Pigment dispersion, method for producing pigment dispersion, and inkjet ink containing said pigment dispersion

Abstract

Provided are: an inkjet ink providing improved wet abrasion resistance of an image on a base material and providing improved storage stability after heating; and a pigment dispersion usable for the inkjet ink.　This pigment dispersion contains at least (A) a pigment, (B) a metal salt, (C) a dispersion resin, and (D) water.

Description

Pigment dispersion, method for producing pigment dispersion, and inkjet ink containing the pigment dispersion

[0001] The present invention relates to a pigment dispersion, a method for producing the pigment dispersion, and an inkjet ink containing the pigment dispersion.

[0002] There is a demand for the development and improvement of aqueous inkjet inks. For example, known inkjet inks and inkjet pigment dispersions that exhibit good abrasion resistance when printed on various substrates such as plastic substrates, that are excellent in filterability and ink ejection properties during inkjet printing, and that do not emit odors during production are disclosed in Patent Document 1.

[0003] WO 2009 / 136547

[0004] However, the inventors' studies revealed that when an inkjet ink such as that described in Patent Document 1 is used to print on a PET film, the printed image peels off when rubbed with a cloth dampened with water, indicating that the water abrasion resistance of the image on the substrate is insufficient. Furthermore, when an ink was prepared using a pigment dispersion such as that described in Patent Document 1 and the storage stability of the ink was examined in an accelerated heating test, the storage stability was found to be insufficient. From the perspective of providing an inkjet ink having improved water abrasion resistance and post-heat storage stability of the image on the substrate, and an inkjet pigment dispersion usable for the inkjet ink, there is room for improvement in the prior art. Therefore, an object of the present invention is to provide an inkjet ink having improved water abrasion resistance and post-heat storage stability of the image on the substrate, and a pigment dispersion usable for the inkjet ink.

[0005] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems of the present invention can be solved by adding a metal salt to a pigment dispersion, and have thus completed the present invention.

[0006] That is, the present invention encompasses the following aspects. [1] A pigment dispersion containing at least a pigment (A), a metal salt (B), a dispersion resin (C), and water (D). [2] The pigment dispersion according to [1], wherein the metal salt (B) comprises an anion moiety and a cation moiety, and the cation moiety is a polyvalent metal ion. [3] The pigment dispersion according to [1] or [2], wherein the metal salt (B) comprises an anion moiety and a cation moiety, and the anion moiety is an ion derived from a compound having an acidic group. [4] The pigment dispersion according to any one of [1] to [3], wherein the content of the pigment (A) in 100% by mass of the pigment dispersion is 10 to 45% by mass. [5] The pigment dispersion according to any one of [1] to [4], wherein the content of the metal salt (B) in 100% by mass of the pigment dispersion is 0.50 to 5.00% by mass. [6] An inkjet ink containing the pigment dispersion according to any one of [1] to [5]. [7] A method for producing a pigment dispersion, comprising: a mixing step of mixing a pigment (A), a metal salt (B), a dispersing resin (C), and water (D) to obtain a mixture; a dispersion step of dispersing the mixture to obtain a dispersion; and a centrifugation step of centrifuging the dispersion. [8] A method for producing a pigment dispersion according to [7], further comprising a degassing step of stirring the dispersion under heating.

[0007] According to the present invention, it is possible to provide an inkjet ink which has improved water abrasion resistance and storage stability after heating of an image on a substrate, and a pigment dispersion which can be used in the inkjet ink.

[0008] The present invention will be described in detail below. Note that the following explanation of the constituent elements is an example for explaining the present invention, and the present invention is not limited to these contents.

[0009] (Pigment Dispersion) The pigment dispersion of the present invention (hereinafter also simply referred to as "dispersion") contains at least a pigment (A), a metal salt (B), a dispersing resin (C), and water (D). The pigment dispersion of the present invention can be used for preparing an inkjet ink. Hereinafter, "pigment (A)" may also be referred to as "component (A)", and the same may also be used for other components. The pigment dispersion of the present invention can be produced as an intermediate product for inkjet ink, and after dilution, is used in inkjet printing as an aqueous inkjet ink.

[0010] <Pigment (A)> Examples of the pigment (A) include quinacridone pigments, phthalocyanine pigments, benzimidazolone pigments, diketopyrrolopyrrole pigments, etc. Examples of quinacridone pigments include C.I. Pigment Violet 19, C.I. Pigment Red 122, and a solid solution of C.I. Pigment Violet 19 and C.I. Pigment Red 122 are preferred. C.I. Pigment Violet 19 and C.I. From the viewpoint of saturation, the mass ratio (C.I. Pigment Violet 19 / C.I. Pigment Red 122) in a solid solution of C.I. Pigment Violet 19 and C.I. Pigment Red 122 is preferably 50 / 50 to 80 / 20, more preferably 55 / 45 to 70 / 30. As a phthalocyanine pigment, for example, B15:3 (copper phthalocyanine) is preferred. As a benzimidazolone pigment, for example, C.I. Pigment Yellow 180 is preferred. As a diketopyrrolopyrrole pigment, for example, C.I. Pigment Red 254 is preferred. Pigment (A) may be a commercially available pigment or a synthesized pigment. One or more types of pigment (A) may be used in combination. The content (pigment content) of the pigment (A) in 100% by mass of the pigment dispersion is preferably from 10 to 45% by mass, and more preferably from 13 to 35% by mass, from the viewpoint of the degree of freedom in ink design.

