Water-based black ink for inkjet recording and printed materials

Abstract

This invention provides a water-based black ink for inkjet recording that allows for printing on colored paper, particularly red-colored paper, while also providing printed materials that exhibit high print density and excellent abrasion resistance. [Solution] An inkjet water-based black ink containing carbon black, cyan pigment, organic solvent, and water, wherein the mass ratio of the cyan pigment content to the carbon black content [cyan pigment / carbon black] exceeds 0.13, and the total mass of the carbon black content and the cyan pigment content is greater than 4% by mass and less than 15% by mass.

Description

[Technical Field]

[0001] This invention relates to a water-based black ink for inkjet recording and printed materials. [Background technology]

[0002] Inkjet recording is a recording method that directly ejects ink droplets from fine nozzles and adheres them to a recording medium to obtain a recorded material containing text or images. This method has become extremely popular due to its numerous advantages, including ease and low cost of full-color printing, the ability to use plain paper as the recording medium, and non-contact operation with respect to the recording medium. In particular, from the perspective of weather resistance and water resistance of the recorded material, inkjet inkjet printers that use pigments as coloring agents are becoming the mainstream. On the other hand, water-based black ink for inkjet recording, which uses pigments as coloring agents, is required to have higher print density, but increasing the print density tends to reduce its abrasion resistance.

[0003] As a technology to address the above problems, for example, Patent Document 1 describes a pigment-dispersed aqueous recording liquid for the purpose of achieving water resistance, weather resistance, light resistance, and both blackness and glossiness of printed materials, wherein the recording liquid contains at least a pigment and a resin, and is characterized in that the resin is contained in parts 60 to 200 parts by weight per 100 parts by weight of pigment, the resin contains a water-dispersible urethane-based resin, the weight fraction of the polyurethane urea portion in the urethane-based resin is 2.0% by weight or less, and the dispersion particle size D50 of the pigment in the recording liquid is 40 to 100 nm.

[0004] Furthermore, for example, Patent Document 2 describes a water-based ink for inkjet recording that improves the dullness of black printed materials, with a DBP oil absorption capacity of 90 cm³. 3 An ink containing polymer particles with carbon black in an amount of 100g or less, wherein the number of particles with a particle size of 0.79 to 5.00 μm present in 1 ml of the ink is 5.0 × 10 5 A water-based ink for inkjet recording is disclosed, having fewer than or equal to 1, and a polymer weight-average molecular weight of 45,000 to 500,000. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-285344 [Patent Document 2] Japanese Patent Publication No. 2009-144007 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, the printing market for high-speed, high-volume, variable information processing (transactions) has seen a surge in printing of invoices, statements, direct mail, etc., and the printing substrates have expanded from white paper to various colored papers such as blue and red. Therefore, there is a need for an inkjet water-based black ink that can produce printed materials with high print density and excellent abrasion resistance, even when using colored paper as the printing substrate. However, Patent Documents 1 and 2 do not focus on printing on a wide variety of printing substrates. The present invention aims to provide a water-based black ink for inkjet recording that can produce printed materials with high print density and excellent abrasion resistance even when printed on colored paper, particularly red-colored paper, and to provide printed materials with high print density and excellent abrasion resistance even when printed on colored paper, particularly red-colored paper, and to solve this problem. [Means for solving the problem]

[0007] The inventors have found that the above problem can be solved by setting the content ratio and total mass of carbon black and cyan pigment within a specific range in an inkjet-based black ink containing carbon black, cyan pigment, an organic solvent, and water.

[0008] In other words, the present invention relates to the following [1] and [2]. [1] A water-based black ink for inkjet recording containing carbon black, cyan pigment, organic solvent, and water, The mass ratio [cyan pigment / carbon black] of the content of the cyan pigment to the content of the carbon black exceeds 0.13, An aqueous black ink for inkjet recording, wherein the total mass of the content of the carbon black and the content of the cyan pigment is more than 4% by mass and less than 15% by mass. [2] A printed matter obtained by using the aqueous black ink for inkjet recording according to [1].

Effects of the Invention

[0009] The present invention provides an aqueous black ink for inkjet recording and a colored paper, particularly a red-colored paper, which can obtain a printed matter with high printing density and excellent rubbing resistance even when printed on a colored paper, particularly a red-colored paper.

Modes for Carrying Out the Invention

[0010] [Aqueous Black Ink for Inkjet Recording] The aqueous black ink for inkjet recording of the present invention (hereinafter, also simply referred to as "black ink") is an aqueous black ink for inkjet recording containing carbon black, a cyan pigment, an organic solvent, and water, wherein the mass ratio [cyan pigment / carbon black] of the content of the cyan pigment to the content of the carbon black exceeds 0.13, and the total mass of the content of the carbon black and the content of the cyan pigment is more than 4% by mass and less than 15% by mass.

