Polymer particle-containing aqueous dispersion for ink

Abstract

The present invention addresses the problem of providing an aqueous dispersion capable of imparting, to an aqueous ink, excellent viscosity stability and high adhesion to PET films and OPP films. Said problem can be solved by an aqueous dispersion for ink, the aqueous dispersion containing polymer particles composed of a polymer (A) that includes a structural unit derived from an aromatic group-containing monomer in an amount of 18-42 mass% and that has a weight average molecular weight of 50,000-100,000.

Description

Aqueous dispersions for inks containing polymer particles

[0001] The present invention relates to an aqueous dispersion for ink containing polymer particles, an aqueous ink containing the aqueous dispersion, and a printed matter obtained using the aqueous ink.

[0002] Inks are broadly classified into two types: organic solvent-based inks, which use an organic solvent as the main solvent component, and water-based inks, which use water as the main solvent component. However, due to environmental considerations, water-based inks have been attracting attention in recent years. In addition, polymers contained in inks are required to exhibit adhesion to printing substrates, and are required to adhere to a wide range of substrates, not only water-absorbent substrates such as paper but also non-water-absorbent substrates such as resin films.

[0003] For example, Patent Document 1 discloses a water-based ink having a copolymer (P) containing an acrylonitrile-derived structural unit (A) and a styrene-derived structural unit (S), and describes that by adjusting the glass transition temperature of the copolymer (P) to 50 to 120°C and adjusting the content of the acrylonitrile-derived structural unit (A) in the copolymer (P) to 8 to 50 mass% of all the structural units of the copolymer (P), the ink has excellent adhesion to a resin film made of polyvinyl chloride.

[0004] JP 2023-62882 A

[0005] Although Patent Document 1 discloses that the aqueous ink containing copolymer (P) can be applied to various resin films, it has not been possible to achieve excellent adhesion with a single ink to both resin films with significantly different polarities, such as polyethylene terephthalate (PET) film and oriented polypropylene (OPP) film. Furthermore, aqueous inks are also required to exhibit a small increase in viscosity even after long-term storage, i.e., good viscosity stability. This is because if an aqueous ink with poor viscosity stability is used as an inkjet ink, there is a concern that the viscosity of the ink after storage may fall outside the appropriate viscosity range for the printer head, making it impossible to eject ink droplets normally.

[0006] Therefore, an object of the present invention is to provide an aqueous dispersion that can impart high adhesion to PET films and OPP films and good viscosity stability to aqueous inks.

[0007] As a result of extensive research to solve the above-mentioned problems, the present inventors have found that by using an aqueous dispersion containing polymer particles constituted of a polymer in which the content of structural units derived from aromatic group-containing monomers and the weight-average molecular weight are adjusted to fall within specific ranges, it is possible to impart high adhesion to PET films and OPP films and good viscosity stability to an aqueous ink, and have completed the present invention.

[0008] That is, the present invention is as follows. [1] An aqueous dispersion for ink containing polymer particles constituted by a polymer (A), wherein the polymer (A) contains 18 to 42 mass % of structural units derived from an aromatic group-containing monomer, and the weight average molecular weight of the polymer (A) is 50,000 to 100,000. [2] The aqueous dispersion for ink according to [1], wherein the aromatic group-containing monomer is a monomer having at least one benzene ring or naphthalene ring and at least one polymerizable unsaturated group in the molecule. [3] The aqueous dispersion for ink according to [1] or [2], wherein the polymer (A) further contains structural units derived from a hydroxyl group-containing monomer, and the content of the structural units derived from the hydroxyl group-containing monomer is 30 to 150 parts by mass per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. [4] The aqueous dispersion for ink according to [3], wherein the hydroxyl group-containing monomer is a monomer having at least one hydroxyl group and at least one (meth)acryloyl group in the molecule. [5] The aqueous dispersion for ink according to any one of [1] to [4], wherein the polymer (A) further contains structural units derived from a cyclic aliphatic group-containing monomer, and the content of the structural units derived from the cyclic aliphatic group-containing monomer is 60 to 180 parts by mass per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. [6] The aqueous dispersion for ink according to [5], wherein the cyclic aliphatic group-containing monomer is a monomer having at least one alicyclic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule, and the alicyclic hydrocarbon ring is a cycloalkyl group, an isobornyl group, or an adamantyl group. [7] The aqueous dispersion for ink according to any one of [1] to [6], wherein the glass transition temperature of the polymer (A) is −10 to 75° C. [8] The aqueous dispersion for ink according to any one of [1] to [7], wherein the acid value of the polymer (A) is 10 mgKOH / g or less. [9] An aqueous ink comprising the aqueous dispersion for ink according to any one of [1] to [8] and a colorant.

[10] The aqueous ink according to [9], wherein the colorant is a white pigment.

[11] A printed matter comprising a printed layer formed from the aqueous ink according to [9] or

[10] .

[12] A method for producing an aqueous ink using the aqueous dispersion according to any one of [1] to [8].

[0009] By using the aqueous dispersion of the present invention, it is possible to impart high adhesion to PET films and OPP films and good viscosity stability to aqueous inks.

[0010] An embodiment of the present invention will be described below, but the present invention is not limited thereto. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B." Furthermore, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylate" means acrylate or methacrylate. The same applies to terms such as "(meth)acryloxy" and "(meth)acryloyl." Furthermore, a "structural unit derived from a specific monomer" corresponds to a structure in which a carbon-carbon double bond in a specific monomer is replaced with a carbon-carbon single bond and two bonds bonded to each carbon. This structure may not only be a structure obtained by polymerizing a specific monomer, but may also be a structural unit derived from a specific monomer obtained by post-modification of a structure obtained by polymerizing a different monomer.

[0011] 1. Polymer Particles The aqueous dispersion for ink of the present invention contains polymer particles constituted of a polymer (A) having a content of structural units derived from an aromatic group-containing monomer of 18 to 42% by mass and a weight average molecular weight of 50,000 to 100,000. Each component constituting the polymer (A) will be described below.

[0012] 1-1. Aromatic Group-Containing Monomer The polymer (A) has structural units derived from an aromatic group-containing monomer. This can improve the viscosity stability of the resulting ink. Although the mechanism behind this is not clear, it is thought that the presence of structural units derived from an aromatic group-containing monomer in the polymer (A) constituting the polymer particles makes it easier to suppress aggregation of the polymer particles when the polymer particles are plasticized by a solvent contained in the ink.

[0013] The aromatic group-containing monomer is preferably a monomer having at least one aromatic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule. Examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, a phenanthrene ring, an anthracene ring, etc., among which a benzene ring or a naphthalene ring is preferred, and a benzene ring is more preferred. Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, a maleimide group, etc., among which a (meth)acryloyl group or a vinyl group is preferred.

[0014] Examples of the aromatic group-containing monomer include styrene-based monomers, aryl (meth)acrylates, aralkyl (meth)acrylates, aryloxy group-containing alkyl (meth)acrylates, and maleimides having an aryl group.

[0015] The styrene-based monomers include those having a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an alkyl group (for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, or a tert-butyl group), 1-4 alkyl group), vinyl group, alkoxysilyl group (e.g., tri-C such as trimethoxysilyl group, triethoxysilyl group, etc. 1-4Examples of the styrene-based monomer include styrene, which may have one or more substituents such as a halogen atom and an alkyl group. The substituent is preferably at least one selected from a halogen atom and an alkyl group. Specific examples of the styrene-based monomer include styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, chlorostyrene, chloromethylstyrene, divinylbenzene, p-styryltrimethoxysilane, and 2-styrylethyltrimethoxysilane. Examples of the aryl(meth)acrylate include aryl(meth)acrylates having an aryl group having 6 to 18 carbon atoms, such as phenyl(meth)acrylate, o-tolyl(meth)acrylate, m-tolyl(meth)acrylate, p-tolyl(meth)acrylate, 2,3-xylyl(meth)acrylate, 2,4-xylyl(meth)acrylate, 2,5-xylyl(meth)acrylate, 2,6-xylyl(meth)acrylate, 3,4-xylyl(meth)acrylate, 3,5-xylyl(meth)acrylate, 1-naphthyl(meth)acrylate, and 2-naphthyl(meth)acrylate. Examples of aralkyl (meth)acrylates include aralkyl (meth)acrylates having an aralkyl group having 7 to 18 carbon atoms, such as benzyl (meth)acrylate, phenylethyl (meth)acrylate, methylbenzyl (meth)acrylate, and naphthylmethyl (meth)acrylate. Examples of aryloxy group-containing alkyl (meth)acrylates include phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, methylphenoxyethyl (meth)acrylate, and 2-naphthoethyl (meth)acrylate. Examples of maleimides having an aryl group include N-phenylmaleimide.

[0016] Among these, as the aromatic group-containing monomer, styrene-based monomers, aryl(meth)acrylates, and aralkyl(meth)acrylates are preferred, with styrene which may have at least one substituent selected from a halogen atom and an alkyl group, aryl(meth)acrylates having an aryl group with 6 to 18 carbon atoms, and aralkyl(meth)acrylates having an aralkyl group with 7 to 18 carbon atoms being more preferred, with styrene, aryl(meth)acrylates having an aryl group with 6 to 10 carbon atoms, and aralkyl(meth)acrylates having an aralkyl group with 7 to 10 carbon atoms being even more preferred, with styrene and benzyl(meth)acrylate being particularly preferred. When the aromatic group-containing monomer is one of the above compounds, the viscosity stability of the resulting ink can be further improved.

[0017] The polymer (A) may contain one or more structural units derived from aromatic group-containing monomers.

[0018] The content of the structural unit derived from the aromatic group-containing monomer in the polymer (A) is 18 to 42% by mass, preferably 20 to 40% by mass. By adjusting the content to 18% by mass or more (preferably 20% by mass or more), the viscosity stability of the resulting ink can be improved, and by adjusting the content to 42% by mass or less (preferably 40% by mass or less), the adhesion to the substrate (particularly OPP film) can be improved.

