Ink set and method for producing printed material

Abstract

To provide an active energy ray-curable inkjet ink set capable of yielding a printed material including a laminate that maintains a balance between excellent adhesion to a substrate and excellent abrasion resistance even after sterilization and disinfection.SOLUTION: A printed material 1 includes a substrate 2, a primer layer 6 formed on the substrate 2, and a colored layer 7 formed on the primer layer 6. The primer layer 6 is formed from a primer ink including a monofunctional monomer with a monocyclic aliphatic group, and the colored layer 7 is formed from a coloring ink including 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a monomer with an acyclic amide bond.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink set and a method for producing a printed matter. [Background technology]

[0002] Patent Document 1 discloses an ink set including a clear ink and a colored ink. The ink set has a composition that takes into consideration adhesion to polypropylene (PP) and polyethylene terephthalate (PET). Both the clear ink and the colored ink contain an amine-containing acrylate and 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA). The clear ink also contains tert-butylcyclohexanol acrylate (TBCHA).

[0003] Patent Document 2 discloses an ink set in which a clear ink containing 3,3,5-triethylcyclohexyl(meth)acrylate (TMCHA) is used as a primer ink and is combined with a colored ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-102692 [Patent Document 2] Japanese Patent Publication No. 2021-161159 Summary of the Invention [Problem to be solved by the invention]

[0005] Printed materials on PP or PE are often used in wet areas. Therefore, they require high adhesion and abrasion resistance to the substrate, even when exposed to sterilization and disinfection with acidic detergents or peroxides. For example, they must be resistant to acidic detergents (inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as sulfamic acid and oxalic acid), peroxides (hydrogen peroxide and peracetic acid), disinfectants (hypochlorous acid water, sodium hypochlorite aqueous solution, etc.), aldehydes, povidone-iodine, catechins, and other agents used in sterilization and disinfection processes (various cleaning and washing detergents).

[0006] In this regard, as in the invention described in Patent Document 1, inks containing amines have good adhesion to non-polar substrates such as PP and PE, but have low resistance to peroxides and other materials used in sterilization and disinfection processes. Therefore, unless a material with high resistance to peroxides and other materials is incorporated into the primer layer, the adhesion of the coating film decreases. On the other hand, if such a material is not incorporated into the colored layer, there is the issue of insufficient scratch resistance.

[0007] Furthermore, in the invention described in Patent Document 2, good curing properties are required because insufficient curing of the UV-curable resin results in low resistance to sterilization and disinfection treatments. Furthermore, unless a material resistant to peroxides is blended into the colored ink, scratch resistance will be poor.

[0008] Therefore, an object of the present invention is to provide an actinic ray-curable inkjet ink set that can provide a printed item having a laminate that can achieve both excellent adhesion to a substrate and excellent abrasion resistance even after a sterilization / disinfection treatment.

[0009] Another object of the present invention is to provide a method for producing a printed item having a laminate obtained using the active energy ray-curable inkjet ink set, which is capable of achieving both excellent adhesion to a substrate and excellent abrasion resistance even after sterilization and disinfection treatment. [Means for solving the problem]

[0010] The ink set of the present invention is an actinic ray-curable inkjet ink set comprising a combination of a clear primer ink and one or more colored inks, wherein the primer ink contains a monofunctional monomer containing a monocyclic aliphatic group, and the colored ink contains 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a monomer having an acyclic amide bond.

[0011] In the ink set of the present invention, the primer ink may contain 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, and the primer ink and the colored ink may each contain 2-(2-vinyloxyethoxy)ethyl (meth)acrylate as a main component.

[0012] In the ink set of the present invention, the primer ink may further contain a monomer having an amide bond.

[0013] In the ink set of the present invention, the monofunctional monomer containing a monocyclic aliphatic group in the primer ink may be t-butylcyclohexanol acrylate or 3,3,5-trimethylcyclohexanol acrylate.

[0014] In the ink set of the present invention, the monomer having a non-cyclic amide bond in the color ink may be acrylamide.

[0015] The method for producing a printed matter of the present invention is a method for producing a printed matter using an actinic ray-curable inkjet ink set comprising a combination of a clear primer ink and one or more colored inks, and comprises a first step of printing the primer ink onto a substrate, and a second step of printing the one or more colored inks onto the primer ink, wherein the primer ink comprises a monofunctional monomer containing a monocyclic aliphatic group, and the colored ink comprises 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a monomer having an acyclic amide bond.

[0016] In the method for producing a printed matter of the present invention, the first step may include a step of irradiating a primer precursor layer formed by printing the primer ink with active energy rays to cause a curing reaction of the primer ink that forms the primer precursor layer, thereby forming a primer layer, and the second step may include a step of irradiating a colored precursor layer formed by printing the colored ink with active energy rays to cause a curing reaction of the colored ink that forms the colored precursor layer, thereby forming a colored layer. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an actinic ray-curable inkjet ink set which can provide a printed item having a laminate which can achieve both excellent adhesion to a substrate and excellent abrasion resistance even after a sterilization / disinfection treatment.

[0018]

[0023] Furthermore, according to the present invention, it is possible to provide a method for producing a printed item having a laminate which is obtained using the actinic energy ray-curable inkjet ink set and which is capable of achieving both excellent adhesion to a substrate and excellent abrasion resistance even after a sterilization / disinfection treatment. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a printed matter produced by a method for producing a printed matter according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a part of the method for producing the printed matter. [Figure 3] FIG. 3 is a diagram showing a process subsequent to the process of FIG. [Figure 4] FIG. 4 is a diagram showing a process subsequent to the process of FIG. [Figure 5] FIG. 5 is a diagram showing a process subsequent to the process of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Ink set] The ink set of the present invention is an actinic ray-curable inkjet ink set. The inks used in the actinic ray-curable inkjet ink set are, for example, UV inks containing polymerizable compounds such as monomers and oligomers (hereinafter, these may be collectively referred to simply as "monomers") that undergo a polymerization reaction and harden when irradiated with ultraviolet light.

[0021] The ink set of the present invention is a combination of (1) a primer ink and (2) one or more colored inks.

[0022] (1) Primer ink The primer ink contains, as a radically polymerizable component, a monofunctional monomer containing at least a monocyclic aliphatic group (a saturated aliphatic group).

[0023] (1-A) Monofunctional Monomer Containing a Monocyclic Aliphatic Group The monocyclic aliphatic group contained in the above-mentioned monofunctional monomer is an independent cycloalkane, and does not include polycyclic compounds in which multiple monocyclic rings are bonded together or ring structures having a bridged structure within the ring. Therefore, the "monocyclic aliphatic group" of the present invention excludes aliphatic groups such as bicyclic compounds, tricyclic compounds, bicyclo rings, and tricyclo rings. Examples of the monocyclic cycloalkane of the present invention include saturated aliphatic hydrocarbon ring structures having 3 to 8 carbon atoms, such as a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a cyclohexene ring, and a cyclooctane ring.

