Aqueous flexographic ink

Abstract

To provide an aqueous flexographic ink capable of realizing excellent plate cleaning properties, high resolubility, and stability over time, and further having superior water rub resistance required for aqueous flexographic inks.SOLUTION: An aqueous flexographic ink, comprising an emulsion-type resin (A) having a core layer and a shell layer, wherein the shell layer contains a rosin resin and / or a polysaccharide, or the emulsion-type resin (A) has a span value of 5 or less as represented by the following formula (1): span value=(D90-D10) / D50.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based flexographic ink and a printed matter using 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 a low ink coverage. When the ink coverage is low, the ink film dries easily on the plate, resulting in the problem of difficulty in removing stains from printing press equipment such as the flexographic plate and the anilox roll. In particular, aqueous flexographic ink compositions containing aqueous acrylic resins significantly deteriorate the plate washability of flexographic plates due to the solubility of the resin. Furthermore, aqueous flexographic ink compositions generally require resolubility, stability over time, and water abrasion resistance, and achieving these properties while also maintaining plate washability is a challenge.

[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, there is no description that the rosin-based resin emulsion has a core-shell structure, and there is a concern that the rosin-based resin emulsion may have insufficient solubility in water. Patent Document 2 discloses an aqueous printing ink composition containing a core-shell structured emulsion resin with an average particle size of 30 to 200 nm, which has an intermediate layer between the core layer and the shell layer and which contains a component obtained from a biomass-derived raw material. However, since the plate cleaning test is evaluated by wiping off the ink coating film that has been swollen with water, there is concern that the ink composition may not have sufficient solubility in water. Patent Documents 3 and 4 disclose water-based flexographic inks that use a composite emulsion of styrene acrylic and polysaccharide. However, there are concerns that the inks described in Patent Documents 3 and 4 also have insufficient solubility in water. Furthermore, Patent Documents 1 to 4 do not conduct any evaluation of stability over time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-108529 [Patent Document 2] Patent Publication No. 2021-107495 [Patent Document 3] Japanese Patent Publication No. 2021-167377 [Patent Document 4] Japanese 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 realizes excellent plate washability, resolubility, and stability over time, and further has excellent water-rubbing resistance, which is required of a water-based flexographic ink. [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 packaging material described below, and have thus completed the present invention.

[0007] That is, the present invention provides a water-based flexographic ink containing an emulsion-type resin (A) having a core layer and a shell layer, The present invention relates to a water-based flexographic ink, wherein the shell layer comprises a rosin resin and / or a polysaccharide.

[0008] The present invention also relates to the above water-based flexographic ink, wherein the emulsion resin (A) has a span value represented by the following formula (1) of 5 or less. Formula (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of emulsion-type resin (A) D50: The cumulative 50% diameter of the volume-based particle size distribution obtained by laser analysis particle size distribution measurement of emulsion-type resin (A) D90: Cumulative 90% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of emulsion-type resin (A)

[0009] The present invention also relates to the above-mentioned water-based flexographic ink, which further contains an extender pigment.

[0010] The present invention also relates to the above-mentioned water-based flexographic ink, wherein the extender pigment comprises at least one selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, kaolin clay, and silica.

[0011] The present invention also relates to the above water-based flexographic ink, wherein the mass ratio of the emulsion-type resin (A) to the extender pigment is 85:15 to 45:55.

[0012] The present invention also relates to the above-mentioned water-based flexographic ink, which further contains a urea compound represented by the following general formula (2): General formula (2) JPEG2025151333000001.jpg2649 [In general formula (2), 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.]

[0013] The present invention also relates to the above water-based flexographic ink, wherein the total mass of the rosin resin and polysaccharide contained in the emulsion resin (A) is 10 to 60 mass % relative to 100 mass % of the emulsion resin (A).

[0014] The present invention also relates to the above-mentioned water-based flexographic ink, which further contains a water-soluble resin, and the water-soluble resin is at least one selected from the group consisting of a water-soluble acrylic resin, a water-soluble rosin resin, and a water-soluble polysaccharide.

[0015] The present invention also relates to a printed matter having a printed layer formed on a substrate using the above-mentioned water-based flexographic ink. [Effects of the Invention]

[0016] The present invention makes it possible to provide a water-based flexographic ink that is excellent in plate washability, resolubility, stability over time, and water abrasion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0017] The water-based flexographic ink of the present invention will be described in detail below.

