Aqueous inkjet ink and printed matter

Abstract

To provide an aqueous inkjet ink which enables obtaining a printed matter suppressed in beading and pinholes, and excellent in laminate strength, and is excellent in standby discharge property.SOLUTION: An aqueous inkjet ink contains a pigment, a binder resin, a water-soluble organic solvent and a surface active agent. The aqueous inkjet ink is such that: the water-soluble organic solvent contains dipropylene glycol monopropyl ether (A), and at least one kind of compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentane diol; the content of the dipropylene glycol monopropyl ether (A) is 1-15 mass% in the total amount of the aqueous inkjet ink; and the entire amount of the content of the water-soluble organic solvent is 8-35 mass% in the total amount of the aqueous inkjet ink.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an aqueous inkjet ink, a printed matter produced using the aqueous inkjet ink, and a method for producing the same. [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 easy to reduce costs and handle small lots of a wide variety of products.

[0003] Inkjet printing, one type of digital printing method, prints images and / or text on a printing substrate (also referred to simply as "substrate" in this disclosure) by ejecting ink droplets from minute nozzles. In this disclosure, the images and / or text 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] 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 film. To date, aqueous inkjet inks have been used to produce prints with practically acceptable print quality on both high-permeability and low-permeability printing substrates. In contrast, when printing on non-permeability substrates such as film, the liquid components present in the aqueous inkjet ink droplets do not penetrate into the printing substrate at all. As a result, when undried aqueous inkjet ink droplets come into contact with each other, a force acts on each droplet in a direction that reduces their surface area, causing the droplets to attract each other and resulting in bead-like aggregation (beading). Beading manifests as white spots (a phenomenon in which the aqueous inkjet ink does not adhere to the printing substrate), uneven density, color bleeding, etc., and therefore significantly reduces the print quality of the printed matter.

[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 adhesion. Furthermore, when a printed matter with insufficient adhesion is laminated to another film via an adhesive (laminating adhesive), the insufficient adhesion may cause delamination between the layers. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-91309 [Patent Document 2] International Publication No. 2020 / 195360 [Patent Document 3] Japanese Patent Publication No. 2022-85548 Summary of the Invention [Problem to be solved by the invention]

[0009] Meanwhile, in the label and packaging markets, which are expected to see future growth within the printing industry, films are often used as printing substrates. Therefore, the ability to produce prints with excellent print quality on non-permeable substrates such as films is extremely important from the perspective of expanding the use of aqueous inkjet inks in these markets. Furthermore, particularly in the packaging market, post-processing such as lamination is often performed on printed materials to be used as packaging materials. From this perspective, "improving lamination suitability" can be said to be an important challenge for aqueous inkjet inks.

[0010] One known method for improving the print quality of printed matter on film is to use a surfactant to reduce the surface tension of the aqueous inkjet ink. The surfactant improves the wetting and spreading of the aqueous inkjet ink on the printing substrate, and the increased surface area associated with this wetting and spreading also improves the drying properties of the aqueous inkjet ink droplets. As a result, adjacent droplets do not come into contact with each other in a wet state, which is thought to suppress beading.

[0011] On the other hand, a method of using a highly hydrophobic surfactant is generally used to wet and spread aqueous inkjet ink on a printing substrate with low surface energy, such as a film. However, when an aqueous inkjet ink containing such a surfactant is dried on the printing substrate, the surfactants may associate with each other. The aqueous inkjet ink is repelled around the associated surfactants, resulting in the formation of pinholes in the printed matter.

[0012] Furthermore, highly hydrophobic surfactants are rapidly oriented at interfaces such as the air-liquid interface and the solid-liquid interface. Therefore, for example, in aqueous inkjet ink present in the vicinity of a nozzle in an inkjet head that is not ejecting aqueous inkjet ink (on standby), the highly hydrophobic surfactants may be excessively oriented at the air-liquid interface, which may deteriorate the ejection stability (standby ejection performance) immediately after returning from standby.

[0013] Furthermore, generally, highly hydrophobic surfactants are present in large amounts on the surface of the dried aqueous inkjet ink film. This means that the surface energy of the ink film is significantly reduced. When a laminate is produced by applying a laminating adhesive or overcoat varnish to such an ink film, the uniformity of the application of these agents deteriorates, which can lead to a decrease in lamination suitability, i.e., a decrease in laminate strength.

[0014] On the other hand, one method for improving the laminate strength of printed matter is to add a resin with binder function (binder resin) to the aqueous inkjet ink. The use of a binder resin improves the adhesion of the ink film to the printing substrate, leading to improved laminate strength. Furthermore, the more the binder resin forms a film, the better the adhesion and laminate strength. However, when the binder resin is used in combination with the highly hydrophobic surfactant described above, an interaction occurs between the two, which inhibits the orientation of the surfactant at the interface, potentially resulting in a deterioration in print image quality.

[0015] Studies have been conducted to date to improve the print quality and laminate strength of printed materials printed on low-permeability printing substrates such as films. For example, Patent Document 1 discloses an ink containing 1,2-propanediol, 1,2-hexanediol, and a polyoxyethylene ether compound as an ink that can prevent beading and improve abrasion resistance in printed materials printed on printing substrates such as polymer films. However, the inventors' studies have revealed that with the ink of Patent Document 1, depending on the structure and specifications of the binder resin used or the printing conditions, the binder resin may not form a sufficient film, resulting in insufficient laminate strength.

[0016] Patent Document 2 discloses an inkjet ink for non-permeable substrates, which contains a pigment coated with a crosslinked pigment dispersion resin, an alkanediol compound (solvent A) having a boiling point of 180 to 200°C, and a monoalcohol compound and / or a glycol monoether compound (solvent B) having a boiling point of 70 to 160°C. It is also claimed that this inkjet ink produces printed matter with excellent drying properties and laminate strength. Because both solvents A and B have low boiling points, as described in Patent Document 2, an inkjet ink having the above composition is believed to have good drying properties. However, depending on the printing and drying conditions, after the inkjet ink is applied to the printing substrate, solvents A and B may dry before the resin component forms a film, resulting in a printed matter with insufficient laminate strength.

[0017] Furthermore, Patent Document 3 discloses a white ink composition containing, as a resin having binder function, 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 makes it possible to produce printed materials with excellent lamination strength and blocking resistance. However, Patent Document 3 does not conduct a detailed evaluation of the ejection stability of the white ink composition, and follow-up tests by the present inventors have shown that stable ejection is difficult depending on the ejection conditions.

[0018] As described above, there has not been a water-based inkjet ink that can suppress beading and pinholes, can produce printed matter with excellent lamination strength, and also has excellent standby ejection properties.

[0019] Therefore, an object of one embodiment of the present disclosure is to provide an aqueous inkjet ink that suppresses beading and pinholes, can produce printed matter with excellent lamination strength, and also has excellent standby ejection properties. [Means for solving the problem]

[0020] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved to a high degree by using an aqueous inkjet ink having the following composition.

[0021] That is, one embodiment of the present disclosure relates to an aqueous inkjet ink as shown in [1] to [6] below, a printed matter obtained using the aqueous inkjet ink as shown in [7] to [9] below, and a method for producing the printed matter as shown in

[10] to

[12] below. [1] An aqueous inkjet ink containing a pigment, a binder resin, a water-soluble organic solvent, and a surfactant, wherein the water-soluble organic solvent contains dipropylene glycol monopropyl ether (A) and at least one compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentanediol, the content of the dipropylene glycol monopropyl ether (A) being 1 to 15 mass% of the total amount of the aqueous inkjet ink, and the total content of the water-soluble organic solvents being 8 to 35 mass% of the total amount of the aqueous inkjet ink. [2] The aqueous inkjet ink according to [1], wherein the ratio of the content of the dipropylene glycol monopropyl ether (A) to the content of the compound (B) (dipropylene glycol monopropyl ether (A) / compound (B)) is 0.15 to 3.0 by mass. [3] The aqueous inkjet ink according to [1] or [2], wherein the total content of the dipropylene glycol monopropyl ether (A) and the compound (B) is 20 to 100 mass % of the total content of the water-soluble organic solvent. [4] The aqueous inkjet ink according to any one of [1] to [3], wherein the total content of the dipropylene glycol monopropyl ether (A) and the compound (B) is 20 to 80 mass % of the total content of the water-soluble organic solvent. [5] The aqueous inkjet ink according to [4], wherein the water-soluble organic solvent further comprises at least one selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether. [6] The aqueous inkjet ink according to any one of [1] to [5], wherein the content of the dipropylene glycol monopropyl ether (A) is 1 to 7 mass % of the total amount of the aqueous inkjet ink. [7] A printed matter comprising a printing substrate and a printing layer, the printing layer being formed by printing the aqueous inkjet ink according to any one of [1] to [6] on the printing substrate. [8] The printed matter described in [7], further comprising a laminate layer, wherein the printing layer is interposed between the printing substrate and the laminate layer. [9] The printed matter described in [8], wherein the printing substrate is a non-permeable substrate.

