Water-based flexographic ink

Abstract

The present invention provides a water-based flexographic ink that is excellent in plate-clogging properties, stability over time, print density, and other properties. [Solution] An aqueous flexographic ink comprising a colorant, an aqueous acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, wherein the content of the colorant is 20 mass% or more in 100 mass% of the aqueous flexographic ink; or an aqueous flexographic ink wherein the solids mass ratio of the colorant to the water-soluble styrene-maleic acid resin is 60:40 to 99:1.

Description

[Technical Field]

[0001] The present invention relates to a water-based flexographic ink and a method for producing the same. [Background technology]

[0002] In recent years, aqueous flexographic printing for packaging applications has increasingly been performed using a high-fine anilox roll and low ink coverage. To maintain high design quality even with a low coverage, high-concentration inks are required. High-concentration inks with low coverage tend to dry the ink film on the printing plate more easily, resulting in problems with difficult-to-remove stains on printing press equipment, such as the flexographic plate and anilox roll (plate tack). In particular, aqueous flexographic ink compositions containing aqueous acrylic resins suffer from significant deterioration in plate tack due to the solubility of the resin. Furthermore, aqueous flexographic ink compositions generally require long-term stability and blocking resistance.

[0003] Patent Document 1 describes an aqueous flexo ink composition containing a colorant, an aqueous acrylic resin, and a styrene-maleic acid emulsion resin, and Patent Document 2 describes an aqueous flexo ink composition containing a colorant and an aqueous acrylic resin. However, neither of these compositions contains a water-soluble styrene-maleic acid resin and has a low colorant content, so there is a concern that plate-binding properties and blocking resistance may decrease when the colorant concentration becomes higher. Patent Document 3 describes titanium oxide, aqueous acrylic resin, and water-soluble styrene-maleic acid resin, but the amount of colorant is small, so there is concern that printing density and blocking resistance may be poor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-167377 [Patent Document 2] Japanese Patent Publication No. 2021-038022 [Patent Document 3] International Publication No. 2021 / 192749 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 is excellent in plate-binding properties, stability over time, print density, and blocking resistance. [Means for solving the problem]

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using the water-based flexographic ink described below, and have thus completed the present invention.

[0007] That is, the present invention provides an aqueous flexographic ink comprising a colorant, an aqueous acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, The present invention relates to an aqueous flexographic ink, wherein the content of the colorant is 20% by mass or more based on 100% by mass of the aqueous flexographic ink.

[0008] That is, the present invention relates to the water-based flexographic ink, wherein the solid content mass ratio between the colorant and the water-soluble styrene-maleic acid resin is 60:40 to 99:1.

[0009] That is, the present invention relates to the above-mentioned water-based flexographic ink, which further contains a urea 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 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 3may form a ring via an alkylene group having 1 to 3 carbon atoms.]

[0010] That is, the present invention relates to the water-based flexographic ink, wherein the solid content ratio between the urea compound represented by the general formula (1) and the water-soluble styrene-maleic acid resin is 40:60 to 80:20.

[0011] That is, the present invention relates to the water-based flexographic ink, wherein the water-based acrylic resin (A) comprises a water-based acrylic resin having a polysaccharide added thereto.

[0012] That is, the present invention relates to the above-mentioned water-based flexographic ink, which further contains a polysaccharide and / or an aqueous rosin resin.

[0013] That is, the present invention relates to the water-based flexo ink, wherein the content of the biomass-derived component is 5% by mass or more based on 100% by mass of the water-based flexo ink.

[0014] That is, the present invention relates to the water-based flexographic ink, wherein the colorant does not contain titanium oxide.

[0015] That is, the present invention relates to the above-mentioned water-based flexographic ink, further comprising a dispersant, wherein the dispersant is a polyether-based dispersant and / or an acetylene-based dispersant.

[0016] That is, the present invention relates to the water-based flexographic ink for use in paper packaging materials.

[0017] That is, the present invention relates to a printed matter having a printed layer formed on a substrate using the above-mentioned water-based flexographic ink.

[0018] That is, the present invention provides a method for producing an aqueous flexographic ink, comprising: a colorant; an aqueous acrylic resin (A); an aqueous medium; and a water-soluble styrene-maleic acid resin, a dispersing step of dispersing a mixed liquid containing the colorant, the aqueous medium, and the water-soluble styrene-maleic acid resin with beads to obtain a dispersion, An addition step of adding an aqueous acrylic resin (A) to the dispersion, The present invention relates to a method for producing a water-based flexographic ink, wherein the content of the colorant is 20% by mass or more based on 100% by mass of the water-based flexographic ink. [Effects of the Invention]

[0019] The present invention makes it possible to provide a water-based flexographic ink that is excellent in plate-binding properties, stability over time, print density, and blocking resistance. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following describes in detail the embodiments of the present invention. However, the following description of the constituent elements is an example of an embodiment of the present invention, and the present invention is not limited to these contents as long as it does not deviate from the gist of the present invention.

[0021] <Water-based flexographic ink> The water-based flexo ink of the present invention is a water-based flexo ink containing a colorant, a water-based acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, and is characterized in that the content of the colorant is 20% by mass or more based on 100% by mass of the water-based flexo ink. By containing a colorant, an aqueous acrylic resin (A), and a water-soluble styrene-maleic acid resin, the water-soluble styrene-maleic acid resin, which has excellent solubility in aqueous media, adsorbs to the colorant and is compatible with the aqueous acrylic resin (A), thereby integrating the colorant and the above-mentioned resin components, thereby controlling drying properties, maintaining a good dispersion state of the high-concentration colorant, and improving durability when formed into a coating film, thereby improving plate-binding properties, stability over time, print density, and blocking resistance. Note that this explanation is based solely on technical considerations and does not limit the invention in any way.

