UV-curable printing ink composition, and production method and cured coating film of same

Abstract

The present invention addresses the problem of providing a UV-curable printing ink composition that has excellent adhesiveness with respect to a base material. Provided is a UV-curable printing ink composition that contains a specific amount of fine polymer particles (A) having a specific configuration.

Description

UV-curable printing ink composition, its manufacturing method, and cured coating

[0001] The present invention relates to a UV-curable printing ink composition, a method for producing the same, and a cured coating.

[0002] BACKGROUND ART Conventionally, UV-curable resin compositions in which an ultraviolet-curable resin and a pigment or the like are mixed have been known (for example, Patent Documents 1 to 3).

[0003] Patent Document 1 discloses a photocurable liquid ink composition for a solder resist, which contains a photocurable resin as an essential component, and is characterized in that polymer fine particles having a Tg of 20°C or less are dispersed in the composition.

[0004] Patent Document 2 discloses a polymerizable compound that is represented by a characteristic general formula.

[0005] Furthermore, Patent Document 3 discloses a resin composition for sealing liquid crystals, which is characterized by containing a rubber-modified unsaturated compound, a coupling agent, a filler, and a photopolymerization initiator as essential components.

[0006] Japanese Unexamined Patent Publication No. 9-137109 Japanese Unexamined Patent Publication No. 2008-274216 Japanese Unexamined Patent Application No. 9-236809

[0007] However, the above-mentioned conventional techniques are not sufficient in terms of adhesion to the substrate, and there is room for further improvement.

[0008] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and an object of the invention is to provide a UV-curable printing ink composition that has excellent adhesion to a substrate.

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0010] a pigment (D) containing a polymer fine particle (A) and a pigment (D), wherein the polymer fine particle (A) comprises a rubber-containing graft copolymer having an elastomer and a graft portion graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers, and the graft portion comprises a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0011] According to one embodiment of the present invention, it is possible to provide a UV-curable printing ink composition that has excellent adhesion to a substrate.

[0012] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0013] 1. Technical Concept of the Present Invention Aqueous printing ink compositions can be used to print on paper, but cannot be used to print on materials that do not penetrate the aqueous printing ink composition, such as plastic materials such as films and molded products, metal materials, and glass materials. Therefore, when printing on non-permeable substrates such as plastic materials, metal materials, and glass materials, solvent-containing inks and UV-curable printing inks are often used.

[0014] Furthermore, aqueous printing ink compositions and solvent-containing printing ink compositions have the disadvantage of requiring a large amount of energy for evaporation and drying. On the other hand, UV-curable printing ink compositions have the advantage of excellent productivity because they are applied to a substrate and then instantly cured by UV irradiation. Furthermore, compared to solvent-containing printing ink compositions, UV-curable printing ink compositions do not require solvent volatilization after application, and the wastewater generated during the manufacturing process does not contain solvent, making them superior in terms of improving the working environment and reducing the environmental impact.

[0015] On the other hand, UV-curable printing ink compositions have problems remaining in terms of adhesion to substrates.

[0016] The above problems will be described in detail below.

[0017] First, UV-curable printing ink compositions are cured by radical polymerization. In radical polymerization, ethylenic double bonds contained in the monomers serving as reactive diluents react with each other to form —C—C— bonds, linking the monomers to each other. However, this polymerization reaction causes a significant volume shrinkage of about 10% before and after curing of the UV-curable printing ink composition. Therefore, residual stress in the cured film (coating film) obtained after curing of the UV-curable printing ink composition can cause the cured film to peel off from the substrate. In other words, conventional UV-curable printing ink compositions have the disadvantage of not having sufficient adhesion to the substrate.

[0018] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and an object of the invention is to provide a novel UV-curable printing ink composition that has excellent adhesion to a substrate.

[0019] SUMMARY OF THE INVENTION As a result of intensive research into solving the above-mentioned problems, the present inventors have newly discovered that a UV-curable printing ink composition having excellent adhesion to a substrate can be obtained by using a UV-curable printing ink composition comprising polymer fine particles (A), the polymer fine particles (A) comprising a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers, the graft moiety comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the UV-curable printing ink composition further comprising a pigment (D), and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition, thereby completing the present invention.

[0020] Furthermore, the present inventors have newly discovered that, when the UV-curable printing ink composition has the above-described configuration, it is possible to achieve both good adhesion of the UV-curable printing ink composition to a substrate and good color development of the cured coating, which has been difficult to achieve up to now.

[0021] [2. UV-curable Printing Ink Composition] A UV-curable printing ink composition according to one embodiment of the present invention is a UV-curable printing ink composition comprising polymer fine particles (A) and a pigment (D), the polymer fine particles (A) comprising a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers, the graft moiety comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0022] In this specification, the “UV-curable printing ink composition” may be referred to as the “printing ink composition,” and the “UV-curable printing ink composition according to one embodiment of the present invention” may be referred to as the “present printing ink composition.” The UV-curable printing ink composition may also be referred to as a UV-curable ink composition for printing, or a UV-curable ink composition for printing.

[0023] In one embodiment of the present invention, a substance obtained by curing the printing ink composition is referred to as a cured coating. A cured coating obtained by curing this printing ink composition also constitutes one embodiment of the present invention. In this specification, a "cured coating according to one embodiment of the present invention" may be referred to as a "cured coating." The cured coating may also be referred to as a cured film, ink film, or ink film, which are synonymous.

[0024] The present printing ink composition has the above-described configuration and thus has the advantage of excellent adhesion to a substrate. In this specification, "excellent adhesion to a substrate" refers to a result of 1 (fair) or higher, i.e., 2 (good) or 1 (fair), when an adhesion test described later in the examples is conducted on a substrate (e.g., a PMMA (polymethyl methacrylate) sheet). That is, the present printing ink composition has the advantage of a result of 1 (fair) or higher, i.e., 2 (good) or 1 (fair), when an adhesion test described later in the examples is conducted on a PMMA sheet substrate.

[0025] The printing ink composition may contain a solvent, but the content of the solvent (e.g., organic solvent) is preferably small. For example, the content of the solvent (e.g., organic solvent) contained in the printing ink composition is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 3 wt% or less, even more preferably 1 wt% or less, and particularly preferably 0.1 wt% relative to 100 wt% of the printing ink composition. When the content of the solvent (e.g., organic solvent) in the printing ink composition is within the above-mentioned range, it has the following advantages: (a) the amount of solvent discharged is reduced or eliminated, thereby reducing the environmental impact; and (b) the drying step for removing the solvent is shortened or eliminated, thereby improving productivity.

[0026] (2-1. Polymer microparticles (A)) The polymer microparticles (A) comprise a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer. By including the polymer microparticles (A), the present printing ink composition has the advantage of being able to provide a cured coating with excellent adhesion. The reason for this is not clear, but it is thought that this is because the polymer microparticles (A) are able to reduce residual stress in the cured coating due to volumetric shrinkage that occurs in the cured coating when the printing ink composition is cured, but one embodiment of the present invention is not limited to this speculation.

[0027] (2-1-1. Elastomer) The elastomer contains one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers. The elastomer may contain natural rubber in addition to the above-mentioned rubbers. The elastomer can also be referred to as an elastic portion or rubber particles. In this specification, (meth)acrylate means acrylate and / or methacrylate.

[0028] The case where the elastomer contains a diene rubber (Case A) will be described below. In Case A, a printing ink composition containing polymer fine particles (A) can provide a cured coating that is excellent in toughness and impact resistance. A cured coating that is excellent in toughness and / or impact resistance can also be said to be a cured coating that is excellent in durability.

[0029] The diene rubber is an elastomer containing, as structural units, structural units derived from a diene monomer. The diene monomer can also be referred to as a conjugated diene monomer. In Case A, the diene rubber may contain, based on 100% by weight of structural units, 50 to 100% by weight of structural units derived from a diene monomer and 0 to 50% by weight of structural units derived from a vinyl monomer other than a diene monomer copolymerizable with the diene monomer. In Case A, the diene rubber may contain, as structural units, structural units derived from a (meth)acrylate monomer in an amount less than the structural units derived from the diene monomer.

[0030] Examples of the diene monomer include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2-chloro-1,3-butadiene, etc. These diene monomers may be used alone or in combination of two or more.

[0031] Examples of vinyl monomers other than diene monomers copolymerizable with diene monomers (hereinafter also referred to as vinyl monomer A) include: (a) vinyl arenes such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; (b) vinyl carboxylic acids such as acrylic acid and methacrylic acid; (c) vinyl cyanides such as acrylonitrile and methacrylonitrile; (d) vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; (e) vinyl acetate; (f) alkenes such as ethylene, propylene, butylene, and isobutylene; and (g) polyfunctional monomers such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and divinylbenzene. The above-mentioned vinyl monomer A may be used alone or in combination of two or more. Among the above-mentioned vinyl monomers A, styrene is particularly preferred.

[0032] In Case A, the diene rubber is preferably butadiene rubber (also referred to as polybutadiene rubber) consisting of structural units derived from 1,3-butadiene, or butadiene-styrene rubber (also referred to as polystyrene-butadiene), which is a copolymer of 1,3-butadiene and styrene. Butadiene rubber is more preferred as the diene rubber. That is, the elastomer is preferably butadiene rubber. According to this configuration, the desired effect of the elastomer of the polymer microparticles (A) containing a diene rubber can be more effectively achieved. Furthermore, butadiene-styrene rubber is more preferred in that the transparency of the resulting cured coating can be enhanced by adjusting the refractive index.

[0033] The case where the elastomer contains a (meth)acrylate rubber (Case B) will be described. In Case B, a wide range of polymer designs for the elastomer are possible by combining a variety of monomers.

[0034] The (meth)acrylate rubber is an elastomer containing, as structural units, structural units derived from (meth)acrylate monomers. In Case B, the (meth)acrylate rubber may contain, per 100% by weight of structural units, 50 to 100% by weight of structural units derived from (meth)acrylate monomers and 0 to 50% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers copolymerizable with the (meth)acrylate monomers. In Case B, the (meth)acrylate rubber may contain, as structural units, structural units derived from diene monomers in an amount less than the structural units derived from the (meth)acrylate monomers.

[0035] Examples of the (meth)acrylate monomer include: (a) alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; (b) aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; (c) 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; (d) glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; (e) alkoxyalkyl (meth)acrylates; (f) allyl alkyl (meth)acrylates such as allyl (meth)acrylate and allyl alkyl (meth)acrylate; and (g) polyfunctional (meth)acrylates such as monoethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. These (meth)acrylate monomers may be used alone or in combination of two or more. Among these (meth)acrylate monomers, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with butyl (meth)acrylate being more preferred.

[0036] In Case B, the (meth)acrylate rubber is preferably one or more selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber, with butyl (meth)acrylate rubber being more preferred. The ethyl (meth)acrylate rubber is a rubber composed of structural units derived from ethyl (meth)acrylate, the butyl (meth)acrylate rubber is a rubber composed of structural units derived from butyl (meth)acrylate, and the 2-ethylhexyl (meth)acrylate rubber is a rubber composed of structural units derived from 2-ethylhexyl (meth)acrylate. This configuration results in a lower glass transition temperature (Tg) of the elastomer, thereby producing polymer microparticles (A) with a low Tg. As a result, (a) a printing ink composition containing the resulting polymer microparticles (A) can provide a cured coating with excellent toughness, and (b) the viscosity of the printing ink composition can be reduced.

[0037] Examples of vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers (hereinafter also referred to as vinyl monomer B) include the monomers listed as vinyl monomer A. The vinyl monomer B may be used alone or in combination of two or more. Among the vinyl monomers B, styrene is particularly preferred.

[0038] The case where the elastomer contains an organosiloxane-based rubber (Case C) will now be described. In Case C, the printing ink composition can provide a cured coating that has sufficient heat resistance and excellent impact resistance at low temperatures.

[0039] Examples of organosiloxane rubbers include (a) organosiloxane polymers composed of alkyl or aryl di-substituted silyloxy units, such as dimethylsilyloxy, diethylsilyloxy, methylphenylsilyloxy, diphenylsilyloxy, and dimethylsilyloxy-diphenylsilyloxy, and (b) organosiloxane polymers composed of alkyl or aryl mono-substituted silyloxy units, such as organohydrogensilyloxy in which some of the alkyl groups in the side chains have been substituted with hydrogen atoms. These organosiloxane polymers may be used alone or in combination of two or more.

[0040] In this specification, a polymer composed of dimethylsilyloxy units is referred to as a "dimethylsilyloxy rubber," a polymer composed of methylphenylsilyloxy units is referred to as a "methylphenylsilyloxy rubber," and a polymer composed of dimethylsilyloxy units and diphenylsilyloxy units is referred to as a "dimethylsilyloxy-diphenylsilyloxy rubber." In Case C, the organosiloxane rubber is preferably one or more selected from the group consisting of dimethylsilyloxy rubber, methylphenylsilyloxy rubber, and dimethylsilyloxy-diphenylsilyloxy rubber (a) because the printing ink composition can provide a cured coating having excellent heat resistance, and (b) more preferably dimethylsilyloxy rubber (b) because it is easily available and economical.

[0041] In Case C, the polymer fine particles (A) preferably contain 80% by weight or more, and more preferably 90% by weight or more, of the organosiloxane rubber relative to 100% by weight of the elastomer contained in the polymer fine particles (A). According to the above configuration, the printing ink composition can provide a cured coating film with excellent heat resistance.

[0042] In one embodiment of the present invention, the elastomer is preferably one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, butadiene-(meth)acrylate rubber, ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, 2-ethylhexyl (meth)acrylate rubber, dimethylsilyloxy rubber, methylphenylsilyloxy rubber, and dimethylsilyloxy-diphenylsilyloxy rubber, and more preferably one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, butyl (meth)acrylate rubber, and dimethylsilyloxy rubber.

[0043] (Crosslinked Structure of Elastomer) Since this allows the dispersion stability of the polymer microparticles (A) in the printing ink composition to be maintained, it is preferable that a crosslinked structure be introduced into the elastomer. A commonly used method can be used to introduce a crosslinked structure into the elastomer, and examples thereof include the following methods. Specifically, in the production of an elastomer, a method can be used in which a crosslinkable monomer such as a polyfunctional monomer and / or a mercapto group-containing compound is mixed with a monomer capable of constituting the elastomer, followed by polymerization. In this specification, the production of a polymer such as an elastomer is also referred to as polymerizing a polymer.

[0044] Other methods for introducing a crosslinked structure into organosiloxane rubber include: (a) using a polyfunctional alkoxysilane compound in combination with other materials when polymerizing the organosiloxane rubber; (b) introducing reactive groups (e.g., (a) mercapto groups and (b) reactive vinyl groups) into the organosiloxane rubber, and then adding (a) an organic peroxide or (b) a polymerizable vinyl monomer to the resulting reaction product to cause a radical reaction; and (c) mixing a crosslinkable monomer such as a polyfunctional monomer and / or a mercapto group-containing compound with other materials when polymerizing the organosiloxane rubber, followed by polymerization.

[0045] A polyfunctional monomer can also be said to be a monomer having two or more radically polymerizable reactive groups in the same molecule. The radically polymerizable reactive group is preferably a carbon-carbon double bond. Examples of polyfunctional monomers include (meth)acrylates having an ethylenically unsaturated double bond, such as allyl alkyl (meth)acrylates and allyloxy alkyl (meth)acrylates, and do not include butadiene. Examples of monomers having two (meth)acrylic groups include ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. Examples of the polyethylene glycol di(meth)acrylates include triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and polyethylene glycol (600) di(meth)acrylate. Examples of monomers having three (meth)acrylic groups include alkoxylated trimethylolpropane tri(meth)acrylates, glycerol propoxy tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate. Examples of the alkoxylated trimethylolpropane tri(meth)acrylates include trimethylolpropane tri(meth)acrylate and trimethylolpropane triethoxy tri(meth)acrylate. Further, examples of monomers having four (meth)acrylic groups include pentaerythritol tetra(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate.Further, examples of monomers having five (meth)acrylic groups include dipentaerythritol penta(meth)acrylate.Further, examples of monomers having six (meth)acrylic groups include ditrimethylolpropane hexa(meth)acrylate.The polyfunctional monomers also include diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, and the like.

[0046] Examples of mercapto group-containing compounds include alkyl group-substituted mercaptans, allyl group-substituted mercaptans, aryl group-substituted mercaptans, hydroxy group-substituted mercaptans, alkoxy group-substituted mercaptans, cyano group-substituted mercaptans, amino group-substituted mercaptans, silyl group-substituted mercaptans, acid group-substituted mercaptans, halo group-substituted mercaptans, and acyl group-substituted mercaptans. As alkyl group-substituted mercaptans, alkyl group-substituted mercaptans having 1 to 20 carbon atoms are preferred, and alkyl group-substituted mercaptans having 1 to 10 carbon atoms are more preferred. As aryl group-substituted mercaptans, phenyl group-substituted mercaptans are preferred. As alkoxy group-substituted mercaptans, alkoxy group-substituted mercaptans having 1 to 20 carbon atoms are preferred, and alkoxy group-substituted mercaptans having 1 to 10 carbon atoms are more preferred. The acid group-substituted mercaptan is preferably an alkyl group-substituted mercaptan having a carboxyl group and 1 to 10 carbon atoms, or an aryl group-substituted mercaptan having a carboxyl group and 1 to 12 carbon atoms.

