Aqueous inkjet ink and printed matter

Abstract

To provide an aqueous inkjet ink which, even when printed on a low-absorbency printing substrate, can produce printed matter free from beading and pinholes and excellent in migration resistance, and also has good intermittent ejection performance.SOLUTION: The aqueous inkjet ink contains a pigment, a binder resin, an acetylenediol-based surfactant (A), and glycol monoethers (B1). The acetylenediol-based surfactant (A) contains 2-600 ppm of an unmodified acetylenediol-based surfactant (A1) and an alkylene oxide-modified acetylenediol-based surfactant (A2) having an HLB value of 6-12. The mass ratio of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenediol-based surfactant (A2) is 0.5-50.SELECTED DRAWING: None

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to an aqueous inkjet ink and a printed matter produced using the aqueous inkjet ink. [Background technology]

[0002] Digital printing is rapidly becoming more popular as printing runs become smaller and market needs become more diverse. Digital printing does not require plates, so it can accommodate small-lot printing, reduce printing costs, and enable the use of smaller printing devices.

[0003] Inkjet printing, a type of digital printing method, is a method in which tiny droplets of ink are ejected from an inkjet head and landed on a printing substrate (also referred to simply as "substrate" in this specification) to print images or text on the printing substrate. The "image" mentioned above includes solid images (images printed at 100% coverage so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard images. Compared to other digital printing methods, inkjet printing is superior in terms of the size and cost of the printing device, ease of full-color printing, and the like, and has been increasingly used in industrial printing applications in recent years.

[0004] Inks used in inkjet printing methods vary widely, including oil-based, solvent-based, actinic radiation-curable, and water-based inks. Until now, solvent-based or actinic radiation-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks due to concerns about the harmful effects on the environment and people.

[0005] In recent years, there has been an increasing demand for the packaging market as a market for water-based inks used in inkjet printing methods (referred to herein as "aqueous inkjet inks"; hereinafter, also simply referred to as "inks"). In the packaging market, paper containers, labels, flexible packaging, and the like are manufactured, sold, and used. The printing substrates used for printing in the packaging market include low-absorbency substrates such as coated paper and art paper, as well as non-absorbency substrates such as polypropylene film, polyethylene terephthalate film, and nylon film. Therefore, in order to promote the development of aqueous inkjet inks in the packaging market, there is a demand for aqueous inkjet inks that can produce printed materials with excellent print image quality and properties that can withstand practical use, even on low-absorbency substrates and non-absorbency substrates.

[0006] In contrast, typical aqueous inkjet inks available to date have been designed for printing on highly absorbent substrates such as plain paper and specialty paper. When such aqueous inkjet inks are used on non-absorbent substrates, the inks do not penetrate and are not absorbed into the substrate. As a result, droplets of the ink that land on the substrate do not dry sufficiently, resulting in droplets attracting and coalescing with each other (beading). Beading can lead to poor solid coverage (the occurrence of areas where the ink is not applied on a printed item with a 100% coverage rate), uneven density, color bleeding, and other problems, resulting in a significant degradation of print quality.

[0007] One known method for suppressing beading is to reduce the surface tension of the aqueous inkjet ink. Surfactants are often used as a material for reducing the surface tension. In particular, to ensure that the surface tension of the aqueous inkjet ink is sufficiently reduced immediately after it lands on the printing substrate, it is preferable to select a compound with a low molecular weight and a high orientation rate toward the droplet surface (interface). However, when using such surfactants, for example, in a nozzle of an inkjet head that is temporarily not performing an ejection operation, the surfactant in the aqueous inkjet ink present near the ejection orifice may rapidly and excessively orient toward the air-liquid interface, causing the aqueous inkjet ink to overflow from the ejection orifice. This phenomenon can lead to ejection defects (deterioration of standby ejection performance) such as nozzle clogging and deflection immediately after the ejection operation is resumed.

[0008] Furthermore, surfactants with low molecular weights and high orientation rates to the droplet surface are generally poorly compatible with water. As a result, when an aqueous inkjet ink containing such a surfactant dries on a printing substrate, the surfactant molecules tend to associate with each other due to changes in the solubility of the surfactant accompanying changes in the composition of the liquid components and a (relative) increase in the amount of the surfactant relative to the total amount (total mass) of the liquid components. The associated surfactants may then cause pinholes in the printed material. Pinholes are a phenomenon in which areas of the printed material where the ink did not adhere appear as exposed spots of the printing substrate.

[0009] Furthermore, when a laminate containing an ink layer is manufactured and used as a package such as a pouch, there is a risk of migration of a low-molecular-weight surfactant with a high orientation rate that is present on the surface of the ink layer and / or that has bled (a phenomenon in which a component seeps out to the surface of a layer over time) onto the surface of the ink layer. This migration refers to the phenomenon in which a low-molecular-weight surfactant with a high orientation rate passes through each layer constituting the laminate and reaches the surface of the laminate. In particular, if migration of the surfactant occurs on the surface that comes into contact with the contents, it may adversely affect the safety of the contents. This could be a fatal problem when the laminate is used for, for example, food packaging or cosmetic packaging.

[0010] As described above, it has conventionally been extremely difficult to simultaneously eliminate all of the bleeding resistance, standby ejection resistance, pinhole resistance, and migration resistance.

[0011] As an example of suppressing beading when printing on low-absorbency or non-absorbency substrates by controlling the type and amount of surfactant, Patent Document 1 discloses an ink composition (set) that uses a silicone surfactant having a specific structure in combination with a nonionic surfactant with an HLB value of 6.0 or more and less than 12.0 (e.g., polyoxyalkylene alkyl ether surfactants such as "Lutensol XL40" manufactured by BASF and "GENAPOL EP2564" manufactured by Clariant). Patent Document 2 also discloses an ink containing a polyoxyalkylene alkyl ether surfactant having a specific structure and an HLB value measured as 5.0 to 13.0. Patent Document 3 also discloses an ink that uses a silicone surfactant and a fluorine-based surfactant in combination with a glycol ether organic solvent. Meanwhile, Patent Documents 1 to 3 specifically evaluate beading on low-absorbency substrates such as coated paper. As described above, when an aqueous inkjet ink is printed on a non-absorbent substrate such as a resin film, the aqueous inkjet ink does not penetrate into the substrate at all, and therefore beading is more likely to occur than when the ink is printed on a low-absorbent substrate. The aqueous inkjet inks specifically disclosed in Patent Documents 1 to 3 above were also not sufficient in terms of improving beading when printed on a non-absorbent substrate.

[0012] Patent Document 4 also discloses an inkjet recording method using an aqueous ink containing a specific acetylene glycol (acetylene diol surfactant) and a nonionic surfactant, with the blending amounts and blending ratios of each component specified. In the main example of the aqueous ink specifically disclosed in Patent Document 4, 2,4,7,9-tetramethyl-5-decyne-4,7-diol is used as the acetylene glycol, and a polyoxyalkylene alkyl ether surfactant such as polyoxyethylene lauryl ether (with 12 moles of ethylene oxide groups added) is used as the nonionic surfactant. Since 2,4,7,9-tetramethyl-5-decyne-4,7-diol corresponds to the aforementioned "compound with a low molecular weight and a high orientation rate toward the droplet surface (air-liquid interface)," the aqueous ink is considered to be effective in suppressing beading. On the other hand, it cannot be said that Patent Document 4 has fully investigated pinhole resistance in particular, and in fact, the pinhole resistance and migration resistance of the above-mentioned water-based ink cannot be said to be good depending on the printing conditions. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 2022-151398 [Patent Document 2] Patent Publication No. 2021-147400 [Patent Document 3] JP 2018-70730 A [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-139004 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide an aqueous inkjet ink that is free from beading or pinholes, can produce printed matter that has excellent migration resistance, and has good standby ejection properties, even when printed on a low-absorbency printing substrate. [Means for solving the problem]

[0015] As a result of extensive research, the present inventors have found that all of the above-mentioned problems can be solved simultaneously and to a high degree by using an aqueous inkjet ink having the following composition.

[0016] That is, one embodiment of the present invention is an aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B), the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12, the content of the unmodified acetylenic diol surfactant (A1) being 2 to 600 ppm relative to the total mass of the aqueous inkjet ink, the water-soluble organic solvent (B) contains a glycol monoether (B1), The aqueous inkjet ink has a ratio (by mass) of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 of 0.5 to 50. Another embodiment of the present invention relates to a printed matter obtained by printing the aqueous inkjet ink of the above embodiment onto a printing substrate. [Effects of the Invention]

[0017] According to an embodiment of the present invention, it is possible to provide an aqueous inkjet ink that is free from beading or pinholes, has excellent migration resistance, and has good standby ejection properties, even when printed on a low-absorbency printing substrate. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes an embodiment of the present invention, specifically, an aqueous inkjet ink (hereinafter simply referred to as "the ink of the present embodiment") and a printed matter obtained by printing with the aqueous inkjet ink. However, the embodiment of the present invention is not limited to the following description, and includes various modifications that are implemented within the scope of the gist of the invention.

[0019] <Water-based inkjet ink> In general, water, the main solvent of aqueous inkjet inks, has high surface tension and is difficult to wet and spread on a printing substrate. Furthermore, when a droplet of aqueous inkjet ink that has landed on a printing substrate comes into contact with an adjacent wet droplet due to its high surface tension and in a wet state, a force acts on each droplet in a direction that reduces the surface area, causing the droplets to attract each other and resulting in beading. Beading can cause uneven density, color mixing, bleeding, and other problems, significantly reducing the quality of the printed material.

[0020] A suitable method for suppressing beading is to use a surfactant that has a small molecular weight and a high orientation rate to the droplet surface (interface). However, such surfactants are generally poorly compatible with water, which can lead to various problems.

[0021] For example, as described above, in aqueous inkjet inks present near the ejection orifices in an inkjet head, surfactants with low molecular weights and high orientation rates may rapidly and excessively orient at the gas-liquid interface, potentially resulting in poor standby ejection performance. Furthermore, during the drying process of the aqueous inkjet ink on the printing substrate, the surfactants with low molecular weights and high orientation rates may associate with each other, potentially resulting in pinholes in the printed material. Furthermore, the surfactants with low molecular weights and high orientation rates are present in large amounts on the surface of the aqueous inkjet ink layer (ink layer) after drying. This may result in the surfactants bleeding onto the surface of a laminate including the ink layer, potentially causing migration.

[0022] On the other hand, if the amount of surfactant used, which has a low molecular weight and a high orientation speed, is reduced in order to suppress deterioration of standby ejection properties, the occurrence of pinholes, and the occurrence of migration, then the occurrence of the above-mentioned beading cannot be suppressed, leading to the occurrence of uneven density, color mixing, bleeding, etc.

[0023] As described above, surfactants with low molecular weights and high orientation speeds are effective in suppressing beading, but there is a trade-off between this and properties such as standby ejection properties, pinhole resistance, and migration resistance.

