Aqueous flexographic ink and printed matter thereof

Abstract

To provide an aqueous flexographic ink excellent in bending resistance, drying resistance, printing density, and temporal stability.SOLUTION: The aqueous flexographic ink contains: at least one selected from the group consisting of a polysaccharide (A1), a styrene-acrylic resin (A2) to which a polysaccharide has been added, and an aqueous rosin resin (B); and a urea-based compound. The urea-based compound is a compound represented by general formula (1). [In the general formula (1), R1 represents an oxygen atom or a sulfur atom; R2 and R3 each independently represent a hydrogen atom, an optionally substituted C1-4 alkyl group, or an optionally substituted C6-9 aryl group; and R2 and R3 may form a ring via a C1-3 alkylene group.]SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based flexographic ink and a printed matter thereof. [Background technology]

[0002] In recent years, in the field of aqueous flexographic printing for packaging applications, there have been an increasing number of cases where flexographic printing is performed using a thin-line anilox roll and a low coating amount of ink. When the coating amount of ink is low, the ink coating film dries easily on the plate, which causes a problem that dirt on printing equipment such as the flexographic plate and the anilox roll is difficult to remove, and therefore drying resistance is required so that the ink does not dry easily even when the coating amount is small. In particular, in aqueous flexographic ink compositions containing aqueous acrylic resins, the deterioration of the cleaning ability of the flexographic plate is significant due to the solubility of the resin. In addition, in general, aqueous flexographic ink compositions are required to have stability over time, print density, and bending resistance.

[0003] Patent Document 1 discloses an aqueous flexographic ink that uses a rosin-based resin emulsion and / or a rosin-based resin neutralized with a volatile basic compound as a binder resin. However, since a large amount of ammonia and the like is used to neutralize the aqueous resin and make it water-soluble, there is a concern that the coating drying property and stability over time may be poor. Patent Document 2 discloses an ink that uses an aqueous acrylic resin emulsion as a binder resin and contains urea or a urea derivative. Patent Documents 3 and 4 disclose aqueous liquid inks that use an aqueous acrylic resin emulsion of a styrene-(meth)acrylic copolymer having a styrene-(meth)acrylic copolymer and a polysaccharide as a binder resin, or an aqueous acrylic resin emulsion of a styrene-(meth)acrylic copolymer to which a modified polysaccharide has been added, and Patent Document 3 describes resolubility and plate washability. However, the resolubility and plate washability described in Patent Document 3 are evaluations of the solubility of the dried coating film in ink or water, and are therefore different from the drying resistance in the present invention. In addition, the inks described in Patent Documents 3 and 4 do not contain a urea compound, and are considered to have an insufficient balance of physical properties such as drying resistance and stability over time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-108529 A [Patent Document 2] Special Publication No. 6-503370 [Patent Document 3] JP 2021-167377 A [Patent Document 4] Patent Publication No. 2022-096161 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a water-based flexographic ink that has both excellent drying resistance and stability over time, and further has excellent bending resistance and printing density, which are required of water-based flexographic inks. [Means for solving the problem]

[0006] As a result of extensive research into the above problems, the present inventors have found that the above problems can be solved by using the packaging material described below, and have thus completed the present invention.

[0007] That is, the present invention provides a composition for producing an aqueous rosin resin, comprising at least one selected from the group consisting of a polysaccharide (A1), a styrene-acrylic resin having a polysaccharide added thereto (A2), and an aqueous rosin resin (B), and a urea-based compound, The present invention relates to an aqueous flexographic ink, wherein the urea compound is a compound represented by the following general formula (1): General formula (1) [ka] [In general formula (1), R 1 represents an oxygen atom or a sulfur atom. R 2 and R 3each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, or an aryl group having 6 to 9 carbon atoms which may have a substituent, provided that R 2 and R 3 may form a ring via an alkylene group having 1 to 3 carbon atoms.]

[0008] The present invention further relates to the water-based flexible ink, which contains an extender pigment.

[0009] The present invention relates to the water-based flex ink, wherein the polysaccharide is at least one selected from the group consisting of maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, and starch derivatives.

[0010] The present invention relates to the water-based flexible ink, wherein a mass ratio of the urea compound to the polysaccharide (A1) is 10:90 to 75:25.

[0011] The present invention relates to the water-based flexible ink, wherein the mass ratio of the urea compound to the styrene-acrylic resin having a polysaccharide added thereto (A2) is 5:95 to 70:30.

[0012] The present invention relates to the water-based flexible ink, wherein a mass ratio of the urea compound to the water-based rosin resin (B) is 5:95 to 70:30.

[0013] The present invention relates to the water-based flex ink, wherein the water-based rosin resin (B) contains a water-soluble rosin resin and / or an aqueous rosin emulsion.

[0014] The present invention relates to the water-based flexible ink, wherein the polysaccharide-added styrene-acrylic resin (A2) has an acid value of solid content of 15 to 100 mgKOH / g.

[0015] The present invention further relates to the water-based flexible ink, which contains a water-based styrene-acrylic resin (C).

