Aqueous inkjet ink and printed matter

Abstract

To provide aqueous inkjet ink which does not cause voids and color mixing bleeding and can obtain a printed matter excellent in water resistance, even in printing on a hardly permeable base material and a non-permeable base material, and is excellent in discharge stability immediately after printing start and after printing cessation for a long time.SOLUTION: The aqueous inkjet ink contains a pigment, a surface active agent (A), a water-soluble organic solvent, and a binder resin, wherein the surface active agent (A) contains a polyoxyalkylene monoalkyl ether-based compound (A-1) having a specific alkyl chain length and a specific number of ethylene oxide groups, and a nonionic surface active agent (A-2) having an HLB value of 1 to 10 (excluding the compound (A-1), and the water-soluble organic solvent contains hexylene glycol.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] With the increasing needs for small-lot printing and reduction of printing costs, the digital printing method that does not require plate making has been rapidly spreading.

[0003] The inkjet printing method, which is one of the above digital printing methods, is a method of printing an image and / or characters on a printing substrate (also simply referred to as "substrate" in the present application) by discharging ink droplets from fine nozzles and applying them to the printing substrate. The inkjet printing method has characteristics such as easy operation of the printing apparatus and low noise during printing. Therefore, a printing apparatus (inkjet printer) employing the inkjet printing method is highly in demand among digital printing methods.

[0004] In the present application, a printing substrate on which an image and / or characters are printed is collectively referred to as a "printed matter". The above "image" also includes seamless images such as solid images and checkered patterns.

[0005] Inks used in the inkjet printing method (referred to as "inkjet inks" in the present application) are classified into solvent-based, water-based, ultraviolet-curable types, etc., depending on their composition. On the other hand, in recent years, the movement to regulate the use of raw materials harmful to humans and the environment has been accelerating. Along with this, there has been an increasing demand for water-based inkjet inks (also simply referred to as "aqueous inkjet inks" in the present application), rather than solvent-based inkjet inks and ultraviolet-curable inkjet inks that use these raw materials.

[0006] Recently, there have also been improvements in the performance of inkjet heads, and the use of inkjet printing methods has been expanding not only in consumer applications but also in industrial printing applications. In particular, in the commercial printing market and the packaging (label / package) printing market, the replacement of plate printing methods such as offset printing and gravure printing with inkjet printing methods is being actively considered.

[0007] However, conventionally, in solid prints (prints with a print rate of 100%) made using water-based inkjet ink on difficult-to-penetrate substrates such as coated paper and art paper, and non-penetrating substrates such as films, there occur phenomena called "white spots" where the water-based inkjet ink does not adhere to the printing substrate, and "bleeding" where water-based inkjet inks with different colors mix together, making it difficult to obtain prints with the same print quality as plate printing methods. This is because water, which is the main solvent of water-based inkjet ink, has a particularly high surface tension, resulting in poor wettability with respect to the above substrates, especially wettability on the order of microseconds (μs).

[0008] Generally, in order to improve the wettability of a substrate, hydrophobic organic solvents and / or surfactants are often used. However, since these components have poor solubility in water, they are prone to foaming and likely to generate bubbles that can contribute to nozzle clogging. Furthermore, when these components orient at the gas-liquid interface formed on the nozzle end face of the inkjet head, there are problems such as destabilizing the gas-liquid interface and causing the meniscus of the aqueous inkjet ink to become unstable. These problems are particularly likely to lead to the occurrence of nozzle clogging (a phenomenon where aqueous inkjet ink is not ejected from the nozzle) immediately after the start of printing. Also, due to the structure of the inkjet head, the diameter of the nozzle is very small, only a few tens of micrometers. In particular, when printing is paused for a long time, while the liquid components (such as water and water-soluble organic solvents) in the aqueous inkjet ink volatilize from the nozzle end face, fresh aqueous inkjet ink may not be sufficiently supplied to the inkjet head. Then, in the aqueous inkjet ink present near the nozzle end face, an increase in the solid content and / or an increase in the proportion of water-soluble organic solvents with a high boiling point may occur, leading to an increase in viscosity due to aggregation and insolubilization of solid components (such as pigments and resins), and nozzle clogging may occur due to this increase in viscosity.

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

[0010] On the one hand, especially in the packaging printing market, it is necessary to ensure that the ink film after drying does not peel off even when the printed matter with water attached is rubbed with a finger or the like. That is, a certain degree of water resistance is required for the ink film after drying. In water-based inkjet ink containing a large amount of water-soluble raw materials, in order to impart water resistance to the ink film after drying, for example, it is necessary to use a binder resin with a large mass average molecular weight to form a strong continuous film of the ink film after drying. On the other hand, when the binder resin is contained in the water-based inkjet ink before printing (liquid) in an amount equal to or more than a certain amount, in the water-based inkjet ink, the binder resins interact with each other, or the binder resin and the pigment dispersion resin interact with each other, which may cause 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 water-based inkjet ink in the packaging printing market, it is necessary to simultaneously solve a plurality of problems, namely, initial ejection stability, standby ejection property, print image quality, and water resistance of the ink film. However, a water-based inkjet ink that can simultaneously and preferably solve all of these problems has not been found so far.

[0012] In the present application, a printed matter without white spots and color mixing is also referred to as a "printed matter with excellent print image 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% by mass of a silicone-based surfactant, with the content of the high-boiling organic solvent being below a certain amount. According to Patent Document 1, the aqueous ink having the above configuration is said to be excellent in continuous dischargeability and suppression of color bleeding (color bleeding in the recorded matter (printed matter)). Further, in the examples of Patent Document 1, in addition to a polyether-modified silicone-based surfactant ("Silface SAG005"), an acetylene diol-based surfactant ("Surfynol 104PG50"), and polyoxyethylene lauryl ether (with an added molar number of ethylene oxide structure of 12 moles, "Emulgen 120") are used as surfactants, and examples of aqueous inks are disclosed (see paragraph number 0090 of Patent Document 1 and Tables 4 to 9).

[0014] Also, the ink used in the image recording method disclosed in Patent Document 2 contains an organic solvent having a specific structure and a defined CLogP value, an acetylene-based surfactant, a polyoxyethylene alkyl ether-based surfactant with an HLB value of 4 to 18, and a polyether-modified silicone-based surfactant. According to Patent Document 2, by the above image recording method, a high-resolution printed matter without graininess and color bleeding (color bleeding) and excellent in abrasion resistance can be obtained. Further, in the examples of Patent Document 2, in addition to "Surfynol 104", "Dynol 604", and "Surfynol DF110D" being used as the above acetylene-based surfactants, "Emulgen 103" and "Emulgen 108" with an added molar number of ethylene oxide structure of 3 moles and 6 moles are used as the above polyoxyethylene alkyl ether-based surfactants.

[0015] Furthermore, Patent Document 3 discloses an aqueous ink containing an acetylene-based surfactant (preferably having an HLB value of 8 or less), other nonionic surfactants, and an aqueous medium, and defining the HLB value, cloud point, etc. of the other nonionic surfactants. The above aqueous ink is less likely to cause ejection failure due to drying and solidification at the nozzles of an inkjet head even in printing after a long printing pause, and is also less likely to cause a decrease in print image quality due to uneven drying when printed on a non-absorbent or poorly absorbent printing substrate. Also, in the aqueous ink specifically disclosed in Patent Document 3, as surfactants, acetylene-based surfactants such as "Surfynol 420" and "Surfynol 104", and polyoxyalkylene monoalkyl ether-based surfactants (the "Emulgen" series) with an added molar number of ethylene oxide structure of 10 or less are used.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0017] However, upon examination by the inventors, it has been found that in the aqueous inkjet inks specifically disclosed in Patent Documents 1 to 3 above, depending on printing conditions and the like, there may be problems with initial ejection stability and standby ejection performance, and there is also a risk of deterioration in the water resistance of the printed matter. The acetylene diol-based surfactants used in these specific examples all correspond to the hydrophobic surfactants described above, and thus are considered to function effectively, for example, in suppressing bleeding in printed matter. However, these surfactants have problems such as being prone to generating bubbles or destabilizing the meniscus of the aqueous inkjet ink as described above, and the above aqueous inkjet inks have not completely solved these problems. Furthermore, although details will be described later, using a hydrophobic surfactant may have an adverse effect on the water resistance of the printed matter depending on the materials used in combination, etc. From this perspective as well, it can be said that there is room for improvement in the aqueous inkjet inks disclosed in the above patent documents.

[0018] As described above, in the technologies described in Patent Documents 1 to 3, the situation was such that not all of the above-described problems were solved at a high level. Therefore, in one embodiment of the present invention, an object is to provide an aqueous inkjet ink that can obtain a printed matter that is free from white spots and bleeding and has excellent water resistance even in printing on a hardly permeable substrate and a non-permeable substrate, and further has excellent ejection stability immediately after the start of printing and after a long printing pause.

Means for Solving the Problems

[0019] As a result of intensive studies by the inventors, it has been found that all of the above-described problems can be solved simultaneously and at a high level by an aqueous inkjet ink having the following configuration.

[0020] That is, one embodiment of the present invention relates to an aqueous inkjet ink shown in the following [1] to [5], and a printed matter manufactured using the above aqueous inkjet ink shown in [6] below. [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)), the water-soluble organic solvent contains hexylene glycol, and it is an aqueous inkjet ink. R 1 -(O-CH2-CH2) n -OH General formula 1 (In general formula 1, R 1 represents an alkyl group having 10 to 25 carbon atoms which may have a branch. Also, n is an integer of 20 to 100.) [2] The aqueous inkjet ink according to [1], wherein the water-soluble organic solvent further contains diols having 2 to 5 carbon atoms. [3] The aqueous inkjet ink according to [1] or [2], wherein the water-soluble organic solvent further contains a compound represented by the following general formula 2. R 2 -(O-CH(CH3)-CH2) m -OH General formula 2 (In general formula 2, R 2 represents an alkyl group having 2 to 4 carbon atoms which may have a branch. Also, m is 1 or 2.) [4] The aqueous inkjet ink according to any one of [1] to [3], wherein the ratio of the content mass of the compound (A-1) to the content mass 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 [1] to [4], wherein the ratio of the sum of the content mass of the hexylene glycol and the content mass of the compound (A-1) to the content mass of the nonionic surfactant (A-2) [(hexylene glycol + compound (A-1)): surfactant (A-2)] is 1:1 to 14:1. A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [5] on a printing substrate.

