JPH05222330A - Flexographic ink binder and flexographic ink composition - Google Patents

Abstract

PURPOSE:To provide the title binder which is excellent in solubility in a solvent mixture having a low dissolving power and in adhesion to a plastic substrate and gives a flexographic ink leaving little solvent behind after printing. CONSTITUTION:The title binder mainly comprises a polyurethane resin obtd. by reacting a high-mol.-wt. polyol, isophorone diisocyanate, and a diamine as a chain extender. The polyol comprises 30-70wt.% polyether diol comprising polyoxypropylene glycol and/or polyoxytetramethylene glycol having a specified mo1.wt. and 70-30wt.% polyester diol prepd. by transesterification of a specific polyester diol with epsilon-caprolactone and having a lactone unit content of 30-80wt.% and an m.p. of 20 deg.C or lower.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a binder for flexographic printing ink and a flexographic printing ink composition.

[0002]

2. Description of the Related Art In flexographic printing, the plate material is rubber or plastic, plate making is easy, and the total cost required for printing is lower than that for gravure printing.
The printing method is widely adopted in the field of using paper as a printing substrate (corrugated board, liner paper, heavy wrapping paper, light wrapping paper, etc.). Further, when a CI (center impression drum) type flexographic printing machine is used, the registration accuracy is better than that of gravure printing, and therefore it is suitable for printing on a flexible substrate such as a plastic film.

However, since the plate material is rubber or plastic, the solvent used is limited. For example, a ketone solvent such as methyl ethyl ketone, which has a high dissolving power, or an aromatic solvent such as toluene or xylene cannot be used because it damages the plate. .. Therefore, a mixed solvent in which alcohol such as isopropyl alcohol or ethanol is used as a main solvent and ester solvent such as ethyl acetate is used as a cosolvent is widely used.

Due to the solubility in the mixed solvent and the like, the binder to be used is also limited, and only alcohol-soluble resins such as nitrocellulose and acrylic resins have been used so far. These do not have sufficient adhesion to polyethylene or polypropylene film, and in order to compensate for this, tackifiers such as polyamide, alkyd and rosin ester resin have been added, but they are unsatisfactory. There is a disadvantage that the amount of residual solvent contained in the film is also large. Therefore, there has been a demand for a binder having good solubility in the mixed solvent, excellent adhesion to a plastic substrate, and a small amount of residual solvent after printing.

On the other hand, in the field of gravure printing inks, a polyurethane resin has been favored as a resin having excellent adhesion to a plastic film and a small amount of residual solvent after printing, but the resin has high polarity and is stable. In order to obtain such a resin solution, it is necessary to use a solvent having a high dissolving power (a solvent such as a ketone type, an aromatic type, an ester type) as a main solvent. Therefore, the polyurethane resin cannot be used as a binder for flexographic printing ink.

JP-B-58-6754 discloses a polyurethane having excellent solubility in an ester solvent and an alcohol solvent, but it is a polyurethane for gravure ink using ethyl acetate as a main solvent. Not applicable to binders for flexographic printing inks.

[0007]

DISCLOSURE OF THE INVENTION The present invention is for flexographic printing ink which has good solubility in the low-solubility mixed solvent, excellent adhesion to a plastic substrate, and a small amount of residual solvent after printing. It was intended to provide a binder and flexographic printing ink composition.

[0008]

In view of the above technical background, the present inventor has conducted diligent studies to solve the problems of the prior art, and as a result, uses a specific polymer diol in combination in a specific ratio, and By using a specific diisocyanate compound as the diisocyanate, a polyurethane resin suitable as a binder for flexographic printing ink that can solve the above problems was found, and the present invention has been completed.

That is, in the present invention, the polymer polyol component (A), the diisocyanate component (B), the chain extender (C)
In a binder for a printing ink containing a polyurethane resin as a main component, obtained by reacting the component (A) with a component (A) of at least one of polypropylene glycol having a molecular weight of 700 to 2500 and polyoxytetramethylene glycol having a molecular weight of 700 to 2500. An ether diol (a-1), a transesterification product of ε-caprolactone with a polyester diol having a side chain glycol having 3 to 10 carbon atoms and adipic acid as essential components, and having an ε-caprolactone content. Is 30-80
Weight%, molecular weight 700-250 with melting point of 20 ° C. or less
0 is a polyester diol (a-2), and the weight percentage of the polyol component used is (a-1) / (a-
2) = 30/70 to 70/30, the component (B) is isophorone diisocyanate, and the component (C) is mainly composed of a polyurethane resin containing diamines as essential components. The present invention relates to a binder for flexographic printing ink. Further, the present invention relates to a flexographic printing ink composition using the binder.

