Ink composition for metal printing

Abstract

[Problem] To provide a white ink composition for metal printing, said ink composition enabling pre-mixing to be finished in a shorter time and having sufficient coating film physical properties such as impact resistance. [Solution] An ink composition for metal printing that may be used comprises a coloring pigment, a resin, a solvent, silica and calcium carbonate, and is characterized in that the coloring pigment contains titanium oxide, the content of the silica is 5 mass% or less relative to the entire composition, and the total content of the silica and the calcium carbonate is 8 mass% or less relative to the entire composition.

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

[0005] Incidentally, metal printing is almost always performed using a white ink composition in addition to the four process colors (yellow, magenta, cyan, and black). This is because the printing target for metal printing is metallic in color, rather than white like paper, and therefore a white ink composition is required to reproduce the white color. Furthermore, in order to enhance the color development of full-color printing using process colors, the entire printing target area may be printed with a white ink composition prior to the printing of the process colors. This white ink composition requires high hiding power to conceal the color of the base, and therefore contains a high concentration of titanium oxide, a white pigment. In fact, the white ink compositions described in Patent Documents 1 to 3 contain high concentrations of titanium oxide, and the invention described in Patent Document 3 is said to use small-particle silica in addition to titanium oxide to further enhance hiding power. Thus, it can be said that white ink compositions tend to contain a high content of solids, such as color pigments and extender pigments, in order to ensure high hiding power.

[0006] Japanese Patent Application Laid-Open No. 6-279722 Japanese Patent Application Laid-Open No. 2011-26404 Japanese Patent Application Laid-Open No. 2021-91806

[0007] As mentioned above, white ink compositions tend to have a high solids content, which can lead to deterioration in the physical properties of the coating film. A typical solution to this problem is to extend the time of the dispersion process (a milling process using a roll mill or the like) to improve the dispersibility of the solids in the ink composition. However, extending the time of the dispersion process leads to an increase in production lead time and reduced productivity. Furthermore, as a step prior to the dispersion process, premixing is performed, in which solids such as pigments are added to and mixed with the varnish, thoroughly blending the solids into the varnish until they are no longer powdery. However, as the solids content increases, this premixing process also takes a long time, which also leads to reduced productivity.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a white ink composition for metal printing that can be premixed in a shorter time and has sufficient coating film properties such as impact resistance.

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by adding calcium carbonate to a white ink composition for metal printing in addition to silica as an extender pigment, and further by limiting the silica content to 5% by mass or less and the total content of silica and calcium carbonate to 8% by mass or less, thereby completing the present invention. Specifically, the present invention provides the following.

[0010] (1) The present invention is an ink composition for metal printing comprising a color pigment, a resin, a solvent, silica, and calcium carbonate, characterized in that the color pigment contains titanium oxide, the content of the silica is 5% by mass or less relative to the total composition, and the total content of the silica and the calcium carbonate is 8% by mass or less relative to the total composition.

[0011] (2) The present invention also provides a solvent 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] (3) The present invention also provides an ink composition for metal printing according to (2), wherein the divalent group represented by AO in general formula (1) is an oxypropylene group.

[0013] (4) The present invention also provides an ink composition for metal printing according to any one of (1) to (3), wherein the silica is surface-hydrophobized silica.

[0014] (5) The present invention also provides an ink composition for metal printing according to any one of (1) to (4), wherein the resin contains an alkyd resin.

[0015] (6) The present invention also provides an ink composition for metal printing according to (5), wherein the alkyd resin has a mass average molecular weight of less than 10,000.

[0016] (7) The present invention also provides an ink composition for metal printing according to item (5) or (6), wherein the alkyd resin has a pentaerythritol skeleton.

[0017] (8) The present invention also provides an ink composition for metal printing according to any one of (5) to (7), further comprising a rosin-modified resin as the resin.

[0018] (9) The present invention also relates to the ink composition for metal printing according to any one of items (1) to (8), which further contains an alkanolamine.

