Aqueous inkjet ink and printed matter

Abstract

An aqueous inkjet ink including a pigment, a polyether-modified siloxane-based surfactant, hexylene glycol, a binder resin, and an organic compound (A) (other than a pigment, a polyether-modified siloxane-based surfactant, hexylene glycol, and a resin), wherein: the organic compound (A) consists of carbon atoms, hydrogen atoms, and oxygen atoms, has a plurality of hydroxyl groups, and has an HLB value of 2.5 to 5.2; and the binder resin includes, among the total mass of resin contained in the aqueous inkjet ink, 50 mass% or more of a resin (B-1) having a glass transition temperature of -70 to 35°C.

Description

Water-based inkjet inks and printed materials

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

[0002] 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] In this disclosure, a printing substrate on which an image and / or text is printed is collectively referred to as a “printed material.” The “image” also includes a solid image and a seamless image such as a checkerboard pattern image.

[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 commercial printing market and the packaging (label / package) printing market, there is active consideration of replacing plate-based printing methods such as offset printing and gravure printing with inkjet printing.

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

[0008] Generally, highly hydrophobic, non-polymeric organic compounds are often used to improve wettability of a printing substrate. These organic compounds orient at the interface with the printing substrate within microseconds, improving wettability of the printing substrate. However, high hydrophobicity also means poor solubility in water, which can lead to the generation of air bubbles in aqueous inkjet inks containing these organic compounds, which can contribute to nozzle clogging. Furthermore, orientation of these organic compounds at the air-liquid interface formed at the nozzle end face of the inkjet head can destabilize the meniscus of the aqueous inkjet ink. These problems are particularly likely to lead to nozzle clogging (a phenomenon in which aqueous inkjet ink is not ejected from the nozzle) immediately after the start of printing. Furthermore, due to the structure of the inkjet head, the nozzle diameter is very small, measuring only a few tens of micrometers. In particular, when printing is paused for an extended period of time, liquid components (water, water-soluble organic solvents, etc.) in the aqueous inkjet ink volatilize from the nozzle end face, 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 an increase in viscosity due to aggregation and insolubilization of solid components (pigments, resins, etc.), and may cause nozzle clogging due to this increase in viscosity.

[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 for the aqueous inkjet ink film (ink film) to not peel off even when a printed material with water attached thereto is rubbed with a finger or the like. In other words, the ink film is required to have a certain degree of water resistance. In aqueous inkjet inks containing a large amount of water-soluble raw materials, one method for imparting water resistance to the ink film after drying is to add a binder resin to the aqueous inkjet ink to form a 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 localized viscosity increase and non-uniform viscoelasticity may occur in the aqueous inkjet ink, resulting in poor ejection stability, and the binder resin may inhibit the orientation of organic compounds, thereby poor wettability 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 water 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 poorly permeable substrates and non-permeable substrates, Patent Document 1 discloses an ink that contains water, an organic solvent, a polysiloxane surfactant having an HLB (Hydrophile-Lipophile Balance) value of 8 or less, and acrylic silicone resin particles, and that can be suitably used in inkjet printing. Furthermore, the examples of Patent Document 1 show examples of inks that use 1,2-propanediol (propylene glycol), 1,3-propanediol, 3-methoxy-3-methylbutanol, 2-methyl-2,4-pentanediol (hexylene glycol), or the like as the organic solvent, and further contain, as other resin particles, a urethane resin emulsion, a polyester resin emulsion, an acrylic-styrene resin emulsion, or the like. Patent Document 1 describes that an ink having the above-described configuration has good storage stability, and that it is possible to produce printed matter that has excellent fixability (ability to suppress 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 properties even on non-water-absorbent recording media (see paragraphs 0014 and 0028 of Patent Document 2).

[0015] JP 2017-115127 A JP 2021-109904 A

[0016] 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 fast, and it is insufficient from the perspective of ensuring wettability on the order of microseconds. Furthermore, the polyoxyalkylene monoallyl ether compounds and acetylene glycol-based surfactants specifically used in the examples of Patent Document 2 (see also paragraphs

[0117] to

[0118] of Patent Document 2) all contain large amounts of ethylene oxide, which is highly hydrophilic. Therefore, the aqueous inkjet ink specifically disclosed in Patent Document 2 also does not contain any non-polymeric hydrophobic organic compounds. Thus, in order 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.

[0017] As described above, the techniques described in Patent Documents 1 and 2 have not yet been able to solve all of the above-mentioned problems to a high degree. Therefore, one object of one embodiment of the present invention is to provide an aqueous inkjet ink that is free from white voids and color bleeding, has excellent water resistance, and is excellent in ejection stability immediately after the start of printing and after a long period of printing pause, even when printing on a poorly permeable substrate or a non-permeable substrate.

[0018] 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.

[0019] That is, some embodiments of the present invention relate to aqueous inkjet inks as shown in [1] to [3] below, and printed matter produced using the aqueous inkjet ink as shown in [4] below. [1] An aqueous inkjet ink comprising a pigment, a polyether-modified siloxane surfactant, hexylene glycol, a binder resin, and an organic compound (A) (excluding the pigment, the polyether-modified siloxane surfactant, the hexylene glycol, and the resin), wherein the organic compound (A) consists only of carbon atoms, hydrogen atoms, and oxygen atoms and has a plurality of hydroxyl groups, the HLB value of the organic compound (A) is 2.5 to 5.2, the binder resin comprises a resin (B-1) having a glass transition temperature of -70 to 35°C, and the content of the resin (B-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 content by mass of the resin (B-1) is 2 to 50, relative to the content by mass of the polyether-modified siloxane surfactant, taken as 1. [3] The aqueous inkjet ink according to [1] or [2], wherein the aqueous inkjet ink does not contain a butylene glycol monoalkyl ether-based water-soluble organic solvent (having an alkyl terminal group with 1 to 4 carbon atoms) or a pentylene glycol monoalkyl ether-based water-soluble organic solvent (having an alkyl terminal group with 1 to 4 carbon atoms), or the total content of the butylene glycol monoalkyl ether-based water-soluble organic solvent (having an alkyl terminal group with 1 to 4 carbon atoms) and the pentylene glycol monoalkyl ether-based water-soluble organic solvent (having an alkyl terminal group with 1 to 4 carbon atoms) is 50% by mass or less relative to the content of the hexylene glycol. [4] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [3] above on a printing substrate.

[0020] The aqueous inkjet ink according to one embodiment of the present invention provides printed matter that is free from white spots and color bleeding and has excellent water resistance, even when printed on poorly permeable substrates and non-permeable substrates, and further has the effect of providing excellent ejection stability immediately after the start of printing and after a long period of printing suspension.

[0021] An aqueous inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "aqueous inkjet ink of an embodiment") will be described below. Note that the present disclosure is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present disclosure.

