Aqueous inkjet ink and printed matter

Abstract

This 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.

Description

Water-based inkjet inks and printed materials

[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.

[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 minute droplets of ink are ejected from an inkjet head and landed on a printing substrate (also simply referred to as "substrate" in this specification) to print images and characters on the printing substrate. The above-mentioned "image" also includes solid images (images printed at a printing rate of 100% 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, etc., and has recently been increasingly used in industrial printing applications.

[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, simply referred to as "inks"). In the packaging market, paper containers, labels, flexible packaging, and the like are manufactured, sold, and used. 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 quality and properties that can withstand practical use, even on low-absorbency substrates and non-absorbency substrates.

[0006] In contrast, typical aqueous inkjet inks that have existed until now 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 aqueous inkjet 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 in a printed item with a 100% coverage rate), uneven density, color bleeding, and other problems, resulting in a significant degradation of print quality.

[0007] A known method for suppressing beading is to reduce the surface tension of the aqueous inkjet ink. Furthermore, surfactants are often used as a material for reducing the surface tension. In particular, to sufficiently reduce the surface tension of the aqueous inkjet ink 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) as the surfactant. However, when using such a surfactant, 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 toward 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 the 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 a low-absorbency or non-absorbency substrate 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 having an HLB value of 6.0 or more but 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 the above Patent Documents 1 to 3 were also not sufficient in terms of improving beading when printed on a non-absorbent substrate.

[0012] Furthermore, Patent Document 4 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. Here, 2,4,7,9-tetramethyl-5-decyne-4,7-diol corresponds to the aforementioned "compound having a small molecular weight and a high rate of orientation to the droplet surface (air-liquid interface)," and therefore, the aqueous ink is considered to be effective in suppressing beading. On the other hand, it cannot be said that Patent Document 4 has sufficiently 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.

[0013] JP 2022-151398 A JP 2021-147400 A JP 2018-70730 A JP 2014-139004 A

[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.

[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 relates to an aqueous inkjet ink containing a pigment, a binder resin, an acetylenic diol surfactant (A), and a water-soluble organic solvent (B), wherein 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, and the water-soluble organic solvent (B) comprises glycol monoethers (B1), and the 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 is 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 on a printing substrate.

[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.

[0018]

[0033] Below, an aqueous inkjet ink (hereinafter also referred to simply as "the ink of this embodiment") and a printed matter obtained by printing with the aqueous inkjet ink are described as embodiments of the present invention. However, the embodiments of the present invention are not limited to the following description, and include various modified examples that are implemented within the scope of the gist of the invention.

[0019] <Aqueous Inkjet Ink> Generally, water, which is the main solvent of aqueous inkjet ink, has a high surface tension and is difficult to 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. When beading occurs, uneven density, color mixing, bleeding, etc. occur, significantly reducing the quality of the printed matter.

[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 inkjet heads, surfactants with low molecular weights and high orientation rates may rapidly and excessively orient at the gas-liquid interface, 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 bleeding of the surfactant 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]

[0010] 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 also contains, as acetylenic diol surfactants, 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 "surfactant with a low molecular weight and a high orientation rate" described above. As described above, surfactants with a low molecular weight and a high orientation rate directly affect the occurrence of pinholes and migration, and therefore, it is preferable that their amount be 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 ejection properties and occurrence of pinholes remains.