[0011] In this specification, "aqueous" means that water occupies the largest proportion in the medium for dispersing the pigment. Also, "recording" is a concept including printing and typing for recording characters and images. Also, "printing" is a concept including printing and typing for recording characters and images, and "printed matter" is a concept including printed materials and typed materials on which characters and images are recorded.

[0012] Conventional black inks increased the concentration of carbon black to improve the printing density, but the rub resistance decreased. Also, when the concentration of carbon black was lowered to improve the rub resistance, the printing density decreased. In particular, in the case of reddish red-colored paper as the printing substrate, it was impossible to improve the printing density while maintaining the rub resistance. In contrast, the black ink of the present invention can obtain a printed matter with high printing density and excellent rub resistance even when printed on red-colored paper. The reason is not clear, but it is presumed to be due to the following reasons. When measuring the chromaticity of conventional black ink in the CIE1976 (L * ,a * ,b * ) color space, it was found that it had a strong yellowish color (b * value was high). Therefore, by using a cyan pigment, which is the complementary color of yellow, together with carbon black in a specific ratio and a specific total amount, it is considered that a printed matter with high printing density can be obtained even when printed on colored paper typified by red paper. Also, it is considered that a printed matter with excellent rub resistance can be obtained because the cyan pigment acts like a binder that binds carbon black. Details of the red-colored paper will be described later.

[0013] <Pigment> The black ink of the present invention contains carbon black and a cyan pigment as pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Among cyan pigments, phthalocyanine pigments are preferred from the viewpoints of improving the printing density on red-colored paper and availability. Examples of phthalocyanine pigments include metal-free phthalocyanine pigments; metal phthalocyanine pigments such as copper, aluminum, nickel, cobalt, iron, titanium, and tin, and unsubstituted or halogen group-substituted phthalocyanine pigments such as chlorine and bromine. Among them, copper phthalocyanine-based cyan pigments are preferred from the viewpoints of improving the printing density on red-colored paper and availability. Carbon black and cyan pigment may be used independently, either individually or in combination of two or more types.

[0014] The black ink of the present invention may optionally contain inorganic pigments other than carbon black, organic pigments other than cyan pigment, and extender pigments. Examples of inorganic pigments other than carbon black include metal oxides, metal sulfides, and metal chlorides. Examples of organic pigments other than cyan pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. Examples of extender pigments include silica, calcium carbonate, and talc. The content of pigments other than carbon black and cyan pigment is preferably 5 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.1 parts by mass or less, and even more preferably substantially absent, per 100 parts of the total content of carbon black and cyan pigment, from the viewpoint of improving the print density on red-colored paper. Here, "substantially absent" means that the pigment is included in the components of the ink but is included unintentionally. In particular, the magenta pigment content in the black ink of the present invention is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0% by mass, from the viewpoint of improving the print density on red-colored paper.

[0015] In this invention, the pigment is dispersed in the ink medium. The form of the pigment in the aqueous ink of the present invention is preferably one or more selected from the group consisting of a pigment dispersed without the use of surfactants or polymer dispersants (hereinafter also referred to as "self-dispersing pigment"), a pigment dispersed with a surfactant, and a pigment dispersed with a polymer dispersant. Among these, the form of the pigment in the aqueous ink of the present invention is more preferably a form dispersed with a polymer dispersant (hereinafter also referred to as "polymer dispersant (a)") from the viewpoint of improving the dispersion stability of the pigment and the print density and abrasion resistance, and the form of polymer particles containing the pigment (hereinafter also referred to as "pigment-containing polymer particles") is even more preferable. Here, there are no particular restrictions on the form of the pigment-containing polymer particles; it is sufficient that the particles are formed by at least a pigment and a polymer dispersant (a). Examples of pigment-containing polymer particle forms include particles in which the pigment is encapsulated in the polymer dispersant (a), particles in which the pigment is uniformly dispersed in the polymer dispersant (a), and particles in which the pigment is exposed on the surface of the polymer dispersant (a) particles, and mixtures thereof are also included.

[0016] (Polymer dispersant (a)) The polymer dispersant (a) may be either a water-soluble polymer or a water-insoluble polymer, but a water-insoluble polymer is preferred from the viewpoint of improving the dispersion stability of the pigment, the print density, and the abrasion resistance. Here, the "water-soluble" and "water-insoluble" properties of the polymer are determined by the amount of resin dissolved in 100g of 25°C water until saturated after drying at 105°C for 2 hours and reaching a constant weight. If the amount dissolved exceeds 10g, it is determined to be "water-soluble," and if it is 10g or less, it is determined to be "water-insoluble." Furthermore, if the polymer dispersant (a) has anionic groups, as described later, and these anionic groups are neutralized by a neutralizing agent, the determination is made by the amount of dissolution measured under conditions where the mass ratio of the polymer dispersant (a) to the neutralizing agent is the same as that in the water-based ink of the present invention. Polymer dispersants (a) may be used individually or in combination of two or more types.

[0017] Examples of polymer dispersants (a) include vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), polyesters, and polyurethanes. Among these, vinyl polymers are preferred as polymer dispersants (a) from the viewpoint of improving print density and abrasion resistance.

