JP3706198B2 - Water-based printing ink binder - Google Patents

Description

（２）接着性
表面処理ポリプロピレンフィルム（ＯＰＰ）および表面処理ポリエステルフィルム（ＰＥＴ）に水性印刷インキを固形分で２〜３μｍの厚みになるようにバーコーターで塗布し、６０℃で１分間乾燥後、塗布面にセロテープ（ニチバン製、１２ｍｍ巾）を貼り、このセロテープの一端をを塗面に対して、直角方向に急速に引き剥がしたときの塗布面状態を観察した。

（３）耐水性試験
接着性試験と同じ方法で得た塗布試験片（ＰＥＴに塗布）を２５℃の水中に２４時間浸漬した後、塗布面にセロテープを貼り、このセロテープの一端をを塗面に対して、直角方向に急速に引き剥がしたときの塗布面状態を観察した。

（４）耐油性
接着性試験と同じ方法で得た塗布試験片（ＰＥＴに塗布）を２５℃の菜種油中に２４時間浸漬した後、塗布面状態を観察した。
評価基準 ○：変化なし ×：艶びけあり
（５）臭気
接着性試験と同じ方法で得た塗布試験片（ＰＥＴに塗布）を５００ｍｌの三角フラスコに封入しゴム栓にて密封し、６０℃の恒温器中で２４時間静置後、ゴム栓を開封し、アミン臭気の有無を検査した。
評価基準 ○：臭気なし ×：臭気あり
【００３６】
【表１】

