WO2025115310A1 - Metal printing ink composition - Google Patents

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

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

For printing on the exterior 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 that contain binder resins such as alkyd resins, polyester resins, and epoxy resins, and organic solvents such as mineral oils or higher alcohols as the main vehicle components.

　Furthermore, these printing surfaces are generally coated with an overprint varnish to improve the adhesion of the ink film, as well as bending resistance, impact resistance, and abrasion resistance. The most widely used overprint varnishes are solvent-type varnishes that contain 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 or similar, and then baked at 150 to 280°C.

However, in recent years, due to issues of 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 the field of metal printing instead of the solvent-based overprint varnishes that have traditionally been used. However, when a water-based overprint varnish is applied over an ink coating 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 coating occur, resulting in a significant decrease in the quality of the coating, such as gloss or adhesion. Therefore, there has been a demand for ink compositions to have excellent suitability for water-based overprint varnishes.

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

Also, depending on the application of the metal print, 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 heating treatment with steam or hot water at 100°C or higher, for the purpose of sterilization. This type of treatment can weaken the printing film of the metal print, and can significantly reduce the impact resistance, which is the ability to maintain the printing film when an impact is applied to the printed surface.

Special Publication No. 5-75031 Special Publication No. 5-40791 Special Publication No. 5-40792 Japanese Patent Application Publication No. 64-60670

The present invention was made in consideration 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 metal print to maintain good impact resistance even after being subjected to retort treatment after printing.

As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by using, in particular, neutral carbon black in a black ink containing carbon black as a coloring pigment, and by using a hydrophobic solvent having a solubility parameter (sp value) of less than 10.00 (cal/cm ³ ) ^1/2 , and have thus completed the present invention. Specifically, the present invention provides the following.

（上記一般式（１）中、各Ａは、それぞれ独立に、分岐を有してもよい炭素数２～４のアルキレン基であり、Ｒは、分岐及び／又は環構造を備えてもよい炭素数１～１３のアルキル基であり、ｎは、２～８の整数である。） (1) The present invention is an ink composition for metal printing comprising carbon black, a resin and a solvent, the carbon black being neutral carbon black, the solvent having a solubility parameter (sp value) of less than 10.00 (cal/ ^cm3 ) ^1/2 and comprising 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 present invention also relates to an ink composition for metal printing as described in (1), in which the resin is an alkyd resin.

(3) The present invention also relates to an ink composition for metal printing as described in (2), in which the mass average molecular weight of the alkyd resin is less than 10,000.

(4) The present invention also relates to an ink composition for metal printing as described in (2) or (3), in which the alkyd resin has a pentaerythritol skeleton.

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

(6) The present invention also relates to an ink composition for metal printing according to any one of items (1) to (5), which further contains an alkanolamine.

(7) The present invention also relates to an ink composition for metal printing according to any one of items (1) to (6), which further contains a rosin-modified resin.

The present invention provides 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 undergoing retort treatment.

Below, one embodiment of the ink composition for metal printing of the present invention will be described. Note that the present invention is not limited to the following embodiment, and can be practiced with appropriate modifications within the scope of the present invention.

The ink composition for metal printing of the present invention (hereinafter, appropriately abbreviated as "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 and 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. In addition, the ink composition of the present invention suppresses the occurrence of misting during printing, and suppresses the occurrence of stains around the printing machine caused by tiny ink droplets generated during printing. Furthermore, the printing film formed by baking treatment after printing with the ink composition of the present invention has good impact resistance even after retort treatment, so the ink composition of the present invention is not only applied to general metal printing, but is also preferably applied 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.

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 represented by general formula (1) with a specific solubility parameter (sp value). Each component is described below.

[Carbon black]
The ink composition of the present invention contains carbon black as a coloring pigment. Various types of carbon black that are acidic, neutral, or alkaline depending on the surface functional group are commercially available, and neutral carbon black is particularly used in the present invention. Note that neutral carbon black in the present invention 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 finding of the present inventors that the impact resistance of the ink film formed on the metal after retort treatment can be improved by using neutral carbon black instead of the acidic carbon black that has been used in ink compositions for metal printing.

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 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 using a glass electrode (German Industrial Standard DIN ISO 787/9).

The amount of carbon black added is, for example, about 5 to 50% by mass of the entire 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.

[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. Among these resins, an alkyd resin is preferably used in the ink composition of the present invention. The alkyd resin may also be used in combination with a rosin-modified resin. These resins will now be described.

