Clear ink composition

Abstract

This invention provides a clear ink composition that exhibits excellent resistance to natural light and is capable of forming a highly hard film. [Solution] A clear ink composition comprising a polymerizable compound, a photopolymerization initiator, and a light stabilizer, wherein the polymerizable compound comprises at least an aminoacrylate (A), the photopolymerization initiator comprises two or more intramolecular cleavage-type photopolymerization initiators (B), the light stabilizer comprises a radical-stable hindered amine-based light stabilizer (C), the amount of the aminoacrylate (A) contained in the clear ink composition is 5.0 to 25.0% by mass, and the amount of the hindered amine-based light stabilizer (C) contained in the clear ink composition is 0.05 to 2.0% by mass.

Description

[Technical Field]

[0001] The present invention relates to a clear ink composition, and more particularly to a clear ink composition that has excellent resistance to natural light and can form a highly hard film. [Background technology]

[0002] A method for controlling the amount of thioxanthone derivatives is known for suppressing discoloration of films formed from photocurable ink compositions. Japanese Patent Publication No. 2020-203976 (Patent Document 1) describes a radiation-curable inkjet composition in which the clear ink contains a polymerizable compound comprising at least one of a monofunctional monomer having a nitrogen-containing heterocyclic structure or a monomer having a hydroxyl group, and the content of the thioxanthone derivative is 0.3% by mass or less of the total amount of the radiation-curable inkjet composition.

[0003] Japanese Patent Publication No. 2014-037542 (Patent Document 2) describes that by using an ink composition containing a polymerizable compound, a photopolymerization initiator, and a surface tension modifier, and without a colorant, and by using (a) an amine-modified reactive oligomer as the polymerizable compound, and (b) a monofunctional (meth)acrylate with a glass transition temperature of 0°C or lower as the cured product on its own, an ink composition for forming a clear layer that has excellent curability and adhesion during thick film printing and possesses both appropriate hardness and appropriate flexibility can be obtained.

[0004] Japanese Patent Publication No. 2018-044163 (Patent Document 3) describes a photocurable clear ink composition containing 5 to 12% by mass of an acylphosphine oxide-based photopolymerization initiator based on the total mass of the clear ink composition, and states that by including a specific amount of the acylphosphine oxide-based photopolymerization initiator, the composition exhibits excellent LED tack-free properties and transparency. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-203976 [Patent Document 2] Japanese Patent Publication No. 2014-037542 [Patent Document 3] Japanese Patent Publication No. 2018-044163 [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors investigated films formed from clear ink and found that while reducing the amount of thioxanthone derivatives, etc., is effective from the viewpoint of preventing discoloration, it was sometimes not possible to obtain a film with sufficient hardness. Furthermore, when a large amount of amine-modified reactive oligomers, such as those described in Patent Document 2, were incorporated into the clear ink, the curability sometimes decreased. With regard to acylphosphine oxide-based photopolymerization initiators, such as those described in Patent Document 3, when these photopolymerization initiators were used alone, the curing speed in response to light was fast, and the ink sometimes unintentionally hardened inside the printer due to indoor lighting or reflected light from UV irradiation (natural light) hitting the nozzle surface.

[0007] Therefore, the object of the present invention is to provide a clear ink composition that has excellent resistance to natural light and can form a highly hard film. [Means for solving the problem]

[0008] As a result of diligent research to achieve the above objective, the inventors have discovered that by using a specific amount of aminoacrylate as a polymerizable compound, two or more intramolecular cleavage-type photopolymerization initiators as photopolymerization initiators, and a specific amount of a radical-stable hindered amine-based photostabilizer as a photostabilizer, it is possible to provide a clear ink composition that has excellent resistance to natural light and can form a highly hard, transparent film, thus completing the present invention.

[0009] Therefore, the clear ink composition of the present invention is a clear ink composition comprising a polymerizable compound, a photopolymerization initiator, and a light stabilizer, The polymerizable compound comprises at least aminoacrylate (A), The photopolymerization initiator comprises two or more intramolecular cleavage type photopolymerization initiators (B), The aforementioned light stabilizer includes a hindered amine-based light stabilizer (C) that is stable as a radical represented by the following formula (I), The amount of aminoacrylate (A) contained in the clear ink composition is 5.0 to 25.0% by mass. The clear ink composition is characterized in that the amount of the hindered amine-based light stabilizer (C) contained in the clear ink composition is 0.05 to 2.0% by mass. [ka] (R represents a hydrogen atom or a hydroxyl group.)

[0010] In a preferred example of the clear ink composition of the present invention, the clear ink composition does not contain a coloring agent.

[0011] In other preferred examples of the clear ink composition of the present invention, the polymerizable compound comprises a monofunctional polymerizable compound (D), a bifunctional polymerizable compound (E), and a trifunctional or higher polymerizable compound (F), wherein the monofunctional polymerizable compound (D), the bifunctional polymerizable compound (E), and the trifunctional or higher polymerizable compound (F) are polymerizable compounds different from the aminoacrylate (A).

[0012] In another preferred example of the clear ink composition of the present invention, the mass ratio (E / F) of the bifunctional polymerizable compound (E) to the trifunctional or more polymerizable compound (F) is 30 / 70 to 70 / 30.

[0013] In other preferred examples of the clear ink composition of the present invention, the three- or more-functional polymerizable compound (F) comprises a four-functional polymerizable compound (G) and a six-functional polymerizable compound (H).

[0014] In another preferred example of the clear ink composition of the present invention, the mass ratio (G / H) of the tetrafunctional polymerizable compound (G) to the hexafunctional polymerizable compound (H) is 80 / 20 to 40 / 60.

[0015] In another preferred example of the clear ink composition of the present invention, at least one of the intramolecular cleavage type photoinitiator (B) is an acylphosphine oxide-based photoinitiator having an ethoxy group.

[0016] In another preferred example of the clear ink composition of the present invention, the acylphosphine oxide-based photoinitiator having an ethoxy group is contained in the clear ink composition at 2 to 10% by mass. [Effect of the Invention]

[0017] According to the present invention, it is possible to provide a clear ink composition that is excellent in resistance to natural light and can form a film with high hardness. [Modes for Carrying Out the Invention]

[0018] Hereinafter, the present invention will be described in detail. The present invention relates to a clear ink composition containing a polymerizable compound, a photoinitiator, and a light stabilizer.

[0019] In the present invention, "clear ink" refers to a clear ink in which the light transmittance at each wavelength in the wavelength range of 380 to 800 nm when a film with a thickness of 30 μm is formed is 80% or more, and the light transmittance is preferably 80% or more, more preferably 90% or more. The light transmittance is measured in accordance with JIS K7361-1:1997 "Plastics - Test method for total light transmittance of transparent materials - Part 1: Single beam method". In this specification, "the clear ink composition of the present invention" is also referred to as "the ink composition of the present invention".

