UV-curable inkjet clear ink composition

Abstract

To provide a clear ink composition which has excellent gloss on a printed surface, low viscosity and excellent curability. [Solution] The ultraviolet-curable inkjet clear ink composition has a viscosity of 5 to 15 mPa·s at 25°C, and contains, per 100 parts by weight of the clear ink composition, 1 to 15 parts by weight of an alicyclic bifunctional monomer, 1 to 10 parts by weight of a trifunctional or higher functional monomer, and 10 to 20 parts by weight of a photopolymerization initiator.

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet-curable inkjet clear ink composition, and more particularly to a low-viscosity ultraviolet-curable inkjet clear ink composition. [Background technology]

[0002] Inkjet printing is a method in which liquid ink is ejected from ink head nozzles to print on a substrate. One type of ink used in inkjet printing is an ultraviolet-curable inkjet ink composition. After being ejected from the ink head nozzles, the ultraviolet-curable inkjet ink composition is cured by crosslinking the polymerizable compound in the ink upon exposure to ultraviolet light, thereby forming a cured coating.

[0003] UV-curable inkjet inks must have a viscosity that allows them to be ejected from ink head nozzles, and they must also have a low viscosity so that small droplets can be ejected stably.

[0004] In recent years, among UV-curable inkjet inks, substantially colorless and transparent inks that are coated on printed color inks have been proposed. Such inks, generally referred to as clear inks, are intended to eliminate uneven gloss caused by differences in reflectance between the color ink layer and the printing substrate, and to impart gloss by smoothing the surface of the color ink layer.

[0005] Patent Document 1 describes a UV-LED-curable clear ink composition for inkjet printing, which contains a photopolymerizable monomer having an amide group and / or an amino group (hereinafter referred to as an "amine-based photopolymerizable monomer") as a photopolymerizable monomer.

[0006] Patent Document 2 describes an inkjet ink composition containing, as polymerizable compounds, a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule. The inkjet ink composition of Patent Document 2 has low viscosity and excellent curability and stretchability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-20457 [Patent Document 2] Japanese Patent Application Publication No. 2018-65911 Summary of the Invention [Problem to be solved by the invention]

[0008] The clear ink composition described in Patent Document 1 contains an amine-based photopolymerizable monomer to achieve UV-LED curing. However, amine-based photopolymerizable monomers have high viscosity. Therefore, it is difficult to further reduce the viscosity of the clear ink composition described in Patent Document 1 in order to further improve ejection stability from the ink head nozzle. Another problem is that cured coatings containing amine-based photopolymerizable monomers tend to yellow over time.

[0009] The inkjet ink composition of Patent Document 2 does not contain an amine-based photopolymerizable monomer, has low viscosity, and exhibits excellent curability. However, in Patent Document 2, the inkjet ink composition is used as a color ink. Therefore, it is unclear whether the inkjet ink composition of Patent Document 2 can eliminate uneven gloss in the printed color ink layer and improve the gloss of the printed surface as an inkjet clear ink composition.

[0010] The present invention solves the above-mentioned conventional problems, and has as its object to provide an ultraviolet-curable inkjet clear ink composition that has excellent gloss on the printed surface, low viscosity, and excellent curability. Hereinafter, the ultraviolet-curable inkjet clear ink composition may be referred to as the "clear ink composition." [Means for solving the problem]

[0011] The present invention provides an ultraviolet-curable inkjet clear ink composition having a viscosity of 5 to 15 mPa·s at 25°C, and containing, per 100 parts by weight of the clear ink composition, 1 to 15 parts by weight of an alicyclic bifunctional monomer, 1 to 10 parts by weight of a trifunctional or higher functional monomer, and 10 to 20 parts by weight of a photopolymerization initiator.

[0012] In one embodiment, the alicyclic bifunctional monomer is at least one selected from the group consisting of tricyclodecane dimethanol di(meth)acrylate and cyclohexane dimethanol diacrylate.

