Photocurable inkjet ink composition

Abstract

The present invention addresses the problem of providing a photocurable inkjet ink composition that is cured adequately by a small amount of photopolymerization initiator, has excellent dischargeability, and can form a cured coating film having excellent friction resistance and alcohol resistance. The means for solving the problem is a photocurable inkjet ink composition containing a polymerizable compound and a photopolymerization initiator. The polymerizable compound contains 5-23 mass% of bifunctional amino acrylates, 55-94 mass% of bifunctional (meth)acrylic monomers other than the bifunctional amino acrylates, and 1-8 mass% of pentafunctional or hexafunctional (meth)acrylic monomers in the polymerizable compound. The content of monofunctional monomers in the polymerizable compound is 5 mass% or less, and the mass ratio (photopolymerization initiator / polymerizable compound) of the photopolymerization initiator and the polymerizable compound is 0.05-0.15.

Description

Photocurable inkjet ink composition

[0001] The present invention relates to a photocurable inkjet ink composition, and particularly to a photocurable inkjet ink composition in which the usage amount of a photopolymerization initiator is reduced.

[0002] As inkjet ink compositions, for example, ink compositions that form images by curing a coating film through irradiation with active energy rays such as ultraviolet rays are known (hereinafter sometimes referred to as photocurable inkjet ink compositions). Since a photocurable inkjet ink composition forms a polymer upon light irradiation and has excellent drying properties, the formed image has advantages such as excellent coating film strength, excellent transferability to the designed image, and suitability for high-speed printing.

[0003] Photocurable inkjet inks have a low viscosity for stable ejection from nozzles, and also have the problem of poor reactivity due to being susceptible to oxygen inhibition. To improve reactivity, a photopolymerization initiator is typically contained at a concentration of 5% to 10%.

[0004] Among photopolymerization initiators, there are substances suspected of being toxic to the human body, such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. Inkjet printing may be performed on products that come into direct contact with food, and it is desirable not to use such photoinitiators.

[0005] Patent Document 1 describes that, regarding an active energy ray-curable inkjet ink composition containing a polymerizable compound polymerizable by active energy rays, it is possible to provide an active energy ray-curable inkjet ink composition containing specific amounts of an aminoacrylate and a bifunctional monomer having two ethylenically double bond groups in the molecule, and a printed matter thereof.

[0006] Patent Document 1, Examples 1, 4, and 6 describe energy ray-curable inkjet ink compositions comprising a difunctional (meth)acrylic monomer and a difunctional aminoacrylate as polymerizable compounds, and acylphosphine compounds other than the aforementioned diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide and thioxanthone compounds as photopolymerization initiators.

[0007] Patent Document 2 describes that an active energy ray-curable inkjet ink composition can be provided containing 2-(2-vinyloxyethoxy)ethyl acrylate (B-1), a bifunctional (meth)acrylate (B-2), and a trifunctional or more polyfunctional (meth)acrylate (B-3) as polymerizable monomers (B).

[0008] Patent Document 2, Examples 17 to 19 describe energy ray-curable inkjet ink compositions containing a pentafunctional or hexafunctional (meth)acrylate (B-3) as a trifunctional or more polyfunctional (meth)acrylate. These ink compositions contain a high concentration of the diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator.

[0009] Japanese Patent Publication No. 2013-159707 Japanese Patent Publication No. 2015-183149

[0010] Photocurable inkjet inks have high chemical activity, and it is necessary to reduce the amount used to improve safety. Therefore, the cured coating film needs to have excellent toughness so that performance is not compromised even when the film thickness is reduced.

[0011] In recent years, the frequency of wiping household items with disinfectant or alcohol has increased in order to improve hygiene in the living environment, such as preventing infectious diseases. Therefore, printed images on household items require hardness that will not be damaged by friction and chemical resistance that will not deteriorate with alcohol. Conventional photocurable inkjet printing films are still insufficient in terms of hardness and alcohol resistance. In particular, when attempting to form a thin cured coating film, the amount of inkjet ink composition used and the coating film thickness decrease, leading to oxygen inhibition and a decrease in curability, making the aforementioned problems apparent.

[0012] The present invention solves the aforementioned problems, and its objective is to provide a photocurable inkjet ink composition that can sufficiently cure with a small amount of photopolymerization initiator, form a cured coating film with excellent discharge properties, abrasion resistance and alcohol resistance, and in particular, can form a cured coating film with excellent abrasion resistance and alcohol resistance even when the film thickness of the cured coating film is thin.

[0013] The present invention provides the following embodiments.

