JP2025136065A - Water-based ink for inkjet printing - Google Patents

Abstract

The present invention provides a water-based ink for ink-jet recording that exhibits excellent ejection stability in ink-jet recording and that can produce printed matter that exhibits excellent abrasion resistance when printed on a low-liquid-absorbency printing medium, and an ink-jet recording method that uses the water-based ink.
[Solution] A water-based ink for ink-jet printing contains a pigment, polyolefin wax particles (W) dispersed with a polymer dispersant (a), and water, wherein the polyolefin wax particles (W) have an acid value of 1 mg KOH/g or more and 100 mg KOH/g or less, and the polyolefin wax particles (W) have an average particle size of 200 nm or more and 3,000 nm or less, and an ink-jet recording method using the water-based ink.
[Selection diagram] None

Description

The present invention relates to a water-based ink for inkjet printing and an inkjet recording method using the water-based ink.

In today's printing industry, with growing awareness of working, printing, and workplace environments, there is a demand for water-based inks in which water accounts for the largest proportion of the vehicle component, from the perspectives of low odor and safety. A variety of water-based inks have been proposed to meet these demands.

For example, Patent Document 1 discloses a water-based ink composition containing a polyolefin wax, a resin dispersion, and water, with the aim of providing a water-based ink composition that has abrasion resistance and the like and that can produce recorded matter with excellent image quality, and in which the content of a predetermined surfactant is 7 parts by mass or less when the total content of the resin of the resin dispersion and the polyolefin wax is taken as 100 parts by mass.
Furthermore, Patent Document 2 discloses an aqueous colorant dispersion that contains a colorant, an acid group-containing resin having an acid value of 1 to 300 mgKOH/g, an aqueous medium, a crosslinking agent, and a basic compound, and that satisfies a neutralization value and a crosslinking value defined by specific formulas, with the aim of providing an aqueous colorant dispersion that is unlikely to lose dispersion stability of the colorant even when there is a temperature change and that can be used to prepare an inkjet recording ink that enables continuous printing. The aqueous colorant dispersion also discloses an inkjet recording ink that contains the aqueous colorant dispersion.
Patent Document 3 discloses an inkjet recording ink that uses a water-soluble dye as a recording agent and contains 0.5 to 15% by weight of synthetic resin fine particles having a specific gravity of 0.9 to 1.05 and an average particle size of 0.2 to 1.0 μm, with the aim of providing an inkjet recording ink that is capable of high-quality image recording and printing and that is highly reliable against clogging and has good storage stability.

Japanese Patent Application Laid-Open No. 2018-162341 Japanese Patent Application Laid-Open No. 2021-109912 Japanese Patent Application Publication No. 8-239605

When printing on low-absorbency print media such as resin films, water-based inks have problems such as slow or no absorption of the ink's liquid components, resulting in long drying times and poor abrasion resistance of the printed material. Among these problems, there is a need for further improvement in abrasion resistance when the printed surface of a print is scratched with a sharp object such as a fingernail. In the case of solvent-based inks, not only do they dry quickly due to the high volatility of the solvent, but the resin components in the ink are dissolved or swelled by the solvent, resulting in increased adhesion to the print medium and improved abrasion resistance. However, this is difficult to achieve with water-based inks. Therefore, various technological developments are required.
Furthermore, in printing by inkjet recording, which has become increasingly popular in recent years, ink droplets are ejected onto a printing medium from extremely fine inkjet nozzles, so there is also a demand for improved ejection stability, which allows ink to be ejected stably without clogging the ink inside the inkjet nozzles.
However, although the technology of Patent Document 1 improves abrasion resistance, it does not provide sufficient ejection stability. Furthermore, although the technology of Patent Document 2 describes that continuous printing is possible, and the technology of Patent Document 3 describes that the technology has high reliability against clogging, the technologies of Patent Documents 2 and 3 do not consider abrasion resistance.
An object of the present invention is to provide a water-based ink for inkjet recording that has excellent ejection stability in inkjet recording and that can give printed matter that has excellent abrasion resistance when printed on a low-liquid-absorbency printing medium, and an inkjet recording method that uses the water-based ink.

The present inventors have discovered that the above-mentioned problems can be solved by containing a pigment, polyolefin wax particles dispersed with a polymer dispersant, and water, and by adjusting the acid value of the polyolefin wax particles to fall within a predetermined range and the average particle size of the polyolefin wax particles to fall within a predetermined range.
That is, the present invention relates to the following [1] and [2].
[1] A composition comprising a pigment, polyolefin wax particles (W) dispersed with a polymer dispersant (a), and water,
the acid value of the polyolefin wax particles (W) is 1 mgKOH/g or more and 100 mgKOH/g or less,
The water-based ink for ink-jet printing, wherein the polyolefin wax particles (W) have an average particle size of 200 nm or more and 3,000 nm or less.
[2] An inkjet recording method in which the water-based ink according to [1] above is used to record on a low-liquid-absorbent print medium.

The present invention provides a water-based ink for inkjet recording that exhibits excellent ejection stability when printed by inkjet recording and that can produce printed matter that exhibits excellent abrasion resistance when printed on a low-liquid-absorbency print medium, as well as an inkjet recording method that uses the water-based ink.

[Water-based ink for inkjet printing]
The water-based ink for ink-jet printing of the present invention (hereinafter also simply referred to as "water-based ink" or "ink") contains a pigment, polyolefin wax particles (W) dispersed with a polymer dispersant (a), and water, wherein the acid value of the polyolefin wax particles (W) is from 1 mg KOH/g to 100 mg KOH/g, and the average particle size of the polyolefin wax particles (W) is from 200 nm to 3,000 nm.
In the present invention, the term "aqueous system" means that water accounts for the largest proportion by mass of the medium.
In the present invention, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid when heated. Here, "semi-solid wax" means that the wax deforms and flows when force is applied to it, but can maintain a certain shape when no force is applied to it. Furthermore, the temperature at which the wax becomes liquid when heated, i.e., the melting point of the wax, is in a temperature range of 45°C or higher.
In the present invention, "printing" is a concept that includes printing and printing that records characters and images, and "printed matter" is a concept that includes printed matter and printed matter on which characters and images are recorded.
Furthermore, the term "low liquid absorption" is a concept that encompasses both low liquid absorption and non-liquid absorption, and refers to a printing medium whose water absorption amount is 0 g/m2 or ^more and less than 10 g/ ^m2 when the printing medium is in contact with pure water for 100 ms, and "high liquid absorption" refers to a printing medium whose water absorption amount is 10 g/m2 or ^more when the printing medium is in contact with pure water for 100 ms, and the water absorption amount can be measured as the amount of transfer when the printing medium is in contact with pure water for 100 ms using an automatic scanning liquid absorption meter (for example, the "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23°C and a relative humidity of 50%.

The water-based ink of the present invention has excellent ejection stability and can produce printed matter with excellent abrasion resistance when printed on a low-liquid-absorbency printing medium. The reason for this is not clear, but is thought to be as follows.
The water-based ink of the present invention contains polyolefin wax particles having a relatively large average particle size of 200 nm or more and 3,000 nm or less. When such a water-based ink is used to form an ink coating on a low-liquid-absorbency printing medium, the frictional resistance of the ink coating can be reduced, thereby improving abrasion resistance. However, polyolefin wax particles having such an average particle size are usually soap-free, meaning they do not use an emulsifier, and therefore do not have sufficient charge repulsion or steric repulsion, making them difficult to eject from very fine inkjet nozzles. Even if used as is, this results in ejection failure or reduced ejection stability.
Therefore, in the water-based ink of the present invention, polyolefin wax particles are dispersed using a polymer dispersant, the acid value of the polyolefin wax particles is adjusted to a specific range, and acid groups are introduced onto the surface of the polyolefin wax particles to impart charge repulsion. This makes it possible to suppress aggregation of the polyolefin wax particles as they pass through extremely fine inkjet nozzles, thereby mitigating and reducing clogging by the ink within the inkjet nozzles, and is believed to achieve both excellent ejection stability and abrasion resistance.

