JP7848596B2 - Aqueous flexographic ink composition containing a urea-based compound. - Google Patents

Description

This invention relates to an aqueous flexographic ink composition comprising an aqueous acrylic resin and a urea-based compound.

In recent years, there has been an increase in the use of high-fine-line anilox rolls and low ink application rates in water-based flexographic printing for packaging applications (Patent Document 1). When the ink application rate is low, the ink film dries more easily on the plate, resulting in difficulty in removing dirt from printing equipment such as flexographic plates and anilox rolls, making cleanability a challenge. In particular, with water-based flexographic ink compositions containing water-based acrylic resins, the cleanability of the flexographic plate is a significant issue due to the solubility of the resin. Furthermore, water-based flexographic ink compositions generally require high print density, resolubility, and bending resistance.

Patent Document 2 discloses an aqueous flexographic ink composition using a water-soluble acrylic resin and an aqueous acrylic resin emulsion as the binder resin. However, aqueous flexographic inks with good physical properties in the printed layer and high print density tend to have insufficient water resistance. This is thought to be related to the large amount of ammonia and other substances used to neutralize and make the aqueous resin water-soluble. On the other hand, for improved cleanability, the water solubility of the binder resin is desirable. However, amine compounds such as ammonia cannot be used in large quantities due to legal restrictions and therefore cannot be used as a means to improve the cleanability of the printing plate.

Patent documents 3 and 4 disclose inks that use an aqueous acrylic resin emulsion as a binder resin and contain urea or a urea derivative. However, the inks described in patent documents 3 and 4 had an insufficient balance of physical properties such as film drying speed and the bending resistance of printed materials.

Japanese Patent Publication No. 2021-167377 Japanese Patent Publication No. 2019-108529 Special Publication No. 6-503370 Special table 2012-506786 publication

The present invention aims to provide an aqueous flexographic ink composition that exhibits excellent flexographic printing suitability and physical properties of the printed layer (bending resistance, resolubility, and coating drying properties), as well as superior plate cleaning performance.

The inventors of this invention have discovered that the above problems can be solved by using the following aqueous flexographic ink composition, and have thus completed the present invention.

In other words, the present invention relates to an aqueous flexographic ink composition comprising an aqueous acrylic resin (A) and a urea-based compound (B),
The aqueous acrylic resin (A) comprises a water-soluble acrylic resin (a1) and an aqueous acrylic resin emulsion (a2).
The content of the aqueous acrylic resin (A) is 10 to 45% by mass of the total mass of the aqueous flexographic ink composition.
This invention relates to an aqueous flexographic ink composition in which the urea-based compound (B) is a compound represented by the following general formula (1).
General formula (1)

[In general formula (1), R ¹ represents an oxygen atom or a sulfur atom.
^R2 and ^R3 each independently represent a hydrogen atom, an optionally substituted C1-C4 alkyl group, or an optionally substituted C6-C9 aryl group.
However, ^R2 and ^R3 may form a ring via an alkylene group having 1 to 3 carbon atoms.

Furthermore, the present invention relates to the above-mentioned aqueous flexographic ink composition, wherein the content of urea-based compound (B) in the total mass of the aqueous flexographic ink composition is 1 to 10% by mass.

Furthermore, the present invention relates to the above-mentioned aqueous flexographic ink composition, wherein the mass ratio of the urea-based compound (B) to the aqueous acrylic resin (A) is 5:95 to 40:60.

Furthermore, the present invention relates to the above-mentioned aqueous flexographic ink composition, wherein the acid value of the water-soluble acrylic resin (a1) is 150 to 350 mg KOH/g.

Furthermore, the present invention relates to a printed material having a printed layer formed on a substrate using the above-described aqueous flexographic ink composition.

This invention makes it possible to provide an aqueous flexographic ink composition that exhibits excellent flexographic printing suitability and physical properties of the printed layer (bending resistance, resolubility, and coating drying properties), as well as superior plate cleaning performance.

The aqueous flexographic ink composition of the present invention will be described in detail below.