[0013] In one embodiment, the tri- or higher functional monomer is at least one selected from the group consisting of pentaerythritol tri(meth)acrylate and trimethylolpropane triacrylate.

[0014] In one embodiment, the photopolymerization initiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0015] In one embodiment, any of the above clear ink compositions further contains a heterocyclic monofunctional monomer having a glass transition temperature (Tg) of 0°C or lower in an amount of 19 to 50 parts by weight per 100 parts by weight of the clear ink composition.

[0016] In one embodiment, the heterocyclic monofunctional monomer is tetrahydrofurfuryl acrylate.

[0017] In one embodiment, any of the above clear ink compositions further contains 0.1 to 40 parts by weight of an alicyclic monofunctional monomer relative to 100 parts by weight of the clear ink composition.

[0018] In one embodiment, the alicyclic monofunctional monomer is at least one selected from the group consisting of isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl acrylate, and 4-tert-butylcyclohexyl acrylate.

[0019] In one embodiment, any of the above clear ink compositions does not contain an amine-based monomer. [Effects of the Invention]

[0020] According to the present invention, there is provided an ultraviolet-curable inkjet clear ink composition that has excellent gloss on the printed surface, low viscosity, and excellent curability. DETAILED DESCRIPTION OF THE INVENTION

[0021] The ultraviolet-curable inkjet clear ink composition of the present invention contains, as photopolymerizable compounds, an alicyclic bifunctional monomer, a trifunctional or higher polyfunctional monomer, and a photopolymerization initiator, and may further contain any other additives, etc., as required.

[0022] The ultraviolet-curable inkjet clear ink composition of the present invention is substantially free of solvent. Here, "substantially free of solvent" does not necessarily mean that a dilution solvent is contained, but that a dilution solvent may inevitably be mixed into the ink during industrial use, for example. In such cases, the content of the solvent contained in the ink composition is 3 wt % or less relative to the total weight of the clear ink composition. Examples of solvents include various known solvents, such as aliphatic solvents such as alcohols, ethers, and ketones, and aromatic solvents such as benzene, toluene, and xylene. Because the clear ink composition of the present invention is solvent-free, no volatile solvent remains in the ink layer, which is preferable from the viewpoint of being free of volatile organic compounds.

[0023] In this specification, a photopolymerizable compound refers to a compound that initiates a photopolymerization reaction and hardens when irradiated with ultraviolet light. Among photopolymerizable compounds, a photopolymerizable monofunctional monomer refers to a compound having one ethylenic double bond in one molecule, a photopolymerizable bifunctional monomer refers to a compound having two ethylenic double bonds in one molecule, and a non-synthetic polyfunctional monomer refers to a compound having three or more ethylenic double bonds in one molecule. In this specification, having an ethylenic double bond means having a (meth)acryloyl group (acryloyl group and / or methacryloyl group).

[0024] <1. Photopolymerizable compound> <1-1. Photopolymerizable monofunctional monomers> The clear ink composition of the present invention contains a photopolymerizable monofunctional monomer. Examples of the photopolymerizable monofunctional monomer include amyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, isomyristyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, neopentyl glycol (meth)acrylic acid benzoate, butoxyethyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, methoxy-triethylene glycol (meth)acrylate, methoxy-polyethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, and phenoxyethyl (meth)acrylate. Acrylate, phenoxy-polyethylene glycol (meth)acrylate, 2-(2-ethoxyethoxyethyl acrylate) nonylphenol ethylene oxide adduct (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 1,4-cyclohexanedimethanol monoacrylate, ethoxylated nonylphenyl acrylate, and the like. These photopolymerizable monofunctional monomers may be used alone or in combination of two or more.

[0025] The photopolymerizable monofunctional monomer preferably has a viscosity of 25 mPa·s or less at 25°C. When the viscosity of the photopolymerizable monofunctional monomer is within this range, it is possible to adjust the viscosity of the clear ink composition to a low level by adjusting the amount used. The viscosity of the photopolymerizable monofunctional monomer is preferably 15 mPa·s or less, and more preferably 10 mPa·s or less.

