JP2022122635A - Water-in-oil emulsion ink - Google Patents

Abstract

To provide a water-in-oil emulsion ink that is applied to a highly water-absorbable printing medium and gives a printed material, which quickly exhibits good fixability just after its printing and has high print density, and a method for producing the water-in-oil emulsion ink.SOLUTION: An water-in-oil emulsion ink has an aqueous phase in an oil phase, the aqueous phase containing a pigment, the water-in-oil emulsion ink having a water content of 10 mass% or more and 25 mass% or less, and the emulsion represented by a formula (1) having a particle size distribution width of 2.0 or less. There is also provided a method for producing the water-in-oil emulsion ink. The particle size distribution width of the emulsion=(D90-D10)/D50 (1) (where, D10, D50 and D90 each denote a particle size corresponding to 10%, 50% and 90% of a cumulative volume frequency of the emulsion particle sizes calculated in an ascending order).SELECTED DRAWING: None

Description

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

The inkjet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and adhered to a printing medium to obtain a printed material on which characters and images are recorded. This method has the advantages of easy and inexpensive full-color printing and non-contact printing. Therefore, in recent years, it has begun to be applied not only to consumer printing for general consumers, but also to commercial and industrial printing fields. there is
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 a water-based ink, the print density is high because the water-absorbing nature of the plain paper is high, but on the other hand, the water contained in the water-based ink causes the fibers of the plain paper to swell, causing the printed matter to curl. There is a problem that it is deformed by
In addition, high-speed printing is required in the fields of commercial printing and industrial printing, and in order to cope with this high-speed printing, a printing machine adopting a line head type inkjet recording system has been developed, and an oil-based pigment ink is used. When the oil-based pigment ink is used for printing on plain paper, deformation of the printed matter can be reduced, but there is a problem that the ink penetrates into the inside of the printed matter and the printing density of the printed matter becomes low.
Therefore, the use of water-in-oil (W/O) emulsion ink is being studied.

For example, Patent Literature 1 discloses an ink jet emulsion ink comprising an oil phase and an aqueous phase, which is capable of obtaining a sufficient optical density of an image when recorded on plain paper and which can reduce paper deformation. A water-in-oil emulsion ink for inkjet is disclosed, wherein the aqueous phase contains water and a colorant, and the colorant is a modified pigment containing a polymer.

JP 2015-189859 A

A water-in-oil emulsion ink has an oil phase as a continuous phase and an aqueous phase emulsified in the oil phase. However, when printing is performed on a highly water-absorbing printing medium such as plain paper, the pigment remains on the surface layer of the printing medium. It was also found that the print density was not sufficient.
The present invention provides a water-in-oil emulsion ink that exhibits good fixability immediately after printing when printed on a highly water-absorbing printing medium, and can produce printed matter with high print density, and the ink in the oil. An object of the present invention is to provide a method for producing a water emulsion ink.

The present inventors have developed a water-in-oil emulsion ink having a water phase in an oil phase, the water phase containing a pigment, and the water content in the water-in-oil emulsion ink being within a predetermined range. The present inventors have found that the above problem can be solved by setting the particle size distribution width of the emulsion represented by the predetermined formula to a predetermined value or less.
That is, the present invention provides the following [1] and [2].
[1] A water-in-oil emulsion ink having an aqueous phase in an oil phase,
the aqueous phase contains a pigment;
The water-in-oil emulsion ink has a water content of 10% by mass or more and 25% by mass or less,
A water-in-oil emulsion ink in which the particle size distribution width of the emulsion represented by the following formula (1) is 2.0 or less.
Emulsion particle size distribution width = (D ₉₀ - D ₁₀ )/D ₅₀ (1)
(In formula (1), D ₁₀ , D ₅₀ and D ₉₀ represent particle diameters corresponding to cumulative volume frequencies of 10%, 50% and 90%, respectively, calculated from the smaller emulsion particle diameter.)
[2] The method for producing a water-in-oil emulsion ink according to [1] above, which comprises 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 exhibits good fixability immediately after printing when printed on a highly water-absorbing printing medium, and can produce printed matter with high print density, and the ink in the oil. A method for producing a water emulsion ink can be provided.

