JP7545320B2 - Water-based ink for ink-jet printing - Google Patents

Description

The present invention relates to a water-based ink for ink-jet printing.

2. Description of the Related Art In the field of commercial printing such as product packaging and advertisements, inkjet recording methods using water-based inks have attracted attention for use with recording media made of resins such as polyethylene terephthalate and polyolefin from the viewpoints of reducing environmental load and saving energy.
Inkjet recording is a recording method in which ink droplets are directly ejected from fine nozzles and deposited on a recording medium to produce a recorded matter on which characters and images are printed. Inkjet recording has many advantages, including the ease of producing full color, low cost, and no contact with the recording medium.
On the other hand, in inkjet recording on resin films and the like that are not white, white inks are used for the purpose of expressing white color and for the purpose of improving visibility. Titanium oxide, which has high hiding power, is generally used as a colorant for white inks, and a polymer dispersant is used for the purpose of improving the dispersibility of pigments such as titanium oxide.

In the ink-jet recording method on a resin film, various proposals have been made to improve the uniformity of solid printing.
For example, Patent Document 1 discloses an inkjet recording method capable of obtaining a good image with excellent solid printing uniformity, which involves recording a first ink and a second ink on a low-liquid-absorbing recording medium by overlapping them, in which the first ink and the second ink are water-based inks containing a colorant, a polymer, and an organic solvent, the static surface tensions and viscosities of the first ink and the second ink satisfy a specific relationship, and an image is formed with one or more first inks, and then a background image is formed with the second ink.

JP 2019-119115 A

In food packaging, non-water-absorbent recording media such as resin films are used, and UV-curable inks and oil-based inks have been widely used in the past. However, UV-curable inks and the like have been problematic because of concerns that polymerization initiators and monomer components in the ink may migrate into food. Even with water-based inks, it is necessary to prevent the migration of low molecular weight components in the water-based ink.
In the conventional techniques such as those disclosed in Japanese Patent Laid-Open No. 2003-233699, the uniformity of solid printing has been improved, but there is still room for improvement in terms of preventing migration of water-based ink.
An object of the present invention is to provide a water-based ink for ink-jet printing which can prevent migration of chemical substances such as surfactants contained in the ink even when recording on a non-water-absorbent recording medium, and which can provide recorded matter which is excellent in image quality such as solid printing uniformity and whiteness.

The present inventors have found that the above problems can be solved by using a surfactant containing an acetylene glycol surfactant and a polyether-modified silicone surfactant in a specific mass ratio.
That is, the present invention provides a water-based ink for ink-jet printing, which contains a white pigment, polymer particles, a water-soluble organic solvent, a surfactant, and water,
the surfactant comprises an acetylene glycol surfactant (a) and a polyether-modified silicone surfactant (s), the content of the acetylene glycol surfactant (a) being 1.2% by mass or more in the water-based ink,
the mass ratio [(s)/(a)] of the polyether-modified silicone-based surfactant (s) to the acetylene glycol-based surfactant (a) is 0.4 or more and 1.2 or less;
A water-based ink for ink-jet printing on a non-water-absorbent recording medium is provided.

The present invention provides a water-based ink for inkjet printing that can prevent migration of chemical substances such as surfactants contained in the ink, even when printing on non-water-absorbent recording media, and can produce printed matter with excellent image quality, such as solid printing uniformity and whiteness.

[Water-based ink for ink-jet printing]
The water-based ink for ink-jet recording for a non-water-absorbent recording medium of the present invention (hereinafter also referred to as "the ink of the present invention") is a water-based ink for ink-jet recording that contains a white pigment, polymer particles, a water-soluble organic solvent, a surfactant, and water,
the surfactant comprises an acetylene glycol surfactant (a) and a polyether-modified silicone surfactant (s), the content of the acetylene glycol surfactant (a) being 1.2% by mass or more in the water-based ink,
The mass ratio [(s)/(a)] of the polyether-modified silicone surfactant (s) to the acetylene glycol surfactant (a) is 0.4 or more and 1.2 or less.

In this specification, the term "water-based" means that water accounts for the largest proportion by mass of the medium in which the pigment is dispersed.
In addition, "recording" is a concept that includes printing and printing out characters and images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters and images are recorded.
The term "non-water absorbing" means that the amount of water absorbed by the recording medium is 1 g/m ² or less when the recording medium is in contact with pure water for 100 ms.

The ink of the present invention can prevent migration of chemical substances such as surfactants contained in the ink even when recording on a non-water-absorbent recording medium, and can obtain recorded matter with excellent image quality such as solid printing uniformity and whiteness. The reason for this is not clear, but is thought to be as follows.
The ink of the present invention contains 1.2 mass % or more of acetylene glycol surfactant (a), but the mass ratio of the polyether-modified silicone surfactant (s) to the acetylene glycol surfactant (a) [(s)/(a)] is controlled to be 0.4 or more and 1.2 or less, and it is believed that the interaction between these two substances makes it possible to prevent migration (transfer) of chemical substances such as low molecular weight surfactants contained in the ink.
Furthermore, in the process of the ink drying on the non-water-absorbent recording medium, a large amount of polyether-modified silicone-based surfactant (s) is present on the surface of the ink coating, which is thought to retain the acetylene glycol-based surfactant (a) having a smaller molecular weight inside the ink coating, making it easier for the ink droplets to wet and spread on the non-water-absorbent recording medium, thereby improving the uniformity of solid printing and whiteness.

