Aqueous inkjet ink and printed matter

Abstract

To provide aqueous inkjet ink which does not cause voids and color mixing bleeding and can obtain a printed matter excellent in water resistance, even in printing on a hardly permeable base material and a non-permeable base material, and is excellent in discharge stability immediately after printing start and after printing cessation for a long time.SOLUTION: The aqueous inkjet ink contains a pigment, a polyether-modified siloxane-based surface active agent, hexylene glycol, a binder resin, and an organic compound (A) (excluding pigment, polyether-modified siloxane-based surface active agent, hexylene glycol and resin), wherein the organic compound (A) is composed of only a carbon atom, a hydrogen atom and an oxygen atom, and has a plurality of hydroxyl groups and an HLB value of 2.5 to 5.2, and the binder resin contains 50 mass% or more of a resin (B-1) having a glass transition temperature of -70 to 35°C in the total mass of a resin contained in the aqueous inkjet ink.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

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

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

[0005] The ink used in the inkjet printing method (referred to as "inkjet ink" in the present application) 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 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 application) instead of solvent-based inkjet ink and ultraviolet-curable inkjet ink that use these raw materials.

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

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

[0008] Generally, in order to improve the wettability of a printing substrate, an organic compound with high hydrophobicity and not being a polymer is often used. The above organic compound is oriented at the interface with the printing substrate on the microsecond order, and the wettability of the printing substrate is improved. However, since high hydrophobicity also means poor solubility in water, in an aqueous inkjet ink containing the above organic compound, bubbles that can cause nozzle clogging are likely to occur. In addition, there are problems such as the meniscus of the aqueous inkjet ink becoming unstable due to the above organic compound being oriented at the gas-liquid interface formed on the nozzle end face of the inkjet head. These problems are particularly likely to lead to the occurrence of nozzle clogging (a phenomenon where aqueous inkjet ink is not ejected from the nozzle) immediately after the start of printing. Also, due to the structure of the inkjet head, the diameter of the nozzle is very small, only several tens of micrometers. In particular, when printing is paused for a long time, while the liquid components (such as water and water-soluble organic solvents) in the aqueous inkjet ink volatilize from the above nozzle end face, fresh aqueous inkjet ink may not be sufficiently supplied to the inkjet head. Then, in the aqueous inkjet ink present near the nozzle end face, an increase in the solid content concentration and / or an increase in the proportion of the water-soluble organic solvent with a high boiling point occur, resulting in an increase in viscosity due to aggregation and insolubilization of solid components (such as pigments and resins), and nozzle clogging associated with the increase in viscosity may occur.

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

[0010] On the one hand, especially in the packaging and printing market, it is necessary to ensure that the film of water-based inkjet ink (ink film) does not peel off even when the printed matter with water adhered to it is rubbed with a finger or the like. That is, a certain degree of water resistance is required for the above ink film. In water-based inkjet inks containing a large amount of water-soluble raw materials, as a method of imparting water resistance to the dried ink film, a method of adding a binder resin to the water-based inkjet ink to form a strong continuous film can be mentioned. On the other hand, when the binder resin is contained in the water-based inkjet ink (liquid) before printing in an amount equal to or more than a certain amount, problems such as local viscosity increase and non-uniformity of viscoelasticity occur in the water-based inkjet ink, resulting in deterioration of ejection stability, and there is a risk of problems such as the binder resin inhibiting the orientation of organic compounds and deteriorating the wettability of the water-based inkjet ink.

[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, initial ejection stability, standby ejection property, print quality, and water resistance of the ink film. However, there has been no situation where a water-based inkjet ink that can simultaneously and suitably solve all of these problems has been found so far.

[0012] In the present application, a printed matter without white spots and color mixing is also referred to as a "printed matter with excellent print quality".

[0013] As an example of the study aimed at improving the printing image quality of printed matter on a hardly permeable substrate and an impermeable substrate, Patent Document 1 discloses an ink containing water, an organic solvent, a polysiloxane surfactant having an HLB value of 8 or less, and acrylic silicone resin particles, which can be suitably used in an inkjet printing method. Further, in the examples of Patent Document 1, as the organic solvent, 1,2-propanediol (propylene glycol), 1,3-propanediol, 3-methoxy-3-methylbutanol, 2-methyl-2,4-pentanediol (hexylene glycol), etc. are used, and further, as other resin particles, examples of inks containing urethane resin emulsion, polyester resin emulsion, acrylic-styrene resin emulsion, etc. are shown. Patent Document 1 describes that the ink having the above configuration has good storage stability, and a printed matter excellent in fixability (suppression of density unevenness) and adhesion can be produced on an impermeable substrate (see paragraph numbers 0006 and 0019 of Patent Document 1).

[0014] Also, Patent Document 2 discloses an aqueous inkjet ink containing an organic solvent selected from ethylene glycol, propylene glycol, 3-methoxy-1-butanol, etc. and a polyoxyalkylene monoallyl ether compound having a specific structure. Further, in the examples of Patent Document 2, in addition to the above organic solvent, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2-methyl-2,4-pentanediol, etc. are included, and further, examples of aqueous inkjet inks containing water-insoluble resins such as urethane resin emulsion and acrylic resin emulsion, and surfactants such as acetylene glycol-based surfactants and silicone-based surfactants are shown. Patent Document 2 describes that the aqueous inkjet ink having the above configuration is excellent in ejection property, and a printed matter having no density unevenness and good wettability can be produced even on a non-absorbent recording medium (see paragraph numbers 0014 and 0028 of Patent Document 2).

Prior Art Documents

Patent Documents

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-115127 [Patent Document 2] Japanese Patent Application Laid-Open No. 2021-109904 [Summary of the Invention] [Problems to be Solved by the Invention]

[0016] However, the ink specifically disclosed in Patent Document 1 does not contain the above-mentioned hydrophobic organic compound that is not a polymer, in addition to the above polysiloxane surfactant. The polysiloxane surfactant used in the above ink is also known to be a material excellent in orientation to the interface and effective in improving the printing quality. However, the orientation speed is not high, and it is not sufficient from the viewpoint of ensuring wettability on the order of microseconds. Further, all of the polyoxyalkylene monoallyl ether compound and the acetylene glycol-based surfactant (see also Paragraph Nos. 0117 to 0118 of Patent Document 2) specifically used in the examples of Patent Document 2 contain a large amount of ethylene oxide having high hydrophilicity. Therefore, the water-based inkjet ink specifically disclosed in Patent Document 2 also does not contain a hydrophobic organic compound that is not a polymer. Thus, in order to produce a printed matter excellent in printing quality regardless of printing conditions such as inkjet printing on a printing substrate having a very small interfacial free energy or high-speed inkjet printing, further improvement including the proper use of a hydrophobic organic compound that is not a polymer is required.

[0017] As described above, the techniques described in Patent Documents 1 and 2 have not reached the situation of solving all of the above-described problems at a high level. Therefore, in one embodiment of the present invention, an object is to provide an aqueous inkjet ink that can obtain a printed matter that is free from white spots and color mixing even in printing on a hardly permeable substrate and a non-permeable substrate, is excellent in water resistance, and is also excellent in ejection stability immediately after the start of printing and after a long printing pause. [Means for Solving the Problems]

[0018] 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 an aqueous inkjet ink having the following configuration.

[0019] That is, one embodiment of the present invention relates to an aqueous inkjet ink shown in the following [1] to [3], and a printed matter produced using the above aqueous inkjet ink shown in the following [4]. [1] An aqueous inkjet ink containing a pigment, a polyether-modified siloxane-based surfactant, hexylene glycol, a binder resin, and an organic compound (A) (excluding pigments, polyether-modified siloxane-based surfactants, hexylene glycol, and resins), wherein the organic compound (A) consists only of carbon atoms, hydrogen atoms, and oxygen atoms and has a plurality of hydroxyl groups, the HLB value of the organic compound (A) is 2.5 to 5.2, the binder resin contains a resin (B-1) having a glass transition temperature of -70 to 35°C, and the content of the resin (B-1) is 50% by mass or more based on the total mass of the resins contained in the aqueous inkjet ink. [2] The aqueous inkjet ink according to [1], wherein the content mass of the resin (B-1) when the content mass of the polyether-modified siloxane-based surfactant is 1 is 2 to 50. [3] The aqueous inkjet ink does not contain a butylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular terminal is 1 to 4) and a pentylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular terminal is 1 to 4), or The total content of the above-mentioned butylene glycol monoalkyl ether-based water-soluble organic solvent (where the carbon number of the alkyl group at the molecular terminal is 1 to 4) and the pentylene glycol monoalkyl ether-based water-soluble organic solvent (where the carbon number of the alkyl group at the molecular terminal is 1 to 4) is 50% by mass or less with respect to the content of the hexylene glycol, the aqueous inkjet ink according to [1] or [2]. [4] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [3] on a printing substrate.

Effects of the Invention

[0020] The aqueous inkjet ink according to one embodiment of the present invention 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, and is also excellent in water resistance. Furthermore, it has the effect of being excellent in ejection stability immediately after the start of printing and after a long printing pause.

Modes for Carrying Out the Invention

[0021] Hereinafter, an aqueous inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "the aqueous inkjet ink of the present embodiment") will be described. The present invention is not limited to the embodiments described below, and includes forms that can be implemented with modifications within the range of not changing the essential part of the present invention.

[0022] Generally, due to the very high surface tension of water, which is the main component of aqueous inkjet ink, it does not wet and spread well on difficult-to-penetrate and non-penetrating substrates, making it difficult to form fine prints. On the other hand, when using organic compounds with a low HLB value, such as surfactants, the organic compounds will orient at the interface with the printing substrate on the microsecond order. As a result, the aqueous inkjet ink can wet and spread well even on difficult-to-penetrate and non-penetrating substrates, especially printing substrates with a very low interfacial free energy, such as polypropylene (PP) films, and an improvement in print quality can be expected. On the other hand, the above organic compounds have problems such as being prone to foaming and generating bubbles that can contribute to nozzle dripping, and there is also a problem that the meniscus of the aqueous inkjet ink may become unstable due to rapid orientation occurring at the gas-liquid interface formed on the nozzle end face of the inkjet head. And these problems lead to deterioration of the initial ejection stability and standby ejection performance.

