WO2025243655A1 - Set of ink composition for metal printing and aqueous overprint varnish, and ink composition for metal printing - Google Patents

Abstract

[Problem] To provide: an ink composition for metal printing which, even when an aqueous overprint varnish having an organic solvent content of less than 10 mass% is applied in a wet-on-wet manner onto an ink coating film in an application amount of 30 mg/dm² or less, can suppress the occurrence of cissing of the varnish on the ink coating film and the deterioration in strength of the coating film; and a set of the ink composition and an overprint varnish. [Solution] An ink composition for metal printing which comprises a coloring pigment, an alkyd resin and a solvent is used, the ink composition for metal printing being characterized in that the solvent includes at least one compound selected from the group consisting of compounds represented by general formula (1) and the alkyd resin is a fatty acid-modified alkyd resin having a fatty acid modification amount of 25-50 mass%. In general formula (1), As each independently represent a C2-4 alkylene group that may be branched, R represents a C1-13 alkyl group that may have a branched and/or cyclic structure, and n is an integer of 2-8.

Description

Set of ink composition for metal printing and water-based overprint varnish, and ink composition for metal printing

For printing on the exterior surfaces of metal materials, such as zinc- or tin-plated iron sheets, aluminum sheets, or metal cans made from these metal materials, metal printing ink compositions are used, the main vehicle components of which are binder resins such as alkyd resins, polyester resins, and epoxy resins, and organic solvents such as mineral oils or higher alcohols.

In addition, these printed surfaces are typically coated with an overprint varnish to improve the ink film's adhesion, bending resistance, impact resistance, abrasion resistance, etc. The most commonly used overprint varnishes are solvent-based, consisting of binder resins such as alkyd resin, polyester resin, acrylic resin, and epoxy resin, hardeners such as melamine resin and benzoguanamine resin, and organic solvents such as mineral oil and cellosolve-based solvents.

When printing on the exterior metal surface, ink is printed using an offset printing machine, dry offset printing machine, etc., and then an overprint varnish is applied wet-on-wet onto the ink coating using a coater, etc., and then baked at 150-280°C.

However, in recent years, due to concerns about air pollution caused by solvents and concerns about hygiene and safety in the printing environment, it has become common to use water-based overprint varnishes rather than the solvent-based ones that have been used traditionally, even in the field of metal printing. However, even water-based overprint varnishes do not contain any solvents at all; hydrophilic organic solvents are used in combination with water. These hydrophilic organic solvents are generally recovered and burned during the thermal drying process after application. Therefore, from the perspective of reducing carbon dioxide emissions, even water-based overprint varnishes are required to reduce the amount of organic solvent contained in the overprint varnish and the amount of overprint varnish applied. However, using overprint varnishes with reduced organic solvents or reducing the amount of overprint varnish applied can lead to problems such as varnish repellency on the ink film and reduced film strength due to uneven application.

As improvements to ink compositions for suppressing cissing of aqueous overprint varnish on ink coatings, various proposals have been made, for example, in Patent Documents 1 to 4. However, in the test examples of the ink compositions proposed in these documents, the amount of varnish applied was always within the normal level of 50 to 60 mg/ ^dm2 , or the amount of organic solvent used in the varnish composition was unknown.

JP 2009-249435 A Japanese Patent Application Publication No. 6-25583 Patent No. 7353551 Patent No. 7368674

The present invention has been made in view of the above circumstances, and aims to provide an ink composition for metallic printing that can suppress varnish cissing on the ink coating and a decrease in coating film strength, even when an aqueous overprint varnish containing less than ¹⁰ % by mass of organic solvent is applied wet-on-wet at an application amount of 30 mg/dm2 or less, and a set of such an ink composition for metallic printing and an overprint varnish. In this invention, the application amount of overprint varnish (mg/ ^dm2 ) means the solids mass (i.e., the mass after drying) of the overprint varnish applied per unit area (1 ^dm2 ).

A smaller amount of organic solvent contained in the aqueous overprint varnish leads to a correspondingly larger amount of water contained in the aqueous overprint varnish. Furthermore, a larger amount of water contained in the aqueous overprint varnish leads to a higher surface tension of the aqueous overprint varnish, which makes it more likely to cause cissing and uneven application when applied wet-on-wet to an ink coating. Meanwhile, when considering the amount of aqueous overprint varnish applied, the greater the amount applied in wet-on-wet application, the less likely cissing and uneven application occurs. Therefore, reducing the amount of organic solvent contained in the aqueous overprint varnish and also reducing the application amount can be said to be extremely strict conditions that make cissing and uneven application more likely. In order to overcome these strict conditions, the inventors have reviewed the formulation of the ink composition that serves as the base for the aqueous overprint varnish and found that by using a solvent selected from the group consisting of compounds represented by the following general formula (1) as the solvent in the ink composition, and using a fatty acid-modified alkyd resin with a fatty acid modification content of 25 to 50% by mass as the resin, it is possible to suppress reduction in coating film strength due to varnish cissing and coating unevenness on the ink coating, even when an aqueous overprint varnish with an organic solvent content of less than ^10% by mass is applied wet-on-wet at a coating amount of 30 mg/dm2 or less. The present invention was made based on these findings and provides the following:

(1) The present invention is an ink composition for metal printing comprising a color pigment, an alkyd resin, and a solvent, characterized in that the solvent comprises at least one compound selected from the group consisting of compounds represented by the following general formula (1), and the alkyd resin is a fatty acid-modified alkyd resin, and the amount of fatty acid modification is 25 to 50 mass%.
(In the above general formula (1), each A is independently an alkylene group having 2 to 4 carbon atoms which may have a branch; R is an alkyl group having 1 to 13 carbon atoms which may have a branched and/or cyclic structure; and n is an integer of 2 to 8.)

