WO2025205000A1 - Aqueous inkjet ink and printed matter - Google Patents

Abstract

This aqueous inkjet ink contains a pigment, a binder resin, an acetylenediol-based surfactant (A), and glycol monoethers (B1). The acetylenediol-based surfactant (A) contains 2-600 ppm of an unmodified acetylenediol-based surfactant (A1) and an alkylene oxide-modified acetylenediol-based surfactant (A2) having an HLB value of 6-12. The mass ratio of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenediol-based surfactant (A2) is 0.5-50.

Description

Water-based inkjet inks and printed materials

Embodiments of the present invention relate to aqueous inkjet inks and printed materials produced using the aqueous inkjet inks.

Digital printing methods are rapidly becoming more popular as printing runs become smaller and market needs become more diverse. Because digital printing methods do not require plates, they are suitable for short-run printing, and they also reduce printing costs and enable the use of more compact printing equipment.

Inkjet printing, a type of digital printing method, is a method in which tiny droplets of ink are ejected from an inkjet head and landed on a printing substrate (also referred to simply as "substrate" in this specification) to print images and text on the printing substrate. The "image" mentioned above includes solid images (images printed at 100% coverage so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard patterns. Compared to other digital printing methods, inkjet printing is superior in terms of the size and cost of the printing equipment, and the ease of achieving full color, and in recent years has been increasingly used in industrial printing applications.

The inks used in inkjet printing methods vary widely, including oil-based, solvent-based, active energy ray-curable, and water-based. Until now, solvent-based or active energy ray-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks due to concerns about and responses to harmful effects on the environment and people.

In recent years, there has been growing demand for the packaging market to be a target for water-based inks used in inkjet printing methods (referred to herein as "aqueous inkjet inks"; hereinafter, simply referred to as "inks"). In this packaging market, paper containers, labels, flexible packaging, and the like are manufactured, sold, and used. Furthermore, the printing substrates used for printing in the packaging market include low-absorbency substrates such as coated paper and art paper, as well as non-absorbency substrates such as polypropylene film, polyethylene terephthalate film, and nylon film. Therefore, in order to further expand the use of aqueous inkjet inks in the packaging market, there is a demand for aqueous inkjet inks that can produce printed materials with excellent print quality and properties that can withstand practical use, even on low-absorbency and non-absorbency substrates.

In contrast, typical aqueous inkjet inks that have existed until now have been designed for printing on highly absorbent substrates such as plain paper and specialty paper. When such aqueous inkjet inks are used on non-absorbent substrates, the ink does not penetrate and is absorbed into the substrate. As a result, droplets of the aqueous inkjet ink that land on the substrate do not dry properly, resulting in the droplets attracting and coalescing together (beading). When beading occurs, solid coverage deteriorates (the occurrence of areas where the ink does not adhere in a print with 100% coverage), uneven density occurs, color mixing and bleeding occur, and print quality is significantly reduced.

One known method for suppressing beading is to reduce the surface tension of the aqueous inkjet ink. Surfactants are often used as a material for reducing this surface tension. In particular, to ensure that the surface tension of the aqueous inkjet ink is sufficiently reduced immediately after it lands on the printing substrate, it is preferable to select a compound with a low molecular weight and a high orientation rate toward the droplet surface (interface). However, when using such surfactants, for example, in nozzles in an inkjet head that are temporarily not ejecting ink, the surfactant in the aqueous inkjet ink present near the ejection port may suddenly and excessively orient toward the air-liquid interface, causing the aqueous inkjet ink to overflow from the ejection port. This phenomenon can lead to ejection problems (deterioration of standby ejection performance), such as nozzle clogs and deflected droplets, immediately after ejection resumes.

Furthermore, surfactants with small molecular weights and a high rate of orientation to the droplet surface are generally not compatible with water. As a result, when an aqueous inkjet ink containing such a surfactant dries on a printing substrate, the surfactant molecules tend to associate with each other due to changes in the solubility of the surfactant accompanying changes in the composition of the liquid components and a (relative) increase in the amount of the surfactant relative to the total amount (total mass) of the liquid components. These associated surfactants can then cause pinholes in the printed material. Pinholes are a phenomenon in which areas of the printed material where the ink did not adhere appear as exposed spots of the printing substrate.

Furthermore, when a laminate containing an ink layer is manufactured and used as packaging such as a pouch (bag), there is a risk of migration of a low-molecular-weight surfactant with a high orientation rate that is present on the surface of the ink layer and/or that has bled (a phenomenon in which a component seeps out to the layer surface over time) onto the surface of the ink layer. This migration refers to the phenomenon in which a low-molecular-weight surfactant with a high orientation rate passes through each layer that makes up the laminate and reaches the surface of the laminate. In particular, if migration of the surfactant occurs on the surface that comes into contact with the contents, it could adversely affect the safety of the contents. This could be a fatal problem when the laminate is used for packaging food or cosmetics, for example.

As described above, it has traditionally been extremely difficult to simultaneously address all of the following requirements: bleeding resistance, standby ejection performance, pinhole resistance, and migration resistance.

As an example of suppressing beading when printing on low-absorbency or non-absorbency substrates by controlling the type and amount of surfactant, Patent Document 1 discloses an ink composition (set) that combines a silicone surfactant with a specific structure and a nonionic surfactant with an HLB value of 6.0 or greater but less than 12.0 (e.g., polyoxyalkylene alkyl ether surfactants such as BASF's "Lutensol XL40" and Clariant's "GENAPOL EP2564"). Patent Document 2 also discloses an ink containing a polyoxyalkylene alkyl ether surfactant with a specific structure and an HLB value measured as 5.0 to 13.0. Patent Document 3 also discloses an ink that combines a silicone surfactant and a fluorine-based surfactant with a glycol ether organic solvent. Meanwhile, Patent Documents 1 to 3 specifically evaluate beading on low-absorbency substrates such as coated paper. As mentioned above, when aqueous inkjet ink is printed on a non-absorbent substrate such as a resin film, the aqueous inkjet ink does not penetrate into the substrate at all, making beading more likely to occur than when printing on a low-absorbent substrate. Even the aqueous inkjet inks specifically disclosed in the above-mentioned Patent Documents 1 to 3 were not sufficient in terms of improving beading when printed on a non-absorbent substrate.

Furthermore, Patent Document 4 discloses an inkjet recording method using an aqueous ink containing a specific acetylene glycol (acetylene diol surfactant) and a nonionic surfactant, with the blending amounts and blending ratios of each component specified. In the main example of the aqueous ink specifically disclosed in Patent Document 4, 2,4,7,9-tetramethyl-5-decyne-4,7-diol is used as the acetylene glycol, and a polyoxyalkylene alkyl ether surfactant such as polyoxyethylene lauryl ether (12 moles of ethylene oxide groups added) is used as the nonionic surfactant. Here, the 2,4,7,9-tetramethyl-5-decyne-4,7-diol corresponds to the aforementioned "compound with a small molecular weight and a high orientation rate to the droplet surface (air-liquid interface)," and therefore the aqueous ink is considered effective in suppressing beading. On the other hand, it cannot be said that Patent Document 4 has fully investigated pinhole resistance in particular, and in fact, the pinhole resistance and migration resistance of the above-mentioned water-based ink cannot be said to be good depending on the printing conditions.

Japanese Patent Application Laid-Open No. 2022-151398 Japanese Patent Application Laid-Open No. 2021-147400 JP 2018-70730 A JP 2014-139004 A

The present invention was made to solve the above-mentioned problems, and its main objective is to provide an aqueous inkjet ink that is free of beading or pinholes, has excellent migration resistance, and has good standby ejection properties, even when printed on low-absorbency printing substrates.

As a result of extensive research, the inventors have discovered that an aqueous inkjet ink having the following composition can simultaneously and to a high degree address all of the above-mentioned issues.

That is, one embodiment of the present invention is an aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B),
the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12;
the content of the unmodified acetylenic diol surfactant (A1) is 2 to 600 ppm relative to the total mass of the aqueous inkjet ink;
the water-soluble organic solvent (B) contains a glycol monoether (B1),
the ratio (by mass) of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 is 0.5 to 50.
Another embodiment of the present invention relates to a printed matter obtained by printing the aqueous inkjet ink of the above embodiment onto a printing substrate.

Embodiments of the present invention provide an aqueous inkjet ink that is free of beading and pinholes, has excellent migration resistance, and exhibits good standby ejection properties, even when printed on low-absorbency printing substrates.

Below, as an embodiment of the present invention, an aqueous inkjet ink (hereinafter also referred to simply as "the ink of this embodiment") and a printed matter printed with this aqueous inkjet ink are described. However, the embodiment of the present invention is not limited to the content of the following description, and also includes various modifications that are implemented within the scope of the gist of the invention.

<Water-based inkjet ink>
In general, water, the main solvent of aqueous inkjet inks, has high surface tension and is difficult to wet and spread on a printing substrate. Furthermore, when a droplet of aqueous inkjet ink that has landed on a printing substrate comes into contact with an adjacent wet droplet due to its high surface tension and in a wet state, a force acts on each droplet in a direction that reduces the surface area, causing the droplets to attract each other and resulting in beading. Beading can cause uneven density, color mixing, bleeding, and other problems, significantly reducing the quality of the printed material.

A suitable method for suppressing beading is to use a surfactant that has a small molecular weight and a high rate of orientation to the droplet surface (interface). However, such surfactants are generally poorly compatible with water, which can lead to various problems.

For example, as mentioned above, in aqueous inkjet ink present near the ejection orifice in an inkjet head, surfactants with low molecular weights and high orientation rates may rapidly and excessively orient at the air-liquid interface, which may result in poor standby ejection performance. Furthermore, as the aqueous inkjet ink dries on the printing substrate, these surfactants with low molecular weights and high orientation rates may associate with each other, potentially causing pinholes in the printed material. Furthermore, these surfactants with low molecular weights and high orientation rates are present in large amounts on the surface of the aqueous inkjet ink layer (ink layer) after drying. This can lead to bleeding of these surfactants onto the surface of the laminate including the ink layer, potentially causing migration.

On the other hand, if the amount of surfactant used, which has a low molecular weight and a high orientation speed, is reduced in order to prevent deterioration of standby ejection properties, the occurrence of pinholes, and the occurrence of migration, the occurrence of the beading mentioned above cannot be prevented, leading to uneven density, color mixing, bleeding, etc.

As mentioned above, while surfactants with low molecular weights and high orientation speeds are effective in suppressing beading, there is a trade-off between these properties and properties such as standby dischargeability, pinhole resistance, and migration resistance.

