Dispersion for water-based inkjet inks and water-based inkjet inks

Abstract

To provide a dispersion for aqueous inkjet inks in which carbon black is highly finely dispersed, enabling the recording of images with excellent storage stability and optical density, and the preparation of aqueous inkjet inks with excellent ejection stability. [Solution] A dispersion for aqueous inkjet ink containing carbon black, specific silica particles, a specific dispersion modifier, and an aqueous medium. The pH of the dispersion for aqueous inkjet ink is within a predetermined range, the content of the carbon black, the silica particles, and the aqueous medium is within a predetermined range relative to the total mass of the dispersion for aqueous inkjet ink, the content of the silica particles and the (meth)acrylic resin per 1 part by mass of carbon black is within a predetermined range, and the predetermined conditions are met when an aqueous inkjet ink is made using the dispersion for aqueous inkjet ink.

Description

[Technical Field]

[0001] This invention relates to a dispersion for aqueous inkjet inks and the ink itself, used in aqueous inkjet inks. [Background technology]

[0002] Printers or printing presses equipped with water-based inkjet inks have become highly functional, leading to a wide range of applications including personal, office, business, record-keeping, color display, and color photography. They are particularly being considered for high-speed industrial printing. Monochrome printing typically uses black ink. Full-color printing typically uses yellow, cyan, magenta, and black inks.

[0003] Text and graphics are generally recorded using black ink. Therefore, black ink is used in larger quantities than yellow, cyan, and magenta inks. Even in full-color printing, the black ink cartridge in printers typically has a particularly high capacity. Furthermore, various types of black ink for inkjet printers have been proposed in recent years.

[0004] Patent Document 1 discloses an inkjet recording solution using modified carbon black in which at least a portion of the surface is coated with a metal oxide, thereby improving print density, ejection performance, and especially scratch resistance when printed on glossy paper or glossy film.

[0005] Patent Document 2 discloses an aqueous inkjet ink composition containing pigment particles, inorganic oxide particles, and a lactam-based solvent, which improves color development, wettability of printed materials, and clogging recovery.

[0006] In Patent Document 3, an inkjet ink containing a pigment, an inorganic oxide colloid, betaines, and water, and having a total concentration (mg / L) of potassium ions and sodium ions in the ink of 500 ppm or less is disclosed for improving clogging recovery and color development properties.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the past, in order to improve the density of black ink for inkjet, studies have been conducted. In Patent Document 1, it aims to improve the printing density by using silica-modified carbon black. However, the ink storage stability test has only been observed based on the average particle size, and the viscosity change has not been studied. In Patent Document 2, it aims to improve color development properties and the like by using silica particles as inorganic oxide particles. However, in this Patent Document 2, the ink storage stability test has not been conducted. In Patent Document 3, it aims to improve color development and the clogging recovery of the ink by using an inorganic oxide colloid which is colloidal silica and betaines. However, in this Patent Document 3, the ink storage stability test has not been conducted either, and compounds containing a quaternary ammonium cation such as betaines have an odor in the crystalline state, and the crystals deposited when the ink is printed on paper and dried cause the odor, so it is not suitable for general printing applications. Also, in any of the patent documents, the relationship between pH and storage stability has not been studied.

[0009] In order to improve the image quality of printed matter, it is required to increase the optical density of the ink. In this case, it has been clarified that the optical density of the printed matter increases by using silica particles. Also, even when using silica particles, the inventors have found conditions for good storage stability of the dispersion liquid by selecting an appropriate dispersant and adjusting the pH.

[0010] An object of the present invention is to provide a dispersion liquid for aqueous inkjet ink in which carbon black is highly finely dispersed and an aqueous inkjet ink, which can record an image excellent in storage stability and optical density and can prepare an aqueous inkjet ink excellent in ejection stability.

Means for Solving the Problems

[0011] That is, according to the present invention, there are provided a dispersion liquid for aqueous inkjet ink and an aqueous inkjet ink shown below. [1] A dispersion liquid for aqueous inkjet ink containing carbon black, silica particles, a dispersion regulator, and an aqueous medium, where the volume average particle diameter of the silica particles is 40 nm or more and 250 nm or less, the dispersion regulator is an aqueous dispersion regulator containing a (meth)acrylic resin, a basic compound, and an aqueous medium and having a pH of 8 or more and 12 or less, the (meth)acrylic resin is a polymer containing a structural unit (i) derived from at least any one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester and a structural unit (ii) derived from a biomass-derived (meth)acrylate, the (meth)acrylic resin has an acid value of 20 mgKOH / g or more and 300 mgKOH / g or less, a number average molecular weight of 1,000 or more and 50,000 or less, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 3.5 or less, in the (meth)acrylic resin, the content of the structural unit (ii) is 50% by mass or more, The biomass-derived (meth)acrylate comprises isobornyl methacrylate and at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. The proportion of isobornyl methacrylate in all of the biomass-derived (meth)acrylates is 40% by mass or more. The pH of the aqueous inkjet ink dispersion is 8 or higher and 11 or lower. With respect to the total mass of the aqueous inkjet ink dispersion, the carbon black content is 10% by mass or more and 20% by mass or less, the silica particle content is 10% by mass or more and 40% by mass or less, and the aqueous medium content is 45% by mass or more and 75% by mass or less. The silica particles are contained in 1 part by mass of carbon black in an amount of 0.5 parts by mass or more and 4 parts by mass or less. The content of the (meth)acrylic resin per 1 part by mass of the carbon black is greater than 0.1 parts by mass and less than or equal to 0.4 parts by mass. Using the aforementioned aqueous inkjet ink dispersion, a water-based inkjet ink containing 5% by mass of diethylene glycol monobutyl ether, 5% by mass of 2-pyrrolidone, 0.75% by mass of propylene glycol monomethyl ether, and 6% by mass of carbon black, with glycerin added to achieve a viscosity of 3 mPa·s to 4 mPa·s, and the remainder diluted with water, was used to print on plain paper. The optical density (OD value) was then measured using this water-based inkjet ink. a In this case, the optical density when printing on plain paper using an aqueous inkjet ink with a carbon black concentration of 6% using the aqueous inkjet ink dispersion which has the same composition as the aqueous inkjet ink dispersion except that it does not contain silica particles is OD. b A dispersion for water-based inkjet ink that satisfies the following conditions: (F1) to (F4). OD a >OD b ...(F1) OD a ≥1 ···(F2) ODb ≥1 ···(F3) 0.03 ≤ OD a -OD b ≤ 0.4 ···(F4) [2] The dispersion for aqueous inkjet ink according to [1], wherein the carbon black is furnace black, channel black, lamp black, or acetylene black derived from petroleum or biomass. [3] The average primary particle diameter of the carbon black is 4 nm or more and 100 nm or less, and the DBP absorption amount is 150 cm 3 / 100 g or less. The dispersion for aqueous inkjet ink according to [1] or [2]. [4] The pH of the dispersion for aqueous inkjet ink when stored at 70°C for one week in a thermostat is 7 or more and 10 or less. The dispersion for aqueous inkjet ink according to any one of [1] to [3]. [5] The basic compound is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonia. The dispersion for aqueous inkjet ink according to any one of [1] to [4]. [6] The water-soluble polar solvent excluding the low-boiling organic solvent having a boiling point of 100°C or less in the aqueous medium is at least one selected from the group consisting of diethylene glycol monobutyl ether and propylene glycol monomethyl ether. The content of the water-soluble polar solvent is 1% by mass or more and 7% by mass or less based on the total mass of the dispersion for aqueous inkjet ink. The dispersion for aqueous inkjet ink according to any one of [1] to [5]. [7] The silica particles are added after taking out the mill base from the disperser or during the preparation of the ink. The dispersion for aqueous inkjet ink according to any one of [1] to [6]. [8] An aqueous inkjet ink using the dispersion for aqueous inkjet ink according to any one of [1] to [7].

