Aqueous inkjet ink and printed matter

Abstract

Provided is an aqueous inkjet ink which contains a pigment, a surfactant (A) and a water-soluble organic solvent (B). The surfactant (A) includes an acetylene diol-based surfactant (A1) which has an ethylene oxide structure and a propylene oxide structure and has an HLB value of 10 or less. The water-soluble organic solvent (B) includes an alkane diol (B1) having 3-5 carbon atoms and a glycol monoether (B2) having 4-10 carbon atoms. The mass ratio of the content of the alkane diol (B1) having 3-5 carbon atoms and the content of the glycol monoether (B2) having 4-10 carbon atoms ((B1) / (B2)) is 0.8-12.

Description

Water-based inkjet inks and printed materials

[0001] An embodiment of the present invention relates to an aqueous inkjet ink and a printed matter formed using the aqueous inkjet ink.

[0002] Digital printing is rapidly becoming more popular as printing runs become smaller and needs become more diverse. Digital printing does not require plates, so it can handle small runs, reduce costs, and enable the use of smaller printing equipment.

[0003] Inkjet printing is a type of digital printing method in which minute droplets of ink are ejected from an inkjet head and landed on a printing substrate (also referred to simply as "substrate" in this application) to form an image and / or characters on the printing substrate. Hereinafter, the printing substrate and the image and / or characters formed on the printing substrate by printing ink are collectively referred to as "printed matter." Note that the above "image" also includes solid images and seamless images such as checkerboard images. Inkjet printing is superior to other digital printing methods in terms of the size and cost of the printing device, running costs during printing, and ease of full-color printing, and has been increasingly used in industrial printing applications in recent years.

[0004] Inks used in inkjet printing methods vary widely, including oil-based, solvent-based, active energy ray-curable, and water-based inks. Until now, solvent-based and active energy ray-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks (inks containing water as the main component) due to concerns about and responses to harmful effects on the environment and people.

[0005] In recent years, there has been an increasing demand for expanded applications of water-based inks used in inkjet printing methods (also referred to as "aqueous inkjet inks" in this application) for packaging applications such as paper containers, labels, and packaging films. For such packaging applications, inks that can produce printed matter with high color reproducibility and print image quality, and that have properties durable enough for practical use, are required not only on poorly permeable substrates such as coated paper and art paper, but also on non-permeable substrates. Examples of such non-permeable substrates include polypropylene films (e.g., biaxially oriented polypropylene (OPP) films), polyethylene terephthalate (PET) films, and nylon films.

[0006] Most aqueous inkjet inks that have been put into practical use to date have been designed for printing on highly permeable substrates such as plain paper and specialty paper. When such aqueous inkjet inks, particularly those that have not undergone any of the processes described below, are used on non-permeable substrates, droplets that land on the substrate remain at high surface tension and do not spread. Furthermore, when adjacent aqueous inkjet ink droplets come into contact with each other in this state, a force acts on each droplet in a direction that reduces their surface area, resulting in beading. Beading is a phenomenon in which aqueous inkjet ink droplets attract each other and coalesce on the printing substrate, resulting in the appearance of a string of beads of different color shading. Printed materials that exhibit beading have significantly reduced print quality.

[0007] Furthermore, when printing on a non-permeable substrate, the aqueous inkjet ink does not penetrate and absorb into the substrate, resulting in insufficient drying of the impacted droplets and insufficient adhesion to the substrate. As a result, when the printed matter is stored in a rolled or stacked state, pressure is applied to the printed surface, causing blocking. Blocking is a phenomenon in which part of the ink layer is taken up by the printing substrate when the printing substrate to which the ink layer is attached is peeled off.

[0008] A common method for improving print image quality and blocking resistance (suppressing the occurrence of blocking) is to reduce the surface tension of aqueous inkjet inks. For example, surface tension can be reduced by adding a surfactant or a water-soluble organic solvent to the aqueous inkjet ink. However, the time it takes for a droplet of aqueous inkjet ink to land on a printing substrate and for another droplet to land in an adjacent position is typically only several hundred microseconds to several tens of milliseconds. Therefore, simply adopting the above-mentioned measures to reduce the static surface tension does not allow the droplets of aqueous inkjet ink to sufficiently wet and spread. As a result, droplets come into contact with each other while the surface tension remains high, resulting in beading.

[0009] For example, Patent Document 1 discloses an aqueous inkjet ink in which dynamic surface tension is controlled by using a polyoxyethylene alkyl ether surfactant. It also discloses that this aqueous inkjet ink suppresses feathering (a phenomenon in which the aqueous inkjet ink irregularly spreads along the fibers of a printing substrate such as fine paper), thereby producing printed matter with excellent print quality and also suppressing deterioration of ejection stability. Indeed, the aqueous inkjet ink is effective in improving print quality on permeable substrates such as those used in the examples of Patent Document 1. However, when the aqueous inkjet ink is used to print on the non-permeable substrate, beading occurs due to droplets coming into contact with each other in a state where they are not sufficiently wetted and spread.

[0010] Patent Literature 2 discloses an aqueous inkjet ink containing an acetylene diol surfactant having an HLB value of 3 or less and a water-soluble organic solvent having an HLB value of 8 or less. It also discloses that the use of this aqueous inkjet ink suppresses whiteout and aggregation unevenness caused by insufficient spreadability of the aqueous inkjet ink on a poorly permeable substrate, thereby producing printed matter with excellent print quality. Indeed, the use of the surfactant and the water-soluble organic solvent reduces image defects such as aggregation unevenness when printing on a poorly permeable substrate. However, when printing on a non-permeable substrate using this aqueous inkjet ink, the surfactant may remain on the surface of the ink layer, resulting in blocking. Furthermore, because the surfactant has a low HLB value and is poorly compatible with water, it is prone to being concentrated and oriented at the air-liquid interface above the nozzle of the inkjet head. As a result, for example, the aqueous inkjet ink may overflow from the nozzle during ejection, resulting in nozzle omission (a phenomenon in which the aqueous inkjet ink is not ejected from the nozzle) and reduced ejection linearity. Details of these issues will be described later.

[0011] JP 2012-211260 A JP 2017-165809 A

[0012] As described above, until now, there has been no aqueous inkjet ink that simultaneously satisfies all of the requirements for print image quality (suppression of beading), blocking resistance, and ejection stability at high levels, particularly for non-permeable substrates.

[0013] Therefore, one embodiment of the present invention provides an aqueous inkjet ink that has excellent ejection stability, suppresses beading even on non-permeable substrates, and can produce printed matter with excellent blocking resistance.

[0014] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by an aqueous inkjet ink having the following composition.

[0015] That is, one embodiment of the present invention relates to an aqueous inkjet ink. Another embodiment of the present invention relates to a printed matter obtained using the aqueous inkjet ink. More specifically, embodiments of the present invention include the following. However, the present invention is not limited to the following embodiments and includes various embodiments.

[0016] [1] An aqueous inkjet ink containing a pigment, a surfactant (A), and a water-soluble organic solvent (B), wherein the surfactant (A) comprises an acetylenic diol surfactant (A1) having a structure represented by the following general formula (1) and having an HLB value of 10 or less, the water-soluble organic solvent (B) comprises an alkanediol (B1) having 3 to 5 carbon atoms and a glycol monoether (B2) having 4 to 10 carbon atoms, and the mass ratio ((B1) / (B2)) of the content of the alkanediol (B1) having 3 to 5 carbon atoms to the content of the glycol monoether (B2) having 4 to 10 carbon atoms is 0.8 to 12.

[0017] General formula (1):

[0018] In general formula (1), R １ and R ２ each represents an alkyl group having 1 to 5 carbon atoms, which may be branched, EO represents an ethylene oxide group, and PO represents a propylene oxide group. Furthermore, m1, m2, n1, and n2 each represent an integer of 1 to 10, and the ratio (m1+n1):(m2+n2) is 1:9 to 9:1. However, the addition pattern of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be block or random.

[0019] [2] The aqueous inkjet ink according to [1], wherein the surfactant (A) further comprises a nonionic surfactant (A2) other than the acetylene diol surfactant (A1).

[0020] [3] The aqueous inkjet ink according to [1] or [2], wherein the content of the acetylene diol surfactant (A1) is 0.1 to 5.0 mass% of the total amount of the aqueous inkjet ink.

[0021] [4] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [3]. The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2023-089969, filed on May 31, 2023, the entire disclosure of which is incorporated herein by reference.

