Metal printing ink composition

Abstract

[Problem] To provide a metal printing ink composition which is capable of reducing occurrence of misting during printing and also maintaining good impact resistance even after a metal printed matter after printing is subjected to a retort treatment. [Solution] Provided is a metal printing ink composition comprising carbon black, a resin, and a solvent. The metal printing ink composition is characterized: in that the carbon black is neutral carbon black and that the solvent has a solubility parameter (sp value) of less than 10.0 (cal / cm3)1 / 2; and by comprising at least one selected from the group consisting of compounds represented by general formula (1). In general formula (1), A is each independently a C2-4 alkylene group that may be branched, R is a C1-13 alkyl group that may be branched and / or may have a cyclic structure, and n is an integer from 2 to 8.

Description

Metal printing ink composition

[0001] The present invention relates to an ink composition for metal printing.

[0002] For printing on the outer metal surfaces of metal materials, such as galvanized or tinned 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.

[0003] Furthermore, these printing surfaces are generally coated with an overprint varnish to improve the ink film's adhesion, bending resistance, impact resistance, abrasion resistance, etc. These overprint varnishes are commonly solvent-based varnishes that contain binder resins such as alkyd resins, polyester resins, acrylic resins, and epoxy resins, hardeners such as melamine resins and benzoguanamine resins, and organic solvents such as mineral oils and cellosolves.

[0004] When printing on the outer surface of a metal, ink is printed using an offset printing machine, dry offset printing machine, or the like, and then an overprint varnish is applied wet-on-wet onto the ink coating using a coater or the like, and then the varnish is baked at 150 to 280°C.

[0005] 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 in place of the solvent-based overprint varnishes that have traditionally been used, even in the field of metal printing. However, when a water-based overprint varnish is applied to an ink film made from a conventional ink composition for metal printing, problems such as the repelling of the water-based overprint varnish or the penetration of the water-based overprint varnish into the ink film occur, resulting in a significant decrease in the quality of the coating film, such as gloss or adhesion. Therefore, ink compositions have been required to have excellent suitability for water-based overprint varnishes.

[0006] As methods for improving suitability for such aqueous overprint varnish, for example, Patent Document 1 proposes the use of an alkylene glycol solvent having 4 to 8 carbon atoms, Patent Document 2 proposes the use of a polyoxyalkylene glycol solvent, Patent Document 3 proposes the use of a polyoxyalkylene alkyl ether organic solvent, and Patent Document 4 proposes the use of a polyoxyalkylene alkyl ester solvent. Although the organic solvents used in these ink compositions are effective in improving the suitability of the ink composition for aqueous overprint varnish, there is room for improvement in that they tend to cause misting during printing, for example.

[0007] Furthermore, depending on the application of the metal printed material, for example, two-piece and three-piece cans used for beverages such as coffee and tea, or canned goods, may be subjected to retort treatment, i.e., pressurization and heat treatment with steam or hot water at 100°C or higher, for the purpose of sterilization, etc. Such treatment can weaken the printed film of the metal printed material, resulting in a significant decrease in impact resistance, which is the ability to maintain the printed film when an impact is applied to the printed surface.

[0008] Japanese Patent Publication No. 5-75031 Publication No. 5-40791 Publication No. 5-40792 Japanese Patent Publication No. 64-60670

[0009] The present invention has been made in view of the above circumstances, and aims to provide an ink composition for metal printing that reduces the occurrence of misting during printing and allows the printed metal print to maintain good impact resistance even after being subjected to retort treatment.

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result, have found that, in black inks using carbon black as a coloring pigment, it is possible to use neutral carbon black, and to produce black inks having a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２ The present inventors have found that the above problems can be solved by using a hydrophobic solvent having a viscosity of less than 1000 MPa, and have completed the present invention. Specifically, the present invention provides the following.

[0011] (1) The present invention provides an ink composition for metal printing comprising carbon black, a resin, and a solvent, wherein the carbon black contains neutral carbon black, and the solvent contains a polymer having a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２ and containing at least one compound selected from the group consisting of compounds represented by the following general formula (1): (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.)

