JP2023122667A - Aqueous ink composition - Google Patents

Abstract

To provide an aqueous ink composition which is excellent in stability with time, water resistance, and flexographic plate washing property, and prevents plate fog of a printed matter.SOLUTION: An aqueous ink composition contains an aqueous resin having an acid group, a pigment and water, wherein total concentration of magnesium ions and calcium ions in the ink composition is 95 mg/L or less. In the aqueous ink composition, pH is 7.5-10.5. In the aqueous ink composition, the aqueous resin having an acid group is an aqueous urethane resin and/or an aqueous acrylic resin.SELECTED DRAWING: None

Description

The present invention relates to aqueous ink compositions.

BACKGROUND ART Conventionally, water-based printing inks have been considered as a means of protecting the global environment, ensuring the safety and security of packaging materials, and responding to stricter regulations. Water-based ink has the following merits because the main component of the dispersion medium (volatile component) in the ink is water. (1) Compared to oil-based inks whose main volatile components are organic solvents, the amount of organic solvents (VOC) released into the atmosphere can be greatly reduced, and the working environment around the printing press can be improved. . (2) The amount of organic solvent remaining in printed matter can be reduced, and contamination of contents can be avoided. For these reasons, especially in gravure printing, where mass production is possible, expansion of applications and markets is expected.

The main problems with water-based inks in gravure printing described in Patent Documents 1 to 3 are the effect of printing on plastic films due to low water wettability, and the printing speed being suppressed due to low water drying properties. low print productivity due to Furthermore, the biggest problem is plate fogging due to the low lubricity of water. Plate fogging occurs when printing ink is supplied to a gravure cylinder on which cells are formed on the surface. This is a phenomenon in which the ink that cannot be sufficiently scraped off with the ink is transferred to the non-image area. Water-based inks with low lubricity tend to damage the doctor and flutter during scraping, generally resulting in poor plate fogging and failing to produce prints of sufficient quality. Lowering the printing speed and increasing the frequency of doctor blade replacement are effective countermeasures, but in the field of gravure printing, which has strengths in mass production, it leads to lower production efficiency and worsening profitability, so it is currently unacceptable. is.

JP-A-2002-178622 JP 2005-272587 A JP 2013-249401 A

An object of the present invention is to provide a water-based ink composition which is excellent in stability over time, water resistance, and flexographic plate washability, and which hardly causes plate fogging in printed matter.

The present inventors conducted extensive studies and found that the problem can be solved by using a water-based ink composition having the following composition, and completed the present invention.

The present invention provides an aqueous ink composition containing an aqueous resin having an acid group, a pigment, and water, wherein the total concentration of magnesium ions and calcium ions in the ink composition is 95 mg/L or less. Regarding the composition.

The present invention also relates to the above water-based ink composition, which has a pH of 7.5 to 10.5.

The present invention also relates to the water-based ink composition, wherein the water-based resin having an acid group is a water-based urethane resin and/or a water-based acrylic resin.

The present invention also relates to the aqueous ink composition, wherein the aqueous resin having acid groups has an acid value of 20 to 150 mgKOH/g.

The present invention also relates to the water-based ink composition, wherein the pigment is an organic pigment.

The present invention also relates to a printed material having a print layer formed of the water-based ink composition on the substrate 1 .

The present invention also relates to a laminate having a substrate 2 on the printed layer of the printed matter according to claim 6 .

The present invention also relates to a printing method, comprising forming a print layer on a substrate using the water-based ink composition according to any one of claims 1 to 5.

INDUSTRIAL APPLICABILITY According to the present invention, it has become possible to provide an aqueous ink composition which is excellent in stability over time, water resistance, and flexographic plate washability, and which hardly causes plate fogging in printed matter.

Preferred embodiments of the present invention will be described below, but the following are examples of embodiments of the present invention, and the present invention is not limited to these embodiments.

In this specification, "aqueous ink composition" may be referred to as "aqueous ink", "ink" or "printing ink", but they have the same meaning. The printed layer made of water-based ink is sometimes simply referred to as "printed layer", "ink layer" or "ink film", but they have the same meaning.

[Ion concentration]
In the present invention, an ink raw material having an acid group is made to have a high molecular weight by forming a pseudo-crosslinked structure with a specific divalent metal ion, and is insolubilized by disappearing the acid group that imparts solubility to the ink raw material. The point is to suppress Therefore, the total concentration of magnesium ions and calcium ions, which are divalent metal ions, is preferably as low as possible. It is more preferably 90 mg/L or less, still more preferably 85 mg/L or less, and particularly preferably 80 mg/L or less. Regarding the point that magnesium ions and calcium ions greatly contribute to the insolubilization, it is considered that, in addition to the experimental facts, the fact that magnesium ions and calcium ions are at the top in the Hofmeister sequence, which is the order of salting-out of proteins, also supports this.

[pH]
In the present invention, the pH value of the ink is preferably 7.5-10.5, more preferably 8.5-10.0. Within this range, plate fogging resistance and ink stability over time are improved. The pH value was measured using a pH meter (D-51T manufactured by Horiba, Ltd.).

[water]
The water-based ink composition of the present invention preferably contains water as a medium, and water is the main component in the medium. Here, that water is the main component means that the content of water is the largest in the liquid medium.
Water is classified into purified water, tap water, and industrial water. Examples of purified water include distilled water purified by cooling water vapor generated by boiling tap water, ion-exchanged water purified by passing tap water through a filter material made of a resin called ion-exchange resin, and reverse osmosis membrane ( RO water filtered using an RO membrane), and ultrapure water that is extremely close to the ethical pure water value that does not contain any impurities specified by the Japanese Pharmacopoeia. , lake water, reservoir water, groundwater, treated sewage water, or seawater. In order to keep the total concentration range of magnesium ions and calcium ions in the present invention, it is preferable to use purified water with a lower total concentration of magnesium ions and calcium ions, considering the contamination of ions from other raw materials. Even industrial water is preferably purified. Also, water other than the above methods and types can be used as long as the total concentration of magnesium ions and calcium ions is within the range of the present invention when the ink composition is prepared.

