Surface printing ink composition, laminate and packaging material

Abstract

To provide a printing ink composition for surface printing, which can form a printing layer having excellent adhesion to a substrate and excellent resistance to heat yellowing, even when the substrate is a polyethylene film that has not been subjected to corona discharge treatment. [Solution] A printing ink composition for surface printing, comprising a binder resin (A), a terpene resin (B), and an organic solvent, wherein the binder resin (A) comprises a nitrocellulose resin (A1) and a polyurethane resin (A2), the terpene resin (B) has a solubility parameter calculated by the Fedors method of 10.0 or less and a softening point of 90°C or more, and the content of the terpene resin (B) converted to solid content is 2 to 25 mass% relative to the total mass of the solid content of the printing ink composition for surface printing.

Description

[Technical Field]

[0001] The present invention relates to a printing ink composition for surface printing, a laminate, and a packaging material. [Background technology]

[0002] Packaging materials using plastic film as a base material are used to package products such as food and daily necessities. For purposes such as decoration and ensuring necessary physical properties, printing is performed on the base material of the packaging material using printing inks such as gravure printing inks.

[0003] Packaging materials often use a simple printed material called a surface printing method, where the surface side of the substrate is printed and the reverse side of the substrate that comes into contact with the contents is left unprinted. In the reverse printing method, where the printing is done on the reverse side of the substrate, the ink layer is protected from external contact by the substrate, whereas in the surface printing method, the ink layer is exposed to the outside. Therefore, inks used in the surface printing method must have better coating properties.

[0004] One of the coating film properties required for printing inks used in surface printing is the adhesion of the ink coating to the substrate. Furthermore, when packaging materials are processed into bags, various methods are known as bag-making methods, a typical example of which is heat sealing. It is also required that the high heat applied during heat sealing does not cause defects in appearance, such as removal of the ink coating or yellowing of the ink coating.

[0005] Known printing inks used for surface printing contain polyurethane resin and nitrocellulose resin as binder resins, and may contain various additives as needed, because they satisfy the various required physical properties and are particularly excellent in oil resistance and printability.

[0006] Patent Document 1 discloses a gravure printing ink composition for surface printing, which contains a pigment, a polyurethane resin, and a curing agent. Patent Document 2 discloses a gravure printing ink composition for surface printing, which contains a pigment, a polyurethane resin, a chelating crosslinking agent, and a fatty acid amide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-196560 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-058979 Summary of the Invention [Problem to be solved by the invention]

[0008] Plastic films used for packaging materials include polyolefin films such as polyethylene films (LLDPE, LDPE, HDPE, etc.) and polypropylene films (OPP, CPP, etc.), polyester films (PET, etc.), polyamide films (ONY, etc.), etc. In addition, a widely used method is to subject the surface of the plastic film to printing to a corona discharge treatment, which generates acidic functional groups on the surface of the plastic film and further improves the adhesion of the ink coating to the substrate.

[0009] Using polyethylene film that has not been corona discharge treated as the base material makes it possible to create a cheaper and simpler packaging material. However, polyethylene film has a smaller solubility parameter (SP value) than other plastic films, and the solubility parameter (SP value) is significantly different from the solubility parameter (SP value) of the ink binder resin. Therefore, if the film is not corona discharge treated, the adhesion of the ink coating will be very weak.

[0010] Patent Documents 1 and 2 state that the addition of a hard resin can improve adhesion to resin films that have not been surface-treated. However, the gravure printing ink compositions for surface printing described in Patent Documents 1 and 2 still do not have sufficient adhesion to polyethylene films that have not been subjected to corona discharge treatment, and further improvements, including other physical properties, are required. On the other hand, terpene resins are sometimes contained in ink compositions, but it has been known that coating films containing terpene resins suffer from poor appearance due to yellowing caused by high heat when subjected to heat processing.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface printing ink composition which is capable of forming a printed layer which has excellent adhesion to a substrate and excellent resistance to heat yellowing, even when the substrate is a polyethylene film which has not been subjected to a corona discharge treatment, and a laminate and a packaging material which use the same. [Means for solving the problem]

[0012] The present invention has the following aspects. [1] A printing ink composition for surface printing, The binder resin (A), the terpene resin (B), and the organic solvent are contained, the binder resin (A) contains a nitrocellulose resin (A1) and a polyurethane resin (A2), the terpene resin (B) has a solubility parameter calculated by the Fedors method of 10.0 or less and a softening point of 90°C or more; A printing ink composition for surface printing, wherein the content of the terpene resin (B) in terms of solid content is 2 to 25 mass % based on the total mass of the solid content of the printing ink composition for surface printing. [2] The printing ink composition for surface printing according to [1], wherein the terpene resin (B) is a polyterpene resin. [3] Further containing a chelating agent (C), The printing ink composition for surface printing according to [1] or [2], wherein the mass ratio of the terpene resin (B) to the chelating agent (C) is 0.5 to 13 in terms of solid content. [4] Further containing a plasticizer (D), The printing ink composition for surface printing according to any one of [1] to [3], wherein the plasticizer (D) has a solidification point of 5°C or lower. [5] The printing ink composition for surface printing according to any one of [1] to [4], wherein the mass ratio of the polyurethane resin (A2) to the nitrocellulose resin (A1) calculated as solid content is 1.0 to 4.0. [6] The surface printing ink composition according to any one of [1] to [5], which is a gravure printing ink composition for surface printing. [7] A laminate comprising a plastic film and a printed layer formed on one surface of the plastic film using the printing ink composition for surface printing described in any one of [1] to [6]. [8] The laminate according to [7], wherein the plastic film is a polyethylene film that has not been subjected to a corona discharge treatment. [9] A packaging material comprising the laminate according to [7] or [8]. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a surface printing ink composition which is capable of forming a printed layer which has excellent adhesion to a substrate and excellent resistance to heat yellowing, even when the substrate is a polyethylene film which has not been subjected to a corona discharge treatment, and a laminate and a packaging material which use the same. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be implemented in various forms without departing from the spirit of the present invention. In this specification, the symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The "coating film" refers to a coating film (printed layer) formed by a printing ink composition. "Solid content" refers to the components (non-volatile components) contained in the printing ink composition, excluding volatile media such as organic solvents, and is the component that will ultimately form the coating film. Solid content is measured in accordance with JIS K 5601-1-2:2008. The contents of all components other than the medium are calculated on a solids basis.