[0012] (2) The present invention also provides an ink composition for metal printing according to the above item (1), wherein the resin is an alkyd resin.

[0013] (3) The present invention also provides the ink composition for metal printing according to (2), wherein the alkyd resin has a mass average molecular weight of less than 10,000.

[0014] (4) The present invention also provides an ink composition for metal printing according to item (2) or (3), wherein the alkyd resin has a pentaerythritol skeleton.

[0015] (5) The present invention also provides an ink composition for metal printing according to any one of items (1) to (4), wherein the divalent group represented by AO in general formula (1) is an oxypropylene group.

[0016] (6) The present invention also provides the ink composition for metal printing according to any one of (1) to (5), further comprising an alkanolamine.

[0017] (7) The present invention also provides the ink composition for metal printing according to any one of (1) to (6), further comprising a rosin-modified resin.

[0018] According to the present invention, there is provided an ink composition for metal printing which reduces the occurrence of misting during printing and allows the printed metal print to maintain good impact resistance even after being subjected to retort treatment.

[0019] An embodiment of the ink composition for metal printing of the present invention will be described below. Note that the present invention is not limited to the following embodiment, and can be practiced by making appropriate modifications within the scope of the present invention.

[0020] The ink composition for metal printing of the present invention (hereinafter referred to as "the ink composition of the present invention") is for metal printing and is preferably applied to printing by the so-called dry offset printing method using a relief plate as the printing plate or the offset printing method using a lithographic plate as the printing plate, but can be applied to all printing methods commonly used in metal printing. Furthermore, the ink composition of the present invention suppresses the occurrence of misting during printing, thereby suppressing the occurrence of staining around the printing machine due to tiny ink droplets generated during printing. Furthermore, a printed film formed by a baking treatment after printing with the ink composition of the present invention retains good impact resistance even after retort treatment. Therefore, the ink composition of the present invention is preferably applied not only to general metal printed materials but also to printing on metals that require retort treatment, such as two-piece and three-piece cans used for beverages such as coffee and tea, and canned goods.

[0021] The ink composition of the present invention comprises carbon black, a resin, and a solvent, and is characterized in that the carbon black is particularly neutral, and the solvent is a glycol monoether solvent having a specific solubility parameter (sp value) and represented by general formula (1). Each component will be described below.

[0022] [Carbon Black] The ink composition of the present invention contains carbon black as a coloring pigment. Various types of carbon black are commercially available that exhibit acidic, neutral, or alkaline properties depending on the surface functional groups. In the present invention, neutral carbon black is particularly used. Note that, in the present invention, neutral carbon black refers to carbon black with a pH in the range of 6.0 to 9.5. The reason for using such neutral carbon black in the present invention is based on the inventors' discovery that by using neutral carbon black instead of the acidic carbon black that has been used in ink compositions for metal printing, the impact resistance of the ink film formed on the metal after retort treatment can be improved.

[0023] The pH of carbon black can be determined by measuring a mixture of carbon black and distilled water with a glass electrode pH meter. Specifically, 1 g of the carbon black to be measured is added to 20 mL of decarbonated distilled water (pH 7.0) and mixed with a magnetic stirrer to prepare an aqueous suspension, and the pH is measured at 25°C with a glass electrode (German Industrial Standard DIN ISO 787 / 9).

[0024] The amount of carbon black added is, for example, about 5 to 50 mass % of the total ink composition, but is not particularly limited. In addition to carbon black, pigments of other colors or ink compositions of other colors may be added to the ink composition as complementary colors.

[0025] [Resin] The resin used in the ink composition of the present invention may be any resin that has been used in ink compositions for metal printing to date, without any particular limitation. Among these resins, alkyd resins are preferably used in the ink composition of the present invention. Furthermore, alkyd resins may be used in combination with rosin-modified resins. These resins will now be described.

[0026] Alkyd resins are condensation polymers of polyhydric alcohols and polybasic acids, a type of polyester, but can also be prepared by condensation polymerization with animal and vegetable oils and / or their fatty acids. In this process, the animal and vegetable oils undergo transesterification with the polyhydric alcohol to form fatty acids, which are then incorporated into the alkyd resin structure. The proportion of the alkyd resin derived from fatty acids of animal and vegetable oils is referred to as the oil length, and the oil length of the alkyd resin used in the present invention is preferably 20 to 50% by mass. Oil-free alkyd resins, which do not contain fatty acid components of animal or vegetable oils, may also be used.

