Water-based inkjet ink using water-soluble acrylic urethane resin and its use

Abstract

To provide aqueous inkjet ink which is excellent in discharge stability from a nozzle of an inkjet head, and gives good printing image quality and excellent adhesive force even after laminate processing and hot water sterilization treatment.SOLUTION: Aqueous inkjet ink contains a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (C), and water (D), wherein the water-soluble acrylic urethane resin (B) has a constitutional unit derived from acrylic diol (b1), a constitutional unit derived from polyisocyanate (b2), and a constitutional unit derived from polyol containing low molecular diol (b3) containing one acid group and two hydroxyl groups and having a molecular weight of 500 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based inkjet ink using a novel water-soluble acrylic urethane resin and uses thereof. [Background technology]

[0002] Because digital printing does not require plates, it is possible to reduce costs and meet short delivery times. Digital printing methods are rapidly becoming more widespread as printing runs become smaller and needs become more diverse. Inkjet printing, one type of digital printing method, ejects and impacts tiny ink droplets from an inkjet head onto a substrate, forming images and characters (collectively referred to as "printed material") on the print medium. Compared to other digital printing methods, inkjet printing offers advantages in terms of the size and cost of the printing device, running costs during printing, and ease of full-color printing, and has been increasingly used in industrial printing applications in recent years.

[0003] Inks used in inkjet printing methods vary widely, including oil-based, solvent-based, active energy ray-curable, and water-based inks. Until now, solvent-based and active energy ray-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks due to concerns about their harmful effects on the environment and people.

[0004] Flexible packaging materials used for packaging food, medicine, cosmetics, etc. are laminates formed by laminating plastic films together or a plastic film (hereinafter simply referred to as "film substrate") with a metallized film or metal foil. Generally, a plastic film with a pre-formed printing layer is laminated with a separately prepared material, such as a plastic film, a metallized film, or a metal foil, to obtain a laminate that can be used as a flexible packaging material. This processing method is called "lamination." To form a printing layer in the laminate, gravure printing or flexographic printing has traditionally been performed on the film substrate. Both gravure printing and flexographic printing are printing methods in which ink is transferred to a pre-formed plate, making them suitable for high-speed printing and mass production.

[0005] Meanwhile, in the flexible packaging market, changes and diversification in consumer needs are leading to a greater variety of products and shorter product life cycles. In addition, environmental and occupational safety concerns have led to a demand for inkjet printing using water-based inks.

[0006] Conventional aqueous inkjet inks use acrylic-based resins as binders, but due to their inherent characteristics, acrylic resins are known to lack flexibility and lack lamination suitability. Other aqueous inkjet inks based on urethane resins have also been reported. Such urethane resin binders for aqueous inkjet inks often use low-molecular-weight compounds containing an acid group and two hydroxyl groups as raw materials to impart hydrophilicity. However, increasing the amount of these low-molecular-weight compounds increases the number of urethane bonds per weight of resin, resulting in a loss of the flexibility inherent to urethane resins and a loss of lamination suitability.

[0007] For these reasons, there is a demand for the development of a resin that can achieve both hydrophilicity and lamination suitability as a binder resin for aqueous inkjet inks, and aqueous inkjet inks that use such resins as binders, and studies are currently underway to achieve this.

[0008] Patent Document 1 discloses an aqueous inkjet ink containing a water-soluble urethane resin as a binder resin, but because the resin has a strong affinity and solubility for water, it has low water resistance and does not provide sufficient laminate strength.

[0009] Patent Document 2 discloses an invention relating to an aqueous acrylic-modified urethane resin that has the properties of both an acrylic resin and a urethane resin, but when used for inkjet ink applications, the printing suitability, such as ejection stability, is insufficient.

[0010] Patent Document 3 discloses an invention relating to an acrylic-urethane resin containing an acid group, but problems remain in terms of ejection stability, solubility of the ink in water, flexibility, and suitability for post-processing.

[0011] Patent Document 4 discloses an invention relating to a water-based inkjet ink using an acrylic-modified polycarbonate-based urethane resin, but there remain problems with the flexibility of the resin and suitability for post-processing. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 2018-197284 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-104315 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-239947 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-038178 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aqueous inkjet ink that exhibits excellent ejection stability from the nozzles of an inkjet head even when printing on non-permeable substrates such as OPP film, PET film, and nylon film used in flexible packaging materials, and that can produce printed matter that maintains good print quality and excellent adhesive strength even after lamination and hot water sterilization. [Means for solving the problem]

[0014] That is, the present invention relates to the following [1] to [4]. [1] An aqueous inkjet ink comprising a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (E), and water (D), and satisfying all of the conditions (1) to (6). (1) The water-soluble acrylic urethane resin (B) A structural unit derived from acrylic diol (b1), A structural unit derived from polyisocyanate (b2), and a structural unit derived from a polyol containing a low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and a molecular weight of 500 or less. (2) The acrylic diol (b1) is A structural unit derived from a chain transfer agent (g) containing one mercapto group and two hydroxyl groups; a structural unit derived from a vinyl monomer (f1) having an acid group, and a structural unit derived from a (meth)acrylate (f2) that does not have an acid group. (3) The acid value of the acrylic diol (b1) is 25 to 310 mgKOH / g. (4) The content of the structural units derived from the chain transfer agent (g) is 1.1 to 9.5 mass %, relative to 100 mass % of the amount of the structural units derived from the acrylic diol (b1). (5) The water-soluble acrylic urethane resin (B) has a weight-average molecular weight of 9,000 to 32,000. (6) The water-soluble acrylic urethane resin (B) has an acid value of 25 to 90 mgKOH / g. [2] The above water-based inkjet ink, wherein the ratio of the amount of acid groups derived from the acid group-containing vinyl monomer (f1) to the amount of acid groups derived from the low-molecular-weight diol (b3), present per unit mass of the water-soluble acrylic urethane resin (B), is 1:4 to 4:1. [3] The water-soluble organic solvent (E) contains at least one selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and 1,2-hexanediol; The above water-based inkjet ink, wherein the total amount of the water-soluble organic solvent (E) is 15 to 35% by mass relative to the total amount of the water-based inkjet ink. [4] A printed matter obtained by printing the above aqueous inkjet ink on a non-permeable substrate. [Effects of the Invention]

[0015] The present invention has made it possible to provide an aqueous inkjet ink that exhibits excellent ejection stability from the nozzles of an inkjet head, even when printing on non-permeable substrates such as OPP film, PET film, and nylon film used in flexible packaging materials, and that can produce printed matter that maintains good print quality and excellent adhesive strength even after lamination and hot water sterilization. DETAILED DESCRIPTION OF THE INVENTION

[0016] The aqueous inkjet ink of the present invention will be described below by way of preferred embodiments. Hereinafter, "aqueous inkjet ink" may be referred to as "aqueous ink" or "ink."

[0017] To obtain a strong ink film, it is common to add a binder resin to the ink. Known binder resin forms for aqueous inkjet inks include water-soluble resins and emulsion resin particles, which are water-insoluble resins. Furthermore, increasing the weight-average molecular weight of the binder resin improves various resistances, such as water resistance, abrasion resistance, and solvent resistance. Therefore, it is known that highly molecular-weighted emulsion resin particles result in ink films with excellent resistance.

[0018] However, water-based inks that use emulsion resin particles as the binder resin can clog inkjet head nozzles and reduce ink ejection stability. This is because the emulsion resin particles in these inks are merely dispersed in the water solvent by an emulsifier, not dissolved, and therefore tend to precipitate on the inkjet head nozzle surface. Furthermore, the strong ink film that solidifies on the nozzle surface cannot be washed away with water, requiring the use of a highly soluble solvent. However, such solvents can deteriorate the inkjet head, its nozzles, and the water-repellent plate themselves.

[0019] In addition, acrylic resins are used as binder resins in conventional aqueous inkjet inks. Acrylic resins are known to form hard, tough coating films, but they lack flexibility, making lamination difficult. Urethane resins, on the other hand, generally consist of hard segments that impart strength to the coating film and soft segments that impart flexibility. Hard segments are derived from structural units of compounds with relatively low molecular weights, such as isocyanates, amines, and chain extenders, and contain a high density of urethane bonds. This allows for cohesive strength through numerous hydrogen bonds, resulting in the formation of a tough coating film. Soft segments are derived from structural units of compounds with relatively high molecular weights, such as polyols. High molecular weights result in less structural crowding and a low density of urethane bonds. This means that there is less cohesion due to hydrogen bonds, allowing the molecules to move freely, resulting in a flexible coating film. Urethane resins are characterized by the ability to form coating films that combine strength and flexibility due to the microphase-separated structure of these two segments.

