JP7608209B2 - Photocurable ink composition for ink-jet printing - Google Patents

Description

The present invention relates to a photocurable ink composition for inkjet printing. More specifically, the present invention relates to a photocurable ink composition for inkjet printing that has little odor, is less likely to cause banding, and provides a printed matter having excellent bending resistance and tackiness when printed on a substrate.

Conventionally, active energy ray curable inks have been developed that are low odor and have excellent bending resistance when printed on a substrate. Patent Document 1 discloses an active energy ray curable ink that contains a photopolymerization initiator and a diallyl phthalate resin.

Incidentally, active energy ray-curable inks containing alkyl 2-allyloxymethylacrylate are known (Patent Document 2).

JP 2016-210975 A JP 2019-2009 A

However, the ink compositions described in Patent Documents 1 and 2 all had insufficient odor relief, were prone to banding during printing, and were prone to cracking when printed on a substrate and folded, and also had insufficient tackiness.

The present invention has been made in consideration of such conventional problems, and aims to provide a photocurable ink composition for inkjet printing that has little odor, is less likely to cause banding, and when printed on a substrate, produces a printed product with excellent bending resistance and tackiness.

The present inventors conducted extensive research to solve the above problems, and discovered that a photocurable ink composition for inkjet printing containing a specific amount of 2-(allyloxymethyl)cyclohexyl acrylate, an acylphosphine oxide-based photopolymerization initiator, a multifunctional photopolymerizable compound, and a nitrogen-containing monofunctional photopolymerizable compound, in which the multifunctional photopolymerizable compound contains an amine-modified oligomer, can solve the above problems, leading to the completion of the present invention. The present invention, which solves the above problems, mainly comprises the following configurations.

(1) A photocurable ink composition for inkjet printing, comprising 5 to 50% by mass of 2-(allyloxymethyl)cyclohexyl acrylate, 5% by mass or more of an acylphosphine oxide-based photopolymerization initiator, 1 to 30% by mass of a multifunctional photopolymerizable compound, and 5 to 35% by mass of a nitrogen-containing monofunctional photopolymerizable compound, the multifunctional photopolymerizable compound including an amine-modified oligomer.

With this configuration, the photocurable ink composition for inkjet printing has little odor, is less prone to banding, has excellent curing properties, and when printed on a substrate, the resulting printed matter has excellent bending resistance and tackiness.

(2) The photocurable ink composition for inkjet printing according to (1), wherein the content of the 2-(allyloxymethyl)cyclohexyl acrylate is 5 to 35% by mass.

With this configuration, the photocurable ink composition for inkjet printing has less odor, is less prone to banding, and the resulting printed matter has better bending resistance and tackiness.

(3) The photocurable ink composition for inkjet printing according to (1) or (2), wherein the acylphosphine oxide photopolymerization initiator includes at least one selected from the group consisting of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

With this configuration, the photocurable inkjet printing ink has a low viscosity, and the resulting print has even better abrasion resistance.

(4) The photocurable ink composition for inkjet printing according to any one of (1) to (3), wherein the content of the amine-modified oligomer is 1.5 to 12% by mass.

With this configuration, the photocurable ink composition for inkjet printing has a relatively low viscosity and excellent curability.

(5) The photocurable ink composition for inkjet printing according to any one of (1) to (4), wherein the content of the multifunctional photopolymerizable compound is 10 to 30% by mass.

With this configuration, the photocurable ink composition for inkjet printing has even better abrasion resistance and tackiness.

(6) The photocurable ink composition for inkjet printing according to any one of (1) to (5), wherein the nitrogen-containing monofunctional photopolymerizable compound contains at least one selected from the group consisting of acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, and N,N-dimethylacrylamide, and the content of the nitrogen-containing monofunctional photopolymerizable compound is 10 to 25% by mass.

With this configuration, the photocurable ink composition for inkjet printing has even better tackiness and can reduce the ink viscosity.

According to the present invention, it is possible to provide a photocurable ink composition for inkjet printing that has little odor, is less likely to cause banding, and has excellent bending resistance and tackiness when printed on a substrate.

<Photocurable ink composition for inkjet printing>
A photocurable ink composition for inkjet printing (hereinafter also referred to as ink composition) according to one embodiment of the present invention contains 5 to 50 mass % of 2-(allyloxymethyl)cyclohexyl acrylate, 5 mass % or more of an acylphosphine oxide-based photopolymerization initiator, 1 to 30 mass % of a polyfunctional photopolymerizable compound, and 5 to 35 mass % of a nitrogen-containing monofunctional photopolymerizable compound. The polyfunctional photopolymerizable compound contains an amine-modified oligomer.