[0027] The alkyd resin used in the present invention is preferably one having a pentaerythritol skeleton in the molecule. The use of an alkyd resin having such a skeleton is preferred because it can improve the impact resistance of the printed film after retort treatment. Such an alkyd resin is prepared using pentaerythritol as the polyhydric alcohol. The alkyd resin used in the present invention may also be prepared using other polyhydric alcohols in addition to pentaerythritol.

[0028] An alkyd resin having a pentaerythritol skeleton in its molecule can be obtained, for example, as a condensation polymer of an acid component consisting of a fatty acid and a polybasic acid with a polyhydric alcohol containing at least pentaerythritol. Next, a method for preparing such an alkyd resin will be described.

[0029] Fatty acids are obtained by hydrolyzing natural fats and oils such as vegetable oils and animal oils. Because they contain one carboxyl group, they can form esters with polyhydric alcohols, as described below. Introducing such fatty acids into alkyd resins can improve the transferability of ink compositions using them and increase the proportion of biomass-derived components. From this perspective, it is preferable to use fatty acids in an amount such that the oil length, which is the ratio (mass %) of the mass of the fatty acid moiety to the mass of the entire resin, is approximately 20 to 50 mass %. A preferred example of such a fatty acid is coconut oil. Various fatty acids can be used, and these can be used alone or in combination of two or more.

[0030] The polybasic acid is a compound having multiple carboxy groups and is a component for condensation polymerization with a polyhydric alcohol (described later) to achieve a 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 acid anhydride, tetrachlorophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, trimellitic anhydride, and methylcyclohexenedicarboxylic anhydride. Among these, phthalic acid or phthalic anhydride is preferred. These polybasic acids may be used alone or in combination of two or more.

[0031] The polyhydric alcohol forms an ester with the acid component, thereby increasing the molecular weight of these components. As the polyhydric alcohol, any of those that have been used in the synthesis of alkyd resins can be used without limitation, and examples thereof include compounds having two or more hydroxyl groups.

[0032] In addition to the above-mentioned pentaerythritol, such compounds include 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. Examples of the polyol include ethylene oxide-modified compounds of bifunctional phenols such as bisphenol A, 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 bisphenol A with ethylene oxide or propylene oxide copolymers, ethylene oxide and propylene oxide copolymer polyether polyols, polycarbonate diols, adamantane diols, polyether diols, polyester diols, and polycaprolactone diols. These may be used alone or in combination of two or more.

[0033] To prepare an alkyd resin, a reaction vessel containing the acid component and polyhydric alcohol is charged with an inert gas such as nitrogen gas, and a small amount of a solvent such as xylene is added and heated. The mixture is then azeotropically distilled with the condensed water to remove the water, resulting in condensation polymerization. Alternatively, an alkyd resin that provides a highly crosslinked, tough cured coating can be obtained by using a condensation polymerization reaction between the acid component and polyhydric alcohol as the first step and a polybasic acid with a functionality of 3 or more, such as trimellitic acid, as the second step. The reaction temperature can be approximately 170 to 250°C, and the reaction time can be approximately 5 to 25 hours, but is not particularly limited. The completion of the reaction can be determined by monitoring the acid value of the reaction mixture over time. That is, the reaction can be considered complete when the decrease in the acid value of the reaction mixture accompanying the condensation polymerization stops. The condensation polymerization reaction can be carried out in a shorter time by distilling the water generated by the condensation polymerization out of the system or by using a reaction catalyst. Examples of the reaction catalyst include tetrabutyl zirconate, monobutyltin oxide, zirconium naphthate, and tetrabutyl titanate.

[0034] The mass average molecular weight of the alkyd resin is preferably less than 10,000, more preferably not more than 8,500, and even more preferably not more than 7,000. As described above, in the present invention, the use of neutral carbon black can improve the impact resistance of the ink film formed on metal after retort treatment, and the use of such an alkyd resin with a relatively low molecular weight is preferable because it can further improve this impact resistance.