(2) The present invention also relates to the ink composition _for metal printing according to item (1), wherein A in the general formula (1) is an ethylene group (-CH ₂ CH ₂ -) or a propylene group (-CH(CH 3 )CH ₂ - or -CH ₂ -CH(CH ₃ )-).

(3) The present invention also relates to a metal printing ink composition according to item (1) or (2), characterized in that the ink composition is used for undercoating printing for applying an aqueous overprint varnish containing less than 10% by mass of organic solvent.

(4) The present invention also relates to an ink composition for metal printing according to any one of items (1) to (3), wherein the content of aromatic compounds in the solvent is less than 10% by mass.

(5) The present invention also relates to an ink composition for metal printing according to any one of items (1) to (4), further comprising a rosin-modified resin.

(6) The present invention also relates to a set comprising an ink composition for metal printing and an aqueous overprint varnish, wherein the ink composition for metal printing comprises a color pigment, an alkyd resin, and a solvent A, and the solvent A comprises at least one selected from the group consisting of compounds represented by the following general formula (1), the alkyd resin is a fatty acid-modified alkyd resin, and the amount of fatty acid modification is 25 to 50 mass %, and the content of organic solvents contained in the aqueous overprint varnish is less than 10 mass % relative to the total amount of the aqueous overprint varnish.
(In the above general formula (1), each A is independently an alkylene group having 2 to 4 carbon atoms which may have a branch; R is an alkyl group having 1 to 13 carbon atoms which may have a branched and/or cyclic structure; and n is an integer of 2 to 8.)

(7) The present invention also relates to the set according to item (6), wherein A in the general formula (1) is an ethylene group (-CH ₂ CH ₂ -) or a propylene group (-CH(CH ₃ )CH ₂ - or -CH ₂ -CH(CH ₃ )-).

(8) The present invention also relates to the set described in item (6) or (7), wherein the content of aromatic compounds in the solvent A is less than 10% by mass.

(9) The present invention also relates to a set according to any one of items (6) to (8), wherein the ink composition for metal printing further contains a rosin-modified resin.

According to the present invention, there is provided an ink composition for metal printing that can suppress varnish cissing on the ink coating and a decrease in coating film strength, even when an aqueous overprint varnish containing less than 10% by mass of organic solvent is applied wet-on-wet at a coating amount of ³⁰ mg/dm2 or less, and a set of such an ink composition for metal printing and an aqueous overprint varnish is provided.

Below, we will explain one embodiment of the metal printing ink composition of the present invention, and one embodiment of a set of the metal printing ink composition and aqueous overprint varnish. The present invention is not limited to the following embodiment, and can be practiced with appropriate modifications within the scope of the present invention. As mentioned above, aqueous overprint varnish is an overprint varnish that contains a combination of a hydrophilic organic solvent and water as the solvent. In this specification, overprint varnish will be abbreviated as OP varnish where appropriate.

<Ink composition for metal printing>
First, one embodiment of the ink composition for metal printing of the present invention will be described. The ink composition of the present invention is for metal printing and is preferably applied to printing using the so-called dry offset printing method, which uses a relief plate as the printing plate, or the offset printing method, which uses a lithographic plate as the printing plate. However, it can be applied to all printing methods commonly used in metal printing. Furthermore, the ink composition of the present invention can suppress cissing and uneven application of an aqueous OP varnish applied wet-on-wet immediately after printing with the ink composition. Therefore, it is not only preferably applicable to two-piece can printing, which employs such printing and coating methods, but also to three-piece can printing. In particular, a major advantage of the ink composition of the present invention is that cissing and uneven application are suppressed even when an aqueous OP varnish containing less than 10% by mass of organic solvent is applied at a coating amount of 30 mg/dm² or ^less . This significantly reduces the amount of carbon dioxide emitted from the organic solvent contained in the aqueous OP varnish during printing.

The ink composition of the present invention is a metal printing ink composition containing a color pigment, an alkyd resin, and a solvent, characterized in that the solvent contains at least one compound selected from the group consisting of compounds represented by the above general formula (1), and the alkyd resin is a fatty acid-modified alkyd resin, the amount of fatty acid modification of which is 25 to 50% by mass. In addition to these components, the ink composition of the present invention can also contain a rosin-modified resin as another resin. Each component is explained below.