【００３７】
【発明の効果】
本発明の水性印刷インキ用バインダ−は、従来のポリウレタン樹脂系水性印刷インキ用バインダーの問題であったインキの再溶解性、耐油性を向上させ、かつ低臭気性であるので、特に包装材等に用いられるプラスチックフィルム用の水性印刷インキ用バインダーとして極めて有用である。
また、本発明のバインダーは、各種基材に対する接着性に優れ、しかも低臭気であることから、上記用途としてだけではなく、塗料用バインダー、接着剤、紙用のコーテング剤等としても有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a binder for aqueous printing inks. More specifically, the present invention relates to a binder for aqueous printing inks that has good ink re-dissolvability, excellent oil resistance of a coating film, and low odor.
[0002]
[Prior art]
Conventionally, as a binder for water-based printing ink, those made of a polyurethane resin emulsion (JP-A 63-37160, JP-A-2-238015, etc.) are known. However, since these are emulsions in which the resin is dispersed in water, if the emulsion particles are aggregated, the re-solubility is poor, and there is a problem of causing plate clogging during printing. Moreover, although what consists of water-soluble polyether type | system | group polyurethane resin (for example, Unexamined-Japanese-Patent No. 55-134635) is proposed, there exists a problem that oil resistance at the time of using ink worsens. As a solution to such a problem, a product obtained by chain-extending a neutralized product of a urethane prepolymer containing a molecular terminal isocyanate group having an average number of functional groups of less than 2 in water (JP-A-7-3199) has been proposed. However, since this is a water-soluble polyurethane resin that uses an organic amine (tertiary amine) as the neutralizing agent, some organic amines remain in the coating film under normal print drying conditions. There was a problem with a bad odor.
[0003]
[Problems to be solved by the invention]
It is an object of the present invention to obtain a good printed matter with good ink re-dissolvability and without clogging during printing, and good oil resistance of the coating film when used as a printed matter and odor such as residual organic amine. An object of the present invention is to provide a binder for water-based printing inks having a very small amount.
[0004]
[Means for Solving the Problems]
As a result of diligent investigations to achieve the above object, the present inventors end-capped a polyurethane resin containing an isocyanate group at the molecular end and an anionic group at the molecular side chain with ammonia, and contained the anionic group in the middle. It was found that the above-mentioned problems can be solved by imparting hydrophilicity and making it water-based, and reached the present invention.
[0005]
That is, the present invention comprises an organic polyisocyanate (a), a polyester polyol (b), a compound (c) having an anionic group and at least two active hydrogen-containing groups in the molecule, and optionally a chain extender (d). A polyurethane resin (A) containing an isocyanate group at a derived molecular end is end-capped with ammonia, and the anionic group is neutralized and dissolved in an aqueous medium. It is a binder for water-based printing ink.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the organic polyisocyanate (a) include (1) aromatic diisocyanate [2,4- or 2,6-tolylene diisocyanate (TDI), 4,4′- or 2,4′-diphenylmethane diisocyanate (MDI), etc. 2) Aliphatic diisocyanates [hexamethylene diisocyanate (HDI), lysine diisocyanate, etc.]; 3) Alicyclic diisocyanates [isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4 ′ -Diisocyanate (hydrogenated MDI, etc.); (4) Aro-aliphatic diisocyanate (xylylene diisocyanate (XDI), α, α, α ', α'-tetramethylxylylene diisocyanate (TMXDI), etc.); Organic diisocyanate Examples thereof include modified products of salts (for example, modified products of isocyanurate, burette, carbodiimide, etc.) and mixtures of two or more thereof. Of these, preferred are alicyclic diisocyanates and araliphatic diisocyanates, and particularly preferred are IPDI, hydrogenated MDI, TMXDI and XDI.
[0007]
As the polyester polyol (b), (1) a low molecular polyol having a number average molecular weight of 500 or less [ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,4-pentanediol, 2, 5-hexanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 2,2,4-trimethyl-1,6hexanediol, 2- Butyl-2-ethylpropylene glycol, 2,2-dimethyloloctane, 2-methyl-1,8-octanediol, 1,9-nonanediol, bishydroxymethylcyclohexane, bishydroxylbenzene, alkyl dialkanolamine, bisphenol A Of alkylene oxides (e.g. Low-mole adducts such as lenoxide and propylene oxide] and polycarboxylic acids (adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, maleic acid, fumaric acid, isophthalic acid, terephthalic acid, dimer acid or these And (2) lactone polyester polyols (polycaprolactone diol, polyvalerolactone diol, etc.), (3) polycarbonate diols, and the like. Among these, preferred are a condensed polyester polyol, a polycaprolactone diol, a polyvalerolactone diol and a polycarbonate diol from a linear or branched low molecular polyol having 5 to 10 carbon atoms and a polyvalent carboxylic acid, particularly preferably. Condensed polyester polyol [polyneopentyl adipate diol, poly (3-methyl-1,5-pentylene adipate) diol, poly (1,4-pentane] from branched low molecular polyol having 5 to 10 carbon atoms and dicarboxylic acid Adipate) diol, poly (2,5-hexaneadipate) diol, poly (2-butyl-2-ethylpropyleneadipate) diol, poly (2,2,4-trimethyl-1,6hexaneadipate) diol and poly (2 -Methyl-1,8-octa Is an adipate) diol].
[0008]
In the present invention, the number average molecular weight of the polyester polyol (b) is usually 500 to 10,000, preferably 700 to 6,000. When the molecular weight is less than 500, the polyurethane resin film becomes hard, and when it is used as an ink, the adhesion to the plastic film is lowered. When it exceeds 10,000, the polyurethane resin film becomes too soft and is applied when used as an ink. The oil resistance and blocking resistance of the film are reduced.
[0009]
Examples of the compound (c) having an anionic group and at least two active hydrogen-containing groups in the molecule include (1) hydroxy acid (glycolic acid, tartaric acid, 4,6-dihydroxyisophthalic acid, α, α-di Methylol propionic acid, α, α-dimethylol butyric acid, α, α-dimethylol nonanoic acid, and carboxyl group-containing polycaprolactone diol obtained by addition polymerization of these with caprolactone monomer); (2) hydroxysulfonic acid (1,7 -Dihydroxynaphthalenesulfonic acid etc.); (3) aminosulfonic acid (2,4-diaminobenzenesulfonic acid etc.) etc. are mentioned. Preferred among these are compounds having two hydroxyl groups and one carboxyl group in the molecule (α, α-dimethylolpropionic acid, α, α-dimethylolbutyric acid and these obtained by addition polymerization of caprolactone monomer. Carboxyl group-containing polycaprolactone diol).
[0010]
When the anionic group of (c) is a carboxyl group, the content of the carboxyl group is usually 1.0 to 7.0% by weight, preferably 1.5 to 6.0% by weight based on the weight of the polyurethane resin (A). %, Particularly preferably 2.0 to 5.0% by weight. If the carboxyl group content is less than 1.0% by weight, a stable aqueous polyurethane resin cannot be obtained. If the carboxyl group content exceeds 7.0% by weight, the water resistance of the film as ink is lowered.
[0011]