[0024] Examples of monofunctional monomers containing a monocyclic aliphatic group include acrylate monomers of secondary alcohols of monocyclic cycloalkanes or alkyl compounds thereof. Such acrylates are resistant to the effects of peroxides used in sterilization and disinfection treatments and have the effect of maintaining adhesion. For example, they maintain good adhesion to non-polar substrates such as polypropylene (PP) and polyethylene (PE), and in particular, they exhibit good adhesion to non-polar substrates that have not been surface-treated with silane coupling agents or corona treatments.

[0025] Examples of the acrylate include cyclohexanol acrylate, methyl cyclohexanol acrylate, ethyl cyclohexanol acrylate, propyl cyclohexanol acrylate, butyl cyclohexanol acrylate, dimethyl cyclohexanol acrylate, and trimethyl cyclohexanol acrylate. These can be used alone or in combination of two or more. Among these, cyclohexanol acrylate is preferred, and specifically preferred are t-butyl cyclohexanol acrylate (TBCHA) and 3,3,5-trimethyl cyclohexanol acrylate (TMCHA).

[0026] The content of the monofunctional monomer containing a monocyclic aliphatic group in the primer ink is, for example, 5% by mass or more, preferably 10% by mass or more, based on the total mass of the monomers contained in the primer ink. The content of the monofunctional monomer containing a monocyclic aliphatic group is, for example, 30% by mass or less, preferably 25% by mass or less, based on the total mass of the monomers contained in the primer ink. More specifically, the content of the monofunctional monomer containing a monocyclic aliphatic group is, for example, 5% by mass or more and 30% by mass or less, preferably 10% by mass or more and 25% by mass or less, based on the total mass of the monomers contained in the primer ink. If the content is less than 5% by mass, sufficient adhesion to the substrate after sterilization / disinfection may not be obtained. On the other hand, if the content exceeds 30% by mass, curing properties may be poor, resulting in insufficient adhesion to the substrate after sterilization / disinfection. When two or more types of monofunctional monomers containing a monocyclic aliphatic group are used in combination, the total content thereof may be within the above range.

[0027] (1-B) 2-(2-vinyloxyethoxy)ethyl (meth)acrylate The primer ink preferably further contains 2-(2-vinyloxyethoxy)ethyl (meth)acrylate (hereinafter, 2-(2-vinyloxyethoxy)ethyl acrylate may be abbreviated as "VEEA" and 2-(2-vinyloxyethoxy)ethyl methacrylate may be abbreviated as "VEEM") as another monomer (radical polymerizable component). If there is little or no VEEA (VEEM), the curing properties of the primer ink may be insufficient, and peeling may occur between the substrate and the primer layer, between the primer layer and the colored ink layer, and especially between the substrate and the primer layer using cellophane tape, similar to interlayer delamination. On the other hand, if there is a large amount of VEEA (VEEM), the primer ink may shrink upon curing and float, resulting in insufficient adhesion to the substrate.

[0028] VEEA (VEEM) is preferably the main component of the primer ink. In other words, VEEA (VEEM) is preferably the monomer contained in the primer ink at the largest blending ratio. The content of VEEA (VEEM) is, for example, 50% by mass or more, and more preferably 65% ​​by mass or less, of the total mass of the monomers contained in the primer ink.

[0029] (1-C) Monomers with an amide bond The primer ink preferably contains a monomer having an amide bond as another monomer (radical polymerizable component). As described below, the color ink of the present invention contains a monomer having an acyclic amide bond as an essential component. By using similar components for the primer ink and color inks used in the same ink set, delamination between the primer ink and color ink can be suppressed. Furthermore, by including a monomer having an amide bond in the primer ink, adhesion to the treated surface of a substrate that has been surface-treated with a silane coupling agent or corona treatment can be improved. On the other hand, as described above, a monofunctional monomer containing a monocyclic aliphatic group exhibits good adhesion to the surface of an untreated substrate. Therefore, by blending both a monofunctional monomer containing a monocyclic aliphatic group and a monomer having an amide bond, the versatility of the substrate can be expanded.

[0030] In the present invention, a monomer having an amide bond (amide bond-containing monomer) may be a monomer containing an amide bond in the narrow sense represented by "-CONR- (R is H or an alkyl group)" or "-RNOC- (R is H or an alkyl group)" in the molecule, or may be a monomer containing an amide bond in the broad sense having an amide bond in the structure, such as a urethane bond represented by "-NHCOO-" or "-COONH-".

[0031] Examples of amide bond-containing monomers include acyclic amide bond-containing monomers and cyclic amide bond-containing monomers. The acyclic amide bond-containing monomer is a monomer in which the N atom constituting the amide bond does not form a ring structure, and the functional group of the monomer may contain a ring structure (e.g., a phenyl group, a cyclohexyl group, etc.). On the other hand, the cyclic amide bond-containing monomer is a monomer in which the N atom constituting the amide bond further forms part of a ring structure. In the present invention, acyclic amide bond-containing monomers are preferably used, and acyclic (meth)acrylamide and acyclic urethane (meth)acrylate are more preferably used.

[0032] Examples of non-cyclic amide bond-containing monomers include (meth)acrylamides such as N,N-dimethylacrylamide (DMAA), hydroxyethylacrylamide, N,N-diethylacrylamide (DEAA), N-isopropylacrylamide (NIPAM), N-[3-(dimethylamino)propyl]acrylamide (DMAPAA), diacetoneacrylamide (DAAM), N-tert-butylacrylamide, N-phenylacrylamide, N-ethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-(isobutoxymethyl)methacrylamide, and N-(triphenylmethyl)methacrylamide. These may be used alone or in combination of two or more.

[0033] Examples of non-cyclic amide bond-containing monomers include urethane (meth)acrylates such as urethane (meth)acrylates obtained by reacting a polyisocyanate with a (meth)acrylate having a hydroxyl group, urethane (meth)acrylates obtained by reacting a polyester of polyisocyanate and a terminal diol with a (meth)acrylate having a hydroxyl group, and urethane (meth)acrylates obtained by reacting a polyisocyanate obtained by reacting a polyol with an excess of diisocyanate with a (meth)acrylate having a hydroxyl group. These can be used alone or in combination of two or more.

[0034] Examples of the cyclic amide bond-containing monomer include N-vinylcaprolactam, N-vinyl-2-pyrrolidone, acryloylmorpholine, etc. These can be used alone or in combination of two or more kinds.

[0035] The content of the amide bond-containing monomer in the primer ink is, for example, 10% by mass or more, and preferably 20% by mass or more, relative to the total mass of the monomers contained in the primer ink. Furthermore, the content of the amide bond-containing monomer in the primer ink is, for example, 50% by mass or less, and preferably 40% by mass or less, relative to the total mass of the monomers contained in the primer ink. More specifically, the content of the amide bond-containing monomer in the primer ink is, for example, 10% by mass or more and 50% by mass or less, and preferably 20% by mass or more and 40% by mass or less, relative to the total mass of the monomers contained in the primer ink. This range is preferable because excessively increasing the amount of the amide bond-containing monomer in the primer ink can cause the amide bond-containing monomers to stabilize with each other, resulting in lower than expected adhesion between the substrate and the primer layer. When two or more amide bond-containing monomers are used in combination, the total content thereof may be within the above range.