[Alkyd resin]
The ink composition of the present invention contains a fatty acid-modified alkyd resin, the fatty acid modification content of which is 25 to 50% by mass. Hereinafter, the fatty acid-modified alkyd resin will also be referred to simply as alkyd resin. Alkyd resins are condensation polymers of polyhydric alcohols and polybasic acids, a type of polyester. However, fatty acid-modified alkyd resins can be synthesized by condensation polymerization with vegetable oils and/or fatty acids. That is, by adding a monobasic fatty acid to the condensation polymer during the formation of the alkyd resin, the fatty acid is incorporated into the alkyd resin structure, thereby synthesizing the fatty acid-modified alkyd resin. Furthermore, by adding a vegetable oil during the formation of the condensation polymer, the vegetable oil undergoes ester exchange with the polyhydric alcohol to form a fatty acid, which is then incorporated into the alkyd resin structure as a fatty acid, thereby synthesizing the fatty acid-modified alkyd resin. The proportion of fatty acid-derived components in the alkyd resin is referred to as the fatty acid modification content. The fatty acid modification content of the alkyd resin used in the present invention is 25 to 50% by mass. A fatty acid modification amount of 25% by mass or more is preferred because it allows the ink composition to maintain good transferability during printing, and a fatty acid modification amount of 50% by mass or less can suppress cissing and coating unevenness when a water-based OP varnish with a low organic solvent content is applied wet-on-wet to the ink coating surface with a small application amount, and can also reduce misting during printing.More preferably, the fatty acid modification amount of the alkyd resin is 25 to 45% by mass.

Fatty acids are obtained by hydrolyzing natural fats and oils such as vegetable oils and animal oils, and because they contain one carboxyl group, they can form esters with the polyhydric alcohols described below. Examples of fatty acids include fatty acids from 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 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, and 12-hydroxystearic acid. Of these, coconut oil fatty acids are preferred. These fatty acids may be used alone or in combination of two or more. Furthermore, the above-mentioned vegetable oils may be used together with or in place of the fatty acids.

Polybasic acids are compounds containing multiple carboxyl groups and are components that undergo condensation polymerization with the polyhydric alcohols described below to achieve high molecular weight. Examples of such polybasic acids include phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, adipic acid, trimellitic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexenedicarboxylic acid, 1,4-cyclohexenedicarboxylic acid, hexahydrophthalic anhydride, 5-sodiosulfoisophthalic acid, fumaric acid, benzoic acid, tert-butylbenzoic acid, tetrahydrophthalic anhydride, maleic anhydride, succinic acid, succinic anhydride, fumaric acid, sebacic acid, azelaic acid, tetrabromophthalic anhydride, methylhimic anhydride, tetrachlorophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, trimellitic anhydride, and methylcyclohexenedicarboxylic anhydride. Of these, isophthalic acid, phthalic acid, phthalic anhydride, trimellitic anhydride, etc. are preferred. These polybasic acids can be used alone or in combination of two or more.

Polyhydric alcohols form esters with the above-mentioned fatty acids and polybasic acids, increasing the molecular weight of these components. Polyhydric alcohols can be any of those that have been used in the synthesis of alkyd resins, without limitation, and include compounds with two or more hydroxyl groups.

Such compounds include pentaerythritol, trimethylolpropane, glycerin, ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, 1,3-butanediol, neopentyl glycol, spiroglycol, dioxane glycol, adamantanediol, 3-methyl-1,5-pentanediol, methyloctanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol. , hexamethylene glycol, octylene glycol, 9-nonanediol, 2,4-diethyl-1,5-pentanediol, ethylene oxide-modified compounds of bifunctional phenols such as bisphenol A, propylene oxide-modified compounds of bifunctional phenols such as bisphenol A, ethylene oxide and propylene oxide copolymer-modified compounds of bisphenol A, copolymer polyether polyols of ethylene oxide and propylene oxide, polycarbonate diol, adamantane diol, polyether diol, polyester diol, polycaprolactone diol, etc. These can be used alone or in combination of two or more.

To prepare alkyd resins, a reaction vessel containing polybasic acids, polyhydric alcohols, and fatty acids and/or vegetable oils is charged with a small amount of a solvent such as xylene, and the mixture is heated while an inert gas such as nitrogen gas is introduced. The mixture is then azeotropically distilled with the condensed water to remove the water, resulting in condensation polymerization. Alternatively, alkyd resins that provide highly crosslinked, tough cured coatings can be obtained by using this condensation polymerization reaction as the first step and then condensing a trifunctional or higher polybasic acid, such as trimellitic acid, in the second step. Reaction temperatures can range from approximately 170 to 250°C, and reaction times can range from approximately 5 to 25 hours, but are not limited thereto. The completion of the reaction can be determined by monitoring the acid value of the reaction mixture over time. The reaction is considered complete when the decrease in the acid value of the reaction mixture accompanying the condensation polymerization stops. The condensation polymerization reaction can be completed in a shorter time by distilling the water produced by the condensation polymerization out of the system or by using a reaction catalyst. Examples of reaction catalysts include tetrabutyl zirconate, monobutyltin oxide, zirconium naphthate, and tetrabutyl titanate.

The content of alkyd resin in the ink composition is preferably 20 to 70% by mass, and more preferably 30 to 60% by mass, of the entire composition. The alkyd resin may also be dissolved in a solvent, as described below, to form a varnish.

[Rosin-modified resin]
In addition to the alkyd resin, other resins may also be used in the ink composition of the present invention. A preferred example of such a resin is a rosin-modified resin. A rosin-modified resin is a resin prepared using rosin as one of its raw materials. Rosin contains a mixture of resin acids such as abietic acid, palustric acid, isopimaric acid, and levopimaric acid. These resin acids contain hydrophilic, chemically active carboxyl groups, and some also contain conjugated double bonds. Therefore, various rosin-modified resins have been prepared by condensation polymerization of a combination of polyhydric alcohols and polybasic acids, by adding a resole (a phenol condensate) to the benzene ring contained in the rosin skeleton, or by Diels-Alder reaction with dienophiles such as maleic anhydride or maleic acid to add a maleic acid or maleic anhydride skeleton. Various rosin-modified resins are commercially available, and they can be obtained and used. By using a rosin-modified resin in the ink composition of the present invention, it is possible to suppress the occurrence of misting during printing and to increase the biomass content in the ink composition without impairing various required performances.

