Water-based inkjet inks and printed matter

Abstract

To provide an aqueous inkjet ink that yields a printed material with high print quality even on low-permeable or impermeable substrates, while also exhibiting superior discharge stability regardless of usage conditions.SOLUTION: An aqueous inkjet ink contains a coloring agent, a water-soluble organic solvent, a surfactant, and water, where the water-soluble organic solvent includes a diol having 2-5 carbon atoms and hexylene glycol, and the surfactant includes an acetylenediol having a HLB value of 10 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] An embodiment of the present invention relates to an aqueous inkjet ink and a printed matter formed using the aqueous inkjet ink. [Background technology]

[0002] 2. Description of the Related Art With the increasing need for short-run printing and reduced printing costs, digital printing methods that do not require plate making are rapidly becoming more and more popular.

[0003] An example of the digital printing method is the inkjet printing method. In the inkjet printing method, droplets of ink are ejected from fine nozzles and applied to a printing substrate (also referred to simply as "substrate" in this disclosure) to print an image and / or characters on the printing substrate. In this disclosure, the printing substrate and the image and / or characters formed on the printing substrate by printing ink are collectively referred to as "printed matter." The above "image" also includes seamless images such as solid images and checkered images. The inkjet printing method has the characteristics that the printing device is easy to operate and produces little noise during printing. Therefore, among the digital printing methods, there is a high demand for printing devices (inkjet printers) that employ the inkjet printing method.

[0004] Inks used in inkjet printing methods (referred to as "inkjet ink" in this disclosure) are classified into solvent-based, water-based, ultraviolet (UV) curing, etc., depending on their composition. Meanwhile, in recent years, there has been an accelerating movement to regulate the use of raw materials that are harmful to humans and the environment. Accordingly, there has been an increasing demand for water-based inkjet inks (also referred to simply as "water-based inkjet inks" in this disclosure) rather than the solvent-based inkjet inks and UV-curing inkjet inks that use the above-mentioned raw materials.

[0005] In recent years, with the improvement of inkjet head performance, the use of inkjet printing has expanded not only for consumer applications but also for industrial printing applications. In particular, in the commercial printing market and the packaging (label and package) printing market, there is active consideration of replacing plate-based printing methods such as offset printing and gravure printing with inkjet printing.

[0006] However, in the past, when printing aqueous inkjet inks on poorly permeable substrates such as coated paper and art paper, and non-permeable substrates such as films, it was difficult to obtain printed matter having the same print quality as that obtained by plate printing. Specifically, when printing by the inkjet printing method, a phenomenon called "bleeding" (mixed color bleeding) in which aqueous inkjet inks of different colors are mixed together is likely to occur. In addition, printed matter using one type of aqueous inkjet ink is likely to have a phenomenon called "beading" (unevenness in shade), in which the shades of colors appear as beads. Furthermore, solid printed matter (printed matter with a printing rate of 100%) produced using one type of aqueous inkjet ink is likely to have a phenomenon called "whiteout," in which the aqueous inkjet ink does not adhere to the printed substrate in some places. These phenomena are due to the fact that water, which is the main solvent of aqueous inkjet ink, has a particularly high surface tension, and therefore the wettability of the aqueous inkjet ink to the substrate, particularly the wettability on the order of microseconds (μs), is poor.

[0007] In general, hydrophobic organic solvents and surfactants are often used to improve wettability to a substrate. However, these hydrophobic materials have poor solubility in water. Therefore, when such hydrophobic materials are used, there is a problem of nozzle missing, which is thought to be caused by instability at the gas-liquid interface of the aqueous inkjet ink or the generation of bubbles. Here, the above-mentioned nozzle missing refers to a phenomenon in which the aqueous inkjet ink is not ejected from the nozzle. Thus, for aqueous inkjet inks used for printing on poorly permeable substrates and non-permeable substrates, it has been necessary to simultaneously solve two problems: increasing wettability to the substrate on the order of μs, and being able to eject the ink from the inkjet head without nozzle missing even after a long printing pause or during continuous printing (having good ejection stability regardless of the conditions of use). However, an aqueous inkjet ink that can simultaneously and suitably solve all of these problems has not been found so far.

[0008] In the present disclosure, the ejection stability after a long period of printing pause is also referred to as “standby ejection property.” Furthermore, the ejection stability during continuous printing is also referred to as “continuous ejection property.”

[0009] For example, Patent Document 1 discloses an ink that contains water as the main solvent but also three or more organic solvents with different water-octanol partition coefficients, and explains that the use of this ink shows good wettability to non-absorbent media (non-permeable substrates). Patent Document 2 discloses an inkjet ink that contains three or more compounds (organic solvents) each having a specific structure and specifies the content ratio of these compounds, and explains that the use of this inkjet ink makes it possible to achieve both wettability and drying properties on non-absorbent media (non-permeable substrates). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2020-125382 A [Patent Document 2] International Publication No. 2022 / 224786 Summary of the Invention [Problem to be solved by the invention]

[0011] However, both of the inks in Patent Documents 1 and 2 are insufficient in terms of wettability on the order of μs. Furthermore, there is a problem in that nozzle missing occurs due to instability of the gas-liquid interface at the nozzle end face of the inkjet head, and all of the above-mentioned problems have not yet been solved at a high level.

[0012] Therefore, an object of one embodiment of the present invention is to provide an aqueous inkjet ink that can provide printed matter with excellent print quality even when printed on poorly permeable substrates and non-permeable substrates, and that further has excellent ejection stability regardless of the conditions of use. [Means for solving the problem]

[0013] As a result of intensive research, the present inventors have found that an aqueous inkjet ink having the following composition can simultaneously solve all of the above-mentioned problems to a high degree.

[0014] That is, one embodiment of the present invention relates to an aqueous inkjet ink. Another embodiment of the present invention relates to a printed matter obtained using the aqueous inkjet ink. More specifically, the embodiments of the present invention include the following. However, the present invention is not limited to the following embodiments and includes various embodiments. [1] A composition comprising a colorant, a water-soluble organic solvent, a surfactant, and water, the water-soluble organic solvent contains a diol having 2 to 5 carbon atoms and hexylene glycol, The aqueous inkjet ink, wherein the surfactant comprises an acetylenic diol having an HLB value of 10 or less. [2] The aqueous inkjet ink according to the above [1], wherein the content of the hexylene glycol is 0.1 to 30 mass % based on the total amount of the aqueous inkjet ink. [3] The aqueous inkjet ink according to the above [1] or [2], wherein the content of the acetylenic diols having an HLB value of 10 or less is 0.1 to 2.0 mass % based on the total amount of the aqueous inkjet ink. [4] A printed matter obtained by printing with the aqueous inkjet ink according to any one of [1] to [3] above.

[0015] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-089968, filed on May 31, 2023, the entire disclosure of which is incorporated herein by reference. Effect of the Invention

[0016] According to the aqueous inkjet ink of one embodiment of the present invention, printed matter with excellent print quality can be obtained even when printing on poorly permeable substrates and non-permeable substrates, and further, excellent ejection stability can be obtained regardless of the usage conditions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An aqueous inkjet ink according to one embodiment of the present invention (hereinafter, simply referred to as "aqueous inkjet ink of this embodiment" or "ink") will be described below. Note that the present invention is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present invention.

