JP7583574B2 - Water-in-oil emulsion ink - Google Patents

Description

The present invention relates to a water-in-oil emulsion ink and a method for producing the water-in-oil emulsion ink.

Inkjet recording is a method of directly ejecting ink droplets from minute nozzles and depositing them on a printing medium to obtain a printed matter on which characters and images are recorded. This method has the advantages of being easy to produce full color, being inexpensive, and not contacting the printed matter, so it is no longer limited to consumer printing, and in recent years it has begun to be applied to commercial and industrial printing fields.
Conventionally, water-based inks using pigments or dyes as colorants have been used as inks for inkjet recording. However, when printing on plain paper using water-based inks, although the print density is high due to the high water absorption of plain paper, there is a problem that the water contained in the water-based ink causes the plain paper fibers to expand, resulting in curling and deformation of the printed matter.
In addition, in the fields of commercial and industrial printing, high-speed printing is required, and in order to meet this demand, printers that employ a line-head type inkjet recording method have been developed and oil-based pigment inks are used. When printing on plain paper using oil-based pigment inks, deformation of the printed matter can be reduced, but there is a problem that the ink penetrates into the interior of the printed matter, resulting in a low print density.
Therefore, the use of water-in-oil (W/O) emulsion inks has been investigated.

For example, Patent Document 1 discloses a W/O type emulsion ink for inkjet recording, which contains 55% by mass or more and 90% by mass or less of an oil phase and 45% by mass or less and 10% by mass or more of an aqueous phase, with the aqueous phase containing water, an aqueous solvent, a colorant, and a resin, for the purpose of providing a W/O type emulsion ink for inkjet recording that can obtain sufficient optical density and the like of an image when recorded on plain paper.
Patent Document 2 discloses an inkjet emulsion ink that is a water-in-oil type emulsion ink consisting of an oil phase and an aqueous phase, the aqueous phase containing water and a colorant, the colorant being a modified pigment containing a polymer, for the purpose of providing an inkjet emulsion ink that can obtain sufficient image optical density and reduce paper deformation when recorded on plain paper.
Patent Literature 3 discloses a water-in-oil emulsion ink for inkjet use, which has an aqueous phase containing water and a liquid organic compound having an acidic group, and an oil phase containing a water-insoluble organic solvent and a basic emulsifier, and at least one of the aqueous phase and the oil phase contains a colorant, for the purpose of providing a water-in-oil emulsion ink for inkjet use which has excellent storage stability and ejection stability and also has a high image density.

JP 2013-194111 A JP 2015-189859 A JP 2017-19998 A

Water-in-oil emulsion inks have an oil phase as the continuous phase, and an aqueous phase is emulsified in the oil phase. When a pigment is contained in the aqueous phase as a colorant, the aqueous phase tends to aggregate, and therefore improvement in storage stability is required. However, the techniques of Patent Documents 1 to 3 do not provide sufficient storage stability when the emulsion ink is stored at high temperatures for a long period of time.
Furthermore, with the techniques of Patent Documents 1 to 3, when printing on plain paper, the print density of the printed matter is insufficient, and deformation of the printed matter cannot be sufficiently reduced.
Furthermore, although it is shown that the water-in-oil emulsion ink of Patent Document 1 has ejection characteristics when the nozzle portion of an inkjet recording device is exposed to the atmosphere and printing is resumed after pausing printing, the ejection stability when continuously printing on a printing medium by an inkjet recording method (hereinafter also referred to as "continuous ejection stability") is insufficient.
In Patent Document 3, ejection stability is evaluated by evaluating the non-ejection of ink when 10 solid images are continuously printed using an inkjet recording device. However, as the number of continuously printed sheets increases, ejection defects become more likely to occur, and therefore further improvement in continuous ejection stability is also required.
An object of the present invention is to provide a water-in-oil emulsion ink which has excellent storage stability, is capable of producing a printed matter with high print density and little deformation after printing when printed on plain paper, and has excellent continuous ejection stability in an inkjet recording system, and a method for producing the water-in-oil emulsion ink.

The present inventors have found that the above problems can be solved by providing a water-in-oil emulsion ink having an aqueous phase containing water and a pigment, and an oil phase containing a water-insoluble organic solvent and an emulsifier, wherein the mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] is within a specific range, and the water content in the water-in-oil emulsion ink is not more than a specific value.
That is, the present invention provides the following [1] and [2].
[1] A water-in-oil emulsion ink having a water phase in an oil phase,
the aqueous phase comprises water, a pigment, and a polymeric dispersant;
a mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] is 1.5 or more and 14 or less;
The oil phase contains a water-insoluble organic solvent and an emulsifier;
The water-in-oil emulsion ink has a water content of 20 mass % or less.
[2] A method for producing a water-in-oil emulsion ink according to the above [1], comprising a step of emulsifying an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium, in an oil phase.

The present invention provides a water-in-oil emulsion ink that has excellent storage stability, can produce printed matter with high print density and little deformation after printing when printed on plain paper, and has excellent continuous ejection stability in inkjet recording methods, and a method for producing the water-in-oil emulsion ink.

[Water-in-oil emulsion ink]
The water-in-oil emulsion ink of the present invention (hereinafter also referred to as "emulsion ink") is a water-in-oil emulsion ink having an aqueous phase in an oil phase which is a continuous phase, the aqueous phase containing water, a pigment, and a polymer dispersant, the mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] being 1.5 or more and 14 or less, the oil phase containing a water-insoluble organic solvent and an emulsifier, and the water content in the water-in-oil emulsion ink being 20 mass % or less.

The water-in-oil emulsion ink of the present invention has excellent storage stability, and when printed on plain paper, it is possible to obtain a printed matter with high print density and little deformation after printing, and has excellent continuous ejection stability in the inkjet recording method. The reason for this is unclear, but is thought to be as follows.
In the present invention, the pigment is dispersed by a polymer dispersant in the aqueous phase, which is the dispersed phase. By setting the mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] to a specific range and setting the water content in the emulsion ink to a specific value or less, it is believed that the entire emulsion ink system is stabilized and the storage stability of the emulsion ink when stored for a long period of time at high temperatures is improved. In addition, since the water content in the emulsion ink is a specific value or less in the present invention, it is believed that deformation of the printed matter when printed on plain paper can be reduced.
Furthermore, by setting the mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] within a specific range, the viscosity of the aqueous phase components can be reduced, making the emulsion finer, and the surface area of the dispersed phase droplet particles relative to the system can be increased. This is thought to promote pigment aggregation when printed on plain paper, thereby improving print density.
Furthermore, a recording device used in an inkjet recording system is usually provided with a filter to prevent foreign matter from entering the ink, which may clog the nozzles of the inkjet head or the ink flow path. In the present invention, as described above, it is believed that since the emulsion can be made fine, clogging of the filter can be suppressed and continuous ejection stability can be improved.

The mass ratio of the pigment to the polymer dispersant in the aqueous phase of the emulsion ink of the present invention [pigment/polymer dispersant], from the viewpoints of reducing the viscosity of the aqueous phase component to make the emulsion fine and improving the print density and continuous ejection stability, is 1.5 or more, preferably 1.6 or more, more preferably 1.9 or more, even more preferably 2.3 or more, still more preferably 3.0 or more, still more preferably 3.3 or more, still more preferably 3.5 or more, still more preferably 3.7 or more, still more preferably 4.0 or more, still more preferably 4.5 or more, still more preferably 4.7 or more, still more preferably 5.0 or more, still more preferably 5.5 or more, still more preferably 6.0 or more, and still more preferably 6.5 or more, and from the viewpoints of improving the dispersion stability of the pigment and improving the storage stability, it is 14 or less, preferably 12 or less, more preferably 10 or less, still more preferably 8 or less, and still more preferably 7 or less.
Here, when the polymer dispersant is a non-crosslinked polymer (a) described later, the mass ratio [pigment/polymer dispersant] is the mass ratio between the pigment and the non-crosslinked polymer (a) in the aqueous phase [pigment/non-crosslinked polymer (a)], and when the polymer dispersant is a crosslinked polymer (A), the mass ratio [pigment/polymer dispersant] is the mass ratio between the pigment and the crosslinked polymer (A) in the aqueous phase [pigment/crosslinked polymer (A)].

The water content in the emulsion ink of the present invention is 20% by mass or less, preferably 17% by mass or less, more preferably 15% by mass or less, even more preferably 13% by mass or less, and even more preferably 12% by mass or less, from the viewpoint of improving storage stability and reducing deformation of printed matter, and is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 9% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of improving print density and continuous ejection stability.

