Ink composition for seamless printing cans, printed and painted seamless cans, and method for manufacturing the same.

Abstract

The objective is to provide an ink composition for seamless printed cans that has a bluish hue that is difficult to express with conventional seamless can printing, and that is excellent in jet blackness, pitting corrosion resistance, on-press stability, and suitability for high-speed printing, as well as a printed and painted seamless can using the same. [Solution] An ink composition for seamless printing cans comprising carbon black, resin, and solvent, wherein the carbon black contains carbon black (CBI) having an average primary particle diameter of 15 nm or more and less than 35 nm, and carbon black (CBII) having an average primary particle diameter of 35 nm or more and 60 nm or less, and the mass ratio of CBI to CBII is 40 / 60 to 95 / 5.

Description

[Technical Field]

[0001] This invention relates to a black ink composition for seamless printed cans and a printed and painted seamless can using the same. In particular, it relates to an ink composition for seamless printed cans that imparts excellent bluish tint and jet blackness to the printed and painted surface, and a printed and painted seamless can using the same. [Background technology]

[0002] Metal containers are used for a wide range of purposes, including beverage containers, general-purpose containers, and confectionery tins. In particular, metal beverage containers offer superior preservation stability of their contents compared to plastic beverage containers, and are therefore used for alcoholic beverages, carbonated drinks, soft drinks, and coffee beverages.

[0003] Metal beverage containers are manufactured using two main methods. One method involves printing and painting a sheet of metal, followed by processes such as cutting and welding to create the desired can shape. The other method involves punching out a metal sheet, shaping it into a bottomed cylindrical form through processes such as ironing, and then printing and painting the body of the cylindrical container. The latter is specifically called a seamless can.

[0004] Seamless cans are generally made of either steel (primarily iron) or aluminum (primarily aluminum). To display images or information about the contents on these seamless cans, methods include printing directly onto the container or attaching a printed film to the container.

[0005] Patent Document 1 describes a metal printing ink composition containing carbon black. Among seamless printing inks used for printing directly onto containers, black inks used for beverage containers such as black coffee require high jet blackness. Furthermore, recently there has been a growing demand for black inks with a bluish hue rather than black inks with a reddish or brownish hue.

[0006] In addition, the ink used for aluminum cans is also required to have pitting corrosion resistance. Pitting corrosion of an aluminum can is a corrosion phenomenon in which the surface of the printed coating film becomes rough or the printed and coated aluminum can develops holes due to the battery action caused by foreign substances adhering to the surface of the aluminum can.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention provides an ink for seamless printed cans that has a blue hue that was conventionally difficult to express in seamless can printing, is excellent in jet blackness and pitting corrosion resistance, and is also excellent in in-flight stability and high-speed printing suitability.

[0009] In order to solve the above problems, in the present invention, carbon blacks with different particle sizes are used in combination to develop an ink for seamless printed cans that is excellent in jet blackness and has a blue hue. In addition, it has been found that by containing acidic carbon black having acidic functional groups introduced on the surface at a specific ratio in all the carbon blacks, the pitting corrosion resistance on aluminum cans is also excellent, and the present invention has been completed.

[0010] That is, the present invention relates to an ink composition for seamless printed cans containing carbon black, a resin, and a solvent, where the carbon black contains carbon black (CBI) having an average primary particle diameter of 15 nm or more and less than 35 nm and carbon black (CBII) having an average primary particle diameter of 35 nm or more and 60 nm or less, and the mass ratio of CBI to CBII is 40 / 60 to 95 / 5.

[0011] Furthermore, the present invention relates to the seamless printing can ink composition in which the content of acidic carbon black in the carbon black is 80% by mass or more.

[0012] Furthermore, the present invention relates to the seamless printing can ink composition in which the difference in the average primary particle diameter between CBI and CBII is 5 nm or more.

[0013] Furthermore, the present invention relates to the seamless printing can ink composition in which the content of carbon black in the ink composition is 20 to 45% by mass.

[0014] Furthermore, the present invention relates to a printed and painted seamless can having a printing layer made of the seamless printing can ink composition provided on a metal printing medium and an overprint layer made of an overprint varnish provided on the printing layer.

