UV-curable aqueous inks, dispersions, UV-curable aqueous compositions, and printed materials

Abstract

Provided is an ultraviolet-curable aqueous ink excellent in terms of coating-film performance, especially alcohol resistance and abrasion resistance.　This ultraviolet-curable aqueous ink comprises an ultraviolet-curable oligomer, a colorant, and a mercapto compound, wherein the ultraviolet-curable oligomer includes a structural unit derived from a compound represented by chemical formula (1). (In formula (1), X is an alkylene group, Y is any of a (meth)acryloyl group, an allyl group, an acyl group, and a hydrogen atom, and n is an integer of 2 or larger.)　Alternatively, this ultraviolet-curable aqueous ink comprises a colorant, a mercapto compound, and the ultraviolet-curable oligomer which includes a structural unit derived from a polyisocyanate compound (A), the compound (A) being a compound having three or more isocyanate groups in the molecule.

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet-curable aqueous ink, to printed materials using this ultraviolet-curable aqueous ink, and further to an ultraviolet-curable aqueous composition and dispersion suitable for this ultraviolet-curable aqueous ink. [Background technology]

[0002] Inkjet printers have several advantages, including the ease of full-color printing, low noise levels, the ability to produce high-resolution images at a low cost, high-speed printing, the ability to print not only on flat surfaces but also on curved surfaces, and the ability to easily print on large areas. For these reasons, they are rapidly gaining popularity not only for personal use but also as commercial inkjet printers for applications such as signage, window films, posters, car wrapping, and wallpaper.

[0003] Commercial inkjet printers require printed materials to have the following characteristics: (1) high image quality, (2) high film durability, (3) high-speed printing, (4) versatility of substrates, and (5) environmental friendliness and safety. When printing large-area materials or materials for outdoor use, excellent coating performance is required, including water resistance, alcohol resistance, coating strength, and lightfastness of the printed film.

[0004] Conventionally, inks used for commercial inkjet printers have included: water-based inks in which pigments are dispersed in an aqueous medium; solvent-based UV inks in which pigments and UV-curable monomers are dispersed or dissolved in an organic solvent; solvent-free UV inks in which pigments are dispersed in UV-curable monomers without a solvent; water-based latex inks in which pigments and resins are dispersed in an aqueous medium; and UV-curable water-based inks in which pigments and UV-curable oligomers are dispersed in an aqueous medium.

[0005] Among these, UV-curable water-based inks possess a relatively good balance of all properties. However, water-based inks generally have inferior coating performance and weak coating strength, making them unsuitable for large-area prints or outdoor use. In such UV-curable water-based inks, an inkjet recording ink has been developed that offers improved abrasion resistance. This inkjet recording ink contains water, a reaction initiator or a crosslinking agent or both, and a compound that reacts with the reaction initiator or the crosslinking agent or both, wherein the reaction initiator or the crosslinking agent or both are contained as a coating coated with a resin, the volume-average particle size of the coating is 50 nm or more and 500 nm or less, and the weight-average molecular weight of the resin is 500 or more and 5000 or less (see Patent Document 1 below). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-163381 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the object of the present invention is to provide an ultraviolet-curable water-based ink that possesses a relatively good balance of all properties, and that exhibits even better coating film performance than conventional inks, particularly superior alcohol resistance and abrasion resistance. [Means for solving the problem]

[0008] As a result of diligent research, the inventors have discovered that by using an ultraviolet-curable oligomer and incorporating a mercapto compound as an additive, it is possible to create an ultraviolet-curable water-based ink with excellent alcohol resistance and abrasion resistance. This invention was achieved based on the above findings, and its gist is as follows.

[0009] [1] A UV-curable aqueous ink comprising at least a UV-curable oligomer, a colorant, and a mercapto compound, wherein the UV-curable oligomer has a structural unit derived from a compound represented by the following formula (1). [Chemical formula] (In formula (1), X is an alkylene group, Y is any one of a (meth)acryloyl group, an allyl group, an acyl group, and a hydrogen atom. n is an integer of 2 or more.)

[0010] [2] The ultraviolet-curable aqueous ink according to [1], wherein the ultraviolet-curable oligomer further has a structural unit derived from a compound containing 4 or more polymerizable unsaturated bonds.

[0011] [3] The ultraviolet-curable aqueous ink according to [1], wherein the ultraviolet-curable oligomer further has a structural unit derived from a polyisocyanate compound (A), and the compound (A) is a compound having 2 or more isocyanate groups in one molecule.

[0012] [4] An ultraviolet-curable aqueous ink containing at least an ultraviolet-curable oligomer, a colorant, and a mercapto compound, wherein the ultraviolet-curable oligomer has a structural unit derived from a polyisocyanate compound (A), and the compound (A) is a compound having 3 or more isocyanate groups in one molecule.

[0013] [5] The ultraviolet-curable aqueous ink according to any one of [1] to [4], wherein the mercapto compound is a secondary thiol.

[0014] [6] The ultraviolet-curable aqueous ink according to any one of [1] to [5], wherein the mercapto compound is a polyfunctional thiol.

[0015] [7] The ultraviolet-curable aqueous ink according to any one of [1] to [6], wherein the content of the mercapto compound is 0.01% by mass or more and 5% by mass or less.

[0016] [8] The ultraviolet-curable aqueous ink according to any one of [1] to [7], further containing one or two or more of a polymerization initiator, a sensitizer, and a surfactant.

[0017] [9] The ultraviolet curable aqueous ink according to any one of [1] to [8], wherein the mercapto compound is encapsulated in the ultraviolet curable oligomer.

[0018]

[10] The ultraviolet curable aqueous ink according to any one of [1] to [9], comprising a polymerization initiator and / or a sensitizer, wherein at least one of the polymerization initiator and / or the sensitizer is encapsulated in the ultraviolet curable oligomer.

[0019]

[11] The ultraviolet curable aqueous ink according to any one of [1] to

[10] , wherein the ultraviolet curable oligomer is nonionic.

[0020]

[12] The ultraviolet curable aqueous ink according to any one of [1] to

[11] , wherein the average particle size of the ultraviolet curable oligomer is 10 nm or more and 200 nm or less.

[0021]

[13] The ultraviolet curable aqueous ink according to any one of [1] to

[12] , wherein the average particle size of the ultraviolet curable oligomer is 10 nm or more and 200 nm or less.

[0022]

[14] A printed matter having a cured product formed from the ultraviolet curable aqueous ink according to any one of [1] to

[13] on a recording medium.

[0023]

[15] A dispersion of an ultraviolet curable oligomer, containing 0.01% by mass or more and 10% by mass or less of a mercapto compound, wherein the ultraviolet curable oligomer has a structural unit derived from a compound represented by the following formula (1). [Chemical formula] (In formula (1), X is an alkylene group, Y is any one of a (meth)acryloyl group, an allyl group, an acyl group, and a hydrogen atom. n is an integer of 2 or more.)

[0024]

[16] A dispersion of an ultraviolet-curable oligomer, containing 0.01% by mass or more and 10% by mass or less of a mercapto compound, wherein the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and the compound (A) is a compound having three or more isocyanate groups in one molecule.

[0025]

[17] The dispersion according to

[15] or

[16] , wherein the mercapto compound is a secondary thiol.

[0026]

[18] A dispersion according to any one of

[15] to

[17] , wherein the mercapto compound is a polyfunctional thiol.

[0027]

[19] An ultraviolet-curable aqueous composition comprising an ultraviolet-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, wherein the ultraviolet-curable oligomer has a structural unit derived from a compound represented by the following formula (1). [ka] (In formula (1), X is an alkylene group, and Y is one of the following: a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

[0028]

[20] An ultraviolet-curable aqueous composition comprising an ultraviolet-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, wherein the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and compound (A) is a compound having three or more isocyanate groups in one molecule.

[0029]

[21] The ultraviolet-curable aqueous composition according to

[19] , wherein the ultraviolet-curable oligomer further comprises structural units derived from a compound containing four or more polymerizable unsaturated bonds.

[0030]

[22] The ultraviolet-curable aqueous composition according to

[19] , wherein the ultraviolet-curable oligomer further comprises a structural unit derived from a polyisocyanate compound (A), and the compound (A) is a compound having two or more isocyanate groups in one molecule.

[0031]

[23] The ultraviolet-curable aqueous composition according to any one of

[19] to

[22] , wherein the mercapto compound is a secondary thiol.

[0032]

[24] The ultraviolet-curable aqueous composition according to any one of

[19] to

[23] , wherein the mercapto compound is a polyfunctional thiol.

[0033]

[25] The ultraviolet-curable aqueous composition according to any one of

[19] to

[24] , wherein the mercapto compound is encapsulated in the ultraviolet-curable oligomer.

[0034]

[26] A UV-curable aqueous composition according to any one of

[19] to

[25] , comprising a polymerization initiator and / or a sensitizer, wherein at least one of the polymerization initiator and / or sensitizer is encapsulated in the UV-curable oligomer.

[0035]

[27] The ultraviolet-curable aqueous composition according to any one of

[19] to

[26] , wherein the ultraviolet-curable oligomer is nonionic. [Effects of the Invention]

[0036] The UV-curable water-based ink of the present invention satisfies the required characteristics of a printing ink in a well-balanced manner, while also exhibiting excellent coating film performance, particularly alcohol resistance and abrasion resistance. [Modes for carrying out the invention]

[0037] One embodiment of the present invention is described below. However, the present invention is not limited to this embodiment.

[0038] In this invention, when expressed as "X~Y" (where X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or greater and Y or less," as well as "preferably greater than X" and "preferably less than Y."

[0039] [UV-curable water-based ink] The ultraviolet-curable aqueous ink of the present invention (hereinafter sometimes referred to as "the ink of the present invention") contains, in the first embodiment of the ink of the present invention, at least an ultraviolet-curable oligomer, a colorant, and a mercapto compound, wherein the ultraviolet-curable oligomer has a structural unit derived from a compound represented by the following formula (1). [ka] (In formula (1), X is an alkylene group, and Y is one of the following: a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

[0040] In a second embodiment of the ink of the present invention, the ink contains at least an ultraviolet-curable oligomer, a colorant, and a mercapto compound, wherein the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and compound (A) is a compound having three or more isocyanate groups in one molecule.

[0041] Although the ink of the present invention is UV-curable, the active energy rays used for curing are not limited to ultraviolet light. When curing the ink of the present invention, curing is not limited to curing by active energy rays; for example, curing may also be done by heat. Furthermore, the ink of the present invention is suitably used for inkjet printing.

[0042] [UV-curable oligomer] The presence or absence of ionicity of the UV-curable oligomer used in this invention is not particularly limited; it may be nonionic or ionic (anionic, cationic, or amphoteric). However, being nonionic can suppress pigment aggregation and improve the storage stability of the ink. Here, nonionic means, for example, that the hydrophilic group of the UV-curable oligomer is composed of ether bonds or hydroxyl groups that do not ionically dissociate in water. Ionic (anionic, cationic, or amphoteric) means, for example, that the UV-curable oligomer has carboxyl groups or amino groups that can ionically dissociate in water. More specifically, an anionic UV-curable oligomer is, for example, a UV-curable oligomer containing a carboxyl group.

[0043] There are no particular limitations on the UV-curable oligomer used in the present invention, but those that have excellent UV curability, fixability, water dispersion stability, pigment aggregation suppression effect, alcohol resistance, etc., are, for example, the following: <1> ~ <3> One of the following is preferable.

[0044] <1> Those having structural units derived from compounds represented by the following formula (1) [ka] (In formula (1), X is an alkylene group, and Y is one of the following: a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

[0045] <2> A compound having a structural unit derived from a polyisocyanate compound (A), wherein compound (A) has three or more isocyanate groups in one molecule.

[0046] <3> A structural unit derived from polyisocyanate compound (A), a structural unit derived from compound (B') shown below, and a structural unit derived from compound (C') shown below.