<Aqueous phase>
The aqueous phase contains water, a pigment, and a polymer dispersant from the viewpoints of improving storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter.
(Pigment)
The pigment according to the present invention may be either an inorganic pigment or an organic pigment, and may be a lake pigment or a fluorescent pigment. If necessary, these pigments may be used in combination with an extender pigment.
Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, pearlescent pigments, etc. In particular, carbon black is preferred for black ink.
The type of carbon black is not particularly limited, and examples thereof include furnace black, lamp black, acetylene black, and channel black.
The DBP oil absorption of the carbon black is preferably 20 mL/100 g or more and 200 mL/100 g or less from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the storage stability, print density and continuous ejection stability.
The DBP oil absorption refers to the oil absorption measured by the DBP method, specifically, a value based on ASTM D2414-65T.

Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.
The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, green, etc. can be used.
Specific examples of preferred organic pigments include one or more product numbers selected from C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green.
Examples of the extender pigment include silica, calcium carbonate, and talc.
The pigments can be used alone or in combination of two or more kinds.

(Polymer Dispersant)
The pigment in the emulsion ink of the present invention is dispersed using a polymer dispersant from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, thereby improving storage stability, print density, and continuous ejection stability, and of reducing deformation of the printed matter.

[Polymer (a)]
The polymer dispersant according to the present invention is not particularly limited as long as it has at least pigment dispersibility, but from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, thereby improving storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, it may be a non-crosslinked polymer (hereinafter also referred to as "non-crosslinked polymer (a)" or "polymer (a)"). From the same viewpoint as above, the polymer (a) preferably contains an acid group.
Examples of the acid group of the polymer (a) include groups that exhibit acidity by dissociating and releasing hydrogen ions, such as a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), and a phosphate group (-OPO ₃ M ₂ ), or dissociated ionic forms thereof (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Among these, the carboxy group (-COOM) is preferred from the viewpoints of improving storage stability, print density, and continuous discharge stability, and of reducing deformation of the printed matter.

The acid value of the polymer (a) is preferably 120 mgKOH/g or more, more preferably 140 mgKOH/g or more, even more preferably 160 mgKOH/g or more, even more preferably 180 mgKOH/g or more, even more preferably 200 mgKOH/g or more, even more preferably 220 mgKOH/g or more, and is preferably 320 mgKOH/g or less, more preferably 300 mgKOH/g or less, and even more preferably 280 mgKOH/g or less, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, and is preferably 320 mgKOH/g or less, more preferably 300 mgKOH/g or less, and even more preferably 280 mgKOH/g or less. If the acid value is within the above range, the amount of acid groups can be sufficient to ensure the dispersion stability of the pigment. It is also preferable from the viewpoint of the balance between the affinity of the polymer (a) with water and the interaction between the polymer (a) and the pigment.
The acid value of the polymer (a) can be measured by the method described in the Examples, or calculated from the mass ratio of the constituent monomers.

At least a portion of the acid groups of the polymer (a) are preferably neutralized from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, the print density, and the continuous ejection stability, and reducing deformation of the printed matter.
Examples of the neutralizing agent used for neutralizing the polymer (a) include alkali metal hydroxides, ammonia, etc. Among them, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, preferred are alkali metal hydroxides, and more preferred are one or more selected from sodium hydroxide and potassium hydroxide.
From the same viewpoint as above, the degree of neutralization is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, still more preferably 45 mol% or more, and is preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 60 mol% or less.
Specifically, the degree of neutralization (mol %) can be calculated by the following formula.
Degree of neutralization (mol %)=[{weight (g) of neutralizing agent added/equivalent weight of neutralizing agent}/[{acid value (mg KOH/g) of polymer (a)×weight (g) of polymer (a)}/(56.1×1,000)]]×100

Examples of polymer (a) include polyester resins, polyurethane resins, vinyl resins, and the like. Among them, vinyl resins are preferred, and vinyl resins containing a structural unit derived from a carboxyl group-containing monomer and a structural unit derived from a hydrophobic monomer are more preferred. The vinyl resin may further contain a structural unit derived from a nonionic monomer.

[Carboxy Group-Containing Monomer]
The carboxyl group-containing monomer is preferably used as a monomer component of the vinyl resin from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, print density, and continuous ejection stability, and reducing deformation of the printed matter.
Examples of the carboxy group-containing monomer include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid, with (meth)acrylic acid being preferred, and acrylic acid being more preferred.
In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.
The carboxyl group-containing monomers can be used alone or in combination of two or more kinds.

[Hydrophobic Monomer]
The hydrophobic monomer is preferably used as a monomer component of the vinyl resin from the viewpoints of improving the adsorption of the polymer to the pigment, improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, the print density, and the continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter.
In this specification, "hydrophobic" means that when a monomer is dissolved to saturation in 100 g of ion-exchanged water at 25° C., the amount of the dissolved hydrophobic monomer is less than 10 g. From the viewpoint of the adsorption of the polymer to the pigment, the amount of the dissolved hydrophobic monomer is preferably 5 g or less, and more preferably 1 g or less.
Examples of the hydrophobic monomer include aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol.
In this specification, the term "(meth)acrylate" refers to at least one selected from acrylate and methacrylate.
The hydrophobic monomers can be used alone or in combination of two or more kinds.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
The styrene-based monomer is preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and more preferably at least one selected from styrene and α-methylstyrene.
The aromatic group-containing (meth)acrylate is preferably at least one selected from phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate, and more preferably benzyl (meth)acrylate.

The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. For example, (meth)acrylates having a straight chain alkyl group such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; (meth)acrylates having a branched chain alkyl group such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and (meth)acrylates having an alicyclic alkyl group such as cyclohexyl (meth)acrylate.

In the present invention, a hydrophobic macromonomer may be used as the hydrophobic monomer constituting the vinyl resin.
The macromonomer is a compound having a number average molecular weight of 500 to 100,000 and having a polymerizable functional group at one end, and can be used as a monomer component of a vinyl resin from the viewpoint of improving the dispersion stability of a pigment in an aqueous phase. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
The number average molecular weight of the macromonomer is preferably from 1,000 to 10,000. The number average molecular weight is measured by gel permeation chromatography using chloroform containing 1 mmol/L dodecyldimethylamine as a solvent and polystyrene as a standard substance.
As the macromonomer, from the viewpoint of dispersion stability of the pigment in the aqueous phase, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferred, and aromatic group-containing monomer-based macromonomers are more preferred.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomers described above in relation to the hydrophobic monomer, and styrene and benzyl (meth)acrylate are preferred, with styrene being more preferred.
The macromonomers can be used alone or in combination of two or more kinds.
Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), and HS-6(S) (product names of Toagosei Co., Ltd.).
The silicone macromonomer may be, for example, an organopolysiloxane having a polymerizable functional group at one end.

From the viewpoints of improving the adsorption of the polymer to the pigment, improving the dispersion stability of the pigment in the aqueous phase, improving storage stability, print density, and continuous discharge stability, and reducing deformation of the printed matter, the hydrophobic monomer is preferably one or more selected from aromatic group-containing monomers, (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol, and aromatic group-containing monomer-based macromonomers, more preferably one or more selected from aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol, even more preferably an aromatic group-containing monomer, and even more preferably one or more selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate.

[Nonionic Monomer]
From the viewpoint of dispersion stability of the pigment in the aqueous phase, a nonionic monomer can be used as a monomer component of the vinyl resin.
Examples of nonionic monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polyalkylene glycol (meth)acrylates such as polypropylene glycol (n=2-30, n indicates the average number of moles of oxypropylene groups added. Hereinafter, n indicates the average number of moles of the oxyalkylene groups added.) (meth)acrylate and polyethylene glycol (n=2-30) (meth)acrylate; alkoxypolyalkylene glycol (meth)acrylates such as methoxypolyethylene glycol (n=1-30) (meth)acrylate; and phenoxy (ethylene glycol-propylene glycol copolymer) (n=1-30, ethylene glycol therein: n=1-29) (meth)acrylate. Among these, polypropylene glycol (n=2-30) (meth)acrylate, alkoxypolyalkylene glycol (meth)acrylate, and phenoxy (ethylene glycol/propylene glycol copolymer) (meth)acrylate are preferred.
The nonionic monomers can be used alone or in combination of two or more kinds.
Specific examples of commercially available nonionic monomers include NK Ester M-20G, 40G, 90G, 230G, and the like, manufactured by Shin-Nakamura Chemical Co., Ltd.; Blemmer PE-90, 200, 350, and the like, Blemmer PME-100, 200, 400, and the like, Blemmer PP-500, 800, 1000, and the like, Blemmer AP-150, 400, 550, and the like, Blemmer 50PEP-300, 50POEP-800B, 43PAPE-600B, and the like, manufactured by NOF Corporation.