[0035] The mass average molecular weight of the resin in the present invention can be measured by gel permeation chromatography (GPC).As an example, Waters Acquity APC (Waters) is used as a GPC device, ACQUITY APC XT 45 1.7 μm 4.6 × 150 mm, ACQUITY APC XT 200 2.5 μm 4.6 × 75 mm, ACQUITY APC XT 900 2.5 μm 4.6 × 75 mm (Waters) is used as a column, tetrahydrofuran is used as a mobile phase, column temperature is 40 ° C, flow rate is 0.8 mL / min, RI detector, sample injection concentration is 10 mg / 5 mL, injection volume is 10 microliters, chromatography is performed under the conditions, and the value can be listed as the mass average molecular weight calculated in terms of polystyrene.

[0036] The content of the alkyd resin in the ink composition is preferably 10 to 40% by mass, more preferably 20 to 40% by mass, based on the total mass of the composition.

[0037] Rosin-modified resins are resins prepared using rosin as one of the 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 combining polyhydric alcohols and polybasic acids and subjecting them to condensation polymerization; adding resols, which are condensates of phenols, to the benzene rings contained in the rosin skeleton; or subjecting dienophiles such as maleic anhydride and maleic acid to a Diels-Alder reaction to add maleic acid or maleic anhydride skeletons. Various types of such rosin-modified resins are commercially available, and they can be obtained and used.

[0038] Examples of rosin-modified resins include rosin ester resins, maleated rosin, fumarated rosin resins, rosin-modified maleic acid resins, rosin-modified fumaric acid resins, rosin-modified phenolic resins, rosin-modified alkyd resins, rosin-modified polyester resins, etc. In the present invention, any of the rosin-modified resins may be used, but among these, rosin ester resins are preferably used.

[0039] The rosin-modified resin used in the present invention preferably has a hydroxyl value of 10 mgKOH / g or more. By including such a rosin-modified resin with a high hydroxyl value in the ink composition of the present invention, the transferability of the ink composition during printing can be further improved. Furthermore, the increased polarity of the composition itself increases its affinity with aqueous OP varnishes, which also have high polarity, thereby suppressing repelling even when the ink composition is 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. The upper limit of the hydroxyl value of the rosin-modified resin is not particularly limited, but an example is about 200 mgKOH / g, preferably about 150 mgKOH / g, and more preferably about 100 mgKOH / g.

[0040] 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 achieve both suppression of repelling when the aqueous OP varnish is applied wet-on-wet and printability such as suppression of misting and smearing. 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.

[0041] The rosin-modified resin is used in the form of a varnish obtained by heating with a solvent 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 may be used in the form of a gelled varnish obtained by dissolving the resin in the varnish during preparation by adding a divalent or higher metal alkoxy compound as a gelling agent to the dissolved varnish. Among these, preparing a dissolved varnish from the rosin-modified resin and using it to prepare an ink composition is preferred, as it can improve the transferability of the ink composition during printing. Furthermore, preparing a gelled varnish from the rosin-modified resin and using it to prepare an ink composition can impart appropriate viscoelasticity to the ink composition, thereby improving flowability and reducing misting, and also forming a tougher cured coating.

[0042] The content of the rosin-modified resin in the ink composition is preferably 5 to 50 mass% relative to the total composition, more preferably 5 to 25 mass% relative to the total composition, and even more preferably 7 to 20 mass% relative to the total composition.

[0043] In addition to the alkyd resin or rosin-modified resin, the ink composition of the present invention can also contain resins conventionally used in preparing ink compositions for metal printing. That is, depending on the required performance, such as printability and coating properties, known resins compatible with the alkyd resin or rosin-modified resin can be used alone or in combination. Examples of such resins include polyester resins, petroleum resins, epoxy resins, ketone resins, amino resins, and benzoguanamine resins.