[0015] [Printing ink composition for surface printing] A printing ink composition for surface printing according to one embodiment of the present invention (hereinafter also simply referred to as "ink composition") contains a binder resin (A), a terpene resin (B), and an organic solvent, as shown below. The ink composition may further contain other components (hereinafter also referred to as "optional components") other than the binder resin (A), the terpene resin (B) and the organic solvent, as necessary.

[0016] <Binder resin (A)> The binder resin (A) contains a nitrocellulose resin (A1) and a polyurethane resin (A2).

[0017] <Nitrocellulose resin (A1)> As the nitrocellulose resin (A1), from the viewpoints of compatibility of the nitrocellulose resin with the ink, stability of the ink composition (ink stability), adhesion of the coating film to the substrate, abrasion resistance, heat resistance, blocking resistance, kneading resistance, and cold kneading resistance, the type and viscosity symbol defined by viscosity measurement in accordance with JIS K 6703:1995 are preferably H1 / 4, H1 / 2, H1, or H2, and more preferably H1 / 2, H1, or H2. If the viscosity symbol of nitrocellulose resin is lower than H1 / 4, the abrasion resistance, heat resistance, and blocking resistance will be slightly reduced. If the viscosity symbol of nitrocellulose resin is higher than H2, the adhesion to the substrate, kneading resistance, cold kneading resistance, and ink stability will be slightly reduced. If the nitrocellulose resin type is L, the compatibility with ink will be slightly reduced.

[0018] The types are defined according to the nitrogen content in the nitrocellulose resin. Nitrocellulose resins with a nitrogen content of 10.7% or more but less than 11.5% are classified as type L. Nitrocellulose resins with a nitrogen content of 11.5% or more and 12.2% or less are classified as type H. The viscosity symbol is defined according to the time (fall time) it takes for a specified steel ball to fall between the marked lines in a nitrocellulose resin solution having a specified solid content concentration. In the case of a nitrocellulose resin of the above type and viscosity symbol H1 / 8, the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content concentration of 25% by mass is 1.6 to 2.9 seconds. In the case of a nitrocellulose resin of the above type and viscosity symbol H1 / 4, the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content concentration of 25% by mass is 3.0 to 8.9 seconds. In the case of a nitrocellulose resin of the above type and viscosity symbol H1 / 2, the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content of 20% by mass is 3.0 to 4.9 seconds, or the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content of 25% by mass is 9.0 to 22.0 seconds. In the case of a nitrocellulose resin of the above type and viscosity symbol H1, the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content concentration of 20% by mass is 5.1 to 9.0 seconds. In the case of a nitrocellulose resin of the type and viscosity symbol H2, the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content of 12.2% by mass is 1.5 to 2.5 seconds, or the time it takes for a steel ball to fall into a nitrocellulose resin solution with a solid content of 20% by mass is 15.0 to 40.0 seconds. The nitrocellulose resin (A1) may be used alone or in combination of two or more kinds.

[0019] <Polyurethane resin (A2)> The polyurethane resin (A2) may be, for example, a thermoplastic polyurethane resin which is a reaction product of a polyisocyanate compound and a polyol compound and is soluble in an organic solvent. The polyurethane resin (A2) can be produced by a conventional method, for example, by reacting a urethane prepolymer, which is a reaction product of a polyisocyanate compound and a polyol compound, with a chain extender and a reaction terminator, if necessary.

[0020] Examples of polyisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4-diphenylether diisocyanate, 2-nitrodiphenyl-4,4-diisocyanate, 2,2-diphenylpropane-4,4-diisocyanate, 3,3-dimethyldiphenylmethane-4,4-diisocyanate, 4,4-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthyl aromatic diisocyanates such as naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, and 3,3-dimethoxydiphenyl-4,4-diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate; and alicyclic diisocyanates such as isophorone diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate. The polyisocyanate compounds may be used alone or in combination of two or more.

[0021] Examples of the polyol compound include polyester polyol, polycarbonate polyol, polyether polyol, etc. One type of polyol compound may be used alone, or two or more types may be used in combination.

[0022] Examples of polyester polyols include polyester polyols and polyesteramide polyols obtained by dehydration polycondensation reaction of polycarboxylic acids with polyhydric alcohols or secondary or tertiary amines. Examples of polycarboxylic acids include succinic acid, adipic acid, sebacic acid, azelaic acid, terephthalic acid, isophthalic acid, orthophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, hexahydroorthophthalic acid, naphthalenedicarboxylic acid, and trimellitic acid, as well as polycarboxylic acids such as their acid esters and their acid anhydrides. One type of polycarboxylic acid may be used alone, or two or more types may be used in combination. Examples of polyhydric alcohols include low molecular weight alcohol compounds such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, ethylene oxide or propylene oxide adducts of bisphenol A, trimethylolpropane, glycerin, and pentaerythritol, as well as low molecular weight amino alcohol compounds such as monoethanolamine and diethanolamine. One type of polyhydric alcohol may be used alone, or two or more types may be used in combination. Examples of secondary and tertiary amines include low molecular weight amine compounds such as hexamethylenediamine, xylylenediamine, and isophoronediamine. The secondary and tertiary amines may be used alone or in combination of two or more. As the polyester polyol, for example, a lactone-based polyester polyol obtained by ring-opening polymerization of a cyclic ester (lactone) monomer such as ε-caprolactone or γ-valerolactone using a low molecular weight alcohol compound, a low molecular weight amino alcohol compound, or the like as an initiator can be used.