As a result of intensive research by the inventors to resolve the above trade-off, they discovered that it is effective to use an unmodified acetylenic diol surfactant (A1), an alkylene oxide-modified acetylenic diol surfactant (A2) having a specific HLB value, and glycol monoethers (B1) in combination, and further specify the amount of the unmodified acetylenic diol surfactant (A1) and the ratio between the amount of the alkylene oxide-modified acetylenic diol surfactant (A2) and the amount of the glycol monoethers (B1), thereby completing the present invention. While the details of the mechanism by which the aqueous inkjet ink having the above-described configuration can effectively resolve the above-mentioned problems are unknown, the inventors speculate as follows.

First, the ink of this embodiment contains an acetylene diol surfactant. Generally, the acetylene groups contained in acetylene diol surfactants do not undergo bond rotation, making the molecular structure less likely to deform, and even the addition of a small amount produces the expected effect.

The ink of this embodiment also contains, as acetylenic diol surfactants, an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12. Of these, the unmodified acetylenic diol surfactant (A1) corresponds to the "surfactant with a low molecular weight and a high orientation rate" described above. As described above, surfactants with a low molecular weight and a high orientation rate are materials that directly affect the occurrence of pinholes and migration, so it is preferable that their amount be small. Therefore, in the ink of this embodiment, it is preferable to adjust the content of the unmodified acetylenic diol surfactant (A1) to a range of 2 to 600 ppm based on the total mass of the aqueous inkjet ink. Note that if no unmodified acetylenic diol surfactant (A1) is used at all, even if the measures described below are taken, the occurrence of beading cannot be completely suppressed, depending on the printing conditions and the printing substrate used. Furthermore, even though it is included, the content of the unmodified acetylenic diol surfactant (A1) contained in the ink of this embodiment is an extremely small amount of 2 to 600 ppm relative to the total mass of the aqueous inkjet ink, so there is still a risk of beading occurring depending on the printing conditions, etc. On the other hand, even small amounts can cause rapid orientation at the interface and association during drying, so the risk of deterioration of standby ejection performance and the occurrence of pinholes remains.

Therefore, the ink of this embodiment uses an unmodified acetylenic diol surfactant (A1), an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12, and glycol monoethers (B1). Both the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1) can emulsify and compatibilize the unmodified acetylenic diol surfactant (A1). Furthermore, both the alkylene oxide-modified acetylenic diol surfactant (A2) and the glycol monoethers (B1) are more hydrophilic than the unmodified acetylenic diol surfactant (A1). As a result, these components facilitate favorable affinity of the unmodified acetylenic diol surfactant (A1) to water, the primary component of aqueous inkjet inks. Furthermore, during drying on the printing substrate, the surfactants are less likely to associate with each other, making it possible to suppress pinholes in the printed material. Furthermore, these surfactants, including the unmodified acetylenic diol surfactant (A1), do not rapidly or excessively orient at the interface, improving standby discharge properties.

On the other hand, emulsification and compatibilization of the unmodified acetylenic diol surfactant (A1) further inhibits the orientation of the unmodified acetylenic diol surfactant (A1) when used in small amounts, which may increase the risk of beading. However, the alkylene oxide-modified acetylenic diol surfactant (A2) is itself a surfactant, and orientation to the interface occurs, although not as rapidly as with the unmodified acetylenic diol surfactant (A1). Additionally, glycol monoethers (B1) have a low surface tension for a water-soluble organic solvent, which contributes to reducing the surface tension of the aqueous inkjet ink on the printing substrate. Therefore, beading is thought to be suppressed.

Furthermore, the inventors have found that by adjusting the ratio of the amount of alkylene oxide-modified acetylenic diol surfactant (A2) to the amount of glycol monoether (B1), beading suppression, pinhole resistance, and standby discharge performance can all be improved simultaneously.

Specifically, in the ink of this embodiment, the ratio (by mass) of the amount of glycol monoethers (B1) to the amount of alkylene oxide-modified acetylenic diol surfactant (A2) is 0.5 to 50. The presence of a certain amount of glycol monoethers (B1) is thought to uniformly reduce surface tension throughout the aqueous inkjet ink, effectively suppressing beading and pinholes. Furthermore, while the detailed mechanism is unknown, rapid and excessive orientation of the surfactant toward the air-liquid interface is effectively suppressed in the aqueous inkjet ink present near the nozzle opening of the inkjet head, thereby improving the standby ejection properties of the aqueous inkjet ink.

As described above, the aqueous inkjet ink having the configuration of this embodiment can simultaneously solve the above-mentioned problems and at a high level.

In addition to the acetylenic diol surfactant described above, the ink of this embodiment can further contain a nonionic surfactant (C) other than an acetylenic diol surfactant. It is generally believed that the nonionic surfactant (C) other than an acetylenic diol surfactant functions effectively in a time region later than the time region in which the acetylenic diol surfactant (A) primarily functions. Because behavior in this time region primarily affects wetting and spreading properties and image density, the use of the nonionic surfactant (C) in combination facilitates the production of printed matter free of beading and pinholes. Furthermore, in aqueous inkjet inks present near the nozzle openings of the inkjet head, the nonionic surfactant (C) is less likely to contribute to rapid and excessive orientation toward the air-liquid interface, which is believed to suppress deterioration of standby ejection performance. Furthermore, it is believed that the interaction between the nonionic surfactant (C) and the unmodified acetylenic diol surfactant (A1) and alkylene oxide-modified acetylenic diol surfactant (A2) allows these surfactants to behave as a single entity. As a result, even if a relatively large amount of unmodified acetylenic diol surfactant (A1) is blended, it is possible to prevent the unmodified acetylenic diol surfactant (A1) from bleeding onto the laminate surface after printing, which is thought to also lead to improved migration.

The aqueous inkjet inks specifically disclosed in the above Patent Documents 1 to 3 differ from the ink of this embodiment in that they contain no acetylenic diol surfactants at all (the specific example in Patent Document 1 does not even use glycol monoethers (B1)). Furthermore, the aqueous inkjet ink specifically disclosed in Patent Document 4 also differs from the ink of this embodiment in that it does not contain glycol monoethers (B1) and furthermore, the content of unmodified acetylenic diol surfactant (A1) ("component (A)" in the examples of Patent Document 4) is significantly greater than 600 ppm, or it does not contain any unmodified acetylenic diol surfactant (A1).

Next, the main components that make up the ink of this embodiment will be described.

<Unmodified acetylene diol surfactant (A1)>
As described above, the unmodified acetylene glycol surfactant (A1) corresponds to a "surfactant with a low molecular weight and a high orientation rate" and is a material necessary for suppressing beading regardless of printing conditions, etc.

In the ink of this embodiment, the content of the unmodified acetylene glycol surfactant (A1) may be in the range of 2 ppm or more, 3 ppm or more, 5 ppm or more, 6 ppm or more, 10 ppm or more, 15 ppm or more, or 20 ppm or more, relative to the total mass of the ink, and the content of the unmodified acetylene glycol surfactant (A1) may be in the range of 600 ppm or less, 450 ppm or less, 400 ppm or less, 200 ppm or less, 100 ppm or less, 65 ppm or less, 45 ppm or less, 30 ppm or less, or 25 ppm or less.
In some embodiments, the unmodified acetylene glycol surfactant (A1) is contained in an amount of 2 to 600 ppm relative to the total mass of the ink. In some embodiments, the content of the unmodified acetylene glycol surfactant (A1) may be preferably 2 to 400 ppm, preferably 3 to 400 ppm, and more preferably 5 to 200 ppm. Using the unmodified acetylene glycol surfactant (A1) in the above range and further using it in combination with a surfactant or glycol monoether (B1) described below can further suppress beading and improve standby discharge properties and pinhole resistance. In addition, since the unmodified acetylene glycol surfactant (A1) is incorporated in a small amount to begin with, it can easily suppress the occurrence of migration in printed materials. Furthermore, in one embodiment, when the content of the unmodified acetylene glycol surfactant (A1) is 6 to 45 ppm, it becomes even easier to achieve both beading suppression, pinhole resistance, and migration resistance.

Specific examples of unmodified acetylene diol surfactants (A1) that can be used in this embodiment include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, and 3,6-diisopropyl Examples of suitable octadecyl compounds include 2,7-dimethyloct-4-yne-3,6-diol, octadec-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, and 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol. Among these, 2,4,7,9-tetramethyl-5-decyne-4,7-diol and/or 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol are preferred from the viewpoint of compatibility with other materials contained in the ink of this embodiment. The above compounds may be used alone or in combination of two or more. The above compounds may be synthesized by conventional methods or commercially available products. Examples of commercially available products include Surfynol 104, Surfynol DF110D, and Surfynol 82 manufactured by Evonik Corporation, and Acetylenol E00 manufactured by Kawaken Fine Chemicals Co., Ltd.

<Alkylene oxide-modified acetylene diol surfactant (A2)>
The ink of this embodiment uses an alkylene oxide-modified acetylenic diol surfactant (A2) in addition to an unmodified acetylenic diol surfactant (A1). As described above, the alkylene oxide-modified acetylenic diol surfactant (A2) emulsifies and compatibilizes the unmodified acetylenic diol surfactant (A1), while also exhibiting surface activity. This allows for the production of printed matter that is free of beading and has excellent pinhole resistance, and also provides an ink that has excellent standby jetting properties. From this perspective, the HLB value of the alkylene oxide-modified acetylenic diol surfactant (A2) is 6 to 12, preferably 7 to 11.5, and more preferably 7 to 11.

The HLB (Hydrophile-Lipophile Balance) value is a parameter that indicates the degree of hydrophilicity of a material. The smaller the HLB value, the more hydrophobic the material, and the higher the HLB value, the more hydrophilic the material. Known methods for determining HLB value include experimental measurement and calculation from molecular structure, including the Griffin method, Davis method, and Kawakami method. In this specification, the value calculated using the Griffin method is used as the HLB value, except in the case of silicone-based surfactants, which will be described later.

The Griffin method is generally used for non-ionic materials and is calculated using the molecular weight of the target material using the following formula (1):

Formula (1):
HLB value = 20 x (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material)

On the other hand, in the case of silicone surfactants, which will be described later, they are generally mixtures containing many compounds, so the HLB value used is the value actually measured using the method described on page 324 of "Surfactant Handbook" (edited by Nishi Ichiro et al., Sangyo Tosho Co., Ltd., 1960).

