Electron beam curable ink and image recording method

Abstract

Provided are: an electron beam-curable ink containing a polymerizable monomer A having a ClogP value of 2.3 or less, and a surfactant, wherein the content of surfactant is 0.3 mass% or more with respect to the total amount of the electron beam-curable ink and the content of a polymerization initiator is less than 1 mass% with respect to the total amount of the electron beam-curable ink; and an image recording method.

Description

[Technical Field]

[0001] The present disclosure relates to an electron beam curable ink and an image recording method. [Background technology]

[0002]

[0003] As one type of image recording method, there is known an image recording method in which ink is applied to a recording medium and the applied ink is irradiated with active energy rays such as ultraviolet rays to cure the ink, thereby obtaining an image. In recent years, it has been considered to replace the active energy rays used for irradiation from ultraviolet rays with electron beams.

[0003] For example, Japanese Patent Application Laid-Open No. 2020-33443 describes that an electron beam curable resin that is cured by electron beam irradiation and is characterized by being composed of a photopolymerizable monomer having a molecular weight of 212 or more, or being composed of the photopolymerizable monomer as the main component mixed with other photopolymerizable materials, is used in ink.

[0004] Furthermore, Japanese Patent Application Laid-Open No. 2016-180072 describes an electron beam-curable inkjet ink containing a colorant and a polymerizable compound, wherein the polymerizable compound contains a monofunctional monomer and / or a bifunctional monomer, the total content of the monofunctional monomer and the bifunctional monomer is 95 to 100 wt % of the total amount of the polymerizable compound, and the viscosity of the ink is 100 mPa·s or less.

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2018-86726 describes a method for forming a cured film, which includes a composition application step of applying a curable composition containing a polymerizable compound onto a recording medium, and an irradiation step of irradiating the curable composition with two or more types of active energy rays, wherein at least an electron beam having an acceleration voltage of 130 kV or less is used as the active energy ray in the irradiation step, and the electron beam is irradiated in the irradiation step so as to achieve an absorbed dose of 20 to 75 kGy. Summary of the Invention [Problem to be solved by the invention]

[0006] In ink images formed by applying ink to a substrate and curing it, it is sometimes necessary to prevent components contained in the ink from eluting from the ink image (i.e., migration).

[0007] According to one embodiment of the present invention, there are provided an electron beam curable ink and an image recording method that can suppress migration. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. <1> An electron beam curable ink comprising a polymerizable monomer A having a ClogP value of 2.3 or less and a surfactant, wherein the content of the surfactant is 0.3 mass% or more relative to the total amount of the electron beam curable ink, and the content of the polymerization initiator is less than 1 mass% relative to the total amount of the electron beam curable ink. <2> The content of the polymerizable monomer A is 20 mass% or more based on the total amount of the electron beam curable ink. <1> The electron beam curable ink according to claim 1. <3> the mass ratio of the content of the polymerizable monomer A to the content of the surfactant is 4 to 100; <1> or <2> The electron beam curable ink according to claim 1. <4> further comprising a polymerizable monomer B having a ClogP value of more than 2.3 and a viscosity of 20 mPa s or less; <1> ~ <3> 10. The electron beam curable ink according to any one of the above items. <5> the mass ratio of the content of the polymerizable monomer A to the content of the polymerizable monomer B is 0.25 to 2.3; <4> The electron beam curable ink according to claim 1. <6> Polymerizable monomer A has a ClogP value of 1.5 or less. <1> ~ <5> 10. The electron beam curable ink according to any one of the above items. <7> The polymerizable monomer A includes a polymerizable monomer containing two or more ethylene oxide chains. <1> ~ <6> 10. The electron beam curable ink according to any one of the above items. <8> The polymerizable monomer A includes a polyfunctional (meth)acrylate containing two or more ethylene oxide chains. <1> ~ <7> 10. The electron beam curable ink according to any one of the above items. <9> The content of polymerizable monomers with a viscosity of 60 mPa·s or more at 25°C is 20 mass% or less of the total amount of the electron beam curable ink. <1> ~ <8> 10. The electron beam curable ink according to any one of the above items. <10> The surfactant is a silicone surfactant. <1> ~ <9> 10. The electron beam curable ink according to any one of the above items. <11> The content of the surfactant is 1.0% by mass to 10% by mass based on the total amount of the electron beam curable ink. <1> ~ <10> 10. The electron beam curable ink according to any one of the above items. <12> The weighted average ClogP value of all polymerizable monomers contained in the ink is 0.9 to 2.5. <1> ~ <11> 10. The electron beam curable ink according to any one of the above items. <13> On the substrate, <1> ~ <12> 1. An image recording method comprising the steps of: applying the electron beam curable ink according to any one of the above items to form an ink film; and irradiating the ink film with an electron beam. <14> In the step of obtaining an ink film, n types of the electron beam curable inks are applied in order, where n is an integer of 2 or more, and the content of surfactant in the mth electron beam curable ink applied is made higher than the content of surfactant in the m-1th electron beam curable ink applied, where m is an integer of 2 to n. <13> The image recording method according to claim 1. [Effects of the Invention]

[0009] According to one embodiment of the present invention, there are provided an electron beam curable ink and an image recording method that can suppress migration. DETAILED DESCRIPTION OF THE INVENTION

[0010] The electron beam curable ink and image recording method according to the present disclosure will be described in detail below.

[0011] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced by the upper or lower limit value of another numerical range described in stages, or may be replaced by a value shown in an example. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In the present disclosure, combinations of preferred aspects are more preferred aspects. In the present disclosure, "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate, "(meth)acryloyl group" is a concept that encompasses both acryloyl group and methacryloyl group, and "(meth)acrylic acid" is a concept that encompasses both acrylic acid and methacrylic acid.

[0012] In the present disclosure, the term "image" generally refers to a film formed using ink, and the term "image recording" refers to the formation of an image (i.e., a film). Additionally, the concept of "image" in this disclosure also includes solid images.

[0013] [Electron beam curable ink] The electron beam curable ink (hereinafter also simply referred to as "ink") of the present disclosure contains a polymerizable monomer A having a ClogP value of 2.3 or less and a surfactant, the content of the surfactant being 0.3 mass% or more relative to the total amount of the electron beam curable ink, and the content of the polymerization initiator being less than 1 mass% relative to the total amount of the electron beam curable ink.

[0014] In the present disclosure, electron beam curable ink refers to ink that is cured by irradiation with an electron beam. The ink of the present disclosure is an electron beam curable ink, and is distinguished from ultraviolet irradiation type ink that is cured by irradiation with ultraviolet light. The ink of the present disclosure can be cured by irradiating with an electron beam under conditions of, for example, an acceleration voltage of 50 kV to 200 kV, a dose of 10 kGy to 100 kGy, and a processing speed of 1 m / min to 200 m / min.

[0015] The ink of the present disclosure can suppress migration. The reason for this effect is presumed to be as follows.

