Aqueous inkjet ink and printed matter

Abstract

To provide an aqueous inkjet ink excellent in remelting property and discharge stability, and excellent in a printing image quality relative to various printing substrates.SOLUTION: An aqueous inkjet ink which contains pigment particles, a surface active agent and an organic solvent is such that: the pigment particles contain pigment and pigment dispersion resin; the pigment dispersion resin has a bridge structure; the surface active agent contains an acetylenediol-based surface active agent (A-1) having an actual measurement HLB value of 6-9, and a siloxane-based surface active agent (A-2) having an actual measurement HLB value of 8-14; and the organic solvent contains 5-8C alkanediol (excluding 5-8C 1,2-alkanediol), and / or (di)propylene glycol monoalkyl ether represented by a specific structural formula.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] The inkjet printing method is a recording method in which ink droplets are directly ejected from a fine nozzle and adhered to a printing substrate to obtain characters and / or images. The inkjet printing method not only has the advantages of low noise of the apparatus and good operability, but also has many advantages such as easy full-colorization, low cost of the printing apparatus, and the ability to print non-contact with various printing substrates, so it has become very popular. In particular, in recent years, it has been widely used not only for household use in offices and homes, but also for commercial printing and industrial printing applications. Among them, the demand for inkjet inks (aqueous inkjet inks) containing water as a main component for the purpose of reducing the environmental impact and the burden on workers is increasing more and more.

[0003] The above "image" also includes seamless images such as solid images and checkered images.

[0004] Aqueous inkjet inks have been developed for a long time using plain paper and special paper as printing substrates. In these applications, it is premised that the liquid component of the aqueous inkjet ink is absorbed into the printing substrate. Therefore, when the above aqueous inkjet ink is printed on a poorly absorbent printing substrate such as those used in the above commercial printing and industrial printing applications, the image bleeds and a printed matter that can withstand actual use cannot be produced.

[0005] For example, coated paper, which is a poorly absorbent printing substrate, has low absorbency for liquid components. Therefore, during printing, if the next droplet lands adjacent to the droplet of the water-based inkjet ink that has landed first before the previously landed droplet dries, a phenomenon (beading) where adjacent droplets coalesce easily occurs. Beading causes color mixing bleeding in printed matter. In addition, some poorly absorbent printing substrates including coated paper have a low surface free energy. When printing on such a printing substrate, it is difficult for the water-based inkjet ink to spread wet on the surface of the printing substrate, which easily leads to the occurrence of white spots (a phenomenon where spots and / or streaks of areas where the water-based inkjet ink does not adhere occur on the printing substrate).

[0006] As a method for improving the above beading, a method of increasing the drying property of the water-based inkjet ink and drying the previously landed droplet before the next droplet lands can be considered. On the other hand, a water-based inkjet ink with high drying property easily dries near the nozzle. As a result, there is a risk that the dried film of the water-based inkjet ink adheres to the outlet of the nozzle. If this adhered dried film continues to exist at the nozzle outlet, it may cause deterioration of the landing accuracy of the water-based inkjet ink and nozzle clogging. Therefore, it is preferable that the water-based inkjet ink used in the inkjet printing method has "redissolvability" that can dissolve the above dried film. However, it can be said that imparting redissolvability to the water-based inkjet ink is an extremely difficult task.

[0007] Also, as another method for improving the above beading, there is a method of reducing the surface tension of the water-based inkjet ink. Generally, highly hydrophobic surfactants and organic solvents are used.

[0008] For example, Patent Document 1 discloses an inkjet recording ink composition containing three types of acetylene diol surfactants with different structures. According to Patent Document 1, it is said that an image with excellent print quality (color unevenness, aggregation, bleeding) and fixing properties (scratch resistance) can be recorded at high speed on various printing base materials with different absorbencies. Further, Patent Document 2 discloses an aqueous ink composition containing a nonionic surfactant with an HLB value of 4 to 14. According to Patent Document 2, for an offset medium on which offset ink may be printed, it is said that a printed matter with excellent wetting spreadability, fineness, printing density, water resistance, rubbing resistance (scratch resistance), etc., and without aggregation can be obtained.

[0009] On the other hand, Patent Document 3 discloses an aqueous ink for inkjet printing aimed at simultaneously solving the above-mentioned redissolubility (redispersibility) and color mixing bleeding. Specifically, Patent Document 3 shows an aqueous ink containing a pigment, a polymer dispersant (preferably including a polymer crosslinked with a crosslinking agent), and a specific water-soluble organic solvent. Further, in Example 2 of Patent Document 3, a specific example of an aqueous ink containing pigment particles containing a polymer dispersant having a crosslinked structure, "Surfynol 440" which is an acetylene diol surfactant, "Silface SAG005" which is a siloxane surfactant, and a water-soluble organic solvent such as 1,6-hexanediol is shown (see paragraph numbers 0068, 0072, Table 2, etc. of Patent Document 3).

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] On the other hand, in the water-based inkjet inks disclosed in Patent Documents 1 and 2 above, the ejection stability, which can be said to be an essential requirement for use in the inkjet printing method, has not been evaluated. Although details will be described later, depending on the materials used in combination, the effects of the highly hydrophobic materials described above may not be fully exhibited, and the ejection stability of the water-based inkjet ink may deteriorate.

[0012] In addition, when the present inventors evaluated the water-based inkjet ink having the configuration of Example 2 of Patent Document 3, although the redissolvability was good, the shape of the droplets of the water-based inkjet ink became distorted (inferior dot roundness), and it was found that white spots occurred depending on the printing conditions.

[0013] As described above, until now, there has been no water-based inkjet ink that simultaneously satisfies all of the ejection stability, redissolvability, dot roundness, and ink wettability (reduction of white spots) at a high level.

[0014] Therefore, in one embodiment of the present invention, an object is to provide a water-based inkjet ink that is excellent in redissolvability and ejection stability and has excellent print quality for various printing substrates. In addition, in another embodiment of the present invention, an object is to provide a printed matter having excellent print quality for various printing substrates.

Means for Solving the Problems

[0015] Based on the background as described above, as a result of intensive studies by the present inventors, the following water-based inkjet ink was found, and the present invention was completed.

[0016] That is, one embodiment of the present invention is a water-based inkjet ink containing pigment particles, a surfactant, and an organic solvent, wherein the pigment particles contain a pigment and a pigment dispersion resin, the pigment dispersion resin has a crosslinked structure, The surfactant includes an acetylene diol-based surfactant (A-1) with a measured HLB value of 6 to 9 and a siloxane-based surfactant (A-2) with a measured HLB value of 8 to 14. The organic solvent includes an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or a glycol monoether represented by the following general formula 1, and relates to an aqueous inkjet ink. General formula 1: R 1 -(O-CH(CH3)-CH2) n -OH (In general formula 1, R 1 is an alkyl group having 2 to 4 carbon atoms, and n is 1 or 2) Another embodiment of the present invention relates to a printed matter printed with the aqueous inkjet ink.

Effects of the Invention

[0017] The aqueous inkjet ink according to one embodiment of the present invention has excellent redissolvability and ejection stability, and has an effect of excellent print quality on various printing substrates, for example, coated paper. Further, the printed matter according to another embodiment of the present invention has an effect of excellent print quality on various printing substrates.

Modes for Carrying Out the Invention

[0018] 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 modified within the range not changing the essential part of the present invention.

[0019] The aqueous inkjet ink of the present embodiment is excellent in redissolvability and ejection stability, and is excellent in print quality for various printing substrates, particularly coated paper. Although the mechanism is not clear, the present inventors presume as follows. However, the present invention is not limited by the following presumption.

[0020] First, the redissolvability will be described. As described above, if the aqueous inkjet ink present near the nozzle dries and the dried film adheres to the outlet of the nozzle, it will cause deterioration of the ejection stability of the aqueous inkjet ink. Therefore, it is preferable that the aqueous inkjet ink has redissolvability. On the other hand, the inventors of the present invention have found that, as one method for improving the above redissolvability, it is important that the pigment dispersion resin that adsorbs and / or coats the pigment does not desorb even after the liquid component in the inkjet ink has evaporated. In the embodiment of the present invention, by using a pigment coated with a pigment dispersion resin having a crosslinked structure, the desorption of the pigment dispersion resin is suppressed, leading to an improvement in redissolvability. In addition, the aqueous inkjet ink of the present embodiment is likely to return the dried film adhered to the outlet of the nozzle to the aqueous inkjet ink, so that it also has excellent ejection stability. Furthermore, it is possible to prevent the phenomenon that a surfactant described later adsorbs to the desorbed pigment dispersion resin and the interfacial orientation of the surfactant is inhibited. And since these surfactants can fully exhibit their functions, it is considered that the wettability of the aqueous inkjet ink is improved and the printing image quality is improved.

[0021] Next, the printing image quality will be described. Generally, surface tension is cited as a factor affecting the printing image quality. The surface tension of the aqueous inkjet ink is mainly controlled by a surfactant. As an example, acetylene diol-based surfactants, siloxane-based surfactants, etc. are used as the surfactant.

[0022] The inventors have found that by using an acetylene diol surfactant (A-1) with a measured HLB value of 6 to 9 and a siloxane surfactant (A-2) with a measured HLB value of 8 to 14, the wettability of the aqueous inkjet ink with respect to the printing substrate is dramatically improved. The acetylene diol surfactant (A-1) with a measured HLB value of 6 to 9 has a low affinity for water and rapidly orientates at the interface. Therefore, when the ink droplets of the aqueous inkjet ink land on the printing substrate, an effect of significantly improving the wettability of the aqueous inkjet ink can be expected. However, when using only the acetylene diol surfactant (A-1), it is difficult to uniformly orient it at the interface, resulting in deterioration of dot roundness and unevenness in the solid portions, and the printed image quality becomes insufficient.

