Aqueous inkjet ink and printed matter

Abstract

To provide aqueous inkjet ink by which a printed matter that has no knockout nor color bleeding and also has excellent water resistance is obtained even if printing is performed onto a hardly permeable substrate and an impermeable substrate, and which furthermore has excellent discharge stability.SOLUTION: Aqueous inkjet ink contains pigment, pigment dispersion resin, surfactant, water-soluble organic solvent and binder resin, where the pigment dispersion resin contains one or more kinds selected from a group consisting of a polymer and a block polymer having a crosslinking structure, the water-soluble organic solvent contains hexylene glycol, and when the total sum of the content (g) of the pigment dispersion resin and the content (g) of the binder resin contained in 100 g of the aqueous inkjet ink is WR(g), and the content of the pigment contained in 100 g of the aqueous inkjet ink is WP(g), a value expressed by WR / WP is 1 to 7.SELECTED DRAWING: None

Description

Technical Field

[0001] Embodiments of the present invention relate to aqueous inkjet ink and 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] As an example of the digital printing method, an inkjet printing method can be mentioned. In the inkjet printing method, ink droplets are ejected from fine nozzles, and by applying the ink to a printing substrate (also simply referred to as "substrate" in the present disclosure), an image and / or characters are formed on the printing substrate. The inkjet printing method has features such as easy operation of the printing apparatus and low noise during printing. Therefore, there is high demand for a printing apparatus (inkjet printer) that employs the inkjet printing method among digital printing methods.

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

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

[0006] Recently, with the improvement of the performance of inkjet heads, the use of inkjet printing 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 from plate printing methods such as offset printing and gravure printing to inkjet printing is being actively considered.

[0007] However, conventionally, when producing solid prints (prints with a print density of 100%) using water-based inkjet inks on difficult-to-penetrate substrates such as coated paper and art paper, and non-penetrating substrates such as films, it has been difficult to obtain prints with the same print quality as plate printing methods. Specifically, when producing solid prints using water-based inkjet inks, a phenomenon called "white spots" occurs easily, where the water-based inkjet ink does not adhere to some areas on the printing substrate. Also, a phenomenon called "bleeding", where water-based inkjet inks with different colors mix together, occurs easily. These phenomena are due to the fact that water, which is the main solvent of water-based inkjet inks, has a particularly high surface tension, resulting in poor wettability of water-based inkjet inks on the above substrates, especially wettability on the order of microseconds (μs).

[0008] Generally, in order to improve the wettability of a printing substrate, a hydrophobic organic solvent and / or a surfactant are often used. However, since these components have poor solubility in water, they are prone to foaming, and thus bubbles that can contribute to nozzle clogging are likely to occur. Furthermore, there are problems such as these components orienting at the gas-liquid interface formed on the nozzle end face of the inkjet head, destabilizing the gas-liquid interface, and destabilizing the meniscus of the aqueous inkjet ink. These problems are particularly likely to lead to the occurrence of nozzle clogging (a phenomenon in which the 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, on the order of several tens of micrometers. In particular, when printing is paused for a long time, while the liquid components (water, organic solvents, etc.) in the aqueous inkjet ink volatilize from the nozzle end face, fresh aqueous inkjet ink may not be sufficiently supplied to the inkjet head. In such a case, 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 the organic solvent with a high boiling point occur, resulting in an increase in viscosity due to aggregation and insolubilization of the solid components (pigments, resins, etc.), and nozzle clogging is likely to occur due to this increase in viscosity.

[0009] In the present disclosure, 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 performance".

[0010] On the one hand, especially in the packaging and 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. That is, the ink film after drying is required to have a certain degree of water resistance. In the case of water-based inkjet inks 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, if a binder resin in an amount of a certain level or more is contained in the water-based inkjet ink before printing (in a liquid state), problems are likely to occur. Specifically, in the water-based inkjet ink, the binder resins interact with each other, or the binder resin interacts with other resins (for example, the free pigment dispersion resin described later), which may deteriorate the ejection stability and / or cause problems such as partially inhibiting the orientation of the surfactant at the gas-liquid interface.

[0011] Thus, in order to expand the use of water-based inkjet inks in the packaging and printing market, it is necessary to simultaneously solve a plurality of problems, namely, the initial ejection stability, standby ejection property, print image quality, and water resistance of the ink film. However, there has been no situation where a water-based inkjet ink that can simultaneously and preferably solve all of these problems has been found so far.

[0012] For example, Patent Document 1 discloses an ink containing three or more organic solvents having different water-octanol partition coefficients. By using this ink, it is described that good wettability can be exhibited with respect to a non-absorbent medium (non-permeable substrate in the present disclosure), and a high-gloss printed matter can be obtained. Patent Document 2 also discloses an inkjet ink containing three or more organic compounds (organic solvents) each having a specific structure, and defining the content and ratio of these organic compounds. It is described that by using this inkjet ink, both wettability and drying property on a non-absorbent ink medium can be achieved. Further, Patent Document 3 discloses an aqueous ink containing an acetylene 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. This aqueous ink is less likely to cause ejection failure due to drying and solidification at the nozzles of the 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 hardly absorbent printing substrate.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0014] However, the inks described in Patent Document 1 and the inkjet inks described in Patent Document 2 have insufficient wettability on the order of μs, and it is difficult to completely prevent the occurrence of bleeding of color mixing described above. For example, the ink specifically disclosed in Patent Document 1 contains dipropylene glycol monopropyl ether, and dipropylene glycol monopropyl ether has a low surface tension. Therefore, depending on the composition of the aqueous inkjet ink, the meniscus of the aqueous inkjet ink present in the nozzle portion of the inkjet head may become unstable, and the standby ejection property may deteriorate. In addition, triethylene glycol and butyl diglycol, which are used in combination with dipropylene glycol monopropyl ether, have a high boiling point under 1 atm, so depending on the printing substrate used, bleeding due to poor drying may occur. This tendency is the same for the inkjet inks specifically disclosed in Patent Document 2. The mainly used 1,5-pentanediol and 1,8-octanediol have a high boiling point under 1 atm. On the other hand, diethylene glycol monohexyl ether has a low surface tension. From this, as in the case of Patent Document 1, in the case of Patent Document 2 as well, there is a possibility that bleeding in the printed matter and / or deterioration of the standby ejection property may occur. Furthermore, the aqueous inkjet inks having the configurations disclosed in Patent Documents 1 to 2 are also in a situation where improvement is required regarding the water resistance of the ink film after drying.

[0015] On the other hand, in the water-based ink specifically disclosed in Patent Document 3, as surfactants, Surfynol 420, Surfynol 104, Emulgen series (polyoxyalkylene monoalkyl ether-based surfactants), etc. are used. Although details will be described later, Surfynol 420 and Surfynol 104 can cause the water-based inkjet ink to wet and spread well even on a printing substrate with very low surface free energy, so they are effective raw materials from the viewpoint of improving the printing image quality. However, as described above, these surfactants have problems such as being prone to generating bubbles or destabilizing the meniscus of the water-based inkjet ink, and the above water-based ink has not completely solved these problems.

[0016] As described above, in the technologies described in Patent Documents 1 to 3, the situation was that not all of the above-described problems were solved at a high level.

[0017] Therefore, in one embodiment of the present invention, there is provided a water-based inkjet ink that can obtain a printed matter that is free from white spots and color bleeding even in printing on a hardly permeable substrate and a non-permeable substrate, has excellent water resistance, and further has excellent ejection stability.

[0018] In the present disclosure, a printed matter free from white spots and color bleeding is also referred to as a "printed matter with excellent printing image quality".

Means for Solving the Problems

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

[0020] That is, one embodiment of the present invention relates to a water-based inkjet ink. Another embodiment of the present invention relates to a printed matter manufactured using the above water-based inkjet ink. More specifically, the embodiments of the present invention include the following. However, the present invention is not limited to the following embodiments and includes various embodiments. [1] An aqueous inkjet ink containing a pigment, a pigment dispersion resin, a surfactant, a water-soluble organic solvent, and a binder resin, wherein the pigment dispersion resin contains one or more selected from the group consisting of a polymer having a crosslinked structure and a block polymer, the water-soluble organic solvent contains hexylene glycol, when the total content (g) of the pigment dispersion resin and the content (g) of the binder resin contained in 100 g of the aqueous inkjet ink is WR (g), and the content of the pigment contained in 100 g of the aqueous inkjet ink is WP (g), an aqueous inkjet ink in which the value represented by WR / WP is 1 to 7. [2] The aqueous inkjet ink according to [1] above, wherein the content of the hexylene glycol is 5 to 90% by mass based on the total amount of the water-soluble organic solvent contained in the aqueous inkjet ink. [3] The aqueous inkjet ink according to [1] or [2] above, wherein the surfactant contains an acetylene diol-based surfactant. [4] The aqueous inkjet ink according to any one of [1] to [3] above, wherein the water-soluble organic solvent further contains diols having 2 to 5 carbon atoms. [5] The aqueous inkjet ink according to any one of [1] to [4] above, further containing wax. [6] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [5] above on a printing substrate.

[0021] The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2023-198146 filed on November 22, 2023, and all the disclosure contents thereof are incorporated herein by reference.

Advantages of the Invention

[0022] According to the aqueous inkjet ink which is one embodiment of the present invention, even in printing on a hardly permeable substrate and a non-permeable substrate, a printed matter without white spots and color bleeding and having excellent water resistance can be obtained, and furthermore, excellent ejection stability can also be obtained.

Mode for Carrying Out the Invention

[0023] Hereinafter, an aqueous inkjet ink according to an embodiment of the present invention (hereinafter also simply referred to as "the aqueous inkjet ink of the present embodiment" or "ink") will be described. Note that the present invention is not limited to the embodiments described below, and includes forms that can be implemented with modifications within a range that does not change the essential part of the present invention.

[0024] The aqueous inkjet ink of the present embodiment having the above-described configuration is excellent in wettability in the order of μs. Therefore, even in printing on a hardly permeable substrate and a non-permeable substrate, a printed matter with excellent print quality, free from white spots and color bleeding, can be obtained. Also, stable ejection is possible even after a long printing pause. Furthermore, the printed matter has excellent water resistance. Although the mechanism is not clear, the present inventors presume as follows. However, the present invention is not limited by the following presumption.

[0025] Generally, due to the very high surface tension of water, which is the main component of aqueous inkjet ink, it does not spread wet on hardly permeable substrates and non-permeable substrates, and it is difficult to form a fine image. On the other hand, when a surfactant is used, the surfactant is oriented at the interface with the printing substrate in a short time such as in the order of μs. As a result, it is possible to make the ink spread well even on hardly permeable substrates and non-permeable substrates, particularly printing substrates with very low interfacial free energy such as polypropylene (PP) films, and an improvement in print quality can be expected. Such an effect is particularly effectively exhibited when a surfactant with low solubility in water is used. On the other hand, surfactants have problems such as being prone to foaming and thus generating bubbles that can cause nozzle clogging. Also, when a surfactant with poor solubility in water is used, orientation occurs at the gas-liquid interface formed on the nozzle end face of the inkjet head, resulting in problems such as destabilization of the meniscus of the aqueous inkjet ink and prone to nozzle clogging.

[0026] 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 an aqueous inkjet ink in an amount equal to or more than a certain amount before printing (liquid), the binder resin may interact with the free pigment dispersion resin, deteriorating the ejection stability, and / or may cause problems such as partially inhibiting the orientation of a surfactant with low solubility in water to the interface. On the other hand, the free pigment dispersion resin in the aqueous inkjet ink also has problems such as inhibiting the formation of the continuous film, and there is a possibility that the water resistance of the printed matter may deteriorate.