[0020] In the present invention, it has been discovered that by introducing a structure derived from an acrylic diol obtained by polymerizing a vinyl monomer into a urethane resin that imparts strength and flexibility to the coating film, the strength of the coating film can be further increased, and that, while being water-soluble, excellent adhesive strength can be maintained even after lamination and hot water sterilization treatment. This makes it possible to obtain an aqueous inkjet ink that is suitable for post-processing and has excellent ejection stability.

[0021] <Water-soluble acrylic urethane resin (B)> The water-soluble acrylic urethane resin is a binder resin composed of an acrylic resin portion and a urethane resin portion, and in the present invention, the acrylic resin portion having structural units derived from an acrylic diol (b1) is grafted to the urethane resin portion. The urethane resin portion further has structural units derived from a polyisocyanate (b2) and structural units derived from a polyol containing a low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and a molecular weight of 500 or less.

[0022] In the present invention, the term "binder resin" refers to the main component of the ink dry film (hereinafter also referred to as "ink film"), and its primary purpose is to bond the ink dry film to the substrate and laminating adhesive. As described below, the aqueous ink used in the present invention contains a pigment dispersion resin. However, the pigment dispersion resin is a resin used primarily for the dispersion stability of the pigment (A), and its purpose is different from that of the binder resin. Therefore, the pigment dispersion resin and the binder resin are distinguished by their adsorption rate to the pigment (A). That is, in a pigment dispersion containing the pigment (A), a resin, and an aqueous medium, where the pigment concentration is 5% by mass and the amount of water is 98% by mass or more of the total amount of the aqueous medium, a resin with an adsorption rate to the pigment of 35% by mass or more is considered to be a pigment dispersion resin, and a resin with an adsorption rate of less than 35% by mass is considered to be a binder resin.

[0023] The pigment dispersion used to measure the adsorption rate can be prepared by, for example, preparing a high-concentration pigment dispersion with a pigment concentration of 20% by mass using the method described in the cyan pigment dispersion preparation example described below, and then diluting the resulting dispersion with water until the pigment concentration reaches 5% by mass. The adsorption rate can be calculated, for example, by subjecting the pigment dispersion to ultracentrifugation (e.g., 30,000 rpm for 4 hours), measuring the amount of resin contained in the supernatant, and then using the following formula (1): WR1 represents the amount of resin contained in the pigment dispersion before ultracentrifugation, and WR2 represents the amount of resin contained in the supernatant. (Equation 1) Adsorption rate (%) = (WR1 - WR2) x 100 / WR1

[0024] In the present invention, the weight-average molecular weight of the water-soluble acrylic urethane resin (B) is 9,000 to 32,000. From the viewpoints of jetting stability, lamination suitability, and high-quality print image, it is preferably 11,000 to 30,000, and more preferably 13,000 to 28,000. When the weight-average molecular weight is 9,000 or more, a dried ink film of sufficient strength can be obtained, and good post-processing suitability can be obtained. When it is 32,000 or less, the structural viscosity of the water-soluble resin is small, and stable jetting properties can be obtained. In other words, when the weight-average molecular weight of the water-soluble acrylic urethane resin (B) is within this range, jetting stability of the water-based ink and good post-processing suitability can be obtained. The weight-average molecular weight of the water-soluble acrylic urethane resin (B) is a polystyrene-equivalent value measured by the method described below.

[0025] In the present invention, the acid value of the water-soluble acrylic urethane resin (B) is 25 to 90 mgKOH / g. When the acid value of the water-soluble acrylic urethane resin (B) is 25 mgKOH / g or more, the resin becomes soluble in water, and can impart resolubility to dried ink. When the acid value is 90 mgKOH / g or less, thickening of the aqueous ink upon drying can be suppressed, and the jetting stability of the aqueous ink can be improved. From the viewpoints of handleability during synthesis and the jetting stability of the aqueous ink using the water-soluble acrylic urethane resin (B), the acid value of the water-soluble acrylic urethane resin (B) is preferably 30 to 80 mgKOH / g, more preferably 35 to 70 mgKOH / g. The acid value of the water-soluble acrylic urethane resin (B) is an actual value measured by the method described below.

[0026] Furthermore, the ratio of the amount of acid groups derived from the acid group-containing vinyl monomer (f1) to the amount of acid groups derived from the low-molecular-weight diol (b3) present per unit mass of the water-soluble acrylic urethane resin (B) is preferably 1:4 to 4:1. When the ratio of the amounts of acid groups derived from each raw material is within this range, the solubility in water due to hydration of the acid groups derived from the acid group-containing vinyl monomer (f1) is increased, resulting in excellent jetting stability. At the same time, a hydrogen-bonding network is favorably formed between the acid groups derived from the low-molecular-weight diol (b3) and the hydrophilic portion of the acrylic urethane resin skeleton, resulting in an aqueous ink with excellent water resistance. A more preferred ratio is 1:3 to 3:1, and an especially preferred ratio is 2:3 to 3:2.

[0027] In this invention, the term "water-soluble resin" refers to a mixture of 1 g of the target resin and 99 g of water that is transparent to the naked eye, or a state in which the particle size cannot be measured using the mixture as a sample. However, the particle size is a volume-based median value measured using a dynamic light scattering method, for example, using a Microtrac-Bell Nanotrac UPA-EX150 at 25°C.

[0028] The water-soluble acrylic urethane resin (B) is synthesized, for example, by addition polymerization (urethane polymerization) of a polyol (a compound having two or more hydroxyl groups) containing an acrylic diol (b1) synthesized by the method described below and a low-molecular-weight diol (b3) having a molecular weight of 500 or less, and a polyisocyanate (b2). After the addition polymerization, the resulting polyol may be further reacted with a chain extender (urea reaction) described below. In this case, the water-soluble acrylic urethane resin (B) will have urea bonds in addition to urethane bonds.

[0029] Next, each material used in the synthesis example of the water-soluble acrylic urethane resin (B) will be described in detail below.

[0030] <Acrylic diol (b1)> The acrylic diol (b1) constituting the water-soluble acrylic urethane resin (B) has a structural unit derived from a chain transfer agent (g) containing one mercapto group and two hydroxyl groups, a structural unit derived from a vinyl monomer (f1) having an acid group, and a structural unit derived from a (meth)acrylate (f2) having no acid group.

[0031] The number average molecular weight of the acrylic diol (b1) is preferably 1,000 to 6,000. When it is 1,000 or more, synthesis is easy and the product can be produced with good reproducibility. When it is 6,000 or less, the molecular weight of the water-soluble acrylic urethane resin (B) can be controlled, and the ejection stability of the water-soluble acrylic urethane resin (B) is improved. A number average molecular weight of 1,500 to 5,500 is more preferable. The number average molecular weight of the acrylic diol (b1) is a polystyrene-equivalent value measured by the method described below.

[0032] The acid value of the acrylic diol (b1) is 25 to 310 mgKOH / g. When the acid value of the acrylic diol (b1) is 25 mgKOH / g or more, it is easy to impart solubility to the water-soluble acrylic urethane resin (B) in water, and when it is 310 mgKOH / g or less, it is easy to synthesize the acrylic diol (b1) in an organic solvent and can suppress the thickening of the water-soluble acrylic urethane resin (B), thereby improving the ejection stability of the water-based ink. From the viewpoint of synthesis, the acid value of the acrylic diol (b1) is preferably 35 to 300 mgKOH / g, more preferably 45 to 280 mgKOH / g. The acid value of the acrylic diol (b1) is an actually measured value measured by the method described below.

[0033] The acrylic diol (b1) used in the present invention can be obtained, for example, by polymerizing a vinyl monomer (f1) having an acid group and a (meth)acrylate (f2) having no acid group in the presence of a chain transfer agent (g) containing one mercapto group and two hydroxyl groups.

[0034] <Vinyl monomer having an acid group (f1)> The vinyl monomer (f1) having an acid group is not particularly limited as long as it has an acid group. For example, carboxy group-containing vinyl monomers such as acrylic acid, methacrylic acid, vinylacetic acid, crotonic acid, cinnamic acid, mesaconic acid, citraconic acid, glutaconic acid, 3-allyloxypropionic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl phthalate, vinyl pyromellitic acid, 5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-nonenoic acid, 9-decenoic acid, 10-undecylenic acid, 11-dodecylenic acid, 17-octadecylenic acid, and oleic acid; 3-(2-allyloxyethoxycarbonyl)propionic acid, 3-(2-allyloxybutoxycarbonyl)propionic acid, 3-(2-vinyloxybutoxycarbonyl)propionic acid, 3-(2-vinyloxy Examples of suitable vinyl monomers include carboxyl group-containing vinyl ether monomers such as (butoxycarbonyl)propionic acid; sulfonic acid group-containing vinyl monomers such as styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and methacrylsulfonic acid; and phosphate group-containing vinyl monomers such as (meth)acryloyloxyalkyl (C1-24) phosphate monoesters such as 2-hydroxyethyl (meth)acryloylphosphate, (meth)acryloyloxyalkyl (C1-24) phosphonic acids such as 2-acryloyloxyethylphosphonic acid, acid phosphooxyethyl (meth)acrylate, and mono(2-hydroxyethyl (meth)acrylate) phosphate. Among the above-listed vinyl monomers, carboxyl group-containing vinyl monomers are preferred from the viewpoints of the wide range of material options and ease of synthesis with (meth)acrylates (f2) that do not have acid groups. In particular, acrylic acid and / or methacrylic acid are more preferred from the viewpoint of ease of handling during synthesis.

