Inkjet recording method

Abstract

To provide an inkjet recording method which achieves both continuous discharge properties of ink and suppression of color mixture.SOLUTION: An inkjet recording method includes a first step of discharging aqueous ink onto a recording medium R from a first recording head 31, using inkjet recording devices 100, 110 and 120 having a conveyance mechanism 10 for conveying a low liquid-absorptive recording medium R, two or more recording heads 31 and 32 for discharging the aqueous ink, and a drier 50 for drying the aqueous ink discharged onto the recording medium R, a second step of drying the aqueous ink discharged onto the recording medium R by the drier 50, while conveying the recording medium R, a third step of discharging the aqueous ink onto the recording medium R from the second recording head 32, and a fourth step of drying the aqueous ink discharged onto the recording medium R by the drier 50, while conveying the recording medium R in this order, and uses the same drier 50, in the second step and the fourth step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method. [Background technology]

[0002] Inkjet recording is a method of directly ejecting ink from fine nozzles in a recording head and depositing it onto a print medium to produce a printed product with characters and images recorded on it. This method offers numerous advantages, including easy and inexpensive full-color printing and non-contact with the print medium. In recent years, this method has been applied not only to consumer printing for general consumers but also to commercial and industrial printing. In the commercial and industrial printing fields, high-speed inkjet printing has been considered in order to increase productivity. This involves providing a linear fixed print head capable of printing across the entire width of the print medium, and using a so-called single-pass method to continuously print rolls or sheets of print medium. Furthermore, in recent years, inkjet printing devices using aqueous inks containing pigments have been considered for this type of printing, from the perspectives of improving the weather resistance and water resistance of printed materials and reducing environmental impact.

[0003] Patent Document 1 discloses an inkjet recording method for the purpose of providing an inkjet recording method capable of easily producing a recorded matter with high image quality that allows the image to be viewed from both sides, the method comprising: a first step of recording colored ink onto a recording medium using an inkjet head to form a first image; a second step of recording background ink using an inkjet head to form a background image that covers the first image; and a third step of recording colored ink using an inkjet head to form a second image, the method including a drying step between the first step and the third step. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-180428 Summary of the Invention [Problem to be solved by the invention]

[0005] In inkjet recording, when a recording medium with low liquid absorption is used, and particularly when a water-based ink is used, the ejected ink is not absorbed by the recording medium and the ink is slowly fixed, which tends to result in the adjacent inks mixing together. Furthermore, when inkjet recording is performed over a long period of time, the recording head that ejects the ink is constantly exposed to the outside air, which causes the problem of some of the nozzles of the recording head becoming clogged.

[0006] An object of the present invention is to provide an inkjet recording method that achieves both continuous ink ejection and suppression of color mixing. [Means for solving the problem]

[0007] The present inventors have discovered that an inkjet recording method can be provided that achieves both continuous ejection and suppression of ink mixing by comprising, in this order: a first step of ejecting an aqueous ink from a first recording head onto a recording medium; a second step of drying the aqueous ink ejected onto the recording medium in a drying device while transporting the recording medium; a third step of ejecting an aqueous ink from a second recording head onto the recording medium; and a fourth step of drying the aqueous ink ejected onto the recording medium in a drying device while transporting the recording medium, and by using the same drying device in the second and fourth steps. That is, the present invention provides the following [1]. [1] An inkjet recording method for recording on a low-liquid-absorbent recording medium using an inkjet recording device comprising a transport mechanism for transporting the recording medium, two or more recording heads for ejecting water-based ink, and a drying device for drying the water-based ink ejected onto the recording medium, the method comprising the following steps, in this order: a first step of ejecting the water-based ink from a first recording head onto the recording medium; a second step of drying the water-based ink ejected onto the recording medium in the drying device while transporting the recording medium; a third step of ejecting the water-based ink from a second recording head onto the recording medium; and a fourth step of drying the water-based ink ejected onto the recording medium in the drying device while transporting the recording medium, wherein the same drying device is used in the second and fourth steps. [Effects of the Invention]

[0008] According to the present invention, an inkjet recording method is provided that achieves both continuous ink ejection properties and suppression of color mixing. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating an inkjet recording method according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating a conventional inkjet recording method. [Figure 3] FIG. 10 is a schematic diagram illustrating an inkjet recording method according to a second embodiment. [Figure 4] FIG. 10 is a schematic diagram illustrating an inkjet recording method according to a third embodiment. [Figure 5] 1A and 1B are diagrams showing print patterns of an example and a comparative example. [Figure 6] FIG. 10 is a diagram showing a print pattern according to an embodiment of the present invention. [Figure 7] FIG. 10 is a schematic diagram for explaining an inkjet recording method according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0011] In this specification, "recording" is a concept that includes printing and printing to record characters and images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters and images are recorded. Furthermore, "low liquid absorption" is a concept that includes low liquid absorption and non-liquid absorption, and the water absorption amount of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g / m. 2 More than 10g / m 2 This means that:

[0012] First, an inkjet recording method according to a first embodiment will be described with reference to FIG. 1. Here, FIG. 1 is a schematic diagram for explaining the inkjet recording method according to the first embodiment. For ease of explanation, the up-down direction is defined based on the normal installation direction of the inkjet recording apparatus 100. Specifically, the down direction is the side of the installation surface (base B) of the transport mechanism 10, i.e., the downward direction on the paper surface of FIG. 1, and the up direction is the upward direction on the paper surface of FIG. 1. Also, for ease of explanation, the thickness of the recording medium R is depicted as being thick in FIG. 1.

[0013] [Inkjet recording method according to the first embodiment] As shown in FIG. 1, the inkjet recording apparatus 100 used in the inkjet recording method according to the first embodiment is configured to include, but is not limited to, a transport mechanism 10 that transports a low-liquid-absorbent recording medium R, two recording heads 30 (a first recording head 31 and a second recording head 32) that eject water-based ink, and a drying device 50 that dries the water-based ink ejected onto the recording medium R.

[0014] As described above, the low-liquid-absorbent recording medium R has a water absorption of 0 g / m when the recording medium is in contact with pure water for 100 ms. 2 More than 10g / m 2The term "film" refers to any of the following, including coated paper, art paper, and transparent synthetic resin film sheets. Examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper. Examples of transparent synthetic resin film sheets include polyester film sheets, vinyl chloride film sheets, polypropylene film sheets, polyethylene film sheets, and nylon film sheets. These film sheets may be biaxially oriented film sheets, uniaxially oriented film sheets, or unoriented film sheets. Among these, the recording medium R may be a polyester film sheet or an oriented polypropylene film sheet, or a polyester film sheet such as a polyethylene terephthalate film sheet that has been subjected to a surface treatment such as corona discharge treatment, or a biaxially oriented polypropylene film sheet. The thickness, width, and depth of the recording medium R can be appropriately changed depending on the intended use of the recorded material.

[0015] Commercially available transparent synthetic resin film sheets can be used, and examples of commercially available products include Lumirror T60 (manufactured by Toray Industries, Inc., polyethylene terephthalate), Taiko FE2001 (manufactured by Futamura Chemical Co., Ltd., corona-treated polyethylene terephthalate), E5100, E5102 (manufactured by Toyobo Co., Ltd., corona-treated polyethylene terephthalate), PVC80B P (manufactured by Lintec Corporation, polyvinyl chloride), KYNAS KEE70CA (manufactured by Lintec Corporation, polyethylene), YUPO SG90 PAT1 (manufactured by Lintec Corporation, polypropylene), FOR, FOR-AQ, FOS, FOS-AQ (manufactured by Futamura Chemical Co., Ltd., corona-treated polypropylene), P2161, P2111, DP053 (manufactured by Toyobo Co., Ltd., corona-treated polypropylene), U1 (manufactured by RM Tocello Co., Ltd., corona-treated polypropylene), and Bonyl RX (manufactured by Kohjin Film & Chemicals Co., Ltd., nylon).