[0019] 1-2. Hydroxyl Group-Containing Monomer The polymer (A) preferably further contains structural units derived from a hydroxyl group-containing monomer. When the polymer (A) contains structural units derived from a hydroxyl group-containing monomer in addition to structural units derived from an aromatic group-containing monomer, the adhesion to substrates (particularly PET films and OPP films) can be further improved.

[0020] The hydroxyl group-containing monomer is preferably a monomer having at least one hydroxyl group and at least one polymerizable unsaturated group in the molecule (but not having an aromatic hydrocarbon ring). Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, and a maleimide group, and among these, a (meth)acryloyl group is preferred.

[0021] Specific examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; halogen-substituted hydroxyalkyl (meth)acrylates such as 3-chloro-2-hydroxypropyl (meth)acrylate; modified hydroxyalkyl (meth)acrylates such as caprolactone-modified 2-hydroxyethyl (meth)acrylate and 2-(meth)acryloyloxyethyl 2-hydroxyethyl phthalate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and hydroxyl group-containing vinyl monomers such as vinyl alcohol and allyl alcohol.

[0022] Among these, the hydroxyl group-containing monomer is preferably a hydroxyalkyl(meth)acrylate, more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group having 1 to 4 carbon atoms, and even more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms. When the hydroxyl group-containing monomer is any of the above compounds, the viscosity stability of the resulting ink can be further improved.

[0023] The polymer (A) may contain one or more structural units derived from a hydroxyl group-containing monomer.

[0024] The content of the structural units derived from the hydroxyl group-containing monomer in the polymer (A) is, for example, 0 to 60% by mass, preferably 10 to 40% by mass, and more preferably 15 to 35% by mass. By adjusting the content of the structural units derived from the hydroxyl group-containing monomer within the above preferred range, adhesion to substrates (particularly PET films and OPP films) can be further improved.

[0025] The content of the structural units derived from the hydroxyl group-containing monomer is preferably 30 to 150 parts by mass, more preferably 50 to 120 parts by mass, and even more preferably 70 to 95 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. By adjusting the content of the structural units derived from the hydroxyl group-containing monomer within the above range, adhesion to substrates (particularly PET films and OPP films) can be further improved. The content of the structural units derived from the hydroxyl group-containing monomer may be 0 to 150 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer.

[0026] 1-3. Cycloaliphatic Group-Containing Monomer The polymer (A) preferably further contains a structural unit derived from a cycloaliphatic group-containing monomer. When the polymer (A) contains a structural unit derived from a cycloaliphatic group-containing monomer in addition to a structural unit derived from an aromatic group-containing monomer, the adhesion to a substrate (particularly an OPP film) can be further improved without reducing the viscosity stability of the resulting ink.

[0027] The cycloaliphatic group-containing monomer is preferably a monomer having at least one alicyclic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule (however, it does not have an aromatic hydrocarbon ring or a hydroxyl group). The alicyclic hydrocarbon ring may be saturated or unsaturated, but is preferably saturated. The alicyclic hydrocarbon ring may be monocyclic or polycyclic, such as bicyclic or tricyclic. In the case of a polycyclic ring, it is preferably a fused ring, and particularly preferably a bridged ring. The alicyclic hydrocarbon ring is preferably a ring having 3 to 10 carbon atoms. Examples of the alicyclic hydrocarbon ring include a cycloalkyl group (particularly a cycloalkyl group having 3 to 10 carbon atoms), an isobornyl group, and an adamantyl group, with a cycloalkyl group having 3 to 10 carbon atoms and an isobornyl group being more preferred. Examples of the polymerizable unsaturated group include a (meth)acryloyl group, a vinyl group, a maleimide group, and the like, with a (meth)acryloyl group being particularly preferred.

[0028] Specific examples of the cyclic aliphatic group-containing monomer include cycloalkyl (meth)acrylates such as cyclopropyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; esters of (meth)acrylic acid and polycyclic alcohols such as isobornyl (meth)acrylate and adamantyl (meth)acrylate; and cycloalkyl group-containing maleimides such as N-cyclohexylmaleimide.

[0029] Among these, as the cycloaliphatic group-containing monomer, cycloalkyl(meth)acrylate and isobornyl(meth)acrylate are preferred, cycloalkyl(meth)acrylate and isobornyl(meth)acrylate having a cycloalkyl group having 3 to 10 carbon atoms are more preferred, and cyclohexyl(meth)acrylate and isobornyl(meth)acrylate are even more preferred. When the cycloaliphatic group-containing monomer is any of the above compounds, adhesion to the substrate can be further improved.

[0030] The polymer (A) may contain one or more structural units derived from a cycloaliphatic group-containing monomer.

[0031] The content of the structural units derived from the cycloaliphatic group-containing monomer in the polymer (A) is, for example, 0 to 60% by mass, preferably 20 to 50% by mass, and more preferably 25 to 45% by mass. By adjusting the content of the structural units derived from the cycloaliphatic group-containing monomer within the above-mentioned preferred range, it is possible to further improve adhesion to substrates (particularly OPP films) without reducing viscosity stability.

[0032] Furthermore, the content of the structural units derived from the cyclic aliphatic group-containing monomer is preferably 60 to 180 parts by mass, more preferably 80 to 160 parts by mass, and even more preferably 100 to 140 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. By adjusting the content of the structural units derived from the cyclic aliphatic group-containing monomer within the above range, adhesion to substrates (particularly OPP films) can be further improved without reducing viscosity stability. The content of the structural units derived from the cyclic aliphatic group-containing monomer may be 0 to 180 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer.

[0033] From the viewpoint of improving the viscosity stability of the resulting ink and improving adhesion to substrates (particularly PET films and OPP films), the polymer (A) preferably contains structural units derived from the hydroxyl group-containing monomer and structural units derived from the cyclic aliphatic group-containing monomer, in addition to structural units derived from the aromatic group-containing monomer. In such a polymer (A), the content of the structural units derived from the hydroxyl group-containing monomer per 100 parts by mass of the structural units derived from the cyclic aliphatic group-containing monomer is preferably 20 to 150 parts by mass, more preferably 40 to 100 parts by mass, and even more preferably 60 to 85 parts by mass.

[0034] The content of the structural units derived from the hydroxyl group-containing monomer relative to 100 parts by mass of the total of the structural units derived from the aromatic group-containing monomer and the structural units derived from the cyclic aliphatic group-containing monomer is, for example, 0 to 150 parts by mass, preferably 15 to 120 parts by mass, and more preferably 25 to 100 parts by mass.

[0035] The total content of the structural units derived from aromatic group-containing monomers, structural units derived from hydroxyl group-containing monomers, and structural units derived from cyclic aliphatic group-containing monomers in the polymer (A) is preferably 20 to 100 mass%, more preferably 35 to 99 mass%, even more preferably 50 to 97 mass%, and still more preferably 75 to 95 mass%.

[0036] 1-4. Other Monomers The polymer (A) may further contain structural units derived from monomers other than aromatic group-containing monomers, hydroxyl group-containing monomers, and cycloaliphatic group-containing monomers (hereinafter referred to as other monomers). The other monomers are monomers other than aromatic group-containing monomers, hydroxyl group-containing monomers, and cycloaliphatic group-containing monomers, and have at least one polymerizable unsaturated group in the molecule. Examples of other monomers include (meth)acrylic acid alkyl esters, nitrogen atom-containing monomers, and acid group-containing monomers.

[0037] Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, 2-pentyl (meth)acrylate, isopentyl (meth)acrylate, and neobutyl (meth)acrylate. Pentyl (meth)acrylate, 3-methyl-2-butyl (meth)acrylate, 3-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-hexyl (meth)acrylate, 3,3-dimethyl-2-butyl (meth)acrylate, 3-methyl-2-pentyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2,4-dimethyl-3-pentyl (meth)acrylate, n-heptyl (meth)acrylate, 2-heptyl (meth)acrylate ) acrylate, 2-methyl-3-hexyl (meth)acrylate, 3-heptyl (meth)acrylate, 5-methyl-2-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2,2-dimethyl-3-hexyl (meth)acrylate, 2,5-dimethyl-3-hexyl (meth)acrylate, 3-octyl (meth)acrylate, 4-octyl (meth)acrylate, Examples of the alkyl (meth)acrylate include 5-methyl-2-heptyl (meth)acrylate, 5-methyl-3-heptyl (meth)acrylate, 6-methyl-2-heptyl (meth)acrylate, 6-methyl-3-heptyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, tridecyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, henicosyl (meth)acrylate, and tetracosyl (meth)acrylate. The polymer (A) may contain one or more structural units derived from an alkyl (meth)acrylate.

[0038] Among them, the (meth)acrylic acid alkyl ester is (meth)acrylic acid C 1-20Further, (meth)acrylic acid alkyl esters having a homopolymer glass transition temperature (Tg) of −20° C. or lower (hereinafter, sometimes referred to as low Tg (meth)acrylic acid alkyl esters) and methacrylic acid C 1-5 At least one selected from alkyl esters is also preferred. 1-5 By appropriately adjusting the content of the structural units derived from alkyl ester, it becomes easy to adjust the glass transition temperature of the polymer (A) to the range described below.

[0039] In this specification, the "glass transition temperature of a homopolymer" may be, for example, a value (when multiple Tg values ​​are listed, the lowest value) described in "POLYMER HANDBOOK THIRD EDITION" (by J. BRANDRUP and E. H. IMMERGUT, 1989, published by John Wiley & Sons, Inc., pp. VI / 209 to VI / 277). For compounds not described in "POLYMER HANDBOOK THIRD EDITION," a value (calculated value) determined by a computer using commercially available glass transition temperature calculation software (for example, "MATERIALS STUDIO" manufactured by Accelrys Software Inc., version: 4.0.0.0, module: Synthia, conditions: calculation with a weight average molecular weight of 100,000) may be used.

