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

Abstract

The present invention provides an inkjet ink with improved water resistance to abrasion of images on a substrate and improved storage stability after heating, as well as a pigment dispersion that can be used in the inkjet ink. [Solution] A pigment dispersion containing at least a pigment (A), a metal salt (B), a dispersion resin (C), and water (D).

Description

[Technical Field]

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

[0002] In the field of inkjet inks, there is a need for the development and improvement of water-based inks. For example, an inkjet ink that exhibits good abrasion resistance when printed on various substrates such as plastic substrates, has excellent filterability and ink ejection properties during inkjet printing, and does not generate odor during manufacturing, and an inkjet pigment dispersion that can be used with the inkjet ink, are known as the inkjet ink and inkjet pigment dispersion described in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2009 / 136547 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the inventors found that when printing on a PET film using inkjet ink as described in Patent Document 1, the printed image peels off when rubbed with a damp cloth, indicating that the water-resistant abrasion performance of the image on the substrate is insufficient. Furthermore, when an ink was prepared using a pigment dispersion as described in Patent Document 1, and its storage stability performance in a heating acceleration test was confirmed, it was found to be insufficient. From the perspective of providing an inkjet ink with improved water-resistant abrasion performance and storage stability after heating of images on a substrate, as well as an inkjet pigment dispersion that can be used in said inkjet ink, there was room for improvement compared to the conventional technology. Therefore, the object of the present invention is to provide an inkjet ink with improved water resistance to abrasion of images on a substrate and improved storage stability after heating, as well as a pigment dispersion that can be used in the inkjet ink. [Means for solving the problem]

[0005] As a result of diligent research to solve the aforementioned problems, the inventors of the present invention have found that the problems of the present invention can be solved by including a metal salt in the pigment dispersion, and have completed the present invention.

[0006] In other words, the present invention encompasses the following embodiments. [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 anionic portion and a cation portion, and the cation portion is a polyvalent metal ion. [3] The pigment dispersion according to [1] or [2], wherein the metal salt (B) comprises an anionic portion and a cation portion, and the anionic portion 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 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 comprising a pigment dispersion as described in any of [1] to [5]. [7] A mixing step of obtaining 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 [the pigment]. [8] A method for producing a pigment dispersion according to [7], further comprising a defoaming step of stirring the dispersion under heating. [Effects of the Invention]

[0007] The present invention provides an inkjet ink with improved water resistance to abrasion of images on a substrate and improved storage stability after heating, as well as a pigment dispersion that can be used in the inkjet ink. [Modes for carrying out the invention]

[0008] The present invention will be described in detail below. The following description of the constituent elements is illustrative for illustrating the present invention, and the present invention is not limited to these elements.

[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 dispersion resin (C), and water (D). The pigment dispersion of the present invention can be used for the preparation of inkjet inks. Hereafter, "pigment (A)" may also be referred to as "component (A)," and the same may be said for other components. The pigment dispersion of the present invention can be manufactured as an intermediate product for inkjet inks and, after dilution, used as an aqueous inkjet ink for inkjet printing.

[0010] <Pigment (A)> Examples of pigments (A) include quinacridone-based pigments, phthalocyanine-based pigments, benzimidazolon-based pigments, and diketopyrrolopyrrole-based pigments. Preferred quinacridone pigments include, for example, CIPigment Violet 19, CIPigment Red 122, and a solid solution of CIPigment Violet 19 and CIPigment Red 122. The mass ratio (C.I. Pigment Violet 19 / C.I. Pigment Red 122) in the 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, from the viewpoint of chroma. As the phthalocyanine-based pigment, for example, B15:3 (copper phthalocyanine) is preferable. As the benzimidazolone-based pigment, for example, C.I. Pigment Yellow 180 is preferable. As the diketopyrrolopyrrole-based pigment, for example, C.I. Pigment Red 254 is preferable. The pigment (A) may be a commercially available product or a synthesized product. One or more kinds of the 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 10 to 45% by mass, more preferably 13 to 35% by mass, from the viewpoint of the freedom of ink design.