(Cyclohexyl 2-(allyloxymethyl)acrylate)
The content of 2-(allyloxymethyl)cyclohexyl acrylate in the ink composition may be 5% by mass or more, and preferably 10% by mass or more. The content of 2-(allyloxymethyl)cyclohexyl acrylate in the ink composition may be 50% by mass or less, and preferably 40% by mass or less, and more preferably 35% by mass or less. When the content of 2-(allyloxymethyl)cyclohexyl acrylate is within the above range, the ink composition has less odor, is less likely to cause banding, and the resulting printed matter has excellent folding resistance and tackiness. In particular, when the content of 2-(allyloxymethyl)cyclohexyl acrylate is 5 to 35% by mass, the ink composition has less odor, is less likely to cause banding, and the resulting printed matter has excellent folding resistance and tackiness.

(Acylphosphine oxide photopolymerization initiator)
The ink composition of the present embodiment contains 5% by mass or more of an acylphosphine oxide-based photopolymerization initiator. There is no particular limitation on the acylphosphine oxide-based photopolymerization initiator. Examples of the acylphosphine oxide-based photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, 2,6-dimethylbenzoyldimethylphosphine oxide, 4-methylbenzoyldiphenylphosphine oxide, 4-ethylbenzoyldiphenyl ... phenylphosphine oxide, 4-isopropylbenzoyldiphenylphosphine oxide, 1-methylcyclohexanoylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,3,3-trimethyl-pentylphosphine oxide, and the like, and preferably includes at least one selected from the group consisting of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. By containing at least one selected from the group consisting of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as the acylphosphine oxide photopolymerization initiator, the ink composition can obtain good curability.

The content of the acylphosphine oxide-based photopolymerization initiator in the ink composition may be 5% by mass or more, and preferably 6% by mass or more. The content of the acylphosphine oxide-based photopolymerization initiator in the ink composition is preferably 15% by mass or less, and more preferably 10% by mass or less. By having the content of the acylphosphine oxide-based photopolymerization initiator within the above range, the ink composition has a low viscosity, and the resulting printed matter has even better abrasion resistance.

(Polyfunctional photopolymerizable compound)
The ink composition of this embodiment contains 1 to 30% by mass of a polyfunctional photopolymerizable compound. The polyfunctional photopolymerizable compound may contain an amine-modified oligomer. By containing an amine-modified oligomer, The ink composition has excellent curing properties, is less susceptible to banding, has excellent tackiness, and provides printed matter with even better folding resistance.

The amine-modified oligomer is not particularly limited. For example, the amine-modified oligomer is a reactive oligomer having an amino group and a functional group that crosslinks or polymerizes by irradiation with actinic rays in the molecule, and is also called a reactive amine coinitiator, a reactive amine synergist, an acrylate-modified amine synergist, an amine acrylate, etc.

There are many commercially available amine-modified oligomers. By way of example, commercially available amine-modified oligomers include CN371, CN373, CN383, CN386, CN501, CN550, and CN551 manufactured by Sartomer; EBECRYL80 and EBECRYL7100 manufactured by Daicel Allnex; GENOMER 5142, GENOMER 5161, and GENOMER 5275 manufactured by RAHN; Miramer AS2010 and Miramer AS5142 manufactured by Miwon; and Etercure 641, Etercure 6410, Etercure 6411, Etercure 6412, Etercure 6413, Etercure 6414, and Etercure 6415 manufactured by Changxing Chemical Co., Ltd. 6417, Etercure 6420, Etercure 6422, Etercure 6423, Etercure 6425, Etercure 6430, Etercure 645, and Etercure 647, etc.

The amine-modified oligomer of this embodiment is preferably an acrylated amine compound such as CN371, CN373, CN383, or CN386 (manufactured by Sartomer), and more preferably CN371, CN386 (manufactured by Sartomer) or EBECRYL80 (manufactured by Daicel-Allnex), which have two or more photopolymerizable functional groups in the molecule. When an amine-modified oligomer is included, the content of the amine-modified oligomer in the ink composition is preferably 3% by mass or more, and more preferably 5% by mass or more. In addition, the content of the amine-modified oligomer in the ink composition is preferably 20% by mass or less, and more preferably 15% by mass or less.