[0022] <Coloring agent> As the colorant, a pigment is preferred, and either an organic pigment or an inorganic pigment can be used, but a pigment other than titanium oxide is more preferred, and an organic pigment is even more preferred. When the above-mentioned raw material is used, plate adhesion, stability over time, and print density tend to be improved. The content of the colorant is 20% by mass or more, preferably 20 to 70% by mass, more preferably 23 to 60% by mass, and even more preferably 25 to 50% by mass, based on 100% by mass of the aqueous flexo ink. When the content of the colorant is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved.

[0023] Specific examples of organic pigments are shown by Colour Index International (CI) numbers. Preferably, CI Pigment Red 57:1, CI Pigment Red 48:1, CI Pigment Red 48:2, CI Pigment Red 48:3, CI Pigment Red 146, CI Pigment Red 242, CI Pigment Yellow 83, CI Pigment Yellow 14, CI Pigment Orange 64, CI Pigment Orange 38, CI Pigment Orange 34, CI Pigment Orange 13, CI Pigment Yellow 180, CI Pigment Yellow 139, CI Pigment Red 185, CI Pigment Red 122, CI Pigment Red 178, CI Pigment Red 149, CI Pigment Red 144, CI Pigment Red 166, CI Pigment Violet 23, CI Pigment Violet 37, CI Pigment Blue 15, CI Pigment Blue 15:1, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 15:6, CI Pigment Green 7, CI Pigment Orange 34, CI Pigment Orange 64, and CI Pigment Black 7, which may be used alone or in combination of two or more.

[0024] (inorganic pigments) Examples of inorganic pigments include zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, aluminum particles, mica, bronze powder, chrome vermilion, yellow lead, cadmium yellow, cadmium red, ultramarine, Prussian blue, red iron oxide, yellow iron oxide, iron black, titanium oxide, and zinc oxide. Aluminum can be either leafing or non-leafing type, with non-leafing type being preferred.

[0025] <Water-soluble styrene-maleic acid resin> Styrene-maleic acid refers to a resin obtained by copolymerizing a styrene monomer and maleic acid. The water-soluble styrene-maleic acid resin preferably has an acid group, and in that case, the acid value is preferably 100 to 300 mgKOH / g, more preferably 120 to 250 mgKOH / g, and even more preferably 150 to 200 mgKOH / g. When the water-soluble styrene-maleic acid resin has an acid group and its acid value is within the above range, the solubility in aqueous media is improved, and as a result, plate-binding properties, print density, and blocking resistance tend to be improved. The weight-average molecular weight of the water-soluble styrene-maleic acid resin is preferably 3,000 to 50,000, and more preferably 5,000 to 30,000. When the weight-average molecular weight of the water-soluble styrene-maleic acid resin is within the above range, plate-binding properties, print density, and blocking resistance tend to be improved. The glass transition temperature of the water-soluble styrene-maleic acid resin is preferably 50 to 120°C, more preferably 60 to 100°C. When the glass transition temperature of the water-soluble styrene-maleic acid resin is within the above range, plate-binding properties, print density, and blocking resistance tend to be improved. The content of the styrene monomer-derived structure in the water-soluble styrene-maleic acid resin is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15 to 70% by mass, and particularly preferably 20 to 40% by mass. When the content of the styrene monomer-derived structure in the water-soluble styrene-maleic acid resin is within the above range, plate-binding properties, stability over time, and print density tend to be improved.

[0026] The solid content of the water-soluble styrene-maleic acid resin is preferably 0.5 to 30% by mass, and more preferably 1 to 10% by mass, based on 100% by mass of the water-based flexo ink.

[0027] The solid content ratio of the colorant to the water-soluble styrene-maleic acid resin is preferably 60:40 to 99:1, and more preferably 80:20 to 95:5. When the solid content ratio of the colorant to the water-soluble styrene-maleic acid resin is within the above range, plate adhesion, print density, and blocking resistance are improved.

[0028] As the water-soluble styrene-maleic acid resin, commercially available products may be used, for example, M-30 manufactured by Seiko PMC Co., Ltd. and Arastar series manufactured by Arakawa Chemical Industries, Ltd.

[0029] <Water-based acrylic resin (A)> The aqueous acrylic resin (A) used in the aqueous flexo ink of the present invention may be either a water-soluble acrylic resin (a1) or an aqueous acrylic emulsion resin (a2), but is preferably an aqueous acrylic emulsion resin (a2). The aqueous acrylic emulsion resin (a2) refers to a resin that is insoluble or poorly soluble in water, but is dispersed in an aqueous medium in the form of particles and stabilized.

[0030] The aqueous acrylic resin (A) preferably has an acid value and is preferably neutralized with a basic compound. Suitable examples of the basic compound include amine compounds and alkali metals. Specific 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.

[0031] Suitable examples of acrylic monomers constituting the aqueous acrylic resin (A) include acrylic acid esters and methacrylic acid esters. For example, suitable examples of 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. Suitable examples of 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. Further, carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid are suitable, and anhydrides and half esters thereof can also be used. 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, or itaconic acid. The aqueous acrylic resin (A) may be one containing the above-mentioned acrylic monomer-derived structure, and may also be one containing a styrene monomer-derived structure and / or a polysaccharide, as described below.

