Ink ejection control device and method

Abstract

To provide an ink discharge control device and method which can suppress the coalescence of ink and improve the quality of a print image such as a solid filling property.SOLUTION: An ink discharge control device comprises: first and third heads 11, 13 which discharge ink to a printing medium to form a print image; a second head 12 which applies processing liquid containing a coagulant of the ink to the printing medium; and a print control device 20 which applies the processing liquid after discharging the ink until the printing rate of a prescribed region in the printing medium reaches a preset threshold by controlling the first to third heads 11 to 13 and performs two-stage ink discharge control of discharging the ink according to the remaining printing rate after the application of the processing liquid.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an ink ejection control device and method for ejecting ink onto a printing medium to form a print image. [Background technology]

[0002] 2. Description of the Related Art Inkjet printing devices have been proposed that perform printing by ejecting ink from an inkjet head onto a print medium such as paper or film.

[0003] When inkjet printing is performed on non-permeable substrates such as film, the ink is not absorbed by the substrate, as opposed to permeable substrates such as cloth, paper, or synthetic paper coated with an absorbent layer, and therefore ink dots coalesce. Coalescence of ink dots is a phenomenon in which adjacent ink dots combine to form a single ink dot.

[0004] In order to prevent such ink dots from coalescing, for example, Patent Document 1 proposes a method of forming a printed image by applying a treatment liquid containing an aggregating agent and then ejecting ink. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-111763 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the case of a non-permeable substrate having a high contact angle with water, such as a polyvinyl chloride film, the treatment liquid has poor wettability with the substrate, and when the treatment liquid is applied to the substrate, the treatment liquid remains on the substrate in the form of droplets that are roughly hemispherical in shape, as shown in Figure 19.

[0007] It has become clear that when ink lands on such droplets of treatment liquid, the following problems arise compared to when ink lands on a thin, wet, and spread layer of treatment liquid.

[0008] The droplets of the treatment liquid have a strong cohesive force because they exist locally. Therefore, when the ink lands and comes into contact with the droplets of the treatment liquid, it immediately coagulates and no dot gain is obtained, as shown in Figure 20. This not only deteriorates the image quality, such as the ability to fill solid areas, but also increases the amount of ink required to obtain the desired image. The ability to fill solid areas is a measure of the extent to which ink dots can be filled on the substrate, such as by the dot gain of the ink.

[0009] Furthermore, when ink lands on droplets of treatment liquid, as shown in FIG. 21, the ink landing position may deviate from the target landing position, or the ink dot shape may become distorted, resulting in a deterioration in image quality.

[0010] Furthermore, if the treatment liquid does not form droplets as described above, but spreads thinly as shown in Figure 22, the ink will wet and spread easily, sufficient dot gain can be obtained, the ink can be dropped close to the targeted position, and the dot shape can be made close to a perfect circle.

[0011] An object of the present invention is to provide an ink ejection control device and method that can improve the image quality of a printed image, such as the ability to fill solid areas, while suppressing ink coalescence. [Means for solving the problem]

[0012] The ink ejection control device of the present invention comprises an ink ejection unit that ejects ink onto a printing medium to form a printed image, a treatment liquid application unit that applies a treatment liquid containing an ink coagulant onto the printing medium, and a control unit that performs two-stage ink ejection control by controlling the ink ejection unit and the treatment liquid application unit to eject ink until the printing rate of a specified area on the printing medium reaches a preset threshold value, then apply the treatment liquid, and after the application of the treatment liquid, eject ink according to the remaining printing rate. Effect of the Invention

[0013] According to the ink ejection control device of the present invention, the ink ejection unit and the treatment liquid application unit are controlled to eject ink until the printing rate of a predetermined area on the printing medium reaches a preset threshold, then the treatment liquid is applied, and after the treatment liquid is applied, ink is ejected according to the remaining printing rate, thereby performing two-stage ink ejection control, so that it is possible to suppress ink coalescence during the first ink ejection, and the subsequent application of the treatment liquid and the second ink ejection can ensure sufficient dot gain and make the dot shape close to a perfect circle, thereby improving the image quality of the printed image, such as solid filling. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an inkjet printing apparatus using an embodiment of an ink ejection control device of the present invention; [Diagram 2] A view of the inkjet printing device shown in Figure 1 from the direction of arrow A. [Diagram 3] FIG. 1 is a top view showing a schematic configuration of a head unit of an inkjet printing apparatus according to a first embodiment; [Figure 4] A block diagram showing the configuration of a control system of an inkjet printing apparatus. [Diagram 5] FIG. 13 is a diagram showing an example of the relationship between the printing rate and the coalescence rate of ink dots. [Figure 6] FIG. 1 is a diagram for explaining a printing operation of an inkjet printing apparatus according to a first embodiment; [Figure 7] FIG. 1 is a diagram for explaining a printing operation of an inkjet printing apparatus according to a first embodiment; [Figure 8] FIG. 1 is a diagram for explaining a printing operation of an inkjet printing apparatus according to a first embodiment; [Figure 9] FIG. 13 is a top view showing a schematic configuration of a head unit of an inkjet printing apparatus according to a second embodiment; [Figure 10] FIG. 11 is a diagram for explaining a printing operation of an inkjet printing apparatus according to a second embodiment; [Figure 11] FIG. 11 is a diagram for explaining a printing operation of an inkjet printing apparatus according to a second embodiment; [Figure 12] Diagrams showing other configuration examples of the head unit [Figure 13] FIG. 13 is a diagram for explaining a printing operation using the head unit shown in FIG. 12; [Figure 14] FIG. 13 is a diagram for explaining a printing operation using the head unit shown in FIG. 12; [Figure 15] FIG. 13 is a diagram for explaining a printing operation using the head unit shown in FIG. 12; [Figure 16] FIG. 13 is a diagram for explaining a printing operation using the head unit shown in FIG. 12; [Figure 17] FIG. 13 is a diagram for explaining a printing operation using the head unit shown in FIG. 12; [Figure 18] Diagrams showing other configuration examples of the head unit [Figure 19] FIG. 13 is a diagram showing an example in which droplets of a treatment liquid are formed; [Figure 20] FIG. 13 is a diagram for explaining ink aggregation when ink lands on droplets of treatment liquid; [Figure 21] FIG. 13 is a diagram for explaining the deviation of the landing position of an ink dot when ink lands on a droplet of treatment liquid; [Figure 22] A diagram showing how the treatment liquid spreads DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An inkjet printing device using a first embodiment of an ink ejection control device of the present invention will be described in detail below with reference to the drawings. The inkjet printing device of this embodiment is characterized by the configuration of the ink ejection control, but first, the configuration of the entire inkjet printing device will be described. Fig. 1 is a schematic configuration diagram of an inkjet printing device 1 of this embodiment. Fig. 2 is a diagram of the inkjet printing device 1 shown in Fig. 1 as viewed from the direction of arrow A. In the following description of the embodiment, the up, down, left, right, front, back, and rear indicated by arrows in Fig. 1 are defined as the up, down, left, right, front, and rear directions of the inkjet printing device 1.