[0023] Therefore, in the embodiments of the present invention, an acetylene diol surfactant (A-1) with a measured HLB value of 6 to 9 and a siloxane surfactant (A-2) with a measured HLB value of 8 to 14 are used in combination to achieve improvement in dot roundness and unevenness. Although the detailed principle is unknown, the siloxane surfactant (A-2) is a surfactant with excellent surface tension reducing ability, similar to the acetylene diol surfactant. On the other hand, due to its high measured HLB value, it is considered to orient at the gas-liquid interface later than the acetylene diol surfactant (A-1). As a result, it is considered that the siloxane surfactant (A-2) orients to eliminate the non-uniformity of orientation caused by the acetylene diol surfactant (A-1), contributing to the uniform spread of ink droplets of the aqueous inkjet ink and the reduction of unevenness in the solid parts. Although the details will be described later, as a preferred embodiment, by using a gemini-type siloxane surfactant as the above siloxane surfactant (A-2), the surface tension reducing ability can be particularly improved. As a result, the wettability of the aqueous inkjet ink containing the gemini-type siloxane surfactant can be significantly improved, and the print quality can be greatly improved. Further, as a preferred embodiment, a both-end polyether-modified siloxane surfactant can also be used as the above siloxane surfactant (A-2). In this case, although the detailed principle is unknown, in addition to the uniform wetting spread on the printing substrate, an improvement in ejection stability can also be achieved.

[0024] On the other hand, when a pigment coated with a pigment dispersion resin having the above cross-linked structure is used in combination with an acetylene diol surfactant and a siloxane surfactant, pinholes (hole-like missing parts generated at the locations where the aqueous inkjet ink should be printed) may occur in the printed matter due to poor compatibility. Moreover, in the aqueous inkjet ink using the above components in combination, the ejection stability may also deteriorate. One of the reasons for the deterioration of the ejection stability is that when the liquid component volatilizes near the nozzle of the inkjet head, the above compatibility balance is disrupted, and in the aqueous inkjet ink present near the nozzle, it is considered that the surfactant is non-uniformly oriented.

[0025] As a result of intensive studies by the present inventors, it has been found that the above-described components are further used in combination with an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or a glycol monoether represented by the above general formula (1). By using these compounds in combination with the acetylene diol-based surfactant and the siloxane-based surfactant, it is considered that the two are more likely to be compatibilized. In addition, since the alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or the glycol monoether represented by the above general formula (1) are all compounds having a low surface tension, the acetylene diol-based surfactant and the siloxane-based surfactant that are compatible with these compounds are likely to be uniformly oriented over the entire surface of the printed matter. As a result, it is considered that pinholes are suppressed in the printed matter. Furthermore, in the inkjet head, it is considered that the meniscus of the aqueous inkjet ink is stabilized and the ejection stability is also improved.

[0026] As described above, in order to simultaneously and highly solve the above-described problems, the aqueous inkjet ink of the present embodiment is essential.

[0027] Note that the water-based inkjet inks specifically disclosed in Patent Documents 1 and 2 described above differ from the present invention in that they do not use crosslinked polymer particles containing a pigment. Further, Patent Documents 1 and 2 do not describe or suggest using a polymer having a crosslinked structure as a dispersion polymer, and that the use of the polymer having such a crosslinked structure improves redissolubility and ejection stability, and further enables the full expression of the effect of a surfactant. On the other hand, the acetylene diol-based surfactant "Surfynol 440" specifically used in the examples of Patent Document 3 (particularly Example 2) has a measured HLB value of 10.5 (see also the examples described later). Therefore, the water-based inkjet ink specifically disclosed in the above examples differs from the water-based inkjet ink of the present embodiment in that it does not contain an acetylene diol-based surfactant (A-1) having a measured HLB value of 6 to 9. Further, as described above, Patent Document 3 aims to improve redissolubility (redispersibility) and color mixing bleeding, but there is no description regarding dot roundness and whiteout, which are problems of the embodiments of the present invention. In particular, there is no description or suggestion in Patent Document 3 regarding the fact that a printed matter excellent in dot roundness can be obtained by using a combination of an acetylene diol-based surfactant (A-1) and a siloxane-based surfactant (A-2) having a specific measured HLB value.

[0028] Subsequently, each component that the water-based inkjet ink according to an embodiment of the present invention may contain will be described in detail below.

[0029] <Pigment particles> The water-based inkjet ink of the present embodiment contains pigment particles. Further, the pigment particles contain a pigment and a pigment dispersion resin having a crosslinked structure.

[0030] In this embodiment, "the pigment-dispersing resin has a crosslinked structure" means that a crosslinked structure is formed between the molecules of the pigment-dispersing resin. By forming a crosslinked structure between the molecules of the pigment-dispersing resin, the pigment is in a state of being coated with the pigment-dispersing resin having a crosslinked structure, and as described above, it becomes easy to suppress the detachment of the pigment-dispersing resin, improve the redissolubility, the ejection stability, etc. Note that the pigment-dispersing resin may have a crosslinked structure within the molecule of the pigment-dispersing resin.

[0031] In the present disclosure, a pigment-dispersing resin having no crosslinked structure between molecules is also referred to as an "uncrosslinked dispersing resin", and a pigment-dispersing resin having a crosslinked structure between molecules is also referred to as a "crosslinked dispersing resin".

[0032] <Pigment> The pigment particles contained in the aqueous inkjet ink of this embodiment contain a pigment. A printed matter produced using an aqueous inkjet ink containing a pigment has a high density. Further, by appropriately drying and / or thickening after landing on the printing substrate, bleeding can be suppressed, and a printed matter with excellent print quality can be obtained.

[0033] In the aqueous inkjet ink of this embodiment, as the above-mentioned pigment, an organic pigment may be used, an inorganic pigment may be used, or both may be used in combination.

[0034] When using an inorganic pigment as the pigment, titanium oxide, zinc white, zinc sulfide, lead white, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, talc, bentonite, carbon black, black iron oxide, cadmium red, red iron oxide, molybdenum red, molybdate orange, chrome vermilion, lead yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chromium green, victoria green, ultramarine, dark blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, cobalt violet, etc. can be used.

[0035] For example, when using carbon black as an inorganic pigment, carbon black produced by either the furnace method or the channel method can be suitably used. Further, among these carbon blacks, those having characteristics such as a primary particle diameter of 11 to 40 nm, a specific surface area by the BET method of 50 to 400 m 2 / g, a volatile content of 0.5 to 10%, a pH value of 2 to 10, etc., can be particularly suitably used.

[0036] On the other hand, specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and perylene pigments. Further, the hue is not particularly limited, and colored pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used.

[0037] Specifically, when exemplifying the pigments that can be used as the above organic pigments by the Color Index, for cyan pigments, C.I.PigmentBlue1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, 64, etc. can be mentioned.

[0038] For magenta pigments, C.I.PigmentRed5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 177, 178, 179, 184, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, 282, C.I.PigmentViolet19, 23, 29, 30, 32, 36, 37, 38, 40, 50, etc. can be mentioned.

[0039] In addition, examples of yellow pigments include C.I.PigmentYellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213, etc.

[0040] In addition, examples of black pigments include aniline black (C.I.PigmentBlack 1), perylene black (C.I.PigmentBlack 31, 32), azomethine azo black, etc. Further, a plurality of colored pigments such as the above cyan pigment, magenta pigment, yellow pigment, and the following brown pigment, orange pigment, etc. can be mixed to form a black pigment.

[0041] In addition, as pigments other than the above, C.I.PigmentGreen 7, 10, 36, C.I.PigmentBrown 3, 5, 25, 26, C.I.PigmentOrange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc. can be used.

[0042] The pigments listed above can be used alone or in combination of two or more. The content of the pigment is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and still more preferably 2 to 7% by mass based on the total mass of the aqueous inkjet ink.

[0043] <Pigment dispersion resin> The above pigment dispersion resin is a resin having a function of dispersing pigments. Both the pigment dispersion resin, that is, the uncrosslinked dispersion resin and the crosslinked dispersion resin, are preferably resins having an acid group in the molecular structure, and the acid group is more preferably a carboxyl group and / or a carboxylate group (R-COO - ). Any resin can be used as the pigment dispersion resin as long as it has an acid group (preferably a carboxyl group and / or a carboxylate group) and has a function of dispersing pigments.

[0044] As described below, as forms of resins generally used in inkjet inks, water-soluble resins and resin fine particles exist. In the present embodiment, as the uncrosslinked dispersion resin, a water-soluble resin or resin fine particles may be used. Also, regarding the crosslinked dispersion resin, both the water-soluble resin and resin fine particles can be used. For example, when there are resin fine particles containing a pigment, it is determined that the resin contained in the resin fine particles is a resin having a function of dispersing the pigment (a pigment dispersion resin). In this case, when there is no crosslinked structure between resin molecules, the resin contained in the resin fine particles is an uncrosslinked dispersion resin, and when there is a crosslinked structure, the resin contained in the resin fine particles is a crosslinked dispersion resin. On the other hand, for example, when using a water-soluble resin as the uncrosslinked dispersion resin, it is possible to confirm whether the water-soluble resin has a function of dispersing a pigment by a method conforming to JIS K 5101-1-4:2004.