[10] A method for producing a printed matter, comprising printing an aqueous inkjet ink on a printing substrate, wherein the aqueous inkjet ink is the aqueous inkjet ink according to any one of [1] to [6].

[11] A method for producing a printed matter according to

[10] , further comprising laminating the printed matter.

[12] The method for producing a printed matter according to

[11] , wherein the printing substrate is a non-permeable substrate. [Effects of the Invention]

[0022] The aqueous inkjet ink according to one embodiment of the present disclosure has the following advantages: beading and pinholes are suppressed, printed matter having excellent lamination strength can be obtained, and standby ejection properties are also excellent. DETAILED DESCRIPTION OF THE INVENTION

[0023] An aqueous inkjet ink according to one embodiment of the present disclosure (also referred to simply as "the aqueous inkjet ink of the present embodiment" in the present disclosure) will be described below. Note that the present disclosure is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present disclosure.

[0024] In general, water, the main solvent of aqueous inkjet inks, has a high surface tension and tends not to wet and spread easily on the printing substrate. Furthermore, when a droplet of aqueous inkjet ink that has landed on the printing substrate comes into contact with an adjacent, wet droplet while still wet, a force acts on each droplet in a direction that reduces the surface area, causing the droplets to attract each other and resulting in beading. As described above, beading can also lead to poor solid coverage, uneven density, color bleeding, and other problems, resulting in a significant degradation of print quality.

[0025]

[0003] A suitable method for suppressing beading is to use a surfactant. Furthermore, in order to wet and spread the aqueous inkjet ink on a printing substrate with low surface energy, such as a film, a highly hydrophobic surfactant can be used. However, as described above, when an aqueous inkjet ink containing such a surfactant is used, pinholes may occur in the printed matter, standby ejection performance may be deteriorated, and lamination suitability may be reduced.

[0026] Another method for improving lamination suitability is to add a resin having a binder function (binder resin) to the aqueous inkjet ink. As described above, when the aqueous inkjet ink containing the binder resin forms a sufficient film on the printing substrate, adhesion and lamination strength are improved.

[0027] A film-forming aid is often used to allow the binder resin to form a sufficient film. Generally, a highly hydrophobic, water-soluble organic solvent is used as the film-forming aid. However, when water in an aqueous inkjet ink present in an inkjet head, particularly in the vicinity of the nozzle, volatilizes preferentially, the highly hydrophobic, water-soluble organic solvent may promote aggregation of the binder resin, or the binder resin once dissolved in the water-soluble organic solvent may re-precipitate as the ink dries. As a result, the inkjet head nozzle may be clogged by the aggregated or precipitated binder resin, resulting in a deterioration in standby ejection performance.

[0028] In general, the use of a humectant (a high-boiling organic solvent) is effective in improving standby ejection properties. However, in ink films prepared using aqueous inkjet inks containing such a humectant, a large amount of the humectant remains, which is likely to deteriorate lamination suitability.

[0029]

[0003] Furthermore, as mentioned above, when an attempt is made to produce a printed matter with reduced beading on a printing substrate with low surface energy, such as a film, pinholes may be generated and lamination suitability may be deteriorated. Furthermore, when a binder resin and a film-forming aid are added to an aqueous inkjet ink to improve lamination suitability, this may lead to deterioration of standby discharge properties. Thus, it has been difficult to achieve high levels of all of beading resistance, pinhole resistance, lamination strength, and standby discharge properties.

[0030] Therefore, in order to solve the above problems, the present inventors have continued their intensive research and have found that dipropylene glycol monopropyl ether (A) and a specific compound (B) are used as water-soluble organic solvents, and furthermore, the blending ratio of these water-soluble organic solvents is specified, which has led to the present invention. Although the details of the mechanism by which the above-mentioned configuration can suitably solve the above problems are unknown, the present inventors speculate as follows.

[0031] First, the aqueous inkjet ink of this embodiment contains dipropylene glycol monopropyl ether (A). Dipropylene glycol monopropyl ether (A) functions as the aforementioned film-forming aid. Meanwhile, in the aqueous inkjet ink of this embodiment, the dipropylene glycol monopropyl ether (A) itself is thought to function like a surfactant. In this case, because the dipropylene glycol monopropyl ether (A) has a low molecular weight, it is thought to be easily oriented at the interface. This improves wetting and spreading on printing substrates with low surface energy, such as films, and makes it possible to suppress the occurrence of beading. Furthermore, because the dipropylene glycol monopropyl ether (A) is a water-soluble organic solvent and is volatile, it is possible to prevent the dipropylene glycol monopropyl ether (A) from remaining on the ink film surface, thereby suppressing a decrease in laminate strength.

[0032] In this way, since dipropylene glycol monopropyl ether (A) can function like a surfactant, the amount of surfactant added to the aqueous inkjet ink can be reduced, making it easier to suppress the occurrence of pinholes.

[0033] On the other hand, as described above, dipropylene glycol monopropyl ether (A) functions as a film-forming aid, and therefore aggregation and precipitation of the binder resin may occur near the nozzles of the inkjet head, and standby discharge properties may be deteriorated.

[0034] Therefore, the aqueous inkjet ink of this embodiment contains at least one compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentanediol as the water-soluble organic solvent. The compound (B) has higher hydrophilicity than, for example, 1,2-alkanediols having the same number of carbon atoms. Meanwhile, the compound (B) has four or more carbon atoms and also possesses moderate hydrophobicity. Therefore, the compound (B) and the dipropylene glycol monopropyl ether (A) are compatible with each other, which is believed to prevent the dipropylene glycol monopropyl ether (A) from localizing in the aqueous inkjet ink. As a result, even when water evaporates from the aqueous inkjet ink near the nozzles of the inkjet head, aggregation and precipitation of the binder resin due to the dipropylene glycol monopropyl ether (A) can be prevented, and standby discharge performance is believed to be improved.

[0035] Furthermore, the compound (B) used in the aqueous inkjet ink of this embodiment is a diol, so it functions as a humectant, but also has moderate hydrophobicity, making it relatively volatile upon drying and less likely to remain in the printed material. Even if trace amounts of compound (B) remain in the printed material, compound (B) without a hydroxyl group at an adjacent position is thought to be more likely to interact with laminating adhesives and overcoat varnishes than 1,2-alkanediols with the same number of carbon atoms. As a result, even when compound (B) is used, it is easy to suppress a decrease in laminate strength.

[0036] As described above, the aqueous inkjet ink having the above-mentioned configuration has been found to solve the above-mentioned problems at a high level.

[0037] Next, each component constituting the aqueous inkjet ink of this embodiment will be described in detail below.

[0038] <Water-soluble organic solvent> The aqueous inkjet ink of this embodiment contains a water-soluble organic solvent. As described above, the water-soluble organic solvent contains dipropylene glycol monopropyl ether (A) and at least one compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentanediol. In this disclosure, 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.

[0039] <Dipropylene glycol monopropyl ether (A)> The content of dipropylene glycol monopropyl ether (A) in the aqueous inkjet ink of this embodiment is 1 to 15 mass % of the total amount of the aqueous inkjet ink, more preferably 2 to 10 mass %, and even more preferably 2 to 7 mass %. By setting the content of dipropylene glycol monopropyl ether within this range, it becomes easy to achieve all of the following: improved standby discharge properties, suppression of beading and pinholes in printed matter, and improved laminate strength.

[0040] ≪Compound (B)≫ The aqueous inkjet ink of this embodiment contains, in addition to the dipropylene glycol monopropyl ether (A), at least one compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentanediol. As described above, these compounds are highly hydrophilic and function as humectants while also possessing moderate hydrophobicity, which is believed to facilitate compatibility with dipropylene glycol monopropyl ether (A). Furthermore, compared to other water-soluble organic solvents that function as humectants, the compound (B) dries relatively quickly and is less likely to remain in printed materials. Even if the compound (B) remains in printed materials, it is likely to interact with laminating adhesives and overcoat varnishes because the carbon atoms containing hydroxyl groups are not adjacent. As a result, the use of compound (B) can achieve both improved standby jetting performance and suppressed deterioration of laminate strength.