[0016] 1, an inkjet printing apparatus 1 of this embodiment includes a base 2, a foot stand 3, a platen 4, a rail section 5, and a head unit 10. In this embodiment, the head unit 10 corresponds to the ink ejection section of the present invention.

[0017] The bases 2 are columnar members extending in the front-rear direction and arranged in parallel with a gap in the left-right direction. Two wheels 2a are provided on the bottom surface of each of the two bases 2.

[0018] A foot stand 3 is provided upright on each base 2. A platen 4 is supported on the upper surfaces of the two foot stands 3 facing each other.

[0019] A front guide 4a and a rear guide 4b formed in an arc shape are provided at the front and rear of the platen 4. A vacuum chamber 4c in which a fan 4d is installed is provided below the platen 4, as shown in Fig. 2. Note that the vacuum chamber 4c is not shown in Fig. 1.

[0020] As the fan 4d in the vacuum chamber 4c rotates, negative pressure is created inside the vacuum chamber 4c, and suction force is generated in suction holes (not shown) formed in the platen 4. The printing medium P is attracted to the platen 4 by the suction force generated in the suction holes of the platen 4.

[0021] 2, a drive roller 6 and a pressure roller 7 are provided behind the platen 4 so as to face each other. Note that the drive roller 6 and the pressure roller 7 are omitted from FIG.

[0022] The drive roller 6 is an elongated roller extending in the extension direction of the platen 4, and is rotated by a transport drive motor 61 (see FIG. 4) which will be described later.

[0023] The pressure roller 7, like the drive roller 6, is an elongated roller extending in the extension direction of the platen 4, and is supported by a lifting mechanism (not shown) so as to be movable up and down.

[0024] Then, the printing medium P on the rear guide 4b is clamped between the drive roller 6 and the pressure roller 7, and as the drive roller 6 rotates with the printing medium P pressed by the pressure roller 7, the printing medium P is sent forward.

[0025] Provided on the front side of the base 2 of the inkjet printing device 1 is a take-up core holder 8 that detachably holds a core 8a that takes up the printing medium P. The take-up core holder 8 is linked to a take-up drive motor 81 (see FIG. 4) via a torque limiter (not shown), and is configured so that the take-up core holder 8 is rotated by the take-up drive motor 81.

[0026] Further, a supply-side core holding section 9 is provided on the rear side of the base 2 of the inkjet printing device 1, which detachably holds a core 9a of a roll of printing medium P. The supply-side core holding section 9 is linked to a supply drive motor 91 (see FIG. 4) via a torque limiter (not shown), and is configured so that the supply-side core holding section 9 is rotated by the supply drive motor 91.

[0027] As shown in Figure 2, the roll (printing medium P) held by the supply side core holding section 9 is pulled out and passed through the rear guide 4b, between the drive roller 6 and the pressure roller 7, over the platen 4, and the front guide 4a so as to be wound onto the core 8a held by the winding side core holding section 8.

[0028] A rail section 5 is installed via a support member (not shown) on the upper part of the two legs 3. The rail section 5 includes a rail (not shown) extending in the left-right direction and a main scanning drive motor 51 (see FIG. 4) that moves the head unit 10 back and forth in the left-right direction on the rail.

[0029] The printing medium P may be a smoothed film such as polyvinyl chloride, nylon, or PET (polyethylene terephthalate). The contact angle of water with polyvinyl chloride is approximately 87°, the contact angle of water with nylon film is approximately 70°, and the contact angle of water with PET is approximately 90°. The present invention is particularly effective when printing on a printing medium P with a contact angle of water of 60° or more.

[0030] Next, the head unit 10 of this embodiment will be described.