[0036] (1-D) Other Monomers The primer ink may further contain other monomers besides the monofunctional monomer containing a monocyclic aliphatic group, VEEA (VEEM), and amide bond-containing monomer. Examples of such monomers include known monofunctional, difunctional, trifunctional, or higher functional polyfunctional monomers and oligomers. Examples include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid, as well as their salts or esters; urethanes; amides and their anhydrides; acrylonitrile; styrene; various unsaturated polyesters; unsaturated polyethers; unsaturated polyamides; and unsaturated urethanes. Examples of the oligomers include oligomers formed from the above-mentioned monomers, such as linear acrylic oligomers; epoxy (meth)acrylates; oxetane (meth)acrylates; aliphatic urethane (meth)acrylates; aromatic urethane (meth)acrylates; and polyester (meth)acrylates. These may be used alone or in combination.

[0037] Other monofunctional or polyfunctional monomers may include, for example, N-vinyl compounds, such as N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof.

[0038] Examples of other monomers include polyfunctional monomers such as ethoxylated pentaerythritol tetraacrylate, etc. By blending a polyfunctional monomer, the hardness of the coating film can be improved.

[0039] The content of other monomers in the primer ink is, for example, the remainder of the monofunctional monomer containing a monocyclic aliphatic group, VEEA (VEEM), and the amide bond-containing monomer. In other words, the blending ratio of the monofunctional monomer containing a monocyclic aliphatic group, VEEA (VEEM), and the amide bond-containing monomer is set preferentially.

[0040] The primer ink is a clear ink in which the content of coloring materials such as pigments and dyes is less than 0.1% by mass, and preferably 0% by mass.

[0041] The primer ink may contain a radical polymerizable additive (component). The additive is not particularly limited, but examples thereof include a radical polymerization initiator, a sensitizer, a radical polymerization inhibitor, and a surfactant.

[0042] (1-E) Radical polymerization initiator When the active energy rays irradiated to the primer ink are light such as ultraviolet rays, the radical polymerization initiator imparts photocurability as active energy ray curability to the primer ink. As the radical polymerization initiator, various compounds that can generate radicals when irradiated with light of any wavelength and cause a radical polymerization reaction of the radically polymerizable component can be used.

[0043] The radical polymerization initiator is not particularly limited, but examples thereof include the various compounds shown below.

[0044] Benzophenones such as benzophenone, hydroxybenzophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone (Michler's ketone), 4,4'-bisdimethylaminobenzophenone (Michler's ketone), 4-methoxy-4'-dimethylaminobenzophenone, and benzophenone compounds represented by general formula (1) of JP 2008-280427 A, or salts thereof.

[0045] Thioxanthones such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2,4-diethylthioxanthone, 4-isopropylthioxanthone, isopropoxychlorothioxanthone, and thioxanthone compounds represented by general formula (2) of JP 2008-280427 A, or salts thereof.

[0046] Anthraquinones such as ethylanthraquinone, benzanthraquinone, aminoanthraquinone, and chloroanthraquinone.

[0047] Acetophenones such as acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxyphenylacetophenone, 4'-dimethylaminoacetophenone, and dimethylhydroxyacetophenone.

[0048] 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, 2-(o-chlorophenyl)-4,5-di(m-methoxyphenyl)imidazole dimer, 2-(o-fluorophenyl)-4,5-diphenylimidazole dimer, 2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer, 2-(p-methoxyphenyl)-4,5-diphenylimidazole dimer, 2-di(p-methoxyphenyl)-5-phenylimidazole Imidazoles such as imidazole dimer, 2-(2,4-dimethoxyphenyl)-4,5-diphenylimidazole dimer, and 2,4,5-triarylimidazole dimer.

[0049] Benzoins such as benzyl dimethyl ketal, 2-benzyl-2-dimethylamino-1-(4-morpholinophenylbutan)-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-hydroxy-2-methyl-1-phenyl-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 9,10-phenanthrenequinone, benzoins, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether, and benzoin-n-butyl ether.

[0050] Acridine derivatives such as 9-phenylacridine and 1,7-bis(9,9′-acridinyl)heptane.

[0051] Phosphine oxides such as bisacylphosphine oxide, bisphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0052] 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}2-methylpropan-1-one, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, methyl benzoyl formate, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trihalomethyltriazine, benzyl, methylbenzoyl, methyl benzoylformate, 2-benzyl-2-dimethylamino-4-morpholinobutyrophenone, and the like.

[0053] The radical polymerization initiators described above can be used alone or in combination of two or more. The content of the radical polymerization initiator can be set as desired. However, in consideration of imparting good photocurability to the primer ink, the content of the radical polymerization initiator is, for example, 0.1% by mass or more and 15% by mass or less, and preferably 1% by mass or more and 10% by mass or less, relative to the total mass of the primer ink. When two or more radical polymerization initiators are used in combination, the total content thereof may be set within the above range.

[0054] (1-F) Sensitizer The photocurable primer ink preferably contains an optional sensitizer, if necessary. The sensitizer becomes excited by irradiation with ultraviolet light or the like, interacts with the radical polymerization initiator, and helps generate radicals in the radical polymerization initiator. In particular, when an LED is used as the light source, its wavelength range is narrow. Therefore, it is preferable to contain a sensitizer to broaden the wavelength range to which the primer ink is sensitive, thereby improving its sensitivity, i.e., to sensitize it.

[0055] Examples of the sensitizer include, among the radical polymerization initiators mentioned above, thioxanthones or salts thereof, such as 2,4-diethylthioxanthone, 1-chloro-4-propoxythioxanthone, and a mixture of 2-isopropylthioxanthone and 4-isopropylthioxanthone; eutectic mixtures of benzophenone and 2,3- and 4-methylbenzophenone; benzophenones or salts thereof, such as methyl-2-benzophenone, benzophenone, 4-benzoyl-4′-methylphenyl sulfide, 4-methylbenzophenone, and 4-phenylbenzophenone; 2-ethylanthraquinone; and 4,4′-bisdiethylaminobenzophenone (Michler's ketone).

[0056] Other sensitizers include, for example, benzoate compounds such as ethyl-4-(dimethylamino)benzoate and 2-ethyl-4-(dimethylaminobenzoate), naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives, stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives, carbostyril, naphthalimide, dibenzothiophene-5,5'-dioxide derivatives, pyrene derivatives, pyridotriazole, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, and triethanolamine.

[0057] As the sensitizer, a compound having an absorption wavelength range suitable for sensitization can be selected from the various sensitizers described above depending on the wavelength range of light from the light source and the absorption wavelength range of the radical polymerization initiator. The above sensitizers can be used alone or in combination of two or more.

[0058] The content of the sensitizer can be set arbitrarily. However, in order to effectively exhibit the sensitizing effect of the sensitizer, the content of the sensitizer is, for example, 0.1% by mass or more and 5% by mass or less, and preferably 0.5% by mass or more and 4% by mass or less, relative to the total mass of the primer ink. When two or more sensitizers are used in combination, the total content thereof may be set within the above range.