[0047] Furthermore, the above <3> UV-curable oligomers like the one described are typically produced by reacting a polyisocyanate compound (A) with compound (B') and compound (C').

[0048] Compound (B'): A compound containing two or more polymerizable unsaturated bonds and capable of binding with polyisocyanate compound (A). Compound (C'): A water-soluble compound that can bind to polyisocyanate compound (A).

[0049] Furthermore, the UV-curable oligomer used in the present invention is preferably one having structural units derived from (meth)acrylate, and in particular, one having structural units derived from polyfunctional (meth)acrylate. Moreover, it is preferable that it has structural units derived from both polyfunctional (meth)acrylate and polyalkylene glycol. That is, from the viewpoint of reactivity, compound (B') is preferably a hydroxyl group-containing polyfunctional (meth)acrylate (B). Also, from the viewpoint of water dispersibility, compound (C') is preferably a polyalkylene glycol (C). Such UV-curable oligomers are usually produced by reacting a polyisocyanate compound (A), a hydroxyl group-containing polyfunctional (meth)acrylate (B), and a polyalkylene glycol (C). In this invention, "(meth)acrylate" means acrylate or methacrylate. In this invention, "structural unit derived from X" refers to a structural unit that is incorporated into the molecular structure of an ultraviolet-curable oligomer by the reaction of compound X with other compounds, using compound X as a raw material. However, "structural unit derived from X" is not necessarily limited to being formed from compound X as a raw material. That is, even if formed from raw materials other than X, it will still be considered an "structural unit derived from X" if its chemical structure is the same.

[0050] In the UV-curable oligomer, the structural unit portion derived from the polyisocyanate compound (A) contributes to the adhesion of the printed film to the recording medium. The structural unit portion derived from compound (B') contributes to UV curability. Furthermore, if compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), the (meth)acryloyl group contained in the structural unit derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) contributes to UV curability. The structural unit portion derived from compound (C') contributes to the water dispersibility of the oligomer in the ink. Furthermore, if the compound (C') is polyalkylene glycol (C), the polyalkylene glycol chain of the structural unit derived from the polyalkylene glycol (C) contributes to the water dispersibility of the oligomer in the ink. The aforementioned UV-curable oligomer is preferable because it contains all of these structural units within the same molecule. Furthermore, since excellent solvent resistance, such as alcohol resistance, can be achieved, it is preferable that the structural units derived from the polyisocyanate compound (A) are bonded to the structural units derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and the structural units derived from the polyalkylene glycol (C) via urethane bonds. As a result, the UV-curable oligomer can be made to have excellent UV curability, coating performance, substrate adhesion, and water dispersion stability.

[0051] As described above, a preferred embodiment of compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B), but a preferred embodiment of compound (B') may also be "a compound (B) containing a hydroxyl group and containing two or more polymerizable unsaturated bonds." The "compound capable of bonding with polyisocyanate compound (A)" in compound (B') may be a compound in which the hydroxyl group of compound (B) is replaced with a carboxyl group, an amino group, etc. Examples of polymerizable unsaturated bonds include carbon-carbon double bonds and carbon-carbon triple bonds, with carbon-carbon double bonds being preferred. More specifically, carbon-carbon double bonds derived from vinyl groups, (meth)acryloyl groups, etc., are examples. The water-soluble compounds in compound (C') include water-soluble polymers, specifically polyglycerin, polyhydroxy(meth)acrylate, polyamine, quaternary amination polystyrene, sulfonated polystyrene, polyether, and polyalkylene glycol. Among these, nonionic water-soluble compounds such as polyglycerin, polyhydroxy(meth)acrylate, and polyalkylene glycol are preferred, with polyalkylene glycol being particularly preferred. Each of these water-soluble compounds may be a copolymer. Compound (C') has the structure of such a water-soluble compound and the structure of a "compound that can be bound to polyisocyanate compound (A)". Here, the structure of the "compound that can be bound to polyisocyanate compound (A)" can be selected from structures similar to those exemplified as compound (B') above.

[0052] Furthermore, structural units derived from the polyisocyanate compound (A) form urethane bonds by bonding with structural units derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B) and structural units derived from the polyalkylene glycol (C). These urethane bonds may be substituted with urea bonds or amide bonds, respectively. To form a urea bond, the hydroxyl group in the hydroxyl-containing polyfunctional (meth)acrylate (B) can be replaced with an amino group as compound (B'), or the hydroxyl-terminated group constituting the polyalkylene glycol (C) can be replaced with an amino group as compound (C'). To form an amide bond, the hydroxyl group in the hydroxyl-containing polyfunctional (meth)acrylate (B) can be replaced with a carboxyl group as compound (B'), or the hydroxyl-terminated group in the polyalkylene glycol (C) can be replaced with a carboxyl group as compound (C'). Alternatively, instead of converting the hydroxyl group in this way, a compound that can already form urea bonds or amide bonds can be used to achieve a substantially similar chemical structure. As mentioned above, the structural units derived from polyisocyanate compound (A) contribute to the adhesion of the printed film to the recording medium. This is thought to be because, as described above, the isocyanate groups in polyisocyanate compound (A) form polar sites such as urethane bonds, urea bonds, or amide bonds in the UV-curable oligomer.

[0053] In the present invention, when the hydroxyl group-containing polyfunctional (meth)acrylate (B) is replaced with the above compound (B') or compound (B"), or when the polyalkylene glycol (C) is replaced with the above compound (C'), the preferred or specific embodiments in such cases can be similarly applied to the preferred or specific embodiments when the hydroxyl group-containing polyfunctional (meth)acrylate (B) or polyalkylene glycol (C) described later is used.

[0054] The following describes each compound that constitutes the UV-curable oligomer. In this invention, "oligomer" is not a term limited to a specific molecular weight range, etc., but is sufficient as long as it has the structure shown below. The ink of the present invention may contain only one type of UV-curable oligomer, or it may contain two or more types.

[0055] <Polyisocyanate compound (A)> Polyisocyanate compound (A) is a compound having a total of two or more isocyanate groups in one molecule.

[0056] The type of polyisocyanate compound (A) is not particularly limited, and examples include linear aliphatic polyisocyanates, aromatic polyisocyanates, and alicyclic polyisocyanates. Among these, polyisocyanate compound (A) is preferably a trimer compound of polyisocyanate from the viewpoint of weather resistance and hardness.

[0057] A linear aliphatic polyisocyanate is a compound having a linear aliphatic structure and two or more isocyanate groups. Linear aliphatic polyisocyanates are preferred from the viewpoint of weather resistance and stretchability. The linear aliphatic structure in linear aliphatic polyisocyanates is not particularly limited, but linear or branched alkylene groups having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, are preferred. Examples of linear aliphatic polyisocyanates include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate, or trimer compounds of these polyisocyanates.

[0058] Aromatic polyisocyanates are compounds having an aromatic structure and two or more isocyanate groups. Aromatic polyisocyanates are preferred from the viewpoint of coating film strength. The aromatic structure in aromatic polyisocyanates is not particularly limited, but an aromatic structure having 6 to 13 carbon atoms is preferred. Examples of aromatic polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, and naphthalene diisocyanate, or trimer compounds of these polyisocyanates.

[0059] Alicyclic polyisocyanates are compounds having an alicyclic structure and two or more isocyanate groups. The alicyclic structure in alicyclic polyisocyanates is not particularly limited, but its carbon number is usually 5 or more, preferably 6 or more, usually 15 or less, preferably 14 or less, and more preferably 13 or less. A cycloalkylene group is particularly preferred for the alicyclic structure. Examples of alicyclic polyisocyanates include diisocyanates having an alicyclic structure such as bis(isocyanate-methyl)cyclohexane, cyclohexane diisocyanate, bis(isocyanate-cyclohexyl)methane, isophorone diisocyanate, or trimer compounds of these polyisocyanates.

[0060] For UV-curable oligomers, only one of these polyisocyanate compounds (A) may be used, or two or more may be used in combination. Furthermore, polyisocyanates having two or more structures from among a linear aliphatic structure, an aromatic structure, and an alicyclic structure may be used as polyisocyanate compound (A).

[0061] As for the polyisocyanate compound (A), those having three or more isocyanate groups are preferred, particularly from the viewpoint of adhesion to the substrate, while those having six or fewer is preferred. Furthermore, as the polyisocyanate compound (A), trimers obtained by a trimer reaction from hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, phenylene diisocyanate, etc., are preferred, and trimers of hexamethylene diisocyanate are particularly preferred. In a second embodiment of the ink of the present invention, the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and it is preferable that the compound (A) is a compound having three or more isocyanate groups in one molecule.

[0062] <Compounds containing polymerizable unsaturated bonds> In compounds containing polymerizable unsaturated bonds, the number of polymerizable unsaturated bonds is preferably 1 or more, more preferably 2 or more, and even more preferably 4 or more. On the other hand, 8 or less is preferred, and 6 or less is more preferred. Furthermore, the compound containing polymerizable unsaturated bonds is preferably a compound that can bond with polyisocyanate compound (A).

[0063] (Compound (B')) Compound (B') is a compound that contains two or more polymerizable unsaturated bonds and is capable of bonding with polyisocyanate compound (A). Compound (B') can be any compound having a hydroxyl group, an amino group, or a carboxyl group. Other examples of compound (B') include polyfunctional vinyl monomers, polyfunctional allyl monomers, and polyfunctional (meth)acrylates. Among these, a hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferred as compound (B').

[0064] <Hydroxyl group-containing polyfunctional (meth)acrylate (B)> Hydroxyl group-containing polyfunctional (meth)acrylate (B) has one or more hydroxyl groups and two or more (meth)acryloyl groups. Specifically, examples include (meth)acrylic acid partial esters of polyhydric alcohols. In the curing reaction, polyfunctional (meth)acrylates containing hydroxyl groups form a good crosslinked structure through the involvement of multiple (meth)acryloyl groups, resulting in good physical properties such as stain resistance and abrasion resistance.

[0065] The number of hydroxyl groups in the hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferably 3 or less, more preferably 2 or less, and even more preferably 1. The number of (meth)acryloyl groups in the hydroxyl group-containing polyfunctional (meth)acrylate (B) is preferably 8 or less, more preferably 6 or less.

[0066] Examples of hydroxyl group-containing polyfunctional (meth)acrylates (B) include pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, 2-hydroxy-1,3-dimethacryloxypropane, and 2-hydroxy-3-acryloyloxypropyl methacrylate.

[0067] For the production of UV-curable oligomers, only one of these hydroxyl group-containing polyfunctional (meth)acrylates (B) may be used, or two or more may be used in combination.

[0068] As for the hydroxyl group-containing polyfunctional (meth)acrylate (B), those having one hydroxyl group and three to five (meth)acryloyl groups are preferred, such as dipentaerythritol penta(meth)acrylate and pentaerythritol tri(meth)acrylate, particularly from the viewpoint of the coating strength of the resulting cured film. Dipentaerythritol penta(meth)acrylate is especially preferred because it forms a good crosslinking structure and enhances the mechanical strength of the cured film.

[0069] <Water-soluble compounds> (Compound (C')) Compound (C') is a water-soluble compound that can bind to polyisocyanate compound (A). Compound (C') is preferably a compound containing one hydroxyl group at its terminus, as this results in good water dispersibility.

[0070] As mentioned above, examples of compound (C') include water-soluble polymers, and among them, polyalkylene glycol (C) is particularly preferred.

[0071] The polyalkylene glycol (C) is not limited, but a monosubstituted structure is preferred. That is, it is preferable that one of the hydroxyl groups of the glycol is substituted. The substituted structure is preferably one that does not bond with the isocyanate. The polyalkylene glycol (C) may be a mixture of a compound with a monosubstituted structure and a compound without a monosubstituted structure.