Examples of rosin-modified resins include rosin ester resin, maleated rosin, fumarated rosin resin, rosin-modified maleic acid resin, rosin-modified fumaric acid resin, rosin-modified phenolic resin, rosin-modified alkyd resin, and rosin-modified polyester resin. In the present invention, any of the rosin-modified resins may be used, but of these, rosin ester resins are preferred.

Furthermore, it is preferable to use a rosin-modified resin with a hydroxyl value of 10 mgKOH/g or more. By including a rosin-modified resin with such a high hydroxyl value in the ink composition of the present invention, the transferability of the ink composition during printing can be further improved. In addition, the increased polarity of the composition itself increases its affinity with water-based OP varnishes, which also have high polarity, and this also has the effect of suppressing repelling and uneven application when applied wet-on-wet. The hydroxyl value of the rosin-modified resin is more preferably 15 mgKOH/g or more, and even more preferably 20 mgKOH/g or more. Furthermore, there is no particular limitation on the upper limit of the hydroxyl value of the rosin-modified resin, but an example would be approximately 200 mgKOH/g, preferably approximately 150 mgKOH/g, and more preferably approximately 100 mgKOH/g.

Furthermore, although not particularly limited, the acid value of the rosin-modified resin is preferably 100 mgKOH/g or less. Having an acid value of 100 mgKOH/g or less is preferable because it can suppress cissing and uneven application when applying an aqueous OP varnish wet-on-wet, while also achieving printability such as suppressing misting and blotching. The acid value of the rosin-modified resin is more preferably 80 mgKOH/g or less, and even more preferably 50 mgKOH/g or less.

The rosin-modified resin is used in the form of a varnish obtained by heating with a solvent, as described below, to dissolve or disperse it. The rosin-modified resin may be used as a dissolved varnish in which it remains dissolved or dispersed in a solvent, or it may be used in the form of a gelled varnish obtained by dissolving the resin in the varnish and adding a divalent or higher metal alkoxy compound as a gelling agent to the dissolved varnish obtained by preparing the varnish. Of these, preparing a dissolved varnish from the rosin-modified resin and using this to prepare the ink composition is preferred, as it improves the transferability of the ink composition during printing. Furthermore, preparing a gelled varnish from the rosin-modified resin and using this to prepare the ink composition imparts appropriate viscoelasticity to the ink composition, thereby improving flowability and reducing misting, and also forming a tougher cured coating.

The content of the rosin-modified resin in the ink composition is preferably 1 to 20% by mass of the entire composition, more preferably 1 to 15% by mass of the entire composition, and even more preferably 2 to 10% by mass of the entire composition.

In addition to the alkyd resins and rosin-modified resins described above, the ink composition of the present invention can also contain resins that have been used in the preparation of ink compositions for metal printing. In other words, known resins can be used alone or in combination of two or more depending on the required performance, such as printability and coating properties. Examples of such resins include polyester resins, petroleum resins, epoxy resins, ketone resins, amino resins, and benzoguanamine resins.

[solvent]
The ink composition of the present invention contains at least one solvent selected from the group consisting of compounds represented by the following general formula (1): Hereinafter, the at least one solvent selected from the group consisting of compounds represented by the following general formula (1) will also be referred to as a specific solvent.

In the general formula (1), each A is independently determined and is an alkylene group having 2 to 4 carbon atoms, which may have a branch. Examples of such alkylene groups include an ethylene group [-(CH ₂ ) ₂ -], a propylene group [-CH ₂ (CH ₃ )-CH ₂ - or -CH ₂ CH ₂ (CH ₃ )-], a trimethylene group [-(CH ₂ ) ₃ -], and an isopropylidene group [-C(CH ₃ ) ₂ -]. Of these, an ethylene group [-(CH ₂ ) ₂ -] or a propylene group [-CH(CH ₃ )CH ₂ - or -CH ₂ -CH(CH ₃ )-] is preferred.

In the above general formula (1), R is an alkyl group having 1 to 13 carbon atoms, which may have a branched and/or cyclic structure. This alkyl group may be an aliphatic group or an alicyclic group. Examples of such alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, hexyl, 2-ethylhexyl, octyl, decyl, and cyclohexyl groups.

In the above general formula (1), n is an integer from 2 to 6. An n of 2 or greater is preferred because it ensures a sufficient boiling point for the specific solvent to provide stability to the ink composition on the printing press, while an n of 6 or less ensures a viscosity suitable for use as a solvent for the ink composition.

Examples of compounds represented by the above general formula (1) include diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol monooctyl ether, diethylene glycol tridecyl ether, triethylene glycol monobutyl ether, triethylene glycol monodecyl ether, tetraethylene glycol monohexyl ether, pentaethylene glycol monobutyl ether, hexaethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monooctyl ether, dipropylene glycol tridecyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monodecyl ether, tetrapropylene glycol monohexyl ether, pentapropylene glycol monobutyl ether, and hexapropylene glycol monomethyl ether. Among these, diethylene glycol monobutyl ether and dipropylene glycol monobutyl ether are preferred. These can be used alone or in combination of two or more.