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a dispersion for aqueous inkjet inks in which carbon black is highly finely dispersed, and an aqueous inkjet ink that can record images with excellent storage stability and optical density, and can prepare an aqueous inkjet ink with excellent ejection stability. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below, and various modifications are possible without departing from the spirit of the invention.

[0014] <Dispersion for water-based inkjet inks> The aqueous inkjet ink dispersion according to this embodiment (hereinafter also simply referred to as "dispersion") contains carbon black, silica particles, a dispersion modifier, and an aqueous medium, wherein the dispersion modifier contains a (meth)acrylic resin, a basic compound, and an aqueous medium, and the pH is 8 or higher and 12 or lower. Furthermore, the dispersion according to this embodiment has a pH of 8 or higher and 11 or lower, a carbon black content of 10% to 20% by mass of the total mass, a silica particle content of 10% to 40% by mass of the total mass, an aqueous medium content of 45% to 75% by mass of the total mass, a silica particle content of 0.5 parts by mass to 4 parts by mass of the total mass per part by mass of carbon black, and a (meth)acrylic resin content of more than 0.1 parts by mass and 0.4 parts by mass or less per part by mass of carbon black. Furthermore, using this aqueous inkjet ink dispersion, a water-based inkjet ink containing 5% by mass of diethylene glycol monobutyl ether, 5% by mass of 2-pyrrolidone, 0.75% by mass of propylene glycol monomethyl ether, and 6% by mass of carbon black, with glycerin added to achieve a viscosity of 3 mPa·s to 4 mPa·s, and the remainder diluted with water, was used to print on plain paper, and the optical density (OD value) was determined to be OD. aFurthermore, when using an aqueous inkjet ink with a carbon black concentration of 6% and an aqueous inkjet ink dispersion that has the same composition as the aqueous inkjet ink dispersion except that it does not contain silica particles, the optical density OD when printed on plain paper is... b When this is the case, the optical density and color development are excellent if the conditions of the following formulas (F1) to (F4) are met. OD a >OD b ...(F1) OD a ≥1 ···(F2) OD b ≥1 ···(F3) 0.03≦OD a -OD b ≤0.4 ···(F4)

[0015] Furthermore, the carbon black and silica particles used in the aqueous inkjet ink dispersion according to this embodiment are often acidic. If the dispersion becomes acidic, the anionic (meth)acrylic resin cannot ionize and precipitates, leading to a decrease in storage stability or optical density. Therefore, by using a dispersion adjuster that has been pre-mixed with a basic compound and adjusted to a pH of 8 to 12 at a liquid temperature of 25°C, the pH of the dispersion can be maintained at a basic level of 8 to 11, allowing the (meth)acrylic resin to act effectively and improving storage stability and optical density. If the pH of the dispersion is less than 8, the dispersion cannot maintain its basicity, resulting in decreased dispersion stability or storage stability. If the pH is greater than 11, a large amount of cationic impurities such as alkali metal ions or ammonium ions will be present in the dispersion, and the pH will become too high, which is undesirable as it will cause significant damage to the inkjet ink ejection head. Furthermore, it is preferable that the pH of the dispersion after storage at 70°C in a constant temperature incubator for one week be between 7 and 10.

[0016] <Carbon Black> Examples of carbon black include furnace black, channel black, lamp black, and acetylene black. Biomass-derived carbon black may also be used. This is an environmentally friendly carbon black that is obtained from living organisms, especially plants, and can achieve carbon neutrality and carbon recycling. There are no particular limitations on the structure of the carbon black or whether or not surface modifications such as oxidation have been performed; conventionally known carbon blacks can be used. Acidic carbon can also be used, but in that case, the dispersion will become acidic unless the pH is adjusted. Therefore, care must be taken to adjust the pH to the basic side, especially to pH 8 to 12 at a liquid temperature of 25°C, in order to maintain the dissolved state of the (meth)acrylic resin, ensure good storage stability, and maintain stable optical density.

[0017] The average primary particle size of carbon black is preferably 4 nm to 100 nm, more preferably 6 nm to 50 nm, and even more preferably 10 nm to 30 nm. If the average primary particle size of carbon black is outside the above range, it becomes difficult to obtain a dispersion with excellent dispersion stability. In this specification, the "average particle size" of carbon black is the average value obtained by measuring any 10 particles from a photograph taken using a transmission electron microscope (TEM). The pH of carbon black is a physical property value measured according to the method shown below. First, 10 mg of water is added to 1 g of carbon black, boiled for 15 minutes, and then cooled to room temperature (25°C). After that, the supernatant is removed by the gradient method or centrifugation method to obtain a muddy substance. Then, the electrode of a glass electrode pH meter is inserted into the obtained muddy substance, and the pH can be measured according to JIS 28802.

