Pigment dispersion liquid and method for producing the same

Abstract

Provided is a pigment dispersion liquid in which biomass-derived carbon black is highly dispersed, which can produce an aqueous inkjet ink having high recording density, and excellent color development and gloss, and excellent jetting stability. A pigment dispersion liquid for producing an aqueous inkjet ink, which contains a pigment, a dispersant, a water-soluble organic solvent, and water. The pigment is biomass-derived carbon black having a number average particle diameter of 80 to 300 nm in a state dispersed in the pigment dispersion liquid, the dispersant is a polymer containing a structural unit (i) derived from a (meth)acrylic acid or the like, and a structural unit (ii) derived from a biomass-derived (meth)acrylate, and at least a part of carboxyl groups of the polymer is neutralized with a base, the polymer has an acid value of 50 to 150 mgKOH / g, and the biomass-derived (meth)acrylate is isobornyl (meth)acrylate or the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a pigment dispersion liquid and a method for producing the same. BACKGROUND

[0002] A printer or a printer equipped with an aqueous ink for inkjet has been used in various fields such as personal use, office use, business use, recording use, color display use, and color photograph use due to its high functionality, and in particular, research on a high-speed printer for industrial use is being promoted. In monochrome printing, black ink is generally used. In addition, in full-color printing, various inks of yellow, cyan, magenta, and black are generally used.

[0003] Note that characters, figures, and the like are basically recorded with black ink. Therefore, the amount of black ink used is larger than that of yellow, cyan, and magenta inks. In addition, even in the case of full-color printing, the cartridge for black ink is particularly large in capacity among the cartridges for inks mounted in a printer or the like. Furthermore, in recent years, various black inks for inkjet have been proposed (Patent Documents 1 to 3).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-10632

[0007] Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2009-67831

[0008] Patent Document 3: Japanese Patent Application Laid-Open (JP-A) No. 2009-504884 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In recent years, from the viewpoint of reduction in carbon dioxide emission, carbon cycle, and carbon neutralization, activities to replace the currently used materials derived from petroleum with materials derived from biomass that enable carbon cycle have become active. Specifically, in addition to various molded articles such as films, there is a strong desire to actively use materials derived from biomass as materials constituting various compositions such as paints and inks. For an aqueous ink for inkjet used for forming an image of a printed matter, the demand for using materials derived from biomass has increased, and in particular, the demand for black ink, which is used in a large amount, has significantly increased.

[0011] Black ink is usually compounded with carbon black as a coloring material. Also, in order to produce an environmentally-considered ink, carbon black derived from biomass is used as a coloring material. However, carbon black derived from biomass has a large particle diameter as compared with carbon black derived from petroleum. Therefore, it is generally difficult to prepare an ink by dispersing carbon black derived from biomass in a liquid medium in a good state. Also, there is a problem that the properties of an image recorded with black ink prepared using carbon black derived from biomass, such as density, color development, and glossiness, are not necessarily sufficient.

[0012] The present application has been made in view of the problems of the prior art, and aims to provide a pigment dispersion liquid in which carbon black derived from biomass is highly dispersed, which can produce an aqueous inkjet ink having excellent discharge stability, capable of recording an image having high density and excellent color development and glossiness. Also, the present application aims to provide a method for producing the pigment dispersion liquid.

[0013] Approach to solving the problem

[0014] That is, according to the present application, the following pigment dispersion liquid is provided.

[0015] [1] A pigment dispersion liquid containing a pigment, a dispersant, a water-soluble organic solvent, and water, which is used for producing an aqueous inkjet ink, wherein the pigment is carbon black derived from biomass having a number average particle diameter of 80 to 300 nm in a state of being dispersed in the pigment dispersion liquid, and the dispersant 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 (meth)acrylic acid ester of biomass origin, and at least a part of carboxyl groups in the polymer is neutralized with a base, the polymer has an acid value of 50 to 150 mgKOH / g, a number average molecular weight of 5,000 to 20,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 2.5 or less, and the content of the structural unit (ii) in the polymer is 50% by mass or more, and the (meth)acrylic acid ester of biomass origin 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.

[0016] [2] The pigment dispersion liquid according to the preceding [1], wherein the dispersant satisfies the following conditions (1) to (3).

[0017] [Condition (1)]

[0018] The dispersant is an A-B block copolymer having a content of structural units derived from the methacrylic monomer of 90 mass% or more, comprising a polymer chain A and a polymer chain B, a number average molecular weight of 5000 to 20000, and a molecular weight distribution of 1.6 or less.

[0019] [Condition (2)]

[0020] The aforementioned polymer chain A is a water-insoluble polymer block having a content of structural units (ii-a) derived from the biomass-derived methacrylic ester of 80 mass% or more, a number average molecular weight of 3000 to 10000, and a molecular weight distribution of 1.6 or less.

[0021] [Condition (3)]

[0022] The aforementioned polymer chain B is a polymer block comprising structural units (i-b) derived from methacrylic acid, and having a content of structural units (ii-b) derived from the biomass-derived methacrylic ester of 40 to 90 mass%, an acid value of 100 to 260 mgKOH / g, a number average molecular weight of 3000 to 10000, and at least a part of carboxyl groups being neutralized by a base.

[0023] [3] The pigment dispersion liquid according to the aforementioned [1] or [2], wherein the biomass-derived (meth)acrylic ester comprises isobornyl methacrylate, and comprises at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate, the ratio of isobornyl methacrylate in all of the biomass-derived (meth)acrylic esters being 40 mass% or more.

[0024] [4] The pigment dispersion liquid according to any one of the aforementioned [1] to [3], wherein the base is a combination of at least either one of sodium hydroxide and potassium hydroxide and ammonia.

[0025] [5] The pigment dispersion liquid according to any one of the aforementioned [1] to [4], wherein the content of the pigment is 10 to 30 mass%, the content of the dispersant is 2 to 10 mass%, the content of the water-soluble organic solvent is 30 mass% or less, and the content of the water is 50 to 80 mass%.

[0026] Further, according to the present application, there is provided a method for producing the pigment dispersion liquid shown below.

[0027] [6] A method for producing a pigment dispersion liquid, which is a method for producing a pigment dispersion liquid containing a pigment, a dispersant, a water-soluble organic solvent, and water for an aqueous inkjet ink, the method for producing the pigment dispersion liquid comprising a step of dispersing a mixture containing a raw material carbon black derived from biomass having a number average particle diameter of primary particles of 20 to 400 nm, the aforementioned dispersant, the aforementioned water-soluble organic solvent, and the aforementioned water, the aforementioned pigment being a carbon black derived from biomass having a number average particle diameter of 80 to 300 nm in a state of being dispersed in the aforementioned pigment dispersion liquid, the aforementioned dispersant being 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, and at least a part of carboxyl groups of the aforementioned polymer being neutralized with a base, the aforementioned polymer having an acid value of 50 to 150 mgKOH / g, a number average molecular weight of 5,000 to 20,000, a molecular weight distribution (weight average molecular weight / number average molecular weight) of 2.5 or less, and a content of the aforementioned structural unit (ii) of 50% by mass or more, and the aforementioned biomass-derived (meth)acrylate being 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.

[0028] Effects of the Invention

[0029] According to the present application, it is possible to provide a pigment dispersion liquid in which biomass-derived carbon black is highly finely dispersed, which can produce an aqueous inkjet ink excellent in discharge stability, which can record an image excellent in color development and glossiness at a high concentration. In addition, according to the present application, it is possible to provide a method for producing the pigment dispersion liquid. DETAILED DESCRIPTION

[0030]

[0031] Hereinafter, an embodiment of the present application will be described, but the present application is not limited to the following embodiment. One embodiment of the pigment dispersion liquid of the present application is as follows: a pigment dispersion liquid containing a pigment, a dispersant, a water-soluble organic solvent, and water for producing an aqueous inkjet ink. Hereinafter, the details of the pigment dispersion liquid of the present embodiment will be described.