[0016] Generally, image recording using an ink containing a polymerizable monomer is performed by applying the ink to a substrate and irradiating the ink applied to the substrate (hereinafter also referred to as "ink film") with active energy rays. In this image recording, when the ink film is irradiated with active energy rays, the polymerizable monomer in the ink film polymerizes and the ink film hardens. As a result, an ink image is obtained, which is a cured ink film. The ink of the present disclosure is an electron beam curable ink, and electron beams are used as the active energy rays.

[0017] The ink of the present disclosure contains a polymerizable monomer A with a ClogP value of 2.3 or less. It is believed that when the ink contains a polymerizable monomer A with a ClogP value of 2.3 or less, oxygen becomes less soluble in the ink, i.e., the amount of dissolved oxygen in the ink is reduced. It is believed that the reduced amount of dissolved oxygen in the ink promotes the polymerization reaction, resulting in excellent curability. The ink of the present disclosure also contains a surfactant, with the surfactant content being 0.3% by mass or more. Therefore, it is believed that the ink film formed by applying the ink to a substrate spreads easily, improving electron beam transparency and, as a result, excellent curability. It is believed that the use of the ink of the present disclosure improves the curability of the ink film, thereby suppressing elution of components contained in the ink. In the present disclosure, elution of components contained in the ink is referred to as "migration."

[0018] On the one hand, the ink disclosed in Patent Document 1 does not contain a surfactant. Further, the content of the surfactant in the ink disclosed in Patent Document 2 is 0.2% by mass, and the content of the surfactant in the ink disclosed in Patent Document 3 is 0.1% by mass. Therefore, when the inks disclosed in Patent Documents 1 to 3 are applied onto a substrate, it is considered that the ink film does not spread, the electron beam permeability is insufficient, and migration is not suppressed.

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

[0020] <Polymerizable monomer A having a ClogP value of 2.3 or less> The ink of the present disclosure contains at least one kind of polymerizable monomer A having a ClogP value of 2.3 or less. Hereinafter, the polymerizable monomer having a ClogP value of 2.3 or less will be simply referred to as "polymerizable monomer A". Further, a polymerizable monomer whose ClogP value is not particularly limited will be simply referred to as "polymerizable monomer".

[0021] In the present disclosure, the ClogP value is calculated using the fragment method. As the calculation software using the fragment method, ChemDraw Professioal 16 is used.

[0022] A polymerizable monomer refers to a monomer having at least one polymerizable group in one molecule. From the viewpoint of curability, the polymerizable group in the polymerizable monomer A is preferably a radical polymerizable group, and more preferably an ethylenically unsaturated group.

[0023] In the present disclosure, a monomer refers to a compound having a molecular weight of 1000 or less. In the present disclosure, the molecular weight of a compound having a molecular weight of 1000 or less can be calculated from the types and numbers of elements constituting the compound.

[0024] The molecular weight of the polymerizable monomer A is preferably 600 or less, and more preferably 300 or less. The lower limit value of the molecular weight of the polymerizable monomer A is, for example, 100.

[0025] The polymerizable monomer A may be any of a monofunctional polymerizable monomer (hereinafter referred to as a "monofunctional monomer"), a bifunctional polymerizable monomer (hereinafter referred to as a "bifunctional monomer"), and a trifunctional or higher functional polymerizable monomer (hereinafter referred to as a "trifunctional or higher functional monomer"). The polymerizable monomer A may also be a combination containing two or more of the monofunctional monomer, the bifunctional monomer, and the trifunctional or higher functional monomer.

[0026] Examples of polymerizable monomers (specifically, monofunctional monomers, bifunctional monomers, and trifunctional or higher monomers) are given below. Polymerizable monomer A may be selected, for example, from the polymerizable monomers exemplified below, so that it has a ClogP value of 2.3 or less. Polymerizable monomer B, which will be described later, may be selected, for example, from the polymerizable monomers exemplified below, so that it has a ClogP value of more than 2.3 and a viscosity of 20 mPa·s or less. Polymerizable monomers other than polymerizable monomer A and polymerizable monomer B, which will be described later, may be selected, for example, from the polymerizable monomers exemplified below, so that it has a ClogP value of more than 2.3 and a viscosity of more than 20 mPa·s.

[0027] -Monofunctional Monomer- Examples of the monofunctional monomer include monofunctional (meth)acrylates, monofunctional (meth)acrylamides, monofunctional aromatic vinyl compounds, monofunctional vinyl ethers, and monofunctional N-vinyl compounds.

[0028] 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, and cyclohexyl (meth)acrylate. , 4-n-butylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, bornyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (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 acrylate, 3-methoxybutyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, 2-(2-butoxyethoxy)ethyl (meth)acrylate, ethyl carbitol (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-phenoxy Dimethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, glycidyl (meth)acrylate, glycidyloxybutyl (meth)acrylate, glycidyloxyethyl (meth)acrylate, glycidyloxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate,4-Hydroxybutyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, phenyl glycidyl ether (meth)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, polypropylene oxide monoalkyl ether (meth)acrylate, 2-methacryloyloxyethyl succinate, 2-methacryloyloxyhexahydrophthalic acid, 2-methacryloyloxy Examples of the ethylene glycol (meth)acrylate include diethyl-2-hydroxypropyl phthalate, butoxydiethylene glycol (meth)acrylate, trifluoroethyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, ethylene oxide-modified (hereinafter referred to as EO-modified) phenol (meth)acrylate, EO-modified cresol (meth)acrylate, EO-modified nonylphenol (meth)acrylate, propylene oxide-modified (hereinafter referred to as 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, and phenoxyethylene glycol (meth)acrylate.

[0029] Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, Nn-butyl(meth)acrylamide, Nt-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.

[0030] 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.

[0031] 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.

[0032] Monofunctional N-vinyl compounds include N-vinylcaprolactam, N-vinylpyrrolidone, N-vinyloxazolidinone, and N-vinyl-5-methyloxazolidinone.

[0033] -Difunctional Monomer- Examples of the bifunctional monomer include bifunctional (meth)acrylate, bifunctional vinyl ether, and bifunctional monomer containing a vinyl ether group and a (meth)acryloyl group.

[0034] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, hexanediol di(meth)acrylate, and heptanediol 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, octanediol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, dodecanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate.

[0035] Examples of bifunctional vinyl ethers include 1,4-butanediol divinyl ether (ClogP value: 1.32), ethylene glycol divinyl ether (ClogP value: 0.66), diethylene glycol divinyl ether (ClogP value: 0.47), triethylene glycol divinyl ether (ClogP value: 0.29), polyethylene glycol divinyl ether (ClogP value: 0.29 or less), propylene glycol divinyl ether (ClogP value: 0.97), and butylene glycol divinyl ether. (ClogP value: 1.32), hexanediol divinyl ether (ClogP value: 2.38), 1,4-cyclohexanedimethanol divinyl ether (ClogP value: 1.66), bisphenol A alkylene oxide divinyl ether (for example, bisphenol A ethylene oxide divinyl ether, ClogP value: 5.35), and bisphenol F alkylene oxide divinyl ether (for example, bisphenol F ethylene oxide divinyl ether, ClogP value: 4.55).