[0027] Therefore, the ink of this embodiment uses an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and glycol monoethers (B1) in addition to the unmodified acetylenic diol surfactant (A1). 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 incorporated in a small amount, which may increase the risk of beading. However, the alkylene oxide-modified acetylenic diol surfactant (A2) itself is 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, and 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 studies 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, 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. The presence of a certain amount of glycol monoethers (B1) is thought to uniformly reduce 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 gas-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 an inkjet head, the nonionic surfactant (C) is less likely to contribute to rapid and excessive orientation toward the gas-liquid interface, which is believed to suppress deterioration of standby ejection performance. 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 the unmodified acetylenic diol surfactant (A1) is blended, the unmodified acetylenic diol surfactant (A1) can be prevented from bleeding onto the surface of the laminate 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 in that 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 acetylene 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. 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, preferably 3 to 400 ppm, and more preferably 5 to 200 ppm. Using the unmodified acetylene glycol surfactant (A1) within 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. Furthermore, since the amount of the unmodified acetylene glycol surfactant (A1) blended is small to begin with, migration in printed materials can also be easily suppressed. 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 Acetylene Diol Surfactant (A2)> In the ink of this embodiment, an alkylene oxide-modified acetylenic diol surfactant (A2) is used in addition to 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 surfactant properties. 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 calculating 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 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 × (sum of molecular weights of hydrophilic portions) ÷ (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, and therefore the HLB value used is the value actually measured by the method described on page 324 of "Handbook of Surfactants" (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 × 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 discharge properties 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 between 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] Specific examples of the alkylene oxide-modified acetylenic diol surfactant (A2) include compounds represented by the following general formula (3).

[0047] General formula (3):

[0048] In general formula (3), R１ 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 rate, 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 a commercially available product may be used. 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 Co., Ltd.; Olfine E1004 manufactured by Nissin Chemical Industry Co., Ltd.; and Acetylenol E40 and Acetylenol E60 manufactured by Kawaken Fine Chemicals Co., Ltd.

[0051] <Other acetylenic 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 simply as "other acetylenic diol surfactants" in this specification). Examples of other acetylenic diol surfactants include alkylene oxide-modified acetylenic diol surfactants having an HLB value of less than 6 and alkylene oxide-modified acetylenic diol surfactants having 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 materials essential to the ink of this embodiment, such as water, the acetylenic diol surfactant (A), and the glycol monoethers (B1), thereby realizing suppression of beading and further improvement of standby ejection properties, and 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, making it easier to suppress pinholes in printed materials and improve standby discharge properties. Furthermore, the orientation speed of these acetylenic diol surfactants to interfaces is suitably maintained, thereby improving solid coverage in printed materials.

[0053] The weighted average HLB value is an average HLB value calculated by weighting according to the content of the target compound. For example, when 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). Furthermore, at least a glycol monoether (B1) is used as the water-soluble organic solvent (B). As described above, the glycol monoether (B1) can emulsify and compatibilize the unmodified acetylenic diol surfactant (A1), and therefore the ink of this embodiment has improved standby ejection properties. Furthermore, the glycol monoether (B1) contributes to a reduction in 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 ３ represents 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. Note that the above "(n / iso)" represents the normal isomer and / or the isomer, and "(n / iso / tert)" represents one or more compounds selected from the group consisting of the normal isomer, the isomer, and the tertiary isomer.

[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 preferably used, because they have an excellent ability to emulsify and compatibilize the unmodified acetylenic diol surfactant (A1), a good balance between low surface tension and a low boiling point at 1 atmospheric pressure, and further have high hydrophilicity, thereby simultaneously realizing suppression of beading, improvement of standby discharge properties, and improvement of 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 the 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 from 0.5 to 20 mass%, more preferably from 1 to 15 mass%, and even more preferably from 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 ejection 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 components 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 in this specification as "other water-soluble organic solvents").