[0032] (Pigment)

[0033] ​The pigment dispersion liquid of the present embodiment contains a pigment in a micro-dispersed state. The pigment is a biomass-derived carbon black having a number average particle diameter of 80 to 300 nm, preferably 90 to 200 nm, in a state dispersed in the pigment dispersion liquid. A "biomass-derived" material is a material obtained using a living organism, particularly a plant, as a raw material. The biomass-derived carbon black is a conventionally known carbon black manufactured from biomass, and is different from a petroleum-derived carbon black, and is an environmentally friendly carbon black that enables carbon neutralization and carbon recycling.

[0034] As the carbon black (raw material carbon black), for example, a carbon black obtained by subjecting a vegetable oil to an incomplete combustion or a thermal cracking reaction at a high temperature, a carbon black obtained by recovering smoke generated by burning a vegetable oil (so-called lamp black), a carbon black obtained by carbonizing a plant or a plant seed as a plant carbon, and the like can be given. As the vegetable oil, palm oil, coconut oil, castor oil, pine tar oil, rapeseed oil, and the like can be given. As the plant carbon, bincho charcoal, bamboo charcoal, plum charcoal, pine charcoal, white birch charcoal, and maple charcoal, and the like can be given. In addition, activated carbon obtained from coconut shells and the like can also be used. Furthermore, oil smoke coal, pine smoke coal, and the like used in inks can also be used. Among them, a carbon black obtained from a non-edible plant is preferably used. The carbon black can have a crystal structure, an amorphous structure, a graphite structure, and the like.

[0035] In manufacturing the pigment dispersion liquid of the present embodiment, a biomass-derived raw material carbon black having a number average particle diameter of primary particles of 20 to 400 nm is used. By using a specific dispersant, a carbon black (raw material carbon black) having a number average particle diameter of primary particles within the above range is dispersed in a liquid medium containing a water-soluble organic solvent and water, and thereby the pigment dispersion liquid of the present embodiment, which contains a carbon black in a dispersed state having a number average particle diameter of 80 to 300 nm and which maintains the dispersed state of the carbon black over a long period of time, can be obtained. The number average particle diameter of the primary particles of the raw material carbon black can be measured by a transmission electron microscope, a scanning electron microscope, X-ray diffraction, and the like. The carbon black can be an acidic carbon black having a surface modified with a carboxyl group, or can be one having a surface modified with a hydroxyl group, a phenolic hydroxyl group, a ketone group, and the like. Hereinafter, the biomass-derived carbon black is also referred to as "biomass carbon black".

[0036] The pigment dispersion liquid of the present embodiment can further contain a pigment other than the above-described biomass-derived carbon black (other pigment). As the other pigment, a petroleum-derived carbon black and the like can be given. By containing a petroleum-derived carbon black, it is expected to complement the function of the biomass-derived carbon black. The ratio of the petroleum-derived carbon black in the entire pigment is preferably 80% by mass or less, and further preferably 50% by mass or less. Note that the pigment dispersion liquid preferably substantially does not contain a petroleum-derived carbon black.

[0037] (Dispersant)

[0038] The dispersant is a component for dispersing pigments in a liquid medium containing a water-soluble organic solvent and water, and is a polymer containing structural unit (i) derived from at least any one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester, and structural unit (ii) derived from a biomass-derived (meth)acrylic acid ester, and at least a part of carboxyl groups is neutralized by a base.

[0039] The polymer contains structural unit (i), and thus, carboxyl groups are introduced in the structure thereof. Also, the acid value of the polymer is 50 to 150 mgKOH / g, and preferably 70 to 200 mgKOH / g. If the acid value is lower than 50 mgKOH / g, even if the carboxyl groups are ionized by neutralization, the polymer does not dissolve in water, and cannot exhibit the performance as a dispersant in an aqueous pigment dispersion liquid, ink. On the other hand, if the acid value exceeds 150 mgKOH / g, the portion dissolved in water becomes more, and thus, the viscosity of the pigment dispersion liquid sometimes becomes excessively high, or the water solubility sometimes becomes excessively high. Thus, even if adsorbed to pigments, the polymer becomes easy to desorb, and the hydrophilic carboxyl groups are excessive, and thus, the water resistance of the recorded image sometimes decreases.

[0040] At least a part of the carboxyl groups in the polymer is neutralized by a base to be ionized, and exhibits the effect of dissolving the polymer (dispersant) in water. The monomer constituting structural unit (i) is at least any one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester. As the itaconic acid monoester, itaconic acid monomethyl ester, itaconic acid monoethyl ester, and the like can be given.

[0041] The monomer constituting structural unit (ii) is a biomass-derived (meth)acrylic acid ester. The biomass-derived (meth)acrylic acid ester 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 cyclic alkyl group having a large number of carbons. The dodecyl group and the octadecyl group are long-chain alkyl groups having high hydrophobicity / oleophilicity. It is considered that the isobornyl group, the dodecyl group, and the octadecyl group exhibit the effect as an adsorption group adsorbed to biomass carbon. The tetrahydrofurfuryl group is a cyclic ether group having a small number of carbons. The ethyl group is an alkyl group having a small number of carbons. It is considered that the tetrahydrofurfuryl group and the ethyl group exhibit the effect of adjusting the solubility of the dispersant in water.

[0042] The biomass-derived (meth)acrylic acid ester is, for example, a monomer obtained using an alcohol derived from a plant. The pigment dispersion liquid of the present embodiment is a dispersion liquid using a large amount of biomass-derived materials, containing biomass carbon black and containing a dispersant composed of a biomass-derived monomer. Thus, the image recorded by the ink prepared using the pigment dispersion liquid of the present embodiment contains a film derived from biomass, and thus, is more environmentally friendly in terms of carbon neutrality and carbon cycle.

[0043] Isobornyl (meth)acrylate is an esterification product using isoborneol as an alcohol. The isoborneol is a plant-derived alcohol obtained from camphene which is obtained from turpentine and the like. Ethyl (meth)acrylate is an esterification product using ethanol as an alcohol. The ethanol is an alcohol obtained by fermenting biomass such as sugar cane, corn and wood. Tetrahydrofurfuryl (meth)acrylate is an esterification product of tetrahydrofurfuryl alcohol. The tetrahydrofurfuryl alcohol is an alcohol obtained industrially by a catalytic hydrogenation reaction of furfuryl alcohol contained in corn cobs and sugar cane residues. Dodecyl (meth)acrylate and octadecyl (meth)acrylate are esterification products of dodecanol and octadecanol, respectively. Dodecanol and octadecanol are alcohols obtained from coconut oil and palm oil.

[0044] The content of the structural unit (ii) in the polymer (dispersant) is 50% by mass or more, and preferably 80 to 95% by mass. By the content of the structural unit (ii) being 50% by mass, it is possible to use the dispersant in consideration of the environment, and it is possible to make an image and the like recorded by an ink containing the polymer as a dispersant into an image in consideration of the environment.

[0045] The biomass-derived (meth)acrylate preferably contains isobornyl methacrylate, and contains at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate and octadecyl methacrylate. Also, the ratio of isobornyl methacrylate in the total biomass-derived (meth)acrylate is preferably 40% by mass or more, and further preferably 45 to 70% by mass. By using a methacrylate as the biomass-derived (meth)acrylate, it is possible to set the glass transition temperature of the resulting polymer to be high, and it is also possible to improve the hydrolysis resistance. In addition, by the ratio of isobornyl methacrylate in the total biomass-derived (meth)acrylate being 40% by mass or more, a group having high hydrophobicity is introduced into the polymer in a large amount, and it is possible to improve the adsorptivity to pigments. Of these, the biomass-derived (meth)acrylate preferably contains isobornyl methacrylate, and contains at least either of ethyl methacrylate and tetrahydrofurfuryl methacrylate.

[0046] The biomass-derived (meth)acrylate can be distinguished from a (meth)acrylate derived from a petroleum material. Further, the compound derived from a petroleum material does not contain carbon 14 14 C) which is one of carbon isotopes. On the other hand, the compound derived from biomass contains carbon 14 14 C). Therefore, it is possible to judge whether or not it is a biomass-derived (meth)acrylate depending on the presence or absence of carbon 14 14 C). As the method for measuring carbon 14 14As a method for measuring C, there are, for example, a beta-ray measurement method and an accelerator mass spectrometry (AMS) method. In particular, for environmental materials, there are standards such as ASTM D6866, CEN 16137, and ISO 16620-2.

