Aqueous inkjet ink and printed matter

Abstract

An aqueous inkjet ink according to the present invention comprises a pigment, an acetylenediol-based compound (A), polyethylene glycol, a binder resin, and an organic compound (B) (excluding the above components and resin), wherein: the HLB value of the acetylenediol-based compound (A) is 7.5-17.5; the organic compound (B) consists only of a carbon atom, a hydrogen atom, and an oxygen atom, has a plurality of hydroxyl groups, and has an HLB value of 2.5-5.2; and the binder resin contains not less than 50 mass% of a resin (C-1) having a glass transition temperature of -60 to 50°C in the total mass of resins in the aqueous inkjet ink.

Description

Water-based inkjet inks and printed materials

[0001] The present disclosure relates to aqueous inkjet inks and printed materials.

[0002] With the increasing need for small-lot printing and reduced printing costs, digital printing methods that do not require plate making are rapidly becoming more popular.

[0003] Inkjet printing, which is one type of digital printing method, is a method of printing images and / or characters on a printing substrate (also simply referred to as "substrate" in this disclosure) by ejecting ink droplets from fine nozzles and applying them to the printing substrate. Inkjet printing has features such as easy operation of the printing device and low noise during printing, and therefore printing devices (inkjet printers) that employ this inkjet printing method are in high demand among digital printing methods.

[0004] The above "image" also includes seamless images such as solid images and checkered pattern images.

[0005] Inks used in inkjet printing methods (referred to as "inkjet inks" in this disclosure) are classified into solvent-based, water-based, ultraviolet-curable, and other types depending on their composition. Meanwhile, in recent years, there has been an accelerating trend toward restricting the use of raw materials that are harmful to humans and the environment. Accordingly, there has been an increasing demand for water-based inkjet inks (also simply referred to as "water-based inkjet inks" in this disclosure) rather than solvent-based inkjet inks and ultraviolet-curable inkjet inks that use these raw materials.

[0006] Recently, with the improvement in the performance of inkjet heads, the use of inkjet printing has been expanding not only for consumer use but also for industrial printing. In particular, in the packaging (label / package) printing market, there is active consideration of replacing plate printing methods such as offset printing and gravure printing with inkjet printing.

[0007] However, in the past, solid prints (prints with a printing rate of 100%) made using aqueous inkjet inks on non-permeable substrates such as plastic films and sheets have suffered from a phenomenon known as "whiteout," in which areas where the aqueous inkjet ink does not adhere to the printing substrate, and a phenomenon known as "color bleeding," in which aqueous inkjet inks of different colors mix together, making it difficult to obtain prints with print quality equivalent to that of plate-based printing. This is because water, the main solvent of aqueous inkjet inks, has a particularly high surface tension, resulting in poor wetting and spreading properties on the printing substrate, particularly on the order of microseconds.

[0008] Generally, highly hydrophobic, non-polymeric organic compounds are often used to improve wetting and spreading properties on a printing substrate. These organic compounds orient at the interface with the printing substrate within microseconds, improving wetting and spreading properties on the printing substrate. However, high hydrophobicity also means poor solubility in water, and aqueous inkjet inks containing these organic compounds are prone to the generation of air bubbles, which can contribute to nozzle clogging (a phenomenon in which aqueous inkjet ink is not ejected from a nozzle). Furthermore, the orientation of these organic compounds at the air-liquid interface formed on the nozzle end surface of an inkjet head can destabilize the meniscus of the aqueous inkjet ink. These problems can easily lead to nozzle clogging immediately after the start of printing and when printing is resumed after a long printing pause. Furthermore, due to the structure of the inkjet head, the nozzle diameter is very small, at just a few tens of micrometers. In particular, during long printing pauses, liquid components in the aqueous inkjet ink (e.g., water, water-soluble organic solvents) volatilize from the nozzle end surface, while fresh aqueous inkjet ink may not be sufficiently supplied to the inkjet head. When this happens, the aqueous inkjet ink present in the vicinity of the nozzle end face will have an increased solid content concentration and / or an increased proportion of water-soluble organic solvents with high boiling points, which will cause the solid components (pigments, resins, etc.) to aggregate, become insolubilized, etc., resulting in an increase in viscosity, and nozzle clogging due to this increase in viscosity may occur.

[0009] In this disclosure, the ejection stability immediately after the start of printing is referred to as "initial ejection stability," and the ejection stability after a long period of printing pause is also referred to as "standby ejection stability."

[0010] On the other hand, particularly in the packaging printing market, it is necessary that the coating (ink film) of the aqueous inkjet ink after drying does not peel off even when the printed material is rubbed hard with a finger or the like. That is, the ink film is required to have a certain degree of abrasion resistance. One method for imparting abrasion resistance to the ink film of an aqueous inkjet ink is to add a binder resin to the aqueous inkjet ink to form a uniform, strong, continuous ink film. On the other hand, if a certain amount or more of binder resin is contained in the aqueous inkjet ink (liquid) before printing, problems such as a local increase in viscosity and non-uniform viscoelasticity may occur in the aqueous inkjet ink, resulting in a deterioration in ejection stability, and the binder resin may inhibit the orientation of the organic compound, thereby worsening the wetting and spreading properties of the aqueous inkjet ink.

[0011] Thus, in order to expand the use of aqueous inkjet inks in the packaging printing market, multiple issues, such as initial ejection stability, standby ejection performance, print image quality, and abrasion resistance of the ink film, must be simultaneously resolved. However, no aqueous inkjet ink that can simultaneously and suitably resolve all of these issues has been discovered to date.

[0012] In this disclosure, a printed matter that is free from white spots and color mixing is also referred to as a "printed matter with excellent print quality."

[0013] As an example of a study aimed at improving the print quality of printed matter on non-permeable substrates, Patent Document 1 discloses an ink suitable for use in inkjet printing, which contains water, an organic solvent, a polysiloxane surfactant having an HLB value of 8 or less, and acrylic silicone resin particles. Patent Document 1 also provides examples of inks that use 1,2-propanediol (propylene glycol), 1,3-propanediol, 3-methoxy-3-methylbutanol, 2-methyl-2,4-pentanediol, or the like as the organic solvent, and further contain urethane resin emulsion, polyester resin emulsion, acrylic-styrene resin emulsion, or the like as other resin particles. Patent Document 1 also describes that inks having the above-described configuration have good storage stability and can produce printed matter that exhibits excellent fixability (suppression of density unevenness) and adhesion to non-permeable substrates (see paragraphs

[0006] and

[0019] of Patent Document 1).

[0014] Patent Document 2 discloses an aqueous inkjet ink containing an organic solvent selected from ethylene glycol, propylene glycol, 3-methoxy-1-butanol, etc., and a polyoxyalkylene monoallyl ether compound having a specific structure. Patent Document 2 also discloses, in its examples, an example of an aqueous inkjet ink that contains, in addition to the organic solvent, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2-methyl-2,4-pentanediol, etc., and further contains a water-insoluble resin such as a urethane resin emulsion or an acrylic resin emulsion, and a surfactant such as an acetylene glycol-based surfactant or a silicone-based surfactant. Patent Document 2 also discloses that the aqueous inkjet ink having the above-described configuration has excellent ejection properties and can produce printed matter with no uneven density and good wetting and spreading properties even on non-water-absorbent recording media (see paragraphs 0014 and 0028 of Patent Document 2).

[0015] On the other hand, as an example of a study aimed at improving the abrasion resistance of printed matter on an impermeable substrate, Patent Document 3 discloses an inkjet ink composition containing a water-soluble polymer having a number-average molecular weight of 1,000 or more, particles having polymerizable groups, a colorant, and water, with a specified ratio of the content of the water-soluble polymer to the content of the particles. Furthermore, the examples of Patent Document 3 show an example of an inkjet ink composition containing polyethylene glycol having a number-average molecular weight of 2,000 to 100,000, an ultraviolet-curable urethane acrylate resin emulsion, water, Olfine E1010 (an acetylene diol surfactant), and the like. Patent Document 3 also describes that an inkjet ink composition having the above-described configuration has excellent ejection stability, and further, that specifying the above-described ratio enables the printed matter to achieve both abrasion resistance and flexibility (see paragraphs 0010, 0014, and 0017 of Patent Document 3).

[0016] Patent Document 4 discloses an ink containing water, a compound having a specific solubility parameter (e.g., 3-butoxy-N,N-dimethylpropionamide, diethylene glycol diethyl ether, 2-pyrrolidone), an alkanediol compound having 3 to 4 carbon atoms, and 3-methoxy-3-methyl-1-butanol. Example 2 of Patent Document 4 describes an ink containing 3-butoxy-N,N-dimethylpropionamide, 1,2-propanediol, 1,3-propanediol, and 3-methoxy-3-methyl-1-butanol, as well as 2-methyl-2,4-pentanediol, a polyurethane resin emulsion having a minimum film-forming temperature of 43°C, and a fluorine-based surfactant. Patent Document 4 also describes that an ink having the above-described configuration has excellent fixability to non-permeable substrates, ejection reliability (standby ejection), and abrasion resistance of printed matter (see paragraphs 0004, 0009, and 0016 of Patent Document 4).

[0017] JP 2017-115127 A JP 2021-109904 A JP 2015-48435 A JP 2020-73665 A

[0018] However, the ink specifically disclosed in Patent Document 1 does not contain the above-mentioned non-polymeric hydrophobic organic compound other than the polysiloxane surfactant. While the polysiloxane surfactant used in the ink is known to have excellent orientation properties at interfaces and is an effective material for improving print quality, its orientation speed is not particularly high, and it is insufficient from the perspective of ensuring wetting and spreading properties on the order of microseconds. Furthermore, the polyoxyalkylene monoallyl ether compounds, acetylene glycol-based surfactants, and silicone-based surfactants specifically used in the examples of Patent Document 2 (see also paragraphs

[0117] to

[0118] of Patent Document 2) are all highly hydrophilic (i.e., have large HLB values, as described below), and, like Patent Document 1, do not contain a non-polymeric hydrophobic organic compound. To produce printed materials with excellent print quality regardless of printing conditions, such as inkjet printing on printing substrates with very low interfacial free energy or high-speed inkjet printing, further improvements, including the mastery of non-polymeric hydrophobic organic compounds, are necessary.

[0019] As with Patent Documents 1 and 2, the inkjet ink composition specifically disclosed in Patent Document 3 does not use a hydrophobic organic compound, and depending on the printing substrate, printing speed, etc., it may be necessary to improve print image quality. On the other hand, the ink specifically disclosed in Patent Document 4 uses a fluorosurfactant together with various water-soluble organic solvents. Fluorosurfactants generally have high hydrophobicity, and as described above, the incorporation of such a fluorosurfactant is considered effective in improving print image quality. However, simply incorporating the hydrophobic organic compound into an aqueous inkjet ink may cause bubbles and meniscus instability, which may deteriorate initial ejection stability and standby ejection stability depending on the device configuration, printing conditions, etc.

[0020] As described above, the techniques described in Patent Documents 1 to 4 have not yet been able to solve all of the above-mentioned problems at a high level. Therefore, an object of one embodiment of the present disclosure is to provide an aqueous inkjet ink that is free from white voids and color bleeding, has excellent abrasion resistance, and also has excellent ejection stability immediately after the start of printing and after a long period of printing pause, even when printing on a non-permeable substrate.

[0021] 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.