[0018] The DBP absorption capacity of carbon black is 150cm 3 It is preferable that the amount be 100g or less, and 130cm 3 It is more preferable that the amount be 100g or less, and 120cm 3 It is even more preferable that the amount of DBP absorption of carbon black is 50cm³ or less.3 If the amount is less than 100g, carbon black tends to aggregate easily in the dispersion, which is undesirable.

[0019] The carbon black content in the dispersion must be between 10% and 20% by mass relative to the total mass of the dispersion, and preferably between 12% and 18% by mass. If the carbon black content in the dispersion is less than 10% by mass, the desired concentration cannot be achieved when forming the ink, resulting in a low carbon black concentration that makes the ink unsuitable. Conversely, if the content exceeds 20% by mass, aggregation is likely to occur, making the dispersion unstable, which is undesirable.

[0020] <Silica particles> The silica particles are not particularly limited, but for example, silica sol or silica particle dispersion can be added to the dispersion according to this embodiment. The silica particles can be added before dispersion, after dispersion, or during the preparation of the aqueous inkjet ink. Commercially available products are not particularly limited, but examples include the Cataloid series from JGC Catalysts & Chemicals, the Seahoster series from Nippon Shokubai Co., Ltd., and the Snowtex series from Nissan Chemical Corporation.

[0021] Volume average particle diameter (D) of silica particles 50The silica particles must be between 40 nm and 250 nm, more preferably between 60 nm and 200 nm, and even more preferably between 70 nm and 150 nm from the viewpoint of dispersion stability, storage stability, and improvement of optical density. If the volume average particle diameter of the silica particles is less than 40 nm, the small particle size will cause the silica particles to penetrate the printing paper when printed, and the ink sealing effect will not be fully realized. On the other hand, if it is greater than 250 nm, the particles will be more prone to settling, which will reduce dispersion stability and storage stability. The silica particle content must be between 10% by mass and 40% by mass relative to the total mass of the dispersion, more preferably between 10% by mass and 30% by mass, and more preferably between 12% by mass and 25% by mass. If the silica particle content is less than 10% by mass, the effect of improving optical density will not be fully realized. On the other hand, if it is greater than 40% by mass, the silica particles will be more prone to settling in the dispersion, which will reduce dispersion stability and storage stability. In this specification, the "average particle diameter" of silica particles refers to the cumulative 50% particle diameter (median diameter (D)) in the particle size distribution based on the volume-average particle diameter. 50 This means )). In this invention, the zeta potential, particle size, and molecular weight were calculated using the dynamic light scattering method with a zeta potential, particle size, and molecular weight measurement system (product name "ELSZ-2000ZS", manufactured by Otsuka Electronics Co., Ltd.).

[0022] <Dispersion modifier> The dispersion modifier contains a (meth)acrylic resin as a dispersant, along with a basic compound and an aqueous medium, and is a component for dispersing carbon black and adjusting the pH. The (meth)acrylic resin is a polymer containing a constituent unit (i) derived from at least one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester, and a constituent unit (ii) derived from biomass-derived (meth)acrylate. Under acidic conditions, the carboxyl groups of the above (meth)acrylic resin cannot be ionized, causing precipitation and preventing the dispersion effect from being obtained, leading to a decrease in storage stability and optical density; therefore, it is necessary to always maintain basicity. When using weak bases such as triisopropanolamine, the pH is 10.8 at a concentration of 100 g / L and a liquid temperature of 25°C. In particular, when adjusting the pH for inks using acidic carbon or acidic silica particles, it was confirmed that basicity could not be maintained after storage tests, resulting in deterioration of storage stability and optical density.

[0023] Since the polymer contains constituent unit (i), a carboxyl group is introduced into its structure. The acid value of the polymer must be between 20 mg KOH / g and 300 mg KOH / g, and preferably between 50 mg KOH / g and 150 mg KOH / g. If the acid value is less than 20 mg KOH / g, the polymer will not dissolve in water even if the carboxyl group is neutralized and ionized, and will not perform as a dispersant in aqueous dispersions or inks. On the other hand, if the acid value is greater than 300 mg KOH / g, the amount that dissolves in water increases, which can lead to excessively high viscosity of the dispersion or excessively high water solubility. As a result, it becomes easier for the polymer to detach even after adsorption to carbon black, and the excess hydrophilic carboxyl group may reduce the water resistance of the recorded image.

[0024] The carboxyl groups in the polymer are ionized by neutralization with a basic compound, which causes the polymer (dispersant) to dissolve in water. The monomer constituting the constituent unit (i) is at least one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester. Examples of itaconic acid monoesters include itaconic acid monomethyl ester and itaconic acid monoethyl ester.

[0025] The monomer constituting unit (ii) is a biomass-derived (meth)acrylate. The biomass-derived (meth)acrylate is at least one selected from the group consisting of isobornyl (meth)acrylate, ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate. The isobornyl group is a hydrophobic cycloalkyl group with a large number of carbon atoms. The dodecyl group and octadecyl group are highly hydrophobic, lipophilic long-chain alkyl groups. The isobornyl group, dodecyl group, and octadecyl group are thought to act as adsorbents that adsorb to biomass carbon. The tetrahydrofurfuryl group is a cyclic ether group with a relatively small number of carbon atoms. The ethyl group is an alkyl group with a relatively small number of carbon atoms. The tetrahydrofurfuryl group and ethyl group are thought to have the effect of adjusting the solubility of the dispersant in water.

[0026] Biomass-derived (meth)acrylates are monomers obtained, for example, using plant-derived alcohols. The dispersion according to this embodiment is a dispersion that uses a large amount of biomass-derived materials, containing biomass carbon black and a dispersant composed of biomass-derived monomers. Therefore, images recorded with ink prepared using the dispersion according to this embodiment contain a biomass-derived film, making them more environmentally friendly from the standpoint of carbon neutrality and carbon recycling.

[0027] Isobornyl (meth)acrylate is an esterified product using isoborneol as the alcohol. This isoborneol is a plant-derived alcohol obtained from camphene, which is obtained from pine resin, etc. Ethyl (meth)acrylate is an esterified product using ethanol as the alcohol. This ethanol is an alcohol obtained by fermenting biomass such as sugarcane, corn, and wood. Tetrahydrofurfuryl (meth)acrylate is an esterified product of tetrahydrofurfuranol. This tetrahydrofurfuranol is an alcohol industrially obtained by a hydrogenation reaction catalyzed by furfural, which is contained in corn cobs or sugarcane bagasse. Dodecyl (meth)acrylate and octadecyl (meth)acrylate are esterified products of dodecyl alcohol and octadecyl alcohol, respectively. Dodecyl alcohol and octadecyl alcohol are alcohols obtained from coconut oil and palm oil, respectively.