(Water-based acrylic resin (A))
In the present invention, aqueous acrylic resin (A) refers to an acrylic resin that is soluble or dispersible in water, and includes water-soluble acrylic resin (a1) and aqueous acrylic resin emulsion (a2).
Among water-soluble acrylic resins (a1), water-soluble styrene-acrylic copolymer resins are preferred, and among aqueous acrylic resin emulsions (a2), styrene-acrylic copolymer resin emulsions are preferred.

The content of the aqueous acrylic resin (A) is preferably 10 to 45% by mass, more preferably 11 to 40% by mass, and even more preferably 12 to 35% by mass, based on the total mass of the ink.

The weight-average molecular weight of the aqueous acrylic resin (A) is preferably 1,500 to 1,500,000, more preferably 5,000 to 1,000,000, and even more preferably 1,000 to 50,000.

(Water-soluble acrylic resin (a1))
In this invention, the water-soluble acrylic resin refers to an acrylic resin obtained by solution polymerization of monomers containing acrylic monomers in an organic solvent, followed by desolventization to dissolve the solid resin under alkaline conditions.

Suitable examples of the above-mentioned acrylic monomers include acrylic acid esters and methacrylic acid esters. For example, suitable 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 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.
In addition, carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, or their anhydrides and half-esters, can also be used.
These can be used individually, or two or more can be used in combination.

Among the above, it is preferable that the acrylic monomers include 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.

Furthermore, the water-soluble acrylic resin (a1) is preferably a water-soluble styrene-acrylic copolymer resin obtained by copolymerizing an acrylic monomer and a styrene monomer. Examples of constituent styrene monomers include styrene, α-methylstyrene, and β-methylstyrene. These may be used individually or in combination of two or more.
In particular, the styrene monomer preferably contains α-methylstyrene.

The water-soluble acrylic resin (a1) preferably has acidic groups, and if it does, its acid value is preferably 150 to 350 mg KOH/g, and more preferably 200 to 300 mg KOH/g. Having an acid value within the above range for the water-soluble acrylic resin (a1) improves the cleanability of the printing plates and anilox rolls.

(Water-based acrylic resin emulsion (a2))
In the present invention, the aqueous acrylic resin emulsion (a2) refers to an acrylic resin that is insoluble or sparingly soluble in water but is dispersed and stabilized by a surfactant or the like. The average particle size of the aqueous acrylic resin emulsion (a2) is preferably 10 to 500 nm, and more preferably 30 to 200 nm.

The aqueous acrylic resin emulsion (a2) preferably has acidic groups, and if it does, the acid value is preferably 30 to 150 mg KOH/g, and more preferably 40 to 100 mg KOH/g.

Furthermore, it is preferable that the acidic group in the aqueous acrylic emulsion (a2) having the acidic group is neutralized with a basic compound. Suitable examples of such basic compounds include amine compounds and alkali metals.

Examples of the above-mentioned amine compounds include ammonia; alkylamines such as diethylamine, triethylamine, and ethylenediamine; and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the above-mentioned alkali metals include sodium hydroxide and potassium hydroxide. These may be used individually or in combination of two or more.

Suitable acrylic monomers for the aqueous acrylic resin emulsion (a2) include acrylic acid esters and methacrylic acid esters. For example, suitable 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 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 individually or in combination of two or more.

Furthermore, carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, or their anhydrides and half-esters, can also be used. These may be used individually or in combination of two or more.

Among the above, it is preferable that the acrylic monomer 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.

Furthermore, the water-soluble acrylic resin is preferably a water-soluble styrene-acrylic copolymer resin, and examples of constituent styrene monomers include styrene, α-methylstyrene, and β-methylstyrene. These may be used individually or in combination of two or more. Among these, the styrene monomer preferably contains α-methylstyrene.

The solid content mass ratio of the aqueous acrylic resin (A) and aqueous acrylic resin emulsion (a2) described above is preferably 70:30 to 50:50, more preferably 65:35 to 50:50, and even more preferably 60:40 to 55:45. This is to improve the suitability for flexographic printing and the balance of physical properties of the printed layer. It is particularly effective in improving bending resistance and redissolvability.