[0022] Generally, aqueous inkjet inks do not wet or spread on poorly permeable or 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 poorly permeable or 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 destabilizing the meniscus of the aqueous inkjet ink due to rapid orientation at the air-liquid interface formed at the nozzle end face of the inkjet head. These drawbacks lead to deterioration in initial ejection stability and standby ejection performance.

[0023] Furthermore, to obtain a printed matter with excellent water resistance, it is preferable that the binder resin form a continuous film in the ink film constituting the printed matter. Generally, the lower the glass transition temperature of the binder resin, the easier it is to form a continuous film. Therefore, from the perspective of forming a continuous film, using a binder resin with a low glass transition temperature is effective. 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 effects cannot be achieved, and the print quality of the printed matter deteriorates. To fully achieve the above-mentioned effects, 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 in the water resistance of the printed matter.

[0024] In contrast, the aqueous inkjet ink of the present embodiment contains an organic compound (A) 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 (B-1) which has a glass transition temperature of −70 to 35° C., as well as hexylene glycol and a polyether-modified siloxane surfactant.

[0025] Hexylene glycol (2-methyl-2,4-pentanediol) has multiple branched alkyl groups and is more hydrophobic than other alkanediols, while also having high solubility in water and a low boiling point at 1 atmosphere. Therefore, it has a higher affinity with the organic compound (A) than alkanediols (e.g., propylene glycol) commonly used in aqueous inkjet inks. As a result, the organic compound (A) is stabilized by hexylene glycol in the aqueous inkjet ink. Furthermore, by suppressing the rapid orientation of the organic compound (A) toward the interface, the generation of bubbles and destabilization of the meniscus are suppressed in the aqueous inkjet ink present in the inkjet head, improving the initial ejection stability and standby ejection performance.

[0026] Furthermore, hexylene glycol also has affinity with the binder resin. Therefore, for example, even after water volatilizes from the aqueous inkjet ink applied to a printing substrate, the affinity between the organic compound (A) and the binder resin via hexylene glycol allows the binder resin to uniformly diffuse together with the organic compound (A) (and the polyether-modified siloxane surfactant described below). In addition, the aqueous inkjet ink of this embodiment contains, as the binder resin, a resin (B-1) that has a low glass transition temperature, i.e., that easily forms a continuous film, and the content of this resin (B-1) is 50 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, thereby improving the water resistance of printed materials. Furthermore, because hexylene glycol itself does not remain in the continuous film but ultimately volatilizes, highly water-resistant printed materials can be produced with low energy.

[0027] In addition, the aqueous inkjet ink of the present embodiment contains a polyether-modified siloxane surfactant. The polyether-modified siloxane surfactant has a highly hydrophobic siloxane chain and a highly hydrophilic polyether chain. Therefore, it is believed that the polyether-modified siloxane surfactant also exhibits affinity similar to that of hexylene glycol. In particular, since the polyether-modified siloxane surfactant has a larger molecular weight than hexylene glycol, it is believed that it has a strong affinity with binder resins having similarly large molecular weights. As a result, the polyether-modified siloxane surfactant suppresses the formation of a film of the binder resin on the nozzle end surface of the inkjet head, improving the initial ejection stability. Furthermore, the polyether-modified siloxane surfactant is oriented at the interface behind the organic compound (A), enabling uniform wetting and spreading of droplets of the aqueous inkjet ink, facilitating the production of printed materials free of whiteout and color bleeding.

[0028] 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.

[0029] As mentioned above, Patent Documents 1 and 2 each provide specific examples of aqueous inkjet inks containing a polyether-modified siloxane surfactant, hexylene glycol, and a resin (B-1), wherein the content of the resin (B-1) is 50% by mass or more of the total mass of the resins contained in the aqueous inkjet ink (e.g., Examples D4-5, D11, E3, E8, E10, and E12 of Patent Document 1, and Inks 7, 15, and 22 of Patent Document 2). However, these specific examples differ from the aqueous inkjet ink of the embodiment in that they do not contain the organic compound (A). Furthermore, the aqueous inkjet ink of the embodiment containing the organic compound (A) can produce printed materials free of whiteout and color bleeding even on printing substrates with very low interfacial free energy, and also has good initial ejection stability, standby ejection properties, and water resistance of printed materials. However, Patent Documents 1 and 2 do not disclose or suggest such a method.

[0030] Next, each component constituting the aqueous inkjet ink according to one embodiment of the present invention will be described in detail below.

[0031] <Organic Compound (A)> The aqueous inkjet ink of the present embodiment contains organic compound (A), which is an organic compound consisting only of carbon, hydrogen, and oxygen atoms and has multiple hydroxyl groups, and has an HLB value of 2.5 to 5.2. During printing, the organic compound (A) quickly orients at the interface with the printing substrate, resulting in printed matter free of white spots and color bleeding, even on poorly permeable and non-permeable substrates. Furthermore, the combined use of hexylene glycol and organic compound (A) 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 binder resin from inhibiting the formation of a continuous film, improving the water resistance of printed matter.

[0032] Pigments, polyether-modified siloxane surfactants, and hexylene glycol are not included in the organic compound (A). Also, resins containing the binder resin (compounds in which one or more polymerizable monomers are linked together by covalent bonds to form a main chain) are also not included in the organic compound (A).

[0033] As described above, the HLB value of the organic compound (A) is 2.5 to 5.2. Furthermore, since the organic compound (A) has good affinity with other components, the initial ejection stability and standby ejection property are improved while suppressing white voids and color bleeding in printed matter, and the water resistance of the printed matter is also improved. From this viewpoint, the HLB value of the organic compound (A) is preferably 3.0 to 5.2, and particularly preferably 3.8 to 5.2.

[0034] In the present disclosure, 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.

[0035] 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, and the larger the HLB value, the more hydrophilic the material.

[0036] Formula (1): HLB value = 20 × (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material)

[0037] The organic compound (A) used in the aqueous inkjet ink of this embodiment is composed only of carbon atoms, hydrogen atoms, and oxygen atoms, and has a plurality of hydroxyl groups. Examples of compounds that can be used as the organic compound (A) include: acetylene diol compounds such as 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), and 3,6-dimethyl-4-octyne-3,6-diol (4.0), as well as ethylene oxide (EO) and / or propylene oxide (PO) adducts thereof; 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; Examples include glycerin fatty acid ester compounds such as glycerol monostearate (3.5), glycerol monobehenate (3.0), and glycerol monooleate (2.8), as well as their ethylene oxide and / or propylene oxide adducts; and 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), 1,2-nonanediol (4.2), and 1,9-nonanediol (4.2). The numbers in parentheses are the HLB values ​​of each material.

