JP7714274B2 - Water-based inkjet ink composition - Google Patents

Description

The present invention relates to an aqueous inkjet ink composition, and more specifically to an aqueous inkjet ink composition that has excellent ejection properties when printing using an inkjet method and enables image printing with good print density.

In conventional aqueous inkjet ink compositions (hereinafter sometimes referred to as "aqueous ink compositions"), the pigment content in the aqueous ink composition has been increased to improve print density when printing on recording media such as plain paper or high-quality plain paper. Various solvents have also been added to improve the penetration of the aqueous ink composition into the recording medium. Furthermore, surfactants have also been added to the aqueous ink composition to appropriately control the wettability of the aqueous ink composition inside the nozzles of the inkjet head, thereby improving the ejection properties of the aqueous ink composition.

Examples of surfactants that can be added to aqueous ink compositions include silicone-based surfactants, fluorine-based surfactants, and acetylene diol-based surfactants. For example, Patent Document 1 describes that by adding an acetylene diol-based surfactant to an aqueous ink composition, it is possible to provide an aqueous ink composition with excellent ejection stability, etc.

However, even with these surfactants, there are cases where the inkjet head nozzles are not sufficiently wetted. In such cases, for example, the meniscus of the ink liquid surface of the aqueous ink composition is drawn too far into the nozzle, making it difficult to maintain its proper shape. This can lead to poor ejection of the aqueous ink composition during inkjet printing, resulting in blurred printed images. While increasing the surfactant content could be considered to improve such ejection problems, this would reduce the surface tension of the aqueous ink composition, causing the aqueous ink composition to wet the nozzle excessively. This would prevent the formation of an appropriate meniscus of the ink liquid surface within the nozzle, resulting in the aqueous ink composition dripping from the nozzle. Furthermore, increasing the surfactant content increases the permeability of the aqueous ink composition into the recording medium, resulting in diffraction and scattering of light in the printed image. This also reduces the amount of colorant remaining on the surface of the recording medium, resulting in reduced print density of the printed image.

Japanese Patent No. 6663069

The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide an aqueous inkjet ink composition that improves ejection properties during inkjet printing, thereby enabling good continuous printing and enabling image printing with good print density.

In order to achieve the above object, the aqueous ink composition for inkjet printing according to the present invention is _{an aqueous ink composition for inkjet printing that contains at least a colorant, a surfactant, a binder, and an aqueous medium, wherein the surfactants are an acetylenic diol surfactant (A) having an HLB in the range of 1 to 4 and represented by the chemical formula (CH3)2CHCH2C ( CH3 )} (OH)CCC( _CH3 )(OH) _CH2CH ( _CH3 ) ₂ , an acetylenic diol surfactant (B) having an HLB in the range of 10 to 15 and represented by the chemical formula ^R1C ( _CH3 )(OH)CCC( _CH3 )(OH) ^R2 (wherein ^R1 and ^R2 each independently represent an alkyl group having 1 to 5 carbon atoms), and an acetylenic diol surfactant (C) having an HLB in the range of 10 to 15 and represented by the chemical formula ( _CH3 ) _2CHCH2C ( _CH3 )( _{OCH2CH2 ) . and} (C) an ethylene oxide adduct of acetylenic diol represented by _the formula _nOHCCC ( _CH3 )( _OCH2CH2 ) _mOHCH2CH ( _CH3 ) ₂ (wherein m and n are integers satisfying 0.5≦m≦25, 0.5≦n≦25, 1≦m+n≦40), wherein the ratio of the contents of the acetylenic diol surfactant (A), the acetylenic diol surfactant (B) and the ethylene oxide adduct of acetylenic diol (C) is in the range of 1.6:1:1 to 3:1:1 by mass of the acetylenic diol surfactant (A):the acetylenic diol surfactant (B):the ethylene oxide adduct of acetylenic diol (C).

According to the above configuration, the surfactant contains an acetylenic diol surfactant (A), an acetylenic diol surfactant (B), and an ethylene oxide adduct of acetylenic diol (C). By adjusting the content ratio of these surfactants to a range of 1.6:1:1 to 3:1:1 by mass, the wettability of the aqueous ink composition inside the nozzle of the inkjet head can be controlled within an appropriate range. That is, this configuration prevents the meniscus of the ink surface of the aqueous ink composition from being excessively drawn into the nozzle, improving ejection performance during printing and enabling good continuous printing. It also prevents the aqueous ink composition from dripping from the nozzle due to excessive wetting inside the nozzle, which could prevent the formation of an appropriately shaped meniscus on the ink surface. Furthermore, this configuration does not require an excessive increase in the surfactant content to improve the wettability of the aqueous ink composition inside the nozzle. This prevents the aqueous ink composition from excessively penetrating into the recording medium. As a result, the occurrence of light diffraction and scattering in the printed image is reduced, and the colorant can remain on the surface layer without excessively penetrating into the recording medium, reducing or preventing a decrease in print density of the printed image.

In the above configuration, it is preferable that the surfactant further contains an alcohol alkoxylate. This further improves the ejection properties of the aqueous ink composition from the nozzle and further suppresses a decrease in the print density of the printed image.