[0022] That is, one embodiment of the present disclosure relates to aqueous inkjet inks shown in [1] to [3] below, and to printed matter produced using the aqueous inkjet inks shown in [4] below. [1] An aqueous inkjet ink comprising a pigment, an acetylenic diol compound (A), polyethylene glycol, a binder resin, and an organic compound (B) (excluding the pigment, the acetylenic diol compound (A), the polyethylene glycol, and the resin), wherein the acetylenic diol compound (A) has an HLB value of 7.5 to 17.5, the organic compound (B) consists only of carbon atoms, hydrogen atoms, and oxygen atoms, and has a plurality of hydroxyl groups, the HLB value of the organic compound (B) is 2.5 to 5.2, the binder resin comprises a resin (C-1) having a glass transition temperature of -60 to 50°C, and the content of the resin (C-1) is 50 mass% or more of the total mass of the resins contained in the aqueous inkjet ink. [2] The aqueous inkjet ink according to [1], wherein the mass content of the polyethylene glycol is 1.0 to 20, when the mass content of the acetylenic diol compound (A) is 1. [3] The aqueous inkjet ink according to [1] or [2], wherein the mass content of the organic compound (B) is 0.05 to 2.0, when the mass content of the acetylenic diol compound (A) is 1. [4] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [3] on a printing substrate.

[0023] The aqueous inkjet ink of one embodiment of the present disclosure has the effect of producing printed matter that is free from white voids and color bleeding and has excellent abrasion resistance, even when printed on a non-permeable substrate, and further has excellent ejection stability immediately after the start of printing and after a long period of printing pause.

[0024] An aqueous inkjet ink according to one embodiment of the present disclosure (hereinafter also simply referred to as "the aqueous inkjet ink of this embodiment") will be described below. Note that the present invention is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present invention.

[0025] Generally, aqueous inkjet inks do not wet or spread on non-permeable substrates due to the extremely high surface tension of their main component, water, making it difficult to form fine prints. In contrast, when organic compounds with a low HLB value, such as surfactants, are used, the organic compounds orient at the interface with the printing substrate within microseconds. As a result, aqueous inkjet inks can wet and spread well even on non-permeable substrates, particularly printing substrates with very low interfacial free energy, such as polypropylene (PP) film, and this can lead to improved print quality. However, these organic compounds have the drawbacks of easily forming bubbles, which can contribute to nozzle clogging, and of rapidly orienting the ink at the air-liquid interface formed at the nozzle end face of the inkjet head, potentially destabilizing the meniscus of the aqueous inkjet ink. These drawbacks lead to deterioration in initial ejection stability and standby ejection performance.

[0026] Furthermore, to obtain a printed material with excellent abrasion resistance, it is preferable that the binder resin form a uniform, continuous ink film constituting the printed material. Generally, the lower the glass transition temperature of the binder resin, the easier it is to form a uniform, continuous film. Therefore, from the perspective of forming such a uniform, continuous film, it is effective to use a binder resin with a low glass transition temperature. On the other hand, binder resins with low glass transition temperatures easily form films, for example, on the nozzle end surfaces of inkjet heads, which may deteriorate the initial ejection stability. Furthermore, the binder resin contained in the aqueous inkjet ink before printing (liquid) may inhibit the orientation of the organic compound at the interface. If the orientation of the organic compound is inhibited, the above-mentioned effect cannot be achieved, and the print quality of the printed material will deteriorate. To fully achieve the above-mentioned effect, one method is to increase the amount of the organic compound added so that a sufficient amount is still oriented at the interface even when inhibited. However, an excessive amount of the organic compound also has the problem of inhibiting the formation of a continuous film of the binder resin, resulting in a deterioration of the abrasion resistance of the printed material.

[0027] In contrast, the aqueous inkjet ink of this embodiment contains an organic compound (B) which is composed only of carbon atoms, hydrogen atoms, and oxygen atoms and has a plurality of hydroxyl groups and has an HLB value of 2.5 to 5.2, and a resin (C-1) which has a glass transition temperature of −60 to 50° C., as well as an acetylene diol compound (A) which has an HLB value of 7.5 to 17.5, and polyethylene glycol.

[0028] Generally, acetylenic diol compounds are used as surfactants. In other words, adding an acetylenic diol compound to an aqueous inkjet ink allows the aqueous inkjet ink to wet and spread well on a printing substrate, improving print quality. On the other hand, the aqueous inkjet ink of this embodiment uses an acetylenic diol compound (A) having an HLB value of 7.5 to 17.5 as the acetylenic diol compound. Thus, the acetylenic diol compound (A) having a relatively large HLB value facilitates stabilization of the organic compound (B) in the aqueous inkjet ink. Furthermore, the presence of the acetylenic diol compound (A) suppresses rapid orientation of the organic compound (B) toward the interface. As a result, the aqueous inkjet ink present in the inkjet head is prevented from generating bubbles and from destabilizing the meniscus, improving initial ejection stability and standby ejection performance.

[0029] Furthermore, the acetylenic diol compound (A) also has affinity with the resin (C-1). Therefore, for example, even after water volatilizes from the aqueous inkjet ink applied to a printing substrate, the organic compound (B) and the resin (C-1) become compatible with each other via the acetylenic diol compound (A), allowing the resin (C-1) to diffuse uniformly together with the organic compound (B). As described above, the aqueous inkjet ink of this embodiment contains, as a binder resin, a resin (C-1) that has a low glass transition temperature, i.e., that easily forms a uniform, continuous film, and the content of the resin (C-1) is 50% by mass or more of the total mass of the resins contained in the aqueous inkjet ink. As a result, it is believed that the aqueous inkjet ink of this embodiment promotes the formation of a continuous ink film, improving the abrasion resistance of printed matter.

[0030] On the other hand, as described above, the acetylenic diol compound (A) also functions as a surfactant. Therefore, for example, in an aqueous inkjet ink that has been left in an inkjet head for a long time without being printed, the acetylenic diol compound (A) may be oriented at the gas-liquid interface, which may deteriorate the standby dischargeability. In particular, if the organic compound (B) is oriented at the gas-liquid interface due to the orientation of the acetylenic diol compound (A), the standby dischargeability may be significantly deteriorated.

[0031] Therefore, the aqueous inkjet ink of this embodiment further contains polyethylene glycol. Polyethylene glycol is a compound consisting only of a hydroxyl group and an ethylene oxide group, and therefore has extremely high affinity with water. It is also believed to have good affinity with the acetylenic diol-based compound (A). As a result, even when the aqueous inkjet ink is left in the inkjet head for a long period of time, orientation of the acetylenic diol-based compound (A) at the gas-liquid interface can be suppressed, thereby preventing deterioration of standby ejection performance. It is also believed that polyethylene glycol diffuses freely within the aqueous inkjet ink. As a result, the polyethylene glycol functions like a plasticizer and promotes film formation of the resin (C-1), resulting in a uniform and continuous ink film and improved abrasion resistance of the printed matter.

[0032] As described above, in order to solve all of the above-mentioned problems at a high level, an aqueous inkjet ink having the above-mentioned configuration is essential. Note that the above-mentioned mechanism is a conjecture by the inventors, and the present invention is not limited by the above conjecture.

[0033] The aqueous inkjet inks specifically disclosed in Patent Documents 1 to 4 differ from the aqueous inkjet ink of the present embodiment in that they do not contain the organic compound (B) or polyethylene glycol. Furthermore, the aqueous inkjet ink specifically disclosed in paragraph

[0104] of Patent Document 3 contains the acetylene diol-based compound (A) "Olfine E1010" and the polyethylene glycol "PEG8000," but, like Patent Documents 1 to 4, does not contain the organic compound (B). As described above, the aqueous inkjet ink of the present embodiment, which contains the organic compound (B), can produce printed materials free of whiteout and color bleeding on printing substrates with very low interfacial free energy. Furthermore, by using the organic compound (B) in combination with the acetylene diol-based compound (A) and polyethylene glycol, it is possible to improve the initial ejection stability and standby ejection performance that can occur when using the organic compound (B). Patent Documents 1 to 4 do not disclose or suggest such a method.

[0034] Next, each component constituting the aqueous inkjet ink according to one embodiment of the present disclosure will be described in detail below.

[0035] <Acetylene Diol Compound (A)> As described above, the aqueous inkjet ink of this embodiment contains an acetylene diol compound (A) having an HLB value of 7.5 to 17.5. By including the acetylene diol compound (A) in the aqueous inkjet ink, the organic compound (B) is stabilized in the aqueous inkjet ink, and rapid orientation of the organic compound (B) to the interface is suppressed, improving the initial ejection stability and standby ejection performance. Furthermore, by uniformly diffusing the resin (C-1) in the aqueous inkjet ink, the formation of a continuous ink film is promoted, improving the abrasion resistance of the printed matter.

[0036] From the viewpoint of suitably achieving the above-mentioned effects, the HLB value of the acetylenic diol compound (A) is preferably 7.5 to 17.5. Furthermore, from the viewpoint of obtaining the effect of improving print image quality due to the function of the acetylenic diol compound (A) as a surfactant in addition to the above-mentioned effects, the HLB value of the acetylenic diol compound (A) is preferably 7.5 to 17.1, more preferably 7.5 to 16.0, particularly preferably 7.5 to 13.5, and may further be 7.9 to 13.2.

[0037] The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that indicate the hydrophilicity / hydrophobicity of a material, and in the present disclosure, the HLB value is calculated using the Griffin method.

[0038] The Griffin method is a method for determining the HLB value using the molecular weight of a material according to the following formula (1): The smaller the HLB value, the more hydrophobic the material is, and the larger the HLB value, the more hydrophilic the material is.

[0039] Formula (1): HLB value = 20 × (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material)

[0040] The acetylene diol compound (A) that can be preferably used in the aqueous inkjet ink of this embodiment is a compound represented by the following general formula (2), in which i1+i2 is an integer of 3 to 30.

[0041] General formula (2):

[0042] In general formula (2), a and b are each 1 or 2. Furthermore, i1 and i2 are each an integer of 0 to 30, and j1 and j2 are each an integer of 0 to 5. The addition mode of the ethylene oxide group and propylene oxide group in each square bracket may be block addition or random addition.

[0043] As the acetylene diol compound (A) represented by the above general formula (2) in which i1 + i2 is an integer of 3 to 30, a compound synthesized by a conventionally known method may be used, or a commercially available product may be used. Examples of the commercially available product include Surfynol 440 (8.1), Surfynol 465 (13.2), Surfynol 485 (17.1), Surfynol 2502 (7.9), Dynol 604 (8.2), and Dynol 607 (11.0), all sold by Evonik Japan K.K. and Nissin Chemical Industry Co., Ltd.; Olfine E1004 (8.8), Olfine E1006 (10.8), Olfine E1010 (13.2), Olfine E1020 (15.9), and Olfine E1030W (17.1), all sold by Nissin Chemical Industry Co., Ltd.; and Acetylenol E40 (8.8), Acetylenol E60 (10.8), Acetylenol E100 (13.2), and Acetylenol E200 (15.9), all sold by Kawaken Fine Chemicals Co., Ltd. The numbers in parentheses are the HLB values ​​of each commercially available product.

[0044] Two or more types of acetylenic diol compounds (A) may be used in combination.

[0045] The total amount of the acetylene diol compound (A) added is preferably from 0.2 to 2.5% by mass, more preferably from 0.3 to 2.0% by mass, and particularly preferably from 0.5 to 1.5% by mass, of the total amount of the aqueous inkjet ink, from the viewpoints of improving the initial ejection stability and standby ejection property and also improving the abrasion resistance of the printed matter.

[0046] Furthermore, since the print quality of the printed matter, the initial ejection stability, and the standby ejection properties are all improved by suitably stabilizing the organic compound (B), the mass content of the organic compound (B) relative to the mass content of the acetylene diol compound (A) taken as 1 is preferably 0.04 to 2.8, more preferably 0.05 to 2.0, particularly preferably 0.1 to 1.5, and may further be 0.1 to 1.2, 0.2 to 1.0, or 0.1 to 0.5.

[0047] Furthermore, from the viewpoint of increasing affinity with polyethylene glycol and improving initial ejection stability, standby ejection property, and abrasion resistance of printed matter, the mass content of the polyethylene glycol is preferably 0.8 to 25, more preferably 1.0 to 20, and particularly preferably 1.4 to 15, relative to the mass content of the acetylene diol compound (A) taken as 1.

