Aqueous inkjet ink and printed matter

Abstract

An aqueous inkjet ink including a pigment, a surfactant (A), a water-soluble organic solvent, and a binder resin, wherein: the surfactant (A) contains a polyoxyalkylene monoalkyl ether-based compound (A-1) having a specific alkyl chain length and number of ethylene oxide groups, and a nonionic surfactant (A-2) (other than said compound (A-1)) having an HLB value of 1-10; and the water-soluble organic solvent includes hexylene glycol.

Description

Water-based inkjet inks and printed materials

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

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

[0003] An example of the digital printing method is the inkjet printing method. In the inkjet printing method, ink droplets are ejected from minute nozzles and applied to a printing substrate (also simply referred to as "substrate" in this disclosure), thereby forming images and / or characters on the printing substrate. The inkjet printing method is characterized by easy operation of the printing device and low noise during printing. Therefore, among digital printing methods, there is high demand for printing devices (inkjet printers) that employ the inkjet printing method.

[0004] In this disclosure, the printing substrate and the image and / or characters formed on the printing substrate by printing ink are collectively referred to as a "printed matter." The above "image" also includes solid images and seamless images such as checkered images.

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

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

[0007] However, in the past, when producing solid prints (prints with a 100% coverage) using aqueous inkjet inks on poorly permeable substrates such as coated paper and art paper, as well as non-permeable substrates such as film, it was difficult to obtain prints with print quality equivalent to that of plate-based printing. Specifically, when producing solid prints using aqueous inkjet inks, a phenomenon known as "whiteout" occurs, in which areas where the aqueous inkjet ink does not adhere to the printed substrate. Furthermore, a phenomenon known as "bleeding," in which aqueous inkjet inks of different colors mix with each other, is likely to occur. These phenomena are due to the poor wettability of the aqueous inkjet ink to the substrate, particularly on the order of microseconds (μs), caused by the uniquely high surface tension of water, the main solvent of aqueous inkjet inks.

[0008] Typically, hydrophobic organic solvents and / or surfactants are used to improve wettability of substrates. However, these components have poor solubility in water and are prone to foaming, resulting in the generation of air bubbles that can contribute to nozzle clogging. Furthermore, these components orient at the air-liquid interface formed at the nozzle end face of the inkjet head, destabilizing the air-liquid interface and destabilizing the meniscus of the aqueous inkjet ink. These problems are particularly likely to lead to nozzle clogging (a phenomenon in which aqueous inkjet ink is not ejected from the nozzle) immediately after the start of printing. Furthermore, due to the structure of the inkjet head, the nozzle diameter is very small, measuring several tens of micrometers. In particular, when printing is paused for an extended period of time, liquid components in the aqueous inkjet ink (water, water-soluble organic solvents, etc.) volatilize from the nozzle end face, while fresh aqueous inkjet ink may not be sufficiently supplied to the inkjet head. When this happens, the aqueous inkjet ink present in the vicinity of the nozzle end face will have an increase in solid content and / or an increase in the proportion of water-soluble organic solvents with high boiling points, which will cause the solid components (pigments, resins, etc.) to aggregate and become insolubilized, resulting in an increase in viscosity, and nozzle clogging due to this increase in viscosity may occur.

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

[0010] On the other hand, particularly in the packaging printing market, it is necessary to ensure that the dried ink film does not peel off even when the printed material to which water has adhered is rubbed with a finger or the like. In other words, the dried ink film is required to have a certain degree of water resistance. In order to impart water resistance to the dried ink film in aqueous inkjet inks containing a large amount of water-soluble ingredients, for example, it is necessary to use a binder resin with a large mass-average molecular weight to make the dried ink film a strong, continuous film. On the other hand, if more than a certain amount of binder resin is contained in the aqueous inkjet ink before printing (liquid), problems are likely to occur. Specifically, interactions between the binder resins or between the binder resin and the pigment dispersion resin in the aqueous inkjet ink may occur, resulting in problems such as deterioration of ejection stability and / or partial inhibition of the orientation of the surfactant at the gas-liquid interface.

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

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

[0013] For example, Patent Document 1 discloses an aqueous ink containing a water-insoluble polymer, a glycol ether-based organic solvent having a specific viscosity and vapor pressure, and 0.005 to 0.3 mass% of a silicone-based surfactant, with the content of the high-boiling organic solvent being kept below a certain amount. Patent Document 1 describes that the aqueous ink having the above-described configuration is excellent in continuous ejection properties and in suppressing color bleeding in recorded matter (printed matter). Furthermore, the examples of Patent Document 1 disclose an example of an aqueous ink that further uses an acetylene diol-based surfactant ("Surfynol 104PG50") and polyoxyethylene lauryl ether ("Emulgen 120", in which the number of moles of ethylene oxide structure added is 12) as surfactants in addition to a polyether-modified silicone-based surfactant ("Silface SAG005") (see paragraph 0090 and Tables 4 to 9 of Patent Document 1).

[0014] The ink used in the image recording method disclosed in Patent Document 2 contains an organic solvent having a specific structure and a specified CLogP value, an acetylene-based surfactant, a polyoxyethylene alkyl ether-based surfactant having an HLB value of 4 to 18, and a polyether-modified silicone-based surfactant. Patent Document 2 describes that the image recording method produces high-resolution prints that are free of graininess and intercolor bleeding (mixed color bleeding) and have excellent abrasion resistance. Furthermore, in the examples of Patent Document 2, "Surfynol 104," "Dynol 604," and "Surfynol DF110D" are used as the acetylene-based surfactants. Other polyoxyethylene alkyl ether-based surfactants used include "Emulgen 103" and "Emulgen 108," which have 3 and 6 moles of ethylene oxide added.

[0015] Furthermore, Patent Document 3 discloses an aqueous ink containing an acetylene-based surfactant (preferably having an HLB value of 8 or less), another nonionic surfactant, and an aqueous medium, wherein the HLB value, cloud point, etc. of the other nonionic surfactant are specified. It is disclosed that the aqueous ink is less likely to suffer from ejection defects due to drying and solidification in the nozzles of an inkjet head, even when printing after a long period of printing rest, and is less likely to suffer from degradation of print quality due to uneven drying when printed on a non-absorbent or poorly absorbent printing substrate. Furthermore, the aqueous ink specifically disclosed in Patent Document 3 uses, as surfactants, acetylene-based surfactants such as "Surfynol 420" and "Surfynol 104," as well as polyoxyalkylene monoalkyl ether surfactants (the "Emulgen" series) in which the number of moles of ethylene oxide added is 10 or less.

[0016] JP 2017-8319 A International Publication No. 2023 / 171302 International Publication No. 2020 / 80121

[0017] However, the inventors' investigations revealed that the aqueous inkjet inks specifically disclosed in the above-mentioned Patent Documents 1 to 3 may not only have problems with initial ejection stability and standby ejection stability depending on the printing conditions, but may also have a risk of deteriorating the water resistance of printed matter. The acetylene diol surfactants used in these specific examples all correspond to the above-mentioned hydrophobic surfactants, and are therefore considered to be effective in suppressing color bleeding in printed matter, for example. However, as mentioned above, these surfactants have problems such as the tendency to generate bubbles or the instability of the meniscus of the aqueous inkjet ink, and the above-mentioned aqueous inkjet inks have not completely resolved these problems. Furthermore, as will be described in more detail below, the use of hydrophobic surfactants may adversely affect the water resistance of printed matter depending on the materials used in combination. From this perspective, too, it can be said that the aqueous inkjet inks disclosed in the above-mentioned Patent Documents leave room for improvement.

[0018] As described above, the techniques described in Patent Documents 1 to 3 have not yet been able to solve all of the above-mentioned problems to a high degree. Therefore, one embodiment of the present invention provides an aqueous inkjet ink that is free from white voids and color bleeding, has excellent water resistance, and is excellent in ejection stability immediately after the start of printing and after a long period of printing pause, even when printing on a poorly permeable substrate or a non-permeable substrate.

[0019] As a result of extensive research, the present inventors have found that all of the above-mentioned problems can be solved simultaneously and to a high degree by using an aqueous inkjet ink having the following composition.

[0020] That is, one embodiment of the present invention relates to an aqueous inkjet ink. Another embodiment of the present invention relates to a printed matter produced using the aqueous inkjet ink. More specifically, the embodiments of the present invention include the following [1] to [6]. However, the present invention is not limited to the following embodiments and includes various embodiments. [1] An aqueous inkjet ink containing a pigment, a surfactant (A), a water-soluble organic solvent, and a binder resin, wherein the surfactant (A) contains a compound (A-1) represented by the following general formula 1 and a nonionic surfactant (A-2) having an HLB value of 1 to 10 (excluding the compound (A-1)), and the water-soluble organic solvent contains hexylene glycol. (General Formula 1) R １ -(O-CH ２ -CH ２ ) ｎ -OH [In general formula 1, R １ represents an alkyl group having 10 to 25 carbon atoms, which may have a branched structure. Also, n is an integer of 20 to 100.] [2] The aqueous inkjet ink according to the above [1], wherein the water-soluble organic solvent further contains a diol having 2 to 5 carbon atoms. [3] The aqueous inkjet ink according to the above [1] or [2], wherein the water-soluble organic solvent further contains a compound represented by the following general formula 2: (General formula 2) R ２ -(O-CH(CH ３ )-CH ２ ) ｍ-OH [In general formula 2, R ２ represents an alkyl group having 2 to 4 carbon atoms, which may have a branched structure. Also, m is 1 or 2.] [4] The aqueous inkjet ink according to any one of the above [1] to [3], wherein the mass ratio of the content of the compound (A-1) to the content of the nonionic surfactant (A-2) [compound (A-1): surfactant (A-2)] is 1:0.5 to 1:20. [5] The aqueous inkjet ink according to any one of the above [1] to [4], wherein the mass ratio of the total content of the hexylene glycol and the content of the compound (A-1) to the content of the nonionic surfactant (A-2) [(hexylene glycol + compound (A-1)): surfactant (A-2)] is 1:1 to 14:1. [6] A printed matter obtained by printing on a printing substrate the aqueous inkjet ink according to any one of the above [1] to [5]. The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-209884, filed December 13, 2023, the entire disclosure of which is incorporated herein by reference.

[0021] The aqueous inkjet ink according to one embodiment of the present invention can provide printed matter that is free from white spots and color bleeding and has excellent water resistance, even when printing on poorly permeable and non-permeable substrates, and can also provide excellent ejection stability both immediately after the start of printing and after a long period of printing rest.