[0035] <(Meth)acrylate (f2) having no acid group> The (meth)acrylate (f2) having no acid group is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cetyl ( alkyl (meth)acrylates such as isobornyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate and other acrylic ester (meth)acrylates; aromatic ester (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate and other aromatic ester (meth)acrylates Ethylenically unsaturated group-containing (meth)acrylates such as allyl (meth)acrylate, 1-methylallyl (meth)acrylate, 2-methylallyl (meth)acrylate, 1-butenyl (meth)acrylate, 2-butenyl (meth)acrylate, 3-butenyl (meth)acrylate, 2-chloroallyl (meth)acrylate, 3-chloroallyl (meth)acrylate, allylphenyl (meth)acrylate, diallyl maleate, diallyl itaconic acid, vinyl (meth)acrylate, vinyl crotonate, and vinyl oleate; perfluoromethylmethyl acrylate perfluoroalkyl group-containing (meth)acrylates having a perfluoroalkyl group having 1 to 20 carbon atoms, such as perfluoroethylmethyl (meth)acrylate, 2-perfluorobutylethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluorooctylethyl (meth)acrylate, 2-perfluoroisononylethyl (meth)acrylate, 2-perfluorononylethyl (meth)acrylate, and 2-perfluorodecylethyl (meth)acrylate;Hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 4-hydroxyvinylbenzene, allyl alcohol, and glycerin mono(meth)acrylate; polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, propoxypolyethylene glycol (meth)acrylate, n-butoxypolyethylene glycol (meth)acrylate, n-pentoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and polypropylene glycol (meth)acrylate. Examples of suitable (meth)acrylates include polyether chain-containing (meth)acrylates such as methyl methacrylate, methoxy polypropylene glycol (meth)acrylate, ethoxy polypropylene glycol (meth)acrylate, propoxy polypropylene glycol (meth)acrylate, n-butoxy polypropylene glycol (meth)acrylate, n-pentoxy polypropylene glycol (meth)acrylate, phenoxy polypropylene glycol (meth)acrylate, polytetramethylene glycol (meth)acrylate, methoxy polytetramethylene glycol (meth)acrylate, phenoxy tetraethylene glycol (meth)acrylate, hexaethylene glycol (meth)acrylate, and methoxy hexaethylene glycol (meth)acrylate. Among these, alkyl (meth)acrylates are preferred due to their mild synthesis. Furthermore, they can impart a highly water-resistant skeleton to the water-soluble acrylic urethane resin structure, resulting in an ink that is highly suitable for post-processing, such as lamination. Even more preferred are (meth)acrylates in which the alkyl group has 6 to 18 carbon atoms.

[0036] <Other vinyl monomers> The acrylic diol (b1) can be polymerized using a vinyl monomer (f1) having an acid group and a (meth)acrylate (f2) not having an acid group, as long as the object of the present invention is not impaired. Examples of the vinyl monomer include α-olefin vinyl monomers such as 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene; aromatic vinyl monomers such as styrene, α-methylstyrene, 2-methylstyrene, and allylbenzene; vinyl monomers containing primary to tertiary amino groups such as (meth)acrylamide and N-vinylpyrrolidone; nitrile vinyl monomers such as (meth)acrylonitrile; and fatty acid vinyl monomers such as vinyl acetate, vinyl butyrate, vinyl propionate, vinyl hexanoate, vinyl laurate, and vinyl stearate.

[0037] The amount of the vinyl monomer (f1) having an acid group used is preferably 5 to 50 mass %, more preferably 5 to 40 mass %, based on the total amount of the acrylic diol (b1), from the viewpoint of ease of handling during synthesis.

[0038] <Chain transfer agent (g)> A chain transfer agent refers to a substance that has the property of accepting a radical from a growing polymer chain in a radical polymerization system and generating a new radical. The acrylic diol (b1) of the present invention contains a structural unit derived from a chain transfer agent (g) having one mercapto group and two hydroxyl groups. By using a chain transfer agent (g) having this structure in the synthesis of the acrylic diol (b1), the chain transfer agent (g) reacts with a vinyl monomer to obtain the acrylic diol (b1) having two hydroxyl groups at the molecular chain terminals. Examples of the chain transfer agent (g) containing one mercapto group and two hydroxyl groups used in the present invention include 3-mercapto-1,2-propanediol, 2-mercapto-1,3-propanediol, 2-mercapto-2-methyl-1,3-propanediol, 2-mercapto-2-ethyl-1,3-propanediol, 2-mercaptoethyl-2-methyl-1,3-propanediol, and 2-mercaptoethyl-2-ethyl-1,3-propanediol.

[0039] The content of the structural units derived from the chain transfer agent (t) contained in the acrylic diol (b1) is 1.1 to 9.5% by mass relative to the total amount of structural units derived from the acrylic diol (b1). When the content of the structural units derived from the chain transfer agent (g) is 1.1% by mass or more relative to the total amount of structural units derived from the acrylic diol (b1), it is easy to control the number average molecular weight of the acrylic diol (b1), making it easier to obtain a desired weight average molecular weight in the synthesis of the water-soluble acrylic urethane resin (B). When the content is 9.5% by mass or less, the acrylic moiety of the acrylic diol (b1) becomes relatively large, the acid groups of the vinyl monomers are easily hydrated, and the solubility of the water-soluble acrylic urethane resin (B) in water is increased. From the viewpoint of handleability during synthesis, the content is preferably 1.5 to 8.5% by mass, more preferably 1.9 to 8.0% by mass.

[0040] <Polymerization initiator> In the polymerization of the acrylic diol (b1), it is preferable to use a radical polymerization initiator (hereinafter referred to as a polymerization initiator). The polymerization initiator may be any one capable of initiating radical polymerization, and known oil-soluble polymerization initiators or water-soluble polymerization initiators can be used.

[0041] Examples of the oil-soluble polymerization initiator include organic peroxides such as benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, tert-butylperoxy(2-ethylhexanoate), tert-butylperoxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxide; and azobis compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 1,1'-azobis-cyclohexane-1-carbonitrile.

[0042] Examples of water-soluble polymerization initiators include ammonium persulfate, potassium persulfate, hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride. These can be used alone or in combination of two or more.

[0043] <Polyisocyanate (b2)> The polyisocyanate used in the present invention is not particularly limited, and any known polyisocyanate can be used, including aromatic, aliphatic, and alicyclic diisocyanates and triisocyanates. Examples include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, and 3,3'-dimethoxy-4,4'. Examples of suitable polyisocyanates include aromatic diisocyanates such as biphenylene diisocyanate, naphthylene-1,5-diisocyanate, tetrahydronaphthylene-1,5-diisocyanate, 4,4'-dibenzyl isocyanate, and xylylene diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; alicyclic diisocyanates such as dicyclohexylmethane diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tolylene diisocyanate; and triisocyanates such as triphenylmethane triisocyanate and lysine triisocyanate. Polyisocyanates may be used singly or in combination of two or more.

[0044] In addition, as the triisocyanate, an adduct or an isocyanurate obtained from an isocyanate compound may be used. The "adduct" is an addition product of an isocyanate compound and trimethylolpropane, and the "isocyanurate" is a trimer of an isocyanate compound.

[0045] <Polyol> The polyol refers to a compound having two or more hydroxyl groups, and in the present invention, includes the acrylic diol (b1) and a low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and a molecular weight of 500 or less.

[0046] <Low molecular weight diol (b3)> The low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and a molecular weight of 500 or less has, as the "acid group" in its molecule, a carboxylic acid (carboxy) group, a sulfonic acid group, a phosphoric acid group, a phosphonic acid group, or the like. Among these, a carboxy group is preferably selected from the viewpoint of improving the ejection stability of the inkjet ink. Furthermore, from the viewpoints of easily adjusting the amount of acid groups derived from the low-molecular-weight diol (b3) and improving the ejection stability of the aqueous inkjet ink, the molecular weight of the low-molecular-weight diol (b3) is preferably 100 to 500, more preferably 100 to 200, and particularly preferably 120 to 160. Examples of low-molecular-weight diols having one acid group and two hydroxyl groups and a molecular weight of 500 or less include dimethylolcarboxylic acid represented by the following general formula 1; aromatic dihydroxycarboxylic acids such as dihydroxybenzoic acid and dihydroxyphenylpropionic acid; and the like.