[0011] <Metal salt (B)> The metal salt (B) is, for example, a compound in which a hydrogen atom of an acid is replaced with a metal ion. The metal salt (B) may preferably consist of an anion part and a cation part. As the cation part, a metal ion is preferable, and a polyvalent metal ion is more preferable. The valence in the polyvalent metal ion is preferably 2 or more, and more preferably 2 to 3. Examples of the divalent metal ion include calcium ion (Ca 2+ ), etc. Examples of the trivalent metal ion include aluminum ion (Al 3+ ), etc. As the anion part, an ion derived from a compound having an acidic group is preferable. Examples of the acidic group include a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group, etc. Examples of the compound having an acidic group include dichlorokynacridone sulfonic acid, copper phthalocyanine cyanine sulfonic acid, C.I. Pigment Yellow 180 sulfonic acid, benzoic acid and the like. From the viewpoint of the affinity with the pigment (A), the metal salt (B) is preferably a derivative of the pigment (A) corresponding to the structure of the pigment (A). For example, when using a phthalocyanine-based pigment, the effect is more pronounced when using a phthalocyanine-based pigment derivative. Further, when using a quinacridone-based pigment, the effect is more pronounced when using a quinacridone-based pigment derivative. Specific examples of the metal salt (B) include, for example, aluminum (Al 3+ ) salt of dichlorokynacridone sulfonic acid, calcium (Ca 2+ ) salt of dichlorokynacridone sulfonic acid, aluminum (Al 3+ ) salt of copper phthalocyanine sulfonic acid, calcium (Ca 2+ ) salt of copper phthalocyanine cyanine sulfonic acid, aluminum (Al 3+ ) salt of C.I. Pigment Yellow 180 sulfonic acid, aluminum (Al 3+ ) salt of benzoic acid and the like. As shown in the examples, when using a quinacridone-based pigment as the pigment (A), the metal salt (B) is preferably a metal salt of dichlorokynacridone sulfonic acid which is a derivative of the pigment (A) corresponding to the structure of the pigment (A) (aluminum (Al 3+ ) salt of dichlorokynacridone sulfonic acid, calcium (Ca 2+ ) salt of dichlorokynacridone sulfonic acid, etc.). [[ID=**************]] Also, as shown in the examples, when using a phthalocyanine-based pigment as the pigment (A), the metal salt (B) is preferably a metal salt of copper phthalocyanine sulfonic acid which is a derivative of the pigment (A) corresponding to the structure of the pigment (A) (aluminum (Al 3+ ) salt of copper phthalocyanine sulfonic acid, etc.). Furthermore, as shown in the examples, when a benzimidazolone-based pigment is used as pigment (A), the metal salt (B) is a metal salt of CI Pigment Yellow 180 (benzimidazolone-based) sulfonic acid, which is a derivative of pigment (A) corresponding to the structure of pigment (A), and aluminum (Al 3+ It is preferable to use salt, etc. The metal salt (B) can be commercially available or synthesized. Metal salt (B) may be one type or two or more types may be used in combination. From the viewpoint of dispersion stability, the content of metal salt (B) in 100% by mass of the pigment dispersion is preferably 0.50 to 5.00% by mass, and more preferably 1.00 to 4.00% by mass. From the viewpoint of dispersion stability, the content of metal salt (B) in the pigment dispersion is preferably 1.00 to 20.00 parts by mass, and more preferably 3.00 to 15.00 parts by mass, per 100 parts by mass of pigment (A). As shown in the examples, for example, when the pigment is a phthalocyanine-based pigment, a metal salt (B) content of 1.00 to 2.00% by mass (or 3 to 7 parts by mass per 100 parts by mass of pigment (A)) yields better results. Furthermore, as shown in the examples, for example, when the pigment is a quinacridone-based pigment, a metal salt (B) content of 2.50 to 3.50% by mass (or 7 to 14 parts by mass per 100 parts by mass of pigment (A)) yields better results. By using a metal salt (B), adhesion can be improved by intermolecular interactions and affinity with carbonyl groups or aromatic rings in PET films, etc. Furthermore, it is presumed that using a metal salt modifies the surface of the pigment (A), improving the affinity between the dispersant (C1) and the pigment (A), and strengthening the physical adsorption between the dispersant (C1) and the pigment (A), thereby improving the solvent resistance and storage stability of the ink.