[0018] The vinyl polymer used as the polymer dispersant (a) is preferably one that contains a structural unit derived from an ionic monomer (a-1) from the viewpoint of improving the dispersion stability of the pigment. Examples of ionic monomers (a-1) include anionic monomers having anionic groups and cationic monomers having cationic groups, but from the viewpoint of improving the dispersion stability of the pigment, anionic monomers having anionic groups are preferred. In this specification, "anionic group" means an anionic group or a group that can be ionized to become an anionic group. Examples of anionic groups include carboxyl groups (-COOM), sulfonic acid groups (-SO3M), and phosphate groups (-OPO3M2). In the above chemical formulas, M represents a hydrogen atom, an alkali metal, an ammonium compound, or an organic ammonium compound. Examples of vinyl polymers include homopolymers of ionic monomers (a-1), copolymers of ionic monomers (a-1) and hydrophobic monomers (a-2), and copolymers of ionic monomers (a-1), hydrophobic monomers (a-2), and nonionic monomers (a-3). Here, "hydrophobic" in the context of hydrophobic monomer (a-2) means that when the monomer is dissolved in 100g of deionized water at 25°C until saturated, the amount dissolved is less than 10g. Furthermore, nonionic monomers (a-3) are monomers that have a high affinity for water and water-soluble organic solvents, and are, for example, monomers that contain hydroxyl groups or polyalkylene glycol chains. If the vinyl polymer is a copolymer, it may be a random copolymer, a block copolymer, an alternating copolymer, or a graft copolymer.

[0019] Examples of ionic monomers (a-1) include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Among these, carboxyl group-containing monomers are preferred from the viewpoint of improving the dispersion stability of the pigment, the print density and abrasion resistance, and from the viewpoint of monomer availability, and (meth)acrylic acid is more preferred. Examples of hydrophobic monomers (a-2) include (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols with 1 to 22 carbon atoms; one or more styrene monomers selected from the group consisting of α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene; aromatic group-containing monomers such as aromatic group-containing (meth)acrylates; and styrene macromonomers. The molecular weight of the aromatic group-containing monomer, preferably styrene monomer, is preferably less than 500. Styrene macromonomers are compounds with a number average molecular weight of 500 to 100,000 having a polymerizable functional group at one end. Among these, hydrophobic monomers (a-2) are preferably styrene monomers from the viewpoint of improving the dispersion stability of the pigment, print density, and abrasion resistance, as well as the availability of monomers, more preferably one or more selected from the group consisting of α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably one or more selected from the group consisting of styrene and α-methylstyrene. Examples of nonionic monomers (a-3) include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxy polyalkylene glycol mono(meth)acrylates such as methoxy polyethylene glycol mono(meth)acrylate and octoxy polyethylene glycol mono(meth)acrylate. In this specification, "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. Also, "(meth)acrylate" means at least one selected from the group consisting of acrylate and methacrylate. Vinyl polymers can be obtained, for example, by addition polymerization of raw material monomers, including an ionic monomer (a-1) and optionally a hydrophobic monomer (a-2) or a nonionic monomer (a-3), using known methods. Each monomer of the vinyl polymer can be used individually or in combination of two or more.

[0020] The polymer dispersant (a) is preferably a vinyl polymer comprising one or more monomer-derived structural units selected from the group consisting of acrylic acid and methacrylic acid, and one or more monomer-derived structural units selected from the group consisting of (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene macromers, from the viewpoint of improving the dispersion stability of the pigment, print density, and abrasion resistance. More preferably, it is a vinyl polymer comprising one or more monomer-derived structural units selected from the group consisting of acrylic acid and methacrylic acid, and one or more monomer-derived structural units selected from the group consisting of (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols having 1 to 22 carbon atoms and aromatic group-containing monomers. Even more preferably, it is a vinyl polymer comprising one or more monomer-derived structural units selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from an aromatic group-containing monomer. Even more preferably, it is a vinyl polymer comprising one or more monomer-derived structural units selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from a styrene monomer.

[0021] When the polymer dispersant (a) has anionic groups, it is preferable that some of the anionic groups of the polymer dispersant (a) are neutralized by a neutralizing agent, from the viewpoint of improving the dispersion stability of the pigment, the print density, and the abrasion resistance. Examples of neutralizing agents include alkali metal hydroxides and amine compounds. Among these, the neutralizing agent is preferably an alkali metal hydroxide, and more preferably sodium hydroxide.

[0022] The polymer dispersant (a) preferably has a crosslinked structure from the viewpoint of improving the dispersion stability of the pigment, the print density, and the abrasion resistance. In this case, the polymer dispersant (a) preferably has a structure that includes a polymer component having a linear two-dimensional structure which may have branched chains, and a component derived from the crosslinking agent. Such a crosslinked structure is thought to be a three-dimensional structure formed by a polymer having a linear two-dimensional structure which may have branched chains, due to the component derived from the crosslinking agent. Examples of polymers having a linear two-dimensional structure which may have branched chains include vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), polyesters, and polyurethanes, with the aforementioned vinyl polymers being preferred. That is, the polymer dispersant (a) is preferably a vinyl polymer crosslinked with a crosslinking agent from the viewpoint of improving the dispersion stability of the pigment, the print density, and the abrasion resistance.

