Aqueous inkjet ink and printed matter

Abstract

To provide an aqueous inkjet ink that shows excellent ejection stability independently of a design resolution of a mounted inkjet head and a droplet volume during ejection, and that makes it possible to obtain a printed matter excellent in solid coverage, blocking resistance, and alcohol resistance.SOLUTION: An aqueous inkjet ink contains a colorant, a binder resin, a water-soluble organic solvent, and a surfactant, wherein the binder resin includes a resin (R1) having a glass transition temperature of 50°C to 130°C, the water-soluble organic solvent includes dipropylene glycol monopropyl ether (S1), the surfactant includes a surfactant having an HLB value of 10 or less, and a ratio of a content of the dipropylene glycol monopropyl ether (S1) is specified with respect to each of a total a content of the water-soluble organic solvent and a total a content of the resin (R1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous inkjet ink and a printed matter produced using the aqueous inkjet ink. [Background technology]

[0002] Unlike plate-based printing methods such as offset printing and gravure printing, digital printing does not require plate-making film or printing plates, making it easier to reduce costs and handle small lots of a wide variety of products.

[0003] Inkjet printing, a type of digital printing method, prints characters and images by ejecting ink droplets from tiny nozzles onto a printing substrate (also referred to simply as "substrate" in this application). In this application, the images and / or characters are collectively referred to as "printed information." The term "image" also includes solid images (images printed at 100% coverage to completely cover the surface of the printing substrate) and seamless images such as checkerboard patterns. Inkjet printing has the advantages of low noise during printing, easy operation of the printing device, and ease of color printing, and is therefore widely used as a method for outputting printed information in offices and homes. Furthermore, with the improvement of inkjet technology, inkjet printing is also being used for industrial purposes.

[0004] Traditionally, solvent inks and UV-curable inks have been used in industrial inkjet printing, but in recent years, there has been a growing demand for water-based inks due to concerns about safety, health, and the environment.

[0005] Water-based inks used in inkjet printing (hereinafter simply referred to as "inkjet inks") have traditionally been intended for use on plain paper, high-quality paper, and specialty paper. Specifically, they contain water as the main component, and a water-soluble organic solvent such as glycerin is added to control the wetting, spreading, and drying properties of the ink on the printing substrate. When a pattern of printing information is printed on a printing substrate using water-based inkjet inks (hereinafter simply referred to as "water-based inkjet inks" or "inks") made of these liquid components, the liquid components penetrate into the printing substrate and dry, fixing the pattern.

[0006] On the other hand, inkjet printing substrates include not only those with high permeability as listed above, but also low-permeability printing substrates such as coated paper, art paper, and lightly coated paper, as well as non-permeability printing substrates such as films. Until now, aqueous inkjet inks have been used to produce printed matter with practical print quality on high-permeability and low-permeability printing substrates. In contrast, when printing on non-permeability substrates such as films, the liquid components present in the droplets of the aqueous inkjet ink do not penetrate into the printing substrate at all. As a result, the undried droplets coalesce and act as a force to reduce the surface area, resulting in whiteouts (a phenomenon in which areas on the printing substrate are not covered with the aqueous inkjet ink), i.e., poor solid coverage.

[0007] Furthermore, when an aqueous inkjet ink is printed on a non-permeable printing substrate, the aqueous inkjet ink does not penetrate at all, making it difficult to obtain sufficient substrate adhesion. Insufficient substrate adhesion to a non-permeable substrate can cause problems such as the film of the aqueous inkjet ink (ink film) peeling off after drying when the printed matter is rubbed, or when the printed matter is stored in a rolled or stacked state, pressure is applied to the printed surface (the surface to which the aqueous inkjet ink is applied), causing blocking (a phenomenon in which part of the ink film is taken up by the printing substrate when the printing substrate or the like that has stuck to the printed surface is peeled off).

[0008] In the label and packaging markets, which are expected to grow in the printing industry, films are often used as printing substrates. Therefore, the ability to produce printed materials with excellent print quality on non-permeable substrates such as films is extremely important from the perspective of expanding aqueous inkjet inks into these markets. Furthermore, when such printed materials are used on materials such as labels and surface-printed packaging, where the printed surface faces outward (the side that consumers can touch), there is a risk of uneven loading and contact with ethanol and other substances. From this perspective, improving blocking resistance and alcohol resistance are also important challenges for aqueous inkjet inks used on such printed materials.

[0009] Furthermore, the label and packaging markets require high productivity and print quality equal to or better than that of plate-based printing. To meet these demands, it is necessary to adopt inkjet heads with high design resolution and small droplet volume during ejection. Therefore, in order to expand the share of aqueous inkjet inks in the above markets, it is also necessary to ensure stable ejection from such inkjet heads.

[0010] Among the above-mentioned problems, a method of adding a resin having a binder function to an aqueous inkjet ink is generally known as a method of improving the adhesion to the printing substrate. In particular, by adjusting the structure and specifications of the resin having a binder function, the ink film becomes stronger, and it becomes possible to obtain printed matter that has excellent adhesion to the substrate as well as excellent blocking resistance, alcohol resistance, etc.

[0011] For example, Patent Document 1 discloses an inkjet ink containing water, a water-soluble organic solvent, pigments, and polycarbonate-modified urethane resin particles. Patent Document 1 claims that the inkjet ink produces printed matter with excellent abrasion resistance, ethanol resistance, and blocking resistance. However, the examples in Patent Document 1 do not evaluate ejection stability. Therefore, when the inkjet ink disclosed in the examples is printed using an inkjet head with a high design resolution, ejection stability may be impaired depending on the printing conditions. Furthermore, the drying time after printing in the examples is extremely long, at 1,800 seconds (30 minutes). The inventors conducted an evaluation under drying conditions that took productivity into account in the label and packaging markets, and found that the blocking resistance and alcohol resistance of printed matter were not necessarily good depending on the printing substrate used.

[0012] Patent Document 2 discloses a white ink composition containing, as a resin having binder properties, an acrylic resin having an acid value of 50 to 100 mgKOH / g and a glass transition temperature of 20 to 50°C. It also states that use of this white ink composition enables the production of printed materials with excellent blocking resistance. However, Patent Document 2 does not include a detailed evaluation of the ejection stability of the white ink composition, and follow-up tests by the present inventors have found that stable ejection is difficult depending on the ejection conditions.

[0013] On the other hand, a method for improving solid printing is known in which a surfactant is blended into the aqueous inkjet ink. In this case, after droplets of the aqueous inkjet ink land on a printing substrate, the surfactant quickly orients on the surface of the droplets, facilitating wetting and spreading of the ink onto the printing substrate, thereby improving solid printing.

[0014] For example, Patent Document 3 discloses an inkjet magenta ink containing a water-soluble organic solvent having a static surface tension of 22 to 32 mN / m, an HLB value of 2 to 8, and a hydroxyl group, and a surfactant having an HLB value of 1.5 to 8. Patent Document 3 also describes that a magenta ink having the above-described configuration can prevent white spots and the like in printed matter printed on poorly absorbent substrates (low-permeability substrates), and can improve ejection stability after long periods of standby. However, it has been found that the blocking resistance and alcohol resistance of printed matter are not necessarily good depending on the structure and specifications of the resin used in combination and the printing substrate used.

[0015] Additionally, Patent Document 4 describes that a water-based inkjet printing ink containing a polypropylene glycol monoalkyl ether, including dipropylene glycol monomethyl ether, and having a specified dipropylene glycol monomethyl ether content relative to the total amount of water-soluble organic solvent, can produce printed matter with excellent image density and substrate adhesion. However, Patent Document 4 does not provide detailed information on the specifications of the resin having binder function. In fact, when the resin specifically disclosed in the examples of Patent Document 4 was reproduced and evaluated, it was found that printed matter with poor blocking resistance and alcohol resistance could be obtained. Furthermore, it was also confirmed that when the water-based ink disclosed in the examples of Patent Document 4 was printed using an inkjet head with a high design resolution and a small droplet volume during ejection, ejection stability could be impaired.

[0016] As described above, there has not been a water-based inkjet ink that has excellent ejection stability regardless of the type of inkjet head used, that suppresses blocking, and that can produce printed matter with excellent solid coverage and alcohol resistance. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2016-6150 A [Patent Document 2] Japanese Patent Publication No. 2022-85548 [Patent Document 3] Japanese Patent Application Publication No. 2019-112608 [Patent Document 4] Japanese Patent Application Publication No. 2020-105299 Summary of the Invention [Problem to be solved by the invention]

[0018] Therefore, an object of one embodiment of the present invention is to provide an aqueous inkjet ink that has excellent ejection stability and is capable of producing printed matter that is excellent in solid coverage, blocking resistance, and alcohol resistance, regardless of the design resolution of the inkjet head used and the amount of droplets ejected. [Means for solving the problem]

[0019] 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.

