JP7513342B2 - Water-based flexographic printing ink composition for reverse printing film - Google Patents

Description

The present invention relates to a water-based flexographic printing ink composition for reverse printing films.

Packaging materials using various plastic films are used for food, confectionery, household goods, pet food, etc., for their functions such as design, economy, content protection, transportability, etc. Furthermore, many packaging materials are printed using gravure printing or flexo printing with the intention of adding designs and messages that will appeal to consumers.
In order to obtain the desired packaging material, front printing is performed, in which printing is done on the surface of the base film of the packaging material, or back printing is performed, in which an adhesive or anchor agent is applied as necessary to the printed surface of the base film of the packaging material and the film is then laminated.
In reverse printing, colored inks and white ink are printed in sequence on various films such as polyester, nylon, and aluminum foil, and then a polyethylene film, polypropylene film, or the like is laminated on the white ink printing layer for the purpose of heat sealing by dry lamination using an adhesive or extrusion lamination using an anchor coating agent (see, for example, Patent Document 1).

Conventionally, water-based flexographic inks have been widely used on permeable, drying stock such as thin paper and cardboard, while gravure printing methods using solvent-based inks have been widely adopted for resin film substrates. In recent years, there has been a demand for the development of environmentally friendly products, and water-based inks have been attracting attention. In the field of printing on resin film substrates, there is also a demand for water-based inks. However, water-based inks that contain a lot of water have high surface tension, making it difficult to wet resin film substrates with low surface free energy, and the leveling properties in particular were poor (see, for example, Patent Documents 2 and 3).

Japanese Patent Application Laid-Open No. 05-097959 Japanese Patent Application Laid-Open No. 08-120205 JP 2015-067818 A

The object of the present invention is to provide a flexographic printing ink composition for reverse printing on resin film substrates by making the ink composition a water-based flexographic printing ink composition.

As a result of intensive research conducted by the present inventors in order to solve the above problems, they have invented the following water-based flexographic printing ink composition for reverse printing film.
1. An ink composition comprising a pigment, an aqueous urethane resin emulsion, a surfactant, a water-soluble organic solvent, and water, and containing 0.1 to 3.0 mass % of an acetylene-based surfactant having an HLB value of 3.0 to 8.0;
The water-based flexographic printing ink composition for reverse printing film contains, as a water-soluble organic solvent, 0.1 to 20 mass % of a water-soluble organic solvent having a boiling point of 60 to 200°C in the ink composition.
2. The water-based flexographic printing ink composition for reverse printing film according to 1., which contains an alkali-soluble water-soluble resin.
3. The water-based flexographic printing ink composition for reverse printing film according to 2., wherein the alkali-soluble water-soluble resin is an acrylic resin.
4. The water-based flexographic printing ink composition for reverse printing film according to any one of 1. to 3., further comprising a carbodiimide-based curing agent and/or an aziridine-based curing agent.

The aqueous flexographic printing ink composition for reverse printing films of the present invention combines a specific resin with a specific surfactant, allowing it to exhibit a good balance of excellent adhesion to resin films, blocking resistance, leveling properties, trapping properties, and boiling resistance.

The water-based flexographic printing ink composition for reverse printing film of the present invention will be described in more detail below.
<Pigments>
In the present invention, various inorganic pigments and/or organic pigments that are generally used in printing inks can be used.
Examples of inorganic pigments include color pigments such as titanium oxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, carbon black, and graphite, and extender pigments such as silica, calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc.
Examples of the organic pigment include soluble azo pigments, insoluble azo pigments, azo lake pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments.
The content of the pigment in the aqueous flexographic printing ink composition for reverse-printed films of the present invention is preferably 0.5 to 50.0% by mass. If the content of the pigment in the aqueous flexographic printing ink composition for reverse-printed films is less than the above range, the coloring power of the ink composition decreases, whereas if it is more than the above range, the viscosity of the ink composition increases, making the printed matter more susceptible to smudging.

<Binder resin>
As the binder resin, an aqueous urethane resin emulsion can be used.

<Water-based urethane resin emulsion>
The aqueous urethane resin emulsion preferably has an acid value of 10 to 100 mgKOH/g. The emulsion also includes hydrosols.
The aqueous urethane resin emulsion is obtained by reacting an organic diisocyanate compound with a polymer diol compound to synthesize a urethane prepolymer, and then reacting with a chain extender and a reaction terminator, and is an acid group-containing urethane resin emulsion obtained by a method of dispersing in water in the presence of an emulsifier, or a method of introducing a free carboxyl group into the molecule and dispersing in water in the presence of a basic compound and, if necessary, an emulsifier. Among these, the acid group-containing urethane resin emulsion obtained by a method of introducing a free carboxyl group into the molecule and dispersing in water in the presence of a basic compound is preferred.

Examples of organic diisocyanate compounds include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, alicyclic diisocyanate compounds such as isophorone diisocyanate, hydrogenated xylylene diisocyanate and 4,4-cyclohexylmethane diisocyanate, araliphatic diisocyanate compounds such as xylylene diisocyanate and tetramethylxylylene diisocyanate, and aromatic diisocyanate compounds such as toluylene diisocyanate and diphenylmethane diisocyanate. Among these, alicyclic or araliphatic diisocyanate compounds are preferred from the viewpoint of improving adhesion to various films and resolubility of aqueous printing inks.

