Inkjet printing method

Abstract

To provide an inkjet printing method which suppresses cracking of a printed coating film after heat shrinkage in printing on a heat-shrinkable resin film substrate.SOLUTION: There is provided an inkjet printing method in which a step 2 is performed after the following step 1 by using an aqueous ink containing a resin (a) having a carboxyl group and an overcoating liquid containing a compound (b) having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond. Step 1: After applying the aqueous ink to a heat-shrinkable resin film substrate using a head (1) by an inkjet ejection method, applying the overcoating liquid to a portion to which the aqueous ink was applied using a head (2) having a resolution lower than the resolution of the head (1) by an inkjet ejection method. Step 2: heating a coating film containing the aqueous ink on the heat-shrinkable resin film substrate and the overcoating liquid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet printing method and a packaging method using a printed matter obtained by the printing method. [Background technology]

[0002] In the fields of commercial printing and industrial printing, in addition to printing on conventional highly liquid-absorbent printing substrates such as plain paper and copy paper, there is a growing demand for printing on low-liquid-absorbent printing substrates such as offset coated paper, and non-liquid-absorbent printing substrates such as resin films made of polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene, nylon, etc. However, when printing on low-absorbent or non-absorbent printing substrates, the liquid components are absorbed slowly or not at all, so the adhesion of the pigment ink to these printing substrates is insufficient, and the image fastness of the printed matter tends to be low. Therefore, in order to improve the image fastness of printed matter using pigment inks, aqueous compositions such as coating liquids to be used in combination with pigment inks 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, with the objective of improving the abrasion resistance, solvent resistance, and substrate adhesion of printed matter; an inkjet recording ink set containing the aqueous composition and a water-based ink; and an inkjet recording method using the aqueous composition and the water-based ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-189867 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, as in Patent Document 1, there have been examples in which a crosslinking agent such as a blocked isocyanate compound, a carbodiimide compound, or an oxazoline compound is printed as an overcoat liquid and heated to promote the crosslinking reaction. However, when printing on heat-shrinkable resin film substrates, which are widely used as packaging substrates for PET bottles and the like, it has been found that the printed coating film is very hard after the crosslinking reaction, and cracks and peeling off may occur in the printed coating film when the heat-shrinkable resin film substrate shrinks. An object of the present invention is to provide an inkjet printing method that, when printing on a heat-shrinkable resin film substrate, prevents cracks from occurring in the printed coating film after heat shrinkage. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by using an aqueous ink containing a resin (a) having a carboxy group and an overcoat liquid containing a compound (b) having two or more reactive groups capable of reacting with the carboxy group of the resin (a) to form a chemical bond, applying the aqueous ink to a heat-shrinkable resin film substrate by an inkjet ejection method using an inkjet head (1), and then applying the overcoat liquid to the area to which the aqueous ink has been applied by an inkjet ejection method using an inkjet head (2) having a resolution lower than that of the inkjet head (1), and then heating the coating film containing the aqueous ink and the overcoat liquid on the film substrate.

[0007] That is, the present invention relates to the following [1] to

[11] . [1] A water-based ink containing a resin (a) having a carboxy group; an overcoat solution containing a compound (b) having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond; An inkjet printing method in which step 2 is carried out after step 1 below. Step 1: A step of applying the water-based ink to a heat-shrinkable resin film substrate by inkjet ejection using a head (1), and then applying the overcoat liquid to the area where the water-based ink has been applied by inkjet ejection using a head (2) having a resolution lower than that of the head (1). Step 2: Heating the coating film containing the water-based ink and the overcoat liquid on the heat-shrinkable resin film substrate [2] The inkjet printing method according to [1], wherein the compound (b) is at least one selected from the group consisting of a polyfunctional carbodiimide compound, a polyfunctional oxazoline compound, and a polyfunctional epoxy compound. [3] The inkjet printing method according to [1] or [2], wherein the printing area of ​​the overcoat liquid is equal to or smaller than the printing area of ​​the water-based ink. [4] The water-based ink is applied onto an image formed on the substrate, The inkjet printing method according to any one of [1] to [3], wherein the water-based ink is a white ink or a clear ink. [5] The inkjet printing method according to any one of [1] to [4], wherein the resolution of the head (2) is 600 dpi or less. [6] The inkjet printing method according to any one of [1] to [5], wherein the difference between the resolution of the head (1) and the resolution of the head (2) is 200 dpi or more. [7] The inkjet printing method according to any one of [1] to [6], wherein the resin (a) is a vinyl resin. [8] The inkjet printing method according to any one of [1] to [7], wherein the overcoat liquid is substantially free of pigment. [9] A water-based ink containing a resin (a) having a carboxy group; an overcoat solution containing a compound (b) having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond; A method for manufacturing printed matter in which step 2 is carried out after step 1 below. Step 1: A step of applying the water-based ink to a heat-shrinkable resin film substrate by inkjet ejection using a head (1), and then applying the overcoat liquid to the area where the water-based ink has been applied by inkjet ejection using a head (2) having a resolution lower than that of the head (1). Step 2: Heating the coating film containing the water-based ink and the overcoat liquid on the heat-shrinkable resin film substrate

[10] A packaging method, comprising: placing a printed matter obtained by the inkjet printing method according to any one of [1] to [8] around an article to be packaged; and then shrinking the heat-shrinkable resin film substrate of the printed matter to obtain a package.

[11] A method for producing a package, comprising arranging a printed matter obtained by the inkjet printing method according to any one of [1] to [8] around a package, and then shrinking the heat-shrinkable resin film substrate of the printed matter. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an inkjet printing method that is excellent in suppressing the occurrence of cracks in the printed coating film after heat shrinkage when printing on a heat-shrinkable resin film substrate, and a packaging method using a printed matter obtained by the printing method. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Inkjet printing method] The inkjet printing method of the present invention (hereinafter also simply referred to as the "printing method") uses an aqueous ink containing a resin (a) having a carboxy group and an overcoat liquid containing a compound (b) having two or more reactive groups capable of reacting with the carboxy group of the resin (a) to form a chemical bond, and performs the following step 2 after step 1. Step 1: A step of applying a water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method using a head (1) (inkjet head (1)), and then applying an overcoat liquid to the area where the water-based ink has been applied by an inkjet ejection method using a head (2) (inkjet head (2)) having a resolution lower than that of the head (1). Step 2: Heating the coating film containing the water-based ink and overcoat liquid on the heat-shrinkable resin film substrate

[0010] The definitions of various terms used in this specification are shown below. The term "water-based" in water-based ink means that water accounts for the largest proportion by mass of the medium contained in the water-based ink. The term "low liquid absorption" in the context of a low liquid absorption resin film substrate is a concept that encompasses both low liquid absorption and non-liquid absorption, and refers to the resin film substrate having a water absorption of 0 g / m when the resin film substrate is in contact with pure water for 100 ms. 2 More than 10g / m 2 The water absorption amount can be measured by the method described in the Examples. "Printing" is a concept that includes printing and printing out characters and images, and "printed matter" is a concept that includes printed matter and printed out matter on which characters and images are recorded. "(Meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. The term "(meth)acrylate" refers to at least one selected from the group consisting of acrylate and methacrylate.

[0011] According to the present invention, it is possible to provide an inkjet printing method that is excellent in suppressing cracking of the printed coating film after heat shrinkage when printing on a heat-shrinkable resin film substrate. The reason for this is not clear, but is thought to be as follows. In the present invention, an aqueous ink containing a resin (a) having a carboxy group is applied to a heat-shrinkable resin film substrate, and then an overcoat liquid containing a compound (b) having two or more reactive groups capable of reacting with the carboxy group of the resin (a) to form a chemical bond is applied to the area where the aqueous ink was applied. In this process, the resolution of the inkjet head (2) that applies the overcoat liquid is lower than the resolution of the inkjet head (1) that applies the aqueous ink. This results in areas with high and low concentrations of compound (b) in the coating film containing the aqueous ink and the overcoat liquid on the heat-shrinkable resin film substrate. As a result, a crosslinking reaction occurs between the carboxy group of the resin (a) and the reactive group of the compound (b), resulting in areas with high and low crosslinking in the resulting printed coating. When this printed material is heat-shrunk, selective shrinkage occurs in the low-crosslinked areas, which is thought to relieve stress within the printed coating and prevent cracking of the printed coating.