[0011] <Metal Salt (B)> The metal salt (B) is, for example, a compound in which a hydrogen atom of an acid is substituted with a metal ion. The metal salt (B) may be composed of an anion moiety and a cation moiety. The cation moiety is preferably a metal ion, and more preferably a polyvalent metal ion. The valence of the polyvalent metal ion is preferably divalent or more, and preferably divalent to trivalent. An example of a divalent metal ion is calcium ion (Ca ２＋ Examples of trivalent metal ions include aluminum ions (Al ３＋ ) and the like. The anion moiety is preferably an ion derived from a compound having an acidic group. Examples of the acidic group include a sulfonic acid group, a carboxylic acid group, and a phosphate group. Examples of compounds having an acidic group include dichloroquinacridone sulfonic acid, copper phthalocyanine cyanine sulfonic acid, C.I. Pigment Yellow 180 sulfonic acid, and benzoic acid. From the viewpoint of affinity with the pigment (A), the metal salt (B) is preferably a derivative of the pigment (A) that corresponds to the structure of the pigment (A). For example, when a phthalocyanine pigment is used, the effect is more pronounced when a phthalocyanine pigment derivative is used. Furthermore, when a quinacridone pigment is used, the effect is more pronounced when a quinacridone pigment derivative is used. Specific examples of the metal salt (B) include aluminum (Al) of dichloroquinacridone sulfonic acid. ３＋ ) salt, calcium dichloroquinacridone sulfonate (Ca ２＋ ) salt, aluminum copper phthalocyanine sulfonate (Al ３＋ ) salt, calcium (Ca) of copper phthalocyanine cyanine sulfonate ２＋ ) salt, C.I. Pigment Yellow 180 aluminum sulfonate (Al ３＋ ) salt, aluminum benzoate (Al ３＋ As shown in the examples, when a quinacridone pigment is used as the pigment (A), the metal salt (B) is a metal salt of dichloroquinacridone sulfonic acid (aluminum salt of dichloroquinacridone sulfonic acid (Al３＋ ) salt and calcium dichloroquinacridone sulfonate (Ca ２＋ As shown in the examples, when a phthalocyanine pigment is used as the pigment (A), the metal salt (B) is a metal salt of copper phthalocyanine sulfonic acid (aluminum (Al) of copper phthalocyanine sulfonic acid), which is a derivative of the pigment (A) corresponding to the structure of the pigment (A). ３＋ As shown in the examples, when a benzimidazolone pigment is used as the pigment (A), the metal salt (B) is a derivative of the pigment (A) that corresponds to the structure of the pigment (A), such as a metal salt of C.I. Pigment Yellow 180 (benzimidazolone) sulfonic acid (aluminum salt of C.I. Pigment Yellow 180 sulfonic acid (Al ３＋) salts, etc.) are preferably used. The metal salt (B) may be commercially available or synthesized. One or more types of metal salt (B) may be used in combination. From the viewpoint of dispersion stability, the content of the metal salt (B) in 100 mass% of the pigment dispersion is preferably 0.50 to 5.00 mass%, and more preferably 1.00 to 4.00 mass%. From the viewpoint of dispersion stability, the content of the metal salt (B) in the pigment dispersion is preferably 1.00 to 20.00 mass parts, and more preferably 3.00 to 15.00 mass parts, relative to 100 mass parts of the pigment (A). As shown in the examples, for example, when the pigment is a phthalocyanine pigment, a content of the metal salt (B) of 1.00 to 2.00 mass% (or 3 to 7 mass parts, relative to 100 mass parts of the pigment (A)) provides better results. Furthermore, as shown in the examples, for example, when the pigment is a quinacridone pigment, better results are obtained when the content of the metal salt (B) is 2.50 to 3.50% by mass (or 7 to 14 parts by mass per 100 parts by mass of the pigment (A)). The use of the metal salt (B) can improve adhesion by forming an affinity through intermolecular interactions with the carbonyl groups or aromatic rings of the PET film or the like. Furthermore, the use of the metal salt modifies the surface of the pigment (A), thereby improving the affinity between the dispersant (C1) described below and the pigment (A) and strengthening the physical adsorption between the dispersant (C1) and the pigment (A). This is presumably why the solvent resistance and storage stability of the ink are improved.

[0012] <Dispersion Resin (C)> The dispersion resin (C) has a structural unit (c1) derived from an acid group-containing monomer and a structural unit (c2) derived from a non-acid group-containing monomer. The dispersion resin (C) can be obtained by polymerizing an acid group-containing monomer and a non-acid group-containing monomer in the presence of any polymerization initiator using a known method such as radical polymerization. The presence of an acid group in the dispersion resin (C) imparts hydrophilicity to the dispersion resin (C), making it possible to stably disperse the pigment in water.

[0013] <<Structural Unit (c1) Derived from Acid Group-Containing Monomer>> In the acid group-containing monomer from which the structural unit (c1) is derived, examples of the acid group include a carboxy group, a sulfonic acid group, a phosphoric acid group, and a thiocarboxy group, and ethylenically unsaturated monomers having these groups can be used as raw material monomers for the structural unit (c1). Examples of ethylenically unsaturated monomers containing a carboxy group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, and 4-vinylbenzoic acid; and polybasic acid unsaturated esters such as vinyl succinate, allyl maleate, vinyl terephthalate, and allyl trimetrite. Examples of ethylenically unsaturated monomers containing a sulfonic acid group include unsaturated carboxylic acid sulfo-substituted alkyl or aryl esters such as 2-sulfoethyl acrylate and 4-sulfophenyl methacrylate; sulfocarboxylic acid unsaturated esters such as vinyl sulfosuccinate; and sulfostyrenes such as styrene-4-sulfonic acid. Among these, as the monomer from which the structural unit (c1) is derived, taking into consideration the availability and price of the raw material monomers, a monomer having a carboxyl group as the acid group is preferred, unsaturated carboxylic acids are more preferred, and acrylic acid or methacrylic acid is preferred. Hereinafter, the term "(meth)acrylic acid" may be used to encompass both acrylic acid and methacrylic acid, and the term "(meth)acrylic acid ester" may be used to encompass both acrylic acid ester and methacrylic acid ester. The same applies to similar acrylic acid compounds. In the present invention, the acid group-containing monomer is preferably acrylic acid or methacrylic acid.