[0047] The polymer used as the dispersant can further include a structural unit other than the structural unit (i) and the structural unit (ii). As the other structural unit, for example, there are a structural unit derived from a radically polymerizable monomer (other monomer) originating from a petroleum material source, and the like. As the other monomer, there are, for example, a vinyl-based monomer such as styrene, vinyltoluene, and the like; a (meth)acrylic acid-based monomer; and the like. As the (meth)acrylic acid-based monomer, there are, for example, a monofunctional (meth)acrylate having a substituent such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, a 2-ethylhexyl group, an octyl group, a decyl group, a dodecyl group, a tridecyl group, a hexadecyl group, an octadecyl group, an isostearyl group, a behenyl group, a cyclohexyl group, a trimethylcyclohexyl group, a t-butylcyclohexyl group, a benzyl group, a methoxyethyl group, a butoxyethyl group, a phenoxyethyl group, a nonylphenoxyethyl group, an isobornyl group, a dicyclopentyl group, a dicyclopentenyl group, a dicyclopentenylethoxy group, a glycidyl group, a 2-hydroxyethyl group, a 2-hydroxypropyl group, a 4-hydroxybutyl group, a dimethylaminoethyl group, a diethylaminoethyl group, a polyethylene glycol, a polypropylene glycol, a polyethylene glycol monomethyl ether, a polypropylene glycol monomethyl ether, a poly-ε-caprolactone, a polydimethylsiloxane, and the like. Among these, for a monomer having a polyalkylene glycol chain, since the polyalkylene glycol chain has biodegradability, it is a monomer that addresses the environment, and thus is preferred. Note that the polymer used as the dispersant preferably consists of substantially only the above-described structural units (i) and (ii).

[0048] The number average molecular weight (Mn) of the polymer used as the dispersant is 5000 to 20000, preferably 6000 to 18000, and further preferably 7000 to 15000. If the Mn of the polymer is less than 5000, it becomes easy to desorb from the pigment, and the dispersion stability of the pigment decreases. On the other hand, if the Mn of the polymer exceeds 20000, the viscosity of the pigment dispersion liquid becomes excessively high, and the particles of the pigment become easy to adsorb to each other, and sometimes aggregate. Note that the number average molecular weight (Mn) and the weight average molecular weight (Mw) in the present specification are both values measured by gel permeation chromatography (GPC) and are polystyrene conversion values.

[0049] The molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer as the dispersant is 2.5 or less, preferably 2.0 or less, and further preferably 1.6 or less. If the molecular weight distribution (PDI) of the polymer exceeds 2.5, the dispersibility of the pigment decreases. By active radical polymerization, the molecular weight of the resulting polymer can be made uniform, or the structure can be controlled. By making the molecular weight of the polymer uniform, a large amount of polymer chains that contribute to the dispersibility of the pigment are contained, with less high-molecular-weight polymers and less low-molecular-weight polymers, and thus this is preferable.

[0050] The dispersant is a polymer in which at least a part of carboxyl groups derived from (meth)acrylic acid, itaconic acid, or the like is neutralized by a base. At least a part of the carboxyl groups is ionized by being neutralized, and thus the polymer easily affines with water and dissolves.

[0051] As the base, ammonia; triethylamine, dimethylaminoethanol, diethanolamine, triethanolamine, aminomethylpropanol, polyethylene glycol polypropylene glycol monoamine, and the like organic amines; coconut amine, octylamine, dodecylamine, stearylamine, oleylamine, dimethyloctylamine, and the like organic monoamines derived from biomass; lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like alkali metal hydroxides; and the like can be given. Among these, the base is preferably at least either one of sodium hydroxide and potassium hydroxide in combination with ammonia. If neutralization is performed with ammonia, the ammonia volatilizes after recording to become the original carboxyl group, and thus the water resistance of the image can be improved. In addition, if neutralization is performed with sodium hydroxide or potassium hydroxide, the carboxyl group is ionic, and thus the polymer easily dissolves in water, and the non-drying property and the redissolvability of the ink can be improved.

[0052] The polymer used as the dispersant can be produced by a method known in the past. Specifically, it is preferable to be synthesized by solution polymerization using a water-soluble organic solvent contained in the pigment dispersion liquid. For example, an azo-based polymerization initiator, a peroxide-based polymerization initiator is used, and polymerization is performed while dropping a monomer into a water-soluble organic solvent or simultaneously dropping a monomer. At the time of polymerization, in order to adjust the molecular weight of the resulting polymer, a chain transfer agent such as a mercaptan, a bromomethyl methacrylate, or the like can be used in combination. In addition, in order to make the molecular weight of the resulting polymer uniform, active radical polymerization can be performed. As the active radical polymerization, an atom transfer radical polymerization, an NMP method using a nitroxyl or the like, a reversible addition fragmentation chain transfer polymerization using a thioester, a thiocarbonic acid ester, or the like, a TERP method using organic tellurium as an initiator, an iodine transfer polymerization using an iodine compound as an initiator, a reversible transfer catalytic polymerization using an inorganic / organic catalyst, a reversible complex-mediated polymerization, a chain transfer polymerization using a cobalt catalyst, and the like can be given.

[0053] The dispersant preferably satisfies the following conditions (1) to (3).

[0054] [Condition (1)]

[0055] The dispersant is an A-B block copolymer having a content of structural units derived from a methacrylic monomer of 90 mass% or more, containing a polymer chain A and a polymer chain B, a number average molecular weight of 5000 to 20000, and a molecular weight distribution of 1.6 or less.

[0056] [Condition (2)]

[0057] The polymer chain A is a water-insoluble polymer block having a content of structural units (ii-a) derived from a biomass-derived methacrylic ester of 80 mass% or more, a number average molecular weight of 3000 to 10000, and a molecular weight distribution of 1.6 or less.

[0058] [Condition (3)]

[0059] The polymer chain B is a polymer block containing structural units (i-b) derived from methacrylic acid and having a content of structural units (ii-b) derived from a biomass-derived methacrylic ester of 40 to 90 mass%, an acid value of 100 to 260 mgKOH / g, a number average molecular weight of 3000 to 10000, and at least a part of carboxyl groups being neutralized by a base.

[0060] The dispersant is an A-B block copolymer containing a polymer chain A (hereinafter, also referred to as "A chain") and a polymer chain B (hereinafter, also referred to as "B chain"). The A chain is a water-insoluble polymer block. In addition, the B chain is a water-soluble polymer block containing structural units (i-b) derived from methacrylic acid, and at least a part of carboxyl groups being neutralized by a base. The A chain is a water-insoluble polymer block, and thus, has high hydrophobicity and easily interacts with water-insoluble pigments. Therefore, the A chain is adsorbed or deposited on the pigments by hydrogen bonding or the like, and can encapsulate the pigments. In addition, the A chain has a high molecular weight, and thus, is not substantially desorbed from the pigments. Furthermore, while the A chain is adsorbed on the pigments, the B chain is dissolved in water, and thus, the micro-dispersed pigments are repelled from each other, and the micro-dispersed state is maintained for a long time. In addition, even if the dispersant is free or dissolved in a liquid medium, since the A chain is water-insoluble and forms particles, the ejection stability of the ink can be improved, and an ink suitable for high-speed printing can be provided.

[0061] The B chain is a water-soluble polymer block. The dispersant is adsorbed on the pigments, and thus, even if the ink containing the dispersant is dried in a recording head or the like, the dispersant is not easily desorbed from the adsorbed pigments. Therefore, the pigments are not substantially aggregated, or the dispersant after desorption does not form a coating film, and thus, the resolubility is excellent, and the dispersed state can be easily recovered by adding an aqueous liquid medium.

