Pigment Dispersant, Pigment Dispersion, and Aqueous Ink Composition for Inkjet

Abstract

To provide: a pigment dispersant which satisfactorily inhibits magenta pigments from aggregating and makes it possible to achieve an aqueous ink that is applicable by ink-jet printing; a pigment dispersion; and an aqueous ink-jet ink composition.SOLUTION: This pigment dispersant is for dispersing magenta pigments. A copolymer of a high-molecular-weight alcohol and an ester or an acrylic dispersant is dispersed in a dispersion medium. The copolymer and the acrylic dispersant have acid values.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a pigment dispersant, a pigment dispersion, and an aqueous ink composition for inkjet, and more particularly, for example, to a pigment dispersant, a pigment dispersion, and an aqueous ink composition for inkjet that can suppress the aggregation of magenta pigments used in aqueous inkjet inks and improve dispersibility.

Background Art

[0002] Aqueous inks used for printing by an inkjet method are required to have ejection stability that can stably eject the aqueous ink without causing poor ejection of the aqueous ink due to aggregation of pigments. Aggregation of pigments also occurs after printing on a recording medium using the aqueous ink. That is, after the droplets of the aqueous ink land on the recording medium, as a result of the aggregation of the pigments, the droplets do not spread sufficiently on the recording medium, and there is a problem that the printing density of the printed image decreases and the hue decreases.

[0003] In response to these problems, for example, Patent Document 1 discloses using a styrene-acrylic acid-methacrylic acid resin (styrene / acrylic acid / methacrylic acid = 77 / 10 / 13) as a pigment dispersant for dispersing quinacridone-based pigments. This pigment dispersant adsorbs on the surface of the quinacridone-based pigment and attempts to suppress the aggregation of the quinacridone-based pigment by the repulsive force due to the steric hindrance of the pigment dispersant, but it is not necessarily a satisfactory dispersion level in aqueous inks used in inkjet printing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a pigment dispersant, a pigment dispersion, and an aqueous ink composition for inkjet that can preferably suppress aggregation of magenta pigments and enable printing by an inkjet method.

Means for Solving the Problems

[0006] The pigment dispersant according to the present invention is a pigment dispersant for dispersing magenta pigments in order to solve the above problems, and a copolymer composed of a polymer alcohol and an ester, or an acrylic dispersant is dispersed in a dispersion medium, and the copolymer composed of the polymer alcohol and the ester and the acrylic dispersant are characterized by having an acid value.

[0007] In the above configuration, it is preferable that the copolymer composed of the polymer alcohol and the ester and the acrylic dispersant do not have an amine value.

[0008] In the above configuration, it is preferable that the acid value of the copolymer composed of the polymer alcohol and the ester and the acrylic dispersant is 10 mgKOH / g or more and 40 mgKOH / g or less.

[0009] In the above configuration, it is preferable that the copolymer composed of the polymer alcohol and the ester is a polyvinyl alcohol-polyacrylic acid copolymer.

[0010] In the above configuration, it is preferable that the polyvinyl alcohol-polyacrylic acid copolymer is DISPERBYK (registered trademark)-2096.

[0011] In the above configuration, it is preferable that the acrylic dispersant is DISPERBYK (registered trademark)-2015.

[0012] In order to solve the above problems, the pigment dispersion according to the present invention is characterized by including a pigment dispersant and the magenta pigment dispersed in the dispersion medium.

[0013] In the above configuration, it is preferable that the magenta pigment contains a quinacridone-based pigment.

[0014] In the above configuration, it is preferable that the quinacridone-based pigment contains at least one of C.I. Pigment Red 122 and C.I. Pigment Violet 19.

[0015] Further, the aqueous ink composition for inkjet according to the present invention is characterized by including the pigment dispersion in order to solve the above problems.

[0016] In the above configuration, it further preferably includes a humectant, and the humectant preferably contains at least one of a polyhydric alcohol having a valence of 3 or more and a glycol-based solvent.

[0017] In the above configuration, it further preferably includes a penetrant, and the penetrant preferably contains at least one of a glycol ether and a heterocyclic compound.

Advantages of the Invention

[0018] According to the present invention, by incorporating a copolymer of a polymer alcohol and an ester or an acrylic-based dispersant having an acid value into the pigment dispersant, the aggregation inhibitory effect on the magenta pigment can be improved as compared with conventional pigment dispersants. As a result, when an ink is prepared using the pigment dispersant having the above configuration as one of the raw materials, the magenta pigment can be well dispersed without aggregation, and an aqueous ink composition for inkjet suitable for printing by an inkjet method can be realized.

[0019] Conventionally, in aqueous ink compositions, there has been a problem that the printing density decreases due to pigment aggregation even after printing on a recording medium. That is, after the droplets of the aqueous ink land on the recording medium, as a result of pigment aggregation, the droplets do not spread sufficiently on the recording medium, and there is a problem that the printing density of the printed image decreases and the hue deteriorates. However, as in the present invention, by containing a copolymer of a polymer alcohol and an ester having only an acid value and no amine value, or an acrylic dispersant as a pigment dispersant, it is possible to suppress the aggregation of magenta pigments on the recording medium even after printing. As a result, it is possible to reduce the reduction in the gamut of the droplets of the aqueous ink composition, and it becomes possible to realize an aqueous ink composition capable of printing with a good printing density (color developability). Moreover, since the reduction in gamut can be suppressed without changing the type of magenta pigment, a change in hue can also be prevented.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0021] (Pigment Dispersant) The pigment dispersant according to the present embodiment will be described below. The pigment dispersant of this embodiment is formed by dispersing a copolymer composed of a high molecular alcohol and an ester, or an acrylic dispersant in a dispersion medium. Further, the copolymer composed of a high molecular alcohol and an ester, and the acrylic dispersant have an acid value and act so as to suppress aggregation with respect to the magenta pigment, and thus it is applicable to printing by an inkjet method, and it is possible to realize an inkjet aqueous ink composition (hereinafter sometimes referred to as "aqueous ink composition") in which the magenta pigment is well dispersed. Here, in this specification, the "inkjet method" means a printing method in which an aqueous ink composition is ejected as droplets from, for example, a known piezo inkjet head, and the droplets are fixed on a recording medium to form a printed image or the like. Incidentally, details of the recording medium will be described later.