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

[0023] The aqueous inkjet ink of this embodiment having the above-described configuration has excellent wettability on the order of μs, and therefore, even when printing on poorly permeable and non-permeable substrates, it is possible to obtain printed matter of excellent print quality without white spots or color bleeding. Furthermore, stable ejection is possible even immediately after the start of printing, and even after a long printing pause. In addition, the printed matter also has excellent water resistance. Although the details of the mechanism are not clear, the inventors speculate as follows. However, the present invention is not limited by the speculation below.

[0024] As described above, aqueous inkjet inks generally do not wet or spread on poorly permeable or non-permeable substrates due to the extremely high surface tension of their main component, water, making it difficult to form fine prints. In contrast, when a surfactant is used, the surfactant orients at the interface with the substrate in a short time, on the order of μs. As a result, the ink can be smoothly wetted and spread on poorly permeable or non-permeable substrates, particularly substrates with very low interfacial free energy, such as polypropylene (PP) film, and improved print quality can be expected. This effect is particularly effective when a surfactant with low solubility in water is used. However, surfactants tend to foam, which can lead to the generation of air bubbles that can contribute to nozzle clogging. Furthermore, when a surfactant with poor solubility in water is used, orientation also occurs at the air-liquid interface formed on the nozzle end surface of the inkjet head, which can destabilize the meniscus of the aqueous inkjet ink. These air bubbles lead to deterioration in standby ejection performance, and the instability of the meniscus leads to deterioration in initial ejection stability.

[0025] Furthermore, to produce printed matter with excellent water resistance, it is necessary to use a binder resin with a large mass-average molecular weight to form a strong, continuous film that is insoluble in water. On the other hand, if such a binder resin is present in a certain amount or more in the aqueous inkjet ink before printing (liquid), the binder resin may cause problems such as partially inhibiting the orientation of surfactants with low water solubility at the interface. To fully utilize the effects of the surfactant, one method is to increase the amount of surfactant added so that sufficient orientation at the interface is still achieved even when inhibited. However, excessive amounts of surfactant also pose the problem of inhibiting the formation of the continuous film, and increasing the amount of surfactant added can result in a deterioration in the water resistance of printed matter.

[0026] The aqueous inkjet ink of this embodiment first contains, as the surfactant (A), a nonionic surfactant (A-2) having an HLB value within a suitable range and a compound (A-1) represented by the general formula (1) above. More specifically, the surfactant (A) contains the compound (A-1) represented by the general formula 1 above and a nonionic surfactant (A-2) having an HLB value of 1 to 10 (excluding the compound (A-1)). That is, in some embodiments, when the compound (A-1) is a nonionic surfactant, it is assumed that the nonionic surfactant (A-2) is a compound different from the compound (A-1). The nonionic surfactant (A-2) corresponds to the surfactant with low solubility in water described above and is capable of imparting excellent permeability and wettability to the aqueous inkjet ink on poorly permeable substrates and non-permeable substrates. In contrast to this, the compound (A-1) has an alkyl chain with a suitable number of carbon atoms as the hydrophobic portion, and also has a polyethylene oxide structure with a suitable number of added moles as the hydrophilic portion.

[0027] When the nonionic surfactant (A-2) is used alone, there is a risk of nozzle clogging due to the generation of bubbles and destabilization of the meniscus of the aqueous inkjet ink near the nozzle, as described above. Furthermore, while the nonionic surfactant (A-2) has a high speed of orientation toward the gas-liquid interface, the uniformity of the orientation is low. In particular, the presence of a binder resin in the aqueous inkjet ink can inhibit the above-described orientation, causing the aqueous inkjet ink to wet and spread unevenly on the printing substrate, which can result in white voids.

[0028] In contrast, the aqueous inkjet ink of this embodiment further uses compound (A-1). In the aqueous inkjet ink, the sufficiently large polyethylene oxide structure present in compound (A-1) has affinity with water, while the alkyl chain has affinity with surfactant (A-2). As a result, in the aqueous inkjet ink, nonionic surfactant (A-2) is stabilized by compound (A-1). Furthermore, the orientation speed toward the interface is suppressed, while enabling uniform orientation at the interface. This suppresses the generation of bubbles and destabilization of the meniscus in the aqueous inkjet ink present in the inkjet head, improving initial ejection stability and standby ejection performance. Furthermore, in the aqueous inkjet ink on the printing substrate, affinity between surfactant (A-2) and binder resin is maintained via compound (A-1) even after the liquid components have volatilized. These factors are thought to prevent the individual materials in the aqueous inkjet ink film (ink film) from becoming non-uniform after drying, resulting in the formation of a uniform and continuous ink film, making it possible to obtain printed materials with excellent water resistance.

[0029] Furthermore, the aqueous inkjet ink of this embodiment uses hexylene glycol as the water-soluble organic solvent. Hexylene glycol (2-methyl-2,4-pentanediol) has multiple branched alkyl groups and is more hydrophobic than other alkanediols, while having high solubility in water and a low boiling point at 1 atmosphere. Therefore, it exhibits a higher orientation toward interfaces than other alkanediols. Furthermore, it has a high affinity with the surfactant (nonionic surfactant (A-2)) that has low solubility in water, while also dissolving well in water and promoting the orientation of the surfactant toward interfaces. As a result, in the presence of hexylene glycol and the compound (A-1), the nonionic surfactant (A-2), which is a surfactant with low solubility in water, can be uniformly distributed within the aqueous inkjet ink. Furthermore, since hexylene glycol is thought to increase the orientation speed of the nonionic surfactant (A-2) to the interface, the decrease in orientation speed caused by the addition of the above-mentioned compound (A-1) is compensated for, and when the aqueous inkjet ink lands on a substrate, the nonionic surfactant (A-2) is oriented to the interface in a short time. As a result, the droplets of the aqueous inkjet ink can be sufficiently wetted and spread, making it possible to obtain printed matter free of white spots and color bleeding.

[0030] As a result of the above, it is believed that hexylene glycol and the compound (A-1) contribute to stabilizing and homogenizing the nonionic surfactant (A-2), thereby preventing foaming and nozzle clogging, improving ejection stability, and enabling the production of printed matter with excellent print quality and water resistance.

[0031] Hexylene glycol also dissolves binder resins well. Therefore, it is believed that, even after the water volatilizes from the aqueous inkjet ink applied to the substrate during drying, the binder resin spreads sufficiently and can flow somewhat freely within the aqueous inkjet ink. As a result, hexylene glycol can promote the formation of a continuous ink film. Furthermore, since hexylene glycol itself does not remain in the continuous film but ultimately volatilizes, highly water-resistant printed materials can be produced with low energy.

[0032] As described above, by constructing the aqueous inkjet ink as described above, all of the above-mentioned problems can be solved to a high degree.

[0033] The aqueous inkjet inks specifically disclosed in the above-mentioned Patent Documents 1 to 3 differ from the aqueous inkjet ink of the present embodiment in that they do not contain the compound (A-1) represented by the above general formula 1 (all of the compounds used in Patent Documents 1 to 3 are compounds in which n in the above general formula 1 is less than 20), and in that they do not use hexylene glycol. Furthermore, Patent Documents 1 to 3 do not describe at all the above-mentioned mechanism, that is, that hexylene glycol and the above-mentioned compound (A-1) contribute to the stabilization and homogenization of the nonionic surfactant (A-2), thereby realizing improvements in initial ejection stability and standby ejection performance, as well as the water resistance of printed matter.

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

[0035] <Surfactant (A)> The aqueous inkjet ink of this embodiment contains, as the surfactant (A), a compound (A-1) represented by general formula 1 and a nonionic surfactant (A-2) having an HLB value of 1 to 10.

[0036] (Compound (A-1)) As described above, the compound (A-1) stabilizes the nonionic surfactant (A-2), thereby suppressing the generation of bubbles and destabilization of the meniscus, and improving the initial ejection stability and standby ejection performance. Furthermore, the affinity of the compound (A-1) with the surfactant (A-2) and the binder resin results in a uniform and continuous ink film, improving the water resistance of the printed matter. Furthermore, in the presence of the compound (A-1) and hexylene glycol, the nonionic surfactant (A-2) can be uniformly present in the aqueous inkjet ink, and the droplets of the aqueous inkjet ink can be sufficiently wetted and spread, making it possible to obtain printed matter free of whiteout and color bleeding.

[0037] From the viewpoints of stabilizing the nonionic surfactant (A-2), facilitating affinity between the surfactant (A-2) and the binder resin, and improving the initial ejection stability, standby ejection properties, and water resistance of the printed matter, n in General Formula 1 is an integer of 20 to 100, and more preferably an integer of 25 to 50.

[0038] From the same viewpoint as that of the value of n in the general formula 1, R １ is an alkyl group having 10 to 25 carbon atoms which may have a branched structure, and preferably an alkyl group having 11 to 22 carbon atoms which may have a branched structure. １ is more preferably an alkyl group having 12 to 22 carbon atoms which may have a branched structure, and particularly preferably an alkyl group having 12 to 16 carbon atoms which may have a branched structure. １ The group represented by the formula (I) is preferably an alkyl group (also referred to as a branched alkyl group) having 10 to 22 carbon atoms and a branched structure, and particularly preferably a branched alkyl group having 11 to 16 carbon atoms. According to such an embodiment, affinity with hexylene glycol, a compound having a branched structure, can be easily improved. Furthermore, by realizing further uniformity of the nonionic surfactant (A-2), printed matter that is free from white voids and color bleeding and has exceptionally excellent water resistance can be easily obtained.

[0039] The compound (A-1) may be obtained by synthesis by a conventionally known method, or a commercially available product may be used. Examples of commercially available products of compound (A-1) include the Emulgen series manufactured by Kao Corporation, the Nonion series manufactured by NOF Corporation, the EMALEX series manufactured by Nippon Emulsion Co., Ltd., the NIKKOL series manufactured by Nikko Chemicals Co., Ltd., the Emulmin series and Sannonik series manufactured by Sanyo Chemical Industries, Ltd., and the Brownon series and Finesurf series manufactured by Aoki Oil & Fat Industries Co., Ltd., but are not limited to these.