[0066] Examples of 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); and polyalkylene glycols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Examples of compounds that can be used include 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; and lactone solvents such as γ-butyrolactone and ε-caprolactone. 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, it is possible to improve the compatibility of the main components of the ink, such as water, the acetylene diol surfactant (A), and the glycol monoethers (B1). It is also possible to achieve further suppression of beading and improvement of standby discharge properties. Among the alkanediols having 2 to 6 carbon atoms, from the viewpoint of particularly exhibiting the above-mentioned effects and improving beading and standby discharge properties, it is preferable to use an alkanediol having a 1-hydroxyethyl group (CH ３ Alkanediols having 2 to 6 carbon atoms and having a 1-hydroxyethyl group (—CH(OH)—) are particularly preferred. 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 preferably used from the viewpoints of excellent compatibility with the acetylene diol surfactant (A) and the glycol monoethers (B1) and high beading suppression. 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 ejection 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, it is even more preferable that the amount of water-soluble organic solvents having a boiling point of 235°C or higher is 2% by mass or less (0 to 2% by mass), and that the amount of water-soluble organic solvents having a boiling point of 210°C or higher is 5% by mass (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 that 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 that is also excellent in 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 an acetylenic diol surfactant can be used in combination. It is believed that the use of the nonionic surfactant (C) interacts with the acetylenic diol surfactant (A), causing the nonionic surfactant (C) and the acetylenic diol surfactant (A) to behave like a single surfactant. As a result, standby ejection 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 the wetting and spreading of ink droplets on the printing substrate and enable the ink droplets to be uniformly wetted and spread, making it easier to obtain printed materials without beading.

[0073] The HLB value of the nonionic surfactant (C) is preferably 6 to 14, and 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, solid filling, standby discharge properties, pinhole resistance, and migration resistance are all excellent. Note that the above expression "(weighted average) HLB value of the nonionic surfactant (C)" indicates that when the ink contains only one type of nonionic surfactant (C), the HLB value of that nonionic surfactant (C) is used. Furthermore, when the ink contains two or more types of nonionic surfactants (C), the weighted average value of the HLB values ​​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%, more preferably 0.3 to 2.5 mass%, and even more preferably 0.5 to 2.0 mass%, relative to the total mass of the ink. 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, this 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 may be a commercially available product. In addition, 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, polyalkylene glycol alkylate surfactants, etc. 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 is likely to interact 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):

[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 When is a methyl group, p is 0.

[0081] General formula (6):

[0082] In 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. ６is 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, 8032 ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Dow Corning Toray 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, and TEGO Examples of such commercially available products include Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Rad 2200, TEGO Rad 2250, TEGO Rad 2300, TEGO Twin 4000, TEGO Twin 4100, and TEGO Twin 4200 manufactured by Shin-Etsu Chemical Co., Ltd.; 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 matter, it is preferable for the acetylenic diol surfactant (A) and the nonionic surfactant (C) to be compatible to some extent. From the above viewpoint, 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 alkenyl group, an optionally branched alicyclic alkyl group having one or more alkyl groups added thereto, and an optionally branched aromatic group having one or more alkyl groups added thereto; 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 the Emulgen series (manufactured by Kao Corporation) such as Emulgen 104P, 105, 106, 108, 109P, 120, 123P, 150, 210, 220, 306P, 320P, and 350; and the Braunon series (manufactured by Aoki Oil & Fat Industries Co., Ltd.) such as Braunon 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, and BN-3. Nonion series 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 (manufactured by NOF Corporation), Lutensol series such as Lutensol XL40, 50, 60, 70, 80, 90, XP30, 40, 50, 60, 70, 80, 90, 100 (manufactured by BASF), Newcol series such as Newcol 2302, 2303, 2305, 2308, 2310, 2320, 2360 (manufactured by Nippon Nyukazai Co., Ltd.), Emulmin Examples of suitable acrylic acid esters include LS-80, LS-90, NL-70, NL-80, NL-90, NL-100, NL-110, Sanonic SS-30, SS-50, SS-70, SS-90, and SS-120 (manufactured by Sanyo Chemical Industries, Ltd.), and Akator 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 commercially available products listed above, diethylene glycol monohexyl ether, triethylene glycol monohexyl ether, and tetraethylene glycol monohexyl ether can also be used. The above-listed products may be used alone or in combination of two or more. Furthermore, the polyoxyalkylene alkyl ether surfactant may be synthesized by a conventionally known synthesis method.