[0014] [1] A photocurable inkjet ink composition comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound contains in an amount of 5 to 23% by mass, preferably 5 to 20% by mass, more preferably 5.5 to 20% by mass, even more preferably 7 to 19% by mass, particularly preferably 9 to 18% by mass, and especially preferably 11 to 17% by mass of a difunctional aminoacrylate, 55 to 94% by mass, preferably 55 to 90% by mass, more preferably 64 to 90% by mass, even more preferably 70 to 88% by mass, particularly preferably 76 to 86% by mass, especially preferably 79 to 84% by mass of a difunctional (meth)acrylic monomer other than the difunctional aminoacrylate, and 1 to 8% by mass, preferably 1 to 7% by mass, more preferably 2 to 6% by mass, even more preferably 3.4 to 5.6% by mass, and especially preferably 3 to 5% by mass of a pentafunctional or hexafunctional (meth)acrylic monomer. A photocurable inkjet ink composition wherein the content of monofunctional monomers in the polymerizable compound is 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, and the mass ratio of the photopolymerization initiator to the polymerizable compound (photopolymerization initiator / polymerizable compound) is 0.05 to 0.15, preferably 0.060 to 0.140, more preferably 0.066 to 0.140, even more preferably 0.070 to 0.130, particularly preferably 0.077 to 0.125, and especially most preferably 0.080 to 0.120.

[0015] [2] The photocurable inkjet ink composition according to embodiment 1, wherein the photopolymerization initiator contains a thioxanthone compound.

[0016] [3] The photocurable inkjet ink composition of embodiment 1 or 2, wherein the photopolymerization initiator does not contain diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and does not contain 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

[0017] [4] A photocurable inkjet ink composition according to any of embodiments 1 to 3, wherein the mass ratio of the photopolymerization initiator to a difunctional (meth)acrylic monomer other than difunctional aminoacrylate (photopolymerization initiator / difunctional (meth)acrylic monomer other than difunctional aminoacrylate) is 0.070 to 0.180, preferably 0.070 to 0.170, more preferably 0.097 to 0.155, even more preferably 0.100 to 0.152, particularly preferably 0.105 to 0.143, and especially preferably 0.110 to 0.130.

[0018] [5] A photocurable inkjet ink composition according to any of embodiments 1 to 4, wherein the mass ratio of the pentafunctional or hexafunctional (meth)acrylic monomer to the difunctional aminoacrylate (pentafunctional or hexafunctional (meth)acrylic monomer / difunctional aminoacrylate) is 0.05 to 0.7, preferably 0.1 to 0.6, more preferably 0.2 to 0.5, and even more preferably 0.3 to 0.4.

[0019] [6] A photocurable inkjet ink composition according to any of embodiments 1 to 5, which does not contain a monofunctional monomer.

[0020] [7] A photocurable inkjet ink composition according to any of embodiments 1 to 6, having a viscosity of 32 mPa·s or less at 25°C.

[0021] [8] The photopolymerization initiator comprises an acylphosphine oxide-based initiator, a photocurable inkjet ink composition according to any one of embodiments 1 to 7.

[0022] [9] A photocurable inkjet ink composition according to any one of embodiments 1 to 8, wherein the photopolymerization initiator comprises bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0023]

[10] A photocurable inkjet ink composition according to any one of embodiments 1 to 9, wherein the polymerizable reactive group of the bifunctional (meth)acrylic monomer is solely a (meth)acryloyl group.

[0024]

[11] A photocurable inkjet ink composition in any of embodiments 1 to 10, wherein a coating film with a thickness of 1.5 μm is cured, and after applying a cotton swab to the surface of the cured coating film and sliding it back and forth 10 times with a load of 5 g, no sliding marks are left on the surface.

[0025]

[12] A photocurable inkjet ink composition that does not contain a trifunctional monomer, any of the photocurable inkjet ink compositions of embodiments 1 to 11.

[0026]

[13] A photocurable inkjet ink composition according to any of embodiments 1 to 12, which does not contain a tetrafunctional monomer.

[0027]

[14] A method for producing a cured coating film, comprising curing a coating film of any of the photocurable inkjet ink compositions in embodiments 1 to 13 using an LED light source having a peak at a specific wavelength.

[0028] According to the present invention, it is possible to provide a photocurable inkjet ink composition that can sufficiently cure with a small amount of photopolymerization initiator, and can form a cured coating film with excellent discharge properties, abrasion resistance, and alcohol resistance. Since the cured coating film formed from the photocurable inkjet ink composition of the present invention has excellent abrasion resistance and alcohol resistance, it can be made thinner than conventional coatings. As a result, the photocurable inkjet ink composition of the present invention can be used in smaller quantities than conventional coatings, improving safety for humans and the environment, as well as energy saving.

[0029] The following describes in detail one embodiment of the present invention, but the scope of the present invention is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the invention. Furthermore, if multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range.