[0032] The aqueous acrylic resin (A) is preferably an aqueous styrene-acrylic resin and / or an aqueous acrylic resin having a polysaccharide added thereto, and more preferably an aqueous styrene-acrylic resin having a polysaccharide added thereto. The aqueous styrene-acrylic resin of the present invention is an aqueous acrylic resin (A) containing a structure derived from a styrene monomer. Examples of the styrene monomer from which the styrene monomer-derived structure is derived include styrene, α-methylstyrene, and β-methylstyrene. Among these, the styrene monomer preferably contains α-methylstyrene. The content of the styrene monomer-derived structure in the aqueous styrene-acrylic resin is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20 to 70% by mass, and particularly preferably 25 to 40% by mass. When the content of the styrene monomer-derived structure in the water-soluble styrene-acrylic resin is within the above range, plate-clogging properties, stability over time, and print density tend to be improved. The polysaccharide-added aqueous acrylic resin may contain a polysaccharide-derived component in its structure, and the content of the polysaccharide-derived component is preferably 5 to 80 mass %, more preferably 10 to 60 mass %, and even more preferably 20 to 40 mass %, of the total mass of the polysaccharide-added aqueous acrylic resin. When the content of the polysaccharide-derived component is within the above range, plate adhesion tends to be improved.

[0033] <Polysaccharide-derived components contained in water-based acrylic resin (A)> The polysaccharides from which the polysaccharide-derived components used in the present invention are derived are not particularly limited, but examples include maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, and starch derivatives. Preferably, the polysaccharide is at least one selected from the group consisting of starch, cellulose, and maltodextrin, and more preferably, starch.

[0034] <Water-soluble acrylic resin (a1)> The water-soluble acrylic resin (a1) used in the present invention refers to an acrylic resin obtained by solution-polymerizing monomers containing an acrylic monomer in an organic solvent, removing the solvent, and dissolving the solid resin under alkaline conditions. The hydroxyl value of the water-soluble acrylic resin (a1) is preferably 200 to 500 mgKOH / g, more preferably 250 to 400 mgKOH / g, and even more preferably 300 to 350 mgKOH / g. When the hydroxyl value of the water-soluble acrylic resin (a1) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The acid value of the water-soluble acrylic resin (a1) is preferably 50 to 350 mgKOH / g, more preferably 100 to 300 mgKOH / g, and even more preferably 150 to 250 mgKOH / g. When the acid value of the water-soluble acrylic resin (a1) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The weight-average molecular weight of the water-soluble acrylic resin (a1) is preferably 2,000 to 200,000, and more preferably 10,000 to 100,000. When the weight average molecular weight of the water-soluble acrylic resin (a1) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved.

[0035] The water-soluble acrylic resin (a1) may be a commercially available product, for example, YL-1098 manufactured by Seiko PMC Corporation or Joncryl 70J manufactured by BASF.

[0036] <Water-based acrylic emulsion resin (a2)> The average particle size of the aqueous acrylic emulsion resin (a2) measured by dynamic light scattering is preferably 10 to 500 nm, more preferably 20 to 300 nm, and even more preferably 30 to 200 nm. The average particle size can be measured, for example, by dynamic light scattering. The hydroxyl value of the aqueous acrylic emulsion resin (a2) is preferably 200 to 500 mgKOH / g, more preferably 250 to 400 mgKOH / g, and even more preferably 300 to 350 mgKOH / g. When the hydroxyl value of the aqueous acrylic emulsion resin (a2) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The acid value of the aqueous acrylic emulsion resin (a2) is preferably 10 to 100 mgKOH / g, and more preferably 30 to 70 mgKOH / g. When the acid value of the aqueous acrylic emulsion resin (a2) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The weight-average molecular weight of the aqueous acrylic emulsion resin (a2) is preferably 50,000 to 2,000,000, more preferably 100,000 to 1,000,000, and even more preferably 200,000 to 800,000. When the weight-average molecular weight of the aqueous acrylic emulsion resin (a2) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The glass transition temperature of the aqueous acrylic emulsion resin (a2) is preferably 10 to 100°C, more preferably 30 to 70°C. When the glass transition temperature of the aqueous acrylic emulsion resin (a2) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved.

[0037] The aqueous acrylic emulsion resin (a2) may be a commercially available product, for example, PE-1304 manufactured by Seiko PMC Corporation or Joncryl 7100 manufactured by BASF.

[0038] The solid content of the aqueous acrylic resin (A) is preferably 1 to 40 mass %, more preferably 5 to 20 mass %, based on 100 mass % of the aqueous flexo ink.

[0039] The solid content ratio of the colorant to the aqueous acrylic resin (A) is preferably 55:45 to 95:5, and more preferably 65:35 to 85:15. When the solid content ratio of the colorant to the aqueous acrylic resin (A) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. The solid content ratio of the aqueous acrylic resin (A) to the water-soluble styrene-maleic acid resin is preferably 55:45 to 95:5, and more preferably 65:35 to 85:15. When the solid content ratio of the aqueous acrylic resin (A) to the water-soluble styrene-maleic acid resin is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved.

[0040] <Urea compounds> The aqueous flexographic ink of the present invention preferably further contains a urea compound represented by the following general formula (1): The urea compound forms an interaction network with the water-soluble styrene-maleic acid resin or the aqueous acrylic resin (A) described above, improving the coating film strength and water retention on the printing plate, which tends to improve plate-cling resistance and blocking resistance.

[0041] 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 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.]

[0042] Examples of the substituent in the alkyl group having 1 to 4 carbon atoms, which may have a substituent, and the aryl group having 6 to 9 carbon atoms, which may have a 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 of these, a hydroxy group is preferred.

[0043] 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 preferred.

[0044] Examples of the aryl group having 6 to 9 carbon atoms include a phenyl group, a tolyl group, and a xylyl group, with a phenyl group being preferred.

[0045] 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.