The constituents of the polyurethane resin which is the binder of the present invention are as follows. First, at least one of polypropylene glycol having a molecular weight of 700 to 2500 and polyoxytetramethylene glycol having a molecular weight of 700 to 2500 is used as the polymer polyol component (A).
A kind of polyether diol (hereinafter referred to as component (a-1)); a polyester diol obtained by subjecting a glycol having 3 to 10 carbon atoms having a side chain and adipic acid to a dehydration esterification reaction and ε-caprolactone A molecular weight of 700 to 25 containing 30 to 80% by weight of ε-caprolactone obtained by an exchange reaction and having a melting point of 20 ° C. or lower.
00 polyester diol (hereinafter referred to as component (a-2)) is essential.

As the component (a-1), a polyether diol other than the above cannot be used. For example,
When an ethylene oxide adduct of bisphenol A or a propylene oxide adduct corresponding thereto is used, the solubility of the polyurethane resin solution is lowered and the object of the present invention cannot be achieved.

Specific examples of the glycol having 3 to 10 carbon atoms, which is the first essential constituent component of the component (a-2), are 1,2-propylene glycol, 1,3-butylene glycol, neopentyl glycol, and 2 -Methyl-
1,3-propylene glycol, 3-methyl-1,5-
Pentanediol, 2,3,5-trimethylpentanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol and the like can be mentioned, and these can be used alone or Can be used together. Up to 30% by weight of these glycols may be substituted with a glycol having no side chain, for example, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1 , 6-hexanediol and the like can be used.

The polybasic acid which is the second essential constituent component of the component (a-2) is limited to adipic acid from the viewpoint of the solubility of the resulting polyurethane resin solution. If phthalic anhydride, isophthalic acid, maleic acid, fumaric acid, sebacic acid, succinic acid, azelaic acid, etc. are used, the solubility of the polyurethane resin solution is lowered and it cannot be used.

The amount of ε-caprolactone used as the third essential constituent in the component (a-2) is the same as that of the component (a-2).
In the range of 30 to 80% by weight. When the content of ε-caprolactone is less than 30% by weight, the water resistance of the obtained polyurethane resin tends to decrease, and 80% by weight is obtained.
If it exceeds, the crystallinity tends to be strong and the solubility tends to decrease.

If the molecular weight of the high molecular weight polyol component (A) is less than 700, the polarity becomes too strong and the solubility decreases, while if it exceeds 2500, the solubility, drying property and blocking resistance tend to decrease. However, neither is preferable.

In the present invention, in addition to the limitation of the various constituent components in the polymer polyol component (A), the proportion of the constituent component used is also limited. That is, the component (a-
The use ratio of 1) and the component (a-2) is (a-1) /
It must be in the range of (a-2) = 30/70 to 70/30 (weight% basis). This is because the stability of the resulting polyurethane resin solution is poor outside this range.

Only isophorone diisocyanate can be used as the component (B) in the polyurethane resin of the present invention. Diisocyanates other than isophorone diisocyanate do not give polyurethane resins having satisfactory solubility.

As the component (C) in the polyurethane resin of the present invention, it is essential to use diamines. Representative examples thereof include ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4′-diamine and the like. Also, 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine,
Di-2-hydroxyethyl ethylenediamine, di-2-
Diamines having a hydroxyl group in the molecule, such as hydroxyethyl propylene diamine, 2-hydroxypropyl ethylene diamine, and di-2-hydroxy propyl ethylene diamine, can be similarly used. Incidentally. The low molecular weight glycols having a side chain and having 3 to 10 carbon atoms described in the above-mentioned polymer diol can also be used in combination with the above diamines.

In the present invention, a chain length terminator can also be used if necessary. Representative examples include dialkylamines such as di-n-butylamine, 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 diol component and isophorone diisocyanate are reacted under conditions of excess isocyanate groups to prepare a prepolymer having isocyanate groups at both ends of the polymer diol. Then, a two-step method of reacting this with a chain extender and, if necessary, a chain length terminating agent in a suitable solvent, and a polymer diol component, isophorone diisocyanate, a chain extender and, if necessary, a chain length terminating agent are used. Although any one-step method in which the reaction is carried out at once in a suitable solvent can be adopted, the former method is preferable for the purpose of obtaining a uniform polymer solution. Further, as the solvent used in the production method, in light of the above-mentioned object of the present invention, ethanol and isopropyl alcohol are used as a main solvent, and an alcohol solvent such as methanol and n-butanol is used as a co-solvent,
An ester solvent such as ethyl acetate or butyl acetate can be used in combination.

