Active energy ray-curable inkjet ink, active energy ray-curable ink set, and image recording method

Abstract

Provided are active energy ray-curable inkjet ink and applications thereof, the active energy ray-curable inkjet ink comprising bifunctional (meth)acrylate having a C5-C9 linear or branched alkylene group, monofunctional (meth)acrylate having a hydroxyl group, and a colorant, wherein the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate is at least 80 mass% with respect to the total amount of polymerizable compounds contained in the active energy ray-curable inkjet ink.

Description

Active energy ray-curable inkjet ink, active energy ray-curable ink set, and image recording method

[0001] The present disclosure relates to an actinic energy ray-curable inkjet ink, an actinic energy ray-curable ink set, and an image recording method.

[0002] 2. Description of the Related Art Conventionally, when an image is recorded on a substrate using ink, a method of curing the ink using active energy rays is known.

[0003] For example, Japanese Patent Application Laid-Open No. 2022-030775 describes a photocurable inkjet printing ink composition that satisfies all of the following requirements A to F: A: The total content of one or more compounds selected from vinylmethyloxazolidinone, N,N-dimethylacrylamide, benzyl acrylate, and N-vinylcaprolactam is 30.0% by mass or more in the photocurable inkjet printing ink composition; B: The total content of one or more compounds selected from saturated hydrocarbon group-containing monofunctional monomers having 6 or more carbon atoms and saturated hydrocarbon group-containing polyfunctional monomers having 6 or more carbon atoms is 15.0% by mass or more in the photocurable inkjet printing ink composition; C: The content of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide is 2.5% by mass or less in the photocurable inkjet printing ink composition. D: The content of ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide in the photocurable ink composition for ink jet printing is 6.5 to 13.0% by mass. E: The content of amine-modified oligomer in the photocurable ink composition for ink jet printing is 0.5 to 15.0% by mass. F: The photocurable ink composition for ink jet printing contains no or 17.0% by mass of a white pigment as a colorant.

[0004] In some cases, image recording materials obtained by applying ink onto a substrate are required to have low odor and excellent water resistance.

[0005] The present disclosure has been made in consideration of these circumstances, and a problem to be solved by one embodiment of the present invention is to provide an actinic energy ray-curable inkjet ink that is low in odor and capable of producing an image recorded product that has excellent water resistance and excellent ejection properties. Another problem to be solved by another embodiment of the present invention is to provide an actinic energy ray-curable ink set that is low in odor and capable of producing an image recorded product that has excellent water resistance and excellent alkali peelability of the image from the substrate and that has excellent ejection properties. Another problem to be solved by another embodiment of the present invention is to provide an image recording method that is low in odor and capable of producing an image recorded product that has excellent water resistance and excellent ejection properties.

[0006] The present disclosure includes the following aspects: <1> An actinic energy ray-curable inkjet ink comprising: a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms; a monofunctional (meth)acrylate having a hydroxyl group; and a colorant, wherein the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate is 80 mass % or more relative to the total amount of polymerizable compounds contained in the actinic energy ray-curable inkjet ink. <2> The actinic energy ray-curable inkjet ink according to <1>, wherein the mass ratio of the content of the bifunctional (meth)acrylate to the content of the monofunctional (meth)acrylate is 0.3 to 3.5. <3> The actinic energy ray-curable ink-jet ink according to <1> or <2>, further comprising, as a polymerization initiator, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, the total content of the polymerization initiators being 5% by mass or more relative to the total amount of the actinic energy ray-curable ink-jet ink. <4> The actinic energy ray-curable ink-jet ink according to any one of <1> to <3>, wherein the molecular weight of the monofunctional (meth)acrylate is 130 to 150. <5> An actinic energy beam-curable ink set comprising: a first ink containing a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant; and a second ink, wherein the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate in the first ink is 80% by mass or more relative to the total amount of polymerizable compounds contained in the first ink, and the second ink is such that, when a cured product of the second ink is immersed in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes each, the pencil hardness of the cured product after immersion in the alkaline aqueous solution of pH 10 is lower than the pencil hardness of the cured product after immersion in water of pH 7. <6> An actinic energy beam-curable ink set according to <5>, wherein the second ink contains at least one acid group-containing compound selected from the group consisting of polymerizable monomers having an acid group and polymers having an acid group, and the total content of the acid group-containing compound is 8% by mass or more relative to the total amount of the second ink.<7> The actinic energy ray-curable ink set according to <5> or <6>, wherein the second ink contains at least one acid group-containing compound selected from the group consisting of polymerizable monomers having an acid group and polymers having an acid group, a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms, and a monofunctional (meth)acrylate having a hydroxyl group, and the total content of the polymerizable monomers having an acid group, the bifunctional (meth)acrylate, and the monofunctional (meth)acrylate is 70 mass % or more based on the total amount of polymerizable compounds contained in the second ink. <8> The actinic energy ray-curable ink set according to any one of <5> to <7>, wherein the mass ratio of the content of the bifunctional (meth)acrylate to the content of the monofunctional (meth)acrylate in the first ink is 0.3 to 3.5. <9> The actinic energy ray-curable ink set according to any one of <5> to <8>, wherein the first ink further contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide as polymerization initiators, and the total content of the polymerization initiators is 5 mass % or more relative to the total amount of the actinic energy ray-curable inkjet ink. <10> The actinic energy ray-curable ink set according to any one of <5> to <9>, wherein the first ink contains a monofunctional (meth)acrylate having a molecular weight of 130 to 150. <11> An image recording method comprising the steps of applying the actinic energy ray-curable inkjet ink according to any one of <1> to <4> onto a substrate by an inkjet recording method, and irradiating the applied actinic energy ray-curable inkjet ink with actinic energy rays. <12> An image recording method using the actinic ray-curable ink set according to any one of <5> to <10>, the method comprising: a step of applying a second ink onto a substrate by an inkjet recording method; a step of irradiating the applied second ink with actinic ray; a step of applying a first ink onto the substrate to which the second ink has been applied by an inkjet recording method; and a step of irradiating the applied first ink with actinic ray.

[0007] According to one embodiment of the present invention, there is provided an actinic energy ray-curable inkjet ink that is capable of producing an image recorded product that has low odor and excellent water resistance, and that has excellent jetting properties. According to another embodiment of the present invention, there is provided an actinic energy ray-curable ink set that is capable of producing an image recorded product that has low odor, excellent water resistance, and excellent alkali peelability of the image from the substrate, and that has excellent jetting properties. According to another embodiment of the present invention, there is provided an image recording method that is capable of producing an image recorded product that has low odor and excellent water resistance, and that has excellent jetting properties.

[0008] The actinic energy ray-curable inkjet ink, actinic energy ray-curable ink set, and image recording method of the present disclosure will be described in detail below.

[0009] In this specification, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0010] As used herein, the amount of each component in a composition refers to the total amount of the components in the composition unless otherwise specified, when the composition contains multiple substances corresponding to each component. In this specification, a combination of two or more preferred aspects is a more preferred aspect. As used herein, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0011] In this specification, the term "image" refers to a film formed by applying ink in general, and "image recording" refers to the formation of an image (i.e., a film). The concept of "image" in this specification also includes a solid image.

[0012] In this specification, the term "(meth)acrylate" encompasses both acrylate and methacrylate, and the term "(meth)acrylic" encompasses both acrylic and methacrylic.

[0013] An actinic ray-curable inkjet ink (hereinafter also simply referred to as "ink") according to one embodiment of the present disclosure comprises a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant, and the total content of the bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms and the monofunctional (meth)acrylate having a hydroxyl group is 80% by mass or more based on the total amount of polymerizable compounds contained in the ink.

[0014] An image recording material can be obtained in which an ink film is formed as an image on a substrate by applying an ink according to an embodiment of the present disclosure to a substrate and then irradiating the substrate with active energy rays. The ink according to an embodiment of the present disclosure contains a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms and a monofunctional (meth)acrylate having a hydroxyl group, and therefore undergoes a polymerization reaction upon irradiation with active energy rays. The bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms tends to have a low odor and low viscosity due to the presence of the linear or branched alkylene group having 5 to 9 carbon atoms. The bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms serves as a diluent in the ink and exhibits excellent ejection properties. Furthermore, the monofunctional (meth)acrylate having a hydroxyl group serves to prevent localized accumulation of water in the ink film and improve water resistance due to the presence of the hydroxyl group. Furthermore, the presence of a monofunctional (meth)acrylate having a hydroxyl group reduces the oxygen concentration in the ink, suppressing polymerization inhibition by oxygen and improving curability, which in turn reduces the amount of unreacted polymerizable compound and reduces odor.

[0015] Furthermore, by having the total content of the bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms and the monofunctional (meth)acrylate having a hydroxyl group be 80 mass% or more, the functions based on the bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms and the monofunctional (meth)acrylate having a hydroxyl group can be fully exerted.

[0016] Another embodiment of the present disclosure is an actinic ray-curable ink set (hereinafter simply referred to as "ink set") that includes a first ink and a second ink, each of which contains a bifunctional (meth)acrylate having a linear or branched alkylene group of 5 to 9 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant, wherein the total content of the bifunctional (meth)acrylate having a linear or branched alkylene group of 5 to 9 carbon atoms and the monofunctional (meth)acrylate having a hydroxyl group is 80 mass% or more relative to the total amount of polymerizable compounds contained in the first ink, and wherein when a cured product of the second ink is immersed in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes, the pencil hardness of the cured product after immersion in the alkaline aqueous solution of pH 10 is lower than the pencil hardness of the cured product after immersion in water of pH 7.

[0017] Using an ink set according to another embodiment of the present disclosure, for example, by applying the first ink and the second ink to a substrate and then irradiating the substrate with active energy rays, an image recording material can be obtained in which an ink film is formed as an image on the substrate. The first ink has a total content of a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms and a monofunctional (meth)acrylate having a hydroxyl group of 80% by mass or more relative to the total amount of polymerizable compounds contained in the first ink. Therefore, as described above, low odor and water resistance can be achieved. Furthermore, when a cured product of the second ink is immersed in water at pH 7 and an alkaline aqueous solution at pH 10 for 5 minutes, the pencil hardness of the cured product after immersion in the alkaline aqueous solution at pH 10 is lower than the pencil hardness of the cured product after immersion in water at pH 7, making the second ink more easily peelable from the substrate by the alkaline aqueous solution. In other words, the resulting image recording material has excellent alkali releasability.

[0018] On the other hand, Japanese Patent Application Laid-Open No. 2022-030775 does not anticipate that the total content of the bifunctional (meth)acrylate having a linear or branched alkylene group with 5 to 9 carbon atoms and the monofunctional (meth)acrylate having a hydroxyl group will be 80 mass% or more relative to the total amount of polymerizable compounds contained in the ink.

[0019] Hereinafter, each component contained in the ink according to an embodiment of the present disclosure will be described.

[0020] [Actinic Energy Ray-Curable Inkjet Ink] The ink according to an embodiment of the present disclosure is an active energy ray-curable ink. That is, the ink according to an embodiment of the present disclosure is cured by irradiation with active energy rays. Examples of active energy rays include gamma rays, beta rays, electron beams, ultraviolet rays, and visible light. Of these, ultraviolet rays are preferred. The ink according to an embodiment of the present disclosure is preferably an ultraviolet ray-curable ink.