[0062] [Condition (1)]

[0063] The dispersant is an A-B block copolymer containing a polymer chain A and a polymer chain B, and the content of structural units derived from a methacrylic monomer is 90 mass% or more. As the methacrylic monomer, methacrylic acid and a methacrylic acid ester as an ester of methacrylic acid, and the like can be given. The A-B block copolymer is a polymer whose structure is precisely controlled, and can be produced by living polymerization, in which living radical polymerization is performed. For producing the A-B block copolymer by living radical polymerization using an organic iodide as an initiating compound and using an organic compound as a catalyst, since an environmentally-considered material can be used and the degree of freedom of polymer design is high, it is preferable. In the case of living radical polymerization using an organic iodide, iodine atoms as a terminal growth group are bonded to tertiary carbon atoms, and thus the content of structural units derived from a methacrylic monomer in the A-B block copolymer is 90 mass% or more. In addition, if the content of structural units derived from a methacrylic monomer is more, the glass transition temperature of the A-B block copolymer becomes higher, and thus the thermal properties such as heat resistance are improved, and a tack-free image can be recorded. Furthermore, the methacrylic monomer has high hydrolysis resistance compared to an acrylic monomer such as an acrylate, and thus is not easily hydrolyzed in an aqueous liquid medium, and is relatively stable. Among them, the content of structural units derived from a methacrylic monomer in the A-B block copolymer is preferably 100 mass%.

[0064] As the methacrylic monomer, methacrylic acid and a biomass-derived methacrylic acid ester are preferably used. Among them, as described above, the biomass-derived (meth)acrylic acid ester preferably contains isobornyl methacrylate, and contains at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. Also, it is preferable that the ratio of isobornyl methacrylate among all the biomass-derived (meth)acrylic acid esters is 40 mass% or more.

[0065] The Mn of the A-B block copolymer is 5000 to 20000, and is preferably 7000 to 15000. If the Mn of the A-B block copolymer is less than 5000, it sometimes becomes easy to be detached from the pigment. On the other hand, if the Mn of the A-B block copolymer exceeds 20000, the viscosity sometimes excessively rises in polymerization, or the viscosity of the pigment dispersion liquid excessively rises.

[0066] The molecular weight distribution (PDI) of the A-B block copolymer is 1.6 or less, and is preferably 1.5 or less. If the PDI of the A-B block copolymer exceeds 1.6, a large amount of the range other than the above-described Mn is contained, and the dispersibility of the pigment sometimes becomes slightly insufficient.

[0067] [Condition (2)]

[0068] The polymer chain A is a water-insoluble polymer block having a content of the structural unit (ii-a) derived from the biomass-derived methacrylic ester of 80% by mass or greater, a number average molecular weight of 3000 to 10000, and a molecular weight distribution of 1.6 or less. That is, the A chain is a polymer block that adsorbs and deposits on the pigment and can encapsulate the pigment.

[0069] In the A chain, the content of the structural unit (ii-a) derived from the biomass-derived methacrylic ester is 80% by mass or greater, and preferably 90% by mass or greater. If the content of the structural unit (ii-a) in the A chain is less than 80% by mass, the consideration for the environment is sometimes slightly insufficient. In addition, as long as the content of the structural unit (ii-a) is 80% by mass or greater, a structural unit derived from a methacrylic ester of a petroleum raw material origin can also be contained. Furthermore, as long as the A chain is a water-insoluble polymer block, a structural unit derived from methacrylic acid, for example, can also be contained at around 0.5 to 5% by mass.

[0070] The Mn of the A chain is 3000 to 10000, and preferably 4000 to 8000. Since the molecular weight of the A chain is large to a certain extent, it is easy to adsorb and deposit on the pigment and can encapsulate the pigment. If the Mn of the A chain is less than 3000, it becomes easy to dissolve in a liquid medium such as a water-soluble organic solvent, and sometimes it becomes easy to desorb from the pigment. On the other hand, if the Mn of the A chain exceeds 10000, the water insolubility is sometimes excessively strong, and sometimes it becomes difficult to adsorb on the pigment.

[0071] The molecular weight distribution (PDI) of the A chain is 1.6 or less, and preferably 1.5 or less. If the PDI of the A chain exceeds 1.6, it becomes to contain a large amount of a polymer block outside the range of the above-mentioned Mn, and sometimes it becomes slightly difficult to improve the dispersibility of the pigment.

[0072] [Condition (3)]

[0073] The polymer chain B is a polymer block that contains a structural unit (i-b) derived from methacrylic acid and contains 40 to 90% by mass of a structural unit (ii-b) derived from a biomass-derived methacrylic ester. Furthermore, the polymer chain B is a water-soluble polymer block having an acid value of 100 to 260 mgKOH / g, a number average molecular weight of 3000 to 10000, and at least a part of carboxyl groups being neutralized by a base and ionized to be dissolved in water.

[0074] The acid value of the B chain is 100 to 260 mgKOH / g, preferably 70 to 200 mgKOH / g. By having the acid value in this range, a polymer block that dissolves in water by neutralizing at least a part of the carboxyl groups can be formed. If the acid value of the B chain is less than 100 mgKOH / g, a large number of isobornyl groups and the like, which are highly hydrophobic groups, are present in the B chain, and thus, even if neutralization is performed, sometimes the B chain cannot be dissolved in water. On the other hand, if the acid value of the B chain exceeds 260 mgKOH / g, the hydrophilicity sometimes becomes excessively high. Thus, the water resistance of the recorded image (dried coating film) sometimes becomes easily reduced, and the content of the structural unit derived from the biomass-derived methacrylate ester is relatively reduced, and thus, the environmental friendliness sometimes decreases.

[0075] Even if the ink containing the A-B block copolymer as a dispersant is dried, the B chain dissolves in water, and thus, by imparting a water-based liquid medium, the dispersed state can be easily recovered. Note that since the A chain, which is water-insoluble, is adsorbed and deposited on the pigment, the ink, even if dried, is not easily desorbed from the pigment, and can be recovered to a good dispersed state.

[0076] The content of the structural unit (ii-b) derived from the biomass-derived methacrylate ester in the B chain is 40 to 90% by mass, preferably 50 to 80% by mass. Thus, the A-B block copolymer is an environmentally friendly dispersant.

[0077] The Mn of the B chain is 3000 to 10000, preferably 4000 to 8000. Note that the "number average molecular weight (Mn) of the B chain" in the present specification is a value obtained by subtracting the number average molecular weight (Mn) of the A chain from the number average molecular weight (Mn) of the entire A-B block copolymer. If the Mn of the B chain is less than 3000, the water solubility of the B chain is slightly insufficient, and the dispersion stability of the pigment sometimes becomes insufficient. On the other hand, if the Mn of the B chain exceeds 10000, even if the A chain is adsorbed to the pigment, the entire polymer becomes easily dissolved in water, and sometimes becomes easily desorbed, and the viscosity of the pigment dispersion liquid sometimes excessively increases.

[0078] The B chain is a water-soluble polymer block in which at least a part of the carboxyl groups is neutralized by a base and ionized to dissolve in water. As the base, the aforementioned ammonia, organic amines, alkali metal hydroxides, and the like can be used. All of the carboxyl groups can be neutralized by the base, or a part of the carboxyl groups can be neutralized within a range in which the B chain can dissolve in water.

[0079] The A-B block copolymer can be produced according to a method known in the art. For example, the A-B block copolymer can be produced by active anion polymerization, active cation polymerization, or active radical polymerization. Among these, the A-B block copolymer is preferably produced by active radical polymerization from the viewpoints of the conditions, materials, and devices, and the like.

[0080] Among the living radical polymerization, there are: atom transfer radical polymerization (ATRP method), radical polymerization with the aid of nitroxide (NMP method), reversible addition fragmentation chain transfer polymerization (RAFT method), organic tellurium-based living radical polymerization (TERP method), reversible transfer catalytic polymerization (RTCP method), reversible complex-mediated polymerization (RCMP method), and the like. Among them, the RTCP method and the RCMP method, which use an organic iodide as an initiating compound and an organic compound as a catalyst, are advantageous in terms of cost, since they do not require heavy metals or special compounds, and are also advantageous in terms of ease of purification and handling.