[0016] The transport mechanism 10 is configured to transport a low-liquid-absorbent recording medium R. As shown in FIG. 1 , the transport mechanism 10 according to this embodiment has a flat upper surface so that the recording medium R can be placed on the upper surface and transported. In this embodiment, the transport mechanism 10 is configured to transport the recording medium R horizontally on a base B, which serves as an installation base, although this is not particularly limited. Specifically, in FIG. 1 , the transport mechanism 10 according to this embodiment transports the recording medium R horizontally from left to right and can move to the position of the transport mechanism 10 indicated by the dashed line. The transport mechanism 10 indicated by the dashed line transports the recording medium R horizontally from right to left and can move to the position of the transport mechanism 10 indicated by the solid line. The means for horizontally reciprocating the transport mechanism 10 is not particularly limited, and any conventionally known means can be appropriately selected and used. The transport mechanism 10 does not have to transport the recording medium R horizontally, but may, for example, have a base B that is an inclined surface and move up and down the base B to reciprocate.

[0017] The base B is a portion having a flat surface that serves as an installation reference for the transport mechanism 10 and the like. The base B may be a floor, a member having a flat surface, or may be inclined. As described above, in this embodiment, the transport mechanism 10 is configured to move horizontally on the base B. Note that if the transport mechanism 10 is a cylindrical transport drum, the recording medium R is transported by the rotation of the transport drum. Therefore, although the base B serves as an installation reference for the transport drum as the transport mechanism 10, the transport drum as the transport mechanism 10 does not normally move on the base B.

[0018] The transport speed of the recording medium R by the transport mechanism 10 can be changed as appropriate depending on the size of the inkjet recording apparatus 100, the type and size of the recording medium R, the type of aqueous ink, etc. The transport speed can be, for example, 5 m / min or more and 100 m / min or less. Note that the recording medium R is usually transported by the transport mechanism 10 at a speed at which proper recording can be performed on the recording medium R, so the transport speed of the recording medium R becomes the recording speed of the recording medium R. Therefore, the recording speed of the recording medium R can be changed as appropriate depending on the size of the inkjet recording apparatus 100, the type and size of the recording medium R, the type of aqueous ink, etc., but can be, for example, 5 m / min or more and 100 m / min or less. In other words, the recording speed of the recording medium R can be 5 m / min or more and 100 m / min or less when converted into the transport speed of the recording medium R. From the viewpoint of achieving both improved quality of the resulting recording material and reduced recording time, the recording speed of the recording medium R can be set to 5 m / min or more, 15 m / min or more, 20 m / min or more, and 100 m / min or less, 80 m / min or less, 60 m / min or less, or 50 m / min or less.

[0019] The transport mechanism 10 may be equipped with a recording medium heating device to heat the recording medium R to a desired temperature. The recording medium heating device may be disposed on the upper surface of the transport mechanism 10, and its location is not particularly limited. If the transport mechanism 10 is equipped with an under-heater as the recording medium heating device, for example, the temperature of the under-heater can be changed appropriately depending on the type of recording medium R and water-based ink, and is not particularly limited, but may be 15°C or higher, 25°C or higher, 30°C or higher, or 35°C or higher, and from the viewpoint of suppressing deformation of the recording medium R, may be 80°C or lower, or 70°C or lower.

[0020] The recording head 30 (inkjet head) ejects water-based ink toward the recording medium R transported by the transport mechanism 10. The recording head 30 may be configured to eject water-based ink from nozzles (not shown). In this embodiment, the recording head 30 includes two recording heads: a first recording head 31 and a second recording head 32. However, the number of recording heads is not particularly limited as long as it is two or more, and may be three, four, or five. As shown in FIG. 1 , although not particularly limited, in this embodiment, the first recording head 31 and the second recording head 32 are arranged across the drying device 50 in the transport direction of the recording medium R. In other words, although not particularly limited, in this embodiment, the drying device 50 is arranged between the first recording head 31 and the second recording head 32 in the transport direction of the recording medium R.

[0021] The aqueous ink ejected from the recording head 30 (31, 32) is an ink whose main solvent is water, i.e., an ink containing 50% by mass or more of water relative to the total mass of the solvent, and the amount of water in the aqueous ink can be, for example, 60% by mass or more. The aqueous ink (hereinafter simply referred to as ink) can be appropriately selected depending on the purpose of the recorded matter. When the ink ejected onto the recording medium R is aqueous ink, the recording head 30 is moistened by the water vapor generated when the ink is dried by the drying device 50 described below, and as a result, an inkjet recording method with excellent continuous ink ejection properties can be provided.

[0022] Examples of aqueous inks include cyan ink, magenta ink, yellow ink, red ink, blue ink, orange ink, green ink, violet ink, black ink, and white ink. While not particularly limited, white ink (white ink) can be used in combination with cyan ink, magenta ink, yellow ink, red ink, blue ink, orange ink, green ink, violet ink, or black ink (non-white ink). Furthermore, although not particularly limited, either the first recording head 31 or the second recording head 32 can be configured to eject a non-white ink, and either the first recording head 31 or the second recording head 32 can be configured to eject a white ink. The inkjet recording method according to this embodiment is effective in suppressing ink color mixing, and is therefore useful because it allows the use of a combination of a non-white ink, in which ink color mixing is easily visible, and a white ink.

[0023] The surface temperature of the recording medium R when recording by ejecting water-based ink onto the recording medium R can be changed appropriately depending on the type of water-based ink and the recording medium R, and is not particularly limited, but can be set to 35° C. or higher, and can be set to 80° C. or lower, 70° C. or lower, or 65° C. or lower from the viewpoint of suppressing deformation of the recording medium R. The surface temperature of the recording medium R can be adjusted to the above temperatures, for example, by arranging an under-heater or the like in the transport mechanism 10.

[0024] The drying device 50 dries the water-based ink ejected onto the recording medium R. The drying device 50 is not particularly limited as long as it can dry the water-based ink ejected onto the recording medium R, but it can be a hot air dryer, a heater dryer, or an IR dryer.

[0025] The inkjet recording method according to the first embodiment includes, in this order, a first step of ejecting water-based ink from a first recording head 31 onto a recording medium R using the inkjet recording apparatus 100 according to the embodiment described above; a second step of drying the water-based ink ejected onto the recording medium R in a drying device 50 while transporting the recording medium R; a third step of ejecting water-based ink from a second recording head 32 onto the recording medium R; and a fourth step of drying the water-based ink ejected onto the recording medium R in the drying device 50 while transporting the recording medium R, and the same drying device 50 is used in the second and fourth steps.

[0026] The first step is a step of ejecting water-based ink from the first recording head 31 onto the recording medium R. In this embodiment, as shown by arrow 1 in Figure 1, the transport mechanism 10, with the recording medium R placed on its upper surface, moves horizontally on the base in the direction in which the first recording head 31 is disposed (to the right on the paper), and when it passes under the first recording head 31, the water-based ink is ejected from the first recording head 31 onto the recording medium R.

[0027] After the first step, the recording medium R onto which the water-based ink has been ejected from the first recording head 31 is dried by the drying device 50 while being transported by the transport mechanism 10 (second step). More specifically, in the second step, as shown by arrow 2 in FIG. 1 , the recording medium R onto which the water-based ink has been ejected from the first recording head 31 is transported in the direction in which the drying device 50 and the second recording head 32 are disposed (toward the right on the paper), and the water-based ink ejected from the first recording head 31 onto the recording medium R is dried by the drying device 50. Then, the second recording head 32 is moistened by the water vapor of the water-based ink dried in the second step. More specifically, water vapor is generated by drying the water-based ink ejected from the first recording head 31 onto the recording medium R in the drying device 50, and since this water vapor tends to flow in the direction of transport of the recording medium R by the transport mechanism 10 (to the right on the page), it tends to flow toward the second recording head 32, and the second recording head 32 in particular is moisturized by the water vapor. Therefore, even if the second recording head 32 is exposed to the outside air for a long period of time and some of the nozzles (not shown) of the second recording head 32 are clogged due to drying, the clogging is eliminated by the water vapor, and ejection defects can be suppressed.