[0048] <Organic Compound (B)> The aqueous inkjet ink of this embodiment contains an organic compound (B) consisting only of carbon, hydrogen, and oxygen atoms, and having multiple hydroxyl groups, the organic compound having an HLB value of 2.5 to 5.2. During printing, the organic compound (B) quickly orients at the interface with the printing substrate, resulting in a printed product free of white spots and color bleeding, even on non-permeable substrates. Furthermore, the combined use of the acetylene diol compound (A) and the organic compound (B) suppresses the generation of bubbles and meniscus instability in the aqueous inkjet ink present in the inkjet head, improving initial ejection stability and standby ejection performance. Furthermore, the combined use of these compounds prevents the formation of a continuous film by the resin (C-1), improving the abrasion resistance of the printed product.

[0049] It should be noted that pigments, acetylene diol compounds (A), and polyethylene glycol are not included in the organic compound (B). Furthermore, resins including the resin (C-1) are also excluded from the organic compound (B).

[0050] In the present disclosure, a "resin" refers to a compound in which one or more types of polymerizable monomers are linked together by covalent bonds to form a main chain, and the compound has a weight average molecular weight of 1,000 or more, which can be measured by the method described below. However, polyethylene glycol, which will be described later, is not included in the "resin" in the present disclosure.

[0051] As described above, the HLB value of the organic compound (B) is 2.5 to 5.2. Furthermore, since the organic compound (B) has good affinity with other components, the HLB value of the organic compound (B) is preferably 2.7 to 5.2, more preferably 3.0 to 5.2, particularly preferably 3.8 to 5.2, and may be 4.0 to 5.2, from the viewpoint of improving the initial ejection stability and standby ejection performance while suppressing white voids and color bleeding in printed matter.

[0052] Examples of compounds that can be used as the organic compound (B) include: acetylene diol compounds represented by the above general formula (2) in which i1 + i2 is 0 or 1 (for example, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (2.7), 2,4,7,9-tetramethyl-5-decyne-4,7-diol (3.0), 5,8-dimethyl-6-dodecaine-5,8-diol (3.0), 3,6-dimethyl-4-octyne-3,6-diol (4.0)); sorbitan fatty acid ester compounds such as sorbitan monostearate (4.7), sorbitan distearate (4.4), and sorbitan monooleate (4.3), as well as ethylene oxide and / or propylene oxide adducts thereof; Glycerin fatty acid ester compounds such as glycerol monostearate (3.5), glycerol monobehenate (3.0), glycerol monooleate (2.8), and their ethylene oxide and / or propylene oxide adducts; medium-chain (e.g., carbon number 7 to 12) alkanediol compounds such as 1,2-heptanediol (5.2), 1,7-heptanediol (5.2), 1,2-octanediol (4.7), 1,8-octanediol (4.7), 2-ethyl-1,3-hexanediol (4.7), 1,2-nonanediol (4.2), 1,9-nonanediol (4.2); cycloalkanediol compounds such as cyclohexanedimethanol (4.7), cyclohexanediethanol (4.0); polypropylene glycol compounds such as dipropylene glycol (5.1), tripropylene glycol (3.5), and the like. The numbers in parentheses are the HLB values ​​of each material.

[0053] Among these compounds, one or more compounds selected from the group consisting of acetylenic diol compounds represented by the above general formula (2) in which i1 + i2 is 0 or 1 and medium-chain alkanediol compounds can be preferably used, from the viewpoints of high affinity with the acetylenic diol compound (A), improved initial ejection stability and standby ejection property, and improved abrasion resistance of printed matter.

[0054] The organic compound (B) has an excellent orientation speed to the interface and good affinity with the acetylene diol-based compound (A). From the viewpoints of suppressing white voids and color mixing in the printed matter, improving the initial ejection stability and standby ejection property, and also improving the abrasion resistance of the printed matter, the molecular weight of the organic compound (B) is preferably 100 to 750, particularly preferably 130 to 650.

[0055] The amount of organic compound (B) added is preferably from 0.05 to 1.6% by mass, more preferably from 0.05 to 1.5% by mass, and particularly preferably from 0.1 to 1% by mass, of the total amount of the aqueous inkjet ink, from the viewpoints that a printed matter that is free from white voids and color bleeding and has excellent abrasion resistance can be obtained, and that the initial ejection stability and standby ejection performance are also improved.

[0056] Furthermore, from the viewpoint of improving the initial ejection stability and standby ejection property, as well as the print image quality of the printed matter, the mass content of the organic compound (B) is preferably 0.03 to 0.40, and particularly preferably 0.05 to 0.30, relative to the mass content of polyethylene glycol described below, which is taken as 1.

[0057] <Other Nonionic Surfactants> The aqueous inkjet ink of this embodiment may contain a nonionic surfactant other than the acetylene diol compound (A) and the surfactant corresponding to the organic compound (B) described above (also referred to as “other nonionic surfactants” in the present disclosure).

[0058] Specific examples of the other nonionic surfactants include acetylene monool surfactants and their ethylene oxide and / or propylene oxide adducts, sorbitan fatty acid ester surfactants and their ethylene oxide and / or propylene oxide adducts (provided that the HLB value is less than 2.5 or more than 5.2), glycerin fatty acid ester surfactants and their ethylene oxide and / or propylene oxide adducts (provided that the HLB value is less than 2.5 or more than 5.2), polyether-modified siloxane surfactants, fluorine-based surfactants, polyoxyalkylene alkyl ether surfactants, polyoxyalkylene alkylamine surfactants, etc.

[0059] Among these, it is preferable to use a polyether-modified siloxane surfactant as the other nonionic surfactant, because it has a high ability to reduce the surface tension of the aqueous inkjet ink, enables the aqueous inkjet ink droplets to wet and spread uniformly, and can easily suppress whiteout and color bleeding in printed materials, and because it has affinity with the binder resin, it suppresses the formation of a binder resin film on the nozzle end face of the inkjet head, improving initial ejection stability. In another embodiment, it is preferable to use a polyoxyalkylene alkyl ether surfactant, because it has high affinity with the organic compound (B), the acetylene diol compound (A), and polyethylene glycol, improving initial ejection stability and standby ejection performance, and also improving the abrasion resistance of printed materials.

[0060] <Polyether-Modified Siloxane-Based Surfactant> When the aqueous inkjet ink of this embodiment contains a polyether-modified siloxane-based surfactant, a compound having a structure represented by the following general formula (3) can be preferably used as the polyether-modified siloxane-based surfactant.

[0061] General formula (3):

[0062] In the general formula (3), m is an integer of 0 to 99, and n is an integer of 1 to 100. However, m+n is an integer of 1 to 100. １ is a methyl group or a structure represented by the following general formula (4), and R ２ is an alkyl group having 1 to 6 carbon atoms (which may be branched), or a structure represented by the following general formula (4): １ When R is a methyl group, m is 0. １ and R ２ At least one of the groups has a structure represented by the following general formula (4) (R １ and R ２ However, both may have a structure represented by the following general formula (4):

[0063] General formula (4):

[0064] In general formula (4), p is an integer of 1 to 6, q is an integer of 1 to 50, and r is an integer of 0 to 50. However, q+r is an integer of 1 to 100. ３ is any one of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acryloyl group, a methacryloyl group, a 3-(acryloyloxy)-2-hydroxypropyl group, and a 3-(methacryloyloxy)-2-hydroxypropyl group. The addition of the ethylene oxide group and the propylene oxide group in the square brackets may be in the form of block addition or random addition.

[0065] In the above general formula (3), R ２ is a structure represented by the general formula (4), and R １Polyether-modified siloxane surfactants (also referred to as "double-end polyether-modified siloxane surfactants" in the present disclosure) in which R is not a structure represented by the above general formula (4) have high affinity with binder resins and are effective in improving the initial ejection stability and the scratch resistance of printed matter. Furthermore, double-end polyether-modified siloxane surfactants are also excellent in uniform orientation at interfaces and can also improve color bleeding, so they are particularly preferably used as polyether-modified siloxane surfactants in the aqueous inkjet ink of this embodiment. On the other hand, in the above general formula (3), R １ is a structure represented by the general formula (4), and R ２ Polyether-modified siloxane surfactants (also referred to as “side-chain polyether-modified siloxane surfactants” in the present disclosure) having a structure other than that represented by the above general formula (4) have a high ability to reduce surface tension and an excellent orientation speed to the interface, and are therefore effective in suppressing white voids in printed materials.

[0066] Examples of commercially available products of the both-end polyether-modified siloxane surfactant include BYK-331, BYK-333, BYK-UV3500, and BYK-3420 manufactured by BYK Japan; TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Japan; Silface SWP001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.; X-22-4952, X-22-4272, and KF-6123 manufactured by Shin-Etsu Chemical Co., Ltd.; and SILWET L-8610 and SILWET L-8620 manufactured by Momentive Performance Materials.

[0067] Commercially available examples of the side chain polyether-modified siloxane surfactant include 8032 ADDITIVE, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, SH 3746, and SH 8400 manufactured by Dow Corning Toray Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-379, BYK-3450, and BYK-3451 manufactured by BYK Japan; and TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, and TEGO Wet 345 manufactured by Evonik Japan Co., Ltd. 280, and Shin-Etsu Chemical Co., Ltd.'s KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6204, KF-6011, KF-6012, KF-6015, KF-6017, and KF-6020.

[0068] The amount of polyether-modified siloxane surfactant added is preferably 0.1 to 4 mass % of the total amount of the aqueous inkjet ink, more preferably 0.2 to 3 mass %, and particularly preferably 0.3 to 2 mass %. When the amount of polyether-modified siloxane surfactant added is within the above range, it becomes easy to improve the initial ejection stability and standby ejection performance, and to obtain printed matter that is free from white voids and color bleeding and has excellent abrasion resistance.

[0069] Furthermore, from the viewpoint of achieving favorable affinity with resin (C-1), improving initial ejection stability, and suppressing white voids and color bleeding in printed matter, the content of resin (C-1) is preferably 3.3 to 72, more preferably 3.5 to 50, and particularly preferably 5.0 to 35, relative to the content of the polyether-modified siloxane surfactant, which is taken as 1.

[0070] <Polyoxyalkylene alkyl ether surfactant> When the aqueous inkjet ink of this embodiment contains a polyoxyalkylene alkyl ether surfactant, a compound having a structure represented by the following general formula (5) can be preferably used as the polyoxyalkylene alkyl ether surfactant. By using a compound represented by the following general formula (5) as the polyoxyalkylene alkyl ether surfactant, the affinity with the organic compound (B), the acetylene diol compound (A), and polyethylene glycol is increased, and the initial ejection stability, standby ejection properties, and abrasion resistance of the printed matter are improved.

[0071] General formula (5):

[0072] In the general formula (5), s is an integer of 10 to 100, and t is an integer of 0 to 50, provided that s>t. ４ is an alkyl group or alkylene group (which may be branched) having 8 to 22 carbon atoms. The addition of the ethylene oxide group and propylene oxide group in the square brackets may be block addition or random addition.

[0073] In particular, from the viewpoint of improving all of the initial ejection stability, standby ejection property, and scratch resistance of the printed matter, s in the above general formula (5) is preferably 20 to 50, and t is preferably 0 to 10. From the same viewpoint, R ４ is preferably an alkyl group having 10 to 22 carbon atoms (which may be branched), and particularly preferably an alkyl group having 12 to 18 carbon atoms (which may be branched).

[0074] The total content of other nonionic surfactants in the aqueous inkjet ink is preferably 0.1 to 3% by mass, and more preferably 0.2 to 2% by mass. If the total content is 0.1% by mass or more, the above-mentioned effects can be reliably achieved, and white voids and color bleeding in printed materials can be easily suppressed, and the abrasion resistance of printed materials can be improved. Furthermore, if the total content of other nonionic surfactants is 3% by mass or less, initial ejection stability and standby ejection performance can be improved.