[0024]

[0009] Therefore, the present inventors have conducted extensive research to resolve the above trade-off, and as a result have found that it is effective to use an unmodified acetylenic diol surfactant (A1), an alkylene oxide-modified acetylenic diol surfactant (A2) having a specific HLB value, and glycol monoethers (B1) in combination, and further specify the amount of the unmodified acetylenic diol surfactant (A1) and the ratio of the amount of the alkylene oxide-modified acetylenic diol surfactant (A2) to the amount of the glycol monoethers (B1), thereby completing the present invention. Although the details of the mechanism by which the above-mentioned problem can be resolved by the aqueous inkjet ink having the above-mentioned configuration are unknown, the present inventors speculate as follows.

[0025] First, the ink of this embodiment contains an acetylene diol surfactant. Generally, the acetylene group contained in an acetylene diol surfactant does not undergo bond rotation, so the molecular structure is less likely to deform, and even the addition of a small amount produces the expected effect.

[0026] The ink of this embodiment contains, as the acetylenic diol surfactant, an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12. Of these, the unmodified acetylenic diol surfactant (A1) corresponds to the aforementioned "surfactant with a low molecular weight and a high orientation rate." As described above, surfactants with a low molecular weight and a high orientation rate directly affect the occurrence of pinholes and migration, so their amount is preferably small. Therefore, in the ink of this embodiment, the content of the unmodified acetylenic diol surfactant (A1) is preferably adjusted to a range of 2 to 600 ppm based on the total mass of the aqueous inkjet ink. Note that if no unmodified acetylenic diol surfactant (A1) is used, even if the measures described below are taken, the occurrence of beading cannot be completely suppressed, depending on the printing conditions and the printing substrate used. Furthermore, even though it is included, the content of the unmodified acetylenic diol surfactant (A1) contained in the ink of this embodiment is an extremely small amount of 2 to 600 ppm relative to the total mass of the aqueous inkjet ink, so there is still a risk of beading occurring depending on the printing conditions, etc. On the other hand, even a small amount can cause rapid orientation at the interface and association during drying, so the risk of deterioration of standby dischargeability and occurrence of pinholes remains.

[0027] Therefore, the ink of this embodiment uses an unmodified acetylenic diol surfactant (A1), an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12, and glycol monoethers (B1). Both the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1) can emulsify and compatibilize the unmodified acetylenic diol surfactant (A1). Furthermore, both the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1) are more hydrophilic than the unmodified acetylenic diol surfactant (A1). As a result, these components facilitate favorable affinity of the unmodified acetylenic diol surfactant (A1) to water, the main component of aqueous inkjet inks. Furthermore, during drying on the printing substrate, the surfactants are less likely to associate with each other, making it possible to suppress pinholes in the printed material. Furthermore, these surfactants, including the unmodified acetylene diol surfactant (A1), are not rapidly and excessively oriented at the interface, and therefore standby discharge properties are improved.

[0028] On the other hand, the emulsification and compatibilization of the unmodified acetylenic diol surfactant (A1) further suppresses the orientation of the unmodified acetylenic diol surfactant (A1) when used in small amounts, which may increase the risk of beading. However, the alkylene oxide-modified acetylenic diol surfactant (A2) is itself a surfactant, and orientation to the interface occurs, although not as rapidly as with the unmodified acetylenic diol surfactant (A1). In addition, the glycol monoethers (B1) have a low surface tension as water-soluble organic solvents, which contribute to a decrease in the surface tension of the aqueous inkjet ink on the printing substrate. Therefore, beading can be suppressed.

[0029] Furthermore, the inventors have conducted research and found that by adjusting the ratio of the amount of the alkylene oxide-modified acetylenic diol surfactant (A2) to the amount of the glycol monoether (B1), all of the beading suppression property, pinhole resistance property, and standby discharge property can be improved simultaneously.

[0030] Specifically, in the ink of this embodiment, the ratio (by mass) of the amount of glycol monoethers (B1) to the amount of alkylene oxide-modified acetylenic diol surfactant (A2) is 0.5 to 50. It is believed that the presence of a certain amount of glycol monoethers (B1) uniformly reduces the surface tension throughout the aqueous inkjet ink, thereby effectively suppressing beading and pinholes. Furthermore, although the detailed mechanism is unknown, in the aqueous inkjet ink present in the vicinity of the ejection orifice of the inkjet head, rapid and excessive orientation of the surfactant toward the air-liquid interface is effectively suppressed, thereby improving the standby ejection properties of the aqueous inkjet ink.

[0031] As described above, the aqueous inkjet ink having the configuration of this embodiment can solve the above-mentioned problems simultaneously and at a high level.

[0032] In addition to the acetylenic diol surfactant described above, the ink of this embodiment may further contain a nonionic surfactant (C) other than the acetylenic diol surfactant. It is generally believed that the nonionic surfactant (C) functions effectively in a time domain later than the time domain in which the acetylenic diol surfactant (A) primarily functions. Because behavior in this time domain primarily affects wetting and spreading properties and image density, the use of the nonionic surfactant (C) in combination facilitates the production of printed matter free of beading and pinholes. Furthermore, in aqueous inkjet inks present near the nozzle openings of the inkjet head, the nonionic surfactant (C) is less likely to contribute to rapid and excessive orientation toward the air-liquid interface, which is believed to suppress deterioration of standby dischargeability. Furthermore, it is believed that the interaction between the nonionic surfactant (C) and the unmodified acetylenic diol surfactant (A1) and the alkylene oxide-modified acetylenic diol surfactant (A2) allows these surfactants to behave as a single entity. As a result, even if a relatively large amount of unmodified acetylenic diol surfactant (A1) is blended, the unmodified acetylenic diol surfactant (A1) can be prevented from bleeding onto the laminate surface after printing, which is thought to also lead to improved migration.

[0033] The aqueous inkjet inks specifically disclosed in Patent Documents 1 to 3 differ from the ink of the present embodiment in that they contain no acetylenic diol surfactants at all (the specific example of Patent Document 1 does not even use glycol monoethers (B1)). The aqueous inkjet ink specifically disclosed in Patent Document 4 also differs from the ink of the present embodiment in that it does not contain glycol monoethers (B1) and further in that the content of unmodified acetylenic diol surfactant (A1) ("component (A)" in the examples of Patent Document 4) is significantly more than 600 ppm, or it does not contain any unmodified acetylenic diol surfactant (A1).

[0034] Next, the main components constituting the ink of this embodiment will be described below.

[0035] <Unmodified acetylenic diol surfactant (A1)> As described above, the unmodified acetylene glycol surfactant (A1) corresponds to a "surfactant with a low molecular weight and a high orientation rate" and is a material necessary for suppressing beading regardless of printing conditions, etc.

[0036] In the ink of this embodiment, the content of the unmodified acetylene glycol surfactant (A1) may be in the range of 2 ppm or more, 3 ppm or more, 5 ppm or more, 6 ppm or more, 10 ppm or more, 15 ppm or more, or 20 ppm or more relative to the total mass of the ink, and the content of the unmodified acetylene glycol surfactant (A1) may be in the range of 600 ppm or less, 450 ppm or less, 400 ppm or less, 200 ppm or less, 100 ppm or less, 65 ppm or less, 45 ppm or less, 30 ppm or less, or 25 ppm or less. In some embodiments, the unmodified acetylene glycol surfactant (A1) is contained in an amount of 2 to 600 ppm relative to the total mass of the ink. In some embodiments, the content of the unmodified acetylene glycol surfactant (A1) may be preferably 2 to 400 ppm, more preferably 3 to 400 ppm, and even more preferably 5 to 200 ppm. Using the unmodified acetylene glycol surfactant (A1) in the above range, and further using it in combination with a surfactant or glycol monoether (B1) described below, can further suppress beading and improve standby discharge properties and pinhole resistance. In addition, since the amount of the unmodified acetylene glycol surfactant (A1) to be incorporated is small to begin with, it can easily suppress the occurrence of migration in printed matter. Furthermore, in one embodiment, when the content of the unmodified acetylene glycol surfactant (A1) is 6 to 45 ppm, it becomes even easier to achieve both beading suppression, pinhole resistance, and migration resistance.

[0037] Specific examples of the unmodified acetylene diol surfactant (A1) that can be used in this embodiment include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 3,6-diisopropyl Examples of suitable octadecyl compounds include 2,7-dimethyloct-4-yne-3,6-diol, octadec-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, and 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol. Among these, 2,4,7,9-tetramethyl-5-decyne-4,7-diol and / or 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol are preferred from the viewpoint of compatibility with other materials contained in the ink of this embodiment. The above compounds may be used alone or in combination of two or more. The above compounds may be synthesized by a conventional method or may be commercially available products, such as Surfynol 104, Surfynol DF110D, and Surfynol 82 manufactured by Evonik Corporation, and Acetylenol E00 manufactured by Kawaken Fine Chemicals Co., Ltd.

[0038] <Alkylene oxide-modified acetylenic diol surfactant (A2)> The ink of this embodiment uses an alkylene oxide-modified acetylenic diol surfactant (A2) together with an unmodified acetylenic diol surfactant (A1). As described above, the alkylene oxide-modified acetylenic diol surfactant (A2) emulsifies and compatibilizes the unmodified acetylenic diol surfactant (A1), while also exhibiting surface activity. This allows for the production of printed matter that is free of beading and has excellent pinhole resistance, and also provides an ink that has excellent standby jetting properties. From this perspective, the HLB value of the alkylene oxide-modified acetylenic diol surfactant (A2) is 6 to 12, preferably 7 to 11.5, and more preferably 7 to 11.

[0039] The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that indicates the degree of hydrophilicity of a material. The smaller the HLB value, the more hydrophobic the material, and the larger the HLB value, the more hydrophilic the material. Known methods for determining the HLB value include experimental measurement and calculation from molecular structure, and methods for calculation from molecular structure include the Griffin method, Davis method, and Kawakami method. In this specification, the value calculated using the Griffin method is used as the HLB value, except in the case of silicone-based surfactants, which will be described later.

[0040] The Griffin method is a method generally used for non-ionic materials, and is calculated using the molecular weight of the target material according to the following formula (1).

[0041] Formula (1): HLB value = 20 × (total molecular weight of hydrophilic parts) ÷ (molecular weight of material)

[0042] On the other hand, in the case of silicone surfactants, which will be described later, they are generally mixtures containing many compounds, so the HLB value used is the value actually measured by the method described on page 324 of "Surfactant Handbook" (edited by Nishi Ichiro et al., Sangyo Tosho Co., Ltd., 1960).

[0043] To explain the specific measurement method, 0.5 g of the target material is dissolved in 5 mL of ethanol, and then the solution is stirred and titrated with a 2% by mass aqueous phenol solution at 25° C. The point at which the solution becomes turbid is set as the endpoint, and the amount of phenol solution (referred to as A (mL)) added up to the endpoint is used to calculate the HLB value according to the following formula (2).

