Aqueous dispersion of acrylic resin particles containing pigment

Abstract

To provide an aqueous dispersion of acrylic resin particles containing a pigment which is excellent in base material adhesion (resistance against tape peelability) of an ink coating film of obtained printed matter when being used for printing a hydrophobic and non-absorbing resin film, and aqueous ink containing the aqueous dispersion.SOLUTION: There are provided [1] an aqueous dispersion of acrylic resin particles containing a pigment, wherein an acrylic resin A constituting the acrylic resin particles includes a structural unit derived from a (meth)acrylic acid (a-1), a structural unit derived from cycloalkyl acrylate (a-2) and a structural unit derived from alkyl (meth)acrylate (a-3) having a glass transition temperature (Tg) when being converted into a single polymer of 10°C or lower, and [2] aqueous ink containing an aqueous dispersion of acrylic resin particles containing a pigment described in [1], and a water-soluble organic solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous dispersion of acrylic resin particles containing a pigment, and an aqueous ink containing the aqueous dispersion. [Background technology]

[0002] Inkjet printing is a method of printing that uses fine nozzles to eject ink droplets, which are then directly applied to a printing substrate to produce printed materials with recorded text and images. This method has become widespread due to its numerous advantages, including ease and low cost of full-color printing, the ability to use various printing substrates such as plain paper, label paper, and resin film, and its non-contact nature. In particular, from the perspective of weather resistance and water resistance of printed materials, methods using pigments as colorants are becoming mainstream.

[0003] For example, Patent Document 1 discloses an inkjet recording ink that provides both high color development on plain paper and glossy paper and high gloss on glossy paper, and contains a carbon black pigment dispersed using a polymer in which water, at least 50% by weight or more of benzyl acrylate or cyclohexyl acrylate or a mixture thereof as polymer components, and 15% by weight or less of (meth)acrylic acid are polymerized, the acid value is 50 mg KOH / g or more and 120 mg KOH / g or less, and the weight-average molecular weight is 20,000 or more and 120,000 or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-222944 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, in the industrial printing market, such as for printing packaging for food products, resin films are mainly used as printing substrates from the standpoint of durability. A unique challenge when using resin films as printing substrates is the adhesion of the ink coating of the resulting printed material to the substrate, particularly its resistance to tape peeling. If the tape peeling resistance of the ink coating of the printed material is insufficient, the ink coating will easily peel off the resin film, impairing the aesthetic appearance of the printed material and reducing the shelf life of the contents of food products, etc. Therefore, there is a need to improve the substrate adhesion (tape peeling resistance) of the ink coating of printed materials obtained when printing on resin films. In particular, when printing on resin films using water-based inks, it is necessary for the ink coating formed by the water-based ink to adhere sufficiently to the resin film. However, when the inkjet recording ink described in Patent Document 1 was used for printing on a hydrophobic and non-absorbent resin film, it was found that the adhesion (tape peel resistance) of the ink coating on the resulting printed material to the substrate was insufficient. The present invention aims to provide an aqueous dispersion of pigment-containing acrylic resin particles, and an aqueous ink containing the aqueous dispersion, which exhibits excellent substrate adhesion (tape peel resistance) of the ink coating of the resulting printed material when used for printing on hydrophobic and non-absorbent resin films. [Means for solving the problem]

[0006] The inventors have found that the above problem can be solved by providing an aqueous dispersion of acrylic resin particles containing a pigment, wherein the acrylic resin constituting the acrylic resin particles includes constituent units derived from (meth)acrylic acid, constituent units derived from cycloalkyl acrylate, and constituent units derived from alkyl (meth)acrylate whose glass transition temperature (Tg) when formed into a homopolymer is below a specific value. In other words, the present invention provides the following [1] and [2]. [1] An aqueous dispersion of acrylic resin particles containing a pigment, An aqueous dispersion of pigment-containing acrylic resin particles, wherein the acrylic resin A constituting the acrylic resin particles contains constituent units derived from (meth)acrylic acid (a-1), constituent units derived from cycloalkyl acrylate (a-2), and constituent units derived from alkyl (meth)acrylate (a-3) having a glass transition temperature (Tg) of 10°C or less when formed into a homopolymer. [2] An aqueous ink comprising an aqueous dispersion of acrylic resin particles containing the pigment described in [1] above, and a water-soluble organic solvent. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an aqueous dispersion of pigment-containing acrylic resin particles, and an aqueous ink containing the aqueous dispersion, which exhibits excellent substrate adhesion (tape peel resistance) of the ink coating film of the resulting printed material when used for printing on hydrophobic and non-absorbent resin films. [Modes for carrying out the invention]