[0023] Also, in order to obtain a printed matter with excellent water resistance, it is preferable that the binder resin forms a continuous film in the ink film constituting the printed matter. Generally, the lower the glass transition temperature of the binder resin, the easier it is to form a continuous film. Therefore, from the perspective of forming a continuous film, it is effective to use a binder resin with a low glass transition temperature. On the other hand, a binder resin with a low glass transition temperature may easily form a film even on the nozzle end face of the inkjet head, for example, which may lead to deterioration of the initial ejection stability. Also, the binder resin contained in the aqueous inkjet ink before printing (in liquid form) may inhibit the orientation of the above organic compounds at the interface. When the orientation of the above organic compounds is inhibited, the above-described effects cannot be exhibited, and the print quality of the printed matter deteriorates. In order to fully exhibit the above-described effects, there is a method, for example, of increasing the addition amount of the above organic compound so that it can still orient in a sufficient amount at the interface even when inhibited. However, an excessive amount of the above organic compound also has a problem of inhibiting the formation of a continuous film of the binder resin, and as a result, the water resistance of the printed matter deteriorates.

[0024] On the other hand, the aqueous inkjet ink of the present embodiment is an organic compound composed only of carbon atoms, hydrogen atoms, and oxygen atoms and having a plurality of hydroxyl groups, and having an HLB value of 2.5 to 5.2, and a resin (B-1) having a glass transition temperature of -70 to 35°C, and further contains hexylene glycol and a polyether-modified siloxane-based surfactant.

[0025] Hexylene glycol (2-methyl-2,4-pentanediol) has a plurality of branched alkyl groups, and has characteristics such as higher hydrophobicity than other alkanediols, higher solubility in water, and lower boiling point under 1 atm. Therefore, its affinity with the above organic compound (A) is higher than that of alkanediols generally used in aqueous inkjet inks (for example, propylene glycol, etc.). As a result, in the aqueous inkjet ink, the organic compound (A) is stabilized by hexylene glycol. In addition, by suppressing the rapid orientation of the organic compound (A) to the interface, the generation of bubbles and the destabilization of the meniscus are suppressed in the aqueous inkjet ink present in the inkjet head, and the initial ejection stability and standby ejection property are improved.

[0026] Furthermore, hexylene glycol also has an affinity with the binder resin. Therefore, for example, even after water has evaporated from the water-based inkjet ink applied on the printing substrate, the organic compound (A) and the binder resin are attracted to each other via hexylene glycol, and the binder resin diffuses uniformly together with the organic compound (A) (and the polyether-modified siloxane surfactant described later). In addition, the water-based inkjet ink of the present embodiment contains a resin (B-1) having a low glass transition temperature, that is, a resin that easily forms a continuous film, as the binder resin, and the content of the resin (B-1) is 50% by mass or more based on the total mass of the resins contained in the water-based inkjet ink. As a result, in the water-based inkjet ink of the present embodiment, it is considered that the formation of a continuous film of the ink film is promoted and the water resistance of the printed matter is improved. Further, 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.

[0027] In addition, the water-based inkjet ink of the present embodiment contains a polyether-modified siloxane surfactant. The polyether-modified siloxane surfactant has a highly hydrophobic siloxane chain and a highly hydrophilic polyether chain. Therefore, it is considered that the polyether-modified siloxane surfactant also exhibits the same affinity as hexylene glycol. In particular, since the polyether-modified siloxane surfactant has a larger molecular weight than hexylene glycol, it is considered to strongly interact with the binder resin having a similarly large molecular weight. As a result, the polyether-modified siloxane surfactant suppresses the film formation of the binder resin on the nozzle end face of the inkjet head, improving the initial ejection stability. In addition, when the polyether-modified siloxane surfactant is oriented at the interface in a manner delayed from the organic compound (A), uniform wet spreading of the droplets of the water-based inkjet ink becomes possible, facilitating the production of a printed matter without white spots and color bleeding.

[0028] As described above, in order to solve all of the above-described problems at a high level, the aqueous inkjet ink having the above-described configuration is essential. Note that the above-described mechanism is a speculation by the present inventors, and the present invention is not limited by the above-described speculation.

[0029] As described above, Patent Documents 1 and 2 include a polyether-modified siloxane-based surfactant, hexylene glycol, and resin (B-1), and the content of the resin (B-1) is 50% by mass or more in the total mass of the resins contained in the aqueous inkjet ink. There are specific examples of aqueous inkjet inks (for example, Examples D4 to D5, D11, E3, E8, E10, E12, etc. of Patent Document 1, Inks 7, 15, 22 of Patent Document 2). However, these specific examples differ from the aqueous inkjet ink of the present embodiment in that they do not contain the organic compound (A). Further, the aqueous inkjet ink of the present embodiment containing the organic compound (A) can produce a printed matter free from white spots and color mixing even on a printing substrate having a very small surface free energy, and has excellent initial ejection stability, standby ejection property, and water resistance of the printed matter. However, such disclosure or suggestion does not exist in Patent Documents 1 and 2.

[0030] Subsequently, each component constituting the aqueous inkjet ink according to an embodiment of the present invention will be described in detail below.

[0031] <Organic Compound (A)> The aqueous inkjet ink of this embodiment is an organic compound composed only of carbon atoms, hydrogen atoms, and oxygen atoms and having a plurality of hydroxyl groups, and contains an organic compound (A) having an HLB value of 2.5 to 5.2. During printing, the organic compound (A) is oriented at the interface with the printing substrate in a short time, so that prints without white bleeding and color bleeding can be obtained even on hard-to-penetrate substrates and non-penetrating substrates. Further, by using hexylene glycol and the organic compound (A) in combination, generation of bubbles and destabilization of the meniscus are suppressed in the aqueous inkjet ink present in the inkjet head, and the initial ejection stability and standby ejection property are improved. Furthermore, by the above combination, the binder resin does not inhibit the formation of a continuous film, and the water resistance of the print is also improved.

[0032] Note that the pigment, polyether-modified siloxane-based surfactant, and hexylene glycol are not included in the organic compound (A). Also, with respect to the resin containing the above binder resin (a compound formed by forming a main chain by covalently linking one or more polymerizable monomers), it is excluded from the organic compound (A).

[0033] As described above, the HLB value of the organic compound (A) is 2.5 to 5.2. Also, from the viewpoint of being easily compatible with other components and improving the initial ejection stability and standby ejection property while suppressing white bleeding and color bleeding in the print, and also improving the water resistance of the print, the HLB value of the organic compound (A) is preferably 3.0 to 5.2, and particularly preferably 3.8 to 5.2.

[0034] The HLB (Hydrophile-Lipophile Balance) value in this application is one of the parameters representing the hydrophilicity and hydrophobicity of a material, and in the present invention, the HLB value is calculated using the Griffin method.

[0035] The Griffin method is a method for obtaining the HLB value using the molecular weight of the target material according to the following formula (1). Note that the smaller the HLB value, the higher the hydrophobicity of the material, and the larger the HLB value, the higher the hydrophilicity of the material.

[0036] Formula (1): HLB value = 20 × (sum of molecular weights of hydrophilic moieties) ÷ (molecular weight of the material)

[0037] In addition, the organic compound (A) used in the aqueous inkjet ink of the present embodiment consists only of carbon atoms, hydrogen atoms, and oxygen atoms, and has a plurality of hydroxyl groups. Examples of the compound that can be used as the organic compound (A) include Acetylenediol compounds such as 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (2.7), 2,4,7,9-tetramethyl-5-decyne-4,7-diol (3.0), 5,8-dimethyl-6-dodecyne-5,8-diol (3.0), 3,6-dimethyl-4-octyne-3,6-diol (4.0), etc., and their ethylene oxide (EO) and / or propylene oxide (PO) adducts; Sorbitan fatty acid ester compounds such as sorbitan monostearate (4.7), sorbitan distearate (4.4), sorbitan monooleate (4.3), etc., and their ethylene oxide and / or propylene oxide adducts; Glycerin fatty acid ester compounds such as glycerol monostearate (3.5), glycerol monobehenate (3.0), glycerol monooleate (2.8), etc., and their ethylene oxide and / or propylene oxide adducts; Medium-chain (for example, having 7 to 12 carbon atoms) alkanediol compounds such as 1,2-heptanediol (5.2), 1,7-heptanediol (5.2), 1,2-octanediol (4.7), 1,8-octanediol (4.7), 1,2-nonanediol (4.2), 1,9-nonanediol (4.2), etc.; Examples include the following. The numerical values in parentheses are the HLB values of the respective materials.

[0038] Among these compounds, from the viewpoint of high affinity with hexylene glycol, improvement in initial ejection stability and standby ejection property, and improvement in water resistance of the printed matter, one or more compounds selected from the group consisting of acetylene diol compounds, ethylene oxide and / or propylene oxide adducts of acetylene diol compounds, and medium-chain alkanediol compounds can be preferably used.

[0039] Since it is excellent in the orientation speed to the interface and has good affinity with hexylene glycol, while suppressing white bleeding and color bleeding in the printed matter, the initial ejection stability and standby ejection property are improved, and from the viewpoint of improving the water resistance of the above printed matter, the molecular weight of the organic compound (A) is preferably 100 to 750, and particularly preferably 130 to 650.

[0040] The addition amount of the organic compound (A) is preferably 0.05 to 1.5% by mass, and particularly preferably 0.1 to 1% by mass in the total amount of the aqueous inkjet ink, from the viewpoint of obtaining a printed matter that has no white bleeding and color bleeding and is excellent in water resistance, and also improving the initial ejection stability and standby ejection property.

[0041] Also, since the affinity between the organic compound (A) and hexylene glycol is improved, while suppressing white bleeding and color bleeding in the printed matter, the initial ejection stability and standby ejection property are improved, and from the viewpoint of improving the water resistance of the above printed matter, when the content mass of the organic compound (A) is 1, the content mass of hexylene glycol is preferably 2 to 200, and more preferably 4 to 50.

[0042] <Polyether-modified siloxane surfactant> The aqueous inkjet ink of the present embodiment contains a polyether-modified siloxane surfactant. As a result of the polyether-modified siloxane surfactant being compatible with the binder resin, film formation of the binder resin on the nozzle end face of the inkjet head is suppressed, and the initial ejection stability is improved. Further, by the polyether-modified siloxane surfactant being oriented at the interface in a form that lags behind the organic compound (A), a printed matter without white spots and color bleeding can be obtained.