[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 a water phase in the oil phase, which is a continuous phase, and the water phase contains a pigment. The content of water in the water-in-oil emulsion ink is 10% by mass or more and 25% by mass or less, and the particle size distribution width of the emulsion represented by the following formula (1) is 2.0 or less.
Emulsion particle size distribution width = (D ₉₀ - D ₁₀ )/D ₅₀ (1)
(In formula (1), D ₁₀ , D ₅₀ and D ₉₀ represent particle diameters corresponding to cumulative volume frequencies of 10%, 50% and 90%, respectively, calculated from the smaller emulsion particle diameter.)
In the present invention, when printing is performed on a highly water-absorbing printing medium, it is also referred to as "initial fixability" to exhibit good fixability immediately after printing.

When the water-in-oil emulsion ink of the present invention is printed on a highly water-absorbing printing medium, it exhibits good fixability immediately after printing, and can provide printed matter with high print density. Although the reason is not clear, it is considered as follows.
In the present invention, by setting the water content in the water-in-oil emulsion ink within a predetermined range, the viscosity of the water phase relative to the viscosity of the oil phase can be set within an appropriate range. The particle size distribution width of the emulsion represented is a predetermined value or less, the particle size distribution width is narrow, and the aqueous phase component dispersed in the oil phase of the water-in-oil emulsion ink is as high as that of plain paper. In contact with a water-absorbent print medium, the speed at which the aqueous phase component penetrates into the print medium fibers can be made uniform, so even in a state where the water is not completely dried immediately after printing, the pigment particles It is speculated that non-uniform adhesion to the print medium fibers can be reduced, and initial fixability and print density can be improved.

In the present invention, the particle size distribution width of the emulsion is represented by the following formula (1).
Emulsion particle size distribution width = (D ₉₀ - D ₁₀ )/D ₅₀ (1)
(In formula (1), D ₁₀ , D ₅₀ and D ₉₀ represent particle diameters corresponding to cumulative volume frequencies of 10%, 50% and 90%, respectively, calculated from the smaller emulsion particle diameter.)
D ₁₀ , D ₅₀ and D ₉₀ used for calculating the particle size distribution width represented by the formula (1) of the emulsion ink are measured by the method described in Examples.
When the particle size distribution width of the emulsion is wide, the value of (D ₉₀ −D ₁₀ )/D ₅₀ is large, and when the particle size distribution width of the emulsion is narrow, (D ₉₀ −D ₁₀ )/D ₅₀ (D ₉₀ −D ₁₀ )/D ₅₀ can be used as an index of the particle size distribution width of the emulsion.
The particle size distribution width represented by the formula (1) of the emulsion ink of the present invention is 2.0 or less, preferably 1.7 or less, more preferably 1.7 or less, from the viewpoint of improving initial fixability and print density. 1.5 or less, more preferably 1.3 or less, still more preferably 1.0 or less, still more preferably 0.7 or less, and from the viewpoint of ease of production, preferably 0.2 or more, more It is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more.

In the present invention, the particle diameter _D50 of the emulsion is preferably 1.5 μm or less, more preferably 1.2 μm or less, and even more preferably 1 μm, from the viewpoint of improving the initial fixability and print density by making the emulsion finer. Below, more preferably 0.8 μm or less, still more preferably 0.6 μm or less, still more preferably 0.4 μm or less, and from the viewpoint of ease of production, preferably 0.1 μm or more, more preferably It is 0.2 μm or more, more preferably 0.25 μm or more, and even more preferably 0.3 μm or more.
The particle size _D50 of the emulsion is measured by the method described in the Examples.

The content of water in the emulsion ink of the present invention is 10% by mass or more, preferably 11% by mass or more, more preferably 12% by mass or more, and even more preferably, from the viewpoint of improving initial fixability and print density. 13% by mass or more, more preferably 14% by mass or more, and 25% by mass or less, preferably 23% by mass or less, more preferably 18% by mass or less, even more preferably 17% by mass or less, and even more Preferably, it is 16% by mass or less.

<Aqueous phase>
The aqueous phase contains a pigment from the viewpoint of print density.
(pigment)
Pigments according to the present invention may be either inorganic pigments or organic pigments, and lake pigments and fluorescent pigments may also be used. In addition, if necessary, they can be used in combination with an extender pigment.
Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide and chromium oxide, and pearl luster pigments. Carbon black is particularly preferred for black ink.
The type of carbon black is not particularly limited and includes furnace black, lamp black, acetylene black, channel black and the like.
The DBP oil absorption of 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. be.
The DBP oil absorption is an oil absorption measured by the DBP method, and specifically, it is 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; Examples include polycyclic pigments such as linone 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, and green can be used.
Specific examples of preferred organic pigments include C.I. I. Pigment Yellow, C.I. I. Pigment Red, C.I. I. pigment orange, C.I. I. pigment violet, C.I. I. pigment blue, and C.I. I. One or more types of each product number selected from Pigment Green.
Examples of extender pigments include silica, calcium carbonate, and talc.
Pigments can be used singly or in combination of two or more.