[Organic solvent]
Although the water-based ink composition of the present invention contains water as a medium, it may contain an organic solvent such as an alcoholic, ketone-based, or ester-based solvent. Solvents are preferred. Specifically, for example, methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, ethylene glycol, propylene glycol, diethylene glycol. Among them, n-propanol and/or isopropyl alcohol are preferred. These may be used alone or in combination of two or more. The content of the organic solvent in the concentrated ink at the time of manufacture and distribution is preferably 20% by mass or less, more preferably 10% by mass or less, in the total mass of the ink from the viewpoint of safety due to flammability. .

At the time of printing, the aqueous ink composition of the present invention is diluted with an aqueous medium so as to obtain a viscosity suitable for printing from a concentrated state at the time of production and distribution. In adjusting the dilution, it is preferable to use an organic solvent in addition to water in order to improve the wettability to plastic films and the drying property, which are problems of water-based inks. The organic solvent is preferably an organic solvent with a boiling point of 100° C. or lower, and more preferably contains an alcohol-based organic solvent with a boiling point of 100° C. or lower. Examples of alcohol-based organic solvents having a boiling point of 100° C. or less include methanol (boiling point 65° C.), ethanol (boiling point 78° C.), n-propanol (hereinafter referred to as NPA) (boiling point 97° C.), and isopropanol (hereinafter referred to as IPA). (boiling point 82° C.), 2-butanol (boiling point 99° C.), t-butanol (boiling point 83° C.). These may be used alone or in combination of two or more. The boiling point of the alcohol-based organic solvent is more preferably 70°C or higher and 100°C or lower. However, the type of alcohol-based organic solvent is not limited to these.

By including the alcohol-based organic solvent having a boiling point of 100°C or less as described above, the contents of these organic solvents and water in the ink film are reduced, and sufficient adhesion between the ink and the substrate is obtained, resulting in a laminate. It is possible to reduce the occurrence of troubles during post-processing such as.

The content of the alcohol-based organic solvent is preferably 3 to 35 mass% of the total mass of the ink during printing, more preferably 5 to 30 mass%, more preferably 8 to 25 mass% of the total mass of the ink during printing. % is more preferred. When the content of the alcohol-based organic solvent is within the above range, it is effective in terms of ink printing speed, transferability and leveling property.

The water-based ink composition of the present invention is suitable even when it contains 5% by mass or less of an organic solvent having a boiling point of over 100°C in the total mass of the ink during printing. organic solvents, glycol organic solvents, and glycol ether organic solvents are preferred. Examples of organic solvents with boiling points exceeding 100° C. include n-butanol, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether. , ethylene glycol mono-n-hexyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono-n-hexyl ether, propylene glycol, propylene glycol monomethyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, propylene glycol isobutyl ether, dipropylene glycol n-butyl ether, tri Propylene glycol n-butyl ether, propylene glycol phenyl ether, and dipropylene glycol dimethyl ether are preferred. These may be used alone or in combination of two or more.

[Aqueous resin]
In the present invention, the aqueous resin functions as a binder resin (binding resin) contained in the ink. The water-based resin should be able to be stably dispersed and dissolved in an aqueous medium, and water-based means water-soluble or in an emulsion state. Water-soluble resins and/or emulsion resins can be suitably used as water-based resins, and a mixture of two or more of them may also be used. Examples of water-based resins include water-based urethane resins, water-based acrylic-modified urethane resins, water-based acrylic-modified urethane urea resins, water-based acrylic resins, water-based styrene-acrylic acid copolymer resins, water-based styrene-maleic acid copolymer resins, and water-based ethylene-acryl. acid copolymer resin, aqueous polyester resin, aqueous shellac, aqueous rosin-modified maleic acid resin, aqueous vinyl chloride-vinyl acetate copolymer resin, aqueous vinyl chloride-acrylic acid copolymer resin, aqueous chlorinated polypropylene resin, aqueous hydroxyethyl cellulose resin, Water-based hydroxypropyl cellulose resins and water-based butyral resins are preferred. These may be used alone or in combination of two or more.

Among the water-based resins, it is preferable to include at least one water-based resin selected from the group consisting of water-based urethane resins, water-based acrylic resins, water-based styrene-acrylic acid copolymer resins, and water-based styrene-maleic acid copolymer resins. and/or a water-based acrylic resin is more preferably included. Further, the water-based urethane resin is particularly preferred from the viewpoint of having no residual acrylic monomer and having viscoelasticity that enables stress relaxation in the laminate. These are preferably contained in an amount of 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more in the total mass of the binder resin.

The aqueous resin in the present invention has an acid group. Since the resin has an acid group, it becomes possible to make the resin water-based. The acid value of the aqueous resin having an acid group is preferably 20 to 150 mgKOH/g, more preferably 20 to 120 mgKOH/g, still more preferably 20 to 100 mgKOH/g, and 25 to 65 mgKOH/g. g is particularly preferred. This is because a good water-based resin can be obtained by the acid value, and the plate entanglement property and the water resistance of the ink film are improved.