[0021] <Bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms> An ink according to an embodiment of the present disclosure contains a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms (hereinafter also referred to as a “specific bifunctional (meth)acrylate”).

[0022] The bifunctional (meth)acrylate means a compound having two (meth)acryloyloxy groups.

[0023] The specific bifunctional (meth)acrylate has a linear or branched alkylene group and a carbon number of 5 to 9, and therefore tends to have low odor and low viscosity. Therefore, by including the specific bifunctional (meth)acrylate, the ink according to one embodiment of the present disclosure has low odor, relatively low viscosity, and excellent ejection properties.

[0024] Examples of the linear or branched alkylene group include a methyl group, an ethyl group, an i-propyl group, an n-butyl group, a t-butyl group, a heptyl group, and a nonyl group. From the same viewpoint as above, the number of carbon atoms in the linear or branched alkylene group is preferably 6 to 8, and more preferably 6.

[0025] From the viewpoint of low odor and low viscosity, the molecular weight of the specific bifunctional (meth)acrylate is preferably 240 to 280.

[0026] The ink may contain only one type of specific bifunctional (meth)acrylate, or two or more types of specific bifunctional (meth)acrylate.

[0027] Examples of the specific bifunctional (meth)acrylate include 3-methyl-1,5-pentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol diacrylate, 1,7-heptanediol diacrylate, 1,8-octanediol diacrylate, and 1,9-nonanediol di(meth)acrylate.

[0028] Among these, from the viewpoint of ejection properties, the specific bifunctional (meth)acrylate is preferably at least one selected from the group consisting of 3-methyl-1,5-pentanediol di(meth)acrylate and 1,6-hexanediol diacrylate, and more preferably 3-methyl-1,5-pentanediol di(meth)acrylate.

[0029] From the viewpoint of reducing odor, the content of the specific bifunctional (meth)acrylate is preferably 10% by mass to 70% by mass, and more preferably 20% by mass to 60% by mass, relative to the total amount of the ink.

[0030] <Monofunctional (meth)acrylate having a hydroxyl group> The ink according to an embodiment of the present disclosure contains a monofunctional (meth)acrylate having a hydroxyl group (hereinafter also referred to as a "specific monofunctional (meth)acrylate").

[0031] The monofunctional (meth)acrylate means a compound having one (meth)acryloyloxy group.

[0032] The specific monofunctional (meth)acrylate has a hydroxyl group, which prevents water from accumulating locally in the ink film and improves water resistance. Furthermore, the presence of the specific monofunctional (meth)acrylate reduces the oxygen concentration in the ink, suppressing polymerization inhibition by oxygen and improving curability. As a result, the amount of unreacted polymerizable compound can be reduced, and odor can be reduced.

[0033] The ink may contain only one type of specific monofunctional (meth)acrylate, or two or more types of specific monofunctional (meth)acrylate.

[0034] The number of hydroxyl groups contained in the specific monofunctional (meth)acrylate is not particularly limited and is, for example, 1 to 6. From the viewpoint of ink viscosity, the number of hydroxyl groups is preferably 1 to 3, and more preferably 1 or 2.

[0035] From the viewpoint of low odor and low viscosity, the molecular weight of the specific monofunctional (meth)acrylate is preferably 130 to 150.

[0036] Examples of the specific monofunctional (meth)acrylate include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, the specific monofunctional (meth)acrylate is preferably 4-hydroxybutyl (meth)acrylate from the viewpoints of water resistance and low odor.

[0037] From the viewpoints of water resistance and low odor, the content of the specific monofunctional (meth)acrylate is preferably 30% by mass to 70% by mass, and more preferably 40% by mass to 50% by mass, relative to the total amount of the ink.

[0038] In an ink according to an embodiment of the present disclosure, the total content of the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate is 80% by mass or more relative to the total amount of polymerizable compounds contained in the ink. A total content of the specific bifunctional (meth)acrylate and the monofunctional (meth)acrylate of 80% by mass or more means that the content of polymerizable compounds other than the specific bifunctional (meth)acrylate and the monofunctional (meth)acrylate in the ink is low. The low content of polymerizable compounds other than the specific bifunctional (meth)acrylate and the monofunctional (meth)acrylate (hereinafter also referred to as "other polymerizable compounds") allows the ink to exhibit low odor and water resistance effects based on the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate.

[0039] From the viewpoint of further exerting the effects of low odor and water resistance, the total content of the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate is preferably 90% by mass or more, more preferably 95% by mass or more. The upper limit of the total content is not particularly limited, and may be 100% by mass. In other words, the polymerizable compounds contained in the ink may be only the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate.

[0040] -Specific Bifunctional (meth)acrylate / Specific Monofunctional (meth)acrylate- The mass ratio of the content of the specific bifunctional (meth)acrylate to the content of the specific monofunctional (meth)acrylate is preferably 0.3 to 3.5, and more preferably 0.5 to 1.3. When this mass ratio is 0.3 or more, odor can be further reduced. When this mass ratio is 3.5 or less, water resistance is further improved.

[0041] <Other Polymerizable Compounds> As described above, from the viewpoint of further improving the effects of low odor and water resistance, it is desirable that the content of other polymerizable compounds is small. However, the ink may contain other polymerizable compounds to the extent that the effects of the present disclosure are not significantly impaired.

[0042] The other polymerizable compound is not particularly limited as long as it is a compound other than the specific bifunctional (meth)acrylate and monofunctional (meth)acrylate and has a polymerizable group.

[0043] From the viewpoint of reactivity with the specific bifunctional (meth)acrylate and monofunctional (meth)acrylate, the polymerizable group in the other polymerizable compound is preferably a radical polymerizable group, more preferably an ethylenically unsaturated group, and even more preferably a (meth)acryloyloxy group. That is, the other polymerizable compound is preferably a radical polymerizable compound, more preferably an ethylenically unsaturated compound, and even more preferably a (meth)acrylate.

[0044] The other polymerizable compound may be a monofunctional polymerizable compound having one polymerizable group, or may be a polyfunctional polymerizable compound having two or more polymerizable groups.

[0045] Monofunctional Polymerizable Compounds Examples of monofunctional polymerizable compounds include monofunctional (meth)acrylates, monofunctional (meth)acrylamides, monofunctional aromatic vinyl compounds, monofunctional vinyl ethers, and monofunctional N-vinyl compounds.

[0046] Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tert-octyl (meth)acrylate, isoamyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-n-butylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, bornyl (meth)acrylate, and isobornyl (meth)acrylate. runyl (meth)acrylate, 2-ethylhexyl diglycol (meth)acrylate, butoxyethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 4-bromobutyl (meth)acrylate, cyanoethyl (meth)acrylate, benzyl (meth)acrylate, butoxymethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, 2-(2-butoxyethoxy)ethyl (meth)acrylate, 2,2,2-tetrafluoroethyl (meth)acrylate, 1H,1H,2H,2H-perfluorodecyl (meth)acrylate, 4-butylphenyl (meth)acrylate, phenyl (meth)acrylate, 2,4,5-tetramethylphenyl (meth)acrylate, 4-chlorophenyl (meth)acrylate, 2-phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, glycidyl (meth)acrylate, glycidyloxybutyl (meth)acrylate, glycidyloxyethyl (meth)acrylate, glycidyloxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, phenyl glycidyl ether (meth)acrylate acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, trimethoxysilylpropyl (meth)acrylate, trimethylsilylpropyl (meth)acrylate, polyethylene oxide monomethyl ether (meth)acrylate, polyethylene oxide (meth)acrylate, polyethylene oxide monoalkyl ether (meth)acrylate, dipropylene glycol (meth)acrylate acrylate, polypropylene oxide monoalkyl ether (meth)acrylate, 2-methacryloyloxyethyl succinate, 2-methacryloyloxyhexahydrophthalic acid, ethoxydiethylene glycol (meth)acrylate, butoxydiethylene glycol (meth)acrylate, trifluoroethyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, ethylene oxide (EO)-modified phenol (meth)acrylate, EO-modified cresol (meth)acrylate, EO-modified nonylphenol (meth)acrylate acrylate, propylene oxide (PO)-modified nonylphenol (meth)acrylate, EO-modified 2-ethylhexyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, (3-ethyl-3-oxetanylmethyl) (meth)acrylate, phenoxyethylene glycol (meth)acrylate, 2-carboxyethyl (meth)acrylate, and 2-(meth)acryloyloxyethyl succinate.

[0047] Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-methylol(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and (meth)acryloylmorpholine.

[0048] Examples of monofunctional aromatic vinyl compounds include styrene, dimethylstyrene, trimethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyrene, acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene, vinyl benzoic acid methyl ester, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-propylstyrene, 3-butylstyrene, 4-butylstyrene, 3-hexylstyrene, 4-hexylstyrene, 3-octylstyrene, 4-octylstyrene, 3-(2-ethylhexyl)styrene, 4-(2-ethylhexyl)styrene, allylstyrene, isopropenylstyrene, butenylstyrene, octenylstyrene, 4-t-butoxycarbonylstyrene, and 4-t-butoxystyrene.

[0049] Examples of monofunctional vinyl ethers include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexylmethyl vinyl ether, 4-methylcyclohexylmethyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, and phenoxypolyethylene glycol vinyl ether.

[0050] Examples of the monofunctional N-vinyl compound include N-vinyl-ε-caprolactam and N-vinylpyrrolidone.

[0051] - Polyfunctional Polymerizable Compound - Examples of polyfunctional polymerizable compounds include polyfunctional (meth)acrylate compounds and polyfunctional vinyl ethers.

[0052] Examples of polyfunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, EO-modified neopentyl glycol di(meth)acrylate, PO-modified neopentyl glycol di(meth)acrylate, EO-modified hexanediol di(meth)acrylate, PO-modified hexanediol di(meth)acrylate, decanediol di(meth)acrylate, dodecanediol di(meth)acrylate, and glycerin di(meth)acrylate. tris(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane EO adduct tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tri(meth)acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly(meth)acrylate, and tris(2-acryloyloxyethyl)isocyanurate.

[0053] Examples of polyfunctional vinyl ethers include 1,4-butanediol divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide divinyl ether, trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, and ditrimethylolpropane. trivinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, EO-added trimethylolpropane trivinyl ether, PO-added trimethylolpropane trivinyl ether, EO-added ditrimethylolpropane tetravinyl ether, PO-added ditrimethylolpropane tetravinyl ether, EO-added pentaerythritol tetravinyl ether, PO-added pentaerythritol tetravinyl ether, EO-added dipentaerythritol hexavinyl ether, and PO-added dipentaerythritol hexavinyl ether.

[0054] <Colorant> The ink according to an embodiment of the present disclosure contains at least one colorant. Examples of the colorant include dyes and pigments. From the viewpoint of durability such as heat resistance, light resistance, and water resistance, the colorant is preferably a pigment.

[0055] When a pigment is used as a colorant, the pigment can be contained in the ink as a pigment dispersion. The pigment dispersion is a liquid obtained by dispersing a pigment in a liquid medium using a dispersant, and contains at least a pigment, a dispersant, and a liquid medium. Details of the dispersant will be described later. The liquid medium may be an organic solvent or a polymerizable compound.

