Metal printing ink composition

Abstract

To provide a metal printing ink composition that exhibits superior transferability during printing and maintains superior impact resistance even after a metal printed material is subjected to retort treatment after printing.SOLUTION: Provided is a metal printing ink composition comprising carbon black, an alkyd resin, and a solvent. The metal printing ink composition used is characterized in that the carbon black is neutral carbon black and that the alkyd resin has a mass average molecular weight of less than 6,000.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] For printing on the outer surface of metal materials, such as galvanized or tinned iron plates, aluminum plates, or metal cans made of these metal materials, an ink composition for metal printing mainly composed of a binder resin such as an alkyd resin, a polyester resin, or an epoxy resin and an organic solvent such as mineral oil or a higher alcohol is used as the main vehicle component.

[0003] In addition, in order to improve the adhesion, flex resistance, impact resistance, abrasion resistance, etc. of the ink coating film on these printing surfaces, coating by overprint varnish is generally performed. As these overprint varnishes, solvent-type ones composed of a binder resin such as an alkyd resin, a polyester resin, an acrylic resin, or an epoxy resin, a curing agent such as a melamine resin or a benzoguanamine resin, and an organic solvent such as mineral oil or a cellosolve type have been widely used.

[0004] When printing on the outer surface of metal, after printing the ink using an offset printing machine, a dry offset printing machine, etc., the overprint varnish is applied wet-on-wet on the ink film using a coater, etc., and then baking is performed at 150 to 280°C.

[0005] However, in recent years, due to the problem of air pollution caused by solvents and the hygiene or safety aspects in the printing work environment, in the field of metal printing as well, it has become common to adopt water-based overprint varnishes instead of the solvent-type overprint varnishes that have been conventionally used. However, when a water-based overprint varnish is applied onto the ink coating film of a conventional ink composition for metal printing, phenomena such as repulsion of the water-based overprint varnish and penetration of the water-based overprint varnish into the ink film occur. As a result, there has been a problem that the quality such as gloss or adhesion of the coating film is significantly deteriorated. Therefore, in the ink composition as well, it has been required to have excellent suitability for water-based overprint varnishes.

[0006] As a method for improving the suitability for such water-based overprint varnishes, for example, Patent Document 1 proposes the use of alkylene glycol solvents having 4 to 8 carbon atoms, Patent Document 2 proposes the use of polyoxyalkylene glycol solvents, Patent Document 3 proposes the use of polyoxyalkylene alkyl ether organic solvents, and Patent Document 4 proposes the use of polyoxyalkylene alkyl ester solvents, respectively.

[0007] By the way, in recent years, in order to improve productivity, high-speed printing has also been attempted in metal printing. From the viewpoint of coping with such high-speed printing, recently, an ink composition having good transferability during printing has been eagerly desired.

[0008] In addition, depending on the use of metal printed matter, for example, in the case of two-piece cans or three-piece cans used for beverages such as coffee and tea or canned goods, retort treatment, that is, pressurization and heat treatment with steam or hot water at 100°C or higher, may be performed for the purpose of sterilization or the like. When such treatment is performed, the printed film of the metal printed matter becomes vulnerable, and the impact resistance, which is the performance of maintaining the printed film when an impact is applied to the printed surface, may be significantly deteriorated.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a metal printing ink composition that has good transferability during printing and can maintain good impact resistance even after the printed metal product has been subjected to retort processing.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that in a black ink using carbon black as a coloring pigment, particularly by using neutral carbon black and an alkyd resin having a mass average molecular weight of less than 6,000, the above problems can be solved, and the present invention has been completed. Specifically, the present invention provides the following.

[0012] (1) The present invention is a metal printing ink composition comprising carbon black, an alkyd resin, and a solvent, wherein the carbon black includes neutral carbon black, and the mass average molecular weight of the alkyd resin is less than 6,000.

[0013] (2) The present invention is also the metal printing ink composition according to item (1), wherein the alkyd resin has a pentaerythritol skeleton.

[0014] (3) The present invention further provides a metal printing ink composition according to item (1) or (2) containing alkanolamine.

[0015] (4) The present invention also provides a metal printing ink composition according to any one of items (1) to (3), characterized by containing at least one selected from the group consisting of compounds represented by the following general formula (1) as the above solvent. [Chemical formula] (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 branch and / or a ring structure, and n is an integer of 2 to 8.)

[0016] (5) The present invention also provides a metal printing ink composition according to item (4), wherein the divalent group represented by AO in the general formula (1) is an oxypropylene group.

