JP7598709B2 - Printing ink composition for laminate and easily tearable laminate - Google Patents

Description

The present invention relates to a printing ink composition for lamination and an easily tearable laminate obtained by printing the printing ink for lamination on a base film, applying an adhesive, and laminating a sealant film.

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

The laminate is then used as a laminated bag for foods such as snacks, soup, miso soup, etc. These laminated bags are opened by human hands to remove the contents. Here, if the tearability is poor, excessive force must be applied when opening the bag, and the bag may tear in an unintended direction, resulting in problems such as spilling of the contents, so good tearability is required.
In particular, in areas where ink is printed, the bonding strength between the ink layer and the adhesive layer is weaker than in areas without ink, and therefore tearability also tends to be poorer.
As a means for improving tearability, it is known that hardening the laminate adhesive layer improves tearability (see, for example, Patent Document 2). However, when inked areas and non-character areas where no ink is printed are mixed, making the adhesive layer hard enough to tear at the inked areas will make the non-character areas too hard, and conversely, matching the non-character areas will result in poor tearability at the inked areas.

In order to solve this problem, it has been proposed to make the ink layer contain a curing agent having two or more functional groups that can react with the same functional groups in the ink layer and the adhesive layer, and to make the ink layer a layer formed from a composition consisting of a compound (a1) having only two or more hydroxyl groups as functional groups in the molecule and a curing agent that reacts with the hydroxyl groups (see, for example, Patent Document 3).
In the examples, the solid content ratio of the polyfunctional isocyanate hardener to the polyurethane resin contained in the ink layer is very low at polyurethane resin:polyfunctional isocyanate hardener = 1:0.25, so although the tearability is improved slightly, there are still problems such as resistance felt when tearing.
Furthermore, the color development of the ink layer using such a compound is not sufficiently good.

In Patent Document 4, a large amount of a curing agent is used in a two-component ink to improve tearability, but the use of a large amount of a curing agent has a large impact on costs, so there is room for improvement.
In Patent Document 5, it is possible to reduce the amount of hardener compared to Patent Document 4, but there is a demand for a further reduction in the amount of hardener while maintaining tearability.

Japanese Patent Application Publication No. 5-97959 JP 2008-274061 A JP 2012-125978 A JP 2017-25143 A Patent No. 6545559

The object of the present invention is to provide a printing ink composition for lamination that exhibits good color development and easy tearability without using a large amount of a curing agent, and an easily tearable laminate that is produced by printing the printing ink for lamination on a base film, applying an adhesive, and laminating a sealant film.

Means of the Invention The present inventors have conducted intensive research to solve the above problems and have invented the following printing ink composition for laminate and laminate.
The present invention relates to
(1) A printing ink composition for laminate containing a pigment, a binder resin, a polyfunctional isocyanate compound as a curing agent, and an organic solvent, characterized in that the binder resin is a polyurethane resin having a reactive group capable of reacting with an isocyanate group of the polyfunctional isocyanate compound, the polyurethane resin is made up of a raw material of a polymer diol, and a polyester diol accounts for 70 mass% or more of the polyurethane resin and the curing agent, and the solid content ratio of the polyurethane resin to the curing agent is polyurethane resin:curing agent=1:0.10-0.90.
(2) The printing ink composition for laminate according to (1), wherein the polyurethane resin is the following (1) or (2), or a mixture of the following (1) and (2):
(1) A polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal, and also having a hydroxyl group. (2) A polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal. (3) The printing ink composition for laminate according to (1) or (2) above, characterized in that the polyfunctional isocyanate compound is a tri- or higher functional isocyanate compound.
(4) The printing ink composition for laminate according to any one of (1) to (3) above, characterized in that the pigment contains rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 20 to 35 g/100 g.
(5) The printing ink composition for laminate according to the above (4), characterized in that the pigment contains rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 25 to 35 g/100 g.
(6) The printing ink composition for laminate according to any one of (1) to (5) above, wherein the organic solvent is a mixed solvent of an ester-based organic solvent and an alcohol-based organic solvent.
(7) An easily tearable laminate comprising a base film, a printed layer made of the printing ink for lamination according to any one of (1) to (6) above, an adhesive layer having a hydroxyl group, and a sealant film laminated in this order.
(8) The easily tearable laminate according to (7) above, which is obtained by printing the printing ink for lamination according to any one of (1) to (6) above on the base film, applying an adhesive containing a resin having a hydroxyl group, and laminating a sealant film.