[0056] As the pigment, any of commercially available organic pigments and inorganic pigments can be used, including, for example, pigments described in "Dictionary of Pigments" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and JP-A Nos. 2002-12607, 2002-188025, 2003-26978, and 2003-342503.

[0057] When the ink contains a colorant, the content of the colorant is preferably 0.5% by mass to 15% by mass, more preferably 1% by mass to 10% by mass, and even more preferably 2% by mass to 5% by mass, relative to the total amount of the ink.

[0058] <Dispersant> When a pigment is used as the colorant, the pigment can be contained in the ink as a pigment dispersion. The pigment can be dispersed in a liquid medium using a dispersant. As the dispersant, a commonly known dispersant can be used. From the viewpoint of dispersion stability, the dispersant is preferably a compound having both a hydrophilic structure and a hydrophobic structure.

[0059] Examples of dispersants include low molecular weight dispersants having a molecular weight of less than 1000, such as higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, polyoxyalkylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene glycols, glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene fatty acid amides, and amine oxides.

[0060] Further, examples of the dispersant include high-molecular-weight dispersants having a molecular weight of 1,000 or more obtained by copolymerizing a hydrophilic monomer and a hydrophobic monomer. From the viewpoint of dispersion stability, the hydrophilic monomer is preferably a dissociable group-containing monomer, and is preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. Examples of the dissociable group-containing monomer include a carboxyl group-containing monomer, a sulfonic acid group-containing monomer, and a phosphate group-containing monomer. From the viewpoint of dispersion stability, the hydrophobic monomer is preferably an aromatic group-containing monomer having an aromatic group and an ethylenically unsaturated bond, or an aliphatic hydrocarbon group-containing monomer having an aliphatic hydrocarbon group and an ethylenically unsaturated bond. The polymer may be either a random copolymer or a block copolymer.

[0061] The dispersant may be a commercially available product. Examples of commercially available products include DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-110, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, and DISPERBYK-182 (all manufactured by BYK Chemie). Examples of the solvent include SOLSPERSE 3000, SOLSPERSE 5000, SOLSPERSE 9000, SOLSPERSE 12000, SOLSPERSE 13240, SOLSPERSE 13940, SOLSPERSE 17000, SOLSPERSE 22000, SOLSPERSE 24000, SOLSPERSE 26000, SOLSPERSE 28000, SOLSPERSE 32000, SOLSPERSE 36000, SOLSPERSE 39000, SOLSPERSE 41000, and SOLSPERSE 71000 (all manufactured by Lubrizol).

[0062] As a dispersing device for dispersing the pigment, a known dispersing device can be used, and examples thereof include a ball mill, a sand mill, a bead mill, a roll mill, a jet mill, a paint shaker, an attritor, an ultrasonic disperser, and a disperser.

[0063] From the viewpoint of dispersion stability, the content of the dispersant relative to the content of the pigment in the ink is preferably 0.05 to 1.0 by mass, and more preferably 0.1 to 0.5.

[0064] <Polymerization initiator> The ink according to an embodiment of the present disclosure may contain at least one polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator that generates radicals.

[0065] Examples of the radical polymerization initiator include alkylphenone compounds, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

[0066] Among these, the polymerization initiator is preferably at least one selected from the group consisting of an acylphosphine compound and a thio compound, more preferably at least one selected from the group consisting of an acylphosphine oxide compound and a thioxanthone compound, and even more preferably a combination of an acylphosphine oxide compound and a thioxanthone compound.

[0067] The acylphosphine oxide compound includes a monoacylphosphine oxide compound and a bisacylphosphine oxide compound.

[0068] Examples of the monoacylphosphine oxide compound include isobutyryldiphenylphosphine oxide, 2-ethylhexanoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, o-toluyldiphenylphosphine oxide, p-t-butylbenzoyldiphenylphosphine oxide, 3-pyridylcarbonyldiphenylphosphine oxide, acryloyldiphenylphosphine oxide, benzoyldiphenylphosphine oxide, pivaloylphenylphosphinic acid vinyl ester, acryloyldiphenylphosphine oxide, benzo ... Examples of the diphenylphosphine oxide include dipoylbisdiphenylphosphine oxide, pivaloyldiphenylphosphine oxide, p-toluyldiphenylphosphine oxide, 4-(t-butyl)benzoyldiphenylphosphine oxide, terephthaloylbisdiphenylphosphine oxide, 2-methylbenzoyldiphenylphosphine oxide, versatoyldiphenylphosphine oxide, 2-methyl-2-ethylhexanoyldiphenylphosphine oxide, 1-methyl-cyclohexanoyldiphenylphosphine oxide, pivaloylphenylphosphine acid methyl ester, and pivaloylphenylphosphine acid isopropyl ester.

[0069] Examples of the bisacylphosphine oxide compound include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-ethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2-naphthylphosphine oxide, and bis(2,6-dichlorobenzoyl). phenyl)-1-naphthylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-chlorophenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)decylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-octylphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)-2, 5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-4-ethoxyphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-4-ethoxyphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2- naphthylphosphine oxide, bis(2-methyl-1-naphthoyl)-4-propylphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, bis(2-methoxy-1-naphthoyl)-4-ethoxyphenylphosphine oxide, bis(2-chloro-1-naphthoyl)-2,5-dimethylphenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0070] Examples of thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dichlorothioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3-(2-methoxyethoxycarbonyl)thioxanthone, 4-butoxycarbonylthioxanthone, and 1-methyl-2-methyl-2-methylthioxanthone. thioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4-di[2-(2-methoxyethoxy)ethoxycarbonyl]thioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, thioxanthone, 2-methyl-6-dimethoxymethylthioxanthone, 2-methyl-6-(1,1-dimethoxybenzyl)thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, n-allylthioxanthone-3,4-dicarboximide, n-octylthioxanthone-3,4-dicarboximide, N-(1,1,3,3-tetramethylthioxanthone), methylbutyl)thioxanthone-3,4-dicarboximide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethylene glycol ester, and 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride.

[0071] The thioxanthone compound may be a commercially available product, such as the SPEEDCURE series manufactured by Lambson (e.g., SPEEDCURE 7010, SPEEDCURE CPTX, SPEEDCURE ITX, etc.).

[0072] From the viewpoint of further reducing odor, the ink according to an embodiment of the present disclosure preferably contains, as a polymerization initiator, at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, and more preferably contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide.

[0073] Furthermore, from the viewpoint of further reducing odor, the total content of at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (preferably the total content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide) is preferably 3.5% by mass or more, and more preferably 5% by mass or more, relative to the total amount of the ink. The upper limit of this total content is not particularly limited, but is, for example, 10% by mass.

[0074] Furthermore, from the viewpoint of further reducing odor, the ink according to an embodiment of the present disclosure preferably contains, as a polymerization initiator, a compound having two or more thioxanthone skeletons in the molecule.

[0075] The content of the compound having two or more thioxanthone skeletons in the molecule is preferably 1% by mass to 10% by mass, and more preferably 2% by mass to 8% by mass, relative to the total amount of the ink.

[0076] <Polymerization Inhibitor> The ink according to an embodiment of the present disclosure preferably contains at least one polymerization inhibitor.

[0077] Examples of the polymerization inhibitor include hydroquinone compounds, phenothiazine, catechols, alkylphenols, alkylbisphenols, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionic acid esters, mercaptobenzimidazole, phosphites, nitrosamine compounds, hindered amine compounds, and nitroxyl radicals.

[0078] Among these, the polymerization inhibitor is more preferably a nitrosamine compound.

[0079] Examples of the nitrosamine compound include N-nitroso-N-phenylhydroxylamine aluminum salt and N-nitroso-N-phenylhydroxylamine, with N-nitroso-N-phenylhydroxylamine aluminum salt being preferred as the nitrosamine compound.

[0080] The content of the polymerization inhibitor is preferably 0.05% by mass to 1% by mass relative to the total amount of the ink, from the viewpoint of improving the stability of the ink over time.

[0081] <Surfactant> The ink according to an embodiment of the present disclosure preferably contains at least one surfactant. The type of surfactant is not particularly limited, and may be any of anionic surfactants, cationic surfactants, and nonionic surfactants.

[0082] In particular, from the viewpoint of further reducing odor, the surfactant is preferably a surfactant having a polymerizable group (hereinafter also referred to as a "polymerizable surfactant").

[0083] From the viewpoint of curability, the polymerizable group in the polymerizable surfactant is preferably a radical polymerizable group. Also, from the viewpoint of curability, the radical polymerizable group is preferably an ethylenically unsaturated group. Among them, the polymerizable group in the polymerizable surfactant is preferably a vinyl group or a (meth)acryloyl group, and more preferably a (meth)acryloyl group.

[0084] From the viewpoint of image quality, the number of polymerizable groups in the polymerizable surfactant is preferably 2 or more, and more preferably 3 or more. The upper limit of the number of polymerizable groups in the polymerizable surfactant is not particularly limited, but is, for example, 5 from the viewpoint of ejection properties when the ink is ejected by an inkjet recording method.

[0085] That is, with regard to the type and number of polymerizable groups, the polymerizable surfactant is preferably a surfactant having two or more (meth)acryloyl groups, and more preferably a surfactant having three or more (meth)acryloyl groups.

[0086] Examples of the polymerizable surfactant include a polymerizable silicone surfactant, a polymerizable fluorine surfactant, and a polymerizable acrylic surfactant.

[0087] Examples of polymerizable silicone surfactants include compounds in which a polymerizable group is bonded to the main chain or side chain of polyether-modified dimethylsiloxane.

[0088] Commercially available polymerizable silicone surfactants include BYK-UV3500, 3505, 3530, 3570, 3575, and 3576 (manufactured by BYK Corporation), Tegorad 2100, 2200, 2250, 2300, 2500, 2600, 2700, 2800, 2010, and 2011 (manufactured by Evonik Corporation), EBECRYL 350 and 1360 (manufactured by Daicel-Allnex Corporation), and KP-410, 411, 412, 413, 414, 415, 416, 418, 420, 422, and 423 (manufactured by Shin-Etsu Silicones Co., Ltd.). Examples of commercially available polymerizable silicone surfactants include BYK-UV3500, 3505, 3530, 3570, 3575, and 3576 (manufactured by BYK Corporation), Tegorad 2100, 2200, 2250, 2300, 2500, 2600, 2700, 2800, 2010, and 2011 (manufactured by Evonik Corporation), EBECRYL 350 and 1360 (manufactured by Daicel-Allnex Corporation), and KP-410, 411, 412, 413, 414, 415, 416, 418, 420, 422, and 423 (manufactured by Shin-Etsu Silicones Co., Ltd.).

[0089] Examples of polymerizable fluorine-based surfactants include compounds having a perfluoroalkyl group and a polymerizable group.

[0090] Commercially available polymerizable fluorosurfactants include, for example, fluorosurfactants having a (meth)acryloyl group, such as Megafac RS-56, RS-72-K, RS-75, RS-76-E, RS-65-NS, RS-78, and RS-90 (manufactured by DIC Corporation).

[0091] Examples of polymerizable acrylic surfactants include compounds in which a polymerizable group is bonded to the side chain of a poly(meth)acrylic structure.

[0092] An example of a commercially available polymerizable acrylic surfactant is CN821 (manufactured by Sartomer).

[0093] The surfactant is preferably a polymerizable silicone surfactant, and more preferably a silicone surfactant having a (meth)acryloyl group.