[0028] The polymer (dispersant) must contain at least 50% by mass of constituent unit (ii), and preferably between 80% and 95% by mass. A 50% by mass content of constituent unit (ii) allows it to be used as an environmentally friendly dispersant, and images and printed materials recorded with inks containing this polymer as a dispersant can be environmentally friendly.

[0029] The biomass-derived (meth)acrylate must contain isobornyl methacrylate and at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. Furthermore, the proportion of isobornyl methacrylate in all biomass-derived (meth)acrylates must be 40% by mass or more, and more preferably 45% by mass or more and 70% by mass or less. By using methacrylate as the biomass-derived (meth)acrylate, the glass transition temperature of the resulting polymer can be set higher and the hydrolysis resistance can be improved. In addition, by setting the proportion of isobornyl methacrylate in all biomass-derived (meth)acrylates to 40% by mass or more, a large number of highly hydrophobic groups are introduced into the polymer, which can improve the adsorption to pigments. In particular, it is preferable that the biomass-derived (meth)acrylate contains isobornyl methacrylate and at least one of ethyl methacrylate and tetrahydrofurfuryl methacrylate.

[0030] Biomass-derived (meth)acrylates can be distinguished from petroleum-derived (meth)acrylates. Furthermore, compounds derived from petroleum materials do not contain carbon-14 (¹⁴C), one of the carbon isotopes. On the other hand, biomass-derived compounds, especially those derived from plant materials, contain carbon-14 (¹⁴C). Therefore, the presence or absence of carbon-14 (¹⁴C) can be used to determine whether or not a (meth)acrylate is biomass-derived. Methods for measuring ¹⁴C include beta-ray spectroscopy and accelerator mass spectrometry (AMS). In particular, for environmental materials, this is also specified in the bio-based concentration test standard ASTM D6866, the European standard CEN16137, and the ISO international standard ISO16620-2, among others.

[0031] The polymer used as a dispersant may further contain other structural units besides structural unit (i) and structural unit (ii). Examples of other structural units include structural units derived from radically polymerizable monomers (other monomers) derived from petroleum materials. Examples of other monomers include vinyl monomers such as styrene and vinyltoluene, and (meth)acrylic acid monomers. Examples of (meth)acrylic acid monomers include monofunctional (meth)acrylates having substituents such as methyl, ethyl, propyl, butyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, hexadecyl, octadecyl, isostearyl, behenyl, cyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxybutyl, dimethylaminoethyl, diethylaminoethyl, polyethylene glycol, polypropylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, polyepsilon caprolactone, and polydimethylsiloxane. Among these, monomers having polyalkylene glycol chains are preferred because the polyalkylene glycol chains are biodegradable and therefore environmentally friendly monomers. Furthermore, it is preferable that the polymer used as a dispersant is substantially composed only of the above-mentioned constituent units (i) and (ii).

[0032] The number-average molecular weight (Mn) of the dispersant polymer must be between 1,000 and 50,000, preferably between 3,000 and 40,000, and more preferably between 5,000 and 20,000. If the Mn of the polymer is less than 1,000, it will easily detach from the pigment, reducing the dispersion stability of the pigment. On the other hand, if the Mn of the polymer is greater than 50,000, the viscosity of the dispersion will become too high, and the carbon black particles may easily adsorb to each other, leading to aggregation. In this specification, both the number-average molecular weight (Mn) and weight-average molecular weight (Mw) are polystyrene-converted values ​​measured by gel permeation chromatography (GPC).

[0033] The molecular weight distribution (PDI = weight-average molecular weight (Mw) / number-average molecular weight (Mn)) of the dispersant polymer must be 3.5 or less, preferably 3.0 or less, and more preferably 2.0 or less. If the molecular weight distribution (PDI) of the polymer is greater than 3.5, the dispersibility of carbon black decreases. Living radical polymerization allows for the standardization of the molecular weight of the resulting polymer and the control of its structure. Standardizing the molecular weight of the polymer is preferable because it reduces the amount of high molecular weight and low molecular weight polymers, and increases the amount of polymer chains that contribute to the dispersibility of carbon black.

[0034] The dispersant is a polymer in which carboxyl groups derived from (meth)acrylic acid or itaconic acid, etc., are neutralized with a basic compound. Because the carboxyl groups are neutralized and ionized, this polymer is highly compatible with and readily soluble in water, and by adjusting its basic properties, the dispersion can be stabilized.

[0035] Examples of basic compounds include ammonia; organic amines such as triethylamine, dimethylaminoethanol, diethanolamine, triethanolamine, aminomethylpropanol, and polyethylene glycol / polypropylene glycol monoamine; biomass-derived organic monoamines such as coconutamine, octylamine, dodecylamine, stearylamine, oleylamine, and dimethyloctylamine; and alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, the basic compound is preferably a combination of ammonia and at least one of sodium hydroxide and potassium hydroxide. Neutralization with ammonia improves the water resistance of the image because the ammonia volatilizes after recording, returning to the original carboxyl group. Neutralization with sodium hydroxide or potassium hydroxide improves the non-drying and re-solubility of the ink because the carboxyl group is ionic, making the polymer more soluble in water.

[0036] Polymers used as dispersants can be produced by conventionally known methods. Specifically, it is preferable to synthesize them by solution polymerization using a water-soluble organic solvent contained in the dispersion. For example, an azo polymerization initiator or a peroxide polymerization initiator is used, and monomers are added dropwise or all at once to a water-soluble organic solvent for polymerization. During polymerization, chain transfer agents such as thiols or bromomethylacrylic acid esters may be used in combination to adjust the molecular weight of the resulting polymer. Alternatively, to ensure uniform molecular weight of the resulting polymers, they may be synthesized by living radical polymerization. Examples of living radical polymerization include atom transfer radical polymerization; NMP method using nitrooxides, etc.; reversible addition-cleavage chain transfer polymerization using thioesters or thiocarbonates, etc.; TERP method using organotellurium as an initiator; iodine transfer polymerization method using iodine compounds as an initiator; reversible transfer catalytic polymerization or reversible catalyst-mediated polymerization using inorganic or organic catalysts; and chain transfer polymerization using cobalt catalysts, etc.

