Ink composition for metal printing, method for producing same, and set of ink composition for metal printing and aqueous overprint varnish

Abstract

[Problem] To provide an ink composition for metal printing which has good transferability during printing, is capable of suppressing cissing of an aqueous overprint varnish having an organic solvent content of less than 10 mass% applied on an ink coating film even when the varnish is applied by a wet-on-wet manner in an amount of 30 mg / dm2 or less, is capable of providing good gloss after varnish application and is capable of preventing yellowing in case of a white ink. [Solution] The problem is solved by using an ink composition for metal printing, comprising a coloring pigment, a resin, bentonite and a solvent, characterized in that the content of the bentonite is 0.1-4 mass% relative to the whole composition and the proportion of an aromatic compound in the entire solvent is less than 50 mass%.

Description

Metal printing ink composition, method for manufacturing the same, and set of metal printing ink composition and aqueous overprint varnish.

[0001] This invention relates to a metal printing ink composition, a method for producing the same, and a set of the metal printing ink composition and an aqueous overprint varnish.

[0002] For printing on the metal exteriors 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, which primarily consist of a binder resin such as alkyd resin, polyester resin, or epoxy resin, and an organic solvent such as mineral oil or higher alcohol as the vehicle components.

[0003] Furthermore, these printed surfaces are generally coated with overprint varnish to improve the adhesion, bending resistance, impact resistance, and abrasion resistance of the ink film. These overprint varnishes are widely used, and are solvent-based types consisting of binder resins such as alkyd resin, polyester resin, acrylic resin, and epoxy resin, hardeners such as melamine resin and benzoguanamine resin, and organic solvents such as mineral oil and cellosolve.

[0004] For printing on the metal exterior, ink is printed using an offset printing press, dry offset printing press, etc., and then an overprint varnish is applied on top of the ink coating using a coater or similar device in a wet-on-wet manner, followed by baking at 150 to 280°C.

[0005] However, in recent years, due to concerns about air pollution caused by solvents and hygiene and safety in the printing work environment, it has become common practice in the field of metal printing to use water-based overprint varnishes instead of the solvent-based ones that were traditionally used. However, even water-based overprint varnishes are not completely solvent-free; they use hydrophilic organic solvents in combination with water. Since these hydrophilic organic solvents are generally recovered and incinerated during the heat drying process after coating, from the perspective of reducing carbon dioxide emissions, it is necessary to reduce the amount of organic solvent contained in the overprint varnish or to reduce the amount of overprint varnish applied, even if it is a water-based type. However, using overprint varnish with a reduced amount of organic solvent or reducing the amount of overprint varnish applied presents problems such as varnish repelling on the ink film and a decrease in film strength due to uneven coating.

[0006] Various improvements to ink compositions for suppressing the repulsion of water-based overprint varnish on ink coatings have been proposed, for example, in Patent Documents 1 to 4. However, in the test examples of the ink compositions proposed in these documents, the varnish coating amount was at a normal level of 50 to 60 mg / dm³. ２ The range of the composition was unclear, or the amount of organic solvent used in the varnish composition was unknown.

[0007] Furthermore, in response to the recent demand for increased productivity, ink compositions are required to have printability suitable for high-speed printing, that is, to possess good transferability even during high-speed printing. However, no ink composition is known that can achieve both this high-speed printability and the suppression of repelling of water-based overprint varnishes with low organic solvent content.

[0008] For example, Patent Document 5 proposes an ink composition that can effectively suppress repelling even when using an aqueous overprint varnish. However, Patent Document 5 does not mention the solvent content in the aqueous overprint varnish, nor does it describe high-speed printability, which is an important quality in the practical operation of can printing, as mentioned above. Furthermore, with the formulation of the ink composition described in Patent Document 5, gloss tended to decrease when an aqueous overprint varnish with a very low solvent content of less than 10% by mass was applied. In addition, when a white ink composition was prepared with this formulation, there was a problem that the white parts tended to yellow during heat drying.

[0009] JP-A-2009-249435 JP-A-6-25583 Patent No. 7353551 Patent No. 7368674 Patent No. 6848120

[0010] The present invention has been made in view of the above circumstances, and provides an aqueous overprint varnish that has good transferability during printing and has an organic solvent content of less than 10% by mass, applied at a coating rate of 30 mg / dm ２ The objective of this invention is to provide a metal printing ink composition that can suppress varnish repellency on the ink film even when wet-on-wet coating is performed, provides good gloss after varnish coating, and suppresses yellowing when used as a white ink. ２ ) is the unit area (1 dm²) ２ This refers to the solid mass (i.e., the mass after drying) of the overprint varnish applied per unit area.

[0011] A low amount of organic solvent in a water-based overprint varnish means a higher amount of water. A higher water content in a water-based overprint varnish leads to a higher surface tension, which makes it more prone to repelling and uneven coating when applied wet-on-wet on an ink film. On the other hand, considering the amount of water-based overprint varnish applied, the more varnish applied in a wet-on-wet application, the less repelling and uneven coating occurs. Therefore, reducing the amount of organic solvent in a water-based overprint varnish and reducing the application amount are extremely challenging conditions that easily lead to repelling and uneven coating. To overcome these challenging conditions, the inventors reviewed the formulation of the ink composition that serves as the base for the water-based overprint varnish and found that adding 0.1 to 4% by mass of bentonite to the total ink composition and keeping the proportion of aromatic compounds in the total solvent content of the ink composition to less than 50% by mass is sufficient. By using such an ink composition, a water-based overprint varnish with an organic solvent content of less than 10% by mass can be applied at a coating rate of 30 mg / dm ２ When wet-on-wet coating is performed as described below, not only is varnish repellency on the ink film suppressed, but good transferability during printing and good gloss after varnish coating are obtained, and furthermore, yellowing is suppressed when white ink is used. The present invention is based on these findings and provides the following.

[0012] (1) The present invention relates to a metal printing ink composition comprising a coloring pigment, a resin, bentonite, and a solvent, characterized in that the bentonite content is 0.1 to 4% by mass of the whole composition, and the proportion of aromatic compounds in the whole solvent is less than 50% by mass.

[0013] (2) The present invention also relates to the metal printing ink composition described in item (1), which comprises at least one selected from the group consisting of compounds represented by the following general formula (1) as the solvent. (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, or a hydrogen atom, and n is an integer of 2 to 25.)

[0014] (3) Further, the present invention is an ink composition for metal printing according to item (1) or (2), which contains a rosin-modified resin having a hydroxyl value of 10 to 100 mgKOH / g as at least a part of the above resin.

[0015] (4) Further, the present invention is an ink composition for metal printing according to item (2), wherein the solubility parameter (sp value) of the above compound is less than 10.50 (cal / cm ３ ) １／２ (5) Further, the present invention is an ink composition for metal printing according to any one of items (1) to (4), which contains an alkyd resin as at least a part of the above resin.

[0016] (6) Further, the present invention is an ink composition for metal printing according to item (3), wherein the above rosin-modified resin is a rosin ester resin.

[0017] (7) Further, the present invention is an ink composition for metal printing according to item (5), wherein the mass average molecular weight of the above alkyd resin is less than 10,000.

[0018] (8) Further, the present invention is an ink composition for metal printing according to item (5) or (7), wherein the fatty acid modification amount of the above alkyd resin is 25 to 50% by mass.

[0019] (9) The present invention is also a method for producing an ink composition for metal printing according to any one of items (1) to (8), characterized in that bentonite is used as one of the components constituting the composition, and the composition is prepared such that the proportion of aromatic compounds in the total solvent contained in the composition is less than 50% by mass.

[0020]

[0021] (10) The present invention is also a set of a metal printing ink composition and an aqueous overprint varnish, wherein the metal printing ink composition is the ink composition described in any one of items (1) to (8), and the content of the organic solvent contained in the aqueous overprint varnish is less than 10% by mass of the total aqueous overprint varnish.

[0022] According to the present invention, an aqueous overprint varnish having good transferability during printing and containing less than 10% by mass of organic solvents can be applied at a coating rate of 30 mg / dm ２ The present invention provides a metal printing ink composition that can suppress varnish repellency on the ink film even when applied using the wet-on-wet method, provides good gloss after varnish application, and suppresses yellowing when used as a white ink.

[0023] The following describes one embodiment of the metal printing ink composition of the present invention, another embodiment of the metal printing ink composition, another embodiment of a set of the metal printing ink composition and aqueous overprint varnish, and another embodiment of a method for manufacturing printed materials. The aqueous overprint varnish, as described above, is an overprint varnish containing a combination of a hydrophilic organic solvent and water as a solvent. In this specification, overprint varnish will be appropriately abbreviated as OP varnish.

[0024] <Metal Ink Composition for Metal Printing> First, an embodiment of the metal ink composition of the present invention will be described. In this specification, the metal ink composition will be referred to as "ink composition" for convenience. The ink composition of the present invention is for metal printing and is preferably applicable to printing using a so-called dry offset printing method using a relief plate as a printing plate or an offset printing method using a flat plate as a printing plate, but can be applied to all printing methods commonly used in metal printing. Further, the ink composition of the present invention has high-speed printing suitability and can suppress repelling and coating unevenness of an aqueous OP varnish coated wet-on-wet immediately after printing with the ink composition. Therefore, it is preferably applicable not only to two-piece can printing in which such printing and coating methods are adopted, but also to three-piece can printing. In particular, in the ink composition of the present invention, when an aqueous OP varnish having an organic solvent content of less than 10% by mass is applied at a coating amount of 30 mg / dm ２ Even when coated below, the suppression of repelling and coating unevenness is a great advantage. Thereby, the amount of carbon dioxide released derived from the organic solvent contained in the aqueous OP varnish can be greatly reduced during printing. Further, according to the ink composition of the present invention, good gloss after coating with the aqueous OP varnish can be obtained, and furthermore, yellowing when used as white ink is suppressed.

[0025] The ink composition of the present invention is an ink composition containing a coloring pigment, a resin, bentonite, and a solvent, wherein the content of the bentonite is 0.1 to 4% by mass with respect to the whole composition, and the ratio of the aromatic compound in the whole solvent is less than 50% by mass. Hereinafter, each component will be described.

[0026] [Resin] As the resin used in the ink composition of the present invention, those that have been used in ink compositions for metal printing so far can be listed without particular limitation. Among such resins, alkyd resins and rosin-modified resins are preferably used in the ink composition of the present invention. Next, these resins will be described.

[0027] Alkyd resins are condensation polymers of polyhydric alcohols and polybasic acids, and are a type of polyester. However, by carrying out condensation polymerization with vegetable oils and / or fatty acids in addition to these, fatty acid-modified types can be synthesized. That is, by including a monobasic acid, such as a fatty acid, when forming the condensation polymer, the fatty acid is incorporated into the structure of the alkyd resin, and a fatty acid-modified alkyd resin is synthesized. Also, by including vegetable oil when forming the condensation polymer, it undergoes transesterification with the polyhydric alcohol to become a fatty acid, which is then incorporated into the structure of the alkyd resin as a fatty acid, resulting in the synthesis of a fatty acid-modified alkyd resin. The proportion of the alkyd resin derived from fatty acids is called the fatty acid modification amount. In the present invention, the fatty acid modification amount of the alkyd resin is preferably about 25 to 50% by mass. A fatty acid modification amount of 25% by mass or more is preferable because it allows for good transferability of the ink composition during printing. Furthermore, a fatty acid modification amount of 50% by mass or less is preferable because it suppresses repelling and uneven coating when a water-based OP varnish with a low organic solvent content is applied wet-on-wet to the ink film surface with a small coating amount, and also reduces misting during printing. More preferably, the fatty acid modification amount of the alkyd resin is 25 to 45% by mass.

[0028] Fatty acids are obtained by hydrolyzing natural oils and fats such as vegetable oils and animal oils, and since they have one carboxyl group, they can form esters with polyhydric alcohols as described below. Examples of fatty acids include those from linseed oil, tuni oil, safflower oil, soybean oil, tall oil, rice bran oil, palm oil, castor oil, dehydrated castor oil, sunflower oil, coconut oil, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, eleostearic acid, and 12-hydroxystearic acid, among which coconut oil fatty acids are preferred. These fatty acids can be used individually or in combination of two or more. In addition, the vegetable oils mentioned above can be used together with or in place of fatty acids.

[0029] Polybasic acids are compounds having multiple carboxyl groups and are components used for condensation polymerization with polyhydric alcohols, as described later, to increase their 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-cyclohexendicarboxylic acid, 1,4-cyclohexendicarboxylic 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, methylhymic anhydride, tetrachlorophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, trimellitic anhydride, and methylcyclohexendicarboxylic acid anhydride. Among these, isophthalic acid, phthalic acid, phthalic anhydride, trimellitic anhydride, and others are preferred. These polybasic acids can be used individually or in combination of two or more.

[0030] Polyhydric alcohols form esters with the fatty acids and polybasic acids mentioned above, thereby increasing the molecular weight of these components. Polyhydric alcohols can be any compound that has been used in the synthesis of alkyd resins, and examples include compounds having two or more hydroxyl groups.

[0031] Examples of such compounds include pentaerythritol, trimethylolpropane, glycerin, ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, 1,3-butanediol, neopentyl glycol, spiroglycol, dioxane glycol, adamantanediol, 3-methyl-1,5-pentanediol, methyloctanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol. Examples include pandiols, octylene glycol, 9-nonanediol, 2,4-diethyl-1,5-pentanediol, ethylene oxide-modified compounds of difunctional phenols such as bisphenol A, propylene oxide-modified compounds of difunctional 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 diols, adamantanediol, polyether diols, polyester diols, and polycaprolactone diols. These can be used individually or in combination of two or more.

[0032] To prepare alkyd resins, one method involves adding a small amount of solvent such as xylene to a reaction vessel containing polybasic acids, polyhydric alcohols, fatty acids, and / or vegetable oils, while introducing an inert gas such as nitrogen gas. The mixture is then heated, and condensation polymerization is carried out while removing the water by azeotropic reaction with the condensed water. Alternatively, this condensation polymerization reaction can be used as the first step, and in the second step, condensation polymerization can be carried out using a polybasic acid with three or more functions, such as trimellitic acid, to obtain an alkyd resin that provides a tough, hardened film with a high degree of crosslinking. The reaction temperature can be around 170 to 250°C, and the reaction time can be around 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 progresses. That is, the reaction should be considered complete when the decrease in the acid value of the reaction mixture due to condensation polymerization stops. The condensation polymerization reaction can be carried out in a shorter time by distilling off the water produced by condensation polymerization or by using a reaction catalyst. Examples of reaction catalysts include tetrabutylzirconate, monobutyltin oxide, zirconium naphthate, and tetrabutyl titanate.

[0033] The mass-average molecular weight of the alkyd resin is preferably less than 10,000. Having a mass-average molecular weight of less than 10,000 improves the transferability of the ink composition during printing and the impact resistance of the printed film after retort processing.

[0034] The alkyd resin content in the ink composition is preferably 20 to 70% by mass of the total composition, and more preferably 25 to 65% by mass of the total composition. The alkyd resin may also be used in the form of a varnish after being dissolved in a solvent as described later.

[0035] 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, palastic acid, isopimal acid, and levopimal acid. These resin acids contain hydrophilic and chemically active carboxyl groups, and some also possess conjugated double bonds. Therefore, various rosin-modified resins are prepared by combining polyhydric alcohols and polybasic acids for condensation polymerization, by adding resol, a phenol condensate, to the benzene ring contained in the rosin skeleton, or by performing a Diels-Alder reaction with dienophiles such as maleic anhydride or maleic acid to add a maleic acid or maleic anhydride skeleton. Various types of such rosin-modified resins are commercially available and can be obtained and used. By using a rosin-modified resin in the ink composition of the present invention, it is possible to suppress the occurrence of misting during printing and to increase the biomass content in the ink composition without impairing various required performance characteristics.

[0036] Examples of rosin-modified resins include rosin ester resins, maleated rosin resins, 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 these rosin-modified resins may be used, but among these, rosin ester resins and maleated rosin resins are preferred, and among rosin ester resins, disproportionated rosin and hydrogenated rosin ester resins are preferred.

[0037] Furthermore, it is preferable to use a rosin-modified resin with a hydroxyl value of approximately 10 to 100 mg KOH / g. By including such a high hydroxyl value rosin-modified resin 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 water-based OP varnish, which is also highly polar, increases, resulting in the effect of suppressing repellency and uneven coating even when applied wet-on-wet. The hydroxyl value of the rosin-modified resin is more preferably 15 mg KOH / g or more, and even more preferably 20 mg KOH / g or more.

[0038] Furthermore, although not particularly limited, the acid value of the rosin-modified resin is preferably 100 mg KOH / g or less. Having an acid value of 100 mg KOH / g or less of the rosin-modified resin is preferable because it allows for both suppression of repelling and uneven coating when water-based OP varnish is applied wet-on-wet, and suppression of printability such as misting and poking. More preferably, the acid value of the rosin-modified resin is 80 mg KOH / g or less, and even more preferably 50 mg KOH / g or less.

[0039] The rosin-modified resin is used in a varnish state, which is dissolved or dispersed by heating with a solvent as described later. The rosin-modified resin may be used as a dissolved varnish, which 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 the varnish may be used in a gelled varnish state. 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, as this improves the transferability of the ink composition during printing. Furthermore, by preparing a gelled varnish from the rosin-modified resin and using it in the preparation of the ink composition, appropriate viscoelasticity is imparted to the ink composition, improving fluidity and reducing misting, as well as forming a tougher cured film.

[0040] The content of rosin-modified resin in the ink composition is preferably 1 to 20% by mass relative to the total composition, more preferably 1 to 15% by mass relative to the total composition, and even more preferably 2 to 10% by mass relative to the total composition.

[0041] Furthermore, in addition to the alkyd resin and rosin-modified resin mentioned above, the ink composition of the present invention may also use resins that have been used to date in the preparation of metal printing ink compositions, as described above. That is, known resins can be used individually or in combination of two or more, depending on the required performance such as printability and coating film properties. Examples of such resins include polyester resins, petroleum resins, epoxy resins, ketone resins, amino resins, and benzoguanamine resins.

[0042] [Bentonite] The ink composition of the present invention contains bentonite. Bentonite is a clay whose main component is montmorillonite, a clay mineral, and various types are commercially available. According to the inventors' studies, adding bentonite to a metal printing ink composition improves the transferability of the ink composition during printing, resulting in good high-speed printing suitability.

[0043] The bentonite content in the ink composition is 0.1 to 4% by mass relative to the total composition. A content of 0.1% by mass or more effectively suppresses yellowing when used as a white ink while a content of 4% by mass or less suppresses the reduction in gloss and the occurrence of yellowing when used as a white ink that can result from excessive bentonite addition. Preferably, the bentonite content in the ink composition is 0.4 to 3.6% by mass, and more preferably 1 to 3.0% by mass, relative to the total composition.

[0044] [Solvent] The ink composition of the present invention contains a solvent, and the proportion of aromatic compounds in the total solvent contained in the ink composition is less than 50% by mass. That is, of the solvent contained in the ink composition of the present invention, 50% or more by mass is a non-aromatic solvent. Conventional ink compositions for metal printing have often used aromatic solvents such as linear alkylbenzene, but according to the inventors' studies, ink compositions that use a large amount of such aromatic solvents tend to cause a decrease in transferability during high-speed printing and a decrease in gloss when water-based OP varnish is applied wet-on-wet. Therefore, in the ink composition of the present invention, the proportion of aromatic compounds in the total solvent contained in the ink composition is less than 50% by mass. The proportion of aromatic compounds in the total solvent contained in the ink composition is preferably 30% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and most preferably 0.

[0045] The solvent used in the ink composition of the present invention is, as described above, any solvent that has been used in the field of ink compositions for metal printing, provided that the proportion of aromatic compounds in the total solvent contained in the ink composition is less than 50% by mass. Examples of such solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, alkylbenzenes, and polyalkylene glycols, all of which have a boiling point range of approximately 230 to 400°C. Among these, the ink composition of the present invention has a solubility parameter (sp value) of 10.50 (cal / cm³). ３ ) １／２ Preferably, at least one compound selected from the group consisting of compounds represented by the following general formula (1) that are less than 10.50 (cal / cm³). ３ ) １／２ A solvent that is less than 9.80 (cal / cm³) and selected from the group consisting of compounds represented by the following general formula (1) is also called a specific solvent. ３ ) １／２ The following are preferable. Furthermore, the lower limit of the sp value for a specific solvent is 8.50 (cal / cm³). ３) １／２ A preferred degree is 9.00 (cal / cm³). ３ ) １／２ A more preferable degree can be cited. Such specific solvents with sp values ​​can also be described as polyalkylene glycol monoalkyl ethers or polyalkylene glycols possessing hydrophobic properties.

[0046]

[0047] In the above general formula (1), each A is independently a branched alkylene group having 2 to 4 carbon atoms. Examples of such alkylene groups include the ethylene group [-(CH4)]. 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 Examples include -]. Among these, the propylene group is preferred. In this case, the divalent group represented by AO in general formula (1) is the oxypropylene group.

[0048] In the above general formula (1), R is a C1-C13 alkyl group which may have a branched and / or cyclic structure, or a hydrogen atom. This alkyl group may be an aliphatic group or an alicyclic group. Examples of such alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, hexyl, 2-ethylhexyl, octyl, decyl, and cyclohexyl groups. When R is an alkyl group, the compound represented by general formula (1) is a polyalkylene glycol monoalkyl ether, and when R is a hydrogen atom, the compound represented by general formula (1) is a polyalkylene glycol.

[0049] In the above general formula (1), n ​​is an integer between 2 and 25. When n is 2 or greater, it is preferable to ensure a sufficient boiling point for the specific solvent to provide stability to the ink composition on the printing press, and when n is 25 or less, a suitable viscosity for the solvent in the ink composition can be achieved.

[0050] Examples of compounds 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, polypropylene glycol monobutyl ether, and polypropylene glycol.

[0051] In the present invention, the sp value used is calculated using the Fedros method (see reference: R.F. Fedros, Polym. Eng. Sci., 14(2) 147 (1974)).

[0052] The solvent content in the ink composition of the present invention is preferably 10 to 50% by mass of the total composition, and more preferably 20 to 45% by mass of the total composition. Furthermore, it is preferable that the content of a specific solvent within the solvent is 15 to 40% by mass of the total composition, and preferably that all of the solvent in the composition is the specific solvent. The inclusion of such a specific solvent in the ink composition of the present invention is preferable because it reduces misting during printing.

[0053] [Coloring Pigments] Coloring pigments are components that impart coloring power to the ink composition. Examples of coloring pigments include organic and / or inorganic pigments that have been conventionally used in printing ink compositions, without any particular limitations. Needless to say, in this invention, white pigments used to give whiteness to the ink composition are also treated as coloring pigments.

[0054] Examples of such coloring pigments include Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 24, 32, 34, 35, 36, 37, 41, 42, 43, 49, 53, 55, 60, 61, 62, 63, 65, 73, 74, 75, 77, 81, 83, 87, 93, 94, 95, 97, 98, 99, 100, 101, 104, 105, 106, 108, 109, 110, 111, 113, 114, 116, 117, 119, 120, 123, 124, 126, 127, 128, 129, 130, 133, 138, 139, 150, 151, 152, 153, 154, 155, 165, 167, 168, 169, 170, 172, 173, 174, 175, 176, 179, 180, 181, 182, 183, 184, 185, 191, 193, 194, 199, 205, 206, 209, 212, 213, 214, 215, 219; Pigment Orange 1, 2, 3, 4, 5, 13, 15, 16, 17, 19, 20, 21, 24, 31, 34, 36, 38, 40, 43, 46, 48, 49, 51, 60, 61, 62, 64, 65, 66, 67, 68, 69, 71 ,72,73,74,81; Pigment Red 1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,17,18,21,22,23,31,32,38,41,48,48:1,48:2,48:3,48:4,48:5,49,52,52:1,52:2,53:1,54,57:1,58,60:1,63,64:1,68,81:1,83,88,89,95,101,104,105,108,112,114,119,122,123,136,144,146,147,149,150,164,166,1 68, 169, 170, 171, 172, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 187, 188, 190, 193, 194, 200, 202, 206, 207, 208, 209, 210, 211, 213, 214, 216, 220, 220, 221, 224, 226, 237, 238, 239, 242, 245, 247, 248, 251, 253, 254, 255, 256, 257, 258, 260, 262, 263, 264, 266, 268, 269, 270, 271, 272, 279;Pigment Violet 1, 2, 3, 3:1, 3:3, 5:1, 13, 15, 16, 17, 19, 23, 25, 27, 29, 31, 32, 36, 37, 38, 42, 50; Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:5, 15:6, 16, 17:1, 24, 24:1, 25, 26, 27, 28, 29, 36, 56, 60, 61, 62, 63, 75, 79, 80; Pigment Examples of pigments include: Green 1, 4, 7, 8, 10, 15, 17, 26, 36, 50; Pigment Brown 5, 6, 23, 24, 25, 32, 41, 42; Pigment Black 1, 6, 7, 9, 10, 11, 20, 26, 28, 31, 32, 34; Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28, etc., as well as glass flakes, pearl pigments, hollow particles, etc. Of the above, glass flakes, pearl pigments, and hollow particles may not generally be treated as coloring pigments, but in this invention, pigments that produce some kind of optical effect are also treated as coloring pigments. Among these, from the perspective of color reproducibility, coating strength, and printability, the following are recommended: Pigment Yellow 13, Pigment Yellow 17, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 139, Pigment Yellow 180, Pigment Yellow 185, Pigment Orange 13, Pigment Orange 16, Pigment Orange 43, Pigment Orange 64, Pigment Red 48:1, Pigment Red 48:2, Pigment Red Preferred pigments include 48:3, Pigment Red 48:4, Pigment Red 53:1, Pigment Red 122, Pigment Red 166, Pigment Red 185, Pigment Red 254, Pigment Red 264, Pigment Violet 23, Pigment Violet 32, Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 15:6, Pigment Green 7, Pigment Black 7, Pigment White 6, etc. Furthermore, in this invention, metal powder pigments used to impart metallic colors such as gold and silver to the ink composition are also treated as coloring pigments. Examples of such metal powder pigments include aluminum flakes, gold powder, bronze powder, and aluminum paste obtained by processing aluminum powder into a paste.

[0055] The amount of coloring pigment added is typically 5 to 50% by mass of the total ink composition, but is not particularly limited. When preparing a yellow ink composition using yellow pigment, a magenta ink composition using magenta pigment, a cyan ink composition using cyan pigment, or a black ink composition using black pigment, it is also possible to use other colored pigments or add other colored ink compositions as complementary colors.

[0056] [Other Components] The ink composition of the present invention may optionally contain other components such as alkanolamines, known curing agents, pigment dispersants, waxes, silica particles, stabilizers, etc.

[0057] By using alkanolamines, the occurrence of misting during printing can be reduced. Examples of alkanolamines include triethanolamine, dibutylethanolamine, methyldiethanolamine, methylethanolamine, and ethyldiethanolamine. When using alkanolamines, their content in the total ink composition is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and even more preferably 0.1 to 1.5% by mass.

[0058] For example, amino resins such as melamine resin and benzoguanamine resin can be used as curing agents.

[0059] Silica particles are SiO ２ These are commercially available as powders, and are readily available in various forms, including those that are untreated, hydrophilic (after hydrophilic treatment), or hydrophobic (after hydrophobic treatment). The silica particle content in the ink composition is preferably 1 to 8% by mass, and more preferably 2 to 5% by mass.

[0060] The ink composition of the present invention can be prepared by conventional methods using a roll mill, ball mill, bead mill, etc., by mixing components such as a coloring pigment, a resin, and a solvent containing a specific solvent. The viscosity of the ink composition can be exemplified by a value of 10 to 70 Pa·s at 25°C measured with a Raleigh viscometer, but is not particularly limited.

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

[0062] Furthermore, as the aqueous OP varnish applied on top of the printed ink composition, commonly used varnishes can be used. Specifically, examples include those using aqueous acrylic resin, aqueous polyester resin, aqueous alkyd resin, aqueous epoxy resin, or two or more modified resins thereof as a binder, with an amino resin used as a curing agent. As previously mentioned, by using the ink composition of the present invention, even when using an aqueous OP varnish with an organic solvent content of less than 10% by mass, it is possible to suppress the repulsion and uneven application of the OP varnish during wet-on-wet application. In other words, the ink composition of the present invention can also be preferably used as a base coat for applying an aqueous OP varnish with an organic solvent content of less than 10% by mass.

[0063] When printing on a metal surface using the ink composition and water-based OP varnish, first, print using the ink composition of the present invention with a dry offset printing press or offset printing press, and while the ink composition is still wet (wet on wet), overcoat with water-based OP varnish using a coater or the like, and then bake at 150 to 280°C for several seconds to several minutes.

[0064] <Method for Manufacturing Metal Printing Ink Composition> Another aspect of the present invention is that the composition is prepared using bentonite as one of its constituent components, and the proportion of aromatic compounds in the total solvent contained in the composition is less than 50% by mass. As this has already been explained, the explanation will be omitted here.

[0065] <Set of Metal Printing Ink Composition and Water-Based Overprint Varnish> The set of the metal printing ink composition and water-based overprint varnish (water-based OP varnish) described above is also part of the present invention. The water-based OP varnish referred to here contains a solvent that is a combination of a hydrophilic organic solvent and water, and the organic solvent content is less than 10% by mass of the total water-based OP varnish. The metal printing ink composition included in this set has already been described, so its description will be omitted here.

[0066] As described above, the ink composition of the present invention suppresses the repulsion and uneven coating of the aqueous OP varnish when an aqueous OP varnish with an organic solvent content of less than 10% by mass is applied wet-on-wet after printing. For this reason, the ink composition of the present invention can preferably be used in combination with an aqueous OP varnish with an organic solvent content of less than 10% by mass. The present invention focuses on this point.

[0067] The water-based OP varnish included in the set can be any type, as long as it contains less than 10% by mass of organic solvent and is used as a coating on the surface of the metal printing ink composition after printing. Since various types of such water-based OP varnishes are commercially available, such commercially available products can be obtained and used in sets with the ink composition of the present invention.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0069] [Preparation of Alkyd Resin Varnish 1] 14.7 parts by mass of trimethylolpropane, 10 parts by mass of coconut oil fatty acid, and 15 parts by mass of isophthalic acid 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 esterification step. Then, 0.82 parts by mass of trimellitic anhydride were added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second esterification step. These esterification reactions were carried out according to conventional methods to obtain alkyd resin 1 with a mass-average molecular weight of 8,785. To this alkyd resin 1, 10 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 1. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm²). ３ ) １／２ This corresponds to the specific solvent in the present invention. Furthermore, the amount of fatty acid modification in the synthesized alkyd resin 1 is 27.7% by mass.

[0070] [Preparation of Alkyd Resin Varnish 2] 14.7 parts by mass of trimethylolpropane, 15.5 parts by mass of coconut oil fatty acid, and 12.9 parts by mass of isophthalic acid 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 esterification step. Then, 0.91 parts by mass of trimellitic anhydride was added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second esterification step. These esterification reactions were carried out according to conventional methods to obtain alkyd resin 2 with a mass-average molecular weight of 4,706. To this alkyd resin 2, 10 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 / cm²). ３ ) １／２ This corresponds to the specific solvent in the present invention. Furthermore, the amount of fatty acid modification in the synthesized alkyd resin 2 is 39.1% by mass.

[0071] [Preparation of Alkyd Resin Varnish 3] 14.7 parts by mass of trimethylolpropane, 18.5 parts by mass of coconut oil fatty acid, and 11.7 parts by mass of isophthalic acid 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 esterification step. Then, 0.95 parts by mass of trimellitic anhydride were added and heated at 165°C for 30 minutes under a nitrogen atmosphere to perform the second esterification step. These esterification reactions were carried out according to conventional methods to obtain alkyd resin 3 with a mass-average molecular weight of 3,477. To this alkyd resin 3, 10 parts by mass of tripropylene glycol monobutyl ether was added to obtain alkyd resin varnish 3. The sp value of this tripropylene glycol monobutyl ether is 9.73 (cal / cm²). ３ ) １／２ This corresponds to the specific solvent in the present invention. Furthermore, the amount of fatty acid modification in the synthesized alkyd resin 3 is 44.6% by mass.

[0072] [Preparation of Alkyd Resin Varnish 4] Alkyd resin varnish 4 was prepared using the same procedure as for the preparation of alkyd resin varnish 1, except that a commercially available linear alkylbenzene was used instead of tripropylene glycol monobutyl ether. The solvent contained in this alkyd resin varnish is an aromatic solvent.

[0073] [Preparation of Rosin-Modified Resin Varnish 1] 63.2 parts by mass of 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 obtain rosin-modified resin varnish 1. The tripropylene glycol monobutyl ether had an sp value of 9.73 (cal / cm³). ３ ) １／２ Therefore, it corresponds to the specific solvent in the present invention.

[0074] [Preparation of Rosin-Modified Resin Varnish 2] 63.2 parts by mass of rosin ester resin (hydroxyl value 40-50 mg KOH / g, acid value 10-20 mg KOH / g, mass-average molecular weight 744, number-average molecular weight 701) and 35.9 parts by mass of tripropylene glycol monobutyl ether were heated at 130°C for 1 hour to dissolve them and obtain rosin-modified resin varnish 2. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm³). ３ ) １／２ Therefore, it corresponds to the specific solvent in the present invention.

[0075] [Preparation of Rosin-Modified Resin Varnish 3] 63.2 parts by mass of maleated rosin resin (hydroxyl value ≈ 0 mg KOH / g, acid value 220 ≤ mg KOH / g, mass-average molecular weight 877, number-average molecular weight 766) and 35.9 parts by mass of tripropylene glycol monobutyl ether were heated at 130°C for 1 hour to dissolve them and obtain rosin-modified resin varnish 3. The sp value of this tripropylene glycol monobutyl ether was 9.73 (cal / cm³). ３ ) １／２ Therefore, it corresponds to the specific solvent in the present invention.

[0076] [Preparation of Rosin-Modified Resin Varnish 4] Rosin-modified resin varnish 4 was prepared using the same procedure as for rosin-modified resin varnish 1, except that a commercially available linear alkylbenzene was used instead of tripropylene glycol monobutyl ether. The solvent contained in this rosin-modified resin varnish is an aromatic solvent.

[0077] [Water-based OP varnish for testing] Water-based OP varnish A was made from PPG iSENSE® series water-based OP varnish (organic solvent content less than 10% by mass) manufactured by PPG, and water-based OP varnish B was made from PPG iSENSE® series water-based OP varnish (organic solvent content 15% by mass or more and 20% by mass or less) manufactured by PPG.

[0078] [Preparation of Ink Composition] The ink compositions of the examples and comparative examples were prepared according to the formulations described in Tables 1 to 3. The numerical values ​​for each component listed in Tables 1 to 3 are in parts by mass. When preparing the ink composition, each component was mixed and then kneaded in a roll mill heated to 40°C. In Tables 1 to 3, "carbon black" is acidic carbon black with an average primary particle size of 24 nm and a DBP oil absorption of 66 mL / 100 g, "titanium dioxide" is titanium dioxide with an average primary particle size of 250 nm and a DBP oil absorption of 18 g / 100 g, "bentonite" is product name CLAYTONE APA (Benton Clay) manufactured by BIC Chemie Japan Co., Ltd., and "specific solvent 1" is tripropylene glycol monobutyl ether (sp value 9.73 (cal / cm³) ３ ) １／２ ) and "Specific Solvent 2" is polypropylene glycol monobutyl ether (BuO-(PO) ｎ -H; sp value 8.90 (cal / cm³) ３ ) １／２ ) (the average value of n is 20), and "Specific Solvent 3" is polypropylene glycol with a number average molecular weight of 400 (sp value 10.3 (cal / cm³) ３ ) １／２ ) and “non-specified solvent” is linear alkylbenzene (aromatic solvent). In addition, in Tables 1 to 3, the percentage values ​​written in parentheses after the names of alkyd resin varnishes 1 to 4, along with the word “fat”, represent the amount of fatty acid modification of the alkyd resin contained in each alkyd resin varnish (mass%), “bentonite content (mass%)” is the amount of bentonite in the total ink composition, and “aromatic solvent content (mass%)” is the proportion of aromatic compounds in the total solvent contained in the ink composition.

[0079] [Transferability Evaluation] For each example and comparative example ink composition, 0.1 cc of the ink composition was applied to a 50 μm thick aluminum substrate using a high-speed color spreader "PM-900PT" (manufactured by Mitsui Electric Seiki Co., Ltd.) at a printing pressure of 90 kgf and a spreading speed of 9 m / s. The resulting applied samples were evaluated according to the following criteria. The evaluation results are shown in the "Transferability" column of Tables 1 to 3. For ease of comparison, the results of this transferability evaluation are also transcribed in the "Transferability" column of Tables 4 and 5. ○: No streaking observed at all △: Streaking observed in less than 50% of the transfer area, but within the range of practical use ×: Streaking observed in 50% or more of the transfer area, poor quality

[0080]

[0081]

[0082]

[0083] [Evaluation of water-based OP varnish repellency] Using the ink compositions and water-based OP varnish combinations described in Tables 4 and 5, the water-based OP varnish was applied at a rate of 25 mg / dm² to the ink composition coating film applied to a metal piece. ２ The surface was coated using a wet-on-wet method, and the presence or absence of repelling or penetration of the applied water-based OP varnish was visually inspected and evaluated. The evaluation criteria were as follows, and the results are shown in the "Repelling Evaluation" column of Tables 4 and 5. The amount of water-based OP varnish applied in this evaluation was 25 mg / dm². ２ The current application rate of water-based OP varnish for two-piece cans, etc., is 50-60 mg / dm ２This is a significantly smaller amount compared to the above, and can be said to be a harsh condition that is likely to cause water-based OP varnish to repel or penetrate. Also, in the "Ink Composition" column of Tables 4 and 5, notations such as "Actual 1" represent "Example 1", notations such as "Ratio 1" represent "Comparative Example 1", and the values ​​shown in the "Organic Solvent Amount" column represent the amount of organic solvent (mass%) contained in the water-based OP varnish used. Furthermore, the items shown as "Reference" in the "Test Number" column of Table 4 use water-based OP varnish B, which is currently widely used and contains a large amount of organic solvent, and serve as a provisional performance target. ○: No repelling is observed at all, and gloss is good △: Almost no repelling is observed, but gloss is slightly reduced ×: Tendency to repel or penetrate of OP varnish is observed

[0084] [Gloss Evaluation] Using the ink compositions described in Tables 4 and 5 and the water-based OP varnish, the water-based OP varnish was applied at a rate of 25 mg / dm² to the ink composition coating film applied to a metal piece. ２ The material was coated using a wet-on-wet method and baked at 200°C for 2 minutes. The gloss of the colored surface of the resulting metal piece was measured using a gloss meter "TMS-724" (manufactured by Ichinen TASCO Corporation). The evaluation criteria were as follows, and the results are shown in the "Gloss" column of Tables 4 and 5. ○: Gloss value of 90 or higher, good quality △: Gloss value of 80 or higher but less than 90, but at a practical level ×: Gloss value of less than 80, poor quality

[0085] [Yellowing Evaluation] For each of the white ink compositions in Examples 10-12 and Comparative Examples 4-5, the combination of the ink composition and aqueous OP varnish described in Table 5 was applied to a metal piece, and the aqueous OP varnish was applied at a rate of 25 mg / dm². ２ The coating was applied using a wet-on-wet method and held in a 200°C oven for 15 minutes. Afterwards, the presence or absence of yellowing of the white ink coating was visually checked. The evaluation criteria were as follows, and the results are shown in the "Yellowing Evaluation" column of Table 5. Note that this test was conducted only on white ink compositions and not on black ink compositions (test numbers 1-9, 13-15). ○: No yellowing observed ×: Yellowing observed

[0086]

[0087]

[0088] As shown in Tables 4 and 5, the ink compositions of the present invention (test numbers 1 to 12) showed good results in all aspects of the evaluation of ink repellency, gloss, and yellowing. On the other hand, the comparative ink compositions (test numbers 13 to 17) showed poor results in at least one of these evaluations, resulting in practical problems. Furthermore, as shown in the test number "Reference" using the ink composition of Comparative Example 1, it can be seen that even with conventional ink compositions, varnish repellency is suppressed if an aqueous OP varnish containing 10% by mass or more of an organic solvent is used.

Claims

1. A metal printing ink composition comprising a coloring pigment, a resin, bentonite, and a solvent, characterized in that the bentonite content is 0.1 to 4% by mass of the whole composition, and the proportion of aromatic compounds in the whole solvent is less than 50% by mass.

2. The metal printing ink composition according to claim 1, comprising, as the solvent, at least one selected from the group consisting of compounds represented by the following general formula (1). (In the above general formula (1), each A is independently a C2-C4 alkylene group which may have branching, R is a C1-C13 alkyl group which may have branching and / or a cyclic structure, or a hydrogen atom, and n is an integer from 2 to 25.) 3. The metal printing ink composition according to claim 1 or 2, comprising, as at least a portion of the resin, a rosin-modified resin having a hydroxyl value of 10 to 100 mg KOH / g.

4. The solubility parameter (sp value) of the compound is 10.50 (cal / cm³). ３ ) １／２ The metal printing ink composition according to claim 2, wherein the amount is less than [amount missing].

5. The metal printing ink composition according to any one of claims 1 to 4, comprising an alkyd resin as at least a portion of the resin.

6. The metal printing ink composition according to claim 3, wherein the rosin-modified resin is a rosin ester resin.

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

8. The metal printing ink composition according to claim 5 or 7, wherein the fatty acid modification amount of the alkyd resin is 25 to 50% by mass.

9. A method for producing a metal printing ink composition according to any one of claims 1 to 8, characterized in that bentonite is used as one of the components constituting the composition, and the composition is prepared such that the proportion of aromatic compounds in the total solvent contained in the composition is less than 50% by mass.

10. A set comprising a metal printing ink composition and an aqueous overprint varnish, wherein the metal printing ink composition is the ink composition according to any one of claims 1 to 8, and the content of the organic solvent contained in the aqueous overprint varnish is less than 10% by mass relative to the total aqueous overprint varnish.

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