[0090] In the case of polyoxyalkylene alkyl ether surfactants, similarly to 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 ​​between 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> The aqueous inkjet ink of this embodiment may further contain surfactants other than the surfactants described above. For example, ionic (anionic or cationic) surfactants, amphoteric surfactants, etc. can be used.

[0093] <Binder Resin> In the ink of this embodiment, a binder resin may be used, as this 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 mass aqueous mixture 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 an emulsifier such as a surfactant or polymer. 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 to form 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, by using a TSKgel column (manufactured by Tosoh Corporation) and a GPC (manufactured by Tosoh Corporation, HLC-8120GPC) equipped with an RI detector, and measuring the weight-average molecular weight in terms of polystyrene using THF as a developing solvent.

[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 re-dissolved in the ink, which makes it easier to suppress 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 has na acid groups with a value of va per molecule and contains Wa mass % of a polymerizable monomer having a molecular weight of Ma among the polymerizable monomers constituting the resin, the acid value (mg KOH / g) can be calculated using the following formula (8):

[0103] Equation (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% by mass, more preferably 1 to 8% by mass, and even more preferably 2 to 6% by mass, relative to the total mass of the ink. When the content of the water-soluble resin is 0.5% by 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, when the content of the water-soluble resin is 10% by 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 Microparticles) 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, by using resin microparticles, a larger amount of resin can be contained in the ink, which makes it easier to improve the abrasion resistance, blocking resistance, and migration resistance of printed matter.

[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 fine 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 addition to the viewpoint of improving the standby discharge property 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, the MFT of the resin microparticles may be further reduced depending on the water-soluble organic solvent added to the ink, and the resin microparticles may adhere to the inkjet head nozzles even at room temperature, causing 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 constituting the emulsion to achieve an MFT of 60°C or higher.

[0110] Furthermore, when a hydrosol is used as the resin fine particles, the possibility of standby dischargeability being deteriorated is not as high as in the case of an emulsion. On the other hand, using a hydrosol with an MFT of 60° C. or higher can reduce factors that can deteriorate standby dischargeability, so it is preferable to set the MFT to 60° C. or higher even in the case of 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, the content thereof is preferably 2 to 15% by mass, and more preferably 4 to 10% by mass, relative to the total mass of the ink. If the content of the emulsion 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 will have excellent standby discharge properties.

[0113] <Pigment> The ink of this embodiment contains a pigment. As the pigment, inorganic pigments and / or organic pigments can be used as desired. These pigments may be used alone or in combination of two or more types. 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 preferred. ２ / g, a volatile content of 0.5 to 10%, a pH of 2 to 10, etc. are suitable. Examples of commercially available products with such specifications include No. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, MCF88 (manufactured by Mitsubishi Chemical Corporation), RAVEN1255 (manufactured by Birla Carbon Corporation), REGAL330R, 400R, 660R, MOGUL L, ELFTEX415 (manufactured by Cabot Corporation), NIPex90, NIPex150T, NIPex160IQ, NIPex170IQ, NIPex75, PrinteX35, PrinteX85, PrinteX90, PrinteX95, PrinteXU (manufactured by Orion Engineered Carbons), and the like, 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 of cyan pigments in terms of color index include C.I. Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, 64, and the like.

[0118] Examples of magenta pigments include C.I. 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, 282, C.I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

[0119] Examples of yellow pigments include C.I. 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 (C.I. Pigment Black 1), perylene black (C.I. 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] In addition to the above pigments, C.I. Pigment Green 7, 10, 36, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, and the like can be mentioned.

