JPH05163452A - Binder for printing ink and printing ink composition - Google Patents

Abstract

PURPOSE:To provide the subject binder excellent in adhesivity, boiling resistance and storage stability, and suitable for plastic films, etc., by adding a prescribed amount of a specified imidazole compound to the solid content of a polyurethane resin. CONSTITUTION:The objective binder comprises (A) 100 pts.wt. of a polyurethane resin obtained by reacting a polymeric polyol such as a polyetherpolyol with a diisocyanate compound such as 4,4'-diphenylmethane diisocyanate and a chain extender such as ethylene diamine and (B) 0.01-50 pts.wt. of an isocyanate compound blocked with an imidazole compound of the formula (X, Y and Z are H, 1-20C alkyl, phenyl, benzyl, dithiocarboxyl, etc.), such as imidazole. The binder is used for the production of printing ink compositions.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a printing ink binder and a printing ink composition.

[0002]

2. Description of the Related Art In recent years, various plastic films have been developed as a packaging material in accordance with the complexity of packaging contents and the sophistication of packaging technology. As a result, a plastic film suitable for the contents can be appropriately selected. Came to be used. As a result, printing inks used for decoration of plastic films or for surface protection have also been required to have high performance.

Polyurethane resins have been widely used as binders for such printing inks. Generally, a printing ink having a polyurethane resin as a binder has excellent adhesive strength to polyester and nylon films alone, but does not have sufficient adhesive strength to polyethylene films and polypropylene films, which are general-purpose films.

In view of the above drawbacks, the polyurethane resin was used alone as a two-component reaction type ink containing a polyisocyanate compound, but the two-component reaction type ink must contain a curing agent immediately before printing. It is inconvenient to handle, and also has the disadvantage that it is practically restricted in terms of pot life (pot life).

Therefore, in the art, it can be used as a one-component ink which does not need to contain a polyisocyanate compound,
Moreover, various polyurethane resins having excellent adhesiveness to various plastic films are being researched and developed.

As described above, various one-pack type inks having good adhesiveness have been developed, and the problem of adhesiveness has been solved to some extent. However, the one-pack type ink is sterilized by boil and retort after food packaging. When applied to the printing of a plastic film used as a packaging base material through a sterilization process, the boil resistance and the retort resistance are still inferior. for that reason,
In the field where the performance is required, the present situation is that two-component reactive inks containing a polyisocyanate compound still occupy the mainstream despite the above problems.

Attempts have been made to improve the boiling resistance and retort resistance by blending a blocked isocyanate compound with a polyurethane resin (JP-A-2-43275). However, oximes such as acetone oxime and 2-butanone oxime described in the publication are
Alternatively, a blocked isocyanate having an active methylene compound such as acetoacetic acid ester or dimethyl malonate as a blocking agent has a high dissociation temperature, so that a sufficient crosslinking effect cannot be obtained, and the boiling resistance and the retort resistance are insufficient.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a printing ink binder having excellent adhesion and boil resistance to various plastic films such as polyester, nylon, polyethylene, and polypropylene as a material to be printed, and one-component printing. It was intended to provide an ink composition.

[0009]

SUMMARY OF THE INVENTION In view of the above technical background, the inventors of the present invention have made intensive studies in order to solve the problems of the prior art by paying attention to the dissociation property of blocked isocyanates. The inventors have found that the above problems can be solved by blending a specific blocked isocyanate compound at a specific ratio and using this as a binder for printing inks, and have completed the present invention.

That is, the present invention relates to a binder for a printing ink containing a polyurethane resin as a main component, which is obtained by reacting a polymer polyol, a diisocyanate compound and a chain extender, with a general formula based on 100 parts by weight of the solid content of the polyurethane resin. :

[0011]

[Chemical 1]

(Wherein X, Y, and Z are any of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a phenyl group, a benzyl group, a dithiocarboxyl group, a hydroxyalkyl group having 1 to 6 carbon atoms, and a formyl group. 0.01 to 50 parts by weight of an isocyanate compound blocked by an imidazole compound represented by the formula (1), X, Y, and Z may be the same group or different groups. The present invention relates to a binder for printing ink, which is characterized by being mixed in parts. Furthermore, the present invention relates to a printing ink composition using the binder.