[0012] [Water-based ink] The water-based ink according to the present invention contains a resin (a) having a carboxy group. The water-based ink may contain a pigment, and the water-based ink according to the present invention may be a black ink, a white ink, a clear ink, or any other colored ink. When the water-based ink contains a pigment, the water-based ink may be used alone in one color tone, or in a combination of two or more different colors.

[0013] (Carboxylic acid group-containing resin (a)) The water-based ink according to the present invention contains a resin (a) (hereinafter simply referred to as "resin (a)") having a carboxyl group (-COOM). The carboxyl group is a group that exhibits acidity by dissociating and releasing a hydrogen ion, or a group in the dissociated ionic form (-COOM). - In the carboxy group (-COOM), M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0014] Examples of the polymer skeleton of resin (a) 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" refers to acrylic or methacrylic. Furthermore, when resin (a) 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 suppressing cracking of the printed coating film after thermal shrinkage, resin (a) is preferably at least one selected from the group consisting of vinyl resins, polyurethane resins, and polyester resins, and more preferably a vinyl resin.

[0015] When the resin (a) is a vinyl resin, examples of the resin (a) include a homopolymer of a carboxy group-containing monomer, a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, and a copolymer of a carboxy group-containing monomer, a hydrophobic monomer, and a nonionic monomer. Here, the hydrophobic monomer is a monomer that dissolves in an amount of less than 10 g when dissolved in 100 g of ion-exchanged water at 25° C. until saturated. The nonionic monomer is a monomer that has a high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxy group or a polyalkylene glycol chain.

[0016] Examples of the carboxy group-containing monomer include vinyl aromatic carboxylic acids such as (meth)acrylic acid and vinylbenzoic acid, with (meth)acrylic acid being preferred. The carboxyl group-containing monomers can be used singly or in combination of two or more.

[0017] Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number average molecular weight of from 500 to 100,000. Among these, 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 from 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 from 1 to 22 carbon atoms and aromatic group-containing monomers, even more preferably a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, still more preferably a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, and still more preferably a (meth)acrylate having an alkyl group having from 1 to 8 carbon atoms. The hydrophobic monomers can be used singly or in combination of two or more.

[0018] Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. The nonionic monomers can be used singly or in combination of two or more.

[0019] Resin (a) preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, and even more 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 a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 8 carbon atoms, and even more preferably a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0020] From the viewpoint of suppressing cracking of the printed coating film after heat shrinkage, the acid value of resin (a) is preferably 3 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more, and from the same viewpoint as above, it is preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, and even more preferably 20 mgKOH / g or less. The acid value of resin (a) can be determined by the method described in the Examples, but it can also be determined by calculation from the mass ratio of the constituent monomers.

[0021] When the resin (a) is a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, the content of the constituent units derived from each monomer component in the resin (a) is as follows. The content of structural units derived from carboxyl group-containing monomers in resin (a) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The content of structural units derived from hydrophobic monomers in resin (a) is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 99.5% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less. The content of the constituent units derived from each monomer component in the resin (a) can be measured by a known method such as NMR. Furthermore, when the resin (a) is produced by polymerizing raw material monomers including a carboxyl group-containing monomer and a hydrophobic monomer, the polymerization proceeds almost quantitatively, and therefore the carboxyl group-containing monomer and the hydrophobic monomer in the raw material monomers can also be used as the content of the constituent units derived from each monomer component in the resin (a).

[0022] The weight average molecular weight of resin (a) is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, still more preferably 50,000 or more, and even more preferably 100,000 or more from the viewpoint of suppressing cracking of the printed coating film after heat shrinkage, and from the same viewpoint as above, is preferably 1,500,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less. The weight average molecular weight can be measured by the method described in the Examples.

[0023] Resin (a) is produced by polymerizing raw material monomers by a known polymerization method, preferably emulsion polymerization or suspension polymerization, more preferably emulsion polymerization.

[0024] From the viewpoint of ink storage stability, the average particle size of the resin (a) particles in the water-based ink is preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more, still more preferably 70 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and still more preferably 130 nm or less. The average particle size of the resin (a) particles in the water-based ink is measured by the method described in the Examples.

[0025] The resin (a) is preferably used as resin particles containing no pigment, and from the viewpoint of improving the productivity of the water-based ink, it is preferably blended into the water-based ink as an aqueous dispersion of polymer particles containing no pigment. The resin (a) may be appropriately synthesized or may be a commercially available product.

[0026] Commercially available aqueous dispersions of pigment-free resin (a) include acrylic resins such as "Neocryl A-1127" (trade name, anionic self-crosslinking waterborne acrylic resin, manufactured by DSM Coating Resins), "Joncryl 390," "Joncryl 7100," "Joncryl 7600," "Joncryl 537J," "Joncryl PDX-7164," "Joncryl 538J," and "Joncryl 780" (trade names, manufactured by BASF Japan Ltd.); styrene / butadiene resins such as "SR-100" and "SR102" (all trade names, manufactured by Nippon A&L Inc.); and vinyl chloride resins such as "Vinyblan 700" and "Vinyblan 701" (trade names, manufactured by Nissin Chemical Industry Co., Ltd.).

[0027] The content of resin (a) in the water-based ink is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.

[0028] (pigment) When the water-based ink contains a pigment, the pigment may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may also be used in combination with extender pigments. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the 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 CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0029] When the aqueous ink contains a pigment, the pigment is dispersed in a medium. The pigment in the aqueous ink according to the present invention may be dispersed using a resin (hereinafter also referred to as a "pigment dispersion resin") or a surfactant as a dispersant, or may be a self-dispersed pigment dispersed without a dispersant. Among these, the pigment in the aqueous ink according to the present invention is preferably dispersed using a pigment dispersion resin, and more preferably in the form of resin particles containing the pigment (hereinafter also referred to as "pigment-containing resin particles"). The form of the pigment-containing resin particles is not particularly limited, as long as they are formed from at least a pigment and a pigment dispersion resin. The pigment-containing resin particles may be particles in which the pigment dispersion resin is adsorbed onto the pigment in the aqueous ink. Examples of the form of the pigment-containing resin particles include particles in which the pigment is encapsulated in the pigment dispersion resin, particles in which the pigment is uniformly dispersed in the pigment dispersion resin, particles in which the pigment is exposed on the surface of the pigment dispersion resin particles, and mixtures thereof.

[0030] When the water-based ink contains a pigment, the content of the pigment in the water-based ink is, from the viewpoint of image density, preferably 3% by mass or more, more preferably 3.5% by mass or more, even more preferably 4% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.

[0031] (pigment dispersion resin) The pigment dispersing resin may be either a water-soluble resin or a water-insoluble resin. Here, regarding the "water-soluble" and "water-insoluble" of a resin, when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g it is judged to be "water-soluble," and if it is 10 g or less it is judged to be "water-insoluble." Furthermore, as described below, if the pigment dispersion resin has anionic groups that are further neutralized with a neutralizer, the solubility is judged from the dissolved amount measured in the presence of a neutralizer such that the mass ratio of the pigment dispersion resin to the neutralizer is the same as that in the water-based ink of the present invention.

[0032] Examples of pigment dispersion resins include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); and condensation resins such as polyester resins and polyurethane resins. The pigment dispersion resin may be an appropriately synthesized product, or a commercially available product. Among these, vinyl resins (hereinafter, vinyl resins as pigment dispersion resins may be referred to as "vinyl resin (c)") are preferred from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage.