[0017] (6) The present invention also provides a metal printing ink composition according to any one of items (1) to (5), wherein the solubility parameter (sp value) of the above solvent is less than 10.00 (cal / cm 3 ) 1 / 2 and is less than.

[0018] (7) The present invention further provides a metal printing ink composition according to any one of items (1) to (6) containing a rosin-modified resin. [Advantages of the Invention]

[0019] According to the present invention, there is provided a metal printing ink composition having good transferability during printing and capable of maintaining good impact resistance even after the printed metal product has been subjected to retort treatment. [Embodiments for Carrying Out the Invention]

[0020] Hereinafter, an embodiment of the ink composition for metal printing of the present invention will be described. It should be noted that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the present invention.

[0021] The ink composition for metal printing of the present invention (hereinafter, appropriately abbreviated as "the ink composition of the present invention") is for metal printing and is preferably applicable to printing by a so-called dry offset printing method using a relief plate as a printing plate or an offset printing method using a lithographic plate as a printing plate. However, it can be applied to all printing methods commonly used in metal printing. In addition, since the ink composition of the present invention is excellent in transferability during printing, it can also well cope with high-speed printing that has been recently popular. Furthermore, the printed film formed by baking after printing with the ink composition of the present invention has good impact resistance even after undergoing retort treatment. Therefore, the ink composition of the present invention is preferably applicable not only to the application to general metal prints but also to printing on metals that require retort treatment, such as two-piece cans and three-piece cans used for beverages such as coffee and tea and canned foods.

[0022] The ink composition of the present invention comprises carbon black, an alkyd resin and a solvent, and is characterized in that it contains a particularly neutral carbon black and an alkyd resin having a mass average molecular weight of less than 10,000.

[0023] [Carbon black] The ink composition of the present invention contains carbon black as a coloring pigment. Various commercially available carbon blacks exhibit acidic, neutral or alkaline properties depending on the difference in their surface functional groups. In the present invention, a particularly neutral carbon black is used. The neutral carbon black in the present invention refers to a carbon black having a pH in the range of 6.0 or more and 9.5 or less.

[0024] The pH of carbon black is determined by measuring a mixture of carbon black and distilled water using a glass electrode pH meter. Specifically, 1 g of the carbon black to be measured is added to 20 mL of distilled water (pH 7.0) from which carbonic acid has been removed, and the mixture is stirred with a magnetic stirrer to prepare an aqueous suspension. The pH is then measured at 25 °C using a glass electrode (German Industrial Standard DIN ISO 787 / 9).

[0025] As the addition amount of carbon black, about 5 to 50% by mass with respect to the whole ink composition is exemplified, but it 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.

[0026] [Alkyd resin] The ink composition of the present invention contains an alkyd resin having a mass average molecular weight of less than 6,000. By including such an alkyd resin, the transferability of the ink composition during printing and the impact resistance of the printed film after retort treatment can be improved. Next, the alkyd resin will be described.

[0027] An alkyd resin is a polycondensate of a polyhydric alcohol and a polybasic acid, and is a type of polyester. However, it can also be prepared by performing polycondensation together with vegetable oils and / or their fatty acids. At this time, the vegetable oil is transesterified with the polyhydric alcohol to become a fatty acid and is incorporated into the structure of the alkyd resin. The ratio derived from the fatty acid of the vegetable oil in the alkyd resin is called the oil length, and the oil length of the alkyd resin used in the present invention is preferably 20 to 50% by mass. Note that an oil-free alkyd resin that does not contain a fatty acid component of vegetable oil may also be used.

[0028] As the alkyd resin used in the present invention, those having a pentaerythritol skeleton in the molecule are preferably mentioned. By using an alkyd resin having such a skeleton, the impact resistance after retort treatment in the printed film can be improved, which is preferable. Such an alkyd resin is prepared by using pentaerythritol as a polyhydric alcohol. In addition, the alkyd resin used in the present invention may be prepared by using other polyhydric alcohols in addition to pentaerythritol.

[0029] The alkyd resin having a pentaerythritol skeleton in the molecule can be obtained, for example, as a polycondensate of an acid component composed 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.

[0030] The fatty acid is obtained by hydrolyzing natural oils and fats such as vegetable oils and animal oils. Since it has one carboxy group, it can form an ester with the polyhydric alcohol described later. By introducing such a fatty acid into the alkyd resin, the transferability of the ink composition using it can be enhanced, or the proportion of biomass-derived components can be increased. From such a viewpoint, it is preferable to use a fatty acid in such an amount 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 %. As such a fatty acid, coconut oil is preferably mentioned. Although various fatty acids can be mentioned, these can be used alone or in combination of two or more.