[0028] In the second step, if the recording medium R onto which the aqueous ink has been ejected from the first recording head 31 is dried by the drying device 50 without being transported by the transport mechanism 10, i.e., if the recording medium R is stopped at the position of the drying device 50 and dried, the water vapor from the aqueous ink dried by the drying device 50 tends to remain near the drying device 50. Therefore, unlike the above-described case, the water vapor does not easily flow toward the second recording head 32, resulting in insufficient moisture retention of the second recording head 32 and, as a result, poor continuous ink ejection performance. Furthermore, if the transportation of the recording medium R is stopped in order to dry the recording medium R onto which the aqueous ink has been ejected from the first recording head 31, inkjet recording takes time and effort, resulting in poor productivity. On the other hand, according to the inkjet recording method of this embodiment, the recording medium R onto which the aqueous ink has been ejected from the first recording head 31 is dried while being transported, resulting in excellent productivity of the recorded material.

[0029] After the second process, the transport mechanism 10 carrying the recording medium R, which has been dried to the extent that the water-based ink ejected from the first recording head 31 does not mix with the water-based ink ejected from the second recording head 32 or has been completely dried, may, although not limited to, move further in the direction in which the second recording head 32 is positioned (to the right on the paper), pass under the second recording head 32 without the water-based ink being ejected from the second recording head 32, and move to the position of the transport mechanism 10 shown by the dashed line in Figure 1.

[0030] In this embodiment, the conveying mechanism 10, which has moved to the position indicated by the dashed line in Figure 1, will convey the recording medium R in the opposite direction (towards the left on the paper) to the conveying direction in the first and second steps (the third and fourth steps described below).

[0031] The third step is a step of ejecting the water-based ink from the second recording head 32 onto the recording medium R. In this embodiment, the transport mechanism 10 moves to the position of the transport mechanism 10 indicated by the dashed line, and then moves horizontally on the base B in the direction in which the second recording head 32 is disposed (to the left on the paper), as indicated by arrow 3 in FIG. 1 , and as it passes under the second recording head 32, the water-based ink is ejected onto the recording medium R.

[0032] After the third step, the recording medium R onto which the water-based ink has been ejected from the second recording head 32 is transported by the transport mechanism 10 and dried by the drying device 50 (fourth step). More specifically, in the fourth step, as indicated by arrow 4 in FIG. 1 , the recording medium R onto which the water-based ink has been ejected from the second recording head 32 is transported in the direction in which the drying device 50 and the first recording head 31 are disposed (toward the left on the page), and the water-based ink ejected from the second recording head 32 onto the recording medium R is dried by the drying device 50. Note that if the water-based ink from the first recording head 31 has not completely dried, the water-based ink from the first recording head 31 may also be dried in the fourth step. Even if the water-based ink from the first recording head 31 has completely dried, the water-based ink may be further dried.

[0033] The first recording head is then moistened by the water vapor of the aqueous ink that is dried in the fourth step. More specifically, water vapor is generated by drying the aqueous ink ejected from the second recording head 32 in the drying device 50, and since this water vapor tends to flow in the direction in which the recording medium R is transported by the transport mechanism 10 (to the left on the page), it tends to flow toward the first recording head 31, and the first recording head 31 in particular is moistened by the water vapor. Therefore, even if some of the nozzles (not shown) of the first recording head 31 are clogged due to drying, the clogging is cleared by the water vapor, and ejection defects can be suppressed.

[0034] With the above-described configuration, the recording medium R onto which the water-based ink has been ejected from the first recording head 31 and the second recording head 32 passes back and forth under the drying device 50. The recording heads 30 (31, 32) are moisturized by the water vapor generated by drying the water-based ink ejected onto the recording medium R in the drying device 50. Note that when the recording medium R passes back and forth under the drying device 50, the number of times it passes back and forth is not particularly limited and can be one or more times.

[0035] A conventional inkjet recording method will now be described. Fig. 2 is a schematic diagram for explaining the conventional inkjet recording method. Components that are the same as or similar to those in the above-described embodiment will be assigned the same reference numerals, and descriptions thereof may be omitted.

[0036] As shown in FIG. 2, an inkjet recording apparatus 200 used in a conventional inkjet recording method includes a transport mechanism 10 that transports a low-liquid-absorbent recording medium R, two recording heads 30 (a first recording head 31 and a second recording head 32) that eject water-based ink, and a drying device 50 that dries the water-based ink ejected onto the recording medium R, with the drying device 50 being configured to be located between the first recording head 31 and the second recording head 32, and having a configuration similar to that of the inkjet recording apparatus 100 according to this embodiment.

[0037] As shown in FIG. 2, in a conventional inkjet recording method, a transport mechanism 10 carrying a recording medium R thereon advances horizontally on a base B in the direction of a first recording head 31 (toward the right on the paper) as indicated by arrow 1. As the transport mechanism 10 passes under the first recording head 31, the aqueous ink is ejected onto the recording medium R. Thereafter, as indicated by arrow 2, the recording medium R onto which the aqueous ink has been ejected from the first recording head 31 is transported in the direction of a drying device 50 and a second recording head 32 (toward the right on the paper) as indicated by arrow 2. The aqueous ink ejected onto the recording medium R from the first recording head 31 is then dried by the drying device 50. Then, as indicated by arrow 3 in FIG. 1, the transport mechanism 10 carrying the recording medium R on which the aqueous ink from the first recording head 31 has dried further advances horizontally on a base B in the direction of a second recording head 32 (toward the right on the paper) as indicated by arrow 3. As the transport mechanism 10 passes under the second recording head 32, the aqueous ink is ejected onto the recording medium R.

[0038] In conventional inkjet recording methods, the water-based ink ejected from the first recording head 31 onto the recording medium R is dried in a drying device 50, generating water vapor. This water vapor tends to flow in the direction of transport of the recording medium R by the transport mechanism 10 (toward the right on the paper), and therefore tends to flow in the direction of placement of the second recording head 32 (toward the right on the paper), thereby moisturizing the second recording head 32. However, because the first recording head 31 is not moisturized, when inkjet recording is performed over a long period of time, some of the nozzles (not shown) of the first recording head 31 become clogged, causing ink ejection problems and making it difficult to obtain a good recorded product. Furthermore, because the water-based ink ejected onto the recording medium R from the second recording head 32 is not dried sufficiently, color mixing with the water-based ink ejected onto the recording medium R from the first recording head 31 easily occurs.

[0039] On the other hand, in the inkjet recording method according to this embodiment, even if some of the nozzles (not shown) of the recording head 31 and the recording head 32 become clogged, the first recording head 31 and the second recording head 32 are moisturized by the water vapor generated by drying the water-based ink, eliminating the clog, making ink ejection failure less likely to occur, and providing excellent continuous ink ejection properties. Furthermore, the water-based ink ejected onto the recording medium R from the second recording head 32 is also dried by the drying device 50, which can suppress color mixing with the water-based ink ejected onto the recording medium R from the first recording head 31. Therefore, the inkjet recording method according to this embodiment can achieve both continuous ink ejection properties and suppression of color mixing.

