Carbon black aqueous dispersion and aqueous ink composition

Abstract

To provide a carbon black aqueous dispersion in which the particle diameter of dispersed carbon black is small, and the dispersibility of carbon black is excellent, and to provide an aqueous ink composition in which the particle diameter of dispersed carbon black is small, the dispersibility of carbon black is excellent, the settling of carbon black can be suppressed even after long-term storage, and the storage stability is excellent.SOLUTION: A carbon black aqueous dispersion or an aqueous ink composition comprises (A) carbon black, (B) water, and (C) a dispersion resin having repeating units represented by formula (1) (in formula (1), R1 is hydrogen or a methyl group).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous carbon black dispersion and an aqueous ink composition for a writing instrument, particularly to an aqueous carbon black dispersion having good pigment dispersibility, and an aqueous ink composition having good pigment dispersibility and good storage stability, which is useful for writing instruments such as felt-tip pens, marking pens, and ballpoint pens. [Background technology]

[0002] When producing an aqueous ink composition for a writing instrument having a black color tone, it is common to produce an aqueous carbon black dispersion using carbon black, which has excellent color development properties and fastness, as a black coloring material, and use the resulting dispersion as a colorant. Since carbon black does not dissolve in water, when producing an aqueous carbon black dispersion, it is necessary to micronize the carbon black using a dispersing machine to reduce the dispersed particle size, and also to use a dispersing resin to stably disperse the carbon black in water as fine particles. Furthermore, in a water-based ink composition containing carbon black as a coloring material, it is necessary that an increase in the dispersed particle size is suppressed even after long-term storage at high or low temperatures.

[0003] Patent Document 1 discloses a water-based pigment dispersion that is characterized by containing at least a pigment, an alkali-soluble resin dispersant, a surfactant, and water. This water-based pigment dispersion is said to be suitable for use as a colorant for inkjet printer inks and writing instrument inks, since the pigment particle size does not change even when the temperature conditions change, from room temperature to high temperatures, or even when the dispersion is subjected to repeated freezing and thawing.

[0004] Patent Document 2 describes a compound comprising carbon black, an aqueous medium, and the following general formula (1): R 1 R 2 NR 3 -(SO3M) n (1) This carbon black aqueous dispersion is said to have excellent dispersibility and dispersion stability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-73787 [Patent Document 2] Japanese Patent Application Publication No. 11-189736 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have discovered that in an aqueous carbon black dispersion containing carbon black and water, a compound represented by the formula (1): [ka] (In formula (1), R 1 is hydrogen or a methyl group. It has been found that by using a dispersion resin having a repeating unit represented by the following formula: Furthermore, the present inventors have discovered that in an aqueous ink composition containing carbon black and water, a dispersing resin represented by the formula (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. The present inventors have found that by using a dispersion resin having a repeating unit represented by the following formula (I), it is possible to reduce the dispersed particle size of carbon black, improve the dispersibility of carbon black, and inhibit settling of carbon black even after long-term storage, thereby providing excellent storage stability.

[0007] One of the problems to be solved by the present invention is to provide an aqueous dispersion of carbon black in which the dispersed particle size of carbon black is small and the dispersibility of carbon black is good. One of the problems to be solved by the present invention is to provide an aqueous ink composition having excellent storage stability, in which the dispersed particle size of carbon black is small, the dispersibility of carbon black is good, and sedimentation of carbon black can be suppressed even after long-term storage. One of the problems to be solved by the present invention is to provide a polymerizable composition comprising carbon black, water, and a polymerizable compound represented by the following formula (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula: The present invention provides an aqueous carbon black dispersion or an aqueous ink composition comprising: [Means for solving the problem]

[0008] As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an aqueous carbon black dispersion and an aqueous ink composition having the following compositions, and have thus completed the present invention. Specifically, the following applies: [Section 1] (A) carbon black, (B) Water; (C) Formula (1): [ka] (In formula (1), R 1 is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula: 1. An aqueous carbon black dispersion comprising: [Section 2] (A) carbon black, (B) Water; (C) Formula (1): [ka] (In formula (1), R 1 is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula: 1. A water-based ink composition comprising: Effect of the Invention

[0009] The present invention provides an aqueous carbon black dispersion in which the dispersed particle size of carbon black is small and the dispersibility of carbon black is good. The present invention provides an aqueous ink composition having excellent storage stability, in which the dispersed particle size of carbon black is small, the dispersibility of carbon black is good, and sedimentation of carbon black can be suppressed even after long-term storage. The mechanism by which the dispersed carbon black particle size is small and the dispersibility of carbon black is good in the carbon black aqueous dispersion of the present invention is unknown, and the mechanism by which the dispersed carbon black particle size is small, the dispersibility of carbon black is good, and sedimentation of carbon black can be suppressed even after long-term storage in the aqueous ink composition of the present invention is excellent in storage stability is also unknown, but the present inventors speculate as follows.

