Ink set for inkjet printing

Abstract

This invention provides an inkjet printing ink kit, an inkjet printing method, and a packaging method for producing prints with excellent scratch resistance and water resistance after heat shrinkage in the printing of heat-shrinkable resin films. The inkjet printing ink kit, the inkjet printing method using the ink kit, and the packaging method using prints obtained by the inkjet printing method all comprise: an aqueous ink containing pigment, and a substantially pigment-free protective coating liquid. The aqueous ink contains a binder resin (Ib) having carboxyl groups, and the protective coating liquid contains a compound (II) having reactive groups capable of crosslinking with the carboxyl groups of the binder resin (Ib). The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the aqueous ink.

Description

TECHNICAL FIELD

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

[0002] In the field of commercial printing or industrial printing, in addition to printing on ordinary paper of the past, high-absorbing printing substrates called copy paper, low-absorbing printing substrates such as offset coated paper, or non-absorbing printing substrates such as resin films of polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), nylon (NY), and the like are required to be printed.

[0003] However, in printing on low-absorbing or non-absorbing printing substrates, there is a tendency that the adhesion of pigment ink to these printing substrates is not sufficient due to slow or no absorption of liquid components, and the image fastness of the printed matter is reduced. Therefore, in order to improve the image fastness of the printed matter produced by pigment ink, an aqueous composition such as a coating liquid used in conjunction with pigment ink has been developed.

[0004] For example, in Japanese Patent Application Publication No. 2019-189867 (Patent Literature 1), as a subject to improve the scratch resistance, solvent resistance, and substrate adhesion of a printed matter, an aqueous composition for inkjet recording containing a blocked isocyanate, at least one compound selected from a carbodiimide compound and an oxazoline compound, and water, an ink set for inkjet recording containing the aqueous composition and an aqueous ink, and an inkjet recording method using the aqueous composition and the aqueous ink are described. SUMMARY

[0005] The present application relates to an ink set for inkjet printing, the ink set for inkjet printing comprising: an aqueous ink containing a pigment, the aqueous ink containing a binder resin (Ib) having a carboxyl group, and a protective layer coating liquid substantially containing no pigment, the protective layer coating liquid containing a compound (II) having a reactive group capable of undergoing a cross-linking reaction with the carboxyl group of the binder resin (Ib), the protective layer coating liquid having a surface tension γ (B) greater than a surface tension γ (A) of the aqueous ink.

[0006] Further, the present application relates to an ink set for inkjet printing, the ink set for inkjet printing comprising: an aqueous ink containing a pigment, the aqueous ink containing a compound (II) having a reactive group capable of undergoing a cross-linking reaction with a carboxyl group of a binder resin (Ib) having a carboxyl group, and a protective layer coating liquid substantially containing no pigment, the protective layer coating liquid containing the binder resin (Ib) having a carboxyl group, the protective layer coating liquid having a surface tension γ (B) greater than a surface tension γ (A) of the aqueous ink. Detailed Implementation

[0007] Previously, there were examples, such as Patent Document 1, of using crosslinking agents such as end-capped isocyanate compounds, carbodiimide compounds, and oxazoline compounds as protective coating liquids for printing, and of promoting the crosslinking reaction by heating.

[0008] However, in the printing of heat-shrinkable resin films, which are widely used as packaging substrates such as plastic bottles, it has been found that the cross-linking reaction initiated by the cross-linking agent occurs unevenly, resulting in uneven strength of the printed coating. Therefore, when the resin film shrinks, the weaker parts of the printed coating are preferentially damaged, impairing the scratch resistance or water resistance of the heat-shrinkable printed material.

[0009] This invention relates to an ink kit, inkjet printing method, and packaging method for inkjet printing, which provides excellent scratch resistance and water resistance of the printed material after heat shrinkage in the printing of heat-shrinkable resin films.

[0010] The inventors have discovered that by using an inkjet printing ink kit comprising a water-based ink containing pigment and a protective coating liquid that is substantially pigment-free, wherein the water-based ink contains a binder resin having carboxyl groups and the protective coating liquid contains a compound having reactive groups capable of crosslinking with the carboxyl groups of the binder resin, and wherein the surface tension of the protective coating liquid is greater than that of the water-based ink, the crosslinking reaction of the binder resin can proceed uniformly, thereby solving the aforementioned problem.

[0011] That is, the present invention relates to the following [1] to [4].

[0012] [1] An ink kit for inkjet printing, wherein the ink kit comprises: a water-based ink containing pigment, and a protective coating liquid that is substantially free of pigment.

[0013] This water-based ink contains a binder resin (Ib) with carboxyl groups.

[0014] The protective coating liquid contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib).

[0015] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0016] [2] An ink kit for inkjet printing, wherein the ink kit comprises: a water-based ink containing pigment, and a protective coating liquid that is substantially free of pigment.

[0017] The water-based ink contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib) having carboxyl groups.

[0018] The protective coating liquid contains a binder resin (Ib) with carboxyl groups.

[0019] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0020] [3] An inkjet printing method, wherein an inkjet printing ink kit as described in [1] or [2] above is used, and includes the following steps 1 and 2.

[0021] Step 1: After applying the water-based ink to the heat-shrinkable resin film substrate by inkjet printing, the protective coating liquid is applied to the portion on which the water-based ink has been applied by inkjet printing.

[0022] Step 2: A step of heating the water-based ink coating and the protective coating liquid coating on the printing substrate formed in Step 1.

[0023] [4] A packaging method wherein, after a printed material obtained by the inkjet printing method described above [3] is disposed around a packaged body, the heat-shrinkable resin film substrate of the printed material is shrunk to obtain a packaged body.

[0024] According to the present invention, an inkjet printing ink kit, an inkjet printing method, and a packaging method are provided that provide excellent scratch resistance and water resistance of the printed matter after heat shrinkage in the printing of heat-shrinkable resin films.

[0025] [Inkjet Recording Ink Kit]

[0026] The ink kit for inkjet recording of the present invention (hereinafter also referred to as the "ink kit") includes: a water-based ink containing pigment (hereinafter also referred to as the "water-based ink" or "ink") and a protective coating liquid that is substantially free of pigment (hereinafter also referred to as the "protective coating liquid"). The water-based ink contains a binder resin (Ib) having a carboxyl group, and the protective coating liquid contains a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the binder resin (Ib). The surface tension γ (B) of the protective coating liquid is greater than the surface tension γ (A) of the water-based ink.

[0027] In this invention, "water-based" in water-based ink means that water accounts for the largest proportion by mass in the medium contained in the water-based ink.

[0028] Furthermore, in this specification, the term "low absorbency" for a low-absorbency printing substrate is a concept that includes both low absorbency and non-absorbency, meaning that the substrate absorbs 0 g / m³ of water when it is in contact with pure water for 100 milliseconds. 2 Above 10g / m 2 The water absorption capacity described above can be measured using the method described in the examples. Furthermore, "printing" includes printing or engraving of text or images, and "printed matter" includes printed matter or engraved matter containing text or images.

[0029] According to the present invention, in printing on heat-shrinkable resin films, the printed material exhibits excellent scratch resistance and water resistance after heat shrinkage. While the reason for this is not definitively established, it can be considered as follows.

[0030] In this invention, the surface tension of the protective coating liquid is greater than that of the water-based ink. Therefore, when the protective coating liquid is applied to the portion of the water-based ink after the water-based ink has been applied to the printing substrate, convection (so-called Marangoni convection) occurs between the water-based ink film and the protective coating liquid film on the printing substrate, driven by the surface tension gradient. As a result, compared to diffusion caused by the concentration difference of compound (II) between the water-based ink film and the protective coating liquid film on the printing substrate, the compound (II) containing reactive groups in the protective coating liquid film is more uniformly distributed into the water-based ink film. This promotes a uniform crosslinking reaction between the carboxyl groups of the binder resin (Ib) contained in the water-based ink film and the reactive groups of compound (II), making it difficult to produce a uniform intensity distribution in the formed printed coating film, and resulting in a printed material with uniform strength of the printed coating film. It is believed that even during heat shrinkage, the weaker areas of the printed coating will not selectively shrink, thus reducing the formation of fine cracks or wrinkles in the printed coating. Consequently, it is speculated that this inhibits embrittlement of the printed coating and improves scratch resistance and water resistance.

[0031] Hereinafter, the scratch resistance and water resistance of heat-shrinked printed materials will be referred to as "scratch resistance" and "water resistance," respectively.

[0032] In this invention, the surface tension γ(B) of the protective coating liquid (hereinafter also referred to as "surface tension γ(B)") is greater than the surface tension γ(A) of the water-based ink (hereinafter also referred to as "surface tension γ(A)").

[0033] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink, from the viewpoint of improving scratch resistance and water resistance, is preferably 1 mN / m or more, more preferably 1.5 mN / m or more, further preferably 2 mN / m or more, further more preferably 3 mN / m or more, further more preferably 5 mN / m or more, and further more preferably 7 mN / m or more. Furthermore, from the same viewpoint as above, it is preferably 20 mN / m or less, more preferably 17 mN / m or less, and further preferably 15 mN / m or less. The surface tension γ(A) of the water-based ink and the surface tension γ(B) of the protective coating liquid are measured using the method described in the examples.

[0034] <Water-based inks>

[0035] The water-based inks of this invention contain pigments and carboxyl-containing binder resins (Ib). The water-based inks can be used alone with an ink having one hue, or in combination with two or more inks having different hues. That is, printed images formed using the water-based inks of this invention can be multi-color printing, such as three-color printing, four-color printing, or printing using four or more inks with different hues.

[0036] (pigment)

[0037] The pigments used in this invention can be any type of inorganic or organic pigment, and lake pigments or fluorescent pigments can also be used. Furthermore, they can be used in combination with extender pigments as needed.

[0038] Specific examples of inorganic pigments include metal oxides such as carbon black, titanium dioxide, iron oxide, iron oxide red, and chromium oxide, as well as pearlescent pigments. Carbon black is particularly preferred in black inks. Examples of carbon black include furnace black, lampblack, acetylene black, and channel black.

[0039] Specific examples of organic pigments include azo lake pigments, insoluble monoazo pigments, insoluble diazo pigments, chelated azo pigments, and other azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, pyrene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindolinone pigments, isoindolineone pigments, quinolineone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

[0040] In achromatic inks, white, black, gray, and other achromatic pigments can be used, while in colored inks, yellow, magenta, cyan, blue, red, orange, green, and other colored pigments can be used.

[0041] As specific examples of preferred organic pigments, examples of numbered products selected from one or more of CI pigments: CI pigment yellow, CI pigment red, CI pigment orange, CI pigment purple, CI pigment blue, and CI pigment green can be listed.

[0042] Examples of pigments that can be used to form a body pigment include silicon dioxide, calcium carbonate, and talc.

[0043] The above pigments can be used alone or in combination of two or more.

[0044] In the water-based inks according to the present invention, pigments are dispersed in a medium. Examples of pigment forms in the water-based inks according to the present invention include those dispersed using a resin (hereinafter also referred to as "pigment dispersion resin") or a surfactant, or self-dispersing pigments dispersed without a dispersant. Among these, the form of pigment in the water-based inks according to the present invention is preferably dispersed using a pigment dispersion resin (hereinafter also referred to as "pigment dispersion resin (Ia)"), and more preferably the form of pigment-containing resin particles (hereinafter also referred to as "pigment-containing resin particles"). Here, the form of the pigment-containing resin particles is not particularly limited, as long as they consist of at least pigment and pigment dispersion resin (Ia) forming particles, specifically particles formed by the adsorption of pigment by the pigment dispersion resin (Ia) in the water-based ink. The forms of pigment-containing resin particles include, for example, particles in which the pigment is encapsulated within the pigment dispersion resin (Ia), particles in which the pigment is uniformly dispersed within the pigment dispersion resin (Ia), particles in which the pigment is exposed on the surface of the pigment dispersion resin (Ia) particles, and mixtures thereof.

[0045] (Pigment dispersion resin (Ia))

[0046] As a pigment dispersion resin (Ia), it can be any type of water-soluble resin and water-insoluble resin.

[0047] Here, the "water-soluble" and "water-insoluble" properties of the resin are determined by dissolving a constant amount of resin dried at 105°C for 2 hours in 100g of water at 25°C until saturation. A solution exceeding 10g is considered "water-soluble," while a solution below 10g is considered "water-insoluble." Furthermore, as described later, when the pigment dispersion resin (Ia) has anionic groups and these anionic groups are neutralized by a neutralizing agent, the amount of solubility is measured under conditions where the neutralizing agent is present, with the mass ratio of the pigment dispersion resin (Ia) to the neutralizing agent being the same as the mass ratio in the water-based ink of the present invention. This amount of solubility is then used for determination.