[0030] <Polymerizable Compounds> The photocurable inkjet ink composition of the present invention contains polymerizable compounds. Polymerizable compounds are compounds that can be polymerized as a reaction product of a polymerization initiator using active energy rays. Examples of active energy rays include visible light, near-ultraviolet light, ultraviolet light, electron beams, alpha rays, gamma rays, and X-rays, among which ultraviolet light and electron beams are preferred. Specifically, polymerizable compounds are preferably compounds having at least one ethylenically double bond selected from the group consisting of acryloyl group, methacryloyl group, vinyl group, allyl group, and vinyl ether group, more preferably compounds having at least one ethylenically double bond selected from the group consisting of acryloyl group, methacryloyl group, and vinyl ether group, and acryloyl group-containing compounds are particularly preferred. Polymerizable compounds may include monofunctional monomers and / or polyfunctional monomers. Specific examples of monomers include (meth)acrylic monomers, which are a general term for (meth)acrylic acid-based radical polymerizable compounds such as acrylic acid ester compounds, acrylamide compounds, methacrylic acid ester compounds, and methacrylamide compounds.

[0031] In this specification, compounds having at least one acryloyl group and / or methacryloyl group, and compounds having at least one acryloyl ester group and / or methacryloyl ester group, are referred to as (meth)acrylic compounds. In one preferred embodiment of the present invention, the ink composition of the present invention preferably contains a (meth)acrylic compound.

[0032] Furthermore, in this specification, "(meth)acrylic compounds" is a general term for "acrylic compounds" and "methacrylic compounds." It is a general term for "(meth)acrylic acid," "(meth)acrylate," "acrylate," and "methacrylate." The terms "(meth)acrylamide" and "(meth)acryloyloxy" have the same meaning.

[0033] (Monofunctional Monomers) Monofunctional monomers are polymerizable compounds that have one ethylenic double bond in one molecule. Among monofunctional monomers, monofunctional (meth)acrylic monomers may be included in amounts that do not impair the function and properties of the inkjet ink composition and coating film.

[0034] Monofunctional (meth)acrylic monomers include, specifically, amyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, isomiristyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, neopentyl glycol (meth)acrylate benzoate, butoxyethyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, methoxy-triethylene glycol (meth)acrylate, methoxy-polyethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate. Examples include phenoxyethyl (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2-(2-ethoxyethoxyethyl acrylate)nonylphenol ethylene oxide adduct (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobonyl (meth)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, and ethoxylated nonylphenyl acrylate. These may be used individually or in combination. Furthermore, the above monomers may be substituted with functional groups such as phosphorus or fluorine.

[0035] From the viewpoint of improving curability, the photocurable inkjet ink composition of the present invention preferably does not contain monofunctional monomers in an amount exceeding 9% by mass in the polymerizable compound. The photocurable inkjet ink composition preferably contains monofunctional monomers of 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, relative to the polymerizable compound, and most preferably does not contain monofunctional monomers at all. "Not containing monofunctional monomers" means that monofunctional monomers are not added with the intention of achieving any technical effect, and for example, the presence of unintentional monofunctional monomers in the material is permissible.

[0036] From the viewpoint of improving curability, the photocurable inkjet ink composition of the present invention preferably does not contain monofunctional monomers in an amount exceeding 9% by mass. Preferably, the photocurable inkjet ink composition has a monofunctional monomer content of 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, and most preferably does not contain monofunctional monomers at all. From a similar viewpoint, the photocurable inkjet ink composition may also have a monofunctional monomer content of 4% by mass or less.

[0037] (Polyfunctional Monomers) A polyfunctional monomer has two or more polymerizable moieties (e.g., ethylenically double bonds) in one molecule. Examples of polyfunctional (meth)acrylic monomers include difunctional (meth)acrylic monomers, trifunctional (meth)acrylic monomers, tetrafunctional (meth)acrylic monomers, pentafunctional (meth)acrylic monomers, and hexafunctional (meth)acrylic monomers. A polyfunctional (meth)acrylic monomer may have a linear structure or an alicyclic structure. A polyfunctional (meth)acrylic monomer having a linear structure does not have a cyclic structure in its molecular structure and has a linear or branched structure. A polyfunctional (meth)acrylic monomer having an alicyclic structure has an alicyclic structure in its molecular structure and may further have a linear structure.

[0038] From the viewpoint of improving the discharge performance of the ink composition, the polyfunctional (meth)acrylic monomer preferably contains a difunctional (meth)acrylic monomer. From the viewpoint of improving the curability of the coating film and improving the abrasion resistance and alcohol resistance of the cured coating film, the polymerizable reactive group of the difunctional (meth)acrylic monomer preferably consists only of an acryloyl group. In order to improve the discharge performance, the difunctional (meth)acrylic monomer needs to have a viscosity suitable for inkjet printing, and for this purpose, a dilutable monomer is preferred, more preferably contains a difunctional (meth)acrylic monomer having a chain structure, and even more preferably contains only a difunctional (meth)acrylic monomer having a chain structure.

[0039] Examples of difunctional (meth)acrylic monomers having a chain-like structure include 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and alkoxylated hexanediol diacrylate. Of these, 1,6-hexanediol diacrylate and dipropylene glycol diacrylate are preferred from the viewpoint of dilutability and safety. These polyfunctional (meth)acrylic monomers having a chain-like structure may be used individually or in combination of two or more.