[0023] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having hydrocarbon groups with 3 to 8 carbon atoms, even more preferably one or more selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less.

[0024] The acid value of polymer dispersant (a) is preferably 50 mg KOH / g or more, more preferably 70 mg KOH / g or more, and even more preferably 100 mg KOH / g or more, from the viewpoint of improving the dispersion stability of the pigment, and preferably 800 mg KOH / g or less, more preferably 500 mg KOH / g or less, even more preferably 300 mg KOH / g or less, and even more preferably 200 mg KOH / g or less, from the viewpoint of improving abrasion resistance. The acid value of polymer dispersant (a) can be determined by the method described in the examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, if polymer dispersant (a) is a vinyl polymer crosslinked with a crosslinking agent, the acid value of polymer dispersant (a) can also be calculated using the following formula. Acid value of polymer dispersant (a) (mgKOH / g) = [Acid value of vinyl polymer before crosslinking (mgKOH / g) × [(100 - Crosslinking rate (mol%)) / 100] In this specification, the crosslinking ratio (mol%) of a vinyl polymer crosslinked with a crosslinking agent is a value calculated from the acid value of the vinyl polymer before crosslinking and the equivalent amount of crosslinkable functional groups of the crosslinking agent.

[0025] The weight-average molecular weight of polymer dispersant (a) is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 40,000 or more, from the viewpoint of improving the dispersion stability of the pigment and improving abrasion resistance, and also preferably 120,000 or less, more preferably 100,000 or less, and even more preferably 80,000 or less, from the same viewpoint as above. The weight-average molecular weight of polymer dispersant (a) can be measured by the method described in the examples.

[0026] The polymer dispersant (a) may be synthesized as appropriate, or a commercially available product may be used. Examples of commercially available polymer dispersants (a) include polyacrylic acid such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.) and styrene / acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690", and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0027] When the pigment in the aqueous ink of the present invention is in the form of pigment-containing polymer particles, it is preferable to disperse the pigment-containing polymer particles with the pigment, polymer dispersant (a), and optionally a neutralizing agent, surfactant, etc., by known methods to form an aqueous dispersion (hereinafter also referred to as "pigment aqueous dispersion") and incorporate it into the aqueous ink. Alternatively, a crosslinking agent may be further added to the obtained pigment aqueous dispersion to crosslink the polymer dispersant (a). The pigment-containing polymer particles contained in the water-based ink of the present invention are preferably those that are less prone to swelling, shrinking, or aggregation between the particles.

[0028] <organic solvents> The black ink of the present invention contains an organic solvent from the viewpoint of print density and scratch resistance. Examples of organic solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, the organic solvent is preferably one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers.

[0029] Preferably, the polyhydric alcohol is one or more selected from the group consisting of diols and polyhydric alcohols of three or higher valency.

[0030] Examples of diols include ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, 1,3-propanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, and dipropylene glycol. Examples of polyhydric alcohols with a valency of 3 or higher include glycerin, trimethylolpropane, and pentaerythritol.

[0031] Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoalkyl ethers such as ethylene glycol monoethyl ether and ethylene glycol monoisopropyl ether; diethylene glycol monoalkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether; tetraethylene glycol monoalkyl ethers such as tetraethylene glycol monomethyl ether; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether; dipropylene glycol monoalkyl ethers such as dipropylene glycol monomethyl ether; and alkylene glycol monoalkyl ethers such as tripropylene glycol monomethyl ether.

[0032] Organic solvents may be used individually or in combination of two or more. Furthermore, from the viewpoint of suppressing the delay in ink drying and further improving scratch resistance, it is preferable to use an organic solvent with a boiling point of less than 260°C. From the same viewpoint, the boiling point of the organic solvent is more preferably 258°C or lower, even more preferably 256°C or lower, preferably 160°C or higher, more preferably 165°C or higher, and even more preferably 170°C or higher.

[0033] Among the above, diols are preferred as organic solvents from the viewpoint of further improving abrasion resistance, and it is preferable that the diols include diols with a boiling point of less than 260°C. One or more diols with a boiling point of less than 260°C are more preferably selected from the group consisting of propylene glycol (boiling point 184°C) and dipropylene glycol (boiling point 254°C), and it is even more preferable to use propylene glycol and dipropylene glycol in combination.

[0034] <Water> The black ink of this invention contains water. As the water used in the black ink of the present invention, pure water or deionized water is preferred from the viewpoint of preventing the contamination of unintended substances.