To explain the specific measurement method, 0.5 g of the target material is dissolved in 5 mL of ethanol, and then the solution is stirred while being titrated at 25°C using a 2% by mass aqueous phenol solution. The endpoint is when the solution becomes cloudy, and the amount of phenol solution (referred to as A (mL)) added up to the endpoint is used to calculate the HLB value using the following formula (2):

Formula (2):
HLB value = 0.89 x A + 1.11

The amount of alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 added is preferably 0.1 to 5 mass% based on the total mass of the ink of this embodiment. Furthermore, from the viewpoint of improving standby ejection properties and suppressing beading and pinholes in printed matter, the amount added is more preferably 0.3 to 2.5 mass%, and even more preferably 0.5 to 2.0 mass%. Furthermore, when the content of unmodified acetylenic diol surfactant (A1) is taken as 1, the content of alkylene oxide-modified acetylenic diol surfactant (A2) is preferably 10 to 5,000 by mass, more preferably 20 to 5,000, even more preferably 50 to 2,000, and particularly preferably 100 to 1,000. When the content of (A2) is adjusted to fall within the above range, a favorable emulsified state is formed between the unmodified acetylenic diol surfactant (A1) and the surfactant function is favorably exhibited, improving standby discharge properties and making it easy to prevent beading and pinholes in printed materials. Furthermore, from the viewpoint of favorably and easily achieving improved solid coverage and pinhole prevention, it is highly preferable that the content of the alkylene oxide-modified acetylenic diol surfactant (A2) be 160 to 800.

Specific examples of the alkylene oxide-modified acetylenic diol surfactant (A2) include compounds represented by the following general formula (3):

General formula (3):

In general formula (3), ^R1 and ^R2 each represent an alkyl group having 1 to 5 carbon atoms, which may be branched, EO represents an ethylene oxide group, and PO represents a propylene oxide group. Furthermore, m1, m2, n1, and n2 each represent an integer of 0 to 30, and m1+n1+m2+n2 is an integer of 1 to 120. However, the addition of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be block or random.

The molecular weight of the alkylene oxide-modified acetylenic diol surfactant (A2) having the structure represented by the above general formula (3) is preferably 300 to 1,200, more preferably 350 to 900, and even more preferably 400 to 700. Alkylene oxide-modified acetylenic diol surfactant (A2) with a molecular weight within the above range orients at the gas-liquid interface at an appropriate speed, making it easier to suppress beading. The molecular weight of the above alkylene oxide-modified acetylenic diol surfactant (A2) refers to the formula weight, which can be determined by calculation.

The alkylene oxide-modified acetylenic diol surfactant represented by the above general formula (3) may be synthesized by a conventionally known method, or a commercially available product may be used. Commercially available examples of the compound represented by general formula (3) include Surfynol 440, Surfynol 2502, Dynol 604, and Dynol 607 manufactured by Evonik; Olfine E1004 manufactured by Nissin Chemical Industry Co., Ltd.; and Acetylenol E40 and Acetylenol E60 manufactured by Kawaken Fine Chemicals Co., Ltd.

<Other acetylene diol surfactants>
The ink of this embodiment may contain an acetylenic diol-based surfactant other than the unmodified acetylenic diol-based surfactant (A1) and the alkylene oxide-modified acetylenic diol-based surfactant (A2) (also referred to herein simply as "other acetylenic diol-based surfactants"). Examples of other acetylenic diol-based surfactants include alkylene oxide-modified acetylenic diol-based surfactants having an HLB value of less than 6 and alkylene oxide-modified acetylenic diol-based surfactants having an HLB value of more than 12. Examples of commercially available products include Surfynol 420, Surfynol 465, and Surfynol 485 manufactured by Evonik; Olfine E1010 manufactured by Nissin Chemical Industry Co., Ltd.; and Acetylenol E13T, Acetylenol E100, and Acetylenol E200 manufactured by Kawaken Fine Chemicals Co., Ltd. Among these, alkylene oxide-modified acetylenic diol surfactants having an HLB value of 14 or more are preferably used from the viewpoint of being able to improve the compatibility of materials essential to the ink of this embodiment, such as water, the acetylenic diol surfactant (A), and the glycol monoethers (B1), thereby realizing suppression of beading and further improvement of standby ejection properties, and being able to improve pinhole resistance by slowly and gently orienting at the interface.

In some embodiments, the weighted average HLB value of the acetylenic diol surfactant (A) is preferably 6.0 to 13.0, more preferably 6.5 to 12.0, and particularly preferably 6.8 to 11.8. By using a combination of an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) (and, if necessary, other acetylenic diol surfactants) so that the weighted average HLB value falls within the above range, these acetylenic diol surfactants are suitably emulsified and compatible, making it easier to suppress pinholes in printed materials and improve standby discharge properties. Furthermore, the orientation speed of these acetylenic diol surfactants to interfaces is optimized, improving solid coverage in printed materials.

The weighted average HLB value is the average HLB value calculated by weighting according to the content of the target compound. For example, if an ink contains three acetylenic diol surfactants, the HLB values of the three acetylenic diol surfactants are A, B, and C, respectively, and the content of the three acetylenic diol surfactants relative to the total mass of the ink is P (mass %), Q (mass %), and R (mass %), the formula for calculating the weighted average HLB value of the acetylenic diol surfactant (A) in the ink is (A x P + B x Q + C x R) ÷ (P + Q + R).

<Water-soluble organic solvent (B)>
The ink of this embodiment contains a water-soluble organic solvent (B). Furthermore, at least a glycol monoether (B1) is used as the water-soluble organic solvent (B). As described above, the glycol monoether (B1) can emulsify and compatibilize the unmodified acetylenic diol surfactant (A1), thereby improving standby ejection properties of the ink of this embodiment. Furthermore, the glycol monoether (B1) contributes to a reduction in the surface tension of the aqueous inkjet ink on the printing substrate, making it easier to suppress beading.

In this specification, the term "water-soluble organic solvent" refers to a solvent that has a solubility of 1% by mass or more in water at 25°C and is liquid at 25°C.

(Glycol monoethers (B1))
Specific examples of the glycol monoethers (B1) include compounds represented by the following general formula (4).

General formula (4):
R ³ -O-(AO) _u -H

In the above general formula (4), ^R3 represents a chain alkyl group having 1 to 4 carbon atoms, which may be branched; AO represents an ethylene oxide group and/or a propylene oxide group; and u represents an integer of 1 to 3.

Specific examples of the compound represented by the general formula (4) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono(n/iso)propyl ether, ethylene glycol mono(n/iso)butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono(n/iso)propyl ether, diethylene glycol mono(n/iso/tert)butyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(n/iso)propyl ether, propylene glycol mono(n/iso/tert)butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono(n/iso)propyl ether, dipropylene glycol mono(n/iso/tert)butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol mono(n/iso/tert)butyl ether, and the like. In particular, from the viewpoint of having good affinity for water and further exhibiting the above-mentioned effects favorably, thereby improving pinhole resistance and beading suppression, one or more compounds selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol mono(n/iso)propyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(n/iso)propyl ether, and dipropylene glycol mono(n/iso)propyl ether can be preferably used.
The above "(n/iso)" represents normal and/or iso forms, and "(n/iso/tert)" represents one or more forms selected from the group consisting of normal, iso, and tertiary forms.

Among these, one or more compounds selected from the group consisting of propylene glycol monomethyl ether, diethylene glycol mono(n/iso)propyl ether, propylene glycol mono(n/iso)propyl ether, and dipropylene glycol mono(n/iso)propyl ether are particularly preferred, as they have excellent emulsifying and compatibilizing capabilities for the unmodified acetylenic diol surfactant (A1), a good balance between low surface tension and a low boiling point at 1 atmosphere, and are also highly hydrophilic, thereby simultaneously suppressing beading, improving standby discharge properties, and improving pinhole resistance.

The glycol monoethers (B1) may be used alone or in combination of two or more types.

From the viewpoint of improving standby ejection properties, beading suppression, and pinhole resistance, as well as improving the drying properties of the aqueous inkjet ink on non-absorbent substrates, the content of glycol monoethers (B1) is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass, relative to the total mass of the ink of this embodiment.

Furthermore, in the ink of this embodiment, the ratio (by mass) of the amount of glycol monoethers (B1) to the amount of alkylene oxide-modified acetylenic diol surfactant (A2) is 0.5 to 50. This ratio is preferably 1.5 to 35, and more preferably 3 to 25. By specifying the blending ratio of the two in this way, it is believed that the surface tension is reduced uniformly throughout the aqueous inkjet ink, and beading and pinholes can be effectively suppressed. This also improves the standby ejection properties of the aqueous inkjet ink.

Furthermore, in this embodiment, the sum of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) and the content of the glycol monoether (B1) is preferably 2 to 20 mass %, more preferably 3 to 15 mass %, and even more preferably 4 to 12 mass %, relative to the total mass of the aqueous inkjet ink. By keeping the ratio of the blend amounts of the two within the above-mentioned ranges and keeping the sum of the blend amounts within the above-mentioned ranges, it is possible to improve standby ejection performance and pinhole resistance while suppressing beading.

(Other water-soluble organic solvents)
The ink of this embodiment may contain, as the water-soluble organic solvent (B), a water-soluble organic solvent other than the glycol monoethers (B1) (also referred to herein as "other water-soluble organic solvents").

Examples of the other water-soluble organic solvents include monohydric alcohols having 1 to 6 carbon atoms, such as ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol, isopentanol, and dimethylbutanol;
Alkanediols having 2 to 6 carbon atoms, such as 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2,4-pentanediol, isoprene glycol (3-methyl-1,3-butanediol), 1,2-hexanediol, and hexylene glycol (2-methyl-2,4-pentanediol);
polyalkylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol;
Methoxybutanols such as 3-methoxy-1-butanol and 3-methoxy-3-methylbutanol;
Nitrogen-containing solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide;
Lactone solvents such as γ-butyrolactone and ε-caprolactone can be used. The compounds listed above may be used alone or in combination of two or more.

When the ink of this embodiment contains another water-soluble organic solvent, it is preferable to use the above-mentioned alkanediols having 2 to 6 carbon atoms as the other water-soluble organic solvent. When an alkanediol having 2 to 6 carbon atoms is used, the compatibility of the main components of the ink, such as water, the acetylene diol surfactant (A), and the glycol monoethers (B1), can be improved. In addition, beading can be suppressed and standby jetting performance can be further improved.
Among alkanediols having 2 to 6 carbon atoms, alkanediols having 2 to 6 carbon atoms and having a 1-hydroxyethyl group (CH ₃ —CH(OH)—) are particularly preferred from the viewpoints of particularly demonstrating the above-mentioned effects and improving beading and standby discharge properties. Examples of alkanediols having 2 to 6 carbon atoms and having a 1-hydroxyethyl group include 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 2,4-pentanediol, and hexylene glycol (2-methyl-2,4-pentanediol). Among these compounds, one or more compounds selected from the group consisting of 1,2-propanediol, 1,3-butanediol, and hexylene glycol are preferred from the viewpoints of excellent compatibility with the acetylene diol surfactant (A) and the glycol monoethers (B1) and high beading suppression properties. In some embodiments, the use of 1,3-butanediol and/or hexylene glycol is particularly preferred.