[0043] Examples of the polyether-modified siloxane surfactant that can be used in the aqueous inkjet ink of the present embodiment include compounds having a structure represented by the following general formula (2).

[0044] General formula (2):

Chemical formula

[0045] In general formula (2), m is an integer from 0 to 99, and n is an integer from 1 to 100. However, m + n is an integer from 1 to 100. Also, R 1 is a methyl group or a structure represented by the following general formula (3), and R 2 is an alkyl group having 1 to 6 carbon atoms (which may have a branch) or a structure represented by the following general formula (3). However, when R 1 is a methyl group, m is 0. Also, at least one of R 1 and R 2 has a structure represented by the following general formula (3) (R 1 and R 2 may both have a structure represented by the following general formula (3).).

[0046] General formula (3):

Chemical formula

[0047] In the general formula (3), p is an integer from 1 to 6, q is an integer from 1 to 50, and r is an integer from 0 to 50. However, q + r is an integer from 1 to 100. Also, R 3 is either a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. The addition pattern of the ethylene oxide group and the propylene oxide group in [ ] may be block or random.

[0048] In the above general formula (2), R 6 has the structure represented by the above general formula (3), and a polyether-modified siloxane-based surfactant in which R 1 does not have the structure represented by the above general formula (3) (also described as "both-terminal polyether-modified siloxane-based surfactant" in the present application) has a high affinity with the binder resin and is effective in terms of improving the initial ejection stability and the water resistance of the printed matter. Further, the both-terminal polyether-modified siloxane-based surfactant is also excellent in the uniform orientation property at the interface and can also improve the bleeding of color mixture. Therefore, in the aqueous inkjet ink of the present embodiment, it can be particularly preferably used as the polyether-modified siloxane-based surfactant. On the other hand, in the above general formula (2), R 1 has the structure represented by the above general formula (3), and a polyether-modified siloxane-based surfactant in which R 2 does not have the structure represented by the above general formula (3) (also described as "side-chain polyether-modified siloxane-based surfactant" in the present application) has a high ability to lower the surface tension and is excellent in the orientation speed at the interface, and thus is effective in suppressing white spots in the printed matter.

[0049] Examples of commercially available products of the above-mentioned both-end polyether-modified siloxane surfactants include BY16-201, SF8427 manufactured by Toray Dow Corning Co., Ltd., BYK-331, BYK-333, BYK-UV3500, BYK-3420 manufactured by BYK Chemie GmbH, TEGO Glide 410, TEGO Glide 432, TEGO Glide435, TEGO Glide440, TEGO Glide450 manufactured by Evonik Degussa GmbH, SILFACE SWP-001, SILFACE SAG003, SILFACE SAG005 manufactured by Nissin Chemical Industry Co., Ltd., and the like.

[0050] Examples of commercially available products of the above-mentioned side-chain polyether-modified siloxane surfactants include SF8428, FZ-2162, 8032ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, SH3773M manufactured by Toray Dow Corning Co., Ltd., BYK-345, BYK-346, BYK-347, BYK-348, BYK-349 manufactured by BYK Chemie GmbH, TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280 manufactured by Evonik Degussa GmbH, KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, KF-643 manufactured by Shin-Etsu Chemical Co., Ltd., and the like.

[0051] The addition amount of the polyether-modified siloxane surfactant is preferably 0.1 to 4% by mass, more preferably 0.2 to 3% by mass, and still more preferably 0.3 to 2% by mass in the total amount of the ink. If the addition amount of the polyether-modified siloxane surfactant is within the above range, it becomes easy to obtain a printed matter with improved initial ejection stability and standby ejection property, and excellent water resistance without white spots and color bleeding.

[0052] Also, from the viewpoint of favorably interacting with the resin (B-1) and achieving improved initial ejection stability and suppression of white spots and color bleeding in printed matter, when the content mass of the polyether-modified siloxane-based surfactant is 1, the content mass of the resin (B-1) is preferably 2 to 50, more preferably 2.5 to 35.

[0053] <Other nonionic surfactants> The aqueous inkjet ink of the present embodiment may contain a polyether-modified siloxane-based surfactant and a nonionic surfactant other than the surfactant corresponding to the above-described organic compound (A) (also described as "other nonionic surfactants" in the present application).

[0054] Specific examples of the above other nonionic surfactants include acetylene diol-based surfactants and their ethylene oxide and / or propylene oxide adducts (provided that those having an HLB value of less than 2.5 or more than 5.2), acetylene monoalcohol-based surfactants and their ethylene oxide and / or propylene oxide adducts, sorbitan fatty acid ester-based surfactants and their ethylene oxide and / or propylene oxide adducts (provided that those having an HLB value of less than 2.5 or more than 5.2), glycerin fatty acid ester-based surfactants and their ethylene oxide and / or propylene oxide adducts (provided that those having an HLB value of less than 2.5 or more than 5.2), fluorine-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyoxyalkylene alkylamine-based surfactants, and the like.

[0055] Among these, from the viewpoint that the affinity with the above-mentioned organic compound (A) and the binder resin is high, the initial ejection stability and the standby ejection property are improved, and the water resistance of the printed matter is also improved, an acetylene diol-based surfactant, an ethylene oxide and / or propylene oxide adduct of an acetylene diol-based surfactant (however, those having an HLB value of less than 2.5 or more than 5.2), and one or more selected from the group consisting of polyoxyalkylene alkyl ether-based surfactants can be preferably used.

[0056] Among them, an acetylene diol-based surfactant and an ethylene oxide and / or propylene oxide adduct of an acetylene diol-based surfactant (however, those having an HLB value of less than 2.5 or more than 5.2) are excellent in the orientation rate to the interface. Therefore, in addition to the above-mentioned effects, the wettability of the aqueous inkjet ink is improved, and it is also preferable to use them from the viewpoint that it becomes easy to obtain a printed matter without white spots and color bleeding. In particular, from the viewpoint that the wettability with respect to non-permeable substrates and difficult-to-permeate substrates is improved and a printed matter having excellent print quality can be obtained, as the acetylene diol-based surfactant and the ethylene oxide and / or propylene oxide adduct of the acetylene diol-based surfactant (however, those having an HLB value of less than 2.5 or more than 5.2), an ethylene oxide and / or propylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and / or an ethylene oxide and / or propylene oxide adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol are preferably used.

[0057] On the other hand, the polyoxyalkylene alkyl ether-based surfactant has a particularly high affinity with the above-mentioned organic compound (A), and can be preferably used from the viewpoint that the initial ejection stability, the standby ejection property, and the water resistance of the printed matter are particularly improved. Also, from these viewpoints, it is preferable to use a compound having a structure represented by the following general formula (4) as the polyoxyalkylene alkyl ether-based surfactant.

[0058] General formula (4): [Chemical formula]

[0059] In general formula (4), s is an integer from 15 to 100, and t is an integer from 0 to 50. However, s > t. Also, R 4 is an alkyl group or an alkylene group having 8 to 22 carbon atoms (however, it may have branches). Note that the addition pattern of the ethylene oxide group and the propylene oxide group in [ ] may be block or random.

[0060] In particular, from the viewpoint of particularly improving the initial ejection stability, standby ejection property, and water resistance of the printed matter, s in the above general formula (4) is preferably 20 to 50, and t is preferably 0 to 10. Also, from the same viewpoint, R 4 in the above general formula (4) is preferably an alkyl group having 10 to 22 carbon atoms (however, it may have branches), and particularly preferably an alkyl group having 12 to 18 carbon atoms (however, it may have branches).

[0061] The total content of other nonionic surfactants in the aqueous inkjet ink is preferably 0.1 to 3% by mass, and more preferably 0.2 to 2% by mass. If the total content is 0.1% by mass or more, the above-described effects can be surely exhibited, and it becomes easy to suppress white bleeding and color mixing bleeding of the printed matter, and the water resistance of the printed matter is also improved. Also, if the total content of other nonionic surfactants is 3% by mass or less, the initial ejection stability and standby ejection property are improved.

[0062] <Hexylene glycol> As described above, the aqueous inkjet ink of the present embodiment contains hexylene glycol. Further, from the viewpoint that all of the ejection stability and the print quality of the printed matter are good, the content of hexylene glycol contained in the aqueous inkjet ink of the present embodiment is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1 to 10% by mass in the total amount of the aqueous inkjet ink.

[0063] <Water-soluble organic solvent> In addition, the aqueous inkjet ink of the present embodiment may contain a water-soluble organic solvent. However, the "water-soluble organic solvent" in the present application shall not include hexylene glycol and the compounds corresponding to the above-described organic compound (A).

[0064] Specific examples of the above-mentioned water-soluble organic solvents include alkanemonoalcohols having 2 to 4 carbon atoms; alkanediols having 2 to 5 carbon atoms; alkanetriols having 3 to 6 carbon atoms; polyethylene glycols (however, those having 2 to 4 ethylene oxide groups); (poly)ethylene glycol monoalkyl ethers (however, those having an alkyl group with 1 to 4 carbon atoms at the molecular terminal and 1 to 3 ethylene oxide groups); (poly)propylene glycol monoalkyl ethers (however, those having an alkyl group with 1 to 4 carbon atoms at the molecular terminal and 1 to 3 propylene oxide groups); butylene glycol monoalkyl ethers (however, those having an alkyl group with 1 to 4 carbon atoms at the molecular terminal); pentylene glycol monoalkyl ethers (however, those having an alkyl group with 1 to 4 carbon atoms at the molecular terminal); (poly)ethylene glycol dialkyl ethers (however, those having alkyl groups with 1 to 4 carbon atoms at both molecular terminals and 1 to 4 ethylene oxide groups); lactams (however, those having a lactam ring composed of 5 to 7 atoms. 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 carbon atom constituting the lactam ring); alkanolamines (however, those having 1 amino group, 1 to 3 hydroxyl groups, and 3 to 9 carbon atoms); etc. These other water-soluble organic solvents may be used alone or in combination of two or more kinds. In the present application, "(poly)ethylene glycol" and "(poly)propylene glycol" respectively represent "ethylene glycol and / or polyethylene glycol" and "propylene glycol and / or polypropylene glycol".