The polyfunctional photopolymerizable compound other than the amine-modified oligomer is not particularly limited. As an example, the polyfunctional photopolymerizable compound other than the amine-modified oligomer is preferably a bifunctional monomer such as hexanediol diacrylate, or a trifunctional monomer such as alkoxy-modified trimethylolpropane triacrylate.

The content of the polyfunctional photopolymerizable compound in the ink composition may be 1% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. The content of the polyfunctional photopolymerizable compound in the ink composition may be 30% by mass or less, and more preferably 25% by mass or less. When the content of the polyfunctional photopolymerizable compound is within the above range, the ink composition has excellent tackiness and abrasion resistance. In particular, when the content of the polyfunctional photopolymerizable compound is 10 to 30% by mass, the ink composition has even more excellent abrasion resistance and tackiness.

The content of the amine-modified oligomer in the ink composition is preferably 1.5% by mass or more, and more preferably 3.0% by mass or more. The content of the amine-modified oligomer in the ink composition is preferably 12% by mass or less, and more preferably 10.0% by mass or less. When the content of the amine-modified oligomer is within the above range, the ink composition has a relatively low viscosity and excellent curability.

(Nitrogen-containing monofunctional photopolymerizable compound)
The ink composition of the present embodiment contains 5 to 35% by mass of a nitrogen-containing monofunctional photopolymerizable compound. The nitrogen-containing monofunctional photopolymerizable compound is not particularly limited. As an example, the nitrogen-containing monofunctional photopolymerizable compound is preferably acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, N,N-dimethylacrylamide, N,N-diethylacrylamide, or isopropylacrylamide, and more preferably at least one selected from the group consisting of acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, and N,N-dimethylacrylamide. By containing at least one selected from the group consisting of acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, and N,N-dimethylacrylamide, the ink composition has excellent tackiness and a relatively low viscosity.

The content of the nitrogen-containing monofunctional photopolymerizable compound in the ink composition may be 5% by mass or more, and preferably 10% by mass or more. The content of the nitrogen-containing monofunctional photopolymerizable compound in the ink composition may be 35% by mass or less, and preferably 25% by mass or less. By having the content of the nitrogen-containing monofunctional photopolymerizable compound within the above range, the ink composition has even better tackiness.

(Optional ingredients)
The ink composition of the present embodiment may further contain optional components in addition to the predetermined amounts of 2-(allyloxymethyl)cyclohexyl acrylate, acylphosphine oxide-based photopolymerization initiator, polyfunctional photopolymerizable compound, and nitrogen-containing monofunctional photopolymerizable compound. The optional components are not particularly limited. For example, the optional components are photopolymerizable compounds other than those described above, photopolymerization initiators other than those described above, sensitizers, additives, pigments, dispersants, etc.

Photopolymerizable Compounds Other Than the Above-mentioned Photopolymerizable compounds other than the above-mentioned that can be blended in the ink composition of the present embodiment are not particularly limited. Examples of the photopolymerizable compounds other than the above-mentioned include monofunctional acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, decyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, cyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, and benzyl acrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3-tetrafluoroethylene acrylate, and the like. Monofunctional halogen-containing acrylates such as trifluoropropyl acrylate, 1H-hexafluoroisopropyl acrylate, 1H,1H,5H-octafluoropentyl acrylate, 1H,1H,2H,2H-heptadecafluorodecyl acrylate, 2,6-dibromo-4-butylphenyl acrylate, 2,4,6-tribromophenoxyethyl acrylate, and 2,4,6-tribromophenol 3EO adduct acrylate, 2-methoxyethyl acrylate, 1,3-butylene glycol methyl ether acrylate, butoxyethyl acrylate, methoxytriethylene glycol acrylate, methoxypoly triethylene glycol #400 acrylate, methoxydipropylene glycol acrylate, methoxytripropylene glycol acrylate, methoxypolypropylene glycol acrylate, ethoxydiethylene glycol acrylate, ethyl carbitol acrylate, 2-ethylhexyl carbitol acrylate, tetrahydrofurfuryl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, cresyl polyethylene glycol acrylate, 2-(vinyloxyethoxy)ethyl acrylate, p-nonyl phenoxy monofunctional ether group-containing acrylates such as β-carboxyethyl acrylate, succinic acid monoacryloyloxyethyl ester, ω-carboxypolycaprolactone monoacrylate, 2-acryloyloxyethyl hydrogen phthalate, 2-acryloyloxypropyl hydrogen phthalate, 2-acryloyloxypropyl hexahydrohydrogen phthalate, 2-acryloyloxypropyl tetrahydrohydrogen phthalate, and the like.

