JP7776579B2 - Water-based flexographic printing ink composition for reverse printing film - Google Patents

Description

The present invention relates to an aqueous flexographic printing ink composition for reverse printing films.

Packaging materials made from various plastic films are used for food, confectionery, household goods, pet food, etc., due to their functionality such as design, economy, content protection, and transportability. Furthermore, many packaging materials are printed using gravure or flexographic printing to impart designs and messages that will appeal to consumers.
To obtain the desired packaging material, front printing is performed on the surface of the base film of the packaging material, or reverse printing is performed by applying an adhesive or anchor agent to the printed surface of the base film of the packaging material as needed and laminating the film.
In reverse printing, colored inks and white inks are printed sequentially onto various films such as polyester, nylon, and aluminum foil, and then a polyethylene film or polypropylene film is laminated onto 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).

Furthermore, traditionally, water-based flexographic inks have been widely used on permeable, dryable substrates such as tissue paper and corrugated 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, resulting in particularly poor leveling properties (see, for example, Patent Documents 2 and 3).

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

The objective of the present invention is to provide a flexographic printing ink composition that can be used for reverse printing on resin film substrates by using an aqueous flexographic printing ink composition as the printing ink composition for reverse printing on films.

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

By combining a specific resin and a specific surfactant, the aqueous flexographic printing ink composition for reverse printing films of the present invention is able to exhibit a good balance of excellent adhesion to resin films, blocking resistance, leveling, trapping, and boiling resistance.

The aqueous 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 colored 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 organic pigments 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 strength of the ink composition will decrease, and if it is more than the above range, the viscosity of the ink composition will increase, making the printed matter more susceptible to smearing.

<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 polymeric diol compound to synthesize a urethane prepolymer, followed by reaction 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 by 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 because they improve adhesion to various films and resolubility in aqueous printing inks.

Polymer 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, with dibasic acid components such as adipic acid and phthalic acid, or by the ring-opening reaction of cyclic ester compounds such as lactones, as well as oxidized Examples of suitable 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 polycarbonate diols and polybutadiene glycols obtained by reacting carbonate components such as alkylene carbonate, diallyl carbonate, and dialkyl carbonate, or phosgene with the above-mentioned low-molecular-weight diol components.

Furthermore, as a polymeric diol compound having a free carboxyl group for making a polyurethane resin aqueous in the presence of a basic compound, a polymeric diol compound obtained by reacting the polymeric 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 500 to 4,000.
In terms of adhesion to plastic films and suitability for lamination, polyester diols and polycarbonate diols are preferably used as the polymeric diol compound, and polyester diols are more preferably used in terms 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 alkanediols, such as 1,4-pentanediol, 2,5-hexanediol, or 3-methyl-1,5-pentanediol, or low-molecular-weight diol compounds, such as ethylene glycol, propylene glycol, 1,4-butanediol, or 1,3-butanediol, can be used alone or in combination of two or more types.

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 mixtures. 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.

A chain extender having a free carboxyl group for making a polyurethane resin water-based in the presence of a basic compound is represented by 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, or aromatic carboxylic acid-containing polyols obtained by reacting phthalic acid, trimellitic acid, pyromellitic acid, or anhydride thereof with a polyol.

Furthermore, to impart higher adhesion to plastic films and excellent lamination strength to printing inks, chain extenders containing hydrazine residues in the molecule can be used, specifically, for example, those represented by 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 general formula (2) can be obtained by a conventional method (JP-B 3-8649), which involves first obtaining a Michael addition compound of a polyamine and a (meth)acrylic acid derivative, and then transesterifying the (meth)acrylic acid ester moiety with hydrazine.
The chain extender having the molecular structure represented by general formula (2) has hydrazine residues remaining in the polyurethane resin even after chain extension, and can provide good adhesiveness by crosslinking with the film surface or the like.

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, with acrylic acid derivatives being preferred from the standpoint of reactivity.

Next, the reaction terminator will be described.
The reaction terminator is used to react with unreacted isocyanate groups after the urethane prepolymer has been chain-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 xylenediamine; and polyamine compounds having primary amino groups at both ends, such as diamines having hydroxyl groups, such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, and N,N'-di(2-hydroxyethyl)ethylenediamine.

