JP7830561B2 - Electron beam curable offset printing ink composition - Google Patents

Description

This invention relates to an electron beam-curable offset printing ink composition and a laminate film using the same.

Active energy ray curing ink compositions harden when irradiated with energy rays such as ultraviolet light, fixing the image to the substrate. Active energy ray curing ink compositions generally have the advantage of being solvent-free and having a low environmental impact, but they may have lower image adhesion to the substrate surface.

On the other hand, offset printing, sometimes called planar printing, is a printing method that basically involves: 1) supplying ink and dampening solution to a plate (planar plate) wrapped around a plate cylinder. Ink (or an oil-water emulsion of ink and dampening solution) adheres to the areas corresponding to the image, and dampening solution adheres to the areas corresponding to the non-image areas; 2) transferring the ink (or the oil-water emulsion of ink and dampening solution) from the ink and dampening solution attached to the plate to a blanket wrapped around a blanket cylinder (offset process); and 3) transferring the ink (or the oil-water emulsion of ink and dampening solution) transferred to the blanket to the substrate (set process). Furthermore, if the ink is an active energy ray-curable ink composition, the ink composition transferred to the substrate is irradiated with active energy rays to cure it and fix the image to the substrate.

Here, the supply ratio of ink to dampening solution to the printing plate is variable depending on the image pattern (e.g., the proportion of the image area). When the supply ratio of ink to dampening solution changes, the emulsification state of the ink and dampening solution may change, or ink may adhere to areas corresponding to non-image areas. A change in the emulsification state of the ink and dampening solution makes ink transfer more difficult. Thus, in offset printing, problems such as deterioration of the printed image quality can occur depending on the supply ratio of ink to dampening solution (Patent Documents 1 and 2).

In offset printing, "water width" refers to the acceptable range of ink-to-dampening water supply ratios that yield good image quality in printed materials. In other words, a wider water width means it's easier to adjust the ink-to-dampening water supply ratio. Improving this water width (i.e., enhancing water width suitability) is one of the common challenges in offset printing ink compositions.

Several active energy ray curable ink compositions for offset printing have been proposed to date (Patent Documents 3-5). Patent Document 3 proposes using an active energy ray curable composition containing a polymerizable compound having a specific (meth)acryloyl group as an offset printing ink. Patent Document 4 describes that a composition containing an acid group-containing urethane (meth)acrylate resin and a metal complex can be used as a raw material for active energy ray curable printing inks, and that such inks can be suitably used for planar offset printing. Patent Document 5 proposes applying a white ink composition containing an acrylate compound-containing ink vehicle, a polyol adhesive composition, a photoinitiator, and a white colorant to digital offset printing.

Japanese Patent Publication No. 2010-229299 Patent No. 6971421 Japanese Patent Publication No. 2020-33465 International Publication No. 2019/17270 Japanese Patent Publication No. 2022-98468

As described above, several active energy ray-curable ink compositions for offset printing have been proposed; however, these proposed ink compositions sometimes failed to address the challenges of offset printing, particularly in ensuring sufficient "water width" suitability. Therefore, the present invention aims to provide an active energy ray (preferably electron beam)-curable ink composition for offset printing that possesses sufficient "water width" suitability. More preferably, the present invention provides an ink composition with high performance in various aspects as an active energy ray-curable ink composition, such as curability, adhesion to the substrate, and lamination suitability. An ink composition with high adhesion to the substrate is preferably used, for example, as an ink for front-side printing, and an ink composition with high lamination suitability can be preferably used, for example, as an ink for back-side printing.

In other words, the present invention relates to the following electron beam curable offset printing ink composition.
<1> An electron beam curable offset printing ink composition comprising a ketone resin (A), a (meth)acrylate compound (B), and an extender pigment (C), substantially free of a photopolymerization initiator, wherein the ketone resin (A) is a resin obtained by condensation of a ketone and formaldehyde, or a hydrogenated thereof.

Furthermore, the present invention preferably relates to the following electron beam curable offset printing ink compositions.
<2> The electron beam curable offset printing ink composition according to <1>, wherein the ketone comprises one or more selected from aromatic ketones, alicyclic ketones, and aliphatic ketones.
<3> The electron beam curable offset printing ink composition according to <1> or <2>, wherein the (meth)acrylate compound (B) comprises one or more polyfunctional (meth)acrylate compounds selected from the group consisting of alkylene oxide-modified trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, alkylene oxide-modified glycerin(meth)acrylate, soybean oil-modified acrylate, and urethane acrylate.
<4> The electron beam curable offset printing ink composition according to any one of <1> to <3>, wherein the content of the extender pigment (C) is 0.1 to 10% by mass with respect to the total mass of the ink composition.
<5> The electron beam curable offset printing ink composition according to any one of <1> to <4> above, wherein the extender pigment (C) comprises one or more selected from the group consisting of calcium carbonate, magnesium carbonate, and magnesium silicate, and silicon dioxide.

The electron beam-curable offset printing ink composition of the present invention can be used for the following applications.
<6> An electron beam curable offset printing ink composition according to any of <1> to <5> above, for use in surface printing.
<7> An electron beam curable offset printing ink composition according to any of <1> to <5> above, for lamination.

The present invention also relates to the following laminate film.
<8> A laminate film comprising a substrate, a printing layer, an adhesive layer, and a sealant layer in this order, wherein the printing layer is a cured layer of an electron beam curable offset printing ink composition as described in any of <1> to <5> above.