[0038] Among these compounds, one or more compounds selected from the group consisting of acetylene diol compounds, ethylene oxide and / or propylene oxide adducts of acetylene diol compounds, and medium-chain alkanediol compounds are preferably used, from the viewpoints of high affinity with hexylene glycol, improved initial ejection stability and standby ejection property, and improved water resistance of printed matter.

[0039] The organic compound (A) has an excellent orientation speed to the interface and good affinity with hexylene glycol, and therefore, while suppressing white voids and color mixing bleeding in printed matter, the initial ejection stability and standby ejection property are improved, and the water resistance of the printed matter is also improved. From these viewpoints, the molecular weight of the organic compound (A) is preferably 100 to 750, and particularly preferably 130 to 650.

[0040] The amount of organic compound (A) added is preferably 0.05 to 1.5% by mass, and particularly preferably 0.1 to 1% by mass, of the total amount of the aqueous inkjet ink, from the viewpoints that a printed matter free from white voids and color bleeding and having excellent water resistance can be obtained, and that the initial ejection stability and standby ejection performance are also improved.

[0041] Furthermore, since the affinity between the organic compound (A) and hexylene glycol is improved, the initial ejection stability and standby ejection performance are improved while white voids and color mixing bleeding in printed matter are suppressed, and the water resistance of the printed matter is also improved. From this viewpoint, the mass content of hexylene glycol is preferably 2 to 200, and more preferably 4 to 50, when the mass content of the organic compound (A) is taken as 1.

[0042] <Polyether-modified siloxane surfactant> The aqueous inkjet ink of this embodiment contains a polyether-modified siloxane surfactant. The polyether-modified siloxane surfactant has affinity for the binder resin, thereby suppressing film formation of the binder resin on the nozzle end surface of the inkjet head and improving initial ejection stability. Furthermore, the polyether-modified siloxane surfactant is oriented at the interface with the organic compound (A) behind it, resulting in a printed product that is free of white spots and color bleeding.

[0043] Examples of polyether-modified siloxane surfactants that can be used in the aqueous inkjet ink of this embodiment include compounds having a structure represented by the following general formula (2).

[0044] General formula (2):

[0045] In the general formula (2), 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 (3), 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 (3): 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 (3) (R １ and R ２ However, both may have a structure represented by the following general formula (3):

[0046] General formula (3):

[0047] In general formula (3), 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 a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. The addition of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be in a block or random manner.

[0048] In the above general formula (2), R ２ is a structure represented by the general formula (3), 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 (3) have high affinity with binder resins and are effective in improving the initial ejection stability and the water 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 the present embodiment. On the other hand, in the above general formula (2), R １ is a structure represented by the above general formula (3), 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 (3) 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.

[0049] Examples of commercially available products of the above-mentioned siloxane surfactants modified at both ends with polyether include BY16-201 and SF8427 manufactured by Dow Corning Toray Co., Ltd.; BYK-331, BYK-333, BYK-UV3500, and BYK-3420 manufactured by BYK-Chemie; TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Degussa; and Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.

[0050] Commercially available examples of the side chain polyether-modified siloxane surfactant include SF8428, FZ-2162, 8032 ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Dow Corning Toray Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 manufactured by BYK-Chemie; and TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, and TEGO Wet manufactured by Evonik Degussa. 280, and Shin-Etsu Chemical Co., Ltd.'s KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, and KF-643.

[0051] The amount of polyether-modified siloxane surfactant added is preferably 0.1 to 4 mass % of the total amount of ink, more preferably 0.2 to 3 mass %, and even more 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 water resistance.

[0052] Furthermore, from the viewpoint of achieving favorable affinity with resin (B-1), improving initial ejection stability, and suppressing white voids and color bleeding in printed matter, the content of resin (B-1) is preferably 2 to 50, and more preferably 2.5 to 35, relative to the content of the polyether-modified siloxane surfactant, which is taken as 1.

[0053] <Other Nonionic Surfactants> The aqueous inkjet ink of the embodiment may contain a nonionic surfactant other than the polyether-modified siloxane surfactant and the surfactant corresponding to the organic compound (A) described above (also referred to as "other nonionic surfactants" in the present disclosure).

[0054] Specific examples of the other nonionic surfactants include acetylene diol 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), 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), fluorine-based surfactants, polyoxyalkylene alkyl ether surfactants, polyoxyalkylene alkylamine surfactants, and the like.

[0055] Among these, one or more surfactants selected from the group consisting of acetylene diol surfactants, ethylene oxide and / or propylene oxide adducts of acetylene diol surfactants (with an HLB value of less than 2.5 or more than 5.2), and polyoxyalkylene alkyl ether surfactants can be preferably used, from the viewpoint that they have high affinity with the organic compound (A) and the binder resin, thereby improving the initial ejection stability and standby ejection property and also improving the water resistance of printed matter.

[0056] Among these, acetylene diol surfactants and ethylene oxide and / or propylene oxide adducts of acetylene diol surfactants (with an HLB value of less than 2.5 or more than 5.2) are preferred because they have excellent orientation speed to the interface, and therefore, in addition to the above-mentioned effects, they improve the wettability of the aqueous inkjet ink, making it easier to obtain printed matter that is free of white voids and color bleeding. In particular, from the viewpoint of improving the wettability of non-permeable substrates and poorly permeable substrates and obtaining printed matter with excellent print quality, it is preferred to use an ethylene oxide and / or propylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and / or an ethylene oxide and / or propylene oxide adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol as the acetylenic diol surfactant and an ethylene oxide and / or propylene oxide adduct of an acetylenic diol surfactant (with an HLB value of less than 2.5 or more than 5.2).

[0057] On the other hand, polyoxyalkylene alkyl ether surfactants are preferably used because they have a particularly high affinity with the organic compound (A) and significantly improve the initial ejection stability, standby ejection properties, and water resistance of printed matter. From these viewpoints, it is preferable to use a compound having a structure represented by the following general formula (4) as the polyoxyalkylene alkyl ether surfactant:

[0058] General formula (4):

[0059] In the general formula (4), s is an integer of 15 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 groups and propylene oxide groups in [ ] may be in a block or random manner.

[0060] In particular, from the viewpoint of significantly improving the initial ejection stability and standby ejection property, as well as the water resistance of the printed matter, s in the above general formula (4) 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).

[0061] 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 are easily suppressed, and the water resistance of printed materials is also improved. Furthermore, if the total content of other nonionic surfactants is 3% by mass or less, initial ejection stability and standby ejection performance are improved.

[0062] <Hexylene Glycol> As described above, the aqueous inkjet ink of this embodiment contains hexylene glycol. Furthermore, in order to ensure good ejection stability and good print quality of printed matter, the content of hexylene glycol in the aqueous inkjet ink of this embodiment is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1 to 10% by mass, of the total amount of the aqueous inkjet ink.