[0015] Furthermore, the present invention relates to a method for manufacturing a printed and painted seamless can, in which the seamless printing can ink composition is dry offset printed or offset printed on a metal printing medium to form a printing layer, and an overprint varnish is applied on the printing layer to form an overprint layer.

Effects of the Invention

[0016] According to the present invention described above, it is possible to provide a seamless printing can ink composition having a bluish tint and excellent jet blackness, in-machine stability, and high-speed printing suitability, and a printed matter printed therefrom, and it is also possible to provide a printed matter showing good pitting corrosion resistance in a seamless can made of an aluminum material.

Modes for Carrying Out the Invention

[0017] The carbon black used in the present invention can be various carbon blacks such as furnace black, channel black, thermal black, acetylene black, etc. manufactured by various manufacturing facilities.

[0018] The carbon black in the ink composition of the present invention is a combination of carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm (CBI) and carbon black with an average primary particle diameter of 35 nm or more and 60 nm or less (CBII). Carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm makes it easy to obtain an ink with high jet blackness, and carbon black with an average primary particle diameter of 20 nm or more and 30 nm or less is more preferable. Carbon black with an average primary particle diameter of 35 nm or more and 60 nm or less makes it easy to obtain an ink with a bluish hue, and carbon black with an average primary particle diameter of 40 nm or more and 50 nm or less is more preferable. By using these in combination, an ink composition for seamless printing cans with excellent jet blackness, bluishness, and suitability for high-speed printing can be obtained.

[0019] Here, the average primary particle diameter refers to the measurement value obtained by electron microscopy. For example, the maximum particle diameter of approximately 2000 to 3000 randomly selected pigment particles is measured using a field emission scanning electron microscope (JEOL JSM-7000F), and the average value of these measurements is taken as the average primary particle diameter. When the average primary particle size of carbon black is represented by a frequency distribution, commercially available carbon black generally shows a symmetrical bell-shaped curve with the average primary particle size as the peak. However, the distribution curve of the average primary particle size of carbon black in the ink composition of the present invention shows an asymmetrical bell-shaped curve. Alternatively, it will have a bell-shaped curve with two or more peaks.

[0020] The difference in average primary particle size between CBI and CBII is preferably 3 nm or more, more preferably 5 nm or more, and more preferably 10 nm or more. This is because it results in superior blackness, bluish tint, and suitability for high-speed printing.

[0021] Furthermore, the nitrogen adsorption specific surface area of ​​CBI is 75-350 m². 2 It is preferable that the value be / g, and 90-180m 2 / g is more preferable. The nitrogen adsorption specific surface area of ​​CBII is 30-70 m². 2 It is preferable that the amount be / g, which is 35-60m 2 / g is more preferable. By using carbon blacks within these ranges in combination, a seamless printing can composition with superior jet blackness, bluish tint, and high-speed printability can be obtained. Here, the nitrogen adsorption specific surface area is defined in accordance with JIS K 6217.

[0022] Examples of CBIs include MA77 (23nm), MA7 (24nm), MA8 (24nm), MA11 (29nm) from Mitsubishi Chemical Corporation, and SpecialBlack5 (20nm), SpecialBlack4 (25nm), SpecialBlack4A (25nm) from Orion Engineered Carbons Co., Ltd., which can be used individually or in combination of two or more types as desired. Examples of CBIIs include MOGUL-E (48nm) from CABOT Corporation, and MA14 (40nm), MA285 (40nm), MA220 (55nm) from Mitsubishi Chemical Corporation, which can be used individually or in combination of two or more types as desired.

[0023] The combined ratio of carbon black described above is such that the mass ratio of CBI to CBII is in the range of 40 / 60 to 95 / 5, more preferably in the range of 50 / 50 to 93 / 7, and even more preferably in the range of 60 / 40 to 90 / 10. Within this range, it is easy to obtain an ink composition for seamless printing cans that has excellent bluish tint, jet blackness, and high-speed printability.