When the polyurethane resin used in the present invention is produced by the two-step method, the conditions for reacting the polymer diol component and isophorone diisocyanate are not limited, except that the isocyanate is in excess. It is preferable that the groups are reacted so that the equivalent ratio is in the range of 1 / 1.2 to 1/4. Further, the conditions for reacting the obtained prepolymer with a chain extender and, if necessary, a chain length terminating agent are as follows: when the free isocyanate group at the terminal of the prepolymer is 1 equivalent. The total equivalent of active hydrogen capable of reacting with the isocyanate group therein is preferably in the range of 0.5 to 2.0 equivalents (particularly, when the active hydrogen is an amino group, 0.5 to 2.0).
It should be in the range of 1.3 equivalents). If the amount of active hydrogen is less than 0.5 equivalent, the drying property, blocking resistance, and film strength are insufficient, and if the amount of active hydrogen exceeds 2.0 equivalents, the chain extender remains unreacted. It remains, and odor tends to remain after printing.

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.

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. In the solvent composition of the polyurethane resin solution, 75% or more of the total amount of solvent is isopropyl alcohol and / or ethanol, and the remaining less than 25% is isopropyl alcohol such as methanol and n-butanol, and alcohol solvents other than ethanol, ethyl acetate, acetic acid. It is an ester solvent such as butyl.

To produce the flexographic printing ink composition of the present invention using the polyurethane resin of the present invention, the polyurethane resin is provided with a colorant, a solvent and, if necessary, an interface for improving ink fluidity and surface film. An activator and a wax may be appropriately mixed and kneaded by using a usual ink manufacturing device such as a ball mill, an attritor, or a sand mill. Further, nitrocellulose, polyamide, acrylic resin, rosin ester and the like may be added within the range not departing from the performance of the present invention. The solvent composition of the present ink composition is also the same as the solvent composition in the binder, and the ink viscosity can be adjusted by appropriately diluting it as long as it is the composition.

[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 In a round bottom flask equipped with a stirrer, a thermometer, a cooling pipe and a nitrogen gas introducing pipe, 350 parts of polypropylene glycol having a molecular weight of 2000 and the molecular weight of 1262 described in Example 2 of Japanese Patent Publication No. 3-57133 were used. 650 parts of polyester diol and 306.4 parts of isophorone diisocyanate were charged and reacted in a nitrogen stream at 130 ° C. for 6 hours to obtain a prepolymer having a free isocyanate value of 4.43%. To this, 526.1 parts of ethyl acetate was added and urethane was added. A uniform solution of the prepolymer was prepared. Then, 1832.5 parts of the above urethane prepolymer solution was added in the presence of a mixture of 93.1 parts of isophorone diamine and 2121.5 parts of isopropyl alcohol, and then the mixture was reacted at 50 ° C. for 3 hours. The polyurethane resin solution A thus obtained had a resin solid content concentration of 35% and a viscosity of 800 cP / 25 ° C. The polyurethane resin solution A was left at 0 ° C. for 1 month,
The solution stability was good and no precipitates or crystals formed.

Production Example 2 In the same round bottom flask as in Production Example 1, 500 parts of polyoxytetramethylene glycol having a molecular weight of 2000 and Japanese Patent Publication No.
500 parts of polyester diol having a molecular weight of 1993 described in Example 3 of -57133 and 222.4 parts of isophorone diisocyanate were charged and reacted at 130 ° C. for 6 hours under a nitrogen stream to form a prepolymer having a free isocyanate value of 3.44%. To this was added 489.4 parts of ethyl acetate to obtain a uniform solution of urethane prepolymer. Then, 62.7 parts of isophoronediamine, di-n-butylamine 31.
The above urethane prepolymer solution 17 in the presence of a mixture of 4 parts and 1958.9 parts of isopropyl alcohol.
11.8 parts was added, and then the mixture was reacted at 50 ° C. for 3 hours. The polyurethane resin solution B thus obtained had a resin solid content concentration of 35% and a viscosity of 650 cP / 25 ° C. The polyurethane resin solution B had good solution stability even after being left at 0 ° C. for 1 month, and did not generate any precipitate or crystal.