[0048] Examples of pigment dispersion resins (Ia) include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinyl styrene compounds); condensation resins such as polyester resins and polyurethane resins. Pigment dispersion resins (Ia) can be appropriately synthesized synthetic products or commercially available products. Among these, from the viewpoint of improving scratch resistance and water resistance, vinyl resins (hereinafter also referred to as "vinyl resins (Ia-1)") are preferred.

[0049] From the viewpoint of improving the dispersion stability of pigments, vinyl resins (Ia-1) preferably contain structural units derived from monomers containing anionic groups. In this specification, "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include carboxyl groups (-COOM), sulfonic acid groups (-SO3M), and phosphate groups (-OPO3M2). In the above chemical formulas, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0050] Examples of vinyl resins (Ia-1) include homopolymers of monomers containing anionic groups, copolymers of monomers containing anionic groups and hydrophobic monomers, copolymers of monomers containing anionic groups, and copolymers of hydrophobic monomers and nonionic monomers. When the vinyl resin (Ia-1) is a copolymer, it can be any of the following: random copolymer, block copolymer, alternating copolymer, and graft copolymer.

[0051] In this specification, "hydrophobic" in a hydrophobic monomer means that when the monomer is dissolved in 100g of ion-exchanged water at 25°C until saturation, the amount dissolved is less than 10g.

[0052] In addition, nonionic monomers are monomers with high affinity for water or water-soluble organic solvents, such as monomers containing hydroxyl groups or polyalkylene glycol chains.

[0053] Examples of monomers containing anionic groups include those containing carboxyl groups, those containing sulfonic acid groups, and those containing phosphate groups. Among these, from the viewpoints of improving the dispersion stability and availability of pigments, monomers containing carboxyl groups are preferred, and (meth)acrylic acid is more preferred.

[0054] Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms; styrene monomers, (meth)acrylates containing aromatic groups, and other monomers containing aromatic groups; and styrene macromonomers. The molecular weight of the monomers containing aromatic groups, preferably styrene monomers, is preferably less than 500. Styrene macromonomers are compounds with a number average molecular weight of 500 to 100,000 or less, having a polymerizable functional group at one end. From the viewpoint of improving the dispersion stability of pigments, the hydrophobic monomer is preferably a styrene monomer, more preferably one or more selected from styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from styrene and α-methylstyrene.

[0055] Examples of nonionic monomers include polyethylene glycol mono(meth)acrylates and other polyalkylene glycol mono(meth)acrylates; methoxy polyethylene glycol mono(meth)acrylates, octoxy polyethylene glycol mono(meth)acrylates and other alkoxy polyalkylene glycol mono(meth)acrylates.

[0056] In addition, "(meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid. Furthermore, "(meth)acrylate" refers to at least one selected from acrylate and methacrylate.

[0057] Furthermore, each monomer of vinyl resin (Ia-1) can be used alone or in combination with two or more monomers.

[0058] When the vinyl resin (Ia-1) is a copolymer, from the viewpoint of improving the dispersion stability of the pigment, the vinyl resin (Ia-1) preferably comprises structural units from one or more monomers containing anionic groups selected from acrylic acid and methacrylic acid, and structural units from one or more hydrophobic monomers selected from (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms, monomers containing aromatic groups, and styrene-based macromonomers. More preferably, it comprises structural units from one or more monomers containing anionic groups selected from acrylic acid and methacrylic acid, and structural units from one or more hydrophobic monomers selected from (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms and monomers containing aromatic groups. Even more preferably, it comprises structural units from one or more monomers containing anionic groups selected from acrylic acid and methacrylic acid, and structural units from monomers containing aromatic groups. Even more preferably, it comprises structural units from one or more monomers containing anionic groups selected from acrylic acid and methacrylic acid, and structural units from styrene-based monomers.

[0059] When the vinyl resin (Ia-1) is a copolymer of anionic monomers and hydrophobic monomers, or a copolymer of anionic monomers, hydrophobic monomers and nonionic monomers, the content of structural units from each monomer component in the vinyl resin (Ia-1) is as follows.

[0060] From the viewpoint of improving the dispersion stability of pigments, the content of structural units from monomers containing anionic groups in vinyl resins (Ia-1) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. Moreover, from the same viewpoint as above, it is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0061] From the viewpoint of improving the dispersion stability of pigments, the content of structural units derived from hydrophobic monomers in vinyl resins (Ia-1) is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Moreover, from the same viewpoint as above, it is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0062] When the vinyl resin (Ia-1) contains structural units derived from nonionic monomers, the content of the structural units derived from nonionic monomers in the vinyl resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of improving the dispersion stability of the pigment.

[0063] Vinyl resins (Ia-1) can be obtained, for example, by addition polymerization of raw material monomers including monomers containing anionic groups, hydrophobic monomers or nonionic monomers using known methods.

[0064] Pigment dispersion resin (Ia) may also have a crosslinked structure. In this case, from the viewpoint of improving the dispersion stability of the pigment, pigment dispersion resin (Ia) preferably has a structure comprising: a polymer having a linear two-dimensional structure that may also have branches, and a component from a crosslinking agent. It is believed that in such a crosslinked structure, the polymer having a linear two-dimensional structure that may also have branches becomes a three-dimensional structure through the component from the crosslinking agent. Examples of polymers having a linear two-dimensional structure that may also have branches include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinyl styrene compounds); condensation resins such as polyester resins and polyurethane resins; and the above-described vinyl resin (Ia-1) is preferred.

[0065] From the viewpoint of improving the dispersion stability of pigments, 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 polyol having 3 to 8 carbon atoms, and even more 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-cyclohexanediethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether.

[0066] When the crosslinking agent is a multifunctional epoxy compound, from the viewpoint of improving the dispersion stability of the pigment, the epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less.

[0067] From the viewpoint of improving the dispersion stability of pigments, the acid value of the pigment dispersion resin (Ia) is preferably 5 mg KOH / g or more, more preferably 50 mg KOH / g or more, and even more preferably 100 mg KOH / g or more. Furthermore, from the same viewpoint, it is preferably 800 mg KOH / g or less. The acid value of the pigment dispersion resin (Ia) can be obtained by the method described in the examples, or it can be calculated based on the mass ratio of the constituent monomers. Furthermore, the acid value of the pigment dispersion resin (Ia) having a cross-linked structure can also be calculated using the following formula.

[0068] The acid value (mgKOH / g) of the pigment dispersion resin (Ia) with cross-linked structure = [acid value (mgKOH / g) of the pigment dispersion resin (Ia) before cross-linking × [(100 - cross-linking rate (mol%)) / 100]

[0069] In this specification, the crosslinking rate (mol%) of the pigment dispersion resin (Ia) having a crosslinked structure is the apparent crosslinking rate calculated based on the acid value of the pigment dispersion resin (Ia) before crosslinking and the equivalent of the crosslinking functional groups of the crosslinking agent.

[0070] From the viewpoint of pigment dispersion stability, the number average molecular weight of the pigment dispersion resin (Ia) is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more. Furthermore, from the same viewpoint as above, it is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The number average molecular weight of the pigment dispersion resin (Ia) can be determined by the method described in the examples.

[0071] From the viewpoint of pigment dispersion stability, the weight-average molecular weight of the pigment dispersion resin (Ia) is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more. Furthermore, 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 weight-average molecular weight of the pigment dispersion resin (Ia) was determined by the method described in the examples.

[0072] Commercially available pigment dispersion resins (Ia) include, for example, polyacrylic acid resins such as "Aron AC-10SL" (manufactured by Toa Synthetic 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 Co., Ltd.).

[0073] In the case where the pigment in the water-based ink of the present invention is in the form of pigment-containing resin particles, the pigment-containing resin particles can be obtained in the form of an aqueous dispersion by dispersing the pigment, pigment dispersion resin (Ia), neutralizing agent as needed, surfactant, etc. using known methods.

[0074] When pigments are incorporated into water-based inks as an aqueous dispersion of pigment-containing resin particles, from the viewpoints of ink ejectibility and storage stability, as well as scratch resistance and water resistance, 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. Furthermore, from the same viewpoints, it is preferably 600 nm or less, more preferably 550 nm or less, even more preferably 500 nm or less, and even more preferably 450 nm or less. The average particle size of the pigment-containing resin particles in the aqueous dispersion is measured using the method described in the examples.

[0075] (Adhesive resin (Ib))

[0076] From the viewpoint of improving scratch resistance and water resistance, the water-based ink of the present invention contains a binder resin (Ib) having a carboxyl group (-COOM) (hereinafter also simply referred to as "binder resin (Ib)"). This carboxyl group can be categorized as an acidic group that releases hydrogen ions upon dissociation, or as an ionic form formed by their dissociation (-COO). － In the above chemical formula, M, like the anionic groups mentioned above, represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0077] From the viewpoint of improving scratch resistance and water solubility, the acid value of the adhesive resin (Ib) is preferably 3 mg KOH / g or more, more preferably 5 mg KOH / g or more, and even more preferably 10 mg KOH / g or more. Furthermore, from the same viewpoint as above, it is preferably 30 mg KOH / g or less, more preferably 25 mg KOH / g or less, and even more preferably 20 mg KOH / g or less. The acid value of the adhesive resin (Ib) can be obtained by the method described in the examples, or it can be calculated based on the mass ratio of the constituent monomers.

[0078] Examples of vinyl resins that can serve as the polymer backbone for adhesive resin (Ib) include (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. Furthermore, "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. Additionally, when the adhesive resin (Ib) is a copolymer, it can be any of the following: random copolymer, block copolymer, alternating copolymer, and graft copolymer.

[0079] From the viewpoint of improving scratch resistance and water resistance, the adhesive resin (Ib) is preferably selected from one or more of vinyl resins having carboxyl groups, polyurethane resins having carboxyl groups, and polyester resins having carboxyl groups, and more preferably from one or more of vinyl resins having carboxyl groups and polyurethane resins having carboxyl groups.

[0080] The vinyl resins with carboxyl groups used in this invention (hereinafter also referred to as "vinyl resins (Ib-1)") preferably contain structural units from carboxyl-containing monomers and structural units from hydrophobic monomers from the viewpoint of improving scratch resistance and water resistance.

[0081] From the viewpoints of improving scratch resistance and water resistance, and from the viewpoints of availability, (meth)acrylic acid is preferred as a carboxyl-containing monomer.

[0082] As the hydrophobic monomer, monomers similar to those exemplified in the pigment dispersion resin (Ia) described above are preferably included. Among these, from the viewpoint of improving scratch resistance and water resistance, the hydrophobic monomer is preferably selected from one or more of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, monomers containing aromatic groups, and styrene-based macromolecular monomers. More preferably, it is selected from one or more of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and monomers containing aromatic groups. Even more preferably, it is a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. Even more preferably, it is a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms. Even more preferably, it is a (meth)acrylate having an alkyl group having 1 to 8 carbon atoms.

[0083] Each monomer of vinyl resin (Ib-1) can be used alone or in combination of two or more monomers.

[0084] For vinyl resins (Ib-1), from the viewpoint of improving scratch resistance and water resistance, it is preferable to include structural units from one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units from one or more hydrophobic monomers selected from (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, monomers containing aromatic groups, and styrene macromolecular monomers. More preferably, it includes structural units from one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units from one or more hydrophobic monomers selected from (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and monomers containing aromatic groups. Even more preferably, it includes structural units from one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid. The above-mentioned structural units of carboxyl-containing monomers and structural units of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms are further preferred to be (meth)acrylate resins comprising structural units of one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units of (meth)acrylates having 1 to 12 carbon atoms. Further preferred to be (meth)acrylate resins comprising structural units of one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units of (meth)acrylates having 1 to 8 carbon atoms. Further preferred to be copolymers of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0085] In the case where the vinyl resin (Ib-1) is a copolymer of a carboxyl-containing monomer and a hydrophobic monomer, the content of structural units from each monomer component in the vinyl resin is as follows.

[0086] The content of structural units derived from carboxyl-containing monomers in vinyl resins (Ib-1) 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 improving scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0087] The content of structural units derived from hydrophobic monomers in vinyl resins (Ib-1) 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 improving scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 99.5% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less.

[0088] From the viewpoint of improving scratch resistance and water resistance, the weight-average molecular weight of the vinyl resin (Ib-1) is preferably 5,000 or more, more preferably 10,000 or more, further preferably 30,000 or more, even more preferably 50,000 or more, even more preferably 100,000 or more, even more preferably 300,000 or more, even more preferably 500,000 or more, and from the same viewpoint as above, preferably 1,500,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less. The weight-average molecular weight can be determined by the method described in the examples.