[0020] The ink composition of the present invention contains a polymerizable compound and a photopolymerization initiator, and can be cured by irradiation with active energy rays such as ultraviolet light, visible light, and electron beams. Therefore, it is suitable as an active energy ray curable ink composition.

[0021] Polymerizable compounds are compounds that have a functional group that exhibits radical polymerization (for example, polymerizable unsaturated groups such as carbon-carbon double bonds that constitute acryloyl, methacryloyl, vinyl, or allyl groups), and can undergo polymerization reactions via the functional group that exhibits radical polymerization. The carbon-carbon double bond that exhibits radical polymerization is also called an "ethylenically unsaturated double bond." Polymerizable compounds may be used individually or in combination of two or more types.

[0022] Polymerizable compounds are classified into monofunctional polymerizable compounds and polyfunctional polymerizable compounds. Examples of monofunctional polymerizable compounds include monofunctional polymerizable monomers having one functional group exhibiting radical polymerization (e.g., monofunctional polymerizable monomers having one polymerizable unsaturated group) and monofunctional polymerizable oligomers having one functional group exhibiting radical polymerization (e.g., monofunctional polymerizable oligomers having one polymerizable unsaturated group). Examples of polyfunctional polymerizable compounds include polyfunctional polymerizable monomers having two or more functional groups exhibiting radical polymerization (e.g., polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups) and polyfunctional polymerizable oligomers having two or more functional groups exhibiting radical polymerization (e.g., polyfunctional polymerizable oligomers having two or more polymerizable unsaturated groups).

[0023] In the ink composition of the present invention, the polymerizable compound preferably contains both a monofunctional polymerizable compound and a polyfunctional polymerizable compound, and more preferably contains a monofunctional polymerizable compound, a difunctional polymerizable compound, and a trifunctional or higher polymerizable compound. A difunctional polymerizable compound is a polyfunctional polymerizable compound having two functional groups that exhibit radical polymerization, and a trifunctional or higher polymerizable compound is a polyfunctional polymerizable compound having three or more functional groups that exhibit radical polymerization.

[0024] The amount of polymerizable compound contained in the ink composition of the present invention is preferably 50 to 98% by mass, and more preferably 70 to 96% by mass. The amount of monofunctional polymerizable compound contained in the ink composition of the present invention is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. The amount of polyfunctional polymerizable compound contained in the ink composition of the present invention is preferably 40 to 85% by mass, and more preferably 45 to 75% by mass. The amount of the bifunctional polymerizable compound contained in the ink composition of the present invention is preferably 5 to 50% by mass. The amount of trifunctional or higher polymerizable compound contained in the ink composition of the present invention is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass.

[0025] In the ink composition of the present invention, the polymerizable compound comprises at least an aminoacrylate. An aminoacrylate is a compound having an amino group and an acryloyl group and / or a methacryloyl group. Here, an amino group refers to a functional group having a -NH2 structure or a functional group in which one or two hydrogen atoms of the -NH2 are substituted with an organic group (e.g., a hydrocarbon group). In the present invention, an aminoacrylate is a compound having one or more amino groups and one or more functional groups exhibiting radical polymerizability, wherein one or more of the functional groups exhibiting radical polymerizability are acryloyl groups or methacryloyl groups. In this specification, aminoacrylate is referred to as component (A) and also as "aminoacrylate (A)".

[0026] Aminoacrylate (A) is a preferred polymerizable compound from the viewpoint of curability because it is less susceptible to oxygen inhibition. On the other hand, the amount of aminoacrylate (A) is important because it can capture radicals from the polymerization chain during polymerization, which can cause tackiness or a decrease in hardness in the film formed from the ink.

[0027] The amount of aminoacrylate (A) contained in the ink composition of the present invention is 5.0 to 25.0% by mass, and preferably 10.0 to 20.0% by mass. When the amount of aminoacrylate (A) is within the above specified range, it is possible to improve the curability of the ink and form a highly hard film while suppressing the occurrence of tack and a decrease in hardness.

[0028] The aminoacrylate (A) preferably has one or more functional groups that exhibit radical polymerization, and more preferably has two to four such groups.

[0029] Aminoacrylate (A) can be obtained by reacting (meth)acrylic acid or (meth)acrylate with an amine compound. Methods for preparing aminoacrylate (A) include, for example, esterification reactions of (meth)acrylic acid or (meth)acryloyl chloride with an alkanolamine, addition reactions of (meth)acrylic acid esters of polyhydric alcohols with monoamines or diamines, and addition reactions of (meth)acrylate with an alkanolamine. There are no particular restrictions on the molecular weight of aminoacrylate (A), but for example, it can be 300 to 5000, more preferably 1000 to 3000.

[0030] Examples of alkanolamines that can be used in the preparation of aminoacrylate (A) include N,N-dimethylethanolamine, diethanolamine, triethanolamine, diisopropanolamine, N-methyldiethanolamine, and 2-amino-2-methyl-1-propanol.

[0031] (Meth)acrylic acid esters of polyhydric alcohols that can be used to prepare aminoacrylate (A) can be prepared, for example, by reacting (meth)acrylic acid with an alcohol having two or more hydroxyl groups. Examples of alcohols having two or more hydroxyl groups include 1,6-hexanediol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol.

[0032] Examples of monoamines that can be used in the preparation of aminoacrylate (A) include methylamine, n-butylamine, n-hexylamine, 2-ethylhexylamine, cyclohexylamine, ethanolamine, and benzylamine.

[0033] Examples of diamines that can be used in the preparation of aminoacrylate (A) include ethylenediamine, tetramethylenediamine, 1,5-pentamethylenediamine, and hexamethylenediamine.

[0034] Aminoacrylate (A) is sometimes also called a reactive amine co-initiator, reactive amine synergist, acrylate-modified amine synergist, or amine acrylate.

[0035] Examples of commercially available aminoacrylate (A) products include "Aron DA (Dimethylaminoethyl Acrylate)" (product name) from Toagosei Co., Ltd., "MIRAMER AS5142" (product name) from MIWON Corporation, "CN371 NS" (product name), "CN550" (product name), and "CN551 NS" (product name) from Arkema Corporation, and "EBECRYL 7100", "EBECRYL 80", "EBECRYL 81" (product name), and "EBECRYL 83" (product name) from Cytec Corporation.

[0036] Aminoacrylate (A) may be used alone or in combination of two or more types.

[0037] In the ink composition of the present invention, the polymerizable compound preferably includes, in addition to aminoacrylate (A), a monofunctional polymerizable compound that does not correspond to aminoacrylate (A), and a polyfunctional polymerizable compound that does not correspond to aminoacrylate (A). More preferably, it includes a monofunctional polymerizable compound that does not correspond to aminoacrylate (A), a difunctional polymerizable compound that does not correspond to aminoacrylate (A), and a trifunctional or higher polymerizable compound that does not correspond to aminoacrylate (A). In this specification, a monofunctional polymerizable compound that does not correspond to aminoacrylate (A) is referred to as component (D) and also as "monofunctional polymerizable compound (D)", a difunctional polymerizable compound that does not correspond to aminoacrylate (A) is referred to as component (E) and also as "difunctional polymerizable compound (E)", and a trifunctional or higher polymerizable compound that does not correspond to aminoacrylate (A) is referred to as component (F) and also as "trifunctional or higher polymerizable compound (F)".

