JP7644562B2 - Electron beam curable inkjet ink, printed matter using the same, and image forming method - Google Patents

Description

The present invention relates to an electron beam curable inkjet ink, a printed matter using the ink, and an image forming method.

The inkjet recording method using an inkjet printer involves ejecting ink droplets from the printer and depositing them onto a recording medium such as paper or resin film to perform printing. This method has rapidly spread in recent years because it is easy to miniaturize and speed up the printer, and it is also being applied for industrial purposes.

One type of inkjet ink is UV-curable inkjet ink, which cures when exposed to UV rays. UV-curable inkjet ink is generally a composition containing a polymerizable compound, a photoinitiator, and a colorant. When droplets of UV-curable inkjet ink are deposited on the surface of a recording medium and the deposited droplets are irradiated with UV rays, the reaction of the polymerizable compound in the ink proceeds, and the droplets are cured to form a cured film on the surface of the recording medium. Compared to solvent-based and water-based inkjet inks, UV-curable inkjet inks have features such as high-speed curing and versatility in substrates, and are therefore expected to be used in packaging materials.

However, unreacted photoinitiators, decomposition products of photoinitiators, unreacted polymerizable compounds, and other low molecular weight compounds remain in the cured film formed by curing UV-curable inkjet ink, causing problems with migration and odor. Therefore, when printing on food packaging materials in particular, it is essential to reduce the amount of unreacted photoinitiators and decomposition products of photoinitiators that tend to emit odors.

Electron beam curable inkjet inks are inkjet inks that solve the problems of migration and odor while maintaining the excellent high-speed curing and substrate versatility of UV-curable inkjet inks.

Electron beam curable inkjet ink can cure ink droplets using the high energy of an electron beam without using a photoinitiator. This prevents migration and odors caused by photoinitiators.

Various studies have been conducted on electron beam curable inkjet inks to take advantage of these features.

Patent Document 1 discloses an electron beam curable inkjet ink that contains a colorant, dipropylene glycol diacrylate as a polymerizable compound, and 2-(2-vinyloxyethoxy)ethyl acrylate. However, when color printing is performed with this ink, the ink droplets of each color land on the substrate and mix with each other before being irradiated with the electron beam, resulting in a decrease in image quality.

Patent Document 2 discloses an electron beam curable inkjet ink that contains a photopolymerizable compound including a trifunctional or higher polyfunctional compound, a linear alkyl aldehyde having 6 to 9 carbon atoms, and a gelling agent, as a technology for solving the problem of mixing of droplets of electron beam curable inkjet ink that land on the surface. However, when this ink is used as a food packaging material, the unreacted linear alkyl aldehyde and gelling agent may migrate into the food, and low migration is insufficient. In addition, the linear alkyl aldehyde inhibits the reactivity of the polymerizable compound, and the scratch resistance of the cured film is also insufficient.

Patent No. 6477113 JP 2019-104845 A

The present invention has been made in consideration of these circumstances, and aims to provide an electron beam curable inkjet ink that has low migration, excellent abrasion resistance, and is capable of forming high quality printed images at high speed.

That is, the present invention relates to the following [1] to [6]. Note that in this application, "(Numerical value 1) to (Numerical value 2)" indicates that the upper and lower limits are included.
[1]
The electron beam curable inkjet ink contains: a polymerizable compound (A) having a long-chain alkyl group having from 6 to 30 carbon atoms in the molecule, a hydrogen-bonding group, and a polymerizable group; a polymerizable compound (B) other than the component (A); and a colorant (C).
[2]
The electron beam curable ink-jet ink according to item [1], wherein the component (A) is a reaction product of an alcohol compound (a) having from 6 to 30 carbon atoms and an isocyanate compound (b) having a (meth)acrylate group.
[3]
The electron beam curable ink-jet ink according to item [1] or [2], wherein the content of the component (A) in the total amount of the electron beam curable ink-jet ink is 0.5 to 90% by weight.
[4]
The electron beam curable inkjet ink according to any one of items [1] to [3] above, wherein the solidification initiation temperature is 20° C. or higher and lower than 100° C.
[5]
A printed matter using the electron beam curable inkjet ink according to any one of items [1] to [4].
[6]
An image forming method comprising the following steps (Step 1) to (Step 3).
(Step 1) A step of heating the electron beam curable inkjet ink according to any one of the preceding items [1] to [4] to a temperature equal to or higher than the ink solidification start temperature. (Step 2) A step of ejecting droplets of the electron beam curable inkjet ink according to any one of the preceding items [1] to [4] from a nozzle of an ejection head and causing the droplets to land on a substrate surface. (Step 3) A step of further irradiating the ink with an electron beam to cure the ink.

The present invention provides an electron beam curable inkjet ink that has low migration, excellent abrasion resistance, and is capable of forming high quality printed images at high speed.

^{The 1} H-NMR chart of Synthesis Example 1 is shown below. 1 shows a chart of the solidification start temperature measurement in Example 1. 1 shows a solidification start temperature measurement chart for Comparative Example 1.

In this specification, "C.I." is an abbreviation for Color Index. In addition, "(meth)acrylate" means "acrylate" and/or "methacrylate." Furthermore, in this specification, "%" and "parts" are all stated on a weight basis unless otherwise specified.

[Electron beam curable inkjet ink]
The electron beam-curable inkjet ink of the present invention contains a polymerizable compound (A) (hereinafter also referred to simply as “component (A)”) having a long-chain alkyl group having from 6 to 30 carbon atoms in the molecule, a hydrogen-bonding group, and a polymerizable group, a polymerizable compound (B) (hereinafter also referred to simply as “component (B)”) other than component (A), and a colorant (C) (hereinafter also referred to simply as “component (C)”).