From the viewpoint of improving the print density, the content of the pigment in the emulsion ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and even more preferably 5% by mass. % or more, and from the viewpoint of lowering the viscosity of the ink when the solvent is volatilized and improving the initial fixability, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less. .

(Polymer Dispersant A)
From the viewpoint of improving the dispersion stability of the pigment in the water phase and improving the initial fixability and print density, the aqueous phase preferably further contains a polymer dispersant A, and the pigment is the same as the above. Therefore, those dispersed with the polymer dispersant A are preferable.
The polymer dispersant A is not particularly limited as long as it has at least pigment dispersibility, and examples thereof include polyester-based resins, polyurethane-based resins, vinyl-based resins, and the like.
As the polymer dispersant A, both a non-crosslinked polymer and a polymer having a crosslinked structure can be used from the viewpoint of initial fixability and print density.
When the polymer dispersant A is a non-crosslinked polymer, the polymer dispersant A is preferably carboxyl from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density. It is a vinyl polymer (a) having a group (hereinafter also simply referred to as "vinyl polymer (a)" or "polymer (a)").

[Vinyl polymer (a) having a carboxy group]
From the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density, the vinyl polymer (a) preferably comprises a structural unit derived from a carboxy group-containing monomer and a hydrophobic monomer derived from It may contain a structural unit and may further contain a structural unit derived from a nonionic monomer.

[Carboxy group-containing monomer]
A carboxy group-containing monomer is preferably used as a monomer component of the polymer (a) from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density.
Carboxy group-containing monomers include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid and the like, preferably (meth)acrylic acid. , more preferably acrylic acid.
As used herein, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.
The carboxy group-containing monomers may be used alone or in combination of two or more.

[Hydrophobic Monomer]
A hydrophobic monomer is used as a monomer component of the polymer (a) from the viewpoint of improving the adsorption of the polymer to the pigment, improving the dispersion stability of the pigment in the aqueous phase, and improving the initial fixability and print density. preferably used.
As used herein, the term "hydrophobic" means that the amount dissolved in 100 g of deionized water at 25° C. until the monomer is saturated is less than 10 g. The dissolved amount of the hydrophobic monomer is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of the adsorption of the polymer to the pigment.
Hydrophobic monomers include aromatic group-containing monomers and (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols.
As used herein, "(meth)acrylate" is at least one selected from acrylate and methacrylate.
The hydrophobic monomers may be used singly or in combination of two or more.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, more preferably at least one selected from styrene-based monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500. The aromatic group-containing monomer may have a substituent containing a heteroatom.
The styrenic monomer is preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, more preferably at least one selected from styrene and α-methylstyrene. is.
Aromatic group-containing (meth)acrylate is preferably at least one selected from phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate, 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, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, (meth)acrylates having a linear alkyl group such as stearyl (meth)acrylate; isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, (meth)acrylates having a branched chain alkyl group such as isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; alicyclic alkyl such as cyclohexyl (meth)acrylate group-containing (meth)acrylates, and the like.

In the present invention, a hydrophobic macromonomer may be used as the hydrophobic monomer constituting the polymer (a).
A macromonomer is a compound having a number average molecular weight of 500 or more and 100,000 or less having a polymerizable functional group at one end. can be used. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, more preferably a methacryloyloxy group.
The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by gel permeation chromatography using chloroform containing 1 mmol/L of dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
From the viewpoint of the dispersion stability of the pigment in the aqueous phase, the macromonomer is preferably an aromatic group-containing monomer-based macromonomer or a silicone-based macromonomer, more preferably an aromatic group-containing monomer-based macromonomer.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomers described in the hydrophobic monomer described above, preferably styrene and benzyl (meth)acrylate, more preferably styrene. .
Macromonomers can be used alone or in combination of two or more.
Specific examples of commercially available styrenic macromonomers include AS-6(S), AN-6(S), HS-6(S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of silicone-based macromonomers include organopolysiloxanes having a polymerizable functional group at one end.