　Alkyd resins are condensation polymers of polyhydric alcohols and polybasic acids, and are a type of polyester, but they can also be prepared by condensation polymerization with animal and vegetable oils and/or their fatty acids. In this case, the animal and vegetable oils are transesterified with the polyhydric alcohol to become fatty acids, which are incorporated into the structure of the alkyd resin. The proportion of the alkyd resin derived from fatty acids of animal and vegetable oils is called the oil length, and the oil length of the alkyd resin used in the present invention is preferably 20 to 50 mass %. Note that oil-free alkyds, which are alkyd resins that do not contain fatty acid components of animal and vegetable oils, may also be used.

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 preferable because it can improve the impact resistance of the printing film after retort treatment. Such an alkyd resin is prepared using pentaerythritol as the polyhydric alcohol. Note that the alkyd resin used in the present invention may be prepared using other polyhydric alcohols in addition to pentaerythritol.

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

Fatty acids are obtained by hydrolysis of natural fats and oils such as vegetable oils and animal oils, and because they have one carboxyl group, they can form esters with polyhydric alcohols, which will be described later. By introducing such fatty acids into alkyd resins, it is possible to improve the transferability of ink compositions using them and to increase the ratio 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 portion to the mass of the entire resin, is about 20 to 50 mass %. A preferred example of such a fatty acid is coconut oil. Various types of fatty acids can be used, and these can be used alone or in combination of two or more types.

A polybasic acid is a compound having multiple carboxy groups, and is a component for polycondensation with a polyhydric alcohol described later to produce a high molecular weight product. 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, phthalic acid or phthalic anhydride is preferred. These polybasic acids can be used alone or in combination of two or more.

The polyhydric alcohol forms an ester with the above acid components, increasing the molecular weight of these components. As the polyhydric alcohol, any of those that have been used in the synthesis of alkyd resins up to now can be used without restriction, and examples of such polyhydric alcohols include compounds with two or more hydroxyl groups.

Such compounds include, in addition to the above-mentioned pentaerythritol, 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, 2-methyl-1,3-propanediol, Examples of the polyether 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, ethylene oxide and propylene oxide copolymer modified compounds of bisphenol A, copolymer polyether polyols of ethylene oxide and propylene oxide, polycarbonate diols, adamantane diols, polyether diols, polyester diols, polycaprolactone diols, etc. These can be used alone or in combination of two or more.

To prepare an alkyd resin, a reaction vessel containing the acid components 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 to remove water by azeotropy with the condensation water. Alternatively, an alkyd resin that provides a highly crosslinked and tough cured film can be obtained by carrying out a condensation polymerization reaction of the acid components and polyhydric alcohol as the first step, and then carrying out a condensation polymerization using a polybasic acid with three or more functional groups such as trimellitic acid as the second step. The reaction temperature can be about 170 to 250°C, and the reaction time can be about 5 to 25 hours, but is not particularly limited. The end of the reaction can be determined by monitoring the acid value of the reaction mixture as the reaction time elapses. In other words, the reaction can be completed 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 reaction catalysts include tetrabutyl zirconate, monobutyltin oxide, zirconium naphthate, and tetrabutyl titanate.

The mass average molecular weight of the alkyd resin is preferably less than 10,000, more preferably 8,500 or less, and even more preferably 7,000 or less. As described above, in the present invention, the impact resistance of the ink film formed on the metal after retort treatment can be improved by using neutral carbon black, but the use of such a relatively low molecular weight alkyd resin is preferable because it can further improve this impact resistance.

The mass average molecular weight of the resin in the present invention can be measured by gel permeation chromatography (GPC). As an example, a Waters Acquity APC (Waters) was used as a GPC device, and columns ACQUITY APC XT 45 1.7 μm 4.6 × 150 mm, ACQUITY APC XT 200 2.5 μm 4.6 × 75 mm, and ACQUITY APC XT 900 2.5 μm 4.6 × 75 mm (Waters) were used as columns, and the values obtained as the mass average molecular weight in terms of polystyrene were obtained under the following conditions: tetrahydrofuran as the mobile phase, column temperature 40°C, flow rate 0.8 milliliters/minute, RI detector, sample injection concentration 10 milligrams/5 milliliters, and injection volume 10 microliters.

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 entire composition.