[0072] The monosubstituted structure is not limited, but from the viewpoint of making the UV-curable oligomer nonionic, polyalkylene glycol monosubstituted ethers are preferred, polyethylene glycol monosubstituted ethers, polytrimethylene glycol monosubstituted ethers, or polypropylene glycol monosubstituted ethers are more preferred, and polyethylene glycol monosubstituted ethers are even more preferred.

[0073] The molecular weight of polyalkylene glycol (C) (meaning the number-average molecular weight if not a single molecular weight) is not limited, but is usually 100 or more, preferably 200 or more, and usually 5000 or less, preferably 2000 or less.

[0074] Among polyalkylene glycol monosubstituted ethers, those that do not contain ionic substituents in the ether portion are more preferred, for example, those represented by the following general formula (1) are even more preferred.

[0075] [ka]

[0076] (In formula (1), X is an alkylene group, Y is one of an alkyl group, a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom, and n is an integer greater than or equal to 2.)

[0077] Specific examples of polyalkylene glycol monosubstituted ethers represented by the above general formula (1) include the following: Y = alkyl group compounds: polyethylene glycol monomethyl ether, polyethylene glycol lauryl ether, polyethylene glycol cetyl ether, polyethylene glycol stearyl ether, polyethylene glycol tridecyl ether, polyethylene glycol oleyl ether, polyethylene glycol octylphenyl ether, polyoxyethylene oleyl cetyl ether, polypropylene glycol monomethyl ether, etc. Y = (meth)acryloyl group: polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) mono(meth)acrylate, poly(ethylene glycol-tetramethylene glycol) mono(meth)acrylate, poly(propylene glycol-tetramethylene glycol) mono(meth)acrylate, etc. Y = Allyl group: Polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, poly(ethylene glycol-propylene glycol) monoallyl ether, etc. Y = Acyl group: Polyethylene glycol monolaurate, polypropylene glycol monolaurate, poly(ethylene glycol-propylene glycol) monolaurate, polyethylene glycol monostearate, polyethylene glycol monooleate, etc.

[0078] Among these, X in general formula (1) is preferably an alkylene group having 1 to 3 carbon atoms, more preferably an ethylene group, a trimethylene group, or a propylene group, and even more preferably an ethylene group from the viewpoint of pigment dispersion stability or storage stability at high temperatures. Furthermore, from the viewpoint of coating film strength, Y is preferably a (meth)acryloyl group, an allyl group, or an acyl group, and more preferably an allyl group.

[0079] In general formula (1), n ​​is usually 2 or more, preferably 5 or more, more preferably 6 or more, and usually 500 or less, preferably 100 or less, and more preferably 50 or less, from the viewpoint of the coating strength of the resulting cured film. In the first embodiment of the ink of the present invention, it is preferable that the ink has a structural unit derived from a compound represented by formula (1), wherein X in formula (1) is an alkylene group, Y is one of a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom, and n is an integer of 2 or more.

[0080] For the production of UV-curable oligomers, one or more of these polyalkylene glycols (C) may be used alone or in combination. The polyalkylene glycols (C) may be a mixture of compounds with different molecular weights (compounds with different n values ​​in general formula (1)).

[0081] <Method for producing UV-curable oligomers> The method for producing UV-curable oligomers is not particularly limited, but it is preferable to produce them by reacting the above-mentioned polyisocyanate compound (A), compound (B'), and compound (C') to form chemical bonds.

[0082] When compound (B') is a hydroxyl group-containing polyfunctional (meth)acrylate (B) and compound (C') is a polyalkylene glycol (C), it is preferable to produce the compound by reacting the above polyisocyanate compound (A), hydroxyl group-containing polyfunctional (meth)acrylate (B), and polyalkylene glycol (C) to form urethane bonds between the isocyanate group of the polyisocyanate compound (A), the hydroxyl group of the hydroxyl group-containing polyfunctional (meth)acrylate (B), and the hydroxyl group of the polyalkylene glycol (C).

[0083] In the present invention, from the viewpoint of pigment dispersion stability and the coating strength of the resulting cured film, it is preferable to use an oligomer in which a polyisocyanate compound (A) is bonded to a polyfunctional (meth)acrylate (B) containing two hydroxyl groups and a polyalkylene glycol (C) forming a urethane bond. Furthermore, this UV-curable oligomer may have additional structures as long as it contains structural units derived from a polyisocyanate compound (A), structural units derived from a hydroxyl group-containing polyfunctional (meth)acrylate (B), and structural units derived from a polyalkylene glycol (C).

[0084] <Weight average molecular weight> From the viewpoint of the performance of the formed coating film and ease of handling, the UV-curable oligomer preferably has a weight-average molecular weight in terms of polystyrene, calculated by gel permeation chromatography (GPC), of 100000 or more, more preferably 2000 or more, more preferably 100000 or less, and more preferably 50000 or less.

[0085] <Average particle size> In the ink, dispersion (oligomer dispersion), and aqueous composition of the present invention, the UV-curable oligomer is preferably present as particles, more preferably as particles with an average particle size of 10 nm to 200 nm, and even more preferably as particles with an average particle size of 20 nm to 150 nm. When the average particle size of the UV-curable oligomer is within the above range, dispersion stability is good. Here, the average particle size of the UV-curable oligomer is, for example, the volume-average particle size (D) measured by a particle size analyzer using the dynamic light scattering method. 50 ) In the examples described later, the average particle size of UV-curable oligomer particles in the UV-curable oligomer aqueous dispersion is measured, but the average particle size of the oligomer particles in this aqueous dispersion is approximately the same as the average particle size of the oligomer particles in the ink. In the ink, dispersion (oligomer dispersion), and aqueous composition of the present invention, as long as the UV-curable oligomer exists as particles, even if aggregation occurs or other substances are contained within the particles, it is included in the above-mentioned state of "existing as particles." Furthermore, the average particle size of the UV-curable oligomer mentioned above refers to the particle size (primary particle size) of the UV-curable oligomer particle.

[0086] The following describes the components of the ink of the present invention other than the UV-curable oligomer.

[0087] [Coloring agent] The ink of the present invention contains a coloring agent. As the colorant used in the ink of the present invention, various dyes or pigments known as colorants for inks can be used, but from the viewpoint of ultraviolet irradiation and long-term storage durability of printed images, it is preferable to use pigments.

[0088] <dye> There are no particular limitations on the dyes that can be used in the present invention, and examples include water-soluble dyes such as acid dyes, direct dyes, and reactive dyes, as well as disperse dyes. Among these, anionic dyes are preferred.

[0089] (water soluble dye) Examples of water-soluble dyes include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, and diphenylmethane dyes. Specific compounds are listed below, but the list is not limited to these examples.

[0090] <CI Acid Yellow> 1, 3, 11, 17, 18, 19, 23, 25, 36, 38, 40, 42, 44, 49, 59, 61, 65, 67, 72, 73, 79, 99, 104, 110, 114, 116, 118, 121, 127, 129, 135, 137, 141, 143, 151, 155, 158, 159, 169, 176, 184, 193, 200, 204, 207, 215, 219, 220, 230, 232, 235, 241, 242, 246 <CI Acid Orange> 3, 7, 8, 10, 19, 24, 51, 56, 67, 74, 80, 86, 87, 88, 89, 94, 95, 107, 108, 116, 122, 127, 140, 142, 144, 149, 152, 156, 162, 166, 168 <CI Acid Red> 88, 97, 106, 111, 114, 118, 119, 127, 131, 138, 143, 145, 151, 183, 195, 198, 211, 215, 217, 225, 226, 249, 251, 254, 256, 257, 260, 261, 265, 266, 274, 276, 277, 289, 296, 299, 315, 318, 336, 337, 357, 359, 361, 362, 364, 366, 399, 407, 415 <CI Acid Violet> 17, 19, 21, 42, 43, 47, 48, 49, 54, 66, 78, 90, 97, 102, 109, 126

[0091] <CI Acid Blue> 1, 7, 9, 15, 23, 25, 40, 62, 72, 74, 80, 83, 90, 92, 103, 104, 112, 113, 114, 120, 127, 128, 129, 138, 140, 142, 156, 158, 171, 182, 185, 193, 199, 201, 203, 204, 205, 207, 209, 220, 221, 224, 225, 229, 230, 239, 249, 258, 260, 264, 278, 279, 280, 284, 290, 296, 298, 300, 317, 324, 333, 335, 338, 342, 350 <CI Acid Green> 9, 12, 16, 19, 20, 25, 27, 28, 40, 43, 56, 73, 81, 84, 104, 108, 109 <CI Acid Brown> 2, 4, 13, 14, 19, 28, 44, 123, 224, 226, 227, 248, 282, 283, 289, 294, 297, 298, 301, 355, 357, 413 <CI Acid Black> 1, 2, 3, 24, 26, 31, 50, 52, 58, 60, 63, 107, 109, 112, 119, 132, 140, 155, 172, 187, 188, 194, 207, 222

[0092] <CI Direct Yellow> 8, 9, 10, 11, 12, 22, 27, 28, 39, 44, 50, 58, 79, 86, 87, 98, 105, 106, 130, 132, 137, 142, 147, 153 <CI Direct Orange> 6, 26, 27, 34, 39, 40, 46, 102, 105, 107, 118 <CI Direct Red> 2, 4, 9, 23, 24, 31, 54, 62, 69, 79, 80, 81, 83, 84, 89, 95, 212, 224, 225, 226, 227, 239, 242, 243, 254 <CI Direct Violet> 9, 35, 51, 66, 94, 95 <CI Direct Blue> 1, 15, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 160, 168, 189, 192, 193, 199, 200, 201, 202, 203, 218, 225, 229, 237, 244, 248, 251, 270, 273, 274, 290, 291 <CI Direct Green> 26, 28, 59, 80, 85 <CI Direct Brown> 44, 106, 115, 195, 209, 210, 222, 223 <CI Direct Black> 17, 19, 22, 32, 51, 62, 108, 112, 113, 117, 118, 132, 146, 154, 159, 169

[0093] <CI Basic Yellow> 1, 2, 11, 13, 15, 19, 21, 28, 29, 32, 36, 40, 41, 45, 51, 63, 67, 70, 73, 91 <CI Basic Orange> 2, 21, 22 <CI Basic Red> 1, 2, 12, 13, 14, 15, 18, 23, 24, 27, 29, 35, 36, 39, 46, 51, 52, 69, 70, 73, 82, 109 <CI Basic Violet> 1, 3, 7, 10, 11, 15, 16, 21, 27, 39 <CI Basic Blue> 1, 3, 7, 9, 21, 22, 26, 41, 45, 47, 52, 54, 65, 69, 75, 77, 92, 100, 105, 117, 124, 129, 147, 151 <CI Basic Green> 1, 4 <CI Basic Brown> 1

[0094] <CI Reactive Yellow> 2, 3, 7, 15, 17, 18, 22, 23, 24, 25, 27, 37, 39, 42, 57, 69, 76, 81, 84, 85, 86, 87, 92, 95, 102, 105, 111, 125, 135, 136, 137, 142, 143, 145, 151, 160, 161, 165, 167, 168, 175, 176 <CI Reactive Orange> 1, 4, 5, 7, 11, 12, 13, 15, 16, 20, 30, 35, 56, 64, 67, 69, 70, 72, 74, 82, 84, 86, 87, 91, 92, 93, 95, 107 <CI Reactive Red> 2, 3, 5, 8, 11, 21, 22, 23, 24, 28, 29, 31, 33, 35, 43, 45, 49, 55, 56, 58, 65, 66, 78, 83, 84, 106, 111, 112, 113, 114, 116, 120, 123, 124, 128, 130, 136, 141, 147, 158, 159, 171, 174, 180, 183, 184, 187, 190, 193, 194, 195, 198, 218, 220, 222, 223, 228, 235 <CI Reactive Violet> 1, 2, 4, 5, 6, 22, 23, 33, 36, 38 <CI Reactive Blue> 2, 3, 4, 5, 7, 13, 14, 15, 19, 21, 25, 27, 28, 29, 38, 39, 41, 49, 50, 52, 63, 69, 71, 72, 77, 79, 89, 104, 109, 112, 113, 114, 116, 119, 120, 122, 137, 140, 143, 147, 160, 161, 162, 163, 168, 171, 176, 182, 184, 191, 194, 195, 198, 203, 204, 207, 209, 211, 214, 220, 221, 222, 231, 235, 236 <CI Reactive Green> 8, 12, 15, 19, 21 <CI Reactive Brown> 2, 7, 9, 10, 11, 17, 18, 19, 21, 23, 31, 37, 43, 46 <CI Reactive Black> 5, 8, 13, 14, 31, 34, 39 <CI Hood Black> 1, 2

[0095] <Pigments> Conventional known organic and inorganic pigments can be used as pigments. Examples include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxandine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye lakes such as basic dye-type lakes and acid dye-type lakes; organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments; and inorganic pigments such as carbon black, titanium dioxide, and iron oxide-based pigments. However, anionic pigments are preferred.