[0040] From the viewpoint of improving ejection performance, the photocurable inkjet ink composition of the present invention preferably contains a difunctional (meth)acrylic monomer other than difunctional aminoacrylate in an amount of 55 to 90% by mass in the polymerizable compound. The content of the difunctional (meth)acrylic monomer in the polymerizable composition is more preferably 70 to 88% by mass, even more preferably 76 to 86% by mass, and most preferably 79 to 84% by mass. From a similar viewpoint, the content of the difunctional (meth)acrylic monomer other than difunctional aminoacrylate in the polymerizable composition may be 55 to 94% by mass, preferably 64 to 90% by mass.

[0041] The photocurable inkjet ink composition of the present invention preferably contains a difunctional (meth)acrylic monomer other than a difunctional aminoacrylate in an amount of 50 to 85 mass% in the composition, from the viewpoint of improving ejection properties. The content of the difunctional (meth)acrylic monomer in the photocurable inkjet ink composition is more preferably 64 to 80 mass%, further preferably 69 to 76 mass%, and most preferably 70 to 74 mass%. The content of the difunctional (meth)acrylic monomer in the photocurable inkjet ink composition may be 55 to 85 mass%, preferably 56 to 79 mass%, from the same viewpoint.

[0042] Examples of polyfunctional (meth)acrylic monomers other than difunctional ones include trifunctional (meth)acrylic monomers such as propoxylated trimethylolpropane tri(meth)acrylate, glycerin propoxy tri(meth)acrylate or pentaerythritol tri(meth)acrylate, tetrafunctional (meth)acrylic monomers such as pentaerythritol tetra(meth)acrylate, pentafunctional (meth)acrylic monomers such as dipentaerythritol hydroxypenta(meth)acrylate, and hexafunctional (meth)acrylic monomers such as dipentaerythritol hexa(meth)acrylate and alkoxylated dipentaerythritol hexaacrylate.

[0043] The polyfunctional (meth)acrylic monomer contains a pentafunctional (meth)acrylic monomer or a hexafunctional (meth)acrylic monomer from the viewpoint of improving the curability of the ink composition. The polymerizable compound preferably contains the pentafunctional or hexafunctional (meth)acrylic monomer in an amount of 1 to 7 mass% from the viewpoint of improving curability. The content of the pentafunctional or hexafunctional (meth)acrylic monomer in the polymerizable compound is more preferably 2 to 6 mass%, further preferably 3.4 to 5.6 mass%, and most preferably 3 to 5 mass%. The content of the pentafunctional or hexafunctional (meth)acrylic monomer in the polymerizable compound may be 1 to 8 mass% from the same viewpoint.

[0044] From the viewpoint of improving curability, the photocurable inkjet ink composition of the present invention preferably contains a pentafunctional or hexafunctional (meth)acrylic monomer in an amount of 0.5 to 6.5% by mass. The content of the pentafunctional or hexafunctional (meth)acrylic monomer in the photocurable inkjet ink composition is more preferably 0.8 to 10% by mass, even more preferably 1 to 6% by mass, and most preferably 2 to 5% by mass. From a similar viewpoint, the content of the pentafunctional or hexafunctional (meth)acrylic monomer in the photocurable inkjet ink composition may be 0.5 to 7% by mass.

[0045] (Difunctional Aminoacrylate) The polymerizable compound contains a difunctional aminoacrylate. A difunctional aminoacrylate refers to a difunctional (meth)acrylate modified by reaction with a first or second amine. The content of the difunctional aminoacrylate in the polymerizable compound is 5 to 20% by mass, more preferably 7 to 19% by mass, even more preferably 9 to 18% by mass, and particularly preferably 11 to 17% by mass. The content of the difunctional aminoacrylate in the polymerizable compound may also be 5 to 23% by mass, preferably 5.5 to 20% by mass.

[0046] From the viewpoint of improving curability, the photocurable inkjet ink composition of the present invention preferably contains a difunctional aminoacrylate in an amount of 5 to 19% by mass. The content of the difunctional aminoacrylate in the photocurable inkjet ink composition is more preferably 7 to 18% by mass, even more preferably 9 to 16% by mass, and most preferably 10 to 14% by mass. From a similar viewpoint, the photocurable inkjet ink composition may contain a difunctional aminoacrylate in an amount of 5 to 20% by mass.

[0047] Difunctional aminoacrylates can be obtained, for example, from Daicel Ornex under the trade name EBECRYL 7100, from Arkema under the trade names CN371 and CN386, from Eternal Materials under the trade names ETERCURE 6410, 6411, 6417, 645, and 647, from IGM Resins under the trade name PHOTOMER 4775, and from Rahn under the trade names Geneomer 5271 and Geneomer 5275.