[0027] Therefore, in the aqueous inkjet ink of the present embodiment, first, 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 when compared with other alkanediols, it has strong hydrophobicity while having high solubility in water and a low boiling point under 1 atm. Therefore, hexylene glycol has a high affinity with the surfactant having low solubility in water described above and is also well dissolved in water. As a result, in the presence of hexylene glycol, even a surfactant with low solubility in water can be uniformly present in the aqueous inkjet ink, and the orientation rate to the interface becomes moderately small. As a result of these, hexylene glycol contributes to the stabilization of the interface, preventing foaming and nozzle dripping, and improving the ejection stability.

[0028] In addition, hexylene glycol also dissolves well the binder resin with a large mass average molecular weight described above. As a result, even after water volatilizes from the aqueous inkjet ink applied on the printing substrate, the binder resin can flow and promote the formation of a continuous 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.

[0029] Furthermore, in the aqueous inkjet ink of the present embodiment, a polymer having a crosslinked structure and / or a block polymer is used as the pigment-dispersing resin. These polymers have a stronger adsorption force to the pigment compared to a pigment dispersion using a random polymer as the pigment-dispersing resin.

[0030] Generally, when a highly hydrophobic water-soluble organic solvent such as hexylene glycol is added to a system containing a pigment dispersed by a pigment-dispersing resin, due to the high resin solubility of hexylene glycol described above, the desorption of the pigment-dispersing resin is promoted. As a result, when using a highly hydrophobic water-soluble organic solvent, there is a risk of problems such as deterioration of dispersion stability and ejection stability, adverse effects on print quality, deterioration of the water resistance of printed matter due to the liberated pigment-dispersing resin, and the like. On the other hand, in the aqueous inkjet ink of the present embodiment, since the adsorption force of the pigment-dispersing resin to the pigment is strong, the above phenomenon is less likely to occur. In addition, it is also possible to prevent the above-described binder resin and the liberated pigment-dispersing resin from interacting with each other. As a result, the meniscus of the aqueous inkjet ink at the nozzle end face of the inkjet head is stabilized, thereby suppressing nozzle clogging. Furthermore, the liberated pigment-dispersing resin no longer inhibits the formation of a continuous film of the binder resin, and the water resistance of the printed matter is further improved.

[0031] In addition, in the aqueous inkjet ink of the present embodiment, the ratio of the total content (WR [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 7. By setting the value represented by WR / WP within the range of 1 to 7, in forming the continuous film, the amount of the pigment that can be a discontinuous point can be adjusted within a suitable range, and a printed matter excellent in water resistance can be easily obtained. Further, as described above, the aqueous inkjet ink of the present embodiment contains hexylene glycol in which the binder resin and the pigment dispersion resin have high solubility. When the aqueous inkjet ink is applied onto a printing substrate, it is considered that first, the water in the ink volatilizes. Therefore, in the aqueous inkjet ink on the printing substrate, the content rate of hexylene glycol increases. As a result, the dissolution of the binder resin proceeds, and it is considered that the binder resin becomes more likely to flow even in the aqueous inkjet ink after most of the water has volatilized. Regarding the pigment dispersion resin, it is softened by hexylene glycol and becomes more likely to be compatible with the binder resin, and as a result, it is considered that it is less likely to adversely affect the formation of the continuous film. Further, by defining the total amount of the binder resin and the pigment dispersion resin with respect to the pigment, it is considered that the pigment is homogenized together with the softened pigment dispersion resin in the presence of the binder resin dissolved in hexylene glycol. Then, as it is, the pigment is fixed onto the printing substrate together with the pigment dispersion resin, resulting in a printed matter in which the pigment is uniformly present, and it is considered that the occurrence of white spots and color bleeding that may occur due to deterioration of uniformity is suppressed. As a result, regardless of the printing substrate or the printing speed, a printed matter having the same print quality and water resistance as those of plate printing can be obtained.

[0032] As described above, according to the aqueous inkjet ink having the configuration of the present embodiment, all of the above-described problems can be solved at a high level.

[0033] Incidentally, the water-based inkjet inks specifically disclosed in Patent Documents 1 to 3 mentioned above differ from the water-based inkjet ink of the present embodiment in that hexylene glycol is not used. Further, regarding the water-based inkjet ink disclosed in Patent Document 1, it also differs from the water-based inkjet ink of the present embodiment in that the value represented by the above WR / WP is less than 1. On the other hand, regarding the water-based inkjet inks disclosed in Patent Document 2 (Examples 25 to 27) and Patent Document 3, there are inks in which the value represented by the above WR / WP is 1 to 7, but all of the pigment dispersion resins used in these water-based inkjet inks are random polymers having no crosslinked structure.

[0034] Hereinafter, each component constituting the water-based inkjet ink according to an embodiment of the present invention will be described in detail.

[0035] <Water-soluble organic solvent> The water-based inkjet ink of the present embodiment contains a water-soluble organic solvent. Further, as described above, the water-soluble organic solvent includes hexylene glycol.

[0036] (Hexylene glycol) From the viewpoint that both the ejection stability and the print quality of the printed matter can be easily improved, the content of hexylene glycol contained in the water-based inkjet ink of the present embodiment is preferably 0.1 to 30% by mass, more preferably 0.6 to 20% by mass, and particularly preferably 1 to 10% by mass with respect to the total amount of the water-based inkjet ink.

[0037] The content of the above hexylene glycol is preferably 5 to 90% by mass, more preferably 10 to 80% by mass, particularly preferably 15 to 50% by mass, and extremely preferably 20 to 40% by mass with respect to 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 the stabilization of the surfactant at the interface can be optimized. As a result, for example, good ejection stability can be obtained even immediately after the start of printing and during continuous printing at high speed. At the same time, the wettability of the printing substrate in the order of μs is improved, thereby improving the print image quality.

[0038] (Diols having 2 to 5 carbon atoms) The aqueous inkjet ink of the present embodiment may further contain diols having 2 to 5 carbon atoms. By including diols having 2 to 5 carbon atoms in the ink, further stabilization of the surfactant can be achieved, and the standby ejection property can be improved. Also, when the aqueous inkjet ink applied on the printing substrate dries, the diols having 2 to 5 carbon atoms dissolve the binder resin together with hexylene glycol. By doing so, an increase in the viscosity of the aqueous inkjet ink can be caused, thereby suppressing bleeding of color mixing. Furthermore, a continuous film formed by the binder resin is likely to be formed, and the water resistance of the printed matter is also improved. Examples of the diols having 2 to 5 carbon atoms include alkanediols having 2 to 5 carbon atoms such as 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, and polyoxyalkylene diols having 2 to 5 carbon atoms such as diethylene glycol and hydroxyethoxypropanol. These compounds may be used alone or in combination of two or more.

[0039] Among these, from the above-described effects, namely, the good ejection stability after a long printing pause and the ability to suppress color bleeding in printed matter, as the diols having 2 to 5 carbon atoms, it is preferable to use alkanediols having 2 to 5 carbon atoms. More preferably, one or more selected from the group consisting of 1,2-ethanediol, 1,2-propanediol, and 1,3-butanediol can be used. Also, from the viewpoint of good ejection stability even immediately after the start of printing and during continuous printing, it is particularly preferable to use 1,2-propanediol.

[0040] From the point that good ejection stability can be easily obtained under all conditions of 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 with respect to the total amount of the aqueous inkjet ink.

[0041] Also, when the aqueous inkjet ink applied on the printing substrate dries, the diols having 2 to 5 carbon atoms contribute, together with hexylene glycol, to the dissolution of the binder resin, the softening of the pigment dispersion resin, and the stabilization of the surfactant. As a result, it becomes easier to provide an aqueous inkjet ink that gives a printed matter without white spots and color bleeding, excellent in water resistance, and further having good ejection stability. From such a viewpoint, in some embodiments, when the content of the above hexylene glycol is 1, the content of the diols having 2 to 5 carbon atoms (that is, the mass ratio of the diols having 2 to 5 carbon atoms / hexylene glycol) is preferably 1 to 6, more preferably 1.5 to 5, and particularly preferably 2 to 4.

[0042] (Other water-soluble organic solvents) The aqueous inkjet ink of the present embodiment may contain a water-soluble organic solvent other than the above hexylene glycol and the diols having 2 to 5 carbon atoms (referred to as "other water-soluble organic solvents" in the present disclosure).

[0043] In the aqueous inkjet ink of this embodiment, as the other water-soluble organic solvents, for example, alkanediols having 6 carbon atoms (excluding hexylene glycol), alkanetriols (however, those having 3 to 6 carbon atoms), polyoxyalkylene diols (however, the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, the number of the oxyalkylene groups is 2 to 4, and those having 2 to 5 carbon atoms are excluded), (poly)oxyalkylene monoalkyl ethers (however, the oxyalkylene group is an oxyethylene group or an oxypropylene group, the number of the oxyalkylene groups is 1 to 4, the number of carbon atoms of the terminal alkyl group is 1 to 4, or the oxyalkylene group is an oxybutylene group or an oxypropylene group, the number of the oxyalkylene groups is 1, and the number of carbon atoms of the terminal alkyl group is 1 to 4), (poly)oxyethylene dialkyl ethers (however, the number of the oxyalkylene groups is 1 to 4, and the number of carbon atoms of each terminal alkyl group is 1 to 4), lactams (however, those having 5 to 7 atoms forming the lactam ring. Further, 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 the carbon atom forming the lactam ring), alkanolamines (however, the number of amino groups is 1, the number of hydroxyl groups is 1 to 3, and the number of carbon atoms is 3 to 9), etc. can be used. These other water-soluble organic solvents may be used alone or in combination of two or more. In the present disclosure, “(poly)oxyalkylene” represents oxyalkylene and / or polyoxyalkylene.

[0044] ((poly)oxyalkylene monoalkyl ethers) In one embodiment, it is preferable to use the above (poly)oxyalkylene monoalkyl ethers as other water-soluble organic solvents in the aqueous inkjet ink of this embodiment. Since the surface tension of the above (poly)oxyalkylene monoalkyl ethers themselves is moderately low, the ejection stability immediately after the start of printing is improved, and it becomes easy to prevent white spots on the printed matter. The above (poly)oxyalkylene monoalkyl ethers are not particularly limited. Specific examples of compounds that can be preferably used include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, butylene glycol monomethyl ether, and the like.

[0045] Among these compounds, compounds having a high affinity with hexylene glycol and having appropriate values for the boiling point and surface tension under 1 atm are preferable in that the ejection stability immediately after the start of printing is improved, and white spots and color bleeding on the printed matter can be easily prevented. In some embodiments, it is preferable to use a compound in which the oxyalkylene group is an oxyethylene group or an oxypropylene group, the carbon number of the terminal alkyl group is 1 to 3, and the carbon number is 4 to 9. Among the compounds listed above, examples of the compounds satisfying the above requirements include ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monopropyl ether.

[0046] Among these compounds, it is preferable to use one or more compounds selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monopropyl ether, that is, (poly)oxypropylene monoalkyl ethers. (Poly)oxypropylene monoalkyl ethers have a strongly hydrophobic oxypropylene group, so they have particularly high affinity with hexylene glycol. Also, compared with compounds having an oxyethylene group, they tend to have a lower boiling point under 1 atm. As a result, the ejection stability immediately after the start of printing and the print image quality are easily improved. Furthermore, as described later, such an effect is particularly improved when the amount of the polymerizable monomer having an aromatic group is within a specific range in the polymer and block polymer having a crosslinked structure.