[0096] (Organic pigments) Examples of specific organic pigments are given below.

[0097] <Pigment for magenta or red> CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 222, etc.

[0098] <Pigment for orange or yellow> CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 128, CI Pigment Yellow 138, CI Pigment Yellow 155, etc.

[0099] <Pigments for green or cyan> CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, CI Pigment Green 7, etc.

[0100] These dyes and pigments may be used individually or in combination of two or more.

[0101] [Mercapto compounds] The ink of the present invention contains a mercapto compound. The ink of the present invention, by containing a mercapto compound, exhibits excellent alcohol resistance and abrasion resistance. The reason for this is presumed to be as follows: In UV-curable aqueous inks, the mercapto compound is thought to act as a chain transfer agent. Specifically, the presence of the mercapto compound increases the crosslinking distance of the UV-curable oligomer, allowing for uniform curing and deep curing of the ink film. This increases the toughness, or flexibility, of the ink film, thereby improving the coating strength and resulting in an ink with excellent alcohol resistance and abrasion resistance.

[0102] A mercapto compound is a compound having one or more thiol groups in its molecule. For example, a monofunctional thiol having one thiol group in its molecule, or a polyfunctional thiol having two or more thiol groups in its molecule, such as a difunctional, trifunctional, or tetrafunctional thiol, may be used, but polyfunctional thiols are preferred. Among these, mercapto compounds having 2 to 4 thiol groups are preferred.

[0103] The monofunctional thiols are not particularly limited, but examples include mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, methyl mercaptopropionate, octyl mercaptopropionate, methoxybutyl mercaptopropionate, tridecyl mercaptopropionate, thioglycolic acid, ammonium thioglycolate, monoethanolamine thioglycolate, sodium thioglycolate, methyl thioglycolate, octyl thioglycolate, methoxybutyl thioglycolate, 2-methyl methyl thioglycolate. Examples include lucaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 5-phenyl-2-benzoxazolethiol, 6-methyl-2-benzoxazolethiol, 4-amino-5-methyl-2-pyridinethiol, thiophenol, 2-mercaptobenzyl alcohol, 2-phenoxythiophenol, 3-mercaptophenanthlene, 3-mercapto-1,2,4-triazole, 2-mercapto-4(3H)-quinazoline, and β-mercaptonaphthalene.

[0104] Polyfunctional thiols are not particularly limited, but examples include alkanepolythiol compounds such as 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,9-nonanedithiol, and decanedithiol; and cycloalkanepolythiol compounds such as 1,2-cyclohexanedithiol; ,4-Butanediol bis(mercaptoacetate), ethylene glycol bis(mercaptoacetate), trimethylolpropane tris(mercaptoacetate), and pentaerythritol tetrakis(mercaptoacetate); 1,4-Butanediol bis(3-mercaptopropionate), ethylene glycol bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(mercaptoacetate); Lythritol tetrakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), ethylene glycol bis(2-mercaptopropionate), 1,2-propylene glycol bis(2-mercaptopropionate), diethylene glycol bis(2-mercaptopropionate), 1,4-butanediol bis(2-mercaptopropionate), 1,8-octanediol bis(2-mercaptopropionate) Lucaptopropionate, trimethylolpropanetris(2-mercaptopropionate), tetraethylene glycol bis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptopropionate), dipentaerythritol hexakis(2-mercaptopropionate), dipentaerythritol hexathiopropionate, and other ester compounds of polyhydric alcohols with mercaptopropionic acid;Ethylene glycol bis(3-mercaptobutyrate), 1,2-propylene glycol bis(3-mercaptobutyrate), diethylene glycol bis(3-mercaptobutyrate), 1,4-butanediol bis(3-mercaptobutyrate), 1,8-octanediolc bis(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptobutyrate), and dipentaerythritol hexakis( 3-mercaptobutyrate; 1,4-bis(3-mercaptobutyryloxy)butane, as well as ethylene glycol bis(2-mercaptoisobutyrate), 1,2-propylene glycol bis(2-mercaptoisobutyrate), diethylene glycol bis(2-mercaptoisobutyrate), 1,4-butanediol bis(2-mercaptoisobutyrate), 1,8-octanediol bis(2-mercaptoisobutyrate), trimethylolpropane tris(2-mercaptoiso 3-mercaptoisobutyrate), pentaerythritol tetrakis(2-mercaptoisobutyrate), dipentaerythritol hexakis(2-mercaptoisobutyrate), ethylene glycol bis(3-mercaptoisobutyrate), 1,2-propylene glycol bis(3-mercaptoisobutyrate), diethylene glycol bis(3-mercaptoisobutyrate), 1,4-butanediol bis(3-mercaptoisobutyrate), 1,8-octanediol bis(3-mercaptoisobutyrate) Ester compounds of mercapto group-containing carboxylic acids and polyhydric alcohols, such as trimethylolpropanetris(3-mercaptoisobutyrate), pentaerythritoltetrakis(3-mercaptoisobutyrate), dipentaerythritolhexakis(3-mercaptoisobutyrate), ethylene glycol bisthioglycolate, ethylene glycol bisthioglycolate, trimethylolpropanetristhioglycolate, and pentaerythritoltetrakisthioglycolate;Aromatic polythiol compounds such as 1,4-dimethylmercaptobenzene, dimercaptobenzene, trimercaptobenzene, 1,4-di(mercaptomethyl)benzene, 1,4-bis(2-mercaptoethyl)benzene, 1,2-benzenedimethanethiol, 1,3-benzenedimethanethiol, 1,4-benzenedimethanethiol, and 2,4,6-trimethyl-1,3-benzenedimethanethiol; 2,4,6-trimercapto-s-triazine, 2,4,6-trimercapto Examples include heterocyclic polythiol compounds such as -1,3,5-triazine, 2-(N,N-dibutylamino)-4,6-dimercapto-s-triazine, and 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione; as well as tris(2-hydroxyethyl) isocyanurate trimercaptopropionate and tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate.

[0105] Furthermore, the mercapto compound may be a primary thiol, a secondary thiol, or a tertiary thiol. Among these, secondary and tertiary thiols are preferred because they have low reactivity and maintain the storage stability of the ink, dispersion, and aqueous composition of the present invention, with secondary thiols being particularly preferred. More specifically, the following mercapto compounds are preferred due to their high curability and excellent storage stability: 1,4-bis(3-mercaptobutyryloxy)butane, 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, pentaerythritol tetrakis(3-mercaptobutyrate), and trimethylolpropane tris(3-mercaptobutyrate), which are polyfunctional secondary thiols.

[0106] Examples of commercially available polyfunctional primary thiols include EGMP-4 (tetraethylene glycol bis(3-mercaptopropionate)), TMMP (trimethylolpropane tris(3-mercaptopropionate)), TEMPIC (tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate), PEMP (pentaerythritol tetrakis(3-mercaptopropionate)), and DPMP (dipentaerythritol hexakis(3-mercaptopropionate)) (all manufactured by Sakai Chemical Industry Co., Ltd.). Examples of commercially available polyfunctional secondary thiols include Karenz MT® BD-1 (1,4-bis(3-mercaptobutyryloxy)butane), NR-1 (1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione), PE-1 (pentaerythritol tetrakis(3-mercaptobutyrate)), and TPMB (trimethylolpropane tris(3-mercaptobutyrate)) (all manufactured by Showa Denko Corporation). Examples of commercially available monofunctional primary thiols include Suncellar M and Suncellar MG (2-mercaptobenzothiazole) (both manufactured by Sanshin Chemical Industry Co., Ltd.).

[0107] Furthermore, from the viewpoint of reducing the odor of inks and printed materials, mercapto compounds with low volatility are preferred. Therefore, the boiling point of the mercapto compound is preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 250°C or higher.

[0108] The molecular weight of the mercapto compound is preferably 150 or more, and more preferably 200 or more. On the other hand, the molecular weight of the mercapto compound is preferably 2000 or less, and more preferably 1500 or less.

[0109] Mercapto compounds may be used individually or in combination of two or more.

[0110] In the ink of the present invention, the mercapto compound is preferably dispersed in a form encapsulated within particles of the UV-curable oligomer. This allows the mercapto compound, which is generally poorly soluble in water, to be suitably incorporated into a water-based ink. To encapsulate the mercapto compound in the UV-curable oligomer, for example, the mercapto compound can be emulsified in the same presence as the UV-curable oligomer.

[0111] [Aqueous medium] The ink of the present invention is a water-based ink, and "water-based ink" means an ink containing a water-based medium. The water-based medium is water and / or a water-soluble organic solvent. The aqueous medium used in the present invention is preferably water, or a mixture of water and a water-soluble organic solvent. Water-soluble organic solvents can be broadly categorized into those that function as moisturizing solvents to enhance the moisture retention and wettability of inks, and those used as aqueous media to adjust ink viscosity, improve handling, and enhance dispensing performance. However, these two categories are not clearly distinguished, and water-soluble organic solvents used as moisturizing solvents can also function as aqueous media. In this invention, a water-soluble organic solvent refers to a compound that is soluble in water. The solubility in water is not limited, but compounds that can dissolve in water in any proportion are preferred. Furthermore, even compounds that do not easily possess solvent properties on their own (for example, compounds that are solid at room temperature or have high viscosity) are included in the category of water-soluble organic solvents if they can be used as a solvent when uniformly mixed with water.

[0112] Examples of water-soluble organic solvents include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0113] Specific examples of water-soluble organic solvents include, for example, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 1,5-pentanediol. Polyhydric alcohols such as 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, etc.; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Examples include polyhydric alcohol alkyl ethers such as monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; and propylene carbonate.

[0114] As a water-soluble organic solvent, it is preferable to use an organic solvent with a boiling point of 250°C or lower, as it not only functions as a moisturizing solvent but also provides good drying properties.

[0115] As water-soluble organic solvents, polyol compounds having 8 or more carbon atoms and glycol ether compounds are also suitably used. Specific examples of polyol compounds with 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol. Specific examples of glycol ether compounds include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0116] These water-soluble organic solvents may be used individually or as a mixture of two or more.

[0117] [Polymerization initiator] The ink of the present invention preferably contains a polymerization initiator. A polymerization initiator is a photoradical polymerization initiator that generates radicals, which are active species, in response to the energy of light (ultraviolet light) received when irradiated with ultraviolet light, thereby initiating the photopolymerization of an ultraviolet-curable oligomer. As a result, the ink present on the surface of the recording medium hardens, and an image can be formed.

[0118] The polymerization initiator may be present in the ink without being encapsulated within the UV-curable oligomer, or it may be present in the ink encapsulated within the UV-curable oligomer particles. Furthermore, it may be present in both of these states.