[0044] [Solvent] The solvent used in the ink composition of the present invention can be any solvent that has been used in the field of inks for metal printing, without any particular limitation. Examples of such solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, alkylbenzenes, polyalkylene glycols, etc., which have a boiling point range of about 230 to 400°C. The ink composition of the present invention is preferably a solvent having a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２and essentially contains at least one compound selected from the group consisting of compounds represented by the following general formula (1): ３ ) １／２ The specific solvent has an sp value of less than 9.80 (cal / cm ３ ) １／２ The lower limit of the sp value in the specific solvent is preferably 8.50 (cal / cm ３ ) １／２ A preferable example is 9.00 (cal / cm ３ ) １／２ A specific solvent having such an sp value can also be said to be a polyalkylene glycol monoalkyl ether having hydrophobic properties. The reason for using such a specific solvent having hydrophobic properties in the present invention is based on the inventors' finding that the occurrence of misting during printing can be significantly reduced by using a hydrophobic polyalkylene glycol monoalkyl ether (i.e., a specific solvent) instead of alkylbenzene-based solvents or hydrophilic polyalkylene glycol monoalkyl ether-based solvents, which have been widely used in the field of ink compositions for metal printing.

[0045]

[0046] In the general formula (1), each A is independently 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 -], propylene group [-CH ２ (CH ３ )-CH ２ - or -CH ２ CH ２ (CH ３ )-], trimethylene group [-(CH ２ ) ３ -], isopropylidene group [-C(CH ３ ) ２-], etc. Among these, a propylene group is preferred. In this case, the divalent group represented by AO in general formula (1) is an oxypropylene group.

[0047] In the 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 not only an aliphatic group but also an alicyclic group. Examples of such an alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a hexyl group, a 2-ethylhexyl group, an octyl group, a decyl group, and a cyclohexyl group.

[0048] In the above general formula (1), n ​​is an integer of 2 to 8. When n is 2 or more, it is possible to ensure a sufficient boiling point of the specific solvent to provide stability to the ink composition on a printing machine, which is preferable, and when n is 8 or less, it is possible to achieve a viscosity that is preferable as a solvent for the ink composition.

[0049] Examples of the compound represented by the general formula (1) include 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.

[0050] The sp value used in the present invention is calculated by the Fedros method (see R. F. Fedros, Polym. Eng. Sci., 14(2)147 (1974)).

[0051] The content of the solvent in the ink composition of the present invention is preferably 10 to 50 mass % relative to the entire composition, and more preferably 20 to 45 mass % relative to the entire composition. Among the solvents, the content of the specific solvent is preferably 15 to 40 mass % relative to the entire composition, and it is preferred that all of the solvents in the composition are the specific solvent.

[0052] The ink composition of the present invention preferably contains an alkanolamine in addition to the above components. By containing an alkanolamine in the ink composition of the present invention, it is possible to reduce misting during printing and improve the impact resistance of the printed film after retort treatment.

[0053] Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, n-butylmonoethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, di-n-butylethanolamine, triisopropanolamine, etc. Among these, triethanolamine is preferred.

[0054] The content of the alkanolamine in the ink composition of the present invention is preferably 0.1 to 3 mass %, more preferably 0.1 to 1 mass part, based on the total mass of the composition.

[0055] Other components that may be added to the ink composition of the present invention, if necessary, include known curing agents; pigment dispersants; waxes; extender pigments such as silica particles, calcium carbonate, benton clay, kaolin, and talc; and stabilizers.

[0056] As the curing agent, for example, an amino resin such as a melamine resin or a benzoguanamine resin can be used.

[0057] Silica particles are SiO ２ These silica particles are commercially available as powders, and are readily available in various forms, including hydrophilic silica particles that have not been surface-treated or that have been hydrophilized, and hydrophobic silica particles that have been hydrophobized. Of these silica particles, hydrophobic silica particles are preferably used in the ink composition of the present invention. The use of hydrophobic silica particles is preferred because it can improve the transferability of the ink composition during printing and increase the fluidity of the ink composition. The content of silica particles in the ink composition is preferably 0.5 to 15% by mass, and more preferably 1 to 5% by mass.

[0058] The ink composition of the present invention can be prepared by mixing the above-mentioned components and using a conventional method, such as a roll mill, a ball mill, a bead mill, etc. The viscosity of the ink composition, as measured at 25°C by a Raley viscometer, can be, for example, 10 to 70 Pa s, but is not particularly limited.