Examples of polymeric diol compounds include polyester diols obtained by polycondensation of low-molecular-weight diol components such as linear glycols such as 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol, branched glycols such as 1,2-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2-ethyl-2-butyl-1,3-propanediol, and ether-based diols such as diethylene glycol and triethylene glycol, and dibasic acid components such as adipic acid and phthalic acid, or by ring-opening reaction of cyclic ester compounds such as lactones, and oxidized ethylene glycol. Examples of the polyether diols include polyether diols obtained by homopolymerizing or copolymerizing ethylene, propylene oxide, tetrahydrofuran, etc., polyalkylene glycols such as polyethylene glycol and polypropylene glycol, polyether diol compounds such as alkylene oxide adducts of bisphenol A with ethylene oxide, propylene oxide, etc., and further include polycarbonate diols and polybutadiene glycols obtained by reacting carbonate components such as alkylene carbonate, diallyl carbonate, and dialkyl carbonate, or phosgene with the low molecular weight diol components.

As a polymer diol compound having a free carboxyl group for making a polyurethane resin aqueous in the presence of a basic compound, a polymer diol compound obtained by reacting the polymer diol component with a tetrabasic acid anhydride such as pyromellitic anhydride, or by ring-opening polymerization of lactones using dimethylolpropionic acid, dimethylolbutanoic acid, or the like as an initiator, can be used.
The number average molecular weight of these polymeric diol compounds is preferably from 500 to 4,000.
In view of adhesion to plastic films and suitability for lamination, polyester diols and polycarbonate diols are preferably used as the polymer diol compound, and polyester diols are more preferably used in view of suitability for boiling and retorting.
Furthermore, for the purpose of obtaining a carboxylic acid group-containing polyurethane resin, a polyol compound having a carboxylic acid group, such as dimethylolpropionic acid or dimethylolbutanoic acid, can be used as a copolymerization component, or an alkanediol, such as 1,4-pentanediol, 2,5-hexanediol, or 3-methyl-1,5-pentanediol, or a low molecular weight diol compound, such as ethylene glycol, propylene glycol, 1,4-butanediol, or 1,3-butanediol, can be used alone or in combination of two or more kinds.

Next, the chain extender used for extending the chain of the urethane prepolymer will be described.
Examples of the chain extender include glycols such as ethylene glycol and propylene glycol; aliphatic and alicyclic diamines such as hydrazine, ethylenediamine, 1,4-butanediamine, aminoethylethanolamine, and isophoronediamine; and N-alkyldiaminoalkylamine compounds such as N-methyldiaminoethylamine and N-ethyldiaminoethylamine, either alone or in mixture. Further, examples of chain extenders that can be used in combination with these include aliphatic polyols such as glycerin, 1,2,3-trimethylolpropane, and pentaerythritol; alicyclic polyols such as 1,3,5-cyclohexanetriol; and aliphatic polyamines such as diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

As a chain extender having a free carboxyl group for making a polyurethane resin aqueous in the presence of a basic compound, the following general formula (1):

(wherein R ¹ represents a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms), or aliphatic carboxylic acid-containing polyols obtained by reacting succinic acid, adipic acid, or the like with a lower polyol, and aromatic carboxylic acid-containing polyols obtained by reacting phthalic acid, trimellitic acid, pyromellitic acid or anhydride thereof with a polyol.

Furthermore, in order to impart higher adhesion to plastic films and superior lamination strength to the printing ink, a chain extender having a hydrazine residue in the molecule can be used, specifically, for example, the following general formula (2):

(wherein ^R2 represents an alkylene group having 2 to 15 carbon atoms, a divalent alicyclic or aromatic group having 6 to 15 carbon atoms, or a residue of a polyethylene polyamine having 3 to 5 nitrogen atoms excluding the primary amino group, and ^R3 represents a hydrogen atom or a methyl group).
The chain extender of the above general formula (2) can be obtained according to a conventional method (JP-B-3-8649), by first obtaining a Michael addition compound of a polyamine and a (meth)acrylic acid derivative, and then subjecting the (meth)acrylic acid ester moiety to ester exchange with hydrazine.
The chain extender having the molecular structure represented by the general formula (2) is capable of obtaining good adhesion by leaving hydrazine residues in the polyurethane resin even after chain extension and crosslinking with the film surface, etc.

Here, examples of polyamines that can be used in the synthesis of polyaminohydrazide include aliphatic diamines having 2 to 15 carbon atoms, such as ethylenediamine, butylenediamine, and trimethylhexamethylenediamine; alicyclic or aromatic diamines having 6 to 15 carbon atoms, such as diaminobenzene, 4,4'-diaminobicyclomethane, 1,4-diaminocyclohexane, 1,4-bis(aminomethyl)cyclohexane, and isophoronediamine; and polyethylene polyamines having 3 to 5 nitrogen atoms, such as diethylenetriamine and triethylenetetramine.