In the above-described configuration, it is preferable that the aqueous medium contains polyoxyethylene glycol with an added mole number of ethylene oxide in the range of 2 to 4. This further improves the ejection properties of the aqueous ink composition from the nozzles and further suppresses a decrease in print density of the printed image.

In the above configuration, the colorant may be at least one of a cyan pigment, a magenta pigment, a yellow pigment, and a black pigment.

In the above-described configuration, it is preferable that the composition further contains a humectant, and that the humectant contains a trihydric or higher polyhydric alcohol. This prevents the aqueous ink composition from drying out, and prevents or reduces clogging near the nozzles of the inkjet head. As a result, the ejection properties of the aqueous ink composition can be further improved.

The above-described configuration preferably further comprises a penetration control agent, which comprises at least one of a glycol-based solvent and a heterocyclic compound having 2 to 5 carbon atoms. This makes it possible to control the permeability of the aqueous ink composition into the recording medium, preventing, for example, the colorant from excessively penetrating the recording medium and remaining on the surface, thereby preventing a decrease in the print density of the printed image.

The aqueous inkjet ink composition of the present invention has the advantage of providing superior ejection properties when printing using an inkjet method, and enabling images to be printed with good density, compared to conventional surfactants such as silicone-based surfactants and fluorine-based surfactants.

(Water-based inkjet ink composition)
The aqueous inkjet ink composition (hereinafter referred to as "aqueous ink composition") according to this embodiment will be described below.

The aqueous ink composition of this embodiment contains at least a colorant, a surfactant, a binder, and an aqueous medium. This aqueous ink composition is suitable for use in inkjet printing. In this specification, the term "inkjet printing" refers to a printing method in which an aqueous ink containing the aqueous ink composition is ejected as droplets from, for example, a known piezoelectric inkjet head, and the droplets are fixed on a recording medium to form a printed image, etc. Details of the recording medium will be provided later.

[Colorant]
Examples of coloring materials include pigments and dyes used in inkjet printing.

The pigment preferably includes at least one of a cyan pigment, a magenta pigment, a yellow pigment, and a black pigment. Examples of inorganic pigments include titanium oxide, iron oxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, ultramarine, Prussian blue, carbon black, graphite, calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc. Examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, thioindigo pigments, triphenylmethane lake pigments, and oxazine lake pigments. These pigments may be used alone or in combination of two or more. The pigments of this embodiment are not limited to the examples given above.

Self-dispersion pigments or resin-dispersion pigments can also be used as pigments. Of these pigments, self-dispersion pigments are preferred from the perspective of increasing print density (image density).

Self-dispersing pigments are pigments in which various functional groups are chemically bonded to the surface of the pigment particles, allowing them to be dispersed in aqueous media without the use of pigment dispersants such as resins or surfactants. There are no particular restrictions on the pigment particles used in self-dispersing pigments, and any of the inorganic and organic pigments mentioned above can be used. There are also no particular restrictions on the functional groups, and examples include hydroxyl groups, quinone groups, carbonyl groups, carboxyl groups, phosphate groups, sulfone groups, amine groups, and salts thereof.

Specific examples of self-dispersible pigments include self-dispersible carbon black, self-dispersible phthalocyanine, self-dispersible quinacridone, and self-dispersible azo.

Resin-dispersed pigments are pigments that can be dispersed in an aqueous medium using a resin dispersant that is soluble in the aqueous medium. There are no particular limitations on the pigments used in resin-dispersed pigments, and any of the inorganic and organic pigments listed above can be used. There are also no particular limitations on the resin dispersants, and examples include polyvinyl alcohols, polyacrylic acid, acrylic acid-acrylonitrile copolymers, vinyl acetate-acrylic acid ester copolymers, acrylic acid-acrylic acid ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers, styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, vinylnaphthalene-acrylic acid copolymers, vinylnaphthalene-maleic acid copolymers, vinyl acetate-maleic acid ester copolymers, vinyl acetate-crotonic acid copolymers, vinyl acetate-acrylic acid copolymers, and salts thereof. These resin dispersants may be used alone or in combination.

The ratio of pigment particles to resin dispersant in resin-dispersed pigments is not particularly limited and can be set appropriately as needed.

Specific examples of resin-dispersed pigments include resin-dispersed carbon black, resin-dispersed phthalocyanine, resin-dispersed quinacridone, and resin-dispersed azo.

Dyes are not particularly limited and include, for example, Red No. 2, Red No. 4, Red No. 40, Red No. 102, Yellow No. 4, Yellow No. 5, Green No. 3, Blue No. 1, chlorophyllin pigments, natural pigments, etc. Chlorophyllin pigments are not particularly limited and include, for example, sodium iron chlorophyllin, sodium copper chlorophyllin, sodium chlorophyllin, etc. Natural pigments are also not particularly limited and include, for example, cochineal pigments, cacao pigments, caramel pigments, etc.

The colorant content affects image density, storage stability, viscosity, pH, and other factors of the aqueous ink composition. Therefore, it is preferable to set the colorant content appropriately, taking these factors into consideration. More specifically, the colorant content is preferably in the range of 1% to 10% by mass, more preferably 3% to 10% by mass, and particularly preferably 4.5% to 7% by mass, calculated as solids relative to the total mass of the aqueous ink composition. By setting the colorant content to 1% by mass or more, a decrease in image density can be suppressed, and this effect is particularly pronounced at 4.5% by mass or more. On the other hand, by setting the colorant content to 10% by mass or less, a decrease in ejection performance due to nozzle clogging can be prevented, and this effect is particularly pronounced at 7% by mass or less.