[0047] (Glass Transition Temperature of Elastomer) The glass transition temperature of the elastomer is preferably 80°C or lower, more preferably 70°C or lower, more preferably 60°C or lower, more preferably 50°C or lower, more preferably 40°C or lower, more preferably 30°C or lower, more preferably 20°C or lower, more preferably 10°C or lower, more preferably 0°C or lower, more preferably -20°C or lower, more preferably -40°C or lower, more preferably -45°C or lower, more preferably -50°C or lower, more preferably -55°C or lower, more preferably -60°C or lower, more preferably -65°C or lower, more preferably -70°C or lower, more preferably -75°C or lower, more preferably -80°C or lower, more preferably -85°C or lower, more preferably -90°C or lower, more preferably -95°C or lower, more preferably -100°C or lower, more preferably -105°C or lower, more preferably -110°C or lower, more preferably -115°C or lower, even more preferably -120°C or lower, and particularly preferably -125°C or lower. In this specification, "glass transition temperature" may also be referred to as "Tg." This configuration allows for the production of polymer microparticles (A) with a low Tg. As a result, the printing ink composition can provide a cured coating with excellent toughness. Furthermore, this configuration allows for the viscosity of the printing ink composition to be further reduced. The Tg of the elastomer can be obtained by performing viscoelasticity measurements using a flat plate made of polymer microparticles (A). Specifically, the Tg can be measured as follows: (1) A dynamic viscoelasticity measurement is performed under tensile conditions on a flat plate made of polymer microparticles (A) using a dynamic viscoelasticity measuring device (e.g., DVA-200, manufactured by IT Measurement & Control Co., Ltd.) to obtain a tan δ graph; (2) The peak temperature of tan δ in the obtained tan δ graph is taken as the glass transition temperature. Here, if multiple peaks are obtained in the tan δ graph, the lowest peak temperature is taken as the glass transition temperature of the elastomer.

[0048] On the other hand, since this can suppress a decrease in the modulus of elasticity (rigidity) of the resulting cured coating, i.e., a cured coating having sufficient modulus of elasticity (rigidity) can be obtained, the Tg of the elastomer is preferably greater than 0°C, more preferably 20°C or greater, even more preferably 50°C or greater, particularly preferably 80°C or greater, and most preferably 120°C or greater.

[0049] The Tg of the elastomer can be determined by the composition of the structural units contained in the elastomer, etc. In other words, the Tg of the resulting elastomer can be adjusted by changing the composition of the monomers used when producing (polymerizing) the elastomer.

[0050] Here, when a homopolymer is prepared by polymerizing only one type of monomer, a group of monomers that provides a homopolymer having a Tg greater than 0°C is referred to as monomer group a. Furthermore, when a homopolymer is prepared by polymerizing only one type of monomer, a group of monomers that provides a homopolymer having a Tg less than 0°C is referred to as monomer group b. An elastomer containing 50 to 100 wt % (more preferably, 65 to 99 wt %) of structural units derived from at least one monomer selected from monomer group a and 0 to 50 wt % (more preferably, 1 to 35 wt %) of structural units derived from at least one monomer selected from monomer group b is referred to as elastomer X. Elastomer X has a Tg greater than 0°C. Furthermore, when the elastomer contains elastomer X, the printing ink composition can provide a cured coating with sufficient rigidity.

[0051] It is also preferable that a crosslinked structure be introduced into the elastic body when the Tg of the elastic body is higher than 0° C. Methods for introducing a crosslinked structure include the methods described above.

[0052] Monomers that can be included in the monomer group a include, but are not limited to, unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; vinyl-substituted aromatic compounds such as α-methylstyrene; ring-alkylated vinyl aromatic compounds such as 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; ring-alkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; ring-ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; and ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene. vinyl halides such as vinyl chloride; aromatic monomers such as acenaphthalene and indene; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate and isopropyl methacrylate; aromatic methacrylates such as phenyl methacrylate; methacrylates such as isobornyl methacrylate and trimethylsilyl methacrylate; methacrylic monomers including methacrylic acid derivatives such as methacrylonitrile; certain acrylic acid esters such as isobornyl acrylate and tert-butyl acrylate; acrylic monomers including acrylic acid derivatives such as acrylonitrile, etc. Further, examples of monomers that can be included in the monomer group a include acrylamide, isopropylacrylamide, N-vinylpyrrolidone, isobornyl methacrylate, dicyclopentanyl methacrylate, 2-methyl-2-adamantyl methacrylate, 1-adamantyl acrylate, and 1-adamantyl methacrylate, which, when made into a homopolymer, can provide a homopolymer having a Tg of 120° C. or higher. These monomers a may be used alone or in combination of two or more.

[0053] Examples of the monomer b include ethyl acrylate, butyl acrylate (also known as butyl acrylate), 2-ethylhexyl acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, 2-hydroxyethyl acrylate, and 4-hydroxybutyl acrylate. These monomers b may be used alone or in combination of two or more. Among these monomers b, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are particularly preferred.

[0054] (Volume Average Particle Diameter of Elastomer) The volume average particle diameter of the elastomer is preferably 0.03 μm to 50.00 μm, more preferably 0.05 μm to 10.00 μm, more preferably 0.08 μm to 2.00 μm, even more preferably 0.10 μm to 1.00 μm, even more preferably 0.10 μm to 0.80 μm, and particularly preferably 0.10 μm to 0.50 μm. When the volume average particle diameter of the elastomer is (a) 0.03 μm or more, an elastomer having the desired volume average particle diameter can be stably obtained, and when (b) 50.00 μm or less, the heat resistance and impact resistance of the resulting cured coating are excellent. The volume average particle diameter of the elastomer can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing the elastomer as a sample. The method for measuring the volume average particle diameter of the elastomer is described in detail in the Examples below.

[0055] (Proportion of Elastomer) The proportion of the elastomer in the polymer microparticles (A), based on 100% by weight of the entire polymer microparticles (A), is preferably 40 to 97% by weight, more preferably 60 to 95% by weight, and even more preferably 70 to 93% by weight. When the proportion of the elastomer is 40% by weight or more, the printing ink composition can provide a cured coating having excellent toughness and impact resistance. When the proportion of the elastomer is 97% by weight or less, the polymer microparticles (A) do not easily aggregate (are less likely to aggregate), and therefore the printing ink composition does not become highly viscous. As a result, the printing ink composition can be easy to handle.

[0056] (Gel content of elastomer) The elastomer is preferably one that can swell in an appropriate solvent but is substantially insoluble in the solvent. Furthermore, in order to enable the polymer fine particles (A) to exist in the form of particles in the printing ink composition and the cured coating, the elastomer is preferably insoluble in the low molecular weight compound (C), the radical polymerizable oligomer resin, and the inert resin (E) described below.

[0057] The elastomer preferably has a gel content of 60 wt % or more, more preferably 80 wt % or more, even more preferably 90 wt % or more, and particularly preferably 95 wt % or more. When the gel content of the elastomer is within this range, the printing ink composition can provide a cured coating having excellent toughness.

[0058] In this specification, the gel content is calculated as follows. First, an aqueous latex containing polymer microparticles (A) is obtained, and then a powder of polymer microparticles (A) is obtained from the aqueous latex. The method for obtaining a powder of polymer microparticles (A) from the aqueous latex is not particularly limited, but an example thereof includes a method of (i) agglomerating the polymer microparticles (A) in the aqueous latex, (ii) dehydrating the obtained agglomerates, and (iii) further drying the agglomerates to obtain a powder of polymer microparticles (A). Next, 2.0 g of the powder of polymer microparticles (A) is dissolved in 50 mL of methyl ethyl ketone (MEK). Thereafter, the obtained MEK solution is separated into a component soluble in MEK (MEK solubles) and a component insoluble in MEK (MEK insolubles). Specifically, the obtained MEK dissolved material is centrifuged using a centrifuge (CP60E, manufactured by Hitachi Koki Co., Ltd.) at a rotation speed of 30,000 rpm for 1 hour to separate the dissolved material into MEK-soluble and MEK-insoluble components. Three sets of centrifugation are performed in total. The weights of the obtained MEK-soluble and MEK-insoluble components are measured, and the gel content is calculated using the following formula: Gel content (%) = (weight of methyl ethyl ketone-insoluble component) / {(weight of methyl ethyl ketone-insoluble component) + (weight of methyl ethyl ketone-soluble component)} × 100.

[0059] (2-1-2. Graft Moiety) In this specification, a polymer grafted to an elastomer is referred to as a graft moiety. The graft moiety includes a polymer containing, as a structural unit, a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers. Because the graft moiety has the above structure, it can fulfill various roles. Examples of the "various roles" include (a) improving the compatibility between the resin component in the printing ink composition and the polymer microparticles (A), (b) improving the dispersibility of the polymer microparticles (A) in the printing ink composition and the cured film, and (c) enabling the polymer microparticles (A) to be dispersed in the state of primary particles in the printing ink composition and the cured film.

[0060] Specific examples of aromatic vinyl monomers include styrene, α-methylstyrene, p-methylstyrene, and divinylbenzene.

[0061] Specific examples of vinyl cyanide monomers include acrylonitrile and methacrylonitrile.

[0062] Specific examples of the (meth)acrylate monomer include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0063] The one or more monomers selected from the group consisting of the aromatic vinyl monomer, the vinyl cyan monomer, and the (meth)acrylate monomer may be used alone or in combination of two or more.

[0064] The graft portion preferably contains, as structural units, structural units derived from aromatic vinyl monomers, structural units derived from vinyl cyan monomers, and structural units derived from (meth)acrylate monomers in a total amount of 10 to 95% by weight, more preferably 30 to 92% by weight, even more preferably 50 to 90% by weight, particularly preferably 60 to 87% by weight, and most preferably 70 to 85% by weight, based on 100% by weight of all structural units.

[0065] The graft moiety preferably includes a structural unit derived from a monomer having a reactive group. The monomer having a reactive group is preferably a monomer having one or more reactive groups selected from the group consisting of epoxy groups, oxetane groups, hydroxyl groups, amino groups, imide groups, carboxylic acid groups, carboxylic anhydride groups, cyclic esters, cyclic amides, benzoxazine groups, and cyanate ester groups, more preferably a monomer having one or more reactive groups selected from the group consisting of epoxy groups, hydroxyl groups, and carboxylic acid groups, and most preferably a monomer having an epoxy group. This configuration allows the graft moiety of the polymer microparticles (A) to be chemically bonded to the low molecular weight compound (C) or the radically polymerizable oligomer resin and inert resin (E) in the resulting printing ink composition. This allows the polymer microparticles (A) to maintain a good dispersion state without agglomerating in the resulting printing ink composition or cured coating.

[0066] Specific examples of the monomer having an epoxy group include glycidyl group-containing vinyl monomers such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and allyl glycidyl ether.

[0067] Specific examples of the monomer having a hydroxyl group include: (a) hydroxy linear alkyl (meth)acrylates (particularly, hydroxy linear C1-6 alkyl (meth)acrylates) such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; (b) caprolactone-modified hydroxy (meth)acrylates; (c) hydroxy branched alkyl (meth)acrylates such as α-(hydroxymethyl)methyl acrylate and α-(hydroxymethyl)ethyl acrylate; and (d) hydroxyl group-containing (meth)acrylates such as mono(meth)acrylates of polyester diols (particularly, saturated polyester diols) obtained from divalent carboxylic acids (such as phthalic acid) and dihydric alcohols (such as propylene glycol).

[0068] Specific examples of the monomer having a carboxylic acid group include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid. As the monomer having a carboxylic acid group, the above-mentioned monocarboxylic acids are preferably used.

[0069] The above-mentioned monomers having a reactive group may be used alone or in combination of two or more.

[0070] The graft portion preferably contains, based on 100% by weight of the graft portion, 0.5 to 90% by weight, more preferably 1 to 50% by weight, even more preferably 2 to 35% by weight, and particularly preferably 3 to 20% by weight, of structural units derived from monomers having a reactive group. When the graft portion contains, based on 100% by weight of the graft portion, 0.5% by weight or more of structural units derived from monomers having a reactive group, the printing ink composition can provide a cured coating having sufficient impact resistance. When the graft portion contains, based on 100% by weight of the graft portion, 90% by weight or less of structural units derived from monomers having a reactive group, the printing ink composition can provide a cured coating having sufficient impact resistance, and has the advantage of exhibiting good storage stability.

[0071] The structural unit derived from a monomer having a reactive group is preferably contained in the graft portion, and more preferably contained only in the graft portion.

[0072] The graft moiety may contain a structural unit derived from a polyfunctional monomer. When the graft moiety contains a structural unit derived from a polyfunctional monomer, it has the following advantages: (a) swelling of the polymer fine particles (A) in the printing ink composition can be prevented, (b) the viscosity of the printing ink composition is reduced, which tends to improve the handleability of the printing ink composition, and (c) the dispersibility of the polymer fine particles (A) in the printing ink composition is improved.

[0073] When the graft portion does not contain a constitutional unit derived from a polyfunctional monomer, the printing ink composition can provide a cured coating that is superior in toughness and impact resistance compared to when the graft portion contains a constitutional unit derived from a polyfunctional monomer.

[0074] Examples of polyfunctional monomers that can be used in the polymerization of the graft portion include the same monomers as the polyfunctional monomers described above. Among these polyfunctional monomers, polyfunctional monomers that can be preferably used in the polymerization of the graft portion include allyl methacrylate, butylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. These polyfunctional monomers may be used alone or in combination of two or more.

[0075] The graft portion preferably contains 1 to 20% by weight, and more preferably 5 to 15% by weight, of structural units derived from polyfunctional monomers, based on 100% by weight of the graft portion.

[0076] In the polymerization of the graft portion, the above-mentioned monomers may be used alone or in combination of two or more.

[0077] The graft moiety may contain, as constituent units, constituent units derived from other monomers in addition to the constituent units derived from the above-mentioned monomers.

[0078] (Glass Transition Temperature of Graft Portion) The glass transition temperature of the graft portion is preferably 190°C or lower, more preferably 160°C or lower, more preferably 140°C or lower, more preferably 120°C or lower, preferably 80°C or lower, more preferably 70°C or lower, more preferably 60°C or lower, more preferably 50°C or lower, more preferably 40°C or lower, more preferably 30°C or lower, more preferably 20°C or lower, more preferably 10°C or lower, more preferably 0°C or lower, more preferably -20°C or lower, more preferably -40°C or lower, more preferably -45°C or lower, more preferably -50°C or lower. ° C. or lower, more preferably −55° C. or lower, more preferably −60° C. or lower, more preferably −65° C. or lower, more preferably −70° C. or lower, more preferably −75° C. or lower, more preferably −80° C. or lower, more preferably −85° C. or lower, more preferably −90° C. or lower, more preferably −95° C. or lower, more preferably −100° C. or lower, more preferably −105° C. or lower, more preferably −110° C. or lower, more preferably −115° C. or lower, even more preferably −120° C. or lower, and particularly preferably −125° C. or lower.

[0079] The glass transition temperature of the graft portion is preferably 0°C or higher, more preferably 30°C or higher, more preferably 50°C or higher, more preferably 70°C or higher, even more preferably 90°C or higher, and particularly preferably 110°C or lower.

[0080] The Tg of the graft portion can be determined by the composition of the structural units contained in the graft portion, etc. In other words, the Tg of the resulting graft portion can be adjusted by changing the composition of the monomers used when producing (polymerizing) the graft portion.

[0081] The Tg of the graft portion can be obtained by performing viscoelasticity measurements using a flat plate made of polymer microparticles (A). Specifically, the Tg can be measured as follows: (1) Using a dynamic viscoelasticity measuring device (e.g., DVA-200, manufactured by IT Measurement & Control Co., Ltd.), dynamic viscoelasticity measurements are performed under tensile conditions on a flat plate made of polymer microparticles (A) to obtain a tan δ graph; (2) The peak temperature of tan δ in the obtained tan δ graph is taken as the glass transition temperature. Here, if multiple peaks are obtained in the tan δ graph, the highest peak temperature is taken as the glass transition temperature of the graft portion.

[0082] (Graft ratio of graft moiety) In one embodiment of the present invention, the polymer microparticles (A) may contain a polymer having the same structure as the graft moiety but not grafted to the elastomer. In this specification, a polymer having the same structure as the graft moiety but not grafted to the elastomer is also referred to as a non-graft polymer. This non-graft polymer also constitutes a part of the polymer microparticles (A) according to one embodiment of the present invention. The non-graft polymer can also be said to be a polymer produced in the polymerization of the graft moiety but not grafted to the elastomer.

[0083] In this specification, the proportion of the polymer grafted to the elastomer, i.e., the proportion of the grafted portion, among the polymers produced in the polymerization of the grafted portion, is referred to as the graft ratio. The graft ratio can also be expressed as (weight of the grafted portion) / {(weight of the grafted portion)+(weight of the non-grafted polymer)}×100.

[0084] The graft ratio of the graft moiety is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. A graft ratio of 70% or more has the advantage that the viscosity of the printing ink composition does not become too high.

[0085] In this specification, the graft ratio is calculated as follows. First, an aqueous latex containing polymer microparticles (A) is obtained, and then a powder of polymer microparticles (A) is obtained from the aqueous latex. Specific methods for obtaining a powder of polymer microparticles (A) from an aqueous latex include (i) coagulating the polymer microparticles (A) in the aqueous latex, (ii) dehydrating the obtained coagulate, and (iii) further drying the coagulate to obtain a powder of polymer microparticles (A). Next, 2 g of the powder of polymer microparticles (A) is dissolved in 50 mL of methyl ethyl ketone (MEK). Thereafter, the obtained MEK solution is separated into a component soluble in MEK (MEK-soluble component) and a component insoluble in MEK (MEK-insoluble component). Specifically, the obtained MEK solution is centrifuged using a centrifuge (CP60E, manufactured by Hitachi Koki Co., Ltd.) at a rotation speed of 30,000 rpm for 1 hour, and the solution is separated into an MEK-soluble fraction and an MEK-insoluble fraction. A total of three sets of centrifugation are performed. Next, 20 ml of the concentrated MEK-soluble fraction is mixed with 200 ml of methanol. An aqueous calcium chloride solution prepared by dissolving 0.01 g of calcium chloride in water is added to the obtained mixture, and the obtained mixture is stirred for 1 hour. The obtained mixture is then separated into a methanol-soluble fraction and a methanol-insoluble fraction, and the weight of the methanol-insoluble fraction is taken as the amount of free polymer (FP).

[0086] The graft ratio was calculated using the following formula: Graft ratio (%)=100−[(FP amount) / {(FP amount)+(weight of MEK insoluble matter)}] / (weight of polymer in grafted portion)×10,000.