[0020] That is, one embodiment of the present invention relates to the aqueous inkjet inks shown in [1] to [4] below, and to the printed matter produced using the aqueous inkjet inks shown in [5] below. [1] A water-based inkjet ink containing a colorant, a resin used for binder purposes, a water-soluble organic solvent, and a surfactant, the resin used for the binder contains a resin (R1) having a glass transition temperature of 50 to 130°C, the water-soluble organic solvent comprises dipropylene glycol monopropyl ether (S1), The surfactant includes a surfactant having an HLB value of 10 or less, the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the water-soluble organic solvent is 8 to 30 mass% on a mass basis, and The aqueous inkjet ink, wherein the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the resin (R1) is 10 to 90 mass % on a mass basis. [2] The aqueous inkjet ink according to [1], wherein the water-soluble organic solvent further contains a compound (S2) represented by the following general formula (1) and having 4 to 8 carbon atoms: General formula (1): H-(O-CH(R 1 )-CH2-O) n -R 2 (In general formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2. [3] The water-based inkjet ink according to [1] or [2], wherein the water-soluble organic solvent further contains a diol compound (S3) having 2 to 6 carbon atoms. [4] The aqueous inkjet ink according to [3], wherein the diol compound (S3) comprises an alkanediol having 3 to 6 carbon atoms. [5] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [4] on a printing substrate. [Effects of the Invention]

[0021] The aqueous inkjet ink according to one embodiment of the present invention has the advantage of being able to produce printed matter that is excellent in ejection stability, solid coverage, blocking resistance, and alcohol resistance, regardless of the design resolution of the inkjet head used and the amount of droplets ejected. DETAILED DESCRIPTION OF THE INVENTION

[0022] An aqueous inkjet ink according to one embodiment of the present invention (also referred to simply as "aqueous inkjet ink of this embodiment" in the present application) will be described below. Note that the present invention is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present invention.

[0023] As described above, adding a resin with binder function to an aqueous inkjet ink generally improves substrate adhesion to the printing substrate. Furthermore, incorporating a certain amount or more of a resin with binder function into the aqueous inkjet ink and using a resin with a high glass transition temperature (Tg) as the resin strengthens the ink film, enabling the production of printed matter with excellent blocking resistance and alcohol resistance. Furthermore, by allowing the resin to form a sufficient film on the printing substrate, the substrate adhesion, blocking resistance, and alcohol resistance described above are further improved. Therefore, the aqueous inkjet ink of this embodiment uses a resin (R1) with a glass transition temperature of 50 to 130°C. The use of resin (R1) makes the ink film less likely to deform, preventing blocking even when high pressure is applied to the printing surface for a long period of time, and also prevents the ink film from detaching from and eluting from the printing substrate when alcohol adheres to the printed matter.

[0024] However, resins with high glass transition temperatures also have high minimum film-forming temperatures (the minimum temperature at which a uniform and continuous film is formed when a solution containing the resin is applied to a substrate and then dried). As a result, aqueous inkjet inks containing such resins have the problem of poor film-forming properties after landing on a printing substrate. An ink film formed without sufficient film formation cannot exhibit sufficient film strength, and the above-mentioned blocking resistance and alcohol resistance are also reduced.

[0025] In such cases, a coalescing agent is typically used to improve film-forming properties. However, most coalescing agents typically used in aqueous inkjet inks are highly water-soluble. Because such coalescing agents have poor affinity for resins, when used in combination with, for example, the aforementioned resins with high glass transition temperatures, the expected improvement in film-forming properties may not be achieved. On the other hand, if the amount of a highly water-soluble coalescing agent is increased to improve film-forming properties, the resin in the aqueous inkjet ink may dissolve in the coalescing agent when water, the main component of the aqueous inkjet ink, evaporates near the nozzles of the inkjet head. This can lead to film formation, aggregation, or other problems in the aqueous inkjet ink near the nozzles, resulting in nozzle clogging and potentially deteriorating ejection stability and solid ink coverage of printed materials. This nozzle clogging is particularly likely to occur in inkjet heads with high design resolution and / or low droplet volume, which are commonly used in recent years, and is therefore an issue requiring improvement.

[0026] As a result of intensive research, the present inventors have discovered dipropylene glycol monopropyl ether (S1) as a suitable coalescent. Compared to the highly water-soluble coalescents that have been used in the past, dipropylene glycol monopropyl ether (S1) has high compatibility with resins while also exhibiting moderately high water solubility. As a result, it functions favorably as a coalescent in aqueous inkjet inks and can stably improve the film-forming properties of resins.

[0027] On the other hand, if the film-forming property is high, for example, even at room temperature, film formation, aggregation, etc. of the resin in the aqueous inkjet ink may occur in the vicinity of the nozzle of the inkjet head, which may cause the above-mentioned ejection stability and solid filling of the printed matter to deteriorate.

[0028] In contrast, the present invention aims to solve the above problem by further using a surfactant having an HLB value of 10 or less. Although the detailed mechanism is unknown, it is believed that surfactants having an HLB value of 10 or less have a high affinity with dipropylene glycol monopropyl ether (S1), and therefore, in the inkjet head, the surfactant suppresses the above-mentioned functional expression of dipropylene glycol monopropyl ether (S1). On the other hand, after droplets of the aqueous inkjet ink land on the printing substrate, as described below, the surfactant having an HLB value of 10 or less quickly orients itself to the droplet surface (air-liquid interface), eliminating components that inhibit the functional expression of dipropylene glycol monopropyl ether (S1), and the dipropylene glycol monopropyl ether (S1) is believed to effectively function as a film-forming aid. In this way, by using dipropylene glycol monopropyl ether (S1) in combination with a surfactant having an HLB value of 10 or less, it is possible to achieve both film-forming properties and prevention of nozzle clogging, even when a resin with a high glass transition temperature is used, and it is possible to improve ejection stability, solid coverage of printed matter, blocking resistance, and alcohol resistance.

[0029] On the other hand, when using an inkjet head with a high design resolution and / or a small droplet volume upon ejection, and / or when printing on a printing substrate with low surface energy, the above-mentioned measures alone may result in insufficient solid coverage of the printed material. Even in these cases, to obtain a printed material with good solid coverage, it is necessary to quickly wet and spread the aqueous inkjet ink on the printing substrate. To achieve this, as described above, a common method is to incorporate a surfactant into the aqueous inkjet ink to reduce the surface tension of the aqueous inkjet ink. As described above, the surfactant used in the aqueous inkjet ink of this embodiment has an HLB value of 10 or less. Surfactants with an HLB value of 10 or less orient extremely quickly to the droplet surface and are therefore effective in wetting and spreading the aqueous inkjet ink. However, surfactants with an HLB value of 10 or less have low solubility in water. As a result, surfactants with an HLB value of 10 or less may localize at the nozzle end surface of the inkjet head, destabilizing the air-liquid interface and potentially resulting in poor ejection stability.

[0030] Common water-soluble organic solvents, especially those with high water solubility, are thought to have low affinity with surfactants with an HLB value of 10 or less and with the resin (R1). On the other hand, dipropylene glycol monopropyl ether (S1) is thought to have high affinity with surfactants with an HLB value of 10 or less, has high compatibility with the resin (R1), and also has moderately high water solubility. Thus, dipropylene glycol monopropyl ether (S1) is thought to be highly compatible with all water-soluble organic solvents, resins (R1), and surfactants with an HLB value of 10 or less. Furthermore, in the aqueous inkjet ink of this embodiment, the ratio of the content of the water-soluble organic solvent to the content of the dipropylene glycol monopropyl ether (S1) and the ratio of the content of the resin (R1) to the dipropylene glycol monopropyl ether (S1) are determined, thereby ensuring the amount of dipropylene glycol monopropyl ether (S1) necessary to stabilize a surfactant with an HLB value of 10 or less in the aqueous inkjet ink. This prevents excessive orientation and localization of the surfactant having an HLB value of 10 or less at the nozzle end surface, thereby improving ejection stability. Furthermore, after droplets of the aqueous inkjet ink land on a printing substrate, the orientation of the surfactant having an HLB value of 10 or less at the interface is not hindered, allowing for sufficient wetting and spreading on the printing substrate, resulting in a printed product with good solid coverage.

[0031] On the other hand, the surfactant remains on the surface of the ink film after drying. In particular, if the surfactant is localized on the surface of the ink film, when a rolled-up printed matter is unrolled for post-processing, the localized surfactant will peel off from the printing substrate, causing blocking and deteriorating abrasion resistance and alcohol resistance.

[0032] In contrast, in the present invention, a predetermined amount of dipropylene glycol monopropyl ether (S1), which has both hydrophilic and hydrophobic properties, is blended, which makes it easier for surfactants with an HLB value of 10 or less to be compatible in the aqueous inkjet ink. That is, in the aqueous inkjet ink of this embodiment, dipropylene glycol monopropyl ether (S1) is thought to function to improve the film-forming properties of the resin as described above, as well as to make the surfactant compatible. As a result, surfactants with an HLB value of 10 or less are no longer excessively localized on the surface of the ink film, making it possible to further improve blocking resistance and alcohol resistance.

[0033] As described above, the aqueous inkjet ink of one embodiment of the present invention has excellent ejection stability, regardless of the design resolution of the inkjet head used and the amount of droplets ejected, and is capable of producing printed matter that is also excellent in solid coverage, blocking resistance, and alcohol resistance.

[0034] Next, each component constituting the aqueous inkjet ink of this embodiment will be described in detail below.

[0035] <Resin> The aqueous inkjet ink of this embodiment contains a resin. The resin includes a resin used as a binder, and the resin used as the binder includes a resin (R1) having a glass transition temperature of 50 to 130°C.

[0036] In general, resins contained in aqueous inkjet inks are used for binder purposes, pigment dispersion purposes, etc. The resins may be used for only one of these purposes, or may serve multiple purposes.

[0037] As described above, the aqueous inkjet ink of this embodiment contains the resin (R1) as a resin used in binder applications in order to strengthen the ink film and improve blocking resistance and alcohol resistance.

[0038] In this application, a resin used for binder purposes is also referred to as a "binder resin," and a resin used for pigment dispersion purposes is also referred to as a "pigment dispersion resin."