By using, as a binder, a composition prepared by blending an isocyanate compound blocked with a specific compound in addition to various polyurethane resins, it is possible to solve the above-mentioned problems which cannot be solved by conventional printing inks. is there.

The constituent components of the polyurethane resin which is the main component of the present invention are as follows. First, as the polymer polyol component, polyether polyols such as polymers or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, etc .; ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1, 3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, octanediol, 1,4-butynediol, diethylene glycol,
Various well-known saturated and unsaturated low-molecular-weight glycols such as triethylene glycol and dipropylene glycol, alkyl glycidyl ethers such as n-butyl glycidyl ether and 2-ethylhexyl glycidyl ether, and monocarboxylic acids such as versatic acid glycidyl ester. Glycidyl esters, dimer diol obtained by reducing dimer acid, and adipic acid, phthalic anhydride, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, glutaric acid, pimelic acid, Polyester polyols obtained by dehydration condensation of dibasic acids such as suberic acid, azelaic acid and sebacic acid, or acid anhydrides or dimer acids corresponding thereto; polyester polyols obtained by ring-opening polymerization of cyclic ester compounds Other polycarbonate polyols, polybutadiene glycols, generally various known polymer polyols used in the production of polyurethane, such as glycols for E by adding ethylene oxide or propylene oxide to bisphenol A are exemplified.
In the case of a polymer polyol obtained from glycols and a dibasic acid among the above, up to 5 mol% of the glycol component can be substituted with the following various polyols. That is, for example, glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, pentaerythritol, sorbitol and the like can be exemplified.

The molecular weights of the various polymer polyols described above are
It is appropriately determined in consideration of the solubility, drying property, blocking resistance, etc. of the resulting polyurethane resin, and usually 500 to 6
It is preferable to set it within the range of 000. When the molecular weight is less than 500, the printability tends to be poor due to the decrease in solubility, while when it exceeds 6000, the drying property and blocking resistance tend to be reduced.

The diisocyanate compound which is another constituent of the polyurethane resin of the present invention includes aromatic, aliphatic and alicyclic diisocyanates. For example,
1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate , 1,
4-phenylene diisocyanate, tolylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, cyclohexane-1, Typical examples thereof include 4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, methylcyclohexane diisocyanate and dimerisocyanate.

Examples of the chain extender include ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, dicyclohexylmethane-4,4'-diamine and dimerdiamine. Other, 2-
Hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine,
The diamines having a hydroxyl group in the molecule such as di-2-hydroxypropylethylenediamine and the low molecular weight glycols described in the section of the polyester diol described above can also be used in the same manner. Further, if necessary, a dialkylamine such as di-n-butylamine as a polymerization terminator,
It is also possible to use dihydroxyalkylamines such as diethanolamine and alcohols such as ethanol and isopropyl alcohol.

As the method for producing the polyurethane resin of the present invention, first, a polymer polyol component and a diisocyanate compound are reacted under the condition of excess isocyanate groups to prepare a prepolymer having isocyanate groups at both ends of the polymer polyol. Then, a two-step method of reacting this with a chain extender and, if necessary, a polymerization terminator in a suitable solvent, a polymer polyol component, a diisocyanate compound, a chain extender and, if necessary, a polymerization terminator are used. Although any one-step method in which the reaction is carried out at once in a different solvent can be adopted, the former method is preferable for the purpose of obtaining a uniform polymer solution. In these production methods, the solvent used is usually an aromatic solvent such as benzene, toluene, xylene, which is well known as a solvent for printing inks.
Ester-based solvents such as ethyl acetate and butyl acetate; alcohol-based solvents such as methanol, ethanol, isopropanol, n-butanol; acetone, methyl ethyl ketone,
Examples thereof include ketone solvents such as methyl isobutyl ketone and mixtures of two or more thereof.