[0014] <<Structural Unit (c2) Derived from Non-Aid Group-Containing Monomer>> Examples of non-acid group-containing monomers from which the structural unit (c2) is derived include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, methylpropyl (meth)acrylate, and butyl (meth)acrylate; unsaturated fatty acid esters such as dimethyl maleate, dimethyl fumarate, 2-hydroxyethyl (meth)acrylate, and 2-aminoethyl (meth)acrylate; unsaturated fatty acid amides such as (meth)acrylamide and N-methyl(meth)acrylamide; unsaturated nitriles such as (meth)acrylonitrile; unsaturated ethers such as vinyl acetate and vinyl propionate; and styrenes such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-t-butylstyrene, 4-methoxystyrene, and 4-chlorostyrene. unsaturated hydrocarbons such as ethylene, propylene, 1-butene, 1-octene, vinylcyclohexane, 4-vinylcyclohexene, etc.; unsaturated halogenated hydrocarbons such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, 3-chloropropylene, etc.; vinyl-substituted heterocyclic compounds such as 4-vinylpyridine, N-vinylcarbazole, N-vinylpyrrolidone, etc.; reaction products of a monomer containing a substituent having an active hydrogen, such as a carboxyl group, a hydroxyl group, an amino group, etc., among the above-exemplified monomers, with an epoxide such as ethylene oxide, propylene oxide, cyclohexene oxide, etc.; reaction products of a monomer containing a substituent having a hydroxyl group, an amino group, etc., among the above-exemplified monomers, with a carboxylic acid such as acetic acid, propionic acid, butanoic acid, hexanoic acid, decanoic acid, dodecanoic acid, etc. Among these, as the monomer from which the structural unit (c2) is derived, (meth)acrylic acid esters and styrenes are preferred, with butyl (meth)acrylate, styrene, or α-methylstyrene being preferred, as these have the effect of increasing the adsorption power of the dispersing resin (C) to the pigment. Furthermore, as the structural unit (c2), it is also preferred to contain methoxypolyethylene glycol monomethacrylate as a monomer, as this has the excellent effect of improving ejection properties. In the present invention, the non-acid group-containing monomer is preferably styrene, butyl acrylate, butyl methacrylate, or 2-hydroxyethyl methacrylate.

[0015] <<Polymerization Initiator>> Examples of the polymerization initiator include organic peroxides, azo compounds, etc. Examples of the organic peroxides include di-t-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, cumene hydroperoxide, isobutyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butyl peroxypivalate, benzoyl peroxide, and methyl ethyl ketone peroxide. Examples of azo compounds include 2,2'-azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexanecarbonitrile) (ABCN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis-2,4-dimethylvaleronitrile (ADVN), 4,4'-azobis-valeric acid, 4,4'-azobis-4-cyanovaleric acid (ACVA), etc. The polymerization initiators may be used alone or in combination of two or more.

[0016] The dispersion resin (C) is preferably, for example, a styrene-acrylic resin. The dispersion resin (C) is preferably non-crosslinked, from the viewpoint of eliminating the need for heat treatment during production. In the present invention, "non-crosslinked dispersion resin (C)" means that the dispersion resin (C) is synthesized and produced without intentionally using a compound generally considered to be a crosslinking agent, or that the dispersion resin (C) is synthesized and produced without undergoing a commonly used crosslinking step. The crosslinking rate of dispersion resin (C) produced without the addition of a crosslinking agent or an intentional crosslinking step is 5% or less, preferably 3% or less, and most preferably 0%. Non-crosslinked dispersion resin (C) is essentially a linear resin. The above crosslinking rate is a theoretical value, and is 100% when the amount of crosslinking agent is 1 molar equivalent, and 50% when the amount is 0.5 molar equivalent.

[0017] From the viewpoint of dispersion stability, the acid value of the dispersion resin (C) is preferably 90 to 150 mg / KOHg, more preferably 100 to 120 mg / KOHg. In this specification, the acid value refers to the amount of acid per 1 g of resin calculated by titrating the acid with an alkali, converted into mg of potassium hydroxide, as measured in accordance with JIS K 0070:1992. From the viewpoint of dispersion stability, the mass average molecular weight of the dispersion resin (C) is preferably 10,000 to 30,000, more preferably 15,000 to 25,000. The mass average molecular weight can be measured by gel permeation chromatography. Specifically, it can be determined using a GPC (HLC-8320, manufactured by Tosoh Corporation) under the following conditions: Column: TSKgel G1000HXL; G2000HXL; G3000HXL; G4000HXL Mobile phase: THF (containing 250 ppm of BHT) Flow rate: 1.0 mL / min Column temperature: 40°C

[0018] In the pigment dispersion of the present invention, the dispersing resin (C) is preferably contained in a state neutralized with a basic compound. Here, a dispersing resin (C) in which the acid group in the structural unit (c1) has been neutralized with a basic compound is particularly referred to as a "dispersant" in this specification.

