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

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

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

The glass transition temperature of a homopolymer formed of the monofunctional polymerizable compound can be measured by the following method. First, a homopolymer having a weight-average molecular weight of 10,000 to 20,000 is produced using the monofunctional polymerizable compound. The glass transition temperature of the homopolymer is measured in conformity with the method described in JIS K 7121:2012. Specifically, the glass transition temperature is measured using a differential scanning calorimeter, such as “DSC-60” produced by Shimadzu Corporation. The above weight-average molecular weight is measured using gel permeation chromatography (GPC). For example, “HLC-8220GPC” produced by Tosoh Corporation is used for GPC, three “TSKgel SuperMultipore HZ-H” columns produced by Tosoh Corporation (4.6 mmID×15 cm) are used as columns, and tetrahydrofuran (THF) is used as an eluant. As for measurement conditions, the sample concentration is set to 0.45% by mass, the flow rate is set to 0.35 ml/min, the sample injection volume is set to 10 μl, and the measurement temperature is set to 40° C. A refractive index (RI) detector is used for detection. Calibration curves are prepared using the eight samples as reference samples: “TSK standard polystyrene F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, “A-2500”, and “A-1000” and “n-propylbenzene” produced by Tosoh Corporation. While the glass transition temperature of the homopolymer varies by the weight-average molecular weight of the homopolymer, the variations are negligibly small when the weight-average molecular weight is 10,000 to 20,000.

The molecular weight of the monofunctional polymerizable compound capable of forming a homopolymer having a Tg of −30° C. to 30° C. is preferably 1,000 or less and is more preferably 500 or less. When the above molecular weight is 1,000 or less, an image having further high flexibility and further high blocking resistance may be recorded.

The monofunctional polymerizable compound capable of forming a homopolymer having a Tg of −30° C. to 30° C. is preferably a monofunctional acrylate in consideration of curability. Examples of the monofunctional acrylate capable of forming a homopolymer having a Tg of −30° C. to 30° C. include benzyl acrylate (6° C.), cyclohexyl acrylate (15° C.), 2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate (−7° C.), tetrahydrofurfuryl acrylate (−15° C.), lauryl acrylate (−30° C.), 3,3,5-trimethylcyclohexyl acrylate (−29° C.), phenoxyethyl acrylate (5° C.), and 2-acryloyloxyethylsuccinic acid (17° C.), where the temperatures in the parentheses are the Tg's of homopolymers of the respective monofunctional acrylates.

The monofunctional polymerizable compound capable of forming a homopolymer having a Tg of −30° C. to 30° C. is particularly preferably phenoxyethyl acrylate in order to further enhance the flexibility of the image.

Compound Selected from Group Consisting of Difunctional (Meth)acrylate and Polymerizable Silicone-Based Surfactant

The ink according to an exemplary embodiment of the present disclosure includes a compound selected from the group consisting of a difunctional (meth)acrylate and a polymerizable silicone-based surfactant. The ink may include only the difunctional (meth)acrylate, only the polymerizable silicone-based surfactant, or both difunctional (meth)acrylate and polymerizable silicone-based surfactant. The blocking resistance of the image may be enhanced in either case. It is particularly preferable that the ink include the polymerizable silicone-based surfactant in order to further enhance blocking resistance.

Difunctional (Meth)acrylate

The difunctional (meth)acrylate is a compound having two (meth)acryloyl groups. The difunctional (meth)acrylate may be any of a compound having two acryloyl groups, a compound having two methacryloyl groups, and a compound having an acryloyl group and a methacryloyl group. In the present disclosure, it is considered that the difunctional (meth)acrylate does not include a silicone structure. Thus, in the present disclosure, the difunctional (meth)acrylate is distinguished from the polymerizable silicone-based surfactant. Thus, a silicone-based surfactant having two acryloyl groups is considered as a polymerizable silicone-based surfactant.

Examples of the difunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, hexanediol di(meth)acrylate, heptanediol di(meth)acrylate, EO-modified neopentyl glycol di(meth)acrylate, PO-modified neopentyl glycol di(meth)acrylate, EO-modified hexanediol di(meth)acrylate, PO-modified hexanediol di(meth)acrylate, octanediol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, dodecanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, and tricyclodecanedimethanol di(meth)acrylate.

The number of carbon atoms included in the difunctional (meth)acrylate excluding the (meth)acryloyl group-portion is preferably 4 to 36 and is more preferably 5 to 15. When the number of the above carbon atoms is 4 or more, the flexibility of the image may be enhanced. When the number of the above carbon atoms is 36 or less, an increase in the viscosity of the ink is limited and the blocking resistance of the image may be enhanced.

Polymerizable Silicone-Based Surfactant

In the present disclosure, the term “polymerizable silicone-based surfactant” refers to a silicone-based surfactant having a polymerizable group.

The polymerizable group included in the polymerizable silicone-based surfactant may be a cationic polymerizable group or a radical polymerizable group. In consideration of curability, the above polymerizable group is preferably a radical polymerizable group. The radical polymerizable group is preferably an ethylenic unsaturated group in consideration of curability. In particular, the polymerizable group included in the polymerizable surfactant is preferably a vinyl group or a (meth)acryloyl group. The polymerizable group is more preferably a (meth)acryloyl group in consideration of curability.

The number of the polymerizable groups included in the polymerizable surfactant is preferably two or more in consideration of blocking resistance. The upper limit for the number of the polymerizable groups included in the polymerizable surfactant is, for example, but not limited to, five in consideration of discharge performance with which the ink is ejected by ink jet recording.

That is, as for the types and number of the polymerizable groups, the polymerizable silicone-based surfactant is preferably a silicone-based surfactant having two or more (meth)acryloyl groups.

Examples of the polymerizable silicone-based surfactant include a compound formed as a result of the above polymerizable groups being bonded to the backbone or side chain of polyether-modified dimethylsiloxane.

Examples of commercial products of the polymerizable silicone-based surfactant include silicone-based surfactants having a (meth)acryloyl group, such as BYK-UV3500, 3505, 3530, 3570, 3575, and 3576 produced by BYK, Tegorad 2100, 2200, 2250, 2300, 2500, 2600, 2700, 2800, 2010, and 2011 produced by Evonik Industries AG, EBECRYL 350 and 1360 produced by Daicel-Allnex Ltd., and KP-410, 411, 412, 413, 414, 415, 416, 418, 420, 422, and 423 produced by Shin-Etsu Chemical Co., Ltd.

The total content of the compound selected from the group consisting of the difunctional (meth)acrylate and the polymerizable silicone-based surfactant in the ink is 0.1% to 2% by mass, is preferably 0.5% to 1.8% by mass, and is further preferably 1.0% to 1.5% by mass of the total amount of the polymerizable compound. When the above total content is 0.1% by mass or more, an image having excellent blocking resistance may be produced. When the above total content is 2% by mass or less, an image having excellent flexibility may be produced.