[0008] [Aqueous dispersion of acrylic resin particles containing pigments] The aqueous dispersion of acrylic resin particles containing the pigment of the present invention (hereinafter also referred to as "pigment-containing acrylic resin particles") (hereinafter also referred to as "aqueous dispersion of the present invention" or "aqueous dispersion") is an aqueous dispersion of acrylic resin particles containing the pigment, wherein the acrylic resin A constituting the acrylic resin particles (hereinafter also referred to as "acrylic resin A") includes constituent units derived from (meth)acrylic acid (a-1), constituent units derived from cycloalkyl acrylate (a-2), and constituent units derived from alkyl (meth)acrylate (a-3) whose glass transition temperature (Tg) when formed into a homopolymer is 10°C or less. In the present invention, the pigment-containing acrylic resin particles are dispersed in an aqueous medium. In this invention, "aqueous system" means that water accounts for the largest proportion by mass in the liquid component. Deionized water, ion-exchanged water, or distilled water are preferably used as the water in the aqueous medium. The aqueous medium may further contain an organic solvent. Examples of such organic solvents include aliphatic alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol; ketones having 3 to 8 carbon atoms such as acetone and methyl ethyl ketone; and ethers such as tetrahydrofuran, which are water-soluble organic solvents. From an environmental standpoint, the water content in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0009] Furthermore, in this invention, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid, and "alkyl (meth)acrylate" refers to alkyl acrylate and / or alkyl methacrylate. In the present invention, "non-absorbent" in the printing substrate means that the amount of water absorbed by the printing substrate during a contact time of 100 milliseconds with pure water is 1 g / m². 2 This means the following: In the context of the present invention, "hydrophobic" in relation to the printing substrate means that the surface free energy (wetting tension) is 45 mN / m or less. The surface free energy (wetting tension) of the printing substrate is measured using a wetting tension test mixture (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in accordance with the wetting tension test method of JIS K6768. In this invention, "substrate adhesion" refers to the tape-peel resistance of the ink coating of a printed material obtained when used for printing on a hydrophobic and non-absorbent resin film, and may be simply referred to as "substrate adhesion."

[0010] According to the present invention, it is possible to provide an aqueous dispersion of pigment-containing acrylic resin particles, and an aqueous ink containing the aqueous dispersion, which exhibits excellent substrate adhesion (tape peel resistance) of the ink coating of the resulting printed material when used for printing on hydrophobic and non-absorbent resin films. The reason for this is not entirely clear, but it is thought to be as follows. The aqueous dispersion of the present invention comprises pigment-containing acrylic resin particles dispersed in an aqueous medium, and the acrylic resin constituting the pigment-containing acrylic resin particles contains constituent units derived from cycloalkyl acrylate. The cycloalkyl ester moiety of this cycloalkyl acrylate has a polarity close to that of the polar functional groups present on the surface of the resin film used as a printing substrate, which is thought to improve the wettability of the aqueous dispersion of the present invention to the resin film when used in an aqueous ink. Furthermore, hydrogen bonds are formed between the polar functional groups and the cycloalkyl ester moiety, and van der Waals interactions can be efficiently expressed between the hydrophobic moiety of the resin film and the cycloalkyl moiety of the cycloalkyl acrylate and the main chain of the acrylic resin containing the constituent units derived from the cycloalkyl acrylate, which is thought to improve the substrate adhesion of the ink coating to the resin film. Furthermore, the alkyl (meth)acrylate-derived structural units contained in the acrylic resin, which have a glass transition temperature (Tg) of 10°C or less when formed into a homopolymer, contribute to increasing the conformational freedom of the cycloalkyl acrylate so that it can strongly interact with the resin film, thereby efficiently enabling strong interactions. In addition, these alkyl (meth)acrylate-derived structural units have the effect of plasticizing the acrylic resin and lowering its glass transition temperature, and also have the effect of easing the stress when the ink coating peels off the printing substrate, thus further improving the adhesion of the ink coating to the resin film.

[0011] <Acrylic resin particles containing pigments> The forms of pigment-containing acrylic resin particles in the aqueous dispersion of the present invention include a form in which acrylic resin A encapsulates the pigment, a form in which the pigment is uniformly dispersed in acrylic resin A, a form in which the pigment is exposed from the surface of the acrylic resin A particles, a form in which acrylic resin A is adsorbed onto the pigment, and mixtures thereof.

[0012] (Pigment) The pigment constituting the pigment-containing acrylic resin particles according to the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferable for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. For white inks, examples include metal oxides such as titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. 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. For achromatic inks, achromatic pigments such as white, black and gray can be used, and for chromatic inks, chromatic pigments such as yellow, magenta, cyan, red, blue, orange and green can be used. The pigments may be used alone or in combination of two or more.

[0013] (Acrylic resin A) Acrylic resin A, which constitutes the pigment-containing acrylic resin particles according to the present invention, comprises, from the viewpoint of improving adhesion to substrates, a structural unit derived from (meth)acrylic acid (a-1), a structural unit derived from cycloalkyl acrylate (a-2), and a structural unit derived from an alkyl (meth)acrylate (a-3) whose homopolymer has a glass transition temperature (Tg) of 10° C. or lower. The above monomers (a-1) to (a-3) may each use the monomer included in each component alone or in combination of two or more.

[0014] [(Meth)acrylic acid (a-1)] (Meth)acrylic acid (a-1) is at least one selected from the group consisting of acrylic acid and methacrylic acid from the viewpoint of improving adhesion to substrates, and is preferably acrylic acid.

[0015] [Cycloalkyl acrylate (a-2)] From the viewpoint of improving adhesion to the substrate, the number of carbon atoms in the cycloalkyl group of cycloalkyl acrylate (a-2) is preferably 4 or more, more preferably 5 or more, and preferably 12 or less, more preferably 8 or less, and even more preferably 7 or less. From the viewpoint of improving substrate adhesion, the cycloalkyl acrylate is preferably one or more selected from the group consisting of cyclopentyl acrylate, cyclohexyl acrylate, and cycloheptyl acrylate, and from the viewpoint of availability and economic efficiency, cyclohexyl acrylate is more preferred.