[0048] The photocurable inkjet ink composition of the present invention contains a 5-functional or 6-functional (meth)acrylic monomer and a 2-functional aminoacrylate, from the viewpoint of improving the friction resistance and alcohol resistance in a thin film, in an amount such that the mass ratio of the 5-functional or 6-functional (meth)acrylic monomer to the 2-functional aminoacrylate is preferably 0.05 to 0.7, more preferably 0.1 to 0.6, still more preferably 0.2 to 0.5, and particularly preferably 0.3 to 0.4.

[0049] <Photopolymerization Initiator> The photocurable inkjet ink composition of the present invention contains a photopolymerization initiator. The photopolymerization initiator refers to a compound that absorbs active energy rays and initiates a photopolymerization reaction (chain polymerization reaction). Examples of the photopolymerization initiator include acylphosphine oxide compounds, alkylphenone compounds, and thioxanthone compounds. From the viewpoint of improving the curability of the photocurable inkjet ink composition, the photopolymerization initiator preferably contains an acylphosphine oxide compound and a thioxanthone compound.

[0050] The photocurable inkjet ink composition of the present invention includes the aforementioned 2-functional aminoacrylate and thioxanthone compound. Thereby, the curability of the photocurable inkjet ink composition is improved, and oxygen inhibition in particular can be suppressed.

[0051] Examples of the acylphosphine oxide compound include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of commercially available products of the acylphosphine oxide compound include "OMNIRAD (registered trademark) TPO", "OMNIRAD (registered trademark) TPO-L" and "OMNIRAD (registered trademark) 819" manufactured by IGM. Among these, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide has been regarded as problematic in terms of safety to the human body, and is preferably not used.

[0052] Examples of alkylphenone compounds include 2,2-dimethoxy-1,2-diphenylethane-1-one and 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one. Commercial alkylphenone compounds include IGM's "OMNIRAD® 651" and "OMNIRAD® 907". Of these, 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one has been raised concerns regarding its safety for human use, and its use is preferable.

[0053] Examples of thioxanthone compounds include thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthe-9-one, 2-chlorothioxanthone, 2-ethylthioxanthone, and 1-chloro-4-propoxythioxanthone.

[0054] The amount of photopolymerization initiator in the photocurable inkjet ink composition of the present invention is such that the mass ratio of the photopolymerization initiator to the polymerizable compound (photopolymerization initiator / polymerizable compound) is 0.05 to 0.15. From the viewpoint of ensuring safety for the human body, it is preferable that the amount of photopolymerization initiator be small, but if the photopolymerization initiator / polymerizable compound is less than 0.05, the curability of the photocurable inkjet ink composition may be insufficient. The photopolymerization initiator / polymerizable compound is preferably 0.060 to 0.140, more preferably 0.070 to 0.130, even more preferably 0.077 to 0.125, and particularly preferably 0.080 to 0.120. The amount of photopolymerization initiator in the photocurable inkjet ink composition may also be such that the mass ratio of the photopolymerization initiator to the polymerizable compound (photopolymerization initiator / polymerizable compound) is 0.066 to 0.140.

[0055] The amount of photopolymerization initiator in the photocurable inkjet ink composition of the present invention is preferably such that the mass ratio of the photopolymerization initiator to the difunctional (meth)acrylic monomer other than difunctional aminoacrylate (photopolymerization initiator / difunctional (meth)acrylic monomer other than difunctional aminoacrylate) is 0.070 to 0.170. The mass ratio is more preferably 0.097 to 0.155, even more preferably 0.100 to 0.152, particularly preferably 0.105 to 0.143, and most preferably 0.110 to 0.130. The amount of photopolymerization initiator in the photocurable inkjet ink composition may also be such that the mass ratio of the photopolymerization initiator to the difunctional (meth)acrylic monomer other than difunctional aminoacrylate (photopolymerization initiator / difunctional (meth)acrylic monomer other than difunctional aminoacrylate) is 0.070 to 0.180.

[0056] <Other Components> In addition to polymerizable compounds and photopolymerization initiators, the ink composition may further contain optional components as needed. Examples of optional components include surfactants (surface tension modifiers), colorants, polymerization inhibitors, dispersants, organic solvents, fixing resins, leveling agents, defoamers, antioxidants, pH adjusters, charge imparters, bactericides, preservatives, deodorants, charge modifiers, wetting agents, and ultraviolet absorbers. These optional components may be used individually or in combination of two or more.