[0038] In the ink composition of the present invention, it is preferable that the polyfunctional polymerizable compound that does not correspond to aminoacrylate (A) is included in a mass ratio of 1.0 to 3.0 times, more preferably 1.5 to 2.5 times, relative to the monofunctional polymerizable compound (D). By including a large amount of the polyfunctional polymerizable compound that does not correspond to aminoacrylate (A) relative to the monofunctional polymerizable compound (D), the hardness of the film formed from the ink can be increased.

[0039] The monofunctional polymerizable compound (D) is preferably a monofunctional polymerizable monomer, and specific examples include isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, 2- (2'-Vinyloxyethoxy)ethyl (meth)acrylate, 2-Hydroxyethyl (meth)acrylate, 2-Hydroxypropyl (meth)acrylate, 2-Hydroxybutyl (meth)acrylate, 4-Hydroxybutyl (meth)acrylate, 6-Hydroxyhexyl (meth)acrylate, 4-t-Butylcyclohexyl (meth)acrylate, Cyclohexyl (meth)acrylate, N-(meth)acryloylmorpholine, Tetrahydrofurfuryl (meth)acrylate, (2-Methyl-2-ethyl-1,3-Dioxolan-4-I Methyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, γ-butyrolactone (meth)acrylate, N-vinylcaprolactam, N-(meth)acryloyloxyethylhexahydrophthalimide, 1-(meth)acryloylpyrrolidine-2-one, 1-(meth)acryloylpiperidine-2-one, N-vinyl-2-pyrrolidone, N-vinylimidazole, dimethylacrylamide, hydroxyethyl (meth)acrylamide, diethylacrylamide, isopropylacrylamide, dimethylami Nopropyl (meth)acrylamide, diacetone acrylamide, Nn-butoxymethylacrylamide, N-isobutoxymethylacrylamide, N-methoxymethylacrylamide, N-methylolacrylamide, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, neopentyl glycol (meth)acrylate benzoate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate,Examples include dicyclopentenyloxyethyl (meth)acrylate, γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropylmethyldiethoxysilane, γ-(meth)acryloxypropylmethyldipropoxysilane, γ-(meth)acryloxybutylphenyldimethoxysilane, γ-(meth)acryloxypropyldimethylmethoxysilane, γ-(meth)acryloxypropyldiethylmethoxysilane, β-(meth)acryloxyethyltrimethoxysilane, β-(meth)acryloxyethyltriethoxysilane, polyoxyethylene mono(meth)acrylate, polyoxypropylene mono(meth)acrylate, polyoxybutylene mono(meth)acrylate, etc., as well as those modified with alkylene glycol. Among these, monofunctional polymerizable monomers with extended alkyl chains or alkylene glycol chains are preferred because the odor is reduced due to the increase in molecular weight compared to before chain extension. Monofunctional polymerizable monomers having a cyclic structure are preferred from the viewpoint of curability and solubility.

[0040] The amount of monofunctional polymerizable compound (D) contained in the ink composition of the present invention is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. Monofunctional polymerizable compound (D) may be used alone or in combination of two or more types.

[0041] Examples of difunctional polymerizable compounds (E) include difunctional polymerizable monomers and difunctional polymerizable oligomers. Examples of polymerizable monomers that fall under the category of difunctional polymerizable compound (E) include 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropyl Examples include ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, PO (propylene oxide) modified neopentyl glycol di(meth)acrylate, cyclohexanedimethanol diacrylate, tricyclodecane dimethanol diacrylate, dimethylol-tricyclodecane di(meth)acrylate, dicyclopentanyl diacrylate, bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

[0042] Examples of polymerizable compounds (F) with three or more functions include polymerizable monomers with three or more functions and polymerizable oligomers with three or more functions. Examples of polymerizable monomers that fall under the category of three- or more functional polymerizable compounds (E) include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, EO-modified diglycerin tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, EO-modified dipentaerythritol hexa(meth)acrylate, and glycerin tri(meth)acrylate.

[0043] The polymerizable oligomers that fall under the category of a bifunctional polymerizable compound (D) or a trifunctional or more polymerizable compound (E) are preferably acrylic oligomers. An acrylic oligomer is an oligomer having an acryloyl group or a methacryloyl group as a functional group that exhibits radical polymerizability.

[0044] The polymerizable oligomer preferably has 2 to 6 functional groups, and its molecular weight is preferably 800 to 20000. The molecular weight of the polymerizable oligomer is the weight-average molecular weight on a polystyrene basis.

[0045] Specific examples of acrylic oligomers include polyurethane acrylic oligomers [acrylic oligomers having multiple urethane bonds (-NHCOO-)], polyester acrylic oligomers [acrylic oligomers having multiple ester bonds (-COO-)], polyepoxy acrylic oligomers [acrylic oligomers having multiple epoxy groups], silicone acrylic oligomers [acrylic oligomers having multiple siloxane bonds (-SiO-)], and polybutadiene acrylic oligomers [acrylic oligomers having multiple butadiene units].

[0046] In addition, the following are known as acrylic oligomers. Beamset 550B, Beamset 575, Beamset AQ-19 (manufactured by Arakawa Chemical Industries, Ltd.) AH-600, UA-306H, UA-306T, UA-306I, UA-510H, UF-8001G (manufactured by Kyoeisha Chemical Co., Ltd.) CN929, CN959, CN962, CN963, CN964, CN965NS, CN966NS, CN980NS, CN981NS, CN982, CN983NS, CN985, CN996NS, CN2920, CN2921, CN8881NS, CN8883NS, CN9001NS, CN973, CN978NS, CN970, CN971, CN972, CN975NS, CN2270, CN2271, CN2273, CN2274 (manufactured by Arkema), U-6LPA, U-10HA, U-10PA, UA-1100H, U-15HA, UA-33H, U-200PA, UA-160TM, UA-290TM, UA-4200, UA-4400, UA-122P (manufactured by Shin-Nakamura Chemical Industries), New Frontier R-1235, R-1220, RST-402, R-1304, R-1214, R-1302XT, GX-8801A, R-1603, R-1150D (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) EBECRYL230, EBECRYL270, EBECRYL280 / 15IB, EBECRYL284, EBECRYL4858, EBECRYL8210, EBECRYL8307, EBECRYL8402, EBECRYL8409, EBECRYL8411, EBECRYL8804, EBECRYL8807, EBECRYL9270, KRM7735, EBECRYL4820, EBECRYL8311, EBECRYL8701, EBECRYL8210, EBECRYL8405, KRM8528 (manufactured by Daicel Ornex Co., Ltd.) UV-1700B, UV-6300B, UV-7550B, UV-7600B, UV-7605B, UV-7610B, UV-7630B, UV-7640B, UV-7650B, UV-6630B, UV-7000B, UV-7510B, UV-3000B, UV-3200B, UV-3300B, UV-3310B, UV-3700B, UV6640B (manufactured by Mitsubishi Chemical Corporation), Arronix M-6100, M-6250, M-6500, M-7100, M-7300K, M-8030, M-8060, M-8100, M-8530, M-8560, M-9050 (manufactured by Toagosei Co., Ltd.)