[0065] When the aqueous inkjet ink of the present embodiment contains the above-described water-soluble organic solvent, the total content thereof is preferably 2 to 40% by mass, more preferably 3 to 30% by mass, and particularly preferably 4 to 25% by mass in the total amount of the aqueous inkjet ink. By setting the total content of the water-soluble organic solvent within the above range, an appropriate viscosity for ejection as an inkjet ink can be maintained. For example, even after a long printing pause, the ejection stability can be made good, and in addition, a printed matter that can be dried with low energy and has good water resistance can be obtained.

[0066] Further, when the aqueous inkjet ink of the present embodiment contains a water-soluble organic solvent, the content of the above hexylene glycol is preferably 3 to 75% by mass, more preferably 10 to 60% by mass, and particularly preferably 15 to 50% by mass in the sum of the content of the water-soluble organic solvent contained in the aqueous inkjet ink and the content of the above hexylene glycol. By setting the content of hexylene glycol within the above range with respect to the total content of the water-soluble organic solvent and hexylene glycol, the stabilization of the organic compound (A) by the co-recorded trial glycol is not inhibited by the water-soluble organic solvent. Therefore, the initial ejection stability and standby ejection property are improved, and at the same time, the wettability of the aqueous inkjet ink on the order of microseconds is improved, so that a printed matter without white spots and bleeding can be obtained.

[0067] In one embodiment, the total content of butylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) and pentylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) contained in the aqueous inkjet ink of the present embodiment is preferably 50% by mass or less (it may not be contained), more preferably 20% by mass or less (it may not be contained), and particularly preferably 10% by mass or less (it may not be contained) with respect to the content of the above hexylene glycol. Butylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) and pentylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) have large hydrophobic groups such as butylene groups and pentylene groups, and have strong hydrophobicity compared to other water-soluble organic solvents, so there is a risk of inhibiting the effects of the above-mentioned hexylene glycol. Therefore, by controlling the total content of butylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) and pentylene glycol monoalkyl ethers (where the alkyl group at the molecular terminal has 1 to 4 carbon atoms), a printed matter with no white spots and no bleeding and excellent water resistance can be obtained. Examples of butylene glycol monoalkyl ethers (however, those where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) include butylene glycol monomethyl ether (methoxybutanol, methoxymethylpropanol, etc.), and examples of pentylene glycol monoalkyl ethers (however, those where the alkyl group at the molecular terminal has 1 to 4 carbon atoms) include pentylene glycol monomethyl ether (methoxypentanol, methoxymethylbutanol, etc.).

[0068] ≪Alkanediols having 2 to 5 carbon atoms≫ In one embodiment, the aqueous inkjet ink of this embodiment may contain alkanediols having 2 to 5 carbon atoms as a water-soluble organic solvent. By containing alkanediols having 2 to 5 carbon atoms, further stabilization of the organic compound (A) can be achieved, and the standby ejection property can be improved. Further, after water has volatilized from the aqueous inkjet ink applied on the printing substrate, it is possible to dissolve a binder resin having a low glass transition temperature together with hexylene glycol. As a result, on the printing substrate, the viscosity of the aqueous inkjet ink increases, and bleeding of the printed colors is suppressed. Further, when using, as the organic compound (A), one or more compounds selected from the group consisting of an acetylenediol-based compound, an ethylene oxide and / or propylene oxide adduct of an acetylenediol-based compound, and a medium-chain alkanediol compound, these organic compounds (A) are particularly stabilized, and in addition to the improvement of the standby ejection property and the suppression of bleeding in the printed matter, the water resistance of the printed matter also becomes good.

[0069] As the alkanediols having 2 to 5 carbon atoms, ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, etc. can be used. These compounds may be used alone, or two or more thereof may be used in combination.

[0070] Among these, from the viewpoints of good ejection stability after a long printing pause and the ability to suppress bleeding in the printed matter, it is preferable to use one or more selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, and 1,3-butanediol. In particular, when using, as the organic compound (A), one or more compounds selected from the group consisting of acetylene diol compounds, ethylene oxide and / or propylene oxide adducts of acetylene diol compounds, and medium-chain alkanediol compounds, it is particularly preferable to use propylene glycol because, in addition to improving the standby ejection property and suppressing the color bleeding in printed matter, the water resistance of the printed matter is further improved.

[0071] From the viewpoint of improving the initial ejection stability and standby ejection property and obtaining a printed matter with excellent water resistance and no white spots, the content of the alkanediols having 2 to 5 carbon atoms is preferably 1 to 30% by mass, more preferably 3 to 25% by mass, and particularly preferably 5 to 22% by mass in the total amount of the aqueous inkjet ink.

[0072] Also, when the aqueous inkjet ink applied on the printing substrate dries, both hexylene glycol and the alkanediols having 2 to 5 carbon atoms contribute to the dissolution of the binder resin and the stabilization of the organic compound (A), so that a printed matter without white spots and color bleeding and having excellent water resistance can be obtained. Furthermore, from the viewpoint of obtaining an aqueous inkjet ink having good initial ejection stability and standby ejection property, when the content mass of hexylene glycol is set to 1, the content mass of the alkanediols having 2 to 5 carbon atoms is preferably 0.2 to 25, more preferably 0.4 to 15, and particularly preferably 1 to 12.

[0073] ≪Specific (Poly)propylene glycol monoalkyl ethers≫ On the one hand, the aqueous inkjet ink of the present embodiment may contain a compound (referred to as "specific (poly)propylene glycol monoalkyl ethers" in the present application) among (poly)propylene glycol monoalkyl ethers, in which the alkyl group at the molecular terminal has 2 to 4 carbon atoms and the number of propylene oxide groups is 1 or 2. Since the specific (poly)propylene glycol monoalkyl ethers have a moderately low surface tension at 25°C, it is easy to improve the initial ejection stability and prevent white spots on printed matter. In addition, since the specific (poly)propylene glycol monoalkyl ethers also function as a film-forming aid for the binder resin, by using the specific (poly)oxypropylene monoalkyl ethers, a uniform and continuous ink film can be obtained, and the water resistance of the printed matter is particularly improved.

[0074] As the specific (poly)propylene glycol monoalkyl ethers, for example, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, propylene glycol monoisobutyl ether, propylene glycol mono-tert-butyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monoisobutyl ether, dipropylene glycol mono-tert-butyl ether can be used. These compounds may be used alone or in combination of two or more.

[0075] Among these compounds, since the boiling point under 1 atm and the surface tension at 25 °C have appropriate values, the ejection stability immediately after the start of printing is improved, and in printed matter, the water resistance is improved and white spots can be prevented. Therefore, it is preferable to use a compound in which the alkyl group at the molecular end is an unbranched alkyl group having 2 or 3 carbon atoms. Among the compounds listed above, those satisfying these requirements include propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol mono-n-propyl ether. Further, by improving the affinity with hexylene glycol, the uniformity and continuous film formation of the ink film are promoted, the water resistance of the printed matter is particularly improved, and bleeding in the printed matter can also be suppressed. Therefore, it is particularly preferable to use a compound in which the alkyl group at the molecular end is an n-propyl group, that is, propylene glycol mono-n-propyl ether and / or dipropylene glycol mono-n-propyl ether. In particular, from the viewpoint of improving the standby ejection property, it is particularly preferable to use dipropylene glycol mono-n-propyl ether as the specific (poly)oxypropylene monoalkyl ethers.

[0076] From the point that all the effects of improving the initial ejection stability, preventing white spots and improving water resistance in the printed matter can be achieved simultaneously, the content of the above specific (poly)propylene glycol monoalkyl ethers is preferably 0.2 to 10% by mass, and particularly preferably 0.5 to 8% by mass in the total amount of the aqueous inkjet ink.

[0077] <Binder resin> ≪Resin (B-1)≫ The aqueous inkjet ink of this embodiment contains a binder resin. Further, as the binder resin, it contains a resin (B-1) having a glass transition temperature of -70 to 35°C, and the content of the resin (B-1) is 50% by mass or more based on the total mass of the resins contained in the aqueous inkjet ink. As described above, by using a certain amount of the resin (B-1) having a low glass transition temperature and being easy to form a continuous film, and by using it in combination with hexylene glycol and a polyether-modified siloxane surfactant, it is possible to achieve both an improvement in the water resistance of the printed matter and an improvement in the initial ejection stability. Further, when the aqueous inkjet ink containing the binder resin is printed on a hardly permeable substrate and a non-permeable substrate, the viscosity of the aqueous inkjet ink greatly increases as the liquid component volatilizes, so that bleeding is suppressed and the printed image quality is improved.

[0078] As described above, the glass transition temperature (Tg) of the resin (B-1) is -70 to 35°C. Further, from the viewpoint that a uniform continuous film can be formed, the water resistance of the printed matter is improved, and the standby ejection property of the aqueous inkjet ink is also improved, the glass transition temperature of the resin (B-1) is preferably -55 to 30°C, and particularly preferably -45 to 25°C.

[0079] The glass transition temperature of the binder resin containing the resin (B-1) can be measured by a method conforming to JIS K 7121. Specifically, about 10 mg of a sample of the target resin is placed in an aluminum sample pan whose mass has been measured in advance, and after measuring the mass again, a lid is placed on it and sealed. Next, this sample container and a sample pan prepared without putting the 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 point 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 point is taken as the glass transition temperature. Note that indium is used for temperature calibration.

[0080] On the other hand, for an acrylic resin, the value calculated by the following formula (5) can be used as the glass transition temperature.

[0081] Formula (5): 1 / Tg = Σ(Wn / Tgn)

[0082] In the above formula (5), Tg represents the glass transition temperature (K) of the resin, Wn represents the mass fraction of the structural unit composed of the polymerizable monomer n constituting the resin, and Tgn represents the glass transition temperature (K) of the homopolymer composed of each polymerizable monomer n. As the above Tgn, for example, the values described in "Polymer Handbook (4th Edition)" (Wiley, 1998) can be used.

[0083] The above resin (B-1) may be a water-soluble resin or resin fine particles. Further, a combination of a water-soluble resin and resin fine particles may be used. Among them, from the viewpoints of improving the initial ejection stability and standby ejection property, and improving the water resistance of the printed matter, the resin (B-1) is preferably resin fine particles.