When these photopolymerizable compounds are included, the content of the photopolymerizable compounds is not particularly limited. As an example, the content of the photopolymerizable compounds in the ink composition is preferably 5% by mass or more, and more preferably 20% by mass or more. Furthermore, the content of the photopolymerizable compounds in the ink composition is preferably 50% by mass or less, and more preferably 40% by mass or less.

Photopolymerization initiators other than those described above Photopolymerization initiators that may be blended in the ink composition of the present embodiment are not particularly limited. Examples of photopolymerization initiators other than those described above include 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyl dimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, and 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one.

When these photopolymerization initiators are included, the content of the photopolymerization initiator is not particularly limited. As an example, the content of the photopolymerization initiator in the ink composition is preferably 0.5% by mass or more. In addition, the content of the photopolymerization initiator in the ink composition is preferably 15% by mass or less, and more preferably 12% by mass or less.

Sensitizer The sensitizer is not particularly limited. For example, the sensitizer is preferably an anthracene-based sensitizer, a thioxanthone-based sensitizer, or the like, more preferably a thioxanthone-based sensitizer. Specifically, the sensitizer is an anthracene-based sensitizer such as 9,10-dibutoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, or 9,10-bis(2-ethylhexyloxy)anthracene, or a thioxanthone-based sensitizer such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, or 4-isopropylthioxanthone. Representative examples of commercially available products include DBA and DEA (manufactured by Kawasaki Chemical Industries, Ltd.) as anthracene-based sensitizers, and DETX and ITX (manufactured by Lambson) as thioxanthone-based sensitizers.

When a sensitizer is included, the content of the sensitizer is not particularly limited. For example, the content of the sensitizer in the ink composition is preferably 0.5% by mass or more, and more preferably 0.8% by mass or more. The content of the sensitizer in the ink composition is preferably 2.0% by mass or less, and more preferably 1.5% by mass or less. When the content of the sensitizer is within the above range, the ink composition has excellent curability and can suppress yellowing of the coating film.

In addition, when a thioxanthone-based sensitizer is included as a sensitizer, the ink composition is likely to change color to yellow. Therefore, since the ink composition has a yellowish hue compared to the color based on the pigment (original hue), it is preferable to appropriately determine the content of the thioxanthone-based sensitizer for each color. Specifically, in the white ink composition and the clear ink composition, which are easily affected by changes in color, it is preferable that the ink composition does not include a thioxanthone-based sensitizer as a sensitizer. In addition, since changes in hue are likely to be a problem in the magenta ink composition and the cyan ink composition, it is preferable to use a photosensitizer in a range that does not cause problems in hue. In addition, since the black ink composition and the yellow ink composition are less likely to affect the hue even if they change color, and have poorer photopolymerizability than other hues, it is preferable to use a thioxanthone-based sensitizer in combination as a photopolymerization initiator.

Additives The ink composition of the present embodiment may contain additives. The additives are not particularly limited. Examples of additives include surface conditioners, surfactants, plasticizers, polymerization inhibitors, UV absorbers, light stabilizers, and antioxidants.

The surface conditioner is not particularly limited. Examples of the surface conditioner include silicone-based surface conditioners, acrylic-based surface conditioners, vinyl-based surface conditioners, fluorine-based surface conditioners, and acetylene glycol-based surface conditioners.

When a surface conditioner is included, the content of the surface conditioner is not particularly limited. As an example, the content of the surface conditioner in the ink composition is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. The content of the surface conditioner in the ink composition is preferably 1.5% by mass or less, and more preferably 1% by mass or less. By having the content of the surface conditioner within the above range, the ink composition has excellent wettability to the substrate and improved abrasion resistance.

Pigment The ink composition of the present embodiment may contain a pigment. There are no particular limitations on the pigment. For example, the pigment may be any of various organic pigments and inorganic pigments.

Organic pigments include dye lake pigments, azo-based, benzimidazolone-based, phthalocyanine-based, quinacridone-based, anthraquinone-based, dioxazine-based, indigo-based, thioindigo-based, perylene-based, perinone-based, diketopyrrolopyrrole-based, isoindolinone-based, nitro-based, nitroso-based, anthraquinone-based, flavanthrone-based, quinophthalone-based, pyranthrone-based, and indanthrone-based pigments.