The printing ink composition for laminate of the present invention is a composition using the above polyurethane resin as a binder resin and a polyfunctional isocyanate compound as a curing agent in such a range that the solid content ratio of the polyurethane resin to the curing agent is polyurethane resin:curing agent=1:0.10 to 0.90. The polyurethane resin has a reactive group capable of reacting with the isocyanate group of the polyfunctional isocyanate compound. Therefore, it is considered that the curing agent in the printing ink composition for laminate reacts with the polyurethane resin in the ink composition and the hydroxyl group of the adhesive layer to increase the bonding strength between the printing layer and the adhesive layer, and the ink layer becomes hard and has good tearability.
In particular, when (1) a polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal and having a hydroxyl group, and/or (2) a polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal, and a polyfunctional isocyanate compound, polyurethane resin, and curing agent are used in such a range that the solids content ratio of polyurethane resin:curing agent is polyurethane resin:curing agent=1:0.10 to 0.90, the polyurethane resin viscosity can be adjusted to a suitable viscosity range for printing ink, and the pigment dispersibility is also good, so that the resin content in the printing ink composition for laminate can be increased.
In addition, since the polyurethane resin has hydroxyl groups, the curing agent in the printing ink composition for laminate reacts with the hydroxyl groups of the adhesive layer to increase the bonding strength between the printing layer and the adhesive layer, making the ink layer harder and improving the tearability.In addition, the pigment dispersibility is improved, which is thought to result in good color development.

The printing ink composition for laminate and the easily tearable laminate of the present invention will be described in more detail below.
First, the printing ink composition for laminate of the present invention will be described.
<Pigments>
As the pigment that can be used in the present invention, various inorganic pigments and/or organic pigments that are generally used in printing inks can be used.
The content of the pigment in the printing ink composition for laminate of the present invention is preferably in the range of 5 to 60% by mass in the ink composition.
If the content of the pigment in the printing ink composition for laminate 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 and the printed matter will be more susceptible to smudging.
The pigment preferably contains rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 20 to 35 g/100 g, and more preferably contains rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 25 to 35 g/100 g.
If the oil absorption is less than 20 g/100 g, the tearability may decrease, whereas if it exceeds 35 g/100 g, the pigment dispersibility may deteriorate.

<Binder resin>
As the binder resin, a polyurethane resin having a reactive group capable of reacting with an isocyanate group of a polyfunctional isocyanate compound, which is a curing agent described below, can be used.
As the polyurethane resin having a reactive group capable of reacting with the isocyanate group of the polyfunctional isocyanate compound, a polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group, and/or a hydroxyl group at the terminal can be used. In particular, (1) a polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at the terminal and a hydroxyl group and/or (2) a polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at the terminal is preferred.
Such polyurethane resins can be obtained by synthesizing a urethane prepolymer by reacting a polyfunctional diisocyanate compound with a polymeric diol compound, and then reacting the resulting urethane prepolymer with (1) an amine compound containing a polyamine compound having at both ends one or more of a primary amino group, a secondary amino group and a tertiary amino group, and an amine compound having a hydroxyl group, or by reacting (2) an amine compound containing a polyamine compound having at both ends one or more of a primary amino group, a secondary amino group and a tertiary amino group.
In this case, examples of the method of reacting the urethane prepolymer with (1) an amine compound containing a polyamine compound having at least one of a primary amino group, a secondary amino group and a tertiary amino group at both ends, and an amine compound having a hydroxyl group, and (2) an amine compound containing a polyamine compound having at both ends one or more of a primary amino group, a secondary amino group and a tertiary amino group, include (A) a method of extending the chain of the urethane prepolymer with a chain extender, and then terminating the reaction with a reaction terminator, and (B) a method of simultaneously reacting the urethane prepolymer with a chain extender and terminating the reaction with a reaction terminator.