[0033] From the viewpoint of improving the dispersion stability of the pigment, the vinyl resin (c) preferably contains a structural unit derived from an anionic group-containing monomer. In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphate group (-OPO3M2). In the carboxy group (-COOM), the sulfonic acid group (-SO3M), and the phosphate group (-OPO3M2), M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Examples of the vinyl resin (c) 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 (c) is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0034] 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, a carboxy group-containing monomer is preferred. Examples of the carboxy group-containing monomer include the monomers exemplified as the carboxy group-containing monomer for the resin (a), and (meth)acrylic acid is preferred.

[0035] Examples of the hydrophobic monomer include the monomers exemplified as the hydrophobic monomer for the resin (a) above. Among these, the hydrophobic monomer is preferably a styrene-based monomer or a styrene-based macromonomer, more preferably at least one selected from the group consisting of styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, divinylbenzene, and a styrene-based macromonomer, and even more preferably at least one selected from the group consisting of styrene and a styrene-based macromonomer.

[0036] Examples of the nonionic monomer include the monomers exemplified as the nonionic monomer for the resin (a) above. Among these, the nonionic monomer is preferably an alkoxypolyalkylene glycol mono(meth)acrylate, and more preferably a methoxypolyethylene glycol mono(meth)acrylate. The respective monomers of the vinyl resin (c) may be used singly or in combination of two or more.

[0037] When the vinyl resin (c) is a copolymer, the vinyl resin (c) preferably contains structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, structural units derived from one or more hydrophobic monomers selected from the group consisting of styrene-based monomers and styrene-based macromers, and a nonionic monomer.

[0038] When the vinyl resin (c) 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 constituent units derived from each monomer component in the vinyl resin (c) is as follows: The content of structural units derived from anionic group-containing monomers in the vinyl resin (c) is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 14% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and from the same viewpoint as above, is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 18% by mass or less. The content of structural units derived from hydrophobic monomers in the vinyl resin (c) is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and from the same viewpoint as above, is preferably 80% by mass or less, more preferably 73% by mass or less, and even more preferably 66% by mass or less. When the vinyl resin (c) contains a structural unit derived from a nonionic monomer, the content of the structural unit derived from a nonionic monomer in the vinyl resin is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and from the same viewpoint as above, is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 27% by mass or less. The vinyl resin (c) 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.

[0039] The pigment dispersion resin may have a crosslinked structure. In this case, the pigment dispersion resin preferably has a structure including a polymer component having a linear two-dimensional structure, which may have a branched chain, and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure, which may have a branched chain, being converted into a three-dimensional structure by a component derived from a crosslinking agent. Examples of polymers having a linear two-dimensional structure, which may have a branched chain, include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; and the above-mentioned vinyl resin (c) is preferred.

[0040] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent weight of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

[0041] From the viewpoint of improving the dispersion stability of the pigment, the acid value of the pigment dispersing resin is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, and even more preferably 80 mgKOH / g or more, and from the same viewpoint as above, it is preferably 800 mgKOH / g or less. The acid value of the pigment dispersing resin can be determined by the method described in the Examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, the acid value of a pigment dispersing resin having a crosslinked structure can also be calculated using the following formula. Acid value of pigment dispersing resin with crosslinked structure (mg KOH / g) = [Acid value of pigment dispersing resin before crosslinking (mg KOH / g) x [(100 - crosslinking rate (mol%)) / 100] In this specification, the crosslinking rate (mol %) of a pigment dispersing resin having a crosslinked structure is an apparent crosslinking rate calculated from the acid value of the pigment dispersing resin before crosslinking and the equivalent weight of the crosslinkable functional group of the crosslinking agent.

[0042] From the viewpoint of pigment dispersion stability, the number average molecular weight of the pigment dispersing resin is preferably 3,000 or more, more preferably 3,500 or more, and even more preferably 4,000 or more, and from the same viewpoint as above, it is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 60,000 or less. The number average molecular weight of the pigment dispersing resin is measured by the method described in the examples.

[0043] Commercially available pigment dispersion resins include, for example, polyacrylic acids such as "Polyacrylic Acid 5,000" and "Polyacrylic Acid 25,000" (both manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); and styrene / acrylic resins such as "Joncryl 67," "Joncryl 611," "Joncryl 678," "Joncryl 680," "Joncryl 690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0044] When the pigment in the water-based ink according to the present invention is in the form of pigment-containing resin particles, the pigment-containing resin particles can be obtained as an aqueous dispersion by dispersing the pigment, pigment dispersing resin, and, if necessary, a neutralizing agent, a surfactant, and the like, by a known method. When the pigment is blended in the aqueous ink as an aqueous dispersion of pigment-containing resin particles, the average particle size of the pigment-containing resin particles in the aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoints of the jetting ability and storage stability of the aqueous ink and of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoints as above, is preferably 600 nm or less, more preferably 550 nm or less, even more preferably 500 nm or less, and still 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.

[0045] When the pigment in the water-based ink is dispersed using a pigment dispersing resin, the content of the pigment dispersing resin in the water-based ink is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, and even more preferably 0.02% by mass or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, from the same viewpoint as above. When the pigment in the water-based ink according to the present invention is in a form dispersed in a pigment dispersing resin, the mass ratio of the pigment content to the total content of the pigment and pigment dispersing resin in the water-based ink according to the present invention [pigment / (pigment+pigment dispersing resin)] is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.65 or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 0.99 or less, more preferably 0.98 or less, from the same viewpoint as above.

[0046] (Water-soluble organic solvent) The water-based ink according to the present invention preferably further contains a water-soluble organic solvent from the viewpoints of improving the jetting properties and storage stability of the water-based ink and suppressing cracking of the printed coating film after thermal shrinkage. The water-soluble organic solvent may be used alone or in combination of two or more. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that, when dissolved in 100 mL of water at 25°C, results in a dissolution volume of 10 mL or more. The boiling point of the water-soluble organic solvent under atmospheric pressure is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and preferably 350°C or lower, more preferably 300°C or lower, even more preferably 250°C or lower. When two or more water-soluble organic solvents are used in combination, the boiling point of the water-soluble organic solvent is a weighted average value weighted by the content (mass %) of each water-soluble organic solvent.

[0047] Examples of water-soluble organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving the jetting properties and storage stability of the water-based ink and suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, one or more solvents selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred. The polyhydric alcohol may be a mixture of two or more compounds included in the concept of polyhydric alcohol. Similarly to the polyhydric alcohol, a mixture of two or more compounds included in the concept of polyhydric alcohol alkyl ether may be used.

[0048] Examples of polyhydric alcohols include ethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

[0049] Examples of polyhydric alcohol alkyl ethers include alkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers. Specific examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.

[0050] When the water-based ink further contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the water-based ink is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, from the viewpoint of improving the jetting properties and storage stability of the water-based ink and of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, and is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less.

[0051] (surfactant) The water-based ink according to the present invention may further contain a surfactant from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage. Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred. The surfactants can be used alone or in combination of two or more. Examples of nonionic surfactants include acetylene-based surfactants, polyoxyalkylene alkyl ether-based surfactants, polyhydric alcohol-based surfactants, fatty acid alkanolamides, silicone-based surfactants, and fluorine-based surfactants. Among these, the surfactant is preferably at least one selected from the group consisting of acetylene-based surfactants and silicone-based surfactants.