[0036] An example of a bifunctional monomer containing a vinyl ether group and a (meth)acryloyl group is 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

[0037] -Trifunctional or higher monomers- Examples of tri- or higher functional monomers include tri- or higher functional (meth)acrylates and tri- or higher functional vinyl ethers.

[0038] Examples of tri- or higher functional (meth)acrylates include trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, PO-modified trimethylolpropane 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.

[0039] Examples of tri- or higher functional vinyl ethers include trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, EO-modified trimethylolpropane trivinyl ether, PO-modified trimethylolpropane trivinyl ether, EO-modified ditrimethylolpropane tetravinyl ether, PO-modified ditrimethylolpropane tetravinyl ether, EO-modified pentaerythritol tetravinyl ether, PO-modified pentaerythritol tetravinyl ether, EO-modified dipentaerythritol hexavinyl ether, and PO-modified dipentaerythritol hexavinyl ether.

[0040] Specific examples of the polymerizable monomer A include the following compounds: Tables 1 and 2 show compounds having a ClogP value of 2.3 or less, along with the structural formula, viscosity, and molecular weight of the compounds.

[0041] In this disclosure, all viscosity values are measured at 25°C.

[0042] [Table 1]

[0043] [Table 2]

[0044] The content of polymerizable monomer A in the ink is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more, relative to the total amount of ink. In addition, taking into account the balance with other components, the content of polymerizable monomer A is preferably 98% by mass or less, more preferably 96% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less, relative to the total amount of ink.

[0045] Polymerizable monomer A is hydrophilic and is believed to have the effect of reducing the amount of dissolved oxygen in the ink. When the content of polymerizable monomer A is 5% by mass or more, it is believed that the effect of reducing the amount of dissolved oxygen in the ink is more pronounced. Therefore, when the content of polymerizable monomer A is 5% by mass or more, the curability is superior and migration is further suppressed. Furthermore, when the content of polymerizable monomer A is 5% by mass or more, the generation of white smoke upon irradiation with an electron beam is further suppressed.

[0046] The ClogP value of polymerizable monomer A is 2.3 or less. When the ClogP value of the polymerizable monomer is 2.3 or less, oxygen is less likely to dissolve in the ink, and the amount of dissolved oxygen in the ink is reduced, resulting in excellent curability and suppressed migration. Furthermore, when the ClogP value of the polymerizable monomer is 2.3 or less, the generation of white smoke when irradiated with an electron beam is suppressed.

[0047] From the same viewpoint as above, the ClogP value of the polymerizable monomer A is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.3 or less, and preferably 0.3 or more, and more preferably 1.0 or more.

[0048] Furthermore, when the ClogP value of the polymerizable monomer A is 0.3 or more, the surface tension of the polymerizable monomer itself does not become too high, and interference between fired droplets is suppressed, which is thought to result in good image quality.

[0049] The polymerizable monomer A preferably contains a polymerizable monomer having an ether structure in the molecule. The ether structure may be a chain ether structure or a cyclic ether structure, but is preferably a chain ether structure.

[0050] Examples of polymerizable monomers having a chain ether structure in the molecule include polymerizable monomers containing an ethylene oxide chain and polymerizable monomers containing a propylene oxide chain. Among these, polymerizable monomer A preferably contains a polymerizable monomer containing an ethylene oxide chain, and more preferably contains a polymerizable monomer containing two or more ethylene oxide chains.

[0051] It is believed that when polymerizable monomer A contains an ethylene oxide chain, radicals are generated, accelerating the polymerization reaction. Therefore, when polymerizable monomer A contains a polymerizable monomer containing two or more ethylene oxide chains, curability is improved and migration is further suppressed. Furthermore, when polymerizable monomer A contains a polymerizable monomer containing two or more ethylene oxide chains, the generation of white smoke upon electron beam irradiation is suppressed.

[0052] In a polymerizable monomer containing an ethylene oxide chain, from the viewpoint of further suppressing migration and further suppressing the generation of white smoke upon irradiation with an electron beam, the number of ethylene oxide chains (i.e., the number of moles of ethylene oxide chains added) is preferably 2 or more, more preferably 2 to 20, even more preferably 3 to 10, and particularly preferably 3 to 6.

[0053] Furthermore, the polymerizable monomer containing two or more ethylene oxide chains is preferably a polyfunctional (meth)acrylate containing two or more ethylene oxide chains. That is, the polymerizable monomer A preferably contains a polyfunctional (meth)acrylate containing two or more ethylene oxide chains. Since the (meth)acryloyl group has high reactivity, it is thought that the polymerization reaction is further accelerated. Therefore, when the polymerizable monomer A contains a polyfunctional (meth)acrylate containing two or more ethylene oxide chains, the curability is more excellent and migration is further suppressed.

[0054] In a polyfunctional (meth)acrylate containing two or more ethylene oxide chains, the number of (meth)acryloyl groups is preferably 2 to 6, and more preferably 2. That is, it is particularly preferable that the polymerizable monomer A contains two or more ethylene oxide chains (preferably 2 to 20, more preferably 3 to 10, and even more preferably 3 to 6) and a polyfunctional (meth)acrylate containing 2 to 6 (preferably 2) (meth)acryloyl groups.

[0055] Among these, the polymerizable monomer A is preferably triethylene glycol divinyl ether, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(2-ethoxyethoxy)-ethyl (meth)acrylate, tetraethylene glycol diacrylate, or triethylene glycol diacrylate, more preferably 2-(2-vinyloxyethoxy)ethyl acrylate, tetraethylene glycol diacrylate, or triethylene glycol diacrylate, and even more preferably tetraethylene glycol diacrylate or triethylene glycol diacrylate.

[0056] <Polymerizable monomer B having a ClogP value exceeding 2.3 and a viscosity of 20 mPa·s or less> The ink of the present disclosure may contain a polymerizable monomer other than the polymerizable monomer A. The polymerizable monomer other than the polymerizable monomer A is a polymerizable monomer having a ClogP value exceeding 2.3.

[0057] The ink of the present disclosure preferably further contains a polymerizable monomer B having a ClogP value exceeding 2.3 and a viscosity of 20 mPa·s or less. Hereinafter, the polymerizable monomer having a ClogP value exceeding 2.3 and a viscosity of 20 mPa·s or less is also simply referred to as "polymerizable monomer B".

[0058] The molecular weight of the polymerizable monomer B is preferably 600 or less, and more preferably 300 or less. The lower limit value of the molecular weight of the polymerizable monomer B is, for example, 100.

[0059] In addition, specific examples of the polymerizable monomer having a ClogP value exceeding 2.3 and a viscosity of 20 mPa·s or less include the following compounds. Table 3 shows the structural formula, viscosity, and molecular weight of the compound together with the compound having a ClogP value exceeding 2.3 and a viscosity of 20 mPa·s or less.

[0060]

Table 3

[0061] When the polymerizable monomer B is contained in the ink, the ink film formed by applying the ink on the substrate is likely to spread, so the permeability of the electron beam is improved, and as a result, the curability is excellent. Therefore, when the polymerizable monomer B is contained in the ink together with the polymerizable monomer A, migration is more suppressed. In addition, when the polymerizable monomer B is contained in the ink, the ink film formed by applying the ink on the substrate is likely to spread, so the roughness of the obtained ink image is suppressed.