[0087] The weight of the polymer other than the graft portion is the charged amount of the monomer constituting the polymer other than the graft portion. The polymer other than the graft portion is, for example, an elastomer. When the polymer microparticles (A) contain a surface-crosslinked polymer described below, the polymer other than the graft portion includes both an elastomer and a surface-crosslinked polymer. The weight of the polymer in the graft portion is the charged amount of the monomer constituting the polymer in the graft portion. In calculating the graft ratio, the method for coagulating the polymer microparticles (A) is not particularly limited, and methods such as using a solvent, using a coagulant, and spraying an aqueous latex can be used.

[0088] When the elastomer and the graft moiety are polymerized in this order in the production of polymer microparticles (A), at least a portion of the graft moiety can cover at least a portion of the elastomer in the resulting polymer microparticles (A). Polymerization of the elastomer and the graft moiety in this order can be said to be multistage polymerization of the elastomer and the graft moiety. The polymer microparticles (A) obtained by multistage polymerization of the elastomer and the graft moiety can also be said to be multistage polymers.

[0089] When the polymer fine particles (A) are multistage polymers, the graft moieties may cover at least a part of the elastomer or may cover the entire elastomer. When the polymer fine particles (A) are multistage polymers, the graft moieties may be partially embedded inside the elastomer.

[0090] When the polymer microparticles (A) are multistage polymers, the elastomer and the graft moieties may form a layer structure. For example, one embodiment of the present invention is one in which the elastomer forms the innermost layer (also referred to as a core layer) and a layer of the graft moieties is formed as the outermost layer (also referred to as a shell layer) outside the elastomer. A structure in which the elastomer forms the core layer and the graft moieties form the shell layer can also be referred to as a core-shell structure. Thus, polymer microparticles (A) in which the elastomer and the graft moieties form a layer structure (core-shell structure) can also be referred to as a multilayer polymer or a core-shell polymer. That is, in one embodiment of the present invention, the polymer microparticles (A) may be multistage polymers and / or multilayer polymers or core-shell polymers. However, as long as the graft moieties are graft-bonded to the elastomer, the polymer microparticles (A) are not limited to the above structure.

[0091] At least a portion of the graft portion preferably covers at least a portion of the elastomer, in other words, at least a portion of the graft portion preferably exists on the outermost side of the polymer fine particles (A).

[0092] (2-1-3. Surface-Crosslinked Polymer) The rubber-containing graft copolymer preferably further comprises a surface-crosslinked polymer in addition to the elastomer and the graft moiety grafted to the elastomer. In other words, the polymer microparticles (A) preferably further comprise a surface-crosslinked polymer in addition to the elastomer and the graft moiety grafted to the elastomer. Hereinafter, one embodiment of the present invention will be described using an example in which the polymer microparticles (A) (e.g., rubber-containing graft copolymer) further comprise a surface-crosslinked polymer. This has the advantages of (a) improving blocking resistance in the production of the polymer microparticles (A) and (b) improving the dispersibility of the polymer microparticles (A) in the printing ink composition. The reasons for this are not particularly limited, but can be presumed as follows: by coating at least a portion of the elastomer with the surface-crosslinked polymer, the exposure of the elastomer portion of the polymer microparticles (A) is reduced, and as a result, the elastomers are less likely to stick to each other, thereby improving the dispersibility of the polymer microparticles (A).

[0093] When the polymer microparticles (A) further contain a surface-crosslinked polymer, they can also have the following effects: (a) reducing the viscosity of the printing ink composition, (b) increasing the crosslink density in the elastomer, and (c) increasing the graft efficiency of the grafted portion. The crosslink density in the elastomer means the degree of the number of crosslinked structures in the entire elastomer.

[0094] The surface cross-linked polymer is composed of a polymer containing, as structural units, 30 to 100% by weight of structural units derived from polyfunctional monomers and 0 to 70% by weight of structural units derived from other vinyl monomers, totaling 100% by weight.

[0095] Examples of polyfunctional monomers that can be used in the polymerization of surface-crosslinked polymers include the same monomers as the polyfunctional monomers described above. Among these polyfunctional monomers, polyfunctional monomers that can be preferably used in the polymerization of surface-crosslinked polymers include allyl methacrylate, ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate (e.g., 1,3-butylene glycol dimethacrylate), butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. These polyfunctional monomers may be used alone or in combination of two or more.

[0096] The polymer fine particles (A) may contain a surface-crosslinked polymer polymerized independently of the polymerization of the rubber-containing graft copolymer, or may contain a surface-crosslinked polymer polymerized together with the rubber-containing graft copolymer. The polymer fine particles (A) may be a multistage polymer obtained by multistage polymerization of an elastomer, a surface-crosslinked polymer, and a graft moiety in this order. In either of these embodiments, the surface-crosslinked polymer can cover at least a portion of the elastomer.

[0097] The surface cross-linked polymer can also be regarded as a part of the elastomer. In other words, the surface cross-linked polymer can also be regarded as a part of the rubber-containing graft copolymer, and can also be called a surface cross-linked polymerization part. When the polymer microparticles (A) contain a surface cross-linked polymer, the graft part may be (a) graft-bonded to an elastomer other than the surface cross-linked polymer, (b) graft-bonded to a surface cross-linked polymer, or (c) graft-bonded to both an elastomer other than the surface cross-linked polymer and the surface cross-linked polymer. When the polymer microparticles (A) contain a surface cross-linked polymer, the volume average particle diameter of the elastomer mentioned above refers to the volume average particle diameter of the elastomer containing the surface cross-linked polymer.

[0098] A case (Case D) will be described in which the polymer microparticles (A) are a multistage polymer obtained by multistage polymerization of an elastomer, a surface-crosslinked polymer, and a graft moiety in this order. In Case D, the surface-crosslinked polymer may cover a part of the elastomer, or the whole of the elastomer. In Case D, a part of the surface-crosslinked polymer may penetrate into the inside of the elastomer. In Case D, the graft moiety may cover a part of the surface-crosslinked polymer, or the whole of the surface-crosslinked polymer. In Case D, a part of the graft moiety may penetrate into the surface-crosslinked polymer. In Case D, the elastomer, the surface-crosslinked polymer, and the graft moiety may have a layer structure. For example, an embodiment in which the elastomer is the innermost layer (core layer), a layer of the surface-crosslinked polymer exists outside the elastomer as an intermediate layer, and a layer of the graft moiety exists outside the surface-crosslinked polymer as an outermost layer (shell layer) is also one embodiment of the present invention.

[0099] (2-1-4. Physical Properties of Polymer Fine Particles (A)) Hereinafter, the physical properties of the polymer fine particles (A) will be described.

[0100] (Volume average particle diameter (Mv) of polymer microparticles (A)) The volume average particle diameter (Mv) of the polymer microparticles (A) is preferably 0.03 μm to 50.00 μm, more preferably 0.05 μm to 10.00 μm, more preferably 0.08 μm to 2.00 μm, even more preferably 0.10 μm to 1.00 μm, even more preferably 0.10 μm to 0.80 μm, and particularly preferably 0.10 μm to 0.50 μm, because this allows for the production of a printing ink composition having the desired viscosity. When the volume average particle diameter (Mv) of the polymer microparticles (A) is within the above range, there is also the advantage that the dispersibility of the polymer microparticles (A) in the printing ink composition is improved. In this specification, the term "volume average particle diameter (Mv) of the polymer microparticles (A)" refers to the volume average particle diameter of the primary particles of the polymer microparticles (A), unless otherwise specified. The volume average particle diameter of the polymer microparticles (A) can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing the polymer microparticles (A) as a sample. The volume average particle diameter of the polymer microparticles (A) will be described in detail in the Examples below. The volume average particle diameter of the polymer microparticles (A) can also be measured by cutting a cured coating of the printing ink composition, photographing the cut surface using an electron microscope or the like, and using the obtained photographed data (photographed image).

[0101] The number distribution of the volume average particle diameter of the polymer fine particles (A) preferably has a half-value width of 0.5 to 1 times the volume average particle diameter, since this allows for a printing ink composition that is low in viscosity and easy to handle.

[0102] (2-1-5. Production method of polymer fine particles (A)) The polymer fine particles (A) can be produced by polymerizing an elastomer, and then graft polymerizing a polymer that constitutes a graft moiety to the elastomer in the presence of the elastomer. Hereinafter, the production method (polymerization method) of the polymer fine particles (A) will be described using as an example a production method of an aqueous latex of the polymer fine particles (A) that can be suitably used in the production of the present printing ink composition described below.

[0103] The polymer microparticles (A) can be produced by known methods, such as emulsion polymerization, suspension polymerization, and microsuspension polymerization. Specifically, the polymerization of the elastomer, the polymerization of the graft moiety (graft polymerization), and the polymerization of the surface-crosslinked polymer in the polymer microparticles (A) can be carried out by known methods, such as emulsion polymerization, suspension polymerization, and microsuspension polymerization. Among these, emulsion polymerization is particularly preferred as a method for producing the polymer microparticles (A). The emulsion polymerization method has the advantages of (a) easy compositional design of the polymer microparticles (A), (b) easy industrial production of the polymer microparticles (A), and (c) easy production of an aqueous latex of the polymer microparticles (A) that can be suitably used in the production of a printing ink composition. Below, the elastomer, graft moiety, and a method for producing a surface-crosslinked polymer of any configuration that can be contained in the polymer microparticles (A) are described.

[0104] (Method for Producing Elastomer) Consider a case where the elastomer contains at least one selected from the group consisting of diene rubber and (meth)acrylate rubber. In this case, the elastomer can be produced by a method such as emulsion polymerization, suspension polymerization, or microsuspension polymerization, and the method described in WO 2005 / 028546 can be used as the production method.

[0105] Consider a case where the elastomer contains an organosiloxane rubber. In this case, the elastomer can be produced by a method such as emulsion polymerization, suspension polymerization, or microsuspension polymerization, and the production method can be, for example, the method described in WO 2006 / 070664.

[0106] (Method for producing the graft portion) The graft portion can be formed, for example, by polymerizing the monomer used to form the graft portion by known radical polymerization. When (a) the elastomer or (b) the polymer microparticle precursor containing the elastomer and the surface-crosslinked polymer is obtained as an aqueous latex, it is preferable to carry out the polymerization of the graft portion by emulsion polymerization. The graft portion can be produced, for example, according to the method described in WO2005 / 028546.

[0107] The graft portion is a graft portion of multiple types (e.g., graft portion １ , graft part ２ , ..., graft part ｎ In this case, the graft portion is made of １ , graft part ２ , ..., graft part ｎ may be polymerized separately by the above-mentioned method, and then mixed and composited to produce a graft portion (composite) consisting of a plurality of types of graft portions. １ , graft part ２ , ..., graft part ｎ may be sequentially polymerized in multiple stages to produce one graft moiety consisting of multiple types of graft moieties.

[0108] (Method for producing surface cross-linked polymer) The surface cross-linked polymer can be formed by polymerizing a monomer used for forming the surface cross-linked polymer by known radical polymerization. When the elastomer is obtained as an aqueous latex, it is preferable to carry out the polymerization of the surface cross-linked polymer by emulsion polymerization.

[0109] When emulsion polymerization is employed as the method for producing the polymer fine particles (A), a known emulsifier (dispersant) can be used for producing the polymer fine particles (A).

[0110] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, polyvinyl alcohol, alkyl-substituted cellulose, polyvinylpyrrolidone, and polyacrylic acid derivatives. Examples of anionic emulsifiers include sulfur-based emulsifiers, phosphorus-based emulsifiers, sarcosinic acid-based emulsifiers, and carboxylic acid-based emulsifiers. Examples of sulfur-based emulsifiers include sodium dodecylbenzenesulfonate (abbreviated as SDBS). Examples of phosphorus-based emulsifiers include sodium polyoxyethylene lauryl ether phosphate.

[0111] When emulsion polymerization is used as the method for producing the polymer microparticles (A), a thermally decomposable initiator can be used to produce the polymer microparticles (A). Examples of the thermally decomposable initiator include known initiators such as (a) 2,2'-azobisisobutyronitrile and (b) peroxides such as organic peroxides and inorganic peroxides. Examples of the organic peroxides include t-butylperoxyisopropyl carbonate, paramenthane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, and t-hexyl peroxide. Examples of the inorganic peroxides include hydrogen peroxide, potassium persulfate, and ammonium persulfate.

[0112] A redox initiator can also be used to produce the polymer microparticles (A). The redox initiator is an initiator that combines (a) a peroxide such as an organic peroxide or an inorganic peroxide with (b) a transition metal salt such as iron (II) sulfate, or a reducing agent such as sodium formaldehyde sulfoxylate or glucose. If necessary, a chelating agent such as disodium ethylenediaminetetraacetate and, if necessary, a phosphorus-containing compound such as sodium pyrophosphate may also be used in combination.

[0113] When a redox initiator is used, polymerization can be carried out even at a low temperature where the peroxide does not substantially decompose thermally, and the polymerization temperature can be set over a wide range. Therefore, it is preferable to use a redox initiator. Among redox initiators, redox initiators using organic peroxides such as cumene hydroperoxide, dicumyl peroxide, paramenthane hydroperoxide, and t-butyl hydroperoxide as the peroxide are preferred. The amount of the initiator used, and when a redox initiator is used, the amounts of the reducing agent, transition metal salt, chelating agent, etc. used can be within known ranges.

[0114] When a polyfunctional monomer is used in polymerization of the elastomer, graft portion, or surface-crosslinked polymer for the purpose of introducing a crosslinked structure into the elastomer, graft portion, or surface-crosslinked polymer, a known chain transfer agent can be used in a known amount range. By using the chain transfer agent, the molecular weight and / or degree of crosslinking of the resulting elastomer, graft portion, or surface-crosslinked polymer can be easily adjusted.

[0115] In addition to the above-mentioned components, a surfactant may be used in the production of the polymer microparticles (A). The type and amount of the surfactant used are within known ranges.

[0116] In the production of the polymer fine particles (A), conditions within known numerical ranges can be appropriately applied as polymerization conditions such as polymerization temperature, pressure, and deoxidation.

[0117] In the present printing ink composition, the content of the polymer fine particles (A) is preferably 1.0 wt % or more, more preferably 1.5 wt % or more, even more preferably 2.0 wt % or more, and particularly preferably 2.5 wt % or more, relative to 100 wt % of the UV-curable printing ink composition. This configuration has the advantage of providing a cured coating with excellent adhesion to the substrate.

[0118] Furthermore, in the present printing ink composition, the content of the polymer fine particles (A) is preferably 10.0 wt % or less, more preferably 8.0 wt % or less, even more preferably 6.0 wt % or less, and particularly preferably 4.0 wt % or less, based on 100 wt % of the UV-curable printing ink composition. This configuration has the advantage of being able to maintain a high level of hardness of the cured coating.

[0119] (2-2. Resin (B)) The printing ink composition preferably further contains a resin (B). The resin (B) is preferably contained in the powder of polymer microparticles (A) described below. In other words, the powder of polymer microparticles (A) preferably contains a resin (B). This configuration has the surprising advantage that the polymer microparticles (A) have excellent dispersibility in the printing ink composition.

[0120] Resin (B) may be, for example, a thermosetting resin, a thermoplastic resin, or any combination of a thermosetting resin and a thermoplastic resin.

[0121] (2-2-1. Thermosetting Resin) The thermosetting resin in resin (B) is not particularly limited, but preferably contains at least one selected from the group consisting of epoxy resins, phenolic resins, polyol resins, and amino-formaldehyde resins. Examples of the thermosetting resin in resin (B) include resins containing polymers obtained by polymerizing aromatic polyester raw materials. In resin (B), only one type of thermosetting resin may be used, or two or more types may be used in combination.

[0122] (Epoxy Resin) The epoxy resin is not particularly limited as long as it has at least one epoxy group in the molecule.

[0123] Specific examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD ​​type epoxy resins, bisphenol S type epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, novolac type epoxy resins, glycidyl ether type epoxy resins of bisphenol A propylene oxide adducts, hydrogenated bisphenol A (or F) type epoxy resins, fluorinated epoxy resins, rubber-modified epoxy resins containing polybutadiene or NBR, flame-retardant epoxy resins such as glycidyl ether of tetrabromobisphenol A, p-oxybenzoic acid glycidyl ether ester type epoxy resins, m-aminophenol type epoxy resins, diaminodiphenylmethane-based epoxy resins, urethane-modified epoxy resins having a urethane bond, various alicyclic epoxy resins, glycidyl ethers of polyhydric alcohols, hydantoin type epoxy resins, epoxidized products of unsaturated polymers such as petroleum resins, and amino-containing glycidyl ether resins. Examples of the polyhydric alcohol include N,N-diglycidylaniline, N,N-diglycidyl-o-toluidine, triglycidyl isocyanurate, polyalkylene glycol diglycidyl ether, and glycerin. Examples of the epoxy resin include epoxy compounds obtained by subjecting the above-mentioned epoxy resins to an addition reaction with bisphenol A (or F), polybasic acids, or the like. The epoxy resin is not limited to these, and commonly used epoxy resins can be used. These epoxy resins may be used alone or in combination of two or more.

[0124] Among the above-mentioned epoxy resins, those having at least two epoxy groups per molecule are preferred because they have high reactivity during curing of the printing ink composition and the resulting cured coating easily forms a three-dimensional network. Furthermore, among epoxy resins having at least two epoxy groups per molecule, those containing bisphenol-type epoxy resins as the main component are preferred because of their excellent economic efficiency and ease of availability.

[0125] (Phenol Resin) The phenol resin is not particularly limited as long as it is a compound obtained by reacting a phenol with an aldehyde. The phenol is not particularly limited, but examples thereof include phenol, orthocresol, meta-cresol, para-cresol, xylenol, para-tertiary butylphenol, para-octylphenol, paraphenylphenol, bisphenol A, bisphenol F, and resorcinol. Particularly preferred phenols include phenol and cresol.

[0126] The aldehydes are not particularly limited, but examples thereof include formaldehyde, acetaldehyde, butylaldehyde, acrolein, and mixtures thereof. As the aldehydes, the above-mentioned substances that are sources of aldehydes or solutions of these aldehydes can also be used. As the aldehydes, formaldehyde is preferred because the operation when reacting phenols with aldehydes is easy.