[0094] The content of the surfactant is preferably 1% by mass to 20% by mass, and more preferably 5% by mass to 15% by mass, based on the total amount of the ink.

[0095] <Additives> The ink according to an embodiment of the present disclosure may contain additives such as a co-sensitizer, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, a solvent, and a basic compound, as needed.

[0096] <Physical Properties> The viscosity of the ink is preferably 0.5 mPa·s to 50 mPa·s, more preferably 5 mPa·s to 40 mPa·s, preferably 7 mPa·s to 35 mPa·s, and even more preferably 8 mPa·s to 30 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0097] The surface tension of the ink is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and even more preferably 25 mN / m to 45 mN / m.

[0098] [Actinic Energy Ray-Curable Ink Set] An ink set according to one embodiment of the present disclosure includes a first ink containing a specific bifunctional (meth)acrylate, a specific monofunctional (meth)acrylate, and a colorant, and a second ink.

[0099] In the first ink, the total content of the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate is 80 mass % or more relative to the total amount of the polymerizable compounds contained in the first ink.

[0100] The first ink is the same as the ink according to an embodiment of the present disclosure, and therefore a description thereof will be omitted. The second ink will be described in detail below.

[0101] When a cured product of the second ink is immersed in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes each, the pencil hardness of the cured product after immersion in the alkaline aqueous solution of pH 10 is lower than the pencil hardness of the cured product after immersion in water of pH 7.

[0102] A cured product of the second ink is prepared under the following conditions. The second ink is applied to a plastic sheet substrate (polyethylene terephthalate substrate, 12 μm thick, "Taiko PET" manufactured by Futamura Chemical Co., Ltd.) using an inkjet recording device (product name "CylinderJET" manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i" manufactured by Konica Minolta, Inc.), and a 100% solid image with a thickness of 6 μm is recorded under conditions of a droplet volume of 10.5 pL (picoliter) and a resolution of 600 × 600 dpi (dots per inch). After the first ink is applied, an exposure amount of 10 mJ / cm is recorded using an LED light source attached to the inkjet recording device. ２ As the LED light source, a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm is used. Then, in an atmosphere with an oxygen concentration of 1% by volume, the LED light source is used to irradiate the sample with ultraviolet light at an exposure dose of 500 mJ / cm. ２ The composition is then irradiated with ultraviolet light at a temperature of 1000 to cure, thereby obtaining a cured product.

[0103] The pencil hardness is measured by immersing a cured product of the second ink in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes, and then conducting a pencil hardness test under the conditions of JIS K 5600 5-4 (1999). The pencil hardness is expressed as 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, and 9H, in order from softest to softest.

[0104] The pencil hardness of the cured product after immersion in an alkaline aqueous solution of pH 10 is lower than the pencil hardness of the cured product after immersion in water of pH 7, which means that the pencil hardness of the former is at least one level lower than the pencil hardness of the latter.

[0105] From the viewpoint of improving alkali strippability, the pencil hardness of the cured product after immersion in an alkaline aqueous solution of pH 10 is preferably at least three levels lower, and more preferably at least five levels lower, than the pencil hardness of the cured product after immersion in water of pH 7.

[0106] From the viewpoint of improving alkaline peelability and ensuring safety, the second ink preferably contains at least one acid group-containing compound selected from the group consisting of polymerizable monomers having acid groups and polymers having acid groups, and the total content of the acid group-containing compounds is preferably 8% by mass or more relative to the total amount of the second ink.

[0107] Furthermore, from the viewpoints of improving alkaline peelability, safety, and low odor, the second ink preferably contains at least one acid group-containing compound selected from the group consisting of polymerizable monomers having acid groups and polymers having acid groups, a specific bifunctional (meth)acrylate, and a specific monofunctional (meth)acrylate.

[0108] <Acid Group-Containing Compound> The second ink preferably contains an acid group-containing compound. When an acid group reacts with an alkali to form a salt, the water solubility improves. Therefore, when the ink contains an acid group-containing compound, alkali strippability improves.

[0109] Examples of the acid group in the acid group-containing compound include a carboxy group, a sulfo group, a phosphonic acid group, a phosphoric acid group, and a sulfonamide group.

[0110] -Polymerizable Monomer Having an Acid Group- In the present disclosure, a "monomer" refers to a compound having a molecular weight of less than 1,000. A "polymerizable monomer" refers to a compound having a molecular weight of less than 1,000 and having a polymerizable group. The molecular weight of a monomer can be calculated based on the type and number of atoms constituting the monomer.

[0111] Examples of polymerizable monomers having a carboxy group include 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-carboxyethyl (meth)acrylate, and (meth)acrylic acid.

[0112] Examples of polymerizable monomers having a sulfo group include 2-hydroxy-3-sulfopropyl(meth)acrylate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl(meth)acrylate, 3-sulfopropyl(meth)acrylate, and 4-styrenesulfonic acid.

[0113] Examples of polymerizable monomers having a phosphoric acid group include 2-phosphonooxyethyl (meth)acrylate and 2-(meth)acryloyloxyethyl acid phosphate.

[0114] Among these, the polymerizable monomer having an acid group is preferably a polymerizable monomer having a carboxy group from the viewpoints of improving alkaline strippability, safety, and low viscosity.

[0115] The polymerizable monomer having an acid group may be a monofunctional polymerizable monomer having an acid group or a polyfunctional polymerizable monomer having an acid group. From the viewpoints of improving alkali strippability, safety, and low viscosity, however, it is preferably a monofunctional polymerizable monomer having an acid group, more preferably a monofunctional polymerizable monomer having a carboxy group, and even more preferably a monofunctional (meth)acrylate having a carboxy group.

[0116] -Polymer Having Acid Groups- In the present disclosure, the term "polymer" refers to a compound having a weight-average molecular weight of 1,000 or more.

[0117] Examples of the polymer having an acid group include a (meth)acrylic copolymer, a polyurethane, a polyvinyl alcohol, a polyvinyl butyral, a polyvinyl formal, a polyamide, a polyester, and an epoxy resin. Of these, the polymer having an acid group is preferably a (meth)acrylic copolymer, a polyurethane, or a polyvinyl butyral.

[0118] In the present disclosure, the term "(meth)acrylic copolymer" refers to a copolymer containing (meth)acrylic acid, (meth)acrylic acid esters (e.g., (meth)acrylic acid alkyl esters, (meth)acrylic acid aryl esters, (meth)acrylic acid allyl esters, etc.), (meth)acrylamide, (meth)acrylamide derivatives, and other (meth)acrylic acid derivatives as structural units. Polyurethane refers to a polymer obtained by a condensation reaction between a polyfunctional isocyanate compound having two or more isocyanate groups and a polyhydric alcohol having two or more hydroxyl groups. Polyvinyl butyral refers to a polymer obtained by reacting polyvinyl alcohol, obtained by partial or complete saponification of polyvinyl acetate, with butyraldehyde under acidic conditions. Polyvinyl butyral also includes polymers having functional groups introduced into the molecule.

[0119] The (meth)acrylic copolymer preferably contains a structural unit having an acid group. Among these, the acid group is preferably a carboxy group. Examples of the structural unit having a carboxy group include a structural unit derived from (meth)acrylic acid and a structural unit derived from a structural unit represented by the following formula 1:

[0120]

[0121] In formula 1, R １ represents a hydrogen atom or a methyl group, R ２ represents a single bond or an (n+1)-valent linking group; A represents an oxygen atom or —NR ３ represents -, and R ３ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms, and n represents an integer of 1 to 5.

[0122] For preferred embodiments and specific examples of the structural unit represented by Formula 1, as well as preferred embodiments of structural units other than the structural unit represented by Formula 1, reference can be made to Japanese Patent Nos. 4,668,111 and 5,588,887.

[0123] In particular, the polymer having an acid group preferably contains a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylic acid alkyl ester. The number of carbon atoms in the alkyl group contained in the (meth)acrylic acid alkyl ester is preferably 1 to 10, and more preferably 1 to 6.

[0124] The weight-average molecular weight of the polymer having an acid group is preferably 1,000 to 1,000,000, more preferably 5,000 to 500,000, and even more preferably 10,000 to 200,000. The weight-average molecular weight refers to a value measured by gel permeation chromatography (GPC). Measurement by gel permeation chromatography (GPC) is performed using an HLC (registered trademark)-8020GPC (manufactured by Tosoh Corporation) as the measuring device, three TSKgel (registered trademark) Super Multipore HZ-H columns (4.6 mm ID x 15 cm, manufactured by Tosoh Corporation) as the columns, and THF (tetrahydrofuran) as the eluent. Measurement is also performed using an RI detector at a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection volume of 10 μl, and a measurement temperature of 40°C. The calibration curve is prepared from eight samples of "Standard Sample TSK Standard, Polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

[0125] From the viewpoint of further improving alkali strippability, the total content of the acid group-containing compounds is preferably 8% by mass or more, more preferably 10% by mass or more, and even more preferably 14% by mass or more, relative to the total amount of the second ink. The upper limit of this total content is, for example, 20% by mass.

[0126] <Bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms> The second ink preferably contains a specific bifunctional (meth)acrylate. Preferred aspects of the specific bifunctional (meth)acrylate contained in the second ink are the same as the preferred aspects of the specific bifunctional (meth)acrylate contained in the ink according to an embodiment of the present disclosure.

[0127] <Monofunctional (meth)acrylate having a hydroxyl group> The second ink preferably contains a specific monofunctional (meth)acrylate. Preferred aspects of the specific monofunctional (meth)acrylate contained in the second ink are the same as the preferred aspects of the specific monofunctional (meth)acrylate contained in the ink according to an embodiment of the present disclosure.

[0128] From the viewpoint of achieving low odor, water resistance, and alkali removability at the same time, it is preferable that the total content of the polymerizable monomer having an acid group, the specific bifunctional (meth)acrylate, and the specific monofunctional (meth)acrylate is 40 mass% or more relative to the total amount of polymerizable compounds contained in the second ink.

[0129] When the content of polymerizable compounds other than the acid group-containing compound, the specific bifunctional (meth)acrylate, and the monofunctional (meth)acrylate (hereinafter also referred to as "other polymerizable compounds A") is low, the effects of alkali strippability, low odor, and water resistance based on the acid group-containing compound, the specific bifunctional (meth)acrylate, and the specific monofunctional (meth)acrylate are more effectively exhibited.

[0130] To enhance the effects of alkali strippability, low odor, and water resistance, the total content of the polymerizable monomer having an acid group, the specific bifunctional (meth)acrylate, and the specific monofunctional (meth)acrylate is preferably 70% by mass or more, and more preferably 90% by mass or more. The upper limit of this total content is not particularly limited and may be 100% by mass. In other words, the polymerizable compounds contained in the second ink may consist only of the polymerizable monomer having an acid group, the specific bifunctional (meth)acrylate, and the specific monofunctional (meth)acrylate.

[0131] <Other polymerizable compounds A> As described above, from the viewpoint of further demonstrating the effects of alkali strippability, low odor, and water resistance, it is desirable that the content of other polymerizable compounds A be small. However, the second ink may contain other polymerizable compounds A.

[0132] Examples of the other polymerizable compound A contained in the second ink include the same polymerizable compounds as those contained in the ink according to an embodiment of the present disclosure.

