JP7619052B2 - Pigment dispersion for inkjet ink, inkjet ink and printed matter - Google Patents

Description

The present invention relates to a pigment dispersion for use in aqueous inkjet inks, an aqueous inkjet ink prepared using the pigment dispersion, and a printed matter that has been inkjet printed using the inkjet ink.

In addition to the perspective of sustainability against the backdrop of worsening air pollution caused by VOCs and the global expansion of global warming, there is a movement to move away from petroleum resources due to concerns about occupational safety and health and flammability, and regulations on the use of organic solvents are becoming increasingly strict. As a result, the printing ink industry is developing water-based inks that replace the organic solvents in solvent-based printing inks with water, and there is also a demand for the development and improvement of water-based inks in inkjet inks.

Meanwhile, the consumption of plastic film packaging is on the rise worldwide due to population growth, rising income levels, and changes in logistics systems, and as a result, the production volume of packaging inks is increasing year by year. Traditionally, solvent-based flexographic inks and solvent-based gravure inks were the mainstream for film package printing. However, these printing methods require plate making, which increases costs and requires time before printing can be completed. For this reason, there is a growing demand for inkjet printing, which does not require plate making and allows on-demand printing, even in film package printing.

However, compared to solvent-based inkjet inks, water-based inkjet inks have problems in that they are still insufficient in adhesion to substrates such as films, in blocking resistance associated with offset of printed images, and in ink ejection from inkjet heads. In particular, the problems of adhesion and blocking resistance are more pronounced when the substrate is a film substrate.
In relation to ink ejection properties, which are a particular issue in inkjet printing, it is known that nozzle clogging occurs during the open time when ink is not ejected during inkjet printing, due to the ink drying in the ejection portion of the inkjet head. Inkjet inks are also desired to have excellent ink resolubility that can reduce the occurrence of nozzle clogging.

In addition, abrasion resistance is a desirable characteristic of inkjet inks for use on film substrates. Reverse printing, in which printing is performed on the reverse side of the film substrate, is the mainstream method of printing on film packages, but surface printing, in which printing is performed on the front side of the film substrate, is faster in terms of printing and processing speed, and is therefore more advantageous when productivity and cost are important. . However, in surface printing, the printed surface comes into contact with the external environment without the substrate, so the printed surface and the ink itself require high abrasion resistance. If an inkjet ink has the above-mentioned characteristics as well as abrasion resistance, it can be used not only for reverse printing on films but also for front printing, increasing its versatility.

JP 2019-196423 A

Patent Document 1 discloses an inkjet ink that has excellent water resistance and alcohol resistance and is capable of film printing. The ink is characterized in that the acid value of the dispersant is neutralized by ammonia, and the resin emulsion has a specific Tg and acid value. In Patent Document 1, the solvent resistance is evaluated by rubbing with a cotton swab moistened with a solvent, and it is clear that a certain degree of abrasion resistance can be obtained with the configuration of Patent Document 1. However, Patent Document 1 does not evaluate the ink ejection properties, adhesion, or blocking resistance. In addition, further improvement in abrasion resistance is desired.

The problem that the present invention aims to solve is to provide an inkjet ink that is excellent in adhesion to various substrates such as plastic substrates, blocking resistance, abrasion resistance, and ink ejection properties during inkjet printing, as well as an inkjet pigment dispersion that can be used in the inkjet ink, and a printed matter that has been inkjet printed with the inkjet ink.

As a result of intensive research aimed at solving the above problems, the inventors discovered that the problems could be solved by a pigment dispersion in which some or all of the acid groups in the dispersion resin are neutralized with ammonia and a crosslinked acrylic resin is used as a binder, thus completing the present invention.

That is, the present invention relates to the following inventions.
(1) A dispersion medium comprising a dispersant (A), a binder resin (B), a pigment (C), and water (D),
The dispersant (A) contains at least a resin (A1) having a structural unit (a1) derived from an acid group-containing monomer,
In the resin (A1), a part or all of the acid groups in the structural unit (a1) are neutralized with ammonia,
A pigment dispersion for inkjet recording, characterized in that the binder (B) contains a crosslinked acrylic resin (B1).
(2) The pigment dispersion for inkjet according to (1), wherein the dispersant (A) has a glass transition temperature of 50 to 120° C. and an acid value of 100 to 300 mgKOH/g.
(3) The pigment dispersion for inkjet according to (1) or (2), wherein the crosslinked acrylic resin (B1) is an acrylic emulsion having a volume average particle size of 20 to 100 nm, a glass transition temperature of 0 to 70° C., and an acid value of 5 to 80 mgKOH/g.
(4) The pigment dispersion for inkjet according to any one of (1) to (3), further comprising an amine compound (E) having a boiling point of 100° C. or higher.
(5) The pigment dispersion for inkjet according to any one of (1) to (4), which is for printing on a plastic substrate.
(6) An ink-jet ink using the ink-jet pigment dispersion according to any one of (1) to (5).
(7) A printed matter printed with the inkjet ink of (6).

According to the present invention, it is possible to obtain an aqueous inkjet ink for printing on plastic substrates that has excellent adhesion to plastic substrates, blocking resistance, and ink ejection properties during inkjet printing.

[Pigment dispersion for inkjet]
The "pigment dispersion for inkjet use" of the present invention (hereinafter sometimes simply referred to as "pigment dispersion" or "dispersion") contains a dispersant (A), a binder resin (B), a pigment (C), and water (D), and is used for preparing an inkjet ink. Hereinafter, "dispersant (A)" will sometimes be referred to as "component (A)", and the other components will sometimes be referred to in the same manner.
The pigment dispersion of the present invention is manufactured as an intermediate product for inkjet inks and, after dilution, is used in inkjet printing as an aqueous inkjet ink.

<Dispersant (A)>
The dispersant (A) contains a resin (A1), and the resin (A1) has at least a structural unit (a1) derived from an acid group-containing monomer, and in the dispersant (A), some or all of the acid groups in the structural unit (a1) are neutralized with ammonia.