The hydrophobic monomer improves the adsorption of the polymer to the pigment, improves the dispersion stability of the pigment in the aqueous phase, and improves the initial fixability and print density. (Meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol, and one or more selected from aromatic group-containing monomer-based macromonomers, more preferably an aromatic group-containing monomer and a hydrocarbon group derived from an aliphatic alcohol One or more selected from (meth)acrylates having a, more preferably aromatic group-containing monomers, still more preferably one or more selected from styrene-based monomers and aromatic group-containing (meth)acrylates .

[Nonionic Monomer]
A nonionic monomer can be used as a monomer component of the polymer (a) from the viewpoint of the dispersion stability of the pigment in the aqueous phase.
Nonionic monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polypropylene glycol (n = 2 to 30, n is the average addition mole of oxypropylene groups The following n indicates the average added mole number of the oxyalkylene group.) Polyalkylene glycol (meth)acrylate such as (meth)acrylate, polyethylene glycol (n = 2 to 30) (meth)acrylate; methoxy Alkoxypolyalkylene glycol (meth)acrylate such as polyethylene glycol (n=1 to 30) (meth)acrylate; 29) (meth)acrylates and the like. Among them, polypropylene glycol (n=2 to 30) (meth)acrylates, alkoxypolyalkylene glycol (meth)acrylates, and phenoxy (ethylene glycol/propylene glycol copolymerization) (meth)acrylates are preferred.
A nonionic monomer can be used individually by 1 type or in combination of 2 or more types.
Specific examples of commercially available nonionic monomers include NK Ester M-20G, 40G, 90G, 230G, etc. of Shin-Nakamura Chemical Co., Ltd., Blenmer PE-90 and 200 of NOF Corporation. , 350, etc., Blenmer PME-100, 200, 400, etc., Blenmer PP-500, 800, 1000, etc., Blenmer AP-150, 400, 550, etc., Blenmer 50PEP-300, 50POEP-800B, 43PAPE-600B and the like.

As described above, the vinyl polymer (a) according to the present invention preferably comprises structural units derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, aromatic group-containing monomers, and aliphatic alcohol-derived (Meth) acrylate having a hydrocarbon group, and a structural unit derived from one or more hydrophobic monomers selected from aromatic group-containing monomer-based macromonomers, and a structural unit derived from a nonionic monomer. Although it may be present, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density, more preferably one or more carboxy groups selected from acrylic acid and methacrylic acid Containing monomer-derived structural units and one or more hydrophobic monomer-derived structural units selected from (meth)acrylates having hydrocarbon groups derived from aromatic group-containing monomers and aliphatic alcohols, more preferably Structural units derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from styrenic monomers and aromatic group-containing (meth)acrylates includes.

(Content of Structural Units Derived from Each Monomer in Vinyl Polymer (a))
The content of the structural unit derived from each monomer in the vinyl polymer (a) is as follows from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density.
The content of structural units derived from a carboxy group-containing monomer in the vinyl polymer (a) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and even more preferably 20% by mass. and preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and even more preferably 40% by mass or less.
The content of structural units derived from hydrophobic monomers in the vinyl polymer (a) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and even more preferably 60% by mass or more. and is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less, and even more preferably 80% by mass or less.
When the vinyl polymer (a) contains a structural unit derived from a macromonomer, the content of the structural unit derived from the macromonomer in the vinyl polymer (a) is preferably 5% by mass or more, more preferably 10% by mass. Above, more preferably 15% by mass or more, preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.
When the vinyl polymer (a) contains a structural unit derived from a nonionic monomer, the content of the structural unit derived from the nonionic monomer in the vinyl polymer (a) is preferably 3% by mass or more, more preferably 5% by mass. % by mass or more, more preferably 7% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.
The content of each monomer-derived structural unit in the vinyl polymer (a) can be measured by analysis such as NMR. In addition, the preferable range of the content of each monomer in the raw material monomers (content as unneutralized amount) in the production of the vinyl polymer (a) is the number of structural units derived from each monomer in the vinyl polymer (a). It can be regarded as the same as the preferred range of content.

The total content of structural units derived from a carboxyl group-containing monomer and structural units derived from a hydrophobic monomer in the vinyl polymer (a) is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass. Above, more preferably 90% by mass or more, preferably 100% by mass or less, even more preferably substantially 100% by mass, and even more preferably 100% by mass.
The mass ratio of the content of the structural unit derived from the carboxy group-containing monomer and the content of the structural unit derived from the hydrophobic monomer in the vinyl polymer (a) [content of the structural unit derived from the carboxy group-containing monomer/hydrophobic monomer-derived is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more, still more preferably 0.4 or more, and preferably 2 or less, More preferably 1.5 or less, still 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, still more preferably 0.5 It is below.