[0031] 3, the head unit 10 of this embodiment includes a first head 11, a second head 12, and a third head 13. In this embodiment, the first head 11 corresponds to the first ink ejection head of the present invention, the second head 12 corresponds to the treatment liquid ejection head (treatment liquid application section) of the present invention, and the third head 13 corresponds to the second ink ejection head, with the first and third heads 11 and 13 constituting an ink ejection section. In this embodiment, the head unit 10 is configured as described above, and therefore two-stage ink ejection control, which will be described later, can be performed by simpler ejection control.

[0032] The first head 11 includes four inkjet heads: a first inkjet head 11a, a second inkjet head 11b, a third inkjet head 11c, and a fourth inkjet head 11d.

[0033] The first to fourth inkjet heads 11a to 11d have a large number of nozzles that eject ink arranged in the front-rear direction (the transport direction of the print medium P). The first to fourth inkjet heads 11a to 11d are inkjet heads that eject ink of different colors, for example, C (cyan), M (magenta), Y (yellow), and K (black). It is preferable to use water-based pigment ink as the ink.

[0034] The second head 12 has a large number of nozzles that eject the treatment liquid arranged in the front-rear direction (the transport direction of the print medium P). The configuration of the second head 12 is the same as that of an inkjet head. The treatment liquid is a liquid that suppresses the coalescence and bleeding of ink droplets and improves color development, and a known liquid (for example, pretreatment agent B described in JP 2020-138456 A) can be used.

[0035] Specifically, the treatment liquid preferably contains at least water, a flocculant, and a surfactant. The flocculant is preferably a cationic water-soluble cationic resin. The flocculant is not limited to the water-soluble cationic resin, but may be a polyvalent metal salt, an organic acid, an inorganic acid, or the like.

[0036] The third head 13 has a configuration similar to that of the first head 11, and includes four inkjet heads: a fifth inkjet head 13a, a sixth inkjet head 13b, a seventh inkjet head 13c, and an eighth inkjet head 13d.

[0037] The fifth to eighth inkjet heads 13a to 13d are also inkjet heads that eject ink of different colors, for example, C (cyan), M (magenta), Y (yellow) and K (black).

[0038] The first head 11, the second head 12, and the third head 13 are arranged side by side in the transport direction of the print medium P (the front-rear direction), as shown in FIG.

[0039] The first to third heads 11 to 13 are held by a carriage 10a, and are installed so that their ejection surfaces are exposed from the carriage 10a.

[0040] Fig. 4 is a block diagram showing the configuration of a control system of the inkjet printing apparatus 1 of this embodiment. The inkjet printing apparatus 1 operates each of the controlled units shown in Fig. 4 in response to a control signal from the print control device 20. In this embodiment, the print control device 20 corresponds to the control unit of the present invention.

[0041] The print control device 20 and the inkjet printing device 1 are connected by a communication line such as a LAN (Local Area Network) or an Internet line, and are configured to be able to communicate with each other. The communication line may be wired or wireless.

[0042] The print control device 20 is composed of a computer equipped with a CPU (Central Processing Unit), a semiconductor memory, a hard disk, etc. The print control device 20 executes a print control program stored in advance in a storage medium such as a semiconductor memory or a hard disk based on an input print job, etc., and controls each part shown in FIG. 4 by operating an electric circuit.

[0043] The print control device 20 performs RIP (Raster Image Processor) processing on the document image to be printed, and generates a print image made of raster data in bitmap format. Then, the print control device 20 controls the first head 11 and the third head 13 to eject ink based on the generated print image.

[0044] The print control device 20 also includes a high print rate region identifying unit 20a. The high print rate region identifying unit 20a identifies a high print rate region in the print image. A high print rate region is a region in which the print rate of the print image is equal to or greater than a preset threshold value.

[0045] In this specification, the printing rate is defined as 100% when a predetermined area on the printing medium P is filled entirely with dots when printed at a predetermined dot density. For example, when printing with a single color of ink, the printing rate is defined as 100% when the predetermined area on the printing medium P is filled entirely with ink dots of a single color, i.e., when a solid image of ink of a single color is formed. Also, when printing with inks of multiple colors, the printing rate is defined as 100% when the predetermined area on the printing medium P is filled with ink dots of each color.

[0046] FIG. 5 is a diagram showing an example of the relationship between the printing rate and the coalescence rate of ink dots when ink is discharged without treatment liquid onto an area of ​​2000 μm×3000 μm. The coalescence rate is the number of coalesced landing dots / total number of landing dots. In the example shown in FIG. 5, if the printing rate is about 45%, the ink dots are less likely to coalesce, so it can be said that the printing rate has little adverse effect on the printed image even without using treatment liquid. For this reason, in this embodiment, the threshold value for the high printing rate area is set to, for example, 40%. Note that the method of setting the threshold value for the high printing rate area is not limited to this, and it is also possible to actually change the printing rate while printing, and set the printing rate just before the ink dots coalesce more when the printed image is visually recognized as the threshold value.

[0047] The print control device 20 then checks whether or not a high printing rate area exists in the print image by identifying the high printing rate area using the high printing rate area identification unit 20a described above, and if a high printing rate area exists, performs two-stage ink ejection control only on the high printing rate area to form a print image. Note that, instead of the printing rate, the ink amount or dot density may be used as a parameter for identifying the high printing rate area, and any parameter related to the ink amount or dot density ejected onto the print medium P is not limited to the printing rate. The two-stage ink ejection control of this embodiment will be described below.