[0018] As described above, the aqueous inkjet ink of the present embodiment having the above-mentioned configuration has excellent wettability to a substrate on the order of μs, so that even when printing on a poorly permeable substrate or a non-permeable substrate, a printed matter with excellent print quality can be obtained. In addition, the inkjet ink has excellent ejection stability even after a long printing pause or during continuous printing. Although the mechanism is not clear, the present inventors speculate as follows. However, the present invention is not limited by the following speculation.

[0019] In general, acetylenic diols are known as surfactants that do not easily foam, and they rarely generate bubbles, which is one of the causes of nozzle clogging. In addition, due to their very stable molecular structure and small molecular weight, they are easily oriented at the interface with the substrate even for a short period of time, such as the order of μs. Among them, acetylenic diols with an HLB value of 10 or less have good wettability with substrates such as PP (polypropylene) films, which have very low interfacial free energy, and are expected to improve print image quality. On the other hand, acetylenic diols with the above HLB value of 10 or less have poor solubility in water. Therefore, when acetylenic diols with the above HLB value of 10 or less are used, there was a problem in the past that the gas-liquid interface at the nozzle end face of the inkjet head becomes unstable, and nozzle clogging is likely to occur. As a result of intensive research by the present inventors, it was found that when diols having 2 to 5 carbon atoms and hexylene glycol are used as the water-soluble organic solvent, acetylenic diols having an HLB value of 10 or less are not destabilized at the gas-liquid interface, and nozzle dropping can be suppressed. Hexylene glycol (2-methyl-2,4-pentanediol) has multiple branched alkyl groups, and is considered to have a high affinity with the above-mentioned acetylenic diols in terms of structural similarity. In addition, since hexylene glycol is a diol, it naturally has a high affinity with diols having 2 to 5 carbon atoms. As a result, it is presumed that hexylene glycol and diols having 2 to 5 carbon atoms protect acetylenic diols having an HLB value of 10 or less, thereby suppressing the above-mentioned destabilization. In addition, since these water-soluble organic solvents have low molecular weights and the above-mentioned high affinity, they can be rapidly oriented at the interface with the substrate together with the acetylene diols having an HLB value of 10 or less, and can achieve wetting and spreading on the order of μs. As a result, printed matter having print quality equivalent to that of plate-based printing can be obtained regardless of the printing substrate and printing speed.

[0020] As described above, the aqueous inkjet ink having the configuration of this embodiment can solve all of the above-mentioned problems to a high degree.

[0021] Each component constituting the aqueous inkjet ink according to one embodiment of the present invention will be described in detail below.

[0022] <Water-soluble organic solvent> The aqueous inkjet ink of this embodiment contains a water-soluble organic solvent. As described above, the water-soluble organic solvent contains a diol having 2 to 5 carbon atoms and hexylene glycol.

[0023] (Diols with 2 to 5 carbon atoms) Examples of the diols having 2 to 5 carbon atoms include alkanediols having 2 to 5 carbon atoms, such as 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, and 3-methyl-1,3-butanediol, as well as polyoxyalkylene diols having 2 to 5 carbon atoms, such as diethylene glycol and hydroxyethoxypropanol. These compounds may be used alone or in combination of two or more. Among them, it is preferable to use alkanediols having 2 to 5 carbon atoms as the diols having 2 to 5 carbon atoms, because the above-mentioned mechanism functions effectively and the ejection stability is good even after a long period of printing suspension. More preferably, one or more selected from the group consisting of 1,2-ethanediol, 1,2-propanediol, and 1,3-butanediol can be used. In addition, it is particularly preferable to use 1,2-propanediol, because the ejection stability is good even during continuous printing.

[0024] In order to achieve excellent ejection stability regardless of the conditions of use, the content of the diols having 2 to 5 carbon atoms is preferably from 0.5 to 30 mass%, more preferably from 2 to 25 mass%, and particularly preferably from 6 to 22 mass%, relative to the total amount of the aqueous inkjet ink.

[0025] (Hexylene glycol) In order to obtain good ejection stability and good print quality of the printed matter, the content of hexylene glycol in the aqueous inkjet ink of this embodiment is preferably 0.1 to 30 mass %, more preferably 0.6 to 24 mass %, and particularly preferably 1 to 20 mass %, relative to the total amount of the aqueous inkjet ink.

[0026] The content of the hexylene glycol is preferably 3 to 70% by mass, more preferably 5 to 50% by mass, and particularly preferably 10 to 30% by mass, based on the total amount of the water-soluble organic solvent contained in the aqueous inkjet ink. By setting the content of hexylene glycol to the above range based on the total amount of the water-soluble organic solvent, it becomes easy to stabilize the acetylenic diols having an HLB value of 10 or less at the gas-liquid interface when used in combination with the diols having 2 to 5 carbon atoms, and good ejection stability can be obtained, for example, even after a long period of printing suspension. In addition, the orientation of the acetylenic diols at the interface with the substrate is optimized, and the wettability to the substrate on the order of μs is also improved.

[0027] The ratio of the content of the diols having 2 to 5 carbon atoms to the content of the hexylene glycol contained in the aqueous inkjet ink (content of diols having 2 to 5 carbon atoms / content of hexylene glycol) is preferably 0.1 to 20. The content ratio is more preferably 0.15 to 8, and particularly preferably 0.2 to 5. By setting the content ratio within the above range, when used in combination with the diols having 2 to 5 carbon atoms, the acetylenic diols having an HLB value of 10 or less can be stabilized at the gas-liquid interface, and good ejection stability can be obtained, for example, even during continuous printing at high speed. In addition, the orientation of the acetylenic diols is optimized, and the wettability to the substrate on the order of μs is also improved.

[0028] In order to achieve both ejection stability and print quality, it is preferable to further consider the drying behavior of the water-soluble organic solvent. Specifically, the ratio (VE2 / VE1) of the energy (VE1) required to evaporate the diol having 2 to 5 carbon atoms to the energy (VE2) required to evaporate the hexylene glycol is preferably 0.05 to 1.5, more preferably 0.1 to 1.1, and particularly preferably 0.2 to 0.9. When hexylene glycol and the diol having 2 to 5 carbon atoms are used in combination so that the ratio of the amount of energy falls within the above range, it is easy to obtain both excellent ejection stability and a printed matter with an excellent printed image. Although the detailed mechanism is unclear, by adjusting the ratio of the amount of energy, it is possible to prevent the water-soluble organic solvent from volatilizing before the effects of affinity with acetylene diols having an HLB value of 10 or less, wetting and spreading on the printing substrate, etc. are achieved. As a result, it is possible to easily improve both the ejection stability and the print image quality of the printed matter, regardless of the type of printing substrate, printing conditions, and printing speed.

[0029] The energy required to evaporate the water-soluble organic solvent can be calculated by the following formula (1-1).

[0030] Formula (1-1): VE = (BP-25) x MP x SH

[0031] In the above formula (1-1), VE is the energy (cal) required to evaporate the target water-soluble organic solvent contained in the aqueous inkjet ink. BP is the boiling point (° C.) of the water-soluble organic solvent at 1 atmospheric pressure. MP is the content (mass %) of the water-soluble organic solvent in the water-based inkjet ink. SH is the specific heat (cal / g·°C) of the above water-soluble organic solvent at 25°C. The above specific heat can be calculated by the Misnar estimation method described later.

[0032] The Missenard estimation method uses the sum of values ​​determined according to the molecular structure and temperature of the target compound as the specific heat (cal / mol·°C) at the above temperature. However, since the unit of specific heat calculated by the Missenard estimation method is "cal / mol·°C", the specific heat value of the target compound obtained by the Missenard estimation method is divided by the molecular weight of the compound in question in the above formula (1-1). An example of values ​​at 25°C determined according to the molecular structure as described above is shown in Table 1 below.

