Ink set for inkjet printing

Abstract

The present invention provides: an ink set for inkjet printing with which, in printing onto a heat-shrinkable resin film, excellent rub fastness and water resistance are achieved in a print article that has been heat-shrunk; an inkjet printing method; and a packaging method.　Provided are: an ink set for inkjet printing comprising a water-based ink that contains a pigment, and an overcoat liquid that contains substantially no pigment, wherein the water-based ink contains a binder resin (Ib) having a carboxy group, the overcoat liquid contains a compound (II) having a reactive group capable of crosslinking with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the water-based ink; an inkjet printing method using the ink set; and a packaging method using a print article obtained by means of the inkjet printing method.

Description

Inkjet printing ink set

[0001] The present invention relates to an ink set for inkjet printing, an inkjet printing method, and a packaging method.

[0002] In the fields of commercial printing and industrial printing, in addition to printing on conventional highly absorbent printing substrates such as plain paper and copy paper, there is a growing demand for printing on low-absorbent printing substrates such as offset coated paper and non-absorbent printing substrates such as resin films such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), and nylon (NY). However, when printing on low-absorbent or non-absorbent printing substrates, the liquid components are absorbed slowly or not at all, so the adhesion of the pigment ink to these printing substrates is insufficient, and the image fastness of the printed matter tends to be low. Therefore, in order to improve the image fastness of printed matter using pigment ink, aqueous compositions such as coating liquids to be used in combination with pigment inks have been developed.

[0003] For example, Japanese Patent Laid-Open No. 2019-189867 (Patent Document 1) describes an aqueous composition for inkjet recording containing a blocked isocyanate, at least one compound selected from a carbodiimide compound and an oxazoline compound, and water, with the objective of improving the abrasion resistance, solvent resistance, and substrate adhesion of printed matter; an inkjet recording ink set containing the aqueous composition and a water-based ink; and an inkjet recording method using the aqueous composition and the water-based ink.

[0004] The present invention relates to an inkjet printing ink set comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a binder resin (Ib) having a carboxy group, the overcoat liquid contains a compound (II) having a reactive group capable of crosslinking with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. The present invention also relates to an inkjet printing ink set comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a compound (II) having a reactive group capable of crosslinking with the carboxy group of the binder resin (Ib), the overcoat liquid contains the binder resin (Ib) having a carboxy group, and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink.

[0005] Conventionally, as in Patent Document 1, there have been examples in which a crosslinking agent such as a blocked isocyanate compound, a carbodiimide compound, or an oxazoline compound is printed as an overcoat liquid and heated to promote the crosslinking reaction. However, when printing on heat-shrinkable resin films widely used as packaging substrates for PET bottles and the like, it has been found that the crosslinking reaction by the crosslinking agent does not occur uniformly, resulting in uneven strength of the printed coating film, and therefore weaker areas of the printed coating film are preferentially destroyed when the resin film shrinks, impairing the abrasion resistance and water resistance of the printed material after heat shrinkage. The present invention relates to an inkjet printing ink set, an inkjet printing method, and a packaging method that, when printing on heat-shrinkable resin films, produce heat-shrunk printed materials with excellent abrasion resistance and water resistance.

[0006] The present inventors have discovered that the above-mentioned problems can be solved by providing an ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a binder resin having a carboxy group, and the overcoat liquid contains a compound having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin, and the surface tension of the overcoat liquid is greater than that of the aqueous ink, thereby allowing the crosslinking reaction of the binder resin to proceed uniformly. That is, the present invention relates to the following [1] to [4]. [1] An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. [2] An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of a binder resin (Ib) having a carboxy group, and the overcoat liquid contains the binder resin (Ib) having a carboxy group, and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. [3] An inkjet printing method using the ink set for inkjet printing according to item [1] or [2] above, comprising the following steps 1 and 2: Step 1: applying the water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method, and then applying the overcoat liquid by an inkjet ejection method to the area where the water-based ink has been applied. Step 2: heating the water-based ink coating film and the overcoat liquid coating film on the printing substrate formed by step 1. [4] A packaging method, comprising arranging a printed matter obtained by the inkjet printing method described in [3] above around an item to be packaged, and then shrinking the heat-shrinkable resin film substrate of the printed matter to obtain a package.

[0007] According to the present invention, it is possible to provide an inkjet printing ink set, an inkjet printing method, and a packaging method that, when printing on a heat-shrinkable resin film, provide a heat-shrunk printed product with excellent abrasion resistance and water resistance.

[0008] [Inkjet Recording Ink Set] The inkjet recording ink set (hereinafter also simply referred to as "ink set") of the present invention comprises a pigment-containing water-based ink (hereinafter also simply referred to as "water-based ink" or "ink") and an overcoat liquid (hereinafter also simply referred to as "overcoat liquid") that is substantially free of pigment, wherein the water-based ink contains a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the water-based ink. In the present invention, the "water-based" aspect of the water-based ink means that water accounts for the largest proportion, by mass, of the medium contained in the water-based ink. Furthermore, in this specification, the "low liquid absorption" of a low liquid-absorbent printing substrate is a concept that encompasses both low liquid absorption and non-liquid absorption, and refers to a printing substrate having a water absorption of 0 g / m when the printing substrate is in contact with pure water for 100 ms. 2 10g / m or more 2 The water absorption amount can be measured by the method described in the Examples. Furthermore, "printing" is a concept that includes printing and printed letters for recording characters and images, and "printed matter" is a concept that includes printed matter and printed letters on which characters and images are recorded.

[0009] According to the present invention, when printing on a heat-shrinkable resin film, the heat-shrunk printed matter has excellent abrasion resistance and water resistance. The reason for this is unclear, but is thought to be as follows. In the present invention, the surface tension of the overcoat liquid is greater than that of the water-based ink. Therefore, when the water-based ink is applied to a printing substrate and then the overcoat liquid is applied to the area where the water-based ink was applied, convection (so-called Marangoni convection) occurs between the water-based ink coating film on the printing substrate and the overcoat liquid coating film, driven by the surface tension gradient. As a result, the compound (II) having a reactive group contained in the overcoat liquid coating film is distributed more uniformly in the water-based ink coating film than in the case where the compound (II) diffuses due to the difference in concentration between the water-based ink coating film on the printing substrate and the overcoat liquid coating film. This promotes a uniform crosslinking reaction between the carboxyl group of the binder resin (Ib) contained in the water-based ink coating film and the reactive group of the compound (II), reducing the likelihood of a distribution in strength of the resulting printed coating film, resulting in a printed matter with a uniform printed coating film strength. It is believed that when such a printed material is thermally shrunk, selective shrinkage does not occur in areas of the printed coating that are weaker in strength, and the occurrence of fine cracks and wrinkles in the printed coating can be reduced. As a result, it is presumed that embrittlement of the printed coating is suppressed and the abrasion resistance and water resistance are improved. Hereinafter, the abrasion resistance and water resistance of the thermally shrunk printed material will also be simply referred to as "abrasion resistance" and "water resistance," respectively.

[0010] In the present invention, the surface tension γ(B) of the overcoat liquid (hereinafter also referred to simply as "surface tension γ(B)") is greater than the surface tension γ(A) of the water-based ink (hereinafter also referred to simply as "surface tension γ(A)"). From the viewpoint of improving abrasion resistance and water resistance, the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink is preferably 1 mN / m or more, more preferably 1.5 nm / m or more, even more preferably 2 mN / m or more, even more preferably 3 mN / m or more, even more preferably 5 mN / m or more, and even more preferably 7 mN / m or more; and from the same viewpoint as above, it is preferably 20 mN / m or less, more preferably 17 mN / m or less, and even more preferably 15 mN / m or less. The surface tension γ(A) of the water-based ink and the surface tension γ(B) of the overcoat liquid are measured by the method described in the examples.

[0011] <Water-based ink> The water-based ink according to the present invention contains a pigment and a binder resin (Ib) having a carboxy group. The water-based ink may be used alone having one color, or in combination with two or more different colors. That is, the printed image formed with the water-based ink according to the present invention may be a multi-color print, for example, a three-color print, a four-color print, or a print using inks having four or more different colors.

[0012] (Pigment) The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may be used in combination with extender pigments. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. Achromatic pigments such as white, black, and gray can be used in achromatic inks, while chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used in chromatic inks. Specific examples of preferred organic pigments include one or more product numbers selected from C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination.

[0013] In the aqueous ink of the present invention, the pigment is dispersed in a medium. The pigment in the aqueous ink of the present invention may be dispersed using a resin (hereinafter also referred to as a "pigment dispersion resin") or a surfactant as a dispersant, or may be dispersed in the form of a self-dispersed pigment without using a dispersant. Among these, the pigment in the aqueous ink of the present invention is preferably dispersed in a pigment dispersion resin (hereinafter also referred to as a "pigment dispersion resin (Ia)"), and more preferably in the form of resin particles containing the pigment (hereinafter also referred to as "pigment-containing resin particles"). The form of the pigment-containing resin particles is not particularly limited, as long as they are formed from at least the pigment and the pigment dispersion resin (Ia), and are particles in which the pigment dispersion resin (Ia) is adsorbed onto the pigment in the aqueous ink. Examples of the form of the pigment-containing resin particles include particles in which the pigment is encapsulated in the pigment dispersion resin (Ia), particles in which the pigment is uniformly dispersed in the pigment dispersion resin (Ia), particles in which the pigment is exposed on the surface of the pigment dispersion resin (Ia) particles, and mixtures thereof.

[0014] (Pigment Dispersion Resin (Ia)) The pigment dispersion resin (Ia) may be either a water-soluble resin or a water-insoluble resin. Here, with regard to the "water-soluble" and "water-insoluble" of a resin, when a resin that has been dried at 105°C for 2 hours and reached a constant weight is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g, it is judged to be "water-soluble," and if the dissolved amount is 10 g or less, it is judged to be "water-insoluble." Furthermore, as described below, when the pigment dispersion resin (Ia) has anionic groups and the anionic groups are further neutralized with a neutralizer, the dissolution amount is judged to be the amount of dissolution measured in the presence of the neutralizer, under conditions such that the mass ratio of the pigment dispersion resin (Ia) to the neutralizer is the same as that in the water-based ink of the present invention.

[0015] Examples of the pigment dispersion resin (Ia) include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); and condensation resins such as polyester resins and polyurethane resins. The pigment dispersion resin (Ia) may be an appropriately synthesized product, or a commercially available product may be used. Among these, the pigment dispersion resin (Ia) is preferably a vinyl resin (hereinafter also referred to as "vinyl resin (Ia-1)") from the viewpoint of improving abrasion resistance and water resistance.

[0016] From the viewpoint of improving the dispersion stability of the pigment, the vinyl resin (Ia-1) preferably contains a structural unit derived from an anionic group-containing monomer. In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Examples of the vinyl resin (Ia-1) include a homopolymer of an anionic group-containing monomer, a copolymer of an anionic group-containing monomer and a hydrophobic monomer, and a copolymer of an anionic group-containing monomer, a hydrophobic monomer, and a nonionic monomer. When the vinyl resin (Ia-1) is a copolymer, it may be a random copolymer, a block copolymer, an alternating copolymer, or a graft copolymer. In this specification, the term "hydrophobic" in the context of a hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of dissolution is less than 10 g. Furthermore, a nonionic monomer is a monomer that has a high affinity for water or a water-soluble organic solvent, such as a monomer containing a hydroxy group or a polyalkylene glycol chain.