[0012] <Dispersion resin (C)> The dispersion resin (C) has constituent units (c1) derived from acid group-containing monomers and constituent units (c2) derived from non-acid group-containing monomers. The dispersed resin (C) can be obtained by polymerizing an acid group-containing monomer and a non-acid group-containing monomer using known methods such as radical polymerization in the presence of any polymerization initiator. The presence of acidic groups in the dispersion resin (C) imparts hydrophilicity to the dispersion resin (C), enabling the stable dispersion of pigments in water.

[0013] <<Constituent unit (c1) derived from acid group-containing monomer>> In the acid group-containing monomer that derives the constituent unit (c1), examples of acid groups include carboxyl groups, sulfonic acid groups, phosphoric acid groups, thiocarboxyl groups, etc., and ethylenically unsaturated monomers having these groups can be used as raw material monomers for the constituent unit (c1). Examples of ethylenically unsaturated monomers containing a carboxyl 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 trimethitate. Examples of ethylenically unsaturated monomers containing a sulfonic acid group include, for example, unsaturated carboxylic acid sulfosubstituted 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. In particular, as monomers that derive the constituent unit (c1), considering the availability and cost of the raw material monomers, monomers having a carboxyl group as an acid group are preferred, unsaturated carboxylic acids are more preferred, and acrylic acid or methacrylic acid is preferred. Hereafter, the term "(meth)acrylic acid" may encompass both acrylic acid and methacrylic acid, and the term "(meth)acrylic acid ester" may encompass both acrylic acid esters and methacrylic acid esters. 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] <<Constituent unit (c2) derived from non-acid group-containing monomer>> Examples of non-acid group-containing monomers that induce the constituent unit (c2) 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, pt-butylstyrene, 4-methoxystyrene, and 4-chlorostyrene. Examples include: unsaturated hydrocarbons such as ethylene, propylene, 1-butene, 1-octene, vinylcyclohexane, and 4-vinylcyclohexene; unsaturated halogenated hydrocarbons such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, and 3-chloropropylene; vinyl-substituted heterocyclic compounds such as 4-vinylpyridine, N-vinylcarbazole, and N-vinylpyrrolidone; reaction products between monomers containing substituents having active hydrogen, such as carboxyl groups, hydroxyl groups, and amino groups, as in the above example monomers, and epoxides such as ethylene oxide, propylene oxide, and cyclohexene oxide; and reaction products between monomers containing substituents having hydroxyl groups, amino groups, etc., as in the above example monomers, and carboxylic acids such as acetic acid, propionic acid, butanoic acid, hexanoic acid, decanoic acid, and dodecanoic acid. In particular, as monomers that induce the constituent unit (c2), (meth)acrylic acid esters and styrenes are preferred, and butyl (meth)acrylate, styrene, or α-methylstyrene are preferred, as they have the effect of increasing the adsorption capacity of the dispersed resin (C) to the pigment. Furthermore, it is preferable to include methoxypolyethylene glycol monomethacrylate as a monomer in the constituent unit (c2) because it has the excellent effect of improving discharge performance. 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 polymerization initiators include organic peroxides and azo compounds. Examples of organic peroxides include di-t-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, cumene hydroperoxide, isobutyl peroxide, laurolyl 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(cyclohexanecarbonitride) (ABCN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis-2,4-dimethylvaleronitrile (ADVN), 4,4'-azobis-valeric acid, and 4,4'-azobis-4-cyanovaleric acid (ACVA). Polymerization initiators may be used alone or in combination of two or more types.