[0062] The ClogP value of polymerizable monomer B is not particularly limited as long as it is greater than 2.3. From the viewpoint of further suppressing the generation of white smoke and migration, the ClogP value of polymerizable monomer B is preferably 10 or less, and more preferably 5 or less.

[0063] From the viewpoint of making the ink film spread more easily, the viscosity of polymerizable monomer B is preferably 20 mPa·s or less, and more preferably 10 mPa·s or less. There are no particular restrictions on the lower limit of the viscosity of polymerizable monomer B, and it is, for example, 1 mPa·s.

[0064] The viscosity of polymerizable monomer B is measured at 25° C. using a digital rotational viscometer, for example, a TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.

[0065] The content of polymerizable monomer B in the ink is preferably 20% by mass to 80% by mass, and more preferably 25% by mass to 70% by mass, based on the total amount of the ink.

[0066] <Other polymerizable monomers> The ink of the present disclosure may contain a polymerizable monomer other than the polymerizable monomer A and the polymerizable monomer B. The polymerizable monomer other than the polymerizable monomer A and the polymerizable monomer B is a polymerizable monomer having a ClogP value of more than 2.3 and a viscosity of more than 20 mPa s.

[0067] Specific examples of polymerizable monomers having a ClogP value greater than 2.3 and a viscosity greater than 20 mPa·s include the following compounds: Table 4 lists compounds having a ClogP value greater than 2.3 and a viscosity greater than 20 mPa·s, along with their structural formulas, viscosities, and molecular weights. The structural formula of caprolactone-modified hydroxypivalic acid neopentyl glycol diacrylate is omitted.

[0068] [Table 4]

[0069] <Polymerizable monomers overall> In the ink of the present disclosure, the weighted average of the ClogP values of all polymerizable monomers contained in the ink is preferably 0.9 to 2.5, and more preferably 1.5 to 2.45. When the weighted average is 0.9 or more, the roughness of the resulting ink image is suppressed. Furthermore, when the weighted average is 2.5 or less, migration is suppressed and the generation of white smoke upon irradiation with an electron beam is suppressed.

[0070] In the present disclosure, the weighted average value of the ClogP values is X calculated by the following formula 1.

[0071] X=ΣS i W i / ΣW i … (Equation 1)

[0072] S i W means the ClogP value of the i-th type (i is an integer of 1 or more) of polymerizable monomer contained in the ink. i means the content (mass %) of the i-th type of polymerizable monomer contained in the ink.

[0073] Furthermore, in the ink of the present disclosure, the content of polymerizable monomers with a viscosity of 60 mPa·s or greater is preferably 20% by mass or less, and more preferably 10% by mass or less, relative to the total amount of the ink. There is no particular lower limit for the content of polymerizable monomers with a viscosity of 60 mPa·s or greater, and it is, for example, 0% by mass. In other words, the ink of the present disclosure does not need to contain, and preferably does not contain, polymerizable monomers with a viscosity of 60 mPa·s or greater.

[0074] When the content of polymerizable monomers with a viscosity of 60 mPa·s or higher is 20% by mass or less, the ink film formed by applying the ink to a substrate spreads easily, improving electron beam permeability and resulting in excellent curing properties. This further suppresses migration. Furthermore, because the ink film formed by applying the ink to a substrate spreads easily, the resulting ink image is less rough.

[0075] The viscosity of the polymerizable monomer is measured at 25° C. using a digital rotational viscometer, for example, a TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.

[0076] <Surfactant> The inks of the present disclosure contain at least one surfactant.

[0077] The surfactant content is 0.3% by mass or more relative to the total amount of ink. When the surfactant content is 0.3% by mass or more, the ink film formed by applying the ink to a substrate spreads easily, improving the electron beam transmittance and, as a result, suppressing migration. In addition, the ink film formed by applying the ink to a substrate spreads easily, suppressing roughness in the resulting ink image.

[0078] From the viewpoint of further suppressing migration and improving image quality, the content of the surfactant is preferably 1.0% by mass to 10% by mass, and more preferably 1.2% by mass to 4.0% by mass, relative to the total amount of ink.

[0079] The type of surfactant is not particularly limited, and may be any of anionic surfactants, cationic surfactants, and nonionic surfactants. Furthermore, the surfactant may be any of silicone-based surfactants, acrylic surfactants, and fluorine-based surfactants. Among these, from the viewpoint of further suppressing migration and improving image quality, the surfactant is preferably a silicone-based surfactant or an acrylic surfactant, and more preferably a silicone-based surfactant.

[0080] An acrylic surfactant is a surfactant containing a structure derived from an acrylic monomer. Examples of acrylic surfactants include BYK361N, BYK350, BYK356, and BYK-UV3535 (all manufactured by BYK).

[0081] Silicone surfactants are surfactants containing a siloxane structure. Examples of silicone surfactants include BYK-UV3500, 3505, 3510, 3530, 3570, 3575, 3576, 3760, 378, 375, 306, 333, 377, 330, 307, 342, 302, 300, 331, 325, 320, 315N, 326, and 322 (all manufactured by BYK); TEGORad 2100, 2200, 2250, 2300, 2500, 2600, 2700, 2010; TEGOGlide 100, 110, 130, 406, 410, 411, 415, 420, 432, 435, 440, 450, 482, A115, B1484, ZG400; and TEGOFlow 300, 370, 425, ATF2, ZFS 460 (all manufactured by Evonik).

[0082] The fluorosurfactant is a surfactant containing a perfluoroalkyl group. Examples of the fluorosurfactant include Megafac F-114, F-251, F-253, F-281, F-410, F-477, F-510, F-551, F-552, F-553, F-554, F-555, F-556, F-557, F-558, F-559, F-560, F-561, F-562, F-563, Examples include F-565, F-568, F-569, F-570, F-572, F-574, F-575, F-576, R-40, R-40-LM, R-41, R-94, RS-56, RS-72-K, RS-75, RS-76-E, RS-76-NS, RS-78, RS-90, and DS-21 (all manufactured by DIC Corporation).

[0083] The surfactant may or may not have a polymerizable group. From the viewpoint of further suppressing migration, the surfactant preferably has a polymerizable group, and more preferably is a silicone surfactant having a polymerizable group.

[0084] An example of the polymerizable group contained in the surfactant is a (meth)acryloyl group.

[0085] In the present disclosure, when a surfactant has a polymerizable group, the molecular weight of the surfactant is more than 1000, and the surfactant is distinguished from the above-mentioned polymerizable monomer.

[0086] <Colorant> The ink of the present disclosure may contain at least one colorant.

[0087] The type of coloring material is not particularly limited, and may be either a pigment or a dye. From the viewpoint of light resistance, the coloring material is preferably a pigment.

[0088] When a pigment is used as the colorant, the pigment can be contained in the ink as a pigment dispersion. The pigment dispersion is a liquid obtained by dispersing the pigment in a liquid medium using a dispersant, and contains at least a pigment, a dispersant, and a liquid medium. Note that when a self-dispersing pigment is used as the pigment, the ink does not need to contain a dispersant.