[0075] <Polyethylene Glycol> The aqueous inkjet ink of this embodiment contains polyethylene glycol. The polyethylene glycol has affinity with water, which is the main component of the aqueous inkjet ink, and the acetylene diol compound (A), which has moderate hydrophilicity, thereby suppressing the orientation of the acetylene diol compound (A) at the gas-liquid interface and improving standby ejection properties. Furthermore, a uniform and continuous ink film is more easily obtained, improving the abrasion resistance of the printed matter.

[0076] In addition, "polyethylene glycol" in the present disclosure refers to a compound having 4 to 300 ethylene oxide groups.

[0077] From the viewpoint of improving the initial ejection stability in addition to the standby ejection property and the abrasion resistance of the printed matter, the number average molecular weight of the polyethylene glycol is preferably 200 to 10,000, more preferably 200 to 4,000, and particularly preferably 200 to 2,000.

[0078] In the aqueous inkjet ink of this embodiment, two or more types of polyethylene glycols having different number average molecular weights may be used in combination.

[0079] From the viewpoint of improving all of the initial ejection stability, standby ejection properties, and abrasion resistance of printed matter, the content of polyethylene glycol contained in the aqueous inkjet ink of this embodiment (when two or more types of polyethylene glycol are contained, the total content) is preferably from 0.5 to 20 mass %, more preferably from 1 to 15 mass %, particularly preferably from 2 to 10 mass %, and may further be from 2 to 8 mass %, or even from 2 to 5 mass %, of the total amount of the aqueous inkjet ink.

[0080] Furthermore, when the aqueous inkjet ink of this embodiment contains polyethylene glycol having a number average molecular weight of MP in an amount of WP [mass %] relative to the total amount of the aqueous inkjet ink, the value expressed by MP x WP is preferably 200 to 10,000, and particularly preferably 500 to 6,000. Aqueous inkjet inks having this value of 200 to 10,000 exhibit particularly excellent initial ejection stability and standby ejection properties. Note that, when the aqueous inkjet ink of this embodiment contains two or more polyethylene glycols, it is preferable that the sum of the MP x WP values ​​calculated for the respective polyethylene glycols falls within the above range.

[0081] Furthermore, from the viewpoint of improving both the print quality and abrasion resistance of the printed matter, when the mass content of polyethylene glycol is taken as 1, the mass content of resin (C-1) is preferably 0.2 to 7.5, more preferably 0.3 to 6.5, and particularly preferably 0.5 to 5.5.

[0082] <Water-soluble organic solvent> The aqueous inkjet ink of this embodiment may contain a water-soluble organic solvent. However, the "water-soluble organic solvent" in this disclosure does not include polyethylene glycol or compounds that fall under the above-mentioned organic compound (B).

[0083] Specific examples of the water-soluble organic solvent include alkane monools having 2 to 4 carbon atoms; alkane diols having 2 to 6 carbon atoms; alkane triols having 3 to 6 carbon atoms; polypropylene glycols (having 2 or 3 propylene oxide groups); (poly)ethylene glycol monoalkyl ethers (having 1 to 4 carbon atoms in the alkyl group at the molecular terminal and 1 to 3 ethylene oxide groups); (poly)propylene glycol monoalkyl ethers (having 1 to 4 carbon atoms in the alkyl group at the molecular terminal and 1 to 3 propylene oxide groups); butylene glycol monoalkyl ethers (having 1 to 4 carbon atoms in the alkyl group at the molecular terminal). Examples of suitable water-soluble organic solvents include: pentylene glycol monoalkyl ethers (wherein the alkyl group at the molecular terminal has 1 to 4 carbon atoms); (poly)ethylene glycol dialkyl ethers (wherein the alkyl groups at the molecular terminals each have 1 to 4 carbon atoms and the number of ethylene oxide groups is 1 to 4); lactams (wherein the lactam ring has 5 to 7 atoms. An alkyl group having 1 to 2 carbon atoms, a hydroxyalkyl group having 1 to 2 carbon atoms, or a vinyl group may be bonded to the nitrogen atom and / or carbon atom that constitutes the lactam ring); alkanolamines (wherein the number of amino groups is 1, the number of hydroxyl groups is 1 to 3, and the number of carbon atoms is 3 to 9); and the like. These other water-soluble organic solvents may be used alone or in combination of two or more. In the present disclosure, "(poly)ethylene glycol" and "(poly)propylene glycol" refer to "ethylene glycol and / or polyethylene glycol" and "propylene glycol and / or polypropylene glycol," respectively.

[0084] When the aqueous inkjet ink of this embodiment contains the above-mentioned water-soluble organic solvents, the total content thereof is preferably 2 to 35 mass %, more preferably 3 to 25 mass %, and particularly preferably 5 to 20 mass %, of the total amount of the aqueous inkjet ink. By keeping the total content of the water-soluble organic solvents within the above range, it is possible to maintain an appropriate viscosity for ejection from the inkjet head, and the initial ejection stability and standby ejection performance are improved. Furthermore, no water-soluble organic solvent remains in the printed matter, resulting in a printed matter with good abrasion resistance.

[0085] <<Alkanediols Having 2 to 6 Carbon atoms>> In one embodiment, the aqueous inkjet ink of this embodiment preferably contains an alkanediol having 2 to 6 carbon atoms as the water-soluble organic solvent. Because alkanediols having 2 to 6 carbon atoms have two hydroxyl groups, they have high affinity with the acetylenic diol compound (A) and polyethylene glycol, which also have hydroxyl groups. As a result, the organic compound (B) and resin (C-1) can be favorably stabilized, resulting in significantly improved initial ejection stability, standby ejection, and abrasion resistance of printed matter. This effect is particularly pronounced when the organic compound (B) is one or more compounds selected from the group consisting of acetylenic diol compounds represented by the above general formula (2) where i1 + i2 is 0 or 1 and medium-chain alkanediol compounds. Furthermore, alkanediols having 2 to 6 carbon atoms volatilize quickly on the printing substrate. As a result, it is easy to obtain printed matter free of color bleeding.

[0086] Examples of the alkanediols having 2 to 6 carbon atoms that can be used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 2-methyl-2,4-pentanediol, and 3-methyl-1,5-pentanediol. These compounds may be used alone or in combination of two or more.

[0087] Among these, it is preferable to use one or more compounds selected from the group consisting of propylene glycol, 1,3-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, and 2-methyl-2,4-pentanediol, because they are easy to balance in drying properties and are excellent in standby jetting properties, abrasion resistance of printed matter, and suppression of mixed color bleeding. In particular, when one or more compounds selected from the group consisting of acetylene diol compounds represented by the above general formula (2) where i1 + i2 is 0 or 1 and medium-chain alkanediol compounds are used as the organic compound (B), it is particularly preferable to use one or more compounds selected from the group consisting of propylene glycol, 1,3-butanediol, and 2-methyl-2,4-pentanediol, because all of the above-mentioned effects, i.e., standby jetting properties, abrasion resistance of printed matter, and suppression of mixed color bleeding, are significantly improved.

[0088] In view of improving the initial ejection stability and standby ejection property, and obtaining printed matter that is free of color bleeding and has excellent abrasion resistance, the content of the alkanediols having 2 to 6 carbon atoms is preferably 1 to 25% by mass, more preferably 3 to 20% by mass, and particularly preferably 5 to 15% by mass, of the total amount of the aqueous inkjet ink.

[0089] Furthermore, since the effects of the polyethylene glycol described above are preferably exhibited, the standby ejection properties of the aqueous inkjet ink are improved, and printed matter with excellent abrasion resistance can be obtained. Therefore, when the mass content of polyethylene glycol is taken as 1, the mass content of the alkanediol having 2 to 6 carbon atoms is preferably 0.2 to 12, and particularly preferably 0.6 to 8.0.

[0090] Specific (poly)propylene glycol monoalkyl ethers The aqueous inkjet ink of this embodiment may also contain (poly)propylene glycol monoalkyl ethers, such as compounds in which the alkyl group at the molecular terminal has 2 to 4 carbon atoms and the number of propylene oxide groups is 1 or 2 (referred to as "specific (poly)propylene glycol monoalkyl ethers" in this disclosure). Specific (poly)propylene glycol monoalkyl ethers have an appropriately low surface tension at 25°C, which makes it easy to improve initial ejection stability and prevent white voids in printed materials. Furthermore, since the specific (poly)propylene glycol monoalkyl ethers also function as film-forming aids for binder resins, a uniform and continuous ink film can be obtained, significantly improving the abrasion resistance of printed materials.

[0091] Examples of specific (poly)propylene glycol monoalkyl ethers that can be used include propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, propylene glycol monoisobutyl ether, propylene glycol mono-tert-butyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monoisobutyl ether, and dipropylene glycol mono-tert-butyl ether. These compounds may be used alone or in combination of two or more.

[0092] Among these compounds, it is preferable to use a compound in which the alkyl group at the molecular terminal is an unbranched alkyl group having 2 or 3 carbon atoms, because these compounds have appropriate boiling points at 1 atmosphere and surface tensions at 25°C, thereby improving ejection stability immediately after the start of printing, improving abrasion resistance in printed matter, and preventing whiteout and color bleeding. Among the compounds listed above, compounds that satisfy these requirements include propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol mono-n-propyl ether. Furthermore, it is particularly preferable to use a compound in which the alkyl group at the molecular terminal is an n-propyl group, i.e., propylene glycol mono-n-propyl ether and / or dipropylene glycol mono-n-propyl ether, because improved affinity with the acetylene diol compound (A) improves standby ejection properties and promotes uniformity and continuous formation of the ink film, thereby improving the abrasion resistance of printed matter. In particular, taking into consideration the improvement of standby discharge properties, it is particularly preferable to use dipropylene glycol mono-n-propyl ether as the specific (poly)oxypropylene monoalkyl ether.

[0093] In order to simultaneously achieve all of the effects of improving the initial ejection stability, preventing white voids in printed matter, and improving abrasion resistance, the content of the specific (poly)propylene glycol monoalkyl ethers is preferably 0.2 to 10 mass%, and particularly preferably 0.5 to 8 mass%, of the total amount of the aqueous inkjet ink.

[0094] <Binder Resin> <Resin (C-1)> The aqueous inkjet ink of this embodiment contains a binder resin. The binder resin includes resin (C-1) having a glass transition temperature of −60 to 50° C., and the content of resin (C-1) is 50 mass% or more of the total mass of the resins contained in the aqueous inkjet ink. As described above, by using a certain amount of resin (C-1), which has a low glass transition temperature and easily forms a uniform continuous film, and by using it in combination with an acetylene diol compound (A) and polyethylene glycol, the abrasion resistance, initial ejection stability, and standby ejection performance of the printed matter are all excellent. Furthermore, when an aqueous inkjet ink containing the binder resin is printed on an impermeable substrate, the viscosity of the aqueous inkjet ink increases significantly as the liquid components volatilize, thereby suppressing color bleeding and improving print image quality.

[0095] In the present disclosure, the term "binder resin" refers to a resin that contributes to the formation of a continuous ink film. Specifically, a resin contained in an aqueous inkjet ink and having a content of 1.5% by mass or more of the total amount of the aqueous inkjet ink is referred to as a "binder resin" in the present disclosure. The content is preferably 2.0% by mass or more, and particularly preferably 2.4% by mass or more, of the total amount of the aqueous inkjet ink.

[0096] As described above, the glass transition temperature (Tg) of the resin (C-1) is −60 to 50° C. Furthermore, from the viewpoints of forming a uniform continuous film, improving the abrasion resistance of the printed matter, and improving the standby discharge properties of the aqueous inkjet ink, the glass transition temperature of the resin (C-1) is preferably −47 to 49° C., more preferably −50 to 40° C., and particularly preferably −40 to 30° C., and may also be −31 to 25° C.