[0133] <Polymerization Initiator> The second ink may contain at least one type of polymerization initiator.

[0134] Examples of the polymerization initiator contained in the second ink include the same polymerization initiator as that contained in the ink according to an embodiment of the present disclosure.

[0135] From the viewpoint of further reducing odor, the second ink preferably contains, as a polymerization initiator, at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, and more preferably contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide.

[0136] Furthermore, from the viewpoint of further reducing odor, the total content of at least one selected from the group consisting of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (preferably the total content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide) is preferably 2% by mass or more, and more preferably 3% by mass or more, relative to the total amount of the second ink. The upper limit of this total content is not particularly limited, but is, for example, 10% by mass.

[0137] Furthermore, from the viewpoint of further reducing odor, the second ink preferably contains, as a polymerization initiator, a compound having two or more thioxanthone skeletons in the molecule.

[0138] The content of the compound having two or more thioxanthone skeletons in the molecule is preferably 0.02% by mass to 1% by mass, and more preferably 0.05% by mass to 0.5% by mass, relative to the total amount of the second ink.

[0139] <Polymerization Inhibitor> The second ink preferably contains at least one type of polymerization inhibitor.

[0140] Examples of the polymerization inhibitor contained in the second ink include the same polymerization inhibitor as that contained in the ink according to an embodiment of the present disclosure.

[0141] From the viewpoint of improving the stability of the second ink over time, the content of the polymerization inhibitor is preferably 0.05% by mass to 0.5% by mass relative to the total amount of the second ink.

[0142] <Surfactant> The second ink preferably contains at least one surfactant.

[0143] Examples of surfactants contained in the second ink include those similar to those contained in the ink according to an embodiment of the present disclosure.

[0144] In particular, from the viewpoint of further reducing odor, the surfactant contained in the second ink is preferably a polymerizable surfactant.

[0145] The content of the surfactant is preferably 1% by mass to 20% by mass, and more preferably 5% by mass to 15% by mass, relative to the total amount of the second ink.

[0146] <Additives> The second ink may contain additives such as a co-sensitizer, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, a solvent, and a basic compound, as needed.

[0147] The second ink preferably does not contain a colorant. As described below, the second ink is preferably applied directly onto the substrate before the first ink is applied. The second ink preferably serves as a primer for removing the image recorded by the first ink containing a colorant with an alkali.

[0148] <Physical Properties> The viscosity of the first ink and the second ink is preferably 0.5 mPa·s to 50 mPa·s, more preferably 5 mPa·s to 40 mPa·s, even more preferably 7 mPa·s to 35 mPa·s, and particularly preferably 8 mPa·s to 30 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0149] The surface tension of the first ink is preferably 60 mN / m or less, more preferably 20 mN / m to 30 mN / m, and even more preferably 20 mN / m to 25 mN / m. The surface tension of the second ink is preferably 60 mN / m or less, more preferably 20 mN / m to 40 mN / m, and even more preferably 23 mN / m to 30 mN / m.

[0150] The surface tension of the second ink is preferably higher than the surface tension of the first ink.

[0151] As will be described later, the order in which the first ink and the second ink are applied onto the substrate is not particularly limited, but from the viewpoints of alkali removability and adhesion to the substrate, the order is preferably the second ink first, then the first ink. When the second ink and the first ink are applied onto the substrate in this order, if the surface tension of the second ink is higher than that of the first ink (in other words, the surface tension of the first ink is lower than that of the second ink), the ink droplets of the first ink will spread more easily, thereby improving image quality.

[0152] [Image Recording Method A] Image recording method A, which is an embodiment of the present disclosure, includes a step of applying the ink (the ink of an embodiment of the present disclosure) onto a substrate using an inkjet recording method, and a step of irradiating the applied ink with actinic energy rays.

[0153] (Step of applying using an inkjet recording method) The type of substrate is not particularly limited, and commonly known substrates can be used as the substrate. Examples of substrates include glass, quartz, and plastic films. Examples of resins constituting the plastic film include cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, acrylic resin, chlorinated polyolefin resin, polyethersulfone resin, polyethylene terephthalate (PET), polyethylene naphthalate, nylon, polyethylene, polystyrene, polypropylene, polycycloolefin resin, polyimide resin, polycarbonate resin, and polyvinyl acetal. The plastic film may be a film containing only one of these resins, or a film containing a mixture of two or more of them.

[0154] The thickness of the substrate is not particularly limited and is, for example, 1 μm to 10 mm. When the substrate is a film, the thickness is preferably 1 μm to 500 μm, more preferably 2 μm to 200 μm, even more preferably 5 μm to 100 μm, and particularly preferably 10 μm to 90 μm. When the substrate is glass, the thickness is preferably 0.1 mm to 10 mm, more preferably 0.15 mm to 8 mm, and even more preferably 0.2 mm to 5 mm.

[0155] The substrate may be a beverage container.

[0156] The material of the beverage container is not particularly limited, and examples thereof include glass and plastic. Among these, the beverage container is preferably a plastic container, and more preferably a PET bottle containing polyethylene terephthalate as a main component.

[0157] The substrate may also be a plastic film that is attached to the surface of a beverage container. The substrate may be subjected to a hydrophilization treatment. Examples of hydrophilization treatments include, but are not limited to, corona treatment, plasma treatment, heat treatment, abrasion treatment, light irradiation treatment (e.g., UV treatment), and flame treatment. Corona treatment can be performed using, for example, a Corona Master (product name "PS-10S", manufactured by Shinko Electric Meter Co., Ltd.). The conditions for the corona treatment may be selected appropriately depending on the type of substrate, etc.

[0158] The inkjet recording method is not particularly limited as long as it is a method capable of recording an image, and any known method can be used. Examples of inkjet recording methods include a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink with it, thereby ejecting the ink using radiation pressure, and a thermal inkjet (Bubble Jet (registered trademark)) method that heats the ink to form bubbles and uses the resulting pressure.

[0159] Inkjet heads used in inkjet recording methods include a shuttle method in which a short serial head is used and recording is performed while the head is scanned in the width direction of the substrate, and a line method in which a line head is used in which recording elements are arranged corresponding to the entire area of ​​one side of the substrate.

[0160] In the line method, a pattern can be formed over the entire surface of a substrate by scanning the substrate in a direction intersecting the arrangement direction of the recording elements, eliminating the need for a transport system such as a carriage for scanning a short head. Furthermore, the line method does not require complex scanning control of the carriage movement and the substrate, and only the substrate moves, making it possible to achieve faster recording speeds than the shuttle method.

[0161] The volume of ink droplets ejected from the inkjet head is preferably 1 pL (picoliter) to 100 pL, more preferably 3 pL to 80 pL, and even more preferably 3 pL to 50 pL.

[0162] (Step of irradiating the applied ink with active energy rays) Examples of active energy rays include gamma rays, beta rays, electron beams, ultraviolet rays, and visible light. Of these, ultraviolet rays are preferred as the active energy rays.

[0163] The peak wavelength of the ultraviolet light is, for example, preferably 200 nm to 405 nm, more preferably 250 nm to 400 nm, and even more preferably 300 nm to 400 nm.

[0164] As light sources for ultraviolet irradiation, various lasers such as mercury lamps, gas lasers, and solid-state lasers are mainly used, and discharge lamps such as mercury lamps, metal halide lamps, and ultraviolet fluorescent lamps are widely known. In addition, semiconductor light sources such as UV-LEDs (ultraviolet light-emitting diodes) and UV-LDs (ultraviolet laser diodes) are small, have a long life, are highly efficient, and are low cost, and are expected to be light sources for ultraviolet irradiation. Among these, the light source for ultraviolet irradiation is preferably a metal halide lamp, a high-pressure mercury lamp, a medium-pressure mercury lamp, a low-pressure mercury lamp, or a UV-LED.

[0165] In the present disclosure, polymerizing only a portion of the polymerizable monomers in the ink is also referred to as “pre-curing,” and the irradiation of active energy rays for pre-curing is also referred to as “pinning exposure.” In the present disclosure, polymerizing substantially all of the polymerizable compounds in the ink is also referred to as “main curing,” and the irradiation of active energy rays for main curing is also referred to as “main exposure.”

[0166] In the step of irradiating the ink with actinic radiation, it is preferable to temporarily cure the ink and then fully cure it. Specifically, it is preferable to apply the ink, then subject the ink to pinning exposure, and finally subject the ink to full exposure.

[0167] The reaction rate of the ink after pinning exposure is preferably 10% to 80%.

[0168] Here, the reaction rate of the ink means the polymerization rate of the polymerizable compound contained in the ink, which is determined by high performance liquid chromatography.

[0169] By ensuring that the ink reaction rate is 10% or more, insufficient dot spreading is suppressed, and as a result, the graininess of the final image is improved.

[0170] Furthermore, by keeping the ink reactivity at 80% or less, interference between ink dots is suppressed, resulting in an improvement in the quality of the image that is ultimately obtained.

[0171] The reaction rate of the ink is preferably 15% or more from the viewpoint of further improving the graininess of the final image.

[0172] From the viewpoint of further improving the image quality of the final image obtained, the ink reactivity is preferably 75% or less, more preferably 50% or less, even more preferably 40% or less, particularly preferably 30% or less, and most preferably 25% or less.

[0173] The reaction rate of the ink after the main exposure is preferably more than 80% and not more than 100%, more preferably 85% to 100%, and even more preferably 90% to 100%. When the reaction rate is more than 80%, the adhesion is further improved.

[0174] The ink reactivity is determined by the following method. A substrate is prepared that has been subjected to the operations up to the end of irradiation of the ink with actinic energy rays. A sample piece (hereinafter referred to as post-irradiation sample piece) measuring 20 mm x 50 mm is cut out from the region of this substrate where the ink film is present. The cut post-irradiation sample piece is immersed in 10 mL of THF (tetrahydrofuran) for 24 hours to obtain an eluate in which the ink has dissolved. The amount of polymerizable compound (hereinafter referred to as "post-irradiation monomer amount X1") is determined for the obtained eluate by high performance liquid chromatography. Separately, the same operation as above is carried out except that the ink on the substrate is not irradiated with actinic energy rays, and the amount of polymerizable compound (hereinafter referred to as "unirradiated monomer amount X1") is determined. The ink reactivity (%) is determined based on the post-irradiation monomer amount X1 and the unirradiated monomer amount X1 using the following formula: Ink reactivity (%) = ((unirradiated monomer amount X1 - post-irradiation monomer amount X1) / unirradiated monomer amount X1) x 100

[0175] The exposure dose of the active energy rays for pinning exposure is set to 10 mJ / cm from the viewpoint of making it easier to achieve the above-mentioned ink reaction rate. ２ ~100 mJ / cm ２ and preferably 20 mJ / cm ２ ~60 mJ / cm ２ It is more preferable that:

[0176] The exposure dose of the active energy rays for the main exposure is 50 mJ / cm from the viewpoint of completely curing the ink. ２ ~1000mJ / cm ２ and preferably 200 mJ / cm ２ ~800 mJ / cm ２ It is more preferable that:

[0177] In the main exposure, from the viewpoint of improving adhesion to the substrate, it is preferable to irradiate with active energy rays in an atmosphere with an oxygen concentration of less than 1% by volume, more preferably 0.5% by volume or less, and even more preferably 0.3% by volume or less.