[0059] The metal for metal printing in the ink composition of the present invention is not particularly limited, but examples thereof include zinc-plated or tin-plated iron sheets, aluminum sheets, and metal cans made of these metal materials.

[0060] The ink composition of 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.

[0061] [Preparation of Alkyd Resin Varnish 1] 5.98 parts by mass of neopentyl glycol, 8.53 parts by mass of pentaerythritol, 11.00 parts by mass of coconut oil fatty acid, 7.30 parts by mass of isophthalic acid, and 6.50 parts by mass of phthalic anhydride were reacted at 220°C under a nitrogen atmosphere until the acid value of the mixture reached 7 mgKOH / g, to perform the first-stage esterification. Then, 0.70 parts by mass of trimellitic anhydride was added, and the mixture was heated at 165°C under a nitrogen atmosphere for 30 minutes to perform the second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain an alkyd resin 1 having a mass average molecular weight of 4,376 and a number average molecular weight of 1,995. To this alkyd resin 1, 15.0 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 1. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0062] [Preparation of Alkyd Resin Varnish 2] 5.00 parts by mass of neopentyl glycol, 9.18 parts by mass of pentaerythritol, 11.00 parts by mass of coconut oil fatty acid, 7.30 parts by mass of isophthalic acid, and 6.50 parts by mass of phthalic anhydride were reacted at 220°C under a nitrogen atmosphere until the acid value of the mixture reached 7 mgKOH / g, to perform the first-stage esterification. Then, 0.70 parts by mass of trimellitic anhydride was added, and the mixture was heated at 165°C under a nitrogen atmosphere for 30 minutes to perform the second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain an alkyd resin 2 having a mass average molecular weight of 4,764 and a number average molecular weight of 2,348. To this alkyd resin 2, 10.0 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 2. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0063] [Preparation of Alkyd Resin Varnish 3] 5.00 parts by mass of neopentyl glycol, 10.80 parts by mass of trimethylolpropane, 11.00 parts by mass of coconut oil fatty acid, 7.30 parts by mass of isophthalic acid, and 6.50 parts by mass of phthalic anhydride were reacted at 220°C under a nitrogen atmosphere until the acid value of the mixture reached 7 mgKOH / g, to perform the first-stage esterification. Then, 0.70 parts by mass of trimellitic anhydride was added, and the mixture was heated at 165°C under a nitrogen atmosphere for 30 minutes to perform the second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain an alkyd resin 3 having a mass average molecular weight of 2,785 and a number average molecular weight of 1,639. To this alkyd resin 3, 10.0 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 3. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0064] [Preparation of Alkyd Resin Varnish 4] 5.98 parts by mass of neopentyl glycol, 8.53 parts by mass of pentaerythritol, 10.10 parts by mass of coconut oil fatty acid, 11.95 parts by mass of isophthalic acid, and 2.48 parts by mass of terephthalic acid were reacted at 220°C under a nitrogen atmosphere until the acid value of the mixture reached 7 mgKOH / g to perform the first-stage esterification. Then, 0.70 parts by mass of trimellitic anhydride was added, and the mixture was heated at 165°C under a nitrogen atmosphere for 30 minutes to perform the second-stage esterification. These esterification reactions were carried out according to conventional methods to obtain an alkyd resin 4 having a mass average molecular weight of 6,049 and a number average molecular weight of 2,591. 21.8 parts by mass of tripropylene glycol monobutyl ether was added to this alkyd resin 4 to obtain alkyd resin varnish 4. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0065] [Preparation of Alkyd Resin Varnish 5] Triethylene glycol monobutyl ether was added to alkyd resin 2 obtained by the procedure for preparing alkyd resin varnish 2 above, instead of tripropylene glycol monobutyl ether, to obtain alkyd resin varnish 5. The sp value of this triethylene glycol monobutyl ether was 10.32 (cal / cm ３ ) １／２ and does not fall under the category of the specific solvent in the present invention.