[0097] The glass transition temperature of the binder resin containing resin (C-1) can be measured by a method conforming to JIS K 7121. Specifically, approximately 10 mg of a sample of the target resin is placed in an aluminum sample pan whose mass has been measured in advance, and the mass is measured again, after which the pan is sealed with a lid. Next, this sample container and a sample pan prepared without the resin are placed in a holder in a Shimadzu DSC-60 (differential scanning calorimeter), and measurements are performed at a temperature increase rate of 10°C / min to obtain a DSC chart. The intersection of the low-temperature baseline and the tangent to the inflection point of the DSC curve is determined, and the temperature of this intersection is taken as the glass transition temperature. Indium is used for temperature calibration.

[0098] On the other hand, for acrylic resins, the value calculated by the following formula (6) can be used as the glass transition temperature.

[0099] Formula (6): 1 / Tg=Σ(Wn / Tgn)

[0100] In the above formula (6), Tg represents the glass transition temperature (K) of the resin, Wn represents the mass fraction of the structural unit consisting of polymerizable monomer n constituting the resin, and Tgn represents the glass transition temperature (K) of the homopolymer consisting of each polymerizable monomer n. For the Tgn, for example, values ​​described in "Polymer Handbook (4th Edition)" (Wiley, 1998) can be used.

[0101] The resin (C-1) may be a water-soluble resin or resin fine particles. A water-soluble resin and resin fine particles may be used in combination. From the viewpoints of improving initial ejection stability and standby ejection performance, as well as improving the abrasion resistance of printed matter, it is preferable that the resin (C-1) be resin fine particles.

[0102] In this disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin," and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin." Furthermore, in this disclosure, among the above-mentioned water-insoluble resins, a resin that is dispersed in particulate form in water and has a volume-based median diameter (also referred to as "D50" in this disclosure) of 10 to 1,000 nm is referred to as a "resin microparticle." Note that D50 in this disclosure is a value measured in a 25°C environment using a dynamic light scattering particle size distribution analyzer such as the "Nanotrac UPA-EX150" manufactured by Microtrac-Bell.

[0103] The resin (C-1) may be any of acrylic resins, styrene resins, maleic anhydride resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymer resins, etc. These resins may be used alone or in combination of two or more.

[0104] Among these, it is preferable to use one or more resins selected from the group consisting of acrylic resins, urethane resins, and polyester resins as resin (C-1).Furthermore, from the viewpoint of being able to produce printed matter having excellent adhesion and abrasion resistance to non-absorbent substrates and also being able to improve standby dischargeability, it is preferable to use an acrylic resin and / or a urethane resin as resin (C-1).

[0105] In the present disclosure, 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. In addition to the polymerizable monomers listed above, a styrene-based monomer may also be used as a polymerizable monomer constituting the acrylic resin. However, resins containing maleic acid (anhydride) (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer are not included in the term "acrylic resin" in the present disclosure. Furthermore, the term "maleic acid (anhydride) resin" refers to a resin using at least maleic acid (anhydride) as a polymerizable monomer. Furthermore, the maleic acid (anhydride) resin may use an α-olefin, a styrene-based monomer, acrylic acid, methacrylic acid, an acrylic acid ester, a methacrylic acid ester, or the like as a polymerizable monomer.

[0106] The acid value of resin (C-1) is preferably 0 to 100 mgKOH / g, more preferably 0.5 to 90 mgKOH / g. It is particularly preferably 1 to 80 mgKOH / g. By setting the acid value within the above range, even if a portion of the aqueous inkjet ink dries near the nozzles of the inkjet head, it is possible to suppress a significant increase in viscosity of the aqueous inkjet ink, thereby improving the ejection stability (particularly standby ejection performance). Furthermore, since the printed matter is less susceptible to the influence of the surrounding environment (humidity, etc.), the abrasion resistance of the printed matter is also improved.

[0107] In this disclosure, 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 disclosure, the acid value used is a value calculated by 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 (7):

[0108] Equation (7): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0109] In the above formula (7), the number "56.11" is the molecular weight of potassium hydroxide.

[0110] Furthermore, when a water-soluble resin is used as the resin (C-1), the mass average molecular weight of the resin (C-1) is preferably 1,000 to 25,000, and more preferably 5,000 to 20,000. By using a resin (C-1) having the above mass average molecular weight, a uniform continuous film can be formed even in a short drying time, and the scratch resistance of the printed matter is improved.

[0111] In the present disclosure, the mass average molecular weight of a compound is measured by a method conforming to JIS K 7252, and is expressed in terms of polystyrene. Specific measurement conditions are shown below. Apparatus used: Tosoh Corporation's "HLC-8320GPC" Columns used: TSKgel (registered trademark) SuperMultiporeHZ-M (3 columns) Column temperature: 40°C Developing solvent: tetrahydrofuran Flow rate: 0.6 mL / min Sample solution concentration: 0.1% by mass Sample solution injection volume: 10 μL

[0112] The preferred content of resin (C-1) contained in the aqueous inkjet ink of this embodiment is preferably 1.5 to 20% by mass, more preferably 2 to 18% by mass, and particularly preferably 5 to 15% by mass, of the total amount of the aqueous inkjet ink, from the viewpoints of improving the initial ejection stability and standby ejection performance, and of obtaining printed matter that is free from color bleeding and has excellent abrasion resistance.

[0113] As described above, the content of resin (C-1) is 50% by mass or more of the total mass of resins contained in the aqueous inkjet ink. When at least half of the resins contained in the aqueous inkjet ink are resin (C-1) with a low glass transition temperature, the ink film becomes a uniform, continuous film, and the abrasion resistance of the printed matter is improved. Furthermore, when the aqueous inkjet ink is printed on an impermeable substrate, the viscosity of the aqueous inkjet ink increases significantly as the liquid components volatilize, thereby suppressing color bleeding and improving print image quality. From the above viewpoints, the content of resin (C-1) is preferably 50% by mass or more of the total mass of resins contained in the aqueous inkjet ink, more preferably 65% ​​by mass or more, and particularly preferably 75% by mass or more.

[0114] <<Other Binder Resins>> The aqueous inkjet ink of this embodiment may contain binder resins other than the resin (C-1) (also referred to as "other binder resins" in the present disclosure).

[0115] The other binder resin may be a water-soluble resin or resin fine particles. The types of resins that can be used as the other binder resin are the same as those in the case of the resin (C-1) described above. In one embodiment, it is preferable to use the same type of resin as the resin (C-1) from the viewpoint of improving the scratch resistance of the printed matter due to its good affinity with the resin (C-1).

[0116] Furthermore, from the viewpoint of improving the scratch resistance of the printed matter and improving standby discharge properties, it is preferable to use a resin having a glass transition temperature of 55 to 130°C as the other binder resin, more preferably a resin having a glass transition temperature of 60 to 120°C, and particularly preferably a resin having a glass transition temperature of 65 to 110°C.

[0117] Furthermore, from the same viewpoint as that of the resin (C-1), that is, from the viewpoint of improving the ejection stability (particularly standby ejection property) and the abrasion resistance of the printed matter, the acid value of the other binder resin is preferably 0 to 100 mgKOH / g, more preferably 0.5 to 90 mgKOH / g, and particularly preferably 1 to 80 mgKOH / g.

[0118] When the aqueous inkjet ink of this embodiment contains another binder resin, the suitable content of the other binder resin is preferably 1.5 to 12 mass %, more preferably 1.5 to 10 mass %, and particularly preferably 2 to 8 mass %, of the total amount of the aqueous inkjet ink, from the viewpoint of improving the initial ejection stability and standby ejection performance.

[0119] <Wax Resin Particles> The aqueous inkjet ink of this embodiment may contain wax resin particles. It is preferable to use polyolefin resin particles as the wax resin particles. Although the detailed reason is unclear, polyolefin resin particles can be stably dispersed in the aqueous inkjet ink even when used in combination with the resin (C-1) described above. Furthermore, polyolefin resin particles are preferably selected from the viewpoint of improving the abrasion resistance, adhesion, etc. of the printed matter.

[0120] As the polyolefin, one or more selected from the group consisting of polyethylene, polypropylene, and polybutene can be suitably used, but polyethylene is particularly preferred because it can improve the scratch resistance of printed matter.

[0121] When wax resin microparticles are used, their D50 is preferably 10 to 200 nm, and more preferably 20 to 180 nm. When the D50 is within the above range, it is possible to improve the abrasion resistance and adhesion of printed matter. Furthermore, since clogging of inkjet head nozzles is prevented, an aqueous inkjet ink with excellent initial ejection stability can be obtained.

[0122] When wax resin microparticles are used, the amount of the wax resin microparticles relative to the total amount of all resins contained in the aqueous inkjet ink (pigment dispersion resin, binder resin, wax resin microparticles, etc.) is preferably 2 to 25% by mass, and particularly preferably 4 to 20% by mass. By keeping the amount within this range, the abrasion resistance and adhesion of printed matter can be improved without deteriorating initial ejection stability and standby ejection properties. Furthermore, even during high-speed printing, printed matter having sufficient abrasion resistance can be obtained while maintaining favorable initial ejection stability and standby ejection properties. Therefore, the amount of the wax resin microparticles relative to the total amount of the aqueous inkjet ink is preferably 0.2 to 2.5% by mass, and particularly preferably 0.5 to 2.0% by mass.

[0123] <Pigment> The aqueous inkjet ink of this embodiment contains a pigment. Any conventionally known organic or inorganic pigment can be used as the pigment, and for example, pigments represented by the following color index names can be used. That is, as red pigments, C.I. Pigment Red 52, 5, 7, 9, 12, 17, 22, 23, 31, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 57:1, 57:2, 112, 122, 123, 146, 147, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 184, 188, 202, 207, 209, 254, 255, 260, 264, 266, 269, 282 can be used; as violet pigments, C.I. As orange pigments, C.I. Pigment Violet 19, 23, 29, 32, 36, 37, 42, 50; as orange pigments, C.I. Pigment Orange 1, 2, 3, 5, 7, 13, 14, 15, 16, 22, 34, 36, 38, 40, 43, 47, 48, 49, 51, 52, 53, 60, 61, 62, 64, 65, 66, 69, 71, 73; as blue pigments, C.I. Pigment Blue 15, 15:3, 15:4, 15:6, 16, 60, 64, 79; as green pigments, C.I. Pigment Green 7, 10, 36, 48; as yellow pigments, C.I. C.I. Pigment Yellow 1, 2, 3, 5, 12, 13, 14, 16, 17, 24, 73, 74, 83, 87, 93, 94, 95, 97, 98, 109, 110, 111, 112, 120, 126, 127, 128, 129, 137, 138, 139, 147, 150, 151, 154, 155, 166, 167, 168, 170, 180, 185, 213; black pigments include C.I. Pigment Black 1, 7, 11; and white pigments include C.I. Pigment White 4, 5, 6, 21, etc. These pigments may be used alone or in combination of two or more. A solid solution of two or more of the pigments listed above may also be used as a pigment.

[0124] The content of the pigment contained in the aqueous inkjet ink of this embodiment is adjusted depending on the intended use of the printed matter produced using the aqueous inkjet ink, but is preferably 0.5 to 30 mass% of the total amount of the aqueous inkjet ink. Furthermore, except for white aqueous inkjet inks (aqueous white inks), the content of the pigment is more preferably 0.5 to 12 mass%, and particularly preferably 1 to 8 mass%, in order to obtain printed matters with high density without deteriorating the jetting stability of the aqueous inkjet ink. On the other hand, in the case of aqueous white inks, the content of the pigment is more preferably 5 to 25 mass%, and particularly preferably 10 to 20 mass%, in order to obtain printed matters with high hiding power without deteriorating the jetting stability of the aqueous white ink.

[0125] <Pigment Dispersion Resin> The aqueous inkjet ink of this embodiment may contain a resin (pigment dispersion resin) used for pigment dispersion purposes. Compared to pigments dispersed without using a pigment dispersion resin (self-dispersed pigments, pigments dispersed with a surfactant, etc.), pigments dispersed using a pigment dispersion resin have excellent dispersion stability, resulting in an aqueous inkjet ink with excellent initial ejection stability and standby ejection stability. In addition, selecting a pigment dispersion resin is preferable because it does not adversely affect the abrasion resistance of printed matter.