[0023] Examples of polycarbonate polyols include those obtained by dehydrochlorination reaction of a low molecular weight alcohol compound with phosgene, and those obtained by transesterification reaction of a low molecular weight alcohol compound with a carbonate compound. Examples of low molecular weight alcohol compounds include the same low molecular weight alcohol compounds used in the synthesis of polyester polyols. Examples of carbonate compounds include diethylene carbonate, dimethyl carbonate, diethyl carbonate, and diphenyl carbonate.

[0024] Examples of polyether polyols include those obtained by ring-opening polymerization of cyclic ethers using hydroxyl group-containing compounds such as low molecular weight alcohol compounds, low molecular weight amine compounds, low molecular weight amino alcohol compounds, and phenols as initiators. Examples of the low molecular weight alcohol compounds, low molecular weight amine compounds, and low molecular weight amino alcohol compounds are the same as the low molecular weight alcohol compounds used in the synthesis of polyester polyols. Examples of cyclic ethers include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide, as well as tetrahydrofuran. Specific examples of polyether polyols include polyoxyethylene polyols, polyoxypropylene polyols, polytetramethylene ether polyols, and polyoxyethylene polyoxypropylene polyols. As the polyether polyol, the above-mentioned polyester polyol or polyester ether polyol using polycarbonate polyol as an initiator can also be used.

[0025] The chain extender may be a compound having two or more functional groups (such as amino groups and hydroxyl groups) in the molecule that are reactive with isocyanate groups. Examples of the chain extender include diamine compounds such as ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, hexamethylenediamine, isophoronediamine, and 2-ethylaminoethylamine; polyamine compounds such as diethylenetriamine and triethylenetetramine; low-molecular-weight diol compounds such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, and triethylene glycol; aminoethylethanolamine; and aminopropylethanolamine. One type of chain extender may be used alone, or two or more types may be used in combination.

[0026] Examples of the reaction terminator include monoalkylamines such as n-propylamine and n-butylamine, dialkylamines such as di-n-butylamine, alkanolamines such as monoethanolamine and diethanolamine, and monoalcohols such as methanol and ethanol. One type of reaction terminator may be used alone, or two or more types may be used in combination.

[0027] The glass transition temperature of the polyurethane resin (A2) is preferably −70 to 0° C., more preferably −60 to −10° C., and even more preferably −50 to −20° C. When the glass transition temperature of the polyurethane resin (A2) is not less than the above lower limit, the blocking resistance, heat resistance, and abrasion resistance are improved, and when it is not more than the above upper limit, the adhesion to the substrate, kneading resistance, and cold kneading resistance are improved. In this specification, the glass transition temperature is determined in accordance with JIS K 7121 by using a differential scanning calorimeter to measure a curve (DSC curve) obtained by heating 10 mg of a sample from −100° C. to 160° C. at a temperature rate of 20° C. / min, and determining the intersection between the baseline and the tangent to the endothermic curve.

[0028] The number average molecular weight of the polyurethane resin (A2) is preferably 1000 to 50000, more preferably 1500 to 30000, and particularly preferably 3000 to 15000. When the number average molecular weight of the polyurethane resin (A2) is at least the above lower limit, the blocking resistance, heat resistance, and abrasion resistance are improved, and when it is at most the above upper limit, the adhesion to the substrate, kneading resistance, and cold kneading resistance are improved. In this specification, the number average molecular weight is a value calculated in terms of standard polystyrene determined by gel permeation chromatography (GPC).

[0029] The hydroxyl value of the polyurethane resin (A2) is preferably 50 mgKOH / g or less, more preferably 40 mgKOH / g or less, and particularly preferably 30 mgKOH / g or less. When the hydroxyl value of the polyurethane resin (A2) is the above upper limit or less, blocking resistance and ink stability are more excellent. In this specification, the hydroxyl value is a value measured in accordance with JIS K 1557-1.

[0030] The amine value of the polyurethane resin (A2) is preferably 10 mgKOH / g or less, more preferably 5 mgKOH / g or less, and particularly preferably 3 mgKOH / g or less. When the amine value of the polyurethane resin (A2) is the above upper limit or less, the printability is more excellent. In this specification, the amine value is a value measured by neutralization titration using hydrochloric acid in accordance with JIS K 7237.

[0031] The storage modulus (E'; dynamic storage modulus) of the polyurethane resin (A2) at a temperature of 100°C and a frequency of 11 Hz is preferably not more than 20, more preferably not more than 10, and particularly preferably not more than 5. When the storage modulus of the polyurethane resin (A2) is not more than the above upper limit, the adhesion to the substrate is better. In this specification, the storage modulus is a value obtained by measuring the dynamic viscoelasticity of a dry film of a sample (film-like sample) using a dynamic viscoelasticity measuring device at a temperature of 100° C. and a frequency of 11 Hz.

[0032] <Terpene Resin (B)> The terpene resin (B) is a resin obtained by polymerization reaction of terpenes. Terpenes include monoterpenes such as α-pinene, β-pinene, limonene, terpinolene, myrcene, and 3-carene, which are mainly obtained from pine trees and oranges, and sesquiterpenes such as longifolene and caryophyllene. Examples of the terpene resin (B) include polyterpene resins synthesized from α-pinene, β-pinene, limonene, etc., aromatic modified terpene resins, terpene phenol resins, hydrogenated polyterpene resins, hydrogenated aromatic modified terpene resins, hydrogenated terpene phenol resins, etc. Among these, polyterpene resins are preferred from the viewpoints of their small solubility parameter and particularly excellent adhesion to polyethylene films that have not been subjected to corona discharge treatment. The terpene resin (B) may be used alone or in combination of two or more kinds.