[0084] In the present application, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin", and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin". Further, in the present application, among the above water-insoluble resins, a resin that is dispersed in a particulate state in water and has a median diameter (also referred to as "D50" in the present application) based on volume of 10 to 1,000 nm is defined as a "resin fine particle". Note that D50 in the present application 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.

[0085] Further, as the type of the above resin (B-1), acrylic resins, styrene resins, (anhydrous) maleic acid resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymer resins, etc. can be arbitrarily used. These resins may be used alone only one kind, or two or more kinds may be used in combination.

[0086] Among these, it is preferable to use at least one selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin as the resin (B-1). Further, from the viewpoint of being able to produce a printed matter excellent in adhesion and water resistance with respect to the soft absorbent base material and the non-absorbent base material, it is preferable to use an acrylic resin and / or a urethane resin as the resin (B-1).

[0087] In the present application, the "acrylic resin" refers to a resin using at least one selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters as polymerizable monomers. In addition to the above-listed polymerizable monomers, a styrene-based monomer may be further used as the polymerizable monomer constituting the acrylic resin. However, a resin containing (anhydrous) maleic acid (at least one selected from "maleic acid" and "anhydrous maleic acid") as the polymerizable monomer is not included in the "acrylic resin" in the present application. Also, the "(anhydrous) maleic acid resin" refers to a resin using at least (anhydrous) maleic acid as the polymerizable monomer. In addition, as the polymerizable monomer of the (anhydrous) maleic acid resin, α-olefins, styrene-based monomers, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, etc. may be further used.

[0088] The acid value of the resin (B-1) is preferably 0 to 100 mgKOH / g, more preferably 0.5 to 80 mgKOH / g. Particularly preferably, it is 1 to 60 mgKOH / g. By setting the acid value within the above range, even if a part of the aqueous inkjet ink dries near the nozzle of the inkjet head, a significant thickening of the aqueous inkjet ink can be suppressed, so that the discharge stability (particularly standby dischargeability) can be improved. Also, the water resistance of the printed matter is improved.

[0089] The "acid value of the resin" in the present application refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In the present application, as the acid value, the value calculated by the following method is used. For example, when the resin contains Wa mass% of a polymerizable monomer having va 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 (6).

[0090] Formula (6): (Acid value) = {(va × na × Wa) ÷ (100 × Ma)} × 56.11 × 1000

[0091] In the above formula (6), the numerical value "56.11" is the molecular weight of potassium hydroxide.

[0092] Further, when a water-soluble resin is used as the resin (B-1), the mass average molecular weight of the resin (B-1) is preferably 1,000 to 25,000, and more preferably 5,000 to 20,000. By using the resin (B-1) having the above mass average molecular weight, a uniform continuous film can be formed even with a short drying time, and the water resistance of the printed matter is improved.

[0093] In the present application, as the mass average molecular weight of the compound, a polystyrene conversion value that can be measured by a method conforming to JIS K 7252 is used. Examples of specific measurement conditions are shown below. · Apparatus used: "HLC-8320GPC" manufactured by Tosoh Corporation · Columns used: TSKgel (registered trademark) SuperMultipore HZ-M (3 columns) · Column temperature: 40 °C · Developing solvent: Tetrahydrofuran · Flow rate: 0.6 mL / min · Concentration of sample solution: 0.1 mass% · Injection volume of sample solution: 10 μL

[0094] The preferred content of the resin (B-1) contained in the aqueous inkjet ink of the present embodiment is 1 to 20% by mass, more preferably 2 to 18% by mass, and particularly preferably 5 to 15% by mass in the total amount of the aqueous inkjet ink, from the viewpoint that the initial ejection stability and standby ejection property can be improved, and a printed matter having no bleeding in color mixing and excellent water resistance can be obtained.

[0095] As described above, the content of the resin (B-1) is 50% by mass or more in the total mass of the resins contained in the aqueous inkjet ink. Since more than half of the resins contained in the aqueous inkjet ink are the resin (B-1) with a low glass transition temperature, the ink film becomes a uniform continuous film, and the water resistance of the printed matter is improved. Further, when the above aqueous inkjet ink is printed on a hardly permeable substrate and a non-permeable substrate, the viscosity of the aqueous inkjet ink greatly increases as the liquid component volatilizes, so bleeding in color mixing is suppressed and the print image quality is improved. From the above viewpoints, the content of the resin (B-1) is more preferably 65% by mass or more, and particularly preferably 75% by mass or more in the total mass of the resins contained in the aqueous inkjet ink.

[0096] ≪Other Binder Resins≫ The aqueous inkjet ink of the present embodiment may contain a binder resin other than the above resin (B-1) (also described as "other binder resin" in the present application).

[0097] The other binder resin may be a water-soluble resin or resin fine particles. Also, the types of resins that can be used as the other binder resin are the same as those in the case of the above resin (B-1). In one embodiment, from the viewpoint that the water resistance of the printed matter is improved because of the good affinity with the resin (B-1), it is preferable to use a resin of the same type as the resin (B-1).

[0098] For example, from the viewpoint of improving the rub resistance of printed matter and achieving good standby ejection performance, as other binder resins, it is preferable to use resins having a glass transition temperature of 50 to 120°C, more preferably resins having a glass transition temperature of 60 to 110°C, and particularly preferably resins having a glass transition temperature of 70 to 100°C.

[0099] Furthermore, from the same viewpoints as those of the above resin (B-1), that is, the viewpoints of improving ejection stability (particularly standby ejection performance) and the water resistance of printed matter, the acid value of the other binder resin is preferably 0 to 100 mgKOH / g, more preferably 0.5 to 80 mgKOH / g. Particularly preferably, it is 1 to 60 mgKOH / g.

[0100] When the aqueous inkjet ink of the present embodiment contains other binder resins, the preferred content of the other binder resins is preferably 1 to 12% by mass, more preferably 1.5 to 10% by mass, and particularly preferably 2 to 8% by mass in the total amount of the aqueous inkjet ink, from the viewpoint of improving initial ejection stability and standby ejection performance.

[0101] <Wax resin fine particles> In addition, the aqueous inkjet ink of the present embodiment may contain wax resin fine particles. Furthermore, as the wax resin fine particles, 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 resin (B-1). Also, it is preferably selected from the viewpoint of improving the rub resistance, adhesion, water resistance, etc. of printed matter.

[0102] As the above polyolefin, one or more selected from the group consisting of polyethylene, polypropylene, and polybutene can be preferably used. In particular, the selection of polyethylene is preferable from the viewpoint of improving the water resistance of printed matter.

[0103] When using wax resin fine particles, the D50 is preferably from 10 to 200 nm, more preferably from 20 to 180 nm. If the D50 is within the above range, improvements in the rub resistance, adhesion, water resistance, etc. of the printed matter can be achieved. Further, since clogging of the inkjet head nozzles does not occur, an aqueous inkjet ink having particularly excellent initial ejection stability can be obtained.

[0104] When using wax resin fine particles, the blending amount of the above wax resin fine particles with respect to the total blending amount of all resins (pigment dispersion resin, binder resin, and wax resin fine particles) contained in the aqueous inkjet ink is preferably 2 to 30% by mass, more preferably 3 to 25% by mass, and particularly preferably 4 to 20% by mass. By keeping within the above range, the rub resistance, adhesion, and water resistance of the printed matter can be improved without deteriorating the initial ejection stability and standby ejection property. In addition, since a printed matter having sufficient water resistance can be obtained even during high-speed printing, the blending amount of the wax resin fine particles with respect to the total amount of the aqueous inkjet ink is preferably 0.2 to 2.5% by mass, and particularly preferably 0.5 to 2% by mass.

[0105] <Pigment> The aqueous inkjet ink of the present embodiment contains a pigment. 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.

[0106] The content of the pigment contained in the aqueous inkjet ink of this embodiment is adjusted according to the intended use of the printed matter produced using the aqueous inkjet ink. For example, it is preferably 0.5 to 30% by mass in the total amount of the aqueous inkjet ink. Also, except in the case of white aqueous inkjet ink (aqueous white ink), from the viewpoint of obtaining a printed matter with a high density without deteriorating the ejection stability of the aqueous inkjet ink, the content of the above pigment is more preferably 0.5 to 12% by mass, and particularly preferably 1 to 8% by mass. On the other hand, in the case of aqueous white ink, from the viewpoint of obtaining a printed matter with high hiding power without deteriorating the ejection stability of the aqueous white ink, the content of the above pigment is more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass.

[0107] <Pigment-dispersing resin> The aqueous inkjet ink of the present embodiment may contain a resin (pigment-dispersing resin) used for pigment dispersion applications. Compared with pigments dispersed without using a pigment-dispersing resin (self-dispersing pigments, pigments dispersed with a surfactant, etc.), the pigments dispersed using a pigment-dispersing resin have excellent dispersion stability, so that the aqueous inkjet ink has excellent initial ejection stability and standby ejection properties. Also, it is preferable to select a pigment-dispersing resin in that it does not adversely affect the water resistance of printed matter.

[0108] Note that the pigment-dispersing resin may also serve as the above-described resin (B-1). Examples of the form in which the pigment-dispersing resin also serves as the resin (B-1) include resin fine particles that contain a pigment and have a glass transition temperature of -70 to 35°C.

[0109] The type of the pigment-dispersing resin is not particularly limited, and for example, acrylic resins, styrene resins, (anhydrous) maleic acid resins, urethane resins, polyester resins, etc. can be arbitrarily used. These resins may be used alone only one kind, or two or more kinds may be used in combination. Among these, from the viewpoints that the initial ejection stability and standby ejection properties can be improved, the material selectivity is large, the resin synthesis is easy, etc., it is preferable to use one or more selected from the group consisting of acrylic resins, (anhydrous) maleic acid resins, and urethane resins. Also, since the affinity with the resin (B-1) is improved, the pigment is less likely to become non-uniform in the aqueous inkjet ink, and the uniformity and continuous film formation of the ink film are not inhibited by the above pigment, so that the water resistance of the printed matter is improved. From this point, it is particularly preferable to use a resin of the same type as the resin (B-1) as the pigment-dispersing resin.