[0126] When a pigment dispersion resin is used, a resin having pigment dispersibility from among the binder resins described above may be used as the pigment dispersion resin. In this case, a resin having pigment dispersibility from among the resin (C-1) described above may be used as the pigment dispersion resin. The content of the resin (C-1) used as the pigment dispersion resin is included in the content of the resin (C-1) in the total mass of the resins described above. However, the pigment dispersion resin is present near the surface of the pigment, and the pigment may inhibit the formation of a continuous film. From the viewpoint that the formation of a uniform continuous film improves the abrasion resistance of printed matter, it is preferable that the pigment dispersion resin be provided as a pigment dispersion liquid in which the pigment and the pigment dispersion resin are dispersed in advance, and then the binder resin is added to the pigment dispersion liquid and blended into the aqueous inkjet ink.

[0127] The type of pigment dispersion resin is not particularly limited, and any of acrylic resins, styrene resins, maleic acid (anhydride) resins, urethane resins, polyester resins, and the like can be used. These resins may be used alone, or two or more may be used in combination. Among these, it is preferable to use one or more selected from the group consisting of acrylic resins, maleic acid (anhydride) resins, and urethane resins, from the viewpoints of improving initial ejection stability and standby ejection performance, wide material selectivity, ease of resin synthesis, and the like. Furthermore, it is particularly preferable to use the same type of resin as the resin (C-1) as the pigment dispersion resin, because the improved affinity with the resin (C-1) makes it difficult for the pigment to become non-uniform within the aqueous inkjet ink, and the uniformity and continuous film formation of the ink film are not inhibited by the pigment, thereby improving the abrasion resistance of the printed matter.

[0128] The pigment dispersion resin may be a resin synthesized by a conventionally known method, or a commercially available product. There are no particular limitations on its structure; for example, resins having a random structure, block structure, graft structure, hyperbranched structure, etc. can be used. In one embodiment, the pigment dispersion resin preferably has a block structure or a graft structure. Pigment dispersion resin free in the aqueous inkjet ink may adsorb to the acetylene diol compound (A), polyethylene glycol, organic compound (B), etc., potentially deteriorating the initial ejection stability, standby ejection stability, and print quality and abrasion resistance of the printed material. Therefore, in the aqueous inkjet ink of this embodiment, a pigment dispersion resin having a block structure or a graft structure, which is less likely to detach from the pigment, can be preferably used. For the same reason, it is also preferable to crosslink the pigment dispersion resin adsorbed on the pigment surface with a crosslinking agent or the like (i.e., use a crosslinked pigment dispersion resin).

[0129] In the aqueous inkjet ink of this embodiment, a water-soluble resin may be selected as the pigment dispersing resin, or a water-insoluble resin may be selected, or a water-soluble resin and a water-insoluble resin may be used in combination.

[0130] When a water-soluble resin is used as the pigment dispersing resin, its acid value is preferably 60 to 400 mgKOH / g, more preferably 70 to 350 mgKOH / g, and particularly preferably 80 to 300 mgKOH / g, and may further be 90 to 300 mgKOH / g or 100 to 300 mgKOH / g. By setting the acid value within the above range, it becomes easy to maintain the dispersion stability of the pigment, and the initial ejection stability and standby ejection performance are improved.

[0131] On the other hand, when a water-insoluble resin is used as the pigment dispersing 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. If the acid value is within the above range, it becomes easy to obtain a printed matter with excellent abrasion resistance.

[0132] In the aqueous inkjet ink of this embodiment, it is preferable to introduce an aromatic group into the pigment dispersion resin, because improved pigment adsorption not only improves the pigment dispersion stability but also suppresses liberation of the pigment dispersion resin, thereby preventing deterioration in initial jetting stability, standby jetting performance, and the print quality of the printed matter. Examples of aromatic groups include, but are not limited to, phenyl, naphthyl, anthryl, tolyl, xylyl, mesityl, and anisyl groups. Of these, one or more groups selected from the group consisting of phenyl, naphthyl, and tolyl are preferably selected from the viewpoint of improving the pigment dispersion stability, initial jetting stability, standby jetting performance, and the print quality of the printed matter.

[0133] From the viewpoint of improving all of the dispersion stability of the pigment, the initial ejection stability and standby ejection properties, and the print image quality of the printed matter, the amount of the aromatic ring-containing polymerizable monomer introduced is preferably 5 to 75 mass %, more preferably 10 to 65 mass %, and particularly preferably 15 to 55 mass %, relative to the total amount of polymerizable monomers constituting the pigment dispersion resin.

[0134] When the pigment dispersion resin does not also serve as the resin (C-1), the blending amount of the pigment dispersion resin is preferably 3 to 80 mass %, more preferably 5 to 70 mass %, and particularly preferably 10 to 60 mass %, relative to the blending amount of the pigment. Furthermore, from the viewpoint of obtaining a printed matter with excellent abrasion resistance, the blending amount of the pigment dispersion resin is preferably 2 to 50 mass %, more preferably 3 to 45 mass %, and particularly preferably 4 to 40 mass %, relative to the blending amount of the resin (C-1).

[0135] <Water> The aqueous inkjet ink of this embodiment contains water. It is preferable to use ion-exchanged water (deionized water) or distilled water as the water. The water content is preferably 45 to 85% by mass, and particularly preferably 50 to 80% by mass, based on the total amount of the aqueous inkjet ink. Water has a low boiling point and therefore volatilizes preferentially from the aqueous inkjet ink. By setting the water content within the above range, after the water volatilizes preferentially on the printing substrate, the acetylene diol compound (A) and polyethylene glycol have favorable affinity with the organic compound (B) and resin (C-1), forming a continuous ink film, thereby improving the scratch resistance of the printed matter.

[0136] <Other Components> The aqueous inkjet ink of this embodiment may contain a pH adjuster and other additives in addition to the components described above. Examples of the other additives include preservatives, ultraviolet absorbers, and infrared absorbers. These components may each be one or more conventionally known compounds.

[0137] <Method for Producing Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. One example is a method in which a pigment dispersion is produced in advance by dispersing a pigment in a medium containing at least water (aqueous medium). Then, water, the acetylene diol compound (A), polyethylene glycol, the organic compound (B), the resin (C-1), and the like are added to the pigment dispersion, and the mixture is thoroughly stirred and mixed, after which coarse particles are removed by techniques such as filtration and centrifugation. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the method described above.

[0138] From the viewpoint that the organic compound (B) and the resin (C-1) are suitably stabilized in the aqueous inkjet ink, and the initial ejection stability, standby ejection properties, print quality, and scratch resistance of the printed matter are all excellent, it is preferable to produce the aqueous inkjet ink by a method in which a mixed solution containing a pigment dispersion, water, the acetylene diol compound (A), and polyethylene glycol is produced, and then the organic compound (B) and the resin (C-1) are added and mixed.

[0139] <Characteristics of Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment preferably has a viscosity at 25°C of 3 to 15 mPa·s. Within this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from inkjet heads with ejection frequencies of approximately 4 to 10 kHz, but also from inkjet heads with high ejection frequencies of approximately 20 to 70 kHz. In particular, when the viscosity of the aqueous inkjet ink of this embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head with a design resolution of 600 dpi or higher is used. In this disclosure, the viscosity is measured at 25°C using a cone-plate rotational viscometer (E-type viscometer, cone angle 1°34') such as the TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

[0140] Furthermore, in order to obtain an aqueous inkjet ink that is excellent in initial ejection stability and print quality of printed matter, the static surface tension of the aqueous inkjet ink of this embodiment at 25° C. is preferably 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m. Note that in the present disclosure, the static surface tension is a value measured in an environment of 25° C. using the Wilhelmy method (plate method) using an "Automatic Surface Tensiometer CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.

[0141] <Aqueous Inkjet Ink Set> Although only one aqueous inkjet ink of this embodiment may be used alone, two or more aqueous inkjet inks may also be combined to form an aqueous inkjet ink set. Examples of such aqueous inkjet ink sets include a four-color aqueous inkjet ink set (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink); and a five-color aqueous inkjet ink set obtained by adding an aqueous white ink to the process color ink set. It is preferable that all of the aqueous inkjet inks constituting the aqueous inkjet ink set satisfy the requirements of the embodiment of the present disclosure described above.

[0142] <Ink-Pretreatment Liquid Set> The aqueous inkjet ink of this embodiment and the aqueous inkjet ink set described above can also be used in a form in which it is combined with a pretreatment liquid containing an aggregating agent (in the form of an ink-pretreatment liquid set). By applying a pretreatment liquid containing an aggregating agent to a printing substrate before printing with the aqueous inkjet ink, it is possible to form a layer (ink aggregation layer) that intentionally aggregates the solid components contained in the aqueous inkjet ink. Then, by landing the aqueous inkjet ink on this ink aggregation layer, it is possible to prevent coalescence of droplets of the aqueous inkjet ink and color bleeding, thereby significantly improving the print quality of the printed matter.

[0143] As the flocculant, for example, a water-soluble inorganic or organic salt containing a polyvalent metal ion, and a resin having a cationic group in which the cationic group equivalent is greater than the anionic group equivalent can be used.

[0144] In the case of a pretreatment liquid that is printed on a printing substrate by being ejected from an inkjet head, the pretreatment liquid preferably contains, in addition to the above-mentioned flocculant, an acetylene diol compound (A), polyethylene glycol, and an organic compound (B). The inclusion of these components in the pretreatment liquid improves the initial ejection stability, standby ejection performance, and wetting and spreading performance on the printing substrate, as in the case of the aqueous inkjet ink of this embodiment. Furthermore, the uniform printing of the pretreatment liquid on the printing substrate significantly improves the print quality of the final print.

[0145] Furthermore, it is particularly preferable that the pretreatment liquid printed on the printing substrate by ejection from an inkjet head contains, in addition to the above-mentioned components, a resin (C-1). When the pretreatment liquid further contains a resin (C-1), it becomes easy to significantly improve the abrasion resistance of the final printed matter obtained while maintaining the initial ejection stability and standby ejection properties in a suitable state.

[0146] The following shows an example of the composition of a pretreatment liquid that is preferably used in a method in which printing is performed on a printing substrate by ejecting the liquid from an inkjet head: Calcium lactate pentahydrate (flocculant) 5.0% by mass Surfynol 2502 (acetylene diol compound (A)) 1.0% by mass Polyethylene glycol (number average molecular weight 600) 10.0% by mass 1,2-octanediol (organic compound (B)) 0.5% by mass Superflex 650 (resin (C-1)) 19.4% by mass Proxel GXL 0.1% by mass Ion-exchanged water 64.0% by mass

[0147] Of the above compositions, "Superflex 650" is urethane resin fine particles (solid content = 26% by mass, glass transition temperature = -17°C) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. "Surfynol 2502" and "Proxel GXL" will be described later.

[0148] <Inkjet Printing Method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. That is, the inkjet printing method performed using the aqueous inkjet ink of this embodiment includes a step of ejecting the ink onto a printing substrate from an inkjet head having fine nozzles (ejecting step). In addition, it is preferable that the aqueous inkjet ink ejected onto the printing substrate is dried by a drying mechanism (drying step).

[0149] <<Discharge Process>> In the discharge process, the inkjet head can be operated in two ways: a shuttle (scan) method in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate while discharging and recording the aqueous inkjet ink; and a single-pass method in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate while discharging and recording the aqueous inkjet ink as the printing substrate passes under a fixedly disposed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may be either a shuttle method or a single-pass method. Of these, the single-pass method is preferably selected because it reduces deviation in the landing position of droplets of the aqueous inkjet ink, improving the print quality of the printed matter, and further enables high-speed printing and provides high productivity as an alternative to plate-based printing.