[0019] The basic compound used to neutralize the acid groups in the structural unit (c1) in the dispersion resin (C) to prepare a dispersant can be, for example, at least one compound selected from the group consisting of alkali metal salt compounds, amine compounds, and alkanolamine compounds. Examples of alkali metal salt compounds include potassium hydroxide. Examples of amine compounds include ammonia, trialkylamines, dialkylamines, monoalkylamines, triarylamines, diarylamines, and monoarylamines. Examples of alkanolamine compounds include methyldiethanolamine (MDEA) and dimethylethanolamine (DMEA). The neutralization rate is determined based on the neutralization rate achieved when the acid groups in the structural unit (c1) are neutralized in theoretical equivalent amounts, which is 100%. The basic compound can be used in an appropriate amount to achieve the desired neutralization rate. From the viewpoint of the water resistance and dispersion stability of the printed coating film, the neutralization rate is preferably 80 to 250%, more preferably 90 to 200%, and even more preferably 100 to 175%.

[0020] The content of the dispersing resin (C) in the pigment dispersion is preferably 5.00 to 25.00 parts by mass, and more preferably 10.00 to 20.00 parts by mass, in terms of solids content per 100 parts by mass of the pigment (A), from the viewpoint of water resistance and dispersion stability of the printed coating film. The content of the dispersing resin (C) in 100 mass% of the pigment dispersion is preferably 2.00 to 8.00 mass%, more preferably 3.00 to 6.00 mass%, from the viewpoint of water resistance and dispersion stability of the printed coating film. As shown in the examples, for example, when a phthalocyanine pigment is used as the pigment, better results are obtained by using a dispersing agent having a neutralization rate with methyldiethanolamine of 145 to 155% (more preferably 150%). Furthermore, as shown in the examples, for example, when a quinacridone pigment is used as the pigment, better results are obtained by using a dispersing agent having a neutralization rate with dimethylethanolamine of 100 to 110% (more preferably 105%).

[0021] <Water (D)> Ion-exchanged water is preferred as the water (D). The water (D) may be used in an appropriate amount so as to obtain the desired amount of pigment.

[0022] <Other Components> Examples of other components include surfactants, waxes, surface tension adjusters, wetting agents, penetrants, antifoaming agents, preservatives, viscosity adjusters, pH adjusters, chelating agents, plasticizers, antioxidants, UV absorbers, etc. Among these, surfactants (E), antifoaming agents (F), preservatives (G), etc. may be contained.

[0023] <<Surfactant (E)>> The surfactant (E) is, for example, preferably an acetylene-based surfactant. From the viewpoints of the wettability of the pigment with the dispersion medium and the water resistance of the printed coating film, the content of the surfactant (E) in the pigment dispersion is preferably 1.50 to 3.50 parts by mass, and more preferably 2.00 to 3.00 parts by mass, per 100 parts by mass of the pigment (A).

[0024] <<Antifoaming Agent (F)>> The content of the antifoaming agent (F) in the pigment dispersion is preferably 0.05 to 0.25 parts by mass, and more preferably 0.10 to 0.20 parts by mass, relative to 100 parts by mass of the pigment (A), from the viewpoints of sufficient defoaming properties and transparency of a printed coating film.

[0025] <<Preservative (G)>> From the viewpoints of sufficient antiseptic properties and safety in using the pigment dispersion, the content of the preservative (G) in the pigment dispersion is preferably 0.10 to 0.50 parts by mass, and more preferably 0.15 to 0.40 parts by mass, relative to 100 parts by mass of the pigment (A).

[0026] <Method for producing pigment dispersion> The method for producing a pigment dispersion of the present invention includes: a mixing step of mixing a pigment (A), a metal salt (B), a dispersing resin (C), and water (D) to obtain a mixture; a dispersion step of dispersing the mixture to obtain a dispersion; and a centrifugation step of centrifuging the dispersion. The method for producing a pigment dispersion of the present invention may further include a degassing step of stirring the dispersion under heating.

[0027] The method for producing the pigment dispersion in the present invention is not particularly limited. For example, the pigment dispersion may be prepared by dispersing components (A) to (D) and optional components such as components (E) to (G) that are added as needed. Alternatively, a pigment dispersion millbase with a high pigment concentration may be prepared in advance using components (A) to (C) and a portion of component (D) or a medium, and optional components such as components (E) to (G) may be added as needed, followed by dilution with an aqueous medium such as component (D) to prepare a pigment dispersion for use in preparing an aqueous inkjet ink. By preparing a pigment dispersion millbase in advance by dispersing the pigment using a stirring / dispersing device and then preparing the pigment dispersion, an aqueous pigment dispersion in which the pigment is dispersed to a desired volume average particle size can be easily obtained.

[0028] Examples of the stirring or dispersing device include an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a Dyno Mill, a Dispermat, an SC Mill, and a Nanomizer. One of these devices may be used alone, or two or more types of devices may be used in combination.

[0029] In the present invention, it is particularly preferable to produce a pigment dispersion through the following steps. (i) Mixing Step: The constituent components of the pigment dispersion (components (A) to (D) and optional components such as components (E) to (G) added as needed) are mixed and stirred to obtain a slurry. (ii) Dispersion Step: The slurry obtained in (i) is subjected to a dispersion treatment. In the present invention, dispersion treatment refers to the use of beads or the like to pulverize and disperse the slurry obtained in (i) by adding beads and stirring them. (iii) Bead Removal Step: After the dispersion treatment, the beads are removed. Thereafter, the amount of water (ion-exchanged water) added to the slurry is adjusted to obtain a dispersion A exhibiting the desired pigment content. (iv) Centrifugation Step: Coarse particles are removed from dispersion A by centrifugation. Thereafter, dispersion A may be filtered using a filter such as a membrane filter. Thereafter, the amount of water (ion-exchanged water) added to dispersion A after the centrifugation step is adjusted to obtain a dispersion B exhibiting the desired pigment content. Dispersion B is the pigment dispersion referred to in the present invention.