<White pigment>
The pigment used in the present invention is a white pigment, and is preferably an inorganic pigment.
Examples of inorganic pigments include metal oxides such as titanium dioxide, zinc oxide, silica, alumina, magnesia, etc., metal sulfates such as calcium sulfate, barium sulfate, etc., and metal carbonates such as calcium carbonate, magnesium carbonate, etc. Among these, from the viewpoint of obtaining high whiteness, metal oxides such as titanium dioxide, zinc oxide, silica, alumina, magnesia, etc. are preferred, one or more selected from titanium dioxide and zinc oxide are more preferred, and titanium dioxide is even more preferred.
The white pigments may be used alone or in combination of two or more kinds.

As the titanium dioxide, rutile type titanium dioxide and anatase type titanium dioxide can be used, but from the viewpoints of stability and availability, rutile type titanium dioxide is preferred.
From the viewpoint of obtaining good dispersibility in the ink of the present invention, titanium dioxide is preferably surface-treated. The surface treatment of titanium dioxide is not particularly limited, and it may be surface-treated with either an organic substance or an inorganic substance. From the viewpoint of avoiding the influence of photocatalysis, titanium dioxide surface-treated with an inorganic substance is preferred, and titanium dioxide surface-treated with silica and alumina is more preferred.
From the viewpoint of whiteness, the average primary particle size of titanium dioxide is preferably 100 nm or more, more preferably 150 nm or more, even more preferably 200 nm or more, and preferably 500 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, and still more preferably 300 nm or less.
The average primary particle size of titanium oxide is measured by the method described in the Examples.
Examples of commercially available rutile titanium dioxide products include Ishihara Sangyo Kaisha, Ltd. (product name: Typeque R, CR, PF series), Sakai Chemical Industry Co., Ltd. (product name: R series), Teika Corporation (product name: JR, MT series), Titan Kogyo Co., Ltd. (product name: KURONOS KR series), and Fuji Titan Kogyo Co., Ltd. (product name: TR series).

The white pigment used in the ink of the present invention is preferably held in a dispersed state in the ink by a polymer dispersant.
The white pigment and polymer dispersant in the ink of the present invention are preferably in the form of polymer particles containing a white pigment (hereinafter also referred to as "pigment-containing polymer particles").
The pigment-containing polymer particles refer to particles in which the polymer dispersant contains the white pigment, particles made of the polymer dispersant and the white pigment and part of the white pigment is exposed on the surface, particles in which the polymer dispersant is adsorbed to part of the white pigment, or mixtures thereof. Among these, particles in which the polymer dispersant contains the white pigment are more preferred.

[Pigment-containing polymer particles]
The polymer dispersant (hereinafter, also referred to as "polymer a") constituting the pigment-containing polymer particles is not particularly limited as long as it has at least the ability to disperse pigments.
Examples of the polymer a include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, polyurethane resins, etc. Among these, vinyl resins are preferred from the viewpoints of dispersion stability and storage stability of the white pigment.
The polymer a may be a water-soluble or water-insoluble polymer.

[Polymer a]
When the polymer a is a vinyl resin, the polymer a preferably contains (a-1) a structural unit derived from an ionic monomer, and more preferably further contains (a-2) a structural unit derived from a hydrophobic monomer and/or (a-3) a structural unit derived from a nonionic monomer.

[(a-1) Ionic Monomer]
As the ionic monomer (a-1), an anionic monomer is preferable. Examples of the ionic monomer include a carboxylic acid monomer and a sulfonic acid monomer, and a carboxylic acid monomer is more preferable.
The carboxylic acid monomer may be at least one selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and is preferably (meth)acrylic acid. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. "(Meth)" in the following description has the same meaning.

[(a-2) Hydrophobic Monomer]
The term "hydrophobic" in the (a-2) hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until it is saturated, the amount of the monomer that dissolves is less than 10 g.
Specific examples of the hydrophobic monomer (a-2) include those described in paragraphs [0020] to [0022] of JP-A-2018-83938. Among these, alkyl (meth)acrylates having an alkyl group having 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group having 6 to 22 carbon atoms, and macromonomers having a polymerizable functional group at one end are preferred, and one or more selected from alkyl (meth)acrylates, styrene, α-methylstyrene, and benzyl (meth)acrylate are more preferred.

[(a-3) Nonionic Monomer]
The nonionic monomer (a-3) is a monomer that has a high affinity for water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxyl group or a polyalkylene glycol chain.
Specific examples of the component (a-3) include those described in paragraph [0018] of JP-A-2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred.
The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more kinds.

(Content of each structural unit in polymer a)
From the viewpoint of improving image quality, the contents of the structural units derived from the components (a-1) to (a-3) in the polymer a are as follows.
The content of the (a-1) component is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and is preferably 100% by mass or less, and more preferably 100% by mass.
The content of the component (a-2) is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, and it is preferable that the component (a-2) is not contained.
The content of the component (a-3) is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, and it is preferable that the component (a-3) is not contained.

(Production of Polymer a)
The polymer a can be produced by copolymerizing a mixture of the above monomer components (a-1) to (a-3) by a known polymerization method, preferably a solution polymerization method.
Although there is no limitation on the solvent used in the solution polymerization method, polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferred.
In the polymerization, a polymerization initiator and a polymerization chain transfer agent can be used. Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble azo polymerization initiators, and examples of the polymerization chain transfer agent include mercaptans.
The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. used, but is preferably 50° C. or higher, more preferably 60° C. or higher, and is preferably 95° C. or lower, more preferably 85° C. or lower.
The polymerization atmosphere is preferably a nitrogen gas or inert gas atmosphere.
It is preferable that the polymer a is neutralized with a neutralizing agent as described below.