[0089] Vinyl resins (Ib-1) are manufactured by polymerizing raw material monomers using a known polymerization method. Examples of preferred polymerization methods include emulsion polymerization and suspension polymerization, with emulsion polymerization being more preferred.

[0090] The polyurethane resin with carboxyl groups used in this invention (hereinafter also referred to as "polyurethane resin (Ib-2)") is preferably an addition polymer of a prepolymer consisting of an organic compound (polyol) component having two or more alcoholic hydroxyl groups in the molecule and a polyisocyanate component, and a dialkyl carboxylic acid component, from the viewpoint of improving scratch resistance and water resistance.

[0091] Examples of dialkylcarboxylic acids include dimethylolbutyric acid, dimethylolpropionic acid, and their salts. Among these, dimethylolpropionic acid is preferred from the viewpoint of improving scratch resistance and water resistance.

[0092] As a polyol component, there are no special restrictions as long as it is a compound with more than two alcoholic hydroxyl groups in its molecule. Examples include polycarbonate polyols, polyester polyols, and polyether polyols.

[0093] Examples of polyisocyanate components include chain-like aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; cyclic aliphatic diisocyanates such as isophorone diisocyanate, hydrogenated phenyl diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aromatic aliphatic diisocyanates such as phenyl diisocyanate and tetramethylphenyl diisocyanate; aromatic diisocyanates such as toluene diisocyanate and diphenylmethane diisocyanate; and modified forms of these diisocyanates (such as those containing carbodiimide, urea diketone, and urea imide).

[0094] For polyurethane resin (Ib-2), from the viewpoint of improving scratch resistance and water resistance, it is more preferable to be an addition polymer of polycarbonate polyol as a polyol component, dicyclohexylmethane 4,4'-diisocyanate as a polyisocyanate component, and dimethylolpropionic acid as a dialkyl carboxylic acid.

[0095] Examples of solvents used in addition polymerization reactions include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. Chain extenders or reaction terminators can also be used in addition polymerization reactions as needed. By using chain extenders, the molecular weight can be further increased. Examples of chain extenders include polyols or polyamines, and examples of reaction terminators include monohydric alcohols or monoamines.

[0096] For polyurethane resin (Ib-2), from the viewpoint of dispersion stability in water-based inks, it is preferable that at least a portion of the carboxyl groups are neutralized by a neutralizing agent.

[0097] Examples of neutralizing agents include alkylamines such as butylamine and triethylamine; alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and inorganic bases such as morpholine, ammonia, and sodium hydroxide.

[0098] The binder resin (Ib) is preferably used in the form of pigment-free resin particles. From the viewpoint of improving the productivity of water-based inks, it is preferable to incorporate it into water-based inks in the form of an aqueous dispersion of pigment-free polymer particles. The binder resin (Ib) can be a suitably synthesized synthetic product or a commercially available product.

[0099] When the binder resin (Ib) is formulated in the form of an aqueous dispersion of pigment-free resin particles, the average particle size of the pigment-free resin particles in the aqueous dispersion, from the perspective of ink preservation stability, is preferably 10 nm or more, more preferably 30 nm or more, further preferably 50 nm or more, and even more preferably 70 nm or more. Furthermore, it is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and even more preferably 130 nm or less. The average particle size of the pigment-free resin particles in the aqueous dispersion is measured by the method described in the examples.

[0100] Commercially available products that are dispersions of pigment-free vinyl resin particles include, for example, acrylic resins such as "Neocryl A-1127" (manufactured by Covestro, trade name, anionic self-crosslinking waterborne acrylic resin), "Joncryl 390", "Joncryl 7100", "Joncryl 7600", "Joncryl 537J", "Joncryl PDX-7164", "Joncryl 538J", and "Joncryl 780" (manufactured by BASF Japan, trade name); styrene / butadiene resins such as "SR-100" and "SR102" (manufactured by Nippon A&L Inc., trade name); and vinyl chloride resins such as "VINYBLAN 700" and "VINYBLAN 701" (manufactured by Nissin Chemical Industry Co., Ltd., trade name).

[0101] Commercially available products that are dispersions of pigment-free polyurethane resin particles include, for example, "NeoRez R-9603" (manufactured by Covestro, trade name), "WBR-2018", and "WBR-2000U" (manufactured by TAISEI FINE CHEMICAL CO.,LTD., trade name).

[0102] Commercially available products that are dispersions of pigment-free polyester resin particles include, for example, “ELITEL KA-5034”, “ELITEL KA-5071S”, “ELITEL KZA-1734”, “ELITEL KZA-6034”, “ELITEL KZA-1449”, “ELITEL KZA-0134”, and “ELITEL KZA-3556” (all manufactured by Unitika Ltd., trade names).

[0103] (Water-soluble organic solvent)

[0104] From the viewpoint of improving the ejectibility and storage stability of water-based inks, and from the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the water-based inks according to the present invention preferably also contain a water-soluble organic solvent. One type of water-soluble organic solvent may be used alone, or two or more may be used in combination.

[0105] In this invention, "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C with a volume of 10 mL or more.

[0106] The boiling point of the water-soluble organic solvent at atmospheric pressure is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher. Moreover, it is preferably 350°C or lower, more preferably 300°C or lower, and even more preferably 250°C or lower.

[0107] When two or more water-soluble organic solvents are used as a water-soluble organic solvent, the boiling point of the water-soluble organic solvent is the weighted average value after weighting the content (mass%) of each water-soluble organic solvent.

[0108] Examples of water-soluble organic solvents include polyols, polyol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving the ejectibility and storage stability of water-based inks, and from the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, one or more selected from polyols and polyol alkyl ethers are preferred.

[0109] Polyols can be used in combination with various other types of polyols. Similarly, the concept of polyol alkyl ethers can also be used in combination with various other types of polyols.

[0110] Examples of polyols 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 3-methyl-1,3,5-pentanetriol (petriol).

[0111] Examples of polyol alkyl ethers include, for instance, alkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers. Specifically, examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, and tripropylene glycol monobutyl ether.

[0112] (surfactant)

[0113] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the water-based inks involved in this invention preferably also contain surfactants.

[0114] Surfactants can be appropriately selected and used within the range that satisfies the relationship between the surface tension γ(A) of the water-based ink and the surface tension γ(B) of the protective coating liquid.

[0115] Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred.

[0116] Surfactants can be used alone or in combination of two or more.

[0117] Examples of nonionic surfactants include acetylene surfactants, polyoxyalkylene alkyl ether surfactants, polyol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorinated surfactants.

[0118] From the perspective of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the surfactant is preferably selected from one or more of acetylene surfactants and silicone surfactants.

[0119] As acetylene surfactants, from the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, preferably include 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyn-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 their ethylene oxide (hereinafter also referred to as "EO") adducts. Among these, more preferably is one or more selected from the EO adducts of 2,4,7,9-tetramethyl-5-decyn-4,7-diol and 2,4,7,9-tetramethyl-5-decyn-4,7-diol, and even more preferably the EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol.

[0120] From the viewpoint of adjusting the surface tension of water-based inks to improve scratch resistance and water resistance, the average molar addition of ethylene oxide in acetylene surfactants (hereinafter also referred to as "average molar addition of EO") is preferably 1 mole or more, more preferably 2 moles or more, and even more preferably 3 moles or more. Moreover, from the same viewpoint as above, it is preferably 35 moles or less, more preferably 30 moles or less, even more preferably 25 moles or less, even more preferably 20 moles or less, even more preferably 15 moles or less, even more preferably 10 moles or less, and even more preferably 5 moles or less.

[0121] From the viewpoint of adjusting the surface tension of water-based inks to improve scratch resistance and water resistance, the HLB value of acetylene surfactants is preferably 1 or more, more preferably 2 or more, further preferably 3 or more, and even more preferably 7 or more. Moreover, from the same viewpoint as above, it is preferably 18 or less, more preferably 15 or less, and even more preferably 10 or less.

[0122] In this invention, the HLB value is used as a hydrophilic-lipophilic balance to represent the affinity of a surfactant for water and oil, and can be obtained by the Griffin method according to the following formula. Alternatively, the values ​​in the catalogs of each product can be referred to.

[0123] HLB value = 20 × [(total formula weight of hydrophilic groups in the surfactant) / (molecular weight of the surfactant)]

[0124] Examples of hydrophilic groups contained in surfactants include hydroxyl and ethylene oxide.

[0125] Commercially available acetylene surfactants include, for example, Surfynol 104PG-50 (50% propylene glycol dilution of 2,4,7,9-tetramethyl-5-decyn-4,7-diol), Surfynol 420 (EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (average EO addition mole: 1), HLB value: 4 (catalog value)), Surfynol 440 (EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (average EO addition mole: 3.5), HLB value: 8 (catalog value)), Surfynol 465 (EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (average EO addition mole: 10), HLB value: 13 (catalog value)), and Surfynol... 485 (EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (average molar number of EO additions: 30), HLB value: 17 (catalog value)).

[0126] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, polyether-modified silicone surfactants are preferred examples of silicone surfactants.

[0127] The polyether group used as a polyether-modified silicone surfactant, preferably polyethyleneoxy, polypropyleneoxy, or polyalkyleneoxy formed by block or random addition of ethyleneoxy and propyleneoxy (trimethyleneoxy or propane-1,2-dioxy), can be a compound with polyether groups branched on the silicone backbone or a compound with polyether groups block-bonded at both ends of the silicone backbone.

[0128] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the HLB value of polyether-modified silicone surfactants is preferably 2 or more, more preferably 6 or more, and even more preferably 10 or more. Moreover, from the same viewpoint, it is preferably 18 or less, more preferably 17 or less, and even more preferably 16 or less.

[0129] Specific examples of polyether-modified silicone surfactants include PEG-3 polydimethylsiloxane, PEG-9 polydimethylsiloxane, PEG-9 methyl ether polydimethylsiloxane, PEG-10 polydimethylsiloxane, PEG-11 methyl ether polydimethylsiloxane, PEG / PPG-20 / 22 butyl ether polydimethylsiloxane, PEG-32 methyl ether polydimethylsiloxane, PEG-9 polydimethylsiloxyethyl polydimethylsiloxane, and lauryl PEG-9 polydimethylsiloxyethyl polydimethylsiloxane.

[0130] Commercially available polyether-modified silicone surfactants include, for example, the "KF" series manufactured by Shin-Etsu Chemical Industry Co., Ltd., the "Silface SAG" series manufactured by Nissin Chemical Industry Co., Ltd., and the "BYK" series manufactured by BYK Chemie Japan KK.

[0131] (water)

[0132] The water-based ink involved in this invention contains water.

[0133] From the viewpoint of preventing the contamination of unintended substances, pure water or ion-exchanged water is preferred as the water used in the water-based inks involved in this invention.

[0134] The water-based inks involved in this invention may also contain various additives such as humectants, wetting agents, penetrants, dispersants, viscosity modifiers, defoamers, preservatives, mildew inhibitors, and rust inhibitors as any component.

[0135] Water-based inks can be obtained by mixing and stirring pigments, binder resins (Ib), water, pigment dispersion resins (Ia) as needed, neutralizers, surfactants, water-soluble organic solvents, etc.

[0136] In the case of pigment-containing resin particles, the pigment-containing resin particles are preferably dispersed by a known method as described above, whereby the pigment, pigment dispersion resin (Ia), neutralizing agent, surfactant, etc., are dispersed to obtain an aqueous dispersion of the pigment-containing resin particles, which is then incorporated into the water-based ink.

[0137] (Composition of water-based inks)

[0138] The pigment content in the water-based ink of the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of image concentration. Moreover, from the viewpoint of scratch resistance and water resistance, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less.

[0139] When the pigment in the water-based ink of the present invention is in the form of a pigment dispersion resin (Ia), from the viewpoint of improving the dispersion stability of the pigment, the content of the pigment dispersion resin (Ia) in the water-based ink of the present invention is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more. Moreover, from the same viewpoint as above, it is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0140] When the pigment in the water-based ink of the present invention is in the form of a pigment dispersion resin (Ia), from the viewpoint of improving the dispersion stability of the pigment, the mass ratio of the pigment content in the water-based ink of the present invention to the total content of pigment and pigment dispersion resin (Ia) [pigment / (pigment + pigment dispersion resin (Ia))] is preferably 0.5 or more, more preferably 0.6 or more, further preferably 0.65 or more, and even more preferably 0.7 or more. Moreover, from the same viewpoint as above, it is preferably 0.99 or less, and more preferably 0.98 or less.

[0141] The content of binder resin (Ib) in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of improving scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.