[0041] In the aqueous inkjet ink of this embodiment, it is preferable to use 2-methyl-2,4-pentanediol as compound (B). Although the detailed mechanism is unknown, using 2-methyl-2,4-pentanediol as compound (B) makes it easy to improve both standby dischargeability and laminate strength. On the other hand, from the viewpoint of significantly improving the standby dischargeability of the aqueous inkjet ink of this embodiment, it is preferable to use 1,3-butanediol and / or 2-methyl-1,3-propanediol as compound (B).

[0042] The content of compound (B) in the aqueous inkjet ink of this embodiment is preferably 2 to 34% by mass, more preferably 3 to 25% by mass, and even more preferably 4 to 20% by mass, of the total amount of the aqueous inkjet ink. By ensuring that the content of compound (B) falls within the above range, dipropylene glycol monopropyl ether (A) is suitably miscible, making it easy to achieve both good standby ejection properties and good laminate strength. Furthermore, the drying properties of the aqueous inkjet ink are improved, and surfactant association can be suppressed, thereby suppressing beading and pinholes in printed materials.

[0043] As described above, it is believed that the compound (B) is compatible with the dipropylene glycol monopropyl ether (A). Furthermore, the dipropylene glycol monopropyl ether (A) is a material that is effective in suppressing beading and pinholes. Therefore, optimizing the blending ratio of the two compounds is believed to enhance both of these effects. Specifically, the ratio of the content of the dipropylene glycol monopropyl ether (A) in the aqueous inkjet ink of this embodiment to the content of the compound (B) in the aqueous inkjet ink of this embodiment (dipropylene glycol monopropyl ether (A) / compound (B)) is preferably 0.15 to 3.0 by mass, more preferably 0.2 to 2.5, and particularly preferably 0.2 to 2.0. By setting the ratio within the above range, the compound (B) appropriately compatibilizes the dipropylene glycol monopropyl ether (A), improving standby discharge properties. Furthermore, it is also easy to obtain printed matter that is free of beading and has excellent lamination strength.

[0044] <Other water-soluble organic solvents> The aqueous inkjet ink of this embodiment may contain water-soluble organic solvents other than the dipropylene glycol monopropyl ether (A) and compound (B) (referred to as "other water-soluble organic solvents" in the present disclosure).

[0045] Specific examples of water-soluble organic solvents that can be used as other water-soluble organic solvents in the aqueous inkjet ink of this embodiment are shown below. Alkanediols include 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 3-methyl-1,3-butanediol, and 3-methyl-1,5-pentanediol. Alkanetriols include glycerin, 1,2,4-butanetriol, and 1,2,6-hexanetriol. Polyalkylene glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. (Poly)alkylene glycol monoalkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl 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, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, and propylene glycol monomethyl ether. ter, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, 1,2-butylene glycol monomethyl ether, 1,3-butylene glycol monomethyl ether, 1,4-butylene glycol monomethyl ether, 1,2-butylene glycol monoethyl ether, 1,3-butylene glycol monoethyl ether, 1,4-butylene glycol monomethyl ether, 1,2-butylene glycol monobutyl ether, 3-methyl-1,3-butylene glycol monomethyl ether. (Poly)alkylene dialkyl ethers include diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, and tetraethylene glycol dimethyl ether. Lactams include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1-(2-hydroxymethyl)-2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-piperidone (δ-valerolactam), N-methyl-2-piperidone, N-vinyl-2-piperidone, ε-caprolactam, and N-vinyl-ε-caprolactam. Alkanolamines include dimethylethanolamine, methyldiethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, triethanolamine, diisopropanolamine, and triisopropanolamine. These water-soluble organic solvents may be used alone or in combination of two or more.

[0046] In the present disclosure, the term "(poly)alkylene glycol" refers to "alkylene glycol" and / or "polyalkylene glycol".

[0047] Among the compounds listed above, it is preferable to include at least one selected from 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, because these compounds have excellent compatibility with dipropylene glycol monopropyl ether (A) and compound (B) and do not inhibit the development of the above-mentioned effects. Among these compounds, the use of propylene glycol monobutyl ether and / or dipropylene glycol monomethyl ether is particularly preferred, as they have good drying properties, making it particularly easy to suppress beading and improve lamination suitability. On the other hand, the use of 1,2-propanediol and / or 1,2-butanediol is particularly preferred, as they suppress drying of the aqueous inkjet ink near the nozzles of the inkjet head, thereby significantly improving standby ejection properties, and they also produce printed matter with excellent lamination suitability. Furthermore, the use of propylene glycol monomethyl ether and / or propylene glycol monopropyl ether is particularly preferred, as they have excellent compatibility with dipropylene glycol monopropyl ether (A) and compound (B), significantly improving the pinhole resistance of printed matter.

[0048] The total content of the dipropylene glycol monopropyl ether (A) and the compound (B) is preferably 20 to 100% by mass, more preferably 25 to 80% by mass, and particularly preferably 30 to 70% by mass, of the total amount of the water-soluble organic solvent in the aqueous inkjet ink. By keeping the total content within the above range, the effects of the dipropylene glycol monopropyl ether (A) and the compound (B) are preferably exhibited, and in particular, it is easy to improve the laminate strength of the printed matter, suppress beading, and improve standby discharge properties.

[0049] Furthermore, the ratio of the content of dipropylene glycol monopropyl ether (A) in the aqueous inkjet ink of this embodiment to the content of other water-soluble organic solvents in the aqueous inkjet ink of this embodiment (dipropylene glycol monopropyl ether (A) / other water-soluble organic solvents) is preferably 0.10 to 1.5 by mass, more preferably 0.10 to 0.80, and particularly preferably 0.10 to 0.50. By setting the value of this ratio within the above range, the other water-soluble organic solvents are favorably compatible with dipropylene glycol monopropyl ether (A), and beading in printed matter can be suppressed, and further, standby jetting performance can be easily improved.

[0050] The total content of water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment is 8 to 35% by mass of the total amount of the aqueous inkjet ink. The total content of the water-soluble organic solvents is more preferably 9 to 30% by mass, and particularly preferably 10 to 25% by mass. By keeping the content within this range, standby ejection properties are improved and it is easy to suppress a decrease in laminate strength due to residual solvent.

[0051] <Resin> <Binder resin> The aqueous inkjet ink of this embodiment contains a resin. The resin contains a resin (binder resin) having a binder function. As described above, by using the binder resin together with dipropylene glycol monopropyl ether (A), it is possible to improve the laminate strength of the printed matter while preventing deterioration of standby dischargeability. In this disclosure, the term "binder function" refers to the function of providing adhesion to the ink film and the printing substrate.

[0052] Generally, water-soluble resins and resin particles are known as the forms of resins used in aqueous inkjet inks. The binder resin contained in the aqueous inkjet ink of this embodiment may be a water-soluble resin or resin particles. Furthermore, a combination of a water-soluble resin and resin particles may be used.

[0053] In this disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin," and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin." Furthermore, 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 disclosure) of 10 to 1,000 nm is referred to as a "resin particle."

[0054] It should be noted that D50 in this disclosure 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.

[0055] Examples of resins that can be used as the binder resin 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.

[0056] Among these resins, the resin used as the binder resin is preferably at least one resin selected from the group consisting of acrylic resin, urethane resin, and polyester resin, because the use of acrylic resin, urethane resin, and polyester resin can easily improve the laminate strength of the printed matter.

[0057] In the present disclosure, "acrylic resin" refers to a resin using at least one polymerizable monomer 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 acrylic resins. Furthermore, "(Maleic anhydride)" in the present disclosure refers to at least one selected from "maleic acid" and "maleic anhydride". Meanwhile, the term "maleic acid resin" in the present disclosure refers to a resin using at least maleic acid (anhydride) as a polymerizable monomer. The maleic acid resin may further use at least one polymerizable monomer selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0058] The glass transition temperature (Tg) of the binder resin is preferably −10 to 100° C., and more preferably 5 to 70° C. By using a resin having the above glass transition temperature, adhesion to the printing substrate and lamination suitability are improved.