(Polyfunctional diisocyanate compound)
As the polyfunctional diisocyanate compound that can be used to obtain the binder resin, aromatic diisocyanate compounds such as tolylene diisocyanate, alicyclic diisocyanate compounds such as 1,4-cyclohexane diisocyanate and isophorone diisocyanate, aliphatic diisocyanate compounds such as hexamethylene diisocyanate, and aromatic aliphatic diisocyanate compounds such as α,α,α',α'-tetramethylxylylene diisocyanate can be used alone or in combination of two or more. Among them, alicyclic diisocyanate compounds, aliphatic diisocyanate compounds, and aromatic aliphatic diisocyanate compounds are more preferred. Furthermore, isocyanate compounds having three or more functionalities can also be used. In addition, it is more preferred that the isocyanate component is a bioisocyanate derived from a plant.

(Polymer diol compound)
Examples of the polymer diol compound that can be used to obtain the binder resin include 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.; polyester diols obtained by condensation reaction of one or more dibasic acids such as adipic acid, sebacic acid, phthalic anhydride, etc. with one or more glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, etc.; and polyester diol compounds such as polycaprolactone diols. These polymer diol compounds can be used singly or in combination of two or more.
In the polymer diol, the polyester diol accounts for 70% by mass or more.
A biopolyol component can be used as the polymer diol compound. Among them, a biopolyester polyol obtained by reacting a short-chain diol component having 2 to 4 carbon atoms with a carboxylic acid component is preferable. It is more preferable that at least one of the short-chain diol component and the carboxylic acid component of the biopolyol component is derived from a plant, and it is even more preferable that both are derived from a plant.
The plant-derived short-chain diol component having 2 to 4 carbon atoms is not particularly limited. As an example, the short-chain diol component may be 1,3-propanediol, 1,4-butanediol, ethylene glycol, etc. obtained from a plant raw material by the following method. These may be used in combination. 1,3-propanediol can be produced from glycerol via 3-hydroxypropylaldehyde (HPA) by a fermentation method in which glucose is obtained by decomposing a plant resource (such as corn, etc.). The 1,3-propanediol compound produced by a biomethod such as the above-mentioned fermentation method can produce useful by-products such as lactic acid, which is safer than the 1,3-propanediol compound produced by the EO production method, and can also be produced at low production costs. 1,4-butanediol can be produced by producing glycol from a plant resource, fermenting it, obtaining succinic acid, and hydrogenating the obtained succinic acid.
Ethylene glycol can also be produced from bioethanol obtained by a conventional method via ethylene.

The plant-derived carboxylic acid component is not particularly limited. For example, the carboxylic acid component may be sebacic acid, succinic acid, lactic acid, glutaric acid, azelaic acid, dimer acid, etc. These may be used in combination. Among these, it is preferable that the carboxylic acid component contains at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid.

In addition to the above-mentioned high molecular weight diol compounds, alkanediols such as 1,4-pentanediol, 2,5-hexanediol, and 3-methyl-1,5-pentanediol, and low molecular weight diol compounds such as ethylene glycol, propylene glycol, 1,4-butanediol, and 1,3-butanediol can be used alone or in combination of two or more kinds.
In addition, in a mixture of an ester-based solvent and an alcohol-based solvent, using a polyether diol compound as the polymer diol compound tends to increase the solubility of the resulting polyurethane resin, which is preferable in that it makes it possible to widely design inks to suit the required performance.
The ratio of the organic diisocyanate compound to the polymer diol compound used is such that the equivalent ratio of isocyanate groups to hydroxyl groups (isocyanate index) is usually in the range of 1.2:1 to 3.0:1, more preferably 1.3:1 to 2.0:1. If the isocyanate index is less than 1.2, the polyurethane resin tends to be soft, and in cases where the blocking resistance is low when the ink is printed, it may be preferable to use the polyurethane resin in combination with another hard resin.

(Chain extender)
As the chain extender that can be used to obtain the binder resin, known chain extenders that are used in polyurethane resins as ink binders can be used, and examples thereof include aliphatic diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, 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; diamines having a hydroxyl group such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, and N,N'-di(2-hydroxyethyl)ethylenediamine; and diol compounds such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, and triethylene glycol.