[0022] The aqueous inkjet ink according to one embodiment of the present invention has excellent ejection stability, and even when applied to a non-permeable substrate, it can suppress beading and provide a printed image with excellent blocking resistance.

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

[0024] As described above, the aqueous inkjet ink of this embodiment having the above-mentioned configuration can simultaneously achieve high levels of ejection stability, as well as beading suppression and blocking resistance in printed materials on non-permeable substrates, etc. Although the mechanism behind this is not clear, the inventors speculate as follows. However, the present invention is not limited to this speculation.

[0025] To suppress beading and improve print quality, it is necessary to reduce the surface tension of the ink immediately after landing. One method for achieving this is to use a surfactant that quickly orients itself to the droplet surface (air-liquid interface). Surfactants with low molecular weights and low water affinity are particularly effective in suppressing beading because they rapidly orient themselves to the air-liquid interface. Among these surfactants, acetylenic diol surfactants contain acetylene groups that do not undergo bond rotation within the molecule. This makes them less susceptible to structural deformation than other surfactants, such as polyoxyethylene alkyl ether surfactants. Therefore, even with a small amount added, a sufficient amount of acetylenic diol surfactant molecules can be oriented at the air-liquid interface. From the perspective of improving print quality, therefore, it is preferable to select an acetylenic diol surfactant with a low molecular weight and low water affinity. Examples of such compounds include unmodified acetylenic diol surfactants and ethylene oxide-modified acetylenic diol surfactants (low molar adducts), as used in Patent Document 2.

[0026] However, naturally, such surfactants are also present in large amounts on the surface of the ink layer. Furthermore, because of their low molecular weight, it is thought that the surfactant molecules move actively when affected by heat (e.g., ambient temperature) or humidity. Therefore, for example, when printed materials are rolled up and stored, blocking is likely to occur.

[0027] To prevent blocking, for example, increasing the molecular weight of the surfactant is effective. However, increasing the molecular weight of an ethylene oxide-modified acetylenic diol makes it too hydrophilic, which reduces the orientation speed to the gas-liquid interface and causes beading. Furthermore, increasing the molecular weight of an unmodified acetylenic diol surfactant makes it unable to exist stably in the aqueous inkjet ink, which may result in precipitation and deterioration of ejection stability.

[0028] Furthermore, the aqueous inkjet ink near the nozzle of the inkjet head also has an air-liquid interface. Therefore, the surfactant may be concentrated and oriented at the air-liquid interface, causing the aqueous inkjet ink to overflow from the nozzle. For example, if the overflow of the aqueous inkjet ink from the nozzle occurs and progresses during continuous ejection, it can cause ejection defects such as nozzle clogging and a decrease in the straightness of ejection.

[0029] As described above, although unmodified acetylenic diol surfactants and ethylene oxide-modified acetylenic diol surfactants (low molar adducts) are effective in improving print image quality, they have the problem of causing deterioration in properties such as blocking resistance and ejection stability.

[0030] In contrast, the aqueous inkjet ink of this embodiment contains, as the acetylenic diol surfactant, an acetylenic diol surfactant (A1) having a structure represented by the above general formula (1) and an HLB value of 10 or less. The acetylenic diol surfactant (A1) includes not only an ethylene oxide structure but also a propylene oxide structure. This propylene oxide structure has both hydrophilic and hydrophobic properties, and therefore, by using it together with the ethylene oxide structure to modify the acetylenic diol surfactant, precise control of the molecular weight and hydrophilicity / hydrophobicity (e.g., HLB value) becomes easier. In particular, by selecting and using an acetylenic diol surfactant (A1) having a structure represented by the above general formula (1) and an HLB value of 10 or less, it becomes possible to maintain hydrophobicity in a molecular weight range where blocking can be suppressed, and an extreme decrease in the orientation speed to the gas-liquid interface is prevented.

[0031] Furthermore, the alkanediol (B1) having 3 to 5 carbon atoms contained in the aqueous inkjet ink of this embodiment is thought to enhance the above-mentioned effect. The alkanediol (B1) having 3 to 5 carbon atoms contains multiple hydroxyl groups and has a small molecular weight. Therefore, while the alkanediol (B1) has a high affinity with water, it does not have excessive affinity with the acetylenic diol surfactant (A1) having an HLB value of 10 or less. The alkanediol (B1) having 3 to 5 carbon atoms also functions to retain moisture on the inkjet head nozzles. As a result, the alkanediol (B1) having 3 to 5 carbon atoms can contribute to improving ejection stability without interfering with the orientation of the acetylenic diol surfactant (A1).

[0032] Furthermore, the aqueous inkjet ink of this embodiment contains glycol monoethers (B2) having 4 to 10 carbon atoms, and the mass ratio of the alkanediols (B1) having 3 to 5 carbon atoms and the glycol monoethers (B2) having 4 to 10 carbon atoms is specified. Although the details are unclear, glycol monoethers having an alkylene oxide structure have a high affinity with the acetylenic diol surfactants (A1) also having ethylene oxide and propylene oxide structures. Furthermore, because the glycol monoethers (B2) having 4 to 10 carbon atoms have a small molecular weight, it is believed that the glycol monoether (B2) molecules exist in close proximity to the acetylenic diol surfactant (A1). As a result, excessive orientation of the acetylenic diol surfactant (A1) at the gas-liquid interface can be suppressed, and it is believed that the aqueous inkjet ink does not overflow from the nozzles even during continuous ejection, and favorable ejection stability can be maintained.

[0033] On the other hand, if the orientation of the acetylenic diol surfactant (A1) is suppressed, there is a risk of beading occurring. However, the glycol monoethers (B2) having 4 to 10 carbon atoms have a lower surface tension than water and other water-soluble organic solvents. Therefore, it is thought that within the droplets of the aqueous inkjet ink on the printing substrate, the glycol monoethers (B2) contribute to a decrease in surface tension together with the acetylenic diol surfactant (A1), thereby suppressing beading.

[0034] As described above, the ink having the configuration of the present invention can solve the above-mentioned problems simultaneously and at a high level.

[0035] Hereinafter, each component constituting the aqueous inkjet ink according to one embodiment of the present invention will be described in detail.

[0036] <Surfactant (A)> (Acetylenic diol surfactant (A1)) As described above, the aqueous inkjet ink of this embodiment contains, as a surfactant, an acetylenic diol surfactant (A1) having a structure represented by the following general formula (1) and having an HLB value of not more than 10. Because the acetylenic diol surfactant (A1) has an ethylene oxide structure and a propylene oxide structure, the molecular weight and hydrophilicity / hydrophobicity can be easily controlled.

[0037] General formula (1):

[0038] In general formula (1), R １ and R ２ each represents an alkyl group having 1 to 5 carbon atoms, which may be branched, EO represents an ethylene oxide group, and PO represents a propylene oxide group. Furthermore, m1, m2, n1, and n2 each represent an integer of 1 to 10, and the ratio (m1+n1):(m2+n2) is 1:9 to 9:1. However, the addition pattern of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be block or random.

[0039] In the above general formula 1, the values ​​of m1, n1, m2, and n2, as well as R １ and R２ By changing the structure of the compound, the HLB value is adjusted to be 10 or less. In particular, in order to obtain a compound having a suitable HLB value and molecular weight (each of which will be described in detail later), the value of m1+n1 in general formula (1) is preferably 2 to 10, and the value of m2+n2 is preferably 1 to 9. Furthermore, the ratio of the number of ethylene oxide structures to the number of propylene oxide structures, represented by (m1+n1):(m2+n2), is preferably 1:2 to 5:1, more preferably 1:1 to 4.5:1, and particularly preferably 1.2:1 to 4:1.

[0040] From the viewpoint of the orientation speed to the gas-liquid interface and the viewpoint of improving blocking resistance, the HLB value is 10 or less, preferably 4 to 9, and more preferably 5 to 8. An HLB value of 10 or less reduces the moisture absorption of the ink layer constituting the printed matter, leading to improved blocking resistance. Furthermore, by using the ink in combination with an alkanediol (B1) having 3 to 5 carbon atoms and a glycol monoether (B2) having 4 to 10 carbon atoms, it is possible to simultaneously suppress beading and improve blocking resistance and ejection stability.

[0041] The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that represent the hydrophilicity / hydrophobicity of a material. There are various methods for calculating the HLB value, such as the Griffin method, the Davis method, and the Kawakami method. In the present application, the value calculated using the Griffin method is used as the HLB value of the acetylene diol surfactant (A1).