Advantages of the Invention

[0021] In one embodiment of the present invention, the aqueous inkjet ink can provide a printed matter that is free from white spots and color bleeding even when printed on a poorly permeable substrate or a non-permeable substrate, has excellent water resistance, and further has excellent ejection stability immediately after the start of printing and after a long printing pause.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, an aqueous inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "the aqueous inkjet ink of the present embodiment") will be described. It should be noted that the present invention is not limited to the embodiments described below, and includes forms that can be implemented with modifications within the range of not changing the essential part of the present invention.

[0023] The aqueous inkjet ink of the present embodiment having the above-described configuration is excellent in wettability on the order of μs, and can provide a printed matter with excellent print quality that is free from white spots and color bleeding even when printed on a poorly permeable substrate or a non-permeable substrate. Also, stable ejection is possible immediately after the start of printing and even after a long printing pause. In addition, the above printed matter also has excellent water resistance. Although the details of the mechanism are not clear, the present inventors presume as follows. However, the present invention is not limited by the following presumption.

[0024] As described above, generally, due to the very high surface tension of water, which is the main component of aqueous inkjet ink, it does not wet and spread on difficult-to-penetrate substrates and non-penetrating substrates, making it difficult to form fine prints. On the other hand, when a surfactant is used, the surfactant aligns at the interface with the substrate in a short time on the order of μs. As a result, it is possible to wet and spread well even on substrates with very low interfacial free energy, such as difficult-to-penetrate substrates and non-penetrating substrates, especially polypropylene (PP) films, etc., and an improvement in print quality can be expected. Such an effect is particularly effectively exhibited by surfactants with low solubility in water. On the other hand, surfactants have problems such as being prone to foaming and generating bubbles that can contribute to nozzle dripping, and when using surfactants with poor solubility in water, orientation also occurs at the gas-liquid interface formed on the nozzle end face of the inkjet head, which may cause the meniscus of the aqueous inkjet ink to become unstable. And the above-mentioned bubbles lead to a deterioration in standby ejection performance, and the destabilization of the above-mentioned meniscus leads to a deterioration in the initial ejection stability.

[0025] In addition, in order to produce a 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 does not dissolve in water. On the other hand, if such a binder resin is contained in a certain amount or more in the aqueous inkjet ink before printing (liquid), there is a risk of causing problems such as the binder resin partially inhibiting the orientation of the surfactant with low solubility in water at the interface. In order to fully exhibit the effect of the surfactant, there is a method of increasing the amount of surfactant added so that it can still be sufficiently oriented at the interface even if it is inhibited. However, an excessive amount of surfactant also has problems such as inhibiting the formation of the above-mentioned continuous film, and increasing the amount of surfactant added deteriorates the water resistance of the printed matter.

[0026] The aqueous inkjet ink of this embodiment first contains, as surfactants, a nonionic surfactant (A-2) having an HLB value within a suitable range and a compound (A-1) represented by the above general formula (1). Among these, the nonionic surfactant (A-2) corresponds to the surfactant having low solubility in water described above, and can impart excellent penetrability and wettability on a hardly penetrable substrate and a non-penetrable substrate to the aqueous inkjet ink. On the other hand, the compound (A-1) has an alkyl chain having a suitable number of carbon atoms as a hydrophobic part, and on the other hand, has a polyethylene oxide structure with a suitable number of added moles as a hydrophilic part.

[0027] When the nonionic surfactant (A-2) is used alone, nozzle clogging may occur due to the generation of bubbles and the destabilization of the meniscus of the aqueous inkjet ink near the nozzle as described above. In addition, although the nonionic surfactant (A-2) has a high rate of orientation at the gas-liquid interface, the uniformity of the orientation is low. In particular, when a binder resin is present in the aqueous inkjet ink, the above-described inhibition of orientation may occur, and the aqueous inkjet ink may spread unevenly on the printing substrate, resulting in the possibility of white spots.

[0028] On the other hand, in the aqueous inkjet ink of the present embodiment, compound (A-1) is further used. In the aqueous inkjet ink, the polyethylene oxide structure of sufficient size present in compound (A-1) is hydrophilic to water, while the alkyl chain is hydrophilic to surfactant (A-2). As a result, in the aqueous inkjet ink, the nonionic surfactant (A-2) is stabilized by compound (A-1). Also, while the orientation rate to the interface is suppressed, it becomes possible to uniformly orient on the interface. Thereby, in the aqueous inkjet ink present in the inkjet head, generation of bubbles and destabilization of the meniscus are suppressed, and the initial ejection stability and standby ejection property are improved. Further, in the aqueous inkjet ink on the printing substrate, even after the liquid component has volatilized, the surfactant (A-2) and the binder resin are hydrophilic via compound (A-1), so that in the film of the aqueous inkjet ink after drying (ink film), it is considered that it becomes possible to obtain a printed matter excellent in water resistance by suppressing non-uniformization of each material and forming a uniform and continuous ink film.

[0029] Furthermore, in the aqueous inkjet ink of the present embodiment, hexylene glycol is used as the water-soluble organic solvent. Hexylene glycol (2-methyl-2,4-pentanediol) has a plurality of branched alkyl groups, and has stronger hydrophobicity compared to other alkanediols, while having high solubility in water and a low boiling point under 1 atm. Therefore, it has a higher orientation property to the interface than other alkanediols. Also, while having a high affinity with the surfactant (nonionic surfactant (A-2)) with low solubility in water described above, it can dissolve well in water and promote the orientation of the surfactant to the interface. As a result, in the presence of hexylene glycol and the above compound (A-1), the nonionic surfactant (A-2), which is a surfactant with low solubility in water, can be uniformly present in the aqueous inkjet ink. Also, since it is considered that the orientation rate of the nonionic surfactant (A-2) to the interface increases due to hexylene glycol, the decrease in the orientation rate due to the addition of the above compound (A-1) is compensated, and when the aqueous inkjet ink lands on the 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, and it becomes possible to obtain a printed matter without white spots and color bleeding.

[0030] As a result of the above, it is considered that hexylene glycol and the above compound (A-1) contribute to the stabilization and homogenization of the nonionic surfactant (A-2), thereby preventing foaming and nozzle dripping, improving ejection stability, and obtaining a printed matter having excellent print quality and water resistance.

[0031] In addition, hexylene glycol can also dissolve the binder resin well. Therefore, even after water has volatilized from the aqueous inkjet ink applied on the substrate during drying, it is considered that the binder resin can spread sufficiently and can flow freely to some extent within the aqueous inkjet ink. As a result, hexylene glycol can promote the formation of a continuous film of the ink film. Furthermore, since hexylene glycol itself does not remain in the continuous film and finally volatilizes, a printed matter with high water resistance can be produced with low energy.

[0032] As described above, in order to solve all of the above-described problems at a high level, an aqueous inkjet ink having the above-described configuration is essential.

[0033] Note that the aqueous inkjet inks specifically disclosed in Patent Documents 1 to 3 described above do not contain the compound (A-1) represented by the general formula 1 (all of those used in Patent Documents 1 to 3 are compounds in which n in the general formula 1 is less than 20), and also do not use hexylene glycol, which is different from the aqueous inkjet ink of the present embodiment. Further, Patent Documents 1 to 3 do not describe at all the above-described mechanism, that is, hexylene glycol and the compound (A-1) contribute to the stabilization and homogenization of the nonionic surfactant (A-2), and can achieve the initial ejection stability and standby ejection property, as well as the improvement of the water resistance of the printed matter.

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

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

[0036] ≪Compound (A-1)≫ As described above, since the above compound (A-1) stabilizes the nonionic surfactant (A-2), the generation of bubbles and the destabilization of the meniscus are suppressed, and the initial ejection stability and the standby ejection property are improved. Further, as a result of the compound (A-1) being compatible with the surfactant (A-2) and the binder resin, a uniform and continuous ink film is formed, and the water resistance of the printed matter is improved. Furthermore, in the presence of the above 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 sufficiently spread by wetting, so that it is possible to obtain a printed matter free from white spots and color bleeding.

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

[0038] Also, from the same viewpoints as those regarding the value of n in General Formula 1 described above, R in General Formula 1 1 The group represented by is an alkyl group having 10 to 25 carbon atoms which may have a branch, and more preferably an alkyl group having 12 to 22 carbon atoms which may have a branch. Further, in one embodiment, from the viewpoint that the affinity with hexylene glycol, which is a compound having a branched structure, can be improved and further homogenization of the nonionic surfactant (A-2) can be achieved, a printed matter free from white spots and color bleeding and having particularly excellent water resistance can be obtained. R in General Formula 1 1 The group represented by is preferably an alkyl group having 10 to 22 carbon atoms which has a branch, and particularly preferably an alkyl group having 11 to 16 carbon atoms which has a branch.

[0039] The above compound (A-1) may be obtained by synthesizing it by a conventionally known method, or a commercially available product may also 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 Emalmin series and the Sun Nonic series manufactured by Sanyo Chemical Industries, Ltd., and the Braunon series and the Fine Surf series manufactured by Aoki Yushi Industry Co., Ltd. However, commercially available products that can be used as compound (A-1) 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. If the content is 0.05% by mass or more, the above-described effects can be surely exhibited. If it is 2% by mass or less, it becomes easy to suppress white spots and color bleeding in the printed matter, and to improve the initial ejection stability and standby ejection property.