[0081] Since, in the case of the RTCP method and the RCMP method, the iodine atom as a terminal growth group is bonded to a tertiary carbon atom, a stabilized radical is easily generated, and it is possible to produce an A-B block copolymer having a specific block structure with good precision and easily using a general apparatus, and thus is preferred. Therefore, in the A-B block copolymer, the content of the structural unit derived from the methacrylic monomer is preferably 90% by mass or more.

[0082] The A-B block copolymer can be produced by any polymerization form such as solvent-free polymerization, solution polymerization, and emulsion polymerization. Among them, solution polymerization in an organic solvent is preferred, and further solution polymerization in the same organic solvent as the water-soluble organic solvent incorporated in the pigment dispersion liquid is preferred. Thereby, the A-B block copolymer can be directly used for the pigment dispersion liquid without being taken out. The above-described RTCP method and the RCMP method can be performed in the water-soluble organic solvent used in the pigment dispersion liquid.

[0083] Any of the polymer blocks in the A chain and the B chain can be polymerized first. It is preferred to polymerize the A chain and then polymerize the B chain. If the B chain is polymerized first, in the case where the polymerization rate is less than 100%, a structural unit derived from a residual monomer can sometimes be introduced into the A chain which is polymerized later. In this case, methacrylic acid as a component of the B chain is introduced into the A chain in a large amount, and thus there is a possibility that the A chain becomes easily soluble in water.

[0084] (Dispersion medium)

[0085] The pigment dispersion liquid of the present embodiment contains a liquid medium including water and a water-soluble organic solvent as a dispersion medium for the pigment. As the water, ion-exchange water, distilled water, purified water, and the like are preferably used. As the water-soluble organic solvent, an alcohol-based solvent, a glycol-based solvent, a glycol ether, an amide-based solvent, a carbonate-based solvent, other polar solvents, and the like can be used.

[0086] As the alcohol-based solvent, methanol, ethanol, isopropanol, propanol, butanol, isobutanol, and the like can be given. As the glycol-based solvent, ethylene glycol, propylene glycol, glycerol, and the like can be given. As the glycol ether, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, 1,3-butanediol, 3-methoxy-3-methyl-1-butanol, and the like can be given.

[0087] As the amide-based solvent, dimethylformamide, dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and the like can be given. As the carbonate-based solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, and the like can be given. As other polar solvents, dimethyl sulfoxide, tetramethyl urea, dimethyl imidazolidinone, and the like can be given.

[0088] As the water-soluble organic solvent, a solvent derived from biomass, a regenerated solvent, a solvent having biodegradability, a green solvent, and the like are preferably used. Specifically, ethanol obtained by saccharifying sugar cane, corn, and cellulose materials and the like, 1,3-butanediol and glycerol as extracts from natural products, 3-methoxy-3-methyl-1-butanol having biodegradability, ethylene glycol, propylene glycol, and their derivatives as regenerated solvents of various materials such as plastic products, and the like can be given.

[0089] The dispersant is preferably produced by solution polymerization using a water-soluble organic solvent contained in the pigment dispersion liquid, the water-based inkjet ink. If these water-soluble organic solvents are used as the polymerization solvent, the polymer solution obtained by polymerization can be directly used to produce the pigment dispersion liquid, and thus, the process can be simplified.

[0090] (Other additives)

[0091] The pigment dispersion liquid of the present embodiment can contain other additives as needed. As the other additives, bases for adjusting pH, surfactants, preservatives, binder components for water-based inkjet inks, and the like can be given.

[0092] As the base, the aforementioned base can be used. In addition, by containing a surfactant, the surface tension of the pigment dispersion liquid, the ink can be maintained within a prescribed range. As the surfactant, a silicone-based, acetylene glycol-based, fluorine-based, alkylene oxide-based, and hydrocarbon-based surfactant, etc. can be given. Among the surfactants, the use of a natural product, a material derived from biomass is preferable. For example, a fatty acid such as palm oil, coconut oil, a polyalkylene glycol ester of a fatty alcohol, and an ether-based surfactant, etc. are preferable in terms of the environment. The surfactant is often the cause of foaming of the ink, or sometimes the cause of the ink being repelled on the surface of the film. In addition, by adding the surfactant, the pigments sometimes become easy to aggregate, and thus, it is preferable to appropriately control the amount of addition of the surfactant.

[0093] As the preservative, sodium benzoate, benzimidazole, thio benzimidazole, potassium sorbate, sodium sorbate, sodium dehydroacetate, thiazole sulfamide, and pyridine thiol oxide, etc. can be given.

[0094] It is also possible to cause the pigment dispersion liquid to contain a binder component for an aqueous inkjet ink in advance. Note that the ink containing the binder component is useful, for example, as an ink for recording an image on paper such as ordinary paper, photo print paper, photo glossy paper, and matte paper. Note that it is preferable to further contain a binder component as a film forming component in an ink for recording an image on a non-absorbing recording medium such as a plastic film, a plastic molded product, a fiber, a cloth, a metal, and a ceramic. By using an ink containing a film forming component, the film forming component forms a coating film, and it is possible to improve the adhesion, dry rub resistance, wet rub resistance, blocking resistance, chemical resistance, solvent resistance, and scratch resistance of the recorded image (dry coating film), etc.

[0095] As the binder component, a polymer such as an acrylic polymer, a styrene acrylic polymer, a urethane polymer, a polyester polymer, and a polyolefin polymer can be used. These polymers can be used in the form of an aqueous solution, an aqueous dispersion, and an emulsion.

[0096] As the acrylic polymer and the styrene acrylic polymer, an emulsion having a dispersed particle diameter (number average particle diameter) of 50 to 200 nm obtained by polymerizing a styrene, a methacrylate, or the like in the presence of a surfactant can be used. These polymers are preferably an A-B block copolymer, an A-B-A block copolymer having a water-insoluble A chain and a water-soluble B chain. The monomer components constituting these polymers preferably contain a (meth)acrylate derived from biomass.

[0097] As the urethane-based polymer, a water dispersion having a dispersed particle diameter (number average particle diameter) of 50 to 200 nm can be obtained by reacting diisocyanate, polyol, short-chain diol, and glycol monocarboxylic acid, and, as necessary, hydrazine, isophorone diamine, and the like, and chain extending, and then self-emulsifying with an alkali water. As the diisocyanate, in addition to isophorone diisocyanate and hexamethylene diisocyanate, lysine diisocyanate derived from a natural material, pentamethylene diisocyanate, and the like are preferable. As the polyol, in addition to polycarbonate diol, castor oil polyol derived from a natural material, and the like are preferable. As the short-chain diol, in addition to diethylene glycol, ethylene glycol, 1,3-propanediol, isosorbide, and the like derived from a natural material are preferable. As the glycol monocarboxylic acid, dimethylolpropionic acid and the like are preferable.

[0098] As the polyester-based polymer, a water dispersion can be obtained by dehydrating or dealcoholizing a diacid such as adipic acid and phthalic acid with a diol such as ethylene glycol, propylene glycol, neopentyl glycol, and cyclohexane dimethanol, and a monomer having a sulfonic acid group such as dimethyl isophthalic acid sodium sulfonate, and then adding water while forcibly stirring.

[0099] As the polyolefin-based polymer, a water dispersion can be obtained by dissolving a maleic acid grafting product or the like in an organic solvent, adding an aqueous alkali solution while forcibly stirring to form a water dispersion, and further performing a de-organic solvent treatment.

[0100] In the pigment dispersion liquid, other additives such as an organic solvent other than the aforementioned water-soluble organic solvent, a leveling agent, a surface tension adjusting agent, an ultraviolet absorber, a light stabilizer, an antioxidant, a dye, a filler, a wax, a thickening agent, an antifoaming agent, a mildew preventive, an antistatic agent, metal fine particles, and a magnetic powder can be contained as necessary.

[0101] (Pigment dispersion liquid)

[0102] The pigment dispersion liquid of the present embodiment can be produced as described above by dispersing a biomass carbon black (raw carbon black) having a number average particle diameter of primary particles of 20 to 400 nm in a dispersion medium using a specific dispersant. Even if the aforementioned raw carbon black having a large number average particle diameter of primary particles, by using a specific dispersant, dispersing in a mechanical manner (physical manner), a pigment dispersion liquid containing a biomass carbon black having a number average particle diameter of 80 to 300 nm in a dispersed state can be obtained.