(Resin (A1))
The resin (A1) has a structural unit (a1) derived from an acid group-containing monomer and a structural unit (a2) other than (a1), and is obtained by polymerizing the acid group-containing monomer and the other monomer using a known method such as radical polymerization. The resin (A1) has an acid group, which gives the resin (A1) hydrophilicity, making it possible to stably disperse the pigment in water.

In the acid group-containing monomer from which the structural unit (a1) is derived, examples of the acid group include a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a thiocarboxyl group, and ethylenically unsaturated monomers having these groups can be used as raw material monomers for the structural unit (a1).
Examples of the ethylenically unsaturated monomer containing a carboxyl group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, and 4-vinylbenzoic acid; and unsaturated polybasic esters such as vinyl succinate, allyl maleate, vinyl terephthalate, and allyl trimetrate.
Examples of ethylenically unsaturated monomers containing a sulfonic acid group include unsaturated carboxylic acid sulfo-substituted alkyl or aryl esters such as 2-sulfoethyl acrylate and 4-sulfophenyl methacrylate; unsaturated sulfocarboxylic acid esters such as vinyl sulfosuccinate; and sulfostyrenes such as styrene-4-sulfonic acid.
Among these, as the monomer from which the structural unit (a1) is derived, taking into consideration the availability and cost of the raw material monomers, a monomer having a carboxyl group as the acid group is preferred, unsaturated carboxylic acids are more preferred, and acrylic acid or methacrylic acid is more preferred.
Hereinafter, the term "(meth)acrylic acid" may include both acrylic acid and methacrylic acid, and the term "(meth)acrylic acid ester" may include both acrylic acid ester and methacrylic acid ester. The same applies to similar acrylic acid compounds.

Examples of the structural unit (a2) other than the structural unit (a1) include ethylenically unsaturated monomers that can be copolymerized with (a1). Examples of such structural units include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and methylpropyl (meth)acrylate; unsaturated fatty acid esters such as dimethyl maleate, dimethyl fumarate, 2-hydroxyethyl (meth)acrylate, and 2-aminoethyl (meth)acrylate; unsaturated fatty acid amides such as (meth)acrylamide and N-methyl(meth)acrylamide; unsaturated nitriles such as (meth)acrylonitrile; unsaturated ethers such as vinyl acetate and vinyl propionate; styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-t-butylstyrene, 4-methoxystyrene, 4-chlorostyrene, unsaturated hydrocarbons such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, 3-chloropropylene, etc.; vinyl-substituted heterocyclic compounds such as 4-vinylpyridine, N-vinylcarbazole, N-vinylpyrrolidone, etc.; reaction products of a monomer containing a substituent having an active hydrogen, such as a carboxyl group, a hydroxyl group, an amino group, etc., among the above-exemplified monomers, with an epoxide, such as ethylene oxide, propylene oxide, cyclohexene oxide, etc.; reaction products of a monomer containing a substituent having a hydroxyl group, an amino group, etc., among the above-exemplified monomers, with a carboxylic acid, such as acetic acid, propionic acid, butanoic acid, hexanoic acid, decanoic acid, dodecanoic acid, etc.
Of these, as the monomer from which the structural unit (a2) is derived, styrenes are preferred, and styrene or α-methylstyrene is preferred, because they have the effect of increasing the adsorptivity of the resin (A1) to the pigment.

As the structural unit (a2), it is preferable that the monomer contains methoxypolyethylene glycol monomethacrylate, since this has the excellent effect of improving the ejection properties.

The resin (A1) may or may not have a crosslinked portion. The resin having a crosslinked portion can be obtained by copolymerizing the above-mentioned monomer with a glycidyl group-containing ethylenically unsaturated monomer such as 2,3-epoxypropyl (meth)acrylate to form a resin having crosslinkability, and then crosslinking the resulting resin by using a curing accelerator as necessary in any step of producing an aqueous pigment dispersion.

The mass average molecular weight of resin (A1) is preferably in the range of 2,000 to 100,000, and particularly preferably in the range of 5,000 to 50,000, in order to provide the pigment dispersion with an appropriate viscosity, improve dispersion stability, and ensure stable printing over a long period of time when used in an inkjet ink.

The acid value of the resin (A1) is preferably from 80 to 350 mgKOH/g, more preferably from 100 to 300 mgKOH/g, and particularly preferably from 180 to 300 mgKOH/g.
The glass transition point of the resin (A1) is preferably from 30 to 130°C, more preferably from 50 to 120°C, and particularly preferably from 80 to 110°C.
By setting the content within the above range, the hydrophilicity and pigment adsorption of the dispersant are well balanced, improving the dispersion stability of the pigment dispersion. Also, the coating strength of the printed matter is increased, improving the abrasion resistance.

In the dispersant (A), some or all of the acid groups in the structural unit (a1) are neutralized with ammonia.
The method of neutralization with ammonia is not particularly limited. For example, the resin (A1) in an organic solvent obtained by monomer synthesis can be neutralized by adding aqueous ammonia and, if necessary, water.
The neutralization may be performed by neutralizing only a part of the acid groups, or may be performed by neutralizing all of the acid groups. Specifically, the neutralization rate is preferably set to 30 to 300%, particularly preferably 60 to 200%, based on the neutralization rate of 100% when the acid groups of the dispersant (A) are neutralized in a theoretical equivalent amount.
Inkjet inks using dispersant (A) neutralized with ammonia become insoluble in water as ammonia volatilizes during the drying process after printing. When ammonia volatilizes, the acid groups in dispersant (A) undergo equilibrium transfer to a non-dissociated state, reducing the hygroscopicity of dispersant (A) and increasing the quick-drying ability of the ink. As a result, adhesion to the substrate and abrasion resistance are improved.

The dispersant (A) may consist of only the resin (A1), or may contain other components in addition to the resin (A1).

In the pigment dispersion of the present invention, the dispersant (A) is preferably contained in an amount of 5 to 100 mass % in terms of non-volatile content, and more preferably 10 to 60 mass %. Within these ranges, a decrease in the dispersion stability of the pigment dispersion caused by an excess or deficiency of the dispersant is suppressed, and a stable state can be maintained even during long-term storage.