[0047] The amount of the difunctional polymerizable compound (E) contained in the ink composition of the present invention is preferably 20 to 65% by mass, and more preferably 30 to 55% by mass. The difunctional polymerizable compound (E) may be used alone or in combination of two or more types.

[0048] The amount of the trifunctional or higher polymerizable compound (F) contained in the ink composition of the present invention is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass. The trifunctional or higher polymerizable compound (F) may be used alone or in combination of two or more types.

[0049] In the ink composition of the present invention, the mass ratio (E / F) of the bifunctional polymerizable compound (E) to the trifunctional or more polymerizable compound (F) is preferably 30 / 70 to 70 / 30. A ratio of 40 / 60 to 60 / 40 is even more preferable. By blending a bifunctional polymerizable compound (E) and a trifunctional or higher polymerizable compound (F) in the specified mass ratio, it is possible to increase the hardness of the film formed from the ink while maintaining adhesion to the substrate.

[0050] In the ink composition of the present invention, it is preferable that the three- or more-functional polymerizable compound (F) includes a four-functional polymerizable compound that does not correspond to aminoacrylate (A) and a six-functional polymerizable compound that does not correspond to aminoacrylate (A). In this specification, the four-functional polymerizable compound that does not correspond to aminoacrylate (A) is referred to as component (G) and also as "four-functional polymerizable compound (G)", and the six-functional polymerizable compound that does not correspond to aminoacrylate (A) is referred to as component (H) and also as "six-functional polymerizable compound (H)". The hardness of the film formed from the ink can be increased by including the four-functional polymerizable compound (G) and the six-functional polymerizable compound (H).

[0051] Examples of tetrafunctional polymerizable compounds (G) include pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, EO-modified diglycerin tetra(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0052] The amount of the tetrafunctional polymerizable compound (G) contained in the ink composition of the present invention is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. The tetrafunctional polymerizable compound (G) may be used alone or in combination of two or more types.

[0053] Examples of hexafunctional polymerizable compounds (H) include dipentaerythritol hexa(meth)acrylate and EO-modified dipentaerythritol hexa(meth)acrylate.

[0054] The amount of the hexafunctional polymerizable compound (H) contained in the ink composition of the present invention is preferably 1 to 15% by mass, and more preferably 3 to 10% by mass. The hexafunctional polymerizable compound (H) may be used alone or in combination of two or more types.

[0055] In the ink composition of the present invention, the mass ratio (G / H) of the tetrafunctional polymerizable compound (G) to the hexafunctional polymerizable compound (H) is preferably 80 / 20 to 40 / 60, and more preferably 75 / 25 to 50 / 50.

[0056] Photopolymerization initiators have the effect of initiating the polymerization of the polymerizable compounds described above when irradiated with active energy rays. The photopolymerization initiators used in the ink composition of the present invention are classified as radical polymerization initiators. Radical polymerization initiators are further classified into two types depending on how they generate radical polymerization initiator species. One is Norrish type I photopolymerization initiators (intramolecular cleavage type photopolymerization initiators) that undergo a cleavage reaction within one molecule under light irradiation, and the other is Norrish type II photopolymerization initiators that generate an initiation radical through a bimolecular reaction between the excited photopolymerization initiator and another molecule (coinitiator). For a classification of photopolymerization initiators, please refer to, for example, Chapter 1, Section 3, Photopolymerization Initiators (pp. 93-103) of the Dictionary of Photo-Applied Technology and Materials, Industrial Technology Service Center Co., Ltd., published April 26, 2006.

[0057] Examples of intramolecular cleavage-type photopolymerization initiators include benzoin-type photopolymerization initiators, benzyl ketal-type photopolymerization initiators, α-hydroxyacetophenone-type photopolymerization initiators, α-aminoacetophenone-type photopolymerization initiators, acylphosphine oxide-type photopolymerization initiators, and oxime ester-type photopolymerization initiators. Norrish type II photopolymerization initiators include hydrogen abstraction-type photopolymerization initiators, and examples of hydrogen abstraction-type photopolymerization initiators include anthraquinone derivatives, benzophenone derivatives, and thioxanthone derivatives.

[0058] In the ink composition of the present invention, the photopolymerization initiator preferably comprises two or more intramolecular cleavage type photopolymerization initiators, and more preferably two or more acylphosphine oxide-based photopolymerization initiators. By using two or more intramolecular cleavage type photopolymerization initiators, preferably two or more acylphosphine oxide-based photopolymerization initiators, the reactivity of the photopolymerization initiator can be controlled, and the curability of the ink can be improved. In this specification, the intramolecular cleavage type photopolymerization initiator is referred to as component (B), and is also referred to as "intramolecular cleavage type photopolymerization initiator (B)" or "photopolymerization initiator (B)".

[0059] Examples of acylphosphine oxide-based photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Omnirad 819 (IGM Resins BV product name)), ethylphenyl(2,4,6-trimethylbenzoyl)phosphine (SPeedCure TPO-L (Arkema product name)), 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (Omnirad TPO H (IGM Resins BV product name)), and (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide (CAS 270586-78-2). Note that "acylphosphine oxide-based photopolymerization initiator" and "acylphosphine oxide type photopolymerization initiator" are synonymous.

[0060] In the ink composition of the present invention, it is preferable that at least one of the intramolecular cleavage-type photopolymerization initiators (B) is a bisacylphosphine oxide-based photopolymerization initiator. Acylphosphine oxide-based photopolymerization initiators mainly include monoacylphosphine oxide-based photopolymerization initiators and bisacylphosphine oxide-based photopolymerization initiators, but bisacylphosphine oxide-based photopolymerization initiators have high reactivity and can provide a high improvement effect on the hardness of the film formed from the ink. However, since bisacylphosphine oxide-based photopolymerization initiators tend to stain the film formed from the ink if they remain, it is particularly preferable to use them in combination with other intramolecular cleavage-type photopolymerization initiators, especially in clear ink compositions.

[0061] Examples of bisacylphosphine oxide-based photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Omnirad 819 (IGM Resins BV product name)).

[0062] The amount of bisacylphosphine oxide-based photopolymerization initiator contained in the ink composition of the present invention is preferably 1 to 6% by mass, and more preferably 3 to 5% by mass. If the amount of bisacylphosphine oxide-based photopolymerization initiator is greater than 6% by mass, there is a concern about poor dissolution and discoloration of the film formed from the ink, and if it is less than 1% by mass, there is a concern about curability.