[0040] The content of compound (A-1) in the aqueous inkjet ink is preferably 0.05 to 2% by mass, and more preferably 0.1 to 1% by mass. When the content is 0.05% by mass or more, the above-mentioned effects can be reliably exhibited, and when the content is 2% by mass or less, white voids and color bleeding in printed matter can be easily suppressed, and initial ejection stability and standby ejection performance can be easily improved.

[0041] (Nonionic Surfactant (A-2)) The surfactant (A-2) has an HLB value of 1 to 10. The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that represent the hydrophilicity and hydrophobicity of a material. Various methods are known for calculating the HLB value, such as the Griffin method, the Davis method, and the Kawakami method, but in the present disclosure, the HLB value is calculated using the Griffin method.

[0042] The Griffin method is generally used for non-ionic materials. In the Griffin method, the molecular weight of the material is used to calculate the HLB value according to the following formula 3. The smaller the HLB value, the more hydrophobic the material is, and the larger the HLB value, the more hydrophilic the material is. (Formula 3) HLB value = 20 x (total molecular weight of hydrophilic parts) ÷ (molecular weight of material)

[0043] The nonionic surfactant (A-2) is not particularly limited as long as it is a surfactant having an HLB value of 1 to 10 and does not correspond to the compound (A-1). On the other hand, from the viewpoint of obtaining printed matter that is free from white voids and color bleeding and has excellent initial ejection stability even on a printing substrate with low permeability, it is preferable for the surfactant (A-2) to contain an acetylene diol surfactant and / or a silicone surfactant, and from the viewpoint of obtaining an aqueous inkjet ink that is particularly excellent in initial ejection stability and standby ejection properties, it is most preferable to use a silicone surfactant.

[0044] Acetylene diol surfactants are preferred because they have excellent orientation speed to the interface, improving the wettability of aqueous inkjet inks and making it easier to obtain printed materials free of white spots and color bleeding. When an acetylene diol surfactant is used as the nonionic surfactant (A-2), it preferably has an HLB value of 1 to 8, more preferably 1 to 4. Specific examples of acetylene diol surfactants having an HLB value of 1 to 4 include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, and 3,6-diisopropyl-2,4,7,9-tetramethyl-5-decyne-4,7-diol. ,7-dimethyloct-4-yne-3,6-diol, octadec-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol, and the like. Among these, from the viewpoint of being able to impart sufficient wettability to aqueous inkjet inks even on poorly permeable printing substrates and obtaining printed matter with excellent print quality, it is preferable to use one or more compounds selected from the group consisting of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The above compounds may be used alone or in combination of two or more. Furthermore, the above compounds may be synthesized by a conventionally known method, or commercially available products may be used.

[0045] The amount of the acetylene diol surfactant added may be preferably 0.1 to 3 mass %, more preferably 0.5 to 2 mass %, and even more preferably 0.8 to 1.5 mass %, based on the total amount of the aqueous inkjet ink.

[0046] On the other hand, although silicone surfactants have a slower orientation speed to the interface than acetylene diol surfactants, they have a high ability to reduce surface tension and are uniformly oriented at the interface, so they can be preferably used from the viewpoints of preventing color bleeding in printed materials and improving initial ejection stability. In the present disclosure, the HLB value of the silicone surfactant is also calculated using the Griffin method.

[0047] When a silicone surfactant is used as the nonionic surfactant (A-2), it is preferable to use a gemini silicone surfactant and / or a polyether-modified silicone surfactant (excluding gemini silicone surfactants). Furthermore, the amount of silicone surfactant added is preferably 0.1 to 5 mass %, more preferably 0.5 to 3 mass %, and even more preferably 0.8 to 2.5 mass %, based on the total mass of the ink.

[0048] (Gemini Silicone Surfactant) Generally, a gemini surfactant has a structure in which surfactants having a hydrophilic structure and a hydrophobic structure are linked by a linking group (spacer) or a covalent bond. In addition, in the case of a gemini silicon surfactant, for example, a siloxane chain (-[SiR ３ R ４ -O] ｘ -, where R ３ and R ４ are each any organic group, and x is an integer of 2 or more.), and the hydrophilic structure (for example, a polyether chain) has the following structure: A structure in which the bonding points between the siloxane chain and the hydrophilic structure are located in the middle of the siloxane chain and in the middle of the hydrophilic structure, respectively. A structure in which multiple siloxane chains are bonded via linking groups or the like (for example, R in the structural formula of the siloxane chain ３ and / or R ４ (At least a part of which is an organic group containing a siloxane chain.) A structure in which a plurality of silicone surfactants each having a plurality of hydrophilic structures share at least a part of the hydrophilic structures.

[0049] Gemini surfactants have superior surface tension reducing ability compared to general surfactants. Therefore, by using a gemini silicone surfactant, it is possible to achieve a surface tension reduction superior to that achieved by general silicone surfactants. As a result, the wettability of aqueous inkjet inks containing gemini silicone surfactants can be significantly improved, making it easier to improve the above-mentioned white voids and color bleeding.

[0050] Examples of commercially available gemini type silicone surfactants include TEGO Twin 4000, TEGO Twin 4100, and TEGO Twin 4200 manufactured by Evonik Degussa, and KF-6100, KF-6104, KF-6105, KF-6106, and KF-6115 manufactured by Shin-Etsu Chemical Co., Ltd.

[0051] (Polyether-modified silicone surfactants (excluding gemini type silicone surfactants)) Examples of the polyether-modified silicone surfactants (excluding gemini type silicone surfactants) that can be used in the aqueous inkjet ink of this embodiment include compounds having a structure represented by the following general formula 4:

[0052]

[0053] In general formula 4, p is an integer of 0 to 99, and q is an integer of 1 to 100. However, p+q is an integer of 1 to 100. ５ is a methyl group or a structure represented by the following general formula 5, and R ６ is an alkyl group having 1 to 6 carbon atoms, or a structure represented by the following general formula 5. ５ When R is a methyl group, p is 0. ５ and R ６ At least one of the groups has a structure represented by the following general formula 5 (R ５ and R ６ may both have a structure represented by the following general formula 5)

[0054]

[0055] In General Formula 5, 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. However, s+t is an integer of 1 to 100. ７ 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.

[0056] The polyether-modified silicone surfactant represented by the above general formula 4 is preferably used, particularly from the viewpoint of improving color bleeding.

[0057] R in the above general formula 4 ６ is a structure represented by general formula 5, and R ５ Examples of commercially available polyether-modified silicone surfactants that do not have a structure represented by general formula 5 include BY16-201 and SF8427 manufactured by Dow Corning Toray Co., Ltd., BYK-331, BYK-333, BYK-UV3500, and BYK-3420 manufactured by BYK-Chemie K.K., TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Degussa A / S, and Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.

[0058] In addition, R in the above general formula 4 ５ is a structure represented by general formula 5, and R ６Examples of commercially available polyether-modified silicone surfactants that do not have the structure represented by general formula 5 include SF8428, FZ-2162, 8032 ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Dow Corning Toray Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 manufactured by BYK-Chemie; and TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, and TEGO Wet 3773M manufactured by Evonik Degussa. 280, and Shin-Etsu Chemical Co., Ltd.'s KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, and KF-643.

[0059] In some embodiments, the content of the surfactant (A) may be 0.1 to 5.0% by mass, more preferably 0.3 to 4.0% by mass, and even more preferably 0.5 to 3.0% by mass, based on the total mass of the aqueous inkjet ink. The surfactant (A) includes a compound (A-1) represented by general formula 1 and a nonionic surfactant (A-2) having an HLB value of 1 to 10, and the total amount of the compound (A-1) and the nonionic surfactant (A-2) based on the total mass of the surfactant (A) may preferably be 60% by mass or more. This total amount may more preferably be 75% by mass or more, and even more preferably be 85% by mass or more. The content may be 100% by mass. The ratio of the content of the compound (A-1) represented by general formula 1 to the content of the nonionic surfactant (A-2) having an HLB value of 1 to 10 used in the aqueous inkjet ink of this embodiment (compound (A-1):surfactant (A-2)) is preferably 1:0.5 to 1:20 by mass. The above ratio is more preferably 1:1.5 to 1:15, and even more preferably 1:2 to 1:10. By blending them in the above-mentioned suitable ratio, the nonionic surfactant (A-2) can be sufficiently stabilized by the compound (A-1), and printed matter having excellent water resistance can be obtained while suppressing white voids and color bleeding in the printed matter.

[0060] Furthermore, since the nonionic surfactant (A-2) can be made uniform within the aqueous inkjet ink and the droplets of the aqueous inkjet ink can be sufficiently wetted and spread, it is possible to obtain printed matter that is free of white voids and color bleeding. Therefore, the ratio of the total content of the hexylene glycol and the compound (A-1) to the content of the nonionic surfactant (A-2) [(hexylene glycol + compound (A-1)): surfactant (A-2)] is preferably 1:1 to 14:1, more preferably 2:1 to 12:1, and particularly preferably 3:1 to 11:1, by mass.

[0061] <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 hexylene glycol.

[0062] (Hexylene Glycol) In order to obtain good ejection stability and good print quality of printed matter, the content of hexylene glycol contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 25 mass %, more preferably 0.6 to 18 mass %, and particularly preferably 1 to 10 mass %, of the total amount of the aqueous inkjet ink.

[0063] Furthermore, the content of the hexylene glycol is preferably 5 to 90% by mass, more preferably 10 to 60% by mass, and particularly preferably 10 to 40% by mass, based on the total mass of the water-soluble organic solvent contained in the aqueous inkjet ink. By ensuring that the content of hexylene glycol relative to the total mass of the water-soluble organic solvent is within the above range, the time required for stabilization of the nonionic surfactant (A-2) at the interface can be optimized. As a result, ejection stability is improved immediately after the start of printing and during high-speed continuous printing, and at the same time, wettability to the printing substrate on the order of μs is improved, thereby improving print image quality.

[0064] (C1 to C5 diols) The aqueous inkjet ink of this embodiment may further contain a C2 to C5 diol. By including a C2 to C5 diol, the nonionic surfactant (A-2) can be further stabilized, improving standby ejection properties. In addition, when the aqueous inkjet ink applied to a printing substrate dries, the binder resin is dissolved together with hexylene glycol, causing an increase in the viscosity of the aqueous inkjet ink, thereby suppressing color bleeding. Examples of the diols having 2 to 5 carbon atoms include alkanediols having 2 to 5 carbon atoms, such as 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, and 3-methyl-1,3-butanediol, as well as polyoxyalkylene diols having 2 to 5 carbon atoms, such as diethylene glycol and hydroxyethoxypropanol. These compounds may be used alone or in combination of two or more.