[0016] The present invention relates to a printed matter having a printed layer formed on a substrate using the above-mentioned water-based flexographic ink. Effect of the Invention

[0017] According to the present invention, it is possible to provide a water-based flexographic ink that is excellent in bending resistance, drying resistance, print density, and stability over time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The water-based flexographic ink of the present invention will be described in detail below.

[0019] [Water-based flexographic ink] The present invention relates to a composition for producing a polysaccharide-based composition comprising at least one selected from the group consisting of a polysaccharide (A1), a styrene-acrylic resin having a polysaccharide added thereto (A2), and an aqueous rosin resin (B), and a urea-based compound; The aqueous flexographic ink is characterized in that the urea compound is a compound represented by the following general formula (1): General formula (1) [ka] [In general formula (1), R 1 R represents an oxygen atom or a sulfur atom. 2 and R 3 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, or an aryl group having 6 to 9 carbon atoms which may have a substituent, provided that R 2 and R 3 may form a ring via an alkylene group having 1 to 3 carbon atoms.]

[0020] By containing at least one selected from the group consisting of polysaccharides (A1), styrene acrylic resins (A2) with polysaccharides added, and aqueous rosin resins (B), and a urea-based compound, (1) the OH groups derived from the polysaccharides and / or the carboxyl groups derived from the aqueous rosin resins (B) form a hydrogen bond network with the urea-based compound, and the network efficiently collects water during the formation of a coating film by printing, thereby slowing down the drying speed, and (2) the cohesive strength of the coating film after formation of the coating film is improved, resulting in excellent bending resistance, drying resistance, print density, and stability over time. Note that the above speculation does not limit the invention in any way. In addition, it is preferable to contain polysaccharides (A1) and / or styrene acrylic resins (A2) with polysaccharides added, and aqueous rosin resin (B).

[0021] The present invention preferably further contains a body pigment. By containing the body pigment, water can be adsorbed on the surface of the body pigment, and excellent drying resistance and print density can be realized by improving the hiding power.

[0022] (Polysaccharide (A1)) The polysaccharide used in the present invention is not particularly limited, but examples thereof include maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, starch derivatives, etc., and it is preferable that the polysaccharide be at least one selected from the group consisting of starch, cellulose, and maltodextrin.

[0023] The content of the polysaccharide (A1) in the aqueous flexo ink is preferably 0.1 to 15 mass%, more preferably 1 to 10 mass%, and even more preferably 3 to 7 mass%, based on the total mass of the aqueous flexo ink. The total content of the solid contents of the binder components including the polysaccharide (A1) in the aqueous flexo ink is preferably 3 to 30 mass%, more preferably 7 to 30 mass%, and even more preferably 10 to 20 mass%, based on the total mass of the aqueous flexo ink.

[0024] (Polysaccharide-added styrene acrylic resin (A2)) The polysaccharide-added styrene-acrylic resin (A2) used in the present invention is an aqueous resin that is soluble or dispersible in water, and may contain a constituent part derived from the polysaccharide and a constituent part derived from the styrene-acrylic resin (a). Examples of such a resin include, but are not limited to, a block polymer of a constituent part derived from a polysaccharide and a constituent part derived from the styrene-acrylic resin (a), a core-shell structure, and the like.

[0025] The acid value of the resin (A2) is preferably 30 to 150 mgKOH / g, more preferably 40 to 120 mgKOH / g, and even more preferably 40 to 100 mgKOH / g. The weight average molecular weight of the resin (A2) is preferably 1500 to 1500000, more preferably 5000 to 1000000, and even more preferably 1000 to 50000. The mass ratio of the polysaccharide to the styrene-acrylic resin is preferably 5:95 to 95:5. The glass transition temperature of the resin (A2) is preferably -20 to 130°C, more preferably 0 to 110°C, and even more preferably 20 to 90°C.

[0026] The content of the resin (A2) in the water-based flexo ink is preferably 10 to 50 mass %, more preferably 12 to 40 mass %, and further preferably 15 to 35 mass %, based on the total mass of the water-based flexo ink.

[0027] <Styrene acrylic resin (a)> The styrene-acrylic resin (a) may be any styrene-acrylic copolymer resin that is soluble or dispersible in water, and includes a water-soluble styrene-acrylic resin (a-1) and / or an aqueous styrene-acrylic emulsion resin (a-2).

[0028] Water-soluble styrene acrylic resin (a-1) The water-soluble styrene-acrylic resin in the present invention refers to a styrene-acrylic copolymer resin obtained by solution-polymerizing monomers including an acrylic monomer and a styrene monomer in an organic solvent, removing the solvent, and dissolving the solid resin under alkaline conditions.

[0029] Suitable examples of the acrylic monomer include acrylic acid esters, methacrylic acid esters, etc. For example, examples of the acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, dimethylaminoethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and glycidyl acrylate, and examples of the methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate. Also usable are carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the anhydrides and half esters thereof. These may be used alone or in combination of two or more.

[0030] Among the above, the acrylic monomer preferably includes methyl acrylate, ethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, maleic acid, and itaconic acid.

[0031] The water-soluble styrene-acrylic resin (a-1) is preferably a water-soluble styrene-acrylic copolymer resin obtained by copolymerizing an acrylic monomer and a styrene monomer, and examples of the constituent styrene monomer include styrene, α-methylstyrene, β-methylstyrene, etc. These may be used alone or in combination of two or more. Among these, the styrene monomer preferably contains α-methylstyrene.