From the viewpoint of dispersion stability, etc., the acid value of polymer a is preferably 200 mgKOH/g or more, more preferably 400 mgKOH/g or more, even more preferably 600 mgKOH/g or more, and is preferably 1000 mgKOH/g or less, more preferably 900 mgKOH/g or less, even more preferably 850 mgKOH/g or less.
The weight average molecular weight of polymer a is preferably 1,500 or more, more preferably 2,000 or more, and even more preferably 2,500 or more, from the viewpoint of preventing migration of chemical substances and improving dispersion stability, and is preferably 30,000 or less, more preferably 20,000 or less, and even more preferably 10,000 or less, from the viewpoint of improving dispersion stability, etc.
The acid value and weight average molecular weight of the polymer a are measured by the method described in the examples.
Commercially available polymer dispersants can also be used, including water-soluble polyacrylic acid such as Aron AC-10SL (trade name) manufactured by Toagosei Co., Ltd., polyacrylic acid manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and special polycarboxylic acids such as Poise 520 and Poise 530 (trade names) manufactured by Kao Corporation.

[Preparation of pigment-containing polymer particles]
The pigment-containing polymer particles can be efficiently produced as a pigment aqueous dispersion by a method having the following step 1.
Step 1: A step of dispersing a pigment mixture containing a white pigment, a polymer dispersant (polymer a), and water to obtain an aqueous dispersion of pigment-containing polymer particles (hereinafter, also referred to as "pigment aqueous dispersion"). If necessary, a crosslinking agent can be added to the obtained pigment aqueous dispersion, and the pigment aqueous dispersion can be further crosslinked.

When the polymer a has acid groups, it is preferable to neutralize at least a part of the acid groups with a neutralizing agent, which is believed to increase the charge repulsion force exhibited after neutralization, suppress the aggregation of white pigment particles in the water-based ink, and improve the dispersion stability.
In the case of neutralization, it is preferable to neutralize so that the pH is 7 or more and 11 or less.
Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred.
The polymer a may be neutralized in advance.
From the viewpoint of improving dispersion stability and storage stability, the amount of the neutralizing agent used is preferably 10 mol % or more, more preferably 15 mol % or more, even more preferably 20 mol % or more, and is preferably 150 mol % or less, more preferably 120 mol % or less, even more preferably 100 mol % or less.
Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where polymer a before neutralization is "polymer a'".
Equivalent amount of neutralizing agent used (mol %)=[{weight (g) of neutralizing agent added/equivalent amount of neutralizing agent}/[{acid value of polymer a′ (mg KOH/g)×weight (g) of polymer (B)}/(56×1,000)]]×100

In the dispersion treatment in step 1, the white pigment particles can be atomized to a desired particle size only by main dispersion using shear stress. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion.
Examples of dispersing machines used for preliminary dispersion include commonly used mixing and stirring machines such as anchor blades, disperser blades, etc. Examples of dispersing machines used for main dispersion include kneading machines such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersing machines such as paint shakers and bead mills.
By controlling the conditions of the dispersion treatment, the average particle size of the pigment particles in the pigment aqueous dispersion can be adjusted.
An organic solvent can also be used in step 1. In the case where an organic solvent is used, the organic solvent may be removed by a known method after a pigment mixture containing a white pigment, a polymer dispersant, an organic solvent, and water is subjected to a dispersion treatment.

From the viewpoint of improving the dispersion stability of the pigment water dispersion, the non-volatile component concentration (solid content concentration) of the obtained pigment water dispersion is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less.
The solids concentration is measured by the method described in the Examples.
From the viewpoint of dispersion stability, the content of the white pigment in the pigment water dispersion is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less.
From the viewpoint of dispersion stability, the content of the polymer dispersant (polymer a) in the pigment water dispersion is preferably 0.2 mass % or more, more preferably 0.4 mass % or more, and is preferably 3 mass % or less, more preferably 2 mass % or less.
From the viewpoint of dispersion stability, the average particle size of the pigment-containing polymer particles is preferably 100 nm or more, more preferably 200 nm or more, and is preferably 500 nm or less, more preferably 400 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in the Examples.

<Polymer Particles>
The ink of the present invention contains polymer particles that do not contain a pigment, from the viewpoint of improving fixability and image quality.
The polymer constituting the polymer particles (hereinafter, also referred to as "polymer b") is not particularly limited as long as it has at least the fixing ability to fix the white pigment to a recording medium.
Examples of the polymer b include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, and polyurethane resins, with vinyl resins being preferred.
Polymer b may be either a water-soluble polymer or a water-insoluble polymer, but is preferably a water-insoluble polymer. Here, the term "water-insoluble" of a polymer means that when a polymer that has been dried at 105° C. for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25° C., the amount of dissolution is less than 10 g. When the polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

Polymer b more preferably contains (b-1) a structural unit derived from an ionic monomer and (b-2) a structural unit derived from a hydrophobic monomer. Polymer b may further contain (b-3) a structural unit derived from a nonionic monomer.
Specific examples and suitable examples of the ionic monomer (b-1) are the same as those of the ionic monomer (a-1) described in the section on polymer A. That is, the component (b-1) is preferably at least one selected from acrylic acid and methacrylic acid.
Specific examples and suitable examples of the hydrophobic monomer (b-2) are the same as those of the hydrophobic monomer (a-2) described in the section on polymer A. That is, the component (b-2) is preferably one or more selected from alkyl (meth)acrylate, styrene, α-methylstyrene, and benzyl (meth)acrylate, more preferably an alkyl (meth)acrylate having an alkyl group having 1 to 18 carbon atoms, particularly preferably 1 to 10 carbon atoms.
Specific examples and preferred examples of the nonionic monomer (b-3) are the same as the specific examples and preferred examples of the nonionic monomer (a-3) explained in the section of the polymer a.
The polymer b can be produced in the same manner as in the above (production of polymer a).
The polymer particles are preferably used in the form of an aqueous dispersion in which the polymer particles are dispersed in an aqueous medium.