[0017] Examples of anionic group-containing monomers include carboxy group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Among these, from the viewpoints of improving the dispersion stability of the pigment and availability, carboxy group-containing monomers are preferred, and (meth)acrylic acid is more preferred. Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number-average molecular weight of from 500 to 100,000. Among these, from the viewpoint of improving the dispersion stability of the pigment, the hydrophobic monomer is preferably a styrene-based monomer, more preferably one or more selected from the group consisting of styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from the group consisting of styrene and α-methylstyrene. Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. The term "(meth)acrylic acid" refers to at least one selected from the group consisting of acrylic acid and methacrylic acid. The term "(meth)acrylate" refers to at least one selected from the group consisting of acrylates and methacrylates. Each of the monomers in the vinyl resin (Ia-1) can be used alone or in combination of two or more.

[0018] When the vinyl resin (Ia-1) is a copolymer, from the viewpoint of improving the dispersion stability of the pigment, the vinyl resin (Ia-1) preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, and more preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid. and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, more preferably structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from aromatic group-containing monomers, and even more preferably structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a styrene-based monomer.

[0019] When the vinyl resin (Ia-1) is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, or a copolymer of an anionic group-containing monomer, a hydrophobic monomer, and a nonionic monomer, the content of the structural units derived from each monomer component in the vinyl resin (Ia-1) is as follows. From the viewpoint of improving the dispersion stability of the pigment, the content of the structural units derived from the anionic group-containing monomer in the vinyl resin (Ia-1) is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and from the same viewpoints as above, it is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less. From the viewpoint of improving the dispersion stability of the pigment, the content of the structural units derived from the hydrophobic monomer in the vinyl resin (Ia-1) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and from the same viewpoints as above, it is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less. When the vinyl resin (Ia-1) contains a structural unit derived from a nonionic monomer, the content of the structural unit derived from a nonionic monomer in the vinyl resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of improving the dispersion stability of the pigment. The vinyl resin (Ia-1) can be obtained, for example, by addition polymerization of raw material monomers including an anionic group-containing monomer, a hydrophobic monomer, or a nonionic monomer by a known method.

[0020] The pigment dispersion resin (Ia) may have a crosslinked structure. In this case, from the viewpoint of improving the dispersion stability of the pigment, the pigment dispersion resin (Ia) preferably has a structure including a polymer component having a linear two-dimensional structure which may have a branched chain and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure which may have a branched chain being converted into a three-dimensional structure by a component derived from a crosslinking agent. Examples of polymers having a linear two-dimensional structure which may have a branched chain include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; and the aforementioned vinyl resin (Ia-1) is preferred.

[0021] From the viewpoint of improving the dispersion stability of the pigment, the crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, from the viewpoint of improving the dispersion stability of the pigment, the epoxy group equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

[0022] From the viewpoint of improving the dispersion stability of the pigment, the acid value of the pigment dispersion resin (Ia) is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, and even more preferably 100 mgKOH / g or more. From the same viewpoint as above, it is preferably 800 mgKOH / g or less. The acid value of the pigment dispersion resin (Ia) can be determined by the method described in the Examples, but it can also be calculated from the mass ratio of the constituent monomers. The acid value of the pigment dispersion resin (Ia) having a crosslinked structure can also be calculated using the following formula: Acid value (mgKOH / g) of pigment dispersion resin (Ia) having a crosslinked structure = [Acid value (mgKOH / g) of pigment dispersion resin (Ia) before crosslinking × [(100 - crosslinking rate (mol %)) / 100]]. In this specification, the crosslinking rate (mol %) of the pigment dispersion resin (Ia) having a crosslinked structure is the apparent crosslinking rate calculated from the acid value of the pigment dispersion resin (Ia) before crosslinking and the equivalent weight of the crosslinkable functional group of the crosslinking agent.

[0023] The number average molecular weight of the pigment dispersing resin (Ia) is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more from the viewpoint of dispersion stability of the pigment, and from the same viewpoint as above, is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The number average molecular weight of the pigment dispersing resin (Ia) is measured by the method described in the examples.

[0024] The weight-average molecular weight of the pigment dispersing resin (Ia) is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more from the viewpoint of pigment dispersion stability, and is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less from the same viewpoint as above. The weight-average molecular weight of the pigment dispersing resin (Ia) is measured by the method described in the examples.

[0025] Commercially available pigment dispersing resins (Ia) include, for example, polyacrylic acids such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); and styrene / acrylic resins such as "Joncryl 67," "Joncryl 611," "Joncryl 678," "Joncryl 680," "Joncryl 690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0026] When the pigment in the aqueous ink according to the present invention is in the form of pigment-containing resin particles, the pigment-containing resin particles can be obtained as an aqueous dispersion by dispersing the pigment, pigment-dispersing resin (Ia), and optionally a neutralizer, surfactant, etc., by a known method. When the pigment is blended in the aqueous ink as an aqueous dispersion of pigment-containing resin particles, the average particle size of the pigment-containing resin particles in the aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoints of the jetting performance and storage stability of the aqueous ink, as well as abrasion resistance and water resistance. From the same viewpoints as above, it is preferably 600 nm or less, more preferably 550 nm or less, even more preferably 500 nm or less, and even more preferably 450 nm or less. The average particle size of the pigment-containing resin particles in the aqueous dispersion is measured by the method described in the Examples.

[0027] (Binder Resin (Ib)) The water-based ink according to the present invention contains a binder resin (Ib) (hereinafter simply referred to as "binder resin (Ib)") having a carboxy group (-COOM) from the viewpoint of improving abrasion resistance and water resistance. The carboxy group is a group that exhibits acidity by dissociating and releasing a hydrogen ion, or a group in the dissociated ionic form (-COOM). - In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium, as in the anionic group described above.

[0028] From the viewpoint of improving abrasion resistance and water resistance, the acid value of the binder resin (Ib) is preferably 3 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more, and from the same viewpoint as above, it is preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, and even more preferably 20 mgKOH / g or less. The acid value of the binder resin (Ib) can be determined by the method described in the examples, but it can also be determined by calculation from the mass ratio of the constituent monomers.

[0029] Examples of the polymer skeleton of the binder resin (Ib) include vinyl resins such as (meth)acrylic resins, styrene resins, styrene / (meth)acrylic resins, butadiene resins, styrene / butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins; polyurethane resins; and polyester resins. The term "(meth)acrylic" refers to acrylic or methacrylic. Furthermore, when the binder resin (Ib) is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. Among these, from the viewpoint of improving abrasion resistance and water resistance, the binder resin (Ib) is preferably one or more selected from the group consisting of vinyl resins having a carboxy group, polyurethane resins having a carboxy group, and polyester resins having a carboxy group, and more preferably one or more selected from the group consisting of vinyl resins having a carboxy group and polyurethane resins having a carboxy group.

[0030] The vinyl resin having a carboxy group used in the present invention (hereinafter also referred to as "vinyl resin (Ib-1)") preferably contains a structural unit derived from a carboxy group-containing monomer and a structural unit derived from a hydrophobic monomer from the viewpoint of improving abrasion resistance and water resistance. As the carboxy group-containing monomer, (meth)acrylic acid is preferred from the viewpoint of improving abrasion resistance and water resistance and from the viewpoint of availability. Preferred examples of the hydrophobic monomer include the same ones as those exemplified for the pigment dispersion resin (Ia) described above. Among them, from the viewpoint of improving abrasion resistance and water resistance, the hydrophobic monomer is preferably one or more selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably one or more selected from the group consisting of (meth)acrylates and aromatic group-containing monomers having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, even more preferably a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, even more preferably a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, and even more preferably a (meth)acrylate having an alkyl group having 1 to 8 carbon atoms. Each monomer of the vinyl resin (Ib-1) can be used alone or in combination of two or more types.

[0031] From the viewpoint of improving abrasion resistance and water resistance, the vinyl resin (Ib-1) preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, and even more preferably structural units derived from one or more hydrophobic monomers selected from the group consisting of acrylic acid and methacrylic acid. The (meth)acrylic resin contains a structural unit derived from the above carboxy group-containing monomer and a structural unit derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and is even more preferably a (meth)acrylic resin containing a structural unit derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and a structural unit derived from a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, and is even more preferably a (meth)acrylic resin containing a structural unit derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and a structural unit derived from a (meth)acrylate having an alkyl group having from 1 to 8 carbon atoms, and is even more preferably a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0032] When the vinyl resin (Ib-1) is a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, the content of the structural units derived from each monomer component in the vinyl resin is as follows. From the viewpoint of improving abrasion resistance and water resistance, the content of the structural units derived from the carboxy group-containing monomer in the vinyl resin (Ib-1) is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and from the same viewpoints as above, it is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less. From the viewpoint of improving abrasion resistance and water resistance, the content of the structural units derived from the hydrophobic monomer in the vinyl resin (Ib-1) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and from the same viewpoints as above, it is preferably 99.5% by mass or less, more preferably 99% by mass or less, even more preferably 98% by mass or less.

[0033] From the viewpoint of improving abrasion resistance and water resistance, the weight average molecular weight of the vinyl resin (Ib-1) is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, even more preferably 50,000 or more, even more preferably 100,000 or more, even more preferably 300,000 or more, and even more preferably 500,000 or more. From the same viewpoint as above, it is preferably 1,500,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less. Measurement of the weight average molecular weight can be performed by the method described in the Examples. The vinyl resin (Ib-1) is produced by polymerizing raw material monomers by a known polymerization method. Preferred polymerization methods include, for example, emulsion polymerization and suspension polymerization, with emulsion polymerization being more preferred.

[0034] The polyurethane resin having a carboxy group (hereinafter also referred to as "polyurethane resin (Ib-2)") used in the present invention is preferably a polyaddition product of a prepolymer composed of an organic compound (polyol) component having two or more alcoholic hydroxyl groups in the molecule and a polyisocyanate component, with a dialkanolcarboxylic acid, from the viewpoint of improving abrasion resistance and water resistance. Examples of dialkanolcarboxylic acids include dimethylolbutanoic acid, dimethylolpropionic acid, and salts thereof. Among these, dimethylolpropionic acid is preferred from the viewpoint of improving abrasion resistance and water resistance.

[0035] The polyol component is not particularly limited as long as it is a compound having two or more alcoholic hydroxyl groups in the molecule, and examples thereof include polycarbonate polyols, polyester polyols, and polyether polyols. Examples of the polyisocyanate component include chain aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; aliphatic diisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; and modified products of these diisocyanates (carbodiimide-, uretdione-, and uretoimine-containing modified products, etc.).

[0036] From the viewpoint of improving abrasion resistance and water resistance, the polyurethane resin (Ib-2) is more preferably a polyaddition product of a polycarbonate polyol as the polyol component, dicyclohexylmethane 4,4'-diisocyanate as the polyisocyanate component, and dimethylolpropionic acid as the dialkanolcarboxylic acid.

[0037] Examples of solvents used in the polyaddition reaction include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. In the polyaddition reaction, a chain extender or a reaction terminator may be used in combination, if necessary. The use of a chain extender can further increase the molecular weight. Examples of chain extenders include polyols and polyamines, and examples of reaction terminators include monoalcohols and monoamines.