[0037] The dispersant content must be between 0.1 parts by mass and 0.4 parts by mass per 1 part by mass of carbon black, and more preferably between 0.15 parts by mass and 0.3 parts by mass. If the dispersant content is less than 0.05 parts by mass, the dispersion effect will be insufficient due to insufficient dispersant, and dispersion stability and storage stability will decrease. If it exceeds 0.4 parts by mass, the viscosity will increase due to excess dispersant, and dispersion stability and storage stability will decrease due to the presence of excess dispersant.

[0038] <Aqueous medium> The aqueous medium used in this embodiment is a combination of water and at least one of a water-soluble polar solvent, excluding low-boiling point organic solvents with a boiling point of 100°C or lower. The water-soluble polar solvent, excluding low-boiling point organic solvents with a boiling point of 100°C or lower, should have a solubility in water of 50g / 100g water (25°C) or higher, and preferably be completely miscible with water. As water, it is preferable to use ion-exchanged water, distilled water, and purified water. As water-soluble polar solvents, it is preferable to use, for example, nitrogen-containing solvents such as glycerin, 2-pyrrolidone, and N-methylpyrrolidone; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, propanediol, butanediol, pentanediol, and hexylene glycol; and glycol monoalkyl ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and propylene glycol monomethyl ether. In particular, it is preferable that it be at least one selected from the group consisting of diethylene glycol monobutyl ether and propylene glycol monomethyl ether. Water and water-soluble polar solvents other than low-boiling point organic solvents with a boiling point of 100°C or lower may be used individually, but it is preferable to use two of them in combination.

[0039] The aqueous medium content must be between 45% and 75% by mass of the total mass of the dispersion, preferably between 55% and 72% by mass, and more preferably between 60% and 70% by mass. If the aqueous medium content is less than 45% by mass, the concentration of carbon black and silica particles becomes too high, increasing viscosity and making it unsuitable for inkjet printing. Furthermore, storage stability deteriorates. If the content exceeds 75% by mass, the concentration of carbon black is too low, resulting in low density during printing, particularly a decrease in optical density.

[0040] Furthermore, the content of water-soluble polar solvents, excluding low-boiling point organic solvents with a boiling point of 100°C or less, is preferably 1% by mass or more and 7% by mass or less, and more preferably 2% by mass or more and 6% by mass or less, relative to the total mass of the dispersion. If the content of water-soluble polar solvents, excluding low-boiling point organic solvents with a boiling point of 100°C or less, is less than 1% by mass, the wettability of the pigment in the initial stages of dispersion in the dispersion will be poor, and the dispersibility of carbon black tends to decrease as the amount of water-soluble polar solvents, excluding low-boiling point organic solvents with a boiling point of 100°C or less, decreases. Also, if it exceeds 7% by mass, a large amount of water-soluble polar solvents, excluding low-boiling point organic solvents with a boiling point of 100°C or less, will be present in the dispersion, which tends to decrease the stability of the dispersant itself or its storage stability. It can also lead to pH instability.

[0041] <Other additives> The dispersion according to this embodiment may contain other additives as needed. Other additives include surfactants, preservatives, and binder components for aqueous inkjet inks. As a preservative, for example, the PROXEL series manufactured by Arcsarda Japan can be used. The amount of preservative added is preferably 0.1% by mass or more and 0.5% by mass or less of the total volume of the dispersion.

[0042] <Method for manufacturing a dispersion for water-based inkjet ink> The dispersion described above can be manufactured according to the method shown below. That is, the method for manufacturing the dispersion according to this embodiment (hereinafter also simply referred to as the "manufacturing method") is a method for manufacturing a dispersion containing carbon black, silica particles, a dispersion modifier, and an aqueous medium, used for preparing aqueous inkjet ink, and comprises a step of dispersing a mixture containing carbon black, silica particles, a dispersion modifier, and an aqueous medium (dispersion step).

[0043] In the dispersion process, first, carbon black, a dispersion modifier, and an aqueous medium are mixed to prepare a mixture. If necessary, a basic compound is added to adjust the pH. Then, the mixture is dispersed using a paint shaker, ball mill, attritor, sand mill, horizontal media mill, colloid mill, roll mill, ultrasonic homogenizer, high-pressure homogenizer, etc., to finely disperse the carbon black and prepare a dispersion. An aqueous medium is added to the prepared dispersion, and if necessary, binder components and other additives are added to adjust the concentration to the desired level. Furthermore, basic compounds may be added to adjust the pH. Finally, by adding various additives such as surfactants and preservatives as necessary, the desired dispersion can be obtained. If the dispersion is insufficient, the carboxylic acid of the (meth)acrylic resin will remain, causing a change in pH in storage stability tests and affecting stability, so sufficient dispersion is necessary.

[0044] In the manufacturing method according to this embodiment, carbon black is dispersed to a predetermined particle size. For the dispersion process, it is preferable to use a mill using media or a high-pressure homogenizer. Larger particles in the dry state are crushed to the predetermined particle size by collision of media or collision of particles under high pressure. In a mill using media, for example, methods such as reducing the size of the media used (grinding media), increasing the packing density of the grinding media, increasing the peripheral speed, increasing the processing time, or decreasing the discharge speed can be employed. In a high-pressure homogenizer, methods such as increasing the pressure or increasing the number of passes can be employed. After the dispersion process, coarse particles may be removed by centrifugation or filtration as needed. Furthermore, it is preferable to add silica particles after removing the mill base from the disperser or during the preparation of the ink.

[0045] <Water-based inkjet ink> The aqueous inkjet ink according to this embodiment (hereinafter also simply referred to as "ink") contains the aforementioned inkjet ink dispersion. Aside from containing the aforementioned dispersion, it is the same as conventionally known inks. The carbon black content in the ink is preferably 4% by mass or more and 10% by mass or less of the total mass of the ink. This makes it possible to prepare an aqueous inkjet ink with high concentration, excellent color development, and superior storage stability that can record images.

[0046] The pH of water-based inkjet ink is preferably between 8 and 11 at a liquid temperature of 25°C, and more preferably between 8 and 10. If the pH of the water-based inkjet ink is less than 8, the dispersion cannot maintain its basicity, and the dispersion stability and storage stability will decrease. If the pH is greater than 11, a large amount of cationic impurities such as alkali metal ions or ammonium ions will be present in the dispersion, and the pH will become too high, which will cause significant damage to the inkjet ink ejection head, and is therefore undesirable.