Examples of the chain extender (d) used as necessary include low molecular polyols and polyamines. Examples of the low molecular polyol include low molecular polyols having an average molecular weight of 500 or less exemplified in the section (b). Polyamines include aliphatic diamines (ethylenediamine, hexamethylenediamine, 1,2-propylenediamine, 2,2,4-trimethylhexamethylenediamine, N- (2-hydroxyethyl) ethylenediamine, etc.); alicyclic diamines ( Isophorone diamine, 4,4′-dicyclohexylmethanediamine, 1,4-diaminocyclohexane, etc.); aromatic diamine (4,4′-diaminodiphenylmethane, etc.); araliphatic diamine (such as xylylenediamine); hydrazine or its Derivatives (such as adipic acid dihydrazide) and mixtures of two or more of these. Of these, preferred are low molecular weight polyols.
[0012]
The concentration of the terminal isocyanate group of the polyurethane resin (A) in the present invention is usually 0.1 to 1.5% by weight, preferably 0.2 to 1.0% by weight, particularly preferably 0.3 to 0.8% by weight. It is. If the isocyanate group concentration is less than 0.1% by weight, the molecular weight of the aqueous polyurethane resin obtained is increased, the re-solubility is lowered when ink is used, and if it exceeds 1.5% by weight, the molecular weight of the aqueous polyurethane resin obtained is When the ink is reduced, the adhesive strength and oil resistance are reduced.
[0013]
Illustrating the production method of the aqueous polyurethane resin in the present invention, the above (a), (b), (c) and, if necessary, (d) are reacted in the presence or absence of an organic solvent to form isocyanate at the molecular end. A polyurethane resin (A) having a group is prepared, and ammonia is added to the (A) to seal the isocyanate group at the molecular end, neutralize an anionic group (carboxyl group, etc.) and then dissolve in an aqueous medium. For example, a method of obtaining an aqueous polyurethane resin by removing an organic solvent as required.
In the production of (A), the equivalent ratio of the total of active hydrogen-containing groups (b), (c) and optionally (d) to the isocyanate group of (a) is usually 1: (1.02- 2), preferably 1: (1.05-1.5).
[0014]
The production method of the polyurethane resin (A) is not particularly limited. (1) One-shot method in which each component is reacted at once or (2) Multistage method in which the components are reacted stepwise [for example, reacting with (b) and (a) After the isocyanate group-terminated prepolymer is formed, the remaining part of the active hydrogen compound is added and further reacted, and the like may be used.
[0015]
In the production of (A), if necessary, a compound having one active hydrogen in the molecule [monoalcohol (eg, methanol, butanol) or monoamine (eg, butylamine, dibutylamine), etc.] can be used in combination.
[0016]
The synthesis reaction of the polyurethane resin (A) is usually carried out at 20 to 140 ° C., preferably 40 to 120 ° C. (However, when polyamine is reacted, it is usually carried out at a temperature of 100 ° C. or less, preferably 0 to 80 ° C. .)
[0017]
To promote the reaction, amine catalysts (triethylamine, N-ethylmorpholine, triethylenediamine, etc.) used in ordinary urethanization reactions, tin-based catalysts (dibutyltin dilaurate, dioctyltin dilaurate, tin octylate, etc.), titanium-based catalysts A catalyst (such as tetrabutyl titanate) may be used.
[0018]
In addition, the reaction is carried out in an organic solvent [ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), esters (ethyl acetate, butyl acetate, ethyl cellosolve acetate, etc.), ethers (dioxane, tetrahydrofuran, etc.). Etc.), hydrocarbons (n-hexane, n-heptane, cyclohexane, tetralin, toluene, xylene, etc.), amides (dimethylformamide, dimethylacetamide, etc.), N-methylpyrrolidone, etc.] The organic solvent may be added during or after the reaction.
[0019]
The number average molecular weight of the aqueous polyurethane resin in the present invention is usually 5,000 to 200,000, preferably 8,000 to 100,000. When the number average molecular weight is less than 5,000, when the ink is used, the blocking resistance of the coating film is poor, and when it exceeds 200,000, the redissolvability of the ink is lowered.
[0020]
The binder for aqueous printing ink of the present invention is usually used as a solution in which the aqueous polyurethane resin is dissolved in an aqueous medium. The resin concentration of the solution is usually 10 to 80% by weight, preferably 20 to 60% by weight. Moreover, a viscosity is 50-100,000 cP / 25 degreeC normally, Preferably it is 100-10,000 cP / 25 degreeC.
[0021]
The resin constituting the binder for aqueous printing inks of the present invention may be the aqueous polyurethane resin alone, or may be used in combination with other aqueous resins as necessary. Other aqueous resins that can be used in combination include acrylic resins, vinyl acetate resins, vinyl chloride resins, styrene maleic acid copolymer resins, and rosin resins.
[0022]
Further, additives such as stabilizers, surfactants, antifoaming agents, preservatives, antifreezing agents, thickeners and the like can be added as necessary. Specific examples thereof include the following.
Stabilizer: Hindered phenol, hydrazine, benzophenone, benzotriazole, oxalic acid anilide, or hindered amine stabilizer.
Surfactant: Nonionic surfactant such as ethylene oxide adduct of nonylphenol, anionic surfactant such as lauryl alcohol sulfate sodium salt, and the like.
Antifoaming agent: A silicone-based or alcohol-based antifoaming agent.
Preservative: Organic nitrogen sulfur compound-based or organic sulfur halogen compound-based preservative.
Antifreeze: ethylene glycol, propylene glycol, etc.
Thickener: cellulose derivative, starch derivative or polyvinyl alcohol.
[0023]
If necessary, a pigment dispersant, water as a solvent and / or alcohols (ethyl alcohol, isopropyl alcohol, etc.) are blended with the binder for water-based printing ink of the present invention, and a normal ink production apparatus such as a sand grinder mill or a ball mill. It can be set as water-based printing ink by kneading | mixing using.
[0024]
An example of the formulation of the aqueous printing ink using the binder of the present invention is as follows (% indicates% by weight).
Binder of the present invention (solid content) 10-30%
5-40% pigment
Other resins 0-10%
Solvent (including solvent in resin component) 40-70%
[0025]
The aqueous printing ink comprising the binder of the present invention may be used as a one-component aqueous printing ink, but can also be used as a two-component aqueous printing ink in combination with a curing agent. Examples of the curing agent include (1) aqueous polyepoxy compounds [bisphenol A glycidyl ether or hydrogenated bisphenol A glycidyl ether aqueous dispersion; ethylene glycol or polyethylene glycol diglycidyl ether; glycerin, polyglycerin, tri Polyglycidyl ethers of polyhydric alcohols such as methylolpropane and sorbitol; polyglycidyl ethers obtained by adding alkylene oxide (2 to 3 carbon atoms) to glycerin, trimethylolpropane, sorbitol, etc., water-soluble ones, etc.], ▲ 2 ▼ Aqueous amino resin [methylol- or alkoxymethylated urea or melamine resin], ③Polyisocyanate compound [IPDI or HDI trimerized to methyl ethyl ketoxime Other aqueous dispersions of the blocked polyisocyanate blocked with such ε- caprolactam], ▲ 4 ▼ like oxazoline compound. Among these, an aqueous polyepoxy compound is preferable.