[0047] Also, from the viewpoint that the above-described effects are particularly preferably exhibited and the ejection stability immediately after the start of printing and the print image quality are particularly improved, among the above-listed (poly)oxypropylene monoalkyl ethers, one or more compounds selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monopropyl ether can be particularly preferably used.

[0048] In some embodiments, the water-soluble organic solvent constituting the aqueous inkjet ink preferably includes hexylene glycol and at least one selected from the group consisting of diols having 2 to 5 carbon atoms and (poly)oxyalkylene monoalkyl ethers. In some embodiments, the water-soluble organic solvent may include hexylene glycol and one or more diols having 2 to 5 carbon atoms. Further, the water-soluble organic solvent may include hexylene glycol and one or more (poly)oxyalkylene monoalkyl ethers. Further, the water-soluble organic solvent may include hexylene glycol, one or more diols having 2 to 5 carbon atoms, and one or more (poly)oxyalkylene monoalkyl ethers. Among them, from the viewpoint of facilitating the improvement of standby ejection property, color bleeding, and water resistance of printed matter, it is more preferable that the water-soluble organic solvent includes hexylene glycol and one or more diols having 2 to 5 carbon atoms. More preferably, the water-soluble organic solvent may include hexylene glycol, one or more diols having 2 to 5 carbon atoms, and one or more (poly)oxyalkylene monoalkyl ethers. As the diols having 2 to 5 carbon atoms, for example, at least one of 1,2-propanediol and 1,5-pentanediol can be used. Among them, from the point that the initial ejection stability is further improved, it is preferable to use at least 1,2-propanediol.

[0049] As the other water-soluble organic solvent contained in the aqueous inkjet ink of the present embodiment, it is preferable to use a water-soluble organic solvent having a static surface tension of 27 to 40 mN / m at 25°C. By using the water-soluble organic solvent having the above surface tension, an appropriate surface tension for ejecting as an inkjet ink can be maintained. Further, for example, even after a long printing pause, good ejection stability can be easily obtained.

[0050] The total content of the water-soluble organic solvent contained in the aqueous inkjet ink of the present embodiment may be 3% by mass or more and 36% by mass or less with respect to the total amount of the aqueous inkjet ink. In some embodiments, the total content is preferably 3 to 33% by mass, more preferably 5 to 30% by mass, and particularly preferably 7 to 30% by mass. In some embodiments, the total content may preferably be 10 to 27% by mass, more preferably 12 to 24% by mass, and still more preferably 13 to 21% by mass. By setting the total content of the water-soluble organic solvent within the above range, an appropriate viscosity for discharging as an inkjet ink can be maintained. Also, for example, even after a long printing pause, good discharge stability can be easily obtained, and furthermore, a printed matter that can be dried with low energy and has good water resistance can be easily obtained.

[0051] In some embodiments, the content of the water-soluble organic solvent having a boiling point of 220°C or higher under 1 atm in the aqueous inkjet ink is preferably 1% by mass or less (it may be 0% by mass) with respect to 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 containing it, setting the blending amount within the above range, it becomes easy to suppress bleeding in, for example, high-speed printing.

[0052] <Surfactant> The aqueous inkjet ink of the present embodiment contains a surfactant.

[0053] Among surfactants, it is preferable to use one or more selected from acetylene diol-based surfactants and siloxane-based surfactants. These surfactants can significantly reduce the surface tension of aqueous inkjet ink in a very short time, and have good wettability with respect to printing substrates with relatively high surface free energy, such as polyethylene terephthalate (PET) films. Therefore, they are preferable in that they facilitate the improvement of the printing image quality of printed matter. Furthermore, it is particularly preferable to use an acetylene diol-based surfactant because a printed matter without white spots and excellent in water resistance can be easily obtained, and the ejection stability is also improved.

[0054] In addition, from the viewpoints that the orientation speed with respect to the interface becomes suitable and it is excellent in the ability to lower the surface tension, so that the wettability with respect to the printing substrate is improved and the printing image quality of the printed matter is improved, and that the water resistance of the printed matter after drying is improved, it is preferable to use a surfactant having an HLB value of 9 or less as the above surfactant. Also, since excessive orientation to the above interface can be suppressed, when used in combination with hexylene glycol, foaming and nozzle dripping are suppressed, and good ejection stability can be easily obtained even after a long printing pause. From this viewpoint, the HLB value is more preferably 4 to 9, and particularly preferably 7 to 9.

[0055] The content of the surfactant having an HLB value of 9 or less (preferably 4 to 9, particularly preferably 7 to 9) contained in the aqueous inkjet ink of the present embodiment is preferably 0.1 to 1.8% by mass, and particularly preferably 0.2 to 1.0% by mass, based on the total amount of the aqueous inkjet ink. When the content of the surfactant having an HLB value of 9 or less (preferably 4 to 9, particularly preferably 7 to 9) is adjusted within the above range, the above-described effects can be obtained more easily, so that the printing image quality is further improved. Furthermore, the ejection stability is good even after a long printing pause or during continuous printing at high speed. Furthermore, the water resistance of the printed matter after drying is also good.

[0056] In the present disclosure, the "HLB (Hydrophilic-Lipophilic Balance) value" is one of the parameters representing the degree of hydrophilicity and hydrophobicity of a material. 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. As methods for obtaining the HLB value, there are a method of actual measurement by experiment and a method of calculation from the molecular structure. As methods of calculation from the molecular structure, there are the Griffin method, the Davis method, the Kawakami method, etc. In the present disclosure, as the HLB value, the value calculated by the Griffin method represented by the following formula (1) is used.

[0057] Formula (1): (HLB value) = 20 × (total molecular weight of hydrophilic moieties) ÷ (molecular weight of the material)

[0058] (Acetylenediol-based surfactant) The acetylenediol-based surfactant preferably used in the aqueous inkjet ink of the present embodiment may be synthesized by a conventionally known method or may be a commercially available product. Examples of such commercially available products include Surfynol (registered trademark) 61, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420, 440, 465, 485, 2502, SE, SE-F, DF-110D, Dynol (registered trademark) 604, 607 (manufactured by Evonik Japan Co., Ltd.), Olfine (registered trademark) E1004, PD-001, PD-002W, PD-004 (manufactured by Nissin Chemical Industry Co., Ltd.), etc. These compounds may be used alone or in combination of two or more. Among them, from the viewpoint of obtaining an aqueous inkjet ink in which the above-described mechanism functions effectively and which is excellent in ejection stability after a long printing pause and the print quality of the printed matter, it is preferable to use one or more selected from the group consisting of Surfynol 440, Surfynol 2502, and Dynol 604, and it is particularly preferable to use Surfynol 2502. These are included in acetylenediols having an HLB value of 7 to 9. Incidentally, Surfynol 440 is an ethylene oxide-modified product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide addition mole number: 3.5). Surfynol 2502 is an ethylene oxide and propylene oxide-modified product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide addition mole number: 5, propylene oxide addition mole number: 2). Dynol 604 is an ethylene oxide-modified product of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (ethylene oxide addition mole number: about 4).

[0059] (Siloxane surfactant) On the other hand, regarding the siloxane surfactant suitably used in the aqueous inkjet ink of the present embodiment, those synthesized by a conventionally known method may be used, or commercially available products may be used. Examples of such commercially available products include TEGO (registered trademark) Wet 270, TEGO Wet 280, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450 manufactured by Evonik Japan Co., Ltd.; Silface SAG002, Silface SAG005, Silface SAG503A, Silface SAG008 manufactured by Nisshin Chemical Industry Co., Ltd.; BYK (registered trademark)-348, BYK-349 manufactured by Big Chemie Japan Co., Ltd., and the like. These compounds may be used alone or in combination of two or more kinds. In some embodiments, among the siloxane surfactants, it is preferable to use a side-chain polyether-modified siloxane surfactant having 4 to 9 silicon (Si) atoms. For example, among the commercially available products listed above, one or more selected from the group consisting of TEGO Wet 270, TEGO Wet 280, BYK-348, and BYK-349 can be preferably used. These are preferable in that they become siloxane surfactants having the above-described suitable HLB values, have good ejection stability even after a long printing pause, and further have good wettability with respect to printing substrates having a very low surface free energy, such as biaxially stretched polypropylene (OPP) films, and a printed matter with excellent print quality can be obtained.

[0060] (Other surfactants) The aqueous inkjet ink of the present embodiment may further contain a surfactant other than the above-described acetylene diol-based surfactant and siloxane-based surfactant (referred to as "other surfactant" in the present disclosure). As the other surfactant, an acetylene monoalcohol-based surfactant, a fluorine-based surfactant, a polyoxyalkylene monoalkyl ether-based surfactant (for example, a surfactant in which the oxyalkylene group is an oxyethylene group and / or an oxypropylene group, the number of the oxyalkylene groups is 5 to 100, and / or the carbon number of the terminal alkyl group is 5 to 22); etc. can be used. These other surfactants may be used alone or in combination of two or more.

[0061] The total content of the surfactant contained in the aqueous inkjet ink of the present embodiment is preferably 0.1 to 3% by mass, more preferably 0.2 to 2.4% by mass, still more preferably 0.3 to 1.8% by mass, and particularly preferably 0.3 to 1.3% by mass with respect to the total amount of the aqueous inkjet ink. By setting the total content of the surfactant within the above range, the print quality is improved and the water resistance of the printed matter after drying becomes good.

[0062] In addition, when an acetylene diol-based surfactant and a surfactant other than the acetylene diol-based surfactant are used in combination as the surfactant, the content of the acetylene diol-based surfactant with respect to the total amount of the surfactant is preferably 30% by mass or more, and particularly preferably 45% by mass or more. When the content of the acetylene diol-based surfactant in the total amount of the surfactant is adjusted within the above range, a printed matter with excellent print quality, free from white spots and color bleeding, can be easily obtained.

[0063] <Pigment> The aqueous inkjet ink of this embodiment contains a pigment.

[0064] As the above 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. Also, a solid solution composed of two or more of the above-listed pigments can be used as a pigment.

[0065] The content of the pigment contained in the aqueous inkjet ink of this embodiment may be adjusted according to the intended use of the printed matter produced using the aqueous inkjet ink. For example, with respect to the total amount of the aqueous inkjet ink, the content of the pigment is preferably 0.5 to 30% by mass. Also, except in the case of white aqueous inkjet ink (aqueous white ink), from the point that a printed matter with a high density can be obtained 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 point that a printed matter with high hiding power can be obtained 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.

[0066] <Pigment dispersion resin> As described above, the aqueous inkjet ink of the present embodiment contains a pigment dispersion resin. In the case of a pigment that does not contain a pigment dispersion resin (self-dispersing pigment) and a pigment using a surfactant as a pigment dispersant (surfactant-dispersed pigment), when water in the ink preferentially volatilizes on the nozzle end face of the inkjet head or on the printing substrate and the proportion of the water-soluble organic solvent increases, the dispersion state of the pigment is destroyed and pigment aggregation is likely to occur. As a result, not only the ejection stability and the print image quality decrease, but also the water resistance of the printed matter may decrease. Therefore, as described above, from the viewpoint of enhancing the adsorptivity to the pigment surface and suppressing the desorption of the pigment dispersion resin in the aqueous inkjet ink, it is preferable to use a polymer having a crosslinked structure and / or a block polymer as the pigment dispersion resin. By using these polymers, it becomes possible to impart dispersion stability even to fine pigments, and to suppress the decrease in ejection stability, print image quality, and water resistance of the printed matter. Also, even when the pigment dispersion resin softens due to hexylene glycol or the like, desorption of the pigment dispersion resin from the pigment can be suppressed. As a result, it becomes possible to easily obtain a printed matter that is particularly excellent in print image quality, color development property, and color reproducibility.

