Ink compositions for metal printing and metal printed materials

Abstract

To provide a metal printing ink composition that exhibits excellent storage stability, transferability, and film properties. [Solution] A metal printing ink composition comprising a resin, a pigment, and a solvent, wherein the resin is an alkyd resin comprising structural units derived from fatty acids and aromatic monocarboxylic acids. A metal printed article having a printing layer made of the metal printing ink composition provided on a metal medium and an overprint layer made of an overprint varnish provided on the printing layer. A method for manufacturing a metal printed article, comprising forming a printing layer on a metal medium by dry offset printing or offset printing of the metal printing ink composition, and forming an overprint layer by coating the printing layer with an overprint varnish.

Description

Technical Field

[0001] The present invention relates to an ink composition for metal printing. More specifically, the present invention relates to an ink composition for metal printing having good storage stability, excellent transferability, and film physical properties, and a metal printed matter using the ink.

Background Art

[0002] Metal containers are widely used in various applications such as beverage containers, general cans, and snack cans. Metal containers are mainly manufactured by two methods. One is a method of printing and coating a sheet-like metal plate and then forming a desired can body through processes such as cutting and welding. The other is a method of punching a metal plate, processing it into a bottomed cylindrical shape through processes such as ironing, and printing and coating the body part. The latter is particularly called a seamless can.

[0003] On the surface of a metal container, an ink composition for metal printing is printed, and various designs and ingredient displays are provided. Printing on a metal container is performed by supplying printing ink from an ink pot, transferring it to the ruled part of the printing plate through a plurality of rolls, and then printing it on the metal substrate after transferring it from the plate to a blanket. Metal printing employs a lithographic offset method or a dry offset method using a resin relief plate.

[0004] Conventionally, alkyd resins have been widely used in ink compositions for metal printing printed by the offset method. Various alkyd resins have been developed to meet the required performance such as printing suitability during high-speed printing, workability when handling the ink composition, and film physical properties when forming a coating film. For example, an alkyd resin with controlled molecular weight (Patent Document 1) has been developed to suppress the thickness of ruled lines and halftone dots, and an alkyd resin with a limited amount of structural units derived from fatty acids (Patent Documents 2 and 3) has been developed to impart aqueous overprint varnish suitability.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Patent No. 7425532 [Patent Document 2] Patent No. 7353551 [Patent Document 3] Patent No. 7368674 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a metal printing ink composition that exhibits good storage stability and excellent transferability and film properties, as well as a metal printed product using the same ink. [Means for solving the problem]

[0007] As a result of diligent research into the aforementioned problems, the inventors have found that the above problems can be solved by using the metal printing ink described below, and have thus come to present invention.

[0008] [1] A metal printing ink composition comprising a resin, a pigment, and a solvent, wherein the resin is an alkyd resin comprising fatty acid-derived structural units and aromatic monocarboxylic acid-derived structural units, and the content of aromatic monocarboxylic acid-derived structural units in the resin is 0.5 to 20% by mass.

[0009] [2] The metal printing ink composition according to [1], wherein the weight-average molecular weight of the resin is in the range of 2,000 to 20,000.

[0010] [3] The metal printing ink composition according to [1] or [2], wherein the mass ratio of structural units derived from fatty acids to structural units derived from aromatic monocarboxylic acids in the resin is 70 / 30 to 98 / 2.

[0011] [4] A metal printed material having a printing layer made of a metal printing ink composition according to any of [1] to [3] provided on a metal medium, and an overprint layer made of an overprint varnish provided on the printing layer.

[0012] [5] A method for manufacturing a metal printed material, comprising forming a printed layer on a metal medium by dry offset printing or offset printing of any of the metal printing ink compositions described in [1] to [3] above, and then applying an overprint varnish on the printed layer to form an overprint layer. [Effects of the Invention]

[0013] According to the present invention described above, it is possible to provide a metal printing ink composition that has excellent storage stability, transferability, and good film properties, as well as a metal printed product using the same. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described in detail below. Note that the embodiments or requirements described are merely examples of embodiments of the present invention and can be modified as appropriate within the scope of the invention.