[0040] The inkjet recording method according to the first embodiment has been described above. Next, an inkjet recording method according to a second embodiment will be described with reference to FIG. 3. FIG. 3 is a schematic diagram for explaining the inkjet recording method according to the second embodiment. As in the above-described case, for convenience of explanation, the up-down direction is defined based on the normal installation direction of the inkjet recording apparatus 110. Specifically, the down direction is the side of the installation surface (base B) of the transport mechanism 10, i.e., the downward direction on the paper surface of FIG. 3, and the up direction is the upward direction on the paper surface of FIG. 3. Also, in FIG. 3, the thickness of the recording medium R is depicted as being thick for convenience of explanation. Furthermore, components that are the same as or similar to those in the above-described embodiments will be assigned the same reference numerals, and their description may be omitted.

[0041] [Inkjet recording method according to the second embodiment] 3, an inkjet recording apparatus 110 used in the inkjet recording method according to the second embodiment is configured to include, but is not limited to, a transport mechanism 10 that transports a low-liquid-absorbent recording medium R, two recording heads 30 (a first recording head 31 and a second recording head 32) that eject water-based ink, and a drying device 50 that dries the water-based ink ejected onto the recording medium R. Unlike the inkjet recording apparatus 100 used in the inkjet recording method according to the first embodiment, this embodiment is configured, but is not limited to, such that the first recording head 31 and the second recording head 32 are arranged adjacent to each other in the transport direction of the recording medium R, and the second recording head 32 and the drying device 50 are arranged adjacent to each other.

[0042] The inkjet recording method according to the second embodiment includes, in this order, a first step of ejecting water-based ink from a first recording head 31 onto a recording medium R using the inkjet recording apparatus 110 according to the above-described embodiment; a second step of drying the water-based ink ejected onto the recording medium R in a drying device 50 while transporting the recording medium R; a third step of ejecting water-based ink from a second recording head 32 onto the recording medium R; and a fourth step of drying the water-based ink ejected onto the recording medium R in the drying device 50 while transporting the recording medium R, and the same drying device 50 is used in the second and fourth steps.

[0043] In this embodiment, as shown by arrow 1 in Figure 3, the conveying mechanism 10, with the recording medium R on its upper surface, moves horizontally on the base in the direction in which the first recording head 31 is disposed (to the right on the paper), and as it passes under the first recording head 31, water-based ink is ejected from the first recording head 31 onto the recording medium R (first step).

[0044] In this embodiment, although not particularly limited, the conveying mechanism 10 carrying the recording medium R onto which the water-based ink has been ejected from the first recording head 31 moves further in the direction where the second recording head 32 and the drying device 50 are arranged (to the right on the paper), passes under the second recording head 32 without the water-based ink being ejected from the second recording head 32, and passes under the drying device 50 without being dried by the drying device 50, and moves to the position of the conveying mechanism 10 shown by the dashed line in Figure 3.

[0045] After the first step, the recording medium R onto which the water-based ink has been ejected from the first recording head 31 is transported by the transport mechanism 10 and dried by the drying device 50 (second step). More specifically, the transport mechanism 10 moves to the position of the transport mechanism 10 indicated by the dashed line, and proceeds in the direction in which the drying device 50 is disposed (leftward on the paper), as indicated by arrow 2 in FIG. 3 . As the recording medium R passes under the drying device 50 while being transported, the water-based ink ejected from the first recording head 31 onto the recording medium R is dried. Note that in this embodiment, the transport direction in the first step (rightward on the paper) and the transport direction in the second step (leftward on the paper) are opposite. Therefore, from the first step to the second step, the transport mechanism 10 carrying the recording medium R passes back and forth under the drying device 50.

[0046] The first recording head 31 and the second recording head 32 are moistened by the water vapor of the aqueous ink dried in the second step. More specifically, water vapor is generated by drying the aqueous ink ejected from the first recording head 31 onto the recording medium R in the drying device 50, and since the water vapor tends to flow in the transport direction of the recording medium R by the transport mechanism 10 (to the left on the page), it tends to flow toward the second recording head 32 and the first recording head 31, and the first recording head 31 and the second recording head 32 are moistened by the water vapor. Therefore, even if some of the nozzles (not shown) of the first recording head 31 and the second recording head 32 are clogged due to drying, the clogging is cleared by the water vapor, and ejection defects can be suppressed.

[0047] After the second process, the transport mechanism 10 carrying the recording medium R, which has been dried to the extent that the water-based ink ejected from the first recording head 31 does not mix with the water-based ink ejected from the second recording head 32 or has been completely dried, moves further in the direction in which the first recording head 31 and the second recording head 32 are arranged (to the left on the paper), passes under the first recording head 31 and the second recording head 32 without ejecting the water-based ink from the first recording head 31 and the second recording head 32, and moves to the position of the transport mechanism 10 shown by the solid line in Figure 3, although this is not particularly limited.

[0048] In this embodiment, the transport mechanism 10 moves to the position indicated by the solid line in Figure 3, and then moves horizontally on the base B in the direction where the second recording head 32 is located (to the right on the paper), as indicated by arrow 3 in Figure 3. After passing under the first recording head 31 without ejecting water-based ink from the first recording head 31, the transport mechanism 10 passes under the second recording head 32, whereupon the water-based ink is ejected onto the recording medium R (third step).

[0049] In this embodiment, although not particularly limited, the conveying mechanism 10 carrying the recording medium R onto which the water-based ink has been ejected from the second recording head 32 moves further in the direction in which the drying device 50 is disposed (to the right on the paper), passes under the drying device 50 without being dried by the drying device 50, and moves to the position of the conveying mechanism 10 shown by the dashed line in Figure 3.

[0050] After the third step, the recording medium R onto which the aqueous ink has been ejected from the second recording head 32 is transported by the transport mechanism 10 and dried by the drying device 50 (fourth step). More specifically, the transport mechanism 10 moves to the position of the transport mechanism 10 indicated by the dashed line, and then proceeds in the direction of the drying device 50 (leftward on the paper) as indicated by arrow 4 in FIG. 3 . While transporting the recording medium R, the aqueous ink ejected from the second recording head 32 onto the recording medium R is dried by the drying device 50. If the aqueous ink from the first recording head 31 is not completely dried, the aqueous ink from the first recording head 31 may also be dried in the fourth step. Even if the aqueous ink from the first recording head 31 is completely dried, the aqueous ink may be further dried. In this embodiment, although not particularly limited, the transport direction in the third step (rightward on the paper) and the transport direction in the fourth step (leftward on the paper) are opposite.

[0051] The first recording head 31 and the second recording head 32 are moistened by the water vapor of the aqueous ink dried in the fourth step. More specifically, water vapor is generated by drying the aqueous ink ejected from the second recording head 32 with the drying device 50. This water vapor tends to flow in the direction of transport of the recording medium R by the transport mechanism 10 (to the right on the paper), and therefore tends to flow toward the second recording head 32 and the first recording head 31, moistening the first recording head 31 and the second recording head 32. Therefore, even if some of the nozzles (not shown) of the first recording head 31 and the second recording head 32 are clogged due to drying, the clogging is eliminated by the water vapor, and ejection defects can be suppressed.

[0052] With the above-described configuration, the recording medium R onto which the water-based ink has been ejected from the first recording head 31 and the second recording head 32 passes back and forth under the drying device 50. The recording heads 30 (31, 32) are moisturized by the water vapor generated by drying the water-based ink ejected onto the recording medium R in the drying device 50. In this embodiment, the recording medium R passes back and forth under the drying device 50 twice, but the number of times is not particularly limited.