[0032] <Water-based styrene-acrylic resin emulsion (a-2)> The aqueous styrene-acrylic resin emulsion (a-2) in the present invention refers to a styrene-acrylic resin that is insoluble or poorly soluble in an aqueous system, but is dispersed and stabilized by a surfactant or the like. Examples of the styrene monomer that constitutes it include styrene, α-methylstyrene, β-methylstyrene, and the like. These may be used alone or in combination of two or more. Among them, it is preferable that the styrene monomer contains α-methylstyrene.

[0033] The aqueous styrene-acrylic resin emulsion (a-2) preferably has an acid group, and the acid group is preferably neutralized with a basic compound. Suitable examples of the basic compound include amine compounds and alkali metals.

[0034] Examples of the amine compound include ammonia, alkylamines such as diethylamine, triethylamine, and ethylenediamine, and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the alkali metal include sodium hydroxide and potassium hydroxide. These may be used alone or in combination of two or more.

[0035] The acrylic monomer constituting the aqueous styrene-acrylic resin emulsion (a-2) is preferably an acrylic acid ester, a methacrylic acid ester, etc., for example, the acrylic acid ester is methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, dimethylaminoethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl acrylate, and the methacrylic acid ester is methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate. These may be used alone or in combination of two or more.

[0036] In addition, carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the like, or their anhydrides or half esters can also be used. These can be used alone or in combination of two or more kinds.

[0037] Among the above, the acrylic monomer preferably includes methyl acrylate, ethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, maleic acid, and itaconic acid.

[0038] The resin (A2) may be a commercially available product, for example, PE-2027, PE-2189, etc. manufactured by Seiko PMC Corporation.

[0039] (Water-based rosin resin (B)) In the present invention, the aqueous rosin resin (B) refers to a rosin resin that is soluble or dispersible in water, and includes a water-soluble rosin resin and an aqueous rosin emulsion. The water-soluble rosin resin refers to a rosin resin obtained by dissolving maleic rosin under alkaline conditions. The aqueous rosin emulsion refers to a rosin resin obtained by dispersing a rosin derivative in water as fine particles in the presence of an emulsifier. The acid value of the aqueous rosin resin (B) is preferably 0 to 350 mgKOH / g. The softening point of the aqueous rosin resin (B) is preferably 80 to 200°C.

[0040] The content of the aqueous rosin resin (B) in the aqueous flexo ink is preferably 0.1 to 20 mass %, more preferably 1 to 15 mass %, and even more preferably 3 to 8 mass %, based on the total mass of the aqueous flexo ink.

[0041] <Water-soluble rosin resin> The water-soluble rosin resin can be a rosin resin having an acid value of 100 to 350 mgKOH / g, which is partially or entirely neutralized with a basic compound and dissolved in water. Examples of the basic compound include ammonia, organic amines, and alkali metal hydroxides. Specifically, the organic amines include alkylamines such as diethylamine, triethylamine, and ethylenediamine, and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Among them, it is preferable to use a combination of volatile and non-volatile basic compounds from the viewpoint of coating film properties and resolubility. The softening point of the water-soluble rosin is preferably 80 to 200°C.

[0042] Specific examples of water-soluble rosin resins include Harima T-80 manufactured by Harima Chemical Industries, Ltd., Sizepine GF and Marquid 32-30WS manufactured by Arakawa Chemical Industries, Ltd.

[0043] <Water-based rosin emulsion> The aqueous rosin emulsion may be prepared by dispersing rosin or a rosin derivative such as a rosin ester, which is made of a material obtained by extraction from a plant, in the form of fine particles in water in the presence of a low molecular weight emulsifier. The acid value of the aqueous rosin emulsion is preferably 0 to 200 mgKOH / g, and more preferably 0 to 100 mgKOH / g. When the acid value is within the above range, the drying resistance is improved. The softening point of the aqueous rosin emulsion is preferably 80 to 200°C.

[0044] Specific examples of the aqueous rosin emulsion include Super Ester NS-121 and NS-100H manufactured by Harima Chemical Industries, Ltd. and Arakawa Chemical Industries, Ltd.

[0045] In the present invention, it is preferable that the composition contains a water-soluble rosin resin and an aqueous rosin emulsion, and the solids ratio between the water-soluble rosin resin and the aqueous rosin emulsion is preferably 70:30 to 10:90, and more preferably 50:50 to 40:60.

[0046] (Urea-based compounds) The water-based flexographic ink of the present invention contains a urea compound represented by the following general formula (1).

[0047] General formula (1) [ka] [In general formula (1), R 1 represents an oxygen atom or a sulfur atom. R 2 and R 3 each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 4 carbon atoms, or an optionally substituted aryl group having 6 to 9 carbon atoms. However, R 2 and R 3 may form a ring via an alkylene group having 1 to 3 carbon atoms.]

[0048] Examples of the substituent include a hydroxy group, an amino group, a carboxyl group, a halogen atom, a cyano group, a thio group, a silyl group, and a nitro group, and among these, a hydroxy group is preferable.