As described above, the polymer (a) according to the present invention is preferably a vinyl resin containing one or more structural units derived from a carboxyl group-containing monomer selected from acrylic acid and methacrylic acid, and one or more structural units derived from a hydrophobic monomer selected from an aromatic group-containing monomer, a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol, and an aromatic group-containing monomer-based macromonomer, and may further contain a structural unit derived from a nonionic monomer. However, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, improving storage stability, print density, and continuous ejection stability, and from the viewpoint of preventing deformation of the printed matter, From the viewpoint of reducing the above, it is more preferable that the vinyl resin contains a structural unit derived from one or more carboxyl group-containing monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from one or more hydrophobic monomers selected from aromatic group-containing monomers and (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol, and even more preferable that the vinyl resin contains a structural unit derived from one or more carboxyl group-containing monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from one or more hydrophobic monomers selected from styrene-based monomers and aromatic group-containing (meth)acrylates.

(Content of structural units derived from each monomer in vinyl resin)
The content of the constituent units derived from each monomer in the vinyl resin is as follows, from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, improving the storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter.
The content of structural units derived from carboxy group-containing monomers in the vinyl resin is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and still more preferably 40% by mass or less.
The content of structural units derived from hydrophobic monomers in the vinyl resin is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.
When the vinyl resin contains a structural unit derived from a macromonomer, the content of the structural unit derived from the macromonomer in the vinyl resin is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.
When the vinyl resin contains a constituent unit derived from a nonionic monomer, the content of the constituent unit derived from the nonionic monomer in the vinyl resin is preferably 3 mass% or more, more preferably 5 mass% or more, even more preferably 7 mass% or more, and preferably 30 mass% or less, more preferably 20 mass% or less, even more preferably 15 mass% or less.
The content of the constituent units derived from each monomer in the vinyl resin can be measured by analysis such as NMR. The preferred range of the content of each monomer in the raw material monomers during the production of the vinyl resin (content as the unneutralized amount) can be considered to be the same as the preferred range of the content of the constituent units derived from each monomer in the vinyl resin.

The total content of the constituent units derived from the carboxy group-containing monomer and the constituent units derived from the hydrophobic monomer in the vinyl resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and is preferably 100% by mass or less, still more preferably substantially 100% by mass, and still more preferably 100% by mass.
The mass ratio of the content of constituent units derived from carboxy group-containing monomers to the content of constituent units derived from hydrophobic monomers in the vinyl resin [content of constituent units derived from carboxy group-containing monomers/content of constituent units derived from hydrophobic monomers] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, still more preferably 0.4 or more, and is preferably 2 or less, more preferably 1.5 or less, even more preferably 1.0 or less, still more preferably 0.9 or less, still more preferably 0.8 or less, still more preferably 0.7 or less, and still more preferably 0.5 or less.

Vinyl resins are produced by copolymerizing raw material monomers using known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, solution polymerization is preferred. There are no restrictions on the chain form of the polymerized monomers, and any polymerization form such as random, block, or graft may be used.

The weight average molecular weight of the polymer (a) is preferably 2,000 or more, more preferably 5,000 or more, even more preferably 7,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, and still more preferably 20,000 or less. When the weight average molecular weight of the polymer (a) is within the above range, the adsorptivity to the pigment is sufficient, and dispersion stability can be exhibited.
The weight average molecular weight of the polymer (a) is measured by the method described in the Examples.

[Crosslinked polymer (A)]
In the present invention, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, thereby achieving both a high pigment concentration in the aqueous phase and a low viscosity of the aqueous phase components, thereby improving storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, it is preferable that the pigment is dispersed by a polymer dispersant, and the polymer dispersant is a crosslinked polymer (A) having a crosslinked structure (hereinafter, also simply referred to as "crosslinked polymer (A)").
From the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, thereby achieving both a high pigment concentration in the aqueous phase and a low viscosity of the aqueous phase components, thereby improving storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, the crosslinked polymer (A) is preferably a polymer crosslinked with a crosslinking agent or a polymer having a self-crosslinking structure into which a crosslinkable group has been introduced, more preferably a polymer crosslinked with a crosslinking agent, and even more preferably a polymer in which the aforementioned non-crosslinked polymer (a) has been crosslinked with a crosslinking agent.
That is, the crosslinked polymer (A) has a structure derived from the crosslinking agent in addition to the constituent units derived from the monomer constituting the polymer (a). The crosslinked polymer (A) has a crosslinked structure, which allows the crosslinked polymer (A) to be firmly adsorbed or fixed to the pigment surface, suppressing the aggregation of the pigment in the aqueous phase, particularly the depletion aggregation, improving the dispersion stability of the pigment in the aqueous phase, and further suppressing the swelling of the polymer, thereby reducing the viscosity of the aqueous phase component and making the emulsion finer, thereby improving the storage stability and continuous discharge stability, and further reducing the water content in the emulsion ink, which is thought to reduce the deformation of the printed matter.

[Crosslinking Agent]
From the viewpoint of reactivity with the polymer (a), the water solubility (mass ratio) of the crosslinking agent is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less. The water solubility (mass ratio) refers to the solubility (%) when 10 parts by mass of the crosslinking agent is dissolved in 90 parts by mass of water at room temperature of 25° C.

The crosslinking agent is preferably a polyfunctional compound, and when the polymer (a) contains an acid group, the crosslinkable functional group of the polyfunctional compound is preferably capable of reacting with the acid group of the polymer (a) to form a covalent bond.The covalent bond is preferably one or more selected from ester bond, thioester bond, amide bond, amino bond, ether bond, thioether bond, carbonyl bond, thiocarbonyl bond and sulfonyl bond, more preferably one or more selected from ester bond, thioester bond and amide bond.The crosslinkable functional group of the polyfunctional compound is not particularly limited as long as it can form the above-mentioned covalent bond.
The molecular weight of the crosslinking agent is preferably 120 or more, more preferably 150 or more, even more preferably 200 or more, from the viewpoints of improving the reactivity, the dispersion stability of the pigment in the aqueous phase, improving the storage stability, the print density, and the continuous ejection stability, and of reducing deformation of the printed matter, and is preferably 2,000 or less, more preferably 1,500 or less, even more preferably 1,000 or less.

The crosslinkable functional group is preferably one or more selected from epoxy group, isocyanate group, aziridino group, amino group and oxazoline group, more preferably epoxy group. The concept of epoxy group includes glycidyl group. That is, the crosslinking agent is preferably a multifunctional epoxy compound, and from the viewpoint of crosslinking efficiency, more preferably a compound having two or more epoxy groups in the molecule, even more preferably a compound having two or more glycidyl ether groups, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.
When the crosslinking agent is a polyfunctional epoxy compound, the epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.
When the crosslinking agent is a polyfunctional epoxy compound, the number of epoxy groups in the crosslinking agent is 2 or more per molecule from the viewpoints of efficiently carrying out a crosslinking reaction to improve the dispersion stability of the pigment in the aqueous phase, improving the storage stability and print density, and reducing deformation of the printed matter, and is preferably 6 or less per molecule, and from the viewpoint of market availability, is more preferably 4 or less, and even more preferably 3 or less.

Specific examples of crosslinking agents include polyglycidyl ethers such as polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, diethylene glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, preferred is one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and more preferred is trimethylolpropane polyglycidyl ether.

The degree of crosslinking of the crosslinked polymer (A) is, from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, reducing the average particle size of the emulsion, improving storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter, preferably 20 mol % or more, more preferably 30 mol % or more, even more preferably 40 mol % or more, still more preferably 45 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less, even more preferably 60 mol % or less, still more preferably 55 mol % or less.
As described above, the degree of crosslinking of the crosslinked polymer (A) is a polymer obtained by crosslinking the polymer (a) with a crosslinking agent, and when the polymer (a) contains an acid group, the degree of crosslinking is calculated from the equivalent of the acid group of the polymer (a) and the equivalent of the crosslinkable functional group of the crosslinking agent, and is expressed as "the number of molar equivalents of the crosslinkable functional group of the crosslinking agent / the number of molar equivalents of the acid group possessed by the polymer (a)".
As described above, when a part of the acid groups of the polymer (a) is neutralized, the neutralized acid groups can also become crosslinking points. Therefore, when the sum of the neutralization degree and the crosslinking degree exceeds 100 mol %, the crosslinking degree is represented by "the number of molar equivalents of the crosslinkable functional groups of the crosslinking agent/the number of molar equivalents of the acid groups of the polymer (a)" as described above, and the neutralization degree of the polymer (a) is a value obtained by subtracting the crosslinking degree from 100 mol %.