[0059] (1-G) Radical polymerization inhibitor The primer ink may contain a radical polymerization inhibitor as needed. The radical polymerization inhibitor prevents the radical polymerizable component from undergoing a radical polymerization reaction and gelling the primer ink during storage of the primer ink or during storage in a sealed package. As the radical polymerization inhibitor, various compounds capable of preventing the above-mentioned gelling can be used.

[0060] Examples of the radical polymerization inhibitor include nitrosamine compounds, hydroquinones, catechols, hindered amines, phenols, phenothiazines, and condensed aromatic ring quinones.

[0061] Examples of nitrosoamine compounds include the ammonium salt of N-nitrosophenylhydroxylamine (ammonium-N-nitrosophenylhydroxylamine), and the aluminum salt of N-nitrosophenylhydroxylamine (aluminum-N-nitrosophenylhydroxylamine).

[0062] Examples of hydroquinones include hydroquinone, hydroquinone monomethyl ether, 1-o-2,3,5-trimethylolhydroquinone, 2-tert-butylhydroquinone, etc. Examples of catechols include catechol, 4-methylcatechol, 4-tert-butylcatechol, etc.

[0063] Examples of the hindered amines include any hindered amines having a polymerization inhibitor effect. Examples of the phenols include phenol, butylhydroxytoluene, butylhydroxyanisole, pyrogallol, alkyl gallate esters, and hindered phenols. Examples of the phenothiazines include phenothiazine. Examples of the condensed aromatic ring quinones include naphthoquinone.

[0064] The radical polymerization inhibitors described above can be used alone or in combination of two or more. The content of the radical polymerization inhibitor is, for example, 0.01% by mass or more and 3% by mass or less, and preferably 0.05% by mass or more and 0.5% by mass or less, relative to the total mass of the primer ink. When two or more radical polymerization inhibitors are used in combination, the total content thereof may be within the above range.

[0065] (1-H) Surfactants Examples of surfactants include silicone-based, fluorine-based, anionic, cationic, nonionic, and amphoteric surfactants. Of these, silicone-based and fluorine-based surfactants are preferred.

[0066] Examples of commercially available silicone surfactants include BYK (registered trademark) 307, 310, 320, 330, 333, 342, and 377 manufactured by BYK Japan Co., Ltd.; and 8029 Additive, 8054 Additive, 205SL, 8032 Additive, 57 Additive, and 8526 Additive manufactured by Dow Corning Toray Co., Ltd.

[0067] Examples of commercially available fluorine-based surfactants include Megafac (registered trademark) F-553, F-554, F-556, F-558, and F-559 manufactured by DIC Corporation, fluorine-containing oligomers and fluorine-containing reactive oligomers under Futergent (registered trademark) manufactured by Neos Corporation, Surflon (registered trademark) manufactured by AGC Sei Chemical Co., Ltd. that does not contain water as a solvent, and LE-604 and LE-605 manufactured by Kyoeisha Chemical Co., Ltd.

[0068] The surfactants described above can be used alone or in combination of two or more. The content of the surfactant, calculated as the amount of the active ingredient in the surfactant, is, for example, 0.1% by mass or more and 3% by mass or less, preferably 0.2% by mass or more and 2% by mass or less, relative to the total mass of the primer ink. When two or more surfactants are used in combination, the total content thereof may be within the above range.

[0069] (1-I) Other additives The primer ink of the present invention may contain additives other than those mentioned above, such as known polymerization accelerators, penetration accelerators, wetting agents (moisturizing agents), fixing agents, antifungal agents, preservatives, antioxidants, chelating agents, and thickeners.

[0070] (2) Colored ink The colored ink contains, as radically polymerizable components, at least 2-(2-vinyloxyethoxy)ethyl (meth)acrylate (VEEA (VEEM)) and a non-cyclic amide bond-containing monomer.

[0071] (2-A) 2-(2-vinyloxyethoxy)ethyl (meth)acrylate VEEA (VEEM) is preferably the main component of the colored ink, that is, VEEA (VEEM) is preferably the monomer contained in the colored ink in the largest proportion.

[0072] If the color ink contains little or no VEEA (VEEM), the color ink will not cure well and will not adhere well to the primer layer, which can lead to delamination between the primer layer and the color ink layer.On the other hand, if the color ink contains a lot of VEEA (VEEM), the color ink will shrink as it cures and float, resulting in insufficient adhesion to the primer layer.

[0073] Therefore, the content of VEEA (VEEM) is, for example, 40% by mass or more, and preferably 50% by mass or more, relative to the total mass of the monomers contained in the color ink. Furthermore, the content of VEEA (VEEM) is, for example, 85% by mass or less, and preferably 75% by mass or less, relative to the total mass of the monomers contained in the color ink. More specifically, the content of VEEA (VEEM) is, for example, 40% by mass or more and 85% by mass or less, and preferably 50% by mass or more and 75% by mass or less, relative to the total mass of the monomers contained in the color ink.

[0074] If the content is less than 40% by mass, the ink viscosity becomes too high due to the increased amount of other highly viscous monomers, which tends to reduce curability. If the curability is reduced, both the initial adhesion to the primer layer and abrasion resistance are insufficient, making it difficult to improve adhesion and abrasion resistance after sterilization and disinfection. On the other hand, if the content exceeds 85% by mass, the ink will cure too hard, causing the colored layer to become too hard and the viscosity to become too low. If the colored ink cures too much, it may shrink and float, resulting in insufficient adhesion to the primer layer. Furthermore, if the ink viscosity is too high, continuous ejection becomes difficult, and if the ink viscosity is too low, mist (splattering) may occur on the printed material. In other words, a large change in ink viscosity can have a significant impact on the ink ejection properties.

[0075] (2-B) Acyclic amide bond-containing monomer Acyclic amide bond-containing monomers are less susceptible to the effects of peroxides used in sterilization and disinfection treatments, and impart excellent abrasion resistance to the colored layer. In addition, they generally impart flexibility to the coating film, preventing it from cracking easily.

[0076] Examples of acyclic amide bond-containing monomers contained in the colored inks include acyclic (meth)acrylamides and acyclic urethane (meth)acrylates, with acyclic (meth)acrylamides being preferred. Examples of acyclic (meth)acrylamides and acyclic urethane (meth)acrylates include the (meth)acrylamides and urethane (meth)acrylates exemplified in the "monomers having a (1-C) amide bond" for the primer inks described above. Specific examples of acyclic amide bond-containing monomers contained in the colored inks include N,N-dimethylacrylamide (DMAA) and N,N-diethylacrylamide (DEAA).

[0077] The content of the acyclic amide bond-containing monomer in the color ink is, for example, 10 parts by mass, and preferably 20 parts by mass or more, when the total mass of the VEEA contained in the color ink is 100. Furthermore, the content of the acyclic amide bond-containing monomer in the color ink is, for example, 80 parts by mass or less, and preferably 70 parts by mass or less, when the total mass of the VEEA contained in the color ink is 100. More specifically, the content of the acyclic amide bond-containing monomer in the color ink is, for example, 10 parts by mass or more and 80 parts by mass or less, and preferably 20 parts by mass or more and 70 parts by mass or less, when the total mass of the VEEA contained in the color ink is 100.