[0049] Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, and among these, a methyl group and an ethyl group are preferable.

[0050] Examples of the aryl group having 6 to 9 carbon atoms include a phenyl group, a tolyl group, and a xylyl group, with the phenyl group being preferred.

[0051] Examples of the alkylene group having 1 to 3 carbon atoms include a methylene group, an ethylene group, and a propylene group, with an ethylene group being preferred.

[0052] Examples of the urea-based compound represented by the general formula (1) include urea, 2-hydroxyethylurea, thiourea, 1,3-dimethylurea, urea derivatives such as ethyleneurea synthesized by reacting ammonium carbamate with a titanium catalyst, and thiourea derivatives such as N-phenylthiourea. Among them, urea, 2-hydroxyethylurea, and 1,3-dimethylurea are preferred, and urea and 1,3-dimethylurea are more preferred. These may be used alone or in combination of two or more.

[0053] The urea compound is preferably used in the range of 1 to 10% by mass, more preferably 3 to 8% by mass, based on the total mass of the ink. The urea compound preferably has a solubility of 20% by mass or more, more preferably 30% by mass or more, in water at 25°C. When the solubility is within the above range, the drying resistance and stability over time are improved. The mass ratio of the urea compound to the polysaccharide (A1) is preferably 10:90 to 75:25, more preferably 25:75 to 70:30, and even more preferably 40:60 to 60:40. The mass ratio of the urea compound to the resin (A2) is preferably 5:95 to 70:30, more preferably 10:90 to 65:35, and even more preferably 20:80 to 60:40. The mass ratio of the urea compound to the aqueous rosin resin (B) is preferably from 5:95 to 70:30, more preferably from 10:90 to 65:35, and further preferably from 20:80 to 60:40.

[0054] (Water-based styrene acrylic resin (C)) In the present invention, by further including an aqueous styrene-acrylic resin (C), it is possible to realize better print density and stability over time due to the effect of improving pigment dispersibility. The aqueous styrene-acrylic resin (C) refers to a styrene-acrylic resin that is soluble or dispersible in water, and includes a water-soluble styrene-acrylic resin (C-1) and / or an aqueous styrene-acrylic emulsion resin (C-2).

[0055] The content of the water-based styrene-acrylic resin (C) is preferably from 10 to 35 mass %, more preferably from 11 to 30 mass %, and even more preferably from 12 to 20 mass %, of the total mass of the ink.

[0056] The weight average molecular weight of the aqueous styrene-acrylic resin (C) is preferably 1,500 to 1,500,000, more preferably 5,000 to 1,000,000, and further preferably 1,000 to 50,000.

[0057] <Water-soluble styrene acrylic resin (C-1)> The water-soluble styrene-acrylic resin in the present invention refers to a styrene-acrylic resin obtained by solution-polymerizing a monomer containing an acrylic monomer in an organic solvent, removing the solvent, and dissolving the solid resin under alkaline conditions. The monomer constituting the water-soluble styrene-acrylic resin (C-1) can be in the form of the above-mentioned (water-soluble styrene-acrylic resin (a-1)).

[0058] The water-soluble styrene-acrylic resin (C-1) preferably has an acid group, and when it has an acid group, the acid value is preferably 150 to 350 mgKOH / g, more preferably 200 to 300 mgKOH / g. When the acid value of the water-soluble styrene-acrylic resin (C-1) is in the above range, the drying resistance is improved.

[0059] <Water-based styrene acrylic resin emulsion (C-2)> The aqueous styrene-acrylic resin emulsion (C-2) in the present invention refers to an acrylic resin that is insoluble or poorly soluble in an aqueous system, but is dispersed and stabilized with a surfactant or the like. The average particle size of the aqueous styrene-acrylic resin emulsion (C-2) is preferably 10 to 500 nm, more preferably 30 to 200 nm. The acid group of the aqueous styrene-acrylic resin emulsion (C-2) is preferably neutralized with a basic compound. The monomer and basic compound constituting the water-soluble styrene-acrylic resin (C-2) can be in the form of the water-soluble styrene-acrylic resin (a-2) described above.

[0060] The aqueous styrene-acrylic resin emulsion (C-2) preferably has an acid group, and when it has an acid group, the acid value is preferably from 30 to 150 mgKOH / g, and more preferably from 40 to 100 mgKOH / g.

[0061] (Liquid medium) The aqueous flexographic ink of the present invention preferably contains a liquid medium. The main component of the liquid medium is preferably water, but a hydrophilic organic solvent can be used in addition to water. Specifically, an alcohol-based organic solvent, a glycol-based organic solvent, etc. can be contained depending on the printing conditions (speed, plate depth, design, drying temperature). The content of the hydrophilic organic solvent is preferably 30% by mass or less based on the total amount of the ink. In the present invention, the term "mainly water" means that the content of water is the largest in the liquid medium, and the term "water-soluble organic solvent" means that the solvent is liquid at 25° C. and has a solubility of 1% by mass or more in water at 25° C.

[0062] Examples of the alcohol-based organic solvent include methanol, ethanol, propanol, isopropanol, isobutanol, normal butanol, tertiary butanol, hexanol, octanol, and decanol. Examples of the glycol-based organic solvent include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monooctyl ether, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, and dibutyl glycol. These may be used alone or in combination of two or more.