When alkanediols having 2 to 6 carbon atoms are used as other water-soluble organic solvents, their content is preferably 1 to 40 mass% relative to the total mass of the ink of this embodiment, more preferably 5 to 35 mass%, and even more preferably 10 to 30 mass%. By ensuring that the content of alkanediols having 2 to 6 carbon atoms is 10 mass% or more, the effects of the acetylene diol surfactant (A) described above can be fully achieved, making it easier to suppress beading, improving moisture retention on the inkjet head, and improving standby ejection properties.

In order to obtain an aqueous inkjet ink that has excellent drying properties even on non-absorbent substrates, as well as excellent beading suppression, standby ejection properties, and pinhole resistance, the amount of water-soluble organic solvents having a boiling point of 235°C or higher contained in the aqueous inkjet ink is preferably 5% by mass or less (0 to 5% by mass), and more preferably 2% by mass or less (0 to 2% by mass). In some embodiments, it is even more preferable that the amount of water-soluble organic solvents having a boiling point of 235°C or higher is 2% by mass or less (0 to 2% by mass), and that the amount of water-soluble organic solvents having a boiling point of 210°C or higher is 5% by mass (0 to 5% by mass). It is particularly preferable that the amount of water-soluble organic solvents having a boiling point of 235°C or higher is 1% by mass or less (0 to 1% by mass), and that the amount of water-soluble organic solvents having a boiling point of 210°C or higher is 2% by mass or less (0 to 2% by mass).

In this specification, the "boiling point" refers to a value at 1 atmosphere and can be measured using, for example, a thermal analyzer. Furthermore, the statement "content (amount blended) is 0% by mass" indicates that the target compound is not contained.

The total content of water-soluble organic solvents contained in the aqueous inkjet ink of this embodiment is preferably 5 to 40% by mass relative to the total mass of the aqueous inkjet ink. In particular, a total content of 10 to 35% by mass is more preferable, from the viewpoint of obtaining an aqueous inkjet ink that can ensure sufficient drying even on a non-absorbent substrate, while also exhibiting excellent beading suppression, standby ejection properties, and pinhole resistance.

<Nonionic Surfactant (C)>
As described above, in this embodiment, in addition to the acetylenic diol surfactant (A), a nonionic surfactant (C) other than the acetylenic diol surfactant can be used in combination. The use of the nonionic surfactant (C) is thought to cause an interaction between the acetylenic diol surfactant (A) and the nonionic surfactant (C) and the acetylenic diol surfactant (A) to behave like a single surfactant. As a result, standby ejection performance can be further improved and pinholes and migration in printed materials can be prevented. Furthermore, the nonionic surfactant (C) is gradually oriented toward the air-liquid interface compared to the acetylenic diol surfactant (A), which can promote wetting and spreading of ink droplets on a printing substrate and enable the ink droplets to be wetted and spread uniformly, making it easier to obtain printed materials without beading.

The HLB value of the nonionic surfactant (C) is preferably 6 to 14, and more preferably 8 to 11. If the HLB value is within this range, a strong interaction occurs, particularly with the alkylene oxide-modified acetylenic diol surfactant (A2), improving standby ejection properties and producing printed matter that is free of pinholes and migration.

When the ink of this embodiment contains a nonionic surfactant (C), the value obtained by dividing the weighted average HLB value of the acetylenic diol surfactant (A) by the (weighted average) HLB value of the nonionic surfactant (C) is preferably 0.5 to 1.8, and more preferably 0.7 to 1.3. When the value obtained by dividing the weighted average HLB value of the acetylenic diol surfactant (A) by the (weighted average) HLB value of the nonionic surfactant (C) is within the above range, the ink will have good solid coverage, standby discharge properties, pinhole resistance, and migration resistance.
The expression "(weighted average value of) the HLB value of the nonionic surfactant (C)" means that when the ink contains one type of nonionic surfactant (C), the HLB value of that nonionic surfactant (C) is used. When the ink contains two or more types of nonionic surfactants (C), the expression means that the weighted average value of the HLB values of the nonionic surfactants (C) calculated by the above-mentioned method is used.

The content of the nonionic surfactant (C) is preferably 0.1 to 5% by mass, more preferably 0.3 to 2.5% by mass, and even more preferably 0.5 to 2.0% by mass, based on the total mass of the ink.
Furthermore, the mass ratio of the content of the nonionic surfactant (C) to the total content of the unmodified acetylenic diol surfactant (A1) and the alkylene oxide-modified acetylenic diol surfactant (A2) is preferably 0.3 to 2.0, more preferably 0.5 to 1.5. More specifically, this mass ratio is a value expressed as "content of nonionic surfactant (C) / {content of unmodified acetylenic diol surfactant (A1) + content of alkylene oxide-modified acetylenic diol surfactant (A2)}".
When the content of the nonionic surfactant (C) and the mass ratio of the content are within the above ranges, the surfactants tend to function as a single surfactant, resulting in good standby ejection properties and making it easier to obtain printed matter that is free of pinholes and migration.

The nonionic surfactant (C) may be synthesized by a conventionally known method, or a commercially available product may be used. Examples of surfactants that can be used as the nonionic surfactant (C) include acetylene monool surfactants, silicone surfactants, fluorine-based surfactants, polyoxyalkylene alkyl ether surfactants, polyoxyalkylene aryl ether surfactants, and polyalkylene glycol alkylate surfactants. These compounds may be used alone or in combination of two or more.

In particular, it is particularly preferable that the ink of this embodiment contains a silicone-based surfactant and/or a polyoxyalkylene alkyl ether-based surfactant as the nonionic surfactant (C). When at least one of these surfactants is used, it easily interacts with the acetylene glycol-based surfactant (A), making it easier to improve standby ejection performance and prevent pinholes and migration, as described above. Furthermore, the surface energy of the ink layer is reduced, making it possible to reduce blocking.

The silicone surfactant preferably used in this embodiment is a compound represented by the following general formula (5):

General formula (5):

In general formula (5), p is an integer of 0 or greater, and q is an integer of 1 or greater. ^R4 is an alkyl group having 1 to 6 carbon atoms or a structure represented by the following general formula (6), and ^R5 is a methyl group or a structure represented by the following general formula (6). However, when ^R5 is a methyl group, p is 0.

General formula (6):

In general formula (6), r is an integer of 1 to 6, s is an integer of 0 to 50, and t is an integer of 0 to 50, provided that s+t is 1 or greater. ^R6 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a (meth)acryloyl group, or a 2-hydroxy-3-((meth)acryloyloxy)propyl group. The addition of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be block or random.

The above silicone surfactants may be synthesized using conventional methods or may be commercially available products. Examples of commercially available products include SF8428, FZ-2162, 8032 ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Dow Corning Toray Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, and BYK-3420 manufactured by BYK-Chemie; and TEGO Wet250, TEGO Wet260, TEGO Wet270, TEGO Wet280, TEGO Glide100, and TEGO Gli manufactured by Evonik. TEGO Glide410, TEGO Glide432, TEGO Glide435, TEGO Glide440, TEGO Glide450, TEGO Rad2200, TEGO Rad2250, TEGO Rad2300, TEGO Twin 4000, TEGO Twin 4100, TEGO Twin 4200 manufactured by Shin-Etsu Chemical Co., Ltd.; KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643 manufactured by Shin-Etsu Chemical Co., Ltd.; and the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd. These commercially available products may be used alone or in combination of two or more.

In order for the nonionic surfactant (C) to behave like a single surfactant with the acetylenic diol surfactant (A), it is preferable for an interaction to occur between the nonionic surfactant (C) and the acetylenic diol surfactant (A). On the other hand, from the perspective of further improving standby dischargeability and suppressing pinholes in printed materials, it is preferable for the acetylenic diol surfactant (A) and the nonionic surfactant (C) to be compatible to a certain extent. From the above perspective, i.e., from the perspective of improving standby dischargeability and making it easier to prevent pinholes and migration, it is preferable to use two or more silicone surfactants in combination as the nonionic surfactant (C). It is particularly preferable to use a combination of the two or more silicone surfactants such that the difference in HLB value between them is 2 or more.

On the other hand, in this embodiment, it is also preferable to use a polyoxyalkylene alkyl ether surfactant as the nonionic surfactant (C). Polyoxyalkylene alkyl ether surfactants have good compatibility with water and acetylene diol surfactants, and can suppress beading and pinholes without affecting these materials.

As the polyoxyalkylene alkyl ether surfactant, for example, a compound represented by the following general formula (7) can be used.

General formula (7):
R ⁷ -O-(EO) _v -H

In the general formula (7), ^R7 represents any one selected from the group consisting of a chain alkyl group having 6 to 22 carbon atoms which may be branched, a chain alkenyl group which may have a branched structure, an alicyclic alkyl group which may have one or more alkyl groups added thereto, and an aromatic group which may have one or more alkyl groups added thereto; EO represents an ethylene oxide group; and v represents an integer of 2 to 100.

Examples of commercially available polyoxyalkylene alkyl ether surfactants include:
Emulgen series (manufactured by Kao Corporation) such as Emulgen 104P, 105, 106, 108, 109P, 120, 123P, 150, 210, 220, 306P, 320P, and 350;
Braunon series such as EL-1502.2, 1505, 1507, 1509, 1515, 1521, 1530, 1540P, CH-302L, 305, 310L, 315L, 320L, 325L, 330L, 340, SR-702L, 705, 707, 711, 715, 720, 730, 750F, BE-5, 10, 20, 30, and BN-3 (manufactured by Aoki Oil & Fat Industries Co., Ltd.);
Nonion series (manufactured by NOF Corporation) such as Nonion K-204, 220, 230, 2100W, P-208, 210, 213, E-202, 205, 212, 215, 230, S-202, 207, 215, 220, EH-204, 208, ID-203, 206, and 209;
Lutensol series (manufactured by BASF), such as Lutensol XL40, 50, 60, 70, 80, 90, XP30, 40, 50, 60, 70, 80, 90, 100, etc.
Newcol series such as Newcol 2302, 2303, 2305, 2308, 2310, 2320, and 2360 (manufactured by Nippon Nyukazai Co., Ltd.);
Emulmin LS-80, LS-90, NL-70, NL-80, NL-90, NL-100, NL-110, Sannonic SS-30, SS-50, SS-70, SS-90, SS-120 (manufactured by Sanyo Chemical Industries, Ltd.),
Examples of such an anti-fungal agent include ADEKA TOLL LA-675B, LA-775, LA-875, LA-975, LA-1275, SO-80, SO-105, SO-120, SO-135, SO-145, and SO-160 (manufactured by ADEKA Corporation).
In addition to the above-mentioned commercially available products, diethylene glycol monohexyl ether, triethylene glycol monohexyl ether, tetraethylene glycol monohexyl ether, etc. can also be used. The above-listed products may be used alone or in combination of two or more. Furthermore, polyoxyalkylene alkyl ether surfactants synthesized by conventionally known synthesis methods may also be used.