[0026] Among photopolymerizable monofunctional monomers, tetrahydrofurfuryl (meth)acrylate, isobornyl acrylate, 3,5,5-trimethylcyclohexyl acrylate (TMCHA), 4-tert-butylcyclohexyl acrylate (TBCHA), 2-(2-ethoxyethoxyethyl acrylate), 2-ethylhexyl (meth)acrylate, etc. are preferred because they have a low viscosity of less than 10 mPa·s at 25°C.

[0027] Among the photopolymerizable monofunctional monomers, isobornyl acrylate, 3,5,5-trimethylcyclohexyl acrylate, and 4-tert-butylcyclohexyl acrylate, which have an alicyclic structure, are particularly preferred because they have excellent dilution properties and improve the tack-free properties of the resulting cured coating.

[0028] The amount of alicyclic monofunctional monomer used is preferably 0.1 to 40 parts by weight per 100 parts by weight of the clear ink composition. Using the alicyclic monofunctional monomer in this range makes it easier to adjust the viscosity of the clear ink composition to a low level. The amount of alicyclic monofunctional monomer used is more preferably 5 to 35 parts by weight, and even more preferably 10 to 30 parts by weight per 100 parts by weight of the clear ink composition.

[0029] The photopolymerizable monofunctional monomer is preferably a heterocyclic monofunctional monomer having a glass transition temperature (Tg) of 0°C or lower. The amount of the heterocyclic monofunctional monomer having a Tg of 0°C or lower used is preferably 19 to 50 parts by weight per 100 parts by weight of the clear ink composition. This provides the cured coating with appropriate hardness and the ink layer (ink coating) with stretchability.

[0030] <1-2. Photopolymerizable bifunctional monomer> The clear ink composition of the present invention contains a photopolymerizable bifunctional monomer. The photopolymerizable bifunctional monomer has higher reactivity than a monofunctional monomer and lower reactivity than a trifunctional or higher polyfunctional monomer. The photopolymerizable bifunctional monomer functions as a viscosity diluent for the trifunctional or higher polyfunctional monomer, while supplementing the reactivity of the monofunctional monomer, thereby imparting hardness and adhesion to the printing substrate to the cured coating while maintaining a low viscosity of the entire clear ink composition.

[0031] Examples of the photopolymerizable bifunctional monomer include 2-hydroxy-3-acryloyloxypropyl(meth)acrylate, hydroxypivalylhydroxypivalate di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 2,methyl-1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 3,methyl-1,5-pentanediol di(meth)acrylate, ethoxylated 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, polyethylene glycol #200 di(meth)acrylate, Examples of photopolymerizable bifunctional monomers include polyethylene glycol #400 di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol #400 di(meth)acrylate, polypropylene glycol #700 di(meth)acrylate, glycerin di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol #600 di(meth)acrylate, polyethylene glycol #1000 di(meth)acrylate, ethoxylated polypropylene glycol #700 di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, tricyclodecane dimethanol diacrylate, etc. These photopolymerizable bifunctional monomers may be used alone or in combination of two or more. Among the bifunctional monomers, alicyclic bifunctional monomers such as cyclohexanedimethanol di(meth)acrylate and tricyclodecanedimethanol diacrylate are preferred from the viewpoint of improving the strength of the cured coating.

[0032] The photopolymerizable bifunctional monomer preferably has a viscosity of 180 mPa·s or less at 25°C. When the viscosity of the photopolymerizable bifunctional monomer is within this range, it is possible to adjust the viscosity of the clear ink composition to a low level by adjusting the amount used. The viscosity of the photopolymerizable bifunctional monomer is preferably 150 mPa·s or less, and more preferably 130 mPa·s or less.