[0042] The Griffin method uses the molecular weight of the target compound to determine the HLB value according to the following formula (2): The smaller the HLB value, the more hydrophobic the target compound is, and the larger the HLB value, the more hydrophilic the target compound is.

[0043] Formula (2): HLB value = 20 × (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material)

[0044] The acetylene diol surfactant (A1) having an HLB value of 10 or less can be a compound represented by the general formula (1). Specific examples include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 3,6-diisopropyl-2,7-dimethyloct-4-yne-3,6-diol, and octadec-1,1,2,3,4,5,6,7,8,9,9,10,11,12,13,14,15,16,17,18,19,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,59,59,59,50,51,52,54,55,58,59,51,52,53,54,55,55,56,57,58,59,59,59,59,59,50,51,52,54,55,57,58,59,59,59,59,50,51,52,52,53,54,55,57,58,59,59,59,50,51,52 Examples of the compounds include ethylene oxide and propylene oxide modified compounds such as cad-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, and 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol. The compounds listed above may be used alone or in combination of two or more. These compounds may be synthesized by known synthesis methods or commercially available products. Among these, from the viewpoint of compatibility with water and the glycol monoethers (B2), it is preferable to use compounds obtained by modifying 2,4,7,9-tetramethyl-5-decyne-4,7-diol and / or 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol with ethylene oxide and propylene oxide.

[0045] The molecular weight of the acetylenic diol surfactant (A1) having a structure represented by the above general formula (1) and an HLB value of 10 or less is preferably 300 to 1,200, more preferably 400 to 900, and even more preferably 450 to 700. The acetylenic diol surfactant (A1) having a molecular weight within the above range has a high orientation rate to the gas-liquid interface, and therefore can suppress beading and prevent deterioration of blocking resistance. Note that the molecular weight in this application refers to formula weight, which can be determined by calculation.

[0046] The content of the acetylene diol surfactant (A1) in the aqueous inkjet ink of this embodiment is preferably 0.1 to 5.0 mass %, more preferably 0.2 to 3.5 mass %, even more preferably 0.3 to 2.5 mass %, particularly preferably 0.5 to 2.0 mass %, and extremely preferably 0.5 to 1.5 mass % of the total amount of the aqueous inkjet ink. By using the acetylene diol surfactant (A1) in the above range, it is possible to simultaneously achieve high levels of beading suppression, ejection stability, and blocking resistance.

[0047] [Other Surfactants] The aqueous inkjet ink of this embodiment may further contain other surfactants other than the acetylene diol surfactant (A1) having an HLB value of 10 or less (i.e., other than the above (A1)).

[0048] In the aqueous inkjet ink of this embodiment, the other surfactant may be one or more selected from the group consisting of ionic (anionic or cationic) surfactants, amphoteric surfactants, and nonionic surfactants (excluding the acetylenic diol surfactant (A1)). In particular, from the viewpoint of compatibility with the glycol monoethers (B2) and the acetylenic diol surfactant (A1), it is preferable to use a nonionic surfactant other than the acetylenic diol surfactant (A1) (also simply referred to as "nonionic surfactant (A2)" in the present application) as the other surfactant.

[0049] <Nonionic Surfactant (A2)> Examples of the nonionic surfactant (A2) that can be used include acetylene diol surfactants (excluding the acetylene diol surfactant (A1)), acetylene monool surfactants, siloxane surfactants, fluorine-containing surfactants, polyoxyalkylene monoalkyl ether surfactants (wherein the oxyalkylene group is an oxyethylene group and / or an oxypropylene group and the number of oxyalkylene groups is 5 to 100 and / or the number of carbon atoms in the terminal alkyl group is 5 to 22); and the like. These other surfactants may be used alone or in combination of two or more.

[0050] Among these, it is preferable to use, as the nonionic surfactant (A2), one or more surfactants selected from the group consisting of acetylenic diol surfactants (excluding the acetylenic diol surfactant (A1)), siloxane surfactants, and polyoxyalkylene monoalkyl ether surfactants (wherein the oxyalkylene group is an oxyethylene group and / or an oxypropylene group and the number of oxyalkylene groups is 5 to 100 and / or the number of carbon atoms in the terminal alkyl group is 5 to 22). These surfactants are preferable because they function in the same way as glycol monoethers (B2) by being compatible with the acetylenic diol surfactant (A1) or by emulsifying the acetylenic diol surfactant (A1), and can be expected to improve both discharge stability and suppress beading.

[0051] Among the above, it is preferable to use a siloxane-based surfactant as the nonionic surfactant (A2). The siloxane-based surfactant has a high compatibility with the acetylene diol-based surfactant (A1), and can significantly improve the ejection stability. Furthermore, after droplets of the aqueous inkjet ink land on a printing substrate, the siloxane-based surfactant orients on the droplet surface with a delay from the orientation of the acetylene diol-based surfactant (A1). As a result, the droplets can be sufficiently wetted and spread, beading can be suppressed to a higher level, and improved blocking resistance can also be expected.

[0052] Furthermore, from the viewpoint of improving the blocking resistance and ejection stability of printed matter, it is preferable to use a siloxane-based surfactant and an acetylenic diol-based surfactant (excluding the acetylenic diol-based surfactant (A1)) in combination as the nonionic surfactant (A2). In one embodiment, the total content of the siloxane-based surfactant and the acetylenic diol-based surfactant (excluding the acetylenic diol-based surfactant (A1)) is preferably 20 to 850 mass%, and particularly preferably 40 to 400 mass%, relative to the content of the acetylenic diol-based surfactant (A1). When the total content is adjusted to fall within the above range, it is possible to easily improve the beading suppression effect and blocking resistance while realizing favorable print image quality.

[0053] In another embodiment, the content of the acetylenic diol surfactant (excluding the acetylenic diol surfactant (A1)) is preferably 10 to 250 mass %, and particularly preferably 25 to 120 mass %, relative to the content of the acetylenic diol surfactant (A1). When the content is adjusted as described above, the effects of the acetylenic diol surfactant (A1) can be suitably exhibited, and all of the suppression of beading and blocking, and improvement of discharge stability can be simultaneously achieved.

[0054] On the other hand, when a siloxane-based surfactant is used as the nonionic surfactant (A2), it is preferable to use it in combination with two or more siloxane-based surfactants with different orientation rates to the interface, from the viewpoint of suppressing beading and easily obtaining printed matter with excellent print quality. Since the orientation rate depends on the molecular structure of the surfactant, examples of the "two or more siloxane-based surfactants with different orientation rates" include two or more modified siloxane-based surfactants with different modified species and / or modified positions; and / or two or more siloxane-based surfactants with different mass-average molecular weights. Furthermore, examples of the "two or more modified siloxane-based surfactants with different modified species and / or modified positions" include a combination of a polyether-modified siloxane-based surfactant having a polyether structure in the side chain and a polyether-modified siloxane-based surfactant having a polyether structure at both ends of the molecular chain.

[0055] On the other hand, an example of the "two or more siloxane-based surfactants with different mass-average molecular weights" is a combination of siloxane-based surfactants whose difference in mass-average molecular weight is 800 to 15,000. From the viewpoint of obtaining printed matter with excellent print quality, the difference in mass-average molecular weight is more preferably 1,200 to 12,000, and particularly preferably 1,500 to 10,000. The mass-average molecular weight of the siloxane-based surfactant can be measured using gel permeation chromatography. Specifically, the measurement can be performed using, for example, a TSKgel column (manufactured by Tosoh Corporation) and an HLC-8120GPC (manufactured by Tosoh Corporation) equipped with an RI detector, using THF as the developing solvent.

[0056] The content of the nonionic surfactant (A2) in the aqueous inkjet ink of this embodiment is preferably 0.1 to 5.0 mass %, more preferably 0.2 to 2.5 mass %, even more preferably 0.4 to 2.0 mass %, and particularly preferably 0.4 to 1.5 mass % of the total amount of the aqueous inkjet ink. By using the nonionic surfactant (A2) within the above range, it is possible to achieve high levels of all of beading suppression, ejection stability, and blocking resistance.

[0057] Examples of commercially available acetylenic diol surfactants (excluding the acetylenic diol surfactant (A1)) that can be used as the nonionic surfactant (A2) include Surfynol 61, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420, 440, 465, 485, SE, SE-F, Dynol 604, and 607 (manufactured by Evonik), and Olfine E1004, E1010, E1020, PD-001, PD-002W, PD-004, PD-005, EXP. 4001, EXP. 4200, EXP. 4123, and EXP. 4300 (manufactured by Nissin Chemical Industry Co., Ltd.). The above-listed products may be used alone or in combination of two or more. These compounds may be synthesized by a conventionally known synthesis method or may be commercially available products.