[0040] The Tg of the low Tg (meth)acrylic acid alkyl ester is −20° C. or lower, preferably −100 to −20° C., and more preferably −80 to −30° C. Examples of the low Tg (meth)acrylic acid alkyl ester include ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, and isononyl acrylate. Of these, n-butyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate are preferred, and 2-octyl acrylate and 2-ethylhexyl acrylate are more preferred.

[0041] Also, methacrylic acid C 1-5 Examples of alkyl esters include methacrylic acid C 1-3 Alkyl esters are preferred, with methyl methacrylate being more preferred.

[0042] The content of the structural units derived from the (meth)acrylic acid alkyl ester (particularly, the low Tg (meth)acrylic acid alkyl ester and the methacrylic acid C 1-5 The total content of structural units derived from alkyl esters (methacrylic acid alkyl esters) may be appropriately adjusted so that the Tg of polymer (A) falls within the range described below, and is, for example, 0 to 600 parts by mass, preferably 5 to 420 parts by mass, and more preferably 10 to 420 parts by mass, relative to 100 parts by mass of the structural units derived from the aromatic group-containing monomers. The total content of structural units derived from aromatic group-containing monomers, structural units derived from hydroxyl group-containing monomers, structural units derived from cyclic aliphatic group-containing monomers, and structural units derived from (meth)acrylic acid alkyl esters in polymer (A) is preferably 60 to 100% by mass, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0043] The nitrogen atom-containing monomer is a monomer having at least a substituent containing a nitrogen atom as a constituent and a polymerizable unsaturated group in the molecule (however, it does not have an aromatic hydrocarbon ring, a hydroxyl group, or an alicyclic hydrocarbon ring). Examples of the nitrogen atom-containing monomer include a nitrogen-based heterocycle-containing monomer, an amino group-containing monomer, and an amide group-containing monomer. Note that, in this specification, a monomer that is an amino group-containing monomer or an amide group-containing monomer but contains a nitrogen-based heterocycle is referred to as a nitrogen-based heterocycle-containing monomer.

[0044] Specific examples of the nitrogen-based heterocycle-containing monomer include vinyl lactam-based monomers such as N-methylvinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinylpyrrolidone, N-vinyl-2-pyrrolidone, and N-(meth)acryloylpyrrolidone; maleimide-based monomers such as maleimide; piperidyl (meth)acrylic monomers such as 2,2,6,6-tetramethyl-4-piperidyl (meth)acrylate and 1,2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate; (meth)acrylic monomers such as 2,2,6,6-tetramethyl-4-piperidyl (meth)acrylate and 1,2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate; aziridinyl group-containing (meth)acrylic monomers such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline; and the like.

[0045] Specific examples of the amino group-containing monomer include amino group-containing (meth)acrylic monomers such as N,N-dimethylaminomethyl (meth)acrylate and N,N-dimethylaminoethyl (meth)acrylate.

[0046] Examples of the amide group-containing monomer include (meth)acrylamide-based monomers such as (meth)acrylamide, N-monomethyl(meth)acrylamide, N-monoethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, methylenebis(meth)acrylamide, N-butoxymethyl(meth)acrylamide, dimethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropylacrylamide, and diacetone acrylamide.

[0047] As the nitrogen atom-containing monomer, a nitrogen-based heterocycle-containing monomer is preferred, a vinyl lactam monomer or a piperidyl(meth)acrylic monomer is more preferred, and N-vinyl-2-pyrrolidone, 2,2,6,6-tetramethyl-4-piperidyl(meth)acrylate, or 1,2,2,6,6-pentamethyl-4-piperidyl(meth)acrylate is even more preferred. From the viewpoint of improving light stability, a nitrogen atom-containing monomer having a hindered amine structure is preferred. As such a monomer, a monomer having a 2,2,6,6-tetraalkylpiperidine ring structure and a polymerizable unsaturated group (e.g., a (meth)acryloyl group, a vinyl group) in the molecule is preferred, a monomer having a 2,2,6,6-tetramethylpiperidine ring structure and a polymerizable unsaturated group (e.g., a (meth)acryloyl group, a vinyl group) is more preferred, and 2,2,6,6-tetramethyl-4-piperidyl(meth)acrylate and 1,2,2,6,6-pentamethyl-4-piperidyl(meth)acrylate are even more preferred.

[0048] The content of the structural units derived from the nitrogen atom-containing monomer is preferably 0 to 40 parts by mass, more preferably 2 to 30 parts by mass, and even more preferably 5 to 25 parts by mass, relative to 100 parts by mass of the structural units derived from the aromatic group-containing monomer.

[0049] The acid group-containing monomer is a monomer having at least one acid group and at least one polymerizable unsaturated group in the molecule (however, it does not have an aromatic hydrocarbon ring, a hydroxyl group, an alicyclic hydrocarbon ring, or a substituent containing a nitrogen atom as a constituent member). Examples of the acid group include a sulfo group and a carboxy group, and a carboxy group is preferred. Examples of the polymerizable unsaturated group include a (meth)acryloyl group and a vinyl group. Specific examples of the acid group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, cinnamic acid, and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monomethyl ester, and itaconic acid monobutyl ester; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, and 2-acryloyloxyethyl hexahydrophthalic acid. Of these, unsaturated monocarboxylic acids are preferred, and (meth)acrylic acid is more preferred.

[0050] The content of the structural units derived from the acid group-containing monomer is preferably 0 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the structural units derived from the aromatic group-containing monomer. Alternatively, it may be 0 to 5 parts by mass, 0 to 4 parts by mass, or 0 to 2 parts by mass. By adjusting the content of the structural units derived from the acid group-containing monomer to be equal to or less than the upper limit, the sedimentation stability of the resulting ink can be improved. Furthermore, by adjusting the content of the structural units derived from the acid group-containing monomer to be equal to or greater than the lower limit, the viscosity stability of the resulting ink can be further improved.

[0051] Other monomers include di(meth)acrylates of alkanediols having 1 to 10 carbon atoms, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate; diC di(meth)acrylates such as diethylene glycol di(meth)acrylate and dipropylene glycol di(meth)acrylate; 2-4 Alkylene glycol di(meth)acrylate: PolyC alkylene glycol di(meth)acrylate having 2 to 4 carbon atoms and having 2 to 50 moles of added alkylene oxide, such as polyethylene glycol di(meth)acrylate having 2 to 50 moles of added ethylene oxide, or polypropylene glycol di(meth)acrylate having 2 to 50 moles of added propylene oxide. 2-4Alkylene glycol di(meth)acrylates; tri(meth)acrylates of trihydric alcohols having 1 to 10 carbon atoms, such as ethoxylated glycerin tri(meth)acrylate, propylene oxide-modified glycerol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and trimethylolpropane triethoxytri(meth)acrylate; tetra(meth)acrylates of tetrahydric alcohols having 1 to 10 carbon atoms, such as pentaerythritol tetra(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate; hexa(meth)acrylates of hexahydric alcohols having 1 to 10 carbon atoms, such as dipentaerythritol hexa(meth)acrylate; 2-(2'-vinyloxyethoxyethyl)(meth)acrylate; (meth)acryloyl group-containing silane coupling agents such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, and 3-(meth)acryloxyethoxypropyltrimethoxysilane; vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane; epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate, α-methylglycidyl (meth)acrylate, and 2-glycidyloxyethyl (meth)acrylate; epoxy group-containing vinyl monomers such as allyl glycidyl ether; Fluoroalkyl (meth)acrylates such as trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, and octafluoropentyl (meth)acrylate; alkoxyalkyl group-containing (meth)acrylates such as methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, and trimethylolpropane tripropoxy (meth)acrylate;Examples of the monomer include carbonyl group-containing (meth)acrylates such as (meth)acryloxyalkylpropenal, acetonyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate acetylacetate, butanediol-1,4-acrylate acetylacetate, and 2-(acetoacetoxy)ethyl (meth)acrylate; vinyl monomers such as vinyl acetate, vinyl chloride, and vinyl benzoate; and olefin monomers such as ethylene and propylene.

[0052] The polymer (A) may contain one or more structural units derived from other monomers.

[0053] 1-5. Physical Properties of Polymer (A) The weight-average molecular weight (Mw) of the polymer (A) is 50,000 to 100,000. By adjusting the Mw of the polymer (A) to 50,000 or more, the viscosity stability of the resulting ink can be improved, and by adjusting the Mw of the polymer (A) to 100,000 or less, film-forming properties can be improved and adhesion to substrates (particularly PET films and OPP films) can be increased. From the viewpoint of further improving adhesion to substrates (particularly PET films and OPP films), the weight-average molecular weight (Mw) of the polymer (A) is more preferably 60,000 to 100,000, and even more preferably 70,000 to 90,000.

[0054] The polymer (A) preferably has a polydispersity (Mw / Mn) calculated using the weight average molecular weight (Mw) and the number average molecular weight (Mn) of 1.0 to 10.0, more preferably 2.0 to 6.0, and even more preferably 3.0 to 4.0. The weight average molecular weight and number average molecular weight can be calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC).

[0055] The glass transition temperature (Tg (°C)) of the polymer (A) is preferably −30 to 100°C, more preferably −20 to 80°C, and even more preferably −10 to 75°C. By adjusting the Tg of the polymer (A) to the above lower limit or more, the blocking resistance of the resulting ink can be improved, and by adjusting the Tg of the polymer (A) to the above upper limit or less, the film-forming properties of the resulting ink can be improved. The glass transition temperature (°C) of the polymer (A) can be calculated from the Tg calculated from the Fox equation shown below: A (K) can be calculated by converting 1 / Tg. A =Σ(Wm / Tgm) / 100 [In the formula, Tg A represents the glass transition temperature (absolute temperature: K) of polymer (A), Wm represents the content (mass%) of monomer m in all monomer components constituting polymer (A), and Tgm represents the glass transition temperature (absolute temperature: K) of a homopolymer of monomer m.