[0053] In the inkjet recording method according to the second embodiment, the aqueous ink ejected from the first recording head 31 onto the recording medium R is dried by the drying device 50, and then the aqueous ink is ejected from the second recording head 32. However, if the aqueous ink ejected from the first recording head 31 and the aqueous ink ejected from the second recording head 32 are unlikely to cause color mixing, the aqueous ink may be ejected from the first recording head 31 onto the recording medium R, and then the aqueous ink may be ejected from the second recording head 32 onto the recording medium R, and then dried by the drying device 50. In this case, too, in order to keep the recording heads 30 (31, 32) moist, the transport mechanism 10 carrying the recording medium R onto which the aqueous inks have been ejected from the first recording head 31 and the second recording head 32 can move to the position of the transport mechanism 10 indicated by the dashed line in FIG. 3 and then transport the recording medium R leftward on the paper toward the position of the transport mechanism 10 indicated by the solid line, while the drying device 50 dries the recording medium R onto which the aqueous inks have been ejected. In this case, the recording medium R passes back and forth under the drying device 50 once, but the number of times is not particularly limited.

[0054] Furthermore, in the inkjet recording method according to the second embodiment, the water-based ink ejected from the first recording head 31 onto the recording medium R is dried in the drying device 50, and then the recording medium R is transported in the direction in which the first recording head 31 and the second recording head 32 are arranged (to the left on the paper), and the recording medium R passes under the second recording head 32 without the water-based ink being ejected from the second recording head 32; however, the water-based ink may be ejected from the second recording head 32 while passing under the second recording head 32 (third step). That is, the third step (arrow 3 in FIG. 3) may be in the same direction as the second step (arrow 2 in FIG. 3) and in the opposite direction to the first step (arrow 1 in FIG. 3). In this case, the transport mechanism 10 transports the recording medium R, on which the aqueous ink ejected from the first recording head 31 has been dried by the drying device 50 after the second process, to the left in FIG. 3 , while passing under the second recording head 32, and ejects aqueous ink from the second recording head 32 onto the recording medium R (third process). The transport mechanism 10 carrying the recording medium R onto which the aqueous ink ejected from the second recording head 32 has been ejected onto the recording medium R from the second recording head 32 (third process). The transport mechanism 10, carrying the recording medium R onto which the aqueous ink has been ejected from the second recording head 32, moves to the position of the transport mechanism 10 indicated by the solid line in FIG. 3 , and then moves in the opposite direction to the third process (toward the right in the drawing) to the position of the transport mechanism 10 indicated by the dashed line. The transport mechanism 10, which has moved to the position of the transport mechanism 10 indicated by the dashed line, then transports the recording medium R in the direction toward the drying device 50 (toward the left in the drawing), while passing under the drying device 50, whereby the aqueous ink is dried by the drying device 50 (fourth process), and the first recording head 31 and the second recording head 32 are moisturized by the generated water vapor. In this case, the recording medium R passes back and forth under the drying device 50 twice, but the number of times is not particularly limited.

[0055] The inkjet recording method according to the second embodiment has been described above. Next, an inkjet recording method according to a third embodiment will be described with reference to FIG. 4. FIG. 4 is a schematic diagram for explaining the inkjet recording method according to the third embodiment. As in the above-described case, for ease of explanation, the up-down direction is defined based on the normal installation direction of the inkjet recording apparatus 120. Specifically, the down direction is the side of the installation surface (base B) of the transport mechanism 10, i.e., the downward direction on the paper surface of FIG. 4, and the up direction is the upward direction on the paper surface of FIG. 4. Also, in FIG. 4, the thickness of the recording medium R is depicted as being thick for ease of explanation. Furthermore, components that are the same as or similar to those in the above-described embodiments will be denoted by the same reference numerals, and their description may be omitted.

[0056] [Inkjet recording method according to the third embodiment] As shown in FIG. 4, an inkjet recording apparatus 120 used in an inkjet recording method according to a third embodiment includes, but is not limited to, a transport mechanism 10 that transports a low-liquid-absorbent recording medium R, three recording heads 30 (a first recording head 31A, a first recording head 31B, and a second recording head 32) that eject water-based inks, and a drying device 50 that dries the water-based inks ejected onto the recording medium R. In this embodiment, but not limited to, the drying device 50 is disposed between the first recording head 31B and the second recording head 32. In this embodiment, but not limited to, either the first recording head 31 (31A, 31B) or the second recording head 32 can eject a non-white ink, and either the first recording head 31 (31A, 31B) or the second recording head 32 can eject a white ink. Alternatively, the first recording head 31 (31A, 31B) may eject non-white ink, and the second recording head 32 may eject white ink.

[0057] The inkjet recording method according to the third embodiment includes, in this order, a first step of ejecting water-based ink from the first recording head 31 (31A, 31B) onto the recording medium R using the inkjet recording apparatus 120 according to the above-described embodiment; a second step of drying the water-based ink ejected onto the recording medium R in a drying device 50 while transporting the recording medium R; a third step of ejecting water-based ink from the second recording head 32 onto the recording medium R; and a fourth step of drying the water-based ink ejected onto the recording medium R in the drying device 50 while transporting the recording medium R, and the same drying device 50 is used in the second and fourth steps.

[0058] In this embodiment, as shown by arrow 1 in FIG. 4, the transport mechanism 10, carrying the recording medium R on its upper surface, moves horizontally on the base in the direction (toward the right on the paper) where the first recording heads 31 (31A, 31B) are arranged. As the transport mechanism passes under the first recording heads 31A and 31B, water-based ink is ejected onto the recording medium R from each of the first recording heads 31 (31A, 31B). The water-based inks ejected from the first recording heads 31 (31A, 31B) can be inks that are less likely to cause color mixing, and can have recording patterns (recording positions) that are spaced apart on the recorded product. This configuration can suppress ink color mixing.

[0059] After the first step, the recording medium R onto which the aqueous ink has been ejected from the first recording head 31 (31A, 31B) is transported by the transport mechanism 10 and dried by the drying device 50 (second step). More specifically, in the second step, as shown by arrow 2 in FIG. 4 , the recording medium R onto which the aqueous ink has been ejected from the first recording head 31 (31A, 31B) is transported in the direction in which the drying device 50 and the second recording head 32 are disposed (toward the right on the paper), and the aqueous ink ejected from the first recording head 31 (31A, 31B) onto the recording medium R is dried by the drying device 50. Then, the second recording head 32 is moistened by the water vapor of the aqueous ink dried in the second step. More specifically, water vapor is generated by drying the water-based ink ejected from the first recording head 31 (31A, 31B) onto the recording medium R in the drying device 50, and since this water vapor tends to flow in the direction of transport of the recording medium R by the transport mechanism 10 (to the right on the page), it tends to flow toward the second recording head 32, and the second recording head 32 in particular is moisturized by the water vapor. Therefore, even if the second recording head 32 is exposed to the outside air for a long time and some of the nozzles (not shown) of the second recording head 32 are clogged due to drying, the clogging is eliminated by the water vapor, and ejection defects can be suppressed.

[0060] After the second process, the transport mechanism 10 carrying the recording medium R, which has been dried to the extent that the water-based ink ejected from the first recording head 31 (31A, 31B) does not mix with the water-based ink ejected from the second recording head 32 or has been completely dried, may, although not limited to, move further in the direction in which the second recording head 32 is positioned (to the right on the paper), pass under the second recording head 32 without the water-based ink being ejected from the second recording head 32, and move to the position of the transport mechanism 10 shown by the dashed line in Figure 4.

[0061] In this embodiment, the conveying mechanism 10 moves to the position indicated by the dashed line in Figure 4 and conveys the recording medium R in the opposite direction (towards the left on the paper) to the conveying direction in the first and second steps (third and fourth steps).

[0062] In this embodiment, the conveying mechanism 10 moves to the position indicated by the dashed line, and then moves horizontally on the base B in the direction in which the second recording head 32 is positioned (to the left of the paper), as indicated by arrow 3 in Figure 4, and as it passes under the second recording head 32, the water-based ink is ejected onto the recording medium R (third step).