<Pigments>
The pigment may be either an inorganic pigment or an organic pigment, and if necessary, an extender pigment may be used in combination with the inorganic pigment or an organic pigment.
The pigments may be used alone or in combination of two or more.
Examples of inorganic pigments include carbon black and metal oxides. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Titanium oxide is preferred for white inks.
Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used.
Specific examples of preferred organic pigments include one or more product numbers selected from the group consisting of C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green.
Examples of extender pigments include silica, calcium carbonate, and talc.

In the present invention, the pigment is dispersed in the ink medium. The form of the pigment in the aqueous ink of the present invention is preferably one or more selected from the group consisting of a pigment dispersed without relying on a surfactant or a polymer dispersant (hereinafter also referred to as a "self-dispersed pigment"), a pigment dispersed with a surfactant, and a pigment dispersed with a polymer dispersant. Among these, from the viewpoint of improving ejection stability, the pigment in the aqueous ink of the present invention is more preferably in a form dispersed with a polymer dispersant (hereinafter also referred to as a "polymer dispersant (b)"), and even more preferably in a form of polymer particles containing the pigment (hereinafter also referred to as "pigment-containing polymer particles").
Here, the form of the pigment-containing polymer particles is not particularly limited, as long as the particles are formed from at least the pigment and the polymer dispersant (b). Examples of the form of the pigment-containing polymer particles include a particle form in which the pigment is encapsulated in the polymer dispersant (b), a particle form in which the pigment is uniformly dispersed in the polymer dispersant (b), a particle form in which the pigment is exposed on the surface of the polymer dispersant (b) particles, and mixtures thereof.

(Polymer Dispersant (b))
The polymer dispersant (b) may be either a water-soluble polymer or a water-insoluble polymer, but is preferably a water-insoluble polymer from the viewpoint of improving ejection stability.
Here, the "water-soluble" and "water-insoluble" polymers are determined as follows: when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g, the polymer is determined to be "water-soluble," and if the dissolved amount is 10 g or less, the polymer is determined to be "water-insoluble." Furthermore, as described below, when the polymer dispersant (b) has an anionic group and the anionic group is further neutralized with a neutralizing agent, the polymer dispersant (b) is determined to be "water-soluble" by the dissolved amount measured in the presence of a neutralizing agent such that the mass ratio of the polymer dispersant (b) to the neutralizing agent is the same as that in the aqueous ink of the present invention.
The polymer dispersant (b) may be used alone or in combination of two or more.

Examples of polymer dispersants (b) include vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), polyesters, and polyurethanes. Among these, vinyl polymers are preferred as polymer dispersants (b) from the viewpoint of improving discharge stability and abrasion resistance.

From the viewpoint of improving the dispersion stability of the pigment and improving the ejection stability, the vinyl polymer used as the polymer dispersant (b) preferably contains a structural unit derived from an ionic monomer (b-1). Examples of the ionic monomer (b-1) include anionic monomers having an anionic group and cationic monomers having a cationic group, but from the viewpoint of improving the dispersion stability of the pigment and improving the ejection stability, an anionic monomer having an anionic group is preferred.
In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), and a phosphate group (-OPO ₃ M ₂ ). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.
Examples of the vinyl polymer include a homopolymer of an ionic monomer (b-1), a copolymer of an ionic monomer (b-1) and a hydrophobic monomer (b-2), and a copolymer of an ionic monomer (b-1), a hydrophobic monomer (b-2), and a nonionic monomer (b-3).
Here, the term "hydrophobic" in the hydrophobic monomer (b-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the monomer dissolved is less than 10 g.
The nonionic monomer (b-3) is a monomer that has a high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxy group or a polyalkylene glycol chain.
When the vinyl polymer is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

Examples of the ionic monomer (b-1) include carboxy group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Among these, carboxy group-containing monomers are preferred, and (meth)acrylic acid is more preferred.
Examples of the hydrophobic monomer (b-2) include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms; one or more styrene-based monomers selected from the group consisting of α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene; aromatic group-containing monomers such as aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number-average molecular weight of from 500 to 100,000. Among these, the hydrophobic monomer (b-2) is preferably a styrene-based monomer, more preferably one or more selected from the group consisting of α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from the group consisting of styrene and α-methylstyrene.
Examples of the nonionic monomer (b-3) include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate.
In this specification, "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid, and "(meth)acrylate" means at least one selected from the group consisting of acrylate and methacrylate.
The vinyl polymer can be obtained by addition polymerization of raw material monomers including, for example, an ionic monomer (b-1) and, if necessary, a hydrophobic monomer (b-2) or a nonionic monomer (b-3) by a known method. Each of the monomers for the vinyl polymer can be used alone or in combination of two or more.

From the viewpoint of improving discharge stability and abrasion resistance, the polymer dispersant (b) is preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers. It is more preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and aromatic group-containing monomers. It is even more preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from an aromatic group-containing monomer. It is even more preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from an aromatic group-containing monomer.

When the polymer dispersant (b) has anionic groups, from the viewpoint of improving ejection stability and abrasion resistance, it is preferable that a portion of the anionic groups of the polymer dispersant (b) be neutralized with a neutralizing agent. Examples of neutralizing agents include alkali metal hydroxides and amine compounds. Among these, the neutralizing agent is preferably an alkali metal hydroxide, and more preferably sodium hydroxide.

From the viewpoint of improving ejection stability, the polymer dispersant (b) preferably has a crosslinked structure. In this case, the polymer dispersant (b) preferably has a structure including a polymer component having a linear two-dimensional structure, which may have branched chains, and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure, which may have branched chains, being transformed into a three-dimensional structure by a component derived from the crosslinking agent. Examples of polymers having a linear two-dimensional structure, which may have branched chains, include vinyl polymers, polyesters, and polyurethanes obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), with the aforementioned vinyl polymers being preferred. In other words, from the viewpoint of improving ejection stability, the polymer dispersant (b) is preferably a vinyl polymer crosslinked with a crosslinking agent.

From the viewpoint of improving ejection stability, the crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether.
When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent weight of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

The acid value of the polymer dispersant (b) is preferably 50 mgKOH/g or more, more preferably 70 mgKOH/g or more, and even more preferably 100 mgKOH/g or more from the viewpoint of improving the dispersion stability of the pigment and thereby improving the ejection stability. From the viewpoint of improving the abrasion resistance, it is preferably 800 mgKOH/g or less, more preferably 500 mgKOH/g or less, even more preferably 300 mgKOH/g or less, and even more preferably 200 mgKOH/g or less. The acid value of the polymer dispersant (b) can be determined by the method described in the Examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, when the polymer dispersant (b) is a vinyl polymer crosslinked with a crosslinking agent, the acid value of the polymer dispersant (b) can also be calculated using the following formula:
Acid value of polymer dispersant (b) (mg KOH/g)=[Acid value of vinyl polymer before crosslinking (mg KOH/g)×[(100−crosslinking rate (mol %))/100]
In this specification, the crosslinking rate (mol %) of a vinyl polymer crosslinked with a crosslinking agent is a value calculated from the acid value of the vinyl polymer before crosslinking and the equivalent weight of the crosslinkable functional group of the crosslinking agent.

The weight-average molecular weight of polymer dispersant (b) is preferably 3,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more, from the viewpoints of improving the dispersion stability of the pigment and thereby improving ejection stability, and of improving abrasion resistance. From the same viewpoints as above, it is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight-average molecular weight of polymer dispersant (b) can be measured by the method described in the examples.

The polymer dispersant (b) may be a suitably synthesized one or a commercially available product.
Commercially available polymer dispersants (b) include, for example, polyacrylic acids such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); and styrene/acrylic resins such as "Joncryl 67,""Joncryl611,""Joncryl678,""Joncryl680,""Joncryl690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

When the pigment in the water-based ink of the present invention is in the form of pigment-containing polymer particles, the pigment-containing polymer particles are preferably blended into the water-based ink as an aqueous dispersion (hereinafter also referred to as "pigment aqueous dispersion") obtained by dispersing the pigment, polymer dispersant (b), and, if necessary, a neutralizing agent, a surfactant, etc., by a known method. If necessary, a crosslinking agent may be further added to the obtained pigment aqueous dispersion to crosslink the polymer dispersant (b).
The pigment-containing polymer particles contained in the water-based ink of the present invention are preferably those that are resistant to swelling and shrinkage of the particles and aggregation between the particles.