[0024] The carbon black in the ink composition of the present invention preferably contains 80% by mass or more of acidic carbon black into which acidic functional groups have been introduced. More preferably 85% or more, and even more preferably 90% or more. The pH of the acidic carbon black is in the range of 2.0 to 6.0, and preferably in the range of 2.5 to 5.0. The pH in this case is the value measured using a glass electrode pH meter for a mixture of carbon black and distilled water. By using acidic carbon black within the above range, the ink composition exhibits good pitting corrosion resistance even when printed on a container made of bare aluminum material that has not been sizing-coated or coated. It is thought that the oxygen on the surface of the carbon black becomes less able to accept electrons released from the aluminum, resulting in less progression of corrosion due to galvanic action. However, the above is based on scientific considerations, and the present invention is not limited to this effect alone. Examples of acidic functional groups include carboxyl groups and phenolic hydroxyl groups.

[0025] The carbon black content in the ink composition of the present invention is in the range of 20 to 45% by mass, more preferably 25 to 40% by mass. By having a carbon black content within this range, the ink composition for seamless printing cans exhibits excellent dispersion stability, and in addition to excellent coating film properties, it also exhibits superior jet blackness and pitting corrosion resistance.

[0026] The solvent used in the seamless printing can ink composition of the present invention can be any solvent suitable for printing inks, such as a high-boiling-point petroleum solvent, an aliphatic hydrocarbon solvent, or a higher alcohol solvent, with the use of a high-boiling-point petroleum solvent being particularly preferred. Furthermore, the above solvents can be used individually or in combination of two or more types as desired.

[0027] High-boiling point petroleum-based solvents are mainly composed of naphthenic or isoparaffinic compounds. Considering environmental impact, non-aromatic solvents that do not contain aromatic compounds are preferable. Among high-boiling point petroleum-based solvents, non-aromatic ones are desirable. Examples of alcohol-based solvents include AF Solvent No. 4 to No. 7 manufactured by Nippon Oil Corporation and Exsol D110 and D130 manufactured by ExxonMobil. In some cases, higher alcohol-based solvents may also be used in combination.

[0028] In addition to petroleum-based solvents, fatty acid esters and other solvents can also be used.

[0029] The solvent content is not particularly limited. For example, the solvent content is preferably 10% by mass or more, and more preferably 15% by mass or more, in the seamless printing can ink composition. Furthermore, the solvent content is preferably 60% by mass or less, and more preferably 50% by mass or less, in the seamless printing can ink composition. By having the solvent content within the above range, the seamless printing can ink composition is easily adjusted to an ink tack value that shows good printability in seamless cans printed at high speed and in large quantities.

[0030] The resin used in the ink composition of the present invention is preferably a fatty acid-modified alkyd resin. Since fatty acid-modified alkyd resins have a high affinity for the particle surface of carbon black, it is easy to obtain a seamless printing can ink that has a bluish hue, excellent jet blackness, and excellent pitting corrosion resistance. Fatty acid-modified alkyd resins are obtained by condensation of a polybasic acid, a polyhydric alcohol, and a fatty acid component.

[0031] The fatty acid component is not particularly limited as long as it is a fatty acid or oil with an iodine value of 100 or less. Examples include coconut oil fatty acid, palm oil fatty acid, palm kernel oil fatty acid, olive oil, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid. Furthermore, from the viewpoint of achieving a deep black color, it is preferable to include a fatty acid or oil having a hydroxyl group as a fatty acid component. Examples include 12-hydroxystearic acid, ricinoleic acid, castor oil fatty acid, hydrogenated castor oil fatty acid, castor oil, and hydrogenated castor oil. These are classified as non-drying oils, which are less likely to produce a characteristic odor due to fatty acid-derived components, and the flavor of the contents of the seamless can is less likely to be impaired.

[0032] Examples of polybasic acids that can be used to make up fatty acid-modified alkyd resins include dibasic acids such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and maleic anhydride, as well as tribasic acids such as trimellitic anhydride and methylcyclohexentricarboxylic acid anhydride. Polybasic acids may be used in combination.

[0033] Examples of polyhydric alcohols that can be used to constitute fatty acid-modified alkyd resins 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. Polyhydric alcohols may be used in combination.

[0034] The method for producing fatty acid-modified alkyd resin is not particularly limited. For example, it can be produced by known methods such as the transesterification method using oil as a raw material, or 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 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 a fatty acid-modified alkyd resin, which is a condensation polymer of the polybasic acid, polyhydric alcohol, and fatty acid component.