[0018] [Water-based flexographic ink] The present invention provides a water-based flexographic ink containing an emulsion-type resin (A) having a core layer and a shell layer, wherein the shell layer contains a rosin resin and / or a polysaccharide. The use of the emulsion-type resin (A) having a core layer and a shell layer improves the compatibility with solvents, resulting in improved plate washability, resolubility, and stability over time. Furthermore, the improved film-forming properties result in good water-based rub resistance.

[0019] (Emulsion-type resin (A) having a core layer and a shell layer) The emulsion-type resin (A) having a core layer and a shell layer in the present invention refers to a resin that is insoluble or slightly soluble in an aqueous system but whose dispersion is stabilized with a surfactant or the like. The weight-average molecular weight of the emulsion-type resin (A) is preferably 1,500 to 1,500,000, more preferably 3,000 to 1,200,000, and even more preferably 5,000 to 1,000,000. When the weight-average molecular weight is within the above range, plate washability, resolubility, and water-rubbing resistance are improved. The glass transition temperature (Tg) of the emulsion-type resin (A) is preferably -40°C to 120°C, more preferably -10 to 100°C, and even more preferably 0 to 90°C. When the weight-average molecular weight is within the above range, plate washability, resolubility, and water-rubbing resistance are improved. The solids content of the emulsion-type resin (A) is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 10% by mass, based on 100% by mass of the aqueous flexo ink. When the content is within the above range, the plate washability, resolubility, and water abrasion resistance are improved.

[0020] The cumulative 50% (D50) of the volume-based particle size distribution of the emulsion resin (A) obtained by laser analysis particle size distribution measurement is preferably 20 to 1,500 nm, more preferably 30 to 700 nm, and even more preferably 50 to 300 nm. When the D50 is within the above range, the plate cleanability, resolubility, and stability over time are improved. The cumulative 10% (D10) of the volume-based particle size distribution is preferably 5 to 1,000 nm, more preferably 10 to 500 nm, and even more preferably 15 to 200 nm. The cumulative 90% (D90) of the volume-based particle size distribution is preferably 100 to 3,000 nm, more preferably 130 to 1,000 nm, and even more preferably 150 to 400 nm. The span value of the emulsion resin (A) as represented by the following formula (1) is preferably 5 or less, more preferably 1 to 3, and even more preferably 1 to 2. When the content is within the above range, the plate washability, resolubility, and stability over time are improved. Formula (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of emulsion-type resin (A) D90: Cumulative 90% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of emulsion-type resin (A)

[0021] The emulsion-type resin (A) can be obtained by a known synthesis method such as emulsion polymerization or solution polymerization. For example, it can be obtained by emulsion polymerization, in which a styrene monomer or an acrylic monomer is dropped into water containing a polysaccharide or a rosin resin, and a polymerization reaction is carried out. In particular, by appropriately selecting the reaction temperature, the monomer dropping rate, the stirring rate, and the synthesis raw materials such as the polysaccharide, the rosin resin, the styrene monomer, and the acrylic monomer, and controlling the reaction rate to be slow, an emulsion-type resin (A) that satisfies the above-mentioned span value can be obtained. The polymerization reaction is preferably carried out at a reaction temperature of 50 to 100°C, the monomer dropping rate during the polymerization reaction is preferably 0.1 to 5 mass% / min for 100 mass% of the dropped monomer, and the stirring speed during the polymerization reaction is preferably 50 to 1000 rpm. The polysaccharide is not particularly limited, but examples thereof include maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, and starch derivatives. The rosin resin is not particularly limited, but is preferably a rosin ester such as maleated rosin or fumarated rosin, or a rosin derivative such as acrylated rosin or hydrogenated rosin. As the styrene monomer, styrene, α-methylstyrene, β-methylstyrene, etc. are preferred. Suitable examples of acrylic monomers include acrylic acid esters and methacrylic acid esters. For example, 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. Preferred examples of methacrylic acid esters include carboxylic acid-containing monomers such as 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, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, as well as anhydrides and half esters thereof.

[0022] The emulsion resin (A) having the core layer and the shell layer preferably has an acid group, and the acid group is preferably neutralized with a basic compound, such as an amine compound or an alkali metal. 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.