[0178] In the step of irradiating with active energy rays, from the viewpoint of image quality, it is preferable to irradiate with active energy rays within 0.1 to 5 seconds from the time the ink lands. When pinning exposure and main exposure are performed, it is preferable to irradiate with active energy rays for pinning exposure within 0.1 to 5 seconds from the time the ink lands. It is more preferable that the time from the time the ink lands to the irradiation with active energy rays (when pinning exposure and main exposure are performed, active energy rays for pinning exposure) is within 0.2 to 1 second.

[0179] [Image Recording Method B] Image recording method B, which is an embodiment of the present disclosure, uses the ink set described above (the ink set, which is an embodiment of the present disclosure), and includes the steps of applying the second ink onto a substrate by inkjet recording; irradiating the applied second ink with actinic energy rays; applying the first ink onto the substrate to which the second ink has been applied by inkjet recording; and irradiating the applied first ink with actinic energy rays.

[0180] The type of substrate, the method of applying the ink by ink jet recording, and the method of irradiating with active energy rays are the same as those in the image recording method A described above.

[0181] The differences from image recording method A will be explained below.

[0182] In image recording method B, it is preferable to apply the second ink, then subject the second ink to pinning exposure, apply the first ink onto the provisionally cured second ink, then apply the first ink, then subject the first ink to pinning exposure, and finally subject the first ink to main exposure. By provisionally curing the second ink, the image quality of the final image obtained is improved.

[0183] Hereinafter, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples as long as it does not depart from the gist of the disclosure.

[0184] Examples 1 to 23, Comparative Examples 1 to 5 Preparation of First Inks C1 to C16, C1a to C5a In preparing the first inks C1 to C16, C1a to C5a (cyan inks), first, a cyan pigment dispersion was prepared.

[0185] A cyan pigment (30 parts by mass), SOLSPERSE 32000 (9 parts by mass) as a dispersant, 3MPDDA (60 parts by mass) as a dispersion medium, and UV22 (1 part by mass) as a polymerization inhibitor were charged into a dispersing machine, Motor Mill M50 (manufactured by Eiger), and a dispersion treatment was carried out using zirconia beads having a diameter of 0.65 mm at a peripheral speed of 9 m / s for 4 hours, thereby obtaining a cyan pigment dispersion.

[0186] Details of the components contained in the cyan pigment dispersion are as follows:

[0187] Cyan pigment: C.I. Pigment Blue 15:4, product name "Heliogen (registered trademark) Blue D 7110 F", Sun Chemical (DIC Corporation); SOLSPERSE 32000: polyethyleneimine-based dispersant (product name "SOLSPERSE 32000", Lubrizol); 3MPDDA: 3-methyl-1,5-pentanediol diacrylate (product name "SR341", Sartomer); UV22: a mixture of 2,6-bis(1,1-dimethylethyl)-4-(phenylmethylene)-2,5-cyclohexadien-1-one and propoxylated glycerin triacrylate (product name "IRGASTAB UV-22", BASF Corporation).

[0188] Although UV22 contains propoxylated glycerin triacrylate as another polymerizable compound, the content of propoxylated glycerin triacrylate is very small, so it is listed in the "polymerization inhibitor" column in the table.

[0189] Next, the prepared cyan pigment dispersion was mixed with the specific bifunctional (meth)acrylate, specific monofunctional (meth)acrylate, other polymerizable compound, polymerization initiator, polymerization inhibitor, and surfactant shown in the table below so that the content of each component was the content (mass %) shown in the table. The mixture was stirred for 20 minutes at 25°C and 5,000 rpm using a mixer (product name "L4R" manufactured by Silverson) to obtain first inks C1 to C16 and C1a to C5a.

[0190] [Preparation of second inks P1 to P8] The specific bifunctional (meth)acrylates, specific monofunctional (meth)acrylates, other polymerizable compounds, polymerization initiators, polymerization inhibitors, and surfactants shown in the table below were mixed so that the content of each component was the content (mass %) shown in the table. The mixture was stirred for 20 minutes at 25°C and 5,000 rpm using a mixer (product name "L4R", manufactured by Silverson) to obtain second inks P1 to P8 (clear inks).

[0191] Details of each component listed in Tables 1 to 5 are as follows. Speedcure 7010L (manufactured by Lambson) was used to prepare the ink. Speedcure 7010L is a mixture of Speedcure 7010 and EOTMPTA, with a mixing ratio of 1:1 by mass. Speedcure 7010 is a polymerization initiator and EOTMPTA is another polymerizable compound, so they will be explained in the columns for polymerization initiators and other polymerizable compounds, respectively.

[0192] <Specific bifunctional (meth)acrylate> The specific bifunctional (meth)acrylate is a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms. 3MPDDA: As described above. HDDA: 1,6-hexanediol diacrylate (product name "Viscoat #230", manufactured by Osaka Organic Chemical Industry Ltd.) NDDA: 1,9-hexanediol diacrylate (product name "Viscoat #260", manufactured by Osaka Organic Chemical Industry Ltd.)

[0193] <Specific monofunctional (meth)acrylate> The specific monofunctional (meth)acrylate is a monofunctional (meth)acrylate having a hydroxyl group. 4-HBA: 4-hydroxybutyl acrylate (product name "4-HBA", manufactured by Osaka Organic Chemical Industry Ltd.) HPA: hydroxypropyl acrylate (product name "HPA", manufactured by Osaka Organic Chemical Industry Ltd.) HEA: hydroxyethyl acrylate (product name "HEA", manufactured by Osaka Organic Chemical Industry Ltd.) HPPA: 2-hydroxy-3-phenoxypropyl acrylate (product name "Etercure 620-100", manufactured by Eternal Chemical Co., Ltd.)

[0194] <Polymerizable monomer having an acid group> A-SA: 2-acryloyloxyethyl succinic acid (product name "NK Ester A-SA", manufactured by Shin-Nakamura Chemical Co., Ltd.)

[0195] <Polymers having acid groups> Polymer A: Binder A described in paragraph 0225 of Japanese Patent No. 5588887 (structural units derived from methacrylic acid:structural units derived from methyl methacrylate=20:80)

[0196] <Other Polymerizable Compounds> The other polymerizable compounds are polymerizable compounds other than the specific bifunctional (meth)acrylates, the specific monofunctional (meth)acrylates, and the polymerizable monomers having an acid group. CTFA: cyclic trimethylolpropane formal acrylate (product name "Viscoat #200", manufactured by Osaka Organic Chemical Industry Ltd.) IBOA: isobornyl acrylate (product name "SR506", manufactured by Sartomer) DDDA: 1,10-decanediol diacrylate (product name "SR595", manufactured by Sartomer) BDDA: 1,4-butanediol diacrylate (product name "Viscoat #195", manufactured by Osaka Organic Chemical Industry Ltd.) THFA: tetrahydrofurfuryl acrylate (product name "Viscoat #150", manufactured by Osaka Organic Chemical Industry Ltd.) EOTMPTA: trimethylolpropane EO adduct triacrylate (50% by mass contained in "product name "Speedcure 7010L", manufactured by Lambson")

[0197] <Polymerization initiator> BAPO: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins B.V.) TPO-L: (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (product name "Omnirad TPO-L", manufactured by IGM Resins B.V.) Speedcure 7010: 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-methylethylene)]}oxymethyl)propane (50% by mass contained in "product name "Speedcure 7010L", manufactured by Lambson") Omni. 907: 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one

[0198] <Polymerization inhibitor> UV12: N-nitroso-N-phenylhydroxylamine aluminum salt (product name "FLORSTAB UV-12", manufactured by Kromachem) UV22: As described above.

[0199] <Surfactants> Tegorad 2010: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2010", manufactured by Evonik) Tegorad 2500: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2500", manufactured by Evonik) Tegorad 2100: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2100", manufactured by Evonik)

[0200] <Colorants> Cyan pigment: As described above.

[0201] <Dispersant> SOLSPERSE 32000: As described above.

[0202] Image recording was performed using the prepared first inks C1 to C16 and C1a to C5a and the prepared second inks P1 to P8. In image recording A, image recording was performed using only the first ink. In image recording B, image recording was performed using both the first ink and the second ink.

[0203] (Image Recording A) Label substrate (polypropylene seal label (product name "7093 / 50 PP Gloss Clear TC AP901 A corona treatment was performed twice on a PET bottle (product name "PET30", manufactured by Ritrama Co., Ltd.) using a Corona Master (product name "PS-10S", manufactured by Shinko Electric Meter Co., Ltd.) under conditions of a treatment voltage of 10 kV and a treatment speed of 50 mm / sec. The corona-treated label substrate was wrapped around the body of a PET bottle (product name "PET500 Round", manufactured by Kokugo Co., Ltd.). The first ink was applied to the corona-treated label substrate using an inkjet recording device (product name "CylinderJET", manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i", manufactured by Konica Minolta, Inc.). Specifically, the first ink was applied to a surface of the label substrate measuring 7 cm in the longitudinal direction of the PET bottle and 5 cm in the circumferential direction of the PET bottle with a droplet volume of 10.5 pL (picoliter) and a resolution of 600 x 600 dpi (dots per After the first ink was applied, an LED light source attached to the inkjet recording apparatus was used to apply an exposure amount of 10 mJ / cm to the recording medium. ２~100 mJ / cm ２ As the LED light source, a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm was used.

[0204] The PET bottle with the image recorded on it was then placed in an exposure machine. The PET bottle was set sideways. The exposure machine is capable of rotating the PET bottle. While rotating the entire image recorded on the PET bottle, it was exposed using an LED light source. The exposure machine was connected to a nitrogen gas generator with a compressor (product name "Maxi-Flow30", manufactured by Inhouse Gas Co.) at a pressure of 0.2 MPa s, and nitrogen was allowed to flow so that the oxygen concentration inside the exposure machine was 1% to 10% by volume. Using an LED light source, an exposure dose of 50 mJ / cm was applied. ２ ~500 mJ / cm ２ The first ink was completely cured by irradiating it with ultraviolet light at a constant pressure (500 mN / cm ２ ~1,000mN / cm ２ The ink is pressed against the image with a constant pressure (a constant value within the range of 0.01 to 0.10) and the ink is then transferred to the plain paper. If no image is transferred, the ink is said to be completely cured.

[0205] In the image recording, the gap between the PET bottle surface and the inkjet head was adjusted to 0.5 mm to 1 mm, and the ejection voltage was adjusted to adjust the ejected droplet velocity to 7 m / s to 9 m / s.

[0206] (Image Recording B) The second ink was applied to the body of a PET bottle (product name "PET500 Round" manufactured by Kokugo Co., Ltd.) using an inkjet recording device (product name "CylinderJET" manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i" manufactured by Konica Minolta, Inc.). Specifically, the second ink was applied to a surface measuring 7 cm in the longitudinal direction of the PET bottle and 5 cm in the circumferential direction of the PET bottle at a droplet volume of 10.5 pL (picoliter) and a resolution of 600 x 600 dpi (dots per inch), thereby recording a 100% solid image with a thickness of 4 to 6 μm. Furthermore, under the same conditions as for the application of the second ink, the first ink was applied to the surface to which the second ink had been applied, thereby recording a 100% solid image with a thickness of 4 to 6 μm. After the second ink was applied and after the first ink was applied, an exposure amount of 10 mJ / cm was applied using an LED light source attached to the inkjet recording apparatus. ２ ~100 mJ / cm ２ As the LED light source, a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm was used.