Furthermore, 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 suitable for use, as well as hydrazine and compounds represented by the following general formula (3):

Alkylene dihydrazines or dihydrazide compounds of saturated aliphatic dibasic acids or unsaturated dibasic acids, represented by the formula (where 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), 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 acid dihydrazide, malonic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, and sebacic acid dihydrazide. Specific examples of dihydrazide compounds of unsaturated dibasic acids include phthalic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide.

A 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 polymeric 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 flexible, and in cases where the blocking resistance or the like is low when the ink is printed, it may be preferable to use it in combination with another hard resin.
The organic diisocyanate compound and the polymeric diol compound are mixed in the above molar ratio, and then the necessity and type of solvent and catalyst, the reaction temperature, etc. are determined depending on the reactivity of the two compounds, and the compounds are reacted by a known method to synthesize a urethane prepolymer. Next, a chain extender and a reaction terminator are added 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 using the above materials and production methods, the polyurethane resin of the present invention is one having a number-average molecular weight of 5,000 to 200,000, preferably 70,000 to 100,000. If the number-average molecular weight is below this range, the resin film will lack elasticity and be brittle. On the other hand, if the number-average molecular weight exceeds this range, the viscosity of an aqueous polyurethane resin dissolved in water in the presence of a basic compound will increase, and the dispersibility of an aqueous polyurethane resin dispersed in water in the presence of an emulsifier and/or a basic compound will decrease.

Next, we will explain how to convert the polyurethane resin of the present invention into an aqueous varnish. First, the method for converting polyurethane resins that do not have free carboxyl groups in their molecules into an aqueous varnish mainly involves dispersing the polyurethane resin in water in the presence of an emulsifier.

To achieve this, the following two methods can be used:
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, and then 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 stopped with a reaction terminator, 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, and these can be used alone or in combination.

On the other hand, 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, is to use a polymeric diol compound having free carboxyl groups and/or a chain extender, dissolving or dispersing the molecules in water at the chain extension stage, and then terminating the reaction. Here, the total amount of polymeric diol compound having free carboxyl groups and 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 will be 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 will be too hard, making it impossible to obtain a printing ink with good film properties.

(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, with ammonia being preferred. 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, as long as the drying performance is not impaired.

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

The aqueous flexographic printing ink composition for reverse printing films of the present invention preferably contains 5 to 25% by weight of aqueous polyurethane resin emulsion solids. If the polyurethane resin solids content is less than this range, adhesion to polyester and nylon films and lamination strength will decrease. On the other hand, if the polyurethane resin solids content is greater than this range, adhesion to polyolefin films and suitability for direct lamination will decrease, which is undesirable.

<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 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 adsorption 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.

Monomers containing hydrophobic groups to improve pigment adsorption are preferably (meth)acrylates with long-chain alkyl groups containing 6 to 20 carbon atoms, with 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, and 2-hydroxystearyl (meth)acrylate being more preferred. Furthermore, styrene-based monomers such as styrene, α-styrene, and vinyltoluene can also 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 such monomers that can be used include (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-methylolacrylamide, cyclohexyl (meth)acrylate, and benzyl (meth)acrylate.
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, while 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 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 abrasion resistance of the resulting printed matter tend to decrease, while if it exceeds 200,000, the viscosity increases, which is undesirable.
The amount of the alkali-soluble resin blended in the aqueous flexographic printing ink composition for reverse printing film is preferably 0.5 to 5.0 mass %, more preferably 1.0 to 3.0 mass %, in terms of solid content.

The acid value is a theoretical acid value calculated arithmetically from the number of milligrams of potassium hydroxide theoretically required to neutralize 1 g of 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 Water 2690 (manufactured by Waters Corporation) as a GPC device and a PLgel 5 μm MIXED-D (manufactured by Agilent Technologies) as a column, and the weight-average molecular weight can be determined as a 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, with ammonia being preferred. 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, as long as the drying performance is not impaired.

<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 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 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 predetermined 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 good balance.
<Other surfactants>
Other surfactants can be added within a range that does not inhibit the effects of the acetylene-based surfactants having an HLB value of 3.0 to 8.0. Examples of other surfactants include acetylene glycol-based 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-based surfactants such as BYK-381, 3441, 302, 307, 325, 331, 333, 342, 345, 346, 347, 348, 349, 378, and 3455 (manufactured by BYK Japan KK), and fluorine-based surfactants.