[0127] When reacting phenols with aldehydes, the molar ratio (F / R) of the phenols (P) to the aldehydes (R) (hereinafter also referred to as the reaction molar ratio) is not particularly limited. When an acid catalyst is used in the reaction, the reaction molar ratio (F / R) is preferably 0.4 to 1.0, more preferably 0.5 to 0.8. When an alkali catalyst is used in the reaction, the reaction molar ratio (F / R) is preferably 0.4 to 4.0, more preferably 0.8 to 2.5. When the reaction molar ratio is equal to or greater than the lower limit, the yield does not become too low, and there is no risk of the molecular weight of the resulting phenolic resin becoming small. On the other hand, when the reaction molar ratio is equal to or less than the upper limit, the molecular weight of the phenolic resin does not become too large, and the softening point does not become too high, so sufficient fluidity can be obtained when heated. Furthermore, when the reaction molar ratio is equal to or less than the upper limit, molecular weight control is easy, and there is no risk of gelation or partial gelation occurring due to the reaction conditions.

[0128] (Polyol Resin) A polyol resin is a compound having two or more active hydrogens at its terminals, and is a polyol having two or more functionalities and a molecular weight of about 50 to 20,000. Examples of polyol resins include aliphatic alcohols, aromatic alcohols, polyether polyols, polyester polyols, polyolefin polyols, and acrylic polyols.

[0129] The aliphatic alcohol may be either a dihydric alcohol or a trihydric or higher alcohol (such as a trihydric alcohol or a tetrahydric alcohol). Examples of dihydric alcohols include (a) alkylene glycols (particularly alkylene glycols having about 1 to 6 carbon atoms) such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and neopentyl glycol, and (b) dehydration condensates of two or more molecules (e.g., about 2 to 6 molecules) of such alkylene glycol compounds (diethylene glycol, dipropylene glycol, tripropylene glycol, etc.). Examples of trihydric alcohols include glycerin, trimethylolpropane, trimethylolethane, and 1,2,6-hexanetriol (particularly trihydric alcohols having about 3 to 10 carbon atoms). Examples of tetrahydric alcohols include pentaerythritol and diglycerin. Further examples include sugars such as monosaccharides, oligosaccharides, and polysaccharides.

[0130] Examples of aromatic alcohols include bisphenols such as bisphenol A and bisphenol F; biphenyls such as dihydroxybiphenyl; polyhydric phenols such as hydroquinone and phenol formaldehyde condensates; and naphthalenediol.

[0131] Examples of polyether polyols include (a) random copolymers or block copolymers obtained by ring-opening polymerization of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, or the like in the presence of one or more active hydrogen-containing initiators, and (b) mixtures of these copolymers. Examples of active hydrogen-containing initiators used in the ring-opening polymerization of polyether polyols include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and bisphenol A; triols such as trimethylolethane, trimethylolpropane, and glycerin; saccharides such as monosaccharides, oligosaccharides, and polysaccharides; sorbitol; and amines such as ammonia, ethylenediamine, urea, monomethyldiethanolamine, and monoethyldiethanolamine.

[0132] Examples of polyester-type polyols include polymers obtained by polycondensing a polybasic acid and / or anhydride of a polybasic acid with a polyhydric alcohol in the presence of an esterification catalyst at a temperature ranging from 150 to 270°C. Examples of the polybasic acid include maleic acid, fumaric acid, adipic acid, sebacic acid, phthalic acid, dodecanedioic acid, isophthalic acid, and azelaic acid. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, and 3-methyl-1,5-pentanediol. Examples of polyester-type polyols include (a) ring-opening polymers of ε-caprolactone, valerolactone, and the like, and (b) active hydrogen compounds having two or more active hydrogen atoms, such as polycarbonate diol and castor oil.

[0133] Examples of polyolefin polyols include polybutadiene polyols, polyisoprene polyols, and hydrogenated products thereof.

[0134] Examples of acrylic polyols include (a) copolymers of hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxybutyl (meth)acrylate, and vinylphenol with (b) general-purpose monomers such as n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, and mixtures of such copolymers.

[0135] Among these polyol resins, polyether polyols are preferred because the printing ink composition has low viscosity and excellent workability, and the printing ink composition can provide a cured coating that has an excellent balance between hardness and toughness.Furthermore, among these polyol resins, polyester polyols are preferred because the printing ink composition can provide a cured coating that has excellent adhesion.

[0136] (Amino-formaldehyde resin) The amino-formaldehyde resin is not particularly limited as long as it is a compound obtained by reacting an amino compound with an aldehyde in the presence of an alkaline catalyst. Examples of the amino compound include melamine; 6-substituted guanamines such as guanamine, acetoguanamine, and benzoguanamine; amine-substituted triazine compounds such as CTU guanamine (3,9-bis[2-(3,5-diamino-2,4,6-triazaphenyl)ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane) and CMTU guanamine (3,9-bis[(3,5-diamino-2,4,6-triazaphenyl)methyl]-2,4,8,10-tetraoxaspiro[5,5]undecane); and ureas such as urea, thiourea, and ethylene urea. Examples of the amino compound that can be used include (a) substituted melamine compounds in which hydrogen atoms on the amino groups of melamine are substituted with alkyl groups, alkenyl groups, and / or phenyl groups (as described in U.S. Pat. No. 5,998,573 (corresponding Japanese Patent Publication No. JP-A-9-143238)), and (b) substituted melamine compounds in which hydrogen atoms on the amino groups of melamine are substituted with hydroxyalkyl groups, hydroxyalkyloxyalkyl groups, and / or aminoalkyl groups (as described in U.S. Pat. No. 5,322,915 (corresponding Japanese Patent Publication No. JP-A-5-202157)). Among the above-mentioned compounds, polyfunctional amino compounds such as melamine, guanamine, acetoguanamine, and benzoguanamine are preferred, as they are industrially produced and inexpensive, with melamine being particularly preferred. The above-mentioned amino compounds may be used alone or in combination of two or more. In addition to these amino compounds, (a) phenols such as phenol, cresol, alkylphenol, resorcinol, hydroquinone, and pyrogallol, and (b) aniline may also be used.

[0137] Examples of the aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and furfural. Formaldehyde and paraformaldehyde are preferred as the aldehydes because they are inexpensive and have good reactivity with the amino compounds listed above. In producing the amino-formaldehyde resin, the aldehydes are preferably used in an amount of 1.1 to 6.0 moles, and particularly preferably 1.2 to 4.0 moles, per mole of the amino compound, per available aldehyde group.

[0138] (Aromatic polyester raw material) Examples of aromatic polyester raw materials include radical polymerizable monomers such as aromatic vinyl compounds, (meth)acrylic acid derivatives, vinyl cyanide compounds, and maleimide compounds, dimethyl terephthalate, and alkylene glycol. In this specification, (meth)acrylic acid means acrylic acid and / or methacrylic acid.

[0139] The thermosetting resin in resin (B) is a compound obtained by bonding an ethylenically unsaturated monomer to a compound having a reactive group (e.g., an epoxy group, an oxetane group, a hydroxyl group, an amino group, an imide group, a carboxylic acid group, a carboxylic anhydride group, a cyclic ester, a cyclic amide, a benzoxazine group, a cyanate ester group, etc.) by a method other than radical polymerization, and also includes compounds having at least one ethylenically unsaturated bond in the molecule. In this specification, a "compound obtained by bonding an ethylenically unsaturated monomer to a compound having a reactive group by a method other than radical polymerization" is sometimes referred to as a "reactive group-ethylenically unsaturated bond-containing monomer." The thermosetting resin in resin (B) also includes a reactive group-ethylenically unsaturated bond-containing monomer.

[0140] The compound having a reactive group also includes thermosetting resins such as the above-mentioned epoxy resins, phenol resins, polyol resins, amino-formaldehyde resins, and resins containing polymers obtained by polymerizing aromatic polyester raw materials. The reactive group-ethylenically unsaturated bond-containing monomer may be a compound obtained by bonding an ethylenically unsaturated monomer to one or more selected from the group consisting of epoxy resins, phenol resins, polyol resins, amino-formaldehyde resins, and polymers obtained by polymerizing aromatic polyester raw materials by a method other than radical polymerization.

[0141] Examples of the reactive group-ethylenically unsaturated bond-containing monomer include unsaturated polyester resins, vinyl ester resins, epoxy acrylates, etc. These may be used alone or in combination of two or more.

[0142] (2-2-2. Thermoplastic Resin) Examples of the thermoplastic resin in the resin (B) include acrylic polymers, vinyl copolymers, polycarbonates, polyamides, polyesters, polyphenylene ethers, polyurethanes, and polyvinyl acetates. These may be used alone or in combination of two or more.

[0143] An acrylic polymer is a polymer whose main component is a structural unit made of an acrylic acid ester monomer. The acrylic acid ester monomer preferably has an ester moiety with 1 to 20 carbon atoms. Examples of the acrylic polymer include (a) a homopolymer of an acrylic acid ester monomer, and (b) a copolymer of an acrylic acid ester monomer with a monomer such as an unsaturated fatty acid, an acrylamide monomer, a maleimide monomer, or vinyl acetate, or a vinyl copolymer (hereinafter also referred to as an acrylic copolymer).

[0144] Examples of acrylic acid ester monomers include methyl acrylate (MA), ethyl acrylate (EA), 2-ethylhexyl acrylate (2EHA), acrylic acid (AA), methacrylic acid (MAA), 2-hydroxyethyl acrylate (2HEA), 2-hydroxyethyl methacrylate (2HEMA), butyl acrylate (BA), methyl methacrylate (MMA), ethyl methacrylate (EMA), n-butyl methacrylate (nBMA), isobutyl methacrylate (iBMA), propyl acrylate, isopropyl acrylate, and isobutyl acrylate. acrylate, t-butyl acrylate, neopentyl acrylate, isodecyl acrylate, lauryl acrylate, tridecyl acrylate, stearyl acrylate, cyclohexyl acrylate, isobornyl acrylate, tricyclodecyl acrylate, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, 2-methoxyethyl acrylate, dimethylaminoethyl acrylate, chloroethyl acrylate, trifluoroethyl acrylate, tetrahydrofurfuryl acrylate, etc. These may be used alone or in combination of two or more.

[0145] In the acrylic copolymer, the ratio of (a) a structural unit derived from an acrylic acid ester monomer (structural unit (a)) to (b) a structural unit derived from a monomer such as an unsaturated fatty acid, an acrylamide monomer, a maleimide monomer, or vinyl acetate, or a vinyl copolymer (structural unit (b)) is preferably 50% by weight to 100% by weight for the structural unit (a) and 0% by weight to 50% by weight for the structural unit (b).

[0146] The acrylic polymer preferably contains 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more of structural units derived from butyl acrylate (BA).

[0147] The vinyl copolymer is obtained by copolymerizing a mixture of vinyl monomers containing at least one selected from the group consisting of an aromatic vinyl monomer, a cyanide vinyl monomer, and an unsaturated carboxylic acid alkyl ester monomer. The vinyl monomer mixture may further contain another monomer (hereinafter also referred to as "monomer C") copolymerizable with the above-mentioned monomer.

[0148] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, and vinyltoluene. These vinyl monomers may be used alone or in combination of two or more. Among these, aromatic vinyl monomers are preferred, and styrene is more preferred, from the viewpoint of easily increasing the refractive index.

[0149] The unsaturated carboxylic acid alkyl ester monomer is not particularly limited. For example, an ester of an alcohol having 1 to 6 carbon atoms with acrylic acid or methacrylic acid is preferred. The ester of an alcohol having 1 to 6 carbon atoms with acrylic acid or methacrylic acid may further have a substituent such as a hydroxyl group or a halogen group.

[0150] Examples of esters of C1 to C6 alcohols with acrylic acid or methacrylic acid include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0151] Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, ethacrylonitrile, etc. These may be used alone or in combination of two or more.

[0152] Monomer C is a vinyl monomer other than the aromatic vinyl monomers, unsaturated carboxylic acid alkyl ester monomers, and vinyl cyanide monomers, and is not particularly limited as long as it does not impair the effects of the present invention. Specific examples of monomer C include unsaturated fatty acids, acrylamide monomers, maleimide monomers, vinyl acetate, and acrylic ester monomers. These may be used alone or in combination of two or more.

[0153] The unsaturated fatty acid may be selected from, for example, itaconic acid, maleic acid, fumaric acid, butenoic acid, acrylic acid, methacrylic acid, and the like.

[0154] The acrylamide monomer may be selected from, for example, acrylamide, methacrylamide, N-methylacrylamide, and the like.

[0155] The maleimide monomer may be selected from, for example, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-dodecylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and the like.

[0156] The method for producing the vinyl copolymer is not particularly limited, but examples thereof include emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization.

[0157] In the method for producing a vinyl copolymer, a polymerization initiator may be used as needed. The polymerization initiator may be, for example, one or more appropriately selected from the group consisting of peroxides, azo compounds, potassium persulfate, etc. The amount of the polymerization initiator to be added is not particularly limited.

[0158] Examples of peroxides include benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl isopropyl carbonate, di-t-butyl peroxide, t-butyl peroctate, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butylperoxy-2-ethylhexanoate. Of these, cumene hydroperoxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclohexane are particularly preferred.

[0159] Examples of azo compounds include azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, 2-cyano-2-propylazoformamide, 1,1'-azobiscyclohexane-1-carbonitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl 2,2'-azobisisobutyrate, 1-t-butylazo-2-cyanobutane, and 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane. Of these, 1,1'-azobiscyclohexane-1-carbonitrile is particularly preferred.

[0160] Specific examples of vinyl copolymers include polyvinyl chloride, chlorinated polyvinyl chloride, polystyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile-N-phenylmaleimide copolymer, α-methylstyrene-acrylonitrile copolymer, polymethyl methacrylate, methyl methacrylate-styrene copolymer, etc. These may be used alone or in combination of two or more.

[0161] Examples of polyester include polyethylene terephthalate and polybutylene terephthalate.

[0162] Resin (B) may be the same resin (a resin having the same composition) as component (E) (a radically polymerizable oligomer resin or an inert resin) described below, or may be a resin different from component (E). It is preferable that component (E) and resin (B) are not phase-separated in the printing ink composition. Resin (B) is preferably a resin that is compatible with component (E).

[0163] When the resin (B) is the same resin as the component (E) described below, there is an advantage that the resin (B) does not affect the various physical properties of the printing ink composition or cured coating containing the obtained powder or granule.

[0164] As an example, consider a case where resin (B) is the same type of resin as component (E). In this case, it is impossible to distinguish component (E) from resin (B) in the printing ink composition. Therefore, from the outside, the printing ink composition appears to contain (a) component (E) but not resin (B), or (b) resin (B) but not component (E). Next, consider a case where resin (B) is a different type of resin from component (E). In this case, component (E) and resin (B) can be distinguished in the printing ink composition. In this case, the printing ink composition may contain component (E) and resin (B) as a resin other than component (E).

[0165] (2-2-3. Others) In this specification, fats and oils and fatty acid esters are also included in resin (B). Resin (B) preferably contains fats and oils, and more preferably consists of fats and oils. Examples of fats and oils that can be suitably used as resin (B) include epoxidized fats and oils such as epoxidized soybean oil and epoxidized linseed oil. These resins may be used alone or in combination of two or more. Resin (B) preferably contains epoxidized soybean oil, and more preferably consists of epoxidized soybean oil. Commercially available epoxidized soybean oils can also be used, such as Adekaiser O-130P manufactured by ADEKA Corporation. Examples of fatty acid esters that can be suitably used as resin (B) include epoxidized fatty acid esters such as epoxidized fatty acid butyl, epoxidized fatty acid 2-ethylhexyl, epoxidized fatty acid octyl ester, and epoxidized fatty acid alkyl ester.

[0166] Epoxidized fats and oils and epoxidized fatty acid esters are sometimes referred to as epoxy plasticizers. That is, in this specification, epoxy plasticizers are also included in resin (B). Examples of epoxy plasticizers other than epoxidized fats and oils and epoxidized fatty acid esters include diepoxystearyl epoxyhexahydrophthalate and di-2-ethylhexyl epoxyhexahydrophthalate.

[0167] The above-mentioned thermosetting resins, thermoplastic resins, mixtures of thermosetting and thermoplastic resins, fats and oils, and fatty acid esters can each be used in combination with an antioxidant. In this specification, the antioxidant is considered to be part of resin (B) only when used in combination with each of the above-mentioned substances. When an antioxidant is used alone, it is not considered to be part of resin (B). The following describes the use of an antioxidant alone instead of resin (B). Because antioxidants are components that do not contribute to crosslinking, the physical properties of the cured film obtained by curing the printing ink composition tend to be inferior. For example, the Tg of the cured film may decrease, or the impact resistance may be poor.

[0168] The antioxidant is not particularly limited and examples thereof include (a) primary antioxidants such as phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, and hydroxylamine-based antioxidants, and (b) secondary antioxidants such as sulfur-based antioxidants and phosphorus-based antioxidants.

[0169] The phenol-based antioxidant may be a hindered phenol-based antioxidant. Examples of the hindered phenol-based antioxidant include compounds having a hindered phenol structure or a mono-hindered phenol structure in the molecule. Commercially available phenol-based antioxidants may also be used, such as Irganox 245 manufactured by BASF Japan Ltd.

[0170] The amine-based antioxidant is not particularly limited, and a wide variety of conventionally known amine-based antioxidants can be used. Specific examples of the amine-ketone compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, and reaction products of diphenylamine and acetone.

[0171] The amine antioxidants also include aromatic amine compounds, such as naphthylamine antioxidants, diphenylamine antioxidants, and p-phenylenediamine antioxidants.

[0172] The lactone-based antioxidant, the hydroxylamine-based antioxidant, and the sulfur-based antioxidant are not particularly limited, and a wide variety of conventionally known antioxidants can be used.

[0173] The phosphorus-based antioxidant is not particularly limited, and a wide variety of conventionally known antioxidants can be used. Phosphoric acid and phosphate esters containing active hydrogen can adversely affect the storage stability of the printing ink composition and the heat resistance of the cured coating film provided by the printing ink composition. Therefore, preferred phosphorus-based antioxidants are alkyl phosphites, aryl phosphites, alkylaryl phosphite compounds, and the like, which do not contain phosphoric acid or phosphate esters in the molecule.