[0023] (Core layer of emulsion-type resin (A)) The core layer of the emulsion type resin (A) preferably contains a polymer of a styrene monomer and / or an acrylic monomer. Examples of styrene monomers constituting the core layer include styrene, α-methylstyrene, and β-methylstyrene. These may be used alone or in combination of two or more. Among these, it is preferable that the styrene monomer contains α-methylstyrene. Suitable acrylic monomers constituting the core layer include acrylic acid esters and methacrylic acid esters. For example, 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. For example, 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. These may be used alone or in combination of two or more. Carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, as well as their anhydrides and half esters, can also be used. These can be used alone or in combination of two or more. 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.

[0024] The content of the styrene monomer and / or acrylic monomer polymer in the core layer of the emulsion type resin (A) is preferably 50% by mass or more, more preferably 70% by mass or more, and preferably 90% by mass or more, based on 100% by mass of the core layer. The core layer of the emulsion type resin (A) may contain a polysaccharide and / or a rosin resin, which will be described later.

[0025] (Shell layer of emulsion-type resin (A)) The shell layer of the emulsion-type resin (A) contains a rosin resin and / or a polysaccharide.

[0026] (Polysaccharides contained in the shell layer of emulsion-type resin (A)) The polysaccharide contained in the shell layer of the emulsion-type resin (A) 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, and more preferably, starch.

[0027] (Rosin resin contained in the shell layer of emulsion-type resin (A)) The rosin resin contained in the shell layer of the emulsion-type resin (A) is not particularly limited, but examples thereof include rosin esters such as maleated rosin and fumarated rosin, and rosin derivatives such as acrylated rosin and hydrogenated rosin. The acid value of the rosin resin contained in the shell layer of the emulsion-type resin (A) is preferably 0 to 350 mg KOH / g. The softening point of the rosin resin is preferably 80 to 200°C.

[0028] The total mass of the rosin resin and polysaccharide contained in the emulsion resin (A) is preferably 10 to 60 mass %, more preferably 15 to 50 mass %, based on 100 mass % of the emulsion resin (A) in terms of solid content mass ratio. When it is in the above range, resolubility, stability over time, and water friction resistance are improved. The total mass of the rosin resin and polysaccharide contained in the shell layer of the emulsion resin (A) is preferably 40 to 90 mass %, more preferably 60 to 80 mass %, based on 100 mass % of the emulsion resin (A) in terms of solid content mass ratio. When it is in the above range, resolubility, stability over time, and water friction resistance are improved. The mass ratio of the core layer to the shell layer of the emulsion-type resin (A) is preferably 90:10 to 40:60, more preferably 80:20 to 45:55, and even more preferably 70:30 to 50:50. When the mass ratio is within the above range, plate washability, resolubility, stability over time, and water abrasion resistance are improved.

[0029] (Water-soluble resin) The water-based flexographic ink of the present invention can further improve its solubility in solvents and film-forming properties of the coating film by further containing a water-soluble resin other than the emulsion-type resin (A), thereby achieving even better plate washability, resolubility, stability over time, and water-rubbing resistance. The water-soluble resin in the present application is soluble or dispersible in water, and specific examples thereof include water-soluble acrylic resins, water-soluble rosin resins, and water-soluble polysaccharides.

[0030] (water-soluble acrylic resin) The water-soluble acrylic resin in the present invention refers to an acrylic resin obtained by solution polymerization of monomers including an acrylic monomer in an organic solvent, followed by desolvation and dissolving the solid resin in water or the like under alkaline conditions. The acrylic monomer constituting the water-soluble acrylic resin can be in the form of the (core layer of emulsion-type resin (A)) described above. The water-soluble acrylic resin can further contain a styrene monomer, and the styrene monomer can be in the form of the (core layer of emulsion-type resin (A)) described above. Furthermore, the water-soluble acrylic resin can be one to which a polysaccharide or a rosin resin is added, and the polysaccharide can be in the form of the (polysaccharide contained in the shell layer of emulsion-type resin (A)) described above, and the rosin resin can be in the form of the (rosin resin contained in the shell layer of emulsion-type resin (A)) described above. The water-soluble acrylic resin is preferably a styrene-acrylic copolymer resin, more preferably a styrene-acrylic copolymer resin with a polysaccharide added thereto and / or a styrene-acrylic copolymer resin with a rosin resin added thereto, and even more preferably a styrene-acrylic copolymer resin with a polysaccharide added thereto. The use of such resins can improve plate washability, resolubility, stability over time, and water abrasion resistance.