[0065] Among these, from the viewpoints of good ejection stability after long periods of printing suspension and suppression of color bleeding in printed matter, it is preferable to use alkanediols having 2 to 5 carbon atoms, and it is even more preferable to use one or more selected from the group consisting of 1,2-ethanediol, 1,2-propanediol, and 1,3-butanediol. On the other hand, from the viewpoint of improving affinity with compound (A-1), which can assist compound (A-1) in homogenizing the nonionic surfactant (A-2) and binder resin in the ink film, thereby improving the uniformity and continuity of the ink film and improving the water resistance of printed matter, it is preferable to use diols having 3 to 5 carbon atoms in which a hydroxyl group is attached to each adjacent carbon atom. From this viewpoint, it is preferable to use one or more selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 2,3-butanediol, and 1,2-pentanediol as the diol having 2 to 5 carbon atoms. It is particularly preferable to use 1,2-propanediol, which satisfies both of the above-mentioned two points and further has good ejection stability immediately after the start of printing and even during continuous printing.

[0066] In order to ensure good ejection stability under all conditions, i.e., immediately after the start of printing, after a long period of printing suspension, and during continuous printing, the content of the diols having 2 to 5 carbon atoms is preferably from 0.5 to 30% by mass, more preferably from 2 to 25% by mass, and particularly preferably from 6 to 22% by mass, based on the total mass of the aqueous inkjet ink.

[0067] Furthermore, when the aqueous inkjet ink applied to a printing substrate dries, both hexylene glycol and the diols having 2 to 5 carbon atoms contribute to dissolving the binder resin, softening the pigment dispersion resin, and stabilizing the nonionic surfactant (A-2), thereby producing printed matter that is free from white voids and color bleeding and has excellent water resistance, and furthermore, providing an aqueous inkjet ink with good ejection stability. From this perspective, when the content of hexylene glycol is taken as 1, the content of the diols having 2 to 5 carbon atoms is preferably 1 to 6, more preferably 1.5 to 5.5, and particularly preferably 2 to 5.

[0068] (Specific (Poly)oxypropylene Monoalkyl Ethers) The aqueous inkjet ink of this embodiment may contain a compound represented by the above general formula 2 (referred to as "specific (poly)oxypropylene monoalkyl ethers" in the present disclosure). The specific (poly)oxypropylene monoalkyl ethers have a structure similar to that of the compound (A-1) and can contribute to the stabilization of the nonionic surfactant (A-2). In addition, the specific (poly)oxypropylene monoalkyl ethers themselves have a moderately low surface tension, which makes it easy to improve the initial ejection stability and prevent white voids in printed matter. Furthermore, the specific (poly)oxypropylene monoalkyl ethers can assist the compound (A-1) in homogenizing the nonionic surfactant (A-2) and binder resin within the ink film, thereby improving the uniformity and continuity of the ink film. Furthermore, the specific (poly)oxypropylene monoalkyl ethers also function as a film-forming aid for the binder resin. From the above, the use of specific (poly)oxypropylene monoalkyl ethers significantly improves the water resistance of printed matter.

[0069] Examples of specific (poly)oxypropylene monoalkyl ethers that can be used include propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, propylene glycol monoisobutyl ether, propylene glycol mono-tert-butyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monoisobutyl ether, and dipropylene glycol mono-tert-butyl ether. These compounds may be used alone or in combination of two or more.

[0070] Among these compounds, R in general formula 2 is preferred because it has a high affinity with compound (A-1) and has a suitable boiling point and surface tension at 1 atmosphere, thereby improving the ejection stability immediately after the start of printing, improving the water resistance of printed matter, and preventing white spots. ２ However, it is preferable to use a compound in which R in general formula 2 is an unbranched alkyl group having 2 or 3 carbon atoms. Among the compounds listed above, compounds that satisfy these requirements include propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol mono-n-propyl ether. Furthermore, by improving the affinity with hexylene glycol, the ink film is made uniform and continuous, which significantly improves the water resistance of the printed matter, and also suppresses color bleeding in the printed matter. ２ is an n-propyl group, i.e., propylene glycol mono-n-propyl ether and / or dipropylene glycol mono-n-propyl ether are particularly preferred. In particular, taking into consideration the improvement of standby dischargeability, it is particularly preferred to use dipropylene glycol monopropyl ether as the specific (poly)oxypropylene monoalkyl ether.

[0071] In order to achieve all of the effects of improving the initial ejection stability, preventing white voids in the printed matter, and improving water resistance at the same time, and in order to achieve good ejection stability under all conditions, namely immediately after the start of printing, after a long period of printing suspension, and during continuous printing, the content of the specific (poly)oxypropylene monoalkyl ethers is preferably 0.2 to 7 mass %, and particularly preferably 0.5 to 5 mass %, based on the total mass of the aqueous inkjet ink.

[0072] (Other Water-Soluble Organic Solvents) The aqueous inkjet ink of this embodiment may further contain water-soluble organic solvents other than the above-mentioned hexylene glycol, the above-mentioned diols having 2 to 5 carbon atoms, and the above-mentioned specific (poly)oxypropylene monoalkyl ethers (referred to as "other water-soluble organic solvents" in the present disclosure).

[0073] In the aqueous inkjet ink of this embodiment, the other water-soluble organic solvents may include alkanediols having 6 carbon atoms (excluding hexylene glycol); alkanetriols (those having 3 to 6 carbon atoms); polyoxyalkylene diols (those in which the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, the number of oxyalkylene groups is 2 to 4, and excluding those having 2 to 5 carbon atoms); (poly)oxyalkylene monoalkyl ethers (those in which the oxyalkylene group is an oxyethylene group or an oxypropylene group, the number of oxyalkylene groups is 1 to 4, and the number of carbon atoms in the terminal alkyl group is 1 to 4 (compounds corresponding to the above-mentioned specific (poly)oxypropylene monoalkyl ethers Examples of suitable water-soluble organic solvents include those in which the oxyalkylene group is an oxybutylene group or an oxypentylene group, the number of oxyalkylene groups is 1, and the terminal alkyl group has 1 to 4 carbon atoms; (poly)oxyethylene dialkyl ethers (in which the number of oxyalkylene groups is 1 to 4, and the terminal alkyl groups each have 1 to 4 carbon atoms); lactams (in which the number of atoms constituting the lactam ring is 5 to 7, and an alkyl group having 1 to 2 carbon atoms, a hydroxyalkyl group having 1 to 2 carbon atoms, or a vinyl group may be bonded to the nitrogen atom and / or carbon atom constituting the lactam ring); alkanolamines (in which the number of amino groups is 1, the number of hydroxyl groups is 1 to 3, and the number of carbon atoms is 3 to 9); and the like. These other water-soluble organic solvents may be used alone or in combination of two or more. In the present disclosure, the terms "(poly)oxyalkylene" and "(poly)oxypropylene" respectively refer to "oxyalkylene and / or polyoxyalkylene" and "oxypropylene and / or polyoxypropylene."

[0074] The total mass of the water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment is preferably 3 to 33 mass%, more preferably 5 to 30 mass%, and particularly preferably 7 to 30 mass%, based on the total mass of the aqueous inkjet ink. By setting the total mass of the water-soluble organic solvents within this range, it is possible to maintain an appropriate viscosity for ejection as an inkjet ink, and to achieve good ejection stability even after, for example, a long period of printing suspension, and to produce printed matter that can be dried with low energy and has good water resistance.

[0075] Furthermore, in the aqueous inkjet ink of this embodiment, the content of the water-soluble organic solvent having a boiling point of 220°C or higher at 1 atmospheric pressure is preferably 5% by mass or less (or may be 0% by mass) based on the total mass of the aqueous inkjet ink. By not including a water-soluble organic solvent having a boiling point of 220°C or higher, or by keeping the blending amount within the above range even if the ink contains one, good color bleeding can be achieved, for example, even in high-speed printing.

[0076] Furthermore, it is preferable that 90% by mass or more of the water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment, based on the total mass, be water-soluble organic solvents having a static surface tension at 25°C of 25 to 50 mN / m. Furthermore, it is even more preferable that 70% by mass or more of the water-soluble organic solvents, based on the total mass, be water-soluble organic solvents having a static surface tension at 25°C of 26 to 40 mN / m, and it is particularly preferable that 90% by mass or more of the water-soluble organic solvents, based on the total mass, be water-soluble organic solvents having a static surface tension at 25°C of 26 to 40 mN / m. By using a water-soluble organic solvent having such a surface tension, it is possible to maintain an appropriate surface tension for ejection as an inkjet ink, thereby improving ejection stability, for example, even after a long period of printing suspension. Furthermore, this helps the aqueous inkjet ink to spread uniformly on the printing substrate, resulting in printed materials with no white spots and excellent water resistance. The static surface tension of the water-soluble organic solvent at 25°C can be measured in the same manner as the static surface tension of the aqueous inkjet ink, as described below.

[0077] Pigment The aqueous inkjet ink of this embodiment contains a pigment.

[0078] As the pigment, any conventionally known organic or inorganic pigment can be used, and for example, pigments represented by the following color index names can be used: red pigments, such as C.I. Pigment Red 52, 5, 7, 9, 12, 17, 22, 23, 31, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 57:1, 57:2, 112, 122, 123, 146, 147, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 184, 188, 202, 207, 209, 254, 255, 260, 264, 266, 269, and 282; violet pigments, such as C.I. As orange pigments, C.I. Pigment Violet 19, 23, 29, 32, 36, 37, 42, 50; as orange pigments, C.I. Pigment Orange 1, 2, 3, 5, 7, 13, 14, 15, 16, 22, 34, 36, 38, 40, 43, 47, 48, 49, 51, 52, 53, 60, 61, 62, 64, 65, 66, 69, 71, 73; as blue pigments, C.I. Pigment Blue 15, 15:3, 15:4, 15:6, 16, 60, 64, 79; as green pigments, C.I. Pigment Green 7, 10, 36, 48; as yellow pigments, C.I. C.I. Pigment Yellow 1, 2, 3, 5, 12, 13, 14, 16, 17, 24, 73, 74, 83, 87, 93, 94, 95, 97, 98, 109, 110, 111, 112, 120, 126, 127, 128, 129, 137, 138, 139, 147, 150, 151, 154, 155, 166, 167, 168, 170, 180, 185, 213; black pigments include C.I. Pigment Black 1, 7, 11; and white pigments include C.I. Pigment White 4, 5, 6, 21, etc. These pigments may be used alone or in combination of two or more. A solid solution of two or more of the pigments listed above may also be used as a pigment.