[0045] Specifically, 600 g of carbon black having a primary particle diameter of 15 to 25 nm, a nitrogen adsorption specific surface area of 120 to 260 m 2 / g, and a DBP absorption amount (granular) of 40 to 80 cm 3 / 100 g, 300 g of the target water-soluble resin, and 2,100 g of water are thoroughly mixed (premixing), and then using a bead mill with a volume of 0.6 L (for example, "Dynomill" manufactured by Simar Enterprises Co., Ltd.) filled with 1,800 g of milling beads (for example, zirconia beads with a diameter of 0.5 mm), dispersion is carried out for 4 hours. After dispersion, the viscosity of the obtained carbon black dispersion at 25°C is measured using an E-type viscometer (for example, "TVE25L-type viscometer" manufactured by Toki Sangyo Co., Ltd.), and then the carbon black dispersion is stored in a forced-air constant-temperature thermostat set at 70°C for one week, and the viscosity is measured again. At this time, if the viscosity of the dispersion immediately after dispersion is 100 mPa·s or less and the absolute value of the viscosity change rate of the carbon black dispersion before and after storage is 10% or less, it is determined that the water-soluble resin has a function of dispersing the pigment.

[0046] Examples of resin types that can be used as pigment-dispersing resins include acrylic, maleic acid, urethane, polyester, etc. Among them, from the perspective of strongly adsorbing to pigments and stabilizing the dispersion state of pigments, it is preferable to use a resin having an aromatic ring in its structure.

[0047] In the present disclosure, the "acrylic resin" refers to a resin using at least one selected from the group consisting of acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters as polymerizable monomers. In addition to the above-listed polymerizable monomers, styrene monomers may be further used as the polymerizable monomers for forming the acrylic resin. On the other hand, a resin containing (anhydrous) maleic acid (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer is excluded from the "acrylic resin" in the present disclosure. The "maleic acid resin" refers to a resin using at least (anhydrous) maleic acid as a polymerizable monomer. In addition, α-olefins, styrene monomers, acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, etc. may be further used as the polymerizable monomers for the maleic acid resin.

[0048] Before performing the crosslinking treatment described below and after performing the crosslinking treatment, it is preferable that at least a part of the acid groups (for example, carboxyl groups) contained in the pigment-dispersing resin are anionic functional groups (for example, carboxylate groups) by neutralization with a basic compound. This is because the pigments can be stably dispersed by the charge repulsion between the anionic functional groups. Examples of the basic compound include ammonia; organic amines such as dimethylaminoethanol, diethanolamine, and triethanolamine; and alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, disodium carbonate, sodium hydrogen carbonate, dipotassium carbonate, and sodium borate. From the viewpoint of achieving excellent dispersion stability of the pigment in the aqueous inkjet ink and suppressing pigment aggregation, it is preferable to use an alkali metal compound, and it is particularly preferable to use sodium hydroxide and / or potassium hydroxide. In addition, the basic compounds listed above can be used alone or in combination of two or more.

[0049] The neutralization of the pigment-dispersing resin is preferably carried out such that the pH becomes 7 to 12 after adding the total amount of the basic compound to a 15 to 25 mass% (for example, 20 mass%) aqueous solution of the pigment-dispersing resin.

[0050] In the present disclosure, the "aqueous solution" refers to a liquid containing an aqueous solvent and components dispersed and / or dissolved in the aqueous solvent. In addition, the pH of the aqueous solution of the pigment-dispersing resin is the value at 25°C and can be measured by a conventional method. For example, it can be measured using a desktop pH meter "F-71" (manufactured by Horiba, Ltd.) using a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

[0051] The suitable addition amount of the basic compound used for neutralizing the pigment-dispersing resin, specifically shown using the neutralization rate, is preferably 10 to 200 mol% and more preferably 40 to 160 mol% from the viewpoint of the dispersion stability of the pigment. Particularly preferably, it is 60 to 120 mol%. Here, the neutralization rate is obtained by dividing the molar amount of the basic groups in the added basic compound by the molar amount of the acid groups in the pigment-dispersing resin and can be determined by the following formula 2. When using a resin in which at least a part is neutralized (for example, containing at least a carboxylate group) as the above pigment-dispersing resin, the calculation of the neutralization rate shall be performed assuming that all the acid groups in the resin are unneutralized (specifically, assuming that the above carboxylate group is a carboxyl group).

[0052] Formula 2:

Number

[0053] Before the crosslinking treatment described later, the weight average molecular weight (Mw) of the pigment-dispersing resin is preferably 5,000 to 100,000. If the weight average molecular weight is 5,000 or more, the dispersion stability will be suitable, and if it is 100,000 or less, the ejection stability will be good. The above weight average molecular weight is more preferably 8,000 to 50,000 and even more preferably 10,000 to 35,000.

[0054] The weight average molecular weight of the above pigment-dispersing resin can be measured by a conventional method. For example, a value measured as the weight average molecular weight in terms of polystyrene, which is measured using GPC (manufactured by Tosoh Corporation, "HLC-8120GPC") equipped with a TSKgel column (manufactured by Tosoh Corporation) and an RI detector and using THF as the developing solvent, is used.

[0055] Also, the acid value of the pigment-dispersed resin before the crosslinking treatment described later is preferably 60 to 180 mgKOH / g, more preferably 70 to 160 mgKOH / g, and particularly preferably 80 to 150 mgKOH / g, from the viewpoint of ensuring the dispersion stability of the pigment and also preferably suppressing the detachment of the pigment-dispersed resin during the dispersion treatment (details will be described later) performed before the crosslinking treatment. By controlling the acid value within the above range, the detachment of the pigment-dispersed resin from the pigment after the crosslinking treatment described later is significantly suppressed, and excellent redissolvability and ejection stability can be obtained.

[0056] The acid value of the pigment-dispersed resin can be measured by a conventional method. For example, about 1 g of the pigment-dispersed resin that has been subjected to acid precipitation treatment in advance is precisely weighed into an Erlenmeyer flask, and further, 50 ml of a distilled water / dioxane = 1 / 9 (mass ratio) mixed solution is added to dissolve the pigment-dispersed resin. This sample solution is titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (titer F). For the titration, a potentiometric titrator (for example, "Automatic Potentiometric Titrator AT-710M" manufactured by Kyoto Electronics Industry Co., Ltd.) is used. Then, using the amount of the potassium hydroxide-ethanol solution (designated as α (mL)) required up to the titration end point, the acid value (mgKOH / g) can be determined from the following formula 3.

[0057] Formula 3: Acid value (mgKOH / g) = (5.611 × α × F) / S

[0058] In formula 3, S is the sampling amount (g) of the pigment-dispersed resin as the sample, α is the amount (ml) of the 0.1 mol / L potassium hydroxide-ethanol solution dropped until the titration end point, and F is the titer of the 0.1 mol / L potassium hydroxide-ethanol solution.

[0059] The content of the pigment dispersion resin with respect to the content of the pigment is preferably 1 to 100% by mass. By setting the content of the pigment dispersion resin to 1% by mass or more with respect to the content of the pigment, the viscosity of the aqueous inkjet ink can be suppressed to a suitable level for inkjet printing applications, and by setting it to 100% by mass or less, the dispersion stability, as well as the storage stability and ejection stability after dispersion, can be made good. More preferably, the content of the pigment dispersion resin is 2 to 50% by mass.

[0060] ≪Pigment dispersion resin having a crosslinked structure≫ The pigment dispersion resin contained in the aqueous inkjet ink of this embodiment has a crosslinked structure. By the crosslinking treatment, the pigment dispersion resin becomes a three-dimensional structure, and the solubility of the pigment dispersion resin decreases. As a result, it becomes possible to suppress the desorption of the pigment dispersion resin from the pigment. Also, this makes it easy to redissolve the aqueous inkjet ink dried near the nozzle.

[0061] Examples of the method for forming the crosslinked structure (crosslinking treatment method) include a method of reacting reactive sites (reactive functional groups such as carboxyl groups and carboxylate groups) of the uncrosslinked dispersion resin adsorbed on the pigment surface in advance with a crosslinking agent or the like to form a crosslinked structure; a method of adsorbing the uncrosslinked dispersion resin having a self-crosslinkable group on the pigment surface in advance and then reacting the self-crosslinkable group; and the like. Among these, the method of reacting with a crosslinking agent or the like can be preferably used because the range of selection of the uncrosslinked dispersion resin that can be used is wide, it is easy to adjust the weight average molecular weight and acid value before the crosslinking treatment as described above, and it is easy to control the crosslinking rate with high accuracy.

[0062] ≪Crosslinking agent≫ Examples of the crosslinking agent include isocyanate compounds, aziridine compounds, carbodiimide compounds, oxetane compounds, oxazoline compounds, epoxy compounds, and the like. Examples of the functional group (reactive functional group) that reacts with the reaction point of the uncrosslinked dispersion resin include isocyanate groups, aziridine groups, carbodiimide groups, oxetane groups, oxazoline groups, epoxy groups, and the like. Among these, one or more functional groups selected from the group consisting of aziridine groups, carbodiimide groups, and epoxy groups are preferable, and at least an epoxy group is more preferable.

[0063] When using a compound having an epoxy group as the crosslinking agent, it is preferable to use a compound having a plurality of epoxy groups in one molecule, more preferably to use a compound having two or more glycidyl ether groups in one molecule, and even more preferably to use a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms. Further, from the viewpoint of being able to more efficiently cause a crosslinking reaction with the reaction point in the pigment dispersion resin in a liquid medium mainly composed of water, the epoxy equivalent of the compound having a plurality of epoxy groups in one molecule is preferably 90 to 300 g / eq., and more preferably 100 to 200 g / eq.

[0064] Specific examples of the compound having a plurality of epoxy groups in one molecule include cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6 - hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 4,4'-diglycidyloxybiphenyl, bisphenol A type diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether, phthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, hydrogenated phthalic acid diglycidyl ester, and the like.