[0063] <Water-soluble organic solvent> The aqueous inkjet ink of the embodiment may contain a water-soluble organic solvent. However, the "water-soluble organic solvent" in the present disclosure does not include hexylene glycol or compounds corresponding to the above-mentioned organic compound (A).

[0064] Specific examples of the water-soluble organic solvent include alkane monools having 2 to 4 carbon atoms; alkane diols having 2 to 5 carbon atoms; alkane triols having 3 to 6 carbon atoms; polyethylene glycols (having 2 to 4 ethylene 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); and butylene glycol monoalkyl ethers (having 1 to 4 carbon atoms in the alkyl group at the molecular terminal). ), 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 can be used. 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.

[0065] When the aqueous inkjet ink of the present embodiment contains the water-soluble organic solvents, the total content thereof is preferably 2 to 40 mass %, more preferably 3 to 30 mass %, and particularly preferably 4 to 25 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 as an inkjet ink, and to ensure good ejection stability even after a long period of printing suspension, and to produce printed matter that can be dried with low energy and has good water resistance.

[0066] Furthermore, when the aqueous inkjet ink of the present embodiment contains a water-soluble organic solvent, the content of the hexylene glycol is preferably 3 to 75 mass %, more preferably 10 to 60 mass %, and particularly preferably 15 to 50 mass %, of the total content of the water-soluble organic solvent and the hexylene glycol contained in the aqueous inkjet ink. By ensuring that the content of hexylene glycol relative to the total content of the water-soluble organic solvent and hexylene glycol is within the above range, the stabilization of organic compound (A) by the hexylene glycol is not inhibited by the water-soluble organic solvent, thereby improving the initial ejection stability and standby ejection performance, and at the same time, improving the wettability of the aqueous inkjet ink on the order of microseconds, thereby enabling the production of printed matter free of white voids and color bleeding.

[0067] In one embodiment, the total content of butylene glycol monoalkyl ethers (terminal alkyl groups having 1 to 4 carbon atoms) and pentylene glycol monoalkyl ethers (terminal alkyl groups having 1 to 4 carbon atoms) contained in the aqueous inkjet ink of this embodiment is preferably 50% by mass or less (can be omitted), more preferably 20% by mass or less (can be omitted), and particularly preferably 10% by mass or less (can be omitted) of the hexylene glycol content. Butylene glycol monoalkyl ethers (terminal alkyl groups having 1 to 4 carbon atoms) and pentylene glycol monoalkyl ethers (terminal alkyl groups having 1 to 4 carbon atoms) have large hydrophobic groups such as butylene and pentylene groups, and are more hydrophobic than other water-soluble organic solvents, which may inhibit the effects of hexylene glycol described above. Therefore, by controlling the total content of butylene glycol monoalkyl ethers (those having 1 to 4 carbon atoms in the alkyl group at the molecular terminal) and pentylene glycol monoalkyl ethers (those having 1 to 4 carbon atoms in the alkyl group at the molecular terminal), it is possible to obtain printed matter that is free of white voids and color bleeding and has excellent water resistance. Examples of butylene glycol monoalkyl ethers (those having 1 to 4 carbon atoms in the alkyl group at the molecular terminal) include butylene glycol monomethyl ether (methoxybutanol, methoxymethylpropanol, etc.), and examples of pentylene glycol monoalkyl ethers (those having 1 to 4 carbon atoms in the alkyl group at the molecular terminal) include pentylene glycol monomethyl ether (methoxypentanol, methoxymethylbutanol, etc.).

[0068] <<Alkanediols Having 2 to 5 Carbon atoms>> In one embodiment, the aqueous inkjet ink of the embodiment may contain an alkanediol having 2 to 5 carbon atoms as the water-soluble organic solvent. The inclusion of an alkanediol having 2 to 5 carbon atoms can further stabilize the organic compound (A) and improve standby jetting properties. Furthermore, after water volatilizes from the aqueous inkjet ink applied to a printing substrate, the binder resin with a low glass transition temperature can be dissolved together with hexylene glycol. As a result, the viscosity of the aqueous inkjet ink on the printing substrate increases, and color bleeding can be suppressed. Furthermore, when one or more compounds selected from the group consisting of acetylene diol compounds, ethylene oxide and / or propylene oxide adducts of acetylene diol compounds, and medium-chain alkanediol compounds are used as the organic compound (A), the organic compound (A) is particularly stabilized, which can improve standby jetting properties, suppress color bleeding in printed matter, and also improve the water resistance of the printed matter.

[0069] Examples of the alkanediols having 2 to 5 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, 2-methyl-1,3-propanediol, and 3-methyl-1,3-butanediol. These compounds may be used alone or in combination of two or more.

[0070] Among these, it is preferable to use one or more selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, and 1,3-butanediol, from the viewpoints of good ejection stability after a long period of printing suspension and suppression of color bleeding in printed matter. In particular, when one or more compounds selected from the group consisting of acetylene diol compounds, ethylene oxide and / or propylene oxide adducts of acetylene diol compounds, and medium-chain alkanediol compounds are used as the organic compound (A), it is particularly preferable to use propylene glycol, from the viewpoints of improving standby ejection properties, suppressing color bleeding in printed matter, and further improving the water resistance of printed matter.

[0071] In view of improving the initial ejection stability and standby ejection property and obtaining printed matter that is free of white voids and has excellent water resistance, the content of the alkanediols having 2 to 5 carbon atoms is preferably from 1 to 30% by mass, more preferably from 3 to 25% by mass, and particularly preferably from 5 to 22% by mass, of the total amount of the aqueous inkjet ink.

[0072] Furthermore, when the aqueous inkjet ink applied to a printing substrate dries, both hexylene glycol and the alkanediol having 2 to 5 carbon atoms contribute to dissolving the binder resin and stabilizing the organic compound (A), thereby enabling printed matter to be obtained that is free from white voids and color bleeding and has excellent water resistance, and further enabling an aqueous inkjet ink to be obtained that has good initial ejection stability and standby ejection properties.From this viewpoint, when the mass content of hexylene glycol is taken as 1, the mass content of the alkanediol having 2 to 5 carbon atoms is preferably 0.2 to 25, more preferably 0.4 to 15, and particularly preferably 1 to 12.

[0073] Specific (poly)propylene glycol monoalkyl ethers Meanwhile, the aqueous inkjet ink of an embodiment may contain, among (poly)propylene glycol monoalkyl ethers, a compound 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 the present disclosure). Specific (poly)propylene glycol monoalkyl ethers have an appropriately low surface tension at 25°C, which makes it easy to improve the initial ejection stability and prevent white voids in printed matter. Furthermore, since specific (poly)propylene glycol monoalkyl ethers also function as film-forming aids for binder resins, the use of specific (poly)oxypropylene monoalkyl ethers makes it possible to obtain a uniform and continuous ink film, and the water resistance of printed matter can be significantly improved.