[0016] The dispersion resin (C) is preferably, for example, a styrene-acrylic resin. The dispersion resin (C) is preferably non-crosslinkable, from the viewpoint of eliminating the need for heat treatment during manufacturing. In the present invention, the term "non-crosslinked dispersion resin (C)" means that the dispersion resin (C) is synthesized and manufactured without the intentional use of compounds commonly used as crosslinking agents, or without undergoing a commonly used crosslinking process. The crosslinking rate of the dispersed resin (C) produced without the addition of a crosslinking agent or an intentional crosslinking process is 5% or less, preferably 3% or less, and most preferably 0%. The non-crosslinked dispersed resin (C) is basically a linear resin. The above crosslinking rate is a theoretical value, and is set to 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 90-150 mg / KOHg, and more preferably 100-120 mg / KOHg. In this specification, the acid value refers to the value obtained by converting the amount of acid in 1 g of resin, calculated by titrating the acid with an alkali, into the number of mg of potassium hydroxide, 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, and more preferably 15,000 to 25,000. The mass-average molecular weight can be measured by gel permeation chromatography. Specifically, it can be determined by using a GPC (Tosoh HLC-8320) and measuring under the following conditions. Columns: TSKgel G1000HXL; G2000HXL; G3000HXL; G4000HXL Mobile phase: THF (contains BHT250ppm) Flow rate: 1.0mL / min. Column temperature: 40℃

[0018] In the pigment dispersion of the present invention, it is preferable that the dispersion resin (C) is contained in a state neutralized by a basic compound. Here, in this specification, a dispersion resin (C) in which the acid group in the constituent unit (c1) is neutralized by a basic compound is referred to as a "dispersant."

[0019] As a basic compound used to neutralize the acid group in the constituent unit (c1) of the dispersion resin (C) to produce a dispersant, at least one compound selected from the group consisting of alkali metal salt compounds, amine compounds, and alkanolamine compounds can be used. 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 defined with the neutralization rate when the acid group in the constituent unit (c1) is neutralized by the theoretical equivalent amount being 100%. For basic compounds, the amount used should be appropriate 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 80-250%, more preferably 90-200%, and even more preferably 100-175%.

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

[0021] <Water(D)> For water (D), ion-exchanged water is preferred, for example. Water (D) should be used in an appropriate amount to obtain the desired amount of pigment.

[0022] <Other ingredients> Other ingredients include, for example, surfactants, waxes, surface tension modifiers, wetting agents, penetrating agents, defoamers, preservatives, viscosity modifiers, pH adjusters, chelating agents, plasticizers, antioxidants, and UV absorbers. In particular, it may contain surfactants (E), defoaming agents (F), preservatives (G), etc.

[0023] <<Surfactant (E)>> As the surfactant (E), an acetylene-based surfactant is preferred, for example. The content of 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 pigment (A), from the viewpoint of wettability of the pigment dispersion medium and water resistance of the printed coating film.

[0024] <<Antifoaming agent (F)>> The content of the defoaming 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, per 100 parts by mass of pigment (A), from the viewpoint of sufficient defoaming properties and transparency of the printed coating film.

[0025] <<Preservative (G)>> From the viewpoint of sufficient preservative properties and safety in the use of the pigment dispersion, the content of 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, per 100 parts by mass of pigment (A).

[0026] <Method for producing pigment dispersions> The method for producing the pigment dispersion of the present invention is as follows: 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, The process includes a centrifugal separation step of centrifuging the dispersion. The method for producing the pigment dispersion of the present invention may further include a defoaming 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, a pigment dispersion may be prepared by dispersing components (A) to (D) with optional components such as components (E) to (G) which are added as needed. Alternatively, a pigment dispersion mill base liquid with a high pigment concentration may be prepared in advance using components (A) to (C) and some of components (D) or a medium, optional components such as components (E) to (G) may be added as appropriate, and the mixture may be diluted with an aqueous medium such as component (D) to prepare a pigment dispersion for preparing an aqueous inkjet ink. By preparing a pigment dispersion mill base liquid in advance by dispersing the pigment using a stirring and dispersion device, an aqueous pigment dispersion in which the pigment is dispersed with a desired volume average particle size can be easily obtained.

[0028] Examples of stirring and dispersion devices include ultrasonic homogenizers, high-pressure homogenizers, paint shakers, ball mills, roll mills, sand mills, sand grinders, Dino mills, Dispermats, SC mills, nanomizers, etc. One of these may be used alone, or two or more types of devices may be used in combination.