[0089] The liquid medium may be, for example, an organic solvent, or the above-mentioned polymerizable monomer contained in the ink.

[0090] The pigment may be either an organic pigment or an inorganic pigment that is commonly available on the market, or may be an invisible pigment that has infrared absorbing properties.

[0091] When the ink of the present disclosure contains a colorant, the content of the colorant is preferably 1% by mass to 20% by mass, and more preferably 2% by mass to 10% by mass, relative to the total amount of the ink.

[0092] When the ink of the present disclosure is a clear ink for recording a clear image, the ink of the present disclosure may be substantially free of coloring materials. In this case, the content of coloring materials may be less than 1% by mass, less than 0.1% by mass, or even 0% by mass, based on the total amount of ink. Note that a clear image refers to an image having a transmittance of 80% or more at a wavelength of 400 nm to 700 nm.

[0093] <Dispersant> When the ink of the present disclosure contains a pigment as a coloring material, it preferably contains at least one dispersant.

[0094] As the dispersant, any 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.

[0095] 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.

[0096] Further, examples of dispersants 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 dissociable group-containing monomers include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. 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.

[0097] 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, DISPERBYK-182 (manufactured by BYK Chemie); and SOLSPERSE3000, SOLSPERSE5000, SOLSPERSE9000, SOLSPERSE12000, SOLSPERSE13240, SOLSPERSE13940, SOLSPERSE17000, SOLSPERSE22000, SOLSPERSE24000, SOLSPERSE26000, SOLSPERSE28000, SOLSPERSE32000, SOLSPERSE36000, SOLSPERSE39000, SOLSPERSE41000, SOLSPERSE71000 (manufactured by Lubrizol) Examples include:

[0098] 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.

[0099] From the viewpoint of dispersion stability, the ratio of the dispersant content to the pigment content in the ink (i.e., dispersant content / pigment content) is preferably 0.05 to 1.0 by mass, and more preferably 0.1 to 0.8.

[0100] <Polymerization initiator> The ink of the present disclosure may contain a polymerization initiator. However, if a polymerization initiator is contained, the content of the polymerization initiator is preferably less than 1% by mass, more preferably less than 0.5% by mass, and even more preferably less than 0.1% by mass, relative to the total amount of the ink. From the viewpoint of further suppressing migration, it is preferable that the ink of the present disclosure does not contain a polymerization initiator. Of the components contained in the ink, the components that cause migration are thought to be the polymerizable monomer and the polymerization initiator. Therefore, when the content of the polymerization initiator is less than 1% by mass, migration can be suppressed.

[0101] Examples of the 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.

[0102] Among these, the polymerization initiator is preferably an acylphosphine compound.

[0103] The acylphosphine oxide compound includes a monoacylphosphine oxide compound and a bisacylphosphine oxide compound.

[0104] 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, pt-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, pivaloylphenylphosphinic acid methyl ester, and pivaloylphenylphosphinic acid isopropyl ester.

[0105] 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). 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, Bis(2,4,6-trimethylbenzoyl)phenylphosphine 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.

[0106] Among these, the acylphosphine oxide compound is preferably bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (product name "Omnirad TPO H", manufactured by IGM Resins BV), or (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (product name "Omnirad TPO-L", manufactured by IGM Resins BV).

[0107] <Other ingredients> The ink of the present disclosure may contain other components in addition to the above components, as needed, such as a sensitizer, a co-sensitizer, a polymerization inhibitor, an ultraviolet absorber, an antioxidant, an anti-fading agent, a conductive salt, an organic solvent, and a basic compound.

[0108] <Physical properties> From the viewpoint of improving ejection properties when applied using an inkjet recording method, the pH of the ink is preferably 7 to 10, and more preferably 7.5 to 9.5. The pH is measured at 25°C using a pH meter, for example, a pH meter manufactured by Toa DKK Corporation (model number "HM-31")

[0109] The viscosity of the ink is preferably 0.5 mPa·s to 30 mPa·s, more preferably 2 mPa·s to 20 mPa·s, preferably 2 mPa·s to 15 mPa·s, and even more preferably 3 mPa·s to 10 mPa·s. The viscosity is measured at 25°C using a viscometer, for example, a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd.

[0110] 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. The surface tension is measured at 25°C using a surface tensiometer, for example, an automatic surface tensiometer (product name "CBVP-Z") manufactured by Kyowa Interface Science Co., Ltd., by the plate method.

[0111] <Relationship between each component> -Polymerizable monomer A / surfactant- The mass ratio of the content of polymerizable monomer A to the content of surfactant (i.e., polymerizable monomer A / surfactant) is preferably from 2 to 150, more preferably from 4 to 100, even more preferably from 5 to 50, and particularly preferably from 10 to 35. When the mass ratio is from 2 to 150, migration is further suppressed, and the resulting ink image is less rough.

[0112] -Polymerizable Monomer A / Polymerizable Monomer B When the ink contains polymerizable monomer B, the mass ratio of the content of polymerizable monomer A to the content of polymerizable monomer B (polymerizable monomer A / polymerizable monomer B) is preferably 0.1 to 4, more preferably 0.25 to 2.3, and even more preferably 0.33 to 2.3. When the mass ratio is 0.1 or more, the generation of white smoke upon irradiation with an electron beam is further suppressed, and migration is further suppressed. When the mass ratio is 4 or less, migration is further suppressed, and roughness of the resulting ink image is further suppressed.

[0113] [Image recording method] The image recording method of the present disclosure preferably includes a step of applying the ink to a substrate to obtain an ink film (hereinafter referred to as the ink application step), and a step of irradiating the ink film with an electron beam (hereinafter referred to as the electron beam irradiation step).

[0114] The image recording method of the present disclosure may include other steps as necessary.

[0115] As described above, the image recording method of the present disclosure uses the ink of the present disclosure, and therefore, the image recording method of the present disclosure achieves the same effects as the ink of the present disclosure.

[0116] <Ink application process> In the ink application step, the ink is applied onto a substrate to obtain an ink film. The type of substrate is not particularly limited, and examples thereof include paper, paper laminated with plastic (e.g., polyethylene, polypropylene, polystyrene, etc.), metal plate (e.g., plate of a metal such as aluminum, zinc, or copper), plastic film (e.g., films of polyvinyl chloride (PVC) resin, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), polypropylene (PP), polycarbonate (PC), polyvinyl acetal, acrylic resin, etc.), paper laminated with or vapor-deposited with the above-mentioned metals, and plastic film laminated with or vapor-deposited with the above-mentioned metals.

[0117] The method for applying the ink is not particularly limited, and examples thereof include known methods such as a coating method, a dipping method, an inkjet recording method, etc. The coating method is carried out using, for example, a bar coater, an extrusion coater, an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, a transfer roll coater, a gravure coater, a kiss roll coater, a cast coater, a spray coater, a curtain coater, or an extrusion coater.

[0118] 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.

[0119] Inkjet heads used in inkjet recording methods include a shuttle method, which uses a short serial head and performs recording by scanning the head in the width direction of the substrate, and a line method, which uses a line head in which recording elements are arranged to correspond to the entire area of one side of the substrate.