<Polyolefin wax particles (W) dispersed with polymer dispersant (a)>
The water-based ink of the present invention contains polyolefin wax particles (W) dispersed in a polymer dispersant (a) (hereinafter also referred to as "polyolefin wax particles (W)") from the viewpoint of improving ejection stability and abrasion resistance. The polyolefin wax particles (W) are composed of a polyolefin wax (w) and the polymer dispersant (a).

(Polyolefin wax (w))
The polyolefin wax (w) constituting the polyolefin wax particles (W) is a wax mainly composed of an olefin monomer. Here, "mainly composed of an olefin monomer" means that the content of the olefin monomer relative to the total components constituting the wax is preferably 50% by mass or more, more preferably 65% by mass or more, and even more preferably 80% by mass or more.
Examples of the olefin-based monomer that is the main component of the polyolefin wax (w) include linear olefins and cyclic olefins, but those containing a linear olefin having from 2 to 6 carbon atoms as the main component are preferred, polyolefin waxes containing ethylene or propylene as the main component are more preferred, and polyethylene waxes containing ethylene as the main component are even more preferred. That is, the polyolefin wax (w) is preferably one or more selected from the group consisting of polyethylene waxes and polypropylene waxes, and more preferably polyethylene wax.

The polyolefin wax (w) is preferably used as an aqueous dispersion dispersed in an aqueous medium. There are no particular limitations on the method for producing the aqueous dispersion of the polyolefin wax (w), but the aqueous dispersion of the polyolefin wax (w) is preferably a soap-free type that does not use an emulsifier, from the viewpoint of adjusting the particle size distribution ((D ₉₀ -D ₁₀ )/D ₅₀ ) of the polyolefin wax particles (W) to improve abrasion resistance.
Commercially available aqueous dispersions of polyolefin wax (w) include "Chemipearl W900,""ChemipearlW950,""ChemipearlW4005,""ChemipearlW500,""ChemipearlW700," and "Chemipearl W401" manufactured by Mitsui Chemicals, Inc.

(Polymer Dispersant (a))
The polyolefin wax particles (W) are composed of a polyolefin wax (w) and a polymer dispersant (a), and the polymer dispersant (a) stably disperses the polyolefin wax (w) in the ink.

The polymer dispersant (a) preferably has an anionic group from the viewpoint of improving ejection stability.
As mentioned above, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), and a phosphate group (-OPO ₃ M ₂ ). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.
Among these, the anionic group is preferably a carboxy group from the viewpoint of improving ejection stability.
Examples of the polymer skeleton of the polymer dispersant (a) include vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), polyesters, and polyurethanes. Among these, from the viewpoint of enhancing the effect of stably dispersing the polyolefin wax particles (W) in the ink and improving the ejection stability, the polymer dispersant (a) is preferably a vinyl polymer having an anionic group, more preferably a vinyl polymer containing a structural unit derived from an anionic monomer (a-1) having an anionic group, and even more preferably a vinyl polymer containing a structural unit derived from an anionic monomer (a-1) having an anionic group and a structural unit derived from a hydrophobic monomer (a-2). When the vinyl polymer is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.
The term "hydrophobic" in the hydrophobic monomer (a-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25°C until saturation occurs, the amount of the monomer dissolved is less than 10 g, as in the case of the above-described hydrophobic monomer (b-2).

Examples of the anionic monomer (a-1) having an anionic group include carboxy group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Among these, carboxy group-containing monomers are preferred, and (meth)acrylic acid is more preferred.

The hydrophobic monomer (a-2) is preferably at least one selected from the group consisting of aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol.
The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having from 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
Examples of styrene-based monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene.
Examples of aromatic group-containing (meth)acrylates include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate.
The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol is preferably one having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and examples thereof include (meth)acrylates having a linear or branched alkyl group having from 1 to 22 carbon atoms; and (meth)acrylates having an alicyclic alkyl group such as cyclohexyl (meth)acrylate.
Among these, from the viewpoint of improving the discharge stability and abrasion resistance, the hydrophobic monomer (a-2) is more preferably at least one selected from the group consisting of a styrene-based monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, even more preferably at least one selected from the group consisting of a styrene-based monomer and a (meth)acrylate having an alicyclic alkyl group, and even more preferably a (meth)acrylate having an alicyclic alkyl group.
From the viewpoint of improving the discharge stability and abrasion resistance, the number of carbon atoms in the alicyclic alkyl group of the (meth)acrylate having an alicyclic alkyl group is preferably 4 or more, more preferably 5 or more, and is preferably 12 or less, more preferably 8 or less, and even more preferably 7 or less.
The (meth)acrylate having an alicyclic alkyl group is preferably at least one selected from the group consisting of cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate, from the viewpoints of improving discharge stability and abrasion resistance, and more preferably cyclohexyl (meth)acrylate from the viewpoints of availability and economy.

The polymer dispersant (a) may contain structural units derived from other monomers in addition to the structural units derived from the anionic monomer (a-1) having an anionic group and the structural units derived from the hydrophobic monomer (a-2).
Examples of such other monomers include nonionic monomers (a-3) such as polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate.
The vinyl polymer can be obtained, for example, by addition polymerization of raw material monomers including an anionic monomer (a-1) having an anionic group, a hydrophobic monomer (a-2), and, if necessary, a nonionic monomer (a-3) by a known method. Each of the monomers for the vinyl polymer can be used alone or in combination of two or more.

From the viewpoint of improving discharge stability and abrasion resistance, the polymer dispersant (a) is preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more monomers selected from the group consisting of aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and more preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more monomers selected from the group consisting of styrene-based monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms. It is a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more monomers selected from the group consisting of styrene-based monomers and (meth)acrylates having an alicyclic alkyl group, and even more preferably a vinyl polymer containing structural units derived from one or more monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a (meth)acrylate having an alicyclic alkyl group.

The acid value of the polymer dispersant (a) is preferably 90 mgKOH/g or more, more preferably 120 mgKOH/g or more, even more preferably 140 mgKOH/g or more, and even more preferably 160 mgKOH/g or more, and is preferably 300 mgKOH/g or less, more preferably 280 mgKOH/g or less, and even more preferably 260 mgKOH/g or less. The acid value of the polymer dispersant (a) can be measured by the method described in the Examples. It may also be calculated from the mass ratio of the constituent monomers, or when using a commercially available product, published values may be referenced.

The weight-average molecular weight of the polymer dispersant (a) is preferably 3,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more, from the viewpoints of improving the dispersion stability of the pigment and thereby improving ejection stability, and of improving abrasion resistance. From the same viewpoints as above, it is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight-average molecular weight of the polymer dispersant (a) can be measured by the method described in the Examples.

When the polymer dispersant (a) has anionic groups, from the viewpoint of improving ejection stability and abrasion resistance, it is preferable that a portion of the anionic groups of the polymer dispersant (a) be neutralized with a neutralizing agent. Examples of neutralizing agents include alkali metal hydroxides and amine compounds. Among these, the neutralizing agent is preferably an alkali metal hydroxide, and more preferably sodium hydroxide.

In the present invention, the polyolefin wax particles (W) are preferably blended in the ink in the form of an aqueous dispersion. A suitable example of a method for producing an aqueous dispersion of polyolefin wax particles (W) is a method in which a polymer dispersant (a), a polyolefin wax (w), and, if necessary, a neutralizing agent are atomized by applying mechanical stress using a dispersing device in the presence of an aqueous medium.
The average particle size of the polyolefin wax particles (W) in the aqueous dispersion is preferably 3,000 nm or less, more preferably 2,000 nm or less, even more preferably 1,000 nm or less, and even more preferably 700 nm or less, from the viewpoint of improving the dispersion stability of the polyolefin wax particles (W) and improving the ejection stability, and is preferably 200 nm or more, more preferably 250 nm or more, and even more preferably 300 nm or more, from the viewpoint of improving the scratch resistance. The average particle size of the polyolefin wax particles (W) in the aqueous dispersion is measured by the method described in the Examples.
The polyolefin wax particles (W) contained in the aqueous ink of the present invention are preferably those that are resistant to swelling, shrinkage, and aggregation of the particles. In this case, the average particle size of the polyolefin wax particles (W) in the aqueous ink of the present invention is considered to be the same as the average particle size of the polyolefin wax particles (W) in the aqueous dispersion.