[0065] The crosslinking agent may be water-soluble or water-insoluble. From the viewpoint that it can react more efficiently with the reaction points of the pigment-dispersing resin in a medium containing water (aqueous medium), the solubility of the crosslinking agent in 100 g of water at 25 °C is preferably 0.1 to 50 g / 100 g H₂O, more preferably 0.2 to 40 g / 100 g H₂O, and still more preferably 0.5 to 30 g / 100 g H₂O.

[0066] From the viewpoints of reducing the detachment of the pigment-dispersing resin from the pigment, improving the redissolubility and ejection stability, and suppressing the inhibition of the function expression of the surfactant by the free pigment-dispersing resin and improving the wettability of the aqueous inkjet ink, the crosslinking agent is preferably added so that the functional group content (mol%) represented by the following formula 4 is 50 to 150 mol%. The above functional group content is more preferably 70 to 120 mol%, and particularly preferably 80 to 100 mol%.

[0067] Formula 4:

Number

[0068] For example, when mixing a crosslinking agent having a plurality of epoxy groups in one molecule and an epoxy equivalent of EE (g / eq.) as EW (g) with a pigment-dispersing resin before crosslinking having an acid value of AV (mg KOH / g) as PW (g), the above functional group content is represented by the following formula 4-2.

[0069] Formula 4-2: Functional group content (mol%) = 100×(EW / EE) / {PW×AV / (56.1×1000)}

[0070] Note that "56.1" in the above formula 4-2 is the molecular weight of potassium hydroxide.

[0071] <Method for producing pigment particles containing a pigment-dispersing resin having a crosslinked structure> As an example of a method for producing pigment particles (crosslinked pigment particles) containing a pigment dispersion resin having a crosslinked structure, for example, a method of sequentially performing a dispersion treatment step and a crosslinking treatment step as shown below can be mentioned. Although optional, a neutralization treatment step as shown below may be performed before the above dispersion treatment step. First, a carboxyl group present in the pigment dispersion resin and a basic compound are mixed in an aqueous medium to neutralize at least a part of the carboxyl group (neutralization treatment step). As described above, by the above neutralization, the carboxyl group present in the pigment dispersion resin becomes a carboxylate group. This pigment dispersion resin having at least a carboxylate group is used in the subsequent steps. Note that the pigment dispersion resin obtained after the neutralization treatment step is in the state of an aqueous solution. Next, a pigment is added to the aqueous solution of the pigment dispersion resin, and after mixing the two, further dispersion treatment is performed (dispersion treatment step). By this dispersion treatment step, an aqueous dispersion of pigment particles (un-crosslinked pigment particles) in which the pigment dispersion resin is chemically adsorbed on at least a part of the surface is obtained. Note that the pigment dispersion resin contained in the un-crosslinked pigment particles is an un-crosslinked dispersion resin. Thereafter, a crosslinking agent is added to the aqueous dispersion of the un-crosslinked pigment particles, and a crosslinking treatment is performed (crosslinking treatment step). By this crosslinking treatment step, an aqueous dispersion of crosslinked pigment particles can be produced.

[0072] <<Neutralization Treatment Step>> As described above, it is preferable that the pigment dispersion resin used in the above dispersion treatment step has an ionized functional group such as a carboxylate group. When using a pigment dispersion resin having no such ionized functional group (for example, a resin having only a carboxyl group as an acid group), it is preferable to neutralize at least a part of the functional group and change it to an ionized functional group by a method such as addition of a basic compound.

[0073] <<Dispersion Treatment Step>> As the disperser used in the dispersion process, any commonly used disperser may be used. For example, a media-type wet disperser, a media-less type wet disperser, a kneader, etc. can be used. Examples of media-type wet dispersers include ball mills, roll mills, sand mills, and bead mills. Examples of media-less type wet dispersers include high-pressure homogenizers. Examples of kneaders include kneaders. Among these, from the viewpoint of crushing and refining coarse particles of the pigment, it is preferable to select a bead mill. Examples of bead mills include Supermill, Sand Grinder, Agitator Mill, Glen Mill, Dyno Mill, Pearl Mill, and Kobol Mill (all are trade names), etc.

[0074] By using the above-listed dispersers, the pigment can be refined to a desired particle size by the collision force and shear stress with the media. Among them, from the viewpoint of obtaining a pigment dispersion liquid with a uniform particle size, it is preferable to pre-disperse (premix) the pigment and the pigment dispersion resin and then further disperse (main dispersion) them with the above-listed dispersers. As the pre-disperser used for premixing, a commonly used mixing and stirring device such as a disper can be used.

[0075] ≪Crosslinking treatment step≫ As described above, by subjecting the pigment dispersion resin adsorbed on the pigment to a crosslinking treatment, pigment particles in which the pigment dispersion resin is crosslinked can be obtained. As a method of the crosslinking treatment, a method of forming a crosslinked structure with a crosslinking agent can be preferably used. Specifically, a method of holding a mixture containing uncrosslinked pigment particles, a crosslinking agent, and water under heating while stirring can be mentioned.

[0076] The temperature during the crosslinking treatment is preferably 50°C to 95°C, more preferably 70°C to 85°C, from the viewpoint of efficiently promoting the crosslinking reaction. Also, the time of the crosslinking treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 5 hours, from the same viewpoint as above.

[0077] The average particle diameter of the crosslinked pigment particles is preferably 60 to 200 nm, more preferably 70 to 175 nm, and particularly preferably 80 to 150 nm from the viewpoint of stable discharge from the nozzle.

[0078] The above average particle diameter is the median diameter on a volume basis, which can be measured by the dynamic light scattering method. For example, it can be measured using "NanoTrack UPA-EX150" manufactured by Microtrac Bell Corporation.

[0079] <Pigment dispersion> The crosslinked pigment particles may be in a state of being dispersed in an aqueous medium, that is, in a state of an aqueous dispersion of the crosslinked pigment particles. Since the discharge stability can be improved, the aqueous inkjet ink of the present embodiment is preferably produced by a method of mixing an aqueous dispersion of the crosslinked pigment particles produced in advance with other raw materials described later.

[0080] In the present disclosure, a composition containing pigment particles and an aqueous medium is referred to as a "pigment dispersion". Therefore, both the aqueous dispersion of the uncrosslinked pigment particles and the aqueous dispersion of the crosslinked pigment particles described above are included in the "pigment dispersion". As described later, the pigment dispersion is used as a raw material for the aqueous inkjet ink, and is different from the aqueous inkjet ink. Specifically, the pigment content of the pigment dispersion and the aqueous inkjet ink is different. For example, the amount of the pigment contained in the pigment dispersion is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and still more preferably 20 to 50% by mass in the total amount of the pigment dispersion. On the other hand, the amount of the pigment contained in the preferred aqueous inkjet ink is as described later. Also, when the amount (mass%) of the pigment contained in the pigment dispersion is PP and the amount (mass%) of the pigment contained in the aqueous inkjet ink is PI, the value represented by PP / PI is preferably 1.5 to 10, and more preferably 2 to 8.

[0081] In the present disclosure, an aqueous dispersion of uncrosslinked pigment particles is particularly referred to as an "uncrosslinked pigment dispersion", and an aqueous dispersion of crosslinked pigment particles is particularly referred to as a "crosslinked pigment dispersion".

[0082] The pigment dispersion may be produced by first manufacturing the above pigment particles in a dry state (solid) and then mixing them with an aqueous medium. It may also be produced by the method for producing pigment particles including a pigment dispersion resin having a crosslinked structure described above.

[0083] The aqueous medium contained in the above pigment dispersion contains at least water. It may also contain an organic solvent (details will be described later) that can be used as a raw material for aqueous inkjet ink. For example, the pigment dispersion may contain ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, etc.

[0084] The pH of the above pigment dispersion is preferably 8 to 12. If the pH is 8 or higher, the anionic functional groups present in the pigment dispersion resin can be stably present, and it is possible to enhance the dispersion stability due to charge repulsion. From this viewpoint, a more preferable pH is 9 to 11. The pH of the pigment dispersion can be measured by the same method as the aqueous solution of the pigment dispersion resin described above.

[0085] <Surfactant> The aqueous inkjet ink of the present embodiment contains, as surfactants, an acetylene diol-based surfactant (A-1) having an actually measured HLB value of 6 to 9 and a siloxane-based surfactant (A-2) having an actually measured HLB value of 8 to 14.

[0086] In the present disclosure, the "HLB (Hydrophilic-Lipophilic Balance) value" is one of the parameters representing the degree of hydrophilicity and hydrophobicity of a material. The smaller the HLB value, the higher the hydrophobicity of the material, and the larger the HLB value, the higher the hydrophilicity of the material. There are methods for calculating the HLB value from the molecular structure and methods for actual measurement by experiments. In the present disclosure, as the HLB value, the value calculated by actual measurement (actual measured HLB value) by the method shown below is used. (1) Dissolve 0.5 g of the surfactant to be measured in 5 mL of ethanol. (2) Titrate the mixture of (1) with a 2% aqueous phenol solution while stirring at 25°C. Then, when the 2% aqueous phenol solution is dropped, the end point is the point where the mixture becomes turbid and does not return to transparency. (3) When the amount of the 2% aqueous phenol solution dropped until the end point is A [mL], the actual measured HLB value is calculated according to the following formula 5.

[0087] Formula 5: Actual measured HLB value = 0.89×A + 1.11

[0088] ≪Acetylenediol-based surfactant (A-1)≫ The aqueous inkjet ink of this embodiment contains an acetylenediol-based surfactant (A-1). Since it has a low affinity for water and is quickly oriented at the gas-liquid interface, resulting in excellent wettability to the printing substrate, the actual measured HLB value of the acetylenediol-based surfactant (A-1) is preferably 6 to 9.