[0035] The styrene-equivalent weight-average molecular weight of the fatty acid-modified alkyd resin is preferably 3,000 to 30,000. Having the weight-average molecular weight of the fatty acid-modified alkyd resin within this range is preferable because it maintains the coating properties of the seamless printing can ink composition and suppresses misting in terms of printability. In this embodiment, the weight-average molecular weight was measured by gel permeation chromatography (GPC).

[0036] In this embodiment, the resin may be a fatty acid-modified alkyd resin, or a conventionally used ink resin. That is, depending on the required performance such as printability and coating film properties, the seamless printing can ink composition can use a known resin that is compatible with the fatty acid-modified alkyd resin. Examples include, in addition to the fatty acid-modified alkyd resin mentioned above, oil-free polyester resin, petroleum resin, epoxy resin, ketone resin, rosin-modified phenol resin, rosin-modified maleic acid resin, melamine resin, benzoguanamine resin, etc.

[0037] The resin content is not particularly limited, as long as it can be adjusted to a predetermined ink tack value. For example, the resin content in the seamless printing can ink composition is preferably 20% by mass or more, and more preferably 30% by mass or more. Furthermore, the resin content is preferably 60% by mass or less, and more preferably 50% by mass or less. By having the resin content within the above range, the seamless printing can ink composition maintains printability performance such as transferability and misting, and also exhibits excellent coating film properties.

[0038] In addition to the components described above, the seamless printing can ink composition of this embodiment may also contain additives commonly used in seamless printing can ink compositions as optional components. These optional components include pigment dispersants, dryers, lubricants, viscosity modifiers, and preservatives. Furthermore, inorganic pigments or organic pigments may be used as needed.

[0039] The method for preparing the seamless printing can ink composition of this embodiment is not particularly limited. For example, the seamless printing can ink composition can be prepared by conventional methods using a three-roll mill, ball mill, bead mill, etc.

[0040] The viscosity of the seamless printing can ink composition of this embodiment is not particularly limited, but is 5 Pa·s to 30 Pa·s, and preferably 7 Pa·s to 20 Pa·s. Here, viscosity was measured using a viscoelasticity measuring device (DiscoveryHR-2, manufactured by T.A. Instruments Japan Co., Ltd.) at a temperature of 30°C and a shear rate of 100 sec. -1 This is the measurement taken at that time.

[0041] The printing method for the ink composition for seamless printed cans of the present invention is not particularly limited, and can be appropriately selected from methods such as a dry offset method using a resin relief plate used for printing printed and painted seamless cans, or an offset method using a waterless lithographic plate.

[0042] The printed and painted seamless can of this embodiment has a printing layer made of an ink composition for seamless printed cans provided on a metal printing medium and an overprint layer made of an overprint varnish provided on the printing layer.

[0043] The metal printing medium on which the ink composition for seamless printed cans of the present invention is printed includes, but is not limited to, aluminum plates, steel plates, and coated plates obtained by laminating these with a polyester film or the like. These substrates may be subjected to chemical treatment, plating, sizing, white coating, silver coating, or the like.

[0044] The process of creating the printing layer is preferably one of the following methods: a dry offset method using a resin relief plate or an offset method using a waterless lithographic plate. By using these printing plates, printed and coated cans printed with the seamless printing ink of the present invention can form clear characters and images on the curved surface of the printed and coated seamless can, even at high-speed printing rates of over 1,000 cans per minute.

[0045] The thickness of the printed layer is not particularly limited. For example, the thickness of the printed layer is preferably 0.3 μm or more, and more preferably 0.4 μm or more. Furthermore, the thickness of the printed layer is preferably 6.0 μm or less, and more preferably 4.0 μm or less. By keeping the thickness of the printed layer within the above range, the manufacturing method for seamless printed cans can prevent problems in the can manufacturing process.

[0046] The process of forming the overprint layer is not particularly limited, but it is preferable to paint using a wet-on-wet method in which the overprint layer is formed without curing the printed layer, and then the coating film is cured.