[Surfactant]
The surfactant contains at least an acetylenic diol surfactant (A), an acetylenic diol surfactant (B), and an ethylene oxide (EO) adduct of acetylenic diol (C).

The acetylene diol surfactant (A) is a compound represented by (CH3)2CHCH2C(CH3)(OH) _CCC ( _CH3 )(OH) _CH2CH ( _CH3 )2, having an HLB (hydrophilic-lipophilic balance) of ₁ to 4, preferably ₂ to _4. Commercially available acetylene diol surfactants (A) are not particularly limited, and examples thereof include Surfynol (registered trademark) 104PA (HLB value: ₄ ) and Surfynol 420 (HLB value: 4) (trade names, manufactured by Air Products Co., Ltd.).

The acetylene diol surfactant (B) is a compound represented by R ¹ C(CH ₃ )(OH)CCC(CH ₃ )(OH)R ² (wherein R ¹ and R ² each independently represent an alkyl group having 1 to 5 carbon atoms) having an HLB in the range of 10 to 15, preferably 12 to 14. In this specification, when a range of carbon atoms is expressed, it is meant that the range includes all integer carbon numbers included in that range. Therefore, for example, an alkyl group having "1 to 3 carbon atoms" means all alkyl groups having 1, 2, and 3 carbon atoms.

The alkyl group may be either a linear alkyl group or a branched alkyl group. More specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group. ^R1 and ^R2 may be the same or different.

Commercially available acetylene diol surfactants (B) are not particularly limited, and examples include Surfynol 465 (HLB value: 13) (trade name, manufactured by Air Products Co., Ltd.).

The EO adduct (C) of acetylenic diol is an adduct in which a predetermined number of moles of ethylene oxide (EO) groups are added to acetylenic diol. More specifically, the EO adduct (C ₎ of acetylenic diol has an HLB in the range of 10 to 15, preferably 12 to 14, and is a compound represented by the chemical formula ( _CH3 ) _{2CHCH2C (} CH3)( _{OCH2CH2 )} nOHCCC( _{CH3 )} ( _{OCH2CH2 )} mOHCH2CH( _CH3 ) ₂ (wherein _m and n are integers satisfying 0.5≦m≦25, 0.5 _≦ n≦25, and 1≦m+n≦40).

Commercially available acetylene diol EO adducts (C) are not particularly limited, and examples include Olfine (registered trademark) E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 13).

In this specification, the HLB value is the HLB value according to the Griffin method, and means the value obtained by the following formula.
HLB value = 20 x (sum of formula weights of hydrophilic groups / molecular weight)
The HLB value falls within the range of 0 to 20, with the larger the HLB value, the stronger the hydrophilicity, and the smaller the HLB value, the stronger the hydrophobicity.

The surfactant content is preferably in the range of 0.1% by mass or more and 5% by mass or less, and more preferably in the range of 0.5% by mass or more and 4% by mass or less, relative to the total mass of the aqueous ink composition. By setting the surfactant content to 0.1% by mass or more, the meniscus of the ink liquid surface of the aqueous ink composition is prevented from being drawn too far into the nozzle, improving ejection properties during inkjet printing and enabling good continuous printing. On the other hand, by setting the surfactant content to 5% by mass or less, the aqueous ink composition is prevented from excessively wetting the nozzle, preventing the aqueous ink composition from dripping from the nozzle. It also suppresses adverse effects on the ejection of the aqueous ink composition due to insoluble surfactant content or poor emulsification.

The ratio of the content of the acetylenic diol surfactant (A), the acetylenic diol surfactant (B), and the EO adduct of acetylenic diol (C) is in the range of 1.6:1:1 to 3:1:1 by mass, and preferably in the range of 2:1:1 to 3:1:1.

The surfactant of this embodiment may also contain other surfactants. Examples of other surfactants include alcohol alkoxylates. The inclusion of alcohol alkoxylates improves ejection properties during inkjet printing, enabling good continuous printing and preventing a decrease in print density. It is preferable that the present invention does not contain silicone-based surfactants or fluorine-based surfactants as other surfactants.

Alcohol alkoxylates are not particularly limited, and examples include alcohol ethoxylate and oleyl alcohol ethoxylate. Commercially available alcohol alkoxylates are also not particularly limited, and examples include ADEKA TOL (registered trademark, manufactured by ADEKA Corporation), CONION (registered trademark, manufactured by New Japan Chemical Co., Ltd.), and DYNWET (registered trademark, manufactured by BYK Japan KK).

When an alcohol alkoxylate is contained in the surfactant, the ratio of the alcohol alkoxylate content to the total mass of the aqueous ink composition is preferably in the range of 0.1 to 2.0, and more preferably in the range of 0.2 to 1.0, based on mass. By further incorporating an alcohol alkoxylate within this range, ejection performance during inkjet printing can be improved and a reduction in print density can be further prevented.