[0052] Preferred acetylene surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide (hereinafter also referred to as "EO") adducts thereof. Among these, more preferred are one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and even more preferred are EO adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0053] Commercially available acetylene surfactants include Surfynol 104PG-50 (2,4,7,9-tetramethyl-5-decyne-4,7-diol diluted with 50% propylene glycol), Surfynol 420 (2,4,7,9-tetramethyl-5-decyne-4,7-diol EO adduct (average number of EO adducts: 1), HLB value: 4 (catalog value)), and Surfynol 440 (2,4,7,9-tetramethyl-5-decyne-4,7-diol). Examples of such compounds include an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 3.5), HLB value: 8 (catalog value)), Surfynol 465 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 10), HLB value: 13 (catalog value)), and Surfynol 485 (an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles of EO added: 30), HLB value: 17 (catalog value)).

[0054] Preferred examples of silicone surfactants include polyether-modified silicone surfactants. Suitable examples of the polyether group in the polyether-modified silicone surfactant include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups (trimethyleneoxy groups or propane-1,2-diyloxy groups) are added in block or random fashion. Compounds in which polyether groups are grafted onto a silicone main chain and compounds in which polyether groups are bonded in block fashion to both ends of a silicone main chain can also be used.

[0055] Specific examples of polyether-modified silicone surfactants include PEG-3 dimethicone, PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG / PPG-20 / 22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, and lauryl PEG-9 polydimethylsiloxyethyl dimethicone. Commercially available polyether-modified silicone surfactants include, for example, the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., the "Silface SAG" series manufactured by Nissin Chemical Industry Co., Ltd., and the "BYK" series manufactured by BYK Japan K.K.

[0056] When the water-based ink further contains a surfactant, the content of the surfactant in the water-based ink is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, from the same viewpoint as above.

[0057] (water) The water-based ink according to the present invention contains water. The water used in the water-based ink according to the present invention is preferably pure water or ion-exchanged water, from the viewpoint of preventing the inclusion of unintended substances.

[0058] The water content in the water-based ink is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0059] The water-based ink according to the present invention may further contain various additives as optional components, such as a humectant, wetting agent, penetrant, dispersant, viscosity adjuster, antifoaming agent, preservative, antifungal agent, and antirust agent.

[0060] The water-based ink can be obtained by mixing and stirring the pigment, resin (a), water, and, if necessary, a pigment dispersing resin, a neutralizing agent, a surfactant, a water-soluble organic solvent, and the like. When pigment-containing resin particles are contained, as described above, it is preferable to disperse the pigment, pigment dispersing resin, and, if necessary, a neutralizing agent, a surfactant, and the like by a known method to obtain an aqueous dispersion of the pigment-containing resin particles, and then blend the resulting dispersion into the water-based ink.

[0061] (Physical properties of water-based ink) The viscosity of the water-based ink according to the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The pH of the water-based ink according to the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. From the viewpoints of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 0.5 or lower, and even more preferably 10 or lower.

[0062] [Overcoat liquid] The overcoat liquid according to the present invention contains a compound (b) (hereinafter simply referred to as "compound (b)") having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond.

[0063] The overcoat liquid according to the present invention preferably contains substantially no pigment. Here, "substantially free of pigment" means that no pigment is intentionally added to the overcoat liquid, and specifically means that the pigment content is preferably 0.1% by mass or less, more preferably 0.01% by mass or less, even more preferably 0.001% by mass or less, and even more preferably 0% by mass.

[0064] (Compound (b)) The reactive group of compound (b) that can react with the carboxy group of resin (a) to form a chemical bond is preferably one or more selected from the group consisting of a carbodiimide group, an oxazoline group, an epoxy group, an isocyanate group, an aziridino group, and an amino group. The concept of an epoxy group includes a glycidyl group. Among these, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, the reactive group is more preferably one or more selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group, even more preferably one or more selected from the group consisting of a carbodiimide group and an oxazoline group, and even more preferably a carbodiimide group. Furthermore, compound (b) may contain one or more types of these reactive groups, and preferably contains one type of reactive group.

[0065] That is, compound (b) is preferably one or more compounds selected from the group consisting of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds, and polyfunctional epoxy compounds, more preferably one or more compounds selected from the group consisting of polyfunctional carbodiimide compounds and polyfunctional oxazoline compounds, and even more preferably a polyfunctional carbodiimide compound. From the viewpoint of suppressing cracking of the printed coating film after heat shrinkage, the reactive group equivalent of compound (b) is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more, and from the viewpoint of blendability into the overcoat liquid, it is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. The reactive group equivalent means the mass of compound (b) per mole of reactive group capable of reacting with a carboxy group of resin (a) to form a chemical bond.

[0066] (Polyfunctional carbodiimide compounds) The polyfunctional carbodiimide compound is a compound having two or more carbodiimide groups in the molecule. As the polyfunctional carbodiimide compound, a polymer containing two or more carbodiimide groups (hereinafter also referred to as a "carbodiimide group-containing polymer") is preferred. The carbodiimide group-containing polymer is preferably one obtained by, for example, blocking the terminal isocyanate groups of a condensation reaction product obtained by a decarboxylation condensation reaction of diisocyanates in the presence of a carbodiimidization catalyst with hydrophilic groups.

[0067] Examples of diisocyanates used in the decarboxylation condensation reaction include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), decamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,5- or 2,6-norbornane diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated tolylene diisocyanate, and 2,4-bis-(8 alicyclic diisocyanates such as (-isocyanatooctyl)-1,3-dioctylcyclobutane (OCDI); araliphatic diisocyanates such as m- or p-xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); and aromatic diisocyanates such as 2,4,6-triisopropylphenyl diisocyanate (TIDI), 4,4'- or 2',4-diphenylmethane diisocyanate (MDI), and 2,4- or 2,6-tolylene diisocyanate (TDI).

[0068] The compound that blocks the terminal isocyanate group of the condensation reaction product is a compound having a functional group that can react with the isocyanate group, such as polyethylene glycol monomethyl ether and polypropylene glycol monomethyl ether. Among these, polyethylene glycol monomethyl ether is preferred from the viewpoint of blendability in the overcoat liquid. The number of moles of ethylene oxide added to the polyethylene glycol monomethyl ether can be adjusted, and the resulting carbodiimide group-containing polymer can be blended in the overcoat liquid as an aqueous solution or emulsion.

[0069] The carbodiimide group equivalent of the carbodiimide group-containing polymer is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more from the viewpoint of suppressing cracking of the printed coating film after heat shrinkage, and is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less from the viewpoint of blendability into an overcoat liquid. The carbodiimide group equivalent means the mass of the carbodiimide group-containing polymer per mole of carbodiimide groups. Commercially available carbodiimide group-containing polymers include, for example, Carbodilite E-02, Carbodilite E-05, and Carbodilite E-07S (all trade names manufactured by Nisshinbo Chemical Inc.).

[0070] (Polyfunctional oxazoline compounds) 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 preferable. From the viewpoint of enhancing reactivity, the number average molecular weight of the oxazoline group-containing polymer is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. Examples of the oxazoline group-containing polymer that can be used include polymers whose main chain has an acrylic skeleton, polymers whose main chain has a styrene / acrylic skeleton, polymers whose main chain has a styrene skeleton, and polymers whose main chain has an acrylonitrile / styrene skeleton.

[0071] From the viewpoint of improving the storage stability of the overcoat solution and suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, the oxazoline group equivalent of the oxazoline group-containing polymer is preferably at least 100, more preferably at least 170, even more preferably at least 200, and is preferably at most 500, more preferably at most 400, even more preferably at most 300. The oxazoline group equivalent means the mass of the oxazoline group-containing polymer per mole of oxazoline groups. Commercially available oxazoline group-containing polymers include, for example, the "Epocross WS" series, such as "Epocross WS-300," "Epocross WS-500," and "Epocross WS-700" (all water-soluble types manufactured by Nippon Shokubai Co., Ltd.).