[0063] After the third step, the recording medium R onto which the aqueous ink has been ejected from the second recording head 32 is transported by the transport mechanism 10 and dried by the drying device 50 (fourth step). More specifically, in the fourth step, as indicated by arrow 4 in FIG. 4 , the recording medium R onto which the aqueous ink has been ejected from the second recording head 32 is transported in the direction (leftward on the paper) toward which the drying device 50 and the first recording head 31 (31A, 31B) are disposed, and the aqueous ink ejected onto the recording medium R from the second recording head 32 is dried by the drying device 50. Note that if the aqueous ink from the first recording head 31 (31A, 31B) has not yet dried completely, the aqueous ink from the first recording head 31 (31A, 31B) may also be dried in the fourth step. Alternatively, even if the aqueous ink from the first recording head 31 (31A, 31B) has already dried completely, the aqueous ink may be further dried.

[0064] The first recording heads (31A, 31B) are moisturized by the water vapor of the aqueous ink dried in the fourth step. More specifically, water vapor is generated by drying the aqueous ink ejected from the second recording head 32 with the drying device 50. This water vapor tends to flow in the transport direction of the recording medium R by the transport mechanism 10 (to the left on the page), and therefore tends to flow toward the first recording heads 31 (31A, 31B), moisturizing the first recording heads 31 (31A, 31B). Therefore, even if some of the nozzles (not shown) of the first recording heads 31 (31A, 31B) are clogged due to drying, the clogging is eliminated by the water vapor, and ejection defects can be suppressed.

[0065] With the above-described configuration, the recording medium R onto which the water-based ink has been ejected from the first recording head 31 (31A, 31B) and the second recording head 32 passes back and forth under the drying device 50. The recording heads 30 (31A, 31B, 32) are moisturized by the water vapor generated by drying the water-based ink ejected onto the recording medium R in the drying device 50. In this embodiment, the recording medium R passes back and forth under the drying device 50 once, but the number of times is not particularly limited.

[0066] While the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various modifications and improvements can be made to the above embodiments. For example, in the above-described embodiment, a sheet is used as the recording medium R, but a long sheet or a rolled sheet can also be used.

[0067] As described above, the inkjet recording method of the present invention comprises, in this order: a first step of ejecting an aqueous ink from a first recording head 31 onto a recording medium R; a second step of drying the aqueous ink ejected onto the recording medium R in a drying device 50 while transporting the recording medium R; a third step of ejecting an aqueous ink from a second recording head 32 onto the recording medium R; and a fourth step of drying the aqueous ink ejected onto the recording medium R in a drying device 50 while transporting the recording medium R. By using the same drying device 50 in the second and fourth steps, it is possible to achieve both continuous ink ejection and suppression of color mixing. [Example]

[0068] In the following examples, comparative examples and production examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0069] (1) Water absorption amount of recording medium when the recording medium is in contact with pure water for 100 ms Using an automatic scanning absorbency meter (KM500win, manufactured by Kumagai Riki Kogyo Co., Ltd.), the amount of transferred water was measured at 23°C and a relative humidity of 50% for a contact time of 100 ms with pure water, and the amount of water absorbed in 100 ms was determined. The measurement conditions are as follows: <Measurement conditions> "Spiral Method" Contact Time (sec): 0.010 to 1.0 Pitch(mm):7 Length Per Sampling(degree):86.29 Start Radius(mm):20 End Radius(mm):60 Min Contact Time(ms):10 Max Contact Time(ms):1000 Sampling Pattern(1-50):50 Number of Sampling Points(>0):19 "Square Head" Slit Span(mm):1 Slit Width(mm):5

[0070] (2) Measurement of weight-average molecular weight of water-insoluble polymers The measurement was performed using a gel permeation chromatography method (GPC system manufactured by Tosoh Corporation (HLC-8120GPC), columns manufactured by Tosoh Corporation (TSK-GEL, α-M × 2), flow rate: 1 mL / min) with an eluent of N,N-dimethylformamide dissolved in phosphoric acid and lithium bromide to concentrations of 60 mmol / L and 50 mmol / L, respectively, and monodisperse polystyrene of known molecular weight as a standard substance.

[0071] (3) Measurement of solids concentration of pigment water dispersion 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm), and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatiles. The mixture was then left in the desiccator for a further 15 minutes, after which the mass was measured. The mass of the sample after devolatilization was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

[0072] (4) Measurement of the average particle size of pigment-containing polymer particles Measurements were performed by cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 accumulations. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 x 10 -3 The results were calculated in mass % (solid content equivalent).

[0073] (5) Measurement of viscosity of water-based ink The viscosity was measured at 32°C using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34' x R24, rotation speed 50 rpm).

[0074] (6) Static surface tension of water-based ink Using a surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., product name: CBVP-Z), a platinum plate was immersed in a cylindrical polyethylene container (diameter 3.6 cm x depth 1.2 cm) containing 5 g of water-based ink, and the static surface tension of the water-based ink was measured at 20°C.

[0075] (7) Measurement of pH of water-based ink The pH of the water-based ink at 25°C was measured using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

[0076] <Production of water-based ink> Production Example 1 (Synthesis of water-insoluble polymer) 16 parts of methacrylic acid (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 30 parts of styrene macromonomer "AS-6S" (manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solids content 50%), and 25 parts of methoxypolyethylene glycol methacrylate "BLEMMER PME-200" (manufactured by NOF Corporation) were mixed to prepare 115 parts of a monomer mixture. In a reaction vessel, 18 parts of methyl ethyl ketone, 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed and mixed, and the atmosphere was thoroughly purged with nitrogen gas. Separately, the remaining 90% (103.5 parts) of the monomer mixture was mixed with 0.27 parts of the chain transfer agent, 42 parts of methyl ethyl ketone, and 3 parts of the polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile) "V-65" (Fujifilm Wako Pure Chemical Industries, Ltd., reagent), and placed in a dropping funnel. The mixture in the reaction vessel was heated to 75°C under a nitrogen atmosphere while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution of 3 parts of the polymerization initiator in 5 parts of methyl ethyl ketone was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. 50 parts of methyl ethyl ketone was then added to obtain a solution of a water-insoluble polymer (weight average molecular weight: 50,000). The solids concentration of the water-insoluble polymer solution was 45% by mass.

[0077] Production Example 2 (Production of aqueous dispersion of black pigment-containing polymer particles) 95.2 parts of the water-insoluble polymer solution obtained in Production Example 1 was diluted with 53.9 parts of methyl ethyl ketone, and 15.0 parts of 5N aqueous sodium hydroxide and 0.5 parts of 25% aqueous ammonia were added as neutralizing agents, along with 341.3 parts of deionized water. 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) were then added as a carbon black pigment to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The resulting pigment mixture was mixed using a disperser blade at 7000 rpm and 20°C for 1 hour. The resulting dispersion was dispersed 15 times using a Microfluidizer "High-Pressure Homogenizer M-140K" (manufactured by Microfluidics) at a pressure of 180 MPa. The resulting pigment-containing polymer particle dispersion was subjected to vacuum decompression at 60°C to remove methyl ethyl ketone, and then a portion of the water was removed. The resulting dispersion was centrifuged. The liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of pigment-containing polymer particles. The solids concentration was 25% by mass. To 100 parts of the resulting aqueous dispersion of pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX321L) and 15.23 parts of deionized water were added, and the mixture was heated at 70°C for 3 hours with stirring to perform a crosslinking treatment. After cooling to room temperature, the liquid layer was filtered through a Minisart syringe filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of black pigment-containing polymer particles (solids concentration: 22.0% by mass). The average particle size of the black pigment-containing polymer particles was 100 nm. The composition and physical properties are shown in Table 1.