[0038] From the viewpoint of dispersion stability in aqueous inks, it is preferable that at least a portion of the carboxyl groups of the polyurethane resin (Ib-2) be neutralized with a neutralizing agent, such as alkylamines such as butylamine and triethylamine; alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; and inorganic bases such as morpholine, ammonia and sodium hydroxide.

[0039] The binder resin (Ib) is preferably used as pigment-free resin particles, and from the viewpoint of improving the productivity of the aqueous ink, it is preferably blended into the aqueous ink as an aqueous dispersion of pigment-free polymer particles. The binder resin (Ib) may be suitably synthesized or a commercially available product. When the binder resin (Ib) is blended as an aqueous dispersion of pigment-free resin particles, the average particle size of the pigment-free resin particles in the aqueous dispersion is preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more, even more preferably 70 nm or more, from the viewpoint of ink storage stability, and is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and even more preferably 130 nm or less. The average particle size of the pigment-free resin particles in the aqueous dispersion is measured by the method described in the Examples.

[0040] Commercially available dispersions of pigment-free vinyl resin particles include, for example, acrylic resins such as "Neocryl A-1127" (trade name, anionic self-crosslinking aqueous acrylic resin, manufactured by Covestro), "Joncryl 390", "Joncryl 7100", "Joncryl 7600", "Joncryl 537J", "Joncryl PDX-7164", "Joncryl 538J", and "Joncryl 780" (trade names, manufactured by BASF Japan Ltd.); styrene / butadiene resins such as "SR-100" and "SR102" (all trade names, manufactured by Nippon A&L Inc.); and vinyl chloride resins such as "Vinyblan 700" and "Vinyblan 701" (trade names, manufactured by Nissin Chemical Industry Co., Ltd.). Commercially available dispersions of pigment-free polyurethane resin particles include, for example, "NeoRez R-9603" (trade name, manufactured by Covestro) and "WBR-2018" and "WBR-2000U" (trade names, manufactured by Taisei Fine Chemical Co., Ltd.). Commercially available dispersions of pigment-free polyester resin particles include, for example, "ELITEL KA-5034," "ELITEL KA-5071S," "ELITEL KZA-1734," "ELITEL KZA-6034," "ELITEL KZA-1449," "ELITEL KZA-0134," and "ELITEL KZA-3556" (all trade names, manufactured by Unitika Ltd.).

[0041] (Water-Soluble Organic Solvent) The water-based ink according to the present invention preferably further contains a water-soluble organic solvent from the viewpoint of improving the jetting properties and storage stability of the water-based ink, and from the viewpoint of adjusting the surface tension of the water-based ink and improving the abrasion resistance and water resistance. The water-soluble organic solvent may be used alone or in combination of two or more. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 10 mL or more. The boiling point of the water-soluble organic solvent under atmospheric pressure is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and preferably 350°C or lower, more preferably 300°C or lower, even more preferably 250°C or lower. When two or more water-soluble organic solvents are used in combination, the boiling point of the water-soluble organic solvents is a weighted average value weighted by the content (mass%) of each water-soluble organic solvent.

[0042] Examples of water-soluble organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving the jetting properties and storage stability of the water-based ink, and from the viewpoint of adjusting the surface tension of the water-based ink and improving the scratch resistance and water resistance, one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred. As for polyhydric alcohols, a mixture of multiple polyhydric alcohols can be used. Similarly to polyhydric alcohols, a mixture of multiple polyhydric alcohol alkyl ethers can also be used.

[0043] Examples of polyhydric alcohols include ethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

[0044] Examples of polyhydric alcohol alkyl ethers include alkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers. Specific examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, and tripropylene glycol monobutyl ether.

[0045] (Surfactant) The aqueous ink according to the present invention preferably further contains a surfactant from the viewpoint of adjusting the surface tension of the aqueous ink and improving abrasion resistance and water resistance. The surfactant can be appropriately selected and used within a range that satisfies the relationship between the surface tension γ(A) of the aqueous ink and the surface tension γ(B) of the overcoat liquid. Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred. The surfactants can be used alone or in combination of two or more. Examples of nonionic surfactants include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants. Among these, the surfactant is preferably at least one selected from the group consisting of acetylene-based surfactants and silicone-based surfactants from the viewpoint of adjusting the surface tension of the aqueous ink and improving abrasion resistance and water resistance.

[0046] From the viewpoint of adjusting the surface tension of the aqueous ink and improving the abrasion resistance and water resistance, preferred acetylene surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide (hereinafter also referred to as "EO") adducts thereof. Among these, more preferred are one or more surfactants selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and even more preferred are EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The average number of moles of ethylene oxide added in the acetylene surfactant (hereinafter also referred to as "average number of moles of EO added") is preferably 1 mole or more, more preferably 2 moles or more, and even more preferably 3 moles or more, from the viewpoint of adjusting the surface tension of the water-based ink and improving the scratch resistance and water resistance, and from the same viewpoint as above, is preferably 35 moles or less, more preferably 30 moles or less, even more preferably 25 moles or less, still more preferably 20 moles or less, still more preferably 15 moles or less, still more preferably 10 moles or less, and still more preferably 5 moles or less.

[0047] The HLB value of the acetylene surfactant is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and even more preferably 7 or more, from the viewpoint of adjusting the surface tension of the water-based ink and improving abrasion resistance and water resistance, and from the same viewpoint as above, is preferably 18 or less, more preferably 15 or less, and even more preferably 10 or less. In the present invention, the HLB value is a value that indicates the affinity of the surfactant for water and oil as a hydrophile-lipophile balance, and can be calculated using the Griffin method using the following formula. The value in the catalog for each product can also be referenced. HLB value = 20 × [(sum of formula weights of hydrophilic groups contained in the surfactant) / (molecular weight of the surfactant)]. Examples of hydrophilic groups contained in surfactants include hydroxyl groups and ethyleneoxy groups.

[0048] Commercially available acetylene surfactants include, for example, Surfynol 104PG-50 (a 50% propylene glycol dilution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol), Surfynol 420 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 1), HLB value: 4 (catalog value)), and Surfynol 440 (2,4,7,9-tetramethyl-5-decyne-4,7-diol). Examples thereof include Surfynol 465 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 3.5), HLB value: 8 (catalog value)), Surfynol 465 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 10), HLB value: 13 (catalog value)), and Surfynol 485 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 30), HLB value: 17 (catalog value)).

[0049] Preferred examples of silicone surfactants include polyether-modified silicone surfactants, from the viewpoint of adjusting the surface tension of the water-based ink and improving the abrasion resistance and water resistance. Suitable polyether groups in polyether-modified silicone surfactants include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups (trimethyleneoxy groups or propane-1,2-diyloxy groups) are added in a block or random manner. Compounds in which polyether groups are grafted onto a silicone main chain and compounds in which polyether groups are bonded in a block manner to both ends of a silicone main chain can be used.

[0050] The HLB value of the polyether-modified silicone surfactant is preferably 2 or more, more preferably 6 or more, and even more preferably 10 or more, from the viewpoint of adjusting the surface tension of the water-based ink and improving the scratch resistance and water resistance, and from the same viewpoint as above, is preferably 18 or less, more preferably 17 or less, and even more preferably 16 or less.

[0051] Specific examples of polyether-modified silicone surfactants include PEG-3 dimethicone, PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG / PPG-20 / 22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, and lauryl PEG-9 polydimethylsiloxyethyl dimethicone. Commercially available polyether-modified silicone surfactants include the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., the "Silface SAG" series manufactured by Nissin Chemical Industry Co., Ltd., and the "BYK" series manufactured by BYK Japan K.K.

[0052] (Water) The water-based ink according to the present invention contains water. The water used in the water-based ink according to the present invention is preferably pure water or ion-exchanged water, from the viewpoint of preventing the inclusion of unintended substances.

[0053] The water-based ink according to the present invention may further contain various additives as optional components, such as a humectant, wetting agent, penetrant, dispersant, viscosity adjuster, antifoaming agent, preservative, antifungal agent, and antirust agent.

[0054] The water-based ink can be obtained by mixing and stirring a pigment, a binder resin (Ib), water, and optionally a pigment-dispersing resin (Ia), a neutralizing agent, a surfactant, a water-soluble organic solvent, etc. When pigment-containing resin particles are contained, as described above, it is preferable to disperse the pigment, the pigment-dispersing resin (Ia), and optionally a neutralizing agent, a surfactant, etc. by a known method to obtain an aqueous dispersion of the pigment-containing resin particles, and then blend it into the water-based ink.

[0055] (Composition of Water-Based Ink) From the viewpoint of image density, the content of the pigment in the water-based ink according to the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, and from the viewpoints of abrasion resistance and water resistance, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less. When the pigment in the water-based ink according to the present invention is in a form dispersed in a pigment dispersing resin (Ia), the content of the pigment dispersing resin (Ia) in the water-based ink according to the present invention is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and from the same viewpoints as above, it is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. When the pigment in the water-based ink according to the present invention is in a form dispersed in the pigment dispersing resin (Ia), the mass ratio of the content of the pigment to the total content of the pigment and the pigment dispersing resin (Ia) in the water-based ink according to the present invention [pigment / (pigment+pigment dispersing resin (Ia))] is, from the viewpoint of improving the dispersion stability of the pigment, preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.65 or more, and still more preferably 0.7 or more, and, from the same viewpoints as above, is preferably 0.99 or less, more preferably 0.98 or less.

[0056] The content of binder resin (Ib) in the water-based ink according to the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more from the viewpoint of improving abrasion resistance and water resistance, and from the same viewpoints as above, is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less. The content of water in the water-based ink according to the present invention is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more from the viewpoint of abrasion resistance and water resistance, and from the same viewpoints as above, is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0033] When the water-based ink according to the present invention further contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the water-based ink according to the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, from the viewpoint of improving the jetting properties and storage stability of the water-based ink, and from the viewpoint of adjusting the surface tension of the water-based ink and improving the abrasion resistance and water fastness of the water-based ink, and is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less. When the water-based ink according to the present invention further contains a surfactant, the content of the surfactant in the water-based ink according to the present invention is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, from the viewpoint of adjusting the surface tension of the water-based ink and improving the abrasion resistance and water fastness of the water-based ink, and from the same viewpoints as above, is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less.

[0057] (Physical Properties of Water-Based Ink) From the viewpoints of improving abrasion resistance and water resistance and of improving image quality, the surface tension γ(A) of the water-based ink according to the present invention is preferably 22 mN / m or more, more preferably 23 mN / m or more, even more preferably 24 mN / m or more, and even more preferably 25 mN / m or more. From the same viewpoints as above, it is preferably 30 mN / m or less, more preferably 29 mN / m or less, even more preferably 28 mN / m or less, and even more preferably 27 mN / m or less. The surface tension is measured by the method described in the Examples. From the viewpoints of jetting stability and dispersion stability, the viscosity of the water-based ink according to the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, and even more preferably 7 mPa·s or less. The viscosity is measured by the method described in the Examples. The pH of the water-based ink according to the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. From the viewpoints of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The pH is measured by the method described in the examples.

[0058] When two or more aqueous inks having different colors are used in combination, there may be a difference in surface tension between the aqueous inks. In this case, from the viewpoint of improving abrasion resistance and water resistance, the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink is preferably larger than the surface tension between the aqueous inks. More specifically, the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink is preferably larger than the surface tension between the aqueous inks by 0.5 mN / m or more, more preferably by 1.0 mN / m or more, and even more preferably by 1.5 mN / m or more.