(Meth)acrylic acid derivatives include alkyl esters, hydroxyalkyl esters, and aminoalkyl esters of acrylic acid or methacrylic acid, and among these, acrylic acid derivatives are preferred in terms of reactivity.

Next, the reaction terminator will be described.
The reaction terminator is used to react with unreacted isocyanate groups after the chain of the urethane prepolymer has been extended with a chain extender, thereby eliminating reactivity.
Examples of reaction terminators that are commonly used include alkylamines such as n-propylamine, n-butylamine, and N,N-di-n-butylamine; alkanolamines such as monoethanolamine and diethanolamine; monoalcohols such as methanol and ethanol; aliphatic diamines such as trimethylenediamine and hexamethylenediamine; alicyclic diamines such as isophoronediamine and 4,4'-dicyclohexylmethanediamine; polyamines such as diethylenetriamine and triethylenetetratriamine; aromatic diamines such as toluylenediamine; aromatic aliphatic diamines such as xylylenediamine; and diamines having hydroxyl groups such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, and N,N'-di(2-hydroxyethyl)ethylenediamine, and other polyamine compounds having primary amino groups at both ends.

The reaction terminator used to introduce hydrazine residues into polyurethane molecules is a compound having a functional group for reacting with an isocyanate group and a hydrazine residue. The aforementioned polyaminohydrazide is preferably used, and other suitable reaction terminators include hydrazine and the following general formula (3):

(wherein X represents an alkylene group having 1 to 8 carbon atoms, or a residue of a saturated or unsaturated dibasic acid having 1 to 10 carbon atoms), alkylene dihydrazine or a dihydrazide compound of a saturated aliphatic dibasic acid or an unsaturated dibasic acid can also be used.

Specific examples of alkylene dihydrazines include methylene dihydrazine, ethylene dihydrazine, and butylene dihydrazine. Specific examples of dihydrazide compounds of saturated aliphatic dibasic acids include oxalic dihydrazide, malonic dihydrazide, glutaric dihydrazide, adipic dihydrazide, and sebacic dihydrazide. Specific examples of dihydrazide compounds of unsaturated dibasic acids include phthalic dihydrazide, fumaric dihydrazide, and itaconic dihydrazide.

The method for producing a polyurethane resin using the above organic diisocyanate compound, polymeric diol compound, chain extender and reaction terminator is described below.

The ratio of the organic diisocyanate compound to the polymer diol compound used is such that the equivalent ratio of isocyanate groups to hydroxyl groups (isocyanate index) is usually in the range of 1.2:1 to 3.0:1, more preferably 1.3:1 to 2.0:1. If the isocyanate index is less than 1.2, the polyurethane resin tends to be soft, and in cases where blocking resistance is low when the ink is printed, it may be preferable to use the polyurethane resin in combination with another hard resin.
Then, the organic diisocyanate compound and the polymer diol compound are mixed in the above molar ratio, and the necessity and type of a solvent and a catalyst, the reaction temperature, etc. are determined according to the reactivity of the two, and the two are reacted by a known method to synthesize a urethane prepolymer. Next, a chain extender and a reaction terminator are reacted in sequence to complete the production.
It is also possible to use the same compound as the chain extender and the reaction terminator, or to add the chain extender and the reaction terminator simultaneously.
The method of producing a polyurethane resin from these urethane prepolymers is preferable because each molecule of the polyurethane resin has a substantially uniform structure and there is little variation in molecular weight.

Among the polyurethane resins obtained from the above materials and manufacturing methods, the polyurethane resin in the present invention has a number average molecular weight of 5,000 to 200,000, preferably 70,000 to 100,000. If the number average molecular weight is less than the above range, the resin film will have poor elasticity and will be brittle, while if the number average molecular weight exceeds the above range, the viscosity of the aqueous polyurethane resin dissolved in water in the presence of a basic compound will increase, and the dispersibility of the aqueous polyurethane resin dispersed in water in the presence of an emulsifier and/or a basic compound will decrease.

Next, a method for converting the polyurethane resin of the present invention into an aqueous varnish will be described. First, the method for converting polyurethane resin that does not have free carboxyl groups in the molecule into an aqueous varnish mainly involves dispersing the polyurethane resin in water in the presence of an emulsifier.

There are two methods available for this:
A method in which a urethane prepolymer obtained by reacting an organic diisocyanate compound with a polymeric diol compound is dispersed in water in the presence of an emulsifier, the chains are extended with a chain extender, and the reaction is terminated with a reaction terminator.
(b) A method in which the urethane prepolymer is dissolved in a water-miscible solvent such as methyl acetate, the chains are extended with a chain extender, the reaction is terminated with a reaction terminator, and then the mixture is mixed with water containing an emulsifier and the solvent is distilled off.
Examples of emulsifiers used in these methods include anionic surfactants such as higher alcohol sulfate salts, alkylbenzene sulfonates, and polyoxyethylene alkyl sulfate salts; and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and sorbitan derivatives. These can be used alone or in combination.