The acid value of the polyolefin wax particles (W) in the aqueous dispersion is preferably 1 mgKOH/g or more, more preferably 2 mgKOH/g or more, even more preferably 5 mgKOH/g or more, and is preferably 100 mgKOH/g or less, more preferably 90 mgKOH/g or less, even more preferably 70 mgKOH/g or less, still more preferably 50 mgKOH/g or less, still more preferably 30 mgKOH/g or less, still more preferably 20 mgKOH/g or less, and still more preferably 15 mgKOH/g or less. The acid value of the polyolefin wax particles (W) in the aqueous dispersion is measured by the method described in the Examples.
The polyolefin wax particles (W) contained in the aqueous ink of the present invention are preferably those that are resistant to swelling, shrinkage, and aggregation of the particles. In this case, the acid value of the polyolefin wax particles (W) in the aqueous ink of the present invention is considered to be the same as the acid value of the polyolefin wax particles (W) in the aqueous dispersion.

That is, from the viewpoint of improving ejection stability, the average particle diameter of the polyolefin wax particles (W) in the aqueous ink of the present invention is 3,000 nm or less, preferably 2,000 nm or less, more preferably 1,000 nm or less, and even more preferably 700 nm or less, and from the viewpoint of improving abrasion resistance, it is 200 nm or more, preferably 250 nm or more, and more preferably 300 nm or more. The average particle diameter of the polyolefin wax particles (W) in the aqueous ink of the present invention is measured by a method similar to that described in the Examples.

The particle size distribution (( _D90 - _D10 )/ _D50 ) of the polyolefin wax particles (W) in the water-based ink of the present invention is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 0.9 or more, and still more preferably 1.0 or more, from the viewpoint of improving abrasion resistance, and is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less, from the same viewpoint as above. The particle size distribution (( _D90 - _D10 )/ _D50 ) of the polyolefin wax particles (W) in the water-based ink of the present invention is measured by the same method as that described in the examples.

The acid value of the polyolefin wax particles (W) in the aqueous ink of the present invention is 1 mgKOH/g or more, preferably 2 mgKOH/g or more, more preferably 5 mgKOH/g or more, and 100 mgKOH/g or less, preferably 90 mgKOH/g or less, more preferably 70 mgKOH/g or less, even more preferably 50 mgKOH/g or less, still more preferably 30 mgKOH/g or less, even more preferably 20 mgKOH/g or less, and even more preferably 15 mgKOH/g or less. The acid value of the polyolefin wax particles (W) in the aqueous ink of the present invention is measured by a method similar to that described in the Examples.

<Water>
The water-based ink of the present invention contains water.
The water used in the water-based ink of the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

In addition to the above components, the water-based ink of the present invention may further contain various commonly used additives, such as fixing aids, water-soluble organic solvents, surfactants, humectants, wetting agents, penetrating agents, antifoaming agents, preservatives, antifungal agents, and anticorrosive agents, as needed.

(Fixing aid)
From the viewpoint of improving abrasion resistance, the water-based ink of the present invention preferably further contains non-pigmented polymer particles as a fixing aid. In the present invention, the non-pigmented polymer particles do not include the polyolefin wax particles (W).
Examples of polymers constituting the pigment-free polymer particles include polyurethanes, polyesters, and vinyl polymers such as (meth)acrylic resins, styrene resins, styrene/(meth)acrylic resins, butadiene resins, styrene/butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins. Among these, vinyl polymers are preferred from the viewpoint of improving abrasion resistance.
From the viewpoint of improving productivity of the ink, the pigment-free polymer particles are preferably blended into the ink as an aqueous dispersion in which they are dispersed in an aqueous medium.

When the polymer constituting the pigment-free polymer particles is a vinyl polymer, the polymer constituting the pigment-free polymer particles is preferably a vinyl polymer containing a constituent unit derived from an ionic monomer and a constituent unit derived from a hydrophobic monomer.
Specific examples of the ionic monomer include the same anionic monomers as the anionic monomer (a-1) having an anionic group described above. Among them, one or more monomers selected from the group consisting of acrylic acid and methacrylic acid are preferred.
Preferred examples of the hydrophobic monomer include the same as the hydrophobic monomer (a-2) described above, and among these, preferred examples include one or more selected from the group consisting of the aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol.
The vinyl polymer can be obtained by addition polymerization of raw material monomers including, for example, an ionic monomer, a hydrophobic monomer, and optionally a nonionic monomer, using a known method such as emulsion polymerization or suspension polymerization. Among these, it is preferable to polymerize by emulsion polymerization and then blend the resulting pigment-free polymer particles into the water-based ink as an aqueous dispersion. Alternatively, commercially available pigment-free polymer particle dispersions can also be used.
Each of the monomers for the vinyl polymer may be used alone or in combination of two or more.

From the viewpoint of dispersion stability, the acid value of the polymer that constitutes the pigment-free polymer particles is preferably 0 mgKOH/g or more, more preferably greater than 0 mgKOH/g. From the viewpoint of improving abrasion resistance, the acid value is preferably 30 mgKOH/g or less, more preferably 20 mgKOH/g or less, even more preferably 10 mgKOH/g or less, and even more preferably 5 mgKOH/g or less. The acid value of the polymer that constitutes the pigment-free polymer particles can be measured by the method described in the Examples. It may also be calculated from the mass ratio of the constituent monomers, or when using commercially available products, published values may be referenced.

The weight-average molecular weight of the polymer that makes up the pigment-free polymer particles is preferably 10,000 or more, more preferably 15,000 or more, from the viewpoint of improving ejection stability and abrasion resistance, and is preferably 100,000 or less, more preferably 50,000 or less, from the same viewpoint as above. The weight-average molecular weight of the polymer that makes up the pigment-free polymer particles can be measured by the method described in the Examples.

The glass transition temperature (Tg) of the acid value of the polymer constituting the pigment-free polymer particles is preferably −5° C. or higher, more preferably 0° C. or higher, even more preferably 5° C. or higher, and still more preferably 10° C. or higher, from the viewpoints of improving the strength of the ink coating film and improving the abrasion resistance, and is preferably 30° C. or lower, more preferably 25° C. or lower, and even more preferably 20° C. or lower, from the viewpoints of forming a good ink coating film and improving the abrasion resistance.
The glass transition temperature of the polymer constituting the pigment-free polymer particles is calculated by the method described in the Examples.

The average particle size of the pigment-free polymer particles in the aqueous dispersion is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more, from the viewpoint of improving the dispersion stability of the pigment-free polymer particles and improving the ejection stability, and is preferably 200 nm or less, more preferably 170 nm or less, and even more preferably 150 nm or less, from the viewpoint of forming a good ink coating film and improving abrasion resistance. The average particle size of the pigment-free polymer particles in the aqueous dispersion can be measured by the method described in the Examples.
The pigment-free polymer particles contained in the water-based ink of the present invention are less likely to swell or shrink, or to aggregate with one another, and the average particle size of the pigment-free polymer particles in the water-based ink of the present invention is considered to be the same as the average particle size of the pigment-free polymer particles in the water-based ink of the present invention. From this perspective, preferred embodiments of the average particle size of the pigment-free polymer particles in the water-based ink of the present invention are the same as the preferred embodiments of the average particle size of the pigment-free polymer particles in the water-based ink of the present invention. The average particle size of the pigment-free polymer particles in the water-based ink of the present invention is also measured by a method similar to that described in the Examples.