[0058] Among these, from the viewpoint of compatibility with water, the alkanediols (B1), and the glycol monoethers (B2), and from the viewpoint of blocking resistance, it is preferable to use a compound obtained by modifying 2,4,7,9-tetramethyl-5-decyne-4,7-diol or 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol with ethylene oxide, such as Surfynol 465, 485, Dynol 604, 607, and Olfine E1010, 1020.

[0059] Examples of commercially available siloxane surfactants that can be used as the nonionic surfactant (A2) are shown below. BY16-201, FZ-77, FZ-2104, FZ-2110, FZ-2162, F-2123, L-7001, L-7002, S F8427, SF8428, SH3749, SH8400, 8032ADDITIVE, SH3773M (manufactured by Toray Dow Corning), TEGO Glide 100, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Twin 4000, TEGO Twin4100, TEGO Wet250, TEGO Wet260, TEGO Wet270, TEGO Wet280 (manufactured by Evonik), SAG-002, SAG-503A (manufactured by Nissin Chemical Industry Co., Ltd.), BYK-331, BYK-333, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-3420, BYK-UV3500, BYK-UV3510 (manufactured by BYK-Chemie), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-6004, KF-6011, KF-6012, KF-6013, KF-6015, KF-6016, KF-6017, KF-6043, KF-615A, KF-640, KF-642, and KF-643 (manufactured by Shin-Etsu Chemical Co., Ltd.). The above-listed products may be used alone or in combination of two or more. Furthermore, these compounds may be synthesized by conventionally known synthesis methods or may be commercially available products.

[0060] Examples of commercially available polyoxyalkylene monoalkyl ether surfactants that can be used as the nonionic surfactant (A2) include the Nonion series (manufactured by NOF Corporation), such as Nonion K-204, 220, 230, 2100W, P-208, 210, 213, S-202, 207, 215, 220, and 250, the Emulgen series (manufactured by Kao Corporation), the Tergitol L series, the Tergitol X series, and the Tergitol TWN series (manufactured by The Dow Chemical Company). The above-listed products may be used alone or in combination of two or more. These compounds may be synthesized by conventionally known synthesis methods, or commercially available products may be used.

[0061] The total content of surfactants contained in the aqueous inkjet ink of this embodiment is preferably 0.1 to 5 mass %, more preferably 0.2 to 4.5 mass %, even more preferably 0.3 to 4 mass %, and particularly preferably 0.4 to 3.5 mass %, based on the total amount of the aqueous inkjet ink.

[0062] <Water-soluble organic solvent (B)> The aqueous inkjet ink of this embodiment contains a water-soluble organic solvent (B). As described above, the water-soluble organic solvent (B) includes an alkanediol (B1) having 3 to 5 carbon atoms and a glycol monoether (B2) having 4 to 10 carbon atoms. In this specification, the term "water-soluble organic solvent" refers to a solvent that has a solubility of 1% by mass or more in water at 25°C and is a liquid at 25°C.

[0063] (C3-C5 Alkanediols (B1)) The C3-C5 alkanediols (B1) exhibit moisturizing properties without inhibiting the orientation of the acetylene diol surfactant (A1), and are therefore thought to contribute to improving ejection stability. Examples of the C3-C5 alkanediols (B1) that can be used include 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, and 2,2-dimethyl-1,3-propanediol. These compounds may be used alone or in combination of two or more.

[0064] The SP value of the alkanediols (B1) having 3 to 5 carbon atoms is 12.0 to 14.0 (cal / cm ３ ) １／２ It is preferable that the viscosity is 12.5 to 14.0 (cal / cm ３ ) １／２ If the alkanediol (B1) is within the above range, it will not have excessive affinity with the acetylenic diol surfactant (A1). As a result, the orientation of the acetylenic diol surfactant (A1) will not be excessively hindered, which not only improves the ejection stability but also contributes to the suppression of beading.

[0065] The "SP value" is an abbreviation for Solubility Parameter. In this specification, it refers to a value calculated by Fedor's estimation method (unit: cal / cm). ３ ) １／２ (Let us say) is used.

[0066] Furthermore, among the alkanediols (B1) having 3 to 5 carbon atoms (preferably alkanediols (B1) having the above-described SP value), it is particularly preferable to use 1,2-propanediol and / or 1,2-butanediol. These water-soluble organic solvents are highly hydrophilic but do not have excessive affinity with the acetylenic diol surfactant (A1). Therefore, the water-soluble organic solvents do not inhibit the orientation of the acetylenic diol surfactant (A1) at the gas-liquid interface, maximizing its effects, which is thought to facilitate the production of printed matter free of beading. Furthermore, after impacting the printing substrate, these water-soluble organic solvents volatilize quickly, resulting in printed matter with excellent drying properties and blocking resistance. In addition, these water-soluble organic solvents have the property of being less likely to disrupt the dispersion state of the pigment (described below), and can prevent deterioration of the storage stability of the aqueous inkjet ink, making them suitable for use.

[0067] The content of the alkanediol (B1) having 3 to 5 carbon atoms contained in the aqueous inkjet ink of this embodiment is preferably 5 to 35 mass %, more preferably 10 to 30 mass %, and even more preferably 10 to 25 mass %, of the total amount of the aqueous inkjet ink.

[0068] (C4 to C10 glycol monoethers (B2)) On the other hand, the aqueous inkjet ink of this embodiment contains a C4 to C10 glycol monoether (B2), which has high affinity with the acetylenic diol surfactant (A1) and can suppress excessive orientation, thereby improving ejection stability. Furthermore, the C4 to C10 glycol monoethers (B2) contribute to reducing the surface tension on the printing substrate together with the acetylenic diol surfactant (A1), thereby suppressing beading. Examples of glycol monoethers (B2) having 4 to 10 carbon atoms that can be used include ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether. These compounds may be used alone or in combination of two or more.

[0069] Among these, it is preferable to use one or more selected from diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether. It is even more preferable to use one or more selected from diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether. These water-soluble organic solvents do not have excessive affinity with water and are easily oriented at the gas-liquid interface. In addition, they have moderate affinity with the acetylenic diol surfactant (A1) (and, if used, the nonionic surfactant (A2)), and by adjusting the orientation speed of these surfactants at the gas-liquid interface, ejection stability is improved. Furthermore, they contribute to reducing the surface tension on the printing substrate together with the acetylenic diol surfactant (A1), thereby suppressing beading. In addition, these water-soluble organic solvents not only have excellent drying properties but also function as film-forming aids for the resins described below, thereby contributing to improved blocking resistance.

[0070] In particular, since the above-mentioned effects are significantly exhibited, in one embodiment, one or more compounds selected from the group consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether are preferably used as the glycol monoethers (B2). Propylene glycol monomethyl ether and / or propylene glycol monoethyl ether are particularly preferred. While propylene glycol monomethyl ether and propylene glycol monoethyl ether are compounds with small molecular weights, they contain a PO group, similar to the acetylenic diol surfactant (A1). Therefore, it is believed that an interaction occurs between these water-soluble organic solvents and the acetylenic diol surfactant (A1), resulting in orientation at the gas-liquid interface while maintaining a favorable compatibilized state. As a result, modest effects are exhibited in terms of discharge stability due to moisturizing or compatibilization, and beading suppression due to improved orientation speed.

[0071] The content of the glycol monoether (B2) having 4 to 10 carbon atoms in the aqueous inkjet ink of this embodiment is preferably from 0.5 to 20 mass%, more preferably from 1 to 15 mass%, and even more preferably from 2 to 10 mass%, of the total amount of the aqueous inkjet ink.

[0072] In the aqueous inkjet ink of this embodiment, from the viewpoint of controlling the affinity of the acetylenic diol surfactant (A1) and simultaneously achieving beading suppression, ejection stability, and blocking resistance, the mass ratio ((B1) / (B2)) of the content of the alkanediols (B1) having 3 to 5 carbon atoms to the content of the glycol monoethers (B2) having 4 to 10 carbon atoms is 0.8 to 12, more preferably 1 to 8, and even more preferably 1.5 to 5. Within the above range, the affinity of the acetylenic diol surfactant (A1) is optimized, and the beading suppression effect can be maximized. Furthermore, by suppressing concentrated orientation of the surfactant at the gas-liquid interface, ejection stability can also be improved. Furthermore, since the aqueous inkjet ink has excellent drying properties, deterioration of blocking resistance can also be prevented.