The content of the specific solvent in the ink composition of the present invention is preferably 10 to 40% by mass of the entire composition, and more preferably 15 to 35% by mass of the entire composition. A content of the specific solvent of 15% by mass or more of the entire composition is preferred because it effectively prevents repelling and uneven application when the water-based OP varnish is applied wet-on-wet.

In addition, in the ink composition of the present invention, it is preferable that the content of aromatic solvents such as linear alkylbenzenes, which have traditionally been used as solvents in ink compositions for metal printing, be less than 10% by mass. By keeping the content of aromatic compound-based solvents to less than 10% by mass, it is possible to effectively suppress cissing and uneven application when applying a water-based OP varnish wet-on-wet, which is preferable.

[Coloring pigments]
The color pigment is a component for imparting coloring power to the ink composition. Examples of the color pigment include, without particular limitation, organic and/or inorganic pigments that have conventionally been used in printing ink compositions.

Such color pigments include Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 24, 32, 34, 35, 36, 37, 41, 42, 43, 49, 53, 55, 60, 61, 62, 63, 65, 73, 74, 75, 77, 81, 83, 87, 93, 94, 95, 97, 98, 99, 100, 101, 104, 105, 1 06, 108, 109, 110, 111, 113, 114, 116, 117, 119, 120, 123, 124, 126, 127, 128, 129, 130, 133, 138, 139, 150, 151, 152, 153, 154, 155, 165, 167, 168, 169, 170, 172, 173, 174, 175, 176, 179, 180, 181, 182, 183, 184 4, 185, 191, 193, 194, 199, 205, 206, 209, 212, 213, 214, 215, 219; Pigment Orange 1, 2, 3, 4, 5, 13, 15, 16, 17, 19, 20, 21, 24, 31, 34, 36, 38, 40, 43, 46, 48, 49, 51, 60, 61, 62, 64, 65, 66, 67, 68, 69, 71, 72, 73, 74, 81; Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32, 38, 41, 48, 48:1, 48:2, 48:3, 48:4, 48:5, 49, 52, 52:1, 52:2, 53:1, 54, 57:1, 58, 60:1, 63, 64:1, 68, 81:1, 83, 88, 89, 95, 101, 1 04, 105, 108, 112, 114, 119, 122, 123, 136, 144, 146, 147, 149, 150, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 187, 188, 190, 193, 194, 200, 202, 206, 207, 208, 20 9, 210, 211, 213, 214, 216, 220, 220, 221, 224, 226, 237, 238, 239, 242, 245, 247, 248, 251, 253, 254, 255, 256, 257, 258, 260, 262, 263, 264, 266, 268, 269, 270, 271, 272, 279; Pigment Violet 1, 2, 3, 3:1, 3:3, 5: 1, 13, 15, 16, 17, 19, 23, 25, 27, 29, 31, 32, 36, 37, 38, 42, 50; Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:5, 15:6, 16, 17:1, 24, 24:1, 25, 26, 27, 28, 29, 36, 56, 60, 61, 62, 63, 75, 79, 80; Pigment Green 1, 4, 7, 8, 1 Pigment Brown 5, 6, 23, 24, 25, 32, 41, 42; Pigment Black 1, 6, 7, 9, 10, 11, 20, 26, 28, 31, 32, 34; Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28, etc., as well as glass flakes, pearl pigments, hollow particles, etc. Among the above, glass flakes, pearl pigments, and hollow particles may not generally be considered as color pigments, but in the present invention, such pigments that provide some kind of optical effect are also considered as color pigments. Among these, from the viewpoint of the color reproducibility, coating film strength and printability, Pigment Yellow 13, Pigment Yellow 17, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 139, Pigment Yellow 180, Pigment Yellow 185, Pigment Orange 13, Pigment Orange 16, Pigment Orange 43, Pigment Orange 64, Pigment Red 48:1, Pigment Red 48:2, Pigment Red Preferred examples of the pigment include Pigment Red 48:3, Pigment Red 48:4, Pigment Red 53:1, Pigment Red 122, Pigment Red 166, Pigment Red 185, Pigment Red 254, Pigment Red 264, Pigment Violet 23, Pigment Violet 32, Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 15:6, Pigment Green 7, Pigment Black 7, and Pigment White 6. Metallic powder pigments used to impart metallic colors such as gold and silver to ink compositions are also considered colored pigments in the present invention. Examples of such metallic powder pigments include aluminum flakes, gold powder, bronze powder, and aluminum paste prepared by processing aluminum powder into a paste.

The amount of color pigment added is, for example, approximately 5 to 50% by mass of the total ink composition, but is not particularly limited. When preparing a yellow ink composition using a yellow pigment, a magenta ink composition using a magenta pigment, a cyan ink composition using a cyan pigment, or a black ink composition using a black pigment, it is also possible to use a pigment of a different color in combination or add an ink composition of a different color as a complementary color.

[Other ingredients]
Other components that can be added to the ink composition of the present invention, if necessary, include alkanolamines, known curing agents, pigment dispersants, solvents other than the above-mentioned specific solvents, waxes, silica particles, stabilizers, and the like.