<Binder Resin (B)>
In the present invention, the binder (B) contains a crosslinked acrylic resin (B1). The binder (B) is added for the purpose of improving the adhesion of the ink to the substrate and the abrasion resistance. If the binder (B) has a pigment dispersing ability, the binder (B) may cause the dispersant (A) to be released from the pigment, thereby decreasing the dispersion stability of the pigment dispersion. Therefore, it is preferable that the binder (B) does not have a pigment dispersing ability.

(Crosslinked acrylic resin (B1))
The crosslinked acrylic resin (B1) used as the binder resin is preferably a crosslinked aqueous acrylic resin emulsion.
Examples of the acrylic emulsion include acrylic emulsion, styrene-acrylic emulsion, acrylic-maleic acid emulsion, and styrene-acrylic-maleic acid emulsion, and acrylic emulsion and styrene-acrylic emulsion are preferred. The emulsion may be of a core-shell type or may be of a type other than the core-shell type.
Examples of the structural unit in the emulsion resin include the structural units (a1) and (a2) described above, as well as those that are copolymerizable therewith.

In the present invention, the acrylic resin (B1) is crosslinked.
As a result of extensive investigations, the present inventors have found that, while the higher the Tg of the acrylic resin (B1), the better the dry abrasion resistance, the lower the Tg of the acrylic resin (B1) is, the lower the dry abrasion resistance is.
However, although the mechanism of action is unclear, it has been found that crosslinking the acrylic resin (B1) improves dry abrasion resistance even when the resin has a low Tg. In addition, good wet abrasion resistance was obtained by crosslinking the acrylic resin regardless of the Tg.
Therefore, by using the crosslinked acrylic resin (B1), even when the acrylic resin (B1) has a low Tg, a pigment dispersion having good abrasion resistance can be obtained in both the dry and wet processes.

As a method for crosslinking the acrylic resin (B1), for example, a method using a crosslinking agent that reacts with the functional groups contained in the acrylic resin (B1) can be mentioned. A crosslinking agent is a compound that has two or more reactive functional groups in the molecule, and specific examples of crosslinking agents include epoxy compounds, hydrazide compounds, and carbodiimide compounds.

The acid value of the acrylic resin (B1) is preferably 5 to 100 mgKOH/g, more preferably 5 to 80 mgKOH/g, and even more preferably 20 to 50 mgKOH/g. If the acid value is less than 5 mgKOH/g, the dispersion stability of the acrylic resin (B1) may decrease. On the other hand, if the acid value exceeds 100 mgKOH/g, the moisture absorption of the printed coating film may increase, and the wet friction resistance of the abrasion resistance may be impaired.

The glass transition point of the acrylic resin (B1) is preferably from 0 to 100°C, more preferably from 0 to 80°C, even more preferably from 0 to 70°C, and particularly preferably from 10 to 40°C.
By setting the drying time within the above range, the drying time after printing can be shortened, which is preferable from the viewpoints of improving the printing speed and saving energy.

The volume average particle diameter of the acrylic resin (B1) is preferably 20 to 100 nm, more preferably 20 to 80 nm. The volume average particle diameter can be measured, for example, by filling a cell with a resin diluted with ion-exchanged water and using a UPA-EX150 under the following conditions.
Loading index: 5±1
Measurement time: 180 seconds Number of measurements: 5 Transmittance: Transmitted Particle refractive index: 1.80
・Shape: True sphere ・Density: 1.00
Solvent refractive index: 1.333
・Viscosity at high temperature: 30℃, 0.797
・Viscosity at low temperature: 20℃, 1.002
Filter: Stand: Norm
Sensitivity: Standard
- UPA compatible mode

Of course, it is also possible to use commercially available products as resin (B1). Examples of commercially available products that can be used include ME-2039 (Seiko PMC Corporation, cross-linked acrylic emulsion).

In the pigment dispersion of the present invention, the binder resin (B) is preferably contained in an amount of 10 to 200% by mass, and more preferably 30 to 150% by mass, calculated as the non-volatile content. This range is preferable because it allows the inkjet ink to have good adhesion to the substrate, abrasion resistance, and blocking resistance even after dilution.

<Pigment (C)>
The pigment (C) is not particularly limited as long as it can be well dispersed in the pigment dispersion, but it is preferable to use one that can be dispersed with an average particle diameter of 50 to 400 nm (details will be described later). For example, organic pigments, inorganic pigments, and dyes that are used in general inks, paints, and recording agents can be used.

Organic pigments include azo, phthalocyanine, anthraquinone, perylene, perinone, quinacridone, thioindigo, dioxazine, isoindolinone, quinophthalone, azomethine azo, dictopyrrolopyrrole, and isoindoline pigments. For indigo ink, it is preferable to use copper phthalocyanine from the standpoint of cost and light resistance.

Inorganic pigments include carbon black, titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, red iron oxide, and mica. In addition, a glittering pigment (Metashine; Nippon Sheet Glass Co., Ltd.) made of glass flakes or aggregated flakes as a base material and coated with a metal or metal oxide can be used. From the standpoint of cost and coloring power, it is preferable to use titanium oxide for white ink, carbon black for black ink, aluminum for gold and silver ink, and mica for pearl ink.

As described above, in the pigment dispersion, the pigment is preferably dispersed with a volume average particle diameter of 50 to 400 nm. The volume average particle diameter of the pigment can be measured by preparing the pigment dispersion and then uniformly dispersing the pigment in the dispersion using a known method such as dynamic light scattering. In particular, the volume average particle diameter of the pigment in the dispersion is preferably 50 to 300 nm, more preferably 50 to 200 nm, even more preferably 50 to 150 nm, and particularly preferably 50 nm or more and less than 100 nm. By having a volume average particle diameter of 50 nm or more, it is possible to suppress the aggregation of the pigment during storage of the pigment dispersion. In addition, by having a volume average particle diameter of 400 nm or less (particularly preferably 100 nm or less), the ink ejection properties are improved.