[0207] The PET bottle with the image recorded on it was then placed in an exposure machine. The PET bottle was set sideways. The exposure machine is capable of rotating the PET bottle. While rotating the entire image recorded on the PET bottle, it was exposed using an LED light source. The exposure machine was connected to a nitrogen gas generator with a compressor (product name "Maxi-Flow30", manufactured by Inhouse Gas Co.) at a pressure of 0.2 MPa s, and nitrogen was allowed to flow so that the oxygen concentration inside the exposure machine was 1% to 10% by volume. Using an LED light source, an exposure dose of 50 mJ / cm was applied. ２ ~500 mJ / cm ２ The first ink and the second ink were completely cured by irradiation with ultraviolet light at 1000 kJ / cm 2 , thereby obtaining a recorded image.

[0208] In the image recording, the gap between the PET bottle surface and the inkjet head was adjusted to 0.5 mm to 1 mm, and the ejection voltage was adjusted to adjust the ejected droplet velocity to 7 m / s to 9 m / s.

[0209] [Evaluation] For each example and comparative example, the image recorded matter obtained by image recording A was used to evaluate water resistance, odor, and flexibility. The ejection properties of the first ink were also evaluated. The image recorded matter obtained by image recording B was used to evaluate water resistance, odor, flexibility, and alkali peelability. The evaluation methods are as follows.

[0210] <Water Resistance> The obtained image-recorded product was immersed in ion-exchanged water at 10°C to 25°C. After 24 hours, the image-recorded product was removed from the ion-exchanged water. The image surface of the removed image-recorded product was scratched with a pencil (hardness H), and visually inspected for image peeling. If image peeling did not occur, the image-recorded product was immersed again in ion-exchanged water, removed after 24 hours, and the image surface of the image-recorded product was scratched with a pencil (hardness H). This operation was repeated up to nine times. If image peeling occurred, the next operation was not performed. The evaluation criteria were as follows: Rank 7 or higher is a level that is practically acceptable. 10: No image peeling occurred after nine operations. 9: Image peeling occurred after nine operations. 8: Image peeling occurred after eight operations. 7: Image peeling occurred after seven operations. 6: Image peeling occurred after six operations. 5: Image peeling occurred after 5 operations. 4: Image peeling occurred after 4 operations. 3: Image peeling occurred after 3 operations. 2: Image peeling occurred after 2 operations. 1: Image peeling occurred after 1 operation.

[0211] <Odor> A 10 cm x 10 cm image sample was cut out from the obtained image recording. Within 10 minutes after the completion of image recording, the image sample was placed in a large-mouthed 500 mL glass bottle, tightly sealed, and left for three days. After three days, a sensory evaluation of odor was conducted. Ten subjects scored the odor using a scale of 50 points for "no odor," 47 points for "very slight odor," 30 points for "slight odor," 20 points for "definite odor," and 0 points for "strong odor." The odor was evaluated based on the total score. The evaluation criteria are as follows: Rank 7 or higher is a level that is acceptable for practical use. 10: 495 points or more 9: 490 points or more but less than 495 points 8: 485 points or more but less than 490 points 7: 480 points or more but less than 485 points 6: 470 points or more but less than 480 points 5: 460 points or more but less than 475 points 4: 450 points or more but less than 460 points 3: 440 points or more but less than 450 points 2: 430 points or more but less than 440 points 1: Less than 430 points

[0212] <Flexibility> 24 hours after image recording, the obtained image-recorded product was bent 180° in an environment of 25°C. After bending, the presence or absence of cracks or peeling at the bent portion was visually confirmed. This operation was performed a maximum of 20 times. If cracks or peeling occurred at the bent portion, the next operation was not performed. The evaluation criteria are as follows: 10: No cracks or peeling occurred after 20 operations; 9: Cracks or peeling occurred after 16 to 20 operations; 8: Cracks or peeling occurred after 12 to 15 operations; 7: Cracks or peeling occurred after 7 to 11 operations; 6: Cracks or peeling occurred after 6 operations; 5: Cracks or peeling occurred after 5 operations; 4: Cracks or peeling occurred after 4 operations; 3: Cracks or peeling occurred after 3 operations; 2: Cracks or peeling occurred after 2 operations. 1: Cracks or peeling occurred after one operation.

[0213] <Ejection Performance> The ejection performance of the first ink was evaluated using an inkjet recording device (product name "CylinderJET", manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i", manufactured by Konica Minolta, Inc.). The number of ejection nozzles before image recording was counted using a nozzle check pattern. In addition, after 10 minutes of image recording, the number of ejection nozzles after image recording was counted using a nozzle check pattern. The number of ejection nozzles before image recording and the number of ejection nozzles after image recording were used to calculate the reduction in the number of ejection nozzles. The same test was performed three times, and the ejection performance was evaluated based on the average value N of the reduction in the number of ejection nozzles. The evaluation criteria were as follows: Reduction in number of ejection nozzles = Number of ejection nozzles before image recording - Number of ejection nozzles after image recording 10: N is less than 1. 9: N is 1 or more and less than 2. 8: N is 2 or more and less than 3. 7: N is 3 or more and less than 4. 6: N is 4 or more and less than 5. 5: N is 5 or more and less than 7. 4: N is 7 or more and less than 10. 3: N is 10 or more and less than 15. 2: N is 15 or more and less than 20. 1: N is 20 or more.

[0214] <Alkali Removal Properties> The obtained image-recorded material was immersed in a 1.5% by mass aqueous solution of sodium hydroxide at 85°C, and the state of peeling was visually observed. The peeling time was the time from the time the image-recorded material was immersed until the image was completely peeled from the image-recorded material. The alkali removability was evaluated based on the peeling time. The shorter the peeling time, the better the alkali removability. The evaluation criteria were as follows: 10: Peeling time was 3 minutes or less. 9: Peeling time was more than 3 minutes and less than 4 minutes. 8: Peeling time was more than 4 minutes and less than 5 minutes. 7: Peeling time was more than 5 minutes and less than 7 minutes. 6: Peeling time was more than 7 minutes and less than 8 minutes. 5: Peeling time was more than 8 minutes and less than 9 minutes. 4: Peeling time was more than 9 minutes and less than 12 minutes. 3: Peeling time was more than 12 minutes and less than 15 minutes. 2: Peeling time was more than 15 minutes and less than 30 minutes. 1: Peeling time was more than 30 minutes.

[0215] Tables 1 to 5 show the evaluation results.

[0216] The evaluation results of the water resistance, odor, and flexibility of the image recorded matter obtained by image recording A, and the evaluation results of the ejection performance of the first ink are shown in the column for the first ink. The evaluation results of the water resistance, odor, flexibility, and alkali peelability of the image recorded matter obtained by image recording B are shown in the column for the second ink.

[0217] In Tables 1 to 4, "specific bifunctional (meth)acrylate + specific monofunctional (meth)acrylate" refers to the total content (mass %) of the specific bifunctional (meth)acrylate and the specific monofunctional (meth)acrylate relative to the total amount of polymerizable compounds contained in the first ink. "Specific bifunctional (meth)acrylate / specific monofunctional (meth)acrylate" refers to the mass ratio of the content of the specific bifunctional (meth)acrylate relative to the content of the specific monofunctional (meth)acrylate in the first ink. Table 3 lists the number of carbon atoms in the alkyl groups of the specific bifunctional (meth)acrylate and other polymerizable compounds. Table 4 lists the molecular weights of the specific monofunctional (meth)acrylate and other polymerizable compounds. In Table 5, "specific bifunctional (meth)acrylate + specific monofunctional (meth)acrylate + polymerizable monomer having an acid group" refers to the total content (mass %) of the specific bifunctional (meth)acrylate, specific monofunctional (meth)acrylate, and polymerizable monomer having an acid group relative to the total amount of polymerizable compounds contained in the second ink. In Table 5, "pencil hardness (water, pH 7)" refers to the pencil hardness after immersing a cured product of the second ink in water, pH 7, for 5 minutes. "pencil hardness (alkaline aqueous solution, pH 10)" refers to the pencil hardness after immersing a cured product of the second ink in an alkaline aqueous solution, pH 10, for 5 minutes. The cured product of the second ink was prepared by the following method. The second ink was applied to a plastic sheet substrate (polyethylene terephthalate substrate, thickness 12 μm, "Taiko PET" manufactured by Futamura Chemical Co., Ltd.) using an inkjet recording device (product name "CylinderJET" manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i" manufactured by Konica Minolta, Inc.) to record a 100% solid image with a thickness of 6 μm under conditions of a droplet volume of 10.5 pL (picoliter) and a resolution of 600 × 600 dpi (dots per inch). After applying the first ink, an exposure amount of 10 mJ / cm was recorded using an LED light source attached to the inkjet recording device. ２ The LED light source used was a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm. Thereafter, the LED light source was used in an atmosphere with an oxygen concentration of 1% by volume, at an exposure dose of 500 mJ / cm.２ The second ink was immersed in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes each, and then subjected to a pencil hardness test under the conditions of JIS K 5600 5-4 (1999) to evaluate the pencil hardness.

[0218]

[0219]

[0220]

[0221]

[0222]

[0223] As shown in Tables 1 to 5, in Examples 1 to 23, the inks contained a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant, and the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate was 80 mass % or more relative to the total amount of polymerizable compounds contained in the ink. Therefore, it was found that the obtained image recorded matter had low odor and excellent water resistance.

[0224] On the other hand, in Comparative Examples 1, 2, and 5, the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate was less than 80% by mass, and therefore low odor and water resistance could not be achieved at the same time.

[0225] In Comparative Example 3, the number of carbon atoms in the bifunctional (meth)acrylate contained in the ink was greater than 9, and it was found that the ink had poor ejection properties. In Comparative Example 4, the number of carbon atoms in the monofunctional (meth)acrylate contained in the ink was less than 5, and it was found that the ink had an odor.

[0226] Examples 101 to 106 First ink C1 (cyan ink), first ink M1 (magenta ink), first ink Y1 (yellow ink), first ink K1 (black ink), first ink W1 (white ink), and second ink P1 (clear ink) were prepared. The methods for preparing the first ink C1 and the second ink P1 were as described above.

[0227] [Preparation of First Inks M1, Y1, K1] First, a magenta pigment dispersion, a yellow pigment dispersion, and a black pigment dispersion were prepared by replacing the cyan pigment in the preparation of the cyan pigment dispersion described above with a magenta pigment, a yellow pigment, and a black pigment, respectively.

[0228] Details of the magenta pigment, yellow pigment, and black pigment are as follows.

[0229] Magenta pigment: C.I. Pigment RED 122, product name "TRM-33", manufactured by Dainichiseika Color & Chemicals Co., Ltd. Yellow pigment: C.I. Pigment Yellow 185, product name "Paliotol Yellow D 1155", manufactured by Sun Chemical (DIC) Corporation Black pigment: Carbon black, product name "MOGUL E", manufactured by CABOT Corporation

[0230] Next, each of the prepared magenta pigment dispersions, yellow pigment dispersions, and black pigment dispersions was mixed with the specific bifunctional (meth)acrylate, specific monofunctional (meth)acrylate, other polymerizable compound, polymerization initiator, polymerization inhibitor, and surfactant listed in Table 6, so that the content of each component was the content (mass %) listed in the table. The mixture was stirred for 20 minutes at 25°C and 5,000 rpm using a mixer (product name "L4R" manufactured by Silverson) to obtain first inks M1, Y1, and K1.