[0048] When performing two-stage ink ejection control on a high printing rate area, the print control device 20 first controls the first head 11 to eject ink onto the printing medium P to form a print image, and ejects ink until the printing rate onto the printing medium P reaches a preset threshold. The preset threshold is a printing rate lower than the printing rate of the final print image, and is set to, for example, 20% to 40%.

[0049] After the first head 11 ejects ink, the print control device 20 controls the second head 12 to eject the treatment liquid onto the high printing rate area.

[0050] Next, after the second head 12 ejects the treatment liquid, the print control device 20 controls the third head 13 to eject ink according to the remaining printing rate onto the area onto which the treatment liquid was ejected. The remaining printing rate is the remaining printing rate until the printing rate of the finally obtained printed image is reached. For example, when the printing rate of the ink ejected by the first head 11 is 40%, the printing rate of the ink ejected by the third head 13 is the remaining 60%.

[0051] As described above, the printing control device 20 of this embodiment ejects ink until the printing rate of the printing medium P reaches a predetermined threshold value, then ejects treatment liquid, and after ejecting the treatment liquid, ejects ink according to the remaining printing rate.

[0052] This ensures sufficient dot gain during the first ink ejection, allowing the ink to land close to the targeted position, and the dot shape to be close to a perfect circle. Next, the treatment liquid is applied and the ink is ejected for the second time, minimizing the adverse effects of ejecting the treatment liquid first, such as a decrease in ink dot gain, misalignment of the landing position, and deterioration of the dot shape, while forming an image in which dot merging and bleeding are suppressed. This makes it possible to improve the image quality of the printed image, such as the ability to fill solid areas.

[0053] Note that for areas of the print image other than the high printing rate area, the print control device 20 controls the first head 11 or the third head 13 to form the print image, or controls both the first head 11 and the third head 13 to form the print image, but controls so as not to eject treatment liquid by the second head 12. In this embodiment, two-stage ink ejection control is performed only for the high printing rate area, and treatment liquid is not ejected in other areas, so that the amount of treatment liquid can be reduced.

[0054] Next, the overall flow of the printing operation of the inkjet printing apparatus 1 of this embodiment will be described with reference to FIGS.

[0055] First, as shown in Figure 2, a roll body is placed on the supply side core body holding section 9, and the roll body (printing medium P) is pulled out and wound around the core body 8a held by the take-up side core body holding section 8, passing through the rear guide 4b, between the drive roller 6 and the pressure roller 7, over the platen 4, and the front guide 4a.

[0056] Then, the printing control device 20 feeds out the printing medium P by rotating the supply side core holding unit 9, the winding side core holding unit 8, and the drive roller 6, and temporarily stops feeding the printing medium P when it reaches the initial printing position.

[0057] Next, the print control device 20 operates the main scanning drive motor 51 to move the head unit 10 in a first direction (for example, to the right) on the rail section 5. Then, as shown in FIG. 6, the print control device 20 operates the first head 11 of the head unit 10 along with the movement of the head unit 10 to eject ink onto the first scan line. At this time, if a high printing rate area exists on the first scan line, ink is ejected into the high printing rate area until the printing rate reaches a predetermined threshold value. Note that the second head 12 and the third head 13 are not operated when the first scan line is scanned.

[0058] Next, the print control device 20 advances the print medium P by one scan line so that the first scan line is positioned directly below the second head 12, as shown in FIG.

[0059] Then, the print control device 20 moves the head unit 10 on the rail portion 5 in a second direction (for example, leftward) opposite to the first direction. At this time, if a high printing rate area exists on the first scan line, the print control device 20 controls the second head 12 to eject treatment liquid only onto the high printing rate area, and does not eject treatment liquid onto areas other than the high printing rate area. Furthermore, if there is no high printing rate area on the first scan line, the print control device 20 does not eject treatment liquid.

[0060] Furthermore, the print control device 20 ejects the treatment liquid onto the first scan line as described above, and also operates the first head 11 to eject ink onto the second scan line that follows the first scan line. The control of ink ejection (printing rate) at this time is the same as that for the first scan line.

[0061] Next, the printing control device 20 feeds the printing medium P by one scan line, and places the first scan line directly below the third head 13, the second scan line directly below the second head 12, and the third scan line following the second scan line directly below the first head 11, as shown in Figure 8.

[0062] Then, the print control device 20 moves the head unit 10 in a first direction on the rail portion 5, and, in conjunction with the movement, operates the first to third heads 11 to 13 to perform a second ink ejection onto the first scan line, eject processing liquid onto the second scan line, and perform a first ink ejection onto the third scan line.

[0063] When a high printing rate area exists in the first scan line, the print control device 20 ejects ink corresponding to the remaining printing rate to the high printing rate area to form a print image. Note that the ejection control of the treatment liquid to the second scan line is the same as that of the first scan line described above. Also, the ink ejection (printing rate) control to the third scan line is the same as that of the first scan line.

[0064] Next, the printing control device 20 feeds the printing medium P by one scan line, and places the second scan line directly below the third head 13, places the third scan line directly below the second head 12, and places the fourth scan line following the third scan line directly below the first head 11.

[0065] Then, the print control device 20 moves the head unit 10 in the second direction on the rail portion 5, and, in conjunction with the movement, operates the first to third heads 11 to 13 to perform a second ink ejection onto the second scan line, eject processing liquid onto the third scan line, and perform a first ink ejection onto the fourth scan line.

[0066] When a high printing rate area exists in the second scan line, the print control device 20 ejects ink corresponding to the remaining printing rate to the high printing rate area to form a print image. Note that the ejection control of the treatment liquid to the third scan line is the same as that of the first scan line described above. Also, the ink ejection (printing rate) control to the fourth line is the same as that of the first scan line.