The pigment content in the aqueous pigment dispersion is not particularly limited, but is preferably 10 to 30% by mass of the total amount of the pigment dispersion. If it is less than 10% by mass, there is a risk that sufficient ink coloring power will not be obtained in the inkjet ink prepared by diluting the pigment dispersion. Furthermore, if it is more than 30% by mass, depending on the type of pigment, the pigment may aggregate during transportation or storage of the dispersion, in which case dispersibility at an average particle size of 50 to 400 nm cannot be guaranteed. Furthermore, there is a concern that the ink ejection properties may deteriorate depending on the degree of dilution.

In the pigment dispersion of the present invention, when the pigment is an organic pigment or carbon black, the pigment concentration is preferably 10 to 30% by mass, and more preferably 10 to 25% by mass. Within these ranges, when the pigment is diluted to prepare an inkjet ink, both ink coloring power and ink dischargeability can be suitably achieved.
When the pigment is an inorganic pigment, the content is preferably from 25 to 60% by mass, and more preferably from 30 to 50% by mass.

<Other optional ingredients>
The pigment dispersion of the present invention may contain other optional components in addition to the above-mentioned components (A) to (C) and water (D), within the range in which the effects of the present invention are not impaired.
Examples of other components include an amine compound (E) having a boiling point of 100° C. or higher, other resins other than the above-mentioned components, solvents other than water, surfactants, waxes, low surface tension organic solvents, wetting agents, penetrating agents, dispersants other than the above-mentioned components, defoamers, preservatives, viscosity adjusters, pH adjusters, chelating agents, plasticizers, antioxidants, and ultraviolet absorbers.

(Amine compound (E) having a boiling point of 100° C. or higher)
The pigment dispersion of the present invention preferably contains an amine compound (E) having a boiling point of 100° C. or higher.
In the pigment dispersion of the present invention, the dispersant (A) is neutralized with ammonia to improve the adhesion to the substrate and the abrasion resistance, but on the other hand, excessive evaporation of ammonia may cause excessive insolubilization of the ink, which may result in clogging of the nozzle. The amine compound (E) has the effect of appropriately neutralizing the acid groups in the insolubilized ink to re-dissolve it in water. In addition, the amine compound (E) having a boiling point of 100° C. or more also has the effect of acting as a wetting agent.
Therefore, by adding the amine compound (E), excessive drying of the ink is suppressed and the ink does not clog the nozzles. As a result, the ejection properties are improved, and it is possible to achieve both ejection properties and abrasion resistance.

Examples of the amine compound (E) include polyalkyleneimines, polyallylamine, (poly)ethylenepolyamines, alkanolamines, and alkylamines.
Among these, alkanolamines are preferred from the viewpoint of pigment dispersibility.

(Polyalkyleneimine)
The polyalkyleneimine is preferably a polyalkyleneimine having an alkylene group having 2 or more and 5 or less carbon atoms.
The polyalkyleneimine is preferably a polyalkyleneimine having an alkylene group with a carbon number of 2 to 4, more preferably polyethyleneimine or polypropyleneimine, and further preferably polyethyleneimine. These may be used alone or in combination.

The number average molecular weight of the polyalkyleneimine is preferably 150 or more, more preferably 500 or more, even more preferably 800 or more, even more preferably 1,000 or more, and preferably 10,000 or less, more preferably 5,000 or less, even more preferably 4,000 or less.
The molecular weight value is determined by the method described in the Examples.

(Polyallylamine)
Examples of polyallylamine include polymers having amino groups on the side chains, such as homopolymers or copolymers of allyl compounds, such as allylamine and dimethylallylamine.
The weight average molecular weight of the polyallylamine is preferably 800 or more, more preferably 1,000 or more, even more preferably 1,500 or more, and is preferably 10,000 or less, more preferably 5,000 or less, even more preferably 4,000 or less.

(Polyethylene polyamine)
Examples of (poly)ethylenepolyamines include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc. Among these, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine are preferred.

(Alkanolamines)
The alkanolamine is preferably an alkanolamine having 2 to 9 carbon atoms. Examples of the alkanolamine include primary alkanolamines such as monoethanolamine, monopropanolamine, and monobutanolamine; secondary monoalkanol amines such as N-methylethanolamine and N-methylpropanolamine; secondary dialkanol amines such as diethanolamine and diisopropanolamine; tertiary monoalkanol amines such as N,N-dimethylethanolamine, N,N-dimethylpropanolamine, and N,N-diethylethanolamine; tertiary dialkanol amines such as N-methyldiethanolamine and N-ethyldiethanolamine; and tertiary trialkanol amines such as triethanolamine and triisopropanolamine. Among these, tertiary alkanolamines having 2 to 9 carbon atoms are preferred, and triisopropanolamine is particularly preferred.

(Alkylamine)
The alkylamine is preferably an alkylamine having a carbon number of 1 to 6. Examples of the alkylamine include primary amines such as propylamine, butylamine, and hexylamine; and secondary amines such as diethylamine and dipropylamine.

In the pigment dispersion of the present invention, the amine compound (E) preferably has a neutralization rate of 30 to 500% relative to the acid groups of the dispersant (A), and is particularly preferably set in the range of 50 to 400%. Within these ranges, the ink will not clog the nozzle and will have excellent adhesion and abrasion resistance.

(Components other than component (E))
The other resin is preferably an aqueous resin suitable for preparing a pigment dispersion, and preferred examples thereof include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic acid ester copolymers, styrene-acrylic resins such as styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, and styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers, styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, vinylnaphthalene-acrylic acid copolymers, and salts of the aqueous resins, which do not fall under the above-mentioned components.

Examples of solvents other than water include alcohol solvents such as methanol, ethanol, n-propanol, and isopropanol; ketone solvents such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycol; and lactam solvents such as N-methyl-2-pyrrolidone.

Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, and among these, anionic surfactants and nonionic surfactants are preferred.

Examples of anionic surfactants include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfate ester salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate ester salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, and polyoxyethylene alkyl ether phosphates. Specific examples of these include dodecylbenzenesulfonates, isopropylnaphthalenesulfonates, monobutylphenylphenol monosulfonates, monobutylbiphenylsulfonates, and dibutylphenylphenol disulfonates.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylol amides, alkyl alkanol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, polyethylene glycol polypropylene glycol block copolymers, and alkylphenol ethoxylates. Among these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, polyethylene glycol polypropylene glycol block copolymers, and alkylphenol ethoxylates are preferred.