[0122] <Pigment Dispersion Resin> In order to maintain the storage stability and standby dischargeability of the ink for a long period of time, the pigment is preferably used in a dispersed state in the ink. Methods for stably dispersing and maintaining the pigment in the ink include (1) a method of covering at least a portion of the pigment surface with a pigment dispersing resin, (2) a method of adsorbing a water-soluble and / or water-dispersible surfactant onto the pigment surface, and (3) a method of chemically and / or physically introducing a hydrophilic functional group onto the pigment surface and dispersing it 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 consistently impart 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, from the viewpoint of strengthening adsorption to the pigment and improving storage stability and standby discharge properties, 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. In this specification, "maleic acid (anhydride)" refers to maleic acid and / or maleic 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 this 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 blending amount of the pigment dispersion resin relative to the blending amount of the pigment is preferably 1 to 120% by mass. By making the ratio of the pigment dispersion resin 1% by mass or more relative to the blending amount of the pigment, the viscosity of the ink can be kept within a range suitable for use in inkjet printing applications, and standby ejection properties can be improved. 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 blending amount of the pigment dispersion resin relative to the blending amount of the pigment is more preferably 2 to 100% by mass, and even more preferably 5 to 50% by mass.

[0128] <Water> In addition to the above-mentioned components, the ink of this embodiment further contains water. 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, relative to 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 Components> In addition to the above components, the ink of the present invention may contain additives such as a pH adjuster, an ultraviolet absorber, a preservative, etc., in order 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 manufacturing the ink of this embodiment containing the above-mentioned components. The following method is an example of a method for manufacturing the ink of this embodiment. The following method includes preparing a pigment dispersion, and then adding and mixing a surfactant and a solvent such as water. However, the ink manufacturing method of this embodiment is not limited to the following method.

[0132] In a typical production method, a pigment dispersion resin and water are mixed to prepare a water-based pigment dispersion resin solution. Next, a pigment and, if necessary, a water-soluble organic solvent are added to the water-based pigment dispersion resin solution, followed by mixing and stirring (premixing), and then a dispersion treatment is performed using a dispersing means described below. Furthermore, if necessary, coarse particles are removed by centrifugation or other treatment to obtain a pigment dispersion. Subsequently, an unmodified acetylenic diol surfactant (A1), an alkylene oxide-modified acetylenic diol surfactant (A2), a binder resin, glycol monoethers (B1), water, and, if necessary, a nonionic surfactant (C), and other components are added to the pigment dispersion, followed by thorough mixing and stirring. 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 printing using an inkjet printing method, it is preferable to use a pigment having an optimal particle size distribution from the perspective 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 ink using a filter or centrifuge after dispersion treatment, and combinations of these methods. The particle size distribution of the ink can be measured using, for example, a Nanotrac UPA-EX150 manufactured by Microtrac-Bell.

[0137] <Ink Set> The inks 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 enhance 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 set may include, as a constituent color, an ink (clear ink) that does not substantially contain a colorant component, i.e., a pigment is excluded from the constituent components of the ink of this embodiment.

[0138] <Ink-Pretreatment Liquid Set> The aqueous inkjet ink of this embodiment can also be used in the form of an ink-pretreatment liquid set in combination with a pretreatment liquid containing an aggregating agent. 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. Then, by landing the ink of this embodiment on this ink aggregation layer, bleeding between ink droplets and uneven density can be prevented, significantly improving the print quality of the printed matter. Furthermore, depending on the material used in the pretreatment liquid, the adhesion and blocking resistance of the printed matter 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. Among these, from the viewpoint of obtaining excellent print image quality, it is preferable to use a metal salt as the flocculant, and Ca ２＋ , 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 additives that can be added to the pretreatment liquid include 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 Material One embodiment of the present invention relates to a printed material obtained by printing the aqueous inkjet ink of this embodiment on a printing substrate. The printed material comprises a printing substrate and a printed layer (ink layer) formed on the printing substrate by printing with the aqueous inkjet ink of this embodiment. <Printed Substrate> As described above, the ink of this embodiment is particularly suitable for use in printing on non-absorbent substrates such as films. When using a non-absorbent substrate as the printing substrate, 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; or film- or sheet-like substrates made of composite materials thereof. These printing substrates may be subjected to surface treatments such as corona treatment and plasma treatment. Alternatively, the pre-coating treatment may be performed using a pre-coating composition (however, different from the above-mentioned pre-treatment liquid) containing one or more resins selected from the group consisting of urethane-based resins, acrylic-based resins, and olefin-based resins.