[0067] (Polymer having a crosslinked structure) The polymer having a crosslinked structure may be a polymer in which a crosslinked structure is introduced into a polymer that can be used as a pigment-dispersing resin. As a method for introducing a crosslinked structure into a polymer that is a pigment-dispersing resin, a method of using a crosslinking agent to form a crosslinked structure is preferable. More specifically, a preferable form of the polymer having a crosslinked structure in the aqueous inkjet ink of the present embodiment is a polymer in which a crosslinked structure is introduced into the molecule by performing a dispersion treatment of a pigment using a polymer having no crosslinked structure (un-crosslinked polymer) and then adding a crosslinking agent to perform a crosslinking treatment. Another form of the polymer having a crosslinked structure may be a polymer into which a crosslinked structure is introduced without using a crosslinking agent. As a method for forming a polymer of such a form, for example, after performing a dispersion treatment of a pigment using a polymer having a polymerizable functional group (for example, an acrylic resin synthesized using a polyfunctional vinyl monomer), a method of introducing a crosslinked structure by bonding the polymerizable functional groups to each other by a reaction can be mentioned. In the aqueous inkjet ink of the present embodiment, compared with the method of not using a crosslinking agent in this way, a method of using a crosslinking agent, that is, a method of performing a dispersion treatment of a pigment using an un-crosslinked polymer and then adding a crosslinking agent to perform a crosslinking treatment can be preferably selected. When the method of using a crosslinking agent is applied, the polymer is densified on the pigment surface, and it becomes possible to easily suppress the desorption of the polymer. Further, the method of using a crosslinking agent is also preferable in that the crosslinking rate (described later) can be easily controlled by controlling the type and amount of the flocculant used and the crosslinking treatment conditions, and the reaction of the polymerizable functional groups during the dispersion treatment can be prevented, and the dispersion treatment can proceed stably.

[0068] In the present disclosure, "a polymer obtained by a method of adding a crosslinking agent to an un-crosslinked polymer to perform a crosslinking treatment" and "a crosslinked product of an un-crosslinked polymer" are used in the same meaning. That is, the above-described "polymer obtained by a method of performing a dispersion treatment of a pigment using an un-crosslinked polymer and then adding a crosslinking agent to perform a crosslinking treatment" and "a crosslinked product of an un-crosslinked polymer after the dispersion treatment of the pigment" are the same.

[0069] As the above uncrosslinked polymer, homopolymers, random polymers, block polymers (details will be described later), graft polymers, alternating polymers, etc. can be arbitrarily used. Further, two or more uncrosslinked polymers may be used in combination, and the two or more uncrosslinked polymers may be crosslinked during crosslinking.

[0070] In some embodiments, the above uncrosslinked polymer preferably has an aromatic group. When an aromatic group is introduced into the above uncrosslinked polymer, even in the state before crosslinking, the uncrosslinked polymer can be sufficiently adsorbed to the pigment, and after crosslinking, the polymer can be present at a high density on the surface of the pigment. Therefore, it is preferable in terms of easily improving the discharge stability. Examples of the aromatic group include, but are not limited to, phenyl group, naphthyl group, anthryl group, tolyl group, xylyl group, mesityl group, anisyl group, etc. Among them, the phenyl group, naphthyl group and tolyl group are preferable in terms of sufficiently ensuring the dispersion stability of the pigment and the discharge stability in the state before crosslinking. Further, the molar amount of the polymerizable monomer having an aromatic group with respect to the total molar amount of the polymerizable monomers constituting the uncrosslinked polymer is preferably 10 to 50 mol%, and more preferably 20 to 40 mol%. In particular, if the above molar amount is 10 to 50 mol%, even in the presence of hexylene glycol, the dispersion stability of the pigment and the discharge stability of the water-based inkjet ink can be easily improved, and further, the printing image quality of the printed matter can also be easily improved. Further, when the crosslinked product of the uncrosslinked polymer having the above molar amount of 10 to 50 mol% is used in combination with the above-mentioned (poly)oxypropylene monoalkyl ethers, the discharge stability immediately after the start of printing and the printing image quality are particularly improved.

[0071] In some embodiments, the mass average molecular weight of the above uncrosslinked polymer is preferably 3,000 to 30,000, and more preferably 5,000 to 30,000. By setting the mass average molecular weight within the above range, the adsorption of the above uncrosslinked polymer to the surface of the pigment is stabilized, and it becomes easy to improve the discharge stability.

[0072] The acid value of the above uncrosslinked polymer is preferably 50 to 300 mgKOH / g, more preferably 60 to 250 mgKOH / g, still more preferably 70 to 200 mgKOH / g, and particularly preferably 70 to 160 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment even in the state before crosslinking, and after crosslinking, the polymer can be present in a high density on the surface of the pigment. Further, when the acid group is used as a crosslinking reaction point described later, it is possible to form a sufficient amount of crosslinked structure. From these facts, when an uncrosslinked polymer having the above acid value within the above range is used, the ejection stability of the aqueous inkjet ink can be easily improved. Furthermore, when the polymer before the above crosslinking treatment is used, since the water solubility of the polymer itself is moderately low, the water resistance of the ink film after drying is less likely to decrease, and the water resistance is good.

[0073] The acid value of the pigment dispersion resin can be measured by a known apparatus. In the present disclosure, the acid value of the pigment dispersion resin is a value measured by a potentiometric titration method in accordance with JIS K 2501. As an example of a specific measurement method, after dissolving the pigment dispersion resin in a toluene-ethanol mixed solvent using AT-610 manufactured by Kyoto Electronics Industry Co., Ltd., it is titrated with a potassium hydroxide solution, and the acid value is calculated from the titration amount up to the end point.

[0074] The above crosslinking agent is preferably a compound having a plurality of reactive functional groups with crosslinking reaction points (for example, carboxy groups and / or carboxylate groups) present in the pigment dispersion resin in one molecule. By using such a compound, the polymer can be present in a high density on the surface of the pigment, and the ejection stability can be improved. As the above crosslinking agent, an aziridine compound, an isocyanate compound, an epoxy compound, an oxetane compound, a carbodiimide compound, and an oxazoline compound can be used. Among them, from the viewpoint that the crosslinking reaction can proceed in the vicinity of the pigment while stably maintaining the dispersion state of the pigment by the uncrosslinked polymer, it is preferable to use an epoxy compound as the crosslinking agent.

[0075] The crosslinking agent may be water-soluble or water-insoluble, but may have a solubility of a certain level or higher from the viewpoint of allowing the crosslinking reaction to proceed more efficiently in a liquid medium mainly composed of water. In some embodiments, the solubility of the crosslinking agent in 100 g of water at 25°C is preferably 0.1 to 50 g / 100 gH 2 O, more preferably 0.2 to 40 g / 100 gH 2 O. The solubility of the crosslinking agent may be more preferably 0.5 to 30 g / 100 gH 2 O. When a crosslinking agent having a solubility of a certain level or higher is used, the crosslinking reaction in a liquid medium mainly composed of water can proceed, and it becomes easier to exhibit the above-described effects, that is, to improve dispersion stability, ejection stability, printing image quality, and water resistance of the printed matter. Further, by using a crosslinking agent having a solubility of 50 g / 100 gH 2 O or less, it is possible to prevent the crosslinking agent from being dispersed in the liquid medium, and it can be surely reacted even with a small amount of addition. As a result, for example, it is possible to easily prevent the ejection stability and printing image quality of the aqueous inkjet ink and the water resistance of the ink film from being deteriorated by the crosslinking agent added in an excessive amount.

[0076] As described above, as the crosslinking agent, a compound having a plurality of epoxy groups in one molecule can be preferably used. The crosslinking agent that can be preferably used may be more preferably a compound having two or more glycidyl ether groups in the molecule, and still more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms. When a compound having a plurality of epoxy groups in one molecule is used as the crosslinking agent, from the viewpoint of enabling more efficient crosslinking reaction with crosslinking reaction points (for example, carboxy groups and / or carboxylate groups) present in the pigment dispersion resin in a liquid medium mainly composed of water, the epoxy equivalent of the above compound is preferably 90 to 300 g / eq., and more preferably 100 to 200 g / eq.

[0077] Specific examples of the compound having a plurality of epoxy groups in the molecule include cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6 - hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 4,4'-diglycidyloxybiphenyl, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, phthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, hydrogenated phthalic acid diglycidyl ester, and the like. Only one of these compounds may be used alone, or two or more thereof may be used in combination.

[0078] Further, it is preferable to add a crosslinking agent so that the crosslinking rate represented by the following formula (2) is 40 to 100 mol%. The above crosslinking rate is more preferably 60 to 100 mol%, and particularly preferably 80 to 100 mol%. By setting the crosslinking rate to 40 mol% or more (preferably 60 mol% or more, particularly preferably 80 mol% or more) and firmly crosslinking the uncrosslinked polymer on the pigment surface, it becomes easy to improve the dispersion stability, ejection stability, printing image quality, and water resistance of the printed matter.

[0079] Formula (2): Crosslinking rate (mol%) = [Number of moles of reactive groups of the crosslinking agent × 100 / Number of moles of crosslinking reaction points (for example, carboxyl group and carboxylate group) of the pigment dispersion resin (uncrosslinked polymer) before crosslinking]

[0080] (Block polymer) A block polymer is a polymer in which two or more types of polymers (blocks) having different structures are bonded. As described above, a block polymer can be adsorbed more strongly on the pigment surface than a general random polymer, and it is possible to suppress the desorption of the block polymer in the aqueous inkjet ink.

[0081] As the block polymer, for example, a polymer having a chain-like molecular chain can be used. Also, when the blocks contained in the block polymer are designated as A, B, C, etc., for example, a two-block polymer such as A-B, a three-block polymer such as A-B-A, A-B-C, a 2×x block polymer represented by (A-B)x (where x is an integer of 2 or more), etc. can be used.

[0082] When using a block polymer, in order to improve the dispersion stability and ejection stability of the pigment, it is preferable to divide the functions possessed by each block. That is, when using a block polymer as a pigment dispersion resin, it is preferable to use a polymer having one or more blocks for preventing the aggregation of the pigment by charge repulsion or the like (hereinafter referred to as "P block") and a block that adsorbs to the pigment (hereinafter referred to as "Q block").

[0083] In order to improve the adsorptivity to the pigment, the ink preferably contains a polymer having an aromatic group. Here, from the above viewpoint, the difference between the molar amount of the polymerizable monomer having an aromatic group with respect to the total molar amount of the polymerizable monomers constituting the P block and the molar amount of the polymerizable monomer having an aromatic group with respect to the total molar amount of the polymerizable monomers constituting the Q block is preferably 5 to 100 mol%. In one embodiment, the above difference is more preferably 5 to 50 mol%, and particularly preferably 10 to 40 mol%. In some embodiments, particularly when the above difference is 5 to 50 mol%, in addition to facilitating the improvement of the dispersion stability of the pigment and the ejection stability of the aqueous inkjet ink, it also facilitates the improvement of the printing image quality of the printed matter. In other embodiments, the difference is preferably 40 to 100 mol%, particularly preferably 60 to 100 mol%. In some embodiments, when the difference is 40 to 100 mol%, the adsorptivity of the block polymer to the pigment is particularly improved. As a result, even when hexylene glycol, which is a highly hydrophobic solvent, is used in combination, it becomes easy to improve the dispersion stability of the pigment, as well as the storage stability and ejection stability of the aqueous inkjet ink.