[0078] If the amount is less than 10 parts by mass, the abrasion resistance after sterilization tends to decrease. On the other hand, if the amount exceeds 80 parts by mass, the content of VEEA (VEEM) in the colored ink decreases and VEEA (VEEM) is no longer the main component, so the curing property of the ink tends to decrease. In addition, the ink itself contains more components other than VEEA, which increases the ink viscosity, and high ink viscosity makes continuous ejection difficult. Note that when two or more types of acyclic amide bond-containing monomers are used in combination, the total content should be within the above range.

[0079] (2-C) Other Monomers The color ink may further contain other monomers besides VEEA (VEEM) and the non-cyclic amide bond-containing monomer. Examples of such monomers include monofunctional, difunctional, trifunctional or higher functional monomers and oligomers exemplified in "(1-D) Other Monomers" for the primer ink.

[0080] The content of other monomers in the color ink is, for example, the remainder of the monofunctional monomer containing a monocyclic aliphatic group, VEEA (VEEM), and the amide bond-containing monomer. In other words, the blending ratio of the monofunctional monomer containing a monocyclic aliphatic group, VEEA (VEEM), and the amide bond-containing monomer is set preferentially.

[0081] (2-D) colorants As the coloring agent in the color ink, various pigments, dyes, etc. of various colors according to the hue of the color ink can be used.

[0082] In particular, in consideration of improving the light resistance of the pattern layer, various inorganic pigments and / or organic pigments are preferred.

[0083] Among these, inorganic pigments include, for example, metal compounds such as iron oxide, and various types of neutral, acidic, and basic carbon blacks produced by known methods such as the contact method, furnace method, and thermal method.

[0084] Examples of organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), polycyclic pigments (such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), dye chelates (such as basic dye chelates and acid dye chelates), nitro pigments, nitroso pigments, and aniline black.

[0085] Specific examples of pigments include the following pigments.

[0086] (yellow pigment) CI Pigment Yellow 1, 2, 3, 12, 13, 14, 14C, 16, 17, 20, 24, 73, 74, 75, 83, 86, 93, 94, 95, 97, 98, 109, 110, 114, 117, 120, 125, 128, 129, 130, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213, 214 (magenta pigment) CI Pigment Red 5, 7, 9, 12, 48(Ca), 48(Mn), 49, 52, 53, 57(Ca), 57:1, 97, 112, 122, 123, 149, 168, 177, 178, 179, 184, 202, 206, 207, 209, 242, 254, 255 (cyan pigment) CI Pigment Blue 1, 2, 3, 15, 15:1, 15:3, 15:4, 15:6, 15:34, 16, 22, 60 (black pigment) CI Pigment Black 7 (orange pigment) CI Pigment Orange 36, 43, 51, 55, 59, 61, 71, 74 (green pigment) CI Pigment Green 7, 36 (Violet pigment) CI Pigment Violet 19, 23, 29, 30, 37, 40, 50 One or more pigments can be used depending on the color of the colored ink.

[0087] For example, when black is expressed using carbon black, a cyan pigment may be added to make it appear more bluish-black.

[0088] The pigment may be surface-treated to improve dispersion stability in the colored ink. Furthermore, the pigment may be used in the production of the colored ink in the form of a liquid pigment dispersion in which the pigment is dispersed in any dispersion medium. A dispersant or the like may be added to the pigment dispersion to disperse the pigment well.

[0089] As the dispersant, any of various dispersants such as polymeric dispersants, surfactants, etc. can be used. As the dispersion medium, any organic solvent or various radical polymerizable components can be used, and it is particularly preferable to use at least one of the above-mentioned radical polymerizable components.

[0090] When a radical polymerizable component is used as the dispersion medium, the proportions of the various radical polymerizable components described above are expressed as values ​​determined taking into consideration the radical polymerizable component as the dispersion medium. The proportion of the colorant such as a pigment can be set as desired depending on the type of colorant, the color of the color ink, etc.

[0091] The color ink may contain a radical polymerizable additive (component) similar to the primer ink. The additive is not particularly limited, but examples thereof include a radical polymerization initiator, a sensitizer, a radical polymerization inhibitor, a surfactant, etc.

[0092] (2-E) Radical polymerization initiator Specific examples of the radical polymerization initiator include the various photoradical polymerization initiators exemplified in the "(1-E) Radical Polymerization Initiator" section of the primer ink described above. It is preferable to select the same radical polymerization initiator as that used in the primer ink. This allows the primer precursor layer made of the primer ink and the color precursor layer made of the color ink to undergo a curing reaction simultaneously. The ratio of the radical polymerization initiator can be set as desired.

[0093] In order to impart good photocurability to the color ink, the proportion of the photoradical polymerization initiator is preferably 3% by mass or more, particularly 5% by mass or more, of the total amount of the color ink, and is preferably 12% by mass or less, particularly 10% by mass or less. When two or more radical polymerization initiators are used in combination, the total proportion thereof may be within the above range. Just do that.

[0094] (2-F) Sensitizer Specific examples of sensitizers include the various sensitizers exemplified in "(1-F) Sensitizer" for the primer ink described above. Among these, it is preferable to select and use any sensitizer having an absorption wavelength range similar to that of the sensitizer for the primer ink, particularly the same sensitizer used in the primer ink. One or more of these sensitizers can be used. The ratio of the sensitizers can be set as desired.

[0095] In order to effectively utilize the sensitizing effect of the sensitizer, the proportion of the sensitizer is preferably 0.1% by mass or more, particularly 1% by mass or more, of the total amount of the color ink, and is preferably 10% by mass or less, particularly 5% by mass or less. When two or more sensitizers are used in combination, the total proportion should be within the above range.

[0096] (2-G) Radical polymerization inhibitor Specific examples of the radical polymerization inhibitor include the various radical polymerization inhibitors exemplified in the above-mentioned primer ink "(1-G) Radical Polymerization Inhibitor," and among them, it is preferable to select and use the same radical polymerization inhibitor as used in the primer ink. One or more of these radical polymerization inhibitors can be used.

[0097] The proportion of the radical polymerization inhibitor is preferably 0.01% by mass or more, particularly 0.05% by mass or more, of the total amount of the color ink, and is preferably 3% by mass or less, particularly 2% by mass or less. When two or more types of radical polymerization inhibitors are used in combination, the total proportion thereof may be within the above range.

[0098] (2-H) surfactants Specific examples of surfactants include the various surfactants exemplified in "(1-H) Surfactant" for the primer ink described above, and it is preferable to select and use the same surfactant as that used in the primer ink. One or more of these surfactants can be used.

[0099] The proportion of the surfactant, calculated as the amount of the active ingredient in the surfactant, is, for example, 0.1% by mass or more and 3% by mass or less, and preferably 0.2% by mass or more and 2% by mass or less, relative to the total mass of the color ink. When two or more surfactants are used in combination, the total content thereof may be within the above range.