[0033] [Table 1]

[0034] (Other water-soluble organic solvents) The aqueous inkjet ink of this embodiment may contain water-soluble organic solvents other than the above-mentioned diols having 2 to 5 carbon atoms and the above-mentioned hexylene glycol (referred to as "other water-soluble organic solvents" in the present disclosure).

[0035] In the aqueous inkjet ink of this embodiment, the other water-soluble organic solvent may be, for example, Alkanediols (excluding those having 2 to 5 carbon atoms and hexylene glycol), Alkanetriols (having 3 to 6 carbon atoms), Polyoxyalkylene diols (excluding those in which the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, the number of said oxyalkylene groups is 2 to 4, and the number of carbon atoms is 2 to 5), (Poly)oxyalkylene monoalkyl ethers (wherein the oxyalkylene group is an oxyethylene group or an oxypropylene group, the number of said oxyalkylene groups is 1 to 4, and the number of carbon atoms in the terminal alkyl group is 1 to 4, or the oxyalkylene group is an oxybutylene group or an oxypentylene group, the number of said oxyalkylene group is 1, and the number of carbon atoms in the terminal alkyl group is 1 to 4), (Poly)oxyethylene dialkyl ethers (wherein the number of oxyalkylene groups is 1 to 4 and the number of carbon atoms in each of the terminal alkyl groups is 1 to 4), Lactams (wherein the number of atoms constituting the lactam ring is 5 to 7. In addition, an alkyl group having 1 to 2 carbon atoms, a hydroxyalkyl group having 1 to 2 carbon atoms, or a vinyl group may be bonded to the nitrogen atom and / or carbon atom constituting the lactam ring), Alkanolamines (having one amino group, one to three hydroxyl groups, and three to nine carbon atoms) and the like can be used. These other water-soluble organic solvents may be used alone or in combination of two or more. In the present disclosure, the term "(poly)oxyalkylene" refers to oxyalkylene and polyoxyalkylene.

[0036] In some embodiments, it is preferable to use a water-soluble organic solvent having a static surface tension of 29 to 50 mN / m at 25° C. as the other water-soluble organic solvent contained in the aqueous inkjet ink. By using a water-soluble organic solvent having the above surface tension, it is possible to maintain an appropriate surface tension for ejection as an inkjet ink. In addition, good ejection stability can be easily obtained, for example, even after a long period of printing suspension. Furthermore, from the viewpoint of improving both the print quality and standby ejection properties of the printed matter, it is also preferable to use a water-soluble organic solvent having a boiling point of 150 to 220° C. at 1 atmospheric pressure as the other water-soluble organic solvent. Therefore, although not particularly limited, among the other water-soluble organic solvents exemplified above, (poly)oxyalkylene monoalkyl ethers having a static surface tension of 29 to 50 mN / m at 25° C. and a boiling point of 150 to 220° C. under 1 atmospheric pressure can be preferably used. Specific examples include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol monoisopropyl ether, 1,3-butylene glycol monomethyl ether, 3-methyl-1,3-butylene glycol monomethyl ether, and the like.

[0037] On the other hand, the total content of the water-soluble organic solvents contained in the aqueous inkjet ink of the present embodiment is preferably 5 to 50% by mass, more preferably 9 to 40% by mass, even more preferably 12 to 35% by mass, and particularly preferably 15 to 30% by mass, based on the total amount of the aqueous inkjet ink. By setting the total content of the water-soluble organic solvents within the above range, it is possible to maintain an appropriate viscosity for ejecting the inkjet ink. In addition, for example, even after a long period of printing suspension, good ejection stability can be easily obtained. In one embodiment, the total content of the water-soluble organic solvents is preferably the total amount of the diols having 2 to 5 carbon atoms and hexylene glycol. In another embodiment, the total content of the water-soluble organic solvents may be the total amount of the diols having 2 to 5 carbon atoms and hexylene glycol, and other water-soluble organic solvents other than these. In this case, the content of the other water-soluble organic solvents is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total content of the water-soluble organic solvents. The content of the other water-soluble organic solvents may be 0% by mass.

[0038] In some embodiments, the aqueous inkjet ink preferably contains a water-soluble organic solvent having a boiling point of 250° C. or higher at 1 atmosphere of pressure in an amount of 5% by mass or less (may be 0% by mass), and most preferably 1% by mass or less (may be 0% by mass), based on the total amount of the aqueous inkjet ink. By not containing a water-soluble organic solvent having a boiling point of 250° C. or higher, or by containing the water-soluble organic solvent in an amount within the above range, it is easy to improve the ejection stability, for example, even after a long period of printing suspension. In addition, water-soluble organic solvents with high boiling points have a high affinity with acetylenic diols having an HLB value of 10 or lower, and there is a risk that the orientation of the acetylenic diols at the gas-liquid interface is inhibited. In contrast, by containing the water-soluble organic solvent having a boiling point of 250° C. or higher in an amount within the above range, the orientation of the acetylenic diols having an HLB value of 10 or lower is not inhibited, and a printed matter with excellent print quality without whiteouts can be easily obtained.

[0039] In the aqueous inkjet ink of this embodiment, the content of the water-soluble organic solvent, which is a heterocyclic compound, is preferably 3% by mass or less (may be 0% by mass) relative to the total amount of the aqueous inkjet ink, and most preferably 1% by mass or less (may be 0% by mass). Since the heterocyclic compound exhibits very high solubility in both hydrophilic and hydrophobic materials, it may dissolve acetylene diols having an HLB value of 10 or less, and may inhibit their orientation at the gas-liquid interface. Therefore, by not including a water-soluble organic solvent, which is a heterocyclic compound, or by setting the amount of the water-soluble organic solvent included within the above range, the orientation of the acetylene diols having an HLB value of 10 or less at the gas-liquid interface is not inhibited, and the print quality of the printed matter is good. In addition, the above-mentioned components are prevented from dissolving in the heterocyclic compound at the nozzle end surface of the inkjet head, and the balance of the existence of these components can be maintained, thereby improving the ejection stability.

[0040] <Surfactant> The aqueous inkjet ink of the present embodiment contains a surfactant. As described above, the surfactant contains acetylenic diols having an HLB value of 10 or less. The aqueous inkjet ink of the present embodiment containing acetylenic diols having an HLB value of 10 or less has excellent wettability on the order of μs, and can obtain printed matter having the same print quality as that obtained by a plate-based printing method even during high-speed printing.

[0041] (Acetylene diols with HLB value of 10 or less) The acetylene diols having an HLB value of 10 or less may be synthesized by a conventionally known synthesis method, or may be commercially available products. Examples of the commercially available products include Surfynol (registered trademark) 61, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420, 440, 2502, SE, SE-F, DF-110D, Dynol (registered trademark) 604, 607 (manufactured by Evonik Japan Co., Ltd.), Olfine (registered trademark) E1004, PD-001, PD-002W, PD-004 (manufactured by Nissin Chemical Industry Co., Ltd.), etc. These compounds may be used alone or in combination of two or more kinds.