[0103] By making the number average particle diameter of the biomass carbon black in a dispersed state 80 to 300 nm, preferably 85 to 130 nm, a pigment dispersion liquid from which an aqueous inkjet ink excellent in ejection stability based on the inkjet method, which can produce an image excellent in optical density, color development, and glossiness at a high concentration, can be produced. If the number average particle diameter (dispersion particle diameter) of the biomass carbon black in the pigment dispersion liquid is less than 80 nm, the optical density (blackness), color development of the recorded image are insufficient. On the other hand, if the number average particle diameter (dispersion particle diameter) of the biomass carbon black in the pigment dispersion liquid exceeds 300 nm, the recording head becomes easily clogged, and the optical density (blackness), color development, and glossiness of the recorded image are insufficient. The number average particle diameter of the dispersed particles (biomass carbon black) in the pigment dispersion liquid can be measured using a dynamic light scattering type particle diameter distribution measuring device.

[0104] The content of the pigment in the pigment dispersion liquid is preferably 10 to 30 mass%, further preferably 12 to 25 mass%. In addition, the content of water in the pigment dispersion liquid is preferably 50 to 80 mass%, further preferably 55 to 75 mass%.

[0105] The content of the water-soluble organic solvent in the pigment dispersion liquid is preferably 30 mass% or less, further preferably 0.5 to 20 mass%. If the content of the water-soluble organic solvent exceeds 30 mass%, the image recorded by the ink produced using the pigment dispersion liquid sometimes becomes difficult to dry.

[0106] The content of the dispersant in the pigment dispersion liquid is preferably 2 to 10 mass%, further preferably 3 to 8 mass%. If the content of the dispersant is less than 2 mass%, the pigment sometimes becomes slightly difficult to be stably dispersed. On the other hand, if the content of the dispersant exceeds 10 mass%, the viscosity becomes excessively high and exhibits non-Newtonian viscosity, and the ink sometimes becomes slightly difficult to be linearly ejected in the inkjet method.

[0107] The content of the dispersant in the pigment dispersion liquid is also preferably set according to the kind, surface properties, and particle diameter of the pigment, and the like. Specifically, the content of the dispersant in the pigment dispersion liquid is preferably set to 5 to 50 parts by mass, further preferably 10 to 30 parts by mass, with respect to 100 parts by mass of the pigment.

[0108] The content of the alkali in the pigment dispersion liquid is preferably an amount in which the content in the ink to be produced becomes 0.5 to 5 mass%. The content of the preservative in the pigment dispersion liquid is preferably an amount in which the content in the ink to be produced becomes 0.05 to 2.0 mass%, further preferably an amount in which it becomes 0.1 to 1.0 mass%. The content of the binder component in the pigment dispersion liquid is preferably an amount in which the content in the ink to be produced becomes 10 to 200 parts by mass, further preferably an amount in which it becomes 20 to 150 parts by mass, with respect to 100 parts of the pigment.

[0109] The viscosity of the pigment dispersion liquid can be appropriately set according to the viscosity of the ink to be prepared, and the like. The viscosity of the pigment dispersion liquid at 25°C is preferably 2.5 to 20 mPa-s, and further preferably 2.6 to 10 mPa-s.

[0110] The surface tension of the pigment dispersion liquid at 25°C is preferably 15 to 45 mN / m, and further preferably 20 to 40 mN / m. The surface tension of the pigment dispersion liquid can be adjusted according to the kind and amount of the water-soluble organic solvent, or by adding a surfactant, and the like.

[0111] The pH of the pigment dispersion liquid at 25°C is preferably 7.0 to 10, and further preferably 8.0 to 9.5. Since the dispersant is neutralized by the base, the dispersant sometimes precipitates when the liquid property of the pigment dispersion liquid is acidic, and the pigments sometimes aggregate.

[0112] <Method for producing pigment dispersion liquid>

[0113] The pigment dispersion liquid described above can be produced according to the method shown below. That is, one embodiment of the method for producing the pigment dispersion liquid of the present application is a method for producing a pigment dispersion liquid containing a pigment, a dispersant, a water-soluble organic solvent, and water, which is used for an aqueous inkjet ink, the method comprising a dispersion treatment step of dispersively treating a mixture containing a raw material carbon black derived from biomass having a number average particle diameter of 20 to 400 nm, preferably 25 to 200 nm, a dispersant, a water-soluble organic solvent, and water.

[0114] In the dispersion treatment step, first, the raw material carbon black (pigment), the dispersant, the water, and the water-soluble organic solvent are mixed to prepare a mixture. Then, the mixture is dispersively treated using a paint shaker, a ball mill, a mortar mill, a sand mill, a horizontal media mill, a colloid mill, a roll mill, an ultrasonic homogenizer, a high-pressure homogenizer, and the like, to micro-disperse the pigment, and to prepare a dispersion liquid. In the prepared dispersion liquid, the water and the water-soluble organic solvent are added, and a binder component and other additives, and the like are added as necessary, to adjust the desired concentration. Furthermore, a base or the like can be added to adjust the pH. Then, by adding various additives such as a surfactant, a preservative, and the like as necessary, the target pigment dispersion liquid can be obtained.

[0115] In the production method of the present embodiment, the raw carbon black, which is a biomass carbon black having a large particle diameter of primary particles, is dispersed in such a manner as to become a prescribed fine particle diameter. In the dispersion treatment, it is preferable to use a grinder using a medium, a high-pressure homogenizer. By collision of the medium, collision of the particles based on high pressure, the large particle diameter is broken down to the prescribed particle diameter in a dry state. In the grinder using a medium, for example, the following methods can be employed: reducing the size of the medium (pulverizing medium) used, increasing the filling rate of the pulverizing medium, increasing the peripheral speed, extending the processing time, slowing the ejection speed, and the like. In the high-pressure homogenizer, the following methods can be employed: increasing the pressure, increasing the number of passes, and the like. After the dispersion treatment, a centrifugal separation treatment, or filtration using a filter, or the like can be performed as needed to remove coarse particles.

[0116] <Usage of the pigment dispersion liquid>

[0117] The pigment dispersion liquid of the present embodiment is useful as a material for producing an aqueous inkjet ink, that is, as a colorant for an aqueous inkjet ink. By using the pigment dispersion liquid of the present embodiment, an aqueous inkjet ink having excellent discharge stability, which can record an image having high concentration and excellent color development and glossiness, can be produced. In addition, the pigment dispersion liquid of the present embodiment is not only useful as an aqueous inkjet ink, but also as a material (colorant) for a printing ink such as an aqueous coating for automobiles and building materials, an aqueous stationery, and an aqueous gravure ink, an aqueous flexographic ink, and the like.

[0118] Examples

[0119] Hereinafter, the present application will be specifically described based on examples, but the present application is not limited to these examples. Note that "parts" and "%" in the examples and comparative examples are mass-based unless otherwise specified.

[0120] <Manufacture of the dispersant>

[0121] (Synthetic Example 1)

[0122] Into a reaction vessel, 300 parts of diethylene glycol (BDG) was placed, and heated to 70°C while bubbling nitrogen. Into another vessel, 120 parts of isobornyl methacrylate (IBXMA), 90 parts of tetrahydrofurfuryl methacrylate (THFMA), 45 parts of lauryl methacrylate (LMA), 45 parts of methacrylic acid (MAA), and 4.5 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (trade name "V-65", manufactured by FUJIFILM Corporation) (V-65) were placed and mixed, homogenized, to prepare a monomer mixture liquid.

[0123] As the IBXMA, a methacrylate obtained by reacting isobornyl alcohol derived from rosin and rosin oil with methacrylic acid (biomass degree 71.4%) was used. As the THFMA, an ester of tetrahydrofurfuryl alcohol obtained by hydrogenating furfuryl alcohol derived from corn cob and the like with methacrylic acid (biomass degree 55.5%) was used. As the LMA, an ester of lauryl alcohol obtained by hydrogen reduction of lauric acid, which is a fraction of fatty acids obtained by hydrolysis of oils and fats such as palm kernel oil, coconut oil, and the like, with methacrylic acid (biomass degree 75.0%) was used.