[0074] 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.

[0075] 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 and improving water resistance and preventing white voids in printed matter. 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 these compounds also have improved affinity with hexylene glycol, thereby promoting the formation of a uniform and continuous ink film, significantly improving the water resistance of printed matter, and suppressing color bleeding in the 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.

[0076] In order to simultaneously achieve all of the effects of improving the initial ejection stability, preventing white voids in printed matter, and improving water 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.

[0077] <Binder Resin> <Resin (B-1)> The aqueous inkjet ink of this embodiment contains a binder resin. The binder resin includes a resin (B-1) having a glass transition temperature of −70 to 35° C., and the content of the resin (B-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 the resin (B-1), which has a low glass transition temperature and easily forms a continuous film, and by using it in combination with hexylene glycol and a polyether-modified siloxane surfactant, it is possible to achieve both improved water resistance of printed matter and improved initial ejection stability. Furthermore, when an aqueous inkjet ink containing the binder resin is printed on a poorly permeable substrate or a non-permeable substrate, the viscosity of the aqueous inkjet ink increases significantly as the liquid components volatilize, thereby suppressing color bleeding and improving print image quality.

[0078] As described above, the glass transition temperature (Tg) of the resin (B-1) is −70 to 35° C. Furthermore, from the viewpoints of forming a uniform continuous film, improving the water resistance of the printed matter, and improving the standby jetting properties of the aqueous inkjet ink, the glass transition temperature of the resin (B-1) is preferably −55 to 30° C., and particularly preferably −45 to 25° C.

[0079] The glass transition temperature of the binder resin containing resin (B-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 baseline is determined, and the temperature of this intersection is taken as the glass transition temperature. Indium is used for temperature calibration.

[0080] On the other hand, for acrylic resins, the value calculated by the following formula (5) can be used as the glass transition temperature.

[0081] Formula (5): 1 / Tg = Σ(Wn / Tgn)

[0082] In the above formula (5), 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.

[0083] The resin (B-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 water resistance of printed matter, it is preferable that the resin (B-1) be resin fine particles.

[0084] 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.

[0085] The resin (B-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.

[0086] 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 the resin (B-1).Furthermore, from the viewpoint of being able to produce printed matter having excellent adhesion and water resistance to poorly absorbent substrates and non-absorbent substrates, it is preferable to use an acrylic resin and / or a urethane resin as the resin (B-1).

[0087] 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.

[0088] The acid value of the resin (B-1) is preferably 0 to 100 mgKOH / g, more preferably 0.5 to 80 mgKOH / g, and particularly preferably 1 to 60 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, a significant increase in viscosity of the aqueous inkjet ink can be suppressed, thereby improving the ejection stability (particularly standby ejection performance). Furthermore, the water resistance of the printed matter can also be improved.

[0089] In the present 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 the present disclosure, the acid value is 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 by the following formula (6):

[0090] Equation (6): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0091] In the above formula (6), the number "56.11" is the molecular weight of potassium hydroxide.

[0092] Furthermore, when a water-soluble resin is used as the resin (B-1), the mass average molecular weight of the resin (B-1) is preferably 1,000 to 25,000, and more preferably 5,000 to 20,000. By using a resin (B-1) having the above mass average molecular weight, a uniform continuous film can be formed even in a short drying time, and the water resistance of the printed matter is improved.

[0093] 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 examples of 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

[0094] The preferred content of resin (B-1) contained in the aqueous inkjet ink of this embodiment is preferably 1 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 water resistance.

[0095] As described above, the content of resin (B-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 (B-1) with a low glass transition temperature, the ink film becomes a uniform, continuous film, and the water resistance of the printed matter is improved. Furthermore, when the aqueous inkjet ink is printed on a poorly permeable substrate or a non-permeable 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 (B-1) is more preferably 65% ​​by mass or more, and particularly preferably 75% by mass or more, of the total mass of resins contained in the aqueous inkjet ink.

[0096] <<Other Binder Resins>> The aqueous inkjet ink of the embodiment may contain binder resins other than the resin (B-1) (also referred to as "other binder resins" in the present disclosure).

[0097] 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 for the resin (B-1) described above. In one embodiment, it is preferable to use the same type of resin as the resin (B-1) from the viewpoint of improving the water resistance of printed matter due to its good affinity with the resin (B-1).

[0098] 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 50 to 120°C as the other binder resin, more preferably a resin having a glass transition temperature of 60 to 110°C, and particularly preferably a resin having a glass transition temperature of 70 to 100°C.

[0099] Furthermore, from the same viewpoint as that of the resin (B-1), that is, from the viewpoint of improving the ejection stability (particularly standby ejection property) and the water 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 80 mgKOH / g, and particularly preferably 1 to 60 mgKOH / g.

[0100] When the aqueous inkjet ink of the embodiment contains another binder resin, the suitable content of the other binder resin is preferably 1 to 12% by mass, more preferably 1.5 to 10% by mass, and particularly preferably 2 to 8% by mass, of the total amount of the aqueous inkjet ink, from the viewpoint of improving the initial ejection stability and standby ejection performance.

[0101] <Wax Resin Particles> The aqueous inkjet ink of the present embodiment may also contain wax resin particles. Furthermore, 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 (B-1) described above. Furthermore, they are preferably selected from the viewpoint of improving the abrasion resistance, adhesion, water resistance, etc. of the printed matter.

[0102] 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 from the viewpoint of improving the water resistance of the printed matter.

[0103] 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 scratch resistance, adhesion, water resistance, etc. of printed matter. Furthermore, since clogging of the inkjet head nozzles is prevented, an aqueous inkjet ink with excellent initial ejection stability can be obtained.

[0104] When wax resin microparticles are used, the amount of the wax resin microparticles relative to the total amount of all resins (pigment dispersion resin, binder resin, and wax resin microparticles) contained in the aqueous inkjet ink is preferably 2 to 30% by mass, more preferably 3 to 25% by mass, and particularly preferably 4 to 20% by mass. By keeping the amount within the above range, the abrasion resistance, adhesion, and water resistance of printed matter can be improved without deteriorating the initial ejection stability and standby ejection performance. Furthermore, since printed matter having sufficient water resistance can be obtained even during high-speed printing, 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% by mass.

[0105] <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.

[0106] The content of the pigment contained in the aqueous inkjet ink of the embodiment is adjusted depending on the intended use of the printed matter produced using the aqueous inkjet ink, but is preferably, for example, 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.

[0107] <Pigment Dispersion Resin> The aqueous inkjet ink of the present 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. Furthermore, selecting a pigment dispersion resin is preferable because it does not adversely affect the water resistance of printed matter.