(Reaction stopper)
Examples of reaction terminators that can be used to obtain the binder resin include 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, 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, monoalkylamines such as n-propylamine and n-butylamine, dialkylamines such as di-n-butylamine, alkanolamines such as monoethanolamine and diethanolamine, and monoalcohols such as ethanol.
To obtain a polyurethane resin having a primary amino group and/or a secondary amino group at both ends, a polyamine having a primary amino group and/or a secondary amino group at both ends is used as a reaction terminator. Examples of such polyamines having a primary amino group and/or a secondary amino group at both ends include aliphatic diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, and hexamethylenediamine, alicyclic diamines such as isophoronediamine and 4,4'-dicyclohexylmethanediamine, polyamines such as diethylenetriamine and triethylenetetratriamine, aromatic diamines such as toluylenediamine, aromatic aliphatic diamines such as xylylenediamine, and diamines having a hydroxyl group such as N-(2-hydroxyethyl)ethylenediamine and N-(2-hydroxyethyl)propylenediamine, and among these, polyamines having a primary amino group such as diethylenetriamine and triethylenetetratriamine are preferred.
To obtain a polyurethane resin having a hydroxyl group, a compound having a hydroxyl group is used as the chain extender and/or the reaction terminator. It is preferable to use a compound having a hydroxyl group as both the chain extender and the reaction terminator. Examples of the chain extender include diamines having a hydroxyl group, such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, and N,N'-di(2-hydroxyethyl)ethylenediamine.
Examples of reaction terminators include diamines having a hydroxyl group, such as N-(2-hydroxyethyl)ethylenediamine, N-(2-hydroxyethyl)propylenediamine, and N,N'-di(2-hydroxyethyl)ethylenediamine; and alkanolamines having a hydroxyl group, such as monoethanolamine and diethanolamine.

In the present invention, the polyurethane resin can be obtained by using the above-mentioned materials and adopting a known method for producing a polyurethane resin. In addition, since the hardness of the obtained polyurethane resin varies depending on the molecular weight, chemical structure, and equivalent ratio of each component, it is possible to adjust the printability and lamination suitability by appropriately selecting and combining these components.
The content of the binder resin in the printing ink composition for lamination during printing is preferably 5 to 15% by mass in terms of solid content. If the content of the binder resin is outside the above range, the tearability tends to decrease.
The polyurethane resin in the printing ink composition for laminate of the present invention preferably has a mass average molecular weight of 10,000 to 70,000, and more preferably 20,000 to 40,000.
Further, as other binder resins, cellulose resins, acrylic resins, vinyl chloride-vinyl acetate copolymers, polyamide resins, adhesive resins, etc. can be added as auxiliary resins. Among these, vinyl chloride-vinyl acetate copolymers are preferred, and from the viewpoint of reaction with the curing agent, vinyl chloride-vinyl acetate copolymers having a hydroxyl group are particularly preferred.

<Curing Agent>
As the curing agent, a multifunctional polyisocyanate compound can be used. Specifically, biuret, isocyanurate, adduct, bifunctional polyfunctional isocyanate compound, isophorone diisocyanate can be used, and examples thereof include 24A-100, 22A-75, TPA-100, TSA-100, TSS-100, TAE-100, TKA-100, P301-75E, E402-808, E405-70B, AE700-100, D101, D201, A201H (manufactured by Asahi Kasei Corporation), Mytech Y260A (manufactured by Mitsubishi Chemical Corporation), Coronate CORONATE HX, Coronate CORONATE HL, Coronate CORONATE L (manufactured by Tosoh Corporation), and Desmodur N75MPA/X (manufactured by Bayer). Among these, isophorone diisocyanate or an adduct thereof is preferred. Furthermore, a trifunctional or higher isocyanate compound can also be used.
It is more preferable that the isocyanate component is a bioisocyanate derived from plants.
The amount of the curing agent used is such that the mass ratio of the polyurethane resin to the curing agent is in the range of polyurethane resin:curing agent=1:0.10 to 0.90 from the viewpoint of tearability, preferably polyurethane resin:curing agent=1:0.13 to 0.40, and more preferably polyurethane resin:curing agent=1:0.15 to 0.35.

<Organic Solvent>
Examples of organic solvents that can be used in the printing ink composition for laminate include toluene, ketone-based organic solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), ester-based organic solvents (e.g., methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate, etc.), alcohol-based organic solvents (e.g., methanol, ethanol, n-propanol, isopropanol, butanol, etc.), and hydrocarbon-based solvents (toluene, methylcyclohexane, etc.).
In consideration of recent environmental issues and the printability and drying properties of the ink, it is particularly preferred to use a mixed organic solvent of an ester-based organic solvent and an alcohol-based organic solvent as the organic solvent for the printing ink composition for lamination during printing, such that the ratio of the ester-based organic solvent/the alcohol-based organic solvent is in the range of 50/50 to 95/5, and preferably 60/40 to 85/15.
Furthermore, from the viewpoint of printability of the ink, it is preferred that the printing ink composition for lamination contains 5% by mass or more, preferably 15% by mass or more, of propyl acetate during printing.