[Polymerizable Compound (A) Having a Long-Chain Alkyl Group Having 6 to 30 Carbon Atoms in the Molecule, a Hydrogen-Bonding Group, and a Polymerizable Group]
Component (A) has 6 to 30 long-chain alkyl groups, a hydrogen-bonding group, and a polymerizable group in the molecule. When the droplets of the electron beam curable inkjet ink of the present invention are ejected from the nozzle of the ejection head and land on the surface of a substrate, the droplets solidify and are less likely to mix with each other due to the inclusion of component (A), so that a high-definition image can be formed. Furthermore, since component (A) has a polymerizable group, it is fixed in the cured film by electron beam irradiation, and low migration can also be achieved.

It is more preferable that the long-chain alkyl group having 6 to 30 carbon atoms is a straight-chain alkyl group having 12 to 22 carbon atoms. With an alkyl group having less than 6 carbon atoms, when ink droplets land on the surface of the substrate, the droplets are less likely to solidify, and the droplets mix together, resulting in poor image quality. With an alkyl group having more than 30 carbon atoms, the abrasion resistance of the cured film is poor. If the carbon number is 6 or more, the ink droplets are more likely to solidify when they land on the surface of the substrate, resulting in a high-quality image, and if the carbon number is 30 or less, the abrasion resistance of the cured film is not insufficient. In addition, an alkyl group having 6 or more carbon atoms also has the effect of lowering the viscosity of the ink.

Examples of hydrogen-bonding groups in component (A) include hydroxyl groups, urethane groups, urea groups, amide groups, carboxyl groups, and ester groups. The presence of hydrogen-bonding groups makes it easier for ink droplets to solidify when they land on the surface of a substrate. Among the hydrogen-bonding groups, hydroxyl groups, urethane groups, and amide groups are preferred, with urethane groups being more preferred from the viewpoint of imparting toughness to the cured film and adhesion to the substrate.

The polymerizable group of component (A) is not particularly limited as long as it undergoes a polymerization reaction upon electron beam irradiation, but examples include acrylic groups, methacrylic groups, vinyl groups, vinyl ether groups, and allyl groups. From the viewpoint of productivity, acrylic groups and methacrylic groups, which have a fast curing rate, are preferred.

The method for obtaining component (A) is not particularly limited, but may be a method of reacting an alcohol compound (a) having 6 to 30 carbon atoms (hereinafter simply referred to as "component (a)") with an isocyanate compound (b) having a (meth)acrylate group (hereinafter simply referred to as "component (b)"), or a method of reacting an isocyanate compound (c) having 6 to 30 carbon atoms (hereinafter simply referred to as "component (c)") with a (meth)acrylate compound (d) having a hydroxyl group (hereinafter simply referred to as "component (d)").

When reacting component (a) with component (b), the desired component (A) can be obtained by mixing component (b) with component (a) so that there are 1.0 to 1.2 equivalents, preferably 1.05 to 1.1 equivalents, of isocyanate groups per equivalent of hydroxyl groups, and reacting at a reaction temperature of 70 to 90°C. When reacting component (c) with component (d), the desired component (A) can be obtained by mixing component (d) with component (c) so that there are 1.0 to 1.2 equivalents, preferably 1.05 to 1.1 equivalents, of hydroxyl groups per equivalent of isocyanate, and reacting at a reaction temperature of 70 to 90°C.

Examples of component (a) include hexyl alcohol, octyl alcohol, tridecanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, behenyl alcohol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 1,18-octadecanediol, 1,20-icosanediol, 1,2-hexanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, 1,2-dodecanediol, 1,2-tetradecanediol, 1,2-hexadecanediol, 1,2-octadecanediol, and 1,2-icosanediol, and preferably those that do not have a branched structure.

Examples of component (b) include 2-isocyanatoethyl methacrylate (Karenz MOI manufactured by Showa Denko K.K.), 2-isocyanatoethyl acrylate (Karenz AOI manufactured by Showa Denko K.K.), 2-(2-methacryloyloxyethyloxy)ethyl isocyanate (Karenz MOI-EG manufactured by Showa Denko K.K.), 1,1-(bisacryloyloxymethyl)ethyl isocyanate (Karenz BEI manufactured by Showa Denko K.K.), etc.

Component (c) includes hexyl isocyanate, heptyl isocyanate, octyl isocyanate, nonyl isocyanate, decyl isocyanate, dodecyl isocyanate, octadecyl isocyanate, hexamethylene diisocyanate, etc., with octadecyl isocyanate (Millionate O, manufactured by Hodogaya Chemical Co., Ltd.) and hexamethylene diisocyanate (HDI) being particularly preferred.

Component (d) may be hydroxy C2-C4 alkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, dimethylolcyclohexyl mono(meth)acrylate, hydroxycaprolactone (meth)acrylate, hydroxyl-terminated polyalkylene glycol (meth)acrylate, glycerin di(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol penta(meth)acrylate, but from the viewpoint of curability, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, hydroxycaprolactone acrylate, glycerin diacrylate, pentaerythritol triacrylate, and dipentaerythritol pentaacrylate are preferred.

In the electron beam curable inkjet ink of the present invention, component (A) may be used alone or in a mixture of two or more kinds in any ratio. The content of component (A) in the total amount of the electron beam curable inkjet ink of the present invention is preferably 0.5 to 90% by weight, more preferably 1 to 80% by weight, particularly preferably 3 to 50% by weight, and most preferably 5 to 20% by weight. If the content is less than 0.5% by weight, the ink droplets are difficult to solidify when they land on the substrate surface, and the droplets mix together, resulting in poor image quality. If the content is more than 90% by weight, the abrasion resistance of the cured film is poor.