Other Polymerizable Compound

The ink according to an exemplary embodiment of the present disclosure may include a polymerizable compound other than the N-vinyl compound, the monofunctional polymerizable compound capable of forming a homopolymer having a Tg of −30° C. to 30° C., or the compound selected from the group consisting of a difunctional (meth)acrylate and a polymerizable silicone-based surfactant.

Examples of the other polymerizable compound include a monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature (Tg) of less than −30° C. and a monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature (Tg) of more than 30° C. The method for measuring Tg is as described above.

Examples of the monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature of less than −30° C. and the monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature of more than 30° C. include the monofunctional polymerizable compounds which are described above as specific examples of the monofunctional polymerizable compound and which have a Tg of less than −30° C. or more than 30° C.

The total content of the monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature of less than −30° C. and the monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature of more than 30° C. (excluding the content of the N-vinyl compound) is 10% by mass or less and is preferably 5% by mass or less of the total amount of the polymerizable compound. The lower limit for the above total content is, for example, but not limited to, 0% by mass. When the above total content is 10% by mass or less, an image having excellent flexibility may be formed.

Examples of the other polymerizable compound also include a multifunctional polymerizable compound other than the difunctional (meth)acrylate.

The multifunctional polymerizable compound is not limited and may be any compound having two or more polymerizable groups. The multifunctional polymerizable compound is preferably a multifunctional radical-polymerizable compound and is more preferably a multifunctional ethylenic unsaturated compound in consideration of curability.

Examples of the multifunctional ethylenic unsaturated compound other than the difunctional (meth)acrylate include (meth)acrylates having three or more functional groups and multifunctional vinyl ethers having two or more functional groups.

Examples of the (meth)acrylates having three or more functional groups include trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-adduct tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tri(meth)acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly(meth)acrylate, and tris(2-acryloyloxyethyl) isocyanurate.

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

The total content of the above multifunctional polymerizable compounds other than the difunctional acrylate is preferably 10% by mass or less and is more preferably 5% by mass or less of the total amount of the polymerizable compound. The lower limit for the total content is not set and is, for example, 0% by mass. When the above total content is 10% by mass or less, the flexibility of the image may be enhanced.

Colorant

The ink according to an exemplary embodiment of the present disclosure includes a colorant. The ink may include only one type of a colorant or two or more types of inks.

Examples of the colorant include a dye and a pigment. The colorant is preferably a pigment in consideration of durability properties, such as heat resistance, light resistance, and water resistance.

In the case where a pigment is used as a colorant, the pigment may be added to the ink in the form of a pigment dispersion liquid. The pigment dispersion liquid is a liquid produced by dispersing a pigment in a liquid medium using a dispersing agent and includes at least a pigment, a dispersing agent, and a liquid medium. Details of the dispersing agent are described below. The liquid medium may be an organic solvent or a polymerizable compound.

Both organic and inorganic pigments that are commonly commercially available may be used as a pigment. Examples of the pigment include the pigments described in “Encyclopedia of Pigments” edited by Seishiro Ito, published in 2000, “Industrial Organic Pigments” by W. Herbst, K. Hunger, JP2002-12607A, JP2002-188025A, JP2003-26978A, and JP2003-342503A.

The content of the colorant is preferably 0.5% to 15% by mass and is more preferably 1% to 10% by mass of the total amount of the ink.

Dispersing Agent

In the case where a pigment is used as a colorant, the pigment can be added to the ink in the form of a pigment dispersion liquid. The pigment can be dispersed in a liquid medium using a dispersing agent. Publicly known dispersing agents may be used. The dispersing agent is preferably a compound having both hydrophilic and hydrophobic structures in consideration of dispersion stability.

Examples of the dispersing agent include low-molecular-weight dispersing agents having a molecular weight of less than 1,000, such as a higher fatty acid salt, an alkyl sulfate, an alkyl ester sulfate, an alkyl sulfonic acid salt, a sulfosuccinic acid salt, a naphthalenesulfonic acid salt, an alkyl phosphate, a polyoxyalkylene alkyl ether phosphate, a polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, a glycerin fatty acid ester, a sorbitan fatty acid ester, a polyoxyethylene fatty acid amide, and amine oxide.

Examples of the dispersing agent also include high-molecular-weight dispersing agents having a weight-average molecular weight of 10,000 or more which are produced by copolymerization of hydrophilic and hydrophobic monomers. The weight-average molecular weight can be determined by the same method as described above. The hydrophilic monomer is preferably a dissociative group-containing monomer and is preferably a dissociative group-containing monomer having a dissociative group and an ethylenic unsaturated bond in consideration of dispersion stability. Examples of the dissociative group-containing monomer include a carboxyl group-containing monomer, a sulfonic group-containing monomer, and a phosphate group-containing monomer. The hydrophobic monomer is preferably an aromatic group-containing monomer having an aromatic group and an ethylenic unsaturated bond or an aliphatic hydrocarbon group-containing monomer having an aliphatic hydrocarbon group and an ethylenic unsaturated bond in consideration of dispersion stability. The polymer may be either a random or block copolymer.

The dispersing agent may be a commercial one. Examples of commercial dispersing agents include:

DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-110, DISPERBYK-111, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, and DISPERBYK-182 (the above are produced by BYK Chemie); and

SOLSPERSE 3000, SOLSPERSE 5000, SOLSPERSE 9000, SOLSPERSE 12000, SOLSPERSE 13240, SOLSPERSE 13940, SOLSPERSE 17000, SOLSPERSE 22000, SOLSPERSE 24000, SOLSPERSE 26000, SOLSPERSE 28000, SOLSPERSE 32000, SOLSPERSE 36000, SOLSPERSE 39000, SOLSPERSE 41000, and SOLSPERSE 71000 (the above are produced by The Lubrizol Corporation).

For dispersing the pigment, publicly known dispersing device can be used. Examples thereof include a ball mill, a sand mill, a bead mill, a roll mill, a jet mill, Paint Shaker, Attritor, an ultrasonic disperser, and Disper.

The ratio of the content of the dispersing agent in the ink relative to the content of the pigment in the ink is preferably 0.05 to 1.0 by mass in consideration of dispersion stability.

Polymerization Initiator

The ink according to an exemplary embodiment of the present disclosure may include at least one polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator that generates radicals.

Examples of the radical polymerization initiator include a light radical polymerization initiator and a thermal radical polymerization initiator. Examples thereof include an alkylphenone compound, an acylphosphine compound, an aromatic onium salt compound, an organic peroxide, a thio compound, a hexaarylbiimidazole compound, a ketoxime ester compound, a borate compound, an azinium compound, a metallocene compound, an active ester compound, a compound having a carbon-halogen bond, and an alkylamine compound.

In particular, the polymerization initiator is preferably at least one selected from the group consisting of an acylphosphine compound and a thio compound and is preferably at least one selected from the group consisting of an acylphosphine oxide compound and a thioxanthone compound.