[0035] [Surfactants] The black ink of the present invention preferably contains a surfactant from the viewpoint of improving print density and scratch resistance. Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants. However, from the viewpoint of improving print density and abrasion resistance, nonionic surfactants are preferred, one or more selected from the group consisting of acetylene glycol-based surfactants and polyoxyalkylene alkyl ether-based surfactants are more preferred, and acetylene glycol-based surfactants are even more preferred. As acetylene glycol-based surfactants, acetylene glycol having 8 to 22 carbon atoms and ethylene oxide adducts of the acetylene glycol are preferred from the viewpoint of improving print density and abrasion resistance, as well as availability, and 2,4,7,9-tetramethyl-5-decine-4,7-diol or its ethylene oxide adduct is more preferred. A specific example of a polyoxyalkylene alkyl ether surfactant is polyoxyethylene lauryl ether. The black ink of the present invention may contain a combination of an acetylene glycol-based surfactant and a polyoxyethylene alkyl ether.

[0036] [Other ingredients] The black ink of the present invention may further contain, if necessary, various additives commonly used in water-based black inks for inkjet recording, such as humectants, wetting agents, penetrating agents, dispersants, viscosity modifiers, defoamers, preservatives, antifungal agents, and rust inhibitors.

[0037] <Content> Carbon black and cyan pigment are included in the black ink of the present invention in a range where the mass ratio of the cyan pigment content to the carbon black content [cyan pigment / carbon black] exceeds 0.13, and the total mass of the carbon black content and cyan pigment content is greater than 4% by mass and less than 15% by mass. If the mass ratio [cyan pigment / carbon black] is 0.13 or less, the print density will be poor when printed on red-colored paper, and the abrasion resistance will also be poor. Furthermore, if the total mass of carbon black and cyan pigment is 4% by mass or less, the print density will not be good on red-colored paper, and if it is 15% by mass or more, the abrasion resistance will not be good.

[0038] The black ink of the present invention exhibits excellent print density when printing on colored paper, particularly reddish colored paper, but is also useful for printing on white paper. The mass ratio of cyan pigment content to carbon black content in the black ink of the present invention [cyan pigment / carbon black] is preferably 0.14 or higher, more preferably 0.16 or higher, even more preferably 0.19 or higher, and even more preferably 0.23 or higher, from the viewpoint of increasing the print density on red-colored paper. Furthermore, the mass ratio [cyan pigment / carbon black] is preferably 0.40 or lower, more preferably 0.30 or lower, even more preferably 0.25 or lower, even more preferably 0.22 or lower, even more preferably 0.18 or lower, and even more preferably 0.15 or lower, from the viewpoint of increasing the print density on white paper. Furthermore, the mass ratio [cyan pigment / carbon black] is 0.14 or higher and 0.25 or lower, even more preferably 0.16 or higher and 0.22 or lower, and even more preferably 0.18 or higher and 0.22 or lower, from the viewpoint of balancing the print density on white paper and the print density on red-colored paper.

[0039] The total mass of carbon black and cyan pigment in the black ink of the present invention is preferably 6% by mass or more, more preferably 7% by mass or more, even more preferably 8.5% by mass or more, and even more preferably 11% by mass or more, from the viewpoint of improving the print density of red-colored paper. Furthermore, the total mass of carbon black and cyan pigment in the black ink is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 9% by mass or less, from the viewpoint of improving scratch resistance. Furthermore, the total mass of carbon black and cyan pigment in the black ink is preferably 6% by mass or more and 12% by mass or less, more preferably 6% by mass or more and 10% by mass or less, and even more preferably 7% by mass or more and 10% by mass or less, from the viewpoint of balancing print density and scratch resistance.

[0040] From the viewpoint of improving the printing density on red-colored paper, the water content in the black ink of the present invention is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 58% by mass or more, and preferably 80% by mass or less, more preferably 77% by mass or less, and even more preferably 72% by mass or less.

[0041] From the viewpoint of improving the printing density on red-colored paper, the organic solvent content of the black ink of the present invention is preferably 10% by mass or more, more preferably 14% by mass or more, even more preferably 17% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0042] When the black ink of the present invention contains a polymer dispersant (a), the content of the polymer dispersant (a) in the black ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and preferably 12% by mass or less, more preferably 9% by mass or less, and even more preferably 6% by mass or less, from the viewpoint of improving print density and abrasion resistance on red-colored paper.

[0043] When the black ink of the present invention contains a surfactant, from the viewpoint of improving the printing density and rubbing resistance on red-colored paper, it is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, still more preferably 0.1% by mass or more, and is preferably 2% by mass or less, more preferably 1% by mass or less, still more preferably 0.5% by mass or less.

[0044] [Method for producing aqueous black ink for inkjet recording] The black ink of the present invention comprises carbon black, a cyan pigment, an organic solvent, and water, and, if necessary, various optional components such as a surfactant. The mass ratio of the blending amount of the cyan pigment to the blending amount of the carbon black [cyan pigment / carbon black] exceeds 0.13, and the total mass of the blending amount of the carbon black and the blending amount of the cyan pigment is 5% by mass or more and 14% by mass or less, and it can be produced by mixing them. The black ink of the present invention is preferably produced by subjecting the components to dispersion treatment by a known method and, if necessary, filtering to remove coarse particles.