<Additives>
The organic solvent-borne gravure printing composition may further contain various additives such as a tackifier, a crosslinking agent, a lubricant, an antiblocking agent, an antistatic agent, and a surfactant.

<Method for producing the printing ink composition for laminate of the present invention>
The printing ink composition for laminate of the present invention can be obtained by producing various materials other than the above-mentioned curing agent using various types of dispersion/kneading devices that are commonly used in the past, and adjusting the contents of each solid material and the combination of the polyurethane resin and the organic solvent to make the viscosity 10 to 1,000 mPa·s. From the viewpoint of stability over time, the curing agent is added at the time of printing, and the organic solvent is added and stirred so that the number of seconds is appropriate depending on the printing conditions at the atmospheric temperature during printing, specifically, until the outflow time in Zahn cup No. 3 is 12 to 23 seconds, preferably about 14 to 16 seconds in high-speed printing.

<Easy-to-tear laminate>
Next, an easily tearable laminate obtained by printing a printing ink for lamination on a base film, applying an adhesive containing a polyester-based adhesive having a hydroxyl group and an isocyanate-based adhesive containing an isocyanate group, and laminating a sealant film will be described.

(Base film)
The base film of the easily tearable laminate of the present invention is not particularly limited, and various types of printing plastic films such as polyolefin films such as polyethylene and polypropylene, polyester films such as polyethylene terephthalate, polylactic acid and polycaprolactone, nylon and vinylon can be used.
Also, a biomass-based film made from a biomass-based resin can be used.

(Laminate printing ink composition)
As the printing ink composition for laminate, the above-mentioned printing ink composition for laminate can be used.

(glue)
An adhesive containing a resin having a hydroxyl group, which has been conventionally used in extrusion lamination and dry lamination, can be used. For example, an adhesive containing a polyester-based adhesive having a hydroxyl group and an isocyanate-based adhesive containing an isocyanate group can be exemplified.
Specifically, adhesives (anchor coating agents) used in extrusion lamination include A-3210/A-3070, A-3210/A3072, A-3210/A-3075 (manufactured by Mitsui Chemicals, Inc.), Secadyne 2710A/Secadyne 2810C(T), Secadyne 2730A/Secadyne 2730B, Secadyne 2710A/Secadyne 2710C (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), LX-500, LX-901, LX747A, etc., and adhesives used in dry lamination include DiCdry LX-401A, 75A, 719, 703VL, 500, 510, etc. (manufactured by DIC Graphics, DiCdry is a registered trademark of DIC Graphics), Takelac/Takenate Examples of the resins include A-909/A-5, A-977/A-92, A-606/A-50, A-515/A-50, A-626/A-50, A-525/A-52, A-666/A-65 (manufactured by Mitsui Chemicals, Inc.), RU-77, 771, 3600, 3900 (manufactured by Rock Paint Co., Ltd.), and the like.
Biomass-based adhesives made from biomass-based materials can also be used.

(Sealant film)
For the sealant film, resins that have been conventionally used as molten resins when lamination means by dry lamination are employed, such as low density polyethylene, LLDPE, ethylene-vinyl acetate copolymer, polypropylene, etc., can be used.
As the plastic film used in the extrusion lamination process by laminating the molded films, a conventionally used film such as a non-oriented plastic film (e.g., a non-oriented polyethylene film, a non-oriented polypropylene film, etc.) can be used.