[0120] 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.

[0121] The droplet volume of ink 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.

[0122] <Electron beam irradiation process> In the electron beam irradiation step, the ink film obtained in the ink application step is irradiated with an electron beam.

[0123] In the electron beam irradiation step, the ink film is irradiated with an electron beam to polymerize the polymerizable monomer in the ink film, thereby obtaining an ink image. The electron beam irradiation can be performed using an electron beam irradiation device.

[0124] The conditions for electron beam irradiation are not particularly limited, and for example, the electron beam is irradiated under conditions of an acceleration voltage of 50 kV to 200 kV, a dose of 10 kGy to 100 kGy, and a processing speed of 1 m / min to 200 m / min.

[0125] The electron beam irradiation may be carried out in an environment with an oxygen concentration of 20% by volume or less (more preferably less than 20% by volume, and even more preferably 5% by volume or less), which suppresses polymerization inhibition by oxygen and further suppresses migration.

[0126] The environment with an oxygen concentration of less than 20% by volume is preferably an environment in the presence of an inert gas (for example, nitrogen gas, argon gas, or helium gas). The amount of exposure to energy rays is not particularly limited, and is, for example, 240 mJ / cm 2 is.

[0127] <Other processes> In the image recording method of the present disclosure, two or more types of ink may be applied in sequence in the ink application step.

[0128] The two or more inks are preferably inks containing a polymerizable monomer, and more preferably, all of them are inks according to the present disclosure.

[0129] When two or more inks are all inks of the present disclosure, it is preferable that the surfactant content in the ink applied later is greater than the surfactant content in the ink applied earlier. The greater the surfactant content, the lower the surface tension of the ink. In other words, if the surfactant content in the second ink applied later is greater than the surfactant content in the first ink applied earlier, the surface tension of the second ink will be lower than the surface tension of the first ink. This suppresses droplet interference when the second ink is applied on the first ink film. As a result, the image quality of the resulting ink image is improved.

[0130] Therefore, in the step of obtaining an ink film in the image recording method of the present disclosure, it is preferable that n types of ink are applied in sequence, where n is an integer of 2 or greater, and the surfactant content in the mth ink applied is greater than the surfactant content in the m-1th ink applied, where m is an integer of 2 to n.

[0131] It is preferable that the first ink applied (i.e., the ink applied m-1th) and the last ink applied (i.e., the ink applied mth) have different hues. When the first ink applied and the last ink applied have different hues, a multi-color image with reduced roughness can be recorded.

[0132] For example, when applying black ink, cyan ink, magenta ink, yellow ink, and white ink, it is preferable to first apply the white ink onto the substrate to obtain a white ink film, then apply the yellow ink onto the white ink film, apply the magenta ink onto the yellow ink film, apply the cyan ink onto the magenta ink film, and apply the black ink onto the cyan ink film.

[0133] Assuming that white ink, yellow ink, magenta ink, cyan ink, and black ink are applied to a substrate in this order, it is preferable that the content of surfactant contained in the yellow ink is greater than the content of surfactant contained in the white ink, the content of surfactant contained in the magenta ink is greater than the content of surfactant contained in the yellow ink, the content of surfactant contained in the cyan ink is greater than the content of surfactant contained in the magenta ink, and the content of silica particles contained in the black ink is greater than the content of surfactant contained in the cyan ink. The surfactant content means the content relative to the total amount of each ink.

[0134] The ink applied later may be applied across the ink film formed by the previously applied ink and the substrate on which the ink film is not formed.

[0135] Furthermore, the ink applied later only needs to be applied onto at least a portion of the ink film formed by the previously applied ink, and does not necessarily need to be applied onto the entire ink film formed by the previously applied ink.

[0136] The method for applying the ink applied later is the same as the method for applying the ink applied earlier, and the preferred embodiments are also the same. [Example]

[0137] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.

[0138] <Examples 1 to 40, Comparative Examples 1 to 4> First, pigment dispersions were prepared. The methods for preparing black pigment dispersion 1, black pigment dispersion 2, cyan pigment dispersion, magenta pigment dispersion, yellow pigment dispersion, and white pigment dispersion were as follows.

[0139] -Preparation of black pigment dispersion 1- 25 parts by mass of black pigment (CI Pigment Black 7), 70 parts by mass of tetraethylene glycol diacrylate (product name "SR268", manufactured by Sartomer), and 5 parts by mass of "SOLSPERSE 32000" were placed in a dispersing machine, Motor Mill M50 (manufactured by Eiger), and dispersion treatment was carried out using zirconia beads with a diameter of 0.65 mm at a peripheral speed of 9 m / s for 8 hours, thereby obtaining black pigment dispersion liquid 1.

[0140] -Preparation of black pigment dispersion 2- Black pigment dispersion 2 was obtained in the same manner as in black pigment dispersion 1, except that tetraethylene glycol diacrylate was changed to 3-methyl-1,5-pentanediol diacrylate (product name "SR341", manufactured by Sartomer).

[0141] -Cyan pigment dispersion- A cyan pigment dispersion was obtained in the same manner as in the preparation of black pigment dispersion 1, except that the black pigment was changed to a cyan pigment (CI Pigment Blue 15:4).

[0142] -Magenta pigment dispersion- A magenta pigment dispersion was obtained in the same manner as in the preparation of black pigment dispersion 1, except that the black pigment was changed to a magenta pigment (CI Pigment Violet 19).

[0143] -Yellow pigment dispersion- A yellow pigment dispersion was obtained in the same manner as in the preparation of black pigment dispersion 1, except that the black pigment was changed to a yellow pigment (CI Pigment Yellow 155).

[0144] -White pigment dispersion- A white pigment dispersion was obtained in the same manner as in the preparation of black pigment dispersion 1, except that the black pigment was changed to a white pigment (CI Pigment White 6).

[0145] Next, the prepared pigment dispersion was mixed with the polymerizable monomer, polymerization initiator, and surfactant shown in Tables 5 to 8 below so that the content (mass %) of each component was as shown in Tables 5 to 8. 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 an ink.

[0146] In Examples 1 to 35 and Comparative Examples 2 to 4, black pigment dispersion 1 was used. In Comparative Example 1, black pigment dispersion 2 was used. In Examples 41 and 42, a cyan pigment dispersion was used. In Examples 51 and 52, a magenta pigment dispersion was used. In Examples 61 and 62, a yellow pigment dispersion was used. In Example 71, a white pigment dispersion was used.

[0147] In Tables 5 to 8, "polymerizable monomer A / surfactant" means the mass ratio of the content of polymerizable monomer A to the content of surfactant. "polymerizable monomer A / polymerizable monomer B" means the mass ratio of the content of polymerizable monomer A to the content of polymerizable monomer B. The weighted average ClogP values of the polymerizable monomers were calculated based on the ClogP values of all polymerizable monomers contained in each ink.

[0148] Details of each component listed in Tables 5 to 8 are as follows.