[0010] The dispersing resin contained in the carbon black aqueous dispersion and the aqueous ink composition of the present invention is a resin represented by the formula (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. When a dispersion resin having a repeating unit represented by formula (1) is used, the carbitol ester chain (-C(=O)O-CH2CH2-O-CH2CH2-O-CH2CH3) in the repeating unit present in the molecule of the dispersion resin improves the water solubility of the dispersion resin itself, and the carbitol ester chain increases the number of steric repulsion action points of the dispersion resin. This is thought to result in the carbon black in the carbon black aqueous dispersion and aqueous ink composition being inhibited from agglomerating and growing into coarse particles, maintaining the small dispersed particle size during dispersion, and improving dispersibility. In addition, due to the carbitol ester chains in the molecules of the dispersion resin contained in the aqueous ink composition, the water solubility of the dispersion resin itself is improved and the number of steric repulsion action points of the dispersion resin is increased, and it is presumed that this maintains the dispersion stability of the carbon black even after the aqueous ink composition is stored for a long period of time under high or low temperature conditions, resulting in an aqueous ink composition with excellent storage stability. However, the present invention is not limited to this speculation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The carbon black aqueous dispersion and the aqueous ink composition of the present invention will be described in detail below.

[0012] [Carbon black aqueous dispersion] The carbon black aqueous dispersion according to the present invention comprises (A) carbon black, (B) water, and (C) a compound represented by the following formula (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula: The carbon black aqueous dispersion comprises: The carbon black aqueous dispersion of the present invention may further contain components such as a water-soluble organic solvent, a surfactant, a preservative, an antifungal agent, etc. Each component will be described in detail below.

[0013] <Carbon black> The type of carbon black contained in the carbon black aqueous dispersion of the present invention is not particularly limited. For example, it is preferable to use furnace black, acetylene black, ketjen black, thermal black, carbon nanotube, graphene, graphite, etc. These carbon blacks can be used alone or in combination of two or more.

[0014] The average primary particle size of carbon black is not particularly limited. For example, it is 60 nm or less. It is preferably 30 nm or less, more preferably 25 nm or less, and preferably 10 nm or more. If the average primary particle size exceeds 60 nm, the handwriting may have a glossy appearance. If the average primary particle size is less than 10 nm, the blackness may decrease. The average primary particle diameter of carbon black is determined by observing carbon black under an electron microscope, calculating the projected area of ​​100 particles, calculating the diameter of a circle that is equal to that area, and then averaging the diameters of the 100 particles to determine the average primary particle diameter. If the pigment is in an agglomerated state, the calculation is based on the primary particles that make up the agglomerated particles. If a commercially available product is used as carbon black, the catalog value may be used.

[0015] The dibutyl phthalate oil absorption of carbon black (hereinafter sometimes referred to as "DBP oil absorption") is not particularly limited. For example, it is 40 ml / 100 g or more and 300 ml / 100 g or less. If the DBP oil absorption is less than 40 ml / 100 g, the carbon black may sink from the paper surface, resulting in a low blackness. If the DBP oil absorption exceeds 300 ml / 100 g, the carbon black may become too bulky, resulting in a low blending amount and a low blackness. The DBP oil absorption can be measured by a method in accordance with JIS K6217-4. A high DBP oil absorption indicates that the primary particles of carbon black are connected and entangled, forming a well-developed "structure."

[0016] The specific surface area of ​​carbon black is determined based on viscosity, dispersibility, etc., and is, for example, 1 m 2 / g or more, preferably 30m 2 / g or more, for example, 500m 2 / g or less, preferably 250m 2 / g or less.

[0017] As the carbon black, various commercially available products can be used. For example, one or more types selected from commercially available products such as NEROX series, Printex series, Color Black series, Special Black series, Toka Black series, SB series, Mitsubishi Carbon Black series, etc. Also, commercially available aqueous dispersions of carbon black can be used.

[0018] The carbon black content in the carbon black aqueous dispersion is not particularly limited. From the viewpoint of blackness and dispersibility, the carbon black content is, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 22% by mass or more, and is, for example, 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 28% by mass or less, based on the total amount of the carbon black aqueous dispersion (100% by mass). If it is less than 5% by mass, it may be difficult to impart a desired color tone (blackness). If it exceeds 50% by mass, the viscosity of the carbon black aqueous dispersion may be high, which may limit the dispersing machine that can be used, and the dispersibility of the carbon black may be reduced.

[0019] <Water> The water contained in the aqueous carbon black dispersion of the present invention functions as a dispersion medium and / or a solvent for dispersing carbon black, dispersing and / or dissolving the dispersion resin, and dispersing and / or dissolving other components such as the water-soluble organic solvent. Examples of water that can be used include tap water, purified water, distilled water, ion-exchanged water, and pure water. Preferably, ion-exchanged water and distilled water are used. The content of water is not particularly limited, and can be appropriately adjusted depending on the content of each component in the carbon black aqueous dispersion, the viscosity of the aqueous carbon black dispersion, etc. In the total amount of the carbon black aqueous dispersion (100 mass%), the content is, for example, 5.0 mass% or more, preferably 10.0 mass% or more, more preferably 20.0 mass% or more, and even more preferably 25.0 mass% or more, and is, for example, 75.0 mass% or less, preferably 60.0 mass% or less, more preferably 50.0 mass% or less, and even more preferably 40.0 mass% or less. If it is less than 5.0 mass%, the viscosity of the carbon black aqueous dispersion may be high, which may limit the dispersing machine that can be used, and the dispersibility of the carbon black may be reduced. If it exceeds 75.0 mass%, the carbon black may be insufficiently wetted, which may deteriorate the dispersibility and dispersion stability of the carbon black.

[0020] <Dispersion resin> The dispersing resin contained in the aqueous carbon black dispersion of the present invention disperses carbon black in a fine particle state and imparts dispersion stability to the dispersed carbon black fine particles. [ka] (In formula (1), R 1 is hydrogen or a methyl group. The dispersing resin has a repeating unit represented by the following formula:

[0021] The dispersing resin having a repeating unit represented by formula (1) is, for example, a repeating unit represented by formula (2); [ka] (In formula (2), R 1 is hydrogen or a methyl group. The monomer represented by the formula (I) can be used as a constituent monomer of the dispersing resin.

