Metallic printing ink composition and metallic printed matter

Abstract

To provide an ink composition for metal printing which has excellent storage stability, transferability and film properties. [Solution] An ink composition for metal printing containing a resin, a pigment, and a solvent, wherein the resin is an alkyd resin containing structural units derived from a fatty acid and an aromatic monocarboxylic acid. A metal printed product having a printed layer made of the ink composition for metal printing provided on a metal medium, and an overprint layer made of an overprint varnish provided on the printed layer. A method for producing a metal printed product, which includes dry offset printing or offset printing the ink composition for metal printing on a metal medium to form a printed layer, and then applying an overprint varnish on the printed layer to form the overprint layer.

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 that has good storage stability and excellent transferability and film properties, and to a metal printed product using the ink. [Background technology]

[0002] Metal containers are used in a wide variety of applications, including beverage containers, general-purpose cans, and candy cans. Metal containers are primarily manufactured using two methods. One method involves printing and painting a sheet metal plate, followed by cutting, welding, and other processes to create the desired can body. The other method involves punching a metal plate, ironing it, and then forming it into a cylindrical shape with a bottom, and then printing and painting the body of the can. The latter method is specifically called a seamless can.

[0003] The surface of a metal container is printed with an ink composition for metal printing, and various designs, ingredient labels, etc. are provided. When printing on a metal container, printing ink is supplied from an ink fountain, transferred to the image area of ​​the plate via multiple rolls, and then transferred from the plate to a blanket, after which it is printed on the metal substrate. Metal printing employs a lithographic offset method or a dry offset method using a resin relief plate.

[0004] Traditionally, alkyd resins have been widely used in ink compositions for metal printing using the offset method. Various alkyd resins have been developed to meet required performance requirements, such as printability during high-speed printing, ease of handling the ink composition, and film properties when formed into a coating. For example, alkyd resins with controlled molecular weights have been developed to suppress thickening of image lines and dots (Patent Document 1), and alkyd resins with a limited amount of fatty acid-derived structural units have been developed to provide suitability for aqueous overprint varnish (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7425532 [Patent Document 2] Patent No. 7353551 [Patent Document 3] Patent No. 7368674 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an ink composition for metallic printing that has good storage stability and excellent transferability and film properties, and a metallic printed product using the ink. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by using the ink for metal printing described below, and have thus achieved the present invention.

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

[0009] [2] The ink composition for metal printing 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 ink composition for metal printing according to [1] or [2], wherein the mass ratio of the structural units derived from fatty acids to the structural units derived from aromatic monocarboxylic acids in the resin is 70 / 30 to 98 / 2.

[0011] [4] A metallic printed matter having a printing layer made of the metallic printing ink composition described in any one of [1] to [3] above provided on a metallic medium, and an overprint layer made of an overprint varnish provided on the printing layer.

[0012] [5] A method for producing a metal printed product, comprising: forming a printed layer on a metal medium by dry offset printing or offset printing the ink composition for metal printing described in any one of [1] to [3] above; and applying an overprint varnish onto the printed layer to form an overprint layer. [Effects of the Invention]

[0013] According to the present invention, it is now possible to provide an ink composition for metallic printing that has excellent storage stability, transferability, and film properties, and a metallic printed product using the same. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes in detail embodiments of the present invention. Note that the embodiments and explanations of the requirements described are examples of embodiments of the present invention, and can be implemented with appropriate modifications within the scope of the present invention.

[0015] (Ink composition for metal printing) The ink composition for metal printing of this embodiment (hereinafter also referred to as the ink composition) contains a resin, a pigment, and a solvent as essential components. When the resin contains an alkyd resin containing structural units derived from a fatty acid and structural units derived from an aromatic monocarboxylic acid, it becomes possible to obtain an ink composition for metal printing that has excellent storage stability, transferability, and 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 whose backbone is a condensate of a polybasic acid and a polyhydric alcohol, modified with a fatty acid (or oil) and an aromatic monocarboxylic acid, resulting in the resin containing structural units derived from the fatty acid and structural units derived from the aromatic monocarboxylic acid.