[0110] As the pigment-dispersing resin, a resin synthesized by a conventionally known method may be used, or a commercially available product may be used. Also, there are no particular restrictions on its structure, and for example, resins having a random structure, block structure, graft structure, hyperbranched structure, etc. can be used. In one embodiment, it is preferable that the pigment-dispersing resin has a block structure or a graft structure. The pigment-dispersing resin released in the aqueous inkjet ink may adsorb to the organic compound (A) and the polyether-modified siloxane-based surfactant, which may deteriorate the initial ejection stability, standby ejection property, and the print image quality of the printed matter. Therefore, in the aqueous inkjet ink of the present embodiment, a pigment-dispersing resin having a block structure or a graft structure, which is less likely to desorb from the pigment, can be preferably used. For the same reason, it is also preferable to crosslink the pigment-dispersing resin adsorbed on the pigment surface with a crosslinking agent or the like (that is, to use a crosslinked pigment-dispersing resin).

[0111] Also, as the pigment-dispersing resin, a water-soluble resin may be selected, a water-insoluble resin may be selected, or a water-soluble resin and a water-insoluble resin may be used in combination.

[0112] When a water-soluble resin is used as the pigment-dispersing resin, its acid value is preferably 60 to 400 mgKOH / g, more preferably 70 to 350 mgKOH / g, and particularly preferably 80 to 300 mgKOH / g. By setting the acid value within the above range, it is possible to maintain the dispersion stability of the pigment and improve the initial ejection stability and standby ejection property.

[0113] On the other hand, when a water-insoluble resin is used as the pigment-dispersing resin, its acid value is preferably 0 to 100 mgKOH / g, more preferably 5 to 90 mgKOH / g, and still more preferably 10 to 80 mgKOH / g. If the acid value is within the above range, it becomes easier to obtain a printed matter with excellent water resistance.

[0114] In the aqueous inkjet ink of the present embodiment, from the viewpoint that by improving the adsorptivity to the pigment, not only the dispersion stability of the pigment is improved, but also the liberation of the pigment dispersion resin is suppressed, and the initial ejection stability, standby ejection property, and deterioration of the printed image quality of the printed matter can be prevented, it is preferable to introduce an aromatic group into the pigment dispersion resin. Examples of the aromatic group include, but are not limited to, a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, and an anisyl group. Among them, one or more selected from the group consisting of a phenyl group, a naphthyl group, and a tolyl group are preferably selected from the viewpoint that all of the dispersion stability of the pigment, the initial ejection stability and standby ejection property, and the printed image quality of the printed matter are good.

[0115] From the viewpoint that all of the dispersion stability of the pigment, the initial ejection stability and standby ejection property, and the printed image quality of the printed matter are improved, the introduction amount of the polymerizable monomer containing an aromatic ring is preferably 5 to 75% by mass, more preferably 10 to 65% by mass, and particularly preferably 15 to 55% by mass with respect to the total amount of the polymerizable monomers constituting the pigment dispersion resin.

[0116] When the pigment dispersion resin does not also serve as the resin (B-1), the blending amount of the pigment dispersion resin is preferably 3 to 80% by mass, more preferably 5 to 70% by mass, and particularly preferably 10 to 60% by mass with respect to the blending amount of the pigment. Further, from the viewpoint of obtaining a printed matter having excellent water resistance, the blending amount of the pigment dispersion resin is preferably 2 to 50% by mass, more preferably 3 to 45% by mass, and particularly preferably 4 to 40% by mass with respect to the blending amount of the resin (B-1).

[0117] <Water> The aqueous inkjet ink of the present embodiment contains water. As the water, it is preferable to use ion-exchanged water (deionized water) or distilled water. Further, the water content is preferably 45 to 85% by mass, particularly preferably 50 to 80% by mass, based on the total amount of the aqueous inkjet ink. Since water has a low boiling point, it volatilizes preferentially from the aqueous inkjet ink. By setting the water content within the above range, after the water volatilizes preferentially on the printing substrate, hexylene glycol and the polyether-modified siloxane-based surfactant, the organic compound (A), and the binder resin are preferably compatible with each other, and as a result, a continuous ink film is formed, improving the water resistance of the printed matter.

[0118] <Other components> The aqueous inkjet ink of the present embodiment may contain a pH adjuster and other additives in addition to the components described above. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds can be used.

[0119] <Method for producing aqueous inkjet ink> The aqueous inkjet ink of the present embodiment can be produced by a conventionally known method. For example, a pigment dispersion in which a pigment is dispersed in a medium (aqueous medium) containing at least water is produced in advance. Then, water, the organic compound (A), the polyether-modified siloxane-based surfactant, hexylene glycol, the binder resin, etc. are added to the pigment dispersion, and after sufficiently stirring and mixing, coarse particles are removed by a method such as filtration or centrifugation. However, the method for producing the aqueous inkjet ink of the present embodiment is not limited to the method described above.

[0120] <Properties of aqueous inkjet ink> The aqueous inkjet ink of this embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. In this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from an inkjet head with a discharge frequency of about 4 to 10 KHz, but also from an inkjet head having a high discharge frequency of about 20 to 70 KHz. In particular, when the viscosity of the aqueous inkjet ink of this embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head having a design resolution of 600 dpi or more is used. In this application, as the viscosity, the value measured in a 25°C environment using a cone plate type rotational viscometer (E-type viscometer, cone angle 1°34’) such as “TVE25L type viscometer” manufactured by Toki Sangyo Co., Ltd. is used.

[0121] Also, from the viewpoint of obtaining an aqueous inkjet ink excellent in initial discharge stability and print image quality of printed matter, the static surface tension of the aqueous inkjet ink of this embodiment at 25°C is preferably 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m. In this application, as the static surface tension, the value measured in a 25°C environment using the Wilhelmy method (plate method) such as “Automatic Surface Tension Meter CBVP-Z” manufactured by Kyowa Interface Science Co., Ltd. is used.

[0122] <Set of Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment may be used alone as a single type, or it can also be used as a set of aqueous inkjet inks combined with two or more types of aqueous inkjet inks. As such a set of aqueous inkjet inks, for example, a set of four-color aqueous inkjet inks (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink); 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 aqueous inkjet inks satisfy the requirements of the embodiment of the present invention described above.

[0123] <Ink - pretreatment liquid set> Also, the aqueous inkjet ink of this embodiment and the set of the above aqueous inkjet inks can 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 the printing substrate before printing the aqueous inkjet ink, a layer (ink flocculation layer) that intentionally aggregates the solid components contained in the aqueous inkjet ink can be formed. Then, by landing the above aqueous inkjet ink on the ink flocculation layer, it is possible to prevent the coalescence and color mixing of the droplets of the aqueous inkjet ink, and significantly improve the printing image quality of the printed matter.

[0124] As the above flocculant, for example, a water - soluble inorganic salt or organic salt containing polyvalent metal ions, and a resin having a cationic group and a cationic group equivalent larger than the anionic group equivalent can be used.

[0125] <Inkjet printing method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. That is, the inkjet printing method performed using the aqueous inkjet ink of this embodiment includes a step of discharging (discharging step) from an inkjet head having fine nozzles onto a printing substrate. Further, the aqueous inkjet ink discharged onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0126] ≪Discharging step≫ As the operation method of the inkjet head in the discharging step, there are a shuttle (scan) method in which the inkjet head is reciprocally scanned in a direction perpendicular to the conveyance direction of the printing substrate while discharging and recording the aqueous inkjet ink, and a single-pass method in which the aqueous inkjet ink is discharged and recorded when the printing substrate passes under a fixedly arranged inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may adopt either the shuttle method or the single-pass method. Among them, the single-pass method is preferably selected because the landing position of the droplets of the aqueous inkjet ink is less likely to shift, the printing image quality of the printed matter is improved, and furthermore, high-speed printing is possible and high productivity as an alternative to plate printing can be exhibited.

[0127] Regarding the discharging method from the inkjet head, a known method can be arbitrarily selected. Examples of the discharging method include a piezo method that utilizes the volume change of a piezoelectric element (piezo element), a thermal method that discharges the aqueous inkjet ink by bubbles generated by heating a heater, a valve method that discharges the pressurized aqueous inkjet ink while opening and closing the lid (valve) of the nozzle with a solenoid, and the like.

[0128] The droplet volume of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing the drying load and improving the print quality. Also, from the viewpoint of improving the print quality, it is preferable to adjust the printing conditions (specifically, the driving frequency and the number of installed inkjet heads, as well as the printing speed) so that the recording resolution of the printed matter is 600 dpi or more, and it is particularly preferable to adjust the printing conditions so that it is 1200 dpi or more.

[0129] <<Drying Process>> Examples of the drying method employed in the drying mechanism used in the drying process include a heat drying method, a hot air drying method, an infrared ray (for example, infrared ray with a wavelength of 700 to 2500 nm) drying method, a microwave drying method, a drum drying method, and the like. In the above drying process, one or more of these methods can be arbitrarily selected and used. Also, when two or more of the above drying methods are employed, each drying method may be used separately (for example, successively) or used simultaneously in combination. For example, by using the heat drying method and the hot air drying method in combination, the aqueous inkjet ink can be dried faster than when each is used alone.

[0130] 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 adopting the heat drying method, the drying temperature is preferably 35 to 100 °C, and when adopting the hot air drying method, the hot air temperature is preferably 50 to 250 °C. Also, from the same viewpoint, when adopting the infrared ray drying method, 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.

[0131] <Printing Substrate> The printing substrate on which the aqueous inkjet ink of the present embodiment is printed is not particularly limited. On the one hand, the aqueous inkjet ink of the present embodiment can be suitably used for hardly permeable substrates and non-permeable substrates. Generally, when hardly permeable substrates and non-permeable substrates are used as printing substrates, since the aqueous inkjet ink does not penetrate (or hardly penetrates), bleeding and deterioration of water resistance are likely to occur in the printed matter. On the other hand, by using the aqueous inkjet ink of the present embodiment, it is possible to obtain a printed matter that is free from bleeding and has excellent water resistance even for hardly permeable substrates and non-permeable substrates.

