Water-based inkjet inks and printed materials

Abstract

Provided is a water-based inkjet ink that is excellent in continuous ejection stability and straight ejection, and that provides excellent print density and print quality for prints on various printing substrates, particularly paper substrates, and further has good resolubility. [Solution] The aqueous inkjet ink comprises pigment particles including a pigment and a pigment dispersing resin that covers at least a portion of the surface of the pigment, an acetylene diol surfactant (B-1) having a measured HLB value of 6 to 9, a siloxane surfactant (B-2), an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms, wherein the pigment dispersing resin comprises a crosslinked reaction product of a polymer (A-1) that has an aromatic ring and an acid group and an acid value of 50 to 160 mg KOH / g, and a compound (A-2) that has multiple glycidyl ether groups in one molecule, and the compound (A-2) is blended in an amount that results in a glycidyl group content of 50 to 200 mol %.

Description

[Technical Field]

[0001] The present disclosure relates to an aqueous inkjet ink and a method for producing an ink using the aqueous inkjet ink. Concerning the printed matter to be produced. [Background technology]

[0002] Inkjet printing, a type of digital printing method, refers to a method in which tiny droplets of ink are ejected and landed on a printing substrate from an inkjet head to form images and / or characters. In recent years, demand for small-lot printing has increased, accelerating the spread of digital printing methods. Because digital printing methods do not require plates, they enable the miniaturization of printing equipment and the ability to handle small lots. Furthermore, inkjet printing is superior to other digital printing methods in terms of the size and cost of the printing equipment, running costs during printing, and ease of full-color printing.

[0003] Inks used in inkjet printing methods (referred to as "inkjet ink" in this disclosure) are generally classified into solvent-based, water-based, ultraviolet (UV)-curing, and other types depending on their composition. In recent years, there has been a movement to restrict the use of raw materials that are harmful to humans and the environment. Accordingly, there has been a shift to water-based inkjet inks (referred to as "water-based inkjet ink" in this disclosure) rather than solvent-based or ultraviolet (UV)-curing inkjet inks, which use raw materials that pose a high risk of contamination and exposure to humans and the environment.

[0004] In recent years, inkjet printing has become increasingly popular not only for office and home use, but also for commercial and industrial printing. When designing aqueous inkjet inks for commercial printing, it is preferable to use pigments as colorants to improve print density and ensure lightfastness and abrasion resistance. However, stably dispersing pigments has been a challenge with conventional aqueous inkjet inks. Furthermore, when liquid components in the ink evaporate near the nozzles of an inkjet head, the pigment dispersion is disrupted, resulting in solidified material that adheres to the nozzles. This can lead to problems such as incorrect ejection in a direction perpendicular to the nozzle surface (deterioration in straight ejection) or failure to achieve continuous, stable ejection (deterioration in continuous ejection stability). Naturally, this loss of stable ejection also leads to a decline in print density and print quality.

[0005] Furthermore, when printing aqueous inkjet inks on paper substrates, which are primarily used in commercial printing applications, it is assumed that the liquid components of the aqueous inkjet ink will penetrate into the paper substrate. Therefore, when printing aqueous inkjet inks on paper substrates with poor permeability, such as coated paper, beading is likely to occur, making it difficult to produce printed materials with print quality acceptable for practical use. Beading is a phenomenon in which, after a droplet of aqueous inkjet ink lands on a printing substrate, another droplet of the same ink lands adjacent to the previous droplet before it penetrates the substrate and dries, causing adjacent droplets to coalesce. Beading causes color bleeding, leading to a decrease in image quality.

[0006] One possible method for improving the beading problem is to increase the drying speed of the aqueous inkjet ink. In this case, the first droplet of aqueous inkjet ink lands on the printing substrate and dries before the next droplet lands. However, aqueous inkjet inks with high drying speeds tend to dry even near the nozzle, increasing the risk of the aforementioned solidification. As described above, if solidified aqueous inkjet ink adheres near the nozzle, it can lead to deterioration in straight-line ejection and continuous ejection stability. Thus, when designing an aqueous inkjet ink for printing on a poorly absorbent printing substrate, achieving both high image quality and straight-line ejection and continuous ejection stability is an extremely difficult challenge.

[0007] Another possible measure to increase the drying speed of aqueous inkjet ink is to add a certain amount of surfactant, for example, to wet and spread the ink on the printing substrate, thereby increasing the surface area of ​​the aqueous inkjet ink droplets. However, in this case, depending on the printing conditions and the printing substrate used, the shape of the droplets (dot shape) after drying may become distorted (dot roundness may be reduced). If the dot shape is distorted, the visibility of fine characters, for example, may be reduced, which may lead to a deterioration in print quality.

[0008] On the other hand, when printing an aqueous inkjet ink on a paper substrate with high permeability, such as high-quality paper, the components contained in the aqueous inkjet ink, mainly the liquid components, penetrate into the interior of the paper substrate, and the pigment in the aqueous inkjet ink also penetrates, resulting in a problem of reduced print density.

[0009] In particular, when using the same aqueous inkjet ink to print on both a poorly permeable printing substrate and a permeable printing substrate, it is necessary to simultaneously solve all of the above-mentioned problems, which has been extremely difficult with conventional techniques.

[0010] As an example of a study on aqueous inkjet inks that can be printed on various types of printing substrates, Patent Document 1 discloses an inkjet recording ink composition containing three types of acetylene diol surfactants with different structures. It is also claimed that use of this ink composition enables high-speed recording of images with excellent print quality (color unevenness, aggregation, and bleeding) and fixation (abrasion resistance) on a variety of printing substrates with different absorbencies. However, when this ink composition is used on a permeable printing substrate, the surfactant reduces the surface tension of the ink composition, which can cause the pigment components to penetrate into the printing substrate, resulting in a decrease in print density. Furthermore, the inventors' investigations have revealed that the ink composition specifically disclosed in the examples of Patent Document 1 may have problems with continuous ejection stability depending on the printing conditions, etc.

[0011] Patent Document 2 discloses an aqueous inkjet ink containing a high-acid-value vinyl polymer as a shear-thinning agent. Furthermore, by using a certain amount of this vinyl polymer, it is possible to produce printed matter with excellent print quality and abrasion resistance, not only on highly hydrophobic, poorly permeable substrates but also on highly permeable printing substrates, and it is also said that the ink jetting stability is also good. Meanwhile, vinyl polymers with high acid values ​​contain many acid groups in their molecules. As a result, the intermolecular interactions formed by these acid groups affect viscoelasticity, and depending on the printing conditions, this may result in poor straight-line ejection and continuous ejection stability. Furthermore, the aqueous inkjet ink specifically disclosed in the examples of Patent Document 2 does not contain a surfactant. Therefore, depending on the poorly permeable substrate used, the print quality may not necessarily be improved.

[0012] Patent Document 3 discloses an aqueous inkjet ink containing a surfactant and an aprotic polar solvent having a specific molecular weight, for printing on offset media. Furthermore, in the examples of Patent Document 3, printing is performed on recycled paper in addition to various types of coated paper (paragraphs 0035 and 0039). However, Patent Document 3 does not evaluate ejection stability. Furthermore, when the present inventors reproduced the aqueous inkjet ink having a surfactant and organic solvent composition specifically disclosed in the examples of Patent Document 3, they found that continuous ejection stability could deteriorate depending on the printing conditions.

[0013] As described above, there has not been a water-based inkjet ink that can produce printed matter with excellent print density and print quality on a variety of printing substrates while maintaining favorable continuous ejection stability and straight ejection properties. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-124238 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-224248 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-268279 Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aqueous inkjet ink that is excellent in continuous ejection stability and straight ejection, that provides excellent print density and print quality of printed matter on various printing substrates, particularly paper substrates, and that also has good resolubility. [Means for solving the problem]

[0016] In light of the above-mentioned background, the present inventors have conducted extensive research and have found an aqueous inkjet ink having the following composition, thereby completing the present invention.

[0017] That is, one embodiment of the present invention relates to the aqueous inkjet inks shown in [1] to [4] below. Another embodiment of the present invention relates to a printed matter produced using the aqueous inkjet ink shown in [5] below. However, the present invention is not limited to the following embodiments, and includes various embodiments that are modified within the scope that does not change the essential parts of the present invention. [1] A water-based inkjet ink comprising pigment particles, a surfactant, and an organic solvent, the pigment particles include a pigment and a pigment dispersing resin that coats at least a portion of the surface of the pigment, the pigment dispersing resin contains a crosslinked reaction product of a polymer (A-1) having an aromatic ring and an acid group and an acid value of 50 to 160 mgKOH / g and a compound (A-2) having a plurality of glycidyl ether groups in one molecule, The surfactant comprises an acetylene diol surfactant (B-1) having a measured HLB value of 6 to 9 and a siloxane surfactant (B-2), the organic solvent contains an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms; An aqueous inkjet ink having a glycidyl group content of 50 to 200 mol % represented by the following formula (1): Formula (1):

number

[0018] The aqueous inkjet ink according to one embodiment of the present invention has the following advantages: excellent continuous ejection stability and linear ejection, excellent print density and print quality of printed matter on a variety of printing substrates, particularly paper substrates, and also good resolubility. DETAILED DESCRIPTION OF THE INVENTION

[0019] An aqueous inkjet ink according to one embodiment of the present invention (hereinafter also simply referred to as "the aqueous inkjet ink of this embodiment") will be described below. Note that the present invention is not limited to the embodiment described below, and includes embodiments that can be modified without changing the essential parts of the present invention.

[0020] The aqueous inkjet ink of this embodiment has excellent resolubility, continuous ejection stability, and straight ejection, and also provides excellent print density and print quality for prints on various printing substrates, particularly paper substrates. Although the mechanism behind this is not clear, the inventors speculate as follows. However, the present invention is not limited by this speculation.

[0021] The aqueous inkjet ink of this embodiment contains a pigment dispersing resin that coats at least a portion of the pigment surface. The polymer (A-1) has an aromatic ring and an acid group and an acid value of 50 to 160 mgKOH / g, and the crosslinked product of the polymer (A-2) has multiple glycidyl ether groups per molecule. Because aromatic rings are easily adsorbed to the pigment, the crosslinked product effectively stabilizes the pigment dispersion. Furthermore, the acid groups present in the polymer cause charge repulsion in the aqueous inkjet ink. Therefore, when the pigment is dispersed using the polymer (A-1) having the above acid value (i.e., before the crosslinking reaction), the pigment dispersion can be stabilized. On the other hand, when the polymer (A-1) is crosslinked using the compound (A-2) having multiple glycidyl ether groups per molecule, the glycidyl ether groups in the compound (A-2) react with the acid groups. This would reduce the number of acid groups in the crosslinking reaction product, i.e., it is believed that the acid value of the crosslinking reaction product would decrease, which could have an adverse effect on the dispersion state of the pigment particles. In response to this, the aqueous inkjet ink of this embodiment further uses in combination an acetylene diol surfactant (B-1) having a measured HLB value of 6 to 9, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms, thereby stabilizing the dispersion state of the pigment particles and avoiding the above-mentioned adverse effects (details will be described later).