[0045] [Printed matter] The printed matter of the present invention is a printed matter using the above-described black ink of the present invention. More specifically, it is a medium in which the black ink of the present invention is loaded into a known inkjet recording apparatus and ejected as ink droplets onto a printing substrate to record characters and images. As described above, the black ink of the present invention has a high printing density on colored paper and excellent rubbing resistance. In particular, when the printing substrate is red-colored paper, the printing density can be increased without impairing the rubbing resistance. Here, the red-colored paper means that the hue angle h in the CIE1976 (L * , a * , b * ) color space is included in the range of 0° or more and 45° or less, and 315° or more and less than 360°, and the h is arctan(b * / a * ). The coordinate values (L * , a * , b *This can be determined by measuring the printing substrate using a spectrophotometer / densitometer.

[0046] Examples of printing substrates include highly absorbent printing substrates such as plain paper and fine paper, low absorbent printing substrates such as art paper and coated paper, and non-absorbent printing substrates such as synthetic resin films. Among these, the black ink of the present invention is particularly suitable for printing on highly absorbent printing substrates such as plain paper and fine paper. Furthermore, "low water absorption" and "non-water absorption" refer to the amount of water absorbed by the printing substrate during a 100 m second contact time with pure water being 10 g / m². 2 This means that the water absorption capacity is 10 g / m². 2 The printing substrate is highly absorbent.

[0047] Inkjet recording devices include thermal and piezo types, but the piezo type is preferred. In other words, the black ink of the present invention is preferably used for piezo inkjet recording. [Examples]

[0048] In the following manufacturing examples, embodiments, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement methods for each physical property are as follows.

[0049] (1) Measurement of the weight-average molecular weight of water-insoluble polymers N,N-dimethylformamide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography) was used as the eluent. Phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent grade) and lithium bromide (manufactured by Tokyo Chemical Industry Co., Ltd., reagent) were dissolved in these solutions at concentrations of 60 mmol / L and 50 mmol / L, respectively. The results were measured using gel chromatography [GPC instrument (HLC-8120GPC) manufactured by Tosoh Corporation, column (TSK-GEL, α-M x 2) manufactured by Tosoh Corporation, flow rate: 1 mL / min], with monodisperse polystyrene of known molecular weight as the standard substance.

[0050] (2) Measurement of the average particle size of polymer particles in an aqueous dispersion Using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), particle size was measured by dynamic light scattering and calculated by cumulant analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, an aqueous pigment dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5) and the solid content concentration was 2 × 10⁻⁶. -4 Water was added to the solution to a mass percentage, and the mixture was stirred using a magnetic stirrer at 25°C for 1 hour.

[0051] (3) Measurement of solid content concentration 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 ml polypropylene container (φ: 40 mm, height: 30 mm). Approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatile components. After that, it was left in the desiccator for another 15 minutes and the mass was measured. The mass of the sample after removal of volatile components was taken as the solid content, and the solid content concentration was obtained by dividing it by the mass of the added sample.

[0052] [Manufacturing Example 1 (Production of Water-Insoluble Polymer Solution)] 16 parts of methacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 15 parts of styrene macromonomer "AS-6S" (manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solids content 50%), 24.5 parts of polyethylene glycol monomethyl ether monomethacrylate "Bremmer PME-200" (NOF Co., Ltd.), and 0.5 parts of polypropylene glycol monomethacrylate "Bremmer PP-1000" (NOF Co., Ltd.) were mixed, and the mixture was thoroughly purged with nitrogen gas to obtain a mixed solution. In the reaction vessel, 10 parts methyl ethyl ketone, 0.02 parts 2-mercaptoethanol (a chain transfer agent), and 20% of the monomer mixture were added and mixed, and the vessel was thoroughly purged with nitrogen gas. Meanwhile, the remaining 80% (80 parts) of the monomer mixture was mixed with 0.08 parts of a chain transfer agent, 42 parts of methyl ethyl ketone, and 0.5 parts of the polymerization initiator 2,2'-azobis(2,4-dimethylvaleronitrile) "V-65" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). This mixture was placed in a dropping funnel, and under a nitrogen atmosphere, the mixture in the reaction vessel was heated to 75°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C following the completion of the dropwise addition, a solution of 3 parts polymerization initiator dissolved in 5 parts methyl ethyl ketone was added. The mixture was then aged for a further 2 hours at 75°C and 2 hours at 80°C, and 50 parts of methyl ethyl ketone were added to obtain a solution of water-insoluble polymer (weight-average molecular weight: 60,000). The solid content concentration of this solution was 45% by mass.