The use of alkanolamines can reduce the occurrence of misting during printing. Examples of alkanolamines include triethanolamine, dibutylethanolamine, and methyldiethanolamine. When using alkanolamines, their content in the total ink composition is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and even more preferably 0.1 to 1.5% by mass.

As a curing agent, for example, an amino resin such as melamine resin or benzoguanamine resin can be used.

Solvents other than the above-mentioned specific solvents include, for example, aliphatic or alicyclic hydrocarbons with a boiling point range of approximately 230 to 400°C, aromatic hydrocarbons such as alkylbenzenes, and higher alcohols. As already mentioned, when aromatic hydrocarbons are used as solvents, it is preferable that their content in the ink composition be less than 10% by mass.

Silica particles are commercially available as _SiO2 powder, and are readily available in hydrophilic forms that have not been surface-treated or that have been hydrophilized, or hydrophobic forms that have been hydrophobized, etc. The content of silica particles in the ink composition is preferably 1 to 8% by mass, and more preferably 2 to 5% by mass.

The ink composition of the present invention can be prepared by mixing the various components, such as color pigments, resins, and solvents including specific solvents, using a roll mill, ball mill, bead mill, or other suitable method. The viscosity of the ink composition, as measured at 25°C using a Raleigh viscometer, can be, for example, 10 to 70 Pa·s, but is not particularly limited.

Metals for use in metal printing with the ink composition of the present invention are not particularly limited, but examples include zinc-plated or tin-plated iron sheets, aluminum sheets, and metal cans made from these metal materials.

Furthermore, the water-based OP varnish to be applied on top of the printed ink composition can be any commonly used one, and specific examples include those that use a water-based acrylic resin, water-based polyester resin, water-based alkyd resin, water-based epoxy resin, or modified resins of two or more of these as a binder in combination with an amino resin as a curing agent. As already mentioned, by using the ink composition of the present invention, it is possible to suppress repelling and uneven application of the OP varnish during wet-on-wet application, even when using a water-based OP varnish with an organic solvent content of less than 10% by mass. In other words, the ink composition of the present invention can also be preferably used for undercoating printing for applying a water-based OP varnish with an organic solvent content of less than 10% by mass.

When printing on a metal surface using the ink composition and water-based OP varnish, first print using the ink composition of the present invention using a dry offset printing machine, offset printing machine, etc., and then overcoat the water-based OP varnish using a coater or the like while the ink composition is still wet (wet-on-wet), and then bake at 150 to 280°C for a few seconds to a few minutes.

<Set of metal printing ink composition and water-based overprint varnish>
The set of the metallic printing ink composition of the present invention and an aqueous overprint varnish (aqueous OP varnish) also constitutes one aspect of the present invention. The aqueous OP varnish referred to here refers to a varnish containing a combination of a hydrophilic organic solvent and water as a solvent, with an organic solvent content of less than 10% by mass. The metallic printing ink composition included in this set has already been described, so further description here will be omitted.

As mentioned above, the ink composition of the present invention suppresses cissing and uneven application of the aqueous OP varnish when it is applied wet-on-wet after printing with an aqueous OP varnish containing less than 10% by mass of organic solvent. For this reason, the ink composition of the present invention can be preferably used in combination with an aqueous OP varnish containing less than 10% by mass of organic solvent. The set of the present invention focuses on this point.

The water-based OP varnish included in the set may be any type, as long as it contains less than 10% by mass of organic solvents and is used by coating the surface of the metal printing ink composition after printing. A variety of such water-based OP varnishes are commercially available, so such commercially available products can be obtained and used to create a set with the ink composition of the present invention.

The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[Preparation of Alkyd Resin Varnish 1]
First-stage esterification was carried out by reacting 14.7 parts by mass of trimethylolpropane, 10 parts by mass of coconut oil fatty acid, and 15 parts by mass of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 0.82 parts by mass of trimellitic anhydride was added, and the mixture was heated at 165°C for 30 minutes under a nitrogen atmosphere to carry out second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain alkyd resin 1. To this alkyd resin 1, 10 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 1. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention. The fatty acid modification content of the synthesized alkyd resin 1 was 27.7% by mass.

[Preparation of Alkyd Resin Varnish 2]
First-stage esterification was performed by reacting 14.7 parts by weight of trimethylolpropane, 15.5 parts by weight of coconut oil fatty acid, and 12.9 parts by weight of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 0.91 parts by weight of trimellitic anhydride was added, and the mixture was heated at 165°C for 30 minutes under a nitrogen atmosphere to perform second-stage esterification. These esterification reactions were performed according to conventional methods to obtain alkyd resin 2. To this alkyd resin 2, 10 parts by weight of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 2. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention. The fatty acid modification content of the synthesized alkyd resin 2 was 39.1% by weight.

[Preparation of Alkyd Resin Varnish 3]
First-stage esterification was performed by reacting 14.7 parts by weight of trimethylolpropane, 18.5 parts by weight of coconut oil fatty acid, and 11.7 parts by weight of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 0.95 parts by weight of trimellitic anhydride was added, and the mixture was heated at 165°C for 30 minutes under a nitrogen atmosphere to perform second-stage esterification. These esterification reactions were performed according to conventional methods to obtain alkyd resin 3. To this alkyd resin 3, 10 parts by weight of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 3. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention. The fatty acid modification content of the synthesized alkyd resin 3 was 44.6% by weight.