[0042] Among the acetylenic diols having an HLB value of 10 or less, it is preferable to use acetylenic diols having an HLB value of 4 to 10, and it is particularly preferable to use acetylenic diols having an HLB value of 7 to 10. When acetylenic diols having an HLB value of 4 to 10 are used, the acetylenic diols themselves are given a certain degree of affinity for water, and the affinity with hexylene glycol and diols having 2 to 5 carbon atoms can be easily improved. As a result, the standby dischargeability and continuous dischargeability can be easily improved while maintaining good print quality of the printed matter. In particular, because the above-mentioned mechanism functions effectively, the ejection stability is good even after a long period of printing suspension, and further, the wettability is good even for substrates with very low interfacial free energy such as PP film, and printed matter with excellent print quality can be obtained regardless of the substrate, it is preferable to use Surfynol 440 and / or Surfynol 2502 as the acetylenic diol having an HLB value of 10 or less, and it is particularly preferable to use Surfynol 2502. Both Surfynol 440 and Surfynol 2502 are compounds included in acetylenic diols having an HLB value of 7 to 10.

[0043] In this disclosure, the term "HLB (Hydrophilic-Lipophilic Balance) value" refers to one of the parameters that indicate the degree of hydrophilicity and hydrophobicity of a material. The smaller the HLB value, the more hydrophobic the material is, and the larger the HLB value, the more hydrophilic the material is. Known methods for determining the HLB value include a method of measuring it experimentally and a method of calculating it from the molecular structure, and the methods of calculating it from the molecular structure include the Griffin method, the Davis method, and the Kawakami method. In this application, the value calculated by the Griffin method, which is represented by the following formula (1), is used as the HLB value.

[0044] Formula (1): (HLB value) = 20 × (sum of molecular weights of hydrophilic parts) ÷ (molecular weight of material)

[0045] The content of acetylenic diols having an HLB value of 10 or less contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 2.0 mass %, and particularly preferably 0.2 to 1.0 mass %, based on the total amount of the aqueous inkjet ink. By setting the content of acetylenic diols having an HLB value of 10 or less within the above range, the print image quality is improved, and ejection stability is also good even after a long printing break or during continuous printing at high speed.

[0046] (Other surfactants) The aqueous inkjet ink of this embodiment may contain surfactants other than the acetylenic diols having an HLB value of 10 or less (referred to as "other surfactants" in the present disclosure).

[0047] In the aqueous inkjet ink of this embodiment, the other surfactants that can be used include acetylenic diol surfactants (excluding acetylenic diols having an HLB value of 10 or less), acetylene monool surfactants, siloxane surfactants, fluorine-based surfactants, polyoxyalkylene monoalkyl ether surfactants (wherein the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, and the number of oxyalkylene groups is 5 to 100 and / or the number of carbon atoms in the terminal alkyl group is 5 to 22). These other surfactants may be used alone or in combination of two or more.

[0048] Among them, in one embodiment, it is preferable to use one or more surfactants selected from acetylenic diol surfactants (excluding acetylenic diols having an HLB value of 10 or less) and siloxane surfactants as the other surfactants, and it is particularly preferable to use a siloxane surfactant. The above embodiment is preferable in that the surface tension of the aqueous inkjet ink can be significantly reduced in a very short time, improving the print quality of the printed matter, and that the wettability to a substrate having a relatively large interfacial free energy, such as a PET (polyethylene terephthalate) film, is good.

[0049] Examples of commercially available siloxane surfactants that can be suitably used include TEGO (registered trademark) Wet 270, TEGO Wet 280, TEGO Twin 4000, TEGO Twin 4100, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Japan Co., Ltd., and the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd. Among these, TEGO Wet 270, TEGO Wet 280, TEGO Twin 4000, and TEGO Twin 4100 are particularly preferably used.

[0050] The total content of the surfactants contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 5 mass %, more preferably 0.2 to 4.5 mass %, even more preferably 0.3 to 4 mass %, and particularly preferably 0.4 to 1.5 mass %, relative to the total amount of the aqueous inkjet ink.

[0051] <Water> The aqueous inkjet ink of this embodiment contains water. The water contained in the ink of this embodiment is preferably ion-exchanged water (deionized water) rather than general water containing various ions. The content of water is preferably 45 to 75 mass % and particularly preferably 50 to 70 mass % based on the total amount of the aqueous inkjet ink. Since water has a low boiling point, it is preferentially evaporated from the nozzle end face of the inkjet head, and the solid concentration at the gas-liquid interface is likely to become high. This may cause the surfactant (particularly those with poor solubility in water, such as acetylene diols with an HLB value of 10 or less) to become non-uniform, which may lead to deterioration of ejection stability. On the other hand, by setting the content of water within the above range, ejection stability is good even after a long period of printing suspension or during continuous printing.

[0052] <Coloring agent> The aqueous inkjet ink of the present embodiment contains a colorant. As the colorant, conventionally known dyes and pigments can be used. Among them, it is preferable to use a pigment, because it can provide a printed matter having high density or hiding power and excellent light resistance, water resistance, etc., and further, it can be appropriately dried and thickened after landing on the substrate, suppressing color mixing between ink colors and improving image quality.

[0053] As the pigment, any conventionally known organic or inorganic pigment can be used. For example, pigments represented by the following color index names can be used. i.e., red pigments, CI Pigment Red 52, 5, 7, 9, 12, 17, 22, 23, 31, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 57:1, 57:2, 112, 122, 123, 146, 147, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 184, 188, 202, 207, 209, 254, 255, 260, 264, 266, 269, 282; Violet pigments include CI Pigment Violet 19, 23, 29, 32, 36, 37, 42, 50; Orange pigments include CI Pigment Orange 1, 2, 3, 5, 7, 13, 14, 15, 16, 22, 34, 36, 38, 40, 43, 47, 48, 49, 51, 52, 53, 60, 61, 62, 64, 65, 66, 69, 71, 73; Blue pigments include CI Pigment Blue 15, 15:3, 15:4, 15:6, 16, 60, 64, and 79; As green pigments, CI Pigment Green 7, 10, 36, 48; Yellow pigments include CI Pigment Yellow 1, 2, 3, 5, 12, 13, 14, 16, 17, 24, 73, 74, 83, 87, 93, 94, 95, 97, 98, 109, 110, 111, 112, 120, 126, 127, 128, 129, 137, 138, 139, 147, 150, 151, 154, 155, 166, 167, 168, 170, 180, 185, 213; Black pigments include CI Pigment Black 1, 7, and 11; White pigments include CI Pigment White 4, 5, 6, 21, etc. These pigments may be used alone or in combination of two or more. A solid solution of two or more of the pigments listed above may also be used as a pigment.

[0054] The content of the pigment contained in the aqueous inkjet ink of the present embodiment may be adjusted depending on the use of the printed matter produced using the aqueous inkjet ink. For example, the content of the pigment is preferably 0.5 to 30% by mass relative to the total amount of the aqueous inkjet ink. In addition, except for the case of a white aqueous inkjet ink (aqueous white ink), the content of the pigment is more preferably 1 to 15% by mass, and particularly preferably 1.5 to 10% by mass, in order to obtain a printed matter with high density without deteriorating the discharge stability of the aqueous inkjet ink. On the other hand, in the case of an aqueous white ink, the content of the pigment is more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass, in order to obtain a printed matter with high concealing property without deteriorating the discharge stability of the aqueous white ink.

[0055] <Resin> The aqueous inkjet ink of the present embodiment may contain a resin. When a resin is used, the viscosity of the ink can be adjusted to a range appropriate for ejection from an inkjet head. Furthermore, when the aqueous inkjet ink is printed on a poorly permeable substrate or a non-permeable substrate and dried, the viscosity increases at a speed of the order of μs, which is preferable in that bleeding and beading can be suppressed and the print image quality can be improved.