(Content of each structural unit in polymer b)
From the viewpoint of improving fixability and image quality, the contents of the structural units derived from the components (b-1) to (b-3) in the polymer b are as follows.
The content of the (b-1) component is preferably 1 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2 mass% or more, and is preferably 20 mass% or less, preferably 15 mass% or less, and preferably 8 mass% or less.
The content of the (b-2) component is preferably 80 mass% or more, more preferably 85 mass% or more, even more preferably 92 mass% or more, and preferably 99 mass% or less, preferably 98.5 mass% or less, and preferably 98 mass% or less.
The content of the component (b-3) is preferably 10% by mass or less, more preferably 5% by mass or less, and it is preferable that the component (b-3) is not contained.

From the viewpoint of improving fixing property and image quality, the acid value of polymer b is preferably 5 mgKOH/g or more, more preferably 8 mgKOH/g or more, even more preferably 10 mgKOH/g or more, and is preferably 100 mgKOH/g or less, more preferably 60 mgKOH/g or less, even more preferably 30 mgKOH/g or less.
From the viewpoint of improving fixability and image quality, the weight average molecular weight of polymer b is preferably 50,000 or more, more preferably 100,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less.
The acid value and weight average molecular weight of the polymer b are measured by the method described in the examples.

From the viewpoint of improving fixability and image quality, the average particle size of the polymer particles in the ink of the present invention is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 60 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less.
The average particle size of the polymer particles is measured by the method described in the Examples.

<Water-soluble organic solvent>
The water-soluble organic solvent used in the present invention mainly serves to impart wetting and spreading properties of the ink to a non-water-absorbent recording medium. The water-soluble organic solvent may be liquid or solid at 25° C., but when the organic solvent is dissolved in 100 mL of water at 25° C., the amount of the dissolved organic solvent is 10 mL or more.
From the viewpoint of preventing migration of chemical substances and improving image quality, the boiling point of the water-soluble organic solvent is preferably 110° C. or higher, more preferably 130° C. or higher, even more preferably 150° C. or higher, and is preferably 250° C. or lower, more preferably 240° C. or lower, even more preferably 235° C. or lower.
From the same viewpoint as above, the water-soluble organic solvent preferably contains one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers.
Examples of polyhydric alcohols include ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-propanediol, 1,4-butanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, 2-ethyl-1,3-hexanediol, and diethylene glycol.
Among these, one or more selected from 1,2-propanediol, 1,2-butanediol, 1,3-propanediol, 1,4-butanediol, and the like are preferred, with 1,2-propanediol being more preferred.

Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and tripropylene glycol monomethyl ether.
Among these, one or more selected from dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether are preferred, and dipropylene glycol monomethyl ether is more preferred.
The water-soluble organic solvent may further contain organic solvents other than those mentioned above, within the range that does not impair the effects of the present invention.

<Surfactant>
The ink of the present invention contains a surfactant from the viewpoint of maintaining the surface tension of the ink at an appropriate level and improving wettability to a recording medium. From the viewpoint of preventing migration of chemical substances and improving image quality, the surfactant further contains an acetylene glycol surfactant (a) and a polyether-modified silicone surfactant (s), the content of the acetylene glycol surfactant (a) in the water-based ink is 1.2% by mass or more, and the mass ratio of the polyether-modified silicone surfactant (s) to the acetylene glycol surfactant (a), [(s)/(a)], is 0.4 to 1.2.

(Acetylene glycol surfactant (a))
Examples of the acetylene glycol surfactant (a) include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, as well as ethylene oxide adducts thereof. Among these, ethylene oxide adducts of acetylene glycol are preferred.
The sum (n) of the average number of moles of ethyleneoxy groups (EO) added in the ethylene oxide adduct is preferably 1 or more, more preferably 1.2 or more, and is preferably 20 or less, more preferably 16 or less, and even more preferably 12 or less.

From the viewpoint of making ink droplets wet and spread easily on a non-water-absorbing recording medium, the HLB (hydrophilic lipophilic balance) value of the acetylene glycol surfactant (a) is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, and is preferably 18 or less, more preferably 15 or less, and even more preferably 13 or less. Here, the HLB value can be determined by the Griffin method.
Commercially available examples of acetylene glycol surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, such as Surfynol 420 (n: 1.3), Surfynol 440 (n: 3.5), Surfynol 465 (n: 10.0), the "Olfine" series, and the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd.

(Polyether-modified silicone surfactant (s))
The polyether-modified silicone surfactant (s) has a structure in which the side chain and/or terminal hydrocarbon group of silicone oil is replaced with a polyether group.As the polyether group, a polyethyleneoxy group, a polypropyleneoxy group, and a polyalkyleneoxy group in which an ethyleneoxy group (EO) and a propyleneoxy group (PO) are added in a block or random manner are suitable, and a compound in which a polyether group is grafted to a silicone main chain, a compound in which silicone and a polyether group are bonded in a block form, etc. can be used.