[0067] Thereafter, the print control device 20 alternately repeats, as described above, between feeding out one scan line of the printing medium P and moving the head unit 10 in the first direction or the second direction on the rail portion 5, while sequentially ejecting a second ink onto the nth scan line, ejecting treatment liquid onto the n-1th scan line, and ejecting a first ink onto the n-1th scan line.

[0068] Next, an inkjet printing device using a second embodiment of the ink ejection control device of the present invention will be described. The inkjet printing device of the second embodiment differs from the inkjet printing device 1 of the first embodiment in the configuration of the head unit 10 and in the method of two-stage ink ejection control. The rest of the configuration is the same as that of the inkjet printing device 1 of the first embodiment. Below, the differences from the inkjet printing device 1 of the first embodiment will be mainly described.

[0069] 9 is a top view of the head unit 15 in the inkjet printing apparatus of the second embodiment. As shown in FIG. 9, the head unit 15 includes a first head 16, a second head 17, and a third head 18.

[0070] The first head 16 of the head unit 15 is similar to the first head 11 of the head unit 10 of the first embodiment. In the head unit 10 of the first embodiment, the second head 12 and the third head 13 are arranged in the front-to-rear direction (the transport direction of the print medium P), but in the head unit 15 of the second embodiment, the second head 17 and the third head 18 are arranged in the left-to-right direction (the movement direction of the head unit 10).

[0071] The configuration and function of the second head 17 is similar to that of the second head 12 of the first embodiment, and ejects treatment liquid onto the printing medium P. The configuration and function of the third head 18 is similar to that of the third head 13 of the first embodiment, and ejects ink for the second time.

[0072] The first to third heads 16 to 18 are held by a carriage 15a, and are installed so that their ejection surfaces are exposed from the carriage 15a.

[0073] In the first embodiment, after the second head 12 ejects the treatment liquid onto the printing medium P, the third head 13 ejects ink onto the printing medium P a second time with an interval of one scan line, but in the second embodiment, the second head 17 and the third head 18 eject the treatment liquid simultaneously. Specifically, while the second head 17 and the third head 18 are scanning the same scan line, the second head 17 and the third head 18 eject the treatment liquid.

[0074] Therefore, the above-mentioned contemporaneity means, for example, that if the width of carriage 15a in the left-right direction is 30 cm and the movement speed of head unit 15 in the left-right direction (direction perpendicular to the transport direction of printing medium P) is 1 m / s, the time it takes carriage 15a to move from one end of the left-right direction to the other is 0.3 s, and therefore contemporaneity means that the time interval between the ejection timing of the treatment liquid and the ejection timing of the second ink is 0.5 s or less, and preferably 0.3 s or less.

[0075] A preferred time interval between the timing of ejecting the treatment liquid and the timing of ejecting the second ink will now be described. In particular, in printing media with a contact angle of water of 60° or more, depending on the amount of treatment liquid ejected, coalescence of the impacted droplets may progress over time immediately after the treatment liquid lands, resulting in uneven coating of the treatment liquid. For this reason, it is preferable that the time interval between the timing of ejecting the treatment liquid and the timing of ejecting the second ink is short, and the time interval is preferably 1 s or less.

[0076] Therefore, the simultaneous timing is preferably 1 s or less, more preferably 0.5 s or less, and even more preferably 0.3 s or less. Note that, as long as it is within the above-mentioned time interval range, it does not matter which of the ejection timing of the treatment liquid and the ejection timing of the second ink is first.

[0077] Next, the overall flow of the printing operation of the inkjet printing apparatus of the second embodiment will be described with reference to FIGS.

[0078] First, as shown in Figure 2, a roll body is placed on the supply side core body holding section 9, and the roll body (printing medium P) is pulled out and wound around the core body 8a held by the take-up side core body holding section 8, passing through the rear guide 4b, between the drive roller 6 and the pressure roller 7, over the platen 4, and the front guide 4a.

[0079] Then, the printing control device 20 feeds out the printing medium P by rotating the supply side core holding unit 9, the winding side core holding unit 8, and the drive roller 6, and temporarily stops feeding the printing medium P when it reaches the initial printing position.

[0080] Next, the print control device 20 operates the main scanning drive motor 51 to move the head unit 15 in a first direction (for example, to the right) on the rail section 5. Then, as shown in FIG. 10, the print control device 20 operates the first head 16 of the head unit 15 along with the movement of the head unit 15 to eject ink onto the first scan line to form a print image. At this time, if a high print rate area exists on the first scan line, ink is ejected into the high print rate area until the print rate reaches a predetermined threshold value. Note that the second head 17 and the third head 18 are not operated when the first scan line is scanned.

[0081] Next, the print control device 20 advances the print medium P by one scan line so that the first scan line is positioned directly below the second head 17 and the third head 18, as shown in FIG.

[0082] Then, the print control device 20 moves the head unit 15 on the rail portion 5 in a second direction (for example, leftward) opposite to the first direction. At this time, if a high printing rate area exists on the first scanning line, the print control device 20 controls the second head 17 to eject treatment liquid only onto the high printing rate area, and does not eject treatment liquid onto areas other than the high printing rate area. Furthermore, if no high printing rate area exists on the first scanning line, the print control device 20 does not eject treatment liquid. Furthermore, the print control device 20 performs a second ink ejection from the third head 18 at the same time as the ejection of treatment liquid from the second head 17 described above.