[0016] [Alkyl (meth)acrylate (a-3)] Alkyl (meth)acrylates (hereinafter also referred to as "alkyl (meth)acrylate (a-3)") having a glass transition temperature (Tg) of 10°C or less when formed into a homopolymer are preferably alkyl (meth)acrylates having an alkyl group with 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, from the viewpoint of improving adhesion to the substrate. Specific examples include one or more selected from the group consisting of methyl acrylate (Tg: 8°C), ethyl acrylate (Tg: -20°C), propyl acrylate (Tg: 3°C), isopropyl acrylate (Tg: -3°C), butyl acrylate (Tg: -55°C), isobutyl acrylate (Tg: -33°C), isopentyl acrylate (Tg: -45°C), hexyl acrylate (Tg: -57°C), octyl acrylate (Tg: -65°C), 2-ethylhexyl acrylate (Tg: -70°C), and benzyl acrylate (Tg: 6°C). Among these, from the viewpoint of improving substrate adhesion, it is more preferable to have one or more selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, and benzyl acrylate, and even more preferably one or more selected from the group consisting of butyl acrylate and isobutyl acrylate. The numbers in parentheses above indicate the glass transition temperature (Tg) when each monomer is formed into a homopolymer. For example, the values ​​listed in the Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used as the glass transition temperature (Tg) for the homopolymers of each monomer.

[0017] Acrylic resin A may contain constituent units derived from other monomers other than monomers (a-1) to (a-3), as long as they do not impede the effects of the present invention. Examples of other monomers include ionic monomers other than monomers (a-1) to (a-3), hydrophobic monomers having aromatic groups, and nonionic monomers.

[0018] (Content of each constituent unit in acrylic resin A) The content of (meth)acrylic acid (a-1) in the raw material monomers constituting acrylic resin A, or the content of constituent units derived from (meth)acrylic acid (a-1) in all constituent units of acrylic resin A, is preferably 13% by mass or more, more preferably 17% by mass or more, even more preferably 23% by mass or more, and preferably 35% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of improving adhesion to the substrate. The content of cycloalkyl acrylate (a-2) in the raw material monomer constituting acrylic resin A, or the content of cycloalkyl acrylate (a-2)-derived constituent units in all constituent units of acrylic resin A, is preferably 25% by mass or more, more preferably 35% by mass or more, even more preferably 45% by mass or more, even more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. The content of alkyl(meth)acrylate(a-3) in the raw material monomer constituting acrylic resin A, or the content of alkyl(meth)acrylate(a-3)-derived constituent units in all constituent units of acrylic resin A, is preferably 0.5% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 17% by mass or more, and preferably 50% by mass or less, more preferably 47% by mass or less, and even more preferably 45% by mass or less.

[0019] The mass ratio of alkyl (meth)acrylate (a-3) content to cycloalkyl acrylate (a-2) content in the raw material monomers constituting acrylic resin A, or the mass ratio of alkyl (meth)acrylate (a-3) content to cycloalkyl acrylate (a-2) content in all constituent units of acrylic resin A [alkyl (meth)acrylate (a-3) / cycloalkyl acrylate (a-2)], is preferably 0.01 or higher, more preferably 0.03 or higher, and even more preferably 0.05 or higher, and from the same viewpoint as above, preferably 1 or lower, more preferably 0.95 or lower, and even more preferably 0.90 or lower.

[0020] Acrylic resin A can be produced by copolymerizing raw material monomers, including the monomers (a-1) to (a-3), etc., using a known polymerization method. The weight-average molecular weight of acrylic resin A is preferably 7,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less, from the viewpoint of improving adhesion to the substrate. From the viewpoint of improving adhesion to the substrate, the acid value of acrylic resin A is preferably 100 mg KOH / g or more, more preferably 140 mg KOH / g or more, even more preferably 180 mg KOH / g or more, and preferably 260 mg KOH / g or less, more preferably 240 mg KOH / g or less, and even more preferably 220 mg KOH / g or less. The weight-average molecular weight and acid value of acrylic resin A are measured by the method described in the examples.

[0021] The glass transition temperature (Tg) of acrylic resin A is preferably -20°C or higher, more preferably -10°C or higher, even more preferably 0°C or higher, and preferably 50°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower, and even more preferably 35°C or lower, from the viewpoint of improving adhesion to the substrate. The glass transition temperature of acrylic resin A, which is a copolymer, can be calculated according to the following Fox equation, based on the mass ratio of each monomer constituting acrylic resin A and the glass transition temperature of the homopolymer when each monomer is made into a homopolymer. 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+···+(W m / Tg m ) W1 + W2 + ...W m =1 In the Fox formula, Tg is the glass transition temperature of acrylic resin A, and Tg1, Tg2, ..., Tg m The glass transition temperature of each monomer when it is used to form a homopolymer is the glass transition temperature of the homopolymer. The unit of temperature is Kelvin (K). Also, W1, W2, ..., W m This represents the mass ratio of each monomer in acrylic resin A. For example, the glass transition temperatures of the homopolymers of each monomer in the Fox equation can be those listed in the Polymer Handbook Third Edition (Wiley-Interscience 1989).

[0022] (Neutralizing agent) It is preferable that the carboxyl groups of acrylic resin A are neutralized with a neutralizing agent. This increases the charge repulsion force of the carboxyl groups that emerge after neutralization, which is thought to suppress aggregation of pigment-containing acrylic resin particles in the aqueous dispersion of the present invention, thereby improving dispersion stability and storage stability. As a neutralizing agent, one or more selected from the group consisting of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds are preferred.