[Aqueous urethane resin]
In addition to the reasons described above, the water-based resin preferably contains a water-based urethane resin from the viewpoint of adhesion to the substrate and pigment dispersibility. When the aqueous resin contains an aqueous urethane resin, the glass transition temperature of the aqueous urethane resin is preferably -30 to 0°C. Here, the glass transition temperature means the maximum value of Tan δ in dynamic viscoelasticity measurement. The hydroxyl value of the aqueous urethane resin is preferably 1 to 15 mgKOH/g.

The water-based urethane resin includes a urethane resin synthesized from a polyol, a hydroxy acid and a polyisocyanate, and a urethane prepolymer synthesized from a polyol, a hydroxy acid and a polyisocyanate and having an isocyanate group at the end and chained with a polyamine. A preferred form is a urethane resin (urethane urea resin) having a urea bond obtained by extension.

Furthermore, in the form of use as a reverse printing ink (ink for lamination), from the viewpoint of lamination strength (adhesive strength between base layers laminated by lamination processing), it is preferable to contain a urethane resin among the water-based resins, and it has a urea bond. More preferably, it contains a urethane resin.

The water-based urethane resin can be made water-soluble by introducing acid groups such as carboxyl groups and sulfonic acid groups into the resin and neutralizing it with a basic compound when reacting a polyol with a polyisocyanate. From the viewpoint of water resistance, the acid group is preferably a carboxyl group.

Methods for introducing carboxyl groups into water-based urethane resins include the use of compounds having active hydrogen capable of reacting with the following anionic groups and isocyanate groups.
Examples of compounds having an active hydrogen capable of reacting with an anionic group and an isocyanate group include 2,2-dimethylolpropanoic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2- dimethylolalkanoic acids such as dimethylolvalerate;
diamine-type amino acids such as glutamine, asparagine, lysine, diaminopropionic acid, ornithine, diaminobenzoic acid, and diaminobenzenesulfonic acid;
Examples include monoamine amino acids such as glycine, alanine, glutamic acid, taurine, aspartic acid, aminobutyric acid, valine, aminocaproic acid, aminobenzoic acid, aminoisophthalic acid, and sulfamic acid. These may be used alone or in combination of two or more.
Among them, 2,2-dimethylolpropanoic acid and/or 2,2-dimethylolbutanoic acid are preferably used from the viewpoint of compatibility and reactivity with other urethane raw materials. In the production of the water-based urethane resin, the hydroxyl groups of polyhydroxycarboxylic acids react with polyisocyanate to form urethane bonds. It is neutralized in the water-based urethane resin and becomes an acid group for making it water-based.

(polyol)
The polyol does not include the hydroxy acid described below. Examples of suitable polyols include polyester polyols, polyether polyols, polylactone polyols, polycarbonate polyols, polyolefin polyols, dimer diols, and hydrogenated dimer diols. These may be used alone or in combination of two or more.
The water-based urethane resin preferably contains structural units composed of at least one polyol selected from polyester polyols, polyether polyols and polycarbonate polyols. The polyol preferably has a number average molecular weight of 500-5000.

《Polyester polyol》
As said polyester polyol, the form which has a structural unit which consists of a diol containing a dibasic acid and a branched diol is preferable. As the dibasic acid, sebacic acid, adipic acid, succinic acid and the like can be preferably used, and the branched diol is one in which at least one of the hydrogen atoms on the carbon atoms of the alkylene glycol has a substituent. Specifically, it consists of propylene glycol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, and 2-methyl-1,3-propanediol. At least one selected from the group is preferably contained in an amount of 50% by mass or more in the total mass of diols.

《Polyether Polyol》
Suitable polyether polyols include polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, and copolymers thereof. It is preferable that the structural unit consisting of these is an aqueous polyurethane resin. The aqueous polyurethane resin preferably contains a structural unit derived from polyethylene glycol, preferably 0.1 to 25% by mass, more preferably 2 to 15% by mass, based on the total mass of the aqueous polyurethane resin. It is more preferable to contain up to 10% by mass.

《Polycarbonate polyol》
The polycarbonate polyol is not limited by the production method or the type of diol that constitutes the polycarbonate polyol, but a polycondensate obtained by transesterification reaction between a diol composed of alkylene glycol and a carbonate compound is preferably exemplified. The polycarbonate polyol is preferably an alicyclic and/or aliphatic polycarbonate diol.

Examples of the diol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, and neopentyl. Glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,10-decane Diol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butynediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, diethylene glycol, polypropylene Glycols, dipropylene glycol and the like are preferred. These may be used alone or in combination of two or more.
Among them, 3-methyl-1,5-pentanediol and other polycarbonate polyols having a branched diol structure are preferred.

Examples of the carbonate compound include dialkyl carbonate, diaryl carbonate, and alkylene carbonate. Specific examples of carbonate compounds include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate and dibutyl carbonate, diaryl carbonates such as diphenyl carbonate, and alkylene carbonates such as ethylene carbonate.

(hydroxy acid)
The hydroxy acid can utilize, but is not limited to, a carboxyl-containing polyol. For example, dimethylolalkanoic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, and the like are suitable. These can be used singly or in combination of two or more. A hydroxy acid is used in the production process of an aqueous polyurethane resin, and its carboxyl group is introduced into the resulting polyurethane resin to have an acid value. Unreacted carboxyl groups are neutralized and rendered aqueous.

(polyisocyanate)
Suitable examples of the polyisocyanate include aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. These may be trimers to form an isocyanurate ring structure.

Aromatic diisocyanates include 1,5-naphthylene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 4,4′-diphenyldimethylmethane diisocyanate, 4,4′-dibenzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyl diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate and the like.