[0022] The dispersion resin may contain, in addition to the monomer represented by formula (2), one or more monomers having an anionic group and one or more other monomers as constituent monomers. Examples of monomers having an anionic group include monomers having a carboxyl group, a sulfonic acid group, and a phosphoric acid group. From the viewpoints of dispersion stability and long-term storage stability, preferred are monomers containing a carboxyl group, such as (meth)acrylic acid and maleic anhydride. Examples of the other monomers include one or more selected from the group consisting of styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene; (meth)acrylic acid ester-based monomers such as (meth)acrylic acid alkyl esters; acrylic acid ester-based monomers having functional groups such as hydroxyethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate; and olefin-based monomers such as ethylene.

[0023] The dispersion resin is preferably a dispersion resin having a repeating unit represented by the formula (1), a repeating unit from a monomer containing a carboxyl group as a monomer having an anionic group, and a repeating unit from a styrene-based monomer, and may further have a repeating unit from a (meth)acrylic acid ester monomer. For example, styrene-(meth)acrylic acid copolymer having a repeating unit represented by the formula (1), styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer having a repeating unit represented by the formula (1), styrene-α-methylstyrene-(meth)acrylic acid copolymer having a repeating unit represented by the formula (1), styrene-(meth)acrylic acid-based resin such as styrene-α-methylstyrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer having a repeating unit represented by the formula (1), etc.

[0024] The content of the repeating unit represented by formula (1) in the dispersed resin is, for example, 0.5 mass% or more, preferably 1 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2.0 mass% or more, based on 100 mass% of all repeating units in the dispersed resin, and is, for example, 15 mass% or less, preferably 10 mass% or less, and more preferably 7 mass% or less. The content of repeating units from anionic group-containing monomers (monomers containing a carboxyl group) in the dispersion resin is, for example, 15.0 mass% or more, preferably 20.0 mass% or more, more preferably 30.0 mass% or more, and for example, 55.0 mass% or less, preferably 50.0 mass% or less, more preferably 45.0 mass% or less, based on 100 mass% of all repeating units in the dispersion resin.

[0025] The weight average molecular weight of the dispersing resin is not particularly limited, and is, for example, 1,000 or more, preferably 1,500 or more, more preferably 2,000 or more, further preferably 5,000 or more, particularly preferably 8,100 or more, and is, for example, 25,000 or less, preferably 20,000 or less, more preferably 12,000 or less.

[0026] The acid value (mgKOH / g) of the dispersion resin is not particularly limited. For example, it is 80 mgKOH / g or more, preferably 100 mgKOH / g or more, more preferably 120 mgKOH / g or more, and even more preferably 170 mgKOH / g or more, and for example, it is 400 mgKOH / g or less, preferably 300 mgKOH / g or less, more preferably 240 mgKOH / g or less, and even more preferably 230 mgKOH / g or less. When the acid value of the dispersion resin is less than 80 mgKOH / g, the water solubility of the dispersion resin decreases, the dispersion stability of the carbon black in the carbon black aqueous dispersion may decrease, and the viscosity of the carbon black aqueous dispersion may increase. When the acid value of the dispersion resin is more than 400 mgKOH / g, a large amount of neutralizing agent is required to neutralize the dispersion resin, which increases the environmental load, and the dispersion stability of the carbon black in the carbon black aqueous dispersion may decrease, and the viscosity of the carbon black aqueous dispersion may increase.

[0027] The dispersion resin is preferably such that an anionic group in the molecule, preferably a carboxyl group, forms a salt (is neutralized). Examples of compounds that form a salt with the anionic group include inorganic bases such as sodium hydroxide and potassium hydroxide, and organic bases such as ammonia, diethylamine, ethylamine, triethylamine, propylamine, isopropylamine, dipropylamine, butylamine, isobutylamine, triethanolamine, diethanolamine, aminomethylpropanol, and morpholine. One or more types of inorganic bases and organic bases can be used, and inorganic bases and organic bases can be used in combination.

[0028] The content of the dispersion resin in the carbon black aqueous dispersion is not particularly limited. For example, it is, for example, 0.5% by mass or more, preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and for example, 15.0% by mass or less, preferably 10.0% by mass or less, more preferably 8.0% by mass or less, based on the total amount of the carbon black aqueous dispersion (100% by mass). If it is less than 0.5% by mass, the dispersibility and dispersion stability of the carbon black may be deteriorated, and if it exceeds 15.0% by mass, the viscosity of the carbon black aqueous dispersion may be too high, and the dispersibility of the carbon black may be deteriorated.

[0029] <Water-soluble organic solvent> The carbon black aqueous dispersion of the present invention may contain a water-soluble organic solvent. The water-soluble organic solvent is an organic solvent that has a solubility in water at 20° C. of 1 g / L or more, preferably 10 g / L or more, more preferably 100 g / L or more, and most preferably is a solvent that is uniformly miscible in any ratio. Examples of the water-soluble organic solvent include monoalcohols, polyhydric alcohols, alkyl ethers of polyhydric alcohols, ketones, ethers, esters, nitrogen-containing compounds, etc. These can be used alone or in combination of two or more.

[0030] Examples of monoalcohols include one or more selected from the group consisting of methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, cyclopentanol, cyclohexanol, and the like.