[Binder]
The binder preferably contains a polyolefin resin dispersion and at least one resin selected from the group consisting of a styrene-acrylic acid resin, a styrene-maleic acid resin, and a polyurethane resin, thereby improving the ejection properties and enabling printing of a print image that is also excellent in abrasion resistance and water resistance.

A polyolefin resin dispersion is a resin dispersion in which polyolefin resin is dispersed in water in the form of an emulsion (latex or dispersion). Adding polyolefin resin to water in the form of an emulsion resin dispersion prevents the water-insoluble polyolefin resin from settling. For example, if powdered polyolefin resin is added to water, the polyolefin resin will settle without dissolving in water. As a result, the composition cannot be ejected from an inkjet head, making printing using the inkjet method difficult.

The polyolefin resin dispersion of this embodiment functions as a binder in the aqueous ink composition. By incorporating a polyolefin resin dispersion, the film formation temperature of an ink layer printed using the aqueous ink composition of this embodiment can be lowered compared to an aqueous ink composition using only a styrene acrylic acid resin, a styrene maleic acid resin, or a polyurethane resin (hereinafter referred to as "styrene acrylic acid resin, etc.") as the binder. As a result, an ink layer using the aqueous ink composition of this embodiment can be sufficiently dried even when dried at a drying temperature of 80°C for a drying time of 10 minutes, and has excellent drying properties. Furthermore, abrasion resistance under the same drying conditions can be improved compared to an ink layer using only a styrene acrylic acid resin, etc.

Examples of the polyolefin resin in the polyolefin resin dispersion include anionic polyolefin resins and nonionic polyolefin resins. Of these, anionic polyolefin resins are preferred in the present invention from the standpoint of abrasion resistance and water resistance.

Anionic polyolefin resins are not particularly limited, and examples include acid-modified polyolefin resins such as maleic anhydride-modified polyolefin resins, chlorinated polyolefin resins, and non-chlorinated polyolefin resins. Commercially available polyolefin resin emulsions can also be used. Examples of such commercially available products include HARDLEN (registered trademark) NZ-1004 (solid content: 30% by mass), HARDLEN NZ-1015 (solid content: 30% by mass) (all manufactured by Toyobo Co., Ltd.), ARROWBASE (registered trademark) DA-1010 (solid content: 25% by mass), ARROWBASE DB-4010 (solid content: 25% by mass) (all manufactured by Unitika Ltd.), SUPERCHLONE (registered trademark) E-415 (solid content: 30% by mass), SUPERCHLONE E-480T (solid content: 30% by mass), and SUPERCHLONE E-604 (solid content: 40% by mass) (all manufactured by Nippon Paper Industries Co., Ltd.).

Styrene acrylic acid resin, styrene maleic acid resin, and polyurethane resin are optional components and function as binders in this embodiment. In this embodiment, these resins are not blended as pigment dispersants.

Styrene-acrylic acid resins are not particularly limited, and examples include polymers containing, as constituent components, 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 within the molecule. Styrene-acrylic acid resins may also contain monomer components other than the styrene-based monomer component and the acrylic acid-based monomer component. In this specification, "(meth)acrylic acid" refers to both "acrylic acid" and "methacrylic acid."

There are no particular limitations on the styrene-maleic acid resin, and examples include polymers containing, as constituent components, 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 within the molecule. Furthermore, the styrene-maleic acid resin may contain monomer components other than the styrene-based monomer component and the maleic acid-based monomer component.

Polyurethane resins are not particularly limited, but examples include polymers containing polyisocyanate, polyol, etc. as constituent components.

In this embodiment, the styrene-acrylic acid resin, styrene-maleic acid resin, and polyurethane resin are blended in an amount, calculated as solids content, of 0.75% by mass or less, preferably 0.6% by mass or less, more preferably 0.3% by mass or less, and particularly preferably 0% by mass, relative to the total mass of the aqueous ink composition. By keeping the content of styrene-acrylic acid resin, etc., calculated as solids content, to 0.75% by mass or less can prevent the film-forming temperature of the ink layer formed by printing with the aqueous ink composition of this embodiment from becoming excessively high. This helps maintain good drying properties. Furthermore, abrasion resistance can be improved compared to when only styrene-acrylic acid resin, etc. is used. Furthermore, for example, in styrene-acrylic acid resin and styrene-maleic acid resin, the ester bonds in the molecules are easily hydrolyzed, while in polyurethane resin, the urethane bonds in the molecules are easily hydrolyzed. Therefore, aqueous ink compositions containing large amounts of these resins tend to result in ink layers printed using the aqueous ink composition having poor water resistance and solvent resistance. However, by limiting the content of styrene acrylic acid resin, etc. to 0.75% by mass or less relative to the total mass of the aqueous ink composition, as in this embodiment, it is possible to suppress or prevent a decrease in the water resistance of the ink layer.

In addition, in this embodiment, it is preferable that the binder consists solely of a polyolefin resin dispersion. This reduces the film formation temperature of the ink layer formed with the aqueous ink composition of this embodiment, allowing it to dry sufficiently even under normal drying conditions, and further improving abrasion resistance. In addition, because it does not contain styrene acrylic acid resin, etc., the water resistance of the ink layer can also be further improved.