[0072] (Multifunctional epoxy compound) A polyfunctional epoxy compound is a compound having two or more epoxy groups in the molecule. As the polyfunctional epoxy compound, a compound containing two or more glycidyl ether groups in the molecule is preferred, a polyglycidyl ether compound of a polyhydric alcohol is more preferred, and a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms is even more preferred. The epoxy group equivalent weight of the polyfunctional epoxy compound is preferably 100 or more, more preferably 120 or more, even more preferably 140 or more, and is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, and still more preferably 200 or less.

[0073] Examples of polyfunctional epoxy compounds include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, the polyfunctional epoxy compound is preferably one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and more preferably 1,6-hexanediol diglycidyl ether.

[0074] The content of compound (b) in the overcoat liquid is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0075] (Water-soluble organic solvent) The overcoat liquid according to the present invention preferably further contains a water-soluble organic solvent from the viewpoints of improving the ejection properties when the overcoat liquid is ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and of adjusting the surface tension of the overcoat liquid to suppress the occurrence of cracks in the printed coating film after thermal shrinkage. Examples of the water-soluble organic solvent include the water-soluble organic solvents exemplified above as the water-soluble organic solvent that may be contained in the water-based ink.

[0076] Among these, the water-soluble organic solvent is preferably at least one selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, from the viewpoint of improving the ejection properties when the overcoat liquid is ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage. Examples of the polyhydric alcohol and polyhydric alcohol alkyl ether include the same ones as those exemplified for the water-based ink.

[0077] When the water-based ink further contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the water-based ink is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, from the viewpoint of improving the jetting properties and storage stability of the water-based ink and from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, and is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less.

[0078] (surfactant) The overcoat liquid according to the present invention may further contain a surfactant from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage. Examples of the surfactant include the surfactants exemplified above as surfactants that may be contained in the water-based ink. Among these, the surfactant is preferably at least one selected from the group consisting of acetylene-based surfactants and silicone-based surfactants, from the viewpoint of improving the ejection properties when the overcoat liquid is ejected by an inkjet ejection method and the storage stability of the overcoat liquid, and from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage. The acetylene-based surfactant and the silicone-based surfactant may be the same as those exemplified for the water-based ink.

[0079] When the overcoat liquid further contains a surfactant, the content of the surfactant in the overcoat liquid is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less.

[0080] (water) The overcoat liquid according to the present invention preferably contains water. The water used in the overcoat solution according to the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

[0081] The water content in the overcoat liquid is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and from the same viewpoint as above, is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0082] The overcoat liquid of the present invention may further contain other components commonly used in overcoat liquids for inkjet printing, such as viscosity modifiers, antifoaming agents, preservatives, antifungal agents, and antirust agents, but preferably does not substantially contain a compound having a functional group capable of crosslinking with compound (b). Examples of resins having such functional groups include those similar to the resin (a) described above. Here, "substantially not containing a compound having a functional group capable of crosslinking with compound (b)" means that there is no resin having a functional group capable of crosslinking with compound (b) intentionally contained in the overcoat liquid, and specifically, the content thereof is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass. The overcoat solution of the present invention can be obtained by mixing and stirring the compound (b), water, and optionally a water-soluble organic solvent, a surfactant, and the other components described above. The compound (b) is preferably formulated as an aqueous solution or emulsion.

[0083] The overcoat liquid according to the present invention preferably contains substantially no pigment. Here, "substantially free of pigment" means that no pigment is intentionally added to the overcoat liquid, and specifically, the pigment content is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass.

[0084] (Physical properties of overcoat liquid) The viscosity of the overcoat solution of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and is preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less.

[0085] [Heat-shrinkable resin film substrate] The heat-shrinkable resin film substrate is preferably a low-liquid-absorbent resin film substrate from the viewpoint of suppressing cracking of the printed coating film after heat shrinkage. A heat-shrinkable resin film substrate is a film substrate that has molecular orientation due to stretching treatment of an unstretched film produced by a known production method, and does not shrink at room temperature but shrinks when heated. Examples of heat-shrinkable resin film substrates include film substrates made of one or a mixture of two or more selected from the group consisting of polyester-based resins, styrene-based resins such as polystyrene and styrene-butadiene copolymers, polylactic acid, olefin-based resins such as polyethylene, polypropylene, and polyolefins, and thermoplastic resins such as vinyl chloride-based resins, and laminated film substrates thereof. The heat-shrinkable resin film substrate is preferably a film substrate made of one material selected from polyester-based resin and polypropylene, or a laminated film substrate made of these materials, more preferably a film substrate made of polyester-based resin or a laminated film substrate made of these materials, and even more preferably a film substrate made of polyethylene terephthalate or a laminated film substrate made of these materials. Commercially available heat-shrinkable resin film substrates include the "Space Clean" series (manufactured by Toyobo Co., Ltd.); the "DXL" series, "Hishipet" series, "PLABIO" and "HybrexDL" (all manufactured by Mitsubishi Chemical Corporation); the "Bonset" series (manufactured by Takiron C.I. Co., Ltd.); and the "Fancy Wrap (PET)" series (manufactured by Gunze Limited).

[0086] <Process 1> In step 1, the water-based ink is applied to a heat-shrinkable resin film substrate by an inkjet ejection method using an inkjet head (1), and then the overcoat liquid is applied to the area to which the water-based ink has been applied by an inkjet ejection method using an inkjet head (2) having a resolution lower than that of the inkjet head (1).

[0087] (inkjet head) In the inkjet printing method of the present invention, the resolution of the inkjet head (2) that ejects the overcoat liquid is lower than the resolution of the inkjet head (1) that ejects the water-based ink, and from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, the difference in resolution between the inkjet head (2) and the inkjet head (1) is preferably 200 dpi or more, more preferably 300 dpi or more, and even more preferably 400 dpi or more. There is no particular upper limit to the difference in resolution between the inkjet head (2) and the inkjet head (1).

[0088] The resolution of the inkjet head (2) is preferably 600 dpi or less, more preferably 500 dpi or less, and even more preferably 400 dpi or less, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and is preferably 360 dpi or more, from the viewpoint of obtaining fine images. The resolution of the inkjet head (1) is not particularly limited as long as it is higher than the resolution of the inkjet head (2), but from the viewpoint of suppressing the occurrence of cracks in the printed coating film after thermal shrinkage, it is preferably 800 dpi or more, more preferably 900 dpi or more, and even more preferably 1000 dpi or more.

[0089] It is preferable that the ejection of the overcoat liquid by the inkjet head (2) and the ejection of the water-based ink by the inkjet head (1) are both performed at a print duty of 100%.

[0090] In step 1, the interval between the ejection of the water-based ink and the ejection of the overcoat liquid depends on the temperature of the inkjet head and the temperature of the heat-shrinkable resin film substrate, but is preferably 0.1 seconds or more, more preferably 1 second or more, and is 30 seconds or less from the viewpoint of suppressing cracking of the printed coating film after heat shrinkage. In step 1, the inkjet method for ejecting the water-based ink and the overcoat liquid is preferably a piezo method from the viewpoint of ejection properties.

[0091] When the water-based ink is a black ink or a colored ink, in step 1, the water-based ink is preferably applied directly to the heat-shrinkable resin film substrate using an inkjet head (1).

[0092] When the water-based ink is a white ink or a clear ink, in step 1, the water-based ink is preferably applied onto an image formed on a heat-shrinkable resin film substrate using an inkjet head (1). Here, "an image formed on a heat-shrinkable resin film substrate" means that the image is sufficiently dried and the components in the image are hardly mixed with the water-based ink and / or overcoat liquid.

[0093] The overcoat liquid is applied to the portion of the heat-shrinkable resin film substrate to which the water-based ink has been applied, and the printing area of ​​the overcoat liquid should be the same as or smaller than the printing area of ​​the water-based ink. From the viewpoint of suppressing cracking of the printed coating film after heat shrinkage, the printing area of ​​the overcoat liquid is preferably 98% or more of the printing area of ​​the water-based ink, more preferably 99% or more, even more preferably 99.5% or more, and preferably 100% or less, more preferably 100%.