[0066] [Preparation of Alkyd Resin Varnish 6] Pentapropylene glycol monobutyl ether was added to alkyd resin 2 obtained by the procedure for preparing alkyd resin varnish 2 above, instead of tripropylene glycol monobutyl ether, to obtain alkyd resin varnish 6. The sp value of pentapropylene glycol monobutyl ether was 9.42 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0067] [Preparation of Alkyd Resin Varnish 7] Alkyd Resin Varnish 7 was obtained by adding tetrapropylene glycol mono-2-ethylhexyl ether instead of tripropylene glycol monobutyl ether to Alkyd Resin 2 obtained by the procedure for preparing Alkyd Resin Varnish 2. The sp value of tetrapropylene glycol mono-2-ethylhexyl ether was 9.32 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0068] [Preparation of Rosin-Modified Resin Varnish 1] 63.2 parts by mass of rosin ester resin (hydroxyl value 20 to 30 mg KOH / g, acid value < 10 mg KOH / g, mass average molecular weight 632, number average molecular weight 565) and 35.9 parts by mass of tripropylene glycol monobutyl ether were heated at 130°C for 1 hour to dissolve them, thereby obtaining Rosin-Modified Resin Varnish 1. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0069] [Preparation of Rosin-Modified Resin Varnish 2] Rosin-modified resin varnish 2 was obtained in the same manner as in the preparation of the above-mentioned rosin-modified resin varnish 1, except that triethylene glycol monobutyl ether was used instead of tripropylene glycol monobutyl ether. The sp value of this triethylene glycol monobutyl ether was 10.32 (cal / cm ３ ) １／２ and does not fall under the category of the specific solvent in the present invention.

[0070] [Preparation of Rosin-Modified Resin Varnish 3] Rosin-modified resin varnish 3 was obtained in the same manner as in the preparation of the above-mentioned Rosin-Modified Resin Varnish 1, except that pentapropylene glycol monobutyl ether was used instead of tripropylene glycol monobutyl ether. The sp value of this pentapropylene glycol monobutyl ether was 9.42 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0071] [Preparation of Rosin-Modified Resin Varnish 4] Rosin-modified resin varnish 4 was obtained in the same manner as in the preparation of the above-mentioned Rosin-Modified Resin Varnish 1, except that tetrapropylene glycol mono-2-ethylhexyl ether was used instead of tripropylene glycol monobutyl ether. The sp value of this tetrapropylene glycol mono-2-ethylhexyl ether was 9.32 (cal / cm ３ ) １／２ and corresponds to the specific solvent in the present invention.

[0072] [Examples 1 to 12, Comparative Examples 1 to 3] Ink compositions of Examples 1 to 12 and Comparative Examples 1 to 3 were prepared by mixing the components according to the formulations shown in Tables 1 to 3 and kneading the resulting mixtures in a three-roll mill. In Tables 1 to 3, "Neutral CB1" refers to HIBLACK 200L (neutral carbon black, primary particle size 28 nm, DBP oil supply amount 62 ml / 100 g, pH 8.0) manufactured by Orion Engineered Carbons, "Neutral CB2" refers to ELFTEX 415 (neutral carbon black, primary particle size 25 nm, DBP oil supply amount 55 ml / 100 g, pH 6.0 to 8.0) manufactured by Cabot Corporation, and "Neutral CB3" refers to Regal 250R (neutral carbon black, primary particle size 25 nm, DBP oil supply amount 55 ml / 100 g, pH 6.0 to 8.0) manufactured by Cabot Corporation. 34 nm, DBP oil amount 48 ml / 100 g, pH 6.0 to 8.0), "Neutral CB4" is Regal 350R (neutral carbon black, primary particle diameter 48 nm, DBP oil amount 46 ml / 100 g, pH 6.0 to 8.0) manufactured by Cabot Corporation, "Acidic CB1" is Mitsubishi Carbon Black MA7 (acidic carbon black, primary particle diameter 24 nm, DBP oil amount 66 ml / 100 g, pH 3.0) manufactured by Mitsubishi Chemical Corporation, and "Acidic CB2" is Mogul E (acidic carbon black, primary particle diameter 48 nm, DBP oil amount 49 ml / 100 g, pH 2.5) manufactured by Cabot Corporation. In addition, in Tables 1 to 3, "Specific Solvent 1" is tripropylene glycol monobutyl ether (sp value 9.73 (cal / cm ３ ) １／２ ), and "specific solvent 2" is pentapropylene glycol monobutyl ether (sp value 9.42 (cal / cm ３ ) １／２), and "specific solvent 3" is tetrapropylene glycol mono-2-ethylhexyl ether (sp value is 9.32 (cal / cm ３ ) １／２ ), and the "non-specific solvent" is triethylene glycol monobutyl ether (sp value 10.32 (cal / cm ３ ) １／２ ), and "silica" refers to surface-hydrophobically treated silica particles (manufactured by Nippon Aerosil Co., Ltd., product name Aerosil R972). The numerical values ​​for each blend amount in Tables 1 to 3 are all in parts by mass.