[0029] Furthermore, in the present invention, it is particularly preferable to produce the pigment dispersion by 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) which may be added as needed) are mixed and stirred to obtain a slurry. (ii) Dispersion process: The slurry obtained in (i) is subjected to a dispersion process. In this invention, dispersion process refers to crushing and dispersing the slurry by adding beads to the slurry obtained in (i) and stirring it using beads or the like. (iii) Bead removal process: After dispersion treatment, the beads are removed. Then, by adjusting the amount of water (ion-exchanged water) added to the slurry, a dispersion A exhibiting the desired pigment content is obtained. (iv) Centrifugal separation step: Coarse particles are removed from dispersion A by centrifugal separation. After that, dispersion A may be filtered using a filter such as a membrane filter. By adjusting the amount of water (ion-exchanged water) added to dispersion A after the centrifugal separation step, dispersion B exhibiting the desired pigment content is obtained. The above-mentioned dispersion B is the pigment dispersion as defined in this invention.

[0030] Furthermore, in the present invention, in step (iii) above, the dispersion A may be stirred under heating to remove foam. In that case, step (iii) above may be replaced with step (iiia) below (in the present invention, step (iiia) which improves the performance of dispersion A is also called the defoaming step). (iiia) Bead removal and defoaming process: After dispersion treatment, the beads are removed. Then, by adjusting the amount of water (ion-exchanged water) added to the slurry, a dispersion A exhibiting the desired pigment content is obtained. Subsequently, dispersion A is stirred under heating.

[0031] The mixing process, dispersion process, centrifugal separation process, and defoaming process described above will be explained below.

[0032] <<Mixing process>> From the viewpoint of fluidity, the mixing temperature in the mixing process is preferably 5 to 40°C. In the mixing process, the peripheral speed is preferably 3.0 to 9.0 m / s from the viewpoint of stirring uniformity.

[0033] <<Dispersion process>> From the viewpoint of bead wear, the dispersion temperature in the dispersion process is preferably 5 to 40°C. In the dispersion process, the frequency is preferably 30 to 50 Hz from the viewpoint of bead abrasion and foaming.

[0034] <<Centrifugal Separation Process>> In the centrifugal separation process, a G value of 3000 to 8000 G is preferred from the viewpoint of coarse particle removal efficiency. In the centrifugal separation process, the temperature is preferably 10 to 50°C from the viewpoint of coarse particle removal efficiency. The dispersion can be diluted before centrifugation if necessary. Furthermore, as described above, if necessary, the pigment dispersion can be obtained by centrifugation and dilution to obtain the desired pigment content.

[0035] <<Defoaming process>> If necessary, a defoaming process may be performed from the standpoint of defoaming. The heating temperature in the defoaming process is preferably 40 to 100°C, and more preferably 45 to 60°C, from the viewpoint of defoaming properties and the boiling point of the dispersion medium. In the defoaming process, the heating time is preferably 30 to 360 minutes from the viewpoint of defoaming properties and dispersion stability. Furthermore, as described above, the dispersion may be diluted as needed before the degassing process, and then subjected to centrifugation.

[0036] <<Other processes>> As described above, if necessary, a step may be taken to filter the pigment dispersion using a membrane filter or cartridge filter to remove impurities.

[0037] (Inkjet ink) Inkjet inks contain inkjet pigment dispersions. As the pigment dispersion for inkjet printing, the pigment dispersion of the present invention described above can be used. Using the pigment dispersion of the present invention, an aqueous inkjet ink can be prepared by diluting it in an aqueous medium so that the pigment (A) content is 1 to 30% by mass. This aqueous medium may be water, a mixture of water and an organic solvent, or an organic solvent alone, similar to component (D). The organic solvent is not particularly limited as long as it is miscible with water. Examples of solvents other than water contained in the inkjet ink according to the present invention include the following: Furthermore, the inkjet ink according to the present invention may also contain a binder resin. Furthermore, the inkjet ink according to the present invention (or the aqueous medium described above) may contain various other components, such as waxes, alkanolamines, and pigment dispersions, as described in the section on waxes, alkanolamines, and pigment dispersions (for example, wetting agents, penetrating agents, preservatives, surface tension modifiers, etc.).