[0031] The weight-average molecular weight of the water-soluble acrylic resin is preferably 1,000 to 100,000, more preferably 1,500 to 50,000, and even more preferably 2,000 to 30,000. When it is within the above range, the plate cleanability, resolubility, stability over time, and water rub resistance are improved. The water-soluble acrylic resin preferably has an acid group, and when it has an acid group, the acid value is preferably 150 to 350 mgKOH / g, and more preferably 200 to 300 mgKOH / g. When it is within the above range, the plate cleanability, resolubility, and stability over time are improved.

[0032] (Water-soluble rosin resin (excluding acrylic resin with added rosin resin)) Water-soluble rosin resins do not include acrylic resins to which rosin resins have been added. Specific examples include rosin esters such as maleated rosin and fumarated rosin, and rosin derivatives such as hydrogenated rosin. Rosin-based resins with an acid value of 100 to 350 mgKOH / g can be used, with the acid value partially or completely neutralized with a basic compound and dissolved in water. Examples of basic compounds include ammonia, organic amines, and alkali metal hydroxides. Specific examples of organic amines include alkylamines such as diethylamine, triethylamine, and ethylenediamine, and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Among these, it is desirable to use a combination of volatile and nonvolatile basic compounds from the viewpoints of coating film properties and resolubility. The softening point of the water-soluble rosin is preferably 80 to 200°C. The water-soluble rosin resin preferably has a weight average molecular weight of 10,000 to 200,000.

[0033] Specific examples of the water-soluble rosin resin include Harima T-80 manufactured by Harima Chemicals Co., Ltd., Sizepine GF and Marquid 32-30WS manufactured by Arakawa Chemical Industries, Ltd.

[0034] (Water-soluble polysaccharides (excluding acrylic resins with polysaccharides added)) As the water-soluble polysaccharide, the form of the polysaccharide described above (the polysaccharide contained in the shell layer of the emulsion-type resin (A)) can be used, except for the acrylic resin to which the polysaccharide is added. The weight-average molecular weight of the water-soluble polysaccharide is preferably 10,000 to 5,000,000.

[0035] The content of the water-soluble resin is preferably 10 to 35% by mass, more preferably 15 to 30% by mass, and even more preferably 17 to 25% by mass, of the total mass of the ink. The solids mass ratio of the emulsion-type resin (A) to the water-soluble resin is preferably 80:20 to 30:70, and more preferably 60:40 to 40:60. When the ratio is within the above range, plate cleanability, resolubility, and stability over time are improved.

[0036] (solvent) The water-based flexographic ink of the present invention preferably contains a solvent. The main component of the solvent is preferably water, but polar organic solvents such as alcohol-based organic solvents and glycol-based organic solvents can be used in addition to water depending on the printing conditions (speed, plate depth, design, drying temperature). The content of the polar organic solvent is preferably 40% by mass or less based on the total mass of the ink. Here, in the present invention, "the main component is water" means that the content of water is the largest in the solvent. The amount of the solvent is preferably 20 to 80% by mass, and more preferably 40 to 70% by mass, based on 100% by mass of the aqueous flexographic ink.

[0037] 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.

[0038] (Pigments (excluding extender pigments)) Pigments used in the aqueous flexographic ink of the present invention can be those conventionally 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. 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 pigments is preferably 1 to 60% by mass of the total mass of the aqueous flexographic ink.