[0056] In the present disclosure, the term "resin" refers to a compound in which one or more types of monomers are linked together by covalent bonds to form a main chain, and which has a mass average molecular weight of 1,000 or more.

[0057] In the present disclosure, the mass average molecular weight of a compound is a polystyrene equivalent value that can be measured by a method in accordance with JIS K 7252. Examples of specific measurement conditions are shown below. Equipment used: Tosoh Corporation "HLC-8320GPC" Columns used: TSKgel (registered trademark) SuperMultiporeHZ-M (3 columns) Column temperature: 40℃ Developing solvent: Tetrahydrofuran ·Flow rate: 0.6mL / min Sample solution concentration: 0.1% by mass Sample solution injection volume: 10μL

[0058] Generally, water-soluble resins and resin microparticles are known as the form of resins used in aqueous inkjet inks. The resin contained in the aqueous inkjet ink of the present embodiment may be a water-soluble resin or resin microparticles. In addition, a combination of a water-soluble resin and resin microparticles may be used.

[0059] In this disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25° C. is referred to as a "water-soluble resin," and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin." In addition, among the above water-insoluble resins, a resin that is dispersed in water in the form of particles and has a volume-based median diameter (also referred to as "D50" in this disclosure) of 10 to 1,000 nm is referred to as a "resin particle."

[0060] In addition, in this disclosure, "D50" is a value measured in an environment of 25°C using a dynamic light scattering particle size distribution measuring device such as "Nanotrac UPA-EX150" manufactured by Microtrac-Bell.

[0061] Examples of resins that can be used in the aqueous inkjet ink of this embodiment include acrylic resins, styrene resins, maleic acid (anhydride)-based resins, styrene-maleic acid (anhydride) resins, olefin-maleic acid (anhydride) resins, urethane resins, polyester resins, vinyl chloride resins, vinyl chloride-vinyl acetate resins, polyolefin resins, vinyl alcohol resins, etc. These resins may be used alone or in combination of two or more.

[0062] In the present disclosure, the term "acrylic resin" refers to a resin using an acrylic acid ester and / or a methacrylic acid ester as a polymerizable monomer (a styrene-based monomer may also be used). Also, the term "maleic acid (anhydride)" refers to at least one selected from "maleic acid" and "maleic anhydride".

[0063] The resin is used for any purpose, for example, a pigment dispersion purpose, a binder purpose, a wax purpose, a thickening purpose, etc. Furthermore, the resin may be used for a single purpose or may have a plurality of purposes.

[0064] The preferred content of the resin contained in the aqueous inkjet ink of this embodiment varies depending on the application of the resin. On the other hand, the total amount of the resin contained in the aqueous inkjet ink is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, even more preferably 4 to 19% by mass, and particularly preferably 5 to 18% by mass, based on the total amount of the aqueous inkjet ink. By setting the total amount of the resin within the above range, after the aqueous inkjet ink lands on the printing substrate, the aqueous inkjet ink thickens mainly around the gas-liquid interface as water evaporates. As a result, color mixing with adjacent aqueous inkjet inks that have landed is suppressed, and the print quality of the printed matter is improved.

[0065] (Pigment dispersion resin) As described above, the aqueous inkjet ink of this embodiment can use a resin used for pigment dispersion (also simply referred to as "pigment dispersion resin" in this disclosure). By selecting and considering the composition and molecular weight of the polymerizable monomer that constitutes the pigment dispersion resin, the covering ability and charge of the pigment dispersion resin can be easily adjusted, so that it is possible to impart dispersion stability to even fine pigments, and further, it is possible to obtain printed matter that is excellent in ejection stability, color development, and color reproducibility.

[0066] The type of pigment dispersion resin is not particularly limited, and the above-mentioned types of resins can be used. Among them, it is preferable to use one or more resins selected from the group consisting of acrylic resins, urethane resins, polyester resins, and polyolefin resins in terms of ejection stability, material selectivity, ease of synthesis, etc.

[0067] The pigment dispersion resin may be synthesized by a known method or may be a commercially available product. There is no particular limitation on the structure, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. may be used. Furthermore, as the pigment dispersion resin, a water-soluble resin or a water-insoluble resin may be selected.

[0068] When a water-soluble resin is used as the pigment dispersion resin, the acid value is preferably more than 100 mgKOH / g and not more than 450 mgKOH / g, more preferably 120 to 400 mgKOH / g. Particularly preferably 150 to 350 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment, and the pigment can be stably discharged from the inkjet head regardless of the use conditions. In addition, the solubility of the pigment dispersion resin in water can be ensured, and the interaction between the pigment dispersion resins becomes favorable, so that the viscosity of the pigment dispersion liquid can be suppressed, which is also preferable in terms of expressing good dischargeability from the inkjet head.

[0069] On the other hand, when a water-insoluble resin is used as the pigment dispersion resin, the acid value is preferably 0 to 100 mgKOH / g, more preferably 5 to 90 mgKOH / g, and even more preferably 10 to 80 mgKOH / g. If the acid value is within the above range, a printed matter having excellent drying properties and good print quality can be obtained.

[0070] The acid value of the resin can be measured by a known device. In the present disclosure, the acid value of the resin is a value measured by potentiometric titration in accordance with JIS K 2501. As a specific example of the measurement method, a method is given in which, using AT-610 manufactured by Kyoto Electronics Manufacturing Co., Ltd., the resin is dissolved in a toluene-ethanol mixed solvent, and then titrated with a potassium hydroxide solution, and the acid value is calculated from the titration amount up to the end point.

[0071] In the aqueous inkjet ink of this embodiment, from the viewpoint of improving the adsorption ability to the pigment and ensuring dispersion stability, it is preferable to introduce an aromatic group into the pigment dispersion resin. Examples of the aromatic group include, but are not limited to, a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, and an anisyl group. Among these, a phenyl group, a naphthyl group, and a tolyl group are preferable from the viewpoint of ensuring sufficient dispersion stability.

[0072] From the viewpoint of improving the dispersion stability and ejection stability of the pigment, as well as the print quality and drying properties of the printed matter, the amount of the aromatic ring-containing monomer introduced is preferably 5 to 75 mass %, more preferably 5 to 65 mass %, and even more preferably 10 to 50 mass %, based on the total amount of monomers constituting the pigment dispersion resin.

[0073] <Other ingredients> The aqueous inkjet ink of the present embodiment may contain a pH adjuster and other additives in addition to the above-mentioned components. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds may be used.

[0074] <Method of manufacturing water-based inkjet ink> The aqueous inkjet ink of the present embodiment can be produced by a conventionally known method. For example, when a water-insoluble colorant (water-insoluble colorant) is used as a colorant, the water-insoluble colorant is dispersed in a medium (aqueous medium) containing at least water to produce a water-insoluble colorant dispersion. On the other hand, when a water-soluble colorant (water-soluble colorant) is used as a colorant, the water-soluble colorant is dissolved in a water-based medium to produce a water-soluble colorant aqueous solution. Then, water, a water-soluble organic solvent, a surfactant, etc. are added to the water-insoluble colorant dispersion and / or the water-soluble colorant aqueous solution, and the mixture is thoroughly stirred and mixed, after which coarse particles are removed by a method such as filtration or centrifugation. However, the method for producing the aqueous inkjet ink of the present embodiment is not limited to the above-mentioned method.