[0100] (2-I) Other additives The color ink of the present invention may contain additives other than those mentioned above, such as known polymerization accelerators, penetration accelerators, wetting agents (moisturizing agents), fixing agents, antifungal agents, preservatives, antioxidants, chelating agents, and thickeners.

[0101] [Printed material] 1 is a schematic diagram of a printed matter 1 produced by a method for producing a printed matter according to one embodiment of the present invention. The printed matter 1 of the present invention produced by the ink set described above includes a substrate 2 and a printed layer 3 formed on the substrate 2.

[0102] The substrate 2 may be, for example, a permeable or non-permeable substrate, and is preferably a non-permeable substrate. Various known substrates that do not absorb or have low absorbency for aqueous inkjet inks can be used as the substrate 2. Non-polar substrates such as PP and PE are particularly preferred. The non-polar substrate may be a substrate that has been surface-treated with a silane coupling agent, corona treatment, or the like.

[0103] Because PP and PE are easy to handle during manufacturing, they can be molded into a wide range of forms, from thin films to parts, using processes such as blow molding, injection molding, rotational molding, and extrusion. Therefore, they are widely used not only for food packaging applications such as films, but also for non-food applications such as bottles, pipes, and cable jackets. In particular, with the mandatory implementation of HACCP (Hazard Analysis and Critical Control Point) by food businesses, there is a growing demand for printing that can withstand cleaning and disinfection procedures for food packaging. This invention is suitable for ink sets for printing on PP and PE products used in such applications.

[0104] The printed surface 4 of the substrate 2 may be smooth or textured, and may be transparent, translucent, or opaque. Two or more types of substrates 2 may be laminated together. A release adhesive layer or the like may be provided on the back surface 5 opposite the printed surface 4 of the substrate 2. After the printing layer 3 is formed, an adhesive layer or the like may be provided to cover the printing layer 3. The substrate 2 may be in the form of a roll or a sheet.

[0105] The printed layer 3 includes a primer layer 6 and a colored layer 7, which are laminated in this order from the printing surface 4 of the substrate 2. The primer layer 6 is a printed layer formed from the primer ink described above. The colored layer 7 is a printed layer formed from the colored ink described above. If necessary, the printed layer 3 may further include a topcoat layer on top of the colored layer 7 to protect the colored layer 7.

[0106] [Manufacturing method for printed matter] 2 to 5 are schematic diagrams showing a part of the method for producing the printed matter 1 in the order of steps.

[0107] The printed matter 1 can be produced, for example, by forming a printed layer 3 on a substrate 2 using a known industrial inkjet printer. More specifically, first, an inkjet ink (e.g., a cartridge) containing the ink set described above is set in the inkjet printer. As the ejection head for the inkjet ink, for example, an on-demand or continuous type, and either a thermal type or a piezo type ejection head can be used. However, in consideration of improving ejection stability, it is preferable to use an on-demand piezo type ejection head.

[0108] Referring to FIG. 2, the primer ink is ejected from an ejection head onto the substrate 2 to form a primer precursor layer 8. Next, referring to FIG. 3, the primer layer 6 is formed by irradiating the monomers in the ink of the primer precursor layer 8 with active energy rays (ultraviolet rays) from an active energy ray source, causing a polymerization reaction and hardening. The active energy ray source can be incorporated into the head of the inkjet printer, for example, or prepared separately from the inkjet printer. Examples of active energy ray sources include ultraviolet lamps, ultraviolet light-emitting diodes, and ultraviolet laser diodes. Here, the emission peak wavelength of the active energy rays is preferably in the range of 350 nm to 420 nm, for example.

[0109] Next, referring to Figure 4, the color inks described above are ejected from an ejection head onto the substrate 2 to form a color precursor layer 9 on the primer layer 6. The color inks may be three colors: cyan (C), magenta (M), and yellow (Y), or four colors (these three colors plus black (K)), or multiple colors. By ejecting such multiple color inks simultaneously or sequentially from multiple nozzles of an on-demand inkjet printer, any color precursor layer 9, from full color to monochrome, can be printed on the primer layer 6.

[0110] Next, referring to FIG. 5, the colored layer 7 is formed by irradiating the colored precursor layer 9 with active energy rays (ultraviolet rays) from an active energy ray source to polymerize and harden the monomers in the ink. The active energy ray source can be incorporated into the inkjet printer head, or can be prepared separately from the inkjet printer. Examples of active energy ray sources include ultraviolet lamps, ultraviolet light-emitting diodes, and ultraviolet laser diodes. Here, the emission peak wavelength of the active energy rays is preferably in the range of 350 nm to 420 nm, for example.

[0111] Through the above steps, the printed matter 1 shown in Fig. 1 is obtained. In the above method, the primer precursor layer 8 and the color precursor layer 9 are cured in separate active energy ray irradiation steps, but the primer precursor layer 8 and the color precursor layer 9 may be laminated in succession and then cured simultaneously in the same active energy ray irradiation step. [Example]

[0112] The present invention will be further explained below based on examples and comparative examples, but the configuration of the present invention is not limited to these examples.

[0113] [Primer Ink 1~13] The components were mixed to obtain the compositions (mass %) shown in Table 1 and stirred until fully dissolved, after which the mixture was filtered using a 5 μm membrane filter to prepare clear primer inks 1 to 13.

[0114] The information on the ingredients used in Table 1 is as follows:

[0115] VEEA is manufactured by Nippon Shokubai Co., Ltd. under the trade name "VEEA-AI."

[0116] The monofunctional monomer containing a monocyclic aliphatic group is t-butylcyclohexanol acrylate (TBCHA) (manufactured by Sartomer Corporation, trade name "SR217"), 3,3,5-trimethylcyclohexanol acrylate (TMCHA) (manufactured by Sartomer Corporation, trade name "SR420"), Isobornyl acrylate (IBXA) (manufactured by Sartomer Corporation, trade name "SR506").

[0117] The amide bond-containing monomer is Diethylacrylamide (DEAA) (KJ Chemicals Co., Ltd.), - Urethane acrylate (manufactured by Sartomer, product name "CN983").

[0118] 1,6-Hexanediol diacrylate is manufactured by Sartomer Corporation under the trade name "SR238."

[0119] The polymerization initiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by Lambson, trade name "A-TPO").

[0120] The sensitizer is 2-isopropylthioxanthone (manufactured by Lambson under the trade name "2-ITX").

[0121] The polymerization inhibitor is manufactured by Kromachem and is available under the trade name "Florstab UV-5."

[0122] The surfactant is a silicone-based surfactant (manufactured by BYK Japan Co., Ltd., trade name "BYK-UV3510").

[0123] [Table 1]

[0124] [Colored inks 1-14] First, the following components were mixed in the proportions shown in Table 2, stirred, and then dispersed using a bead mill to prepare a black pigment dispersion.