[0039] In this application, the term "binder resin" refers to a resin that can impart strength (fastness) and / or adhesion to a printing substrate to an ink film. As mentioned above, a strong ink film also has excellent blocking resistance and alcohol resistance. Examples of the binder resin include resins that constitute the main component of the ink film. On the other hand, examples of pigment-dispersing resins include resin microparticles that encapsulate pigments ("resin microparticles" will be described later), resins that have an adsorption rate for pigments of 35% by mass or more, and the like.

[0040] As an example of a method for measuring the adsorption rate for the pigment, a pigment dispersion (or an ink containing no solids other than the resin being investigated) diluted with water as necessary is centrifuged until the supernatant becomes transparent (for example, a 5 mL sample is centrifuged at 80,000 rpm for 4 hours), and the amount of resin contained in the recovered supernatant is then measured (for example, the supernatant is left to stand in a 100°C environment to completely remove the liquid components, and the mass of the evaporation residue is measured and used as the amount of resin).The adsorption rate can then be calculated by subtracting the amount of resin contained in the supernatant from the amount of resin (referred to as WR0 [g]) contained in the pigment dispersion (or ink) that has been centrifuged, and then dividing the resulting value by WR0.

[0041] <Resin (R1)> As described above, the glass transition temperature (Tg) of the resin (R1) is 50 to 130° C., more preferably 80 to 130° C., and particularly preferably 90 to 130° C. By using a resin (R1) having the above glass transition temperature, the ejection stability as well as the blocking resistance and alcohol resistance of the printed matter are improved, as described above.

[0042] The glass transition temperature of a resin can be measured using a method in accordance with JIS K 7121:2012. Specifically, approximately 10 mg of the target resin sample is placed in an aluminum sample pan whose mass has been measured in advance, and the mass is measured again. The pan is then sealed with a lid. This sample container and a sample pan prepared without the resin are then placed in a holder in a Shimadzu DSC-60 (differential scanning calorimeter). Measurements are performed at a temperature increase rate of 10°C / min to obtain a DSC chart. The intersection of the low-temperature baseline and the tangent to the inflection point of the DSC curve is then determined, and the temperature at this intersection is taken as the glass transition temperature. Indium is used for temperature calibration.

[0043] On the other hand, for acrylic resins, the value calculated by the following formula (2) can be used as the glass transition temperature.

[0044] Formula (2): 1 / Tg = Σ(Wn / Tgn)

[0045] In the above formula (2), Tg represents the glass transition temperature (K) of the resin, Wn represents the mass fraction of the structural unit consisting of polymerizable monomer n that constitutes the resin, and Tgn represents the glass transition temperature (K) of the homopolymer of each structural unit. For the Tgn, for example, values ​​described in "Polymer Handbook (4th Edition)" (Wiley, 1998) can be used.

[0046] The acid value of the resin (R1) is preferably 0 to 100 mgKOH / g, more preferably 0 to 80 mgKOH / g, and particularly preferably 5 to 60 mgKOH / g. By setting the acid value of the resin (R1) within the above range, film formation and aggregation of the aqueous inkjet ink in the vicinity of the nozzles of the inkjet head can be prevented, making it easier to improve ejection stability, and also improving the blocking properties and alcohol resistance of the printed matter.

[0047] In this application, the "acid value of a resin" refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In this application, the acid value is calculated using the following method. For example, if a resin contains Wa mass% of a polymerizable monomer having na acid groups with a valence of va per molecule and a molecular weight of Ma, the acid value (mg KOH / g) can be calculated using the following formula (3):

[0048] Formula (3): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0049] In the above formula (3), the number "56.11" is the molecular weight of potassium hydroxide.

[0050] Generally, water-soluble resins and resin particles are known as the forms of resins used in aqueous inkjet inks. The resin (R1) may be a water-soluble resin or resin particles. Furthermore, a combination of a water-soluble resin and resin particles may be used.

[0051] In this application, 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, among the water-insoluble resins, a resin that is dispersed in water in the form of particles and has a volume-based median diameter (also referred to as "D50" in this application) of 10 to 1,000 nm is referred to as a "resin particle."

[0052] In this application, D50 is a value measured in an environment of 25°C using a dynamic light scattering particle size distribution measuring device such as "Nanotrac UPA-EX150" manufactured by Microtrac-Bell.

[0053] When the resin (R1) is a fine resin particle, in order to achieve a high level of both ejection stability and the strength of the printed matter, which affects blocking resistance and alcohol resistance, the D50 of the fine resin particles is preferably 10 to 300 nm or less, more preferably 20 to 250 nm or less, and even more preferably 25 to 200 nm or less.

[0054] Examples of resins that can be used as the resin (R1) include acrylic resins, styrene resins, maleic acid resins, urethane resins, polyester resins, vinyl chloride resins, vinyl chloride-vinyl acetate resins, polyolefin resins, vinyl alcohol resins, etc. These resins may be used alone or in combination of two or more.

[0055] Among these resins, 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 (R1), because the use of these resins can easily improve the blocking resistance and alcohol resistance of printed matter.

[0056] In this application, 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 (styrene, styrene derivatives, etc. may also be used). However, resins containing maleic acid (anhydride) as a polymerizable monomer are excluded from the above-mentioned acrylic resin. In addition, "(Maleic anhydride)" in the present application refers to at least one selected from "maleic acid" and "maleic anhydride". Meanwhile, the term "maleic acid resin" in the present application refers to a resin using at least maleic acid (anhydride) as a polymerizable monomer. The maleic acid resin may further use one or more polymerizable monomers selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0057] From the viewpoint of obtaining an aqueous inkjet ink that is excellent in all of ejection stability, solid coverage of printed matter, blocking resistance, and alcohol resistance, the content of the resin (R1) contained in the aqueous inkjet ink of this embodiment is preferably 1.4 to 18 mass %, more preferably 2.2 to 15 mass %, and particularly preferably 2.5 to 10 mass %, calculated as solid content, of the total amount of the aqueous inkjet ink.

[0058] Furthermore, from the viewpoints of improving the substrate adhesion of the ink film to the printing substrate and obtaining printed matter with excellent blocking resistance, alcohol resistance, etc., the content of resin (R1) is preferably 50 to 100 mass % of the total amount of resins contained in the aqueous inkjet ink, and more preferably 60 to 90 mass %.

[0059] Other binder resins The aqueous inkjet ink of this embodiment may contain a binder resin other than the above-mentioned resin (R1), i.e., a resin having a glass transition temperature of less than 50°C and / or a resin having a glass transition temperature of more than 130°C. In the present application, binder resins other than resin (R1) are also referred to as "other binder resins." When the aqueous inkjet ink of this embodiment contains other binder resins, it becomes easy to significantly improve the blocking resistance and alcohol resistance of printed matter.

[0060] The acid value of the other binder resin is preferably 0 to 100 mgKOH / g, more preferably 0 to 80 mgKOH / g, and particularly preferably 5 to 60 mgKOH / g. By adjusting the acid value of the other binder resin within the above acid value range, it is possible to simultaneously improve the ejection stability, as well as the blocking resistance and alcohol resistance of the printed matter.

[0061] On the other hand, the other binder resin may be a water-soluble resin or resin particles, or a combination of a water-soluble resin and resin particles may be used.

[0062] The types of resins that can be used as the other binder resins are the same as those for the resin (R1). Among these resins, it is preferable to use one or more resins selected from the group consisting of acrylic resins, urethane resins, polyester resins, and polyolefin resins as the resin (R1). This is because the use of these resins can easily improve the blocking resistance and alcohol resistance of printed matter.

[0063] When the aqueous inkjet ink of this embodiment contains another binder resin, from the viewpoint of obtaining an aqueous inkjet ink that is excellent in all of ejection stability, blocking resistance of printed matter, and alcohol resistance of printed matter, the content of the other binder resin is preferably 0.5 to 8 mass %, more preferably 1 to 6 mass %, and particularly preferably 1.5 to 5 mass %, calculated as solid content, of the total amount of the aqueous inkjet ink.

[0064] Furthermore, from the viewpoint of fully exerting the effects of the resin (R1) described above and obtaining an aqueous inkjet ink that is excellent in all of ejection stability, solid coverage of printed matter, blocking resistance, and alcohol resistance, when the aqueous inkjet ink of this embodiment contains another binder resin, the content of the other binder resin is preferably 5 to 25 mass %, and more preferably 8 to 18 mass %, of the total amount of binder resin contained in the aqueous inkjet ink.

[0065] From the viewpoint of obtaining an aqueous inkjet ink that is excellent in all of ejection stability, solid coverage of printed matter, blocking resistance, and alcohol resistance, the total content of binder resins contained in the aqueous inkjet ink of this embodiment is preferably 1.5 to 25 mass %, more preferably 2.0 to 20 mass %, and particularly preferably 2.5 to 16 mass %, calculated as solid content, of the total amount of the aqueous inkjet ink.

[0066] For the same reasons as above, the total content of the binder resins is preferably 50 to 100% by mass, and more preferably 65 to 95% by mass, of the total amount of resins contained in the aqueous inkjet ink.

[0067] <Pigment dispersion resin> When the aqueous inkjet ink of this embodiment contains a pigment as a colorant, it is preferable to use a pigment dispersing resin, as this allows for easy adjustment and improvement of ejection stability. The pigment dispersing resin may contain a resin other than the resin used for the binder (resin (R1) and other binder resins), or the resin used for the binder may also be used for pigment dispersion (in other words, resin (R1) and / or other binder resins may also serve as pigment dispersing resins).