[0056] The acid value of the polymer (A) is preferably 10 mgKOH / g or less, more preferably 7 mgKOH / g or less, even more preferably 3 mgKOH / g or less, and particularly preferably 0 mgKOH / g. By adjusting the acid value of the polymer (A) within the above range, the sedimentation stability of the resulting ink can be improved. The acid value of the polymer (A) indicates the number of milligrams of potassium hydroxide required to neutralize the acid groups contained in 1 g of the polymer (A). The acid value can be calculated from the amounts of the monomer components constituting the polymer (A), i.e., by measuring the number of milligrams of potassium hydroxide required to neutralize the acid groups contained in 1 g of the monomer components charged to synthesize the polymer (A).

[0057] The polymer particles contained in the aqueous dispersion for ink of the present invention are composed of the polymer (A). The content of the polymer (A) in the polymer particles is, for example, 90 to 100% by mass, preferably 95% by mass or more, and more preferably 98% by mass or more.

[0058] The shape of the polymer particles is not particularly limited, but is usually spherical. The shape can be measured using a transmission electron microscope or a scanning electron microscope. The polymer particles may have a single-layer structure or a multi-layer structure (e.g., a core-shell structure), but a single-layer structure is preferred.

[0059] The average particle size of the polymer particles is preferably 20 to 300 nm, more preferably 35 to 200 nm, and even more preferably 50 to 100 nm. By adjusting the average particle size of the polymer particles within the above range, it becomes easier to incorporate the polymer particles at a high concentration while maintaining the viscosity of the ink within an appropriate range, and when used for inkjet printing, it is possible to improve the ejection stability. Note that the average particle size of the polymer particles may be determined by the volume-based cumulant average particle size measured by dynamic light scattering.

[0060] The aqueous dispersion for ink of the present invention contains polymer particles composed of the polymer (A), and specifically, is a dispersion in which polymer particles composed of the polymer (A) are dispersed in an aqueous solvent. The polymer particles are substantially composed of the polymer (A), and the content of the polymer (A) in the polymer particles is, for example, 95 to 100 mass %, and preferably 98 to 100 mass %.

[0061] 2-1. Polymer Particles From the viewpoint of handleability, the content of the polymer particles in the aqueous ink dispersion of the present invention is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, and even more preferably 30 to 65% by mass. The content of the polymer particles can be determined as the non-volatile content (solid content) of the aqueous ink dispersion; that is, it is preferable to adjust the solid content of the aqueous ink dispersion to be within the above range.

[0062] The nonvolatile content can be calculated by any known method, and may be calculated as the mass obtained by subtracting the mass of volatile components from the total mass of the aqueous ink dispersion according to the following formula 1. Alternatively, as described in the Examples, 1 g of the aqueous ink dispersion may be weighed and dried in a hot air dryer at 110°C for 1 hour, and the resulting residue is used as the nonvolatile content, and the nonvolatile content may be calculated according to the following formula 2. Formula 1: [Amount of nonvolatile content in aqueous ink dispersion (% by mass)] = ([Total mass of aqueous ink dispersion - Mass of volatile components] ÷ [Total mass of aqueous ink dispersion]) × 100 Formula 2: [Amount of nonvolatile content in aqueous ink dispersion (% by mass)] = ([Mass of residue] ÷ [Mass of 1 g of aqueous ink dispersion]) × 100

[0063] 2-2. Water-Based Solvent The water-based solvent contained in the aqueous dispersion for ink of the present invention may be water or a mixed solvent of water and a water-soluble organic solvent. A water-soluble organic solvent refers to an organic solvent that dissolves in water at a concentration of 0.01% by mass or more at room temperature and normal pressure. In this specification, room temperature means 25°C, and normal pressure means 1 atmosphere. The water content in the water-based solvent is preferably 10 to 100% by mass, more preferably 25% by mass or more, even more preferably 60% by mass or more, and particularly preferably 90% by mass or more. The remainder is preferably the water-soluble organic solvent. As the water, ion-exchanged water (deionized water), distilled water, pure water, etc. can be used.

[0064] Examples of the water-soluble organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and tert-butyl alcohol (preferably C 1-4alcohol); glycols such as propylene glycol, 1,3-propanediol, 1,2-hexanediol, dipropylene glycol, tripropylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; glycerin; ethylene glycol monoalkyl ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoisobutyl ether, etc.); 1-4 alkyl ether), propylene glycol monoalkyl ether (for example, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol monobutyl ether, propylene glycol monoisobutyl ether, etc.) 1-4 alkylene glycol monoalkyl ethers (preferably C alkyl ethers) 2-4 Alkylene glycol mono C 1-4 diethylene glycol monoalkyl ethers (e.g., diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, etc.); 1-4 alkyl ethers), dipropylene glycol monoalkyl ethers (for example, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monoisobutyl ether, and other dipropylene glycol mono C 1-4 Dialkylene glycol monoalkyl ethers (preferably diC alkyl ethers) 2-4Alkylene glycol mono C 1-4 alkyl ethers); polyethylene glycol monoalkyl ethers (for example, polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polyethylene glycol monopropyl ether, polyethylene glycol monoisopropyl ether, polyethylene glycol monobutyl ether, polyethylene glycol monoisobutyl ether, etc.); 1-4 alkyl ether), polypropylene glycol monoalkyl ether (for example, polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monopropyl ether, polypropylene glycol monoisopropyl ether, polypropylene glycol monobutyl ether, polypropylene glycol monoisobutyl ether, etc.) 1-4 alkyl ethers) and the like (preferably polyC 2-4 Alkylene glycol mono C 1-4 Examples of water-soluble organic solvents include: alkyl ethers; heterocycles such as 2-pyrrolidone and N-methyl-2-pyrrolidone; and ketones such as acetone and methyl ethyl ketone. The number of moles of alkylene oxide added in the polyalkylene glycol monoalkyl ether is preferably 2 to 10, and more preferably 2 to 4. These water-soluble organic solvents may be used alone or in combination of two or more.

[0065] Among these water-soluble organic solvents, propylene glycol, glycerin, diethylene glycol, triethylene glycol, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, polyethylene glycol (number of moles of ethylene oxide added=2 to 4) monobutyl ether, and 2-pyrrolidone are preferred, and propylene glycol, triethylene glycol, polyethylene glycol (number of moles of ethylene oxide added=2 to 4) monobutyl ether, and 2-pyrrolidone are more preferred.

[0066] From the viewpoint of handleability, the content of the aqueous solvent in the aqueous dispersion for ink of the present invention is preferably 30 to 900 parts by mass, more preferably 50 to 400 parts by mass, and even more preferably 70 to 250 parts by mass, relative to 100 parts by mass of the polymer particles.

[0067] 2-3. Other Additives The aqueous dispersion for ink of the present invention may contain additives such as chain transfer agents, such as compounds having a thiol group, e.g., tert-dodecyl mercaptan, pH buffers, chelating agents, etc. The amount of the additives cannot be determined in general because it differs depending on the type and purpose, but is usually preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the polymer particles.

[0068] 2-4. Method for Producing Aqueous Dispersion for Ink The aqueous dispersion for ink of the present invention is preferably produced by emulsion polymerization of monomer components (aromatic group-containing monomer, and optionally hydroxyl group-containing monomer, cyclic aliphatic group-containing monomer, and other monomers) in an aqueous solvent in the presence of an emulsifier and a polymerization initiator. The types, combinations, and blending ratios of preferred monomer components used in emulsion polymerization are the same as those described above for the preferred monomers for forming polymer (A). Specific means and conditions for carrying out emulsion polymerization can be appropriately selected and adopted from means and techniques used in conventionally known emulsion polymerization methods. A preferred production method is described in detail below.

[0069] The emulsifier used in the emulsion polymerization may be a conventionally known emulsifier, such as a nonionic emulsifier, an anionic emulsifier, a cationic emulsifier, or an amphoteric emulsifier. These emulsifiers may be used alone or in combination of two or more. Furthermore, an emulsifier containing a polymerizable unsaturated group in the molecule may also be used. Examples of the polymerizable unsaturated group include a group having an ethylenically unsaturated double bond. Incidentally, an emulsifier containing a polymerizable unsaturated group is also referred to as a reactive emulsifier. A polymeric emulsifier may also be used. Among the above emulsifiers, nonionic emulsifiers or anionic emulsifiers are preferred. From the viewpoint of improving water resistance and image uniformity, anionic emulsifiers containing a polymerizable unsaturated group or nonionic emulsifiers containing a polymerizable unsaturated group are more preferred, and anionic emulsifiers containing a polymerizable unsaturated group are even more preferred.

[0070] Examples of the anionic emulsifier include alkyl sulfate salts such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonate salts such as ammonium dodecyl sulfonate, sodium dodecyl sulfonate and sodium alkyl diphenyl ether disulfonate; alkyl aryl sulfonate salts such as ammonium dodecyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium dodecyl naphthalene sulfonate; polyoxyethylene alkyl sulfonate salts; polyoxyethylene alkyl ether sulfate salts; polyoxyethylene alkyl aryl ether sulfate salts; polyoxyethylene polycyclic phenyl ether sulfate ester salts; dialkyl sulfosuccinate salts; arylsulfonic acid-formalin condensates; fatty acid salts such as ammonium laurate and sodium stearylate; sulfates or salts thereof having an allyl group such as bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfonate salts, propenyl-alkyl sulfosuccinate ester salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts, and sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene; sulfate ester salts of allyloxymethyl alkoxyethyl polyoxyethylene, and polyoxyalkylene alkenyl ether ammonium sulfate salts.

[0071] Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, condensates of polyethylene glycol and polypropylene glycol, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides, condensates of ethylene oxide and aliphatic amines, and polyoxyalkylene alkenyl ethers.

[0072] Examples of polymer emulsifiers include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate; and copolymers containing one or more of the monomers constituting these polymers as copolymerization components.