[0015] (Ink composition for metal printing) The metal printing ink composition of this embodiment (hereinafter also referred to as the ink composition) contains a resin, a pigment, and a solvent as essential components. By including an alkyd resin containing fatty acid-derived structural units and aromatic monocarboxylic acid-derived structural units, it is possible to obtain a metal printing ink composition with excellent storage stability, transferability, and good film properties. Each component will be described below.

[0016] <Resin> The alkyd resin of this embodiment functions as a binder component in the ink composition and is a resin modified with a condensate of a polybasic acid and a polyhydric alcohol as its backbone, and with a fatty acid (or oil) and an aromatic monocarboxylic acid. As a result, the resin contains constituent units derived from fatty acids and constituent units derived from aromatic monocarboxylic acids.

[0017] The content of aromatic monocarboxylic acid-derived structural units in the alkyd resin is 0.5 to 20% by mass. When structural units derived from aromatic monocarboxylic acids are included, and the content is within the above range, storage stability, transferability, and film properties are good. This is because the aromatic monocarboxylic acid-derived structural units improve solubility in solvents, which is thought to affect the storage stability and transferability of the ink composition. Furthermore, the improved hardness of the resin is thought to improve the film properties of the ink composition. In addition, including aromatic monocarboxylic acid-derived structural units makes it easier to adjust the molecular weight of the resin to a suitable range, which has the advantage of making it easier to balance the above-mentioned properties. The content of aromatic monocarboxylic acid-derived structural units is preferably 1 to 15% by mass, and more preferably 2 to 10% by mass. When it is within this range, storage stability, transferability, and film properties are even better. Note that the above effects are based on chemical considerations and are not limited to this range. If the content of aromatic monocarboxylic acid-derived structural units is less than 0.5% by mass, the solubility with solvents is poor, and the ink composition tends to have poor storage stability and transferability. If the content of aromatic monocarboxylic acid-derived structural units is more than 20% by mass, there are too many rigid structural units, which worsens the solubility with solvents, and the ink composition tends to have poor storage stability and transferability.

[0018] Aromatic monocarboxylic acids are aromatic compounds having one carboxyl group in one molecule. Examples include benzoic acid, methylbenzoic acid, dimethylbenzoic acid, ethylbenzoic acid, and para-t-butylbenzoic acid. Among these, benzoic acid and para-t-butylbenzoic acid are preferred, with benzoic acid being more preferred. These can be used individually or in combination of two or more.

[0019] The oils and fatty acids include linseed oil, castor oil, safflower oil, soybean oil, tall oil, sake lees oil, palm oil, castor oil, dehydrated castor oil, sunflower oil, coconut oil, fatty acids of these oils, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, eleostearic acid, 12-hydroxystearic acid, etc. Among these, linseed oil fatty acid, coconut oil fatty acid, palm oil fatty acid, palm kernel oil fatty acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid are preferred, and coconut oil fatty acid, palm kernel oil fatty acid, capric acid, lauric acid, and myristic acid are more preferred. The oils and fatty acids may be used alone or in combination of two or more.

[0020] The mass ratio of the structural unit derived from fatty acid and the structural unit derived from aromatic monocarboxylic acid contained in the alkyd resin is preferably from 70 / 30 to 98 / 2, more preferably from 80 / 20 to 95 / 5. When the mass ratio of the structural unit derived from fatty acid and the structural unit derived from aromatic monocarboxylic acid contained in the alkyd resin is within the above range, the ink composition has good storage stability and excellent transferability and film physical properties.

[0021] The total content of the structural unit derived from fatty acid and the structural unit derived from aromatic monocarboxylic acid contained in the alkyd resin is preferably 20 to 65% by mass based on the total mass of the alkyd resin, more preferably 30 to 55% by mass. When the total content of the structural unit derived from fatty acid and the structural unit derived from aromatic monocarboxylic acid is within the above range, the ink composition has excellent transferability and film physical properties.

[0022] The polybasic acids include aromatic dibasic acids such as phthalic anhydride, isophthalic acid, and terephthalic acid; alicyclic dibasic acids such as tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 1,4 - cyclohexanedicarboxylic acid; aliphatic dibasic acids such as succinic anhydride, maleic anhydride, hymic anhydride, adipic acid, sebacic acid, azelaic acid, and fumaric acid; polybasic acids such as trimellitic anhydride and methylcyclohexenetricarboxylic anhydride. Among these, phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, adipic acid, and sebacic acid are preferred, and phthalic anhydride and isophthalic acid are more preferred. The polybasic acids may be used alone or in combination of two or more.