[0108] The pigment dispersion resin may also serve as the resin (B-1) described above. An example of a pigment dispersion resin that also serves as the resin (B-1) is resin fine particles that contain a pigment and have a glass transition temperature of −70 to 35° C.

[0109] The type of pigment-dispersing 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 in combination of two or more. Among these, it is preferable to use one or more resins 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 (B-1) as the pigment-dispersing resin, because the improved affinity with the resin (B-1) makes it difficult for the pigment to become non-uniform within the aqueous inkjet ink, and the uniformity and continuous formation of the ink film are not inhibited by the pigment, thereby improving the water resistance of the printed matter.

[0110] The pigment dispersion resin may be a resin synthesized by a conventional method, or a commercially available product. There are no particular limitations on its structure; for example, resins having a random structure, a block structure, a graft structure, a hyperbranched structure, or the like 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 organic compound (A) and the polyether-modified siloxane surfactant, potentially deteriorating the initial ejection stability, standby ejection stability, and print quality 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, is preferably used. For the same reason, it is also preferable to crosslink the pigment dispersion resin adsorbed to the pigment surface with a crosslinking agent or the like (i.e., to use a crosslinked pigment dispersion resin).

[0111] As the pigment dispersing resin, a water-soluble resin may be selected, a water-insoluble resin may be selected, or a water-soluble resin and a water-insoluble resin may be used in combination.

[0112] 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. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment, and the initial ejection stability and standby ejection performance are improved.

[0113] 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 water resistance.

[0114] In the aqueous inkjet ink of the present embodiment, it is preferable to introduce an aromatic group into the pigment dispersion resin, because improved pigment adsorption not only improves the dispersion stability of the pigment 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 dispersion stability of the pigment, initial jetting stability, standby jetting performance, and the print quality of the printed matter.

[0115] 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.

[0116] When the pigment dispersion resin does not also serve as the resin (B-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 water 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 (B-1).

[0117] <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, so it 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 hexylene glycol and polyether-modified siloxane surfactant have favorable affinity with the organic compound (A) and the binder resin, forming a continuous ink film, thereby improving the water resistance of the printed matter.

[0118] <Other Components> In addition to the components described above, the aqueous inkjet ink of this embodiment may contain a pH adjuster and other additives. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds may be used.

[0119] <Method for Producing Aqueous Inkjet Ink> The aqueous inkjet ink of the present embodiment can be produced by a conventionally known method. One example is a method in which a pigment dispersion is produced by dispersing a pigment in a medium containing at least water (aqueous medium). Water, organic compound (A), a polyether-modified siloxane surfactant, hexylene glycol, a binder resin, and the like are then added to the pigment dispersion, followed by thorough stirring and mixing, and then removing coarse particles by techniques such as filtration and centrifugation. However, the method for producing the aqueous inkjet ink of the present embodiment is not limited to the above-described method.

[0120] <Characteristics of Aqueous Inkjet Ink> The aqueous inkjet ink of the present 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 the present embodiment is 4 to 10 mPa·s at 25°C, 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 the present 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.

[0121] 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 an embodiment is preferably 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m at 25° C. In the present disclosure, the static surface tension is a value measured in an environment of 25° C. using the Wilhelmy method (plate method) with an "Automatic Surface Tensiometer CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.

[0122] <Aqueous Inkjet Ink Set> In an embodiment, a single aqueous inkjet ink may be used alone, or two or more aqueous inkjet inks may 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); or 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 invention described above.

[0123] <Ink-Pretreatment Liquid Set> The aqueous inkjet ink of the 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.

[0124] 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.

[0125] <Inkjet Printing Method> The aqueous inkjet ink of the embodiment is used in the inkjet printing method described above. That is, the inkjet printing method performed using the aqueous inkjet ink of the embodiment includes a step of ejecting the aqueous inkjet 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).

[0126] <<Discharge Process>> The inkjet head operation methods in the discharge process include 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 ink is discharged and recording is performed as the printing substrate passes under a fixedly disposed inkjet head. The inkjet head equipped with the aqueous inkjet ink of the embodiment may employ either the shuttle method or the 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] <Printing substrate> The printing substrate onto which the aqueous inkjet ink of the embodiment is printed is not particularly limited. On the other hand, the aqueous inkjet ink of the embodiment can be suitably used on a poorly permeable substrate and a non-permeable substrate. Generally, when a poorly permeable substrate or a non-permeable substrate is used as the printing substrate, the aqueous inkjet ink does not (or penetrates poorly), and therefore, the printed matter is likely to suffer from color bleeding and deterioration of water resistance. In contrast, by using the aqueous inkjet ink of the embodiment, it is possible to obtain a printed matter that is free from color bleeding and has excellent water resistance, even on a poorly permeable substrate or a non-permeable substrate.

[0132] In the present disclosure, the permeability of a printing substrate is determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. Specifically, the amount of pure water absorption measured by the following method for a contact time of 100 msec is 1 g / m ２ A printing substrate with a density of less than 1 g / m is called an "impermeable substrate." ２ 6g / m or more ２ A printing substrate with a permeability of less than 6 g / m is called a "hard-to-penetrate substrate." ２ A printing substrate that satisfies the above criteria is referred to as a "permeable substrate." The water absorption of a printing substrate can be measured using a dynamic scanning absorptivity meter (for example, the "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the following conditions, using a printing substrate approximately 15 to 20 cm square as a sample, in an environment of 23°C and 50% RH. Measurement method: Spiral scanning Measurement start radius: 20 mm Measurement end radius: 60 mm Contact time: 10 to 1,000 msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) Scanning interval: 7 mm Rotating table speed switching angle: 86.3 degrees Headbox conditions: width 5 mm, slit width 1 mm

[0133] Examples of impermeable substrates and poorly permeable substrates include plastic films and sheets such as polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene film, nylon film, polystyrene film, and polystyrene sheet; coated paper such as coated paper, art paper, and cast paper; and metals such as aluminum, iron, stainless steel, and titanium.

[0134] 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.

[0135] 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, as this improves the wettability of the aqueous inkjet ink of the embodiment, and results in a printed product with excellent print quality and drying properties, and with a uniform printed surface, which also has good abrasion resistance and water resistance.

[0136] <Printed Matter> The aqueous inkjet ink of the embodiment can be used to produce printed matter, and the inkjet printing method described above can be used as a method for producing the printed matter.

[0137] The aqueous inkjet ink of the 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.

[0138] <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. 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 (5) was 53°C, and the acid value of the acrylic pigment dispersion resin calculated using the above formula (6) was 104 mgKOH / g.

[0139] 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.

[0140] <Production Example of Magenta Pigment Dispersion> 450 g of C.I. Pigment Red 122 (DIC Corporation, "FASTOGEN SUPER MAGENTA RTS"), 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. Then, every certain time (for example, every hour), the D50 of the mixture was measured using the above-mentioned device, and the circulatory dispersion was terminated when the D50 reached 180 nm or less, thereby producing a magenta pigment dispersion with a pigment concentration of 15%.

[0141] <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 Lysopac Yellow 5515C (C.I. Pigment Yellow 155 manufactured by Vibrants) was used as the pigment.

[0142] <Production Example of Acrylic Binder Resin 1> 40 parts of ion-exchanged water and 0.2 parts of the emulsifier Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were charged into a reaction vessel equipped with a thermometer, condenser, stirrer, and dropping funnel. Meanwhile, in a separate mixing vessel equipped with a stirrer, polymerizable monomers (25 parts of methyl methacrylate, 10 parts of butyl acrylate, 50 parts of butyl methacrylate, 2.5 parts of acrylic acid, and 12.5 parts of benzyl methacrylate); 53 parts of ion-exchanged water; and 1.8 parts of the emulsifier Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were charged and thoroughly stirred and mixed to form an emulsion. Five portions of the emulsion were taken and added to the reaction vessel. The contents of the reaction vessel were then heated to 60°C, the atmosphere in the reaction vessel was purged with nitrogen gas, and then 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 (5) was 32°C, and the acid value of acrylic binder resin 1 calculated using the above formula (6) was 20 mgKOH / g.

[0143] <Production Example of Acrylic Binder Resins 2 to 4> Aqueous dispersions of acrylic binder resins 2 to 4 (each with a solids concentration of 30%), which are resin fine particles, were obtained using the same materials and method as for the acrylic binder resin 1, except that the types and amounts of polymerizable monomers used to prepare the emulsions were changed as shown in Table 1 below.

[0144]

[0145] 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 (5)) and acid values ​​(calculated using the above formula (6)) of acrylic binder resins 1 to 4.

[0146] <Production Examples of Acetylene Diol Compounds 1 to 3> Using the method described in Examples 6 to 9 of JP 2001-215690 A, compounds in which an ethylene oxide group and a propylene oxide group 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 to 3) by adjusting the amounts of ethylene oxide and propylene oxide and the synthesis conditions (pressure, temperature, time). Specifically, three 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; 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; and acetylenic diol compound 3 (HLB value 1.8) in which 1.5 moles of ethylene oxide groups and 7.5 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0147] <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 so as to obtain the formulation shown in each column of Table 2 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 (M) and an aqueous yellow ink (Y) were produced by producing aqueous inkjet inks using the magenta pigment dispersion and the yellow pigment dispersion, respectively.

[0148] When producing the aqueous inkjet ink, each raw material was added while stirring the mixture in the mixing vessel. The raw materials were added in the order listed in the top row of each column in Table 1. 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. For components containing two or more raw materials, the order of addition of the raw materials within that component was arbitrary.

[0149]

[0150]

[0151]

[0152]

[0153] The meanings of the abbreviations and details of the product names listed in Table 1 above are as follows. In Table 1, "HLB" represents the HLB value, "Tg" represents the glass transition temperature, and "Nv" represents the solid content concentration. Furthermore, "EO" represents "ethylene oxide," and "PO" represents "propylene oxide." Surfynol DF110D: 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (acetylene diol compound (surfactant), manufactured by Evonik Japan Co., Ltd., HLB value = 2.7) Surfynol 420: A compound in which 1.3 moles of ethylene oxide groups are added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (acetylene diol compound (surfactant), manufactured by Evonik Japan Co., Ltd., 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) 1,6-HexD: 1,6-hexanediol (HLB value = 5.8) BYK-3420: a 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) Surfynol 465: a compound in which 10 moles of ethylene oxide groups are added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (acetylene diol compound (surfactant), HLB value = 13.2, manufactured by Evonik Japan) Nonion K-230: a surfactant represented by general formula (4) in which 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) QE-1042: acrylic resin microparticles manufactured by Seiko PMC Co., Ltd. (solid content=40.5%, glass transition temperature=53°C) Proxel GXL: 1,2-benzisothiazol-3-one in dipropylene glycol solution (1,2-benzisothiazol-3-one:dipropylene glycol:water=2:6:2, preservative manufactured by Arch Chemicals)

[0154] [Examples 1 to 57, Comparative Examples 1 to 8] 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 Table 1 above.

[0155] <Evaluation 1: Evaluation of Discharge Stability (Initial Ejection)> An inkjet ejection device equipped with a Kyocera Corporation inkjet head "KJ4B-QA" (design resolution 600 dpi) installed in an environment of 25°C was filled with the aqueous magenta ink or aqueous yellow ink constituting the above-mentioned aqueous inkjet ink set, and a nozzle check pattern was printed to confirm that the ink was being ejected normally from all nozzles. Next, a solid print with a print coverage of 100% was performed on OK topcoat paper under printing conditions of a frequency of 30 kHz and 600 x 600 dpi. The resulting solid print was then evaluated for discharge stability (initial ejection) by checking with a magnifying glass whether the aqueous inkjet ink had been applied to the area where it was originally supposed to be printed. The evaluation criteria were as follows, with ◎, ○, ○△, and △ representing usable ink. The above evaluation was performed separately for the aqueous magenta ink and aqueous yellow ink constituting the aqueous inkjet ink set. Table 2 also lists the results of poor evaluations of the water-based magenta inks and water-based yellow inks that were evaluated. ⊚: In the solid print, no chipping was observed in the area that was 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 was observed in the area that was to be printed first. ○△: In the solid print, chipping of more than 1 cm and 1.5 cm was observed in the area that was to be printed first. △: In the solid print, chipping of more than 1.5 cm and 2 cm was observed in the area that was to be printed first. ×: In the solid print, chipping of more than 2 cm was observed in the area that was to be printed first.