[0174] Other conventionally known substances may also be used as the antioxidant, including various substances described in "Antioxidant Handbook" published by Taiseisha (first edition published on October 25, 1976) and "Polymer Additives Handbook" published by CMC Publishing (edited by Toru Haruna, first edition published on November 7, 2010).

[0175] Resin (B) is preferably one or more selected from the group consisting of thermosetting resins, mixtures of thermosetting resins and antioxidants, thermoplastic resins, mixtures of thermoplastic resins and antioxidants, oils and fats, mixtures of oils and antioxidants, fatty acid esters, mixtures of fatty acid esters and antioxidants, epoxy curing agents, and mixtures of epoxy curing agents and antioxidants, more preferably one or more selected from the group consisting of epoxy resins, acrylic polymers, mixtures of epoxy resins and antioxidants, mixtures of acrylic polymers and antioxidants, and mixtures of epoxy plasticizers and antioxidants, still more preferably one or more selected from the group consisting of mixtures of epoxy resins and antioxidants, mixtures of acrylic polymers and antioxidants, and mixtures of epoxy plasticizers and antioxidants, and particularly preferably a mixture of epoxy plasticizers and antioxidants. This configuration allows the (a) printing ink composition to provide a cured coating with excellent heat resistance, and has the advantage of improving the dispersibility of polymer microparticles (A) in the printing ink composition.

[0176] (2-2-4. Physical Properties of Resin (B)) Resin (B) is not particularly limited in other properties as long as it is a liquid, semi-solid, or solid having a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25°C. Note that "resin (B) has a viscosity of 100 mPa·s to 1,000,000 mPa·s at 25°C" means "resin (B) at 25°C has a viscosity of 100 mPa·s to 1,000,000 mPa·s."

[0177] When resin (B) is a liquid, the viscosity of resin (B) at 25°C is preferably 750,000 mPa·s or less, more preferably 700,000 mPa·s or less, more preferably 500,000 mPa·s or less, more preferably 350,000 mPa·s or less, more preferably 300,000 mPa·s or less, more preferably 250,000 mPa·s or less, more preferably 100,000 mPa·s or less, more preferably 75,000 mPa·s or less, more preferably 50,000 mPa·s or less, more preferably 30,000 mPa·s or less, more preferably 25,000 mPa·s or less, even more preferably 20,000 mPa·s or less, and particularly preferably 15,000 mPa·s or less. According to the above-mentioned configuration, the resin (B) has an advantage of being excellent in fluidity.

[0178] Furthermore, the viscosity of the resin (B) at 25°C is more preferably 100 mPa·s or more, more preferably 200 mPa·s or more, more preferably 300 mPa·s or more, more preferably 400 mPa·s or more, more preferably 500 mPa·s or more, even more preferably 750 mPa·s or more, even more preferably 1000 mPa·s or more, and particularly preferably 1500 mPa·s or more. According to this configuration, the resin (B) does not impregnate the polymer fine particles (B). Therefore, the resin (B) can prevent the polymer fine particles (B) from fusing together.

[0179] The viscosity of resin (B) at 25°C is more preferably 100 mPa·s to 750,000 mPa·s, more preferably 100 mPa·s to 700,000 mPa·s, more preferably 100 mPa·s to 350,000 mPa·s, more preferably 100 mPa·s to 300,000 mPa·s, more preferably 100 mPa·s to 50,000 mPa·s, even more preferably 100 mPa·s to 30,000 mPa·s, and particularly preferably 100 mPa·s to 15,000 mPa·s.

[0180] When resin (B) is semi-solid at 25° C., resin (B) can also be said to be semi-liquid at 25° C., and resin (B) can also be said to have a viscosity of greater than 1,000,000 mPa s at 25° C. When resin (B) is semi-solid or solid at 25° C., the resulting composition has the advantage of being less sticky and easier to handle.

[0181] The viscosity of the resin (B) can be measured using a viscometer. The method for measuring the viscosity of the resin (B) will be described in detail in the examples below.

[0182] Resin (B) is preferably a resin having an endothermic peak of 25°C or less in a differential scanning calorimetry (DSC) thermogram, more preferably a resin having an endothermic peak of 0°C or less.

[0183] (2-3. Radically polymerizable oligomer resin and / or inert resin (E)) In one embodiment of the present invention, the printing ink composition preferably comprises a radically polymerizable oligomer resin and / or inert resin (E). This configuration has the advantage of being able to provide a printing ink composition and a cured coating that are excellent in the viscosity and fluidity of the printing ink composition, as well as in chemical properties such as the film strength and adhesion of the cured coating, and in printability. In this specification, "radical polymerizable oligomer resin and / or inert resin (E)" may be referred to as "component (E)".

[0184] In this specification, the radically polymerizable oligomer resin in component (E) refers to a resin that can be polymerized by radicals and has a molecular weight of 10,000 or less. The radically polymerizable oligomer is an oligomer resin obtained by reacting a linear polymer having a reactive substituent with a (meth)acrylic compound having a reactive substituent to introduce a photocrosslinkable group such as a (meth)acryloyl group and a photopolymerizable group into the linear polymer. Examples of reactive substituents in linear polymers having reactive substituents include functional groups such as hydroxyl groups, carboxyl groups, and amino groups, as well as structures derived from acid anhydrides. Examples of reactive substituents in (meth)acrylic compounds having reactive substituents include hydroxyl groups, isocyanate groups, aldehyde groups, and epoxy groups. For example, radically polymerizable oligomer resins include half-esterified compounds obtained by reacting (a) a linear polymer containing a structure derived from an acid anhydride, such as a styrene-maleic anhydride copolymer and an α-olefin-maleic anhydride copolymer, with (b) a (meth)acrylic compound having a hydroxyl group, such as a hydroxyalkyl (meth)acrylate. The radically polymerizable oligomer resin is not particularly limited, but from the viewpoints of (a) the physical and chemical properties of the cured film (ink film) and (b) the printability of the printing ink composition itself (e.g., ease of application or spraying, viscosity), it is preferable for the radically polymerizable oligomer resin to contain at least one selected from the group consisting of alkyd acrylates, urethane-modified acrylates, polyester acrylates, and epoxy acrylates, and it is more preferable for the resin to consist solely of at least one selected from this group.

[0185] In this specification, the inert resin in component (E) refers to a solid resin that is not reactive itself. The inert resin is not particularly limited, but from the viewpoints of (a) the physical and chemical properties of the cured film (ink film) and (b) the printability of the printing ink composition itself (e.g., ease of application, viscosity), it is preferable that the inert resin contains, for example, (i) one or more resins selected from the group consisting of diallyl phthalate resin, acrylic resin, urethane resin, epoxy resin, phenolic resin, cellulose ester resin, and polyester resin, and more preferably is composed of only one or more resins selected from this group, and (ii) it is more preferable that the inert resin contains at least one of diallyl phthalate resin and acrylic resin, and even more preferably is composed of at least one of diallyl phthalate resin and acrylic resin.

[0186]

[0023] The total content of the radical-polymerizable oligomer resin and the inert resin in the printing ink composition is preferably 0.5 wt% to 50.0 wt%, more preferably 1.0 wt% to 30.0 wt%, even more preferably 1.0 wt% to 20.0 wt%, and particularly preferably 1.0 wt% to 10.0 wt%, based on 100 wt% of the printing ink composition. This configuration has the advantages of (a) excellent physical and chemical properties of the cured film (ink film), and (b) excellent printability of the printing ink composition itself (ease of application, viscosity, etc.).

[0187] (2-4. Low Molecular Weight Compound (C)) In one embodiment of the present invention, the printing ink composition preferably contains a low molecular weight compound (C). In this specification, the "low molecular weight compound (C)" may be referred to as the "component (C)".

[0188] In one embodiment of the present invention, the low molecular weight compound (C) has at least one polymerizable unsaturated bond in its molecule. Because of this structure, the low molecular weight compound (C) itself can be cured when the printing ink composition is cured. Furthermore, when a radically polymerizable oligomer resin is included as component (E), a curing reaction can also occur between component (C) and the radically polymerizable oligomer resin of component (E) when the printing ink composition is cured. Therefore, the low molecular weight compound (C) can also function as a polymerizable monomer that crosslinks the cured coating.

[0189] The low molecular weight compound (C) preferably has at least one polymerizable unsaturated bond in the molecule, more preferably has two polymerizable unsaturated bonds in the molecule, further preferably has three polymerizable unsaturated bonds in the molecule, and particularly preferably has six polymerizable unsaturated bonds in the molecule. This configuration has the advantage of increasing the curing rate.

[0190] In one embodiment of the present invention, the low molecular weight compound (C) has a molecular weight of less than 1,000. Because of this configuration, the low molecular weight compound (C) can function as a reactive diluent in the printing ink composition. For example, the low molecular weight compound (C) can function as a diluent (solvent) for adjusting the viscosity of the printing ink composition to an appropriate level (reducing the viscosity to an appropriate level). In other words, the inclusion of the low molecular weight compound (C) in the printing ink composition provides the advantage of excellent handleability.

[0191] The molecular weight of the low molecular weight compound (C) is preferably less than 1,000, more preferably less than 900, even more preferably less than 800, and particularly preferably less than 700. This configuration has the advantage of making it easier to adjust the viscosity of the printing ink composition.

[0192] In applications requiring high curing speed and high cured film hardness, it is preferable to use a low molecular weight compound (C) having at least three polymerizable unsaturated bonds per molecule as a reactive diluent. However, in the past, when a large amount of a low molecular weight compound (C) having at least three polymerizable unsaturated bonds per molecule (e.g., 10 parts by weight or more per 100% by weight of the printing ink composition) was used, the shrinkage of the cured film accompanying the curing of the printing ink composition became significant, and the residual stress generated in the cured film tended to deteriorate the adhesion of the cured film. However, by including the above-mentioned polymer microparticles (A), the present printing ink composition can reduce the residual stress in the cured film even when it contains a large amount of a low molecular weight compound (C) having at least three polymerizable unsaturated bonds per molecule. Therefore, the present printing ink composition has the advantages of excellent curing speed, high cured film hardness, and excellent adhesion to the substrate.

[0193] In one embodiment of the present invention, the low molecular weight compound (C) preferably contains 5% by weight or more, more preferably 10% by weight or more, still more preferably 15% by weight or more, and particularly preferably 20% by weight or more of a low molecular weight compound having at least three polymerizable unsaturated bonds per molecule, based on 100% by weight of the low molecular weight compound (C). This configuration has the advantage of increasing the curing rate.

[0194] Specific examples of the low molecular weight compound (C) include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethoxylated 1,6-hexanediol diacrylate, neopentyl glycol di(meth)acrylate, polypropylene glycol diacrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanediol diacrylate, tetraethylene glycol diacrylate, 2-n-butyl-2- Ethyl-1,3-propanediol diacrylate, dimethylol tricyclodecane diacrylate, neopentyl glycol hydroxypivalate diacrylate, 1,3-butylene glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, propoxylated bisphenol A di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, dimethyloldicyclopentane diacrylate, trimethylolpropane triacrylate, trimethylolpropane hydroxypivalate triacrylate Ethoxylated phosphate triacrylate, ethoxylated tripropylene glycol diacrylate, neopentyl glycol modified trimethylolpropane diacrylate, stearic acid modified pentaerythritol diacrylate, pentaerythritol triacrylate, tetramethylolpropane triacrylate, tetramethylolmethane triacrylate, pentaerythritol tetraacrylate, caprolactone modified trimethylolpropane triacrylate, ethoxylated isocyanuric acid triacrylate, tri(2-hydroxyethyl) Socyanurate) triacrylate, propoxylated glyceryl triacrylate, tetramethylolmethane tetraacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, neopentyl glycol oligoacrylate, 1,4-butanediol oligoacrylate, 1,6-Hexanediol oligoacrylate, trimethylolpropane oligoacrylate, pentaerythritol oligoacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, isobutyl acrylate, t-butyl acrylate, isooctyl acrylate, cyclohexyl acrylate, 2-methoxyethyl acrylate, methoxytriethylene glycol acrylate, 2-ethoxyethyl acrylate, tetrahydrofurfuryl acrylate, 3-methoxybutyl acrylate, benzyl acrylate, ethoxyethoxyethyl acrylate, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydipropylene glycol acrylate, methylphenoxyethyl acrylate, dipropylene glycol acrylate, β-carboxyethyl acrylate, ethyl diglycol acrylate Acrylate, trimethylolpropane formal monoacrylate, 4-t-butylcyclohexyl acrylate, tri(meth)allyl isocyanurate, imide acrylate, isoamyl acrylate, ethoxylated succinic acid acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, tribromophenyl acrylate, ethoxylated tribromophenyl acrylate, trifluoroethyl acrylate, ω-carboxypolycaprolactone monoacrylate, acryloylmorpholine, ethoxylated neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, phenoxydiethylene glycol acrylate, vinylpyrrolidone, N-vinylformamide, 1,4-cyclohexanedimethanol monoacrylate, etc. Component (C) is not limited to these. These compounds may be used alone, or two or more may be used in combination as needed. It is particularly preferable that component (C) contains one or more compounds selected from the group consisting of low molecular weight compounds having at least three or more polymerizable unsaturated bonds in one molecule, or be composed solely of one or more compounds selected from this group. This configuration has the advantage of increasing the curing speed.

[0195] The content of the low molecular weight compound (C) is not particularly limited, but is preferably 5 wt % to 90 wt %, more preferably 7 wt % to 80 wt %, more preferably 10 wt % to 70 wt %, more preferably 15 wt % to 60 wt %, even more preferably 15 wt % to 50 wt %, and particularly preferably 20 wt % to 40 wt %, relative to 100 wt % of the printing ink composition. The content of the low molecular weight compound (C) may be 30 wt % or more, or even 40 wt % or more, relative to 100 wt % of the printing ink composition. This configuration has the advantage of making it easier to adjust the viscosity of the printing ink composition.

[0196] (2-5. Pigment (D)) In one embodiment of the present invention, the printing ink composition contains a pigment (D). This configuration has the advantage of being able to impart color to the printing ink composition. In this specification, "pigment (D)" may be referred to as "component (D)".

[0197] The pigment (D) used in one embodiment of the present invention is not particularly limited, and any known pigment can be used. For example, pigments described in "Pigment Dictionary" edited by Seijiro Ito (published in 2000), "Industrial Organic Pigments" by W. Herbst and K. Hunger, and JP-A Nos. 2002-12607, 2002-188025, 2003-26978, and 2003-342503 can be used.

[0198] The content of the pigment (D) in the printing ink composition is 1 wt % or more, preferably 2 wt % or more, more preferably 3 wt % or more, and even more preferably 5 wt % or more, relative to 100 wt % of the printing ink composition. This configuration has the advantage that the cured coating obtained by curing the printing ink composition has excellent color development properties.

[0199] (2-6. Photopolymerization initiator (F)) In one embodiment of the present invention, the printing ink composition preferably contains a photopolymerization initiator (F). This configuration has the advantage that the printing ink composition can be cured by exposure to light. In this specification, the "photopolymerization initiator (F)" may be referred to as the "component (F)".

[0200] The photopolymerization initiator (F) used in one embodiment of the present invention is not particularly limited, and known photopolymerization initiators can be used. For example, Bruce M. Monroe et al., Chemical Review, 93, 435 (1993). R. S. Davidson, Journal of Photochemistry and Biology A: Chemistry, 73.81 (1993). J. P. Faussier, "Photoinitiated Polymerization - Theory and Applications": Rapra Review vol. 9, Report, Rapra Technology (1998). and M. Tsunooka et al., Prog. Polym. Sci., 21, 1 (1996). It is also possible to use compounds used in chemically amplified photoresists and photocationic polymerization, as described in Organic Electronics Materials Research Group, "Organic Materials for Imaging," Bunshin Publishing (1993), pp. 187-192. Furthermore, it is also possible to use compounds described in F. D. Saeva, Topics in Current Chemistry, 156, 59 (1990). G. G. Maslak, Topics in Current Chemistry, 168, 1 (1993). H. Photopolymerization initiators described in B. Shuster et al., JACS, 112, 6329 (1990) and I. D. F. Eaton et al., JACS, 102, 3298 (1980) can be used. From the viewpoint of curability, the photopolymerization initiator (F) preferably contains one or more selected from the group consisting of alkylacetophenone-based polymerization initiators, alkylphenyl ketone-based polymerization initiators, benzoin alkyl ether-based polymerization initiators, benzophenone-based polymerization initiators, thioxanthone-based polymerization initiators, and anthraquinone-based polymerization initiators, or is preferably composed of only one or more selected from the group.

[0201] The content of the photopolymerization initiator (F) in the printing ink composition is preferably 0.1 to 30.0% by weight, more preferably 0.5 to 20.0% by weight, and even more preferably 1.0 to 20.0% by weight, relative to 100% by weight of the printing ink composition. This configuration has the advantage of good curability.

[0202] The content of the photopolymerization initiator (F) in the printing ink composition is preferably 0.1 wt % or more, more preferably 0.5 wt % or more, more preferably 1.0 wt % or more, even more preferably 1.5 wt % or more, still more preferably 2.0 wt % or more, and particularly preferably 2.5 wt % or more, relative to 100 wt % of the printing ink composition. This configuration has the advantage that the curable composition has excellent both curability and adhesion.

[0203]

[0023] In the printing ink composition, the content of the low molecular weight compound (C) having at least three polymerizable unsaturated bonds in one molecule is preferably 2 wt% or more, more preferably 5 wt% or more, even more preferably 7.5 wt% or more, and particularly preferably 10 wt% or more, relative to 100 wt% of the printing ink composition. This configuration has the advantage that the curable composition has excellent both curability and adhesion.

[0204] (2-7. Additives) The printing ink composition may contain other optional components in addition to the components described above, as necessary. Examples of other optional components include a photopolymerization inhibitor, wax, leveling agent, photoinitiator assistant, sensitizer, active energy ray curing catalyst, filler, matting agent, defoaming agent, dispersant, surface conditioner, antistatic agent, antioxidant, conductive agent, silicon, flame retardant, plasticizer, thermal conductivity improver, silane coupling agent, etc.