[0094] The equivalent ratio of compound (b) used, calculated from the following formula, is preferably 0.5 or more, more preferably 1 or more, and even more preferably 2 or more, from the viewpoint of suppressing cracking of the printed coating film after thermal shrinkage, and is preferably 10 or less, more preferably 7 or less, and even more preferably 4 or less, from the same viewpoint as above. Equivalent ratio of compound (b) used=[(volume of droplets of overcoat liquid dispensed × content of compound (b) in overcoat liquid) / reactive group equivalent of compound (b)] / [(volume of droplets of water-based ink dispensed × content of resin (a) in water-based ink × (acid value of resin (a) / (56.11 × 1000))] In addition, when the pigment dispersing resin has a carboxy group, the carboxy group can also undergo a crosslinking reaction with compound (b). In the present invention, the equivalent ratio of compound (b) used is calculated as the equivalent ratio of the reactive group of compound (b) to the carboxy group of resin (a).

[0095] <Process 2> Step 2 is a step of heating the coating film containing the water-based ink and overcoat liquid on the heat-shrinkable resin film substrate formed in Step 1. Step 1 allows the resin (a) and compound (b) to be uniformly mixed in the coating film containing the water-based ink and overcoat liquid, and a crosslinking reaction between the carboxyl group of the resin (a) and the reactive group of the compound (b) proceeds, resulting in a printed matter with a printed coating film having uniform strength. The heat treatment in step 2 is preferably also a treatment for drying the coating film containing the water-based ink and the overcoat liquid formed in step 1. Methods for the heat treatment in step 2 include a method of blowing gas adjusted to the desired temperature onto the coating film formed on the heat-shrinkable resin film substrate, a method of passing the heat-shrinkable resin film substrate on which the coating film has been formed through a gas atmosphere adjusted to the desired temperature, a method of irradiating the coating film formed on the heat-shrinkable resin film substrate with an infrared heater, and a method of heating the heat-shrinkable resin film substrate on which the coating film has been formed using a platen heater. The heating temperature is preferably 40°C or higher, more preferably 50°C or higher, and preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 70°C or lower. The heating time is preferably 30 seconds or longer, more preferably 1 minute or longer, and preferably 10 minutes or shorter, more preferably 7 minutes or shorter, and even more preferably 5 minutes or shorter.

[0096] [Manufacturing method for printed matter] The method for producing a printed matter of the present invention uses an aqueous ink containing a resin (a) having a carboxy group and an overcoat liquid containing a compound (b) having two or more reactive groups capable of reacting with the carboxy group of the resin (a) to form a chemical bond, and carries out the following step 1 followed by step 2. Step 1: A step in which an aqueous ink is applied to a heat-shrinkable resin film substrate by an inkjet ejection method using an inkjet head (1), and then an overcoat liquid is applied to the area to which the aqueous ink has been applied by an inkjet ejection method using an inkjet head (2) having a resolution lower than that of the inkjet head (1). Step 2: Heating the coating film containing the water-based ink and overcoat liquid on the heat-shrinkable resin film substrate

[0097] In the method for producing a printed matter, the water-based ink, the overcoat liquid, the heat-shrinkable resin film substrate, the inkjet head, and steps 1 and 2 are the same as those in the inkjet printing method.

[0098] [Packaging method] In the present invention, the printed matter obtained by the inkjet printing method can be used in a method for packaging an item to be packaged. A preferred packaging method is to arrange a printed matter obtained by inkjet printing around the object to be packaged, and then shrink the heat-shrinkable resin film substrate of the printed matter to obtain a package. The printed matter obtained by the inkjet printing method of the present invention is able to exhibit excellent image fastness because cracking of the printed coating film after thermal shrinkage is suppressed, even if the printed coating film is provided on the opposite side of the surface where the resin film substrate and the packaged item come into contact.

[0099] The heating temperature for shrinkage is preferably 60° C. or higher, more preferably 70° C. or higher, even more preferably 80° C. or higher, and preferably 200° C. or lower, more preferably 150° C. or lower, even more preferably 130° C. or lower, and even more preferably 110° C. or lower. This heating temperature is preferably a temperature at which the printed matter can be used without any problems even if shrinkage occurs. The heating time for shrinkage is preferably 3 seconds or more, more preferably 5 seconds or more, even more preferably 7 seconds or more, and preferably 5 minutes or less, more preferably 3 minutes or less, even more preferably 1 minute or less.

[0100] [Manufacturing method of packaging body] In the present invention, the printed matter obtained by the inkjet printing method can be used in the method for producing a package. A preferred method for producing a package is to arrange a printed material obtained by inkjet printing around the item to be packaged, and then shrink the heat-shrinkable resin film substrate of the printed material to produce the package. The printed matter obtained by the inkjet printing method of the present invention is prevented from cracking in the printed coating after thermal shrinkage, and therefore can exhibit excellent image fastness even if the printed coating is provided on the opposite side of the surface where the resin film substrate and the packaged item come into contact, making it possible to produce packages with excellent image fastness. The heating temperature and heating time for shrinkage may be the same as those for the above-mentioned packaging method. [Example]

[0101] In the following Production Examples, Preparation Examples, Examples and Comparative Examples, "parts" means "parts by mass" unless otherwise specified. Measurements of various physical properties were carried out by the following methods.

[0102] [Measurement of resin acid value] The resin was dissolved in a titration solvent (toluene:acetone = 2:1 (volume ratio)) mixed with toluene and acetone in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0103] [Measurement of number average molecular weight and weight average molecular weight of resin] The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H," "TSKgel SuperAW3000," and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: 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)" (both manufactured by Tosoh Corporation) The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring the mixture with a magnetic stirrer at 25°C for 10 hours, and filtering the mixture through a syringe filter "DISMIC-13HP" (manufactured by Advantech Co., Ltd., pore size: 0.2 μm, material: PTFE).

[0104] [Measurement of the average particle size of pigment-containing resin particles in aqueous dispersion and the average particle size of resin (a) particles having a carboxy group in aqueous dispersion] Cumulant analysis was performed using a laser particle analysis system (Otsuka Electronics Co., Ltd., "ELS-8000") to measure the average particle size. -3 A dispersion diluted with water to a mass % (solid content equivalent) was used. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion medium, and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing resin particles in the aqueous dispersion or the average particle size of the particles of resin (a) having a carboxy group in the aqueous dispersion.

[0105] [Measurement of solid concentration] Using an infrared moisture meter ("FD-230" manufactured by Kett Electric Laboratory Co., Ltd.), 5 g of the measurement sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and the moisture content (mass%) of the measurement sample was measured, and the solid content (mass%) was calculated using the following formula. Solid concentration (mass%) = 100 - moisture content of measurement sample (mass%)

[0106] [Measurement of viscosity of water-based ink] The viscosity of the water-based ink at 32°C was measured using an E-type viscometer ("TV-25" manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34'×R24, rotation speed 50 rpm).

[0107] [Measurement of pH of water-based ink] The pH of the water-based ink at 25°C was measured using a tabletop pH meter ("F-71" manufactured by Horiba Ltd.) equipped with a pH electrode ("6337-10D" manufactured by Horiba Ltd.).

[0108] [Measurement of water absorption of heat-shrinkable resin film substrate when heat-shrinkable resin film substrate is in contact with pure water for 100 ms] Using an automatic scanning absorbency meter (KM500win manufactured by Kumagai Riki Kogyo Co., Ltd.), the amount of transferred water was measured at 23°C and 50% relative humidity for a contact time of 100 ms with pure water, and the amount of water absorbed in 100 ms was defined as the water absorption. The measurement conditions are as follows: "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

[0109] [Preparation of aqueous dispersion of pigment-containing resin particles] Production Example 1-1 (Production of pigment dispersing resin (1)) 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. In a reaction vessel, 18 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were mixed and thoroughly purged with nitrogen gas. Separately, a mixture of the remaining 90% (103.5 parts) of the monomer mixture with 0.27 parts of the chain transfer agent, 42 parts of MEK, and 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was placed in a dropping funnel. Under a nitrogen atmosphere, the mixture in the reaction vessel was heated to 75°C with stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution of 3 parts of the polymerization initiator in 5 parts of MEK was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. An additional 50 parts of MEK was added to obtain a solution of pigment dispersion resin (1) (weight average molecular weight: 50,000). The solids concentration of the pigment dispersion resin (1) solution was 45% by mass.