[0079] The content of the pigment contained in the aqueous inkjet ink of this embodiment may be adjusted depending on the intended use of the printed matter produced using the aqueous inkjet ink. For example, the content of the pigment is preferably 0.5 to 30% by mass, based on the total mass 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, and particularly preferably 1.5 to 10% by mass, in order to obtain printed matters with high density without deteriorating the jetting stability of the aqueous inkjet ink. On the other hand, in the case of aqueous white inks, the content of the pigment is more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass, in order to obtain printed matters with high hiding power without deteriorating the jetting stability of the aqueous white ink.

[0080] <Pigment Dispersion Resin> The aqueous inkjet ink of this embodiment may contain a resin (pigment dispersion resin) used for pigment dispersion purposes. Compared to dispersions containing pigments dispersed without using a pigment dispersion resin (such as dispersions of self-dispersed pigments or dispersions of pigments dispersed with a surfactant), pigments dispersed using a pigment dispersion resin have excellent dispersion stability, resulting in an aqueous inkjet ink with excellent initial ejection stability and standby ejection properties. Selecting a pigment dispersion resin is also preferable from the viewpoint of improving the water resistance of printed matter. Furthermore, from the viewpoint of preventing detachment of the pigment dispersion resin from the pigment, the liberated pigment dispersion resin is adsorbed by the compound (A-1) and the nonionic surfactant (A-2), thereby preventing deterioration in initial ejection stability, standby ejection properties, and the print image quality of printed matter, the pigment dispersion resin is preferably a polymer having a crosslinked structure and / or a block polymer.

[0081] The type of pigment dispersion resin is not particularly limited, and any of acrylic resins, styrene resins, maleic acid (anhydride) resins, urethane resins, polyester resins, polyolefin resins, and the like can be used. These resins may be used alone or in combination of two or more. Among these, it is preferable to use one or more resins selected from the group consisting of acrylic resins, maleic acid (anhydride) resins, and urethane resins, in terms of improving initial ejection stability and standby ejection performance, wide material selectivity, ease of resin synthesis, and the like. Furthermore, acrylic resins and / or maleic acid (anhydride) resins are particularly preferred because they have a high affinity with compound (A-1), making it difficult for the pigment to become non-uniform within the aqueous inkjet ink, thereby preventing the pigment from interfering with the uniformity and continuous formation of the ink film, improving the water resistance of printed materials, and improving the initial ejection stability and standby ejection performance of the aqueous inkjet ink.

[0082] In the present disclosure, the term "acrylic resin" refers to a resin using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters (styrene and / or styrene derivatives may also be used). However, resins containing maleic acid (anhydride) (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer are excluded from the term "acrylic resin." Furthermore, the term "maleic acid (anhydride) resin" refers to a resin using at least maleic acid (anhydride) as a polymerizable monomer. Furthermore, the maleic acid (anhydride) resin may also use one or more polymerizable monomers selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0083] The pigment dispersing resin may be synthesized by a known method or may be a commercially available product. There are no particular limitations on its structure, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. may be used. Furthermore, either a water-soluble resin or a water-insoluble resin may be selected as the pigment dispersing resin.

[0084] In this disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin," and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin."

[0085] When a water-soluble resin is used as the pigment dispersion resin, its acid value is preferably 50 to 300 mgKOH / g, more preferably 60 to 250 mgKOH / g. It is particularly preferably 70 to 160 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment, and stable ejection from the inkjet head is possible regardless of the use conditions. Furthermore, this is preferable in that the solubility of the pigment dispersion resin in water can be ensured and the interaction between the pigment dispersion resins can be favorable, thereby reducing the viscosity of the pigment dispersion and achieving good ejection properties from the inkjet head.

[0086] On the other hand, when a water-insoluble resin is used as the pigment dispersing resin, its acid value is preferably 0 to 100 mgKOH / g, more preferably 5 to 90 mgKOH / g, and even more preferably 10 to 80 mgKOH / g. When the acid value is within the above range, a printed matter having excellent water resistance can be obtained.

[0087] In this disclosure, the "acid value of a resin" refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In this disclosure, the acid value used is a value calculated by the following method. For example, if a resin has na acid groups with a value of va per molecule and contains Wa mass% of a polymerizable monomer having a molecular weight of Ma among the polymerizable monomers constituting the resin, the acid value (mg KOH / g) can be calculated using the following formula 6:

[0088] (Equation 6) (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0089] In the above formula 6, the number "56.11" is the molecular weight of potassium hydroxide.

[0090] In the aqueous inkjet ink of this embodiment, it is preferable to introduce an aromatic group into the pigment dispersing resin, from the viewpoint of improving the adsorption ability to the pigment and ensuring the dispersion stability of the pigment and the ejection stability of the aqueous inkjet ink. Examples of aromatic groups include, but are not limited to, a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, and an anisyl group. Of these, a phenyl group, a naphthyl group, or a tolyl group is preferable, from the viewpoint of ensuring sufficient dispersion stability and ejection stability.

[0091] From the viewpoint of improving the dispersion stability and ejection stability of the pigment, as well as the print quality and drying properties of the printed matter, the amount of the aromatic ring-containing monomer incorporated is preferably 5 to 75 mass %, more preferably 10 to 65 mass %, and even more preferably 15 to 55 mass %, relative to the total amount of monomers constituting the pigment dispersion resin.

[0092] <Binder Resin> The aqueous inkjet ink of this embodiment contains a binder resin. After printing the aqueous inkjet ink containing the binder resin on a poorly permeable substrate or a non-permeable substrate, the viscosity increases at a speed on the order of μs, thereby suppressing bleeding and improving print image quality. Furthermore, when the aqueous inkjet ink dries, the binder resin forms a continuous film, thereby improving the water resistance of the printed matter.

[0093] The binder resin contained in the aqueous inkjet ink of this embodiment may be a water-soluble resin or resin particles. Also, a water-soluble resin and resin particles may be used in combination.

[0094] In this disclosure, "resin microparticles" refers to the above-mentioned water-insoluble resins that are dispersed in particulate form in water and have a volumetric median diameter (also referred to as "D50" in this disclosure) of 10 to 1,000 nm. In this disclosure, D50 is a value measured in an environment of 25°C using a dynamic light scattering particle size distribution analyzer such as the "Nanotrac UPA-EX150" manufactured by Microtrac-Bell.

[0095] When a water-soluble resin is used as the binder resin, the weight average molecular weight of the binder resin is preferably 1,000 to 25,000, and more preferably 5,000 to 20,000. By using a binder resin having the above weight average molecular weight, a strong continuous film can be formed even with a short drying time, and water resistance can be improved.

[0096] In the present disclosure, the mass average molecular weight of a compound is measured by a method conforming to JIS K 7252, and is expressed in terms of polystyrene. Specific examples of measurement conditions are shown below. Apparatus used: Tosoh Corporation's "HLC-8320GPC" Columns used: TSKgel (registered trademark) SuperMultiporeHZ-M (3 columns) Column temperature: 40°C Developing solvent: tetrahydrofuran Flow rate: 0.6 mL / min Sample solution concentration: 0.1% by mass Sample solution injection volume: 10 μL

[0097] The binder resin may be any of acrylic resins, styrene resins, maleic anhydride resins, urethane resins, polyester resins, vinyl chloride resins, vinyl chloride-vinyl acetate resins, and the like. These resins may be used singly or in combination. Among these, it is preferable to use one or more resins selected from the group consisting of acrylic resins, urethane resins, and polyester resins as the binder resin. Furthermore, from the viewpoints of achieving both adhesion and abrasion resistance to soft absorbent substrates and non-absorbent substrates (e.g., film substrates such as PP and PET, which will be described later), as well as improving ejection stability, it is preferable to use an acrylic resin as the binder resin. In this case, it is particularly preferable that the amount of the acrylic resin be 50% by mass or more relative to the total mass of the binder resins in the aqueous inkjet ink.

[0098] The glass transition temperature (Tg) of the binder resin is preferably 50 to 120°C, more preferably 60 to 110°C, and particularly preferably 70 to 100°C. By using a binder resin having the above glass transition temperature, even when printing on a printing substrate with low heat resistance and drying the aqueous inkjet ink on the printing substrate at a low temperature of about 70°C, the binder resin forms a solid film and / or the binder resin molecular chains become entangled with each other, thereby improving the abrasion resistance and water resistance of the printed matter. Furthermore, since the binder resin molecular chains do not become entangled with each other during ejection, stable ejection is possible even after leaving the ink to stand for a long period of time.

[0099] The glass transition temperature of the binder resin can be measured by a method conforming to JIS K 7121. Specifically, approximately 10 mg of a sample of the binder resin of interest 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 binder resin are placed in a holder in a Shimadzu DSC-60 (differential scanning calorimeter), and measurements are performed at a temperature increase rate of 10°C / min to obtain a DSC chart. The intersection of the low-temperature baseline and the tangent to the inflection point of the baseline is then determined, and the temperature of this intersection is taken as the glass transition temperature. Indium is used for temperature calibration.

[0100] On the other hand, for acrylic resins, the value calculated by the following formula 7 can be used as the glass transition temperature.

[0101] (Formula 7) 1 / Tg = Σ(Wn / Tgn)

[0102] In the above formula 7, Tg represents the glass transition temperature (K) of the resin, Wn represents the mass fraction of the structural unit consisting of polymerizable monomer n constituting the resin, and Tgn represents the glass transition temperature (K) of the homopolymer consisting of each polymerizable monomer n. For the Tgn, for example, values ​​described in "Polymer Handbook (4th Edition)" (Wiley, 1998) can be used.

[0103] The acid value of the binder resin is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, and may even be 0 mgKOH / g. The acid value of the binder resin is preferably 0 to 100 mgKOH / g, and more preferably 0 to 80 mgKOH / g. It is particularly preferably 10 to 60 mgKOH / g. By setting the acid value within the above range, even if a portion of the aqueous inkjet ink dries in the vicinity of the nozzles of the inkjet head, a significant increase in viscosity of the aqueous inkjet ink can be suppressed, thereby improving the ejection stability.