[0231] [Preparation of First Ink W1] White pigment (60 parts by mass), SOLSPERSE 41000 (9 parts by mass) as a dispersant, 3MPDDA (30 parts by mass) as a dispersion medium, and UV-22 (1 part by mass) as a polymerization inhibitor were charged into a dispersing machine, Motor Mill M50 (manufactured by Eiger), and a dispersion treatment was carried out using zirconia beads with a diameter of 0.65 mm at a peripheral speed of 9 m / s for 4 hours, to obtain a white pigment dispersion.

[0232] Details of each component contained in the white pigment dispersion are as follows.

[0233] White pigment: titanium oxide, product name "KRONOS 2300", manufactured by KRONOS SOLSPERSE 41000: product name "SOLSPERSE 41000", manufactured by Lubrizol

[0234] Next, the prepared white pigment dispersion was mixed with the specific bifunctional (meth)acrylate, specific monofunctional (meth)acrylate, other polymerizable compound, polymerization initiator, polymerization inhibitor, and surfactant listed in Table 6 so that the content of each component was the content (mass %) listed in Table 6. The mixture was stirred for 20 minutes at 25°C and 5,000 rpm using a mixer (product name "L4R" manufactured by Silverson) to obtain a first ink W1.

[0235]

[0236] [Image Recording] Example 101 Using an inkjet recording device (product name "CylinderJET," manufactured by Tritec Corporation) and an inkjet head (product name "KM1800i," manufactured by Konica Minolta, Inc.), the prepared primer (Pr1) was applied to the body of a PET bottle (product name "PET500 Maru," manufactured by Kokugo Co., Ltd.). Specifically, the second ink P1 was applied to an area measuring 7 cm in the longitudinal direction of the PET bottle and 5 cm in the circumferential direction of the PET bottle at a droplet volume of 10.5 pL (picoliter) and a resolution of 600 x 600 dpi (dots per inch), thereby recording a 100% solid image with a thickness of 6 μm. Furthermore, under the same conditions as for the application of the second ink P1, the first ink W1 was applied to the surface on which the second ink P1 had been recorded, thereby recording a 100% white solid image with a thickness of 6 μm. Furthermore, the first ink K1 was applied onto the surface onto which the first ink W1 had been applied, thereby recording a black solid image with a thickness of 2 μm. The first ink C1 was applied onto the surface onto which the first ink K1 had been applied, thereby recording a cyan solid image with a thickness of 2 μm. The first ink M1 was applied onto the surface onto which the first ink C1 had been applied, thereby recording a magenta solid image with a thickness of 2 μm. The first ink Y1 was applied onto the surface onto which the first ink M1 had been applied, thereby recording a yellow solid image with a thickness of 2 μm. After applying the second ink P1, after applying the first ink W1, after applying the first ink K1, after applying the first ink C1, after applying the first ink M1, and after applying the first ink Y1, an exposure amount of 10 mJ / cm was used using an LED light source attached to the inkjet recording apparatus. ２ ~100 mJ / cm ２ Specifically, after the application of the second ink P1, the ink was irradiated with ultraviolet light at a dose of 10 mJ / cm ２ , and after application of the first ink W1, 20 mJ / cm ２ , and after application of the first ink K1, 20 mJ / cm ２ , and 20 mJ / cm after application of the first ink C1 ２ , and 20 mJ / cm after application of the first ink M1 ２ , and after application of the first ink Y1, 100 mJ / cm ２The exposure was performed using a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm as the LED light source. The PET bottle on which the image was recorded was then placed in the exposure machine. The PET bottle was set sideways. The exposure machine is capable of rotating the PET bottle. The entire image recorded on the PET bottle was exposed using the LED light source while being rotated. The exposure machine was connected to a nitrogen gas generator with a compressor (product name "Maxi-Flow30", manufactured by Inhouse Gas Co.) at a pressure of 0.2 MPa s, and nitrogen was flowed so that the oxygen concentration inside the exposure machine was 1% by volume or less. An exposure dose of 200 mJ / cm was used using the LED light source. ２ The ink was completely cured by irradiation with ultraviolet light at 1000 kJ / min, to obtain a recorded image.

[0237] During the image recording, the gap between the PET bottle surface and the inkjet head was adjusted to 0.5 mm to 1 mm. The ejection voltage was also adjusted to adjust the ejected droplet velocity to 7 m / s to 9 m / s. The PET bottle was previously subjected to corona treatment twice using a Corona Master (product name "PS-10S", manufactured by Shinko Electric Meter Co., Ltd.) at a treatment voltage of 10 kV and a treatment speed of 50 mm / s.

[0238] Example 102 An image recording was obtained in the same manner as in Example 101, except for the following. The second ink P1 was applied, and a 100% solid image with a thickness of 4 μm was recorded. The first ink W1 was applied, and a 100% white solid image with a thickness of 4 μm was recorded. After applying the second ink P1, after applying the first ink W1, and after applying the first ink Y1, an exposure amount of 10 mJ / cm was recorded using an LED light source attached to the inkjet recording apparatus. ２ ~100 mJ / cm ２ Specifically, after the application of the second ink P1, the ink was irradiated with ultraviolet light at a dose of 10 mJ / cm ２ , and after application of the first ink W1, 20 mJ / cm ２ , and after application of the first ink Y1, 100 mJ / cm ２ It was decided.

[0239] Example 103 An image recording was obtained in the same manner as in Example 101, except for the following: An LED light source was used, and the exposure dose was 500 mJ / cm ２ UV light was irradiated.

[0240] Example 104 An image recording material was obtained in the same manner as in Example 101, except for the following: After applying the second ink P1, an exposure amount of 10 mJ / cm was applied using an LED light source attached to the inkjet recording apparatus. ２ UV light was irradiated.

[0241] Example 105 An image recording material was obtained in the same manner as in Example 101, except for the following: After applying the second ink P1 and after applying the first ink W1, an exposure amount of 10 mJ / cm was applied using an LED light source attached to the inkjet recording apparatus. ２ ~100 mJ / cm ２ Specifically, after the application of the second ink P1, the ink was irradiated with ultraviolet light at a dose of 10 mJ / cm ２ , and after application of the first ink W1, 20 mJ / cm ２ It was decided.

[0242] Example 106 An image recording material was obtained in the same manner as in Example 101, except for the following: After applying the second ink P1, after applying the first ink W1, and after applying the first ink K1, an exposure amount of 10 mJ / cm was applied using an LED light source attached to the inkjet recording apparatus. ２ ~100 mJ / cm ２ Specifically, after the application of the second ink P1, the ink was irradiated with ultraviolet light at a dose of 10 mJ / cm ２ , and after application of the first ink W1, 20 mJ / cm ２ , and after application of the first ink K1, 20 mJ / cm ２ It was decided.

[0243] The obtained image-recorded matter was evaluated for water resistance, odor, flexibility, and alkali peelability using the same evaluation methods as in Example 1. The ejection properties of the first inks M1, Y1, K1, and W1 were also evaluated using the same evaluation methods as in Example 1. Table 7 shows the evaluation results.

[0244]

[0245] As shown in Table 7, even when two or more first inks were used, the resulting image recordings had low odor and were excellent in water resistance, flexibility, and alkali peelability. Furthermore, the ejection properties of the first inks M1, Y1, K1, and W1 were all good.

[0246] The disclosure of Japanese Patent Application No. 2022-194438, filed on December 5, 2022, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. The composition comprises a bifunctional (meth)acrylate having a linear or branched alkylene group having 6 to 8 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant, the total content of the bifunctional (meth)acrylate and the monofunctional (meth)acrylate is 80 mass % or more based on the total amount of polymerizable compounds contained in the actinic energy ray-curable inkjet ink.

2. 2. The actinic ray-curable inkjet ink according to claim 1, wherein a mass ratio of the content of the bifunctional (meth)acrylate to the content of the monofunctional (meth)acrylate is 0.3 to 3.

5.

3. 2. The actinic energy ray-curable inkjet ink according to claim 1, further comprising phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide as polymerization initiators, the total content of the polymerization initiators being 5 mass % or more with respect to the total amount of the actinic energy ray-curable inkjet ink.

4. 2. The actinic ray-curable inkjet ink according to claim 1, wherein the monofunctional (meth)acrylate has a molecular weight of 130 to 150.

5. a first ink containing a bifunctional (meth)acrylate having a linear or branched alkylene group having 6 to 8 carbon atoms, a monofunctional (meth)acrylate having a hydroxyl group, and a colorant; and a second ink, the first ink contains the bifunctional (meth)acrylate and the monofunctional (meth)acrylate in a total amount of 80 mass % or more of the polymerizable compounds contained in the first ink; The second ink is an actinic ray-curable ink set, wherein when a cured product of the second ink is immersed in water of pH 7 and an alkaline aqueous solution of pH 10 for 5 minutes each, the pencil hardness of the cured product after immersion in the alkaline aqueous solution of pH 10 is lower than the pencil hardness of the cured product after immersion in water of pH 7.

6. 6. The actinic ray-curable ink set according to claim 5, wherein the second ink contains at least one acid group-containing compound selected from the group consisting of polymerizable monomers having an acid group and polymers having an acid group, and the total content of the acid group-containing compound is 8 mass % or more with respect to the total amount of the second ink.

7. 6. The actinic ray-curable ink set according to claim 5, wherein the second ink comprises at least one acid group-containing compound selected from the group consisting of polymerizable monomers having an acid group and polymers having an acid group, a bifunctional (meth)acrylate having a linear or branched alkylene group having 5 to 9 carbon atoms, and a monofunctional (meth)acrylate having a hydroxyl group, and the total content of the polymerizable monomers having an acid group, the bifunctional (meth)acrylate, and the monofunctional (meth)acrylate is 70 mass % or more relative to the total amount of the polymerizable compounds contained in the second ink.

8. 6. The actinic ray-curable ink set according to claim 5, wherein the first ink has a mass ratio of the content of the bifunctional (meth)acrylate to the content of the monofunctional (meth)acrylate of 0.3 to 3.

5.

9. 6. The actinic ray-curable ink set according to claim 5, wherein the first ink further contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide as polymerization initiators, and the total content of the polymerization initiators is 5 mass % or more with respect to the total amount of the first ink.

10. 6. The actinic ray-curable ink set according to claim 5, wherein the first ink contains a monofunctional (meth)acrylate having a molecular weight of 130 to 150.

11. applying the actinic ray-curable inkjet ink according to any one of claims 1 to 4 onto a substrate by an inkjet recording method; and irradiating the applied actinic energy ray-curable inkjet ink with actinic energy rays.

12. The active energy ray-curable ink set according to any one of claims 5 to 10 is used, applying the second ink onto a substrate by an inkjet recording method; irradiating the applied second ink with actinic energy rays; applying the first ink onto the substrate to which the second ink has been applied by an inkjet recording method; irradiating the applied first ink with actinic energy rays; An image recording method comprising:

13. An inkjet head and an LED light source, An inkjet recording apparatus used in the image recording method according to claim 11.