[0047] The ink can contain various additives commonly used in water-based inkjet inks. Examples of additives include surfactants, organic solvents / humectants, pigment derivatives, dyes, leveling agents, defoamers, UV absorbers, binder components such as emulsions, preservatives, and antibacterial agents.

[0048] The physical properties of the ink are adjusted as appropriate to match the performance of the inkjet printer, etc. For example, the surface tension of the ink is preferably between 20 mN / m and 40 mN / m. Regarding the optical density (OD value) of the ink, when using an aqueous inkjet ink dispersion containing 5% by mass of diethylene glycol monobutyl ether, 5% by mass of 2-pyrrolidone, 0.75% by mass of propylene glycol monomethyl ether, and 6% by mass of carbon black, with glycerin added to achieve a viscosity of 3 mPa·s to 4 mPa·s, and the remainder diluted with water, the optical density when printed on plain paper is measured as the OD value. a Furthermore, when using an aqueous inkjet ink with a carbon black concentration of 6% and an aqueous inkjet ink dispersion that has the same composition as the aqueous inkjet ink dispersion except that it does not contain silica particles, the optical density OD when printed on plain paper is... b In this case, the following conditions must be met: Formulas (F1) to (F4). OD a >OD b ...(F1) OD a ≥1 ···(F2) OD b ≥1 ···(F3) 0.03≦OD a -OD b ≤0.4 ···(F4) OD a -OD b A value of less than 0.03 is undesirable because it results in poor optical concentration after silica particle addition. On the other hand, OD a -OD bIf the value exceeds 0.4, the average particle size of the carbon black in the ink becomes too small, which is undesirable because it can lead to aggregation and other deteriorations in storage stability. Optical density can be measured using a commercially available optical densitometer. In this specification, measurements were taken using the above-mentioned plain paper with a HAMMERMILL Copy Plus (manufactured by Hammermill).

[0049] It should be noted that the optical density measured may not necessarily show the same trend depending on the type of paper. For example, as shown in Japanese Patent Publication No. 2005-350586, which illustrates the difference in optical density between printing with HAMMERMILL Copy Plus (manufactured by Hammermill) used in this embodiment and printing with Xerox P paper (manufactured by Fuji Xerox), it is known that the color development differs depending on the printing substrate.

[0050] <Recording medium> The ink according to this embodiment can be applied to inkjet printers for consumer, industrial, or textile printing applications. Examples of media (recording media) to be printed on include plain paper, glossy paper, matte paper, plastic films such as PET or polyvinyl chloride, fibers such as cotton or polyester, and metal plates such as aluminum. Because the ink according to this embodiment contains silica particles, it has a sealing effect that prevents ink penetration into the recording medium; therefore, it is preferable to use an absorbent recording medium. Among these, neutral paper, which is less prone to aggregation after ink application, is particularly preferred. Furthermore, using the ink according to this embodiment, images with excellent color development can be recorded at high speed even on paper containing a large amount of inorganic fillers. Moreover, because the ink according to this embodiment is suitable for high-speed printing, it can be applied to inkjet printers for mass printing of food packaging and packaging materials. In addition to being an aqueous inkjet ink, it can also be used as a material for printing inks such as aqueous paints for automobiles or building materials, aqueous stationery, aqueous gravure inks, or aqueous flexographic inks. [Examples]

[0051] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0052] <Preparing the materials> The following carbon black, silica particles, and dispersant were prepared.

[0053] (Carbon Black) CB-1: Product name "#40", manufactured by Mitsubishi Chemical Corporation, average primary particle size 24 nm, nitrogen adsorption specific surface area 115 m² 2 / g, DBP absorption 110cm 3 / 100g, pH 7.5 CB-2: Product name "MA100", manufactured by Mitsubishi Chemical Corporation, average primary particle size 24 nm, nitrogen adsorption specific surface area 110 m² 2 / g, DBP absorption 100cm 3 / 100g, pH 3.5

[0054] (Silica particles) Si-1: Product name "SI-45P", manufactured by JGC Catalysts & Chemicals, volume average particle size (D 50 ) 45 nm, aqueous dispersion with a solid content concentration of 40% by mass. Si-2: Product name "SI-80P", manufactured by JGC Catalysts & Chemicals Co., Ltd., volume average particle size (D 50 ) 80 nm, aqueous dispersion with a solid content concentration of 40% by mass. Si-3: Product name "KE-P10", manufactured by Nippon Shokubai Kasei Co., Ltd., volume average particle size (D 50 )100nm, powder Si-4: Product name "SI-30P", manufactured by JGC Catalysts & Chemicals Co., Ltd., volume average particle size (D 50 ) 15 nm, aqueous dispersion with a solid content concentration of 40% by mass. Si-5: Product name "KE-P30", manufactured by Nippon Shokubai Kasei Co., Ltd., volume average particle size (D 50 )300nm, powder

[0055] (Dispersion modifier) Dispersion modifier D: Product name "Floren GW-1500", manufactured by Kyoeisha Chemical Co., Ltd., styrene-maleic acid resin, 100% solids content.

[0056] (Dispersion modifier A) 141.1 parts of DEGmBE (diethylene glycol monobutyl ether), 141.1 parts of PGME (propylene glycol monomethyl ether), 61.0 parts of IBXMA (isobornyl methacrylate), 61.0 parts of LMA (lauryl methacrylate), 3.0 parts of iodine, 5.8 parts of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", manufactured by Fujifilm Corporation) (V-70), and 0.3 parts of N-iodosuccinimide (NIS) were placed in a reaction vessel. The mixture was heated to 45°C while bubbling nitrogen and polymerized for 4 hours to form the A chain (polymer). A sample of the A chain was measured and found to have a manganese content of 3,500, a PDI of 1.24, and a polymerization rate of approximately 100%.

[0057] A mixture of 56.2 parts IBXMA, 28.2 parts EMA (ethyl methacrylate), 28.2 parts LMA, and 47.7 parts MAA was added and polymerized at 45°C for 4 hours to form the B chain and obtain the AB block copolymer. The Mn of the AB block copolymer was 8,600, the PDI was 1.40, the acid value was 110.3 mgKOH / g, the content of constituent unit (ii) was 83.1%, the proportion of isobornyl methacrylate in the biomass-derived (meth)acrylate was 49.9%, and the polymerization rate was approximately 100%. In addition, the Mn of the B chain (total Mn - Mn of the A chain) was 5,300, and the acid value of the B chain calculated from the blending values ​​considering the polymerization rate was 159.2 mgKOH / g. After cooling to room temperature, 111.0 parts of 10% sodium hydroxide aqueous solution (50 mol% relative to the carboxyl groups contained), 16.9 parts of 28% ammonia aqueous solution (50 mol% relative to the carboxyl groups contained), and 436.6 parts of deionized water were added to obtain dispersion modifier A. The resulting solution had a solid content of 22.1%, a basic compound content of 18.0 g / L, and a pH of 9.5.