[0047] Overprint varnishes are not particularly limited and conventionally known varnishes can be used. Examples include thermosetting overprint varnishes such as polyester-melamine, polyester-epoxy-melamine, and polyester-acrylic-melamine varnishes, which are commonly used for seamless printing cans. They may also be water-based or solvent-based.

[0048] The thickness of the coating film, including the printing layer and the overprint layer, is not particularly limited. For example, the thickness of the coating film is preferably 3.0 μm or more, and more preferably 6.0 μm or more. Furthermore, the thickness of the coating film is preferably 30.0 μm or less, and more preferably 20.0 μm or less. By having the coating film thickness within the above range, the resulting printed and coated seamless cans will have excellent appearance, such as gloss, and it is easy to obtain a coating film with excellent coating properties for the purpose of protecting the ink layer.

[0049] The baking conditions in the process of baking and curing the paint film are not particularly limited. For example, the baking conditions may involve a first baking at a temperature of 180°C to 300°C for about 3 to 90 seconds, and a second baking at a temperature of 180°C to 300°C for about 30 to 150 seconds. However, depending on the type of can, baking may be done only once. This results in the production of a printed and painted seamless can consisting of a multi-layer coating.

[0050] For the printed and painted seamless cans and test panels of the present invention, L * a * b * In the color system (CIE1976), L * and b * are evaluated by the values obtained by measurement. In the L * a * b * color system, lightness is represented by L * , hue by a * and b * .

[0051] L * The larger the value of L, the lighter the color, and the smaller the value, the darker the color. In the case of black ink, the smaller the L * value, the better the blackness is shown. The black ink composition is transferred onto a metal printing medium with a film thickness of 2 μm, and then an overprint varnish is applied and baked and cured. The L * value of the printed matter is preferably 15.0 or less, and more preferably 10.0 or less.

[0052] a * and b * values indicate the direction of the color. a * (+) represents the hue in the red direction, and a * (-) represents the hue in the green direction. b * (+) represents the hue in the yellow direction, and b * (-) represents the hue in the blue direction. In the case of black ink, the smaller the b * value, the more blueish the black ink is shown. The black ink composition is transferred onto a metal printing medium with a film thickness of 2 μm, and then an overprint varnish is applied and baked and cured. The b * value of the printed matter is preferably 2.0 or less, and more preferably 1.5 or less.

Examples

[0053] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited thereto. Hereinafter, the numbers in the tables are based on mass.

[0054] An ink composition for seamless printing cans was prepared using the following formulation.

[0055] <Synthesis of fatty acid-modified alkyd resin> 10.5 parts of 12-hydroxystearic acid, 24.5 parts of coconut oil fatty acid, 35.6 parts of phthalic anhydride, 18.2 parts of pentaerythritol, and 18.2 parts of trimethylolpropane were esterified by conventional methods to obtain a fatty acid-modified alkyd resin with a fatty acid content of 35%, an acid value of 4.3 mgKOH / g, and a weight-average molecular weight of 7,800. The amount of dewatering was 7.0%. The above-mentioned fatty acid-modified alkyd resin was used in Examples 1-30 and Comparative Examples 1-5.

[0056] <Preparation of Printing Ink Composition> Using the obtained fatty acid-modified alkyd resin, seamless printing can inks for the examples and comparative examples were prepared with the formulations shown in Tables 1 and 2. The carbon black used was the one listed below, the solvent was linear alkylbenzene manufactured by Nippon Oil Corporation, and the additive was Solspers 20000 manufactured by Lubrizol Corporation.

[0057] CB(A): MA77 manufactured by Mitsubishi Chemical Corporation (average primary particle diameter 23 nm, specific surface area 130 m²) 2 ( / g, pH 2.5) CB(B): MOGUL-E manufactured by CABOT Corporation (average primary particle diameter 48 nm, specific surface area 57 m²) 2 ( / g, pH 2.5) CB(C): Mitsubishi Chemical Corporation #47 (average primary particle size 23 nm, specific surface area 132 m²) 2 ( / g, pH 7.5) CB(D): REGAL350R manufactured by CABOT Corporation (average primary particle size 48 nm, specific surface area 58 m²) 2 ( / g, pH 7.0) CB(E): MA11 manufactured by Mitsubishi Chemical Corporation (average primary particle diameter 29 nm, specific surface area 92 m²) 2 ( / g, pH 2.5) CB(F): MA14 manufactured by Mitsubishi Chemical Corporation (average primary particle diameter 40 nm, specific surface area 56 m²) 2 ( / g, pH 3.0) Note that CB(A), CB(B), CB(E), and CB(F) are acidic carbon blacks with an acid treatment applied to the surface, while CB(C) and CB(D) are neutral carbon blacks without an acid treatment applied to the surface.