[0073] [Evaluation of misting amount] For each of the ink compositions of the Examples and Comparative Examples, 2.6 cc of the ink composition was applied to the rotating roller of an ink meter, smoothed evenly, and then rotated at 1200 rpm for 3 minutes. During this time, a piece of white paper was placed under the roller, and the amount of ink composition adhering to its surface due to misting was compared. The measurement was carried out with the roller maintained at 40°C. The change in mass of the white paper before and after the measurement was determined, and this was taken as the amount of misting (mg). The greater the change in mass of the white paper before and after the measurement, the greater the amount of ink composition scattered, so the smaller this value, the better the result. Based on the calculated amount of misting (mg), the evaluation was carried out according to the following criteria. The evaluation results are shown in the "Misting" column of Tables 1 to 3. ○: The amount of misting was less than 5 mg △: The amount of misting was 5 mg or more but less than 10 mg ×: The amount of misting was 10 mg or more

[0074] [Evaluation of impact resistance after retort treatment] For each of the Examples and Comparative Examples, 0.2 cc of the ink composition was applied to a 50 μm-thick aluminum substrate using an RI paint coater to obtain a painted product. Then, a retort overprint varnish (manufactured by AkzoNobel) was applied to the painted surface of the painted product using a No. 0.4 bar coater (Meyer bar), and the painted product was held in an oven at 240°C for 2 minutes to obtain a retort sample. The retort sample was then retorted at 125°C for 30 minutes using an autoclave (high-pressure steam sterilizer, HG-50 manufactured by Hirayama Seisakusho Co., Ltd.) to obtain a retort-treated product. The retorted product was subjected to impacts at four locations from the opposite side of the painted surface using a DuPont impact tester (Toyo Seiki Seisakusho Co., Ltd., product name H-50) under the following conditions: impact point diameter: 1 / 4Φ (6.35 mm), weight: 300 g, weight drop height: 50 mm. The degree of peeling of the coating film on the painted surface was evaluated according to the following criteria. The results are shown in the "Impact resistance after retort" column in Tables 1 to 3. ○: The coating film did not peel off at all four locations where it came into contact with the impact point. ×: At least a portion of the coating film peeled off at one or more locations where it came into contact with the impact point, exposing the aluminum substrate.

[0075]

[0076]

[0077]

[0078] As is clear from Tables 1 to 3, by combining neutral carbon black with a specific solvent that satisfies the specified solubility parameters to form an ink composition for metal printing, it is understood that misting suitability and impact resistance after retort are improved.

Claims

1. An ink composition for metal printing comprising carbon black, a resin and a solvent, wherein the carbon black comprises neutral carbon black, and the solvent comprises a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２ and containing at least one compound selected from the group consisting of compounds represented by the following general formula (1): (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 said resin is an alkyd resin.

3. The ink composition for metal printing according to claim 2, wherein the alkyd resin has a mass average molecular weight of less than 10,000.

4. The ink composition for metal printing according to claim 2 or 3, wherein the alkyd resin has a pentaerythritol skeleton.

5. The ink composition for metal printing according to any one of claims 1 to 4, wherein the divalent group represented by AO in general formula (1) is an oxypropylene group.

6. The ink composition for metal printing according to any one of claims 1 to 5, further comprising an alkanolamine.

7. The ink composition for metal printing according to any one of claims 1 to 6, further comprising a rosin-modified resin.

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