From the viewpoint of making it easier for ink droplets to wet and spread on a non-water-absorbent recording medium, the HLB value of the polyether-modified silicone surfactant (s) is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less.
Specific examples of polyether-modified silicone surfactants include Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd., KF series (KF-353, KF-355A, KF-642, etc.) manufactured by Shin-Etsu Chemical Co., Ltd., and BYK-348 manufactured by BYK Japan K.K.

In the present invention, in the process of drying the ink on a non-water-absorbent recording medium, a large amount of polyether-modified silicone-based surfactant (s) is present on the surface of the ink coating film, and the acetylene glycol-based surfactant (a) having a smaller molecular weight is retained inside the ink coating film, so that it is considered that migration of chemical substances such as low-molecular-weight surfactants contained in the ink can be prevented, but the efficiency is improved by reducing the affinity between the acetylene glycol-based surfactant (a) and the polyether-modified silicone-based surfactant (s). Therefore, the HLB value of the acetylene glycol-based surfactant (a) and the HLB value of the silicone-based surfactant (s) are preferably 2 or more apart, more preferably 3 or more apart, as determined by the Griffin method.
In the present invention, the above surfactants can be used in combination of two or more kinds, and among them, it is preferable to use one type of silicone surfactant (s) and two types of acetylene glycol surfactant (a) in combination. In addition, surfactants other than the above can be contained within a range that does not impair the effects of the present invention.

The ink of the present invention can be efficiently produced by mixing a white pigment, preferably polymer particles containing a white pigment, polymer particles not containing a pigment, a water-soluble organic solvent, a surfactant, water, and, as necessary, various additives such as a preservative, a pH adjuster, a viscosity adjuster, an antifoaming agent, and an anti-rust agent. There are no particular limitations on the method of mixing them.

(Content of each component in the ink of the present invention)
The contents of the various components in the ink of the present invention are as follows, from the viewpoint of preventing migration of chemical substances and improving image quality.
(White pigment content)
The content of the white pigment in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 2.5% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.
The content of the pigment-containing polymer particles in the ink of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and is preferably 18% by mass or less, more preferably 16% by mass or less, even more preferably 14% by mass or less, and still more preferably 12% by mass or less.

(Polymer Particle Content)
The content of the polymer particles not containing a pigment in the ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

(Content of Water-soluble Organic Solvent)
The content of the polyhydric alcohol in the ink of the present invention is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.
The content of the polyhydric alcohol alkyl ether in the ink of the present invention is preferably 1 mass % or more, more preferably 2 mass % or more, even more preferably 3 mass % or more, and is preferably 20 mass % or less, more preferably 15 mass % or less, even more preferably 10 mass % or less.
The total content of the water-soluble organic solvents in the ink of the present invention is preferably 16% by mass or more, more preferably 22% by mass or more, even more preferably 28% by mass or more, and is preferably 65% by mass or less, more preferably 55% by mass or less, even more preferably 45% by mass or less.

(Surfactant content)
The content of the acetylene glycol surfactant (a) in the ink of the present invention is 1.2 mass % or more, preferably 1.3 mass % or more, more preferably 1.4 mass % or more, even more preferably 1.5 mass % or more, and is preferably 5 mass % or less, more preferably 4 mass % or less, even more preferably 3 mass % or less.
The content of the polyether-modified silicone surfactant (s) in the ink of the present invention is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, even more preferably 0.6% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less.
The total content of surfactants in the ink of the present invention is preferably 1.4% by mass or more, more preferably 1.7% by mass or more, even more preferably 2.1% by mass or more, and is 10% by mass or less, preferably 8% by mass or less, more preferably 6% by mass or less.
The mass ratio of the polyether-modified silicone-based surfactant (s) to the acetylene glycol-based surfactant (a) [(s)/(a)] is 0.4 or more, preferably 0.45 or more, more preferably 0.5 or more, even more preferably 0.6 or more, and is 1.2 or less, preferably 1.15 or less, more preferably 1.1 or less, even more preferably 1.0 or less.

The water content in the ink of the present invention is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and is preferably 75% by mass or less, more preferably 65% by mass or less, even more preferably 55% by mass or less.
The ink of the present invention may contain various additives such as preservatives, pH adjusters, viscosity adjusters, defoamers, rust inhibitors, etc. as optional components depending on the application. In such cases, a part of the water content may be replaced with the various additives.

(Physical properties of the ink of the present invention)
From the viewpoints of storage stability and improvement in image quality, the viscosity of the ink of the present invention at 32° C. is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 5 mPa·s or more, and is preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The viscosity of the water-based ink can be measured using an E-type viscometer.
From the viewpoints of storage stability and improvement in image quality, the pH of the ink of the present invention is preferably 7.0 or more, more preferably 7.2 or more, and even more preferably 7.5 or more, and from the viewpoints of member resistance and skin irritation, it is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less. The pH of the water-based ink can be measured by a conventional method.

[Inkjet recording method]
The ink of the present invention can be loaded into a known inkjet recording device such as a piezoelectric type as a water-based ink for inkjet recording on a non-water-absorbent recording medium, and ejected as ink droplets onto a recording medium to obtain a high-quality recorded matter.
Examples of non-water-absorbent recording media include synthetic resin films. Examples of synthetic resin films include films of polyester, polyvinyl chloride, polyolefin, nylon, etc. These films may be biaxially oriented, uniaxially oriented, or non-oriented. Among these, polyethylene terephthalate (PET) films and polypropylene films are preferred, and films whose surfaces have been subjected to corona discharge treatment are more preferred.