Inorganic pigments include colored pigments such as titanium oxide, red ocher, antimony red, cadmium yellow, cobalt blue, ultramarine, Prussian blue, iron black, chromium oxide green, carbon black, and graphite (including achromatic colored pigments such as white and black), and extender pigments such as calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc.

Specific examples of pigments for each representative hue of the ink composition of this embodiment are as follows. Yellow pigments are C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 42, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 108, 109, 114, 120, 128, 129, 138, 139, 150, 151, 155, 166, 180, 184, 185, 213, etc., and C.I. Pigment Yellow 150, 155, 180, 213, etc. are preferred.

The magenta pigment is C.I. Pigment Red 5, 7, 12, 19, 22, 38, 48:1, 48:2, 48:4, 49:1, 53:1, 57, 57:1, 63:1, 101, 102, 112, 122, 123, 144, 146, 149, 168, 177, 178, 179, 180, 184, 185, 190, 202, 209, 224, 242, 254, 255, 270, C.I. Pigment Violet 19, etc., and preferably C.I. Pigment Red 122, 202, Pigment Violet 19, etc.

Cyan pigments include C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 18, 22, 27, 29, 60, etc., and preferably C.I. Pigment Blue 15:4, etc.

Black pigments include carbon black (C.I. Pigment Black 7), etc.

The white pigment is titanium oxide, aluminum oxide, etc., and preferably titanium oxide that has been surface-treated with various materials such as alumina and silica.

When a pigment is included, the content of the pigment is not particularly limited. For example, the content of the pigment other than white in the ink composition is preferably 0.5% by mass or more, and more preferably 2.0% by mass or more. The content of the pigment other than white in the ink composition is preferably 10% by mass or less, and more preferably 7% by mass or less. On the other hand, the content of the white pigment in the ink composition is preferably 8% by mass or more, and more preferably 10% by mass or more. The content of the white pigment in the ink composition is preferably 18% by mass or less, and more preferably 15% by mass or less. When the content of the pigment is within the above range, the ink composition has excellent color reproducibility.

Dispersant The ink composition of the present embodiment may contain a dispersant. There is no particular limitation on the dispersant. Examples of the dispersant include polyvinyl alcohol, acrylic acid resins, styrene-acrylic acid resins, and vinyl acetate resins. Examples of the acrylic acid resins include polyacrylic acid, acrylic acid-acrylonitrile copolymers, and acrylic acid-acrylic acid alkyl ester copolymers.

When a dispersant is included, the content of the dispersant is not particularly limited. For example, the content of the dispersant is preferably 10% by mass or more, and more preferably 15% by mass or more, relative to 100% by mass of the pigment. The content of the dispersant is preferably 60% by mass or less, and more preferably 50% by mass or less, relative to 100% by mass of the pigment. When the content of the dispersant is within the above range, the ink composition has excellent dispersion stability.

Returning to the description of the ink composition as a whole, the ink composition of this embodiment preferably has a viscosity of 20.0 mPa·s or less at 25°C, and more preferably 15.0 mPa·s or less. The ink composition may contain a viscosity adjuster or the like as necessary. In this embodiment, the viscosity can be measured at 25°C using an E-type viscometer (RE100L type viscometer, manufactured by Toki Sangyo Co., Ltd.).

<Method of preparing ink composition>
The method for preparing the ink composition of the present embodiment is not particularly limited. For example, the ink composition may be prepared by dispersing and mixing using a dispersing machine such as a wet circulation mill, a bead mill, a ball mill, a sand mill, an attritor, a roll mill, a DCP mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a high-pressure homogenizer (such as a Microfluidizer, Nanomizer, Ultimizer, Genus PY, or DeBEE2000), or a pearl mill.

<Method of manufacturing printed matter>
Next, a method for producing a printed matter using the ink composition of this embodiment will be described.

The method for producing a printed matter of this embodiment includes a step of printing the ink composition described above onto a substrate using an inkjet method.

The substrate is not particularly limited. Examples of the substrate include resin substrates, paper, capsules, gels, metal foils, glass, wood, cloth, and the like. The ink composition of the present embodiment exhibits excellent bending resistance even when the substrate is folded after being printed on. Therefore, the ink composition is particularly suitable for use when the substrate is a substrate used for applications in which it is folded, such as a cardboard sheet.