[0075] <Characteristics of water-based inkjet ink> The aqueous inkjet ink of the present embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. In this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from an inkjet head having an ejection frequency of about 4 to 10 KHz, but also from an inkjet head having a high ejection frequency of about 20 to 70 KHz. In particular, when the aqueous inkjet ink of the present embodiment has a viscosity of 4 to 10 mPa·s at 25°C, the aqueous inkjet ink can be stably ejected even when an inkjet head having a design resolution of 600 dpi or more is used. In the present disclosure, the viscosity is measured in a 25°C environment using a cone-plate type rotational viscometer (E-type viscometer, cone angle 1°34') such as the "TVE25L type viscometer" manufactured by Toki Sangyo Co., Ltd.

[0076] In order to obtain an aqueous inkjet ink excellent in ejection stability and print quality of printed matter, the aqueous inkjet ink of this embodiment preferably has a static surface tension of 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m, at 25° C. In the present disclosure, the static surface tension is a value measured in an environment at 25° C. using the Wilhelmy method (plate method) with an automatic surface tensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0077] Furthermore, when the aqueous inkjet ink of the present embodiment contains a water-insoluble colorant, in order to achieve both high levels of ejection stability and high levels of density or hiding power of the printed matter, the median diameter (D50) of the water-insoluble colorant on a volume basis is preferably 30 to 450 nm, more preferably 50 to 400 nm, and particularly preferably 70 to 350 nm.

[0078] <Water-based inkjet ink set> The aqueous inkjet ink of the present embodiment may be used alone, or may be used as an aqueous inkjet ink set by combining two or more aqueous inkjet inks. Examples of the aqueous inkjet ink set include a set of four aqueous inkjet inks (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink); a set of five aqueous inkjet inks obtained by adding an aqueous white ink to the process color ink set; and the like. It is preferable that all the aqueous inkjet inks constituting the aqueous inkjet ink set satisfy the requirements of the above-mentioned embodiment of the present invention.

[0079] <Ink-pretreatment liquid set> The aqueous inkjet ink of this embodiment and the aqueous inkjet ink set can also be used in a form combined with a pretreatment liquid containing an aggregating agent (in the form of an ink-pretreatment liquid set). By applying a pretreatment liquid containing an aggregating agent onto a printing substrate before printing with the aqueous inkjet ink, a layer (ink aggregating layer) that intentionally aggregates solid components contained in the aqueous inkjet ink can be formed. Then, by landing the aqueous inkjet ink on the ink aggregating layer, it is possible to prevent the droplets of the aqueous inkjet ink from coalescing and mixing, and to significantly improve the print quality of the printed matter.

[0080] As the flocculant, for example, water-soluble inorganic or organic salts containing polyvalent metal ions, and resins having cationic groups and in which the cationic group equivalent is greater than the anionic group equivalent can be used.

[0081] <Inkjet printing method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. A printing method using the inkjet printing method typically includes an ink ejection step and a drying step of the ejected ink. In the above printing method, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). In addition, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0082] (Discharge process) In the above-mentioned ejection step, an example of the operation method of the inkjet head is a shuttle (scan) method in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate to eject and record the aqueous inkjet ink. Another example of the operation method is a single-pass method in which the aqueous inkjet ink is ejected and recorded when the printing substrate passes under a fixedly arranged inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may adopt either the shuttle method or the single-pass method. Among them, the single-pass method is preferably selected because the landing position of the droplets of the aqueous inkjet ink is less likely to shift, improving the print quality of the printed matter, and further because high-speed printing is possible and high productivity can be achieved as an alternative to plate-based printing.

[0083] The method of ejection from the inkjet head can be selected from any known methods, such as a piezoelectric method that utilizes the volume change of a piezoelectric element, a thermal method that ejects water-based inkjet ink by bubbles generated by heating a heater, and a valve method that ejects pressurized water-based inkjet ink by opening and closing a nozzle cover (valve) with a solenoid.

[0084] The amount of droplets of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing the drying load and improving the print quality. In addition, from the viewpoint of improving the print quality, it is preferable to adjust the printing conditions (specifically, the driving frequency and number of inkjet heads, and the printing speed). In some embodiments, the printing conditions may be adjusted so that the recording resolution of the printed matter is preferably 600 dpi or more, more preferably 1200 dpi or more.

[0085] (drying process) Examples of drying methods that can be used in the drying mechanism in the drying step include heat drying, hot air drying, infrared drying (for example, infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. In the drying step, one or more of these methods can be arbitrarily selected and used. When two or more of the above drying methods are used, the drying methods may be used separately (for example, consecutively) or simultaneously. For example, by using the heat drying method and the hot air drying method in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[0086] In particular, from the viewpoint of preventing bumping of the liquid components in the aqueous inkjet ink and obtaining a printed matter with excellent print quality, when a heat drying method is employed, the drying temperature is preferably 35 to 100° C. When a hot air drying method is employed, the hot air temperature is preferably 50 to 250° C. From the same viewpoint, when an infrared drying method is employed, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared rays is in the wavelength region of 700 to 2200 nm.

[0087] <Printed material> A printed matter according to one embodiment of the present invention has a printing substrate and a printing layer containing an image or characters formed by printing the aqueous inkjet ink according to this embodiment on the printing substrate. The printing can be suitably carried out according to an inkjet printing method. The details of the printing method and printing conditions are as described above. (Printing base material) The printing substrate on which the aqueous inkjet ink of the present embodiment is printed is not particularly limited. In some embodiments, the printing substrate may be a poorly permeable substrate or a non-permeable substrate. In general, printing on poorly permeable substrates and non-permeable substrates is prone to bleeding or beading, which tends to deteriorate the print quality. In contrast, by using the aqueous inkjet ink of the present embodiment, a printed matter having print quality equivalent to that of plate printing can be obtained even on poorly permeable substrates and non-permeable substrates, and even in high-speed printing.

[0088] The permeability of a printing substrate can be determined by the amount of water absorption measured by a dynamic scanning absorptiometer. In the present disclosure, it is defined as the amount of pure water absorbed at a contact time of 100 msec, measured by the following method. Specifically, when the amount of water absorption is 1 g / m 2 A printing substrate with a water absorption of less than 1 g / m is called a "non-permeable substrate". 2 More than 6g / m 2 A printing substrate with a water absorption of less than 6g / m2 is called a "hardly permeable substrate." 2 The printing substrate described above is referred to as a "permeable substrate." The water absorption of the printing substrate can be measured, for example, using a dynamic scanning absorptiometer (e.g., "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the conditions shown below, using a sample of the printing substrate approximately 15 to 20 cm square, in an environment of 23°C and 50% RH. Measurement method: Spiral Method ·Measurement start radius: 20mm Measurement end radius: 60mm ·Contact time: 10~1,000msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of contact time) Scanning distance: 7mm Rotating table speed switching angle: 86.3 degrees Head box conditions: width 5mm, slit width 1mm

[0089] Examples of non-permeable substrates and poorly permeable substrates include plastic films and sheets such as polyvinyl chloride sheets, polyethylene terephthalate (PET) films, polypropylene films, polyethylene films, polyethylene sheets, nylon films, nylon sheets, polystyrene films, polystyrene sheets, and polyvinyl alcohol films; coated papers such as coated paper, art paper, and cast paper; metals such as aluminum, iron, stainless steel, and titanium; and glass.