The electron beam-curable offset printing ink composition of the present invention can form an image on a substrate by printing it using an offset printing method and curing it with an electron beam. Furthermore, because the electron beam-curable offset printing ink composition of the present invention has high water-width compatibility in offset printing, it can form high-quality images even when offset printing conditions vary. More preferably, the electron beam-curable offset printing ink composition of the present invention has good lamination compatibility and can be preferably used, for example, as an ink for forming the printed layer in a laminate film.

[1. Electron beam curable offset printing ink composition]
The electron beam-curable offset printing ink composition of the present invention (the ink composition of the present invention) contains a ketone resin (A), a (meth)acrylate compound (B), and an extender pigment (C), and may contain any other components. However, it is preferable that the ink composition of the present invention substantially does not contain a photopolymerization initiator.

[1-1. Ketone resin (A)]
The ketone resin (A) contained in the ink composition of the present invention is a resin obtained by a condensation reaction between a ketone and formaldehyde, or by a hydrogenation reaction of said resin. The condensation reaction between a ketone and formaldehyde refers to a reaction in which formaldehyde is added to the α-carbon of a ketone, etc., causing the ketone to be converted to hydroxymethyl ( _-CH2OH ), and then the hydroxymethyl further attacks the α-carbon of another ketone, etc., resulting in a linkage with a methylene (-CH2-) chain. The conditions for the condensation reaction in the production of the ketone resin (A) are not particularly limited, and for example, it can be obtained by reacting a ketone and formaldehyde in the presence of an alkali.

The ketones subjected to the condensation reaction are not particularly limited as long as they can react with formaldehyde, and include aromatic ketones, alicyclic ketones, and aliphatic ketones, with aromatic ketones and alicyclic ketones being preferred.

Examples of aromatic ketones include acetophenone or its derivatives, benzophenone or its derivatives, methyl naphthyl ketone, propiophenone, and the like.

Examples of acetophenone derivatives include o-hydroxymethoxyacetophenone, m-hydroxymethoxyacetophenone, p-hydroxymethoxyacetophenone, o-aminoacetophenone, m-aminoacetophenone, p-aminoacetophenone, 2'-trifluoromethylacetophenone, 3'-trifluoromethylacetophenone, p-t-butylacetophenone, 4'-cyclohexylacetophenone, 2'-phenylacetophenone, 3-acetylbiphenyl, 4-acetylbiphenyl, 2'-(benzyloxy)acetophenone, 3-benzyloxyacetophenone, 4'-(benzyloxyacetophenone) This includes diluentyl acetophenone, 2'-fluoroacetophenone, 3'-fluoroacetophenone, 4'-fluoroacetophenone, 2'-bromoacetophenone, 3'-bromoacetophenone, 4'-bromoacetophenone, 3'-nitroacetophenone, 2'-iodoacetophenone, 3'-iodoacetophenone, 4-iodoacetophenone, p-nitroacetophenone, 2-bromoacetophenone, 2-hydroxy-1-phenylethonone, 2-phenylacetophenone, 2,2,2-trifluoroacetophenone, 4'-(imidazole-1-1yl)acetophenone, etc.

Examples of benzophenone derivatives include dihydroxybenzophenone, 2-methylbenzophenone, p-methylbenzophenone, 2-(trifluoromethyl)benzophenone, 3-(trifluoromethyl)benzophenone, 3,3'-bis(trifluoromethyl)benzophenone, 4,4'-di-tert-butylbenzophenone, 3-fluorobenzophenone, 3,3'-difluorobenzophenone, 4-fluorobenzophenone, 4,4'-difluorobenzophenone, 3-chlorobenzophenone, 2,2'-dichlorobenzophenone, 3,3'-dichlorobenzophenone, and p-chlorobenzophenone. This includes bromobenzophenone, 3-bromobenzophenone, 4-bromobenzophenone, 4,4'-dibromobenzophenone, 2-iodobenzophenone, 3-iodobenzophenone, 4-iodobenzophenone, 3-hydroxybenzophenone, p-hydroxybenzophenone, bis(4-hydroxy)benzophenone, 2-aminobenzophenone, 3-aminobenzophenone, 4-aminobenzophenone, 2-(molifornomethyl)benzophenone, 4-morpholinobenzophenone, p-nitrobenzophenone, 3,3'-dinitrobenzophenone, p-cyanobenzophenone, etc.

Examples of alicyclic ketones include compounds having a cyclopentanone skeleton, a cyclohexanone skeleton, and a cyclooctanone skeleton, which may be substituted with lower alkyl groups or halogen atoms. For example, alicyclic ketones having a cyclohexanone skeleton include cyclohexanone, 2-methylcyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone, 2-ethylcyclohexanone, 2-n-butylcyclohexanone, 3-n-butylcyclohexanone, 3-tert-butylcyclohexanone, 4-n-butylcyclohexanone, 4-sec-butylcyclohexanone, 4-tert-butylcyclohexanone, 2,6-dimethylcyclohexanone, 3,3,5-trimethylcyclohexanone, 2,4,6-trimethylcyclohexanone, 2-chlorocyclohexanone, 3-chlorocyclohexanone, 4-chlorocyclohexanone, 2-fluorocyclohexanone, 2-bromocyclohexanone, and 2-iodocyclohexanone.