Aliphatic diisocyanates include butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate and lysine diisocyanate.

Alicyclic diisocyanates include cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, and norbornane diisocyanate. , m-tetramethylxylylene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, dimer diisocyanate obtained by converting the carboxyl group of dimer acid to an isocyanate group, and the like.

Among them, at least one selected from trimers of tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, bis(isocyanatomethyl)cyclohexane, hexamethylene diisocyanate and hexamethylene diisocyanate is preferable. These polyisocyanates can be used alone or in combination of two or more.

(polyamine)
Compounds that can be used as the polyamine include various known amines, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, di-2-hydroxypropylethylenediamine, ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4'-diamine, and dimer diamine obtained by converting the carboxyl group of dimer acid to an amino group. are preferably mentioned, and these can be used alone or in combination of two or more.

(Reaction terminator)
A reaction terminator can also be used in combination with the polyamine. Examples of the reaction terminator include dialkylamines such as di-n-dibutylamine, monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, tri(hydroxymethyl)aminomethane, 2-amino- Amines having a hydroxyl group such as 2-ethyl-1,3-propanediol, N-di-2-hydroxyethylethylenediamine, N-di-2-hydroxyethylpropylenediamine, N-di-2-hydroxypropylethylenediamine, and further Examples include monoamine amino acids such as glycine, alanine, glutamic acid, taurine, aspartic acid, aminobutyric acid, valine, aminocaproic acid, aminobenzoic acid, aminoisophthalic acid, and sulfamic acid.

(Neutralizer)
To make the polyurethane resin water-soluble, it is preferable to neutralize the carboxyl group and other ionizable groups in the resin with a basic compound. Basic compounds include sodium hydroxide, potassium hydroxide, ammonia, methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, ethanolamine, propanolamine, diethanolamine, N-methyldiethanolamine, dimethylamine, diethylamine, triethylamine, N,N-dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, morpholine and the like, and these may be used alone. Well, you may use 2 or more types together. Ammonia is preferred from the viewpoint of water resistance of printed matter and residual odor.

(Synthesis method)
Polyurethane resins are appropriately produced by known methods. Examples thereof include an acetone method using an organic solvent that is inert to isocyanate and hydrophilic, and a non-solvent synthesis method that does not use any solvent. For example, the method described in JP-A-2013-234214 can be used as appropriate.

[Water-based acrylic resin]
It is also preferred that the water-based resin includes a water-based acrylic resin. Aqueous acrylic resins have acrylic monomer constitutional units. Furthermore, acrylic resins obtained by copolymerizing styrene-based monomers, maleic acid-based monomers, etc. are also preferable.
The water-based acrylic resin has an acid group, and is preferably rendered water-based in the presence of an emulsifier and/or a basic compound, and a carboxyl group is particularly preferred as the acid group. Methods for introducing carboxyl groups include the following ethylenically unsaturated compounds having carboxyl groups as monomers, polymerizable unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid and crotonic acid, and their These can be used alone or in combination of two or more.

Examples of the acrylic monomer include benzyl acrylate, benzyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol acrylate, phenoxydiethylene glycol methacrylate, phenoxytetraethyleneglycol acrylate, phenoxytetraethyleneglycol methacrylate, phenoxyhexaethyleneglycol acrylate, phenoxyhexa aromatic alkyl group-containing acrylic monomers such as ethylene glycol methacrylate, phenyl acrylate and phenyl methacrylate;
Furthermore, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, heptyl (meth) acrylate, hexyl ( meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl ( linear or branched alkyl group-containing acrylic monomers such as meth)acrylates,
Alicyclic alkyl group-containing acrylic monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate,
fluorinated alkyl group-containing acrylic monomers such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate;
(Meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl -(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide Acrylamide, N,N-di(propoxymethyl)acrylamide, N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide acrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N- amide group-containing acrylic monomers such as dimethylacrylamide and N,N-diethylacrylamide;
2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono (meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, allyl hydroxyl group-containing acrylic monomers such as alcohols,
Polyethylene glycol monoacrylate (manufactured by NOF Corporation, Blemmer PE-90, 200, 350, 350G, AE-90, 200, 400, etc.) Polyethylene glycol/polypropylene glycol monoacrylate (manufactured by NOF Corporation, Blemmer 50PEP-300, 70PEP- 350, etc.) and polyethylene oxide group-containing acrylic monomers such as methoxy polyethylene glycol monoacrylate (manufactured by NOF Co., Ltd., Blenmer PME-400, 550, 1000, 4000, etc.).

Among the above acrylic monomers, one or more selected from the group consisting of (meth)acrylic acid alkyl esters, (meth)acrylic acid alkylamides, and (meth)acrylic acid hydroxyalkyl esters is preferable. The number of carbon atoms in the alkyl group constituting the alkyl ester or the like is preferably 1-18.

Examples of suitable styrene-based monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene and m-methylstyrene, and preferred maleic acid-based monomers include maleic anhydride and maleic acid. It may be an alkyl ester having 1 to 18 carbon atoms, an alkylamide having 1 to 18 carbon atoms, or a hydroxyalkyl ester having 2 to 4 carbon atoms. Furthermore, the water-based acrylic resin may further use, as a reactive component, known monomers other than those described above that are generally used as a reactive component for water-based acrylic resins.

Using each of these reaction components, an acrylic resin can be produced by a known production method, a method using a known emulsifier or a protective colloid of a polymer, a method of introducing a carboxyl group into the molecule, and neutralization with a basic compound. It can be made water-based by a method or the like. Examples of the basic compound include those exemplified in the production of the water-based urethane resin, among which amine compounds are preferred, and ammonia is preferred. Further, the aqueous acrylic resin is preferably an aqueous emulsion.