[0084] In addition, the molar amount of the polymerizable monomer having an aromatic group is preferably larger in the Q block, which is the block adsorbed to the pigment, than in the P block. Further, similar to the case of the uncrosslinked polymer described above, the aromatic group preferably has a phenyl group, a naphthyl group, or a tolyl group.

[0085] In addition, in order to improve the adsorptivity to the pigment, the molar amount of the polymerizable monomer having an aromatic group with respect to the total molar amount of the polymerizable monomers constituting the Q block is preferably 10 to 100 mol%. In one embodiment, the molar amount of the polymerizable monomer having an aromatic group is more preferably 10 to 75 mol%, and particularly preferably 20 to 60 mol%. In some embodiments, when the molar amount is 10 to 75 mol%, in addition to improving the dispersion stability of the pigment and the ejection stability of the aqueous inkjet ink, it also becomes easy to improve the printing image quality of the printed matter. In other embodiments, the molar amount contained is preferably 40 to 100 mol%, particularly preferably 60 to 100 mol%. In some embodiments, when the molar amount contained is 40 to 100 mol%, the adsorptivity of the block polymer to the pigment is particularly improved. As a result, even when hexylene glycol, which is a highly hydrophobic solvent, is used in combination, it becomes easy to improve the dispersion stability of the pigment, as well as the storage stability and ejection stability of the aqueous inkjet ink. Further, when a block polymer having a Q block with the molar amount contained of 40 to 100 mol% is used in combination with the above-described (poly)oxypropylene monoalkyl ethers, the ejection stability immediately after the start of printing and the print image quality are particularly improved.

[0086] In the above block polymer, the molar amount of the polymerizable monomer having an aromatic group relative to the total molar amount of the polymerizable monomers constituting the P block is preferably 20 mol% or less, particularly preferably 10 mol% or less. In one embodiment, the molar amount of the polymerizable monomer having an aromatic group may be 0 mol%. Note that when the molar amount of the polymerizable monomer having an aromatic group is 0 mol%, it means that the polymerizable monomer having the aromatic group is not contained in the block polymer. When the content of the polymerizable monomer having an aromatic group is within the above range, the characteristics as a block polymer can be sufficiently exhibited, and even in the presence of hexylene glycol, which is a highly hydrophobic solvent, the adsorptivity of the block polymer to the pigment can be easily increased. Therefore, it is preferable from the viewpoint of improving the dispersion stability of the pigment and the ejection stability of the aqueous inkjet ink.

[0087] Furthermore, from the viewpoint of improving the storage stability and ejection stability of the aqueous inkjet ink, it is preferable that the acid value of the P block is larger than the acid value of the Q block. Specifically, the difference between the acid value of the P block and the acid value of the Q block is preferably 10 to 450 mgKOH / g, more preferably 30 to 430 mgKOH / g, and particularly preferably 50 to 400 mgKOH / g.

[0088] In addition, when the glass transition temperature of the Q block, which is a block adsorbed to the pigment, is low, for example, when aqueous inkjet ink is stored at room temperature, the block polymer is likely to desorb from the pigment surface, and the water resistance of the ink film also tends to decrease. Although the detailed mechanism is unknown, it is considered that the softened block polymer dissolves in highly hydrophobic hexylene glycol, promoting desorption from the pigment. Also, it is thought that when the ink film is formed in a state where the block polymer is likely to desorb from the pigment, the ink film becomes more easily broken by an external force in the presence of water. From these viewpoints, that is, from the viewpoints of improving the dispersion stability of the pigment, the ejection stability of the aqueous inkjet ink, and the water resistance of the printed matter, the glass transition temperature of the Q block is preferably 50 to 120°C, and particularly preferably 50 to 100°C. The method for measuring and calculating the glass transition temperature is the same as that for the binder resin described later. However, when measuring the glass transition temperature of the Q block, a polymer having the same composition as the Q block is used as the sample instead of the block polymer itself.

[0089] From the viewpoints of improving the dispersion stability and ejection stability of the pigment, as well as the print image quality and drying property of the printed matter, the molar amount of the polymerizable monomer containing an aromatic group with respect to the molar amount of the polymerizable monomer constituting the block polymer is preferably 5 to 75 mol%, more preferably 10 to 60 mol%, still more preferably 15 to 50 mol%, and particularly preferably 20 to 50 mol%.

[0090] In some embodiments, in addition to the points of improving the storage stability and ejection stability of the aqueous inkjet ink, from the point of improving the water resistance of the ink film, the acid value of the block polymer used in the aqueous inkjet ink is preferably 60 to 150 mgKOH / g, and particularly preferably 60 to 130 mgKOH / g.

[0091] Also, even when used in combination with hexylene glycol, the glass transition temperature of the above block polymer is preferably 40 to 105°C, and particularly preferably 45 to 90°C, from the viewpoints of improving the dispersion stability of the pigment, the ejection stability of the water-based inkjet ink, and the water resistance of the ink film. The method for measuring and calculating the glass transition temperature of the block polymer is the same as that for the binder resin described later.

[0092] Further, the mass average molecular weight of the above block polymer is preferably 3,000 to 35,000, and more preferably 5,000 to 30,000. By setting the mass average molecular weight within the above range, the adsorption of the above block polymer onto the pigment surface is stabilized, and the dispersion stability of the pigment and the ejection stability of the water-based inkjet ink are improved.

[0093] The molecular weight distribution of the above block polymer is preferably 1.0 or more and 2.0 or less, and more preferably 1.0 or more and 1.7 or less. By setting the molecular weight distribution within the above range, the content ratio of high molecular weight polymers that can deteriorate the dispersibility and ejection stability of the pigment, and low molecular weight polymers that can reduce the density and print image quality of the printed matter can be reduced.

[0094] In some embodiments, as an example of a block polymer that can be preferably used, the molar amount of the polymerizable monomer having an aromatic group in the P block is 10 mol% or less, the glass transition temperature of the Q block is 50 to 100°C, the difference between the acid value of the above P block and the acid value of the above Q block is 50 to 400 mgKOH / g, and further, the molar amount of the polymerizable monomer containing an aromatic group in the block polymer is 20 to 50 mol%. Such block polymers are also used in some embodiments of the examples described later.

[0095] The method for synthesizing the block polymer is not limited, but living polymerization is preferred, and living radical polymerization is more preferred. Further, in the living radical polymerization method, depending on the method for stabilizing the polymerization growing end, there are a method using a sulfur-based reversible chain transfer method (RAFT method), a method using an organic tellurium compound (TERP method), a method using a transition metal catalyst (ATRP method), a nitroxide-mediated radical polymerization method (NMP method), etc. Among these, since the polymerization of not only conjugated monomers (polymerizable monomers having a substituent with a resonance stabilization effect) but also polymerizable monomers other than the conjugated monomers can be controlled, the use of the RAFT method is preferred.

[0096] (Properties common to polymers and block polymers having a crosslinked structure, etc.) The type of the pigment dispersion resin is not particularly limited, and examples thereof include acrylic resins, styrene resins, (anhydrous) maleic acid-based resins, styrene-(anhydrous) maleic acid resins, olefin-(anhydrous) maleic acid resins, urethane resins, polyester resins, polyolefin resins, polyvinyl alcohol resins, etc. These resins may be used alone or in combination of two or more. Among them, from the viewpoints of ejection stability, the magnitude of material selectivity, ease of synthesis, etc., it is preferable to use one or more selected from the group consisting of acrylic resins, polyester resins, styrene-(anhydrous) maleic acid resins, and olefin-(anhydrous) maleic acid resins.

[0097] In the present disclosure, the "acrylic resin" refers to a resin using an acrylate ester and / or a methacrylate ester as a polymerizable monomer (a styrene-based monomer may be further used). Further, "(anhydrous) maleic acid" refers to at least one selected from "maleic acid" and "maleic anhydride". In some embodiments, the polymer having a crosslinked structure is obtained by reacting a polymer obtained by reacting one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, and (anhydrous) maleic acid, styrene or benzyl methacrylate, and one or more polymerizable monomers selected from the group consisting of 1-octadecene, methyl methacrylate, lauryl methacrylate, and cyclohexyl maleimide, with a crosslinking agent such as an epoxy compound. It is preferably crosslinked. Also, in some embodiments, in the block polymer, the P block is preferably composed of one or more polymerizable monomers selected from the group consisting of benzyl methacrylate, stearyl methacrylate, butyl methacrylate, and methacrylic acid. On the other hand, the Q block is preferably composed of one or more polymerizable monomers selected from the group consisting of benzyl methacrylate, styrene, cyclohexyl methacrylate, 2-ethylhexyl acrylate, butyl methacrylate, and methacrylic acid.

[0098] Generally, as the form of the resin used in the aqueous inkjet ink, a water-soluble resin and a water-insoluble resin are known. The pigment dispersion resin contained in the aqueous inkjet ink of the present embodiment may be a water-soluble resin or a water-insoluble resin. When the pigment dispersion resin is a polymer having a crosslinked structure, it means an uncrosslinked (before crosslinking treatment) polymer.

[0099] In the present disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin", and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin". Among the above water-insoluble resins, a resin that is dispersed in a particulate form in water and has a median diameter (also referred to as "D50" in the present disclosure) based on volume of 10 to 1,000 nm is referred to as a "resin fine particle".

[0100] Also, "D50" in the present disclosure is a value measured in an environment at 25°C using a dynamic light scattering particle size distribution measuring device such as "NanoTrac UPA-EX150" manufactured by Microtrac Bell Co., Ltd.

[0101] The pigment-dispersing resin may be synthesized by a known method or may be a commercially available product.

[0102] From the viewpoint of improving the dispersion stability and ejection stability of the pigment, the content of the pigment-dispersing resin is preferably 10 to 80% by mass, and particularly preferably 15 to 50% by mass, based on the content of the pigment.

[0103] <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 and a non-permeable substrate, the viscosity increases at a speed on the order of μs, so bleeding is suppressed and the printed image quality is improved. Further, when the aqueous inkjet ink dries, the binder resin forms a continuous film, thereby improving the water resistance of the printed matter.

[0104] The binder resin contained in the aqueous inkjet ink of the present embodiment may be a water-soluble resin or resin fine particles (water-insoluble resin). Further, a combination of a water-soluble resin and resin fine particles may be used.

[0105] 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 the binder resin having the above mass average molecular weight, a strong continuous film can be obtained even with a short drying time, and the water resistance is improved.

[0106] In the present disclosure, as the mass average molecular weight of the compound, a polystyrene conversion 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 · Column 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

[0107] Also, as the type of the binder resin, acrylic resin, styrene resin, (anhydrous) maleic acid resin, styrene-(anhydrous) maleic acid resin, olefin-(anhydrous) maleic acid resin, urethane resin, polyester resin, vinyl chloride resin, vinyl chloride-vinyl acetate resin, polyolefin resin, 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 one or more selected from the group consisting of acrylic resin, urethane resin, and polyester resin as the binder resin. Further, from the viewpoint of achieving both adhesion to the film substrate and abrasion resistance, and improving ejection stability, it is preferable to use acrylic resin as the binder resin. In that case, the amount of the acrylic resin is particularly preferably 50 mass% or more based on the total amount of the binder resin in the aqueous inkjet ink.

[0108] The glass transition temperature (Tg) of the binder resin is preferably 50 to 120°C, and particularly preferably 60 to 110°C. By using the binder resin having the above glass transition temperature, the abrasion resistance and water resistance of the printed matter are improved, and at the time of ejection, since the binder resins do not get entangled with each other, stable ejection is possible even after long-term standing.

[0109] 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. 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.

[0110] On the other hand, for an acrylic resin, the value calculated by the following formula (3) can be used as the glass transition temperature.