[0019] According to the present invention, a white ink composition for metal printing is provided which can be premixed in a shorter time and has sufficient coating properties such as impact resistance.

[0020] 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.

[0021] 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, a printed film formed by a baking treatment after printing with the ink composition of the present invention has good impact resistance not only in its original state but also after retort treatment. Therefore, the ink composition of the present invention is preferably applied not only to general metal printed matters 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.

[0022] The ink composition of the present invention is a metal printing ink composition comprising a color pigment, a resin, a solvent, silica, and calcium carbonate, and is characterized in that the color pigment contains titanium oxide, the content of the silica is 5% by mass or less based on the total composition, and the total content of the silica and the calcium carbonate is 8% by mass or less based on the total composition. Each component will be explained below.

[0023] [Coloring Pigment] The ink composition of the present invention contains titanium oxide as a coloring pigment. Examples of titanium oxide that have been used in ink compositions to date are not particularly limited. Examples of such titanium oxide include anatase-type titanium oxide and rutile-type titanium oxide, with rutile-type titanium oxide being preferred from the viewpoint of achieving higher hiding power. The titanium oxide may be surface-treated with a metal oxide such as alumina, silica, or zirconia, and the average particle size thereof may preferably be, for example, about 0.1 μm to 0.5 μm.

[0024] The content of titanium oxide in the ink composition is preferably about 10 to 60% by mass, more preferably about 20 to 50% by mass, and even more preferably about 30 to 45% by mass, based on the total mass of the composition.

[0025] [Resin] The resin used in the ink composition of the present invention can be any resin that has been used in ink compositions for metal printing, without any particular limitation. Among these resins, alkyd resins and rosin-modified resins are preferably used in the ink composition of the present invention. Next, these resins will 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, and because they have 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 fatty acid. 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, 2-methylpropanediol, 3-methylpentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 2-methylpropanediol, 1,3-methylpentanediol, 1,3-methylpentanediol, 1,4-methylpentanediol, 1,5-methylpentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-methylpentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-methylpentanediol, 1,3-methylpentanediol, 1,4-methylpentanediol, 1,5 ...5-methylpentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-methylpentanediol, 1,5-methylpentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-methylpentanediol, 1,5-methyl ,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- and propylene oxide-copolymerized compounds of bisphenol A, copolymerized polyether polyols of ethylene oxide and propylene oxide, polycarbonate diol, adamantane diol, polyether diol, polyester diol, polycaprolactone diol, etc. 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 8,500 or less, and even more preferably 7,000 or less.

[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 1 to 20 mass% relative to the total composition, more preferably 1 to 10 mass% relative to the total composition, and even more preferably 2 to 5 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 ink compositions 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 particularly suitable for use in ink compositions containing aliphatic hydrocarbons, alicyclic hydrocarbons, alkylbenzenes, polyalkylene glycols, etc., which have a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２A preferred example of the compound is at least one selected from the group consisting of compounds having a solubility parameter (sp value) of less than 10.00 (cal / cm 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 The specific solvent having such an sp value can also be said to be a polyalkylene glycol monoalkyl ether having hydrophobic properties.

[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% by mass, more preferably 20 to 45% by mass, based on the total mass of the composition. Among the solvents, the content of the specific solvent is preferably 15 to 40% by mass, based on the total mass of the composition, and it is preferable that all of the solvents in the composition are specific solvents. By including such a specific solvent in the ink composition of the present invention, misting during printing can be reduced, which is preferable.

[0052] [Silica] The ink composition of the present invention contains silica. Silica contributes to improving the hiding power of the ink composition of the present invention. The silica used in the present invention is preferably in the form of extremely fine particles with an average primary particle diameter of 100 nm or less, and may be hydrophilic silica in which the particle surface is covered with silanol groups, or surface-hydrophobized silica in which the silanol groups present on the particle surface are modified with an alkyl group or the like. Of these, fumed silica with an average primary particle diameter of 10 to 30 nm and surface-hydrophobized can be preferably used.

[0053] The content of silica in the ink composition of the present invention is 5% by mass or less. By having the silica content of 5% by mass or less, the premixing time in the production stage of the ink composition can be shortened. Furthermore, the lower limit of the silica content in the ink composition of the present invention is preferably about 0.1% by mass, more preferably about 1% by mass, and even more preferably about 2% by mass.

[0054] [Calcium Carbonate] The ink composition of the present invention contains calcium carbonate. Calcium carbonate contributes to improving the hiding power of the ink composition of the present invention. Such calcium carbonate may be in the form of powder particles, and its average primary particle diameter is preferably 70 nm or less. A primary particle diameter of 70 nm or less of calcium carbonate is preferred because it can ensure sufficient storage stability of the ink composition. Furthermore, the lower limit of the primary particle diameter of calcium carbonate is preferably about 10 nm, more preferably about 20 nm, and even more preferably about 30 nm.

[0055] The calcium carbonate used in the present invention is preferably one whose particle surface has been modified by chemical modification. In this case, preferred examples of the treatment agent used for the modification include fatty acids and rosin acids. Various types of such modified calcium carbonate are commercially available, including the Hakuenka series manufactured by Shiraishi Calcium.

[0056] The content of calcium carbonate in the ink composition of the present invention is preferably about 2 to 6% by mass, and more preferably about 3 to 6% by mass.

[0057] In the present invention, the total content of the silica and calcium carbonate must be 8% by mass or less relative to the total composition. By making the total content of the silica and calcium carbonate 8% by mass or less relative to the total composition, the impact resistance of the coating film obtained using the ink composition of the present invention can be made sufficient. The total content of the silica and calcium carbonate is preferably 7.5% by mass or less.

[0058] [Other Components] 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, misting during printing can be reduced.

[0059] 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.

[0060] 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.

[0061] Other components that may be added to the ink composition of the present invention include, if necessary, known curing agents; pigment dispersants; waxes; extender pigments such as silica particles, benton clay, kaolin, and talc; stabilizers, and the like.

[0062] As the curing agent, for example, an amino resin such as a melamine resin or a benzoguanamine resin can be used.

[0063] To prepare the ink composition of the present invention, the above-mentioned components are first mixed and stirred until the powder components, such as titanium oxide, silica, and calcium carbonate, are no longer powdery. As already explained, this process is called premixing, and is a process for thoroughly blending the solvent and varnish with the powder components. The mixture obtained by premixing is then milled using a roll mill, ball mill, bead mill, or the like to obtain the ink composition of the present invention. The viscosity of the ink composition is, for example, 10 to 70 Pa·s at 25°C as measured by a Raley viscometer, but is not particularly limited.

[0064] 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.

[0065] 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.

[0066] [Preparation of Alkyd Resin Varnish] 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 with 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 to prepare an alkyd resin varnish. 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.

[0067] [Preparation of Rosin-Modified Resin Varnish] 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 a rosin-modified resin varnish. 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.

[0068] [Examples 1 to 6, Comparative Examples 1 to 8] First, the components were mixed according to the formula of "Component 1" shown in Tables 1 and 2, and premixing was performed. Premixing was performed by heating the components other than the powder to about 60°C while stirring with a stirring blade, and then gradually adding the powder while continuing stirring and heating, and finishing when the powder had disappeared. The mixture obtained by premixing was kneaded in a three-roll mill, and then "Component 2" shown in Tables 1 and 2 was added and mixed well, thereby preparing the ink compositions of Examples 1 to 6 and Comparative Examples 1 to 8. In Tables 1 and 2, the "specific solvent" was tripropylene glycol monobutyl ether (sp value 9.73 (cal / cm ３ ) １／２ ), where "titanium oxide" is titanium oxide having an average primary particle diameter of 250 nm and a DBP oil absorption of 18 g / 100 g, and "silica" is Aerosil R972 (surface-hydrophobized silica, average primary particle diameter of 0.016 μm, specific surface area of ​​110±20 m) manufactured by Nippon Aerosil Co., Ltd. ２ / g), "clay" is manufactured by BYK Japan K.K. under the trade name CLAYTONE APA (Benton clay), "Calcium Carbonate 1" is manufactured by Shiraishi Calcium Co., Ltd. under the trade name Hakuenka O (rosin acid-treated calcium carbonate, average primary particle diameter 30 nm), "Calcium Carbonate 2" is manufactured by Shiraishi Calcium Co., Ltd. under the trade name Hakuenka CC (fatty acid-treated calcium carbonate, average primary particle diameter 50 nm), "Calcium Carbonate 3" is manufactured by Shiraishi Calcium Co., Ltd. under the trade name Hakuenka T-DD (rosin acid-treated calcium carbonate, average primary particle diameter 80 nm), "Calcium Carbonate 4" is manufactured by Shiraishi Calcium Co., Ltd. under the trade name Hakuenka DD (rosin acid-treated calcium carbonate, average primary particle diameter 50 nm), and "Calcium Carbonate 5" is manufactured by Shiraishi Calcium Co., Ltd. under the trade name Viscoexcel 30 (fatty acid-treated calcium carbonate, average primary particle diameter 30 nm).

[0069] [Evaluation of premixing suitability] When the ink compositions of each Example and Comparative Example were prepared according to the above procedure, the time required for premixing was measured, and the premixing suitability was evaluated based on the measurement results according to the following criteria. The evaluation results are shown in the "premixing suitability" column of Tables 1 and 2. ○: The time required for premixing was less than 10 minutes △: The time required for premixing was 10 minutes or more but less than 15 minutes ×: The time required for premixing was 15 minutes or more

[0070] [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 retort-treated product was subjected to impacts at four locations from the opposite side of the drawn 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 drawn surface was evaluated according to the following criteria. The results are shown in the "Impact resistance" column in Tables 1 and 2. ○: 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 at one or more locations where it came into contact with the impact point peeled off, exposing the aluminum substrate.

[0071]

[0072]

[0073] As shown in Tables 1 and 2, it can be seen that in Examples 1 to 6, which are the ink compositions of the present invention, all evaluation items were within practical ranges, whereas there were problems in terms of manufacturing and impact resistance in Comparative Examples 1 to 8. From the above, it was demonstrated that the ink composition of the present invention allows premixing to be completed in a shorter time, and provides a coating film with good impact resistance after printing.

Claims

1. An ink composition for metal printing comprising a color pigment, a resin, a solvent, silica, and calcium carbonate, wherein the color pigment contains titanium oxide, the content of the silica is 5% by mass or less based on the total composition, and the total content of the silica and the calcium carbonate is 8% by mass or less based on the total composition.

2. The solvent has a solubility parameter (sp value) of 10.00 (cal / cm ３ ) １／２ 2. The ink composition for metal printing according to claim 1, wherein the total amount of the ink composition is less than 100 wt %, and the ink composition 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.) 3. The ink composition for metal printing according to claim 2, wherein the divalent group represented by AO in general formula (1) is an oxypropylene group.

4. The ink composition for metal printing according to any one of claims 1 to 3, wherein the silica is surface-hydrophobized silica.

5. The ink composition for metal printing according to any one of claims 1 to 4, wherein the resin contains an alkyd resin.

6. The ink composition for metal printing according to claim 5, wherein the weight average molecular weight of said alkyd resin is less than 10,000.

7. The ink composition for metal printing according to claim 5, wherein the alkyd resin has a pentaerythritol skeleton.

8. The ink composition for metal printing according to claim 5, wherein the resin further contains a rosin-modified resin.

9. The ink composition for metal printing according to any one of claims 1 to 8, further comprising an alkanolamine.

Images