Other surfactants that can be used include silicon-based surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; and biosurfactants such as spiculisporic acid, rhamnolipids, and lysolecithin.

These surfactants can be used alone or in combination of two or more. In consideration of the dissolution stability of the surfactant, it is preferable that the HLB is in the range of 7 to 20.

Commercially available fluorine-based surfactants include Novec FC-4430, FC-4432 (all manufactured by Sumitomo 3M), Zonyl FSO-100, FSN-100, FS-300, FSO (all manufactured by DuPont), EF-TOP EF-122A, EF-351, 352801, 802 (manufactured by Gemco), Megafac F-470, F-1405, F474, F-444 (manufactured by DIC), Surflon S-111, S-112, S-113, S These include 121, S131, S132, S-141, S-145 (manufactured by Asahi Glass), Ftergent series (manufactured by Neos), Fluorad FC series (manufactured by Minnesota Mining and Manufacturing Company), Monflor (manufactured by Imperial Chemical Industries), and Licowet VPF series (manufactured by Farbewerke Hoechst).

Examples of silicone surfactants include KF-351A, KF-642, Olfin PD-501, Olfin PD-502, Olfin PD-570 (manufactured by Shin-Etsu Chemical Co., Ltd.), BYK347, and BYK348 (manufactured by BYK Japan).

Examples of polyoxyethylene alkyl ether surfactants include the BT series (Nikko Chemicals), the Nonipol series (Sanyo Chemical), the D- and P-series (Takemoto Oil & Fat), the EMALEX DAPE series (Nippon Emulsion), and the Pegnol series (Toho Chemical Industry). Examples of polyethylene glycol alkyl ester surfactants include Pegnol (Toho Chemical Industry).

Examples of acetylene glycol surfactants include Olfin E1010, STG, and Y (all manufactured by Nissin Chemical Co., Ltd.), and Surfynol 104, 82, 420, 440, 465, 485, and TG (manufactured by Air Products and Chemicals Inc.).

Examples of waxes include plant and animal waxes such as carnauba wax, candelilla wax, beeswax, rice wax, and lanolin; mineral waxes such as montan wax and ozokerite; paraffin wax, a so-called petroleum wax; and synthetic waxes such as carbon wax, Hoechst wax, polyolefin wax, silicone wax, and stearic acid amide, as well as natural and synthetic wax emulsions and blended waxes such as α-olefin-maleic anhydride copolymers. These waxes have the effect of imparting slip properties to the surface of the formed recording material and improving abrasion resistance. These waxes can be used alone or in combination. Of these, silicone wax, polyolefin wax, and paraffin wax are preferably used.

Commercially available silicone waxes include, for example, SM8706EX, SM7036EX, SM7060EX, SM7025EX, SM490EX, SM8701EX, SM8709SR, SM8716SR, IE-7045, IE-7046T, SH7024, BY22-744EX, BY22-818EX, FZ-4658, FZ-4634EX, FZ-4602 (all trade names, manufactured by Dow Corning Toray Co., Ltd.), POLON-MF-14, POLON-MF-14EC, and POLON-MF-2. 3POLON-MF-63, POLON-MF-18T, POLON-MF-56, POLON-MF-49, POLON-MF-33A, POLON-MF-55T, POLON-MF-28T, POLONMF-50, POLON-MK-206, POLON-SR-CONC, KM-9771, KM-9774, KM-2002-T, KM-2002-L-1, KM-9772, KS-7002, KS-701, X-51-1264 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), etc.

Examples of polyolefin waxes include waxes and copolymers thereof made from olefins such as ethylene, propylene, and butylene or their derivatives, specifically, polyethylene-based waxes, polypropylene-based waxes, polybutylene-based waxes, and the like. Polyolefin waxes can be used alone or in combination of two or more. Among these, polyethylene-based waxes are preferred from the viewpoint of being less likely to react with the crosslinkable groups of the urethane resin particles having the above-mentioned crosslinkable groups and being excellent in ejection stability.

Commercially available polyolefin waxes include, for example, the AQUACER series, such as AQUACER 513 (polyethylene wax, average particle size 100 nm to 200 nm, melting point 130°C, solid content 30%), AQUACER 507, AQUACER 515, AQUACER 840, and AQUACER 1547 (all trade names, manufactured by BYK Japan Co., Ltd.), and Hi-Tech E-7025P, Hi-Tech E- Examples include the Hitech series, such as Hitech E-6213, Hitech E-6500, Hitech E-6314, Hitech E-9460, Hitech E-9015, Hitech E-4A, Hitech E-5403P, and Hitech E-8237 (all trade names, manufactured by Toho Chemical Industry Co., Ltd., polyethylene wax); Nopcoat PEM-17 (trade name, manufactured by San Nopco Ltd., polyethylene emulsion, average particle size 40 nm); and ULTRALUBE E-843N (trade name, manufactured by Keim Additec Surface GmbH, polyethylene wax).

Paraffin wax is a type of petroleum wax. Here, paraffin refers to an alkane with 20 or more carbon atoms, and paraffin wax refers to a mixture of hydrocarbons with a molecular weight of about 300 to 500, mainly consisting of straight-chain paraffinic hydrocarbons with 20 to 30 carbon atoms, and containing a small amount of isoparaffin. When the ink contains paraffin wax, it gives the recorded material slip properties and water repellency, which improves abrasion resistance.

Commercially available paraffin wax products include, for example, AQUACER 537 and AQUACER 539 (both trade names, manufactured by BYK Japan Co., Ltd.).

It is preferable that the wax is contained in the pigment dispersion in a fine particle state, that is, in an emulsion state or a suspension state. This makes it easier to adjust the viscosity of the ink to an appropriate range for ejection using an inkjet head, and also makes it easier to ensure ejection stability and intermittent ejection characteristics during recording.