[0041] ≪Nonionic surfactant (A-2)≫ The above surfactant (A-2) has an HLB value of 1 to 10. The HLB (Hydrophile-Lipophile Balance) value is one of the parameters representing the hydrophilicity and hydrophobicity of a material. As methods for calculating the HLB value, various methods such as the Griffin method, the Davis method, and the Kawakami method are known. In the present application, the HLB value is calculated using the Griffin method.

[0042] Generally, the Griffin method is used for nonionic materials. In the Griffin method, the molecular weight of the target material is used, and the HLB value is obtained by the following formula 3. Note that the smaller the HLB value, the higher the hydrophobicity of the material, and the larger the HLB value, the higher the hydrophilicity of the material. HLB value = 20 × (sum of molecular weights of hydrophilic moieties) ÷ (molecular weight of the material) Formula 3

[0043] The above nonionic surfactant (A-2) is a surfactant having an HLB value of 1 to 10 and is not particularly limited as long as it does not correspond to the above compound (A-1). On the other hand, from the viewpoint that even on a poorly permeable printing substrate, a printed matter without white spots and color mixing and excellent in initial ejection stability can be obtained, as the above surfactant (A-2), it preferably contains an acetylene diol-based surfactant and / or a silicone-based surfactant. From the viewpoint that an aqueous inkjet ink particularly excellent in initial ejection stability and standby ejection property can be obtained, it is most preferable to use a silicone-based surfactant.

[0044] Since acetylene diol - based surfactants are excellent in the orientation speed to the interface, the wettability of aqueous ink - jet inks is improved, and it becomes easy to obtain printed matter without white streaks and color bleeding, so they can be preferably used. When using an acetylene diol - based surfactant as the nonionic surfactant (A - 2), the HLB value is preferably from 1 to 8, more preferably from 1 to 4. Specific examples of acetylene diol - based surfactants having an HLB value of 1 to 4 include, for example, 2,4,7,9 - tetramethyl - 5 - decyne - 4,7 - diol, 2,5,8,11 - tetramethyl - 6 - dodecyne - 5,8 - diol, hexadeca - 8 - yn - 7,10 - diol, 4,7 - dipropyl - dec - 5 - yn - 4,7 - diol, 6,9 - dimethyl - tetradeca - 7 - yn - 6,9 - diol, 3,6 - diisopropyl - 2,7 - dimethylocta - 4 - yn - 3,6 - diol, octadeca - 9 - yn - 8,11 - diol, 7,10 - dimethylhexadeca - 8 - yn - 7,10 - diol, 5,8 - dibutyldodeca - 6 - yn - 5,8 - diol, 4,7 - diisobutyl - 2,9 - dimethyl - dec - 5 - yn - 4,7 - diol, 5,14 - diethyl - 8,11 - dimethyloctadeca - 9 - yn - 8,11 - diol, etc. Among them, from the viewpoint that it can impart sufficient wettability even on a difficult - to - penetrate printing substrate to aqueous ink - jet inks and a printed matter with excellent print quality can be obtained, 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, hexadeca - 8 - yn - 7,10 - diol, and 2,4,7,9 - tetramethyl - 5 - decyne - 4,7 - diol. Note that only one kind of the above - mentioned compounds may be used, or two or more kinds may be used in combination. Also, the above - mentioned compounds may be those synthesized by a conventionally known method or commercially available products.

[0045] The addition amount of the acetylene diol - based surfactant is preferably 0.1 to 3% by mass in the total amount of the aqueous ink - jet ink, more preferably 0.5 to 2% by mass, and still more preferably 0.8 to 1.5% by mass.

[0046] On the one hand, although the silicon-based surfactant has a slower orientation speed at the interface than the acetylene diol-based surfactant, it has a high ability to lower the surface tension and can be preferably used from the viewpoints of reducing color bleeding in printed matter and improving the initial ejection stability. In the present application, the HLB value of the silicon-based surfactant is also calculated using the Griffin method.

[0047] When using a silicon-based surfactant as the nonionic surfactant (A-2), it is preferable to use a gemini-type silicon-based surfactant and / or a polyether-modified silicon-based surfactant (excluding those that are gemini-type silicon-based surfactants). Furthermore, the addition amount of the silicon-based surfactant is preferably 0.1 to 5% by mass in the total amount of the ink, more preferably 0.5 to 3% by mass, and still more preferably 0.8 to 2.5% by mass.

[0048] ≪Gemini-Type Silicon-Based Surfactant≫ Generally, a gemini-type surfactant has a structure in which surfactants having hydrophilic and hydrophobic structures are linked by a linking group (spacer) or a covalent bond. Also, in the case of a gemini-type silicon-based surfactant, for example, a hydrophobic structure represented by a siloxane chain ( -[SiR 3 R 4 -O] x - However, R 3 and R 4 are each an arbitrary organic group, and x is an integer of 2 or more.). And, a hydrophilic structure (for example, a polyether chain) has the following structure. · A structure in which the bonding points of the siloxane chain and the hydrophilic structure are present in the middle of the above siloxane chain and in the middle of the above hydrophilic structure, respectively. · A plurality of siloxane chains are bonded via a linking group or the like (for example, at least a part of R 3 and / or R 4 in the structural formula of the above siloxane chain is an organic group containing a siloxane chain). · In a plurality of silicone-based surfactants each having a plurality of hydrophilic structures, a structure in which at least a part of the hydrophilic structures is shared.

[0049] Gemini-type surfactants are superior in surface tension reduction ability to general surfactants. Therefore, by using a Gemini-type silicone-based surfactant, a reduction in surface tension superior to that of general silicone-based surfactants can be achieved. As a result, the wettability of an aqueous inkjet ink containing the Gemini-type silicone-based surfactant can be significantly improved, and it becomes easier to improve the above-mentioned white streaks and color bleeding.

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

[0051] ≪Polyether-modified silicone-based surfactant (excluding Gemini-type silicone-based surfactant)≫ Examples of the above polyether-modified silicone-based surfactant (excluding those that are Gemini-type silicone-based surfactants) that can be used in the aqueous inkjet ink of the present embodiment include compounds having a structure represented by the following general formula 4.

[0052]

Chemical formula

[0053] In general formula 4, p is an integer from 0 to 99, and q is an integer from 1 to 100. However, p + q is an integer from 1 to 100. Also, R 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. However, when R 5 is a methyl group, p is 0. Also, R5 and R 6 at least one of them 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]

Chemical formula

[0055] In general formula 5, r is an integer from 1 to 6, s is an integer from 1 to 50, and t is an integer from 0 to 50. However, s + t is an integer from 1 to 100. Also, R 7 is either a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. Note that the addition pattern of the ethylene oxide group and the propylene oxide group in [ ] may be block or random.

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

[0057] R in the above general formula 4 6 has a structure represented by general formula 5, and examples of commercially available products of polyether-modified silicone-based surfactants where R 5 does not have a structure represented by general formula 5 include BY16 - 201, SF8427 manufactured by Toray Dow Corning, BYK - 331, BYK - 333, BYK - UV3500, BYK - 3420 manufactured by BYK Chemie, TEGO Glide 410, TEGO Glide 432, TEGO Glide435, TEGO Glide440, TEGO Glide450 manufactured by Evonik Degussa, Silface SWP - 001, Silface SAG003, Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd., etc.

[0058] Also, R in the above general formula 4 5 has 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, SH3773M manufactured by Toray Dow Corning Co., Ltd., BYK-345, BYK-346, BYK-347, BYK-348, BYK-349 manufactured by BYK-Chemie GmbH, TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280 manufactured by Evonik Degussa GmbH, KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, KF-643 manufactured by Shin-Etsu Chemical Co., Ltd., and the like.

[0059] The ratio (Compound (A-1): Surfactant (A-2)) 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 the present embodiment is preferably 1:0.5 to 1:20 by mass ratio. The above ratio is more preferably 1:1.5 to 1:15, and even more preferably 1:2 to 1:10. By blending at the above-described preferred ratio, the nonionic surfactant (A-2) can be sufficiently stabilized by the compound (A-1), and a printed matter excellent in water resistance can be obtained while suppressing white spots and color bleeding in the printed matter.

[0060] In addition, the nonionic surfactant (A-2) can be homogenized in the aqueous inkjet ink, and the droplets of the aqueous inkjet ink can spread sufficiently, so that it is possible to obtain a printed matter without white spots and color bleeding. Therefore, the ratio of the sum of the 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 preferably 1:1 to 14:1, more preferably 2:1 to 12:1, and particularly preferably 3:1 to 11:1 in terms of mass ratio.

[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 includes hexylene glycol.

[0062] ≪Hexylene glycol≫ From the viewpoints of both good ejection stability and good print image quality of the printed matter, the content of hexylene glycol contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 25% by mass, more preferably 0.6 to 18% by mass, and particularly preferably 1 to 10% by mass in the total amount of the aqueous inkjet ink.

[0063] In addition, 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 in the total amount of the water-soluble organic solvent contained in the aqueous inkjet ink. By setting the content of hexylene glycol within the above range with respect to the total amount of the water-soluble organic solvent, the time required for stabilizing at the interface of the nonionic surfactant (A-2) can be optimized. As a result, immediately after the start of printing and during continuous printing at high speed, the ejection stability is good, and at the same time, the wettability to the printing substrate in the order of μs is improved, thereby improving the print image quality.