[0078] Production Example 3 (Production of aqueous dispersion of cyan pigment-containing polymer particles) In Production Example 2, the black pigment was changed to a cyan pigment (manufactured by DIC Corporation, PB15:3), and an aqueous dispersion of cyan pigment-containing polymer particles (solid content concentration: 22.0% by mass) was obtained under the conditions shown in Table 1. The composition and physical properties are shown in Table 1.

[0079] Production Example 4 (Production of aqueous dispersion of white pigment-containing polymer particles) A 2-L plastic container was charged with a mixture of 6 g of polyacrylic acid (PAA; Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight 5,000) as a polymer dispersant, 4.2 g of 5N sodium hydroxide solution, and 4.8 g of deionized water (polymer neutralization degree 50 mol%). 300 g of titanium dioxide: CI Pigment White 6 (PW6; Ishihara Sangyo Kaisha, Ltd., product name: CR-80, rutile type, Al·Si treated, average particle size: 0.25 μm), 255 g of water, and 1,000 g of zirconia beads were added, and the mixture was dispersed for 8 hours using a benchtop pot mill stand (AS ONE Corporation). The zirconia beads were removed using a metal mesh, and the solid concentration and pH were adjusted with deionized water and 5N sodium hydroxide solution to obtain an aqueous dispersion of white pigment-containing polymer particles with an average particle size of 328 nm (solid concentration: 40.0%, pigment introduction rate: 98%, pH: 9.0). The composition and physical properties are shown in Table 1.

[0080] [Table 1]

[0081] Manufacturing Example 5 (Manufacturing Black Ink) A mixture of 46.3 parts (pigment content: 7.0% by weight) of the aqueous dispersion of black pigment-containing polymer particles obtained in Production Example 2 (solid content: 22.0% by weight), 24.0 parts of propylene glycol, 3.0 parts of diethylene glycol monoisobutyl ether, 0.3 parts of a silicone surfactant (Shin-Etsu Chemical Co., Ltd., product name: SAG-005), and 0.3 parts of an acetylene surfactant (Nissin Chemical Industry Co., Ltd., Surfynol 104PG50, active ingredient: 50% by weight) was added, and deionized water was added to bring the total ink volume to 100 parts. The mixture was filtered through a MiniSart syringe filter (acetylcellulose membrane filter: 5 μm opening diameter, Sartorius) to obtain a black ink as an aqueous ink. The composition and physical properties are shown in Table 2.

[0082] Production Example 6 (Production of cyan ink) A cyan ink was produced in the same manner as in Production Example 5, except that the aqueous dispersion of pigment-containing polymer particles was changed to the aqueous dispersion of cyan pigment-containing polymer obtained in Production Example 3. The composition, physical properties, etc. of the ink are shown in Table 2.

[0083] Production Example 7 (Production of White Ink) A white ink was produced in the same manner as in Production Example 5, except that the aqueous dispersion of pigment-containing polymer particles was changed to the aqueous dispersion of white pigment-containing polymer particles obtained in Production Example 4 and the amounts of each component were changed as shown in Table 2. The composition, physical properties, etc. of the ink are shown in Table 2.

[0084] [Table 2]

[0085] <Examples and Comparative Examples> The recording medium was a corona-treated PET (manufactured by Futamura Chemical Co., Ltd., Taiko FE2001, polyester film, thickness 12 μm, water absorption of the recording medium when the recording medium was in contact with pure water for 100 ms) was 0 g / m 2 ) and the water-based ink obtained above were used to carry out the various evaluations using a print evaluation device with the following settings. (Common setting conditions for print evaluation devices) The temperature of an underheater (manufactured by Kawai Electric Manufacturing Co., Ltd.) was set to 40°C, and the surface temperature of the recording medium was set to 50°C.

[0086] Example 1 The print evaluation device used in this example is the same as the inkjet recording device 100 shown in FIG. In a single-pass printing evaluation system (Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and a hot air blower as a dryer, the first inkjet head was filled with black ink and the second inkjet head with white ink in a temperature environment of 25±1°C and relative humidity of 30±5%. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform as a transport mechanism to heat the recording medium. The recording medium was fixed on the underheater with glue so that its longitudinal direction was aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 5, with two solid colors overlapping perpendicularly. In Figure 5, the solid image in the horizontal direction of the paper was printed with black ink, and the solid image in the vertical direction of the paper was printed with white ink. Explaining with reference to Figure 1, a solid image was printed using black ink while the recording medium R was being transported in the direction where the first inkjet head 31 was disposed (first step). Then, while the recording medium R was being further transported, the black ink solid image was dried using a hot air blower as the drying device 50 (second step). Next, while the recording medium R was being further transported in the direction where the second inkjet head 32 was disposed, a solid image was printed using white ink (third step), and the white ink solid image was further dried using a hot air drying device as the drying device 50 (fourth step), thereby obtaining a recorded product.

[0087] Example 2 The print evaluation device used in this example is the same as the inkjet recording device 110 shown in FIG. In a single-pass printing evaluation system (Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and a hot air blower as a dryer, the first inkjet head was filled with black ink and the second inkjet head with white ink in a temperature environment of 25±1°C and relative humidity of 30±5%. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform as a transport mechanism to heat the recording medium. The recording medium was fixed on the underheater with glue so that its longitudinal direction was aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 5 so that the two colors of the two-color solid image overlapped perpendicularly. Explaining this with reference to Fig. 3, while the recording medium R was being transported in the direction where the first inkjet head 31 was disposed, a solid image was printed using black ink (first step), and the recording medium R was then passed underneath the first inkjet head 31 without being printed on by the second inkjet head 32 or dried by a hot air blower serving as the drying device 50, and then moved to the position of the transport mechanism 10 shown by the dashed line in Fig. 3. Thereafter, while the recording medium R was being transported in the direction where the hot air drying device serving as the drying device 50 was disposed (to the left in Fig. 3), the black ink solid image was dried by the hot air blower serving as the drying device 50 (second step). Next, the recording medium R was returned to its initial position (the position of the transport mechanism 10 shown by the solid line in Fig. 3), and then while being transported in the direction where the second inkjet head 32 was disposed (to the right in Fig. 3), a solid image was printed using white ink (third step), and the recording medium R was then transported in the direction where the second inkjet head 32 was disposed (to the right in Fig. 3), without being dried by a hot air blower serving as the drying device 50, and then moved to the position of the transport mechanism 10 shown by the dashed line in Fig. 3. Thereafter, the recording medium R was transported in the direction in which the hot air drying device serving as the drying device 50 was disposed (to the left of the paper in Figure 3), and the white ink solid image was dried by the hot air drying device serving as the drying device 50 (fourth step), thereby obtaining a recorded matter.

[0088] Example 3 The print evaluation device used in this example is the same as the inkjet recording device 120 shown in FIG. In a single-pass printing evaluation device (manufactured by Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and a hot air blower as a dryer, the first inkjet head (the first inkjet head designated by reference numeral 31A in Figure 4) was filled with black ink, the second inkjet head (the first inkjet head designated by reference numeral 31B in Figure 4) with cyan ink, and the second inkjet head with white ink, in an environment of 25±1°C and 30±5% relative humidity. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform as a transport mechanism to heat the recording medium, and the recording medium was fixed on the underheater with glue so that its longitudinal direction was aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 6, with two of the three solid colors overlapping perpendicularly. In Figure 6, the dark solid image in the horizontal direction of the paper is made with black ink, the light solid image in the horizontal direction of the paper is made with cyan ink, and the solid image in the vertical direction of the paper is made with white ink. Explaining with reference to Fig. 4, a solid image was printed using black ink and cyan ink while the recording medium R was being transported in the direction where the first inkjet heads 31A and 31B were disposed (first step). Then, while the recording medium R was being further transported, the black ink solid image and the cyan ink solid image were dried using a hot air blower as the drying device 50 (second step), and the transport table was moved to the position of the transport mechanism 10 shown by the dashed line in Fig. 4. Next, a solid image was printed using white ink while the recording medium R was being transported in the direction where the second inkjet head 32 was disposed (third step), and the white ink solid image was further dried using a hot air drying device as the drying device 50 (fourth step), thereby obtaining a recorded product.