Production Example 3 600 parts of polypropylene glycol having a molecular weight of 1000 and JP-B-3-5713 were placed in a round bottom flask similar to that of Production Example 1.
400 parts of polyester diol having a molecular weight of 2025 as described in Example 4 of No. 3, isophorone diisocyanate 354.
1 part was charged and reacted under a nitrogen stream at 130 ° C. for 6 hours to obtain a prepolymer having a free isocyanate value of 4.94%. 544.1 parts of ethyl acetate was added to this to prepare a uniform solution of a urethane prepolymer. Then, 66.1 parts of isophoronediamine, 27.2 parts of 2-hydroxyethylethylenediamine and isopropyl alcohol 2194.2.
1898.2 parts of the above urethane prepolymer solution was added in the presence of a mixture of parts, and then reacted at 50 ° C. for 3 hours. Polyurethane resin solution C thus obtained
Has a resin solid content of 35% and a viscosity of 550 cP / 25.
It was ℃. This polyurethane resin solution C is 1 at 0 ° C.
Even after being left for a month, the solution stability was good and no precipitates or crystals were formed.

Production Example 4 In the same round bottom flask as in Production Example 1, 500 parts of polyoxytetramethylene glycol having a molecular weight of 2,000 and Japanese Patent Publication No.
-57133, 500 parts of polyester diol having a molecular weight of 1262 described in Example 2, neopentyl glycol 3
Charge 0 parts, 415 parts of isophorone diisocyanate,
It was made to react at 130 ° C. for 6 hours under a nitrogen stream to form a prepolymer having a free isocyanate value of 5.43%, and 591.6 parts of ethyl acetate was added thereto to obtain a uniform solution of urethane prepolymer. Then, 83.5 parts of isophorone diamine,
2036.6 parts of the above urethane prepolymer solution was added in the presence of a mixture of 29.6 parts of 2-hydroxyethylethylenediamine, 29.0 parts of di-n-butylamine and 2371.9 parts of isopropyl alcohol, and then at 50 ° C. The reaction was carried out for 3 hours. The polyurethane resin solution D thus obtained had a resin solid content concentration of 35% and a viscosity of 1
It was 400 cP / 25 ° C. The polyurethane resin solution D had good solution stability even after standing at 0 ° C. for 1 month, and did not generate any precipitate or crystal.

Production Example 5 In a round bottom flask similar to that of Production Example 1, Japanese Examined Patent Publication No.
1000 parts of polyester diol having a molecular weight of 1993 and isophorone diisocyanate 22 described in Example 3 of 3
2.8 parts were charged and reacted at 130 ° C. for 6 hours under a nitrogen stream to obtain a prepolymer having a free isocyanate value of 3.44%. To this, 483.4 parts of ethyl acetate was added to prepare a uniform solution of urethane prepolymer. .. Then 63 parts of isophorone diamine and isopropyl alcohol 1949.2
1706.2 parts of the above urethane prepolymer solution was added in the presence of a mixture of parts, and then the mixture was reacted at 50 ° C. for 3 hours. Polyurethane resin solution E thus obtained
Has a resin solid content of 35% and a viscosity of 900 cP / 25
It was ℃. This polyurethane resin solution E was inferior in solution stability, and a resin precipitate had already formed after 1 day at 0 ° C.

Production Example 6 A round bottom flask similar to that of Production Example 1 was charged with 1000 parts of polyoxytetramethylene glycol having a molecular weight of 2000 and 222 parts of isophorone diisocyanate, and reacted at 130 ° C. for 6 hours under a nitrogen stream to give a free isocyanate value of 3 ．
43% prepolymer and ethyl acetate 483
Was added to prepare a uniform solution of urethane prepolymer. Then, 1705 parts of the above urethane prepolymer solution was added in the presence of a mixture of 62.7 parts of isophorone diamine and 1947.5 parts of isopropyl alcohol, and then the mixture was reacted at 50 ° C. for 3 hours. The polyurethane resin solution F thus obtained had a resin solid content concentration of 35% and a viscosity of 850 cP / 25 ° C. The polyurethane resin solution F was inferior in solution stability and a resin precipitate had already formed after 1 day at 0 ° C.

Production Example 7 A propylene oxide adduct 655 of bisphenol A having a molecular weight of 1900 was placed in the same round bottom flask as in Production Example 1.
Parts, 345 parts of polyethylene adipate diol having a molecular weight of 2000 and 230 parts of isophorone diisocyanate were charged and reacted at 130 ° C. for 6 hours under a nitrogen stream to form a prepolymer having a free isocyanate value of 3.53%, to which 487 parts of ethyl acetate was added. To obtain a uniform solution of urethane prepolymer. Then, in the presence of a mixture of 65.5 parts of isophorone diamine and 1963.9 parts of isopropyl alcohol, the above urethane prepolymer solution 1717 is added.
Parts were added and then reacted at 50 ° C. for 3 hours. The polyurethane resin solution G thus obtained had a resin solid content concentration of 35% and a viscosity of 1000 cP / 25 ° C. The polyurethane resin solution F was inferior in solution stability and a resin precipitate had already formed after 1 day at 0 ° C.