(Water-soluble organic solvent)
The water-based ink of the present invention preferably further contains a water-soluble organic solvent from the viewpoint of improving ejection stability and abrasion resistance. The water-soluble organic solvent may be used alone or in combination of two or more.
In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 10 mL or more.
The boiling point of the water-soluble organic solvent under atmospheric pressure is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and is preferably 350°C or lower, more preferably 300°C or lower, even more preferably 250°C or lower.
When two or more water-soluble organic solvents are used in combination, the boiling point of the water-soluble organic solvents is a weighted average value weighted by the content (mass %) of each water-soluble organic solvent.

Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving ejection stability and abrasion resistance, one or more solvents selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.
The polyhydric alcohol may be a mixture of two or more compounds included in the concept of polyhydric alcohol. Similarly to the polyhydric alcohol, a mixture of two or more compounds included in the concept of polyhydric alcohol alkyl ether may be used.

Examples of polyhydric alcohols include ethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

Examples of polyhydric alcohol alkyl ethers include alkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers. Specific examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.

(Surfactant)
The water-based ink of the present invention preferably further contains a surfactant from the viewpoint of improving ejection stability and abrasion resistance.
Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred.
The surfactants can be used alone or in combination of two or more.
Examples of nonionic surfactants include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants.
Among these, the surfactant is preferably at least one selected from the group consisting of acetylene-based surfactants and silicone-based surfactants.

Preferred acetylene surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide (hereinafter also referred to as "EO") adducts thereof. Among these, more preferred are one or more surfactants selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and even more preferred are EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

Preferred examples of silicone surfactants include polyether-modified silicone surfactants. Examples of the polyether group in polyether-modified silicone surfactants include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups (trimethyleneoxy groups or propane-1,2-diyloxy groups) are attached in a block or random manner. Compounds in which polyether groups are grafted onto a silicone main chain and compounds in which polyether groups are attached in a block manner to both ends of a silicone main chain can also be used.

Commercially available acetylene surfactants include the "Surfynol" series. Commercially available silicone surfactants include the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., the "Silface SAG" series manufactured by Nissin Chemical Industry Co., Ltd., and the "BYK" series manufactured by BYK Japan KK.

(Content of each component in water-based ink)
The content of the pigment in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of print density, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, from the viewpoint of improving ejection stability and abrasion resistance.
The content of the pigment-containing polymer particles in the water-based ink of the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and still more preferably 5% by mass or more, from the viewpoint of print density, and is preferably 16% by mass or less, more preferably 11% by mass or less, and even more preferably 9% by mass or less, from the viewpoint of improving ejection stability and abrasion resistance.
The mass ratio of the content of the pigment to the total content of the pigment and polymer dispersant (b) in the water-based ink of the present invention [pigment/(pigment+polymer dispersant (b))] is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, from the viewpoint of print density, and is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less, from the viewpoint of improving ejection stability and abrasion resistance.

The content of polyolefin wax particles (W) in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.7% by mass or more, from the viewpoint of improving abrasion resistance, and is preferably 7% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and still more preferably 1% by mass or less, from the viewpoint of improving ejection stability.
In the present invention, the content of the polymer dispersant (a) relative to 100 parts by mass of the polyolefin wax (w) contained in the polyolefin wax particles (W) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more, from the viewpoint of improving the ejection stability, and is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, from the viewpoint of improving the ejection stability and the abrasion resistance.

The content of pigment-free polymer particles in the water-based ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of improving abrasion resistance, and is preferably 10% by mass or less, more preferably 9% by mass or less, and even more preferably 8% by mass or less, from the viewpoint of improving ejection stability.

The content of polyolefin wax particles (W) in the total amount of solids in the water-based ink of the present invention is, from the viewpoint of improving abrasion resistance, preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and still more preferably 4% by mass or more, and from the viewpoint of improving ejection stability, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and still more preferably 10% by mass or less.
Here, when the water-based ink of the present invention contains polymer particles containing a pigment and polymer particles containing no pigment, the total amount of solids in the water-based ink is preferably the combined content of the polyolefin wax particles (W), the polymer particles containing a pigment, and the polymer particles containing no pigment.

When the water-based ink of the present invention contains pigment-free polymer particles, the mass ratio of the content of polyolefin wax particles (W) to the total content of polyolefin wax particles (W) and pigment-free polymer particles in the water-based ink [polyolefin wax particles (W)/(polyolefin wax particles (W) + pigment-free polymer particles)] is preferably 0.01 or more, more preferably 0.03 or more, and even more preferably 0.07 or more, from the viewpoint of improving jetting stability and abrasion resistance, and is preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.3 or less, and even more preferably 0.2 or less, from the viewpoint of improving jetting stability.

The content of the water-soluble organic solvent in the water-based ink of the present invention is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving ejection stability, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of improving abrasion resistance.

From the viewpoint of improving ejection stability and abrasion resistance, the content of surfactant in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, and even more preferably 1% by mass or more; and from the same viewpoint as above, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

From the viewpoint of improving ejection stability and abrasion resistance, the water content in the water-based ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, and from the same viewpoint as above, it is preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[Inkjet recording method]
From the viewpoint of ejection stability, the water-based ink of the present invention is used as a water-based ink for ink-jet printing.
The inkjet recording method using the water-based ink of the present invention (hereinafter also referred to as the "inkjet recording method of the present invention") is a method of recording on a print medium using the water-based ink described above. In the inkjet recording method of the present invention, a piezo system is preferred as a system for ejecting the water-based ink from the viewpoint of ejection performance.
The printing medium used in the inkjet recording method of the present invention includes highly liquid-absorbent plain paper, low liquid-absorbent coated paper, and resin film. Among these, low liquid-absorbent printing media are preferred from the viewpoint of abrasion resistance.
Examples of coated paper include general-purpose glossy paper and multicolor form glossy paper.
Examples of the resin film include films made of synthetic resins. Examples of such synthetic resins include polyolefin resins such as polyethylene resins and polypropylene resins; polyester resins such as polyethylene terephthalate resins; and polyvinyl chloride resins. The resin film may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film, or may be a corona discharge-treated film.
Among these, from the viewpoint of abrasion resistance, low-liquid-absorbency printing media using synthetic resins are preferred, and low-liquid-absorbency printing media using one or more synthetic resins selected from the group consisting of polyethylene resin, polypropylene resin, and polyethylene terephthalate resin are more preferred.

In the following production examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement and calculation methods for each physical property are as follows:

(1) Measurement of the weight-average molecular weight of the polymer The weight-average molecular weight was determined by gel permeation chromatography under the following conditions.
GPC device: "HLC-8320GPC" manufactured by Tosoh Corporation
Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guard column Super AW-H" manufactured by Tosoh Corporation
Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60 mmol/L and 50 mmol/L, respectively. Flow rate: 0.5 mL/min
Standard substance: monodisperse polystyrene kits with known molecular weights "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (manufactured by Tosoh Corporation)
Measurement sample: 0.1 g of polymer was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter (membrane filter material: hydrophilic PTFE, pore size 0.2 µm, "DISMIC-13HP" manufactured by Advantec Co., Ltd.) and used.

(2) Measurement of Acid Value of Polymer and Acid Value of Polyolefin Wax Particles (W) The resin was dissolved in a titration solvent (toluene:acetone=2:1 (volume ratio)) prepared by mixing toluene and acetone in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide/ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH/g) was calculated from the titration amount of the potassium hydroxide solution up to the endpoint.