[0046] Examples of urea compounds 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 these, urea, 2-hydroxyethylurea, and 1,3-dimethylurea are preferred, and urea and 1,3-dimethylurea are more preferred. These compounds may be used alone or in combination of two or more.

[0047] The content of the urea compound is preferably in the range of 1 to 10% by mass, more preferably 5 to 8% by mass, of the total mass of the ink. When the content of the urea compound is in the above range, plate adhesion, print density, and blocking resistance tend to be improved. Furthermore, the urea compound preferably has a solubility in water at 25°C of 20% by mass or more, more preferably 30% by mass or more. The solid content ratio of the urea compound to the water-soluble styrene-maleic acid resin is preferably 40:60 to 80:20, and more preferably 50:50 to 70:30. When the solid content ratio of the urea compound to the water-soluble styrene-maleic acid resin is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved. The solid content ratio of the urea compound to the aqueous acrylic resin (A) is preferably 40:60 to 90:10, and more preferably 60:40 to 80:20. When the solid content ratio of the urea compound to the aqueous acrylic resin (A) is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved.

[0048] <Polysaccharides> The aqueous flexo ink of the present invention preferably contains a polysaccharide. 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, and starch derivatives. Preferably, the polysaccharide is at least one selected from the group consisting of starch, cellulose, and maltodextrin. The polysaccharide may be the same as the polysaccharide-derived component contained in the aqueous acrylic resin (A) described above in the section on aqueous acrylic resin (A).

[0049] The content of polysaccharides in the aqueous flexo ink is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 3 to 12% by mass, based on the total mass of the aqueous flexo ink. When the content is within the above range, plate adhesion tends to be improved.

[0050] <Water-based rosin resin> The aqueous flexographic ink of the present invention preferably contains an aqueous rosin resin. In the present invention, the term "aqueous rosin resin" refers to a rosin resin that is soluble or dispersible in water, and includes water-soluble rosin resins and aqueous rosin emulsions. The water-soluble rosin resin refers to a rosin resin obtained by dissolving maleated 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 is preferably 0 to 350 mgKOH / g. When the acid value of the aqueous rosin resin is within the above range, plate adhesion and blocking resistance tend to be improved. The softening point of the aqueous rosin resin is preferably 80 to 200°C. When the softening point of the aqueous rosin resin is within the above range, plate adhesion and blocking resistance tend to be improved.

[0051] The content of the aqueous rosin resin in the aqueous flexo ink is preferably 0.1 to 20 mass %, more preferably 1 to 15 mass %, and even more preferably 3 to 12 mass %, of the total mass of the aqueous flexo ink. When the content of the aqueous rosin resin in the aqueous flexo ink is within the above range, plate adhesion resistance and blocking resistance tend to be improved.

[0052] <Water-soluble rosin resin> The water-soluble rosin resin can be prepared by neutralizing a portion or all of the acid value of a rosin-based resin having an acid value of 100 to 350 mgKOH / g with a basic compound and dissolving the resin in water. Examples of basic compounds include ammonia, organic amines, and alkali metal hydroxides. Specific examples of the organic amine include alkylamines such as diethylamine, triethylamine, and ethylenediamine, and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. Among these, it is desirable to use a combination of volatile and nonvolatile basic compounds in terms of coating film properties and resolubility. The softening point of the water-soluble rosin is preferably 80 to 200°C. When the softening point of the water-soluble rosin is within the above range, plate adhesion and blocking resistance tend to be improved.

[0053] Specific examples of water-soluble rosin resins include Harima T-80 manufactured by Harima Chemicals, and Sizepine GF and Marquid 32-30WS manufactured by Arakawa Chemicals.

[0054] <Water-based rosin emulsion> The aqueous rosin emulsion can be prepared by dispersing rosin or a rosin derivative such as a rosin ester, which is obtained by extracting a plant, in water as fine particles in the presence of a low-molecular-weight emulsifier. The acid value of the aqueous rosin emulsion is preferably 0 to 200 mg KOH / g, and more preferably 0 to 100 mg KOH / g. When the acid value of the aqueous rosin emulsion is within the above range, plate adhesion and blocking resistance tend to be improved. The softening point of the aqueous rosin emulsion is preferably 80 to 200°C. When the softening point of the aqueous rosin emulsion is within the above range, plate adhesion and blocking resistance tend to be improved.

[0055] Specific examples of aqueous rosin emulsions include Super Ester NS-121 and NS-100H manufactured by Arakawa Chemical Industries, Ltd.

[0056] <Aqueous medium> The aqueous flexographic ink of the present invention preferably contains an aqueous medium. The aqueous medium is preferably mainly composed of water, but a polar organic solvent can be used in addition to water. Specifically, the polar organic solvent may be an alcohol-based organic solvent, a glycol-based organic solvent, or the like, depending on the printing conditions (speed, plate depth, design, drying temperature). The content of the polar organic solvent is preferably 30% by mass or less based on the total amount of the ink. When the content of the polar organic solvent is within the above range, plate adhesion and stability over time tend to be improved.

[0057] Examples of the alcohol-based organic solvent include methanol, ethanol, propanol, isopropanol, isobutanol, normal butanol, tertiary butanol, hexanol, octanol, and decanol. Examples of glycol-based organic solvents 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.

[0058] <Additives> The aqueous flexographic ink of the present invention may contain various additives as needed, such as dispersants, waxes, extender pigments, leveling agents, antifoaming agents, and film-forming aids. Specifically, various additives can be added, such as hydrocarbon waxes such as polyethylene wax to improve abrasion resistance, inorganic fine particles and adhesive resins, extender pigments such as kaolin, aluminum hydroxide, clay and talc to improve drying properties and coating film hiding power, 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.