[0023] The polyhydric alcohols include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,6 - hexanediol, bisphenol A, and hydrogenated bisphenol A; trihydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, and tris(2 - hydroxyethyl)isocyanurate; polyhydric alcohols with a valence of 4 or more such as pentaerythritol and dipentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0024] The styrene - equivalent weight - average molecular weight of the alkyd resin is preferably 2,000 to 20,000, and more preferably 5,000 to 15,000. When the weight - average molecular weight of the fatty acid - modified alkyd resin is within the above range, the ink composition is likely to retain film physical properties, has good solubility in solvents, and also has excellent storage stability and transferability. In this embodiment, the weight - average molecular weight is a value measured by gel permeation chromatography (GPC).

[0025] The method for producing alkyd resin is not particularly limited. For example, known methods for producing alkyd resin include the transesterification method using oil as a raw material and the fatty acid method using fatty acids as a raw material. In one example, the fatty acid described above, a polybasic acid, and a polyhydric alcohol are charged together with xylene in a reaction vessel equipped with a stirrer, reflux condenser, and thermometer, and the temperature is raised to 240°C while stirring under a nitrogen atmosphere to carry out the esterification reaction. After confirming that the desired acid value is achieved, the reaction is terminated to obtain alkyd resin.

[0026] The resin content in the ink composition is not particularly limited. It is sufficient that it can be adjusted to a predetermined ink tack value suitable for metal printing. For example, the resin content in the ink composition is preferably 15 to 60% by mass, and more preferably 20 to 50% by mass. By having a resin content within the above range, the ink composition maintains printability performance such as on-press stability and also exhibits excellent film properties.

[0027] <Solvent> As the solvent in this embodiment, known solvents used in metal printing ink compositions can be used. The solvent may be used alone or two or more solvents may be used in combination.

[0028] High-boiling-point petroleum-based solvents with boiling points of approximately 200°C to 400°C, such as aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons, can be used as solvents. In addition to petroleum-based solvents, higher alcohols, fatty acid esters, etc., can also be used.

[0029] The solvent content is not particularly limited. For example, the solvent content is preferably 10 to 60% by mass, and more preferably 15 to 50% by mass, in the ink composition. By having the solvent content within the above range, the ink composition is easily adjusted to an ink tack value that shows good printability in metal printing.

[0030] <Pigments> The pigments in this embodiment are not particularly limited. Known inorganic or organic pigments for printing inks can be used. The pigments may be used alone or in combination of two or more.

[0031] Inorganic and organic pigments are preferably heat-resistant, light-resistant, and retort-resistant. Examples of inorganic pigments include titanium dioxide, silica, and carbon black. Examples of organic pigments include phthalocyanine pigments, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and quinophthalone pigments.

[0032] The pigment content in the ink composition is adjusted as appropriate depending on the type and purpose. For example, titanium dioxide, which exhibits a white color, is preferably present in an amount of 10 to 70% by mass, more preferably 20 to 60% by mass; carbon black, which exhibits a black color, is preferably present in an amount of 10 to 50% by mass, more preferably 20 to 40% by mass; and organic pigments are preferably present in an amount of 10 to 50% by mass, more preferably 15 to 40% by mass. By having the pigment content within the above ranges, the ink composition exhibits good coloring power, opacity, and excellent dispersion stability.

[0033] <Other ingredients> In addition to the above components, the ink composition of this embodiment may contain additives that are commonly used in ink compositions. Examples include pigment dispersants, extender pigments, dryers, acid catalysts, waxes, viscosity modifiers, and preservative stabilizers.

[0034] • How to adjust printing inks The method for preparing the ink composition in this embodiment is not particularly limited. For example, the ink composition can be prepared by conventional methods using a three-roll mill, a ball mill, a bead mill, etc.