[0063] In the ink composition of the present invention, it is preferable that at least one of the intramolecular cleavage-type photopolymerization initiators (B) is an acylphosphine oxide-based photopolymerization initiator having an ethoxy group. Such photopolymerization initiators have an ethoxy group (CH2CH2O) in their molecule and have high solubility in the ink composition. Therefore, when using multiple types of intramolecular cleavage-type photopolymerization initiators (B), it is effective to use an acylphosphine oxide-based photopolymerization initiator having an ethoxy group in order to ensure the solubility of the photopolymerization initiators. The ethoxy group (CH2CH2O) in the molecule may be bonded to a carbon atom or to a heteroatom (an atom other than carbon), such as a phosphorus atom. Since acylphosphine oxide-based photopolymerization initiators having an ethoxy group may not have sufficient curability, it is particularly preferable to use them in combination with an intramolecular cleavage-type photopolymerization initiator that has high curability.

[0064] Examples of acylphosphine oxide-based photopolymerization initiators containing an ethoxy group include ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate (SPeedCure TPO-L (Arkema product name)).

[0065] The amount of ethoxy-group-containing acylphosphine oxide-based photopolymerization initiator contained in the ink composition of the present invention is preferably 2 to 10% by mass, and more preferably 3 to 8% by mass. If the amount of ethoxy-group-containing acylphosphine oxide-based photopolymerization initiator is greater than 10% by mass, unreacted ethoxy-group-containing acylphosphine oxide-based photopolymerization initiator may reduce the hardness of the coating film formed from the ink.

[0066] From the viewpoint of ensuring solubility of the photopolymerization initiator while achieving high reactivity, the ink composition of the present invention preferably contains both a bisacylphosphine oxide-based photopolymerization initiator and an acylphosphine oxide-based photopolymerization initiator having an ethoxy group. Furthermore, the mass ratio (B1 / B2) of the bisacylphosphine oxide-based photopolymerization initiator (B1) to the acylphosphine oxide-based photopolymerization initiator (B2) having an ethoxy group is preferably 10 / 90 to 75 / 25, and more preferably 40 / 60 to 60 / 40.

[0067] The ink composition of the present invention may contain a thioxanthone derivative as a sensitizer to improve the curability of the acylphosphine oxide-based photopolymerization initiator. However, from the viewpoint of suppressing discoloration of the coating film formed from the ink composition, the amount of thioxanthone derivative is preferably 0 to 0.2% by mass.

[0068] Examples of thioxanthone derivatives include 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone.

[0069] The ink composition of the present invention preferably does not contain 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide. It is desirable to avoid using this photopolymerization initiator due to concerns about reproductive toxicity.

[0070] The ink composition of the present invention contains a radical-stable hindered amine-based light stabilizer. In the present invention, "radical-stable light stabilizer" means a light stabilizer that is stable in a state where it has unpaired electrons in its molecule. The radical-stable hindered amine-based light stabilizer can reduce the curability of the ink composition to ultraviolet irradiation, and the curing speed can be adjusted by the amount added. Furthermore, when the polymerization reaction is delayed by using the radical-stable hindered amine-based light stabilizer, the hardness of the film formed from the ink can be maintained without decreasing. In this specification, the radical-stable hindered amine-based light stabilizer is referred to as component (C), and is also referred to as "radical-stable hindered amine-based light stabilizer (C)", "hindered amine-based light stabilizer (C)", or "light stabilizer (C)".

[0071] Printers equipped with UV-curing ink can perform gloss-finish printing using clear ink. While there are various methods for gloss-finish printing, the basic principle is that after dispensing clear ink onto the substrate, it is not cured immediately but allowed to mature over time. This allows the dispensed clear ink droplets to coalesce and become smooth, after which a coating film is formed by UV irradiation. Challenges with this method include appearance defects caused by flying debris while the droplets are coalescing, and corrosion of the substrate itself. Generally, to solve these problems, a method is employed in which weak UV irradiation is performed immediately after dispensing the clear ink onto the substrate to pre-cur it. The ink composition of the present invention can also be used as printer ink in printing methods that include such pre-curing.

[0072] The amount of hindered amine-based light stabilizer (C) contained in the ink composition of the present invention is 0.05 to 2.0% by mass, preferably 0.10 to 1.00% by mass. The hindered amine-based light stabilizer (C) may be used alone or in combination of two or more types. If the amount of hindered amine-based light stabilizer (C) is less than 0.05% by mass, a sufficient reduction in curing speed cannot be obtained, and the glossy print will fully harden during the preliminary curing stage, making it impossible to form a smooth film. On the other hand, if the amount of hindered amine-based light stabilizer (C) exceeds 2.0% by mass, the curing speed will decrease significantly, and the hardness of the film formed from the ink will decrease.

[0073] Examples of hindered amine-based light stabilizers (C) that are stable as radicals include 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and 2,2,6,6-tetramethylpiperidine-1-oxyl.

[0074] The ink composition of the present invention may contain a hindered amine-based light stabilizer (C) that is stable as a radical, as well as a hindered amine-based light stabilizer that is not stable as a radical. The hindered amine-based light stabilizer (C) that is stable as a radical is a compound represented by the following formula (I). [ka] (R represents a hydrogen atom or a hydroxyl group.) Furthermore, hindered amine light stabilizers that do not fall under the category of radical-stable hindered amine light stabilizers (C) are hindered amine compounds having one or more skeletons represented by the following formula (II) or formula (II'). [ka] (R1 represents one of the following: a hydrogen atom, a hydroxyl group, or a hydrocarbon group which may contain a heteroatom.) R2 represents either a hydrogen atom, a methyl group, or an alkoxyl group. [ka] (R3 represents either a hydrogen atom, a methyl group, or an alkoxyl group.)

[0075] The ink composition of the present invention preferably contains a polymerization inhibitor. Examples of polymerization inhibitors include hydroquinone compounds, phenolic compounds, phenothiazine compounds, and nitroso compounds.

[0076] Specific examples of polymerization inhibitors include phenol compounds such as phenol, o-, m- or p-cresol, 2-t-butyl-4-methylphenol, 6-t-butyl-2,4-dimethylphenol, 2,6-di-t-butyl-4-methylphenol, 2-t-butylphenol, 4-t-butylphenol, 2,4-di-t-butylphenol, 2-methyl-4-t-butylphenol, 4-t-butyl-2,6-dimethylphenol, hydroquinone, hydroquinone monomethyl ether, methylhydroquinone, 2,5-di-t-butylhydroquinone, 2-methyl-p-hydroquinone, and 2,3-di- Examples include hydroquinone compounds such as methylhydroquinone, trimethylhydroquinone, 4-methylbenzcatechin, t-butylhydroquinone, 3-methylbenzcatechin, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, t-butylhydroquinone, benzoquinone, t-butyl-p-benzoquinone, and 2,5-diphenyl-p-benzoquinone; phenothiazine compounds such as phenothiazine; and nitroso compounds such as N-nitroso-N-phenylhydroxylamine ammonium and N-nitroso-N-phenylhydroxylamine aluminum salt.