On the other hand, as a method for introducing free carboxyl groups into polyurethane molecules and dispersing them in water in the presence of a volatile basic compound and, if necessary, an emulsifier, a method can be used in which the polymeric diol compound having free carboxyl groups and/or a chain extender are used to dissolve or disperse the polyurethane molecules in water at the chain extension stage, and then the reaction is terminated. Here, the total amount of the polymeric diol compound having free carboxyl groups and the chain extender used is in a range that results in an acid value of the polyurethane resin of 5 to 100, more preferably 10 to 60.

If the acid value is lower than the above range, it becomes difficult for the resulting polyurethane resin to maintain a stable self-emulsified state in an aqueous system. On the other hand, if the acid value exceeds the above range, the resulting resin film becomes too hard, and a printing ink with good film properties cannot be obtained.

(Basic Compound)
In the urethane resin used in the present invention, in which free carboxyl groups have been introduced into the polyurethane molecule, some or all of the carboxyl groups are neutralized with a basic compound.
The basic compound is preferably a volatile basic compound. Examples of the volatile basic compound include organic amines such as ammonia, triethylamine, N,N-dimethylethanolamine, and monoethanolamine, and among these, ammonia is preferable. Inorganic alkali compounds such as sodium hydroxide and potassium hydroxide, and non-volatile amine compounds such as triethylenediamine, diethanolamine, triethanolamine, diethylenetriamine, and diazabicyclooctene can also be used in combination within a range in which the drying performance is not reduced.

Of the aqueous urethane resin emulsions obtained by the above methods, when high drying properties and water resistance are required, it is generally advantageous to use an aqueous polyurethane resin emulsion dispersed in water in the presence of a volatile basic compound, whereas when pigment dispersibility and print reproducibility are required, it is advantageous to use an aqueous polyurethane resin emulsion dispersed in water in the presence of an emulsifier, in which case it is more desirable to use a pigment dispersing resin or a pigment dispersant in combination.

In the aqueous flexographic printing ink composition for reverse printing film of the present invention, the solid content of the aqueous polyurethane resin emulsion is preferably 5 to 25% by weight. If the polyurethane resin solid content is less than the above range, the adhesion to polyester and nylon films and the lamination strength decrease, while if it is more than the above range, the adhesion to polyolefin films and the suitability for direct lamination decrease, which is not preferable.

<Alkali-soluble water-soluble resin>
The alkali-soluble resin (alkali-soluble, water-soluble resin) that can be used in the present invention is an alkali-soluble resin in which a part or all of the acid groups have been neutralized with a basic compound.
The monomer components constituting such an alkali-soluble resin include a monomer having a carboxyl group, a monomer containing a hydrophobic group for improving the adsorptivity to the pigment, and another polymerizable monomer.

Examples of monomers having a carboxyl group that can be used include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-carboxyethyl (meth)acrylate, 2-carboxypropyl (meth)acrylate, maleic anhydride, maleic acid monoalkyl ester, citraconic acid, citraconic anhydride, and citraconic acid monoalkyl ester.

As a monomer containing a hydrophobic group to improve the adsorption to the pigment, preferably, a (meth)acrylate having a long-chain alkyl group having 6 to 20 carbon atoms, more preferably 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, 2-hydroxystearyl (meth)acrylate, etc., can be used. Furthermore, as a styrene-based monomer, styrene, α-styrene, vinyl toluene, etc. can be used.

The other polymerizable monomer is a monomer that can be used within a range that does not impair the properties of the alkali-soluble resin, and examples of (meth)acrylic acids such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, and hexyl (meth)acrylate, hydroxyethyl (meth)acrylate, acrylamide, N-methylol acrylamide, cyclohexyl (meth)acrylate, and benzyl (meth)acrylate can be used.
Among these, acrylic resins such as styrene-acrylic resin, acrylic resin, and acrylic-maleic acid copolymer are preferred.

The acid value of the alkali-soluble resin is preferably 40 to 300 mgKOH/g, more preferably 70 to 250 mgKOH/g. If the acid value of the alkali-soluble resin is lower than 40 mgKOH/g, the dispersion stability of the resulting aqueous dispersion of the alkali-soluble resin may decrease, whereas if it is higher than 300 mgKOH/g, the hydrophilicity may become too high, resulting in decreased storage stability and water resistance.
The molecular weight of the alkali-soluble resin is preferably in the range of a weight average molecular weight of 3,000 to 200,000, and more preferably 10,000 to 50,000. If the weight average molecular weight of the alkali-soluble resin is less than 3,000, the dispersion stability of the pigment and the scratch resistance of the resulting printed matter tend to decrease, whereas if it exceeds 200,000, the viscosity increases, which is undesirable.
The amount of the alkali-soluble resin in the aqueous flexographic printing ink composition for reverse printing film is preferably 0.5 to 5.0% by mass, more preferably 1.0 to 3.0% by mass, in terms of solid content.

The acid value is a theoretical acid value calculated arithmetically from the amount of potassium hydroxide (mg) theoretically required to neutralize 1 g of the alkali-soluble resin based on the composition of the monomers used to synthesize the alkali-soluble resin.
The weight average molecular weight can be measured by gel permeation chromatography (GPC). For example, chromatography is performed using a GPC device Water 2690 (manufactured by Waters Corporation) and a column PLgel 5 μm MIXED-D (manufactured by Agilent Technologies Corporation), and the weight average molecular weight can be calculated as polystyrene equivalent.