[0030] In the present invention, in the above step (iii), dispersion A may be subjected to a stirring treatment under heating to defoam. In this case, the above step (iii) may be the following step (iiia) (note that in the present invention, the step (iiia) for improving the performance of dispersion A is also referred to as a defoaming step). (iiia) Bead removal step and defoaming step: After the dispersion treatment, the beads are removed. Thereafter, dispersion A having a desired pigment content is obtained by adjusting the amount of water (ion-exchanged water) added to the slurry. Thereafter, dispersion A is subjected to a stirring treatment under heating.

[0031] The mixing step, the dispersion step, the centrifugation step, and the degassing step will be described below.

[0032] <<Mixing Step>> In view of fluidity, the mixing temperature in the mixing step is preferably 5 to 40° C. In view of uniform stirring, the peripheral speed in the mixing step is preferably 3.0 to 9.0 m / s.

[0033] <<Dispersion Step>> In view of bead abrasion, the dispersion temperature in the dispersion step is preferably 5 to 40° C. In view of bead abrasion and foaming, the frequency in the dispersion step is preferably 30 to 50 Hz.

[0034] <<Centrifugation Step>> The G in the centrifugation step is preferably 3000 to 8000 G from the viewpoint of coarse particle removal efficiency. The temperature in the centrifugation step is preferably 10 to 50°C from the viewpoint of coarse particle removal efficiency. If necessary, the dispersion can be diluted before centrifugation. Furthermore, as described above, if necessary, after centrifugation, the dispersion can be diluted to the desired pigment content to obtain a pigment dispersion.

[0035] <<Degassing Step>> If necessary, a deegassing step may be performed from the viewpoint of degassing. The heating temperature in the deegassing step is preferably 40 to 100°C, more preferably 45 to 60°C, from the viewpoint of deegassing ability and the boiling point of the dispersion medium. The heating time in the deegassing step is preferably 30 to 360 minutes from the viewpoint of deegassing ability and dispersion stability. Furthermore, as described above, the deegassing step may be performed after diluting the dispersion liquid if necessary, and then the dispersion may be subjected to centrifugation.

[0036] <<Other Steps>> As described above, if necessary, a step of filtering the pigment dispersion using a membrane filter or cartridge filter may be carried out to remove dust.

[0037] (Inkjet Ink) The inkjet ink contains an inkjet pigment dispersion. The pigment dispersion of the present invention described above can be used as the inkjet pigment dispersion. An aqueous inkjet ink can be prepared by diluting the pigment dispersion of the present invention with an aqueous medium so that the content of pigment (A) is 1 to 30% by mass. This aqueous medium may be water, as with component (D), a mixture of water and an organic solvent, or an organic solvent alone. The organic solvent is not particularly limited as long as it is miscible with water. Examples of solvents other than water that may be contained in the inkjet ink of the present invention include those listed below. The inkjet ink of the present invention may also contain a binder resin. The inkjet ink of the present invention (or the aqueous medium) may also contain various other components, such as wax, alkanolamine, and the optional components described in the section on the pigment dispersion (e.g., humectant, penetrant, preservative, surface tension modifier, etc.).

[0038] <Solvents Other Than Water> Examples of solvents other than water include alcohol solvents such as methanol, ethanol, n-propanol, and isopropanol; ketone solvents such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycols; and lactam solvents such as N-methyl-2-pyrrolidone.

[0039] <Binder Resin> A binder resin may be added for the purpose of further improving the adhesion of the ink to the substrate and the abrasion resistance. For example, an acrylic resin is preferred as the binder resin. From the viewpoint of the water resistance and dispersion stability of the printed coating film, the acid value of the binder resin is preferably 5 to 50 mgKOH / g, and more preferably 10 to 40 mgKOH / g. From the viewpoint of the strength of the printed coating film, the glass transition temperature (Tg) of the binder resin is preferably 5 to 50°C, and more preferably 10 to 40°C. The glass transition temperature (Tg) of the binder resin can be measured according to JIS K7121:2021.

[0040] <Wax> Examples of waxes include plant and animal waxes such as carnauba wax, candelilla wax, beeswax, rice wax, and lanolin; mineral waxes such as montan wax and ozokerite; paraffin wax, a so-called petroleum wax; synthetic waxes such as carbon wax, Hoechst wax, polyolefin wax, silicone wax, and stearic acid amide; and natural and synthetic wax emulsions and blended waxes such as α-olefin-maleic anhydride copolymers. These waxes have the effect of imparting slip properties to the surface of the formed recording material and improving abrasion resistance. These waxes can be used alone or in combination. Among these, silicone wax, polyolefin wax, paraffin wax, and the like are preferably used.

[0041] <Alkanolamine> As the alkanolamine, for example, an alkanolamine having from 2 to 9 carbon atoms is preferred. Examples of alkanolamines include primary alkanolamines such as monoethanolamine, monopropanolamine, and monobutanolamine; secondary alkanolamines such as monoalkanol secondary amines such as N-methylethanolamine and N-methylpropanolamine; and secondary alkanolamines such as dialkanol secondary amines such as diethanolamine and diisopropanolamine; and tertiary alkanolamines such as monoalkanol tertiary amines such as N,N-dimethylethanolamine, N,N-dimethylpropanolamine, and N,N-diethylethanolamine; dialkanol tertiary amines such as N-methyldiethanolamine and N-ethyldiethanolamine; and trialkanol tertiary amines such as triethanolamine and triisopropanolamine. Among these, tertiary alkanolamines having from 2 to 9 carbon atoms are preferred, and triisopropanolamine is particularly preferred.