[0111] Formula (3): 1 / Tg = Σ(Wn / Tgn)

[0112] In the above formula (3), 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 above 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.

[0113] 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. Therefore, it is possible to easily improve the discharge stability. Also, the water resistance of the printed matter is improved.

[0114] In the present disclosure, the "acid value of the resin" 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 disclosure, 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 acid groups per molecule and na in one molecule and a molecular weight of Ma in the polymerizable monomers constituting the resin, the acid value (mgKOH / g) is obtained by the following formula (4).

[0115] Formula (4): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0116] In the above formula (4), the numerical value "56.11" is the molecular weight of potassium hydroxide.

[0117] From the viewpoint of achieving all of the print image quality, water resistance, and ejection stability of the printed matter, the content of the binder resin is preferably 1.5 to 20% by mass, and particularly preferably 3.5 to 18% by mass, based on the total amount of the aqueous inkjet ink.

[0118] <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 also from the viewpoint that the abrasion resistance and water resistance of the printed matter can be remarkably improved.

[0119] As the above polyolefin, one or more selected from the group consisting of polyethylene, polypropylene, and polybutene can be preferably used. In particular, when polyethylene is selected, it is preferable in that the water resistance of the printed matter can be remarkably improved.

[0120] When using wax, its D50 is preferably from 10 to 200 nm, more preferably from 20 to 180 nm. If the D50 is within the above range, it becomes possible to preferably exhibit the above-described functions. Further, since clogging at the inkjet head nozzles does not occur, an aqueous inkjet ink excellent in ejection stability can be obtained.

[0121] When using wax, the blending amount of the above 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 the blending amount within the above range, the functions of the respective resins are not inhibited from each other. Further, since a printed matter having sufficient water resistance can be obtained even during high-speed printing, the blending amount of wax with respect to the total amount of the aqueous inkjet ink is preferably 0.5 to 1.5% by mass.

[0122] <Water> The aqueous inkjet ink of the present embodiment contains water. The water contained in the ink of the present embodiment is preferably ion-exchanged water (deionized water), not general water containing various ions. Further, the water content is preferably 45 to 85% by mass, 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 printing pause, and during continuous printing.

[0123] <wr wp> In some embodiments, for the aqueous inkjet ink, the ratio of the total content (WR [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 7. As described above, by setting the value represented by WR / WP within the range of 1 to 7, in forming the continuous film, the amount of the pigment that can be a discontinuous point can be adjusted within a suitable range, and a printed matter with excellent water resistance can be obtained. Further, since the pigment can be uniformly present in the aqueous inkjet ink, the occurrence of white spots and color bleeding is suppressed, and a print quality equivalent to that of plate printing can be obtained. Furthermore, from the viewpoint that the viscosity increase at the nozzle interface is suppressed even after a long printing pause and the ejection stability is good, the value represented by the above WR / WP is particularly preferably 1 to 4.

[0124] <Other components> The aqueous inkjet ink of the present embodiment may contain a pH adjuster and other additives in addition to the above-described components. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds can be used.

[0125] <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 produced by dispersing a pigment in a medium (aqueous medium) containing at least water using a polymer and / or block polymer having a crosslinked structure. In some embodiments, when manufacturing an aqueous inkjet ink containing a polymer having a crosslinked structure, it is preferable to obtain a pigment dispersion by dispersing the pigment and the polymer before crosslinking treatment and then adding a crosslinking agent to perform crosslinking treatment. Then, water, hexylene glycol, a binder resin, a surfactant, 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 method described above.

[0126] <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, stable ejection of droplets of the aqueous inkjet ink can be achieved not only from an inkjet head with a ejection frequency of about 4 to 10 KHz, but also from an inkjet head with a high ejection 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 higher is used. In the present disclosure, 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 the “TVE25L type viscometer” manufactured by Toki Sangyo Co., Ltd. is used.

[0127] Also, from the viewpoint of obtaining an aqueous inkjet ink excellent in ejection 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 disclosure, as the static surface tension, a value measured in a 25°C environment using the Wilhelmy method (plate method) with an automatic surface tension meter "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. or the like is used.

[0128] <Set of aqueous inkjet inks> The aqueous inkjet ink of the present embodiment may be used alone as a single type, or may be used as a set of two or more types of aqueous inkjet inks combined. As the set of the aqueous inkjet inks, for example, a set of four-color aqueous inkjet inks (process color ink set) composed of a cyan-colored aqueous inkjet ink (aqueous cyan ink), a magenta-colored aqueous inkjet ink (aqueous magenta ink), a yellow-colored aqueous inkjet ink (aqueous yellow ink), and a black-colored aqueous inkjet ink (aqueous black ink); a set of five-color aqueous 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 aqueous inkjet inks constituting the set of the aqueous inkjet inks satisfy the requirements of the above-described embodiment of the present invention.

[0129] <Ink - pretreatment liquid set> The aqueous inkjet ink of the present embodiment and the set of the aqueous inkjet ink 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 the pretreatment liquid containing a flocculant onto a printing substrate before printing with the aqueous inkjet ink, a layer (ink flocculation layer) for intentionally flocculating the solid components contained in the aqueous inkjet ink can be formed. Then, by landing the aqueous inkjet ink on the ink flocculation layer, the coalescence and color mixing of the droplets of the aqueous inkjet ink can be prevented, and the print quality of the printed matter can be significantly improved.

[0130] As the above-mentioned 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.

[0131] <Inkjet printing method> The aqueous inkjet ink of the present embodiment is used in the above-described inkjet printing method. The printing method by the inkjet printing method typically includes an ink ejection step and a drying step of the ejected ink. In the above printing method, the aqueous inkjet ink of the present 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).

[0132] (Ejection step) As an example of the operation method of the inkjet head in the above ejection process, there is 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 aqueous inkjet ink. As another example of the operation method, there is a single-pass method in which the aqueous inkjet ink is ejected and recorded when the printing substrate passes under a fixedly arranged inkjet head. The inkjet head equipped with the aqueous inkjet ink of the present 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 quality of the printed matter is improved, and furthermore, high-speed printing is possible and high productivity as an alternative to plate printing can be exhibited.

[0133] 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 aqueous inkjet ink by bubbles generated by heating a heater, a valve method that ejects pressurized aqueous inkjet ink while opening and closing the lid (valve) of the nozzle with a solenoid, and the like.

[0134] 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 printing quality. Also, from the viewpoint of improving the printing quality, it is preferable to adjust the printing conditions (specifically, the drive frequency and the number of installations of the inkjet head, as well as the printing speed). In some embodiments, the printing conditions may be adjusted so that the recording resolution of the printed matter is preferably 600 dpi or more, more preferably 1200 dpi or more.

[0135] (Drying process) As drying methods employed in the drying mechanism used in the drying process, there are a heating 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. Further, when two or more of the above drying methods are employed, each drying method may be used separately (for example, successively) or may be used in combination simultaneously. For example, by using the heating drying method and the hot air drying method in combination, the aqueous inkjet ink can be dried faster than when each is used alone.

[0136] In particular, from the viewpoint of preventing the bumping of the liquid component in the aqueous inkjet ink and obtaining a printed matter with excellent print quality, when the heating drying method is employed, the drying temperature is preferably 35 to 100 °C. When the hot air drying method is employed, the hot air temperature is preferably 50 to 250 °C. From the same viewpoint, 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 range of 700 to 2200 nm.

[0137] <Printed matter> A printed matter according to an embodiment of the present invention has a printing substrate and a printing layer including an image or characters formed by printing the aqueous inkjet ink of the present embodiment on the printing substrate. The printing can be preferably carried out in accordance with an inkjet printing method. Details of the printing method and printing conditions are as described above. (Printing substrate) The printing substrate on which the aqueous inkjet ink of the present embodiment is printed is not particularly limited. In some embodiments, the printing substrate may be a hardly permeable substrate and a non-permeable substrate. Generally, printing on a hardly permeable substrate and a non-permeable substrate is likely to cause color bleeding and uneven shading, and the print quality is likely to deteriorate. On the other hand, by using the aqueous inkjet ink of the present embodiment, a printed matter having a print quality equivalent to that of relief printing can be obtained even for a hardly permeable substrate and a non-permeable substrate, and even for high-speed printing.

[0138] The permeability of the printing substrate can be determined by the water absorption measured by a dynamic scanning wicking meter. In the present disclosure, it is defined by the water absorption of pure water at a contact time of 100 msec measured by the following method. Specifically, if the water absorption is less than 1 g / m 2 the printing substrate is referred to as a "non-permeable substrate". If the water absorption is 1 g / m 2 or more and less than 6 g / m 2 the printing substrate is referred to as a "semi-permeable substrate". If the water absorption is 6 g / m 2 or more, the printing substrate is referred to as a "permeable substrate". Note that the water absorption of the printing substrate can be measured at 23°C and 50% RH using a dynamic scanning wicking meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the conditions shown below, with a printing substrate sized approximately 15 - 20 cm square as the sample. · Measurement method: Spiral Method · Measurement start radius: 20 mm · Measurement end radius: 60 mm · Contact time: 10 - 1,000 msec · Number of sampling points: 19 (measured to be approximately equally spaced with respect to the square root of the contact time) · Scanning interval: 7 mm · Speed switching angle of the rotating table: 86.3 degrees · Head box conditions: width 5 mm, slit width 1 mm

[0139] Examples of non-permeable substrates and semi-permeable substrates include plastic films and sheets such as polyvinyl chloride sheets, polyethylene terephthalate (PET) films, polypropylene films, polyethylene films, polyethylene sheets, nylon films, nylon sheets, polystyrene films, polystyrene sheets, polyvinyl alcohol films; coated papers such as coated paper, art paper, cast paper; metals such as aluminum, iron, stainless steel, titanium; glass; and the like.

[0140] The above-listed printing substrates may have a smooth surface or may have irregularities. Further, the above-listed printing substrates may be any of transparent, translucent, and opaque. Furthermore, the shape of the above-listed printing substrates may be in the form of a roll or in the form of single sheets. In addition, a laminate obtained by laminating two or more of the above-listed printing substrates together 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.

[0141] Surface modification such as corona treatment and plasma treatment may be performed on the printing surface of the above-listed printing substrates. When surface modification is performed, it is preferable in that the wettability of the aqueous inkjet ink of the present embodiment is improved, the printed image quality and drying property are excellent, and a printed matter with good abrasion resistance and substrate adhesion can be easily obtained along with the uniformity of the printed matter surface.

Examples

[0142] Examples and comparative examples will be 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.

[0143] <Production Example of Pigment-Dispersing Resin 1> Into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, 26 parts of 1-octadecene, which is a polymerizable monomer, 13 parts of maleic anhydride, 30.5 parts of cyclohexyl maleimide, and 30.5 parts of styrene, and 100 parts of methyl ethyl ketone (organic solvent) were charged and purged with nitrogen. Next, while stirring the contents in the reaction vessel, the mixture was heated until the internal temperature reached 130°C. After reaching 130°C, 1.0 part of t-butyl peroxy-2-ethylhexanoate (radical polymerization initiator) was added dropwise over 2 hours while continuing stirring. After the dropwise addition, the polymerization reaction was continued with stirring for an additional 1 hour while maintaining the internal temperature at 130°C. After confirming that the polymerization conversion rate reached 95% by mass or more through the measurement of the solid content, it was cooled until the internal temperature reached around 60°C. After cooling, 12 parts of ion-exchanged water and 0.01 part of diazabicycloundecene (catalyst) were added to the reaction vessel, and while stirring the contents, it was heated until the internal temperature reached 80°C. After the internal temperature reached 80°C, the ring-opening reaction of maleic anhydride was carried out by maintaining the internal temperature at 80°C while continuously stirring for 4 hours, and Pigment Dispersant Resin 1 was synthesized. The weight-average molecular weight of Pigment Dispersant Resin 1 measured by the method described above was 28,000, and the acid value was 149 mgKOH / g. Thereafter, the amount of potassium hydroxide required to make the neutralization rate 100% calculated from the acid value of the obtained pigment dispersant resin was added, and further ion-exchanged water was added so that the non-volatile content concentration became 20%. Next, this solution was heated to 50°C, stirred for 1 hour, and then cooled again to obtain an aqueous solution of Pigment Dispersant Resin 1 (non-volatile content concentration: 20% by mass).