[0063] (Pigments (excluding extender pigments)) The pigments used in the aqueous flexographic ink of the present invention may be those that have been used in aqueous flexographic printing ink compositions.Specific examples of inorganic pigments include colored pigments such as titanium oxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine blue, carbon black, and graphite.In addition, examples of organic pigments include oil-soluble azo pigments, insoluble azo pigments, azo lake pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments.These pigments may be used alone or in combination of two or more. The content of the pigment is preferably 1 to 60% by mass based on the total mass of the water-based flexographic ink.

[0064] (Extender pigment) The water-based flexographic ink of the present invention preferably contains a body pigment. The body pigment is preferably contained in an amount of 0.1 to 10% by mass, more preferably 1 to 5% by mass, based on the total mass of the ink. By containing the body pigment, it is expected that the drying resistance and print density can be improved. The body pigment used preferably contains one or more types of body pigments selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, kaolin clay, and silica. Among these, barium sulfate is preferred from the viewpoint of the stability over time of the ink. The body pigment such as barium sulfate preferably has an average particle size of 0.01 to 0.9 μm, more preferably 0.1 to 0.7 μm. Here, the average particle size refers to a value measured by an electron microscope, and can be measured, for example, by using a field emission scanning electron microscope (JSM-7000F manufactured by JEOL Ltd.) or the like to obtain an average value of particle sizes of 10 randomly selected body pigment particles.

[0065] (Additives) The water-based flexographic ink of the present invention may contain various additives, such as dispersants, waxes, extender pigments, leveling agents, antifoaming agents, and film-forming assistants, if necessary. Specifically, various additives can be added, such as hydrocarbon waxes such as polyethylene wax to improve abrasion resistance; extender pigments such as calcium carbonate, kaolin, barium sulfate, aluminum hydroxide, clay, and talc to improve drying properties and coating film hiding properties; inorganic fine particles and adhesive resins (acrylic resin, vinyl acetate resin) to impart anti-slip properties; leveling agents to improve leveling properties; antifoaming agents to impart antifoaming properties; basic compounds such as sodium hydroxide and potassium hydroxide to impart resolubility; and film-forming aids.

[0066] <Dispersant> The aqueous flexographic ink of the present invention preferably contains a dispersant as required. As the dispersant, it is preferable to use a surfactant such as a polyether compound or an acetylene glycol compound.

[0067] For example, in the case of polyether-based compounds, copolymerized polyethers are suitable, and although not limited thereto, compounds in the form of copolymerization of polypropylene glycol (propylene oxide) and polyethylene glycol (ethylene oxide) are preferred. The weight average molecular weight of the polypropylene glycol-polyethylene glycol copolymer resin is preferably 500 to 30,000, and if the weight average molecular weight is greater than 500, the pigment dispersibility is improved, and if it is less than 30,000, the leveling property is improved. The weight average molecular weight is more preferably in the range of 1,000 to 5,000. In addition, the amount of ethylene oxide added is preferably 10 to 95% by mass in the whole molecule. If the amount of ethylene oxide added is greater than 10%, the stability over time is improved, and if it is less than 95%, the drying resistance is improved. From the viewpoint of achieving both stability over time and drying resistance, the amount of ethylene oxide added is more preferably 30 to 90% by mass.

[0068] Acetylene glycol compounds are also preferred, and acetylene glycol compounds having ethylene oxide and / or propylene oxide are preferred. As acetylene glycol compounds, the Surfynol series (manufactured by Air Products Co., Ltd.) are commercially available.

[0069] The dispersant is preferably used in the range of 0.1 to 10% by mass, more preferably 1 to 8% by mass, based on the total mass of the ink. When used in the above range, the ink has improved stability over time and resistance to drying.

[0070] <Hydrocarbon wax> The hardness (penetration) of the hydrocarbon wax at 25°C as specified by JISK2207 is 12 or less, preferably 0.5 to 8, more preferably 1 to 5, even more preferably 2 to 4, and particularly preferably 2.5 to 3.5. When it is within the above range, the bending resistance and drying resistance are good. The density of the hydrocarbon wax at 23°C as specified by JISK7112 (Method B) is 900 to 990 kg / m 3is preferably 925 to 990 kg / m 3 It is more preferable that the melting point is within the above range. When it is within the above range, the bending resistance and drying resistance are good. The melting point of the hydrocarbon wax in DSC measurement is preferably 90 to 150°C, more preferably 100 to 125°C. When it is within the above range, the bending resistance and drying resistance are good. The melting point of the hydrocarbon wax refers to the melting point of the peak top (minimum value) of the endothermic peak in the DSC temperature rise curve. The average particle size of the hydrocarbon wax is preferably 0.5 to 12 μm, more preferably 1 to 10 μm, and even more preferably 1.5 to 4 μm. The average particle size of the hydrocarbon wax refers to the D50 value measured by laser diffraction / light scattering method.

[0071] The content of the hydrocarbon wax in the water-based flexographic ink of the present invention is preferably 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, based on 100 mass % of the ink. When it is within the above range, the bending resistance and drying resistance are good.