[0033] If one of the multiple photopolymerizable bifunctional monomers used has a high viscosity, the viscosity of the clear ink composition can be adjusted to a low level by using in combination with the other photopolymerizable bifunctional monomer with a low viscosity of less than 10 mPa·s at 25° C. An example of such a low-viscosity photopolymerizable bifunctional monomer is the aliphatic bifunctional monomer 1,6-hexanediol di(meth)acrylate.

[0034] Among the aliphatic bifunctional monomers, tricyclodecane dimethanol diacrylate and cyclohexane dimethanol di(meth)acrylate, which have an alicyclic structure, are particularly preferred because they improve the tack-free properties and strength of the cured coating.

[0035] The amount of the alicyclic bifunctional monomer used is 1 to 15 parts by weight per 100 parts by weight of the clear ink composition. By using the alicyclic bifunctional monomer in this amount, the viscosity of the clear ink composition can be adjusted to a low level while maintaining the curability. The amount of the alicyclic bifunctional monomer used is preferably 3 to 15 parts by weight, more preferably 3 to 10 parts by weight per 100 parts by weight of the clear ink composition.

[0036] <1-3. Photopolymerizable polyfunctional monomers> The clear ink composition of the present invention contains a photopolymerizable polyfunctional monomer. Examples of the photopolymerizable polyfunctional monomer include ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate (TMPTA), pentaerythritol tri(meth)acrylate (PETA), tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, glyceryl tri(meth)acrylate, and ethylene oxide-, propylene oxide-, and caprolactone-modified versions of these. These photopolymerizable polyfunctional monomers can be used alone or in combination.

[0037] Among the photopolymerizable polyfunctional monomers, ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, and trimethylolpropane tri(meth)acrylate (TMPTA) are preferred because they have relatively low viscosity, and pentaerythritol tri(meth)acrylate (PETA) is preferred from the viewpoint of improving the curability of the coating film. By appropriately combining these photopolymerizable polyfunctional monomers with the monofunctional and bifunctional monomers, it is possible to obtain a clear ink composition that has excellent curability while maintaining a low viscosity as a whole.

[0038] The amount of photopolymerizable polyfunctional monomer used is 1 to 10 parts by weight per 100 parts by weight of the clear ink composition. By using the photopolymerizable polyfunctional monomer in this range, the viscosity can be adjusted to a low level while maintaining the curability of the clear ink composition. The amount of photopolymerizable polyfunctional monomer used is preferably 3 to 10 parts by weight per 100 parts by weight of the clear ink composition.

[0039] <2. Photopolymerization initiator> The clear ink composition of the present invention contains at least one of an alkylphenone compound and a thioxanthone compound as a photopolymerization initiator, which allows the photopolymerization reaction of the clear ink composition to be initiated by ultraviolet irradiation.

[0040] Examples of the alkylphenone compounds include α-aminoalkylphenones and benzyl methyl ketals. Specific examples include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-methyl-1-[4-(methoxythio)phenyl]-2-morpholinopropan-2-one, and 2,2-dimethoxy-1,2-diphenylethan-1-one. These compounds can be used alone or in combination. Commercially available alkylphenone compounds include Irgacure 369, Irgacure 907, and Irgacure 651 manufactured by Ciba.

[0041] Examples of the thioxanthone compounds include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These compounds can be used alone or in combination. Commercially available thioxanthone compounds include KAYACUREDETX-S manufactured by Nippon Kayaku Co., Ltd. and Chivacure ITX manufactured by Double Bond Chemical Co., Ltd.

[0042] In addition to the above, the clear ink composition according to the present invention may further contain a conventionally known photopolymerization initiator such as an acylphosphine oxide compound, an aryl alkyl ketone, an oxime ketone, an acylphosphine oxide, an acylphosphonate, S-phenyl thiobenzoate, titanocene, an aromatic ketone, benzyl, a quinone derivative, or a ketocoumarin.