[0017] The content of aromatic monocarboxylic acid-derived structural units in the alkyd resin is 0.5 to 20% by mass in the alkyd resin. When aromatic monocarboxylic acid-derived structural units are contained and the content is within the above range, the storage stability, transferability, and film properties are good. The reason for this is believed to be that the aromatic monocarboxylic acid-derived structural units improve solubility in solvents, which affects the storage stability and transferability of the ink composition. Furthermore, the improved hardness of the resin is believed to improve the film properties of the ink composition. Furthermore, the inclusion of aromatic monocarboxylic acid-derived structural units makes it easy to adjust the molecular weight of the resin within a suitable range, which has the advantage of making it easier to balance the various physical properties mentioned above. The content of aromatic monocarboxylic acid-derived structural units is preferably 1 to 15% by mass, more preferably 2 to 10% by mass. Within the above range, the storage stability, transferability, and film properties are better. The above effects are based on chemical considerations and are not limited to these ranges. If the content of structural units derived from aromatic monocarboxylic acid is less than 0.5% by mass, the ink composition will have poor solubility in solvents and will tend to have poor storage stability and transferability.If the content of structural units derived from aromatic monocarboxylic acid is more than 20% by mass, the ink composition will have too many rigid structural units, which will tend to have poor solubility in solvents and will tend to have poor storage stability and transferability.

[0018] The aromatic monocarboxylic acid is an aromatic compound having one carboxyl group in one molecule. Examples thereof 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, and benzoic acid is more preferred. These may be used alone or in combination of two or more.

[0019] Examples of oils and fatty acids include linseed oil, tung oil, safflower oil, soybean oil, tall oil, rice bran oil, palm oil, castor oil, dehydrated castor oil, sunflower oil, and coconut oil, as well as the fatty acids contained therein, such as 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, linoleic acid, ricinoleic acid, eleostearic acid, and 12-hydroxystearic acid. Among these, linseed oil fatty acids, coconut oil fatty acids, palm oil fatty acids, palm kernel oil fatty acids, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid are preferred, with coconut oil fatty acids, palm kernel oil fatty acids, capric acid, lauric acid, and myristic acid being more preferred. The oils and fatty acids may be used alone or in combination.

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

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

[0022] Examples of 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, himic anhydride, adipic acid, sebacic acid, azelaic acid, and fumaric acid; and polybasic acids such as trimellitic anhydride and methylcyclohexene tricarboxylic anhydride. Among these, phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, adipic acid, and sebacic acid are preferred, with phthalic anhydride and isophthalic acid being 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; and tetrahydric or higher alcohols 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 maintain its film properties, has good solubility in solvents, and is excellent in 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 an alkyd resin is not particularly limited. Examples of methods for producing an alkyd resin include known methods such as the transesterification method using oil as a raw material and the fatty acid method using fatty acids as a raw material. For example, the fatty acid, polybasic acid, and polyhydric alcohol described above are charged together with xylene into a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, and the mixture is heated to 240°C with stirring under a nitrogen atmosphere to carry out an esterification reaction. After confirming that the desired acid value has been reached, the reaction is terminated to obtain an alkyd resin.

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

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

[0028] The solvent may be a high-boiling petroleum-based solvent such as an aliphatic hydrocarbon, an alicyclic hydrocarbon, or an aromatic hydrocarbon, having a boiling point of about 200° C. to 400° C. In addition to petroleum-based solvents, higher alcohols, fatty acid esters, etc. may also be used.

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

[0030] <Pigments> The pigment of this embodiment is 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] The inorganic pigments and organic pigments preferably have heat resistance, light resistance, and retort resistance. Inorganic pigments include titanium oxide, silica, carbon black, etc. Organic pigments include phthalocyanine pigments, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, etc.

[0032] The content of the pigment in the ink composition is adjusted appropriately depending on the type and purpose. For example, the content of titanium oxide, which exhibits white color, in the ink composition is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, the content of carbon black, which exhibits black color, is preferably 10 to 50% by mass, more preferably 20 to 40% by mass, and the content of organic pigments is preferably 10 to 50% by mass, more preferably 15 to 40% by mass. By keeping the content of the pigment within the above ranges, the ink composition exhibits good coloring power and hiding power, and also has excellent dispersion stability.

[0033] <Other ingredients> In addition to the components described above, the ink composition of this embodiment may contain additives that are typically added to ink compositions, such as pigment dispersants, extender pigments, driers, acid catalysts, waxes, viscosity modifiers, and storage stabilizers.

[0034] ·How to adjust printing ink The method for preparing the ink composition of the present embodiment is not particularly limited. For example, the ink composition can be prepared by a conventional method using a three-roll mill, a ball mill, a bead mill, or the like.