[0124] After 1 / 3 of the prepared monomer mixture was added dropwise into the reaction vessel, the remaining monomer mixture was further added dropwise over 2 hours, and polymerization was carried out at 70°C for 8 hours to obtain a liquid containing a polymer. A part of the obtained liquid was sampled, and the molecular weight of the polymer was measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a developing solvent. As a result, the number average molecular weight (Mn) of the polymer was 15800, the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.98, and the polymerization rate was about 100%. The polymerization rate was calculated as follows: a part of the obtained liquid was weighed into an aluminum pan, dried in an air-drying oven at 150°C for 3 hours, and calculated from the remaining part.

[0125] A part of the obtained liquid was sampled, and homogenized by adding a toluene / ethanol (= 1 / 1 (volume ratio)) mixed solvent. A few drops of a 1% phenothalin / ethanol solution were added, and titrated with a 0.1 N (0.1 mol / L) potassium hydroxide ethanol solution to measure the acid value of the polymer. As a result, the acid value of the polymer was 97.8 mgKOH / g. In the solution containing the polymer, a mixed solution of 28% ammonia water 34.9 parts (relative to 100 mol% of the contained carboxyl group) and water 114.2 parts was added to neutralize, and an aqueous solution of dispersant D-1 was obtained. The solid content of the obtained aqueous solution was 40.1%, and the pH was 8.9.

[0126] (Synthetic Examples 2 to 4, Comparative Synthetic Examples 1 to 3)

[0127] Using the kinds and amounts (unit: parts) of various materials shown in Table 1, in addition to the same as in the aforementioned Synthetic Example 1, an aqueous solution of dispersants D-2 to 4, comparative dispersants HD-1 to 3 was obtained. The physical properties and the like of the obtained dispersants are shown in Table 1. Note that the meanings of the abbreviations in Table 1 are shown below.

[0128] • MPG: propylene glycol monomethyl ether

[0129] • LSH: lauryl mercaptan

[0130] • EMA: ethyl methacrylate (esterification product of biomass's ethanol and methacrylic acid, biomass degree 33.3%)

[0131] • StMA: stearyl methacrylate (esterification product of stearyl alcohol obtained from palm kernel oil, coconut oil, etc. and methacrylic acid, biomass degree 81.8%)

[0132] • ITME: monoethyl itaconate (monoesterification product of itaconic acid obtained by fermenting starch using biomass's ethanol, biomass degree 100%)

[0133] Table 1

[0134]

[0135] (Synthetic Example 5)

[0136] Into a reaction vessel were put BDG 283.1 parts, IBXMA 59.6 parts, THFMA 59.6 parts, iodine 2.0 parts, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", manufactured by FUJIFILM Corporation) (V-70) 3.6 parts, and N-iodosuccinimide (NIS) 0.1 part. While bubbling nitrogen, the temperature was raised to 45°C, and polymerization was performed for 4 hours to form an A chain (polymer). The Mn of the A chain measured by sampling a part thereof was 4900, the PDI was 1.19, and the polymerization rate was about 100%.

[0137] A mixture of IBXMA 59.5 parts, THFMA 59.5 parts, and MAA 30.2 parts was added, and polymerization was performed at 45°C for 4 hours to form a B chain, to obtain an A-B block copolymer. The Mn of the A-B block copolymer was 10800, the PDI was 1.26, the acid value was 73.2 mgKOH / g, and the polymerization rate was about 100%. In addition, the Mn of the B chain (Mn of the whole - Mn of the A chain) was 5900, and the acid value of the B chain calculated from the compounding value taking the polymerization rate into account was 132.0 mgKOH / g. After cooling to room temperature, a mixture of sodium hydroxide 14.0 parts and water 125.8 parts was added to perform neutralization, to obtain an aqueous solution of dispersant D-5. The solid content of the obtained aqueous solution was 41.6%, and the pH was 10.2.

[0138] (Synthetic Examples 6 to 8)

[0139] Using the kinds and amounts (unit: parts) of various materials shown in Table 2, and in addition, in the same manner as in the aforementioned Synthetic Example 5, aqueous solutions of dispersants D-6 to 8 were obtained. The physical properties, etc. of the obtained dispersants are shown in Table 2.

[0140] Table 2

[0141]

[0142] Preparation of dispersant

[0143] (Dispersant HD-4)

[0144] An aqueous solution (solid content 35.0%) of styrene-maleic anhydride copolymer (styrene / maleic anhydride = 1 / 1 (mol ratio), Mn 5000, acid value 470.0 mgKOH / g) neutralized with ammonia was prepared as an aqueous solution of dispersant HD-4. This dispersant HD-4 was a high-acid-value dispersant (polymer) manufactured from a material derived from petroleum.

[0145] Preparation of pigment dispersion liquid (1)

[0146] (Example 1)

[0147] An aqueous solution of dispersant D-1 89.1 parts and ion exchange water 337.8 parts were mixed to obtain a transparent liquid. To the obtained solution, carbon black (C.I. Pigment Black 6, trade name "PRINTEX Nature", manufactured by Orion Engineered Carbons S.A., number average particle diameter of primary particles 27 nm, oil absorption 68 cm 3 / 100 g) 150 parts were added, dry stirring was performed for 30 minutes using a disperser, and a grind base was prepared. This carbon black was a biomass-derived carbon black (raw material carbon black). Using a horizontal medium dispersion machine (trade name "DYNO-MILL 0.6 liter ECM type", manufactured by SHINMARU ENTERPRISES Co., Ltd., zirconia beads with a diameter of 0.5 mm), a dispersing treatment of 5 passes was performed at a peripheral speed of 10 m / s, and the pigment was sufficiently dispersed in the grind base. Water 256.4 parts were added, and adjustment was performed so that the pigment concentration became 18%. After centrifugal separation treatment (7500 rpm, 20 minutes) of the grind base, filtration was performed using a membrane filter with a pore size of 5 μm. Dilution was performed with water, and an inkjet-use pigment dispersion liquid-1 with a pigment concentration of 14% was obtained.

[0148] The number average particle diameter of the pigment in the pigment dispersion liquid-1 was 116.6 nm as measured using a particle size analyzer (trade name "NICOMP 380ZLS-S", manufactured by International Business Machines Corp.), and it was confirmed that the pigment was finely dispersed. The viscosity of the pigment dispersion liquid-1 was 2.7 mPa-s, and the pH was 8.4. The viscosity of the pigment dispersion liquid-1 was a value at 25°C measured using an E-type viscometer at 60 rpm. The number average particle diameter of the pigment in the pigment dispersion liquid-1 after storage at 70°C for 1 week was 116.5 nm, and the viscosity was 2.6 mPa-s. It was thus confirmed that the storage stability of the pigment dispersion liquid-1 was very good.

[0149] (Examples 2 to 8, Comparative Examples 1 to 4, Reference Examples 1 to 3)

[0150] Using the dispersants of the kinds shown in Table 3, and excepting this, in the same manner as in the aforementioned Example 1, pigment dispersions -2 to -8, pigment dispersions -1H to -4H were obtained. Further, using the dispersants of the kinds shown in Table 3, and using C.I. Pigment Black 7 (trade name "Printex 85", manufactured by Orion Engineered Carbons S.A., number average particle diameter of primary particles 16 nm, oil absorption amount 54 cm 3 / 100 g) as carbon black, and excepting this, in the same manner as in the aforementioned Example 1, pigment dispersions -1S to -3S were obtained. This carbon black is a carbon black derived from petroleum (raw material carbon black). The properties of each of the obtained pigment dispersions are shown in Table 3. Further, the criteria for "Evaluation" in Table 3 are shown below. Note that "O" is pass, and "Δ" and "X" are fail.

[0151] O: The pigment is finely dispersed, and even if stored at 70°C for 1 week, the number average particle diameter of the pigment and the viscosity do not greatly change.