[0150] The method of ejection from the inkjet head can also be selected from any known methods, such as a piezoelectric method that utilizes the volume change of a piezoelectric element, a thermal method that ejects aqueous inkjet ink by bubbles generated by heating a heater, and a valve method that ejects pressurized aqueous inkjet ink by opening and closing a nozzle cover (valve) with a solenoid.

[0151] The volume of droplets of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing the drying load, improving print quality, etc. Furthermore, from the viewpoint of improving print quality, it is preferable to adjust the printing conditions (specifically, the driving frequency and number of inkjet heads installed, and the printing speed) so that the recording resolution of the printed matter is 600 dpi or higher, and it is particularly preferable to adjust the printing conditions so that the resolution is 1200 dpi or higher.

[0152] Drying Process Examples of drying methods employed in the drying mechanism used in the drying process include heat drying, hot air drying, infrared drying (e.g., infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. One or more of these methods can be selected and used as desired in the drying process. When two or more of the above drying methods are used, they may be used separately (e.g., consecutively) or simultaneously. For example, by using heat drying and hot air drying in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[0153] In particular, from the viewpoint of preventing bumping of the liquid components in the aqueous inkjet ink and obtaining printed matter with excellent print quality, when a heat drying method is employed, it is preferable that the drying temperature be 35 to 100° C., and when a hot air drying method is employed, it is preferable that the hot air temperature be 50 to 250° C. From the same viewpoint, when an infrared drying method is employed, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared rays be in the wavelength region of 700 to 2200 nm.

[0154] <Printing substrate> The printing substrate onto which the aqueous inkjet ink of this embodiment is printed is not particularly limited. On the other hand, the aqueous inkjet ink of this embodiment can be suitably used on non-permeable substrates. Generally, when a non-permeable substrate is used as the printing substrate, the aqueous inkjet ink does not penetrate, and therefore, the printed matter is likely to suffer from color bleeding and deterioration of abrasion resistance. In contrast, by using the aqueous inkjet ink of this embodiment, it is easy to obtain a printed matter that is free from color bleeding and has excellent water resistance, even on a non-permeable substrate.

[0155] Examples of impermeable substrates include plastic films and sheets such as polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene film, nylon film, polystyrene film, and polystyrene sheet; metals such as aluminum, iron, stainless steel, and titanium; and glass.

[0156] The aqueous inkjet ink of this embodiment can also be used for printing on printing substrates other than the above-mentioned impermeable substrates. Examples of printing substrates other than impermeable substrates include paper such as high-quality paper, plain paper, recycled paper, liner paper, coated paper, art paper, and cast paper.

[0157] The printing substrates listed above may have a smooth or uneven surface. The printing substrates may be transparent, translucent, or opaque. The printing substrates may be in the form of rolls or sheets. Two or more of the printing substrates listed above may be bonded together to form the printing substrate. A release adhesive layer or the like may be provided on the side opposite the printed surface, or an adhesive layer or the like may be provided on the printed surface after printing.

[0158] The improved wetting and spreading properties of the aqueous inkjet ink of this embodiment improve the print quality and drying properties, and the uniformity of the printed surface results in a printed product with good abrasion resistance and water resistance. Therefore, it is also preferable to subject the printing surface of the printing substrates listed above to surface modification such as corona treatment and plasma treatment before printing.

[0159] For example, when the above-mentioned plastic film and sheet are subjected to a corona treatment, the discharge amount of the corona treatment is 20 to 1,000 W·min / m ２ It is preferable to set the range to 30 W to 800 W·min / m ２ By setting the discharge amount in the corona treatment within the above range, damage to the printing substrate is suppressed, and the print quality and abrasion resistance of the printed matter are improved.

[0160] <Printed Material> A printed material produced using the aqueous inkjet ink of this embodiment has a printing substrate and a printed layer containing an image and / or characters formed on the printing substrate. The printed layer is a layer formed by drying the aqueous inkjet ink of this embodiment printed on the printing substrate, i.e., a layer consisting of an ink film. In one embodiment, the inkjet printing method described above can be used as a method for printing the aqueous inkjet ink of this embodiment to produce a printed material.

[0161] The aqueous inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0162] <Example of Production of an Aqueous Solution of Acrylic Pigment Dispersion Resin> 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. After the atmosphere inside the reaction vessel was purged with nitrogen gas, the contents inside the reaction vessel were heated to 75°C, and a polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C, thereby obtaining 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, and the contents of the reaction vessel were heated until the temperature reached 75°C. A polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C, thereby obtaining an acrylic pigment dispersion resin 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. The contents of the reaction vessel were then cooled to room temperature, and 17 parts of dimethylaminoethanol were added to neutralize the acrylic pigment dispersion resin. 150 parts of ion-exchanged water were then added. The contents were then heated to azeotrope 2-butanone with ion-exchanged water, thereby distilling off the 2-butanone. Ion-exchanged water was then added to adjust the solids concentration to 20%, thereby obtaining an aqueous solution of the acrylic pigment dispersion resin. Furthermore, the mass average molecular weight of the acrylic pigment dispersion resin measured by the method described above was 23,000, the glass transition temperature of the acrylic pigment dispersion resin calculated using the above formula (6) was 53°C, and the acid value of the acrylic pigment dispersion resin calculated using the above formula (7) was 104 mgKOH / g.

[0163] In the present disclosure, the term "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

[0164] <Production Example of Magenta Pigment Dispersion> 450 g of C.I. Pigment Red 122 (DIC Corporation, "FASTOGEN SUPER MAGENTA RG"), 560 g of an aqueous solution of acrylic pigment dispersion resin, and 1,990 g of ion-exchanged water were added to a mixing vessel (volume 10 L) equipped with a stirrer and stirred (premixed) for 1 hour. Next, circulatory dispersion of the mixture was initiated using a Shinmaru Enterprises "Dyno Mill" (volume 0.6 L) filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. The D50 of the mixture was measured using the above-mentioned device at regular intervals (for example, every hour), and circulatory dispersion was terminated when the D50 reached 180 nm or less, thereby producing a magenta pigment dispersion with a pigment concentration of 15%.

[0165] <Production Example of Yellow Pigment Dispersion> A yellow pigment dispersion having a pigment concentration of 15% was obtained using the same raw materials and method as for the magenta pigment dispersion, except that C.I. Pigment Yellow 74 ("Inkjet Yellow 5GX-W" manufactured by Heubach) was used as the pigment.

[0166] <Production Example of Cyan Pigment Dispersion> A cyan pigment dispersion having a pigment concentration of 15% was obtained using the same raw materials and method as for the magenta pigment dispersion, except that C.I. Pigment Blue 15:3 ("FASTOGEN BLUE LA5380" manufactured by DIC Corporation) was used as the pigment and circulatory dispersion was continued until D50 reached 150 nm or less.

[0167] <Production Example of Acrylic Binder Resin 1> A reaction vessel equipped with a thermometer, condenser, stirrer, and dropping funnel was charged with 40 parts of ion-exchanged water and 0.2 parts of the emulsifier Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). Meanwhile, a separate mixing vessel equipped with a stirrer was charged with polymerizable monomers (52 parts of methyl methacrylate, 36 parts of butyl acrylate, 11 parts of methacrylic acid, and 1 part of sodium p-toluenesulfonate); 53 parts of ion-exchanged water; and 1.8 parts of the emulsifier Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). The contents were then heated to 60°C, the atmosphere in the reaction vessel was purged with nitrogen gas, and 3 parts of a 5% aqueous solution of potassium persulfate and 4 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate the polymerization reaction. After the polymerization reaction began, the temperature of the contents in the reaction vessel was maintained at 60°C, and the remaining emulsion, 2 parts of a 5% aqueous solution of potassium persulfate, and 6 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added dropwise over 1.5 hours. After the addition was completed, stirring was continued for another 2 hours. The contents in the reaction vessel were then cooled to room temperature, and diethylaminoethanol was added until the pH of the contents reached 8.5. Ion-exchange water was then added to adjust the solids concentration to 30%, thereby obtaining an aqueous dispersion of acrylic binder resin 1, which is resin microparticles. The glass transition temperature of acrylic binder resin 1 calculated using the above formula (6) was 28°C, and the acid value of acrylic binder resin 1 calculated using the above formula (7) was 74 mgKOH / g.

[0168] <Production Example of Acrylic Binder Resins 2 to 7> Aqueous dispersions of acrylic binder resins 2 to 7 (solid content concentration of 30% each), which are resin fine particles, were obtained using the same materials and method as for the acrylic binder resin 1, except that the type and amount of polymerizable monomer used to prepare the emulsion were changed as shown in Table 1 below.

[0169]

[0170] Table 1 above also lists the type and amount of polymerizable monomer used in producing acrylic binder resin 1, as well as the glass transition temperatures (calculated using the above formula (6)) and acid values ​​(calculated using the above formula (7)) of acrylic binder resins 1 to 7.

[0171] <Production Examples of Acetylene Diol Compounds 1 and 2> Using the method described in Examples 6 to 9 of JP 2001-215690 A, compounds in which ethylene oxide groups and propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol ("Surfynol 104" manufactured by Evonik Japan K.K.) were synthesized using the diol as a starting material (acetylene diol compounds 1 and 2) by adjusting the amounts of ethylene oxide and propylene oxide and the synthesis conditions (pressure, temperature, time). Specifically, two types of compounds were produced: acetylenic diol compound 1 (HLB value 2.7) in which 3 moles of ethylene oxide groups and 11 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol; and acetylenic diol compound 2 (HLB value 5.0) in which 3.5 moles of ethylene oxide groups and 4 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0172] <Production of Water-Based Inkjet Ink Set> Using the pigment dispersion produced by the method described above, each raw material was added to a mixing vessel equipped with a stirrer to obtain the formulation shown in each column of Tables 2-1 to 2-6 below. After all raw materials were added, stirring and mixing was continued until the mixture became sufficiently uniform. The mixture was then filtered through a membrane filter with a pore size of 0.8 μm to produce an aqueous inkjet ink. Aqueous inkjet ink sets consisting of an aqueous magenta ink, an aqueous yellow ink, and an aqueous cyan ink were produced by producing aqueous inkjet inks using the magenta pigment dispersion, yellow pigment dispersion, and cyan pigment dispersion, respectively.

[0173] When producing aqueous inkjet inks, each raw material was added while stirring the mixture in the mixing vessel. In addition, in each column of Tables 2-1 to 2-6, the components were added in the order listed, starting with the component listed in the top row. However, when producing an aqueous inkjet ink that did not contain one or more of these components, that component was not added, and the next component was added in the order listed. Furthermore, for components containing two or more raw materials, the order of addition of the components within that component was arbitrary.