[0044] Formula (2): HLB value = 0.89 x A + 1.11

[0045] The amount of alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 added is preferably 0.1 to 5 mass% relative to the total mass of the ink of this embodiment. Furthermore, from the viewpoints of improving standby dischargeability and suppressing beading and pinholes in printed matter, the amount added is more preferably 0.3 to 2.5 mass%, and even more preferably 0.5 to 2.0 mass%. Furthermore, when the content of unmodified acetylenic diol surfactant (A1) is taken as 1, the content of alkylene oxide-modified acetylenic diol surfactant (A2) is preferably 10 to 5,000 by mass, more preferably 20 to 5,000, even more preferably 50 to 2,000, and particularly preferably 100 to 1,000. When the content of (A2) is adjusted to the above range, a suitable emulsified state is formed with the unmodified acetylenic diol surfactant (A1), and the surfactant function is suitably exhibited, thereby improving standby dischargeability and easily preventing beading and pinholes in printed matter. Furthermore, from the viewpoint of suitably and easily realizing improved solid filling and prevention of pinholes, it is extremely preferable that the content of the alkylene oxide-modified acetylenic diol surfactant (A2) is 160 to 800.

[0046] A specific example of the alkylene oxide-modified acetylenic diol surfactant (A2) is a compound represented by the following general formula (3).

[0047] General formula (3): [ka]

[0048] In general formula (3), R 1 and R 2 each represents an alkyl group having 1 to 5 carbon atoms, which may be branched, EO represents an ethylene oxide group, and PO represents a propylene oxide group. Furthermore, m1, m2, n1, and n2 each represent an integer of 0 to 30, and m1+n1+m2+n2 is an integer of 1 to 120. However, the addition pattern of the ethylene oxide groups and propylene oxide groups in [ ] may be block or random.

[0049] The molecular weight of the alkylene oxide-modified acetylenic diol surfactant (A2) having a structure represented by the above general formula (3) is preferably 300 to 1,200, more preferably 350 to 900, and even more preferably 400 to 700. The alkylene oxide-modified acetylenic diol surfactant (A2) having a molecular weight within the above range orients at the gas-liquid interface at a suitable speed, making it easy to suppress beading. The molecular weight of the alkylene oxide-modified acetylenic diol surfactant (A2) refers to the formula weight, which can be determined by calculation.

[0050] The alkylene oxide-modified acetylenic diol surfactant represented by the general formula (3) may be synthesized by a conventionally known method or may be a commercially available product. Examples of commercially available products of the compound represented by the general formula (3) include Surfynol 440, Surfynol 2502, Dynol 604, and Dynol 607 manufactured by Evonik Corporation; Olfine E1004 manufactured by Nissin Chemical Industry Co., Ltd.; and Acetylenol E40 and Acetylenol E60 manufactured by Kawaken Fine Chemicals Co., Ltd.

[0051] <Other acetylene diol surfactants> The ink of this embodiment may contain acetylenic diol surfactants other than the unmodified acetylenic diol surfactant (A1) and the alkylene oxide-modified acetylenic diol surfactant (A2) (also referred to herein simply as "other acetylenic diol surfactants"). Examples of other acetylenic diol surfactants include alkylene oxide-modified acetylenic diol surfactants with an HLB value of less than 6 and alkylene oxide-modified acetylenic diol surfactants with an HLB value of more than 12. Examples of commercially available products include Surfynol 420, Surfynol 465, and Surfynol 485 manufactured by Evonik; Olfine E1010 manufactured by Nissin Chemical Industry Co., Ltd.; and Acetylenol E13T, Acetylenol E100, and Acetylenol E200 manufactured by Kawaken Fine Chemicals Co., Ltd. Among these, alkylene oxide-modified acetylenic diol surfactants having an HLB value of 14 or more are preferably used from the viewpoint of being able to improve the compatibility of the materials essential to the ink of this embodiment, such as water, the acetylenic diol surfactant (A), and the glycol monoethers (B1), thereby suppressing beading and further improving standby ejection properties, and from the viewpoint of being able to improve pinhole resistance by slowly and gently orienting at the interface.

[0052] In some embodiments, the weighted average HLB value of the acetylenic diol surfactant (A) is preferably 6.0 to 13.0, more preferably 6.5 to 12.0, and particularly preferably 6.8 to 11.8. By using a combination of an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) (and, if necessary, other acetylenic diol surfactants) so that the weighted average HLB value falls within the above range, these acetylenic diol surfactants are suitably emulsified and compatible, which facilitates the suppression of pinholes in printed materials and the improvement of standby dischargeability. Furthermore, the orientation speed of these acetylenic diol surfactants to interfaces is suitably maintained, which also improves solid coverage in printed materials.

[0053] The weighted average HLB value is the average HLB value calculated by weighting according to the content of the target compound. For example, if an ink contains three acetylenic diol surfactants, the HLB values ​​of the three acetylenic diol surfactants are A, B, and C, respectively, and the contents of the three acetylenic diol surfactants relative to the total mass of the ink are P (mass%), Q (mass%), and R (mass%), respectively, the formula for calculating the weighted average HLB value of the acetylenic diol surfactant (A) in the ink is (A×P+B×Q+C×R)÷(P+Q+R).

[0054] <Water-soluble organic solvent (B)> The ink of this embodiment contains a water-soluble organic solvent (B). The water-soluble organic solvent (B) contains at least a glycol monoether (B1). As described above, the glycol monoether (B1) can emulsify and compatibilize the unmodified acetylenic diol surfactant (A1), thereby improving standby ejection properties of the ink of this embodiment. Furthermore, the glycol monoether (B1) contributes to reducing the surface tension of the aqueous inkjet ink on the printing substrate, making it easier to suppress beading.

[0055] In this specification, the term "water-soluble organic solvent" refers to a solvent that has a solubility in water at 25°C of 1% by mass or more and is liquid at 25°C.

[0056] (Glycol monoethers (B1)) Specific examples of the glycol monoethers (B1) include compounds represented by the following general formula (4).

[0057] General formula (4): R 3 -O-(AO) u -H

[0058] In the above general formula (4), R 3represents an optionally branched chain alkyl group having 1 to 4 carbon atoms; AO represents an ethylene oxide group and / or a propylene oxide group; and u represents an integer of 1 to 3.

[0059] Specific examples of the compound represented by the general formula (4) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono(n / iso)propyl ether, ethylene glycol mono(n / iso)butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono(n / iso)propyl ether, diethylene glycol mono(n / iso / tert)butyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(n / iso)propyl ether, propylene glycol mono(n / iso / tert)butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono(n / iso)propyl ether, dipropylene glycol mono(n / iso / tert)butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol mono(n / iso / tert)butyl ether, and the like. In particular, from the viewpoint of having good affinity for water and further exhibiting the above-mentioned effects favorably, thereby improving pinhole resistance and beading suppression, one or more compounds selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol mono(n / iso)propyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(n / iso)propyl ether, and dipropylene glycol mono(n / iso)propyl ether can be preferably used. The above "(n / iso)" represents normal and / or iso isomers, and "(n / iso / tert)" represents one or more selected from the group consisting of normal, iso, and tertiary isomers.

[0060] Among these, one or more compounds selected from the group consisting of propylene glycol monomethyl ether, diethylene glycol mono(n / iso)propyl ether, propylene glycol mono(n / iso)propyl ether, and dipropylene glycol mono(n / iso)propyl ether are particularly preferred, as they have excellent emulsifying and compatibilizing capabilities for the unmodified acetylenic diol surfactant (A1), a good balance between low surface tension and a low boiling point at 1 atmospheric pressure, and are also highly hydrophilic, thereby simultaneously achieving suppression of beading, improved standby discharge properties, and improved pinhole resistance.

[0061] The glycol monoethers (B1) may be used alone or in combination of two or more kinds.

[0062] From the viewpoint of improving all of standby ejection properties, beading suppression properties, and pinhole resistance, and further from the viewpoint of improving the drying properties of the aqueous inkjet ink on a non-absorbent substrate, the content of the glycol monoethers (B1) is preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %, and even more preferably 2 to 10 mass %, relative to the total mass of the ink of this embodiment.

[0063] Furthermore, in the ink of this embodiment, the ratio (by mass) of the amount of glycol monoethers (B1) to the amount of alkylene oxide-modified acetylenic diol surfactant (A2) is 0.5 to 50. This ratio is preferably 1.5 to 35, and more preferably 3 to 25. By specifying the blending ratio of the two in this manner, it is believed that the surface tension is uniformly reduced throughout the aqueous inkjet ink, and beading and pinholes can be suitably suppressed. This also improves the standby discharge properties of the aqueous inkjet ink.

[0064] Furthermore, in this embodiment, the sum of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) and the content of the glycol monoether (B1) is preferably 2 to 20 mass %, more preferably 3 to 15 mass %, and even more preferably 4 to 12 mass %, relative to the total mass of the aqueous inkjet ink. By keeping the ratio of the blending amounts of the two within the above-mentioned ranges and keeping the sum of the blending amounts within the above-mentioned ranges, it is possible to improve standby discharge performance and pinhole resistance while suppressing beading.

[0065] (Other water-soluble organic solvents) The ink of this embodiment may contain, as the water-soluble organic solvent (B), a water-soluble organic solvent other than the glycol monoethers (B1) (also referred to herein as "other water-soluble organic solvents").

[0066] Examples of the other water-soluble organic solvents include monohydric alcohols having 1 to 6 carbon atoms, such as ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, isopentanol, and dimethylbutanol; Alkanediols having 2 to 6 carbon atoms, such as 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2,4-pentanediol, isoprene glycol (3-methyl-1,3-butanediol), 1,2-hexanediol, and hexylene glycol (2-methyl-2,4-pentanediol); polyalkylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol; Methoxybutanols such as 3-methoxy-1-butanol and 3-methoxy-3-methylbutanol; nitrogen-containing solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; Lactone solvents such as γ-butyrolactone, ε-caprolactone, etc. The compounds listed above may be used alone or in combination of two or more.

[0067] When the ink of this embodiment contains other water-soluble organic solvents, it is preferable to use the above-mentioned alkanediols having 2 to 6 carbon atoms as the other water-soluble organic solvents. When an alkanediol having 2 to 6 carbon atoms is used, the compatibility of the main components of the ink, such as water, the acetylene diol surfactant (A), and the glycol monoethers (B1), can be improved. In addition, beading can be suppressed and standby discharge performance can be further improved. Among alkanediols having 2 to 6 carbon atoms, alkanediols having 2 to 6 carbon atoms and having a 1-hydroxyethyl group (CH3-CH(OH)-) are particularly preferred, as they significantly exhibit the above-mentioned effects and improve beading and standby discharge properties. Examples of alkanediols having 2 to 6 carbon atoms and having a 1-hydroxyethyl group include 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 2,4-pentanediol, and hexylene glycol (2-methyl-2,4-pentanediol). Among these compounds, one or more compounds selected from the group consisting of 1,2-propanediol, 1,3-butanediol, and hexylene glycol are preferred, as they have excellent compatibility with the acetylene diol surfactant (A) and the glycol monoethers (B1) and are highly effective in suppressing beading. In some embodiments, the use of 1,3-butanediol and / or hexylene glycol is particularly preferred.