(Basic Compound)
As the basic compound for neutralizing the alkali-soluble resin used in the present invention, any of the conventionally known compounds can be used.
The basic compound is preferably a volatile basic compound. Examples of the volatile basic compound include organic amines such as ammonia, triethylamine, N,N-dimethylethanolamine, and monoethanolamine, and among these, ammonia is preferable. Inorganic alkali compounds such as sodium hydroxide and potassium hydroxide, and non-volatile amine compounds such as triethylenediamine, diethanolamine, triethanolamine, diethylenetriamine, and diazabicyclooctene can also be used in combination within a range in which the drying performance is not reduced.

<Acetylene-based surfactants with HLB values of 3 to 8>
In order to improve both blocking resistance and leveling properties, it is necessary to contain an acetylene-based surfactant having an HLB value of 3.0 to 8.0. Examples of such surfactants include Surfynol 104E, 104H, 104A, 104PA, 104PG-50, 104S, SE, SE-F465, and 485, which are based on the compound represented by the following formula (4).

The content of the acetylene-based surfactant having an HLB value of 3.0 to 8.0 in the aqueous flexographic printing ink composition for reverse printing film is 0.1 to 5.0 mass %, preferably 0.1 to 3.0 mass %, and more preferably 0.1 to 1.5 mass %.
By blending a prescribed amount of such an acetylene surfactant having an HLB value of 3 to 8, blocking resistance, leveling properties and trapping properties can be exhibited in a well-balanced manner.
<Other surfactants>
Other surfactants may be added within a range that does not inhibit the effect of the acetylene surfactant having an HLB value of 3.0 to 8.0. Examples of other surfactants include acetylene glycol surfactants and derivatives thereof, such as Surfynol 465 and 485, each having an HLB value of less than 3.0 or more than 8.0, silicon surfactants such as BYK-381, 3441, 302, 307, 325, 331, 333, 342, 345, 346, 347, 348, 349, 378, and 3455 (manufactured by BYK Japan Co., Ltd.), and fluorine-based surfactants.

<Water-soluble organic solvent with boiling point of 60 to 200°C>
As the aqueous solvent, water-soluble organic solvents used together with water can include, for example, monoalcohols, polyhydric alcohols, lower alkyl ethers of polyhydric alcohols, ketones, ethers, esters, nitrogen-containing compounds, etc. These may be used alone or in combination of two or more kinds.
Examples of the monoalcohols include methanol (65° C.), ethanol (78° C.), n-propanol (97° C.), n-butanol (118° C.), n-pentanol (138° C.), n-hexanol (157° C.), n-heptanol (176° C.), n-octanol (195° C.), or isomers thereof, cyclopentanol (139° C.), cyclohexanol (161° C.), and the like. Preferably, an alcohol having an alkyl group with 1 to 6 carbon atoms can be used.
As the polyhydric alcohol, ethylene glycol (197° C.), propylene glycol (188° C.), etc. can be used.
Examples of the lower alkyl ethers of the polyhydric alcohols include ethylene glycol monomethyl ether (125° C.), ethylene glycol monoisopropyl ether (142° C.), ethylene glycol monobutyl ether (171° C.), ethylene glycol monoisobutyl ether (161° C.), diethylene glycol monomethyl ether (194° C.), propylene glycol monomethyl ether (121° C.), propylene glycol monopropyl ether (150° C.), dipropylene glycol monomethyl ether (187° C.), diethylene glycol dimethyl ether (162° C.), diethylene glycol methyl ethyl ether (176° C.), diethylene glycol diethyl ether (189° C.), etc. The numbers in parentheses indicate the boiling points.
Of these, it is preferable to employ ethanol, n-propanol, propylene glycol n-propyl ether, ethylene glycol monobutyl ether, propylene glycol, and propylene glycol monomethyl ether.
The content of the water-soluble organic solvent in the aqueous flexographic printing ink composition for reverse printing film is 0.1 to 20% by mass, preferably 1.0 to 10.0% by mass, and more preferably 2.0 to 7.0% by mass. If the water-soluble organic solvent is not contained, the leveling property will decrease, and if it exceeds 20% by mass, poor drying and blocking resistance will decrease.
Furthermore, when a water-soluble organic solvent having a boiling point exceeding 200° C. is added, there is a possibility that poor drying or reduced blocking resistance may occur, and when a water-soluble organic solvent having a boiling point of less than 60° C. is added, there is a possibility that reduced leveling properties may occur. By using a water-soluble organic solvent having such a boiling point range in the above-mentioned content range, it becomes possible to handle the ink composition as a non-hazardous material.
<Curing Agent>
Furthermore, the aqueous flexographic printing ink composition for reverse printing film of the present invention preferably contains a curing agent such as a carbodiimide-based curing agent or an aziridine-based curing agent in order to impart boiling resistance.
As the carbodiimide-based curing agent, water-soluble types such as Carbodilite V-02, V-02-L2, SV-02, V-04, and V-10, and emulsion types such as Carbodilite E-02, E-03A, and E-05 (all manufactured by Nisshinbo Chemical Co., Ltd.) can be used.
The aziridine-based curing agent is not particularly limited as long as it is a compound containing at least two aziridine groups (aziridinyl groups) in the molecule, and examples thereof include trimethylolpropane-tris[3-(1-aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl)butyrate], trimethylolpropane-tris[3-(1-(2-methyl)aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl) -2-methylpropionate], pentaerythritol-tris[3-(1-aziridinyl)propionate], pentaerythritol-tetra[3-(1-aziridinyl)propionate], tris(1-(2-methyl)aziridinyl)phosphine oxide, tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, ethylene glycol-bis[3-(1-aziridinyl)propionate], polyethylene glycol-bis[3-(1-aziridinyl ) propionate], propylene glycol bis[3-(1-aziridinyl) propionate], polypropylene glycol bis[3-(1-aziridinyl) propionate], tetramethylene glycol bis[3-(1-aziridinyl) propionate], polytetramethylene glycol bis[3-(1-aziridinyl) propionate], N,N'-tetramethylene bisethylene urea, N,N'-hexamethylene bisethylene urea, N,N'-phenylene bi Examples of the bis(1-aziridine)amide include bis[1-(2-ethyl)aziridinyl]benzene-1,3-carboxylic acid amide, N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), and bis[1-(2-ethyl)aziridinyl]benzene-1,3-carboxylic acid amide. These may be used alone or in combination of two or more. Among these, polyaziridines having three or more aziridinyl groups, such as trimethylolpropane-tris[3-(1-aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl)butyrate], trimethylolpropane-tris[3-(1-(2-methyl)aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl)-2-methylpropionate], pentaerythritol-tris[3-(1-aziridinyl)propionate], and pentaerythritol-tetra[3-(1-aziridinyl)propionate], are preferably used. In addition, as the polyfunctional aziridine compound, an aziridine prepolymer obtained by reacting at least one selected from polyesters and polycarbonates having two or more functional groups capable of reacting with an aziridinyl group with an aziridine compound having two or more aziridinyl groups may be used. Furthermore, when the resin has a hydroxyl group, an isocyanate crosslinking agent may be used in combination.
When these curing agents are blended, they are preferably used in the range of 0.1 to 1 equivalent, more preferably 0.1 to 0.7 equivalent, relative to 1 equivalent of the acid group in the aqueous urethane resin emulsion. If the amount used is less than 0.1 equivalent, the coating strength tends to decrease, whereas if it is more than 1 equivalent, the pot life (stability over time) tends to decrease.