[0038] <Solvents other than water> Other solvents besides water include, for example, 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> Binder resin may be added to further improve the adhesion of the ink to the substrate and its abrasion resistance. As the binder resin, an acrylic resin is preferred, for example. The acid value of the binder resin is preferably 5 to 50 mg KOH / g, and more preferably 10 to 40 mg KOH / g, from the viewpoint of water resistance and dispersion stability of the printed coating film. From the viewpoint of print coating strength, 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-based waxes such as carnauba wax, candelilla wax, beeswax, rice wax, and lanolin; mineral waxes such as montane wax and ozokerite; paraffin wax, which is a so-called petroleum-based 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 slipperiness to the surface of the formed recording and improving abrasion resistance. These waxes can be used individually or in mixtures of multiple types. Among these, silicone wax, polyolefin wax, and paraffin wax are preferred.

[0041] <Alkanolamine> As for alkanolamines, those having 2 to 9 carbon atoms are 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 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 2 to 9 carbon atoms are preferred, and triisopropanolamine is particularly preferred.

[0042] <Humectant> There are no particular limitations on the wetting agent, but those that are miscible with water and have an effect of preventing clogging of the inkjet printer head are preferred. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol 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-di Examples include diol compounds such as ol, 1,2-heptanediol, 1,2-nonanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-nonanediol, and 1,2-octanediol; 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 provides safety and exhibits excellent ink drying and ejection performance. The content of the wetting agent in the ink is preferably 3 to 50% by mass.

[0043] <Penetrating agent> Examples of penetrating agents 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 amount of penetrating agent in the ink is preferably 0.01 to 10% by mass.

[0044] <Inkjet ink manufacturing method> The method for producing inkjet ink according to the present invention is not particularly limited. For example, inkjet ink can be obtained by mixing the pigment dispersion of the present invention with a binder resin, water, and other components such as solvents other than water, waxes, alkanolamines, wetting agents, and penetrating agents, which may be added as needed.

[0045] <Application of inkjet ink> The inkjet ink of the present invention exhibits excellent adhesion to various substrates (plastic substrates). There are no particular restrictions on the plastic substrate, and examples include 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 represented by aliphatic polyester resins such as poly(ethylene succinate) and poly(butylene succinate); polyolefin resins such as polypropylene and polyethylene; and thermoplastic resins such as polyvinyl chloride, polyimide resin, polyarylate resin, or mixtures thereof. Among these, polyethylene terephthalate (PET) and oriented polypropylene (OPP, biaxially oriented polypropylene) can be preferably used.

[0046] Furthermore, the plastic substrate may be a plastic film. The plastic film may be either an unstretched film or a stretched film, and its manufacturing method is not limited. The film thickness is also not particularly limited, but is usually in the range of 1 to 500 μm. Furthermore, the printed surface of the film may be subjected to corona discharge treatment. Additionally, silica, alumina, or the like may be deposited on the printed surface.

[0047] According to the present invention, it is possible to provide an inkjet ink with improved water resistance to scratching and storage stability after heating of images formed on substrates such as PET and OPP, and to provide a pigment dispersion that can be used to manufacture the inkjet ink. [Examples]

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

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

[0050] <Pigment (A)> • Quinacridone pigment: Solid solution of CIPigment Violet 19 and CIPigment Red 122 (mass ratio (CIPigment Violet 19 / CIPigment Red 122) = 65 / 35), manufactured by DIC Corporation. • Phthalocyanine pigment: B15:3 (copper phthalocyanine), manufactured by DIC Corporation. • Benzimidazolone-based pigment: CI Pigment Yellow 180, manufactured by DIC Corporation.

[0051] <Metal salt (B)> • Metal salt (B-1): Aluminum (Al) dichloroquinacridone sulfonic acid 3+ )salt • Metal salt (B-2): Aluminum (Al) copper phthalocyanine sulfonic acid 3+ )salt • Metal salt (B-3): CI Pigment Yellow 180 Aluminum (Al) sulfonic acid 3+ )salt • Metal salt (B-4): Calcium (Ca) dichloroquinacridone sulfonic acid 2+ )salt

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

[0053] <<Synthesis of Dispersed Resin (C)>> 600 g of isopropyl alcohol (IPA) was placed in a 2 L stainless steel flask, and nitrogen was blown in at 20 mL / min. The mixture was heated to 80°C using an oil bath while stirring at 100 rpm. The following pre-mixed substances were added dropwise to the flask at a rate of 2 g / min: 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-azobisvaleric acid, and 0.33 g of 3-mercapto-1,2-propanediol (thioglycerol). Subsequently, stirring was continued for 16 hours while maintaining the internal temperature at 80°C to obtain a dispersion resin (C) with a non-volatile content of 45% by mass, an acid value of 110 mg KOH / g, and a mass-average molecular weight of 20,000.