[0068] The acid value of the pigment dispersion resin is preferably 70 to 450 mgKOH / g, more preferably 120 to 400 mgKOH / g, and particularly preferably 150 to 350 mgKOH / g. By setting the acid value within this range, it is possible to maintain the dispersion stability of the pigment, and stable ejection from the inkjet head is possible regardless of the usage conditions. This is also advantageous in that it enhances affinity with dipropylene glycol monopropyl ether (S1), and the pigment dispersed by the pigment dispersion resin is uniformly dispersed in the aqueous inkjet ink, thereby improving the blocking resistance and alcohol resistance of the printed matter.

[0069] The pigment dispersing resin may be a water-soluble resin or resin particles, or a combination of a water-soluble resin and resin particles.

[0070] In addition, examples of resins that can be used as the pigment dispersing resin include acrylic resins, styrene resins, maleic acid resins, urethane resins, polyester resins, polyolefin resins, etc. These resins may be used alone or in combination of two or more.

[0071] Among these resins, it is preferable to use one or more resins selected from the group consisting of acrylic resins, urethane resins, and polyester resins as the pigment dispersing resin. The use of these resins increases the affinity with the resin (R1) and also improves the affinity with the dipropylene glycol monopropyl ether (S1), so that the pigment dispersed by the pigment dispersing resin is uniformly dispersed in the aqueous inkjet ink, improving the blocking resistance and alcohol resistance of the printed matter.

[0072] From the viewpoints of pigment dispersion stability and ejection stability, as well as blocking resistance and alcohol resistance in printed matter, the content of the pigment dispersing resin in the aqueous inkjet ink of this embodiment is preferably 1 to 50 mass % in terms of solid content, and more preferably 2 to 35 mass % relative to the pigment content.

[0073] <Water-soluble organic solvent> The aqueous inkjet ink of this embodiment contains a water-soluble organic solvent, and as described above, the water-soluble organic solvent contains dipropylene glycol monopropyl ether (S1). Note that in this application, the term "water-soluble organic solvent" refers to a solvent that has a solubility of 1% by mass or more in water at 25°C and is liquid at 25°C.

[0074] <Dipropylene glycol monopropyl ether (S1)> The content of dipropylene glycol monopropyl ether (S1) in the aqueous inkjet ink of this embodiment is preferably 0.9 to 8 mass %, more preferably 1.2 to 7 mass %, and even more preferably 1.5 to 6 mass % of the total amount of the aqueous inkjet ink. By keeping the content of dipropylene glycol monopropyl ether (S1) within the above range, the function as a film-forming aid is suitably exhibited, and by suitably compatibilizing surfactants with an HLB value of 10 or less, the blocking resistance and alcohol resistance of printed matter are improved.

[0075] On the other hand, as described above, the content of dipropylene glycol monopropyl ether (S1) is preferably specified with respect to each of the content of resin (R1) and the content of surfactant having an HLB value of 10 or less.

[0076] Specifically, from the viewpoint of making the dipropylene glycol monopropyl ether (S1) function as a film-forming aid for the resin (R1) to improve the blocking resistance and alcohol resistance of printed matter, and further from the viewpoint of being able to maintain good ejection stability of the aqueous inkjet ink, the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the resin (R1) is preferably from 10 to 90 mass%, more preferably from 20 to 80 mass%, and even more preferably from 30 to 70 mass% on a mass basis.

[0077] Furthermore, from the viewpoints of ensuring a certain amount of dipropylene glycol monopropyl ether (S1), suppressing excessive orientation of the surfactant having an HLB value of 10 or less at the nozzle end surface of the inkjet head, improving ejection stability, and not hindering the orientation of the surfactant having an HLB value of 10 or less at the interface after droplets of the aqueous inkjet ink have landed on the printing substrate, resulting in a printed matter with good solid coverage, the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the water-soluble organic solvent is preferably 8 to 30 mass %, more preferably 9 to 28 mass %, and even more preferably 10 to 26 mass %.

[0078] <Water-soluble organic solvent (S2) represented by general formula (1)> In one embodiment, the aqueous inkjet ink of this embodiment preferably contains, in addition to the dipropylene glycol monopropyl ether (S1), a compound (S2) represented by the following general formula (1) and having 4 to 8 carbon atoms:

[0079] General formula (1): H-(O-CH(R 1 )-CH2-O) n -R 2

[0080] In the above general formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2.

[0081] The compound (S2) has high affinity with dipropylene glycol monopropyl ether (S1), surfactants with an HLB value of 10 or less, and water. Therefore, excessive orientation of the surfactant with an HLB value of 10 or less can be suppressed at the nozzle end surface of the inkjet head, while at the same time, film formation and aggregation of the resin at the nozzle end surface caused by dipropylene glycol monopropyl ether (S1) can be suppressed, thereby improving ejection stability. Furthermore, the compound (S2) has a higher evaporation rate than the dipropylene glycol monopropyl ether (S1), and therefore dries quickly when the aqueous inkjet ink lands on the printing substrate. This allows the surfactant with an HLB value of 10 or less to function optimally, improving solid coverage and also effectively demonstrating the film-forming effect of dipropylene glycol monopropyl ether (S1).

[0082] Examples of compounds that can be used as the compound (S2) represented by the above general formula (1) and having 4 to 8 carbon atoms include ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monotertiary butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, etc. These compounds may be used alone or in combination of two or more. Among these compounds, it is preferable to use one or more compounds selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Although the detailed mechanism is unknown, the use of these compounds improves ejection stability and solid coverage of printed matter.

[0083] When the aqueous inkjet ink of this embodiment contains the compound (S2), the content thereof is preferably 0.3 to 10 mass %, and more preferably 0.5 to 5 mass %, of the total amount of the aqueous inkjet ink.

[0084] <Diol compounds with 2 to 6 carbon atoms (S3)> Meanwhile, in addition to the above-described compound (S2), the aqueous inkjet ink of this embodiment also preferably uses a diol compound (S3) having 2 to 6 carbon atoms. The above-described compound (S2) and diol compound (S3) can also be used in combination. The diol compound (S3) has both hydrophilic properties due to its multiple hydroxyl groups and hydrophobic properties due to its alkylene groups. Because the diol compound (S3) is particularly hydrophilic compared to the above-described water-soluble organic solvents, it is particularly effective in improving ejection stability. Meanwhile, since the diol compound (S3) does not have a high affinity for surfactants with an HLB value of 10 or less, after impacting the printing substrate, the surfactant with an HLB value of 10 or less quickly orients at the interface, improving solid coverage in the printed matter. Furthermore, since the diol compound (S3) has a high affinity with the dipropylene glycol monopropyl ether (S1), the resin (R1) can be homogenized in the aqueous inkjet ink via the dipropylene glycol monopropyl ether (S1), which is thought to facilitate improvement in the blocking resistance and alcohol resistance of the resulting printed matter.

[0085] In the aqueous inkjet ink of this embodiment, it is preferable to use alkanediols having 3 to 6 carbon atoms as the diol compound (S3), and it is particularly preferable to use 1,2-propanediol and / or 1,2-butanediol. These compounds are particularly hydrophilic but do not have excessive affinity with surfactants, so they do not inhibit the orientation of the surfactant at the interface, maximizing its effectiveness and making it easier to obtain printed matter with good solid coverage. Furthermore, after landing on the printing substrate, these compounds volatilize without leaving any residue, resulting in printed matter with excellent blocking resistance and alcohol resistance.

[0086] From the viewpoint of suitably achieving the above-mentioned effects and improving the ejection stability, blocking resistance, and alcohol resistance of the printed matter, the content of the diol compound (S3) having 2 to 6 carbon atoms is preferably from 5 to 27 mass%, more preferably from 7 to 25 mass%, and even more preferably from 9 to 23 mass%, of the total amount of the aqueous inkjet ink.

[0087] <Other water-soluble organic solvents> The aqueous inkjet ink of this embodiment may contain water-soluble organic solvents other than the dipropylene glycol monoalkyl ether solvent (S1), the compound (S2), and the diol compound (S3) (referred to as "other water-soluble organic solvents" in this application).

[0088] In the aqueous inkjet ink of the present embodiment, as the other water-soluble organic solvents, alkanetriols (however, those having 3 to 6 carbon atoms); polyalkylene glycols (however, those having 7 to 9 carbon atoms and having an alkylene glycol group of ethylene glycol group (ethylene oxide group) or propylene glycol group (propylene oxide group)); polyethylene glycol monoalkyl ethers (however, those having 3 or 4 ethylene oxide groups and having a terminal alkyl group with 1 to 4 carbon atoms), tripropylene glycol monoalkyl ethers (however, those having a terminal alkyl group with 1 to 4 carbon atoms); alkylene glycol dialkyl ethers (however, having an alkylene glycol group of ethylene glycol group or propylene glycol group, having 1 to 4 of such alkylene glycol groups, and having a terminal alkyl group with 1 to 4 carbon atoms each); lactams (however, those having 5 to 7 atoms constituting the lactam ring. Also, a C1-C2 alkyl group, a C1-C2 hydroxyalkyl group, or a vinyl group may be bonded to the nitrogen atom and / or carbon atom constituting the lactam ring); alkanolamines (however, having 1 amino group, having 1 to 3 hydroxyl groups, and having 3 to 9 carbon atoms); etc. can be used. These other water-soluble organic solvents may be used alone or in combination of two or more.

[0089] The total content of the water-soluble organic solvents contained in the aqueous inkjet ink of the present embodiment is preferably 10 to 30% by mass, more preferably 11 to 28% by mass, and still more preferably 12 to 26% by mass in the total amount of the aqueous inkjet ink. By setting the total content of the water-soluble organic solvents within the above range, an aqueous inkjet ink excellent in ejection stability, and all of solid filling of printed matter, blocking resistance, and alcohol resistance can be obtained.