[0142] From the viewpoint of scratch resistance and water resistance, the water content in the water-based inks involved in this invention is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more. Moreover, from the same viewpoint as above, it is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0143] In cases where the water-based ink of the present invention also contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the water-based ink of the present invention, from the viewpoint of improving the sprayability and storage stability of the water-based ink, and from the viewpoint of adjusting the surface tension of the water-based ink to improve scratch resistance and water resistance, is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, and further preferably 40% by mass or less.

[0144] When the water-based ink according to the present invention also contains a surfactant, the content of the surfactant in the water-based ink according to the present invention, from the viewpoint of adjusting the surface tension of the water-based ink to improve scratch resistance and water resistance, 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. Moreover, from the same viewpoint as above, it is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less.

[0145] (Physical properties of water-based inks)

[0146] The surface tension γ(A) of the water-based ink according to the present invention is preferably 22 mN / m or more, more preferably 23 mN / m or more, further preferably 24 mN / m or more, and even more preferably 25 mN / m or more, from the viewpoints of improving scratch resistance and water resistance and improving image quality. Furthermore, from the same viewpoints, it is preferably 30 mN / m or less, more preferably 29 mN / m or less, even more preferably 28 mN / m or less, and even more preferably 27 mN / m or less. The above surface tension is measured by the method described in the examples.

[0147] 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, and even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, and even more preferably 7 mPa·s or less, from the viewpoint of spraying stability and dispersion stability. The above viscosity was measured by the method described in the examples.

[0148] 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. Furthermore, from the viewpoint of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The above pH values ​​were measured using the methods described in the examples.

[0149] When water-based inks are used in combination with two or more inks of different shades, differences in surface tension can also exist between the water-based inks.

[0150] At this point, from the viewpoint of improving scratch resistance and water resistance, the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is preferably greater than the surface tension between the individual water-based inks. More specifically, the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is preferably 0.5 mN / m or more, more preferably 1.0 mN / m or more, and even more preferably 1.5 mN / m or more compared to the surface tension between the individual water-based inks.

[0151] <Protective Coating Liquid>

[0152] The protective coating liquid involved in this invention is substantially free of pigments and contains compound (II) (hereinafter also referred to as "compound (II)"), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib).

[0153] The protective coating liquid involved in this invention is substantially free of pigments.

[0154] Here, "substantially free of pigment" means that the pigment content in the protective coating liquid involved in the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass.

[0155] (Compound (II))

[0156] The reactive group of compound (II) is preferably selected from one or more of carbodiimide, oxazoline, epoxy, isocyanate, aziridinyl, and amino groups. Furthermore, the concept of epoxy group includes glycidyl groups. From the viewpoint of improving scratch resistance and water resistance, the reactive group is more preferably selected from one or more of carbodiimide, oxazoline, and epoxy groups, even more preferably selected from one or more of carbodiimide and oxazoline groups, and even more preferably carbodiimide. That is, compound (II) is preferably selected from one or more of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds, and polyfunctional epoxy compounds, more preferably selected from one or more of polyfunctional carbodiimide compounds and polyfunctional oxazoline compounds, and even more preferably a polyfunctional carbodiimide compound.

[0157] The reactive group equivalent of compound (II) is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more, from the viewpoint of improving scratch resistance and water resistance. Moreover, from the viewpoint of its compatibility in the protective coating liquid, it is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. The reactive group equivalent refers to the mass of compound (II) per mole of reactive group.

[0158] [Multifunctional carbodiimide compounds]

[0159] Polyfunctional carbodiimide compounds are compounds having two or more carbodiimide groups in their molecules. From the viewpoint of improving scratch resistance and water resistance, polymers containing two or more carbodiimide groups (hereinafter also referred to as "polymers containing carbodiimide groups") are preferred as polyfunctional carbodiimide compounds.

[0160] The polymer containing carbodiimide groups is preferably obtained by capping the terminal isocyanate groups of the condensation product obtained by decarbonation condensation reaction in the presence of a carbodiimide catalyst of diisocyanate type with hydrophilic groups.

[0161] Examples of diisocyanates used in decarbonation condensation reactions include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), decamethyl diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,5- or 2,6-norbornene diisocyanate, hydrogenated phenyl diisocyanate (H6XDI), and hydrogenated toluene diisocyanate; 2,4'-dicyclohexylmethane diisocyanate, etc. Alicyclic diisocyanates such as bis-(8-isocyanate octyl)-1,3-dioctylcyclobutane (OCDI); aromatic aliphatic diisocyanates such as meta- or p-phenylenedimethyl diisocyanate (XDI) and tetramethylphenyl diisocyanate (TMXDI); aromatic diisocyanates such as 2,4,6-triisopropylphenyl diisocyanate (TIDI), 4,4'- or 2',4-diphenylmethane diisocyanate (MDI), and 2,4- or 2,6-toluene diisocyanate (TDI).

[0162] The compound used to cap the terminal isocyanate group of the above-mentioned condensation reactant is a compound having a functional group capable of reacting with the isocyanate group; examples include polyethylene glycol monomethyl ether and polypropylene glycol monomethyl ether. Among these, polyethylene glycol monomethyl ether is preferred from the viewpoint of its coordination in the protective coating solution. The molar number of ethylene oxide additions to the polyethylene glycol monomethyl ether can be adjusted so that the resulting polymer containing carbodiimide groups is in the form of an aqueous solution or an emulsion, and is then incorporated into the protective coating solution.

[0163] From the viewpoint of improving scratch resistance and water resistance, the carbodiimide equivalent of the polymer containing carbodiimide groups is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more. Furthermore, from the viewpoint of compatibility in the protective coating liquid, it is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. Additionally, the carbodiimide equivalent refers to the mass of the polymer containing carbodiimide groups per mole of carbodiimide groups.

[0164] Commercially available products containing carbodiimide groups include, for example, Carbodilite E-02, Carbodilite E-05, and Carbodilite E-07S (all manufactured by Nisshinbo Chemical Inc., trade names).

[0165] [Multifunctional oxazoline compounds]

[0166] Polyfunctional oxazoline compounds are compounds having two or more oxazoline groups in their molecule. Polymers containing two or more oxazoline groups are preferred as polyfunctional oxazoline compounds (hereinafter also referred to as "oxazoline-containing polymers").

[0167] The number-average molecular weight of the oxazoline-containing polymer is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less, from the viewpoint of improving crosslinking reactivity with carboxyl groups and improving scratch resistance and water resistance.

[0168] As a polymer containing an oxazoline group, polymers with an acrylic backbone, polymers with a styrene / acrylic backbone, polymers with a styrene backbone, and polymers with an acrylonitrile / styrene backbone can be used, for example.

[0169] From the viewpoint of improving the storage stability of the protective coating solution and enhancing scratch resistance and water resistance, the oxazoline equivalent of the oxazoline-containing polymer is preferably 100 or more, more preferably 170 or more, and even more preferably 200 or more. Furthermore, it is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. The oxazoline equivalent refers to the mass of oxazoline-containing polymer per mole of oxazoline.

[0170] Commercially available products containing oxazoline groups include, for example, the "Epocros WS" series such as "Epocros WS-300", "Epocros WS-500", and "Epocros WS-700" (all of which are manufactured by Nippon Shokubai Co., Ltd. and are water-soluble).

[0171] [Multifunctional epoxides]

[0172] Multifunctional epoxy compounds are compounds with two or more epoxy groups in their molecules.

[0173] From the viewpoint of improving scratch resistance and water resistance, compounds having two or more glycidyl ether groups in the molecule are preferred as multifunctional epoxy compounds, polyglycidyl ether compounds of polyols are more preferred, and polyglycidyl ether compounds of polyols having 3 or more but less than 8 carbon atoms are even more preferred.

[0174] From the viewpoint of improving scratch resistance and water resistance, the epoxy group equivalent of the multifunctional epoxy compound is preferably 100 or more, more preferably 120 or more, and even more preferably 140 or more. Moreover, it is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, and even more preferably 200 or less.

[0175] Examples of multifunctional 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-cyclohexanediethanol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether. From the viewpoint of improving scratch resistance and water resistance, the multifunctional epoxy compound is preferably selected from one or more of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanediethanol diglycidyl ether, and diethylene glycol diglycidyl ether, more preferably 1,6-hexanediol diglycidyl ether.

[0176] (Water-soluble organic solvent)

[0177] From the viewpoints of improving the ejectibility of the protective coating liquid when it is ejected by inkjet printing and the storage stability of the protective coating liquid, and from the viewpoints of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the protective coating liquid according to the present invention preferably also contains a water-soluble organic solvent.

[0178] In this invention, "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C or more as described above.

[0179] From the viewpoint of spray stability, storage stability and drying properties, the boiling point of the water-soluble organic solvent is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher. Moreover, it is preferably 350°C or lower, more preferably 300°C or lower, and even more preferably 250°C or lower.

[0180] When two or more water-soluble organic solvents are used as a water-soluble organic solvent, the boiling point of the water-soluble organic solvent is the weighted average value after weighting the content (mass%) of each water-soluble organic solvent.

[0181] As a water-soluble organic solvent, similar to water-based inks, examples include polyols, polyol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoints of improving the ejectibility of the protective coating liquid when it is ejected by inkjet printing and the storage stability of the protective coating liquid, and from the viewpoints of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, one or more selected from polyols and polyol alkyl ethers are preferred.

[0182] Polyols can be used in combination with various types encompassed by the concept of polyols. Similarly, like polyols, various types encompassed by the concept of polyol alkyl ethers can also be used in combination.

[0183] As polyols and polyol alkyl ethers, the same polyols and polyol alkyl ethers exemplified in water-based inks are preferred.

[0184] (surfactant)

[0185] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the protective coating liquid involved in this invention may also contain surfactants.

[0186] Surfactants can be appropriately selected and used within the range that satisfies the relationship between the surface tension γ(A) of the water-based ink and the surface tension γ(B) of the protective coating liquid.

[0187] From the perspective of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, surfactants such as nonionic surfactants, anionic surfactants, and amphoteric surfactants can be used, with nonionic surfactants being preferred.

[0188] Surfactants can be used alone or in combination of two or more.

[0189] Examples of nonionic surfactants include acetylene surfactants, polyoxyalkylene alkyl ether surfactants, polyol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorinated surfactants.

[0190] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the surfactant is preferably selected from one or more of acetylene surfactants and silicone surfactants.

[0191] As acetylene surfactants, preferably include 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyn-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 their EO adducts. More preferably, one or more EO adducts selected from 2,4,7,9-tetramethyl-5-decyn-4,7-diol and 2,4,7,9-tetramethyl-5-decyn-4,7-diol are preferred.

[0192] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the average molar number of EO added to the acetylene surfactant is preferably 1 mole or more. Moreover, from the same viewpoint, it is preferably 35 moles or less, more preferably 30 moles or less, even more preferably 25 moles or less, even more preferably 20 moles or less, even more preferably 15 moles or less, even more preferably 10 moles or less, even more preferably 5 moles or less, even more preferably 3 moles or less, and even more preferably 2 moles or less.

[0193] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the HLB value of the acetylene surfactant is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. Moreover, from the same viewpoint as above, it is preferably 18 or less, more preferably 15 or less, even more preferably 10 or less, even more preferably 7 or less, and even more preferably 5 or less.

[0194] In this invention, the HLB value, as described above, can be obtained using the Griffin method according to the above formula. Alternatively, the catalog value for each product can be referred to.

[0195] Commercially available products that are acetylene surfactants can be the same as those exemplified in water-based inks.

[0196] As silicone surfactants, polyether-modified silicone surfactants are preferred examples.

[0197] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the HLB value of the polyether-modified silicone surfactant is preferably 2 or more, more preferably 3 or more, further preferably 4 or more, further more preferably 6 or more, further more preferably 8 or more, further more preferably 10 or more, and preferably 18 or less, more preferably 17 or less, and further preferably 16 or less.

[0198] Specific examples and commercially available products of polyether-modified silicone surfactants can be cited as those illustrated in the section on water-based inks.

[0199] (water)

[0200] The protective coating liquid involved in this invention preferably contains water.

[0201] From the viewpoint of preventing the contamination of unintended substances, pure water or ion-exchanged water is preferred as the water used in the protective coating liquid of the present invention.

[0202] The protective coating liquid involved in this invention may also contain other components commonly used in protective coating liquids used in inkjet printing, such as viscosity modifiers, defoamers, preservatives, mildew inhibitors, and rust inhibitors, but preferably does not substantially contain a carboxyl-containing resin capable of crosslinking with compound (II). Examples of such carboxyl-containing resins include the same resins as the adhesive resin (Ib) described above.