[Polymerizable compound (B) other than component (A)]
The electron beam curable inkjet ink of the present invention contains, as component (B), a polymerizable compound other than component (A). Examples of component (B) include alkyl (meth)acrylates having 5 to 25 carbon atoms, such as isooctyl (meth)acrylate, isoamyl (meth)acrylate, lauryl (meth)acrylate, isodecyl (meth)acrylate, stearyl (meth)acrylate, cetyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, and tridecyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, (meth)acrylamide, N-hydroxyethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, acryloylmorpholine, allyloxymethyl methyl acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, and 2-methylpropanediol. (Meth)acrylates having a cyclic skeleton such as -(2-vinyloxyethoxy)ethyl, phenyl glycidyl (meth)acrylate, tricyclodecane (meth)acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl acrylate, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl acrylate, 1-adamantyl methacrylate, polypropylene oxide modified nonylphenyl (meth)acrylate, and dicyclopentadieneoxyethyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as 4-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; alkyl (meth)acrylates such as ethoxydiethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polypropylene oxide modified nonylphenyl (meth)acrylate and other polyalkylene glycol (meth)acrylates, caprolactone modified tetrafurfuryl (meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2-n-butyl-2-ethyl- Di(meth)acrylates of aliphatic hydrocarbon diols having 5 to 12 carbon atoms, such as 1,3-propanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and tricyclodecane dimethanol di(meth)acrylate; dioxane glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkylene oxide-modified bisphenol A-type di(meth)acrylate, caprolactone-modified hydroxypivalic acid neopentyl glycol di(meth)acrylate; trimethylol C2-10 alkane tri(meth)acrylates, such as trimethylolpropane tri(meth)acrylate and trimethyloloctane tri(meth)acrylate; trimethylolpropane polyethoxy tri(meth)acrylate; acrylate, trimethylol C2-10 alkane polyalkoxy tri(meth)acrylate such as trimethylolpropane polypropoxy tri(meth)acrylate and trimethylolpropane polyethoxy polypropoxy tri(meth)acrylate, tris[(meth)acroyloxyethyl]isocyanurate, pentaerythritol tri(meth)acrylate, alkylene oxide modified trimethylolpropane tri(meth)acrylate such as ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol polyethoxy tetra(meth)acrylate, pentaerythritol polypropoxy tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, di-trimethylolpropane tri(meth)acrylate, (meth)acrylate compounds such as methylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy (meth)acrylate oligomers, aliphatic urethane (meth)acrylate oligomers, aromatic urethane (meth)acrylate oligomers, and polyester (meth)acrylate oligomers; monofunctional vinyl ethers including butyl vinyl ether, butyl propenyl ether, butyl butenyl ether, hexyl vinyl ether, ethylhexyl vinyl ether, phenyl vinyl ether, benzyl vinyl ether, ethyl ethoxy vinyl ether, acetyl ethoxy ethoxy vinyl ether, cyclohexyl vinyl ether, and adamantyl vinyl ether; vinyl ether compounds having a functional group, bifunctional vinyl ether compounds including ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol vinyl ether, butylene divinyl ether, dibutylene glycol divinyl ether, neopentyl glycol divinyl ether, cyclohexanediol divinyl ether, cyclohexanedimethanol divinyl ether, norbornyl dimethanol divinyl ether, isovinyl divinyl ether, divinyl resorcinol, and divinyl hydroquinone, as well as glycerin trivinyl ether, glycerin ethylene oxide adduct trivinyl ether (the number of moles of ethylene oxide added is 6), trimethylolpropane trivinyl ether, and the like. vinyl ether compounds such as trifunctional or higher vinyl ether compounds including ether, trivinyl ether ethylene oxide adduct trivinyl ether (the number of moles of ethylene oxide added is 3), pentaerythritol trivinyl ether, ditrimethylolpropane hexavinyl ether, and oxyethylene adducts thereof; aromatic vinyl compounds such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, indene, divinylbenzene, and diallyl phthalate; vinyl ester compounds such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, and divinyl adipate; and allyl compounds such as allyl acetate, allyl benzoate, diallyl adipate, diallyl terephthalate, diallyl isophthalate, and diallyl phthalate.

From the viewpoint of reactivity and solubility of component (A), acryloylmorpholine, allyloxymethyl methyl acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(2-vinyloxyethoxy)ethyl methacrylate, phenylglycidyl (meth)acrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polytetramethylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, and ethylene oxide modified trimethylolpropane triacrylate are particularly preferred.

From the viewpoint of imparting flexibility to the ink after curing, lauryl acrylate, isodecyl acrylate, stearyl acrylate, cetyl acrylate, isomyristyl acrylate, isostearyl acrylate, tridecyl acrylate, polypropylene glycol diacrylate, polyethylene glycol diacrylate, polytetramethylene glycol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanediol diacrylate, 1,12-dodecanediol diacrylate, aliphatic urethane acrylate oligomer, and aromatic urethane acrylate oligomer are particularly preferred.

In the electron beam curable inkjet ink of the present invention, component (B) may be used alone or in a mixture of two or more kinds in any ratio. The content of component (B) in the total amount of the electron beam curable inkjet ink of the present invention is preferably 10 to 99.5% by weight, more preferably 20 to 99% by weight, and particularly preferably 50 to 95% by weight.

[Colorant (C)]
The electron beam curable inkjet ink of the present invention contains a colorant as component (C). As component (C), a dye or a pigment can be used, and from the viewpoint of obtaining an image with good weather resistance, the colorant is preferably a pigment. The pigment can be selected from, for example, a yellow pigment, a red or magenta pigment, a blue or cyan pigment, and a black pigment depending on the color of the image to be formed, and examples of the pigment include inorganic pigments, organic pigments, extender pigments, and hollow particles.

Examples of the inorganic pigments include carbon black, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides.