[0090] The printing substrates listed above may have a smooth surface or may have irregularities. The printing substrates may be transparent, semi-transparent, or opaque. The printing substrate may be in the form of a roll or a sheet. In addition, a laminate obtained by bonding two or more of the printing substrates listed above to each other may be used as the printing substrate. A peelable adhesive layer or the like may be provided on the opposite side of the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing.

[0091] The printing surface of the printing substrates listed above may be subjected to surface modification such as corona treatment and plasma treatment. When the surface is modified, the wettability of the aqueous inkjet ink of the present embodiment is improved, and a printed matter having excellent print quality and drying properties and excellent abrasion resistance and adhesion to the substrate can be easily obtained due to the uniformity of the printed surface, which is preferable. EXAMPLES

[0092] The aqueous inkjet ink of the present embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0093] <Production of Water-Soluble Colorant (Pigment) Dispersion> 450 g of carbon black ("PrinteX85" manufactured by Orion Engineered Carbons), 90 g of acrylic resin, and 2,460 g of water were charged into a mixing vessel (volume 10 L) equipped with a stirrer and stirred (premixed) for 1 hour to obtain a reaction mixture. The acrylic resin was a random polymer of styrene / acrylic acid / behenyl acrylate = 45 / 30 / 25 (mass ratio) in which all acid groups had been neutralized with dimethylaminoethanol, with an acid value of about 230 mgKOH / g and a mass average molecular weight of 20,000. Next, the reaction mixture was circulated and dispersed using a Shinmaru Enterprises "Dyno Mill" (volume: 0.6 L) filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. The D50 of the reaction mixture was measured using the above-mentioned device at regular intervals (for example, every hour), and the circulated dispersion was stopped when the D50 became 120 nm or less. A black pigment dispersion was produced by this method.

[0094] In addition, a cyan pigment dispersion was produced using the same materials and method as the black pigment dispersion, except that LIONOL BLUE 7358G (CI Pigment Blue 15:3) manufactured by Toyo Color Co., Ltd. was used as the pigment and circulation dispersion was carried out until the D50 became 180 nm or less.

[0095] <Manufacturing of water-based inkjet ink sets> Using the water-soluble colorant (pigment) dispersion liquid produced by the above-mentioned method, each raw material was charged into a mixing vessel equipped with a stirrer so as to obtain the compounding formulation shown in each column of Table 2. After charging, the raw materials were heated to 50°C and further mixed for 1 hour. Next, filtration was performed using a membrane filter with a pore size of 0.8 μm to produce sets 1 to 52 of aqueous inkjet inks. Each set consisted of an aqueous black ink (K) and an aqueous cyan ink (C). In producing these inks, a black pigment dispersion liquid and a cyan pigment dispersion liquid were used, respectively.

[0096] In the production of the aqueous inkjet ink set, each raw material was added while stirring the mixture in the mixing container. The components listed in each column of Table 2 were added in the order listed from top to bottom. However, when producing an aqueous inkjet ink that does not contain one or more of these components, the component in question was not added, and the next component was added in the order listed. In addition, for components that contain two or more types of raw materials, the order of addition of the components within that component was arbitrary.

[0097] [Table 2]

[0098] [Table 2]

[0099] [Table 2]

[0100] [Table 2]

[0101] Here, the meanings of the abbreviations and details of the product names listed in Table 2 are as follows. In Table 2, "bp" represents the boiling point, and "Nv" represents the solid content concentration. Furthermore, VE1 represents the energy required to evaporate diols having 2 to 5 carbon atoms, VE2 represents the energy required to evaporate hexylene glycol, and (VE2 / VE1) represents the ratio thereof. (Diols with 2 to 5 carbon atoms) EG: Ethylene glycol (specific heat: 0.556 cal / g°C, boiling point: 198°C) 1,2-PD: 1,2-propanediol (specific heat: 0.574 cal / g°C, boiling point: 188°C) 1,2-BD: 1,2-butanediol (specific heat: 0.559 cal / g°C, boiling point: 191°C) 1,3-BD: 1,3-butanediol (specific heat: 0.559cal / g°C, boiling point: 207°C) 1,5-PeD: 1,5-Pentanediol (specific heat: 0.526cal / g°C, boiling point: 239°C) (Hexylene glycol) Specific heat: 0.555cal / g°C, boiling point: 196°C (Other water-soluble organic solvents) 3-Methyl-1,3-butylene glycol monomethyl ether (boiling point: 173°C, surface tension: 30mN / m) Diethylene glycol monoethyl ether: (boiling point: 202°C, surface tension: 32mN / m) Diethylene glycol methyl ethyl ether: (boiling point: 179°C, surface tension: 24mN / m) Glycerin: (boiling point: 290°C, surface tension: 62mN / m) 2-Pyrrolidone: (boiling point: 245℃, surface tension: 45mN / m) (Acetylene diol surfactant) Surfynol 485: Acetylene diol manufactured by Evonik Japan, HLB value: 17 Surfynol 465: Acetylene diol manufactured by Evonik Japan, HLB value: 13 Olfine E1006: Acetylene diol manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 11 Olfine E1004: Acetylene diol manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 9 Surfynol 2502: Acetylene diol manufactured by Evonik Japan, HLB value: 8 Surfynol 440: Acetylene diol manufactured by Evonik Japan, HLB value: 8 Surfynol 420: Acetylene diol manufactured by Evonik Japan, HLB value: 4 Surfynol 104: Acetylene diol manufactured by Evonik Japan, HLB value: 3 (Siloxane surfactant) TEGO Wet 280: Siloxane surfactant manufactured by Evonik Japan TEGO Twin 4100: Siloxane surfactant manufactured by Evonik Japan (Other ingredients) Proxel GXL: 1,2-benzisothiazol-3-one in dipropylene glycol (1,2-benzisothiazol-3-one:dipropylene glycol:water = 2:6:2, a preservative manufactured by Arch Chemicals) (resin) Resin A (for binder use): Resin produced by reproducing the manufacturing example of binder resin 24 in JP 2020-180178 A (used in the form of a resin solution with a solid content of 30%). The acid value of the obtained resin A was 29.5 mg KOH / g, the hydroxyl value was 21.5 mg KOH / g, and the mass average molecular weight was 17,500. Resin B (for binder): Seiko PMC QE-1042 (acrylic resin particles, solid content: 40.5%, acid value: 33 mg KOH / g)

[0102] [Examples 1 to 43, Comparative Examples 1 to 9] The aqueous inkjet ink set produced by the above-mentioned method was used to carry out the following evaluations. The evaluation results are shown in Table 2.