[0089] As the acetylene diol-based surfactant (A-1), for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (however, those with an ethylene oxide addition molar number of 1.5 moles or less), 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, etc. can be used. Further, examples of commercially available products that can be used as the acetylene diol-based surfactant (A-1) include Surfynol DF-110D, Surfynol 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420 (manufactured by Evonik Japan Co., Ltd.), Acetylenol E00, E13T (manufactured by Kawaken Fine Chemicals Co., Ltd.), etc. These compounds may be used alone only one type, or two or more types may be used in combination.

[0090] From the viewpoint of ensuring excellent printing image quality, the content of the acetylene diol-based surfactant (A-1) in the aqueous inkjet ink is preferably 0.1 to 5% by mass, more preferably 0.3 to 3% by mass. Particularly preferably, it is 0.5 to 2% by mass.

[0091] ≪Siloxane-based surfactant (A-2)≫ The aqueous inkjet ink of the present embodiment contains a siloxane-based surfactant (A-2) having an actually measured HLB value of 8 to 14. Since the siloxane-based surfactant (A-2) can be oriented to supplement the non-uniform orientation of the acetylene diol-based surfactant (A-1), it is effective for reducing dot roundness and unevenness. From this point, the difference between the actually measured HLB value of the acetylene diol-based surfactant (A-1) and the actually measured HLB value of the siloxane-based surfactant (A-2) is preferably 2 to 7.

[0092] As the above-mentioned siloxane surfactant (A-2), gemini-type siloxane surfactants, both-terminal polyether-modified siloxane surfactants, side-chain polyether-modified siloxane surfactants, etc. can be used. Among them, although the details are unknown, the siloxane surfactant (A-2) preferably contains a gemini-type siloxane surfactant and / or a both-terminal polyether-modified siloxane surfactant because unevenness can be reduced with a small addition amount, a printed matter with good dot roundness can be obtained, and furthermore, the ejection stability of the aqueous inkjet ink is improved.

[0093] Also, from the viewpoints of further enhancing the effects of dot roundness, wettability, and unevenness reduction, obtaining a printed matter with particularly excellent print quality, and maintaining and improving ejection stability, the aqueous inkjet ink of the present embodiment preferably contains two or more types of siloxane surfactants (A-2), more preferably, one or more of them are gemini-type siloxane surfactants and / or both-terminal polyether-modified siloxane surfactants (excluding those that are gemini-type siloxane surfactants). Further, from the viewpoint of obtaining an aqueous inkjet ink that is excellent in wettability, redissolvability, and ejection stability on a printing substrate and has good dot roundness, the above-mentioned siloxane surfactant (A-2) particularly preferably contains one or more types of gemini-type siloxane surfactants and one or more types of both-terminal polyether-modified siloxane surfactants (excluding those that are gemini-type siloxane surfactants).

[0094] ≪Gemini-Type Siloxane Surfactant≫ Generally, a gemini surfactant has a structure in which surfactants having a hydrophilic structure and a hydrophobic structure are linked by a linking group (spacer) or a covalent bond. In the case of a gemini-type siloxane surfactant, for example, a hydrophobic structure represented by a siloxane chain (-[O-SiR 1 R 2 x -. However, R 1 and R 2 ​are each an arbitrary organic group, and x is an integer of 2 or more. ), and the hydrophilic structure (for example, a polyether chain) has the following structure. · A structure in which the bonding points between the siloxane chain and the hydrophilic structure are present in the middle of the siloxane chain and the middle of the hydrophilic structure, respectively. · A plurality of siloxane chains are bonded via a linking group or the like (for example, at least a part of R 1 and / or R 2 in the structural formula of the siloxane chain is an organic chain containing a siloxane chain). · A structure in which, in a plurality of siloxane-based surfactants each having a plurality of hydrophilic structures, a part of the hydrophilic structures is shared.

[0095] Gemini-type surfactants are excellent in surface tension reduction ability compared to general surfactants. Therefore, by using a Gemini-type siloxane-based surfactant, a surface tension reduction superior to that of non-Gemini siloxane-based surfactants can be achieved. As a result, the wettability of the aqueous inkjet ink containing the Gemini-type siloxane-based surfactant can be significantly improved, and the improvement of the above-described dot roundness and unevenness can be achieved.

[0096] Examples of commercially available Gemini-type siloxane-based surfactants having an actually measured HLB value of 8 to 14 include, but are not limited to, TEGOTwin4100 and TEGOTwin4200 manufactured by Evonik Japan Co., Ltd.

[0097] ≪Both-terminal polyether-modified siloxane-based surfactant (excluding those that are Gemini-type siloxane-based surfactants)≫ The both-terminal polyether-modified siloxane-based surfactant has a structure in which polyether chains are bonded to both ends of a polysiloxane skeleton. The aqueous inkjet ink containing the both-terminal polyether-modified siloxane-based surfactant improves the printing image quality by uniformizing the wet spreading on the printing substrate, and also has good ejection stability. As the both-terminal polyether-modified siloxane-based surfactant, a compound represented by the following general formula 6 can be preferably used.

[0098] General formula 6: [Chem.]

[0099] In general formula 6, l represents an integer from 1 to 100, and R 3 represents a structure represented by the following general formula 7.

[0100] General formula 7: [Chem.]

[0101] In general formula 7, p represents an integer from 1 to 6, q represents an integer from 1 to 100, and r represents an integer from 0 to 80. However, p + r is an integer of 1 or more. Also, R 4 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a methacryloyl group, or an acryloyl group. However, the addition pattern of the ethylene oxide group (OC2H4) and propylene oxide group (OC3H6) in [ ] may be block or random.

[0102] Examples of commercially available products of the compound represented by the above general formula 6 and having a measured HLB value of 8 to 14 include, but are not limited to, BYK-333, BYK-UV3500, BYK-3420 manufactured by BYK Chemie, and TEGO Glide 440, TEGO Glide 450 manufactured by Evonik Japan.

[0103] <<Side-chain polyether-modified siloxane-based surfactant (excluding gemini-type siloxane-based surfactants)>> As the above siloxane surfactant (A-2), a side-chain polyether-modified siloxane surfactant (however, excluding gemini-type siloxane surfactants) can be used. Even if the side-chain polyether-modified siloxane surfactant has a relatively low molecular weight, it shows high orientation in an aqueous medium and can achieve excellent wettability. As the side-chain polyether-modified siloxane surfactant, it is preferable to use a surfactant represented by the following general formula 8.

[0104] General formula 8:

Chemical formula

[0105] In general formula 8, m is an integer of 0 or more, n is an integer of 1 or more, and m + n is an integer of 1 to 100. Also, R 5 has the structure represented by the above general formula 7, and R 6 represents an alkyl group having 1 to 6 carbon atoms.

[0106] As commercially available products of compounds represented by the above general formula 8 and having an actually measured HLB value of 8 to 14, BYK-347, BYK-348, BYK-349, BYK-3451 manufactured by BYK Chemie, TEGOWet240, TEGOWet250, TEGOWet260 manufactured by Evonik Japan, etc. can be mentioned, but it is not limited thereto.

[0107] From the viewpoint of ensuring excellent printing image quality, the content of the siloxane surfactant (A-2) in the aqueous inkjet ink is preferably 0.1 to 5% by mass, more preferably 0.3 to 3.5% by mass. Particularly preferably, it is 0.5 to 2.5% by mass.

[0108] Also, from the viewpoint of obtaining a printed matter with excellent dot roundness and no white spots, when the content mass of the acetylene diol surfactant (A-1) contained in the aqueous inkjet ink (when two or more acetylene diol surfactants (A-1) are included, the total content mass) is taken as 1, the content mass of the siloxane surfactant (A-2) (when two or more siloxane surfactants (A-2) are included, the total content mass) is preferably 0.3 to 3, and particularly preferably 0.5 to 2.

[0109] <Organic solvent> ≪Specific organic solvent≫ The aqueous inkjet ink of the present embodiment contains an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or the glycol monoether represented by the above general formula 1. In the present disclosure, these organic solvents are collectively referred to as "specific organic solvents". Since all of the specific organic solvents have a low surface tension, the acetylene diol surfactant (A-1) and the siloxane surfactant (A-2) that are compatible with the specific organic solvent diffuse along with the wetting spread of the specific organic solvent and are likely to be uniformly oriented on the interface. As a result, pinholes are easily suppressed in the printed matter. In addition, since the meniscus of the aqueous inkjet ink in the inkjet head is stabilized, the ejection stability is also improved.

[0110] As alkanediols having 5 to 8 carbon atoms (excluding 1,2-alkanediols having 5 to 8 carbon atoms), 1,3-pentanediol, 1,4-pentanediol, 2,3-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,3-hexanediol, 1,4-hexanediol, 2,3-hexanediol, 3,4-hexanediol, 1,5-hexanediol, 2,2-dimethyl-1,3-pentanediol, 2-methyl-1,3-pentanediol, 3-methyl-1,3-butanediol, 2-methyl-2,4-pentanediol (hexylene glycol), 2-ethyl-1,3-hexanediol, 1,3-octanediol, etc. can be mentioned, but it is not limited thereto. Among them, from the viewpoint that the above-described mechanism functions effectively, the surfactant in the aqueous inkjet ink can be uniformly oriented, and the ejection stability is also improved, it is particularly preferable to use an alkanediol having a particularly small surface tension, that is, a surface tension at 25 ° C of 20 to 30 mN / m. On the other hand, although the detailed mechanism is unknown, from the viewpoint of suitably solubilizing the above-described surfactant and particularly improving the ejection stability, a compound having a quaternary carbon atom (a carbon atom bonded to four atoms other than hydrogen atoms) can be preferably used. Among the above-listed compounds, as a compound having a surface tension at 25 ° C of 20 to 30 mN / m and having a quaternary carbon atom, 3-methyl-1,3-butanediol and 2-methyl-2,4-pentanediol (hexylene glycol) can be mentioned.