[0031] A polybasic acid is a compound having a plurality of carboxy groups and is a component for undergoing polycondensation with a polyhydric alcohol described later to increase its 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-sodium sulfoisophthalic acid, fumaric acid, benzoic acid, tert-butylbenzoic acid, tetrahydrophthalic anhydride, maleic anhydride, succinic acid, succinic anhydride, fumaric acid, sebacic acid, azelaic acid, tetrabromophthalic anhydride, methyl hymic anhydride, tetrachlorophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, trimellitic anhydride, methylcyclohexenedicarboxylic anhydride, and the like. Among these, phthalic acid or phthalic anhydride is preferably mentioned. These polybasic acids can be used alone or in combination of two or more.

[0032] A polyhydric alcohol forms an ester with the above acid component and increases the molecular weight of these components. As the polyhydric alcohol, those that have been used for the synthesis of alkyd resins can be used without limitation, and examples include compounds having two or three or more hydroxyl groups.

[0033] Examples of 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-methylpropanediol 1,3, 3-methylpentanediol 1,5, 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, propylene oxide copolymer-modified compounds of bisphenol A, copolymer polyether polyols of ethylene oxide and propylene oxide, polycarbonate diol, adamantanediol, polyether diol, polyester diol, polycaprolactone diol, and the like. These can be used alone or in combination of two or more kinds.

[0034] To prepare an alkyd resin, a method can be cited in which a small amount of a solvent such as xylene is added to a reaction kettle charged with these acid components and polyhydric alcohol, and heating is carried out while flowing an inert gas such as nitrogen gas, and azeotroping with condensed water to remove water while performing polycondensation. Further, taking the polycondensation reaction of these acid components and polyhydric alcohol as the first stage, and as the second stage, by performing polycondensation using a polybasic acid having three or more functional groups such as trimellitic acid, an alkyd resin that gives a highly crosslinked and tough cured film can also be obtained. The reaction temperature can be about 170 to 250 °C, and the reaction time can be about 5 to 25 hours, but it is not particularly limited. The completion of the reaction can be determined by monitoring the acid value of the reaction mixture according to the passage of the reaction time. That is, the reaction may be terminated when the decrease in the acid value of the reaction mixture accompanying polycondensation stops. The polycondensation reaction can be carried out in a shorter time by distilling out the water generated by polycondensation outside the system or using a reaction catalyst. Examples of the reaction catalyst include tetrabutyl zirconate, monobutyltin oxide (monobutyl tin oxide), zirconium naphthate, tetrabutyl titanate, and the like.

[0035] As described above, the mass average molecular weight of the alkyd resin used in the present invention is less than 6,000. As this mass average molecular weight, less than 5,500 can be preferably cited, and less than 5,000 can be more preferably cited.

[0036] The weight-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 the GPC apparatus, and 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) are used as the columns, respectively. Chromatography is performed under the conditions of using tetrahydrofuran as the mobile phase, a column temperature of 40°C, a flow rate of 0.8 milliliters / minute, an RI detector, a sample injection concentration of 10 milligrams / 5 milliliters, and an injection volume of 10 microliters, and the value obtained as the weight-average molecular weight in terms of polystyrene can be cited.

[0037] As the content of the alkyd resin in the ink composition, 10 to 40% by mass is preferably cited with respect to the entire composition, and 20 to 40% by mass is more preferably cited with respect to the entire composition.

[0038] The ink composition of the present invention preferably further contains a rosin-modified resin in addition to the above alkyd resin.

[0039] The rosin-modified resin is a resin prepared using rosin as one of the raw materials. Rosin contains resin acids such as abietic acid, palustric acid, isopimaric acid, and levopimaric acid as a mixture. These resin acids contain hydrophilic and chemically active carboxyl groups, and some of them have conjugated double bonds. Therefore, various rosin-modified resins are prepared by, for example, condensation polymerization by combining polyhydric alcohols and polybasic acids, adding resole, which is a condensate of phenol, to the benzene ring contained in the rosin skeleton, or performing a Diels-Alder reaction with maleic anhydride or maleic acid, which is a dienophile, to add a maleic acid or maleic anhydride skeleton. Such rosin-modified resins are commercially available in various types, and it is also possible to obtain and use them.