[0047] (General formula 1) RC(CH2OH)2-COOH

[0048] In the above general formula 1, R is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0049] Among the above, from the viewpoints of ease of urethane polymerization, hydrophilicity after conversion into an aqueous ink, and resolubility, it is preferable to use, as the low-molecular-weight diol (b3), one or more selected from the group consisting of dimethylolpropionic acid, dimethylolbutyric acid (dimethylolcarboxylic acids represented by the above general formula 1 in which R is a methyl group or an ethyl group), and hydroxybenzoic acid.

[0050] <Polyol without acid group> The acrylic urethane resin of the present invention may contain, in addition to the acrylic diol (b1) and the low-molecular-weight diol (b3) having a molecular weight of 500 or less, a structural unit derived from a polyol having no acid group. Examples of polyols having no acid group include low-molecular-weight diols such as polycarbonate polyol, polyester polyol, polyether polyol, polyurethane polyol, polyethylene glycol, polypropylene glycol, polyesteramide polyol, ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol, and low-molecular-weight triols such as trimethylolpropane and glycerin. These may be used alone or in combination of two or more.

[0051] Among the polyols having no acid groups, polycarbonate polyols are preferably used, because the high cohesive force of the carbonate groups makes it possible to obtain aqueous inkjet inks with excellent water resistance, abrasion resistance, and solvent resistance.

[0052] Examples of polycarbonate polyols include condensates of a carbonate component such as alkylene carbonate, diallyl carbonate, or dialkyl carbonate, or phosgene with a low molecular weight polyol such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, pentanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, octanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butynediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, diethylene glycol, polypropylene glycol, or dipropylene glycol.

[0053] Examples of polyester polyols include reaction products of polycarboxylic acids such as terephthalic acid, isophthalic acid, adipic acid, azelaic acid, and sebacic acid, or their dialkyl esters, or mixtures thereof, with glycols such as ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, polyoxyethylene glycol, polyoxypropylene glycol, and polytetramethylene ether glycol, or mixtures thereof; or ring-opening polymerization products of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone). Furthermore, vegetable oils such as castor oil and polyester compounds having hydroxyl groups derived from the vegetable oils can also be used as polyester polyols.

[0054] Examples of polyether polyols include compounds obtained by polymerizing an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran using a low-molecular-weight polyol such as water, ethylene glycol, propylene glycol, trimethylolpropane, or glycerin as an initiator.

[0055] <Chain extender> In the synthesis of the water-soluble acrylic urethane resin (B), it is preferable to use a chain extender that does not react with the polyol and has two or more groups that react with unreacted isocyanate groups derived from the polyisocyanate that do not form urethane bonds. The use of a chain extender forms urea bonds, resulting in an aqueous inkjet ink with better water resistance and abrasion resistance. Examples of chain extenders include ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, dicyclohexylmethane-4,4'-diamine, N-ethyl-N-(2-hydroxyethyl)-p-phenylenediamine, 2-hydroxyethylethylenediamine, N-(2-aminoethyl)ethanolamine, 2-hydroxyethylpropylenediamine, 1,3-diamino-2-propanol, and N Examples of known compounds include N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)-1,3-propanediamine, N-(2-hydroxypropyl)ethylenediamine, N,N-bis(2-hydroxyethyl)ethylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, di-2-hydroxypropylethylenediamine, and dimer diamines in which the carboxy groups of dimer acids are converted to amino groups. These compounds may be used alone or in combination of two or more.

[0056] <Method for measuring number average molecular weight (Mn) and weight average molecular weight (Mw)> The number average molecular weight (Mn) of the acrylic diol (b1) and the weight average molecular weight (Mw) of the water-soluble acrylic urethane resin (B) were measured by gel permeation chromatography (GPC) in terms of standard polystyrene. The measurement equipment and conditions were as follows. However, depending on the type of polymer, a more appropriate carrier (eluent) and a suitable column were selected. Other details were based on JIS K7252-1 to 4:2008. For poorly soluble polymer compounds, measurements were performed at a soluble concentration under the following conditions. Column: TOSO HTSKgel Super HZM-H, TOSOHTSKgelSuperHZ4000 and A combination of TOSOHTSKgelSuperHZ2000. Carrier: Tetrahydrofuran Measurement temperature: 40℃ Carrier flow rate: 1.0 mL / min Sample concentration: 0.1% by mass Detector: RI (refractive index) detector Injection volume: 0.1mL

[0057] <Acid value measurement method> The acid value was measured in accordance with JIS K0070 by the following method. 0.5 to 2 g of sample was precisely weighed out (solid content: Sg), and 10 mL of neutral ethanol was added to dissolve the sample. The resulting solution was subjected to potentiometric titration with 0.1 mol / L ethanolic potassium hydroxide solution (potency: F). The point at which the potential difference curve reached its maximum was taken as the endpoint, and the titer (A mL) at this point was used to calculate the acid value according to (Equation 2). (Formula 2) Acid value (mmol / g)=(A×F×0.1) / S

[0058] <Pigment (A)> As the pigment (A), either an inorganic pigment or an organic pigment can be used. These pigments can be used alone or in combination of two or more. Examples of inorganic pigments include white pigments such as titanium oxide, zinc white, zinc sulfide, calcium carbonate, precipitated barium sulfate, and alumina white, and black pigments such as carbon black and iron oxide.

[0059] Titanium oxide is preferably used as the white pigment. Either anatase or rutile titanium oxide can be used, but the rutile type is preferred in order to improve the hiding power of printed matter. Titanium oxide produced by either the chlorine method or the sulfuric acid method may be used, but titanium oxide produced by the chlorine method is preferred because it has a higher degree of whiteness.

[0060] It is more preferable that the titanium oxide has its surface treated with an inorganic compound and / or an organic compound. Examples of inorganic compounds include compounds of silicon (Si), aluminum, zirconium, tin, antimony, and titanium, and hydrated oxides thereof. Examples of organic compounds include polyhydric alcohols, alkanolamines or their derivatives, higher fatty acids or their metal salts, and organometallic compounds. Among these, polyhydric alcohols or their derivatives are more preferably used because they can highly hydrophobize the titanium oxide surface and improve dispersion stability.

[0061] It is also suitable to use hollow resin particles as the white pigment. Hollow resin particles have a smaller specific gravity (apparent density) than titanium oxide and the like, and are therefore less likely to settle over time, resulting in an ink with excellent storage stability. Furthermore, to obtain a white ink that combines storage stability and opacity, hollow resin particles and titanium oxide may be used in combination as pigments.

[0062] As the black pigment, carbon black (CI Pigment Black 7) manufactured by the furnace method or the channel method is preferably used. For example, these carbon blacks have a primary particle diameter of 11 to 40 nm and a specific surface area measured by the BET method of 50 to 400 m 2 Suitable examples of such a material include Nos. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, and MCF88 (all manufactured by Mitsubishi Chemical Corporation); RAVEN 1080 and 1255 (all manufactured by Birla Carbon Corporation); REGAL 330R, 400R, 660R, MOGUL L, and ELFTEX 415 (all manufactured by Cabot Corporation); and Nipex 90, 150T, 160IQ, 170IQ, 75, PrinteX 85, 95, 90, and 35 (all manufactured by Orion Engineered Carbons).

[0063] In addition to carbon black, other black pigments that can be used include aniline black, lumogen black, azomethine azo black, etc. A black pigment can also be obtained by using a plurality of chromatic pigments, such as cyan pigments, magenta pigments, yellow pigments, brown pigments, and orange pigments, which will be described later.

[0064] Examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, and fluorescent pigments.

[0065] Specific examples of cyan pigments in terms of color index include CI Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 22, 60, 64, and the like.

[0066] Examples of magenta pigments include CI Pigment Red 5, 7, 12, 31, 48, 49, 52, 53, 57, 112, 120, 122, 146, 147, 149, 150, 168, 170, 184, 185, 188, 202, 209, 238, 242, 254, 255, 264, 269, and 282; and CI Pigment Violet 19, 23, 29, 30, 37, 40, and 50.

[0067] Further, examples of yellow pigments include CI Pigment Yellow 10, 11, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, and 213.

[0068] In addition to the above, other special colors such as orange pigments, green pigments, and brown pigments can also be used. Specific examples include CI Pigment Orange 16, 36, 38, 40, 43, 62, 63, 64, and 71, CI Pigment Green 7, 10, and 36, and Pigment Brown 23, 25, and 26.

[0069] In the aqueous ink of the present invention, a mixture of the above pigments can be used to achieve a suitable hue and color development of the printed matter. For example, to improve the color tone at low printing rates in a black ink using carbon black, a small amount of one or more pigments selected from cyan pigments, magenta pigments, orange pigments, and brown pigments can be added.