[0023] Among these, it is preferable that the carboxyl group of acrylic resin A is neutralized with an amine compound. The amine compound plasticizes acrylic resin A and lowers the glass transition temperature of the acrylic resin, thereby easing the stress when the ink coating peels off the printing substrate, and thus improving substrate adhesion (tape peel resistance). Suitable examples of amine compounds include inorganic amines and organic amines. A suitable example of an inorganic amine is ammonia. Suitable examples of organic amines include alkylamines, alkanolamines, aminoalkanediols, alkoxyamines, and heterocyclic amines. Examples of alkylamines include ethylamine (boiling point at 1 atmosphere: 16.6°C), diethylamine (55.5°C), triethylamine (89.7°C), n-propylamine (48°C), di-n-propylamine (108°C), isopropylamine (33°C), diisopropylamine (84°C), n-butylamine (78°C), tert-butylamine (44.5°C), sec-butylamine (63°C), n-pentylamine (104°C), n-hexylamine (130°C), N,N-dimethylethylamine (37°C), N,N-diethylmethylamine (62°C), and N,N-dimethylbutylamine (93°C). Examples of alkanolamines include monoethanolamine (same: 170°C), diethanolamine (same: 217°C), triethanolamine (same: 335°C), n-propanolamine (same: 188°C), isopropanolamine (same: 160°C), 2-amino-2-methyl-1-propanol (same: 165°C), N-methylethanolamine (same: 155°C), N-ethylethanolamine (same: 169°C), Nn-butylethanolamine (same: 199°C), and N-methyldiethanolamine (same: 1 Examples include N-(2-aminoethyl)ethanolamine (251°C), N,N-dimethylethanolamine (245°C), N,N-diethylethanolamine (162°C), N,N-dimethylpropanolamine (164°C), N,N-dimethylisopropanolamine (125°C), 2-(dimethylamino)-2-methyl-1-propanol (163°C), N-(2-aminoethyl)ethanolamine (125°C), and 2-(2-aminoethoxy)ethanol (223°C). Examples of aminoalkanediols include 2-amino-1,3-propanediol (temperature: 302°C), 2-amino-2-ethyl-1,3-propanediol (temperature: 294°C), 3-(methylamino)-1,2-propanediol (temperature: 254°C), and 3-(dimethylamino)-1,2-propanediol (temperature: 217°C). Examples of alkoxyamines include 3-methoxypropylamine (at 116°C) and 3-ethoxypropylamine (at 132°C). Examples of heterocyclic amines include pyrrolidine (same: 87°C), piperidine (same: 106°C), piperazine (same: 106°C), 1-(2-hydroxyethyl)piperazine (same: 246°C), and morpholine (same: 129°C).

[0024] The boiling point of the amine compound at 1 atmosphere is preferably 270°C or lower, more preferably 260°C or lower, even more preferably 250°C or lower, and preferably 40°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and even more preferably 120°C or higher, from the viewpoint of improving adhesion to the substrate. When two or more organic amines are used, the boiling points of the organic amines are calculated as a weighted average value.

[0025] Among these, from the viewpoint of improving adhesion to the substrate, the neutralizing agent is more preferably one or more selected from the group consisting of ammonia and organic amines having a boiling point of 250°C or less, even more preferably an organic amine having a boiling point of 250°C or less, and even more preferably an alkanolamine having a boiling point of 250°C or less.

[0026] From the viewpoint of improving adhesion to the substrate, the degree of neutralization of the carboxyl groups in acrylic resin A is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and preferably less than 100 mol%, more preferably 90 mol% or less, even more preferably 70 mol% or less, even more preferably 50 mol% or less, and even more preferably 40 mol% or less. Here, the degree of neutralization can be determined by the following formula (1) as the equivalent amount of neutralizing agent used relative to the carboxyl groups of acrylic resin A. When the equivalent amount of neutralizing agent used is 100 mol% or less, it is synonymous with the degree of neutralization. When the equivalent amount of neutralizing agent used exceeds 100 mol%, it means that the neutralizing agent is in excess relative to the carboxyl groups of acrylic resin A, and in this case, the degree of neutralization of acrylic resin A is considered to be 100 mol%. Amount of neutralizing agent used (mol%) = [{Mass of neutralizing agent added (g) / Equivalent amount of neutralizing agent} / [{Acid value of acrylic resin A (mgKOH / g) × Mass of vinyl polymer (g)} / (56 × 1000)]] × 100 (1)

[0027] (Production of aqueous dispersion of pigment-containing acrylic resin particles) The aqueous dispersion of the present invention can be efficiently produced by a method that includes a step of dispersing a pigment mixture containing a pigment, acrylic resin A, and water (hereinafter also referred to as "step 1"). Step 1 is preferably carried out by dispersing a pigment mixture containing a pigment, acrylic resin A, organic solvent, water, and optionally a neutralizing agent, surfactant, etc., to obtain a pigment dispersion, and then removing the organic solvent from the pigment dispersion by a known method. The dispersion process in step 1 can be carried out by known methods using kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers (manufactured by Microfluidics), paint shakers, bead mills, and other media-type dispersers.

[0028] (Content and physical properties of each component in the aqueous dispersion) From the viewpoint of improving substrate adhesion, the solid content of the aqueous dispersion of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0029] The pigment content in the aqueous dispersion of the present invention is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and preferably 20% by mass or less, more preferably 17% by mass or less, and even more preferably 15% by mass or less, from the viewpoint of printing density.

[0030] The mass ratio of the pigment content to the total content of the pigment and acrylic resin A in the aqueous dispersion of the present invention [pigment / (pigment + acrylic resin A)] is preferably 0.45 or higher, more preferably 0.50 or higher, even more preferably 0.55 or higher, and preferably 0.80 or lower, more preferably 0.75 or lower, even more preferably 0.70 or lower, and even more preferably 0.65 or lower, from the viewpoint of improving adhesion to the substrate.

[0031] From the viewpoint of reducing environmental impact, the water content in the aqueous dispersion of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 93% by mass or less, more preferably 87% by mass or less, and even more preferably 82% by mass or less.

[0032] From the viewpoint of ink storage stability, the average particle size of the pigment-containing acrylic resin particles in the aqueous dispersion of the present invention is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 100 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 130 nm or less. The average particle size of pigment-containing acrylic resin particles in the aqueous dispersion of the present invention is measured by the method described in the examples.

[0033] The aqueous dispersion of the present invention can be suitably used by incorporating it into aqueous inks for various printing applications, such as inkjet printing, flexographic printing, and gravure printing. Among these, it is preferable to use it in aqueous inks for inkjet printing from the viewpoint of ink discharge performance and substrate adhesion.

[0034] [Water-based ink] The water-based ink of the present invention (hereinafter also referred to as "the ink of the present invention") contains an aqueous dispersion of acrylic resin particles containing the pigment and a water-soluble organic solvent.

[0035] <Water-soluble organic solvents> Water-soluble organic solvents are organic solvents that can be mixed with water in any proportion. Water-soluble organic solvents can be used individually or in combination of two or more types. The boiling point of the water-soluble organic solvent is preferably 90°C or higher, more preferably 150°C or higher, even more preferably 180°C or higher, and preferably 260°C or lower, more preferably 250°C or lower, even more preferably 240°C or lower, and even more preferably 230°C or lower. When two or more water-soluble organic solvents are used, the boiling point value is a weighted average value weighted by the content (mass%) of each water-soluble organic solvent. Examples of water-soluble organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, the water-soluble organic solvent preferably includes one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, from the viewpoint of improving adhesion to the substrate.

[0036] Examples of polyhydric alcohols include ethylene glycol, propylene glycol, alkanediols such as 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol; polyalkylene glycols such as diethylene glycol and triethylene glycol; glycerin; and trimethylolpropane. Among these, the polyhydric alcohol is preferably one or more selected from the group consisting of propylene glycol, 1,2-hexanediol, triethylene glycol, and glycerin, and more preferably propylene glycol.

[0037] Examples of polyhydric alcohol ethers include (poly)alkylene glycol monoalkyl ethers such as monoalkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers; and (poly)alkylene glycol dialkyl ethers such as monoalkylene glycol dialkyl ethers and dialkylene glycol dialkyl ethers. The alkylene oxide group of the polyhydric alcohol ether can be one or more selected from the group consisting of ethylene oxide groups and propylene oxide groups, with the ethylene oxide group being more preferred. Polyvalent glycol ethers have at least one hydrocarbon group having 2 to 8 carbon atoms.

[0038] Examples of (poly)alkylene glycol monoalkyl ethers include ethylene glycol monoalkyl ethers such as ethylene glycol monoisopropyl ether (boiling point: 142°C), ethylene glycol mono-n-butyl ether (boiling point: 171°C), ethylene glycol monoisobutyl ether (boiling point: 161°C), and ethylene glycol mono-n-hexyl ether (boiling point: 208°C); diethylene glycol monoethyl ether (boiling point: 202°C), diethylene glycol monoisopropyl ether (boiling point: 207°C), diethylene glycol mono-n-butyl ether (boiling point: 231°C), and diethylene glycol monoisobutyl ether ( Preferably, one or more are selected from the group consisting of diethylene glycol monoalkyl ethers such as diethylene glycol mono-n-hexyl ether (boiling point: 259°C), triethylene glycol monoalkyl ethers such as triethylene glycol monobutyl ether (boiling point: 271°C), propylene glycol monoalkyl ethers such as propylene glycol mono-n-propyl ether (boiling point: 150°C), dipropylene glycol monoalkyl ether, tripropylene glycol monoalkyl ether, and ethylene glycol aryl ethers such as ethylene glycol monobenzyl ether (boiling point: 256°C). Examples of (poly)alkylene glycol dialkyl ethers include diethylene glycol dialkyl ethers such as diethylene glycol methyl ethyl ether (boiling point: 176°C) and diethylene glycol diethyl ether (boiling point: 189°C).

[0039] The water-soluble organic solvent preferably contains one or more selected from diethylene glycol monoalkyl ethers and diethylene glycol dialkyl ethers, more preferably contains diethylene glycol monoalkyl ethers, and even more preferably contains one or more selected from the group consisting of diethylene glycol monoethyl ether (boiling point: 202°C), diethylene glycol monoisopropyl ether (boiling point: 207°C), diethylene glycol mono-n-butyl ether (boiling point: 231°C), diethylene glycol monoisobutyl ether (boiling point: 220°C), and diethylene glycol monohexyl ether (boiling point: 259°C), and even more preferably contains one or more selected from the group consisting of diethylene glycol monoisopropyl ether (boiling point: 207°C), diethylene glycol mono-n-butyl ether (boiling point: 231°C), and diethylene glycol monoisobutyl ether (boiling point: 220°C).

[0040] When the water-soluble organic solvent contains one or more selected from diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether, the total content of diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether in the water-soluble organic solvent is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0041] When the water-soluble organic solvent contains diethylene glycol monoalkyl ether, the content of diethylene glycol monoalkyl ether in the water-soluble organic solvent is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of improving adhesion to the substrate.

[0042] From the viewpoint of improving adhesion to the substrate, the water-soluble organic solvent preferably contains an alkanediol, and more preferably contains one or more selected from diethylene glycol monoalkyl ethers and diethylene glycol dialkyl ethers and an alkanediol. When the water-soluble organic solvent contains one or more selected from diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether and an alkanediol, the mass ratio of the total content of diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether in the ink of the present invention to the content of the alkanediol [total content of diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether / alkanediol content] is preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, and preferably 0.40 or less, more preferably 0.30 or less, even more preferably 0.25 or less, and even more preferably 0.20 or less.

[0043] The ink of the present invention may optionally contain various additives such as fixing resins, surfactants, humectants, wetting agents, wetting / penetrating agents, viscosity modifiers, defoaming agents, preservatives, fungicides, and rust inhibitors. Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants. Among these, nonionic surfactants are preferred. Examples of nonionic surfactants include polyoxyalkylene alkyl ether type surfactants, acetylene glycol type surfactants, polyhydric alcohol type surfactants, fatty acid alkanolamides, silicone type surfactants, and fluorine type surfactants.

[0044] The ink of the present invention can be manufactured by mixing an aqueous dispersion of pigment-containing acrylic resin particles, a water-soluble organic solvent, and, if necessary, various additives such as water and surfactants.

[0045] (Content and physical properties of each component of water-based ink) From the viewpoint of improving adhesion to the substrate, the content of pigment-containing acrylic resin particles in the ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 20% by mass or less, more preferably 17% by mass or less, and even more preferably 15% by mass or less.

[0046] From the viewpoint of printing density, the pigment content in the ink of the present invention is preferably 4.5% by mass or more, more preferably 5.0% by mass or more, even more preferably 5.5% by mass or more, and preferably 8.5% by mass or less, more preferably 8.0% by mass or less, and even more preferably 7.5% by mass or less.

[0047] The mass ratio of the pigment content to the total content of pigment and acrylic resin A in the ink of the present invention [pigment / (pigment + acrylic resin A)] is preferably 0.45 or more, more preferably 0.50 or more, even more preferably 0.55 or more, and preferably less than or equal to, more preferably 0.75 or less, even more preferably 0.70 or less, and even more preferably 0.65 or less.

[0048] From the viewpoint of reducing environmental impact, the water content in the ink of the present invention is preferably 45% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0049] The content of the water-soluble organic solvent in the ink of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0050] If the ink of the present invention contains a surfactant, the surfactant content in the ink is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and preferably 3% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less.

[0051] From the viewpoint of storage stability of the ink, the average particle size of the pigment-containing acrylic resin particles in the ink of the present invention is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 100 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 130 nm or less. The average particle size of the pigment-containing acrylic resin particles in the ink of the present invention is measured by the method described in the examples.

[0052] The viscosity of the ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, and even more preferably 7 mPa·s or less. The viscosity of water-based inks can be measured using an E-type viscometer. The pH of the ink of the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. Furthermore, from the viewpoint of material resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The pH of water-based ink can be measured by conventional methods.

[0053] The ink of the present invention can be used as an ink for various printing applications such as inkjet printing, gravure printing, and flexographic printing, but from the viewpoint of ink ejection performance and substrate adhesion, it is preferable to use it as a water-based ink for inkjet printing. When the aqueous ink of the present invention is used for inkjet printing, the aqueous ink can be loaded into a known inkjet printing apparatus and ejected as ink droplets onto a printing substrate such as a resin film, as described later, to print images and the like. Piezoelectric, thermal, or electrostatic methods can all be used for ejecting the ink droplets.

[0054] From the viewpoint of substrate adhesion, a resin film is preferred as the printing substrate used in printing with the ink of the present invention. In other words, the water-based ink of the present invention is preferably used in printing where a resin film is used as the printing substrate. Examples of resin films include transparent synthetic resin films, such as polyester films like polyethylene terephthalate film; vinyl chloride film; polyolefin films like polypropylene film and polyethylene film; and polyamide films like nylon film. These resin films may be stretched films such as biaxially oriented films and uniaxially oriented films, or unstretched films. Furthermore, it is preferable to use resin films that have undergone surface treatment such as corona discharge treatment, from the viewpoint of imparting polar functional groups to the surface of the resin film to improve the wettability of water-based inks to the resin film and to improve adhesion to the substrate by forming hydrogen bonds between the polar functional groups and the cycloalkyl ester moieties. Among these, resin films with a surface free energy of 45 mN / m or less are preferred, one or more selected from the group consisting of polyester film, stretched polypropylene film, and polyethylene film are more preferred, and one or more selected from the group consisting of corona discharge treated polyethylene terephthalate (PET) film, corona discharge treated biaxially oriented polypropylene (OPP) film, and corona discharge treated polyethylene (PE) film are even more preferred. [Examples]

[0055] In the following manufacturing examples, embodiments, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement and calculation methods for each physical property are as follows.

[0056] (1) Measurement of the weight-average molecular weight of acrylic resin A The results were obtained by gel permeation chromatography. The measurement conditions are shown below. GPC device: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation. Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of acrylic resin A 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 "DISMIC-13HP" (PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0057] (2) Measurement of the acid value of acrylic resin A Acrylic resin A was dissolved in a titration solvent of toluene and acetone (2:1) using a potentiometric automatic titrator (manufactured by Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610). The solution was then titrated with a 0.1N potassium hydroxide / ethanol solution using potentiometric titration, with the inflection point on the titration curve as the endpoint. The acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution titrated to the endpoint.

[0058] (3) Calculation of the glass transition temperature of acrylic resin A The glass transition temperature of acrylic resin A, which is a copolymer, can be calculated according to the Fox equation below from the mass ratio of each monomer constituting acrylic resin A and the glass transition temperature of the homopolymer obtained when each monomer is formed into a homopolymer. 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+···+(W m / Tg m ) W1+W2+···W m =1 In the Fox equation above, Tg is the glass transition temperature of acrylic resin A, and Tg1, Tg2, ···, Tg m is the glass transition temperature of the homopolymer obtained when each monomer is formed into a homopolymer. The unit of temperature is K. Further, W1, W2, ···, W m represent the mass ratio of each monomer in acrylic resin A. As the glass transition temperature of the homopolymer of each monomer in the Fox equation, for example, values described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0059] (4) Measurement of solid content concentration 10.0 g of sodium sulfate that had been subjected to constant weight treatment in a desiccator was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm), about 1.0 g of the sample was added thereto and mixed, then accurately weighed, maintained at 105°C for 2 hours to remove volatile components, further left to stand in the desiccator for 15 minutes, and the mass was measured. The mass of the sample after removal of volatile components was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration (%).