[0203] Here, "substantially free of carboxyl-containing resins capable of cross-linking with compound (II)" means that the content of carboxyl-containing resins capable of cross-linking with compound (II) in the protective coating liquid of the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass.

[0204] The protective coating liquid of the present invention can be obtained by mixing compound (II), water, a water-soluble organic solvent as needed, a surfactant, and other components mentioned above, and then stirring. Compound (II) is preferably formulated in the form of an aqueous solution or an emulsion.

[0205] (Composition of the protective coating liquid)

[0206] From the viewpoint of improving scratch resistance and water resistance, the content of compound (II) in the protective coating liquid involved in this invention is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, further more preferably 7% by mass or more, and further more preferably 8% by mass or more. Moreover, from the same viewpoint as above, it is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less.

[0207] When the protective coating liquid involved in the present invention contains a water-soluble organic solvent, from the viewpoint of improving scratch resistance and water resistance, the content of the water-soluble organic solvent in the protective coating liquid involved in the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. Moreover, from the same viewpoint as above, it is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0208] When the protective coating liquid involved in the present invention contains a surfactant, the content of the surfactant in the protective coating liquid involved in the present invention, from the viewpoint of improving scratch resistance and water resistance, is preferably 3% by mass or less, more preferably 2.5% by mass or less, even more preferably 2% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less.

[0209] When the protective coating liquid involved in the present invention contains water, the water content in the protective coating liquid involved in the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of improving scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0210] (Physical properties of the protective coating liquid)

[0211] The surface tension γ(B) of the protective coating liquid according to the present invention is preferably 27 mN / m or more, more preferably 29 mN / m or more, further preferably 31 mN / m or more, and even more preferably 33 mN / m or more, from the viewpoint of improving scratch resistance and water resistance. Furthermore, from the same viewpoint, it is preferably 44 mN / m or less, more preferably 42 mN / m or less, and even more preferably 40 mN / m or less. The above surface tension was measured by the method described in the examples.

[0212] [Another implementation of an inkjet recording ink kit]

[0213] Another embodiment of the inkjet recording ink kit of the present invention (hereinafter also referred to as "another embodiment") comprises: an aqueous ink containing pigment and a protective coating liquid that is substantially free of pigment, the aqueous ink containing compound (II) having reactive groups capable of crosslinking with the carboxyl groups of a binder resin (Ib) having carboxyl groups, the protective coating liquid containing a binder resin (Ib) having carboxyl groups, and the surface tension γ (B) of the protective coating liquid being greater than the surface tension γ (A) of the aqueous ink.

[0214] According to another embodiment of the present invention, in printing on heat-shrinkable resin films, the printed material exhibits excellent scratch resistance and water resistance after heat shrinkage. While the reason is not explicitly stated, it can be considered as follows.

[0215] In this invention, the surface tension of the protective coating liquid is greater than that of the water-based ink. Therefore, when the protective coating liquid is applied to the portion of the water-based ink after it has been applied to the printing substrate, convection (so-called Marangoni convection) occurs between the water-based ink film on the printing substrate and the protective coating liquid film, driven by the surface tension gradient. As a result, compared to diffusion caused by the concentration difference of compound (II) between the water-based ink film and the protective coating liquid film on the printing substrate, the compound (II) containing reactive groups in the water-based ink film is more uniformly distributed into the protective coating liquid film. This promotes a uniform crosslinking reaction between the carboxyl groups of the binder resin (Ib) contained in the protective coating liquid film and the reactive groups of compound (II), making it difficult to produce a uniform intensity distribution in the formed printed coating film, and resulting in a printed material with uniform strength of the printed coating film. It is believed that even during heat shrinkage, the weaker areas of the printed coating will not selectively shrink, thus reducing the occurrence of microcracks or wrinkles in the printed coating. Consequently, it is speculated that this inhibits embrittlement of the printed coating and improves scratch resistance and water resistance.

[0216] In another embodiment of the present invention, the surface tension γ(B) of the protective coating liquid (hereinafter also referred to as "surface tension γ(B)") is greater than the surface tension γ(A) of the water-based ink (hereinafter also referred to as "surface tension γ(A)").

[0217] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is the same as that of the water-based ink involved in the inkjet recording ink of the present invention.

[0218] <Another embodiment of water-based ink>

[0219] Another embodiment of the present invention relates to a water-based ink containing a pigment and a compound (II) having reactive groups capable of crosslinking with the carboxyl groups of a binder resin (Ib) having carboxyl groups. The water-based ink can be used alone with a single hue, or in combination with two or more inks having different hues. That is, the printed image formed using the water-based ink of the present invention can be multi-color printing, such as three-color printing, four-color printing, or printing using inks with four or more different hues.

[0220] In another embodiment of the present invention, the pigment in the water-based ink is the same as that in the water-based ink for inkjet recording of the present invention described above. Furthermore, in another embodiment of the present invention, the pigment dispersion resin (Ia) is the same as that in the water-based ink for inkjet recording of the present invention described above.

[0221] In another embodiment of the present invention, the water-based ink containing a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the binder resin (Ib) having a carboxyl group is the same as the compound (II) of the protective coating liquid involved in the inkjet recording ink of the present invention.

[0222] From the viewpoint of improving the ejectibility and storage stability of water-based inks, and from the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the water-based ink according to another embodiment of the present invention preferably further contains a water-soluble organic solvent. The water-soluble organic solvent may be used alone or in combination with two or more types. In the water-based ink according to another embodiment of the present invention, the water-soluble organic solvent is the same as the water-soluble organic solvent of the water-based ink according to the inkjet recording ink of the present invention described above.

[0223] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of water-based inks, the water-based ink according to another embodiment of the present invention preferably further contains a surfactant. In the water-based ink according to another embodiment of the present invention, the surfactant is the same as the surfactant in the water-based ink according to the inkjet recording ink of the present invention described above.

[0224] Another embodiment of the present invention relates to a water-based ink containing water.

[0225] In another embodiment of the present invention, the water in the water-based ink is the same as the water in the water-based ink for inkjet recording of the present invention described above.

[0226] In another embodiment of the present invention, the water-based ink may also contain, as an arbitrary component, various additives or fixing resins such as humectants, wetting agents, penetrants, dispersants, viscosity modifiers, defoamers, preservatives, mildew inhibitors, and rust inhibitors.

[0227] Another embodiment of the present invention relates to a water-based ink which can be obtained by mixing and stirring a pigment, a compound (II) having a reactive group that can crosslink with the carboxyl group of a binder resin (Ib) having a carboxyl group, water, a pigment dispersion resin (Ia) as needed, a neutralizer, a surfactant, a water-soluble organic solvent, etc.

[0228] In the case of pigment-containing resin particles, the pigment-containing resin particles are preferably dispersed by a known method as described above, whereby the pigment, pigment dispersion resin (Ia), neutralizing agent, surfactant, etc., are dispersed to obtain an aqueous dispersion of the pigment-containing resin particles, which is then incorporated into the water-based ink.

[0229] (Composition of water-based ink according to another embodiment)

[0230] The pigment content in the water-based ink according to another embodiment of the present invention is the same as that in the water-based ink for inkjet recording according to the present invention described above.

[0231] In another embodiment of the present invention, the pigment in the water-based ink is in the form of a pigment dispersion resin (Ia) dispersed in the water-based ink. The content of the pigment dispersion resin (Ia) in the water-based ink of the other embodiment of the present invention is the same as that in the water-based ink of the inkjet recording ink of the present invention described above.

[0232] In another embodiment of the present invention, the pigment in the water-based ink is in the form of a pigment dispersion resin (Ia), and the mass ratio of the pigment content in the water-based ink according to the other embodiment of the present invention to the total content of pigment and pigment dispersion resin (Ia) [pigment / (pigment + pigment dispersion resin (Ia))] is the same as that in the water-based ink for inkjet recording according to the present invention described above.

[0233] In another embodiment of the present invention, the content of the compound (II) having a reactive group capable of crosslinking with the carboxyl group of the adhesive resin (Ib) having a carboxyl group is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 1.2% by mass or more, and even more preferably 1.5% by mass or more, and from the same viewpoint as above, preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0234] The water content in the water-based ink according to another embodiment of the present invention is the same as that in the water-based ink for inkjet recording according to the present invention described above.

[0235] In another embodiment of the present invention, the water-based ink further contains a water-soluble organic solvent. The content of the water-soluble organic solvent in the water-based ink of the present invention is the same as that in the water-based ink of the inkjet recording ink of the present invention described above.

[0236] In another embodiment of the present invention, the water-based ink further contains a surfactant, and the surfactant content in the water-based ink of the present invention is the same as that in the water-based ink of the inkjet recording ink of the present invention described above.

[0237] (Physical properties of water-based inks according to another embodiment)

[0238] The surface tension γ(A) of the water-based ink in another embodiment of the present invention is the same as that of the water-based ink for inkjet recording of the present invention described above.

[0239] The viscosity of the water-based ink at 32°C in another embodiment of the present invention is the same as that of the water-based ink involved in the inkjet recording ink of the present invention described above.

[0240] The pH of the water-based ink in another embodiment of the present invention is the same as that of the water-based ink for inkjet recording of the present invention described above.

[0241]

[0242] Another embodiment of the present invention relates to a protective coating liquid that is substantially free of pigments and contains a binder resin (Ib) having carboxyl groups.

[0243] The protective coating liquid involved in this invention is substantially free of pigments.

[0244] In another embodiment of the present invention, the binder resin (Ib) having carboxyl groups in the protective coating liquid is the same as the binder resin (Ib) of the water-based inks involved in the inkjet recording inks of the present invention.

[0245] From the viewpoints of improving the ejectibility of the protective coating liquid when it is ejected by inkjet printing and the storage stability of the protective coating liquid, and from the viewpoints of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the protective coating liquid according to another embodiment of the present invention preferably further contains a water-soluble organic solvent.

[0246] In another embodiment of the present invention, the water-soluble organic solvent in the protective coating liquid is the same as that in the protective coating liquid of the inkjet recording ink of the present invention described above.

[0247] From the viewpoint of improving scratch resistance and water resistance by adjusting the surface tension of the protective coating liquid, the protective coating liquid according to another embodiment of the present invention may also contain a surfactant.

[0248] Surfactants can be appropriately selected and used within the range that satisfies the relationship between the surface tension γ(A) of the water-based ink and the surface tension γ(B) of the protective coating liquid.

[0249] In another embodiment of the present invention, the surfactant used in the protective coating liquid is the same as that used in the protective coating liquid of the inkjet recording ink of the present invention.

[0250] In another embodiment of the present invention, the protective coating liquid preferably contains water.

[0251] In another embodiment of the present invention, the water in the protective coating liquid is the same as the water in the protective coating liquid of the inkjet recording ink of the present invention.

[0252] Another embodiment of the present invention may contain other components such as viscosity modifiers, defoamers, preservatives, mildew inhibitors, and rust inhibitors commonly used in protective coating liquids used in inkjet printing.

[0253] The protective coating liquid of the present invention can be obtained by mixing and stirring a carboxyl-containing binder resin (Ib), water, a water-soluble organic solvent as needed, a surfactant, and other components mentioned above. Compound (II) is preferably formulated in the form of an aqueous solution or an emulsion.

[0254] (Composition of the protective coating liquid according to another embodiment)

[0255] In another embodiment of the present invention, the content of the carboxyl-containing binder resin (Ib) in the protective coating liquid 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 scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0256] In another embodiment of the present invention, when the protective coating liquid contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the protective coating liquid of the other embodiment of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving scratch resistance and water resistance. Moreover, from the same viewpoint as above, it is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0257] In another embodiment of the present invention, if the protective coating liquid contains a surfactant, the surfactant content in the protective coating liquid of the other embodiment of the present invention is the same as that in the protective coating liquid of the inkjet recording ink of the present invention described above.

[0258] In another embodiment of the present invention, if the protective coating liquid contains water, the water content in the protective coating liquid of the other embodiment of the present invention is the same as that in the protective coating liquid of the inkjet recording ink of the present invention described above.

[0259] (Physical properties of the protective coating liquid in another embodiment)

[0260] The surface tension γ(B) of the protective coating liquid in another embodiment of the present invention is the same as that of the protective coating liquid in the inkjet recording ink of the present invention described above.

[0261] Inkjet printing method

[0262] (Process 1)

[0263] Step 1 is a process of applying water-based ink to a printing substrate by inkjet spraying, and then applying a protective coating liquid to the portion of the substrate that has been coated with the water-based ink by inkjet spraying.