[0022] The acid value of the copolymer composed of a high molecular alcohol and an ester, and the acrylic dispersant is preferably 75 mgKOH / g or less, and more preferably 10 mgKOH / g or more and 40 mgKOH / g or less. By setting the acid value to 75 mgKOH / g or less, it becomes possible to produce an aqueous ink composition in which the dispersibility of the magenta pigment is further improved. Incidentally, when two or more kinds of the copolymer composed of a high molecular alcohol and an ester, or the acrylic dispersant are used in combination, the acid value is obtained as an average of each pigment dispersant. Further, in this specification, the "acid value" means, for example, in the case of an acrylic dispersant, the mass (unit: mg) of potassium hydroxide (KOH) required to neutralize the free acid in 1 g of the solid content of the acrylic dispersant, and it can be determined by a potentiometric titration method in accordance with JIS K 0070.

[0023] The copolymer composed of a polymer alcohol and an ester in this embodiment, and the acrylic dispersant are not particularly limited as long as they have an acid value, but those having no amine value are preferably used. As a result, even on a recording medium after printing by an inkjet method, aggregation of the magenta pigment is suppressed, and reduction in the color gamut of the printed image can be reduced without changing the hue. In this specification, the "amine value" means, for example, in the case of an acrylic dispersant, the mass (unit: mg) of potassium hydroxide (KOH) equivalent to the amount of base per 1 g of the solid content of the acrylic dispersant, and can be determined by a potentiometric titration method according to JIS K 7237.

[0024] Examples of the copolymer composed of a polymer alcohol and an ester having an acid value and no amine value include polyvinyl alcohol-polyacrylic acid copolymers. Further, as the polyvinyl alcohol-polyacrylic acid copolymer, for example, commercially available products such as DISPERBYK (registered trademark)-2096 (acid value 40 mgKOH / g) manufactured by BYK-Chemie GmbH can be used. DISPERBYK (registered trademark)-194N (acid value 75 mgKOH / g) is also included.

[0025] As the acrylic dispersant having an acid value and no amine value, one or more selected from polyacrylic acid (acrylic acid polymer) and acrylic acid copolymers can be preferably used. As the polyacrylic acid, those containing acrylic acid as a monomer component are preferred. As the acrylic acid copolymer, those copolymerized with other monomer components such as styrene in addition to the acrylic acid are preferred.

[0026] Commercially available products can be used as the acrylic dispersant having an acid value and no amine value. For example, DISPERBYK (registered trademark)-2015 (acid value 10 mgKOH / g) manufactured by BYK-Chemie GmbH can be mentioned.

[0027] The molecular weights of the copolymer composed of a high molecular alcohol and an ester, and the acrylic dispersant are not particularly limited, but are preferably set from the viewpoint of increasing the adsorption rate to the magenta pigment etc.

[0028] In the pigment dispersant according to this embodiment, a dispersion medium for dispersing a copolymer composed of a high molecular alcohol and an ester, or an acrylic dispersant is included. Examples of the dispersion medium include water. More specifically, pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis permeated water, distilled water, etc., or those from which ionic impurities such as ultrapure water have been removed are mentioned. In particular, water sterilized by ultraviolet irradiation or hydrogen peroxide addition etc. is suitable because it can prevent the generation of mold and bacteria over a long period. Also, the content of the dispersion medium is not particularly limited and can be set as appropriate according to need.

[0029] Also, as the dispersion medium, a mixed solution of water and a water-soluble organic solvent may be used. The water-soluble organic solvent is not particularly limited, and examples include ethyl alcohol, n-butyl alcohol, isobutyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, propylene glycol, polyethylene glycol, glycerin, etc. Furthermore, the blending amount when a water-soluble organic solvent is used in combination with the dispersion medium is not particularly limited and can be set as appropriate according to need.

[0030] The content of the copolymer composed of a high molecular alcohol and an ester, or the acrylic dispersant is preferably 50 mass% or more and 100 mass% or less, more preferably 65 mass% or more and 100 mass% or less, and particularly preferably 80 mass% or more and 100 mass% or less with respect to the total mass of the pigment dispersant. By making the content 50 mass% or more, the chroma can be improved, and the effect is particularly remarkable when it is 80 mass% or more.

[0031] (Pigment Dispersion and Method for Producing the Same) Next, the pigment dispersion according to this embodiment will be described below. The pigment dispersion of the present embodiment can be used, for example, in an aqueous ink composition suitable for printing by an inkjet method, and at least includes the above-described pigment dispersant and a pigment composed of a magenta pigment dispersed in a dispersion medium.

[0032] In the present embodiment, the pigment is composed of a magenta pigment used in printing by an inkjet method. By using the pigment, the light resistance and water resistance can be improved as compared with the case where a dye is used as a coloring material. The magenta pigment is not particularly limited, but in the present embodiment, a quinacridone-based pigment as an organic pigment is preferable.