In the following manufacturing examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

(1) Measurement of average primary particle diameter of titanium oxide The average primary particle diameter of titanium oxide was measured by extracting 500 primary particles of titanium oxide by image analysis using a transmission electron microscope "JEM-2100" (manufactured by JEOL Ltd.), measuring their particle diameters, and calculating the average of the particle diameters to obtain the number average particle diameter. Note that, when titanium oxide has a major axis and a minor axis, the major axis was used for the calculation.

(2) Measurement of Weight-Average Molecular Weight of Polymer Using a solution of phosphoric acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent) and lithium bromide (manufactured by Tokyo Chemical Industry Co., Ltd., reagent) dissolved in N,N-dimethylformamide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) to concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, the measurement was performed by gel chromatography method [GPC apparatus (HLC-8120GPC) manufactured by Tosoh Corporation, columns (TSK-GEL, α-M × 2 columns) manufactured by Tosoh Corporation, flow rate: 1 mL/min] using monodisperse polystyrene with a known molecular weight as a standard substance.

(3) Measurement of acid value of polymer The resin was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1 N potassium hydroxide/ethanol solution by potentiometric titration, with the inflection point on the titration curve being the end point. The acid value (mg KOH/g) was calculated from the titration amount of the potassium hydroxide solution up to the end point.

(4) Measurement of average particle size of pigment-containing polymer particles and polymer particles The particle size was measured by dynamic light scattering using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), and calculated by cumulant method analysis.
The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was 5 x ^10-3 mass% (converted into solid content concentration), and the obtained cumulant average particle size was taken as the average particle size of the polymer particles.

(5) Measurement of solid content concentration of aqueous dispersion 10.0 g of sodium sulfate, which had been brought to a constant weight in a desiccator, was weighed out into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample was added thereto and mixed, and then accurately weighed, maintained at 105° C. for 2 hours to remove volatile matter, and further left in the desiccator for 15 minutes, and the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the mass of the sample added to obtain the solid content concentration.

Production Example 1 (Production of Water Dispersion of White Pigment-Containing Polymer Particles A)
In a 5L plastic container, 2500 g of water-soluble polyacrylic acid (Toagosei Co., Ltd., Aron AC-10SL, weight average molecular weight: 3000, acid value: 779 mg KOH/g, solid content concentration 40%) as a polymer dispersant and 3.57 g of ion-exchanged water were added, the container was cooled in an ice bath, and the solution was neutralized by slowly adding 1666.43 g of a 5N aqueous sodium hydroxide solution while stirring at 100 rpm (neutralization degree: 60 mol%). Ion-exchanged water was added to the neutralized aqueous solution to adjust the solid content concentration to 20%, and a neutralized aqueous solution of an acrylic acid-based dispersant was obtained.
In a 2L poly container, 30.0 g of the neutralized aqueous solution of the acrylic acid-based dispersant obtained above, 300 g of C.I. Pigment White 6 (manufactured by Ishihara Sangyo Kaisha, Ltd., titanium oxide, product name: Typeque CR-80, rutile type, Al-Si treatment, average primary particle diameter 250 nm), 306 g of water were added, 1000 g of zirconia beads were added, and dispersion was performed for 8 hours using a tabletop pot mill stand (As One Corporation). The zirconia beads were removed using a metal mesh, and the solid content concentration was adjusted with ion-exchanged water to obtain an aqueous dispersion of white pigment-containing polymer particles A (solid content concentration: 40%, pigment: 39.2%, polymer dispersant: 0.8%, average particle size: 300 nm).

Production Example 2 (Production of Water-Insoluble Polymer a Solution)
A monomer mixture was prepared by mixing 61.6 parts of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 128.8 parts of styrene, and 9.6 parts of α-methylstyrene. 20 parts of methyl ethyl ketone (MEK), 0.3 parts of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of the monomer mixture were placed in a reaction vessel and mixed, followed by thorough nitrogen gas replacement.
Meanwhile, a mixture of the remaining 90% of the monomer mixture, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and 2.2 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., product name: V-65) was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C while being stirred under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours had elapsed at 65°C from the end of the dropping, a solution in which 0.3 parts of the polymerization initiator was dissolved in 5 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and at 70°C for 2 hours, to obtain a water-insoluble polymer a solution (number average molecular weight of polymer a: 10,500, acid value: 239 mgKOH/g).

Preparation Example 1 (Preparation of Water Dispersion of Polymer Particles Containing Black Pigment)
(1) 58.1 parts of the polymer obtained by drying the water-insoluble polymer a solution obtained in Production Example 2 under reduced pressure was mixed with 71.5 parts of MEK, and 23.6 parts of 5N aqueous sodium hydroxide solution (sodium hydroxide solid content 16.9%) was added to neutralize the ratio of the mole number of sodium hydroxide to the mole number of carboxyl groups of the polymer to 40 mol% (neutralization degree: 40 mol%). 695.1 parts of ion-exchanged water was added, and 200g of carbon black pigment (C.I. Pigment Black 7, manufactured by Cabot Corporation, product name: MONARCH 717) was added thereto, and the mixture was stirred for 60 minutes using Disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper: product name) at 20°C with Disper blade rotating at 7000 rpm.
The resulting mixture was subjected to a dispersion treatment at a pressure of 150 MPa for nine passes using a Microfluidizer (trade name, manufactured by Microfluidics Corporation).
(2) 1000 g of the dispersion obtained in (1) was placed in a 2 L eggplant flask, 666.7 g of ion-exchanged water was added (solid concentration: 15.0%), and the organic solvent was removed by holding for 3 hours at a pressure of 0.09 MPa in a warm bath adjusted to 32°C at a rotation speed of 50 rpm using a rotary distillation apparatus (manufactured by Tokyo Rikakikai Co., Ltd., product name: Rotary Evaporator N-1000S). Further, the warm bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa, and the mixture was concentrated until the solid concentration reached 25.0%.