The addition amount of the curing agent is usually 0 to 30% by weight, preferably 0 to 20% by weight, based on the weight of the aqueous polyurethane resin.
[0026]
The aqueous printing ink using the binder of the present invention is particularly suitable as a special gravure ink and a flexographic ink because it is excellent in re-solubility and oil resistance and has a low odor compared to conventional aqueous printing inks. Examples of the application target of the ink include polyester film, nylon film, polypropylene film, polyethylene film, polyvinyl chloride film, cellophane film and the like.
[0027]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this. In the following, “part” means “part by weight” and “%” means “% by weight”.
[0028]
Example 1
In a pressure polymerization apparatus equipped with a thermometer and a stirrer, 772 parts of poly (3-methylpentaneadipate) diol (Kurapol P-4010; manufactured by Kuraray Co., Ltd.) having a number average molecular weight of 4,000, 1,4-butane 19 parts of diol, 119 parts of dimethylolpropionic acid, 290 parts of IPDI and 800 parts of acetone were charged and reacted at 80 ° C. for 10 hours with stirring to obtain an acetone solution of an NCO-terminated polyurethane resin having an NCO content of 0.30%. The obtained acetone solution was cooled to 30 ° C. and 49 parts of 28% ammonia water was added. Next, 1765 parts of water was added to the acetone solution, and acetone was removed at 50 to 60 ° C. under reduced pressure to obtain an aqueous polyurethane resin solution having a solid content of 40.0% and a viscosity of 660 cP / 25 ° C. The number average molecular weight (hereinafter the same) of this resin measured by gel permeation chromatography (GPC) was 15,000.
[0029]
Using the obtained aqueous polyurethane resin solution as a binder, a printing ink was prepared according to the following formulation.
Aqueous polyurethane resin solution 100 parts Pigment (rutile titanium oxide) 80 parts Isopropanol 30 parts Water 90 parts Ceramic balls 150 parts The above raw material mixture is put into a steel can with an internal volume of 500 ml, and paint conditioner (manufactured by Red Devil) Was kneaded for 1 hour to obtain a printing ink [1].
[0030]
Example 2
In a pressure polymerization reactor equipped with a thermometer and a stirrer, 618 parts of polyneopentyl adipate diol having a number average molecular weight of 2,000, 20 parts of 1,4-butanediol, 102 parts of dimethylolpropionic acid, 290 parts of IPDI and 670 of acetone Then, an acetone solution of an NCO group-terminated polyurethane resin having an NCO content of 0.20% was obtained. The obtained acetone solution was cooled to 30 ° C. and 42 parts of 28% ammonia water was added. Next, 1515 parts of water was added to the acetone solution, and acetone was removed at 50-60 ° C. under reduced pressure to obtain an aqueous polyurethane resin solution having a solid content of 40.0% and a viscosity of 460 cP / 25 ° C. The number average molecular weight of this resin was 28,000.
Printing ink [2] was obtained in the same manner as in Example 1 except that the obtained resin solution was used as a binder.
[0031]
Example 3
In a pressure polymerization apparatus equipped with a thermometer and a stirrer, 309 parts of poly-ε-caprolactone diol having a number average molecular weight of 2,000, 309 parts of polyneopentyl adipate diol having a number average molecular weight of 2,000, bisphenol A having a molecular weight of 350 78 parts of propylene oxide adduct, 102 parts of dimethylolpropionic acid, 290 parts of IPDI, and 720 parts of acetone were allowed to react with stirring at 80 ° C. for 10 hours, and an acetone solution of an NCO-terminated polyurethane resin having an NCO content of 0.40% was prepared. Obtained. The obtained acetone solution was cooled to 30 ° C. and 42 parts of 28% ammonia water was added. Next, 1584 parts of water was added to the acetone solution, and acetone was removed at 50 to 60 ° C. under reduced pressure to obtain an aqueous polyurethane resin solution having a solid content of 40.0% and a viscosity of 410 cP / 25 ° C. The number average molecular weight of this resin was 13,000.
Printing ink [3] was obtained in the same manner as in Example 1 except that the obtained resin solution was used as a binder.
[0032]
Example 4
6 parts of “Denacol EX-521” (manufactured by Nagase Kasei Co., Ltd., water-soluble polyepoxy compound) was added to 100 parts of the printing ink obtained in Example 1 to obtain a printing ink [4].
[0033]
Comparative Example 1
A pressure polymerization reactor equipped with a thermometer and a stirrer was charged with 618 parts of polybutylene adipate diol having a number average molecular weight of 2,000, 102 parts of dimethylolpropionic acid, 290 parts of IPDI and 672 parts of acetone, and stirred at 80 ° C. for 10 minutes. The reaction was performed for an hour to obtain an acetone solution of an NCO group-terminated polyurethane resin having an NCO content of 1.50%. The obtained acetone solution was cooled to 30 ° C. and 70 parts of triethylamine was added. Next, a solution obtained by adding 120 parts of ethylenediamine to 1692 parts of water is added to the acetone solution, and acetone is removed at 50 to 60 ° C. under reduced pressure to obtain a polyurethane resin aqueous solution having a solid content of 40.0% and a viscosity of 5,000 cP / 25 ° C. Obtained. Since the molecular terminal of this resin was not sealed, it became high molecular weight by extension reaction and became insoluble in tetrahydrofuran, and the molecular weight could not be measured.
A printing ink [5] was obtained in the same manner as in Example 1 except that the obtained resin solution was used as a binder.
[0034]
Comparative Example 2
A pressure polymerization vessel equipped with a thermometer and a stirrer is charged with 618 parts of polypropylene glycol having a number average molecular weight of 2,000, 27 parts of 1,4-butanediol, 102 parts of dimethylolpropionic acid, 290 parts of IPDI and 690 parts of acetone. The mixture was reacted for 20 hours at 80 ° C. with stirring to obtain an acetone solution of a polyurethane resin having an NCO content of 0.02%. The obtained acetone solution was cooled to 30 ° C. and 42 parts of 28% ammonia water was added. Next, 1523 parts of water was added to the acetone solution, and acetone was removed at 50-60 ° C. under reduced pressure to obtain an aqueous polyurethane resin solution having a solid content of 40.0% and a viscosity of 2,000 cP / 25 ° C. The molecular weight of this resin was 250,000.
Printing ink [6] was obtained in the same manner as in Example 1 except that the obtained resin solution was used as a binder.
[0035]
Performance Test Examples The following performance tests were performed using the printing inks [1] to [6] obtained in Examples 1 to 4 and Comparative Examples 1 and 2, respectively. The results are shown in Table 1.
<Performance test items and test methods>
(1) Aqueous printing ink was applied to a re-dissolvable glass plate with a bar coater so as to have a thickness of 2 to 3 μm in solid content, and left at room temperature for 2 minutes to make the ink surface semi-dry, and then used aqueous printing. The ink was dropped and mixed with a glass rod, and the solubility of the ink coating was observed.