[0111] On the one hand, examples of the glycol monoether represented by the general formula 1 include, but are not limited to, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, etc. Among them, since the above-mentioned acetylene diol-based surfactant (A-1) and siloxane-based surfactant (A-2) can be preferably compatibilized, in addition to the improvement of the discharge stability, the redissolution property is also improved. Therefore, as the glycol monoether represented by the general formula 1, it is preferable to use a compound in which n in the general formula 1 is 2. Specific examples of the compound in which n in the general formula 1 is 2 include dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether. Among these compounds, since the above-mentioned effects are particularly preferably exhibited, the aqueous inkjet ink particularly preferably contains dipropylene glycol monopropyl ether.

[0112] Only one kind of the above-mentioned specific organic solvent may be used, or two or more kinds may be used in combination. Further, the total content of the specific organic solvent is preferably 0.5 to 25% by mass, more preferably 1 to 20% by mass, particularly preferably 2 to 15% by mass in the total amount of the aqueous inkjet ink.

[0113] The inkjet ink of this embodiment can preferably contain organic solvents other than specific organic solvents. Examples of the organic solvents other than those described above include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, γ-butyrolactone, 2-pyrrolidone, etc., but are not limited thereto. Also, only one of these organic solvents may be used, or two or more thereof may be used in combination.

[0114] <Binder resin> The aqueous inkjet ink of this embodiment preferably contains a resin used for binder applications (also referred to as "binder resin" in the present disclosure) in order to improve drying properties and impart scratch resistance.

[0115] As described above, generally, as the forms of resins used in aqueous inkjet inks, water-soluble resins and resin fine particles are known. The binder resin contained in the aqueous inkjet ink of this embodiment may be a water-soluble resin, may be resin fine particles, or may be a combination of a water-soluble resin and resin fine particles.

[0116] In the present disclosure, a resin having a solubility of 1 g or more in 100 g of water at 25°C is referred to as a "water-soluble resin", and a resin having a solubility of less than 1 g is referred to as a "water-insoluble resin". Among the above water-insoluble resins, a resin that is dispersed in the form of particles in water and has a median diameter (also referred to as "D50" in the present disclosure) based on volume of 10 to 1,000 nm is referred to as a "resin fine particle".

[0117] The D50 of the resin fine particles can be measured by the same apparatus and method as in the case of the average particle diameter of the crosslinked pigment particles described above.

[0118] Examples of the types of binder resins that can be used in the aqueous inkjet ink of the present embodiment include acrylic, styrene, maleic acid, urethane, polyester, vinyl chloride, vinyl chloride-vinyl acetate, polyolefin, vinyl alcohol, and the like. These resins may be used alone or in combination of two or more.

[0119] When the aqueous inkjet ink of the present embodiment contains a binder resin, the type of resin used as the binder resin is preferably one or more selected from the group consisting of acrylic, urethane, and polyester among those listed above.

[0120] The preferred content of the binder resin contained in the aqueous inkjet ink of the present embodiment is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and particularly preferably 2 to 10% by mass in the total amount of the aqueous inkjet ink.

[0121] <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.

[0122] <Water> The water contained in the aqueous inkjet ink of the present embodiment is preferably ion-exchanged water and / or reverse osmosis water. Further, the content of water contained in the aqueous inkjet ink is preferably 30 to 90% by mass in the total amount of the aqueous inkjet ink.

[0123] <Method for producing aqueous inkjet ink> The aqueous inkjet ink of the present embodiment can be produced by a conventionally known method. For example, water, an organic solvent, an acetylene-based surfactant (A-1), a siloxane-based surfactant (A-2), etc. are added to an aqueous dispersion of crosslinked pigment particles produced by the method described above, and after sufficiently stirring and mixing, a method of removing coarse particles by means such as filtration and centrifugation can be mentioned. However, the method for producing the aqueous inkjet ink of the present embodiment is not limited to the method described above.

[0124] <Properties of aqueous inkjet ink> The aqueous inkjet ink of the present embodiment preferably has a viscosity at 25°C of 3 to 15 mPa·s. In this viscosity range, droplets of the aqueous inkjet ink can be stably ejected not only from an inkjet head having a discharge frequency of about 4 to 10 KHz, but also from an inkjet head having a high discharge frequency of about 20 to 70 KHz. In particular, when the viscosity of the aqueous inkjet ink of the present embodiment at 25°C is 4 to 10 mPa·s, the aqueous inkjet ink can be stably ejected even when an inkjet head having a design resolution of 600 dpi or more is used. In the present disclosure, as the viscosity, a value measured in a 25°C environment using a cone plate type rotational viscometer (E-type viscometer, cone angle 1°34’) such as the “TVE25L type viscometer” manufactured by Toki Sangyo Co., Ltd. is used.

[0125] Also, from the viewpoint of obtaining an aqueous inkjet ink excellent in ejection stability and print image quality of printed matter, the static surface tension of the aqueous inkjet ink of the present embodiment at 25°C is preferably 18 to 35 mN / m, and particularly preferably 20 to 30 mN / m. In the present disclosure, as the static surface tension, a value measured in a 25°C environment using the Wilhelmy method (plate method), such as the "Automatic Surface Tension Meter CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd., is used.

[0126] <Set of aqueous inkjet inks> The aqueous inkjet ink of the present embodiment may be used alone as only one type, but can also be used as a set of two or more types of aqueous inkjet inks combined. As such a set of aqueous inkjet inks, for example, a set of four-color aqueous inkjet inks (process color ink set) composed 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) can be mentioned.

[0127] <Inkjet recording method> The aqueous inkjet ink of the present embodiment is used in an inkjet printing method. That is, the aqueous inkjet ink of the present embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). Further, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0128] ≪Ejection step≫ In the above ejection process, as the operation mode of the inkjet head, there are a shuttle (scan) mode in which the inkjet head is reciprocally scanned in a direction perpendicular to the conveyance direction of the printing substrate while ejecting and recording aqueous inkjet ink, and a single-pass mode in which the printing substrate is passed under a fixedly arranged inkjet head while ejecting and recording aqueous inkjet ink. The inkjet head equipped with the aqueous inkjet ink of the present embodiment may adopt either the shuttle mode or the single-pass mode. Among them, the single-pass mode is preferably selected from the viewpoint that the landing position of the droplets of the aqueous inkjet ink is less likely to shift and the print image quality of the printed matter is improved.

[0129] Regarding the ejection method from the inkjet head as well, a known method can be arbitrarily selected. Examples of the ejection method include a piezo method that utilizes the volume change of a piezoelectric element (piezo element), a thermal method that ejects aqueous inkjet ink by bubbles generated by heating a heater, a valve method that ejects pressurized aqueous inkjet ink while opening and closing the lid (valve) of the nozzle with a solenoid, and the like.

[0130] The droplet volume of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing the drying load and improving the print image quality. Further, from the viewpoint of improving the print image quality, it is preferable to adjust the printing conditions (specifically, the drive 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.

[0131] ≪Drying process≫ As drying methods employed in the drying mechanism used in the drying process, there are heat drying methods, hot air drying methods, infrared ray (for example, infrared rays with a wavelength of 700 to 2500 nm) drying methods, microwave drying methods, drum drying methods, and the like. In the above drying process, one or more of these methods can be arbitrarily selected and used. Further, when two or more of the above drying methods are employed, each drying method may be used separately (for example, successively) or may be used in combination simultaneously. For example, by using a heat drying method and a hot air drying method in combination, water-based inkjet ink can be dried more quickly than when each is used alone.

[0132] <<Printing substrate>> The printing substrate on which the water-based inkjet ink of the present embodiment is printed can be suitably used for permeable substrates and hardly permeable substrates. Among them, from the viewpoint of obtaining a printed matter with excellent printing quality, it is preferable to use a paper substrate as the printing substrate.

[0133] Examples of permeable substrates include uncoated papers such as newsprint, medium-quality paper, high-quality paper, and recycled paper; fabrics such as cotton, chemical fiber textiles, silk, hemp, and non-woven fabrics; and leather. Among them, uncoated papers such as newsprint, medium-quality paper, high-quality paper, and recycled paper can be preferably used from the point of obtaining a printed matter with excellent printing quality.

[0134] Examples of hardly permeable substrates include coated papers such as coated paper, art paper, and cast paper. Among them, coated paper can be preferably used from the point of obtaining a printed matter with excellent printing quality.

[0135] The above-listed printing substrates may have a smooth surface or a surface with irregularities. Further, the printing substrate may be in the form of a roll or a single sheet. Furthermore, a material obtained by laminating two or more of the above-listed printing substrates 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.

[0136] From the viewpoint of improving the wettability of the water-based inkjet ink of the present embodiment and obtaining a printed matter excellent in printing quality and drying property, 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.

[0137] That is, the present invention relates to a water-based inkjet ink shown in the following [1] to [5], and a printed matter manufactured using the above water-based inkjet ink shown in the following [6]. [1] A water-based inkjet ink containing pigment particles, a surfactant, and an organic solvent, wherein the pigment particles contain a pigment and a pigment dispersion resin, the pigment dispersion resin has a crosslinked structure, the surfactant contains an acetylene diol-based surfactant (A-1) having a measured HLB value of 6 to 9 and a siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14, the organic solvent contains an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or a glycol monoether represented by the following general formula 1, a water-based inkjet ink. General formula 1: R 1 -(O-CH(CH3)-CH2) n -OH (In general formula 1, R 1 is an alkyl group having 2 to 4 carbon atoms, and n is 1 or 2) [2] The water-based inkjet ink according to [1], wherein the siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14 contains a gemini-type siloxane-based surfactant. [3] The water-based inkjet ink according to [1] or [2], wherein the siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14 contains a both-end polyether-modified siloxane-based surfactant (excluding those which are gemini-type siloxane-based surfactants). [4] An aqueous inkjet ink according to [2] or [3], comprising two or more kinds of siloxane surfactants (A-2) having an actually measured HLB value of 8 to 14. [5] The aqueous inkjet ink according to [4], wherein the siloxane surfactant (A-2) having an actually measured HLB value of 8 to 14 includes a gemini-type siloxane surfactant and a both-terminal polyether-modified siloxane surfactant (excluding those which are gemini-type siloxane surfactants). [6] A printed matter obtained by printing the aqueous inkjet ink according to any one of [1] to [5].