[0043] Examples of the photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1-hydroxy-cyclohexyl-phenyl-ketone 1,2-octanedione-[4-(phenylthio)-2-(o-benzoyloxime)], bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and 2,4,6-trimethylbenzoyl-phosphine oxide.

[0044] Among these, acylphosphine oxide compounds such as 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO) and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide are particularly preferred because they make the cured coating less susceptible to yellowing.

[0045] The amount of photopolymerization initiator used in the clear ink composition according to the present invention is 10 to 20 parts by weight, and more preferably 10 to 13 parts by weight, per 100 parts by weight of the clear ink composition, taking into consideration the curing properties of the coating film that is formed.

[0046] <3. Additives> <3-1. Polymerization inhibitors> The polymerization inhibitor may further contain a phenol-based antioxidant, a phosphorus-based antioxidant, a hydroquinone monoalkyl ether, etc. Examples of such polymerization inhibitors include hydroquinone monomethyl ether, hydroquinone, t-butylcatechol, and pyrogallol.

[0047] <3-2. Surface conditioners> The clear ink composition of the present invention may further contain a silicone-based compound having a polydimethylsiloxane structure as a surface conditioner. By using a silicone-based compound as a surface conditioner together with the polymerizable compound, the liquid properties such as the surface tension of the ink can be adjusted to ranges suitable for inkjet printing methods.

[0048] Examples of the silicone-based compound include BYK-UV3500, BYK-UV3510, and BYK-UV3570 manufactured by BYK-Chemie, Tego-Rad2100, Tego-Rad2200N, Tego-Rad2250, Tego-Rad2300, Tego-Rad2500, Tego-Rad2600, and Tego-Rad2700 manufactured by Degussa, and UCR-L72 and UCR-L93 manufactured by Kyoeisha Chemical Co., Ltd. These compounds contain a polydimethylsiloxane structure having an ethylenic double bond in the molecule, and therefore can further improve adhesion.

[0049] <3-3. Other additives> The clear ink composition according to the present invention may further contain known general additives, such as surfactants, leveling agents, antifoaming agents, antioxidants, pH adjusters, charge-imparting agents, bactericides, preservatives, deodorizers, charge adjusters, humectants, antiskinning agents, and fragrances, as needed.

[0050] <4. Manufacturing method> The clear ink composition of the present invention can be produced using a conventionally known process.

[0051] For example, the various photopolymerizable compounds, photopolymerization initiators, polymerization inhibitors, and surface conditioners, as well as other additives if necessary, are added and uniformly mixed using a stirrer. Examples of stirrers include a three-one motor, a magnetic stirrer, a disperser, and a homogenizer. The clear ink composition may also be mixed using a mixer such as a line mixer. Furthermore, the clear ink composition may also be mixed using a disperser such as a bead mill or a high-pressure jet mill in order to further refine the particles in the clear ink composition.

[0052] The clear ink composition of the present invention has a viscosity at 25°C of 5 to 15 mPa·s. If the viscosity of the clear ink composition is less than 5 mPa·s, the ejection stability will decrease, and if it exceeds 15 mPa·s, the gloss of the printed surface will decrease. The viscosity of the clear ink composition is preferably 6 to 12 mPa·s, and more preferably 7 to 10 mPa·s. The viscosity of the clear ink composition can be adjusted taking into account the viscosity of the components and the amounts used.

[0053] <5. Manufacturing method of cured film> A cured film of the clear ink composition can be produced, for example, by forming a coating film on the surface of a substrate to be printed using an inkjet system and then curing the coating film by irradiating it with ultraviolet light. Examples of means for irradiating the coating film with ultraviolet light include a mercury lamp and a metal halide lamp. [Example]

[0054] The present invention will be explained in more detail below based on examples. However, the present invention is not limited to these examples. Numerical values ​​in the examples are by weight unless otherwise specified. Viscosity values ​​are measured at 25°C.