The content of the polyolefin resin dispersion is 1.2% by mass or more, in solids content, relative to the total mass of the aqueous ink composition, preferably 1.5% by mass or more and 6% by mass or less, and more preferably 3% by mass or more and 4.5% by mass or less. By making the content of the polyolefin resin dispersion in solids content 1.2% by mass or more, it is possible to maintain good abrasion resistance. Furthermore, by making the content of the polyolefin resin emulsion in solids content 6% or less, it is possible to maintain good ejection properties of the aqueous ink composition from an inkjet head.

[Aqueous medium]
The aqueous medium used in the aqueous ink composition of this embodiment is water, which is preferably pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water from which ionic impurities have been removed.

The aqueous medium may also be a mixed solution of water and a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited, and specific examples include 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; and N-methylpyrrolidone and 1,3-dimethyl-2-imidazolidinone. Of these water-soluble organic solvents, from the viewpoint of improving the jetting properties of the aqueous ink composition and preventing a decrease in print density, polyoxyethylene glycols having 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 solvents can be used alone or in combination of two or more.

The content of the aqueous medium is not particularly limited, but is typically 5% by mass or more and 50% by mass or less, and preferably 5% by mass or more and 45% by mass or less, relative to the total mass of the aqueous ink composition. Furthermore, when a mixed solution of water and a water-soluble organic solvent is used as the aqueous medium, the ratio of water to 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.

[Other additives]
The aqueous ink composition of this embodiment may contain other additives as long as the effects of the present invention are not impaired. Examples of additives include humectants, penetrating (controlling) agents, pigment dispersants, water-soluble resins, pH adjusters, chelating agents, preservatives, viscosity adjusters, antifoaming agents, dispersion stabilizers, anti-reducing agents, and antioxidants. Except for the humectants and penetrating agents, the contents of these additives are not particularly limited and can be set appropriately as needed (the contents of the humectants and penetrating agents will be described below).

Examples of humectants include trivalent or higher polyhydric alcohols. There are no particular limitations on trivalent or higher polyhydric alcohols, and examples include polyethylene glycol, glycerin, polyglycerin, etc. Of these, high-boiling-point water-soluble polyhydric alcohols such as glycerin and polyglycerin are preferred from the perspective of preventing the nozzle surface from drying out. These humectants can be used alone or in combination of two or more.

The amount of humectant added 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, relative to the total mass of the aqueous ink composition. A humectant content of 1% by mass or more prevents clogging near the nozzles of the inkjet head when printing using the inkjet method, further improving ejection performance; this effect is particularly pronounced at 5% by mass or more. On the other hand, a humectant content of 20% by mass or less allows the viscosity of the aqueous ink composition to be appropriately controlled; this effect is particularly pronounced at 15% by mass or less.

Examples of penetration (control) agents include glycol-based solvents and heterocyclic compounds having 2 to 5 carbon atoms. Glycol-based solvents having 2 to 5 carbon atoms are not particularly limited, and examples include ethylene glycol and propylene glycol. Furthermore, heterocyclic compounds are not particularly limited, and examples 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.

The amount of penetration (control) agent added 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, relative to the total mass of the aqueous ink composition. By making the content of the penetration (control) agent 1% by mass or more, the aqueous ink composition can maintain sufficient penetration into the recording medium, and this effect is particularly pronounced at 5% by mass or more. On the other hand, by making the content of the penetration (control) agent 20% by mass or less, it is possible to prevent the colorant from penetrating excessively into the recording medium and remaining in the surface layer, thereby preventing a decrease in the print density of the printed image. In addition, it is possible to prevent the viscosity of the aqueous ink composition from becoming excessively high, and to maintain the stability of the aqueous ink composition. These effects are particularly pronounced at 15% by mass or less.

When using the aforementioned self-dispersed pigment or resin-dispersed pigment as the colorant, the incorporation of a pigment dispersant into the aqueous ink composition can be omitted. When using a pigment other than a self-dispersed pigment or a resin-dispersed pigment, it is preferable to incorporate a pigment dispersant into the aqueous ink composition. There are no particular restrictions on the pigment dispersant, and any known dispersant can be used as appropriate.

[others]
In consideration of the ejection properties from the inkjet nozzle, the viscosity of the aqueous ink composition of this embodiment is preferably 3 mPa·s to 6 mPa·s, and more preferably 3.5 mPa·s to 5.7 mPa·s, when ejected from the inkjet nozzle. By keeping the viscosity of the aqueous ink composition within this range, clogging of the inkjet nozzle can be further suppressed, thereby maintaining good ejection properties. The viscosity of the aqueous ink composition can be measured, for example, using a viscometer (trade name: VISCOMATE MODEL VM-10A, manufactured by SEKONIC CORPORATION) at a measurement temperature of 25°C.

The aqueous ink composition of this embodiment can be used as an aqueous ink composition that can form an ink layer on the surface of a recording medium to form a printed image. Furthermore, the aqueous ink composition of this embodiment can be included in the final product, an aqueous inkjet ink, or can be used as the aqueous inkjet ink itself.