[0142] <Method for producing printed matter> The ink of the present embodiment is used in a printing method in which the ink is ejected from the nozzles of an inkjet head and droplets of the ink are deposited on a substrate. Furthermore, in this specification, a printing substrate on which an image and / or text is printed and which is produced by such a printing method is referred to as a "printed matter." In other words, the ink of the present 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 in combination. 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> If necessary, the surface of the printed matter of this embodiment may be subjected to a post-coating treatment. 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 permeability to the interface of a printed material, and 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 to the interface of a printed material obtained using the ink of this embodiment, for example, to the printed layer (printed area) and the pretreatment liquid layer (non-printed area), and also provide excellent laminate strength to a laminated printed material (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 materials obtained with the ink of the present invention, and the laminate strength of laminated printed materials (laminates), it is preferable that the polyisocyanate component contains a polyether-based urethane resin terminated with an isocyanate group. From the same viewpoints 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. Alternatively, a film having a vapor-deposited metal (oxide) layer such as aluminum oxide may be used.

[0150] Representative embodiments of the present invention are described below. <1> An aqueous inkjet ink containing a pigment, a binder resin, an acetylenic diol surfactant (A), and a water-soluble organic solvent (B), wherein 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, and the water-soluble organic solvent (B) comprises glycol monoethers (B1), and the 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 is 0.5 to 50. <2> The aqueous inkjet ink according to <1> above, 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 monoethers (B1) is 2 to 20% by mass, based on the total mass of the aqueous inkjet ink. <3> The aqueous inkjet ink according to <1> or <2> above, further comprising a nonionic surfactant (C) other than the acetylenic diol surfactant. <4> The aqueous inkjet ink according to any one of <1> to <3> above, 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> The aqueous inkjet ink according to any one of <1> to <4> above, wherein 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 5000. <6> The aqueous inkjet ink according to <5> above, wherein 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 5000.<7> A printed matter having a printing substrate and a printing layer formed on the printing substrate using the aqueous inkjet ink described in any one of <1> to <6> above. 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.

[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> 90 parts of butanol was charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. Next, the reaction vessel was heated to 110°C, and then a mixture of polymerizable monomers (30 parts of acrylic acid, 35 parts of behenyl acrylate, and 35 parts of styrene) and 4 parts of a polymerization initiator (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After completion of the addition, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 110°C. Thereafter, 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, thereby obtaining a solution of pigment dispersion resin 1. Next, the contents of the reaction vessel were cooled to room temperature, and then 38 parts of dimethylaminoethanol was added to neutralize the pigment dispersion resin 1, followed by the addition of 100 parts of ion-exchanged water. Thereafter, the contents were heated to 100°C or higher to form an azeotrope of butanol with the ion-exchanged water and distill off the butanol. Next, ion-exchanged water was 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-Soluble Solution 2> 56 parts of 2-butanone were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer. Next, 56 parts of benzyl methacrylate as a polymerizable monomer, 0.3 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 2.2 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid were charged. The atmosphere inside the reaction vessel was purged with nitrogen gas, and the contents of the reaction vessel were heated to 75°C. A polymerization reaction was then carried out for 3 hours while maintaining the internal temperature at 75°C, yielding a polymer (A block) composed of benzyl methacrylate. After completion of the polymerization reaction, 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 charged into the reaction vessel. The atmosphere inside the reaction vessel was again purged with nitrogen gas. The contents of the reaction vessel were then heated to 75°C, after which a polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C. In this manner, a pigment dispersion resin 2 having an A-B block structure in which a copolymer (block B) composed of butyl methacrylate and methacrylic acid was added to the A block was obtained. The contents of the reaction vessel were then cooled to room temperature, and 17 parts of dimethylaminoethanol was added to neutralize the pigment dispersion resin 2. Then, 150 parts of ion-exchanged water was added. The contents were then heated to azeotrope 2-butanone with 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 a water-based 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 Liquid 1> 20 parts of LIONOGEN BLUE FG-7358G (C.I. Pigment Blue 15:3, manufactured by Toyocolor Co., Ltd.), 15 parts of Pigment Dispersion Resin Water-Based Solution 1, and 65 parts of ion-exchanged water were mixed and pre-dispersed using a Disper, and then main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm, thereby obtaining Cyan Pigment Dispersion Liquid 1.