Examples of low surface tension organic solvents include glycol ether compounds such as diethylene glycol mono (alkyl having 1 to 8 carbon atoms) ether, triethylene glycol mono (alkyl having 1 to 8 carbon atoms) ether, propylene glycol mono (alkyl having 1 to 6 carbon atoms) ether, and dipropylene glycol mono (alkyl having 1 to 6 carbon atoms) ether, which can be used alone or in a mixture of two or more kinds.

Specifically, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monot-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monot-butyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, diethylene glycol monooctyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol Examples of the ethylene glycol monopentyl ether include triethylene glycol monohexyl ether, triethylene glycol monoheptyl ether, triethylene glycol monooctyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol mono-isopropyl ether, propylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopentyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono-isopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopentyl ether, and dipropylene glycol monohexyl ether.

Glycol ethers, surfactants, etc. can be used to adjust the surface tension of the ink. Specifically, they can be added appropriately so that the surface tension of the ink is 15 mN/m to 30 mN/m or less, and the amount of surfactant added is preferably in the range of about 0.1 to 10 mass% of the aqueous pigment dispersion, more preferably 0.3 to 2 mass%. It is even more preferable for the surface tension to be in the range of 16 to 28, and most preferably in the range of 18 to 25.

The wetting agent is not particularly limited, but is preferably one that is miscible with water and has an effect of preventing clogging of the inkjet printer head. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,2-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methylpentane-2,4-diol, and the like. Examples of suitable inks include diol compounds such as 1,2-heptanediol, 1,2-nonanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-nonanediol, and 1,2-octanediol, and nitrogen-containing heterocyclic compounds such as 1,4-butanediol, 1,3-butanediol, mesoerythritol, pentaerythritol, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, and ε-caprolactam. Among these, inks containing propylene glycol and 1,3-butyl glycol are safe and have excellent effects on ink drying properties and ejection performance.
The content of the wetting agent in the ink is preferably 3 to 50% by mass.

Examples of penetrating agents include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether. The content of the penetrating agent in the pigment dispersion is preferably 0.01 to 10% by mass.

<Method of producing pigment dispersion>
The method for producing the pigment dispersion in the present invention is not limited in any way.
The pigment dispersion may be prepared by dispersing components (A) to (D) and optional components such as component (E) that are added as necessary, or a pigment dispersion millbase liquid having a high pigment concentration may be prepared in advance using a portion of components (A), (C) and (D) excluding component (B) or a medium, and then component (B) and optional components are added as appropriate, and the pigment dispersion for preparing an aqueous inkjet ink may be prepared by diluting with an aqueous medium such as component (D). By preparing a pigment dispersion after dispersing the pigment using a stirring/dispersing device to prepare a pigment dispersion millbase liquid in advance, an aqueous pigment dispersion in which the pigment is dispersed with a desired volume average particle size can be easily obtained.
Hereinafter, the latter method of preparing a pigment dispersion mill base liquid and then converting it into a pigment dispersion will be described.

The following method can be used to produce the pigment dispersion millbase.
(1) A method of preparing a pigment dispersion millbase by adding a pigment to an aqueous medium, optionally containing a pigment dispersant, and then dispersing the pigment in the aqueous medium using a stirring and dispersing device.
(2) A method in which a pigment and, if necessary, a pigment dispersant are kneaded using a kneading machine such as a two-roll mill or a mixer, the resulting kneaded mixture is added to an aqueous medium, and a pigment dispersion millbase is prepared using a stirring and dispersing device.
(3) A method in which a pigment dispersant is dissolved in an organic solvent compatible with water, such as methyl ethyl ketone or tetrahydrofuran, and a pigment is added to the resulting solution, the pigment is dispersed in the organic solution using a stirring/dispersing device, and then an aqueous medium is used to effect phase inversion emulsification, after which the organic solvent is distilled off to prepare a pigment dispersion millbase.

Examples of stirring/dispersing devices include ultrasonic homogenizers, high-pressure homogenizers, paint shakers, ball mills, roll mills, sand mills, sand grinders, Dyno Mills, Dispermats, SC Mills, Nanomizers, etc., and any one of these may be used alone or two or more types of devices may be used in combination.

<Inkjet ink>
The pigment dispersion of the present invention is used and diluted with an aqueous medium so that the pigment content is 1 to 30% by mass to prepare an aqueous inkjet ink. This aqueous medium may be water, as with component (D), a mixture of water and an organic solvent, or an organic solvent only. There are no particular restrictions on the organic solvent as long as it is miscible with water, and examples of the organic solvent include those mentioned above as optional components for "solvents other than water."

<Printed materials>
Since the inkjet ink of the present invention has excellent adhesion to various substrates, it is possible to suitably produce a printed item having a plastic substrate and a printed layer formed by the inkjet ink.

Examples of plastic substrates include polyamide resins such as Ny6, nylon 66, and nylon 46; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate; biodegradable resins such as polyhydroxycarboxylic acids such as polylactic acid, aliphatic polyester resins such as poly(ethylene succinate) and poly(butylene succinate); polyolefin resins such as polypropylene and polyethylene, polyimide resins, polyarylate resins, and mixtures thereof; and plastic substrates and laminates thereof made of thermoplastic resins. Among these, substrates made of polyester, polyamide, polyethylene, and polypropylene are preferably used.

The plastic substrate may be a plastic film. The plastic film may be an unstretched film or a stretched film, and the manufacturing method is not limited. The thickness of the film is not particularly limited, but is usually in the range of 1 to 500 μm.
The printed surface of the film is preferably subjected to a corona discharge treatment, and silica, alumina, etc. may be vapor-deposited on the printed surface.

The printed matter of the present invention has good adhesion to plastic substrates and can be produced by inkjet printing, making it suitable for use as a packaging material. In particular, it has excellent design properties and on-demand printability, making it particularly suitable for use in food packaging. In addition, since the inkjet ink of the present invention has excellent abrasion resistance, the printed matter of the present invention can also be made into a surface-printed printed matter in which inkjet printing is performed on the surface that will become the surface.