[0073] Examples of reactive emulsifiers include propenyl-alkyl sulfosuccinate salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts (e.g., Sanyo Chemical Industries, Ltd., trade name: ELEMINOL RS-30, etc.), polyoxyethylene alkylpropenylphenyl ether sulfonate salts (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: AQUALON HS-10, etc.), sulfonate salts of allyloxymethyl alkyloxypolyoxyethylene (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: AQUALON KH-10, etc.), polyoxyethylene styrenated propenylphenyl ether sulfate ester ammonium (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: AQUALON AR-10, etc.), anionic emulsifiers having a polymerizable unsaturated group, such as sulfonate salts of allyloxymethyl nonylphenoxyethyl hydroxypolyoxyethylene (e.g., manufactured by ADEKA, trade name: ADEKA REASOAP SE-10, etc.), allyloxymethyl alkoxyethyl hydroxypolyoxyethylene sulfate ester salts (e.g., manufactured by ADEKA, trade name: ADEKA REASOAP SR-10, SR-30, etc.), bis(polyoxyethylene polycyclic phenyl ether) methacrylated sulfonate salts (e.g., manufactured by Nippon Nyukazai Co., Ltd., trade name: ANTOX MS-60, etc.), and polyoxyalkylene alkenyl ether ammonium sulfate (e.g., manufactured by Kao Corporation, trade name: LATEMUL PD-104, LATEMUL PD-105, etc.); nonionic emulsifiers having a polymerizable unsaturated group, such as polyoxyethylene styrenated propenyl phenyl ether (for example, trade name: Aqualon AN-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), allyloxymethyl alkoxyethyl hydroxypolyoxyethylene (for example, trade name: Adeka Reasop ER-20, manufactured by ADEKA), polyoxyethylene alkylpropenyl phenyl ether (for example, trade name: Aqualon RN-20, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), allyloxymethyl nonylphenoxyethyl hydroxypolyoxyethylene (for example, trade name: Adeka Reasop NE-10, manufactured by ADEKA), and polyoxyalkylene alkenyl ether (for example, trade name: Latemul PD-420, Latemul PD-430, manufactured by Kao Corporation).

[0074] When a reactive emulsifier is used in the production of polymer (A), polymer (A) contains structural units derived from the reactive emulsifier. The content of the structural units derived from the reactive emulsifier in polymer (A) is preferably 0.5 to 10 mass%, more preferably 1.0 to 8 mass%, and even more preferably 1.5 to 6 mass%.

[0075] The amount of the emulsifier used is, for example, preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8 parts by mass, and even more preferably 1.5 to 6 parts by mass, per 100 parts by mass of the monomer component. If necessary, protective colloids can be used alone or together with the emulsifier.

[0076] The polymerization initiator used in the emulsion polymerization is not limited to, but examples include azo-based polymerization initiators such as azobisisobutyronitrile, 2,2-azobis(2-methylbutyronitrile), 2,2-azobis(2,4-dimethylvaleronitrile), 2,2-azobis(2-diaminopropane) hydrochloride, 4,4-azobis(4-cyanovaleric acid), and 2,2-azobis(2-methylpropionamidine); persulfates such as ammonium persulfate and potassium persulfate; and peroxide-based polymerization initiators such as hydrogen peroxide, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, and ammonium peroxide, but are not limited to these examples. These polymerization initiators may be used alone or in combination of two or more.

[0077] The amount of the polymerization initiator used in the emulsion polymerization is preferably 0.01 to 3 parts by mass, more preferably 0.05 to 2 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the monomer component. If it is necessary to increase the polymerization rate or lower the reaction temperature, a reducing agent such as a soluble sulfite or ascorbic acid, or a metal compound that generates heavy metal ions in water, such as ferrous sulfate, can be combined with the peroxide polymerization initiator or persulfate to form a redox initiator.

[0078] The reaction temperature during the emulsion polymerization can be appropriately set taking into consideration the weight-average molecular weight of the resulting polymer (A), the blending ratio of the monomer components, the type of polymerization initiator, and the like. The reaction temperature is, for example, 0 to 100°C, preferably 50 to 95°C, and more preferably 60 to 90°C, and the reaction time is, for example, 0.5 to 30 hours, preferably 1 to 20 hours, and more preferably 3 to 10 hours. The reaction pressure is also not particularly limited and may be normal pressure (atmospheric pressure), reduced pressure, or increased pressure. The polymerization reaction is desirably carried out under an atmosphere of an inert gas such as nitrogen gas.

[0079] The aqueous solvent used in the emulsion polymerization may be the same as the aqueous solvent described above as the aqueous solvent contained in the aqueous dispersion for ink of the present invention, and the preferred embodiments thereof are also the same. The amount of the aqueous solvent used in the emulsion polymerization is not limited, but is preferably 20 to 300 parts by mass, more preferably 40 to 200 parts by mass, per 100 parts by mass of the monomer component.

[0080] Specific examples of the emulsion polymerization include monomer dropping polymerization, pre-emulsion dropping polymerization, seed polymerization, and multi-stage polymerization.

[0081] If necessary, an appropriate amount of additives such as a chain transfer agent, e.g., a compound having a thiol group such as tert-dodecyl mercaptan, a pH buffer, a chelating agent, etc., may be added to the reaction system in the emulsion polymerization. The amount of the additive varies depending on the type of additive and cannot be determined in general, but is usually preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the monomer component.

[0082] 3. Water-Based Ink The water-based ink of the present invention contains the above-described aqueous dispersion for ink and a colorant.

[0083] 3-1. Polymer Particles As described above, the aqueous ink of the present invention contains the aqueous ink dispersion described above; that is, the aqueous ink of the present invention contains the polymer particles described above. The content of the polymer particles in the aqueous ink can be set depending on the properties required of the ink, but is preferably 5 to 40% by mass, and more preferably 8 to 25% by mass. The content of the polymer particles in the solid content of the aqueous ink is preferably 15 to 90% by mass, more preferably 25 to 75% by mass, and even more preferably 35 to 55% by mass. By setting the content of the polymer particles in the aqueous ink or the solid content of the aqueous ink within the above range, it becomes easier to achieve both substrate adhesion and viscosity stability. In this specification, the solid content of the aqueous ink refers to the components of the aqueous ink excluding the solvent.

[0084] 3-2. Colorant The hue of the colorant may be, for example, achromatic colors such as white, black, and gray, or chromatic colors such as yellow, magenta, cyan, blue, red, orange, and green, with white being preferred. In the present technical field, a packaging film with improved visibility may be produced by solid printing a white ink obtained using a colorant with a white hue over a wide area of ​​a resin film, and then printing a non-white ink (color ink) on top of that. The aqueous ink of the present invention exhibits high adhesion to resin films (particularly PET films and OPP films), and therefore can be suitably used as a white ink having a large contact surface with such resin films.

[0085] The colorant may be either a pigment or a dye, and these may be used alone or in combination of two or more. Among these, pigments are preferred because of their excellent weather resistance. When a pigment is used, the pigment may be used in the form of a pigment dispersion such as a paste. Examples of pigments include organic pigments and inorganic pigments. Furthermore, if necessary, these pigments can also be used in combination with an extender pigment.

[0086] Examples of organic pigments include azo pigments such as benzidine and Hansa Yellow, diazo pigments, azomethine pigments, methine pigments, anthraquinone pigments, phthalocyanine pigments such as phthalocyanine blue, perinone pigments, perylene pigments, diketopyrrolopyrrole pigments, thioindigo pigments, iminoisoindoline pigments, isoindolinone pigments such as iminoisoindolinone, dioxazine pigments, quinacridone pigments such as quinacridone red and quinacridone violet, flavanthrone pigments, indanthrone pigments, anthrapyrimidine pigments, carbazole pigments, monoarylide yellow, diarylide yellow, benzimidazolone yellow, tolyl orange, naphthol orange, quinophthalone pigments, etc. Preferred organic pigments include, for example, C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Examples of such pigments include C.I. Pigment Blue, C.I. Pigment Green, and the like.

[0087] Examples of inorganic pigments include titanium dioxide, antimony trioxide, zinc oxide such as zinc white, lithopone, white lead, red iron oxide, black iron oxide, chromium oxide green, carbon black, yellow lead, molybdenum red, ferric ferrocyanide (Prussian blue), ultramarine, and lead chromate. Other examples of inorganic pigments include flat-shaped pigments such as mica, clay, aluminum powder, talc, and aluminum silicate, and extender pigments such as calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, and magnesium carbonate. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0088] Among the pigments, inorganic pigments are preferred, white pigments are more preferred, and at least one selected from titanium dioxide, antimony trioxide, zinc oxide such as zinc white, lithopone, white lead, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, magnesium carbonate, clay, talc, and aluminum silicate is even more preferred. Among these, titanium dioxide is preferred from the viewpoint of having a high refractive index and excellent hiding power, and titanium dioxide having a rutile crystal structure is more preferred.

[0089] The volume average particle diameter of the pigment is preferably 10 to 1,000 nm, more preferably 20 to 500 nm, from the viewpoints of dispersion stability, color development, and hiding power. In particular, when the pigment is a white pigment, the volume average particle diameter of the white pigment is preferably 100 to 500 nm, more preferably 150 to 450 nm, and even more preferably 200 to 400 nm, from the viewpoint of superior hiding power.

[0090] The volume average particle diameter of the pigment refers to the volume average particle diameter of the pigment in the aqueous ink of the present invention. The volume average particle diameter of the pigment can be measured using a laser diffraction / scattering particle size distribution analyzer or dynamic light scattering. For example, the volume-based cumulant average particle diameter measured using dynamic light scattering can be used. However, in cases where measurement using dynamic light scattering is difficult, such as with black pigments, the 50% particle diameter in the volume-based particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer can be used as the volume average particle diameter.