[0070] These pigments are preferably contained in an amount ranging from 2% to 20% by mass, more preferably from 2.5% to 15% by mass, and particularly preferably from 3% to 10% by mass, relative to the total amount of the ink, except in the case of white ink. Furthermore, in the case of white ink, the pigment content is preferably from 5% to 40% by mass, more preferably from 8% to 30% by mass, relative to the total amount of the white ink. By keeping the pigment content at 2% by mass or more (5% by mass or more for white ink), sufficient color development (opacity for white ink) can be achieved even in single-pass printing. Furthermore, by keeping the pigment content at 20% by mass or less (40% by mass or less for white ink), the ink viscosity can be kept within a range suitable for inkjet printing, and good storage stability of the ink can be maintained, resulting in long-term ejection stability.

[0071] <Pigment dispersing resin> Methods for stably dispersing and maintaining pigment (A) in aqueous ink include (1) a method in which at least a portion of the pigment surface is coated with a water-soluble or water-insoluble pigment dispersing resin, (2) a method in which a water-soluble and / or water-dispersible surfactant is adsorbed onto the pigment surface and dispersed, and (3) a method in which hydrophilic functional groups are chemically or physically introduced onto the pigment surface, allowing the pigment to disperse in the ink without a dispersing resin or surfactant (self-dispersing pigment).

[0072] In the water-based ink of the present invention, it is preferable to use the above method (1), i.e., the pigment dispersion resin, because the covering ability of the pigment dispersion resin for the pigment and the charge of the pigment dispersion resin can be easily adjusted by selecting and considering the composition and molecular weight of the polymerizable monomers that make up the resin, making it possible to impart dispersion stability to even fine pigments, and furthermore, to obtain printed matter with excellent ejection stability, color development, and color reproducibility.

[0073] The type of the pigment dispersing resin is not particularly limited, and examples thereof include (meth)acrylic, styrene (meth)acrylic, (maleic anhydride)-based, styrene (maleic anhydride)-based, α-olefin (maleic anhydride)-based, urethane-based, and ester-based resins. Among these, from the viewpoint of strengthening pigment adsorption and stabilizing the pigment dispersion, it is preferable to use one or more resins selected from α-olefin (maleic anhydride)-based, (meth)acrylic, and styrene (meth)acrylic resins. In this specification, "(maleic anhydride)" refers to maleic acid or maleic anhydride.

[0074] Furthermore, the pigment dispersion resin preferably contains structural units derived from a monomer containing an aromatic ring structure. This is advantageous in that it improves adhesive strength by utilizing the π-cation interaction formed between the aromatic ring structure contained in the pigment dispersion resin and the nitrogen atoms in the urethane bonds contained in the laminating adhesive composition, and in that it ensures and improves the dispersion stability of the pigment in aqueous inks. The amount of structural units derived from a monomer containing an aromatic ring structure is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, and particularly preferably 20 to 70% by mass, based on the total amount of the pigment dispersion resin.

[0075] The weight-average molecular weight of the pigment dispersion resin is preferably 5,000 to 100,000. It is more preferably 10,000 to 50,000, and even more preferably 15,000 to 30,000. Having a weight-average molecular weight within this range allows the pigment to be stably dispersed in water, and viscosity adjustment when applied to aqueous inks is easy. In particular, when the weight-average molecular weight is 5,000 or more, the pigment dispersion resin is less likely to dissolve in the water-soluble organic solvent added to the aqueous ink, resulting in strong adsorption of the pigment dispersion resin to the pigment and excellent dispersion stability. Furthermore, when the weight-average molecular weight is 100,000 or less, the viscosity during dispersion is kept low, and ejection stability from the inkjet head is excellent, enabling stable printing over a long period of time.

[0076] When a water-soluble resin is used as the pigment dispersing resin, its acid value is preferably 60 to 400 mgKOH / g. By setting the acid value within the above range, the dispersion stability of the pigment and the storage stability of the ink can be made favorable. The acid value is more preferably 120 to 350 mgKOH / g, and even more preferably 150 to 300 mgKOH / g. 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. The acid value of the pigment dispersing resin can be measured in the same manner as in the case of the binder resin described above.

[0077] In the present invention, the blending amount of the pigment dispersing resin is preferably 1 to 50% by mass relative to the pigment. By blending the pigment dispersing resin in an amount of 1 to 50% by mass relative to the pigment, the viscosity of the pigment dispersion can be reduced, and the viscosity stability and dispersion stability of the pigment dispersion and water-based ink can be improved. The blending amount of the pigment dispersing resin relative to the pigment is more preferably 2 to 45% by mass, and even more preferably 4 to 35% by mass.

[0078] <Water-soluble organic solvent (E)> The aqueous ink of the present invention contains a water-soluble organic solvent to improve ejection stability by suppressing ink adhesion on the nozzles of an inkjet head and to improve drying properties on non-permeable substrates. Furthermore, the water-soluble organic solvent can improve the dispersion stability of the aqueous ink, resulting in an ink with excellent ejection properties and storage stability. In the present invention, the term "water-soluble organic solvent" refers to an organic compound that is used to dissolve and / or disperse substances, is liquid at 25°C and 1 atmosphere, and has a solubility in water at 25°C under 1 atmosphere of 1 g / 100 g H2O or more.

[0079] The water-soluble organic solvent (E) is not particularly limited and any known solvent can be used. However, from the viewpoint of compatibility and affinity with the pigment dispersion resin and other material components, such as surfactants added as needed, it is preferable for the water-soluble organic solvent to contain an alkyl polyol solvent. In particular, the boiling point of the water-soluble organic solvent at 1 atmosphere is preferably 100°C or higher but lower than 240°C. A boiling point of 100°C or higher improves the jetting properties, dispersion stability, and moisture retention of the aqueous ink. A boiling point of lower than 240°C improves the drying properties of the aqueous ink, preventing color bleeding, and improving the abrasion resistance and processability of printed materials. Specifically, the water-soluble organic solvent is preferably at least one selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and 1,2-hexanediol. These water-soluble organic solvents have a strong affinity with the acrylic portion of the water-soluble acrylic urethane resin, preventing the aqueous ink from drying out in the inkjet head and suppressing nozzle clogging, thereby improving ejection stability.

[0080] The boiling point at 1 atmospheric pressure can be measured using a thermal analyzer such as a DSC (differential scanning calorimetry) analyzer.

[0081] Other water-soluble solvents that can be used in the present invention include alkyl polyol solvents, such as 1,2-ethanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methylpentane-2,4-diol, 2-ethyl-1,3-hexanediol, diethylene glycol, and dipropylene glycol. Examples of glycol ether solvents include glycol monoalkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monomethyl ether; and glycol dialkyl ethers such as diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, and tetraethylene glycol dimethyl ether.

[0082] From the viewpoint of ensuring ejection stability from the inkjet head and sufficient adhesive strength during lamination, the total amount of water-soluble organic solvents is preferably 15% by mass or more and 35% by mass or more, and more preferably 17% by mass or more and 30% by mass or less, relative to the total amount of the water-soluble organic solvents. By making the total amount of water-soluble organic solvents 15% by mass or more, a water-based ink with excellent ink moisture retention and ejection stability can be obtained, and by making it 35% by mass or less, a water-based ink with good drying properties and good color bleeding, and with good adhesive strength and good print image quality after lamination can be obtained.

[0083] <Surfactant> The aqueous ink of the present invention preferably contains a surfactant to adjust the surface tension, ensure wettability on the film substrate, and improve print quality. On the other hand, if the surface tension is too low, the nozzle surface of the inkjet head will become wet with the aqueous ink, impairing ejection stability. Therefore, the selection of the type and amount of surfactant is important. From the viewpoint of ensuring optimal wettability and achieving stable ejection from the inkjet head, it is preferable to use surfactants such as siloxane-based, acetylene-based, acrylic-based, fluorine-based, and polyoxyalkylene alkyl ether-based surfactants, with siloxane-based and / or acetylene-based surfactants being particularly preferred. The amount of surfactant added is preferably 0.05% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 3.0% by mass or less, based on the total amount of the aqueous ink. A content of 0.05% by mass or more allows the surfactant to fully exert its functions, while a content of 5.0% by mass or less allows the storage stability and ejection stability of the aqueous ink to be maintained at an appropriate level.

[0084] <Other ingredients> In addition to the above components, additives such as pH adjusters, antifoaming agents, preservatives, infrared absorbers, ultraviolet absorbers, crosslinking agents, thickeners, etc. may be added as needed. The amount of these additives added is preferably 0.01% by mass or more and 10% by mass or less based on the total mass of the water-based ink.

[0085] <Ink preparation method> The ink of the present invention, which is composed of the above-mentioned components, can be prepared by the following methods, but the method for preparing the ink of the present invention is not limited to these.

[0086] First, a pigment and, if necessary, a water-soluble organic solvent (E) are added to an aqueous solution containing at least a pigment dispersion resin and water, and the mixture is stirred (premixed), followed by dispersion treatment using a dispersion means described below, and, if necessary, centrifugal separation to obtain a pigment dispersion. Next, if necessary, a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (E), water (D), and, if necessary, the components listed above are appropriately added to the pigment dispersion, and the mixture is thoroughly stirred and mixed, followed by filtration to obtain the ink of the present invention.