[0068] When an alkanediol having 2 to 6 carbon atoms is used as the other water-soluble organic solvent, the content thereof is preferably 1 to 40 mass %, more preferably 5 to 35 mass %, and even more preferably 10 to 30 mass %, relative to the total mass of the ink of this embodiment. By setting the content of the alkanediol having 2 to 6 carbon atoms to 10 mass % or more, the effect of the acetylene diol surfactant (A) described above can be fully exerted, making it easier to suppress beading, improving the moisture retention on the inkjet head, and improving standby discharge properties.

[0069] In order to obtain an aqueous inkjet ink that has excellent drying properties even on non-absorbent substrates, as well as excellent beading suppression, standby discharge properties, and pinhole resistance, the amount of water-soluble organic solvents having a boiling point of 235°C or higher contained in the aqueous inkjet ink is preferably 5% by mass or less (0 to 5% by mass), and more preferably 2% by mass or less (0 to 2% by mass). In some embodiments, the amount of water-soluble organic solvents having a boiling point of 235°C or higher is more preferably 2% by mass or less (0 to 2% by mass), and the amount of water-soluble organic solvents having a boiling point of 210°C or higher is even more preferably 5% by mass or less (0 to 5% by mass). It is particularly preferable that the amount of water-soluble organic solvents having a boiling point of 235°C or higher is 1% by mass or less (0 to 1% by mass), and the amount of water-soluble organic solvents having a boiling point of 210°C or higher is 2% by mass or less (0 to 2% by mass).

[0070] In this specification, the "boiling point" refers to a value at 1 atmosphere and can be measured using, for example, a thermal analyzer. Furthermore, the expression "content (blending amount) is 0 mass%" means that the target compound is not contained.

[0071] The total content of water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment is preferably 5 to 40% by mass relative to the total mass of the aqueous inkjet ink, and more preferably 10 to 35% by mass, from the viewpoint of obtaining an aqueous inkjet ink that can ensure sufficient drying even on a non-absorbent substrate and also has excellent beading suppression, standby ejection properties, and pinhole resistance.

[0072] <Nonionic surfactant (C)> As described above, in this embodiment, in addition to the acetylenic diol surfactant (A), a nonionic surfactant (C) other than the acetylenic diol surfactant can be used in combination. The use of the nonionic surfactant (C) is thought to cause an interaction between the acetylenic diol surfactant (A) and the nonionic surfactant (C) and the acetylenic diol surfactant (A) to behave like a single surfactant. As a result, standby discharge performance can be further improved and pinholes and migration in printed materials can be prevented. Furthermore, the nonionic surfactant (C) is gradually oriented toward the air-liquid interface compared to the acetylenic diol surfactant (A), which can promote wetting and spreading of ink droplets on the printing substrate. Furthermore, since the ink droplets can be uniformly wetting and spreading, it is easy to obtain printed materials without beading.

[0073] The HLB value of the nonionic surfactant (C) is preferably 6 to 14, more preferably 8 to 11. When the HLB value is within the above range, a strong interaction occurs particularly with the alkylene oxide-modified acetylenic diol surfactant (A2), improving standby discharge properties and providing printed matter free of pinholes and migration.

[0074] When the ink of this embodiment contains a nonionic surfactant (C), the value obtained by dividing the weighted average HLB value of the acetylenic diol surfactant (A) by the (weighted average) HLB value of the nonionic surfactant (C) is preferably 0.5 to 1.8, and more preferably 0.7 to 1.3. When the value obtained by dividing the weighted average HLB value of the acetylenic diol surfactant (A) by the (weighted average) HLB value of the nonionic surfactant (C) is within the above range, the ink will have good coverage, standby discharge properties, pinhole resistance, and migration resistance. The expression "(weighted average) HLB value of nonionic surfactant (C)" means that when the ink contains one type of nonionic surfactant (C), the HLB value of that nonionic surfactant (C) is used. When the ink contains two or more types of nonionic surfactants (C), the expression means that the weighted average HLB value of the nonionic surfactants (C), calculated by the above-mentioned method, is used.

[0075] The content of the nonionic surfactant (C) is preferably 0.1 to 5 mass % relative to the total mass of the ink, more preferably 0.3 to 2.5 mass %, and even more preferably 0.5 to 2.0 mass %. Furthermore, the mass ratio of the content of the nonionic surfactant (C) to the total content of the unmodified acetylenic diol surfactant (A1) and the alkylene oxide-modified acetylenic diol surfactant (A2) is preferably 0.3 to 2.0, more preferably 0.5 to 1.5. More specifically, the mass ratio is a value expressed as "content of nonionic surfactant (C) / {content of unmodified acetylenic diol surfactant (A1)+content of alkylene oxide-modified acetylenic diol surfactant (A2)}". When the content of the nonionic surfactant (C) and the mass ratio of the content are within the above ranges, the surfactants tend to function as a single surfactant, resulting in good standby ejection properties and making it easier to obtain printed matter that is free of pinholes and migration.

[0076] The nonionic surfactant (C) may be synthesized by a conventionally known method, or a commercially available product may be used. Examples of surfactants that can be used as the nonionic surfactant (C) include acetylene monool surfactants, silicon surfactants, fluorine surfactants, polyoxyalkylene alkyl ether surfactants, polyoxyalkylene aryl ether surfactants, and polyalkylene glycol alkylate surfactants. These compounds may be used alone or in combination of two or more.

[0077] In particular, it is particularly preferable that the ink of this embodiment contains a silicone surfactant and / or a polyoxyalkylene alkyl ether surfactant as the nonionic surfactant (C). When at least one of these surfactants is used, it easily interacts with the acetylene glycol surfactant (A), making it easier to improve the standby discharge performance and prevent pinholes and migration as described above. Furthermore, the surface energy of the ink layer is reduced, making it possible to reduce blocking.

[0078] The silicone surfactant preferably used in this embodiment is a compound represented by the following general formula (5).

[0079] General formula (5): [ka]

[0080] In general formula (5), p is an integer of 0 or more, and q is an integer of 1 or more. 4 is an alkyl group having 1 to 6 carbon atoms or a structure represented by the following general formula (6), and R 5 is a methyl group or a structure represented by the following general formula (6), where R 5 If is a methyl group, p is 0.

[0081] General formula (6): [ka]

[0082] In the general formula (6), r is an integer of 1 to 6, s is an integer of 0 to 50, and t is an integer of 0 to 50, provided that s+t is 1 or more. 6 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a (meth)acryloyl group, or a 2-hydroxy-3-((meth)acryloyloxy)propyl group. The addition of the ethylene oxide groups and propylene oxide groups in [ ] may be in a block or random manner.

[0083] The silicone surfactant may be synthesized by a conventionally known method or may be a commercially available product. Examples of commercially available products include SF8428, FZ-2162, 8032ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Toray Dow Corning Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, and BYK-3420 manufactured by BYK-Chemie; and TEGO Wet250, TEGO Wet260, TEGO Wet270, TEGO Wet280, TEGO Glide100, TEGO Glide410, TEGO Glide432, TEGO Glide435, TEGO Glide440, TEGO Glide450, TEGO Rad2200, and TEGO Examples include Rad2250, TEGO Rad2300, TEGO Twin 4000, TEGO Twin 4100, and TEGO Twin 4200; KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, and KF-643 manufactured by Shin-Etsu Chemical Co., Ltd.; and the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd. These commercially available products may be used alone or in combination of two or more.

[0084] In order for the nonionic surfactant (C) to behave like a single surfactant with the acetylenic diol surfactant (A), it is preferable for an interaction to occur between the nonionic surfactant (C) and the acetylenic diol surfactant (A). On the other hand, from the viewpoint of further improving standby dischargeability and suppressing pinholes in printed materials, it is preferable for the acetylenic diol surfactant (A) and the nonionic surfactant (C) to be compatible to some extent. From the above viewpoints, i.e., from the viewpoint of improving standby dischargeability and facilitating the prevention of pinholes and migration, it is preferable to use two or more silicone surfactants in combination as the nonionic surfactant (C). Furthermore, it is particularly preferable to use a combination of the two or more silicone surfactants such that the difference in HLB value between them is 2 or more.

[0085] On the other hand, in this embodiment, it is also preferable to use a polyoxyalkylene alkyl ether surfactant as the nonionic surfactant (C). Polyoxyalkylene alkyl ether surfactants have good compatibility with water and acetylene diol surfactants, and can suppress beading and pinholes without affecting these materials.

[0086] As the polyoxyalkylene alkyl ether surfactant, for example, a compound represented by the following general formula (7) can be used.

[0087] General formula (7): R 7 -O-(EO) v -H

[0088] In the above general formula (7), R 7 represents any one selected from the group consisting of an optionally branched chain alkyl group having 6 to 22 carbon atoms, an optionally branched chain alkenyl group, an optionally branched chain alicyclic alkyl group to which one or more alkyl groups may be added, and an aromatic group to which one or more alkyl groups may be added; EO represents an ethylene oxide group; and v represents an integer of 2 to 100.

[0089] Examples of commercially available polyoxyalkylene alkyl ether surfactants include: Emulgen series (manufactured by Kao Corporation) including Emulgen 104P, 105, 106, 108, 109P, 120, 123P, 150, 210, 220, 306P, 320P, and 350 Braunon series such as EL-1502.2, 1505, 1507, 1509, 1515, 1521, 1530, 1540P, CH-302L, 305, 310L, 315L, 320L, 325L, 330L, 340, SR-702L, 705, 707, 711, 715, 720, 730, 750F, BE-5, 10, 20, 30, BN-3 (manufactured by Aoki Oil & Fat Industries Co., Ltd.), Nonion series (manufactured by NOF Corporation) such as K-204, 220, 230, 2100W, P-208, 210, 213, E-202, 205, 212, 215, 230, S-202, 207, 215, 220, EH-204, 208, ID-203, 206, 209, etc. Lutensol series (manufactured by BASF), such as Lutensol XL40, 50, 60, 70, 80, 90, XP30, 40, 50, 60, 70, 80, 90, 100, Newcol series such as Newcol 2302, 2303, 2305, 2308, 2310, 2320, and 2360 (manufactured by Nippon Nyukazai Co., Ltd.), Emulmin LS-80, LS-90, NL-70, NL-80, NL-90, NL-100, NL-110, Sannonic SS-30, SS-50, SS-70, SS-90, SS-120 (manufactured by Sanyo Chemical Industries, Ltd.), Examples include Adekatal LA-675B, LA-775, LA-875, LA-975, LA-1275, SO-80, SO-105, SO-120, SO-135, SO-145, and SO-160 (manufactured by ADEKA Corporation). In addition to the above-mentioned commercially available products, diethylene glycol monohexyl ether, triethylene glycol monohexyl ether, tetraethylene glycol monohexyl ether, etc. can also be used. The above-listed products may be used alone or in combination of two or more. Furthermore, polyoxyalkylene alkyl ether surfactants synthesized by conventionally known synthesis methods may also be used.