[0031] Examples of polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-heptanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, butylene glycol, dibutylene glycol, and glycerin.

[0032] Examples of alkyl ethers of polyhydric alcohols include ethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol methylethyl ether, diethylene glycol diethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and triethylene glycol monopropyl. and glycol dialkyl ethers such as dimethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol butyl methyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol butyl methyl ether, and tetraethylene glycol diethyl ether.

[0033] Examples of the esters include one or more selected from the group consisting of γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, and the like.

[0034] Examples of nitrogen-containing solvents include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, ε-caprolactam, 3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, N,N-dimethyl-β-methoxypropionamide, N,N-dimethyl-β-ethoxypropionamide, N,N-dimethyl-β-butoxypropionamide, N,N-dimethyl-β-pentoxypropionamide, N,N-dimethyl-β-hexoxypropionamide, and N,N-dimethyl-β ... and N,N-dimethyl-β-hexoxypropionamide, N,N-dimethyl-β-octoxypropionamide, N,N-diethyl-β-butoxypropionamide, N,N-diethyl-β-pentoxypropionamide, N,N-diethyl-β-hexoxypropionamide, N,N-diethyl-β-heptoxypropionamide, N,N-diethyl-β-octoxypropionamide, and the like.

[0035] Of these, ethylene glycol, propylene glycol, glycerin, and 1,6-hexanediol are preferred.

[0036] The content of the water-soluble organic solvent is not particularly limited and is, for example, 0% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, and for example, 20.0% by mass or less, preferably 15.0% by mass or less, more preferably 10% by mass or less, based on 100% by mass of the carbon black aqueous dispersion.

[0037] <Colorants other than carbon black> The carbon black aqueous dispersion of the present invention may contain a colorant other than carbon black, if necessary, to impart a black hue and an aesthetic black tone. Any colorant may be used without particular limitation as long as it has properties such as good sedimentation stability in the aqueous dispersion and excellent storage stability. The colorant is preferably one that is used in aqueous ink compositions, particularly aqueous ink compositions for writing instruments. As colorants other than carbon black, for example, inorganic pigments, organic pigments, dyes, colored resin spheres, etc. of any color tone can be used. The content of the colorant other than carbon black is not particularly limited. The colorant can be contained so that the color tone of the carbon black aqueous dispersion becomes the desired color tone.

[0038] Examples of the inorganic pigment include one or more selected from the group consisting of graphite, titanium oxide, zinc oxide, red iron oxide, yellow iron oxide, ultramarine blue, dark blue, metal powders such as aluminum powder and bronze powder, extender pigments such as talc, silica, alumina, mica, and aluminosilicate, fluorescent pigments, glass flakes, and lustrous pigments. Examples of the organic pigment include one or more selected from the group consisting of coloring pigments such as phthalocyanine-based, azo-based, quinacridone-based, anthraquinone-based, quinacridone-based, isoindolinone-based, diketopyrrolopyrrole-based, dioxane-based, indigo-based, thioindigo-based, perinone-based, perylene-based, indolenone-based, and azomethine-based, and fluorescent pigments. The dye may be any of direct dyes, acid dyes, food dyes, and basic dyes, and water-soluble dyes are preferred. For example, one or more selected from the group consisting of coloring dyes and fluorescent dyes such as anthraquinone-based, methine-based, carbonium-based, and metal complex salt-based are included. The colored resin spheres are those obtained by coloring resin spheres such as spherical, amorphous, hollow, and flat shapes with one or more colorants exhibiting any color tone. Examples of the resin material for forming the colored resin spheres include polyethylene, polypropylene, vinyl chloride, polymethacrylate, benzoguanamine, melamine resin, and nylon. Examples of the colorant for coloring the colored resin spheres include one or more selected from the group consisting of the above-mentioned inorganic pigments, organic pigments, and dyes.

[0039] <pH adjuster> The carbon black aqueous dispersion may contain a pH adjuster to adjust the pH value, prevent gelation, etc. Examples of the pH adjuster include one or more selected from the group consisting of alkali metal hydroxides or aqueous solutions thereof, such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, salts, such as sodium carbonate, sodium phosphate, sodium acetate, and sodium benzoate, amine compounds, such as triethanolamine, aminomethylpropanol, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine, and triethylamine, and ammonia (water). The content of the pH adjuster in the aqueous carbon black dispersion is not particularly limited, and is an amount that makes the pH of the aqueous carbon black dispersion, for example, from 6.0 to 10.0.

[0040] <Other additives> The carbon black aqueous dispersion of the present invention may contain, as necessary, other additives in addition to the carbon black, water, dispersing resin, water-soluble organic solvent, colorant other than carbon black, and pH adjuster, such as one or more additives selected from the group consisting of resins other than the dispersing resin, dispersants, viscosity adjusters (thickeners), anti-agglomeration agents, and defoamers.

[0041] <Applications of carbon black aqueous dispersions> The carbon black aqueous dispersion of the present invention can be used for various applications. For example, it can be used for coloring dispersions, varnish colorants, paints, coatings, ink compositions, and paper and fiber materials. It is preferably used as an aqueous ink composition, particularly preferably as an aqueous ink composition for writing instruments.

[0042] [Water-based ink composition] The aqueous ink composition of the present invention comprises (A) carbon black, (B) water, and (C) a compound represented by the following formula (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. and a dispersion resin having a repeating unit represented by the formula: The water-based ink composition of the present invention may further contain a water-soluble organic solvent, a colorant other than carbon black, and a pH adjuster. It may also contain other additives. Each component will be described in detail below.