[0055] The raw materials used in the clear ink composition of the present invention are as follows. <Photopolymerizable compound> (Heterocyclic monofunctional monomer) THFA: tetrahydrofurfuryl acrylate ("Sartomer SR285" (trade name) manufactured by Arkema, viscosity: 6 cps, Tg: -12°C) (alicyclic monofunctional monomer) IBXA: isobornyl acrylate ("IBXA" (trade name) manufactured by Osaka Organic Chemical Industry, Ltd., viscosity: 9 cps, Tg: 97°C) TMCHA: 3,3,5-trimethylcyclohexyl acrylate ("Sartomer SR420" (trade name) manufactured by Arkema, viscosity: 2.7, Tg: 43°C) TBCHA: 4-tert-butylcyclohexyl acrylate ("Sartomer SR217" (trade name) manufactured by Arkema, viscosity: 4.6, Tg: 65°C) (alicyclic dimonofunctional monomer) DCPDA: Tricyclodecane dimethanol diacrylate ("Sartomer SR833" (trade name) manufactured by Arkema, viscosity: 130, Tg: 180°C) CHDMDA: cyclohexanedimethanol diacrylate ("Sartomer CD406" (trade name) manufactured by Arkema, viscosity: 25, Tg: 21°C) (aliphatic bifunctional monomer) HDDA: 1,6-hexanediol diacrylate ("Sartomer SR238" (trade name) manufactured by Arkema, viscosity: 9, Tg: 43°C) (Other bifunctional monomers) GC1100Z: Amine-modified oligomer ("GC1100Z" (trade name) manufactured by Qualipoly Chemical Co., Ltd., viscosity: 1000, Tg: -25°C) (polyfunctional monomer) PETA: Trimethylolpropane triacrylate (Arkema "Sartomer SR444" (trade name), viscosity: 520, Tg: 103°C) TMPTA: pentaerythritol triacrylate ("Sartomer SR351" (trade name) manufactured by Arkema, viscosity: 106, Tg: 62°C) <Photopolymerization initiator> TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (BASF "IRGACURE TPO" (trade name)) <Polymerization inhibitor> HTEMPO: 2,2,6,6-tetramethylpiperidinol ("HYDROXY-TEMPO" (trade name) manufactured by Evonik Degussa Japan) <Surface conditioner> BYK-UV3500: Polyether-modified polydimethylsiloxane (BYK-Chemie "BYK-UV3500" (trade name))

[0056] (Examples 1 to 22 and Comparative Examples 1 to 13) [Production of clear ink composition] The photopolymerizable monofunctional monomer, photopolymerizable bifunctional monomer, photopolymerizable multifunctional monomer, photopolymerizable initiator, polymerization inhibitor, and surface conditioner were weighed out and placed in a 100cc plastic bottle in the amounts shown in Tables 1 to 3, and the mixture was stirred for 30 minutes using a magnetic stirrer. After stirring, the mixture was suction filtered using a glass filter (manufactured by Kiriyama Seisakusho) to produce a clear ink composition. In Comparative Examples 5 to 7, an amine-modified oligomer was further added to produce the clear ink composition.

[0057] Tables 1 to 4 show the components and blending ratios of the clear ink compositions used in each of the examples and comparative examples.

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] [Table 4]

[0062] [Evaluation of Clear Ink Composition] Each of the obtained clear ink compositions was subjected to various evaluations as follows, and the results are shown in Tables 1 to 4.

[0063] [viscosity] The viscosity of each clear ink composition produced in each of the Examples and Comparative Examples was measured. The viscosity was measured using a viscometer (Toki Sangyo Co., Ltd., "R100 Type Viscometer" (product name)) at 25°C and a cone rotation speed of 20 rpm. The measured viscosity was evaluated according to the following criteria.