<Other additives>
In addition, various additives such as pigment dispersants, anti-blocking agents such as ethylene-acrylic acid copolymers, defoamers, and antistatic agents can also be added depending on the requirements for ink performance.

<Production of Water-Based Flexographic Printing Ink Composition for Reverse Printing Film>
A typical method for producing an aqueous flexographic printing ink composition for reverse printing film using the various materials described above is to mix and knead the pigment, binder resin, aqueous solvent, and, if necessary, pigment dispersant, and then add and mix the remaining specified materials such as a curing agent.

<Printed materials>
The aqueous flexographic printing ink composition for reverse printing film obtained by the above method can be used for printing on a plastic film by a flexographic printing method.
Examples of plastic films onto which the aqueous flexographic printing ink composition for reverse printing film of the present invention is printed include various plastic films such as polyolefin, polyester and nylon, and those that have been surface-treated, such as by corona discharge treatment, are particularly preferred.

<Laminated printed matter>
Furthermore, as a method for laminating a printed matter of the aqueous flexographic printing ink composition for reverse printing film of the present invention, any of the following can be used: a normal extrusion lamination method in which the aqueous printing ink composition of the present invention is printed on the various films mentioned above, and then an imine-, isocyanate-, polybutadiene-, titanate-, or other anchor coating agent is applied to the printed surface, and molten polyethylene resin is laminated; a dry lamination method in which a urethane-, or other adhesive is applied to the printed surface, and then a plastic film is laminated; and a direct lamination method in which the aqueous printing ink composition of the present invention is printed on a polypropylene film, and then molten polypropylene resin is directly laminated on the printed surface.

The water-based flexographic printing ink composition for reverse-printed films of the present invention is water-based and has good lamination suitability for any lamination method.

When laminating using the usual extrusion lamination and dry lamination methods, using a water-based anchor coating agent or adhesive will result in a laminated product with less residual solvent, which is more advantageous in terms of food hygiene, etc.

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 addition, unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass".
(Production of aqueous urethane resin emulsion)
In a four-neck flask equipped with a thermometer, a stirrer, a cooling tube, and a nitrogen inlet tube, 300 parts of polyneopentyl adipate diol having a number average molecular weight of 1,000 and 133.2 parts of isophorone diisocyanate were charged, and while introducing nitrogen gas, the mixture was reacted at 100 to 105° C. for 4 hours with stirring, and then 24.1 parts of dimethylolpropionic acid was charged and reacted at 100 to 110° C. for 2 hours. After confirming that the dimethylolpropionic acid had completely reacted, the mixture was cooled to 100° C., and 1128 parts of water and 20.2 parts of triethylamine were charged to make the mixture aqueous, and the reaction was stopped with 34.8 parts of dihydrazine adipate, to obtain an aqueous polyurethane resin solution with a solid content of 30% and a resin acid value of 24.