<Water-soluble organic solvent with a boiling point of 60 to 200°C>
Examples of the aqueous solvent that can be used together with water include water-soluble organic solvents such as 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.
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), etc., and preferably, alcohols 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 boiling points.
Of these, it is preferable to use 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 films 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 ability will decrease, and if it exceeds 20% by mass, poor drying and reduced blocking resistance will occur.
Furthermore, when a water-soluble organic solvent with 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 with a boiling point of less than 60° C. is added, there is a possibility that leveling properties may decrease. By using a water-soluble organic solvent with a boiling point in this range within 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 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 Inc.) can be used.
The aziridine 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], nate], 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'- Examples thereof include tetramethylene bisethylene urea, N,N'-hexamethylene bisethylene urea, N,N'-phenylene bisethylene urea, N,N'-toluylene bisethylene urea, N,N'-diphenyl-4,4'-bisethylene urea, 3,3'-dimethyldiphenyl-4,4'-bisethylene urea, diphenylmethane P,P-bisethylene urea, N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), bis[1-(2-ethyl)aziridinyl]benzene-1,3-carboxylic acid amide, and the like. 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. Alternatively, the polyfunctional aziridine compound may be an aziridine prepolymer obtained by reacting at least one selected from polyesters and polycarbonates having two or more functional groups reactive with aziridinyl groups with an aziridine compound having two or more aziridinyl groups. Furthermore, when the resin has a hydroxyl group, an isocyanate crosslinking agent may be used in combination.
When these curing agents are added, they are preferably used in the range of 0.1 to 1 equivalent, and more preferably 0.1 to 0.7 equivalents, per equivalent of the acid groups in the aqueous urethane resin emulsion. If the amount used is less than 0.1 equivalent, the coating strength tends to decrease, while 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, antifoaming agents, antistatic agents and the like can also be added depending on the ink performance requirements.

<Production of aqueous 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 involves mixing and kneading the pigment, binder resin, aqueous solvent, and, if necessary, pigment dispersant, and then adding and mixing the remaining predetermined materials such as a curing agent.

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

<Laminated printed matter>
Furthermore, methods that can be used to laminate a printed material printed with the aqueous flexographic printing ink composition for reverse-printing film of the present invention include a conventional extrusion lamination method in which the aqueous printing ink composition of the present invention is printed on the various films described above, and then an imine-, isocyanate-, polybutadiene-, or titanate-based anchor coating agent is applied to the printed surface, and then molten polyethylene resin is laminated thereon; a dry lamination method in which a urethane-based or other adhesive is applied to the printed surface, and then a plastic film is laminated thereon; 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 laminated directly on the printed surface.

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

When laminating using standard extrusion lamination and dry lamination methods, using a water-based anchor coating agent or adhesive will result in laminated products 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. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."
(Production of aqueous urethane resin emulsion)
A four-neck flask equipped with a thermometer, stirrer, condenser, and nitrogen inlet tube was charged with 300 parts of polyneopentyl adipate diol having a number average molecular weight of 1,000 and 133.2 parts of isophorone diisocyanate, and the mixture was reacted for 4 hours at 100-105°C with stirring while introducing nitrogen gas. Next, 24.1 parts of dimethylolpropionic acid was charged and the mixture was reacted for 2 hours at 100-110°C. After confirming that the dimethylolpropionic acid had completely reacted, the mixture was cooled to 100°C, and 1,128 parts of water and 20.2 parts of triethylamine were charged to make the mixture aqueous. The reaction was then stopped with 34.8 parts of dihydrazine adipate, yielding an aqueous polyurethane resin solution with a solids 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 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)
Curing agent 1: SU-125F (aziridine-based curing agent, solid content 25%, manufactured by Meisei Chemical Industry Co., Ltd.)
Curing agent 2: Carbodilite E-02 (carbodiimide curing agent, solid content 40%, manufactured by Nisshinbo Chemical Inc.)
Curing agent 3: Carbodilite E-05 (carbodiimide curing agent, solid content 40%, manufactured by Nisshinbo Chemical Inc.)