[0090] <Surfactant> <Surfactant with an HLB value of 10 or less> The aqueous inkjet ink of this embodiment contains a surfactant having an HLB value of not more than 10. From the viewpoint of the orientation speed onto the droplet surface, the ability to suppress deterioration in the ejection stability of the aqueous inkjet ink when used in combination with dipropylene glycol monopropyl ether (S1), and the viewpoint of further improving blocking resistance, the HLB value is preferably 3 to 9, and more preferably 4 to 8. In particular, surfactants with an HLB value of 10 or less (preferably 9 or less, more preferably 8 or less) orient to the droplet surface at a high rate, and therefore, after orientation, components that inhibit the functional expression of dipropylene glycol monopropyl ether (S1) disappear, allowing the dipropylene glycol monopropyl ether (S1) to function satisfactorily as a film-forming aid. As a result, it is easy to obtain an aqueous inkjet ink with excellent film-forming properties, even when a resin with a high glass transition temperature is used.

[0091] The HLB (Hydrophile-Lipophile Balance) value in this application is one of the parameters that represent the hydrophilicity and hydrophobicity of a material. There are various methods for calculating the HLB value, such as the Griffin method, the Davis method, and the Kawakami method. In this application, the value calculated using the Griffin method is used as the HLB value of a surfactant.

[0092] In the Griffin method, the HLB value is calculated using the molecular weight of the target compound according to the following formula (4): The smaller the HLB value, the more hydrophobic the target compound is, and the larger the HLB value, the more hydrophilic the compound is.

[0093] Formula (4): HLB value = 20 × (total molecular weight of hydrophilic parts) ÷ (molecular weight of material)

[0094] Any conventionally known surfactant can be used as the surfactant having an HLB value of 10 or less, and it is particularly preferable to use a nonionic surfactant. Since a nonionic surfactant can easily have an HLB value of 10 or less, it is easy to achieve the above-mentioned effects. Furthermore, the use of a nonionic surfactant easily improves alcohol resistance.

[0095] Further, examples of the types of compounds that can be used as the nonionic surfactant include acetylene diol-based surfactants, acetylene monool-based surfactants, siloxane-based surfactants, fluorine-based surfactants, polyethylene glycol monoalkyl ether-based surfactants, polyethylene glycol alkylamine-based surfactants, glycerin fatty acid ester-based surfactants, and sorbitan fatty acid ester-based surfactants.

[0096] The "polyethylene glycol monoalkyl ether surfactant" includes compounds in which the alkyl group at the molecular terminal has 6 or more carbon atoms and has a total of two or more ethylene oxide groups. The "polyethylene glycol alkylamine surfactant" includes compounds in which the alkyl group at the molecular terminal has 6 or more carbon atoms and has a total of two or more ethylene oxide groups. The "polyethylene glycol monoalkyl ether surfactant" and the "polyethylene glycol alkylamine surfactant" may both have a propylene oxide group.

[0097] The surfactants listed above may be used alone or in combination of two or more. Examples of the combination of two or more surfactants include a combination of one or more surfactants selected from the group consisting of an acetylenic diol surfactant and a siloxane surfactant, an acetylenic diol surfactant and a polyethylene glycol monoalkyl ether surfactant, an acetylenic diol surfactant and a glycerin fatty acid ester surfactant, a siloxane surfactant and a polyethylene glycol monoalkyl ether surfactant, a siloxane surfactant and a glycerin fatty acid ester surfactant, and a polyethylene glycol monoalkyl ether surfactant and a glycerin fatty acid ester surfactant.

[0098] In the aqueous inkjet ink of this embodiment, it is preferable to use one or more surfactants selected from the group consisting of acetylene diol surfactants, siloxane surfactants, and polyethylene glycol monoalkyl ether surfactants as the surfactant having an HLB value of 10 or less. The use of these surfactants not only particularly improves solid coverage, blocking resistance, and alcohol resistance in printed matter, but also makes it easier to obtain an aqueous inkjet ink with excellent ejection stability regardless of the design resolution of the inkjet head used or the droplet volume during ejection.

[0099] <Acetylene diol surfactants with an HLB value of 10 or less> Examples of acetylene diol surfactants having an HLB value of 10 or less include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, and 3,6-diisopropyl-2,7-dimethyloct-4-yne-3,6-diol. , octadec-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol, and ethylene oxide and / or propylene oxide modified versions of the above-listed compounds. However, the above-listed compounds may be used alone or in combination of two or more. Furthermore, these compounds may be synthesized by conventionally known synthesis methods or may be commercially available products. Examples of commercially available products include Surfynol 61, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420, 440, 2502, SE, SE-F, Dynol 604 (manufactured by Evonik Chemical Industry Co., Ltd.), Olfine E1004, PD-001, PD-002W, and PD-004 (manufactured by Nissin Chemical Industry Co., Ltd.).

[0100] Among these, it is preferable to select one or more selected from the group consisting of Surfynol 440, Surfynol 2502, Dynol 604, and Olfine E1004 as the acetylenic diol having an HLB value of 10 or less, because the above-mentioned mechanism functions effectively and is effective in wetting and spreading the aqueous inkjet ink, and further because the affinity with dipropylene glycol monopropyl ether (S1) is improved, resulting in good ejection stability. It is more preferable to use Surfynol 2502 and / or Dynol 604, and it is particularly preferable to use Surfynol 2502.

[0101] Surfynol 440 is an ethylene oxide modified product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of ethylene oxide groups added: 3.5), Surfynol 2502 is an ethylene oxide and propylene oxide modified product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of ethylene oxide groups added: 5, average number of moles of propylene oxide groups added: 2), Dynol 604 is an ethylene oxide modified product of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (average number of moles of ethylene oxide groups added: 4), and Olfine E1004 is an ethylene oxide modified product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of ethylene oxide groups added: 4).

[0102] <Siloxane surfactants with an HLB value of 10 or less> When the aqueous inkjet ink of this embodiment contains a siloxane-based surfactant having an HLB value of 10 or less, a compound having a structure represented by the following general formula (5) can be used as the siloxane-based surfactant having an HLB value of 10 or less.

[0103] General formula (5): [ka]

[0104] In the general formula (5), p is an integer of 0 to 99, and q is an integer of 1 to 100, provided that p+q is an integer of 1 to 100. 3 is an alkyl group having 1 to 6 carbon atoms or a structure represented by the following general formula (6), and R 4 is a methyl group or a structure represented by the following general formula (6), where R 4 When R is a methyl group, p is 0. 3 and R 4 At least one of the groups has a structure represented by the following general formula (6) (R 3 and R4 However, both may have a structure represented by the following general formula (6).

[0105] General formula (6): [ka]

[0106] In the general formula (6), r is an integer of 1 to 6, s is an integer of 1 to 50, and t is an integer of 0 to 50, provided that s+t is an integer of 1 to 100. 5 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.

[0107] The siloxane-based surfactant having an HLB value of 10 or less may be used alone or in combination of two or more kinds. In addition, those synthesized by a conventionally known synthesis method may be used, or commercially available products may be used.

[0108] When the aqueous inkjet ink of this embodiment contains a siloxane surfactant having an HLB value of 10 or less, from the viewpoint of improving solid coverage, blocking resistance, and alcohol resistance in printed matter, it is preferable to use a side-chain polyether-modified siloxane having 4 to 12 silicon atoms and at least 1 to 10 ethylene oxide groups as the siloxane surfactant having an HLB value of 10 or less.

[0109] <Polyethylene glycol monoalkyl ether surfactants with an HLB value of 10 or less> When the aqueous inkjet ink of the present embodiment contains a polyethylene glycol monoalkyl ether-based surfactant having an HLB value of 10 or less, as the polyethylene glycol monoalkyl ether-based surfactant, those synthesized by a conventionally known synthesis method may be used, or commercially available products may be used. Hereinafter, examples of commercially available products of polyethylene glycol monoalkyl ether-based surfactants having an HLB value of 10 or less include Emulgen series such as Emulgen 103, 104P, 105, 306P, etc. (manufactured by Kao Corporation), Braunon series such as Braunon EL-1502.2, 1503P, CH-302L, 305, SR-702L, 705, BE-5, etc. (manufactured by Aoki Yushi Kogyo Co., Ltd.), Nonion series such as Nonion K-204, S-202, ID-203, HT-505, 507, etc. (manufactured by NOF Corporation), Lutensol series such as Lutensol XP30 (manufactured by BASF), Newcol series such as Newcol 2302, 2303, 2304, 2502, NT-3, etc. (manufactured by Nippon Emulsion Co., Ltd.), and the like. Only one of the above-listed products may be used, or two or more kinds may be used in combination.

[0110] The content of the surfactant having an HLB value of 10 or less contained in the aqueous inkjet ink of the present embodiment is preferably 0.2 to 4.0% by mass, more preferably 0.3 to 3.5% by mass, and particularly preferably 0.5 to 3.0% by mass in the total amount of the aqueous inkjet ink. By using within the above range, it becomes possible to achieve all of ejection stability, solid filling in printed matter, and blocking resistance at a high level.

[0111] <Surfactant with an HLB value greater than 10> The aqueous inkjet ink of the present embodiment may contain a surfactant other than the surfactant having an HLB value of 10 or less, that is, a surfactant having an HLB value greater than 10. Any conventionally known surfactant can be used as the surfactant having an HLB value of greater than 10. In particular, when a nonionic surfactant is used as the surfactant having an HLB value of 10 or less, it is preferable to use a nonionic surfactant for the surfactant having an HLB value of greater than 10. By using nonionic surfactants for both, the mutual affinity is improved, making it easier to improve ejection stability. Furthermore, nonionic surfactants are preferably used in view of their improved resistance to alcohol.