[0144] The above-mentioned "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

[0145] [Examples 1 to 42, Comparative Examples 1 to 5] <Production Example of Magenta Pigment Dispersion Liquid 1> 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 Pigment Dispersant Resin 1 (non-volatile content concentration: 20% by mass), and 55 parts of ion-exchanged water were put into a mixing container. After stirring (pre-dispersing) the contents for 1 hour, the main dispersion was carried out using a 0.6 L dyno mill filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. After the main dispersion, 33.3 parts of ion-exchanged water was added to the obtained pigment dispersion liquid, and while heating at 60°C, a part of the ion-exchanged water and the total amount of methyl ethyl ketone were distilled off under reduced pressure. Thereafter, ion-exchanged water was added so that the pigment concentration became 15%, and Magenta Pigment Dispersion Liquid 1 with a pigment concentration of 15% by mass was obtained.

[0146] <Production Example of Magenta Pigment Dispersion Liquid 2> 93.3 parts of the above-mentioned magenta pigment dispersion 1, 1.2 parts of Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 140 (g / eq.)) as a crosslinking agent, and 5.5 parts of ion-exchanged water were added to a mixing container. Then, the contents were heated to 80 °C while stirring, and after reaching the temperature, stirring was continued for 3 hours to carry out a crosslinking reaction. Thereafter, ion-exchanged water was added to adjust the pigment concentration to 14% by mass, thereby obtaining a magenta pigment dispersion 2 (pigment concentration 14% by mass) in which the pigment-dispersing resin was crosslinked (crosslinking rate 90 mol%).

[0147] <Production Examples of Yellow Pigment Dispersions 1 to 2> A yellow pigment dispersion 1 with a pigment concentration of 15% by mass was obtained by the same materials and method as the above-mentioned magenta pigment dispersion 1, except that Lysopac Yellow 5515C (C.I. Pigment Yellow 155 manufactured by Vibrantz) was used as the pigment. Further, a yellow pigment dispersion 2 (pigment concentration 14% by mass) in which the pigment-dispersing resin was crosslinked (crosslinking rate 90 mol%) was obtained by the same materials and method as the above-mentioned magenta pigment dispersion 2, except that the yellow pigment dispersion 1 was used instead of the above-mentioned magenta pigment dispersion 1.

[0148] <Production Example of Pigment-Dispersing Resin 2> 56 parts of 2-butanone was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer. Next, 56 parts of benzyl methacrylate as a polymerizable monomer, 0.3 part of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 2.2 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid were respectively added. After replacing the inside of the reaction vessel with nitrogen gas, the contents in the reaction vessel were heated until they reached 75 °C. Then, a polymer (A block) of benzyl methacrylate was obtained by carrying out a polymerization reaction for 3 hours while maintaining the internal temperature at 75 °C. After completion of the above polymerization reaction, the content was cooled to room temperature, and then 44 parts of 2-butanone; 28 parts of butyl methacrylate as a polymerizable monomer, and 16 parts of methacrylic acid were respectively charged into the reaction vessel. After replacing the inside of the reaction vessel with nitrogen gas again, the content in the reaction vessel was heated until it reached 75°C. Then, by carrying out a polymerization reaction for 3 hours while maintaining the internal temperature at 75°C, a pigment-dispersing resin 2 having an A-B block structure in which a copolymer (block B) composed of butyl methacrylate and methacrylic acid was added to the above A block was obtained. Thereafter, after cooling the content in the reaction vessel to room temperature, 17 parts of dimethylaminoethanol was added to neutralize the pigment-dispersing resin 2. Then, 150 parts of ion-exchanged water was further added. Thereafter, the mixture was heated, 2-butanone was azeotroped with ion-exchanged water to distill off the 2-butanone, and then ion-exchanged water was added to adjust the non-volatile content concentration to 20% by mass, thereby obtaining an aqueous solution (non-volatile content concentration 20% by mass) of the pigment-dispersing resin 2.

[0149] The mass average molecular weight of the obtained pigment-dispersing resin 2 was 23,000, the acid value was 104 mgKOH / g, and the molecular weight dispersity was 1.4.

[0150] <Production Example of Magenta Pigment Dispersion 3 and Yellow Pigment Dispersion 3> A magenta pigment dispersion 3 having a pigment concentration of 15% by mass was obtained by the same materials and method as the above magenta pigment dispersion 1 except that the aqueous solution of the pigment-dispersing resin 2 was used instead of the aqueous solution of the pigment-dispersing resin 1. Also, a yellow pigment dispersion 3 having a pigment concentration of 15% by mass was obtained by the same materials and method as the above magenta pigment dispersion 3 except that Lysopac Yellow 5515C (C.I. Pigment Yellow 155 manufactured by Vibrantz) was used as the pigment.

[0151] <Production 1 of Aqueous Inkjet Ink Set> Using the pigment dispersion prepared by the method described above, each raw material was put into a mixing container equipped with a stirrer so as to obtain the formulation described in each column of Table 1. After all the materials were put in, the mixture was heated with stirring until it reached 50°C, and further stirred and mixed for another 1 hour while maintaining the temperature of the mixture at 50°C. Then, filtration was carried out using a membrane filter with a pore size of 0.8 μm to produce an aqueous inkjet ink. In addition, for the production of the above aqueous inkjet ink, each of the above magenta pigment dispersion and yellow pigment dispersion was used, and a set of aqueous inkjet inks composed of aqueous magenta ink (M) and aqueous yellow ink (Y) was produced using the respective inks thus produced.

[0152] In the production of the aqueous inkjet ink, each raw material was put in while stirring the mixture in the mixing container. Also, in each column of Table 1, the described components were put in order from the top. However, when producing an aqueous inkjet ink that does not contain one or more of these components, the next component was put in order without putting in the said component. Also, regarding components containing two or more types of raw materials, the order of putting in within the said component was arbitrary.

[0153]

Table 1

[0154]

Table 1

[0155]

Table 1

[0156] The meanings of the abbreviations and the details of the product names described in Table 1 are as shown below. In Table 1, "bp" represents the boiling point, "HLB" represents the HLB value, and "Nv" represents the solid content concentration. (Diols having 2 to 5 carbon atoms) · 1,2-PD: 1,2-propanediol (boiling point: 188 °C) · 1,5-PeD: 1,5-pentanediol (boiling point: 239 °C) (Other water-soluble organic solvents) · PGM: Propylene glycol monomethyl ether (boiling point: 121 °C) · PGP: Propylene glycol monopropyl ether (boiling point: 150 °C) · DPGP: Dipropylene glycol monopropyl ether (boiling point: 210 °C) · EDG: Diethylene glycol monoethyl ether (boiling point: 196 °C) · BDG: Diethylene glycol monobutyl ether (boiling point: 231 °C) (Acetylenediol-based surfactants) · Surfynol 104: Acetylenediol-based surfactant manufactured by Evonik Japan, HLB value: 3.0 · Surfynol 420: Acetylenediol-based surfactant manufactured by Evonik Japan, HLB value: 4.0 · Surfynol 440: Acetylenediol-based surfactant manufactured by Evonik Japan, HLB value: 8.1 · Acetylenol E40: Acetylenediol-based surfactant manufactured by Kawaken Fine Chemicals, HLB value: 8.8 · Acetylenol E60: Acetylenediol-based surfactant manufactured by Kawaken Fine Chemicals, HLB value: 10.8 · Surfynol 2502: Acetylenediol-based surfactant manufactured by Evonik Japan, HLB value: 7.8 (Siloxane-based surfactants) · TEGO Wet 280: Siloxane-based surfactant manufactured by Evonik Japan, HLB value: 3 - 5 (Other surfactants) · FS-300: Fluorine-based surfactant manufactured by DuPont, solid content 40% (Resins) · Resin A: A resin produced by replicating the production example of Binder Resin 1 in JP-A-2018-203802 (used in the form of a resin solution with a solid content concentration of 35%). The acid value of Resin A was 49 mgKOH / g, and the glass transition temperature was 81°C. · Resin B: A resin produced by replicating the production example of Binder Resin 34 in JP-A-2018-203802 (used in the form of a resin solution with a solid content concentration of 35%). The acid value of Resin B was 49 mgKOH / g, and the glass transition temperature was 42°C. · Pes resin A-615GE: A polyester resin manufactured by Takamatsu Yushi Co., Ltd., with a solid content of 25% and a glass transition temperature of 47°C (Pigment dispersion) Dispersion 1: The previously prepared magenta pigment dispersion 1 and yellow pigment dispersion 1 were used. Dispersion 2: The previously prepared magenta pigment dispersion 2 and yellow pigment dispersion 2 were used. Dispersion 3: The previously prepared magenta pigment dispersion 3 and yellow pigment dispersion 3 were used. (Other components) · AQ515: AQUACER515, a polyethylene wax emulsion manufactured by BYK Japan Co., Ltd., with a solid content of 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) (Specifications) In Table 1, WR represents the sum of the mass of the binder resin and the mass of the pigment dispersion resin. The mass of the pigment dispersion resin is a value calculated from the proportion of the pigment dispersion resin in the pigment dispersion with respect to the blending amount of the pigment dispersion. Also in Table 1, the total amount of the water - soluble organic solvent represents the proportion of the total amount of the water - soluble organic solvent with respect to the total mass of the ink.

[0157] Using the set of aqueous inkjet inks manufactured by the above - described method, the following evaluations were performed. The evaluation results are shown in Table 1.

[0158] <Evaluation 1: Evaluation of ejection stability (initial stage)> An inkjet ejection device equipped with an inkjet head "KJ4B-1200" (designed resolution 1200 dpi, nozzle diameter 20 μm) manufactured by Kyocera Corporation and installed in an environment at 25°C 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 evaluation of ejection stability (initial stage) was carried out by checking with a magnifying glass whether the aqueous inkjet ink was applied to the part where the aqueous inkjet ink should be printed first. The evaluation criteria were as follows, and evaluations A, B, and C+ were considered practically usable. The above evaluations were performed separately with the aqueous magenta ink and aqueous yellow ink that constitute the set of the aqueous inkjet ink. Also, in Table 1, the results of the aqueous magenta ink and aqueous yellow ink for which the evaluation results were poor were described. (Evaluation criteria) A: In the solid print, no chipping was observed in the part that should be printed first. B: In the solid print, chipping less than 1 mm was observed in the part that should be printed first. C+: In the solid print, chipping of 1 mm or more and less than 5 mm was observed in the part that should be printed first. C: In the solid print, chipping of 5 mm or more and less than 1 cm was observed in the part that should be printed first. D: In the solid print, chipping of 1 cm or more was observed in the part that should be printed first.