<Easily tearable laminate and easily tearable laminate bag>
The easily tearable laminate and the easily tearable laminate bag of the present invention will now be described.
First, a desired pattern, characters, etc. are printed on the above-mentioned printing substrate using a general gravure printing method or flexographic printing method or the like with the printing ink composition for lamination of the present invention.
The resulting printed matter is then laminated with a heat-fusible polymer called a sealant. There are two main methods used for this lamination.
The first method is an extrusion lamination method in which a printing ink composition for lamination is used for printing, and after or before the printed portion is cured with a curing agent, an adhesive (also called an anchor coating agent) is applied to the surface of the resulting printed layer, and then a heat-fusible polymer is laminated as a molten resin. The extrusion lamination method involves applying an adhesive (for example, an adhesive containing a polyester-based adhesive having a hydroxyl group and an isocyanate-based adhesive containing an isocyanate group) to the surface of the printed layer, and then laminating the molten resin using a known extrusion laminator. Furthermore, the molten resin can be used as an intermediate layer, and other materials can be laminated to form a sandwich-like laminate. Note that it is preferable to use an isocyanate-based anchor coating agent as an adhesive, rather than an imine-based anchor coating agent, in terms of superior adhesive strength.
The second is dry lamination, which involves printing with a printing ink composition for lamination, applying an adhesive (e.g., an adhesive containing a polyester adhesive having a hydroxyl group and an isocyanate adhesive containing an isocyanate group) to the surface of the printed layer after or before curing the printed portion with a curing agent, and then laminating a non-stretched plastic film. In particular, lamination can be performed using a multi-layer film in which a metal foil used in retort applications is sandwiched in advance.
The easily tearable laminate obtained by these methods is then finally heat-sealed at its sealant surfaces with a heat sealer or the like to form an easily tearable laminate bag.
A common feature of these two methods is that, when printing is performed with a printing ink composition for lamination and the printed portion is cured with a curing agent, and then an adhesive is applied, the printing ink composition for lamination and the adhesive may be cured by different functional groups, i.e., by different curing mechanisms, or a curing agent having the same functional group may be used. As a result, it becomes possible to select a more appropriate combination of the printing ink composition for lamination and the adhesive.
On the other hand, when printing is performed using a printing ink composition for lamination and an adhesive is applied before the printed portion is cured with a curing agent, the printing ink composition for lamination and the adhesive may each use a curing agent having the same functional group acting thereon.

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 polyurethane resin varnish)
Production Example of Polyurethane Resin Varnish A (Polymer Diol: 100% by mass of Polyester Diol, Terminal Primary Amino Groups, Terminal Hydroxyl Groups)
A four-neck flask equipped with a stirrer, a cooling tube, and a nitrogen gas inlet tube was charged with 400 parts by weight of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000, 33.3 parts by weight of isophorone diisocyanate, and 0.04 parts by weight of tetrabutyl titanate, and reacted for 6 hours at 80 to 90 ° C. while introducing nitrogen gas. The mixture was allowed to cool to near room temperature, and 824 parts by weight of propyl acetate and 206 parts by weight of isopropyl alcohol were added, followed by adding 7.6 parts by weight of isophorone diamine to extend the chain, and then adding 0.37 parts by weight of monoethanolamine to react, and then adding 0.41 parts by weight of diethylene triamine to stop the reaction, thereby obtaining a polyurethane resin varnish A having a solid content of 30% by weight.

Production Example of Polyurethane Resin Varnish B (Polymer diol: 100% by mass of polyester diol, terminal primary amino group, hydroxyl group in molecule and at terminal)
A four-neck flask equipped with a stirrer, a cooling tube and a nitrogen gas inlet tube was charged with 400 parts by weight of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000, 33.3 parts by weight of isophorone diisocyanate, and 0.04 parts by weight of tetrabutyl titanate, and reacted for 6 hours at 80 to 90 ° C. while introducing nitrogen gas. After cooling to near room temperature, 822 parts by weight of propyl acetate and 205 parts by weight of isopropyl alcohol were added, and then a mixture of 3.8 parts by weight of isophorone diamine and 2.3 parts by weight of aminoethylethanolamine was added to extend the chain, and 0.37 parts by weight of monoethanolamine was added to react, and then 0.41 parts by weight of diethylenetriamine was added to stop the reaction, and a polyurethane resin varnish B having a solid content of 30% by weight was obtained.

Production Example of Polyurethane Resin Varnish C (Polymer Diol: Polyester Diol/Polyether Diol=80/20 (mass ratio), Terminal Primary Amino Group, Terminal Hydroxyl Group)
In the production example of polyurethane resin varnish A, 400 parts by mass of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000 was changed to a mixture of 320 parts by mass of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000 and 80 parts by mass of polypropylene glycol having an average molecular weight of 2000, thereby obtaining polyurethane resin varnish C having a solid content of 30% by mass.