[0039] (extender pigment) The aqueous flexo ink of the present invention preferably contains a body pigment. By including the body pigment, the emulsion-type resin (A) is adsorbed onto the surface of the body pigment, thereby improving plate cleanability, resolubility, and stability over time. The content of the body pigment is preferably 0.1 to 10 mass %, more preferably 1 to 5 mass %, based on the total mass of the ink. When the content is within the above range, plate cleanability, resolubility, and stability over time are improved. Known body pigments can be used as the extender pigment, but it is preferable to include at least one selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, kaolin clay, and silica, more preferably at least one selected from the group consisting of barium sulfate, calcium carbonate, and silica, and even more preferably barium sulfate. When the above extender pigment is included, plate cleanability, resolubility, and stability over time are improved. The average particle size of the extender pigment, such as barium sulfate, is preferably 0.01 to 5 μm, more preferably 0.05 to 3 μm, and even more preferably 0.1 to 0.7 μm. When the average particle size is within the above range, the plate washability, resolubility, and stability over time are improved. Here, the average particle size refers to a value measured by electron microscopy, and can be measured, for example, by averaging the particle sizes of 10 randomly selected extender pigment particles using a field emission scanning electron microscope (JEOL JSM-7000F). The solid mass ratio of the emulsion resin (A) to the extender pigment is preferably 85:15 to 35:65, and more preferably 80:20 to 60:40. When it is in the above range, the plate cleanability and resolubility are improved.

[0040] (Urea-based compounds) The aqueous flexographic ink of the present invention preferably further contains a urea compound represented by the following general formula (2): By containing the urea compound, the urea compound and the emulsion-type resin (A) form a hydrogen-bond network, improving plate cleanability, resolubility, and stability over time. General formula (2) [ka] [In general formula (2), R 1 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.]

[0041] 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, with a hydroxy group being preferred. 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, with a methyl group and an ethyl group being preferred. 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. 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.

[0042] Examples of urea compounds represented by the general formula (2) 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.

[0043] The urea compound is preferably used in a range of 1 to 10% by mass, more preferably 3 to 8% by mass, of the total mass of the ink. Within this range, plate washability, resolubility, and stability over time are improved. Furthermore, the urea compound (B) preferably has a solubility in water at 25°C of 20% by mass or more, more preferably 30% by mass or more. Within this range, plate washability and stability over time are improved. The mass ratio of the urea compound to the emulsion-type resin (A) is preferably 10:90 to 75:25, more preferably 15:85 to 70:30, and even more preferably 20:80 to 60:40. When it is in the above range, the plate cleanability, resolubility, and stability over time are improved.

[0044] (additives) The aqueous flexographic ink of the present invention may contain various additives as needed, such as dispersants, waxes, tackifiers, leveling agents, antifoaming agents, and film-forming aids. Specifically, various additives may be added, such as hydrocarbon waxes such as polyethylene wax to improve water-friction resistance, tackifiers to improve water-friction resistance, leveling agents to improve leveling, antifoaming agents to impart antifoaming properties, basic compounds such as sodium hydroxide and potassium hydroxide to impart resolubility, and film-forming aids.

[0045] (dispersant) The aqueous flexographic ink of the present invention preferably contains a dispersant from the viewpoints of improving plate washability, resolubility, and stability over time. As the dispersant, it is preferable to use a surfactant such as a polyether compound or an acetylene glycol compound.

[0046] For example, polyether-based compounds are preferably copolymerized polyethers, 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. When it is within this range, the plate cleanability, resolubility, and stability over time are improved. The weight-average molecular weight is more preferably in the range of 1,000 to 5,000. Furthermore, the amount of ethylene oxide added is preferably 10 to 95 mass% of the total molecule, and more preferably 30 to 90 mass%. When it is within the above range, the plate cleanability, resolubility, and stability over time are improved. Acetylene glycol-based compounds are also preferred, and acetylene glycol-based compounds containing ethylene oxide and / or propylene oxide are preferred. As acetylene glycol-based compounds, the Surfynol series (manufactured by Air Products Co., Ltd.) is commercially available.

[0047] The dispersant is preferably used in the range of 0.1 to 10% by mass, more preferably 1 to 8% by mass, of the total mass of the ink, which improves plate washability, resolubility, and stability over time.

[0048] (hydrocarbon wax) Examples of hydrocarbon waxes include polyethylene wax and Fischer-Tropsch wax. 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 it is within the above range, the plate cleanability, redissolvability, and water abrasion resistance are 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 softening point of the hydrocarbon wax is 50 to 200°C, more preferably 90 to 130°C. When the softening point is within the above range, the plate cleanability, redissolution property, and water-rubbing resistance are improved. When the softening point is within the above range, the plate cleanability, redissolution property, and water-rubbing resistance are improved. When the softening point is within the above range, the melting point of the hydrocarbon wax measured by DSC is preferably 90 to 150°C, more preferably 100 to 125°C. When the softening point is within the above range, the plate cleanability, redissolution property, and water-rubbing resistance are 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. When the softening point is within the above range, the plate cleanability, redissolution property, and water-rubbing resistance are improved. The average particle size of the hydrocarbon wax refers to the D50 value measured by the laser diffraction / light scattering method.