[0035] The shape of the ink composition in this embodiment varies depending on the type and content of the resin, pigment, solvent, and additives. For example, a tack value of 4 to 12 is preferred, and a tack value of 5 to 10 is more preferred. Here, the tack value is shown as the value obtained by rotating a digital incomometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 1 minute under the conditions of 1.31 cc of ink, room temperature of 25°C, roller temperature of 30°C, and rotation speed of 400 rpm. A tack value within the above range provides excellent resistance to aggregation and misting.

[0036] The flow value is preferably 25 to 50, and more preferably 30 to 45. Here, the flow value is the value obtained by measuring the spreading diameter (unit: mm) after 60 seconds at room temperature of 25°C using a spread meter (manufactured by Yasuda Seiki Seisakusho Co., Ltd.). A flow value within the above range indicates good transferability.

[0037] • Manufacturing method of metal printed materials The printing method for the ink composition of this embodiment is not particularly limited, and can be appropriately selected from a dry offset method using a resin relief plate or a waterless lithographic plate, or an offset method using a watered lithographic plate. The film thickness of the ink composition is arbitrary, but it should be in the range of 0.5 to 6 μm. By having the film thickness of the ink composition within the above range, metal printed materials can be obtained that exhibit excellent on-press stability, misting resistance, good coloring power, and good opacity.

[0038] Furthermore, the metal printing medium on which the ink composition of this embodiment is printed includes, but is not limited to, aluminum plates, steel plates, and coated plates laminated with polyester film or the like. These substrates may be subjected to chemical treatment, plating, or base coating such as sizing paint, white paint, or silver paint.

[0039] The manufacturing method for a metal printed article of this embodiment includes the steps of forming a printed layer on a substrate using an ink composition, applying an overprint varnish to the printed layer, and then performing a curing treatment. The printed coated article of the present invention comprises a printed layer formed on a substrate using a printing ink composition and an overprint layer formed using an overprint varnish. The curing treatment is preferably performed by heat curing, and although the heating conditions are not particularly limited, as an example, the first baking condition involves heating at a temperature of 180°C to 300°C for about 3 to 90 seconds, and the second baking condition involves heating at a temperature of 180°C to 300°C for about 30 to 150 seconds.

[0040] Thermosetting varnishes are preferred for overprinting, and conventionally known overprinting varnishes for metal containers can be used without particular limitations. Examples include polyester-melamine, polyester-epoxy-melamine, and polyester-acrylic-melamine varnishes. The overprinting varnish may be either water-based or solvent-based. [Examples]

[0041] The present invention will be described below based on examples and comparative examples, but the present invention is not limited to these examples. Note that the figures in the following tables are based on mass.

[0042] The details of the raw materials used and the synthesis method are as follows:

[0043] <Resin> The resin was synthesized according to the following procedure, and its composition is shown in Table 1. (Synthesis of alkyd resin) • Alkyd resin 1 (Example 1) 42.0 parts of coconut oil fatty acid, 0.5 parts of benzoic acid, 32.5 parts of phthalic anhydride, and 32.5 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 19,000 and a number-average molecular weight of 3,000. The amount of dewatered resin was 7.5 parts. • Alkyd resin 2 (Example 2) 42.0 parts of coconut oil fatty acid, 2.0 parts of benzoic acid, 31.0 parts of phthalic anhydride, and 32.0 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 12,000 and a number-average molecular weight of 2,400. The amount of dewatered resin was 7.0 parts. • Alkyd resin 3 (Example 3) 42.0 parts of coconut oil fatty acid, 5.0 parts of benzoic acid, 29.0 parts of phthalic anhydride, and 32.0 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 8,000 and a number-average molecular weight of 2,000. The amount of dewatered resin was 8.0 parts. • Alkyd resin 4 (Example 4) 42.0 parts of coconut oil fatty acid, 10.0 parts of benzoic acid, 25.0 parts of phthalic anhydride, and 31.0 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 5,000 and a number-average molecular weight of 1,100. The amount of dewatered material was 8.0 parts. • Alkyd resin 5 (Example 5) 42.0 parts of coconut oil fatty acid, 15.0 parts of benzoic acid, 21.0 parts of phthalic anhydride, and 30.5 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 3,500 and a number-average molecular weight of 1,000. The amount of dewatered resin was 8.5 parts. • Alkyd resin 6 (Example 6) 42.0 parts of coconut oil fatty acid, 5.0 parts of para-t-butylbenzoic acid, 29.0 parts of phthalic anhydride, and 31.5 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 8,200 and a number-average molecular weight of 2,600. The amount of dewatered resin was 7.5 parts. • Alkyd resin 7 (Example 7) 42.0 parts of coconut oil fatty acid, 5.0 parts of benzoic acid, 15.0 parts of phthalic anhydride, 15.0 parts of isophthalic acid, and 32.0 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 11,000 and a number-average molecular weight of 2,700. The amount of dewatered resin was 9.0 parts. • Alkyd resin 8 (Example 8) 42.0 parts myristic acid, 5.0 parts benzoic acid, 29.0 parts phthalic anhydride, and 31.5 parts pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 9,500 and a number-average molecular weight of 2,100. The amount of dewatered resin was 7.5 parts. • Alkyd resin 9 (Comparative Example 1) 42.0 parts of coconut oil fatty acid, 33.0 parts of phthalic anhydride, and 33.0 parts of pentaerythritol were esterified by a conventional method to obtain an alkyd resin with a weight-average molecular weight of 25,000 and a number-average molecular weight of 3,300. The amount of dewatered resin was 8.0 parts. • Alkyd resin 10 (Comparative Example 2) 42.0 parts of coconut oil fatty acid, 0.2 parts of benzoic acid, 32.7 parts of phthalic anhydride, and 32.6 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 20,000 and a number-average molecular weight of 2,900. The amount of dewatered resin was 7.5 parts. • Alkyd resin 11 (Comparative Example 3) 42.0 parts of coconut oil fatty acid, 30.0 parts of benzoic acid, 8.5 parts of phthalic anhydride, and 28.5 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 1,800 and a number-average molecular weight of 850. The amount of dewatered resin was 9.0 parts. • Alkyd resin 12 (Comparative Example 4) 42.0 parts of coconut oil fatty acid, 5.0 parts of abietic acid, 29.0 parts of phthalic anhydride, and 32.0 parts of pentaerythritol were esterified by a conventional method to obtain an alkyd resin with a weight-average molecular weight of 9,500 and a number-average molecular weight of 2,300. The amount of dewatered resin was 8.0 parts. • Alkyd resin 13 (Comparative Example 5) 42.0 parts of coconut oil fatty acid, 10.0 parts of abietic acid, 25.0 parts of phthalic anhydride, and 31.0 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 7,500 and a number-average molecular weight of 2,000. The amount of dewatered resin was 8.0 parts. • Alkyd resin 14 (Comparative Example 6) 42.0 parts of coconut oil fatty acid, 5.0 parts of acetic acid, 28.0 parts of phthalic anhydride, and 33.5 parts of pentaerythritol were esterified by conventional methods to obtain an alkyd resin with a weight-average molecular weight of 6,300 and a number-average molecular weight of 1,500. The amount of dewatered resin was 8.5 parts. • Alkyd resin 15 (Comparative Example 7) 42.0 parts of coconut oil fatty acid, 29.0 parts of phthalic anhydride, and 36.0 parts of pentaerythritol were esterified by a conventional method to obtain an alkyd resin with a weight-average molecular weight of 5,500 and a number-average molecular weight of 1,100. The amount of dewatered resin was 7.0 parts.

[0044] [Table 1]

[0045] <Solvent> • LAB (Linear alkylbenzene, manufactured by Mitsui & Co., Ltd.)

[0046] <Pigments> • LIONOL BLUE FG-7351 (Phthalocyanine Blue 15:3, manufactured by Toyo Color Co., Ltd.)

[0047] <Preparation of printing ink composition> Using the obtained alkyd resins 1 to 15, metal printing inks for the examples and comparative examples were prepared according to the formulations shown in Table 2.

[0048] <Rating> The metal printing ink compositions of Examples 1-8 and Comparative Examples 1-7 were evaluated according to the following procedure, and the results are shown in Table 2.