[0073] In order to simultaneously achieve all of improved ejection stability, suppressed beading, and improved blocking resistance, it is preferable to further consider the drying behavior of the water-soluble organic solvent. Specifically, the amount of energy required to evaporate the alkanediol (B1) having 3 to 5 carbon atoms is preferably 1.2 to 20 times, more preferably 2.5 to 16 times, and particularly preferably 3.5 to 13 times, the amount of energy required to evaporate the glycol monoether (B2) having 4 to 10 carbon atoms.

[0074] Although the detailed mechanism is unknown, by using an alkanediol (B1) having 3 to 5 carbon atoms and a glycol monoether (B2) having 4 to 10 carbon atoms in combination so that the energy ratio falls within the above range, it is possible to prevent the water-soluble organic solvent from volatilizing before the effects of controlling affinity with the acetylenic diol surfactant (A1), adjusting the orientation speed of the acetylenic diol surfactant (A1), and the like are achieved. Furthermore, as the aqueous inkjet ink dries on the printing substrate, the balance between the amount of the alkanediol (B1) and the amount of the glycol monoether (B2) does not fluctuate significantly. As a result, it is possible to improve ejection stability, suppress beading in printed materials printed on non-permeable substrates, and improve blocking resistance.

[0075] The energy required to evaporate the water-soluble organic solvent can be calculated by the following formula (3).

[0076] Formula (3): VE=(BP-25)×MP×SH

[0077] In the above formula (3), VE is the energy (cal) required to evaporate the target water-soluble organic solvent contained in the aqueous inkjet ink. BP is the boiling point (°C) of the water-soluble organic solvent at 1 atmosphere. MP is the content (mass%) of the water-soluble organic solvent in the aqueous inkjet ink. SH is the specific heat (cal / g°C) of the water-soluble organic solvent at 25°C. Furthermore, a value calculated by the Missenard estimation method can be used as the specific heat.

[0078] The Missenard estimation method uses the sum of values ​​determined according to the molecular structure and temperature of a target compound as the specific heat (cal / mol °C) at that temperature. However, the unit of the specific heat calculated by the Missenard estimation method is "cal / mol °C." Therefore, in the above formula (3), the specific heat value of the target compound obtained by the Missenard estimation method is divided by the molecular weight of the compound. Note that examples of values ​​at 25 °C determined according to the molecular structure are shown in Table 1.

[0079]

[0080] (Other Water-Soluble Organic Solvents) The aqueous inkjet ink of this embodiment may contain water-soluble organic solvents other than the alkanediol (B1) having 3 to 5 carbon atoms and the glycol monoether (B2) having 4 to 10 carbon atoms (referred to as "other water-soluble organic solvents" in the present application).

[0081] In the aqueous inkjet ink of this embodiment, the other water-soluble organic solvents may include alkanediols having 6 carbon atoms; alkanetriols (having 3 to 6 carbon atoms); polyoxyalkylene diols (having 2 to 4 oxyalkylene groups as oxyethylene or oxypropylene groups); glycol monoethers ((poly)oxyalkylene monoalkyl ethers) (having 1 to 4 oxyalkylene groups as oxyethylene or oxypropylene groups as oxyalkylene groups, and having 1 to 4 carbon atoms in the terminal alkyl group, those having 11 or more carbon atoms); glycol diethers ((poly)oxyethylene dialkyl ethers) (provided that the number of oxyalkylene groups is 1 to 4 and the number of carbon atoms in the terminal alkyl groups is 1 to 4); lactams (provided that the number of atoms constituting the lactam ring is 5 to 7, and an alkyl group having 1 to 2 carbon atoms, a hydroxyalkyl group having 1 to 2 carbon atoms, or a vinyl group may be bonded to the nitrogen atom and / or carbon atom constituting the lactam ring); alkanolamines (provided that the number of amino groups is 1, the number of hydroxyl groups is 1 to 3, and the number of carbon atoms is 3 to 9); and the like can be used. These other water-soluble organic solvents exemplified above may be used alone or in combination of two or more.

[0082] In the present application, the term "(poly)oxyalkylene" refers to oxyalkylene and polyoxyalkylene.

[0083] The total content of water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment is preferably 5 to 50 mass %, more preferably 9 to 40 mass %, even more preferably 12 to 35 mass %, and particularly preferably 15 to 30 mass %, of the total amount of the aqueous inkjet ink.

[0084] <Resin> The aqueous inkjet ink of this embodiment preferably contains a resin.

[0085] Generally, water-soluble resins and resin microparticles are known as the forms of resins used in aqueous inkjet inks. In the aqueous inkjet ink of this embodiment, the resin contained in the aqueous inkjet ink of this embodiment may be a water-soluble resin or resin microparticles. Furthermore, a combination of a water-soluble resin and resin microparticles may be used.

[0086] In this specification, a resin having a solubility of 1 g or more in 100 g of water at 25° C. is referred to as a "water-soluble resin," and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin." Furthermore, among the water-insoluble resins, a resin that is dispersed in water in the form of particles and has a volume-based median diameter (also referred to as "D50" in this application) of 10 to 1,000 nm is referred to as a "resin particle."

[0087] In this specification, D50 is a value measured in an environment of 25° C. using a dynamic light scattering particle size distribution analyzer such as the Nanotrac UPA-EX150 manufactured by Microtrac Bell.

[0088] Examples of resins that can be used in the aqueous inkjet ink of this embodiment include acrylic resins, styrene resins, maleic acid (anhydride)-based resins, styrene-maleic acid (anhydride) resins, olefin-maleic acid (anhydride) resins, urethane resins, polyester resins, vinyl chloride resins, vinyl chloride-vinyl acetate resins, polyolefin resins, vinyl alcohol resins, etc. These resins may be used alone or in combination of two or more.

[0089] In this specification, the term "acrylic resin" refers to a resin using an acrylic acid ester and / or a methacrylic acid ester as a polymerizable monomer (a styrene-based monomer may also be used). Furthermore, the term "maleic acid (anhydride)" refers to at least one selected from "maleic acid" and "maleic anhydride."

[0090] The resin is used for any purpose, such as a pigment dispersion purpose, a binder purpose, a wax purpose, a thickening purpose, etc. The resin may be used for a single purpose or may have multiple purposes. In particular, from the viewpoint of improving blocking resistance, the resin is preferably used for a binder purpose and / or a pigment dispersion purpose.

[0091] (Binder Resin) In one embodiment, it is preferable to add a resin used as a binder (also referred to as "binder resin" in the present application) to the aqueous inkjet ink in order to improve the coating film resistance and blocking resistance of the printed matter. When the aqueous inkjet ink of this embodiment contains a binder resin, the type of resin used as the binder resin may be one of those listed above. In particular, it is preferable that the binder resin is one or more types selected from the group consisting of acrylic resins, urethane resins, and polyester resins. Furthermore, the resin is preferably in the form of resin fine particles.

[0092] The content of the binder resin in the aqueous inkjet ink of this embodiment is preferably 0.1 to 20 mass %, more preferably 0.2 to 15 mass %, even more preferably 0.3 to 12 mass %, and particularly preferably 0.5 to 10 mass %, of the total amount of the aqueous inkjet ink.

[0093] (Pigment Dispersion Resin) When the aqueous inkjet ink of this embodiment contains a pigment as a colorant, the blocking resistance of the printed matter can be improved by using a resin used for pigment dispersion (also referred to herein as a "pigment dispersion resin"). In this case, the type of resin used as the pigment dispersion resin may be one of those listed above. In particular, the pigment dispersion resin is preferably one or more resins selected from the group consisting of styrene-maleic anhydride resins, olefin-maleic anhydride resins, and acrylic resins.

[0094] <Colorant> [Pigment] The aqueous inkjet ink of this embodiment contains a colorant. In addition, it is preferable that the colorant contains a pigment, as this will result in printed matter with high density or hiding power and excellent light resistance, water resistance, etc.