(3) Calculation of Glass Transition Temperature (Tg) of Polymer The glass transition temperature of a polymer can be calculated from the mass ratio of each monomer constituting the polymer and the glass transition temperature of the homopolymer when each monomer is made into a homopolymer according to the following Fox equation.
1/Tg=(W ₁ /Tg ₁ )+(W ₂ /Tg ₂ )+...+(W _m /Tg _m )
W ₁ +W ₂ +...W _m =1
In the Fox equation, Tg is the glass transition temperature of the polymer, and _Tg1 , _Tg2 , ..., _Tgm are the glass transition temperatures of the homopolymers obtained by homopolymerizing each monomer. The unit of temperature is K. Furthermore, _W1 , _W2 , ..., _Wm represent the mass ratio of each monomer in the polymer. As the glass transition temperature of the homopolymer of each monomer in the Fox equation, for example, the values described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

(4) Measurement of Solids Concentration Approximately 10 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ = 40 mm, height = 30 mm), and the combined mass of the container and sodium sulfate (referred to as "mass M1") was precisely weighed. Approximately 1 g of sample was added thereto and mixed thoroughly, after which the combined mass of the container, sodium sulfate, and sample (referred to as "mass M2") was precisely weighed, maintained at 105°C for 2 hours to remove volatiles, and then left in the desiccator for 15 minutes, after which the mass (referred to as "mass M3") was precisely weighed. The mass of the sample after devolatilization was taken as the solids content, and the solids concentration (%) was calculated according to the following formula:
Solid content concentration (%) = [(mass M3 - mass M1) / (mass M2 - mass M1)] x 100

(5) Measurement of the average particle size of pigment-containing polymer particles in a pigment aqueous dispersion and the average particle size of pigment-free polymer particles in a pigment aqueous dispersion. Measurements were performed by cumulant analysis using a laser particle analysis system (Otsuka Electronics Co., Ltd., "ELSZ-1000"). The sample was diluted with water to a measurement concentration of approximately 5 x ^10-3 % (equivalent to solids concentration). The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 165°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion medium, and the obtained cumulant average particle size was taken as the average particle size of pigment-containing polymer particles in a pigment aqueous dispersion or the average particle size of pigment-free polymer particles in a pigment aqueous dispersion.

(6) Measurement of average particle size and particle size distribution of polyolefin wax particles (W) in aqueous dispersion Using a laser diffraction/scattering particle size distribution analyzer ("LA950" manufactured by Horiba, Ltd.), water was used as the dispersion medium, the circulation rate was set to "5" and the ultrasonic intensity was set to "3", and measurement was performed after 1 minute of irradiation. The volume median particle size ( _D50 ) value at this time was taken as the average particle size of the polyolefin wax particles (W) in the aqueous dispersion. In addition, ( _D90 - _D10 )/ _D50 was taken as the particle size distribution of the polyolefin wax particles (W).

(Preparation of aqueous dispersion of polymer dispersant (a))
Production Example 1-1
A monomer mixture was prepared by mixing 24.2 parts of acrylic acid and 75.8 parts of cyclohexyl methacrylate. Five parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 2.5 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% (10 parts) of the monomer mixture were placed in a reaction vessel and mixed, followed by thorough nitrogen gas replacement.
Meanwhile, a dropping funnel was charged with a mixture of the remaining 90% (90 parts) of the monomer mixture, 2.25 parts of the polymerization chain transfer agent, 75 parts of MEK, and 2 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo-based radical polymerization initiator. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 77°C with stirring, and the mixture in the dropping funnel was added dropwise over 5 hours. After completion of the dropping, a solution in which 0.5 parts of the polymerization initiator was dissolved in 5 parts of MEK was added, and the mixture was further reacted at 77°C for 2 hours. Finally, MEK was added to give a solids concentration of 55%, yielding a solution of acrylic acid/cyclohexyl methacrylate copolymer (hereinafter referred to as "vinyl polymer P1"). The acid value of the vinyl polymer P1 was 180 mgKOH/g and the weight-average molecular weight was 16,000.
100 g of the vinyl polymer P1 solution obtained above was charged, and while stirring (200 rpm) with a stirring blade, a 5N aqueous solution of sodium hydroxide was added dropwise to a neutralization degree of 60 mol%, followed by adding 372 g of ion-exchanged water dropwise at 10 mL/min. Thereafter, the solvent and water were removed using an evaporator to obtain an aqueous dispersion of vinyl polymer P1 (average particle size: 15 nm, solid content: 20%) as polymer dispersant (a).

Production Example 1-2
100.0 g of a styrene/acrylic acid copolymer ("JONCRYL 690" manufactured by BASF, weight average molecular weight: 16,500, acid value: 240 mgKOH/g), 339.0 g of ion-exchanged water, and 60.9 g of a 5N aqueous sodium hydroxide solution so as to give a degree of neutralization of 60% were charged, and the mixture was stirred (200 rpm) at 90°C for 5 hours to obtain an aqueous dispersion of vinyl polymer P2 (average particle size: 15 nm, solid content: 20%) as polymer dispersant (a).

(Preparation of aqueous dispersion of pigment-free polymer particles)
Production Example 2-1
A monomer mixture was prepared by mixing 3 g of acrylic acid, 110 g of cyclohexyl methacrylate, 82 g of n-butyl acrylate, and 2 g of tert-butylacrylamide. A reaction vessel was charged with 220 g of ion-exchanged water, 5 g of a polymerizable surfactant (polyoxyalkylene alkenyl ether ammonium sulfate, manufactured by Kao Corporation under the trade name "Latemul PD-104") as an emulsifier, 30 g of a 4% aqueous solution of potassium persulfate (KPS) as a polymerization initiator, and 10% (19.7 parts) of the monomer mixture, and the mixture was heated to 80°C while stirring (200 rpm) with a stirring blade. Next, 124 g of ion-exchanged water, 10 g of the polymerizable surfactant, and the remaining (177.3 parts) of the monomer mixture were added dropwise over 3 hours, and after aging for 2 hours, 82 g of ion-exchanged water and 2.8 g of a 25% aqueous ammonia solution were added to obtain an aqueous dispersion of pigment-free polymer particles obtained by emulsion polymerization (average particle size: 125 nm, solids concentration: 30%). The glass transition temperature (Tg) of the vinyl polymer (acrylic acid/cyclohexyl methacrylate/n-butyl acrylate/tert-butylacrylamide copolymer) constituting the pigment-free polymer particles, calculated using the Fox formula described above, was 15°C and the weight-average molecular weight was 18,000.

(Production of Pigment Water Dispersion (Water Dispersion of Cyan Pigment-Containing Polymer Particles))
Production Example 3-1
A mixture of 514.3 parts of a styrene/acrylic acid copolymer ("JONCRYL 690" manufactured by BASF, weight average molecular weight: 16,500, acid value: 240 mgKOH/g) as a polymer dispersant (b), 262.4 parts of a 5N aqueous sodium hydroxide solution so as to have a degree of neutralization of 50 mol%, and 4760 parts of ion-exchanged water was added, and the mixture was heated at 90°C for 8 hours while stirring (200 rpm) with a stirring blade. Thereafter, 1200 parts of a cyan pigment (C.I. Pigment Blue 15:3, "FASTOGEN BLUE TGR-SD" manufactured by DIC Corporation) was added, and the mixture was stirred (6400 rpm) at 15°C for 1 hour using a Homodisper (manufactured by Primix Corporation). The obtained mixture was subjected to 10-pass dispersion treatment at 15°C and a pressure of 150 MPa using a Microfluidizer (trade name, manufactured by Microfluidics Corporation), to obtain an aqueous dispersion (d1) of cyan pigment-containing polymer particles in which the cyan pigment was dispersed in the polymer dispersant (b).
Next, 123.4 parts (degree of crosslinking: 40 mol%) of trimethylolpropane polyglycidyl ether ("EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) as a crosslinking agent was added and mixed, and the mixture was heated at 90°C for 90 minutes while stirring (200 rpm) with a stirring blade. Thereafter, the mixture was cooled to 25°C, centrifuged, and filtered through a 5 µm acetyl cellulose membrane filter. Ion-exchanged water was added to obtain an aqueous dispersion (D1) (solids concentration: 25%) of cyan pigment-containing polymer particles in which the cyan pigment was dispersed by the polymer dispersant (b) having a crosslinked structure.