Examples of the acylphosphine oxide compound include a monoacylphosphine oxide compound and a bisacylphosphine oxide compound.

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

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

Among these, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (e.g., “Omnirad TPO-H” produced by IGM Resins B.V.) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (e.g., “Omnirad 819” produced by IGM Resins B.V.) are preferable as an acylphosphine oxide compound.

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

The thioxanthone compound may be a commercial one. Examples of the commercial product include SPEEDCURE series produced by Lambson, such as SPEEDCURE 7010, SPEEDCURE CPTX, and SPEEDCURE ITX.

The content of the polymerization initiator is preferably 2% by mass or more and is more preferably 5% by mass or more of the total amount of the ink in order to enhance curability. The upper limit for the content of the polymerization initiator is, for example, but not limited to, 15% by mass.

Polymerization Inhibitor

The ink according to an exemplary embodiment of the present disclosure preferably includes at least one type of a polymerization inhibitor.

Examples of the polymerization inhibitor include a hydroquinone compound, phenothiazine, a catechol, an alkylphenol, an alkylbisphenol, zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionic acid ester, mercaptobenzimidazole, a phosphite, a nitrosamine compound, a hindered amine compound, and nitroxyl radicals.

In particular, the polymerization inhibitor is further preferably a nitrosamine compound.

Examples of the nitrosamine compound include an N-nitroso-N-phenylhydroxylamine aluminum salt and N-nitroso-N-phenylhydroxylamine. In particular, the nitrosamine compound is preferably an N-nitroso-N-phenylhydroxylamine aluminum salt.

The content of the polymerization inhibitor is preferably 0.05% to 1.0% by mass of the total amount of the ink in order to enhance the temporal stability of the ink.

Additive

The ink according to an exemplary embodiment of the present disclosure may optionally include the following additives as needed: a resin, a cosensitizer, an ultraviolet absorber, an antioxidant, an antifade agent, a conductive salt, a solvent, a basic compound, and the like.

The viscosity of the ink is preferably 0.5 to 50 mPa·s, is more preferably 5 to 40 mPa·s, is preferably 7 to 35 mPa·s, and is further preferably 8 to 30 mPa·s. The above viscosity is measured at 25° C. with a viscometer. Examples of the viscometer that can be used include a viscometer “TV-22” produced by Toki Sangyo Co., Ltd.

The surface tension of the ink is preferably 60 mN/m or less, is more preferably 20 to 50 mN/m, and is further preferably 25 to 45 mN/m. The above surface tension is measured by a Wilhelmy plate method at 25° C. with a surface tensiometer. Examples of the surface tensiometer that can be used include an automatic surface tensiometer “DY-300” produced by Kyowa Interface Science Co., Ltd.

Ink Set

An ink set according to an exemplary embodiment of the present disclosure preferably includes the above-described ink and a pretreatment liquid. The pretreatment liquid is a liquid applied to a substrate before the ink is applied to the substrate. Applying the pretreatment liquid to the substrate before the application of the ink enhances flexibility under repeated folding and bending.

First Aspect

In the first aspect, the pretreatment liquid preferably includes a polymerizable compound and a polyester resin. When the pretreatment liquid includes a polyester resin, adhesiveness to the substrate is increased. This is because the polyester resin reduces the likelihood of a residual stress being generated due to the shrinkage on curing.

Polyester Resin

A polyester resin is a polymer including a backbone having ester linkages. A polyester resin is commonly produced by the reaction of a dicarboxylic acid with a polyol. Examples of the dicarboxylic acid include fumaric acid, itaconic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, sulfoisophthalic acid, naphthalenedicarboxylic acid, tetrahydrophthalic acid, and cyclohexanedicarboxylic acid. Examples of the polyol include ethylene glycol, propylene glycol, glycerin, hexanetriol, butanediol, hexanediol, 1,4-cyclohexanedimethanol, bisphenol A, and hydrogenated bisphenol A.

In particular, the polyester resin is preferably a polyester resin produced by the reaction of a dicarboxylic acid having a ring structure with a polyol having a ring structure. Examples of such a polyester resin include “DIACRON FC1588” produced by Mitsubishi Chemical Corporation, “Nichigo-POLYESTER TP219” produced by Mitsubishi Chemical Corporation, “UVAD081” produced by Osaka Soda Co., Ltd., and “DIACRON ER-535” produced by Mitsubishi Chemical Corporation.

The polyester resins and raw materials for the polyester resins are described in, for example, “Handbook of Polyester Resin” (Eiichiro Takiyama, The Nikkan Kogyo Shimbun, Ltd., Showa 63 (1988)).

Examples of the polyester resin include polyesters, such as polyhydroxybutyrate (PHB), polycaprolactone (PCL), polycaprolactone butylene succinate, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene succinate carbonate, polyethylene terephthalate succinate, polybutylene adipate terephthalate, polytetramethylene adipate terephthalate, polybutylene adipate terephthalate, polyethylene succinate (PES), polyglycolic acid (PGA), and polylactic acid (PLA); carbonate copolymers of aliphatic polyesters; and copolymers of aliphatic polyesters with polyamides.

The weight-average molecular weight of the polyester resin is, for example, 1,500 to 10,000. The above weight-average molecular weight is determined by the same method as described above.

The content of the polyester resin is preferably 0.5% to 15% by mass and is more preferably 1% to 10% by mass of the total amount of the pretreatment liquid.

Polymerizable Compound

The polymerizable compound included in the pretreatment liquid is not limited and may be a monofunctional or multifunctional polymerizable compound. Examples of the monofunctional and multifunctional polymerizable compounds are the same as those of the monofunctional and multifunctional polymerizable compounds that can be included in the above-described ink.

In order to further increase the adhesiveness between the substrate and the image, the proportion of the monofunctional polymerizable compound to the polymerizable compounds included in the pretreatment liquid is preferably 80% by mass or more and is more preferably 90% by mass or more. The upper limit for the above proportion is not set and may be 100% by mass.

In order to reduce odors, the polymerizable compound included in the pretreatment liquid is preferably a monofunctional polymerizable compound including at least one structure selected from the group consisting of a cyclic ether structure and an alicyclic structure, is more preferably a monofunctional polymerizable compound including a cyclic ether structure, and is further preferably a monofunctional (meth)acrylate including a cyclic ether structure.

Examples of the cyclic ether structure include a furan ring structure, a pyran ring structure, an oxirane ring structure, an oxetane ring structure, a dioxane ring structure, a dioxolane ring structure, and a morpholine ring structure.

The number of carbon atoms constituting the ring of the alicyclic structure is not limited and is preferably 5 to 10. Examples of the alicyclic structure include a cyclohexane ring structure, a dicyclopentanyl ring structure, a dicyclopentenyl ring structure, a norbornane ring structure, an isobornane ring structure, a norbornene ring structure, an isobornene ring structure, and an adamantane ring structure.