[0077] The amount of polymerization inhibitor contained in the ink composition of the present invention is preferably within the range of 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. Too much polymerization inhibitor may cause curing failure. The lower limit of the polymerization inhibitor content is, for example, 0.01% by mass or more, and preferably 0.1% by mass or more. The polymerization inhibitor may be used alone or in combination of two or more types.

[0078] The clear ink composition of the present invention may contain colorants such as dyes and pigments, as long as it is a clear ink, but it is preferable that it does not contain colorants. Extender pigments and rust-preventive pigments can also be used in the ink composition of the present invention.

[0079] The ink composition of the present invention may optionally contain a pigment dispersant to disperse the pigment. The pigment dispersant content is, for example, 0.1 to 5% by mass of the ink composition. The pigment dispersant may be used alone or in combination of two or more types.

[0080] The ink composition of the present invention may further contain a surface modifier from the viewpoint of improving wettability, etc. A surface modifier is a substance that has hydrophilic and hydrophobic parts in its molecular structure and can adjust the surface tension of the ink composition when added.

[0081] Surface modifiers that can be used in the ink composition of the present invention include, specifically, anionic surface modifiers such as dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts; nonionic surface modifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers; cationic surface modifiers such as alkylamine salts and quaternary ammonium salts; acrylic surface modifiers; silicone surface modifiers; and fluorine-based surface modifiers. Silicone-based and acrylic surface modifiers are particularly preferred, and commercially available products from companies such as Bic Chemie, Evonik, and Toray Dow Corning can be used. Furthermore, in the case of silicone-based surface modifiers, it is preferable that they be polyether-modified silicone oils with an HLB of 7.6 to 12.

[0082] The amount of surface modifier can be appropriately selected depending on the intended use, but it is preferably 0.01 to 1% by mass in the ink composition. The surface modifier may be used alone or in combination of two or more types.

[0083] Specific examples of the surface conditioner include BYK-300, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-315N, BYK-320, BYK-322, BYK-323, BYK-325, BYK-326, BYK-330, BYK-331, BYK-333, BYK-342, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-350, BYK-354, BYK-355, BYK-356, BYK-358N, BYK-361N, BYK-370, BYK-375, BYK-377, BYK-378, BYK-381, BYK-392, BYK-394, BYK-399, BYK-3440, BYK-3441, BYK-3455, BYK-3550, BYK-3560, BYK-3565, BYK-3760, BYK-DYNWET 800N, BYK-SILCLEAN 3700, BYK-SILCLEAN 3701, BYK-SILCLEAN 3720, BYK-UV3500, BYK-UV3505, BYK-UV3510, BYK-UV3530, BYK-UV3535, BYK-UV3570, BYK-UV3575, BYK-UV3576 (all manufactured by BYK Chemie Japan Co., Ltd.), TEGO Flow 300, TEGO Flow 370, TEGO Flow 425, TEGO Flow ATF 2, TEGO Flow ZFS 460, TEGO Glide 100, TEGO Glide 110, TEGO Glide 130, TEGO Glide 406, TEGO Glide 410, TEGO Glide 411, TEGO Glide 415, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Glide 482, TEGO GlideA 115, TEGO GlideB 1484, TEGO GlideZG 400 (all manufactured by Evonik Japan Co., Ltd.), 501W ADDITIVE, FZ-2104, FZ-2110, FZ-2123, FZ-2164, FZ-2191, FZ-2203, FZ-2215, FZ-2222, FZ-5609, L-7001, L-7002, L-7604, OFX-0193, OFX-0309 FLUID, OFX-5211 FLUID, SF 8410 FLUID, SH3771, SH 3746 FLUID, SH 8400 FLUID, SH 8700 FLUID, Y-7006 (all manufactured by Toray Dow Corning), Examples include KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6004, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, X-22-2516, X-22-4515 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0084] The ink composition of the present invention may contain an ultraviolet absorber. The ultraviolet absorber has the effect of absorbing ultraviolet light and preventing degradation caused by ultraviolet light. Examples of ultraviolet absorbers include cyanoacrylate compounds, benzophenone compounds, benzoate compounds, benzotriazole compounds, hydroxyphenyltriazine compounds, benzylidene camphor compounds, and inorganic fine particles.

[0085] Examples of UV absorbers include: 2,4-dihydroxybenzophenone, 2-Hydroxy-4-methoxybenzophenone, 2-Hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-Hydroxy-4-octoxybenzophenone, 2-Hydroxy-4-dodecyloxybenzophenone-2-Hydroxy-4-benzyloxybenzophenone, Bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-Hydroxy-4-methoxy-2'-carboxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole 2-[2'-hydroxy-3',5'-bis(α,α-(dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2,2'-methylene-bis[4-(1,1,3,3-tetramethylbutyl)-6-(2N-benzotriazole-2-yl)phenol], A condensate of methyl-3-[3-t-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionate and polyethylene glycol, 2-(2-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2,6-di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate, Examples include hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate.

[0086] The ink composition of the present invention may also contain a resin. The resin plays a role in capturing solid components such as pigments and forming a film on the substrate, thereby contributing to improved adhesion of the ink composition to the substrate.

[0087] Specific examples of resins include polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, chlorinated rubber, chlorinated polyethylene resin, chlorinated polypropylene resin, chlorinated ethylene-vinyl acetate resin, acrylic resin, polystyrene resin, polyamide resin, polyurethane resin, polyolefin resin, silicone resin, fluororesin, epoxy resin, polyester resin, ketone resin, phenolic resin, polyvinyl alcohol, polyvinyl alcohol derivatives (anionic modified polyvinyl alcohol, etc.), cellulose, cellulose derivatives (hydroxymethylcellulose, hydroxyethylcellulose, cellulose acetate, etc.), rosin-based resins, alkyd resins, alginic acid, alginic acid derivatives (propylene glycol alginate, etc.), etc. Modified products of these resins are also included. For example, for resins containing hydroxyl groups, modifications such as hydroxyalkyl etherification and carboxylic acid modification can be used.

[0088] The amount of resin contained in the ink composition of the present invention is preferably within the range of 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. Too much resin may cause curing failure. The resin may be used alone or in combination of two or more types.

[0089] The ink composition of the present invention may optionally contain other additives such as silane coupling agents, antioxidants, plasticizers, rust inhibitors, solvents, antibacterial agents, antiviral agents, viscosity modifiers, fillers, defoaming agents, charge control agents, stress relievers, penetrating agents, light guides, luminescence agents, magnetic materials, and phosphors.

[0090] The ink composition of the present invention can be prepared by mixing various components as needed. Furthermore, it is preferable to filter the ink composition using a filter to prevent nozzle clogging of the print head due to impurities.