[0022] Furthermore, in the pigment dispersion resin after crosslinking, the bond derived from the acid group in the polymer (A-1) (for example, an ester bond when the acid group is a carboxy group) and the hydroxy group and ether bond derived from the glycidyl ether group in the compound (A-2) are located close to each other. Meanwhile, paper substrates generally contain polyvalent metal salts derived from fillers, pigments, sizing agents, etc. Therefore, when the aqueous inkjet ink of this embodiment is printed on such a paper substrate, it is believed that interactions occur between the polyvalent metal ions derived from the polyvalent metal salts and the bond, hydroxy group, and ether bond. As a result, even when printing on a paper substrate with high permeability, for example, the aqueous inkjet ink is less likely to penetrate into the paper substrate, improving the print density of the printed product.

[0023] On the other hand, with regard to the polymer (A-1) and compound (A-2), the aqueous inkjet ink of this embodiment satisfies the requirement that the glycidyl group content represented by the above formula (1) be 50 to 200 mol %. When the glycidyl group content is within the above range, a sufficient amount of crosslinked structure is formed, which prevents the pigment dispersing resin from being detached from the pigment, and allows dispersion stability to be maintained even after some of the liquid components in the aqueous inkjet ink have evaporated.

[0024] Here, resolubility will be explained. As mentioned above, one of the causes of poor ejection of aqueous inkjet inks is the adhesion of the aqueous inkjet ink to the vicinity of the nozzle. In order to prevent poor ejection, it is important that even if the aqueous inkjet ink partially adheres, the adhered matter can be redissolved, that is, the aqueous inkjet ink has resolubility. As a result of studies by the present inventors, it was found that resolubility can be improved by designing the aqueous inkjet ink so that the pigment dispersing resin does not detach from the pigment even after some of the liquid components in the aqueous inkjet ink have evaporated.

[0025] As described above, the aqueous inkjet ink according to an embodiment of the present invention uses a pigment whose surface is at least partially coated with a pigment dispersing resin that has been crosslinked with compound (A-2) so that the glycidyl group content is 50 to 200 mol %, thereby suppressing detachment of the pigment dispersing resin and improving resolubility.

[0026] Next, we will discuss print quality. Print quality is significantly affected by the surface tension of the aqueous inkjet ink. Furthermore, surfactants are a factor that determines the surface tension of aqueous inkjet inks. Through research, the inventors discovered that the use of an acetylene diol-based surfactant (B-1) with a measured HLB value of 6 to 9 in combination with a siloxane-based surfactant (B-2) in the aqueous inkjet ink of this embodiment significantly improves the print quality of printed materials using the aqueous inkjet ink. Although the acetylene diol-based surfactant (B-1) with a measured HLB value of 6 to 9 is highly hydrophobic and quickly aligns to interfaces, the acetylene diol-based surfactant (B-1) alone does not provide sufficient wettability to the printing substrate or dot circularity, making it difficult to obtain printed materials with high print quality. On the other hand, the siloxane-based surfactant (B-2) is an effective material for improving the wettability and dot circularity, although it aligns to interfaces more slowly than the acetylene diol-based surfactant (B-1). In contrast, the aqueous inkjet ink of this embodiment uses both surfactants in combination to improve print quality. The presumed mechanism is that the siloxane-based surfactant (B-2) functions to emulsify the acetylenic diol-based surfactant (B-1). That is, the siloxane-based surfactant (B-2) is rapidly oriented at the interface together with the acetylenic diol-based surfactant (B-1), which is thought to significantly improve wettability to the printing substrate and dot roundness.

[0027] As described above, the aqueous inkjet ink of this embodiment is believed to suppress detachment of the pigment dispersion resin from the pigment. This prevents the surfactant from being adsorbed onto the detached pigment dispersion resin, which would inhibit the surfactant from being oriented at the interface. As a result, each surfactant can fully exert its aforementioned functions, which is believed to facilitate an improvement in the print quality of the printed matter.

[0028] The siloxane surfactant (B-2) preferably has a measured HLB value of 1 to 8. As the siloxane surfactant (B-2), gemini siloxane surfactants, side chain polyether-modified siloxane surfactants, and both terminal polyether-modified siloxane surfactants can be preferably used.

[0029] On the other hand, aqueous inkjet inks that simply combine a pigment at least partially coated with the above-described pigment dispersion resin having a crosslinked structure with an acetylene diol surfactant (B-1) and a siloxane surfactant (B-2) may have poor straight-line ejection properties. Furthermore, if ejection is continued while straight-line ejection properties are poor, the aqueous inkjet ink may accumulate in part of the nozzle opening. If this deposit increases or dries up, it may clog (part of) the nozzle opening, making stable ejection impossible. In other words, continuous ejection stability may be impaired.

[0030] Here, "good straight-line ejection properties" means that the aqueous inkjet ink is ejected in a direction perpendicular to the nozzle surface, and "poor straight-line ejection properties" means that the aqueous inkjet ink is ejected in a direction oblique to the nozzle surface.

[0031] One possible reason for the poor ejection straightness is poor compatibility between the constituent materials. Pigment particles at least partially coated with a crosslinked pigment dispersion resin have low compatibility with highly hydrophobic surfactants, such as acetylene diol-based surfactants (B-1). Therefore, it is thought that the acetylene diol-based surfactant (B-1) and siloxane-based surfactant (B-2) are unlikely to be uniformly oriented at the interface of the aqueous inkjet ink near the nozzle orifice. Under such conditions, the aqueous inkjet ink is not ejected stably and straight, making it difficult for the aqueous inkjet ink droplets to land in the intended positions on the printing substrate (resulting in poor landing accuracy). Furthermore, depending on the siloxane-based surfactant (B-2) used in combination, the emulsification state described above may become unstable, potentially preventing sufficient improvement in print quality. On the other hand, as mentioned above, the combined use of the highly hydrophobic acetylene diol-based surfactant (B-1) and siloxane-based surfactant (B-2) is essential to obtain printed materials with excellent print quality.

[0032] As a result of extensive research, the present inventors have found that the above-mentioned components can be further combined with an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms. While the detailed mechanism is unknown, it is believed that the combined use of an alkanediol having 5 to 8 carbon atoms and a glycol ether having 4 to 10 carbon atoms improves the compatibility between the pigment particles and the highly hydrophobic surfactant. This is believed to result in the acetylene diol surfactant (B-1) and further the siloxane surfactant (B-2) being uniformly oriented at the interface, improving properties such as straight-line ejection and continuous ejection stability. Furthermore, the improved compatibility is also effective in stabilizing the dispersion state of the pigment particles.

[0033] It is preferable to use an alkanediol containing a branched alkyl group and not a 1,2-alkanediol as the alkanediol having 5 to 8 carbon atoms. This is thought to be because the alkanediol has a similar structure to the acetylene diol surfactant (B-1) and has a high affinity, thereby contributing particularly effectively to improving the compatibility.

[0034] Furthermore, in the aqueous inkjet ink of this embodiment, in addition to the alkanediol having 5 to 8 carbon atoms and the glycol ether having 4 to 10 carbon atoms, an alkanediol having 3 to 4 carbon atoms is also used in combination. Because the alkanediol having 5 to 8 carbon atoms and the glycol ether having 4 to 10 carbon atoms do not necessarily have a high affinity with water, these components may cause a deterioration in continuous ejection stability or may result in insufficient stabilization of the emulsified state as described above, which may deteriorate the straight ejection performance, print image quality, etc. Therefore, by using an alkanediol having 3 to 4 carbon atoms, which has a high affinity with water, the components with poor affinity with water are stabilized within the aqueous inkjet ink, thereby achieving improvements in continuous ejection stability, straight ejection performance, print image quality, etc.

[0035] As described above, the aqueous inkjet ink of this embodiment has excellent resolubility. That is, a dried film that has adhered to the nozzle orifice can be easily redissolved in the aqueous inkjet ink. From this perspective, the aqueous inkjet ink of this embodiment also has excellent straight-line ejection properties and continuous ejection stability.

[0036] As described above, the aqueous inkjet ink of this embodiment is essential to simultaneously and highly effectively solve the above-mentioned problems.

[0037] Next, the components that may be contained in the aqueous inkjet ink according to one embodiment of the present invention will be described below. This will be explained in detail.

[0038] <Pigment particles> The aqueous inkjet ink of this embodiment contains pigment particles. The pigment particles further contain a pigment and a pigment dispersion resin that coats at least a portion of the surface of the pigment. The pigment dispersion resin further contains a crosslinked reaction product of a polymer (A-1) having an aromatic ring and an acid group and an acid value of 50 to 160 mgKOH / g, and a compound (A-2) having multiple glycidyl ether groups in one molecule.

[0039] In the present disclosure, the phrase "the pigment dispersion resin comprises a crosslinked reaction product of a polymer (A-1) and a compound (A-2) having multiple glycidyl ether groups per molecule" means that a crosslinked structure is formed between the polymer (A-1) molecules. The formation of a crosslinked structure between the polymer (A-1) molecules results in at least a portion of the pigment surface being coated with the pigment dispersion resin having a crosslinked structure, thereby achieving the aforementioned benefits of suppressing detachment of the pigment dispersion resin, improving resolubility, and improving print quality. The polymer (A-1) may have a crosslinked structure within the polymer (A-1) molecule.

[0040] In the present disclosure, "coated" refers to the state in which the surface of the pigment is covered with the pigment dispersing resin. However, "coated" also includes a state in which the surface of the pigment is only partially covered, in addition to a state in which the surface of the pigment is completely covered. Furthermore, in the present disclosure, when simply referring to an "acid group," the "acid group" is used as a general term to refer to non-anionized acid groups (e.g., carboxy groups, sulfo groups, etc.) and anionized acid groups (e.g., carboxylate groups, sulfonate groups, etc.).

[0041] <Pigments> The pigment particles contained in the aqueous inkjet ink of this embodiment contain a pigment. Printed matter produced using the aqueous inkjet ink containing the pigment has high density. Furthermore, by coating at least a portion of the pigment surface with the pigment dispersion resin and using it in combination with the surfactant and organic solvent described above, printed matter with excellent print quality can be obtained.