[0033] Also, the quinacridone-based pigment is not particularly limited, and examples thereof include C.I. Pigment Red 122, C.I. Pigment Red 202, C.I. Pigment Red 206, C.I. Pigment Red 207, C.I. Pigment Red 209, and C.I. Pigment Violet 19. Among these quinacridone-based pigments, from the viewpoint of the chroma characteristics, C.I. Pigment Red 122 and C.I. Pigment Violet 19 are preferable.

[0034] The content of the pigment affects the image density, the storage stability, the viscosity, and the pH of the aqueous ink composition. Therefore, the content of the pigment is preferably set appropriately in consideration of these points. More specifically, the content of the pigment is preferably in the range of 1% by mass to 10% by mass in terms of solid content based on the total mass of the aqueous ink composition, more preferably in the range of 3% by mass to 10% by mass, and particularly preferably in the range of 4.5% by mass to 7% by mass. By setting the content of the coloring material to 1% by mass or more, a decrease in the image density can be suppressed, and the effect is particularly remarkable when it is 4.5% by mass or more. On the other hand, by setting the content of the coloring material to 10% by mass or less, a decrease in the ejection property due to nozzle clogging can be prevented, and the effect is particularly remarkable when it is 7% by mass or less.

[0035] The content of the copolymer composed of a polymer alcohol and an ester contained in the pigment dispersion, or the acrylic dispersant, can be appropriately set from the viewpoint of improving the dispersibility of the magenta pigment. In the case of this embodiment, the content of these compounds is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 25% by mass or less, based on 100% by mass of the magenta pigment. By setting the content to 1% by mass or more, the dispersibility of the magenta pigment in the dispersion medium can be maintained well. On the other hand, by setting the content to 50% by mass or less, for example, when the pigment dispersion of this embodiment is used in an aqueous ink composition, an excessive increase in the viscosity of the aqueous ink composition can be suppressed, and good ejection stability can be maintained. In particular, when it is 25% by mass or less, the effect is more remarkable.

[0036] In the method for producing the pigment dispersion of this embodiment, the mixing method and the addition order of the magenta pigment, the pigment dispersant, and other additives to be blended as required are not particularly limited. For example, the magenta pigment, the pigment dispersant, and water as the dispersion medium can be mixed at once, and the mixture can be subjected to a dispersion treatment using a normal disperser.

[0037] The dispersion time in the dispersion treatment is not particularly limited and can be set as appropriate according to the need. The disperser used in the dispersion treatment of the magenta pigment is not particularly limited as long as it is a commonly used disperser. Specifically, for example, a ball mill, a roll mill, a sand mill, a bead mill, a paint shaker, a nanomizer, etc. can be mentioned.

[0038] In addition, the pigment dispersion of this embodiment includes not only the form of an aqueous ink composition (details will be described later), but also the form of a pigment dispersion liquid for preparing the aqueous ink composition.

[0039] (Aqueous Ink Composition for Inkjet and Its Manufacturing Method) The aqueous ink composition of this embodiment is an aqueous ink containing at least a pigment dispersion and an aqueous medium.

[0040] [Pigment Dispersion]

[0041] The content of the pigment dispersion is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and particularly preferably 30% by mass or more and 40% by mass or less with respect to the total mass of the aqueous ink composition. By setting the content of the pigment dispersion to 10% by mass or more, the coloring power can be improved, and the effect is particularly remarkable when it is 30% by mass or more. Further, by setting the content of the pigment dispersion to 60% by mass or less, the dispersibility can be improved, and the effect is particularly remarkable when it is 40% by mass or less.

[0042] [Aqueous Medium] Examples of the aqueous medium used in the aqueous ink composition of the present embodiment include water. As the water, it is preferable to use pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis permeated water, distilled water, or water from which ionic impurities such as ultrapure water have been removed.

[0043] In addition, as the aqueous medium, a mixed solution of water and a water-soluble organic solvent may be used. The water-soluble organic solvent is not particularly limited. Specifically, for example, alcohols such as methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-propyl alcohol, and isopropyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, ethylene glycol methyl ether, ethylene glycol ethyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, triethylene glycol monomethyl ether, and triethylene glycol monoethyl ether; polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, 1,2,6-hexanetriol, thiodiglycol, polyethylene glycol, polypropylene glycol, glycerin, diglycerin, and polyglycerin; N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, etc. Among these water-soluble organic solvents, from the viewpoints of improving the ejectability of the aqueous ink composition and preventing the reduction of printing density, polyoxyethylene glycol with an added mole number of ethylene oxide of 2 to 4, more specifically, diethylene glycol, triethylene glycol, and tetraethylene glycol are preferred, diethylene glycol and triethylene glycol are more preferred, and triethylene glycol is particularly preferred. The water-soluble organic solvent can be used alone or in combination of two or more.

[0044] The content of the aqueous medium is not particularly limited, but usually it is 5% by mass or more and 50% by mass or less, preferably 5% by mass or more and 45% by mass or less, based on the total mass of the aqueous ink composition. When a mixed solution of water and a water-soluble organic solvent is used as the aqueous medium, the ratio of water to the water-soluble organic solvent is preferably in the range of 10:90 to 50:50, more preferably in the range of 20:80 to 40:60, and even more preferably in the range of 30:70 to 40:60.