[0072] Polyethylene wax The polyethylene wax is not particularly limited, but examples thereof include high-density polymerized polyethylene, low-density polymerized polyethylene, oxidized polyethylene, acid-modified polyethylene, and special monomer-modified polyethylene. The polyethylene wax has a density of 925 to 990 kg / m at 23° C. as specified in JIS K7112 (B method). 3 and the melt viscosity at 140°C measured in accordance with JIS K6862 is preferably 50 to 8000 mPa s. The polyethylene wax may have an acid value. If it has an acid value, the acid value is preferably 0.5 to 70 mgKOH / g. The polyethylene wax preferably has a melting point in DSC measurement of 90 to 150°C, more preferably 100 to 125°C.

[0073] Fischer-Tropsch wax is a wax produced by the Fischer-Tropsch process using carbon monoxide and hydrogen as raw materials, and is composed of a nearly saturated, unbranched, linear molecular structure. Due to its linear structure, it has a high melting point, low viscosity, and is hard. Fischer-Tropsch wax hardly deteriorates even when exposed to heat for a long period of time, and shows extremely high thermal stability. The number average molecular weight of Fischer-Tropsch wax is preferably 400 to 2000. In addition, Fischer-Tropsch wax has a density of 925 to 990 kg / m at 23°C as specified in JIS K7112 (Method B). 3 The Fischer-Tropsch wax may have an acid value. When the Fischer-Tropsch wax has an acid value, the acid value is preferably 0.5 to 50 mgKOH / g. The Fischer-Tropsch wax preferably has a melting point of 90 to 130°C, more preferably 100 to 120°C, as measured by DSC.

[0074] (Method of manufacturing water-based flexographic ink) The method for producing the water-based flexographic ink of the present invention will be described. The water-based flexographic ink of the present invention can be produced, for example, by mixing and stirring water, pigment, dispersant, water-soluble resin, etc., dispersing the pigment using various mills such as a bead mill, pearl mill, sand mill, ball mill, attritor, roll mill, etc., and then adding and mixing predetermined materials and additives such as a resin emulsion, water-soluble resin, rosin-based resin, etc. The ink can be obtained by mixing and stirring the ink. It is preferable to use a bead mill for dispersing the pigment.

[0075] (Flexographic printing method) Flexographic printing methods include the two-roll method, doctor method, and doctor chamber method. In the doctor method and doctor chamber method, an aqueous flexographic ink composition is supplied to an anilox roll having cells formed on its surface, and excess aqueous flexographic ink is scraped off the anilox roll surface with a doctor blade, and the ink is finally printed on a substrate through a resin plate. When the aqueous flexographic ink of the present invention is printed by the flexographic printing method, a printed matter having excellent aesthetic appearance can be obtained even on a paper substrate having a rough surface.

[0076] (Flexographic printing method; Anilox roll) The anilox used in the flexographic printing used in the method for producing a flexographic printed matter of the present invention may be a ceramic anilox roll with cell engraving, a chrome-plated anilox roll, or the like. The shape of the cells may be a honeycomb pattern, a diamond pattern, a helical pattern, or the like, and any pattern may be used. The role of the anilox is to receive a fixed amount of ink supplied from the doctor chamber (or fountain roll) uniformly and then transfer it to the printing plate. The screen ruling of the anilox roll is preferably 50 to 2000 lines / inch, more preferably 100 to 1200 lines / inch.

[0077] (Flexographic printing method; flexographic plate) The plate used in the flexographic printing used in the method for producing a flexographic printed matter of the present invention includes a photosensitive resin plate that utilizes ultraviolet curing by a UV light source, or an elastomer material plate that uses a direct laser engraving method. Any sleeve or cushion tape can be used to attach the plate. The screen ruling of the flexographic plate is preferably 80 to 200 lines / inch, more preferably 125 to 175 lines / inch.

[0078] (Flexographic printing method; printing machine) Flexographic printing machines include CI type multicolor flexographic printing machines, unit type multicolor flexographic printing machines, etc., and ink supply methods include chamber methods and two-roll methods, and an appropriate printing machine can be used. The printing speed is preferably 50 to 500 m / min, and more preferably 100 to 300 m / min.

[0079] (Printed matter having a printing layer formed with water-based flexographic ink) An example of a method for producing a printed matter having a printing layer formed with an aqueous flexographic ink is printing on the surface of paper or resin, in particular, printing on paper containers such as paper cups, paper plates, and other paper containers, or paper containers whose surfaces are covered with a resin layer, thin paper for food packaging, or materials thereof, using the above-mentioned aqueous flexographic ink with a flexographic printing machine. In this case, the substrate to be printed may be any of food packaging such as wrapping paper or paper bags, paper products such as paper containers having a resin layer such as polyolefin laminated on the surface, paper products such as paper containers having a resin layer such as a resin coating layer of polyolefin on the surface, and paper products such as uncoated paper containers that do not have a resin layer on the surface.

[0080] (base material) Examples of the substrate for printing (printing material) include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and nylon, cellophane, paper, aluminum foil, and films and sheets made of composite materials thereof. In the present invention, a paper substrate is particularly preferred. The paper substrate is preferably a paper substrate selected from uncoated paper, one-side gloss kraft paper in which one side of the substrate is treated, bleached kraft paper, unbleached kraft paper, and the like. EXAMPLES

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass". The figures for the amounts of each material in the tables are also "parts by mass". The units of hydroxyl value and acid value are mgKOH / g.