(Method for producing aqueous inkjet ink composition)
The aqueous ink composition of this embodiment can be produced by mixing a colorant, a surfactant, a binder, an aqueous medium, and other additives, if necessary, in any order. For example, when a pigment is used as the colorant, the pigment, surfactant, binder, and aqueous medium are mixed together, and the mixture is subjected to a dispersion treatment using a conventional disperser. The dispersion time is not particularly limited, but is preferably set so that the average dispersed particle diameter of the dispersed pigment falls within a specific range.

The dispersing machine used in dispersing the pigment is not particularly limited, as long as it is a commonly used dispersing machine. Specific examples include a ball mill, roll mill, sand mill, bead mill, paint shaker, and Nanomizer.

Next, the dispersion obtained by the dispersion process is further mixed with the other additives mentioned above using an appropriate method, thereby obtaining an aqueous ink composition using a pigment as the colorant.

The method for mixing the materials is not particularly limited; for example, the materials can be added sequentially to a container equipped with a stirring device such as a disper, mechanical stirrer, or magnetic stirrer, and then stirred and mixed. The filtration method is also not particularly limited; for example, centrifugal filtration, filter filtration, etc. can be used.

(Recording medium)
The recording medium is not particularly limited, and any conventionally known recording medium can be used, including, for example, printing paper such as coated paper, art paper, and matte paper, and film.

The following provides a detailed description of preferred embodiments of the present invention. However, unless otherwise specified, the materials, contents, etc. described in the following examples do not limit the scope of the present invention to these.

Example 1
As shown in Table 1, the emulsion contained 40% by mass (solid content: 6% by mass) of a self-dispersing black pigment (solid content concentration: 15% by mass), 10% by mass (solid content: 1.5% by mass) of an anionic polyolefin resin emulsion (trade name: HARDLEN (registered trademark) NZ-1004, manufactured by Toyobo Co., Ltd., solid content concentration: 30% by mass), 0.8% by mass of an acetylene diol surfactant (A) (trade name: SURFYNOL (registered trademark) 104PA, manufactured by Air Products Co., Ltd.), and 0.5% by mass of an acetylene diol surfactant (B). An aqueous ink composition according to this example was prepared by mixing an acetylene diol surfactant (B) (trade name: Surfynol 465, manufactured by Air Products Co., Ltd.), 0.5 mass% of an EO adduct of acetylene diol (C) (trade name: Olfine (registered trademark) E1010, manufactured by Nissin Chemical Industry Co., Ltd.), 5 mass% of diethylene glycol monobutyl ether (trade name: Hisolve DB, manufactured by Toho Chemical Industry Co., Ltd.), 5 mass% of triethylene glycol, and 38.2 mass% of water.

Example 2
As shown in Table 1, in this example, the content of the acetylene diol surfactant (A) was changed to 1 mass %, and the content of water was changed to 38 mass %. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 1.

Example 3
As shown in Table 1, in this example, the content of the acetylene diol surfactant (A) was changed to 1.2% by mass, and the content of water was changed to 37.8% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 1.

Example 4
As shown in Table 1, in this example, the content of the acetylene diol surfactant (A) was changed to 1.5% by mass, and the content of water was changed to 37.5% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 1.

Example 5
As shown in Table 1, in this example, 0.5% by mass of alcohol alkoxylate (product name: DYNWET (registered trademark) 800N, manufactured by BYK Japan KK) was further added as a surfactant, and the water content was changed to 37.5% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

(Comparative Example 1)
As shown in Table 2, in this comparative example, the content of the acetylene diol surfactant (A) was changed to 0.5% by mass, and the content of water was changed to 38.5% by mass. Except for these, the aqueous ink composition of this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 2)
As shown in Table 2, in this comparative example, the content of the acetylene diol surfactant (A) was changed to 2% by mass, and the content of water was changed to 37% by mass. Except for these, the aqueous ink composition according to this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 3)
As shown in Table 2, in this comparative example, only 1% by mass of the acetylene diol surfactant (A) was added as the surfactant, and the water content was changed to 39% by mass. Except for these, the aqueous ink composition according to this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 4)
As shown in Table 2, in this comparative example, only 2% by mass of the acetylene diol surfactant (B) was added as the surfactant, and the water content was changed to 38% by mass. Except for these, the aqueous ink composition according to this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 5)
As shown in Table 2, in this comparative example, only 2% by mass of the acetylene diol EO adduct (C) was added as a surfactant, and the water content was changed to 38% by mass. Except for these, the aqueous ink composition of this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 6)
As shown in Table 2, in this comparative example, only 1 mass % of the acetylene diol surfactant (A) and 0.5 mass % of the acetylene diol EO adduct (C) were added as surfactants, and the water content was changed to 38.5 mass %. Except for these, the aqueous ink composition of this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 7)
As shown in Table 2, in this comparative example, only 1 mass % of the acetylenic diol surfactant (A) and 0.5 mass % of the acetylenic diol surfactant (B) were added as surfactants, and the water content was changed to 38.5 mass %. Except for these, the aqueous ink composition of this comparative example was prepared in the same manner as in Example 1.

(Comparative Example 8)
As shown in Table 2, in this comparative example, only 0.5% by mass of the acetylene diol surfactant (B) and 0.5% by mass of the acetylene diol EO adduct (C) were added as surfactants, and the water content was changed to 39% by mass. Except for these, the aqueous ink composition of this comparative example was prepared in the same manner as in Example 1.