[0205] Note that, as components other than the polymer microparticles (A) and the resin (B), commercially available products may be used. Examples of such commercially available products include offset UV ink (FD LPC PR i CM, manufactured by Toyo Ink Co., Ltd.) and inkjet UV ink (LH-100, manufactured by Mimaki Engineering Co., Ltd.). This configuration has the advantage of producing high-quality printed matter.

[0206] (2-8. Method for producing printing ink composition) The printing ink composition can be produced by mixing the above-mentioned components. For example, (a) a method for producing a printing ink composition by mixing a powder containing polymer microparticles (A) and optionally a resin (B) with components other than the polymer microparticles (A) and the resin (B) (or commercially available products containing each component) (Method 1), or (b) a method for producing a printing ink composition by mixing a dispersion in which polymer microparticles (A) are dispersed in component (C) and a resin, etc. (also referred to as a masterbatch), with components other than the above (and optionally further component (C)) (or commercially available products containing each component) (Method 2).

[0207] A method for producing a UV-curable printing ink composition according to one embodiment of the present invention may be configured as follows: the method comprises the steps of preparing a powder containing polymer fine particles (A); and mixing the powder with a pigment (D) to prepare a UV-curable printing ink composition, wherein the polymer fine particles (A) comprise a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers, the graft moiety comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0208] Furthermore, a method for producing a UV-curable printing ink composition according to another embodiment of the present invention may be configured as follows: the method comprises the steps of preparing a dispersion containing polymer fine particles (A); and mixing the dispersion with a pigment (D) to prepare a UV-curable printing ink composition, wherein the polymer fine particles (A) comprise a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers, the graft moiety comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0209] The printing ink composition may be produced by either method 1 or method 2. Method 1 is preferred from the viewpoint of not restricting the formulation.

[0210]

[0023] When Method 1 is adopted, a UV-curable print ink composition according to one embodiment of the present invention may be in the following form: a UV-curable print ink composition comprising a print ink composition comprising powder particles of polymer fine particles (A) dispersed therein, and comprising a pigment (D), the polymer fine particles (A) comprising a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers, the graft moiety comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable print ink composition is 1 wt % or more, relative to 100 wt % of the UV-curable print ink composition.

[0211] (2-8-1. Method 1) (Granular Powder) In this specification, the term "granular powder" includes both powder and granules, and refers to an aggregate of powder, granules, etc. Furthermore, when specifically distinguishing between the two, "powder" refers to a volume average particle diameter of 0.01 mm to 0.1 mm, and "granules" refers to a volume average particle diameter of 0.1 mm to 10 mm. However, the granular powder may contain coarse particles of 10 mm or more. Furthermore, a "volume average particle diameter" in the range of less than 10 μm can be measured using a dynamic light scattering (DLS) particle size distribution analyzer Nanotrac Wave II-EX150 (manufactured by Microtrack Bell Co., Ltd.), and a "volume average particle diameter" in the range of 10 μm or more can be measured using a laser diffraction particle size distribution analyzer Microtrac MT3000 II (manufactured by Microtrack Bell Co., Ltd.).

[0212] (Method for Producing Powder and Granules) A ​​method for producing powder and granules according to one embodiment of the present invention, in other words, a process for preparing powder and granules containing polymer microparticles (A), includes an aggregation process for preparing aggregates containing polymer microparticles (A) and a drying process for flash-drying or freeze-drying the aggregates. The polymer microparticles (A) include a rubber-containing graft copolymer having an elastomer and a graft moiety grafted to the elastomer. The elastomer preferably includes one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers. The graft moiety preferably includes a polymer containing, as a structural unit, a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers. The "method for producing powder and granules according to one embodiment of the present invention" may also be referred to as the "present manufacturing method."

[0213] The present production method has the above-described configuration, and therefore has the advantage of being able to provide a powder or granule that exhibits excellent dispersibility of the polymer microparticles (A) in a printing ink composition. In other words, the present production method has the above-described configuration, and therefore has the advantage of being able to provide a powder or granule that can provide a printing ink composition in which the polymer microparticles (A) are uniformly dispersed.

[0214] Each step of the production method will be described in detail below, but matters other than those described below (e.g., various components and their amounts added) are not particularly limited. As mentioned above, the powder or granule preferably further contains a resin (B). An example of a method for producing a powder or granule containing a resin (B) will be described in detail below.

[0215] (Aggregation Step) The aggregation step is not particularly limited as long as aggregates containing the polymer fine particles (A) and the resin (B) can be finally obtained, in other words, as long as the finally obtained aggregates contain the polymer fine particles (A) and the resin (B).

[0216] The aggregation step may include, for example, the following steps in order: a preparation step (a1) of preparing an aqueous latex containing polymer fine particles (A) and a resin (B); and an aggregation step (a2) of aggregating both the polymer fine particles (A) and the resin (B) in the obtained aqueous latex.

[0217] The preparation step (a1) is not particularly limited as long as it can produce an aqueous latex containing polymer microparticles (A) and resin (B). Examples of methods for producing an aqueous latex containing polymer microparticles (A) and resin (B) include (i) a method of adding resin (B) to a reaction solution during the polymerization step of polymer microparticles (A), (ii) a method of adding resin (B) to an aqueous latex of polymer microparticles (A), and (iii) a method of polymerizing resin (B) in an aqueous latex of polymer microparticles (A).

[0218] The method of adding resin (B) to the reaction solution or aqueous latex of polymer microparticles (A) during the polymerization process of polymer microparticles (A) is not particularly limited. For example, (i) a method of directly adding resin (B) to the reaction solution or the aqueous latex, (ii) a method of separately preparing an aqueous latex containing resin (B) and then adding the aqueous latex containing resin (B), and (iii) a method of separately preparing a solution containing resin (B) and then adding the solution containing resin (B), etc. are included. As a method of adding resin (B), a method of separately preparing an aqueous latex containing resin (B) to the reaction solution or the aqueous latex and then adding the aqueous latex containing resin (B) is preferred.

[0219] In the case where the aggregation step (a2) is an embodiment in which a coagulant is used, the timing of adding the resin (B) to the aqueous latex of the polymer microparticles (A) may be before or after adding the coagulant, or the resin (B) may be added to the polymer microparticles (A) together with the coagulant.

[0220] A preferred method for obtaining an aqueous latex containing polymer fine particles (A) and resin (B) is to add resin (B) in the form of an aqueous latex to an aqueous latex of polymer fine particles (A).

[0221] The aggregation step (a2) is not particularly limited as long as it can obtain aggregates containing polymer microparticles (A) and resin (B). The method for aggregating the polymer microparticles (A) and resin (B) in the aqueous latex is not particularly limited. Examples of such methods include known methods such as a method using a coagulant, a method using a solvent, and a method of spraying an aqueous latex. Here, the mixture containing the aggregates containing polymer microparticles (A) and resin (B) and the aqueous solvent obtained by aggregating the polymer microparticles (A) and resin (B) in the aqueous latex is also referred to as a slurry.

[0222] In order to improve the blocking resistance and to improve the dispersibility of the polymer fine particles (A) in the printing ink composition, it is preferable that the aggregation of the polymer fine particles (A) and the resin (B) in the aqueous latex is carried out in the presence of an anti-blocking agent.

[0223] The aggregating step (a2) preferably employs a method using a coagulant, in other words, it is preferable to use a coagulant in the aggregating step of the present production method.

[0224] The coagulant is not particularly limited as long as it has the property of being able to aggregate (also referred to as coagulation or solidification) the polymer fine particles (A) and the resin (B) in the aqueous latex by contacting the aqueous latex containing the polymer fine particles (A) and the resin (B). Examples of the coagulant include an aqueous solution of an inorganic salt, an aqueous solution of an inorganic acid, an aqueous solution of an organic salt, an aqueous solution of an organic acid, and a polymer coagulant.

[0225] Examples of inorganic salts include chloride salts, bromide salts, iodide salts, sulfate salts, nitrate salts, ammonium salts, and phosphate salts. Specific examples of inorganic salts include sodium chloride, potassium chloride, lithium chloride, sodium bromide, potassium bromide, lithium bromide, potassium iodide, sodium iodide, potassium sulfate, sodium sulfate, ammonium sulfate, ammonium chloride, sodium nitrate, potassium nitrate, calcium chloride, ferrous sulfate, magnesium sulfate, zinc sulfate, copper sulfate, barium chloride, ferrous chloride, ferric chloride, magnesium chloride, ferric sulfate, aluminum sulfate, potassium alum, and iron alum.

[0226] Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0227] Examples of organic salts include acetates, citrates, formates, gluconates, lactates, oxalates, tartrates, etc. of alkali metals or alkaline earth metals. Specific examples of organic acid salts include sodium acetate, calcium acetate, sodium formate, calcium formate, etc.

[0228] Examples of organic acids include acetic acid and formic acid.

[0229] The polymeric coagulant is not particularly limited as long as it is a polymeric compound having a hydrophilic group and a hydrophobic group, and may be any of anionic, cationic, or nonionic polymeric coagulants. Cationic polymeric coagulants are preferred because they can further enhance the effects of one embodiment of the present invention. Cationic polymeric coagulants may be polymeric coagulants having cationic groups in the molecule, i.e., polymeric coagulants that exhibit cationic properties when dissolved in water. Examples of cationic polymeric coagulants include polyamines, polydicyandiamides, cationic starch, cationic poly(meth)acrylamides, water-soluble aniline resins, polythioureas, polyethyleneimines, quaternary ammonium salts, polyvinylpyridines, and chitosan.

[0230] As the coagulant, only one of the above-mentioned compounds may be used, or two or more of them may be used in combination. Among the above-mentioned compounds, aqueous solutions of monovalent or divalent inorganic salts or inorganic acids such as sodium chloride, potassium chloride, sodium sulfate, ammonium chloride, calcium chloride, magnesium chloride, magnesium sulfate, barium chloride, hydrochloric acid, and sulfuric acid are preferably used as the coagulant. There are no particular limitations on the method of adding the coagulant, and it can be added all at once, in portions, or continuously.

[0231] The polymer microparticles (A) and the resin (B) can be aggregated by contacting an aqueous latex containing the polymer microparticles (A) and the resin (B) with a coagulant or a solution of the coagulant (e.g., an aqueous solution). The method for contacting the aqueous latex containing the polymer microparticles (A) and the resin (B) with the coagulant or the solution of the coagulant is not particularly limited. Examples of such methods include (i) a method in which the aqueous latex containing the polymer microparticles (A) and the resin (B) is contacted with a coagulant or a solution of the coagulant (hereinafter referred to as aggregation method 1), and (ii) a method in which droplets containing the polymer microparticles (A) and the resin (B) obtained by spraying the aqueous latex containing the polymer microparticles (A) and the resin (B) are contacted with a coagulant or a solution of the coagulant (hereinafter referred to as aggregation method 2).

[0232] Aggregation method 1 is a method using an aqueous latex containing polymer fine particles (A) and resin (B) as a liquid phase, in other words, a method in which the aqueous latex containing polymer fine particles (A) and resin (B) is not sprayed. In this specification, aggregation method 1 is also referred to as "liquid phase coagulation."

[0233] Aggregation method 1 will be specifically described. Specific examples of aggregation method 1 include (1-i) a method of adding a coagulant to an aqueous latex containing polymer microparticles (A) and a resin (B), (1-ii) a method of mixing an aqueous latex containing polymer microparticles (A) and a resin (B) with a coagulant solution, and (1-iii) a method of spraying a coagulant or a coagulant solution into an aqueous latex containing polymer microparticles (A) and a resin (B). The method (1-iii) can also be said to be a method of spraying a coagulant or a coagulant solution in the presence of polymer microparticles (A) and a resin (B). Aggregation method 1 produces an aqueous latex containing polymer microparticles (A), a resin (B), and a coagulant.

[0234] Aggregation method 1 may further include a step of heating the obtained aqueous latex (aqueous latex containing polymer microparticles (A), resin (B), and a coagulant). The step of heating the aqueous latex containing polymer microparticles (A), resin (B), and a coagulant has the advantage of being able to lower the water content of the obtained aggregates and / or being able to reduce the amount of fine powder in the obtained granular product. The temperature (heating temperature) of the aqueous latex obtained by heating the aqueous latex containing polymer microparticles (A), resin (B), and a coagulant in the heating step is not particularly limited.

[0235] Aggregation method 2 is a method of spraying an aqueous latex containing polymer fine particles (A) and resin (B), in other words, a method of using an aqueous latex containing polymer fine particles (A) and resin (B) in the form of droplets. In this specification, aggregation method 2 is also referred to as "vapor phase coagulation."

[0236] Aggregation method 2 will be specifically described. Specific examples of aggregation method 2 include (2-i) a method of spraying an aqueous latex containing polymer fine particles (A) and resin (B) into a coagulant or a solution of the coagulant, and (2-ii) a method of spraying an aqueous latex containing polymer fine particles (A) and resin (B) and also spraying a coagulant or a solution of the coagulant. The method (2-i) can also be said to be a method including a polymer fine particle spraying step of spraying an aqueous latex containing polymer fine particles (A) and resin (B) in the presence of a coagulant.

[0237] The method (2-ii) will be specifically described. The method (2-ii) can include the following aspects: (2-ii-a) a method of contacting droplets containing polymer microparticles (A) and / or resin (B) obtained by spraying with droplets containing a coagulant obtained by spraying; (2-ii-b) a method of spraying an aqueous latex containing polymer microparticles (A) and resin (B) into a region (space) where droplets containing the coagulant obtained by spraying are present; and (2-ii-c) a method of spraying a coagulant solution into a region (space) where droplets containing polymer microparticles (A) and / or resin (B) obtained by spraying are present. Here, the region (space) where droplets containing the coagulant are present can also be referred to as being in the presence of the coagulant. Furthermore, the region (space) where droplets containing polymer microparticles (A) and / or resin (B) are present can also be referred to as being in the presence of polymer microparticles (A) and resin (B). Therefore, the method (2-ii) can also be said to be a method comprising a polymer fine particle spraying step of spraying an aqueous latex containing polymer fine particles (A) and resin (B) in the presence of a coagulant, and a coagulant spraying step of spraying a coagulant or a solution containing a coagulant in the presence of polymer fine particles (A) and resin (B).

[0238] The agglomeration step in this production method is preferably carried out by agglomeration method 2, i.e., "gas-phase coagulation." In other words, the agglomeration step in this production method preferably further includes a polymer microparticle spraying step in which an aqueous latex containing polymer microparticles (A) and resin (B) is sprayed in the presence of a coagulant. This configuration has the advantage of being able to produce powder or granules in which the proportion of granules with a volume average particle diameter of 1000 μm or more or granules with a volume average particle diameter of 600 μm or more is low relative to the total amount of powder or granules. In addition to the polymer microparticle spraying step, the agglomeration step in this production method more preferably further includes a coagulant spraying step in which a coagulant or a solution containing a coagulant is sprayed in the presence of polymer microparticles (A) and resin (B). This configuration has the advantage of being able to produce powder or granules in which the proportion of granules with a volume average particle diameter of 1000 μm or more or granules with a volume average particle diameter of 600 μm or more is low relative to the total amount of powder or granules.

[0239] The above-described preparation step (a1) and aggregation step (a2) can produce a slurry containing aggregates comprising the polymer fine particles (A) and the resin (B). The aggregation step may further include a recovery step (a3) ​​of recovering the obtained aggregates, i.e., the aggregates comprising the polymer fine particles (A) and the resin (B), from the slurry.

[0240] The recovery step (a3) ​​is not particularly limited as long as it can separate the aqueous solvent of the slurry from the aggregates, and any known method can be used. Examples of the recovery step (a3) ​​include a method of filtering the slurry and a method of centrifugal dehydration of the slurry.

[0241] Another embodiment of the aggregation step includes, for example, a step including the following steps in order: an aggregation step (b1) of aggregating polymer microparticles (A) in an aqueous latex containing only polymer microparticles (A); a recovery step (b2) of recovering the resulting aggregates of polymer microparticles (A); and a mixing step (b3) of mixing the recovered aggregates of polymer microparticles (A) with a resin (B).

[0242] The aggregation step (b1) may be the same as the aggregation step (a2) described above, including a preferred embodiment, except that an aqueous latex containing only polymer fine particles (A) is used instead of the aqueous latex containing polymer fine particles (A) and resin (B).

[0243] The recovery step (b2) may be the same as the recovery step (a3) ​​described above, including preferred embodiments, except that the aggregates contain only polymer fine particles (A) rather than polymer fine particles (A) and resin (B).

[0244] In the mixing step (b3), the method for mixing the recovered aggregates of polymer fine particles (A) with the resin (B) is not particularly limited, and examples of the method include mechanical mixing methods using a planetary mixer, a planetary mixer, a disperser, etc.

[0245] (Moisture Content of Aggregates) The aggregates containing the polymer microparticles (A) and the resin (B) obtained in the aggregation step may contain moisture. The moisture content of the aggregates is preferably 10% to 70%, more preferably 20% to 60%, more preferably 30% to 60%, even more preferably 30% to 50%, and particularly preferably 30% to 40%, relative to the total weight (100% by weight) of the aggregates. The moisture content of the aggregates can be measured by drying the obtained aggregates in an oven at 120°C for 1 hour and comparing the weights before and after drying.

[0246] (Drying Step) The drying step is a step of drying the aggregates containing the polymer fine particles (A) and the resin (B) obtained in the above-mentioned aggregation step. In this production method, the drying step involves air drying or freeze-drying the aggregates.

[0247] In this specification, flash drying refers to drying aggregates while they are airborne in a certain space. The method of flash drying is not particularly limited, and any conventionally known method can be used. One example of flash drying is a method in which aggregates are placed in a container and gas at a predetermined temperature is fed into the container, thereby drying the aggregates while they are airborne in the container.

[0248] The atmospheric temperature when the drying step is carried out is not particularly limited. Since a printing ink composition in which the resulting powder or granule has superior dispersibility to the polymer microparticles (A) can be provided, the drying step is preferably carried out at 100°C or less, more preferably at 90°C or less, more preferably at 80°C or less, more preferably at 70°C or less, more preferably at 60°C or less, more preferably at 50°C or less, more preferably at 40°C or less, more preferably at 30°C or less, more preferably at 20°C or less, even more preferably at 10°C or less, and particularly preferably at 0°C or less.