[0091] The pigment is preferably stabilized in dispersion in the aqueous ink with a dispersant. The dispersant is preferably an ionic dispersant, and more preferably a polymer dispersant. Examples of polymer dispersants include poly(meth)acrylic acid (salts) such as poly(meth)acrylic acid and poly(meth)acrylate salts; copolymers of (meth)acrylic acid (salts) with one or more of the monomer components other than (meth)acrylic acid (salts), such as (meth)acrylic acid alkyl esters, (meth)acrylamide, styrene, maleic acid, maleic anhydride, maleic acid esters, and vinyl acetate; polyvinyl alcohol; and polyvinylpyrrolidone. The dispersant may have an acid value. From the viewpoint of reducing the viscosity of the aqueous ink, improving the dispersion stability, and suppressing an increase in electrical conductivity, the acid value of the dispersant is preferably 150 mgKOH / g or less, more preferably 100 mgKOH / g or less, and even more preferably 50 mgKOH / g or less. The lower limit is not particularly limited, but may be 5 mgKOH / g or more, preferably 6 mgKOH / g or more, and more preferably 7 mgKOH / g or more. As the dispersant, commercially available products may be used, and examples thereof include Disperbyk-102, Disperbyk-111, Disperbyk-190, Disperbyk-191, Disperbyk-194N, Disperbyk-2010, Disperbyk-2012, and Disperbyk-2015 manufactured by BYK Japan, and TEGO Dispers-715W, TEGO Dispers-750W, and TEGO Dispers-755W manufactured by BASF, and Efka 6230 manufactured by BASF, and among these, Disperbyk-190, Disperbyk-191, Disperbyk-194N, Disperbyk-2010, Disperbyk-2015, and TEGO Dispers-750W are preferred.

[0092] Examples of dyes include, but are not limited to, C.I. Solvent Black, C.I. Solvent Red, C.I. Solvent Yellow, C.I. Solvent Blue, C.I. Solvent Green, C.I. Solvent Orange, and C.I. Solvent Violet.

[0093] The content of the colorant in the solid content of the aqueous ink of the present invention is preferably from 5 to 80% by mass, more preferably from 20 to 70% by mass, and even more preferably from 35 to 60% by mass.

[0094] 3-3. Water-Based Solvent The water-based ink of the present invention contains a water-based solvent as a solvent. The water-based solvent acts as a diluent to adjust the viscosity of the water-based ink. The content of the water-based solvent in the water-based ink of the present invention is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 95 to 100% by mass, based on 100% by mass of all solvents contained in the water-based ink of the present invention.

[0095] The aqueous solvent may be a solvent derived from the aqueous solvent contained in the aqueous dispersion for ink described above, or may be a mixed solvent of a solvent derived from the aqueous solvent and another aqueous solvent. Specific examples of the aqueous solvent contained in the aqueous ink of the present invention include the same aqueous solvents as those described as the aqueous solvent contained in the aqueous dispersion for ink.

[0096] From the viewpoints of controlling the wetting and spreading of the aqueous ink onto the substrate, improving print image quality, and enhancing ejection stability, it is preferable that the aqueous solvent contained in the aqueous ink contains a water-soluble organic solvent. The content of the water-soluble organic solvent in the aqueous solvent is preferably 20 to 65% by mass, more preferably 30 to 55% by mass. Furthermore, the content of the water-soluble organic solvent in the aqueous ink is preferably 15 to 45% by mass, more preferably 20 to 40% by mass, and even more preferably 25 to 35% by mass.

[0097] In particular, from the viewpoints of improving print image quality and the safety of the aqueous ink, the water-soluble organic solvent is preferably a water-soluble organic solvent having a boiling point of 150°C or higher, and more preferably a water-soluble organic solvent having a boiling point of 180°C or higher. Furthermore, from the viewpoint of improving the drying properties of the aqueous ink, the boiling point of the water-soluble organic solvent is preferably 270°C or lower, and more preferably 240°C or lower. That is, the boiling point of the water-soluble organic solvent is preferably 150 to 270°C, and more preferably 180 to 240°C. Specific examples of the water-soluble organic solvent include propylene glycol, diethylene glycol, triethylene glycol, glycerin, diethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether, and propylene glycol and dipropylene glycol monomethyl ether are more preferred.

[0098] The content of the aqueous solvent in the aqueous ink of the present invention may be set according to the desired viscosity of the aqueous ink, and is not particularly limited. From the viewpoint of handleability, however, it is, for example, 40 to 90% by mass, preferably 50 to 88% by mass, and more preferably 55 to 85% by mass.

[0099] The aqueous ink of the present invention may further contain additives within the scope of not impairing the object of the present invention. For example, the aqueous ink may contain additives such as surfactants, dispersants, crosslinking agents, leveling agents, UV absorbers, UV stabilizers, thickeners, humectants, plasticizers, stabilizers, defoamers, antioxidants, crosslinking accelerators, pH adjusters, and preservatives in appropriate amounts.

[0100] As the surfactant, known surfactants such as acetylene glycol surfactants, silicone surfactants, and fluorine surfactants can be used.

[0101] As the dispersant, the same dispersants as those explained above can be used.

[0102] As the crosslinking agent, from the viewpoint of improving the coating film strength, an oxazoline group-containing compound, a carbodiimide group-containing compound, or the like can be preferably used. Examples of the oxazoline group-containing compound include EPOCROS WS-500, EPOCROS WS-700, EPOCROS K-2010, EPOCROS K-2020, and EPOCROS K-2030, all manufactured by Nippon Shokubai Co., Ltd. Examples of the carbodiimide group-containing compound include Carbodilite SV-02, Carbodilite V-02, Carbodilite V-02-L2, Carbodilite E-02, and Carbodilite E-05, all manufactured by Nisshinbo.

[0103] When the above additives are added, their content is not particularly limited, but is preferably 0.01 to 5% by mass, and more preferably 0.05 to 3% by mass, in the aqueous ink of the present invention. In particular, when a surfactant is added, its content is, for example, 0.01 to 2% by mass, based on 100% by mass of the aqueous ink. Furthermore, when a dispersant is added, its content is, for example, 0.3 to 3% by mass, based on 100% by mass of the aqueous ink. Furthermore, when a crosslinking agent is added, its content is preferably 0.1 to 15% by mass, and more preferably 1 to 10% by mass, based on 100% by mass of the aqueous ink.

[0104] The aqueous ink of the present invention may further contain, within the scope of the object of the present invention, other binder resins other than the polymer (A), such as vinyl resins, (meth)acrylic resins, olefin resins, urethane resins, fluorine-containing resins, silicone resins, epoxy resins, phenoxy resins, phenolic resins, xylene resins, etc. As the olefin resin, polyolefin waxes can be used from the viewpoint of improving abrasion resistance, and examples of polyolefin waxes include AQUACER 497, AQUACER 515, AQUACER 531, and AQUACER 1547 manufactured by BYK Corporation.

[0105] It should be noted that polymer particles composed of the aforementioned polymer (A) are also included in the binder resin in the aqueous ink of the present invention. The content of polymer particles composed of the polymer (A) in 100% by mass of the binder resin contained in the ink of the present invention is preferably 70 to 100% by mass, more preferably 85% by mass or more, and even more preferably 95% by mass or more. The other binder resins are also preferably added as polymer particles composed of the resin.

[0106] 3-5. Physical Properties of the Water-Based Ink The viscosity of the water-based ink of the present invention, when measured using an E-type viscometer at a temperature of 25°C and a rotation speed of 10 rpm, is preferably in the range of 2 to 20 mPa·s, and more preferably in the range of 2 to 15 mPa·s. By adjusting the viscosity of the water-based ink within the above range, clogging of the nozzles of an inkjet head can be suppressed when the water-based ink is applied to inkjet printing. The water-based ink of the present invention has good viscosity stability. The difference in viscosity of the water-based ink of the present invention before and after storage at 50°C for 4 weeks is preferably less than 2 mPa·s, more preferably less than 1.0 mPa·s, and even more preferably less than 0.5 mPa·s.

[0107] 3-6. Method for Producing Aqueous Ink There are no particular limitations on the method for producing the aqueous ink of the present invention. For example, the aqueous ink of the present invention can be produced using the aqueous dispersion for ink, specifically by mixing the aqueous dispersion for ink and a colorant, as well as an aqueous solvent and other additives that are used as needed. An example of a method for producing an aqueous ink is shown below, but the method is not limited thereto.

[0108] First, the aqueous dispersion for ink is prepared. The aqueous dispersion for ink can be produced by a conventional emulsion polymerization method as described above.

[0109] When a pigment is used as the colorant, it is preferable to prepare a pigment dispersion in which the pigment is dispersed in an aqueous solvent. The pigment dispersion can be produced, for example, by mixing the pigment and a dispersant in an aqueous solvent such as water, and dispersing the mixture using a bead mill or the like. The dispersant may be the same as the dispersants described above.

[0110] The content of the pigment in the pigment dispersion is not particularly limited, but is preferably 5 to 80% by mass relative to 100% by mass of the pigment dispersion. In particular, when the pigment is a white pigment, the content of the white pigment in the pigment dispersion is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass. Furthermore, from the viewpoints of dispersion stability and blocking resistance, the content of the dispersant is preferably 2 to 10 parts by mass, more preferably 2 to 5 parts by mass, relative to 100 parts by mass of the pigment.

[0111] The pigment dispersion may also contain a surfactant. The surfactant may be the same as the surfactant described above. The content of the surfactant in the pigment dispersion is preferably 0.01 to 1% by mass.

[0112] Next, the aqueous dispersion for ink, other colorants such as pigment dispersions and / or dyes, and an aqueous solvent and other additives used as needed are mixed. When mixing, the other colorants and other additives may be added as they are or as a solution diluted with a solvent or the like. The method and order of mixing the above components are not particularly limited. After mixing, centrifugation, filtration, or the like may be performed as needed.

[0113] 4. Printed Material The present invention also encompasses printed materials including a printed layer (image) formed from the aqueous ink. The printed material preferably has a printed layer formed from the aqueous ink laminated on a substrate.

[0114] Examples of the substrate include paper; paper (coated paper, etc.) laminated with a resin film such as polyethylene, polypropylene, polystyrene, etc.; metal plates such as aluminum, zinc, copper, etc.; polyolefin films such as polyethylene film, oriented polypropylene (OPP) film, and non-oriented polypropylene film (CPP), polyester films such as polyethylene terephthalate (PET) film, polyvinyl chloride film, nylon film, cellulose film, polystyrene film, polycarbonate film, polyvinyl acetal film, and acrylic resin film; paper having a metal coating; and resin films having a metal coating. Among these, resin films are preferred, more preferably polyolefin films and polyester films, and even more preferably OPP films and PET films.