(Liquid medium)
The aqueous flexographic ink composition of the present invention preferably contains a liquid medium. The main component of the liquid medium is preferably water, but in addition to water, a water-soluble organic solvent can be used. Specifically, depending on the printing conditions (speed, plate depth, design, drying temperature), it may contain an alcohol-based organic solvent, a glycol-based organic solvent, etc. The content of the water-soluble organic solvent is preferably 30% by mass or less of the total amount of ink.
In this invention, "the main component is water" means that water is the most abundant component in the liquid medium. Furthermore, a water-soluble organic solvent refers to a substance that is liquid at 25°C and has a solubility of 1% by mass or more in water at 25°C.

Examples of alcohol-based organic solvents include methanol, ethanol, propanol, isopropanol, isobutanol, n-butanol, tert-libutanol, 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, dipropyl 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 can be used individually, or two or more can be used in combination.

(Pigment)
Pigments used in the aqueous flexographic ink composition of the present invention can be those conventionally used in aqueous flexographic printing ink compositions. Specifically, examples of inorganic pigments include colored pigments such as titanium dioxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, carbon black, and graphite, as well as extender pigments such as calcium carbonate and barium titanate. 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 may be used individually or in combination of two or more.
The content of the above pigment is preferably 1 to 60% by mass of the total mass of the aqueous flexographic ink composition.

(Additives)
Various additives may be used in the aqueous flexographic ink composition of the present invention as needed. Examples include dispersants, waxes, extender pigments, leveling agents, defoaming agents, and film-forming aids.
Specifically, various additives can be added, such as a dispersion of wax resin fine particles including polyethylene wax to improve abrasion resistance, extender pigments such as calcium carbonate, kaolin, barium sulfate, aluminum hydroxide, clay, and talc to improve drying properties and film opacity, inorganic fine particles and adhesive resins (acrylic resin, vinyl acetate resin) to provide anti-slip properties, leveling agents to improve leveling properties, defoaming agents to provide anti-foaming properties, basic compounds such as sodium hydroxide and potassium hydroxide to provide resolubility, and film-forming aids.

(Dispersant)
The aqueous flexographic ink composition of the present invention may contain, as necessary, a dispersant in addition to the dispersant sometimes used to disperse the aqueous acrylic resin emulsion (a2). Preferably, a surfactant such as a polyether compound or an acetylene glycol compound is used as the dispersant.

For example, among polyether compounds, copolymerized polyethers are preferred, and are not limited to them, but compounds in which polypropylene glycol (propylene oxide) and polyethylene glycol (ethylene oxide) are copolymerized are preferred. The weight-average molecular weight of the polypropylene glycol-polyethylene glycol copolymer resin is preferably 500 to 30,000. A weight-average molecular weight greater than 500 improves pigment dispersibility, while a weight-average molecular weight less than 30,000 improves leveling properties. More preferably, the weight-average molecular weight is in the range of 1,000 to 5,000. Furthermore, the amount of ethylene oxide added is preferably 10 to 95% by mass of the total molecule. A higher amount of ethylene oxide added improves dispersion stability, while a lower amount than 95% improves water resistance and drying properties. From the viewpoint of achieving both dispersion stability and water resistance/drying properties, a weight-average molecular weight of 30 to 90% by mass is more preferable.

Acetylene glycol compounds are also preferred, and acetylene glycol compounds containing ethylene oxide and/or propylene oxide are particularly suitable. The Surfinol series (manufactured by Air Products Corporation) is a commercially available acetylene glycol compound.

The dispersant is preferably used in an amount of 0.1 to 10% by mass of the total ink mass, and more preferably in an amount of 1 to 8% by mass. This is to improve the gloss of the pigment and maintain blocking resistance.

(Urea compound (B))
The aqueous flexographic ink composition of the present invention contains a urea-based compound (B) represented by the following general formula (1). This suppresses drying on the printing plate and anilox roller, and improves the cleanability of the printing plate. This effect is thought to be due to the hydration of the urea-based compound (B) with water in the liquid medium of the aqueous flexographic ink composition.