[0090] In the case of polyoxyalkylene alkyl ether surfactants, as in the case of the silicone surfactants described above, it is preferable to use two or more polyoxyalkylene alkyl ether surfactants in combination, in order to improve standby ejection properties and to easily prevent pinholes and migration, and to use them in combination so that the difference in HLB values ​​of the two or more polyoxyalkylene alkyl ether surfactants is 2 or more.

[0091] For the same reason, i.e., to improve standby ejection properties and facilitate prevention of pinholes and migration, it is also preferable that the ink of this embodiment uses a silicone surfactant and a polyoxyalkylene alkyl ether surfactant in combination, and that the difference in HLB value between the silicone surfactant and the polyoxyalkylene alkyl ether surfactant is 2 or more.

[0092] <Other surfactants> Furthermore, the aqueous inkjet ink of this embodiment may contain surfactants other than the surfactants described above, and for example, ionic (anionic or cationic) surfactants, amphoteric surfactants, etc. can be used.

[0093] <Binder resin> The ink of this embodiment may contain a binder resin, which can significantly improve the scratch resistance and migration resistance of the printed matter.

[0094] Generally, water-soluble resins and hydrosols and emulsions, which are types of water-insoluble resins, are known as binder resins used in aqueous inkjet inks. Here, "water-soluble resin" refers to a pigment dispersion resin whose 1% by weight aqueous solution is transparent to the naked eye at 25°C. Furthermore, "hydrosol" refers to a "water-insoluble resin" (a resin that is not water-soluble) that contains acidic and / or basic functional groups in its structure and is dispersed in a dispersion medium without the use of emulsifiers such as surfactants or polymers. Meanwhile, "emulsion" refers to a form in which the emulsifier is adsorbed and / or bonded to the resin surface, forcibly dispersing the resin in a dispersion medium. In this specification, the hydrosols and emulsions are collectively referred to as "resin microparticles."

[0095] (Water-soluble resin) In some embodiments, it is preferable to use a water-soluble resin and / or hydrosol as the binder resin for forming the ink. These resins have affinity with aqueous media (mediums consisting of liquids containing at least water) without the use of an emulsifier, and at least a portion of the resin swells and / or dissolves in the aqueous medium. Therefore, clogging due to precipitation of the resin near the nozzles of the inkjet head is unlikely to occur, and an ink with excellent standby ejection properties can be easily provided. Furthermore, these resins can function as compatibilizers for the unmodified acetylenic diol surfactant (A1), thereby suppressing the occurrence of pinholes in printed materials.

[0096] Examples of resins that can be used as the water-soluble resin and hydrosol include acrylic resins, urethane resins, and polyester resins. Among these, acrylic resins are preferred in consideration of the storage stability and standby discharge properties of the ink, as well as the abrasion resistance of the printed matter.

[0097] In this specification, the term "acrylic resin" refers to a resin using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters (a styrene-based monomer may also be used).

[0098] In this embodiment, the water-soluble resin may be a resin synthesized by a conventionally known method or a commercially available product. There are no particular limitations on the structure of the resin, and any resin having, for example, a random structure, a block structure, a comb structure, a star structure, or the like may be used.

[0099] When a water-soluble resin is used as the binder resin, the weight-average molecular weight of the water-soluble resin is preferably in the range of 5,000 to 50,000, and more preferably in the range of 10,000 to 40,000. When the weight-average molecular weight of the water-soluble resin is 5,000 or more, the abrasion resistance of the printed matter is improved and beading is easily suppressed. Furthermore, when the weight-average molecular weight of the water-soluble resin is 50,000 or less, an ink with good standby ejection properties from an inkjet head can be easily obtained.

[0100] The weight-average molecular weight of the resin can be measured by a conventional method, for example, using a TSKgel column (manufactured by Tosoh Corporation) and a GPC (manufactured by Tosoh Corporation, HLC-8120GPC) equipped with an RI detector, and THF as the developing solvent, as a weight-average molecular weight converted into polystyrene.

[0101] The acid value is also important when selecting a water-soluble resin. When a water-soluble resin is used as a binder resin, its acid value is preferably 5 to 80 mgKOH / g, and more preferably 15 to 50 mgKOH / g. By setting the acid value to 5 mgKOH / g or more, even if the resin solidifies near the nozzle of the inkjet head, it can be redissolved in the ink, which makes it easier to prevent clogging of the nozzle and improves standby discharge performance. Furthermore, if the acid value is 80 mgKOH / g or less, printed matter with excellent water resistance and abrasion resistance can be obtained, and the resin can easily function as a compatibilizer for the unmodified acetylenic diol surfactant (A1), making it easier to obtain printed matter without pinholes.

[0102] The "acid value of a resin" refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In this specification, the acid value is calculated using the following method. For example, if a resin contains Wa mass% of polymerizable monomers having na acid groups with a valence of va per molecule and a molecular weight of Ma, the acid value (mgKOH / g) can be calculated using the following formula (8):

[0103] Formula (8): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0104] In the above formula (8), the number "56.11" is the molecular weight of potassium hydroxide.

[0105] In the ink of this embodiment, the content of the water-soluble resin is preferably 0.5 to 10 mass% relative to the total mass of the ink, more preferably 1 to 8 mass%, and even more preferably 2 to 6 mass%. If the content of the water-soluble resin is 0.5 mass% or more, the unmodified acetylene diol surfactant (A1) can be sufficiently compatibilized, improving the storage stability of the ink and suppressing pinholes in printed matter. Furthermore, if the content of the water-soluble resin is 10 mass% or less, the viscosity of the ink can be kept within a suitable range and an ink with excellent standby discharge properties can be easily obtained.

[0106] (Resin fine particles) On the other hand, resin microparticles such as hydrosols and emulsions generally have a higher molecular weight than water-soluble resins. Furthermore, when the same amount of resin is blended, resin microparticles can lower the viscosity of the ink compared to water-soluble resins. Therefore, the use of resin microparticles allows a larger amount of resin to be incorporated into the ink, making it easier to improve the abrasion resistance, blocking resistance, and migration resistance of printed materials.

[0107] Among the resins used as resin microparticles, types of resins that can be used as emulsions include acrylic resins, urethane resins, polyester resins, styrene-butadiene resins, acrylonitrile-butadiene resins, vinyl chloride resins, polyolefin resins, etc. Among these, in consideration of maintaining the storage stability of the ink and facilitating improvement in the abrasion resistance and blocking resistance of printed matter, emulsions of one or more resins selected from the group consisting of acrylic, urethane, polyester, and polyolefin resins can be preferably used.

[0108] Furthermore, when using a hydrosol as the resin particles, it is preferable to use one or more resins selected from the group consisting of acrylic, urethane, and polyester resins from the viewpoint of improving the scratch resistance of the printed matter. Furthermore, in consideration of the viewpoint of improving the standby discharge property as described above, it is particularly preferable to use an acrylic resin.

[0109] However, when the binder resin in the ink is resin microparticles, especially when an emulsion is used, the minimum film-forming temperature (MFT) of the resin microparticles must be taken into consideration. When resin microparticles with a low MFT are used, depending on the water-soluble organic solvent added to the ink, the MFT of the resin microparticles may further decrease, causing the resin microparticles to adhere near the nozzles of the inkjet head, even at room temperature, resulting in clogging. In particular, in the case of emulsions, once a film is formed, it is difficult to redissolve the emulsion in the ink, so the adhered emulsion may impair standby discharge performance. To avoid such problems, it is preferable to adjust the type and amount of polymerizable monomers that make up the emulsion to ensure the MFT of the emulsion is 60°C or higher.

[0110] Furthermore, when a hydrosol is used as the resin microparticles, the standby dischargeability is less likely to deteriorate than when an emulsion is used. On the other hand, using a hydrosol with an MFT of 60°C or higher can reduce factors that can deteriorate the standby dischargeability, so it is preferable to set the MFT to 60°C or higher even when using a hydrosol.

[0111] The MFT can be measured, for example, by an MFT tester manufactured by Tester Sangyo Co., Ltd.

[0112] When an emulsion is used in the ink of this embodiment, its content is preferably 2 to 15% by mass, more preferably 4 to 10% by mass, based on the total mass of the ink. If the emulsion content is 2% by mass or more, the abrasion resistance and blocking resistance are improved, and if it is 15% by mass or less, the viscosity of the ink can be kept within a suitable range and the ink has excellent standby discharge properties.

[0113] <Pigments> The ink of this embodiment contains a pigment. The pigment may be an inorganic pigment and / or an organic pigment. These pigments may be used singly or in combination of two or more. The pigment content is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass, based on the total mass of the ink.

[0114] When an inorganic pigment is used as the pigment, specific examples thereof include titanium oxide, zinc white, zinc sulfide, white lead, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, talc, bentonite, carbon black, black iron oxide, cadmium red, red iron oxide, molybdenum red, molybdate orange, chrome vermilion, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, Prussian blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, and cobalt violet.

[0115] Among the carbon blacks listed above, those produced by the furnace method or the channel method can be used. Among them, carbon black produced by the furnace method or the channel method, which has a primary particle diameter of 11 to 40 nm and a specific surface area measured by the BET method of 50 to 400 m, is particularly preferred. 2Suitable examples of such a polymer include those having properties such as a viscosity of 1 / g, a volatile content of 0.5 to 10%, and a pH of 2 to 10. Commercially available polymers having such specifications include Nos. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, and MCF88 (manufactured by Mitsubishi Chemical Corporation), RAVEN 1255 (manufactured by Birla Carbon Corporation), REGAL 330R, 400R, 660R, MOGUL L, and ELFTEX 415 (manufactured by Cabot Corporation), NIPex 90, NIPex 150T, NIPex 160IQ, NIPex 170IQ, NIPex 75, PrinteX 35, PrinteX 85, PrinteX 90, PrinteX 95, and PrinteX U (manufactured by Orion Engineered Carbons), all of which can be preferably used.

[0116] On the other hand, examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, fluorescent pigments, and the like.

[0117] Specific examples based on the color index include cyan pigments such as CI Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, and 64.

[0118] Examples of magenta pigments include CI Pigment Red 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 176, 177, 178, 179, 184, 185, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, and 282, and CI Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

[0119] Further, examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, and 213.

[0120] Examples of black pigments include aniline black (CI Pigment Black 1), perylene black (CI Pigment Black 31, 32), azomethine azo black, etc. A black pigment can also be prepared by mixing a plurality of chromatic pigments such as the cyan pigments, magenta pigments, and yellow pigments described above, and the brown pigments and orange pigments described below.

[0121] Examples of pigments other than those mentioned above include CI Pigment Green 7, 10, 36, CI Pigment Brown 3, 5, 25, 26, CI Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, and the like.