[0058] For IBXMA, we used methacrylate (biomass content 71.4%) obtained by reacting isoborneol, which is derived from pine resin or pine essential oil, with methacrylic acid. For LMA, we used an ester of lauryl alcohol (biomass content 75.0%) obtained by hydrogen-reducing lauric acid, a fractional distillate of fatty acids obtained by hydrolyzing oils such as palm kernel oil and coconut oil, with methacrylic acid. For EMA, we used an ester of itaconic acid (biomass content 33.3%) obtained by fermenting starch, with biomass ethanol and methacrylic acid.

[0059] (Dispersion modifier B) After cooling to room temperature, the solution was prepared in the same manner as dispersant A, except that 55.5 parts of 10% sodium hydroxide aqueous solution (25 mol% relative to the carboxyl groups contained), 8.5 parts of 28% ammonia aqueous solution (25 mol% relative to the carboxyl groups contained), and 500.6 parts of deionized water were added. The resulting solution had a solid content of 22.1%, a basic compound content of 9.0 g / L, and a pH of 8.2.

[0060] (Dispersion modifier C) The solution was prepared in the same manner as dispersant A, except that after cooling to room temperature, 22.2 parts of 10% sodium hydroxide aqueous solution (10 mol% relative to the carboxyl groups contained), 2.8 parts of 28% ammonia aqueous solution (10 mol% relative to the carboxyl groups contained), and 539.6 parts of deionized water were added. The resulting solution had a solid content of 22.1%, a basic compound content of 3.6 g / L, and a pH of 7.3, with some resin precipitated.

[0061] <Manufacturing of dispersions for water-based inkjet inks> (Example 1) 169.7 parts of dispersion modifier A and 55.3 parts of deionized water were mixed to obtain a clear liquid. 150 parts of CB-1 and 375 parts of Si-1 (150 parts of silica purity) were added to the resulting solution, and the mixture was stirred for 30 minutes using a disperser to prepare a mill base. Using a horizontal media disperser (product name "DinoMill MultiLab type", manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.3 mm), a total of 11 pass-type dispersions were performed at a peripheral speed of 8.5 m / s to thoroughly disperse the pigment in the mill base. When removing the mill base from the disperser, 132.4 parts of water were added to adjust the pigment concentration to 17%, and the mixture was heat-treated in a constant temperature bath at 70°C for 17 hours. After cooling to room temperature with water, the mill base was centrifuged (7,500 rpm, 10 minutes), 189.1 parts of deionized water were added, and the mixture was filtered through a membrane filter with a pore size of 10 μm. A dispersion for aqueous inkjet ink with a carbon black concentration of 14% was obtained.

[0062] Visual inspection of the obtained dispersion confirmed that there was no sedimentation of carbon black and silica particles, indicating fine dispersion. The viscosity of the water-based inkjet ink dispersion was 5.8 mPa·s, and the pH was 8.6. The viscosity of the water-based inkjet ink dispersion was measured at 25°C using an E-type viscometer under conditions of 50 revolutions per minute.

[0063] (Examples 2-11, Reference Examples 1 and 2, and Comparative Examples 1-11) A dispersion for aqueous inkjet ink was obtained in the same manner as in Example 1 described above, except that the types of materials shown in Tables 1 and 2 were used. The results are shown in Tables 1 and 2.

[0064] (Example 12) A dispersion for aqueous inkjet ink was obtained in the same manner as in Example 1 described above, except that the silica particles were added after the mill base was removed from the disperser, rather than before dispersion. The results are shown in Table 1.

[0065] <Evaluation Method> (Storage stability of average particle size of dispersion) The dispersion of the obtained aqueous inkjet ink was stored in a constant temperature incubator at 70°C for one week. Visual observation results were used to determine the dispersion storage stability, which is shown in Tables 1 and 2. The criteria for "dispersion storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: No particle sedimentation occurred. △: Some particles have settled. ×: Most of the particles settled.

[0066] (Viscosity storage stability of dispersions) Tables 1 and 2 show the viscosity storage stability of the obtained aqueous inkjet ink dispersion after being stored in a constant temperature incubator at 70°C for one week. The criteria for "viscosity storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: The rate of change in viscosity was within ±5%. △: The rate of change in viscosity was greater than ±5% and less than or equal to ±10%. ×: The rate of change in viscosity was greater than ±10%.

[0067] (pH storage stability of dispersion) Tables 1 and 2 show the pH storage stability of the obtained aqueous inkjet ink dispersion after being stored in a constant temperature incubator at 70°C for one week. The criteria for "pH storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: The rate of change in pH was within ±5%. △: The rate of change in pH was greater than ±5% and less than or equal to ±10%. ×: The rate of change in pH was greater than ±10%.

[0068] [Table 1]

[0069] [Table 2]

[0070] <Ink preparation> (Example 13) 42.9 parts of the aqueous inkjet ink dispersion of the type shown in Table 3, 5 parts of DEGmBE, 0.8 parts of PGME, 5 parts of 2-pyrrolidone, 8 parts of glycerin, 1 part of surfactant (product name "Surfinol 465", manufactured by Air Product Co., Ltd.), and 37.4 parts of water were mixed to a carbon black concentration of 6%. After thorough stirring, the mixture was filtered through a 10 μm pore size membrane filter to prepare the aqueous inkjet ink. The results are shown in Table 3.

[0071] (Examples 14-26, Reference Examples 3 and 4, and Comparative Examples 12-22) Aqueous inkjet inks were prepared in the same manner as in Example 13, except that the types of materials shown in Tables 3-5 were used to achieve a carbon black concentration of 6%. The results are shown in Tables 3-5. Note that the optical density of Reference Examples 3 and 4 is OD. b It becomes a value.