[0049] The content of the hydrocarbon wax in the aqueous flexographic ink of the present invention is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on 100% by mass of the ink. When the content is within the above range, the plate cleanability, resolubility, and water abrasion resistance are improved.

[0050] (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.

[0051] 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 has a melting point of 90 to 130°C, more preferably 100 to 120°C, as measured by DSC.

[0052] (Method for manufacturing water-based flexographic ink) The method for producing the water-based flexo ink of the present invention will now be described. The water-based flexo ink of the present invention can be produced, for example, by stirring and mixing a solvent, pigment (excluding the extender pigment), extender pigment, dispersant, emulsion resin (A), water-soluble resin, etc., followed by dispersing the pigment using a mill such as a bead mill, pearl mill, sand mill, ball mill, attritor, or roll mill, and then adding predetermined materials and additives such as emulsion resin (A) and water-soluble resin, followed by stirring and mixing. It is preferable to use a bead mill for dispersing the pigment.

[0053] The viscosity of the water-based flexographic ink of the present invention is preferably 10 to 20 seconds at 25°C using Zahn cup No. 3.

[0054] [Method for producing a printed matter having a printed layer formed with aqueous 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.

[0055] (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. 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 a flexographic printing method, a printed product with excellent aesthetic appeal can be obtained even on a substrate with a rough surface such as paper.

[0056] (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.

[0057] (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.

[0058] (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 an appropriate printing press such as FlexiProop can be used. The printing speed is preferably 50 to 500 m / min, and more preferably 100 to 300 m / min.

[0059] (base material) Examples of printing substrates (printed materials) include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and nylon, cellophane, paper, aluminum foil, and films and sheets made from composite materials thereof, food packaging such as wrapping paper and 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 polyolefin resin coating on the surface, and paper products such as uncoated paper containers without a resin layer on the surface. In the present invention, paper substrates are particularly preferred. Paper substrates are preferably selected from uncoated paper, one-side gloss kraft paper with a treated surface, bleached kraft paper, unbleached kraft paper, liner paper, and the like. [Example]

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. In these examples, unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass." The numerical values ​​for the amounts of each material in the tables are also "parts by mass." The units for hydroxyl value and acid value are mgKOH / g.

[0061] (Particle size distribution measurement) The particle size distribution of the emulsion-type resin (A) was measured using water as the dispersion medium with a laser diffraction / scattering particle size distribution measuring device (Microtrac MT-3000EX(II) manufactured by Microtrac-Bell Corporation). From the volume frequency particle size distribution curve obtained, the cumulative 10% diameter of the particle size distribution (D10), median diameter (cumulative 50% diameter of the particle size distribution, D50), and cumulative 90% diameter of the particle size distribution (D90) were calculated, and the span value of the particle size distribution ((D90-D10) / D50) was calculated from the obtained values.

[0062] (Example 1) [Preparation of water-based flexographic ink S1] First, a mixture of the following raw materials was kneaded and dispersed in a bead mill. ·Wednesday: 28 parts ·PigmentBlack7: 18 copies Barium sulfate (Sakai Chemical Industry Co., Ltd., Variace B-35, average particle size 0.3 μm, solid content 100%): 4 parts ·Urea: 4 parts PEG-PPG (copolymer resin of polyethylene glycol (PEG) and polypropylene glycol (PPG), PEG / PPG=40 / 60, weight average molecular weight 2800, solid content 100%): 2.5 parts Acetylene glycol (100% solids): 0.5 parts Styrene acrylic resin solution SAC11: 17 parts Next, the following raw materials were further added and mixed by stirring to obtain a water-based flexographic ink S1. Styrene acrylic resin solution SAC 1:15 parts Styrene acrylic resin solution SAC10: 5 parts Polyethylene wax (average particle size 4 μm, softening point 110°C): 3 parts Nonionic surfactant (60% solids): 2 parts Triethanolamine: 1 part

[0063] (Examples 2 to 21, Comparative Examples 1 to 3) [Preparation of Water-Based Flexographic Inks S2 to S24] Water-based flexographic inks S2 to S24 were obtained in the same manner as in Example 1, except that the raw materials and formulations shown in Tables 2-1 and 2-2 were changed. In the tables, values ​​without units indicate parts, and blank spaces indicate no formulation. The various conditions for the emulsion-type resin (A) solution, emulsion-type resin solutions other than emulsion-type resin (A), and water-soluble resin solutions are as shown in Table 1.