[0059] In one embodiment, two or more resins with different glass transition temperatures (Tg) can be used in combination, from the viewpoint of improving both the laminate strength and standby ejection properties, and further accelerating the drying of the aqueous inkjet ink, thereby suppressing beading in printed matter. Specifically, it is preferable to use in combination a resin with a glass transition temperature of 20°C or less and a resin with a glass transition temperature higher than 20°C. The difference in glass transition temperatures of the resins used in combination is preferably 15 to 150°C, and particularly preferably 30 to 130°C.

[0060] The glass transition temperature of a resin can be measured using a method conforming to JIS K 7121. Specifically, approximately 10 mg of the target resin sample is placed in an aluminum sample pan whose mass has been measured in advance, and after the mass is measured again, the pan is sealed with a lid. Next, this sample container and a sample pan prepared without the resin are placed in a holder in a Shimadzu DSC-60 (differential scanning calorimeter), and measurements are performed at a temperature increase rate of 10°C / min to obtain a DSC chart. The intersection of the low-temperature baseline and the tangent to the inflection point of the DSC curve is then determined, and the temperature at this intersection is taken as the glass transition temperature. Indium is used for temperature calibration.

[0061] On the other hand, for acrylic resins, the value calculated by the following formula 1 can be used as the glass transition temperature.

[0062] Formula 1: 1 / Tg = Σ(Wn / Tgn)

[0063] In the above formula 1, 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.

[0064] When an acrylic resin is used as the binder resin, its acid value 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 acrylic resin within the above range, even if a portion of the aqueous inkjet ink dries near the nozzle of the inkjet head, a significant increase in viscosity of the aqueous inkjet ink can be suppressed, making it easier to improve standby ejection properties and also suppressing beading in printed matter.

[0065] In this disclosure, the "acid value of a resin" refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In this disclosure, the acid value used is a value calculated by the following method. For example, if a resin contains Wa mass% of polymerizable monomers 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 2:

[0066] Formula 2: (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0067] In the above formula 2, the number "56.11" is the molecular weight of potassium hydroxide.

[0068] In one embodiment, when the aqueous inkjet ink of this embodiment contains an acrylic resin as a binder resin, it is preferable that the acrylic resin has a hydroxyl group. It is believed that the acrylic resin having a hydroxyl group forms an interaction with the dipropylene glycol monopropyl ether (A), the compound (B), etc. This interaction is believed to optimize the viscoelasticity of the aqueous inkjet ink and greatly improve the standby jetting properties of the aqueous inkjet ink.

[0069] From the viewpoint of obtaining an aqueous inkjet ink that is excellent in all of standby ejection properties, beading resistance of printed matter, and lamination suitability, the content of the binder resin contained in the aqueous inkjet ink of this embodiment is preferably 0.3 to 15 mass %, more preferably 1 to 14 mass %, and particularly preferably 2 to 13 mass %, calculated as solid content, of the total amount of the aqueous inkjet ink.

[0070] Furthermore, the ratio of the content of the dipropylene glycol monopropyl ether (A) to the content of the binder resin (dipropylene glycol monopropyl ether (A) / binder resin) is preferably 0.3 to 2.3 by mass, and particularly preferably 0.5 to 1.5. When the value of the above ratio is within the above range, the dipropylene glycol monopropyl ether (A) functions favorably as a film-forming aid for the binder resin, improving the laminate strength of the printed material. Furthermore, aggregation and precipitation of the binder resin near the nozzles of the inkjet head can be suppressed, preventing deterioration of standby discharge properties.

[0071] From the viewpoint of improving adhesion to the printing substrate and improving lamination strength, and further from the viewpoint of accelerating the drying of the aqueous inkjet ink and suppressing beading in printed matter, the content of the binder resin is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, of the total amount of resin contained in the aqueous inkjet ink.

[0072] <Pigment dispersion resin> From the viewpoint of easily improving the standby jetting properties of the aqueous inkjet ink and the laminate strength of printed matter, the pigment contained in the aqueous inkjet ink of this embodiment is preferably dispersed in a resin used for pigment dispersion (also referred to as a "pigment dispersion resin" in the present disclosure). The pigment dispersion resin may also serve as a binder resin.

[0073] Examples of resins used for dispersing pigments include resin microparticles that encapsulate pigments, and resins (which may be water-soluble resins or resin microparticles) that have an adsorption rate for pigments of 35% by mass or more. As an example of a method for measuring the adsorption rate for a pigment, a pigment dispersion (or an ink that does not contain any solid content other than the resin being investigated) diluted with water as needed 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 (WR0 [g]) contained in the pigment dispersion (or ink) that has been centrifuged, and then dividing the resulting value by WR0.

[0074] 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, vinyl alcohol resins, etc. These resins may be used alone or in combination of two or more.

[0075] Among these resins, the resin used for pigment dispersion is preferably at least one resin selected from the group consisting of acrylic resin, styrene resin, maleic acid resin, and polyester resin, because the use of such a resin improves the adsorption of the pigment dispersion resin to the pigment, thereby improving standby discharge properties.

[0076] The acid value of the pigment dispersion resin is preferably 80 to 400 mgKOH / g, more preferably 100 to 350 mgKOH / g, and particularly preferably 115 to 300 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment and facilitate improvement of standby discharge properties. Furthermore, the affinity between the pigment dispersion resin and the printing substrate is improved, and the affinity between the pigment dispersion resin and the binder resin is also improved via compound (B) and the like, thereby improving the laminate strength of the printed material.

[0077] The content of the pigment dispersing resin contained in the aqueous inkjet ink of this embodiment is preferably 1 to 40 mass % and more preferably 2 to 30 mass % in terms of solid content relative to the pigment content, from the viewpoint of being able to improve all of the pigment dispersion stability, standby ejection properties, and lamination strength of printed matter.

[0078] <Surfactant> In the aqueous inkjet ink of this embodiment, a surfactant (hereinafter also simply referred to as "activator") is used to ensure wetting and spreading on the printing substrate and to suppress beading.

[0079] Any conventionally known surfactant can be used as the surfactant. In particular, in consideration of suppressing beading and pinholes and improving standby discharge properties, it is preferable to use a nonionic surfactant.

[0080] In addition, 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, polyethylene glycol monoaryl ether-based surfactants, glycerin fatty acid ester-based surfactants, and sorbitan fatty acid ester-based surfactants.

[0081] 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 monoaryl 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", the "polyethylene glycol monoaryl ether surfactant", and the "polyethylene glycol alkylamine surfactant" may each have a propylene oxide group.

[0082] 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 at least one 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 polyethylene glycol monoaryl 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 polyethylene glycol monoaryl 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.

[0083] Among the surfactants listed above, it is preferable to use at least one selected from the group consisting of acetylene diol surfactants, siloxane surfactants, polyethylene glycol monoalkyl ether surfactants, and polyethylene glycol monoaryl ether surfactants, from the viewpoints that they have a high ability to reduce surface tension, ensure excellent wetting and spreading properties regardless of the printing substrate used, and can suitably suppress beading.

[0084] Furthermore, from the viewpoints of easily obtaining printed matter free of beading and pinholes and improving the laminate strength of the printed matter, it is preferable to use a siloxane surfactant in combination with at least one selected from the group consisting of an acetylenic diol surfactant, a polyethylene glycol monoalkyl ether surfactant, and a polyethylene glycol monoaryl ether surfactant, and it is particularly preferable to use a siloxane surfactant in combination with an acetylenic diol surfactant. Furthermore, it is preferable that the surfactant used in the aqueous inkjet ink of this embodiment has a hydrophobic group and a hydrophilic group in one molecule. Therefore, for the siloxane surfactant, a compound having an ethylene oxide group on a side chain and / or at both ends of the polydimethylsiloxane chain can be preferably used, and for the acetylenic diol surfactant, a compound having an ethylene oxide group can be preferably used.

[0085] The total content of surfactants contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 5% by mass, and more preferably 0.2 to 4% by mass, of the total amount of the aqueous inkjet ink. By keeping the total content of surfactants within this range, it is possible to improve the standby ejection properties of the aqueous inkjet ink, as well as the beading resistance, pinhole resistance, and lamination suitability of the printed matter. For example, the total content of the surfactants may be 0.1 to 2% by mass, 0.1 to 1.5% by mass, or 0.1 to 1% by mass.