[0104] The content of the binder resin in the aqueous inkjet ink of this embodiment is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, and particularly preferably 5 to 18% by mass, based on the total mass of the aqueous inkjet ink. When the content of the binder resin is adjusted to be within the above range, standby ejection properties can be improved and color bleeding in printed matter can be easily prevented.

[0105] Furthermore, in the aqueous inkjet ink of this embodiment, the ratio of the sum ([g]) of the pigment dispersion resin content and the binder resin content to the pigment content (WP [g]) contained in 100 g of the aqueous inkjet ink, i.e., the value expressed as WR / WP, is preferably 1 to 4. By adjusting the value expressed as WR / WP to be within the range of 1 to 4, the amount of pigment that may become discontinuous points when forming a continuous film upon drying of the aqueous inkjet ink can be adjusted within a suitable range, making it possible to obtain printed matter with excellent water resistance. Furthermore, the ejection stability of the aqueous inkjet ink can be easily improved.

[0106] <Wax> The aqueous inkjet ink of this embodiment preferably contains a wax. Furthermore, it is preferable to use polyolefin resin microparticles as the wax. Although the detailed reason is unclear, polyolefin resin microparticles can be stably dispersed in the aqueous inkjet ink even when used in combination with the pigment dispersion resin described above. Furthermore, they are preferably selected because they can significantly improve the abrasion resistance and water resistance of printed matter.

[0107] The polyolefin may be at least one selected from the group consisting of polyethylene, polypropylene, and polybutene. Among these, polyethylene is particularly preferred because it can significantly improve the water resistance of printed matter.

[0108] When a wax is used, its D50 is preferably 10 to 200 nm, and more preferably 20 to 180 nm. When the D50 is within the above range, the above-mentioned functions can be suitably exhibited. Furthermore, clogging of the inkjet head nozzles is prevented, resulting in an aqueous inkjet ink with excellent initial ejection stability.

[0109] When a wax is used, the amount of the wax relative to the total mass of all resins (pigment dispersion resin, binder resin, and wax) contained in the aqueous inkjet ink is preferably 3 to 30% by mass, and more preferably 6 to 20% by mass. Adjusting the amount of wax to fall within the above range can prevent the functions of the individual resins from interfering with each other. Furthermore, since printed matter having sufficient water resistance can be obtained even during high-speed printing, the amount of wax relative to the total mass of the aqueous inkjet ink is preferably 0.5 to 1.5% by mass.

[0110] <Water> The aqueous inkjet ink of this embodiment contains water. It is preferable to use ion-exchanged water (deionized water) as the water, rather than ordinary water containing various ions. The water content is preferably 45 to 85% by mass, and particularly preferably 50 to 80% by mass, relative to the total mass of the aqueous inkjet ink. Because water has a low boiling point, it volatilizes preferentially from the nozzle end face of the inkjet head, which tends to increase the solids concentration at the gas-liquid interface. By adjusting the water content within the above range, good ejection stability is achieved under all conditions: immediately after the start of printing, after a long printing break, and during continuous printing.

[0111] <Other Components> The aqueous inkjet ink of this embodiment may contain, in addition to the components described above, a pH adjuster and other additives. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds may be used.

[0112] <Method for Producing Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. One example is a method in which a pigment dispersion is produced by pre-dispersing a pigment in a medium containing at least water (aqueous medium). Then, water, a water-soluble organic solvent, compound (A-1), a nonionic surfactant (A-2), a binder resin, and the like are added to the pigment dispersion, and the mixture is thoroughly stirred and mixed. Subsequently, coarse particles are removed by a technique such as filtration or centrifugation. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the above-described method.

[0113] <Characteristics of Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment preferably has a viscosity at 25°C of 3 to 15 mPa·s. Within this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from inkjet heads with ejection frequencies of approximately 4 to 10 kHz, but also from inkjet heads with high ejection frequencies of approximately 20 to 70 kHz. In particular, when the viscosity of the aqueous inkjet ink of this embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head with a design resolution of 600 dpi or higher is used. In this disclosure, the viscosity is measured at 25°C using a cone-plate rotational viscometer (E-type viscometer, cone angle 1°34') such as the TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

[0114] Furthermore, in order to obtain an aqueous inkjet ink that is excellent in ejection stability and print quality of printed matter, the aqueous inkjet ink of this embodiment preferably has a static surface tension of 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m, at 25° C. In the present disclosure, the static surface tension is a value measured in an environment of 25° C. using the Wilhelmy method (plate method) with an "Automatic Surface Tensiometer CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.

[0115] <Aqueous Inkjet Ink Set> Although only one aqueous inkjet ink of this embodiment may be used alone, two or more aqueous inkjet inks may also be combined to form an aqueous inkjet ink set. Examples of such aqueous inkjet ink sets include a four-color aqueous inkjet ink set (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink); and a five-color aqueous inkjet ink set obtained by adding an aqueous white ink to the process color ink set. It is preferable that all of the aqueous inkjet inks constituting the aqueous inkjet ink set satisfy the requirements of the embodiment of the present invention described above.

[0116] <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, it is possible to form a layer (ink aggregation layer) that intentionally aggregates solid components contained in the aqueous inkjet ink. Next, by landing the aqueous inkjet ink on the ink aggregation layer, it is possible to prevent coalescence of droplets of the aqueous inkjet ink and color bleeding, thereby significantly improving the print quality of printed matter.

[0117] 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.

[0118] <Inkjet Printing Method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. A printing method using the inkjet printing method typically includes an ink ejection step and a drying step of the ejected ink. In the above printing method, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). In addition, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0119] (Discharge Process) In the discharge process, one example of the operation method of the inkjet head is a shuttle (scan) method in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate, while discharging and recording the aqueous inkjet ink. Another example of the operation method is a single-pass method in which the aqueous inkjet ink is discharged and recording is performed as the printing substrate passes under a fixedly disposed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may be either a shuttle method or a single-pass method. Of these, the single-pass method is preferably selected because it is less likely to cause deviation in the landing position of droplets of the aqueous inkjet ink, improving the print quality of the printed matter, and further because it enables high-speed printing and can demonstrate high productivity as an alternative to plate-based printing.

[0120] The method of ejection from the inkjet head can also be selected from any known methods, such as a piezoelectric method that utilizes the volume change of a piezoelectric element, a thermal method that ejects aqueous inkjet ink by bubbles generated by heating a heater, and a valve method that ejects pressurized aqueous inkjet ink by opening and closing a nozzle cover (valve) with a solenoid.

[0121] The droplet volume of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing drying load and improving print quality. Furthermore, from the viewpoint of improving print quality, it is preferable to adjust the printing conditions (specifically, the drive frequency and number of inkjet heads, and the printing speed). In some embodiments, the printing conditions may be adjusted so that the recording resolution of the printed matter is preferably 600 dpi or higher, more preferably 1200 dpi or higher.

[0122] (Drying Step) Examples of 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. One or more of these methods can be selected and used as desired in the drying step. Furthermore, when two or more of the above drying methods are used, they may be used separately (for example, consecutively) or simultaneously. For example, by using heat drying and hot air drying in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[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 employed, the drying temperature is preferably 35 to 100° C. When a hot air drying method is employed, the hot air temperature is preferably 50 to 250° C. From the same viewpoint, when an infrared drying method is employed, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared rays is in the wavelength region of 700 to 2200 nm.

[0124] (Printing Substrate) The printing substrate onto which the aqueous inkjet ink of this embodiment is printed is not particularly limited. In some embodiments, the printing substrate may be a poorly permeable substrate or a non-permeable substrate. Generally, printing on poorly permeable substrates and non-permeable substrates is prone to color bleeding and unevenness in density, resulting in poor print quality. In contrast, by using the aqueous inkjet ink of this embodiment, printed matter having print quality equivalent to that of plate-based printing can be obtained even on poorly permeable substrates and non-permeable substrates, and even at high speeds.

[0125] In the present disclosure, the permeability of a printing substrate can be determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. In the present disclosure, it is defined as the amount of pure water absorption measured by the following method in a contact time of 100 msec. Specifically, when the amount of water absorption is 1 g / m ２ A printing substrate with a water absorption of less than 1 g / m is called an "impermeable substrate." ２ 6g / m or more ２ A printing substrate with a water absorption of less than 6 g / m is called a "hard-to-penetrate substrate." ２ A printing substrate that satisfies the above criteria is referred to as a "permeable substrate." The water absorption of a printing substrate can be measured, for example, using a dynamic scanning absorptivity meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the following conditions, using a printing substrate measuring approximately 15 to 20 cm square as a sample, in an environment of 23°C and 50% RH. Measurement method: Spiral scanning Measurement start radius: 20 mm Measurement end radius: 60 mm Contact time: 10 to 1,000 msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) Scanning interval: 7 mm Rotating table speed switching angle: 86.3 degrees Headbox conditions: width 5 mm, slit width 1 mm

[0126] Examples of impermeable substrates and poorly permeable substrates include plastic films and sheets such as polyvinyl chloride sheets, polyethylene terephthalate (PET) films, polypropylene films, polyethylene films, polyethylene sheets, nylon films, nylon sheets, polystyrene films, polystyrene sheets, and polyvinyl alcohol films; coated papers such as coated paper, art paper, and cast paper; metals such as aluminum, iron, stainless steel, and titanium; and glass.

[0127] The printing substrates listed above may have a smooth surface or may have an uneven surface. The printing substrates may be transparent, translucent, or opaque. The printing substrates may be in the form of a roll or sheets. Additionally, a laminate obtained by bonding two or more of the printing substrates listed above to each other may be used as the printing substrate. A release adhesive layer or the like may be provided on the side opposite the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing.

[0128] The printing surface of the printing substrates listed above may be subjected to surface modification such as corona treatment or plasma treatment. Surface modification is preferable in that it improves the wettability of the aqueous inkjet ink of this embodiment, and makes it easy to obtain printed matter that is excellent in print quality and drying properties, and that also has good abrasion resistance and substrate adhesion due to the uniformity of the printed surface.

[0129] <Printed Material> The aqueous inkjet ink of this embodiment can be used to produce a printed material. The inkjet printing method described above can be used to produce the printed material. In some embodiments, the printed material has a printing substrate and a printed layer containing an image or characters formed on the printing substrate by printing the aqueous inkjet ink of this embodiment. Printing can be suitably carried out according to an inkjet printing method. Details of the printing method and printing conditions are as described above.

[0130] 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.