(2) Adhesive surface-treated polypropylene film (OPP) and surface-treated polyester film (PET) were coated with water-based printing ink with a bar coater to a thickness of 2 to 3 μm and dried at 60 ° C. for 1 minute. A cellophane tape (made by Nichiban, width 12 mm) was applied to the coated surface, and the coated surface state was observed when one end of the cellophane was rapidly peeled in a direction perpendicular to the coated surface.

(3) Water resistance test A coating test piece (applied to PET) obtained by the same method as in the adhesion test was immersed in water at 25 ° C for 24 hours, and then a cello tape was applied to the coated surface, and one end of this cello tape was coated. On the other hand, the state of the coated surface when it was peeled off rapidly in the perpendicular direction was observed.

(4) A coated test piece (coated on PET) obtained by the same method as in the oil-resistant adhesion test was immersed in rapeseed oil at 25 ° C. for 24 hours, and then the coated surface state was observed.
Evaluation criteria ○: No change ×: There is glossiness (5) An application test piece (applied to PET) obtained by the same method as the odor adhesion test is sealed in a 500 ml Erlenmeyer flask and sealed with a rubber stopper, 60 ° C After standing for 24 hours in an incubator, the rubber stopper was opened and the presence or absence of amine odor was examined.
Evaluation criteria ○: No odor ×: Odor [0036]
[Table 1]