[0064] [Table 1]

[0065] The other raw materials listed in Tables 2-1 and 2-2 are as follows: Calcium carbonate: average particle size 1μm, oil absorption 40ml / 100g ·Silica: Average particle size 4μm, oil absorption 200ml / 100g Magnesium carbonate: Konoshima Chemical Co., Ltd., Magthermo MS-S, average particle size 1.2 μm Kaolin clay: Engelhard UW90, average particle size 0.5 μm

[0066] (evaluation) The following evaluations were carried out using the water-based flexographic inks S1 to 24 and printed matter having a printed layer formed using the water-based flexographic inks S1 to 24. The evaluation results are shown in Tables 2-1 and 2-2.

[0067] (Plate cleaning ability) Water-based flexographic inks S1 to S24 were applied to flexographic resin plates using a bar coater (Miyya bar #4). The flexographic resin plates were then left to stand at 25°C and washed with water every 15 minutes, with the washout time being evaluated. <Evaluation criteria> 5: After washing with water 60 minutes after the coating has dried, 95% or more of the total area of ​​the flexographic resin plate is ink-free. 4: After rinsing with water 45 minutes after the coating has dried, the ink-free area of ​​the total area of ​​the flexographic resin plate is 95% or more, but after rinsing with water 60 minutes after the coating has dried, the ink-free area of ​​the total area of ​​the flexographic resin plate is less than 95%. 3: After rinsing with water 30 minutes after the coating dried, the ink-free area of ​​the total area of ​​the flexographic resin plate was 95% or more, but after rinsing with water 45 minutes after the coating dried, the ink-free area of ​​the total area of ​​the flexographic resin plate was less than 95%. 2: After rinsing with water 15 minutes after the coating dried, the ink-free area of ​​the total area of ​​the flexographic resin plate was 95% or more, but after rinsing with water 30 minutes after the coating dried, the ink-free area of ​​the total area of ​​the flexographic resin plate was less than 95%. 1: After washing with water 15 minutes after the coating has dried, the area of ​​the flexographic resin plate that is free of ink is less than 95% of the total area. The industrially applicable levels are rated 3, 4 and 5 above.

[0068] (Re-soluble) Water-based flexographic inks S1 to S24 were applied to a polyethylene terephthalate (PET) film (Toyobo E5100, 12 μm thick) that had been corona discharge-treated on one side using a bar coater (Miyya bar #4), and then left to stand at 25°C for 30 minutes to form a coating. The same water-based flexographic ink was then dropped onto the coating and wiped off. The area ratio of the ink coating area remaining on the substrate after wiping to the area of ​​the ink coating before wiping was then calculated. <Evaluation criteria> 5: The remaining ink film area ratio is less than 1% 4: The area ratio of remaining ink film is 1% or more but less than 5% 3: The remaining ink film area ratio is 5% or more but less than 10% 2: The remaining ink film area ratio is 10% or more but less than 30% 1: The remaining ink film area ratio is 30% or more The industrially applicable levels are rated 3, 4 and 5.

[0069] (Stability over time) First, the viscosity of each of the water-based flexographic inks S1 to 24 immediately after production was measured at 25°C using a Zahn Cup No. 4 at 25°C to obtain the ink viscosity before storage. Next, the water-based flexographic inks S1 to 24 were stored under the following storage conditions, and then the viscosity of each ink after storage under Condition 1 or Condition 2 was measured using a Zahn Cup No. 4 at 25°C to obtain the ink viscosity after storage under each condition. Next, for each ink, the absolute value of the difference between the ink viscosity after storage under Condition 1 or Condition 2 and the ink viscosity before storage was calculated, and the larger absolute value of the difference was taken as the viscosity change of the ink. The stability over time was evaluated based on the following criteria. <Storage conditions> Condition 1: Store in a refrigerator at 5°C for one week Condition 2: Store in a 40°C oven for one week <Evaluation criteria> 5: Viscosity change is less than 3 seconds 4: Viscosity change is 3 seconds or more but less than 5 seconds 3: Viscosity change is 5 seconds or more but less than 7 seconds 2: Viscosity change is 7 seconds or more but less than 10 seconds 1: Viscosity change exceeds 10 seconds The industrially applicable levels are rated 3, 4 and 5 above.