In the case of polyoxyalkylene alkyl ether surfactants, as in the case of the silicone surfactants described above, it is preferable to use two or more polyoxyalkylene alkyl ether surfactants in combination so that the difference in HLB values between the two or more polyoxyalkylene alkyl ether surfactants is 2 or more, as this improves standby ejection properties and makes it easier to prevent pinholes and migration.

Furthermore, for the same reason, namely, to improve standby ejection properties and facilitate the prevention of pinholes and migration, it is also preferable that the ink of this embodiment uses a silicone surfactant and a polyoxyalkylene alkyl ether surfactant in combination, and that the difference in HLB value between the silicone surfactant and the polyoxyalkylene alkyl ether surfactant is 2 or more.

<Other surfactants>
Furthermore, the aqueous inkjet ink of this embodiment may contain surfactants other than the surfactants described above. For example, ionic (anionic or cationic) surfactants, amphoteric surfactants, etc. can be used.

<Binder resin>
The ink of this embodiment may contain a binder resin, which can significantly improve the scratch resistance and migration resistance of the printed matter.

Generally, water-soluble resins and hydrosols and emulsions, which are types of water-insoluble resins, are known as binder resins used in aqueous inkjet inks. Here, "water-soluble resin" refers to a pigment dispersion resin whose 1% by weight aqueous mixture is transparent to the naked eye at 25°C. Furthermore, "hydrosol" refers to a "water-insoluble resin" (a resin that is not water-soluble) that contains acidic and/or basic functional groups in its structure and is dispersed in a dispersion medium without the use of emulsifiers such as surfactants or polymers. Meanwhile, "emulsion" refers to a resin that is forcibly dispersed in a dispersion medium by adsorbing and/or bonding the emulsifier to the resin surface. In this specification, the above hydrosols and emulsions are collectively referred to as "resin microparticles."

(Water-soluble resin)
In some embodiments, it is preferable to use a water-soluble resin and/or hydrosol as the binder resin for forming the ink. These resins have affinity with aqueous media (mediums consisting of liquids containing at least water) without the use of an emulsifier, and at least a portion of the resin swells and/or dissolves in the aqueous medium. Therefore, clogging due to precipitation of the resin near the nozzles of the inkjet head is unlikely to occur, and an ink with excellent standby ejection properties can be easily provided. Furthermore, these resins can function as compatibilizers for the unmodified acetylenic diol surfactant (A1), thereby suppressing the occurrence of pinholes in printed materials.

Types of resins that can be used as water-soluble resins and hydrosols include acrylic resins, urethane resins, and polyester resins. Among these, acrylic resins are preferred, taking into consideration the storage stability and standby discharge properties of the ink, as well as the abrasion resistance of the printed material.

In this specification, "acrylic resin" refers to a resin that uses one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters (a styrene-based monomer may also be used).

In this embodiment, the water-soluble resin may be a resin synthesized by a conventionally known method, or a commercially available product. There are no particular restrictions on the structure, and any resin having a random structure, block structure, comb structure, star structure, etc. can be used.

When a water-soluble resin is used as the binder resin, the weight-average molecular weight of the water-soluble resin is preferably in the range of 5,000 to 50,000, and more preferably in the range of 10,000 to 40,000. When the weight-average molecular weight of the water-soluble resin is 5,000 or more, the abrasion resistance of the printed matter is improved and beading is easily suppressed. Furthermore, when the weight-average molecular weight of the water-soluble resin is 50,000 or less, an ink with good standby ejection properties from an inkjet head can be easily obtained.

The weight-average molecular weight of a resin can be measured by standard methods. For example, it is the value measured as the weight-average molecular weight converted into polystyrene using a TSKgel column (manufactured by Tosoh Corporation) and a GPC (HLC-8120GPC, manufactured by Tosoh Corporation) equipped with an RI detector, using THF as the developing solvent.

When selecting a water-soluble resin, the acid value is also important. When using a water-soluble resin as a binder resin, it is preferable that the acid value be 5 to 80 mgKOH/g, and more preferably 15 to 50 mgKOH/g. By setting the acid value to 5 mgKOH/g or more, even if the resin solidifies near the nozzle of the inkjet head, it can be re-dissolved in the ink, which makes it easier to prevent clogging of the nozzle and improves standby ejection performance. Furthermore, an acid value of 80 mgKOH/g or less not only produces printed matter with excellent water resistance and abrasion resistance, but also functions more easily as a compatibilizer for the unmodified acetylenic diol surfactant (A1), making it easier to produce printed matter without pinholes.

The "acid value of a resin" refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize the acid groups contained in 1 g of the resin. In this specification, the value calculated using the following method is used as the acid value. For example, if a resin has na acid groups with a value of va per molecule and contains Wa mass% of polymerizable monomers with a molecular weight of Ma among the polymerizable monomers that make up the resin, the acid value (mg KOH/g) can be calculated using the following formula (8):

Formula (8):
(Acid value) = {(va x na x Wa) ÷ (100 x Ma)} x 56.11 x 1000

In the above formula (8), the number "56.11" is the molecular weight of potassium hydroxide.

In the ink of this embodiment, the content of the water-soluble resin is preferably 0.5 to 10% by mass, more preferably 1 to 8% by mass, and even more preferably 2 to 6% by mass, relative to the total mass of the ink. If the content of the water-soluble resin is 0.5% by mass or more, the unmodified acetylene diol surfactant (A1) can be sufficiently compatibilized, improving the storage stability of the ink and suppressing pinholes in printed materials. Furthermore, if the content of the water-soluble resin is 10% by mass or less, the viscosity of the ink can be kept within a suitable range, and an ink with excellent standby ejection properties can be easily obtained.

(Resin fine particles)
On the other hand, resin microparticles such as hydrosols and emulsions generally have a higher molecular weight than water-soluble resins. Furthermore, when the same amount of resin is blended, resin microparticles can lower the viscosity of the ink compared to water-soluble resins. Therefore, the use of resin microparticles allows a larger amount of resin to be incorporated into the ink, making it easier to improve the abrasion resistance, blocking resistance, and migration resistance of printed materials.

Among the resins used as resin microparticles, types of resins that can be used as emulsions include acrylic resins, urethane resins, polyester resins, styrene-butadiene resins, acrylonitrile-butadiene resins, vinyl chloride resins, polyolefin resins, etc. Among these, emulsions of one or more resins selected from the group consisting of acrylic, urethane, polyester, and polyolefin resins are preferred, considering that they maintain the storage stability of the ink and easily improve the abrasion resistance and blocking resistance of printed materials.

Furthermore, when using a hydrosol as the resin microparticles, it is preferable to use one or more resins selected from the group consisting of acrylic, urethane, and polyester resins, from the viewpoint of improving the scratch resistance of printed matter. Furthermore, when further considering the viewpoint of improving standby discharge properties as mentioned above, it is particularly preferable to use an acrylic resin.

However, when the binder resin in the ink is resin microparticles, particularly when an emulsion is used, the minimum film-forming temperature (MFT) of the resin microparticles must be taken into consideration. If resin microparticles with a low MFT are used, the MFT of the resin microparticles may decrease further depending on the water-soluble organic solvent added to the ink, and the resin microparticles may adhere near the nozzles of the inkjet head, even at room temperature, causing clogging. In particular, in the case of emulsions, once a film is formed, it is difficult to redissolve the resin in the ink, so there is a risk that the emulsion's standby discharge performance will be impaired due to the adhered emulsion. To avoid such problems, it is preferable to adjust the type and amount of polymerizable monomers that make up the emulsion to set the MFT of the emulsion to 60°C or higher.

Furthermore, when using hydrosol as the resin microparticles, the possibility of standby discharge performance deteriorating is not as high as in the case of emulsion. On the other hand, using a hydrosol with an MFT of 60°C or higher can reduce factors that can deteriorate standby discharge performance, so it is preferable to set the MFT to 60°C or higher even in the case of hydrosol.

The above MFT can be measured, for example, using an MFT tester manufactured by Tester Sangyo Co., Ltd.

When an emulsion is used in the ink of this embodiment, its content is preferably 2 to 15% by mass, and more preferably 4 to 10% by mass, relative to the total mass of the ink. If the emulsion content is 2% by mass or more, abrasion resistance and blocking resistance will be improved, and if it is 15% by mass or less, the ink viscosity can be kept within a suitable range and the ink will have excellent standby ejection properties.

<Pigments>
The ink of this embodiment contains a pigment. The pigment may be an inorganic pigment and/or an organic pigment. These pigments may be used alone or in combination of two or more. The pigment content 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 ink.

When inorganic pigments are used, specific examples include titanium oxide, zinc oxide, 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, and cobalt violet.

Of the carbon blacks listed above, those produced by the furnace method or the channel method can be used. Among them, carbon black produced by the furnace method or the channel method and having properties such as a primary particle size of 11 to 40 nm, a specific surface area measured by the BET method of 50 to 400 m ² /g, a volatile content of 0.5 to 10%, and a pH of 2 to 10 are preferred. Examples of commercially available products having these specifications include No. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, MCF88 (manufactured by Mitsubishi Chemical Corporation), RAVEN1255 (manufactured by Birla Carbon Corporation), REGAL330R, 400R, 660R, MOGUL L, ELFTEX415 (manufactured by Cabot Corporation), NIPex90, NIPex150T, NIPex160IQ, NIPex170IQ, NIPex75, PrinteX35, PrinteX85, PrinteX90, PrinteX95, PrinteXU (manufactured by Orion Engineered Carbons), and the like, all of which can be preferably used.

On the other hand, examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, fluorescent pigments, etc.

Specific examples based on the color index include cyan pigments such as C.I. Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, and 64.

Magenta pigments include C.I. Pigment Red 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 176, 177, 178, 179, 184, 185, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, and 282, and C.I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

Yellow pigments include C.I. 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.

Furthermore, examples of black pigments include aniline black (C.I. Pigment Black 1), perylene black (C.I. Pigment Black 31, 32), azomethine azo black, etc. Furthermore, a black pigment can be produced by mixing multiple chromatic pigments, such as the cyan pigments, magenta pigments, and yellow pigments listed above, as well as the brown pigments and orange pigments listed below.

Other pigments besides those mentioned above include C.I. Pigment Green 7, 10, 36, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc.

<Pigment dispersing resin>
In order to maintain the storage stability and standby dischargeability of the ink for a long period of time, the pigment is preferably used in a dispersed state in the ink. Methods for stably dispersing and maintaining the pigment in the ink include (1) a method in which at least a portion of the pigment surface is coated with a pigment dispersing resin, (2) a method in which a water-soluble and/or water-dispersible surfactant is adsorbed onto the pigment surface, and (3) a method in which a hydrophilic functional group is chemically and/or physically introduced onto the pigment surface, and the pigment is dispersed in the ink without a pigment dispersing resin or surfactant (self-dispersing pigment).