[0119] The polymerization initiator may be either a lipid-soluble polymerization initiator (hereinafter sometimes referred to as "lipid-soluble initiator") or a water-soluble polymerization initiator (hereinafter sometimes referred to as "water-soluble initiator"). Here, "lipid-soluble initiator" refers to polymerization initiators that are compatible with UV-curable oligomers or dissolve in organic solvents, and "water-soluble initiator" refers to those that dissolve in water at a concentration of 1% by mass or more. The same applies to "lipid-soluble sensitizers" and "water-soluble sensitizers" described later.

[0120] The polymerization initiators used in the present invention are not limited to the following, but include, for example, aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having carbon-halogen bonds, and alkylamine compounds.

[0121] Among these, the polymerization initiator preferably contains at least one of an acylphosphine oxide compound and a thioxanthone compound. Using such a polymerization initiator tends to improve the curability of the ink.

[0122] Lipid-soluble polymerization initiators include, but are not limited to, acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, p,p'-bisdiethylaminobenzophenone, Michler ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}2-methylpropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-di Examples include methylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-ylphenyl)butan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]2-morpholinopropan-1-one, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, methylbenzophyllate, azobisisobutyrillonitrile, benzoyl peroxide, and di-tert-butyl peroxide.

[0123] Examples of water-soluble polymerization initiators include, but are not limited to, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, sodium phenyl(2,4,6-trimethylbenzoyl)phosphinate, and 2-(3-dimethylamino-2-hydroxypropoxy)-3,4-dimethyl-9H-thioxanthon-9-one metochloride.

[0124] Examples of commercially available polymerization initiators include GENOPOL TX-2 from RAHN, and Irgacure 369, Irgacure 500, and Irgacure 2959 from Ciba Specialty Chemicals.

[0125] Polymerization initiators may be used individually or in combination of two or more. For example, a lipid-soluble initiator and a water-soluble initiator may be used in combination, with the lipid-soluble initiator encapsulated in UV-curable oligomer particles and the water-soluble initiator dissolved in an aqueous medium. In addition to the photoradical polymerization initiators mentioned above, thermal radical polymerization initiators may also be used in combination as polymerization initiators.

[0126] [Surfactants] The ink of the present invention preferably contains a surfactant for the flatness of the formed coating film and for wettability with the substrate.

[0127] Any of the following surfactants can be used: silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants.

[0128] There are no particular restrictions on silicone-based surfactants, and they can be appropriately selected depending on the purpose. Among them, those that do not decompose even at high pH are preferred, and examples include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end modified polydimethylsiloxane. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants. Polyether-modified silicone-based surfactants can also be used as silicone-based surfactants, and examples include compounds in which a polyalkylene oxide structure is introduced into the Si side chain of dimethylsiloxane.

[0129] As for fluorine-based surfactants, compounds with 2 to 16 fluorine-substituted carbon atoms are preferred, and compounds with 4 to 16 fluorine-substituted carbon atoms are more preferred. As fluorine-based surfactants, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl alkylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains are preferred because they have low foaming properties. Examples of perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonate salts. Examples of perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acid and perfluoroalkyl carboxylic acid salts. Examples of perfluoroalkyl phosphate ester compounds include perfluoroalkyl phosphate esters and perfluoroalkyl phosphate ester salts. Examples of perfluoroalkyl alkylene oxide adducts include perfluoroalkyl ethylene oxide adducts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains include sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains and salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains. Examples of counterions for the salts of these fluorinated surfactants include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, and NH(CH2CH2OH)3.

[0130] Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains are more preferred because they have particularly low foaming properties, and fluorine-based surfactants represented by the following general formulas (3A) and (3B) are particularly preferred.

[0131] CF3CF2(CF2CF2) s -CH2CH2O(CH2CH2O) t H …(3A) In the compound represented by general formula (3A), s is preferably an integer between 0 and 10 in order to impart water solubility, and t is preferably an integer between 0 and 40 in order to impart water solubility.

[0132] C r F 2r+1 -CH2CH(OH)CH2-O-(CH2CH2O) c -Z …(3B) In the compound represented by the general formula (3B), Z is H, or C d F 2d+1 where d is an integer of 1 or more and 6 or less, or CH2CH(OH)CH2-C e F 2e+1 where e is an integer of 4 or more and 6 or less, or C f H 2f+1 where f is an integer of 1 or more and 19 or less. Also, r is an integer of 1 or more and 6 or less, and c is an integer of 4 or more and 14 or less.

[0133] Commercially available products can be used as the fluorosurfactant. Examples of commercially available products include, for example, Surfron S-111, S-112, S-113, S-121, S-131, S-132, S-141, S-145 (all manufactured by Asahi Glass Co., Ltd.); Fluorad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F-470, F-1405, F-474 (all manufactured by DIC Corporation); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR (all manufactured by DuPont); FT-11, FT-250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omnova), Neugen FN-1287 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Unidine DSN-403N (manufactured by Daikin Industries, Ltd.), LE-604, LE-605, LE-606, LE-607 (manufactured by Kyoeisha Chemical Co., Ltd.), etc.

[0134] Examples of the amphoteric surfactant include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, etc.

[0135] Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, acetylene alcohol derivatives, and acetylene glycol derivatives.

[0136] Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, and salts of polyoxyethylene alkyl ether sulfate.

[0137] These can be used individually or in combination of two or more types.

[0138] As mentioned above, there are no particular restrictions on the silicone-based surfactant, and it can be appropriately selected depending on the purpose. However, polyether-modified silicone-based surfactants having polyoxyethylene groups and polyoxyethylene-polyoxypropylene groups as modifying groups are particularly preferred because they exhibit good properties as aqueous surfactants.

[0139] Such surfactants may be synthesized as appropriate, or commercially available products may be used. Commercially available products can be obtained from companies such as BIC Chemie Inc., Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.

[0140] There are no particular restrictions on the polyether-modified silicone surfactant, and it can be appropriately selected depending on the purpose. For example, one example is a polyalkylene oxide structure, represented by the general formula (2) below, introduced into the Si side chain of dimethylpolysiloxane.

[0141] [ka]

[0142] (In formula (2), p, q, a, and b represent integers. R and R' represent hydrocarbon groups.)

[0143] Commercially available polyether-modified silicone surfactants can be used. Examples of commercially available products include KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), SAG001, SAG002, SAG003, SAG005, SAG503, SAG008 (Nisshin Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Toray Dow Corning Silicone Co., Ltd.), BYK-33, BYK-387 (Big Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicone Co., Ltd.).

[0144] [Sensitizer] The ink of the present invention may contain a sensitizer. When a sensitizer is present in the ink together with a polymerization initiator, the sensitizer in the system absorbs active energy rays and enters an excited state, which then comes into contact with the polymerization initiator, promoting the decomposition of the polymerization initiator and enabling a more sensitive curing reaction. The sensitizer may be lipid-soluble, like the polymerization initiator, or it may be water-soluble. If it is a lipid-soluble sensitizer, it can be encapsulated within the particles of the UV-curable oligomer.

[0145] As sensitizers, you can use aliphatic amines, amines having aromatic groups, or cyclic amine compounds such as piperidine, thioxanthone compounds, alkoxyanthracene compounds, urea compounds such as o-tolylthiourea, sulfur compounds such as sodium diethylthiophosphate or soluble salts of aromatic sulfinic acid, nitrile compounds such as N,N'-disubstituted-p-aminobenzonitrile, phosphorus compounds such as tri-n-butylphosphine or sodium diethyldithiophosphate, Michler ketones, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, nitrogen compounds such as formaldehyde or condensates of acetaldehyde and diamines.

[0146] These sensitizers may be used individually or in combination of two or more.

[0147] [Other oligomers, resins, monomers] In addition to the above components, the ink of the present invention may optionally contain oligomer components other than UV-curable oligomers, any resin components, and any monomer components (collectively referred to as "other resin components"). The other resin components may be encapsulated within the UV-curable oligomer particles, dissolved in an aqueous medium, or dispersed individually or compounded with other components in the ink.

[0148] [Other additives] In addition to the components described above, the ink of the present invention may optionally contain other additives. Other known additives include, for example, anti-fading agents, emulsifying stabilizers, penetration enhancers, UV absorbers, preservatives, antifungal agents, rust inhibitors, pH adjusters, viscosity adjusters, dispersants, dispersion stabilizers, defoamers, solid wetting agents, and chelating agents. These various additives may be added directly after the ink is prepared or added during the ink preparation process. For other additives, refer to paragraphs 0088 to 0096 of Japanese Patent Publication No. 2010-65205 and paragraphs 0083 to 0090 of Japanese Patent Publication No. 2010-70669 as appropriate.

[0149] [Content of each ingredient] The water content in the ink of the present invention is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of ink drying properties and ejection reliability, it is usually 10% by mass or more, preferably 20% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less. Furthermore, if the ink of the present invention contains a water-soluble organic solvent, there are no particular limitations on its content (the total content of the water-soluble organic solvent used as both a moisturizing solvent and a water-based medium). It can be appropriately selected depending on the type and purpose of the water-soluble organic solvent used. However, from the viewpoint of drying properties, discharge reliability, and wettability with the substrate, it is usually 10% by mass or more, usually 50% by mass or less, and preferably 40% by mass or less.

[0150] From the viewpoint of drying properties and ejection reliability, the ink of the present invention is adjusted so that the total solid content concentration of components other than the aqueous medium, which is water and / or a water-soluble organic solvent, is usually 5% by mass or more, preferably 7% by mass or more, more preferably 9% by mass or more, usually 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0151] Furthermore, when a mixture of water and a water-soluble organic solvent is used as the aqueous medium, the ratio of water to the water-soluble organic solvent (the total of the water-soluble organic solvent used as both a moisturizing solvent and the water-soluble organic solvent used as the aqueous medium) is preferably such that the ratio of water to water-soluble organic solvent is typically 1:0.05 to 1:1.5 (mass ratio), more preferably 1:0.1 to 1:1.2 (mass ratio), and more preferably 1:0.15 to 1:1.1 (mass ratio), from the viewpoint of improving drying properties and discharge properties.

[0152] The content of the UV-curable oligomer in the ink of the present invention is usually 3% by mass or more, preferably 5% by mass or more, and more preferably 7% by mass or more, from the viewpoint of the resulting printed coating performance and UV curability, while from the viewpoint of ejection stability, it is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 12% by mass or less. Furthermore, from a similar viewpoint, the content of UV-curable oligomers in the total solid content of the ink of the present invention is usually 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and usually 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less.

[0153] Here, the total solid content in the ink of the present invention can be rephrased as the constituent components of the cured film (printed film) formed by the ink of the present invention, and the above numerical range can be similarly adopted. The content of each component in the total solid content is approximately equal to the content of that component in the cured film (printed film) formed by the ink of the present invention. Therefore, the fact that the content of UV-curable oligomers in the total solid content of the ink of the present invention is typically 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and typically 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less, can be treated in the same way as the content of components derived from UV-curable oligomers in the cured film (printed film) formed by the ink of the present invention being typically 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and typically 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less. The same applies to the content of the following colorants, mercapto compounds, and other ingredients.

[0154] The colorant content in the ink of the present invention is usually 0.1% by mass or more, preferably 1% by mass or more, and usually 8% by mass or less, preferably 6% by mass or less, from the viewpoint of improving image density, good fixation and ejection stability. Furthermore, from a similar viewpoint, the content of the colorant in the total solid content of the ink of the present invention is usually 1% by mass or more, preferably 5% by mass or more, and usually 40% by mass or less, preferably 30% by mass or less.

[0155] The content of the mercapto compound in the ink of the present invention is usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.08% by mass or more, and particularly preferably 0.30% by mass or more, from the viewpoint of alcohol resistance and abrasion resistance, while from the viewpoint of manufacturing stability, it is usually 5% by mass or less, preferably 4% by mass or less, and more preferably 3% by mass or less. Furthermore, from a similar viewpoint, the content of the mercapto compound in the total solid content of the ink of the present invention is usually 0.05% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, and more preferably 15% by mass or less.