[0057] (Surfactants) For the purpose of adjusting the wettability of the ink to the recording medium and / or the nozzle substrate of the inkjet head, the ink composition may contain surfactants. Examples of surfactants include silicone compounds. Preferred silicone compounds include, for example, silicone compounds having a dimethylsiloxane structure, and more preferably polyether-modified polydimethylsiloxane. Examples of commercially available surfactants include BYK-350, 352, 354, 355, 358N, 361N, 381N, 381, 392, BYK-300, 302, 306, 307, 310, 315, 320, 322, 323, 325, 330, 331, 333, 337, 340, 344, 348, 370, 375, 377, 378, 355, 356, 357, 390, UV3500, UV3510, and UV3570 from BYK Chemie, Tegorad-2100, 2200, 2250, 2500, and 2700 from Tego Chemie, and TEGO (registered trademark) from Evonik Degussa. Examples of surfactants include, but are not limited to, "Glide 100, 110, 130, 403, 406, 410, 411, 415, 432, 435, 440, 450, and 482." These surfactants may be used individually or in combination of two or more. From the viewpoint of maintaining good compatibility, it is preferable to use two or more surfactants. By using two or more surfactants in combination, good compatibility is maintained even when the ink composition is stored for a long period of time, so that the ink composition can spread sufficiently on the recording medium and maintain the wide color reproducibility that is a characteristic of pigments.

[0058] From the viewpoint of improving the wettability of the ink composition of the present invention to the recording medium, the surfactant content is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the ink composition, more preferably 0.05 parts by mass or more and 3 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2 parts by mass or less.

[0059] (Polymerization inhibitors) For the purpose of controlling the progress of the photopolymerization reaction, the ink composition may contain polymerization inhibitors. Examples of polymerization inhibitors include hindered amine compounds, hydroquinone compounds, catechol compounds, and phenolic compounds. Hindered amine compounds include compounds having a piperidine skeleton, and hindered amine polymerization inhibitors having a 2,2,6,6-tetramethylpiperidinyl group. Examples of hindered amine compounds include esters of 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, bis(1-oxyl-2,2,6,6-tetramethylpiperidinyl-4-yl) sebacate, and bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) decandioate. Among these, bis(1-oxyl-2,2,6,6-tetramethylpiperidine-N-oxyl), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and bis(1-oxyl-2,2,6,6-tetramethylpiperidinyl-4-yl) sebacate having an N-hydroxy-2,2,6,6-tetramethylpiperidinyl group are preferred. Examples of hydroquinone compounds include hydroquinone, methylhydroquinone, hydroquinone monomethyl ether, tert-butylhydroquinone, and ditert-butylhydroquinone. Examples of catechol compounds include catechol, methylcatechol, and tert-butylcatechol. Examples of phenolic compounds include phenol, 3,5-ditert-butyl-4-hydroxytoluene (butylhydroxytoluene (BHT)), cresol, and methoquinone. These may be used individually or in combination.

[0060] From the viewpoint of achieving both storage stability and curability of the ink composition of the present invention, the content of the polymerization inhibitor is preferably 0.05 parts by mass or more and 5 parts by mass or less, preferably 0.20 parts by mass or more and 2 parts by mass or less, and more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the ink composition.

[0061] (Coloring agent) Examples of coloring agents include pigments and dyes. From the viewpoint of improving the weather resistance of the formed image, pigments (more specifically, organic pigments and inorganic pigments, etc.) are preferred.

[0062] Examples of black colorants include carbon black. Commercially available black colorants include Toka Black from Tokai Carbon Co., Ltd.; HCF, MCF, RCF, LFF, SCF from Mitsubishi Chemical Corporation; Color Black, Special Black, and Printex from Degussa-Hürss Corporation; Raven from Columbia Chemicals Corporation; and Monarch and Regal from Cabot Corporation.

[0063] Examples of cyan colorants include copper phthalocyanine compounds, anthraquinone compounds, and basic dye lake compounds. Examples of cyan colorants include C.I. Pigment Blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, or 66).

[0064] Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, or arylamide compounds. Examples of yellow colorants include C.I. Pigment Yellow (1, 3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 138, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, 185, 191, 194, and 214).

[0065] Examples of magenta colorants include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolon compounds, thioindigo compounds, or perylene compounds. Examples of magenta colorants include C.I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 150, 166, 168, 177, 184, 185, 202, 206, 220, 221, or 254).

[0066] Examples of white colorants include white organic pigments (more specifically, pigment white 6, 18, 21, etc.) and white inorganic pigments (more specifically, basic lead carbonate, zinc oxide, titanium oxide, and strontium titanate, etc.).

[0067] From the viewpoint of improving the dispersibility of the pigment in the ink composition, the average dispersion particle size of the pigment is preferably 20 to 250 nm, and more preferably 50 to 230 nm.

[0068] The coloring agent content is preferably 0.5 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the ink composition, more preferably 1.0 part by mass or more and 20 parts by mass or less, and even more preferably 2.0 parts by mass or more and 15 parts by mass or less.