[0035] The form of the ink composition of this embodiment varies depending on the type and content of resin, pigment, solvent, and additives. For example, the tack value is preferably 4 to 12, and more preferably 5 to 10. Here, the tack value is the value measured using a digital incometer (manufactured by Toyo Seiki Seisakusho, Ltd.) with 1.31 cc of ink, at a room temperature of 25°C, a roller temperature of 30°C, and a rotation speed of 400 rpm for 1 minute. A tack value within the above range provides excellent agglomeration resistance and misting resistance.

[0036] The flow value is preferably 25 to 50, and more preferably 30 to 45. Here, the flow value indicates the value measured using a horizontal plate viscometer (spread meter) (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) at room temperature of 25°C and after 60 seconds, as the spread diameter (unit: mm). When the flow value is in the above range, good transferability is exhibited.

[0037] ·Metal printing method The printing method for the ink composition of this embodiment is not particularly limited, and can be appropriately selected from dry offset methods using resin relief plates or waterless lithographic plates, and offset methods using water-based lithographic plates. The film thickness of the ink composition is optional, but should be in the range of 0.5 to 6 μm. By ensuring that the film thickness of the ink composition is in the above range, a metal print can be obtained that is excellent in on-press stability and misting resistance, and exhibits good coloring power and hiding power.

[0038] Furthermore, examples of metal printing media on which the ink composition of the present embodiment is printed include, but are not limited to, aluminum plates, steel plates, and coated plates obtained by laminating these with polyester films, etc. These substrates may be subjected to chemical conversion treatment, plating treatment, or base coating such as size coating, white coating, or silver coating.

[0039] The method for producing a metal printed product of this embodiment includes the steps of providing a printing layer on a substrate using an ink composition, applying an overprint varnish to the printing layer, and then performing a curing treatment. The printed / coated product of the present invention also includes, on a substrate, a printing layer formed using a printing ink composition and an overprint layer formed using an overprint varnish. The curing treatment is preferably heat curing, and although the heating conditions are not particularly limited, one example includes a first baking step at a temperature of 180°C to 300°C for approximately 3 to 90 seconds, and a second baking step at a temperature of 180°C to 300°C for approximately 30 to 150 seconds.

[0040] The overprint varnish is preferably a thermosetting one, and any conventionally known overprint varnish for metal containers can be used without any particular limitation. Examples include polyester-melamine, polyester-epoxy-melamine, and polyester-acrylic-melamine varnishes. The overprint varnish may be either water-based or solvent-based. [Example]

[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 numbers in the tables below are based on mass.

[0042] Details of the raw materials used and the synthesis method are as follows.

[0043] <Resin> The resin was synthesized as follows, and the 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 in a conventional manner 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 dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 12,000 and a number average molecular weight of 2,400. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 8,000 and a number average molecular weight of 2,000. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 5,000 and a number average molecular weight of 1,100. The amount of dehydration 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 in a conventional manner 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 dehydration 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 in a conventional manner 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 dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 11,000 and a number average molecular weight of 2,700. The amount of dehydration was 9.0 parts. Alkyd Resin 8 (Example 8) 42.0 parts of myristic acid, 5.0 parts of benzoic acid, 29.0 parts of phthalic anhydride, and 31.5 parts of pentaerythritol were esterified in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 9,500 and a number average molecular weight of 2,100. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 25,000 and a number average molecular weight of 3,300. The amount of dehydration 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 in a conventional manner 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 dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 1,800 and a number average molecular weight of 850. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 9,500 and a number average molecular weight of 2,300. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 7,500 and a number average molecular weight of 2,000. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 6,300 and a number average molecular weight of 1,500. The amount of dehydration 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 in a conventional manner to obtain an alkyd resin having a weight average molecular weight of 5,500 and a number average molecular weight of 1,100. The amount of dehydration was 7.0 parts.

[0044] [Table 1]

[0045] <Solvent> LAB (Linear Alkyl Benzene, 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 of Examples and Comparative Examples were prepared according to the formulations shown in Table 2.

[0048] <Evaluation> The ink compositions for metallic printing of Examples 1 to 8 and Comparative Examples 1 to 7 were evaluated in the following manner, and the results are shown in Table 2.