[0152] Δ: The pigment is finely dispersed, but the viscosity exceeds 4.0 mPa-s, or the number average particle diameter of the pigment and the viscosity greatly change after storage at 70°C for 1 week.

[0153] X: The pigment is finely dispersed, but the number average particle diameter of the pigment increases, or the viscosity increases after storage at 70°C for 1 week.

[0154] Table 3

[0155]

[0156] <Preparation of ink>

[0157] (Evaluation Examples 1 to 11)

[0158] The pigment dispersion of the kind shown in Table 4, 28.7 parts, BDG, 1.5 parts, 2-pyrrolidone, 5 parts, glycerol, 20.0 parts, a surfactant (trade name "SURFYNOL 465", manufactured by Air Products), 1 part, and water, 44.8 parts were mixed. After sufficient stirring, filtration was performed using a membrane filter having a pore size of 5 μm, and inks I-1 to I-11 for inkjet were prepared.

[0159] (Resolubility)

[0160] A drop of each ink was dropped on a glass plate. After drying at 60°C for 24 hours, ion-exchanged water was added, and the resolubility of the ink was evaluated in accordance with the evaluation criteria shown below. The results are shown in Table 4. Note that "O" and "D" were taken as passing.

[0161] O: A fine film was visible, but the state of the original dispersion liquid was restored.

[0162] O: A fine film was visible, but the state of the original dispersion liquid was restored.

[0163] D: The film detached and peeled off.

[0164] X: Not dissolved.

[0165] (ejection property)

[0166] Each ink was filled into a cartridge, and mounted on an inkjet printer (trade name "EM930C", manufactured by Seiko Epson Corporation). A solid image was printed on (i) a dedicated glossy paper for photos (PGPP) and (ii) a general paper (trade name "4024", manufactured by Xerox Corporation) in a print mode of "Photo 720 dpi". The ejection state of the ink at the time of printing was observed, and the ejection property of the ink was evaluated in accordance with the evaluation criteria shown below. The results are shown in Table 4. Note that "O" was taken as passing.

[0167] O: Ejected without problems.

[0168] X: Spattering occurred halfway, or the droplet ejection did not go straight.

[0169] (determination of optical density and 20° gloss)

[0170] An optical densitometer (trade name "Macbeth RD-914", manufactured by Gretag Macbeth LLC) was used to determine the optical density (OD value) and 20° gloss of an image recorded on PGPP, and the optical density (OD value) of an image recorded on a general paper. The results are shown in Table 4. Note that each physical value was measured 5 times, and the average value was calculated.

[0171] (scratch resistance)

[0172] The surface of an image recorded on PGPP was wiped with a finger, and the scratch resistance of the image was evaluated in accordance with the evaluation criteria shown below. The results are shown in Table 4. Note that "O" and "D" were taken as passing.

[0173] O: The ink did not adhere to the finger.

[0174] Δ: Ink adheres to the finger, but the image is not distorted.

[0175] X: Striations are generated in the image.

[0176] Table 4

[0177]

[0178] <Manufacture of pigment dispersion liquid (2)>

[0179] (Example 9)

[0180] Bamboo charcoal (trade name "Fine Bamboo Charcoal Powder", manufactured by the Synergy Group Trust Co., Ltd., number average particle diameter of primary particles: 350 nm) was used as the carbon black (raw material carbon black), and otherwise, in the same manner as in the aforementioned Example 8, a pigment dispersion liquid-9 was obtained. Note that the number average particle diameter of the pigment in the pigment dispersion liquid-9 was measured at the middle of the manufacture and after the manufacture (at the middle of the dispersion treatment (1 to 5 passes), after the filtration / centrifugal separation treatment, and after storage at 70°C for 1 week). The results are shown in Table 5.

[0181] Table 5

[0182]

[0183] As shown in Table 5, even in the case where the bamboo charcoal having a large primary particle diameter was used as the raw material carbon black, a pigment dispersion liquid having excellent dispersion stability could be obtained in the same manner as in Example 8.

[0184] In addition, an ink for inkjet was prepared using the manufactured pigment dispersion liquid-9 in the same manner as in the aforementioned evaluation example, and various evaluations were performed. As a result, with respect to the redissolution, the ejection, and the rub-off resistance, the same evaluation results as in the ink I-8 prepared using the pigment dispersion liquid-8 were obtained. In addition, the optical density (OD value) of the image recorded on the PGPP was 1.81, and the 20° gloss was 38.3. Furthermore, the optical density (OD value) of the image recorded on the plain paper was 0.99. Thus, it was confirmed that the characteristics of the image were slightly inferior to those of the image recorded with the ink I-8, but were within a practical range.

[0185] Industrial applicability

[0186] The biomass-derived carbon black of the pigment dispersion liquid of the present application is highly finely dispersed, and is useful as a material for preparing an aqueous inkjet ink.

Claims

1. A pigment dispersion, comprising pigment, dispersant, water-soluble organic solvent and water, used for preparing water-based inkjet inks. The pigment is biomass-derived carbon black with a number average particle size of 80–300 nm, dispersed in the pigment dispersion. The dispersant is a polymer comprising structural units (i) derived from at least one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester, and structural units (ii) derived from biomass-derived (meth)acrylic acid esters, wherein at least a portion of the carboxyl groups is neutralized by a base. The polymer has an acid value of 50–150 mg KOH / g, a number-average molecular weight of 5000–20000, and a molecular weight distribution of less than 2.

5. In the polymer, the content of the structural unit (ii) is 50% by mass or more. The biomass-derived (meth)acrylates include isobornyl methacrylate and at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. The proportion of isoborneol methacrylate in all of the biomass-derived (meth)acrylates is 40% by mass or more.

2. The pigment dispersion according to claim 1, wherein, The dispersant satisfies the following conditions (1) to (3), Condition (1): The dispersant is an AB block copolymer derived from methacrylic acid monomers, comprising polymer chains A and B, with a number average molecular weight of 5000–20000 and a molecular weight distribution of less than 1.

6. Condition (2): The polymer chain A is a water-insoluble polymer block derived from biomass-derived methacrylate structural units (ii-a) with a content of 80% by mass or more, a number average molecular weight of 3000-10000, and a molecular weight distribution of less than 1.

6. Condition (3): The polymer chain B is a polymer block comprising a structural unit (ib) derived from methacrylic acid and a structural unit (ii-b) derived from biomass-derived methacrylate, with a content of 40-90% by mass, an acid value of 100-260 mg KOH / g, a number-average molecular weight of 3000-10000, and at least a portion of the carboxyl group being neutralized by a base.

3. The pigment dispersion according to claim 1 or 2, wherein, The base is a combination of at least one of sodium hydroxide and potassium hydroxide with ammonia.

4. The pigment dispersion according to claim 1 or 2, wherein, The pigment content is 10-30% by mass. The content of the dispersant is 2-10% by mass. The content of the water-soluble organic solvent is less than 30% by mass. The water content is 50-80% by mass.

5. A method for manufacturing a pigment dispersion, which is a method for preparing a pigment dispersion containing pigment, dispersant, water-soluble organic solvent and water for use in preparing water-based inkjet inks. The manufacturing method includes a step of dispersing a mixture containing biomass-derived carbon black with a primary particle size of 20–400 nm, the dispersant, the water-soluble organic solvent, and water. The pigment is biomass-derived carbon black with a number average particle size of 80–300 nm, dispersed in the pigment dispersion. The dispersant is a polymer comprising structural units (i) derived from at least one of (meth)acrylic acid, itaconic acid, and itaconic acid monoester, and structural units (ii) derived from biomass-derived (meth)acrylic acid esters, wherein at least a portion of the carboxyl groups is neutralized by a base. The polymer has an acid value of 50–150 mg KOH / g, a number-average molecular weight of 5000–20000, and a molecular weight distribution of less than 2.

5. In the polymer, the content of the structural unit (ii) is 50% by mass or more. The biomass-derived (meth)acrylates include isobornyl methacrylate and at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, dodecyl methacrylate, and octadecyl methacrylate. The proportion of isoborneol methacrylate in all of the biomass-derived (meth)acrylates is 40% by mass or more.

Images