[0091] The ink composition of the present invention preferably has a viscosity of 5 to 25 mPa·s at 40°C, and more preferably 5 to 20 mPa·s. Good ejection performance can be obtained if the ink viscosity at 40°C is within the above specified range. The ink viscosity can be measured using a cone-plate viscometer. The temperature at which the ink is ejected is preferably 30°C to 50°C.

[0092] The ink composition of the present invention preferably has a surface tension of 20 to 35 mN / m at 25°C, and more preferably 23 to 33 mN / m. Good ejection performance can be obtained if the ink surface tension at 25°C is within the above specified range. The ink surface tension can be measured by the plate method.

[0093] The present invention aims to provide a clear ink composition that exhibits excellent resistance to natural light and is capable of forming a highly hard film.

[0094] The pencil hardness of the film surface produced from the ink composition of the present invention is preferably 4H or more and 6H or less. Here, the pencil hardness is measured in accordance with JIS K 5600-5-4:1999 (ISO / DIS 15184:1996).

[0095] When the clear ink composition of the present invention is applied to a PET film using a bar coater #3, it can withstand 100 mW / cm² of light using a 385 nm LED lamp. 2 , 200 mJ / cm 2 When cured, it did not harden, 1000 mW / cm² 2 , 1000 mJ / cm 2 When cured, it is preferable that the pencil hardness be 3H or higher. Clear ink compositions that satisfy this condition exhibit excellent smoothness when printing gloss-like finishes.

[0096] The clear ink composition of the present invention was used to form a film on white polycarbonate using a bar coater #5, and then heated using a 385nm LED lamp at 1000mW / cm². 2 , 1000 mJ / cm 2The color difference between the surface of the film produced by curing and the surface of the white polycarbonate paper is preferably 5 or less, and more preferably 3 or less.

[0097] Various printing methods can be used to print the ink composition of the present invention, including gravure printing, offset printing, flexographic printing, screen printing, coater printing, and inkjet printing, but inkjet printing is particularly preferred. Various inkjet printers can be used for inkjet printing. Examples of inkjet printers include those that eject the ink composition using a charge control system or a piezo system. Large-format inkjet printers, specifically those intended for printing on articles produced on industrial lines, can also be suitably used.

[0098] The layer formed by printing using the ink composition of the present invention is cured by irradiation with active energy rays such as ultraviolet light. High-pressure mercury lamps, metal halide lamps, LED lamps, etc., can be used as the light source for the active energy rays. Furthermore, the wavelength of the active energy rays irradiated to cure this layer preferably overlaps with the absorption wavelength of the photopolymerization initiator, and the dominant wavelength of the active energy rays is preferably 350-400 nm. The integrated light intensity of the active energy rays is 100-2000 mJ / cm². 2 It is preferable that it be within the range.

[0099] Examples of substrates on which printing with the ink composition of the present invention is performed include plastic substrates such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyolefin, such as polypropylene (PP); metal substrates such as steel, galvanized steel, tin-plated steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, titanium, titanium alloy; inorganic substrates other than metals such as cement, mortar, concrete, slate, gypsum, calcium silicate, glass, ceramic, calcium carbonate, marble, artificial marble; wood substrates such as wood; paper substrates; and composite substrates that combine two or more of these substrates. Examples of composite substrates include wood fiber reinforced cement board, fiber reinforced cement board, fiber reinforced cement-calcium silicate board, metal substrates that have undergone various surface treatments, such as oxidation treatment, and plastic substrates whose surfaces are coated with inorganic materials (for example, plastic substrates coated with glass).

[0100] The substrate can take on various shapes, such as two-dimensional substrates like films, sheets, or plates, or three-dimensional substrates with complex shapes. The surface of the substrate may be smooth or it may have irregularities.

[0101] The substrate may have undergone pretreatment such as degreasing, chemical treatment, or polishing on its surface, or it may have been coated with a sealer or primer.

[0102] Specific examples of base materials include plastic materials such as PVC sheets, tarpaulins, corrugated plastic sheets, and acrylic sheets; paper types such as coated paper (specifically resin-coated paper), art paper, cast paper, lightly coated paper, fine paper, synthetic paper, and inkjet paper; wood-based building materials such as veneers, plywood, particleboard, and medium-density fiberboard (MDF); inorganic building materials such as ceramic siding boards, flexible boards, calcium silicate boards, gypsum slag barlite boards, wood chip cement boards, pulp cement boards, precast concrete boards, autoclaved lightweight concrete (ALC) boards, and gypsum boards; and metal building materials such as aluminum, iron, and stainless steel, as well as PCM steel sheets, tiles, and glass sheets.

[0103] A substrate on which printing is performed using the ink composition of the present invention may have an additional film formed on part or all of its surface. For example, a film formed by paint, a film formed by ink, etc., may be formed. The additional film may contain resins, pigments, ultraviolet absorbers, radical scavengers, antioxidants, plasticizers, rust inhibitors, anti-algal agents, antifungal agents, antibacterial agents, antiviral agents, fillers, charge control agents, light guides, brightening agents, magnetic materials, phosphors, waxes, etc.

[0104] Examples of paints and inks used to form further films include organic solvent-based paints and inks using organic solvents as the main solvent, water-based paints and inks using water as the main solvent, photocurable paints and inks using polymerizable compounds, powder paints, and various other paints and inks. In the case of photocurable inks, examples of components that can be used include those that can be used in the ink composition of the present invention as described above.

[0105] The means for forming further films are not particularly limited. For example, in the case of paints, various coating methods such as air spraying, airless spraying, roll coaters, flow coaters, and electrostatic coatings can be used. In the case of inks, various printing methods such as gravure printing, offset printing, flexographic printing, screen printing, coater printing, and inkjet printing can be used. [Examples]

[0106] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0107] (Example of clear ink composition preparation) Mixtures containing the components shown in Tables 1-3 were stirred and dissolved until homogenized, then filtered to prepare the clear ink compositions of Examples 1-18 and Comparative Examples 1-5. The results of the following evaluation tests—curing state, hardness of the clear printed material (hardness of the coating film), tack, color difference with a white carbonate board, and natural light resistance—are shown in Tables 1-3, respectively.