Production Example 8 The same round bottom flask as in Production Example 1 was charged with 500 parts of polypropylene glycol having a molecular weight of 1500, 500 parts of polyethylene adipate diol having a molecular weight of 1500 and 295.8 parts of isophorone diisocyanate at 130 ° C. under a nitrogen stream. Reaction for 6 hours Free isocyanate value 4.3
1% prepolymer, to which ethyl acetate 520.
7 parts was added to obtain a uniform solution of urethane prepolymer.
Then, 1816.5 parts of the above urethane prepolymer solution was added in the presence of a mixture of 89.2 parts of isophorone diamine and 2099.5 parts of isopropyl alcohol, and then the mixture was reacted at 50 ° C. for 3 hours. The polyurethane resin solution H thus obtained had a resin solid content concentration of 35.
%, The viscosity was 1200 cP / 25 ° C. This polyurethane resin solution H was inferior in solution stability and a resin precipitate had already formed after 1 day at 0 ° C.

Examples 1 to 4 Phthalocyanine blue 10 parts Polyurethane resin solutions A to D obtained in Production Examples 1 to 50 50 parts Ethyl acetate 5 parts Isopropyl alcohol 35 parts Mixtures of the above composition were each kneaded with a paint shaker, A blue printing ink was prepared. To the obtained indigo printing ink, 5 parts of ethyl acetate and 35 parts of isopropyl alcohol were further added to adjust the viscosity.
Indigo blue ink was made. The indigo ink of Comparative Example 1 is a conventional nitrified cotton polyamide type flexo ink. Corona discharge treated nylon film (NY), polyethylene terephthalate (PET) film, corona discharge treated polypropylene film (OPP), corona discharge treated by using a rubber roller equipped with a 165 line anilox roller for these five indigo printing inks. The color was spread on a polyethylene film (PE).

(Cellophane Tape Adhesion Test) One day after the color development, a cellophane adhesive tape was adhered to the color development surface, and the state of the ink film when strongly peeled off was evaluated as follows. ◎ ------ There is no abnormality in the ink film. ○ ------ 80% or more of the ink film remained. △ ------ 50% or more of the ink film remained. × ------ Less than 50% of the ink film remains.

(Residual Solvent Test) After one day of color development, 300 cm ² of each color development product was placed in a 300 ml Erlenmeyer flask and sealed, and then kept at 140 ° C. for 10 minutes, after which the gas in the flask was quantified by gas chromatography. .

[0037]

According to the present invention, a binder for flexographic printing ink and a flexographic ink having good solubility in a low-solubility mixed solvent, excellent adhesion to a plastic substrate, and a small amount of residual solvent after printing. The great effect that a printing ink composition is obtained is exhibited.

[0038]

[Table 1]

Claims (4)

[Claims] 1. A binder for a printing ink containing a polyurethane resin as a main component obtained by reacting a polymer polyol component (A), a diisocyanate component (B) and a chain extender (C), wherein the component (A) has a molecular weight. 700-250
0 polypropylene glycol and molecular weight 700-25
At least one kind of polyether diol (a-1) of polyoxytetramethylene glycol of No. 00, a polyester diol having a side chain-containing glycol having 3 to 10 carbon atoms and adipic acid as essential constituents, and ε- A transesterification product with caprolactone,
-Caprolactone content 30-80% by weight, melting point 2
It is a polyester diol (a-2) having a molecular weight of 700 to 2500, which is 0 ° C. or less, and the weight percentage of the polyol component used is (a-1) / (a-2) = 30/70 to
70/30, the component (B) is isophorone diisocyanate, and the component (C) is mainly composed of a polyurethane resin containing diamines as essential components. 2. The binder for flexographic printing ink according to claim 1, which contains isopropyl alcohol and / or ethanol as a solvent component in the binder in an amount of 75% or more based on the total amount of the solvent. 3. A flexographic printing ink composition comprising the binder for flexographic printing ink according to claim 1. 4. The flexographic printing ink composition according to claim 3, wherein isopropyl alcohol and / or ethanol is contained as a solvent component in the ink composition in an amount of 75% or more based on the total amount of the solvent.