[0043] The carbon black, water, dispersion resin having a repeating unit represented by formula (1), water-soluble organic solvent, colorant other than carbon black, and pH adjuster contained in the aqueous ink composition of the present invention may each be one or more of the same materials as those described above in the section [Aqueous Carbon Black Dispersion].

[0044] <Other additives> The aqueous ink composition of the present invention may contain other additives as necessary. The other additives are not particularly limited as long as they are used in aqueous ink compositions for writing instruments. For example, one or more additives selected from the group consisting of resins other than the dispersion resin, dispersants, surfactants, viscosity adjusters (thickeners), preservatives and mildew inhibitors, rust inhibitors, wetting agents, etc. may be mentioned. Furthermore, lubricants, defoamers, leveling agents, anti-aggregating agents, ultraviolet absorbers, infrared absorbers, antioxidants, etc. may be used in appropriate amounts as necessary.

[0045] (Resins and dispersants other than dispersing resins) The aqueous ink composition may contain a resin / dispersant other than the dispersing resin for the purposes of increasing the viscosity and fixing the handwriting on a suitable writing surface when the solvent evaporates after writing on the writing surface, and for the purposes of stabilizing the dispersion of pigments such as carbon black. Dispersion resins and resins / dispersants other than dispersion resins have the effect of preventing pigment precipitation by stabilizing the pigment after dispersion, and at the same time function as vehicles / binders for forming a coating film of the water-based ink composition.

[0046] The resin / dispersant other than the dispersing resin is not particularly limited as long as it is used in an aqueous ink composition, particularly an aqueous ink composition for writing instruments, and commercially available products may be used. For example, one or more resins selected from the group consisting of (meth)acrylic acid resins, maleic acid resins, styrene-(meth)acrylic acid resins, styrene-maleic acid resins, styrene-maleic acid ester resins (emulsions), (meth)acrylic acid ester resins, polyvinyl alcohol resins, water-soluble urethane resins, (meth)acrylic acid ester resins, cellulose resins such as sodium carboxymethylcellulose, vinyl acetate resins, etc., resin solutions, or resin emulsions may be used.

[0047] The content of the resin / dispersant other than the dispersing resin in the aqueous ink composition is not particularly limited. It is, for example, 0% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and for example, 30% by mass or less, preferably 10% by mass or less, based on the total amount of the aqueous ink composition. If it exceeds 30% by mass, it may act as a flocculant and cause pigment aggregation. If pigment aggregation occurs, there is a risk of pigment sedimentation occurring in the ink.

[0048] (Surfactant) The aqueous ink composition of the present invention may contain a surfactant in order to improve storage stability, adjust viscosity, and improve pigment dispersibility. The surfactant may be any of anionic, nonionic, and amphoteric surfactants. For example, one or more selected from the group consisting of anionic surfactants such as sulfonic acid surfactants (e.g., alkylarylsulfonic acid (salt), sulfosuccinic acid ester, sulfosuccinic acid diester, etc.), phosphorus surfactants (e.g., alkyl phosphate ester, alkyl ether phosphate ester, alkylaryl phosphate ester, etc.), nonionic surfactants such as ether surfactants (polyoxyalkylene alkyl ether, etc.), acetylene glycol surfactants, and ester surfactants (polyoxyalkylene fatty acid ester, polyoxyalkylene alkylaryl ether, sorbitan fatty acid ester, glycerin fatty acid ester, etc.), and fluorine-based surfactants may be used. In the present invention, among these surfactants, one or more selected from the group consisting of anionic surfactants (e.g., sulfonic acid surfactants) and nonionic surfactants (e.g., acetylene glycol surfactants) are preferably used in terms of wetting / penetrating function, emulsifying function, dispersing function, etc.

[0049] (Viscosity modifier (thickener)) The aqueous ink composition may contain a viscosity modifier (thickener) for adjusting the viscosity. The viscosity modifier (thickener) is not particularly limited as long as it is used in aqueous ink compositions, particularly aqueous ink compositions for writing instruments. For example, one or more selected from the group consisting of polysaccharides and derivatives thereof, such as xanthan gum, welan gum, succinoglycan (rheosan), diutan gum, guar gum, locust bean gum and derivatives thereof, cellulose-based polymers, crosslinkable acrylic acid polymers, alkali-thickening acrylic resins, urethane association-type thickeners, N-vinylacetamide resins, inorganic fine particles, etc. may be mentioned. The content of the viscosity modifier (thickener) in the aqueous ink composition is not particularly limited and is appropriately set so that the aqueous ink composition has an appropriate viscosity depending on the application. For example, the content is 0% by mass or more, preferably 0.1% by mass or more, and for example, 10.0% by mass or less, preferably 8.0% by mass or less, based on the total amount of the ink composition.