The vinyl polymer (a) is produced by copolymerizing raw material monomers by known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Among these polymerization methods, the solution polymerization method is preferred. Moreover, there is no restriction on the chain mode of the polymerization monomers, and any polymerization mode such as random, block, or graft may be used.

The acid value of the vinyl polymer (a) is preferably 120 mgKOH/g or more, more preferably 140 mgKOH/g or more, from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density. , more preferably 160 mgKOH/g or more, still more preferably 180 mgKOH/g or more, still more preferably 200 mgKOH/g or more, still more preferably 220 mgKOH/g or more, and preferably 320 mgKOH/g or less, more preferably It is 300 mgKOH/g or less, more preferably 280 mgKOH/g or less, still more preferably 250 mgKOH/g or less. When the acid value is within the above range, the amount of carboxyl 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 between the vinyl polymer (a) and water and the interaction between the vinyl polymer (a) and the pigment.
The acid value of the vinyl polymer (a) can be measured by the method described in Examples. Moreover, it can be calculated from the mass ratio of the constituent monomers.

At least part of the carboxy groups of the vinyl polymer (a) improve the dispersion stability of the pigment in the aqueous phase, narrow the particle size distribution width of the emulsion, and improve initial fixability and print density. Therefore, it is preferably neutralized.
The counter ion of the neutralized carboxy group of the vinyl polymer (a) is preferably an alkali metal cation, more preferably sodium, from the viewpoint of improving the dispersion stability of the pigment and improving the initial fixability and print density. One or more selected from ions (Na ⁺ ) and potassium ions (K ⁺ ), more preferably sodium ions.

The weight average molecular weight of the vinyl polymer (a) is preferably 2,000 or more, more preferably 5,000 or more, still more preferably 7,000 or more, and preferably 100,000 or less, more preferably 50,000 or more. 000 or less, more preferably 30,000 or less, and even more preferably 20,000 or less. When the weight-average molecular weight of the polymer (a) is within the above range, it has sufficient adsorptive power to pigments and can exhibit dispersion stability.
The weight average molecular weight of polymer (a) is measured by the method described in Examples.

[Vinyl polymer (a') having a crosslinked structure]
The polymer dispersant A is preferably a polymer having a crosslinked structure from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase and improving the initial fixability and print density.
Since the polymer dispersant A has a crosslinked structure, the polymer dispersant A is strongly adsorbed or immobilized on the surface of the pigment, and aggregation of the pigment in the aqueous phase, especially depletion aggregation, is suppressed. It improves the dispersion stability of the pigment, suppresses the swelling of the polymer, reduces the viscosity of the aqueous phase component, makes the emulsion finer, and narrows the particle size distribution of the emulsion. It is thought that the properties and print density can be further improved.
From this point of view, the polymer dispersant A is preferably a polymer crosslinked with a crosslinking agent or a polymer having a self-crosslinking structure introduced with a crosslinkable group, more preferably a polymer crosslinked with a crosslinking agent, More preferred is a vinyl polymer (a') obtained by cross-linking the aforementioned vinyl polymer (a) having a carboxyl group with a cross-linking agent. That is, the polymer dispersant A is more preferably a vinyl polymer (a′) having a crosslinked structure containing a structure derived from the vinyl polymer (a) and a structure derived from a crosslinker (hereinafter simply “vinyl polymer (a′)” or "polymer (a')").

[Crosslinking agent]
From the viewpoint of reactivity with the polymer (a), the cross-linking agent preferably has a water content (mass ratio) of 50% or less, more preferably 40% or less, and still more preferably 35% or less, And it is preferably 5% or more, more preferably 10% or more. The water solubility % (mass ratio) refers to the dissolution rate (%) when 10 parts by mass of the cross-linking agent is dissolved in 90 parts by mass of water at room temperature of 25°C.