[0058] The TV values ​​listed in the table indicate the ink tack value, measured using a digital incomometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) with an ink volume of 1.31cc, room temperature of 25°C, roller temperature of 30°C, and rotation speed of 400rpm for 1 minute. The FV values ​​indicate the ink flow value, measured using a parallel plate viscometer (spread meter) (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) at room temperature of 25°C and measured the diameter of the spread after 60 seconds (unit: mm).

[0059] Test panels were prepared for the printing inks prepared in Examples 1-30 and Comparative Examples 1-5 using the method described below. These test panels were then used to evaluate the blackness, hue, and pitting corrosion resistance. On-press stability was also evaluated.

[0060] <Jet Black> For the printing inks prepared in Examples 1-30 and Comparative Examples 1-5, a high-speed printability tester (PM904PT, manufactured by SMT Corporation) was used to determine if the ink film thickness on the substrate was 2 μm. The design was uniformly transferred to a test rubber roll, then transferred to an aluminum plate at a printing speed of 8 m / s. Immediately afterward, a thermosetting overprint varnish was applied to the printing ink layer at a speed of 2 m / s to a thickness of 13 μm. The print coating film was then baked at 200°C for 3 minutes to create the coating. This coating film was measured using a spectrophotometer (X-rite), and L * a * b * L in color systems * The evaluation was based on numerical values. (Evaluation Criteria) A:L * The color measurement result is 10 or less, and the blackness is good. B:L * The color measurement result is greater than 10 and 15 or less, and does not pose a quality problem. C:L * Products with a color measurement result greater than 15, exhibiting significantly poor blackness, and therefore unsuitable for commercial use. The ratings for practical use are A and B.

[0061] <Hue> For the printing inks prepared in Examples 1-30 and Comparative Examples 1-5, a high-speed printability tester (PM904PT, manufactured by SMT Corporation) was used to uniformly transfer the ink film thickness to a test rubber roll on the substrate to 2 μm. This was then transferred to an aluminum plate at a printing speed of 8 m / s. Immediately afterward, a thermosetting overprint varnish was applied to the printing 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. This printed coating film was measured using a spectrophotometer (X-rite), and L * a * b * b in the color system * The evaluation was based on numerical values. (Evaluation Criteria) A:b * The color measurement result is 1.5 or less, and it has a strong blue tint. B:b * Colorimetric values ​​greater than 1.5 and less than or equal to 2.0, indicating a slightly bluish tint. C:b * Colorimetric values ​​greater than 2.0 indicate a weaker blue tint. The ratings for practical use are A and B.

[0062] <Pitting corrosion resistance> For the printing inks prepared in Examples 1-30 and Comparative Examples 1-5, an RI tester (manufactured by Kokubo Precision Co., Ltd.) was used to uniformly transfer the ink film thickness to a test rubber roll on the substrate to 2 μm, and then transferred it to an aluminum plate. Subsequently, a thermosetting overprint varnish was applied to the printing ink layer to a thickness of 13 μm. After that, the printed coating film was prepared by baking at 200°C for 3 minutes. The printed coating plate was then immersed in a 1% sodium chloride aqueous solution at 40°C for 168 hours. After that, the coating plate was removed, cellophane adhesive tape was applied to the printed area, and then the tape was removed. The condition of the ink in the printed area (corrosion status) was visually determined. (Evaluation Criteria) A: A state in which no paint peeling occurs at all. B: Very slight paint peeling is observed, but it does not affect the quality. C: Slight paint peeling is observed, but this does not affect the quality. D: Slight peeling of the coating is observed, making the product unusable. E: Obvious paint peeling is observed, rendering the product unusable. The ratings for practical use are A, B, and C.