[0059] <Dispersant> The aqueous flexographic ink of the present invention preferably contains a dispersant as needed. The dispersant is not particularly limited, but it is preferable to use a surfactant such as a polyether-based dispersant or an acetylene glycol-based dispersant.

[0060] <Polyether-based dispersant> Suitable polyether-based dispersants include, but are not limited to, copolymerized polyethers. A copolymer of polypropylene glycol (propylene oxide) and polyethylene glycol (ethylene oxide) is preferred. When the polyether-based dispersant is the above-mentioned compound, plate adhesion and print density tend to be improved. When the polyether-based dispersant is a copolymer of polypropylene glycol (propylene oxide) and polyethylene glycol (ethylene oxide), the ratio of ethylene oxide to propylene oxide (EO / PO ratio) is preferably 50 / 50 to 99 / 1, more preferably 70 / 30 to 90 / 10. When the ratio of ethylene oxide to propylene oxide (EO / PO ratio) is within the above range, plate adhesion and print density tend to be improved. The weight-average molecular weight of the polyether-based dispersant is preferably 500 to 30,000, more preferably 5,000 to 15,000. When the weight average molecular weight of the polyether-based dispersant is within the above range, plate-holding resistance and print density tend to be improved. The cloud point of the polyether-based dispersant is preferably 50 to 130° C., and more preferably 70 to 110° C. When the cloud point of the polyether-based dispersant is within the above range, plate-holding resistance and print density tend to be improved.

[0061] <Acetylene-based dispersant> The acetylene-based dispersant is a nonionic compound having an acetylene group, and a preferred form is an acetylene glycol-based compound having ethylene oxide and / or propylene oxide. When the acetylene-based dispersant is the above-mentioned compound, plate adhesion and print density tend to be improved. As the acetylene glycol-based compound, the Surfynol series (manufactured by Air Products Co., Ltd.) is commercially available. The acetylene-based dispersant preferably has an HLB value in the range of 1 to 17, more preferably in the range of 3 to 10, and even more preferably in the range of 4 to 8. When the HLB value of the acetylene-based dispersant is in the above range, plate adhesion resistance and stability over time are improved.

[0062] The dispersant content is preferably in the range of 0.1 to 10% by mass, more preferably 1 to 8% by mass, of the total mass of the ink. When the dispersant content is in the above range, plate adhesion and print density tend to be improved. The solid content ratio of the dispersant to the water-soluble styrene-maleic acid resin is preferably 1:99 to 50:50, and more preferably 10:90 to 30:70. When the solid content ratio of the dispersant to the water-soluble styrene-maleic acid resin is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved.

[0063] <Hydrocarbon wax> The hydrocarbon wax may be a known wax such as polyethylene wax, Fischer-Tropsch wax, or paraffin wax. Among these, polyethylene wax and / or Fischer-Tropsch wax are preferred, and polyethylene wax is more preferred. The hardness (penetration) of the hydrocarbon wax at 25°C as specified in JIS K2207 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 the hardness (penetration) of the hydrocarbon wax at 25°C as specified in JIS K2207 is within the above range, blocking resistance tends to be improved. The density of the hydrocarbon wax at 23°C as specified in JIS K7112 (Method B) is 900 to 990 kg / m 3 It is preferable that the density is 925 to 990 kg / m 3 It is more preferable that the density at 23°C of the hydrocarbon wax as specified in JIS K7112 (Method B) is within the above range, the blocking resistance tends to be improved. The melting point of the hydrocarbon wax as measured by DSC is preferably 90 to 150°C, more preferably 100 to 125°C. When the melting point of the hydrocarbon wax as measured by DSC is within the above range, the blocking resistance tends to be improved. The melting point of the hydrocarbon wax refers to the melting point at 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 as measured by laser diffraction / light scattering.

[0064] The content of the hydrocarbon wax in the aqueous 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 the content of the hydrocarbon wax is within the above range, blocking resistance tends to be improved.

[0065] <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 (Method B). 3 The polyethylene wax preferably has a melt viscosity of 50 to 8000 mPa·s at 140°C measured in accordance with JIS K6862. 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 of 90 to 150°C, more preferably 100 to 125°C, as measured by DSC.

[0066] <Fischer-Tropsch wax> Fischer-Tropsch wax is a wax produced using carbon monoxide and hydrogen as raw materials by the Fischer-Tropsch process, and consists of a nearly saturated, unbranched, linear molecular structure. This linear structure gives it a high melting point, low viscosity, and hardness. Fischer-Tropsch wax shows almost no deterioration even when exposed to heat for long periods of time, and exhibits extremely high thermal stability. Fischer-Tropsch wax preferably has a number average molecular weight of 400 to 2000. Fischer-Tropsch wax also has a density at 23°C specified in JIS K7112 (Method B) of 925 to 990 kg / m 3 Preferably, the Fischer-Tropsch wax has an acid value of 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.

[0067] <Water-based flexographic ink manufacturing method> The method for producing an aqueous flexo ink of the present invention is a method for producing an aqueous flexo ink containing a colorant, an aqueous acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, and is characterized in that it includes a dispersing step of dispersing a mixed liquid containing the colorant, the aqueous medium, and the water-soluble styrene-maleic acid resin into beads to obtain a dispersion, and an adding step of adding the aqueous acrylic resin (A) to the dispersion, and the content of the colorant is 20% by mass or more in 100% by mass of the aqueous flexo ink.