[0125] Black pigment: CI Pigment Black 8 (carbon black manufactured by Mitsubishi Chemical Corporation, product name "MA-8") Dispersant: Lubrizol, product name "Solsperse 32000" Dispersion medium: VEEA (manufactured by Nippon Shokubai Co., Ltd., product name "VEEA-AI")

[0126] [Table 2]

[0127] Next, the components were mixed to obtain the composition (mass %) shown in Table 3 and stirred until fully dissolved. After that, the mixture was filtered using a 5 μm membrane filter to prepare a black (K) colored ink.

[0128] The information on the ingredients used in Table 3 is as follows:

[0129] VEEA is manufactured by Nippon Shokubai Co., Ltd. under the trade name "VEEA-AI."

[0130] The amide bond-containing monomer is Diethylacrylamide (DEAA) (KJ Chemicals Co., Ltd.), Urethane acrylate (manufactured by Sartomer, product name "CN983"), Acryloylmorpholine (ACMO) (manufactured by KJ Chemicals Co., Ltd.).

[0131] 1,6-Hexanediol diacrylate is manufactured by Sartomer Corporation under the trade name "SR238."

[0132] The polymerization initiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by Lambson, trade name "A-TPO").

[0133] The sensitizer is 2-isopropylthioxanthone (manufactured by Lambson under the trade name "2-ITX").

[0134] The polymerization inhibitor is manufactured by Kromachem and is available under the trade name "Florstab UV-5."

[0135] The surfactant is a silicone-based surfactant (manufactured by BYK Japan Co., Ltd., trade name "BYK-UV3510").

[0136] In Table 3, the blending ratio of the pigment dispersion indicates only the pigment content, and the amount of VEEA in the pigment dispersion is shown as a total amount including VEEA as the radical polymerizable component.

[0137] [Table 3]

[0138] [Examples 1 to 20 and Comparative Examples 1 to 7] Ink sets according to the examples and comparative examples were prepared in the combinations shown in Tables 4 and 5 and loaded into a piezo inkjet printer equipped with a piezo head. Next, the primer ink was ejected onto the substrate 2 in a solid pattern to print a primer precursor layer 8. The substrate 2 was a laminate film of 12 μm PET and 30 μm LLDPE, with the LLDPE surface corona-treated. The printing conditions were a printing speed of 50 m / min, a resolution of 600 × 600, and four passes. The substrate 2 on which the primer precursor layer 8 had been formed was then transferred to an ultraviolet irradiation device, where the primer ink was cured by ultraviolet irradiation to form a primer layer 6. The ultraviolet irradiation conditions were a wavelength of 350 nm to 420 nm and a conveying speed of 25 m / min.

[0139] Next, under normal temperature and pressure, colored ink was ejected onto the substrate 2 on which the primer layer 6 had been formed in a solid pattern to print a colored precursor layer 9 on the primer layer 6. The printing conditions were a printing speed of 50 m / min, a resolution of 600 x 600, and four passes. Thereafter, the substrate 2 on which the colored precursor layer 9 had been formed was transferred to an ultraviolet irradiation device, and a curing process was performed by ultraviolet irradiation to cure the colored ink, thereby forming a colored layer 7. The ultraviolet irradiation conditions were a wavelength of 350 nm to 420 nm and a transport speed of 25 m / min.

[0140] As a result, an evaluation sample was prepared in which an A4 solid pattern sample image consisting of a laminate (printed layer 3) of a primer layer 6 and a colored layer 7 was recorded on a substrate 2 made of PE. The obtained evaluation sample was then evaluated as follows.

[0141] [Evaluation test] (1) Cellophane tape adhesion evaluation Each evaluation sample was prepared according to the Japanese Industrial Standard JIS K5600-5-6 :1999 The cross-cut test described in "General Test Methods for Paints - Part 5: Mechanical Properties of Coating Films - Section 6: Adhesion (Cross-Cut Method)" was carried out. The evaluation criteria for adhesion are as follows. The evaluation results are shown in Tables 4 and 5. "Good": Classification was 0 to 2. "△": Classification was 3 to 4. "X": Classification was 5. (2) Scratch test evaluation The coating film of each evaluation sample was rubbed back and forth five times with a paper clip (Gachadama (registered trademark)), and the change in the coating film before and after the rub was evaluated. The evaluation criteria for the scratch test are as follows. The evaluation results are shown in Tables 4 and 5. "Good": No change in the coating. "△": Slight (thin or intermittent) scratches remained on the coating film. "X": A (clear or solid) scratch remained on the coating film. (3) Evaluation of cellophane tape adhesion after sterilization Each evaluation sample was immersed in a solvent containing an acidic detergent (9.7% hydrochloric acid) and a surfactant (polyoxyethylene alkyl ether) for 30 minutes, and then an adhesion test was conducted using the same method as in "(1) Evaluation of cellophane tape adhesion" above. The evaluation criteria were also the same as in "(1) Evaluation of cellophane tape adhesion" above. The evaluation results are shown in Tables 4 and 5. (4) Scratch test evaluation after sterilization Each evaluation sample was immersed in a solvent containing an acidic detergent (9.7% hydrochloric acid) and a surfactant (polyoxyethylene alkyl ether) for 30 minutes, and then an adhesion test was conducted using the same method as in "(2) Scratch Test Evaluation" above. The evaluation criteria were also the same as in "(2) Scratch Test Evaluation" above. The evaluation results are shown in Tables 4 and 5.

[0142] [Table 4]

[0143] [Table 5]

[0144] [Evaluation results] First, referring to Tables 4 and 5, the results of Examples 1 to 20 show that if the primer ink contains a monofunctional monomer containing at least a monocyclic aliphatic group and the colored ink contains VEEA (VEEM) and a monomer having an acyclic amide bond, it is possible to form a printing layer 3 that has both excellent adhesion to the substrate 2 and excellent abrasion resistance both before and after sterilization and disinfection treatment.

[0145] More specifically, referring to Table 4, a comparison between Example 1 and Comparative Example 1 shows that even though the primer ink contains a monofunctional monomer containing an aliphatic group with a ring structure, Comparative Example 1, which is IBXA having a crosslinked structure within the ring and a bicyclic aliphatic group, has lower adhesion to the substrate 2 both before and after sterilization treatment compared to Example 1, which has a monocyclic aliphatic group.

[0146] Furthermore, a comparison between Comparative Example 1 and Comparative Example 2 revealed that in Comparative Example 1, due to the presence of the three-dimensional structure of IBXA, the adhesion before sterilization treatment (initial stage) was not worse than in Comparative Example 2, which did not contain any monofunctional monomers having a ring-structured aliphatic group, but the adhesion after sterilization treatment decreased.

[0147] A comparison between Example 2 and Comparative Example 2 revealed that even when the primer ink did not contain a monofunctional monomer containing a monocyclic aliphatic group, adhesion to the substrate 2 was low both before and after the sterilization and disinfection treatment.

[0148] A comparison between Example 1 and Comparative Example 3 revealed that when the primer ink did not contain a monofunctional monomer containing a monocyclic aliphatic group and also did not contain a monomer having an amide bond, not only did the adhesion before and after the sterilization treatment decrease, but the abrasion resistance after the sterilization treatment also decreased.