[0042] <Humectant> The humectant is not particularly limited, but is preferably one that is miscible with water and has the effect of preventing clogging of the inkjet printer head. Examples include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,2-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methylpentane-2,4-diol, and the like. Examples of suitable humectants include diol compounds such as 1,2-heptanediol, 1,2-nonanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-nonanediol, and 1,2-octanediol, and nitrogen-containing heterocyclic compounds such as 1,4-butanediol, 1,3-butanediol, mesoerythritol, pentaerythritol, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, and ε-caprolactam. Among these, the inclusion of propylene glycol and 1,3-butyl glycol ensures safety and exhibits excellent effects in terms of ink drying properties and ejection performance. The content of the humectant in the ink is preferably 3 to 50% by mass.

[0043] <Penetrant> Examples of penetrants include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether. The content of the penetrant in the ink is preferably 0.01 to 10% by mass.

[0044] <Method for Producing Inkjet Ink> The method for producing the inkjet ink of the present invention is not particularly limited. For example, an inkjet ink can be obtained by mixing the pigment dispersion of the present invention, a binder resin, water, and other components, such as a solvent other than water, a wax, an alkanolamine, a wetting agent, and a penetrating agent, which are added as needed.

[0045] The inkjet ink of the present invention has excellent adhesion to various substrates (plastic substrates). The plastic substrate is not particularly limited, and examples thereof include plastic substrates made of polyamide resins such as Ny6, nylon 66, and nylon 46; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate; polyhydroxycarboxylic acids such as polylactic acid; biodegradable resins typified by aliphatic polyester resins such as poly(ethylene succinate) and poly(butylene succinate); polyolefin resins such as polypropylene and polyethylene; thermoplastic resins such as polyvinyl chloride, polyimide resins, polyarylate resins, and mixtures thereof, and laminates thereof. Among these, polyethylene terephthalate (PET) and oriented polypropylene (OPP, biaxially oriented polypropylene) can be preferably used.

[0046] The plastic substrate may also be a plastic film. The plastic film may be an unstretched film or a stretched film, and the manufacturing method is not limited. The thickness of the film is also not particularly limited, but is generally in the range of 1 to 500 μm. The printed surface of the film may be subjected to a corona discharge treatment. Silica, alumina, etc. may also be vapor-deposited on the printed surface.

[0047] According to the present invention, it is possible to provide an inkjet ink that exhibits improved water abrasion resistance and improved storage stability after heating for images formed on a substrate such as PET or OPP, and it is also possible to provide a pigment dispersion that can be used to produce the inkjet ink.

[0048] The present invention will be described in more detail below using examples. Of course, the present invention should not be limited to the scope of these examples. Hereinafter, "parts" and "%" are by mass unless otherwise specified.

[0049] (Materials Used) The following materials were used in the examples.

[0050] <Pigments (A)> Quinacridone pigment: solid solution of C.I. Pigment Violet 19 and C.I. Pigment Red 122 (mass ratio (C.I. Pigment Violet 19 / C.I. Pigment Red 122) = 65 / 35), manufactured by DIC Corporation Phthalocyanine pigment: B15:3 (copper phthalocyanine), manufactured by DIC Corporation Benzimidazolone pigment: C.I. Pigment Yellow 180, manufactured by DIC Corporation

[0051] <Metal Salt (B)> Metal Salt (B-1): Aluminum dichloroquinacridone sulfonate (Al ３＋ ) salt Metal salt (B-2): aluminum (Al) phthalocyanine sulfonic acid salt ３＋ ) salt Metal salt (B-3): C.I. Pigment Yellow 180 sulfonic acid aluminum (Al ３＋ ) salt Metal salt (B-4): calcium salt of dichloroquinacridone sulfonic acid (Ca ２＋ )salt

[0052] <Dispersant> A dispersant was prepared as follows.

[0053] <<Synthesis of Dispersion Resin (C)>> 600 g of isopropyl alcohol (IPA) was placed in a 2 L stainless steel flask, nitrogen was blown in at 20 mL / min, and the mixture was heated to 80 ° C. using an oil bath while stirring at 100 rpm. A mixture of 82.7 g of methacrylic acid, 153.25 g of styrene, 88.65 g of butyl methacrylate, 73.44 g of 2-hydroxyethyl methacrylate, 88.65 g of butyl acrylate, 6.58 g of 2,2-azobis(2-methylbutyronitrile), 6.58 g of 4,4-azobis-valeric acid, and 0.33 g of 3-mercapto-1,2-propanediol (thioglycerol) was added dropwise to the flask at 2 g / min. Thereafter, stirring was continued for 16 hours while maintaining the internal temperature at 80°C, to obtain a dispersion resin (C) having a nonvolatile content of 45% by mass, an acid value of 110 mgKOH / g, and a mass average molecular weight of 20,000.

[0054] <<Preparation of Dispersant (C-1)>> 1284.58 g of ion-exchanged water, 315.42 g of methyldiethanolamine (MDEA, boiling point 247°C), and 2000 g of dispersion resin (C) were placed in a 10 L glass separable flask and stirred. An additional 3300 g of ion-exchanged water was then added, and the mixture was heated with stirring to distill off the IPA and water, yielding Dispersant (C-1) (resin content: 18.82 mass%, basic compound: MDEA, neutralization rate: 150%).

[0055] <<Preparation of Dispersant (C-2)>> Dispersant (C-2) (resin content: 18.82 mass%, basic compound: MDEA, neutralization rate: 105%) was obtained in the same manner as in <<Preparation of Dispersant (C-1)>> above, except that the amount of methyldiethanolamine (MDEA, boiling point 247°C) was changed to 220.79 g.