When the ink is a black ink and the pigment is an inorganic pigment, the inorganic pigment contained in the black ink is preferably carbon black such as thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon Co.; the Monarch series, Regal series, and Mogul series manufactured by Cabot Corporation; the ColorBlack series, Printex series, SpecialBlack series, and Nerox series manufactured by Orion Engineered Carbons Co.; and the MA series, MCF series, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, and No. 2300 manufactured by Mitsubishi Chemical Corporation.
When the ink is a white ink and the pigment is an inorganic pigment, examples of the inorganic pigment contained in the white ink include oxides, nitrides, and oxynitrides of metals such as zinc, silicon, aluminum, titanium, strontium, and zirconium; and inorganic compounds such as various types of glass and silica, and titanium dioxide and zinc oxide are preferred.

The above organic pigments include, for example, various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone, with disazo being preferred.

The organic pigments include, for example, yellows such as C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 155, 180, 185, 193, 199, 202, and 213; C.I. Reds such as C.I. Pigment Red 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, 269, 272; Blues such as C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80; Violets such as C.I. Pigment Violet 19, 23, 29, 37, 38, 50; Examples of pigments include orange pigments such as C.I. Pigment Orange 13, 16, 43, 68, 69, 71, and 73; green pigments such as C.I. Pigment Green 7, 36, and 54; and black pigments such as C.I. Pigment Black 1.

Examples of the above-mentioned extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. Extender pigments are often used in combination with other colorants.

The hollow particles may be any of the known hollow particles described in, for example, U.S. Patent No. 4,880,465, Japanese Patent No. 3,562,754, Japanese Patent No. 6026234, Japanese Patent No. 5459460, JP-A-2003-268694, and Japanese Patent No. 4902216, and are particularly preferably used as white pigments.

The disperse dye may be a known disperse dye or a known oil-soluble dye. The known disperse dye is preferably a C.I. Dispers-based disperse dye. Specific examples thereof include C.I. Dispers Yellow 9, 23, 33, 42, 49, 54, 58, 60, 64, 66, 71, 76, 79, 83, 86, 90, 93, 99, 114, 116, 119, 122, 126, 149, 160, 163, 165, 180, 183, 186, 198, 200, 211, 224, 226, 227, 231, 237 and other yellows; Reds such as C.I. Dispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283; Oranges such as C.I. Dispers Orange 9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97; Violets such as C.I. Dispers Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1; Examples of disperse dyes of blue colors include Dispers Blue 27, 56, 60, 79:1, 87, 143, 165, 165:1, 165:2, 181, 185, 197, 202, 225, 257, 266, 267, 281, 341, 353, 354, 358, 364, 365, and 368.
As the known solvent dye, C.I. Solvent-based disperse dyes are preferred.

The average particle size of component (C) is preferably 30 nm to 300 nm, and more preferably 50 nm to 250 nm. In this specification, the average particle size refers to the average particle size of particles measured using a laser light scattering method.

In the electron beam curable inkjet ink of the present invention, component (C) may be used alone or in a mixture of two or more kinds in any ratio. The content of component (C) in the total amount of the electron beam curable inkjet ink of the present invention is preferably 0.1 to 40% by weight, more preferably 0.5 to 20% by weight, particularly preferably 1 to 10% by weight, and most preferably 2 to 7% by weight.

[Optional ingredients]
The electron beam curable inkjet ink of the present invention may contain, as optional components, various additives such as a surface tension adjuster, a pigment dispersant, an ultraviolet absorber, an antifoaming agent, an antioxidant, a light stabilizer (for example, a hindered amine compound, etc.), a silane coupling agent, a metal adhesion imparting agent, and an organic solvent, as appropriate.

(Surface tension adjuster)
The electron beam curable inkjet ink of the present invention may further contain a surfactant as a surface tension adjuster. Examples of the surfactant include anionic, nonionic, silicone, and fluorine-based surfactants. Among these, a surfactant selected from the group consisting of nonionic and silicone surfactants is preferred.

The above anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acylamino acids or salts thereof, N-acylmethyltaurines, alkyl sulfates polyoxyalkyl ether sulfates, alkyl sulfates polyoxyethylene alkyl ether phosphates, rosin acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, alkyl phosphates, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, dioctyl sulfosuccinates, etc.

Examples of the nonionic surfactants include ether-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyethylene distyrenated phenyl ether (for example, Emulgen A-60, A-90, and A-500 manufactured by Kao Corporation); ester-based surfactants such as polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; and acetylene glycol (or acetylene alcohol)-based surfactants such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyne-3-ol (for example, Surfynol manufactured by Evonik Japan Co., Ltd.). 104, 104PG50, 82, 420, 440, 465, 485, Olfin STG, etc.); polyglycol ethers, etc.

Examples of silicone surfactants include polyether-modified siloxane, polyether-modified polydimethylsiloxane, etc. Examples of such products include Dynol 960 and 980 manufactured by Air Products Co., Ltd.; Silface SAG001, SAG002, SAG003, SAG005, SAG503A, SAG008, SAG009, SAG010, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 manufactured by Nissin Chemical Co., Ltd.; and BYK Additives & Examples of such products include BYK-306, 307, 333, 347, 348, BYK-UV3500, UV-3510, UV-3530, UV3570, 345, 347, 348, 349, 3455, LP-X23288, LP-X23289, and LP-X23347 manufactured by Evonik Instruments; and TEGO Twin 4000, TEGO Wet KL 245, 250, 260, 265, 270, 280, TEGO Rad 2010, 2011, 2100, 2200N, 2250, 2300, 2500, 2600, and 2700 manufactured by Evonik Tego Chemie.

Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains. Specific examples of commercially available products include Capstone FS-30 and FS-31 (manufactured by Chemours).

Among the above surfactants, surfactants containing a polymerizable group are preferred from the viewpoint of migration, and examples thereof include BYK-UV3500, BYK-UV3510, BYK-UV3530, BYK-UV3570, TEGO Rad 2010, 2011, 2100, 2200N, 2250, 2300, 2500, 2600, and 2700.