[0033] The solubility parameter (hereinafter also referred to as "SP value") of the terpene resin (B) is 10.0 or less, preferably 9.5 or less, and more preferably 9.0 or less. The SP value of the terpene resin (B) is important for improving adhesion to polyethylene film that has not been subjected to corona discharge treatment. When the SP value of the terpene resin (B) is equal to or less than the above upper limit, the adhesion to polyethylene film that has not been subjected to corona discharge treatment is excellent. This is thought to be because the addition of the terpene resin (B) to the binder resin (A) reduces the SP value of the resin as a whole, approaching the SP value of polyethylene film that has not been subjected to corona discharge treatment, thereby significantly improving compatibility with the film, and because the terpene resin (B) contributes to adhesion not only chemically but also physically due to its plasticity and adhesiveness. The lower limit of the SP value of the terpene resin (B) is not particularly limited, but from the viewpoint of miscibility with the binder resin (A), it is preferably 8.0 or more. In this specification, the SP value is calculated by the Fedors method. The SP value was calculated by the Fedors method using Δei (cal / mol) and Δvi (cm) as described in Polymer Engineering and Science, February 1974, Vol. 14, No. 2, pp. 147-154. 3 / mol) into the following formula: SP value = (ΣΔei / ΣΔvi) 1 / 2

[0034] The softening point of the terpene resin (B) is 90°C or higher, more preferably 95°C or higher, and particularly preferably 110°C or higher. When the softening point of the terpene resin (B) is above the above lower limit, the resin exhibits excellent heat yellowing resistance, blocking resistance, and heat resistance. The content of low-molecular-weight components in the terpene resin affects the softening point. A high content of low-molecular-weight components increases tackiness, resulting in reduced blocking resistance. Furthermore, low-molecular-weight components yellow when exposed to high heat due to thermal degradation caused by changes in molecular structure or oxidation, thereby reducing heat yellowing resistance. Low-molecular-weight components also have a negative effect on coating film strength, resulting in reduced abrasion resistance. Therefore, by using a terpene resin (B) having a softening point above the above limit, the influence of low-molecular-weight components can be suppressed, resulting in a coating film with the above-mentioned excellent physical properties. The higher the softening point of the terpene resin (B), the better, and the upper limit is not particularly limited, but is, for example, 135°C or lower. In this specification, the softening point is a value measured in accordance with JIS K 2207.

[0035] The glass transition temperature of the terpene resin (B) is preferably at least 45° C., more preferably at least 55° C., and even more preferably at least 60° C. When the glass transition temperature of the terpene resin (B) is at least the above lower limit, the resin has better heat yellowing resistance, blocking resistance, and heat resistance. The higher the glass transition temperature of the terpene resin (B), the better. There is no particular upper limit to the glass transition temperature, but it is, for example, 80° C. or lower.

[0036] <Organic solvents> Examples of organic solvents include aromatic organic solvents such as toluene and xylene; aliphatic hydrocarbon organic solvents such as cyclohexane and methylcyclohexane; ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, and isobutyl acetate; alcohol organic solvents such as methanol, ethanol, n-propanol, isopropanol, and n-butanol; and glycol ether organic solvents such as ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether.

[0037] From an environmental perspective, the organic solvent is preferably an organic solvent that is substantially free of toluene (a non-toluene organic solvent). That is, the ink composition is preferably a non-toluene ink composition that is substantially free of toluene. The organic solvent is more preferably an organic solvent that is substantially free of aromatic organic solvents such as toluene and xylene. "Substantially free" means that it is not intentionally added.

[0038] From the viewpoint of stably dissolving the binder resin (A), the organic solvent preferably contains an ester-based organic solvent and an alcohol-based organic solvent. The content of the ester-based organic solvent in the organic solvent is preferably 50 to 95 mass % based on the total mass of the organic solvent, and the content of the alcohol-based organic solvent in the organic solvent is preferably 5 to 50 mass % based on the total mass of the organic solvent.

[0039] <Optional ingredients> [Chelating agent (C)] For the purpose of further improving heat resistance, blocking resistance, abrasion resistance, and adhesion to plastic films, a chelating agent (C) may be contained in the ink composition. Examples of the chelating agent (C) include metal chelate compounds. Examples of the metal component of the metal chelate compound include titanium, zirconium, aluminum, iron, etc. Among these, titanium is preferred from the viewpoints of cost, stability, and excellent coating film properties. Examples of titanium chelate compounds include tetraisopropyl titanate, tetra-normal-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, tetramethyl titanate, tetrahexyl titanate, tetraheptyl titanate, tetrastearyl titanate, triethanolamine titanate, titanium acetylacetate, titanium ethylacetoacetate, titanium lactate, octylene glycol titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, titanium dodecylbenzenesulfonate compounds, and n-butyl phosphate titanium ester. Among these, titanium acetylacetonate and n-butyl phosphate titanium ester are preferred because of their particularly excellent heat resistance, blocking resistance, abrasion resistance, and adhesion to plastic films. The chelating agent (C) may be used alone or in combination of two or more kinds.

[0040] [Plasticizer (D)] For the purpose of further improving the resistance to rubbing and cold rubbing, a plasticizer (D) may be contained in the ink composition. The plasticizer (D) is not particularly limited, but examples thereof include phthalate esters, adipic acid esters, trimellitic acid esters, aliphatic dibasic acid esters, phosphate esters, ricinoleic acid esters, sebacic acid esters, azelaic acid esters, maleic acid esters, fumaric acid esters, benzoic acid esters, polyesters, citrate esters, acetate esters, sulfonamides, mixed-group dibasic acid esters, and vegetable oil derivatives such as epoxidized vegetable oil. The plasticizer (D) may be used alone or in combination of two or more kinds.