[0059] <Overcoat Liquid> The overcoat liquid according to the present invention is substantially free of pigment and contains a compound (II) (hereinafter also simply referred to as "compound (II)") having a reactive group capable of crosslinking with a carboxy group of the binder resin (Ib). The overcoat liquid according to the present invention is substantially free of pigment. Here, "substantially free of pigment" means that the content of the pigment in the overcoat liquid according to the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and still more preferably 0% by mass.

[0060] (Compound (II)) The reactive group of compound (II) is preferably one or more selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, an isocyanate group, an aziridino group, and an amino group. The concept of an epoxy group includes a glycidyl group. Among these, from the viewpoint of improving abrasion resistance and water resistance, the reactive group is more preferably one or more selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group, even more preferably one or more selected from the group consisting of a carbodiimide group and an oxazoline group, and even more preferably a carbodiimide group. That is, compound (II) is preferably one or more selected from the group consisting of a polyfunctional carbodiimide compound, a polyfunctional oxazoline compound, and a polyfunctional epoxy compound, more preferably one or more selected from the group consisting of a polyfunctional carbodiimide compound and a polyfunctional oxazoline compound, and even more preferably a polyfunctional carbodiimide compound. From the viewpoint of improving abrasion resistance and water resistance, the reactive group equivalent of compound (II) is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more, and from the viewpoint of blendability into an overcoat solution, it is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. The reactive group equivalent means the mass of compound (II) per mole of reactive group.

[0061] [Polyfunctional carbodiimide compound] The polyfunctional carbodiimide compound is a compound having two or more carbodiimide groups in the molecule. As the polyfunctional carbodiimide compound, from the viewpoint of improving abrasion resistance and water resistance, a polymer containing two or more carbodiimide groups (hereinafter also referred to as "carbodiimide group-containing polymer") is preferred. The carbodiimide group-containing polymer is preferably one obtained by, for example, blocking the terminal isocyanate group of a condensation reaction product obtained by decarboxylation condensation reaction of diisocyanates in the presence of a carbodiimidization catalyst with a hydrophilic group.

[0062] Examples of diisocyanates used in the decarboxylation condensation reaction include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), decamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,5- or 2,6-norbornane diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated tolylene diisocyanate, and 2,4-bis-(8 alicyclic diisocyanates such as m- or p-xylylene diisocyanate (XDI) and tetramethyl xylylene diisocyanate (TMXDI); and aromatic diisocyanates such as 2,4,6-triisopropylphenyl diisocyanate (TIDI), 4,4'- or 2',4-diphenylmethane diisocyanate (MDI), and 2,4- or 2,6-tolylene diisocyanate (TDI).

[0063] The compound that blocks the terminal isocyanate group of the condensation reaction product is a compound having a functional group that can react with the isocyanate group, such as polyethylene glycol monomethyl ether and polypropylene glycol monomethyl ether. Among these, polyethylene glycol monomethyl ether is preferred from the viewpoint of blendability in the overcoat liquid. The number of moles of ethylene oxide added to the polyethylene glycol monomethyl ether can be adjusted, and the resulting carbodiimide group-containing polymer can be blended in the overcoat liquid as an aqueous solution or emulsion.

[0064] The carbodiimide group equivalent of the carbodiimide group-containing polymer is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more from the viewpoint of improving abrasion resistance and water resistance, and is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less from the viewpoint of blendability into an overcoat solution. The carbodiimide group equivalent means the mass of the carbodiimide group-containing polymer per mole of carbodiimide group. Commercially available carbodiimide group-containing polymers include, for example, Carbodilite E-02, Carbodilite E-05, and Carbodilite E-07S (all trade names manufactured by Nisshinbo Chemical Inc.).

[0065] [Polyfunctional Oxazoline Compound] A polyfunctional oxazoline compound is a compound having two or more oxazoline groups in the molecule. As the polyfunctional oxazoline compound, a polymer containing two or more oxazoline groups (hereinafter also referred to as "oxazoline group-containing polymer") is preferred. From the viewpoint of enhancing crosslinking reactivity with carboxy groups and improving abrasion resistance and water resistance, the number average molecular weight of the oxazoline group-containing polymer is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. Examples of oxazoline group-containing polymers that can be used include polymers whose main chain has an acrylic skeleton, polymers whose main chain has a styrene / acrylic skeleton, polymers whose main chain has a styrene skeleton, and polymers whose main chain has an acrylonitrile / styrene skeleton.

[0066] From the viewpoint of improving the storage stability of the overcoat solution and improving the abrasion resistance and water resistance, the oxazoline group equivalent of the oxazoline group-containing polymer is preferably 100 or more, more preferably 170 or more, even more preferably 200 or more, and preferably 500 or less, more preferably 400 or less, even more preferably 300 or less. The oxazoline group equivalent means the mass of the oxazoline group-containing polymer per mole of oxazoline groups. Examples of commercially available oxazoline group-containing polymers include the "Epocross WS" series, such as "Epocross WS-300," "Epocross WS-500," and "Epocross WS-700" (all manufactured by Nippon Shokubai Co., Ltd., water-soluble types).

[0067] [Polyfunctional Epoxy Compound] The polyfunctional epoxy compound is a compound having two or more epoxy groups in the molecule. From the viewpoint of improving abrasion resistance and water resistance, the polyfunctional epoxy compound is preferably a compound containing two or more glycidyl ether groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms. From the viewpoint of improving abrasion resistance and water resistance, the epoxy group equivalent of the polyfunctional epoxy compound is preferably 100 or more, more preferably 120 or more, even more preferably 140 or more, and preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, and even more preferably 200 or less.

[0068] Examples of polyfunctional epoxy compounds include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, from the viewpoint of improving abrasion resistance and water resistance, the polyfunctional epoxy compound is preferably one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and more preferably 1,6-hexanediol diglycidyl ether.

[0069] (Water-Soluble Organic Solvent) The overcoat liquid according to the present invention preferably further contains a water-soluble organic solvent from the viewpoints of improving the ejection properties of the overcoat liquid when ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and from the viewpoint of adjusting the surface tension of the overcoat liquid to improve abrasion resistance and water resistance. In the present invention, as described above, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 10 mL or more. From the viewpoints of ejection stability, storage stability, and drying properties, the boiling point of the water-soluble organic solvent is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher, and is preferably 350°C or lower, more preferably 300°C or lower, and even more preferably 250°C or lower. When two or more water-soluble organic solvents are used in combination, the boiling point of the water-soluble organic solvent is a weighted average value weighted by the content (mass%) of each water-soluble organic solvent.

[0070] As with the aqueous ink, examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving the ejection properties when the overcoat liquid is ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and from the viewpoint of adjusting the surface tension of the overcoat liquid to improve the abrasion resistance and water resistance, one or more types selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred. A mixture of multiple polyhydric alcohols can be used. Similarly to the polyhydric alcohols, a mixture of multiple polyhydric alcohol alkyl ethers can also be used. Preferred examples of the polyhydric alcohols and polyhydric alcohol alkyl ethers include those exemplified for the aqueous ink.

[0071] (Surfactant) The overcoat liquid according to the present invention may further contain a surfactant from the viewpoint of adjusting the surface tension of the overcoat liquid and improving its abrasion resistance and water resistance. The surfactant can be appropriately selected and used within a range that satisfies the relationship between the surface tension γ(A) of the water-based ink and the surface tension γ(B) of the overcoat liquid. From the viewpoint of adjusting the surface tension of the overcoat liquid and improving its abrasion resistance and water resistance, examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred. The surfactants can be used alone or in combination of two or more. Examples of nonionic surfactants include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants. Among these, from the viewpoint of adjusting the surface tension of the overcoat liquid and improving its abrasion resistance and water resistance, the surfactant is preferably at least one selected from the group consisting of acetylene-based surfactants and silicone-based surfactants.

[0072] Preferred acetylene surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and EO adducts thereof. Among these, more preferred are one or more surfactants selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The average number of moles of EO added in the acetylene surfactant is preferably 1 mole or more from the viewpoint of adjusting the surface tension of the overcoat liquid and improving the abrasion resistance and water resistance, and from the same viewpoint as above, is preferably 35 moles or less, more preferably 30 moles or less, even more preferably 25 moles or less, still more preferably 20 moles or less, still more preferably 15 moles or less, still more preferably 10 moles or less, still more preferably 5 moles or less, still more preferably 3 moles or less, and still more preferably 2 moles or less.

[0073] The HLB value of the acetylene-based surfactant is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, from the viewpoint of adjusting the surface tension of the overcoat liquid and improving abrasion resistance and water resistance, and from the same viewpoint as above, is preferably 18 or less, more preferably 15 or less, even more preferably 10 or less, still more preferably 7 or less, and even more preferably 5 or less. In the present invention, the HLB value can be determined from the above formula using the Griffin method, as described above. The catalog values ​​of each product can also be referenced. Commercially available acetylene-based surfactants include those similar to those exemplified for the water-based ink.

[0074] Preferred examples of silicone surfactants include polyether-modified silicone surfactants. From the viewpoint of adjusting the surface tension of the overcoat liquid and improving abrasion resistance and water resistance, the HLB value of the polyether-modified silicone surfactant is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, still more preferably 6 or more, still more preferably 8 or more, and still more preferably 10 or more, and is preferably 18 or less, more preferably 17 or less, and still more preferably 16 or less. Specific examples and commercially available products of polyether-modified silicone surfactants include the same as those exemplified for the water-based ink.

[0075] (Water) The overcoat solution according to the present invention preferably contains water. The water used in the overcoat solution according to the present invention is preferably pure water or ion-exchanged water, from the viewpoint of preventing the inclusion of unintended substances.

[0076] The overcoat solution of the present invention may further contain other components commonly used in overcoat solutions for inkjet printing, such as viscosity modifiers, antifoaming agents, preservatives, antifungal agents, and anticorrosive agents. However, it is preferable that the overcoat solution is substantially free of resins having carboxy groups capable of crosslinking with compound (II). Examples of such resins having carboxy groups include those similar to the binder resin (Ib) described above. Here, "substantially free of resins having carboxy groups capable of crosslinking with compound (II)" means that the content of resins having carboxy groups capable of crosslinking with compound (II) in the overcoat solution of the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass. The overcoat solution of the present invention can be obtained by mixing and stirring compound (II), water, optionally a water-soluble organic solvent, a surfactant, and the other components described above. Compound (II) is preferably formulated as an aqueous solution or emulsion.

[0077] (Composition of Overcoat Solution) From the viewpoint of improving abrasion resistance and water resistance, the content of Compound (II) in the overcoat solution according to the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, still more preferably 7% by mass or more, and still more preferably 8% by mass or more, and from the same viewpoints as above, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the overcoat solution according to the present invention contains a water-soluble organic solvent, from the viewpoint of improving abrasion resistance and water resistance, the content of the water-soluble organic solvent in the overcoat solution according to the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and from the same viewpoints as above, it is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the overcoat solution of the present invention contains a surfactant, the content of the surfactant in the overcoat solution of the present invention is, from the viewpoint of improving abrasion resistance and water resistance, preferably 3% by mass or less, more preferably 2.5% by mass or less, even more preferably 2% by mass or less, still more preferably 1.5% by mass or less, still more preferably 1% by mass or less, and still more preferably 0.5% by mass or less. When the overcoat solution of the present invention contains water, the content of water in the overcoat solution of the present invention is, from the viewpoint of improving abrasion resistance and water resistance, preferably 30% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more, and from the same viewpoint as above, preferably 80% by mass or less, more preferably 75% by mass or less, and still more preferably 70% by mass or less.