(3) The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 7,000 rpm for 20 minutes using a high-speed refrigerated centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20° C.), and the liquid layer was then filtered through a 5 μm membrane filter (manufactured by Sartorius, product name: Minisart).
61.6 g of ion-exchanged water was added to 400 g of the obtained filtrate (carbon black pigment: 76.0 g, water-insoluble polymer a: 22.1 g), 1.08 g of Proxel LVS (Arch Chemicals Japan Co., Ltd., antifungal agent, active content 20%) was further added, and 5.2 g of a crosslinking agent (trimethylolpropane polyglycidyl ether, Nagase ChemteX Corporation, trade name: Denacol EX-321L, epoxy equivalent: 129, water solubility: 27 mass%) was further added, and the mixture was stirred for 3 hours at 70 ° C. After cooling to 25 ° C., the mixture was filtered through the 5 μm filter, and further ion-exchanged water was added to obtain an aqueous dispersion of polymer particles containing a black pigment (solid concentration: 18%, pigment: 14%, polymer: 4%, average particle size: 90 nm).

Preparation Example 2 (Production of Water Dispersion of Polymer Particles B)
In a reaction vessel equipped with a dropping funnel, 0.5 parts of methacrylic acid, 14.5 parts of methyl methacrylate, 5.0 parts of 2-ethylhexyl acrylate, 11.1 parts of LATEMURU E-118B (polyoxyethylene alkyl ether sodium sulfate, manufactured by Kao Corporation, surfactant), 0.2 parts of potassium persulfate (polymerization initiator), and 382.8 parts of ion-exchanged water were mixed and substituted with nitrogen gas to obtain an initial charge monomer solution. Also, 9.5 parts of methacrylic acid, 275.5 parts of methyl methacrylate, 95.0 parts of 2-ethylhexyl acrylate, 35.1 parts of LATEMURU E-118B, 0.6 parts of potassium persulfate, and 183.0 parts of ion-exchanged water were mixed to obtain a dropping monomer solution, which was placed in a dropping funnel and substituted with nitrogen gas.
Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was heated from room temperature to 80° C. over 30 minutes while stirring, and the monomer in the dropping funnel was gradually dropped into the reaction vessel over 3 hours while maintaining the temperature at 80° C. After the dropping was completed, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. The mixture was then filtered through a 200 mesh to obtain an aqueous dispersion of water-insoluble polymer particles B (solid content: 44.1%, average particle size: 100 nm).
The polymer b constituting the polymer particles B had a weight average molecular weight of 700,000, a glass transition temperature of 50° C., and an acid value of 15 mgKOH/g.

Example 1 (Preparation of Water-Based Ink 1)
25.50 g (solid content: 10.2 g) of an aqueous dispersion of white pigment-containing polymer particles A obtained in Production Example 1 (solid content concentration: 40%), 9.07 g (solid content: 4.0 g) of an aqueous dispersion of polymer particles B obtained in Preparation Example 2 (solid content concentration: 44.1%), 6.0 g of dipropylene glycol monomethyl ether, 31.0 g of 1,2-propanediol, 0.75 g of acetylene glycol surfactant S420 (product name: Surfynol 420), acetylene glycol monomethyl ether, 1.0 g of ... [0113] 0.75 g of ethylene glycol-based surfactant S465 (product name: Surfynol 465), 1.20 g of polyether-modified silicone surfactant SAG005 (product name: Silface SAG005), and ion-exchanged water were added to a total amount of 100 g to obtain water-based ink 1 (solids concentration: 16.9%, white pigment-containing polymer particles (white pigment: 10.0%, polymer 0.2%), polymer particles: 4.0%, average particle size: 310 nm).

Details of the surfactants used are as follows:
[Acetylene glycol surfactant (a)]
S420: Product name: Surfynol 420, manufactured by Nissin Chemical Industry Co., Ltd.
Surfynol 104 (2,4,7,9-tetramethyl-5-decyne-4,7-diol, average number of moles of EO added: 0 moles, active content 100%) adduct of ethylene oxide (20%), average number of moles of ethylene oxide added: 1.3, active content 100%, HLB: 4
S465: Product name: Surfynol 465, manufactured by Nissin Chemical Industry Co., Ltd.
Ethylene oxide (65%) adduct of Surfynol 104, average number of moles of ethylene oxide added: 10, active content 100%, HLB: 13
[Polyether-modified silicone surfactant (b)]
SAG005: manufactured by Nissin Chemical Industry Co., Ltd., product name: Silface SAG005, HLB: 7, active content 100%

Examples 2 to 4 and Comparative Examples 1 to 3 (Preparation of Water-Based Inks 2 to 4 and 11 to 13)
Water-based inks 2 to 4 and 11 to 13 were obtained in the same manner as in Example 1, except that the compositions in Example 1 were changed to those shown in Table 1.

Reference Example 1 (Preparation of Water-Based Ink 21)
Water-based ink 21 was obtained in the same manner as in Example 1, except that the composition was changed to that shown in Table 1, using the water dispersion (solids concentration: 18%) of polymer particles containing the black pigment obtained in Preparation Example 1.