[0056] <<Preparation of Dispersant (C-3)>> Dispersant (C-3) (resin content: 18.82 mass%, basic compound: potassium hydroxide, neutralization rate: 105%) was obtained in the same manner as in <<Preparation of Dispersant (C-1)>> above, except that 315.42 g of methyldiethanolamine (MDEA, boiling point 247°C) was changed to 103.95 g of potassium hydroxide.

[0057] <<Preparation of Dispersant (C-4)>> Dispersant (C-4) (resin content: 18.82 mass%, basic compound: MDEA, neutralization rate: 200%) was obtained in the same manner as in <<Preparation of Dispersant (C-1)>> above, except that the amount of methyldiethanolamine (MDEA, boiling point 247°C) was changed to 420.56 g.

[0058] <<Preparation of Dispersant (C-5)>> Dispersant (C-5) (resin content: 18.82 mass%, basic compound: DMEA, neutralization rate: 105%) was obtained in the same manner as in <<Preparation of Dispersant (C-1)>> above, except that 315.42 g of methyldiethanolamine (MDEA, boiling point 247°C) was changed to 165.16 g of dimethylethanolamine (DMEA, boiling point 133°C).

[0059] <<Preparation of Dispersant (C-6)>> Dispersant (C-6) (resin content: 18.82 mass%, basic compound: MDEA, neutralization rate: 200%) was obtained in the same manner as in <<Preparation of Dispersant (C-1)>> above, except that the amount of dimethylethanolamine (DMEA, boiling point 133°C) was changed to 314.59 g.

[0060] (Example 1) A pigment dispersion and an inkjet ink were produced and evaluated as follows. <Production of Pigment Dispersion> 474.58 g of ion-exchanged water, 557.92 g of dispersant (C-1), 17.5 g of Surfynol 465 as a surfactant (E), 0.805 g of BYK-019 as an antifoaming agent (F), 1.87 g of Proxel GXL(S) as a preservative (G), 35 g of metal salt (B-1), and 665 g of a quinacridone pigment were placed in a 5 L stainless steel container (18 cm diameter), and the mixture was stirred for 1 hour using a Dispermat (CV3-PLUS manufactured by VMA-GETZMANN) under conditions of 35°C and a peripheral speed of 6.3 m / s (stirring blade: 8 cm diameter), to obtain a slurry. The slurry was then placed in an SC100 mill (manufactured by Nippon Coke Corporation), and 440 g of 0.5 mm diameter zirconia beads (manufactured by Nikkato Corporation, YTZ) were added. Dispersion treatment was carried out for 2 hours at 35°C and a frequency of 45 Hz. After dispersion treatment, the beads were removed, and the resulting dispersion was adjusted with ion-exchanged water to a pigment content of 29% by mass. Coarse particles were then removed using a centrifuge (manufactured by Kokusan Co., Ltd., H-200B, 6000G, 30 minutes, 20°C or lower), and the resulting mixture was filtered using a membrane filter with a pore size of 8 μm (manufactured by Merck Millipore, nitrocellulose). Ion-exchanged water was then added to obtain a pigment dispersion with a pigment content of 27% by mass.

[0061] In Example 5, after the materials were added, a Dispermat (CV3-PLUS manufactured by VMA-GETZMANN) was used to stir for 1 hour at 20°C and a peripheral speed of 4.1 m / s (stirring blade: 8 cmΦ) to obtain a slurry. The slurry was then placed in an SC100 mill (manufactured by Nippon Coke Company), and 440 g of Φ0.5 mm zirconia beads (manufactured by Nikkato Corporation, YTZ) were added. Dispersion treatment was carried out for 2 hours at 35°C and a frequency of 35 Hz. After the dispersion treatment, the beads were removed and the resulting dispersion was adjusted with ion-exchanged water to a pigment content of 15% by mass, and then stirred at 50°C for 3 hours with a stirrer (Three-One Motor, manufactured by Shinto Scientific Co., Ltd.). Thereafter, coarse particles were removed using a centrifuge (H-200B, manufactured by Kokusan Co., Ltd., 6000 G, 30 minutes, 20°C or less), and the mixture was filtered using a membrane filter with a pore size of 8 μm (nitrocellulose, manufactured by Merck Millipore Co., Ltd.), and ion-exchanged water was added to obtain a pigment dispersion with a pigment content of 13% by mass.

[0062] <Preparation of Inkjet Ink> The obtained pigment dispersion, binder resin, wax, water, propylene glycol, 1.3-butanediol, 1.2-hexanediol, diethylene glycol monobutyl ether, and triisopropyl alcohol amine were mixed to prepare an inkjet ink. The pigment content was 5% by mass, the binder resin (acrylic emulsion, manufactured by Seiko PMC Corporation, acid value: 30 mgKOH / g, glass transition temperature (Tg): 20°C) was 2.5% by mass, and the wax (modified polyethylene wax emulsion, Aquacer 531, manufactured by BYK Corporation) was 1.3% by mass, based on the total amount (100% by mass) of the prepared inkjet ink.