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 and chemically active carboxyl groups, and some of them have conjugated double bonds. For this reason, various rosin-modified resins are prepared by combining polyhydric alcohols and polybasic acids and condensing them, adding resol, which is a condensation product of phenol, to the benzene ring contained in the rosin skeleton, or by carrying out a Diels-Alder reaction with dienophiles such as maleic anhydride and maleic acid to add maleic acid or maleic anhydride skeletons. Various types of rosin-modified resins are commercially available, and it is possible to obtain and use them.

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

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 improved, and the composition itself has a high polarity, which increases its affinity with water-based OP varnishes, which also have a high polarity, and this also has the effect of suppressing repelling even when the 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.

Although not particularly limited, the acid value of the rosin-modified resin is preferably 100 mgKOH/g or less. The acid value of the rosin-modified resin is preferably 100 mgKOH/g or less, since this allows both suppression of repelling when the aqueous OP varnish is applied wet-on-wet and printability such as suppression of misting and blotting to be achieved. 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 a state in which it is dissolved or dispersed by heating with a solvent described later to form a varnish. 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 a state in which a divalent or higher metal alkoxy compound is added as a gelling agent to the dissolved varnish obtained by dissolving the resin when preparing the varnish, and it is used in a state in which it is formed into a gelled varnish. Among these, it is preferable to prepare a dissolved varnish from the rosin-modified resin and use this to prepare the ink composition, since this can improve the transferability of the ink composition during printing. In addition, by preparing a gelled varnish from the rosin-modified resin and using this to prepare the ink composition, the ink composition is given an appropriate viscoelasticity, which can improve the flowability and reduce misting, and can form a tougher cured coating.

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

In addition to the above alkyd resins and rosin-modified resins, the ink composition of the present invention can also contain resins that have been used in the preparation of conventional ink compositions for metal printing. In other words, depending on the required performance such as printability and coating properties, known resins that are compatible with the above alkyd resins and rosin-modified resins 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.

[solvent]
The solvent used in the ink composition of the present invention may be any solvent that has been used in the field of ink for metal printing, without any particular limitation. Examples of such solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, alkylbenzenes, polyalkylene glycols, etc., each having a boiling point range of about 230 to 400° C. Among these, the ink composition of the present invention essentially contains at least one compound having a solubility parameter (sp value) of less than 10.00 (cal/cm ³ ) ^1/2 and selected from the group consisting of compounds represented by the following general formula (1). Hereinafter, at least one solvent having a solubility parameter (sp value) of less than 10.00 (cal/cm ³ ) ^1/2 and selected from the group consisting of compounds represented by the following general formula (1) is also referred to as a specific solvent. The sp value of the specific solvent is preferably 9.80 (cal/cm ³ ) ^1/2 or less. The lower limit of the sp value in the specific solvent is preferably about 8.50 (cal/cm ³ ) ^1/2 , and more preferably about 9.00 (cal/cm ³ ) ^1/2 . A specific solvent having such an sp value can 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 finding of the present inventors 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 an alkylbenzene-based solvent or a hydrophilic polyalkylene glycol monoalkyl ether-based solvent, which have been widely used in the field of ink compositions for metal printing.

In the above 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 -], 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 -]. Among these, a propylene group is preferred. In this case, the divalent group represented by AO in general formula (1) is an oxypropylene group.

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 not only an aliphatic group but also 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 8. It is preferable that n is 2 or more, because this ensures a sufficient boiling point of the specific solvent to provide stability to the ink composition on the printing machine, and it is preferable that n is 8 or less, because this ensures a viscosity that is favorable for the solvent of the ink composition.

Examples of the compound represented by the above 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, hexapropylene glycol monomethyl ether, etc.

In addition, the sp value used in this invention is calculated by the Fedros method (see R.F. Fedros, Polym. Eng. Sci., 14(2)147(1974)).

The content of the solvent in the ink composition of the present invention is preferably 10 to 50% by mass, more preferably 20 to 45% by mass, based on the entire composition. Among the solvents, the content of the specific solvent is preferably 15 to 40% by mass, based on the entire composition, and it is preferable that all of the solvents in the composition are specific solvents.

The ink composition of the present invention preferably contains an alkanolamine in addition to the above-mentioned 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.

Alkanolamines include monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, n-butylmonoethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, di-n-butylethanolamine, triisopropanolamine, etc. Among these, triethanolamine is preferred.

The content of alkanolamine in the ink composition of the present invention is preferably 0.1 to 3 mass % of the entire composition, and more preferably 0.1 to 1 mass part.