[0086] Furthermore, the ratio of the content of the dipropylene glycol monopropyl ether (A) to the total content of the surfactants (dipropylene glycol monopropyl ether (A) / surfactant) is preferably 1.3 to 7.8 by mass, and particularly preferably 2.0 to 7.2. When the value of the ratio is within the above range, the dipropylene glycol monopropyl ether (A) functions to assist the surfactant, and the occurrence of beading and pinholes can be suppressed.

[0087] <Siloxane surfactants> When the aqueous inkjet ink of this embodiment contains a siloxane surfactant, as described above, a compound having an ethylene oxide group at a side chain and / or at both ends of a polydimethylsiloxane chain can be suitably used as the siloxane surfactant. Specifically, a compound having a structure represented by the following general formula 3 can be suitably used as the siloxane surfactant.

[0088] General formula 3: [ka]

[0089] In General Formula 3, 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. 1 is a methyl group or a structure represented by the following general formula 4, and R 2 is an alkyl group having 1 to 6 carbon atoms, or a structure represented by the following general formula 4, where R 1 When R is a methyl group, p is 0. 1 and R 2 At least one of the groups has a structure represented by the following general formula 4 (R 1 and R 2 However, both may have a structure represented by the following general formula 4).

[0090] General formula 4: [ka]

[0091] In general formula 4, 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. 3 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. The addition of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be in a block or random manner.

[0092] The siloxane surfactant may be used alone or in combination of two or more kinds. In addition, those synthesized by conventionally known synthesis methods may be used, or commercially available products may be used.

[0093] When the aqueous inkjet ink of this embodiment contains a compound having a structure represented by the above general formula 3 as a siloxane-based surfactant, in order to easily suppress beading and pinholes in printed matter, it is preferable to use a compound having a structure represented by the above general formula 3 in which R 1 is a methyl group, and R 2 is a structure represented by the above general formula 4, p is 0, and q is an integer of 10 to 30, and compounds that can be used particularly preferably.

[0094] When the aqueous inkjet ink of this embodiment contains a siloxane surfactant, the content thereof is preferably 0.1 to 3.0 mass %, more preferably 0.3 to 2.5 mass %, and particularly preferably 0.5 to 2.0 mass %, of the total amount of the aqueous inkjet ink. By using the siloxane surfactant within the above range, it is possible to achieve high levels of beading resistance, pinhole resistance, lamination suitability, and standby discharge performance.

[0095] <Acetylene diol surfactant> Examples of the acetylene diol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 3,6-diisopropyl-2,7-dimethyloct-4-yne-3,6-diol, and octadeca- Examples of suitable compounds include 5,8-dibutyl-2,9-dimethyl-octadec-9-yne-8,11-diol, 5,8-dibutyl-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, and 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol, as well as ethylene oxide and / or propylene oxide modified versions of the compounds listed above. The compounds listed above may be used alone or in combination. 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, 465, 485, 2502, SE, SE-F, Dynol 604, 607 (manufactured by Evonik Chemical Industry Co., Ltd.), Olfine E1004, E1006, E1010, E1020, PD-001, PD-002W, PD-004, EXP.4200, and EXP.4123 (manufactured by Nissin Chemical Industry Co., Ltd.).

[0096] Among these, it is preferable to use a compound having an HLB value of 4 to 13 as the acetylenic diol surfactant, more preferably a compound having an HLB value of 7 to 11, and particularly preferably a compound having an HLB value of 7 to 9, because this allows for the production of printed matter that is free of pinholes and beading, the printed matter has good lamination suitability, and furthermore has excellent affinity with dipropylene glycol monopropyl ether and good continuous discharge properties.

[0097] Among the commercially available acetylene diol surfactants listed above, those having an HLB value of 7 to 11 include Surfynol 440 (HLB value = 8), Surfynol 2502 (HLB value = 8), Dynol 604 (HLB value = 8), Olfine E1004 (HLB value = 8), and Olfine E1006 (HLB value = 11). Among these, it is preferable to select at least one surfactant selected from the group consisting of Surfynol 440, Surfynol 2502, Dynol 604, and Olfine E1004, which have an HLB value of 7 to 9. It is more preferable to use Surfynol 2502 and / or Dynol 604, and it is particularly preferable to use Surfynol 2502. Compared to other compounds, Surfynol 2502 has a large molecular weight and a large number of added moles of ethylene oxide groups. Therefore, it is considered that compatibility with the dipropylene glycol monopropyl ether (A) can easily realize improvements in standby discharge properties and lamination suitability of printed matter.

[0098] 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).

[0099] The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that indicate the degree of hydrophilicity of a material. The smaller the HLB value, the more hydrophobic the material, and the larger the HLB value, the more hydrophilic the material. In this disclosure, the HLB value is calculated using the Griffin method. Specifically, the sum of the molecular weights of the hydrophilic portions contained in the target material is divided by the molecular weight of the material, and the calculated value is multiplied by 20 to obtain the HLB value.

[0100] When the aqueous inkjet ink of this embodiment contains an acetylene diol surfactant, the content thereof is preferably 0.1 to 2.0 mass %, more preferably 0.2 to 1.5 mass %, of the total amount of the aqueous inkjet ink. By using the surfactant within this range, it is possible to achieve high levels of beading resistance, lamination suitability, and standby dischargeability.

[0101] Furthermore, when the aqueous inkjet ink of this embodiment contains an acetylenic diol surfactant, the ratio of the content of dipropylene glycol monopropyl ether (A) to the content of the acetylenic diol surfactant (dipropylene glycol monopropyl ether (A) / acetylenic diol surfactant) is preferably from 2 to 25 by mass, more preferably from 4 to 14, and particularly preferably from 4 to 10. By setting the value of the ratio within the above range, the other water-soluble organic solvent is favorably compatible with the dipropylene glycol monopropyl ether (A), and it is possible to easily suppress beading in printed matter, improve laminate strength, and further improve standby discharge properties.

[0102] <Polyethylene glycol monoalkyl ether surfactants> When the aqueous inkjet ink of the present embodiment contains a polyethylene glycol monoalkyl ether surfactant, the polyethylene glycol monoalkyl ether surfactant may be synthesized by a conventionally known synthesis method, or may be a commercially available product. Examples of commercially available polyethylene glycol monoalkyl ether surfactants include the Emulgen series (manufactured by Kao Corporation), such as the Emulgen 100 series, 200 series, 300 series, 700 series, 1100 series, and LS-100 series; the Braunon series (manufactured by BE series, CH series, EH series, EL series, LI series, OX series, and SR series); the Finesurf series (manufactured by Aoki Oil Industries Co., Ltd.), such as the Finesurf 200 series, 320, 400, 500, 600-70, D series, FO series, NE series, and TD series; the Safetycut series (manufactured by Aoki Oil Industries Co., Ltd.), such as the Safetycut ID series and ND series; the Nonion series (manufactured by Nonion B series, K series, P series, S series, EH series, HT series, and ID series); the Persoft NK series; Dispanol TOC (manufactured by NOF Corporation); and Lutensol. Examples include the Rutensol series (manufactured by BASF), such as the A series, M series, AO series, AT series, ON series, XA series, XL series, and XP series, and the Newcol series (manufactured by Nippon Nyukazai Co., Ltd.), such as the Newcol 1000 series, 1300 series, 1600 series, 1800 series, and 2300 series. The above-listed products may be used alone or in combination of two or more.

[0103] The content of the polyethylene glycol monoalkyl ether surfactant in the aqueous inkjet ink of this embodiment is preferably 0.1 to 3.0 mass %, more preferably 0.15 to 2.5 mass %, and particularly preferably 0.2 to 2.0 mass % of the total amount of the aqueous inkjet ink. By using it within the above range, it becomes easy to achieve high levels of all of the following, in particular, suppression of pinholes in printed matter, improvement of lamination strength, and improvement of standby discharge properties.

[0104] <Polyethylene glycol monoaryl ether surfactants> When the aqueous inkjet ink of this embodiment contains a polyethylene glycol monoaryl ether surfactant, the polyethylene glycol monoaryl ether surfactant may be synthesized by a conventionally known synthesis method, or a commercially available product may be used. Examples of commercially available polyethylene glycol monoaryl ether surfactants include the Emulgen series (manufactured by Kao Corporation), such as the Emulgen A series and B-66; the Blaunon series (manufactured by Aoki Oil & Fat Industries Co., Ltd.), such as the Blaunon BA series, BN series, DP series, DSP series, N series, NK series, PH series, TSP series, and KTSP-16; and the Blaunon series (manufactured by Nippon Nyukazai Co., Ltd.), such as the Nyukol 600 series, 700 series, 2600 series, B series, and CMP series. The above-listed products may be used alone or in combination of two or more.