[0053] [Manufacturing Example 2 (Manufacturing of K-1, an aqueous dispersion of carbon black-containing polymer particles)] 95.6 parts of the water-insoluble polymer solution obtained in Production Example 1 were dissolved in 53.9 parts of methyl ethyl ketone. To this solution, 14.8 parts of 5N sodium hydroxide aqueous solution and 341.3 parts of deionized water were added as neutralizing agents. Further, 100 parts of carbon black (Cabot Corporation, trade name: Monarch 717) were added to obtain a pigment mixture. The degree of neutralization was 75.5 mol%. The pigment mixture was mixed using a disperser blade at 2600 rpm and 20°C for 1 hour. The resulting dispersion was subjected to 15-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer "High-Pressure Homogenizer M-7115" (Microfluidics Corporation).

[0054] The obtained dispersion of carbon black-containing polymer particles was subjected to reduced pressure at 60°C to remove methyl ethyl ketone, and then some water was removed to achieve a solid content concentration of 25% by mass. The dispersion was then centrifuged, and the liquid layer was filtered through a "Minisart syringe filter" (Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion of carbon black-containing polymer particles. To 100 parts of the obtained aqueous dispersion of carbon black-containing polymer particles, 0.45 parts of Denacol EX321L (Nagase ChemteX Corporation) and 10.0 parts of deionized water were added, and the mixture was heated at 70°C for 3 hours while stirring. After cooling to room temperature, the liquid layer was filtered through a "Minisart syringe filter" (Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion of carbon black-containing polymer particles K-1 (solid content concentration 23.0%, pigment 15.8%, polymer 7.2%). The average particle size of the carbon black-containing polymer particles was 100 nm.

[0055] [Manufacturing Example 3 (Manufacturing of C-1 aqueous dispersion of cyanide pigment-containing polymer particles)] In Production Example 2, the carbon black was replaced with a copper phthalocyanine-based cyanide pigment (manufactured by DIC, product name: Fastogen Blue TGR-SD). The same process as in Production Example 2 was carried out to obtain an aqueous dispersion of cyanide pigment-containing polymer particles C-1 (solids content 23.0%, pigment 15.8%, polymer 7.2%). The average particle size of the cyan pigment-containing polymer particles was 90 nm.

[0056] [Manufacturing Example 4 (Manufacturing of K-2, an aqueous dispersion of carbon black-containing polymer particles)] By removing some of the water from the aqueous dispersion of carbon black-containing polymer particles K-1 (solid content concentration 23%) obtained in Production Example 2, so that the solid content concentration became 28% by mass, an aqueous dispersion of carbon black-containing polymer particles K-2 was obtained.

[0057] [Manufacturing Example 5 (Manufacturing of aqueous dispersion of cyanide pigment-containing polymer particles C-2)] By removing some of the water from the aqueous dispersion of cyanide pigment-containing polymer particles C-1 (solid content concentration 23%) obtained in Production Example 3, so that the solid content concentration became 28% by mass, an aqueous dispersion of cyanide pigment-containing polymer particles C-2 was obtained.

[0058] [Example 1] 41.7 parts of an aqueous dispersion of carbon black-containing polymer particles obtained in Production Example 2, 5.7 parts of an aqueous dispersion of cyanide pigment-containing polymer particles obtained in Production Example 3, 13.9 parts of propylene glycol (PG; manufactured by AGC), 7.0 parts of dipropylene glycol (DPG; manufactured by ADEKA), and 0.2 parts (in form) of an acetylene glycol-based surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name: Surfinol 104PG50, PG (50% by mass) solution) as a nonionic surfactant were combined. Deionized water was then added and mixed to a total volume of 100 parts. The resulting mixture was filtered using a 25 mL needleless syringe fitted with a 1.2 μm filter (acetylcellulose membrane, outer diameter 2.5 cm, manufactured by Sartorius) to remove coarse particles and obtain water-based ink 1.

[0059] [Examples 2-7 and Comparative Examples 1-4] Aqueous inks for Examples 2-7 and Comparative Examples 1-4 were obtained in the same manner as in Example 1, except that the formulation composition was changed as shown in Table 1.

[0060] The obtained water-based inks were evaluated for print density and abrasion resistance using the following method, and the results are shown in Table 1.

[0061] (Inkjet recording method) In an environment with a temperature of 23±1℃ and a relative humidity of 50±5%, a printing evaluation device (manufactured by Trytech Co., Ltd.) equipped with an inkjet head (Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) was filled with water-based ink. The head voltage was set to 26V, frequency to 20kHz, appropriate amount of ejected liquid to 12pL, head temperature to 32℃, resolution to 600dpi, number of pre-ejection flushing cycles to 200, and negative pressure to -4.0kPa. The recording medium was fixed to the transport table under reduced pressure with its longitudinal direction and transport direction being the same. A print command was transferred to the printing evaluation device, and a 5cm square solid image with a duty cycle of 100% was printed.