[0040] Examples of the rosin-modified resin include rosin ester resin, maleated rosin, fumarated rosin resin, rosin-modified maleic acid resin, rosin-modified fumaric acid resin, rosin-modified phenol resin, rosin-modified alkyd resin, rosin-modified polyester resin, and the like. In the present invention, any rosin-modified resin may be used, but among them, rosin ester resin is preferably used.

[0041] As the rosin-modified resin used in the present invention, those having a hydroxyl value of 10 mgKOH / g or more are preferably used. By including such a rosin-modified resin having 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, as the polarity of the composition itself increases, the affinity for the highly polar aqueous OP varnish also increases, and the effect of suppressing repelling even when it is wet-on-wet coated is also achieved. 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 for example, it is about 200 mgKOH / g, preferably about 150 mgKOH / g, and more preferably about 100 mgKOH / g.

[0042] Also, although not particularly limited, the acid value of the rosin-modified resin is preferably 100 mgKOH / g or less. When the acid value of the rosin-modified resin is 100 mgKOH / g or less, it is preferable because it can achieve both suppression of repelling when the aqueous OP varnish is wet-on-wet coated and printing suitability such as suppression of misting and overflowing. 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.

[0043] The rosin-modified resin is used in a state where it is dissolved or dispersed by being heated together with a solvent described later to form a varnish. The rosin-modified resin may be used as a dissolved varnish that remains dissolved or dispersed in the solvent, or when preparing the varnish, a divalent or higher metal alkoxy compound may be added as a gelling agent to the dissolved varnish obtained by dissolving the resin, and it may be used in a state of being a gelled varnish. Among these, it is preferable to prepare a dissolved varnish from the rosin-modified resin and use it in the preparation of the ink composition, because the transferability of the ink composition during printing can be improved. Also, by preparing a gelled varnish from the rosin-modified resin and using it in the preparation of the ink composition, appropriate viscoelasticity can be imparted to the ink composition, fluidity can be improved and misting can be reduced, and a stronger and tougher cured film can be formed.

[0044] As the content of the rosin-modified resin in the ink composition, 5 to 50% by mass is preferably mentioned with respect to the whole composition, 5 to 25% by mass is more preferably mentioned with respect to the whole composition, and 7 to 20% by mass is even more preferably mentioned with respect to the whole composition.

[0045] In addition to the above-mentioned alkyd resin and rosin-modified resin, the ink composition of the present invention can also be used in combination with resins conventionally used in the preparation of metal printing ink compositions. That is, according to the required performance such as printing suitability and coating film physical properties, known resins compatible with the above-mentioned alkyd resin and rosin-modified resin can be used alone or in a mixture of plural. Examples of such resins include polyester resins, petroleum resins, epoxy resins, ketone resins, amino resins, benzoguanamine resins, and the like.

[0046] [Solvent] As the solvent used in the ink composition of the present invention, those that have been used in the field of metal printing ink organisms so far can be mentioned without particular limitation. Examples of such solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, alkylbenzenes, polyalkylene glycols, etc. having a boiling point range of about 230 to 400 °C. Among these, the solubility parameter (sp value) is 10.00 (cal / cm3 ) 1 / 2 is less than, and at least one selected from the group consisting of compounds represented by the following general formula (1) can be preferably mentioned. Hereinafter, the solubility parameter (sp value) is 10.00 (cal / cm 3 ) 1 / 2 is less than, and at least one solvent 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 in the specific solvent is 9.80 (cal / cm 3 ) 1 / 2 is preferably the following. Further, as the lower limit value of the sp value in the specific solvent, 8.50 (cal / cm 3 ) 1 / 2 is preferably mentioned, and 9.00 (cal / cm 3 ) 1 / 2 is more preferably mentioned. The specific solvent having such an sp value can also be called a polyalkylene glycol monoalkyl ether having a hydrophobic property.

[0047]

Chemical formula

[0048] 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 an alkylene group 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 -), an isopropylidene group [-C(CH 3 ) 2 -], etc. Among these, a propylene group is preferably mentioned. In this case, the divalent group represented by AO in the general formula (1) becomes an oxypropylene group.

[0049] In the general formula (1) above, R is an alkyl group having 1 to 13 carbon atoms which may have a branched and / or cyclic structure. Note that this alkyl group may be an alicyclic group as well as an aliphatic 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, a cyclohexyl group, and the like.

[0050] In the general formula (1) above, n is an integer of 2 to 8. When n is 2 or more, it is preferable because a sufficient boiling point of a specific solvent can be ensured to impart the stability of the ink composition on the printing machine. When n is 8 or less, a preferable viscosity can be obtained as the solvent of the ink composition.