[0049] [Table 2]

[0050] <Storage Stability> The ink compositions of the examples and comparative examples were left to stand for one week at an ambient temperature of 60°C, and the separation of the solvent was observed visually. (Evaluation Criteria) A: The solvent has not separated. B: A very slight separation of the solvent is observed, but this does not affect the quality. C: Slight separation of the solvent is observed, but this does not affect the quality. D: Clear separation of the solvent is observed. The ratings for practical use are A, B, and C.

[0051] <Metastatic> Using a high-speed printability tester (PM904PT, manufactured by SMT Co., Ltd.), 0.2 cc of the ink compositions of the examples and comparative examples were supplied to a roll, homogenized, and then transferred to a test rubber roll. Subsequently, the mixture was transferred to an aluminum plate at a printing speed of 8.0 m / s. Immediately afterward, a thermosetting overprint varnish was applied to the print ink layer at a speed of 2 m / s to a film thickness of 13 μm. The printed coating film was then baked at 200°C for 3 minutes to produce the printed coating film. (Evaluation Criteria) A: The ink composition is uniformly transferred to the substrate. B: The ink composition has been uniformly transferred to the substrate, but the substrate surface is slightly exposed. C: The ink composition has not been uniformly transferred to the substrate, and the substrate surface is slightly exposed. D: The ink composition is not uniformly transferred to the substrate, and the amount transferred is small, resulting in noticeable exposure of the substrate surface. The ratings for practical use are A, B, and C.

[0052] <Film properties> Test panels were prepared using the ink compositions of the examples and comparative examples. Using an RI tester (manufactured by Kokubo Precision Co., Ltd.) and a four-part roll, 0.1 cc of ink composition was spread onto an aluminum plate, and a solvent-based overprint varnish was applied using a simple roll coater, resulting in a solvent-based overprint varnish of approximately 50 mg to 60 mg / 100 cm in solid content. 2To achieve this, the coating was applied to the printing ink layer using a wet-on-wet method and then heated and cured in an electric oven. For the baking and drying conditions, the test panel was first baked at 200°C for 30 seconds, and then second baked at 200°C for 120 seconds. The pencil hardness of the prepared test panels was evaluated in accordance with JIS K 5600-5-4, using pencils for pencil hardness testing (manufactured by Mitsubishi Pencil Co., Ltd.) in an environment of 25°C room temperature. (Evaluation Criteria) A: Pencil hardness of 3H or higher. B: Pencil hardness is H or higher and 2H or lower. C: Pencil hardness HB or higher, F or lower D: Pencil hardness B or lower. The ratings for practical use are A, B, and C.

[0053] The formulation designs for the examples and comparative examples are as follows. (Examples 1-8) The material comprises a resin, a pigment, and a solvent, wherein the resin is an alkyd resin containing structural units derived from fatty acids and structural units derived from aromatic monocarboxylic acids, and the content of structural units derived from aromatic monocarboxylic acids in the resin is 0.5 to 20% by mass. (Comparative Examples 1, 4-7) A difference from the example composition is that the resin does not contain structural units derived from aromatic monocarboxylic acids. (Comparative Examples 2 and 3) A difference from the example composition is that the content of structural units derived from aromatic monocarboxylic acids in the resin is not in the range of 0.5 to 20% by mass.

Claims

1. A metal printing ink composition comprising a resin, a pigment, and a solvent, wherein the resin is an alkyd resin comprising fatty acid-derived structural units and aromatic monocarboxylic acid-derived structural units, and the content of aromatic monocarboxylic acid-derived structural units in the resin is 0.5 to 20% by mass.

2. The metal printing ink composition according to claim 1, wherein the weight-average molecular weight of the resin is in the range of 2,000 to 20,000.

3. The metal printing ink composition according to claim 1, wherein the mass ratio of structural units derived from fatty acids to structural units derived from aromatic monocarboxylic acids in the resin is 70 / 30 to 98 / 2.

4. A metallic printed material having a printing layer made of a metal printing ink composition according to any one of claims 1 to 3 provided on a metal medium, and an overprint layer made of an overprint varnish provided on the printing layer.

5. A method for manufacturing a metal printed material, comprising forming a printed layer on a metal medium by dry offset printing or offset printing with a metal printing ink composition according to any one of claims 1 to 3, and then applying an overprint varnish on the printed layer to form an overprint layer.

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