Example 6
In this example, the penetrant was changed to triethylene glycol dimethyl ether, as shown in Table 3. Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 7
In this example, the penetrant was changed to triethylene glycol monomethyl ether, as shown in Table 3. Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

(Example 8)
In this example, the penetrant was changed to propylene glycol monopropyl ether, as shown in Table 3. Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 9
In this example, the water-soluble organic solvent was changed to diethylene glycol, as shown in Table 3. Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 10
As shown in Table 3, in this example, the colorant was changed to a resin-dispersed black pigment (solid content concentration: 16% by mass) at 40% by mass (solid content equivalent: 6.4% by mass). Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 11
As shown in Table 4, in this example, the binder was changed to 10% by mass (solid content: 3% by mass) of styrene acrylic acid resin (trade name: JONCRYL 96J, manufactured by BASF Japan Ltd., solid content concentration: 30% by mass). Otherwise, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

Example 12
As shown in Table 4, in this example, the binder was changed to 10% by mass (solid content: 3% by mass) of styrene maleic acid resin (product name: SMA 1440H, manufactured by TOTAL Corporation, solid content concentration: 30% by mass). Otherwise, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

Example 13
As shown in Table 4, in this example, the binder was changed to 10% by mass of a nonionic polyolefin resin (product name: AQUACER (registered trademark) 515, manufactured by BYK Japan KK). Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 14
As shown in Table 4, in this example, the binder was changed to 10% by mass of a nonionic polyolefin resin (product name: AQUACER (registered trademark) 531, manufactured by BYK Japan KK). Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 15
As shown in Table 4, in this example, the binder was changed to 10% by mass of a nonionic polyolefin resin (product name: AQUACER (registered trademark) 551, manufactured by BYK Japan KK). Otherwise, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

Example 16
As shown in Table 4, in this example, the binder was changed to 10% by mass of polyurethane resin (product name: WBR-016U, manufactured by Taisei Fine Chemical Co., Ltd.) Except for this, the aqueous ink composition according to this example was prepared in the same manner as in Example 2.

(Example 17)
As shown in Table 5, in this example, 9% by mass (solid content equivalent: 2.7% by mass) of an anionic polyolefin resin emulsion (trade name: HARDLEN (registered trademark) NZ-1004, manufactured by Toyobo Co., Ltd., solid content concentration: 30% by mass) and 1% by mass (solid content equivalent: 0.3% by mass) of a styrene acrylic acid resin (trade name: JONCRYL 96J, manufactured by BASF Japan Ltd., solid content concentration: 30% by mass) were used as the binder. Except for this, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

(Example 18)
As shown in Table 5, in this example, 8% by mass (solid content equivalent: 2.7% by mass) of an anionic polyolefin resin emulsion (trade name: HARDLEN (registered trademark) NZ-1004, manufactured by Toyobo Co., Ltd., solid content concentration: 30% by mass) and 2% by mass (solid content equivalent: 0.3% by mass) of a styrene acrylic acid resin (trade name: JONCRYL 96J, manufactured by BASF Japan Ltd., solid content concentration: 30% by mass) were used as the binder. Except for this, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

Example 19
As shown in Table 5, in this example, 7% by mass (solid content equivalent: 2.7% by mass) of an anionic polyolefin resin emulsion (trade name: HARDLEN (registered trademark) NZ-1004, manufactured by Toyobo Co., Ltd., solid content concentration: 30% by mass) and 3% by mass (solid content equivalent: 0.3% by mass) of a styrene acrylic acid resin (trade name: JONCRYL 96J, manufactured by BASF Japan Ltd., solid content concentration: 30% by mass) were used as the binder. Except for this, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

(Example 20)
As shown in Table 5, in this example, the content of the polyolefin resin emulsion was changed to 3% by mass (solid content: 0.9% by mass), and the content of water was changed to 45% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

(Example 21)
As shown in Table 5, in this example, the content of the polyolefin resin emulsion was changed to 5% by mass (solid content: 0.9% by mass), and the content of water was changed to 43% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

Example 22
As shown in Table 5, in this example, the content of the polyolefin resin emulsion was changed to 15% by mass (solid content: 0.9% by mass), and the content of water was changed to 33% by mass. Except for these, the aqueous ink composition of this example was prepared in the same manner as in Example 2.

(Dischargeability)
Using the aqueous ink compositions of Examples 1 to 22 and Comparative Examples 1 to 8, inkjet printing was performed on inkjet wood-free paper (product name: Next-IJ, manufactured by Nippon Paper Industries Co., Ltd.). Specifically, printing was performed using a single-pass (one-pass) method using an inkjet printer (product name: PX-105, manufactured by Epson Corporation). Printing was performed in an environment with an air temperature of 25°C and a relative humidity of 60%. After that, hot air at a temperature of 80°C was directly applied to the printed surface for 10 minutes to thoroughly dry it. In this way, samples according to each Example and Comparative Example were prepared. Then, the ink layer of each sample was evaluated for ejection properties. The results are shown in Tables 1 to 5.