(Pigment Dispersant)
The electron beam curable inkjet ink of the present invention can use a pigment dispersant. Examples of the pigment dispersant include a polyurethane skeleton, a polyacrylic skeleton, a polyester skeleton, a polyamide skeleton, a polyimide skeleton, and a polyurea skeleton. Specific examples include Solsperse 24000GR, 32000, 33000, 35000, 39000, 41000, 53000, and J180 (manufactured by Lubrizol), and Ajisper PB821, 822, 824, 827, and 711 (manufactured by Ajinomoto Fine-Techno Co., Ltd.).

(Ultraviolet absorber)
The electron beam curable inkjet ink of the present invention may contain an ultraviolet absorbing agent in order to improve weather resistance. Examples of the ultraviolet absorbing agent include benzophenone-based ultraviolet absorbing agents, benzotriazole-based ultraviolet absorbing agents, salicylate-based ultraviolet absorbing agents, hydroxyphenyltriazine-based ultraviolet absorbing agents, cyanoacrylate-based ultraviolet absorbing agents, and nickel complex salt-based ultraviolet absorbing agents. Among them, 2-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole (product name: RUVA-93, manufactured by Otsuka Chemical Co., Ltd.), which contains a polymerizable group, is preferred because of its low migration risk.

(Antioxidants)
Specific examples of the antioxidant include BHT, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, N,N-hexyl Examples of the monomer include samethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tris-(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, octylated diphenylamine, 2,4-bis[(octylthio)methyl-O-cresol, isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], dibutylhydroxytoluene, and 4-allyl-2,6-di-t-butylphenol. However, 4-allyl-2,6-di-t-butylphenol (trade name: TRIAM-100, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) containing a polymerizable group is preferable because of its low migration risk.

(Light stabilizer)
Specific examples of the light stabilizer include 1,2,2,6,6-pentamethyl-4-piperidyl alcohol, 2,2,6,6-tetramethyl-4-piperidyl alcohol, 1,2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol, and 3,9-bis(2-hydroxy-1,1-dimethyl)-2,3-diaminetetracarboxylic acid. ethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane mixed ester, decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 1-[2-[3-(3,5-di-tert-butyl-4-hydroxy 1,2,2,6,6-Pentamethyl-4-piperidinyl-methacrylate, Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, Decanedioic acid bis(2,2,6,6-tetramethyl-1(octyloxy)-4-piperidinyl)ester, Reaction products of 1,1-dimethylethyl hydroperoxide with octane, N,N',N'',N''' -tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, polycondensate of dibutylamine/1,3,5-triazine/N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, poly[[6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6, 6-Tetramethyl-4-piperidyl)imino]], polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, 2,2,4,4-tetramethyl-20-(β-lauryloxycarbonyl)ethyl-7-oxa-3,20-diazadispiro[5,1,11,2]heneicosan-21-one, β-alanine, N-(2,2,6,6-tetramethyl-4-piperidinyl)-dodecyl ester/tetradecyl ester, N-acetyl-3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)pyrrolidine-2,5-dione, 2,2,4,4-tetramethyl-7-oxa-3,20-di Azadispiro[5,1,11,2]heneicosan-21-one, 2,2,4,4-tetramethyl-21-oxa-3,20-diazadicyclo-[5,1,11,2]-heneicosane-20-propanoic acid dodecyl ester/tetradecyl ester, propanedioic acid, [(4-methoxyphenyl)-methylene]-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester, higher fatty acid esters of 2,2,6,6-tetramethyl-4-piperidinol, 1,3-benzenedicarboxamide, hindered amines such as N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl), benzofurafine compounds such as octabenzone, phenol compounds, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole, 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole, methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) Examples of suitable compounds include reaction products of propionate and polyethylene glycol, benzotriazole compounds such as 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol, benzoates such as 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate, and triazine compounds such as 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol. However, 1,2,2,6,6-pentamethyl-4-piperidyl (meth)acrylate (trade name: LA-82, manufactured by ADEKA CORPORATION) containing a polymerizable group is preferred because of its low migration risk.

(Silane coupling agent)
The electron beam curable inkjet ink of the present invention may contain a silane coupling agent in order to improve the adhesion to the substrate. Specific examples of the silane coupling agent include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-(2-aminoethyl)3-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, N-(2-aminoethyl)3-aminopropylmethyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, N-(2-(vinylbenzyl)phenyl)phenyl, and the like. Silane coupling agents such as (amino)ethyl)3-aminopropyltrimethoxysilane hydrochloride, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, and 3-chloropropyltrimethoxysilane; isopropyl(N-ethylaminoethylamino)titanate, isopropyltriisostearoyltitanate, titanium di(dioctylpyrophosphate)oxyacetate, and tetraisopropyldi(dioctylphosphite). Titanium coupling agents such as titanate and neoalkoxytri(p-N-(β-aminoethyl)aminophenyl)titanate; Zr-acetylacetonate, Zr-methacrylate, Zr-propionate, neoalkoxyzirconate, neoalkoxytrisneodecanoylzirconate, neoalkoxytris(dodecanoyl)benzenesulfonylzirconate, neoalkoxytris(ethylenediaminoethyl)zirconate, neoalkoxytris(m-aminophenyl)zirconate, ammonium zirconium carbonate, Al-acetylacetonate, Al-methacrylate, Al-propionate, etc. Examples of suitable coupling agents include zirconium or aluminum coupling agents. However, vinyltrimethoxysilane (trade name: KBM-1003, manufactured by Shin-Etsu Chemical Co., Ltd.), 3-methacryloxypropylmethyldimethoxysilane (trade name: KBM-502, manufactured by Shin-Etsu Chemical Co., Ltd.), 3-methacryloxypropyltrimethoxysilane (trade name: KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.), 3-methacryloxypropyltriethoxysilane (trade name: KBE-503, manufactured by Shin-Etsu Chemical Co., Ltd.), and 3-acryloxypropyltrimethoxysilane (trade name: KBM-5103, manufactured by Shin-Etsu Chemical Co., Ltd.), which contain a polymerizable group, are preferred because they have a low migration risk.