Printed matter was produced by the following inkjet printing method using the water-based inks obtained in Examples 1 to 4, Comparative Examples 1 to 3, and Reference Example 1, and the set-off migration, solid uniformity of the image, and whiteness were evaluated. The results are shown in Table 1.
The amount of each component in Table 1 is the effective amount (solid content).

<Creating printed matter>
(Inkjet printing method)
In an environment of temperature 25±1° C. and relative humidity 30±5%, the water-based ink was filled into a print evaluation device (manufactured by Tritec Corporation) equipped with an inkjet print head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezoelectric type).
The print head applied voltage was set to 26 V, the drive frequency to 20 kHz, the amount of ejected liquid to be discharged to be 12 pL, the print head temperature to be 32° C., the resolution to be 600 dpi, the number of flushings before ejection to be 200, and the negative pressure to be -4.0 kPa. An A4-sized film heater (manufactured by Kawai Electric Works Ltd.) was fixed on the transport table so that the printing medium (manufactured by Futamura Chemical Co., Ltd., "FOR-AQ", OPP film) could be heated, and the printing medium was fixed on the film heater with glue so that the longitudinal direction of the printing medium was the same as the transport direction.
The heating temperature of the film heater was set to 40°C.
A print command was transferred to the print evaluation device, and the ink was ejected to perform printing. After that, the print was dried for 5 seconds in a hot air dryer at 60° C. to obtain a print.

<Evaluation of set-off migration>
Under the above printing conditions, a solid image of 10 cm x 10 cm was printed with 100% ink duty, and two printed sheets were stacked so that the printed surface and the non-printed surface were in contact. The stacked printed sheets were wrapped in aluminum foil, a load of 1 kg/ ^dm2 was applied, and the sheets were left standing at 40°C for one week. Thereafter, the sheets were fixed in a one-sided elution vessel (MK-10 type, manufactured by Maeda Manufacturing Co., Ltd.) containing 50 parts by weight of 95% ethanol in advance, so that 50 ^cm2 of the non-printed surface that had been in contact with the printed surface was in contact with 95% ethanol, the vessel was sealed, and the vessel was left standing at 60°C for seven days. After leaving the vessel for seven days, the 95% ethanol was removed from the one-sided elution vessel.
Using a gas chromatograph mass spectrometer (manufactured by Agilent Technology, product name: 6890N Network GC) and a calibration curve of the acetylene glycol surfactant prepared in advance, the amount of acetylene glycol surfactant transferred (migration amount) to 95% ethanol was quantified, and the set-off migration was evaluated according to the following evaluation criteria.
(Evaluation Criteria)
3: The amount of the acetylene glycol surfactant eluted from the solid image was 10 ppb or less.
2: The amount of acetylene glycol surfactant eluted from the solid image was more than 10 ppb and 50 ppb or less.
1: The amount of acetylene glycol surfactant eluted from the solid image exceeded 50 ppb.
If the evaluation result is 3 or 2, the set-off migration is at a level acceptable for practical use.

<Evaluation of solid printing uniformity>
Under the above printing conditions, a solid image was printed with 100% ink duty and left for one day, after which it was visually checked for unevenness or streaks and the solid printing uniformity of the image was evaluated according to the following evaluation criteria.
(Evaluation Criteria)
◯: No unevenness or streaks were observed, and the solid printing uniformity was good.
△: There are unevenness and streaks, but it can still be used.
×: There are unevenness and streaks, which are problematic in practical use.

<Evaluation of Whiteness>
Under the above printing conditions, a solid image was printed with 100% ink duty, and after leaving it for one day, the whiteness was evaluated visually on a black drawing paper according to the following evaluation criteria.
(Evaluation Criteria)
◯: No black color is observed, and the whiteness is high.
△: A little black color is observed, but it can be actually used.
x: A considerable amount of black is observed, which is problematic in practical use as a white printed matter.

From Table 1, it can be seen that the water-based inks obtained in the examples have less migration of chemical substances such as surfactants to articles containing solvents, compared to the water-based inks obtained in the comparative examples, and can produce printed matter with excellent image quality such as solid printing uniformity and whiteness.

Claims (6)

A water-based ink for ink-jet printing, comprising a white pigment, polymer particles, a water-soluble organic solvent, a surfactant, and water,
The surfactant comprises an acetylene glycol surfactant (a) and a polyether-modified silicone surfactant (s),
the content of the acetylene glycol surfactant (a) in the water-based ink is 1.2% by mass or more;
the mass ratio [(s)/(a)] of the polyether-modified silicone-based surfactant (s) to the acetylene glycol-based surfactant (a) is 0.4 or more and 1.2 or less;
Water-based inks for ink-jet printing on non-water-absorbent recording media. The water-based ink for ink-jet printing according to claim 1, wherein the acetylene glycol surfactant (a) is an ethylene oxide adduct of acetylene glycol, and the average number of moles of ethylene oxide added is 1 or more and 20 or less. The water-based ink for ink-jet printing according to claim 1 or 2, wherein the content of the acetylene glycol surfactant (a) in the water-based ink is 1.3% by mass or more and 5% by mass or less. The water-based ink for ink-jet printing according to any one of claims 1 to 3, wherein the water-soluble organic solvent is at least one selected from polyhydric alcohols and polyhydric alcohol alkyl ethers. The water-based ink for ink-jet printing according to any one of claims 1 to 4, wherein the white pigment is in the form of polymer particles containing the white pigment. The water-based ink for ink-jet recording according to any one of claims 1 to 5, wherein the non-water-absorbent recording medium is a polyethylene terephthalate film or a polypropylene film.