[0041] The freezing point of the plasticizer (D) is preferably 5°C or lower, more preferably -5°C or lower, and even more preferably -10°C or lower. When the freezing point of the plasticizer (D) is equal to or lower than the above upper limit, the cold kneading resistance is superior. In low-temperature environments, the ink coating hardens and loses flexibility, which frequently causes the coating to crack when kneaded and fall off. However, by including a plasticizer with a low freezing point, it is possible to maintain flexibility even in low-temperature environments without losing it, which is thought to result in excellent cold kneading resistance. The lower the freezing point of the plasticizer (D), the better. There is no particular lower limit to the freezing point, but it is, for example, −60° C. or higher. In this specification, the freezing point is a value measured in accordance with JIS K 0065:1992.

[0042] [Hydrocarbon wax] To further improve rub resistance, the ink composition may contain a hydrocarbon wax. Examples of hydrocarbon waxes include polyethylene wax, Fischer-Tropsch wax, paraffin wax, microcrystalline wax, and polypropylene wax. Among these, polyethylene wax and Fischer-Tropsch wax are preferred. Examples of polyethylene wax include high-density polymerized polyethylene, low-density polymerized polyethylene, oxidized polyethylene, acid-modified polyethylene, and special monomer-modified polyethylene. Fischer-Tropsch wax is a wax produced by the Fischer-Tropsch process using carbon monoxide and hydrogen as raw materials. It has a nearly saturated, unbranched, linear molecular structure. The hydrocarbon waxes may be used alone or in combination of two or more.

[0043] The penetration (hardness) of the hydrocarbon wax at 25°C as specified in JIS K 2207 is preferably from 0.1 to 30, more preferably from 0.1 to 28, and particularly preferably from 0.1 to 25. When the penetration (hardness) of the hydrocarbon wax is the above upper limit or less, the abrasion resistance and printability are more excellent.

[0044] [Pigment] If necessary, the ink composition may contain a pigment. The ink composition may be a medium ink composition that does not substantially contain a coloring material such as a pigment.

[0045] Examples of pigments include extender pigments, inorganic pigments, and organic pigments. Examples of extender pigments include silica, barium sulfate, kaolin, clay, calcium carbonate, and magnesium carbonate. Examples of inorganic pigments include white pigments such as titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, and silica; black pigments such as carbon black and iron black; and various color inorganic pigments such as aluminum particles, mica, bronze powder, chrome vermilion, yellow lead, cadmium yellow, cadmium red, ultramarine, Prussian blue, red iron oxide, yellow iron oxide, and zinc oxide. Examples of organic pigments include soluble azo pigments, insoluble azo pigments, azo pigments, phthalocyanine pigments, halogenated phthalocyanine pigments, anthraquinone pigments, anthanthrone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, perylene pigments, perinone pigments, quinacridone pigments, thioindigo pigments, dioxazine pigments, isoindolinone pigments, quinophthalone pigments, azomethine azo pigments, flavanthrone pigments, diketopyrrolopyrrole pigments, isoindoline pigments, and indanthrone pigments. The pigments may be used alone or in combination of two or more.

[0046] [Other optional ingredients] If necessary, the ink composition may contain other optional components in addition to those described above. Other optional components include, for example, fatty acid amides, chlorinated polyolefin resins, resin beads, rosin derivatives, antifoaming agents, dispersants, pigment derivatives, antisettling agents, ultraviolet absorbers, antioxidants, antistatic agents, leveling agents, thickeners, stabilizers, and the like. The other optional components may be used alone or in combination of two or more.

[0047] <Content of each ingredient> The content of the binder resin (A) in terms of solid content is preferably 20 to 80 mass %, more preferably 25 to 75 mass %, and even more preferably 30 to 70 mass %, based on the total mass of the solid content of the ink composition. When the content of the binder resin (A) is equal to or greater than the above lower limit, the adhesion to the substrate, abrasion resistance, and printability are superior, and when it is equal to or less than the above upper limit, the heat resistance and blocking resistance are superior. The content of the binder resin (A) in terms of solid content is preferably from 5 to 30 mass %, more preferably from 8 to 25 mass %, and even more preferably from 10 to 20 mass %, relative to the total mass of the ink composition.

[0048] The mass ratio (hereinafter also referred to as "A2 / A1") expressed in terms of solid content, expressed as polyurethane resin (A2) / nitrocellulose resin (A1), is preferably 1.0 to 4.0, more preferably 1.0 to 3.0, and even more preferably 1.0 to 2.5. When A2 / A1 is equal to or greater than the above lower limit, adhesion to substrates, ink stability, kneading resistance, cold kneading resistance, oil resistance, and printability are superior, and when it is equal to or less than the above upper limit, blocking resistance, heat resistance, and abrasion resistance are superior.

[0049] The content of the terpene resin (B) in terms of solid content is 2 to 25 mass %, preferably 3 to 20 mass %, and more preferably 5 to 18 mass %, relative to the total mass of the solid content of the ink composition. When the content of the terpene resin (B) is at least the above lower limit, the ink composition has excellent adhesion to polyethylene film that has not been subjected to corona discharge treatment, and when the content is at most the above upper limit, the ink composition has excellent heat yellowing resistance, blocking resistance, and heat resistance. The content of the terpene resin (B) in terms of solid content is preferably 0.8 to 5.5 mass %, more preferably 1.2 to 4.8 mass %, and even more preferably 2 to 4 mass %, relative to the total mass of the ink composition.