General formula (1)

[In general formula (1), R ¹ represents an oxygen atom or a sulfur atom.
^R2 and ^R3 each independently represent a hydrogen atom, an optionally substituted C1-C4 alkyl group, or an optionally substituted C6-C9 aryl group.
However, ^R2 and ^R3 may form a ring via an alkylene group having 1 to 3 carbon atoms.

Examples of substituents in the C1-C4 alkyl groups and C6-C9 aryl groups, which may have substituents, include hydroxyl groups, amino groups, carboxyl groups, halogen atoms, cyano groups, thio groups, silyl groups, and nitro groups, with hydroxyl groups being preferred.

Examples of C1-C4 alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl groups, with methyl and ethyl groups being preferred.

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

Examples of alkylene groups having 1 to 3 carbon atoms include methylene, ethylene, and propylene groups, with ethylene being preferred.

Examples of urea-based compounds (B) represented by the general formula (1) above include urea, 2-hydroxyethylurea, thiourea, 1,3-dimethylurea, ethylene urea derivatives 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, with urea and 1,3-dimethylurea being more preferred. These may be used individually or in combination of two or more.

The urea-based compound (B) is preferably used in an amount of 1 to 10% by mass, and more preferably in an amount of 5 to 8% by mass, based on the total mass of the ink. Furthermore, the urea-based compound (B) is preferably soluble in water at 25°C at 20% by mass or more, and more preferably at 30% by mass or more, in order to suppress the drying of the ink film. The mass ratio of the urea-based compound (B) to the aqueous acrylic resin (A) is preferably 5:95 to 40:60, more preferably 10:90 to 30:70, and even more preferably 15:85 to 25:75.

(Method for producing aqueous flexographic ink composition)
The method for producing the aqueous flexographic ink composition of the present invention will now be described. The method for producing the aqueous flexographic ink composition of the present invention involves, for example, stirring and mixing water, pigment, dispersant, and water-soluble resin, then dispersing the pigment using various mixing machines, such as a bead mill, pearl mill, sand mill, ball mill, attritor, or roll mill, and finally adding and stirring predetermined materials and additives such as a resin emulsion, water-soluble resin, or rosin-based resin. It is preferable to use a bead mill for pigment dispersion.

(Flexographic printing method)
Examples of flexographic printing methods include the two-roll method, the doctor method, and the doctor chamber method. In both the doctor method and the doctor chamber method, the aqueous flexographic ink composition is supplied to an anilox roll on which cells are formed on the surface, and after a process in which excess aqueous flexographic ink on the surface of the anilox roll is scraped off by a doctor blade, the ink is finally printed on the substrate through a resin plate. When the aqueous flexographic ink composition of the present invention is printed using a flexographic printing method, a printed material with excellent aesthetic appeal can be obtained even on paper substrates with rough surfaces.

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

(Flexographic printing method; flexographic plate)
Examples of flexographic printing plates used in the manufacturing method of flexographic printed materials of the present invention include photosensitive resin plates that utilize ultraviolet curing by a UV light source or elastomer material plates that use a direct laser engraving method. Any type of sleeve or cushioning tape can be used to attach the plate. The screen ruling of the flexographic plate is preferably 80 to 200 lines/inch, and more preferably 125 to 175 lines/inch.

(Flexographic printing method; printing press)
Flexographic printing presses include CI-type multi-color flexographic printing presses and unit-type multi-color flexographic printing presses. Ink supply methods include chamber type and two-roll type, and an appropriate printing press can be used. The printing speed is preferably 50 to 500 m/min, and more preferably 100 to 300 m/min.

(Printed material having a printed layer formed with an aqueous flexographic ink composition)
Examples of methods for manufacturing printed materials having a printed layer formed with an aqueous flexographic ink composition include printing on the surface of paper or resin, particularly on paper containers such as paper cups and paper plates, or on paper containers whose surfaces are coated with a resin layer, thin paper for food packaging, or materials thereof, using the aqueous flexographic ink composition and a flexographic printing press.
In this case, the printed material may be any of the following: food packaging such as wrapping paper or paper bags; paper products such as paper containers having a resin layer such as polyolefin laminated to the surface; paper products such as paper containers having a resin coating layer such as polyolefin on the surface; or paper products such as uncoated paper containers that do not have a resin layer on the surface.