[0249] In flash drying, the ambient temperature during the drying step can be adjusted by changing the temperature inside the container containing the aggregates and / or the temperature of the gas sent into the container.

[0250] In flash drying, the gas to be fed into the container is not particularly limited, and examples of the gas include air, nitrogen, a mixture of nitrogen and air, a mixture of nitrogen and oxygen, and rare gases.

[0251] The freeze-drying method is not particularly limited, and any conventionally known method can be used. When freeze-drying is used as the drying step, the drying step can be easily carried out at 0°C or below.

[0252] The time for the drying step is not particularly limited and can be set appropriately depending on the degree of drying of the aggregate. The drying time can be, for example, 1 minute to 3 hours, but is preferably 1 minute to 1 hour, more preferably 1 minute to 30 minutes, even more preferably 1 minute to 20 minutes, and particularly preferably 1 minute to 10 minutes. The drying step may be carried out, for example, until the temperature of the aggregate (powder / granule) reaches 40°C.

[0253] In this specification, the mode of drying by leaving an aggregate containing polymer fine particles (A) and resin (B) stationary in a container such as an oven, as in the conventional technology, is also referred to as "stationary drying".

[0254] (Washing Step) The present production method preferably further includes a step of washing the aggregates obtained in the agglomeration step between the agglomeration step and the drying step. By washing the aggregates, powder or granules with a low content of impurities and the like can be obtained. In the washing step, the aggregates are more preferably washed with water, and even more preferably washed with ion-exchanged water or pure water.

[0255] The washing step may be any step for washing the aggregates, and the specific method is not particularly limited. Specific methods for the washing step include, for example, a method of mixing the aggregates with water and stirring them with a stirrer, a method of kneading the aggregates with water using a kneader, a method of mixing the aggregates with water using a planetary mixer, a method of spraying water onto the aggregates, and a method of washing the cake with a pressure filter. Various kneaders can be used, such as a batch kneader, a continuous kneader, an extrusion kneader, and an extruder.

[0256] The washing time is not particularly limited and can be, for example, 1 second to 60 minutes. The washing time is preferably 1 second to 45 minutes, more preferably 1 second to 30 minutes, still more preferably 1 minute to 30 minutes, even more preferably 3 minutes to 30 minutes, particularly preferably 5 minutes to 30 minutes, and particularly preferably 10 minutes to 30 minutes.

[0257] The number of washing cycles is not particularly limited and may be, for example, 1 to 10. The number of washing cycles is preferably 1 to 6, more preferably 1 to 5, even more preferably 1 to 4, and most preferably 1 to 3.

[0258] The amount of washing water is not particularly limited, and can be, for example, 0.1 to 1000 parts by weight relative to 1 part by weight of the aggregate. The amount of washing water is preferably 1 to 1000 parts by weight relative to 1 part by weight of the aggregate, more preferably 1 to 500 parts by weight, more preferably 1 to 200 parts by weight, more preferably 10 to 200 parts by weight, even more preferably 15 to 200 parts by weight, and particularly preferably 20 to 200 parts by weight. The amount of washing water is also preferably 1 to 10 parts by weight relative to 1 part by weight of the aggregate, also preferably 2 to 10 parts by weight, and also preferably 2 to 5 parts by weight. Furthermore, washing by kneading the aggregate with water using a kneader is more preferred, as this allows for less washing water to be used.

[0259] The temperature of the cleaning water is not limited, and for example, room temperature or heated water can be used as appropriate. Since warm water has a higher cleaning effect, it is preferable to use heated cleaning water. The temperature of the cleaning water can be, for example, 10°C to 100°C, preferably 15°C to 100°C, more preferably 20°C to 100°C, more preferably 40°C to 100°C, more preferably 40°C to 90°C, even more preferably 40°C to 85°C, even more preferably 40°C to 80°C, and particularly preferably 40°C to 70°C.

[0260] In the washing step, the method for removing the washing water is not limited, and examples thereof include methods such as draining the washing water, vacuum filtration, oil-water separation, filter press, centrifugation, belt press, screw press, membrane separation, and squeeze dehydration.

[0261] The objects to be washed include all impurities contained in the aggregates, and are not particularly limited. Examples include impurities derived from emulsifiers (e.g., phosphorus-based emulsifiers, sulfonic acid-based emulsifiers), and, when a coagulant is used, impurities derived from the coagulant.

[0262] (Temperature) It is preferable that the aggregates and powder particles containing polymer microparticles (A) and resin (B) are handled (manipulated) in a temperature environment below the glass transition temperature of the grafted portion of the polymer microparticles (A) throughout the production method. In other words, the shorter the time that the aggregates and powder particles containing polymer microparticles (A) and resin (B) are exposed to a temperature environment equal to or higher than the glass transition temperature of the grafted portion of the polymer microparticles (A), the better. According to this configuration, a printing ink composition can be provided in which the resulting powder particles have better dispersibility than the polymer microparticles (A) (i.e., the polymer microparticles (A) are more uniformly dispersed).

[0263] In this production method, the time (period) during which the aggregates and powder particles containing polymer microparticles (A) and resin (B) are exposed to a temperature environment equal to or higher than the glass transition temperature of the grafted portion of polymer microparticles (A) can be shortened by adjusting the following temperatures: the temperature of the aqueous latex containing polymer microparticles (A), the temperature of the aqueous latex containing polymer microparticles (A) and resin (B) (aqueous latex before addition of coagulant), the temperature of the aqueous solution of coagulant, the temperature of the aqueous latex containing polymer microparticles (A), resin (B) and coagulant, the heating temperature in the heating step, the drying temperature in the drying step, the temperature of the washing water in the washing step, etc.

[0264] The temperature below the glass transition temperature of the graft portion of the polymer microparticles (A) varies depending on the composition of the graft portion and is appropriately set depending on the composition of the graft portion. The aggregates and granules containing the polymer microparticles (A) and the resin (B) are preferably handled in an environment below 90°C, more preferably below 80°C, and even more preferably below 70°C throughout the production method. That is, the above-mentioned temperatures are preferably below 90°C, more preferably below 80°C, more preferably below 70°C, more preferably below 60°C, more preferably below 50°C, and even more preferably below 40°C.

[0265] The content of resin (B) in the powder or granule is preferably 50 to 99 wt % of the polymer microparticles (A) and 1 to 50 wt % of the resin (B), where the total of the polymer microparticles (A) and the resin (B) is 100 wt %. The content of resin (B) in the powder or granule can be appropriately set within the above-mentioned numerical range depending on the type of resin (B) and the physical properties of resin (B) (solid, semi-solid, liquid, viscosity, etc.). If resin (B) is liquid at 25°C and the content of resin (B) in the powder or granule is high, the powder or granule may not be obtained. If resin (B) is liquid at 25°C and the content of resin (B) in the powder or granule is high, the fluidity (smoothness) of the powder or granule may be deteriorated.

[0266] The content of the resin (B) in the powder or granule will be explained from the viewpoint of excellent blocking resistance. When the total of the polymer fine particles (A) and the resin (B) is 100% by weight, it is more preferable that the polymer fine particles (A) are 55 to 99% by weight and the resin (B) is 1 to 45% by weight, it is more preferable that the polymer fine particles (A) are 60 to 99% by weight and the resin (B) is 1 to 40% by weight, it is more preferable that the polymer fine particles (A) are 65 to 99% by weight and the resin (B) is 1 to 35% by weight, it is more preferable that the polymer fine particles (A) are 70 to 99% by weight and the resin (B) is 1 to 30% by weight, and it is more preferable that the polymer fine particles (A) are 70 to 99% by weight and the resin (B) is 1 to 30% by weight. It is more preferable that the polymer fine particles (A) are 75 to 99% by weight and the resin (B) is 1 to 25% by weight, it is more preferable that the polymer fine particles (A) are 80 to 99% by weight and the resin (B) is 1 to 20% by weight, it is even more preferable that the polymer fine particles (A) are 85 to 99% by weight and the resin (B) is 1 to 15% by weight, it is even more preferable that the polymer fine particles (A) are 90 to 99% by weight and the resin (B) is 1 to 10% by weight, it is particularly preferable that the polymer fine particles (A) are 95 to 99% by weight and the resin (B) is 1 to 5% by weight.

[0267] The content of the resin (B) in the powder or granule will be explained from the viewpoint of improving the dispersibility of the polymer microparticles (A) in the printing ink composition. When the total of the polymer microparticles (A) and the resin (B) is taken as 100% by weight, the polymer microparticles (A) are preferably 50 to 97% by weight and the resin (B) is 3 to 50% by weight, more preferably 50 to 95% by weight and the resin (B) is 5 to 50% by weight, still more preferably 50 to 92% by weight and the resin (B) is 8 to 50% by weight, still more preferably 50 to 90% by weight and the resin (B) is 10 to 50% by weight, and still more preferably 50 to 90% by weight and the resin (B) is 10 to 50% by weight. It is more preferable that the polymer microparticles (A) are 0 to 87% by weight and the resin (B) is 13 to 50% by weight, it is more preferable that the polymer microparticles (A) are 50 to 85% by weight and the resin (B) is 15 to 50% by weight, it is even more preferable that the polymer microparticles (A) are 50 to 82% by weight and the resin (B) is 18 to 50% by weight, it is even more preferable that the polymer microparticles (A) are 50 to 80% by weight and the resin (B) is 20 to 50% by weight, it is particularly preferable that the polymer microparticles (A) are 60 to 80% by weight and the resin (B) is 20 to 40% by weight.

[0268] In addition, when the printing ink composition is obtained by Method 1, the content of resin (B) in the printing ink composition (the content of resin (B) when the total of polymer microparticles (A) and resin (B) is 100% by weight) can be said to be the same as the content of resin (B) in the powder or granule (the content of resin (B) when the total of polymer microparticles (A) and resin (B) is 100% by weight).

[0269] (Anti-blocking Agent) When the polymer fine particles (A) are used as a powder, the powder preferably further contains an anti-blocking agent. According to this configuration, the resulting powder has (a) excellent anti-blocking properties and (b) excellent dispersibility of the polymer fine particles (A) in the printing ink composition.

[0270] The antiblocking agent is not particularly limited as long as it exhibits the effects of one embodiment of the present invention. Examples of the antiblocking agent include antiblocking agents composed of inorganic fine particles such as silicon dioxide, titanium oxide, aluminum oxide, zirconium oxide, aluminum silicate, diatomaceous earth, zeolite, kaolin, talc, calcium carbonate, calcium phosphate, barium sulfate, and magnesium hydrosilicate; antiblocking agents composed of organic fine particles; and oil-based antiblocking agents such as polyethylene wax, higher fatty acid amide, metal soap, and silicone oil. Among these, antiblocking agents composed of fine particles are preferred, and antiblocking agents composed of organic fine particles are more preferred. As the antiblocking agent composed of organic fine particles, antiblocking agents composed of organic fine particles of a polymer containing, as a constituent unit, a constituent unit derived from one or more monomers selected from aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers are particularly preferred.

[0271] Antiblocking agents consisting of fine particles are generally in the form of fine particles dispersed in a liquid or in a colloidal state. The fine particles in the antiblocking agent usually have a volume average particle diameter (Mv) of 10 μm or less, preferably 0.05 μm to 10.00 μm. The content of the antiblocking agent is preferably 0.01 wt % to 5.00 wt %, more preferably 0.50 wt % to 3.00 wt %, based on the total weight (100 wt %) of the powder or granule.

[0272] (Other Optional Components) The present powder or granule may contain other optional components in addition to the components described above, as necessary. Examples of other optional components include the various components described in the section (2-2-5. Additives) below.

[0273] The antiblocking agent and other optional components can be added as appropriate during any step in the production method of the present powder or granule. For example, the antiblocking agent and other optional components can be added to the aqueous suspension (aqueous latex) of the polymer fine particles (A) or the polymer fine particles (A) and the resin (B) before or after coagulation. The antiblocking agent and other optional components can also be added to the powder or granule containing the polymer fine particles (A), the resin (B), or the polymer fine particles (A) and the resin (B).

[0274] (2-8-2. Method 2) (Dispersion (Masterbatch)) Examples of a method for producing a dispersion, in other words, a step for preparing a dispersion containing polymer microparticles (A), include the following methods (steps) (i) and (ii): (i) (i-1) a method (step) of obtaining an aqueous latex containing polymer microparticles (A), (i-2) subsequently contacting the aqueous latex with component (C) and / or a resin (oligomer), and (i-3) subsequently removing unnecessary components such as water from the obtained mixture; and (ii) (ii-1) a method (step) of obtaining an aqueous latex containing polymer microparticles (A), (ii-2) subsequently extracting the polymer microparticles (A) in the aqueous latex with an organic solvent, (ii-2) subsequently mixing the obtained organic solvent solution of the polymer microparticles (A) with component (C) and / or a resin (oligomer), and (ii-3) subsequently removing the organic solvent from the obtained mixture. As a method for producing a polymer particle dispersion composition, it is preferable to use the method described in WO 2005 / 028546.

[0275] A preferred embodiment of the method for producing a dispersion, in other words, a step for preparing a dispersion containing polymer microparticles (A), includes, for example, the following steps in order: (i) a first step of preparing an aqueous latex containing polymer microparticles (A) (in other words, preparing polymer microparticles (A) by emulsion polymerization); (ii) a second step of mixing the aqueous latex containing polymer microparticles (A) (specifically, the reaction mixture obtained after producing polymer microparticles (A) by emulsion polymerization) with an organic solvent having a solubility in water of 5% by weight to 40% by weight at 20°C, followed by adding excess water to the resulting mixture and mixing the resulting mixture to aggregate the polymer microparticles (A); (iii) a third step of separating and recovering the aggregated polymer microparticles (A) from the mixture (liquid phase), and then mixing the recovered polymer microparticles (A) again with an organic solvent to obtain an organic solvent solution of the polymer microparticles (A); and (iv) a fourth step of further mixing the resulting organic solvent solution with component (C) and / or a resin (oligomer), followed by distilling off the organic solvent.

[0276] A method for producing a UV-curable print ink composition according to one embodiment of the present invention includes a step of mixing the powder or granules described in the (Powder or Granule) section or the dispersion described in the (2-8-2. Method 2) section with components other than the polymer microparticles (A) and the resin (B). A method for producing a print ink composition according to one embodiment of the present invention may also include a step of mixing the powder or granules obtained by the powder or granule production method described in the (Powder or Granule Production Method) section or the dispersion described in the (2-8-2. Method 2) section with components other than the polymer microparticles (A) and the resin (B). These configurations make it possible to obtain a print ink composition in which the polymer microparticles (A) are uniformly dispersed in the components other than the polymer microparticles (A) and the resin (B).

[0277] Regarding the method for producing the printing ink composition, the various components and specific steps are not particularly limited, and the above explanations are used as appropriate.

[0278] A specific method for mixing the powder or the dispersion described in Section (2-8-2. Method 2) with components other than the polymer microparticles (A) and the resin (B), in other words, a process for preparing a printing ink composition using the powder or a process for preparing a printing ink composition using the dispersion, will be described below. Examples of such a method (process) include methods using a rotation-revolution mixer, a planetary mixer, a disperser, or the like. A preferred method for mixing the powder and the components other than the polymer microparticles (A) and the resin (B) is, for example, a method using a rotation-revolution mixer at 2000 rpm for 40 minutes.

[0279] (2-4. Uses) The UV-curable printing ink composition according to one embodiment of the present invention can be suitably used as a printing ink (printing ink).

[0280] [3. Cured Coating] The cured coating according to one embodiment of the present invention is preferably obtained by curing the UV-curable printing ink composition described in [2. UV-curable Printing Ink Composition]. This configuration has the advantage that the cured coating is less likely to peel off from the substrate.

[0281] In recent years, there has been a shift toward LED lamps, which enable instantaneous lighting and energy savings, as a light source for curing UV-curable printing ink compositions to obtain cured films. However, LED lamps have lower output than UV lamps. Therefore, to enable curing using an LED lamp, the UV-curable printing ink composition must contain large amounts of a photopolymerization initiator, a polyfunctional monomer, and the like, and must have superior curability (high sensitivity). There is a trade-off between the curability and adhesion of a curable composition, and UV-curable printing ink compositions containing large amounts of a photopolymerization initiator, a polyfunctional monomer (e.g., a low-molecular-weight compound (C) having at least three polymerizable unsaturated bonds in one molecule), and the like, have the disadvantage of poor adhesion to substrates.

[0282] On the other hand, the present printing ink composition solves the above-mentioned problems and has the advantage of excellent adhesion to a substrate. In other words, the present cured coating is less likely to peel off from a substrate.

[0283] The light source used to cure the printing ink composition, i.e., the light source used to obtain a cured coating from the printing ink composition, is not particularly limited, but is preferably a high-pressure mercury lamp, a metal halide lamp, or a UV-LED lamp. It is also possible to use an EB (electron beam) lamp as the light source. When an EB (electron beam) lamp is used, the organic molecules can be decomposed by the electron beam to initiate radical polymerization, and therefore there is no need to include a photopolymerization initiator.

[0284] The method for printing the UV-curable printing ink composition onto a substrate is not particularly limited, but examples thereof include offset printing, screen printing, flexographic printing, and IJ printing.

[0285] An embodiment of the present invention may have the following configuration.

[0286] [1] A UV-curable printing ink composition comprising polymer fine particles (A) and a pigment (D), the polymer fine particles (A) comprising a rubber-containing graft copolymer having an elastomer and a graft portion graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers, the graft portion comprising a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0287] [2] The UV-curable printing ink composition according to [1], further comprising a resin (B).

[0288] [3] The UV-curable printing ink composition according to [1] or [2], further comprising a low-molecular-weight compound (C), which (i) has at least one polymerizable unsaturated bond in the molecule, and (ii) has a molecular weight of less than 1,000.

[0289] [4] The UV-curable printing ink composition according to [3], wherein the low molecular weight compound (C) contains 5% by weight or more of a low molecular weight compound having at least three polymerizable unsaturated bonds in one molecule, relative to 100% by weight of the low molecular weight compound (C).