Examples of the (meth)acrylate including a cyclic ether structure include acryloylmorpholine, cyclic trimethylolpropane formal (meth)acrylate, 1,4-dioxaspiro[4,5]decan-2-ylmethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate.

The content of the monofunctional polymerizable compound including at least one structure selected from the group consisting of a cyclic ether structure and an alicyclic structure is preferably 70% to 90% by mass and is more preferably 80% to 85% by mass of the total amount of the pretreatment liquid.

It is also preferable that the pretreatment liquid include a polymerizable silicone-based surfactant as a polymerizable compound. When the pretreatment liquid includes a polymerizable silicone-based surfactant, the bleeding of the image may be reduced. Moreover, the rubfastness of the image may be enhanced.

Examples of the polymerizable silicone-based surfactant are the same as those of the polymerizable silicone-based surfactant that can be included in the above-described ink.

The content of the polymerizable silicone-based surfactant is preferably 3% to 20% by mass and is more preferably 5% to 15% by mass of the total amount of the pretreatment liquid.

The content of the polymerizable compound is preferably 70% to 95% by mass and is more preferably 80% to 90% by mass of the total amount of the pretreatment liquid in consideration of curability.

In the first aspect, the pretreatment liquid may further include a component other than the polymerizable compound or the polyester resin. Examples of the other component include a polymerization initiator, a polymerization inhibitor, and an additive. Examples of the polymerization initiator, the polymerization inhibitor, and the additive are the same as those of the polymerization initiator, the polymerization inhibitor, and the additive that can be included in the above-described ink.

Second Aspect

In the second aspect, the pretreatment liquid preferably includes a polymerizable compound including a polymerizable compound A having an acid group. When the pretreatment liquid includes the polymerizable compound A having an acid group, adhesiveness to the substrate may be increased. This is presumably because the acid group included in the polymerizable compound A interacts with the surface of the substrate.

Examples of the acid group included in the polymerizable compound having an acid group include a carboxyl group, a sulfo group, a phosphonic acid group, a phosphate group, and a sulfonamide group.

Examples of polymerizable compounds having a carboxyl group include 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-carboxyethyl (meth)acrylate, and (meth)acrylic acid.

Examples of polymerizable compounds having a sulfo group include 2-hydroxy-3-sulfopropyl (meth)acrylate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, and 4-styrenesulfonic acid.

Examples of polymerizable compounds having a phosphate group include 2-phosphonoxyethyl (meth)acrylate and 2-(meth)acryloyloxyethyl acid phosphate.

Among these, the polymerizable compound A having an acid group is preferably a polymerizable compound having a carboxyl group.

The polymerizable compound A having an acid group may be a monofunctional or multifunctional polymerizable compound having an acid group. In particular, the polymerizable compound A is preferably a monofunctional polymerizable compound having an acid group, is more preferably a monofunctional polymerizable compound having a carboxyl group, and is further preferably a monofunctional (meth)acrylate having a carboxyl group.

The content of the polymerizable compound A having an acid group is preferably 3% to 20% by mass and is more preferably 5% to 15% by mass of the total amount of the ink.

In the second aspect, the pretreatment liquid may further include a polymerizable compound other than the polymerizable compound A having an acid group.

The other polymerizable compound is not limited and may be a monofunctional or multifunctional polymerizable compound. Examples of the monofunctional and multifunctional polymerizable compounds are the same as those of the monofunctional and multifunctional polymerizable compounds that can be included in the above-described ink.

The other polymerizable compound preferably includes a monofunctional polymerizable compound in order to further increase the adhesiveness between the substrate and the image.

In order to reduce odors, the other polymerizable compound included in the pretreatment liquid is preferably a monofunctional polymerizable compound including at least one structure selected from the group consisting of a cyclic ether structure and an alicyclic structure, is more preferably a monofunctional polymerizable compound including a cyclic ether structure, and is further preferably a monofunctional (meth)acrylate including a cyclic ether structure.

The content of the monofunctional polymerizable compound including at least one structure selected from the group consisting of a cyclic ether structure and an alicyclic structure is preferably 65% to 85% by mass and is more preferably 70% to 80% by mass of the total amount of the pretreatment liquid.

It is also preferable that the pretreatment liquid include a polymerizable silicone-based surfactant as another polymerizable compound.

Examples of the polymerizable silicone-based surfactant are the same as those of the polymerizable silicone-based surfactant that can be included in the above-described ink.

The content of the polymerizable silicone-based surfactant is preferably 3% to 20% by mass and is more preferably 5% to 15% by mass of the total amount of the pretreatment liquid.

The content of the polymerizable compound is preferably 70% to 95% by mass and is more preferably 80% to 90% by mass of the total amount of the pretreatment liquid in consideration of curability.

In order to further increase the adhesiveness between the substrate and the image, the proportion of the monofunctional polymerizable compound to the polymerizable compounds included in the pretreatment liquid is preferably 80% by mass or more and is more preferably 90% by mass or more. The upper limit for the above proportion is not set and may be 100% by mass.

In the second aspect, the pretreatment liquid may further include a component other than the polymerizable compound. Examples of the other component include a polymerization initiator, a polymerization inhibitor, and an additive. Examples of the polymerization initiator, the polymerization inhibitor, and the additive are the same as those of the polymerization initiator, the polymerization inhibitor, and the additive that can be included in the above-described ink.

In another aspect, the pretreatment liquid may include both polyester resin and polymerizable compound A having an acid group.

The viscosity of the pretreatment liquid is preferably 0.5 to 50 mPa·s, is more preferably 5 to 40 mPa·s, is preferably 7 to 35 mPa·s, and is further preferably 8 to 30 mPa·s. The above viscosity is measured at 25° C. with a viscometer. Examples of the viscometer that can be used include a viscometer “TV-22” produced by Toki Sangyo Co., Ltd.

The surface tension of the pretreatment liquid is preferably 60 mN/m or less, is more preferably 20 to 50 mN/m, and is further preferably 25 to 45 mN/m. The above surface tension is measured by a Wilhelmy plate method at 25° C. with a surface tensiometer. Examples of the surface tensiometer that can be used include an automatic surface tensiometer “DY-300” produced by Kyowa Interface Science Co., Ltd.

Image Recording Method

An image recording method according to a first exemplary embodiment of the present disclosure preferably includes a step of applying the above-described ink to a substrate by ink jet recording (hereinafter, this step is also referred to as “ink application step” and a step of irradiating the ink with an active energy ray (hereinafter, this step is also referred to as “active energy ray curing step”).

Ink Application Step

In the ink application step, the ink is applied to a substrate by ink jet recording.

The type of the substrate is not limited; publicly known substrates can be used. Examples of the substrate include glass, quartz, and a plastic film. Examples of the resin constituting the plastic film include cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, an acrylic resin, a chlorinated polyolefin resin, a polyether sulfone resin, polyethylene terephthalate (PET), polyethylene naphthalate, nylon, polyethylene, polystyrene, polypropylene, a polycycloolefin resin, a polyimide resin, a polycarbonate resin, and polyvinyl acetal. The plastic film may be a film that includes only one of the above resins and may be a film composed of a mixture of two or more of the above resins.