(Base material)
Examples of substrates (substrates for printing) include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and nylon, cellophane, paper, aluminum foil, or films and sheets made of composite materials thereof. In the present invention, paper substrates are particularly preferred. The paper substrate is preferably selected from uncoated paper, one-sided glossy kraft paper (where one side of the substrate is treated), bleached kraft paper, unbleached kraft paper, and the like.

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

(Acid value and hydroxyl value)
The calculation was performed according to JIS K0070.

(Example 1) [Preparation of aqueous flexographic ink composition S1]
A mixture of 28 parts water, 18 parts Pigment Black 7, 5 parts urea compound, 2 parts PEG-PPG (a copolymer resin of polyethylene glycol (PEG) and polypropylene glycol (PPG), weight-average molecular weight 2800; PEG:PPG = 40:60; solids content 100%), 1 part acetylene glycol (Surfinol SE manufactured by Nisshin Chemical Industry Co., Ltd., solids content 80%), and 15 parts water-soluble acrylic resin (acid value 240 mg KOH/g, solids content 28%) was kneaded and dispersed in a bead mill. Then, 27 parts of aqueous acrylic resin emulsion (hydroxyl acid value 50 mg KOH/g, solids content 47%), 3 parts polyethylene wax, and 1 part triethanolamine were added and stirred to obtain aqueous flexographic ink composition S1.

[Printing of water-based flexographic ink composition S1]
The aqueous flexographic ink composition S1 obtained above was printed on the surface of a substrate of unbleached kraft paper (Nippon Paper Industries Co., Ltd.'s double-sided kraft K, basis weight 70 g/ ^m² ) using a small flexi-purf printing press equipped with a 200 line/inch anilox roll and a solid plate made of photosensitive resin at a printing speed of 50 m/s to obtain a printed material.

(Examples 2-15) [Preparation of aqueous flexographic ink compositions S2-S15]
An aqueous flexographic ink composition was obtained in the same manner as in Example 1, except that the raw materials and formulations listed in Table 1 were changed. In the table, numbers without unit labels represent parts, and blank spaces indicate that an ingredient was not included in the formulation.

[Printing of water-based flexographic ink compositions S2 to S15]
The aqueous flexographic ink compositions S2 to S15 listed in Table 1 were printed in the same manner as in Example 1, and printed materials were obtained using a flexi-purifier printing machine.

(Comparative Examples 1-3) [Aqueous flexographic ink compositions T1-T3]
An aqueous flexographic ink composition was obtained in the same manner as in Example 1, except that the raw materials and formulations listed in Table 1 were changed. In the table, numbers without units represent parts, and blank spaces indicate that an ingredient was not included.

[Printing of water-based flexographic ink compositions T1 to T3]
The aqueous flexographic ink compositions T1 to T3 listed in Table 1 were printed in the same manner as in Example 1, and printed materials were obtained using a flexi-purifier printing machine.

(evaluation)
The following evaluations were performed using the inks and printed materials obtained in the above examples and comparative examples. The evaluation results are shown in Table 1.

(Bending resistance)
The inks obtained in the examples and comparative examples were applied to unbleached kraft paper (Nippon Paper Industries Co., Ltd.'s double-sided kraft K; basis weight 70 g/ ^m² ) using a flexible pulp printing press to form a colored coating and evaluate its bending resistance. The substrate was folded so that the printed side was on the inside, and then folded so that the printed side was on the outside, and the degree of cracking of the ink coating on the printed side was evaluated. The criteria are as follows.
5. No creases will form on the printed surface.
It has a bending resistance level that is between 4:5 and 3.
3. On the printed surface, cracks in the printed layer occur only at the fold.
It has a bending resistance level that is intermediate between 2:3 and 1.
1: Cracks or chips in the printed layer on the printed surface, excluding the fold lines.
The above ratings indicate levels of industrial applicability: 3, 4, and 5.