[0063] <On-board stability> For the printing inks prepared in Examples 1-30 and Comparative Examples 1-5, 1.31 cc of ink was uniformly placed on the rubber roll of a digital incomometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the time it took for the tack value to reach its maximum was measured under conditions of 40°C and 1200 rpm to evaluate on-machine stability. It should be noted that inks with a longer time to reach their maximum value exhibit less solvent leaching from the ink, resulting in less change in ink fluidity and viscosity on the ink roller and blanket, and thus superior on-machine stability. (Evaluation Criteria) A: The maximum value will be reached after 20 minutes. B: The maximum value is reached between 10 minutes and 20 minutes. C: Maximum value in less than 10 minutes The ratings for practical use are A and B.

[0064] <High-speed printing suitability (inking property)> For the printing inks prepared in Examples 1-30 and Comparative Examples 1-5, 0.2 cc of ink was supplied to a leveling roll using a high-speed printability tester (PM904PT, manufactured by SMT Corporation) to homogenize it, then transferred to a test rubber roll, and subsequently transferred to an aluminum plate at a printing speed of 8 m / s. Immediately afterward, a thermosetting overprint varnish was applied to the printing 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: It adequately conceals the base material and has good adhesion. B: Slight ink leakage is observed. C: Some noticeable ink fading is visible. D: There is ink leakage, or the aluminum substrate is not sufficiently covered, resulting in poor ink adhesion. The ratings for practical use are A, B, and C.

[0065] [Table 1] JPEG2026065684000002.jpg223158

[0066] [Table 2]

[0067] The formulation designs for the examples and comparative examples are as follows. (I) Table 1 (Examples 1-30) • Contains fatty acid-modified alkyd resin, carbon black, and solvent, and the carbon black component contained in the ink composition (1) Carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm, and average primary particles Contains carbon black with a diameter of 35 nm or more and less than 60 nm. (2) The mass ratio of carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm to carbon black with an average primary particle diameter of 35 nm or more and less than 60 nm is 40 / 60 to 95 / 5 (II) Table 2 (Comparative Examples 1 to 4) The difference from the example composition is that it does not contain carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm, or carbon black with an average primary particle diameter of 35 nm or more and less than 60 nm. (III) Table 2 (Comparative Example 5) One difference between the compositions of the examples is that the mass ratio of carbon black with an average primary particle diameter of 15 nm or more and less than 35 nm to carbon black with an average primary particle diameter of 35 nm or more and less than 60 nm is not in the range of 40 / 60 to 95 / 5.

[0068] As shown in Tables 1 and 2, when using the seamless printing can ink composition described in the examples of the present invention, it was possible to obtain a seamless printing can ink composition that exhibited high jet blackness, a bluish tint, excellent pitting corrosion resistance, practical on-press stability, and excellent suitability for high-speed printing, compared to when using the seamless printing can ink composition of the comparative example.

Claims

1. An ink composition for seamless printing cans comprising carbon black, resin, and solvent, wherein the carbon black contains carbon black (CBI) having an average primary particle diameter of 15 nm or more and less than 35 nm, and carbon black (CBII) having an average primary particle diameter of 35 nm or more and 60 nm or less, and the mass ratio of CBI to CBII is 40 / 60 to 95 / 5. A seamless ink composition for printing cans characterized by the following.

2. The seamless printing can ink composition according to claim 1, wherein the content of acidic carbon black in the carbon black is 80% by mass or more.

3. The seamless printing can ink composition according to claim 1, wherein the difference in average primary particle size between CBI and CBII is 5 nm or more.

4. The seamless printing can ink composition according to claim 1, wherein the carbon black content in the ink composition is 20 to 45% by mass.

5. A seamless printed can having a printing layer made of an ink composition for seamless printed cans according to any one of claims 1 to 4, provided on a metal printing medium, and an overprint layer made of an overprint varnish provided on the printing layer.

6. A method for manufacturing a printed and painted seamless can, comprising: forming a printed layer on a metal printing medium by dry offset printing or offset printing with the seamless printed can ink composition according to any one of claims 1 to 4; and forming an overprint layer by applying an overprint varnish on the printed layer.

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