Ink set for inkjet printing

Abstract

To provide an ink set for inkjet printing which is excellent in scratch resistance and water resistance of a heat-shrunk printed matter, in printing on a heat-shrinkable resin film, an inkjet printing method, and a packaging method.SOLUTION: There are provided an ink set for inkjet printing which contains aqueous ink containing a pigment, and an overcoat liquid substantially containing no 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 that is crosslinking reactive with the carboxy group of the binder resin (Ib), and surface tension γ (B) of the overcoat liquid is larger than surface tension γ (A) of the aqueous ink; an inkjet printing method using the ink set; and a packaging method using a printed matter obtained by the inkjet printing method.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In the fields of commercial printing and industrial printing, in addition to printing on conventional highly absorbent printing substrates called plain paper and copy paper, there has been a 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, in printing on low absorbent or non-absorbent printing substrates, since the absorption of liquid components is slow or not absorbed, the adhesion of pigment ink to these printing substrates is not sufficient, and the image fastness of printed matter tends to be low. Therefore, in order to improve the image fastness of printed matter with pigment ink, aqueous compositions such as coating liquids used in combination with pigment ink have been developed.

[0003] For example, 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, an ink set for inkjet recording containing the aqueous composition and an aqueous ink, and an inkjet recording method using the aqueous composition and the aqueous ink, with the aim of improving the rubbing resistance, solvent resistance, and substrate adhesion of printed matter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventionally, as in Patent Document 1, there is an example 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, in printing on a heat-shrinkable resin film widely used as a packaging base material such as a PET bottle, the crosslinking reaction by the crosslinking agent does not occur uniformly, and unevenness occurs in the strength of the printed coating film. Therefore, when the resin film shrinks, the weak parts of the strength of the printed coating film are preferentially broken, and it has been found that the abrasion resistance and water resistance of the printed matter after heat shrinkage are impaired. An object of the present invention is to provide an ink set for inkjet printing, an inkjet printing method, and a packaging method that are excellent in abrasion resistance and water resistance of a printed matter after heat shrinkage in printing on a heat-shrinkable resin film.

Means for Solving the Problems

[0006] The present inventors have found an ink set for inkjet printing including an aqueous ink containing a pigment and an overcoat liquid substantially free of a 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 the surface tension of the aqueous ink, whereby the crosslinking reaction of the binder resin proceeds uniformly and the above problems can be solved. That is, the present invention relates to the following [1] to [4]. [1] An ink set for inkjet printing including an aqueous ink containing a pigment and an overcoat liquid substantially free of a 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 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 the 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, the overcoat liquid contains a binder resin (Ib) having a carboxy group, and an ink set for inkjet printing, wherein 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, comprising the following steps 1 and 2, using the ink set for inkjet printing according to [1] or [2] above. Step 1: After applying the aqueous ink to a heat-shrinkable resin film substrate by an inkjet ejection method, applying the overcoat liquid to the portion where the aqueous ink has been applied by an inkjet ejection method. Step 2: A step of heating the coating film of the aqueous ink and the coating film of the overcoat liquid on the printed substrate formed in Step 1. [4]A packaging method, wherein after arranging a printed matter obtained by the inkjet printing method according to [3] above around an object to be packaged, the heat-shrinkable resin film substrate of the printed matter is shrunk to obtain a package. [Advantages of the Invention]

[0007] According to the present invention, there can be provided an ink set for inkjet printing, an inkjet printing method, and a packaging method, which are excellent in scratch resistance and water resistance of a heat-shrunk printed matter in printing on a heat-shrinkable resin film. [Embodiments for Carrying Out the Invention]

[0008] [Ink Set for Inkjet Recording] The ink set for inkjet recording of the present invention (hereinafter, also simply referred to as "ink set") includes an aqueous ink containing a pigment (hereinafter, also simply referred to as "aqueous ink" or "ink") and an overcoat liquid substantially free of a pigment (hereinafter, also simply referred to as "overcoat liquid"), 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 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. In the present invention, "aqueous" of the aqueous ink means that water occupies the largest proportion by mass in the medium contained in the aqueous ink. Also, in this specification, "low liquid-absorbing property" of the low liquid-absorbing printing substrate is a concept including low liquid-absorbing property and non-liquid-absorbing property, and the water absorption amount of the printing substrate at a contact time of 100 msec between the printing substrate and pure water is 0 g / m 2 10 g / m or more 2 as follows. The water absorption amount can be measured by the method described in the examples. Also, "printing" is a concept including printing and typing for recording characters and images, and "printed matter" is a concept including printed matter and typed matter on which characters and images are recorded.

[0009] According to the present invention, in printing on a heat-shrinkable resin film, the printed matter after heat shrinkage is excellent in scratch resistance and water resistance. The reason is not clear, but it is considered as follows. In the present invention, the surface tension γ(B) of the overcoat liquid (hereinafter also simply referred to as "surface tension γ(B)") is greater than the surface tension γ(A) of the aqueous ink (hereinafter also simply referred to as "surface tension γ(A)"). Therefore, when the overcoat liquid is applied to the portion where the aqueous ink has been applied after the aqueous ink is applied to the printing substrate, convection (so-called Marangoni convection) occurs with the gradient of the surface tension between the coating film of the aqueous ink on the printing substrate and the coating film of the overcoat liquid as the driving force. As a result, the compound (II) having a reactive group contained in the coating film of the overcoat liquid is more uniformly distributed in the coating film of the aqueous ink compared to the diffusion based on the concentration difference of the compound (II) between the coating film of the aqueous ink on the printing substrate and the coating film of the overcoat liquid, and the uniform crosslinking reaction between the carboxy group of the binder resin (Ib) contained in the coating film of the aqueous ink and the reactive group of the compound (II) is promoted, making it difficult to generate a non-uniform distribution of the strength of the formed printing coating film, and enabling the production of a printed matter with a uniform strength of the printing coating film. Such a printed matter is considered to be able to reduce the occurrence of fine cracks and wrinkles in the printing coating film because even when heat-shrunk, the portions with weak strength of the printing coating film do not selectively shrink. As a result, it is presumed that embrittlement of the printing coating film is suppressed and scratch resistance and water resistance are improved. Hereinafter, the scratch resistance and water resistance of the heat-shrunk printed matter are also simply referred to as "scratch resistance" and "water resistance", respectively.

[0010] In the present invention, the surface tension γ(B) of the overcoat liquid (hereinafter also simply referred to as "surface tension γ(B)") is greater than the surface tension γ(A) of the aqueous ink (hereinafter also simply referred to 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 aqueous ink is preferably 1 mN / m or more, more preferably 1.5 mN / m or more, still 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 from the viewpoint of improving scratch resistance and water resistance, and is preferably 20 mN / m or less, more preferably 17 mN / m or less, still more preferably 15 mN / m or less from the same viewpoint as above. The surface tension γ(A) of the aqueous 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 can be used alone or in combination of two or more inks having different hues. That is, the printed image formed by 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 hues.

[0012] (Pigment) The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment can also be used. Further, if necessary, they can be used in combination with a extender pigment. Specific examples of the inorganic pigment include, for example, carbon black, titanium oxide, iron oxide, red iron oxide, metal oxides such as chromium oxide, and nacreous pigments. Particularly in the case of black ink, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of the organic pigment include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; 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 perylene pigments. In the case of achromatic ink, achromatic pigments such as white, black, and gray can be used, and in the case of chromatic ink, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. 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 the extender pigment include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0013] In the aqueous ink according to the present invention, the pigment is dispersed in the medium. The form of the pigment in the aqueous ink according to the present invention includes a form dispersed by a resin (hereinafter also referred to as "pigment-dispersing resin") or a surfactant as a dispersant, or a form of a self-dispersing pigment dispersed without using a dispersant. Among these, as the form of the pigment in the aqueous ink according to the present invention, a form dispersed by a pigment-dispersing resin (hereinafter also referred to as "pigment-dispersing resin (Ia)") is preferable, and a form of resin particles containing a pigment (hereinafter also referred to as "pigment-containing resin particles") is more preferable. Here, the form of the pigment-containing resin particles is not particularly limited, and it is sufficient that the particles are formed by at least a pigment and a pigment-dispersing resin (Ia), and the particles are those in which the pigment-dispersing resin (Ia) is adsorbed to the pigment in the aqueous ink. Examples of the form of the pigment-containing resin particles include a particle form in which the pigment is encapsulated in the pigment-dispersing resin (Ia), a particle form in which the pigment is uniformly dispersed in the pigment-dispersing resin (Ia), a particle form in which the pigment is exposed on the surface of the pigment-dispersing resin (Ia) particles, etc., and mixtures thereof are also included.

[0014] (Pigment-dispersing resin (Ia)) The pigment-dispersing resin (Ia) may be either a water-soluble resin or a water-insoluble resin. Here, with respect to the "water-solubility" and "water-insolubility" of the resin, when the resin dried at 105 °C for 2 hours until 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 as "water-soluble", and if it is 10 g or less, it is judged as "water-insoluble". Further, when the pigment-dispersing resin (Ia) has an anionic group and the anionic group is neutralized with a neutralizing agent as described later, the dissolved amount measured under the condition that the neutralizing agent is present under the condition that the mass ratio of the pigment-dispersing resin (Ia) to the neutralizing agent is the same as that in the aqueous ink according to the present invention is used for judgment.

[0015] Examples of the pigment-dispersing 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. As the pigment-dispersing resin (Ia), those synthesized as appropriate may be used, or commercially available products may be used. Among these, from the viewpoint of improving scratch resistance and water resistance, the vinyl resin (hereinafter also referred to as "vinyl resin (Ia-1)") is preferable as the pigment-dispersing resin (Ia).

[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 the present specification, the "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of the anionic group include a carboxy group (-COOM), a sulfonic acid group (-SO 3 M), and a phosphoric acid group (-OPO 3 M 2 ). 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 any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. In the present specification, the "hydrophobicity" of the hydrophobic monomer means that when the monomer is dissolved until saturated in 100 g of ion-exchanged water at 25°C, the dissolved amount is less than 10 g. The nonionic monomer is a monomer having a high affinity for water or a water-soluble organic solvent, and is, for example, a monomer containing a hydroxy group or a polyalkylene glycol chain.

[0017] Examples of the anionic group-containing monomer include a carboxy group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer. Among these, from the viewpoints of improving the dispersion stability of the pigment and availability, a carboxy group-containing monomer is preferable, and (meth)acrylic acid is more preferable. Examples of the hydrophobic monomer include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 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 number average molecular weight of 500 or more and 100,000 or less and having a polymerizable functional group at one end. Among these, the hydrophobic monomer is preferably a styrene-based monomer from the viewpoint of improving the dispersion stability of the pigment, more preferably at least one selected from the group consisting of styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and still more preferably at least one selected from the group consisting of styrene and α-methylstyrene. Examples of the nonionic monomer 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. Note that “(meth)acrylic acid” means at least one selected from the group consisting of acrylic acid and methacrylic acid. Also, “(meth)acrylate” means at least one selected from the group consisting of acrylate and methacrylate. Each monomer of 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 a structural unit derived from at least one anionic group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from at least one hydrophobic monomer selected from the group consisting of (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, an aromatic group-containing monomer, and a styrene-based macromer. More preferably, it contains a structural unit derived from at least one anionic group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from at least one hydrophobic monomer selected from the group consisting of (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and an aromatic group-containing monomer. Even more preferably, it contains a structural unit derived from at least one anionic group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from an aromatic group-containing monomer. Even more preferably, it contains a structural unit derived from at least one anionic group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit 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 unit 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 unit 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 viewpoint as above, preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less. The content of the structural unit 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, still more preferably 60% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and from the same viewpoint as described above, it is preferably 90% by mass or less, more preferably 85% by mass or less, still 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 the nonionic monomer in the vinyl resin is preferably 20% by mass or less, more preferably 10% by mass or less, still 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 containing a constituent component of a polymer having a linear two-dimensional structure which may have a branched chain and a constituent component derived from a crosslinking agent. Such a crosslinked structure is considered to be a three-dimensional structure formed by a polymer having a linear two-dimensional structure which may have a branched chain and a constituent component derived from a crosslinking agent. Examples of the polymer 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 above-described vinyl resin (Ia-1) is preferred.

[0021] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule from the viewpoint of improving the dispersion stability of the pigment, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms, and still more preferably one or more 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, the epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, still more preferably 150 or less from the viewpoint of improving the dispersion stability of the pigment.

[0022] The acid value of the pigment dispersion resin (Ia) is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, still more preferably 100 mgKOH / g or more from the viewpoint of improving the dispersion stability of the pigment, and preferably 800 mgKOH / g or less from the same viewpoint as above. The acid value of the pigment dispersion resin (Ia) can be determined by the method described in the examples, but can also be calculated from the mass ratio of the constituent monomers. Further, the acid value of the pigment dispersion resin (Ia) having a crosslinked structure can also be calculated by the following formula. Acid value (mgKOH / g) of the pigment dispersion resin (Ia) having a crosslinked structure = [Acid value (mgKOH / g) of the 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 an apparent crosslinking rate calculated from the acid value of the pigment dispersion resin (Ia) before crosslinking and the equivalent 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, still more preferably 5,000 or more, from the viewpoint of the dispersion stability of the pigment, and, from the same viewpoint as above, is preferably 100,000 or less, more preferably 50,000 or less, still 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, still more preferably 5,000 or more, from the viewpoint of the dispersion stability of the pigment, and, from the same viewpoint as above, is preferably 100,000 or less, more preferably 80,000 or less, still more preferably 60,000 or less. The weight average molecular weight of the pigment-dispersing resin (Ia) is measured by the method described in the examples.

[0025] Examples of commercially available products of the pigment-dispersing resin (Ia) include polyacrylic acid such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); styrene / acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690", "Joncryl 819" (all of the above are manufactured by BASF Japan Ltd.).

[0026] When the form of 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 subjecting a pigment, a pigment-dispersing resin (Ia), a neutralizing agent, a surfactant, etc., as required, to a dispersion treatment by a known method. When the pigment is formulated 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, still more preferably 70 nm or more, from the viewpoints of the ejection property and storage stability of the aqueous ink, and the rubbing resistance and water resistance. And from the same viewpoints as above, it is preferably 600 nm or less, more preferably 550 nm or less, still 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)) From the viewpoint of improving the rubbing resistance and water resistance, the aqueous ink according to the present invention contains a binder resin (Ib) having a carboxy group (-COOM) (hereinafter, also simply referred to as "binder resin (Ib)"). The carboxy group is a group that exhibits acidity by dissociating to release hydrogen ions, or their dissociated ionic form (-COO - ). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium, similar to the aforementioned anionic group.

[0028] From the viewpoint of improving the rubbing 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, still more preferably 10 mgKOH / g or more, and from the same viewpoints as above, it is preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, still 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 can also be calculated 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. Note that “(meth)acrylic” means acrylic or methacrylic. 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 at least one 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 at least one 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. From the viewpoints of improving abrasion resistance and water resistance and availability, (meth)acrylic acid is preferable as the carboxy group-containing monomer. Examples of the hydrophobic monomer preferably include the same ones as those exemplified in the aforementioned pigment dispersion resin (Ia). Among these hydrophobic monomers, from the viewpoint of improving rubbing resistance and water resistance, the hydrophobic monomer is preferably at least one 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 at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and aromatic group-containing monomers, still 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-based resin (Ib-1) can be used alone or in combination of two or more.

[0031] 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 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, from the viewpoint of improving scratch resistance and water resistance. More preferably, it 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 1 to 22 carbon atoms and aromatic group-containing monomers. Even more preferably, it is 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 (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. Even more preferably, it is 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 (meth)acrylates having an alkyl group having 1 to 12 carbon atoms. Even more preferably, it is 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 (meth)acrylates having an alkyl group having 1 to 8 carbon atoms. Even more preferably, it is 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 scratch resistance and water resistance, the content of the structural unit 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, still more preferably 2% by mass or more, and from the same viewpoint as above, preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less. From the viewpoint of improving scratch resistance and water resistance, the content of the structural unit 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, still more preferably 95% by mass or more, and from the same viewpoint as above, preferably 99.5% by mass or less, more preferably 99% by mass or less, still more preferably 98% by mass or less.

[0033] From the viewpoint of improving scratch 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, still 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, even more preferably 500,000 or more, and from the same viewpoint as above, preferably 1,500,000 or less, more preferably 1,000,000 or less, still more preferably 800,000 or less. The measurement of the weight-average molecular weight can be carried out 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 examples of the polymerization method include, for example, an emulsion polymerization method and a suspension polymerization method, and more preferably an emulsion polymerization method.

[0034] As the polyurethane resin having a carboxy group used in the present invention (hereinafter, also referred to as "polyurethane resin (Ib-2)"), from the viewpoint of improving scratch resistance and water resistance, 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 and a dialkanol carboxylic acid is preferable. Examples of the dialkanol carboxylic acid 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, uretoimine - containing modified products, etc.).

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

[0037] Examples of the solvent used in the polyaddition reaction include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. In the polyaddition reaction, a chain extender and a reaction terminator may be used in combination as necessary. By using a chain extender, the molecular weight can be further increased. Examples of the chain extender include polyols and polyamines, and examples of the reaction terminator include monoalcohols and monoamines.

[0038] From the viewpoint of dispersion stability in the aqueous ink, it is preferable that at least a part of the carboxy groups of the polyurethane resin (Ib-2) is neutralized with a neutralizing agent. Examples of the neutralizing agent include 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 resin particles not containing a pigment, and from the viewpoint of improving the productivity of the aqueous ink, it is preferably formulated in the aqueous ink as an aqueous dispersion of polymer particles not containing a pigment. The binder resin (Ib) may be appropriately synthesized or a commercially available product may be used. When the binder resin (Ib) is formulated as an aqueous dispersion of resin particles not containing a pigment, the average particle diameter of the resin particles not containing a pigment in the aqueous dispersion is preferably 10 nm or more, more preferably 30 nm or more, still more preferably 50 nm or more, even more preferably 70 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, even more preferably 130 nm or less, from the storage stability of the ink. The average particle diameter of the resin particles not containing a pigment in the aqueous dispersion is measured by the method described in the examples.

[0040] Examples of commercially available dispersions of vinyl resin particles containing no pigment include, for example, "Neocryl A-1127" (manufactured by Covestro, trade name, anionic self-crosslinking aqueous acrylic resin), "Joncryl 390", "Joncryl 7100", "Joncryl 7600", "Joncryl 537J", "Joncryl PDX-7164", "Joncryl 538J", "Joncryl 780" (manufactured by BASF Japan Ltd., trade name), etc. acrylic resins; "SR-100", "SR102" (above, manufactured by Japan A&R Co., Ltd., trade name), etc. styrene / butadiene resins; "Vinibran 700", "Vinibran 701" (manufactured by Nisshin Chemical Industry Co., Ltd., trade name), etc. vinyl chloride resins. Examples of commercially available dispersions of polyurethane resin particles containing no pigment include, for example, "NeoRez R-9603" (manufactured by Covestro, trade name), "WBR-2018", "WBR-2000U" (manufactured by Daisheng Fine Chemical Co., Ltd., trade name). Examples of commercially available dispersions of polyester resin particles containing no pigment include, for example, "Elytel KA-5034", "Elytel KA-5071S", "Elytel KZA-1734", "Elytel KZA-6034", "Elytel KZA-1449", "Elytel KZA-0134", "Elytel KZA-3556" (above, manufactured by Unitika Ltd., trade name).

[0041] (Water-soluble organic solvent) From the viewpoints of improving the ejection property and storage stability of the aqueous ink, and adjusting the surface tension of the aqueous ink to improve the rubbing resistance and water resistance, the aqueous ink according to the present invention preferably further contains a water-soluble organic solvent. The water-soluble organic solvent can be used alone or in combination of two or more. In the present invention, the "water-soluble organic solvent" refers to an organic solvent whose dissolution amount is 10 mL or more when the organic solvent is dissolved in 100 mL of water at 25°C. The boiling point of the water-soluble organic solvent under atmospheric pressure is preferably 150 °C or higher, more preferably 160 °C or higher, still more preferably 170 °C or higher, and preferably 350 °C or lower, more preferably 300 °C or lower, still more preferably 250 °C or lower. When two or more water-soluble organic solvents are used in combination as the water-soluble organic solvent, the boiling point of the water-soluble organic solvent is the weighted average value weighted by the content (% by mass) of each water-soluble organic solvent.

[0042] 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 viewpoints of improving the dischargeability and storage stability of the aqueous ink, and adjusting the surface tension of the aqueous ink to improve the rubbing resistance and water resistance, it is preferably at least one selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers. A plurality of polyhydric alcohols included in the concept of polyhydric alcohols can be mixed and used. Similarly, a plurality of polyhydric alcohol alkyl ethers included in the concept of polyhydric alcohol alkyl ethers can be mixed and used.

[0043] Examples of the polyhydric alcohol 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 pentaerythritol.

[0044] Examples of the polyhydric alcohol alkyl ether include alkylene glycol monoalkyl ether, dialkylene glycol monoalkyl ether, and trialkylene glycol monoalkyl ether. Specifically, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol mono isobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol mono isobutyl 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 can be mentioned.

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

[0046] Examples of the acetylene-based surfactant 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-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, and ethylene oxide (hereinafter also referred to as "EO") adducts thereof. Among these, more preferably, it is at least one 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 still more preferably, it is an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The average number of moles of ethylene oxide added (hereinafter also referred to as "average EO addition mole number") of the acetylene-based surfactant is preferably 1 mole or more, more preferably 2 moles or more, still more preferably 3 moles or more, and from the same viewpoint as above, preferably 35 moles or less, more preferably 30 moles or less, still more preferably 25 moles or less, even more preferably 20 moles or less, even more preferably 15 moles or less, even more preferably 10 moles or less, and even more preferably 5 moles or less, from the viewpoint of adjusting the surface tension of the aqueous ink and improving the rubbing resistance and water resistance.

[0047] The HLB value of the acetylene-based surfactant is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, even more preferably 7 or more, and from the same viewpoint as above, preferably 18 or less, more preferably 15 or less, and still more preferably 10 or less, from the viewpoint of adjusting the surface tension of the aqueous ink and improving the rubbing resistance and water resistance. In the present invention, the HLB value is a value indicating the affinity of a surfactant for water and oil as the Hydrophile-Lypophile Balance, and can be obtained from the following formula by the Griffin method. Also, the catalog values of each product can be referred to. HLB value = 20 × [(total formula weight of hydrophilic groups contained in the surfactant) / (molecular weight of the surfactant)] Examples of the hydrophilic groups contained in the surfactant include a hydroxy group and an ethyleneoxy group.

[0048] Examples of commercially available acetylene-based surfactants include Surfynol 104PG-50 (50% propylene glycol diluted product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol), Surfynol 420 (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)), Surfynol 440 (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 (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)), Surfynol 485 (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] As the silicone-based surfactant, from the viewpoint of adjusting the surface tension of the aqueous ink and improving the rubbing resistance and water resistance, a polyether-modified silicone-based surfactant is preferably mentioned. As the polyether group of the polyether-modified silicone surfactant, for example, a polyethyleneoxy group, a polypropyleneoxy group, or a polyalkyleneoxy group in which an ethyleneoxy group and a propyleneoxy group (trimethyleneoxy group or propane-1,2-diyl group) are added in a block or random manner is suitable, and a compound in which a polyether group is grafted to the silicone main chain or a compound in which polyether groups are block-bonded to both ends of the silicone main chain can be used.

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

[0051] Specific examples of the polyether-modified silicone surfactant 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, lauryl PEG-9 polydimethylsiloxyethyl dimethicone. Commercially available products of the polyether-modified silicone surfactant include, for example, the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., the "Silface SAG" series manufactured by Nichi-Shin Chemical Industry Co., Ltd., and the "BYK" series manufactured by BYK-Chemie Japan Co., Ltd.

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

[0053] The aqueous ink according to the present invention may further contain various additives such as a humectant, a wetting agent, a penetrant, a dispersant, a viscosity modifier, an antifoaming agent, a preservative, a fungicide, and a rust inhibitor as optional components.

[0054] The aqueous ink can be obtained by mixing a pigment, a binder resin (Ib), water, a pigment dispersion resin (Ia) as required, a neutralizing agent, a surfactant, a water-soluble organic solvent, etc. and stirring them. When pigment-containing resin particles are included, the pigment-containing resin particles are preferably dispersed by a known method using a pigment, a pigment dispersion resin (Ia), a neutralizing agent, a surfactant, etc. as described above to obtain an aqueous dispersion of the pigment-containing resin particles, and then incorporated into the aqueous ink.

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

[0056] From the viewpoint of improving the abrasion resistance and water resistance, the content of the binder resin (Ib) in the aqueous ink according to the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and from the same viewpoint as above, preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less. From the viewpoint of abrasion resistance and water resistance, the water content in the aqueous ink according to the present invention is preferably 35% by mass or more, more preferably 40% by mass or more, still more preferably 45% by mass or more, and from the same viewpoint as above, preferably 65% by mass or less, more preferably 60% by mass or less, still more preferably 55% by mass or less. When the aqueous ink according to the present invention further contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the aqueous ink according to the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, from the viewpoints of improving the ejection property and storage stability of the aqueous ink and adjusting the surface tension of the aqueous ink to improve the abrasion resistance and water resistance, and preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less. When the aqueous ink according to the present invention further contains a surfactant, the content of the surfactant in the aqueous ink according to the present invention is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, from the viewpoint of adjusting the surface tension of the aqueous ink to improve the abrasion resistance and water resistance, and from the same viewpoint as above, preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less.

[0057] (Physical properties of aqueous ink) The surface tension γ(A) of the aqueous ink according to the present invention is preferably 22 mN / m or more, more preferably 23 mN / m or more, still more preferably 24 mN / m or more, and even more preferably 25 mN / m or more, from the viewpoints of improving scratch resistance and water resistance and improving image quality. And from the same viewpoints as above, it is preferably 30 mN / m or less, more preferably 29 mN / m or less, still 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. The viscosity of the aqueous ink according to the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, still more preferably 4 mPa·s or more, from the viewpoints of ejection stability and dispersion stability. And it is preferably 12 mPa·s or less, more preferably 9 mPa·s or less, still more preferably 7 mPa·s or less. The viscosity is measured by the method described in the examples. The pH of the aqueous ink according to the present invention is preferably 7.0 or more, more preferably 7.2 or more, still more preferably 7.5 or more. Also, from the viewpoints of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, still more preferably 9.5 or less. The pH is measured by the method described in the examples.

[0058] When the aqueous ink is used in combination with those having two or more different colors, there may be a difference in surface tension between the aqueous inks. At this time, 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 from the viewpoints of improving scratch resistance and water resistance. 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 0.5 mN / m or more larger than the surface tension between the aqueous inks, more preferably 1.0 mN / m or more larger, and still more preferably 1.5 mN / m or more larger.

[0059] <Overcoat liquid> The overcoat liquid according to the present invention substantially does not contain a pigment and contains a compound (II) (hereinafter also simply referred to as "compound (II)") having a reactive group capable of undergoing a crosslinking reaction with a carboxy group of a binder resin (Ib). The overcoat liquid according to the present invention substantially does not contain a pigment. Here, "substantially does not contain a 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, still more preferably 0.01% by mass or less, and even more preferably 0% by mass.

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

[0061] [Polyfunctional carbodiimide compound] A polyfunctional carbodiimide compound is a compound having two or more carbodiimide groups in the molecule. 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 as the polyfunctional carbodiimide compound. The carbodiimide group-containing polymer is preferably obtained by blocking the terminal isocyanate groups of a condensation product obtained by a decarboxylation condensation reaction in the presence of a carbodiimidization catalyst of diisocyanates with a hydrophilic group.

[0062] Examples of the diisocyanates used in the decarboxylation condensation reaction include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), decamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as 4,4'-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,5- or 2,6-norbornane diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated tolylene diisocyanate, 2,4-bis-(8-isocyanatooctyl)-1,3-dioctylcyclobutane (OCDI); aromatic aliphatic diisocyanates such as m- or p-xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI); aromatic diisocyanates such as 2,4,6-triisopropylphenyl diisocyanate (TIDI), 4,4'- or 2',4-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-tolylene diisocyanate (TDI).

[0063] Examples of the compound for blocking the terminal isocyanate group of the condensation reactant include compounds having a functional group capable of reacting 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 compatibility with the overcoat liquid. By adjusting the number of moles of ethylene oxide added to the polyethylene glycol monomethyl ether, the resulting carbodiimide group-containing polymer can be formulated into the overcoat liquid in the form of an aqueous solution or an emulsion.

[0064] From the viewpoint of improving scratch resistance and water resistance, the carbodiimide group equivalent of the carbodiimide group-containing polymer is preferably 100 or more, more preferably 170 or more, still more preferably 200 or more, and from the viewpoint of compatibility with the overcoat liquid, it is preferably 500 or less, more preferably 400 or less, still more preferably 300 or less. The carbodiimide group equivalent means the mass of the carbodiimide group-containing polymer per mole of the carbodiimide group. Examples of commercially available carbodiimide group-containing polymers include Carbodilite E-02, Carbodilite E-05, and Carbodilite E-07S (all manufactured by Nisshinbo Chemical Inc., trade names).

[0065] [Polyfunctional oxazoline compound] The 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 the crosslinking reactivity with the carboxy group and improving scratch 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, still more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, still more preferably 30,000 or less. As the oxazoline group-containing polymer, for example, a polymer having an acrylic backbone, a polymer having a styrene / acrylic backbone, a polymer having a styrene backbone, or a polymer having an acrylonitrile / styrene backbone can be used.

[0066] From the viewpoints of improving the storage stability of the overcoat liquid and improving the scratch resistance and water resistance, the oxazoline group equivalent of the oxazoline group-containing polymer is preferably 100 or more, more preferably 170 or more, still more preferably 200 or more, and preferably 500 or less, more preferably 400 or less, still more preferably 300 or less. The oxazoline group equivalent means the mass of the oxazoline group-containing polymer per mole of the oxazoline group. Examples of commercially available products of the oxazoline group-containing polymer include the "Epocros WS" series such as "Epocros WS-300", "Epocros WS-500", and "Epocros WS-700" (above, manufactured by Nippon Shokubai Co., Ltd., water-soluble type).

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

[0068] Examples of the polyfunctional epoxy compound 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 type diglycidyl ether. Among these, from the viewpoint of improving abrasion resistance and water resistance, the polyfunctional epoxy compound is preferably at least one 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) From the viewpoints of improving the ejection property when ejecting the overcoat liquid by an inkjet ejection method and the storage stability of the overcoat liquid, and adjusting the surface tension of the overcoat liquid to improve abrasion resistance and water resistance, it is preferable that the overcoat liquid according to the present invention further contains a water - soluble organic solvent. In the present invention, the "water - soluble organic solvent" refers to an organic solvent whose dissolution amount is 10 mL or more when the organic solvent is dissolved in 100 mL of water at 25°C, as described above. From the viewpoints of ejection stability, storage stability, and drying property, the boiling point of the water - soluble organic solvent is preferably 150°C or higher, more preferably 160°C or higher, still more preferably 170°C or higher, and preferably 350°C or lower, more preferably 300°C or lower, still more preferably 250°C or lower. When two or more water-soluble organic solvents are used in combination as the water-soluble organic solvent, the boiling point of the water-soluble organic solvent is the weighted average value weighted by the content (% by mass) of each water-soluble organic solvent.

[0070] Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds, similar to the aqueous ink. Among these, from the viewpoints of improving the ejection property when ejecting the overcoat liquid by an inkjet ejection method and the storage stability of the overcoat liquid, and adjusting the surface tension of the overcoat liquid to improve the scratch resistance and water resistance, it is preferably at least one selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers. A plurality of polyhydric alcohols included in the concept of polyhydric alcohols can be mixed and used. Similarly, a plurality of polyhydric alcohol alkyl ethers included in the concept of polyhydric alcohol alkyl ethers can be mixed and used. Preferred examples of the polyhydric alcohol and the polyhydric alcohol alkyl ether are the same as 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 to improve the scratch 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 aforementioned aqueous ink and the surface tension γ(B) of the overcoat liquid. Examples of the surfactant include nonionic surfactants, anionic surfactants, and amphoteric surfactants from the viewpoint of adjusting the surface tension of the overcoat liquid to improve the scratch resistance and water resistance, and nonionic surfactants are preferred. The surfactant can be used alone or in combination of two or more. Examples of nonionic surfactants include acetylene surfactants, polyoxyalkylene alkyl ether surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorosurfactants. Among these, from the viewpoint of adjusting the surface tension of the overcoat liquid and improving scratch resistance and water resistance, the surfactant is preferably at least one selected from the group consisting of acetylene surfactants and silicone surfactants.

[0072] Examples of acetylene surfactants preferably 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 - hexyne - 3 - ol, 2,4 - dimethyl - 5 - hexyne - 3 - ol, and EO adducts thereof. Among these, more preferably, it is at least one 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. From the viewpoint of adjusting the surface tension of the overcoat liquid and improving scratch resistance and water resistance, the average number of moles of EO added to the acetylene surfactant is preferably 1 mole or more, and from the same viewpoint as above, it is preferably 35 moles or less, more preferably 30 moles or less, still more preferably 25 moles or less, even more preferably 20 moles or less, even more preferably 15 moles or less, even more preferably 10 moles or less, even more preferably 5 moles or less, even more preferably 3 moles or less, even more preferably 2 moles or less.

[0073] From the viewpoint of adjusting the surface tension of the overcoat liquid and improving scratch resistance and water resistance, the HLB value of the acetylene surfactant is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and from the same viewpoint as above, it is preferably 18 or less, more preferably 15 or less, still more preferably 10 or less, even more preferably 7 or less, even more preferably 5 or less. In the present invention, as described above, the HLB value can be determined from the above formula by the Griffin method. Alternatively, the catalog value of each product can also be referred to. Examples of commercially available acetylene-based surfactants include the same ones as those exemplified for aqueous inks.

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

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

[0076] The overcoat liquid according to the present invention can further contain other components such as a viscosity modifier, an antifoaming agent, a preservative, a fungicide, and a rust preventive, which are commonly used in overcoat liquids used in inkjet printing and the like. However, it is preferably substantially free of a resin having a carboxy group capable of crosslinking with compound (II). Examples of such a resin having a carboxy group include the same ones as the binder resin (Ib) described above. Here, "substantially free of a resin having a carboxy group capable of crosslinking with compound (II)" means that the content of the resin having a carboxy group capable of crosslinking with compound (II) in the overcoat liquid according to the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, still more preferably 0.01% by mass or less, and even more preferably 0% by mass. The overcoat liquid according to the present invention can be obtained by mixing compound (II), water, a water-soluble organic solvent, a surfactant, and the other components described above as necessary and stirring them. Compound (II) is preferably formulated as an aqueous solution or an emulsion.

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

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

[0079] [Another aspect of the inkjet recording ink set] Another aspect of the inkjet recording ink set of the present invention (hereinafter, also simply referred to as "another aspect") includes an aqueous ink containing a pigment and an overcoat liquid substantially free of a pigment. 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, 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.

[0080] According to another aspect of the present invention, in printing on a heat-shrinkable resin film, the printed matter after heat shrinkage is excellent in scratch resistance and water resistance. The reason is not clear, but it is considered as follows. In the present invention, the surface tension of the overcoat liquid is greater than the surface tension of the aqueous ink. Therefore, when the overcoat liquid is applied to the portion where the aqueous ink has been applied after the aqueous ink is applied to the printing substrate, convection (so-called Marangoni convection) occurs with the gradient of the surface tension between the coating film of the aqueous ink on the printing substrate and the coating film of the overcoat liquid as the driving force. As a result, the compound (II) having a reactive group contained in the coating film of the aqueous ink is more uniformly distributed in the coating film of the overcoat liquid compared to the diffusion based on the concentration difference of the compound (II) between the coating film of the aqueous ink on the printing substrate and the coating film of the overcoat liquid, and the uniform cross-linking reaction between the carboxy group of the binder resin (Ib) contained in the coating film of the overcoat liquid and the reactive group of the compound (II) is promoted, and it is difficult to generate a distribution of the strength of the formed printing coating film, and a printed matter having a uniform strength of the printing coating film can be obtained. Such a printed matter is considered to be able to reduce the occurrence of fine cracks and wrinkles in the printing coating film because even when heat-shrunk, the portion with a weak strength of the printing coating film does not selectively shrink. As a result, it is presumed that embrittlement of the printing coating film is suppressed and scratch resistance and water resistance are improved.

[0081] In another aspect of the present invention, the surface tension γ(B) of the overcoat liquid (hereinafter, also simply referred to as "surface tension γ(B)") is greater than the surface tension γ(A) of the aqueous ink (hereinafter, also simply referred to 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 aqueous ink is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above.

[0082] <Aqueous ink according to another aspect> The aqueous ink according to another aspect of the present invention contains a pigment and a compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy groups of a binder resin (Ib) having carboxy groups. The aqueous ink can be used alone or in combination of two or more having different hues. That is, the printed image formed by the aqueous 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 hues.

[0083] In the aqueous ink according to another aspect of the present invention, the pigment is the same as the pigment of the aqueous ink for inkjet recording according to the present invention described above. Further, in another aspect of the present invention, the pigment dispersion resin (Ia) is the same as the pigment dispersion resin (Ia) of the aqueous ink for inkjet recording according to the present invention described above.

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

[0085] The aqueous ink according to another aspect of the present invention preferably further contains a water-soluble organic solvent from the viewpoints of improving the ejection property and storage stability of the aqueous ink, and adjusting the surface tension of the aqueous ink to improve the rub resistance and water resistance. The water-soluble organic solvent can be used alone or in combination of two or more. In the aqueous 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 aqueous ink for inkjet recording according to the present invention described above.

[0086] The aqueous ink according to another aspect of the present invention preferably further contains a surfactant from the viewpoint of adjusting the surface tension of the aqueous ink to improve the rub resistance and water resistance. In the aqueous ink according to another aspect of the present invention, the surfactant is the same as the surfactant of the aqueous ink for inkjet recording according to the present invention described above.

[0087] The aqueous ink according to another aspect of the present invention contains water. In the aqueous ink according to another aspect of the present invention, the water is the same as the water in the aqueous ink for inkjet recording of the present invention described above.

[0088] The aqueous ink according to another aspect of the present invention may further contain various additives such as a humectant, a wetting agent, a penetrant, a dispersant, a viscosity modifier, an antifoaming agent, a preservative, a fungicide, a rust preventive, etc. and a fixing resin as optional components.

[0089] The aqueous ink according to another aspect of the present invention can be obtained by mixing a pigment, a compound (II) having a reactive group capable of crosslinking reaction with the carboxy group of the binder resin (Ib) having a carboxy group, water, a pigment dispersion resin (Ia) as required, a neutralizing agent, a surfactant, a water-soluble organic solvent, etc. and stirring. When pigment-containing resin particles are included, the pigment-containing resin particles are preferably dispersed by a known method using a pigment, a pigment dispersion resin (Ia), a neutralizing agent, a surfactant, etc. as described above to obtain an aqueous dispersion of the pigment-containing resin particles, and then blended into the aqueous ink.

[0090] (Composition of the aqueous ink according to another aspect) The content of the pigment in the aqueous ink according to another aspect of the present invention is the same as that in the case of the aqueous ink for inkjet recording of the present invention described above. When the form of the pigment in the aqueous ink according to another aspect of the present invention is a form dispersed with the pigment dispersion resin (Ia), the content of the pigment dispersion resin (Ia) in the aqueous ink according to another aspect of the present invention is the same as that in the case of the aqueous ink for inkjet recording of the present invention described above. When the form of the pigment in the aqueous ink according to another aspect of the present invention is a form dispersed with 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 aqueous ink according to another aspect of the present invention [pigment / (pigment + pigment dispersion resin (Ia))] is the same as that in the case of the aqueous ink for inkjet recording of the present invention described above.

[0091] From the viewpoint of improving the abrasion resistance and water resistance, the content of the 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 according to another aspect of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 1.2% by mass or more, and even more preferably 1.5% by mass or more. From the same viewpoint as above, it is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0092] The water content in the aqueous ink according to another aspect of the present invention is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above. When the aqueous 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 aqueous ink according to the present invention is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above. When the aqueous ink according to another aspect of the present invention further contains a surfactant, the content of the surfactant in the aqueous ink according to the present invention is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above.

[0093] (Physical properties of the aqueous ink according to another aspect) The surface tension γ(A) of the aqueous ink according to another aspect of the present invention is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above. The viscosity of the aqueous ink according to another aspect of the present invention at 32°C is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above. The pH of the aqueous ink according to another aspect of the present invention is the same as in the case of the aqueous ink for inkjet recording according to the present invention described above.

[0094] <Overcoat liquid according to another aspect> The overcoat liquid according to another aspect of the present invention substantially does not contain a pigment and contains a binder resin (Ib) having a carboxy group. The overcoat liquid according to the present invention substantially does not contain pigments.

[0095] In the overcoat liquid according to another aspect of the present invention, the binder resin (Ib) having a carboxy group is the same as the binder resin (Ib) of the aqueous ink according to the inkjet recording ink of the present invention described above.

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

[0097] From the viewpoint of adjusting the surface tension of the overcoat liquid to improve the rubbing resistance and water resistance, the overcoat liquid according to another aspect of the present invention may further contain a surfactant. The surfactant can be appropriately selected and used within a range that satisfies the relationship between the surface tension γ(A) of the aforementioned aqueous 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 the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0098] The overcoat liquid according to another aspect of the present invention preferably contains water. In the overcoat liquid according to another aspect of the present invention, the water is the same as the water of the overcoat liquid according to the inkjet recording ink of the present invention described above.

[0099] The overcoat liquid according to another aspect of the present invention can further contain other components such as a viscosity modifier, an antifoaming agent, a preservative, a fungicide, and a rust preventive, which are usually used in overcoat liquids used in inkjet printing. The overcoat liquid according to the present invention can be obtained by mixing a binder resin (Ib) having a carboxy group, water, a water-soluble organic solvent, a surfactant, and the other components as required, and stirring them. Compound (II) is preferably formulated as an aqueous solution or an emulsion.

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

[0101] When the overcoat liquid according to another aspect 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 aspect of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, from the viewpoint of improving scratch resistance and water resistance, and, from the same viewpoint as above, preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less. When the overcoat liquid according to another aspect of the present invention contains a surfactant, the content of the surfactant in the overcoat liquid according to another aspect of the present invention is the same as in the case of the overcoat liquid for inkjet recording according to the present invention described above. When the overcoat liquid according to another aspect of the present invention contains water, the content of water in the overcoat liquid according to another aspect of the present invention is the same as in the case of the overcoat liquid for inkjet recording according to the present invention described above.

[0102] (Physical properties of the overcoat liquid according to another aspect) The surface tension γ(B) of the overcoat liquid according to another aspect of the present invention is the same as in the case of the overcoat liquid for inkjet recording according to 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 an inkjet ejection method and then applying an overcoat liquid to the portion to which the aqueous ink has been applied by an inkjet ejection method. In Step 1, the ejection interval between the aqueous ink and the overcoat liquid depends on the temperature of the inkjet head and the temperature of the printing substrate, but is preferably 0.1 second or more, more preferably 1 second or more, and, from the viewpoint of improving scratch resistance and water resistance, is 30 seconds or less. In Step 1, as the inkjet method for ejecting the aqueous ink and the overcoat liquid, the piezo method is preferable from the viewpoint of ejection properties.

[0104] The use equivalent ratio of Compound (II) calculated from the following formula is preferably 0.5 or more, more preferably 1 or more, still more preferably 2 or more, even more preferably 2.5 or more, even more preferably 3 or more, even more preferably 3.5 or more, even more preferably 4 or more, and, from the same viewpoint as above, is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, from the viewpoint of improving scratch resistance and water resistance. Use equivalent ratio of Compound (II) = 〔(Drop amount of overcoat liquid injected × Content of Compound (II) in overcoat liquid) / Equivalent of reactive group of Compound (II)〕 / 〔(Drop amount of aqueous ink injected × Content of binder resin (Ib) in aqueous ink × (Acid value of binder resin (Ib) / (56.11×1000)))〕 When the pigment dispersion resin (Ia) has a carboxy group, the carboxy group can also undergo a crosslinking reaction with Compound (II), but in the present invention, the use equivalent ratio of Compound (II) is calculated as the equivalent ratio of the reactive group of Compound (II) to the carboxy group of the binder resin (Ib).

[0105] In addition, the equivalent amount of Compound (II) used when another embodiment of the ink set for inkjet recording of the present invention is used is calculated by the following formula. The equivalent amount of Compound (II) used when another embodiment of the ink set for inkjet recording of the present invention is used is the same as when the above-described ink for inkjet recording of the present invention is used. Equivalent ratio of Compound (II) used = [(amount of aqueous ink droplet ejected × content of Compound (II) in aqueous ink) / equivalent of reactive group of Compound (II)] / [(amount of overcoat liquid droplet ejected × content of binder resin (Ib) in overcoat liquid × (acid value of binder resin (Ib) / (56.11 × 1000))]

[0106] Examples of the printing substrate include ordinary paper with high liquid absorbency, coated paper with low liquid absorbency, and non-liquid-absorbent resin films. From the viewpoints of abrasion resistance and water resistance, a low liquid absorbency printing substrate is preferable, one or more selected from the group consisting of coated paper and resin films is more preferable, and a resin film is even more preferable. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper. Examples of the resin film include one or more selected from the group consisting of polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. The surface for forming the printed image of the resin film may be corona-treated.

[0107] From the viewpoints of abrasion resistance and water resistance, the resin film is preferably a heat-shrinkable resin film that shrinks by heating. The heat-shrinkable resin film has molecular orientation by stretching an unstretched film formed by a known film-forming method, and does not shrink at room temperature but shrinks by heating. Examples of the heat-shrinkable resin film include polyester-based resins; styrene-based resins such as polystyrene and styrene-butadiene copolymers; polylactic acid; olefin-based resins such as polyethylene, polypropylene, and polyolefins; films composed of one or a mixture of two or more selected from the group consisting of thermoplastic resins such as vinyl chloride-based resins, and laminated films thereof. Examples of commercially available heat-shrinkable resin films include the "Space Screen" series (manufactured by Toyobo Co., Ltd.); the "DXL" series, "Hishipet" series, "PLABIO", "HybrexDL" (manufactured by Mitsubishi Chemical Corporation); the "Bonset" series (manufactured by Takiron Cea, Inc.); the "Fancy Wrap (PET)" series (manufactured by Gunze, Ltd.), and the like.

[0108] (Step 2) Step 2 is a step of heating the coating film of the aqueous ink and the coating film of the overcoat liquid on the printed substrate formed in Step 1. By this Step 2, the compound (II) contained in the overcoat liquid on the printed substrate is distributed to the coating film of the aqueous ink, and the crosslinking reaction between the carboxy group of the binder resin (Ib) and the reactive group of the compound (II) proceeds, so that a printed matter with uniform strength of the printed coating film can be obtained. Further, in the inkjet printing method of the present invention, when an inkjet set of another aspect of the present invention is used, by this Step 2, the compound (II) contained in the aqueous ink on the printed substrate is distributed to the coating film of the overcoat liquid, and the crosslinking reaction between the carboxy group of the binder resin (Ib) and the reactive group of the compound (II) proceeds, so that a printed matter with uniform strength of the printed coating film can be obtained. The heat treatment in Step 2 is preferably also a treatment for drying the coating film of the aqueous ink and the coating film of the overcoat liquid on the printed substrate formed in Step 1. Examples of the method of heat treatment in Step 2 include a method of spraying a gas adjusted to a desired temperature onto the coating film formed on the printed substrate, a method of passing the printed substrate having the coating film formed thereon through a gas atmosphere adjusted to a desired temperature, a method of irradiating the coating film formed on the printed substrate with an infrared heater, and a method of heating the printed substrate having the coating film formed thereon 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 the influence on the printed substrate, it is preferably 100°C or lower, more preferably 90°C or lower, and still more preferably 70°C or lower. The heating time is preferably 30 seconds or more, more preferably 1 minute or more, from the viewpoints of rub resistance and water resistance, and is preferably 10 minutes or less, more preferably 7 minutes or less, still more preferably 5 minutes or less, from the viewpoint of productivity.

[0109] [Packaging method] In the present invention, when the printed substrate is a heat-shrinkable resin film, the above ink set for inkjet printing is preferably used for the packaging method of the object to be packaged. As the packaging method, a method is preferable in which after arranging the printed matter obtained by the above inkjet printing method around the object to be packaged, 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, still more preferably 80°C or higher, from the viewpoint of productivity, and is preferably 200°C or lower, more preferably 150°C or lower, still more preferably 130°C or lower, even more preferably 110°C or lower, from the viewpoint of preventing the influence on the resin film substrate. This heating temperature is preferably below the temperature at which the printed matter can be used without problems even when shrinkage occurs. The heating time for shrinking is preferably 3 seconds or more, more preferably 5 seconds or more, still more preferably 7 seconds or more, from the viewpoint of shrinking the resin film substrate, and is preferably 5 minutes or less, more preferably 3 minutes or less, still more preferably 1 minute or less, from the viewpoint of productivity.

[0111] Regarding the above 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 a 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 crosslinking reaction with the carboxy group of the binder resin (Ib). An ink set for inkjet printing, wherein 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 a 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, the overcoat liquid contains a binder resin (Ib) having a carboxy group, An ink set for inkjet printing, wherein 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> above, 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> above, 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> above, wherein the reactive group equivalent of the compound (II) is 100 or more and 500 or less. <6> The ink set for inkjet printing according to any one of <1> to <5> above, wherein the compound (II) is at least one selected from the group consisting of a polyfunctional carbodiimide compound, a polyfunctional oxazoline compound, and a polyfunctional epoxy compound. <7> The ink set for inkjet printing according to any one of <1> to <6> above, wherein the compound (II) is a polyfunctional carbodiimide compound. <8> The inkjet printing ink set according to any one of <1> to <7>, wherein the binder resin (Ib) is at least one 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 inkjet printing ink set according to <8>, wherein the vinyl resin (Ib-1) is a (meth)acrylic resin containing a structural unit derived from at least one carboxy group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid and a structural unit derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. <10> The inkjet printing ink set according to <8> or <9>, wherein the weight average molecular weight of the vinyl resin (Ib-1) is 10,000 or more and 800,000 or less. <11> The inkjet printing ink set 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 inkjet printing ink set according to any one of <1> to <8>, wherein the binder resin (Ib) is an adduct of dimethylolpropionic acid, a polycarbonate polyol, and dicyclohexylmethane 4,4'-diisocyanate. <13> An inkjet printing ink set including an aqueous ink containing a pigment and an overcoat liquid substantially free of a pigment. The aqueous ink contains, as a binder resin (Ib) having a carboxy group, a (meth)acrylic resin containing a structural unit derived from at least one carboxy group-containing monomer selected from the group consisting of acrylic acid and methacrylic acid and a structural unit derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, and the weight average molecular weight of the (meth)acrylic resin is 10,000 or more and 800,000 or less. The overcoat liquid contains a polyfunctional carbodiimide compound as the compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib). 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. An ink set for inkjet printing. <14> An ink set for inkjet printing, comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of a pigment. The aqueous ink contains a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate as the binder resin (Ib) having a carboxy group, and the weight average molecular weight of the copolymer is 10,000 or more and 800,000 or less. The overcoat liquid contains a polyfunctional carbodiimide compound as the compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib). 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. An ink set for inkjet printing. <15> An ink set for inkjet printing, comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of a pigment. The aqueous ink contains a polyurethane resin (Ib-2) having a carboxy group as the binder resin (Ib) having a carboxy group. The overcoat liquid contains a polyfunctional carbodiimide compound as the compound (II) having a reactive group capable of undergoing a crosslinking reaction with the carboxy group of the binder resin (Ib). 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. An ink set for inkjet printing. <16> An ink set for inkjet printing, comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of the pigment. The aqueous ink contains an adduct obtained by polyaddition of dimethylolpropionic acid, a polycarbonate polyol, and dicyclohexylmethane 4,4'-diisocyanate as a binder resin (Ib) having a carboxy group. The overcoat liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of crosslinking reaction with the carboxy group of the binder resin (Ib). 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. An ink set for inkjet printing. <17> An inkjet printing method, comprising the following step 1 and step 2, using the ink set for inkjet printing according to any one of <1> to <16>. Step 1: A step of applying the aqueous ink to a heat-shrinkable resin film substrate by an inkjet ejection method, and then applying the overcoat liquid to the portion where the aqueous ink is applied by an inkjet ejection method. Step 2: A step of heating the coating film of the aqueous ink and the coating film of the overcoat liquid on the printed substrate formed in step 1. <18> A packaging method, in which a printed matter obtained by the inkjet printing method according to <17> is disposed around an object to be packaged, and then the heat-shrinkable resin film substrate of the printed matter is shrunk to obtain a package. <19> Use as an ink set for inkjet printing, comprising an aqueous ink containing a pigment and an overcoat liquid substantially free of the pigment. 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 reaction with the carboxy group of the binder resin (Ib). Use as an ink set for inkjet printing, wherein 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 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 the carboxy group of a binder resin (Ib) having a carboxy group, the overcoat liquid contains a binder resin (Ib) having a carboxy group, Use as an ink set for inkjet printing, wherein 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 <1> to <16>, having an inkjet head filled with the aqueous ink and an inkjet head filled with the overcoat liquid. <22> The inkjet printing apparatus according to <21>, further having a processing unit for heating the coating film of the aqueous ink and the coating film of the overcoat liquid on the printing substrate.

Examples

[0112] In the following production examples, preparation examples, examples and comparative examples, "parts" means "parts by mass" unless otherwise specified. The measurements of various physical properties were carried out by the following methods.

[0113] [Measurement of acid value of resin] Using a potentiometric automatic titrator (manufactured by Kyoto Electronics Industry Co., Ltd., motor-driven burette, model number: APB-610), the resin was dissolved in a titration solvent obtained by mixing toluene and acetone [toluene:acetone = 2:1 (volume ratio)], and titrated with a 0.1N potassium hydroxide / ethanol solution. The inflection point on the titration curve was taken as the end point. The acid value (mgKOH / g) was calculated from the titration volume up to the end point of the potassium hydroxide solution.

[0114] [Measurement of the number-average molecular weight and weight-average molecular weight of the resin] It was determined by gel permeation chromatography. The measurement conditions are shown below. GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 0.5 mL / min Standard substances: 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)" (manufactured by Tosoh Corporation as above) For the measurement sample, 0.1 g of the polymer was mixed with 10 mL of the above eluent in a glass vial, stirred with a magnetic stirrer at 25 °C for 10 hours, and the filtered solution using a syringe filter "DISMIC-13HP" (manufactured by Advantec Co., Ltd., pore size: 0.2 μm, material: PTFE) was used.

[0115] [Measurement of the average particle diameter of pigment-containing resin particles in the aqueous dispersion and the average particle diameter of resin particles not containing pigment in the aqueous dispersion] Cumulant analysis was performed using a laser particle analysis system ("ELS-8000" manufactured by Otsuka Electronics Co., Ltd.) to measure the average particle diameter. The dispersion diluted with water was used so that the concentration of the particles to be measured was 5×10 -3 mass% (in terms of solid content concentration). The measurement conditions were a temperature of 25 °C, an angle of 90° between the incident light and the detector, and an integration count of 100 times. The refractive index of water (1.333) was input as the refractive index of the dispersion medium, and the obtained cumulant average particle diameter was taken as the average particle diameter of the pigment-containing resin particles in the aqueous dispersion or the average particle diameter of the resin particles not containing pigment in the aqueous dispersion.

[0116] [Measurement of solid content concentration] Using an infrared moisture meter (manufactured by Kett Scientific Laboratory Co., Ltd., "FD-230"), 5 g of the measurement sample was dried under the conditions of a drying temperature of 150°C and a measurement mode of 96 (monitoring time: 2.5 minutes / variation width: 0.05%). After that, 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 the measurement sample

[0117] [Measurement of the surface tension γ(A) of the aqueous ink and the surface tension γ(B) of the overcoat liquid] Using a surface tension meter (manufactured by Kyowa Interface Science Co., Ltd., "CBVP-Z"), a platinum plate was immersed in a cylindrical polyethylene container (diameter: 3.6 cm × depth: 1.2 cm) containing 5 g of the aqueous ink or overcoat liquid adjusted to 20°C, and the static surface tension at 20°C was measured by the Wilhelmy method. The surface tension γ(A) of the aqueous ink or the surface tension γ(B) of the overcoat liquid was obtained.

[0118] [Measurement of the viscosity of the aqueous ink] Using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., "TV-25", standard cone rotor 1°34’×R24, rotation speed: 50 rpm), the viscosity of the aqueous ink at 32°C was measured.

[0119] [Measurement of the pH of the aqueous ink] Using a desktop pH meter (manufactured by Horiba, Ltd., "F-71") with a pH electrode (manufactured by Horiba, Ltd., "6337-10D"), the pH of the aqueous ink at 25°C was measured.

[0120] [Measurement of the water absorption amount of the printing substrate at a contact time of 100 msec between the printing substrate and pure water] Using an automatic scanning liquid absorber (manufactured by Kumagai Riki Kogyo Co., Ltd., "KM500win"), the transfer amount at a contact time of 100 msec of pure water was measured under the conditions of 23°C and a relative humidity of 50%, and the water absorption amount at 100 msec was obtained. The measurement conditions are shown below. "Spiral Method" Contact Time (seconds): 0.010~1.0 Pitch (mm): 7 Length Per Sampling(degree):86.29 Start Radius(mm):20 End Radius(mm):60 Min Contact Time(m seconds):10 Max Contact Time(m seconds):1,000 Sampling Pattern(1~50):50 Number of Sampling Points(>0):19 「Square Head」 Slit Span(mm):1 Slit Width(mm):5

[0121] 〔Production of Pigment Dispersing Resin (Ia)〕 Production Example 1-1 (Production of Water-insoluble Polymer (a1) Having Carboxy Group) 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of styrene macromonomer (“AS-6S” manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solid 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 solution. 18 parts of methyl ethyl ketone (hereinafter referred to as “MEK”), 0.03 part of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture solution were placed in a reaction vessel and mixed, and sufficient nitrogen gas substitution was carried out. On the other hand, 90% (103.5 parts) of the remaining monomer mixture, 0.27 part of the chain transfer agent, 42 parts of MEK, and 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fuji Film Wako Pure Chemical Corporation) as a polymerization initiator were mixed, and the resulting mixture was placed in a dropping funnel. While stirring the mixture in the reaction vessel under a nitrogen atmosphere, the temperature was raised to 75°C, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours had elapsed at 75°C from the end of the addition, a solution prepared by dissolving 3 parts of the polymerization initiator 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. Then, 50 parts of MEK were added to obtain a solution of a water-insoluble polymer (a1) having a carboxy group (weight average molecular weight: 50,000). The solid content concentration of the solution of the water-insoluble polymer (a1) having a carboxy group was 45% by mass.

[0122] [Production of Aqueous Dispersion of Pigment-Containing Resin Particles] Production Example 2-1 (Production of Aqueous Dispersion (D1) of White Pigment-Containing Resin Particles) Into a 250 mL polyethylene bottle, a mixture prepared by previously mixing and dissolving 0.3 g of polyacrylic acid (PAA; manufactured by Fuji Film Wako Pure Chemical Corporation, Mw: 5,000 (catalog value)) as a pigment dispersion resin (Ia), 0.21 g of a 5N aqueous sodium hydroxide solution (sodium hydroxide solid content 16.9% by mass, manufactured by Fuji Film Wako Pure Chemical Corporation), and 1 g of ion-exchanged water was introduced. Next, 15 g of titanium oxide (rutile type, "KURONOSKR-380" manufactured by Titanium Industry Co., Ltd., Al·Si-treated, average primary particle diameter: 355 nm (catalog value 300 - 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 dispersion was carried out at 250 rpm for 8 hours using a tabletop pot mill stand (manufactured by AS ONE Corporation). Thereafter, the zirconia beads were removed using a mesh, and the solid content concentration was adjusted with water to obtain an aqueous dispersion (D1) of white pigment-containing resin particles (solid content concentration: 30% by mass, mass ratio [pigment / (pigment + pigment dispersion resin (Ia))]: 0.98). The average particle diameter 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 a solution of the water-insoluble polymer (a1) having a carboxy group obtained in Production Example 1-1 as the pigment-dispersing resin (Ia) and 53.9 parts of MEK were mixed, and 15.0 parts of a 5N aqueous sodium hydroxide solution, 0.5 part of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water were added thereto as neutralizing agents. Further, 100 parts of C.I. Pigment Black 7 (P.B.7, manufactured by Cabot Corporation) as a black pigment was added to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed at 7,000 rpm for 1 hour under the conditions of 20 °C using a dispersing blade, and then subjected to a dispersion treatment at a pressure of 180 MPa for 15 passes using a high-pressure homogenizer "Microfluidizer M-140K" (manufactured by Microfluidics) to obtain a dispersion-treated product. The obtained dispersion-treated product was removed of MEK at 60 °C under reduced pressure, and further a part of water was removed, followed by centrifugation. The liquid layer portion was recovered and filtered through a filter "Mini Sartorius Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion of black pigment-containing polymer particles. The solid content concentration was 25% by mass. To 100 parts of the obtained aqueous dispersion of black pigment-containing polymer particles, 0.45 part of trimethylolpropane polyglycidyl ether ("Denacol EX-321L", epoxy equivalent 130, manufactured by Nagase ChemteX Corporation) as a crosslinking agent and 15.23 parts of ion-exchanged water were added, and heat treatment was performed at 70 °C for 3 hours while stirring. After cooling to room temperature, the liquid layer portion was recovered and filtered through a filter "Mini Sartorius 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% by mass, mass ratio [pigment / (pigment + pigment-dispersing resin (Ia) having a crosslinked structure)]: 0.69). The average particle diameter of the black pigment-containing polymer particles in the obtained aqueous dispersion K was 100 nm.

[0124] 〔Production of an Aqueous Dispersion of Resin Particles Containing No Pigment and Composed of Binder Resin (Ib)〕 Production Example 3-1 (Production of an Aqueous Dispersion (d1) of Acrylic Resin Particles Containing No Pigment) Into a reaction vessel equipped with a dropping funnel, the monomers shown in the "Initial Charge Monomer Solution" in Table 1, sodium polyoxyethylene alkyl ether sulfate (Kao Corporation's "Latemul E-118B") (hereinafter referred to as "Latemul E-118B") as an emulsifier, potassium persulfate as a polymerization initiator, and ion-exchanged water were added and mixed, and nitrogen gas substitution was performed to obtain an initial charge monomer solution. Separately, the monomers, emulsifier, polymerization initiator, and ion-exchanged water shown in the "Dropping Monomer Solution" in Table 1 were mixed to obtain a dropping monomer solution. Then, the dropping monomer solution was placed in a dropping funnel and nitrogen gas substitution was performed. Under a nitrogen atmosphere, while stirring the initial charge monomer solution in the reaction vessel, the temperature was raised from room temperature to 80 °C over 30 minutes, and while maintaining at 80 °C, the dropping monomer solution in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After completion of the dropping, stirring was carried out for 1 hour while maintaining the temperature in the reaction vessel. Then, filtration was performed through a 200-mesh sieve to obtain an aqueous dispersion (d1) of acrylic resin particles containing no pigment (solid content concentration: 44.1 mass%, acid value: 16 mgKOH / g, weight average molecular weight of acrylic resin: 750,000, average particle size: 95 nm).

[0125]

Table 1

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

[0127] 〔Production of Aqueous Ink〕 Ink Production Example 1 (Production of Aqueous Ink W-1) 34.00 g of an aqueous dispersion (D1) of white pigment-containing resin particles obtained in Production Example 2-1 (solid content concentration: 30% by mass), 12.81 g of an aqueous dispersion (d1) of acrylic resin particles not containing a pigment obtained in Production Example 3-1 (solid content concentration: 44.1% by mass), 30.00 g of propylene glycol (hereinafter referred to as "PG"), 3.00 g of diethylene glycol mono isobutyl ether (manufactured by Nippon Emulsifier Co., Ltd.) (hereinafter referred to as "iBDG"), 1.00 g of an acetylene glycol-based surfactant "Surfinol 440" (manufactured by Nissin Chemical Industry Co., Ltd., EO (3.5 mol) adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB value: 8 (catalog value), active ingredient 100% by mass), 1.00 g of a polyether-modified silicone-based 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 was added so that the total amount became 100.00 g. The obtained mixed solution was filtered through a filter "Mini Sartorius Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain an aqueous ink W-1 (viscosity: 5.6 mPa·s, pH: 8.2).

[0128] Ink Production Examples 2 to 4 (Production of Aqueous Inks W-2, K-1, and W-3) Ink Production Example 1 was repeated except that the composition shown in Table 2 was changed to obtain each aqueous ink.

[0129]

Table 2

[0130] Preparation Examples 1 to 12 (Preparation of Overcoat Liquids OC-1 to OC-12) The components were mixed according to the composition shown in Table 3, and the obtained mixed solution was filtered through a filter "Mini Sartorius Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain each overcoat liquid. Each notation in Tables 2 and 3 is as follows. (Compound (II)) [Polyfunctional Carbodiimide Compound] Carbodilite E-07S: Polyvalent carbodiimide compound (carbodiimide group equivalent: 234, active ingredient: 40% by mass, manufactured by Nisshinbo Chemical Inc.) Carbodilite E-02: Carbodiimide group-containing polymer (carbodiimide group equivalent: 445, emulsion / dispersion type, active ingredient: 40% by mass, manufactured by Nisshinbo Chemical Inc.) Carbodilite E-05: Carbodiimide group-containing polymer (carbodiimide group equivalent: 313, emulsion / dispersion type, active ingredient: 40% by mass, manufactured by Nisshinbo Chemical Inc.) [Polyfunctional oxazoline compound] Epocros WS-700: Oxazoline group-containing polymer (oxazoline group equivalent: 220, polymer main chain: acrylic, number average molecular weight: 20,000, water-soluble type, active ingredient: 25% by mass, manufactured by Nippon Shokubai Co., Ltd.) [Polyfunctional epoxy compound] Denacol EX-212: 1,6-Hexanediol diglycidyl ether (epoxy group equivalent: 151, active ingredient: 100% by mass, manufactured by Nagase ChemteX Corporation) (Surfactant) Surfynol 420: Acetylene glycol-based 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 Nisshin Chemical Industry Co., Ltd.) KF-6011: Polyether-modified silicone-based surfactant (PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value), manufactured by Shin-Etsu Chemical Co., Ltd.)

[0131]

Table 3

[0132] Examples 1 to 13 and Comparative Example 1 Using the combinations of the aqueous ink and the overcoat liquid shown in Table 4 as ink sets, and using the heat-shrinkable PET film "Space Screen SP809" (manufactured by Toyobo Co., Ltd., heat shrinkage rate (90 °C, 10 seconds): 50%, water absorption: 10 g / m2 Using the following, printed matter was produced by the following method, and the following evaluation was performed on each of the obtained printed matters. The results are also shown in Table 4.

[0133] (Inkjet printing) [Inkjet printing conditions] A printing evaluation apparatus equipped with three inkjet heads ("KJ4B-HD06MHG-STDV" manufactured by Kyocera Corporation, piezo type) and an underheater for heating the printing substrate from the back side of the surface of the printing substrate facing the inkjet heads was filled with aqueous ink in the first two inkjet heads in the front row and overcoat liquid in the inkjet head in the last row. The distance between the underheater and the printing substrate was set to 0.2 mm, the distance between the inkjet head 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 temperature 25±1°C and relative humidity 30±5%, a head application voltage of 26 V, a head drive frequency of 10 kHz, a head temperature of 32°C, a head resolution of 600 dpi, a pre-discharge flushing number of 200 shots, and a negative pressure of -4.0 kPa were set, and the printing substrate was fixed to the printing evaluation apparatus in a direction such that the longitudinal direction and the conveyance direction of the printing substrate were the same. The appropriate discharge amounts of the discharged liquids of the first two inkjet heads filled with aqueous ink were each set to 12 pL, and the appropriate discharge amount of the discharged liquid of the inkjet head in the last row filled with overcoat liquid was set to 5 pL. [Step 1] A printing command was transferred to the printing evaluation apparatus, and aqueous ink and overcoat liquid were discharged in the order of aqueous ink and overcoat liquid, and the solid image of the overcoat liquid was overprinted on the same location as the solid image of the aqueous ink. The discharge interval between the aqueous ink and the overcoat liquid was set to 1 second. In the examples and comparative examples, the use equivalent ratio of compound (II) calculated by the following formula is shown in Table 4. (In the case of Examples 1 to 11 and Comparative Example 1) Usage equivalent ratio of compound (II) = 〔(Overcoat liquid injection drop volume (5 pl) × Content of compound (II) in overcoat liquid) / Equivalent weight of reactive group of compound (II)〕 / 〔(Aqueous ink injection drop volume (24 pL) × Content of binder resin (Ib) in aqueous ink × (Acid value of binder resin (Ib) / (56.11 × 1000)))〕 (In the case of Example 12) Usage equivalent ratio of compound (II) = 〔(Aqueous ink injection drop volume × Content of compound (II) in aqueous ink) / Equivalent weight of reactive group of compound (II)〕 / 〔(Overcoat liquid injection drop volume × Content of binder resin (Ib) in overcoat liquid × (Acid value of binder resin (Ib) / (56.11 × 1000)))〕 〔Step 2〕 Next, the printed matter was obtained by heat-treating and drying it in a warm air dryer at 60 °C for 1 minute. 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〕 For each of the obtained printed matters, while measuring the load at the fingertip during the abrasion test with a mass measuring instrument ("GX-6100" manufactured by A&D Company, Limited), a load of 300 g was applied with the tip of the index finger and rubbed, and the surface state after reciprocating the printed surface 50 times was visually confirmed, and the abrasion resistance was evaluated according to the following evaluation criteria. (Evaluation criteria) A: No change on the entire surface B: No change in more than 90% of the target area C: No change in more than 70% of the target area D: More than 50% change in the target area If the evaluation is C or higher, there is no practical problem with the abrasion resistance.

[0135] 〔Evaluation of water resistance of printed matter before shrinkage〕 Each obtained printed matter was cut into test pieces of 3×3 cm, and the test pieces were immersed in ion-exchanged water contained in a screw tube manufactured by Maru EM Co., Ltd., and left at room temperature for 24 hours. Then, the test pieces of the printed matter were taken out from the screw tube, and while measuring the load with a fingertip using a mass measuring instrument ("GX-6100" manufactured by A&D Co., Ltd.), a load of 300 g was applied with the tip of the index finger and rubbed, and the surface state after reciprocating the printed surface 10 times was visually confirmed, and the abrasion resistance was evaluated according to the evaluation criteria shown below. (Evaluation Criteria) A: No change on the entire surface B: No change in more than 90% of the target area C: No change in more than 70% of the target area D: Change in more than 50% of the target area If the evaluation is C or higher, there is no practical problem with water resistance.

[0136] (Preparation of Shrunken Printed Matter) Samples were prepared using each obtained printed matter in accordance with the test described in JIS Z 1709-1995. The samples were cut out such that the solid image portion of the printed matter had a winding direction MD (vertical) of 100 mm and a width direction TD (horizontal) of 100 mm. The heat medium liquid in the above standard was changed to water, and the sample was immersed in hot water heated to 90°C for 10 seconds for thermal shrinkage, and then immersed in normal temperature water for 5 seconds for cooling. After this sample was left to stand and dried for 24 hours in an environment of 23°C and 50% humidity, the same abrasion resistance and water resistance tests as those of the printed matter before shrinkage were carried out.

[0137]

Table 4

[0138] From Table 4, it can be seen that the ink sets of the examples are particularly excellent in the abrasion resistance and water resistance of the thermally shrunk printed matter as compared with the comparative examples. In Examples 1 to 4, the type and blending amount of the surfactant contained in the overcoat liquid were changed to adjust the surface tension γ(B) of the overcoat liquid. However, the abrasion resistance and water resistance before shrinkage were both evaluated as the same "A". Also, in Examples 1 to 4, the abrasion resistance and water resistance after shrinkage improved as the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink increased. From this, the results of the abrasion resistance and water resistance of the printed matter after shrinkage in Examples 1 to 4 are not due to the change in the type and blending amount of the surfactant, but due to the occurrence of Marangoni convection due to the difference Δγ between the surface tension γ(B) of the overcoat liquid and the surface tension γ(A) of the aqueous ink. The compound (II) having a reactive group contained in the coating film of the overcoat liquid is uniformly distributed in the coating film of the aqueous ink, and a uniform crosslinking reaction between the carboxy group of the binder resin (Ib) and the reactive group of the compound (II) is promoted, resulting in a printed matter with uniform strength of the printed coating film. It is considered that this is why a printed matter could be obtained. Also, in Example 13, the aqueous ink contains a compound (II) having a reactive group capable of crosslinking with the carboxy group of the binder resin (Ib) having a carboxy group, and the overcoat liquid is an ink set containing the binder resin (Ib) having a carboxy group. It can be seen that in this ink set as well, the abrasion resistance and water resistance of the printed matter after heat shrinkage can be improved.

Industrial Applicability

[0139] According to the present invention, an inkjet printing ink set, an inkjet printing method, and a packaging method capable of improving the abrasion resistance and water resistance of a printed matter after heat shrinkage in printing on a heat-shrinkable resin film can be provided.

Claims

1. This is an inkjet printing method using an inkjet printing ink set that includes a water-based ink containing pigment and an overcoat liquid that substantially does not contain pigment. The aqueous ink contains a binder resin (Ib) having a carboxyl group, The overcoat liquid contains compound (II) having a reactive group that can crosslink with the carboxyl group of the binder resin (Ib), The surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink, and the inkjet printing method includes the following step 1: Step 1: After applying a water-based ink to a printing substrate using an inkjet ejection method, the overcoat liquid is applied to the portion where the water-based ink has been applied using an inkjet ejection method. An inkjet printing method in which the discharge interval between the water-based ink and the overcoat liquid is 0.1 seconds or more and 30 seconds or less.

2. An inkjet printing method using an ink set for inkjet printing, comprising a water-based ink containing a pigment and an overcoat liquid substantially free of pigment. The aqueous ink contains a binder resin (Ib) having a carboxyl group, The overcoat liquid contains compound (II) having a reactive group that can crosslink with the carboxyl group of the binder resin (Ib), An inkjet printing method wherein the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the aqueous ink, and the inkjet printing method includes the following steps 1 and 2. Step 1: The water-based ink is applied to a heat-shrinkable resin film substrate by an inkjet ejection method, and then the overcoat liquid is applied to the portion to which the water-based ink has been applied by an inkjet ejection method. Step 2: A step of heating the water-based ink coating and the overcoat liquid coating on the heat-shrinkable resin film substrate formed in Step 1.

3. The inkjet printing method 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 aqueous ink is 1.5 mN / m or more.

4. The inkjet printing method according to claim 1 or 2, wherein the reactive group equivalent of compound (II) is 100 or more and 500 or less.

5. The inkjet printing method according to claim 1 or 2, wherein the compound (II) is a polyfunctional carbodiimide compound.

6. The binder resin (Ib) is a vinyl resin (Ib-1) having a carboxyl group, The inkjet printing method according to claim 1 or 2, wherein the vinyl resin (Ib-1) is a (meth)acrylic resin comprising a constituent unit derived from one or more carboxyl group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and a constituent unit derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms.

7. The inkjet printing method according to claim 6, wherein the weight-average molecular weight of the vinyl resin (Ib-1) is 10,000 or more and 800,000 or less.

8. A packaging method comprising arranging a printed material obtained by the inkjet printing method described in claim 2 around a package to be packaged, and then shrinking the heat-shrinkable resin film substrate of the printed material to obtain a package.

9. This ink set for inkjet printing includes a water-based ink containing pigment and an overcoat liquid that is substantially free of pigment. The aqueous ink contains a binder resin (Ib) having a carboxyl group, The overcoat liquid contains compound (II) having a reactive group that can crosslink with the carboxyl group of the binder resin (Ib), An inkjet printing ink set in which the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the water-based ink, and the surface tension γ(B) is 33 mN / m or more.

10. An inkjet printing apparatus for use in the inkjet printing method according to claim 1 or 2, comprising an inkjet head filled with the aqueous ink and an inkjet head filled with the overcoat liquid.

11. The inkjet printing apparatus according to claim 10, further comprising a processing unit for heating the water-based ink coating film and the overcoat liquid coating film on the printing substrate.

12. Use as an inkjet printing ink set comprising a water-based ink containing a pigment and an overcoat liquid substantially free of pigment, The aqueous ink contains a binder resin (Ib) having a carboxyl group, The overcoat liquid contains compound (II) having a reactive group that can crosslink with the carboxyl group of the binder resin (Ib), Use as an inkjet printing ink set in which the surface tension γ(B) of the overcoat liquid is greater than the surface tension γ(A) of the water-based ink, and the surface tension γ(B) is 33 mN / m or more.