[0054] <<Preparation of Dispersant (C-1)>> 1284.58g of deionized water, 315.42g of methyldiethanolamine (MDEA, boiling point 247℃), and 2000g of dispersion resin (C) were added to a 10L glass separable flask and stirred. Subsequently, 3300g of deionized water was added, and the mixture was heated while stirring to remove the IPA and water by distillation, yielding the dispersant (C-1) (resin content: 18.82% by mass, basic compound: MDEA, neutralization rate: 150%).

[0055] <<Preparation of Dispersant (C-2)>> Dispersant (C-2) (resin content: 18.82% by mass, basic compound: MDEA, neutralization rate: 105%) was obtained in the same manner as in the above <<Preparation of dispersant (C-1)>>, 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% by mass, basic compound: potassium hydroxide, neutralization rate: 105%) was obtained in the same manner as in the above <<Preparation of dispersant (C-1)>>, except that 315.42 g of methyldiethanolamine (MDEA, boiling point 247°C) was replaced with 103.95 g of potassium hydroxide.

[0057] <<Preparation of Dispersant (C-4)>> Dispersant (C-4) (resin content: 18.82% by mass, basic compound: MDEA, neutralization rate: 200%) was obtained in the same manner as in the above <<Preparation of dispersant (C-1)>>, 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% by mass, basic compound: DMEA, neutralization rate: 105%) was obtained in the same manner as in the above <<Preparation of dispersant (C-1)>>, except that 315.42 g of methyldiethanolamine (MDEA, boiling point 247°C) was replaced with 165.16 g of dimethylethanolamine (DMEA, boiling point 133°C).

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

[0060] (Example 1) The manufacturing and evaluation tests of pigment dispersions and inkjet inks were carried out as follows. <Manufacturing of pigment dispersions> In a 5L stainless steel container (18cmΦ), 474.58g of deionized water, 557.92g of dispersant (C-1), 17.5g of Surfinol 465 as surfactant (E), 0.805g of BYK-019 as defoaming agent (F), 1.87g of Proxel GXL(S) as preservative (G), 35g of metal salt (B-1), and 665g of quinacridone pigment were added. The mixture was then stirred for 1 hour using a dispermat (VMA-GETZMANN CV3-PLUS) at 35℃ and a peripheral speed of 6.3m / s (agitator blade: 8cmΦ) to obtain a slurry. Subsequently, the slurry was placed in an SC100 mill (manufactured by Nippon Coke Co., Ltd.), 440g of Φ0.5mm zirconia beads (manufactured by Nikkatoh, YTZ) were added, and the mixture was dispersed for 2 hours under conditions of 35℃ and a frequency of 45Hz. After dispersion treatment, the beads were removed, and the resulting dispersion was adjusted with deionized water to a pigment content of 29% by mass. Subsequently, coarse particles were removed using a centrifuge (H-200B, 6000G, 30 minutes, below 20°C), filtered through an 8μm pore size membrane filter (Merck Millipore, nitrocellulose), and deionized water was added to obtain a pigment dispersion with a pigment content of 27% by mass.