[0050] When the ink composition contains a chelating agent (C), the mass ratio (hereinafter also referred to as "B / C") of terpene resin (B) to chelating agent (C) in terms of solid content is preferably 0.5 to 13, more preferably 1.0 to 10, and even more preferably 2.0 to 5.0. When B / C is equal to or greater than the lower limit, adhesion to non-corona-treated polyethylene film and cold-friction resistance are superior. When B / C is equal to or less than the upper limit, heat yellowing resistance, blocking resistance, and abrasion resistance are superior. In particular, B / C is important from the perspective of achieving both excellent adhesion to non-corona-treated polyethylene film and excellent blocking resistance. While the terpene resin (B) is important for improving adhesion to non-corona-treated polyethylene film, it also reduces blocking resistance due to tackiness derived from low-molecular-weight components. Therefore, by using a chelating agent capable of forming a strong coating film by crosslinking, it is possible to achieve excellent adhesion to non-corona-treated polyethylene film and excellent blocking resistance.

[0051] When the ink composition contains a plasticizer (D), the content of the plasticizer (D) in terms of solid content is preferably 0.5 to 15 mass %, more preferably 1 to 12 mass %, and even more preferably 2 to 10 mass %, relative to the total mass of the solid content of the ink composition. When the content of the plasticizer (D) is equal to or greater than the above lower limit, sufficient improvements in kneading resistance and cold kneading resistance can be expected, and when it is equal to or less than the above upper limit, better blocking resistance, heat resistance, and abrasion resistance can be achieved. The content of the plasticizer (D) in terms of solid content is preferably from 0.1 to 5.0 mass %, more preferably from 0.3 to 4.0 mass %, and even more preferably from 0.5 to 3.0 mass %, relative to the total mass of the ink composition.

[0052] When the ink composition contains a hydrocarbon wax, the content of the hydrocarbon wax is preferably 0.5 to 3.5 mass%, more preferably 0.7 to 3 mass%, and particularly preferably 1 to 2.5 mass%, based on the total mass of the solids of the ink composition. When the content of the hydrocarbon wax is equal to or greater than the lower limit, further improvement in abrasion resistance can be expected. When the content of the hydrocarbon wax is equal to or less than the upper limit, better printability and heat resistance can be achieved.

[0053] When the ink composition contains a pigment, the content of the pigment may be set to an amount sufficient to ensure the ink's coloring strength, etc. The content of the pigment is usually set to a range of 1 to 80% by mass relative to the total mass of the solid content of the ink composition.

[0054] <Manufacturing method> The ink composition of this embodiment can be obtained, for example, by mixing a nitrocellulose resin (A1), a polyurethane resin (A2), a terpene resin (B), and, if necessary, optional components. The method for mixing the components is not particularly limited, and various methods can be used to mix the components. For example, a method can be used in which the nitrocellulose resin (A1), the polyamide resin (A2), the terpene resin (B), and optional components, if necessary, are dissolved or dispersed in an organic solvent. The method for dissolving or dispersing the components in the organic solvent is not particularly limited, and can be carried out using a known disperser. Examples of dispersers include paint shakers, ball mills, attritors, sand mills, bead mills, dyno mills, roll mills, ultrasonic mills, and high-pressure collision dispersers. In this case, one type of disperser can be used to perform the dispersion treatment once or multiple times, or two or more types of dispersers can be used in combination to perform the dispersion treatment multiple times.

[0055] <Action and effect> The ink composition of the present embodiment described above contains the nitrocellulose resin (A1), the polyurethane resin (A2), and the terpene resin (B), and therefore can form a coating film that has excellent adhesion to the substrate and excellent resistance to heat yellowing, even if the substrate is a polyethylene film that has not been subjected to corona discharge treatment. The coating film formed also has excellent coating film properties such as blocking resistance, cold rubbing resistance, and abrasion resistance.

[0056] <Application> The ink composition of the present embodiment is for surface printing and is suitable as an ink for printing on the surface side of a substrate that will become a packaging material (i.e., the side that does not come into contact with the product to be packaged). In particular, it is ideal as an ink (gravure printing ink) for printing on the surface side of a substrate by gravure printing.

[0057] Although the ink composition of this embodiment can form a coating film with excellent adhesion to polyethylene film that has not been subjected to corona discharge treatment, the substrate to be printed on is not particularly limited. The substrate may or may not be subjected to corona discharge treatment. In addition to corona discharge treatment, surface treatments that generate polar functional groups on the substrate surface, such as plasma treatment, are known. The substrate may or may not be subjected to such surface treatment. The material of the substrate is also not limited, and examples thereof include various plastics such as polyolefins such as polyethylene (PE) and polypropylene (PP), polyesters such as polyethylene terephthalate (PET), polystyrene (PS), and polyamide (NY). Examples of PE include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). One type of plastic may be used alone, or two or more types may be used in combination.

[0058] The substrate is preferably a plastic film. Examples of plastics constituting the plastic film include those similar to those mentioned above. The plastic film may or may not be stretched. Examples of stretched plastic films include biaxially stretched PP film (OPP) and biaxially stretched NY film (ONY). One type of plastic film may be used alone, or two or more types may be stuck together. The thickness of the plastic film is, for example, 5 to 150 μm. The ink composition of this embodiment can form a coating film with excellent adhesion to PE film that has not been subjected to corona discharge treatment, and therefore, a PE film that has not been subjected to corona discharge treatment is suitable as the plastic film.

[0059] A laminate including a plastic film and a printed layer is obtained by printing on one side (surface) of a plastic film using the ink composition of this embodiment. The one side of the plastic film is the front side when the plastic film is used as a packaging material. The print layer is typically formed on one surface of the plastic film, and is typically located on the outermost surface of the laminate, with no other layers formed on top of the print layer. The laminate may or may not further have another layer on the other surface (rear surface) of the plastic film.