Examples of aliphatic ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl methyl ketone, diethyl ketone, t-butyl methyl ketone, chloroacetone, 1,1,1-trifluoroacetone, 3-bromo-1,1,1-trifluoroacetone, hexafluoroacetone, hydroxyacetone, 2-cyclopentenyl-1-acetone, 1-(1-adamantyl)acetone, 1-(4-methylpiperazine-1-yl)acetone, 1-(1-piperidinyl)acetone, and 1-morpholine-4-ylacetone.

The ketone resin (A) may be a resin obtained by hydrogenating a resin that is a condensation reaction product of a ketone and formaldehyde. In this condensation reaction, the carbonyl group (-C(=O)-) derived from the ketone is reduced by the hydrogenation reaction to produce a hydroxyl group (-CH(-OH)-). Furthermore, the ketone resin (A) may be a resin obtained by hydrogenating the condensation reaction product and then crosslinking the hydroxyl groups via a linker.

The ketone resin (A) may be a commercially available resin. Examples of commercially available ketone resins (A) include the TEGO VARIPLUS series (VARIPLUS AP, SK, CA, TC, etc.) (EVONIK), K90 (Arakawa Chemical Industries), the Halon series (Halon 80, 110H, etc.) (Honshu Chemical Co.), and the Laropal series (Laropal A81, 101, K80, etc.) (BASF).

The content of ketone resin (A) in the ink composition of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the solid content ratio of the mass of the ink composition; on the other hand, it is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. Ketone resin (A) can improve the curability of the ink composition of the present invention, the adhesion of the ink composition to the substrate to be printed (especially resin film, etc.), and the lamination suitability, and further improve the offset printing suitability (especially the water-width suitability) of the ink composition of the present invention.

The ketone resin (A) preferably has a glass transition temperature (Tg) of 200°C or lower, more preferably 150°C or lower, and even more preferably 100°C or lower; on the other hand, it is preferably 30°C or higher. By keeping the glass transition temperature of the ketone resin below a certain level, the lamination suitability of the ink composition of the present invention can be improved.

The ketone resin (A) should have a hydroxyl value (mgKOH/g) of 0 or higher, preferably 1.0 or higher; however, it is preferably 500 or lower, more preferably 300 or lower, and even more preferably 100 or lower. Ketone resin (A) with a hydroxyl value below a certain level may easily improve the offset printing suitability (particularly water-width suitability) of the ink composition.

[1-2. (Meth)acrylate compounds (B)]
The (meth)acrylate compound (B) contained in the ink composition of the present invention may be any compound having a (meth)acrylate group that undergoes a curing reaction when irradiated with an electron beam. The (meth)acrylate group refers to a methacrylic group and/or an acrylic group. The (meth)acrylate compound (B) may have one or more (meth)acrylate groups, but it is preferable to have two or more (meth)acrylate groups, and more preferably to have two or three (meth)acrylate groups. Furthermore, the (meth)acrylate compound (B) may be a monomer or an oligomer.

Specific examples of monofunctional (meth)acrylate compounds (B) include ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, isoamyl (meth)acrylate, isodecyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycoside. This includes methyl (meth)acrylate, nonylphenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, diethylaminoethyl (meth)acrylate, nonylphenoxyethyl tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, etc.

Specific examples of polyfunctional (meth)acrylate compounds (B) include 1,4-butanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, ethylene glycol di(meth)acrylate, and diethylene glycol Di(meth)acrylates of dihydric alcohols such as di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; di(meth)acrylate of polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, tris(2-hydroxyethyl) isocyanurate di(meth)acrylate, and di(meth) diols obtained by adding 4 moles or more of ethylene oxide or propylene oxide to 1 mole of neopentyl glycol. Acrylates, di(meth)acrylates of diols obtained by adding 2 moles of ethylene oxide or propylene oxide to 1 mole of bisphenol A; poly(meth)acrylates of trivalent or higher polyhydric alcohols such as trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol poly(meth)acrylate; 3 moles of glycerin This includes poly(meth)acrylates of polyoxyalkylene polyols such as triol triacrylates obtained by adding 1 or more moles of ethylene oxide or propylene oxide, triol diacrylates or tri(meth)acrylates obtained by adding 3 or more moles of ethylene oxide or propylene oxide to 1 mole of trimethylolpropane, and di(meth)acrylates of diols obtained by adding 4 or more moles of ethylene oxide or propylene oxide to 1 mole of bisphenol A; and vegetable oil (e.g., soybean oil) epoxy acrylates.

Specific examples of oligomeric (meth)acrylate compounds (B) include amine-modified polyether acrylates, amine-modified epoxy acrylates, amine-modified aliphatic acrylates, amine-modified polyester acrylates, amino (meth)acrylates and other amine-modified acrylates, thiol-modified polyester acrylates, thiol (meth)acrylates and other thiol-modified acrylates, polyester (meth)acrylates, polyether (meth)acrylates, polyolefin (meth)acrylates, polystyrene (meth)acrylates, epoxy (meth)acrylates, urethane (meth)acrylates, and the like.

Preferably, at least a portion of (meth)acrylate compound (B) is a polyfunctional (meth)acrylate compound. For example, 50% or more by mass, more preferably 60% or more by mass, and even more preferably 80% or more by mass of (meth)acrylate compound (B) is a polyfunctional (meth)acrylate compound. Polyfunctional (meth)acrylate compounds can enhance the electron beam curability of the ink composition. Suitable examples of polyfunctional (meth)acrylate compounds include alkylene oxide-modified trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkylene oxide-modified glycerin (meth)acrylate, soybean oil-modified acrylate, urethane acrylate, and the like.