[0290] [5] The UV-curable printing ink composition according to any one of [1] to [4], further comprising a radical-polymerizable oligomer resin and / or an inert resin (E), and the total content of the radical-polymerizable oligomer resin and the inert resin (E) in the UV-curable printing ink composition is 0.5% by weight or more, relative to 100% by weight of the UV-curable printing ink composition.

[0291] [6] The UV-curable printing ink composition according to any one of [1] to [5], further comprising a photopolymerization initiator (F), and the content of the photopolymerization initiator (F) in the UV-curable printing ink composition is 1.0 wt % or more, relative to 100 wt % of the UV-curable printing ink composition.

[0292] [7] The UV-curable printing ink composition according to any one of [1] to [6], wherein the content of the polymer fine particles (A) is 1.0% by weight or more, based on 100% by weight of the UV-curable printing ink composition.

[0293] [8] The UV-curable printing ink composition according to any one of [1] to [7], wherein the content of the polymer fine particles (A) is 10.0% by weight or less, based on 100% by weight of the UV-curable printing ink composition.

[0294] [9] The UV-curable printing ink composition according to any one of [1] to [8], wherein the elastic material is butadiene rubber.

[0295]

[10] The UV-curable printing ink composition according to any one of [1] to [9], wherein the polymer fine particles (A) have a volume average particle diameter of 0.03 μm to 50.00 μm.

[0296]

[11] The UV-curable printing ink composition according to [2], wherein the resin (B) is epoxidized soybean oil.

[0297]

[12] A cured coating obtained by curing the UV-curable printing ink composition according to any one of [1] to

[11] .

[0298]

[13] A method for producing a UV-curable printing ink composition, comprising the steps of: preparing a powder containing polymer fine particles (A); and mixing the powder with a pigment (D) to prepare a UV-curable printing ink composition, wherein the polymer fine particles (A) comprise a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers, and the graft moiety comprises a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0299]

[14] A method for producing a UV-curable printing ink composition, comprising the steps of preparing a dispersion containing polymer fine particles (A), and mixing the dispersion with a pigment (D) to prepare a UV-curable printing ink composition, wherein the polymer fine particles (A) comprise a rubber-containing graft copolymer having an elastomer and a graft moiety graft-bonded to the elastomer, the elastomer comprising one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers, and the graft moiety comprises a polymer comprising a structural unit derived from one or more monomers selected from the group consisting of aromatic vinyl monomers, vinyl cyan monomers, and (meth)acrylate monomers, and the content of the pigment (D) in the UV-curable printing ink composition is 1 wt % or more relative to 100 wt % of the UV-curable printing ink composition.

[0300] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these. One embodiment of the present invention can be practiced with appropriate modifications within the scope of the above-mentioned or below-mentioned purpose, and all such modifications are included within the technical scope of the present invention. In the following examples and comparative examples, "parts" and "%" mean parts by weight or % by weight.

[0301] <Evaluation Method> First, the evaluation methods for the printing ink compositions produced in the Examples and Comparative Examples will be described below. In the following description, unless otherwise specified, the term "polymer fine particles" includes both polymer fine particles (A) which are polymer fine particles according to one embodiment of the present invention and polymer fine particles outside the scope of the present invention.

[0302] (Method for preparing a cured coating made of a printing ink composition) The printing ink composition obtained in each of the Examples and Comparative Examples was applied to a PMMA sheet to a thickness of 30 μm. The resulting PMMA sheet was irradiated with ultraviolet light to cure the printing ink composition, thereby forming a cured coating made of the printing ink composition on the PMMA sheet.

[0303] (Method for measuring the adhesion of a cured coating made from a printing ink composition) First, a cutter was used to cut 10 vertical and 10 horizontal grid-like incisions into the cured coating formed on a PMMA sheet, each grid square measuring 1 mm vertically and 1 mm horizontally. Next, cellophane tape (manufactured by Nichiban Co., Ltd.) was applied to the cured coating so that all of the grid-like incisions were covered. Finally, the cellophane tape was peeled off the cured coating, and the number of squares on the PMMA sheet where the cured coating remained covering 80% or more of the total area of ​​each square was visually counted. The adhesion of the printing ink composition was evaluated based on the number of squares using the following criteria. The results are shown in Table 1. 2 (Good): The number of squares on the PMMA sheet where the cured coating remains on an area of ​​80% or more of the total area of ​​each square is 80 or more. 1 (Acceptable): The number of squares on the PMMA sheet where the cured coating remains on an area of ​​80% or more of the total area of ​​each square is 50 to 80. 0 (Unacceptable): The number of squares on the PMMA sheet where the cured coating remains on an area of ​​80% or more of the total area of ​​each square is 50 or less.

[0304] <1. Preparation of Elastic Body> (Production Example 1-1: Preparation of Polybutadiene Rubber Latex (R-1)) 200 parts by weight of deionized water, 0.03 parts by weight of tripotassium phosphate, 0.002 parts by weight of disodium ethylenediaminetetraacetate (EDTA), 0.001 parts by weight of ferrous sulfate heptahydrate, and 1.55 parts by weight of sodium dodecylbenzenesulfonate (SDBS) as an emulsifier were charged into a pressure-resistant polymerization vessel. Next, while stirring the charged raw materials, the gas inside the pressure-resistant polymerization vessel was replaced with nitrogen, thereby thoroughly removing oxygen from inside the pressure-resistant polymerization vessel. Thereafter, 100 parts by weight of butadiene (Bd) was charged into the pressure-resistant polymerization vessel, and the temperature inside the pressure-resistant polymerization vessel was raised to 45°C. Thereafter, 0.03 parts by weight of paramenthane hydroperoxide (PHP) was charged into the pressure-resistant polymerization reactor, followed by 0.10 parts by weight of sodium formaldehyde sulfoxylate (SFS) to initiate polymerization. Fifteen hours after the start of polymerization, the polymerization was terminated by devolatilization under reduced pressure to remove the remaining monomers that had not been used in the polymerization. During the polymerization, PHP, EDTA, and ferrous sulfate heptahydrate were each added to the pressure-resistant polymerization reactor in desired amounts and at desired times. This polymerization yielded an aqueous latex (R-1) containing an elastomer composed primarily of polybutadiene rubber. The volume average particle size of the elastomer contained in the resulting aqueous latex was 70 nm.

[0305] (Production Example 1-2: Preparation of Polybutadiene Rubber Latex (R-2)) Into a pressure-resistant polymerization vessel, 7 parts by weight (solids content) of the polybutadiene rubber latex (R-1) obtained above, 200 parts by weight of deionized water, 0.03 parts by weight of tripotassium phosphate, 0.002 parts by weight of EDTA, and 0.001 parts by weight of ferrous sulfate heptahydrate were charged. Next, while stirring the charged raw materials, the gas inside the pressure-resistant polymerization vessel was replaced with nitrogen, thereby thoroughly removing oxygen from inside the pressure-resistant polymerization vessel. Thereafter, 93 parts by weight of Bd were charged into the pressure-resistant polymerization vessel, and the temperature inside the pressure-resistant polymerization vessel was raised to 45°C. Thereafter, 0.02 parts by weight of PHP was charged into the pressure-resistant polymerization vessel, followed by 0.10 parts by weight of SFS, to initiate polymerization. 30 hours after the start of polymerization, devolatilization was carried out under reduced pressure to remove remaining monomers that had not been used in the polymerization, thereby terminating the polymerization. During the polymerization, PHP, EDTA, ferrous sulfate heptahydrate, and SDBS were each added to the pressure polymerization reactor in desired amounts and at desired times. The polymerization yielded an aqueous latex (R-2) containing an elastomer primarily composed of polybutadiene rubber. The volume average particle size of the elastomer contained in the resulting aqueous latex was 195 nm.

[0306] 2. Preparation of Polymer Microparticles (A) (Polymerization of Graft Portion) (Production Example 2-1: Preparation of Polymer Microparticle Latex (L-1)) 230 parts by weight of the polybutadiene rubber latex (R-2) (containing 80 parts by weight of an elastomer mainly composed of polybutadiene rubber) and 103 parts by weight of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The gas in the glass reactor was replaced with nitrogen, and the charged raw materials were stirred at 60°C. Next, 0.003 parts by weight of EDTA, 0.0007 parts by weight of ferrous sulfate heptahydrate, and 0.14 parts by weight of SFS were added to the glass reactor and stirred for 10 minutes. Thereafter, a mixture of 19 parts by weight of methyl methacrylate (MMA), 1 part by weight of butyl acrylate, and 0.1 parts by weight of t-butyl hydroperoxide (BHP) was continuously added to the glass reactor over 80 minutes. Then, 0.012 parts by weight of BHP was added to the glass reactor, and the mixture in the glass reactor was stirred for an additional hour to complete the polymerization. Through the above operations, an aqueous latex (L-1) containing polymer microparticles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer microparticles (A) contained in the obtained aqueous latex was 200 nm. The solids concentration (concentration of polymer microparticles (A)) in the obtained aqueous latex (L-1) was 30%.

[0307] 3. Preparation of Powder and Granules (Production Example 3-1) (i) Water, (ii) a mixture of 67 parts by weight of epoxidized soybean oil (ADEKA Corporation, Adeka Cizer O-130P) as resin (B) and 33 parts by weight of triethylene glycol bis[3-(-t-butyl-4-hydroxy-5-methylphenyl)propionate] (Irganox 245, BASF Japan Ltd.) as antioxidant, and (iii) SDBS as emulsifier were mixed together using a homogenizer to prepare an aqueous emulsion (S-1) (resin (B) content: 50%). Additionally, 4 parts by weight of calcium acetate was dissolved in 600 parts by weight of ion-exchanged water adjusted to 70°C. Next, 333 parts by weight of aqueous latex (L-1), corresponding to 100 parts by weight of polymer microparticles (A), and 22.2 parts by weight of the aqueous emulsion (S-1) (corresponding to 11.1 parts by weight of resin (B)) were added to 600 parts by weight of the ion-exchanged water to obtain a slurry containing a coagulum containing polymer microparticles (A). Next, the slurry was centrifuged to obtain a wet powder of the coagulum. Furthermore, using the obtained wet powder, a total of two cycles were repeated: adding the wet powder to 500 parts by weight of ion-exchanged water and centrifuging the resulting mixture to obtain a wet powder. Finally, the wet powder was dried in a dryer at 50°C for 48 hours to obtain a powder (P-1) containing polymer microparticles (A) and resin (B). When the total of polymer microparticles (A) and resin (B) was 100% by weight, powder (P-1) contained 90% by weight of polymer microparticles (A) and 10% by weight of resin (B).

[0308] 4. Preparation of Masterbatch (Step 1) A mixing tank (volume: 1 L) equipped with a stirrer was used as the apparatus. Methyl ethyl ketone (MEK) was used as the organic solvent partially soluble in water. After the temperature inside the mixing tank was raised to 30°C, 126 parts by weight of MEK was added to the mixing tank. Thereafter, while stirring the MEK inside the mixing tank, 143 parts by weight of the latex (L-1) of polymer microparticles (A) was added to the mixing tank. The added raw materials were uniformly mixed to obtain a mixture (mixture M) of an aqueous latex containing polymer microparticles (A) and an organic solvent partially soluble in water. Next, while stirring the mixture M, 200 parts by weight of water (469 parts by weight in total) was added to the mixing tank at a feed rate of 80 parts by weight / min, bringing the mixture M into contact with the water. After the water supply was completed, stirring was promptly stopped, and floating aggregates (aggregates of polymer microparticles (A)) were formed in the aqueous phase, and a slurry containing the aggregates was obtained.

[0309] (Second Step) Next, the aggregates were separated and recovered from the aqueous phase. Specifically, 350 parts by weight of the aqueous phase was discharged from a discharge port at the bottom of the mixing tank while leaving the aggregates in the mixing tank, thereby obtaining aggregates. 150 parts by weight of MEK was added to the obtained aggregates (polymer microparticle (A) dope) and mixed to obtain a first organic solvent dispersion containing polymer microparticles (A). The obtained first organic solvent solution was 277 parts by weight (containing 42.9 parts by weight of polymer microparticles (A)).

[0310] (Step 3) 277 parts by weight of the obtained first organic solvent dispersion (containing 42.9 parts by weight of polymer microparticles (A)) was charged with 0.1716 parts by weight of 2,6-di-t-butyl-p-cresol, and the resulting mixture was mixed. Next, 64 parts by weight of acryloylmorpholine (molecular weight 141.17), which is the low molecular weight compound (C), was charged into the resulting mixture, and the resulting mixture was mixed to obtain a second organic solvent dispersion. In the third step, when the total of the polymer microparticles (A) and the low molecular weight compound (C) is 100 wt%, the polymer microparticles (A) were 40 wt% and the low molecular weight compound (C) was 60 wt%. The polymer microparticles (A) and the low molecular weight compound (C) were mixed at a blending ratio of 60 wt%.

[0311] (Step 4) MEK was distilled off under reduced pressure from the obtained second organic solvent dispersion to obtain a masterbatch (M-1). The masterbatch (M-1) contained 40 wt % of the polymer fine particles (A) and 60 wt % of the low molecular weight compound (C), assuming that the total of the polymer fine particles (A) and the low molecular weight compound (C) was 100 wt %.

[0312] 5. Production of UV-curable printing ink composition Example 1 100% by weight of offset UV ink (FD LPC PR i CM, manufactured by Toyo Ink Co., Ltd.) was mixed with 2.0% by weight of powder (P-1) in a three-roll mill to produce a printing ink composition.

[0313] The offset UV ink contains, based on 100% by weight of the offset UV ink, 20% by weight or more of the (C) component, 1% by weight or more of a pigment as the (D) component, 1.0% by weight or more of the (E) component, and 1.0% by weight or more of the (F) component.

[0314] Example 2 A printing ink composition was prepared by mixing 100% by weight of offset UV ink (FD LPC PR i CM, manufactured by Toyo Ink Co., Ltd.) with 5.0% by weight of masterbatch (M-1) in a three-roll mill.

[0315] Example 3 A printing ink composition was prepared by mixing 100% by weight of inkjet UV ink (LH-100, manufactured by Mimaki Engineering Co., Ltd.) with 1.0% by weight of powder (P-1) in a three-roll mill.

[0316] The inkjet UV ink contains, based on 100% by weight of the inkjet UV ink, 20% by weight or more of the (C) component, 1% by weight or more of a pigment as the (D) component, 0.5% by weight or more of the (E) component, and 1.0% by weight or more of the (F) component.

[0317] Example 4 A printing ink composition was prepared by mixing 100% by weight of inkjet UV ink (LH-100, manufactured by Mimaki Engineering Co., Ltd.) with 2.0% by weight of powder (P-1) in a three-roll mill.

[0318] Comparative Example 1 Neither the polymer fine particles (A) nor the resin (B) was used, and only an offset UV ink (FD LPC PR i CM, manufactured by Toyo Ink Co., Ltd.) was used.

[0319] Comparative Example 2 Neither the polymer fine particles (A) nor the resin (B) was used, and only an inkjet UV ink (LH-100, manufactured by Mimaki Engineering Co., Ltd.) was used.

[0320] A UV-curable printing ink composition according to one embodiment of the present invention can be suitably used as a printing ink (printing ink).

Claims

1. A step of preparing a powder containing polymer fine particles (A); and mixing the powder and a pigment (D) to prepare a UV-curable printing ink composition. the polymer fine particles (A) contain a rubber-containing graft copolymer having an elastomer and a graft portion graft-bonded to the elastomer, the elastic body includes at least one rubber selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers, the graft portion includes a polymer including a structural unit derived from one or more monomers selected from the group consisting of an aromatic vinyl monomer, a vinyl cyan monomer, and a (meth)acrylate monomer; A method for producing a UV curable printing ink composition, wherein a content of the pigment (D) in the UV curable printing ink composition is 1% by weight or more relative to 100% by weight of the UV curable printing ink composition.

2. A method for producing a UV-curable printing ink composition as described in claim 1, wherein the UV-curable printing ink composition further contains a resin (B).

3. The UV-curable printing ink composition further contains a low molecular weight compound (C), The low molecular weight compound (C) is (i) having at least one polymerizable unsaturated bond in the molecule; and The method for producing a UV-curable printing ink composition according to claim 1 or 2, wherein (ii) the molecular weight is less than 1,000.

4. A method for producing a UV-curable printing ink composition as described in claim 3, wherein the low molecular weight compound (C) contains 5% by weight or more of a low molecular weight compound having at least three polymerizable unsaturated bonds in one molecule, out of 100% by weight of the low molecular weight compound (C).

5. The UV-curable printing ink composition further comprises a radical polymerizable oligomer resin and / or an inert resin (E), 3. The method for producing a UV curable printing ink composition according to claim 1, wherein a total content of the radical polymerizable oligomer resin and the inert resin (E) in the UV curable printing ink composition is 0.5% by weight or more relative to 100% by weight of the UV curable printing ink composition.

6. The UV-curable printing ink composition further contains a photopolymerization initiator (F), 3. The method for producing a UV curable printing ink composition according to claim 1, wherein a content of the photopolymerization initiator (F) in the UV curable printing ink composition is 1.0% by weight or more relative to 100% by weight of the UV curable printing ink composition.

7. A method for producing a UV-curable printing ink composition as described in claim 1 or 2, wherein the content of the polymer microparticles (A) is 1.0 weight % or more relative to 100 weight % of the UV-curable printing ink composition.

8. A method for producing a UV-curable printing ink composition as described in claim 1 or 2, wherein the content of the polymer microparticles (A) is 10.0 weight % or less relative to 100 weight % of the UV-curable printing ink composition.

9. A method for producing a UV-curable printing ink composition as described in claim 1 or 2, wherein the elastomer is butadiene rubber.

10. The method for producing a UV-curable printing ink composition according to claim 1 or 2, wherein the volume average particle diameter of the polymer microparticles (A) is 0.03 μm to 50.00 μm.

11. A method for producing a UV-curable printing ink composition as described in claim 2, wherein the resin (B) is made of epoxidized soybean oil.