[0045] [Additive] In the aqueous ink composition of the present embodiment, other additives may be blended as long as the effects of the present invention are not impaired. Examples of the additives include surfactants, binders, humectants, penetration (control) agents, water-soluble resins, pH adjusters, chelating agents, preservatives, viscosity adjusters, defoaming agents, dispersion stabilizers, anti-reducing agents, antioxidants, and the like. Except for surfactants, binders, humectants, and penetration agents, the contents of these additives are not particularly limited and can be set as appropriate according to need (the contents of surfactants, binders, humectants, and penetration agents will be described later).

[0046] 1. Surfactant The surfactant is not particularly limited, and examples thereof include fluorine-based surfactants, silicone-based surfactants, and acetylene diol-based surfactants. These surfactants can be used alone or in combination of two or more.

[0047] The fluorine-based surfactant is not particularly limited, and examples thereof include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds. Commercially available fluorine-based surfactants include, for example, F-410, 444, 553 (manufactured by DIC Corporation, trade names), FS-65, 34, 35, 31, 30 (manufactured by DuPont Kabushiki Kaisha, trade names), BYK-340 (manufactured by BYK-Chemie Japan Co., Ltd., trade name), and the like. These fluorine-based surfactants can be used alone or in combination of two or more.

[0048] The silicone-based surfactant is not particularly limited, and examples thereof include polysiloxane-based compounds, polyether-modified organosiloxanes, and the like. Commercially available silicone-based surfactants include, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349 (above, manufactured by BYK-Chemie Japan Co., Ltd., trade name), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (above, manufactured by Shin-Etsu Chemical Co., Ltd., trade name), and the like. These silicone-based surfactants can be used alone or in combination of two or more.

[0049] The acetylene diol-based surfactant is not particularly limited, and examples thereof include compounds having an acetylene diol skeleton, compounds obtained by adding ethylene oxide to an acetylene diol-based compound, and the like. Commercially available acetylene diol-based surfactants include, for example, Surfynol® 104PA, Surfynol 420, Surfynol 440, Surfynol 465 (above, manufactured by Air Products Co., Ltd., trade name), Olfine® E1010, Olfine STG (above, manufactured by Nisshin Chemical Industry Co., Ltd., trade name), and the like. These acetylene diol-based surfactants can be used alone or in combination of two or more.

[0050] Among the surfactants described above, from the viewpoints of the ejection property of the aqueous ink composition and the environment, etc., silicone-based surfactants and acetylene diol-based surfactants are preferred.

[0051] The content of the surfactant is preferably in the range of 0.1% by mass or more and 5% by mass or less, more preferably in the range of 0.5% by mass or more and 4% by mass or less, based on the total mass of the aqueous ink composition. When the content of the surfactant is 0.1% by mass or more, when printing by an inkjet method, it is possible to prevent ejection failure due to poor meniscus formation at the nozzles in the inkjet head and further prevent clogging of the nozzles. Particularly when it is 0.5% by mass or more, the effect is more remarkable. Thereby, the ejection property can be improved. On the other hand, when the content of the surfactant is 5% by mass or less, it is possible to suppress the adverse effect on the ejection of the aqueous ink composition due to insoluble components or poor emulsification of the surfactant. Particularly when it is 4% by mass or less, the effect is more remarkable.

[0052] 2. Binder The binder is not particularly limited, and examples thereof include polyolefin resin dispersions, styrene acrylic resins, styrene maleic resins, and polyurethane resins. By containing a binder, the ejection property can be improved, and it is possible to print a printed image excellent in rubbing resistance and water resistance. Note that styrene acrylic resins, styrene maleic resins, and polyurethane resins function as binders and are not blended as pigment dispersants.

[0053] The polyolefin resin dispersion is a resin dispersion in which a polyolefin resin is dispersed in water in the form of an emulsion (latex or dispersion). By adding the polyolefin resin to water in the form of an emulsion resin dispersion, it is possible to prevent the polyolefin resin that does not dissolve in water from settling. For example, when a powdery polyolefin resin is added to water, the resulting composition is a composition in which the polyolefin resin settles without dissolving in water. As a result, the composition cannot be ejected from the inkjet head, and printing by the inkjet method becomes difficult.

[0054] The polyolefin resin dispersion of this embodiment functions as a binder in the aqueous ink composition. By blending the polyolefin resin dispersion, in the ink layer printed using the aqueous ink composition of this embodiment, for example, compared with the case of an aqueous ink composition using only a styrene acrylic resin, a styrene maleic acid resin, or a polyurethane resin (hereinafter referred to as "styrene acrylic resin etc.") as a binder, the film-forming temperature can be lowered. Thereby, in the ink layer using the aqueous ink composition of this embodiment, for example, even when dried at a drying temperature of 80 °C and a drying time of 10 minutes, it can be sufficiently dried and has excellent drying properties. Also, the rub resistance under the same drying conditions can be improved compared with the case of using only a styrene acrylic resin etc.

[0055] Examples of the polyolefin resin in the polyolefin resin dispersion include anionic polyolefin resins and nonionic polyolefin resins. Among these, in the present invention, anionic polyolefin resins are preferred from the viewpoints of rub resistance and water resistance.

[0056] The anionic polyolefin resin is not particularly limited, and examples thereof include acid-modified polyolefin resins such as maleic anhydride-modified polyolefin resins, chlorinated polyolefin resins, and non-chlorinated polyolefin resins. Also, commercially available products can be used as the polyolefin resin emulsion. Examples of such commercially available products include Hardlen (registered trademark) NZ-1004 (solid content concentration: 30% by mass), Hardlen NZ-1015 (solid content concentration: 30% by mass) (both manufactured by Toyobo Co., Ltd., trade name), Arrow Base (registered trademark) DA-1010 (solid content concentration: 25% by mass), Arrow Base DB-4010 (solid content concentration: 25% by mass) (both manufactured by Unitika Ltd., trade name), Super Cron (registered trademark) E-415 (solid content concentration: 30% by mass), Super Cron E-480T (solid content concentration: 30% by mass), Super Cron E-604 (solid content concentration: 40% by mass) (all manufactured by Nippon Paper Industries Co., Ltd., trade name), etc.