[0089] Comparative Example 1 The print evaluation device used in this comparative example is the same as the inkjet recording device 210 shown in FIG. In a temperature environment of 25±1°C and relative humidity of 30±5%, a single-pass printing evaluation device (Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and two hot air blowers was loaded. The first inkjet head was filled with black ink, and the second inkjet head with white ink. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform to heat the recording medium. The recording medium was glued onto the underheater with its longitudinal axis aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 5 so that the two colors of the two-color solid image overlapped perpendicularly. Explaining with reference to Fig. 7, a solid image was printed using black ink while the recording medium R was being transported in the direction where the first inkjet head 31 was disposed (first step). Thereafter, while the recording medium R was being further transported, the black ink solid image was dried using a hot air blower as the drying mechanism 50 (second step), and while the recording medium R was being further transported in the direction where the second inkjet head 32 was disposed, a solid image was printed using white ink (third step), and while the recording medium R was being further transported, the white ink solid image was dried using a hot air dryer as the drying mechanism 50 (fourth step), thereby obtaining a recorded product.

[0090] Comparative Example 2 The print evaluation device used in this comparative example is the same as the inkjet recording device 200 shown in FIG. In a single-pass printing evaluation system (Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and a hot air blower as a dryer, the first inkjet head was filled with black ink and the second inkjet head with white ink in a temperature environment of 25±1°C and relative humidity of 30±5%. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform as a transport mechanism to heat the recording medium. The recording medium was fixed on the underheater with glue so that its longitudinal direction was aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 5 so that the two colors of the two-color solid image overlapped perpendicularly. Explaining with reference to FIG. 2, a solid image was printed using black ink while the recording medium R was transported in the direction where the first inkjet head 31 was disposed (first step). Next, while the recording medium R was further transported, the black ink solid image was dried using a hot air blower as the drying device 50 (second step). While the recording medium R was further transported in the direction where the second inkjet head 32 was disposed, a solid image was printed using white ink (third step), thereby obtaining a recorded product. Note that drying was not performed in the fourth step.

[0091] Comparative Example 3 The print evaluation device used in this comparative example is the same as the inkjet recording device 100 shown in FIG. In a temperature environment of 25±1°C and relative humidity of 30±5%, a single-pass printing evaluation device (Kao Corporation) equipped with an inkjet head (Kyocera Corporation, "KJ4B-1200," piezo type) and a hot air blower as a dryer was loaded with black ink in the first inkjet head and white ink in the second inkjet head. Using a printing software program, the droplet volume was adjusted to 3 pL and the resolution to 1200 dpi by changing the piezoelectric element drive voltage waveform of the head. An A4-sized underheater was fixed on the transport platform as a transport mechanism to heat the recording medium. The recording medium was fixed on the underheater with glue so that its longitudinal direction was aligned with the transport direction. The recording medium transport speed was 30 m / min. The image was printed in the pattern shown in Figure 5 so that the two colors of the two-color solid image overlapped perpendicularly. Referring to FIG. 1, a solid image was printed using black ink while the recording medium R was being conveyed in the direction where the first inkjet head 31 was disposed (first step). The recording medium R was further conveyed, and the conveying table serving as the conveying mechanism 10 was stopped for 30 seconds under the hot air blowing device serving as the drying device 50 to dry the black ink solid image (second step). The conveying table was then moved to the position of the conveying mechanism 10 indicated by the dashed line in FIG. 1. Next, a solid image was printed using white ink while the recording medium R was being conveyed in the direction where the second inkjet head 32 was disposed (third step). The recording medium R was further conveyed, and the conveying table serving as the conveying mechanism 10 was stopped for 30 seconds under the hot air blowing device serving as the drying device 50 to dry the white ink solid image (fourth step), resulting in a recorded product.

[0092] <Evaluation of ink color mixing in recorded materials> In the areas of the resulting recorded material where solid print images of different colors intersect at right angles, where color mixing may occur, the width of the area where one color encroaches on the solid image of the other color that intersects at right angles was measured. The average values ​​obtained for each color combination were calculated, and the degree of color mixing was compared using these average values. Evaluation was based on the following criteria. A: The average protrusion width is less than 150 μm, and almost no color mixing is observed. B: The average protrusion width is 150 μm or more and less than 200 μm, and color mixing is visible, but does not pose a problem in practical use. C: The average protrusion width is 200 μm or more, color mixing is visible, and there is a problem in practical use.

[0093] <Evaluation of continuous ejection> In Examples 1 to 3 and Comparative Examples 1 to 3, printing was performed continuously on 500 sheets of recording medium to obtain a recorded product. After that, a print check pattern was printed to determine whether ejection had been performed from all nozzles (2656 nozzles), and the number of missing nozzles was counted to evaluate the continuous ejection property according to the following evaluation criteria. 3: No missing nozzles 2: Missing nozzles 1-9 1: 10 or more nozzle chips

[0094] The above evaluation results of the recorded materials of the Examples and Comparative Examples are shown in Table 3.

[0095] [Table 3]

[0096] As shown in Table 3, the inkjet recording method of the present invention can achieve both continuous ink ejection and suppression of color mixing. [Explanation of symbols]

[0097] 1: conveying direction of the first process, 2: conveying direction of the second process, 3: conveying direction of the third process, 4: conveying direction of the fourth process, 100: Inkjet recording device, 10: conveying mechanism, 30: recording head (31 (31A, 31B): first recording head, 32: second recording head) 50: Drying equipment, B: base, R: recording medium

Claims

1. a conveying mechanism for conveying a low-liquid-absorbent recording medium; two or more recording heads that eject water-based ink; a drying device that dries the water-based ink ejected onto the recording medium; An inkjet recording method for recording on the recording medium using an inkjet recording apparatus comprising: a first step of ejecting a water-based ink from a first recording head onto the recording medium; a second step of drying the water-based ink ejected onto the recording medium in the drying device while conveying the recording medium; a third step of ejecting the water-based ink from a second recording head onto the recording medium; a fourth step of drying the water-based ink ejected onto the recording medium in the drying device while conveying the recording medium; in that order, An inkjet recording method, wherein the same drying device is used in the second step and the fourth step.

2. The inkjet recording method according to claim 1 , wherein the recording medium onto which the water-based ink has been ejected passes back and forth under the drying device.

3. 3. The inkjet recording method according to claim 1, wherein the recording head is moistened by water vapor generated by drying the water-based ink ejected onto the recording medium in the drying device.

4. 3. The inkjet recording method according to claim 1, wherein the transport mechanism is capable of horizontally reciprocating the recording medium, and the transport direction in the first step and the second step is opposite to the transport direction in the third step and the fourth step.

5. 3. The inkjet recording method according to claim 1, wherein the second recording head is moistened by the water vapor of the water-based ink dried in the second step, and the first recording head is moistened by the water vapor of the water-based ink dried in the fourth step.

6. The inkjet recording method according to claim 1 or 2, wherein the water content in the water-based ink is 60% by mass or more.

7. 3. The inkjet recording method according to claim 1, wherein either the first recording head or the second recording head ejects a non-white ink, and either the first recording head or the second recording head ejects a white ink.

8. 3. The inkjet recording method according to claim 1, wherein the recording speed of the recording medium is 5 m / min or more and 100 m / min or less in terms of a conveying speed of the recording medium.

9. 3. The inkjet recording method according to claim 1, wherein the drying device is a hot air dryer, a heater dryer, or an IR dryer.

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