[0156] <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 water-based magenta ink or water-based yellow ink constituting the water-based inkjet ink set, and the pump was operated to fill the inkjet head and flow channels with the water-based 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 considered usable. The above evaluation was carried out for each of the aqueous magenta ink and aqueous yellow ink that made up the aqueous inkjet ink set. Table 2 also lists the results of the aqueous magenta inks and aqueous yellow inks that were evaluated and had poor evaluation results. ◎: No nozzle clogs at all ○: 1 to 4 nozzle clogs occurred △: 5 to 9 nozzle clogs occurred ×: 10 or more nozzle clogs occurred

[0157] <Preparation of Magenta / Yellow Gradient Printed Material> An inkjet ejection device was prepared, in which two 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 set of aqueous inkjet inks was filled in the order of aqueous magenta ink and aqueous yellow ink from the upstream side in the transport direction. Furthermore, an A4-size (21 cm wide x 30 cm long) OPP film (Mitsui Chemicals Tohcello Inc.'s "OPU-1" (thickness 20 μm) or Futamura Chemical Co., Ltd.'s "FOR-AQ" (thickness 20 μm)) was fixed on a conveyor as the printing substrate, with the corona-treated surface facing up. The conveyor was then driven at 50 m / min, and as the printing substrate passed below the installation section of the inkjet heads, the aqueous inkjet ink sets were each ejected at a drop volume of 2.6 pL, to print a magenta / yellow gradation image. Immediately after printing, the printed printing substrate was placed in a constant-temperature incubator set at 70°C and dried for 3 minutes to produce a magenta / yellow gradation print. The "magenta / yellow gradation image" refers to a 5 cm wide x 30 cm long magenta gradation image printed using aqueous magenta ink (with a printing rate varied in 10% increments between 10 and 100%) and a 5 cm wide x 30 cm long yellow gradation image printed using aqueous yellow ink, arranged adjacent to each other with their long sides touching. The two types of OPP film described above were used as printing substrates, and a magenta / yellow gradation image was printed on each of them.

[0158] <Evaluation 3: Evaluation of print quality (whiteout)> The magenta / yellow gradation print produced by the method described above was visually observed. The print quality of the magenta / yellow gradation print was evaluated by checking for the presence or absence of whiteout at a printing rate of 100%. The evaluation criteria were as follows, with ◎, ○, ○△, and △ being considered usable. The above evaluation was performed for each of the two types of printing substrates on which the magenta / yellow gradation print was printed. ◎: No white spots were observed on either of the two types of printing substrates, and on both the printed portion of the magenta gradation image and the printed portion of the yellow gradation image. ○: Slight white spots were observed on either the printed portion of the magenta gradation image or the printed portion of the yellow gradation image on only one of the two types of printing substrates. ○△: Slight white spots were observed on either the printed portion of the magenta gradation image and the printed portion of the yellow gradation image on only one of the two types of printing substrates. △: Clear white spots were observed on either the printed portion of the magenta gradation image and the printed portion of the yellow gradation image on at least one of the two types of printing substrates. ×: Clear white spots were observed on both of the printed portion of the magenta gradation image and the printed portion of the yellow gradation image on both of the two types of printing substrates.

[0159] <Evaluation 4: Evaluation of print quality (color bleeding)> The magenta / yellow gradation print produced by the method described above was visually observed. The print quality (color bleeding) of the magenta / yellow gradation print was evaluated by checking the coverage rate 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 be observed. The evaluation criteria were as follows, with ◎, ○, ○△, and △ being considered usable. Table 2 also lists the results of the two types of printing substrates that were evaluated, with the poorest evaluation results. ◎: No mixed color bleeding was observed on both printing substrates even at a printing rate of 80%. ○: Mixed color bleeding was observed on at least one printing substrate at a printing rate of 80%, but on both printing substrates no mixed color bleeding was observed on a printing rate of 70%. ○△: Mixed color bleeding was observed on at least one printing substrate at a printing rate of 70%, but on both printing substrates no mixed color bleeding was observed on a printing rate of 60%. △: Mixed color bleeding was observed on one of the printing substrates at a printing rate of 60%. ×: Mixed color bleeding was observed on both printing substrates at a printing rate of 60%.

[0160] <Evaluation 5: Evaluation of Water Resistance> 20 μL of the above aqueous inkjet ink was dropped onto an OPP film (FOR-AQ, 20 μm thick) manufactured by Futamura Chemical Co., Ltd., and coated using an automatic coater ("PI-1210" manufactured by Tester Sangyo Co., Ltd.) equipped with an SA-203 bar coater (ROD No. 3). The OPP film coated with the aqueous inkjet ink was then placed in a constant temperature incubator set at 70°C, where the printed substrate was allowed to dry for 3 minutes. The ink film was then rubbed back and forth over a 1 cm width with a cotton swab moistened with ion-exchange water, and the number of times the cotton swab was rubbed back and forth until the ink film at the rubbed area was completely peeled off was counted. The above evaluation was performed at five locations on the same ink film, and the water resistance was evaluated by calculating the average number of reciprocating motions. The evaluation criteria were as follows, with ◎, ○, and △ indicating practical use. The evaluation was carried out for each of the water-based magenta ink and the water-based yellow ink, and the results of those with poor evaluation results are shown in Table 1. ◎: The ink film did not peel off even after 20 rubbings ○: The ink film peeled off after 11 to 19 rubbings △: The ink film peeled off after 6 to 10 rubbings ×: The ink film peeled off even after 5 or fewer rubbings

[0161] As shown in Table 2 above, the aqueous inkjet inks (sets) of Examples 1 to 57 having the configuration of the present disclosure were superior in ejection stability to the aqueous inkjet inks of Comparative Examples 1 to 8, and also had good solid coverage and little color mixing. Furthermore, the water resistance of the ink film was also good. These results confirmed that the aqueous inkjet inks having the configuration of the present disclosure are excellent aqueous inkjet inks that combine ejection stability, print quality of printed matter, and water resistance.

[0162] Although the present disclosure has been described with reference to the above several embodiments, the present disclosure is not limited to the above several embodiments. Various changes can be made to the configuration and details of the present disclosure within the scope of the present disclosure.

[0163] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-209885, filed December 13, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. An aqueous inkjet ink comprising a pigment, a polyether-modified siloxane-based surfactant, hexylene glycol, a binder resin, and an organic compound (A) (excluding the pigment, the polyether-modified siloxane-based surfactant, the hexylene glycol, and the resin), wherein the organic compound (A) is composed only of carbon atoms, hydrogen atoms, and oxygen atoms, and has a plurality of hydroxyl groups, the HLB value of the organic compound (A) is 2.5 to 5.2, the binder resin comprises a resin (B-1) having a glass transition temperature of -70 to 35°C, and the content of the resin (B-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 claim 1, wherein the content by mass of said resin (B-1) is 2 to 50, relative to the content by mass of said polyether-modified siloxane-based surfactant being 1.

3. The aqueous inkjet ink according to claim 1 or 2, wherein the aqueous inkjet ink does not contain a butylene glycol monoalkyl ether-based water-soluble organic solvent (one in which the alkyl group at the molecular terminal has 1 to 4 carbon atoms) and a pentylene glycol monoalkyl ether-based water-soluble organic solvent (one in which the alkyl group at the molecular terminal has 1 to 4 carbon atoms), or the total content of the butylene glycol monoalkyl ether-based water-soluble organic solvent (one in which the alkyl group at the molecular terminal has 1 to 4 carbon atoms) and the pentylene glycol monoalkyl ether-based water-soluble organic solvent (one in which the alkyl group at the molecular terminal has 1 to 4 carbon atoms) is 50 mass% or less of the content of the hexylene glycol.

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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