It is preferable that at least a portion of the (meth)acrylate compound (B) contained in the ink composition of the present invention is a compound with a low glass transition temperature (for example, 100°C or less, preferably 60°C or less). For example, 50% by mass or more, more preferably 60% by mass or more, of the (meth)acrylate compound (B) is a compound with a low glass transition temperature. A (meth)acrylate compound (B) with a low glass transition temperature can improve the lamination suitability of the ink composition. Examples of (meth)acrylate compounds (B) with a low glass transition temperature include di- or tri(meth)acrylates of triols obtained by adding 3 moles or more of ethylene oxide or propylene oxide to 1 mole of trimethylolpropane.

The content of (meth)acrylate compound (B) in the ink composition of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on the solid content ratio of the mass of the ink composition; on the other hand, it is preferably 65% by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less.

In the ink composition of the present invention, the total content of the ketone resin (A) and the (meth)acrylate compound (B) is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the mass of the ink composition; on the other hand, it is preferably 95% by mass or less, and even more preferably 85% by mass or less. Furthermore, the content ratio ((A):(B)) of the ketone resin (A) and the (meth)acrylate compound (B) in the ink composition of the present invention is preferably in the range of 1.0:0.5 to 1.0:15.0, more preferably in the range of 1.0:0.7 to 1.0:5.0, and even more preferably in the range of 1.0:1.0 to 1.0:2.0.

[1-3. Extender Pigments (C)]
The extender pigment (C) contained in the ink composition of the present invention is an inorganic fine particle, and examples of extender pigment (C) include titanium dioxide, graphite, zinc, lime carbonate powder, calcium carbonate, gypsum, clay, silica (silicon dioxide), diatomaceous earth, talc, kaolin, alumina white, barium sulfate, aluminum stearate, magnesium carbonate, magnesium silicate, barite powder, and glass beads.

The extender pigment (C) preferably contains a combination of calcium carbonate, magnesium carbonate, or magnesium silicate and silica (silicon dioxide). This combination of extender pigments can reduce the stringiness (tendency to string) of the ink composition.

The content of the extender pigment (C) in the ink composition of the present invention is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and even more preferably 3.0% by mass or more, relative to the mass of the ink composition; on the other hand, it is preferably 10% by mass or less.

The extender pigment (C) can adjust the rheological properties of the ink composition of the present invention. Furthermore, by localizing on the surface (outer surface) of the cured coating film formed by the ink composition of the present invention, the extender pigment (C) can prevent sticking of printed materials.

[1-4. Other optional components]
The ink composition of the present invention may contain any other components; examples of any other components include colorants, pigment dispersants, polymerization inhibitors, surfactants, solvents, waxes, ultraviolet absorbers, antibacterial agents, resins other than ketone resin (A), etc.

The coloring agent may be a coloring pigment or a dye. The coloring pigment may be an inorganic or organic pigment. Examples of inorganic pigments include colored pigments such as titanium dioxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, carbon black, and graphite, as well as extender pigments such as silica, calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc. Examples of organic pigments include soluble azo pigments, insoluble azo pigments, azo lake pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments. Examples of dyes include dye lakes such as basic reaction-type lakes and acid dye-type lakes, and nitro pigments.

The pigment dispersant may be a polymer-based dispersant. Preferably, the polymer-based pigment dispersant is a pigment dispersant containing basic groups. Examples of pigment dispersants containing basic groups include polymer-based pigment dispersants such as basic group-containing polyester-based pigment dispersants, basic group-containing acrylic-based pigment dispersants, basic group-containing urethane-based pigment dispersants, and basic group-containing carbodiimide-based pigment dispersants, as well as anionic surfactants. The polymer-based pigment dispersant is not particularly limited, but may be a linear polymer having a pigment-affinity moiety consisting of basic groups at least at the ends of the main chain (one or both ends) in a block or graft structure.

Polymerization inhibitors can prevent polymerization reactions from occurring during storage of the ink composition and suppress thickening of the ink composition. Examples of polymerization inhibitors include phenolic compounds (including quinone compounds) such as dibutylhydroxytoluene, tocopherol acetate, nitrosamine compounds, benzotriazole, and hindered amines; among these, quinone compounds and nitrosamine compounds are more preferably exemplified. The content ratio of the polymerization inhibitor in the ink composition is appropriately set depending on the type of polymerization inhibitor, but for example, in the case of quinone compounds, it may be about 0.3 to 2.0 parts by mass when the total curable component is 100 parts by mass.

Examples of surfactants include nonionic surfactants, cationic surfactants, anionic surfactants, and betaine surfactants. Specific examples of surfactants include silicone-based surfactants such as polyether-modified silicone oil, polyester-modified polydimethylsiloxane, and polyester-modified methylalkylpolysiloxane, as well as fluorine-based surfactants and acetylene-based surfactants. These surfactants can be used individually or in combination of two or more types.

The ink composition of the present invention is curable by electron beam irradiation and may or may not contain a polymerization initiator; in fact, it is preferable that it does not. Examples of polymerization initiators include acylphosphine oxide compounds, thioxanthone compounds, aromatic ketones, aromatic onium salt compounds, organic peroxides, thio compounds (such as compounds containing a thiophenyl group), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

The ink composition of the present invention may or may not contain a solvent such as water or an organic solvent, or it may contain a small amount of solvent (for example, 3% by mass or less relative to the mass of the ink composition).