[0122] <Pigment dispersing resin> In order to maintain the storage stability and standby dischargeability of the ink for a long period of time, the pigment is preferably dispersed in the ink before use. Methods for stably dispersing and maintaining the pigment in the ink include (1) a method in which at least a portion of the pigment surface is coated with a pigment dispersing resin, (2) a method in which a water-soluble and / or water-dispersible surfactant is adsorbed onto the pigment surface, and (3) a method in which hydrophilic functional groups are chemically and / or physically introduced onto the pigment surface, and the pigment is dispersed in the ink without a pigment dispersing resin or surfactant (self-dispersing pigment).

[0123] For the ink of this embodiment, method (1) above, i.e., the method using a pigment dispersion resin, is preferably selected. This is because the pigment covering ability and charge of the pigment dispersion resin can be easily adjusted by selecting and considering the composition, weight average molecular weight, etc. of the polymerizable monomers that make up the resin, making it possible to impart stable storage stability to even fine pigments, and furthermore, to obtain printed matter that is excellent in standby jetting properties, color development, and color reproducibility.

[0124] Examples of the pigment dispersing resin include acrylic resins, styrene-maleic acid (anhydride) resins, α-olefin-maleic acid (anhydride) resins, urethane resins, and polyester resins. Among these, it is preferable to use one or more resins selected from acrylic resins, styrene-maleic acid (anhydride) resins, and α-olefin-maleic acid (anhydride) resins, from the viewpoint of strengthening adsorption to the pigment and improving storage stability and standby discharge properties. In this specification, "maleic acid (anhydride)" refers to maleic acid and / or maleic acid anhydride.

[0125] When a water-soluble resin is used as the pigment dispersion resin, its acid value is preferably 60 to 400 mgKOH / g. By setting the acid value within the above range, the dispersion stability of the pigment, as well as the storage stability and standby dischargeability of the ink, can be favorably achieved. The acid value is more preferably 100 to 350 mgKOH / g, and even more preferably 120 to 300 mgKOH / g. On the other hand, when a water-insoluble resin is used as the pigment dispersion resin, its 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. An acid value within the above range not only enables printed matter to be obtained with excellent drying properties and water resistance, but also improves the dispersion stability of the pigment and the standby dischargeability of the ink. The acid value of the pigment dispersion resin can be measured in the same manner as for the binder resin described above.

[0126] The weight-average molecular weight of the pigment dispersion resin is preferably 5,000 to 100,000. By setting the weight-average molecular weight to 5,000 or more, the dispersion stability of the pigment and the storage stability of the ink can be made favorable. Furthermore, by setting the weight-average molecular weight to 100,000 or less, the standby discharge properties can be made favorable. The weight-average molecular weight is more preferably in the range of 10,000 to 50,000, and even more preferably in the range of 15,000 to 30,000. The weight-average molecular weight of the pigment dispersion resin can be measured in the same manner as in the case of the binder resin described above.

[0127] The amount of pigment dispersing resin relative to the amount of pigment is preferably 1 to 120% by mass. By making the ratio of pigment dispersing resin 1% by mass or more relative to the amount of pigment, the viscosity of the ink can be kept within a range suitable for use in inkjet printing applications, improving standby discharge properties. Furthermore, by making the ratio 120% by mass or less, the dispersion stability of the pigment and the storage stability of the ink can be improved. The amount of pigment dispersing resin relative to the amount of pigment is more preferably 2 to 100% by mass, and even more preferably 5 to 50% by mass.

[0128] <Water> The ink of this embodiment further contains water in addition to the above-mentioned components. The water contained in the ink of this embodiment is preferably ion-exchanged water (deionized water) rather than ordinary water containing various ions. The content of water contained in the ink is preferably adjusted taking into account the content of liquid media other than water, such as the water-soluble organic solvent (B).

[0129] In some embodiments, the amount of water contained in the ink is preferably in the range of 20 to 90% by mass, and may be 30 to 80% by mass, based on the total mass of the ink. In some embodiments, the content of the aqueous medium containing water and the water-soluble organic solvent (B) in the total mass of the ink may be in the range of 25 to 95% by mass. The content of the aqueous medium may be preferably 35 to 92% by mass, and more preferably 50 to 88% by mass. In some embodiments, the ratio (mass ratio) of water to the water-soluble organic solvent (B) in the aqueous medium may be preferably 50 / 50 to 95 / 5, more preferably 55 / 45 to 90 / 10, and even more preferably 60 / 40 to 85 / 15.

[0130] <Other ingredients> In addition to the above components, the ink of the present invention may contain additives such as pH adjusters, UV absorbers, preservatives, etc., to impart desired physical properties as needed. The amount of these additives added is preferably 0.01% by mass or more and 10% by mass or less, based on the total mass of the ink.

[0131] <Ink manufacturing method> One embodiment of the present invention relates to a method for producing the ink of this embodiment containing the above-mentioned components. An example of a method for producing the ink of this embodiment is the following method. The method includes preparing a pigment dispersion, and then adding and mixing a surfactant and a solvent such as water. However, the method for producing the ink of this embodiment is not limited to the following method.

[0132] In a typical production method, first, a pigment dispersion resin and water are mixed to produce a pigment dispersion resin aqueous solution. Next, a pigment and, if necessary, a water-soluble organic solvent or the like are added to the pigment dispersion resin aqueous solution, and the mixture is mixed and stirred (premixed), and then a dispersion treatment is performed using a dispersing means described below. If necessary, a centrifugal separation treatment or the like is then performed to remove coarse particles, thereby obtaining a pigment dispersion liquid. Thereafter, the unmodified acetylenic diol surfactant (A1), the alkylene oxide-modified acetylenic diol surfactant (A2), the binder resin, the glycol monoethers (B1), water, and, if necessary, the nonionic surfactant (C) and other components are added to the pigment dispersion, and the mixture is thoroughly mixed and stirred. The resulting mixture is then filtered to remove coarse particles, thereby obtaining the desired ink.

[0133] In this specification, the term "aqueous solution" refers to a solution containing an aqueous solvent (a liquid medium containing at least water) and components dispersed and / or dissolved in the aqueous solvent.

[0134] As described above in the ink manufacturing method, it is effective to perform a premixing treatment before performing a dispersion treatment, as the premixing treatment improves the wetting and spreading properties of the pigment surface and promotes the adsorption of the pigment dispersing resin to the pigment surface, and is therefore preferably carried out.

[0135] The dispersing machine that can be used for dispersing the pigment may be any commonly used dispersing machine. Examples include a ball mill, a roll mill, a sand mill, a bead mill, and a Nanomizer. Of these, a bead mill is preferably used. Examples of bead mills include a Super Mill, a sand grinder, an agitator mill, a grain mill, a Dyno Mill, a pearl mill, and a Cobol Mill (all trade names).

[0136] Since the ink of this embodiment is intended for use in inkjet printing, it is preferable to use a pigment with an optimal particle size distribution from the viewpoint of preventing nozzle clogging, etc. Methods for obtaining a pigment with the desired particle size distribution include reducing the size of the grinding media in the disperser mentioned above, increasing the packing rate of the grinding media, extending the dispersion treatment time, classifying the dispersion using a filter or centrifuge, etc., after dispersion treatment, and combinations of these methods. The particle size distribution of the ink can be measured, for example, using a Nanotrac UPA-EX150 manufactured by Microtrac-Bell.

[0137] <Ink set> The ink of this embodiment may be used in a single color, or may be used as an ink set combining multiple colors depending on the application. While the combination is not particularly limited, a full-color image can be obtained by using three colors: cyan, yellow, and magenta. The addition of black ink can improve the sense of black and increase the visibility of characters, etc. Color reproducibility can also be improved by adding colors such as orange and green. When printing on a printing substrate other than white, a clear image can be obtained by using a white ink in combination. Furthermore, the ink of this embodiment may be an ink set containing, as a constituent color, an ink that substantially does not contain a colorant component (clear ink) by excluding pigments from the constituent components of the ink.

[0138] <Ink-pretreatment liquid set> The aqueous inkjet ink of this embodiment can also be used in combination with a pretreatment liquid containing an aggregating agent, forming an ink-pretreatment liquid set. By applying a pretreatment liquid containing an aggregating agent to a printing substrate, a layer (ink aggregation layer) can be formed that intentionally aggregates the solid components contained in the ink. By then landing the ink of this embodiment on the ink aggregation layer, bleeding between ink droplets and uneven density can be prevented, significantly improving the print quality of the printed material. Furthermore, depending on the material used in the pretreatment liquid, the adhesion and blocking resistance of the printed material can also be improved.

[0139] In this specification, the term "flocculant" refers to a component contained in an aqueous inkjet ink that can disrupt the dispersion state of pigments and cause them to flocculate, and / or insolubilize resins contained in the aqueous inkjet ink, thereby thickening the aqueous inkjet ink. The flocculant used in the pretreatment liquid combined with the ink of this embodiment preferably contains one or more selected from metal salts and cationic polymer compounds, from the viewpoint of significantly improving print image quality. Of these, from the viewpoint of obtaining excellent print image quality, it is preferable to use a metal salt as the flocculant, and Ca2+ , Mg 2+ , Zn 2+ , and Al 3+ It is particularly preferred that the pretreatment liquid contains one or more salts of polyvalent metal ions selected from the group consisting of: When a metal salt is used as the flocculant, the content thereof is preferably 2 to 30 mass %, and particularly preferably 3 to 25 mass %, based on the total mass of the pretreatment liquid.

[0140] Other pretreatment liquids may contain, as appropriate, water-soluble organic solvents, surfactants, pH adjusters, antifoaming agents, thickeners, preservatives, etc. The water-soluble organic solvents and surfactants that can be used in the pretreatment liquid are the same as those for the inks described above. When the pretreatment liquid contains a surfactant, from the viewpoint of obtaining printed matter with excellent blocking resistance and migration resistance, it is preferable that the pretreatment liquid contain an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12.

[0141] <2> printed matter One embodiment of the present invention relates to a printed matter obtained by printing the aqueous inkjet ink of the present embodiment onto a printing substrate. The printed matter has a printing substrate and a printed layer (ink layer) formed on the printing substrate by printing with the aqueous inkjet ink of the present embodiment. <Printing base material> As described above, the ink of this embodiment is particularly suitable for printing on non-absorbent substrates such as films. When using such non-absorbent substrates as printing substrates, specific examples include polyolefin resins such as polyethylene, biaxially oriented polypropylene (OPP), and non-axially oriented polypropylene (CPP); polyester resins such as polyethylene terephthalate (PET), polycarbonate, and polylactic acid; polystyrene resins such as polystyrene, AS resin, and ABS resin; polyamide resins such as nylon; chlorine-containing resins such as polyvinyl chloride and polyvinylidene chloride; cellophane; and film or sheet substrates made of composite materials thereof. These printing substrates may be subjected to surface treatments such as corona treatment and plasma treatment. Furthermore, they may be pre-coated with a pre-coating composition (different from the pre-treatment liquid) containing one or more resins selected from the group consisting of urethane resins, acrylic resins, and olefin resins.