[0112] When a nonionic surfactant is used as the surfactant having an HLB value of greater than 10, the types of compounds that can be used as the nonionic surfactant are the same as those described above for surfactants having an HLB value of 10 or less. Among them, it is preferable to use an acetylene diol surfactant as the nonionic surfactant having an HLB value of greater than 10, because it has excellent affinity with dipropylene glycol monopropyl ether (S1), improves discharge stability, and further improves blocking resistance and alcohol resistance.

[0113] When an acetylene diol surfactant having an HLB value of more than 10 is used, one synthesized by a conventionally known synthesis method may be used, or a commercially available product may be used. Examples of such commercially available products include Surfynol 465, 485, Dynol 607 (manufactured by Evonik), Olfine E1006, E1010, E1020, EXP.4200, and EXP.4123 (manufactured by Nissin Chemical Industry Co., Ltd.). The compounds listed above may be used alone or in combination of two or more.

[0114] The total amount of surfactants contained in the aqueous inkjet ink of this embodiment is preferably 0.3 to 5 mass %, more preferably 0.4 to 4 mass %, and particularly preferably 0.5 to 3 mass % of the total amount of the aqueous inkjet ink. By keeping the total amount of surfactants within the above range, the ejection stability of the aqueous inkjet ink, as well as the solid filling, blocking resistance, and abrasion resistance of the printed matter are all improved.

[0115] Furthermore, from the viewpoint of improving all of the ejection stability, solid coverage of printed matter, and blocking resistance, the ratio of the content of surfactants having an HLB value of 10 or less to the content of surfactants having an HLB value of more than 10 (content of surfactants having an HLB value of 10 or less / content of surfactants having an HLB value of more than 10) is preferably 0.3 to 3, and particularly preferably 0.5 to 2, by mass.

[0116] <Coloring agent> The aqueous inkjet ink of this embodiment contains a colorant. Pigments and / or dyes can be used as the colorant, but it is preferable for the aqueous inkjet ink of this embodiment to contain a pigment, as this improves the blocking resistance and alcohol resistance of the printed matter. Furthermore, 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. Namely, as red pigments, CI 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, 144, 146, 147, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 184, 185, 188, 202, 207, 209, 221, 254, 255, 260, 264, 266, 269, 282; Violet pigments include CI Pigment Violet 19, 23, 29, 32, 36, 37, 42, and 50; As orange pigments, CI 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, CI Pigment Blue 15, 15:3, 15:4, 15:6, 16, 60, 64, 79; As green pigments, CI Pigment Green 7, 10, 36, 48; Yellow pigments include CI Pigment Yellow 1, 2, 3, 5, 12, 13, 14, 16, 17, 24, 73, 74, 83, 87, 93, 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, and 213; Black pigments include CI Pigment Black 1, 7, and 11; White pigments include CI Pigment White 4, 5, 6, 21, and the like. These pigments may be used alone or in combination of two or more. Also, a solid solution of two or more of the pigments listed above may be used as a pigment.

[0117] In one embodiment, the aqueous inkjet ink of this embodiment preferably uses a condensed disazo pigment as the pigment. While the detailed mechanism is unclear, it is believed that dipropylene glycol monopropyl ether and the condensed disazo pigment exhibit good compatibility, while dipropylene glycol monopropyl ether (S1) inhibits the adsorption of surfactants with an HLB value of 10 or less to the pigment surface, thereby preventing the dispersion of the condensed disazo pigment from being disrupted. As a result, the jetting stability of the aqueous inkjet ink is improved, and the condensed disazo pigment is uniformly present in the ink film without localization, thereby improving the density, blocking resistance, and alcohol resistance of the printed material. Among the pigments listed above, examples of condensed disazo pigments include red pigments such as CI Pigment Red 144, 166, and 221, and yellow pigments such as CI Pigment Yellow 93, 95, 128, 155, and 166.

[0118] The content of the pigment in the aqueous inkjet ink of this embodiment is adjusted depending on the intended use of the printed matter produced using the aqueous inkjet ink, but is preferably 0.5 to 30% by 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 1 to 15% by mass, even more preferably 1.2 to 10% by mass, and particularly preferably 1.5 to 8% by mass, in order to obtain printed matters with excellent density, print quality, and blocking resistance 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% by mass, even more preferably 10 to 22% by mass, and particularly preferably 12 to 20% by mass, in order to obtain printed matters with excellent hiding power and blocking resistance without deteriorating the jetting stability of the aqueous white ink.

[0119] <Other ingredients> In addition to the components described above, the aqueous inkjet ink of this embodiment may contain one or more components selected from the group consisting of a pH adjuster, a preservative, a crosslinking agent, an ultraviolet absorber, and an infrared absorber. These components may each be one or more conventionally known compounds.

[0120] <Method for manufacturing water-based inkjet ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. For example, when a pigment is used as the colorant, a pigment dispersion is produced by dispersing the pigment in a medium containing at least water (aqueous medium) using a pigment dispersing resin. On the other hand, when a dye is used as the colorant, a dye solution is produced by dissolving the dye in an aqueous medium. Water, resin (R1), dipropylene glycol monopropyl ether (S1), a surfactant with an HLB value of 10 or less, and the like are then added to the pigment dispersion and / or dye solution, followed by thorough stirring and mixing, followed by removal of coarse particles by techniques such as filtration and centrifugation. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the above-described method.

[0121] <Characteristics of water-based inkjet ink> The aqueous inkjet ink of this embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. This viscosity range allows stable ejection of droplets of the aqueous inkjet ink, 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 aqueous inkjet ink of this embodiment has a viscosity of 4 to 10 mPa·s at 25°C, the aqueous inkjet ink can be ejected stably even when an inkjet head with a design resolution of 1,200 dpi or higher is used. In this application, 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.

[0122] Furthermore, in order to obtain an aqueous inkjet ink that is excellent in ejection stability and solid coverage of printed matter, the aqueous inkjet ink of this embodiment preferably has a static surface tension of 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m, at 25° C. In the present application, 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 such as the CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0123] Furthermore, when the aqueous inkjet ink of this embodiment contains a pigment as a colorant, in order to achieve high levels of ejection stability, blocking resistance, alcohol resistance, and density or hiding power in the printed matter, the volume-based median diameter (D50) of the pigment is preferably 30 to 450 nm, more preferably 50 to 350 nm, and particularly preferably 70 to 300 nm.

[0124] <Water-based inkjet ink set> The aqueous inkjet ink of this embodiment may be used alone, or two or more aqueous inkjet inks may be combined to form an aqueous inkjet ink set. Examples of 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 that further includes a white aqueous inkjet ink (aqueous white ink) in addition to the process color ink set. It is more 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.

[0125] <Ink-pretreatment liquid set> The aqueous inkjet ink of this embodiment and the aqueous inkjet ink set described above can also be used in a form 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, a layer (ink aggregation layer) can be formed that intentionally aggregates solid components (pigments, binder resins, etc.) contained in the aqueous inkjet ink. By depositing the aqueous inkjet ink on the ink aggregation layer, coalescence and color mixing of droplets of the aqueous inkjet ink can be prevented, and excessive wetting and spreading can be suppressed, significantly improving the print quality of printed matter, including solid fills.

[0126] 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.

[0127] <Inkjet printing method> The aqueous inkjet ink of this embodiment is used in an inkjet printing system. An example of a method (inkjet printing method) performed in this inkjet printing system is a method including, in this order, a step of ejecting the aqueous inkjet ink of this embodiment onto a printing substrate (an ejecting step), and a step of drying the aqueous inkjet ink on the printing substrate using a drying mechanism (a drying step).

[0128] ≪Discharge process≫ In the ejection step, the aqueous inkjet ink is ejected from an inkjet head. The inkjet head can be operated in two ways: a shuttle (scan) method, in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate, to eject the aqueous inkjet ink and perform recording; and a single-pass method, in which the aqueous inkjet ink is ejected and performed as the printing substrate passes below a fixed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment is preferably selected for the single-pass method, as this method is less likely to cause deviation in the landing position of aqueous inkjet ink droplets, thereby improving the print quality of the printed matter.

[0129] The method of ejection from the inkjet head can also be selected from any known methods, such as a piezoelectric method that uses 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.

[0130] The droplet volume of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, more preferably 0.5 to 16 picoliters, from the viewpoints of reducing drying load and improving print quality of printed matter, including solid fills. Furthermore, from the viewpoint of achieving both print quality and ejection stability of printed matter, including solid fills, it is preferable to use an inkjet head with a design resolution of 150 to 1,600 dpi, more preferably an inkjet head with a design resolution of 300 to 1,200 dpi, and particularly preferably an inkjet head with a design resolution of 600 to 1,200 dpi. Furthermore, it is particularly preferable to adjust the printing conditions (specifically, the drive frequency and number of inkjet heads, and the printing speed) so that the recording resolution of the printed matter is 1,200 dpi or higher. In one embodiment, from the viewpoint of improving ejection stability and solid coverage of printed matter, when the design resolution of the inkjet head used in the inkjet printing method is DR [dpi], it is preferable that the droplet volume of the aqueous inkjet ink ejected from the inkjet head is (600 / DR) [picoliters] or more, and more preferably (4,800 / DR) [picoliters].