For the ink of this embodiment, method (1) above, i.e., the method using a pigment dispersion resin, is preferably selected. This is because the pigment coverage and charge of the pigment dispersion resin can be easily adjusted by selecting and considering the composition and weight average molecular weight of the polymerizable monomers that make up the resin, making it possible to impart stable storage stability even to fine pigments, and also to obtain printed matter with excellent standby ejection properties, color development, and color reproducibility.

Examples of the pigment dispersion resin include acrylic resins, styrene-maleic acid (anhydride) resins, α-olefin-maleic acid (anhydride) resins, urethane resins, and polyester resins. Among these, it is preferable to use one or more resins selected from acrylic resins, styrene-maleic acid (anhydride) resins, and α-olefin-maleic acid (anhydride) resins, as these resins strengthen adsorption to the pigment and improve storage stability and standby discharge properties. In this specification, "maleic acid (anhydride)" refers to maleic acid and/or maleic anhydride.

When a water-soluble resin is used as the pigment dispersion resin, its acid value is preferably 60 to 400 mgKOH/g. By keeping the acid value within this range, pigment dispersion stability, as well as ink storage stability and standby discharge properties can be optimized. The acid value is more preferably 100 to 350 mgKOH/g, and even more preferably 120 to 300 mgKOH/g. On the other hand, when a water-insoluble resin is used as the pigment dispersion resin, its acid value is preferably 0 to 100 mgKOH/g, more preferably 5 to 90 mgKOH/g, and even more preferably 10 to 80 mgKOH/g. An acid value within the above range not only produces printed matter with excellent drying properties and water resistance, but also improves pigment dispersion stability and ink standby discharge properties. The acid value of the pigment dispersion resin can be measured in the same manner as for the binder resin described above.

The weight-average molecular weight of the pigment dispersion resin is preferably 5,000 to 100,000. A weight-average molecular weight of 5,000 or more can ensure favorable pigment dispersion stability and ink storage stability. Furthermore, a weight-average molecular weight of 100,000 or less can ensure favorable standby ejection properties. The weight-average molecular weight is more preferably in the range of 10,000 to 50,000, and even more preferably in the range of 15,000 to 30,000. The weight-average molecular weight of the pigment dispersion resin can be measured in the same manner as for the binder resin described above.

The amount of pigment dispersion resin relative to the amount of pigment is preferably 1 to 120% by mass. By making the ratio of pigment dispersion resin 1% or more by mass relative to the amount of pigment, the ink viscosity can be kept within a range suitable for use in inkjet printing applications, improving standby ejection properties. Furthermore, by making it 120% or less by mass, the pigment dispersion stability and ink storage stability can be improved. The amount of pigment dispersion resin relative to the amount of pigment is more preferably 2 to 100% by mass, and even more preferably 5 to 50% by mass.

<Water>
The ink of this embodiment further contains water in addition to the above-mentioned components. The water contained in the ink of this embodiment is preferably ion-exchanged water (deionized water) rather than ordinary water containing various ions. The content of water contained in the ink is preferably adjusted taking into account the content of liquid media other than water, such as the water-soluble organic solvent (B).

In some embodiments, the amount of water contained in the ink is preferably in the range of 20 to 90% by mass, and may be 30 to 80% by mass, relative to the total mass of the ink. In some embodiments, the content of the aqueous medium containing water and the water-soluble organic solvent (B) in the total mass of the ink may be in the range of 25 to 95% by mass. The content of the aqueous medium may preferably be 35 to 92% by mass, and more preferably 50 to 88% by mass. In some embodiments, the ratio (mass ratio) of water to the water-soluble organic solvent (B) in the aqueous medium may preferably be 50/50 to 95/5, more preferably 55/45 to 90/10, and even more preferably 60/40 to 85/15.

<Other ingredients>
In addition to the above components, the ink of the present invention may contain additives such as a pH adjuster, an ultraviolet absorber, and a preservative, if necessary, in order to impart desired physical properties. The amount of these additives added is preferably 0.01% by mass or more and 10% by mass or less, based on the total mass of the ink.

<Ink manufacturing method>
One embodiment of the present invention relates to a method for producing the ink of this embodiment containing the above-mentioned components. An example of a method for producing the ink of this embodiment is the following method. The method includes preparing a pigment dispersion, and then adding and mixing a surfactant and a solvent such as water. However, the method for producing the ink of this embodiment is not limited to the following method.

In a typical production method, first, a pigment dispersion resin and water are mixed to produce a pigment dispersion resin aqueous solution. Next, a pigment and, if necessary, a water-soluble organic solvent or the like are added to the pigment dispersion resin aqueous solution, and the mixture is mixed and stirred (premixed), and then a dispersion treatment is performed using a dispersing means described below. If necessary, coarse particles are removed by centrifugation or the like to obtain a pigment dispersion liquid.
Thereafter, the unmodified acetylenic diol surfactant (A1), the alkylene oxide-modified acetylenic diol surfactant (A2), the binder resin, the glycol monoethers (B1), water, and, if necessary, the nonionic surfactant (C) and other components are added to the pigment dispersion, and the mixture is thoroughly mixed and stirred. The resulting mixture is then filtered to remove coarse particles, thereby obtaining the desired ink.

In this specification, the term "aqueous solution" refers to a solution containing an aqueous solvent (a liquid medium containing at least water) and components dispersed and/or dissolved in the aqueous solvent.

As described in the ink manufacturing method above, it is effective to perform a premixing process before performing the dispersion process. This is preferable because it improves the wetting and spreading properties of the pigment surface and promotes the adsorption of the pigment dispersing resin to the pigment surface.

Furthermore, any commonly used dispersing machine can be used for dispersing the pigment. Examples include ball mills, roll mills, sand mills, bead mills, and Nanomizers, with bead mills being preferred. Examples of bead mills include Super Mills, Sand Grinders, Agitator Mills, Grain Mills, Dyno Mills, Pearl Mills, and Cobol Mills (all trade names).

Since the ink of this embodiment is intended for use in inkjet printing, it is preferable to use a pigment with an optimal particle size distribution from the perspective of preventing nozzle clogging, etc. Methods for obtaining a pigment with the desired particle size distribution include reducing the size of the grinding media in the disperser mentioned above, increasing the packing rate of the grinding media, extending the dispersion treatment time, classifying the ink using a filter or centrifuge after dispersion treatment, and combinations of these methods. The particle size distribution of the ink can be measured using, for example, a Nanotrac UPA-EX150 manufactured by Microtrac-Bell.

<Ink set>
The inks of this embodiment may be used in a single color, or may be used as an ink set combining multiple colors depending on the application. While the combination is not particularly limited, a full-color image can be obtained by using three colors: cyan, yellow, and magenta. The addition of black ink can enhance the sense of black and increase the visibility of characters, etc. Color reproducibility can also be improved by adding colors such as orange and green. When printing on a printing substrate other than white, a clear image can be obtained by using a white ink in combination. Furthermore, the ink set of this embodiment may include, as a constituent color, an ink (clear ink) that does not substantially contain a colorant component, excluding pigments from the constituent components of the ink.

<Ink-pretreatment liquid set>
The aqueous inkjet ink of this embodiment can also be combined with a pretreatment liquid containing an aggregating agent and used in the form of an ink-pretreatment liquid set. By applying a pretreatment liquid containing an aggregating agent to a printing substrate, a layer (ink aggregation layer) can be formed that intentionally aggregates the solid components contained in the ink. Then, by landing the ink of this embodiment on this ink aggregation layer, bleeding between ink droplets and uneven density can be prevented, significantly improving the print quality of the printed matter. Furthermore, depending on the material used in the pretreatment liquid, the adhesion and blocking resistance of the printed matter can also be improved.

As used herein, the term "flocculant" refers to a component contained in an aqueous inkjet ink that disrupts the dispersion state of pigments, causing them to flocculate, and/or insolubilizes resins contained in the aqueous inkjet ink, thereby thickening the aqueous inkjet ink. The flocculant used in the pretreatment liquid combined with the ink of this embodiment preferably contains one or more selected from metal salts and cationic polymer compounds, from the viewpoint of significantly improving print image quality. Of these, from the viewpoint of obtaining excellent print image quality, it is preferable to use a metal salt as the flocculant, and it is particularly preferable to use a salt of one or more polyvalent metal ions selected from the group consisting of Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , and Al ³⁺ . When a metal salt is used as the flocculant, its content is preferably 2 to 30% by mass, and particularly preferably 3 to 25% by mass, relative to the total mass of the pretreatment liquid.

Other pretreatment liquids may contain water-soluble organic solvents, surfactants, pH adjusters, antifoaming agents, thickeners, preservatives, etc. as appropriate. The water-soluble organic solvents and surfactants that can be used in the pretreatment liquid are the same as those for the inks described above. Furthermore, if the pretreatment liquid contains a surfactant, from the perspective of obtaining printed matter with excellent blocking resistance and migration resistance, it is preferable that the pretreatment liquid contain an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) with an HLB value of 6 to 12.

One embodiment of the present invention relates to a printed material obtained by printing the aqueous inkjet ink of the present embodiment onto a printing substrate. The printed material has a printing substrate and a printed layer (ink layer) formed on the printing substrate by printing using the aqueous inkjet ink of the present embodiment.
<Printing base material>
As described above, the ink of this embodiment is particularly suitable for printing on non-absorbent substrates such as films. When using the non-absorbent substrate as the printing substrate, specific examples include polyolefin resins such as polyethylene, biaxially oriented polypropylene (OPP), and non-axially oriented polypropylene (CPP); polyester resins such as polyethylene terephthalate (PET), polycarbonate, and polylactic acid; polystyrene resins such as polystyrene, AS resin, and ABS resin; polyamide resins such as nylon; chlorine-containing resins such as polyvinyl chloride and polyvinylidene chloride; cellophane; and film or sheet substrates made of composite materials thereof. These printing substrates may be subjected to surface treatments such as corona treatment and plasma treatment. Furthermore, they may be subjected to a pre-coating treatment with a pre-coating composition (however, different from the pre-treatment liquid described above) containing one or more resins selected from the group consisting of urethane resins, acrylic resins, and olefin resins.

<Method of manufacturing printed matter>
The ink of this embodiment is used in a printing method in which ink droplets are ejected from the nozzles of an inkjet head and deposited on a substrate. Furthermore, a printed substrate on which an image and/or text is printed, produced by such a printing method, is referred to herein as a "printed matter." In other words, the ink of this embodiment can be used to produce printed matters.

Furthermore, in the production of printed matter, after the ink of this embodiment has been applied to a substrate, it is preferable to dry the ink on the substrate using a drying mechanism. Drying methods used in the drying mechanism include heat drying, hot air drying, infrared drying (for example, infrared with a wavelength of 700 to 2500 nm), microwave drying, and drum drying. The above drying methods may be used alone, or multiple methods may be used in succession, or they may be used in combination simultaneously. For example, by using heat drying and hot air drying in combination, the ink can be dried more quickly than when each method is used alone.