When the polyurethane resin used in the present invention is produced by the two-step method, the conditions for reacting the high molecular weight polyol component and the diisocyanate compound are not limited, except that the isocyanate is in excess. It is preferable that the groups are reacted so that the equivalent ratio is within the range of 1 / 1.2 to 1/3. The conditions for reacting the obtained prepolymer with a chain extender and optionally a polymerization terminator are also not limited, but when the free isocyanate group at the end of the prepolymer is 1 equivalent, The total equivalent of active hydrogen capable of reacting with the isocyanate group in the extender is preferably in the range of 0.5 to 2.0 equivalents (particularly when active hydrogen is an amino group, 0.5 to 1.3). It should be within the equivalent range). When the amount of active hydrogen is less than 0.5 equivalent, the dryness, blocking resistance, and film strength are insufficient, and the amount of active hydrogen is 2.0.
If the amount exceeds the equivalent amount, the chain extender remains unreacted and odor tends to remain on the printed matter.

The number average molecular weight of the polyurethane resin obtained as described above is preferably in the range of 5,000 to 100,000. If the molecular weight is less than 5000, the printing ink using this as a binder is inferior in the drying property, blocking resistance, film strength, oil resistance, etc., while if it exceeds 100,000, the viscosity of the polyurethane resin solution increases. Or the gloss of the printing ink tends to decrease. Further, it is preferable that the polyurethane resin has a hydroxyl group or an amino group in the molecule. This is because, when the isocyanate compound blocked by the imidazole compound represented by the general formula is dissociated, the produced isocyanate group reacts with these hydroxyl groups and amino groups, so that a stronger crosslinked structure can be obtained. By using a diamine having a hydroxyl group and / or a monoamine having a hydroxyl group as the chain extender or the chain terminator, a polyurethane resin having a hydroxyl group in the molecule can be obtained. Use amines as a chain extender and employ chain extension conditions such that the number of amino groups in the chain extender is more than 1 and 1.3 or less per 1 equivalent of free isocyanate groups at the end of the prepolymer. Thereby, a polyurethane resin having an amino group in the molecule is obtained.

The concentration of resin solids in the polyurethane resin solution obtained as described above is not particularly limited and is appropriately determined in consideration of workability at the time of printing and is usually 15 to 60% by weight. The viscosity is 50 to 10,000 cP / 25 ° C.
Is practically preferable.

Examples of the imidazole compound as the blocking agent represented by the above general formula include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 4-formylimidazole, and 2
-Ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2- Phenyl-4,5-dihydroxymethylimidazole, imidazole-4-dithiocarboxylic acid, 4-methylimidazole-5-dithiocarboxylic acid, 2-ethylimidazole-4-dithiocarboxylic acid,
2-Phenylimidazole-4-dithiocarboxylic acid and the like can be mentioned.

In the present invention, the blocked isocyanate compound is a compound obtained by reacting the isocyanate group of the polyisocyanate compound with approximately the same amount of the imidazole compound. Examples of the polyisocyanate compound include various diisocyanate compounds that are constituent components of the polyurethane resin, addition products of these diisocyanate compounds with polyhydric alcohols or water, and polymers of these diisocyanate compounds. More specifically, an adduct of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate, tolylene diisocyanate trimer by isocyanurate bond, carbodiimide-modified diphenylmethane diisocyanate (liquid MDI), polymethylene polyphenyl isocyanate (crude) MDI), triphenylmethane-4,
4 ', 4 "-triisocyanate, hexamethylene diisocyanate trimer by burette bond, hexamethylene diisocyanate trimer by isocyanurate bond, adduct of trimethylolpropane 1 mol and hexamethylene diisocyanate 3 mol, trimethylolpropane 1 Mol of isophorone diisocyanate, 3 mol of isophorone diisocyanate by isocyanurate bond, adduct of 1 mol of trimethylolpropane and 3 mol of xylylene diisocyanate, 1 mol of trimethylolpropane and 1,3-bis ( An adduct with 3 mol of isocyanate methyl) cyclohexane and the like can be mentioned.