[0064] ≪Diols with 2 to 5 carbon atoms≫ The aqueous inkjet ink of this embodiment may further contain diols with 2 to 5 carbon atoms. By containing diols with 2 to 5 carbon atoms, further stabilization of the nonionic surfactant (A-2) can be achieved, and the standby ejection property can be improved. Also, when the aqueous inkjet ink applied on the printing substrate dries, it dissolves the binder resin together with hexylene glycol and causes an increase in the viscosity of the aqueous inkjet ink, thereby suppressing bleeding in color mixing. As the diols with 2 to 5 carbon atoms, alkanediols with 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, 3-methyl-1,3-butanediol, etc., and polyoxyalkylene diols with 2 to 5 carbon atoms such as diethylene glycol, hydroxyethoxypropanol, etc. can be used. These compounds may be used alone, or two or more of them may be used in combination.

[0065] Among these, from the viewpoints of good ejection stability after a long printing pause and the ability to suppress bleeding in the printed matter, it is preferable to use alkanediols with 2 to 5 carbon atoms, and it is 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, in order to improve the affinity with the compound (A-1), it is possible to assist the homogenization of the nonionic surfactant (A-2) and the binder resin in the ink film by the compound (A-1). From the viewpoint that the water resistance of the printed matter can be improved by improving the uniformity and continuity of the ink film, it is preferable that the diols having 3 to 5 carbon atoms have hydroxyl groups added to adjacent carbon atoms. From this viewpoint, as the diols having 2 to 5 carbon atoms, 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. And from the viewpoint that both of the above-mentioned two viewpoints are satisfied, and further, the ejection stability is good even immediately after the start of printing and during continuous printing, it is particularly preferable to use 1,2-propanediol.

[0066] From the viewpoint that the ejection stability is good under all conditions immediately after the start of printing, after a long printing pause, and during continuous printing, the content of the diols having 2 to 5 carbon atoms is preferably 0.5 to 30% by mass, more preferably 2 to 25% by mass, and particularly preferably 6 to 22% by mass in the total amount of the aqueous inkjet ink.

[0067] Also, when the aqueous inkjet ink applied on the printing substrate dries, both hexylene glycol and the diols having 2 to 5 carbon atoms contribute to the dissolution of the binder resin, the softening of the pigment dispersion resin, and the stabilization of the nonionic surfactant (A-2). From the viewpoint of obtaining a printed matter that is free from white spots and color bleeding and has excellent water resistance, and further has good ejection stability, when the content of the above-mentioned hexylene glycol is 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 the present embodiment may contain a compound represented by the above general formula 2 (referred to as "specific (poly)oxypropylene monoalkyl ethers" in the present application). The specific (poly)oxypropylene monoalkyl ethers have a structure similar to that of compound (A-1), can contribute to the stabilization of the nonionic surfactant (A-2), and since the surface tension of the specific (poly)oxypropylene monoalkyl ethers themselves is moderately low, it becomes easy to improve the initial ejection stability and prevent white spots on the printed matter. In addition, the specific (poly)oxypropylene monoalkyl ethers can assist the homogenization of the nonionic surfactant (A-2) and the binder resin in the ink film by the compound (A-1), and the uniformity and continuity of the ink film are improved. Furthermore, the specific (poly)oxypropylene monoalkyl ethers also function as a film-forming aid for the binder resin. From the above, by using the specific (poly)oxypropylene monoalkyl ethers, the water resistance of the printed matter is remarkably improved.

[0069] Examples of the specific (poly)oxypropylene monoalkyl ethers 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, since they have a high affinity for compound (A-1) and have appropriate values for the boiling point and surface tension under 1 atm, the ejection stability immediately after the start of printing is improved, and in the printed matter, the water resistance is improved and white spots can be prevented. Therefore, R in General Formula 2 2 is preferably a compound that is an unbranched alkyl group having 2 or 3 carbon atoms. Among the above-listed compounds, those 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. Further, by improving the affinity with hexylene glycol, the homogenization and continuous film formation of the ink film are promoted, the water resistance of the printed matter is particularly improved, and bleeding in the printed matter can also be suppressed. Therefore, R in General Formula 2 2 is a compound having an n-propyl group, that is, propylene glycol mono-n-propyl ether and / or dipropylene glycol mono-n-propyl ether are particularly preferably used. In particular, from the viewpoint of improving the standby ejection property, it is particularly preferable to use dipropylene glycol monopropyl ether as the specific (poly)oxypropylene monoalkyl ethers.

[0071] From the point that all the effects of improving the initial ejection stability, preventing white spots and improving water resistance in the printed matter can be achieved simultaneously, and from the point that the ejection stability is good under all conditions immediately after the start of printing, after a long printing pause, and during continuous printing, the content of the above specific (poly)oxypropylene monoalkyl ethers is preferably 0.2 to 7% by mass, and particularly preferably 0.5 to 5% by mass in the total amount of the aqueous inkjet ink.

[0072] <<Other water-soluble organic solvents>> The aqueous inkjet ink of the present embodiment may contain the above hexylene glycol and water-soluble organic solvents other than the above diols having 2 to 5 carbon atoms (referred to as "other water-soluble organic solvents" in the present application).

[0073] In the aqueous inkjet ink of the present embodiment, as the other water-soluble organic solvents, alkanediols having 6 carbon atoms (excluding hexylene glycol); alkanetriols (where the number of carbon atoms is 3 to 6); polyoxyalkylene diols (where the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, and the number of the oxyalkylene groups is 2 to 4, excluding those having 2 to 5 carbon atoms); (poly)oxyalkylene monoalkyl ethers (where the oxyalkylene group is an oxyethylene group or an oxypropylene group, the number of the oxyalkylene groups is 1 to 4, and the carbon number of the terminal alkyl group is 1 to 4 (excluding the compounds corresponding to the specific (poly)oxypropylene monoalkyl ethers), or the oxyalkylene group is an oxybutylene group or an oxypentylene group, the number of the oxyalkylene groups is 1, and the carbon number of the terminal alkyl group is 1 to 4); (poly)oxyethylene dialkyl ethers (where the number of the oxyalkylene groups is 1 to 4, and the carbon number of each terminal alkyl group is 1 to 4); lactams (where the number of atoms constituting the lactam ring is 5 to 7. Also, 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 (where the number of amino groups is 1, the number of hydroxyl groups is 1 to 3, and the carbon number is 3 to 9); etc. can be used. These other water-soluble organic solvents may be used alone or in combination of two or more. In the present application, "(poly)oxyalkylene" and "(poly)oxypropylene" respectively represent "oxyalkylene and / or polyoxyalkylene" and "oxypropylene and / or polyoxypropylene".

[0074] The total content of the water-soluble organic solvent contained in the aqueous inkjet ink of the present embodiment is preferably 3 to 33% by mass, more preferably 5 to 30% by mass, and particularly preferably 7 to 30% by mass in the total amount of the aqueous inkjet ink. By setting the total content of the water-soluble organic solvent within the above range, an appropriate viscosity for ejection as an inkjet ink can be maintained, and for example, even after a long printing pause, the ejection stability can be made good. Moreover, a printed matter that can be dried with low energy and has good water resistance can be obtained.

[0075] Further, in the aqueous inkjet ink of the present embodiment, the content of the water-soluble organic solvent having a boiling point of 220°C or higher under 1 atm is preferably 5% by mass or less (it may be 0% by mass) in the total amount of the aqueous inkjet ink. By not containing a water-soluble organic solvent having a boiling point of 220°C or higher or, even if it contains, setting the blending amount within the above range, for example, even in high-speed printing, the bleeding is good.

[0076] Furthermore, it is preferable that 90% by mass or more of the total content of the water-soluble organic solvent contained in the aqueous inkjet ink of the present embodiment is a water-soluble organic solvent having a static surface tension of 25 to 50 mN / m at 25°C. Further, it is more preferable that 70% by mass or more of the total content of the water-soluble organic solvent is a water-soluble organic solvent having a static surface tension of 26 to 40 mN / m at 25°C, and it is particularly preferable that 90% by mass or more of the total content of the water-soluble organic solvent is a water-soluble organic solvent having a static surface tension of 26 to 40 mN / m at 25°C. By using the water-soluble organic solvent having the above surface tension, an appropriate surface tension for ejection as an inkjet ink can be maintained, and for example, even after a long printing pause, the ejection stability can be made good. In addition, it will assist the uniform wet spreading of the aqueous inkjet ink on the printing substrate, resulting in a printed matter without white spots and excellent in water resistance. Note that 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 described later.

[0077] <Pigment> The water-based inkjet ink of this embodiment contains a pigment.

[0078] As the above-mentioned pigment, conventionally known organic and inorganic pigments can be arbitrarily used. For example, pigments represented by the following Color Index names can be used. That is, as red pigments, C.I. Pigment Red 52, 5, 7, 9, 12, 17, 22, 23, 31, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 57:1, 57:2, 112, 122, 123, 146, 147, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 184, 188, 202, 207, 209, 254, 255, 260, 264, 266, 269, 282; As violet 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. 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; As black pigments, C.I. Pigment Black 1, 7, 11; and As white pigments, C.I. Pigment White 4, 5, 6, 21, etc. These pigments may be used alone, or two or more of them may be used in combination. Further, a solid solution composed of two or more of the above-listed pigments can also be used as a pigment.

[0079] The content of the pigment contained in the aqueous inkjet ink of this embodiment is adjusted according to the intended use of the printed matter produced using the aqueous inkjet ink. For example, it is preferably 0.5 to 30% by mass in the total amount of the aqueous inkjet ink. Further, except in the case of white aqueous inkjet ink (aqueous white ink), from the viewpoint of obtaining a printed matter with high density without deteriorating the ejection stability of the aqueous inkjet ink, the content of the above pigment is more preferably 1 to 15% by mass, and particularly preferably 1.5 to 10% by mass. On the other hand, in the case of aqueous white ink, from the viewpoint of obtaining a printed matter with high hiding power without deteriorating the ejection stability of the aqueous white ink, the content of the above pigment is more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass.