The cross-linking agent is preferably a polyfunctional compound, and the cross-linkable functional groups of the polyfunctional compound are preferably capable of reacting with the carboxy groups of the polymer (a) to form covalent bonds. The covalent bond is preferably one or more selected from an ester bond, a thioester bond, an amide bond, an amino bond, an ether bond, a thioether bond, a carbonyl bond, a thiocarbonyl bond and a sulfonyl bond, more preferably an ester bond, It is one or more selected from a thioester bond and an amide bond. The crosslinkable functional group of the polyfunctional compound is not particularly limited as long as it can form the covalent bond described above.
The molecular weight of the cross-linking agent is preferably 120 or more, more preferably 150 or more, and still more preferably 150 or more, from the viewpoints of easiness of reaction, improvement of dispersion stability of the pigment in the aqueous phase, and improvement of initial fixability and print density. It is 200 or more, and preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 1,000 or less.

The crosslinkable functional group is preferably one or more selected from an epoxy group, an isocyanate group, an aziridino group, an amino group and an oxazoline group, more preferably an epoxy group. In addition, the concept of an epoxy group includes a glycidyl group. That is, the cross-linking agent is preferably a polyfunctional epoxy compound, more preferably a compound having two or more epoxy groups in the molecule, still more preferably a compound having two or more glycidyl ether groups, still more preferably, from the viewpoint of cross-linking efficiency. is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group of 3 to 8 carbon atoms.
When the cross-linking agent is a polyfunctional epoxy compound, the epoxy equivalent of the cross-linking agent is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 200 or less. , more preferably 150 or less.
When the cross-linking agent is a polyfunctional epoxy compound, the number of epoxy groups in the cross-linking agent allows for efficient cross-linking reaction, improves the dispersion stability of the pigment in the aqueous phase, and improves the initial fixability and print density. From the viewpoint of increasing the number of molecules, the number per molecule is 2 or more, and preferably 6 or less per molecule, and from the viewpoint of market availability, the number is more preferably 4 or less, and still more preferably 3 or less.

Specific examples of cross-linking agents include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, and neopentyl. Polyglycidyl ethers such as 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 etc. Among these, preferably trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol di It is one or more selected from glycidyl ether and diethylene glycol diglycidyl ether, more preferably trimethylolpropane polyglycidyl ether.

The degree of crosslinking of the vinyl polymer (a′) is preferably 30 mol from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, reducing the average particle size of the emulsion, and improving the initial fixability and print density. % or more, more preferably 40 mol% or more, still more preferably 50 mol% or more, still more preferably 60 mol% or more, and preferably 80 mol% or less, more preferably 75 mol% or less, still more preferably It is 73 mol % or less.
The degree of cross-linking of the vinyl polymer (a′) is the degree of cross-linking calculated from the equivalent weight of the carboxyl groups of the polymer (a) and the equivalent weight of the cross-linking functional groups of the cross-linking agent, and is expressed as “moles of the cross-linking functional groups of the cross-linking agent. It is represented by the number of equivalents/the number of molar equivalents of carboxy groups in the polymer (a).
As described above, when the carboxy groups of the polymer (a) are partially neutralized, the neutralized carboxy groups can also serve as cross-linking points. %, the degree of cross-linking is represented by "the number of molar equivalents of the crosslinkable functional group of the cross-linking agent/the number of molar equivalents of the carboxyl groups possessed by the polymer (a)" as described above, and the degree of neutralization of the polymer (a) is a value obtained by subtracting the degree of cross-linking from 100 mol %.

The acid value of the vinyl polymer (a′) is preferable from the viewpoint of improving the dispersion stability of the pigment in the aqueous phase, narrowing the particle size distribution width of the emulsion, and improving the initial fixability and print density. is 70 mgKOH/g or more, more preferably 80 mgKOH/g or more, still more preferably 90 mgKOH/g or more, still more preferably 100 mgKOH/g or more, still more preferably 110 mgKOH/g or more, and preferably 200 mgKOH/g or less , more preferably 180 mgKOH/g or less, still more preferably 160 mgKOH/g or less, still more preferably 140 mgKOH/g or less, still more preferably 130 mgKOH/g or less. When the acid value is within the above range, the amount of carboxyl 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 between the vinyl polymer (a') and water and the interaction between the vinyl polymer (a') and the pigment.
The acid value of the vinyl polymer (a') can be measured by the method described in Examples.
Also, the acid value of the vinyl polymer (a') can be determined by the following formula.
Acid value of vinyl polymer (a′) (mgKOH/g)=[acid value of polymer (a) (mgKOH/g)]×[100−degree of cross-linking (mol %)]/100
Here, the acid value of the polymer (a) can be calculated from the mass ratio of the constituent monomers. As described above, the degree of cross-linking is represented by "the number of molar equivalents of crosslinkable functional groups of the cross-linking agent/the number of molar equivalents of carboxyl groups possessed by the polymer (a)".