[0049] [Table 2]

[0050] <Storage stability> The ink compositions of the examples and comparative examples were allowed to stand at an ambient temperature of 60° C. for one week, and then the state of solvent separation was visually observed. (Evaluation criteria) A: The solvent is not separated. B: A very small amount of solvent separation is observed, but this does not pose a quality problem. C: A small amount of solvent separation is observed, but this does not pose a quality problem. D: Clear solvent separation is observed. The practical evaluations are A, B and C.

[0051] <Metastatic> Using a high-speed printability tester (PM904PT manufactured by SMT Corporation), 0.2 cc of the ink compositions of the Examples and Comparative Examples was supplied to a roll, homogenized, and then transferred to a test rubber roll. The ink composition was then transferred to an aluminum plate at a printing speed of 8.0 m / s. Immediately thereafter, a thermosetting overprint varnish was applied to the printed ink layer at a speed of 2 m / s to a film thickness of 13 μm. The printed coating was then baked at 200°C for 3 minutes to produce a printed coating film. (Evaluation criteria) A: The ink composition is transferred uniformly to the substrate. B: The ink composition is transferred uniformly to the substrate, but the substrate surface is slightly exposed. C: The ink composition was not uniformly transferred to the substrate, and the substrate surface was slightly exposed. D: The ink composition was not uniformly transferred to the substrate, and the amount transferred was small, resulting in noticeable exposure of the substrate surface. The practical evaluations 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-section roll, 0.1 cc of the ink composition was spread on an aluminum plate, and the solvent-based overprint varnish was applied to the aluminum plate using a simple roll coater until the solid content of the solvent-based overprint varnish was 50 mg to 60 mg / 100 cm. 2The coating was applied wet-on-wet onto the printed ink layer so that the coating was cured by heating in an electric oven. The baking and drying conditions were as follows: the first baking was performed by maintaining the test panel at 200°C for 30 seconds, and then the second baking was performed by maintaining the test panel at 200°C for 120 seconds. The pencil hardness of the prepared test panel was evaluated in accordance with JIS K 5600-5-4 using a pencil hardness test pencil (manufactured by Mitsubishi Pencil Co., Ltd.) at room temperature of 25°C. (Evaluation criteria) A: Pencil hardness of 3H or higher. B: Pencil hardness is H or higher and 2H or lower. C: Pencil hardness is HB or higher and F or lower D: Pencil hardness is B or less. The practical evaluations are A, B and C.

[0053] The formulations of the examples and comparative examples are as follows: Examples 1 to 8 The composition comprises a resin, a pigment, and a solvent, the resin being an alkyd resin containing structural units derived from a fatty acid and structural units derived from an aromatic monocarboxylic acid, and the content of the structural units derived from an aromatic monocarboxylic acid in the resin is 0.5 to 20 mass %. (Comparative Examples 1, 4 to 7) The difference from the compositions of the examples is that the resin does not contain structural units derived from aromatic monocarboxylic acid. (Comparative Examples 2 and 3) The difference from the compositions of the examples is that the content of structural units derived from aromatic monocarboxylic acid in the resin is not in the range of 0.5 to 20% by mass.

Claims

1. An ink composition for metal printing comprising a resin, a pigment, and a solvent, wherein the resin is an alkyd resin containing structural units derived from a fatty acid and structural units derived from an aromatic monocarboxylic acid, the total content of the structural units derived from the fatty acid and the structural units derived from the aromatic monocarboxylic acid being 30 to 55 mass% based on the total mass of the alkyd resin, the aromatic monocarboxylic acid being at least one selected from the group consisting of benzoic acid, methylbenzoic acid, dimethylbenzoic acid, ethylbenzoic acid, and para-t-butylbenzoic acid, and the content of the structural units derived from the aromatic monocarboxylic acid in the resin being 0.5 to 20 mass%, The weight average molecular weight of the resin is in the range of 2,000 to 20,000, the solvent is at least one selected from the group consisting of high-boiling petroleum solvents having a boiling point of 200°C to 400°C, higher alcohols, and fatty acid esters; The ink composition for metal printing has a resin content of 15 to 60% by mass and a solvent content of 10 to 60% by mass.

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

3. A metallic printed product comprising a printed layer formed on a metallic medium and comprising the ink composition for metallic printing according to claim 1 or 2, and an overprint layer formed on the printed layer and comprising an overprint varnish.

4. A method for producing a metal printed product, comprising: forming a printed layer on a metal medium by dry offset printing or offset printing the ink composition for metal printing according to claim 1 or 2; and applying an overprint varnish onto the printed layer to form an overprint layer.

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