[0060] The printed layer can be formed by a known method. For example, an ink composition is applied to one side of a plastic film and dried to form a printed layer. The process of applying the ink composition and drying it may be repeated two or more times. The thickness of the printed layer is, for example, 0.2 to 3 μm. The method for applying the ink composition is not particularly limited, and known application methods such as gravure printing, flexographic printing, brush coating, gravure coating, die coating, bar coating, spray coating, flow coating, dip coating, spin coating, and curtain coating can be used. Among these, gravure printing is preferred from the viewpoint of high quality and productivity. Therefore, the ink composition of this embodiment is preferably a gravure printing ink composition. Any known drying method can be used as long as it can remove the organic solvent contained in the ink composition, such as reduced pressure drying, pressure drying, heat drying, air drying, etc. The temperature for heat drying is, for example, 30 to 150°C.

[0061] The resulting laminate is suitable for use as a packaging material, particularly as a flexible packaging material. "Flexible packaging" refers to packaging materials made of flexible materials, i.e., flexible packages, and is used to package food, daily necessities, etc. [Example]

[0062] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0063] [Raw materials used] <Nitrocellulose resin (A1)> A1-1: Nobel, product name "DHX30-50", solid content: 70%, type and viscosity symbol: H1 / 2. A1-2: Nobel, product name "DHL5 / 15", solid content: 70%, type and viscosity code: H2.

[0064] <Polyurethane resin (A2)> A2-1: Seikabond A-155, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., solid content: 70%, number average molecular weight: 8000, hydroxyl value: 21.4 mg KOH / g, amine value: 0 mg KOH / g. A2-2: Arakawa Chemical Industries, Ltd., trade name "Yuriano 3262", solid content: 70%, number average molecular weight: 2000, hydroxyl value: 0 mg KOH / g, amine value: 0 mg KOH / g.

[0065] <Pigments> Pigment 1: Titanium oxide, manufactured by Teika Corporation, product name "Titanix JR-600A". Pigment 2: CI Pigment Blue 15:4, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "4933GN-EP".

[0066] <Terpene Resin (B)> B-1: Polyterpene resin, SP value: 8.86, softening point: 125±5°C, solid content 50% by mass (methylcyclohexane solution). B-2: Polyterpene resin, SP value: 8.86, softening point: 100±5°C, solid content 50% by mass (methylcyclohexane solution). B-3: Aromatic modified terpene resin, SP value: 9.19, softening point: 125±5°C, solid content 50% by mass (methylcyclohexane solution). B-4: Terpene phenol resin, SP value: 9.83, softening point: 115±5°C, solid content 50% by mass (methylcyclohexane solution). B-5: Polyterpene resin, SP value: 8.86, softening point: 80±5°C, solid content 50% by mass (methylcyclohexane solution). B-6: Terpene phenol resin, SP value: 10.24, softening point: 115±5°C, solid content 50% by mass (methylcyclohexane solution). All of these terpene resins used were commercially available products.

[0067] <Chelating agent (C)> C-1: Matsumoto Fine Chemical Co., Ltd., product name "Orgatics TC-100", solid content 75%.

[0068] <Plasticizer (D)> D-1: Manufactured by Daihachi Chemical Industry Co., Ltd., product name "BXA-N", solid content: 100%, freezing point: -19°C. D-2: Manufactured by Daihachi Chemical Industry Co., Ltd., product name "DMP", solid content: 100%, freezing point: 0°C. D-3: ADEKA CORPORATION, product name "ADEKA Cizer O-130P", solid content: 100%, freezing point: 5°C.

[0069] <Organic solvents> A mixed solvent of ethyl acetate (EtAC): n-propyl acetate (NPAC): isopropanol (IPA) = 6:2:2 (mass ratio).

[0070] <Other ingredients> Hydrocarbon wax: Mitsui Chemicals, Inc., product name "Hiwax 110P", solids content: 100%, penetration: 25. Fatty acid amide: Manufactured by Nippon Fine Chemical Co., Ltd., product name "Neutron S", solid content: 100%. Antifoaming agent: BYK, product name "BYK-1751", solid content: 100%.

[0071] [Examples 1 to 18, Comparative Examples 1 to 5] <Preparation of Ink Composition> The components were mixed to obtain the compositions shown in Tables 1 to 4, and the resulting mixtures were kneaded in a paint shaker to obtain ink compositions.

[0072] <Creating printed materials> The ink composition was diluted with the same organic solvent as used in preparing the ink composition so that the viscosity at 25°C measured using a Zahn cup #3 was 16 seconds, thereby preparing a printing ink. The prepared printing ink was applied to the untreated side of a polyethylene film (RM Tocello Co., Ltd., product name "TUX HC", thickness: 60 μm) using a gravure printing press (manufactured by Matsuo Sangyo Co., Ltd., product name "K Printing Proofer") equipped with a Helio 175 lines / inch gravure engraving plate. The film was then dried at 50°C for 10 seconds to form a printed layer, resulting in a printed product.

[0073] <Evaluation of adhesion to untreated polyethylene film> Cellophane tape (manufactured by Nichiban Co., Ltd.) was applied to the surface of the printed layer of the resulting print, and then the cellophane tape was quickly peeled off. The condition of the printed layer remaining on the substrate was visually inspected and the adhesion of the printed layer to the untreated polyethylene film was evaluated according to the following criteria: 3 to 5 was considered acceptable. 5: The printing layer has not peeled off at all. 4: The ratio of the area of ​​the peeled printing layer to the total area of ​​the printing layer is more than 0% and 5% or less. 3: The ratio of the area of ​​the peeled printing layer to the total area of ​​the printing layer is more than 5% and less than 20%. 2: The ratio of the area of ​​the peeled printing layer to the total area of ​​the printing layer is more than 20% and less than 50%. 1: The ratio of the area of ​​the peeled printing layer to the total area of ​​the printing layer is more than 50%.