[Preparation of Alkyd Resin Varnish 4]
First-stage esterification was performed by reacting 14.7 parts by weight of trimethylolpropane, 25 parts by weight of coconut oil fatty acid, and 9.3 parts by weight of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 1.04 parts by weight of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform second-stage esterification. These esterification reactions were performed according to conventional methods to obtain alkyd resin 4. To this alkyd resin 4, 10 parts by weight of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 4. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention. The fatty acid modification content of the synthesized alkyd resin 4 was 54.7% by weight.

[Preparation of Alkyd Resin Varnish 5]
First-stage esterification was carried out by reacting 14.7 parts by weight of trimethylolpropane, 8.12 parts by weight of coconut oil fatty acid, and 15.69 parts by weight of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 0.8 parts by weight of trimellitic anhydride was added, and the mixture was heated at 165°C for 30 minutes under a nitrogen atmosphere to carry out second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain alkyd resin 5. To this alkyd resin 5, 10 parts by weight of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 5. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention. The fatty acid modification content of the synthesized alkyd resin 5 was 23.0% by weight.

[Preparation of Alkyd Resin Varnish 6]
First-stage esterification was performed by reacting 14.7 parts by weight of trimethylolpropane, 18.5 parts by weight of coconut oil fatty acid, and 11.7 parts by weight of isophthalic acid under a nitrogen atmosphere at 220°C until the acid value of the mixture reached 7 mgKOH/g. Then, 0.95 parts by weight of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform second-stage esterification. These esterification reactions were performed according to conventional methods to obtain alkyd resin 6. To this alkyd resin 6, 10 parts by weight of commercially available linear alkylbenzene was added to obtain alkyd resin varnish 6. Note that this linear alkylbenzene does not fall under the category of a specified solvent in the present invention and is an aromatic solvent. The fatty acid modification content of the synthesized alkyd resin 6 was 44.6% by weight.

[Preparation of rosin-modified resin varnish]
A rosin-modified resin varnish was obtained by dissolving 63.2 parts by mass of a rosin ester resin (hydroxyl value 20-30 mgKOH/g, acid value <10 mgKOH/g, mass average molecular weight 632, number average molecular weight 565) and 35.9 parts by mass of tripropylene glycol monobutyl ether by heating at 130°C for 1 hour. Note that this tripropylene glycol monobutyl ether corresponds to the specified solvent in the present invention.

[Test water-based OP varnish]
Varnish A was a PPG iSENSE™ series aqueous OP varnish (organic solvent content less than 10% by mass) manufactured by PPG, and Varnish C was a PPG iSENSE™ series aqueous OP varnish (organic solvent content 15% by mass to 20% by mass) also manufactured by PPG. Furthermore, an aqueous OP varnish (organic solvent content less than 1.1% by mass) was prepared from a mixture of 47 parts by mass of Joncryl PDX7615 manufactured by BASF Japan Ltd., 47 parts by mass of Elitel KT-8803 manufactured by Unitika Ltd., and 6 parts by mass of Cymel 303LF manufactured by Allnex Corporation, and was designated Varnish B. Of these varnishes, Varnish A and Varnish B are aqueous OP varnishes with an organic solvent content of less than 10% by mass, and Varnish C is an aqueous OP varnish with an organic solvent content of 10% by mass or more (15 to 20% by mass).

[Preparation of ink composition]
Ink compositions of Examples and Comparative Examples were prepared according to the formulations shown in Tables 1 and 2. The numerical values for each blend amount shown in Tables 1 and 2 are in parts by mass. In preparing the ink compositions, the components were mixed and then kneaded using a roll mill heated to 40°C. In Tables 1 and 2, "carbon black" refers to acidic carbon black having an average primary particle size of 24 nm and a DBP oil absorption of 66 mL/100 g, "titanium oxide" refers to titanium oxide having an average primary particle size of 250 nm and a DBP oil absorption of 18 g/100 g, "phthalocyanine blue" refers to commercially available phthalocyanine blue 15:3, "specific solvent 1" refers to tripropylene glycol monobutyl ether, "specific solvent 2" refers to triethylene glycol monobutyl ether, and "non-specific solvent" refers to linear alkylbenzene (aromatic solvent). In addition, in Tables 1 and 2, the percentage values written in parentheses after the names of alkyd resin varnishes 1 to 6 are the fatty acid modified amounts (mass %) of the alkyd resin contained in each alkyd resin varnish.

[Metastatic evaluation]
For each of the ink compositions of the Examples and Comparative Examples, 0.1 cc of the ink composition was applied to a 50 μm thick aluminum substrate using a high-speed ink-drawer "PM-900PT" (manufactured by Mitsui Electric Seiki Co., Ltd.) at a printing pressure of 90 kgf and a drawing speed of 9 m/s. The resulting drawn-down inks were evaluated according to the following criteria. The evaluation results are shown in the "Transferability" column of Tables 1 and 2.
○: No smearing was observed. △: Smearing was observed in less than 50% of the transfer area, but within the practical range. ×: Smearing was observed in 50% or more of the transfer area, and it was poor.