The ejection properties were evaluated according to the following criteria.
○: Dischargeable without problems △: Slight printing disturbances ×: Discharge not possible or significant printing disturbances

(Print density)
As in the case of evaluating the ejection properties, inkjet printing was carried out on inkjet wood-free paper using each of the aqueous ink compositions of Examples 1 to 22 and Comparative Examples 1 to 8. In this way, samples according to each Example and Comparative Example were prepared.

Next, the image density (print density) of the printed image was measured using a reflection densitometer (product name: Exact, manufactured by Videojet X-Rite Inc.). The image density was measured for each of 10 randomly selected areas in the printed image, and the arithmetic mean of the obtained measurements was used as the print density to be evaluated. The results are shown in Tables 1 to 5.

(result)
As can be seen from Examples 1 to 4, the aqueous ink compositions of Examples 1 to 4, which contained all of the acetylenic diol surfactant (A), the acetylenic diol surfactant (B), and the ethylene oxide adduct of acetylenic diol (C) as surfactants, and in which the content ratio of these surfactants was within the range of 1.6:1:1 to 3:1:1, exhibited good jetting properties and were confirmed to suppress a decrease in print density of printed images (see Table 1). Furthermore, as can be seen from Example 5, when an alcohol alkoxylate was further contained as a surfactant in addition to these three surfactant components, excellent jetting properties and print density were also confirmed (see Table 1). On the other hand, when the acetylenic diol surfactant (A), the acetylenic diol surfactant (B), and the ethylene oxide adduct of acetylenic diol (C) were not all contained simultaneously as surfactants, as in Comparative Examples 3 to 8, or when all three surfactant components were contained, as in Comparative Examples 1 and 2, when the content ratio was outside the range of 1.6:1:1 to 3:1:1, ejection defects occurred, and it was also confirmed that the print density decreased in some Comparative Examples (see Table 2).

Furthermore, as can be seen from Examples 6 to 10, when triethylene glycol dimethyl ether, triethylene glycol monomethyl ether, or propylene glycol monopropyl ether was used as the penetrant, when diethylene glycol was used as the water-soluble organic solvent, and when a resin-dispersed black pigment was used as the colorant, good ejection properties were observed and printing at high print density was confirmed (see Table 3).

Furthermore, as can be seen from Examples 11 to 19, when styrene-acrylic acid resin, styrene-maleic acid resin, nonionic polyolefin, or polyurethane resin was used as the binder, and when an anionic polyolefin resin emulsion was used in combination with styrene-acrylic acid resin, it was confirmed that good jetting properties were exhibited and printing at high print density was possible (see Tables 4 and 5). Furthermore, as can be seen from Examples 20 to 22, when an anionic polyolefin resin emulsion was used as the binder and its content was changed to 3%, 5%, or 15% by mass, it was confirmed that good jetting properties were exhibited and printing at high print density was possible (see Table 5).

Claims (6)

An aqueous inkjet ink composition comprising at least a colorant, a surfactant, a binder, and an aqueous medium,
The surfactant is
an acetylene diol surfactant (A) having an HLB in the range of 1 to 4 and represented by the chemical formula (CH ₃ ) ₂ CHCH ₂ C(CH _{3 )} (OH)CCC(CH ₃ )(OH)CH ₂ CH(CH 3 ) ₂ ;
an acetylene diol surfactant (B) having an HLB in the range of 10 to 15 and represented by the chemical formula R ¹ C(CH ₃ )(OH)CCC(CH ₃ )(OH)R ² (wherein R ¹ and R ² each independently represent an alkyl group having 1 to 5 carbon atoms);
an ethylene _{oxide adduct (C) of acetylene diol having an HLB in the range of 10 to 15 and represented by the chemical formula (CH 3 ) 2 CHCH 2 C(CH 3 ) ( OCH 2 CH 2 ) n OHCCC} (CH 3 )(OCH 2 CH 2 ) _m OHCH ₂ CH(CH ₃ ) ₂ (wherein m and n are integers satisfying 0.5≦m≦25, 0.5≦n≦25, and 1≦m+n≦40);
Including,
The aqueous inkjet ink composition has a content ratio of the acetylenic diol surfactant (A), the acetylenic diol surfactant (B), and the ethylene oxide adduct of acetylenic diol (C) of the acetylenic diol surfactant (A):the acetylenic diol surfactant (B):the ethylene oxide adduct of acetylenic diol (C) in the range of 1.6:1:1 to 3:1:1 on a mass basis. The aqueous inkjet ink composition according to claim 1, wherein the surfactant further comprises an alcohol alkoxylate. The aqueous inkjet ink composition according to claim 1 or 2, wherein the aqueous medium contains polyoxyethylene glycol having an added mole number of ethylene oxide in the range of 2 to 4. The aqueous inkjet ink composition according to any one of claims 1 to 3, wherein the colorant includes at least one of a cyan pigment, a magenta pigment, a yellow pigment, and a black pigment. It also contains moisturizers,
5. The aqueous inkjet ink composition according to claim 1, wherein the humectant contains a trihydric or higher polyhydric alcohol. Further comprising a penetration control agent,
6. The aqueous inkjet ink composition according to claim 1, wherein the penetration control agent comprises at least one of a glycol solvent having 2 to 5 carbon atoms and a heterocyclic compound.