The present invention will be specifically explained below with reference to examples and comparative examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[Synthesis Example of Dispersion]
(Synthesis Example 1: Synthesis Example of Styrene Acrylic Resin 1)
600 parts of methyl ethyl ketone was charged into the reaction vessel of an automatic polymerization reactor (polymerization tester DSL-2A S type, manufactured by Todoroki Sangyo Co., Ltd.) having a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introduction device at the top, and the inside of the reaction vessel was replaced with nitrogen while stirring. After the temperature inside the reaction vessel was raised to 80 ° C. while maintaining a nitrogen atmosphere, a mixture of 160 parts of styrene, 80 parts of α-methylstyrene, 124 parts of acrylic acid, 36 parts of Blenmar PME-100 (manufactured by NOF Corp.), and 44 parts of "Perbutyl O" (active ingredient peroxy 2-ethylhexanoate t-butyl, manufactured by Nippon Oil & Fats Co., Ltd.) was dropped over 4 hours from the dropping device. After the end of the dropping, the reaction was continued for another 15 hours at the same temperature to obtain a methyl ethyl ketone solution of styrene acrylic resin.
To the methyl ethyl ketone solution of the styrene-acrylic resin obtained above, 83 parts of 28% aqueous ammonia and 550 parts of ion-exchanged water were gradually added as neutralizing agents to neutralize the carboxyl groups in the styrene-acrylic resin, and then the methyl ethyl ketone was distilled off under reduced pressure to obtain a styrene-acrylic resin 1 having a non-volatile content of 40% by mass. The acid value of this styrene-acrylic resin 1 was 240 mgKOH/g and the glass transition temperature was 91° C.

(Synthesis Examples 2 to 5: Synthesis Examples of Styrene Acrylic Resins 2 to 5)
Styrene-acrylic resins 2 to 5 were obtained in the same manner as in Synthesis Example 1 except that the monomer composition and neutralizing agent were changed according to Table 1.
In the table below, Blemmer PME-100 is methoxypolyethylene glycol monomethacrylate (manufactured by NOF Corporation).

[Synthesis example of binder resin]
(Synthesis Example 6: Synthesis Example of Water-Based Polyurethane 1)
In a nitrogen-substituted vessel equipped with a thermometer, a nitrogen gas inlet tube, and a stirrer, 964 parts by mass of 1,6-hexanediol-based polycarbonate diol (weight average molecular weight: 2,000), 43 parts by mass of dimethylolpropionic acid, and 558 parts by mass of methyl ethyl ketone were added and mixed uniformly. Next, 295 parts by mass of dicyclohexylmethane diisocyanate was added, followed by 0.05 parts by mass of tin dioctylate, and the mixture was reacted at 70° C. for about 4 hours to obtain a methyl ethyl ketone solution of urethane prepolymer 1 having an isocyanate group at the molecular end.
33 parts by mass of triethylamine was added to the methyl ethyl ketone solution of urethane prepolymer 1 obtained above to neutralize the carboxyl groups in the urethane prepolymer 1, and then 2,516 parts by mass of ion-exchanged water was gradually added. Next, 11.0 parts by mass of an 80% aqueous hydrazine solution was added and reacted. After completion of the reaction, the methyl ethyl ketone was distilled off under reduced pressure to obtain an aqueous polyurethane 1 having a non-volatile content of 40% by mass. This aqueous polyurethane 1 had a volume average particle size of 98 nm, an acid value of 10 mgKOH/g, and a glass transition temperature of -29°C.

[Production Example of Mill Dispersion 1]
In a mixing tank, 250 parts of styrene acrylic resin 1 as a dispersion resin, 55 parts of isopropyl alcohol, 710 parts of ion-exchanged water, and 500 parts of FASTOGEN BLUE SBG-SD (pigment blue 15:3, manufactured by DIC Corporation) were charged and mixed with a disperser (TK Homo Disper 20 type, manufactured by Tokushu Kika Kogyo Co., Ltd.). The resulting mixture was circulated and dispersed (a method in which the dispersion liquid discharged from the dispersion device is returned to the mixing tank) using a dispersion device filled with zirconia beads having a diameter of 0.3 mm (Pico Mill, model: PCM-LR, manufactured by Asada Iron Works Co., Ltd.). During the dispersion process, the dispersion temperature was controlled to be kept below 30 ° C. by passing cold water through the cooling jacket, and the rotor peripheral speed of the dispersion device was fixed at 12 m / sec to disperse for 2 hours. After the dispersion was completed, the stock dispersion liquid was extracted from the mixing tank and distilled under reduced pressure to remove the isopropyl alcohol and a portion of the water, thereby obtaining Mill Dispersion 1 (pigment concentration 33%).

[Production Examples of Mill Dispersions 2 to 5]
Mill Dispersions 2 to 5 were obtained in the same manner as above, except that the dispersing resin of Mill Dispersion 1 was changed to styrene acrylic resins 2 to 5, respectively.

[Example 1: Production Example of Pigment Dispersion 1]
45 parts of mill dispersion 1, 24.5 parts of ME-2039 (manufactured by Seiko PMC Corporation, crosslinked acrylic emulsion, volume average particle size 63 nm, acid value 42 mg KOH/g, glass transition temperature 8°C, non-volatile content 49%) as a binder, 3.9 parts of ULTRALUBE E-843N (manufactured by keim additec surface GmbH, polyethylene wax) as a wax, 0.2 parts of Proxel GXL (S) (manufactured by Lonza Japan Co., Ltd.) as a preservative, and 26.4 parts of ion-exchanged water were charged and stirred for 30 minutes with a paint shaker (Toyo Seiki Seisakusho Co., Ltd., amplitude 750/min) to obtain pigment dispersion 1 having a pigment content of 15% by mass.

[Examples 2 to 4 and Comparative Examples 1 to 7: Production Examples of Pigment Dispersions]
Pigment dispersions 2 to 4 (Examples 2 to 4) and comparative dispersions 1 to 7 (Comparative Examples 1 to 7) were obtained in the same manner as above, except that the formulation of Example 1 was changed according to Tables 2 and 3.