Production example of polyurethane resin varnish D (100% polyester diol in polymer diol, primary amino group at terminal, no hydroxyl group)
In the production example of polyurethane resin varnish A, monoethanolamine was changed to dibutylamine to obtain polyurethane resin varnish D having a solid content of 30 mass %.

Production example of polyurethane resin varnish E (100% polyester diol in high molecular weight diol, no primary amino groups at the ends, hydroxyl groups at both ends (i.e., two hydroxyl groups))
In the production example of polyurethane resin varnish A, diethylenetriamine was changed to monoethanolamine to obtain polyurethane resin varnish E having a solid content of 30 mass %.

Production Example of Polyurethane Resin Varnish F (Polymer Diol: Polyester Diol/Polyether Diol=50/50 (mass ratio), Terminal Primary Amino Group, Terminal Hydroxyl Group)
In the production example of polyurethane resin varnish A, 400 parts by mass of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000 was changed to a mixture of 200 parts by mass of 3-methyl-1,5-pentylene adipate diol having an average molecular weight of 2000 and 200 parts by mass of polypropylene glycol having an average molecular weight of 2000, thereby obtaining polyurethane resin varnish F having a solid content of 30% by mass.

Polyurethane Resin Varnish G Manufacturing Example (Polyurethane Resin Varnish A with reduced molecular weight: for Helio 200 wire)
In the production example of polyurethane resin varnish A, the amount of isophorone diamine was changed to 6.8 parts by mass, the amount of monoethanolamine to 0.73 parts by mass, and the amount of diethylenetriamine to 0.82 parts by mass, thereby obtaining polyurethane resin varnish G having a solids content of 30% by mass.

(Pigment)
Titanium oxide A (rutile type titanium oxide treated with silica and alumina, oil absorption 29g/100g)
Titanium oxide B (rutile type titanium oxide treated with only alumina, oil absorption 29g/100g)

(vinyl chloride resin varnish)
20 parts by mass of a vinyl chloride-vinyl acetate copolymer having a hydroxyl group (product name: Solvine TA3, manufactured by Nissin Chemical Industry Co., Ltd.) was dissolved in a mixed organic solvent consisting of 40 parts by mass of methyl ethyl ketone, 20 parts by mass of ethyl acetate, and 20 parts by mass of propyl acetate to obtain a vinyl chloride-vinyl acetate resin varnish A having a solid content of 20%.

(Production of printing ink composition for laminate)
35 parts by mass of pigments A to B, 30 parts by mass of polyurethane resin varnishes A to G, and 10 parts by mass of the mixed solvent were kneaded using a paint conditioner, and the remainder of the mixed solvent 1 was further added and mixed according to the formulation in Table 1. 100 parts by mass of each mixture was diluted with a curing agent (product name "Mytech NY260A", manufactured by Mitsubishi Chemical Corporation) and mixed solvent 2 according to the formulation in Table 1 at the time of printing, and the viscosity was adjusted to 15 seconds using Zahn cup #3 manufactured by Rigo Co., Ltd., to prepare the printing ink compositions for laminate of Examples 1 to 10 and Comparative Examples 1 to 4.

<Performance evaluation>
For the printing ink compositions for laminate of Examples 1 to 8 and Comparative Examples 1 to 4, printing was performed on the treated surface of ONY#15 (manufactured by Toyobo Co., Ltd., N-1102, thickness 15 μm, hereinafter referred to as the base film) at a printing speed of 100 m/min using a gravure printing machine (manufactured by Azumaya Manufacturing Co., Ltd.) equipped with an engraving plate (Helio 175 lines) for the printing ink compositions for laminate of Examples 9 to 10, and an engraving plate (Helio 200 lines) for the printing ink compositions for laminate of Examples 9 to 10.

(Dry lamination)
An adhesive containing a polyester-based adhesive having a hydroxyl group and an isocyanate-based adhesive containing an isocyanate group (A-515/A-50 ethyl acetate solution, manufactured by Mitsui Chemicals, Inc.) was applied to each of the printed materials of Examples 1 to 10 and Comparative Examples 1 to 4, and a sealant film LLDPE#50 (L-4104, manufactured by Toyobo Co., Ltd.) was laminated using a dry laminator to obtain a laminate.