[0131] ≪Drying process≫ Drying methods employed in the drying mechanism used in the drying step include heat drying, hot air drying, infrared drying (for example, infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. In the drying step, one or more of these methods can be selected and used as desired. When two or more of the drying methods are used, they may be used separately (for example, consecutively) or simultaneously. For example, by using a heat drying method and a hot air drying method in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[0132] 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 used, it is preferable that the drying temperature be 35 to 100° C., and when a hot air drying method is used, it is preferable that the hot air temperature be 50 to 250° C. From the same viewpoint, when an infrared drying method is used, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared rays is in the wavelength range of 700 to 1500 nm.

[0133] <Printing base material> The printing substrate onto which the aqueous inkjet ink of this embodiment is printed is not particularly limited, and any known substrate such as a permeable substrate, a low-permeable substrate, or a non-permeable substrate can be used.

[0134] In this application, 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 More than 6g / m 2 Printing substrates with a permeability of less than 6 g / m are called "low permeability substrates." 2 The printing substrate described above is referred to as a "permeable substrate." The water absorption of the 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 conditions shown below, 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 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

[0135] Examples of permeable substrates include uncoated paper such as wood paper, medium-grade paper, fine paper, recycled paper, and plain paper; fabrics such as cotton, synthetic fiber fabrics, silk, hemp, and nonwoven fabrics; leather; etc. Among these, uncoated paper such as wood paper, medium-grade paper, fine paper, and recycled paper is preferably used because it allows prints with excellent print quality to be obtained.

[0136] Examples of non-permeable substrates and low-permeable substrates include plastic substrates; coated paper such as coated paper, art paper, lightly coated paper, and cast paper; metals such as aluminum, iron, stainless steel, and titanium; and glass.

[0137] Examples of the plastic substrate include polyester films made of polyethylene terephthalate, polyethylene naphthalate, etc., polyolefin films made of polyethylene, polypropylene, etc., polyamide films made of nylon, etc., polystyrene films, polyvinyl alcohol films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, polylactic acid films, etc. Among these, polyester films, polyolefin films, and polyamide films are preferably used.

[0138] The plastic substrate may also be a film coated with polyvinylidene chloride or the like to provide barrier properties, or a film having a metal layer such as aluminum or a vapor-deposited layer made of a metal oxide such as silica or alumina. Furthermore, an anti-fog film produced by kneading an anti-fog agent into the film or by coating the film may also be used.

[0139] The plastic substrate may be an unstretched film, or may be one that has been stretched uniaxially or biaxially.

[0140] 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.

[0141] The printing surface of the printing substrate listed above may be untreated, but it is also preferable to subject it to various treatments for improving adhesion, such as corona discharge treatment, ozone treatment, low-temperature plasma treatment, flame treatment, glow discharge treatment, etc., in order to improve the wetting and spreading properties of the aqueous inkjet ink of this embodiment, to obtain a printed product with excellent solid coverage and drying properties, and further to obtain a printed product with good blocking resistance and alcohol resistance due to the uniformity of the printed surface. [Example]

[0142] The aqueous inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0143] <Resin 1 manufacturing example> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 72.4 parts of 2-butanone, and the atmosphere inside the reaction vessel was replaced with nitrogen gas and then heated to 80°C. Next, a mixture of polymerizable monomers (10 parts of styrene, 10 parts of methacrylic acid, 25 parts of butyl acrylate, 40 parts of methyl methacrylate, and 15 parts of stearyl methacrylate) and 4 parts of polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise over 2 hours. After the addition was completed, the reaction vessel was maintained at 80°C while the polymerization reaction was allowed to proceed for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 2 hours at 80°C to obtain a solution of Resin 1. After cooling the solution of Resin 1 to 50°C, 10.3 parts of dimethylaminoethanol was added to neutralize the carboxyl groups present in Resin 1, and then 140 parts of water was added. Thereafter, the mixture was heated to 78°C or higher and azeotroped with water to distill off 2-butanone, and the solids concentration was adjusted to 30% with water, thereby obtaining an aqueous solution of Resin 1 (solids concentration 30%). The mass average molecular weight of the resin 1 was measured using a GPC (HLC-8120GPC, manufactured by Tosoh Corporation) equipped with a TSKgel column (manufactured by Tosoh Corporation) and an RI detector, using THF as a developing solvent, and was found to be approximately 14,000. The acid value of the resin 1, calculated from the above formula 3, was 65.2 (mgKOH / g). The glass transition temperature (Tg) of the resin 1, calculated from the above formula 2, was 39.7°C.

[0144] In the present application, the term "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

[0145] <Production Examples of Resins 2 to 7> Aqueous solutions of resins 2 to 7 (each with a solids concentration of 30%) were produced in the same manner as for resin 1 described above, except that the polymerizable monomers used were changed as shown in Table 1 below.

[0146] [Table 1]

[0147] The above Table 1 also lists the weight average molecular weight, acid value, and glass transition temperature of Resins 1 to 7. The meanings of the abbreviations used in the above Table 1 are as follows. ·MAA: methacrylic acid BA: Butyl acrylate MMA: Methyl methacrylate STMA: Stearyl methacrylate IB-X: Isobornyl methacrylate St: Styrene

[0148] <Production example of Resin 8 (AB block polymer)> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 20 parts of 2-butanone, followed by the addition of polymerizable monomers (10.0 parts of methacrylic acid and 10.0 parts of methyl methacrylate), a polymerization initiator (0.9 parts of 2,2'-azobisisobutyronitrile), and a RAFT agent (3.6 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid). The atmosphere in the reaction vessel was purged with nitrogen gas, and the vessel was heated to 75°C. The polymerization reaction was carried out over 3 hours while maintaining the temperature at 75°C, yielding a copolymer (A block) composed of methacrylic acid and methyl methacrylate.

[0149] After completion of the polymerization reaction, the reaction vessel was cooled to room temperature, and then 60 parts of 2-butanone and 55 parts of polymerizable monomers, methyl methacrylate and 25 parts of styrene, were added to the reaction vessel. The atmosphere in the reaction vessel was again replaced with nitrogen gas, and the reaction vessel was heated to 75°C. A polymerization reaction was carried out for 3 hours while maintaining the temperature at 75°C, thereby obtaining Resin 8, which has an AB block structure in which a copolymer (block B) composed of methyl methacrylate and styrene was added to the A block.

[0150] Thereafter, the inside of the reaction vessel was cooled to room temperature, and then 10.3 parts of dimethylaminoethanol was added to the reaction vessel to neutralize the carboxyl groups present in the above-mentioned resin 8, and then 200 parts of water was added. Thereafter, the mixture was heated to 78°C or higher and azeotroped with water to distill off 2-butanone, and then the solids concentration was adjusted with water to 30%, thereby obtaining an aqueous solution of resin 8 (solids concentration 30%).

[0151] The mass average molecular weight of Resin 8 was approximately 15,000, measured in the same manner as Resin 1. The acid value of Resin 8, calculated from Equation 3 above, was 65.2 (mgKOH / g), and the glass transition temperature (Tg) of Resin 8, calculated from Equation 2 above, was 106.1°C.

[0152] <Production of Resin 9> Using the materials and method described in Production Example 2 of Patent Document 4, a "pigment-free aqueous dispersion of polymer particles B" (solids concentration: 44%) was produced. This polymer particles B was then used as "resin 9" to produce the aqueous inkjet ink shown below. The acid value of resin 9, calculated from the above formula 3, was 16.3 (mgKOH / g), and the glass transition temperature (Tg) of resin 9, calculated from the above formula 2, was -16.3°C.

[0153] <Synthesis of acetylene diol compound 1> Acetylene diol compound 1 was synthesized using the method described in Example 6 of JP 2001-215690 A. Acetylene diol compound 1 is a compound represented by the following general formula (7), in which u1 + v1 is 6 and u2 + v2 is 1, and ethylene oxide groups (C2H4O) and propylene oxide groups (C3H6O) are added randomly. The HLB value of acetylene diol compound 1, calculated by the Griffin method, is 9.6.

[0154] General formula (7): [ka]

[0155] <Production of Yellow Pigment Dispersion> 450 g of CI Pigment Yellow 155 (FERRO's "Lysopure Yellow 5518P"), 115 g of Resin 10 (a random polymer of styrene / acrylic acid / behenyl methacrylate = 45 / 25 / 30 (mass ratio) in which all acid groups had been neutralized with dimethylaminoethanol, acid value 194.6 mg KOH / g, mass average molecular weight 20,000), and 2,435 g of water were charged into a mixing vessel (volume 10 L) equipped with a stirrer and premixed for 1 hour. Next, the mixture was circulated and dispersed using a Shinmaru Enterprises "Dynomill" (volume 0.6 L) filled with 1,800 g of 0.5 mm diameter zirconia beads. Then, every certain time (for example, every hour), the D50 (median diameter on a volume basis) of the mixture was measured in a 25°C environment using a Nanotrac UPA-EX150 manufactured by Microtrac Bell, and the circulatory dispersion was terminated when the D50 became 150 nm or less, thereby producing a yellow pigment dispersion.

[0156] <Production of white pigment dispersion> 3,000 g of titanium dioxide (Ishihara Sangyo Kaisha, Ltd., "Tipake CR-60"), 300 g of Resin 10, and 2,700 g of water were added to a mixing vessel (10 L volume) equipped with a stirrer and stirred (premixed) for 1 hour. Next, the mixture was circulated and dispersed using a Shinmaru Enterprises "Dynomill" (0.6 L volume) filled with 1,800 g of 0.5 mm diameter zirconia beads. The D50 of the mixture was measured at regular intervals (e.g., every hour) using the same equipment as for the yellow pigment dispersion. The circulatory dispersion was terminated when the D50 reached 250 nm or less, producing a white pigment dispersion.