[0078] (Physical Properties of Overcoat Solution) From the viewpoint of improving abrasion resistance and water resistance, the surface tension γ(B) of the overcoat solution according to the present invention is preferably 27 mN / m or more, more preferably 29 mN / m or more, even more preferably 31 mN / m or more, and still more preferably 33 mN / m or more, and from the same viewpoint as above, is preferably 44 mN / m or less, more preferably 42 mN / m or less, and even more preferably 40 mN / m or less. The surface tension is measured by the method described in the examples.

[0079] Another embodiment of the ink set for inkjet recording of the present invention (hereinafter also simply referred to as "another embodiment") comprises a water-based ink containing a pigment and an overcoat liquid that is substantially free of pigment, wherein the water-based ink contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of a binder resin (Ib) having a carboxy group, the overcoat liquid contains the binder resin (Ib) having a carboxy group, and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the water-based ink.

[0080] According to another aspect of the present invention, when printing on a heat-shrinkable resin film, the heat-shrunk printed matter has excellent abrasion resistance and water resistance. The reason for this is unclear, but is thought to be as follows. In the present invention, the surface tension of the overcoat liquid is greater than that of the water-based ink. Therefore, when the water-based ink is applied to a printing substrate and then the overcoat liquid is applied to the area where the water-based ink was applied, convection (so-called Marangoni convection) occurs between the water-based ink coating film on the printing substrate and the overcoat liquid coating film, driven by the surface tension gradient. As a result, the compound (II) having a reactive group contained in the water-based ink coating film is distributed more uniformly in the overcoat liquid coating film than in the case where the compound (II) diffuses due to the difference in concentration between the water-based ink coating film on the printing substrate and the overcoat liquid coating film. This promotes a uniform crosslinking reaction between the carboxyl group of the binder resin (Ib) contained in the overcoat liquid coating film and the reactive group of the compound (II), reducing the likelihood of a distribution in strength of the resulting printed coating film, resulting in a printed matter with a uniform printed coating film strength. It is believed that when such a printed material is subjected to thermal shrinkage, selective shrinkage does not occur in areas of the printed coating film that are weaker in strength, and the occurrence of fine cracks and wrinkles in the printed coating film can be reduced, which is presumably to suppress embrittlement of the printed coating film and improve abrasion resistance and water resistance.

[0081] In another embodiment of the present invention, the surface tension γ(B) of the overcoat liquid (hereinafter also referred to simply as "surface tension γ(B)") is greater than the surface tension γ(A) of the water-based ink (hereinafter also referred to simply as "surface tension γ(A)") The difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink is the same as in the case of the water-based ink according to the ink-jet recording ink of the present invention described above.

[0082] <Water-Based Ink According to Another Aspect> The water-based ink according to another aspect of the present invention contains a pigment and a compound (II) having a reactive group capable of crosslinking with a carboxy group of a binder resin (Ib) having a carboxy group. The water-based ink may be used alone having one color, or in combination with inks having two or more different colors. In other words, the printed image formed with the water-based ink according to the present invention may be a multicolor print, for example, a three-color print, a four-color print, or a print using inks having four or more different colors.

[0083] In another aspect of the present invention, the pigment in the water-based ink is the same as that in the water-based ink for ink-jet recording of the present invention. Also, in another aspect of the present invention, the pigment dispersing resin (Ia) is the same as that in the water-based ink for ink-jet recording of the present invention.

[0084] In the water-based ink according to another embodiment of the present invention, the compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of the binder resin (Ib) having a carboxy group is the same as the compound (II) in the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0085]

[0033] The water-based ink according to another aspect of the present invention preferably further contains a water-soluble organic solvent from the viewpoint of improving the jetting properties and storage stability of the water-based ink, and from the viewpoint of adjusting the surface tension of the water-based ink and improving the scratch resistance and water resistance. The water-soluble organic solvent may be used alone or in combination of two or more. In the water-based ink according to another aspect of the present invention, the water-soluble organic solvent is the same as the water-soluble organic solvent of the water-based ink according to the inkjet recording ink of the present invention described above.

[0086] The water-based ink according to another aspect of the present invention preferably further contains a surfactant, from the viewpoint of adjusting the surface tension of the water-based ink and improving the abrasion resistance and water resistance of the water-based ink. In the water-based ink according to another aspect of the present invention, the surfactant is the same as the surfactant in the water-based ink according to the ink jet recording ink of the present invention described above.

[0087] The water-based ink according to another embodiment of the present invention contains water. The water in the water-based ink according to another embodiment of the present invention is the same as the water in the water-based ink according to the ink-jet recording ink of the present invention described above.

[0088] The water-based ink according to another embodiment of the present invention may further contain, as optional components, various additives such as a humectant, a wetting agent, a penetrating agent, a dispersant, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, and an antirust agent, and a fixing resin.

[0089] An aqueous ink according to another embodiment of the present invention can be obtained by mixing and stirring a pigment, a compound (II) having a reactive group capable of crosslinking with a carboxy group in a binder resin (Ib) having a carboxy group, water, and, if necessary, a pigment dispersion resin (Ia), a neutralizer, a surfactant, a water-soluble organic solvent, etc. When pigment-containing resin particles are contained, as described above, it is preferable to disperse the pigment, pigment dispersion resin (Ia), and, if necessary, a neutralizer, a surfactant, etc., by a known method to obtain an aqueous dispersion of the pigment-containing resin particles, and then blend this into the aqueous ink.

[0090] (Composition of Water-Based Ink According to Another Aspect) The content of the pigment in the water-based ink according to another aspect of the present invention is the same as in the case of the water-based ink relating to the inkjet recording ink of the present invention described above. When the pigment in the water-based ink according to another aspect of the present invention is in a form dispersed in the pigment dispersion resin (Ia), the content of the pigment dispersion resin (Ia) in the water-based ink according to another aspect of the present invention is the same as in the case of the water-based ink relating to the inkjet recording ink of the present invention described above. When the pigment in the water-based ink according to another aspect of the present invention is in a form dispersed in the pigment dispersion resin (Ia), the mass ratio of the content of the pigment to the total content of the pigment and the pigment dispersion resin (Ia) in the water-based ink according to another aspect of the present invention [pigment / (pigment+pigment dispersion resin (Ia))] is the same as in the case of the water-based ink relating to the inkjet recording ink of the present invention described above.

[0091] The content of the compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group in the binder resin (Ib) having a carboxy group related to another embodiment of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.2% by mass or more, and still more preferably 1.5% by mass or more, from the viewpoint of improving the abrasion resistance and water resistance, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and still more preferably 5% by mass or less, from the same viewpoint as above.

[0092] The content of water in the water-based ink according to another aspect of the present invention is the same as that in the water-based ink according to the inkjet recording ink of the present invention described above. When the water-based ink according to another aspect of the present invention further contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the water-based ink according to the present invention is the same as that in the water-based ink according to the inkjet recording ink of the present invention described above. When the water-based ink according to another aspect of the present invention further contains a surfactant, the content of the surfactant in the water-based ink according to the present invention is the same as that in the water-based ink according to the inkjet recording ink of the present invention described above.

[0093] (Physical properties of water-based ink according to another embodiment) The surface tension γ(A) of the water-based ink according to another embodiment of the present invention is the same as that of the water-based ink according to the inkjet recording ink of the present invention described above. The viscosity at 32°C of the water-based ink according to another embodiment of the present invention is the same as that of the water-based ink according to the inkjet recording ink of the present invention described above. The pH of the water-based ink according to another embodiment of the present invention is the same as that of the water-based ink according to the inkjet recording ink of the present invention described above.

[0094] <Overcoat Liquid According to Another Aspect> An overcoat liquid according to another aspect of the present invention contains substantially no pigment and contains a binder resin (Ib) having a carboxy group. The overcoat liquid according to the present invention contains substantially no pigment.

[0095] In the overcoat liquid according to another embodiment of the present invention, the binder resin (Ib) having a carboxy group is the same as the binder resin (Ib) in the water-based ink according to the ink-jet recording ink of the present invention described above.

[0096] The overcoat liquid according to another aspect of the present invention preferably further contains a water-soluble organic solvent, from the viewpoints of improving the ejection properties when the overcoat liquid is ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and of adjusting the surface tension of the overcoat liquid to improve the abrasion resistance and water resistance. In the overcoat liquid according to another aspect of the present invention, the water-soluble organic solvent is the same as that in the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0097] The overcoat liquid according to another aspect of the present invention may further contain a surfactant in order to adjust the surface tension of the overcoat liquid and improve its abrasion resistance and water resistance. The surfactant can be appropriately selected and used within a range that satisfies the relationship between the surface tension γ(A) of the water-based ink and the surface tension γ(B) of the overcoat liquid. In the overcoat liquid according to another aspect of the present invention, the surfactant is the same as that in the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0098] The overcoat liquid according to another embodiment of the present invention preferably contains water. In the overcoat liquid according to another embodiment of the present invention, the water is the same as that in the overcoat liquid according to the ink jet recording ink of the present invention.

[0099] The overcoat liquid according to another embodiment of the present invention may further contain other components commonly used in overcoat liquids used in inkjet printing, such as a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, and an antirust agent. The overcoat liquid according to the present invention can be obtained by mixing and stirring a binder resin (Ib) having a carboxy group, water, and optionally a water-soluble organic solvent, a surfactant, and the other components described above. Compound (II) is preferably formulated as an aqueous solution or emulsion.

[0100] (Composition of Overcoat Liquid According to Another Aspect) The content of the binder resin (Ib) having a carboxy group in the overcoat liquid according to another aspect of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving abrasion resistance and water resistance, and is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, from the same viewpoint as above.

[0101] When the overcoat liquid according to another embodiment of the present invention contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the overcoat liquid according to another embodiment of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving abrasion resistance and water resistance, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the same viewpoints as above. When the overcoat liquid according to another embodiment of the present invention contains a surfactant, the content of the surfactant in the overcoat liquid according to another embodiment of the present invention is the same as in the case of the overcoat liquid according to the inkjet recording ink of the present invention described above. When the overcoat liquid according to another embodiment of the present invention contains water, the content of water in the overcoat liquid according to another embodiment of the present invention is the same as in the case of the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0102] (Physical Properties of Overcoat Liquid of Another Aspect) The surface tension γ(B) of the overcoat liquid according to another aspect of the present invention is the same as that of the overcoat liquid according to the ink jet recording ink of the present invention described above.

[0103] [Inkjet printing method] (Step 1) Step 1 is a step of applying an aqueous ink to a printing substrate by inkjet ejection, and then applying an overcoat liquid by inkjet ejection to the area where the aqueous ink has been applied. In Step 1, the ejection interval between the aqueous ink and the overcoat liquid is preferably 0.1 seconds or more, more preferably 1 second or more, depending on the temperature of the inkjet head and the temperature of the printing substrate, and is 30 seconds or less from the viewpoint of improving abrasion resistance and water resistance. In Step 1, the inkjet method for ejecting the aqueous ink and the overcoat liquid is preferably a piezo method from the viewpoint of ejection performance.