Example 1
(1) Preparation of aqueous dispersion of polyolefin wax particles (W) Aqueous dispersion of polyethylene wax (Mitsui Chemicals, Inc. "Chemipearl W900", solid content: 40%, acid value 0 mg KOH / g, no emulsifier) 500 g, 460 g of ion-exchanged water, and the content of polymer dispersant (a) was 5 parts by mass relative to the content of 100 parts by mass of polyolefin wax (w), and 50 g of aqueous dispersion of vinyl polymer P2 as polymer dispersant (a) was added, and stirred for 10 minutes (200 rpm). Then, using a microfluidizer (manufactured by Microfluidics, trade name), 5 passes were performed at a pressure of 150 MPa at 15 ° C. to obtain an aqueous dispersion of polyethylene wax particles (W1) dispersed in vinyl polymer P2 (solid content concentration: 20%, polyolefin wax (w) content: 19%, polymer dispersant (a) content: 1%). The physical properties of the polyethylene wax particles (W1) were an average particle size of 390 nm, a particle size distribution of 1.0, and an acid value of 11.4 mgKOH/g.
(2) Preparation of Water-Based Ink 2 g of the aqueous dispersion of polyethylene wax particles (W1) obtained in (1) above, 20 g of the aqueous dispersion of cyan pigment-containing polymer particles obtained in Production Example 3-1, 26.7 g of the aqueous dispersion of pigment-free polymer particles obtained in Production Example 2-1, 13 g of propylene glycol (hereinafter referred to as "PG"), 2 g of diethylene glycol monoisobutyl ether (hereinafter referred to as "iBDG") (manufactured by Nippon Nyukazai Co., Ltd.), 1 g of "Surfynol 440" (manufactured by Nissin Chemical Industry Co., Ltd.) as an acetylene-based surfactant, 1 g of "KF6011" (manufactured by Shin-Etsu Chemical Co., Ltd.) as a polyether-modified silicone-based surfactant, and 34.3 g of ion-exchanged water were mixed so that the content of polyolefin wax particles (W) in the water-based ink was 0.4%, to obtain Water-Based Ink 1.

Example 2
(1) The same procedure as in (1) of Example 1 was carried out to obtain an aqueous dispersion (W1) of polyethylene wax particles dispersed in vinyl polymer P2.
(2) Water-based ink 2 was obtained in the same manner as in (2) of Example 1, except that the amount of the water dispersion of polyethylene wax particles (W1) was changed to 4 g so that the content of polyolefin wax particles (W) in the water-based ink was 0.8%, and the amount of ion-exchanged water was also changed to 32.3 g.

Example 3
(1) The same procedure as in (1) of Example 1 was carried out to obtain an aqueous dispersion of polyethylene wax particles (W1) dispersed in vinyl polymer P2.
(2) Water-based ink 3 was obtained in the same manner as in (2) of Example 1, except that the amount of the water dispersion of polyethylene wax particles (W1) was changed to 25 g so that the content of polyolefin wax particles (W) in the water-based ink was 5%, and the amount of ion-exchanged water was further changed to 11.3 g.

Example 4
(1) In Example 1 (1), the amount of the aqueous dispersion of vinyl polymer P2 used as polymer dispersant (a) was changed to 10 g so that the content of polymer dispersant (a) was 1 part by mass per 100 parts by mass of polyolefin wax (w), and the amount of ion-exchanged water was changed to 492 g. The same procedure was followed to obtain an aqueous dispersion of polyethylene wax particles (W2) dispersed in vinyl polymer P2 (solids concentration: 20%, polyolefin wax (w) content: 19.8%, polymer dispersant (a) content: 0.2%). The physical properties of the polyethylene wax particles (W2) were an average particle size of 390 nm, a particle size distribution of 1.0, and an acid value of 2.4 mg KOH/g.
(2) Aqueous ink 4 was obtained in the same manner as in (2) of Example 2, except that the aqueous dispersion of polyethylene wax particles (W1) was changed to the aqueous dispersion of polyethylene wax particles (W2) obtained above.

Example 5
(1) In Example 1 (1), the amount of the aqueous dispersion of vinyl polymer P2 used as polymer dispersant (a) was changed to 500 g so that the content of polymer dispersant (a) was 50 parts by mass per 100 parts by mass of polyethylene wax (w), and the amount of ion-exchanged water was changed to 100 g. An aqueous dispersion of polyethylene wax particles (W3) dispersed in vinyl polymer P2 (solids concentration: 20%, polyolefin wax (w) content: 13.4%, polymer dispersant (a) content: 6.6%) was obtained. The physical properties of the polyethylene wax particles (W3) were an average particle size of 390 nm, a particle size distribution of 1.0, and an acid value of 80.0 mg KOH/g.
(2) Next, in (2) of Example 2, water-based ink 5 was obtained in the same manner as above, except that the water dispersion of polyethylene wax particles (W1) was replaced with the water dispersion of polyethylene wax particles (W3) obtained above.

Example 6
(1) In the same manner as in (1) of Example 1, except that the aqueous dispersion of vinyl polymer P2 was replaced with the aqueous dispersion of vinyl polymer P1 as the polymer dispersant (a), an aqueous dispersion of polyethylene wax particles (W4) dispersed in vinyl polymer P1 (solids concentration: 20%, polyolefin wax (w) content: 19%, polymer dispersant (a) content: 1%) was obtained. The physical properties of the polyethylene wax particles (W4) were an average particle size of 390 nm, a particle size distribution of 1.0, and an acid value of 8.6 mgKOH/g.
(2) Aqueous ink 6 was obtained in the same manner as in (2) of Example 2, except that the aqueous dispersion of polyethylene wax particles (W1) was changed to the aqueous dispersion of polyethylene wax particles (W4) obtained above.

Example 7
(1) In Example 1(1), an aqueous dispersion of polyethylene wax particles (W5) dispersed with vinyl polymer P2 (solids concentration: 20%, polyolefin wax (w) content: 19%, polymer dispersant (a) content: 1%) was obtained in the same manner as in Example 1(1), except that "Chemipearl W900" was replaced with "Chemipearl W950" (manufactured by Mitsui Chemicals, Inc., aqueous dispersion of polyethylene wax, solids concentration: 40%, acid value: 0 mgKOH/g, no emulsifier). The physical properties of the polyethylene wax particles (W5) were an average particle size of 600 nm, a particle size distribution of 1.1, and an acid value of 11.4 mgKOH/g.
(2) Water-based ink 7 was obtained in the same manner as in (2) of Example 2, except that the water dispersion of polyethylene wax particles (W1) was changed to the water dispersion of polyethylene wax particles (W5) obtained above.

Example 8
(1) In Example 1(1), an aqueous dispersion of polyethylene wax particles (W6) dispersed with vinyl polymer P2 (solid concentration: 20%, polyolefin wax (w) content: 19%, polymer dispersant (a) content: 1%) was obtained in the same manner as in Example 1(1), except that "Chemipearl W900" was replaced with "Chemipearl W500" (manufactured by Mitsui Chemicals, Inc., aqueous dispersion of polyethylene wax, solid concentration: 40%, acid value: 0 mgKOH/g, no emulsifier). The physical properties of the polyethylene wax particles (W6) were an average particle size of 2600 nm, a particle size distribution of 1.2, and an acid value of 11.4 mgKOH/g.
(2) Aqueous ink 8 was obtained in the same manner as in (2) of Example 2, except that the aqueous dispersion of polyethylene wax particles (W1) was changed to the aqueous dispersion of polyethylene wax particles (W6) obtained above.

Comparative Example 1
(2) In Example 2(2), a water-based ink C1 was obtained in the same manner as in Example 2(2), except that the aqueous dispersion of polyethylene wax particles (W1) was replaced with "Chemipearl 900" (Mitsui Chemicals, Inc., aqueous dispersion of polyethylene wax, solids concentration: 40%, acid value: 0 mgKOH/g, no emulsifier) diluted two-fold with ion-exchanged water (solids concentration: 20%). The physical properties of "Chemipearl 900" were an average particle diameter of 400 nm, a particle size distribution of 1.1, and an acid value of 0 mgKOH/g.