[0132] In the present application, the permeability of the printing substrate is determined by the water absorption measured by a dynamic scanning liquid absorber. Specifically, the water absorption of pure water at a contact time of 100 msec measured by the following method is less than 1 g / m 2 The printing substrate is defined as a "non-permeable substrate", and the printing substrate with a water absorption of 1 g / m 2 or more and less than 6 g / m 2 is defined as a "hardly permeable substrate", and the printing substrate with a water absorption of 6 g / m 2 or more is defined as a "permeable substrate". The water absorption of the printing substrate can be measured under the environment of 23°C and 50% RH using a dynamic scanning liquid absorber (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the conditions shown below, with a printing substrate sized about 15 to 20 cm square as a sample. · Measurement method: Spiral Method · Measurement start radius: 20 mm · Measurement end radius: 60 mm · Contact time: 10 to 1,000 msec · Sampling points: 19 (measured at approximately equal intervals with respect to the square root of the contact time) · Scanning interval: 7 mm · Rotation table speed switching angle: 86.3 degrees · Head box conditions: width 5 mm, slit width 1 mm

[0133] Examples of the non-permeable substrate and the hardly permeable substrate include plastic films and sheets such as polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene film, nylon film, polystyrene film, and polystyrene sheet; coated papers such as coated paper, art paper, and cast paper; metals such as aluminum, iron, stainless steel, and titanium; and the like.

[0134] The above-listed printing substrates may have a smooth surface or a surface with irregularities. Also, the above-listed printing substrates may be transparent, translucent, or opaque. Furthermore, the above-listed printing substrates may be in the form of a roll or a single sheet. In addition, a combination of two or more of the above-listed printing substrates adhered to each other may be used as the printing substrate. Also, a release adhesive layer or the like may be provided on the side opposite to the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing.

[0135] From the viewpoint of improving the wettability of the aqueous inkjet ink of the present embodiment, having excellent print quality and drying properties, and obtaining a printed matter with good rubbing resistance and water resistance along with the uniformity of the surface of the printed matter, it is also preferable to perform surface modification such as corona treatment and plasma treatment on the printing surface of the above-listed printing substrates before printing.

[0136] <Printed matter> The aqueous inkjet ink of the present embodiment can be used for manufacturing printed matter. Also, as a method for manufacturing the above-mentioned printed matter, the inkjet printing method described above can be used.

Examples

[0137] Examples and comparative examples are given below to more specifically explain the aqueous inkjet ink of the present embodiment. In the following description, "parts" and "%" represent "parts by mass" and "mass %", respectively, unless otherwise specified.

[0138] <Production example of an aqueous solution of an acrylic pigment dispersion resin> 56 parts of 2-butanone were charged into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer. Next, 56 parts of benzyl methacrylate, which is a polymerizable monomer, 0.3 parts of 2,2'-azobisisobutyronitrile, which is a polymerization initiator, and 2.2 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid were each 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, and a polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C to obtain a polymer (A block) composed of benzyl methacrylate. After completion of the above polymerization reaction, the contents were cooled until they reached room temperature, and then 44 parts of 2-butanone, 28 parts of butyl methacrylate, and 16 parts of methacrylic acid were each added to the reaction vessel. After replacing the inside of the reaction vessel with nitrogen gas again, the contents in the reaction vessel were heated until they reached 75°C, and a polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C to obtain an acrylic pigment dispersion resin 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. Thereafter, after the contents in the reaction vessel were cooled until they reached room temperature, 17 parts of dimethylaminoethanol was added to neutralize the acrylic pigment dispersion resin, and further 150 parts of ion-exchanged water was added. Thereafter, the contents were 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 solid content concentration to 20% to obtain an aqueous solution of the acrylic pigment dispersion resin. The mass average molecular weight of the acrylic pigment dispersion resin measured by the method described above was 23,000, the glass transition temperature of the acrylic pigment dispersion resin calculated using the above formula (5) was 53°C, and the acid value of the acrylic pigment dispersion resin calculated using the above formula (6) was 104 mgKOH / g.

[0139] In the present application, the "aqueous solution" refers to a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium.

[0140] <Production Example of Magenta Pigment Dispersion Liquid> 450 g of C.I. Pigment Red 122 (“FASTOGEN SUPER MAGENTA RTS” manufactured by DIC Corporation), 560 g of an aqueous solution of an acrylic pigment dispersion resin, and 1,990 g of ion-exchanged water were charged into a mixing container (volume: 10 L) equipped with a stirrer, and stirred (premixed) for 1 hour. Next, circulation dispersion of the mixture was started using “Dyno-Mill” (volume: 0.6 L) manufactured by Shinmaru Enterprises Co., Ltd. filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. Then, the D50 of the above mixture was measured using the above-described apparatus every certain period (for example, 1 hour), and when the D50 became 180 nm or less, the circulation dispersion was terminated, thereby producing a magenta pigment dispersion having a pigment concentration of 15%.

[0141] <Production Example of Yellow Pigment Dispersion> A yellow pigment dispersion having a pigment concentration of 15% was obtained by the same raw materials and method as the above magenta pigment dispersion, except that Lysopac Yellow 5515C (C.I. Pigment Yellow 155 manufactured by Vibrantz Corporation) was used as the pigment.

[0142] <Production Example of Acrylic Binder Resin 1> 40 parts of ion-exchanged water and 0.2 part of Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), an emulsifier, were charged into a reaction vessel equipped with a thermometer, a condenser, a stirrer, and a dropping funnel. On the other hand, 25 parts of methyl methacrylate, 10 parts of butyl acrylate, 50 parts of butyl methacrylate, 2.5 parts of acrylic acid, and 12.5 parts of benzyl methacrylate; 53 parts of ion-exchanged water; and 1.8 parts of Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), an emulsifier, were charged into another mixing container equipped with a stirrer, and well stirred and mixed to obtain an emulsion. Five parts of the above emulsion were taken and put into the above reaction vessel. Then, it was heated until the temperature of the contents in the reaction vessel reached 60°C. After replacing the inside of the reaction vessel with nitrogen gas, 3 parts of a 5% aqueous solution of potassium persulfate and 4 parts of a 1% aqueous solution of sodium metabisulfite were added to initiate the polymerization reaction. After the start of the polymerization reaction, while maintaining the temperature of the contents in the reaction vessel at 60°C, the remaining of the above emulsion, 2 parts of a 5% aqueous solution of potassium persulfate, and 6 parts of a 1% aqueous solution of sodium metabisulfite were added dropwise over 1.5 hours. After the completion of the dropwise addition, stirring was continued for another 2 hours. Then, after cooling the contents in the reaction vessel until it reached room temperature, diethylaminoethanol was added until the pH of the contents reached 8.5. And, ion-exchanged water was added and adjusted so that the solid content concentration became 30%, whereby an aqueous dispersion of acrylic binder resin 1, which is resin fine particles, was obtained. Incidentally, the glass transition temperature of acrylic binder resin 1 calculated using the above formula (5) was 32°C, and the acid value of acrylic binder resin 1 calculated using the above formula (6) was 20 mgKOH / g.

[0143] <Production Examples of Acrylic Binder Resins 2 to 4> Except that the types and addition amounts of the polymerizable monomers used in the preparation of the emulsion were changed as shown in Table 1 below, aqueous dispersions (each having a solid content concentration of 30%) of acrylic binder resins 2 to 4, which are resin fine particles, were obtained by the same materials and method as the above acrylic binder resin 1.

[0144]

Table 1

[0145] In addition, Table 1 above also shows the types and addition amounts of the polymerizable monomers used in the production of acrylic binder resin 1, as well as the glass transition temperatures (calculated using the above formula (5)) and acid values (calculated using the above formula (6)) of acrylic binder resins 1 to 4.

[0146] <Production Examples of Acetylenediol Compounds 1 to 3> Using the methods described in Examples 6 to 9 of Japanese Patent Application Laid-Open No. 2001-215690, 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol 104 manufactured by Evonik Japan) as a diol was used as a starting material, and by adjusting the amounts of ethylene oxide and propylene oxide, as well as the synthesis conditions (pressure, temperature, time), compounds (acetylene diol-based compounds 1 to 3) in which ethylene oxide groups and propylene oxide groups were added to the 2,4,7,9-tetramethyl-5-decyne-4,7-diol were synthesized. Specifically, an acetylene diol-based compound 1 (HLB value 2.7) in which 3 moles of ethylene oxide groups and 11 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol, an acetylene diol-based compound 2 (HLB value 5.0) in which 3.5 moles of ethylene oxide groups and 4 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and an acetylene diol-based compound 3 (HLB value 1.8) in which 1.5 moles of ethylene oxide groups and 7.5 moles of propylene oxide groups were added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol were produced.

[0147] <Production of an aqueous inkjet ink set> Using the pigment dispersions produced by the method described above, each raw material was put into a mixing container equipped with a stirrer so as to have the formulation described in each column of Table 2 below. After all the raw materials were put in, stirring and mixing were continued until the mixture became sufficiently uniform. Thereafter, an aqueous inkjet ink was produced by filtering with a membrane filter having a pore size of 0.8 μm. By producing an aqueous inkjet ink with each of the above magenta pigment dispersion and yellow pigment dispersion, an aqueous inkjet ink set consisting of an aqueous magenta ink (M) and an aqueous yellow ink (Y) was produced, respectively.

[0148] In the production of the aqueous inkjet ink, while stirring the mixture in the mixing container, each raw material was charged. Also, in each column of Table 1, the components described in the upper row were charged in order. However, when producing an aqueous inkjet ink that does not contain one or more of these components, the next component was charged in order without charging the said component. Also, regarding components containing two or more types of raw materials, the charging order within the said component was made arbitrary.