[0070] (Water friction resistance) Water-based flexographic inks S1 to 24 were printed at a printing speed of 50 m / min using Flexiproof (cell volume 13 cc) on unbleached kraft paper (kraft paper made from unbleached kraft pulp, Nippon Paper Industries Co., Ltd., unglazed kraft K, basis weight 120 g / m). 2 ) and left to stand at 25°C for 24 hours to form a coating. Next, a Gakushin-type rub fastness tester was used to test the 2.5 cm x 17 cm printed surface, with five drops of water dropped onto a Kanakin cloth (this was used as the base paper) and the water rub resistance was evaluated from the ratio of the exposed area of ​​the base paper after three back and forth strokes with a load of 200 g. Evaluation Criteria 5: The exposed area ratio of the base paper is less than 1%. 4: The exposed area ratio of the base paper is 1% or more and less than 5%. 3: The exposed area ratio of the base paper is 5% or more and less than 10%. 2: The exposed area ratio of the base paper is 10% or more and less than 20%. 1: The exposed area ratio of the base paper is 20% or more. The industrially applicable levels are rated 3, 4 and 5 above.

[0071] [Table 2-1]

[0072] [Table 2-2]

[0073] The above results show that Comparative Example 1, which did not contain a rosin resin and / or polysaccharides in the emulsion resin (A), had poor resolubility, plate cleanability, and stability over time. Comparative Example 2, which contained polysaccharides in the intermediate layer but did not contain a rosin resin and / or polysaccharides in the shell layer, had poor plate cleanability, resolubility, and stability over time. Comparative Example 3, which used an emulsion resin without a core layer or shell layer, had poor plate cleanability. On the other hand, Examples that had a core layer and a shell layer and in which the shell layer contained an emulsion resin (A) containing a rosin resin and / or polysaccharides had good resolubility, plate cleanability, stability over time, and water rub resistance.

Claims

1. An aqueous flexographic ink comprising an emulsion-type resin (A) having a core layer and a shell layer, The water-based flexographic ink, wherein the shell layer comprises a rosin resin and / or a polysaccharide.

2. 2. The water-based flexographic ink according to claim 1, wherein the emulsion resin (A) has a span value represented by the following formula (1) of 5 or less: Formula (1): Span value = (D90 - D10) / D50 D10: cumulative 10% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of the emulsion-type resin (A) D50: cumulative 50% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of the emulsion-type resin (A) D90: cumulative 90% diameter of the volume-based particle size distribution obtained by laser analytical particle size distribution measurement of the emulsion-type resin (A)

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

4. 4. The water-based flexographic ink according to claim 3, wherein the extender pigment comprises at least one selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, kaolin clay, and silica.

5. 4. The water-based flexographic ink according to claim 3, wherein the solids mass ratio of the emulsion-type resin (A) to the extender pigment is 85:15 to 35:

65.

6. The water-based flexographic ink according to claim 1 or 2, further comprising a urea compound represented by the following general formula (2): General formula (2) [In general formula (2), 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.]

7. 3. The water-based flexographic ink according to claim 1, wherein the total mass of the rosin resin and polysaccharide contained in the emulsion-type resin (A) is 10 to 60 mass % in terms of solid content mass ratio, relative to 100 mass % of the emulsion-type resin (A).

8. 3. The water-based flexographic ink according to claim 1, wherein the mass ratio of the core layer to the shell layer of the emulsion-type resin (A) is 90:10 to 40:

60.

9. 3. The water-based flexographic ink according to claim 1, further comprising a water-soluble resin, the water-soluble resin being at least one selected from the group consisting of a water-soluble acrylic resin, a water-soluble rosin resin, and a water-soluble polysaccharide.

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

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