[0080] <Pigment-dispersing resin> The aqueous inkjet ink of this embodiment may contain a resin used for pigment dispersion (pigment-dispersing resin). Compared with a dispersion containing a pigment dispersed without using a pigment-dispersing resin (a dispersion of a self-dispersing pigment, a dispersion of a pigment dispersed with a surfactant, etc.), the pigment dispersed using a pigment-dispersing resin has excellent dispersion stability, so that it becomes an aqueous inkjet ink excellent in initial ejection stability and standby ejection property. Also, from the viewpoint of improving the water resistance of the printed matter, it is preferable to select a pigment-dispersing resin. Further, by suppressing the desorption of the pigment-dispersing resin from the pigment, it is possible to suppress the free pigment-dispersing resin from adsorbing to the compound (A-1) and the nonionic surfactant (A-2), and to prevent the initial ejection stability, standby ejection property, and print image quality of the printed matter from deteriorating. From this viewpoint, the above pigment-dispersing resin is preferably a polymer having a crosslinked structure and / or a block polymer.

[0081] The type of the pigment-dispersing resin is not particularly limited. For example, acrylic resins, styrene resins, (anhydrous) maleic acid resins, urethane resins, polyester resins, polyolefin resins, etc. can be arbitrarily used. These resins may be used alone, or two or more of them may be used in combination. Among them, in terms of the points that the initial ejection stability and standby ejection property can be improved, the material selectivity is large, and the resin synthesis is easy, etc., it is preferable to use one or more selected from the group consisting of acrylic resins, (anhydrous) maleic acid resins, and urethane resins. Further, since it has a high affinity with the compound (A-1) and it is difficult for the pigment to become non-uniform in the aqueous inkjet ink, the homogenization and continuous film formation of the ink film are not inhibited by the above pigment, and the water resistance of the printed matter is improved, and also from the point that the initial ejection stability and standby ejection property of the aqueous inkjet ink can be improved, acrylic resins and / or (anhydrous) maleic acid resins can be particularly preferably used.

[0082] In the present application, the "acrylic resin" refers to a resin using, as a polymerizable monomer, one or more selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters (further, styrene and / or styrene derivatives may be used). However, a resin containing (anhydrous) maleic acid (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer shall be excluded from the "acrylic resin". The "(anhydrous) maleic acid resin" refers to a resin using at least (anhydrous) maleic acid as a polymerizable monomer. The (anhydrous) maleic acid resin may further use, as a polymerizable monomer, one or more 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 is no particular limitation on its structure, and for example, resins having a random structure, a block structure, a comb structure, a star structure, etc. can be used. Further, as the pigment-dispersing resin, a water-soluble resin or a water-insoluble resin may be selected.

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

[0085] When a water-soluble resin is used as the pigment-dispersing resin, its acid value is preferably 50 to 300 mgKOH / g, more preferably 60 to 250 mgKOH / g. Particularly preferably, it is 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 it can be stably discharged from the inkjet head regardless of the use conditions. Further, the solubility of the pigment-dispersing resin in water can be ensured, and the interaction between the pigment-dispersing resins becomes suitable, so that the viscosity of the pigment dispersion can be suppressed, which is also preferable from the viewpoint of exhibiting good dischargeability 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 still more preferably 10 to 80 mgKOH / g. If the acid value is within the above range, a printed matter with excellent water resistance can be obtained.

[0087] The "acid value of the resin" in the present application is the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In the present application, as the acid value, the value calculated by the following method is used. For example, when the resin contains Wa mass% of a polymerizable monomer having va valent acid groups and a molecular weight of Ma in the polymerizable monomers constituting the resin, the acid value (mgKOH / g) is obtained by the following formula 6.

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

[0089] In the above Formula 6, the numerical value "56.11" is the molecular weight of potassium hydroxide.

[0090] In the aqueous inkjet ink of the present embodiment, from the viewpoint that the adsorption ability to the pigment is improved and the dispersion stability of the pigment and the ejection stability of the aqueous inkjet ink can be ensured, it is preferable to introduce an aromatic group into the pigment dispersion resin. Examples of the aromatic group 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. Among them, a phenyl group, a naphthyl group, and a tolyl group are preferable from the viewpoint that sufficient dispersion stability and ejection stability can be ensured.

[0091] From the viewpoints of improving the dispersion stability and ejection stability of the pigment, as well as the printing image quality and drying property of the printed matter, the introduction amount of the monomer containing an aromatic ring is preferably 5 to 75% by mass, more preferably 10 to 65% by mass, and even more preferably 15 to 55% by mass with respect to the total amount of the monomers constituting the pigment dispersion resin.

[0092] <Binder resin> The aqueous inkjet ink of the present embodiment contains a binder resin. After printing the aqueous inkjet ink containing the binder resin on a hardly permeable substrate or a non-permeable substrate, the viscosity increases at a speed on the order of μs, so bleeding is suppressed and the printing image quality is improved. Also, 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 the present embodiment may be a water-soluble resin or resin fine particles. Also, a combination of a water-soluble resin and resin fine particles may be used.

[0094] In the present application, the "resin fine particles" refer to the resin among the above-described water-insoluble resins that are dispersed in a particulate form in water and have a median diameter (also referred to as "D50" in the present application) based on volume of 10 to 1,000 nm. Further, D50 in the present application is a value measured at 25°C using a dynamic light scattering particle size distribution measuring device such as "NanoTrac UPA-EX150" manufactured by Microtrac BEL Corporation.

[0095] When a water-soluble resin is used as the binder resin, the mass 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 mass average molecular weight, a strong continuous film with high strength can be obtained even with a short drying time, and the water resistance is improved.

[0096] In the present application, as the mass average molecular weight of the compound, a polystyrene equivalent value measured by a method conforming to JIS K 7252 is used. Examples of specific measurement conditions are shown below. · Apparatus used: "HLC-8320GPC" manufactured by Tosoh Corporation · Columns used: TSKgel (registered trademark) SuperMultipore HZ-M (3 columns) · Column temperature: 40°C · Developing solvent: Tetrahydrofuran · Flow rate: 0.6 mL / min · Concentration of sample solution: 0.1 mass% · Injection volume of sample solution: 10 μL

[0097] Further, as the types of the above binder resin, acrylic resins, styrene resins, (anhydrous) maleic acid resins, urethane resins, polyester resins, vinyl chloride resins, vinyl chloride-vinyl acetate resins, etc. can be arbitrarily used. These resins may be used alone only one kind, or two or more kinds may be used in combination. Among these, it is preferable to use at least one selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin as the binder resin. Further, from the viewpoints of achieving both adhesion and abrasion resistance to the soft absorbent substrate and the non-absorbent substrate (for example, film substrates such as PP and PET described later) and improving ejection stability, it is preferable to use an acrylic resin as the binder resin. In that case, the amount of the acrylic resin is particularly preferably 50% by mass or more based on the total amount of the binder resin 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 the binder resin having the above glass transition temperature, even when drying the aqueous inkjet ink on the printing substrate at a low temperature of about 70°C in printing on a printing substrate with low heat resistance, the binder resin forms a firm film and / or the binder resin molecular chains are intertwined, thereby improving the abrasion resistance and water resistance of the printed matter. Further, at the time of ejection, since the binder resin molecular chains do not get entangled with each other, stable ejection is possible even after long-term standing.

[0099] The glass transition temperature of the binder resin can be measured by a method conforming to JIS K 7121. Specifically, about 10 mg of a sample of the target binder resin is placed in an aluminum sample pan whose mass has been measured in advance, and after measuring the mass again, a lid is placed on it and sealed. Next, this sample container and a sample pan prepared without putting the binder resin are set in a holder in a "DSC-60" (differential scanning calorimeter) manufactured by Shimadzu Corporation, and then measurement is performed under a temperature rising condition of 10°C / min to obtain a DSC chart. Then, the intersection of the baseline on the low temperature side and the tangent line at the inflection point of the baseline is obtained, and the temperature of the intersection is taken as the glass transition temperature. Note that indium is used for temperature calibration.

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

[0101] 1 / Tg = Σ(Wn / Tgn) Formula 7

[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 composed of the polymerizable monomer n constituting the resin, and Tgn represents the glass transition temperature (K) of the homopolymer composed of each polymerizable monomer n. As the above Tgn, for example, the values described in "Polymer Handbook (4th Edition)" (Wiley, 1998) can be used.

[0103] The acid value of the binder resin is preferably 0 to 100 mgKOH / g, more preferably 0 to 80 mgKOH / g. Particularly preferably, it is 10 to 60 mgKOH / g. By setting the acid value within the above range, even if a part of the aqueous inkjet ink dries near the nozzle of the inkjet head, a significant thickening of the aqueous inkjet ink can be suppressed, so that the ejection stability can be improved.

[0104] The preferred content of the binder resin contained in the aqueous inkjet ink of the present embodiment is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, and particularly preferably 5 to 18% by mass in the total amount of the aqueous inkjet ink, from the viewpoint that the standby ejection property can be improved and the color bleeding in the printed matter can be prevented.

[0105] In addition, for the aqueous inkjet ink of the present embodiment, the ratio of the total content ([g]) of the pigment dispersion resin and the binder resin to the content (WP [g]) of the pigment contained in 100 g of the aqueous inkjet ink, that is, the value represented by WR / WP is preferably 1 to 4. By setting the value represented by WR / WP within the range of 1 to 4, when forming a continuous film during drying of the aqueous inkjet ink, the amount of pigment that can become a discontinuous point can be adjusted within a suitable range, and a printed matter with excellent water resistance can be obtained. Furthermore, the ejection stability of the aqueous inkjet ink is improved.

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

[0107] As the above polyolefin, one or more selected from the group consisting of polyethylene, polypropylene, and polybutene can be preferably used. In particular, selecting polyethylene is preferable because it can significantly improve the water resistance of the printed matter.

[0108] When using wax, its D50 is preferably 10 to 200 nm, and more preferably 20 to 180 nm. If D50 is within the above range, the above-described functions can be preferably exhibited. In addition, since clogging of the inkjet head nozzle does not occur, an aqueous inkjet ink with particularly excellent initial ejection stability can be obtained.

[0109] When using wax, the blending amount of the wax with respect to the total blending amount of all resins (pigment dispersion resin, binder resin, and wax) contained in the aqueous inkjet ink is preferably 3 to 30% by mass, and preferably 6 to 20% by mass. By keeping within the above range, the functions of the respective resins are not inhibited from each other. Also, since a printed matter having sufficient water resistance can be obtained even during high-speed printing, the blending amount of the wax with respect to the total amount of the aqueous inkjet ink is preferably 0.5 to 1.5% by mass.

[0110] <Water> The aqueous inkjet ink of the present embodiment contains water. As the water, it is preferable to use ion-exchanged water (deionized water) rather than general water containing various ions. Further, the water content is preferably 45 to 85% by mass, and particularly preferably 50 to 80% by mass with respect to the total amount of the aqueous inkjet ink. Since water has a low boiling point, it preferentially volatilizes from the nozzle end face of the inkjet head, and the solid content concentration at the gas-liquid interface tends to increase. On the other hand, by setting the water content within the above range, the ejection stability becomes good under all conditions immediately after the start of printing, after a long-term printing pause, and during continuous printing.

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

[0112] <Method for Producing Aqueous Inkjet Ink> The aqueous inkjet ink of the present embodiment can be manufactured by a conventionally known method. For example, a pigment dispersion is first produced by dispersing a pigment in a medium containing at least water (aqueous medium). Then, water, a water-soluble organic solvent, compound (A-1), nonionic surfactant (A-2), a binder resin, etc. are added to the pigment dispersion, and after sufficient stirring and mixing, coarse particles are removed by methods such as filtration and centrifugation. However, the manufacturing method of the aqueous inkjet ink of the present embodiment is not limited to the above-described method.

[0113] <Properties of Aqueous Inkjet Ink> The aqueous inkjet ink of the present embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. In this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from an inkjet head with a discharge frequency of about 4 to 10 KHz, but also from an inkjet head having a high discharge frequency of about 20 to 70 KHz. In particular, when the viscosity of the aqueous inkjet ink of the present embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head having a design resolution of 600 dpi or more is used. In the present application, as the viscosity, a value measured in a 25°C environment using a cone-plate type rotational viscometer (E-type viscometer, cone angle 1°34’) such as “TVE25L type viscometer” manufactured by Toki Sangyo Co., Ltd. is used.

[0114] Also, from the viewpoint of obtaining an aqueous inkjet ink excellent in discharge stability and print image quality of printed matter, the static surface tension of the aqueous inkjet ink of the present embodiment at 25°C is preferably 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m. In the present application, as the static surface tension, a value measured in a 25°C environment using the Wilhelmy method (plate method) with an “Automatic Surface Tensiometer CBVP-Z” manufactured by Kyowa Interface Science Co., Ltd. is used.

[0115] <Set of Aqueous Inkjet Ink> The water-based inkjet ink of this embodiment may be used alone as only one type, or may also be used as a set of water-based inkjet inks combined with two or more water-based inkjet inks. As such a set of water-based inkjet inks, for example, a set of four-color water-based inkjet inks (process color ink set) composed of a cyan water-based inkjet ink (aqueous cyan ink), a magenta water-based inkjet ink (aqueous magenta ink), a yellow water-based inkjet ink (aqueous yellow ink), and a black water-based inkjet ink (aqueous black ink); a set of five-color water-based inkjet inks obtained by further adding an aqueous white ink to the process color ink set; and the like can be mentioned. It is preferable that all the water-based inkjet inks constituting the set of water-based inkjet inks satisfy the requirements of the above-described embodiment of the present invention.

[0116] <Ink-Pretreatment Liquid Set> Further, the water-based inkjet ink of this embodiment and the set of the above water-based inkjet inks can also be used in a form combined with a pretreatment liquid containing a flocculant (in the form of an ink-pretreatment liquid set). By applying a pretreatment liquid containing a flocculant onto a printing substrate before printing with the water-based inkjet ink, a layer (ink flocculation layer) for intentionally aggregating the solid components contained in the water-based inkjet ink can be formed. Then, by landing the water-based inkjet ink on the ink flocculation layer, it is possible to prevent the coalescence and color mixing of the droplets of the water-based inkjet ink, and significantly improve the printing image quality of the printed matter.

[0117] As the above flocculant, for example, a water-soluble inorganic salt or organic salt containing polyvalent metal ions, and a resin having a cationic group and a cationic group equivalent larger than the anionic group equivalent can be used.

[0118] <Inkjet Recording Method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. That is, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). Further, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0119] ≪Ejection step≫ As the operation method of the inkjet head in the ejection step, there are a shuttle (scan) method in which the inkjet head is reciprocally scanned in a direction perpendicular to the conveyance direction of the printing substrate while ejecting and recording the aqueous inkjet ink, and a single-pass method in which the aqueous inkjet ink is ejected and recorded when the printing substrate passes under a fixed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may adopt either the shuttle method or the single-pass method. Among them, the single-pass method is preferably selected because the landing position of the droplets of the aqueous inkjet ink is less likely to shift, the printing image quality of the printed matter is improved, and furthermore, high-speed printing is possible and high productivity as a substitute for plate printing can be exhibited.

[0120] Regarding the ejection method from the inkjet head, a known method can be arbitrarily selected. Examples of the ejection method include a piezo method that utilizes the volume change of a piezoelectric element (piezo element), a thermal method that ejects the aqueous inkjet ink by bubbles generated by heating a heater, and a valve method that ejects the pressurized aqueous inkjet ink while opening and closing the nozzle lid (valve) with a solenoid, etc.

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

[0122] <<Drying Process>> Examples of the drying method employed in the drying mechanism used in the drying process include a heat drying method, a hot air drying method, an infrared ray (for example, infrared ray with a wavelength of 700 to 2500 nm) drying method, a microwave drying method, a drum drying method, and the like. In the above drying process, one or more of these methods can be arbitrarily selected and used. Also, when two or more of the above drying methods are employed, each drying method may be used separately (for example, successively) or used simultaneously in combination. For example, by using the heat drying method and the hot air drying method in combination, the aqueous inkjet ink can be dried faster than when each is used alone.

[0123] In particular, from the viewpoints of preventing the bumping of the liquid component in the aqueous inkjet ink and obtaining a printed matter with excellent print quality, when the heat drying method is employed, the drying temperature is preferably 35 to 100 °C, and when the hot air drying method is employed, the hot air temperature is preferably 50 to 250 °C. Also, from the same viewpoints, when the infrared ray drying method is employed, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared ray exists in the wavelength region of 700 to 2200 nm.

[0124] <<Printing Substrate>> The printing substrate on which the aqueous inkjet ink of the present embodiment is printed is not particularly limited. On the other hand, even for difficult-to-penetrate or non-penetrating substrates where color bleeding and uneven shading are likely to occur and the printing quality is likely to deteriorate, and even for high-speed printing, by using the aqueous inkjet ink of the present embodiment, a printed matter having a printing quality equivalent to that of plate printing can be obtained.

[0125] In the present application, the permeability of the printing substrate is determined by the water absorption measured by a dynamic scanning liquid absorbency meter. Specifically, the water absorption of pure water at a contact time of 100 msec, measured by the following method, is less than 1 g / m 2 A printing substrate is defined as a "non-penetrating substrate", a printing substrate with 1 g / m 2 or more and less than 6 g / m 2 is defined as a "difficult-to-penetrate substrate", and a printing substrate with 6 g / m 2 or more is defined as a "penetrating substrate". Note that the water absorption of the printing substrate can be measured in an environment of 23°C and 50% RH using a dynamic scanning liquid absorbency meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the conditions shown below, with a printing substrate sized about 15 to 20 cm square as a sample. · Measurement method: Spiral Method · Measurement start radius: 20 mm · Measurement end radius: 60 mm · Contact time: 10 to 1,000 msec · Sampling points: 19 (measured at approximately equal intervals with respect to the square root of the contact time) · Scanning interval: 7 mm · Rotation table speed switching angle: 86.3 degrees · Head box conditions: width 5 mm, slit width 1 mm

[0126] Examples of the non-permeable substrate and the hardly permeable substrate 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, polyvinyl alcohol films, etc.; coated papers such as coated paper, art paper, cast paper, etc.; metals such as aluminum, iron, stainless steel, titanium, etc.; glass; and the like.

[0127] The above-listed printing substrates may have a smooth surface or a rough surface. Also, the above printing substrates may be transparent, translucent, or opaque. Furthermore, the above printing substrates may be in the form of a roll or a single sheet. In addition, a combination of two or more of the above-listed printing substrates adhered to each other may be used as the printing substrate. Also, a release adhesive layer or the like may be provided on the side opposite to the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing.

[0128] From the viewpoint of improving the wettability of the aqueous inkjet ink of the present embodiment, being excellent in printing image quality and drying property, and obtaining a printed matter with good rubbing resistance and substrate adhesion along with the homogenization of the surface of the printed matter, it is also preferable to perform surface modification such as corona treatment and plasma treatment on the printing surface of the above-listed printing substrates.

[0129] <Printed matter> The aqueous inkjet ink of the present embodiment can be used for manufacturing printed matter. Also, as a method for manufacturing the above printed matter, the inkjet recording method described above can be used.