[0095] As the pigment, any conventionally known organic or inorganic pigment can be used, and for example, pigments represented by the following color index names can be used. Specifically, 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 can be used; as violet pigments, C.I. As orange pigments, C.I. Pigment Violet 19, 23, 29, 32, 36, 37, 42, 50; as orange pigments, C.I. Pigment Orange 1, 2, 3, 5, 7, 13, 14, 15, 16, 22, 34, 36, 38, 40, 43, 47, 48, 49, 51, 52, 53, 60, 61, 62, 64, 65, 66, 69, 71, 73; as blue pigments, C.I. Pigment Blue 15, 15:3, 15:4, 15:6, 16, 60, 64, 79; as green pigments, C.I. Pigment Green 7, 10, 36, 48; as yellow pigments, C.I. C.I. Pigment Yellow 1, 2, 3, 5, 12, 13, 14, 16, 17, 24, 73, 74, 83, 87, 93, 94, 95, 97, 98, 109, 110, 111, 112, 120, 126, 127, 128, 129, 137, 138, 139, 147, 150, 151, 154, 155, 166, 167, 168, 170, 180, 185, 213; 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 in combination of two or more. Furthermore, a solid solution consisting of two or more of the pigments listed above can also be used as a pigment.

[0096] The content of the pigment contained in the aqueous inkjet ink of this embodiment may be adjusted depending on the intended use of the printed matter produced using the aqueous inkjet ink. In one embodiment, the content of the pigment is preferably 0.5 to 30% by mass of the total amount of the aqueous inkjet ink. In the case of inks other than white aqueous inkjet inks (aqueous white inks), the content of the pigment is more preferably 1 to 15% by mass, and particularly preferably 1.5 to 10% by mass, in order to obtain printed matters with high density without deteriorating the jetting stability of the aqueous inkjet ink. On the other hand, in the case of aqueous white inks, the content of the pigment is more preferably 5 to 25% by mass, and particularly preferably 10 to 20% by mass, in order to obtain printed matters with high hiding power without deteriorating the jetting stability of the aqueous white ink.

[0097] <Other Components> The aqueous inkjet ink of this embodiment may contain, in addition to the components described above, a pH adjuster, a preservative, and other additives. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. For each of these components, one or more conventionally known compounds may be used.

[0098] <Water> The water contained in the aqueous inkjet ink of this embodiment is preferably ion-exchanged water and / or reverse osmosis water. The content of water contained in the aqueous inkjet ink is preferably 30 to 90 mass % of the total amount of the aqueous inkjet ink, and particularly preferably 45 to 85 mass %.

[0099] <Method for Producing Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. For example, when a water-insoluble colorant (water-insoluble colorant) is used as the colorant, the water-insoluble colorant is dispersed in a medium containing at least water (aqueous medium) to produce a water-insoluble colorant dispersion. On the other hand, when a water-soluble colorant (water-soluble colorant) is used as the colorant, the water-soluble colorant is dissolved in a water-based medium to produce an aqueous colorant solution. Then, water, a surfactant (A), a water-soluble organic solvent (B), and the like are added to the water-insoluble colorant dispersion and / or the aqueous water-soluble colorant solution, followed by thorough stirring and mixing, and then removing coarse particles by techniques such as filtration and centrifugation. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the above-described method.

[0100] <Characteristics of Aqueous Inkjet Ink> The aqueous inkjet ink of this embodiment preferably has a viscosity at 25°C of 3 to 15 mPa·s. Within this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from inkjet heads with ejection frequencies of approximately 4 to 10 kHz, but also from inkjet heads with high ejection frequencies of approximately 20 to 70 kHz. In particular, when the viscosity of the aqueous inkjet ink of this embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head with a design resolution of 600 dpi or higher is used. In this specification, the viscosity is measured at 25°C using a cone-plate rotational viscometer (E-type viscometer, cone angle 1°34') such as the TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

[0101] In order to obtain an aqueous inkjet ink that is excellent in ejection stability and print quality of printed matter, the aqueous inkjet ink of this embodiment preferably has a static surface tension of 18 to 35 mN / m, and particularly preferably 21 to 32 mN / m, at 25° C. In this specification, the static surface tension is a value measured in an environment of 25° C. using the Wilhelmy method (plate method) with an automatic surface tensiometer such as the CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0102] When the aqueous inkjet ink of this embodiment contains a water-insoluble colorant, in order to achieve both high levels of ejection stability and high levels of density or hiding power of the printed matter, the volume-based median diameter (D50) of the water-insoluble colorant is preferably 30 to 450 nm, more preferably 50 to 400 nm, and particularly preferably 70 to 350 nm.

[0103] <Aqueous Inkjet Ink Set> Although only one aqueous inkjet ink of this embodiment may be used alone, two or more aqueous inkjet inks may also be combined to form an aqueous inkjet ink set. Examples of such aqueous inkjet ink sets include a four-color aqueous inkjet ink set (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink); and a five-color aqueous inkjet ink set obtained by adding an aqueous white ink to the process color ink set. It is preferable that all of the aqueous inkjet inks constituting the aqueous inkjet ink set satisfy the requirements of the embodiment of the present invention described above.

[0104] <Ink-Pretreatment Liquid Set> The aqueous inkjet ink of this embodiment and the aqueous inkjet ink set described above can also be used in a form combined with a pretreatment liquid containing an aggregating agent (in the form of an ink-pretreatment liquid set). By applying a pretreatment liquid containing an aggregating agent to a printing substrate before printing with the aqueous inkjet ink, it is possible to form a layer (ink aggregation layer) that intentionally aggregates solid components contained in the aqueous inkjet ink. Then, by landing the aqueous inkjet ink on this ink aggregation layer, it is possible to prevent coalescence and color mixing of droplets of the aqueous inkjet ink, and significantly improve the print quality of the printed matter.

[0105] As the flocculant, for example, a water-soluble inorganic or organic salt containing a polyvalent metal ion, and a resin having a cationic group in which the cationic group equivalent is greater than the anionic group equivalent can be used.

[0106] <Inkjet Printing Method> The aqueous inkjet ink of this embodiment is used in the inkjet printing method described above. A printing method using the inkjet printing method typically includes an ink ejection step and a drying step of the ejected ink. In the above printing method, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). In addition, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0107] (Discharge Process) One example of an operation method for the inkjet head in the discharge process is a shuttle (scan) method, in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate, while discharging and recording the aqueous inkjet ink. Another example of an operation method is a single-pass method, in which the aqueous inkjet ink is discharged and recording is performed as the printing substrate passes under a fixedly disposed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may be either a shuttle method or a single-pass method. Of these, the single-pass method is preferably selected because it is less likely to cause deviation in the landing position of droplets of the aqueous inkjet ink, thereby improving the print quality of the printed matter.

[0108] The method of ejection from the inkjet head can also be selected from any known methods, such as a piezoelectric method that utilizes the volume change of a piezoelectric element, a thermal method that ejects aqueous inkjet ink by bubbles generated by heating a heater, and a valve method that ejects pressurized aqueous inkjet ink by opening and closing a nozzle cover (valve) with a solenoid.

[0109] The volume of droplets of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing drying load and improving print quality. Furthermore, from the viewpoint of improving print quality, it is preferable to adjust the printing conditions (specifically, the drive frequency and number of inkjet heads, and the printing speed). In one embodiment, the printing conditions may be adjusted so that the recording resolution of the printed matter is preferably 600 dpi or higher, more preferably 1200 dpi or higher.

[0110] (Drying Step) Examples of drying methods employed in the drying mechanism used in the drying step include heat drying, hot air drying, infrared drying (for example, infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. In the drying step, one or more of these methods can be selected and used as desired. Furthermore, when two or more of the above drying methods are used, the drying methods may be used separately (for example, consecutively) or simultaneously. For example, by using heat drying and hot air drying in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[0111] In particular, from the viewpoint of preventing bumping of the liquid components in the aqueous inkjet ink and obtaining printed matter with excellent print quality, when a heat drying method is employed, the drying temperature is preferably 35 to 100° C. When a hot air drying method is employed, the hot air temperature is preferably 50 to 250° C. From the same viewpoint, when an infrared drying method is employed, it is preferable that 50% or more of the integrated value of the total output of the irradiated infrared rays is in the wavelength region of 700 to 1500 nm.

[0112] <Printed Material> A printed material, which is one embodiment of the present invention, has a printing substrate and a printing layer containing an image or characters formed by printing the aqueous inkjet ink of this embodiment on the printing substrate. Printing can be suitably carried out according to an inkjet printing method. Details of the printing method and printing conditions are as described above. (Printed Material) The printing substrate onto which the aqueous inkjet ink of this embodiment is printed is not particularly limited, and any known substrate, such as a permeable substrate, a poorly permeable substrate, or a non-permeable substrate, can be used.