[0264] In step 1, the spray interval between the water-based ink and the protective coating liquid also depends on the temperature of the inkjet head and the temperature of the printing substrate, but it is preferably 0.1 seconds or more, more preferably 1 second or more, and from the viewpoint of improving scratch resistance and water resistance, it is 30 seconds or less.

[0265] In step 1, from the viewpoint of ejection performance, a piezoelectric method is preferred as the inkjet method for ejecting water-based ink and protective coating liquid.

[0266] From the viewpoint of improving scratch resistance and water resistance, the usage equivalent ratio of compound (II) calculated by the following formula is preferably 0.5 or more, more preferably 1 or more, further preferably 2 or more, further preferably 2.5 or more, further preferably 3 or more, further preferably 3.5 or more, further preferably 4 or more, and from the same viewpoint as above, it is preferably 10 or less, more preferably 8 or less, and further preferably 6 or less.

[0267] The usage equivalent ratio of compound (II) = [(droplet volume of protective coating liquid × content of compound (II) in the protective coating liquid) / equivalent of reactive groups of compound (II)] / [(droplet volume of water-based ink × content of binder resin (Ib) in the water-based ink × (acid value of binder resin (Ib) / (56.11 × 1000))]

[0268] In addition, when the pigment dispersion resin (Ia) has a carboxyl group, the carboxyl group can also undergo a crosslinking reaction with the compound (II). However, in this invention, the equivalent ratio of the compound (II) is calculated as the equivalent ratio of the reactive group of the compound (II) to the carboxyl group of the binder resin (Ib).

[0269] Furthermore, in another embodiment of the inkjet recording ink kit of the present invention, the usage equivalent of compound (II) is calculated using the following formula. The usage equivalent of compound (II) in another embodiment of the inkjet recording ink kit of the present invention is the same as that in the case of using the inkjet recording ink of the present invention described above.

[0270] The usage equivalent ratio of compound (II) = [(droplet amount of water-based ink × content of compound (II) in water-based ink) / equivalent of reactive groups of compound (II)] / [(droplet amount of protective coating liquid × content of binder resin (Ib) in protective coating liquid × (acid value of binder resin (Ib) / (56.11 × 1000))]

[0271] Examples of printing substrates include ordinary paper with high absorbency, coated paper with low absorbency, and resin film without absorbency. From the viewpoint of scratch resistance and water resistance, printing substrates with low absorbency are preferred, and those selected from coated paper and resin film are more preferred, and resin film is even more preferred.

[0272] Examples of coated papers include general glossy paper and multi-color glossy paper.

[0273] The resin film can be selected from at least one of polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. The surface of the printed image formed on the resin film can also be corona treated.

[0274] From the viewpoint of scratch resistance and water resistance, the resin film is preferably a heat-shrinkable resin film that shrinks when heated.

[0275] Heat-shrinkable resin films are films that have molecular orientation obtained by stretching an unstretched film produced using a known method, and which do not shrink at room temperature but can shrink upon heating. Examples of heat-shrinkable resin films include films and laminates thereof composed of one or more of the following: polyester resins; styrene resins such as polystyrene and styrene-butadiene copolymers; polylactic acid; olefin resins such as polyethylene, polypropylene, and polyolefins; and thermoplastic resins such as vinyl chloride resins.

[0276] Commercially available heat-shrinkable resin films include the "SPACECLEAN" series (manufactured by Toyobo Co., Ltd.); the "DXL" series, the "HISHIPET" series, "PLABIO", and "HybrexDL" (all manufactured by Mitsubishi Chemical Co., Ltd.); the "BONSET" series (manufactured by CI TAKIRON Corporation); and the "Fancy wrap (PET)" series (manufactured by Gunze Limited).

[0277] (Process 2)

[0278] Step 2 is a process of heating the water-based ink coating and the protective coating liquid coating formed on the printing substrate in Step 1. Through this step 2, the compound (II) contained in the protective coating liquid on the printing substrate is distributed to the water-based ink coating, and the carboxyl groups of the binder resin (Ib) undergo a cross-linking reaction with the reactive groups of compound (II), resulting in a printed material with uniform strength of the printed coating.

[0279] Furthermore, in the inkjet printing method of the present invention, when using the inkjet kit of another embodiment of the present invention, through this step 2, the compound (II) contained in the water-based ink on the printing substrate is distributed to the coating film of the protective layer coating liquid, and the cross-linking reaction between the carboxyl group of the binder resin (Ib) and the reactive group of the compound (II) is carried out, so that a printed material with uniform strength of the printed coating film can be obtained.

[0280] The heat treatment in step 2 is preferably a process to dry the coating film of water-based ink and the coating film of protective coating liquid on the printing substrate formed in step 1.

[0281] Methods for heating treatment in step 2 include blowing a gas at a desired temperature onto the coating formed on the printing substrate, passing the printing substrate with the coating formed through a gas atmosphere at a desired temperature, irradiating the coating formed on the printing substrate with an infrared heater, and heating the printing substrate with the coating formed using a hot plate.

[0282] From a production point of view, the heating temperature is preferably 40°C or higher, more preferably 50°C or higher, and from the point of view of preventing the impact on the printing substrate, it is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 70°C or lower.

[0283] From the viewpoint of scratch resistance and water resistance, the heating time is preferably 30 seconds or more, more preferably 1 minute or more, and from the viewpoint of productivity, it is preferably 10 minutes or less, more preferably 7 minutes or less, and even more preferably 5 minutes or less.

[0284] [Packaging Method]

[0285] In this invention, when the printing substrate is a heat-shrinkable resin film, the ink kit for inkjet printing described above is preferably used in the packaging method of the packaged object.

[0286] As a packaging method, it is preferable to place the printed material obtained by the inkjet printing method described above around the packaged object, and then shrink the heat-shrinkable resin film substrate of the printed material to obtain the packaged object.

[0287] From a production point of view, the heating temperature for causing shrinkage is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. Furthermore, from the viewpoint of preventing damage to the resin film substrate, it is preferably 200°C or lower, more preferably 150°C or lower, even more preferably 130°C or lower, and even more preferably 110°C or lower. This heating temperature is preferably below a temperature at which the printed material can be used without problems even if shrinkage occurs.

[0288] The heating time for shrinking the resin film substrate is preferably 3 seconds or more, more preferably 5 seconds or more, and even more preferably 7 seconds or more, and from a production point of view, preferably 5 minutes or less, more preferably 3 minutes or less, and even more preferably 1 minute or less.

[0289] Regarding the above-described embodiments, the present invention also discloses the following contents.

[0290] <1> An ink kit for inkjet printing, wherein,

[0291] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0292] This water-based ink contains a binder resin (Ib) with carboxyl groups.

[0293] The protective coating liquid contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib).

[0294] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0295] <2> An ink kit for inkjet printing, wherein,

[0296] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0297] The water-based ink contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib) having carboxyl groups.

[0298] The protective coating liquid contains a binder resin (Ib) with carboxyl groups.

[0299] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0300] <3> The ink kit for inkjet printing described in <1> or <2> above, wherein the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is 1.5 mN / m or more.

[0301] <4> The ink kit for inkjet printing as described in any one of <1> to <3> above, wherein the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is more than 7 mN / m and less than 15 mN / m.

[0302] <5> The ink kit for inkjet printing as described in any one of <1> to <4> above, wherein the reactive group equivalent of the compound (II) is 100 to 500.

[0303] <6> The ink kit for inkjet printing as described in any one of <1> to <5> above, wherein the compound (II) is selected from one or more of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds and polyfunctional epoxy compounds.

[0304] <7> The ink kit for inkjet printing as described in any one of <1> to <6> above, wherein the compound (II) is a polyfunctional carbodiimide compound.

[0305] <8> The ink kit for inkjet printing as described in any one of <1> to <7> above, wherein the binder resin (Ib) is selected from one or more vinyl resins (Ib-1) having carboxyl groups and polyurethane resins (Ib-2) having carboxyl groups.

[0306] <9> The ink kit for inkjet printing described in <8> above, wherein the vinyl resin (Ib-1) is a (meth)acrylic resin comprising structural units from one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units from (meth)acrylic esters having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms.

[0307] <10> The ink kit for inkjet printing described in <8> or <9> above, wherein the weight-average molecular weight of the vinyl resin (Ib-1) is more than 10,000 and less than 800,000.

[0308] <11> The ink kit for inkjet printing as described in any one of <1> to <8> above, wherein the binder resin (Ib) is a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0309] <12> The ink kit for inkjet printing as described in any one of <1> to <8> above, wherein the binder resin (Ib) is an addition polymer of dimethylolpropionic acid, polycarbonate polyol, and dicyclohexylmethane 4,4'-diisocyanate.

[0310] <13> An ink kit for inkjet printing, wherein,

[0311] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0312] This water-based ink contains a (meth)acrylic resin as a carboxyl-containing binder resin (Ib). The (meth)acrylic resin comprises structural units derived from one or more carboxyl-containing monomers selected from acrylic acid and methacrylic acid, and structural units derived from (meth)acrylic esters having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms. The weight-average molecular weight of the (meth)acrylic resin is 10,000 to 800,000.

[0313] The protective coating liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the adhesive resin (Ib).

[0314] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is more than 7 mN / m and less than 15 mN / m.

[0315] <14> An ink kit for inkjet printing, wherein,

[0316] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0317] This water-based ink contains a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate as a carboxyl-containing binder resin (Ib), the copolymer having a weight-average molecular weight of 10,000 to 800,000.

[0318] The protective coating liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the adhesive resin (Ib).

[0319] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is more than 7 mN / m and less than 15 mN / m.

[0320] <15> An ink kit for inkjet printing, wherein,

[0321] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0322] This water-based ink contains a carboxyl-containing polyurethane resin (Ib-2) as a carboxyl-containing binder resin (Ib).

[0323] The protective coating liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the adhesive resin (Ib).

[0324] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is more than 7 mN / m and less than 15 mN / m.

[0325] <16> An ink kit for inkjet printing, wherein,

[0326] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0327] This water-based ink contains an addition polymer of dimethylolpropionic acid, polycarbonate polyols, and dicyclohexylmethane 4,4'-diisocyanate as a carboxyl-containing binder resin (Ib).

[0328] The protective coating liquid contains a polyfunctional carbodiimide compound as a compound (II) having a reactive group capable of crosslinking with the carboxyl group of the adhesive resin (Ib).

[0329] The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is more than 7 mN / m and less than 15 mN / m.

[0330] <17> An inkjet printing method, wherein,

[0331] The inkjet printing method uses the inkjet printing ink kit described in any one of <1> to <16> above, and includes the following steps 1 and 2.

[0332] Step 1: After applying the water-based ink to the heat-shrinkable resin film substrate by inkjet printing, the protective coating liquid is applied to the portion on which the water-based ink has been applied by inkjet printing.

[0333] Step 2: A step of heating the water-based ink coating and the protective coating liquid coating on the printing substrate formed in Step 1.

[0334] <18> A packaging method wherein, after a printed material obtained by the inkjet printing method described in <17> is disposed around a packaged body, the heat-shrinkable resin film substrate of the printed material is shrunk to obtain a packaged body.

[0335] <19> As an ink kit for inkjet printing, among which,

[0336] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0337] This water-based ink contains a binder resin (Ib) with carboxyl groups.

[0338] The protective coating liquid contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib).

[0339] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0340] <20> As an ink kit for inkjet printing, among which,

[0341] The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free.

[0342] The water-based ink contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib) having carboxyl groups.

[0343] The protective coating liquid contains a binder resin (Ib) with carboxyl groups.

[0344] The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

[0345] <21> An inkjet printing apparatus, wherein the inkjet printing apparatus is used for the inkjet printing ink kit of <1> to <16> above, and has an inkjet head filled with the water-based ink and an inkjet head filled with the protective coating liquid.

[0346] <22> The inkjet printing apparatus described in <21> above further includes a processing unit for heating the coating film of water-based ink and the coating film of protective coating liquid on the printing substrate.

[0347] Example

[0348] In the following manufacturing examples, preparation examples, embodiments, and comparative examples, "parts" are used unless otherwise specified as "parts by mass". Various physical properties were determined by the following methods.

[0349] [Determination of the acid value of resin]

[0350] Using an automatic potentiometric titration apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., electric burette, model: APB-610), the resin was dissolved in a titration solvent consisting of toluene and acetone (toluene:acetone = 2:1 (volume ratio)), and titrated with a 0.1N potassium hydroxide / ethanol solution. The inflection point on the titration curve was taken as the endpoint. The acid value (mgKOH / g) was calculated based on the titration volume of the potassium hydroxide solution up to the endpoint.

[0351] [Determination of number-average and weight-average molecular weight of resins]

[0352] The determination was performed by gel permeation chromatography. The determination conditions are as follows.