[0083] Furthermore, the print control device 20 ejects the treatment liquid and the second ink onto the first scan line as described above, and also operates the first head 16 to eject ink onto the second scan line following the first scan line. The control of the ink ejection (printing rate) at this time is the same as that for the first scan line.

[0084] Next, the printing control device 20 feeds the printing medium P by one scan line, positions the second scan line directly below the second head 17 and the third head 18, and positions the third scan line, which is next to the second scan line, directly below the first head 16.

[0085] Then, the print control device 20 moves the head unit 15 on the rail section 5 in the first direction, and operates the first to third heads 16 to 18 in conjunction with the movement, thereby causing the second head 17 to eject treatment liquid simultaneously with the second ink ejection from the third head 18 onto the second scan line. The print control device 20 also causes the first head 16 to eject ink onto the third scan line. The second ink ejection (printing rate) control and treatment liquid ejection onto the second scan line are the same as those for the first scan line. The first ink ejection (printing rate) control onto the third scan line is the same as those for the first scan line.

[0086] Thereafter, the print control device 20 alternately repeats the process of feeding out one scan line of the printing medium P and moving the head unit 10 in the first direction and the second direction on the rail portion 5, in the same manner as described above, while sequentially performing a second ink ejection and treatment liquid ejection onto the nth scan line, and a first ink ejection onto the n-1th scan line.

[0087] According to the inkjet printing apparatus of the second embodiment, like the inkjet printing apparatus 1 of the first embodiment, it is possible to suppress the coalescence of ink and improve the image quality of the printed image, such as the solid filling property. Furthermore, since the ejection of the treatment liquid and the ejection of the second ink are performed at the same time, it is possible to suppress the coalescence of the droplets of the treatment liquid that have landed, and also to shorten the total printing time.

[0088] The configuration of the head unit is not limited to the configurations of head units 10, 15 shown in Figures 3 and 7, and may be, for example, a configuration like head unit 30 shown in Figure 12. Head unit 30 shown in Figure 12 includes a first head 31, a second head 32, and a third head 33.

[0089] The first head 31 of the head unit 30 is similar to the first head 16 of the head unit 15 of the second embodiment. And, in the head unit 15 of the second embodiment, the second head 17 and the third head 18 are arranged side by side in the left-right direction (the movement direction of the head unit 10) and are arranged at the same position in the front-rear direction (the transport direction of the print medium P), but in the head unit 30, the second head 32 and the third head 33 are arranged with their positions shifted in the front-rear direction.

[0090] The configuration and function of the second head 32 is similar to that of the second head 17 of the second embodiment, and ejects treatment liquid onto the printing medium P. The configuration and function of the third head 33 is similar to that of the third head 18 of the second embodiment, and ejects ink for the second time.

[0091] When a print image is formed using the head unit 30 shown in Fig. 12, after the first ink ejection onto the first scan line is completed by the first head 31 as shown in Fig. 13, ejection of treatment liquid from the second head 32 is started from the point in time when the printing medium P reaches the position shown in Fig. 14, thereby starting ejection of treatment liquid onto the first scan line. Also, by starting ink ejection from the first head 31, the first ink ejection onto the second scan line next to the first scan line is started.

[0092] When using the head unit 30 shown in FIG. 12, unlike the first and second embodiments, ink or treatment liquid is not ejected from all of the nozzles aligned in the front-to-rear direction during one movement of the head units 10, 15, but rather ink or treatment liquid is ejected only from the nozzles corresponding to the printing area of ​​the ink or treatment liquid.

[0093] Then, when the printing medium P reaches the position shown in Fig. 15, the third head 33 starts a second ink ejection, thereby starting a second ink ejection onto the first scan line. Then, the second head 32 continues ejecting treatment liquid until the printing medium P reaches the position shown in Fig. 16, thereby completing the ejection of treatment liquid onto the first scan line. At this time, the first head 31 completes the first ink ejection onto the second scan line. From this time, the first head 31 starts ejecting ink onto the third scan line, which is the next to the second scan line.

[0094] Next, a second ink ejection from the third head 33 is started until the print medium P reaches the position shown in FIG. 17, thereby completing printing on the first scan line.

[0095] Thereafter, in the same manner as described above, the feeding of the printing medium P and the movement of the head unit 30 in the first direction and the second direction are alternately repeated, and a first ink ejection, an ejection of the treatment liquid, and a second ink ejection are sequentially performed onto a specified scanning line.

[0096] It should be noted that the inkjet head for ejecting ink the first time and the inkjet head for ejecting ink the second time do not necessarily need to be provided separately, and may be configured, for example, as in the head unit 40 shown in Fig. 18, including a first head 41 for ejecting ink and a second head 42 for ejecting treatment liquid. In the case of such a configuration, it is sufficient to selectively control the nozzles for ejecting ink from the first head 41 and the nozzles for ejecting treatment liquid from the second head 42 so as to obtain printing results similar to those of the head units 10, 15, and 30 described above.

[0097] In addition, in the above description, the treatment liquid is ejected from a second head similar to an inkjet head, but the method of applying the treatment liquid is not limited to this, and a coating method such as spray coating may also be used. EXAMPLES

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0099] Examples 1 to 5 shown in Table 1 are examples in which printed images were formed using the inkjet printing apparatus 1 of the first embodiment. [Table 1]

[0100] For the evaluation in Table 1 above, an aqueous pigment ink K was used as the ink, and each of the components shown in Table 2 below was premixed in the ratio (solid content equivalent) shown in Table 2 below, and the resulting mixture was passed through a membrane filter with a pore size of 3 μm.