[1-5. Physical Properties of Ink Compositions]
The viscosity of the ink composition of the present invention is preferably 100.0 Pa·s or less, and more preferably 1.0 Pa·s to 90.0 Pa·s. This viscosity may be the viscosity measured using a cone plate viscometer under conditions of 25°C and a shear rate of 100/s. If the viscosity is greater than the above value, the fluidity and transferability of the ink composition will decrease, which may reduce the stability of the ink composition supplied to the roller in offset printing and cause problems with print workability. Furthermore, if the viscosity is greater than the above value, the leveling ability of the ink composition transferred to the substrate to be printed will decrease, which may cause quality problems such as deterioration of gloss, and is therefore undesirable. In addition, as the viscosity of the ink composition increases, the tack value of the ink also increases, which may result in poor transfer to the substrate to be printed and may prevent stable print workability.

The ink composition of the present invention has the property of hardening when irradiated with an electron beam (curability). The degree of curability is not particularly limited, but it is preferable that, for example, when formed into a coating film, it hardens completely at an irradiation dose of 20 to 40 kGy.

[1-6. Method for manufacturing ink composition]
The ink composition of the present invention can be obtained by dissolving a ketone resin (A) in a (meth)acrylate compound (B), dispersing an extender pigment (C), and mixing in other optional components. The mixing method and the like are not particularly limited.

[2. Printing method of the present invention]
The printing method of the present invention comprises the steps of offset printing the ink composition of the present invention onto a substrate to be printed (offset printing step) and curing the offset printed coating film with an electron beam (curing step).

The substrate to be printed in the offset printing process is not particularly limited and may include resin substrates, metal substrates, paper substrates, etc. Examples of metals used in metal substrates include aluminum, zinc, copper, iron, tin, etc. Paper substrates may include synthetic paper, art paper, coated paper, cast paper, newsprint, resin-laminated paper, metal-metallized paper, metal oxide-metallized paper, etc.

Considering the effects of the present invention, such as improved adhesion to the substrate to be printed and improved lamination suitability, a resin substrate, particularly a resin film, is sometimes preferable. While there are no particular limitations on the resins constituting the resin substrate, examples include films or sheets of polyester resin (e.g., polyethylene terephthalate), acrylic resin, vinyl chloride resin, vinylidene chloride resin, polyvinyl alcohol, polyethylene, polypropylene, polyacrylonitrile, ethylene vinyl acetate copolymer, ethylene vinyl alcohol copolymer, ethylene methacrylic acid copolymer, nylon, polylactic acid, polycarbonate, cellophane, aluminum foil, and various other resins conventionally used as printing substrates. The resin film may be subjected to stretching (uniaxial stretching, biaxial stretching, etc.).

The offset printing process may be carried out in accordance with known printing methods, but for example, it may include: A) a step of supplying the ink composition and dampening solution of the present invention to the printing plate; B) a step of transferring the ink composition supplied to the plate to a blanket (offset step); and C) a step of fixing the ink composition transferred to the blanket to the substrate to be printed (set step).

The dampening solution supplied to the printing plate is a water-based solution, and may contain additional components. Examples of these additional components include pH adjusters, water-soluble organic solvents, chelating compounds, and water-soluble polymers.

In step A, which involves supplying the ink composition and dampening solution to the printing plate, for example, the ink composition can be supplied to the plate wrapped around the plate cylinder via an ink roller, and the dampening solution via a water roller. The plate has areas where the ink composition adheres (lipophilic image areas) and areas where the dampening solution adheres (hydrophilic non-image areas). The ink composition adheres to the image areas of the plate, and the adhering ink composition is often an emulsion of the ink composition and dampening solution (water-in-oil emulsion).

Furthermore, in the offset printing process, the supply ratio of ink composition to dampening water supplied to the printing plate is not constant but variable. When this supply ratio changes, the emulsification state of the emulsion in the ink composition adhering to the image area of the plate may change, and the ink composition may also adhere to the non-image areas of the plate. As a result, the quality of the image printed on the substrate may deteriorate. In contrast, the ink composition of the present invention exhibits minimal change in the emulsification state of the emulsion even when the supply ratio of ink composition to dampening water changes, and the ink composition is less likely to adhere to the non-image areas of the plate. While the mechanism is not limited, it can be considered that the high polarity of the ketone resin (A) contained in the ink composition of the present invention stabilizes the emulsification state with the dampening water.

The ink composition (or emulsion with dampening solution) adhering to the image area of the plate is transferred to the blanket (Step B). The dampening solution adhering to the non-image area of the plate is collected without being transferred to the blanket cylinder. Furthermore, the ink composition (or emulsion with dampening solution) transferred to the blanket is typically pressed against the substrate by the impression cylinder, fixing it to the substrate and forming a coating (Step C).

The coating film formed on the substrate by offset printing is cured by irradiation with an electron beam, becoming a cured film and fixing as an image. The acceleration voltage of the electron beam used for irradiation is preferably in the range of 80kV to 170kV, and more preferably in the range of 80kV to 110kV, in order to effectively suppress the penetration of the electron beam into the substrate and minimize damage to the substrate. Furthermore, the irradiation dose of the electron beam is preferably in the range of 20 to 40kGy to ensure reliable curing of the coating film while suppressing poor adhesion to the substrate due to excessive curing.

[3. Uses of Ink Compositions]
The ink composition of the present invention is printed on a substrate to be printed and cured to form a printed layer, thereby providing a printed material. The ink composition may be printed on the reverse side, on the front side, or in any other form.