[0037]
【The invention's effect】
The binder for water-based printing inks of the present invention improves the re-solubility and oil resistance of the ink, which has been a problem of conventional polyurethane resin-based water-based printing ink binders, and has low odor. It is extremely useful as a binder for water-based printing inks for plastic films used in the above.
Further, since the binder of the present invention is excellent in adhesiveness to various substrates and has low odor, it is useful not only as the above-mentioned application but also as a coating binder, adhesive, paper coating agent, and the like. .

Claims (5)

Molecular end derived from organic polyisocyanate (a), polyester polyol (b), compound (c) having an anionic group and at least two active hydrogen-containing groups in the molecule, and optionally a chain extender (d) A water-based printing ink comprising: a polyurethane resin (A) containing an isocyanate group in an aqueous polyurethane resin which is end-capped with ammonia and neutralized with an anionic group and dissolved in an aqueous medium. Binder. The binder for aqueous printing inks according to claim 1, wherein the anionic group of (c) is a carboxyl group. The binder for aqueous printing inks according to claim 2, wherein the content of carboxyl groups is 1.0 to 7.0% by weight based on the weight of the polyurethane resin (A). The binder for an aqueous printing ink according to any one of claims 1 to 3, wherein the isocyanate group concentration of (A) is 0.1 to 1.5% by weight. The binder for water-based printing inks in any one of Claims 1-4 used for printing ink for plastic films.