<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-2161 manufactured by Toyobo Co., Ltd., thickness 25 μm
NY: Nylon film, manufactured by Toyobo Co., Ltd., N-1102, thickness 15 μm

<Water-based flexographic printing blue ink composition for reverse printing>
A blue pigment (C.I. Pigment Blue 15:4), 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 the water-based blue 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, trade 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 compositions for reverse printing films (Examples 1 to 10, 13 to 16, Comparative Examples 1 to 7) were printed on the treated surface of each film using a flexographic printing machine under the conditions below, followed by drying to obtain printed matter. The resulting printed matter was used to evaluate substrate adhesion, blocking resistance, leveling ability, and boiling resistance. Specific evaluation methods are described below.
(Printing method/printing 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>
The treated surface of the film was printed and dried using a flexographic printing machine under the conditions below with aqueous flexographic printing indigo ink compositions for reverse-printing films (Examples 1 to 10, 13 to 16, Comparative Examples 1 to 7). Next, aqueous flexographic printing white ink compositions for reverse-printing films (Examples 11 and 12, Comparative Examples 8 and 9) were printed and dried under the conditions below to obtain the overprints shown in Table 1, and after obtaining prints, the overprinting suitability was evaluated. Specific evaluation methods are described below.
(Printing method/printing 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 by 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 from the film at all.
B: Less than 20% of the area of the printed film peeled off from the film.
C: 20% or more but 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 peeled off from the film.

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

(Leveling ability)
The solid portion of the print was observed under magnification, 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: Missing points were noticeable.
D: There were many missing dots 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 overprinting ink was observed.
D: Overprint ink bleeding and wavy patterns were observed.

(Boiling resistance)
One day after printing, each PET film print and each NY film print was coated with a urethane adhesive (Takelac A-616/Takenate A-65, manufactured by Mitsui Chemicals Polyurethanes) in an amount of 2.0 g/ ^m2 in solids, and then a non-oriented polypropylene film (RXC-22, 60 μm thick, manufactured by Tocello Co., Ltd.) was attached using a dry laminating machine and left to stand at 40°C for 3 days to obtain a dry laminate. This dry laminate was made into a bag, filled with water, heat-sealed, and then immersed in hot water at 90°C for 30 minutes. Boiling resistance was evaluated based on whether the laminate film floated.
A: No lamination lifting is observed.
B: Pinholes or thin, short laminations are observed in some areas.
C: Long stripes of raised lamination are observed over the entire surface.

The above results show that Examples 1 to 16, which are examples in accordance with the present invention, provided aqueous flexographic printing ink compositions for reverse-printed films that were excellent in substrate adhesion, blocking resistance, leveling, trapping, and boiling resistance. In contrast, the ink compositions 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, exhibited poor leveling properties. Furthermore, Comparative Examples 5, 6, 8, and 9, which contained only an acetylene-based surfactant with an HLB value outside the range of 3.0 to 8.0 as a surfactant, exhibited poor or even worse leveling properties.
Furthermore, Comparative Example 2, which contained an excess amount of an acetylene-based surfactant with an HLB value of 3.0 to 8.0, resulted in poor blocking resistance and trapping properties. Comparative Example 4, which contained an excess amount of a water-soluble organic solvent with a boiling point of 60 to 200°C, and Comparative Example 7, which contained no water-soluble organic solvent with a boiling point of 60 to 200°C but contained a water-soluble organic solvent outside this boiling point range, resulted in poor blocking resistance.

Claims (5)

A pigment,
an alkali-soluble water-soluble resin;
an aqueous urethane resin emulsion;
an acetylene-based surfactant having an HLB value of 3.0 to 8.0;
a water-soluble organic solvent having a boiling point of 60 to 200°C;
Water and
An aqueous flexographic printing ink composition for reverse printing films, comprising:
the content of the acetylene surfactant is 0.1 to 3.0% by mass based on the total mass of the ink composition;
the water-soluble organic solvent comprises a polyhydric alcohol selected from ethylene glycol and propylene glycol, or ethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, propylene glycol monomethyl ether, or propylene glycol monopropyl ether;
The content of the water-soluble organic solvent is 0.1 to 20% by mass based on the total mass of the ink composition. The water-based flexographic printing ink composition for reverse printing films according to claim 1, wherein the alkali-soluble water-soluble resin is an acrylic resin. The aqueous flexographic printing ink composition for reverse printing film according to claim 1 or 2, further comprising a carbodiimide-based curing agent and/or an aziridine-based curing agent. The aqueous flexographic printing ink composition for reverse printing films according to claim 1 or 2, wherein the number average molecular weight of the aqueous urethane resin in the aqueous urethane resin emulsion is in the range of 70,000 to 200,000. The aqueous flexographic printing ink composition for reverse printing film according to claim 1 or 2, except when the aqueous urethane resin in the aqueous urethane resin emulsion contains an acrylic resin portion.