[0159] <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 top coat paper under the 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 evaluations A, B, C+, and C were considered usable in actual use. The above evaluations were performed respectively 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 evaluations of the aqueous magenta ink and the aqueous yellow ink for which the evaluation results were poor were described. (Evaluation Criteria) A: In the solid print printed after a 1-hour standby, no chipping was observed in the portion that should have been printed first. B: In the solid print printed after a 1-hour standby, chipping less than 1 cm was observed in the portion that should have been printed first. C+: In the solid print printed after a 1-hour standby, chipping of 1 cm or more and less than 3 cm was observed in the portion that should have been printed first. C: In the solid print printed after a 1-hour standby, chipping of 3 cm or more and less than 5 cm was observed in the portion that should have been printed first. D: In the solid print printed after a 1-hour standby, chipping of 5 cm or more was observed in the portion that should have been printed first.

[0160] <Production of Magenta / Yellow Gradation Print An inkjet ejection device was prepared in which two inkjet heads "KJ4B-1200" (designed resolution 1200 dpi, nozzle diameter 20 μm) manufactured by Kyocera Corporation were arranged side by side along the conveyance direction of the printing substrate. From the upstream side in the conveyance direction, sets of aqueous magenta ink and aqueous yellow ink were filled in order. Also, on the conveyor, an OPP film (''OPU-1'' manufactured by Mitsui Chemicals Toagosei Co., Ltd., thickness 20 μm) with an A4 size (width 21 cm × length 30 cm) 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 inks were ejected under the condition of a drop volume of 2.6 pL each to print a magenta / yellow gradation image. Next, immediately after printing, the printed printing substrate was put into a forced-air constant-temperature thermostat set at 70°C and dried for 3 minutes to produce a magenta / yellow gradation print. Note that the above "magenta / yellow gradation image" refers to a magenta color gradation image (an image in which the printing rate was changed in steps of 10% between 10% and 100%) with a width of 5 cm × a length of 30 cm printed using aqueous magenta ink, and a yellow color gradation image with a width of 5 cm × a length of 30 cm printed using aqueous yellow ink, which were arranged adjacent to each other such that their long sides were 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 print was produced in the same manner as above.

[0161] <Evaluation 3: Evaluation of Printing Image Quality (White Speckles) The magenta / yellow gradation print manufactured by the method described above was visually observed. Then, by confirming the presence or absence of white speckles at a printing rate of 100%, the printing image quality of the magenta / yellow gradation print was evaluated. The evaluation criteria were as follows, and evaluations A, B, C+, and C were considered acceptable for actual use. The above evaluations were performed on each of the two types of printing substrates on which magenta / yellow gradient prints were printed. (Evaluation Criteria) A: No white spots were observed in both of the two types of printing substrates, and in both the printed part of the magenta color gradient image and the printed part of the yellow color gradient image. B: Slight white spots were observed in either the printed part of the magenta color gradient image or the printed part of the yellow color gradient image on only one of the two types of printing substrates. C+: Slight white spots were observed in both the printed part of the magenta color gradient image and the printed part of the yellow color gradient image on only one of the two types of printing substrates. C: Obvious white spots were observed in both the printed part of the magenta color gradient image and the printed part of the yellow color gradient image on at least one of the two types of printing substrates. D: Obvious white spots were observed in both of the two types of printing substrates, and in both the printed part of the magenta color gradient image and the printed part of the yellow color gradient image.

[0162] <Evaluation 4: Evaluation of Print Image Quality (Color Bleeding)> The magenta / yellow gradient prints produced by the method described above were visually observed. Then, the print image quality of the magenta / yellow gradient prints was evaluated by checking the printing rate at the location where color bleeding started to be seen at the boundary between the printed part of the magenta color gradient image and the printed part of the yellow color gradient image. The evaluation criteria were as follows, and evaluations A, B, and C+ were considered acceptable for actual use. Also, Table 1 shows the results of the evaluation for the printing substrate with the worse evaluation result among the two types of printing substrates for which the evaluation was performed. (Evaluation Criteria) A: No color bleeding was observed even at a printing rate of 80% for both printing substrates. B: Color bleeding was observed at a printing rate of 80% for at least one of the printing substrates. C+: In at least one printing substrate, bleeding was observed at a printing rate of 70%. C: In at least one printing substrate, bleeding was observed at a printing rate of 60%. D: In both printing substrates, bleeding was observed at a printing rate of 60%.

[0163] <Evaluation 5: Evaluation of water resistance> 20 μL of the above aqueous inkjet ink was dropped onto an OPP film (FOR-AQ, thickness 20 μm) manufactured by Futamura Chemical Co., Ltd., and coated using an automatic coater (PI-1210 manufactured by Tester Sangyo Co., Ltd.) equipped with an SA-203 bar coater (ROD No. 3). Then, the OPP film coated with the aqueous inkjet ink was placed in a forced-air constant-temperature thermostat set at 70°C, and the printed substrate after printing was inserted and dried for 3 minutes. Then, a cotton swab moistened with ion-exchanged water was used to rub the ink film back and forth with a width of 1 cm, and the number of times the cotton swab was reciprocated until the ink film at the rubbed area was completely peeled off was counted. The above evaluation was performed at 5 locations within the same ink film, and the water resistance was evaluated by obtaining the average value of the number of reciprocations. The evaluation criteria were as follows, and evaluations A+, A, B, C+, and C were considered suitable for actual use. The 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. (Evaluation criteria) A+: The coated film did not peel off even after rubbing 40 times. A: The coated film peeled off between 30 and 39 times. B: The coated film peeled off between 21 and 29 times. C+: The coated film peeled off between 11 and 20 times. C: The coated film peeled off between 6 and 10 times. D: The coated film peeled off within 5 times.

[0164] [Examples 43 to 85] <Production Examples of Pigment-Dispersed Resins 3 to 15> The polymerization monomers used and their charged amounts were changed as described in Table 2, and synthesis was carried out in the same manner as the above-described pigment dispersion resin 1 to obtain aqueous solutions of pigment dispersion resins 3 to 15 (each having a non-volatile content concentration of 20% by mass).

[0165]

Table 2

[0166]

Table 2

[0167] Table 2 also describes the composition of the above-described pigment dispersion resins, as well as the mass average molecular weight, acid value, and molar amount of the polymerizable monomer having an aromatic group in each pigment dispersion resin. The details of the cross-linking agents described in Table 2 are as follows. · Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 140 (g / eq.)) · Denacol EX-313 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 141 (g / eq.)) · Denacol EX-612 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 166 (g / eq.)) · Denacol EX-614B (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 173 (g / eq.))

[0168] <Production Examples of Magenta Pigment Dispersions 4 to 23> Except for using the above-described pigment dispersion resins 3 to 15, magenta pigment dispersions 5 to 7, 11, 15 to 23 (before cross-linking treatment), and yellow pigment dispersions 5 to 7, 11, 15 to 23 (before cross-linking treatment, each having a pigment concentration of 15% by mass) were produced by the same raw materials and method as magenta pigment dispersion 1 and yellow pigment dispersion 1. Then, except that Magenta Pigment Dispersion Liquid 1 or Yellow Pigment Dispersion Liquid 1, or Magenta Pigment Dispersion Liquids 5 to 7, 11, 15 to 23 (before crosslinking treatment) or Yellow Pigment Dispersion Liquids 5 to 7, 11, 15 to 23 (before crosslinking treatment); the crosslinking agent described in Table 2; and ion-exchanged water were used in the compounding amounts described in the "Crosslinking Treatment" row in Table 2, Magenta Pigment Dispersion Liquids 4 to 23 and Yellow Pigment Dispersion Liquids 4 to 23 (each with a pigment concentration of 14% by mass), in which the pigment-dispersed resin was crosslinked, were produced by the same materials and methods as Magenta Pigment Dispersion Liquid 2 and Yellow Pigment Dispersion Liquid 2, respectively.

[0169] <Production Examples of Pigment-Dispersed Resins 16 to 38> Except that the types and charged amounts of the polymerizable monomers used were changed as described in Table 3, synthesis was carried out in the same manner as the above Pigment-Dispersed Resin 2 to obtain aqueous solutions of Pigment-Dispersed Resins 16 to 38 (each with a non-volatile content concentration of 20% by mass).

[0170]

Table 3

[0171]

Table 3

[0172] Table 3 also describes the composition of the above-mentioned Pigment-Dispersed Resin 2. Table 3 also shows the mass average molecular weight, molecular weight dispersity, molar amount of polymerizable monomer having an aromatic group, acid value, and glass transition temperature of each pigment-dispersed resin. Regarding the molar amount of polymerizable monomer having an aromatic group and the acid value, the values of each block, the difference in values between blocks, and the values for the entire pigment-dispersed resin are also described. Regarding the glass transition temperature, the values of each block and the value for the entire pigment-dispersed resin are also described. The details of the abbreviations described in Table 3 above are as follows. ·BzMA: Benzyl methacrylate ·St: Styrene ·CHMA: Cyclohexyl methacrylate · 2HEA: 2-Ethylhexyl acrylate · BMA: Butyl methacrylate · SMA: Stearyl methacrylate · MAA: Methacrylic acid

[0173] <Production Examples of Magenta Pigment Dispersion 24 - 46 and Yellow Pigment Dispersion 24 - 46> Magenta pigment dispersions 24 - 46 and yellow pigment dispersions 24 - 46 (each with a pigment concentration of 15% by mass) were produced by the same materials and methods as those of magenta pigment dispersion 3 and yellow pigment dispersion 3, except that the aqueous solutions of pigment dispersion resins 16 - 38 were used instead of the aqueous solution of pigment dispersion resin 2.

[0174] <Production 2 of Aqueous Inkjet Ink Set> An aqueous inkjet ink set was produced with the same raw materials and amounts charged as in Example 3, except that the magenta pigment dispersion and yellow pigment dispersion used were changed to those described in Table 4.

[0175] <Production 3 of Aqueous Inkjet Ink Set> An aqueous inkjet ink set was produced with the same raw materials and amounts charged as in Example 8, except that the magenta pigment dispersion and yellow pigment dispersion used were changed to those described in Table 5.

[0176] Then, using the obtained aqueous inkjet ink set, the above-described Evaluations 1 - 5 were conducted. The evaluation results were as shown in Tables 4 - 5 below.

[0177]

Table 4

[0178]

Table 5

[0179] As shown in Tables 1, 4, and 5 above, the aqueous inkjet inks (ink sets) of Examples 1 to 85 having the configuration of the present invention were superior in ejection stability compared to the aqueous inkjet inks of Comparative Examples 1 to 5, and had good solid filling and little color mixing. Furthermore, the water resistance of the ink film was also good. From these results, it was confirmed that the aqueous inkjet ink having the configuration of the present embodiment is an excellent aqueous inkjet ink having both ejection stability, print image quality of printed matter, and water resistance.< / wr>

Claims

1. An aqueous inkjet ink comprising a pigment, a pigment dispersing resin, a surfactant, a water-soluble organic solvent, and a binder resin, the pigment dispersing resin contains at least one polymer selected from the group consisting of a polymer having a crosslinked structure and a block polymer, the water-soluble organic solvent comprises hexylene glycol, The aqueous inkjet ink has a value expressed by WR / WP, in which WR (g) is the sum of the content (g) of the pigment dispersion resin and the content (g) of the binder resin contained in 100 g of the aqueous inkjet ink, and WP (g) is the content of the pigment contained in 100 g of the aqueous inkjet ink, and the value expressed by WR / WP is 1 to 7.

2. 2. The aqueous inkjet ink according to claim 1, wherein the content of the hexylene glycol is 5 to 90 mass % based on the total content of the water-soluble organic solvent contained in the aqueous inkjet ink.

3. The aqueous inkjet ink according to claim 1 or 2, wherein the surfactant comprises an acetylenic diol-based surfactant.

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

5. The aqueous inkjet ink according to claim 1 or 2, further comprising a wax.

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

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