[0051] 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, hexapropylene glycol monomethyl ether, and the like.

[0052] Note that as the sp value in the present invention, the one calculated by the Fedros method is used (see the literature: R.F. Fedros, Polym. Eng. Sci., 14(2) 147 (1974)).

[0053] 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 whole composition. Among the solvents, the content of the specific solvent is preferably 15 to 40% by mass based on the whole composition, and it is preferable that all of the solvents in the composition are the specific solvent. It is preferable that the ink composition of the present invention contains such a specific solvent because misting during printing can be reduced.

[0054] In addition to the above components, the ink composition of the present invention preferably contains an alkanolamine. By containing an alkanolamine in the ink composition of the present invention, both the reduction of misting during printing and the impact resistance after retort treatment in the printed film can be improved.

[0055] Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, n-butylmonoethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, di-n-butylethanolamine, triisopropanolamine and the like. Among these, triethanolamine is preferably mentioned.

[0056] The content of the alkanolamine in the ink composition of the present invention is preferably 0.1 to 3% by mass, more preferably 0.1 to 1 part by mass, based on the whole composition.

[0057] In the ink composition of the present invention, as other components, a known curing agent; a pigment dispersant; a wax; extender pigments such as silica particles, calcium carbonate, bentonite clay, kaolin, talc; a stabilizer and the like can be added as necessary.

[0058] As the curing agent, for example, amino resins such as melamine resin and benzoguanamine resin can be used.

[0059] The silica particles are SiO 2It is commercially available as a powder, and it is possible to easily obtain those that are not particularly surface-treated or are hydrophilic ones that have been hydrophilized, hydrophobic ones that have been hydrophobicized, etc. Among these silica particles, in the ink composition of the present invention, hydrophilic silica particles are preferably used. By using hydrophilic silica particles, the transferability of the ink composition during printing can be made better, 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, more preferably 1 to 5% by mass.

[0060] The ink composition of the present invention can be prepared by mixing the above-mentioned respective components by a conventional method using a roll mill, a ball mill, a bead mill, etc. The viscosity of the ink composition can be exemplified by a value at 25°C measured by a rotational viscometer of 10 to 70 Pa·s, but is not particularly limited.

[0061] The metal for metal printing in the ink composition of the present invention is not particularly limited, and examples thereof include galvanized or tinned iron plates, aluminum plates, or metal cans made of these metal materials.

Examples

[0062] Hereinafter, the ink composition of the present invention will be described more specifically by showing examples, but the present invention is not limited to the following examples at all.

[0063] [Preparation of Alkyd Resin Varnish 1] 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 carry out the first-stage esterification. Then, 0.70 part by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to carry out the second-stage 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 4,764 and a number average molecular weight of 2,348. To this alkyd resin 1, 10.0 parts by mass of tripropylene glycol monobutyl ether was added to obtain an alkyd resin varnish 1. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm 3 ) 1 / 2 and it corresponds to the specific solvent in the present invention.

[0064] [Preparation of alkyd resin varnish 2] 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 carry out the first-stage esterification. Then, 0.70 part by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to carry out the second-stage esterification. These esterification reactions were carried out according to a conventional method to obtain an alkyd resin 2 having a mass average molecular weight of 4,376 and a number average molecular weight of 1,995. To this alkyd resin 2, 15.0 parts by mass of tripropylene glycol monobutyl ether was added to obtain an alkyd resin varnish 2. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm 3 ) 1 / 2 and it corresponds to the specific solvent in the present invention.

[0065] [Preparation of alkyd resin varnish 3] 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 in 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 for 30 minutes in a nitrogen atmosphere to perform the second-stage 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 6,049 and a number average molecular weight of 2,591. To this alkyd resin 3, 21.8 parts by mass of tripropylene glycol monobutyl ether and 2.0 parts by mass of triethanolamine were added to obtain an alkyd resin varnish 3. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm 3 ) 1 / 2 and it corresponds to the specific solvent in the present invention.

[0066] [Preparation of Rosin-Modified Resin Varnish] 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 were heated at 130°C for 1 hour to dissolve them, and a rosin-modified resin varnish was obtained. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm 3 ) 1 / 2 and it corresponds to the specific solvent in the present invention.