(Water-soluble acrylic resin)
Styrene-lauryl methacrylate-acrylic acid copolymer (acid value 100 mg KOH/g, weight average molecular weight 11,000, ammonia neutralization, solid content 28% by mass)

(Acetylene-based surfactant)
Acetylenic surfactant 1: 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB value 4
Acetylenic surfactant 2: Ethylene oxide adduct of acetylene surfactant 1, HLB value 6
Acetylenic surfactant 3: Ethylene oxide adduct of acetylene surfactant 1, HLB value 13
Acetylenic surfactant 4: Ethylene oxide adduct of acetylene surfactant 1, HLB value 17

(Hardening agent)
Hardener 1: SU-125F (aziridine-based hardener, solid content 25%, manufactured by Meisei Chemical Industry Co., Ltd.)
Hardener 2: Carbodilite E-02 (carbodiimide hardener, solid content 40%, manufactured by Nisshinbo Chemical Co., Ltd.)
Hardener 3: Carbodilite E-05 (carbodiimide hardener, solid content 40%, manufactured by Nisshinbo Chemical Co., Ltd.)

<Film>
PET: Polyethylene terephthalate film with corona discharge treatment on one side, manufactured by Toyobo Co., Ltd., E-5101, thickness 12 μm
OPP: Corona-discharged biaxially oriented polypropylene film, P-216 manufactured by Toyobo Co., Ltd.
1. Thickness: 25 μm
NY: Nylon film, Toyobo Co., Ltd., N-1102, thickness 15 μm

<Water-based flexographic printing blue ink composition for reverse printing>
Indigo pigment (C.I. Pigment Blue 15:4), water-soluble acrylic resin, and aqueous polyurethane resin solution were kneaded using a paint conditioner manufactured by Red Devil Co., Ltd., and then an acetylene-based surfactant, a water-soluble organic solvent, and a curing agent were added and stirred to obtain water-based flexographic indigo ink compositions for reverse printing of Examples 1 to 10, 13 to 16, and Comparative Examples 1 to 7 shown in Table 1.

<Water-based flexographic printing white ink composition for reverse printing>
A white pigment (titanium oxide, product name "R-960", manufactured by DuPont), a water-soluble acrylic resin, and an aqueous polyurethane resin solution were kneaded using a paint conditioner manufactured by Red Devil Co., Ltd., and then an acetylene-based surfactant, a water-soluble organic solvent, and a curing agent were added and stirred to obtain water-based flexographic printing white ink compositions for reverse printing of Examples 11 and 12 and Comparative Examples 8 and 9 shown in Table 1.

<Production of printed matter 1>
The aqueous flexographic printing indigo ink composition for reverse printing film (Examples 1-10, 13-16, Comparative Examples 1-7) was printed on the treated surface of each film using a flexographic printer under the following conditions, followed by drying to obtain a print. The obtained prints were used to evaluate substrate adhesion, blocking resistance, leveling property, and boiling resistance. Specific evaluation methods are shown below.
(Printing method and conditions)
Printing room environment: Temperature 25°C, humidity 50%
Coating machine: Flexographic printing machine
Coating speed: 150 m/min
Printing plate: Solid plate Drying temperature: 55°C

<Production of printed matter 2>
On the treated surface of the film, a water-based flexographic printing indigo ink composition for reverse printing film (Examples 1 to 10, 13 to 16, Comparative Examples 1 to 7) was printed and dried under the conditions below using a flexographic printing machine. Next, a water-based flexographic printing white ink composition for reverse printing film (Examples 11, 12, Comparative Examples 8 and 9) was printed and dried under the conditions below so as to obtain the overprinting shown in Table 1, to obtain a print, and then the overprinting suitability was evaluated. The specific evaluation method is shown below.
(Printing method and conditions)
Printing room environment: Temperature 25°C, humidity 50%
Coating machine: Flexographic printing machine
Coating speed: 150 m/min
Printing plate: Indigo and white printing plate: Solid plate Drying temperature: 55°C

(Adhesion to substrate)
Adhesion was evaluated based on the degree to which the printed film peeled off from the film when cellophane tape was applied to the printed surface and then quickly peeled off.
A: The printed film does not peel off at all from the film.
B: Less than 20% of the area of the printed film peeled off from the film.
C: 20% or more and less than 50% of the area of the printed film peeled off from the film.
D: 50% or more of the area of the printed film was peeled off from the film.

(Blocking resistance)
The printed and non-printed surfaces were put together, clamped in a vice and left at 40° C. for one day before being peeled off by hand, and blocking resistance was evaluated from the degree of ink peeling and the strength of the peeling resistance.
A: The printed film does not peel off at all, and no peel resistance is felt.
B: The printed film did not peel off at all, but some resistance to peeling was felt.
C: The printing film peeled off slightly, and there was a strong resistance to peeling.
D: The printing film was almost completely peeled off, and there was a strong resistance to peeling.