[0060] (5) Measurement of average particle diameter of pigment-containing acrylic resin particles in aqueous dispersion or aqueous ink Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle diameter was taken as the average particle diameter of pigment-containing acrylic resin particles in the aqueous dispersion or aqueous ink. For the measurement sample, the concentration of the particles to be measured was 5×10 -3A dispersion solution diluted with water to a concentration of % (converted to solid content) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent.

[0061] (6) Viscosity of aqueous dispersions and aqueous inks Using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34'×R24, rotation speed 50 rpm), aqueous dispersions were measured at 20°C and aqueous inks at 32°C.

[0062] (Manufacturing of acrylic resin A) Manufacturing Example 1 In a reaction vessel equipped with a stirrer, reflux condenser, and dropping tank, the initial charges were 0.98 parts acrylic acid, 2.03 parts cyclohexyl acrylate, 0.69 parts methyl acrylate, 5.00 parts methyl ethyl ketone (hereinafter referred to as "MEK"), and 0.56 parts water. The reaction vessel was then stirred for 10 minutes while maintaining its temperature at 77°C. Next, a mixture of 8.83 parts acrylic acid, 18.34 parts cyclohexyl acrylate, 6.17 parts methyl acrylate, 45.03 parts MEK, 5.00 parts water, 0.56 parts 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, and 0.41 parts 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was complete, the polymerization reaction was carried out for 1 hour, and then the reaction was terminated by cooling to room temperature to obtain a solution of acrylic resin A1' (resin solids concentration 40%). To 28.60 parts of the obtained acrylic resin A1' solution, 3.68 parts of MEK were added to dilute it so that the resin solids content concentration was 35%. Next, 1.08 parts of N,N-dimethylethanolamine (hereinafter referred to as "DMAE") was added so that the degree of neutralization of the carboxyl groups of acrylic resin A1' was 30 mol%, and the mixture was stirred at 25°C. After that, 66.60 parts of water were added over 1 hour. After the addition was complete, the MEK was removed by distillation using an evaporator to obtain an aqueous dispersion of acrylic resin A1 (DMAE neutralized) (resin solids content concentration 25%). The physical properties of acrylic resin A1 are shown in Table 1.

[0063] Manufacturing Examples 2-17 and Comparative Manufacturing Examples 1-3 In Production Example 1, aqueous dispersions of each acrylic resin A (resin solids concentration 25%) were obtained in the same manner as in Production Example 1, except that the monomer composition and neutralizing agent constituting acrylic resin A were changed to the conditions shown in Table 1, and the amount of neutralizing agent was changed as necessary so that the degree of neutralization of acrylic resin A was 30 mol%. The terms used in Table 1 are as follows: DMAE: N,N-dimethylethanolamine (boiling point 134°C) MDEA: N-methyldiethanolamine (boiling point 245°C) NH3: Ammonia NaOH: Sodium hydroxide

[0064] (Manufacturing of aqueous dispersions) Example 1-1 61.69 parts of an aqueous dispersion of acrylic resin A1 (DMAE neutralized) obtained in Production Example 1 (resin solids content 25%) were added to 2.95 parts of MEK and 12.78 parts of deionized water. Furthermore, 22.58 parts of cyanide pigment (manufactured by DIC Corporation, product name: Fastogen Blue CA5380 15:3) were added to obtain a pigment mixture (ratio of the mass of pigment to the total mass of pigment and acrylic resin A [pigment / (pigment + acrylic resin A)] = 0.59). The resulting pigment mixture was mixed using a disperser blade at 7000 rpm and 20°C for 1 hour. It was then subjected to a 10-pass dispersion treatment at a pressure of 180 MPa using a microfluidizer (Microfluidics, high-pressure homogenizer, product name: M-140K) to obtain a pigment dispersion. From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and some water was further removed by centrifugation. The liquid layer was then filtered through a membrane filter (Sartorius, product name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and an aqueous dispersion D1 of pigment-containing acrylic resin particles (total concentration of pigment and acrylic resin A: 22%) was obtained. Table 1 shows the average particle size of the pigment-containing acrylic resin particles in the obtained aqueous dispersion D1 and the viscosity of the aqueous dispersion D1 at 20°C.

[0065] Examples 1-2 to 1-17 and Comparative Examples 1-1 to 1-3 In Example 1-1, aqueous dispersions of pigment-containing acrylic resin particles D2-D17 and DC1-DC3 (all with a total concentration of pigment and acrylic resin A of 22%) were obtained in the same manner as in Example 1, except that the type or amount of acrylic resin A was changed as shown in Table 1. The average particle size of the pigment-containing acrylic resin particles in each of the obtained aqueous dispersions and the viscosity of each aqueous dispersion at 20°C are shown in Table 1.

[0066] [Table 1]

[0067] (Preparation of water-based ink) Example 2-1 To obtain the ink composition shown in Table 2, 12 parts of an aqueous dispersion of pigment-containing acrylic resin particles D1 (7 parts pigment content) as the total of pigment and acrylic resin A, 22 parts of propylene glycol, 4 parts of diethylene glycol monoisobutyl ether, 1 part of an acetylene glycol-based surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name: Surfinol 440 (ethylene oxide (3.5 mol) adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol, effective content 100%)), and ion-exchanged water were added to the mixture to a total of 100 parts. After stirring, the mixture was filtered through a membrane filter (trade name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink 1.