[0068] <Dispersion process> In the dispersion step, the colorant, styrene-maleic acid resin, and water are mixed by stirring, and then the pigment is dispersed using a known bead disperser, such as a Mighty Mill (MHG-5) manufactured by Inoue Seisakusho Co., Ltd. In the dispersion step, the components described above in the <Water-based flexographic ink>, such as the aqueous acrylic resin (A) and dispersant, may be added. In the dispersion step, the solid content ratio of the colorant to the styrene-maleic acid resin is preferably 60:40 to 99:1, and more preferably 80:20 to 95:5. When the solid content ratio of the colorant to the styrene-maleic acid resin is within the above range, plate adhesion, print density, and blocking resistance are improved.

[0069] <Addition process> The aqueous acrylic resin (A) is added to the dispersion obtained in the above-mentioned <Dispersion Step>, and the mixture is mixed and stirred. In the addition step, various components described in the above-mentioned <Water-Based Flexographic Ink> can also be added. A known mixer, such as a Homodisper manufactured by Primix Corporation, can be used for the mixing and stirring. In the addition step, the solids ratio of the colorant to the aqueous acrylic resin (A) is preferably 55:45 to 95:5, and more preferably 65:35 to 85:15. When the solids ratio of the colorant to the aqueous acrylic resin (A) is within the above range, plate adhesion, print density, and blocking resistance tend to be improved. In the addition step, the solids ratio of the aqueous acrylic resin (A) to the water-soluble styrene-maleic acid resin is preferably 55:45 to 95:5, and more preferably 65:35 to 85:15. When the solid content ratio of the aqueous acrylic resin (A) to the water-soluble styrene-maleic acid resin is within the above range, plate adhesion, stability over time, print density, and blocking resistance tend to be improved.

[0070] (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 surface of the anilox roll with a doctor blade. The ink is then passed through a resin plate and finally printed onto a substrate. When the aqueous flexographic ink of the present invention is printed using the flexographic printing method, a printed product with excellent aesthetic appeal can be obtained even on paper substrates with a rough surface.

[0071] (Flexographic printing method; Anilox roll) The anilox roll used in the flexographic printing method of the present invention for producing a flexographic printed product can be a ceramic anilox roll with engraved cells, a chrome-plated anilox roll, or the like. The cell shape can be a honeycomb pattern, a diamond pattern, a helical pattern, or any other pattern. The role of the anilox roll is to receive a uniform, fixed amount of ink supplied from the doctor chamber (or fountain roll) 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.

[0072] (Flexographic printing method; Flexographic plate) The flexographic printing plate used in the method for producing a flexographic printed product of the present invention may be a photosensitive resin plate that utilizes ultraviolet curing with 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.

[0073] (Flexographic printing method; printing machine) Flexographic printing presses include CI type multicolor flexographic printing presses and unit type multicolor flexographic printing presses, and ink supply systems include chamber systems and two-roll systems, and any suitable printing press can be used. The printing speed is preferably 50 to 500 m / min, and more preferably 100 to 300 m / min.

[0074] <Printed matter having a printing layer formed with water-based flexographic ink> Examples of methods for producing printed matter having a printing layer formed with an aqueous flexographic ink include printing on the surface of paper or resin, particularly paper containers such as paper cups and paper plates, paper containers whose surfaces are coated with a resin layer, thin paper for food packaging, or materials made from these materials, 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.

[0075] <Base material> Examples of substrates for printing (printed materials) include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and nylon, cellophane, paper, and aluminum foil, as well as films and sheets made of composite materials of these. In the present invention, paper substrates are particularly preferred. Paper substrates are preferably 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. The basis weight of the paper substrate is 30 to 300 g / m 2 It is preferable that the density is 50 to 200 g / m 2 It is more preferable that: [Example]

[0076] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the present invention, parts and % represent parts by mass and % by mass unless otherwise noted. Furthermore, "NV." represents the mass % of non-volatile content.

[0077] <<Measurement of hydroxyl value>> In the present application, the hydroxyl value is the number of mg of potassium hydroxide required to acetylate the hydroxyl groups contained in 1 g of resin solid content and neutralize the acetic acid bonded to the hydroxyl groups, and is measured in accordance with JIS K0070.

[0078] <<Acid value measurement>> In the present invention, the acid value is the number of milligrams of potassium hydroxide required to neutralize the acidic groups contained in 1 g of resin solid content, and is measured in accordance with JIS K0070.

[0079] <<Measurement of Glass Transition Temperature>> In the present invention, the glass transition temperature was measured by simultaneous thermogravimetry and differential thermal analysis (TG-DTA) using a DTG-60A manufactured by Shimadzu Corporation. Specifically, the glass transition temperature was determined as the temperature at the inflection point in the baseline shift of the DTA curve under conditions of a nitrogen atmosphere, a measurement temperature range of −100 to 200°C, and a heating rate of 1°C / min.

[0080] <<Measurement of weight-average molecular weight>> In the present invention, the weight-average molecular weight can be determined as a converted molecular weight using polyethylene glycol as a standard substance, and the measuring equipment used was a GPC apparatus (Shodex GPC-401 manufactured by Showa Denko K.K.), a column (Shodex OHpak LB-805 manufactured by Showa Denko K.K.), and an RI (differential refractometer) as a detector. The eluent used was a 0.1N aqueous solution of NaNO3, and the column temperature was 35°C, and the flow rate was 3 mL / min.

[0081] <Measuring average particle size> In the present invention, the average particle size can be measured by a dynamic light scattering method using a particle size distribution measuring device, MT3300EXII manufactured by MicrotracMRB, in water in accordance with JIS Z8825-2013.