The acid value of the crosslinked polymer (A) is preferably 70 mgKOH/g or more, more preferably 80 mgKOH/g or more, even more preferably 90 mgKOH/g or more, even more preferably 100 mgKOH/g or more, even more preferably 110 mgKOH/g or more, and is preferably 200 mgKOH/g or less, more preferably 180 mgKOH/g or less, even more preferably 160 mgKOH/g or less, even more preferably 140 mgKOH/g or less, and even more preferably 130 mgKOH/g or less, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase to reduce the average particle size of the emulsion, improving storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter. If the acid value is in the above range, the amount of acid groups can be made sufficient to ensure the dispersion stability of the pigment. It is also preferable from the viewpoint of the balance between the affinity of the crosslinked polymer (A) with water and the interaction between the crosslinked polymer (A) with the pigment.
The acid value of the crosslinked polymer (A) can be measured by the method described in the Examples.
When the crosslinked polymer (A) is a polymer obtained by crosslinking the polymer (a) with a crosslinking agent, the acid value of the crosslinked polymer (A) can also be calculated by the following formula.
Acid value of crosslinked polymer (A) (mg KOH/g)=[acid value of polymer (a) (mg KOH/g)]×[100−degree of crosslinking (mol %)]/100
Here, the acid value of the polymer (a) can be calculated from the mass ratio of the constituent monomers. Also, the degree of crosslinking is expressed as "the molar equivalent number of the crosslinkable functional group of the crosslinking agent/the molar equivalent number of the acid group of the polymer (a)" as described above.

At least a part of the acid groups of the crosslinked polymer (A) is preferably neutralized from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, reducing the average particle size of the emulsion, improving storage stability, print density and continuous discharge stability, and reducing deformation of the printed matter. Examples of the neutralizing agent used for neutralizing the crosslinked polymer (A) include the same ones as those exemplified for the polymer (a) described above.
The counter ion of the neutralized acid group of the crosslinked polymer (A) is preferably an alkali metal cation, more preferably one or more selected from sodium ion (Na ⁺ ) and potassium ion (K ⁺ ), from the viewpoint of improving the dispersion stability of the pigment and improving storage stability and continuous ejection stability.
Regarding the degree of neutralization of the crosslinked polymer (A), a part of the acid groups of the crosslinked polymer (A) may be neutralized, or all of the acid groups may be neutralized.

The form of the polymer (a) or crosslinked polymer (A) in the aqueous phase of the emulsion ink of the present invention may be in a state where it is adsorbed to the pigment, in a state where it contains the pigment (including a particle form in which the pigment is encapsulated and a particle form in which the pigment is uniformly dispersed), or in a form where the pigment is not adsorbed. From the viewpoint of improving the dispersion stability of the pigment and reducing the average particle size of the emulsion, the form of particles in which the pigment is contained in the polymer (a) (hereinafter also referred to as "pigment-containing polymer particles") or particles in which the pigment is contained in the crosslinked polymer (A) (hereinafter also referred to as "pigment-containing crosslinked polymer particles") is preferred in the present invention, the form of pigment-containing crosslinked polymer particles is more preferred, and the form of particles in which the pigment is encapsulated in the crosslinked polymer (A) is even more preferred.

(Surfactant)
In the emulsion ink of the present invention, it is preferable to contain a surfactant in the aqueous phase. It is considered that the surfactant improves the dispersion stability of the pigment in the aqueous phase, reduces the energy of the interface between the aqueous phase and the oil phase, contributes to the formation of a fine and stable dispersed phase, and refines the emulsion, thereby improving the storage stability, print density, and continuous ejection stability. From this viewpoint, the surfactant is preferably a nonionic surfactant, more preferably one or more selected from acetylene glycol surfactants, polyoxyalkylene alkyl ether surfactants, polyether-modified silicone surfactants, and fluorine-based surfactants, even more preferably one selected from acetylene glycol surfactants and polyether-modified silicone surfactants, and even more preferably an acetylene glycol surfactant.
The HLB (hydrophilic-lipophilic balance) value of the nonionic surfactant is preferably 6 or more, more preferably 8 or more, even more preferably 10 or more, still more preferably 12 or more, and is preferably 20 or less, more preferably 18 or less.
The HLB value indicates the affinity of a surfactant to water and oil, and can be calculated by the Griffin method from the following formula: In the following formula, examples of the "hydrophilic group contained in the surfactant" include a hydroxyl group and an ethyleneoxy group.
HLB = 20 x [(total formula weight of hydrophilic groups contained in surfactant)/(molecular weight of surfactant)]

The acetylene glycol surfactant is preferably an ethylene oxide (hereinafter also referred to as "EO") adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, an EO adduct of 3,6-dimethyl-4-octyne-3,6-diol, an EO adduct of 2,5-dimethyl-3-hexyne-2,5-diol, an EO adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and an EO adduct of 3,5-dimethyl-1-hexyne-2,5-diol. The EO adduct is at least one selected from the group consisting of an EO adduct of cin-3-ol, more preferably at least one selected from the group consisting of an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, an EO adduct of 3,6-dimethyl-4-octyne-3,6-diol, and an EO adduct of 2,5-dimethyl-3-hexyne-2,5-diol, and still more preferably an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.
The average number of moles of EO added of the above-mentioned EO adduct used as the acetylene glycol surfactant is preferably 5 or more, more preferably 6 or more, even more preferably 7 or more, still more preferably 8 or more, and is preferably 40 or less, more preferably 36 or less, even more preferably 32 or less.

Commercially available acetylene glycol surfactants include Surfynol 465 (average 10 moles of EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB: 13) and Surfynol 485 (average 30 moles of EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB: 17) manufactured by Nissin Chemical Industry Co., Ltd., and Acetylenol E8 manufactured by Kawaken Fine Chemical Co., Ltd. 1 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with an average of 8.1 moles of EO, HLB: 13.0), E100 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with an average of 10 moles of EO, HLB: 13.9), E200 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with an average of 20 moles of EO, HLB: 16.4), etc.

The polyether-modified silicone surfactant is preferably one having a structure in which the side chain and/or terminal hydrocarbon group of the silicone oil is replaced with a polyether group.As the polyether group, a polyethyleneoxy group, a polypropyleneoxy group, or a polyalkyleneoxy group in which an ethyleneoxy group (EO) and a propyleneoxy group (trimethyleneoxy group or propane-1,2-diyloxy group; PO) are added in a block or random manner is preferable, and a compound in which a polyether group is grafted onto a silicone main chain, a compound in which a silicone and a polyether group are bonded in a block form, etc. can be used.
Commercially available polyether-modified silicone surfactants include KF-353, KF-355A, KF-642, and the like manufactured by Shin-Etsu Chemical Co., Ltd.; Silface SAG005, and the like manufactured by Nissin Chemical Industry Co., Ltd.; FZ-2191, and the like manufactured by NUC Corporation; and BYK-348, and the like manufactured by BYK Japan K.K.

(Water-soluble organic solvent)
It is preferred that the aqueous phase of the emulsion ink of the present invention further contains a water-soluble organic solvent from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, thereby reducing the average particle size of the emulsion, improving storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter.
The water-soluble organic solvent refers to an organic solvent that, when dissolved in 100 mL of water at 25° C., dissolves in an amount of 10 mL or more.
The water-soluble organic solvent is preferably one that is normally used in the aqueous phase of water-in-oil emulsion inks and is miscible with water in any ratio, and examples of such solvents include alkanols having from 1 to 4 carbon atoms, polyhydric alcohols, polyhydric alcohol alkyl ethers, ketones, cyclic ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. Of these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are more preferred.
The boiling point of the water-soluble organic solvent is preferably 60° C. or higher, more preferably 90° C. or higher, and even more preferably 150° C. or higher, and is preferably 350° C. or lower, more preferably 330° C. or lower, and even more preferably 310° C. or lower.
The water-soluble organic solvent may be used alone or in combination of two or more kinds, so long as it is miscible with water in any ratio.

In the present invention, the aqueous phase may contain an oil-in-water polymer emulsion, a viscosity modifier, an antifoaming agent, a preservative, an antifungal agent, an antirust agent, etc., to the extent that the effects of the present invention are not impaired.

<Oil phase>
The oil phase of the emulsion ink of the present invention contains a water-insoluble organic solvent and an emulsifier from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase, thereby finely dispersing the emulsion, improving storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter.