[0174]

[0175]

[0176]

[0177]

[0178]

[0179]

[0180] The meanings of the abbreviations and details of the product names listed in Tables 2-1 to 2-6 above are as follows. In Tables 2-1 to 2-6, "HLB" represents the HLB value, "Tg" represents the glass transition temperature, and "Nv" represents the solids concentration. Furthermore, "PEGn" in Tables 2-1 to 2-6 represents polyethylene glycol with a number average molecular weight of n. Surfynol 485: A compound in which an average of 30 moles of ethylene oxide groups have been added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (an acetylenic diol compound manufactured by Evonik Japan, HLB value = 17.1). Acetylenol E200: A compound in which an average of 20 moles of ethylene oxide groups have been added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (an acetylenic diol compound manufactured by Kawaken Fine Chemicals, HLB value = 15.9). Surfynol 465: A compound in which an average of 10 moles of ethylene oxide groups have been added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (an acetylenic diol compound manufactured by Evonik Japan, HLB value = 13.2). Dynol 607: a compound in which an average of 7 moles of ethylene oxide groups are added to 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (acetylene diol compound manufactured by Evonik Japan, HLB value = 11.0); Acetylenol E60: a compound in which an average of 6 moles of ethylene oxide groups are added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (acetylene diol compound manufactured by Kawaken Fine Chemicals, HLB value = 10.8); Surfynol 2502: a compound in which an average of 5 moles of ethylene oxide groups and 2 moles of propylene oxide groups are added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (acetylene diol compound manufactured by Evonik Japan, HLB value = 7.9). Surfynol DF110D: 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (acetylene diol compound (surfactant), manufactured by Evonik Japan, HLB value = 2.7) Surfynol 420: 2,4,7,9-tetramethyl-5-decyne-4,Compounds in which an average of 1.3 moles of ethylene oxide groups are added to 7-diol (acetylene diol compound (surfactant), manufactured by Evonik Japan, HLB value = 4.0) 1,7-HepD: 1,7-heptanediol (medium-chain alkanediol compound, HLB value = 5.2) 1,2-OctD: 1,2-octanediol (medium-chain alkanediol compound, HLB value = 4.7) 1,8-OctD: 1,8-octanediol (medium-chain alkanediol compound, HLB value = 4.7) 1,9-NonD: 1,9-nonanediol (medium-chain alkanediol compound, HLB value = 4.2) BYK-3420: siloxane surfactant modified at both ends with polyether (manufactured by BYK Japan) BYK-333: a siloxane surfactant modified at both ends with polyether (manufactured by BYK Japan) BYK-348: a side chain polyether modified siloxane surfactant (manufactured by BYK Japan) KF-6015: a side chain polyether modified siloxane surfactant (manufactured by Shin-Etsu Silicones Co., Ltd.) Nonion K-230: a surfactant represented by the general formula (5) where R, ４is an alkyl group having 12 carbon atoms, s=30, and t=0 (manufactured by NOF Corporation, HLB value=17.5) Takelac W-6061: urethane resin microparticles manufactured by Mitsui Chemicals, Inc. (solid content=30%, glass transition temperature=25°C) Takelac W-6110: urethane resin microparticles manufactured by Mitsui Chemicals, Inc. (solid content=32%, glass transition temperature=-20°C) SF470: Superflex 470 (urethane resin microparticles manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content=38%, glass transition temperature=-31°C) SF300: Superflex 300 (urethane resin microparticles manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content=30%, glass transition temperature=-42°C) Elitel KT-0507: polyester resin microparticles manufactured by Unitika Ltd. (solid content=25%, glass transition temperature=-25°C) AQUACER 515: Wax resin microparticles manufactured by BYK Japan (oxidized polyethylene resin microparticles, solid content = 35%, D50 = 30 nm) Proxel GXL: 1,2-benzisothiazol-3-one dipropylene glycol-water solution (1,2-benzisothiazol-3-one: dipropylene glycol: water = 2:6:2, preservative manufactured by Arch Chemicals)

[0181] [Examples 1 to 99, Comparative Examples 1 to 6] The aqueous inkjet ink sets produced by the methods described above were used to carry out the following evaluations, and the evaluation results are shown in Tables 2-1 to 2-6 above.

[0182] <Evaluation 1: Evaluation of ejection stability (initial ejection)> An inkjet ejection device equipped with a Kyocera inkjet head "KJ4B-QA" (design resolution 600 dpi) was placed in an environment of 25°C, and the aqueous cyan ink constituting the aqueous inkjet ink set described above was filled. A nozzle check pattern was then printed to confirm that the ink was ejected normally from all nozzles. Next, a nozzle check pattern was printed using OK top coat + paper (Oji Paper Co., Ltd. coated paper, basis weight 104.7 g / m) under printing conditions of a frequency of 30 kHz and 600 x 600 dpi. ２) was subjected to solid printing with a printing rate of 100%. The obtained solid print was then visually and with a magnifying glass to check whether the aqueous cyan ink was applied to the area where the aqueous cyan ink was supposed to be printed first, and the ejection stability (initial ejection) was evaluated. The evaluation criteria were as follows, with ◎, ○, and △ being considered usable. ◎: In the solid print, no chipping was observed in the area where the aqueous cyan ink was supposed to be printed first, or chipping was observed but the length was 3 mm or less. ○: In the solid print, chipping of more than 3 mm and 1 cm or less was observed in the area where the aqueous cyan ink was supposed to be printed first. △: In the solid print, chipping of more than 1 cm and 2 cm or less was observed in the area where the aqueous cyan ink was supposed to be printed first. ×: In the solid print, chipping of more than 2 cm was observed in the area where the aqueous cyan ink was supposed to be printed first.

[0183] <Evaluation 2: Evaluation of Standby Dischargeability> An inkjet head "Samba G3L" (design resolution 1,200 dpi) manufactured by FUJIFILM Dimatix was installed in an inkjet discharge device placed in an environment of 25°C. Furthermore, a pump, a tube, and an ink tank were prepared, and the ink supply port of the Samba G3L was connected to the pump, the pump to the ink tank, and the ink tank to the ink discharge port of the Samba G3L. Next, the ink tank was filled with the aqueous cyan ink constituting the aqueous inkjet ink set, and the pump was operated to fill the inkjet head and the flow paths with the aqueous inkjet ink. A nozzle check pattern was printed, and after confirming that ink was being discharged normally from all nozzles, the inkjet discharge device was allowed to stand by for one hour with the pump running. After one hour, a nozzle check pattern was printed again, and the number of missing nozzles was visually counted to evaluate standby dischargeability. The evaluation criteria were as follows, with ◎, ○, and △ being usable: ◎: No missing nozzles at all ○: 1 to 4 missing nozzles occurred △: 5 to 9 missing nozzles occurred ×: 10 or more missing nozzles occurred

[0184] <Preparation of Printed Material> An inkjet ejection device was prepared, in which three Kyocera Corporation inkjet heads "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) were arranged along the transport direction of the printing substrate. Each inkjet head was filled with a set of aqueous inkjet inks in the following order from the upstream side in the transport direction: aqueous cyan ink, aqueous magenta ink, and aqueous yellow ink. Furthermore, an OPP film ("OP U-1" manufactured by RM Tocello Co., Ltd., thickness 20 μm) cut to A4 size (width 21 cm x length 30 cm) was fixed on a conveyor as the printing substrate, with the corona-treated side facing up. The conveyor was then driven at 50 m / min, and as the printing substrate passed below the inkjet head installation section, the aqueous inkjet inks were ejected at a drop volume of 2.6 pL, respectively, to print a three-color gradation image or a three-color overlay print image. Immediately after printing, the printed substrate was placed in a constant temperature incubator set at 70°C and dried for 3 minutes to produce a three-color gradation image print and a three-color overprinted image print. The "three-color gradation image" refers to an image in which a cyan gradation image (5 cm wide x 25 cm long) printed using aqueous cyan ink (with a printing rate varied in 10% increments between 10 and 100%), a magenta gradation image (5 cm wide x 25 cm long) printed using aqueous magenta ink, and a yellow gradation image (5 cm wide x 25 cm long) printed using aqueous yellow ink are arranged adjacent to each other in the order cyan, magenta, and yellow, with their long sides touching. Furthermore, the above-mentioned "three-color superimposed printed image" refers to an image in which a halftone image (width 10 cm x length 20 cm) with a printing rate of 60% using aqueous cyan ink, a halftone image (width 10 cm x length 20 cm) with a printing rate of 60% using aqueous magenta ink, and a halftone image (width 10 cm x length 20 cm) with a printing rate of 60% using aqueous yellow ink are all printed so that they overlap each other (total printing rate 180%).

[0185] <Evaluation 3: Evaluation of print quality (whiteout)> The three-color gradation image print produced by the method described above was visually observed. The print quality of the three-color gradation image print was evaluated by checking for the presence or absence of whiteout in the areas printed at a coverage rate of 100%. The evaluation criteria were as follows, with ⊚, ◯, and Δ being usable. ⊚: No whiteout was observed in any of the printed areas of the cyan gradation image, the magenta gradation image, and the yellow gradation image. ◯: Slight whiteout was observed in at least one of the printed areas of the cyan gradation image, the magenta gradation image, and the yellow gradation image. Δ: Obvious whiteout was observed in only one of the printed areas of the cyan gradation image, the magenta gradation image, and the yellow gradation image. ×: Obvious whiteout was observed in two or more of the printed areas of the cyan gradation image, the magenta gradation image, and the yellow gradation image.

[0186] <Evaluation 4: Evaluation of Print Quality (Color Bleeding)> The three-color gradation image print produced by the method described above was visually observed. The print quality (color bleeding) of the three-color gradation image print was evaluated by checking the coverage rate at the boundary between the printed portion of the cyan gradation image and the printed portion of the magenta gradation image, and at the boundary between the printed portion of the magenta gradation image and the printed portion of the yellow gradation image, where color bleeding began to appear. The evaluation criteria were as follows, with ◎, ○, and △ indicating usable prints. Tables 2-1 to 2-6 list the results of the poorest evaluation results for the boundary between cyan and magenta and the boundary between magenta and yellow that were evaluated. ◎: No color bleeding was observed even at a printing rate of 80%. ○: Color bleeding was observed at a printing rate of 80%, but not at a printing rate of 70%. △: Color bleeding was observed at a printing rate of 70%, but not at a printing rate of 60%. ×: Color bleeding was observed at a printing rate of 60%.

[0187] <Evaluation 5: Evaluation of Scratch Resistance> The three-color overprinted image print produced by the method described above was rubbed strongly with a finger a predetermined number of times. The state of the print after rubbing was then visually inspected to evaluate the rub resistance of the three-color overprinted image print. The evaluation criteria were as follows, with ⊚, ○, and △ being considered usable. ⊚: No peeling of the printed layer or exposure of the printed substrate occurred even after rubbing strongly with a finger 20 times. ○: No peeling of the printed layer or exposure of the printed substrate occurred even after rubbing strongly with a finger 15 times, but peeling of the printed material and / or exposure of the printed substrate occurred after rubbing 20 times. △: No peeling of the printed layer or exposure of the printed substrate occurred even after rubbing strongly with a finger 10 times, but peeling of the printed material and / or exposure of the printed substrate occurred after rubbing 15 times. ×: Peeling of the printed layer and / or exposure of the printed substrate occurred after rubbing strongly with a finger 10 times.

[0188] As shown in Tables 2-1 to 2-6 above, the aqueous inkjet inks (sets) of Examples 1 to 99 had superior ejection stability compared to the aqueous inkjet inks of Comparative Examples 1 to 6, and also had good solid coverage and little color mixing. Furthermore, the abrasion resistance of the printed layer was also good. These results confirmed that the aqueous inkjet inks having the configurations of the present disclosure are excellent aqueous inkjet inks that combine ejection stability, print quality of printed matter, and abrasion resistance.

[0189] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0190] This disclosure is related to the subject matter described in Japanese Patent Application No. 2024-127605, filed August 2, 2024, the entire disclosure of which is incorporated herein by reference.

Claims

1. An aqueous inkjet ink comprising a pigment, an acetylenic diol compound (A), polyethylene glycol, a binder resin, and an organic compound (B) (excluding the pigment, the acetylenic diol compound (A), the polyethylene glycol, and the resin), wherein the HLB value of the acetylenic diol compound (A) is 7.5 to 17.5, the organic compound (B) consists only of carbon, hydrogen, and oxygen atoms and has multiple hydroxyl groups, the HLB value of the organic compound (B) is 2.5 to 5.2, the binder resin comprises a resin (C-1) having a glass transition temperature of -60 to 50°C, and the content of the resin (C-1) is 50% by mass or more of the total mass of the resins contained in the aqueous inkjet ink.

2. The aqueous inkjet ink according to claim 1, wherein the mass of the polyethylene glycol is 1.0 to 20, relative to the mass of the acetylene diol compound (A) taken as 1.

3. The aqueous inkjet ink according to claim 1 or 2, wherein the mass content of said organic compound (B) is 0.05 to 2.0 when the mass content of said acetylene diol compound (A) is taken as 1.

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

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