[0156] If the ink of the present invention contains a polymerization initiator, its content is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.4% by mass or more, and usually 8% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. By having the polymerization initiator content within this range, the curing speed can be sufficiently improved and residual polymerization initiator and discoloration derived from the polymerization initiator can be avoided. Furthermore, from a similar viewpoint, the content of polymerization initiator in the total solid content of the ink of the present invention is usually 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, usually 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 8% by mass or less.

[0157] When the ink of the present invention contains a surfactant, there are no particular restrictions on its content, and it can be appropriately selected depending on the purpose. However, in terms of excellent wettability, ejection stability, and improved image quality, the surfactant content in the ink is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. Furthermore, from a similar viewpoint, the surfactant content in the total solid content of the ink of the present invention is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less.

[0158] If the ink of the present invention contains a sensitizer, its content is usually 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and usually 4% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.7% by mass or less. If the content of the sensitizer is within the above range, the effect of the sensitizer can be sufficiently obtained. Furthermore, from a similar viewpoint, the sensitizer content in the total solid content of the ink of the present invention is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and usually 8% by mass or less, preferably 6% by mass or less, and more preferably 5% by mass or less.

[0159] [Ultraviolet curable water-based composition] The ultraviolet-curable aqueous composition of the present invention (hereinafter sometimes referred to as "the aqueous composition of the present invention") contains, in the first embodiment of the aqueous composition of the present invention, an ultraviolet-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, and a mercapto compound, wherein the ultraviolet-curable oligomer has a structural unit derived from a compound represented by the following formula (1). [ka] (In formula (1), X is an alkylene group, and Y is one of the following: a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

[0160] In a second embodiment of the aqueous composition of the present invention, the composition contains an ultraviolet-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, and a mercapto compound, wherein the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and compound (A) is a compound having three or more isocyanate groups in one molecule.

[0161] The UV-curable aqueous composition of the present invention is an aqueous composition and contains an aqueous medium similar to the ink of the present invention. Furthermore, in the aqueous composition of the present invention, the UV-curable oligomer is preferably nonionic, and a UV-curable oligomer having structural units derived from the polyisocyanate compound (A), structural units derived from the compound (B') shown below, and structural units derived from the compound (C') shown below is preferred, and a UV-curable oligomer having structural units derived from the polyisocyanate compound (A), structural units derived from the hydroxyl group-containing polyfunctional (meth)acrylate (B), and structural units derived from the polyalkylene glycol (C) is particularly preferred. In other words, the aqueous composition of the present invention described above corresponds to an embodiment of the ink of the present invention that does not contain a colorant, and the ultraviolet-curable oligomer, mercapto compound, aqueous medium, polymerization initiator, sensitizer, surfactant, and other additives contained in the aqueous composition of the present invention are the same as those described in the section on the ink of the present invention described above, and their content is also the same as the content of each component excluding the colorant in the ink of the present invention described above.

[0162] The form in which the aqueous composition of the present invention is used is not particularly limited, but a preferred form of use is to prepare the ink of the present invention by adding the aforementioned colorants to the aqueous composition of the present invention. The added colorants may be one color or two or more colors. By optionally adding two or more colorants, the color of the ink can be adjusted to a desired color. Furthermore, the aqueous composition of the present invention can be used as a clear ink.

[0163] [Ink manufacturing method] There are no particular limitations on the method for manufacturing the ink of the present invention, but one method involves preparing a dispersion in which ultraviolet-curable oligomer particles (hereinafter sometimes referred to as "oligomer particles") are dispersed in an aqueous medium (hereinafter sometimes referred to as "oligomer dispersion") and a dispersion in which a coloring agent such as a pigment is dispersed in an aqueous medium (hereinafter sometimes referred to as "pigment dispersion"), and then mixing the oligomer dispersion and the pigment dispersion with a polymerization initiator (water-soluble initiator), other additives, and an organic solvent. Another method involves adding a coloring agent to the aqueous composition of the present invention, but inks with similar performance can be obtained regardless of which method is used for manufacturing.

[0164] A first embodiment of the dispersion of the present invention is a dispersion of an ultraviolet-curable oligomer, characterized in that it contains 0.01% by mass or more and 10% by mass or less of a mercapto compound, and the ultraviolet-curable oligomer has structural units derived from a compound represented by the following formula (1). [ka] (In formula (1), X is an alkylene group, and Y is one of the following: a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.) A second embodiment of the dispersion of the present invention is a dispersion of an ultraviolet-curable oligomer, which contains 0.01% by mass or more and 10% by mass or less of a mercapto compound, wherein the ultraviolet-curable oligomer has structural units derived from a polyisocyanate compound (A), and compound (A) is a compound having three or more isocyanate groups in one molecule.

[0165] When preparing the oligomer dispersion, it is preferable to first add and mix a mercapto compound and a lipid-soluble initiator and / or lipid-soluble sensitizer to the UV-curable oligomer to form an emulsion in which these are encapsulated in oligomer particles, and then further add and mix a water-soluble initiator and / or water-soluble sensitizer. Alternatively, after forming an emulsion by adding and mixing the mercapto compound to the UV-curable oligomer, a water-soluble initiator, a water-soluble sensitizer, a lipid-soluble initiator, and a lipid-soluble sensitizer may be added and mixed in an appropriate combination. Furthermore, the lipid-soluble initiator and lipid-soluble sensitizer can also be mixed with other components as a solution obtained by dissolving them separately in an organic solvent at a concentration of approximately 0.1% to 10% by mass. The content of the mercapto compound in the oligomer dispersion is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 8% by mass or less. Furthermore, when mercapto compounds are encapsulated in oligomer particles, the amount of mercapto compounds in the oligomer dispersion is preferably the same as described above.

[0166] In addition to encapsulating the mercapto compound in the UV-curable oligomer as described above, the mercapto compound may also be included by adding it to a dispersion of UV-curable oligomers. In this case, the amount of mercapto compound added to the dispersion of UV-curable oligomer should be such that it results in the preferred content described above in the ink of the present invention. For example, it is used in an amount of 0.1% to 10% by mass relative to the UV-curable oligomer.

[0167] <Preparation of oligomer dispersion> The oligomer dispersion can be prepared by mixing an ultraviolet-curable oligomer with an aqueous medium (preferably water). By adjusting the temperature and stirring speed at this time, the average particle size of the resulting oligomer particles can be adjusted. From the viewpoint of ease of handling, it is preferable that the oligomer particle concentration of the oligomer dispersion prepared in this manner is approximately 10% by mass or more and 30% by mass or less.

[0168] As mentioned above, when preparing this oligomer dispersion, a dispersion of oligomer particles containing the mercapto compound can be obtained by adding and mixing only the mercapto compound, or the mercapto compound with a lipid-soluble initiator and / or a lipid-soluble sensitizer. In this case, in order to prevent the formation of initiator-only particles that do not contain oligomers, it is preferable to mix at least the UV-curable oligomer and the lipid-soluble initiator before mixing with an aqueous medium such as water. When oligomer particles containing a lipid-soluble initiator are used, from the viewpoint of manufacturing stability, it is preferable that the content of the lipid-soluble initiator in the oligomer particles be approximately 0.1% to 8% by mass relative to the UV-curable oligomer. Similarly, to prevent the formation of particles of mercapto compounds alone that do not contain oligomers, it is preferable to mix at least the UV-curable oligomer and the mercapto compound before mixing with an aqueous medium such as water. When oligomer particles containing mercapto compounds are used, from the viewpoint of manufacturing stability, the content of the mercapto compound in the oligomer particles is preferably 0.1% by mass or more and 30% by mass or less relative to the UV-curable oligomer. In the present invention, multiple types of oligomer dispersions containing different encapsulated compounds can be prepared and used by mixing them. Alternatively, an oligomer dispersion containing only an ultraviolet-curable oligomer without any encapsulated compounds can be mixed with an oligomer dispersion containing all the compounds or a mixture of multiple types of oligomer dispersions containing different encapsulated compounds.

[0169] <Preparation of Pigment Dispersion> Pigment dispersions can be prepared by adding a coloring agent such as a pigment to an aqueous medium such as water and mixing the mixture. The concentration of colorants such as pigments in the pigment dispersion is usually 5% by mass or more, preferably 10% by mass or more, and usually 40% by mass or less, preferably 35% by mass or less, from the viewpoint of handling and storage stability.

[0170] Commercially available pigment dispersions may be used as is.

[0171] [Method for producing aqueous compositions] There are no particular limitations on the method for producing the aqueous composition of the present invention, but one method is to prepare an oligomer dispersion in the same manner as in the ink production method of the present invention described above, and then mix the prepared oligomer dispersion with one or more of a polymerization initiator (water-soluble initiator), a sensitizer, and a surfactant, as well as other additives and organic solvents as needed.

[0172] As mentioned above, when preparing the oligomer dispersion, the mercapto compound alone, or the mercapto compound with a lipid-soluble initiator and / or lipid-soluble sensitizer, can be encapsulated within the oligomer particles by adding and mixing them together. Alternatively, the lipid-soluble initiator and lipid-soluble sensitizer can be dissolved separately in an organic solvent at a concentration of approximately 0.1% to 10% by mass and mixed with other components. The method for preparing the oligomer dispersion, and the method for preparing a dispersion of oligomer particles containing only a mercapto compound, or a mercapto compound and a lipid-soluble initiator and / or lipid-soluble sensitizer, are the same as in the method for producing the ink of the present invention described above.

[0173] [Ink viscosity] The ink of the present invention exhibits excellent pigment dispersion stability, allowing for low ink viscosity. As a result, good ink ejection is achieved even during high-speed printing. The viscosity of the ink of the present invention at 25°C is preferably 25 mPa·sec or less, more preferably 20 mPa·sec or less, and even more preferably 10 mPa·sec or less. The lower limit is not particularly limited, but is preferably 1 mPa·sec or more, and more preferably 2 mPa·sec or more.

[0174] [Viscosity of aqueous compositions] The viscosity of the aqueous composition of the present invention at 25°C is preferably 50 mPa·sec or less, more preferably 30 mPa·sec or less, and even more preferably 20 mPa·sec or less. The lower limit is not particularly limited, but is preferably 0.5 mPa·sec or more, and more preferably 1 mPa·sec or more.

[0175] [Ink container] The ink of the present invention can be contained in ink cartridges or ink bottles, which eliminates the need to directly touch the ink during tasks such as ink transport and ink replacement, thus preventing contamination of hands and clothing. It also prevents foreign matter such as dust from contaminating the ink. The shape, size, and material of the ink container itself are not particularly limited and should be suitable for the inkjet printer to which it is applied, for example. However, it is desirable that the material be a light-shielding material that does not transmit light, or that the container be covered with a light-shielding sheet or the like.

[0176] [Inkjet recording method] The inkjet recording method using the ink of the present invention preferably comprises the steps of: ejecting the ink of the present invention from the ejection nozzle of an inkjet printer and adhering it to a recording medium; heating the recording medium to which the ink has been adhering; and irradiating the ink adhering to the recording medium with active energy rays. The step of adhering the ink of the present invention to the recording medium only requires that the ink be adhering to the recording medium in a mist-like or spray-like manner, and is not necessarily limited to using an inkjet printer.

[0177] <Recording medium> The ink of the present invention is not particularly limited to the recording medium to which it is applied. It can form high-quality printed images with good adhesion to a variety of substrates, such as polyesters like polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), and other plastic materials, as well as paper, textiles (cloth and fabrics), leather, glass, ceramics, wood, metals, or composite materials thereof.