[0087] In the above-mentioned ink preparation method, it is effective to perform premixing before the dispersion treatment, as the premixing operation is preferable because it improves the wettability of the pigment surface and promotes the adsorption of the pigment dispersing resin to the pigment surface.

[0088] The dispersing machine used for dispersing the pigment (A) may be any commonly used dispersing machine, such as a ball mill, a roll mill, a sand mill, a bead mill, or a Nanomizer, among which a bead mill is preferably used. Examples of bead mills include a Super Mill, a sand grinder, an agitator mill, a grain mill, a Dyno Mill, a Pearl Mill, and a Cobol Mill (all of which are trade names).

[0089] Since the ink of the present invention is for inkjet printing, it is preferable to use a pigment with an optimal particle size distribution from the viewpoint of nozzle clogging resistance, etc. Methods for obtaining a pigment with the desired particle size distribution include reducing the size of the grinding media in the disperser as mentioned above, increasing the packing rate of the grinding media, extending the processing time, classifying the ink after grinding using a filter or centrifuge, or a combination of these methods. The particle size distribution of the ink can be measured, for example, using a Nanotrac UPA-EX150 manufactured by Microtrac-Bell.

[0090] <Ink set> The ink of the present invention may be used in a single color, or may be used as an ink set combining multiple colors depending on the application. While the combination is not particularly limited, a combination of two or more colors with different hues is preferred. For example, a full-color image can be obtained by using three colors: cyan, yellow, and magenta. The addition of black ink can improve the sense of black and increase the visibility of text, etc. Color reproducibility can also be improved by adding colors such as orange, green, and violet. The use of white ink in combination can produce clear images when printing on file substrates other than white, and can improve the hiding power of contents when used as a laminate for flexible packaging materials. The ink of the present invention may also include an ink (clear ink) that does not contain pigments and therefore does not substantially contain colorant components.

[0091] The aqueous ink of the present invention can also be used in combination with a pretreatment liquid containing a flocculant in the form of an ink-pretreatment liquid set. The pretreatment liquid containing a flocculant can form a layer (ink flocculation layer) on a substrate, which is a recording medium, that intentionally flocculates the solid components contained in the ink. By depositing the aqueous ink of the present invention on the ink flocculation layer, bleeding between ink droplets and color unevenness can be prevented, significantly improving print quality. Furthermore, depending on the material used in the pretreatment liquid, the adhesion and lamination suitability of the printed material can also be improved.

[0092] In the present invention, the term "flocculant" refers to a component contained in the aqueous ink that can disrupt the dispersion state of the pigment and cause it to flocculate, and / or insolubilize the binder resin and thicken the aqueous ink. From the viewpoint of improving the print quality, the flocculant used in the pretreatment liquid to be combined with the aqueous ink of the present invention preferably contains one or more selected from metal salts and cationic polymer compounds. Among these, it is preferable to use a metal salt, and Ca 2+ , Mg 2+ , Zn 2+ , and Al 3+ It is particularly preferred that the pretreatment liquid contains one or more salts of polyvalent metal ions selected from the group consisting of: When a metal salt is used as the flocculant, the content thereof is preferably 2 to 25 mass %, and particularly preferably 3 to 20 mass %, based on the total mass of the pretreatment liquid.

[0093] Other additives that may be added to the pretreatment liquid include water-soluble organic solvents, surfactants, pH adjusters, antifoaming agents, thickeners, and preservatives.

[0094] The aqueous ink is printed onto the film substrate using an inkjet printing method. A single-pass printing method is preferred. The single-pass printing method requires fewer scans than inkjet printing (multi-pass printing), which involves multiple scans of the inkjet head, allowing for faster printing speeds. This method is also suitable for industrial applications requiring high printing speeds. It is also suitable because high-quality prints can be obtained at a high recording resolution of 600 dpi or higher. Note that "recording resolution" is expressed in units of dpi (dots per inch) and represents the number of aqueous inkjet ink droplets printed per inch. In this specification, "recording resolution" refers to both the recording resolution in the transport direction of the substrate and the recording resolution in the direction perpendicular to the transport direction within the substrate plane (hereinafter referred to as the recording width direction).

[0095] When printing with aqueous ink using a one-pass printing method, the drop volume of the aqueous ink depends largely on the performance of the inkjet head, but to obtain printed matter with excellent print quality and adhesive strength, it is preferably in the range of 0.6 to 60 pL, more preferably 1 to 50 pL, and particularly preferably 1.4 to 40 pL. Furthermore, to obtain high-quality images, it is particularly preferable to use an inkjet head with gradation specifications that allows the drop volume to be changed.

[0096] <Non-permeable base material> The substrate on which the ink of the present invention is printed is not particularly limited, and any known substrate can be used. Among them, from the viewpoint of resistance to hot water sterilization treatment, non-permeable substrates or poorly permeable substrates are suitable, and the ink of the present invention can be particularly preferably used for non-permeable substrates. In this specification, the permeability of a recording medium 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 Recording media with a permeability of less than 1 to 10 g / m are considered "impermeable substrates." 2 The recording medium having the above properties is called a "hardly permeable substrate."

[0097] The amount of water absorbed by a recording medium can be measured, for example, under the following conditions: Using a dynamic scanning absorptivity meter, a KM500win manufactured by Kumagai Riki Kogyo Co., Ltd., and using a recording medium approximately 15-20 cm square at 23°C and 50% RH, the amount of transferred pure water is measured under the conditions shown below. Measurement method: Spiral method ·Measurement start radius: 20mm Measurement end radius: 60mm ·Contact time: 10~1,000msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) Scanning interval: 7mm Rotating table speed change angle: 86.3 degrees Headbox conditions: width 5mm, slit width 1mm

[0098] Examples of impermeable or poorly permeable substrates include plastic substrates such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyethylene, nylon, polystyrene, and polyvinyl alcohol; coated paper substrates such as coated paper, art paper, and cast paper; metal substrates such as aluminum, iron, stainless steel, and titanium; and glass substrates. Polyethylene terephthalate or nylon, which are impermeable substrates, are particularly suitable as substrates for printing with the ink of the present invention. Hydrogen bonding between the ester bond of polyethylene terephthalate or the amide bond of nylon and the acid group of the water-soluble acrylic urethane resin maintains good adhesive strength even after lamination and hot water sterilization.

[0099] The substrate may have a smooth or textured surface, and may be transparent, translucent, or opaque. Two or more of these recording media may be laminated together. A release adhesive layer may be provided on the side opposite the printed surface, or an adhesive layer may be provided on the printed surface after printing. The recording medium used in the inkjet recording method of the present invention may be in the form of a roll or sheets.

[0100] From the viewpoint of improving the wettability, image quality, and drying properties of the aqueous inkjet ink of the present invention, and from the viewpoint of making the surface of the printed matter uniform and improving the abrasion resistance and adhesion, it is also preferable to subject the non-permeable substrates or poorly permeable substrates exemplified above to a surface modification method such as corona treatment or plasma treatment. [Example]

[0101] The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the scope of the invention. In the examples and comparative examples, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0102] <Synthesis of acrylic diol (b1-1)> [Synthesis Example 1] A reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube was charged with 360 parts by mass of butyl methacrylate (manufactured by Mitsubishi Chemical Corporation) as the (meth)acrylate (f2) without an acid group, 140 parts by mass of methacrylic acid (manufactured by Mitsubishi Chemical Corporation) as the vinyl monomer (f1) with an acid group, 300 parts by mass of 2-butanone (hereinafter referred to as MEK) (manufactured by Maruzen Petrochemical Co., Ltd.) as an organic solvent, and 28 parts by mass of 1-thioglycerol (manufactured by Asahi Chemical Industry Co., Ltd.) as a chain transfer agent (g). The atmosphere in the reaction vessel was purged with nitrogen gas, and the reaction vessel was heated to 65°C and stirred. After stirring for 15 minutes, 50 parts by mass of MEK and 0.15 parts by mass of 2,2'-azobisisobutyronitrile were mixed and added to the reaction vessel, followed by a 12-hour reaction. GPC measurement and acid value measurement revealed that an acrylic diol (b1-1) was obtained with a number average molecular weight of 2000 and an acid value of 171 mgKOH / g.

[0103] <Synthesis of acrylic diols (b1-2) to (b1-8) and (b'1-9) to (b'1-12)> [Synthesis Example 2] to [Synthesis Example 8], [Comparative Synthesis Example 1] to [Comparative Synthesis Example 4] Acrylic diols (b1-2) to (b1-8) and (b'1-9) to (b'1-12) were obtained by synthesis in the same manner as for the acrylic diol (b1-1) according to the compositions and parts by weight of the ingredients in Table 1.