[0082] (Acid value and hydroxyl value) Calculated in accordance with JIS K0070.

[0083] <Polysaccharide (A1)> Maltodextrin <Polysaccharide-added styrene acrylic resin (A2)> Water-soluble styrene acrylic resin SAC1 (polysaccharides contained: starch, acid value 30mgKOH / g, glass transition temperature 85℃, solid content 48%) Water-based styrene acrylic resin emulsion SAC2 (polysaccharides contained: starch, acid value 50mgKOH / g, glass transition temperature 30℃, solid content 48%) Water-based styrene acrylic emulsion SAC3 (polysaccharides included: starch, acid value 10mgKOH / g, glass transition temperature 40℃, solid content 48%) Water-based styrene acrylic emulsion SAC4 (polysaccharides contained: starch, acid value 120mgKOH / g, glass transition temperature 50℃, solid content 48%) Water-based styrene acrylic emulsion SAC5 (polysaccharides included: cellulose, acid value 40mgKOH / g, glass transition temperature 55℃, solid content 48%) <Water-based rosin resin (B)> Water-soluble rosin resin: Sizevine E (Arakawa Chemical Co., Ltd., solids content 30%) Water-based rosin emulsion (Arakawa Chemical, Super Ester NS-121, softening point: 120°C, solids content 49%) <Other ingredients> Styrene acrylic emulsion SAC7 (acid value 100mgKOH / g, glass transition temperature 16℃, solid content 28%) Acrylic resin emulsion AC1 (Seiko PMC, PE-1126) ·Silica: Average particle size 4μm, oil absorption 200ml / 100g Calcium carbonate: average particle size 1μm, oil absorption 40ml / 100g

[0084] (Example 1) [Preparation of water-based flexographic ink S1] A mixture of 28 parts of water, 18 parts of Pigment Black 7, 2 parts of barium sulfate (Sakai Chemical Industry Co., Ltd., Variace B-35, average particle size 0.3 μm, solid content 100%), 5 parts of a urea compound, 2 parts of PEG-PPG (copolymer resin of polyethylene glycol (PEG) and polypropylene glycol (PPG) (weight average molecular weight 2800; PEG:PPG=40:60; solid content 100%), 1 part of acetylene glycol (Nissin Chemical Industry Co., Ltd., Surfynol SE, solid content 80%), and 15 parts of water-soluble styrene acrylic resin SAC6 (acid value 240 mg KOH / g, solid content 28%) was kneaded and dispersed using a bead mill, and then 15 parts of aqueous styrene acrylic resin emulsion SAC2, 10 parts of aqueous rosin emulsion (solid content 49%), 3 parts of polyethylene wax, and 1 part of triethanolamine were added and mixed by stirring to obtain aqueous flexographic ink S1.

[0085] (Examples 2 to 15, Comparative Examples 1 to 3) [Preparation of Water-Based Flexographic Inks S2 to S18] Water-based flexographic inks S2 to S18 were obtained in the same manner as in Example 1, except for changing the raw materials and compositions shown in Table 1. In the table, values ​​without units indicate parts, and blanks indicate that no ingredients were added.

[0086] (Creation of printed matter) The water-based flexographic inks S1 to 18 obtained above were printed on a small flexiproof printing machine equipped with a 200 line / inch anilox roll and a solid plate made of photosensitive resin. Unbleached kraft paper: kraft paper made from unbleached kraft pulp (Nippon Paper Industries, Ltd., unglazed kraft K basis weight 70 g / m 2 ) at a printing speed of 50 m / s to obtain a printed matter.

[0087] (evaluation) The inks and printed matter obtained in the above Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Table 1.

[0088] (Bending resistance) The inks obtained in the examples and comparative examples were printed on unbleached kraft paper: kraft paper using unbleached kraft pulp (unbleached kraft K, manufactured by Nippon Paper Industries Co., Ltd.; basis weight 70 g / m) using a Flexi Proofer printing machine. 2 ) and a coating film was formed, and folding resistance was evaluated. The substrate was folded so that the printed surface was on the inside, and then folded again so that the printed surface was on the outside, and the degree of cracking of the ink coating film on the printed surface was evaluated. The criteria are as follows: 5: No creases on the printed surface. It has a bending resistance level between 4:5 and 3. 3: Cracks in the printed layer occur only at the fold on the printed surface. It has a bending resistance that is intermediate between 2:3 and 1. 1: Cracks or chips occur in the printed layer on the printed surface other than in the fold areas. The industrially applicable levels above are rated 3, 4 and 5.