[0057] The styrene acrylic resin is not particularly limited. For example, as its constituent components, a polymer containing at least one styrene-based monomer component selected from the group consisting of styrene and its derivatives and at least one acrylic acid-based monomer component selected from the group consisting of (meth)acrylic acid and its derivatives in the molecule can be mentioned. Further, the styrene acrylic resin may contain monomer components other than the styrene-based monomer component and the acrylic acid-based monomer component.

[0058] The styrene maleic acid resin is not particularly limited. For example, as its constituent components, a polymer containing at least one styrene-based monomer component selected from the group consisting of styrene and its derivatives and at least one maleic acid-based monomer component selected from the group consisting of maleic acid and its derivatives in the molecule can be mentioned. Further, the styrene maleic acid resin may contain monomer components other than the styrene-based monomer component and the maleic acid-based monomer component.

[0059] The polyurethane resin is not particularly limited. For example, a polymer containing polyisocyanate, polyol, etc. in its constituent components can be mentioned.

[0060] When blending styrene acrylic resin, styrene maleic acid resin, and / or polyurethane resin, the content thereof is 0.75% by mass or less, preferably 0.6% by mass or less, more preferably 0.3% by mass or less in terms of solid content based on the total mass of the aqueous ink composition. By setting the content of the styrene acrylic resin or the like to 0.75% by mass or less in terms of solid content, it is possible to suppress the film-forming temperature of the ink layer formed by printing with the aqueous ink composition of the present embodiment from becoming excessively high. Thereby, good drying properties can be maintained. Also, the abrasion resistance can be improved as compared with the case where only the styrene acrylic resin or the like is used. Further, for example, in the styrene acrylic resin and the styrene maleic acid resin, the ester bond in the molecule is easily hydrolyzed, and in the polyurethane resin, the urethane bond in the molecule is easily hydrolyzed. Therefore, in an aqueous ink composition containing a large amount of these resins, the water resistance and solvent resistance of the ink layer printed using the aqueous ink composition are not good. However, by suppressing the content of the styrene acrylic resin or the like to 0.75% by mass or less based on the total mass of the aqueous ink composition as in the present embodiment, it is possible to suppress or prevent the water resistance of the ink layer from decreasing.

[0061] Also, in the present embodiment, it is preferable that the binder consists only of a polyolefin resin dispersion. Thereby, the film-forming temperature of the ink layer formed by the aqueous ink composition of the present embodiment can be reduced, and sufficient drying can be achieved even under normal drying conditions, and the abrasion resistance can be further improved. Further, since it does not contain a styrene acrylic resin or the like, the water resistance of the ink layer can be further improved.

[0062] The content of the polyolefin resin dispersion is 1.2% by mass or more, preferably 1.5% by mass or more and 6% by mass or less, more preferably 3% by mass or more and 4.5% by mass or less, in terms of solid content based on the total mass of the aqueous ink composition. By setting the content of the polyolefin resin dispersion in terms of solid content to 1.2% by mass or more, good abrasion resistance can be maintained. In addition, by setting the content of the polyolefin resin emulsion in terms of solid content to 6% by mass or less, good dischargeability of the aqueous ink composition from the inkjet head can be maintained.

[0063] 3. Humectant The humectant is not particularly limited, and examples thereof include polyhydric alcohols having a valence of 3 or more. The polyhydric alcohol having a valence of 3 or more is not particularly limited, and examples thereof include polyethylene glycol, glycerin, and polyglycerin. Among these, from the viewpoint of preventing drying of the nozzle surface, high-boiling water-soluble polyhydric alcohols such as glycerin and polyglycerin are preferable. These humectants can be used alone or in combination of two or more.

[0064] The addition amount of the humectant is preferably in the range of 1% by mass or more and 20% by mass or less, more preferably in the range of 5% by mass or more and 15% by mass or less, based on the total mass of the aqueous ink composition. By setting the content of the humectant to 1% by mass or more, clogging near the nozzles of the inkjet head can be prevented when printing by the inkjet method, and the discharge performance can be further improved. In particular, when it is 5% by mass or more, the effect is more remarkable. On the other hand, by setting the content of the humectant to 20% by mass or less, the viscosity of the aqueous ink composition can be appropriately controlled, and in particular, when it is 15% by mass or less, the effect is more remarkable.

[0065] 4. Penetrant The penetration (control) agent is not particularly limited, and examples thereof include glycol solvents having 2 to 5 carbon atoms and heterocyclic compounds. The glycol solvent having 2 to 5 carbon atoms is not particularly limited, and examples thereof include ethylene glycol and propylene glycol. Further, the heterocyclic compound is not particularly limited, and examples thereof include nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-hydroxyethyl-2-pyrrolidone. The exemplified penetration (control) agents can be used alone or in combination of two or more.