(Non-water-soluble organic solvent)
The water-insoluble organic solvent refers to an organic solvent that, when dissolved in 100 mL of water at 25° C., dissolves in an amount of less than 10 mL.
As the water-insoluble organic solvent, either a non-polar organic solvent or a polar organic solvent can be used. These can be used alone or in combination of two or more kinds as long as they form a single continuous phase.

Examples of non-polar organic solvents include aliphatic hydrocarbon solvents such as paraffin-based, isoparaffin-based, and naphthenic solvents, and petroleum-based hydrocarbon solvents such as alicyclic hydrocarbon solvents and aromatic hydrocarbon solvents.
The initial boiling point of the non-polar organic solvent is preferably 90° C. or higher, more preferably 150° C. or higher, and is preferably 300° C. or lower, more preferably 250° C. or lower.
Commercially available non-polar organic solvents include the Isopar (trade name) series and Exxol (trade name) series (both manufactured by ExxonMobil Corporation); and the AF Solvent (trade name) series (manufactured by JXTG Nippon Oil & Energy Corporation).

Examples of the polar organic solvent include ester-based solvents and higher alcohol-based solvents.
The ester solvent is preferably a fatty acid ester solvent. Examples of the fatty acid ester solvent include fatty acid esters having 13 to 30 carbon atoms, such as isononyl isononanoate, isodecyl isononanoate, isotridecyl isononanoate, methyl laurate, isopropyl laurate, hexyl laurate, 2-ethylhexyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, isobutyl oleate, methyl linoleate, ethyl linoleate, isobutyl linoleate, butyl stearate, 2-ethylhexyl stearate, isopropyl isostearate, methyl soybean oil, isobutyl soybean oil, methyl tall oil, isobutyl tall oil, propylene glycol monocaprate, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, trimethylolpropane tri-2-ethylhexanoate, and glyceryl tri-2-ethylhexanoate.
Examples of higher alcohol solvents include higher alcohols having 12 to 20 carbon atoms, such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol.

From the viewpoint of improving the dispersion stability of the pigment in the aqueous phase to make the emulsion fine, improving the storage stability, print density and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter, the non-water-soluble organic solvent preferably includes an ester-based solvent, and more preferably includes an aliphatic ester-based solvent.
From the viewpoints of improving the dispersion stability of the pigment in the aqueous phase to make the emulsion fine, improving storage stability, print density and continuous ejection stability, and reducing deformation of the printed matter, the content of the ester solvent in the water-insoluble organic solvent is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, and is preferably 100% by mass or less, still more preferably 100% by mass.

(emulsifier)
There are no particular limitations on the emulsifier as long as it is contained in the oil phase and can emulsify the aqueous phase to form a water-in-oil emulsion, but lipophilic emulsifiers such as surfactants and polymer dispersants are preferred.
The lipophilic surfactant is preferably a nonionic surfactant having an HLB value of 6 or less. Examples of the nonionic surfactant include sorbitan fatty acid esters such as sorbitan monooleate, sorbitan sesquioleate, and sorbitan monostearate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; glycerin fatty acid esters such as glycerol monostearate and glycerol monooleate; polyoxyethylene glycerin fatty acid esters such as polyoxyethylene sorbit fatty acid ester and polyoxyethylene glycerin vegetable oil fatty acid ester; sucrose fatty acid esters such as sucrose stearate, sucrose palmitate, sucrose oleate, sucrose erucate, and sucrose laurate; polyethylene glycol fatty acid esters; polyglycerin condensed ricinoleate; polyoxyethylene alkyl ethers; polyoxyethylene alkylphenyl ethers; polyoxyethylene alkylamines/fatty acid amides; and polyoxyethylene polyoxypropylene alkyl ethers.
The lipophilic surfactants can be used alone or in combination of two or more kinds.

Examples of lipophilic polymer dispersants include polyester polyimines, polyester polyamines, polyalkylol aminoamides and their salts, polyether polyamines, hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, modified polyurethanes, modified poly(meth)acrylates, polyether ester-type anionic surfactants, naphthalene sulfonate formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, stearylamine acetate, and the like. Among these, one or more selected from polyester polyimines, polyester polyamines, polyalkylol aminoamides and their salts, and polyether polyamines are preferred, and polyester polyimines are more preferred. These may be used alone or in combination of two or more.

The polyester polyimine is preferably an amide or salt formed by reacting a polyalkyleneimine such as polyethyleneimine with a polyester having a carboxyl group such as a polymer of hydroxystearic acid or a polymer of a cyclic ester, and includes a dispersant having a graft structure in which two or more polyester chains are bonded as branches to a polyalkyleneimine chain as a backbone. When the non-water-soluble organic solvent contains an ester-based solvent, the steric repulsion of the polyester chain of the polyester polyimine in the oil phase suppresses the interaction between the dispersed phase droplet particles, and the coalescence of the dispersed phase droplet particles is suppressed, which is thought to stabilize the entire emulsion ink system and improve storage stability, print density, and continuous discharge stability.
Commercially available lipophilic polymer dispersants include, for example, the Solsperse (trade name) series manufactured by Lubrizol Japan Co., Ltd.; the Efka (trade name) series manufactured by Efka Chemicals; the Disparlon (trade name) series manufactured by Kusumoto Chemicals Co., Ltd.; and the Ajisper (trade name) series manufactured by Ajinomoto Co., Inc.

In the present invention, it is preferable that the oil phase does not contain a colorant such as a pigment, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, refining the emulsion, improving storage stability, print density, and continuous ejection stability, and from the viewpoint of reducing deformation of the printed matter.

[Method of manufacturing water-in-oil emulsion ink]
The water-in-oil emulsion ink of the present invention can be produced by mixing an oil phase component and an aqueous phase component and emulsifying the aqueous phase. Among these, from the viewpoints of improving the dispersion stability of the pigment in the aqueous phase to make the emulsion fine, improving storage stability, print density, and continuous discharge stability, and reducing deformation of printed matter, it is preferable to obtain the ink by a method including a step of emulsifying an aqueous pigment dispersion in which the pigment is dispersed in an aqueous medium (hereinafter also referred to as "aqueous pigment dispersion") in an oil phase.
The "aqueous medium" in the aqueous pigment dispersion means a medium in which water accounts for the largest proportion of the medium in which the pigment is dispersed.

When the pigment is dispersed in a non-crosslinked polymer (a), the aqueous pigment dispersion is preferably produced efficiently by a method including the following step 1.
Step 1: A step of dispersing a pigment mixture containing a pigment, a polymer (a) and water to obtain an aqueous pigment dispersion in which the pigment is dispersed in an aqueous medium by the polymer (a).

(Step 1)
Specifically, step 1 is preferably carried out by a method (1) in which a pigment mixture obtained by mixing a previously prepared aqueous dispersion of polymer (a) with a pigment is subjected to a dispersion treatment, or a method (2) in which a pigment mixture containing a pigment, polymer (a), an organic solvent, water, and, if necessary, a neutralizing agent, a surfactant, etc. is subjected to a dispersion treatment to obtain a dispersion, and then the organic solvent is removed from the dispersion, etc. Among these, method (1) is preferred from the viewpoints of improving storage stability, print density, and continuous ejection stability, and of reducing deformation of the printed matter.

In the case of the method (1), it is preferable to have the following step 1-1 before the step 1.
Step 1-1: A step of neutralizing a part of the acid groups of the polymer (a) with a neutralizing agent to obtain an aqueous dispersion of the polymer (a) (hereinafter, also referred to as "aqueous polymer dispersion (D)"). The preferred neutralizing agent used for neutralization in step 1-1 and the degree of neutralization of the polymer (a) are as described above. From the viewpoint of promoting sufficient and uniform neutralization, the neutralizing agent is preferably used in the form of an aqueous solution.

In the dispersion treatment in step 1, the 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.
As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used.
Examples of means for applying shear stress used in the present dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When the dispersion treatment is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the treatment pressure and the number of passes, and the cumulant average particle size of the aqueous pigment dispersion described below can also be adjusted.
From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less.
The number of passes is preferably 3 or more, more preferably 7 or more, from the viewpoint of reducing the particle size of the pigment, and is preferably 30 or less, more preferably 20 or less, from the viewpoint of the dispersion stability of the pigment.
When the pigment mixture contains an organic solvent, the organic solvent can be removed by a known method to obtain an aqueous pigment dispersion. It is preferable that the organic solvent in the obtained aqueous pigment dispersion is substantially removed, but it may remain as long as it does not impair the object of the present invention. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

(Step 2)
In the present invention, when the pigment is dispersed by the crosslinked polymer (A), the aqueous pigment dispersion is preferably obtained by a method including, after step 1, preferably step 1-1, and further including the following step 2 after step 1.
Step 2: A step of adding a crosslinking agent to the aqueous pigment dispersion obtained in step 1, and crosslinking the polymer (a) with the crosslinking agent to obtain an aqueous pigment dispersion in which the pigment is dispersed in the crosslinked polymer (A).