[0115] The surface of the resin film on which the printing layer is laminated (i.e., the surface on which the aqueous ink of the present invention is printed) may be chemically or physically modified by corona treatment, anchor coat treatment, or the like. This improves adhesion to the printing layer formed from the aqueous ink of the present invention. In particular, corona-treated polyolefin films and corona-treated polyester films are preferred, and corona-treated OPP films and corona-treated PET films are more preferred.

[0116] The thickness of the substrate is not particularly limited, but is preferably 1 to 500 μm, more preferably 2 to 200 μm, even more preferably 5 to 100 μm, and particularly preferably 10 to 90 μm.

[0117] The printed matter can be produced by printing the aqueous ink onto a substrate. The printing method is not particularly limited, and flexographic printing, offset printing, lithographic printing, gravure printing, screen printing, inkjet printing, etc. can be used. In particular, digital printing is preferred because it does not require plate making and is resource and energy saving, and inkjet printing is more preferred among them. An example of a method for producing a printed matter by inkjet printing is shown below, but the method is not limited thereto.

[0118] Inkjet-printed printed materials can be produced by a production method including a printing layer formation step in which the aqueous ink of the present invention is applied to a substrate using an inkjet printer to form a printing layer. The inkjet printer used in the printing layer formation step is not particularly limited, and any conventionally known inkjet printer can be used. The inkjet printer may be of any type, such as a piezoelectric type, a thermal type, or a charge change control type (continuous ejection type). When a piezoelectric type inkjet printer is used, the ink ejection conditions, etc., are not particularly limited.

[0119] In the printing layer forming step, the aqueous ink of the present invention is ejected from the nozzle openings of the inkjet printer head and adheres to the substrate to form a printing layer (image).

[0120] It is preferable to further heat and dry the substrate on which the printing layer has been formed in the printing layer forming step at a temperature above room temperature. Heat treatment at a temperature above room temperature can promote the removal of volatile components, such as the solvent derived from the aqueous ink, contained in the printing layer formed on the substrate, and can promote the fixation of the printing layer. In addition, the adhesion of the printing layer can be further improved by film formation (fusion) of the binder resin (polymer particles composed of polymer (A)) contained in the aqueous ink.

[0121] The heating may be carried out simultaneously with the printing layer forming step, or after the printing layer forming step. Alternatively, both may be combined. For example, a method of carrying out heating simultaneously with the printing layer forming step includes a method of carrying out the printing layer forming step while heating the substrate. When heating is carried out after the printing layer forming step, preferred examples include a heating method using a heating dryer, a heating method using a heat press, a heating method using an infrared lamp, and a method using steam such as atmospheric steam or high-pressure steam. Among these, the heating method is preferably carried out after the printing layer forming step, since carrying out the heating simultaneously with the printing layer forming step may cause disturbances in the airflow.

[0122] The heating temperature (drying temperature) is preferably 30 to 120° C., more preferably 50 to 110° C. The heating time (drying temperature) may be appropriately set depending on the drying temperature, but from the viewpoint of productivity, it is, for example, 10 seconds to 1 hour, preferably 30 seconds to 10 minutes.

[0123] This application claims the benefit of priority based on Japanese Patent Application No. 2023-218604, filed on December 25, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-218604, filed on December 25, 2023, are incorporated herein by reference.

[0124] The present invention will now be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0125] The physical properties of the aqueous dispersions obtained in the examples and comparative examples and the polymer particles contained in the aqueous dispersions were measured as follows.

[0126] <Glass Transition Temperature of Polymer> The glass transition temperature (Tg) of the polymer constituting the polymer particles contained in the aqueous dispersion was calculated based on the Fox equation expressed by the following formula, using the glass transition temperatures of the homopolymers of each monomer used in the monomer components constituting the polymer: 1 / Tg A =Σ(Wm / Tgm) / 100 [In the formula, Tg A represents the glass transition temperature (absolute temperature: K) of the polymer, Wm represents the content (mass%) of monomer m in all the monomer components constituting the polymer, and Tgm represents the glass transition temperature (absolute temperature: K) of a homopolymer of monomer m.

[0127] <Acid value of polymer> The acid value of the polymer constituting the polymer particles contained in the aqueous dispersion was obtained by approximating the acid value as the number of mg of potassium hydroxide required to neutralize the acid groups present in 1 g of the monomer component constituting the polymer.

[0128] <Nonvolatile content (NV value) of aqueous dispersion> The nonvolatile content of the aqueous dispersion was calculated by weighing 1 g of the aqueous dispersion, drying it in a hot air dryer at 110°C for 1 hour, and defining the resulting residue as the nonvolatile content according to the following formula: [Nonvolatile content (mass%) in aqueous dispersion] = ([mass of residue] ÷ [mass of aqueous dispersion (1 g)]) × 100

[0129] <Weight-Average Molecular Weight of Polymer> The weight-average molecular weight of the polymer constituting the polymer particles contained in the aqueous dispersion was determined from a gel permeation chromatography chart prepared using a gel permeation chromatography equipped with an RI detector (manufactured by Tosoh Corporation, product number: HLC-8120GPC, column: TSKgel G-5000HXL and TSKgel GMHXL-L used in series, developing solvent: tetrahydrofuran (THF)), and a calibration curve prepared using standard polystyrenes F-450, A-5000, A-1000, and A-300 manufactured by Tosoh Corporation.

[0130] The average particle size (hydrodynamic diameter) of the polymer particles contained in the aqueous dispersion was measured at a measurement temperature of 25°C using a multi-analyte nanoparticle size measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: nanoSAQLA), which is a particle size measurement device using a dynamic light scattering method, by determining an autocorrelation function using a photon correlation method and then calculating the average particle size by cumulant analysis.

[0131] [Preparation of Aqueous Dispersion] [Example 1] 1,050 parts of deionized water was charged into a flask equipped with a dropping funnel, a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser. A pre-emulsion for dropping, consisting of 381 parts of deionized water, 80 parts of a 25% aqueous solution of an emulsifier [reactive emulsifier, manufactured by ADEKA, trade name: ADEKA REASOAP SR-10], 300 parts of styrene, 250 parts of 2-ethylhexyl acrylate, 450 parts of methyl methacrylate, and 10 parts of tert-dodecyl mercaptan, was prepared and added to the dropping funnel. 74 parts, or 5% of the total amount, was added to the flask. The temperature was raised to 80°C while slowly blowing in nitrogen gas. Next, 30 parts of a 5% aqueous ammonium persulfate solution was added, and polymerization was initiated. Thereafter, the remainder of the pre-emulsion for dropping and 30 parts of a 5% aqueous ammonium persulfate solution were uniformly added dropwise to the flask over 180 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 80°C for 120 minutes, and the pH was adjusted to 8 by adding 25% aqueous ammonia to terminate the polymerization. The resulting reaction solution was cooled to room temperature and then filtered through a 300-mesh wire mesh to prepare an aqueous dispersion containing polymer particles. The nonvolatile content (NV value) of this aqueous dispersion was 40% by mass. The average particle size of the polymer particles contained in the aqueous dispersion was 100 nm, and the polymer constituting the polymer particles had an acid value of 0 mgKOH / g, a glass transition temperature of 37°C, and a weight-average molecular weight of 83,000.

[0132] [Examples 2 to 18, Comparative Examples 1 to 4] Aqueous dispersions were prepared in the same manner as in Example 1, except that the types and amounts of the monomer components, emulsifiers, and chain transfer agents were changed as shown in Tables 1 and 2.

[0133] [Preparation of White Paste A] 424 parts of deionized water, 535 parts of JR-403 [titanium oxide, manufactured by Teika Corporation], 40 parts of Disperbyk-190 [dispersant, acid value 10 mg KOH / g, active ingredient concentration 40%, manufactured by BYK Japan], 1 part of Olfine D-10 [surfactant, manufactured by Nissin Chemical Industry Co., Ltd.], and 200 parts of glass beads (diameter 1 mm) were mixed in a Disper at a rotation speed of 3000 min -1 After dispersing for 120 minutes at 40°C, the mixture was filtered through a 300-mesh wire screen to prepare a white paste A.

[0134] [Preparation of Water-Based Inks] [Experimental Examples 1 to 14, Comparative Experimental Examples 1 to 4] 32.5 parts of each of the aqueous dispersions obtained in Examples 1 to 14 and Comparative Examples 1 to 4 was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 50°C, 27.2 parts of White Paste A, 15 parts of propylene glycol (hereinafter, PG), 15 parts of dipropylene glycol monomethyl ether (hereinafter, MFDG), 0.8 parts of BYK-3480 [manufactured by BYK Japan, surfactant], and deionized water to bring the total to 100 parts were added, and the mixture was stirred for a further 30 minutes, and then filtered through a 3 μm filter [manufactured by Advantec Co., Ltd., MCP-3-C10S] to prepare an aqueous ink.

[0135] [Experimental Example 15] 3.7 parts of a polyolefin wax [AQUACER 515, manufactured by BYK Japan, non-volatile content 35% by mass] was added to 29.3 parts of the aqueous dispersion obtained in Example 15, and the mixture was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 50°C, 27.2 parts of White Paste A, 15 parts of PG, 15 parts of MFDG, 0.8 parts of BYK-3480 [a surfactant manufactured by BYK Japan], and deionized water to a total of 100 parts were added, and the mixture was stirred for a further 30 minutes, followed by filtration through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to prepare an aqueous ink. Details are shown in Table 2.