[0113] In this embodiment, the permeability of the printing substrate is determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. Specifically, the amount of pure water absorption measured by the following method for a contact time of 100 msec is 1 g / m ２ A printing substrate with a water absorption of less than 1 g / m is called an "impermeable substrate." ２ 6g / m or more ２ A printing substrate with a water absorption of less than 6 g / m is called a "hard-to-penetrate substrate." ２A printing substrate that satisfies the above criteria is referred to as a "permeable substrate." The water absorption of a printing substrate can be measured, for example, using a dynamic scanning absorptivity meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) set under the following conditions, using a printing substrate measuring approximately 15 to 20 cm square as a sample, in an environment of 23°C and 50% RH. Measurement method: Spiral scanning Measurement start radius: 20 mm Measurement end radius: 60 mm Contact time: 10 to 1,000 msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) Scanning interval: 7 mm Rotating table speed switching angle: 86.3 degrees Headbox conditions: width 5 mm, slit width 1 mm

[0114] Examples of permeable substrates include uncoated paper such as sawdust paper, medium-grade paper, fine paper, and recycled paper; fabrics such as cotton, synthetic fiber fabrics, silk, hemp, and nonwoven fabrics; leather; etc. Among these, uncoated paper such as sawdust paper, medium-grade paper, fine paper, and recycled paper is preferably used because it allows prints with excellent print quality to be obtained.

[0115] Examples of impermeable substrates or poorly permeable substrates include plastic films and sheets such as polyvinyl chloride sheets, polyethylene terephthalate (PET) films, polypropylene films, polyethylene films, polyethylene sheets, nylon films, nylon sheets, polystyrene films, polystyrene sheets, and polyvinyl alcohol films; coated papers such as coated paper, art paper, and cast paper; metals such as aluminum, iron, stainless steel, and titanium; and glass.

[0116] The printing substrates listed above may have a smooth or uneven surface. The printing substrates may be transparent, translucent, or opaque. Furthermore, the printing substrates may be in the form of rolls or sheets. Additionally, two or more of the printing substrates listed above may be bonded together and used as the printing substrate. A release adhesive layer or the like may be provided on the side opposite the printed surface, or an adhesive layer or the like may be provided on the printed surface after printing.

[0117] The printing surface of the printing substrates listed above may be subjected to surface modification such as corona treatment or plasma treatment. Surface modification is advantageous in that it improves the wetting and spreading properties of the aqueous inkjet ink of this embodiment, and provides a printed product with excellent print quality and drying properties, and with a uniform printed surface, it also provides good abrasion resistance and adhesion to the substrate.

[0118] The aqueous inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0119] <Production Example of Binder Resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 72.4 parts of 2-butanone and purged with nitrogen gas. The reaction vessel was heated to 80°C, and a mixture of 15 parts of styrene, 4.5 parts of methacrylic acid, 5.0 parts of 2-hydroxyethyl methacrylate, 20 parts of stearyl methacrylate, 55.5 parts of methyl methacrylate, and 4 parts of a polymerization initiator, V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise over 2 hours. After completion of the dropwise addition, the mixture was allowed to react at 80°C for 3 hours, after which 0.6 parts of V-601 was added, and the reaction was continued for another 2 hours at 80°C to obtain a solution of binder resin 1. The binder resin 1 solution was cooled to 50°C, and 4.7 parts of dimethylaminoethanol was added to neutralize the carboxyl groups, followed by the addition of 140 parts of water. Thereafter, the mixture was heated to 78°C or higher and azeotropically distilled with water to remove 2-butanone, and the solid content was adjusted to 30%, thereby obtaining an aqueous solution (solid content 30%) of binder resin 1. The weight average molecular weight of the binder resin 1 was measured using a GPC (HLC-8120GPC, manufactured by Tosoh Corporation) equipped with a TSKgel column (manufactured by Tosoh Corporation) and an RI detector, using THF as a developing solvent, and was found to be approximately 17,000.

[0120] In the present application, the term "aqueous solution" refers to a solution containing an aqueous solvent (a medium consisting of a liquid containing at least water) and components dispersed and / or dissolved in the aqueous solvent.

[0121] <Synthesis of acetylenic diol surfactant 1> Acetylene diol surfactant 1 was synthesized using the method described in Example 4 of JP-A No. 2001-215690. Acetylene diol surfactant 1 is a surfactant represented by the general formula (1), １ is a methyl group, R ２ is an isobutyl group, m1+n1 is 5, m2+n2 is 2, and it is a compound in which ethylene oxide groups and propylene oxide groups are added in block form. The HLB value of acetylene diol surfactant 1 is 7.8, and the molecular weight is 563.

[0122] <Synthesis of Acetylene Diol-Based Surfactants 2 to 11> Acetylene diol-based surfactants 2 to 11 were synthesized by using the methods described in Examples 6 and 14 of JP 2001-215690 A and further adjusting the amounts of ethylene oxide and propylene oxide used. The structures and HLB values ​​of acetylene diol-based surfactants 2 to 11 are as shown in Table 2.

[0123]

[0124] <Preparation of Pigment Dispersion> 450 g of carbon black ("PrinteX85" manufactured by Orion Engineered Carbons), 90 g of acrylic resin (a random polymer of styrene / acrylic acid / behenyl acrylate = 45 / 30 / 25 (mass ratio), in which all acid groups had been neutralized with dimethylaminoethanol, an acid value of approximately 230 mg KOH / g, and a mass average molecular weight of 20,000), and 2,460 g of water were placed in a mixing vessel (volume 10 L) equipped with a stirrer and stirred (premixed) for 1 hour. Next, circulatory dispersion of the mixture was initiated using a "Dynomill" (volume 0.6 L) manufactured by Shinmaru Enterprises, Inc., filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. The D50 of the mixture was measured using the above-mentioned device at regular intervals (e.g., every hour), and the circulatory dispersion was terminated when the D50 reached 120 nm or less, thereby producing a pigment dispersion.

[0125] <Production of aqueous inkjet inks> Using the pigment dispersions produced by the method described above, each raw material was charged into a mixing vessel equipped with a stirrer so as to obtain the formulation shown in each column of Table 3. After charging, the mixture was heated to 50°C and further mixed for 1 hour, and then filtered through a membrane filter with a pore size of 0.8 μm to produce aqueous inkjet inks 1 to 60.

[0126] When producing the aqueous inkjet ink, each raw material was added while stirring the mixture in the mixing vessel. The raw materials were added in the order listed in each column of Table 3, starting with the component listed in the top row. However, when producing an aqueous inkjet ink that did not contain one or more of these components, that component was not added, and the next component was added in the order listed. For components containing two or more raw materials, the order of addition of the raw materials within that component was arbitrary.

[0127]

[0128]

[0129]

[0130]

[0131] The meanings of the abbreviations and details of the product names listed in Table 3 above are as follows. In Table 3, "bp" represents the boiling point (unit: °C), and "HLB" represents the HLB value. 1,2-PD: 1,2-propanediol (SP value: 13.5 (cal / cm ３ ) １／２ , boiling point: 188°C, specific heat: 0.574 cal / g °C) 1,2-BD: 1,2-butanediol (SP value: 12.8 (cal / cm ３ ) １／２ , boiling point: 191°C, specific heat: 0.559 cal / g °C) 1,3-BD: 1,3-butanediol (SP value: 12.8 (cal / cm ３ ) １／２ , boiling point: 207°C, specific heat: 0.559 cal / g °C) 1,5-PentD: 1,5-pentanediol (SP value: 12.4 (cal / cm ３ ) １／２, boiling point: 239°C, specific heat: 0.526 cal / g °C) Gly: glycerin (SP value: 16.4 (cal / cm ３ ) １／２ , boiling point: 290°C, specific heat: 0.539 cal / g °C) DEG: diethylene glycol (SP value: 15.0 (cal / cm ３ ) １／２ , boiling point: 244°C, specific heat: 0.519 cal / g °C) EB: ethylene glycol monobutyl ether (SP value: 10.8 (cal / cm ３ ) １／２ , boiling point: 171°C, specific heat: 0.519 cal / g °C) PM: propylene glycol monomethyl ether (SP value: 11.3 (cal / cm ３ ) １／２ , boiling point: 121°C, specific heat: 0.557 cal / g °C) PE: propylene glycol monoethyl ether (SP value: 10.9 (cal / cm ３ ) １／２ , boiling point: 132°C, specific heat: 0.547 cal / g °C) PnP: propylene glycol monopropyl ether (SP value: 10.7 (cal / cm ３ ) １／２ , boiling point: 150°C, specific heat: 0.539 cal / g°C)