[0104] [Table 1]

[0105] The monomers and reagents listed in Table 1 are shown below. ·MAA: methacrylic acid BMA: Butyl methacrylate 2EHMA: 2-ethylhexyl methacrylate LMA: Lauryl methacrylate SMA: Stearyl methacrylate 1-TG: 1-thioglycerol (molecular weight 108) AIBN: 2,2'-azobisisobutyronitrile MEK:2-butanone

[0106] <Synthesis of Water-Soluble Acrylic Urethane Resin (B-1)> [Synthesis Example 9] A reaction vessel equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel was charged with 147 parts by mass of polycarbonate polyol C-2090 (Kuraray Co., Ltd., a condensate of 1,6-hexanediol and 3-methyl-1,5-pentanediol), 14 parts by mass of dimethylol butanoic acid (Kadotoku Corporation), 49 parts by mass of acrylic diol (b1-1), 56 parts by mass of isophorone diisocyanate, and 220 parts by mass of MEK while introducing nitrogen gas. The mixture was then heated to 75°C. With stirring, 0.02 parts by mass of tin 2-ethylhexanoate was added, and the mixture was further heated to 80°C. After reacting for 3 hours, a urethane resin with terminal isocyanate was obtained and cooled to 40°C. Next, 3 parts by mass of amino alcohol EA (Nippon Nyukazai Co., Ltd.) and 50 parts by mass of MEK were added dropwise over 1 hour, and the mixture was further aged for 3 hours to obtain a urethane resin solution. Next, 8 parts by mass of 28% ammonia water and 500 parts by mass of ion-exchanged water were added dropwise to the urethane resin solution over 1 hour to neutralize it and make it water-soluble, and then the entire amount of MEK was distilled at 50°C under reduced pressure to obtain a water-soluble acrylic urethane resin (B-1) with an acid value of 50 mgKOH / g and a weight-average molecular weight of 17000. Water was added again to make the solution an aqueous solution with a resin solids content of 25%.

[0107] <Synthesis of Water-Soluble Acrylic Urethane Resins (B-2) to (B-19) and (B'-20) to (B'-28)> [Synthesis Example 10] to [Synthesis Example 27], [Comparative Synthesis Example 5] to [Comparative Synthesis Example 13] Water-soluble acrylic urethane resins (B-2) to (B-19) and (B'-20) to (B'-28) were obtained by synthesis in the same manner as for water-soluble acrylic urethane resin (B-1) according to the compositions and charged mass parts in Table 2.

[0108] It should be noted that the acrylic diol (b'1-10) was highly hydrophilic and insoluble in MEK, a solvent, and therefore a water-soluble acrylic urethane resin was not synthesized using the acrylic diol (b'1-10).

[0109] [Table 2]

[0110] The reagents listed in Table 2 are as follows: PC: Polycarbonate polyol C-2090 manufactured by Kuraray Co., Ltd. PE: Polyester polyol P-2010 manufactured by Kuraray Co., Ltd. DMBA: Dimethylolbutanoic acid 14BD: 1,4-butanediol IPDI: Isophorone diisocyanate HDI: Hexamethylene diisocyanate AEA: Amino alcohol EA manufactured by Nippon Nyukazai Co., Ltd. IPDA: Isophoronediamine

[0111] <Production example of cyan pigment dispersion> 20 parts by mass of Lionol Blue 7358G (CI Pigment Blue 15:3) manufactured by Toyocolor Co., Ltd., 15 parts by mass of an aqueous solution of pigment dispersion resin (solids concentration 30%), and 65 parts by mass of water were mixed and pre-dispersed using a disper, and then main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads with a diameter of 0.5 mm, to obtain a cyan pigment dispersion.

[0112] <Production example of black pigment dispersion> A pigment dispersion (black) was obtained in the same manner as for the cyan pigment, except that CI Pigment Black 7 (Printex 85 manufactured by Orion Engineered Carbons) was used as the pigment.

[0113] <Production example of magenta pigment dispersion> A pigment dispersion (magenta) was obtained in the same manner as for the cyan dispersion, except that CI Pigment Red 122 (FASTGEN SUPER MAGENTA RGT, manufactured by DIC Corporation) was used as the pigment.

[0114] <Production example of pigment dispersion yellow> A pigment dispersion (yellow) was obtained in the same manner as for the cyan pigment, except that CI Pigment Yellow 14 (Lionol Yellow TT-1405G, manufactured by Toyocolor Co., Ltd.) was used as the pigment.

[0115] <Production example of white pigment dispersion> 40 parts of CR-90-2 (titanium oxide) manufactured by Ishihara Sangyo Kaisha, Ltd., 30 parts of an aqueous solution of pigment dispersion resin (solid content concentration 30%), and 30 parts of water were mixed, and dispersed in the same manner as in the cyan pigment dispersion to obtain a white pigment dispersion.

[0116] <Production of Ink C1> [Manufacturing Example 1] 25 parts by weight of cyan pigment dispersion, 20 parts by weight of an aqueous solution of water-soluble acrylic urethane resin (B-1), 25 parts by weight of 1,2-propanediol, 1 part by weight of TEGOWet 280 (manufactured by Evonik), and 1 part by weight of Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) were added sequentially to a mixing vessel, and ion-exchanged water was added to adjust the total ink to 100 parts by weight, followed by stirring in a disperser until sufficiently uniform. The mixture was then filtered through a membrane filter with a pore size of 1 μm to remove coarse particles that could cause head clogging, producing Ink C1.

[0117] <Production of inks C2 to C25, K26, M27, Y28, W29, C30 to C41> [Production Examples 2] to [Production Examples 29], [Comparative Production Examples 1] to [Comparative Production Examples 11] Inks C2 to C25, K26, M27, Y28, W29, and C30 to C40 were produced in the same manner as in Production Example 1, except that the materials listed in Table 3 were used.

[0118] [Table 3]

[0119] The reagents listed in Table 3 are as follows: PG: 1,2-propanediol MB: 3-Methoxybutanol 12BD: 1,2-butanediol 12HD: 1,2-hexanediol TEGOWet 280: Evonik siloxane surfactant SF465: Surfynol 465 manufactured by Nissin Chemical Industry Co., Ltd.

[0120] [Example 1] An inkjet head KJ4B-1200 (Kyocera Corporation, resolution 1200 dpi, maximum drive frequency 64 kHz) was installed above a conveyor capable of transporting printing substrates, and the aqueous inkjet ink prepared above was filled in. Next, a form substrate was fixed onto the conveyor, and the conveyor was driven at 50 m / min. The aqueous inkjet ink was ejected as the substrate passed the area where the inkjet head was installed, and the following printing was performed. The drop volume during printing was 2.5 pL, and the printed material was placed in an air oven at 70°C and dried for 3 minutes.

[0121] A nozzle check pattern was printed to confirm that ink was being ejected normally from all nozzles. After leaving the printer in a 25°C environment for 1 minute, a solid print was performed with a frequency of 40 kHz and a resolution of 1200 x 1200 dpi at a printing rate of 100%. The evaluation results are shown in Table 4.

[0122] [Example 2] to [Example 29], [Comparative Example 1] to [Comparative Example 11] First, solid printing with a printing rate of 100% was performed with cyan ink, producing a printed matter with a printing rate of 100%, using the same inkjet printer and printing conditions as in Example 1. The obtained evaluation results are shown in Table 4.

[0123] <Evaluation 1: Redissolution test of dried and solidified ink> 0.3g of ink was added to a 30g small aluminum container and dried and solidified for the specified time in an air oven at 35°C. After drying for 1 hour under the above conditions, none of the inks adhered to the fingertips when touched. 10g of maintenance liquid was then added and left to stand for 1 hour, after which the ink was visually observed to see if it dissolved in the maintenance liquid, and the resolubility of the dried and solidified ink was evaluated. The evaluation criteria are as follows, with ◎ and 〇 being in the range of practical use. ◎:Even if the ink is dried and hardened for 12 hours in an air oven at 35°C, no maintenance is required. It dissolved in the liquid. 〇: Ink dried and solidified in an air oven at 35℃ for 12 hours showed no signs of dissolving in the maintenance liquid. However, the ink that had been dried and solidified for 6 hours dissolved. △: Ink dried and solidified in an air oven at 35°C for 6 hours was soluble in the maintenance liquid. However, it dissolved in the ink that had been dried and solidified for 1 hour. ×: Even if the ink is dried for 1 hour in an air oven at 35°C, it will not adhere to the maintenance liquid. It did not dissolve.

[0124] <Evaluation 2: Initial ejection performance evaluation> Initial dischargeability was evaluated by visually and with a magnifying glass to check whether the initial part of a 100% solid print was printed. The evaluation criteria are as follows, with ⊚ and ◯ being in the practically usable range. A PET film (FE2001, 12 μm thick) manufactured by Futamura Chemical Co., Ltd. was used as the film substrate. The results are shown in Table 4. ◎: No chipping was found at the beginning of the stamping, even when checked visually and with a magnifying glass. 〇: No chips are visible to the naked eye, but chips less than 1 mm are found when inspected with a magnifying glass △: Chips of 1mm or more but less than 5mm were visually confirmed at the beginning of the shot ×: A chip of 5 mm or more was visually confirmed at the beginning of the shot.