[0069] (Dispersant) For the purpose of dispersing the colorant in the ink composition, the ink composition may contain a dispersant (more specifically, a pigment dispersion, etc.). Examples of dispersants include polyvinyl alcohol, acrylic acid resins, styrene-acrylic acid resins, and vinyl acetate resins. Examples of acrylic acid resins include polyacrylic acid, acrylic acid-acrylonitrile copolymer, and acrylic acid-alkyl acrylate copolymer. Examples of styrene-acrylic acid resins include styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene-acrylic acid-alkyl acrylate copolymer. Examples of vinyl acetate resins include vinyl acetate-ethylene copolymer and vinyl acetate-maleic acid copolymer.

[0070] From the viewpoint of ensuring good dispersion stability of the ink composition and maintaining the same quality as the initial state even after a long period of time, the dispersant content is preferably 0.1 parts by mass or more and 3 parts by mass or less, and more preferably 0.5 parts by mass or more and 1.5 parts by mass or less, per 100 parts by mass of the ink composition.

[0071] <Method for preparing a light-curing inkjet ink composition> Conventional known preparation methods can be used to prepare the ink composition. The following describes a preferred preparation method when the ink composition contains a pigment as a coloring agent. A primary dispersion is prepared by pre-mixing the coloring agent, a portion of the polymerizable compound, and any optional components (more specifically, pigment dispersants, etc.) using a disperser, and then dissolving or dispersing each component. Examples of dispersers include dispersers, container-driven media mills (more specifically, ball mills, centrifugal mills, and planetary ball mills, etc.), high-speed rotary mills (more specifically, sand mills, etc.), and media stirring mills (more specifically, stirring tank type mills, etc.).

[0072] Next, the remaining polymerizable compound, photopolymerization initiator, surfactant (surface tension modifier), and additives as needed (more specifically, gelling inhibitors, etc.) are added to the obtained primary dispersion and mixed uniformly using a stirrer. Examples of stirrers include a dispenser, a three-way motor, a homogenizer, and a magnetic stirrer. In this way, an ink composition can be obtained. Alternatively, the ink composition may be mixed using a mixer such as a line mixer. Furthermore, the ink composition may 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 ink composition.

[0073] <Viscosity of Inkjet Ink Composition> The viscosity of the ink composition of the present invention at 25°C, as measured with a TV-100 viscometer, is 10 to 50 mPa·s. If the viscosity is less than 10 mPa·s, the curing properties of the photocurable inkjet ink composition may be insufficient, and if it exceeds 50 mPa·s, it may become difficult to discharge stably from the nozzle. The viscosity is preferably 30 mPa·s or less, more preferably 15 to 30 mPa·s, even more preferably 17 to 28 Pa·s, and particularly preferably 20 to 25 Pa·s. The viscosity of the ink composition at 25°C, as measured with a TV-100 viscometer, may be 32 mPa·s or less, preferably 13 to 32 mPa·s, and more preferably 16 to 30 mPa·s.

[0074] <Ink Set> The ink set includes a photocurable inkjet ink composition. The ink set includes a photocurable inkjet color ink composition of multiple colors (for example, cyan, magenta, yellow, black, and white). The photocurable inkjet color ink composition is, for example, a photocurable inkjet ink composition containing a colorant.

[0075] The present invention will be further described below using examples. However, the present invention is not limited in any way to the scope of the examples. Unless otherwise specified, "%" refers to "mass percent" and "parts" refers to "parts by mass".

[0076] [1. Preparation of Ink Composition] (1) Raw Materials The following materials were prepared as raw materials for the ink composition.

[0077]

[0078] (2) Preparation of the pigment dispersion Fifteen parts of pigment, seven.5 parts of pigment dispersant, and seventy-seven parts of dipropylene glycol diacrylate were placed in a plastic bottle. The contents of the plastic bottle were stirred using a high-speed mixer until uniform to obtain a mill base. Next, the mill base was dispersed for two hours using paint conditioner (manufactured by Toyo Seiki Co., Ltd.) to obtain a pigment dispersion.

[0079] (3) Preparation of the ink composition A photopolymerization initiator, polymerizable compound, polymerization inhibitor, and surface modifier were further added to a plastic bottle containing the pigment dispersion in amounts corresponding to the compositions (parts by mass) shown in Table 2 or Table 3. The pigment dispersion and the additionally added components were stirred for 30 minutes using a magnetic stirrer to obtain a mixture. After stirring, the mixture was filtered by suction using a glass filter (manufactured by Kiriyama Seisakusho) to prepare the ink composition.

[0080] [2. Performance Evaluation] (1) Viscosity The viscosity of the ink composition was measured using a TV-100 viscometer (manufactured by Toki Sangyo Co., Ltd.) in accordance with JIS Z8803, under conditions of a temperature of 25°C and a cone rotation speed of 5 rpm. The obtained viscosities (unit: mPa·s) are shown in Tables 2 and 3.