[0157] <Production of Water-Based Inkjet Inks 1-113> Using the pigment dispersion liquid produced by the above method, each raw material was charged into a mixing vessel equipped with a stirrer so as to obtain the formulation shown in each column of Tables 2-1 to 2-7 below. After charging, the mixture was heated to 50°C and mixed for an additional hour, and then filtered through a membrane filter with a pore size of 0.8 μm to produce aqueous inkjet inks 1 to 113.

[0158] When producing aqueous inkjet inks, each raw material was added while stirring the mixture in the mixing vessel. In addition, in each column of Tables 2-1 to 2-7, the ingredients were added in the order listed, starting with the top row. However, when producing an aqueous inkjet ink that did not contain one or more of these ingredients, that ingredient was not added, and the next ingredient was added in the order listed. Furthermore, for ingredients containing two or more ingredients, the order of addition of the ingredients within that ingredient was arbitrary.

[0159] [Table 2-1]

[0160] [Table 2-2]

[0161] [Table 2-3]

[0162] [Table 2-4]

[0163] [Table 2-5]

[0164] [Table 2-6]

[0165] [Table 2-7]

[0166] Here, the meanings of the abbreviations and details of the product names listed in Tables 2-1 to 2-7 above are as follows: In Tables 2-1 to 2-7, "Tg" represents the glass transition temperature. MDG: Diethylene glycol monomethyl ether EDG: Diethylene glycol monoethyl ether BDG: Diethylene glycol monobutyl ether PGM: Propylene glycol monomethyl ether PnP: Propylene glycol monopropyl ether PnB: Propylene glycol monobutyl ether DPM: Dipropylene glycol monomethyl ether MEDG: Diethylene glycol methyl ethyl ether AMP: 2-amino-2-methyl-1-propanol SF104: Surfynol 104 (acetylene diol manufactured by Evonik Japan, HLB value: 3) SF2502: Surfynol 2502 (acetylene diol manufactured by Evonik Japan, HLB value: 8) SF440: Surfynol 440 (acetylene diol manufactured by Evonik Japan, HLB value: 8.1) TW280: TEGO Wet280 (manufactured by Evonik Japan, a polyether-modified siloxane with ethylene oxide groups in the side chain) SAG005: Silface SAG005 (manufactured by Nissin Chemical Industry Co., Ltd., a polyether-modified siloxane with ethylene oxide groups in the side chain) Emulgen 102KG (Kao Corporation polyethylene glycol monoalkyl ether surfactant (polyoxyethylene lauryl ether), HLB value: 6.3) SF465: Surfynol 465 (acetylene diol manufactured by Evonik Japan, HLB value: 13) Proxel GXL: 1,2-benzisothiazol-3-one in dipropylene glycol (1,2-benzisothiazol-3-one: dipropylene glycol: water = 2:6:2, preservative manufactured by Arch Chemicals)

[0167] [Examples 1 to 94, Comparative Examples 1 to 19] The above water-based inkjet inks 1 to 113 were used to carry out the following evaluations 1 to 4. The evaluation results were as shown in Tables 2-1 to 2-7.

[0168] <Evaluation 1: Evaluation of ejection stability> An inkjet printing device equipped with a Kyocera inkjet head "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) was placed above the conveyor in an environment of 25°C. After filling the inkjet head with each of the above aqueous inkjet inks, a nozzle check pattern was printed to confirm that there were no missing nozzles (a phenomenon in which aqueous inkjet ink was not ejected from the nozzles of the inkjet head). Next, a printing substrate, OPP film (FOR, 20 μm thick) manufactured by Futamura Chemical Co., Ltd., cut into A4 size (21 cm wide x 30 cm long) was fixed on the conveyor. Thereafter, the conveyor was driven at a constant speed, and as the printing substrate passed under the installation area of ​​the inkjet head, the aqueous inkjet ink was ejected at a drop volume of 2 pL to print a solid image. After printing one solid image, the printing device was left to stand for 10 minutes in a 25°C environment without printing again. After that, a nozzle check pattern was printed again and the number of missing nozzles was visually counted to evaluate the ejection stability. The evaluation criteria were as follows, with ◎, ○, and △ indicating that the ink was usable. ◎: No nozzle missing at all ○: 1 to 4 nozzles missing △: 5 to 9 nozzles were missing ×: 10 or more nozzles were missing

[0169] <Creating printed materials> An inkjet printing apparatus equipped with a Kyocera Corporation inkjet head "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) was prepared above a conveyor at 25°C. The inkjet head was filled with each of the aqueous inkjet inks. The same OPP film as used in Evaluation 1 was fixed onto the conveyor. The conveyor was then driven at a speed of 50 m / min. As the printing substrate passed under the inkjet head, the aqueous inkjet ink was ejected at a drop volume of 2 pL, printing a 100% solid image measuring 15 cm wide x 30 cm long. The printed substrate was then immediately placed in a constant temperature incubator with a blower set at 70°C and dried for 1 minute to produce a printed product.

[0170] <Evaluation 2: Evaluation of solid filling> A backing (a white backing if printed with water-based black ink, or a black backing if printed with water-based white ink) was attached to the non-printed side of the solid print produced by the above method, and then the number of streaks (white streaks 1 cm or longer) was visually observed from the printed side to evaluate the solid filling. The evaluation criteria were as follows, with ◎, ○, and △ being considered usable. ◎: Not a single streak was observed ○: 1 to 4 missing lines were observed △: 5 to 9 missing lines were observed ×: More than 10 missing lines were observed

[0171] <Evaluation 3: Evaluation of blocking resistance> The solid print produced by the above method was cut into a 4cm x 4cm square, and the printed surface was then overlapped with the unprinted surface of the same type of OPP film used for printing. This overlapping piece was then used as a test piece, and a blocking test was carried out using a constant load permanent deformation tester ("CO-201" manufactured by Tester Sangyo Co., Ltd.). The blocking test conditions were a load of 10 kg / cm2 The test was conducted under the following conditions: ambient temperature 40°C, ambient humidity 80% RH, and standing time 24 hours. After 24 hours, the test piece was removed from the constant-load permanent deformation tester, and the overlapping printed substrate was instantly peeled off while maintaining a 90-degree angle. Blocking resistance was evaluated based on the feel upon peeling (peel resistance) and the appearance of the printed surface after peeling (visual inspection). The evaluation criteria were as follows, with ◎, ○, and △ indicating practical use. ◎: There was no peel resistance, and no part of the water-based inkjet ink layer adhered to the non-printed surface of the printing substrate. ○: There was slight resistance when peeling, but no part of the water-based inkjet ink layer adhered to the non-printed surface of the printing substrate. △: Part of the water-based inkjet ink layer was attached to the non-printed surface of the printing substrate, and the extent of this was 30% or less of the area of ​​the overlapping portion. ×: Part of the aqueous inkjet ink layer was attached to the non-printed surface of the printing substrate, and the extent of this was more than 30% of the area of ​​the overlapping portion.

[0172] <Evaluation 4: Evaluation of alcohol resistance> The printed surface of the solid print produced by the method described above was rubbed back and forth over a width of approximately 1 cm with a cotton swab moistened with a 60% by weight aqueous ethanol solution. The number of times the cotton swab was rubbed back and forth until the aqueous inkjet ink film completely peeled off the print substrate was counted. The above evaluation was performed at five locations on the same print, and the alcohol resistance was evaluated by calculating the average number of times the swab was rubbed. The evaluation criteria were as follows, with ◎, ○, and △ indicating that the product was usable. ◎: The coating film did not peel off even after rubbing 20 times ○: The coating peeled off after 11 to 19 times △: The coating peeled off after 6 to 10 times ×: The coating film peeled off after 5 times or less

[0173] As shown in each example in Tables 2-1 to 2-7, it was confirmed that the aqueous inkjet ink having the constitution of the present invention is excellent in all of ejection stability, solid coverage of printed matter, blocking resistance, and alcohol resistance.

[0174] Water-based inkjet ink 113 (Comparative Example 19) is a reproduction of the water-based inkjet ink described in Example 2 of Patent Document 4, except for the composition and blending amount of the pigment dispersion. As a result of the evaluation, it was confirmed that the coating film did not have sufficient strength, the blocking resistance and alcohol resistance did not reach a level sufficient for practical use, and the ejection stability was also not sufficient for practical use.

Claims

1. A water-based inkjet ink containing a colorant, a resin used for binder purposes, a water-soluble organic solvent, and a surfactant, The resin used for the binder contains a resin (R1) having a glass transition temperature of 50 to 130°C, the water-soluble organic solvent contains dipropylene glycol monopropyl ether (S1), The surfactant includes a surfactant having an HLB value of 10 or less, the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the water-soluble organic solvent is 8 to 30% by mass on a mass basis, and the ratio of the content of the dipropylene glycol monopropyl ether (S1) to the total content of the resin (R1) is 10 to 90 mass % on a mass basis.

2. The aqueous inkjet ink according to claim 1, wherein the water-soluble organic solvent further contains a compound (S2) represented by the following general formula (1) and having 4 to 8 carbon atoms: General formula (1): H-(O-CH(R 1 )-CH 2 -O) n -R 2 (In general formula (1), R 1 represents a hydrogen atom or a methyl group, R 2 represents an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2.

3. 3. The aqueous inkjet ink according to claim 1, wherein the water-soluble organic solvent further comprises a diol compound (S3) having 2 to 6 carbon atoms.

4. The aqueous inkjet ink according to claim 3, wherein the diol compound (S3) comprises an alkanediol having 3 to 6 carbon atoms.

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

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