[0050] (Anti-septic and anti-fungal agent) The aqueous ink composition may contain an antiseptic / antifungal agent to suppress spoilage and mold growth. The antiseptic / antifungal agent is not particularly limited as long as it is used in aqueous ink compositions. For example, one or more types selected from the group consisting of isothiazolin-based, pentachlorophenol-based, cresol-based, propylene glycol-based, iodine-based, and other antiseptic / antifungal agents may be mentioned. For example, one or more selected from the group consisting of chloroacetamide, 2-pyridinethiol-1-oxide sodium salt, sodium dehydroacetate, sodium benzoate, sodium sorbate, potassium sorbate, 2-bromo-2-nitropropane-1,3-diol, 3-iodo-2-propynyl butylcarbamate, 1,2-benzisothiazolin-3(2H)-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one thiabendazole, phenoxyethanol, sodium fluoride, 4-(2-nitrobutyl)morpholine, 1,3-dimorpholino-2-ethyl-2-nitripropane, etc. may be mentioned. In the present invention, it is preferable to use an isothiazoline-based preservative (particularly a benzoisothiazoline-based preservative) and an organic iodine-based fungicide in combination. The content of the preservative / antifungal agent in the aqueous ink composition is not particularly limited, and is, for example, 0 mass % or more, preferably 0.01 mass % or more, and 2.00 mass % or less, preferably 1.00 mass % or less, relative to the total amount of the aqueous ink composition.

[0051] (rust inhibitor) The aqueous ink composition may contain a rust inhibitor to suppress corrosion of the metal constituting the refill. The rust inhibitor is not particularly limited as long as it is used in aqueous ink compositions, particularly aqueous ink compositions for writing instruments. For example, one or more types selected from the group consisting of benzotriazole, tolyltriazole, dicyclohexylammonium nitrate, etc. may be mentioned. The content of the rust inhibitor in the aqueous ink composition is not particularly limited, and is, for example, in the range of 0 mass % or more, preferably 0.01 mass % or more, and 2.00 mass % or less, preferably 1.00 mass % or less, relative to the total amount of the aqueous ink composition.

[0052] (Wetting agent) The aqueous ink composition may contain a humectant to adjust drying properties, etc. The humectant is not particularly limited as long as it is used in aqueous ink compositions, particularly aqueous ink compositions for writing instruments. For example, one or more selected from the group consisting of glycols such as glycerin, diglycerin, triglycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol, sugars such as sorbitol, mannitol, sucrose, glucose, and reduced starch hydrolysates, ureas such as urea, phosphates such as sodium pyrophosphate, and derivatives thereof can be used. The content of the wetting agent in the aqueous ink composition is not particularly limited and is appropriately set so that the drying property, etc. of the aqueous ink composition is appropriate for the application. For example, the content is 0% by mass or more, preferably 0.1% by mass or more, and for example, 40.0% by mass or less, preferably 25.0% by mass or less, based on the total amount of the aqueous ink composition.

[0053] <color tone> The color tone of the coating film of the water-based ink composition of the present invention is preferably black to gray. * a * b * Lightness L in color system * The value is preferably 0 to 80. L * a * b * The color system is a chromaticity a, which indicates the hue and saturation in a three-dimensional approximately uniform color space defined in JIS Z 8781-4. * value, chromaticity b * Value and lightness L * It consists of values. Lightness L * The closer the value is to 0, the more black the color is, and the closer the value is to 100, the more white the color is. chromaticity a * The larger the positive value, the stronger the red color, and the larger the negative value, the stronger the green color. chromaticity b * The larger the positive value, the stronger the yellow color, and the larger the negative value, the stronger the blue color.

[0054] The aqueous ink composition of the present invention may contain, as a pigment, a pigment having a blue, red, green, purple, yellow, or other color tone in addition to carbon black (black pigment) so that the coating film thereof has a black or gray color tone with a slight blue, red, green, purple, yellow, or other color tone.

[0055] The coating film of the water-based ink composition of the present invention, L * a * b * Chromaticity a, which indicates the hue and saturation in the color system * Value and chromaticity b * The value is not particularly limited. For black tone areas, lightness L * The value range is 0 to less than 30. For gray tone areas, lightness L * The value range is, for example, 30 or more, preferably 35 or more, more preferably 40 or more, and, for example, 80 or less, preferably 70 or less, more preferably 65 or less. chromaticity a * The value range is, for example, -20.0 or more, preferably -15.0 or more, more preferably -6.0 or more, and for example, +20.0 or less, preferably +15.0 or less, more preferably -0.5 or less. For example, the chromaticity a * A value in the range of -6.0 to -0.5 represents an achromatic color range, a value closer to -20.0 represents a greenish color range, and a value closer to +20.0 represents a reddish color range. chromaticity b *The value range is, for example, -20.0 or more, preferably -15.0 or more, more preferably +3.0 or more, and for example, +20.0 or less, preferably +15.0 or less, more preferably +10.0 or less. For example, chromaticity b * When the value is in the range of +3.0 or more and +10.0 or less, it becomes an achromatic color tone range. For example, the closer it is to -20.0, the more bluish the color tone range becomes, and for example, the closer it is to +20.0, the more yellowish the color tone range becomes. L * a * b * Lightness L in the color space * Value, chromaticity a * Value and chromaticity b * The value can be measured by using a spectrophotometer.

[0056] <Viscosity> The viscosity of the aqueous ink composition of the present invention can be appropriately set. For example, it can be in the range of 1 mPa·s to 10,000 mPa·s, preferably 2 mPa·s to 10,000 mPa·s, more preferably 3 mPa·s to 5,000 mPa·s (E-type rotational viscometer (for example, manufactured by Toki Sangyo Co., Ltd., TVE-type viscometer, 3°R14 cone, 0.5 rpm)). If the viscosity of the aqueous ink composition is less than 1 mPa·s, the fluidity of the ink may become too high and may become uncontrollable, and there may be problems in terms of sedimentation stability and the like. If the viscosity of the aqueous ink composition exceeds 10,000 mPa·s, the viscosity may become too high, and there may be problems in terms of ink handleability, sedimentation stability, bleeding of handwriting, manufacturing cost, and the like.