When the substrate is a cardboard sheet such as a C liner or K liner, the ink composition may be applied directly to the cardboard sheet, or may be applied after providing a primer layer on the cardboard sheet or performing corona discharge treatment or the like. That is, in recent years, waste paper or recycled paper may be used for cardboard sheets in consideration of the environment. When a K liner is used as the cardboard sheet, the surface has rough unevenness, the color is unclear, and the ink has high permeability when printed. Therefore, when the ink composition is printed on the cardboard sheet, the brown color of the liner base paper, which is the base, is likely to cause a decrease in print quality. In particular, if the color of the base appears in the printed area, the inkjet image will look dull and the appearance of the printed matter may be impaired. In order to eliminate the above-mentioned unevenness, etc., a primer layer is appropriately provided on such cardboard sheets.

The primer layer is provided for the purpose of adjusting the whiteness and color of the liner paper that constitutes the cardboard sheet and increasing the whiteness of the base. The primer layer can be formed by applying a precoat agent that contains a pigment and an adhesive.

There is no particular limitation on the pigment. Examples of pigments include titanium dioxide (anatase, rutile), as well as extender pigments such as aluminum hydroxide, barium sulfate, calcium carbonate, amorphous silica, and clay. The content of the white pigment is preferably 20 to 85 parts by mass, and more preferably 20 to 80 parts by mass, per 100 parts by mass of the precoat agent.

In this embodiment, the binder resin used in the precoat agent for the cardboard is preferably an aqueous resin. The aqueous resin is preferably a natural resin, a synthetic resin, etc., and more preferably a starch derivative, casein, shellac, a polyvinyl alcohol derivative, an acrylic resin, or a maleic acid resin. More specifically, the aqueous resin is preferably an aqueous acrylic resin copolymerized with acrylic acid or methacrylic acid and its alkyl ester, or styrene as the main monomer component, an aqueous styrene-acrylic resin, an aqueous styrene-maleic acid resin, an aqueous styrene-acrylic acid-maleic acid resin, an aqueous polyurethane resin, an aqueous polyester resin, etc. The content of the binder resin is preferably 1 to 25 parts by mass, more preferably 1 to 15 parts by mass, per 100 parts by mass of the precoat agent.

The aqueous medium that can be used in the precoat agent of this embodiment is water or a mixture of water and a water-miscible solvent. The water-miscible solvent is a lower alcohol, a polyhydric alcohol, and an alkyl ether or alkyl ester thereof. Specifically, the water-miscible solvent is a lower alcohol such as methyl alcohol, ethyl alcohol, normal propyl alcohol, isopropyl alcohol, etc.; a polyhydric alcohol such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, glycerin, etc.; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoacetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monoacetate, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, etc.

In addition to the components listed above, the precoat used in this embodiment may contain various additives such as film-forming agents, pigment dispersants or pigment dispersing resins, antiblocking agents, wetting agents, viscosity adjusters, pH adjusters, defoamers, and general surfactants, as needed.

The method of producing a precoat agent using these various materials is not particularly limited. As an example, a typical method of producing a precoat agent is to mix and knead a white pigment, an aqueous binder resin, water, a water-miscible solvent if necessary, and a pigment dispersant or a pigment dispersing resin, and then add and mix additives, water, a water-miscible solvent if necessary, and the remaining specified materials.

The precoat agent of this embodiment can be easily obtained by mixing the required amounts of each of the above components and mixing and dispersing them using a high-speed mixer such as a homomixer or lab mixer, or a dispersing machine such as a three-roll mill or bead mill.

When a primer layer is provided, the thickness of the primer layer (amount of application of the precoat agent) is not particularly limited. The primer layer preferably has a solids application amount in the range of 0.1 to 5 g/ ^m2 . By having the thickness of the primer layer (amount of application of the precoat agent) within the above range, the whiteness and color of the corrugated board sheet can be easily adjusted appropriately.

Returning to the explanation of the ink composition, the method for curing the ink composition is not particularly limited. For example, the ink composition can be cured by irradiating it with light after being ejected onto a substrate. The light source for irradiating the light is not particularly limited. For example, the light source may be ultraviolet light, an electron beam, visible light, a light-emitting diode (LED), or the like.

Specifically, the ink composition is ejected onto a substrate by supplying the ink composition to a printer head of an inkjet printer and ejecting the ink composition from the printer head onto the substrate so that the coating has a thickness of 1 to 20 μm. The ink composition is exposed to light and cured (cured as an image) by irradiating the ink composition applied to the substrate as an image with light.