[0149] <Polymerizable Monomer A> 4-HBA: 4-hydroxybutyl acrylate (product name "4-HBA", manufactured by Osaka Organic Chemical Industry Ltd.) VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate (product name "VEEA", manufactured by Nippon Shokubai Co., Ltd.) Tetraethylene glycol diacrylate (product name "SR268", manufactured by Sartomer) Triethylene glycol diacrylate (product name "SR272", manufactured by Sartomer) 2-(butylcarbamoyloxy)ethyl acrylate (product name "Genomer 1122", manufactured by Rahn)

[0150] <Polymerizable Monomer B> 3MPDDA: 3-methyl-1,5-pentanediol diacrylate (product name "SR341", manufactured by Sartomer) LA: Lauryl acrylate (product name "SR335", manufactured by Sartomer)

[0151] <Other polymerizable monomers> Caprolactone-modified hydroxypivalic acid neopentyl glycol diacrylate (product name: KAYARAD HX220, manufactured by Nippon Kayaku Co., Ltd.)

[0152] <Polymerization initiator> Ominirad 819: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IGM Resins BV)

[0153] <Black pigment> CIPigment Black 7

[0154] <Cyan pigment> CIPigment Blue 15:4

[0155] <Magenta pigment> CI Pigment Violet 19

[0156] <Yellow pigment> CIPigment Yellow 155

[0157] <White pigment> CIPigment White 6

[0158] <Dispersant> SOLSPERSE32000: Polyethyleneimine polymer (manufactured by Lubrizol)

[0159] <Surfactant> Acrylic surfactant with polymerizable group: Product name "BYK-UV3535", manufactured by BYK Acrylic surfactant without polymerizable groups: Product name "BYK-361N" manufactured by BYK Silicone surfactant 1 without polymerizable groups: Product name "BYK-378" manufactured by BYK Silicone surfactant 2 without polymerizable groups: Product name "BYK-3760" manufactured by BYK Silicone surfactant 3 without polymerizable groups: Product name "TEGO (registered trademark) Glide 450", manufactured by Evonik Silicone surfactant 4 without polymerizable groups: Product name "TEGO (registered trademark) Glide 432", manufactured by Evonik Silicone surfactant 1 having a polymerizable group: Product name "TEGO (registered trademark) Rad 2010", manufactured by Evonik Silicone surfactant 2 having a polymerizable group: Product name "TEGO (registered trademark) Rad 2500", manufactured by Evonik Silicone surfactant 3 having a polymerizable group: Product name "TEGO (registered trademark) Rad 2700", manufactured by Evonik Fluorosurfactant with polymerizable groups: Product name "Megafac RS-76-NS", manufactured by DIC Corporation

[0160] [Image recording] An inkjet recording device with a piezoelectric inkjet nozzle was used to record images on a substrate (product name: "Viewful UV TP-188N" manufactured by Kimoto Co., Ltd.). The ink supply system consisted of a main tank, supply piping, an ink supply tank immediately preceding the inkjet head, a filter, and a piezoelectric inkjet head. The ink supply tank and the inkjet head were insulated and heated. Temperature sensors were installed near the ink supply tank and the inkjet head nozzle, respectively, to maintain a constant temperature of 50°C ± 2°C at the nozzle. The piezoelectric inkjet head was driven to eject multi-size dots ranging from 1 to 60 pL (picoliters) at a resolution of 1,200 x 1,200 dpi. Here, dpi refers to the number of dots per 2.54 cm. A 20 cm x 20 cm solid image was recorded by ejecting the ink. Thereafter, the film was irradiated with electron beams using an electron beam irradiation device (manufactured by Iwasaki Electric Co., Ltd.) under conditions of an acceleration voltage of 90 kV, a dose of 30 kGy, a processing speed of 5 m / min, and an oxygen concentration of 300 ppm or less, to obtain an image recording.

[0161] The obtained image recording material was used to evaluate migration and image quality. It was also evaluated for the generation of white smoke when irradiated with an electron beam. The evaluation results are shown in Tables 5 to 8.

[0162] <Migration> A circle with a diameter of 10 cm was cut out from the image recording. An unstretched polypropylene substrate (model number "FHK2-L", manufactured by Futamura Chemical Co., Ltd., thickness 20 μm) was laminated onto the ink image of the cut-out image recording. The laminate was placed in a migration tester, and 95% by mass ethanol was used as the extraction solvent. After a test at 40°C for 10 days, the content of the polymerizable monomer contained in the ink used in the image recording was measured in the ethanol. If the ink also contained a polymerization initiator, the content of the polymerizable monomer and polymerization initiator in the ethanol was measured. The evaluation criteria were as follows. If the evaluation results for the polymerizable monomer and polymerization initiator corresponded to different ranks, the lower rank was used. Rank 5 means that migration was most suppressed. 5: None of the components were detected. 4: The content of the component most frequently detected among the polymerizable monomers was less than 5 ppb, or the content of the component most frequently detected among the polymerization initiators was less than 10 ppb. 3: The content of the component most frequently detected among the polymerizable monomers was 5 ppb or more and less than 10 ppb, or the content of the component most frequently detected among the polymerization initiators was 10 ppb or more and less than 100 ppb. 2: The content of the component most frequently detected among the polymerizable monomers was 10 ppb or more and less than 20 ppb, or the content of the component most frequently detected among the polymerization initiators was 100 ppb or more and less than 500 ppb. 1: The content of the component most frequently detected among the polymerizable monomers was 20 ppb or more, or the content of the component most frequently detected among the polymerization initiators was 500 ppb or more.

[0163] <Image quality (graininess)> The ink image in the image recording was visually observed and evaluated for graininess, using the following evaluation criteria: Rank 5 means the best image quality. 5: No roughness was observed across the entire image, and it was uniform. 4: The image had slight, minute graininess, but was generally uniform. 3: Slight graininess was observed in the image. 2: The image had noticeable graininess. 1: The image was uneven and had a lot of roughness with strong contrast.

[0164] <White smoke generation> During exposure using electron beams, the degree of white smoke generation was visually observed. If no white smoke generation was confirmed, the electron beam irradiation device was visually inspected for dirt. The evaluation criteria were as follows: Rank 5 means that white smoke generation was most suppressed. 5: No white smoke was observed, and the electron beam irradiation equipment was not dirty. 4: No white smoke was observed, but the electron beam irradiation device was slightly dirty. 3: A small amount of white smoke was observed. 2: White smoke came out. 1: A lot of white smoke came out.

[0165] [Table 5]

[0166] [Table 6]

[0167] [Table 7]

[0168] [Table 8]

[0169] [Table 9]

[0170] In Examples 1 to 35, 41, 42, 51, 52, 61, 62, and 71, a polymerizable monomer A having a ClogP value of 2.3 or less and a surfactant are contained, the content of the surfactant is 0.3% by mass or more relative to the total amount of the electron beam curable ink, and the content of the polymerization initiator is less than 1% by mass relative to the total amount of the electron beam curable ink, and therefore it was found that migration was suppressed.

[0171] On the other hand, in Comparative Example 1, since polymerizable monomer A was not contained, migration was not suppressed and white smoke was generated when irradiated with an electron beam.