[0064] ◎: Less than 10 mPa·s, 〇: Less than 12 mPa·s, △: Less than 15 mPa·s, ×: 15 mPa·s or more

[0065] Next, a white polyethylene terephthalate (PET) film was prepared, and an appropriate amount of the clear ink composition was placed on the surface of the white layer, followed by forming a coating film using a bar coater. An ultraviolet LED lamp (NCCU001E manufactured by Nichia Corporation) was used as the irradiation means, irradiating the coating film with a wavelength of 365 nm and an integrated light intensity of 200 mJ / cm. 2 The resin was cured by irradiating it with light under the conditions of 16 passes.

[0066] The cured coating obtained was evaluated for curability, tack-free property, gloss (60°), yellowing (visual), and yellowing (b * ) was evaluated.

[0067] [Curability] The cured coating was gently rubbed with a cotton swab all the way to the edge of the printed area, and the curability was evaluated according to the following criteria. S (particularly good): The ink does not stick to the cotton swab at all, and no scratches are left on the coating. A (Good): No ink sticks to the cotton swab, and slight scratches remain on the coating. B (Good): A small amount of ink is left on the cotton swab. C (Poor): Ink sticks to the cotton swab.

[0068] [Tack-free] The cured coating was touched with a finger and evaluated according to the following criteria. S (particularly good): The coating film is not sticky at all. A (Good): The coating film is slightly non-sticky. B (Good): The coating film is slightly sticky in some areas. C (Poor): The entire coating film where the adhesive sheet was attached was sticky.

[0069] [Glossiness (60°)] The gloss of the cured coating was measured at 60° using a gloss meter (BYK Gardner "micro-TRI-gloss" (trade name)) and evaluated according to the following criteria. ◎: 98 or above, 〇: 95 or above, △: 90 or above, ×: below 90

[0070] [Yellowing] The color of the cured coating was checked visually or by UV LED lamp after 3 hours. * The visual evaluation criteria are as follows: ◯ (good) and △ (good) indicate that the yellowing is at a level that poses no practical problem. ○: When yellowing is not observed compared to the initial state △: Only slight yellowing is observed compared to the initial state ×: If it appears yellow compared to the initial state

[0071] Next, the degree of yellowing (b * The color value was measured using a colorimeter (X-Rite 939 (trade name) manufactured by X-Rite Corporation) under a light source of D65 / 10°C visual field.

[0072] As shown by Examples 1 to 22 in Tables 1 and 2, the clear ink compositions containing alicyclic difunctional monomers and trifunctional monomers according to the present invention have a low viscosity of less than 12 mPa·s at 25°C. Furthermore, all of them exhibit good gloss. Therefore, the clear ink compositions of these examples have excellent ejection stability and provide printed surfaces with excellent gloss.

[0073] Reducing the blending ratio of the alicyclic monofunctional monomer (isobornyl acrylate (IBXA)) resulted in a slight decrease in the tack-free properties of the clear ink composition (Example 1, Comparative Example 1). Reducing the blending ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) and increasing the blending ratio of the alicyclic monofunctional monomer (isobornyl acrylate (IBXA)) improved gloss (Examples 1 to 3). Replacing the alicyclic monofunctional monomer from isobornyl acrylate (IBXA) with 3,3,5-trimethylcyclohexyl acrylate (TMCHA) further improved tack-free properties (Examples 5 to 8). Replacing 4-tert-butylcyclohexyl acrylate (TBCHA) resulted in a slight decrease in gloss but improved curability (Examples 9 to 11).

[0074] Decreasing the blending ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) and increasing the blending ratio of the alicyclic bifunctional monomer (tricyclodecane dimethanol di(meth)acrylate (DCPDA)) improved the tack-free properties and gloss (Examples 12 to 14). The same was true when the blending ratio of cyclohexane dimethanol di(meth)acrylate (CHDMDA) was increased (Examples 15 to 17).