Since the ink according to an exemplary embodiment of the present disclosure enables recording of images having excellent flexibility, the ink can be applied to a substrate that is deformable at room temperature. The images having excellent flexibility can follow the deformation of the substrate which occurs at room temperature and, therefore, cracks are unlikely to be formed in the images.

Since the ink can be applied to substrates deformable at room temperature, the substrate is preferably composed of a metal, a plastic, synthetic leather, or a rubber and is more preferably composed of a rubber.

The thickness of the substrate is not limited. Since the ink according to an exemplary embodiment of the present disclosure enables recording of images having excellent flexibility, the ink can be applied to a thick substrate. The lower limit for the thickness of the substrate is, for example, 1 μm. Since the ink can be applied to a thick substrate, the thickness of the substrate is preferably 1 mm or more. The upper limit for the thickness of the substrate is, for example, 5 mm.

The type of ink jet recording is not limit, and any ink jet recording method with which an image can be recorded may be used. Examples of the ink jet recording method include a charge control ink jet method in which an electrostatic attractive force is used for ejecting an ink, a drop-on-demand (pressure pulse) ink jet method in which the vibration pressure of a piezoelectric element is used, an acoustic ink jet method in which an electrical signal is converted into an acoustic beam, an ink is irradiated with the acoustic beam, and the ink is ejected using the resulting radiation pressure, and a thermal ink jet (Bubble Jet (registered trademark)) method in which an ink is heated to form bubbles and the resulting pressure is used.

Examples of the ink jet head used in the ink jet recording method include a shuttle-type ink jet recording method in which a short serial head is used and recording is performed while the head is moved in the width direction of a substrate and a line-type ink jet recording method in which a line head that includes recording elements arranged to cover the entirety of a side of a substrate is used.

In the line-type ink jet recording method, a pattern can be formed over the entire surface of a substrate by scanning the substrate in a direction orthogonal to the direction in which the recording elements are arranged. This eliminates the need to use a transporting system for moving the short head, such as a carriage. In addition, in the line-type ink jet recording method, it becomes not necessary to perform a complex control over the movement of the carriage and the scanning of the substrate. That is, only the substrate is moved. This increases the recording speed compared with the shuttle system.

The amount of droplets of the ink which are ejected from an ink jet head is preferably 1 to 100 pL (picoliter), is more preferably 3 to 80 pL, and is further preferably 3 to 50 pL.

Active Energy Ray Curing Step

In the active energy ray curing step, the ink is irradiated with an active energy ray.

Examples of the active energy ray include a γ-ray, a β-ray, an electron beam, ultraviolet radiation, and visible light. Among these, ultraviolet radiation is preferably used as an active energy ray.

The peak wavelength of ultraviolet radiation is preferably, for example, 200 to 405 nm, is more preferably 250 to 400 nm, and is further preferably 300 to 400 nm. Note that the term “peak wavelength” used herein refers to the wavelength at which the maximum strength occurs in a waveform having the highest intensity in the ultraviolet region (e.g., 200 to 405 nm).

The light sources commonly used for ultraviolet irradiation are a mercury lamp, a gas laser, and a solid-state laser. A mercury lamp, a metal halide lamp, and an ultraviolet fluorescent lamp are broadly known. Compact, long-life, high-efficiency, and low-cost ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are considered as promising light sources for ultraviolet irradiation. In particular, the light source for ultraviolet irradiation is preferably a metal halide lamp, a high-pressure mercury lamp, a medium-pressure mercury lamp, a low-pressure mercury lamp, or a UV-LED.

In the present disclosure, polymerizing only a part of the polymerizable compound included in the ink is referred to as “partial curing”, and irradiating the ink with an active energy ray to perform partial curing is referred to as “pinning exposure”.

In the present disclosure, polymerizing substantially the entirety of the polymerizable compound included in the ink is referred to as “full curing”, and irradiating the ink with an active energy ray to perform full curing is referred to as “full exposure”.

In the active energy ray irradiation step, it is preferable to partially cure the ink and subsequently fully cure the ink. Specifically, it is preferable to perform the pinning exposure of the ink subsequent to the application of the ink and finally perform the full exposure.

The reaction rate of the ink subsequent to the pinning exposure is preferably 10% to 80%.

Note that the term “reaction rate” of the ink used herein refers to the rate of polymerization of the polymerizable compound included in the ink which is determined by high-performance liquid chromatography.

When the reaction rate of the ink is 10% or more, the droplet settling interference between ink dots can be reduced and, as a result, the quality of the final image may be enhanced.

When the reaction rate of the ink is 80% or less, the possibility of ink dots failing to spread to a sufficient degree is reduced and, consequently, the final image may be improved in terms of graininess.

The reaction rate of the ink is preferably 15% or more in order to further enhance the quality of the final image.

The reaction rate of the ink is preferably 75% or less, is more preferably 50% or less, is preferably 40% or less, is more preferably 30% or less, and is further preferably 25% or less in order to further improve the final image in terms of graininess.

The reaction rate of the ink subsequent to the full exposure is preferably more than 80% and 100% or less, is more preferably 85% to 100%, and is further preferably 90% to 100%.

When the above reaction rate is more than 80%, adhesiveness may be further enhanced.

The reaction rate of the ink is determined by the following method.

A substrate including an ink deposited thereon, the ink having been irradiated with an active energy ray, is prepared. A sample piece having a size of 20 mm×50 mm is taken from a region of the substrate in which the ink film is present (hereinafter, this sample piece is referred to as “irradiated sample piece”). The irradiated sample piece is immersed in 10 mL of tetrahydrofuran (THF) for 24 hours in order to prepare a solution containing an eluted ink. This solution is subjected to high-performance liquid chromatography in order to measure the amount of polymerizable compound (hereinafter, this amount is referred to as “amount of compound X1 after irradiation”).

Subsequently, the same operation as described above is performed, except that the ink deposited on a substrate is not irradiated with an active energy ray, and the amount of polymerizable monomer is measured (hereinafter, this amount is referred to as “amount of compound X1 before irradiation”).

The ink reaction rate (%) is calculated using the following formula on the basis of the amount of compound X1 after irradiation and the amount of compound X1 before irradiation.

Ink reaction rate (%)=((Amount of compound X1 before irradiation−Amount of compound X1 after irradiation)/Amount of compound X1 before irradiation)×100

The amount of exposure of the active energy ray used for the pinning exposure is preferably 10 to 100 mJ/cm²and is more preferably 20 to 60 mJ/cm²in order to achieve the above-described ink reaction rate with further ease.

The amount of exposure of the active energy ray used for the full exposure is preferably 50 to 1,000 mJ/cm²and is more preferably 200 to 800 mJ/cm²in order to fully cure the ink.