[0131] <Example of Production of an Aqueous Solution of Acrylic Pigment Dispersion Resin> 90 parts of butanol was charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. Next, the reaction vessel was heated to 110°C, and then a mixture of polymerizable monomers (30 parts of acrylic acid, 35 parts of behenyl acrylate, and 35 parts of styrene) and 4 parts of a polymerization initiator (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After completion of the addition, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 110°C. Thereafter, 0.4 parts of V-601 was added, and the polymerization reaction was continued for 1 hour while maintaining the internal temperature at 110°C, to obtain a solution of an acrylic pigment dispersion resin. The contents of the reaction vessel were then cooled to room temperature, and 38 parts of dimethylaminoethanol was added to neutralize the acrylic pigment dispersion resin. 100 parts of ion-exchanged water was then added. The contents were then heated to above 100°C to azeotrope butanol and ion-exchanged water. The butanol was then distilled off, and ion-exchanged water was added to adjust the solids concentration to 20%, yielding an aqueous solution of the acrylic pigment dispersion resin. The "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium. The molecular weight of the resulting acrylic pigment dispersion resin was 16,000, and the acid value was 234 mgKOH / g.

[0132] <Production Example of Magenta Pigment Dispersion> 20 parts of FASTOGEN SUPER MAGENTA RTS (C.I. Pigment Red 122 manufactured by DIC Corporation) as a pigment, 25 parts of the previously prepared aqueous solution of acrylic pigment dispersion resin, and 55 parts of water were charged into a mixing vessel and pre-dispersed with a stirrer. After that, main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm, to obtain a magenta pigment dispersion having a pigment concentration of 15%.

[0133] <Production Example of Yellow Pigment Dispersion> A yellow pigment dispersion having a pigment concentration of 15% was obtained using the same raw materials and method as for the magenta pigment dispersion, except that Lysopac Yellow 5515C (C.I. Pigment Yellow 155 manufactured by Vibrants) was used as the pigment.

[0134] <Production Example of Aqueous Solutions of Acrylic Binder Resins 1 and 2> Aqueous solutions of acrylic binder resin 1 were produced by reproducing the production example of fixer resin 1 in JP 2018-203802 A. However, the degree of adjustment of the solids concentration with water after distilling off toluene was changed so that the solids concentration of the aqueous solution of acrylic binder resin 1 was 35%. The acid value of the acrylic binder resin 1 was 49 mg KOH / g and the glass transition temperature was 81°C. Furthermore, a water-based solution of acrylic binder resin 2 (solids concentration 35%) was produced in the same manner as the acrylic binder resin 1 by reproducing the production example of fixer resin 34 in JP 2018-203802 A, except that the solids concentration was adjusted to 35%. The acid value of the acrylic binder resin 2 was 49 mg KOH / g and the glass transition temperature was 42°C.

[0135] <Production of Aqueous Inkjet Ink Set> The pigment dispersion produced by the method described above, the aqueous binder resin solution, and the raw materials listed in Table 1 were added to a mixing vessel equipped with a stirrer so as to obtain the formulation shown in each column. After all the raw materials were added, the mixture was heated to 50°C while stirring, and the mixture was stirred and mixed for an additional hour while maintaining the temperature at 50°C. The resulting reaction solution was then filtered through a membrane filter with a pore size of 0.8 μm to produce an aqueous inkjet ink. Aqueous inkjet ink sets consisting of an aqueous magenta ink (M) and an aqueous yellow ink (Y) were produced by producing aqueous inkjet inks using the magenta pigment dispersion and the yellow pigment dispersion, respectively.

[0136] When producing the aqueous inkjet ink, each raw material was added while stirring the mixture in the mixing vessel. The raw materials were added in the order listed in the top row of each column in Table 1. However, when producing an aqueous inkjet ink that did not contain one or more of these components, that component was not added, and the next component was added in the order listed. For components containing two or more raw materials, the order of addition of the raw materials within that component was arbitrary.

[0137]

[0138]

[0139]

[0140] The meanings of the abbreviations and details of the product names listed in Table 1 above are as follows. In Table 1, "bp" represents the boiling point, "Nv" represents the solid content concentration, and "HLB" represents the HLB value. The boiling points listed in Table 1 are values ​​at 1 atmosphere. <Water-soluble organic solvents> Hexylene glycol: boiling point of 196°C at 1 atmosphere, surface tension of 27mN / m at 25°C 1,2-PD: 1,2-propanediol (boiling point of 188°C at 1 atmosphere, surface tension of 37mN / m at 25°C) 1,5-PeD: 1,5-pentanediol (boiling point of 239°C at 1 atmosphere, surface tension of 42mN / m at 25°C) PnP: propylene glycol monopropyl ether (boiling point of 150°C at 1 atmosphere, surface tension of 26mN / m at 25°C) DPnP: dipropylene glycol monopropyl ether (boiling point of 212°C at 1 atmosphere, surface tension of 26mN / m at 25°C) DPnB: dipropylene glycol monobutyl ether (boiling point at 1 atmosphere: 230°C, surface tension at 25°C: 24 mN / m) iPDG: diethylene glycol monoisopropyl ether (boiling point at 1 atmosphere: 207°C, surface tension at 25°C: 30 mN / m) Glycerin: boiling point at 1 atmosphere: 290°C, surface tension at 25°C: 65 mN / m <Compound (A-1)> Nonion K-220: a compound represented by the general formula (1) where R １is an alkyl group having 12 carbon atoms, and n=20 (surfactant manufactured by NOF Corporation, solid content 100%). Nonion K-230: a compound in which R １ is an alkyl group having 12 carbon atoms, and n=30 (surfactant manufactured by NOF Corporation, solid content 100%). Emulgen 1150S-60: a compound in which R １ is an alkyl group having 11 carbon atoms, and n=50 (surfactant manufactured by Kao Corporation, solid content 60%). Brownon BE-30: a compound represented by the general formula (1) where R １ is an alkyl group having 22 carbon atoms, and n=30 (surfactant manufactured by Aoki Oil & Fat Industries Co., Ltd., solid content 100%). Nonion K-2100: a compound in which R １ is an alkyl group having 12 carbon atoms, and n=100 (surfactant manufactured by NOF Corporation, solid content 50%). Brownon BE-20: a compound in which R １ is an alkyl group having 22 carbon atoms, and n=20 (surfactant manufactured by Aoki Oil & Fat Industries Co., Ltd., solid content 100%). Nonion B-250: a compound in which R １ is an alkyl group having 22 carbon atoms, and n=50 (surfactant manufactured by NOF Corporation, solid content 100%). Emalex 120: a compound in which R １ is an alkyl group having 16 carbon atoms, and n=20 (surfactant manufactured by Nippon Emulsion Co., Ltd., solid content 100%). Emalex 130: a compound represented by the general formula (1), １ is an alkyl group having 16 carbon atoms, and n=30 (surfactant manufactured by Nippon Emulsion Co., Ltd., solid content 100%). Emalex 630: a compound represented by the general formula (1), １ is an alkyl group having 18 carbon atoms, and n=30 (surfactant manufactured by Nippon Emulsion Co., Ltd., solid content 100%). Emalex 640: a compound represented by the general formula (1), １ is an alkyl group having 18 carbon atoms, and n=40 (surfactant manufactured by Nippon Emulsion Co., Ltd., solid content 100%). Emulgen 150: a compound represented by the general formula (1), １is an alkyl group having 12 carbon atoms, and n=50 (surfactant manufactured by Kao Corporation, solid content 100%) <Surfactants (A-2)> Surfynol 104: an acetylene diol-based surfactant manufactured by Evonik Japan, HLB value=3.0 Surfynol 440: an acetylene diol-based surfactant manufactured by Evonik Japan, HLB value=8.1 TEGO Twin 4100: a gemini type silicone-based surfactant manufactured by Evonik Japan (HLB value=0 to 2) TEGO Wet 280: a silicone-based surfactant manufactured by Evonik Japan (R in the above general formula 4) ５ is a structure represented by general formula 5, and R ６ a polyether-modified silicone surfactant having a structure other than that represented by general formula 5, HLB value = 3 to 5); TEGO Glide 440: a silicone surfactant manufactured by Evonik Japan (R ６ is a structure represented by general formula 5, and R ５ (polyether-modified silicone surfactant having a structure not represented by general formula 5, HLB value = 3 to 5) <Other surfactants> Surfynol 465: acetylene diol surfactant manufactured by Evonik Japan, HLB value = 13.2 <Resins> A-615GE: PES Resin A-615GE (polyester resin manufactured by Takamatsu Oil & Fat Co., Ltd., solid content 25%, glass transition temperature 47°C) <Waxes> AQ515: AQUACER 515, polyethylene wax emulsion manufactured by BYK Japan, solid content 35% <Preservatives> Proxel GXL: 1,2-benzisothiazol-3-one in dipropylene glycol solution (1,2-benzisothiazol-3-one:dipropylene glycol:water=2:6:2, preservative manufactured by Arch Chemicals. Dipropylene glycol is a water-soluble organic solvent with a boiling point of 232°C at 1 atmosphere and a surface tension of 36 mN / m at 25°C.)

[0141] [Examples 1 to 50, Comparative Examples 1 to 7] The aqueous inkjet ink sets produced by the methods described above were used to carry out the following evaluations, and the evaluation results are shown in Table 1 above.

[0142] <Evaluation 1: Evaluation of Discharge Stability (Initial Printing)> An inkjet ejection device equipped with a Kyocera Corporation inkjet head "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) installed in an environment of 25°C was filled with the aqueous magenta ink or aqueous yellow ink constituting the above aqueous inkjet ink set. Next, a nozzle check pattern was printed, and after confirming that ink was being ejected normally from all nozzles, the device was left for 1 minute. Thereafter, a solid print with a print rate of 100% was performed on OK topcoat paper under printing conditions of a frequency of 40 kHz and 1200 × 1200 dpi. The resulting solid print was then evaluated for discharge stability (initial print) by checking with a magnifying glass whether the aqueous inkjet ink had been applied to the area where it was originally supposed to be printed. The evaluation criteria were as follows, with ratings of "A" and "B" deemed the print suitable for practical use. The above evaluation was carried out for each of the aqueous magenta ink and the aqueous yellow ink that make up the aqueous inkjet ink set. Table 1 also lists the results of the aqueous magenta ink and the aqueous yellow ink that received poor evaluation results. (Evaluation criteria) A: No chipping was observed in the area that should have been printed first in the solid print. B: A chipping of less than 1 cm was observed in the area that should have been printed first in the solid print. D: A chipping of 1 cm or more was observed in the area that should have been printed first in the solid print.