When printing with an ink composition using the front side, the printed layer is exposed on the surface of the printed material, therefore high adhesion between the printed layer and the substrate is required. The printed layer obtained from the ink composition of the present invention exhibits high adhesion to the substrate, making it suitable for use in front-side printing. On the other hand, when printing with an ink composition using the back side, the printed material generally has a laminate layer covering the printed layer. Therefore, printed materials obtained by back-side printing require high laminate strength (the laminate layer is resistant to peeling). The printed layer obtained from the ink composition of the present invention can be strongly bonded to the laminate layer via an adhesive, making it suitable for use in back-side printing.

The mechanism by which the ink composition of the present invention improves the adhesion and lamination suitability of the printed layer is not particularly limited, but generally, ketone resins are also used as adhesive components, and it can be assumed that their adhesive function is being exhibited.

The ink composition of the present invention may also be used as an ink composition for lamination. That is, by fixing a cured product of the ink composition of the present invention onto a substrate film (the substrate to be printed) to form an image, applying an adhesive to cover the cured product to form an adhesive layer, and then laminating a sealant layer onto the adhesive layer, a laminate film (a laminated film containing, in this order, a substrate film, a cured product layer of the ink composition, an adhesive layer, and a sealant layer) can be obtained.

The substrate film, which is the printing substrate, is preferably made of resin, but is not particularly limited and can be selected according to the intended use of the resulting laminate film. The adhesive layer is a cured product of an adhesive composition, but the composition of the adhesive composition is not particularly limited. The sealant layer, which is arranged to cover the adhesive layer, is preferably made of resin, for example, polyolefin, but can be selected according to the intended use of the laminate film.

The sealant layer may be formed by dry lamination, solvent-free lamination, or extrusion lamination. In order to effectively exhibit the effects of the ink composition of the present invention (high adhesion to the substrate and high lamination suitability), it is sometimes preferable to form the sealant layer by the dry lamination method.

The laminate film obtained in this manner has the advantage of easily ensuring sufficient lamination strength because it exhibits high adhesion between the substrate to be printed and the cured ink composition layer, as well as high adhesion between the cured ink composition layer and the adhesive layer. Furthermore, the resulting laminate film can be used in a variety of applications, such as food packaging, lithium-ion battery pouches, building material sheets, and other lamination applications.

The present invention will be described in more detail below with reference to examples, but these examples are not intended to limit the scope of the present invention. The numerical values for the formulations shown in each table are in parts by mass.

[A. Preparation of electron beam curable offset printing ink composition]
The material components used to prepare the electron beam-curable offset printing ink compositions for each example and comparative example are shown below.

A-1. Resins (ketone resins and other resins)
• AP: Condensation resin of acetophenone and formaldehyde (product name "TEGO VARIPLUS AP (EVONIK)") Hydroxyl value 5 mg KOH/g
SK: Hydrogenated version of AP (product name "TEGO VARIPLUS SK (EVONIK)"), hydroxyl value 325 mg KOH/g
• CA: Condensation resin of cyclohexanone and formaldehyde (product name "TEGO VARIPLUS CA (EVONIK)") Hydroxyl value 110 mg KOH/g
TC: Condensation resin of cyclohexanone skeleton-containing ketone (3,3,5-trimethylcyclohexanone) and formaldehyde (product name "TEGO VARIPLUS TC (EVONIK)") Hydroxyl value ~10 mg KOH/g
• Daiso DAP A: Polymer of diallyl phthalate (product name "Daiso DAP A (Osaka Soda Co.)")
・VS-1063: Polystyrene, Mw=5,500 (Product name: "VS-1063 (Seiko PMC Company)")
• MSB: Sucrose benzoate (product name "MIRAMER SB (Miwon Co.)")

A-2. Polymerizable compounds ((meth)acrylate compounds)
• M3130: Triacrylate of the ethylene oxide 3-mol adduct of trimethylolpropane (product name "MIRAMER M3130 (Miwon Co.)")
• M3160: Triacrylate of a 6-mol ethylene oxide adduct of trimethylolpropane (product name "MIRAMER M3160 (Miwon Co.)")
• M3190: Triacrylate of a 9-mol ethylene oxide adduct of trimethylolpropane (product name "MIRAMER M3190 (Miwon Co.)")
• M340: Pentaerythritol triacrylate (product name "MIRAMER M340 (Miwon Co.)")
• M360: Triacrylate of a 3-mol propylene oxide adduct of trimethylolpropane (product name "MIRAMER M360 (Miwon Co.)")
• M320: Triacrylate of a 3-mol adduct of glycerin with propylene oxide (product name "MIRAMER M320 (Miwon Co.)")
PE310: Soybean oil epoxy acrylate (product name "MIRAMER PE310 (Miwon Co.)")
• PU5000: Aliphatic trifunctional acrylate (product name "MIRAMER PU5000 (Miwon Co.)")
• M170: Ethoxydiethylene glycol acrylate (product name "MIRAMER M170 (Miwon Co.)")
• M144: Phenol ethylene oxide modified acrylate (product name "MIRAMER M144 (Miwon Co.)")
• M1140: Isobornyl acrylate (product name "MIRAMER M1140 (Miwon Co.)")