[0101] Details of the raw materials listed in Table 2 are as follows. "CAB-O-JET 200": Cabot Corporation, water-based self-dispersing black pigment dispersion "Takelac W-5661": Urethane resin emulsion manufactured by Mitsui Chemicals, Inc. "Silface SAG002": Silicone surfactant manufactured by Nissin Chemical Industry Co., Ltd. [Table 2]

[0102] The processing liquid used was a processing liquid containing a water-soluble cationic resin.

[0103] The treatment liquid used in the evaluations in Table 1 above was obtained by premixing the components shown in Table 3 below in the ratios shown in Table 3 below, and passing the resulting mixture through a membrane filter with a pore size of 3 μm.

[0104] Details of the raw materials listed in Table 3 below are as follows: "Sharol DC-303P": Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., cationic water-soluble resin, active ingredient content 41% (polydiallyldimethylammonium chloride) "Dipropylene glycol": Fujifilm Wako Pure Chemical Corporation "1,2-butanediol": manufactured by Tokyo Chemical Industry Co., Ltd. "Silface SAG002": Silicone surfactant manufactured by Nissin Chemical Industry Co., Ltd. [Table 3]

[0105] The printing medium used was a white polyvinyl chloride film.

[0106] A black solid image was formed as the printed image. The dot density of the printed black ink was 600 dpi x 1200 dpi (dot density at a target print rate of 100%).

[0107] The above-mentioned printed image was formed using the inkjet printing apparatus 1 of the first embodiment, and then the printed image was dried at 100°C for 1 minute using a hot air heater, after which the solid filling performance was evaluated. The solid filling performance increases as the ink wets and spreads well, the ink landing accuracy is high, and the ink dot shape approaches a perfect circle.

[0108] The evaluation criteria for solid filling performance were as follows: when the print was visually observed from a distance of 30 cm, a level where no white spots (uncolored areas of the white polyvinyl chloride film) were visible was given an "A", a level where white spots were visible was given a "B", and a level where white spots were noticeable or white streaks occurred was given a "C".

[0109] The threshold value of the printing rate of the first ink ejection and the presence or absence of ejection of the treatment liquid are as shown in Table 1. As shown in Examples 1 to 4, when the printing rate of the first ink ejection was 25% to 40%, the solid filling performance was evaluated as "A". Furthermore, as shown in Example 5, when the printing rate of the first ink ejection was set to 20%, the printing rate of the first ink ejection was lower than in Examples 1 to 4, so that a sufficient dot gain could be ensured, ink could be landed close to the targeted position, and the number of dots that could be made to have a dot shape close to a perfect circle was smaller than in Examples 1 to 4, and the solid filling performance was evaluated as "B".

[0110] Comparative Example 1 shown in Table 1 is a case where a print image is formed by discharging ink twice without treatment liquid, Comparative Example 2 is a case where a print image is formed by discharging ink only once without treatment liquid, and Comparative Example 3 is a case where a print image is formed by discharging ink only once after discharging treatment liquid first. In Comparative Examples 1 to 3, the solid filling performance was evaluated as "C". In Comparative Examples 1 and 2, since no treatment liquid was used, the ink dots were not fixed and moved and merged, so that the solid filling performance was deteriorated to the extent that the white of the background was visible. In Comparative Example 3, since the treatment liquid was discharged first and then the ink was discharged, the treatment liquid was present on the printing medium P first, so that the ink that landed around the treatment liquid did not obtain dot gain, and the impact position was shifted from the target impact position due to the influence of the presence of the treatment liquid, and the ink dot shape became distorted, so that the solid filling performance was deteriorated.

[0111] Next, Examples 6 to 11 shown in Table 4 below are examples in which printed images were formed using the inkjet printing apparatus 1 of the second embodiment. In other words, these are examples in which the ejection timing of the treatment liquid and the second ink ejection timing are simultaneous. [Table 4]

[0112] The threshold value of the printing rate of the first ink ejection and the presence or absence of ejection of the treatment liquid are as shown in Table 4. As shown in Example 6 and Example 7, when the printing rate of the first ink ejection was 40% and 35%, the solid filling evaluation was "B". That is, in Example 6 and Example 7, the solid filling evaluation was slightly deteriorated compared to Example 1 and Example 2, which have the same threshold value of the printing rate of the first ink ejection. This is because in Example 6 and Example 7, the treatment liquid and ink are ejected simultaneously when the printing rate of the first ink ejection is high at 40% and 35%, and therefore the second ink is ejected in an area where the treatment liquid is not sufficiently applied (because an area with a printing rate of 50% or more in FIG. 5 occurs locally), and there are areas where the coalescence of dots cannot be suppressed, and this is thought to reduce the effect of improving the solid filling by the two-stage ink ejection control.

[0113] As shown in Examples 8 to 10, when the printing rate of the first ink ejection was 20% to 30%, the solid filling performance was evaluated as "A." In Examples 8 to 10, the treatment liquid and ink are ejected simultaneously at a lower printing rate of the first ink ejection than in Examples 6 and 7, and therefore the treatment liquid exerts a sufficient coalescence suppression effect before the ink coalescence progresses (because there is a margin before an area with a printing rate of 50% or more appears in FIG. 5), which is thought to have improved the solid filling performance evaluation.