[0353] GPC Unit: Tosoh Corporation "HLC-8320GPC"

[0354] Chromatographic columns: TSKgel SuperAWM-H, TSKgel SuperAW3000, and TSKgel guardcolum Super AW-H, all manufactured by Tosoh Corporation.

[0355] Eluent: A liquid in which phosphoric acid and lithium bromide are dissolved in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively.

[0356] Flow rate: 0.5 mL / min

[0357] Standard materials: Monodisperse polystyrene kits with known molecular weights, "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (all manufactured by Tosoh Corporation).

[0358] The sample was tested by mixing 0.1 g of polymer with 10 mL of the above eluent in a glass vial and stirring with a magnetic stirrer at 25 °C for 10 hours. The liquid was then filtered through a syringe filter "DISMIC-13HP" (Advantech Co., Ltd., pore size: 0.2 μm, material: PTFE).

[0359] [Determination of the average particle size of pigment-containing resin particles in an aqueous dispersion and the average particle size of pigment-free resin particles in an aqueous dispersion]

[0360] The average particle size was determined by cumulative analysis using a laser particle analysis system (ELS-8000, manufactured by Otsuka Electronics Co., Ltd.). The concentration of the particles measured reached 5 × 10⁻⁶. -3 The dispersion diluted with water was measured by mass % (conversion of solid component concentration). The measurement conditions were: temperature 25°C, incident light angle with detector 90°, cumulative measurements 100, and the refractive index of water (1.333) was used as the input refractive index of the dispersion medium. The resulting cumulative average particle size was taken as the average particle size of either the pigment-containing resin particles or the pigment-free resin particles in the aqueous dispersion.

[0361] [Determination of solid component concentration]

[0362] Using an infrared moisture meter (Kett Electric Laboratory Co., Ltd. "FD-230"), 5g of the test sample was dried at a drying temperature of 150℃ and in test mode 96 (monitoring time 2.5 min / variable range 0.05%). The moisture content (mass%) of the test sample was then measured, and the concentration of solid components (mass%) was calculated using the following formula.

[0363] Solid component concentration (mass%) = 100 - moisture content of the sample (mass%)

[0364] [Determination of surface tension γ(A) of water-based ink and surface tension γ(B) of protective coating liquid]

[0365] Using a surface tension meter (“CBVP-Z” manufactured by Kyowa Interface Science Co., Ltd.), a platinum plate was immersed in a cylindrical polyethylene container (3.6 cm in diameter × 1.2 cm in depth) containing 5 g of water-based ink or protective coating liquid adjusted to 20 °C. The static surface tension at 20 °C was measured using the Wilhelmy method and denoted as the surface tension γ(A) of the water-based ink or the surface tension γ(B) of the protective coating liquid.

[0366] [Viscosity Measurement of Water-Based Inks]

[0367] The viscosity of water-based ink at 32°C was measured using an E-type viscometer (Toki Sangyo Co., Ltd. "TV-25", standard conical rotor 1°34'×R24, rotation speed 50 rpm).

[0368] [pH Measurement of Water-Based Inks]

[0369] The pH of water-based ink at 25°C was measured using a benchtop pH meter ("F-71" manufactured by Horiba Ltd.) equipped with a pH electrode ("6337-10D" manufactured by Horiba Ltd.).

[0370] [Determination of water absorption of printing substrate during 100ms of contact time between printing substrate and pure water]

[0371] Using an automatic scanning absorbent meter (Kumagai Riki Kogyo Co., Ltd. "KM500win"), the amount of water transferred when the contact time with pure water was 100 minutes was measured under conditions of 23°C and 50% relative humidity. The absorbance was defined as the amount of water absorbed in 100 minutes. The measurement conditions are as follows.

[0372] "Spiral Method"

[0373] Contact time (seconds): 0.010~1.0

[0374] Pitch (mm): 7

[0375] Length per sampling (degrees): 86.29

[0376] Starting Radius (mm): 20

[0377] End Radius (mm): 60

[0378] Minimum Contact Time (milliseconds): 10

[0379] Maximum Contact Time (milliseconds): 1,000

[0380] Sampling Pattern (1-50): 50

[0381] Number of Sampling Points (>0): 19

[0382] "Square Head"

[0383] Slit span (mm): 1

[0384] Slit Width (mm): 5

[0385] [Manufacturing of Pigment Dispersion Resin (Ia)]

[0386] Manufacturing Example 1-1 (Manufacturing of a water-insoluble polymer (a1) with carboxyl groups)

[0387] 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of styrene macromonomer (AS-6S manufactured by Toa Synthetic Co., Ltd., number average molecular weight 6,000, solid content 50% by mass) and 25 parts of methoxy polyethylene glycol methacrylate (Blemmer PME-200 manufactured by Nippon Oil Co., Ltd.) were mixed to prepare 115 parts of monomer mixture.

[0388] 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 above monomer mixture were added to the reaction vessel and mixed thoroughly with nitrogen gas.

[0389] On the other hand, the remaining 90% (103.5 parts) of the above-mentioned monomer mixture, along with 0.27 parts of the above-mentioned chain transfer agent, 42 parts of MEK, and 3 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) (manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd., "V-65") as a polymerization initiator, were added to a dropping funnel. Under a nitrogen atmosphere, the mixture in the reaction vessel was stirred while the temperature was raised to 75°C, and the mixture was added dropwise to the dropping funnel over 3 hours. After 2 hours at 75°C from the end of the titration, a solution of 3 parts of the above-mentioned polymerization initiator dissolved in 5 parts of MEK was added. The mixture was then aged at 75°C for 2 hours, then at 80°C for 2 hours, and finally 50 parts of MEK were added to obtain a solution of a carboxyl-containing water-insoluble polymer (a1) (weight average molecular weight: 50,000). The solid content concentration of the solution of the carboxyl-containing water-insoluble polymer (a1) was 45% by mass.

[0390] [Preparation of aqueous dispersions of pigment-containing resin particles]

[0391] Manufacturing Example 2-1 (Manufacturing of an aqueous dispersion (D1) of resin particles containing white pigment)

[0392] In a 250 mL polyethylene bottle, a mixture was prepared by mixing and dissolving 0.3 g of polyacrylic acid (PAA; manufactured by Fujifilm and Kogyo Pure Chemical Industries Co., Ltd., Mw: 5,000 (list value)) as pigment dispersion resin (Ia), 0.21 g of 5N sodium hydroxide aqueous solution (sodium hydroxide solid content 16.9% by mass, manufactured by Fujifilm and Kogyo Pure Chemical Industries Co., Ltd.), and 1 g of deionized water. Then, 15 g of titanium dioxide (rutile type, manufactured by Titan Kogyo, Ltd., "KURONOSKR-380", Al·Si treated, average primary particle size: 355 nm (list value 300~500 nm)) as white pigment and 14.3 g of deionized water were added. Finally, 369 g of 2 mm zirconia beads were added. The mixture was dispersed at 250 rpm for 8 hours using a benchtop mill stand (AS ONE Corporation). Then, the zirconia beads were removed using a sieve, and the solid content concentration was adjusted with water to obtain an aqueous dispersion (D1) of resin particles containing white pigment (solid content concentration: 30% by mass, mass ratio [pigment / (pigment + pigment dispersion resin (Ia))]: 0.98). The average particle size of the resin particles containing white pigment in the obtained aqueous dispersion was 325 nm.

[0393] Manufacturing Example 2-2 (Manufacturing of an aqueous dispersion (D2) of resin particles containing black pigment)

[0394] A solution of 95.2 parts of a carboxyl-containing water-insoluble polymer (a1) obtained in Example 1-1 as a pigment dispersion resin (Ia) was mixed with 53.9 parts of MEK. 15.0 parts of a 5N sodium hydroxide aqueous solution, 0.5 parts of 25% ammonia, and 341.3 parts of deionized water were added as neutralizing agents. Then, 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) as a black pigment were added to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed for 1 hour at 7,000 rpm and 20°C using a dispersing vane. Then, it was dispersed 15 times using a high-pressure homogenizer, "Microfluidizer M-140K" (manufactured by Microfluidics), at a pressure of 180 MPa to obtain a dispersion.

[0395] The obtained dispersion was subjected to reduced pressure at 60°C to remove MEK, followed by partial water removal. Centrifugation was then performed, and the liquid layer was recovered. Coarse particles were removed by filtration using a "Minisart Syringe Filter" (manufactured by Sartorius, pore size: 5μm, material: cellulose acetate), yielding an aqueous dispersion of polymer particles containing black pigment. The solids concentration was 25% by mass.

[0396] To a ratio of 100 parts to the obtained aqueous dispersion of polymer particles containing black pigment, 0.45 parts of trimethylolpropane polyglycidyl ether (DENACOL EX-321L, manufactured by Nagase ChemteX Corporation, epoxy equivalent 130) and 15.23 parts of deionized water were added, and the mixture was heated at 70°C for 3 hours while stirring. After cooling to room temperature, the liquid layer was recovered and filtered using a "Minisart Syringe Filter" (manufactured by Sartorius Corporation, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion K of polymer particles containing black pigment (solid content concentration 22% by mass, mass ratio [pigment / (pigment + pigment dispersion resin with cross-linked structure (Ia))]: 0.69). The average particle size of the polymer particles containing black pigment in the obtained aqueous dispersion K was 100 nm.

[0397] [Preparation of an aqueous dispersion of pigment-free resin particles composed of binder resin (Ib)]

[0398] Manufacturing Example 3-1 (Manufacturing of an aqueous dispersion (d1) of acrylic resin particles without pigment)

[0399] In a reaction vessel equipped with a dropping funnel, the monomers shown in Table 1 “Initial Monomer Solution”, sodium polyoxyethylene alkyl ether sulfate (manufactured by Kao Corporation, “LATEMUL E-118B”) (hereinafter referred to as “LATEMULE-118B”) as emulsifier, potassium persulfate as polymerization initiator, and deionized water are added and mixed, and nitrogen is purged to obtain the initial monomer solution.

[0400] Separately mix the monomers, emulsifiers, polymerization initiators and ion-exchanged water shown in Table 1 to obtain a monomer addition solution. Then, put the monomer addition solution into a dropping funnel and purge with nitrogen.

[0401] Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was stirred while the temperature was raised from room temperature to 80°C over 30 minutes. While maintaining this temperature, the monomer solution from the dropping funnel was slowly added dropwise into the reaction vessel over 3 hours. After the addition was complete, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. Then, it was filtered through a 200-mesh sieve to obtain an aqueous dispersion (d1) of pigment-free acrylic resin particles (solids concentration: 44.1% by mass, acid value: 16 mg KOH / g, weight-average molecular weight of acrylic resin: 750,000, average particle size: 95 nm).

[0402] [Table 1]

[0403]

[0404] Manufacturing Example 3-2 (Manufacturing of an aqueous dispersion (d2) of polyurethane resin particles without pigment)

[0405] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen purging tube, 125.0 g of a polycarbonate polyol ("DURANOL T-6002" manufactured by Asahi Kasei Corporation, molecular weight: 2,000, hydroxyl value: 56.1 mgKOH / g), 36.1 g of dicyclohexylmethane 4,4'-diisocyanate, and 80.5 g of methyl ethyl ketone (MEK) were added. The mixture was reacted at 75°C for 1 hour to obtain a MEK solution containing the prepolymer. Further, 4.8 g of dimethylolpropionic acid, 4.3 g of triethylamine, and MEK were added, and the mixture was reacted at 75°C for 1 hour. The solution was then cooled to 45°C, and 0.8 g of deionized water and ethylenediamine were mixed in. The emulsified dispersion was desolventized by vacuum evaporation at 50°C for 2 hours to obtain an aqueous dispersion (d2) of polyurethane resin particles without pigment (solid content concentration: 20% by mass, acid value: 16 mg KOH / g, average particle size: 88 nm).

[0406] [Manufacturing of water-based inks]

[0407] Example 1 of ink manufacturing (manufacturing of water-based ink W-1)

[0408] Add 34.00 g of the aqueous dispersion (D1) (solid content concentration: 30% by mass) of resin particles containing white pigment obtained in Manufacturing Example 2-1, 12.81 g of the aqueous dispersion (d1) (solid content concentration: 44.1% by mass) of acrylic resin particles without pigment obtained in Manufacturing Example 3-1, 30.00 g of propylene glycol (hereinafter referred to as "PG"), 3.00 g of diethylene glycol monoisobutyl ether (manufactured by Nippon Emulsifier Co., Ltd.) (hereinafter referred to as "iBDG"), and acetylene glycol surfactant "Surfynol". 1.00 g of EO (3.5 mol) adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol, manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 8 (list value), 100% by mass of active ingredient; 1.00 g of polyether-modified silicone surfactant "KF-6011" (PEG-11 methyl ether polydimethylsiloxane, manufactured by Shin-Etsu Chemical Industry Co., Ltd., HLB value: 14.5 (list value)); and 100.00 g of deionized water. The resulting mixture was filtered using a "Minisart Syringe Filter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain water-based ink W-1 (viscosity: 5.6 mPa·s, pH: 8.2).