[0142] <Manufacturing method for printed matter> The ink of this embodiment is used in a printing method in which ink droplets are ejected from the nozzles of an inkjet head and deposited on a substrate. Furthermore, a printed substrate on which an image and / or text is printed, produced by such a printing method, is referred to herein as a "printed matter." In other words, the ink of this embodiment can be used to produce printed matters.

[0143] Furthermore, in the production of printed matter, after the ink of this embodiment is applied to a substrate, it is preferable to dry the ink on the substrate using a drying mechanism. Drying methods used in the drying mechanism include heat drying, hot air drying, infrared drying (e.g., infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. The above drying methods may be used alone, or multiple methods may be used in succession, or they may be used simultaneously. For example, by using heat drying and hot air drying in combination, the ink can be dried more quickly than when each method is used alone.

[0144] <Post-coating treatment> The printed matter of this embodiment may be subjected to a post-coating treatment on the surface of the printed matter, if necessary. Specific examples of the post-coating treatment include coating or printing with a post-coating composition, and lamination using a dry lamination method, a solventless lamination method, an extrusion lamination method, or the like. Any of these methods may be selected, or a combination of two or more may be used.

[0145] When a post-coating treatment is performed on a printed material by coating and printing the post-coating composition, the coating and printing method may be either a method of printing without contact with the printing substrate, such as inkjet printing, or a method of printing by bringing the post-coating composition into contact with the printing substrate. Furthermore, when the method of printing without contact with the printing substrate is selected, it is preferable to use, as the post-coating composition, an ink (clear ink) that is obtained by excluding the pigment from the ink of the present invention and that does not substantially contain a colorant component.

[0146] When a printed material is laminated, the adhesive used to laminate the sealant substrate is preferably composed of a mixture of a polyol component and a polyisocyanate component.

[0147] The polyol component is a resin component having multiple hydroxyl groups, and polyurethane resins and polyester resins are preferably used in view of coatability, wettability and spreadability at the interface of printed matter, and the laminate strength developed after aging. Among these, it is preferable that the polyol component contains a polyester polyol, because these resins provide good wettability and spreadability at the interface of printed matter obtained using the ink of this embodiment, for example, at the printed layer (printed area) and the pretreatment liquid layer (non-printed area), and also provide excellent laminate strength for laminated printed matter (laminate). The polyol component may be a single component, or multiple components may be used in combination.

[0148] Furthermore, the polyisocyanate component reacts with the polyol component to form a urethane bond, thereby increasing the molecular weight of the adhesive layer and improving the laminate strength. In particular, from the viewpoints of compatibility with the polyol component, wetting and spreading properties at the interface of printed matter obtained with the ink of the present invention, and the laminate strength of the laminated printed matter (laminate), it is preferable that the polyisocyanate component contains a polyether-based urethane resin having an isocyanate group terminal. From the same viewpoint as above, the blending amount of the polyisocyanate component is preferably 50 to 80% by mass relative to the polyol component. The polyisocyanate component may be a single component, or multiple components may be used in combination.

[0149] Examples of the sealant substrate used in the lamination process include polypropylene films and polyethylene films such as CPP films and linear short-chain branched polyethylene (LLDPE) films. Films with a metal (oxide) vapor-deposited layer such as aluminum oxide may also be used.

[0150] Representative embodiments of the present invention will be described below. <1> An aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B), the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12; the content of the unmodified acetylenic diol surfactant (A1) is 2 to 600 ppm relative to the total mass of the aqueous inkjet ink; the water-soluble organic solvent (B) contains a glycol monoether (B1), The aqueous inkjet ink has a ratio (by mass) of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 of 0.5 to 50. <2> the total content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and the content of the glycol monoether (B1) is 2 to 20% by mass based on the total mass of the aqueous inkjet ink; <1> 1. The aqueous inkjet ink according to claim 1. <3> Furthermore, the above-mentioned surfactant (C) contains a nonionic surfactant other than an acetylene diol surfactant. <1> or <2> 1. The aqueous inkjet ink according to claim 1. <4> the content of the unmodified acetylenic diol surfactant (A1) is 2 to 400 ppm based on the total amount of the aqueous inkjet ink; <1> ~ <3> 10. The aqueous inkjet ink according to claim 9, wherein the ink is a water-based ink. <5> the ratio (by mass) of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 10 to 5,000; <1> ~ <4> 10. The aqueous inkjet ink according to claim 9, wherein the ink is a water-based ink. <6> the ratio (by mass) of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 20 to 5,000; <5> 1. The aqueous inkjet ink according to claim 1. <7> a printing substrate, and the above-mentioned <1> ~ <6> and a printed layer formed using the aqueous inkjet ink according to any one of the above items. The present invention is related to the subject matter described in Japanese Patent Application No. 2024-053810, filed on March 28, 2024, the disclosure of which is incorporated herein by reference. [Example]

[0151] The present invention will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" are by mass unless otherwise specified.

[0152] <Production Example of Pigment Dispersion Resin Water-Based Solution 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 90 parts of butanol, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. The reaction vessel was then heated to 110°C, and a mixture of polymerizable monomers (30 parts of acrylic acid, 35 parts of behenyl acrylate, and 35 parts of styrene) and a polymerization initiator (4 parts of V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition was completed, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 110°C. Then, 0.4 parts of V-601 was added, and the polymerization reaction was continued for 1 hour while maintaining the internal temperature of the reaction vessel at 110°C, yielding a solution of pigment dispersion resin 1. Next, the contents of the reaction vessel were cooled to room temperature, and 38 parts of dimethylaminoethanol was added to neutralize the pigment dispersion resin 1. Then, 100 parts of ion-exchanged water was added. The contents were then heated to above 100°C, and the butanol was distilled off by azeotroping with the ion-exchanged water. Ion-exchanged water was then added to adjust the solids concentration to 50%, thereby obtaining an aqueous pigment dispersion resin solution 1 with a solids concentration of 50%. The resulting pigment dispersion resin 1 had a weight-average molecular weight of 16,000 and an acid value of 234 mgKOH / g.

[0153] <Production Example of Pigment Dispersion Resin Water-Based Solution 2> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 56 parts of 2-butanone. Next, 56 parts of benzyl methacrylate (polymerizable monomer), 0.3 parts of 2,2'-azobisisobutyronitrile (polymerization initiator), and 2.2 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid (polymerization initiator) were added. The atmosphere inside the reaction vessel was replaced with nitrogen gas, and the contents were heated to 75°C. After that, the polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C, yielding a polymer (A block) composed of benzyl methacrylate. After the polymerization reaction was completed, the contents were cooled to room temperature, and then 44 parts of 2-butanone, 28 parts of butyl methacrylate, and 16 parts of methacrylic acid were added to the reaction vessel. The atmosphere inside the reaction vessel was again purged with nitrogen gas, and the contents were then heated to 75°C. The polymerization reaction was then carried out for 3 hours while maintaining the internal temperature at 75°C. In this way, pigment dispersion resin 2 was obtained, which has an AB block structure in which a copolymer (block B) composed of butyl methacrylate and methacrylic acid was added to the A block. The contents of the reaction vessel were then cooled to room temperature, and 17 parts of dimethylaminoethanol were added to neutralize the pigment dispersion resin 2. Then, 150 parts of ion-exchanged water were added. The contents were then heated to azeotrope 2-butanone with the ion-exchanged water, and the 2-butanone was distilled off. Ion-exchanged water was then added to adjust the solids concentration to 50%, thereby obtaining an aqueous pigment dispersion resin solution 2 with a solids concentration of 50%. The resulting pigment dispersion resin had a weight-average molecular weight of 23,000 and an acid value of 104 mgKOH / g.

[0154] <Production example of cyan pigment dispersion 1> 20 parts of LIONOGEN BLUE FG-7358G (CI Pigment Blue 15:3, manufactured by Toyocolor Co., Ltd.), 15 parts of aqueous pigment dispersion resin solution 1, and 65 parts of ion-exchanged water were mixed and pre-dispersed using a disper. After that, main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads with a diameter of 0.5 mm, and cyan pigment dispersion 1 was obtained.

[0155] <Production example of cyan pigment dispersion 2> Cyan pigment dispersion liquid 2 was produced using the same materials and method as for the above-mentioned cyan pigment dispersion liquid 1, except that pigment dispersion resin water-based solution 2 was used instead of pigment dispersion resin water-based solution 1.

[0156] <Production example of binder resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 72.4 parts of 2-butanone, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. The reaction vessel was then heated to 80°C, and a mixture of polymerizable monomers (15 parts styrene, 4.5 parts methacrylic acid, 5.0 parts 2-hydroxyethyl methacrylate, 20 parts stearyl methacrylate, 55.5 parts methyl methacrylate) and 4 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 80°C. Then, 0.6 parts of V-601 was added, and the polymerization reaction was continued for 2 hours while maintaining the internal temperature at 80°C, yielding a solution of binder resin 1. Next, the contents of the reaction vessel were cooled to 50°C, and then 4.7 parts of dimethylaminoethanol were added to neutralize the binder resin 1. Then, 140 parts of water were added. The contents were then heated to 78°C or higher, and 2-butanone was azeotroped with water to distill off the 2-butanone. Water was then added to adjust the solids concentration to 30%, yielding an aqueous solution of binder resin 1 with a solids concentration of 30%. The weight-average molecular weight of the resulting binder resin 1 was 17,000.

[0157] <Synthesis of unmodified acetylenic diol surfactant (A1)> Using the method described in Example 1 of JP 2002-356451 A and using methyl isobutyl ketone as the raw material ketone, 2,4,7,9-tetramethyl-5-decyne-4,7-diol (unmodified acetylenic diol compound 1, HLB value = 3.0) was synthesized. Similarly, using methyl isoamyl ketone as the raw material ketone, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (unmodified acetylenic diol compound 2, HLB value = 2.7) was synthesized.

[0158] <Synthesis of alkylene oxide-modified acetylenic diol surfactant (A2)> Using the method described in Example 1 of U.S. Pat. No. 3,268,593, alkylene oxide-modified acetylenic diol surfactants (modified acetylenic diol compounds 1-6) with different amounts of ethylene oxide modification were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time) starting from the unmodified acetylenic diol compound 1 (2,4,7,9-tetramethyl-5-decyne-4,7-diol). Furthermore, using unmodified acetylenic diol compound 2 (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol) starting from the unmodified acetylenic diol compound 2 (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol), ethylene oxide-modified acetylenic diol surfactants (modified acetylenic diol compounds 7-14) were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time). Furthermore, by utilizing the method described in Example 1 of JP-A No. 2001-215690, and using modified acetylenic diol compounds 5, 6, 10, and 11 as starting materials, ethylene oxide-propylene oxide modified acetylenic diol surfactants (modified acetylenic diol compounds 15 to 18) were synthesized in which a propylene oxide group was added to the modified acetylenic diol compounds 5, 6, 10, and 11.