[0103] <Evaluation 1: Evaluation of ejection stability (standby ejection property)> An inkjet ejection device equipped with a Kyocera inkjet head "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) was filled with the water-based black ink or water-based cyan ink constituting the water-based inkjet ink set. After filling, the water-based black ink or water-based cyan ink was pressurized until it oozed from the nozzle of the inkjet head, the nozzle plate was wiped, and immediately a nozzle check pattern was printed at a frequency of 40 kHz. Then, for those nozzles in which there were no missing nozzles in the nozzle check pattern, a solid image (printing rate 100%) with a printing width of 10 cm and a length of 30 cm was immediately printed. Note that OK topcoat paper was used as the printing substrate, and the printing conditions were a frequency of 40 kHz, a conveyor driving speed of 50 m / min, and a resolution of 1200×1200 dpi. After printing, the inkjet ejection device was left to stand by for 1 hour in an environment of 25° C., and then a solid image was printed again using the same printing substrate and printing conditions as above. At that time, the standby ejection property was evaluated by visually checking whether the starting portion of the solid print was printed. The evaluation criteria are as follows, and a rating of "C+" or higher is deemed usable. The above evaluation was carried out for each of the water-based black ink and water-based cyan ink that make up the water-based inkjet ink set. Table 1 also lists the results of the water-based black ink and water-based cyan ink that received poor evaluation results. (Evaluation Criteria) A: No missing nozzles were found in the nozzle check pattern, and no missing nozzles were found at the beginning of the printout immediately after printing the nozzle check pattern and after waiting for one hour. B: No missing nozzles were found in the nozzle check pattern, and no chipping was found at the beginning of the solid print printed immediately after printing the nozzle check pattern. However, a chipping of less than 3 cm was found at the beginning of the solid print printed after waiting one hour. C+: No missing nozzles were found in the nozzle check pattern. Also, no chipping was found at the beginning of the solid printout printed immediately after printing the nozzle check pattern. However, chipping of 3 cm to less than 5 cm was found at the beginning of the solid printout printed after waiting for 1 hour. C: No missing nozzles were found in the nozzle check pattern, and no chipping was found at the beginning of the solid print printed immediately after printing the nozzle check pattern. However, a chipping of 5 cm or more was found at the beginning of the solid print printed after waiting one hour. D+: No missing nozzles were found in the nozzle check pattern, but a chip was found at the beginning of the printout in the solid print made immediately after printing the nozzle check pattern. D: One or more missing nozzles were found in the nozzle check pattern.

[0104] <Evaluation 2: Evaluation of ejection stability (continuous ejection)> An inkjet ejection device having the same configuration as in Evaluation 1 above was filled with the water-based black ink or water-based cyan ink constituting the water-based inkjet ink set. After filling, the water-based black ink or water-based cyan ink was pressurized until it oozed from the nozzle of the inkjet head, the nozzle plate was wiped, and immediately, a nozzle check pattern was printed under the condition of a frequency of 40 kHz. Then, for those in which there were no nozzle missing in the nozzle check pattern, 10 solid images (printing rate 100%) with a printing width of 10 cm and a length of 30 cm were immediately printed in succession. Note that OK topcoat paper was used as the printing substrate, and the printing conditions were a frequency of 40 kHz, a conveyor driving speed of 50 m / min, and a resolution of 1200 x 1200 dpi. Then, the continuous ejection property was evaluated by visually checking whether each of the 10 solid prints was printed without missing. The evaluation criteria are as follows, and a rating of "B" or higher is deemed usable. The above evaluation was carried out for each of the water-based black ink and water-based cyan ink that make up the water-based inkjet ink set. Table 1 also lists the results of the water-based black ink and water-based cyan ink that received poor evaluation results. (Evaluation Criteria) A: No missing nozzles were found in the nozzle check pattern, and no missing ink was found on any of the 10 solid prints. B+: No nozzles were found to be missing in the nozzle check pattern, but nozzles were missing from the 10th sheet of solid prints printed immediately after the nozzle check pattern was printed. B: No nozzles were found to be missing in the nozzle check pattern, but nozzles were missing from the 9th sheet of solid prints printed immediately after the nozzle check pattern was printed. C: No nozzle missing was confirmed in the nozzle check pattern, but a nozzle missing occurred on any of the 4th to 8th solid prints printed immediately after printing the nozzle check pattern. D+: No nozzle missing was confirmed in the nozzle check pattern, but a nozzle missing occurred on one of the first to third solid prints printed immediately after printing the nozzle check pattern. D: One or more missing nozzles were found in the nozzle check pattern.

[0105] <Creating black / cyan gradation prints> An inkjet discharge device was prepared by arranging two Kyocera inkjet heads "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) along the transport direction of the substrate, and a set of water-based inkjet inks was filled in the order of water-based black ink and water-based cyan ink from the upstream side of the transport direction. In addition, an A4 size (width 21 cm x length 30 cm) OPP film (Mitsui Chemicals Tohcello biaxially oriented polypropylene film "OPU-1": thickness 20 μm) was fixed on the conveyor as the printing substrate. Next, the conveyor was driven at 50 m / min, and when the printing substrate passed under the installation part of the inkjet head, the set of the aqueous inkjet inks was discharged under the condition of a drop volume of 2.6 pL, and a black / cyan gradation image was printed. More specifically, as an image, a black gradation image (width 5 cm x length 30 cm) printed with a printing rate of 10 to 100% at 10% intervals, and a cyan gradation image (width 5 cm x length 30 cm) printed with a printing rate of 10 to 100% at 10% intervals, and an aqueous cyan ink was printed with a printing rate of 10 to 100%, were arranged side by side to obtain an image. Then, the printing substrate after the printing was immediately placed in a constant temperature incubator set at 70 ° C. and dried for 3 minutes to produce a black / cyan gradation print.

[0106] <Evaluation 3: Evaluation of print quality (beading, whiteout)> The black / cyan gradation prints produced by the above-mentioned method were visually observed, and the print ratio was checked for the area where unevenness in shading (beading) began to appear. For prints where unevenness in shading was not observed at a print ratio of 80%, the presence or absence of blank spaces at a print ratio of 100% was further checked to evaluate the print quality of the black / cyan gradation prints. The evaluation criteria were as follows, and a rating of "C" or higher was deemed usable. Table 1 shows the evaluation results of the ink that had the worst evaluation result among the inks that make up the water-based inkjet ink set. (Evaluation Criteria) A: No unevenness in density was observed at a printing rate of 80%, and no blank areas were observed at a printing rate of 100%. B: No unevenness in density was observed at a printing rate of 80%, but blank areas were observed at a printing rate of 100%. C: No unevenness in shading was observed at a print rate of 70%, but unevenness in shading was observed at a print rate of 80%. D+: No unevenness in shading was observed at a print rate of 60%, but unevenness in shading was observed at a print rate of 70%. D: Uneven shading was observed at a printing rate of 60%.

[0107] As shown in Table 2 above, the aqueous inkjet inks of Examples 1 to 43 having the configuration of this embodiment have superior ejection stability and produce superior printed images with no beading or blank spots observed, compared to the aqueous inkjet inks of Comparative Examples 1 to 9. From these results, it was found that the aqueous inkjet inks having the configuration of this embodiment are excellent aqueous inkjet inks that combine excellent print quality and excellent ejection stability.

Claims

1. The composition includes a colorant, a water-soluble organic solvent, a surfactant, and water, the water-soluble organic solvent comprises a diol having 2 to 5 carbon atoms and hexylene glycol; a ratio of the content of the diols having 2 to 5 carbon atoms to the content of the hexylene glycol (content of the diols having 2 to 5 carbon atoms / content of hexylene glycol) is 0.15 to 8; The surfactant contains an acetylenic diol having an HLB value of 10 or less, An aqueous inkjet ink, comprising a water-soluble organic solvent having a boiling point of 250° C. or higher at one atmospheric pressure, the content of which is 5% by mass or less based on the total amount of the aqueous inkjet ink.

2. 2. The aqueous inkjet ink according to claim 1, wherein the content of the hexylene glycol is 0.1 to 30% by mass based on the total amount of the aqueous inkjet ink.

3. 3. The water-based inkjet ink according to claim 1, wherein the content of the acetylenic diol having an HLB value of 10 or less is 0.1 to 2.0% by mass based on the total amount of the water-based inkjet ink.

4. A printed matter obtained by printing with the aqueous inkjet ink according to claim 1 or 2.

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