(Metal Adhesion Promoters)
The electron beam curable inkjet ink of the present invention may contain a metal adhesion promoter in order to improve adhesion to metal substrates such as aluminum, etc. Specific examples of metal adhesion promoters include ethylene oxide modified phenoxylated (meth)acrylate phosphate, ethylene oxide modified butoxylated (meth)acrylate phosphate, ethylene oxide modified octyloxylated (meth)acrylate phosphate, ethylene oxide modified di(meth)acrylate phosphate, ethylene oxide modified tri(meth)acrylate phosphate, and caprolactone modified ethylene oxide modified di(meth)acrylate phosphate, with ethylene oxide modified dimethacrylate phosphate (trade name: KAYAMER PM-2, manufactured by Nippon Kayaku Co., Ltd.) and caprolactone modified ethylene oxide modified dimethacrylate phosphate (trade name: KAYAMER PM-21, manufactured by Nippon Kayaku Co., Ltd.) being easily available and having a low migration risk, being preferred.

(Organic Solvent)
The electron beam curable inkjet ink of the present invention may contain an organic solvent in order to adjust the storage stability, ejection stability, flying properties of the ink, etc. Examples of the organic solvent include alcohols, ketones, ethers, esters, nitrogen-containing compounds, amides, etc.

[Method for preparing electron beam curable inkjet ink]
The electron beam curable inkjet ink of the present invention can be prepared by a conventionally known method. A suitable preparation method for the electron beam curable inkjet ink of the present invention containing a pigment as a colorant will be described below. A dispersing machine is used to premix component (C), a part of component (B), and any other component (more specifically, a pigment dispersant, etc.) as necessary, and each component is dissolved or dispersed to prepare a primary dispersion. Examples of dispersing machines include a disperser, a container-driven media mill (more specifically, a ball mill, a centrifugal mill, a planetary ball mill, etc.), a high-speed rotary mill (more specifically, a sand mill, etc.), and a media stirring mill (more specifically, a stirring tank type mill, etc.).

Next, component (A), the remaining component (B), and the above-mentioned additives, if necessary, are added to the obtained primary dispersion liquid, and mixed uniformly using a stirrer. Examples of the stirrer include a Disper, a Three-One Motor, a homogenizer, and a magnetic stirrer. In this manner, an electron beam curable inkjet ink can be obtained. The electron beam curable inkjet ink may also be mixed using a mixer such as a line mixer. Furthermore, in order to further refine the particles in the electron beam curable inkjet ink, the electron beam curable inkjet ink may also be mixed using a dispersing machine such as a bead mill or a high-pressure jet mill.

[Physical Properties]
The electron beam curable inkjet ink of the present invention preferably has a viscosity of 100 mPa·s or less, and more preferably 30 mPa·s or less, at a temperature of 60° C. or higher. In the present invention, the viscosity can be measured using an E-type viscometer (TV-22, manufactured by Toki Sangyo Co., Ltd.).

In the electron beam curable inkjet ink of the present invention, the ink solidification start temperature is preferably 20°C or more and less than 100°C. When the ink solidification start temperature is 20°C or more, the ink solidifies quickly after landing on the substrate, thereby suppressing ink bleeding. When the ink solidification start temperature is less than 100°C, the ink melted by heating can be ejected from the inkjet head, allowing the ink to be ejected more stably. The ink solidifies more quickly and can be ejected at a lower temperature. From the viewpoint of energy load, it is more preferable that the ink solidification start temperature is 30°C or more and less than 80°C.

The ink solidification start temperature can be determined by measuring the change in heat quantity of the ink using a differential scanning calorimeter. In the present invention, the ink sample was held at 90°C for 3 minutes, and then cooled at a rate of 10°C/min. The temperature at which the heat generation peak rose was determined as the ink solidification start temperature.

[Image forming method]
The process for producing a printed matter using the electron beam curable inkjet ink of the present invention will be described.
In the method for producing a printed matter of the present invention, an image is formed on the surface of a substrate by the following (Step 1) to (Step 3).
(Step 1) heating an electron beam curable inkjet ink to a temperature equal to or higher than the ink solidification start temperature;
(Step 2) ejecting ink droplets from the nozzles of an ejection head and causing them to land on the surface of a substrate;
(Step 3) A step of curing the ink by irradiating it with an electron beam.

(Step 1)
In this process, the ink tank, the inkjet head, the flow path connecting the ink tank and the inkjet head, etc. are heated to a temperature equal to or higher than the ink solidification temperature. If the ink does not have a viscosity that allows it to be ejected from the inkjet head even when the ink is at or above the ink solidification temperature, the ink is heated to a temperature at which it can be ejected.

(Step 2)
The electron beam curable inkjet ink of the present invention is preferably ejected by an inkjet method.
As a means for discharging ink by the inkjet method, it is preferable to use an inkjet head. As an inkjet head, for example, a charge control type that uses electrostatic attraction to discharge ink, a drop-on-demand type (pressure pulse type) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet type that converts an electric signal into an acoustic beam and irradiates the ink to discharge ink using radiation pressure, a thermal inkjet (Bubble Jet (registered trademark)) type that heats the ink to form bubbles and uses the generated pressure, etc. are preferably used, and the pressure pulse type that uses a piezoelectric element is particularly preferable. In addition, it is also possible to use a multi-pass type, a single-pass type (one-pass printing type), etc.