[0155] <Production Example of Cyan Pigment Dispersion Liquid 2> Cyan pigment dispersion liquid 2 was produced using the same raw materials and method as for the above-mentioned Cyan Pigment Dispersion Liquid 1, except that the Pigment Dispersion Resin Water-Soluble Solution 2 was used instead of the Pigment Dispersion Resin Water-Soluble Solution 1.

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

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

[0158] Synthesis of Alkylene Oxide-Modified Acetylene 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 to 6) with different amounts of ethylene oxide modification were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time) using the unmodified acetylenic diol compound 1 (2,4,7,9-tetramethyl-5-decyne-4,7-diol) as a starting material. Furthermore, ethylene oxide-modified acetylenic diol surfactants (modified acetylenic diol compounds 7 to 14) were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time) using the unmodified acetylenic diol compound 2 (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol) as a starting material. Furthermore, by utilizing the method described in Example 1 of JP-A-2001-215690, 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 shown in Table 1.

[0160]

[0161] <Production Example of Water-Based Inkjet Inks 1 to 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-based surfactant manufactured by BYK-Chemie, HLB value = 10.2), 0.2 parts of TEGO Glide 100 (a silicone-based 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 charged into a mixing vessel, and then additional ion-exchanged water was added so that the total amount added was 100 parts. The mixture was then stirred using a disper mixer until it was sufficiently uniform, and then filtered using a membrane filter with a pore size of 1 μm to remove coarse particles that may cause head clogging, thereby producing water-based 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]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[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. Furthermore, the "remaining amount" in Table 2 represents the amount required to bring the total mass of the mixture to 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 (urethane emulsion manufactured by DSM, solids concentration = 33%, MFT less than 0°C) TEGO Wet 280 (silicone surfactant manufactured by Evonik, HLB value = 9.8) BYK 349 (silicone surfactant manufactured by BYK, HLB value = 10.2) BYK 3420 (silicone surfactant manufactured by BYK, HLB value = 13.8) BYK 3451 (silicone surfactant manufactured by BYK, 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) BRAWNON EL-1502.2 (polyoxyethylene lauryl ether manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 6.3) BRAWNON EL-1505 (polyoxyethylene lauryl ether manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 10.5) BRAWNON EL-1515 (polyoxyethylene lauryl ether manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 14.9) BRAWNON EL-1530 (polyoxyethylene lauryl ether manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 17.4) BRAWNON BN-3 (polyoxyethylene-β-naphthol ether manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 9.6) Lutensol XP30 (polyoxyethylene isodecyl ether manufactured by BASF, HLB value = 9.1) Lutensol XP40 (polyoxyethylene isodecyl ether manufactured by BASF, HLB value = 10.5) Lutensol XP100 (polyoxyethylene isodecyl ether manufactured by BASF, 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] <Evaluation 1: Solid Beading (Beading)> An inkjet ejection device equipped with a Kyocera Corporation head (KJ4B-1200) installed in an environment of 25°C and 50% RH was filled with each of the aqueous inkjet inks prepared above. A nozzle check pattern was printed, and after confirming that the aqueous inkjet ink was being ejected normally from all nozzles, the device was left to stand for 1 minute. Subsequently, a solid print was performed at a printing frequency of 40 kHz and 1200 x 1200 dpi on a PET film (FE2001, thickness 12 μm) manufactured by Futamura Chemical Co., Ltd., with a printing rate of 100%, and the printed PET film was then dried in an air oven at 85°C for 1 minute to obtain a solid print. The solid print was then evaluated for solid beading by visually checking the number of streaks (areas where the ink did not adhere to the printing substrate and appeared streaky). As mentioned above, when beading occurs, it appears as a deterioration in solid filling, so the degree of beading can be confirmed by evaluating the solid filling. The evaluation criteria are as follows. Evaluations of "A+", "A", "B", and "C" were considered to be in the usable range. (Evaluation criteria) A+: Two or fewer streaks were visible to the naked eye. A: Three to five streaks were visible to the naked eye. B: Six to ten streaks were visible to the naked eye. C: Eleven to twenty streaks were visible to the naked eye. D: 21 or more streaks were visible to the naked eye.