The glass transition temperature of the acrylic resin is preferably -20 to 150°C, more preferably -10 to 130°C. This is because the glass transition temperature range improves the adhesion to the substrate. Further, the weight average molecular weight of the aqueous acrylic resin is preferably 5,000 to 700,000, more preferably 8,000 to 500,000, and further preferably 8,000 to 200,000. preferable.

[Pigment]
Either an organic pigment or an inorganic pigment may be used as the pigment, but the organic pigment is more preferable because contamination with calcium ions and magnesium ions derived from the pigment can be suppressed by avoiding calcium salts and magnesium salts. When the organic pigment is contained in an amount of 50% by mass or more based on the total amount of all pigments, the organic pigment is preferably contained in an amount of 70% by mass or more, more preferably 80% by mass or more. When the inorganic pigment content exceeds 50% by mass in the total mass of all pigments, the inorganic pigment content is preferably 70% by mass or more, more preferably 80% by mass or more.

(organic pigment)
Examples of organic pigments include organic pigments used in general inks, paints, recording agents, and the like. Examples include azo, phthalocyanine, anthraquinone, perylene, perinone, quinacridone, thioindigo, dioxazine, isoindolinone, quinophthalone, azomethineazo, dictropyrrolopyrrole, and isoindoline groups. . These pigments may be used alone or in combination of two or more. Specifically, it is preferable to avoid Pigment Red 48:1, which is a calcium salt soluble azo pigment, and use Pigment Red 146, which is a naphthol-based insoluble azo pigment.

(Inorganic pigment)
Suitable inorganic pigments include titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, aluminum hydroxide, chromium oxide, silica, carbon black, aluminum, and mica (mica). Titanium oxide is preferred as the white pigment in terms of coloring power, hiding power, chemical resistance, and weather resistance. Although aluminum is in the form of powder or paste, it is preferable to use it in the form of paste in terms of handling and safety.
Extender pigments such as barium sulfate, calcium carbonate, and aluminum hydroxide are also preferably used. Extender pigments are preferably used as extenders to improve fluidity, strength and optical properties.

(Ratio of pigment and resin in water-based ink)
In the water-based ink composition of the present invention, the mass ratio of the pigment to the water-based resin (pigment/water-based resin) is preferably in the range of 1-7. Specifically, when the organic pigment is contained in an amount of 50% by mass or more in all pigments, the mass ratio (pigment/aqueous resin) is preferably in the range of 1 to 5, more preferably in the range of 1 to 4. Preferably, it is more preferably in the range of 1-3. When the inorganic pigment exceeds 50% by mass in the total mass of all pigments, the ratio is preferably in the range of 1.5 to 7, more preferably in the range of 2 to 5.2. A range of 5 to 4 is more preferred. This is because by keeping the content within this range, good density, printability, and lamination strength can be obtained.

[Curing agent]
The water-based resin used in the water-based ink composition of the present invention can be crosslinked with a curing agent to improve adhesion to the substrate, laminate strength, and water resistance. Since the water-based resin has an acid group, it is preferable to use a hydrazine-based compound, a carbodiimide compound, or an epoxy compound as the curing agent.
Preferred hydrazine-based compounds are dihydrazide adipic acid, dihydrazide sebacate, dihydrazide isophthalate and other dihydrazide compounds.
A carbodiimide compound is a compound having a carbodiimide group, and examples thereof include Carbodilite E-02, E-03A, SV-02, V-02, V02-L2 and V-04 manufactured by Nisshinbo.
An epoxy compound means a compound having an epoxy group, and examples thereof include alicyclic epoxies such as ADEKA ADEKA RESIN EP-4000, EP-4005 and 7001.
The content of the curing agent is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, based on the total mass of the ink.

[Additive]
The aqueous ink composition of the present invention may contain additives. Additives include pigment dispersants, pigment derivatives, neutralizers, leveling agents, defoaming agents, waxes, silane coupling agents, rust inhibitors, preservatives, plasticizers, infrared absorbers, ultraviolet absorbers, and fragrances. , flame retardants, and the like.

[Production of water-based ink]
The method for producing the water-based ink of the present invention is not particularly limited, but it can be preferably produced by mixing or dispersing the ingredients using a ball mill, an attritor, a bead mill, or the like. For example, it can be produced by mixing a pigment, an aqueous resin, and water with a disper for about 20 minutes and then dispersing them with a sand mill or other bead mill for about 10 to 60 minutes.

The viscosity of the water-based ink produced by the above method is in the range of 10 mPa s or more from the viewpoint of preventing sedimentation of the pigment and appropriately dispersing it, and 1000 mPa s or less from the viewpoint of work efficiency during ink production and printing. is preferably The viscosity measured at 25° C. with a Brookfield viscometer can be used as the viscosity.

[Production of printed matter]
The printed matter in this embodiment has a printed layer formed on the surface of a substrate to be printed using the water-based ink of the present invention. The water-based ink of the present invention is preferably printed using a plate system such as gravure printing or flexographic printing, depending on the intended printed matter.

The substrate to be printed (referred to as substrate 1) includes, for example, polyolefin substrates such as polyethylene and polypropylene, polyethylene terephthalate substrates, polyester substrates such as polylactic acid, polycarbonate substrates, polystyrene substrates, and AS resin substrates. material, polystyrene resin base material such as ABS resin, polyamide base material such as nylon base material, polyvinyl chloride base material, polyvinylidene chloride base material, cellophane base material, paper base material, aluminum base material, etc., or a combination of these A film-like substrate made of a material, or a vapor-deposited substrate obtained by vapor-depositing an inorganic compound such as silica, alumina, or aluminum on a polyethylene terephthalate or nylon film can be used. Among them, it is preferable to use a stretched substrate. The base material (referred to as base material 2) used in the production of the later-described laminate may be the same as base material 1, and may be the same or different.

The method for producing a plastic substrate printed matter in this embodiment includes the step of printing on the surface of a wound plastic substrate using the water-based ink described above. After printing, processes such as lamination, slitting (cutting unnecessary width portions), and bag-making (cutting and heat-sealing to form bags) can be carried out.

Both of the gravure printing method and the flexographic printing method are roll-up printing methods, enabling high-speed printing and excellent productivity.
Gravure printing usually uses a gravure plate with cells (recesses) for expressing patterns and/or characters on the peripheral surface of a cylindrical cylinder. material) is passed between the gravure plate and the impression cylinder to transfer the printing ink filled in the cells to the material to be printed, thereby reproducing patterns and/or characters on the material to be printed. be.
In flexographic printing, ink is supplied directly from a container for storing printing ink or via an ink supply pump or the like to an anilox roller having an uneven surface. It is transferred to the plate surface by contact with the plastic substrate, and finally transferred to the plastic substrate by contact between the plate surface and the plastic substrate to form a pattern and/or characters.

Since the substrate is of a winding type, it is in the form of a roll with a specified width. Therefore, it differs from the sheet form in which each sheet is cut in advance. The width of the substrate is appropriately selected based on the plate width of the printing machine to be used and the width of the image (pattern) portion of the gravure plate. When multiple colors of printing inks are printed in layers, the printing order of the inks is not particularly limited.

When printing in gravure and flexographic printing methods, in the case of reverse printing, which is preferably used for lamination, the web plastic substrate is first printed with colored ink and then printed with white ink. is common. When multiple colors of ink are used, for example, printing can be performed in the order of black, cyan, magenta, and yellow, but there is no particular limitation. In large-sized printing presses, special colors and the like can be used in addition to the basic colors. That is, a large-sized printing press has a plurality of printing units corresponding to 5 to 10 colors, one printing unit is provided with ink of one color, and 5 to 10 colors of overprinting can be performed at one time.

[Laminate]
The laminate in the present invention can be obtained through a step of laminating a substrate on the printed layer of the printed matter. It can be obtained by applying an anchor coating agent, a molten resin, an adhesive, or the like on the printed layer, drying it, and bonding it to the substrate 2 . The substrate 2 may be the same as or different from the substrate 1 described above. In the laminate, the printed layer made of water-based ink is positioned as an intermediate layer, and the layer structure at that time is, for example, (base material 1/printed layer/adhesive layer/base material 2).

As the lamination method, (1) an extrusion lamination method in which an anchor coating agent is applied on the printed layer of the obtained printed material as necessary, and then the molten resin and the base material 2 are laminated in this order, or (2) A dry lamination method of applying an adhesive on the printed layer of the obtained printed matter, drying it if necessary, and then laminating the base material 2, and the like. Low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and the like can be used as the molten resin, and imine, isocyanate, polybutadiene, and titanate adhesives can be used as the anchor coating agent. As the adhesive, a urethane adhesive is suitable, and a two-liquid adhesive is more suitable. For example, ether-based urethane adhesives and ester-based urethane adhesives correspond to this.

A laminated laminate can be preferably used as a packaging material, and is suitably used as a general packaging material and particularly as a packaging material for food.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples as long as it does not depart from the technical idea of the present invention. In addition, parts and % in the present invention represent parts by mass and % by mass unless otherwise specified.

(water used)
The following water was used in the examples.
Purified water (purified by reverse osmosis membrane method): magnesium ion 0.03 mg/L, calcium ion 0.05 mg/L, total 0.08 mg/L
Tap water: magnesium ion 9 mg/L, calcium ion 25 mg/L, total 34 mg/L
Industrial water (ground water): magnesium ion 30 mg/L, calcium ion 80 mg/L, total 110 mg/L
The amount of each metal ion was determined by inductively coupled plasma (ICP) emission spectrometry. In addition, it can be similarly measured by ion chromatography.

(Inductively coupled plasma (ICP) emission spectroscopy)
About 0.25 g of the ink was weighed and put into a decomposition vessel, mixed with 5 ml of a 70% nitric acid aqueous solution in the decomposition vessel, and allowed to stand overnight. After standing, decomposition operation was performed using MARS5 manufactured by CEM, and the sample was taken out after being allowed to cool and injected into a 50 ml volumetric flask by gravity filtration. Then, while washing the filter paper with ion-exchanged water, the sample was diluted to 50 ml and measured with SPECTRO ICP-OES manufactured by SPECT ROBLUE.

(ion chromatograph)
The ink was diluted with purified water to a measurable range, and the content of magnesium ions and calcium ions in the ink was measured using an ion chromatograph (2010i, manufactured by DIONEX) and a column (IonPacAS4A, manufactured by DIONEX).

(Aqueous Urethane Synthesis Example 1)
Kuraray Polyol C2050 (3-methyl-1,5-pentanediol and 1,6- Polycarbonate diol having a number average molecular weight of 2000 consisting of hexanediol-derived units) 221.4 parts, PEG2000 (polyethylene glycol having a number average molecular weight of 2000) 10.8 parts, 2,2-dimethylolbutanoic acid (DMBA) 33.3 parts, and 225 parts of methyl ethyl ketone (MEK) were mixed, and while stirring, 91.7 parts of isophorone diisocyanate (IPDI) was added dropwise over 1 hour and allowed to react at 80° C. for 4 hours to obtain a terminal isocyanate prepolymer solvent solution. The resulting isocyanate-terminated prepolymer was cooled to 30° C., and a mixture of 2.7 parts of N-(2-aminoethyl)-2-aminoethanol (AEA) and 250 parts of isopropanol (IPA) was gradually added at room temperature. and reacted at 40° C. for 2 hours to obtain a solvent-type polyurethane resin solution. Next, 13.6 parts of 28% aqueous ammonia and 1,080 parts of purified water are gradually added to the above solvent-type polyurethane resin solution to neutralize it, and then methyl ethyl ketone and isopropanol are distilled off under reduced pressure, followed by purified water. was added to adjust the solid content to obtain an aqueous polyurethane resin solution PU1 having a solid content of 30%.

(Aqueous Urethane Synthesis Examples 2-6)
PUs 2 to 6 were obtained in the same manner as in Synthesis Example 1 of water-based urethane using the composition of raw materials shown in Table 1.

(Aqueous Urethane Synthesis Example 7)
49.2 parts of polytetramethylene glycol with a number average molecular weight of 2000 (PTG2000) and a 31.2 parts of polyethylene glycol (PEG2000), 13.1 parts of 2,2-dimethylolbutanoic acid (DMBA), 8.3 parts of bis(2-hydroxypropyl)aniline (PDIA), and 1,4-cyclohexanedimethanol 1.8 parts of (CHDM) was charged, purged with dry nitrogen, and heated to 100°C. With stirring, 37.7 parts of isophorone diisocyanate (IPDI) was added dropwise over 20 minutes, and the temperature was gradually raised to 140°C. Further reaction was performed for 180 minutes to obtain a urethane resin. Next, while cooling, 3.2 parts of 28% aqueous ammonia and 420.5 parts of purified water were added to obtain an aqueous urethane resin solution (PU7).

(Aqueous Urethane Synthesis Examples 8-18)
PUs 8 to 18 were obtained in the same manner as in Synthesis Example 7 of water-based urethane using the raw material composition shown in Table 2.

(Aqueous Acrylic Synthesis Example 1)
150 parts of isopropyl alcohol was charged into a reaction vessel equipped with a stirring device, a thermometer, a dropping device and a reflux condenser, and the temperature was raised to 78° C., acrylic acid (AA) 16 parts, n-butyl acrylate (BA) 59 parts, methacryl. After 25 parts of methyl acid (MMA) and 3 parts of 2,2'-azobisisobutyronitrile (ABN-R manufactured by Nippon Finechem Co., Ltd.) were added dropwise over 2 hours, the mixture was reacted at 78°C for 4 hours. Next, isopropyl alcohol was distilled off under reduced pressure, and 10.0 parts of 28% aqueous ammonia, 186.7 parts of purified water, and 33.3 parts of isopropyl alcohol were added to obtain aqueous acrylic resin solution AC1.

(Aqueous Acrylic Synthesis Examples 2-4)
AC2 to AC4 were obtained in the same manner as in Water-Based Acrylic Synthesis Example 1 with the raw material composition shown in Table 3.

The abbreviations in Tables 1 to 3 are as follows.
PCD (MPD/HD=9/1) 2000: Kuraray Polyol C-2050 manufactured by Kuraray Co., Ltd. (polycarbonate diol having a number average molecular weight of 2000 consisting of units derived from 3-methyl-1,5-pentanediol and 1,6-hexanediol)
PEG2000: polyethylene glycol with a number average molecular weight of 2000 DMBA: dimethylolbutanoic acid PDO: 1,3-propanediol MEK: methyl ethyl ketone IPDI: isophorone diisocyanate IPA: isopropanol AEA: N-(2-aminoethyl)-2-aminoethanol PTG2000: Polytetramethylene glycol with a number average molecular weight of 2000 PDIA: N,N-bis(2-hydroxypropyl)aniline CHDM: Cyclohexane dimethanol AA: Acrylic acid BA: n-butyl acrylate MMA: Methyl methacrylate ABN-R: Nippon Finechem Company ABN-R (2,2'-azobisisobutyronitrile)

(Example 1)
13 parts of an insoluble azo pigment Pigment Red 146 (LIONOL RED 5620 manufactured by Toyocolor Co., Ltd.), 40 parts of an aqueous urethane resin solution (PU1), 7 parts of n-propanol, and 20 parts of purified water were stirred and mixed, and dispersed in a sand mill for 30 minutes. After that, 10 parts of aqueous polyurethane resin solution (PU1), 6.6 parts of purified water, 2 parts of polyethylene wax (Chemipearl W300 manufactured by Mitsui Chemicals, Inc.), 0.2 parts of adipic acid dihydrazide, acetylene glycol surfactant (Evonik Industries) 1.0% of Surfynol 420) was stirred and mixed to obtain water-based gravure ink M1. Furthermore, purified water: isopropanol = 65:35 diluted solvent and a carbodiimide compound (Carbodiimide E-02 manufactured by Nisshinbo Co., Ltd.) were blended in an aqueous gravure ink M1: diluted solvent: carbodiimide compound = 100:50:3 ratio. A diluted ink M1-1 was obtained.

(Examples 2-14, Comparative Examples 1-5, Examples 15-27, Comparative Examples 6-10)
Aqueous gravure inks M2 to M19 and W1 to W18 were obtained in the same manner as in Example 1, except that the raw materials and blending ratios shown in Tables 4 and 5 were used. Magnesium ion and calcium ion content was determined for each ink by inductively coupled plasma (ICP) emission spectroscopy.