To produce the binder for a printing ink of the present invention using the above-mentioned polyurethane resin and the blocked isocyanate compound of the present invention, the blocked isocyanate compound of the present invention is usually added to 0.1 parts by weight per 100 parts by weight of the solid content of the polyurethane resin. 01 to 50 parts by weight, preferably 0.5
It suffices to add and mix it at a ratio of up to 20 parts by weight. Further, in order to produce the printing ink composition of the present invention, a colorant, a solvent, and if necessary, a surfactant for improving the ink fluidity and the surface film, and a wax are appropriately added to the binder. The kneading may be carried out by using an ordinary ink producing device such as a ball mill, an attritor, or a sand mill. Further, nitrocellulose, vinyl chloride-vinyl acetate copolymer, polyamide, acrylic resin, chlorinated polypropylene and the like may be added within the range not departing from the performance of the present invention. The compounding ratio of the blocked isocyanate compound of the present invention is 0.0 based on 100 parts by weight of the solid content of the polyurethane resin.
If it is less than 1 part by weight, almost no improvement effect is observed in the boil resistance, and if it is used in excess of 50 parts by weight, the effect of excessive use is not recognized, which is a problem in terms of drying property. Is not preferred because it causes

[0025]

EXAMPLES The present invention will be described in detail below with reference to production examples, examples and comparative examples, but the present invention is not limited to these examples. In the examples, all parts and% are by weight unless otherwise specified.

Production Example 1 A round-bottomed flask equipped with a stirrer, a thermometer and a nitrogen gas inlet tube was charged with 1000 parts of poly (1,2-propylene adipate) glycol having a molecular weight of 2000 and 222 parts of isophorone diisocyanate, and under a nitrogen stream. Was reacted at 100 ° C. for 6 hours to form a prepolymer having a free isocyanate value of 3.36%, and 815 parts of methyl ethyl ketone was added thereto to obtain a uniform solution of urethane prepolymer. Then, 88.7 parts of isophorone diamine, 12 methyl ethyl ketone
The above urethane prepolymer solution 203 in the presence of a mixture of 24 parts and 1019 parts of isopropyl alcohol.
7 parts was added and then reacted at 50 ° C. for 3 hours. The polyurethane resin solution thus obtained had a resin solid content concentration of 30% and a viscosity of 650 cP / 25 ° C.

Production Example 2 A reactor similar to that used in Production Example 1 was charged with 1000 parts of poly (butylene adipate) glycol having a molecular weight of 2000 and 222 parts of isophorone diisocyanate, and reacted at 100 ° C. for 6 hours under a nitrogen stream to obtain a free isocyanate value of 3 .4
A 0% prepolymer was prepared, and 815 parts of methyl ethyl ketone was added thereto to prepare a uniform solution of the urethane prepolymer. Then, the above urethane prepolymer solution 2037 in the presence of a mixture of 39.4 parts of isophoronediamine, 24.0 parts of 2-hydroxyethylethylenediamine, 8.3 parts of di-n-butylamine, 1197 parts of methyl ethyl ketone and 1006 parts of isopropyl alcohol. Parts were added and then reacted at 50 ° C. for 3 hours. The polyurethane resin solution thus obtained has a resin solid content of 30
%, The viscosity was 3800 cP / 25 ° C.

Production Example 3 A reactor similar to that of Production Example 1 was charged with 1000 parts of polyoxytetramethylene glycol having a molecular weight of 1000 and 333 parts of isophorone diisocyanate, and the mixture was placed under a nitrogen stream for 10 minutes.
The reaction was carried out at 0 ° C for 10 hours to give a free isocyanate value of 3.10.
% Prepolymer with 8% methyl ethyl ketone
89 parts were added to obtain a uniform solution of urethane prepolymer. Then, 2222 parts of the above urethane prepolymer solution was added in the presence of a mixture of 71.6 parts of isophorone diamine, 14.9 parts of diethanolamine, 1319 parts of methyl ethyl ketone and 1104 parts of isopropyl alcohol, and then reacted at 50 ° C. for 3 hours. .. The polyurethane resin solution thus obtained has a resin solid content of 30
%, The viscosity was 740 cP / 25 ° C.