[0143] <Evaluation 2: Evaluation of Discharge Stability (Standby Discharge)> An inkjet discharge device equipped with a Kyocera Corporation inkjet head "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) installed in an environment of 25°C was filled with the water-based magenta ink or water-based yellow ink constituting the above-mentioned water-based inkjet ink set. After filling, the water-based magenta ink or water-based yellow ink was pressurized until it oozed out from the nozzles of the inkjet head. Next, the nozzle plate to which the oozed water-based inkjet ink had adhered was wiped, and the inkjet discharge device was then left to stand by for 1 hour. Thereafter, a solid image was printed on OK topcoat paper under printing conditions of a frequency of 40 kHz, a conveyor drive speed of 50 m / min, and a resolution of 1200 × 1200 dpi. The resulting solid prints were then visually inspected to determine whether the aqueous inkjet ink was applied to the area where it was supposed to be printed first, thereby evaluating standby ejection performance. The evaluation criteria were as follows, with "A," "B," and "C" being considered usable. The above evaluation was performed for each of the aqueous magenta ink and aqueous yellow ink that constituted the aqueous inkjet ink set. Table 1 also lists the results of the aqueous magenta ink and aqueous yellow ink that received poor evaluation results. (Evaluation Criteria) A: In the solid print printed after waiting for 1 hour, no chipping was observed in the area where it was supposed to be printed first. B: In the solid print printed after waiting for 1 hour, chipping of less than 3 cm was observed in the area where it was supposed to be printed first. C: In the solid print printed after waiting for 1 hour, chipping of 3 cm or more but less than 5 cm was observed in the area where it was supposed to be printed first. D: In the solid print printed after waiting for 1 hour, chipping of 5 cm or more was observed in the area where it was supposed to be printed first.

[0144] <Preparation of Magenta / Yellow Gradient Printed Material> An inkjet ejection device was prepared, in which two Kyocera Corporation inkjet heads "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) were arranged side by side along the transport direction of the substrate. Each set of aqueous inkjet inks was loaded in the order of aqueous magenta ink and aqueous yellow ink from the upstream side in the transport direction. Furthermore, an A4-size (21 cm wide x 30 cm long) OPP film ("OPU-1" manufactured by Mitsui Chemicals Tohcello, Inc., thickness 20 μm) was fixed on the conveyor as the printing substrate. The conveyor was then driven at 50 m / min, and as the printing substrate passed below the installation position of the inkjet heads, the aqueous inkjet ink set was ejected at a drop volume of 2.6 pL, printing a magenta / yellow gradation image. Immediately after printing, the printed printing substrate was placed in a constant temperature incubator with a blower set at 70°C and dried for 3 minutes to produce a magenta / yellow gradation print. The "magenta / yellow gradation image" refers to a 5 cm wide x 30 cm long magenta gradation image printed using aqueous magenta ink (with a printing rate varied in 10% increments between 10 and 100%) and a 5 cm wide x 30 cm long yellow gradation image printed using aqueous yellow ink, arranged adjacent to each other with their long sides in contact. Furthermore, a magenta / yellow gradation print was produced using a Futamura Chemical OPP film (FOR-AQ, thickness 20 μm) as the printing substrate, using the same method as above.

[0145] <Evaluation 3: Evaluation of print quality (whiteout)> The magenta / yellow gradation print produced by the method described above was visually observed. The print quality of the magenta / yellow gradation print was evaluated by checking for the presence or absence of whiteout at a printing rate of 100%. The evaluation criteria were as follows, with "A," "B," "C+," and "C" being considered usable. The above evaluation was performed on each of the two types of printing substrates on which the magenta / yellow gradation print was printed. A: No white spots were observed on either of the two types of printing substrates, and on both the printed areas of the magenta gradation image and the printed areas of the yellow gradation image. B: Slight white spots were observed on either the printed areas of the magenta gradation image or the printed areas of the yellow gradation image on only one of the two types of printing substrates. C+: Slight white spots were observed on either the printed areas of the magenta gradation image and the printed areas of the yellow gradation image on only one of the two types of printing substrates. C: Clear white spots were observed on either the printed areas of the magenta gradation image and the printed areas of the yellow gradation image on at least one of the two types of printing substrates. D: Clear white spots were observed on either the printed areas of the magenta gradation image and the printed areas of the yellow gradation image on both of the two types of printing substrates.

[0146] <Evaluation 4: Evaluation of print quality (bleeding)> The magenta / yellow gradation print produced by the method described above was visually observed. The print quality of the magenta / yellow gradation print was evaluated by checking the coverage rate at the boundary between the printed portion of the magenta gradation image and the printed portion of the yellow gradation image where bleeding began to occur. The evaluation criteria were as follows, with "A," "B," "C+," and "C" being considered usable. Table 1 also lists the results of the two types of substrates evaluated that had the poorest evaluation results. (Evaluation criteria) A: No color bleeding was observed on both substrates even at a printing rate of 80%. B: Color bleeding was observed on at least one substrate at a printing rate of 80%. C+: Color bleeding was observed on at least one substrate at a printing rate of 70%. C: Color bleeding was observed on at least one substrate at a printing rate of 60%. D: Color bleeding was observed on both substrates at a printing rate of 60%.

[0147] <Evaluation 5: Evaluation of Water Resistance> An inkjet ejection device equipped with two Kyocera Corporation KJ4B-1200 inkjet heads (design resolution 1200 dpi, nozzle diameter 20 μm) arranged in the conveyance direction of the printing substrate was installed in an environment of 25°C, and an aqueous magenta ink and an aqueous yellow ink were filled in this order from the upstream inkjet head. In addition, an OPP film (FOR-AQ, thickness 20 μm) manufactured by Futamura Chemical Co., Ltd. was fixed on the conveyor. Thereafter, the conveyor was driven at 50 m / min, and as the printing substrate passed below the installation section of the inkjet head, one of the aqueous inkjet inks was ejected at a drop volume of 2.6 pL to print a monochrome solid image (printing rate 100%) measuring 20 cm wide and 20 cm long. Immediately after printing, the printed substrate was placed in a constant-temperature, air-blowing incubator set at 70°C and dried for 3 minutes to produce a monochrome solid print. Test pieces were then cut from the resulting monochrome solid print and placed in a Tester Sangyo AB-301 Gakushin-type rub fastness tester. A test attachment white cotton cloth (Kanakin No. 3) thoroughly moistened with ion-exchange water was attached to a friction element (weight: 200 g). The friction element was subjected to various loads and shaken several times. The condition of the print surface and the degree of coloring of the cotton cloth were then visually inspected to evaluate rub resistance. The evaluation criteria were as follows, with "A," "B," "C+," and "C" representing usable inks. The above evaluations were performed for both the aqueous magenta ink and the aqueous yellow ink, and Table 1 lists the results of those with poor evaluation results.(Evaluation criteria) A: Even after shaking the friction element 20 times with a 300g weight placed on it (500g in total), there were no abrasion marks on the printed surface and no discoloration on the cotton cloth. B: Even after shaking the friction element 10 times with a 300g weight placed on it (500g in total), there were no abrasion marks on the printed surface and no discoloration on the cotton cloth, but after shaking the element 20 times under the same load conditions, there were abrasion marks on the printed surface and / or discoloration on the cotton cloth. C+: Even after shaking the friction element 5 times with a 300g weight placed on it (500g in total), there were no abrasion marks on the printed surface and no discoloration on the cotton cloth, but after shaking the element 10 times under the same load conditions, there were abrasion marks on the printed surface and / or discoloration on the cotton cloth. C: After shaking the friction element five times without placing a weight (load 200 g), there were no abrasion marks on the printed surface and no discoloration of the cotton cloth was observed, but after shaking the friction element five times with a 300 g weight placed on the friction element (total 500 g), abrasion marks on the printed surface and / or discoloration of the cotton cloth were observed. D: After shaking the friction element five times without placing a weight (load 200 g), abrasion marks on the printed surface and / or discoloration of the cotton cloth were observed.

[0148] As shown in Table 1 above, the aqueous inkjet inks (sets) of Examples 1 to 50 having the configuration of the present invention were superior in ejection stability, had good solid coverage, and exhibited little color mixing, compared to the aqueous inkjet inks of Comparative Examples 1 to 7. Furthermore, the water resistance of the ink film was also good. These results confirmed that the aqueous inkjet inks having the configuration of the present invention are excellent aqueous inkjet inks that combine ejection stability, print quality, and water resistance of printed matter.

Claims

1. An aqueous inkjet ink comprising a pigment, a surfactant (A), a water-soluble organic solvent, and a binder resin, wherein the surfactant (A) comprises a compound (A-1) represented by the following general formula 1, and a nonionic surfactant (A-2) having an HLB value of 1 to 10 (excluding the compound (A-1)), and the water-soluble organic solvent comprises hexylene glycol. (General Formula 1) R １ -(O-CH ２ -CH ２ ) ｎ -OH [In general formula 1, R １ represents an alkyl group having 10 to 25 carbon atoms which may have a branched structure, and n is an integer of 20 to 100.

2. The water-based inkjet ink according to claim 1, wherein the water-soluble organic solvent further comprises a diol having 2 to 5 carbon atoms.

3. The aqueous inkjet ink according to claim 1, wherein the water-soluble organic solvent further contains a compound represented by the following general formula 2: ２ -(O-CH(CH ３ )-CH ２ ) ｍ -OH [In general formula 2, R ２ represents an alkyl group having 2 to 4 carbon atoms which may have a branched structure, and m is 1 or 2.

4. The aqueous inkjet ink according to any one of claims 1 to 3, wherein the mass ratio of the content of said compound (A-1) to the content of said nonionic surfactant (A-2) [compound (A-1):surfactant (A-2)] is from 1:0.5 to 1:

20.

5. The aqueous inkjet ink according to any one of claims 1 to 3, wherein the mass ratio of the sum of the content of said hexylene glycol and the content of said compound (A-1) to the content of said nonionic surfactant (A-2) [(hexylene glycol + compound (A-1)):surfactant (A-2)] is 1:1 to 14:

1.

6. A printed matter obtained by printing the aqueous inkjet ink according to any one of claims 1 to 3 on a printing substrate.

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