[0138] The present invention is related to the subject matter described in Japanese Patent Application No. 2023-209882 filed on December 13, 2023, the disclosure of which is incorporated herein by reference.

Examples

[0139] 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.

[0140] <Production Example of Pigment-Dispersing Resin 1> 93.4 parts of methyl ethyl ketone was charged into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. After heating the inside of the reaction vessel to 110 °C, a mixture of 25 parts of styrene, 25 parts of acrylic acid, 20 parts of methyl methacrylate, 30 parts of lauryl methacrylate, and 6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.), which is a polymerization initiator, was added dropwise to the reaction vessel over 2 hours. After the addition was completed, the reaction was continued for 3 hours while maintaining the inside of the reaction vessel at 110 °C, then 0.6 part of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 °C for 1 hour to synthesize Pigment Dispersing Resin 1. For the obtained Pigment Dispersing Resin 1, the weight average molecular weight measured by the method described above was 29,000, and the acid value was 196 mgKOH / g. Thereafter, from the acid value of the above Pigment Dispersing Resin 1, the amount of potassium hydroxide required to make the neutralization rate 100% was calculated, and an aqueous potassium hydroxide solution having a concentration of 48 mass% containing an amount of potassium hydroxide equal to the obtained amount was added. Then, ion-exchanged water was added so that the solid content concentration became 20%, and the mixture was stirred at 50 °C for 1 hour to obtain an aqueous solution (solid content concentration 20%) of Pigment Dispersing Resin 1.

[0141] <Production Examples of Pigment Dispersing Resins 2 to 10> Aqueous solutions (all having a solid content concentration of 20%) of Pigment Dispersing Resins 2 to 10 were obtained by using the same raw materials and operations as those of Pigment Dispersing Resin 1, except that the monomers described in Table 1 were used as the polymerizable monomers. Note that Pigment Dispersing Resins 1 to 10 are uncrosslinked dispersion resins.

[0142]

Table 1

[0143] The abbreviations described in Table 1 are as follows. Also, the weight average molecular weights and acid values of Pigment Dispersing Resins 1 to 10 are also described in Table 1. ·St: Styrene ·AA: Acrylic acid ·MMA: Methyl methacrylate ·LMA: Lauryl methacrylate

[0144] <Production Example 1 of Aqueous Dispersion of Uncrosslinked Pigment Particles> 20 parts of LIONOL BLUE FG-7351 (C.I. Pigment Blue 15:3 manufactured by Toyo Color Co., Ltd.), which is a pigment, 25 parts of an aqueous solution of Pigment Dispersing Resin 1 (solid content concentration: 20%), and 55 parts of ion-exchanged water were mixed and preliminarily dispersed with a disper. After that, main dispersion was carried out using a 0.6 L dyno mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. After the main dispersion, 33.3 parts of ion-exchanged water was added to the obtained pigment dispersion. Further, while heating at 60°C, a part of water and methyl ethyl ketone contained in the above aqueous solution of Pigment Dispersing Resin 1 were distilled off under reduced pressure, and then ion-exchanged water was added and adjusted so that the pigment concentration became 15%, whereby an aqueous dispersion 1 of cyan uncrosslinked pigment particles (pigment concentration: 15%) was obtained.

[0145] <Production Examples 2 to 10 of Aqueous Dispersion of Uncrosslinked Pigment Particles> Aqueous dispersions 2 to 10 of cyan uncrosslinked pigment particles were obtained by the same raw materials and method as the above aqueous dispersion 1 of uncrosslinked pigment particles, except that aqueous solutions of Pigment Dispersing Resins 2 to 10 were used instead of the aqueous solution of Pigment Dispersing Resin 1. Note that the pigment concentration was 15% in all cases.

[0146] <Production Example 1 of Aqueous Dispersion of Crosslinked Pigment Particles> 93.3 parts of the aqueous dispersion 1 of uncrosslinked pigment particles obtained above, 1.5 parts of Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140 g / eq.), which is a crosslinking agent (an amount such that the functional group content ratio represented by the above formula 4 is 90 mol%), and 5.2 parts of ion-exchanged water were mixed. While stirring the mixture, it was heated to 80°C and then the crosslinking treatment was carried out by holding at 80°C for 3 hours. Thereafter, ion-exchanged water was added and adjusted so that the pigment concentration became 14%, whereby an aqueous dispersion 1 of cyan crosslinked pigment particles (pigment concentration: 14%) was obtained.

[0147] <Production Examples 2 to 14 of Aqueous Dispersion of Crosslinked Pigment Particles> The aqueous dispersions 2 to 14 of crosslinked cyan pigment particles were obtained in the same manner as the aqueous dispersion 1 of crosslinked pigment particles, except that the type of the aqueous dispersion of uncrosslinked pigment particles used and the addition amounts of the respective raw materials were changed as described in Table 2. Note that all the pigment concentrations were 14%.

[0148]

Table 2

[0149] <Production Example of Binder Resin 1> Using the method described in Example 21 of International Publication No. 2008 / 139980, binder resin 1, which is an A-B block polymer, was produced. Specifically, in the polymerization of the first block, methacrylic acid was used as the polymerizable monomer, and the reaction was carried out at 80°C for 2 hours and then reprecipitated to obtain a first block copolymer with iodine added. The weight average molecular weight (Mw) of the first block copolymer was 6,000. Next, the above first block copolymer and, as polymerizable monomers, styrene, methyl methacrylate, and lauryl methacrylate were used at a mass ratio of 15:65:15, and the reaction was carried out at 80°C for 2.5 hours and then reprecipitated to obtain binder resin 1 in which the iodine-added site of the above first block was substituted with a second block composed of styrene, methyl methacrylate, and lauryl methacrylate. Note that the weight average molecular weight (Mw) of the binder resin 1 was 18,000 and the acid value was 40. Then, the binder resin 1 obtained above was mixed and stirred with 1.5 times the amount (mass ratio) of ion-exchanged water and completely dissolved to obtain an aqueous solution (solid content concentration 40%) of binder resin 1, which is an A-B block polymer.

[0150] <Production of Aqueous Inkjet Ink> The raw materials described in Table 3 were mixed while stirring with a disper and stirred until sufficiently uniform, and then filtered through a 0.8-μm membrane filter to remove coarse particles that could cause head clogging, thereby producing an aqueous inkjet ink.

[0151]

Table 3

[0152]

Table 3

[0153]

Table 3

[0154]

Table 3

[0155]

Table 3

[0156]

Table 3

[0157]

Table 3

[0158]

Table 3

[0159]

Table 3

[0160] The abbreviations described in Table 3 are as follows. · Surfynol DF110D (an acetylene diol-based surfactant manufactured by Evonik Japan, measured HLB value = 6.4) · Surfynol 104 (an acetylene diol - based surfactant manufactured by Evonik Japan, measured HLB value = 7.9) · Surfynol 420 (an acetylene diol - based surfactant manufactured by Evonik Japan, measured HLB value = 8.3) · Surfynol 440 (an acetylene diol - based surfactant manufactured by Evonik Japan, measured HLB value = 10.5) · TEGOTwin 4100 (a gemini - type siloxane - based surfactant manufactured by Evonik Japan, measured HLB value = 8.1) · TEGOTwin 4200 (a gemini - type siloxane - based surfactant manufactured by Evonik Japan, measured HLB value = 8.2) · TEGOTwin 4000 (a gemini - type siloxane - based surfactant manufactured by Evonik Japan, measured HLB value = 2.0) · TEGOGlide 440 (a both - ends polyether - modified siloxane - based surfactant manufactured by Evonik Japan, measured HLB value = 12.1) · BYK - 3420 (a both - ends polyether - modified siloxane - based surfactant manufactured by BYK - Chemie Japan, measured HLB value = 13.8) · TEGOGlide 100 (a both - ends polyether - modified siloxane - based surfactant manufactured by Evonik Japan, measured HLB value = 7.1) · BYK - 348 (a side - chain polyether - modified siloxane - based surfactant manufactured by BYK - Chemie Japan, measured HLB value = 12.2) · BYK - 349 (a side - chain polyether - modified siloxane - based surfactant manufactured by BYK - Chemie Japan, measured HLB value = 10.2) · Propylene glycol (Surface tension: 36.5 mN / m) · 1,5 - Pentanediol (Surface tension: 42.2 mN / m) · 1,3 - Octanediol (Surface tension: 35.0 mN / m) · 3 - Methyl - 1,5 - pentanediol (Surface tension: 38.1 mN / m) · 3 - Methyl - 1,3 - butanediol (Surface tension: 29.9 mN / m) · Hexylene glycol (2 - Methyl - 2,4 - pentanediol, Surface tension: 29.1 mN / m) · 1,2 - Butanediol (Surface tension: 31.6 mN / m) · 1,2 - Hexanediol (Surface tension: 26.5 mN / m) · Dipropylene glycol monopropyl ether (Surface tension: 25.6 mN / m) · Propylene glycol monoethyl ether (Surface tension: 26.3 mN / m) · Propylene glycol monopropyl ether (Surface tension: 25.9 mN / m) · Propylene glycol monobutyl ether (Surface tension: 26.3 mN / m) · Propylene glycol monomethyl ether (Surface tension: 26.7 mN / m) · Diethylene glycol monoisobutyl ether (Surface tension: 24.7 mN / m) · Diethylene glycol monobutyl ether (Surface tension: 27.9 mN / m)

[0161] [Examples 1 - 98, Comparative Examples 1 - 11] Using the aqueous inkjet inks of Examples 1 - 98 and Comparative Examples 1 - 11 manufactured above, the following evaluations were conducted. The evaluation method for the prepared aqueous inkjet inks is as shown below. Also, the evaluation results were as shown in Table 3 above.