[0159] The details of the modified acetylenic diol compounds 1 to 18 produced above (starting material, number of moles of ethylene oxide group and propylene oxide group added, and HLB value) are as shown in Table 1.

[0160] [Table 1]

[0161] <Production examples of water-based inkjet inks 1-114> 25 parts of ion-exchanged water, 20 parts of 1,2-propanediol, 5 parts of propylene glycol monomethyl ether, 1 part of modified acetylenic diol compound 11, 1.0 part of BYK-349 (a silicone surfactant manufactured by BYK-Chemie, HLB value = 10.2), 0.2 parts of TEGO Glide 100 (a silicone surfactant manufactured by Evonik, HLB value = 6.8), 16.7 parts of aqueous binder resin 1 solution, and 25 parts of cyan pigment dispersion 1 were sequentially added to a mixing vessel, and then additional ion-exchanged water was added to bring the total amount to 100 parts.The mixture was then stirred using a disper mixer until sufficiently uniform, and then filtered through a membrane filter with a pore size of 1 μm to remove coarse particles that could cause head clogging, producing aqueous inkjet ink 1.

[0162] Furthermore, water-based inkjet inks 2 to 114 were produced in the same manner as in the production example of water-based inkjet ink 1, except that the raw materials listed in Table 2 were used.

[0163] [Table 2]

[0164] [Table 2-1]

[0165] [Table 2-2]

[0166] [Table 2-3]

[0167] [Table 2-4]

[0168] [Table 2-5]

[0169] [Table 2-6]

[0170] In Table 2, "Nv" represents the solid content concentration, "HLB" represents the HLB value, "Mw" represents the molecular weight, and "bp" represents the boiling point at 1 atmosphere. Also, the "remaining amount" in Table 2 represents the amount required to make the total mass of the mixture 100 parts. Details of the product names listed in Table 2 are as follows: NeoCryl A-1127 (acrylic emulsion manufactured by DSM, solids concentration = 44%, MFT = 7°C) NeoRez R-600 (DSM urethane emulsion, solids concentration = 33%, MFT below 0°C) TEGO Wet 280 (silicone surfactant manufactured by Evonik, HLB value = 9.8) BYK 349 (a silicone surfactant manufactured by BYK Chemie, HLB value = 10.2) BYK 3420 (a silicone surfactant manufactured by BYK Chemie, HLB value = 13.8) BYK 3451 (BYK-Chemie silicone surfactant, HLB value = 10.8) TEGO Glide 100 (silicone surfactant manufactured by Evonik, HLB value = 6.8) TEGO Glide 440 (silicone surfactant manufactured by Evonik, HLB value = 12.7) TEGO Twin 4200 (silicone surfactant manufactured by Evonik, HLB value = 8.2) Brownon EL-1502.2 (Aoki Oil & Fat Co., Ltd. polyoxyethylene lauryl ether, HLB value = 6.3) Brownon EL-1505 (Aoki Oil & Fat Co., Ltd., polyoxyethylene lauryl ether, HLB value = 10.5) Brownon EL-1515 (Aoki Oil & Fat Co., Ltd. polyoxyethylene lauryl ether, HLB value = 14.9) Brownon EL-1530 (Aoki Oil & Fat Co., Ltd., polyoxyethylene lauryl ether, HLB value = 17.4) Brownon BN-3 (Aoki Oil & Fat Co., Ltd., polyoxyethylene-β-naphthol ether, HLB value = 9.6) Lutensol XP30 (BASF polyoxyethylene isodecyl ether, HLB value = 9.1) Lutensol XP40 (BASF polyoxyethylene isodecyl ether, HLB value = 10.5) Lutensol XP100 (BASF polyoxyethylene isodecyl ether, HLB value = 14.7)

[0171] [Examples 1 to 107, Comparative Examples 1 to 7] The aqueous inkjet inks prepared above were evaluated as follows. The evaluation results are shown in Table 3.

[0172] <Rating 1: Solid filling (beading)> The aqueous inkjet inks prepared above were loaded into an inkjet ejection device equipped with a Kyocera Corporation head (KJ4B-1200) installed in an environment of 25°C and 50% RH. A nozzle check pattern was printed, and after confirming that the aqueous inkjet ink was ejecting normally from all nozzles, the device was left to stand for 1 minute. Subsequently, a solid print with 100% coverage was performed on a PET film (FE2001, 12 μm thick) manufactured by Futamura Chemical Co., Ltd. at a frequency of 40 kHz and 1200 × 1200 dpi. The printed PET film was then dried in an air oven at 85°C for 1 minute to obtain a solid print. The number of streaks (areas where the ink did not adhere to the printing substrate and appear streaky) present on the resulting solid print was visually confirmed to evaluate the solid print. As mentioned above, beading manifests as a deterioration in solid print, and the degree of beading can be confirmed by evaluating the solid print. The evaluation criteria are as follows. The ratings of "A+", "A", "B", and "C" were considered to be within the practical range. (Evaluation criteria) A+: Two or fewer streaks were visually observed. A: Three to five streaks were visible to the naked eye. B: 6 to 10 streaks were visible to the naked eye. C: 11 to 20 lines were visible to the naked eye. D: 21 or more lines were visually confirmed.

[0173] <Evaluation 2: Standby discharge> The aqueous inkjet inks prepared above were each filled into an inkjet ejection device equipped with a Kyocera head (KJ4B-1200) installed in an environment of 25°C and 50% RH. A nozzle check pattern was printed, and after confirming that the aqueous inkjet ink was ejecting normally from all nozzles, the device was left to stand for 30 minutes. Thereafter, a nozzle check pattern was printed again, and the number of nozzles from which the aqueous inkjet ink was not ejected (number of missing nozzles) was counted to evaluate standby ejection performance. The evaluation criteria are as follows: "A," "B," and "C" were considered to be in the practical range. (Evaluation criteria) A: The number of missing nozzles was 0 B: The number of missing nozzles was 1 to 5 C: The number of missing nozzles was 6 to 10. D: The number of missing nozzles was 10 or more.

[0174] <Rating 3: Pinhole resistance> Using the same printing conditions and printing substrate as in Evaluation 1 above, 10 solid prints with a printing rate of 100% were produced. The number of pinholes present in the obtained solid prints was then visually confirmed, and pinhole resistance was evaluated by counting the total number of pinholes present in the 10 prints. The evaluation criteria were as follows: "A", "B", and "C" were considered to be in the practical range. (Evaluation criteria) A: There were no pinholes at all. B: The total number of pinholes was 1 to 2 C: The total number of pinholes was 3 to 5. D: The total number of pinholes was 6 or more.

[0175] Furthermore, for aqueous inkjet inks that were rated "A" for pinhole resistance, an additional evaluation was conducted using the method described below. Specifically, 30 solid prints were produced using the same printing conditions and printing substrate as in Evaluation 1 above, and the number of pinholes present in the 30 solid prints was visually confirmed. If no pinholes were present in the 30 solid prints, or if the total number of pinholes present in the 30 solid prints was one, the pinhole resistance was rated "A+." Naturally, aqueous inkjet inks rated "A+" are usable.

[0176] <Rating 4: Migration resistance> Using the same printing conditions as in Evaluation 1 above, solid printing was carried out at a printing rate of 100% on an OPP film (FOS-AQ, thickness 40 μm) manufactured by Futamura Chemical Co., Ltd. Next, the obtained print was placed in a migration cell (MigraCell (registered trademark) MC60 manufactured by Gassner Glastechnik) with the non-printed surface (OPP film surface) facing up, and 50 mL of 95% ethanol was added. The contact area between the non-printed surface of the solid print and the 95% ethanol was 0.5 dm 2The migration cell was then placed in a 40°C oven for 10 days, after which the 95% ethanol solution was removed and concentrated to 2 mL or less under conditions of 40°C and 50 mmHg. When the amount of the concentrated ethanol solution was less than 2 mL, it was placed in a 2 mL volumetric flask and filled up with 95% ethanol. The ethanol solution after concentration and filling up was used as a sample, and the amount (total amount) of acetylene diol surfactant (A) contained per mL of the ethanol solution after concentration and filling up was quantified using a gas chromatograph mass spectrometer (Agilent 7890A / 5975C manufactured by Agilet Technologies) to evaluate migration resistance. The evaluation criteria were as follows: "A," "B," and "C" were considered to be within the range of practical use. (Evaluation criteria) A: The amount of acetylene diol surfactant (A) eluted was 0.1 μg / mL or less. B: The amount of acetylene diol surfactant (A) eluted was greater than 0.1 μg / mL and less than 1.0 μg / mL. C: The amount of acetylene diol surfactant (A) eluted was greater than 1.0 μg / mL and less than 3.0 μg / mL. D: The amount of acetylene diol surfactant (A) eluted was more than 3.0 μg / mL.

[0177] [Table 3]

[0178] [Table 3-1]

[0179] [Table 3-2]

[0180] As is clear from Examples 1 to 107, the aqueous inkjet inks of the present embodiment, which contain 2 to 600 ppm of unmodified acetylenic diol surfactant (A1), and further contain alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and glycol monoethers (B1) in a predetermined blending ratio (mass ratio), exhibited good solid filling without beading, excellent pinhole resistance and migration resistance, and good standby ejection properties.

[0181] On the other hand, in the aqueous inkjet ink 1 containing no unmodified acetylenic diol surfactant (A1), even when the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1) were used in a suitable mass ratio range, beading occurred, resulting in poor solid coverage (Comparative Example 1). Conversely, in the aqueous inkjet inks 43 to 45 and 48 containing 2 to 600 ppm of the unmodified acetylenic diol surfactant (A1) but not containing at least one of the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1), problems such as poor solid coverage, poor standby ejection performance, and the occurrence of pinholes occurred (Comparative Examples 4 to 7).

Claims

1. An aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B), the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12; the content of the unmodified acetylenic diol surfactant (A1) is 2 to 600 ppm relative to the total mass of the aqueous inkjet ink; the water-soluble organic solvent (B) contains a glycol monoether (B1), the mass ratio of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 is 0.5 to 50.

2. 2. The aqueous inkjet ink according to claim 1, wherein the sum of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and the content of the glycol monoether (B1) is 2 to 20 mass % relative to the total mass of the aqueous inkjet ink.

3. The aqueous inkjet ink according to claim 1 or 2, further comprising a nonionic surfactant (C) other than the acetylene diol surfactant.

4. 3. The aqueous inkjet ink according to claim 1, wherein the content of the unmodified acetylenic diol surfactant (A1) is 2 to 400 ppm based on the total mass of the aqueous inkjet ink.

5. 3. The aqueous inkjet ink according to claim 1, wherein the mass ratio of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 10 to 5,000.

6. 6. The aqueous inkjet ink according to claim 5, wherein the mass ratio of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 20 to 5,000.

7. A printed matter comprising a printing substrate and a printing layer formed on the printing substrate using the aqueous inkjet ink according to claim 1 or 2.

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