[0409] Examples of ink manufacturing 2-4 (manufacturing of water-based inks W-2, K-1 and W-3)

[0410] The same operation was performed, except that the formulation was changed to that shown in Table 2 in Ink Manufacturing Example 1, to obtain various water-based inks.

[0411] [Table 2]

[0412]

[0413] Preparation Examples 1-12 (Preparation of Protective Coating Liquids OC-1 to OC-12)

[0414] The mixtures were prepared according to the formulations shown in Table 3. The resulting mixtures were then filtered through a "Minisart SyringeFilter" (manufactured by Sartorius, pore size: 5.0 μm, material: cellulose acetate) to obtain the coating solutions for each protective layer.

[0415] The labels in Tables 2 and 3 are described below.

[0416] (Compound (II))

[0417] [Multifunctional carbodiimide compounds]

[0418] Carbodilite E-07S: A multi-carbodiimide compound (carbodiimide equivalent: 234, active ingredient 40% by mass, manufactured by Nisshinbo Chemical Inc.)

[0419] Carbodilite E-02: A polymer containing carbodiimide groups (carbodiimide equivalent: 445, emulsion / dispersion type, active ingredient 40% by mass, manufactured by Nisshinbo Chemical Inc.)

[0420] Carbodilite E-05: A polymer containing carbodiimide groups (carbodiimide equivalent: 313, emulsion / dispersion type, active ingredient 40% by mass, manufactured by Nisshinbo Chemical Inc.)

[0421] [Multifunctional oxazoline compounds]

[0422] Epocros WS-700: A polymer containing oxazoline groups (oxazoline equivalent: 220, polymer backbone: acrylic acid, number average molecular weight: 20,000, water-soluble type, active ingredient 25% by mass, manufactured by Nippon Shokubai Co., Ltd.)

[0423] [Multifunctional epoxides]

[0424] DENACOL EX-212: 1,6-Hexanediol diglycidyl ether (epoxy equivalent: 151, active ingredient 100% by mass, manufactured by Nagase ChemteX Corporation)

[0425] (surfactant)

[0426] Surfynol 420: An ethynylene glycol surfactant (EO adduct of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (average EO addition moles: 1), HLB value: 4 (catalog value), manufactured by Nissin Chemical Industry Co., Ltd.)

[0427] KF-6011: Polyether-modified silicone surfactant (PEG-11 methyl ether polydimethylsiloxane, HLB value: 14.5 (catalog value), manufactured by Shin-Etsu Chemical Co., Ltd.)

[0428] [Table 3]

[0429]

[0430] Examples 1-13 and Comparative Example 1

[0431] The combination of water-based ink and protective coating liquid shown in Table 4 was used as an ink kit. The heat-shrinkable PET film “SPACECLEAN SP809” (manufactured by Toyobo Co., Ltd., heat shrinkage rate (90℃, 10 seconds): 50%, water absorption: 10g / m³) was used as the printing substrate. 2 The following methods were used to produce printed materials, and the resulting printed materials were evaluated as follows. The results are shown in Table 4.

[0432] (Inkjet printing)

[0433] [Inkjet Printing Conditions]

[0434] In a printing evaluation apparatus equipped with three inkjet heads (KJ4B-HD06MHG-STDV, piezoelectric type, manufactured by Kyocera Corporation) and a bottom heater that heats the printing substrate from the face and back sides opposite the inkjet heads, water-based ink is filled in the first two inkjet heads, and a protective coating liquid is filled in the last inkjet head. The distance between the bottom heater and the printing substrate is set to 0.2 mm, the distance between the inkjet head and the printing substrate is set to 1.0 mm, and the surface temperature of the bottom heater is set to 40°C.

[0435] In an environment with a temperature of 25±1℃ and a relative humidity of 30±5%, the printhead voltage is set to 26V, the printhead drive frequency to 10kHz, the printhead temperature to 32℃, the printhead resolution to 600dpi, the number of pre-spray rinses to 200, and the negative pressure to -4.0kPa. The printing substrate is fixed to the printing evaluation device with the long side of the printing substrate facing the same direction as the conveying direction.

[0436] Set the ejection liquid volume of the first two inkjet heads filled with water-based ink to 12 pL each, and set the ejection liquid volume of the last inkjet head filled with protective coating liquid to 5 pL.

[0437] [Process 1]

[0438] A printing command is transmitted to the aforementioned printing evaluation device, and water-based ink and protective coating liquid are sprayed out in the order of water-based ink and protective coating liquid. The solid image of the protective coating liquid is printed overlaid at the same position as the solid image of the water-based ink. The spray interval between the water-based ink and the protective coating liquid is set to 1 second.

[0439] In the examples and comparative examples, the equivalent ratio of compound (II) calculated by the following formula is shown in Table 4.

[0440] (The cases of Examples 1-11 and Comparative Example 1)

[0441] The usage equivalent ratio of compound (II) = [(the amount of protective coating liquid injected (5 pL) × the content of compound (II) in the protective coating liquid) / the equivalent of reactive groups of compound (II)] / [(the amount of water-based ink injected (24 pL) × the content of binder resin (Ib) in the water-based ink × (the acid value of binder resin (Ib) / (56.11 × 1000))]

[0442] (Case of Example 12)

[0443] The usage equivalent ratio of compound (II) = [(droplet amount of water-based ink × content of compound (II) in water-based ink) / equivalent of reactive groups of compound (II)] / [(droplet amount of protective coating liquid × content of binder resin (Ib) in protective coating liquid × (acid value of binder resin (Ib) / (56.11 × 1000))]

[0444] [Process 2]

[0445] Next, the printed material was dried by heat treatment in a 60°C warm air dryer for 1 minute, thereby obtaining the printed material. The scratch resistance and water resistance of the obtained printed material before shrinkage were evaluated according to the following method.

[0446] [Evaluation of the scratch resistance of the printed material before shrinkage]

[0447] For each printed material obtained, the fingertip load during the scratch test was measured using a mass measuring instrument (A&D Company, Ltd. "GX-6100"), while a load of 300g was applied to the nail tip of the index finger for scratching. The surface condition after 50 back-and-forth strokes on the printed surface was visually confirmed, and the scratch resistance was evaluated according to the evaluation criteria shown below.

[0448] (Evaluation Criteria)

[0449] A: No change at all

[0450] B: Over 90% of the affected area remained unchanged.

[0451] C: More than 70% of the affected area remained unchanged.

[0452] D: More than 50% of the affected area has changed.

[0453] If the rating is C or higher, then the scratch resistance is not a problem in practical use.

[0454] [Evaluation of the water resistance of the printed material before shrinkage]

[0455] Each printed material was cut into 3×3cm test pieces. The test pieces were immersed in ion-exchanged water in a threaded tube manufactured by Maruemu Corporation and left at room temperature for 24 hours. Then, the test pieces of the printed materials were removed from the threaded tube, and while measuring the load on the fingertip using a mass meter (A&D Company, Ltd. "GX-6100"), a 300g load was applied with the tip of the index fingernail to scratch the surface. The surface condition after 10 back-and-forth strokes was visually confirmed, and the scratch resistance was evaluated according to the evaluation criteria shown below.

[0456] (Evaluation Criteria)

[0457] A: No change at all

[0458] B: Over 90% of the affected area remained unchanged.

[0459] C: More than 70% of the affected area remained unchanged.

[0460] D: More than 50% of the affected area has changed.

[0461] If the rating is C or above, then the water resistance is not a problem in practical applications.

[0462] (Preparation of the shrunken printed material)

[0463] Following the test described in JIS Z 1709-1995, test specimens were prepared using the obtained printed materials. For each specimen, the solid image portion of the printed material was cut out with a roll direction MD (longitudinal) of 100 mm and a width direction TD (horizontal) of 100 mm.

[0464] The heat transfer medium in the above standard was changed to water. The sample was immersed in hot water heated to 90°C for 10 seconds to cause thermal shrinkage. Then, the sample was immersed in room temperature water for 5 seconds to cool it. The sample was then left to stand at 23°C and 50% humidity for 24 hours to dry. After that, the same scratch resistance and water resistance tests were performed as on the printed material before shrinkage.

[0465] [Table 4]

[0466]

[0467] As shown in Table 4, the ink kits of the embodiments, compared with the comparative examples, exhibit superior scratch resistance and water resistance, especially in the heat-shrinked printed materials.

[0468] In Examples 1-4, there were instances where the surface tension γ(B) of the protective coating liquid was adjusted by changing the type and amount of surfactant contained in the protective coating liquid, and the scratch resistance and water resistance before shrinkage were both rated as "A". Furthermore, in Examples 1-4, the greater the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink, the better the scratch resistance and water resistance after shrinkage. Therefore, it can be concluded that the improved scratch resistance and water resistance of the printed materials after shrinkage in Examples 1-4 were not due to changes in the type and amount of surfactant, but rather due to the Marangoni convection caused by the difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink. This convection allows the reactive compound (II) contained in the protective coating liquid film to be uniformly distributed into the water-based ink film, promoting a uniform cross-linking reaction between the carboxyl groups of the binder resin (Ib) and the reactive groups of compound (II), thereby resulting in printed materials with uniform strength of the printed coating film.

[0469] Furthermore, Example 13 is an ink kit containing a compound (II) with a reactive group that can crosslink with the carboxyl group of a carboxyl-containing binder resin (Ib), and the protective coating liquid contains an ink kit containing a carboxyl-containing binder resin (Ib). This ink kit can also improve the scratch resistance and water resistance of the printed material after heat shrinkage.

[0470] Industrial availability

[0471] According to the present invention, an ink kit, inkjet printing method, and packaging method are provided for inkjet printing, which can improve the scratch resistance and water resistance of the printed material after heat shrinkage in the printing of heat-shrinkable resin films.

Claims

1. An ink kit for inkjet printing, wherein, The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free. This water-based ink contains a binder resin (Ib) with carboxyl groups. The protective coating liquid contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib). The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

2. An ink kit for inkjet printing, wherein, The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free. The water-based ink contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib) having carboxyl groups. The protective coating liquid contains a binder resin (Ib) with carboxyl groups. The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

3. The ink kit for inkjet printing as described in claim 1 or 2, wherein, The difference Δγ between the surface tension γ(B) of the protective coating liquid and the surface tension γ(A) of the water-based ink is greater than 1.5 mN / m.

4. The ink kit for inkjet printing as described in any one of claims 1 to 3, wherein, The reactive group equivalent of the compound (II) is more than 100 and less than 500.

5. The ink kit for inkjet printing as described in any one of claims 1 to 4, wherein, The compound (II) is selected from one or more of polyfunctional carbodiimide compounds, polyfunctional oxazoline compounds, and polyfunctional epoxy compounds.

6. The ink kit for inkjet printing as described in any one of claims 1 to 5, wherein, The compound (II) is a polyfunctional carbodiimide compound.

7. An inkjet printing method, wherein, The inkjet printing method uses the inkjet printing ink kit according to any one of claims 1 to 6, and includes the following steps 1 and 2. Step 1: After applying the water-based ink to the heat-shrinkable resin film substrate by inkjet printing, the protective coating liquid is applied to the portion on which the water-based ink has been applied by inkjet printing. Step 2: A step of heating the water-based ink coating and the protective coating liquid coating on the printing substrate formed in Step 1.

8. A packaging method, wherein, After the printed material obtained by the inkjet printing method of claim 7 is placed around the packaged body, the heat-shrinkable resin film substrate of the printed material is shrunk to obtain the packaged body.

9. As an ink kit for inkjet printing, wherein, The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free. This water-based ink contains a binder resin (Ib) with carboxyl groups. The protective coating liquid contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib). The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

10. An application as an ink kit for inkjet printing, wherein, The inkjet printing ink kit includes: a water-based ink containing pigment, and a protective coating liquid that is substantially pigment-free. The water-based ink contains compound (II), which has reactive groups capable of crosslinking with the carboxyl groups of the adhesive resin (Ib) having carboxyl groups. The protective coating liquid contains a binder resin (Ib) with carboxyl groups. The surface tension γ(B) of the protective coating liquid is greater than the surface tension γ(A) of the water-based ink.

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