Other components that may be added to the ink composition of the present invention, as necessary, include known hardeners; pigment dispersants; waxes; extender pigments such as silica particles, calcium carbonate, bentonite clay, kaolin, and talc; stabilizers, etc.

As a hardener, for example, amino resins such as melamine resin and benzoguanamine resin can be used.

Silica particles are commercially available as _SiO2 powder, and are easily available in the form of hydrophilic particles that have not been surface-treated or that have been hydrophilized, and hydrophobic particles that have been hydrophobized. Among these silica particles, hydrophobic silica particles are preferably used in the ink composition of the present invention. By using hydrophobic silica particles, the transferability of the ink composition during printing can be improved, and the fluidity of the ink composition can be increased, which is preferable. 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.

The ink composition of the present invention can be prepared by mixing the above-mentioned components and using a roll mill, ball mill, bead mill, or the like in a conventional manner. The viscosity of the ink composition is, for example, 10 to 70 Pa·s at 25°C as measured by a Raleigh viscometer, but is not particularly limited.

The metals used for metal printing in the ink composition of the present invention are not particularly limited, but examples include galvanized or tinned iron sheets, aluminum sheets, and metal cans made of these metal materials.

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.

[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 of esterification, and then 0.70 parts by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second stage of esterification. These esterification reactions were carried out according to a conventional method to obtain an alkyd resin 1 having a mass average molecular weight of 4,376 and a number average molecular weight of 1,995. 15.0 parts by mass of tripropylene glycol monobutyl ether was added to this alkyd resin 1 to obtain an alkyd resin varnish 1. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal/ ^cm3 ) ^1/2 , which corresponds to the specific solvent in the present invention.

[Preparation of alkyd resin varnish 2]
Neopentyl glycol 5.00 parts by mass, pentaerythritol 9.18 parts by mass, coconut oil fatty acid 11.00 parts by mass, isophthalic acid 7.30 parts by mass, and phthalic anhydride 6.50 parts by mass were reacted at 220 ° C. under a nitrogen atmosphere until the acid value of the mixture reached 7 mg KOH / g to perform the first stage esterification, and then trimellitic anhydride 0.70 parts by mass was added and heated at 165 ° C. for 30 minutes under a nitrogen atmosphere to perform the second stage esterification. These esterification reactions were carried out according to a conventional method to obtain 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 is 9.73 (cal / cm ³ ) ^{1 / 2} , which corresponds to the specific solvent in the present invention.

[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 of esterification, and then 0.70 parts by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second stage of esterification. These esterification reactions were carried out according to a conventional method to obtain an alkyd resin 3 having a mass average molecular weight of 2,785 and a number average molecular weight of 1,639. 10.0 parts by mass of tripropylene glycol monobutyl ether was added to this alkyd resin 3 to obtain an alkyd resin varnish 3. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal/ ^cm3 ) ^1/2 , which corresponds to the specific solvent in the present invention.

[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 of esterification, and then 0.70 parts by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second stage of esterification. These esterification reactions were carried out according to a conventional method 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 an alkyd resin varnish 4. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal/ ^cm3 ) ^1/2 , which corresponds to the specific solvent in the present invention.

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

[Preparation of alkyd resin varnish 6]
Pentapropylene glycol monobutyl ether was added instead of tripropylene glycol monobutyl ether to alkyd resin 2 obtained by the procedure for preparing alkyd resin varnish 2, thereby obtaining alkyd resin varnish 6. The sp value of pentapropylene glycol monobutyl ether is 9.42 (cal/cm ³ ) ^1/2 , and corresponds to the specified solvent in the present invention.

[Preparation of alkyd resin varnish 7]
Tetrapropylene glycol mono-2-ethylhexyl ether was added instead of tripropylene glycol monobutyl ether to alkyd resin 2 obtained by the procedure for preparing alkyd resin varnish 2 described above to obtain alkyd resin varnish 7. The sp value of tetrapropylene glycol mono-2-ethylhexyl ether is 9.32 (cal/cm ³ ) ^1/2 , and corresponds to the specified solvent in the present invention.

[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, obtaining rosin modified resin varnish 1. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal/ ^cm3 ) ^1/2 , which corresponds to the specified solvent in the present invention.

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

[Preparation of Rosin-Modified Resin Varnish 3]
Except for using pentapropylene glycol monobutyl ether instead of tripropylene glycol monobutyl ether, a rosin modified resin varnish 3 was obtained in the same manner as in the preparation of the rosin modified resin varnish 1. The sp value of this pentapropylene glycol monobutyl ether was 9.42 (cal/cm ³ ) ^1/2 , which corresponds to the specified solvent in the present invention.