Comparative Example 2
(1) In the same manner as in (1) of Example 1, except that the aqueous dispersion of vinyl polymer P2 was changed to 10 g of surfactant "Surfynol 440" (manufactured by Nissin Chemical Industry Co., Ltd., active content: 100%) and the amount of ion-exchanged water was changed to 500 g, an aqueous dispersion of surfactant-dispersed polyethylene wax particles (WC1) (solid content: 20%, polyolefin wax content: 19%, surfactant content: 1%) was obtained. The physical properties of the polyethylene wax particles (WC1) were an average particle size of 390 nm, a particle size distribution of 1.0, and an acid value of 0 mgKOH/g.
(2) In Example 2 (2), a water-based ink C2 was obtained in the same manner as above, except that the water dispersion of polyethylene wax particles (W1) was replaced with the water dispersion of polyethylene wax particles (WC1) obtained above.

Comparative Example 3
(1) In Example 1(1), "CHEMIPEARL 900" was replaced with "AQUACER 531" (manufactured by BYK Corporation, polyethylene wax emulsion, nonionic, solids concentration: 45%), the blending amount was changed to 420 g, and the blending amount of ion-exchanged water was changed to 530 g. The same procedure was followed to obtain an aqueous dispersion of polyethylene wax particles (WC2) dispersed with vinyl polymer P2 (solids concentration: 20%, polyolefin wax content: 19.0%, polymer dispersant (a) content: 1%). The physical properties of the polyethylene wax particles (WC2) were an average particle size of 170 nm, a particle size distribution of 0.3, and an acid value of 11.4 mg KOH/g.
(2) In Example 2 (2), a water-based ink C3 was obtained in the same manner as above, except that the water dispersion of polyethylene wax particles (W1) was replaced with the water dispersion of polyethylene wax particles (WC2) obtained above.

Comparative Example 4
(1) In Example 1(1), the procedure was repeated except that "Chemipearl W900" was replaced with "Hitec E-6500" (manufactured by Toho Chemical Industry Co., Ltd., aqueous dispersion of polyethylene wax, nonionic, solids concentration: 35%), the amount of ion-exchanged water was changed to 340 g, and the amount of aqueous dispersion of vinyl polymer P2 was changed to 45 g, resulting in an aqueous dispersion of polyethylene wax particles (WC3) dispersed in vinyl polymer P2 (solids concentration: 20%, polyolefin wax content: 19%, polymer dispersant (a) content: 1%). The physical properties of the polyethylene wax particles (WC3) were an average particle size of 70 nm, a particle size distribution of 0.3, and an acid value of 11.4 mg KOH/g.
(2) In Example 2 (2), a water-based ink C4 was obtained in the same manner as above, except that the water dispersion of polyethylene wax particles (W1) was replaced with the water dispersion of polyethylene wax particles (WC3) obtained above.

[evaluation]
The water-based inks obtained in the examples and comparative examples were evaluated according to the following (1) and (2). The results are shown in Table 1.

(1) Evaluation of Ejection Stability In an environment of 25±1°C temperature and 30±5% relative humidity, each water-based ink was loaded into a printing evaluation device (manufactured by Tritec Corporation) equipped with an inkjet head (Kyocera Corporation "KJ4B-HD06MHG-STDV", piezo type). The settings were head voltage 26V, drive frequency 10 kHz, ejection liquid volume 12 pL, head temperature 32°C, resolution 600 dpi, pre-ejection flushing count 200, and negative pressure -4.0 kPa. Corona-discharge-treated OPP film (product number: FOR-AQ, count: #20, manufactured by Futamura Chemical Co., Ltd.) was fixed to the conveying table under reduced pressure as the printing medium, with the longitudinal direction and conveying direction of the printing medium aligned. A printing command was transferred to the printing evaluation device, and 10 solid images (4 cm x 4 cm) were printed 10 times at 100% duty. Thereafter, a print check pattern that could be used to determine whether ejection had occurred from all nozzles (2,656 nozzles) was printed on paper, and the number of missing nozzles (nozzles that were not ejecting normally) was counted, and ejection stability was evaluated according to the following evaluation criteria.
6: No missing nozzles. 5: The number of missing nozzles is 1 to 10.
4: The number of missing nozzles is 11 or more and 60 or less. 3: The number of missing nozzles is 61 or more and 100 or less.
2: The number of missing nozzles is 101 or more.
1: Discharge becomes impossible before printing a solid image 10 times.
The fewer the number of missing nozzles, the more excellent the ejection stability. If the above evaluation is 3 or higher (the number of missing nozzles is 100 or less), the ink can be used for practical purposes.

(2) Evaluation of Scratch Resistance Using a gravure proofing machine ("K Printing Proofer" manufactured by RK Print Coat Instruments Ltd.), a 250L, 10 μm deep Honeycomb gravure plate was used, and each water-based ink was printed at a speed of 15 m/min on a corona discharge-treated OPP film (product number: FOR-AQ, count: #20, manufactured by Futamura Chemical Co., Ltd.), and then dried at 60 ° C. for 1 hour to obtain a print for scratch resistance evaluation. Next, the ink coating film formed on the printed surface of the print for scratch resistance evaluation was vigorously scratched with the tip of a fingernail, and the presence or absence of peeling of the ink coating film was visually confirmed, and the scratch resistance was evaluated according to the following evaluation criteria.
5: The ink coating film is not peeled off at all when rubbed with a fingernail.
4: The underlying print medium is not visible due to fingernail scratching, and the ink coating is not peeled off, but fingernail scratch marks are visible on the ink coating.
3: The ink film peels slightly when rubbed with a fingernail.
2: When rubbed with a fingernail, about 50% of the ink coating peeled off from the printed area.
1: Almost all of the ink coating in the printed area is removed by rubbing with a fingernail.
If the above evaluation is 3, the ink coating film of the printed matter is suitable for practical use in applications where the ink coating film is not subject to significant abrasion, and if the above evaluation is 4, the ink coating film of the printed matter is suitable for practical use in applications where the ink coating film is subject to abrasion.
The evaluation of abrasion resistance was carried out using gravure prints in order to evaluate the water-based inks of the comparative examples, which are difficult to eject. It is estimated that the same results as for gravure prints can be obtained when using prints obtained by inkjet recording.

From Table 1, it can be seen that the water-based inks of Examples 1 to 8 are superior to the water-based inks of Comparative Examples 1 to 4 in ejection stability and abrasion resistance.
On the other hand, Comparative Example 1 does not use polymer dispersant (a), so the ejection stability is inferior to that of the Examples, and Comparative Example 2 uses a surfactant instead of polymer dispersant (a), so the ejection stability is inferior to that of the Examples.
Furthermore, it can be seen that in Comparative Examples 3 and 4, the average particle size of the polyolefin wax particles dispersed with the polymer dispersant is less than 200 nm, and therefore the abrasion resistance is poor.

Claims (9)

A pigment, polyolefin wax particles (W) dispersed with a polymer dispersant (a), and water,
the acid value of the polyolefin wax particles (W) is 1 mgKOH/g or more and 100 mgKOH/g or less,
The water-based ink for ink-jet printing, wherein the polyolefin wax particles (W) have an average particle size of 200 nm or more and 3,000 nm or less. The water-based ink according to claim 1, wherein the particle size distribution of the polyolefin wax particles (W) is 0.5 or greater. The water-based ink according to claim 1, wherein the content of the polyolefin wax particles (W) is 0.1% by mass or more and 7% by mass or less. The water-based ink according to claim 1, wherein the content of the polymer dispersant (a) per 100 parts by mass of the polyolefin wax (w) contained in the polyolefin wax particles (W) is 0.5 parts by mass or more and 60 parts by mass or less. The water-based ink according to any one of claims 1 to 4, wherein the polymer dispersant (a) is a vinyl polymer containing a structural unit derived from an anionic monomer (a-1) having an anionic group and a structural unit derived from a hydrophobic monomer (a-2). The water-based ink according to any one of claims 1 to 4, wherein the acid value of the polymer dispersant (a) is 90 mg KOH/g or more and 300 mg KOH/g or less. The water-based ink according to any one of claims 1 to 4, wherein the pigment is dispersed in a polymer dispersant (b). The water-based ink according to any one of claims 1 to 4, wherein the content of polyolefin wax particles (W) in the total amount of solids in the water-based ink is 1% by mass or more and 40% by mass or less. An inkjet recording method using the water-based ink described in any one of claims 1 to 4 to record on a low-liquid-absorbent print medium.