(Resolubility)
The inks obtained in the examples and comparative examples were applied to polyethylene terephthalate (PET) film (E5100, manufactured by Toyobo Co., Ltd.; 12 μm thick) that had been subjected to corona discharge treatment on one side using a bar coater, forming a colored coating film. The resolubility of the dried coating film in the same ink composition was then evaluated.
5. After wiping, the ratio of the ink coating surface area to the substrate is less than 1%.
4. After wiping, the ratio of the ink coating surface area to the substrate is 1% or more and less than 5%.
3. After wiping, the ratio of the ink coating surface area to the substrate is 5% or more and less than 10%.
2. After wiping, the ratio of the ink coating surface area to the substrate is 10% or more and less than 30%.
1. After wiping, the ratio of the ink coating surface area to the substrate is 30% or more.
The above ratings indicate levels of industrial applicability: 3, 4, and 5.

(paint film drying)
The inks obtained in the examples and comparative examples were spread onto flexographic resin plates using Miyabar (#4) to form a coating film, and the degree of ink drying was visually evaluated by touch after 1 minute at room temperature. The criteria are as follows.
5. The ratio of the ink coating surface area to the flexographic resin plate in the area touched by a finger is 30% or more.
4. In the area touched by a finger, the ratio of the ink coating surface area to the flexographic resin plate is 10% or more and less than 30%.
3. In the area touched by a finger, the ratio of the ink coating surface area to the flexographic resin plate is 5% or more but less than 10%.
2. In the area touched by a finger, the ratio of the ink coating surface area to the flexographic resin plate is 1% or more and less than 5%.
1: The ratio of ink coating surface area to flexographic resin plate in the area touched by a finger is less than 1%.
The above ratings indicate levels of industrial applicability: 3, 4, and 5.

(Printing plate cleanability)
The inks obtained in the examples and comparative examples were applied to polyethylene terephthalate (PET) film (E5100, manufactured by Toyobo Co., Ltd.; 12 μm thick) that had been treated with corona discharge on one side using a bar coater to form a coating film. Water was then dropped onto the dried coating film and wiped off, and the solubility of the dried coating film in water was evaluated to assess the cleanability of the printing plate. The criteria are as follows.
5. After wiping, the ratio of the ink coating surface area to the substrate is less than 1%.
4. After wiping, the ratio of the ink coating surface area to the substrate is 1% or more and less than 5%.
3. After wiping, the ratio of the ink coating surface area to the substrate is 5% or more and less than 10%.
2. After wiping, the ratio of the ink coating surface area to the substrate is 10% or more and less than 30%.
1. After wiping, the ratio of the ink coating surface area to the substrate is 30% or more.
The above ratings indicate levels of industrial applicability: 3, 4, and 5.

Based on these results, it was confirmed that the aqueous flexographic ink composition of the present invention exhibits excellent flexographic printability and physical properties of the printed layer (bending resistance, resolubility, and film drying properties), and also provides good plate cleaning.

Claims (4)

A water-based flexographic ink composition comprising a water-based acrylic resin (A) and a urea-based compound (B),
The aqueous acrylic resin (A) comprises a water-soluble acrylic resin (a1) and an aqueous acrylic resin emulsion (a2).
The content of the aqueous acrylic resin (A) is 10 to 45% by mass of the total mass of the aqueous flexographic ink composition.
The urea-based compound (B) is a compound represented by the following general formula (1),
An aqueous flexographic ink composition in which the content of the urea-based compound (B) in the total mass of the aqueous flexographic ink composition is 0.5 to 12% by mass .
General formula (1)

[In general formula (1), R ¹ represents an oxygen atom or a sulfur atom.
^R2 and ^R3 each independently represent a hydrogen atom, an optionally substituted C1-C4 alkyl group, or an optionally substituted C6-C9 aryl group.
However, ^R2 and ^R3 may form a ring via an alkylene group having 1 to 3 carbon atoms. The aqueous flexographic ink composition according to claim 1, wherein the mass ratio of the urea-based compound (B) to the aqueous acrylic resin (A) is 5:95 to 40:60. The aqueous flexographic ink composition according to claim 1, wherein the acid value of the water-soluble acrylic resin (a1) is 150 to 350 mg KOH/g. A printed article having a printed layer formed on a substrate using the aqueous flexographic ink composition described in any one of claims 1 to 3.