[0062] <Evaluation of print density on high-quality paper> Using each water-based ink, the above 100% duty cycle solid images were formed on two types of A4-sized fine paper (manufactured by Nippon Paper Industries, product name: Japanese Color Fine Paper <Thin> White and Light Pink) using the following inkjet recording method. The obtained images were left to stand for 1 hour to obtain printed materials. Printing on white fine paper was performed only with the water-based inks of the example. Subsequently, the print density at a total of five locations—the center and the four corners of the printed area—was measured using a spectrophotometer (manufactured by X-Rite, product name: X-Rite eXact, conditions: light source D50, field of view 2°, density standard DIN, white base "Abs", built-in filter "No", ISO status A). The average value of the print density at any five locations on the printed surface of the obtained printed material was calculated as the print density on fine paper. In Table 1, light pink high-quality paper is referred to as "red-toned high-quality paper," and white high-quality paper is referred to as "white-toned high-quality paper." Furthermore, CIE1976(L) is applied to any 10 locations on the light pink fine paper. * ,a * ,b * ) Coordinate values ​​in the color space (L * ,a * ,b * The coordinate values ​​(L) were measured and the average value was calculated. * ,a * ,b * When the h h in ) was determined, it was confirmed to fall within the range of 0° to 45° and 315° to less than 360°.

[0063] <Criteria for evaluating abrasion resistance> An image was formed on high-quality paper (manufactured by Nippon Paper Industries, product name: Japanese Color High-Quality Paper <Thin> Light Pink) using the same method as the inkjet recording method used to evaluate the print density on high-quality paper described above, and a 5cm square 100% duty solid image was obtained. After the obtained image was left to stand for 1 hour, a 1cm square piece of high-quality paper was pressed against it, and a load of 2kg was applied to rub off the printed surface. The abrasion resistance was evaluated from the change in the printed surface after the test (absorption rate (%)). The evaluation criteria for abrasion resistance are as follows: A: Scratching was observed in 0% to less than 10% of the test area. B: Scratching was observed in 10% to less than 20% of the test area. C: Scratching was observed in 20% to less than 25% of the test area. D: Scratching was observed in more than 25% of the test area.

[0064] The scraping rate (%) was calculated as follows: Before and after the scraping test, solid images were captured at 640 x 480 pixels using the portable magnifying camera "PIAS-II" (manufactured by Quality Engineering Associates). The image area was calculated using the image analysis software "Image-J," and the scraping rate (%) was calculated using the following formula. Scratch rate (%) = [1 - (Remaining area of ​​solid image after scratch test) / (Initial area of ​​solid image before scratch test)] × 100

[0065] [Table 1]

[0066] As can be seen from Table 1, the printed materials using the water-based ink in the examples exhibit high print density and excellent abrasion resistance, regardless of whether red or white high-quality paper is used. A comparison of Examples 1-4 shows that, when the total mass of carbon black and cyan pigment remains constant, the larger the mass ratio [cyan pigment / carbon black], the higher the print density on red-toned fine paper. Furthermore, a comparison of Example 6 with Comparative Example 2 shows that, despite having a lower carbon black content than Comparative Example 2, Example 6 maintains print density on white-toned fine paper. Additionally, although Example 6 and Comparative Example 2 have the same total mass of carbon black and cyan pigment, Example 6 exhibits superior abrasion resistance, likely because the cyan pigment acts as a binder, binding the carbon black together. Furthermore, a comparison of Examples 3 and 5-7 shows that, while the mass ratio [cyan pigment / carbon black] remains constant, the total mass of carbon black and cyan pigment increases, resulting in higher print density regardless of whether red or white high-quality paper is used. [Industrial applicability]

[0067] According to the present invention, an inkjet water-based black ink that can produce printed materials with high print density and excellent abrasion resistance, and printed materials with high print density and excellent abrasion resistance can be obtained.

Claims

1. A water-based black ink for inkjet recording containing carbon black, cyan pigment, organic solvent, and water, The mass ratio of the cyan pigment content to the carbon black content [cyan pigment / carbon black] exceeds 0.

13. A water-based black ink for inkjet recording, wherein the total mass of the carbon black content and the cyan pigment content is greater than 4% by mass and less than 15% by mass.

2. The aqueous black ink for inkjet recording according to claim 1, wherein the content of an organic solvent with a boiling point of 260°C or higher is 3% by mass or less.

3. The aqueous black ink for inkjet recording according to claim 1 or 2, wherein the organic solvent contains a diol with a boiling point of less than 260°C.

4. The water-based black ink for inkjet recording according to claim 1 or 2, wherein the mass ratio of the cyan pigment content to the carbon black content [cyan pigment / carbon black] is 0.4 or less.

5. A printed material using water-based black ink for inkjet recording according to claim 1 or 2.

6. The printed material according to claim 5, wherein the printing substrate is red-colored paper. Here, the aforementioned red-colored paper is CIE1976(L ＊ , a ＊ , b ＊ ) The h h in the color space is included in the range of 0° to 45° and 315° to less than 360°, and the h is arctan(b ＊ / a ＊ )

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