[0089] (Dry resistance) The inks obtained in the Examples and Comparative Examples were spread on a flexographic resin plate using a Mayer bar (#4) to form a coating, and after one minute at 40°C, the ink was visually evaluated by touching with a finger for drying condition. The criteria are as follows. Compared to tests at room temperature, 40°C represents an excessive condition because the drying speed of water is greatly increased. 5: The ink coating adhesion area ratio to the flexographic resin plate is 30% or more in the area touched by the finger. 4: In the area touched by the finger, the ink coating adhesion area ratio to the flexographic resin plate is 10% or more and less than 30%. 3: In the area touched by the finger, the ink coating adhesion area ratio to the flexographic resin plate is between 5% and 10%. 2: In the area touched by the finger, the ink coating adhesion area ratio to the flexographic resin plate is between 1% and 5%. 1: Within the area touched by the finger, the ink coating adhesion area ratio to the flexographic resin plate is less than 1%. The industrially applicable levels above are rated 3, 4 and 5.

[0090] (Print density) The inks obtained in the examples and comparative examples were printed on a Flexiproof printing machine using unbleached kraft paper: kraft paper using unbleached kraft pulp (Nippon Paper Industries Co., Ltd., unbleached kraft K, basis weight 70 g / m 2 ) was applied to form a coating, and the print density (color development) was evaluated using a colorimeter. For the measurements, a PANTONE X-Rite eXact spectrophotometer was used. The measurement conditions were: illuminant / observer field of view: D50 / 2°, density status: ISO status E, density white standard: absolute value, and the L of the printed surface was * , a * , b * The standard color L * , a * , b * The measured values ​​were 31.20, -3.20, and -22.60, respectively, and the color difference ΔE * ab was calculated using the following formula (1). Equation (1)ΔE * ab = [(ΔL * )2+(Δa * )2+(Δb * )2] 1 / 2 5: ΔE measured with an X-Rite eXact spectrophotometer * ab is less than 0.4. 4:ΔE * ab is greater than or equal to 0.4 and less than 0.8. 3:ΔE * ab is greater than or equal to 0.8 and less than 1.6. 2:ΔE * ab is greater than or equal to 1.6 and less than 3.2. 1:ΔE * ab is 3.2 or more. The industrially applicable levels above are rated 3, 4 and 5.

[0091] (Stability over time) The inks obtained in the examples and comparative examples were stored in ovens at 5° C. and 40° C. for one week, and the ink viscosity and condition were then evaluated. 5: After one week, the viscosity change is less than 3 seconds compared to the viscosity of the ink before storage. 4: After one week, the viscosity of the ink has changed by more than 3 seconds but less than 5 seconds compared to the viscosity before storage. 3: After one week, the ink viscosity has changed by more than 5 seconds but less than 7 seconds compared to the viscosity before storage. 2: After one week, the viscosity of the ink has changed by more than 7 seconds but less than 10 seconds compared to the viscosity before storage. 1: After one week, the ink viscosity has changed by more than 10 seconds compared to the viscosity before storage. The industrially applicable levels above are rated 3, 4 and 5.

[0092] [Table 1]

[0093] From the above results, Comparative Example 1 did not contain any of the polysaccharide (A1), the styrene acrylic resin with a polysaccharide added thereto (A2), and the aqueous rosin resin (B), and therefore had poor folding resistance, drying resistance, and print density. Comparative Examples 2 and 3 did not contain any urea-based compound, and therefore had poor drying resistance and stability over time. On the other hand, in the examples, since the composition contains at least one selected from the group consisting of polysaccharides (A1), styrene acrylic resins having polysaccharides added thereto (A2), and aqueous rosin resins (B), and a urea-based compound, the composition has good bending resistance, drying resistance, print density, and stability over time.

Claims

1. The composition contains at least one selected from the group consisting of polysaccharides (A1), styrene-acrylic resins having polysaccharides added thereto (A2), and aqueous rosin resins (B), and a urea-based compound; The aqueous flexographic ink, wherein the urea compound is a compound represented by the following general formula (1): General formula (1) 【Chemistry 1】 [In general formula (1), R １ represents an oxygen atom or a sulfur atom. R ２ and R ３ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, or an aryl group having 6 to 9 carbon atoms which may have a substituent. ２ and R ３ may form a ring via an alkylene group having 1 to 3 carbon atoms.]

2. The water-based flexible ink according to claim 1, further comprising an extender pigment.

3. 3. The water-based flex ink according to claim 1 or 2, wherein the polysaccharide is at least one selected from the group consisting of maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, and starch derivatives.

4. The water-based flexographic ink according to claim 1 or 2, wherein a mass ratio of the urea compound to the polysaccharide (A1) is from 10:90 to 75:

25.

5. 3. The water-based flexographic ink according to claim 1, wherein a mass ratio of the urea compound to the styrene-acrylic resin having the polysaccharide added thereto (A2) is 5:95 to 70:

30.

6. 3. The water-based flexographic ink according to claim 1, wherein a mass ratio of the urea compound to the water-based rosin resin (B) is from 5:95 to 70:

30.

7. 3. The water-based flexographic ink according to claim 1, wherein the water-based rosin resin (B) comprises a water-soluble rosin resin and / or an aqueous rosin emulsion.

8. The water-based flexographic ink according to claim 1 or 2, wherein the polysaccharide-added styrene-acrylic resin (A2) has an acid value of 15 to 100 mg KOH / g.

9. The water-based flexographic ink according to claim 1 or 2, further comprising an aqueous styrene-acrylic resin (C).

10. A printed matter having a printed layer formed on a substrate using the water-based flexographic ink according to claim 1 or 2.

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