[0114] However, as shown in Example 11, when the printing rate of the first ink ejection is 15%, the printing rate of the first ink ejection is low, so that the dot gain can be sufficiently ensured, the ink can be landed at a position close to the target, and the number of dots that can be made to have a dot shape close to a perfect circle is smaller than in Examples 8 to 10. This reduces the improvement effect of the solid filling property, and the solid filling property was evaluated as "B".

[0115] As can be seen from Examples 6 to 11, when the timing of ejecting the treatment liquid and the timing of the second ink ejection were synchronized, the solid filling performance could be evaluated as "A" by adjusting the balance between the printing rate of the first ink ejection and the printing rate of the second ink ejection.

[0116] In Example 6, when heating was performed during printing, the coalescence of dots could be suppressed, and the solid filling performance was evaluated as "A." Heating was performed using a heater installed in the printing device, and heating was performed at 40°C.

[0117] The present invention further discloses the following supplementary notes. (Additional Note)

[0118] The ink ejection control device of the present invention comprises an ink ejection unit that ejects ink onto a printing medium to form a printed image, a treatment liquid application unit that applies a treatment liquid containing an ink coagulant onto the printing medium, and a control unit that controls the ink ejection unit and the treatment liquid application unit to perform two-stage ink ejection control in which ink is ejected until the printing rate of a specified area on the printing medium reaches a preset threshold value, and then the treatment liquid is applied and ink is ejected according to the remaining printing rate at the same time.

[0119] In addition, the ink ejection control device of the invention can be provided with a high printing rate area identification unit that identifies high printing rate areas within a printed image where the printing rate is equal to or greater than a predetermined threshold value, and the control unit can perform two-stage ink ejection control only for high printing rate areas within the printed image.

[0120] In addition, in the ink ejection device of the present invention, the ink ejection section can include a first ink ejection head that ejects ink before the treatment liquid is applied, a second ink ejection head that ejects ink after the treatment liquid is applied, and a treatment liquid ejection head that ejects the treatment liquid.

[0121] The ink ejection control method of the present invention ejects ink until the printing rate of a specified area on a printing medium reaches a preset threshold value, then applies a treatment liquid containing an ink coagulant to the printing medium, and ejects ink according to the remaining printing rate after the application of the treatment liquid. [Explanation of symbols]

[0122] 1 Inkjet printing device 2 Base 2a wheels 3 pedestal 4 Platen 4a Front guide 4b Rear guide 4c Vacuum chamber 4d fan 5 Rail section 6 Drive roller 7 Pressure roller 8. Winding side core holder 8a Core body 9 Supply side core holding part 9a Core body 10,15,30,40 Head Unit 10a, 15a Carriage 11 First Head 11a first inkjet head 11b Second inkjet head 11c The third inkjet head 11d The fourth inkjet head 12 Second Head 13 The Third Head 13a 5th inkjet head 13b 6th inkjet head 13c 7th Inkjet Head 13d 8th Inkjet Head 16 First Head 17 Second Head 18 The Third Head 20 Printing control device 20a High printing rate area identification part 31 First Head 32 Second Head 33 The Third Head 41 First Head 42 Second Head 51 Main scanning drive motor 61 Transport drive motor 81 Winding drive motor 91 Supply drive motor P Print media

Claims

1. an ink ejection unit that ejects ink onto a print medium to form a print image; a treatment liquid applying unit that applies a treatment liquid containing a coagulant for the ink to the print medium; a control unit that controls the ink ejection unit and the treatment liquid application unit to eject ink until a printing rate of a predetermined area in the print medium reaches a preset threshold value, and then applies the treatment liquid, and ejects ink according to the remaining printing rate after the application of the treatment liquid, performing two-stage ink ejection control; a high printing rate area specifying unit that specifies a high printing rate area in the print image in which the printing rate is equal to or higher than a preset threshold value; An ink ejection control device, wherein the control unit performs the two-stage ink ejection control only for the high printing rate area in the printed image, and performs ink ejection control for areas in the printed image other than the high printing rate area without applying the treatment liquid.

2. an ink ejection unit that ejects ink onto a print medium to form a print image; a treatment liquid applying unit that applies a treatment liquid containing a coagulant for the ink to the print medium; an ink ejection control device comprising: a control unit that controls the ink ejection unit and the treatment liquid application unit to eject ink until the printing rate of a high printing rate area in the printing medium reaches a preset threshold value, and then performs two-stage ink ejection control to simultaneously apply the treatment liquid and eject ink according to the remaining printing rate, and that performs ink ejection control without applying the treatment liquid to areas in the printed image other than the high printing rate area.

3. 3. The ink ejection control device according to claim 1, wherein the ink ejection section comprises a first ink ejection head that ejects ink before the treatment liquid is applied, a second ink ejection head that ejects ink after the treatment liquid is applied, and a treatment liquid ejection head that ejects the treatment liquid.

4. An ink ejection control method including a step of ejecting ink onto a print medium to form a print image, and a step of applying a treatment liquid containing a coagulant for the ink onto the print medium, Identifying a high print rate area in the print image, the high print rate area having a print rate equal to or greater than a preset threshold value; An ink ejection control method in which ink is ejected only into the high printing rate area until the printing rate reaches a preset threshold, and then the treatment liquid is applied, and after the application of the treatment liquid, ink is ejected according to the remaining printing rate, and ink ejection control is performed without applying the treatment liquid to areas in the printed image other than the high printing rate area.

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