[0162] [Evaluation of ejection stability] Each aqueous inkjet ink was filled into an inkjet ejection device installed in an environment at 25°C and equipped with a head (KJ4B - 1200) manufactured by Kyocera. After printing a nozzle check pattern and confirming that the aqueous inkjet ink was ejected normally from all nozzles, solid printing with a printing rate of 100% was continuously performed 100 sheets at a printing condition of 1200×1200 dpi and a drop volume of 3 pl on OK top coat + paper manufactured by Oji Paper Co., Ltd. Then, the nozzle check pattern was printed again, and the ejection stability was evaluated by visually counting the number of clogged nozzles. The driving frequency of the above inkjet head was set to two conditions of 40 kHz and 64 kHz, and the evaluation was performed at each driving frequency. Also, the evaluation criteria were as follows, and D or above was defined as the practical usable range. A: There was no nozzle detachment at all B: There were 1 to 3 nozzle detachments C: There were 4 to 6 nozzle detachments D: There were 7 to 9 nozzle detachments E: There were 10 or more nozzle detachments

[0163] <Evaluation of redissolution property> One drop of each ink was dropped onto a glass plate and placed in a thermo-hygrostat set at a temperature of 50 °C and a humidity of 40% for drying. After a predetermined time had elapsed, the glass plate was taken out of the thermo-hygrostat, pure water was dropped onto the (dried) film, and it was visually confirmed whether it returned to the aqueous inkjet ink. Then, the redissolution property was evaluated by changing the standing time in the thermo-hygrostat and performing the above evaluation. The evaluation criteria were as follows, and C or above was defined as the practical application range. A+: Even after drying for 40 minutes, it visually returned to a uniform aqueous inkjet ink, and there were no foreign substances such as dried films and pigment aggregates A: Even after drying for 30 minutes, it visually returned to a uniform aqueous inkjet ink, and there were no foreign substances such as dried films and pigment aggregates. However, when dried for 40 minutes, foreign substances were observed visually after dropping pure water B: Even after drying for 20 minutes, it visually returned to a uniform aqueous inkjet ink, and there were no foreign substances such as dried films and pigment aggregates. However, when dried for 30 minutes, foreign substances were observed visually after dropping pure water C: Even after drying for 10 minutes, it visually returned to a uniform aqueous inkjet ink, and there were no foreign substances such as dried films and pigment aggregates. However, when dried for 20 minutes, foreign substances were observed visually after dropping pure water E: After drying for 10 minutes, foreign substances such as dried films and pigment aggregates were observed visually

[0164] <Evaluation of dot roundness> An inkjet ejection device used in the above ejection stability evaluation was filled with each aqueous inkjet ink. Next, printing of a gradation image was performed using the same printing conditions as in the above ejection stability evaluation and the same type of printing substrate. The "gradation image" is an image in which the printing rate is continuously changed from 5% to 60% within a predetermined area. After printing the gradation image, an OK top coat + paper printed with the aqueous inkjet ink was put into a 70°C air oven and dried for 1 minute to obtain a gradation printed matter. Then, a portion with a printing rate of 10% in the gradation printed matter was observed with an image evaluation device ("PIAS-II" manufactured by Quality Engineering Associates), and the roundness of the dots was measured. The closer the roundness is to 1, the more circular it is, which means it shows a good dot shape. The evaluation criteria are as follows, and a region of C or higher was defined as the practical use region. A: The roundness was 1 or more and 2 or less B: The roundness was more than 2 and 3 or less C: The roundness was more than 3 and 3.5 or less E: The roundness was greater than 3.5

[0165] <Evaluation of wettability> An inkjet ejection device used in the above ejection stability evaluation was filled with each aqueous inkjet ink. Next, a solid image with a printing rate of 100% was printed using the same printing conditions as in the above ejection stability evaluation and the same type of printing substrate. After printing the solid image, the printed matter was dried for 1 minute using a 70°C air oven. Then, the degree of whiteout of the obtained solid printed matter was confirmed visually and with a magnifying glass to evaluate the wettability. The evaluation criteria are as follows, and an evaluation of C or higher was defined as the practical use region. A: No whiteout was visible visually or with a magnifying glass B: Slight whiteout was visible with a magnifying glass, but no whiteout was visible visually C: Slight whiteout was visible visually E: Obvious whiteout was visible visually

[0166] As can be confirmed from Table 3, the water-based inkjet inks evaluated in Examples 1 to 98 had practical levels of quality in all aspects of redissolution property, ejection stability, dot roundness, and wettability. In particular, in the water-based inkjet inks of Examples 23, 26, 37, 38, 40, 52, 53, 55, 66 to 68, 89 to 93, and 96, in the evaluation of ejection stability in an inkjet head with a driving frequency of 40 kHz, they were at the "A" level, and in the evaluations of redissolution property, dot roundness, and wettability, they were at the "A" or "A+" level. In solving the above-described problems of the present invention, as the siloxane-based surfactant (A-2), it is extremely preferable to use a gemini-type siloxane-based surfactant and a both-terminal polyether-modified siloxane-based surfactant in combination, to set the content mass (total amount) of the siloxane-based surfactant (A-2) to 0.5 to 2 when the content mass (total amount) of the acetylene diol-based surfactant (A-1) contained in the water-based inkjet ink is set to 1, and to set the functional group content ratio (mol%) represented by the above formula 4 to 70 to 120 mol%. As a result, it was shown that this is extremely suitable.

[0167] Among the above-listed examples, in the water-based inkjet inks of Examples 23, 26, 37, 52, 66, 93, and 96, in all evaluations including the evaluation of ejection stability in an inkjet head with a driving frequency of 64 kHz, they were at the "A" or "A+" level. In these water-based inkjet inks, in addition to the above-described elements, as a specific organic solvent, they contain one or more compounds selected from the group consisting of 3-methyl-1,3-butanediol, 2-methyl-2,4-pentanediol (hexylene glycol), and dipropylene glycol monopropyl ether, and it was confirmed that these compounds are particularly effective materials in solving the above-described problems of the present invention.

[0168] On the other hand, Comparative Example 1 is a system in which the pigment dispersion resin is not crosslinked. Since the adsorption of the pigment dispersion resin to the pigment is insufficient, it was confirmed that the printed image quality and redissolution property are impaired by the desorbed pigment dispersion resin, and it does not have a quality suitable for practical use in all qualities.

[0169] On the other hand, in Comparative Examples 2, 9, and 10 that do not contain the siloxane surfactant (A-2), the acetylene diol surfactant could not be uniformly oriented at the gas-liquid interface, and the wettability and dot roundness on the coated paper were not satisfactory. In addition, deterioration of the ejection stability, presumably due to non-uniform orientation of the acetylene diol surfactant near the nozzle, was also confirmed.

[0170] Conversely, in Comparative Examples 3 and 8 that do not contain the acetylene diol surfactant (A-1), not only was the wettability insufficient, but the printed matter had poor dot roundness.

[0171] In addition, the aqueous inkjet inks of Comparative Examples 4 to 7 and 11 do not contain an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or the glycol monoether represented by the above general formula 1 as an organic solvent. As a result of the evaluation, the surfactant could not be sufficiently solubilized, and the ejection stability was impaired due to non-uniform orientation of the surfactant at the nozzle interface, and deterioration of the printed image quality was also observed. In addition, the aqueous inkjet ink of Comparative Example 11 further does not contain the acetylene diol surfactant (A-1), and it was confirmed that, similar to Comparative Examples 3 and 8, the dot roundness and wettability did not reach a practical level.

Claims

1. 1. An aqueous inkjet ink comprising pigment particles, a surfactant, and an organic solvent, The pigment particles include a pigment and a pigment dispersing resin, The pigment dispersing resin has a crosslinked structure, The surfactant comprises an acetylene diol-based surfactant (A-1) having a measured HLB value of 6 to 9 and a siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14; The organic solvent comprises an alkanediol having 5 to 8 carbon atoms (excluding 1,2-alkanediol having 5 to 8 carbon atoms) and / or a glycol monoether represented by the following general formula 1: General formula 1: R 1 -(O-CH(CH 3 )-CH 2 ) n -OH (In general formula 1, R 1 is an alkyl group having 2 to 4 carbon atoms, and n is 1 or 2.

2. 2. The aqueous inkjet ink according to claim 1, wherein the siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14 comprises a gemini type siloxane-based surfactant.

3. The aqueous inkjet ink according to claim 1, wherein the siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14 includes a siloxane-based surfactant modified at both ends with polyether (excluding gemini siloxane-based surfactants).

4. The aqueous inkjet ink according to claim 1, comprising two or more types of siloxane-based surfactants (A-2) having a measured HLB value of 8 to 14.

5. The aqueous inkjet ink according to claim 4, wherein the siloxane-based surfactant (A-2) having a measured HLB value of 8 to 14 comprises a gemini siloxane-based surfactant and a siloxane-based surfactant both ends of which are modified with polyether (excluding gemini siloxane-based surfactants).

6. A printed matter obtained by printing with the aqueous inkjet ink according to any one of claims 1 to 5.

Images