In step 2, the preferred crosslinking agent and degree of crosslinking are as described above.
The temperature of the crosslinking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, and even more preferably 60° C. or higher, and is preferably 95° C. or lower, more preferably 85° C. or lower, and even more preferably 75° C. or lower.
From the viewpoints of completion of the crosslinking reaction and economic efficiency, the time for the crosslinking treatment is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, and is preferably 12 hours or less, more preferably 10 hours or less, even more preferably 8 hours or less.

From the viewpoint of improving dispersion stability and facilitating the production of ink, the non-volatile component concentration (solid content concentration) of the aqueous pigment dispersion is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less. The solid content concentration of the aqueous pigment dispersion is measured by the method described in the examples.

[0053] From the viewpoints of reducing coarse particles, refining the emulsion, and improving storage stability, print density, and ejection stability, the cumulant average particle size of the aqueous pigment dispersion is preferably 50 nm or more, more preferably 60 nm or more, even more preferably 70 nm or more, still more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 130 nm or less, still more preferably 100 nm or less, and still more preferably less than 100 nm.
The cumulant average particle size of the aqueous pigment dispersion is measured by the method described in the Examples.

The aqueous pigment dispersion is preferably a dispersion in which pigment-containing polymer particles are dispersed in an aqueous medium. The form of the pigment-containing polymer particles is not particularly limited as long as the particles are formed from at least the pigment and the non-crosslinked polymer (a) or the crosslinked polymer (A), but as described above, the form of the particles is preferably a form in which the pigment is encapsulated in the polymer (a) or the crosslinked polymer (A).
The aqueous pigment dispersion may contain 1% by mass or more and 10% by mass or less of glycerin, polyethylene glycol or the like as a moisturizing agent to prevent drying, and may also contain additives such as antifungal agents.
The above-mentioned additives may be added when the pigment is dispersed in the polymer (a), or may be added after the pigment is dispersed or after crosslinking.

In the present invention, when the aqueous phase of the emulsion ink contains the above-mentioned surfactant, water-soluble organic solvent, or optional component, the aqueous pigment dispersion can be mixed with the surfactant, water-soluble organic solvent, or optional component as necessary, or the water content can be adjusted to prepare an aqueous phase component, and then the aqueous phase component and an oil phase component can be mixed and emulsified to prepare an emulsion ink.
The mixing mass ratio of the aqueous phase component to the oil phase component [aqueous phase component/oil phase component] is, from the viewpoint of productivity and from the viewpoint of obtaining a stable emulsion, preferably 5/95 or more, more preferably 10/90 or more, even more preferably 15/85 or more, still more preferably 20/80 or more, and is preferably 45/65 or less, more preferably 40/60 or less, more preferably 35/65 or less, still more preferably 30/70 or less, and still more preferably 25/75 or less.

From the viewpoint of refining the emulsion and improving storage stability, print density and continuous ejection stability, and from the viewpoint of using the emulsion ink for inkjet recording, the viscosity of the aqueous phase component at 25°C is preferably 300 mPa·s or less, more preferably 200 mPa·s or less, even more preferably 150 mPa·s or less, still more preferably 100 mPa·s or less, still more preferably 70 mPa·s or less, still more preferably 50 mPa·s or less, still more preferably 40 mPa·s or less, still more preferably 35 mPa·s or less, and is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, still more preferably 15 mPa·s or more, and still more preferably 20 mPa·s or more.
The viscosity of the aqueous phase component is measured by the method described in the Examples.

If necessary, the emulsion ink of the present invention may further contain various additives commonly used in water-in-oil emulsion inks, such as a humectant, wetting agent, penetrating agent, dispersant, surfactant, viscosity modifier, defoamer, preservative, antifungal agent and rust inhibitor, and may further be subjected to filtration treatment using a filter or the like.
The contents and physical properties of each component in the emulsion ink of the present invention are as follows.

From the viewpoint of improving print density, the content of the pigment in the emulsion ink is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and still more preferably 5% by mass or more, and from the viewpoint of reducing the ink viscosity when the solvent evaporates and improving storage stability and continuous ejection stability, the content of the pigment in the emulsion ink is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less.
The pigment content in the aqueous phase of the emulsion ink is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving print density, and is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of reducing the ink viscosity when the solvent evaporates and improving storage stability and continuous ejection stability.

The total content of the pigment and the polymer (a) or the crosslinked polymer (A) in the emulsion ink is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 6% by mass or more, and is preferably 18% by mass or less, more preferably 13% by mass or less, even more preferably 10% by mass or less.

When a surfactant is contained in the aqueous phase of the emulsion ink, the content of the surfactant in the emulsion ink is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, from the viewpoint of improving storage stability, print density, and continuous ejection stability, and is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less.

The content of the water-soluble organic solvent in the emulsion ink is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of adjusting the viscosity of the emulsion ink, improving the storage stability and continuous ejection stability, and reducing deformation of the printed matter, and is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of improving the print density.

The content of the water-insoluble organic solvent in the emulsion ink is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 65% by mass or more, from the viewpoint of adjusting the viscosity of the emulsion ink, improving storage stability, and reducing deformation of the printed matter, and is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, from the viewpoint of improving print density.

The content of the emulsifier in the emulsion ink is preferably 0.3% by mass or more, more preferably 0.7% by mass or more, and even more preferably 1% by mass or more, from the viewpoint of refining the emulsion and improving storage stability, print density, and continuous ejection stability, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of adjusting the viscosity of the emulsion ink.

From the viewpoints of reducing coarse particles, refining the emulsion, and improving storage stability, print density, and ejection stability, the cumulant average particle size of the pigment particles in the aqueous phase of the emulsion ink is preferably 50 nm or more, more preferably 60 nm or more, even more preferably 70 nm or more, still more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 130 nm or less, still more preferably 100 nm or less, and still more preferably less than 100 nm.
The cumulant average particle size of the pigment particles in the aqueous phase of the emulsion ink can be determined, for example, by subjecting the emulsion ink to centrifugal separation under conditions that maintain the dispersed state of the pigment particles in the aqueous phase, demulsifying the emulsion ink to separation into an aqueous phase and an oil phase, recovering the aqueous phase component, and measuring the cumulant average particle size of the pigment particles in the aqueous phase component by the method described in the examples.
The centrifugation conditions capable of maintaining the dispersion state of the pigment particles in the aqueous phase can be set by observing the dispersion state of the pigment particles under a microscope before and after the centrifugation treatment.

In the present invention, the average particle size of the emulsion is, from the viewpoint of refining the emulsion to improve storage stability, print density and continuous ejection stability, and from the viewpoint of reducing deformation of printed matter, preferably 2.0 μm or less, more preferably 1.7 μm or less, even more preferably 1.2 μm or less, still more preferably 1 μm or less, still more preferably 0.8 μm or less, still more preferably 0.6 μm or less, still more preferably 0.5 μm or less, and still more preferably 0.3 μm or less, and from the viewpoint of ease of production, preferably 0.1 μm or more, more preferably 0.2 μm or more, and still more preferably 0.25 μm or more.
The average particle size of the emulsion is measured by the method described in the Examples.

The viscosity of the emulsion ink of the present invention at 25°C is preferably 2 mPa·s or more, more preferably 5 mPa·s or more, even more preferably 7 mPa·s or more, and still more preferably 9 mPa·s or more, and from the viewpoint of using the emulsion ink for inkjet recording, preferably 20 mPa·s or less, more preferably 17 mPa·s or less, even more preferably 15 mPa·s or less, and still more preferably 13 mPa·s or less.
The viscosity of the emulsion ink is measured by the method described in the examples.

From the viewpoint of continuous ejection stability, the emulsion ink of the present invention is preferably used for inkjet recording. The emulsion ink can be loaded into a known inkjet recording device and ejected as ink droplets onto a printing medium to record an image or the like.
The printing medium to be used includes highly water-absorbent plain paper, low water-absorbent coated paper, and non-water-absorbent resin film. The coated paper includes general-purpose glossy paper, multicolor foam gloss paper, etc. The resin film is preferably at least one selected from polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. The resin film may be a corona-treated substrate.
Among these, plain paper is preferred from the viewpoints of print density and deformation of printed matter.

In the following Preparation Examples, Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.
Various physical properties were measured by the following methods.