Production Example 4 A reactor similar to that of Production Example 1 was charged with 1000 parts of polycaprolactone glycol having a molecular weight of 2000, 52 parts of neopentyl glycol, and 291 parts of 1,3-bis (isocyanatomethyl) cyclohexane, under a nitrogen stream. To 1
The reaction was carried out at 00 ° C for 10 hours to obtain a free isocyanate value of 3.1.
A 0% prepolymer was prepared, and 895 parts of methyl ethyl ketone was added thereto to prepare a uniform solution of urethane prepolymer. Then, 73.3 parts of isophoronediamine, di-n-
Butylamine 10.2 parts, methyl ethyl ketone 1329
2238 parts of the above urethane prepolymer solution was added in the presence of a mixture consisting of 1 part of isopropyl alcohol and 1115 parts of isopropyl alcohol, and then reacted at 50 ° C. for 3 hours. The polyurethane resin solution thus obtained has a resin solids concentration of 3
The viscosity was 0% and the viscosity was 800 cP / 25 ° C.

Example 1 Titanium white (rutile type) 30 parts Polyurethane resin solution obtained in Preparation Example 1 50 parts Toluene 10 parts Isopropyl alcohol 10 parts 2-Methylimidazole 2 mol and isophorone diisocyanate 1 mol 2 parts The mixture having the above composition was kneaded with a paint shaker to prepare a white printing ink. To the obtained white printing ink, 35 parts of toluene and 15 parts of isopropyl alcohol were further added to adjust the viscosity. This white printing ink was applied to a discharge surface of a corona discharge treated nylon film (NY) having a thickness of 15 μm and a thickness of 11 using a simple gravure printing machine equipped with a gravure plate having a plate depth of 30 μm.
Printing was performed on one side of μm polyethylene terephthalate (PET) and dried at 40 to 50 ° C. to obtain a printing film.
Then, the solid content of 25 on the printing surface of the obtained printing film.
% Of a polyurethane adhesive was applied and dried at a coating amount of 3 g / m ² , and then a 60 μm polyethylene film was dry laminated with a laminator to obtain a laminated film. The laminate strength (adhesive strength) of the thus obtained laminate film and the suitability for boiling at 100 ° C. were evaluated. The evaluation results are shown in Table 1.

Boilability (1) Evaluation by change in appearance of film Laminated film was observed for change in appearance after boiling at 100 ° C. for 30 minutes. ○ ------ There is no abnormality in the film. × ------ Part of the film is delaminated or blistered. (2) Change due to laminating strength (adhesive strength) After laminating film was boiled at 100 ° C for 30 minutes, it was cut into a width of 15 mm and a peeling tester was used to speed 300 mm
The T-type peel strength was measured in / min and compared with the strength before boiling. (Unit: g / 15mm)

The stability of the white printing ink was evaluated by the following method. The evaluation results are shown in Table 1. Storage stability A diluted ink whose viscosity was adjusted by adding 35 parts of toluene and 15 parts of isopropyl alcohol was allowed to stand at 25 ° C for 1 month, and the initial viscosity and the viscosity after 1 month were compared and evaluated. ○ ------ The viscosity after one month is within 1.5 times the initial viscosity. × ------ The viscosity after 1 month is more than twice the initial viscosity. Stability of residual meat Add 1 part of water to diluted ink whose viscosity was adjusted by adding 35 parts of toluene and 15 parts of isopropyl alcohol. 4
The sample was left at 0 ° C. for 1 week, and the initial viscosity and the viscosity after 1 week were compared and evaluated. ○ ------ The viscosity after 1 week is within 1.5 times the initial viscosity. × ------ The viscosity after 1 week is more than twice the initial viscosity.