<Post-coating treatment>
The printed matter of this embodiment may be subjected to a post-coating treatment on the surface of the printed matter, if necessary. Specific examples of the post-coating treatment include coating or printing with a post-coating composition, and lamination using a dry lamination method, a solventless lamination method, an extrusion lamination method, or the like. Any of these methods may be selected, or a combination of two or more may be used.

When post-coating a printed item by applying and printing a post-coating composition, the coating and printing method may be either a method in which printing is performed without contact with the printing substrate, such as inkjet printing, or a method in which the post-coating composition is brought into contact with the printing substrate. Furthermore, when the method of printing the post-coating composition without contact with the printing substrate is selected, it is preferable to use, as the post-coating composition, an ink (clear ink) that is substantially free of colorant components, i.e., the ink of the present invention, from which pigments have been removed.

Furthermore, when laminating printed materials, it is preferable that the adhesive used to laminate the sealant substrate be composed of a mixture of a polyol component and a polyisocyanate component.

The polyol component is a resin component having multiple hydroxyl groups, and polyurethane resins and polyester resins are preferably used in view of coatability, wetting and spreading properties and permeability to the interface of printed matter, and the laminate strength developed after aging. In particular, it is preferable for the polyol component to contain polyester polyol, as this provides good wetting and spreading properties to the interface of printed matter obtained with the ink of this embodiment, such as the printed layer (printed area) and pretreatment liquid layer (non-printed area), and also provides excellent laminate strength to the laminated printed matter (laminate). The polyol component may be a single component, or multiple components may be used in combination.

Furthermore, the polyisocyanate component reacts with the polyol component to form urethane bonds, thereby increasing the molecular weight of the adhesive layer and improving laminate strength. In particular, from the standpoints of compatibility with the polyol component, wetting and spreading at the interface of printed materials obtained with the ink of the present invention, and laminate strength of laminated printed materials (laminates), it is preferable that the polyisocyanate component contain a polyether-based urethane resin terminated with an isocyanate group. From the same standpoint, the blending amount of the polyisocyanate component is preferably 50 to 80% by mass relative to the polyol component. The polyisocyanate component may be a single component, or multiple components may be used in combination.

Note that examples of sealant substrates used in the above lamination process include polypropylene films and polyethylene films, such as CPP film and linear short-chain branched polyethylene (LLDPE) film. Films with a vapor-deposited metal (oxide) layer, such as aluminum oxide, may also be used.

Representative embodiments of the present invention will be described below.
<1> An aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B),
the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12;
the content of the unmodified acetylenic diol surfactant (A1) is 2 to 600 ppm relative to the total mass of the aqueous inkjet ink;
the water-soluble organic solvent (B) contains a glycol monoether (B1),
the ratio (by mass) of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 is 0.5 to 50.
<2> The aqueous inkjet ink according to <1> above, wherein the total content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and the content of the glycol monoether (B1) is 2 to 20% by mass, based on the total mass of the aqueous inkjet ink.
<3> The aqueous inkjet ink according to <1> or <2>, further comprising a nonionic surfactant (C) other than the acetylene diol surfactant.
<4> The aqueous inkjet ink according to any one of <1> to <3>, wherein the content of the unmodified acetylenic diol surfactant (A1) is 2 to 400 ppm based on the total amount of the aqueous inkjet ink.
<5> The aqueous inkjet ink according to any one of <1> to <4> above, wherein the ratio (by mass) of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 10 to 5,000.
<6> The aqueous inkjet ink according to the above <5>, wherein the ratio (by mass) of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 20 to 5,000.
<7> A printed matter comprising a printing substrate and a printing layer formed on the printing substrate using the aqueous inkjet ink described in any one of <1> to <6> above.
The present invention is related to the subject matter described in Japanese Patent Application No. 2024-053810, filed on March 28, 2024, the disclosure of which is incorporated herein by reference.

The present invention will be explained in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" are by mass unless otherwise specified.

<Production Example of Pigment Dispersion Resin Water-Based Solution 1>
A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 90 parts of butanol, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. Next, the reaction vessel was heated to 110°C, and then a mixture of polymerizable monomers (30 parts of acrylic acid, 35 parts of behenyl acrylate, and 35 parts of styrene) and 4 parts of a polymerization initiator (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After completion of the addition, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 110°C. Thereafter, 0.4 parts of V-601 was added, and the polymerization reaction was continued for 1 hour while maintaining the internal temperature of the reaction vessel at 110°C, thereby obtaining a solution of pigment dispersion resin 1.
Next, the contents of the reaction vessel were cooled to room temperature, and then 38 parts of dimethylaminoethanol was added to neutralize the pigment dispersion resin 1, followed by the addition of 100 parts of ion-exchanged water. Thereafter, the contents were heated to 100°C or higher to form an azeotrope of butanol with the ion-exchanged water and distill off the butanol. Next, ion-exchanged water was added to adjust the solids concentration to 50%, thereby obtaining an aqueous pigment dispersion resin solution 1 with a solids concentration of 50%. The resulting pigment dispersion resin 1 had a weight-average molecular weight of 16,000 and an acid value of 234 mgKOH/g.

<Production Example of Pigment Dispersion Resin Water-Based Solution 2>
A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 56 parts of 2-butanone. Next, 56 parts of benzyl methacrylate as a polymerizable monomer, 0.3 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 2.2 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid were charged. The atmosphere inside the reaction vessel was purged with nitrogen gas, and the contents of the reaction vessel were heated until they reached 75°C. After that, a polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C, thereby obtaining a polymer (A block) composed of benzyl methacrylate.
After completion of the polymerization reaction, the contents were cooled to room temperature, and then 44 parts of 2-butanone, 28 parts of butyl methacrylate, and 16 parts of methacrylic acid were charged into the reaction vessel. The atmosphere inside the reaction vessel was again purged with nitrogen gas, and the contents inside the reaction vessel were then heated until they reached 75°C, after which the polymerization reaction was carried out for 3 hours while maintaining the internal temperature at 75°C. In this way, a pigment dispersion resin 2 was obtained, which had an A-B block structure in which a copolymer (block B) composed of butyl methacrylate and methacrylic acid was added to the A block.
The contents of the reaction vessel were then cooled to room temperature, and 17 parts of dimethylaminoethanol was added to neutralize the pigment dispersion resin 2. Then, 150 parts of ion-exchanged water was added. The contents were then heated to azeotrope 2-butanone with the ion-exchanged water, and the 2-butanone was distilled off. Ion-exchanged water was then added to adjust the solids concentration to 50%, thereby obtaining an aqueous pigment dispersion resin solution 2 with a solids concentration of 50%. The weight-average molecular weight of the resulting pigment dispersion resin was 23,000, and the acid value was 104 mgKOH/g.

<Production Example of Cyan Pigment Dispersion Liquid 1>
20 parts of LIONOGEN BLUE FG-7358G (C.I. Pigment Blue 15:3, manufactured by Toyocolor Co., Ltd.), 15 parts of pigment dispersion resin aqueous solution 1, and 65 parts of ion-exchanged water were mixed and pre-dispersed using a disper, and then main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm, to obtain cyan pigment dispersion liquid 1.

<Production Example of Cyan Pigment Dispersion Liquid 2>
Cyan pigment dispersion liquid 2 was produced using the same materials and method as for the above-mentioned cyan pigment dispersion liquid 1, except that pigment dispersion resin water-based solution 2 was used instead of pigment dispersion resin water-based solution 1.

<Production Example of Binder Resin 1>
A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 72.4 parts of 2-butanone, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. Next, the reaction vessel was heated to 80°C, and then a mixture of polymerizable monomers (15 parts of styrene, 4.5 parts of methacrylic acid, 5.0 parts of 2-hydroxyethyl methacrylate, 20 parts of stearyl methacrylate, 55.5 parts of methyl methacrylate), and 4 parts of V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added dropwise to the reaction vessel over 2 hours. After completion of the addition, the polymerization reaction was continued for 3 hours while maintaining the internal temperature at 80°C. Thereafter, 0.6 parts of V-601 was added, and the polymerization reaction was continued for 2 hours while maintaining the internal temperature at 80°C, to obtain a solution of binder resin 1.
Next, the contents of the reaction vessel were cooled to 50°C, and then 4.7 parts of dimethylaminoethanol were added to neutralize the binder resin 1, and then 140 parts of water were added. Thereafter, the contents were heated to 78°C or higher, and 2-butanone was azeotroped with water to distill off the 2-butanone, and water was added to adjust the solids concentration to 30%, thereby obtaining an aqueous solution of binder resin 1 with a solids concentration of 30%. The weight average molecular weight of the obtained binder resin 1 was 17,000.

<Synthesis of Unmodified Acetylene Diol Surfactant (A1)>
2,4,7,9-tetramethyl-5-decyne-4,7-diol (unmodified acetylenic diol compound 1, HLB value = 3.0) was synthesized by utilizing the method described in Example 1 of JP 2002-356451 A and using methyl isobutyl ketone as the raw material ketone. Similarly, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (unmodified acetylenic diol compound 2, HLB value = 2.7) was synthesized by using methyl isoamyl ketone as the raw material ketone.

<Synthesis of alkylene oxide-modified acetylene diol surfactant (A2)>
Using the method described in Example 1 of U.S. Pat. No. 3,268,593, alkylene oxide-modified acetylenic diol surfactants (modified acetylenic diol compounds 1 to 6) with different amounts of ethylene oxide modification were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time) using the unmodified acetylenic diol compound 1 (2,4,7,9-tetramethyl-5-decyne-4,7-diol) as a starting material. Furthermore, using the unmodified acetylenic diol compound 2 (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol) as a starting material, ethylene oxide-modified acetylenic diol surfactants (modified acetylenic diol compounds 7 to 14) were synthesized by adjusting the amount of ethylene oxide and synthesis conditions (pressure, temperature, and time). Furthermore, by utilizing the method described in Example 1 of JP-A-2001-215690, modified acetylenic diol compounds 5, 6, 10, and 11 as starting materials, ethylene oxide-propylene oxide modified acetylenic diol surfactants (modified acetylenic diol compounds 15 to 18) were synthesized in which a propylene oxide group was added to the modified acetylenic diol compounds 5, 6, 10, and 11.

The details of the modified acetylenic diol compounds 1 to 18 produced above (starting material, number of moles of ethylene oxide groups and propylene oxide groups added, and HLB value) are shown in Table 1.

<Production Examples of Water-Based Inkjet Inks 1 to 114>
25 parts of ion-exchanged water, 20 parts of 1,2-propanediol, 5 parts of propylene glycol monomethyl ether, 1 part of modified acetylenic diol compound 11, 1.0 part of BYK-349 (a silicone surfactant manufactured by BYK-Chemie, HLB value = 10.2), 0.2 parts of TEGO Glide 100 (a silicone surfactant manufactured by Evonik, HLB value = 6.8), 16.7 parts of aqueous binder resin 1 solution, and 25 parts of cyan pigment dispersion 1 were sequentially charged into a mixing vessel, and then additional ion-exchanged water was added so that the total amount added was 100 parts. The mixture was then stirred using a disper mixer until it was sufficiently uniform, and then filtered using a membrane filter with a pore size of 1 μm to remove coarse particles that may cause head clogging, thereby producing aqueous inkjet ink 1.

In addition, water-based inkjet inks 2 to 114 were produced in the same manner as in the production example for water-based inkjet ink 1, except that the raw materials listed in Table 2 were used.

In Table 2, "Nv" represents the solid content concentration, "HLB" represents the HLB value, "Mw" represents the molecular weight, and "bp" represents the boiling point at 1 atmosphere. Also, the "remaining amount" in Table 2 represents the amount required to bring the total mass of the mixture to 100 parts.
Details of the product names listed in Table 2 are as follows:
NeoCryl A-1127 (acrylic emulsion manufactured by DSM, solid content = 44%, MFT = 7°C)
NeoRez R-600 (urethane emulsion manufactured by DSM, solids concentration = 33%, MFT less than 0°C)
TEGO Wet 280 (silicone surfactant manufactured by Evonik, HLB value = 9.8)
BYK 349 (a silicone surfactant manufactured by BYK-Chemie, HLB value = 10.2)
BYK 3420 (a silicone surfactant manufactured by BYK-Chemie, HLB value = 13.8)
BYK 3451 (a silicone surfactant manufactured by BYK-Chemie, HLB value = 10.8)
TEGO Glide 100 (silicone surfactant manufactured by Evonik, HLB value = 6.8)
TEGO Glide 440 (silicone surfactant manufactured by Evonik, HLB value = 12.7)
TEGO Twin 4200 (silicone surfactant manufactured by Evonik, HLB value = 8.2)
Brownon EL-1502.2 (polyoxyethylene lauryl ether, manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 6.3)
Brownon EL-1505 (polyoxyethylene lauryl ether, manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 10.5)
Brownon EL-1515 (polyoxyethylene lauryl ether, manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 14.9)
Brownon EL-1530 (polyoxyethylene lauryl ether, manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 17.4)
Brownon BN-3 (polyoxyethylene-β-naphthol ether, manufactured by Aoki Oil & Fat Co., Ltd., HLB value = 9.6)
Lutensol XP30 (BASF polyoxyethylene isodecyl ether, HLB value = 9.1)
Lutensol XP40 (BASF polyoxyethylene isodecyl ether, HLB value = 10.5)
Lutensol XP100 (BASF polyoxyethylene isodecyl ether, HLB value = 14.7)

[Examples 1 to 107, Comparative Examples 1 to 7]
The aqueous inkjet inks prepared above were evaluated as follows. The evaluation results are shown in Table 3.

<Rating 1: Beading>
The aqueous inkjet inks prepared above were each filled into an inkjet ejection device equipped with a Kyocera Corporation head (KJ4B-1200) installed in an environment of 25°C and 50% RH. A nozzle check pattern was printed, and after confirming that the aqueous inkjet ink was ejecting normally from all nozzles, the device was left to stand for 1 minute. Subsequently, a solid print with a printing rate of 100% was performed on a PET film (FE2001, thickness 12 μm) manufactured by Futamura Chemical Co., Ltd. under printing conditions of a frequency of 40 kHz and 1200 x 1200 dpi. The printed PET film was then dried in an air oven at 85°C for 1 minute to obtain a solid print. The number of streaks (areas where the ink did not adhere to the printing substrate and appeared streaky) present on the obtained solid print was then visually confirmed to evaluate the solid print. As mentioned above, the occurrence of beading manifests as a deterioration in solid print, and the degree of beading can be confirmed by evaluating the solid print. The evaluation criteria are as follows: Evaluations of "A+", "A", "B", and "C" were considered to be in the practical range.
(Evaluation criteria)
A+: Two or fewer streaks were visually observed.
A: 3 to 5 streaks were visible to the naked eye.
B: 6 to 10 streaks were visually confirmed.
C: 11 to 20 streaks were visually confirmed.
D: 21 or more streaks were visually confirmed.

<Evaluation 2: Standby Dischargeability>
Each of the aqueous inkjet inks prepared above was filled into an inkjet ejection device equipped with a Kyocera head (KJ4B-1200) installed in an environment of 25°C and 50% RH. A nozzle check pattern was printed, and after confirming that the aqueous inkjet ink was being ejected normally from all nozzles, the device was left to stand for 30 minutes. Thereafter, a nozzle check pattern was printed again, and the number of nozzles from which the aqueous inkjet ink was not ejected (number of missing nozzles) was counted to evaluate standby ejection performance. The evaluation criteria were as follows. A rating of "A,""B," or "C" was considered to be within the practical range.
(Evaluation criteria)
A: The number of missing nozzles was 0. B: The number of missing nozzles was 1 to 5. C: The number of missing nozzles was 6 to 10. D: The number of missing nozzles was 10 or more.

<Evaluation 3: Pinhole resistance>
Ten solid prints with a printing rate of 100% were produced using the same printing conditions and printing substrate as in Evaluation 1 above. The number of pinholes present in the obtained solid prints was then visually confirmed, and the pinhole resistance was evaluated by counting the total number of pinholes present in the 10 prints. The evaluation criteria were as follows: "A", "B", and "C" were considered to be in the practical range.
(Evaluation criteria)
A: There were no pinholes. B: The total number of pinholes was 1 to 2. C: The total number of pinholes was 3 to 5. D: The total number of pinholes was 6 or more.

Furthermore, for aqueous inkjet inks that were rated "A" for pinhole resistance above, additional evaluation was conducted using the method described below. Specifically, 30 solid prints were produced using the same printing conditions and printing substrate as in Evaluation 1 above, and the number of pinholes present in the 30 solid prints was visually confirmed. If there were no pinholes present in the 30 solid prints, or if the total number of pinholes present in the 30 solid prints was one, the pinhole resistance was rated "A+". Naturally, aqueous inkjet inks that received an "A+" rating are usable.

<Evaluation 4: Migration Resistance>
Using the same printing conditions as in Evaluation 1 above, solid printing was carried out at a printing rate of 100% on an OPP film (FOS-AQ, thickness 40 μm) manufactured by Futamura Chemical Co., Ltd.
Next, the non-printed surface (OPP film surface) of the obtained print was placed in a migration cell (MigraCell (registered trademark) MC60 manufactured by Gassner Glastechnik) with the non-printed surface (OPP film surface) facing up, and 50 mL of 95% ethanol was added. The contact area between the non-printed surface of the solid print and the 95% ethanol was 0.5 dm2. The migration cell was then left to stand in a 40°C oven for 10 days, after which the 95% ethanol solution was removed and concentrated to 2 mL or less under conditions of 40°C and 50 mmHg. Furthermore, if the amount of ethanol solution after concentration was less than 2 mL, it was placed in a 2 mL volumetric flask and filled up with 95% ethanol. The ethanol solution after concentration and fill-up was used as a sample, and the amount (total amount) of the acetylene diol surfactant (A) contained per mL of the ethanol solution after concentration and fill-up was quantified using a gas chromatograph mass spectrometer (Agilent 7890A/5975C manufactured by Agilent Technologies), thereby evaluating migration resistance. The evaluation criteria were as follows. Evaluations of "A,""B," and "C" were considered to be within the range of practical use.
(Evaluation criteria)
A: The amount of eluted acetylenic diol surfactant (A) was 0.1 μg/mL or less. B: The amount of eluted acetylenic diol surfactant (A) was more than 0.1 μg/mL and 1.0 μg/mL or less. C: The amount of eluted acetylenic diol surfactant (A) was more than 1.0 μg/mL and 3.0 μg/mL or less. D: The amount of eluted acetylenic diol surfactant (A) was more than 3.0 μg/mL.

As is clear from Examples 1 to 107, the aqueous inkjet ink of this embodiment, which contains 2 to 600 ppm of unmodified acetylenic diol surfactant (A1), and further contains alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and glycol monoethers (B1) in a specified blending ratio (mass ratio), exhibited good solid coverage without beading, excellent pinhole resistance and migration resistance, and good standby ejection properties.

On the other hand, in aqueous inkjet ink 1, which did not contain any unmodified acetylenic diol surfactant (A1), beading occurred, resulting in poor solid coverage, even when alkylene oxide-modified acetylenic diol surfactant (A2) and glycol monoethers (B1) were used in the appropriate mass ratio range (Comparative Example 1). Conversely, aqueous inkjet inks 43 to 45 and 48, which contained 2 to 600 ppm of unmodified acetylenic diol surfactant (A1) but did not contain at least one of alkylene oxide-modified acetylenic diol surfactant (A2) and glycol monoethers (B1), exhibited problems such as poor solid coverage, poor standby ejection performance, and the occurrence of pinholes (Comparative Examples 4 to 7).

Claims (7)

An aqueous inkjet ink containing a pigment, a binder resin, an acetylene diol surfactant (A), and a water-soluble organic solvent (B),
the acetylenic diol surfactant (A) comprises an unmodified acetylenic diol surfactant (A1) and an alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12;
the content of the unmodified acetylenic diol surfactant (A1) is 2 to 600 ppm relative to the total mass of the aqueous inkjet ink;
the water-soluble organic solvent (B) contains a glycol monoether (B1),
the mass ratio of the content of the glycol monoethers (B1) to the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 is 0.5 to 50. The aqueous inkjet ink according to claim 1, wherein the sum of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 and the content of the glycol monoethers (B1) is 2 to 20% by mass, based on the total mass of the aqueous inkjet ink. The aqueous inkjet ink according to claim 1 or 2, further comprising a nonionic surfactant (C) other than an acetylenic diol surfactant. The aqueous inkjet ink according to any one of claims 1 to 3, wherein the content of the unmodified acetylenic diol surfactant (A1) is 2 to 400 ppm based on the total mass of the aqueous inkjet ink. The aqueous inkjet ink according to any one of claims 1 to 4, wherein the mass ratio of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 10 to 5,000. The aqueous inkjet ink according to claim 5, wherein the mass ratio of the content of the alkylene oxide-modified acetylenic diol surfactant (A2) having an HLB value of 6 to 12 to the content of the unmodified acetylenic diol surfactant (A1) is 20 to 5,000. A printed matter having a printing substrate and a printing layer formed on the printing substrate using the aqueous inkjet ink described in any one of claims 1 to 6.