[0075] The gloss level was also good when the compounding ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was reduced and the compounding ratio of the polyfunctional monomer was increased (Examples 18 to 22). However, when the compounding ratio was high, the tack-free property was significantly reduced due to the viscosity of the polyfunctional monomer, and yellowing (b * ) values ​​have worsened.

[0076] When the compounding ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was increased and the compounding ratio of the alicyclic bifunctional monomer (tricyclodecane dimethanol di(meth)acrylate (DCPDA)) was decreased, the curability decreased (Example 2, Comparative Example 2). This was also the case when the compounding ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was increased and the compounding ratio of the polyfunctional monomer (pentaerythritol tri(meth)acrylate (PETA)) was decreased (Example 2, Comparative Example 3). When the compounding ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was decreased and the compounding ratio of the polyfunctional monomer (pentaerythritol tri(meth)acrylate (PETA)) was increased, the curability decreased and yellowing (b * ) also became worse (Example 2, Comparative Example 4).

[0077] When the compounding ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was reduced and the compounding ratio of the amine-modified oligomer was increased, the viscosity increased and yellowing was also observed (Example 2, Comparative Examples 5 to 7).

[0078] When a thioxanthone-based photopolymerization sensitizer was used as the photopolymerization initiator, yellowing was significant (Example 2, Comparative Examples 8 and 9).

[0079] When the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was not included at all and the blending ratio of the aliphatic bifunctional monomer (1,6-hexanediol di(meth)acrylate (HDDA)) was increased instead, the curability decreased (Example 2, Comparative Example 10). Conversely, when the blending ratio of the heterocyclic monofunctional monomer (tetrahydrofurfuryl acrylate (THFA)) was increased and the blending ratio of the aliphatic bifunctional monomer (1,6-hexanediol di(meth)acrylate (HDDA)) was decreased, the curability remained good, but the tack-free property decreased (Example 2, Comparative Example 11).

[0080] Evaluations of the clear ink compositions described in Examples 1 and 4 of Patent Document 3 are shown as Comparative Examples 12 and 13, respectively (Comparative Examples 12 and 13). In comparison with these, it can be seen that the clear ink composition of the present invention exhibits excellent effects in terms of viscosity, curability, and gloss.

Claims

1. The ultraviolet-curable inkjet clear ink composition has a viscosity of 5 to 15 mPa·s at 25°C, and contains, relative to 100 parts by weight of the clear ink composition, 1 to 15 parts by weight of an alicyclic bifunctional monomer, 1 to 10 parts by weight of a trifunctional or higher functional monomer, and 10 to 20 parts by weight of a photopolymerization initiator.

2. The clear ink composition according to claim 1, wherein the alicyclic bifunctional monomer is at least one selected from the group consisting of tricyclodecane dimethanol di(meth)acrylate and cyclohexane dimethanol diacrylate.

3. The clear ink composition according to claim 1 or 2, wherein the tri- or higher functional monomer is at least one selected from the group consisting of pentaerythritol tri(meth)acrylate and trimethylolpropane triacrylate.

4. The clear ink composition according to any one of claims 1 to 3, wherein the photopolymerization initiator is an acylphosphine-based photopolymerization initiator.

5. 5. The clear ink composition according to claim 1, further comprising a heterocyclic monofunctional monomer having a glass transition temperature (Tg) of 0°C or less in an amount of 19 to 50 parts by weight per 100 parts by weight of the clear ink composition.

6. The clear ink composition according to claim 5 , wherein the heterocyclic monofunctional monomer is tetrahydrofurfuryl acrylate.

7. The clear ink composition according to any one of claims 1 to 6, further comprising 0.1 to 40 parts by weight of an alicyclic monofunctional monomer relative to 100 parts by weight of the clear ink composition.

8. 8. The clear ink composition according to claim 7, wherein the alicyclic monofunctional monomer is at least one selected from the group consisting of isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl acrylate, and 4-tert-butylcyclohexyl acrylate.

9. The clear ink composition according to any one of claims 1 to 8, which does not contain an amine-based monomer.

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