[0081] Furthermore, when the viscosity of the ink composition at 25°C is 30 mPa·s or less, the ejection stability of the ink composition was evaluated as being at a level that poses no practical problems. This is because, when the viscosity of the ink composition at 25°C is 30 mPa·s or less, the ink composition is stably ejected from the nozzles of the inkjet head under the standard operating conditions of the inkjet recording device (usually 40°C). In one embodiment, when the viscosity of the ink composition at 25°C is 32 mPa·s or less, the ejection stability of the ink composition was evaluated as being at a level that poses no practical problems. This is because, when the viscosity of the ink composition at 25°C is 32 mPa·s or less, the ink composition is stably ejected from the nozzles of the inkjet head under the standard operating conditions of the inkjet recording device (usually 40°C).

[0082] (2) The curable ink composition was applied to a transparent PET film (HK-33WF, manufactured by Higashiyama Film Co., Ltd.) at a spreading speed of 2 cm / second using an OSP1.5 wireless bar (manufactured by OSG System Products Co., Ltd.) or a (No. 0.7) wire bar (manufactured by Toyo Seiki Co., Ltd.) in a constant temperature room at 25°C and 30% humidity. The thickness of the coated film was approximately 1.5 μm.

[0083] Furthermore, the coating was applied to a transparent PET film at a spreading speed of 2 cm / second using either an OSP6.0 wireless bar or a (No. 3) wire bar. The thickness of the coated film was approximately 6 μm.

[0084] In Example 1 and Comparative Example 1, a 6 μm coating was also performed.

[0085] Using a UV LED (Fosseon FJ100), the irradiance was 1100 mW / cm². ２ Total luminous intensity: 40 mJ / cm ２ The coating film was cured by irradiating it with ultraviolet light, forming a cured coating film on the substrate.

[0086] A cotton swab was applied to the surface of the cured coating and slid back and forth 10 times under a load of 5g. The surface condition was then visually observed. The curability was evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3.

[0087] A: No sliding marks observed B: Sliding marks observed (3) Alcohol resistance The cured coating was slid and evaluated in the same manner as the curing test described above, except that a cotton swab soaked in 100% alcohol was used. The evaluation results are shown in Tables 2 to 6.

[0088]

[0089]

[0090]

[0091]

[0092]

Claims

1. A photocurable inkjet ink composition comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound contains 5 to 23% by mass of a difunctional aminoacrylate, 55 to 94% by mass of a difunctional (meth)acrylic monomer other than the difunctional aminoacrylate, and 1 to 8% by mass of a pentafunctional or hexafunctional (meth)acrylic monomer, the content of monofunctional monomers in the polymerizable compound is 5% by mass or less, and the mass ratio of the photopolymerization initiator to the polymerizable compound (photopolymerization initiator / polymerizable compound) is 0.05 to 0.

15.

2. The photocurable inkjet ink composition according to claim 1, wherein the photopolymerization initiator comprises a thioxanthone compound.

3. The photocurable inkjet ink composition according to claim 1 or 2, wherein the photopolymerization initiator does not contain diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and does not contain 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

4. The photocurable inkjet ink composition according to any one of claims 1 to 3, wherein the mass ratio of the photopolymerization initiator to the difunctional (meth)acrylic monomer other than the difunctional aminoacrylate (photopolymerization initiator / difunctional (meth)acrylic monomer other than the difunctional aminoacrylate) is 0.070 to 0.

180.

5. The photocurable inkjet ink composition according to any one of claims 1 to 4, wherein the mass ratio of the pentafunctional or hexafunctional (meth)acrylic monomer to the difunctional aminoacrylate (pentafunctional or hexafunctional (meth)acrylic monomer / difunctional aminoacrylate) is 0.05 to 0.

7.

6. A photocurable inkjet ink composition according to any one of claims 1 to 5, which does not contain a monofunctional monomer.

7. A photocurable inkjet ink composition according to any one of claims 1 to 6, having a viscosity of 32 mPa·s or less at 25°C.

8. The photocurable inkjet ink composition according to any one of claims 1 to 7, wherein the photopolymerization initiator comprises an acylphosphine oxide-based initiator.

9. The photocurable inkjet ink composition according to any one of claims 1 to 8, wherein the photopolymerization initiator comprises bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

10. The photocurable inkjet ink composition according to any one of claims 1 to 9, wherein the polymerizable reactive group of the difunctional (meth)acrylic monomer is solely a (meth)acryloyl group.

11. A photocurable inkjet ink composition according to any one of claims 1 to 10, wherein a coating film with a thickness of 1.5 μm is cured, and after applying a cotton swab to the surface of the cured coating film and sliding it back and forth 10 times with a load of 5 g, no sliding marks are left on the surface.

12. A photocurable inkjet ink composition according to any one of claims 1 to 11, which does not contain a trifunctional monomer.

13. A photocurable inkjet ink composition according to any one of claims 1 to 12, which does not contain a tetrafunctional monomer.

14. A method for producing a cured coating film, comprising curing a coating film of a photocurable inkjet ink composition according to any one of claims 1 to 13 using an LED light source having a peak at a specific wavelength.

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