[0105] The content of the polyethylene glycol monoalkyl ether surfactant in the aqueous inkjet ink of this embodiment is preferably 0.1 to 3.0 mass %, more preferably 0.15 to 2.5 mass %, and particularly preferably 0.2 to 2.0 mass % of the total amount of the aqueous inkjet ink. By using it within the above range, it becomes easy to achieve high levels of both suppression of beading and pinholes in printed matter and improvement of laminate strength.

[0106] <Pigments> The aqueous inkjet ink of this embodiment contains a pigment. Any conventionally known organic or inorganic pigment can be used as the pigment, and for example, pigments represented by the following color index names can be used. 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.

[0107] In one embodiment, the aqueous inkjet ink of this embodiment preferably uses a condensed disazo pigment as the pigment. While the detailed mechanism is unknown, it is believed that dipropylene glycol monopropyl ether and the condensed disazo pigment exhibit good compatibility, while compound (B) suppresses the destruction of the dispersion state of the condensed disazo pigment. As a result, the standby ejection properties of the aqueous inkjet ink are improved, and the condensed disazo pigment is uniformly present in the ink film without localization, thereby improving the laminate strength 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.

[0108] 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. In addition, 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, beading resistance, and laminate strength 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 high hiding power and laminate strength without deteriorating the jetting stability of the aqueous white ink.

[0109] <Other ingredients> In addition to the components described above, the aqueous inkjet ink of this embodiment may contain at least one component selected from the group consisting of a pH adjuster, a preservative, a crosslinking agent, an ultraviolet absorber, and an infrared absorber. Each of these components may be one or more conventionally known compounds.

[0110] <Method for manufacturing water-based inkjet ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. For example, a pigment dispersion is produced by dispersing a pigment in a medium containing at least water (aqueous medium) using a pigment dispersing resin. Water, a binder resin, dipropylene glycol monopropyl ether (A), compound (B), a surfactant, and the like are then added to the pigment dispersion, followed by thorough stirring and mixing, and then coarse particles are removed by filtration, centrifugation, or the like. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the above-described method.

[0111] <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 disclosure, the viscosity is measured at 25°C using a cone-plate rotational viscometer (E-type viscometer, cone angle 1°34') such as the TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

[0112] Furthermore, in order to obtain an aqueous inkjet ink that exhibits excellent standby ejection properties and excellent beading resistance and pinhole resistance in 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 disclosure, the static surface tension is measured in an environment of 25° C. using the Wilhelmy method (plate method) using an automatic surface tensiometer such as the CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0113] In order to improve standby discharge properties and laminate strength, 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.

[0114] <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 disclosure described above.

[0115] <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, thereby significantly improving the print quality of the printed matter, such as by suppressing beading.

[0116] 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.

[0117] <Inkjet printing method> In this embodiment, a method for producing a printed matter includes printing an aqueous inkjet ink onto a printing substrate, where the aqueous inkjet ink is the aqueous inkjet ink of this embodiment described above. The method may further include laminating the printing substrate. The printing substrate may be a permeable substrate, a low-permeable substrate, or a non-permeable substrate. Even a non-permeable substrate can provide adhesion of the printing substrate and lamination strength.

[0118] 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).

[0119] ≪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.

[0120] 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.

[0121] 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. Furthermore, from the viewpoints of simultaneously suppressing beading in printed matter and improving standby ejection performance, 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 printed matter is 1,200 dpi or higher. In one embodiment, from the viewpoint of achieving both suppression of beading in the printed matter and improvement of standby ejection properties, as well as improvement of the lamination strength of the 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, in the range of (4,800 / DR) [picoliters].

[0122] ≪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 above drying methods are used, they may be used separately (e.g., consecutively) or in combination. 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.

[0123] 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.

[0124] <Printed material> The aqueous inkjet ink of this embodiment can be used to produce a printed matter (a printing substrate on which printed information is recorded). The inkjet printing method described above can be used to produce the printed matter. The printed matter includes a printing substrate and a printing layer, and the printing layer is formed by printing the aqueous inkjet ink of this embodiment onto the printing substrate. The printed matter may further include a laminate layer, and the printing layer may be interposed between the printing substrate and the laminate layer. The laminate layer may include a sealant substrate and a laminating adhesive. In another embodiment, the printed matter may further include an overcoat varnish layer on the surface of the printing layer. The printing substrate may be a permeable substrate, a low-permeable substrate, or a non-permeable substrate; however, even a non-permeable substrate can provide adhesion of the printing substrate and laminate strength.

[0125] <Printing base material> The printing substrate on which the aqueous inkjet ink of this embodiment is printed is not particularly limited, and any known substrate can be used, such as a permeable substrate, a low-permeable substrate, a non-permeable substrate, etc. Among these, the aqueous inkjet ink of this embodiment is particularly suitable for use on a non-permeable substrate, from the viewpoint of optimally achieving the effects described above. Examples of the impermeable substrate include polyolefin resins such as polyethylene, biaxially oriented polypropylene (OPP), and non-axially oriented polypropylene (CPP); polyester resins such as polyethylene terephthalate (PET), polycarbonate, and polylactic acid; polystyrene resins such as polystyrene, AS resin, and ABS resin; polyamide resins such as nylon; chlorine-containing resins such as polyvinyl chloride and polyvinylidene chloride; cellophane; and film or sheet-like materials made from composite materials of these. These printing substrates may be surface-treated, such as by corona treatment or plasma treatment, or may be coated with a resin such as a urethane resin, an acrylic resin, or a polyolefin resin to suppress beading.

[0126] <Coating treatment> On the other hand, if necessary, the printed surface of a printed material produced using the aqueous inkjet ink of this embodiment can be subjected to a coating treatment. Specific examples of such coating treatment include application and printing of a coating composition, and lamination using a dry lamination method, a solventless lamination method, an extrusion lamination method, etc. When performing the coating treatment, any one of these methods may be selected, or a combination of two or more may be used.

[0127] The coating composition may contain a colorant component, or may not contain the colorant component. A specific example of a coating composition that does not contain a colorant component is the overcoat liquid disclosed in JP 2023-96217 A. In this disclosure, a coating composition that does not contain a colorant component and that provides a glossy layer after coating is referred to as an overcoat varnish. When the aqueous clear ink described below satisfies the above-mentioned requirements, the aqueous clear ink is included in the overcoat varnish.

[0128] When a coating treatment is performed on a printed material by applying and printing a coating composition, the coating and printing method may be either a method of printing without contact with the printing substrate, such as inkjet printing, or a method of printing by bringing the coating composition into contact with the printing substrate. Furthermore, when a method of printing without contact with the printing substrate is selected, it is preferable to use, as the coating composition, an aqueous inkjet ink (aqueous clear ink) that does not substantially contain a colorant component, which is the aqueous inkjet ink of this embodiment except for the pigment.

[0129] Furthermore, when a printed matter is laminated, the adhesive (laminating adhesive) used to laminate the sealant substrate is preferably composed of a mixture of a polyol component and a polyisocyanate component.

[0130] The polyol component is a resin component having a hydroxyl group, and polyurethane resins and polyester resins are preferably used in view of coatability, wettability and permeability to the interface of a printed material, and the laminate strength developed after aging. Among these, it is preferable that the polyol component contains a polyester polyol, because the aqueous inkjet ink of this embodiment provides good wettability and spreadability to the interface of a printed material, for example, the printed surface, and also provides excellent laminate strength for a laminated printed material (laminate). The polyol component may be a single component, or multiple components may be used in combination.

[0131] Furthermore, the polyisocyanate component reacts with the polyol component to form a urethane bond, thereby increasing the molecular weight of the adhesive layer and improving the laminate strength. In particular, from the viewpoints of compatibility with the polyol component, wettability and spreadability at the interface of a printed material obtained using the aqueous inkjet ink of this embodiment, and improving the laminate strength of the laminate, it is preferable that the polyisocyanate component contains a polyether-based urethane resin having an isocyanate group terminal. From the same viewpoint, the blending amount of the polyisocyanate component is preferably 50 to 80% by mass relative to the polyol component. The polyisocyanate component may be a single component or a combination of multiple components.