A-3. Extender pigment T-DD: Calcium carbonate (product name "Hakuenka T-DD (Shiraishi Calcium Co.)")
• L-1: Talc (Product name "L-1 (Nippon Talc Co., Ltd.)")
CP-102: Silica (Product name: "Rheoroseal CP102 (Tokuyama Corporation)")

A-4. Others - Pigment MA-70 (Carbon Black, Product Name MA-70, Manufactured by Mitsubishi Chemical Corporation)
• Pigment dispersant Solspers 33000 (Basic functional group-containing copolymer, amine value 43.0 mg KOH/g, acid value 27 mg KOH/g, active ingredient 100% by mass, manufactured by Lubrizol Nippon Co., Ltd.)
• Polymerization inhibitor BHT (dibutylhydroxytoluene)

The active energy ray-curable printing ink compositions of the examples and comparative examples were obtained by blending each component to the composition (mass%) shown in Tables 1 to 3 and kneading the mixture in a three-roll mill.

[B. Evaluation of electron beam curable offset printing ink compositions]
The ink compositions of each example and comparative example were evaluated as shown in B-1 to B-5. The results are shown in Tables 1 to 3.

B-1. Water Width Suitability Printed materials were prepared on printing paper using the ink compositions of each example and comparative example, according to the following procedure and conditions.
• Printing press: Komori Corporation, full-size, single-sided, four-color press; Print rotation speed: 12,000 sph
• Printing plate: Fujifilm Global Graphic Systems Co., Ltd. XP-F (CTP plate) AM175 lines • Printing paper: Nippon Paper Industries Co., Ltd. OK Coat L

First, printing was started with the dampening solution flow rate dial set to 30. After printing 10,000 sheets, the dampening solution flow rate dial was reduced to 15 (the amount of dampening solution supplied was decreased). The ink stain density (OD value) in the blank areas (non-image areas) of the printed materials obtained when the dial value was reduced was measured, and the suitability of the water width was evaluated according to the following criteria.

5: Ink stain density of plain area is less than 0.01 4: Ink stain density of plain area is 0.01 or more and less than 0.05 3: Ink stain density of plain area is 0.05 or more and less than 0.1 2: Ink stain density of plain area is 0.1 or more and less than 0.2 1: Ink stain density of plain area is 0.2 or more

B-2. Density Stability Printed materials were prepared using the ink compositions of each example and comparative example under the same conditions as in B-1 above. However, the dampening water supply amount was changed in 10% increments between 10% and 60% (increasing the dampening water supply amount), and the print density (OD value) of the image area of the printed material obtained at each dampening water supply amount was measured. The dampening water supply amount represents the rotation speed (%) of the water roller. The rate of decrease in optical density (OD value) was calculated using the following formula.

5: The rate of decrease in concentration is 0%. 4: The rate of decrease in concentration is greater than 0% and 5% or less. 3: The rate of decrease in concentration is greater than 5% and 10% or less. 2: The rate of decrease in concentration is greater than 10% and 15% or less. 1: The rate of decrease in concentration is greater than 15%.

B-3. Curability Printed materials were prepared using the ink compositions of each example and comparative example under the same conditions as in B-1 above. However, electron beam irradiation (EB irradiation device; acceleration voltage 90 kV, irradiation dose 30 kGy) was repeated until the ink coating printed on the material cured, and the number of passes was counted. Curing of the ink coating was determined when the ink did not adhere when the coating was rubbed with a cotton swab.

5:1 pass, 4:2 pass, 3:3 pass, 2:4 pass, 1:5 or more passes.

B-4. Tape Adhesion 0.1 cc of the ink composition of each example and comparative example was taken and spread onto the following films using an RI spreading machine (two-part roll, manufactured by Akira Seisakusho Co., Ltd.) to form an ink coating. The ink coating was then irradiated with an electron beam (irradiated with an electron beam until the ink coating hardened, similar to the curing test in B-3 above) to obtain a cured film and a printed material.
• OPP: Stretched polypropylene film (product name "P2161 (Toyobo Co., Ltd.)")
MDOPE: Uniaxially oriented polyethylene film (JINDAL Co., Ltd.)
• OPA: Stretched nylon film (product name "Emblem ONM-15 (Unitika Corporation)") • PET: Polyethylene terephthalate film (product name "E-5102 (Toyobo Co., Ltd.)")

Cellophane tape (manufactured by Nichiban Co., Ltd., product name: Cellotape®) was applied to the cured surface of the obtained printed material and peeled off in one swift motion. The area of the peeled-off cured film was evaluated on a five-point scale according to the following criteria. Note that a smaller peeled area indicates better adhesion between the cured film and the resin film.

5: No peeling at all 4: Peeled hardened film covers more than 0% but less than or equal to 20% of the area 3: Peeled hardened film covers more than 20% but less than or equal to 50% of the area 2: Peeled hardened film covers more than 50% but less than or equal to 75% of the area 1: Peeled hardened film covers more than 75% of the area

B-5. Lamination Suitability In the same manner as in B-4, 0.1 cc of the ink composition of each example and comparative example was taken and spread onto each film using an RI color spreader (two-part roll, manufactured by Akira Seisakusho Co., Ltd.) to form an ink coating film. The ink coating film was then irradiated with an electron beam to obtain printed materials. An adhesive (Takelac A969V/Takenate A-5, manufactured by Mitsui Chemicals, Inc.) was applied to the cured film surface of the obtained printed materials in an amount equal to 3.5 g/ ^m² as solid content, and an unoriented polypropylene film ("GLC", manufactured by Mitsui Chemicals Tohcello Co., Ltd., 40 μm thick) was laminated using a dry laminating machine. The tensile strength of the obtained laminated film (laminate film) was measured using a tensile testing machine (Yasuda Seiki Seisakusho Co., Ltd.) at a measurement temperature of 25°C and a tensile speed of 200 mm/min.