(Extrusion Lamination)
An adhesive (A-3210/A-3070 (manufactured by Mitsui Chemicals)) was applied to each of the printed materials of Examples 1 to 10 and Comparative Examples 1 to 4, and molten polyethylene was laminated thereon using an extrusion laminator to obtain a laminate.

(Color development)
The laminate printing ink compositions of Examples 1 to 10 and Comparative Examples 1 to 4 were printed on the above-mentioned base film using a gravure printing machine with a 175-line printing plate, and the color development of each printed matter was visually observed and evaluated according to the following evaluation criteria, using the color development of the laminate printing ink composition of Comparative Example 3 as the standard.
◯: The color development is clearly clearer than that of Comparative Example 3. ×: The color development is not clearer than that of Comparative Example 3.

(Tearability)
Each of the laminates of Examples 1 to 10 and Comparative Examples 1 to 4 obtained by dry lamination and extrusion lamination was left at 40° C. for 3 days, and then cut with a cutter and torn by hand to evaluate ease of tearing.
○: Can be torn without resistance. ○△: Slight resistance is felt when torn, but can be torn without any problems. △: Resistance is felt when torn, or the sealant stretches slightly, but can be torn. ×: The sealant stretches or cannot be torn at all.

Curing agent: Isophorone diisocyanate (IPDI adduct) (Mitsubishi Chemical Corporation, Mytec NY260A)
Mixed solvents 1 and 2: ethyl acetate/propyl acetate/isopropyl alcohol = 50/25/25 (mass ratio)

The laminates of each example printed using the printing ink composition for lamination of the present invention showed good color development whether a 175-line or 200-line printing plate was used, and also showed good tearability without resistance whether the lamination was performed by dry lamination or extrusion lamination.
In contrast, in Comparative Examples 1 and 2, in which the ratio of the curing agent to the polyurethane resin used was less than the range in the present invention, the color development was good, but the tearability was poor, and the sealant stretched slightly, but was only able to be torn. In Comparative Example 3, in which a polyurethane resin having a hydroxyl group at the end but no amino group was used, the color development was not good, and in addition, resistance was felt when torn. In Comparative Example 4, in which the polyester diol was 50% by mass in the polymer diol, which is the raw material for the polyurethane resin, the tearability was poor.

Claims (7)

A printing ink composition for laminate, comprising a pigment, a binder resin, a polyfunctional isocyanate compound as a curing agent (excluding cases where the polyfunctional isocyanate compound has an alkoxysilyl group), and an organic solvent,
the binder resin is a polyurethane resin having a reactive group capable of reacting with an isocyanate group of the polyfunctional isocyanate compound, a polyester diol accounts for 70 mass% or more of a polymer diol that is a raw material of the polyurethane resin, and the polyester diol contains 1,4-butanediol as a raw material thereof,
A printing ink composition for laminate, wherein the solid content ratio of the polyurethane resin to the curing agent is polyurethane resin:curing agent=1:0.10 to 0.90, and the polyurethane resin is the following (1) or (2), or a mixture of the following (1) and (2) (excluding the case where the printing ink composition for laminate contains a vinyl chloride-vinyl acetate copolymer resin):
(1) A polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal, and also having a hydroxyl group. (2) A polyurethane resin having at least one of a primary amino group, a secondary amino group, and a tertiary amino group at its terminal. 2. The printing ink composition for laminate according to claim 1 , wherein the polyfunctional isocyanate compound is a tri- or higher functional isocyanate compound. 3. The printing ink composition for laminate according to claim 1, wherein the pigment comprises rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 20 to 35 g/100 g. 4. The printing ink composition for laminate according to claim 3 , wherein the pigment contains rutile-type titanium dioxide treated with silica and alumina and having an oil absorption of 25 to 35 g/100 g. 5. The printing ink composition for laminate according to claim 1, wherein the organic solvent is a mixed solvent of an ester-based organic solvent and an alcohol-based organic solvent. 13. An easily tearable laminate comprising a substrate film, a printed layer made of the printing ink for lamination according to claim 1, an adhesive layer having a hydroxyl group, and a sealant film laminated in this order. The easily tearable laminate according to claim 6, characterized in that it is obtained by printing the printing ink for lamination according to any one of claims 1 to 5 on the base film, applying an adhesive containing a resin having a hydroxyl group, and laminating a sealant film.