[0057] <pH value> The pH of the aqueous ink composition of the present invention is not particularly limited, but is preferably 6.0 to 10.0. When the pH value approaches the acidic side of less than 6.0, the stability of the ink composition over time may deteriorate, and corrosion of the metal members in contact with the ink composition may easily occur. When the pH value approaches the strong alkali side exceeding 10.0, the ink composition tends to fade and discolor easily, and there may be a risk of not obtaining good handwriting. Taking into consideration the stability over time, color development, writing properties, etc. of the ink composition, the pH value is preferably 6.5 to 9.5. The pH value may be, for example, a value measured at 20° C. using a commercially available pH meter. The pH value can be adjusted with a pH adjuster.

[0058] <Method for producing water-based ink composition> The method for producing the water-based ink composition of the present invention is not particularly limited, and any method for producing a water-based ink composition known in the art can be used. For example, the ink can be prepared by putting all of the components constituting the aqueous ink composition into a container and mixing, stirring, and dispersing them using equipment such as a ball mill, bead mill, roll mill, Henschel mixer, planetary mixer, homomixer, propeller mixer, homogenizer, high-pressure homogenizer, kneader, or dissolver. For example, some of the components of the aqueous ink composition, such as a pigment, a water-soluble organic solvent, water, a dispersant, etc., are placed in a container and mixed, stirred, and dispersed using the mixing and stirring device to produce a pigment dispersion, and then the remaining components are added and mixed and stirred to prepare the aqueous ink composition. In the method for producing the aqueous ink composition, coarse particles, gas, and bubbles may be removed by performing operations such as filtration, centrifugation, and degassing. In the production of the aqueous ink composition, means such as heating, cooling, pressurization, decompression, and inert gas replacement may also be employed. Furthermore, an aging step may be performed after the production of the aqueous ink composition.

[0059] <Applications of water-based ink composition> The aqueous ink composition of the present invention can be used, for example, as an aqueous ink composition for writing instruments or printing. It is preferably used as an aqueous ink composition for writing instruments such as an aqueous marking pen (aqueous felt-tip pen) or an aqueous ballpoint pen. In particular, it is preferably used as an ink composition for an aqueous marking pen or an aqueous felt-tip pen.

[0060] An aqueous marking pen (aqueous felt tip pen) using the aqueous ink composition of the present invention is an aqueous pen that has a pen tip consisting of a fiber core or a plastic core and an ink reservoir, in which the aqueous ink composition is stored. Examples of water-based marking pens (water-based felt-tip pens) include writing implements called felt-tip pens, which have a pen tip made of a fiber bundle, a sintered body, or a plastic, and which are provided with an ink storage means in the body of a so-called core made of felt or a fiber bundle impregnated with ink, and which supply ink from such ink storage means to the pen tip by utilizing capillary action, thereby enabling writing, so-called core-type pens. Also included are non-core-type or so-called free-ink-type pens in which ink is stored as it is in a cylindrical body and supplied to the pen tip. The water-based ink composition according to the present invention is suitably used for any of these water-based marking pens (water-based felt-tip pens). EXAMPLES

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

[0062] [Components] The following components were used to form the carbon black aqueous dispersions and the aqueous ink compositions described in the examples. Carbon black: Monarch 800 (average primary particle size 17 nm) manufactured by Cabot Corporation Water-soluble organic solvent: Ethylene glycol Dispersion resin A: 63% by mass of a styrene-based monomer, 28% by mass of acrylic acid and a resin of formula (2); [ka] (In formula (2), R 1 is hydrogen or a methyl group. A 20% by mass aqueous solution of a copolymer (weight average molecular weight 7,300, acid value 150 mgKOH / g) obtained from a monomer composition consisting of 9% by mass of total monomers represented by the formula: Dispersion resin B: a 20% by mass aqueous solution of a copolymer (weight average molecular weight 8,500, acid value 215 mgKOH / g) obtained from a monomer composition consisting of 53% by mass of a styrene-based monomer, 48% by mass of acrylic acid, and 4% by mass of the total monomers represented by the formula (2) Dispersion resin C: 20% by mass aqueous solution of a copolymer obtained from a monomer composition consisting of 56% by mass of a styrene-based monomer and 44% by mass of acrylic acid Dispersion resin D: 20% by mass aqueous solution of a copolymer obtained from a monomer composition consisting of 29% by mass of a styrene-based monomer and 71% by mass of acrylic acid · Antiseptic and antifungal agent A: Benzisothiazoline-based preservative · Antiseptic and antifungal agent B: Organic iodine-based antifungal agent

[0063] [Example 1-1] <Preparation of Pigment Dispersion 1A> A 20% by mass aqueous dispersion of 29.8 parts of water, 20.0 parts of a water-soluble organic solvent, and 25.0 parts of dispersion resin A was placed in a beaker and stirred for 60 minutes. Then, 25.0 parts of carbon black was added to the beaker and stirred for another 60 minutes, followed by degassing to obtain a premix. The obtained premix was placed in a thin film swirling high-speed mixer ("Filmix 80" manufactured by Primix Corporation) and stirred at a peripheral speed of 40 m / sec for 30 seconds to prepare pigment dispersion A.