As described above, the ink composition of this embodiment has little odor, is less likely to cause banding, and when printed on a substrate, the resulting printed matter has excellent bending resistance and tackiness.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

The raw materials and preparation methods used are shown below.
2-(allyloxymethyl)cyclohexyl acrylate: AOMA-CH, manufactured by Nippon Shokubai Co., Ltd. 2-(allyloxymethyl)methyl acrylate: AOMA, manufactured by Nippon Shokubai Co., Ltd. (multifunctional photopolymerizable compound)
CN371: Amine-modified oligomer manufactured by Sartomer, EO(3)-modified trimethylolpropane triacrylate, PO(3)-modified trimethylolpropane triacrylate, hexanediol diacrylate (nitrogen-containing monofunctional photopolymerizable compound)
Acryloylmorpholine Vinylmethyloxazolidinone Vinylcaprolactam (other photopolymerizable compounds)
Isobornyl acrylate, benzyl acrylate, lauryl acrylate, ethyl carbitol acrylate (acylphosphine oxide photopolymerization initiator)
TPO: 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (manufactured by Lambson)
TPOL: ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide Omnirad 819: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resins B.V.)
(Other photopolymerization initiators)
Omnirad 184: 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins B.V.)
(Sensitizer)
DETX: 2,4-diethylthioxanthone (Lambson)
(Additives)
BYK-315N: Polyester-modified polymethylalkylsiloxane, solid content 25% by mass, solvent component: mixture of methoxypropyl acetate and phenoxyethanol in a mass ratio of 1/1 (manufactured by BYK-Chemie)
(Pigment)
PB15:4: Pigment Blue 15:4
PR122: Pigment Red 122
PY155: Pigment Yellow 155
PBk7: Pigment Black 7
(Dispersant)
SS32000: Solsperse 32000 (manufactured by Lubrizol)

(Photocurable ink composition for ink-jet printing)
The materials were mixed and stirred so as to obtain the composition (mass %) shown in Table 1, thereby obtaining photocurable ink compositions for ink-jet printing of Examples 1 to 11 and Comparative Examples 1 to 6.

(Substrate)
PET film: E5100, manufactured by Toyobo Co., Ltd. PVC plate: T938, manufactured by Takiron C.I. Co., Ltd.

<Evaluation of Photocurable Ink Composition for Inkjet Printing and Printed Matter>
The photocurable ink compositions for inkjet printing of Examples 1 to 11 and Comparative Examples 1 to 6 were evaluated for viscosity, coating odor, curability, bending resistance, banding, tackiness, and abrasion resistance according to the following evaluation methods and criteria. The results are shown in Table 1.

(Measurement of Viscosity of Photocurable Ink Composition for Inkjet Printing)
The viscosity of the photocurable ink composition for ink jet printing was measured using an E-type viscometer (RE100L type viscometer, manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25° C. and a rotor rotation speed of 20 rpm.

(Paint film odor)
The photocurable ink composition for ink-jet printing obtained in each of the Examples and Comparative Examples was applied to the surface of a PET film using a bar coater No. 6, and then irradiated with ultraviolet light to obtain a cured coating film.
The resulting cured coating film was cut to a size of 8 cm x 12 cm, placed in a 24 cm x 34 cm zipper bag, and left at 25°C for 1 hour. The bag was then opened and the odor at the opening was evaluated on the following 5-point scale.
5: No odor was detected.
4: A slight odor was detected.
3: Moderate odor was felt.
2: A strong odor was detected.
1: A very strong odor was felt.
Ten people performed the same evaluation, and the arithmetic mean value of the evaluation results was obtained.

(Curing property)
The photocurable ink composition for inkjet printing obtained in the Examples and Comparative Examples was printed on the surface of a PET film using a commercially available inkjet printer, and a cured coating film was obtained by irradiating with ultraviolet light at 1500 mJ/ ^cm2 . The obtained coating film was rubbed with a cotton swab, and the curability was evaluated based on the marks left and the touch according to the following evaluation criteria.
○: No marks or stickiness were left behind.
△: No marks were left, but there was some stickiness.
×: Marks were left behind and there was a lot of stickiness.

(Bending resistance)
The photocurable ink composition for ink-jet printing obtained in each of the Examples and Comparative Examples was applied to the surface of a PET film using a bar coater No. 12, and then irradiated with ultraviolet light to obtain a cured coating film.
The resulting coating film was folded 180 degrees and the state of the coating film was visually evaluated according to the following evaluation criteria.
A: No cracks were observed in the coating.
△: Slight cracking of the coating film.
×: The coating film was cracked.