Specific examples of substrates include glass, quartz, aluminum, paper (e.g., ordinary paper without an ink-receiving layer, media used in gravure printing or offset printing, etc., paper for inkjet printing with an ink-receiving layer, film for inkjet printing, glossy paper, etc.), plastic film (e.g., polyolefin resin, polyamide resin, polyester resin, polycycloolefin resin, cellulose acetate, acrylic resin, chlorinated polyolefin resin, polyethersulfone resin, polyethylene, polystyrene, polycarbonate resin, polyethylene naphthalate, nylon, polyvinyl acetal, etc.), etc. Among these, polyolefin resin, polyamide resin, and polyester resin are preferable for packaging, and polypropylene, polyethylene, polyethylene terephthalate, and nylon are more preferable.

The surface of the substrate may be uneven, which may result in deterioration of image quality. For this reason, when used as a printing substrate, it is preferable to homogenize the substrate by subjecting it to a surface modification treatment. As the surface modification treatment, a known surface modification treatment selected from corona discharge treatment, plasma treatment, and frame treatment is preferable. Here, it is generally known that the effect of the surface modification treatment decreases over time. For this reason, it is preferable to carry out the surface modification treatment step and the inkjet recording step consecutively, and it is preferable to carry out the surface modification treatment step immediately before the inkjet recording step. It is also preferable to modify the outermost surface of the substrate by using a pretreatment agent or the like.

(Step 3)
In the method for producing a printed matter of the present invention, the deposited ink is irradiated with an electron beam to cure it.

The accelerating voltage of the electron beam should be such that it delivers sufficient energy to the inside of the ink to sufficiently cause a reaction of the polymerizable compound, but does not cause significant deterioration of the substrate. For example, from the viewpoint of minimizing migration while suppressing deterioration of the substrate, the accelerating voltage of the electron beam is preferably 10 to 150 kV, and more preferably 30 to 120 kV.

When electron beams are used in the atmosphere, there is a risk of decomposing oxygen and generating large amounts of ozone, so the electron beam irradiation device is used under low oxygen concentrations. In the present invention, the oxygen concentration is preferably 1000 ppm or less. Furthermore, if the oxygen concentration is 50 to 500 ppm, the ink can be sufficiently cured and a sufficient printing speed can be maintained, which is even more preferable in terms of quality and productivity.

The electron beam curable inkjet ink of the present invention has low migration and high abrasion resistance, making it suitable for printing on various packages and other types of printing.

In inkjet image forming methods, small individual dots are preferred in order to obtain high-definition, high-resolution images. To obtain small dots, ultraviolet-curing inkjet systems may include a process called pinning. This is a process in which ink is ejected from a nozzle and irradiated with ultraviolet light immediately after it lands on the substrate. This allows dots to be formed quickly after landing, making it possible to obtain images with small dot diameters, and achieving high image quality with ultraviolet-curing inkjet ink. On the other hand, with electron beam-curing inkjet ink, pinning curing with ultraviolet light is not possible, and the dot diameter becomes large, making it difficult to obtain high-resolution image quality.

The ink of the present invention solidifies from the liquid state immediately after impact, making it possible to suppress the spread of dots on the substrate, i.e., to obtain small dot diameters. This can be easily confirmed by dropping a fixed amount of ink droplets onto a glass substrate and measuring the dot diameter.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, unless otherwise specified, "parts" and "%" in the text are based on weight.

[Synthesis Example 1]
In a flask equipped with a thermometer, a condenser, and a stirrer, 408.31 g of methyl ethyl ketone, 267.19 g of stearyl alcohol (NAA-45 manufactured by NOF Corporation, hydroxyl value 210 mg KOH/g), and 141.12 g of 2-isocyanatoethyl acrylate (Karens AOI-VM manufactured by Showa Denko K.K., molecular weight 141.12) were charged and reacted at 80 ° C. The isocyanate content after 8 hours of reaction was determined by adding an excess of amine and back titrating with hydrochloric acid, and it was confirmed that the value was less than 0.1% of the residual amount of isocyanate calculated from the calculated value. Next, methyl ethyl ketone was distilled off under reduced pressure to obtain a solid reaction product (A-1). The ¹ H-NMR chart of the obtained reaction product (A-1) is shown in FIG. 1.
^1H -NMR (400MHz, CDCl3) δ (ppm) = 6.42 (d, 1H), 6.12 (q, 1H), 5.84 (d, 1H), 4.95 (br, 1H), 4.22 (t, 2 H), 4.03 (t, 2H), 3.46 (q, 2H), 1.58 (br, 2H), 1.23 (br, 32H), 0.86 (t, 3H)

[Preparation Example 1]: Preparation of Dispersion 10 g of Solsperse 32000 (manufactured by Lubrizol) and 70 g of dipropylene glycol diacrylate (DPGDA) were charged in a dispersion vessel and adjusted by stirring to a uniform liquid. 20 g of C.I. Pigmnet Blue 15:4 (manufactured by Dainichiseika Chemicals Co., Ltd. CHROMOFINE BLUE 4851) was added thereto, and 100 g of 0.3 mm glass beads were further added, and dispersion treatment was performed for 6 hours with a sand mill. After the dispersion treatment, dipropylene glycol diacrylate was added so that the pigment concentration was 12%, and the glass beads used for dispersion were removed by filtering with glass fiber filter paper GA-100 (manufactured by Toyo Roshi Co., Ltd.) to prepare a pigment dispersion with a concentration of 12%.

[Preparation Example 2]: Preparation of Ink A-1 obtained in Synthesis Example 1, the pigment dispersion obtained in Preparation Example 1, BYK-UV3510 (manufactured by BYK Chemie, polyether-modified polydimethylsiloxane), dipropylene glycol diacrylate (DPGDA), and stearyl alcohol (NAA-45 manufactured by NOF Corporation, hydroxyl value 210 mgKOH/g) were used and mixed so that the components in the ink were as shown in Table 1, and then impurities were filtered out using a 3 μm membrane filter, thereby obtaining the inkjet inks of Example 1 and Comparative Examples 1 and 2.