At least part of the carboxyl groups of the vinyl polymer (a') improves the dispersion stability of the pigment in the aqueous phase, narrows the particle size distribution width of the emulsion, and improves initial fixability and print density. From the point of view, it is preferably neutralized.
The counter ion of the neutralized carboxyl group of the vinyl polymer (a′) is preferably an alkali metal cation, more preferably an alkali metal cation, from the viewpoint of improving the dispersion stability of the pigment and improving the initial fixability and print density. It is one or more selected from sodium ions (Na ⁺ ) and potassium ions (K ⁺ ), more preferably sodium ions.
As for the degree of neutralization of the vinyl polymer (a'), the carboxy groups of the vinyl polymer (a') may be partially neutralized or all of the carboxy groups may be neutralized.

In the aqueous phase of the emulsion ink of the present invention, the vinyl polymer (a) or vinyl polymer (a′) exists in a state of being adsorbed to the pigment, a state of containing the pigment (encapsulating the pigment (capsule (including particles in which the pigment is uniformly dispersed), and a form in which 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, in the present invention, the pigment is a particle containing a vinyl polymer (a) (hereinafter also referred to as a "pigment-containing polymer particle") or a vinyl polymer. The form of particles containing (a′) (hereinafter also referred to as “pigment-containing crosslinked polymer particles”) is preferred, and the form of pigment-containing crosslinked polymer particles is more preferred, and the pigment is encapsulated in the vinyl polymer (a′). More preferred is the form of particles.

The total content of the pigment and polymer dispersant A in the emulsion ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 6% by mass or more, and preferably 18% by mass. % by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less.

The mass ratio [pigment/polymer dispersant A] between the pigment and polymer dispersant A in the emulsion ink of the present invention is preferably 1.5 or more, more preferably 2 or more, and still more preferably 2 or more, from the viewpoint of improving print density. is 2.5 or more, more preferably 3 or more, and from the viewpoint of improving the initial fixability, it is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and even more preferably 5 or less. More preferably 4.5 or less, still more preferably 4 or less.
Here, when the polymer dispersant A is a non-crosslinked vinyl polymer (a), the mass ratio [pigment/polymer dispersant A] is the mass ratio [pigment/vinyl polymer (a)], and when the polymer dispersant A is a vinyl polymer (a′) having a crosslinked structure, the mass ratio [pigment/polymer dispersant A] is the ratio of the pigment to the vinyl polymer (a′). mass ratio [pigment/vinyl polymer (a′)].

(Surfactant)
The emulsion ink of the present invention preferably contains a surfactant in the aqueous phase. Surfactants improve the dispersion stability of pigments in the water phase, reduce the energy of the interface between the water phase and the oil phase, contribute to the formation of a fine and stable dispersed phase, and increase the particle size distribution width of the emulsion. can be made narrower, and the initial fixability and print density can be improved. From this point of view, the surfactant is preferably a nonionic surfactant, more preferably an acetylene glycol surfactant, a polyoxyalkylene alkyl ether surfactant, a polyether-modified silicone surfactant, and One or more selected from fluorine-based surfactants, more preferably one selected from acetylene glycol-based surfactants and polyether-modified silicone-based surfactants, still more preferably acetylene glycol-based surfactants is.
The HLB (hydrophilic-lipophilic balance) value of the nonionic surfactant is preferably 6 or more, more preferably 8 or more, still more preferably 10 or more, still more preferably 12 or more, and preferably 20 or less, It is more preferably 18 or less.
The HLB value is a value that indicates the affinity of a surfactant for water and oil, and can be obtained from the following equation according to Griffin's method. In the following formula, the "hydrophilic group contained in the surfactant" includes, for example, a hydroxyl group and an ethyleneoxy group.
HLB = 20 x [(sum of formula weights of hydrophilic groups contained in surfactant)/(molecular weight of surfactant)]

The acetylene glycol-based surfactant is preferably an ethylene oxide (hereinafter also referred to as "EO") adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl- EO adduct of 4-octyne-3,6-diol, EO adduct of 2,5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecine-5 EO adduct of ,8-diol and EO adduct of 3,5-dimethyl-1-hexyn-3-ol, more preferably 2,4,7,9-tetramethyl- EO adduct of 5-decyne-4,7-diol, EO adduct of 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2,5-diol and more preferably an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.
The EO average added mole number of the above-mentioned EO adduct used as an acetylene glycol-based surfactant is preferably 5 or more, more preferably 6 or more, still more preferably 7 or more, and even more preferably 8 or more, and It is preferably 40 or less, more preferably 36 or less, still more preferably 32 or less.