[0066] The addition amount of the penetration (control) agent is preferably in the range of 1% by mass or more and 20% by mass or less, and more preferably in the range of 5% by mass or more and 15% by mass or less, based on the total mass of the aqueous ink composition. By setting the content of the penetration (control) agent to 1% by mass or more, sufficient permeability of the aqueous ink composition to the recording medium can be maintained, and particularly when it is 5% by mass or more, the effect is more remarkable. On the other hand, by setting the content of the penetration (control) agent to 20% by mass or less, it is possible to suppress the excessive penetration of the coloring material into the recording medium and its non-residual in the surface layer portion, and to prevent the printing density of the printed image from decreasing. Further, it is possible to suppress the excessive increase in the viscosity of the aqueous ink composition and maintain the stability of the aqueous ink composition. These effects are particularly remarkable when it is 15% by mass or less.

[0067] 5. pH adjuster The pH adjuster is added for the purpose of adjusting the pH of the aqueous ink composition. The pH adjuster is not particularly limited, and examples thereof include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid; inorganic bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia; organic bases such as triethanolamine, diethanolamine, monoethanolamine, triisopropanolamine, diisopropanolamine, and tris(hydroxymethyl)aminomethane; and organic acids such as adipic acid, citric acid, succinic acid, and lactic acid. The exemplified pH adjusters can be used alone or in combination of two or more.

[0068] [Others] Considering the ejection property from the inkjet nozzles, the viscosity of the aqueous ink composition of the present embodiment is preferably 3 mPa·s to 6 mPa·s, more preferably 3.5 mPa·s to 5.7 mPa·s, when ejected from the inkjet nozzles. By setting the viscosity of the aqueous ink composition within the above numerical range, the occurrence of clogging in the inkjet nozzles can be further suppressed, and good ejection property can be maintained. Incidentally, the viscosity of the aqueous ink composition can be obtained by measuring, for example, using a viscometer (trade name: VISCOMATE MODEL VM-10A, manufactured by Sekonic Corporation), under the condition of a measurement temperature of 25°C.

[0069] The aqueous ink composition of the present embodiment can be used as an aqueous ink composition capable of forming a printed image by forming an ink layer on the surface of a recording medium. Further, the aqueous ink composition of the present embodiment can be used not only when it is included in the aqueous ink for inkjet which is the final product, but also as the aqueous ink for inkjet itself.

[0070] [Method for manufacturing an aqueous ink composition for inkjet] The aqueous ink composition of the present embodiment can be produced by mixing the above-described respective components by an appropriate method. That is, for example, additives and the like described above are added to the pigment dispersion, and further diluted with an aqueous medium. Thereafter, it is sufficiently stirred, and filtration is performed as necessary to remove coarse particles and foreign matters that cause clogging. Thereby, the aqueous ink composition according to the present embodiment can be obtained.

[0071] Incidentally, the mixing method of each material is not particularly limited. For example, the materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer, and stirred and mixed. Also, the filtration method is not particularly limited, and for example, centrifugal filtration, filter filtration, etc. can be employed.

[0072] (Recording medium) The recording medium is not particularly limited, and conventionally known ones can be adopted. Specifically, for example, printing papers such as coated paper, art paper, and matte paper, and films and the like can be mentioned.

Example

[0073] Hereinafter, preferred embodiments of the present invention will be exemplarily described in detail. However, the materials, contents, etc. described in the following examples do not limit the scope of the present invention only to them unless otherwise specifically limited.

[0074] (Example 1) In this example, 19.2 g of C.I. Pigment Red 122 (PR122, Cinquasia® Magenta D 4550 J, manufactured by BASF Japan Ltd.) as a magenta pigment, 5.16 g of an acrylic dispersant (trade name: DISPERBYK-2015, manufactured by BYK Chemie GmbH, acid value 10 mgKOH / g), and 7.2 g of propylene glycol were added to a container, and further 88.44 g of pure water was added. Subsequently, the mixed solution in the container was dispersed with a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) at room temperature for 2 hours (dispersion time). Also, 210 g of zirconia beads (average particle size 0.5 mm) were mixed during the dispersion. Thereby, the pigment dispersion A according to this example was prepared. Incidentally, the content of the acrylic dispersant with respect to the magenta pigment was 26.875% by mass.

[0075] (Example 2) In this example, 18 g of C.I. Pigment Violet 19 (PV19, Cinquasia® Red L 4105 HD, manufactured by BASF Japan Ltd.) as a magenta pigment, 6.6 g of an acrylic dispersant (trade name: DISPERBYK-2015, manufactured by BYK-Chemie GmbH, acid value 10 mg KOH / g), and 7.2 g of propylene glycol were added to a container, and further 88.2 g of pure water was added. Subsequently, the mixed solution in the container was dispersed with a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) at normal temperature for 2 hours (dispersion time). Also, 210 g of zirconia beads (average particle size 0.5 mm) were mixed during the dispersion. Thus, the pigment dispersion B according to this example was prepared. Incidentally, the content of the acrylic dispersant with respect to the magenta pigment was 36.667 mass%.

[0076] (Example 3) In this example, the content of the acrylic dispersant as a pigment dispersant was changed to 3.6 g, and the content of pure water was changed to 90 g. Otherwise, the pigment dispersion C according to this example was prepared in the same manner as in Example 1. Incidentally, the content of the pigment dispersant with respect to the magenta pigment was 18.75 mass%.

[0077] (Example 4) In this example, 18 g of C.I. Pigment Violet 19 (PV19, Cinquasia® Red L 4105 HD, manufactured by BASF Japan Ltd.) as a magenta pigment, 3.6 g of an acrylic dispersant (trade name: DISPERBYK-2015, manufactured by BYK-Chemie GmbH, acid value 10 mg KOH / g) as a pigment dispersant, and 7.2 g of propylene glycol were added to a container, and further 91.2 g of pure water was added. Subsequently, the mixed solution in the container was dispersed with a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) at normal temperature for 2 hours (dispersion time). Also, 210 g of zirconia beads (average particle size 0.5 mm) were mixed during the dispersion. Thus, the pigment dispersion D according to this example was prepared. Incidentally, the content of the pigment dispersant with respect to the magenta pigment was 20 mass%.