[0132] Examples of sealant substrates used in the lamination process include polypropylene films and polyethylene films such as CPP films and linear short-chain branched polyethylene (LLDPE) films. Films with a vapor-deposited metal (oxide) layer such as aluminum oxide may also be used. [Example]

[0133] 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.

[0134] <Production of binder resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 72.4 parts of 2-butanone and purged with nitrogen gas. After heating the reaction vessel to 80°C, a mixture of polymerizable monomers (4.5 parts methacrylic acid, 5.0 parts 2-hydroxyethyl methacrylate, 90.5 parts methyl methacrylate), and 12 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise over 2 hours. After completion of the dropwise addition, the temperature inside the reaction vessel was maintained at 80°C, and the polymerization reaction was continued for 3 hours. An additional 0.6 parts of V-601 was then added, and the polymerization reaction was continued for 2 hours at 80°C, yielding a solution containing binder resin 1. After cooling the solution of binder resin 1 to 50°C, 4.7 parts of dimethylaminoethanol was added to neutralize the carboxyl groups present in the binder resin, and then 140 parts of ion-exchanged water was added. Thereafter, the solution was heated to 78°C or higher, and 2-butanone was distilled off. After that, the solids concentration was adjusted to 30% with ion-exchanged water, and an aqueous solution of binder resin 1 (solids concentration 30%) was obtained. The glass transition temperature (Tg) of binder resin 1 calculated using the above formula 1 was 103°C. The acid value of binder resin 1 calculated using the above formula 2 was 29 (mgKOH / g). Furthermore, the weight average molecular weight of binder resin 1 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 (tetrahydrofuran) as a developing solvent, was approximately 7,000.

[0135] In the present disclosure, the term "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

[0136] <Production of Yellow Pigment Dispersion 1> 450 g of CI Pigment Yellow 155 (FERRO "Lysopure Yellow 5518P"), 115 g of Resin 2 (a block polymer of benzyl methacrylate / / acrylic acid / / methyl methacrylate / / butyl acrylate = 65 / / 15 / / 10 / / 10 (weight ratio) in which all acid groups were neutralized with dimethylaminoethanol, acid value 116.8 mg KOH / g, weight average molecular weight 24,000. Note that " / / " indicates the block boundary. Note that within each block, the polymerizable monomers are randomly polymerized) and 2,435 g of water were added to a mixing vessel (10 L) equipped with a stirrer and premixed for 1 hour. Next, the mixture was circulated and dispersed using a Shinmaru Enterprises "Dynomill" (0.6 L) filled with 1,800 g of 0.5 mm diameter zirconia beads. Then, the D50 of the mixture was measured at regular intervals (for example, every hour) using the above-mentioned device, and the circulatory dispersion was terminated when the D50 became 150 nm or less, thereby producing yellow pigment dispersion liquid 1.

[0137] <Production of Yellow Pigment Dispersion Liquid 2> Yellow pigment dispersion 2 was produced using the same materials and method as for the above yellow pigment dispersion 1, except that resin 3 (a random polymer of styrene / α-methylstyrene / acrylic acid / butyl acrylate = 27.5 / 25 / 27.5 / 20 (mass ratio), in which all acid groups had been neutralized with potassium hydroxide, acid value 214.1 mgKOH / g, and mass average molecular weight 14,000) was used instead of resin 2.

[0138] <Production of Yellow Pigment Dispersion 3> A reaction vessel was charged with 93.3 parts of Yellow Pigment Dispersion 2 obtained by the method described above, 0.7 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation), and 6.0 parts of ion-exchanged water. The contents of the reaction vessel were then heated to 80°C while stirring. After reaching 80°C, stirring was continued for 3 hours while maintaining the temperature, resulting in a reaction (crosslinking reaction) between the carboxy groups in Resin 3 and the epoxy groups in the trimethylolpropane polyglycidyl ether. The internal temperature of the reaction vessel was then cooled to below 30°C, and ion-exchanged water was added to adjust the solids concentration, yielding Yellow Pigment Dispersion 3 (pigment concentration 14%).

[0139] <Production of water-based inkjet inks 1-159> Using the yellow pigment dispersions 1 to 3 produced by the method described above, each raw material was charged into a mixing vessel equipped with a stirrer to obtain the formulation shown in each column of Tables 1-1 to 1-9 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 159.

[0140] 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 1-1 to 1-9, the ingredients were added in the order listed, starting with the ingredient listed in 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 component was arbitrary.

[0141] [Table 1-1]

[0142] [Table 1-2]

[0143] [Table 1-3]

[0144] [Table 1-4]

[0145] [Table 1-5]

[0146] [Table 1-6]

[0147] [Table 1-7]

[0148] [Table 1-8]

[0149] [Table 1-9]

[0150] In Tables 1-1 to 1-9 above, "Nv" represents the solids concentration, "Tg" represents the glass transition temperature, and "AV" represents the acid value. Furthermore, "remaining amount" refers to the amount required to make the total amount of aqueous inkjet ink added 100% by mass. Details of the product names listed in Tables 1-1 to 1-9 above are as follows: Neocryl A-1127: Covestro acrylic resin microparticles (solids concentration 30%, glass transition temperature 103°C, acid value 29mgKOH / g) Neocryl A-662: Acrylic resin microparticles manufactured by Covestro (solid concentration 44%, glass transition temperature 5°C, acid value 18mgKOH / g) Neocryl A-639: Covestro acrylic resin microparticles (solids concentration 40%, glass transition temperature 95°C, acid value 24mgKOH / g) Superflex 870: urethane resin particles manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (solids concentration 30%, glass transition temperature 78°C) Superflex 420: urethane resin particles manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (solids concentration 32%, glass transition temperature -10°C) Superflex 470: urethane resin particles manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (solids concentration 38%, glass transition temperature -31°C) BYK-3420: siloxane surfactant manufactured by BYK-Chemie (in the above general formula 3, R 1 is a methyl group, and R 2 is a compound having a structure represented by the above general formula 4, where p is 0 and q is an integer of 10 to 30) TEGO Glide 440: a siloxane surfactant manufactured by Evonik (in the above general formula 3, R 1 is a methyl group, and R 2 is a compound having a structure represented by the above general formula 4, where p is 0 and q is an integer of 10 to 30) BYK-349: siloxane surfactant manufactured by BYK-Chemie (in the above general formula 3, R 1 is a methyl group, and R 2 is a structure represented by the above general formula 4, and is not a compound in which p is 0 and q is an integer of 10 to 30) Surfynol 104: Evonik acetylene diol surfactant Surfynol 440: Evonik acetylene diol surfactant Surfynol 2502: Evonik acetylene diol surfactant Surfynol 465: Evonik acetylene diol surfactant Emulgen 104P: Kao Corporation polyethylene glycol monoalkyl ether surfactant (polyoxyethylene lauryl ether) Emulgen 108: Kao Corporation polyethylene glycol monoalkyl ether surfactant (polyoxyethylene lauryl ether) Emulgen 306P: Kao Corporation polyethylene glycol monoalkyl ether surfactant (polyoxyethylene stearyl ether) Brownon N502: Aoki Oil & Fat Co., Ltd. Polyethylene glycol monoaryl ether surfactant (polyoxyethylene nonylphenyl ether) Brownon N504: Aoki Oil & Fat Co., Ltd. Polyethylene glycol monoaryl ether surfactant (polyoxyethylene nonylphenyl ether) Brownon N507: Aoki Oil & Fat Co., Ltd. Polyethylene glycol monoaryl ether surfactant (polyoxyethylene nonylphenyl ether) 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)

[0151] [Examples 1 to 142, Comparative Examples 1 to 17] The above-mentioned water-based inkjet inks 1 to 159 were used to carry out the following evaluations 1 to 4. The evaluation results are shown in Tables 2-1 to 2-3.

[0152] <Evaluation 1: Standby discharge> The aqueous inkjet inks prepared above were filled into an inkjet ejection device equipped with a Kyocera head (KJ4B-1200) installed in an environment of 25°C and 50% RH. A nozzle check pattern was printed to confirm that the aqueous inkjet ink was ejected normally from all nozzles, and the ejection device was then left to stand for 30 minutes. A nozzle check pattern was then printed again to check the number of nozzles from which the aqueous inkjet ink was not ejected (number of missing nozzles), thereby evaluating standby ejection performance. The evaluation criteria are as follows, with ◎, ○, and △ being considered practical. ◎: The number of missing nozzles was 0 ○: The number of missing nozzles was 1 to 5 △: The number of missing nozzles was 6 to 9 ×: The number of missing nozzles was 10 or more.