[0136] [Experimental Example 16] 2.6 parts of an oxazoline-based crosslinking agent [WS-700, manufactured by Nippon Shokubai Co., Ltd., nonvolatile content 25% by mass] was added to 30.9 parts of the aqueous dispersion obtained in Example 16, and the mixture was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 50°C, 27.2 parts of White Paste A, 15 parts of PG, 15 parts of MFDG, 0.8 parts of BYK-3480 [a surfactant manufactured by BYK Japan], and deionized water to a total of 100 parts were added, and the mixture was stirred for a further 30 minutes, followed by filtration through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to prepare an aqueous ink. Details are shown in Table 2.

[0137] [Experimental Example 17] 1.6 parts of a carbodiimide crosslinking agent [Nisshinbo Chemical Co., Ltd., Carbodilite SV-02, non-volatile content 40%] was added to 30.9 parts of the aqueous dispersion obtained in Example 17, and the mixture was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 50°C, 27.2 parts of White Paste A, 15 parts of PG, 15 parts of MFDG, 0.8 parts of BYK-3480 [a surfactant manufactured by BYK Japan], and deionized water to a total of 100 parts were added, and the mixture was stirred for a further 30 minutes, followed by filtration through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to prepare an aqueous ink. Details are shown in Table 2.

[0138] [Experimental Example 18] 3.7 parts of a polyolefin wax [AQUACER 515, manufactured by BYK Japan, non-volatile content 35% by mass] and 1.6 parts of a carbodiimide crosslinking agent [Carbodilite SV-02, manufactured by Nisshinbo Chemical Inc., non-volatile content 40%] were added to 27.6 parts of the aqueous dispersion obtained in Example 18, and the mixture was mixed in a homodisper at a rotation speed of 1000 min -1 While stirring at 50°C, 27.2 parts of White Paste A, 15 parts of PG, 15 parts of MFDG, 0.8 parts of BYK-3480 [a surfactant manufactured by BYK Japan], and deionized water to a total of 100 parts were added, and the mixture was stirred for a further 30 minutes, followed by filtration through a 3 μm filter [MCP-3-C10S manufactured by Advantec Co., Ltd.] to prepare an aqueous ink. Details are shown in Table 2.

[0139] [Preparation of Inkjet Printed Material] A corona-treated PET film (manufactured by Futamura Chemical Co., Ltd., trade name: Taiko Polyester Film FE2001) or a corona-treated OPP film (manufactured by Futamura Chemical Co., Ltd., trade name: FOR-AQ) was used as the substrate. A solid image of aqueous ink was printed on the substrate by inkjet recording at a coverage of 100% (40 pL, 360 × 360 dpi), and immediately thereafter, the printed substrate was dried for 2 minutes in a dryer at 100 ° C. to obtain a printed material. Printing was performed using a print evaluation device (manufactured by ImageXpert Co., Ltd.) equipped with an inkjet printhead (manufactured by SII Printec Co., Ltd., product number: RC1536) in air at a temperature of 25 ± 1 ° C. and a relative humidity of 30 ± 5%.

[0140] -Evaluation Method- <Adhesion> Adhesive tape (Nichiban Co., Ltd., Cellotape (registered trademark) No. 405, 24 mm wide) was applied to the solid image area of ​​each printed matter at room temperature, left to stand for 1 minute, and then peeled off in a 180° direction. The evaluation area was scanned using a printer scanner against a black background, and then image analysis software (Image Analyzer) was used to calculate the peel rate (%) = area of ​​black area / total area of ​​evaluation area × 100. The peel rate (%) was rounded to the nearest integer. Adhesion was evaluated from the obtained peel rate based on the following evaluation criteria. The results of the adhesion evaluation when a corona-treated PET film was used as the substrate are shown in Tables 1 and 2 as PET adhesion, and the results of the adhesion evaluation when a corona-treated OPP film was used as the substrate are shown in Tables 1 and 2 as OPP adhesion. [Evaluation Criteria] 5: The peel rate of the printed image was 0%. 4: The peel rate of the printed image was 1 to 20%. 3: The peeling rate of the printed image is 21 to 50%. 2: The peeling rate of the printed image is 51 to 75%. 1: The peeling rate of the printed image is 76 to 100%.

[0141] <Viscosity Stability> The aqueous ink was placed in a glass bottle and stored for 4 weeks in a thermostatic chamber with the internal temperature set to 50°C. The viscosity of the aqueous ink was measured before and after storage using an E-type viscometer at a temperature of 25°C and a rotation speed of 10 rpm. The viscosity stability was evaluated based on the obtained viscosity in accordance with the following evaluation criteria. The results are shown in Tables 1 and 2. [Evaluation Criteria] 5: The difference in viscosity before and after storage is less than 0.5 mPa·s 4: The difference in viscosity before and after storage is 0.5 mPa·s or more but less than 1.0 mPa·s 3: The difference in viscosity before and after storage is 1.0 mPa·s or more but less than 2.0 mPa·s 2: The difference in viscosity before and after storage is 2.0 mPa·s or more but less than 3.0 mPa·s 1: The difference in viscosity before and after storage is 3.0 mPa·s or more

[0142] <Overall evaluation> The total score for each test item was used as the index for the overall evaluation.

[0143]

[0144]

[0145] The abbreviations in Tables 1 and 2 above represent the following compounds: St: styrene BzA: benzyl acrylate CHMA: cyclohexyl methacrylate IBOA: isobornyl acrylate HEMA: 2-hydroxyethyl methacrylate HPA: hydroxypropyl acrylate 2EHA: 2-ethylhexyl acrylate 2OA: 2-octyl acrylate MMA: methyl methacrylate AA: acrylic acid LA-82: 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, UV stabilizer manufactured by ADEKA, trade name: Adeka STAB LA-82 SR-10: reactive emulsifier manufactured by ADEKA, trade name: Adeka Reasoap SR-10 t-DM: tert-dodecyl mercaptan

[0146] The results in Tables 1 and 2 show that the aqueous inks of Experimental Examples 1 to 18, which used aqueous dispersions (Examples 1 to 18) containing polymer particles composed of a polymer having 18 to 42 mass% of structural units derived from an aromatic group-containing monomer and a weight-average molecular weight of 50,000 to 100,000, were able to achieve both high adhesion to PET films and OPP films and good viscosity stability. In particular, compared to the aqueous ink of Comparative Experimental Example 1, which used an aqueous dispersion (Comparative Example 1) containing polymer particles composed of a polymer with a low content of structural units derived from an aromatic group-containing monomer, the aqueous inks of Experimental Examples 1 to 18, which used aqueous dispersions (Examples 1 to 18) containing polymer particles composed of a polymer with such a content adjusted to 18 to 42 mass%, had improved viscosity stability. Furthermore, the aqueous ink of Comparative Experimental Example 2, which used an aqueous dispersion (Comparative Example 2) containing polymer particles composed of a polymer with a high content of structural units derived from an aromatic group-containing monomer, did not have sufficient adhesion to OPP film, while the aqueous inks of Experimental Examples 1 to 18, which used aqueous dispersions containing polymer particles composed of a polymer in which the content was adjusted to 18 to 42 mass% (Examples 1 to 18), exhibited high adhesion to both PET film and OPP film substrates. Furthermore, compared to the aqueous ink of Comparative Experimental Example 3, which used an aqueous dispersion (Comparative Example 3) containing polymer particles composed of a polymer with a low weight-average molecular weight, the aqueous inks of Experimental Examples 1 to 18, which used aqueous dispersions containing polymer particles composed of a polymer adjusted to a weight-average molecular weight of 50,000 to 100,000, had improved viscosity stability. Furthermore, compared to the aqueous ink of Comparative Experimental Example 4, which used an aqueous dispersion containing polymer particles composed of a polymer with a large weight-average molecular weight (Comparative Example 4), the aqueous inks of Experimental Examples 1 to 18, which used aqueous dispersions containing polymer particles composed of a polymer adjusted to have a weight-average molecular weight of 50,000 to 100,000 (Examples 1 to 18), resulted in improved adhesion to both PET film and OPP film.

Claims

1. An aqueous ink dispersion containing polymer particles composed of a polymer (A), wherein the polymer (A) has a structural unit derived from an aromatic group-containing monomer in an amount of 18 to 42% by mass, and the weight average molecular weight of the polymer (A) is 50,000 to 100,000.

2. The aqueous ink dispersion according to claim 1, wherein the aromatic group-containing monomer is a monomer having at least one benzene ring or naphthalene ring and at least one polymerizable unsaturated group in the molecule.

3. The aqueous ink dispersion according to claim 1, wherein the polymer (A) further contains a structural unit derived from a hydroxyl group-containing monomer, and the content of the structural unit derived from the hydroxyl group-containing monomer is 30 to 150 parts by mass with respect to 100 parts by mass of the structural unit derived from the aromatic group-containing monomer.

4. The aqueous ink dispersion according to claim 3, wherein the hydroxyl group-containing monomer is a monomer having at least one hydroxyl group and at least one (meth)acryloyl group in the molecule.

5. The aqueous ink dispersion according to claim 1, wherein the polymer (A) further contains a structural unit derived from a cyclic aliphatic group-containing monomer, and the content of the structural unit derived from the cyclic aliphatic group-containing monomer is 60 to 180 parts by mass with respect to 100 parts by mass of the structural unit derived from the aromatic group-containing monomer.

6. The aqueous ink dispersion according to claim 5, wherein the cyclic aliphatic group-containing monomer is a monomer having at least one alicyclic hydrocarbon ring and at least one polymerizable unsaturated group in the molecule, and the alicyclic hydrocarbon ring is a cycloalkyl group, an isobornyl group, or an adamantyl group.

7. The aqueous ink dispersion according to claim 1, wherein the glass transition temperature of the polymer (A) is -10 to 75°C.

8. The aqueous ink dispersion according to claim 1, wherein the acid value of the polymer (A) is 10 mgKOH / g or less.

9. An aqueous ink containing the aqueous ink dispersion according to any one of claims 1 to 8 and a colorant.

10. The aqueous ink according to claim 9, wherein the colorant is a white pigment.

11. A printed matter containing a printed layer formed from the aqueous ink according to claim 9.

12. A method for producing an aqueous ink using the aqueous dispersion according to any one of claims 1 to 8.

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