[0104] The equivalent ratio of compound (II) used, calculated from the following formula, is preferably 0.5 or more, more preferably 1 or more, even more preferably 2 or more, still more preferably 2.5 or more, still more preferably 3 or more, still more preferably 3.5 or more, and still more preferably 4 or more, from the viewpoint of improving abrasion resistance and water resistance, and is preferably 10 or less, more preferably 8 or less, and still more preferably 6 or less, from the same viewpoint as above. Usage equivalent ratio of compound (II)=[(volume of droplets of overcoat liquid injected×content of compound (II) in overcoat liquid) / reactive group equivalent of compound (II)] / [(volume of droplets of water-based ink injected×content of binder resin (Ib) in water-based ink×(acid value of binder resin (Ib) / (56.11×1000))]. Note that, when the pigment dispersion resin (Ia) has a carboxy group, the carboxy group can also undergo a crosslinking reaction with compound (II). However, in the present invention, the usage equivalent ratio of compound (II) is calculated as the equivalent ratio of the reactive group of compound (II) to the carboxy group of binder resin (Ib).

[0105] Furthermore, the usage equivalent of compound (II) when another embodiment of the ink jet recording ink set of the present invention is used is calculated by the following formula. The usage equivalent of compound (II) when another embodiment of the ink jet recording ink set of the present invention is used is the same as when the ink jet recording ink of the present invention is used as described above. Usage equivalent ratio of compound (II) = [(volume of droplets of water-based ink ejected x content of compound (II) in water-based ink) / reactive group equivalent of compound (II)] / [(volume of droplets of overcoat liquid ejected x content of binder resin (Ib) in overcoat liquid x (acid value of binder resin (Ib) / (56.11 x 1000))]

[0106] Examples of printing substrates include highly absorbent plain paper, low-absorbent coated paper, and non-absorbent resin films. From the viewpoint of abrasion resistance and water resistance, low-absorbent printing substrates are preferred, and one or more selected from the group consisting of coated paper and resin films are more preferred, with resin films being even more preferred. Examples of coated paper include general-purpose glossy paper and multicolor foam gloss paper. Examples of resin films include one or more selected from the group consisting of polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. The surface of the resin film on which the printed image is formed may be corona-treated.

[0107] From the viewpoint of abrasion resistance and water resistance, the resin film is preferably a heat-shrinkable resin film that shrinks upon heating. Heat-shrinkable resin films are films that have molecular orientation due to stretching treatment of an unstretched film produced by a known manufacturing method, and do not shrink at room temperature but shrink upon heating. Examples of heat-shrinkable resin films include films made of one or a mixture of two or more selected from the group consisting of polyester-based resins; styrene-based resins such as polystyrene and styrene-butadiene copolymers; polylactic acid; olefin-based resins such as polyethylene, polypropylene, and polyolefins; and thermoplastic resins such as vinyl chloride-based resins, as well as laminate films thereof. Commercially available heat-shrinkable resin films include the "Space Clean" series (manufactured by Toyobo Co., Ltd.); the "DXL" series, "Hishipet" series, "PLABIO," and "Hybrex DL" (all manufactured by Mitsubishi Chemical Corporation); the "Bonset" series (manufactured by Takiron C.I. Co., Ltd.); and the "Fancy Wrap (PET)" series (manufactured by Gunze Limited).

[0108] (Step 2) Step 2 is a step of heating the aqueous ink coating film and the overcoat liquid coating film on the printing substrate formed in Step 1. Step 2 distributes compound (II) contained in the overcoat liquid on the printing substrate into the aqueous ink coating film, causing a crosslinking reaction between the carboxy group of the binder resin (Ib) and the reactive group of compound (II) to proceed, resulting in a printed product with a uniform strength of the printed coating film. Furthermore, when an inkjet set according to another aspect of the present invention is used in the inkjet printing method of the present invention, Step 2 distributes compound (II) contained in the aqueous ink on the printing substrate into the overcoat liquid coating film, causing a crosslinking reaction between the carboxy group of the binder resin (Ib) and the reactive group of compound (II), resulting in a printed product with a uniform strength of the printed coating film. It is preferable that the heating treatment in Step 2 also serves as a treatment for drying the aqueous ink coating film and the overcoat liquid coating film on the printing substrate formed in Step 1. Examples of methods for the heat treatment in step 2 include a method of blowing a gas adjusted to a desired temperature onto the coating film formed on the printing substrate, a method of passing the printing substrate on which the coating film has been formed through a gas atmosphere adjusted to a desired temperature, a method of irradiating the coating film formed on the printing substrate with an infrared heater, and a method of heating the printing substrate on which the coating film has been formed with a platen heater. From the viewpoint of productivity, the heating temperature is preferably 40°C or higher, more preferably 50°C or higher, and from the viewpoint of preventing effects on the printing substrate, it is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 70°C or lower. From the viewpoint of abrasion resistance and water resistance, the heating time is preferably 30 seconds or higher, more preferably 1 minute or higher, and from the viewpoint of productivity, it is preferably 10 minutes or lower, more preferably 7 minutes or lower, and even more preferably 5 minutes or lower.

[0109] [Packaging method] In the present invention, when the printing substrate is a heat-shrinkable resin film, the ink set for inkjet printing described above is preferably used in a method for packaging an article to be packaged, in which a printed matter obtained by the inkjet printing method described above is arranged around the article to be packaged, and then the heat-shrinkable resin film substrate of the printed matter is shrunk to obtain a package.

[0110] The heating temperature for shrinking is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher from the viewpoint of productivity, and is preferably 200°C or lower, more preferably 150°C or lower, even more preferably 130°C or lower, and even more preferably 110°C or lower from the viewpoint of preventing effects on the resin film substrate. This heating temperature is preferably a temperature at which the printed matter can be used without problems even if shrinkage occurs. The heating time for shrinking is preferably 3 seconds or higher, more preferably 5 seconds or higher, and even more preferably 7 seconds or higher from the viewpoint of shrinking the resin film substrate, and is preferably 5 minutes or shorter, more preferably 3 minutes or shorter, and even more preferably 1 minute or shorter from the viewpoint of productivity.

[0111] In relation to the above-described embodiments, the present invention further discloses the following: <1> An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. <2> An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a compound (II) having a reactive group capable of crosslinking with a carboxy group of a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a binder resin (Ib) having a carboxy group, and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. <3> The ink set for inkjet printing according to <1> or <2>, wherein the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink is 1.5 mN / m or more. <4> The ink set for inkjet printing according to any one of <1> to <3>, wherein the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink is 7 mN / m or more and 15 mN / m or less. <5> The ink set for inkjet printing according to any one of <1> to <4>, wherein the compound (II) has a reactive group equivalent weight of 100 or more and 500 or less. <6> The ink set for inkjet printing according to any one of <1> to <5>, wherein the compound (II) is one or more compounds selected from the group consisting of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds, and polyfunctional epoxy compounds. <7> The ink set for inkjet printing according to any one of <1> to <6>, wherein the compound (II) is a polyfunctional carbodiimide compound.<8> The ink set for inkjet printing according to any one of <1> to <7>, wherein the binder resin (Ib) is at least one resin selected from the group consisting of a vinyl resin (Ib-1) having a carboxy group and a polyurethane resin (Ib-2) having a carboxy group. <9> The ink set for inkjet printing according to <8>, wherein the vinyl resin (Ib-1) is a (meth)acrylic resin containing structural units derived from at least one carboxy group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms. <10> The ink set for inkjet printing according to <8> or <9>, wherein the weight-average molecular weight of the vinyl resin (Ib-1) is from 10,000 to 800,000. <11> The ink set for inkjet printing according to any one of <1> to <8>, wherein the binder resin (Ib) is a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate. <12> The ink set for inkjet printing according to any one of <1> to <8>, wherein the binder resin (Ib) is a polyaddition product of dimethylolpropionic acid, a polycarbonate-based polyol, and dicyclohexylmethane 4,4'-diisocyanate.<13> An ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the water-based ink contains, as a binder resin (Ib) having a carboxy group, a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and structural units derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and the (meth)acrylic resin has a weight-average molecular weight of from 10,000 to 800,000, the overcoat liquid contains, as a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of the binder resin (Ib), a polyfunctional carbodiimide compound, and a difference Δγ between a surface tension γ(B) of the overcoat liquid and a surface tension γ(A) of the water-based ink is from 7 mN / m to 15 mN / m. <14> An ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid substantially not containing a pigment, wherein the water-based ink contains, as a binder resin (Ib) having a carboxy group, a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate, and the weight-average molecular weight of the copolymer is 10,000 or more and 800,000 or less, the overcoat liquid contains, as a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of the binder resin (Ib), a polyfunctional carbodiimide compound, and the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink is 7 mN / m or more and 15 mN / m or less.<15> An ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid that does not substantially contain a pigment, wherein the water-based ink contains a polyurethane resin (Ib-2) having a carboxy group as the binder resin (Ib) having a carboxy group, and the overcoat liquid contains a polyfunctional carbodiimide compound as the compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of the binder resin (Ib), and the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink is 7 mN / m or more and 15 mN / m or less. <16> An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a polyaddition product of dimethylolpropionic acid, a polycarbonate polyol, and dicyclohexylmethane 4,4'-diisocyanate as a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of the binder resin (Ib), and the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink is 7 mN / m or more and 15 mN / m or less. <17> An inkjet printing method using the ink set for inkjet printing according to any one of <1> to <16> above, and comprising the following steps 1 and 2: Step 1: applying the water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method, and then applying the overcoat liquid by an inkjet ejection method to the area where the water-based ink has been applied. Step 2: heating the water-based ink coating film and the overcoat liquid coating film on the printing substrate formed by step 1. <18> A packaging method, comprising arranging a printed matter obtained by the inkjet printing method described in <17> around an item to be packaged, and then shrinking the heat-shrinkable resin film substrate of the printed matter to obtain a package.<19> Use as an inkjet printing ink set comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a binder resin (Ib) having a carboxy group, and the overcoat liquid contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. <20> Use as an inkjet printing ink set comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the aqueous ink contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib) having a carboxy group, and the overcoat liquid contains a binder resin (Ib) having a carboxy group, and the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink. <21> An inkjet printing apparatus for use with the ink set for inkjet printing according to any one of <1> to <16>, the inkjet printing apparatus comprising an inkjet head filled with the water-based ink and an inkjet head filled with the overcoat liquid. <22> The inkjet printing apparatus according to <21>, further comprising a processing section that heats a coating of the water-based ink and a coating of the overcoat liquid on a printing substrate.

[0112] In the following Production Examples, Preparation Examples, Examples and Comparative Examples, "parts" means "parts by mass" unless otherwise specified. Measurements of various physical properties were carried out by the following methods.

[0113] [Measurement of Acid Value of Resin] Using an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), the resin was dissolved in a titration solvent consisting of a mixture of toluene and acetone [toluene:acetone=2:1 (volume ratio)] and titrated with a 0.1 N potassium hydroxide / ethanol solution. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration amount of the potassium hydroxide solution up to the endpoint.