[0078] (Example 5) In this example, 15 g of C.I. Pigment Violet 19 (PV19, Cinquasia® Red L 4105 HD, manufactured by BASF Japan Ltd.) as a magenta pigment, 9. 5 g of DISPERBYK-194N (trade name, manufactured by BYK-Chemie GmbH, acid value 75 mg KOH / g), and 7.2 g of propylene glycol were added to a container, and further 68.3 g of pure water was added. Subsequently, the mixed solution in the container was dispersed with a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) at room temperature for 2 hours (dispersion time). Also, 175 g of zirconia beads (average particle size 0.5 mm) were mixed during the dispersion. Thereby, the pigment dispersion E according to this example was prepared. Incidentally, the content of DISPERBYK-194N with respect to the magenta pigment was 63.3% by mass.

[0079] (Example 6) In this example, a polyvinyl alcohol-polyacrylic acid copolymer (trade name: DISPERBYK-2096, manufactured by BYK-Chemie GmbH, acid value 40 mg KOH / g) was used instead of DISPERBYK-194N, and its content was changed to 0.1 g. Also, the content of pure water was changed to 77.7 g. Otherwise, the pigment dispersion F according to this example was prepared in the same manner as in the example 5 The content of the pigment dispersant with respect to the magenta pigment was 0.7% by mass.

[0080] (Comparative Example 1) In this comparative example, 16 g of C.I. Pigment Red 122 (PR122, Cinquasia® Magenta D 4550 J, manufactured by BASF Japan Ltd.) as a magenta pigment, 0.8 g of a pigment dispersant (trade name: DISPERBYK-193, manufactured by BYK-Chemie GmbH, no acid value, no amine value), and 7.2 g of propylene glycol were added to a container, and further 76 g of pure water was added. Subsequently, the mixed solution in the container was dispersed with a disperser (paint shaker, manufactured by Asada Iron Works Co., Ltd.) at normal temperature for 2 hours (dispersion time). Also, 175 g of zirconia beads (average particle size 0.5 mm) were mixed during the dispersion. However, in this comparative example, the magenta pigment aggregated into a paste form, and a pigment dispersion could not be obtained. Incidentally, the content of the pigment dispersant with respect to the magenta pigment was 5.0% by mass.

[0081] (Comparative Example 2) In this comparative example, DISPERBYK-2061 (trade name, manufactured by BYK-Chemie GmbH, amine value 3 mg KOH / g) was used instead of DISPERBYK-193, and its content was changed to 4 g. Also, the content of pure water was changed to 72.8 g. Otherwise, the pigment dispersion G according to this comparative example was prepared in the same manner as in Comparative Example 1. Incidentally, the content of the pigment dispersant with respect to the magenta pigment was 25% by mass.

[0082] (Comparative Example 3) In this comparative example, DISPERBYK-2055 (trade name, manufactured by BYK-Chemie GmbH, amine value 40 mg KOH / g) was used instead of DISPERBYK-193, and its content was changed to 3.5 g. Also, the content of pure water was changed to 73.3 g. Otherwise, the pigment dispersion H according to this comparative example was prepared in the same manner as in Comparative Example 1. Incidentally, the content of the pigment dispersant with respect to the magenta pigment was 21.9% by mass.

[0083] (Comparative Example 4) In this comparative example, C.I. Pigment Violet 19 (PV19, Cinquasia® Red L 4105 HD, manufactured by BASF Japan Ltd.) was used as the magenta pigment, and its content was changed to 15 g. Also, the content of pure water was changed to 77 g. Otherwise, the pigment dispersion I according to this comparative example was prepared in the same manner as in Comparative Example 1. The content of the pigment dispersant with respect to the magenta pigment was 5.3% by mass.

[0084] (Comparative Example 5) In this comparative example, DISPERBYK-2061 (trade name, manufactured by BYK-Chemie GmbH, amine value 3 mg KOH / g) was used instead of DISPERBYK-193, and its content was changed to 4 g. Also, the content of pure water was changed to 73.8 g. Otherwise, the pigment dispersion J according to this comparative example was prepared in the same manner as in Comparative Example 4. The content of the pigment dispersant with respect to the magenta pigment was 26.7% by mass.

[0085] (Comparative Example 6) In this comparative example, DISPERBYK-2055 (trade name, manufactured by BYK-Chemie GmbH, amine value 40 mg KOH / g) was used instead of DISPERBYK-193, and its content was changed to 3.5 g. Also, the content of pure water was changed to 74.3 g. Otherwise, the pigment dispersion K according to this comparative example was prepared in the same manner as in Comparative Example 1. The content of the pigment dispersant with respect to the magenta pigment was 23.3% by mass.

[0086]

Table 1

[0087]

Table 2

[0088] (Examples 7 - 11) In Examples 7 to 11, using the pigment dispersions shown in Table 3, other additives were added so as to obtain the blending ratios shown in Table 4, and an aqueous ink composition for inkjet (hereinafter referred to as "aqueous ink composition") according to each example was prepared.

[0089] (Comparative Examples 7 to 10) In Comparative Examples 7 to 10, using the pigment dispersions shown in Table 3, other additives were added so as to obtain the blending ratios shown in Table 4, and an aqueous ink composition according to each comparative example was prepared.