[0132] PnB: Propylene glycol monobutyl ether (SP value: 10.4 (cal / cm ３ ) １／２ , boiling point: 170°C, specific heat: 0.533 cal / g °C) MDG: diethylene glycol monomethyl ether (SP value: 11.2 (cal / cm ３ ) １／２ , boiling point: 193°C, specific heat: 0.513 cal / g °C) EDG: diethylene glycol monoethyl ether (SP value: 10.9 (cal / cm ３ ) １／２ , boiling point: 202°C, specific heat: 0.510 cal / g °C) BDG: diethylene glycol monobutyl ether (SP value: 10.5 (cal / cm ３ ) １／２, boiling point: 231°C, specific heat: 0.505 cal / g °C) HDG: diethylene glycol monohexyl ether (SP value: 10.2 (cal / cm ３ ) １／２ , boiling point: 258°C, specific heat: 0.501 cal / g °C) TEB: triethylene glycol monobutyl ether (SP value: 10.3 (cal / cm ３ ) １／２ , boiling point: 278°C, specific heat: 0.497 cal / g°C)

[0133] Surfynol 440: an acetylene diol surfactant manufactured by Evonik Japan (in general formula (1), R １ is a methyl group, R ２ is an isobutyl group, m1+n1 is 3 to 4, and m2+n2 is 0, HLB value: 8.1 (average value)) Surfynol 485: an acetylene diol surfactant manufactured by Evonik Japan Co., Ltd. (in general formula (1), R １ is a methyl group, R ２ is an isobutyl group, m1 + n1 is 30, and m2 + n2 is 0, HLB value: 17.1)

[0134] TEGO Wet 280: a siloxane-based surfactant manufactured by Evonik Japan BYK-3420: a siloxane-based surfactant manufactured by BYK Japan TEGO Glide 100: a siloxane-based surfactant manufactured by Evonik Japan TEGO Glide 440: a siloxane-based surfactant manufactured by Evonik Japan

[0135] Emal 20C: Polyoxyethylene (3) lauryl ether sodium sulfate aqueous solution (solid content 25%, anionic surfactant manufactured by Kao Corporation) Proxel GXL: 1,2-benzisothiazol-3-one dipropylene glycol aqueous solution (1,2-benzisothiazol-3-one:dipropylene glycol:water=2:6:2, preservative manufactured by Arch Chemicals)

[0136] <Preparation of Printed Material> An inkjet printing apparatus was prepared in which a Kyocera Corporation inkjet head "KJ4B-1200" (design resolution 1,200 dpi, nozzle diameter 20 μm) was installed above a conveyor, and the inkjet head was filled with the aqueous inkjet ink listed in Table 2. Furthermore, a piece of OPP film pre-cut to A4 size (21 cm wide x 30 cm long) was fixed onto the conveyor as a printing substrate. The conveyor was then driven at a speed of 50 m / min, and as the printing substrate passed below the installation location of the inkjet head, the aqueous inkjet ink was ejected at a drop volume of 2 pL to print an image. The printed printing substrate was then immediately placed in a constant temperature incubator set at 70°C and dried for 1 minute to produce a printed material.

[0137] The following two types of prints were produced using the above method. For each aqueous inkjet ink, the following two types of prints were produced: Solid print: a print with a coverage of 100% (width 15 cm x length 30 cm) Gradient print: a print in which a gradation image with a coverage of 5-80% was printed in an area of ​​10 cm width x 30 cm length.

[0138] [Examples 1 to 51, Comparative Examples 1 to 9] Using the printed matter produced by the above-described method, the following evaluations 1 and 2 were carried out. Furthermore, using the above-described aqueous inkjet ink, the following evaluation 3 was carried out. The results of these evaluations are shown in Table 3.

[0139] <Evaluation 1: Beading Evaluation> The gradation print produced by the method described above was visually observed, and beading was evaluated by checking the printing rate at the point where unevenness in density began to be observed. The evaluation criteria were as follows, with a rating of "C" or higher being deemed usable. (Evaluation criteria) AA: No unevenness in density was observed even at a printing rate of 90%. A: No unevenness in density was observed at a printing rate of 80%, but unevenness in density was observed at a printing rate of 70%. B: No unevenness in density was observed at a printing rate of 70%, but unevenness in density was observed at a printing rate of 80%. C: No unevenness in density was observed at a printing rate of 60%, but unevenness in density was observed at a printing rate of 70%. D: Unevenness in density was observed at a printing rate of 60%.

[0140] <Evaluation 2: Evaluation of Blocking Resistance> The solid print produced by the method described above was cut into a 4 cm x 4 cm square, and then the printed surface was superimposed on the non-printed surface of the same printing substrate (OPP film) as that used for printing. Next, this superimposed piece was used as a test piece, and a blocking test was carried out using a constant load permanent deformation tester ("CO-201" manufactured by Tester Sangyo Co., Ltd.). The conditions for the blocking test were a load of 10 kg / cm ２The test was conducted at an ambient temperature of 40°C, an ambient humidity of 80% RH, and a standing time of 36 hours. After 24 hours, the test piece was removed from the constant-load permanent deformation tester, and the overlapping printing substrate was instantaneously peeled off while maintaining a 90-degree angle. Blocking resistance was evaluated based on the feel upon peeling (peel resistance) and the appearance of the printed surface after peeling (visual inspection). The evaluation criteria were as follows, and a rating of "B" or higher was deemed usable. (Evaluation criteria) AA: There was no resistance to peeling, and no part of the aqueous inkjet ink layer adhered to the non-printed surface of the printed substrate. A: There was slight resistance when peeling, but no part of the aqueous inkjet ink layer adhered to the non-printed surface of the printed substrate. B: Part of the aqueous inkjet ink layer adhered to the non-printed surface of the printed substrate, and the extent was 10% or less of the area of ​​the overlapped parts. C: Part of the aqueous inkjet ink layer adhered to the non-printed surface of the printed substrate, and the extent was more than 10% but 30% or less of the area of ​​the overlapped parts. D: Part of the aqueous inkjet ink layer adhered to the non-printed surface of the printed substrate, and the extent was more than 30% of the area of ​​the overlapped parts.

[0141] <Evaluation 3: Evaluation of ejection stability> The inkjet printing device used to produce the printed matter was filled with the aqueous inkjet inks listed in Table 2. A nozzle check pattern was printed, and after confirming that there were no missing nozzles, 300 solid prints were produced using the method described above. Thereafter, a nozzle check pattern was printed again, and the number of missing nozzles was visually counted to evaluate the ejection stability. The evaluation criteria were as follows, and a rating of "B" or higher was deemed practically usable. (Evaluation criteria) AA: No missing nozzles at all A: 1 to 9 missing nozzles B: 10 to 19 missing nozzles C: 20 to 49 or more missing nozzles D: 50 or more missing nozzles

[0142] As shown in Table 3 above, the aqueous inkjet inks of Examples 1 to 51 having the configuration of the present invention were superior in ejection stability compared to the inks of Comparative Examples 1 to 9. Furthermore, the printed matter exhibited good suppression of beading (image quality) and also had excellent anti-blocking properties.

Claims

1. An aqueous inkjet ink containing a pigment, a surfactant (A), and a water-soluble organic solvent (B), wherein the surfactant (A) comprises an acetylene diol surfactant (A1) having a structure represented by the following general formula (1) and an HLB value of 10 or less, the water-soluble organic solvent (B) comprises an alkanediol (B1) having 3 to 5 carbon atoms and a glycol monoether (B2) having 4 to 10 carbon atoms, and the mass ratio ((B1) / (B2)) of the content of the alkanediol (B1) having 3 to 5 carbon atoms to the content of the glycol monoether (B2) having 4 to 10 carbon atoms is 0.8 to 12. General formula (1): (In the general formula (1), R １ and R ２ each represents an alkyl group having 1 to 5 carbon atoms which may be branched, EO represents an ethylene oxide group, and PO represents a propylene oxide group. In addition, m1, m2, n1, and n2 each represent an integer of 1 to 10, and (m1+n1):(m2+n2)=1:9 to 9:

1. However, the addition pattern of the ethylene oxide groups and propylene oxide groups in the parentheses may be block or random.) 2. The aqueous ink-jet ink according to claim 1, wherein the surfactant (A) further comprises a nonionic surfactant (A2) other than the acetylene diol surfactant (A1).

3. The aqueous inkjet ink according to claim 1 or 2, wherein the content of the acetylene diol surfactant (A1) is 0.1 to 5.0 mass % of the total amount of the aqueous inkjet ink.

4. A printed matter obtained by printing with the aqueous inkjet ink according to claim 1 or 2.

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