In the full exposure, it is preferable to irradiate the ink with an active energy ray in an atmosphere having an oxygen concentration of less than 1% by volume in order to increase adhesiveness to the substrate. The above oxygen concentration is more preferably 0.5% by volume or less and is further preferably 0.3% by volume or less.

In the active energy ray irradiation step, it is preferable to irradiate the ink with an active energy ray 0.1 to 5 seconds after the ink has landed on the substrate in consideration of image quality. In the case where both pinning exposure and full exposure are performed, it is preferable to irradiate the ink with an active energy ray for pinning exposure 0.1 to 5 seconds after the ink has landed on the substrate. The time interval from when the ink has landed on the substrate to when the ink is irradiated with an active energy ray (in the case where both pinning exposure and full exposure are performed, the active energy ray for pinning exposure) is more preferably 0.2 to 1 second.

An image recording method in which the above-described ink set is used is described below.

In the image recording method according to a second embodiment of the present disclosure, the above-described ink set is used. The image recording method preferably includes a step of applying the pretreatment liquid and the ink to a substrate by ink jet recording and a step of performing irradiation with an active energy ray subsequent to application of the pretreatment liquid and subsequent to application of the ink.

The step of applying the pretreatment liquid and the step of applying the ink are the same as the ink application step described above.

In the active energy ray irradiation step, it is preferable to perform pinning exposure of the pretreatment liquid subsequent to the application of the pretreatment liquid, apply the ink to the partially cured pretreatment liquid, then perform pinning exposure of the ink, and finally perform full exposure.

The preferable aspects of pinning exposure and full exposure are the same as the preferable aspects of pinning exposure and full exposure performed in the active energy ray curing step described above.

EXAMPLES

The present disclosure is described further specifically with reference to Examples below. It should be noted that the present disclosure is not limited by Examples below without departing from the summary of the present disclosure.

Details of each of the components of the inks prepared in Examples and Comparative Examples are as described below.

Monofunctional Polymerizable Compounds

- NVC: N-Vinylcaprolactam (produced by BASF SE)
- PEA: Phenoxyethyl acrylate (“SR339A”, produced by Sartomer)
- CHA: Cyclohexyl acrylate (“Viscoat #155, CHA”, produced by Osaka Organic Chemical Industry Ltd.)
- TMCHA: Trimethylcyclohexyl acrylate (“SR420”, produced by Sartomer)
- THFA: Tetrahydrofurfuryl acrylate (“SR285”, produced by Sartomer)
- LA: Lauryl acrylate (“SR335”, produced by Sartomer)
- CTFA: Cyclic trimethylolpropane formal acrylate (“SR531”, produced by Sartomer)
- IBOA: Isobornyl acrylate (“SR506”, produced by Sartomer)
- 4-HBA: 4-Hydroxybutyl acrylate (“4-HBA”, produced by Osaka Organic Chemical Industry Ltd.)
- IOA: Isooctyl acrylate (“SR440”, produced by Sartomer)
- A-SA: 2-Acryloyloxyethylsuccinic acid (“NK-Ester A-SA”, produced by Shin-Nakamura Chemical Co., Ltd.; Polymerizable compound A having an acid group)
  
  Difunctional Polymerizable Compounds
- HDDA: 1,6-Hexanediol diacrylate (“Viscoat #230, HDDA”, produced by Osaka Organic Chemical Industry Ltd.)
- DDDA: 1,10-Decanediol diacrylate (“A-DOD-N”, produced by Shin-Nakamura Chemical Co., Ltd.)
- PEGDA200: Polyethylene glycol #200 diacrylate (“A-200”, produced by Shin-Nakamura Chemical Co., Ltd.)
- PEGDA600: Polyethylene glycol #600 diacrylate (“A-600”, produced by Shin-Nakamura Chemical Co., Ltd.)
- PPGDA700: Polypropylene glycol #700 diacrylate (“APG-700”, produced by Shin-Nakamura Chemical Co., Ltd.)
- NPGDA: Neopentyl glycol diacrylate (“Lightacrylate NP-A”, produced by Kyoeisha Chemical Co., Ltd.)
- TCDDMDA: Tricyclodecane dimethanol diacrylate (“EBECRYL 130”, produced by Daicel-Allnex Ltd.)
- HMPA: 2-Hydroxy-3-methacrylpropyl acrylate (“701A”, produced by Shin-Nakamura Chemical Co., Ltd.)
- PEGDA1000: Polyethylene glycol #1000 diacrylate (“A-1000”, produced by Shin-Nakamura Chemical Co., Ltd.)
  
  Polymerizable Silicone-Based Surfactants
- TEGO Rad 2100 (produced by Evonik Industries AG)
- TEGO Red 2010 (produced by Evonik Industries AG)
  
  Pigments
- White pigment: Titanium dioxide (“KRONOS 2300”, produced by Kronos Worldwide, Inc.)
- Cyan pigment: Pigment Blue 15:4 (“Heliogen Blue D 7110 F”, produced by BASF SE Japan)
- Magenta pigment: “Cinquasia Magenta L 4540”, produced by BASF SE Japan)
- Yellow pigment: Pigment Yellow 155 (“Inkjet Yellow 4GC”, produced by Clariant AG)
- Black pigment: Carbon black (“Mogul E”, produced by Cabot Corporation)
  
  Dispersing Agents
- SOLSPERSE 41000 (produced by The Lubrizol Corporation)
- SOLSPERSE 32000 (produced by The Lubrizol Corporation)
- Efka 7731 (produced by BASF SE Japan)
- BYKJET 9151 (produced by BYK)
  
  Polymerization Initiators
- Omn.184: 1-Hydroxycyclohexyl-phenyl ketone (“Omnirad 184”, produced by IGM Resins B.V.)
- Omn.819: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (“Omnirad 819”, produced by IGM Resins B.V.)
- ITX: Isopropylthioxanthone (“SPEEDCURE ITX”, produced by Lambson Ltd.)
- TPO: 2,4,6-Trimethylbenzoyldiphenylphosphine oxide (“Omnirad TPO-H”, produced by IGM Resins B.V.)
  
  Polymerization Inhibitor
- UV12: N-Nitroso-N-phenylhydroxylamine aluminum salt (“FLORSTAB UV12”, produced by Kromachem Ltd.)
  
  Additive
- BR113: Acrylic resin (“Dianal BR113”, produced by Mitsubishi Chemical Corporation)
  
  Preparation of Inks

Example 1

A white pigment dispersion liquid was prepared. Specifically, the following components were charged into a disperser “Motormill M50” produced by Eiger Torrance Ltd. The resulting mixture was subjected to a dispersion treatment for 4 hours at a rotation speed of 9 m/s with zirconia beads having a diameter of 0.65 mm to form a white pigment dispersion liquid.