[0149] Even when the primer ink contains a monomer having an amide bond, it was found that Examples 1 and 2, which contain acrylamide, have better adhesion to the substrate 2 after sterilization and disinfection treatment than Example 3, which does not contain acrylamide. This is thought to be because the inclusion of a monomer having acrylamide, as in Examples 1 and 2, improves adhesion to the treated surface (printed surface 4) of the surface-treated PE substrate (PE film).

[0150] A comparison between Example 2 and Example 4 revealed that the primer ink containing VEEA (VEEM) had better adhesion to the substrate 2 both before and after sterilization treatment than the primer ink not containing VEEA (VEEM). This is thought to be because VEEA (VEEM) imparts sufficient curing properties to the primer ink, suppressing delamination between the substrate 2 and the primer layer 6.

[0151] A comparison of Examples 6 to 9 revealed that when the content of the monofunctional monomer containing a monocyclic aliphatic group relative to the total mass of the monomers contained in the primer ink is 5% by mass or more and 30% by mass or less, particularly excellent adhesion and abrasion resistance can be exhibited both before and after sterilization. Near the lower limit of 5% by mass, as in Example 6, the amount of TBCHA, an active ingredient, is low, so it is thought that sufficient adhesion to the substrate 2 cannot be obtained after sterilization. On the other hand, near the upper limit of 30% by mass, as in Example 9, it is thought that the curing properties of the primer ink deteriorate, resulting in insufficient adhesion to the substrate 2 after sterilization.

[0152] Comparison of Examples 1 and 2 with Example 10 revealed that when the primer ink did not contain a monomer having an amide bond, the adhesion to the substrate 2 after sterilization and disinfection treatment decreased.

[0153] Next, referring to Table 5, a comparison of Examples 1, 11, and 12 with Comparative Example 4 revealed that even though the colored ink contained an amide bond-containing monomer, Comparative Example 4, which used the cyclic amide bond-containing monomer ACMO, did not provide practically sufficient abrasion resistance after sterilization. This is thought to be because the acyclic amide bond-containing monomers used in Examples 1, 11, and 12 were less susceptible to the effects of peroxides used in sterilization and disinfection, and could impart excellent abrasion resistance to the colored layer 7, whereas the cyclic amide bond-containing monomers were significantly affected by peroxides. However, it was found that, among the acyclic amide bond-containing monomers, the acrylamide used in Examples 1 and 11 exhibited particularly excellent abrasion resistance even after sterilization and disinfection, compared to the urethane acrylate used in Example 12.

[0154] A comparison between Example 11 and Comparative Example 5 revealed that even if the color ink contained acyclic acrylamide, if it did not contain any VEEA (VEEM), the adhesion and abrasion resistance both before and after sterilization treatment were significantly reduced. This is thought to be because the constituent monomers of the primer ink (containing VEEA as the main component) and the color ink (containing no VEEA) were significantly different, causing delamination between the primer layer 6 and the color layer 7.

[0155] Comparison of Examples 1, 11, and 12 with Comparative Example 6 revealed that if the colored ink did not contain any amide bond-containing monomers, the scratch resistance after sterilization treatment was significantly reduced.

[0156] A comparison between Example 1 and Comparative Example 7 revealed that even if the primer ink contains a monofunctional monomer containing at least a monocyclic aliphatic group and the colored ink contains a monomer having VEEA (VEEM) and an acyclic amide bond, if the stacking order of the primer layer 6 and the colored layer 7 is reversed, the adhesion to the substrate 2 both before and after the sterilization and disinfection treatment is significantly reduced. In other words, it was found that it is difficult to obtain the desired adhesion even when the primer ink of the present invention is used in the overcoat layer that covers the colored layer 7.

[0157] A comparison of Examples 13 to 16 revealed that when the content of VEEA (VEEM) in the color ink relative to the total mass of the monomers contained in the color ink was 40% by mass or more and 85% by mass or less, particularly excellent adhesion and abrasion resistance could be exhibited both before and after sterilization. At a lower limit of 40% by mass, as in Example 13, curability tended to decrease. When curability decreased, both the initial adhesion and abrasion resistance to the substrate were insufficient, and as a result, it was thought that it became difficult to improve adhesion and abrasion resistance after sterilization. On the other hand, at an upper limit of 85% by mass, as in Example 16, the ink cured excessively, causing the color layer 7 to become too hard and the viscosity to become too low. As a result, the color ink shrank upon curing and floated, resulting in insufficient adhesion to the substrate 2.

[0158] A comparison of Examples 17 to 20 revealed that, when the total mass of VEEA contained in the colored ink is taken as 100, the content of the acyclic amide bond-containing monomer in the colored ink is 20 parts by mass or more and 70 parts by mass or less, and thus excellent adhesion and abrasion resistance can be exhibited both before and after sterilization. At 13.7 parts by mass (<20 parts by mass) as in Example 17, the amount of DEAA, an active ingredient, is low, which is thought to have reduced abrasion resistance after sterilization. On the other hand, at 78.6 parts by mass (>70 parts by mass) as in Example 20, the content of VEEA (VEEM) in the colored ink is reduced, which is thought to have reduced curing properties, resulting in reduced adhesion and abrasion resistance both before and after sterilization. [Explanation of symbols]

[0159] 1 Printed matter 2 Base material 3 printing layer 4 Print side 5 Back side 6 Primer layer 7 Colored layer 8. Primer precursor layer 9 Colored precursor layer

Claims

1. An actinic radiation curable inkjet ink set comprising a combination of a clear primer ink and one or more color inks, The primer ink contains a monofunctional monomer containing a monocyclic aliphatic group, The color inks include 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a monomer having a non-cyclic amide bond.

2. The primer ink contains 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2. The ink set according to claim 1, wherein the primer ink and the color ink each contain 2-(2-vinyloxyethoxy)ethyl (meth)acrylate as a main component.

3. The ink set according to claim 2 , wherein the primer ink further comprises a monomer having an amide bond.

4. 2. The ink set according to claim 1, wherein the monofunctional monomer containing a monocyclic aliphatic group of the primer ink is t-butylcyclohexanol acrylate or 3,3,5-trimethylcyclohexanol acrylate.

5. The ink set according to any one of claims 1 to 4, wherein the monomer having a non-cyclic amide bond in the color ink is acrylamide.

6. A method for producing a printed matter using an actinic energy ray curable inkjet ink set comprising a combination of a clear primer ink and one or more color inks, comprising: A first step of printing the primer ink on a substrate; a second step of printing the one or more colored inks onto the primer ink; The primer ink contains a monofunctional monomer containing a monocyclic aliphatic group, The color ink contains 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a monomer having a non-cyclic amide bond.

7. the first step includes a step of irradiating a primer precursor layer formed by printing the primer ink with active energy rays to cause a curing reaction of the primer ink forming the primer precursor layer, thereby forming a primer layer; The method for producing a printed matter according to claim 6, wherein the second step includes a step of irradiating the color precursor layer formed by printing the color ink with active energy rays to cause a curing reaction of the color ink that forms the color precursor layer, thereby forming a color layer.

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