[0072] (Reference examples 5~9) Aqueous inkjet inks were prepared in the same manner as in Example 13, except that the types of materials shown in Table 4 were used to achieve a carbon black concentration of 7%. The results are shown in Table 4. For Reference Examples 7 and 8, printed materials were obtained using plain paper (neutral paper) (product name "Xerox P paper", manufactured by Fuji Xerox Corporation).

[0073] <Evaluation Method> (Storage stability of average particle size of ink) The dispersed storage stability of the obtained water-based inkjet inks, as determined by visual observation after storage in a constant temperature incubator at 70°C for one week, is shown in Tables 3-5. The criteria for "dispersed storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: No particle sedimentation occurred. △: Some particles have settled. ×: Most of the particles settled.

[0074] (Ink viscosity and storage stability) Tables 3-5 show the viscosity storage stability of the obtained water-based inkjet inks after being stored in a constant temperature incubator at 70°C for one week. The criteria for "viscosity storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: The rate of change in viscosity was within ±5%. △: The rate of change in viscosity was greater than ±5% and less than or equal to ±10%. ×: The rate of change in viscosity was greater than ±10%.

[0075] (pH storage stability of ink) Tables 3-5 show the pH storage stability of the obtained water-based inkjet inks after being stored in a constant temperature incubator at 70°C for one week. The criteria for "pH storage stability" in the tables are shown below. "○" and "△" indicate passing grades, while "×" indicates failing grades. ○: The rate of change in pH was within ±5%. △: The rate of change in pH was greater than ±5% and less than or equal to ±10%. ×: The rate of change in pH was greater than ±10%.

[0076] (Measurement of optical density) The obtained water-based inkjet inks were filled into cartridges and installed in an inkjet printer (product name "PX-S270T," manufactured by Seiko Epson). A solid image was printed on plain paper (neutral pH paper) (product name "HAMMERMILL Copy Plus," manufactured by Hammermill) to obtain printed materials. The optical density (OD value) of the obtained printed materials was measured using an optical densitometer (product name "i1PRO," manufactured by x-rite). The results are shown in Tables 3-5. Each physical property was measured six times, and the average value was calculated for each measurement of the OD value. a The value was used. Also, the measurement results for Reference Examples 3 and 4 were OD b These are the values. For reference examples 7-9, the printed materials were obtained using plain paper (acid-free paper) (product name "Xerox P paper", manufactured by Fuji Xerox Corporation).

[0077] [Table 3]

[0078] Table 4

[0079] Table 5

Claims

1. A dispersion for aqueous inkjet ink containing carbon black, silica particles, a dispersion modifier, and an aqueous medium, The volume-average particle diameter of the silica particles is 40 nm or more and 250 nm or less. The aforementioned dispersion modifier is an aqueous dispersion modifier containing a (meth)acrylic resin, a basic compound, and an aqueous medium, and having a pH of 8 or higher and 12 or lower. The (meth)acrylic resin is a polymer comprising a constituent unit (i) derived from at least one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester, and a constituent unit (ii) derived from biomass-derived (meth)acrylate. The (meth)acrylic resin has an acid value of 20 mg KOH / g or more and 300 mg KOH / g or less, a number-average molecular weight of 1,000 or more and 50,000 or less, and a molecular weight distribution (weight-average molecular weight / number-average molecular weight) of 3.5 or less. The (meth)acrylic resin contains 50% by mass or more of the constituent unit (ii), The biomass-derived (meth)acrylate comprises isobornyl methacrylate and at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. The proportion of isobornyl methacrylate in all of the biomass-derived (meth)acrylates is 40% by mass or more. The pH of the aqueous inkjet ink dispersion is 8 or higher and 11 or lower. The carbon black content is 10% to 20% by mass relative to the total mass of the aqueous inkjet ink dispersion, the silica particle content is 10% to 40% by mass, and the aqueous medium content is 45% to 75% by mass. The silica particles are contained in 1 part by mass of carbon black in an amount of 0.5 parts by mass or more and 4 parts by mass or less. The content of the (meth)acrylic resin per 1 part by mass of the carbon black is greater than 0.1 parts by mass and less than or equal to 0.4 parts by mass. Using the aforementioned aqueous inkjet ink dispersion, a water-based inkjet ink containing 5% by mass of diethylene glycol monobutyl ether, 5% by mass of 2-pyrrolidone, 0.75% by mass of propylene glycol monomethyl ether, and 6% by mass of carbon black, with glycerin added to achieve a viscosity of 3 mPa·s to 4 mPa·s, and the remainder diluted with water, was used to print on plain paper. The optical density (OD value) was then measured. ａ In this case, the optical density when printing on plain paper using an aqueous inkjet ink with a carbon black concentration of 6%, using the aqueous inkjet ink dispersion which has the same composition as the aqueous inkjet ink dispersion except that it does not contain silica particles, is OD ｂ A dispersion for water-based inkjet ink that satisfies the following conditions: formulas (F1) to (F4). OD ａ >OD ｂ ・・・(F1) OD ａ ≧1 ・・・(F2) OD ｂ ≧1 ・・・(F3) 0.03≦OD ａ -OD ｂ ≦0.4 ・・・(F4)

2. The aqueous inkjet ink dispersion according to claim 1, wherein the carbon black is a furnace black, channel black, lamp black, or acetylene black derived from petroleum or biomass.

3. The average primary particle diameter of the carbon black is 4 nm or more and 100 nm or less, and the DBP absorption amount is 150 cm ３ / 100 g or less, and the dispersion liquid for aqueous inkjet ink according to claim 1.

4. The aqueous inkjet ink dispersion according to claim 1, wherein the pH of the aqueous inkjet ink dispersion after being stored in a constant temperature incubator at 70°C for one week is 7 or more and 10 or less.

5. The aqueous inkjet ink dispersion according to claim 1, wherein the basic compound is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonia.

6. The aqueous inkjet ink dispersion according to claim 1, wherein the aqueous medium contains at least one water-soluble polar solvent selected from the group consisting of diethylene glycol monobutyl ether and propylene glycol monomethyl ether, excluding low-boiling point organic solvents having a boiling point of 100°C or less, and the content of the water-soluble polar solvent is 1% by mass or more and 7% by mass or less with respect to the total mass of the aqueous inkjet ink dispersion.

7. The aqueous inkjet ink dispersion according to claim 1, wherein the silica particles are added after removing the mill base from the disperser or during the preparation of the ink.

8. A water-based inkjet ink using the water-based inkjet ink dispersion according to any one of claims 1 to 7.

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