[Preparation of Rosin-Modified Resin Varnish 4]
Except for using tetrapropylene glycol mono-2-ethylhexyl ether instead of tripropylene glycol monobutyl ether, rosin modified resin varnish 4 was obtained in the same manner as in the preparation of rosin modified resin varnish 1. The sp value of this tetrapropylene glycol mono-2-ethylhexyl ether was 9.32 (cal/cm ³ ) ^1/2 , which corresponds to the specified solvent in the present invention.

[Examples 1 to 12, Comparative Examples 1 to 3]
Each ink composition of Examples 1 to 12 and Comparative Examples 1 to 3 was prepared by mixing the components according to the formulations in Tables 1 to 3 and kneading the resulting mixture with a three-roll mill. In addition, in Tables 1 to 3, "Neutral CB1" is HIBLACK200L (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" is ELFTEX415 (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" is Regal250R (neutral carbon black, primary particle size "Neutral CB4" is Regal 350R (neutral carbon black, primary particle size 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 size 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 size 48 nm, DBP oil amount 49 ml/100 g, pH 2.5) manufactured by Cabot Corporation. In Tables 1 to 3, "specific solvent 1" is tripropylene glycol monobutyl ether (sp value 9.73 (cal/cm ³ ) ^1/2 ), "specific solvent 2" is pentapropylene glycol monobutyl ether (sp value 9.42 (cal/cm ³ ) ^1/2 ), "specific solvent 3" is tetrapropylene glycol mono-2-ethylhexyl ether (sp value 9.32 (cal/cm ³ ) ^1/2 ), "non-specific solvent" is triethylene glycol monobutyl ether (sp value 10.32 (cal/cm ³ ) ^1/2 ), and "silica" is surface-hydrophobically treated silica particles (manufactured by Nippon Aerosil Co., Ltd., product name Aerosil R972). The numerical values of each blend amount in Tables 1 to 3 are all parts by mass.

[Misting amount evaluation]
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 the ink meter and uniformly spread, and then rotated at 1200 rpm for 3 minutes. During this time, a blank sheet of paper was placed under the roller, and the amount of the ink composition adhering to the surface due to misting was compared. The measurement was performed with the roller kept at 40°C. The change in mass of the blank sheet before and after the measurement was determined, and this was taken as the misting amount (mg). The greater the change in mass of the blank sheet before and after the measurement, the greater the amount of the ink composition scattered, so the smaller this value, the better the result. Based on the calculated misting amount (mg), evaluation was performed 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 and less than 10 mg. ×: The amount of misting was 10 mg or more.

[Evaluation of impact resistance after retort treatment]
For each of the Examples and Comparative Examples, 0.2 cc of the ink composition was spread on an aluminum substrate having a thickness of 50 μm using an RI spreader to obtain a spread product. Then, a retort overprint varnish (manufactured by AkzoNobel) was applied to the spread surface of the spread product using a No. 0.4 bar coater (Meyer bar), and the product was kept in an oven at 240° C. for 2 minutes to obtain a retort sample. Then, the retort sample was retorted using an autoclave (high-pressure steam sterilizer, HG-50 manufactured by Hirayama Seisakusho Co., Ltd.) at 125° C. for 30 minutes to obtain a retort-treated product. The retorted product was subjected to impacts at four points 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, and 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.
○: In all four locations, the coating film at the location in contact with the impact core did not peel off. ×: In one or more of the four locations, at least a portion of the coating film at the location in contact with the impact core peeled off, exposing the aluminum base material.

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 possible to obtain good misting suitability and impact resistance after retort.

Claims (7)

A metal printing ink composition comprising carbon black, a resin and a solvent,
The carbon black includes neutral carbon black,
The ink composition for metal printing is characterized in that the solvent has a solubility parameter (sp value) of less than 10.00 (cal/cm ³ ) ^1/2 and contains 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.) The ink composition for metal printing according to claim 1, wherein the resin is an alkyd resin. The ink composition for metal printing according to claim 2, wherein the mass average molecular weight of the alkyd resin is less than 10,000. The ink composition for metal printing according to claim 2 or 3, wherein the alkyd resin has a pentaerythritol skeleton. 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. The ink composition for metal printing according to any one of claims 1 to 5 further contains an alkanolamine. The ink composition for metal printing according to any one of claims 1 to 6 further contains a rosin-modified resin.