(Banding)
The photocurable ink compositions for inkjet printing obtained in the Examples and Comparative Examples were printed on the surface of a PVC film using a commercially available inkjet printer, and the coating film cured by irradiation with ultraviolet light was measured for gloss at a measurement angle of 60° using a variable angle glossmeter (product name: GlossMeter VG7000, manufactured by Nippon Denshoku Industries Co., Ltd.), and evaluated according to the following evaluation criteria.
A: The measured value was 15.0 or more.
Δ: The measured value was 10.0 or more and less than 15.0.
×: The measured value was less than 10.0.

(tackiness)
The photocurable ink composition for ink-jet printing obtained in each of the Examples and Comparative Examples was applied to the surface of each of the two PET films using a bar coater No. 4, and then irradiated with ultraviolet light to obtain a cured coating film.
The two resulting cured coating films on the surfaces of the PET films were temporarily overlapped with each other, and after 30 seconds, they were peeled off by hand. The degree of sticking was evaluated according to the following evaluation criteria.
A: No tack was observed.
Δ: Slight tack was observed.
×: Tack was observed.

(Abrasion resistance)
The photocurable ink composition for inkjet printing obtained in the Examples and Comparative Examples was applied to the surface of a PVC plate (T938, manufactured by Takiron C.I. Co., Ltd.) using a bar coater No. 6, and then irradiated with ultraviolet light to obtain a cured coating film.
The resulting coating film was rubbed 100 times against a white bleached cloth using a Gakushin fastness tester at a load of 500 g and a speed of 60 rpm. The degree of peeling of the coating film and the degree of color transfer to the white bleached cloth were evaluated according to the following evaluation criteria.
◯: No color transfer occurred or color transfer occurred over less than 5% of the fabric area.
Δ: Color transfer occurred over 5% or more and less than 70% of the fabric area.
x: Color transfer occurred over 70% or more of the fabric area.

As shown in Table 1, the photocurable inkjet printing ink composition of the present invention has a low odor, excellent curing properties, is less likely to cause banding, and has excellent folding resistance and tackiness of the printed matter obtained when printed on a substrate. On the other hand, the photocurable inkjet printing ink composition of Comparative Example 1, which does not contain 2-(allyloxymethyl)cyclohexyl acrylate, has a strong odor and has poor results in folding resistance and tackiness. The photocurable inkjet printing ink composition of Comparative Example 2, which contains an excess of 2-(allyloxymethyl)cyclohexyl acrylate, has poor results in tackiness. The photocurable inkjet printing ink composition of Comparative Example 3, which contains 2-(allyloxymethyl)methyl acrylate instead of 2-(allyloxymethyl)cyclohexyl acrylate, has a strong odor. The photocurable inkjet printing ink composition of Comparative Example 4, which contains a low content of acylphosphine oxide-based photopolymerization initiator, has poor results in curing properties. The photocurable inkjet printing ink composition of Comparative Example 5, which does not contain an amine-modified oligomer, has poor results in curing properties and tackiness. The photocurable inkjet printing ink composition of Comparative Example 6, which does not contain a nitrogen-containing monofunctional photopolymerizable compound, showed poor curing results.

Claims (6)

Contains 5 to 50 mass % of cyclohexyl 2-(allyloxymethyl)acrylate;
Contains 5% by mass or more of an acylphosphine oxide-based photopolymerization initiator,
Contains 1 to 30% by mass of a multifunctional photopolymerizable compound;
Contains 5 to 35% by mass of a nitrogen-containing monofunctional photopolymerizable compound,
The photocurable ink composition for ink-jet printing, wherein the multifunctional photopolymerizable compound contains an amine-modified oligomer. The photocurable ink composition for inkjet printing according to claim 1, wherein the content of the 2-(allyloxymethyl)cyclohexyl acrylate is 5 to 35% by mass. The photocurable ink composition for inkjet printing according to claim 1 or 2, wherein the acylphosphine oxide photopolymerization initiator includes at least one selected from the group consisting of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, ethoxy(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. The photocurable ink composition for inkjet printing according to any one of claims 1 to 3, wherein the content of the amine-modified oligomer is 1.5 to 12 mass %. The photocurable ink composition for inkjet printing according to any one of claims 1 to 4, wherein the content of the multifunctional photopolymerizable compound is 10 to 30 mass %. the nitrogen-containing monofunctional photopolymerizable compound includes at least one selected from the group consisting of acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, and N,N-dimethylacrylamide;
6. The photocurable ink composition for ink-jet printing according to claim 1, wherein the content of the nitrogen-containing monofunctional photopolymerizable compound is 10 to 25% by mass.