[0068] Examples 2-2 to 2-19 and Comparative Examples 2-1 to 2-3 In Example 2-1, water-based inks 2-19 and C1-C3 were obtained in the same manner as in Example 2-1, except that the ink formulation composition was changed as shown in Table 2. The average particle size and viscosity of each water-based ink are shown in Table 2.

[0069] The water-based inks 1-19 and C1-C3 obtained in the above examples and comparative examples were used to evaluate the adhesion to the substrate using the method described below. The results are shown in Table 2.

[0070] <Evaluation of substrate adhesion> Using a printing evaluation device (Seiko Epson Corporation, inkjet printer, PX105, piezo type), an A4-sized film heater (Kawai Electric Works Co., Ltd.) was fixed to the printing substrate discharge section so that the area where the ink is injected could be heated to 50°C. The printing substrate used was a resin film cut to A4 size, as shown below. In an environment with a temperature of 25±1℃ and a relative humidity of 30±5%, the water-based inks of the examples and comparative examples were filled into the cartridge of the printing evaluation apparatus. A 50mm x 50mm solid image was printed with 100% ink duty, and the printed material was dried on a film heater for 3 minutes at a temperature of 50℃. A 50mm long, 15mm wide tape, "Nicetack No. 4" (registered trademark) (manufactured by Nichiban Co., Ltd.), was attached to the printed surface of the obtained printed material, leaving a 1cm margin and extending 4cm. A T-type peel test was performed using a Tensilon universal material tester (manufactured by A&D Co., Ltd., product name: RTC-1150A), and the peel strength (N / 15mm), an indicator of substrate adhesion, was measured. The substrate adhesion was evaluated according to the following evaluation criteria. A rating of A in the evaluation criteria below indicates excellent adhesion to the substrate, while an E rating indicates poor adhesion to the substrate. (Printing base material) PET film: Corona discharge treated PET film (manufactured by Futamura Chemical Co., Ltd., product number: FE2001, film thickness: 20 μm) OPP film: Corona discharge treated OPP film (manufactured by Futamura Chemical Co., Ltd., product number: FOR-AQ, film thickness: 20 μm) LDPE film: Corona discharge treated LDPE film (manufactured by Skyfilm Co., Ltd., product number: HR611, film thickness: 30 μm) (Evaluation Criteria) A:2.5N / 15mm or more B: 2.0N / 15mm or more, 2.5N / less than 15mm C: 1.5N / 15mm or more, 2.0N / less than 15mm D: 1.0N / 15mm or more, less than 1.5N / 15mm E: 1.0N / less than 15mm

[0071] [Table 2]

[0072] Table 2 shows that the aqueous ink using the aqueous dispersion in the examples exhibits superior substrate adhesion (tape peel resistance) of the ink coating on hydrophobic and non-absorbent resin films compared to the aqueous ink using the aqueous dispersion in the comparative examples.

Claims

1. An aqueous dispersion of acrylic resin particles containing a pigment used in an inkjet printing water-based ink used in printing on a resin film having a water absorption capacity of 1 g / m² or less as a printing substrate, The acrylic resin A constituting the acrylic resin particles includes constituent units derived from (meth)acrylic acid (a-1), constituent units derived from cycloalkyl acrylate (a-2), and constituent units derived from alkyl (meth)acrylate (a-3) whose glass transition temperature (Tg) when formed into a homopolymer is 10°C or less. The acid value of the acrylic resin A is 180 mg KOH / g or more and 260 mg KOH / g or less. Aqueous dispersion of acrylic resin particles containing pigment.

2. An aqueous dispersion of acrylic resin particles containing the pigment described in claim 1, wherein the carboxyl group of the acrylic resin A is neutralized with an amine compound.

3. An aqueous dispersion of acrylic resin particles containing the pigment according to claim 1, wherein the content of cycloalkyl acrylate (a-2)-derived structural units in all structural units of the acrylic resin A is 25% by mass or more and 85% by mass or less.

4. A water-based ink comprising an aqueous dispersion of acrylic resin particles containing the pigment described in any one of claims 1 to 3, and a water-soluble organic solvent.

5. The aqueous ink according to claim 4, wherein the water-soluble organic solvent contains an alkanediol.

6. Acrylic resin particles containing a pigment used in an inkjet printing water-based ink used in printing on a resin film having a water absorption capacity of 1 g / m² or less as a printing substrate, The acrylic resin A constituting the acrylic resin particles includes constituent units derived from (meth)acrylic acid (a-1), constituent units derived from cycloalkyl acrylate (a-2), and constituent units derived from alkyl (meth)acrylate (a-3) whose glass transition temperature (Tg) when formed into a homopolymer is 10°C or less. Acrylic resin particles containing a pigment, wherein the acid value of the acrylic resin A is 180 mg KOH / g or more and 260 mg KOH / g or less.

7. A method for producing acrylic resin particles containing the pigment described in Claim 6, A method for producing pigment-containing acrylic resin particles, comprising the step of dispersing a pigment mixture containing acrylic resin A, a pigment, and water, which includes a component unit derived from (meth)acrylic acid (a-1), a component unit derived from cycloalkyl acrylate (a-2), and a component unit derived from alkyl (meth)acrylate (a-3) having a glass transition temperature (Tg) of 10°C or less when formed into a homopolymer, and having an acid value of 180 mg KOH / g or more and 260 mg KOH / g or less.

8. A water-based ink comprising acrylic resin particles containing the pigment described in claim 6, and a water-soluble organic solvent.

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