[Evaluation of repelling of water-based OP varnish]
Using the combinations of ink compositions and water-based OP varnishes shown in Tables 3 and 4, the water-based OP varnish was applied wet-on-wet to a coating of the ink composition drawn onto a metal piece at a coating amount of 25 mg/ ^dm2 , and the applied water-based OP varnish was visually inspected for cissing and seepage and evaluated. The evaluation criteria were as follows, and the results are shown in the "Capping Evaluation" column in Tables 3 and 4. Note that the coating amount of water-based OP varnish in this evaluation, 25 mg/ ^dm2 , is significantly less than the coating amount of water-based OP varnish currently commonly used on two-piece cans and the like (50 to 60 mg/ ^dm2 ), and can be said to be a severe condition that is likely to cause cissing and seepage of the water-based OP varnish. Furthermore, in the "Ink Composition" column of Tables 3 and 4, notations such as "Ex. 1" represent "Example 1" etc., notations such as "Ratio 1" represent "Comparative Example 1" etc., and the numerical values shown in the "Organic Solvent Amount" column represent the amount of organic solvent (% by mass) contained in the water-based OP varnish used. Furthermore, the "Reference" shown in the "Test Number" column of Tables 3 and 4 is a test using the currently widely used water-based OP varnish C, which contains a large amount of organic solvent, and serves as a tentative performance target.
○: No cissing is observed and gloss is good. △: Almost no cissing is observed, but gloss is slightly reduced. ×: There is a tendency for cissing and OP varnish to seep in.

[Pencil hardness]
The metal pieces that had been coated with aqueous OP varnish in the above-mentioned evaluation of repellency of aqueous OP varnish were baked by heating at 200°C for 2 minutes in an electric oven. The metal pieces were then returned to room temperature, and the pencil hardness of the drawn surface was measured in accordance with JIS K5600-5-4. The results are shown in the "Pencil hardness" column in Tables 3 and 4.

As shown in Tables 3 and 4, the ink compositions of Examples 1 to 7 did not experience cissing or penetration of the aqueous OP varnish, even when an aqueous OP varnish containing less than 10% by mass was applied at a low application rate of 25 mg/ ^dm² , and the pencil hardness after baking was sufficient. Furthermore, as shown in Tables 1 and 2, the ink compositions of Examples 1 to 7 also exhibited good transferability and sufficient performance in terms of printability. Among these, the ink composition of Example 7, which contained a rosin-modified resin, achieved the above-described favorable results. Therefore, it is understood that the application of a rosin-modified resin to the ink composition of the present invention can increase the biomass content in the ink composition without causing a decrease in various performance characteristics. On the other hand, the ink composition of Comparative Example 1, which contained an alkyd resin varnish with a fatty acid modification content exceeding 50% by mass, not only experienced cissing when applied with the aqueous OP varnish, but also exhibited a significantly poor pencil hardness of B after baking. Furthermore, the ink composition of Comparative Example 2, which contains an alkyd resin with a fatty acid modification amount of less than 25% by mass, exhibited good cissing when applied with aqueous OP varnish and good pencil hardness after baking, but showed poor transferability as shown in Table 2, indicating that basic printability was insufficient. Furthermore, the ink composition of Comparative Example 3, which does not contain the specific solvent of the present invention, was found to exhibit cissing when applied with aqueous OP varnish.

Claims (9)

An ink composition for metal printing comprising a color pigment, an alkyd resin, and a solvent, wherein the solvent comprises at least one compound selected from the group consisting of compounds represented by the following general formula (1), and the alkyd resin is a fatty acid-modified alkyd resin, and the amount of fatty acid modification is 25 to 50 mass%.
(In the above general formula (1), each A is independently an alkylene group having 2 to 4 carbon atoms which may have a branch; R is an alkyl group having 1 to 13 carbon atoms which may have a branched and/or cyclic structure; and n is an integer of 2 to 8.) 2. The ink composition for metal printing according to claim 1, wherein A in said general formula (1) is an ethylene group (--CH ₂ CH ₂ --) or a propylene group (--CH(CH ₃ )CH ₂ -- or --CH ₂ --CH(CH ₃ )--). The metal printing ink composition according to claim 1 or 2, characterized in that it is used for undercoating printing for applying an aqueous overprint varnish containing less than 10% by mass of organic solvent. The ink composition for metal printing according to any one of claims 1 to 3, wherein the content of aromatic compounds in the solvent is less than 10% by mass. The ink composition for metal printing according to any one of claims 1 to 4, further comprising a rosin-modified resin. A set of an ink composition for metal printing and an aqueous overprint varnish,
The ink composition for metal printing comprises a color pigment, an alkyd resin, and a solvent A, and the solvent A comprises at least one selected from the group consisting of compounds represented by the following general formula (1), the alkyd resin is a fatty acid-modified alkyd resin, and the amount of fatty acid modification is 25 to 50 mass %,
A set characterized in that the content of organic solvents contained in the aqueous overprint varnish is less than 10 mass % based on the total amount of the aqueous overprint varnish.
(In the above general formula (1), each A is independently an alkylene group having 2 to 4 carbon atoms which may have a branch; R is an alkyl group having 1 to 13 carbon atoms which may have a branched and/or cyclic structure; and n is an integer of 2 to 8.) 7. The set according to claim 6, wherein A in the general formula (1) is an ethylene group (-CH ₂ CH ₂ -) or a propylene group (-CH(CH ₃ )CH ₂ - or -CH ₂ -CH(CH ₃ )-). The set according to claim 6 or 7, wherein the content of aromatic compounds in solvent A is less than 10% by mass. The set described in any one of claims 6 to 8, characterized in that the ink composition for metal printing further contains a rosin-modified resin.