- White pigment . . . 50 parts by mass
- Dispersing agent (“SOLSPERSE 41000”, produced by The Lubrizol Corporation) . . . 3.53 parts by mass
- PEA . . . 45.47 parts by mass
- UV12 . . . 1 part by mass

Subsequently, the following components were mixed together. The resulting mixture was stirred for 20 minutes at 25° C. and 5,000 rotations/min using a mixer “L4R” produced by Silverson to form a white ink.

- White pigment dispersion liquid . . . 15 parts by mass
- PEA . . . 49.6 parts by mass
- HDDA . . . 1 part by mass
- NVC . . . 21.5 parts by mass
- BR113 . . . 2.4 parts by mass
- UV12 . . . 0.42 parts by mass
- Omni.184 . . . 2.8 parts by mass
- TPO . . . 8 parts by mass

Examples 2 to 17 and Comparative Examples 1 to 6

Inks were each prepared as in Example 1, except that the contents of the polymerizable compounds in the ink were adjusted to the contents described in Tables 1 to 3. Tables 1 to 3 list the proportions (mass %) of the components relative to the total amount of the polymerizable compound. In Examples 2 to 17 and Comparative Examples 1 to 6, the types and contents of components of the ink which were other than the polymerizable compound were the same as in Example 1.

Image Recording

One of the white inks was charged into the white throttle of an ink jet recording apparatus “Acuity LED 1600R” produced by FUJIFILM Corporation. The substrates used were a synthetic leather sheet “Cappuccino” produced by Yamaplas Co., Ltd. (thickness: 1 mm) and a stainless steel sheet “Stainless Steel Sheet” produced by Yahata Neji Corporation (thickness: 1 mm). The application of the ink was performed under the following conditions: 1,200 dpi×1,200 dpi, 48 passes, and bidirectional printing. A 100% solid image was recorded. Note that “dpi” is an abbreviation for “dot per inch”.

By adjusting the lampworking of the ink jet recording apparatus, the ink deposited on the substrate was irradiated with ultraviolet radiation (peak wavelength: 385 nm) for pinning exposure and ultraviolet radiation (peak wavelength: 385 nm) for full exposure in this order. The amount of exposure for pinning exposure was set to 400 mJ/cm². The amount of exposure for full exposure was set to 1,200 mJ/cm².

Thus, the ink deposited on the substrate was subjected to pinning exposure and full exposure in this order under the above-described conditions. Hereby, an image recorded article was prepared. An image recorded article formed by recording an image on a synthetic leather sheet is referred to as “image recorded article 1”, while an image recorded article formed by recording an image on a stainless steel sheet is referred to as “image recorded article 2”.

Evaluations

Each of the image recorded articles prepared in Examples and Comparative Examples was evaluated in terms of flexibility, blocking resistance, and adhesiveness. The evaluation methods were as described below.

Flexibility

The image recorded article 1 was bent 180° at room temperature (23° C.). After bending, the image was visually inspected for the occurrence of cracking or detachment of the image.

The image recorded article 2 was bent 90° at room temperature (23° C.) by press forming. After bending, the image was visually inspected for the occurrence of cracking or detachment of the image. After bending, the image was visually inspected for the occurrence of cracking or detachment of the image.

The following evaluation standard was employed.

- A: Cracking and detachment did not occur at all.
- B: At least one of cracking and detachment occurred slightly.
- C: Occurrence of at least one of cracking and detachment was obviously confirmed.
  
  Blocking Resistance

The image recorded articles 1 and 2 were inspected for the stickiness of the surface of the image by hands. The following evaluation standard was employed.

- A: Stickiness was not confirmed at all.
- B: Slight stickiness was confirmed.
- C: Considerable stickiness was confirmed.
  
  Adhesiveness

The image recorded articles 1 and 2 were subjected to a cross hatch test in conformity with ISO 2409 (Cross cut test). In the cross hatch test, cut intervals were set to 1 mm and 25 square lattices with a side of 1 mm were created. The adhesiveness evaluation was conducted on the basis of the proportion (%) of detached lattices. The proportion (%) of detached lattices was calculated using the following formula. In the formula below, the total number of lattices is 25.

Proportion of detached lattices (%)=[(Number of detached lattices)/(Total number of lattices)]×100

The following evaluation standard was employed.

- A: The proportion (%) of detached lattices was 0%.
- B: The proportion (%) of detached lattices was more than 0% and 5% or less.
- C: The proportion (%) of detached lattices was more than 5%.

Tables 1 to 3 list the evaluation results.

Tables 1 to 3 list the glass transition temperature (Tg) of a homopolymer formed of each of the monofunctional polymerizable compounds other than the N-vinyl compound. Tables 1 to 3 also list the number of carbon atoms included in each of the difunctional (meth)acrylates excluding the (meth)acryloyl group-portion. The results of evaluations of the image recorded article 1 are described in the column of “Synthetic leather”, while the results of evaluations of the image recorded article 2 are described in the column of “Metal”.