[0173] <Evaluation 2: Standby Dischargeability> Each of the aqueous inkjet inks prepared above was filled into an inkjet discharge 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 being discharged 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 discharged (number of clogged nozzles) was counted to evaluate the standby dischargeability. The evaluation criteria were as follows. A rating of "A", "B", or "C" was considered to be within the range of practical use. (Evaluation Criteria) A: The number of clogged nozzles was 0 B: The number of clogged nozzles was 1 to 5 C: The number of clogged nozzles was 6 to 10 D: The number of clogged nozzles was 10 or more

[0174] <Evaluation 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 are as follows. Evaluations of "A", "B", and "C" were considered to be in the practical range. (Evaluation Criteria) A: No pinholes were found 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, additional evaluation was carried out 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] <Evaluation 4: Migration Resistance> Using the same printing conditions as in Evaluation 1 above, a solid print was performed with a printing rate of 100% on an OPP film (FOS-AQ, 40 μm thick) manufactured by Futamura Chemical Co., Ltd. Next, the non-printed surface (OPP film surface) of the obtained print was placed in a migration cell (MigraCell (registered trademark) MC60 manufactured by Gassner Glastechnik) with the non-printed 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 dm2. Thereafter, the migration cell was left to stand 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. Furthermore, if the amount of ethanol solution after concentration 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 fill-up was used as a sample, and the amount (total amount) of acetylenic diol surfactant (A) contained per mL of the ethanol solution after concentration and fill-up was quantified using a gas chromatograph mass spectrometer (Agilent 7890A / 5975C manufactured by Agilent Technologies) to evaluate migration resistance. The evaluation criteria were as follows. Evaluations of "A," "B," and "C" were considered to be within the range of practical use. (Evaluation Criteria) A: The amount of eluted acetylenic diol surfactant (A) was 0.1 μg / mL or less. B: The amount of eluted acetylenic diol surfactant (A) was more than 0.1 μg / mL and 1.0 μg / mL or less. C: The amount of eluted acetylenic diol surfactant (A) was more than 1.0 μg / mL and 3.0 μg / mL or less. D: The amount of eluted acetylenic diol surfactant (A) was more than 3.0 μg / mL.

[0177]

[0178]

[0179]

[0180] As is clear from Examples 1 to 107, the aqueous inkjet inks of the present embodiment, which contain 2 to 600 ppm of the unmodified acetylenic diol surfactant (A1), and further contain the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and the glycol monoethers (B1) in a predetermined blending ratio (mass ratio), exhibited good solid filling without beading, were excellent in pinhole resistance and migration resistance, and also had 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 acetylenic diol surfactant (A), and a water-soluble organic solvent (B), wherein 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, and the water-soluble organic solvent (B) comprises a glycol monoether (B1), and the mass ratio of the content of the glycol monoether (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. 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 % based on 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 an acetylene diol surfactant.

4. The aqueous inkjet ink according to any one of claims 1 to 3, 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. The aqueous inkjet ink according to any one of claims 1 to 4, 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. 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 having a printing substrate and a printing layer formed on the printing substrate using the aqueous inkjet ink according to any one of claims 1 to 6.

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