[0153] <Evaluation 2: Beading resistance> An inkjet printing device equipped with a Kyocera inkjet head (KJ4B-1200) was placed above the conveyor in an environment of 25°C and 50% RH. After filling each with the aqueous inkjet ink prepared above, a nozzle check pattern was printed to confirm that the aqueous inkjet ink was being ejected normally from all nozzles, and then the printing device was left to stand for 1 minute. Then, a solid print was performed at a printing frequency of 40 kHz and a resolution of 1,200 x 1,200 dpi on a PET film (FE2001, 12 μm thick) manufactured by Futamura Chemical Co., Ltd. After printing, the PET film was left to stand in an air oven at 85°C for 1 minute to dry the aqueous inkjet ink, thereby obtaining a solid print. The beading resistance was evaluated by visually checking the number of streaks (areas where the ink did not adhere to the printing substrate and appeared streaky) present on the solid print. The evaluation criteria are as follows, with ◎, ○, and △ being in the practical range. ⊚: Five or fewer streaks were visually observed. ○: 6 to 10 streaks were visually confirmed. △: 11 to 20 lines were visually confirmed. ×: 21 or more streaks were visually observed.

[0154] <Rating 3: Pinhole resistance> Ten solid prints with a 100% printing rate were produced using the same printing conditions and printing substrate as in Evaluation 2 above. The number of pinholes in each of the resulting solid prints was visually checked, and the total number of pinholes present on the 10 solid prints was calculated to evaluate pinhole resistance. The evaluation criteria are as follows, with ◎, ○, and △ being considered within the practical range. ◎: No pinholes were found on any of the 10 solid prints ○: The total number of pinholes was 1 to 2 △: The total number of pinholes was 3 to 5 ×: The total number of pinholes was 6 or more

[0155] <Evaluation 4: Evaluation of laminate strength> Using the same printing conditions as in Evaluation 2 above, and using a PET film (FE2001, thickness 12 μm) manufactured by Futamura Chemical Co., Ltd. as the printing substrate, a solid print with a printing rate of 100% was produced. Next, a solventless laminating adhesive (EA-N373A / B manufactured by Toyo-Morton) was applied to the printed surface of the solid print using a solventless test coater at a temperature of 60°C and a coating speed of 50 m / min (coating amount: 2 g / m 2 Furthermore, the corona-treated surface of a non-oriented polypropylene film (CPP) "FHK2" (manufactured by Futamura Chemical, thickness 25 μm) was superimposed on the coated surface of the above laminating adhesive, and then aging was carried out for one day in an environment of 40°C and 80% RH to cure the solventless laminating adhesive composition and produce a laminated product. The resulting laminated product was then cut into a length of 300 mm and a width of 15 mm to prepare test pieces. Using an Instron tensile tester, the test pieces were pulled at a peel rate of 300 mm / min in a 25°C environment to measure the T-peel strength (N). This test was performed five times, and the average value was calculated to evaluate the laminate strength. The evaluation criteria were as follows, with ◎, ○, △, and ▽ being in the practical range. ◎: Adhesive force 1.5N or more ○: Adhesive strength 1.0N or more, less than 1.5N △: Adhesion strength 0.6N or more, less than 1.0N ▽: Adhesive strength 0.3N or more, less than 0.6N ×: Adhesion strength less than 0.3N

[0156] [Table 2-1]

[0157] [Table 2-2]

[0158] [Table 2-3]

[0159] As a result of the evaluation, it was confirmed that the aqueous inkjet inks of Examples 1 to 142 having the above-mentioned configurations had practically acceptable quality in all of the standby ejection properties, beading resistance, pinhole resistance, and lamination strength.

[0160] [Examples 143 to 169] Using a portion of the aqueous inkjet ink produced above, the following evaluations 1B and 3B were further carried out. The evaluation results are shown in Table 3.

[0161] <Evaluation 1B: Standby ejection 2> An additional evaluation of standby dischargeability was carried out in the same manner as in Evaluation 1, except that the same inkjet discharge device as in Evaluation 1 above was used and the resting time after printing the nozzle check pattern was changed to 60 minutes. The evaluation criteria are as follows, with ◎ and ○ ratings being in the practically preferable range, and ◎+ rating being in the practically particularly preferable range. ⊚+: The number of missing nozzles was 0. ◎: The number of missing nozzles was 1 to 5 ○: The number of missing nozzles was 6 to 9 △: The number of missing nozzles was 10 to 19 ×: The number of missing nozzles was 20 or more.

[0162] <Evaluation 3B: Pinhole resistance 2> An additional evaluation of pinhole resistance was carried out in the same manner as in Evaluation 3 above, except that the same printing conditions and printing substrate as in Evaluation 2 above were used and the number of solid prints produced was 30. The evaluation criteria are as follows, with ◎ and ○ ratings being in the practically preferable range, and ◎+ rating being in the particularly practically preferable range. ◎+: No pinholes were found on any of the 30 solid prints. ◎: The total number of pinholes was 1 to 2 ○: The total number of pinholes was 3 to 5 △: The total number of pinholes was 6 to 9 ×: The total number of pinholes was 10 or more

[0163] [Table 3]

[0164] As a result of the evaluation, it was confirmed that standby discharge properties were significantly improved by using 1,3-butanediol and / or 2-methyl-1,3-propanediol as compound (B), a compound with an HLB value of 7 to 9 as the acetylene diol surfactant, and an acrylic resin having a hydroxyl group as the binder resin. It was also confirmed that pinhole resistance was significantly improved by using propylene glycol monomethyl ether and / or propylene glycol monopropyl ether as other water-soluble organic solvents.

[0165] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0166] This disclosure is related to the subject matter described in Japanese Patent Application No. 2024-090799, filed June 4, 2024, the entire disclosure of which is incorporated herein by reference.

Claims

1. An aqueous inkjet ink containing a pigment, a binder resin, a water-soluble organic solvent, and a surfactant, the water-soluble organic solvent contains dipropylene glycol monopropyl ether (A) and at least one compound (B) selected from the group consisting of 1,3-butanediol, 2-methyl-1,3-propanediol, and 2-methyl-2,4-pentanediol; the content of the dipropylene glycol monopropyl ether (A) is 1 to 15% by mass based on the total amount of the aqueous inkjet ink, The aqueous inkjet ink has a total content of the water-soluble organic solvents of 8 to 35% by mass based on the total amount of the aqueous inkjet ink.

2. 2. The aqueous inkjet ink according to claim 1, wherein the ratio of the content of the dipropylene glycol monopropyl ether (A) to the content of the compound (B) (dipropylene glycol monopropyl ether (A) / compound (B)) is 0.15 to 3.0 on a mass basis.

3. 3. The aqueous inkjet ink according to claim 1, wherein the total content of the dipropylene glycol monopropyl ether (A) and the compound (B) is 20 to 100 mass % of the total content of the water-soluble organic solvent.

4. 4. The aqueous inkjet ink according to claim 3, wherein the total content of the dipropylene glycol monopropyl ether (A) and the compound (B) is 20 to 80 mass % of the total content of the water-soluble organic solvent.

5. 5. The aqueous inkjet ink according to claim 4, wherein the water-soluble organic solvent further comprises at least one selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether.

6. 3. The aqueous inkjet ink according to claim 1, wherein the content of the dipropylene glycol monopropyl ether (A) is 1 to 7% by mass based on the total amount of the aqueous inkjet ink.

7. A printed matter comprising a printing substrate and a printing layer, the printing layer being formed by printing the aqueous inkjet ink according to claim 1 or 2 onto the printing substrate.

8. The printed matter according to claim 7 , further comprising a laminate layer, wherein the printing layer is interposed between the printing substrate and the laminate layer.

9. The printed matter according to claim 8 , wherein the printing substrate is a non-porous substrate.

10. A method for producing a printed matter, comprising printing an aqueous inkjet ink onto a printing substrate, wherein the aqueous inkjet ink is the aqueous inkjet ink according to claim 1 or 2.

11. The method for producing a printed matter according to claim 10, further comprising laminating the printed matter.

12. The method for producing a printed matter according to claim 11 , wherein the printing substrate is a non-porous substrate.

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