[0172] In Comparative Example 2, the surfactant content was 0.2 mass %, so migration was not suppressed and the image quality was poor.

[0173] In Comparative Example 3, since no surfactant was contained, migration was not suppressed and the image quality was poor.

[0174] In Comparative Example 4, the content of the polymerization initiator was 1% by mass, so migration was not suppressed.

[0175] In Example 20, since the content of polymerizable monomer A was 20 mass% or more, it was found that migration was suppressed and the generation of white smoke was suppressed when irradiated with an electron beam, compared to Example 19.

[0176] In Example 24, the mass ratio of the content of polymerizable monomer A to the content of surfactant was 100 or less, and therefore it was found that the image quality was superior to that of Example 18.

[0177] In Example 28, the mass ratio of the content of polymerizable monomer A to the content of surfactant was 4 or more, and therefore, it was found that migration was suppressed and image quality was superior compared to Example 29.

[0178] In Example 20, the mass ratio of the content of polymerizable monomer A to the content of polymerizable monomer B was 0.25 or more, and therefore it was found that migration was suppressed and the generation of white smoke upon irradiation with an electron beam was suppressed compared to Example 19. Furthermore, in Example 23, the mass ratio of the content of polymerizable monomer A to the content of polymerizable monomer B was 2.3 or less, and therefore it was found that migration was suppressed and image quality was superior compared to Example 24.

[0179] In Example 4, since the ClogP value of polymerizable monomer A was 1.5 or less, it was found that migration was suppressed and the generation of white smoke was suppressed when irradiated with an electron beam, compared to Example 13.

[0180] In Examples 2 to 4, the image quality was found to be superior to that of Example 1 because the polymerizable monomer A contained a polymerizable monomer containing two or more ethylene oxide chains.

[0181] In Examples 3 and 4, it was found that migration was more suppressed than in Example 2 because the polymerizable monomer A contained a polyfunctional (meth)acrylate containing two or more ethylene oxide chains.

[0182] In Example 17, the content of polymerizable monomers having a viscosity of 60 mPa·s or more was 20 mass % or less, and therefore, compared with Example 16, it was found that the image quality was superior.

[0183] In Examples 4 and 7 to 12, the surfactant was a silicone surfactant, and therefore, it was found that the image quality was superior to that of Examples 5 and 6, and migration was suppressed compared to Example 35.

[0184] In Example 24, the surfactant content was 1.0 mass % or more, and therefore migration was suppressed and image quality was superior compared to Example 18. In Example 28, the surfactant content was 10 mass % or less, and therefore migration was suppressed and image quality was superior compared to Example 29.

[0185] In Example 2, the weighted average value of the ClogP values of all polymerizable monomers contained in the ink was 0.9 or more, and therefore, it was found that image quality was superior to Example 1. In Example 13, the weighted average value of the ClogP values of all polymerizable monomers contained in the ink was 2.5 or less, and therefore, it was found that, when irradiated with an electron beam, the generation of white smoke was suppressed compared to Example 14.

[0186] [Example 101 and Example 102] In order to record a multi-color image, the inks prepared in the above examples were used to record the image.

[0187] [Image recording] In Example 101, the white ink of Example 71 was ejected onto a substrate to record a 20 cm x 20 cm solid image. Thereafter, using an electron beam irradiation device (manufactured by Iwasaki Electric Co., Ltd.), electron beam irradiation was performed under conditions of an acceleration voltage of 90 kV, a dose of 30 kGy, a processing speed of 5 m / min, and an oxygen concentration of 300 ppm or less. Next, the yellow ink of Example 61, the magenta ink of Example 51, the cyan ink of Example 41, and the black ink of Example 33 were ejected in this order, and after each ejection, the ink was irradiated with an electron beam in the same manner as after ejection of the white ink, to obtain a recorded image. In Example 102, the white ink of Example 71, the yellow ink of Example 62, the magenta ink of Example 52, the cyan ink of Example 42, and the black ink of Example 34 were ejected in this order, and after each ejection, they were irradiated with an electron beam in the same manner as in Example 101, to obtain an image recording material.

[0188] The image quality of the obtained image recording was evaluated in the same manner as in the image quality evaluation described above. The evaluation results are shown in Table 10.

[0189] [Table 10]

[0190] As shown in Table 10, in Example 102, the surfactant content in the ink applied later was greater than the surfactant content in the ink applied earlier, and therefore the image quality was found to be superior to that of Example 101.

[0191] The disclosure of Japanese Patent Application No. 2021-013235, filed on January 29, 2021, 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 was specifically and individually indicated to be incorporated by reference.

Claims

1. The composition contains a polymerizable monomer A having a ClogP value of 2.3 or less and a surfactant, the polymerizable monomer A includes at least one selected from the group consisting of triethylene glycol diacrylate and tetraethylene glycol diacrylate, the content of the surfactant is 0.3% by mass or more relative to the total amount of the electron beam curable ink, The content of the polymerization initiator is less than 1 mass % based on the total amount of the electron beam curable ink.

2. 2. The electron beam curable ink according to claim 1, wherein the content of the polymerizable monomer A is 20% by mass or more based on the total amount of the electron beam curable ink.

3. 3. The electron beam curable ink according to claim 1, wherein a mass ratio of the content of the polymerizable monomer A to the content of the surfactant is 4 to 100.

4. 4. The electron beam-curable ink according to claim 1, further comprising a polymerizable monomer B having a ClogP value of more than 2.3 and a viscosity of 20 mPa·s or less.

5. 5. The electron beam curable ink according to claim 4, wherein the mass ratio of the content of the polymerizable monomer A to the content of the polymerizable monomer B is 0.25 to 2.

3.

6. 6. The electron beam curable ink according to claim 1, wherein the polymerizable monomer A has a ClogP value of 1.5 or less.

7. 7. The electron beam curable ink according to claim 1, wherein the content of the polymerizable monomer having a viscosity of 60 mPa s or more at 25° C. is 20 mass % or less, based on the total amount of the electron beam curable ink.

8. 8. The electron beam curable ink according to claim 1, wherein the surfactant is a silicone surfactant.

9. 9. The electron beam curable ink according to claim 1, wherein the content of the surfactant is 1.0% by mass to 10% by mass with respect to the total amount of the electron beam curable ink.

10. 10. The electron beam curable ink according to claim 1, wherein the weighted average value of the ClogP values of all polymerizable monomers contained in the ink is 0.9 to 2.

5.

11. the surfactant is a surfactant having a polymerizable group, The electron beam curable ink according to any one of claims 1 to 10, wherein the polymerizable group is a (meth)acryloyl group.

12. A step of applying the electron beam curable ink according to any one of claims 1 to 11 onto a substrate to obtain an ink film; irradiating the ink film with an electron beam; An image recording method comprising:

13. In the step of obtaining the ink film, n types of the electron beam curable inks are applied in order, where n is an integer of 2 or more, 13. The image recording method according to claim 12, wherein, when m is an integer from 2 to n, the content of surfactant in the electron beam curable ink applied m-th is greater than the content of surfactant in the electron beam curable ink applied m-1-th.

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