[0178] <Heating process> In the heating process, it is preferable to heat the recording medium to which the ink of the present invention is attached to 40°C or higher. More preferably, the heating temperature is 45°C or higher, and even more preferably 50°C or higher. By performing the above heating, volatile components such as water in the ink can be dried, and the curability tends to be further improved. There is no particular upper limit to the heating temperature, but since the presence of a heating means generally tends to cause the ink on the nozzle surface to dry out, resulting in poor ejection, it is preferable to keep it at 120°C or lower, and more preferably at 100°C or lower. Here, the heating temperature is the surface temperature of the recording surface of the recording medium.

[0179] The heating method is not particularly limited, but examples include ceramic heaters, halogen heaters, quartz tube heaters, and the like.

[0180] The timing of heating may be before, during, or after the ink of the present invention is applied to the recording medium, but it is more preferable to continue heating throughout all processes before, during, and after application.

[0181] <Irradiation process> In the irradiation process, the polymerization reaction of the UV-curable oligomer is initiated by irradiation with active energy rays. Furthermore, the polymerization initiator contained in the ink decomposes upon irradiation with active energy rays, generating initiator species such as radicals, acids, and bases. The polymerization reaction of the UV-curable oligomer is then accelerated by the function of these initiator species. If a sensitizer is present in the ink along with the polymerization initiator, the sensitizer in the system absorbs the active energy rays and becomes excited. This excites the polymerization initiator, accelerating its decomposition and enabling a more sensitive curing reaction.

[0182] Mercury lamps, metal halide lamps, and gas / solid-state lasers are widely known as light sources (active energy sources). On the other hand, there is a strong desire for mercury-free alternatives from an environmental protection standpoint, and replacing them with GaN-based semiconductor ultraviolet light-emitting devices is extremely useful both industrially and environmentally. Furthermore, ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have long lifespans, are highly efficient, and are low-cost, making them promising light sources for UV-curable inkjet printers. Among these, UV-LEDs are preferred.

[0183] The emission peak wavelength of the irradiated active energy source is preferably in the range of 350 to 450 nm, and the irradiation energy is 20 J / cm². 2 For example, 0.5 to 10 J / cm 2 It is preferable.

[0184] Note that there may be one or more emission peak wavelengths within the above wavelength range. Furthermore, the irradiation process is not limited to the intentional process described above, but may also be, for example, exposed to sunlight outdoors. Also, if the reactivity (curability) of the UV-curable oligomer of the present invention is high, the heating process alone may suffice, without the irradiation process. In other words, the ink of the present invention only needs to be UV-curable and is not limited to being used in a printing method that includes an irradiation process.

[0185] [Application] The ink of the present invention is water-based, making it environmentally friendly and safe. It satisfies the required characteristics of printing inks, such as inkjet printing inks, in a well-balanced manner, while also exhibiting excellent coating performance, particularly alcohol resistance and abrasion resistance. Therefore, it can be used in a variety of applications, including posters, road signs, signboards, billboards, various outdoor and indoor display boards, building materials (exterior, interior, walls, floors, ceilings, windows, etc.), vehicle exteriors (automobiles, trains, aircraft, etc.), furniture and office automation equipment surface materials, and printed paper materials. [Examples]

[0186] An embodiment of the present invention is described below. However, the present invention is not limited to this embodiment. First, examples and comparative examples of the first embodiment of the present invention will be described.

[0187] [Preparation of UV-curable oligomer 1] A nonionic UV-curable oligomer 1 was prepared by reacting 0.4 moles of a hexamethylene diisocyanate trimer with 0.8 moles of dipentaerythritol pentaacrylate and 0.4 moles of polyethylene glycol monoallyl ether (n=30-40 in the general formula (1) above).

[0188] [Preparation of lipid-soluble initiator solution] To 100 parts by mass of diethylene glycol monoisobutyl ether as a water-soluble organic solvent, 1 part by mass of GENOPOL TX-2 manufactured by RAHN was added as a lipid-soluble initiator, and the mixture was completely dissolved while stirring at 40°C to obtain a lipid-soluble initiator solution.

[0189] [Mercapto compounds] The following compounds were used as mercapto compounds. (1) Secondary tetrafunctional thiol Pentaerythritol tetrakis(3-mercaptobutyrate) Karenz MT (registered trademark), PE-1, manufactured by Showa Denko Corporation (2) Primary tetrafunctional thiol Pentaerythritol tetra(3-mercaptopropionate) manufactured by Mitsubishi Chemical Corporation, jER Cure®, QX40

[0190] [Example 1] The UV-curable oligomer 1 was kept at 60°C, and the secondary tetrafunctional thiol described in (1) above was added in the composition ratio shown in Table 1 below. While stirring, deionized water that had been preheated to 60°C was added dropwise to form an aqueous dispersion. The average particle size (D) of the UV-curable oligomer particles in this aqueous dispersion was determined. 50The particle size distribution was measured using a MICROTRAC UPA (MODEL: 9340-UPA, manufactured by Nikkiso Co., Ltd.) and found to be 39 nm. To the aforementioned aqueous dispersion, ion-exchanged water, 1,2-butanediol as a humectant solvent, diethylene glycol monoisobutyl ether as a water-soluble organic solvent, a lipid-soluble initiator, a water-soluble initiator, a water-soluble sensitizer, Neugen FN1287 manufactured by Daiichi Kogyo Seiyaku as a surfactant [1], LE-605 manufactured by Kyoeisha Chemical as a surfactant [2], and EMACOL SF CYAN AE2034F manufactured by Sanyo Shikiso as a pigment dispersion were added and mixed in the composition ratios shown in Table 1 below to obtain ink composition solution 1.

[0191] [Preparation of a lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1] UV-curable oligomer 1 in the composition ratio shown in Table 1 and GENOPOL TX-2 manufactured by RAHN as a lipid-soluble initiator were kept at 60°C, and the secondary tetrafunctional thiol from (1) above was added. While stirring and mixing, ion-exchanged water that had been preheated to 60°C was added dropwise to obtain a lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1. The average particle size (D) of the UV-curable oligomer particles in this lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1 was measured. 50 The value was measured in the same manner as in Example 1 and was found to be 39 nm.

[0192] [Example 2] To the aforementioned lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1, ion-exchanged water, 1,2-butanediol as a moisturizing solvent, a water-soluble initiator, a water-soluble sensitizer, Neugen FN1287 manufactured by Daiichi Kogyo Seiyaku as a surfactant [1], LE-605 manufactured by Kyoeisha Chemical as a surfactant [2], and EMACOL SF CYAN AE2034F manufactured by Sanyo Shikiso as a pigment dispersion, were added and mixed in the composition ratios shown in Table 1 below to obtain ink composition solution 2.

[0193] [Example 3] Ink composition liquid 3 was obtained in the same manner as in Example 2, except that the secondary tetrafunctional thiol in (1) above was replaced with the primary tetrafunctional thiol in (2) above.

[0194] [Example 4] Ink composition liquid 4 was obtained in the same manner as in Example 2, except that the blending ratio of the secondary tetrafunctional thiol in (1) above was changed as shown in Table 1 below.

[0195] [Comparative Example 1] Ink composition liquid 5 was obtained in the same manner as in Example 1, except that the secondary tetrafunctional thiol mentioned in (1) above was not added.

[0196] [Comparative Example 2] Ink composition liquid 6 was obtained in the same manner as in Example 2, except that the secondary tetrafunctional thiol mentioned in (1) above was not added.

[0197] [Example 5] Ink composition solution 7 was obtained by mixing equal amounts of ink composition solution 2 and ink composition solution 6.

[0198] [Table 1]

[0199] [Evaluation of ink composition solution] The ink compositions obtained in Examples 1-5 and Comparative Examples 1-2 were evaluated as follows, and the results are shown in Table 2.

[0200] <Evaluation of alcohol resistance and abrasion resistance of cured films> A cured film was formed using method (1) below, alcohol resistance was evaluated using method (2), and abrasion resistance was evaluated using method (3).

[0201] (1) LED curing Applying the ink composition solution prepared above to a PVC film using a bar coater to a film thickness of 15 μm for approximately 50 cm 2 After coating and heating at 80°C for 10 minutes, apply 7 J / cm² with an LED having a peak wavelength of 385 nm. 2 A cured film was formed by irradiating the area with ultraviolet light of the specified irradiation energy.

[0202] (2) Evaluation of the alcohol resistance of the cured film The obtained cured film was used to evaluate the alcohol resistance. The evaluation was carried out by visually observing the presence or absence of color transfer to the absorbent cotton when the absorbent cotton was immersed in absolute ethanol and rubbed on the surface of the cured film without load or with a 200 g load, and evaluated according to the following evaluation criteria. The results are shown in Table 2. In this evaluation test, cases of "△" or above were evaluated as passing. ◎: No color transfer to the absorbent cotton in any of the tests. ○: No color transfer to the absorbent cotton without load, and slightly color transfer to the absorbent cotton with a 200 g load. △: No color transfer to the absorbent cotton without load, and color transfer to the absorbent cotton with a 200 g load. ×: No color transfer to the absorbent cotton without load, and the coating film peels off and the substrate is exposed with a 200 g load. ××: There is color transfer to the absorbent cotton or exposure of the coating film without load, which is a problem in practical use.

[0203] (3) Evaluation of the abrasion resistance of the cured film The obtained cured film was used to evaluate the abrasion resistance. The evaluation was carried out using a tribogear HEIDON-14DR (manufactured by Shin-Tong Scientific Co., Ltd.) friction and wear tester. A lapping film sheet with a particle size of #1000 (manufactured by Trasco Nakayama Co., Ltd.) was set on a circular terminal with a ground contact surface diameter of 27 mm. When the surface of the cured film was rubbed with a 400 g load for 10 reciprocations in 10 seconds over a test distance of 50 mm, the peeling of the cured film was binarized with image analysis software, and the ratio (%) of the peeled part to the area of the cured film was determined. The results are shown in Table 2. In this evaluation test, 2.00% or less was considered passing.

[0204]

Table 2

[0205] From Tables 1 and 2, it was found that the ink of the present invention containing a mercapto compound is excellent in alcohol resistance and abrasion resistance, and can form a printed image with excellent coating film performance. In contrast, Comparative Examples 1 and 2, which did not contain mercapto compounds, were found to have inferior alcohol resistance and abrasion resistance.

[0206] [Preparation of UV-curable oligomer 2] Nonionic UV-curable oligomer 2 was prepared by reacting 0.75 moles of isophorone diisocyanate with 0.90 moles of dipentaerythritol pentaacrylate and 0.52 moles of polyethylene glycol (n=15-25 in the general formula (1) above). [Preparation of UV-curable oligomer 3] An anionic, UV-curable oligomer 3 containing a carboxyl group was prepared by reacting 0.87 moles of isophorone diisocyanate, 1.0 mole of dipentaerythritol pentaacrylate, 0.30 moles of polyethylene glycol (n=10-20 in the general formula (1) above), 0.13 moles of 2,2-bis(hydroxymethyl)propionic acid, and 0.12 moles of 2,2-bis(hydroxymethyl)butyric acid.

[0207] [Preparation of Lipid-Soluble Initiator-Encapsulated UV-Curable Oligomer Aqueous Dispersion 2] Lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 2 was obtained in the same manner as lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1, except that UV-curable oligomer 1 was replaced with UV-curable oligomer 2. The average particle size (D50) of the UV-curable oligomer particles in this aqueous dispersion was measured using a particle size analyzer (Nanotrac Wave II EX-150, manufactured by Microtrac-Bell Co., Ltd.) and was found to be 30 nm.

[0208] [Preparation of UV-curable oligomer aqueous dispersion 3 containing a lipid-soluble initiator] Lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 3 was obtained in the same manner as lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 1, except that UV-curable oligomer 1 was replaced with UV-curable oligomer 3, and 1.25 molar equivalents of sodium hydroxide were added to 1 molar equivalent of carboxyl groups contained in UV-curable oligomer 3 to neutralize it. The average particle size (D50) of the UV-curable oligomer particles in this aqueous dispersion was measured using a particle size analyzer (Nanotrac Wave II EX-150, manufactured by Microtrac-Bell Co., Ltd.) and was found to be 160 nm.