[0063] <Various Evaluation Tests> <<Abrasion Resistance Test>> First, a coating film was prepared on a PET film (E5100, manufactured by Toyobo Co., Ltd.) and an OPP film (P2161, manufactured by Toyobo Co., Ltd.) using the prepared inkjet ink. The coating film was prepared as follows. First, each film was prepared as a 25 cm x 12 cm strip. Next, the inkjet ink was applied to the strip using a bar coater (No. 6, manufactured by R.D. Specialties). The film was then heated and air-dried with a hair dryer for 1 minute, and then dried in a constant temperature dryer at 90°C for 10 minutes. The dried coating film was then cut into a 15 cm x 4 cm piece to obtain a test piece. Next, abrasion resistance was evaluated using a Gakushin-type abrasion fastness tester (AB-301, manufactured by Tester Sangyo Co., Ltd.) in accordance with JIS K5701-1:2000. Specifically, one test piece was set in the tester, and using PPC paper (trade name "PPC PAPER High White") (for dry evaluation) and a water-moistened No. 3 gold duster (for wet evaluation) as the friction element, the test was performed under the conditions of a load of 200 g, 100 strokes for the dry evaluation, and 10 strokes for the wet evaluation. The print after the test was scanned with a scanner and evaluated according to the following evaluation criteria using image processing software imageJ. [Evaluation criteria] A: Peeling was less than 20%. B: Peeling occurred of 20% or more but less than 50%. C: Peeling occurred of 50% or more but less than 70%. D: Peeling occurred of 70% or more.

[0064] <<Storage Stability>> First, the viscosity of the inkjet ink was measured immediately after production. Next, the produced inkjet ink was stored statically in a thermostatic chamber at 70°C for one week. Thereafter, the viscosity of the inkjet ink was measured again, and the storage stability was evaluated according to the following calculation (Equation 1) and evaluation criteria: Storage stability = |1 - (viscosity after storage) / (viscosity before storage)| x 100 (Equation 1) [Evaluation criteria] A: 0 or more and less than 5 B: 5 or more and less than 25 C: 25 or more and less than 35 D: 35 or more

[0065] The results of the evaluation test of the inkjet ink in Example 1 are shown in Table 1. In Table 1, "parts by mass" indicates the amount added relative to 100 parts by mass of the pigment (A). In Table 1, the description of water (D) is omitted.

[0066] In Example 1 of Table 1, the content (parts by mass) of the dispersing resin (C) indicates the amount added relative to 100 parts by mass of the pigment (A), and x was calculated using the following formula: 665:100 = (557.92 × 18.82%):x x = 15.79

[0067] In Example 1 in Table 1, the pigment content (mass%) was adjusted by adding ion-exchanged water as described above to prepare a pigment dispersion with a pigment content of 27 mass%. Therefore, in Example 1 in Table 1, the content (mass%) of metal salt (B) is the result of calculating y using the following formula: 665:35=(27%):(y%) y=1.42. In addition, in Example 1 in Table 1, the content (mass%) of dispersing resin (C) is the result of calculating z using the following formula: 665:(557.92×18.82%)=(27%):(z%) z=4.26.

[0068] (Examples 2 to 11, Comparative Example 1) Pigment dispersions and inkjet inks were produced in the same manner as in Example 1, except that the amounts of the pigment (A), metal salt (B), and dispersant (C) listed in Table 1 were adjusted. Note that in the inkjet ink of Example 5, the content of the binder resin was set to 1.25% by mass.

[0069]

[0070] The results of the examples confirmed that inkjet inks containing the pigment dispersions of the present invention exhibited excellent abrasion resistance when printed on substrates such as PET and OPP. Furthermore, the inkjet inks also exhibited excellent storage stability. Among these, Examples 3 and 10 showed favorable results. In Example 3, a phthalocyanine pigment was used as the pigment (A), and the use of a phthalocyanine pigment derivative as the metal salt (B) is believed to have contributed to the favorable results. The use of an aluminum sulfonate derivative as the metal salt (B) is also believed to have contributed to the favorable results. The use of a dispersant with a neutralization rate of 150% with methyldiethanolamine is also believed to have contributed to the favorable results. The content of the metal salt (B) within the range of 1 to 2% by mass is also believed to have contributed to the favorable results. In Example 10, a quinacridone pigment was used as the pigment (A), and the use of a quinacridone pigment derivative as the metal salt (B) is also believed to have contributed to the favorable results. The use of an aluminum sulfonate derivative as the metal salt (B) is also believed to have contributed to the favorable results. The use of a dispersant with a neutralization rate of 105% with dimethylethanolamine is also believed to have contributed to the favorable results. The content of the metal salt (B) within the range of 2.5 to 3.5 mass% is also believed to have contributed to the favorable results.

Claims

1. A pigment dispersion containing at least a pigment (A), a metal salt (B), a dispersion resin (C), and water (D), A pigment dispersion in which the dispersion resin (C) is neutralized with an amine compound or an alkanolamine compound.

2. The pigment dispersion according to claim 1, wherein the metal salt (B) comprises an anionic portion and a cation portion, and the cation portion is a polyvalent metal ion.

3. The pigment dispersion according to claim 1, wherein the metal salt (B) comprises an anionic portion and a cationic portion, and the anionic portion is an ion derived from a compound having an acidic group.

4. The pigment dispersion according to claim 1, wherein the content of the pigment (A) in 100% by mass of the pigment dispersion is 10 to 45% by mass.

5. The pigment dispersion according to claim 1, wherein the content of the metal salt (B) in 100% by mass of the pigment dispersion is 0.50 to 5.00% by mass.

6. An inkjet ink comprising a pigment dispersion according to any one of claims 1 to 5.

7. A mixing step to obtain a mixture by mixing a pigment (A), a metal salt (B), a dispersion resin (C), and water (D), A dispersion step to obtain a dispersion by dispersing the mixture, A centrifugal separation step of centrifuging the dispersion, A method for producing a pigment dispersion containing, A method for producing a pigment dispersion, wherein the dispersion resin (C) is neutralized with an amine compound or an alkanolamine compound.

8. The method for producing a pigment dispersion according to claim 7, further comprising a defoaming step of stirring the dispersion under heating.