Examples

[0130] Examples and comparative examples are given below to more specifically explain the aqueous inkjet ink of the present embodiment. In the following description, "parts" and "%" represent "parts by mass" and "mass %", respectively, unless otherwise specified.

[0131] <Production example of an aqueous solution of an acrylic pigment dispersion resin> 90 parts of butanol was charged into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, and the inside of the reaction vessel was purged with nitrogen gas. Next, after heating the inside of the reaction vessel to 110 °C, a mixture of 30 parts of acrylic acid, 35 parts of behenyl acrylate, and 35 parts of styrene, which are polymerizable monomers; and 4 parts of V-601 (manufactured by Fuji Film Wako Pure Chemical Corporation), which is a polymerization initiator, was dropped into the above reaction vessel over 2 hours. After the dropping was completed, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 110 °C. Then, 0.4 part 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. Next, after cooling the contents in the reaction vessel to room temperature, 38 parts of dimethylaminoethanol was added to neutralize the acrylic pigment dispersion resin, and then 100 parts of ion-exchanged water was added. Thereafter, the contents were heated to 100 °C or higher, butanol was azeotroped with ion-exchanged water to distill off the butanol, and then ion-exchanged water was added to adjust the solid content concentration to 20% to obtain an aqueous solution of an acrylic pigment dispersion resin. The molecular weight of the obtained acrylic pigment dispersion resin was 16,000, and the acid value was 234 mgKOH / g.

[0132] <Production Example of Magenta Pigment Dispersion Liquid> 20 parts of FASTOGEN SUPER MAGENTA RTS (C.I. Pigment Red 122 manufactured by DIC Corporation), which is a pigment, 25 parts of an aqueous solution of an acrylic pigment dispersion resin, and 55 parts of water were charged into a mixing vessel, and after preliminary dispersion with a stirrer, the main dispersion was carried out using a dyno mill with a volume of 0.6 L filled with 1,800 g of zirconia beads having a diameter of 0.5 mm to obtain a magenta pigment dispersion liquid having a pigment concentration of 15%.

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

[0134] <Production Example of Aqueous Solution of Acrylic Binder Resin 1 to 2> By replicating the production example of Fixing Resin 1 in JP-A-2018-203802, an aqueous solution of Acrylic Binder Resin 1 was produced. However, the degree of adjustment of the solid content concentration with water after distilling off toluene was changed so that the solid content concentration of the above aqueous solution of Acrylic Binder Resin 1 became 35%. The acid value of Resin 1 was 49 mgKOH / g, and the glass transition temperature was 81°C. In addition, while replicating the production example of Fixing Resin 34 in the above JP-A-2018-203802 and making the solid content concentration 35%, an aqueous solution (solid content concentration 35%) of Acrylic Binder Resin 2 was produced in the same manner as the above Acrylic Binder Resin 1. The acid value of Acrylic Binder Resin 2 was 49 mgKOH / g, and the glass transition temperature was 42°C.

[0135] <Production of Set of Aqueous Inkjet Ink> Using the pigment dispersion produced by the method described above, each raw material was put into a mixing container equipped with a stirrer so as to have the formulation described in each column of Table 1 below. After all the materials were put in, the mixture was heated to 50°C while stirring, and while maintaining the temperature of the mixture at 50°C, it was further stirred and mixed for 1 hour. Then, an aqueous inkjet ink was produced by filtering with a membrane filter having a pore size of 0.8 μm. By producing an aqueous inkjet ink with each of the above magenta pigment dispersion and yellow pigment dispersion, a set of aqueous inkjet inks consisting of aqueous magenta ink (M) and aqueous yellow ink (Y) was produced, respectively.

[0136] In the production of the aqueous inkjet ink, each raw material was charged while stirring the mixture in the mixing vessel. Also, in each column of Table 1, the components described in the upper row were charged in order. However, when producing an aqueous inkjet ink that does not contain one or more of these components, the next component was charged in order without charging the said component. Also, regarding components containing two or more types of raw materials, the charging order within the said component was made arbitrary.

[0137] [Table 1]

[0138] [Table 1]

[0139] [Table 1]

[0140] The meanings of the abbreviations and the details of the product names described in Table 1 above are as shown below. Also, in Table 1, "bp" represents the boiling point, "Nv" represents the solid content concentration, and "HLB" represents the HLB value. Also, the boiling points shown in Table 1 are values under 1 atm. ·Hexylene glycol: Boiling point at 1 atm: 196°C, surface tension at 25°C: 27 mN / m ·1,2-PD: 1,2-propanediol (boiling point at 1 atm: 188°C, surface tension at 25°C: 37 mN / m) ·1,5-PeD: 1,5-pentanediol (boiling point at 1 atm: 239°C, surface tension at 25°C: 42 mN / m) ·PnP: Propylene glycol monopropyl ether (boiling point at 1 atm: 150°C, surface tension at 25°C: 26 mN / m) ·DPnP: Dipropylene glycol monopropyl ether (boiling point at 1 atm: 212°C, surface tension at 25°C: 26 mN / m) · DPnB: Dipropylene glycol monobutyl ether (boiling point at 1 atm: 230 °C, surface tension at 25 °C: 24 mN / m) · iPDG: Diethylene glycol mono-isopropyl ether (boiling point at 1 atm: 207 °C, surface tension at 25 °C: 30 mN / m) · Glycerin: Boiling point 290 °C at 1 atm, surface tension 65 mN / m at 25 °C · Nonion K-220: A compound where R in general formula (1) 1 is an alkyl group with 12 carbon atoms and n = 20 (surfactant manufactured by NOF Corporation, solid content 100%) · Nonion K-230: A compound where R in general formula (1) 1 is an alkyl group with 12 carbon atoms and n = 30 (surfactant manufactured by NOF Corporation, solid content 100%) · Emulgen 1150S-60: A compound where R in general formula (1) 1 is an alkyl group with 11 carbon atoms and n = 50 (surfactant manufactured by Kao Corporation, solid content 60%) · Braunon BE-30: A compound where R in general formula (1) 1 is an alkyl group with 22 carbon atoms and n = 30 (surfactant manufactured by Aoki Yushi Kogyo Co., Ltd., solid content 100%) · Nonion K-2100: A compound where R in general formula (1) 1 is an alkyl group with 12 carbon atoms and n = 100 (surfactant manufactured by NOF Corporation, solid content 50%) · Surfynol 104: An acetylene diol-based surfactant manufactured by Evonik Japan Co., Ltd., HLB value = 3.0 · Surfynol 440: An acetylene diol-based surfactant manufactured by Evonik Japan Co., Ltd., HLB value = 8.1 · TEGO Twin 4100: A gemini-type silicone-based surfactant manufactured by Evonik Japan Co., Ltd. (HLB value = 0 - 2) · TEGO Wet 280: A silicone-based surfactant manufactured by Evonik Japan Co., Ltd. (R in the above general formula 4 5 has the structure represented by general formula 5, and R 6 does not have the structure represented by general formula 5, a polyether-modified silicone-based surfactant, HLB value = 3 - 5) ·TEGO Glide 440: A silicone surfactant manufactured by Evonik Japan Co., Ltd. (R in the general formula 4 above 6 has a structure represented by the general formula 5, and a polyether-modified silicone surfactant in which R 5 does not have a structure represented by the general formula 5, HLB value = 3 - 5) Surfynol 465: An acetylene diol surfactant manufactured by Evonik Japan Co., Ltd., HLB value = 13.2 ·A-615GE: Pes resin A-615GE (a polyester resin manufactured by Takamatsu Oil & Fat Co., Ltd., solid content 25%, glass transition temperature 47°C) ·AQ515: AQUACER515, a polyethylene wax emulsion manufactured by BYK Japan Co., Ltd., solid content 35% ·Proxel GXL: A dipropylene glycol - aqueous solution of 1,2 - benzisothiazol - 3 - one (1,2 - benzisothiazol - 3 - one:dipropylene glycol:water = 2:6:2, a preservative manufactured by Arch Chemicals. Note that dipropylene glycol is a water - soluble organic solvent with a boiling point of 232°C under 1 atm and a surface tension of 36 mN / m at 25°C.)

[0141] [Examples 1 - 43, Comparative Examples 1 - 7] Using the set of aqueous inkjet inks manufactured by the method described above, the evaluations shown below were carried out. Also, the evaluation results were as shown in Table 1 above.

[0142] <Evaluation 1: Evaluation of ejection stability (initial)> An inkjet ejection device installed in an environment of 25°C and equipped with an inkjet head "KJ4B-1200" manufactured by Kyocera (design resolution 1200 dpi, nozzle diameter 20 μm) was filled with aqueous magenta ink or aqueous yellow ink that constitutes the set of the above aqueous inkjet ink. Next, a nozzle check pattern was printed, and after confirming that ink was being ejected normally from all nozzles, it was left for 1 minute. Then, solid printing with a printing rate of 100% was performed on OK topcoat paper under printing conditions of a frequency of 40 kHz and 1200×1200 dpi. And for the obtained solid print, the ejection stability (initial) was evaluated by checking with a magnifying glass whether the aqueous inkjet ink was applied to the part where the aqueous inkjet ink should have been printed first. The evaluation criteria were as follows, and ◎ and ○ were considered usable in actual use. The above evaluation was performed separately with the aqueous magenta ink and the aqueous yellow ink that constitute the set of the aqueous inkjet ink. Also, in Table 1, the results of the evaluation of the aqueous magenta ink and the aqueous yellow ink that had a poor evaluation result were described. ◎: In the solid print, no missing parts were found in the part that should have been printed first. ○: In the solid print, a missing part less than 1 cm was found in the part that should have been printed first. ×: In the solid print, a missing part of 1 cm or more was found in the part that should have been printed first.