(Leveling ability)
The solid portion of the print was magnified and observed, and the leveling ability of the print was evaluated visually.
A: There was no unevenness in the shade and it was uniform.
B: There was slight unevenness in the shade.
C: There were noticeable missing points.
D: Many dots were missing, and wavy patterns were observed.

(Trapping ability)
Using a flexographic printing machine, the diluted indigo ink containing each additive was printed, and then the diluted white ink was printed, and the resulting prints were visually evaluated.
A: There was no unevenness in the shade and it was uniform.
B: There was slight unevenness in the shade.
C: Bleeding of the overprinted ink was observed.
D: Blurring of the overprinted ink and wavy patterns were observed.

(Boiling resistance)
A urethane adhesive (Takelac A-616/Takenate A-65, manufactured by Mitsui Chemicals Polyurethanes) was applied to each PET film print and each NY film print one day after printing in an amount of 2.0 g/ ^m2 in solid content, and then a non-oriented polypropylene film (RXC-22, thickness 60 μm, manufactured by Tocello) was attached using a dry laminator and left for 3 days at 40°C to obtain a dry laminate. This dry laminate was made into a bag, filled with water and heat-sealed, and then immersed in hot water at 90°C for 30 minutes to evaluate boil resistance based on the presence or absence of lifting of the laminate film.
A: No peeling of the lamination is observed at all.
B: Pinholes or short, thin laminations are observed in some areas.
C: Long streaks of lamination are observed over the entire surface.

According to the above results, according to Examples 1 to 16, which are examples according to the present invention, it was possible to obtain an aqueous flexographic printing ink composition for reverse printing film, which was excellent in substrate adhesion, blocking resistance, leveling property, trapping property, and boiling resistance. In contrast, the ink composition of Comparative Example 1, which did not contain an acetylene-based surfactant with an HLB value of 3.0 to 8.0, and Comparative Example 3, which did not contain a water-soluble organic solvent with a boiling point of 60 to 200°C, showed poor leveling properties. Furthermore, according to Comparative Examples 5, 6, 8, and 9, which contained only an acetylene-based surfactant not in the range of an HLB value of 3.0 to 8.0 as a surfactant, the leveling properties were deteriorated or further deteriorated.
Furthermore, Comparative Example 2, which contained an excess of an acetylene-based surfactant with an HLB value of 3.0 to 8.0, exhibited deteriorated blocking resistance and trapping properties, while Comparative Example 4, which contained an excess of a water-soluble organic solvent having a boiling point of 60 to 200° C., and Comparative Example 7, which contained no water-soluble organic solvent having a boiling point of 60 to 200° C. but contained a water-soluble organic solvent outside this boiling point range, exhibited deteriorated blocking resistance.

Claims (6)

It contains pigment, water-based urethane resin emulsion, surfactant, water-soluble organic solvent, and water.
The ink composition contains 0.1 to 3.0 mass % of an acetylene-based surfactant having an HLB value of 3.0 to 8.0,
the ink composition contains 0.1 to 20 mass% of a water-soluble organic solvent having a boiling point of 60 to 200°C as the water-soluble organic solvent (excluding cases where 1-butanol or isobutanol is contained), and the water-soluble organic solvent contains a polyhydric alcohol and/or a lower alkyl ether of a polyhydric alcohol;
The aqueous urethane resin in the aqueous urethane resin emulsion contains an acrylic resin portion.
A water-based flexographic printing ink composition for reverse printing films. It contains pigment, water-based urethane resin emulsion, surfactant, water-soluble organic solvent, and water.
The ink composition contains 0.1 to 3.0 mass % of an acetylene-based surfactant having an HLB value of 3.0 to 8.0,
the ink composition contains, as a water-soluble organic solvent, a water-soluble organic solvent having a boiling point of 60 to 200°C in an amount of 0.1 to 20 mass%, and the water-soluble organic solvent contains a polyhydric alcohol and/or a lower alkyl ether of a polyhydric alcohol;
The aqueous urethane resin in the aqueous urethane resin emulsion is a resin obtained by reacting a urethane prepolymer, which is a reaction product of an organic diisocyanate compound and a polymeric diol compound, with a chain extender containing glycols or aliphatic or alicyclic diamines.
A water-based flexographic printing ink composition for reverse printing films. The water-based flexographic printing ink composition for reverse printing film according to claim 1 or 2, which contains an alkali-soluble water-soluble resin. The aqueous flexographic printing ink composition for reverse printing film according to claim 3, wherein the alkali-soluble water-soluble resin is an acrylic resin. The aqueous flexographic printing ink composition for reverse printing film according to any one of claims 1 to 4 further contains a carbodiimide-based curing agent and/or an aziridine-based curing agent. The aqueous flexographic printing ink composition for reverse printing film according to any one of claims 1 to 5, wherein the polyhydric alcohol is one or more selected from the group consisting of ethylene glycol and propylene glycol, and the lower alkyl ether of the polyhydric alcohol is one or more selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether.