Ink composition

Abstract

To provide an ink composition containing a diketopyrrolopyrrole pigment that exhibits excellent drying performance of a printed matter, suppresses bleeding of an ink image on the printed matter, and has favorable weather resistance.SOLUTION: An ink composition contains at least a glycol ether solvent, a nitrogen-containing heterocyclic compound, a diketopyrrolopyrrole pigment, and a vinyl chloride-vinyl acetate copolymer resin, wherein an amount of the nitrogen-containing heterocyclic compound in the ink composition is within a range of 1 to 15 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink composition containing a diketopyrrolopyrrole pigment, and more particularly to an ink composition that provides excellent drying properties for printed matter, prevents bleeding of printed ink images, and has good weather resistance. [Background technology]

[0002] Inkjet inks containing diketopyrrolopyrrole pigments are known to produce high saturation in printed materials and are used as red and orange inks. Among these, non-aqueous diketopyrrolopyrrole pigment inks using organic solvents as a medium have been widely studied due to their high saturation in printed materials.

[0003] Japanese Patent Laid-Open Publication No. 2017-132889 (Patent Document 1) relates to a non-aqueous inkjet composition containing a diketopyrrolopyrrole pigment, an organic solvent, and a vinyl chloride resin, the organic solvent containing a glycol ether and a cyclic lactone, and the pigment having an average particle size of 100 to 240 nm. Patent Document 1 describes that even when printed on a low-absorbency recording medium using the non-aqueous inkjet composition, the resulting recorded material has excellent saturation and ejection stability. It also describes that the inclusion of a glycol ether improves dispersion stability and ejection stability, and that the inclusion of a glycol monoether in particular improves the wetting and spreading properties of the ink containing the diketopyrrolopyrrole compound pigment, tending to further improve saturation.

[0004] Japanese Patent Laid-Open Publication No. 2017-132890 (Patent Document 2) relates to a non-aqueous inkjet composition containing a diketopyrrolopyrrole pigment and an organic solvent containing a glycol monoether and a saturated hydrocarbon having an alicyclic structure. Patent Document 2 describes that the non-aqueous inkjet composition can produce recorded matter with excellent storage stability and high color saturation. It also describes that the organic solvent contains a glycol monoether, which ensures sufficient wettability and spreadability of the resulting recorded matter, and that the composition contains a saturated hydrocarbon having an alicyclic structure, which maintains good dispersibility of the red colorant.

[0005] Japanese Patent Laid-Open No. 2022-159265 (Patent Document 3) relates to a non-aqueous ink composition that contains a pigment, a pigment dispersant, and an organic solvent and is ejected by an inkjet method. Patent Document 3 describes that the non-aqueous ink composition has high storage stability and high cleaning recovery because the diketopyrrolopyrrole pigment has a pH in the range of 3 to 9.

[0006] Japanese Patent Laid-Open Publication No. 2023-133066 (Patent Document 4) relates to a non-aqueous ink composition to be ejected by an inkjet method, which contains a diketopyrrolopyrrole pigment, a pigment dispersant, an organic solvent, and a resin. The non-aqueous ink composition is characterized by containing the pigment and the pigment dispersant in specific ratios. Patent Document 4 describes that the non-aqueous ink composition containing a diketopyrrolopyrrole pigment is likely to have poor ejection properties and storage stability, resulting in a decrease in the gloss and coating resistance of the printed surface of the resulting printed matter, which may result in the non-aqueous ink composition not meeting the properties required for an inkjet method. It also describes that the pigment dispersant improves dispersion stability, thereby improving ejection properties and storage stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-132889 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-132890 [Patent Document 3] Japanese Patent Publication No. 2022-159265 [Patent Document 4] Japanese Patent Publication No. 2023-133066 Summary of the Invention [Problem to be solved by the invention]

[0008] Although these patent documents describe excellent techniques for ink compositions containing diketopyrrolopyrrole pigments, there is still room for improvement in terms of obtaining printed matter that is excellent in drying properties, bleeding resistance, and weather resistance.

[0009] Therefore, an object of the present invention is to provide an ink composition using a diketopyrrolopyrrole pigment, which has excellent drying properties for printed matter, is resistant to bleeding of printed ink images, and has good weather resistance. [Means for solving the problem]

[0010] The present inventors conducted extensive research to achieve the above-mentioned objective. Because glycol ether-based solvents have low surface tension and viscosity and excellent pigment wetting and dispersion stability, they were selected as the solvent for ink compositions containing diketopyrrolopyrrole pigments. Furthermore, they discovered that the combined use of a nitrogen-containing heterocyclic compound, which has excellent resin solubility and pigment dispersion stability, with a glycol ether-based solvent reduces image bleeding and improves drying properties. On the other hand, they discovered that a high amount of nitrogen-containing heterocyclic compound resulted in reduced weather resistance due to partial dissolution of the diketopyrrolopyrrole pigment, and therefore specified the amount of nitrogen-containing heterocyclic compound. Furthermore, they discovered that the use of a vinyl chloride-vinyl acetate copolymer resin reduces bleeding when used in combination with a glycol ether-based solvent and a nitrogen-containing heterocyclic compound, and also provides excellent weather resistance and image gloss.

[0011] Therefore, the ink composition of the present invention is an ink composition containing at least a glycol ether solvent, a nitrogen-containing heterocyclic compound, a diketopyrrolopyrrole pigment, and a vinyl chloride-vinyl acetate copolymer resin, The ink composition is characterized in that the amount of the nitrogen-containing heterocyclic compound in the ink composition is within a range of 1 to 15% by mass.

[0012] In a preferred embodiment of the ink composition of the present invention, the nitrogen-containing heterocyclic compound is a compound containing an amide bond or a urea bond.

[0013] In another preferable embodiment of the ink composition of the present invention, the amount of solids in the ink composition is within the range of 4 to 20% by mass.

[0014] In another preferred embodiment of the ink composition of the present invention, the viscosity at 25°C is in the range of 2.5 to 7.0 mPa·s. [Effects of the Invention]

[0015] The ink composition of the present invention can provide an ink composition that has excellent drying properties for printed matter, that prevents bleeding of printed ink images, and that has good weather resistance. DETAILED DESCRIPTION OF THE INVENTION

[0016] The ink composition according to an embodiment of the present invention will now be described.

[0017] The ink composition of the present invention is an ink composition containing a diketopyrrolopyrrole pigment.

[0018] The ink composition of the present invention is preferably a non-aqueous ink composition, and more preferably a non-aqueous ink composition for inkjet printing.

[0019] In this specification, the term "non-aqueous ink composition" refers to an ink composition that is substantially free of water, although it is permissible for a small amount of water to be unavoidably mixed in during the manufacturing process or storage.

[0020] In this specification, an ink composition for inkjet printing means an ink composition that can be used for printing with an inkjet printer.

[0021] The ink composition of the present invention contains a diketopyrrolopyrrole pigment. Diketopyrrolopyrrole pigments are a type of organic pigment that exhibits reddish or orangeish colors. Diketopyrrolopyrrole pigments have excellent initial color reproducibility, color development, and sharpness, and can produce printed materials with little change in color tone over time. Diketopyrrolopyrrole pigments refer to pigments based on substituted or unsubstituted diketopyrrolopyrrole. Diketopyrrolopyrrole pigments that can be suitably used in the present invention include CI Pigment Orange 71, 73, and 81, and CI Pigment Red 254, 255, 264, 270, 272, 283, and 291. Commercially available diketopyrrolopyrrole pigments in combination with other pigments can also be suitably used. Commercially available products include the Irgazin (registered trademark) Orange series (2038, D2905, EH1287, K2910, K2990, L2990HD, L2999HD, L3250HD) manufactured by BASF. These pigments may be used singly or in combination of two or more.

[0022] The content of the diketopyrrolopyrrole pigment in the ink composition of the present invention is preferably from 1% to 15% by mass, more preferably from 1% to 10% by mass, and even more preferably from 1% to 5% by mass.

[0023] Furthermore, from the viewpoints of weather resistance and dispersion stability, the diketopyrrolopyrrole pigment contained in the ink composition of the present invention preferably has a 50% by volume particle size (hereinafter simply referred to as D50) of 450 nm or less, more preferably 10 to 350 nm, and even more preferably 100 to 260 nm.

[0024] In this specification, the 50% volume particle size refers to the 50% particle size (D50) of the volume-based particle size distribution (also simply referred to as D50), and can be determined from the particle size distribution measured using a dynamic light scattering measuring device (e.g., NANOTRAC WAVE II, manufactured by Microtrac-Bell). The particle size in this specification is expressed as a sphere-equivalent diameter measured by dynamic light scattering.

[0025] The ink composition of the present invention contains a glycol ether-based solvent. The use of a glycol ether-based solvent reduces the surface tension or viscosity of the ink composition, improving the wetting properties of the ink. The glycol ether-based solvent is also suitable in terms of the dispersion stability of the pigment. In this specification, the glycol ether-based solvent is referred to as component (A), and is also referred to as "(A) glycol ether-based solvent."

[0026] In this specification, glycol ether solvents refer to ether compounds having an oxyalkylene structure based on glycols such as ethylene glycol and propylene glycol, and also include compounds having the oxyalkylene structure as a repeating unit. Glycol ether solvents include those having hydroxyl groups at both ends of the molecule and those in which the hydrogen atoms of the hydroxyl groups at one or both ends of the molecule are substituted with a substituent such as an alkyl group or an acyl group.

[0027] Glycol ether solvents are organic solvents with low viscosity, relatively high flash points, and good drying properties, and are preferably used as the main solvent in the ink composition of the present invention. The preferred flash points of glycol ether solvents are 50°C or higher and 75°C or lower. In this specification, the flash points are those measured by the tag-closed method.

[0028] The glycol ether solvent preferably contains a glycol ether solvent represented by the following general formula (1). R1-(OR2)nO-R3 (1) In formula (1), n is an integer between 1 and 4, R1 is hydrogen, an alkyl group having 1 to 8 carbon atoms which may be branched, or an acyl group having 1 to 4 carbon atoms; R2 is an alkylene group having 1 to 4 carbon atoms which may be branched, R3 is hydrogen, an alkyl group having 1 to 4 carbon atoms which may be branched, or an acyl group having 1 to 4 carbon atoms.

[0029] In the ink composition of the present invention, the amount of component (A) is preferably in the range of 1% by mass to 99% by mass, more preferably in the range of 50% by mass to 99% by mass, and even more preferably in the range of 85% by mass to 99% by mass. The component (A) may be used alone or in combination of two or more types.

[0030] The glycol ether solvent preferably contains a glycol ether solvent having a boiling point of less than 200°C. In this specification, the "glycol ether solvent having a boiling point of less than 200°C" is referred to as component (A-1), and is also referred to as "(A-1) glycol ether solvent having a boiling point of less than 200°C." Component (A-1) preferably has a boiling point of 150 to 200°C, more preferably 160 to 190°C. In this specification, the boiling point refers to the boiling point at 1 atmosphere. Use of component (A-1) can reliably improve the drying properties of the ink.

[0031] The glycol ether solvent of component (A-1) is preferably a solvent corresponding to the glycol ether solvent represented by the above general formula (1), more preferably contains a dialkylene glycol dialkyl ether or a dialkylene glycol monoalkyl ether acetate, and even more preferably contains at least one selected from diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, and propylene glycol monomethyl ether acetate.

[0032] In the ink composition of the present invention, the amount of component (A-1) is preferably within a range of 50 to 98% by mass, and more preferably within a range of 80 to 97% by mass. The component (A-1) may be used alone or in combination of two or more types.

[0033] The glycol ether solvent preferably contains a glycol ether solvent having a boiling point of 220° C. or more and less than 300° C. In this specification, the "glycol ether solvent having a boiling point of 220° C. or more and less than 300° C." is referred to as component (A-2), and is also referred to as "(A-2) glycol ether solvent having a boiling point of 220° C. or more and less than 300° C.." Component (A-2) prevents the ink from drying out in the head section, improves re-ejection properties, and contributes to improving the gloss of printed matter.

[0034] Examples of the component (A-2) include diethylene glycol, triethylene glycol, tripropylene glycol, polypropylene glycol, diethylene glycol-2-ethylhexyl ether, diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, dipropylene glycol, ethylene glycol monophenyl ether, triethylene glycol monomethyl ether, and diethylene glycol dibutyl ether.

[0035] In the ink composition of the present invention, the amount of component (A-2) is preferably within a range of 0.1 to 5.0% by mass, and more preferably within a range of 0.1 to 2.0% by mass. The component (A-2) may be used alone or in combination of two or more.

[0036] The ink composition of the present invention contains a nitrogen-containing heterocyclic compound. In this specification, the nitrogen-containing heterocyclic compound is referred to as component (B) and is also referred to as the "(B) nitrogen-containing heterocyclic compound." The nitrogen-containing heterocyclic compound has excellent resin solubility and pigment dispersion stability. When used in combination with a glycol ether-based solvent, it can reduce image bleeding and improve drying properties. In particular, nitrogen-containing heterocyclic compounds are organic solvents that have a high ability to dissolve resins such as vinyl chloride-vinyl acetate copolymer resins (described below) and vinyl chloride resins, which are commonly used for printing surfaces (in other words, have excellent resin solubility). While this can potentially degrade the design of the printed surface, the use of a glycol ether-based solvent in the ink composition of the present invention in combination with a resin in a range of 1 to 15% by mass allows the ink to penetrate into the substrate in the thickness direction (longitudinal direction) without spreading. Thus, the combined use of a nitrogen-containing heterocyclic compound and a glycol ether-based solvent reduces the amount of solvent remaining on the surface of the printed material, allowing the surface to dry easily and reducing image bleeding.

[0037] The nitrogen-containing heterocyclic compound is preferably an amide bond or urea bond-containing compound. Specific examples of the amide bond-containing compound corresponding to component (B) include N-methylcaprolactam, N-acetylcaprolactam, ε-caprolactam, N-vinylcaprolactam, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone, 1-cyclohexyl-2-pyrrolidone, 2-oxazolidone, N-ethyl-ε-caprolactam, N-propyl-ε-caprolactam, N-methyl-ε-caprolactam, and N-acetyl-ε-caprolactam. The urea bond-containing compound corresponding to component (B) is preferably an imidazolidinone solvent, and specific examples include 2-imidazolidinone and 1,3-dimethyl-2-imidazolidinone. As the urea bond-containing compound corresponding to component (B) used in the present invention, 1,3-dimethyl-2-imidazolidinone is particularly preferred.

[0038] In the ink composition of the present invention, the amount of component (B) is in the range of 1% by mass to 15% by mass, preferably in the range of 1.4% by mass to 10% by mass, and more preferably in the range of 1.8% by mass to 7% by mass. To obtain the effects of (B), the amount of component (B) in the ink composition is preferably 1% by mass or more. On the other hand, if the content of component (B) in the ink composition of the present invention is greater than 15% by mass, a portion of the diketopyrrolopyrrole pigment dispersed in the ink will be dissolved, resulting in a decrease in the weather resistance of printed materials obtained using the ink. Fading is particularly likely to occur when exposed outdoors. The component (B) may be used alone or in combination of two or more types.

[0039] In the ink composition of the present invention, the nitrogen-containing heterocyclic compound is preferably a nitrogen-containing heterocyclic compound that results in a pH of greater than 7.0 when the mixture is composed of 50 parts by mass of water, 47.5 parts by mass of diethylene glycol ethyl methyl ether, and 12.5 parts by mass of the nitrogen-containing heterocyclic compound. A nitrogen-containing heterocyclic compound that results in a pH of the mixture of 7.0 to 10.0 is more preferred, and a nitrogen-containing heterocyclic compound that results in a pH of the mixture of 7.0 to 9.5 is even more preferred. Diethylene glycol ethyl methyl ether is a common glycol ether-based solvent. Using a nitrogen-containing heterocyclic compound in the ink composition of the present invention that results in a pH of the mixture of greater than 7.0 prevents the pH range of the ink adhered to the head from becoming acidic, thereby suppressing head corrosion.

[0040] In the ink composition of the present invention, the mass ratio of the component (A) to the component (B) is preferably 5-98, and more preferably 9-50.

[0041] The ink composition of the present invention may further contain an organic solvent that has a boiling point of less than 150° C. and does not fall under component (A-1), component (A-2), or component (B). Organic solvents with a boiling point of less than 150° C. are preferred from the viewpoint of improving the drying properties of the ink.

[0042] Examples of organic solvents that have a boiling point below 150°C and do not fall under the category of component (A-1), component (A-2), or component (B) include propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, cyclopentanone, etc. Such organic solvents may be contained in component (A), and preferably have excellent compatibility with components (A) and (B).

[0043] In the ink composition of the present invention, the amount of organic solvent having a boiling point of less than 150°C and not corresponding to component (A-1), component (A-2), or component (B) is preferably in the range of 0.1 to 2.0% by mass, more preferably in the range of 0.5 to 1.5% by mass. Such organic solvents may be used alone or in combination of two or more.

[0044] The ink composition of the present invention preferably does not contain γ-butyrolactone.

[0045] The ink composition of the present invention contains a vinyl chloride-vinyl acetate copolymer resin. In this specification, the vinyl chloride-vinyl acetate copolymer resin is referred to as component (C), and is also referred to as "(C) vinyl chloride-vinyl acetate copolymer resin." Vinyl chloride-vinyl acetate copolymer resins have high solubility in nitrogen-containing heterocyclic compounds and excellent compatibility with glycol ether solvents. They also exhibit excellent dispersion stability of diketopyrrolopyrrole pigments and excellent coating film properties after drying. Therefore, when used in combination with glycol ether solvents, nitrogen-containing heterocyclic compounds, and diketopyrrolopyrrole pigments, they can provide printed materials with excellent weather resistance, blocking resistance, abrasion resistance, and gloss.

[0046] The amount of vinyl chloride-vinyl acetate copolymer resin in the ink composition of the present invention is preferably 1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 15% by mass or less, and even more preferably 1% by mass or more and 5% by mass or less. If it is more than 30% by mass, the storage stability of the ink may decrease, and if it is less than 1% by mass, the scratch resistance and weather resistance of the printed matter may decrease. The vinyl chloride-vinyl acetate copolymer resin may be used alone or in combination of two or more types.

[0047] The vinyl chloride-vinyl acetate copolymer resin preferably has a weight-average molecular weight / number-average molecular weight (molecular weight distribution) of 2.0 to 8.0, more preferably 2.3 to 7.0. A molecular weight distribution of less than 2.0 may result in reduced abrasion resistance and weather resistance of printed matter, while a molecular weight distribution of more than 8.0 may result in reduced solubility in solvents, leading to poorer ink ejection stability and storage stability. Furthermore, the vinyl chloride-vinyl acetate copolymer resin preferably has a weight-average molecular weight of 20,000 to 90,000, more preferably 30,000 to 80,000, and even more preferably 40,000 to 80,000. When the weight-average molecular weight is within the above-specified range, solvent solubility can be further improved. In particular, a weight-average molecular weight of 20,000 or more contributes to improved weather resistance, while a weight-average molecular weight of less than 90,000 facilitates solvent solubility. In the present invention, the weight average molecular weight, number average molecular weight and molecular weight distribution are values ​​measured by gel filtration chromatography, using polystyrene as the standard substance and tetrahydrofuran as the mobile phase.

[0048] Vinyl chloride-vinyl acetate copolymer resins can be synthesized using known polymerization methods such as suspension polymerization and emulsion polymerization, but emulsion polymerization using a polymerization initiator having an ionic group at its end is preferred from the viewpoint of adjusting the molecular weight distribution. Furthermore, to adjust the molecular weight distribution, it is preferable to use a polymerization initiator in combination with a chain transfer agent, and by appropriately adjusting the amount of the chain transfer agent used, it becomes possible to easily adjust the molecular weight distribution.

[0049] In the (C) vinyl chloride-vinyl acetate copolymer resin, the mass ratio (a / b) of vinyl chloride units (a) to vinyl acetate units (b) is preferably 70 / 30 to 95 / 5, more preferably 80 / 20 to 90 / 10. The vinyl chloride units are monomer units derived from vinyl chloride, and the vinyl acetate units are monomer units derived from vinyl acetate. By ensuring that the proportion of vinyl chloride units in the total monomer units constituting the resin is 70% by mass or more, high weather resistance and bleeding-free printed matter are easily obtained. On the other hand, if the proportion exceeds 90% by mass, solubility in solvents decreases.

[0050] When a resin solution containing 20% ​​by weight of vinyl chloride-vinyl acetate copolymer resin and 80% by weight of diethylene glycol ethyl methyl ether is prepared, the haze value of the resin solution is preferably 10.0% or less, more preferably 5.0% or less. If the haze value exceeds 10.0%, the solubility in solvents decreases, which may result in poor ink ejection stability and storage stability. Furthermore, by maintaining the haze value at 10.0% or less, weather resistance is more easily achieved. The haze value of the resin solution is closely related to the molecular weight distribution of the vinyl chloride-vinyl acetate copolymer resin. For example, if the molecular weight distribution is less than 3.0 or more than 8.0, the solubility of the vinyl chloride-vinyl acetate copolymer resin decreases, and the haze value may increase significantly. The haze value can be measured using a haze meter. In the present invention, the haze value is measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) for a resin solution prepared under conditions of a stirring temperature of 30°C, a stirring speed of 500 to 1,200 rpm, and a stirring time of 2 hours.

[0051] By using the glycol ether solvent, the nitrogen-containing heterocyclic compound, and the vinyl chloride-vinyl acetate copolymer resin in combination, it is possible to provide an ink composition that exhibits excellent drying properties for printed matter, that is resistant to bleeding of printed ink images, and that has good weather resistance.

[0052] The ink composition of the present invention preferably contains a synergist from the viewpoint of improving the dispersion stability and color development of the pigment. A synergist is a compound in which a specific substituent, such as a sulfate group, a sulfonamide group, a sulfonic acid group and its salt, a phthalimide group, a phthalimidemethyl group, an amino group, or a triazine group, is introduced into an organic pigment, and is also called a pigment derivative. Known pigment derivatives (synergists) include azo-based, phthalocyanine-based, and quinacridone-based synergists.

[0053] In the ink composition of the present invention, the amount of synergist is preferably in the range of 0.001% by mass to 0.5% by mass, and more preferably in the range of 0.005% by mass to 0.2% by mass. The synergist may be used alone or in combination of two or more types.

[0054] The ink composition of the present invention preferably contains a pigment dispersant from the viewpoint of improving the dispersion stability of the pigment. The content of the pigment dispersant in the ink composition is, for example, 0.1% by mass to 5% by mass. The pigment dispersants may be used alone or in combination of two or more.

[0055] The pigment dispersant is preferably a polymer dispersant having an acid value and an amine value, or a basic dispersant having an amine value of less than 40.

[0056] In this specification, "acid value" refers to the number of milligrams of potassium hydroxide (unit: mgKOH / g) required to neutralize the acidic components present in 1 g of sample, and can be measured by the method specified in JIS K2501: 2003. "Amine value" refers to the number of milligrams of potassium hydroxide (unit: mgKOH / g) equivalent to the amount of hydrochloric acid or perchloric acid required to neutralize the basic components contained in 1 g of sample, and can be measured by the method specified in JIS K2501: 2003.

[0057] A dispersant with an acid value means a dispersant with an acid value of 2 mg KOH / g or more. A dispersant with an amine value means a dispersant with an amine value of 2 mg KOH / g or more. A polymer dispersant means a dispersant made of a polymer with a weight average molecular weight of 4,000 or more.

[0058] For polymer dispersants having an acid value and an amine value, the acid value is preferably 5 to 20 mg KOH / g, the amine value is preferably 5 to 50 mg KOH / g, and the weight average molecular weight is preferably 5,000 to 15,000. Examples of polymer dispersants having an acid value and an amine value include SOLSPERSE 24000, 28000, 32000, 32500, 32600, 33000, 35100, 35200, 37500, and 39000 (all manufactured by Lubrizol Corporation), DISPERBYK-142, 145, 2001, 2020, 2025, and 9076 (all manufactured by BYK Japan Co., Ltd.), and AJISPER PB821, PB822, PB824, PB827, PB831, and PB881 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.). Using a polymer dispersant with both an acid value and an amine value increases the dispersion stability of the diketopyrrolopyrrole pigment and improves the stability of the pigment in vinyl chloride-vinyl acetate copolymer resins, glycol ether solvents, and nitrogen-containing heterocyclic compounds, making it easier to obtain printed materials with excellent weather resistance.

[0059] For basic dispersants with an amine value of less than 40, the amine value is preferably 10 mgKOH / g or more and less than 40 mgKOH / g. Examples of basic dispersants with an amine value of less than 40 include SOLSPERSE 32000, 35100, and 39000 (all manufactured by Lubrizol Corporation), DISPERBYK-162, 163, 168, and 2050 (all manufactured by BYK Japan Co., Ltd.), and AJISPER PB821, PB822, PB824, and PB881 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.). Because diketopyrrolopyrrole pigments are difficult to ensure dispersion stability, using them in combination with nitrogen-containing heterocyclic compounds with high solubility makes it even more difficult to ensure dispersion stability. However, by using a basic dispersant with an amine value of less than 40, particularly a polymer dispersant with both an amine value and an acid value of less than 40, it becomes easier to ensure dispersion stability in diketopyrrolopyrrole pigment inks that contain nitrogen-containing heterocyclic compounds, making it easier to obtain printed materials with excellent weather resistance.

[0060] The ink composition of the present invention may contain, as other components, additives such as ultraviolet absorbers, radical scavengers, surface modifiers, viscosity modifiers, antioxidants, plasticizers, rust inhibitors, solvents, fillers, antifoaming agents, charge control agents, stress relaxation agents, penetrating agents, light-guiding materials, glittering materials, magnetic materials, fluorescent materials, antibacterial agents, antiviral agents, and anti-algae agents, as needed.

[0061] In the ink composition of the present invention, the amount of solids contained in the ink composition is preferably in the range of 4% to 20% by mass, more preferably in the range of 4.5% to 15% by mass, and even more preferably in the range of 5% to 10% by mass. When the amount of solids is within the above-specified range, the ink jetting stability, drying properties, and coating film properties are favorable. If the solids content is greater than 20% by mass, this is undesirable in terms of ink jetting stability during inkjet printing. Furthermore, if the solids content is less than 4% by mass, this is undesirable in terms of ensuring drying properties during printing. In this specification, the term "solid content" refers to the components excluding volatile components such as solvents, and is the component that will ultimately form the printed matter. In the present invention, the solid content refers to the components that remain when the ink composition is dried at 150°C for 60 minutes.

[0062] The viscosity of the ink composition of the present invention at 25°C is preferably in the range of 2.5 mPa·s to 7.0 mPa·s, more preferably 2.8 mPa·s to 6.5 mPa·s, and even more preferably 3.0 mPa·s to 6.0 mPa·s. When the viscosity of the ink composition at 25°C is within the above-specified range, good ejection stability can be obtained. The viscosity of the ink can be measured using a cone-plate viscometer. In this specification, the viscosity of the ink is also referred to as "viscosity (R)".

[0063] The ink composition of the present invention preferably has a surface tension at 25°C of 20 mN / m to 35 mN / m, more preferably 23 mN / m to 33 mN / m, and even more preferably 25 mN / m to 30 mN / m. If the ink surface tension at 25°C is within the above-specified range, good ejection stability and wettability to the printed surface can be obtained. The surface tension of the ink can be measured by a plate method.

[0064] The ink composition of the present invention can be prepared by mixing various components appropriately selected as needed, and, if necessary, filtering the resulting mixture using a filter having a pore size of not more than about 1 / 10 of the nozzle diameter of the inkjet printhead to be used.

[0065] The ink composition of the present invention is preferably used as a red ink or an orange ink. It is particularly preferably used as an orange ink. The ink composition of the present invention can be used alone for printing, or can be used in printing as an ink set in combination with other inks. For example, the ink composition of the present invention can be combined with basic color inks such as cyan ink, magenta ink, yellow ink, and black ink, as well as light cyan ink, light magenta ink, light yellow ink, light black ink, green ink, white ink, and metallic ink.

[0066] The substrate on which printing is performed using the ink composition of the present invention is not particularly limited, but suitable examples include substrates used in industrial lines and commercial printing. The substrate may be in the form of, for example, a film, a sheet, or a plate. Examples of substrate materials include plastics such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, and acrylic resin, particularly polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polypropylene (PP); metals such as iron, stainless steel, and aluminum; wood; cement; concrete; gypsum; calcium silicate; calcium carbonate; and glass. Specific examples of substrates include vinyl chloride sheets, tarpaulin, plastic cardboard, acrylic boards, flexible boards, calcium silicate boards, gypsum slag barite boards, calcium carbonate boards, wood chip cement boards, precast concrete boards, lightweight foamed concrete (ALC) boards, gypsum boards, tiles, and glass plates. Among these, polyvinyl chloride substrates and tarpaulin substrates are preferred. (B) Nitrogen-containing heterocyclic compounds have high penetration into polyvinyl chloride substrates and tarpaulin substrates, resulting in a printed layer that is less likely to bleed.

[0067] Printing using the ink composition of the present invention is preferably carried out by inkjet printing. Various inkjet printers can be used for inkjet printing. Examples of inkjet printers include inkjet printers that eject the ink composition using a charge control system or a piezoelectric system. Large-format inkjet printers, specifically inkjet printers designed for printing on products produced on industrial lines, can also be suitably used. [Example]

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

[0069] Mixtures containing each component in the amounts (parts by mass) shown in Table 1 were kneaded in a bead mill for 3 hours to prepare orange inks or red inks containing diketopyrrolopyrrole pigments in Examples 1 to 9 and Comparative Examples 1 to 5. Similarly, magenta inks, yellow inks, and cyan inks were prepared using the components and amounts (parts by mass) shown in Table 2.

[0070] The diketopyrrolopyrrole pigments used are shown below. Pigment Orange 71 Pigment Red 254 The solvents used are listed below, with the boiling point of each solvent shown in parentheses. Diethylene glycol ethyl methyl ether (boiling point 176°C) Diethylene glycol diethyl ether (boiling point 188°C) Triethylene glycol (boiling point 287°C) 1,3-Dimethylimidazolidinone (boiling point 220°C) 2-pyrrolidone (boiling point 250°C) γ-butyrolactone (boiling point 204°C) 3-Methoxy-N,N-dimethylpropionamide (boiling point 215°C) The resins used are shown below. VINNOL H15 / 42 (vinyl chloride-vinyl acetate copolymer resin, manufactured by Wacker Chemie) Solvin C (vinyl chloride-vinyl acetate copolymer resin, manufactured by Nissin Chemical Industry Co., Ltd.) Dianall BR-87 (acrylic resin, manufactured by Mitsubishi Chemical Corporation) The dispersants used are shown below. Solsperse 32000 (Polycaprolactone-based polymer dispersant, acid value: 15.5 mg KOH / g, amine value: 31.2 mg KOH / g, manufactured by Lubrizol)

[0071] <Drying> Each of the inks listed in Table 1 was applied using a bar coater #7 onto a glossy PVC sheet heated to 45°C. After application, the applied surface was rubbed with a finger and the drying time was evaluated according to the following criteria. The results are shown in Table 1. (standard) ◎: The time it takes for the coating to not come off when rubbed with a finger is less than 2 minutes, measured immediately after application. ○: The time it takes for the coating film to not come off when rubbed with a finger is less than 3 minutes, measured immediately after application. △: The time it takes for the coating to not come off when rubbed with a finger is 3 minutes or more but less than 5 minutes measured immediately after application. ×: The time it takes for the coating film to not come off even when rubbed with a finger is 5 minutes or more, measured immediately after application.

[0072] <Bleeding resistance> Using various orange or red inks listed in Table 1 and the ink set prepared above, a solid image of a 300% mixture of CMY colors listed in Table 2 was printed adjacent to a 100% solid image of orange or red ink. Bleed resistance was evaluated according to the following criteria, and the results are shown in Table 1. When inks rated as "good" were used, the image was less likely to bleed. (standard) ◯: No bleeding was observed between adjacent colors. ×: Bleeding was observed between adjacent colors.

[0073] <Weather resistance> A 5 cm x 5 cm square solid image of the orange or red ink prepared in Table 1 was printed at 100% density with a recording resolution of 720 x 720 dpi on a polyvinyl chloride substrate (PVC100MP, manufactured by Lintec Corporation) using a large-format inkjet printer. The color was measured using a spectrophotometer (SpectroEye, manufactured by X-Rite). The image was then subjected to a weather resistance test under the following test 1) conditions using an accelerated weather resistance tester, a Super UV Tester (Eye Super UV Tester W Type SUV-W23, manufactured by Iwasaki Electric Co., Ltd.). The image after the test was measured in the same manner as before the test, and the color difference (ΔE) between the image before and after the test was determined. The observed color difference (ΔE) was used to evaluate weather resistance according to the following evaluation criteria 2), and the results are shown in Table 1. 1) Conditions Light source: Water-cooled metal halide lamp Illuminance: 100mW / cm2 Wavelength: 295~450nm Temperature: 60℃ (irradiation), 30℃ (condensation) Humidity: 50% (irradiation), 90% (condensation) Cycle: 6 hours of irradiation, 2 hours of dew Shower: 30 seconds before and after condensation Test duration: 200 hours 2) Evaluation criteria ◎: The color difference between the initial state and after the weather resistance test is within 3. ◯: The color difference between the initial color and the color after the weather resistance test is more than 3 but not more than 5. ×: The color difference between the initial color and the color after the weather resistance test is more than 5.

[0074] <Gloss of printed matter> A 100% solid image was printed using a large-format inkjet printer with the orange or red ink listed in Table 1. The resulting print was dried at 60°C for 1 hour, and then the 20° gloss was measured using a BYK gloss meter. The gloss of the print was evaluated according to the following criteria, and the results are shown in Table 1. (standard) ◎: Gloss value is 40 or more 〇: Gloss value is 30 or more ×: Gloss value less than 30

[0075] <Discharge stability> For the orange ink or red ink listed in Table 1, a nozzle check pattern image was printed using a large format inkjet printer, and then a 100% solid image was printed for 1,000 hours. After printing, a nozzle check pattern was printed again, and ejection stability was evaluated according to the following criteria. The results are shown in Table 1. (standard) ◎: Missing or irregularities in the nozzle check pattern are less than 1%. ○: Missing or irregularities in the nozzle check pattern are less than 5%. △: Nozzle check pattern is missing or distorted in 5% to 10% of cases. ×: Missing or disordered nozzle check pattern exceeds 10%.

[0076] [Table 1]

[0077] [Table 2]

Claims

1. An ink composition comprising at least a glycol ether solvent, a nitrogen-containing heterocyclic compound, a diketopyrrolopyrrole pigment, and a vinyl chloride-vinyl acetate copolymer resin, The ink composition is characterized in that the amount of the nitrogen-containing heterocyclic compound in the ink composition is within the range of 1 to 15 mass %.

2. 2. The ink composition according to claim 1, wherein the nitrogen-containing heterocyclic compound is a compound containing an amide bond or a urea bond.

3. 3. The ink composition according to claim 1, wherein the amount of solids in the ink composition is in the range of 4 to 20% by mass.

4. 3. The ink composition according to claim 1, wherein the viscosity at 25° C. is in the range of 2.5 to 7.0 mPa·s.

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