[0108] (A) Aminoacrylate • EBECRYL 7100 (manufactured by Daicel Ornex), bifunctional aminoacrylate • EBECRYL 80 (manufactured by Daicel Ornex), a tetrafunctional amine-modified highly reactive polyether acrylate. (B) Intramolecular cleavage polymerization initiator Ominirad 819 (Omnirad 380) (manufactured by IGM Resins BV), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide Omnirad TPO-L (manufactured by IGM Resins BV), ethyl (2,4,6-trimethylbenzoyl)-phenylphosphonate • Ominirad TPO H (manufactured by IGM Resins BV), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (C) Hindered amine-based light stabilizers TEMPOL (EVONIK) 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical (D) Monofunctional polymerizable compounds • Light acrylate THF-A (manufactured by Kyoeisha Chemical Co., Ltd.), tetrahydrofurfuryl acrylate • Light acrylate PO-A (manufactured by Kyoeisha Chemical Co., Ltd.), phenoxyethyl acrylate (E) 2-functional polymerizable compound · Light Acrylate 1,6-HX-A (manufactured by Kyoeisha Chemical Co., Ltd.), 1,6-hexanediol diacrylate · DPGDA (manufactured by Daicel Ornex Co., Ltd.), dipropylene glycol diacrylate (F) Polymerizable compounds with 3 or more functional groups: (G) 4-functional polymerizable compound · Light Acrylate PE-4A (manufactured by Kyoeisha Chemical Co., Ltd.), pentaerythritol tetraacrylate (F) Polymerizable compounds with 3 or more functional groups: (H) 6-functional polymerizable compound · Light Acrylate DPE-6A (manufactured by Kyoeisha Chemical Co., Ltd.), dipentaerythritol hexaacrylate (I) Other materials · BHT (manufactured by Seiko Chemical Co., Ltd.), butylated hydroxytoluene · MEHQ (manufactured by Seiko Chemical Co., Ltd.), 4-methoxyphenol · BYK-UV 3500 (manufactured by Big Chemie), silicone-based surface conditioner

[0109] <Hardened state> Based on the formulations described in Tables 1 to 3, clear ink compositions of Examples 1 to 18 and Comparative Examples 1 to 5 were prepared respectively. Subsequently, a commercially available PET film (HK-33WF manufactured by Toyama Film: 70 mm × 150 mm × thickness 188 μm) was coated with the clear ink composition prepared with a bar coater #5, and then irradiated with active energy rays (LED 385 nm) at the following two irradiation intensities respectively to obtain clear prints. · 100 mW / cm 2 , 200 mJ / cm 2 · 1000 mW / cm 2 , 1000 mJ / cm 2

[0110] Each of the prepared clear prints was rubbed with a cotton swab, and the hardened state was evaluated according to the following criteria. 100 mW / cm 2 , 200 mJ / cm 2 In the case of ◎ : Liquid state ○: Jelly-like △: Scratch marks appear, but it hardens. ×: No trace was left when rubbed with a cotton swab; it has completely hardened. 1000 mW / cm 2 , 1000 mJ / cm 2 in the case of, ◎: No marks are left when rubbed with a cotton swab, and it is completely hardened. ○: Scratch marks appear, but it hardens. △: Jelly-like ×: Liquid state

[0111] <Hardness of clear printed materials> For each clear printed material produced using the method described above, the pencil hardness of the printed material was measured in accordance with JIS K 5600-5-4:1999. If the hardness was less than H or if there were undissolved ink particles, it was indicated with "-".

[0112] <Tack> Based on the formulations described in Tables 1 to 3, clear ink compositions for Examples 1 to 18 and Comparative Examples 1 to 5 were prepared, respectively. Subsequently, the prepared clear ink compositions were applied to a commercially available PET film (Higashiyama Film HK-33WF: 70 mm x 150 mm x 188 μm thick) using a bar coater #5, and then subjected to a 1000 mW / cm² coating. 2 , 1000 mJ / cm 2 Clear printed material was obtained by irradiating the material with an active energy ray (LED 385nm) at this intensity.

[0113] Each clear printed material produced was touched and evaluated according to the following criteria. ◎: No pleats ○: Slightly pleated ×: With pleats

[0114] <Color difference ΔE compared to white polycarbonate sheet> Based on the formulations described in Tables 1 to 3, clear ink compositions for Examples 1 to 18 and Comparative Examples 1 to 5 were prepared, respectively. After applying the prepared clear print to white polycarbonate (70 mm x 150 mm, 2 mm thick) purchased from TP Giken using a bar coater #5, a 1000 mW / cm² load was applied. 2 , 1000 mJ / cm 2 Clear printed material was obtained by irradiating the material with an active energy ray (LED 385nm) at this intensity.

[0115] Using an X-Rite CH-8105 colorimeter, the L, a, and b values ​​were measured, and the ΔE value was calculated.

[0116] <Natural light resistance test> Based on the formulations described in Tables 1 to 3, clear ink compositions for Examples 1 to 18 and Comparative Examples 1 to 5 were prepared, respectively. Subsequently, 5 g of ink was placed in a colorless, transparent glass bottle (Maruemu Co., Ltd., screw-top tube No. 3), and the state was checked after being left under fluorescent light for 1 hour.

[0117] The ink that had been left standing was visually inspected and evaluated according to the following criteria. ◎: No hardened material ○: The material has hardened, but more than half of it is still liquid. ×: More than half has hardened.

[0118] [Table 1]

[0119] [Table 2]

[0120] [Table 3]

Claims

1. A clear ink composition comprising a polymerizable compound, a photopolymerization initiator, and a light stabilizer, The polymerizable compound comprises at least aminoacrylate (A), The photopolymerization initiator comprises two or more intramolecular cleavage type photopolymerization initiators (B), The light stabilizer comprises a hindered amine-based light stabilizer (C) that is stable as a radical represented by the following formula (I), and the amount of the aminoacrylate (A) contained in the clear ink composition is 5.0 to 25.0% by mass. A clear ink composition wherein the amount of the hindered amine-based light stabilizer (C) contained in the clear ink composition is 0.05 to 2.0% by mass. 【Chemistry 1】 (R represents a hydrogen atom or a hydroxyl group.)

2. The clear ink composition according to claim 1, wherein the clear ink composition does not contain a coloring agent.

3. The clear ink composition according to claim 1 or 2, wherein the polymerizable compound comprises a monofunctional polymerizable compound (D), a difunctional polymerizable compound (E), and a trifunctional or higher polymerizable compound (F), and the monofunctional polymerizable compound (D), the difunctional polymerizable compound (E), and the trifunctional or higher polymerizable compound (F) are polymerizable compounds different from the aminoacrylate (A).

4. The clear ink composition according to claim 3, wherein the mass ratio (E / F) of the bifunctional polymerizable compound (E) to the trifunctional or more polymerizable compound (F) is 30 / 70 to 70 / 30.

5. The clear ink composition according to claim 3, wherein the three- or more-functional polymerizable compound (F) comprises a four-functional polymerizable compound (G) and a six-functional polymerizable compound (H).

6. The clear ink composition according to claim 5, wherein the mass ratio (G / H) of the tetrafunctional polymerizable compound (G) to the hexafunctional polymerizable compound (H) is 80 / 20 to 40 / 60.

7. The clear ink composition according to claim 1 or 2, wherein at least one of the intramolecular cleavage-type photopolymerization initiators (B) is an acylphosphine oxide-based photopolymerization initiator having an ethoxy group.

8. The clear ink composition according to claim 1 or 2, comprising 2 to 10% by mass of the ethoxy group-containing acylphosphine oxide-based photopolymerization initiator described in claim 7.

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