(1) Measurement of Acid Value of Polymer (a) or Crosslinked Polymer (A) The measurement was performed in accordance with JIS K0070, except that the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of ethanol and toluene [ethanol:toluene=1:1 (volume ratio)].

(2) Measurement of Weight-Average Molecular Weight of Polymer (a) Using a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, a weight-average molecular weight of polymer (a) was measured by gel permeation chromatography (GPC apparatus (model: HLC-8320GPC, manufactured by Tosoh Corporation), columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H, all trade names manufactured by Tosoh Corporation), flow rate: 0.5 mL/min) using a monodisperse polystyrene kit with known molecular weights [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick B (F-100), F-200), F-100, F-200, F-300, F-400, F-500, F-600, F-700, F-800, F-900, F-1000, F-1000, F-2000, F-3000, F-400, F-500, F-600, F-700, F-800, F-900, F-10 ... C (F-288, F-40, F-4, A-5000, A-500), all of which are product names manufactured by Tosoh Corporation).
The measurement sample was prepared by mixing 0.1 g of polymer (a) with 10 mL of the eluent in a glass vial, stirring the mixture with a magnetic stirrer at 25° C. for 10 hours, and filtering the mixture with a syringe filter (product name: DISMIC-13HP, membrane filter material: hydrophilic PTFE, pore size 0.2 μm, manufactured by Advantec Co., Ltd.).

(3) Measurement of solid content concentration 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, after which it was accurately weighed, maintained at 105° C. for 2 hours to remove volatile matter, and then left in a desiccator at room temperature (25° C.) for 15 minutes, after which the mass was measured. The mass of the sample after removal of volatile matter was taken as the solid content, and divided by the mass of the sample added to obtain the solid content concentration.

(4) Measurement of cumulant average particle diameter Cumulant analysis was performed using a laser particle analysis system (model: ELS-8000, manufactured by Otsuka Electronics Co., Ltd.) to measure the cumulant average particle diameter. 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 medium. The concentration of the measurement sample was 5 x ^10-3 % (converted into solids concentration).

(5) Average particle size of emulsion The volume median particle size ( _D50 ) measured using a laser diffraction/scattering particle size measuring device "Mastersizer 3000" (manufactured by Malvern Panalytical) was taken as the average particle size of the emulsion. The measurement sample was prepared by adding hexyl laurate (product name: Exepar HL, manufactured by Kao Corporation, viscosity at 20°C 6.8 mPa·s) to an emulsion ink and adjusting the concentration to give a scattering intensity of 5 to 15%. The measurement was performed under conditions of a particle refractive index of 1.59 (absorption coefficient 0.1, density 1 g/ ^cm3 ) and a dispersion medium refractive index of 1.44.

(6) Viscosity of Water Phase Component and Water-in-Oil Emulsion Ink The viscosity was measured at 25° C. using an E-type viscometer (model: TV-25, manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34′×R24, rotation speed 50 rpm).

<Preparation of Polymer (a)>
Preparation Example 1
A raw material monomer was prepared by mixing 19.2 parts of acrylic acid, 70.8 parts of styrene, and 10.0 parts of α-methylstyrene. A reaction vessel was charged with 10 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the raw material monomer, and the atmosphere was thoroughly replaced with nitrogen gas.
Meanwhile, a mixture of the remaining raw material monomer (90%), 0.27 parts of the polymerization chain transfer agent, 40 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (product name: V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2,2'-azobis(2,4-dimethylvaleronitrile)) (hereinafter referred to as "V-65") was placed in a dropping funnel, and the raw material monomer 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 stirring for 2 hours from the end of the dropping while maintaining the contents in the reaction vessel at 65°C, a solution in which 0.15 parts of the polymerization initiator was dissolved in 2.5 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 solution of a polymer (a1) having a carboxy group. The weight average molecular weight and acid value are shown in Table 1.

Preparation Example 2
A solution of a polymer (a2) having a carboxy group was obtained in the same manner as in Preparation Example 1, except that the raw material monomer composition was changed as shown in Table 1. The weight average molecular weight and acid value are shown in Table 1.

Preparation Example 3
37.0 parts of methacrylic acid, 33.0 parts of benzyl acrylate, 40.0 parts of styrene macromer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6,000, solid content concentration 50%) (hereinafter referred to as "styrene macromer") (20.0 parts as solid content), and 10.0 parts of polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: Blenmer PP-800, average number of moles of propylene oxide added: 13, terminal: hydroxyl group) (hereinafter referred to as "PP-800") were mixed to prepare a raw material monomer. In a reaction vessel, 10 parts of MEK, 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the raw material monomer were added and mixed, and nitrogen gas replacement was performed sufficiently.
Meanwhile, a mixed solution of the remaining raw material monomers (90%), 0.27 parts of the polymerization chain transfer agent, 40 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (V-65) was placed in a dropping funnel, and the subsequent procedures were carried out in the same manner as in Preparation Example 1 to obtain a solution of a polymer (a3) having a carboxy group. The weight average molecular weight and acid value are shown in Table 1.

<Production of polymer aqueous dispersion (D) (step 1-1)>
Production Example 1-1
The polymer solution obtained in Preparation Example 1 was dried under reduced pressure to obtain 80.0 parts of polymer (a1), and 316.0 parts of ion-exchanged water and 25.3 parts of 5N aqueous sodium hydroxide solution were added to neutralize the ratio of the number of moles of sodium hydroxide to the number of moles of carboxyl groups of polymer (a1) to 50 mol% (neutralization degree: 50 mol%). Then, the mixture was heated at 90°C for 5 hours while stirring at 150 rpm to obtain a polymer aqueous dispersion (D1) (solid concentration: 20%).

Production Examples 1-2 to 1-3
Polymer aqueous dispersions (D2) and (D3) (solid concentration: 20% and degree of neutralization: 50 mol%) were obtained in the same manner as in Production Example 1-1, except that the type of polymer (a), the amount of the aqueous sodium hydroxide solution, and the amount of ion-exchanged water were changed as shown in Table 2.

<Production of Water-Based Pigment Dispersion (Step 1 and Step 2)>
Production Example 2-1
(Step 1)
400.0 parts of ion-exchanged water and 100.0 parts of black pigment (carbon black, trade name: MONARCH717, manufactured by Cabot Corporation, DBP oil absorption 53 mL/100 g) were added to 211.1 parts of the polymer aqueous dispersion (D2) obtained in Production Example 1-2, and the mixture was stirred for 60 minutes using a Disper (manufactured by Asada Iron Works Co., Ltd., trade name: Ultra Disper) at 20 ° C. with a Disper blade rotating at 7,000 rpm. The resulting mixture was subjected to 10 pass dispersion treatment at a pressure of 200 MPa using a Microfluidizer (manufactured by Microfluidics, trade name) to obtain a dispersion treatment product.
The obtained dispersion was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to remove coarse particles, and then an aqueous pigment dispersion (i-1) having a solid content concentration of 20% was obtained.
(Step 2)
100.0 parts (solids concentration 20%) of the obtained water-based pigment dispersion (i-1) was placed in a screw-capped glass bottle, and 1.66 parts of trimethylolpropane polyglycidyl ether (product name: Denacol EX-321, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 139, water solubility: 27%) (hereinafter referred to as "EX-321") as a crosslinking agent was added so that 50 mol % of all carboxy groups in the polymer (a2) were crosslinked (crosslinking degree 50 mol %), and the bottle was sealed and heated at 70° C. for 5 hours while stirring with a stirrer. After 5 hours had passed, the temperature was lowered to room temperature, and the mixture was filtered using a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and further concentrated under reduced pressure so that the pigment content in the obtained aqueous pigment dispersion was 36.0 mass %, thereby obtaining an aqueous black pigment dispersion (hereinafter also referred to as "black pigment dispersion") Bk-I (mass ratio of pigment to crosslinked polymer (A) [pigment/crosslinked polymer (A)]=1.9, solid content concentration of 54.1%, cumulant average particle size: 95 nm).

Manufacturing Examples 2-2 to 2-10
Black pigment dispersions Bk-II to Bk-X were obtained in the same manner as in Production Example 2-1, except that the type and amount of the polymer aqueous dispersion (D) and the amount of the crosslinking agent were changed as shown in Table 3.