[0125] <Evaluation 3: Intermittent ejection evaluation> After printing a solid image at 100% coverage, the inkjet ejection device was left to stand by for a certain period of time in an environment of 25°C, after which a nozzle check pattern was printed and the ink was visually inspected for any missing nozzles to evaluate intermittent ejection. The evaluation criteria are as follows, with ◎ and ◯ being in the practical usable range. The results are shown in Table 4. ◎: No missing nozzles even after waiting for 2 hours 〇: There were no nozzle missing issues when printing after waiting for 1 hour, but after waiting for 2 hours When printing after that, nozzles were missing. △: When printing after waiting for 1 hour, 1 to 9 nozzles were missing. ×: When printing after waiting for 1 hour, 10 or more nozzles were missing

[0126] <Evaluation 4: Laminate strength (adhesion) evaluation> Using a test coater, a laminating adhesive (TM-265L / CAT-RT37 manufactured by Toyo-Morton Co., Ltd.) was applied to the printed surface of a film substrate with a solid print rate of 100% at a temperature of 60°C and a coating speed of 50 m / min. Since the laminating adhesive contains a solvent component, the solvent component was dried after application, and the coating amount after drying was 2.5 g / m. 2 Furthermore, a sealant film was superimposed on the surface coated with the laminating adhesive, and the laminate was then aged for 2 days in an environment of 40°C to cure the laminating adhesive composition, thereby producing a laminated laminate. <Film substrate> Futamura Chemical Co., Ltd. PET film "FE2001" (Thickness: 12 μm, referred to as "PET" in Table 4 and below) Unitika nylon film "Emblem ON" (Thickness 15 μm, listed as "NY" in Table 4) <Sealant film> Futamura Chemical Co., Ltd. non-stretched polypropylene film "FHK2" (Thickness: 25 μm, referred to as "CPP" in Table 4 and below) Mitsui Chemicals Tocello Linear Low-Density Polyethylene Film "TUX-FC-D" (Thickness: 40 μm, listed as "LLDPE" in Table 4)

[0127] The laminated laminate thus produced was cut into a length of 300 mm and a width of 15 mm to prepare test pieces. Using an Instron tensile tester, the laminate was pulled at a peel rate of 300 mm / min in an environment of 25°C, and the T-peel strength (N) between the film substrate (PET) and the sealant film (CPP) was measured. This test was performed five times, and the average value was calculated to evaluate the adhesive strength. The evaluation criteria were as follows, with ◎ and ◯ being in the practical usable range. The results are shown in Table 4. ◎: Adhesive force 1.5N or more 〇: Adhesive strength 0.6N or more, less than 1.5N △: Adhesion strength 0.3N or more, less than 0.6N ×: Adhesion strength less than 0.3N

[0128] <Evaluation 5: Adhesion strength evaluation after hot water sterilization treatment> Two laminated sheets are placed together with the sealant film facing inward, and then heated at 150°C and 2 kg / cm using a heat sealer. 2 The container was sealed for 1 second to create a tare. This was then sterilized in hot water at 95°C for 30 minutes using a Hisaka Seisakusho "RCS-40RTGN" high-temperature, high-pressure cooking sterilization tester. After the test, the laminate strength was evaluated in the same manner as described above. The results are shown in Table 4.

[0129] <Evaluation 6: Appearance evaluation> The laminate test pieces used in the adhesive strength evaluation after hot water sterilization were visually observed from the film substrate side to evaluate their appearance. The evaluation criteria were as follows, with ⊚ and ◯ being in the practical usable range. The results are shown in Table 4. ◎: There is no delamination or bubbling in the laminate, or there is delamination or bubbling in less than 3% of the area Good: Delamination and bubbling occurred in an area of ​​3% or more but less than 20% of the laminate. △: Delamination and bubbling occurred in an area of ​​20% or more but less than 50% of the laminate. ×: Delamination and bubbles are present in 50% or more of the laminated surface area.

[0130] [Table 4]

[0131] In Comparative Example 1, the acid value of the acrylic diol was low and the amount of low-molecular-weight diol contained in the water-soluble acrylic urethane resin was high, resulting in an increased number of urethane bonds and poor discharge stability. As a result of the poor discharge, gaps appeared in the solid print, and the expected adhesive strength was not achieved. In Comparative Example 2, the amount of 1-thioglycerol was low, resulting in a large Mn of the acrylic diol and a large Mw of the water-soluble acrylic urethane resin, resulting in poor resolubility, discharge stability, and adhesive strength, making it unusable. In Comparative Example 3, the amount of 1-thioglycerol was high, resulting in a small Mn of the acrylic diol and a small Mw of the water-soluble acrylic urethane resin, resulting in poor water solubility, dischargeability, and adhesive strength of the water-soluble acrylic urethane resin. In Comparative Example 4, the acid value of the water-soluble acrylic urethane resin was low, resulting in poor resolubility, and therefore poor post-processing suitability. In Comparative Example 5, the acid value of the water-soluble acrylic urethane resin was high, resulting in increased viscosity, resulting in poor discharge stability and poor adhesive strength after hot water sterilization. In Comparative Example 6, the water-soluble acrylic urethane resin had a small Mw, and while resolubility and ejection stability were good, the resin properties could not be fully realized, resulting in poor adhesion and appearance after hot water sterilization. In Comparative Example 7, the water-soluble acrylic urethane resin had a large Mw, and therefore poor ejection stability and subsequent post-processing suitability were also poor. In Comparative Example 8, the water-soluble acrylic urethane resin did not contain low-molecular-weight diol (b3), resulting in an imbalance in the hydrophilicity of the main chain and side chains, resulting in the formation of an emulsion in water, resulting in poor initial ejection and intermittent ejection. In Comparative Example 9, ink C38 was produced using a water-soluble acrylic urethane that did not contain acrylic diol (b1). This resulted in poor ejection stability due to the large number of urethane bonds, resulting in poor post-processing suitability. In Comparative Example 10, ink C40 did not contain water-soluble acrylic urethane resin (B). It had excellent resolubility and ejection stability, but did not adhere, resulting in poor post-processing suitability, such as adhesion. Comparative Example 11 was ink C41 containing no water-soluble organic solvent (E), which was poor in resolubility and ejection stability, and also had poor suitability for subsequent post-processing.

[0132] In contrast to the comparative examples, Examples 1 to 29 were made of a suitable combination of a binder resin and a water-soluble organic solvent, had excellent ejection stability from the nozzle of the inkjet head, maintained good adhesive strength even after lamination and hot water sterilization, and no change in appearance was observed, so all were within the range of practical use.

Claims

1. An aqueous inkjet ink comprising a pigment (A), a water-soluble acrylic urethane resin (B), a water-soluble organic solvent (E), and water (D), and satisfying all of the conditions (1) to (6). (1) The water-soluble acrylic urethane resin (B) is A structural unit derived from acrylic diol (b1), A structural unit derived from polyisocyanate (b2), and and a structural unit derived from a polyol containing a low-molecular-weight diol (b3) having one acid group and two hydroxyl groups and a molecular weight of 500 or less. (2) The acrylic diol (b1) is A structural unit derived from a chain transfer agent (g) containing one mercapto group and two hydroxyl groups; a structural unit derived from a vinyl monomer (f1) having an acid group, and a structural unit derived from a (meth)acrylate (f2) that does not have an acid group. (3) The acid value of the acrylic diol (b1) is 25 to 310 mgKOH / g. (4) The content of the structural units derived from the chain transfer agent (g) is 1.1 to 9.5% by mass, relative to 100% by mass of the structural units derived from the acrylic diol (b1). (5) The water-soluble acrylic urethane resin (B) has a weight average molecular weight of 9,000 to 32,000. (6) The water-soluble acrylic urethane resin (B) has an acid value of 25 to 90 mgKOH / g.

2. 2. The aqueous inkjet ink according to claim 1, wherein the ratio of the amount of acid groups derived from the acid group-containing vinyl monomer (f1) to the amount of acid groups derived from the low-molecular-weight diol (b3), present per unit mass of the water-soluble acrylic urethane resin (B), is 1:4 to 4:

1.

3. the water-soluble organic solvent (E) contains at least one selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and 1,2-hexanediol; 3. The aqueous inkjet ink according to claim 1, wherein the total amount of the water-soluble organic solvent (E) is 15 to 35% by mass relative to the total amount of the aqueous inkjet ink.

4. A printed matter obtained by printing the aqueous inkjet ink according to any one of claims 1 to 3 onto a non-permeable substrate.

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