Examples 2 to 5 The amount of the reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate in Example 1 was 0.07 part in Example 2, 0.15 part in Example 3, and Four
Then, white printing ink was prepared as 1.0 part and as 3.0 part in Example 5, respectively, and evaluated. The results are shown in Table 1.

Example 6 In Example 1, the polyurethane resin solution obtained in Production Example 2 was used in place of the polyurethane resin solution obtained in Production Example 1, and a reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate. Instead of imidazole 2
A white printing ink was prepared and evaluated in the same manner except that the reaction product of 1 mol of hexamethylene diisocyanate was used. The results are shown in Table 1.

Example 7 In Example 1, the polyurethane resin solution obtained in Production Example 3 was used in place of the polyurethane resin solution obtained in Production Example 1, and a reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate. A white printing ink was prepared and evaluated in the same manner except that the reaction product of 2-phenylimidazole (2 mol) and xylylenediisocyanate (1 mol) was used instead of. The results are shown in Table 1.

Example 8 In Example 1, the polyurethane resin solution obtained in Production Example 4 was used in place of the polyurethane resin solution obtained in Production Example 1, and a reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate. In place of 3 mol of 2-heptadecyl imidazole and triphenylmethane-4,
A white printing ink was prepared and evaluated in the same manner except that the reaction product of 1 mol of 4 ', 4 "-triisocyanate was used. The results are shown in Table 1.

Example 9 In Example 8, 2-ethyl-4-methylimidazole 3 was used instead of the reaction product of 3 mol of 2-heptadecylimidazole and 1 mol of triphenylmethane-4,4 ', 4 "-triisocyanate. Moles and triphenylmethane-4,
A white printing ink was prepared and evaluated in the same manner except that the reaction product of 1 mol of 4 ', 4 "-triisocyanate was used. The results are shown in Table 1.

Comparative Example 1 In Example 1, a white printing ink was prepared and evaluated without adding the reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate. The results are shown in Table 1.

Comparative Example 2 At the time of printing the white printing ink prepared in Comparative Example 1, 2 parts of isophorone diisocyanate was added to evaluate as a two-component printing ink. The results are shown in Table 1.

COMPARATIVE EXAMPLE 3 In Example 1, instead of the reaction product of 2 mol of 2-methylimidazole and 1 mol of isophorone diisocyanate,
A white printing ink was prepared and evaluated in the same manner except that the reaction product of diethyl malonate and isophorone diisocyanate described in JP-A-2-43275 was used. The results are shown in Table 1.
Shown in.

[0041]

According to the present invention, a printing ink having excellent adhesiveness to various plastic films such as polyester, nylon film, polyethylene and polypropylene as a material to be printed and having excellent boil resistance and storage stability. The great effect that a binder for ink and a one-pack type printing ink composition can be obtained.

[0042]

[Table 1]

Claims (5)

[Claims] 1. A binder for a printing ink containing a polyurethane resin as a main component, which is obtained by reacting a high molecular weight polyol, a diisocyanate compound and a chain extender, with a general formula: 1] (In the formula, X, Y, and Z each represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a phenyl group, a benzyl group, a dithiocarboxyl group, a hydroxyalkyl group having 1 to 6 carbon atoms, or a formyl group. , X, Y, and Z may be the same group or different groups.) 0.01 to 50 parts by weight of an isocyanate compound blocked by an imidazole compound represented by A binder for printing ink, which is characterized in that 2. The blending ratio of the blocked isocyanate compound is 100 parts by weight of the solid content of the polyurethane resin,
The printing ink binder according to claim 1, which is 0.5 to 20 parts by weight. 3. The binder for printing ink according to claim 1, wherein the polyurethane resin has a hydroxyl group in the molecule. 4. The binder for a printing ink according to claim 1, wherein the polyurethane resin has an amino group in its molecule. 5. A printing ink composition comprising the printing ink binder according to any one of claims 1 to 4.