[0067] [Examples 1 - 5, Comparative Examples 1 - 3] The respective ink compositions of Examples 1 to 5 and Comparative Examples 1 to 3 were prepared by mixing each component according to the formulations in Tables 1 and 2 and kneading the resulting mixture with a three-roll mill. In Tables 1 and 2, "Neutral CB1" is HIBLACK 200L (neutral carbon black, primary particle size 28 nm, DBP absorption 62 ml / 100 g, pH 8.0) manufactured by Orion Engineered Carbons, "Neutral CB2" is ELFTEX 415 (neutral carbon black, primary particle size 25 nm, DBP absorption 55 ml / 100 g, pH 6.0 or more and 8.0 or less) manufactured by Cabot, "Neutral CB3" is Regal 250R (neutral carbon black, primary particle size 34 nm, DBP absorption 48 ml / 100 g, pH 6.0 or more and 8.0 or less) manufactured by Cabot, "Neutral CB4" is Regal 350R (neutral carbon black, primary particle size 48 nm, DBP absorption 46 ml / 100 g, pH 6.0 or more and 8.0 or less) manufactured by Cabot, "Acidic CB1" is Mitsubishi Carbon Black MA7 (acidic carbon black, primary particle size 24 nm, DBP absorption 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 absorption 49 ml / 100 g, pH 2.5) manufactured by Cabot. Also, in Tables 1 and 2, the "specific solvent" is tripropylene glycol monobutyl ether (sp value 9.73 (cal / cm 3 )) 1 / 2 ) and the "silica" is surface-hydrophobically treated silica particles (product name Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.). The numerical values of each compounding amount in Tables 1 and 2 are all in parts by mass.

[0068] [Transferability Evaluation] For each of the ink compositions of each example and comparative example, 0.1 cc of the ink composition was applied onto an aluminum substrate with a thickness of 50 μm using a high-speed color development machine "PM-900PT" (manufactured by Mitsui Electric Precision Co., Ltd.) at a printing pressure of 90 kgf and a color development speed of 9 m / s. Each of the resulting color-developed products was evaluated according to the following criteria. The evaluation results are shown in the "Transferability" column of Tables 1 and 2. ○: No bleeding is observed at all △: Fuzzing was observed at less than 50% of the transfer area, but it is within the practical range. ×: Fuzzing was observed at 50% or more of the transfer area, indicating a defect.

[0069] [Impact resistance evaluation after retort treatment] For each of the examples and comparative examples, 0.2 cc of the ink composition was spread on an aluminum substrate with a thickness of 50 μm using an RI color development machine to obtain a color-developed product. Subsequently, a retort overprint varnish (manufactured by AkzoNobel) was applied to the color-developed surface of the color-developed product using a #0.4 bar coater (Mayer bar), and the product was held in an oven at 240 °C for 2 minutes to obtain a retort sample. Then, the retort sample was subjected to a retort treatment 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 obtained retort-treated product was subjected to impact on four locations from the opposite side of the color-developed surface under the conditions of a striker diameter of 1 / 4Φ (6.35 mm), a weight of 300 g, and a weight drop height of 50 mm using a DuPont impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name H-50), and the degree of peeling of the coating film on the color-developed surface side was evaluated according to the following criteria. The results are shown in the "Impact resistance after retort" columns of Tables 1 and 2. ○: For all four locations, the coating film at the contact point with the striker did not peel off. ×: For one or more of the four locations, at least a part of the coating film at the contact point with the striker peeled off, exposing the aluminum substrate.

[0070]

Table 1

[0071]

Table 2

[0072] As is clear from Tables 1 and 2, it can be understood that by combining neutral carbon black and an alkyd resin having a mass average molecular weight of less than 6,000 to form an ink composition for metal printing, the ink transferability during printing and the impact resistance after retort become good.

Claims

1. An ink composition for metal printing comprising carbon black, an alkyd resin, and a solvent, wherein the carbon black includes neutral carbon black, and the alkyd resin has a mass average molecular weight of less than 6,000. An ink composition for metal printing characterized by this.

2. The ink composition for metal printing according to Claim 1, wherein the alkyd resin has a pentaerythritol skeleton.

3. Furthermore, the ink composition for metal printing according to Claim 1, which contains alkanolamine.

4. The ink composition for metal printing according to Claim 1, characterized in that it contains at least one selected from the group consisting of compounds represented by the following general formula (1) as the solvent. 【Chemical 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 branch and / or a ring structure, and n is an integer of 2 to 8.)

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

6. The solubility parameter (sp value) of the solvent is less than 10.00 (cal / cm ３ ). １／２ The ink composition for metal printing according to claim 1, wherein the ink composition is less than

7. Furthermore, the ink composition for metal printing according to Claim 1, which contains a rosin-modified resin.