TABLE 1

Number

of
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-

carbon
ple
ple
ple
ple
ple
ple
ple

Tg(° C.)
atoms
1
2
3
4
5
6
7

Monofunctional
NVC
—
—
27.2
5.0
45
27.2
27.2
27.2
27.2

polymerizable
PEA
5
—
71.5
93.7
53.7
—
—
—
—

compound
CHA
15
—
—
—
—
71.5
—
—
—

TMCHA
29
—
—
—
—
—
71.5
—
—

THFA
−15
—
—
—
—
—
—
71.5
—

LA
−30
—
—
—
—
—
—
—
71.5

Difunctional
HDDA
—
6
1.3
1.3
1.3
1.3
1.3
1.3
1.3

(meth)acrylate

Evaluations
Flexibility
Synthetic leather
A
A
A
A
A
A
A

Metal
A
A
A
A
A
A
A

Blocking
Synthetic leather
A
B
B
A
A
A
A

resistance
Metal
A
B
B
A
A
A
A

Adhesiveness
Synthetic leather
A
C
C
B
B
B
B

Metal
A
C
C
B
B
B
B

TABLE 2

Number

of
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-
Exam-

Tg
carbon
ple
ple
ple
ple
ple
ple
ple
ple
ple
ple

(° C.)
atoms
8
9
10
11
12
13
14
15
16
17

Monofunctional
NVC
—
—
27.2
27.2
27.2
27.2
27.2
27.2
27.2
27.2
25.5
25.5

polymerizable
PEA
5
—
71.5
71.5
71.5
71.5
71.5
71.5
71.5
71.5
73.3
73.3

compound

Difunctional
DDDA
—
10
1.3
—
—
—
—
—
—
—
—
—

(meth)acrylate
PEGDA200
—
8
—
1.3
—
—
—
—
—
—
—
—

PEGDA600
—
28
—
—
1.3
—
—
—
—
—
—
—

PPDA700
—
36
—
—
—
1.3
—
—
—
—
—
—

NPGDA
—
5
—
—
—
—
1.3
—
—
—
—
—

TCDDMDA
—
12
—
—
—
—
—
1.3
—
—
—
—

HMPA
—
3
—
—
—
—
—
—
1.3
—
—
—

PEGDA1000
—
46
—
—
—
—
—
—
—
1.3
—
—

Polymerizable
Tegorad2100
—
—
—
—
—
—
—
—
—
—
1.2
—

silicone-based
Tegorad2010
—
—
—
—
—
—
—
—
—
—
—
1.2

surfactant

Evaluations
Flexibility
Synthetic leather
A
A
A
A
A
A
B
A
A
A

Metal
A
A
A
A
A
A
B
A
A
A

Blocking
Synthetic leather
A
A
A
A
A
A
A
B
A
A

resistance
Metal
A
A
A
A
A
A
A
B
A
A

Adhesiveness
Synthetic leather
B
B
B
B
B
B
A
C
A
A

Metal
B
B
B
B
B
B
A
C
A
A

TABLE 3

Number
Com-
Com-
Com-
Com-
Com-
Com-

of carbon
parative
parative
parative
parative
parative
parative

Tg(° C.)
atoms
Example 1
Example 2
Example 3
Example 4
Example 5
Example 6

Monofunctional
NVC
—
—
27.2
27.2
27.2
27.2
27.2
27.2

polymerizable
PEA
5
—
—
—
—
—
72.8
69.8

compound
CTFA
32
—
71.5
—
—
—
—
—

IBOA
88
—
—
71.5
—
—
—
—

4-HBA
−32
—
—
—
71.5
—
—
—

IOA
−54
—
—
—
—
71.5
—
—

Difunctional
HDDA
—
6
1.3
1.3
1.3
1.3
—
3

(meth)acrylate

Evaluations
Flexibility
Synthetic leather
C
C
A
A
A
C

Metal
C
C
A
A
A
C

Blocking
Synthetic leather
A
A
C
C
C
A

resistance
Metal
A
A
C
C
C
A

Adhesiveness
Synthetic leather
B
B
C
C
C
B

Metal
B
B
C
C
C
B

As described in Tables 1 and 2, in Examples 1 to 17, where the ink included a polymerizable compound and a colorant, the polymerizable compound including an N-vinyl compound, a monofunctional polymerizable compound capable of forming a homopolymer having a Tg of −30° C. to 30° C., and a compound selected from the group consisting of a difunctional (meth)acrylate and a polymerizable silicone-based surfactant, wherein the total content of a monofunctional polymerizable compound capable of forming a homopolymer having a Tg of less than −30° C. and a monofunctional polymerizable compound capable of forming a homopolymer having a Tg of more than 30° C. excluding the N-vinyl compound was 10% by mass or less of the total amount of the polymerizable compound, and the total content of the compound selected from the group consisting of the difunctional (meth)acrylate and the polymerizable silicone-based surfactant was 0.1% to 2% by mass of the total amount of the polymerizable compound, images having excellent flexibility and excellent blocking resistance were formed.

In contrast, as described in Table 3, it was confirmed that, in Comparative Examples 1 and 2, where the total content of the monofunctional polymerizable compound capable of forming a homopolymer having a Tg of more than 30° C. was more than 10% by mass, the flexibility of the images was poor.

It was confirmed that, in Comparative Examples 3 and 4, where the total content of the monofunctional polymerizable compound capable of forming a homopolymer having a Tg of less than −30° C. was more than 10% by mass, the blocking resistance of the images was poor.

It was confirmed that, in Comparative Example 5, where the ink did not include the compound selected from the group consisting of a difunctional (meth)acrylate and a polymerizable silicone-based surfactant, the blocking resistance of the images was poor.

It was confirmed that, in Comparative Example 6, where the total content of the compound selected from the group consisting of a difunctional (meth)acrylate and a polymerizable silicone-based surfactant was more than 2% by mass of the total amount of the polymerizable compound, the flexibility of the images was poor.

It was confirmed that, in Example 1, where the content of the N-vinyl compound was 10% to 35% by mass of the total amount of the polymerizable compound and the content of the monofunctional polymerizable compound capable of forming a homopolymer having a glass transition temperature of −30° C. to 30° C. was 60% to 85% by mass of the total amount of the polymerizable compound, blocking resistance was excellent compared with Example 2 or 3.

It was confirmed that, in Example 1, where the ink included phenoxyethyl acrylate, adhesiveness was excellent compared with any of Examples 4 to 7.

It was confirmed that, in Example 1, where the number of carbon atoms included in the difunctional (meth)acrylate excluding the (meth)acryloyl group-portion was 4 or more, flexibility was excellent compared with Example 14. It was also confirmed that, in Example 1, where the number of carbon atoms included in the difunctional (meth)acrylate excluding the (meth)acryloyl group-portion was 36 or less, blocking resistance was excellent compared with Example 15.

Example 101

A cyan pigment dispersion liquid, a magenta pigment dispersion liquid, a yellow pigment dispersion liquid, and a black pigment dispersion liquid were each prepared as in the preparation of the white pigment dispersion liquid, except that the components of the white pigment dispersion liquid were changed to the following components.

Cyan Pigment Dispersion Liquid

- Cyan pigment . . . 30 parts by mass
- PEA . . . 52 parts by mass
- SOLSPERSE 32000 (produced by Noveon) . . . 17 parts by mass
- UV12 . . . 1 part by mass
  
  Magenta Pigment Dispersion Liquid
- Magenta pigment . . . 30 parts by mass
- PEA . . . 56 parts by mass
- SOLSPERSE 32000 . . . 12.5 parts by mass
- UV12 . . . 1.5 parts by mass
  
  Yellow Pigment Dispersion Liquid
- Yellow pigment . . . 33.9 parts by mass
- PEA . . . 58.2 parts by mass
- SOLSPERSE 32000 . . . 6.8 parts by mass
- UV12 . . . 1.1 parts by mass
  
  Black Pigment Dispersion Liquid
- Black pigment . . . 40 parts by mass
- PEA . . . 45.47 parts by mass
- Efka7731 . . . 3.53 parts by mass
- UV12 . . . 1 part by mass

A cyan ink, a magenta ink, a yellow ink, and a black ink were each prepared as in the preparation of the white ink, except that the components of the white ink were changed to the following components.

Cyan Ink

- Cyan pigment dispersion liquid . . . 8.3 parts by mass
- PEA . . . 58.07 parts by mass
- HDDA . . . 1 part by mass
- NVC . . . 21.7 parts by mass
- BR113 . . . 2.98 parts by mass
- UV12 . . . 0.35 parts by mass
- ITX . . . 1 part by mass
- Omni.184 . . . 2.8 parts by mass
- Omni.819 . . . 3.8 parts by mass
  
  Magenta Ink
- Magenta pigment dispersion liquid . . . 13.5 parts by mass
- PEA . . . 55.24 parts by mass
- HDDA . . . 1 part by mass
- NVC . . . 21.7 parts by mass