[0110] Production Example 1-2 (Production of Water Dispersion (D1) of Black Pigment-Containing Resin Particles) 95.2 parts of the pigment dispersion resin (1) solution obtained in Production Example 1-1 was mixed with 53.9 parts of MEK, to which 15.0 parts of 5N aqueous sodium hydroxide, 0.5 parts of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water were added as neutralizers. 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) were then added as a black pigment to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed using a disperser blade at 7,000 rpm and 20°C for 1 hour, and then dispersed using a high-pressure homogenizer "Microfluidizer M-140K" (manufactured by Microfluidics) for 15 passes at a pressure of 180 MPa to obtain a dispersion. The obtained dispersion was subjected to vacuum treatment at 60°C to remove MEK, and then some of the water was removed. The mixture was centrifuged, and the liquid layer was recovered and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of particles containing a black pigment and pigment dispersing resin (1). The solid content was 25% by mass. To 100 parts of the resulting aqueous dispersion of particles containing black pigment and pigment dispersion resin (1), 0.45 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321L, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 130) as a crosslinker and 15.23 parts of ion-exchanged water were added and heated at 70°C for 3 hours with stirring. After cooling to room temperature, the liquid layer was collected and filtered through a Mini Sart Syringe Filter (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of black pigment-containing resin particles (D1) (solids concentration: 22% by mass, mass ratio [pigment / (pigment + crosslinked pigment dispersion resin (1)]: 0.69). The average particle size of the black pigment-containing resin particles in the resulting aqueous dispersion (D1) was 100 nm.

[0111] Production Example 2 (Production of Water Dispersion (D2) of White Pigment-Containing Resin Particles) A 250 mL polyethylene bottle was charged with a mixture of 0.3 g of polyacrylic acid (PAA; Fujifilm Wako Pure Chemical Industries, Mw: 5,000 (catalog value)) as a pigment dispersion resin, 0.21 g of 5N sodium hydroxide solution (sodium hydroxide solids content: 16.9 wt%, Fujifilm Wako Pure Chemical Industries, Ltd.), and 1 g of ion-exchanged water. Next, 15 g of titanium dioxide (rutile type, Titan Kogyo Co., Ltd. "KURONOSKR-380", Al·Si treated, average primary particle size: 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 the mixture was dispersed for 8 hours at 250 rpm using a benchtop pot mill (AS ONE Corporation). The zirconia beads were then removed using a mesh, and the solid content was adjusted with water to obtain an aqueous dispersion (D2) of white pigment-containing resin particles (solid content: 30% by mass, mass ratio [pigment / (pigment + pigment-dispersed resin)]: 0.98). The average particle size of the white pigment-containing resin particles in the obtained aqueous dispersion was 325 nm.

[0112] [Preparation of aqueous dispersion of resin (a) having carboxy groups] Production Example 3 (Production of Water Dispersion (d1) of Resin (a) Having Carboxy Groups) In a reaction vessel equipped with a dropping funnel, the monomers shown in "Initial Charge Monomer Emulsion" in Table 1, sodium polyoxyethylene alkyl ether sulfate ("Latemul E-118B" manufactured by Kao Corporation) (hereinafter referred to as "Latemul E-118B") as an emulsifier, potassium persulfate as a polymerization initiator, and ion-exchanged water were placed and mixed, and the interior was replaced with nitrogen gas to obtain an initial charge monomer emulsion. Separately, the monomers, emulsifiers, polymerization initiators, and ion-exchanged water shown in the "Monomer emulsion to be added" column of Table 1 were mixed to obtain a monomer emulsion to be added, and the resulting emulsion was then placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer emulsion in the reaction vessel was heated from room temperature to 80°C over 30 minutes while stirring. While maintaining the temperature at 80°C, the monomer emulsion in the dropping funnel was gradually added dropwise to the reaction vessel over 3 hours. After the addition was completed, the mixture was stirred for 1 hour while maintaining the temperature inside the reaction vessel. The mixture was then filtered through a 200-mesh filter to obtain an aqueous dispersion (d1) of resin (a) having carboxy groups (solid content: 44.1% by mass). The acid value of resin (a) was 16 mg KOH / g, the weight-average molecular weight was 750,000, and the average particle size of resin (a) particles in aqueous dispersion (d1) was 95 nm.

[0113] [Table 1]

[0114] [Production of Water-Based Ink] Production Example 4-1 (Production of Water-Based Ink BK-1) 46.30 g of the water dispersion (D1) of black pigment-containing resin particles obtained in Production Example 1 (solid content concentration: 45% by mass), 12.81 g of the water dispersion (d1) of resin (a) having a carboxy group obtained in Production Example 3 (solid content concentration: 44.1% by mass), 30.00 g of propylene glycol (referred to as "PG" in Table 2), 3.00 g of diethylene glycol monoisobutyl ether (manufactured by Nippon Nyukazai Co., Ltd.) (referred to as "iBDG" in Table 2), acetylene glycol surfactant "Surfynol 44 A mixture of 1.00 g of "SF-440" (manufactured by Nissin Chemical Industry Co., Ltd., 2,4,7,9-tetramethyl-5-decyne-4,7-diol adduct with EO (3.5 mol), HLB value: 8 (catalog value), active content: 100% by mass) and 1.00 g of "KF-6011" (manufactured by Shin-Etsu Chemical Co., Ltd., PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value)) was added with ion-exchanged water to a total weight of 100.00 g. The resulting mixture was filtered through a "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain the aqueous black ink BK-1 (viscosity: 5.6 mPa·s, pH: 9.6).

[0115] Production Example 4-2 (Production of Water-Based Ink W-1) White water-based ink W-1 (viscosity: 5.6 mPa·s, pH: 8.2) was obtained in the same manner as in Ink Production Example 1, except that 34.00 g of water dispersion (D2) of white pigment-containing resin particles (solid content: 30% by mass) was used instead of water dispersion (D1) of black pigment-containing resin particles.

[0116] Production Example 4-3 (Production of Water-Based Ink CL-1) Water-based clear ink CL-1 (viscosity: 3.1 mPa·s, pH: 8.0) was obtained in the same manner as in Ink Production Example 1, except that 1.00 g of 5N aqueous sodium hydroxide solution was used instead of the water dispersion (D1) of black pigment-containing resin particles.

[0117] [Table 2]

[0118] Production Example 5 (Production of Overcoat Solution OC-1) The mixture was mixed with 12.50 g of a polyvalent carbodiimide compound "Carbodilite E-07S" (carbodiimide group equivalent: 234, active content 40% by mass, manufactured by Nisshinbo Chemical Inc.), 39.00 g of propylene glycol, 1.00 g of an acetylene glycol surfactant "Surfynol 440" (manufactured by Nisshin Chemical Industry Co., Ltd., 2,4,7,9-tetramethyl-5-decyne-4,7-diol EO (3.5 mol) adduct, HLB value: 8 (catalog value), active content 100% by mass), and 1.00 g of a polyether-modified silicone surfactant "KF-6011" (manufactured by Shin-Etsu Chemical Co., Ltd., PEG-11 methyl ether dimethicone, HLB value: 14.5 (catalog value)), and ion-exchanged water to bring the total amount to 100.00 g. The resulting mixture was filtered through a filter "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain overcoat liquid OC-1.

[0119] (inkjet printing) [Inkjet printing conditions] A printing evaluation device equipped with three piezoelectric inkjet heads (head 1a (resolution 1200 dpi), head 1b (resolution 1200 dpi), and head 2 (resolution shown in Table 3), from the front in the printing direction) and an underheater that heats the heat-shrinkable resin film substrate from the back side of the surface of the heat-shrinkable resin film substrate facing the inkjet heads was filled with the water-based inks and overcoat liquid shown in Table 3. The distance between the underheater and the heat-shrinkable resin film substrate was set to 0.2 mm, the distance between the inkjet heads and the heat-shrinkable resin film substrate was set to 1.0 mm, and the surface temperature of the underheater was set to 40°C. In an environment with a temperature of 25±1°C and a relative humidity of 30±5%, the settings were: head applied voltage 26V, head drive frequency 10kHz, head temperature 32°C, head resolution 600dpi, pre-ejection flushing count 200 shots, and negative pressure -4.0kPa, and the printing substrate was fixed to the printing evaluation device so that the longitudinal direction of the printing substrate was the same as the transport direction. Using a printing software program, the droplet volume of head 1a was adjusted to 3 pL, and that of head 1b was adjusted to 3 pL by changing the piezoelectric element drive voltage waveform of each head. For head 2, the droplet volume was adjusted to 1.5 pL when the resolution was 1200 dpi and 7 pL when the resolution was 600 dpi.

[0120] Examples 1 and 2 and Comparative Examples 1 and 2 Heat-shrinkable resin film substrate: Heat-shrinkable PET film "Space Clean SP809" (manufactured by Toyobo Co., Ltd., heat shrinkage rate (90°C, 10 seconds): 50%, water absorption: 10 g / m 2 A solid image was printed on the substrate (described below) using head 1a with water-based black ink BK-1 in an area of ​​10 cm x 10 cm at a print duty of 100%, and the solid image was completely dried by heating it for 1 minute in a hot air dryer at 60°C. [Process 1] A print command was transferred to the print evaluation device, and heads 1b and 2 were used to print solid images of the water-based inks and overcoat liquid shown in Table 3, each with a print duty of 100%, in that order, overlaid on the solid image of the water-based black ink BK-1 prepared above. The ejection interval between the water-based inks and the overcoat liquid was 1 second. [Process 2] Next, the coating film containing the water-based ink and the overcoat liquid was dried by heat treatment in a hot air dryer at 60° C. for 1 minute to obtain a printed matter.

[0121] Example 3 and Comparative Example 3 [Process 1] A print command was transferred to the print evaluation device, and a heat-shrinkable PET film "Space Clean SP809" (manufactured by Toyobo Co., Ltd., heat shrinkage rate (90°C, 10 seconds): 50%, water absorption: 10 g / m) was used as a heat-shrinkable resin film substrate. 2 A solid image with a printing duty of 100% was printed on a 10cm x 10cm area of ​​a substrate (see below) by overlapping the water-based ink BK-1 and the overcoat liquid OC-1 in this order using heads 1b and 2. The interval between the ejection of the water-based ink and the overcoat liquid was 1 second. [Process 2] Next, the coating film containing the water-based ink and the overcoat liquid was dried by heat treatment in a hot air dryer at 60° C. for 1 minute to obtain a printed matter.

[0122] [Evaluation of cracking of printed coating film after thermal shrinkage] A sample was prepared using each of the obtained prints in accordance with the test described in JIS Z 1709-1995. The sample was cut out from the solid image portion of the print so that it was 100 mm in the winding direction MD (vertical) and 100 mm in the width direction TD (horizontal). The heat transfer liquid in the standard was changed to water, and the sample was immersed in hot water heated to 90°C for 10 seconds to cause thermal shrinkage, and then immersed in water at room temperature for 5 seconds to cool. This sample was left to dry for 24 hours in an environment of 23°C and 50% humidity, yielding a shrunk printed matter.

[0123] The heat-shrunk printed material obtained using the above method was fixed in place, and air was sprayed onto the solid image area from a 45° angle above using an air duster gun (K-60, manufactured by Kinki Seisakusho) at a pressure of 0.05 MPa and a flow rate of 120 L / min for 30 seconds. The occurrence of cracks in the printed coating after heat shrinkage was evaluated using the following evaluation criteria. The area of ​​the portion peeled from the image refers to the total area of ​​the portion peeled from the solid image relative to the area of ​​the entire solid image. The results are shown in Table 3. (Evaluation criteria) A: No peeled parts from the image B: The area of ​​the part peeled off from the image is less than 5% C: The area of ​​the part peeled off from the image is 5% or more but less than 10% D: The area of ​​the part peeled off from the image is 10% or more but less than 20% E: The area of ​​the part peeled off from the image is 20% or more. If the evaluation is A to C, the printed matter will not be a problem for practical use after heat shrinkage.

[0124] [Table 3]

[0125] From Table 3, it can be seen that the printing methods of the examples are superior to the comparative examples in suppressing cracking of the printed coating film after thermal shrinkage. [Industrial Applicability]

[0126] According to the present invention, it is possible to provide an inkjet printing method that is excellent in suppressing the occurrence of cracks in a printed coating film when printing on a heat-shrinkable resin film substrate, and a packaging method that uses a printed matter obtained by the printing method.

Claims

1. a water-based ink containing a resin (a) having a carboxy group; an overcoat solution containing a compound (b) having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond; An inkjet printing method comprising carrying out the following step 2 after step 1: Step 1: A step of applying the water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method using a head (1), and then applying the overcoat liquid to the area where the water-based ink has been applied by an inkjet ejection method using a head (2) having a resolution lower than that of the head (1). Step 2: Heating the coating film containing the water-based ink and the overcoat liquid on the heat-shrinkable resin film substrate

2. The inkjet printing method according to claim 1, wherein the compound (b) is at least one selected from the group consisting of a polyfunctional carbodiimide compound, a polyfunctional oxazoline compound, and a polyfunctional epoxy compound.

3. The inkjet printing method according to claim 1 , wherein the printing area of ​​the overcoat liquid is equal to or smaller than the printing area of ​​the water-based ink.

4. the application of the water-based ink is carried out on an image formed on the substrate, 2. The inkjet printing method according to claim 1, wherein the water-based ink is a white ink or a clear ink.

5. 2. The inkjet printing method according to claim 1, wherein the resolution of the head (2) is 600 dpi or more.

6. 2. The inkjet printing method according to claim 1, wherein the difference between the resolution of the head (1) and the resolution of the head (2) is 200 dpi or more.

7. The inkjet printing method according to claim 1 , wherein the resin (a) is a vinyl resin.

8. The ink jet printing method of claim 1 , wherein the overcoat liquid is substantially free of pigment.

9. a water-based ink containing a resin (a) having a carboxy group; an overcoat solution containing a compound (b) having two or more reactive groups capable of reacting with the carboxyl group of the resin (a) to form a chemical bond; A method for producing a printed matter, comprising carrying out the following step 2 after step 1: Step 1: A step of applying the water-based ink to a heat-shrinkable resin film substrate by an inkjet ejection method using a head (1), and then applying the overcoat liquid to the area where the water-based ink has been applied by an inkjet ejection method using a head (2) having a resolution lower than that of the head (1). Step 2: Heating the coating film containing the water-based ink and the overcoat liquid on the heat-shrinkable resin film substrate

10. A packaging method, comprising: placing a printed matter obtained by the inkjet printing method according to any one of claims 1 to 8 around an article to be packaged; and then shrinking the heat-shrinkable resin film substrate of the printed matter to obtain a package.

11. A method for producing a package, comprising: placing a printed matter obtained by the inkjet printing method according to any one of claims 1 to 8 around a package; and then shrinking the heat-shrinkable resin film substrate of the printed matter.

Images