[0074] <Evaluation of heat yellowing resistance> The printed layer of the obtained printed matter was placed on a soft aluminum foil, and a heat seal tester (manufactured by Tester Sangyo, product name "TP-701-C Heat Seal Tester") was used to measure the temperature at 120 to 150°C and 2 kg / cm2 on the aluminum foil. 2 After that, the state of the printed layer was checked and the heat yellowing resistance was evaluated according to the following evaluation criteria. A score of 3 to 5 was considered acceptable. 5: No yellowing was observed. 4: Yellowing was observed at 150°C. 3: Yellowing was observed at 140°C. 2: Yellowing was observed at 130°C. 1: Yellowing was observed at 120°C.

[0075] <Evaluation of blocking resistance> The printed and non-printed surfaces of the printed material were overlapped before drying, and the pressure was 4 kg / cm 2The samples were then stored for 24 hours in a thermostatic chamber at 40°C and 80% humidity under a load of 1000 kJ / cm2. The printed and non-printed surfaces were then peeled apart and the blocking resistance was evaluated according to the following criteria. A rating of 3 to 5 was considered acceptable. "Ink transfer to the non-printed surface" refers to the ink film peeling off from the substrate while remaining attached to the non-printed surface when the printed and non-printed surfaces are peeled apart. 5: No ink is transferred to the non-printed surface. 4: Ink absorption onto non-printed surfaces is greater than 0% and less than 5% of the total area of ​​the ink coating. 3: Ink absorption onto non-printed surfaces is more than 5% and less than 20% of the total area of ​​the ink coating. 2: Ink absorption onto non-printed surfaces is more than 20% and less than 50% of the total area of ​​the ink coating. 1: Ink absorption onto non-printed surfaces exceeds 50% of the total area of ​​the ink coating.

[0076] <Evaluation of cold tolerance> The resulting prints were stored in a freezer at -20°C for one day, then vigorously rubbed in the freezer so that the surfaces of the prints touched each other, and their cold-rubbing resistance was evaluated according to the following criteria. A score of 3 to 5 was considered acceptable. 5: The printed layer has not fallen off at all. 4: The ratio of the area of ​​the fallen printed layer to the total area of ​​the printed layer is more than 0% and 5% or less. 3: The ratio of the area of ​​the fallen printed layer to the total area of ​​the printed layer is more than 5% and less than 20%. 2: The ratio of the area of ​​the fallen printed layer to the total area of ​​the printed layer is more than 20% and less than 50%. 1: The ratio of the area of ​​the fallen printed layer to the total area of ​​the printed layer is more than 50%.

[0077] <Evaluation of abrasion resistance> The printed surface of the resulting print was subjected to a rub resistance test using a Gakushin-type rub fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301"), in which a load of 200 gf was applied and a black cloth (gold cloth No. 3) was rubbed back and forth 100 times. After that, the appearance of the printed layer was visually inspected, and rub resistance was evaluated according to the following evaluation criteria. A score of 3 to 5 was considered pass. 5: The area of ​​the printed layer that has migrated to the black cloth (gold cloth No. 3) is less than 5%. 4: The area of ​​the printed layer that has migrated to the black cloth (gold cloth No. 3) is 5% or more but less than 10%. 3: The area of ​​the printed layer that has migrated to the black cloth (gold cloth No. 3) is 10% or more but less than 30%. 2: The area of ​​the printed layer that has migrated to the black cloth (gold cloth No. 3) is 30% or more but less than 60%. 1: The area of ​​the printed layer that has migrated to the black cloth (gold cloth No. 3) is 60% or more.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4]

[0082] In the table, the blending amount of each ingredient indicates the blending amount of the active ingredient. The blending amount is expressed in mass %. The "balance" of organic solvent is the amount that makes the total of all ingredients 100 mass %. "NV." indicates solid content (non-volatile content). [Industrial Applicability]

[0083] The printed layer formed from the ink composition of this embodiment has excellent adhesion to the substrate and excellent heat yellowing resistance, even if the substrate is a polyethylene film that has not been subjected to corona discharge treatment. Therefore, the ink composition of this embodiment is useful as a printing ink for surface printing.

Claims

1. A printing ink composition for surface printing, comprising: The binder resin (A), the terpene resin (B), and the organic solvent are contained, the binder resin (A) contains a nitrocellulose resin (A1) and a polyurethane resin (A2), the terpene resin (B) has a solubility parameter calculated by the Fedors method of 10.0 or less and a softening point of 90°C or more; a surface printing ink composition, wherein the content of the terpene resin (B) in terms of solid content is 2 to 25 mass % relative to the total mass of the solid content of the surface printing ink composition.

2. 2. The printing ink composition for surface printing according to claim 1, wherein the terpene resin (B) is a polyterpene resin.

3. Further containing a chelating agent (C), 2. The printing ink composition for surface printing according to claim 1, wherein a mass ratio of the terpene resin (B) to the chelating agent (C) is 0.5 to 13 in terms of solid content.

4. Further containing a plasticizer (D), 2. The printing ink composition for surface printing according to claim 1, wherein the plasticizer (D) has a freezing point of 5°C or lower.

5. 2. The printing ink composition for surface printing according to claim 1, wherein the mass ratio of the polyurethane resin (A2) to the nitrocellulose resin (A1) is 1.0 to 4.0 in terms of solid content.

6. The surface printing ink composition according to any one of claims 1 to 5, which is a gravure printing ink composition for surface printing.

7. A laminate comprising a plastic film and a printed layer formed on one surface of the plastic film using the printing ink composition for surface printing according to claim 6.

8. 8. The laminate according to claim 7, wherein the plastic film is a polyethylene film that has not been subjected to a corona discharge treatment.

9. A packaging material comprising the laminate according to claim 7.

Images