[0061] In Example 5, after adding the materials, the mixture was stirred for 1 hour using a disperser mat (VMA-GETZMANN CV3-PLUS) at 20°C and a peripheral speed of 4.1 m / s (agitator blade: 8 cmΦ) to obtain a slurry. Subsequently, the slurry was placed in an SC100 mill (manufactured by Nippon Coke Co., Ltd.), 440g of Φ0.5mm zirconia beads (manufactured by Nikkatoh, YTZ) were added, and the mixture was dispersed for 2 hours under conditions of 35℃ and 35Hz. After the dispersion treatment, the beads were removed, and the resulting dispersion was adjusted with deionized water to a pigment content of 15% by mass. The mixture was then stirred at 50°C for 3 hours using a stirrer (Three One Motor, manufactured by Shinto Kagaku Co., Ltd.). Subsequently, coarse particles were removed using a centrifuge (H-200B, 6000G, 30 minutes, below 20°C), filtered through an 8um pore size membrane filter (Merck Millipore, nitrocellulose), and deionized water was added to obtain a pigment dispersion with a pigment content of 13% by mass.

[0062] <Manufacturing of inkjet inks> An inkjet ink was produced by mixing the obtained pigment dispersion with a binder resin, wax, water, propylene glycol, 1,3-butanediol, 1,2-hexanediol, diethylene glycol monobutyl ether, and triisopropyl alcohol amine. In total inkjet ink produced (100% by mass), the pigment content was 5% by mass, the binder resin (acrylic emulsion, manufactured by Seikoh PMC, acid value: 30 mg KOH / g, glass transition temperature (Tg): 20°C) was 2.5% by mass, and the wax (modified polyethylene wax emulsion, Aquacer 531, manufactured by BYK) was 1.3% by mass.

[0063] <Various evaluation tests> <<Abrasion Resistance Test>> First, coatings were prepared using inkjet inks manufactured on PET film (Toyobo Co., Ltd., E5100) and OPP film (Toyobo Co., Ltd., P2161). The coating was prepared as follows. First, each film was prepared as a strip measuring 25cm x 12cm. Next, inkjet ink was applied to strips of film using a bar coater (RD Specialties, No. 6). Then, after heating and air-drying with a hairdryer for 1 minute, it was dried in a 90°C constant temperature dryer for 10 minutes. Subsequently, the dried paint film was cut into 15cm x 4cm pieces to obtain test specimens. Next, in accordance with JIS K5701-1:2000, the abrasion resistance was evaluated using a JSPS-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., AB-301). Specifically, one test specimen was set in the testing machine, and PPC paper (product name "PPC PAPER High White") (for dry evaluation) and a water-moistened metal cloth No. 3 (for wet evaluation) were used as the friction element. The test was conducted under the conditions of a load of 200g, 100 cycles for the dry evaluation, and 10 cycles for the wet evaluation. The degree of ink peeling on the printed materials after the test was evaluated by scanning the printed materials and using the image processing software imageJ according to the following evaluation criteria. [Evaluation Criteria] A: Less than 20% peeling. B: There was peeling of 20% to less than 50%. C: There was peeling of 50% to less than 70%. D: There was more than 70% peeling.

[0064] <<Storage Stability>> First, we measured the viscosity of the inkjet ink immediately after manufacturing. Next, the manufactured inkjet ink was left to stand in a constant temperature bath at 70°C for one week. Subsequently, the viscosity of the inkjet ink was measured again, and its storage stability was evaluated according to the following calculation (Equation 1) and evaluation criteria. Storage stability = |1 - (viscosity after storage) / (viscosity before storage)| × 100 (Equation 1) [Evaluation Criteria] A: 0 or more, less than 5 B: 5 or more and less than 25 C: 25 or more and less than 35 D:35 or more

[0065] Table 1 shows the results of the evaluation test of the inkjet ink in Example 1. In Table 1, "parts by mass" indicates the amount added relative to 100 parts by mass of pigment (A). Also, water (D) is not listed in Table 1.

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

[0067] In Example 1 of 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% by mass. Therefore, In Example 1 of Table 1, the content (mass%) of the metal salt (B) was calculated by determining y using the following formula. 665:35=(27%):(y%) y = 1.42 Furthermore, in Example 1 of Table 1, the content (mass%) of the dispersed resin (C) was determined by calculating z using the following formula. 665:(557.92×18.82%)=(27%):(z%) z = 4.26

[0068] (Examples 2-11, Comparative Example 1) A pigment dispersion and an inkjet ink were prepared 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. In the inkjet ink of Example 5, the binder resin content was set to 1.25% by mass.

[0069] [Table 1]

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

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 [the pigment].

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

Images