[0082] <<Method for calculating the solid mass content of biomass-derived components>> In the present invention, the biomass-derived component refers to an aqueous acrylic resin with added polysaccharides, polysaccharides, aqueous rosin resin, etc., and the solid mass content thereof can be calculated using the following (Equation 1). The solid mass content of the biomass-derived component is preferably 5% by mass or more, based on 100% by mass of the total solids content of the aqueous flexo ink. (Formula 1) Solid mass content of biomass-derived components (%) = (total solid mass of biomass components in water-based flexo ink (g)) / (total solid mass in water-based flexo ink (g)) × 100

[0083] Example 1: Preparation of water-based flexographic ink V1 A mixture of 16.6 parts water, 10 parts water-soluble styrene-maleic acid resin SM1, 30 parts colorant (phthalocyanine blue, manufactured by Ramdev Chemical Industries, product name: Ramafast Blue WP / L-143), 0.8 parts polyether-based dispersant (dispersant, polyoxyethylene polyoxypropylene glycol copolymer, weight average molecular weight 8,750, EO / PO ratio: 80 / 20, cloud point 90°C, solids content 100%) manufactured by Aoki Oil & Fat Industries Co., Ltd., and 0.2 parts acetylene diol was kneaded and dispersed in a bead mill, and then mixed with 5 parts urea-based compound (urea) and aqueous acrylic emulsion resin AC1 (styrene-acrylic resin with an average particle size of 150 μm containing 30% by mass of polysaccharide-derived components). 23 parts of resin emulsion, acid value 50 mgKOH / g, glass transition temperature 55°C, solids content 50% by mass, 10 parts of aqueous rosin resin (manufactured by Arakawa Chemical Industries, Ltd., rosin emulsion resin, anionic, softening point: 120°C, solids content 50%), 1.5 parts of nonionic surfactant (manufactured by Nippon Nyukazai Co., Ltd., polycyclic phenyl copolymer, solids content 60%), 0.2 parts of preservative (1,2-benzisothiazolin-3-one, solids content 20%), 1.5 parts of polyethylene wax (solids content 40%), 0.6 parts of silicone antifoaming agent (solids content 25%), and 0.6 parts of triethanolamine were added and mixed with stirring to obtain aqueous flexo ink V1.

[0084] <Examples 2 to 26, Comparative Examples 1 to 4> Preparation of Water-Based Flexographic Inks V2 to 30 Water-based flexographic inks V2 to 30 were obtained in the same manner as in Example 1, except that the raw materials and blending ratios shown in Table 1 were used. The properties of the raw materials used are as follows: Water-soluble styrene-maleic acid resin SM1 (acid value: 190 mg KOH / g, glass transition temperature: 83°C, weight average molecular weight: 12,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM2 (acid value: 180 mg KOH / g, glass transition temperature: 120°C, weight average molecular weight: 12,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM3 (acid value: 185 mg KOH / g, glass transition temperature: 30°C, weight average molecular weight: 12,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM4 (acid value: 190 mg KOH / g, glass transition temperature: 83°C, weight average molecular weight: 50,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM5 (acid value: 193 mg KOH / g, glass transition temperature: 83°C, weight average molecular weight: 2,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM6 (acid value: 100 mg KOH / g, glass transition temperature: 83°C, weight average molecular weight: 12,000, neutralizer: ammonia, solid content: 35%) Water-soluble styrene-maleic acid resin SM7 (acid value: 300 mg KOH / g, glass transition temperature: 83°C, weight average molecular weight: 12,000, neutralizer: ammonia, solid content: 35%) Styrene-maleic acid resin emulsion SM8 (acid value: 42 mg KOH / g, glass transition temperature: 91°C, neutralizer: ammonia, solid content: 35%) Water-based acrylic emulsion resin AC2 (styrene-acrylic resin emulsion with an average particle size of 150 μm, no polysaccharide-derived components, acid value: 50 mg KOH / g, glass transition temperature: 51°C, solid content: 50%) Water-based acrylic emulsion resin AC3 (styrene-acrylic resin emulsion with an average particle size of 150 μm, no polysaccharide-derived components, acid value: 200 mg KOH / g, glass transition temperature: 80°C, solid content: 35%) Water-soluble acrylic resin AC4 (acid value: 40 mg KOH / g, glass transition temperature: 79°C, weight average molecular weight: 10,000, neutralizer: ammonia, solid content: 35%) Acetylene-based dispersant (manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol-based, HLB value 8, solids content 100%) Acrylic dispersant (manufactured by Toagosei, polyacrylic acid type, 100% solids) Polysaccharides (maltodextrin aqueous solution, solids 50%)

[0085] (Evaluation of water-based flexographic ink) The resulting water-based flexographic inks V1 to 30 were evaluated as described below, and the evaluation results are shown in Tables 1-1 to 1-3.

[0086] (Stability over time) The inks obtained in the examples and comparative examples were stored in an oven at 40°C for one week, and then the ink viscosity was evaluated. The ink viscosity was evaluated at 25°C using a Zahn cup #4 (manufactured by Rigo Co., Ltd.). A: The change in viscosity between one week and before storage is less than 3 seconds. B: The change in viscosity between the ink after one week and before storage is 3 seconds or more but less than 5 seconds. C: The change in viscosity between the ink after one week and before storage is 5 seconds or more but less than 7 seconds. D: The change in viscosity between the ink after one week and before storage is 7 seconds or more. The industrially applicable levels are rated as A, B and C.