[0064] [Example 1-2; Comparative Examples 1-1 and 1-2] <Preparation of Pigment Dispersions 2A to 4A> Pigment dispersions 2A to 4A were prepared in the same manner as in Example 1-1, except that dispersion resin B (Example 1-2), dispersion resin C (Comparative Example 1-1), or dispersion resin D (Comparative Example 1-2) was used instead of dispersion resin A.

[0065] [Evaluation of carbon black dispersibility in pigment dispersions 1A to 4A] For the obtained pigment dispersions 1A to 4A, the 10% cumulative volume particle size, 50% cumulative volume particle size (d50; median size), and 90% cumulative volume particle size (d90) of the carbon black in each pigment dispersion were measured using a particle size distribution measuring device (Microtrac's "Microtrac MT3000II") to evaluate the dispersibility. The results are shown in Table 1. In pigment dispersions 1A to 4A, when the 50% cumulative volume particle size (d50; median size) of the carbon black in each pigment dispersion is 1.70 μm or less, it is rated A (pass), and when it exceeds 1.70 μm, it is rated C (fail).

[0066] [Table 1]

[0067] [Example 2-1] <Preparation of Water-Based Ink Composition 1B> A 20% by mass aqueous dispersion of 29.8 parts of water, 20.0 parts of a water-soluble organic solvent, and 25.0 parts of dispersion resin A was placed in a beaker and stirred for 60 minutes. Then, 25.0 parts of carbon black was added to the beaker and stirred for another 60 minutes, followed by degassing to obtain a premix. The obtained premix was mixed in a bead mill (Willy A. Bachofen's "Dyno Mill KDL") to obtain pigment dispersion 1B. To the obtained pigment dispersion 1B, 0.1 parts of preservative / antifungal agent A and 0.1 parts of preservative / antifungal agent B were added, and the mixture was stirred for 30 minutes in a bead mill (Willy A. Bachofen's "Dynomill KDL") and then degassed to obtain aqueous ink composition 1B.

[0068] [Example 2-2; Comparative Example 2-1] <Preparation of Water-Based Ink Compositions 2B and 3B> Water-based ink compositions 2B and 3B were prepared in the same manner as in Example 2-1, except that Dispersion Resin B (Example 2-2) and Dispersion Resin C (Comparative Example 2-1) were used instead of Dispersion Resin A.

[0069] [Evaluation of storage stability of water-based ink compositions 1B to 3B] For the resulting water-based ink compositions 1B to 3B, the 50% cumulative volume particle diameter (d50; median diameter) of the carbon black in each water-based ink composition immediately after production was measured using a particle size distribution measuring device (Microtrac MT3000II, manufactured by Microtrac). Next, each water-based ink composition was divided into two, one was stored at 50°C for 4 weeks, and the other was stored at 5°C for 4 weeks, and then the 50% cumulative volume particle size (d50; median size) of the carbon black in each water-based ink composition was measured using a particle size distribution measuring device (Microtrac MT3000II, manufactured by Microtrac Co., Ltd.) and the storage stability was evaluated from the change in d50 immediately after production. The results are shown in Table 2. For aqueous ink compositions 1B to 3B, if no pigment precipitation occurs after storage for 4 weeks at 50°C or 4 weeks at 5°C and each d50 (nm) is within 150% of the d50 (nm) immediately after production, the composition is rated A (passed); if pigment precipitation is observed with the naked eye or any of the d50 (nm) exceeds 150% of the d50 (nm) immediately after production, the composition is rated C (failed).

[0070] [Table 2] (For the water-based ink composition 3B, d50 was not measured because pigment precipitation was visually observed after storage at 50°C for 4 weeks.)

[0071] From Table 1, Equation (1); [ka] (In formula (1), R 1 is hydrogen or a methyl group. It was found that pigment dispersions 1A and 2A, which contain dispersion resin A and dispersion resin B, which are dispersion resins having repeating units represented by the following formula, have good dispersibility for carbon black, judging from the measurement results of the dispersed particle size (d50; median size) of carbon black. On the other hand, pigment dispersions 3A and 4A, which contain dispersion resins C and D that do not have the repeating unit represented by formula (1), were found to have poor dispersibility of carbon black, based on the measurement results of the dispersed particle size (d50; median size) of carbon black.

[0072] As can be seen from Table 2, the aqueous ink compositions 1B and 2B obtained from pigment dispersions 1A and 2A containing dispersion resin A and dispersion resin B, which are dispersion resins having a repeating unit represented by formula (1), showed good storage stability, as shown in the measurement results of the dispersed particle diameter (d50; median diameter) of carbon black after storage for 4 weeks at 5°C and the dispersed particle diameter (d50; median diameter) of carbon black after storage for 4 weeks at 50°C, as well as in both cases showing only a small change in the dispersed particle diameter of carbon black and no pigment sedimentation. On the other hand, in the case of aqueous ink composition 3B obtained from pigment dispersion 3B containing dispersion resin C, which is a dispersion resin that does not have a repeating unit represented by formula (1), sedimentation of carbon black (pigment sedimentation) was visually confirmed after storage at 50°C for 4 weeks, indicating that the storage stability was poor.

Claims

1. (A) carbon black, (B) water; (C) the following formula (1); 【Chemistry 1】 (In formula (1), R １ is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula:

1. An aqueous carbon black dispersion comprising:

2. (A) carbon black, (B) water; (C) the following formula (1); 【Chemistry 2】 (In formula (1), R １ is hydrogen or a methyl group. A dispersion resin having a repeating unit represented by the formula:

1. A water-based ink composition comprising:

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