The inkjet inks of Example 1 and Comparative Examples 1 and 2 were subjected to the various tests shown below, and the results are shown in Table 1.

(Viscosity Measurement)
The viscosity was measured at 50° C. using an E-type viscometer (TV-22, manufactured by Toki Sangyo Co., Ltd.).

(Measurement of solidification start temperature)
Using a differential scanning calorimeter (DSC Q2000: manufactured by TA Instruments), the solidification start temperature was measured by holding the inkjet ink (2 mg) at 90° C. for 3 minutes and then cooling to −20° C. at 10° C./min. The measurement chart for Example 1 is shown in FIG. 2, and the measurement chart for Comparative Example 1 is shown in FIG. 3. The solidification start temperature of the ink of Example 1 was 36° C. No exothermic peak associated with solidification was observed for the ink of Comparative Example 1.

(image quality)
Using a micropipette, 20 μL droplets of inkjet ink were dropped from a height of 5 mm onto a glass substrate and a polyethylene terephthalate film (E5102: manufactured by Toyobo), and the spread of the droplets after 5 minutes was measured and used as the dot diameter. Each experiment was performed six times, and the average value was calculated. The experiments were performed in a laboratory set at 25° C., and the inks of Example 1 and Comparative Example 2 were preheated to 60° C. before use.

(Preparation of evaluation test pieces)
A 10 cm square glass plate was placed on a hot plate at 60° C., and the inkjet ink heated to 60° C. was applied to the glass plate to a thickness of 20 μm over an area of 8 cm square using a bar coater heated to 60° C. Next, electron beam curing was performed in an atmosphere with an oxygen concentration of 300 ppm under conditions of an acceleration voltage of 100 kV and a dose of 50 kGy to obtain a test piece.

(Abrasion resistance)
The prepared test pieces were rubbed reciprocally 10 times under a load of 300 g using a Gakushin type rub fastness tester RT-200 manufactured by Daiei Scientific Instruments Co., Ltd., and the cured surface was visually observed and evaluated according to the following criteria.
A: Almost no scratches were observed on the printed image.
B: Slight scratches were observed on the printed image.
C: Very large scratches were observed on the printed image.

(Adhesion)
Using the prepared test pieces, a 1 cm wide piece of Cellotape (registered trademark) was attached to a length of 5 cm on the cured surface, and after peeling off the Cellotape (registered trademark) surface was visually observed and evaluated according to the following evaluation criteria.
A: No printed matter adhered B: Slightly no printed matter adhered C: Printed matter adhered

(Solvent resistance)
The cured surface of the prepared test piece was rubbed with a cotton swab soaked in 95% ethanol, and evaluated according to the following criteria.
A: The cotton swab is not stained, and there are no rubbing marks on the surface of the printed material. B: The cotton swab is not stained, but there are faint rubbing marks on the surface of the printed material. C: The cotton swab is stained, and there are rubbing marks on the surface of the printed material.

(Migration property)
A 3 cm x 5 cm test piece was cut out from the prepared test piece using a laser cutter, and its weight (W1) was measured. This was left in refluxing methyl ethyl ketone for about 8 hours to extract the eluted components, and then dried at 80°C for 3 hours and at 120°C for 5 hours, and its weight (W2) was measured.
Weight reduction rate (%) = (W1-W2) x 100/W1
A: Weight loss rate is less than 2% B: Weight loss rate is 2% to less than 5% C: Weight loss rate is 5% or more

The ink of Example 1 achieved good results in all evaluations. On the other hand, the ink of Comparative Example 1, which does not contain component (A), does not have a solidification initiation temperature, and as a result, there were issues with image quality. The ink of Comparative Example 2, in which component (A) was changed to stearyl alcohol, resulted in issues with solvent resistance, migration, etc.

The electron beam curable inkjet ink of the present invention has low migration, excellent abrasion resistance and excellent image quality, and is expected to be a useful electron beam curable inkjet ink for food and pharmaceutical packaging.

Claims (6)

The composition comprises a polymerizable compound (A) having a long-chain alkyl group having from 6 to 30 carbon atoms in the molecule, a hydrogen-bonding group, and a polymerizable group, a polymerizable compound (B) other than the component (A), and a colorant (C),
the component (B) is one or more selected from neopentyl glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polytetramethylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, and ethylene oxide-modified trimethylolpropane triacrylate;
the weight loss rate calculated by the following formula (1) when the cured product is left in methyl ethyl ketone under reflux for 8 hours is less than 2%,
1. An electron beam curable inkjet ink comprising :
Weight reduction rate (%) = (W1-W2) x 100/W1...Formula (1) The electron beam curable inkjet ink according to claim 1, wherein the component (A) is a reaction product of an alcohol compound (a) having 12 to 30 carbon atoms and an isocyanate compound (b) having a (meth)acrylate group. The electron beam curable inkjet ink according to claim 1 or 2, wherein the content of component (A) in the total amount of the electron beam curable inkjet ink is 0.5 to 90% by weight. The electron beam curable inkjet ink according to any one of claims 1 to 3, wherein the solidification initiation temperature is 20°C or higher and lower than 100°C. A printed matter using the electron beam curable inkjet ink according to any one of claims 1 to 4. An image forming method comprising the following steps (Step 1) to (Step 3).
(Step 1) A step of heating the electron beam curable inkjet ink according to any one of claims 1 to 4 to a temperature equal to or higher than the ink solidification start temperature. (Step 2) A step of ejecting droplets of the electron beam curable inkjet ink according to any one of claims 1 to 4 from a nozzle of an ejection head and landing them on a substrate surface. (Step 3) A step of further irradiating the ink with an electron beam to cure it.

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