[0087] (tangle resistance) The inks obtained in the examples and comparative examples were printed at a printing speed of 300 m / min for 2000 m, using unbleached kraft paper: kraft paper using unbleached kraft pulp (Nippon Paper Industries Co., Ltd., unglazed kraft paper K, basis weight 70 g / m 2 ) The plate entanglement in the 1% halftone dot area of ​​the printed matter obtained by flexographic printing was visually observed and evaluated according to the following criteria. Evaluation Criteria A: There is no thickening of the 1% halftone dots and a clear image is formed. B: The 1% halftone dots are slightly thickened and the halftone dots are not connected. C: 1% The shape of the halftone dots is distorted and some dot bridging is observed. D: 1% The shape of the halftone dots is distorted and dot bridges are clearly visible. The industrially applicable levels are rated as A, B and C.

[0088] (Print density) The inks obtained in the examples and comparative examples were printed on unbleached kraft paper (unbleached kraft paper made by Nippon Paper Industries Co., Ltd., unglazed kraft paper with a basis weight of 70 g / m) using a Flexiproof printing machine. 2 The color was developed on the surface of the ink, a coating was formed, and the print density (color development) was evaluated using a colorimeter. A PANTONE X-RiteeXact spectrophotometer was used for the measurements. 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. * , a * , b * In addition, 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 (2). Equation (2)ΔE * ab =[(ΔL * ) 2 +(Δa * ) 2 +(Δb * ) 2 ] 1 / 2 Evaluation Criteria A:ΔE * ab is less than 0.4. B:ΔE * ab is greater than or equal to 0.4 and less than 0.8. C:ΔE * ab is greater than or equal to 0.8 and less than 1.6. D:ΔE * ab is 1.6 or more The industrially applicable levels are rated as A, B and C.

[0089] (blocking resistance) The inks obtained in the examples and comparative examples were printed on a K liner (basis weight: 250 g / m) using a Flexiproof printing machine. 2) and dried at room temperature for 24 hours to create a printed matter, which was then cut into two 40mm square pieces. The water-based flexographic ink coated surfaces of the two pieces were placed together and pressed at a temperature of 40°C and a load of 100kg / cm using a small heat press machine H30-10D manufactured by AS ONE Corporation. 2 After leaving the printed matter to stand for 12 hours under the pressure conditions (meaning a significantly excessive load), the two overlapping printed matter sheets were peeled away from each other, and the exposed state of the K liner was visually observed and evaluated according to the following criteria. Evaluation Criteria A: The exposed area percentage of the K liner surface is less than 1%. B: The exposed area percentage of the K liner surface is 1% or more and less than 10%. C: The exposed area percentage of the K liner surface is 10% or more and less than 30%. D: The exposed area percentage of the K liner surface is 30% or more. The industrially applicable levels are rated as A, B and C.

[0090] [Table 1-1]

[0091] [Table 1-2]

[0092] [Table 1-3]

[0093] From the above results, Comparative Example 1 had poor print density and blocking resistance because the colorant content was less than 20% by mass. Comparative Example 2 contained a water-soluble styrene-maleic acid resin but no aqueous acrylic resin (A), so it had poor print density and blocking resistance. Comparative Example 3 contained a styrene-maleic acid resin emulsion but no water-soluble styrene-maleic acid resin, so it had poor plate holding properties and print density. Comparative Example 4 contained an aqueous acrylic resin (A) but no water-soluble styrene-maleic acid resin, so it had poor plate holding properties, stability over time, and print density. On the other hand, in the examples, the inks contained a colorant, an aqueous acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, and the amount of colorant in the aqueous flexographic ink was 20% by mass or more, and therefore the inks exhibited good plate adhesion, stability during printing, print density, and blocking resistance.

Claims

1. An aqueous flexographic ink comprising a colorant, an aqueous acrylic resin (A), an aqueous medium, and a water-soluble styrene-maleic acid resin, The water-based flexographic ink has a content of the colorant of 20% by mass or more relative to 100% by mass of the water-based flexographic ink.

2. 2. The water-based flexographic ink according to claim 1, wherein the solids mass ratio of the colorant to the water-soluble styrene-maleic acid resin is 60:40 to 99:

1.

3. The water-based flexographic ink according to claim 1 or 2, further comprising a urea 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.]

4. 4. The water-based flexographic ink according to claim 3, wherein the solid content mass ratio of the urea compound represented by the general formula (1) to the water-soluble styrene-maleic acid resin is 40:60 to 80:

20.

5. The water-based flexographic ink according to claim 1 or 2, wherein the water-based acrylic resin (A) comprises a water-based acrylic resin having a polysaccharide added thereto.

6. The water-based flexographic ink according to claim 1 or 2, further comprising a polysaccharide and / or an aqueous rosin resin.

7. 3. The water-based flexo ink according to claim 1, wherein the solid mass content of the biomass-derived component is 5% by mass or more relative to 100% by mass of the total solid content of the water-based flexo ink.

8. 3. The water-based flexographic ink according to claim 1, wherein the colorant does not contain titanium oxide.

9. 3. The water-based flexographic ink according to claim 1, further comprising a dispersant, wherein the dispersant is a polyether-based dispersant and / or an acetylene-based dispersant.

10. The water-based flexographic ink according to claim 1 or 2, which is for use in paper packaging materials.

11. A printed matter having a printed layer formed on a substrate using the aqueous flexographic ink according to claim 1 or 2.

12. A method for producing an aqueous flexographic ink, comprising: a colorant; an aqueous acrylic resin (A); an aqueous medium; and a water-soluble styrene-maleic acid resin, the method comprising: a dispersing step of dispersing a mixed liquid containing the colorant, the aqueous medium, and the water-soluble styrene-maleic acid resin with beads to obtain a dispersion; an addition step of adding an aqueous acrylic resin (A) to the dispersion, a content of the colorant in the aqueous flexographic ink is 20% by mass or more based on 100% by mass of the aqueous flexographic ink.

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