The component names used in the above table are as follows:
M-141: Seiko PMC Corporation, non-crosslinked acrylic emulsion, volume average particle size 71 nm, acid value 19 KOHmg/g, glass transition temperature 15°C, non-volatile content 40%
QE-1042: Seiko PMC Corporation, non-crosslinked acrylic emulsion, volume average particle size 31 nm, acid value 33 KOHmg/g, glass transition temperature 53°C, non-volatile content 40%

[Examples 5 to 8 and Comparative Examples 8 to 14: Production Examples of Ink Compositions]
Using the pigment dispersions 1 to 4 and comparative dispersions 1 to 7 obtained above, respectively, the compositions shown in Tables 4 to 5 below were formulated and stirred for 30 minutes with a paint shaker to produce ink compositions 1 to 4 (Examples 5 to 8) and comparative ink compositions 1 to 7 (Comparative Examples 8 to 14).
Using the ink composition of each example obtained, printed matter for evaluation was prepared, and the blocking resistance, adhesion to substrate, scratch resistance, and nozzle clogging were evaluated. The evaluation results are shown in Tables 4 and 5. The method for preparing the printed matter for evaluation and the method for evaluating it will be described in detail later.

<Preparation of printed matter for evaluation>
The ink composition was filled into an ink cartridge of an inkjet printer (MJ-510C, manufactured by Seiko Epson Corporation), and a solid pattern was printed on a corona-treated polyethylene terephthalate (PET) film (Ester E5100, manufactured by Toyobo Co., Ltd., thickness 12 μm) or a corona-treated biaxially stretched polypropylene (OPP) film (Pylen P2161, manufactured by Toyobo Co., Ltd., thickness 20 μm). The film was then dried with a dryer and further dried in an oven at 90° C. for 10 minutes to obtain a print.

<Blocking resistance>
The film was cut to a size of 4 cm x 4 cm so that the printed and non-printed surfaces of the PET film prints were in contact, and then the films were overlapped. A load of 5 kgf/cm2 was applied and the film was left in an environment of 50°C for 24 hours. After that, the state of ink transfer (set-off) to the non-printed side when the film was peeled off was visually judged based on the area ratio (%) of the set-off area.
⊚: No transfer to the non-printed surface was observed.
◯: Transfer due to offset is observed, although only slightly, less than 5%.
Δ: Transfer due to offset of 5% or more and less than 20% is observed.
x: Transfer due to offset of 20% or more is observed.

<Abrasion resistance>
The abrasion resistance of OPP film prints was evaluated using a Gakushin-type abrasion fastness tester (AB-301, manufactured by Tester Sangyo Co., Ltd.) in accordance with JIS K5701-1:2000. The prints were set in the tester, and the dry abrasion test was performed using PPC paper as the abrasion paper, a load of 200 g, and 100 reciprocations, while the wet abrasion test was performed using Kanakin No. 3 paper moistened with ion-exchanged water as the abrasion paper, a load of 200 g, and 10 reciprocations. After the test, the degree of ink peeling from the prints was visually evaluated according to the following evaluation criteria.
⊚: No peeling occurred at all.
A: Less than 1% peeling occurred.
Δ: Peeling occurred at 1% or more and less than 5%.
x: Peeling occurred in 5% or more and less than 10%.

<Adhesion to substrate>
After leaving the print for one day, cellophane tape (12 mm width, manufactured by Nichiban) was applied to the printed surface, and one end of the cellophane tape was quickly peeled off in a direction perpendicular to the printed surface. The remaining rate of the printed film was visually evaluated based on the area ratio and the appearance.
⊚: The printing film does not peel off at all.
◯: 80% or more but less than 90% of the printed film remained on the film.
Δ: 50% or more but less than 80% of the printed film remained on the film.
x: Less than 50% of the printed film remained on the film.

<Evaluation of ink ejection properties>
After printing the equivalent of 10 A4 solid sheets using the above-mentioned inkjet printing procedure, a check pattern was printed and the non-ejecting nozzles were evaluated according to the following criteria.
A: Less than 1% of non-ejecting nozzles B: 1% or more but less than 3% or less than 5% of non-ejecting nozzles C: 3% or more but less than 5% of non-ejecting nozzles D: 5% or more of non-ejecting nozzles

As is clear from the above results, it was confirmed that the inkjet inks of Examples 5 to 8, which used the pigment dispersions of Examples 1 to 4 according to the present invention, were excellent in all of adhesion to plastic substrates, blocking resistance, ink ejection properties, and abrasion resistance.
On the other hand, the ink-jet inks of Comparative Examples 8 to 14, which used the comparative dispersions of Comparative Examples 1 to 7, were inferior in any of the above characteristics.
Therefore, it was confirmed that the inkjet pigment dispersion and inkjet ink of the present invention can be suitably used for inkjet printing. In addition, it was confirmed that the pigment dispersion and ink of the present invention have high substrate adhesion to plastic substrates and are therefore suitable for printing on plastic films for packaging, and that they can also be used for surface printing due to their high abrasion resistance.

Claims (7)

The composition contains a dispersant (A), a binder resin (B), a pigment (C), and water (D),
The dispersant (A) contains at least a resin (A1) having a structural unit (a1) derived from an acid group-containing monomer,
In the resin (A1), a part or all of the acid groups in the structural unit (a1) are neutralized with ammonia,
The binder (B) contains a crosslinked acrylic resin (B1) ,
The crosslinked acrylic resin (B1) has an acid value of 5 to 50 mgKOH/g;
A pigment dispersion for inkjet use, characterized in that the binder (B) is contained in an amount of 10 to 30 mass % calculated as non-volatile content . The pigment dispersion for inkjet according to claim 1, wherein the glass transition temperature of the dispersant (A) is 50 to 120°C and the acid value is 100 to 300 mgKOH/g. 3. The pigment dispersion for inkjet according to claim 1, wherein the crosslinked acrylic resin (B1) is an acrylic emulsion having a volume average particle size of 20 to 100 nm and a glass transition temperature of 0 to 70 ° C. The pigment dispersion for inkjet according to any one of claims 1 to 3 further contains an amine compound (E) having a boiling point of 100°C or higher. The inkjet pigment dispersion according to any one of claims 1 to 4, which is for printing on a plastic substrate. An inkjet ink using the inkjet pigment dispersion according to any one of claims 1 to 5. A printed matter printed with the inkjet ink according to claim 6.