[0149]

Table 2

[0150]

Table 2

[0151]

Table 2

[0152]

Table 2

[0153] The meanings of the abbreviations and the details of the product names described in Table 1 above are as shown below. Also, in Table 1, "HLB" represents the HLB value, "Tg" represents the glass transition temperature, and "Nv" represents the solid content concentration. Further, "EO" represents "ethylene oxide" and "PO" represents "propylene oxide". · Surfynol DF110D: 2,5,8,11 - tetramethyl - 6 - dodecyne - 5,8 - diol (an acetylene diol - based compound (surfactant) manufactured by Evonik Japan Co., Ltd., HLB value = 2.7) · Surfynol 420: A compound in which 1.3 moles of ethylene oxide groups are added to 2,4,7,9 - tetramethyl - 5 - decyne - 4,7 - diol (an acetylene diol - based compound (surfactant) manufactured by Evonik Japan Co., Ltd., HLB value = 4.0) · 1,7-HepD: 1,7-heptanediol (medium-chain alkane diol compound, HLB value = 5.2) · 1,2-OctD: 1,2-octanediol (medium-chain alkane diol compound, HLB value = 4.7) · 1,6-HexD: 1,6-hexanediol (HLB value = 5.8) · BYK-3420: Both-terminal polyether-modified siloxane surfactant (manufactured by BYK-Chemie Japan) · BYK-333: Both-terminal polyether-modified siloxane surfactant (manufactured by BYK-Chemie Japan) · BYK-348: Side-chain polyether-modified siloxane surfactant (manufactured by BYK-Chemie Japan) · KF-6015: Side-chain polyether-modified siloxane surfactant (manufactured by Shin-Etsu Silicone Co., Ltd.) · Surfynol 465: A compound in which 10 moles of ethylene oxide groups are added to 2,4,7,9-tetramethyl-5-decyne-4,7-diol (an acetylene diol-based compound (surfactant) manufactured by Evonik Japan, HLB value = 13.2) · Nonion K-230: In the general formula (4), R 4 is an alkyl group having 12 carbon atoms, and s = 30, t = 0 (manufactured by NOF Corporation, HLB value = 17.5) · Takelac W-6061: Urethane resin fine particles manufactured by Mitsui Chemicals, Inc. (solid content concentration = 30%, glass transition temperature = 25°C) · Takelac W-6110: Urethane resin fine particles manufactured by Mitsui Chemicals, Inc. (solid content concentration = 32%, glass transition temperature = -20°C) · SF470: Superflex 470 (urethane resin fine particles manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content concentration = 38%, glass transition temperature = -31°C) · SF300: Superflex 300 (urethane resin fine particles manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content concentration = 30%, glass transition temperature = -42°C) · QE-1042: Acrylic resin fine particles manufactured by Starlight PMC Co., Ltd. (solid content concentration = 40.5%, glass transition temperature = 53°C) ·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)

[0154] [Examples 1 - 57, Comparative Examples 1 - 8] Using the set of aqueous inkjet inks manufactured by the above - described method, the following evaluations were carried out. Also, the evaluation results were as shown in Table 1 above.

[0155] <Evaluation 1: Evaluation of ejection stability (initial stage)>[ An inkjet ejection device equipped with an inkjet head "KJ4B - QA" (designed resolution 600 dpi) manufactured by Kyocera, installed in an environment at 25°C, was filled with aqueous magenta ink or aqueous yellow ink that constitutes the set of the above - mentioned aqueous inkjet inks. After that, a nozzle check pattern was printed, and it was confirmed that ink was ejected normally from all nozzles. Next, solid printing with a printing rate of 100% was performed on OK top - coat paper under printing conditions of a frequency of 30 kHz and 600×600 dpi. Then, regarding the obtained solid print, the ejection stability (initial stage) was evaluated 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 ◎, ○, ○Δ, and Δ were considered to be usable in actual use. The above evaluations were performed for the aqueous magenta ink and the aqueous yellow ink that constitute the set of aqueous inkjet inks, respectively. Also, in Table 2, the results of those aqueous magenta inks and aqueous yellow inks with poor evaluation results were described. ◎: In the solid print, in the part that should be printed first, no chipping was observed, or if chipping was observed, its length was 3 mm or less ○: In the solid print, in the part that should be printed first, chipping exceeding 3 mm and not exceeding 1 cm was observed ○Δ: In the solid print, in the part that should be printed first, chipping exceeding 1 cm and not exceeding 1.5 cm was observed △: In the solid print, a chip of more than 1.5 cm and not more than 2 cm was found in the part that should have been printed first. ×: In the solid print, a chip of more than 2 cm was found in the part that should have been printed first.

[0156] <Evaluation 2: Evaluation of standby ejection performance> An inkjet head "Samba G3L" (designed resolution 1,200 dpi) manufactured by FUJIFILM Dimatix was installed in an inkjet ejection device installed in an environment of 25°C. Furthermore, a pump, a tube, and an ink tank were prepared, and the ink supply port of the Samba G3L was connected to the pump, the pump to the ink tank, and the ink tank to the ink discharge port of the Samba G3L. Next, the ink tank was filled with aqueous magenta ink or aqueous yellow ink that constitutes the set of the aqueous inkjet ink. The pump was operated to fill the inkjet head and the flow path with the aqueous inkjet ink. After printing a nozzle check pattern and confirming that ink was being ejected normally from all nozzles, the inkjet ejection device was allowed to stand by for 1 hour with the pump operating. Then, after 1 hour, the nozzle check pattern was printed again, and the number of missing nozzles was visually counted to evaluate the standby ejection performance. The evaluation criteria were as follows, and ◎, ○, and △ were considered usable in actual use. The above evaluation was performed with the aqueous magenta ink and the aqueous yellow ink that constitute the set of the aqueous inkjet ink, respectively. Also, in Table 2, the results of the evaluation were described for the aqueous magenta ink and the aqueous yellow ink for which the evaluation results were poor. ◎: There was no missing nozzle. ○: 1 to 4 missing nozzles occurred. △: 5 to 9 missing nozzles occurred. ×: 10 or more missing nozzles occurred.

[0157] <Production of magenta / yellow gradient print> An inkjet ejection device was prepared by arranging two inkjet heads "KJ4B-1200" (designed resolution 1200 dpi, nozzle diameter 20 μm) manufactured by Kyocera Corporation side by side along the conveyance direction of the printing substrate. From the upstream side in the conveyance direction, sets of each aqueous inkjet ink were filled in the order of aqueous magenta ink and aqueous yellow ink. Also, on the conveyor, as the printing substrate, an A4 size (width 21 cm × length 30 cm) OPP film (manufactured by Mitsui Chemicals Toagosei Co., Ltd. "OPU-1" (thickness 20 μm), or "FOR-AQ" (thickness 20 μm) manufactured by Futamura Chemical Co., Ltd.) was fixed with the corona-treated surface facing upward. Then, the conveyor was driven at 50 m / min, and when the printing substrate passed under 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. And 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 printed matter. The "magenta / yellow gradation image" refers to a magenta color gradation image (an image with the printing rate changed at intervals of 10% between 10% and 100%) with a width of 5 cm × length of 30 cm printed using aqueous magenta ink, and a yellow color gradation image with a width of 5 cm × length of 30 cm printed using aqueous yellow ink, which are arranged adjacent to each other such that their long sides are in contact. Also, the above two types of OPP films were used as the printing substrate, and a magenta / yellow gradation image was printed on each of them.

[0158] <Evaluation 3: Evaluation of Printing Image Quality (White Speckles)> The magenta / yellow gradient printed matter produced by the method described above was visually observed. Then, by checking the presence or absence of white spots at a printing rate of 100%, the print quality of the magenta / yellow gradient printed matter was evaluated. The evaluation criteria were as follows, and ◎, ○, ○Δ, and Δ were considered to be practically usable. The above evaluation was performed on each of the two types of printing substrates on which the magenta / yellow gradient printed matter was printed. ◎: 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. ○: 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. ○Δ: 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. Δ: 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. ×: 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.

[0159] <Evaluation 4: Evaluation of Print Quality (Color Bleeding)> The magenta / yellow gradient printed matter produced by the method described above was visually observed. Then, by checking the printing rate at the location where color bleeding began 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 print quality (color bleeding) of the magenta / yellow gradient printed matter was evaluated. The evaluation criteria were as follows, and ◎, ○, ○Δ, and Δ were considered to be practically usable. Also, Table 2 shows the results of the evaluation of the two types of printing substrates with the worse evaluation results. ◎: No color bleeding was observed even at a printing rate of 80% for both printing substrates. ○: In at least one type of printing substrate, bleeding was observed at a printing rate of 80%, but bleeding was not observed at a printing rate of 70% for both printing substrates. ○△: In at least one type of printing substrate, bleeding was observed at a printing rate of 70%, but bleeding was not observed at a printing rate of 60% for both printing substrates. △: Bleeding was observed at a printing rate of 60% in one of the printing substrates. ×: Bleeding was observed at a printing rate of 60% for both printing substrates.

[0160] <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 a 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 oven set at 70 °C, and the printed substrate after printing was put in 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 average value of the number of reciprocations was obtained to evaluate the water resistance. The evaluation criteria were as follows, and ◎, ○, and △ 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. ◎: The ink film did not peel off even after rubbing 20 times. ○: The ink film peeled off when rubbed 11 - 19 times. △: The ink film peeled off when rubbed 6 - 10 times. ×: The ink film peeled off even when the number of rubs was 5 times or less.

[0161] As shown in Table 2 above, the aqueous inkjet inks (sets) of Examples 1 to 57 having the configuration of the present invention were superior in ejection stability compared to the aqueous inkjet inks of Comparative Examples 1 to 8, 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 invention is an excellent aqueous inkjet ink that combines ejection stability, print image quality of printed matter, and water resistance.

Claims

1. An aqueous inkjet ink comprising a pigment, a polyether-modified siloxane surfactant, hexylene glycol, a binder resin, and an organic compound (A) (excluding pigments, polyether-modified siloxane surfactants, hexylene glycol, and resins), wherein the organic compound (A) consists only of carbon atoms, hydrogen atoms, and oxygen atoms and has a plurality of hydroxyl groups, the HLB value of the organic compound (A) is 2.5 to 5.2, the binder resin contains a resin (B-1) having a glass transition temperature of -70 to 35°C, the content of the resin (B-1) is 50% by mass or more based on the total mass of the resins contained in the aqueous inkjet ink.

2. The aqueous inkjet ink according to Claim 1, wherein the content mass of the resin (B-1) is 2 to 50 when the content mass of the polyether-modified siloxane surfactant is 1.

3. The aqueous inkjet ink does not contain a butylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular end is 1 to 4) and a pentylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular end is 1 to 4), or the total content of the butylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular end is 1 to 4) and the pentylene glycol monoalkyl ether-based water-soluble organic solvent (wherein the carbon number of the alkyl group at the molecular end is 1 to 4) is 50% by mass or less relative to the content of the hexylene glycol.

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

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