[0114] [Measurement of number average molecular weight and weight average molecular weight of resin] The number average molecular weight and weight average molecular weight of resin were determined by gel permeation chromatography under the following measurement conditions. GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide to concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 0.5 mL / min Standard substance: monodisperse polystyrene kits with known molecular weights "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (all manufactured by Tosoh Corporation) The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring the mixture with a magnetic stirrer at 25°C for 10 hours, and filtering the mixture through a syringe filter "DISMIC-13HP" (manufactured by Advantec Co., Ltd., pore size: 0.2 μm, material: PTFE).

[0115] [Measurement of the average particle size of pigment-containing resin particles in aqueous dispersion and the average particle size of pigment-free resin particles in aqueous dispersion] The average particle size was measured by cumulant analysis using a laser particle analysis system ("ELS-8000" manufactured by Otsuka Electronics Co., Ltd.). －３ The measurement was performed under the following conditions: temperature 25°C, angle between incident light and detector 90°, and number of integrations 100. The refractive index of water (1.333) was input as the refractive index of the dispersion medium, and the obtained cumulant average particle size was taken as the average particle size of pigment-containing resin particles in the aqueous dispersion or the average particle size of pigment-free resin particles in the aqueous dispersion.

[0116] [Measurement of solid content concentration] Using an infrared moisture meter (FD-230 manufactured by Kett Electric Laboratory Co., Ltd.), 5 g of the measurement sample was dried under conditions of a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and then the moisture content (mass %) of the measurement sample was measured, and the solid content concentration (mass %) was calculated using the following formula: Solid content concentration (mass %) = 100 - Moisture content (mass %) of measurement sample

[0117] [Measurement of Surface Tension γ(A) of Water-Based Ink and Surface Tension γ(B) of Overcoat Liquid] Using a surface tensiometer ("CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.), a platinum plate was immersed in a cylindrical polyethylene container (diameter 3.6 cm x depth 1.2 cm) containing 5 g of water-based ink or overcoat liquid adjusted to 20°C, and the static surface tension at 20°C was measured by the Wilhelmy method, and this was taken as the surface tension γ(A) of the water-based ink or the surface tension γ(B) of the overcoat liquid.

[0118] [Measurement of Viscosity of Water-Based Ink] The viscosity of the water-based ink at 32° C. was measured using an E-type viscometer ("TV-25" manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34'×R24, rotation speed 50 rpm).

[0119] [Measurement of pH of Water-Based Ink] The pH of the water-based ink at 25°C was measured using a tabletop pH meter ("F-71" manufactured by Horiba Ltd.) equipped with a pH electrode ("6337-10D" manufactured by Horiba Ltd.).

[0120] [Measurement of Water Absorption of Printing Substrate During 100 ms Contact Time Between Printing Substrate and Pure Water] Using an automatic scanning absorption meter ("KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.), the amount of transfer during 100 ms of pure water contact was measured under conditions of 23°C and 50% relative humidity, and this was taken as the water absorption during 100 ms. The measurement conditions are as follows: "Spiral Method" Contact Time (seconds): 0.010 to 1.0 Pitch (mm): 7 Length Per Sampling (degrees): 86.29 Start Radius (mm): 20 End Radius (mm): 60 Min Contact Time (ms): 10 Max Contact Time (ms): 1,000 Sampling Pattern (1 to 50): 50 Number of Sampling Points (>0): 19 "Square Head" Slit Span (mm): 1 Slit Width (mm): 5

[0121] [Production of Pigment Dispersion Resin (Ia)] Production Example 1-1 (Production of Water-Insoluble Polymer (a1) Having a Carboxy Group) 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of a styrene macromonomer ("AS-6S" manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solids content 50% by mass), and 25 parts of methoxypolyethylene glycol methacrylate ("Blemmer PME-200" manufactured by NOF Corporation) were mixed to prepare 115 parts of a monomer mixture. Into a reaction vessel, 18 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed and mixed, and the inside of the vessel was thoroughly purged with nitrogen gas. Meanwhile, a mixture of the remaining 90% (103.5 parts) of the monomer mixture with 0.27 parts of the chain transfer agent, 42 parts of MEK, and 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was placed in a dropping funnel, and the mixture in the reaction vessel was heated to 75°C with stirring under a nitrogen atmosphere, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution of 3 parts of the polymerization initiator dissolved in 5 parts of MEK was added, and the mixture was further aged at 75°C for 2 hours and at 80°C for 2 hours, and then 50 parts of MEK was added to obtain a solution of a water-insoluble polymer (a1) having a carboxy group (weight average molecular weight: 50,000). The solids concentration of the solution of the water-insoluble polymer (a1) having a carboxy group was 45% by mass.

[0122] [Production of Water Dispersion of Pigment-Containing Resin Particles] Production Example 2-1 (Production of Water Dispersion (D1) of White Pigment-Containing Resin Particles) A mixed solution prepared by mixing and dissolving 0.3 g of polyacrylic acid (PAA; manufactured by FUJIFILM Wako Pure Chemical Industries, Mw: 5,000 (catalog value)) as a pigment dispersion resin (Ia), 0.21 g of a 5 N aqueous sodium hydroxide solution (sodium hydroxide solids content 16.9 mass%, manufactured by FUJIFILM Wako Pure Chemical Industries, and 1 g of ion-exchanged water was charged into a 250 mL polyethylene bottle, and then 15 g of titanium oxide (rutile type, "KURONOSKR-380" manufactured by Titan Kogyo Co., Ltd., Al / Si treated, average primary particle size: 355 nm (catalog value 300 to 500 nm)) as a white pigment and 14.3 g of ion-exchanged water were added. Finally, 369 g of 2 mm zirconia beads were added, and the mixture was dispersed for 8 hours at 250 rpm using a benchtop pot mill stand (AS ONE Corporation). The zirconia beads were then removed using a mesh, and the solid content was adjusted with water to obtain an aqueous dispersion (D1) of white pigment-containing resin particles (solid content: 30% by mass, mass ratio [pigment / (pigment+pigment-dispersed resin (Ia)]: 0.98). The average particle size of the white pigment-containing resin particles in the obtained aqueous dispersion was 325 nm.

[0123] Production Example 2-2 (Production of Aqueous Dispersion (D2) of Black Pigment-Containing Resin Particles) 95.2 parts of the solution of the water-insoluble polymer (a1) having a carboxy group obtained in Production Example 1-1 as the pigment dispersion resin (Ia) was mixed with 53.9 parts of MEK, and 15.0 parts of a 5N aqueous sodium hydroxide solution, 0.5 parts of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water were added thereto as neutralizing agents, and 100 parts of C.I. Pigment Black 7 (P.B.7, manufactured by Cabot Corporation) was further added as a black pigment to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed for 1 hour using a disper blade under conditions of 7,000 rpm and 20°C, and then dispersed using a high-pressure homogenizer "Microfluidizer M-140K" (manufactured by Microfluidics) at a pressure of 180 MPa for 15 passes to obtain a dispersion. The obtained dispersion was subjected to vacuum treatment at 60°C to remove MEK, and then a portion of the water was removed. The mixture was centrifuged, and the liquid layer was recovered and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of black pigment-containing polymer particles. The solids concentration was 25% by mass. To 100 parts of the obtained aqueous dispersion of black pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, epoxy equivalent: 130) as a crosslinking agent and 15.23 parts of ion-exchanged water were added, and the mixture was heated at 70°C for 3 hours with stirring. After cooling to room temperature, the liquid layer was recovered and filtered through a filter "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion K of black pigment-containing polymer particles (solid content concentration 22 mass%, mass ratio [pigment / (pigment + pigment-dispersing resin (Ia) having a crosslinked structure)]: 0.69). The average particle size of the black pigment-containing polymer particles in the obtained aqueous dispersion K was 100 nm.

[0124] [Production of aqueous dispersion of pigment-free resin particles composed of binder resin (Ib)] Production Example 3-1 (production of aqueous dispersion (d1) of pigment-free acrylic resin particles) In a reaction vessel equipped with a dropping funnel, the monomers shown in "Initial charged monomer solution" in Table 1, polyoxyethylene alkyl ether sodium sulfate ("Latemul E-118B" manufactured by Kao Corporation) as an emulsifier (hereinafter referred to as "Latemul E-118B"), potassium persulfate as a polymerization initiator, and ion-exchanged water were placed and mixed, and nitrogen gas replacement was performed to obtain an initial charged monomer solution. Separately, the monomers, emulsifier, polymerization initiator, and ion-exchanged water shown in "Monomer solution to be dropped" in Table 1 were mixed to obtain a dropping monomer solution, and the dropping monomer solution was then placed in a dropping funnel, and nitrogen gas replacement was performed. Under a nitrogen atmosphere, the temperature of the initially charged monomer solution in the reaction vessel was raised from room temperature to 80°C over 30 minutes while stirring, and while maintaining the temperature at 80°C, the monomer solution in the dropping funnel was gradually added dropwise into the reaction vessel over 3 hours. After completion of the addition, the mixture was stirred for 1 hour while maintaining the temperature inside the reaction vessel. The mixture was then filtered through a 200 mesh filter to obtain a pigment-free aqueous dispersion (d1) of acrylic resin particles (solid concentration: 44.1% by mass, acid value: 16 mg KOH / g, weight average molecular weight of acrylic resin: 750,000, average particle size: 95 nm).

[0125]

[0126] Production Example 3-2 (Production of aqueous dispersion (d2) of urethane resin particles not containing a pigment) Into a four-neck flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 125.0 g of polycarbonate polyol ("Duranol T-6002" manufactured by Asahi Kasei Corporation, molecular weight: 2,000, hydroxyl value: 56.1 mg KOH / g) as the polyol component, 36.1 g of dicyclohexylmethane 4,4'-diisocyanate as the diisocyanate component, and 80.5 g of methyl ethyl ketone were added, and the mixture was allowed to react at 75°C for 1 hour to obtain an MEK solution containing a prepolymer. Furthermore, 4.8 g of dimethylolpropionic acid, 4.3 g of triethylamine, and methyl ethyl ketone were added, and the mixture was allowed to react at 75°C for 1 hour. Next, this solution was cooled to 45°C, and subsequently, ion-exchanged water and 0.8 g of ethylenediamine were mixed. This emulsion dispersion was distilled under reduced pressure at 50°C for 2 hours to remove the solvent, thereby obtaining an aqueous dispersion (d2) of urethane resin particles containing no pigment (solid content concentration: 20 mass%, acid value: 16 mgKOH / g, average particle size: 88 nm).

[0127] [Production of Water-Based Inks] Ink Production Example 1 (Production of Water-Based Ink W-1) 34.00 g of the water dispersion (D1) (solid content: 30% by mass) of white pigment-containing resin particles obtained in Production Example 2-1, 12.81 g of the water dispersion (d1) (solid content: 44.1% by mass) of pigment-free acrylic resin particles obtained in Production Example 3-1, 30.00 g of propylene glycol (hereinafter referred to as "PG"), 3.00 g of diethylene glycol monoisobutyl ether (manufactured by Nippon Nyukazai Co., Ltd.) (hereinafter referred to as "iBDG"), acetylene glycol-based surfactant The mixture was mixed with 1.00 g of a surfactant "Surfynol 440" (manufactured by Nissin Chemical Industry Co., Ltd., 2,4,7,9-tetramethyl-5-decyne-4,7-diol with EO (3.5 mol), HLB value: 8 (catalog value), active content: 100% by mass), 1.00 g of a polyether-modified silicone surfactant "KF-6011" (manufactured by Shin-Etsu Chemical Co., Ltd., PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value)), and ion-exchanged water to a total amount of 100.00 g. The resulting mixture was filtered through a filter "Minisart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate), to obtain water-based ink W-1 (viscosity: 5.6 mPa s, pH: 8.2).