[0042] In the aqueous inkjet ink of this embodiment, an organic pigment may be used as the pigment. Alternatively, inorganic pigments may be used, or both may be used in combination.

[0043] When an inorganic pigment is used as the pigment, titanium oxide, zinc white, zinc sulfide, white lead, 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, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, Prussian blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, cobalt violet, and the like can be used.

[0044] For example, when carbon black is used as an inorganic pigment, carbon black produced by either the furnace method or the channel method can be suitably used. In addition, these carbon blacks have a primary particle diameter of 11 to 40 nm and a specific surface area according to the BET method of 50 to 400 m. 2 Carbon black having properties such as a volatile content of 0.5 to 10% and a pH value of 2 to 10 can be particularly preferably used.

[0045] 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; and 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 threne pigments. Furthermore, the hue is not particularly limited, and chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used.

[0046] Specific examples of pigments that can be used as the organic pigments, in terms of color index, include cyan and blue pigments such as CI Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, and 64.

[0047] Furthermore, examples of red pigments and violet pigments include CI Pigment Red 2, 5, 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, and 282, and CI Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

[0048] Furthermore, examples of yellow pigments include CI Pigment Yellow 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, and 213.

[0049] Examples of black pigments include aniline black (CI Pigment Black 1), perylene black (CI Pigment Black 31, 32), azomethine azo black, etc. A mixture of multiple chromatic pigments such as the above blue pigments, red pigments, violet pigments, and yellow pigments, as well as the below-mentioned brown pigments and orange pigments, can also be used as a black pigment.

[0050] Examples of pigments other than those listed above include CI Pigment Green 7, 10, 36, CI Pigment Brown 3, 5, 25, 26, CI Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, and the like.

[0051] 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 even more preferably 2 to 7% by mass, based on the total mass of the aqueous inkjet ink.

[0052] <Pigment dispersing resin> The pigment dispersing resin is a resin that has the function of dispersing a pigment. In the case of the aqueous inkjet ink of this embodiment, the pigment dispersing resin is a crosslinked reaction product of a polymer (A-1) that has an aromatic ring and an acid group and an acid value of 50 to 160 mgKOH / g and a compound (A-2) that has multiple glycidyl ether groups in one molecule. In the aqueous inkjet ink of this embodiment, any resin that has the function of dispersing a pigment can be used as the pigment dispersing resin together with the crosslinked reaction product.

[0053] <Polymer (A-1)> As described above, the polymer (A-1) has an acid group in its molecular structure. It is also preferable that the crosslinked product has an acid group remaining in its molecular structure. Furthermore, in both the polymer (A-1) and the crosslinked product, the acid group is preferably a carboxyl group and / or a carboxylate group (R-COO - ) is more preferable.

[0054] The acid value of the polymer (A-1) is 50 to 160 mgKOH / g, preferably 60 to 140 mgKOH / g, and more preferably 80 to 130 mgKOH / g, from the viewpoint of further improving resolubility and print image quality by significantly suppressing detachment of the polymer (A-1) from the pigment.

[0055] Furthermore, when acid groups remain in the crosslinking reaction product, the crosslinking reaction product has an acid value of preferably 10 to 90 mgKOH / g, particularly preferably 15 to 70 mgKOH / g, from the viewpoints of increasing compatibility with the acetylene diol surfactant (B-1) and improving continuous ejection stability and straight ejection properties.

[0056] The acid value of polymer (A-1) can be measured by standard methods. For example, approximately 1 g of polymer (A-1), which has been previously acid-precipitated, is precisely weighed into an Erlenmeyer flask, and 50 ml of a 1:9 (by mass) mixture of distilled water and dioxane is added to dissolve the polymer (A-1). This sample solution is then titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (potency F). A potentiometric measuring device (e.g., the Kyoto Electronics Manufacturing Co., Ltd. "Automatic Potentiometric Titrator AT-710M") is used for the titration. The acid value (mgKOH / g) can then be calculated using the amount of potassium hydroxide-ethanol solution (α (mL)) required to reach the titration endpoint using the following equation (2):

[0057] Formula (2): Acid value (mgKOH / g)=(5.611×α×F) / S

[0058] In equation (2), S is the amount (g) of sample polymer (A-1) collected, α is the amount (ml) of 0.1 mol / L potassium hydroxide ethanol solution added until the titration ends, and F is the titer of the 0.1 mol / L potassium hydroxide ethanol solution.

[0059] On the other hand, as will be described later, resins generally used in aqueous inkjet inks include water-soluble resins and water-insoluble resins. In this embodiment, either a water-soluble resin or a water-insoluble resin may be used as the polymer (A-1). The crosslinked reaction product may also be either a water-soluble resin or a water-insoluble resin. Therefore, for example, a crosslinked reaction product obtained by crosslinking the water-soluble polymer (A-1) may be in the form of a water-insoluble resin. Furthermore, for example, a crosslinked reaction product obtained by crosslinking the water-insoluble polymer (A-1) may be used (naturally, the crosslinked reaction product is in the form of a water-insoluble resin).

[0060] A method for determining whether a resin contained in an aqueous inkjet ink functions as a pigment dispersing resin is described below. For example, in an aqueous inkjet ink, a resin that covers at least a portion of the surface of a pigment is a resin that functions to disperse the pigment, i.e., a pigment dispersing resin. In this case, if the resin does not have a crosslinked structure between resin molecules, the resin is a polymer (A-1), and if it has a crosslinked structure, the resin is a crosslinked reaction product.

[0061] On the other hand, for example, when a water-soluble resin is used as the polymer (A-1), and adsorption and desorption from the pigment surface are in equilibrium, it can be confirmed by a method in accordance with JIS K 5101-1-4:2004 whether the water-soluble resin has the function of dispersing the pigment.

[0062] Specifically, the primary particle diameter is 15 to 25 nm, the nitrogen adsorption specific surface area is 120 to 260 m2 / g, and the DBP absorption amount (granular) is 40 to 80 cm 3 600 g of carbon black (100 g / 100 g), 200 g of the target resin, and 2,200 g of water are thoroughly mixed (premixed), and then dispersed for 4 hours using a 0.6 L bead mill (e.g., Shinmaru Enterprises' "Dyno Mill") filled with 1,800 g of grinding beads (e.g., 0.5 mm diameter zirconia beads). After dispersion, the viscosity of the resulting carbon black dispersion at 25°C is measured using an E-type viscometer (e.g., Toki Sangyo's "TVE25L Viscometer"). The carbon black dispersion is then stored in a constant-temperature, ventilated incubator set at 70°C for one week, and the viscosity is measured again. If the viscosity of the dispersion immediately after dispersion is 100 mPa·s or less and the absolute value of the viscosity change of the carbon black dispersion before and after storage is 10% or less, the resin is deemed to have the ability to disperse pigments.

[0063] Examples of resins that can be used as the polymer (A-1) include acrylics, maleic acid resins, urethane resins, polyester resins, etc. Furthermore, with regard to the types of resins that can be used as the polymer (A-1), any of the above-listed resins can be used as long as it has an aromatic ring and an acid group and has an acid value of 50 to 160 mgKOH / g, as described below.

[0064] In the present disclosure, the term "acrylic resin" refers to a resin using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters. In addition to the polymerizable monomers listed above, a styrene-based monomer may also be used as the polymerizable monomer for forming the acrylic resin. Meanwhile, resins containing maleic acid (anhydride) (at least one selected from "maleic acid" and "maleic acid anhydride") as a polymerizable monomer are excluded from the "acrylic resin" of the present disclosure. Furthermore, the term "maleic acid-based resin" refers to a resin using at least maleic acid (anhydride) as a polymerizable monomer. The maleic acid-based resin may also use, as a polymerizable monomer, an α-olefin, a styrene-based monomer, acrylic acid, methacrylic acid, an acrylic acid ester, a methacrylic acid ester, or the like.

[0065] As described above, it is preferable that both the polymer (A-1) and the crosslinking reaction product after the crosslinking treatment have acid groups remaining in their molecular structures. In this case, it is preferable that at least a portion of the non-anionized acid groups contained in these resins be neutralized with a basic compound to become anionized acid groups. This is because the charge repulsion between the anionized acid groups allows for stable dispersion of pigment particles and improves continuous ejection stability, linear ejection, resolubility, and other properties. 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, sodium bicarbonate, dipotassium carbonate, and sodium borate. Among these, alkali metal compounds are preferred because they can easily achieve dispersion stability of pigment particles in aqueous inkjet inks and further improve continuous ejection stability, linear ejection, resolubility, and other properties. The basic compounds listed above can be used alone or in combination.

[0066] The amount of the basic compound added when neutralizing the polymer (A-1) and the crosslinking reaction product is preferably such that the pH of a 20% by mass aqueous solution of the polymer (A-1) and the crosslinking reaction product after the total amount of the basic compound is added is 7 to 12.

[0067] In the present disclosure, the term "aqueous solution" refers to a liquid containing an aqueous solvent and components dispersed and / or dissolved in the aqueous solvent. The pH of the aqueous solution is a value at 25°C and can be measured by a conventional method. For example, it can be measured using a tabletop pH meter "F-71" (manufactured by Horiba Ltd.) that uses a pH electrode "6337-10D" (manufactured by Horiba Ltd.).

[0068] On the other hand, the preferred amount of the basic compound used to neutralize the polymer (A-1) and the crosslinking reaction product can be specifically expressed in terms of the neutralization ratio. From the viewpoints of improving the dispersion stability and resolubility of the pigment particles, as well as the continuous ejection stability and linear ejection performance, the neutralization ratio is preferably 10 to 200 mol%, more preferably 40 to 160 mol%, and particularly preferably 60 to 120 mol%. Here, the neutralization ratio is calculated by dividing the molar amount of basic groups in the added basic compound by the molar amount of acid groups in the target resin (polymer (A-1) or crosslinking reaction product), and can be calculated using the following formula (3): When using at least a partially neutralized resin (e.g., containing at least carboxylate groups) as the polymer (A-1) and the crosslinking reaction product, the neutralization ratio is calculated assuming that all acid groups in the resin are unneutralized (e.g., assuming that all carboxylate groups in the resin molecule are carboxyl groups).

[0069] Formula (3):

number

[0070] The content of polymer (A-1) relative to the content of the pigment is preferably 1 to 100% by mass. By making the content of polymer (A-1) relative to the content of the pigment 1% by mass or more, the viscosity of the aqueous inkjet ink can be controlled to a level suitable for inkjet printing applications, and resolubility can also be improved. Furthermore, by making the content 100% by mass or less, dispersion stability, storage stability after dispersion, and continuous ejection stability can be improved. The content of polymer (A-1) is more preferably 2 to 50% by mass.

[0071] ≪Compound (A-2)≫ The compound (A-2) having a plurality of glycidyl ether groups in one molecule is used to crosslink the polymer (A-1), and is a material also known as a "crosslinking agent."

[0072] The epoxy equivalent of compound (A-2) is preferably 90 to 300 g / eq., more preferably 100 to 200 g / eq., from the viewpoint of enabling more efficient reaction with the acid groups in polymer (A-1) in a liquid medium containing water (aqueous medium). Efficient reaction of compound (A-2) makes it easier to achieve the glycidyl group content requirement described below. This also facilitates improvements in the dispersion stability, resolubility, print density, print image quality, and continuous ejection stability of pigment particles.

[0073] The compound (A-2) may be water-soluble or water-insoluble, but from the viewpoint of being able to react more efficiently with the acid groups in the polymer (A-1) in an aqueous medium, the solubility 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 even more preferably 0.5 to 30 g / 100 g H2O.

[0074] Specific examples of compounds having multiple glycidyl ether 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'-diglycidyloxybiphenol, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, phthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, and hydrogenated phthalic acid diglycidyl ester.

[0075] In the aqueous inkjet ink of this embodiment, compound (A-2) is added so that the glycidyl group content represented by the following formula (1) is 50 to 200 mol %. By incorporating compound (A-2) so that the glycidyl group content is 50 to 200 mol %, detachment of the crosslinked reaction product from the pigment can be reduced, improving resolubility and continuous discharge stability. Furthermore, the free polymer (A-1) is less likely to inhibit the surfactant's functionality, improving the print quality of the aqueous inkjet ink. Furthermore, sufficient amounts of hydroxy groups and ether bonds derived from glycidyl ether groups are formed in the crosslinked reaction product, improving the print density of the printed material. From these perspectives, compound (A-2) is more preferably added so that the glycidyl group content represented by the following formula (1) is 70 to 120 mol %, and particularly preferably 80 to 100 mol %. Formula (1):

number

[0076] Other pigment dispersion resins As described above, the aqueous inkjet ink of this embodiment may contain a pigment dispersing resin other than the crosslinking reaction product (referred to as "other pigment dispersing resins" in the present disclosure). For example, the crosslinking reaction product and the polymer (A-1) may be used in combination, that is, the crosslinking reaction product and the polymer (A-1) may coexist in the aqueous inkjet ink.

[0077] From the viewpoint of optimally achieving the effects of the crosslinking reaction product described above, the content of other pigment dispersion resins contained in the aqueous inkjet ink of this embodiment is preferably 80% by mass or less (or may be 0% by mass) relative to the content of the crosslinking reaction product, more preferably 50% by mass or less, and particularly preferably 25% by mass or less.

[0078] <Method for producing pigment particles containing crosslinking reaction product> An example of a method for producing pigment particles (crosslinked pigment particles) containing a pigment and a crosslinking reaction product is a method in which a dispersion treatment step and a crosslinking treatment step are carried out in this order, as shown below. Optionally, a neutralization treatment step as shown below may be carried out before the dispersion treatment step.

[0079] First, the non-anionized acid groups present in the polymer (A-1) are mixed with a basic compound in an aqueous medium to neutralize at least a portion of the non-anionized acid groups (neutralization step). As described above, the non-anionized acid groups present in the polymer (A-1) are converted to anionized acid groups by the neutralization. This pigment dispersion resin having at least anionized acid groups is used in the subsequent steps. The polymer (A-1) obtained after the neutralization step is in the form of an aqueous solution. Next, the pigment is added to the aqueous solution of the polymer (A-1), and the two are mixed, followed by a further dispersion treatment (dispersion treatment step).The dispersion treatment step produces an aqueous dispersion of pigment particles (uncrosslinked pigment particles) having the polymer (A-1) chemically adsorbed to at least a portion of the pigment surface. Thereafter, the compound (A-2) is added to the aqueous dispersion of the uncrosslinked pigment particles to carry out a crosslinking treatment (crosslinking treatment step).By this crosslinking treatment step, an aqueous dispersion of crosslinked pigment particles can be produced.

[0080] <Dispersion processing process> The disperser used in the dispersion treatment may be any commonly used disperser, such as a media-type wet disperser, a media-less wet disperser, or a kneader. Examples of media-type wet dispersers include paint shakers, ball mills, roll mills, bead mills, and attritors; examples of media-less wet dispersers include high-pressure homogenizers and ultrasonic dispersers; and examples of kneaders include kneaders. Among these, it is preferable to select a bead mill from the viewpoint of crushing and refining coarse pigment particles. Examples of bead mills include a super mill, a sand grinder, an agitator mill, a grain mill, a dyno mill, a pearl mill, and a cobol mill (all trade names).

[0081] Using the disperser listed above, the pigment can be pulverized to a desired particle size by the collision force with the media or shear stress. From the viewpoint of obtaining a pigment dispersion with a uniform particle size, it is preferable to pre-disperse (premix) the pigment and polymer (A-1) and then further disperse (main dispersion) using the disperser listed above. A commonly used mixing and stirring device such as a disperser can be used as the pre-disperser used for pre-mixing.

[0082] <Crosslinking process> As described above, by subjecting the polymer (A-1) adsorbed to the pigment to a crosslinking treatment, pigment particles in which the pigment dispersing resin is crosslinked can be obtained. Furthermore, a method of forming a crosslinked structure using a compound (A-2) can be suitably used as the crosslinking treatment method. Specifically, a method can be used in which a mixture containing uncrosslinked pigment particles, the compound (A-2), and water is heated and stirred.

[0083] 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. The time for 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.

[0084] From the viewpoint of enabling stable ejection from a nozzle, the average particle size of the crosslinked pigment particles is preferably 60 to 200 nm, more preferably 70 to 175 nm, and particularly preferably 80 to 150 nm.

[0085] The average particle size is the volume-based median diameter, which can be measured by dynamic light scattering, for example, using a Microtrac-Bell Nanotrac UPA-EX150 at 25°C.

[0086] <Pigment dispersion> The crosslinked pigment particles may be dispersed in an aqueous medium, i.e., in the form of an aqueous dispersion of crosslinked pigment particles. The aqueous inkjet ink of this embodiment is preferably produced by mixing a previously produced aqueous dispersion of crosslinked pigment particles with other raw materials, as this can improve continuous ejection stability.

[0087] In the present disclosure, a composition containing pigment particles and an aqueous medium is referred to as a "pigment dispersion." Therefore, the above-described aqueous dispersion of uncrosslinked pigment particles and the above-described aqueous dispersion of crosslinked pigment particles are both included in the "pigment dispersion." As will be described later, the pigment dispersion is used as a raw material for aqueous inkjet ink, and is different from the aqueous inkjet ink. Specifically, the pigment dispersion and the aqueous inkjet ink differ in the pigment content. For example, the amount of pigment contained in the pigment dispersion is preferably 10 to 60 mass% of the total amount of the pigment dispersion, more preferably 15 to 55 mass%, and even more preferably 20 to 50 mass%. The preferred amount of pigment contained in the aqueous inkjet ink is as described below. Furthermore, when the amount of pigment contained in the pigment dispersion (% by mass) is PP and the amount of pigment contained in the aqueous inkjet ink (% by mass) is PI, the value expressed as PP / PI is preferably 1.5 to 10, and more preferably 2 to 8.

[0088] The pigment dispersion may be produced by first preparing pigment particles in a dry state (solid) and then mixing them with an aqueous medium, or may be produced by the above-mentioned method for producing pigment particles containing a crosslinked reaction product.

[0089] The aqueous medium contained in the pigment dispersion contains at least water. It may also contain an organic solvent (described in detail below) that can be used as a raw material for aqueous inkjet inks. 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.

[0090] The pH of the pigment dispersion is preferably 8 to 12. If the pH is 8 or higher, the anionized acid groups present in the pigment dispersion resin can be stably present, and dispersion stability due to charge repulsion can be improved. From this viewpoint, the pH is more preferably 9 to 11. The pH of the pigment dispersion can be measured in the same manner as for the aqueous solution of polymer (A-1) described above.

[0091] <Surfactant> The aqueous inkjet ink of this embodiment contains, as surfactants, an acetylene diol surfactant (B-1) having a measured HLB value of 6 to 9, and a siloxane surfactant (B-2).

[0092] The "HLB (Hydrophilic-Lipophilic Balance) value" is one of the parameters that indicates the degree of hydrophilicity and hydrophobicity of a material. The smaller the HLB value, the more hydrophobic the material, and the larger the HLB value, the more hydrophilic the material. The HLB value can be calculated from the molecular structure or measured experimentally. In this disclosure, the HLB value used is the value calculated by actual measurement using the method described below (measured HLB value). (1) Dissolve 0.5 g of the target surfactant in 5 mL of ethanol. (2) At 25°C, the mixture from (1) is titrated with a 2% aqueous phenol solution while stirring. The endpoint is when the mixture becomes cloudy and no longer returns to a transparent state upon dropwise addition of the 2% aqueous phenol solution. (3) When the amount of 2% phenol aqueous solution dropped up to the end point is A [mL], calculate the measured HLB value according to the following formula (4).

[0093] Formula (4): Actual HLB value = 0.89 x A + 1.11

[0094] <Acetylene diol surfactant (B-1)> The aqueous inkjet ink of this embodiment contains an acetylenic diol surfactant (B-1) having a measured HLB value of 6 to 9. The measured HLB value of the acetylenic diol surfactant (B-1) is preferably 6 to 8, because it has low affinity with water and quickly orients at the gas-liquid interface, resulting in excellent wettability to the printing substrate and improved print density.

[0095] Examples of the acetylenic diol surfactant (B-1) that can be used include 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 (provided that the number of moles of ethylene oxide added is 1.5 moles or less), and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol. Commercially available examples of the acetylenic diol surfactant (B-1) include Surfynol DF-110D, Surfynol 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, and 420 (manufactured by Evonik Japan Co., Ltd.), and Acetylenol E00 and E13T (manufactured by Kawaken Fine Chemicals Co., Ltd.). These compounds may be used alone or in combination of two or more.

[0096] From the viewpoint of ensuring excellent print quality, the content of the acetylene diol surfactant (B-1) in the aqueous inkjet ink is preferably 0.1 to 5 mass %, more preferably 0.3 to 3 mass %, and particularly preferably 0.5 to 2 mass %.

[0097] <Siloxane surfactant (B-2)> As described above, the aqueous inkjet ink of this embodiment contains a siloxane-based surfactant (B-2). The siloxane-based surfactant (B-2) can be oriented to compensate for the non-uniform orientation of the acetylenic diol-based surfactant (B-1), and is therefore effective in improving dot circularity and reducing unevenness. In particular, the measured HLB value of the siloxane-based surfactant (B-2) is preferably 1 to 8, because the siloxane-based surfactant (B-2) has an increased affinity with the more hydrophobic acetylenic diol-based surfactant (B-1), allowing it to be rapidly oriented at the interface together with the acetylenic diol-based surfactant (B-1), improving wettability to the printing substrate and dot circularity, thereby improving print image quality.

[0098] As described above, the siloxane surfactant (B-2) can be a gemini siloxane surfactant, a siloxane surfactant modified at both ends with polyether, a side-chain polyether-modified siloxane surfactant, etc. Among these, it is preferable that the siloxane surfactant (B-2) contains a gemini siloxane surfactant and / or a siloxane surfactant modified at both ends with polyether, because even with a small amount of addition, unevenness can be reduced and printed matter with good dot circularity and wettability can be obtained, and the ejection stability of the aqueous inkjet ink is also improved.

[0099] <Gemini siloxane surfactants> 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 addition, in the case of a gemini siloxane surfactant, for example, a siloxane chain (-[O-SiR 1 R 2 ] x-, where R 1 and R 2 are each an arbitrary organic group, and x is an integer of 2 or more.) and a hydrophilic structure (for example, a polyether chain) has the following structure: A structure in which the bonding points between the siloxane chain and the hydrophilic structure are located in the middle of the siloxane chain and the middle of the hydrophilic structure, respectively. Multiple siloxane chains are bonded via linking groups, etc. (for example, R 1 and / or R 2 at least a portion of which is an organic chain containing a siloxane chain). A structure in which multiple siloxane chains each have multiple hydrophilic structures and share some of the hydrophilic structures.

[0100] Gemini surfactants have superior surface tension reducing ability compared to general surfactants. Therefore, the use of gemini siloxane surfactants can achieve a superior reduction in surface tension compared to non-gemini siloxane surfactants. As a result, the wettability and dot roundness of aqueous inkjet inks containing gemini siloxane surfactants can be significantly improved, enabling a significant improvement in print image quality.

[0101] Examples of commercially available gemini siloxane surfactants include, but are not limited to, TEGOTwin4000, TEGOTwin4100, and TEGOTwin4200 manufactured by Evonik Japan Co., Ltd.

[0102] <<Both-end polyether modified siloxane surfactants (Gemini type siloxane surfactants) (excluding surfactants) A dual-end polyether-modified siloxane surfactant has a structure in which polyether chains are bonded to both ends of a polysiloxane skeleton. Aqueous inkjet inks containing dual-end polyether-modified siloxane surfactants improve print quality by uniformly spreading the ink on the printing substrate and improving dot roundness, and also improve continuous ejection stability, although the details are unclear. A compound represented by the following general formula (5) is preferably used as the dual-end polyether-modified siloxane surfactant.

[0103] General formula (5): [ka]

[0104] In general formula (5), l represents an integer of 1 to 100, and R 3 represents a structure represented by the following general formula (6).

[0105] General formula (6): [ka]

[0106] In the general formula (5), p represents an integer of 1 to 6, q represents an integer of 1 to 100, and r represents an integer of 0 to 80, provided that p+r is an integer of 1 or more. 4 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a methacryloyl group, or an acryloyl group, provided that the addition of the ethylene oxide groups (OC2H4) and propylene oxide groups (OC3H6) in the brackets may be in a block or random manner.

[0107] Examples of commercially available products of the compound represented by general formula (5) include, but are not limited to, BYK-333, BYK-UV3500, and BYK-3420 manufactured by BYK-Chemie; TEGOGlide 100, TEGOGlide 432, TEGOGlide 440, and TEGOGlide 450 manufactured by Evonik Japan; and KF-6004, KF-6123, X-22-4952, and X-22-4272 manufactured by Shin-Etsu Chemical Co., Ltd.

[0108] <Side chain polyether modified siloxane surfactant (Gemini type siloxane interface (Excluding those that are activators)≫ The siloxane surfactant (B-2) may be a side-chain polyether-modified siloxane surfactant (excluding gemini siloxane surfactants). Side-chain polyether-modified siloxane surfactants, even with relatively low molecular weight, exhibit high orientation in aqueous media and can achieve excellent wettability. It is preferable to use a surfactant represented by the following general formula (7) as the side-chain polyether-modified siloxane surfactant:

[0109] General formula (7): [ka]

[0110] In the general formula (7), 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. 5 is a structure represented by the above general formula (6), and R 6 represents an alkyl group having 1 to 6 carbon atoms.

[0111] Commercially available products of the compound represented by the general formula (7) include BYK-345, BYK-347, BYK-348, BYK-349, BYK-3450, and BYK-3451 manufactured by BYK-Chemie; TEGOWet 240, TEGOWet 250, TEGOWet 260, TEGOWet 270, and TEGOWet 280 manufactured by Evonik Japan; Examples of such fluoropolymers include, but are not limited to, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, LKF-643, KF-644, KF-945, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, and X-22-4515.

[0112] From the viewpoint of ensuring excellent print quality, the content of the siloxane surfactant (B-2) in the aqueous inkjet ink is preferably 0.1 to 5% by mass, more preferably 0.3 to 3.5% by mass, and particularly preferably 0.5 to 2.5% by mass.

[0113] Other surfactants The aqueous inkjet ink of this embodiment may contain surfactants other than the acetylene diol surfactant (B-1) and the siloxane surfactant (B-2) (also referred to as "other surfactants" in the present disclosure).

[0114] As the other surfactant, one or more surfactants selected from the group consisting of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants (excluding the acetylenic diol surfactant (B-1) and the siloxane surfactant (B-2)) can be used. In particular, from the viewpoint of excellent compatibility with the acetylenic diol surfactant (B-1) and the siloxane surfactant (B-2), and improving continuous discharge stability, discharge straightness, and print quality of printed matter, it is preferable to use a nonionic surfactant other than the acetylenic diol surfactant (B-1) and the siloxane surfactant (B-2) (also simply referred to as "nonionic surfactant (B-3)" in the present disclosure) as the other surfactant.

[0115] Examples of the nonionic surfactant (B-3) that can be used include acetylene diol surfactants (excluding the acetylene diol surfactant (B-1)), acetylene monool surfactants, fluorine-containing surfactants, polyoxyalkylene monoalkyl ether surfactants (specifically, compounds having ethylene oxide groups and / or propylene oxide groups, in which the total number of moles of ethylene oxide groups and propylene oxide groups added is 5 to 100, and the alkyl or alkenyl group at the molecular terminal has 5 to 22 carbon atoms). These other surfactants may be used alone or in combination of two or more.

[0116] Among these, it is preferable to use the above polyoxyalkylene monoalkyl ether surfactants as the nonionic surfactant (B-3) because they have excellent affinity with the acetylene diol surfactant (B-1), and also provide good continuous ejection stability, straight ejection, print quality of printed matter, and resolubility.

[0117] When the aqueous inkjet ink of this embodiment contains a polyoxyalkylene monoalkyl ether surfactant as the nonionic surfactant (B-3), the content thereof is preferably 0.1 to 2% by mass, more preferably 0.2 to 1.5% by mass, and particularly preferably 0.3 to 1.2% by mass, in order to suitably exhibit the above-mentioned effects.

[0118] <Organic solvents> <Specific organic solvents> The aqueous inkjet ink of this embodiment contains, as organic solvents, an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms. In the present disclosure, these organic solvents are collectively referred to as "specific organic solvents." The alkanediols having 5 to 8 carbon atoms and the glycol ethers having 4 to 10 carbon atoms have low surface tension and are highly compatible with pigment particles, the acetylene diol surfactant (B-1), and the siloxane surfactant (B-2). Therefore, these surfactants diffuse uniformly as the aqueous inkjet ink droplets printed on the printing substrate spread. Furthermore, this diffusion facilitates uniform orientation of the surfactants at the interface. As a result, the straightness of ejection, continuous ejection stability, and print image quality are improved. Furthermore, the alkanediols having 3 to 4 carbon atoms are highly water-soluble, allowing the alkanediols having 5 to 8 carbon atoms, the glycol ethers having 4 to 10 carbon atoms, the acetylene diol surfactant (B-1), and other materials to be stabilized within the aqueous inkjet ink. This also stabilizes the meniscus of the aqueous inkjet ink within the inkjet head. As a result, the straightness of ejection, continuous ejection stability, and print image quality are also improved.

[0119] Examples of alkanediols having 5 to 8 carbon atoms include, but are not limited to, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,3-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 2,3-hexanediol, 3,4-hexanediol, 1,5-hexanediol, 1,2-octanediol, 1,3-octanediol, 3-methyl-1,3-butanediol, 2-methyl-1,3-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol (hexylene glycol), 2,2-dimethyl-1,3-pentanediol, and 2-ethyl-1,3-hexanediol.

[0120] Although the detailed mechanism is unknown, the use of alkanediols other than 1,2-alkanediols among these improves print quality such as dot circularity, continuous ejection stability, and straight ejection, as well as print density. Among these, it is preferable to use alkanediols having a structure containing a branched alkyl group. Alkanediols having a structure containing a branched alkyl group are believed to have a high affinity with the acetylene diol surfactant (B-1), which promotes uniform orientation of the acetylene diol surfactant (B-1) at the interface, improving straight ejection, continuous ejection stability, and print quality of printed materials. Examples of alkanediols having a structure containing a branched alkyl group that are not 1,2-alkanediols include 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol (hexylene glycol), and 2-ethyl-1,3-hexanediol. Furthermore, among these, from the viewpoint of improving the print density and print quality of printed matter, it is particularly preferable to select one or more compounds selected from the group consisting of alkanediols having 5 to 6 carbon atoms, specifically 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-2,4-pentanediol (hexylene glycol).

[0121] On the other hand, it is also preferable to use an alkanediol with a small surface tension, i.e., a surface tension of 20 to 30 mN / m at 25°C, because the above-mentioned mechanism can be effectively functioned to uniformly orient the surfactant in the aqueous inkjet ink at the interface, thereby improving the straight-line ejection property and continuous ejection stability.

[0122] The content of the alkanediol having 5 to 8 carbon atoms is preferably 0.5 to 10 mass % of the total amount of the aqueous inkjet ink, and particularly preferably 1 to 8 mass %. By keeping the content of the alkanediol having 5 to 8 carbon atoms within the above range, the above-mentioned mechanism functions effectively.

[0123] On the other hand, examples of glycol ethers having 4 to 10 carbon atoms include, but are not limited to, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, and triethylene glycol monobutyl ether.

[0124] Among these, it is preferable that the alkyl group at the molecular terminal has 3 to 4 carbon atoms, because this allows for favorable compatibility between the acetylenic diol surfactant (B-1) and the siloxane surfactant (B-2), thereby improving continuous discharge stability and straight discharge, as well as resolubility. Furthermore, it is more preferable to use propylene glycol monoalkyl ether and / or dipropylene glycol monoalkyl ether, and it is particularly preferable to use dipropylene glycol monoalkyl ether, because this allows the above-mentioned mechanism to function effectively and the surfactant in the aqueous inkjet ink to be uniformly oriented at the interface, thereby improving straight discharge, continuous discharge stability, and print image quality, as well as resolubility. For these reasons, it is preferable that the aqueous inkjet ink of this embodiment contains, as the glycol ether having 4 to 10 carbon atoms, dipropylene glycol monopropyl ether and / or dipropylene glycol monobutyl ether, which are dipropylene glycol monoalkyl ethers having an alkyl group at the molecular terminal with 3 to 4 carbon atoms.

[0125] The content of the glycol ether having 4 to 10 carbon atoms is preferably 0.1 to 10 mass % of the total amount of the aqueous inkjet ink, and particularly preferably 0.5 to 7 mass %. By keeping the content of the alkanediol having 5 to 8 carbon atoms within the above range, the above-mentioned mechanism functions effectively.

[0126] Examples of alkanediols having 3 to 4 carbon atoms include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, etc. Among these, it is preferable to select 1,2-alkanediol because it has high affinity with water and therefore the above-mentioned effects are preferably exhibited.

[0127] The content of the alkanediol having 3 to 4 carbon atoms is preferably 5 to 25 mass % of the total amount of the aqueous inkjet ink, and particularly preferably 7 to 20 mass %. By keeping the content of the alkanediol having 5 to 8 carbon atoms within the above range, the above-mentioned mechanism functions effectively.

[0128] <Other organic solvents> The aqueous inkjet ink of this embodiment may contain organic solvents other than the specific organic solvents described above (referred to as "other organic solvents" in this disclosure).

[0129] Examples of the other organic solvents include monohydric alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-methoxy-2-butanol, 2-methoxy-1-butanol, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol; polyalkylene glycols such as diethylene glycol, triethylene glycol, and dipropylene glycol; glycol diethers such as diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; and nitrogen-containing heterocyclic solvents such as 2-pyrrolidone, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0130] The total mass of the organic solvent contained in the aqueous inkjet ink of this embodiment is preferably 6 to 45 mass %, and particularly preferably 9 to 35 mass %.

[0131] <Binder resin> The aqueous inkjet ink of this embodiment preferably contains a resin used as a binder ("binder resin") to improve drying properties, impart abrasion resistance, and further improve print density of printed matter.

[0132] As described above, water-soluble resins and resin microparticles are generally known as the forms of resins used in aqueous inkjet inks. The binder resin contained in the aqueous inkjet ink of this embodiment may be a water-soluble resin or resin microparticles. Furthermore, a combination of a water-soluble resin and resin microparticles may be used.

[0133] In this 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." Furthermore, among the water-insoluble resins, a resin that is dispersed in water in the form of particles and has a volume-based median diameter (also referred to as "D50" in this disclosure) of 10 to 1,000 nm is referred to as a "resin particle."

[0134] The D50 of the resin fine particles can be measured using the same device and method as in the case of measuring the average particle size of the crosslinked pigment particles described above.

[0135] Examples of types of binder resins that can be used in the aqueous inkjet ink of this embodiment include acrylic, styrene, maleic acid, urethane, polyester, vinyl chloride, vinyl chloride-vinyl acetate, polyolefin, polyvinyl alcohol, etc. These resins may be used alone or in combination of two or more.

[0136] When the aqueous inkjet ink of this embodiment contains a binder resin, the type of resin used as the binder resin is preferably one or more types selected from the group consisting of acrylic, urethane, and polyester resins, among those listed above.

[0137] The content of the binder resin in the aqueous inkjet ink of this embodiment is preferably 0.1 to 20 mass % of the total amount of the aqueous inkjet ink, more preferably 1 to 15 mass %, and particularly preferably 2 to 10 mass %.

[0138] <Other ingredients> The aqueous inkjet ink of this embodiment may contain, in addition to the above-mentioned components, a pH adjuster and other additives. Examples of the other additives include a crosslinking agent, a preservative, an ultraviolet absorber, and an infrared absorber. These components may each be one or more conventionally known compounds.

[0139] <Water> The water contained in the aqueous inkjet ink of this embodiment is preferably ion-exchanged water and / or reverse osmosis water, and the content of water contained in the aqueous inkjet ink is preferably 30 to 90 mass % of the total amount of the aqueous inkjet ink.

[0140] <Method for manufacturing water-based inkjet ink> The aqueous inkjet ink of this embodiment can be produced by a conventionally known method. One example is a method in which water, an acetylene-based surfactant (B-1), a siloxane-based surfactant (B-2), an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, a glycol ether having 4 to 10 carbon atoms, or the like is added to an aqueous dispersion of crosslinked pigment particles produced by the method described above, and the mixture is thoroughly stirred and mixed, followed by removing coarse particles by filtration, centrifugation, or the like. However, the method for producing the aqueous inkjet ink of this embodiment is not limited to the method described above.

[0141] <Characteristics of water-based inkjet ink> The aqueous inkjet ink of this embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. This viscosity range allows stable ejection of aqueous inkjet ink droplets not only from inkjet heads with ejection frequencies of approximately 4 to 10 kHz, but also from inkjet heads with high ejection frequencies of approximately 20 to 70 kHz. In particular, when the aqueous inkjet ink of this embodiment has a viscosity of 4 to 10 mPa·s at 25°C, the aqueous inkjet ink can be ejected stably even when an inkjet head with a design resolution of 600 dpi or higher is used. In this disclosure, the viscosity is measured at 25°C using a cone-plate rotational viscometer (E-type viscometer, cone angle 1°34') such as the TVE25L viscometer manufactured by Toki Sangyo Co., Ltd.

[0142] Furthermore, in order to obtain an aqueous inkjet ink that is excellent in ejection stability and print quality of printed matter, the aqueous inkjet ink of this embodiment preferably has a static surface tension of 18 to 35 mN / m, and particularly preferably 20 to 30 mN / m, at 25° C. In the present disclosure, the static surface tension is a value measured in an environment of 25° C. using the Wilhelmy method (plate method) using an automatic surface tensiometer such as the CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[0143] <Water-based inkjet ink set> Although the aqueous inkjet ink of this embodiment may be used alone, two or more aqueous inkjet inks may be combined to form an aqueous inkjet ink set. Examples of the aqueous inkjet ink set include a four-color aqueous inkjet ink set (process color ink set) consisting of a cyan aqueous inkjet ink (aqueous cyan ink), a magenta aqueous inkjet ink (aqueous magenta ink), a yellow aqueous inkjet ink (aqueous yellow ink), and a black aqueous inkjet ink (aqueous black ink).

[0144] <Inkjet recording method> The aqueous inkjet ink of this embodiment is used in an inkjet printing method. That is, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). Furthermore, the aqueous inkjet ink ejected onto the printing substrate is preferably dried by a drying mechanism (drying step).

[0145] ≪Discharge process≫ In the ejection process, the inkjet head can be operated in two ways: a shuttle (scan) method, in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate while ejecting and recording the aqueous inkjet ink; and a single-pass method, in which the inkjet head is scanned back and forth in a direction perpendicular to the transport direction of the printing substrate while ejecting and recording the aqueous inkjet ink as the printing substrate passes below a fixedly disposed inkjet head. The inkjet head equipped with the aqueous inkjet ink of this embodiment may be either a shuttle method or a single-pass method. Of these, the single-pass method is preferably selected because it is less likely to cause deviation in the landing position of aqueous inkjet ink droplets, improving the print quality of printed matter, and further enabling high-speed printing and achieving high productivity.

[0146] The method of ejection from the inkjet head can also be selected from any known methods, such as a piezoelectric method that uses the volume change of a piezoelectric element, a thermal method that ejects aqueous inkjet ink by bubbles generated by heating a heater, and a valve method that ejects pressurized aqueous inkjet ink by opening and closing a nozzle cover (valve) with a solenoid.

[0147] The volume of droplets of the aqueous inkjet ink ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoints of reducing the drying load and improving print quality. Furthermore, from the viewpoint of improving print quality, it is preferable to adjust the printing conditions (specifically, the driving frequency and number of inkjet heads installed, and the printing speed) so that the recording resolution of the printed matter is 600 dpi or higher, and particularly preferably 1200 dpi or higher.

[0148] ≪Drying process≫ Examples of drying methods used in the drying mechanism used in the drying step include heat drying, hot air drying, infrared drying (e.g., infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. One or more of these methods can be selected and used as desired in the drying step. When two or more of the above drying methods are used, they may be used separately (e.g., consecutively) or simultaneously. For example, by using heat drying and hot air drying in combination, the aqueous inkjet ink can be dried more quickly than when each method is used alone.

[0149] ≪Printing base material≫ Any conventionally known printing substrate can be used as the printing substrate on which the aqueous inkjet ink of this embodiment is printed. Among these, it is preferable to use a paper substrate as the printing substrate, from the viewpoint of obtaining a printed matter excellent in print density and print quality.

[0150] Examples of paper substrates include uncoated paper such as sawdust paper, medium-quality paper, fine paper, plain paper, and recycled paper; packaging paper such as kraft paper; cardboard base paper such as liner and cardboard; and coated paper such as coated paper, art paper, and cast paper. Of these, uncoated paper such as fine paper, plain paper, and recycled paper, and coated paper such as coated paper are preferably used because they can produce printed matter with excellent print quality.

[0151] The paper substrates listed above may have a smooth or uneven surface. The paper substrates may be in the form of rolls or sheets. Furthermore, a release adhesive layer or the like may be provided on the side opposite the printed surface, or an adhesive layer or the like may be provided on the printed surface after printing.

[0152] In order to improve the wettability of the aqueous inkjet ink of this embodiment and obtain printed matter with excellent print quality and drying properties, it is also possible to subject the printing surface of the paper substrates listed above to surface modification such as corona treatment and plasma treatment. [Example]

[0153] The aqueous inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0154] <Production of dispersion resin> The "dispersion resins" shown below all correspond to the polymer (A-1) described above. These dispersion resins were obtained by synthesis using the method described below.

[0155] <Production example of dispersion resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of methyl ethyl ketone and purged with nitrogen gas. The contents of the reaction vessel were heated to 110°C, and a mixture of polymerizable monomers (25 parts styrene, 20 parts acrylic acid, 35 parts methyl methacrylate, and 20 parts lauryl methacrylate) and 6 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition, the temperature of the contents of the reaction vessel was maintained at 110°C and the polymerization reaction was continued for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110°C, yielding a solution containing dispersion resin 1 precursor. The acid value of the resulting dispersion resin 1 precursor was 155 mgKOH / g. The amount of potassium hydroxide required to achieve a neutralization rate of 100 mol% was calculated from the acid value of the dispersion resin 1 precursor, and a 48% by mass aqueous potassium hydroxide solution containing an equal amount of potassium hydroxide was added to the solution to convert the carboxy groups present in the dispersion resin 1 precursor to carboxylate groups (neutralization treatment). After neutralization, 150 parts of ion-exchanged water was added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Ion-exchanged water was then added to obtain a 20% solids solution of dispersion resin 1.

[0156] <Production Examples of Dispersion Resins 2 to 4> Aqueous solutions of dispersion resins 2 to 4 (each with a solids concentration of 20%) were obtained using the same raw materials and procedures as for dispersion resin 1, except that the polymerizable monomers listed in Table 1-1 were used as the polymerizable monomers.

[0157] [Table 1-1]

[0158] The abbreviations listed in Table 1-1 are as follows: Table 1-1 also lists the acid values ​​of Dispersion Resins 1 to 4. St: Styrene AA: Acrylic acid MMA: Methyl methacrylate LMA: Lauryl methacrylate

[0159] <Production example of dispersion resin 5> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of methyl ethyl ketone and purged with nitrogen gas. The contents of the reaction vessel were heated to 110°C, and then a mixture of polymerizable monomers (25 parts styrene, 20 parts acrylic acid, 35 parts maleic anhydride, and 20 parts lauryl methacrylate) and 6 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition, the temperature of the contents of the reaction vessel was maintained at 110°C, and the polymerization reaction was continued for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110°C, yielding a solution containing a dispersion resin 5 precursor. Next, the temperature in the reaction vessel was lowered to 60°C, and then 10 parts of water and 0.05 parts of diazabicycloundecene were added to the resulting solution. The reaction vessel was then heated to 80°C while stirring the solution. After reaching 80°C, the solution was maintained at that temperature for 5 hours, allowing the maleic anhydride structure contained in the dispersion resin 5 precursor to be hydrolyzed (ring-opened) by water. The acid value of the dispersion resin 5 precursor after ring-opening was 325 mgKOH / g. The amount of potassium hydroxide required to achieve a neutralization rate of 100 mol% was calculated from the acid value of the dispersion resin 5 precursor after ring opening. A 48% by mass aqueous solution of potassium hydroxide containing an equal amount of potassium hydroxide was then added to the solution, converting the carboxy groups present in the dispersion resin 5 precursor to carboxylate groups (neutralization treatment). After neutralization, 140 parts of ion-exchanged water was added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Ion-exchanged water was then added to obtain a 20% solids solution of dispersion resin 5.

[0160] <Production Examples of Dispersion Resins 6 to 8> Aqueous solutions of dispersion resins 6 to 8 (each with a solids concentration of 20%) were obtained using the same raw materials and procedures as for dispersion resin 5, except that the polymerizable monomers listed in Table 1-2 were used as the polymerizable monomers.

[0161] [Table 1-2]

[0162] The abbreviation "Manh" in Table 1-2 stands for maleic anhydride. The meanings of other abbreviations are the same as in Table 1-1 above. Table 1-1 also lists the acid values ​​of dispersion resins 5 to 8.

[0163] <Production Example of Aqueous Dispersion 1 of Uncrosslinked Pigment Particles> 600 g of LIONOL BLUE FG-7351 pigment (CI Pigment Blue 15:3, manufactured by Toyocolor Co., Ltd.), 750 g of an aqueous solution of Dispersion Resin 1 (20% solids concentration), and 1,650 g of ion-exchanged water were mixed and stirred for 1 hour (pre-dispersion). After this, circulation dispersion was initiated using a 0.6 L bead mill (Dyno Mill, manufactured by Shinmaru Enterprises) filled with 1,800 g of 0.5 mm diameter zirconia beads. The median diameter was then measured at 25°C by volume using a Microtrac-Bell Nanotrac UPA-EX150 at regular intervals (e.g., every hour). The circulation dispersion was terminated when the median diameter reached 150 nm or less. Then, 1,000 g of ion-exchanged water was added to the resulting pigment dispersion. Further, while heating at 60°C, a portion of the ion-exchanged water and all of the methyl ethyl ketone contained in the aqueous solution of pigment dispersion resin 1 were distilled off under reduced pressure, and then ion-exchanged water was added to adjust the pigment concentration to 15%, thereby obtaining an aqueous dispersion 1 of cyan uncrosslinked pigment particles (pigment concentration 15%).

[0164] <Production Examples of Aqueous Dispersions 2 to 8 of Uncrosslinked Pigment Particles> Aqueous dispersions 2 to 8 of cyan uncrosslinked pigment particles were obtained using the same materials and method as for the aqueous dispersion 1 of uncrosslinked pigment particles, except that the aqueous solutions of dispersion resins 2 to 8 were used instead of the aqueous solution of dispersion resin 1. The pigment concentration was all 15%.

[0165] <Production Example of Aqueous Dispersion 1 of Crosslinked Pigment Particles> 93.3 parts of the aqueous dispersion 1 of uncrosslinked pigment particles obtained above, 1.15 parts of Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent 140 g / eq., solubility at 25°C 27 g / 100 g HO) corresponding to compound (A-2) (an amount equivalent to 85 mol% of the glycidyl group content represented by formula (1) above), and 5.55 parts of ion-exchanged water were mixed, and the mixture was heated to 80°C with stirring and then maintained at 80°C for 3 hours to carry out a crosslinking treatment. Subsequently, ion-exchanged water was added to adjust the pigment concentration to 14%, thereby obtaining an aqueous dispersion 1 of cyan crosslinked pigment particles (pigment concentration 14%).

[0166] <Production Examples of Aqueous Dispersions 2 to 12 of Crosslinked Pigment Particles> Aqueous dispersions 2 to 12 of cyan crosslinked pigment particles were obtained in the same manner as for aqueous dispersion 1 of crosslinked pigment particles, except that the type of aqueous dispersion of uncrosslinked pigment particles used and the amount of each raw material added were changed as shown in Table 2. The pigment concentration was all 14%.

[0167] [Table 2]

[0168] In Table 2, "Denacol EX-313" is an epoxy compound manufactured by Nagase ChemteX Corporation (epoxy equivalent 141 g / eq., solubility at 25°C 99 g / 100 g H2O), and "Denacol EX-612" is an epoxy compound manufactured by Nagase ChemteX Corporation (epoxy equivalent 166 g / eq., solubility at 25°C 42 g / 100 g H2O).

[0169] <Production example of binder resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of butanol and purged with nitrogen gas. The contents of the reaction vessel were heated to 110°C, and a mixture of polymerizable monomers (6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 10 parts styrene) and 6 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition, the contents of the reaction vessel were maintained at 110°C and the polymerization reaction was continued for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110°C to obtain a solution of binder resin 1 precursor. Next, the binder resin 1 precursor solution was cooled to room temperature, and 7.1 parts of dimethylaminoethanol was added to neutralize the carboxyl groups present in the binder resin 1 precursor. 100 parts of ion-exchanged water was then added. The mixture was then heated to 100°C, and the temperature was maintained after reaching 100°C, causing the butanol to form an azeotrope with water and distill off the butanol. The solids concentration was then adjusted to 40% using ion-exchanged water, yielding an aqueous solution of binder resin 1. The weight-average molecular weight of the resulting binder resin 1 was 19,000 and the acid value was 47 mgKOH / g.

[0170] <Production of water-based inkjet inks> The raw materials listed in each column of Tables 3-1 to 3-6 were added to a mixing vessel equipped with a stirrer. Each raw material was added while stirring the contents of the mixing vessel with the stirrer. After all the raw materials were added, they were stirred at room temperature until they were sufficiently uniform. The mixture was then filtered through a 0.8 μm membrane filter to remove coarse particles that could cause head clogging, thereby producing an aqueous inkjet ink.

[0171] [Table 3-1]

[0172] [Table 3-2]

[0173] [Table 3-3]

[0174] [Table 3-4]

[0175] [Table 3-5]

[0176] [Table 3-6]

[0177] The abbreviations used in Tables 3-1 to 3-6 are as follows: In Tables 3-1 to 3-6, "(A-1) acid value" refers to the acid value (unit: mgKOH / g) of the dispersing resin (corresponding to polymer (A-1)) used in producing the crosslinked pigment particles, and "GL content" refers to the content (unit: mol%) of glycidyl groups in the crosslinked pigment particles. Surfynol DF110D (acetylene diol surfactant manufactured by Evonik Japan, actual HLB value = 6.4) Surfynol 104 (acetylene diol surfactant manufactured by Evonik Japan, actual HLB value = 7.9) Surfynol 420 (acetylene diol surfactant manufactured by Evonik Japan, actual HLB value = 8.3) TEGOTwin4200 (Evonik Japan Gemini type siloxane interface) Activator, actual HLB value = 8.2) TEGOTwin4000 (Evonik Japan Gemini type siloxane interface) Activator, measured HLB value = 2.0) TEGOGlide 440 (Evonik Japan Co., Ltd.) Xanthane surfactant, actual HLB value = 12.5) TEGOGlide 100 (Evonik Japan Co., Ltd., polyether-modified silica gel) Xanthane surfactant, measured HLB value = 7.1) BYK348 (side-chain polyether-modified siloxane surfactant manufactured by BYK Japan, actual HLB value = 13.0) TEGOWET 270 (Evonik Japan Co., Ltd., double-ended polyether-modified siloxane surfactant, measured HLB value = 3.3) Propylene glycol (surface tension: 36.5 mN / m) 1,2-butanediol (surface tension: 31.6 mN / m) 2-Methyl-1,5-pentanediol (surface tension: mN / m) 3-Methyl-1,3-butanediol (surface tension: 29.9 mN / m) 2-Methyl-2,4-pentanediol (surface tension: 29.1 mN / m) 1,2-Hexanediol (surface tension: 26.0 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) Diethylene glycol monobutyl ether (surface tension: 27.9 mN / m)

[0178] [Examples 1 to 48, Comparative Examples 1 to 5] The aqueous inkjet inks produced above were evaluated as follows, and the evaluation results are shown in Tables 3-1 to 3-6 above.

[0179] <Evaluation of continuous ejection stability> Each aqueous inkjet ink was filled into an inkjet ejection device equipped with a Kyocera inkjet head (KJ4B-1200) placed in a 25°C environment. A nozzle check pattern was printed to confirm that the aqueous inkjet ink was ejecting normally from all nozzles, and then 100 consecutive solid prints were performed at 100% coverage on Oji Paper OK topcoat + paper under printing conditions of 1200 x 1200 dpi, a drive frequency of 40 kHz, and a drop volume of 3 pL. Thereafter, the nozzle check pattern was printed again, and the number of missing nozzles was visually counted to evaluate the continuous ejection stability. The evaluation criteria were as follows, with D or higher being considered to be in the practical range. A: No missing nozzles at all B: 1 to 3 nozzles were missing C: 4 to 6 nozzles were missing D: 7 to 9 nozzles were missing E: 10 or more nozzles were missing

[0180] <Evaluation of ejection straightness> The inkjet ejection device used in the continuous ejection stability evaluation was filled with each aqueous inkjet ink. A nozzle check pattern was printed to confirm that the aqueous inkjet ink was ejecting normally from all nozzles. Then, five 25 cm long one-dot lines (line images in which dots made of droplets of aqueous inkjet ink extend parallel to the transport direction of the printing substrate) were simultaneously printed on OK topcoat + paper manufactured by Oji Paper Co., Ltd. under printing conditions of 1200 x 1200 dpi, a driving frequency of 40 kHz, and a drop volume of 3 pL. The five 1-dot lines obtained were then observed, and the number of locations where the droplets had landed off the 1-dot line was counted to evaluate the straightness of the ejection. The evaluation criteria were as follows, with C or higher being considered to be in the practical range. A: The total number of misaligned bullets was 25 or less. B: The total number of misaligned bullets was 26 to 70. C: The total number of misaligned bullets was between 71 and 125. D: The total number of misaligned bullets was 126 or more.

[0181] <Evaluation of resolubility> A drop of each aqueous inkjet ink was placed on a glass plate and then placed in a thermo-hygrostat set at a temperature of 50°C and a humidity of 40% RH to dry. After a predetermined time had passed, the glass plate was removed from the thermo-hygrostat, and pure water was dropped onto the dried film. Visual inspection was performed to determine whether the ink reverted to the aqueous inkjet ink. The resolubility was evaluated by varying the time the ink was left in the thermo-hygrostat. The evaluation criteria were as follows, with a grade of C or higher considered to be within the practical range. A: Even after drying for 30 minutes, the ink returned to a uniform aqueous inkjet ink, and no foreign matter such as a dried film or pigment aggregates was observed. B: Even after drying for 20 minutes, the ink returned to a uniform aqueous inkjet ink, and no foreign matter such as a dried film or pigment aggregates was observed visually. However, when the dried film that had been dried for 30 minutes was used, the above foreign matter was visually observed after pure water was dripped on it. C: Even after drying for 10 minutes, the ink returned to a uniform aqueous inkjet ink, and no foreign matter such as a dried film or pigment aggregates was observed visually. However, when the dried film that had been dried for 20 minutes was used, the above foreign matter was visually observed after pure water was dripped on it. D: After drying for 10 minutes, foreign matter such as dried film or pigment aggregates was visually observed.

[0182] <Print quality evaluation 1 (dot roundness)> Each aqueous inkjet ink was filled into the inkjet ejection device used in the continuous ejection stability evaluation. Next, a gradation image was printed using the same printing conditions and the same type of printing substrate as the solid printing performed in the continuous ejection stability evaluation. The "gradation image" refers to an image in which the printing rate continuously changes from 5 to 60% within a predetermined area. After printing the gradation image, the OK topcoat and paper on which the aqueous inkjet ink was printed were placed in a constant temperature incubator set at 70°C and dried for 1 minute to obtain a gradation print. A portion of the gradation print with a printing rate of 10% was then observed using an image evaluation device ("PIAS-II" manufactured by Quality Engineering Associates) to measure the circularity of the dots. The closer the circularity is to 1, the more circular the dot is, indicating a good dot shape. Furthermore, a good dot shape indicates good print quality. The evaluation criteria were as follows, with a grade of C or higher considered to be within the practical range. A: Roundness was between 1 and 2 B: Roundness was greater than 2 and less than 3 C: Roundness was greater than 3 and less than 3.5 D: Roundness was greater than 3.5

[0183] <Evaluation of print quality 2 (wettability)> Each aqueous inkjet ink was filled into the inkjet ejection device used in the continuous ejection stability evaluation. Next, a solid image with a coverage of 100% was printed using the same printing conditions and the same type of printing substrate as in the solid printing performed in the continuous ejection stability evaluation. After printing the solid image, the OK topcoat and paper on which the aqueous inkjet ink had been printed were placed in a constant temperature incubator set at 70°C and dried for 1 minute to obtain a solid print. The degree of whiteout on the resulting solid print was then evaluated visually and with a magnifying glass to evaluate wettability. Whiteout is generally considered a type of printing defect, and poor wettability can cause uneven density, etc. Therefore, reducing whiteout and improving wettability are effective in improving print quality. The evaluation criteria were as follows, with a rating of C or higher considered to be within the practical range. A: No white spots were observed visually or with a magnifying glass. B: Slight white spots were observed with a magnifying glass, but no white spots were observed with the naked eye. C: Slight white spots were observed visually D: White spots were clearly observed by visual inspection

[0184] <Evaluation of print density on high-quality paper> Each aqueous inkjet ink was filled into the inkjet printing device used for the continuous discharge stability evaluation. Next, a solid image with a coverage rate of 100% was printed on OK Prince wood-free paper (high-quality paper) manufactured by Oji Paper Co., Ltd. under the same printing conditions as the solid print performed in the continuous discharge stability evaluation. After printing the solid image, the OK Prince wood-free paper with the aqueous inkjet ink printed on it was placed within 10 seconds in a constant-temperature incubator set at 60°C and dried for 1 minute to obtain a gradient print. The print was then placed in a 60°C air oven. After drying for 1 minute, the print was removed from the oven and the print density (OD value) of the resulting solid print was measured under the same conditions as in Evaluation 1. The evaluation criteria were as follows, with a rating of B or higher considered to be within the practical range. A:OD value 1.3 or more B: OD value 1.1 or more and less than 1.3 C:OD value less than 1.1

[0185] As can be seen from Tables 3-1 to 3-6, the aqueous inkjet inks evaluated in Examples 1 to 48 all had practically acceptable quality in terms of continuous ejection stability, straight ejection, resolubility, dot circularity, wettability, and print density. In particular, the aqueous inkjet inks of Examples 24 and 27 to 30 achieved an "A" rating in all evaluations of continuous ejection stability, straight ejection, resolubility, dot circularity, wettability, and print density on fine paper. These results demonstrate that the combined use of a gemini siloxane surfactant and a siloxane surfactant modified at both ends with polyether as the siloxane surfactant (B-2), and the glycidyl group content of 70 to 120 mol% represented by the above formula 1, are extremely suitable for solving the problems described above.

[0186] On the other hand, Comparative Example 1 is a system in which the pigment dispersing resin is not crosslinked. It is believed that the pigment dispersion stability is poor because the pigment dispersing resin does not adsorb sufficiently to the pigment, and as a result, it was confirmed that the system does not have the quality suitable for practical use in all evaluation items, including poor resolubility, print image quality, and print density on high-quality paper.

[0187] Furthermore, in Comparative Example 2, which does not contain the acetylene diol surfactant (B-1), there is no surfactant with high hydrophobicity and high orientation speed to the interface, so the dots lacked circularity and wettability to the printing substrate, and the continuous ejection stability and straight ejection were also poor.

[0188] On the other hand, in Comparative Example 3, which contained the acetylenic diol surfactant (B-1) but not the siloxane surfactant (B-2), the acetylenic diol surfactant (B-1) could not be uniformly oriented at the gas-liquid interface, and the dot roundness was not practically sufficient. In addition, deterioration in continuous ejection stability and ejection straightness was also confirmed, which is presumed to be due to the non-uniform orientation of the acetylenic diol surfactant near the nozzle.

[0189] Additionally, the aqueous inkjet ink of Comparative Example 4 does not contain an alkanediol having 5 to 8 carbon atoms, and the aqueous inkjet ink of Comparative Example 5 does not contain a glycol ether having 4 to 10 carbon atoms. Evaluation results showed that the surfactants could not be sufficiently compatibilized, and in both cases, deterioration in continuous ejection stability occurred, which is thought to be due to non-uniform orientation of the surfactants at the nozzle interface, and deterioration in print image quality was also observed.

Claims

1. 1. A water-based inkjet ink comprising pigment particles, a surfactant, and an organic solvent, the pigment particles include a pigment and a pigment dispersing resin that coats at least a portion of the surface of the pigment, the pigment dispersing resin comprises a crosslinked reaction product of a polymer (A-1) having an aromatic ring and an acid group and an acid value of 50 to 160 mgKOH / g with a compound (A-2) having a plurality of glycidyl ether groups in one molecule, The surfactant comprises an acetylene diol surfactant (B-1) having a measured HLB value of 6 to 9 and a siloxane surfactant (B-2), the organic solvent comprises an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms; An aqueous inkjet ink, comprising a glycidyl group content of 50 to 200 mol % represented by the following formula (1): Formula (1): [Equation 1]

2. 2. The aqueous inkjet ink according to claim 1, wherein the siloxane surfactant (B-2) comprises a gemini siloxane surfactant.

3. 3. The aqueous inkjet ink according to claim 1, wherein the alkanediol having 5 to 8 carbon atoms contains a branched alkyl group and is not a 1,2-alkanediol.

4. 3. The aqueous inkjet ink according to claim 1, wherein the glycol ether having 4 to 10 carbon atoms comprises a propylene glycol monoalkyl ether in which the alkyl group at the molecular terminal has 3 to 4 carbon atoms, and / or a dipropylene glycol monoalkyl ether in which the alkyl group at the molecular terminal has 3 to 4 carbon atoms.

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

Images