Furthermore, each ink was diluted in the same manner as in Example 1 to obtain aqueous gravure diluted inks M2-1 to M19-1 and W1-1 to W18-1, respectively. Each number of water-based gravure diluted ink is obtained by adding "-1" to the end of the number of water-based gravure ink before dilution.

Furthermore, a water-based gravure dilution ink M1-1 was filled in the printing unit of a gravure printing machine, and a gravure plate with a screen line number of 250 lines having a shadow part with a cell depth of 15 μm was used. (manufactured by FOR-AQ, film thickness 20 μm) at a printing speed of 120 m/min to obtain prints of water-based gravure dilution ink M1-1. Aqueous gravure dilution inks M2-1 to M19-1 and W1-1 to W18-1 were also printed in the same manner.

Abbreviations in Tables 4 and 5 are as follows.
Insoluble azo pigment Pigment Red146: LIONOL RED 5620 manufactured by Toyocolor Co., Ltd.
Soluble azo pigment Pigment Red 48:1: LIONOL RED 4804G manufactured by Toyocolor Co., Ltd.
Polyethylene wax: Chemipearl W300 manufactured by Mitsui Chemicals
Acetylene glycol-based surfactant: Surfynol 420 manufactured by Evonik Industries
Titanium oxide: Titanix JR-800 manufactured by Tayca Corporation

(Stability over time)
Each of the aqueous gravure inks M1 to M19 and W1 to W18 obtained in Examples and Comparative Examples was stored at 40° C. for 7 days, and evaluated by observing the state before and after storage and measuring the viscosity. Viscosity was confirmed by the number of seconds of outflow using a Zahn cup #4. Table 6 shows the results.
[Evaluation criteria]
A. No liquid separation or sedimentation, viscosity change less than 1 second (excellent)
B. There is some liquid separation, but no precipitation, and the viscosity change is 1 second or more and less than 2 seconds (good)
C. Liquid separation and sedimentation are slightly observed, viscosity change is 2 seconds or more and less than 5 seconds (practical use possible)
D. Liquid separation and sedimentation are slightly observed, viscosity change is 5 seconds or more and less than 10 seconds (slightly poor)
E. Severe liquid separation and sedimentation were observed, and the viscosity change was more than 10 seconds (poor).
Note that A, B, and C are ranges that pose no problem in practice.

(water resistance)
For the prints of M1-1 to M19-1 and W1-1 to W18-1 obtained in Examples and Comparative Examples, the 100% solid printed portion is rubbed with a cotton swab soaked with water, and the ink is removed by the cotton swab. evaluated the number of times. Table 6 shows the results.
[Evaluation criteria]
AA. 5 times or more (very good)
A. 4 times (excellent)
B. 3 times (good)
C. 2 times (practical)
D. Ink is partially removed in one pass (slightly poor)
E. The ink can be completely removed in one pass (defective)
Incidentally, AA, A, B and C are within practically non-problematic ranges.

(Plate fogging)
During printing of M1-1 to M19-1 and W1-1 to W18-1 obtained in Examples and Comparative Examples, the area of the plate fogging portion was visually determined after 90 minutes of idling of the plate in the gravure printing machine. , made an evaluation. Table 6 shows the results.
[Evaluation criteria]
AA. No plate fogging area (extremely good)
A. Plate fogging area is less than 2% (excellent)
B. Plate fogging area of 2% or more and less than 5% (good)
C. Plate fogging area of 5% or more and less than 10% (practical use possible)
D. Plate fogging area of 10% or more and less than 25% (slightly poor)
E. Plate fogging area is 25% or more (defective)
Incidentally, AA, A, B and C are within practically non-problematic ranges.

(flexo plate washability)
The water-based gravure inks M1, M11, M16, and M19 were subjected to simple evaluation of plate washability when used as flexographic inks as follows. The ink was spread on an OPP film (FOR-AQ above) and dried for 10 minutes at room temperature. Next, water, n-propanol, and Magiclean (a special solvent for plate washing, manufactured by Kao Corporation) were dripped onto the coating film to examine the solubility of the coating film, and a simple evaluation of the plate washing property. did. Evaluation criteria are shown below. The practical level is C or higher.
A. Dissolves in water alone.
B. Dissolves in n-propanol alone.
C. Dissolve with Magiclean.
D. Even Magiclean does not dissolve it.
As a result, M1 was rated C, M11 was rated B, M16 was rated D, and M19 was rated D, which were good within the scope of the present invention.

As described above, the present invention has made it possible to provide a water-based gravure ink that is excellent in stability over time and water resistance, and that hardly causes plate fogging in printed matter. In addition, it has become possible to provide a water-based flexographic ink with excellent plate washability.

Claims (8)

An aqueous ink composition comprising an aqueous resin having an acid group, a pigment, and water, wherein the total concentration of magnesium ions and calcium ions in the aqueous ink composition is 95 mg/L or less. 2. The aqueous ink composition according to claim 1, having a pH of 7.5 to 10.5. 3. The water-based ink composition according to claim 1, wherein the water-based resin having an acid group is a water-based urethane resin and/or a water-based acrylic resin. The water-based ink composition according to any one of claims 1 to 3, wherein the acid value of the water-based resin having acid groups is 20 to 150 mgKOH/g. The aqueous ink composition according to any one of claims 1 to 4, wherein the pigment is an organic pigment. A printed material having a print layer formed of the water-based ink composition according to any one of claims 1 to 5 on a substrate 1. A laminate having a substrate 2 on the printed layer of the printed matter according to claim 6. A printing method, comprising forming a printed layer on a substrate using the aqueous ink composition according to any one of claims 1 to 5.