[0128] Ink Production Examples 2 to 4 (Production of Water-Based Inks W-2, K-1, and W-3) Each water-based ink was obtained in the same manner as in Ink Production Example 1, except that the formulations were changed to those shown in Table 2.

[0129]

[0130] Preparation Examples 1 to 12 (Preparation of Overcoat Solutions OC-1 to OC-12) The components were mixed according to the formulations shown in Table 3, and the resulting mixtures were filtered through a "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain the respective overcoat solutions. The symbols in Tables 2 and 3 are as follows. (Compound (II)) [Polyfunctional carbodiimide compounds] Carbodilite E-07S: polyvalent carbodiimide compound (carbodiimide group equivalent: 234, active content 40% by mass, manufactured by Nisshinbo Chemical Inc.) Carbodilite E-02: carbodiimide group-containing polymer (carbodiimide group equivalent: 445, emulsion / dispersion type, active content 40% by mass, manufactured by Nisshinbo Chemical Inc.) Carbodilite E-05: carbodiimide group-containing polymer (carbodiimide group equivalent: 313, emulsion / dispersion type, active content 40% by mass, manufactured by Nisshinbo Chemical Inc.) [Polyfunctional oxazoline compounds] Epocross WS-700: oxazoline group-containing polymer (oxazoline group equivalent: 220, polymer main chain: acrylic, number average molecular weight: 20,000, water-soluble type, active content 25% by mass, manufactured by Nippon Shokubai Co., Ltd.) [Polyfunctional epoxy compounds] Denacol EX-212: 1,6-hexanediol diglycidyl ether (epoxy group equivalent: 151, active content 100% by mass, manufactured by Nagase ChemteX Corporation) (Surfactants) Surfynol 420: acetylene glycol surfactant (EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 1), HLB value: 4 (catalog value), manufactured by Nissin Chemical Industry Co., Ltd.) KF-6011: polyether-modified silicone surfactant (PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value), manufactured by Shin-Etsu Chemical Co., Ltd.)

[0131]

[0132] Examples 1 to 13 and Comparative Example 1 The combinations of water-based inks and overcoat liquids shown in Table 4 were used as ink sets, and the printing substrate was a heat-shrinkable PET film "Space Clean SP809" (manufactured by Toyobo Co., Ltd., heat shrinkage rate (90°C, 10 seconds): 50%, water absorption: 10 g / m 2Each of the resulting prints was evaluated as follows. The results are also shown in Table 4.

[0133] (Inkjet Printing) [Inkjet Printing Conditions] A printing evaluation device equipped with three inkjet heads (Kyocera Corporation, "KJ4B-HD06MHG-STDV," piezo type) and an underheater that heats the printing substrate from the backside of the surface of the printing substrate facing the inkjet heads was loaded with a water-based ink in the first two inkjet heads and an overcoat liquid in the last inkjet head. The distance between the underheater and the printing substrate was set to 0.2 mm, the distance between the inkjet heads and the printing substrate was set to 1.0 mm, and the surface temperature of the underheater was set to 40°C. Under an environment of 25±1°C and 30±5% relative humidity, the settings were: head applied voltage 26V, head drive frequency 10 kHz, head temperature 32°C, head resolution 600 dpi, pre-ejection flushing count 200 shots, and negative pressure -4.0 kPa. The printing substrate was fixed to the printing evaluation device so that the longitudinal direction of the printing substrate was the same as the transport direction. The droplet volume of the two inkjet heads in the front row filled with water-based ink was set to 12 pL each, and the droplet volume of the inkjet head in the last row filled with overcoat liquid was set to 5 pL. [Step 1] A print command was transferred to the print evaluation device, and the water-based ink and overcoat liquid were ejected in that order, and a solid image of the overcoat liquid was printed superimposed on the same location as the solid image of the water-based ink. The ejection interval between the water-based ink and the overcoat liquid was set to 1 second. In the examples and comparative examples, the equivalent ratio of compound (II) used, calculated by the following formula, is shown in Table 4.(In the case of Examples 1 to 11 and Comparative Example 1) Equivalent ratio of compound (II) used=[(volume of droplets of overcoat liquid injected (5 pL)×content of compound (II) in overcoat liquid) / reactive group equivalent of compound (II)] / [(volume of droplets of water-based ink injected (24 pL)×content of binder resin (Ib) in water-based ink×(acid value of binder resin (Ib) / (56.11×1000))] (In the case of Example 12) Equivalent ratio of compound (II) used=[(volume of droplets of water-based ink injected×content of compound (II) in water-based ink) / reactive group equivalent of compound (II)] / [(volume of droplets of overcoat liquid injected×content of binder resin (Ib) in overcoat liquid×(acid value of binder resin (Ib) / (56.11×1000))] [Step 2] The printed matter was then dried by heat treatment in a hot air dryer at 60° C. for 1 minute to obtain a printed matter. The abrasion resistance and water resistance of the obtained printed matter before shrinkage were evaluated by the following methods.

[0134] [Evaluation of abrasion resistance of printed matter before shrinkage] Each of the obtained printed matters was rubbed with the tip of the index finger under a load of 300 g while measuring the load with the fingertip during the rub test using a mass measuring device (GX-6100 manufactured by A&D Co., Ltd.), and the printed surface was rubbed back and forth 50 times. After the rub, the surface condition was visually inspected and the rub resistance was evaluated according to the following evaluation criteria: (Evaluation criteria) A: No change on the entire surface B: No change in 90% or more of the target area C: No change in 70% or more of the target area D: Change in 50% or more of the target area A rating of C or higher indicates that there is no practical problem with respect to rub resistance.

[0135] [Evaluation of Water Resistance of Printed Matter Before Shrinkage] Each of the obtained printed materials was cut into a 3 x 3 cm test piece, which was immersed in ion-exchanged water contained in a screw tube manufactured by Maruemu Co., Ltd. and left at room temperature for 24 hours. The printed test piece was then removed from the screw tube, and while measuring the load at the fingertip using a mass measuring device ("GX-6100" manufactured by A&D Co., Ltd.), the test piece was rubbed with the tip of the index finger under a load of 300 g. After 10 strokes of the printed surface, the surface condition was visually confirmed and the rub resistance was evaluated according to the following evaluation criteria: (Evaluation Criteria) A: No change on the entire surface B: No change in 90% or more of the target area C: No change in 70% or more of the target area D: Change in 50% or more of the target area If the evaluation score is C or higher, there is no practical problem with respect to water resistance.

[0136] (Preparation of Shrunk Printed Material) Samples were prepared using each of the obtained printed materials in accordance with the test described in JIS Z 1709-1995. The samples were cut out from the solid image portion of the printed material, measuring 100 mm in the winding direction MD (vertical) and 100 mm in the width direction TD (horizontal). The heat transfer liquid in the standard was changed to water, and the sample was immersed in hot water heated to 90°C for 10 seconds to cause thermal shrinkage, and then immersed in water at room temperature for 5 seconds to cool. The sample was left to dry for 24 hours in an environment of 23°C and 50% humidity, and then subjected to the same abrasion resistance and water resistance tests as for the printed material before shrinkage.

[0137]

[0138] Table 4 shows that the ink sets of the Examples are superior to the Comparative Examples in abrasion resistance and water resistance, particularly for thermally shrunk printed matter. In Examples 1 to 4, the type and amount of surfactant contained in the overcoat liquid was changed to adjust the surface tension γ(B) of the overcoat liquid, but the abrasion resistance and water resistance before shrinkage were all rated "A." Furthermore, in Examples 1 to 4, the abrasion resistance and water resistance after shrinkage improved the larger the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink. From this, it is believed that the results of the abrasion resistance and water resistance of the shrunk printed matter in Examples 1 to 4 were not due to changes in the type or amount of surfactant, but rather due to the Marangoni convection caused by the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink, which caused the compound (II) having a reactive group contained in the coating of the overcoat liquid to be uniformly distributed throughout the coating of the water-based ink, promoting a uniform cross-linking reaction between the carboxy groups of the binder resin (Ib) and the reactive groups of the compound (II), thereby obtaining printed matter with a uniform strength of the printed coating. Furthermore, in Example 13, an ink set was used in which the water-based ink contained a compound (II) having a reactive group capable of cross-linking with the carboxy groups of the binder resin (Ib) having a carboxy group, and the overcoat liquid contained a binder resin (Ib) having a carboxy group. It can be seen that this ink set also improved the abrasion resistance and water resistance of heat-shrunk printed matter.

[0139] According to the present invention, it is possible to provide an inkjet printing ink set, an inkjet printing method, and a packaging method that can improve the abrasion resistance and water resistance of a heat-shrunk printed matter when printing on a heat-shrinkable resin film.

Claims

1. An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, the aqueous ink containing a binder resin (Ib) having a carboxy group, the overcoat liquid containing a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ(B) of the overcoat liquid being greater than the surface tension γ(A) of the aqueous ink.

2. An ink set for inkjet printing comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of pigment, the aqueous ink containing a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of a binder resin (Ib) having a carboxy group, the overcoat liquid containing a binder resin (Ib) having a carboxy group, and the surface tension γ (B) of the overcoat liquid being greater than the surface tension γ (A) of the aqueous ink.

3. The ink set for ink-jet printing according to claim 1 or 2, wherein the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the water-based ink is 1.5 mN / m or more.

4. The ink set for ink-jet printing according to any one of claims 1 to 3, wherein the compound (II) has a reactive group equivalent of 100 or more and 500 or less.

5. The ink set for ink-jet printing according to any one of claims 1 to 4, wherein the compound (II) is at least one selected from the group consisting of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds, and polyfunctional epoxy compounds.

6. The ink set for ink-jet printing according to any one of claims 1 to 5, wherein the compound (II) is a polyfunctional carbodiimide compound.

7. An inkjet printing method using the ink set for inkjet printing according to any one of claims 1 to 6, comprising the following steps 1 and 2. Step 1: applying the water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method, and then applying the overcoat liquid by an inkjet ejection method to the portion to which the water-based ink has been applied. Step 2: heating the coating film of the water-based ink and the coating film of the overcoat liquid formed on the printing substrate by step 1.

8. A packaging method, comprising arranging the printed matter obtained by the inkjet printing method according to claim 7 around an item to be packaged, and then shrinking the heat-shrinkable resin film substrate of the printed matter to obtain a package.

9. Use as an ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid substantially free of pigment, the water-based ink containing a binder resin (Ib) having a carboxy group, the overcoat liquid containing a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib), and the surface tension γ (B) of the overcoat liquid being greater than the surface tension γ (A) of the water-based ink.

10. Use as an ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid substantially free of pigment, wherein the water-based ink contains a compound (II) having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of a binder resin (Ib) having a carboxy group, the overcoat liquid contains a binder resin (Ib) having a carboxy group, and the surface tension γ (B) of the overcoat liquid is greater than the surface tension γ (A) of the water-based ink.

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