<Production of water-in-oil emulsion ink>
Example 1
An aqueous phase component was prepared by mixing 16.7 parts of the black pigment dispersion Bk-I obtained in Production Example 2-1, 2.0 parts of Surfynol 465 (trade name, EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, average EO addition mole number: 10, HLB: 13, manufactured by Nissin Chemical Industry Co., Ltd.) as a surfactant, 2.0 parts of glycerin (concentrated glycerin for cosmetics, manufactured by Kao Corporation) as a water-soluble organic solvent, and 1.8 parts of ion-exchanged water.
Separately, 74.5 parts of hexyl laurate (product name: Exepar HL, manufactured by Kao Corporation) as a water-insoluble organic solvent and 3.0 parts of Solsperse 11200 (product name, polymer dispersant, active content 50%, manufactured by Lubrizol Corporation) as an emulsifier were mixed to prepare an oil phase component.
Using a homogenizer (product name: ULTLRA-TURRAX, model: T25 digital, shaft generator (model: S25N-25F), both manufactured by IKA Japan Co., Ltd.), the aqueous phase component was added dropwise to the oil phase component while stirring it at 5,000 rpm. The mixture was then stirred at 12,000 rpm for 3 minutes to obtain water-in-oil emulsion ink Bk-1 having a pigment content of 6.0%. The mass ratio of the pigment to the crosslinked polymer (A) in the aqueous phase of the emulsion ink Bk-1 [pigment/crosslinked polymer (A)], the water content, and the average particle size of the emulsion are shown in Table 4.

Examples 2 to 9, Comparative Examples 1 to 3
Water-in-oil emulsion inks with a pigment content of 6.0% were obtained in the same manner as in Example 1, except that the types or amounts of the components constituting the oil phase component and the aqueous phase component were changed as shown in Table 4. Table 4 shows the mass ratio of the pigment to the crosslinked polymer (A) in the aqueous phase of each emulsion ink [pigment/crosslinked polymer (A)], the water content, and the average particle size of the emulsion.
The Isopar M in Table 4 is as follows:
Isopar M (product name, isoparaffin solvent, manufactured by Ando Parachemie Co., Ltd.)

<Evaluation test of water-in-oil emulsion ink>
The emulsion inks obtained in the examples and comparative examples were evaluated for storage stability, deformation of printed matter, print density, and continuous ejection stability. The results are shown in Table 4.

[Evaluation of storage stability]
The obtained emulsion ink was placed in a 100 mL screw vial and stored at 60° C. After standing, the emulsion ink was visually observed for separation of the oil and water phases and flocculated sediment, and evaluated according to the following criteria.
(Evaluation Criteria)
A: Even after storage for one week, there was no separation of the oil and water phases of the emulsion ink, and no flocculated sediment.
B: After one day of storage, there was no separation of the oil and water phases of the emulsion ink, and no flocculated sedimentation, but after one week of storage, there was separation of the oil and water phases of the emulsion ink, or there was flocculated sedimentation.
C: Immediately after preparation of the emulsion ink, there was no separation of the oil and water phases or no flocculated sediment, but after storage for 1 day, there was separation of the oil and water phases of the emulsion ink or no flocculated sediment.
D: Separation of the oil phase and the water phase or flocculation and sedimentation were observed immediately after preparation of the emulsion ink.

[Evaluation of deformation (curl amount) of printed matter]
The obtained emulsion ink was filled into an inkjet printer (product name: Business Printer PX-105, manufactured by Seiko Epson Corporation), and a solid image was printed on plain paper (product name: Xerox Business 4200 Copy Paper, manufactured by Fuji Xerox Co., Ltd.) under an environment of room temperature of 23°C and relative humidity of 50% RH. The obtained print was placed on a horizontal table with the printed surface facing up, and left for one day under the same environmental conditions. After leaving for one day, the heights of the four corners of the print from the horizontal table were measured, and the average value was calculated as the curl amount, and the deformation of the print was evaluated. The smaller the curl amount, the smaller the deformation of the print, indicating that the deformation of the print was reduced. A curl amount of 2.0 mm or less is suitable for practical use.

[Evaluation of Print Density]
The obtained emulsion ink was filled into an inkjet printer (Business Printer PX-105), and a 1 cm x 1 cm solid image was printed on plain paper (Xerox Business 4200 copy paper) under an environment of room temperature 23°C and relative humidity 50% RH, and the obtained print was left for one day under the same conditions. The print density of the print after being left for one day was measured using an optical densitometer (product name: SpectroEye, manufactured by GretagMacbeth). The measurement was performed at 10 arbitrary points on the print, changing the measurement location, and the average value was taken as the print density.

[Evaluation of Continuous Discharge Stability]
The obtained emulsion ink was filled into an inkjet printer (Business Printer PX-105), and a nozzle check pattern image in which 105 oblique lines corresponding to the diagonal portions of a 0.6 cm x 3.5 cm rectangle were arranged in parallel at 0.3 cm intervals on plain paper (Xerox Business 4200 copy paper) was continuously printed at a printing speed of one sheet per 20 seconds under an environment of room temperature of 23°C and relative humidity of 50% RH, and the occurrence of nozzle chipping was visually observed and evaluated according to the following criteria.
(Evaluation Criteria)
A: No nozzle chipping occurred even after printing 200 sheets.
B: Nozzle missing occurred between 100 and 199 printed sheets.
C: Nozzle chipping occurred between 10 and 99 printed sheets.
D: Nozzle chipping occurred up to the 9th printed sheet.
In the above evaluation criteria, a rating of A or B is suitable for practical use, a rating of C is acceptable for practical use, and a rating of D increases the frequency of nozzle cleaning, making it problematic for practical use.

From Table 4, it can be seen that, compared to Comparative Examples 1 to 3, Examples 1 to 9 have a mass ratio [pigment/crosslinked polymer (A)] of the pigment in the aqueous phase of the emulsion ink to the crosslinked polymer (A) used as a polymer dispersant of 1.5 to 14, and the water content in the emulsion ink is 20 mass% or less, so that they have excellent storage stability and continuous ejection stability, high print density, and small curl amount, suppressing deformation of the printed matter. In addition, the viscosity of the emulsion inks of Examples 1 to 9 was all within the appropriate range for inkjet recording.

The emulsion ink of the present invention and the method for producing the emulsion ink have excellent storage stability and continuous ejection stability, and when printed on plain paper, it is possible to obtain a printed matter with high print density and little deformation after printing. Furthermore, the emulsion ink of the present invention is useful for inkjet recording.

Claims (10)

A water-in-oil emulsion ink having a water phase in an oil phase,
the aqueous phase comprises water, a pigment, and a polymeric dispersant;
a mass ratio of the pigment to the polymer dispersant in the aqueous phase [pigment/polymer dispersant] is 2.3 or more and 14 or less;
The oil phase contains a water-insoluble organic solvent and an emulsifier;
The water-in-oil emulsion ink has a water content of 20 mass % or less. The water-in-oil emulsion ink according to claim 1, wherein the polymer dispersant is a crosslinked polymer (A) having a crosslinked structure. The water-in-oil emulsion ink according to claim 2, wherein the acid value of the crosslinked polymer (A) is 70 mg KOH/g or more and 200 mg KOH/g or less. The water-in-oil emulsion ink according to claim 3, in which at least a portion of the acid groups of the crosslinked polymer (A) are neutralized. The water-in-oil emulsion ink according to any one of claims 2 to 4, wherein the crosslinked polymer (A) is a polymer obtained by crosslinking a non-crosslinked polymer (a) with a crosslinking agent. A water-in-oil emulsion ink according to any one of claims 1 to 5, in which the average particle size of the emulsion is 2.0 μm or less. The water-in-oil emulsion ink according to any one of claims 1 to 6, wherein the non-water-soluble organic solvent contains an ester-based solvent, and the content of the ester-based solvent in the non-water-soluble organic solvent is 60% by mass or more. The water-in-oil emulsion ink according to any one of claims 1 to 7, which is for inkjet recording. The method for producing a water-in-oil emulsion ink according to any one of claims 1 to 8, comprising a step of emulsifying an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium, in an oil phase. 10. The method for producing a water-in-oil emulsion ink according to claim 9, wherein the aqueous pigment dispersion is obtained by a method including the following steps 1-1, 1, and 2:
Step 1-1: A step of neutralizing a portion of the acid groups of the polymer (a) with a neutralizing agent to obtain an aqueous dispersion of the polymer (a). Step 1: A step of mixing the aqueous dispersion of the polymer (a) obtained in step 1-1 with a pigment to obtain a pigment mixture, and then dispersing the pigment mixture to obtain an aqueous pigment dispersion in which the pigment is dispersed in an aqueous medium by the polymer (a). Step 2: A step of adding a crosslinking agent to the aqueous pigment dispersion obtained in step 1, crosslinking the polymer (a) with the crosslinking agent, and obtaining an aqueous pigment dispersion in which the pigment is dispersed by the crosslinked polymer (A).