5: Peel strength of 1.5 N/15 mm or more 4: Peel strength of 1.0 N/15 mm or more, and less than 1.5 N/15 mm 3: Peel strength of 0.5 N/15 mm or more, and less than 1.0 N/15 mm 2: Peel strength of 0.1 N/15 mm or more, and less than 0.5 N/15 mm 1: Peel strength of less than 0.1 N/15 mm

Comparative Examples 1-8 in Table 4 are ink compositions that do not contain ketone resin but contain other resins; however, in all cases, tape adhesion and lamination suitability are poor. In contrast, Examples 1-31 in Tables 1-3 are ink compositions that contain ketone resin, and they exhibit good tape adhesion and lamination suitability. Thus, it is clear that ketone resin imparts tape adhesion and lamination suitability to ink compositions.

Furthermore, Comparative Examples 2-8 in Table 3 all showed poor evaluations of water-to-liquid compatibility and also deteriorated in curability. In contrast, Examples 1-31 in Tables 1-3 show improvements in all aspects. Thus, it can be seen that ketone resins improve both the water-to-liquid compatibility and curability of ink compositions.

The ink compositions of Examples 22-24 (Table 3), which contained monofunctional compounds as polymerizable compounds, showed slightly reduced electron beam curability. In contrast, the ink compositions of Examples 1-21 (Tables 1 and 2), which also contained monofunctional compounds as polymerizable compounds, all exhibited sufficient electron beam curability. Thus, it is clear that including polyfunctional compounds is preferable to obtain electron beam curable ink compositions with high curability.

In Examples 25 and 26 (Table 3), where the content of polymerizable compound was low relative to the ketone resin (weight ratio "ketone resin:polymerizable compound" of 45:25), the curability by electron beam was slightly reduced. In Examples 1 to 21 (Tables 1 and 2), where the weight ratio "ketone resin:polymerizable compound" was 30:40, the curability by electron beam was sufficient. On the other hand, as the content of polymerizable compound relative to the ketone resin increased, the water-to-water compatibility and concentration stability of the ink composition decreased, and curability also tended to decline. Furthermore, the evaluation of adhesion and lamination suitability also deteriorated (see Examples 27 to 31 (Table 3)). Thus, the ratio of ketone resin to polymerizable compound can be appropriately set according to the physical properties required of the ink composition.

As can be seen from the comparison of Examples 1-4 (Table 1) and Examples 8-11 (Table 1), the inclusion of AP and TC among the ketone resins results in higher evaluations of water-to-water ratio suitability and concentration stability. Thus, it is suggested that including ketone resins with low hydroxyl values tends to improve water-to-water ratio suitability and concentration stability, although the mechanism of improvement is not particularly limited.

Furthermore, as shown in Examples 1 to 31, it can be seen that by arbitrarily combining multiple types of ketone resins and multiple types of polymerizable compounds, a sufficiently effective ink composition can be obtained.

The electron beam-curable offset printing ink composition of the present invention, when used as an offset printing ink, can print images with high adhesion to the substrate as high-quality images. Furthermore, the electron beam-curable offset printing ink composition of the present invention can be used for front-side printing, back-side printing, and other printing methods. For example, by using the electron beam-curable offset printing ink composition of the present invention as a laminating ink, a laminate film with high lamination strength can be obtained, and the resulting laminate film can be used for various applications.

Claims (7)

An electron beam curable offset printing ink composition comprising a ketone resin (A), a (meth)acrylate compound (B), and an extender pigment (C),
The electron beam curable offset printing ink composition contains no water or contains 3% by mass or less of water relative to the ink composition, and the electron beam curable offset printing ink composition may or may not contain a photopolymerization initiator.
The content of the extender pigment (C) is 0.1% by mass or more and 10% by mass or less based on the total mass of the ink composition.
The extender pigment (C) comprises one or more selected from the group consisting of calcium carbonate, magnesium carbonate, and magnesium silicate, and silicon dioxide.
The ketone resin (A) is a resin obtained by the condensation of ketone and formaldehyde, or a hydrogenated product thereof .
The mass content ratio of the ketone resin (A) to the (meth)acrylate compound (B), "ketone resin (A):(meth)acrylate compound (B)", is in the range of 1.0:0.5 to 1.0:2.0 .
Electron beam curable offset printing ink composition. The electron beam-curable offset printing ink composition according to claim 1, wherein the content of the extender pigment (C) is 1.0% by mass or more and 10% by mass or less, based on the total mass of the ink composition. The electron beam-curable offset printing ink composition according to claim 1 or 2, wherein the ketone comprises one or more selected from aromatic ketones, alicyclic ketones, and aliphatic ketones. The electron beam curable offset printing ink composition according to claim 1 or 2, wherein the (meth)acrylate compound (B) comprises one or more polyfunctional (meth)acrylate compounds selected from the group consisting of alkylene oxide-modified trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkylene oxide-modified glycerin(meth)acrylate, soybean oil-modified acrylate, and urethane acrylate. An electron beam-curable offset printing ink composition according to claim 1 or 2, for use in surface printing. An electron beam-curable offset printing ink composition according to claim 1 or 2, for use in lamination. A laminate film comprising a substrate, a printing layer, an adhesive layer, and a sealant layer in this order,
A laminate film in which the printing layer is a cured product layer of the electron beam curable offset printing ink composition described in claim 1 or 2.