[0209] [Example 6] Ion-exchanged water, the aforementioned lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion 2, diethylene glycol ethyl methyl ether as a moisturizing solvent, propylene glycol as a water-soluble organic solvent, a water-soluble initiator, a water-soluble sensitizer, BYK-347 manufactured by Bic Chemie Japan as a surfactant, and EMACOL SF CYAN AE2034F manufactured by Sanyo Shikyou as a pigment dispersion were added and mixed in the composition ratios shown in Table 3 to obtain ink composition solution 8.

[0210] [Example 7] Ink composition solution 9 was obtained in the same manner as in Example 6, except that lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion solution 2 was replaced with lipid-soluble initiator-encapsulated UV-curable oligomer aqueous dispersion solution 3.

[0211] [Comparative Example 3] Ink composition solution 10 was obtained in the same manner as in Example 6, except that the secondary tetrafunctional thiol mentioned in (1) above was not added.

[0212] [Comparative Example 4] Ink composition solution 11 was obtained in the same manner as in Example 7, except that the secondary tetrafunctional thiol mentioned in (1) above was not added.

[0213] [Table 3]

[0214] [Evaluation of ink composition solution] The ink compositions obtained in Examples 6-7 and Comparative Examples 3-4 were evaluated as follows, and the results are shown in Table 4.

[0215] <Evaluation of alcohol resistance and abrasion resistance of cured films> A cured film was formed by the method of (1) below, and the abrasion resistance was evaluated by the method of (2) and the alcohol resistance was evaluated by the method of (3).

[0216] (1) LED curing A cured film was formed on each of a PVC film and a polymethyl methacrylate (PMMA) film by the method described above.

[0217] (2) Evaluation of the abrasion resistance of the cured film The abrasion resistance was evaluated using the cured film on the PVC film and the cured film on the PMMA film obtained above. The evaluation was performed using a tribogear HEIDON-14DR (manufactured by Shinto Kagaku Co., Ltd.) friction and wear tester. A BONSTAR steel wool No0000 manufactured by Nippon Steel Wool Co., Ltd. was set on a circular terminal with a ground contact surface diameter of 27 mm. When the surface of the cured film was rubbed at a test distance of 50 mm for 10 reciprocations in 10 seconds under a load of 400 g, the peeling of the cured film was binarized with image analysis software, and the ratio (%) of the peeled portion in the area of the cured film was determined. The results are shown in Table 4. Since this test using BONSTAR steel wool is a more severe wear condition than the test using the wrapping film sheet described above, in this evaluation test, for the cured film on the PVC film, a value of 10.00% or less was considered qualified, and for the cured film on the PMMA film, a value of 0.25% or less was considered qualified. In addition, since it is considered that the PMMA film is a material to which ink adheres more easily than the PVC film in the case of the PVC film and the case of the PMMA film, separate acceptance criteria were provided for each.

[0218] (3) Evaluation of the alcohol resistance of the cured film The alcohol resistance was evaluated using the cured film on the PVC film obtained above. The evaluation was performed by visually observing the presence or absence of color transfer to absorbent cotton when absorbent cotton was immersed in absolute ethanol and rubbed on the surface of the cured film without load or under a load of 200 g, and the evaluation was performed according to the following evaluation criteria. The results are shown in Table 4. In this evaluation test, a case of "△" or more was evaluated as qualified. ◎: No color transfer to the absorbent cotton was observed in any of the tests. ○: No color transfer to the cotton wool without load; slight color transfer to the cotton wool with a 200g load. △: No color transfer to the cotton wool under no load; color transfer to the cotton wool occurred under a 200g load. ×: No color transfer to the cotton wool without load; under a 200g load, the coating peels off and the base material is exposed. ××: Color transfer to absorbent cotton or exposure of the coating occurs without any load, which poses a practical problem.

[0219] [Table 4]

[0220] Table 4 shows that the ink of the present invention, which contains a mercapto compound, can form printed images with excellent alcohol resistance and abrasion resistance, and superior coating performance, regardless of the structure of the UV-curable oligomer. Furthermore, it was found that the ink of the present invention exhibits excellent abrasion resistance and high versatility as a substrate, regardless of whether it is applied to PVC film or PMMA film. In contrast, Comparative Examples 3 and 4, which did not contain mercapto compounds, were found to have inferior abrasion resistance and alcohol resistance, as well as inferior versatility as a substrate.

[0221] Next, examples and comparative examples of the second embodiment of the present invention will be described.

[0222] [Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-2] An ink composition solution was obtained in the same manner as in Examples 1-5 and Comparative Examples 1-2 described above.

[0223] [Table 5]

[0224] [Evaluation of ink composition solution] The alcohol resistance and abrasion resistance of the cured films of the ink compositions obtained in Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-2 were evaluated using the same method as described above for Examples 1 to 5 and Comparative Examples 1 to 2, and the results are shown in Table 6.

[0225] [Table 6]

[0226] Table 6 shows that the ink of the present invention, which contains a mercapto compound, has excellent alcohol resistance and abrasion resistance, and can form printed images with excellent coating film performance. In contrast, Comparative Examples 2-1 and 2-2, which did not contain mercapto compounds, were found to have inferior alcohol resistance and abrasion resistance.

Claims

1. It contains at least an ultraviolet-curable oligomer, a colorant, and a mercapto compound, The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') containing two or more polymerizable unsaturated bonds and capable of binding to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') capable of binding to the polyisocyanate compound (A), represented by the following formula (1). A UV-curable aqueous ink in which structural units derived from compound (A) are bonded to structural units derived from compound (B') and structural units derived from (C') via urethane bonds, urea bonds, or amide bonds. 【Chemistry 1】 (In formula (1), X is an alkylene group, and Y is one of a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

2. The UV-curable aqueous ink according to Claim 1, wherein the compound (B') is a compound containing four or more polymerizable unsaturated bonds.

3. The UV-curable aqueous ink according to Claim 1, wherein the compound (A) is a compound having two or more isocyanate groups in one molecule.

4. It contains at least an ultraviolet-curable oligomer, a colorant, and a mercapto compound, The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') that contains two or more polymerizable unsaturated bonds and can bind to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') that can bind to the polyisocyanate compound (A). The structural unit derived from compound (A) is an ultraviolet-curable oligomer that is bonded to the structural unit derived from compound (B') and the structural unit derived from (C') via urethane bonds, urea bonds, or amide bonds. A UV-curable aqueous ink in which the compound (A) is a compound having three or more isocyanate groups in one molecule.

5. The UV-curable aqueous ink according to any one of claims 1 to 4, wherein the mercapto compound is a secondary thiol.

6. The UV-curable aqueous ink according to any one of claims 1 to 5, wherein the mercapto compound is a polyfunctional thiol.

7. The ultraviolet-curable aqueous ink according to any one of claims 1 to 6, wherein the content of the mercapto compound is 0.01% by mass or more and 5% by mass or less.

8. Furthermore, the UV-curable aqueous ink according to any one of claims 1 to 7 further comprises one or more polymerization initiators, sensitizers, and surfactants.

9. The ultraviolet-curable aqueous ink according to any one of claims 1 to 8, wherein the mercapto compound is encapsulated in the ultraviolet-curable oligomer.

10. The ultraviolet-curable aqueous ink according to any one of claims 1 to 9, comprising a polymerization initiator and / or a sensitizer, wherein at least one of the polymerization initiator and / or sensitizer is encapsulated in the ultraviolet-curable oligomer.

11. The ultraviolet-curable aqueous ink according to any one of claims 1 to 10, wherein the ultraviolet-curable oligomer is nonionic.

12. The ultraviolet-curable aqueous ink according to any one of claims 1 to 11, wherein the ultraviolet-curable oligomer exists as particles.

13. The ultraviolet-curable aqueous ink according to any one of claims 1 to 12, wherein the average particle size of the ultraviolet-curable oligomer is 10 nm or more and 200 nm or less.

14. A printed article having a cured product formed from an ultraviolet-curable aqueous ink according to any one of claims 1 to 13 on a recording medium.

15. A dispersion of ultraviolet-curable oligomers used in inks, It contains 0.01% by mass or more and 10% by mass or less of a mercapto compound. The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') containing two or more polymerizable unsaturated bonds and capable of binding to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') capable of binding to the polyisocyanate compound (A), represented by the following formula (1). A dispersion in which structural units derived from compound (A) are bonded to structural units derived from compound (B') and structural units derived from (C') via urethane bonds, urea bonds, or amide bonds. 【Chemistry 1】 (In formula (1), X is an alkylene group, and Y is one of a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

16. A dispersion of ultraviolet-curable oligomers used in inks, It contains 0.01% by mass or more and 10% by mass or less of a mercapto compound. The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') that contains two or more polymerizable unsaturated bonds and can bind to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') that can bind to the polyisocyanate compound (A). The structural unit derived from compound (A) is an ultraviolet-curable oligomer that is bonded to the structural unit derived from compound (B') and the structural unit derived from (C') via urethane bonds, urea bonds, or amide bonds. A dispersion in which the compound (A) has three or more isocyanate groups in one molecule.

17. The dispersion according to claim 15 or 16, wherein the mercapto compound is a secondary thiol.

18. The dispersion according to any one of claims 15 to 17, wherein the mercapto compound is a polyfunctional thiol.

19. A UV-curable aqueous composition for use in inks, comprising a UV-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, and a mercapto compound, The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') containing two or more polymerizable unsaturated bonds and capable of binding to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') capable of binding to the polyisocyanate compound (A), represented by the following formula (1). A UV-curable aqueous composition in which structural units derived from compound (A) are bonded to structural units derived from compound (B') and structural units derived from (C') via urethane bonds, urea bonds, or amide bonds. 【Chemistry 1】 (In formula (1), X is an alkylene group, and Y is one of a (meth)acryloyl group, an allyl group, an acyl group, or a hydrogen atom. n is an integer greater than or equal to 2.)

20. A UV-curable aqueous composition for use in inks, comprising a UV-curable oligomer, one or more of a polymerization initiator, a sensitizer, and a surfactant, and a mercapto compound, The UV-curable oligomer has a structural unit derived from a polyisocyanate compound (A), a structural unit derived from a compound (B') that contains two or more polymerizable unsaturated bonds and can bind to the polyisocyanate compound (A), and a structural unit derived from a water-soluble compound (C') that can bind to the polyisocyanate compound (A). The structural unit derived from compound (A) is an ultraviolet-curable oligomer that is bonded to the structural unit derived from compound (B') and the structural unit derived from (C') via urethane bonds, urea bonds, or amide bonds. An ultraviolet-curable aqueous composition in which compound (A) is a compound having three or more isocyanate groups in one molecule.

21. The ultraviolet-curable aqueous composition according to claim 19, wherein the compound (B') is a compound containing four or more polymerizable unsaturated bonds.

22. The ultraviolet-curable aqueous composition according to claim 19, wherein the compound (A) is a compound having two or more isocyanate groups in one molecule.

23. The ultraviolet-curable aqueous composition according to any one of claims 19 to 22, wherein the mercapto compound is a secondary thiol.

24. The ultraviolet-curable aqueous composition according to any one of claims 19 to 23, wherein the mercapto compound is a polyfunctional thiol.

25. The ultraviolet-curable aqueous composition according to any one of claims 19 to 24, wherein the mercapto compound is encapsulated in the ultraviolet-curable oligomer.

26. The ultraviolet-curable aqueous composition according to any one of claims 19 to 25, comprising a polymerization initiator and / or a sensitizer, wherein at least one of the polymerization initiator and / or sensitizer is encapsulated in the ultraviolet-curable oligomer.

27. The ultraviolet-curable aqueous composition according to any one of claims 19 to 26, wherein the ultraviolet-curable oligomer is nonionic.

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