[0090]

Table 3

[0091]

Table 4

[0092] (Evaluation of Printed Images) For the aqueous ink compositions of Examples 7, 9 to 11 and Comparative Examples 7 to 10, gamut evaluation and magenta chroma evaluation were carried out by the following methods.

[0093] Using each aqueous ink composition, printing was performed by an inkjet method on high-quality inkjet paper. Specifically, printing was performed in a single-pass (one-pass) method using an inkjet printer (trade name: PX-105, manufactured by Epson Co., Ltd.).

[0094] Next, for the images printed on the samples of each example and comparative example, using a color difference meter (model number: X-Rite eXact, manufactured by X-Rite Co., Ltd.), L * a * b * values in the L color system * , a * , b * were measured respectively. Also, the magenta chroma (C * ) was calculated by the following formula (JIS Z 8729) based on the measured values of color characteristics. C* ={(a *2 )+(b *2 )} 1 / 2

[0095] In addition, in the L * a * b * color space system, the lightness is represented by L * , and the hue and chroma are represented by a * and b * . Regarding the evaluation of the magenta chroma, it can be said that the higher the value of C * , the better the chroma of the printed image. The results are shown in FIGS. 1 to 4. FIG. 1 is an L * a * b * color space chromaticity diagram of the printed image using the aqueous ink compositions according to Example 7 and Comparative Example 10. FIG. 2 is a graph showing the measured values (L * , C * ) of the printed image using the aqueous ink compositions according to Example 7 and Comparative Example 10. FIG. 3 is an L * a * b * color space chromaticity diagram of the printed image using the aqueous ink compositions according to Examples 9 to 11 and Comparative Examples 7 to 9. FIG. 4 is a graph showing the measured values (L * , C * ) of the printed image using the aqueous ink compositions according to Examples 9 to 11 and Comparative Examples 7 and 8.

[0096] As can be seen from FIGS. 1 and 3, in the printed images using the aqueous ink compositions according to each example, it was confirmed that the hue and chroma were good and the printing density was high. In particular, in the aqueous ink compositions according to Examples 7, 9, and 11 using a pigment dispersant having an acid value of 10 mgKOH / g or 40 mgKOH / g and no amine value, compared with the aqueous ink compositions according to Comparative Examples 8 to 10 using a pigment dispersant having no acid value, the printing density was high and it was confirmed that the reduction of gamut due to aggregation was suppressed.

[0097] Also, as can be seen from FIGS. 2 and 4, in the printed images using the aqueous ink compositions according to each example, the lightness L * and the chroma C *showed good values. In particular, in the aqueous ink compositions according to Examples 7, 9, and 11 using a pigment dispersant having an acid value of 10 mgKOH / g or 40 mgKOH / g and no amine value, it was confirmed that the magenta chroma was good as compared with the aqueous ink compositions according to Comparative Examples 7 and 8 using a pigment dispersant having no acid value.

Claims

1. An aqueous ink composition for inkjet containing a pigment dispersion and a binder, wherein the pigment dispersion is a pigment dispersant for dispersing a magenta pigment, which is a copolymer composed of a high molecular alcohol and an ester, or an acrylic dispersant dispersed in a dispersion medium, the magenta pigment dispersed in the dispersion medium, and contains the copolymer composed of the high molecular alcohol and the ester and the acrylic dispersant have an acid value, the binder is a polyolefin resin dispersion, an aqueous ink composition for inkjet.

2. The aqueous ink composition for inkjet according to claim 1, wherein the copolymer composed of the high molecular alcohol and the ester and the acrylic dispersant have no amine value.

3. The aqueous ink composition for inkjet according to claim 1 or 2, wherein the acid value of the copolymer composed of the high molecular alcohol and the ester and the acrylic dispersant is 10 mgKOH / g or more and 40 mgKOH / g or less.

4. The aqueous ink composition for inkjet according to any one of claims 1 to 3, wherein the copolymer composed of the high molecular alcohol and the ester is a polyvinyl alcohol-polyacrylic acid copolymer.

5. The aqueous ink composition for inkjet according to claim 4, wherein the polyvinyl alcohol-polyacrylic acid copolymer is DISPERBYK (registered trademark)-2096.

6. The aqueous ink composition for inkjet according to any one of claims 1 to 3, wherein the acrylic dispersant is DISPERBYK (registered trademark)-2015.

7. The pigment dispersant is a copolymer composed of the high molecular alcohol and the ester, or only the acrylic dispersant is dispersed in the dispersion medium, The aqueous ink composition for inkjet according to any one of claims 1 to 3, wherein the acrylic dispersant is DISPERBYK (registered trademark)-2015.

8. The pigment dispersant is a copolymer composed of the high molecular alcohol and the ester only dispersed in the dispersion medium, the aqueous ink composition for inkjet according to any one of claims 1 to 3.

9. The aqueous ink composition for inkjet according to any one of claims 1 to 8, wherein the magenta pigment contains a quinacridone-based pigment.

10. The aqueous ink composition for inkjet according to claim 9, wherein the quinacridone-based pigment contains at least one of C.I. Pigment Red 122 and C.I. Pigment Violet 19.

11. further comprising a humectant, The aqueous ink composition for inkjet according to any one of claims 1 to 10, wherein the humectant contains at least one of a polyhydric alcohol having a valence of 3 or more and a glycol-based solvent.

12. further comprising a penetrant, The aqueous ink composition for inkjet according to any one of claims 1 to 11, wherein the penetrant contains at least one of a glycol ether and a heterocyclic compound.

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