[0143] <Evaluation 2: Evaluation of ejection stability (standby ejection property)> An inkjet ejection device installed in an environment of 25°C and equipped with an inkjet head "KJ4B-1200" manufactured by Kyocera (design resolution 1200 dpi, nozzle diameter 20 μm) was filled with aqueous magenta ink or aqueous yellow ink that constitutes the set of the above aqueous inkjet ink. After filling, the aqueous magenta ink or aqueous yellow ink was pressurized until the aqueous magenta ink or aqueous yellow ink oozed out from the nozzles of the inkjet head. Next, after wiping the nozzle plate to which the oozed aqueous inkjet ink adhered, the inkjet ejection device was allowed to stand by for 1 hour. Then, solid image printing was performed on OK topcoat paper under printing conditions of a frequency of 40 kHz, a conveyor driving speed of 50 m / min, and a resolution of 1200×1200 dpi. And for the obtained solid print, the standby ejection property was evaluated by visually checking whether the aqueous inkjet ink was applied to the portion where the aqueous inkjet ink should have been printed first. The evaluation criteria were as follows, and ◎, ○, and △ were regarded as practically usable. The above evaluation was performed separately with the aqueous magenta ink and the aqueous yellow ink that constitute the set of the aqueous inkjet ink. Also, in Table 1, the results were described for the aqueous magenta ink and the aqueous yellow ink for which the evaluation results were poor among those for which the evaluation was performed. ◎: In the solid print printed after standing by for 1 hour, no chipping was observed in the portion that should have been printed first. ○: In the solid print printed after standing by for 1 hour, chipping less than 3 cm was observed in the portion that should have been printed first. △: In the solid print printed after standing by for 1 hour, chipping of 3 cm or more and less than 5 cm was observed in the portion that should have been printed first. ×: In the solid print printed after standing by for 1 hour, chipping of 5 cm or more was observed in the portion that should have been printed first.

[0144] <Production of Magenta / Yellow Gradation Print> An inkjet ejection device was prepared by arranging two inkjet heads "KJ4B-1200" (design resolution 1200 dpi, nozzle diameter 20 μm) manufactured by Kyocera Corporation side by side along the conveyance direction of the substrate. From the upstream side in the conveyance direction, sets of each aqueous inkjet ink were filled in the order of aqueous magenta ink and aqueous yellow ink. Also, on the conveyor, an OPP film of A4 size (width 21 cm × length 30 cm) (manufactured by Mitsui Chemicals Toagosei Co., Ltd., "OPU-1", thickness 20 μm) was fixed as the printing substrate. Then, the conveyor was driven at 50 m / min, and when the printing substrate passed below the installation part of the inkjet head, the sets of the aqueous inkjet ink were ejected under the condition of a drop volume of 2.6 pL each to print a magenta / yellow gradation image. And immediately after printing, the printed substrate after printing was put into a forced-air constant-temperature thermostat set at 70°C and dried for 3 minutes to produce a magenta / yellow gradation printed matter. The "magenta / yellow gradation image" refers to a magenta color gradation image (an image in which the printing rate is changed in steps of 10% between 10% and 100%) with a width of 5 cm and a length of 30 cm printed using aqueous magenta ink, and a yellow color gradation image with a width of 5 cm and a length of 30 cm printed using aqueous yellow ink, which are arranged adjacent to each other such that their long sides are in contact with each other. Also, an OPP film (FOR-AQ, thickness 20 μm) manufactured by Futamura Chemical Co., Ltd. was used as the printing substrate, and a magenta / yellow gradation printed matter was produced in the same manner as above.

[0145] <Evaluation 3: Evaluation of Printing Image Quality (White Missing)> The magenta / yellow gradation printed matter manufactured by the method described above was visually observed. And by confirming the presence or absence of white missing at a printing rate of 100%, the printing image quality of the magenta / yellow gradation printed matter was evaluated. The evaluation criteria were as follows, and ◎, ○, ○△, and △ were considered usable in actual use. The above evaluation was performed for each of the two types of printing substrates on which the magenta / yellow gradation printed matter was printed. ◎: No white spots were observed in both of the two types of printing substrates, and in both the printed area of the magenta gradation image and the printed area of the yellow gradation image. ○: In only one of the two types of printing substrates, slight white spots were observed in either the printed area of the magenta gradation image or the printed area of the yellow gradation image. 〇△: In only one of the two types of printing substrates, slight white spots were observed in both the printed area of the magenta gradation image and the printed area of the yellow gradation image. △: In at least one of the two types of printing substrates, obvious white spots were observed in both the printed area of the magenta gradation image and the printed area of the yellow gradation image. ×: In both of the two types of printing substrates, obvious white spots were observed in both the printed area of the magenta gradation image and the printed area of the yellow gradation image.

[0146] <Evaluation 4: Evaluation of Print Image Quality (Color Bleeding)> The magenta / yellow gradation printed matter produced by the method described above was visually observed. Then, by checking the printing rate at the boundary between the printed area of the magenta gradation image and the printed area of the yellow gradation image where color bleeding started to be seen, the print image quality of the magenta / yellow gradation printed matter was evaluated. The evaluation criteria are as follows, and ◎, ○, ○△, and △ were considered practically usable. Also, in Table 1, the results of the substrate with the worse evaluation result among the two types of substrates for which the evaluation was conducted were described. ◎: In both substrates, no color bleeding was observed even at a printing rate of 80%. ○: In at least one substrate, color bleeding was observed at a printing rate of 80%. ○△: In at least one substrate, color bleeding was observed at a printing rate of 70%. △: In at least one substrate, color bleeding was observed at a printing rate of 60%. ×: In both substrates, color bleeding was observed at a printing rate of 60%.

[0147] <Evaluation 5: Evaluation of Water Resistance> Two inkjet heads KJ4B-1200 (designed resolution 1200 dpi, nozzle diameter 20 μm) manufactured by Kyocera Corporation were arranged side by side in the conveyance direction of the printing substrate, and the inkjet ejection device was installed in an environment at 25°C. The upstream inkjet head was filled with aqueous magenta ink and aqueous yellow ink in this order. Also, an OPP film (FOR-AQ, thickness 20 μm) manufactured by Futamura Chemical Co., Ltd. was fixed on the conveyor. Then, the conveyor was driven at 50 m / min, and when the above printing substrate passed below the installation part of the inkjet head, either one of the above aqueous inkjet inks was ejected under the condition of a drop volume of 2.6 pL, and a solid-color solid image (printing rate 100%) with a size of 20 cm in width and 20 cm in length was printed. Immediately after printing, the printed substrate after printing was put into a forced-air constant-temperature thermostat set at 70°C and dried for 3 minutes to produce a solid-color solid print. Next, test pieces were cut out from the obtained solid-color solid prints and set on an AB-301 Kagakushin-type friction fastness tester manufactured by Tester Sangyo Co., Ltd. Then, a test attached white cotton cloth (Kanakin No. 3) sufficiently moistened with ion-exchanged water was attached to the friction element (self-weight 200 g), the load applied to the friction element was changed, and after oscillating a predetermined number of times, the state of the printed surface and the degree of coloring of the cotton cloth were visually confirmed to evaluate the rub resistance. The evaluation criteria were as follows, and ◎, ○, ○△, and △ were considered usable in actual use. The above evaluation was performed for each of the aqueous magenta ink and the aqueous yellow ink, and Table 1 shows the results of those with poor evaluation results. ◎: Even after placing a 300 g weight on the friction element (total 500 g) and oscillating 20 times, there were no rubbing marks on the printed surface and no coloring on the cotton cloth was observed. ○: Even after placing a 300 g weight on the friction element (total 500 g) and oscillating 10 times, there were no rubbing marks on the printed surface and no coloring on the cotton cloth was observed. However, after oscillating 20 times under the same load condition, rubbing marks on the printed surface and / or coloring on the cotton cloth were observed. ○△: Even after placing a 300 g weight on the friction element (total 500 g) and performing 5 reciprocating oscillations, there were no rubbing marks on the printed surface and no coloring on the cotton cloth. However, after performing 10 reciprocating oscillations under the same load conditions, rubbing marks on the printed surface and / or coloring on the cotton cloth were observed. △: After performing 5 reciprocating oscillations without placing a weight on the friction element (load 200 g), there were no rubbing marks on the printed surface and no coloring on the cotton cloth. However, after placing a 300 g weight on the friction element (total 500 g) and performing 5 reciprocating oscillations, rubbing marks on the printed surface and / or coloring on the cotton cloth were observed. ×: After performing 5 reciprocating oscillations without placing a weight on the friction element (load 200 g), rubbing marks on the printed surface and / or coloring on the cotton cloth were observed.

[0148] As shown in Table 1 above, the water-based inkjet inks (sets) of Examples 1 to 43 having the configuration of the present invention were superior in ejection stability compared to the water-based inkjet inks of Comparative Examples 1 to 7. Also, the solid filling was good and the color mixing was less. Furthermore, the water resistance of the ink film was also good. From these results, it was confirmed that the water-based inkjet ink having the configuration of the present invention is an excellent water-based inkjet ink that combines ejection stability, print image quality of printed matter, and water resistance.

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) 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)), the water-soluble organic solvent contains hexylene glycol, the aqueous inkjet ink. R 1 -(O-CH 2 -CH 2 ) n -OH General formula 1 (In General Formula 1, R 1 represents an alkyl group having 10 to 25 carbon atoms which may have a branch. Further, n is an integer of 20 to 100.)

2. The aqueous inkjet ink according to claim 1, wherein the water-soluble organic solvent further contains diols 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. R 2 -(O-CH(CH 3 ))-CH 2 ) m -OH General formula 2 (In General Formula 2, R 2 represents an alkyl group having 2 to 4 carbon atoms which may have a branch. Also, m is 1 or 2.)

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

20.

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