Commercially available acetylene glycol-based surfactants include Surfynol 465 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with EO average of 10 mol added product, HLB: 13), 485 (EO average 30 mol adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB: 17), manufactured by Kawaken Fine Chemicals Co., Ltd. Acetylenol E81 (2,4,7,9-tetramethyl-5-decyne-4,7-diol EO average 8.1 mol adduct, HLB: 13.0), E100 (2,4,7,9) -Tetramethyl-5-decyne-4,7-diol EO average 10 mol adduct, HLB: 13.9), E200 (2,4,7,9-tetramethyl-5-decyne-4,7- EO average 20 mol adduct of diol, HLB: 16.4) and the like.

As polyether-modified silicone-based surfactants, those having a structure in which side chains and/or terminal hydrocarbon groups of silicone oil are substituted with polyether groups are preferred. As the polyether group, a polyethyleneoxy group, a polypropyleneoxy group, an ethyleneoxy group (EO) and a propyleneoxy group (trimethyleneoxy group or propane-1,2-diyloxy group; PO) are added blockwise or randomly. A polyalkyleneoxy group is preferable, and a compound in which a polyether group is grafted to a silicone main chain, a compound in which a silicone and a polyether group are bonded in a block form, or the like can be used.
Commercially available polyether-modified silicone surfactants include KF-353, KF-355A, KF-642, etc. manufactured by Shin-Etsu Chemical Co., Ltd.; Silface SAG005, etc. manufactured by Nisshin Chemical Co., Ltd.; and BYK-348 manufactured by BYK-Chemie Japan.

When the water phase of the emulsion ink of the present invention contains a surfactant, the content of the surfactant in the emulsion ink is preferably 0.5% by mass or more from the viewpoint of improving initial fixability and print density. , more preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and 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, it is 3% by mass or less.

(Water-soluble organic solvent)
From the viewpoint of initial fixability and print density, the aqueous phase of the emulsion ink of the invention preferably further contains a water-soluble organic solvent.
A water-soluble organic solvent is an organic solvent that dissolves in 100 mL of water at 25° C. in an amount of 10 mL or more.
As the water-soluble organic solvent, those which are usually used in the aqueous phase of water-in-oil emulsion inks and which are miscible with water in any proportion are preferred, such as alkanols, polyhydric alcohols and polyhydric alcohol alkyls having 1 to 4 carbon atoms. Ethers, ketones, cyclic ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds and the like. Among these, more preferably one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers.
The boiling point of the water-soluble organic solvent is preferably 60°C or higher, more preferably 90°C or higher, still more preferably 150°C or higher, and preferably 350°C or lower, more preferably 330°C or lower, still more preferably 310°C. It is below.
The water-soluble organic solvents can be used singly or in combination of two or more as long as they are miscible with water at any ratio.

The content of the water-soluble organic solvent in the emulsion ink of the present invention is preferably 0.5% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of adjusting the viscosity of the emulsion ink and improving the initial fixability and print density. 1.0% by mass or more, more preferably 1.5% by mass or more, and 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.

In the present invention, the aqueous phase may contain an oil-in-water polymer emulsion, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, an anticorrosive, etc., as long as the effects of the present invention are not impaired.

<Oil phase>
The oil phase of the emulsion ink of the present invention improves the dispersion stability of the pigment in the aqueous phase, narrows the particle size distribution width of the emulsion, and improves initial fixability and print density. contains a toxic organic solvent.

(Water-insoluble organic solvent)
The water-insoluble organic solvent refers to an organic solvent that dissolves less than 10 mL in 100 mL of water at 25°C.
Both non-polar organic solvents and polar organic solvents can be used as the water-insoluble organic solvent. These may be used singly or in combination of two or more as long as they form a single continuous phase.

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

Examples of polar organic solvents include ester oils and higher alcohols.
Examples of ester oils include fatty acid monoesters composed of fatty acids having 8 to 22 carbon atoms and monohydric alcohols having 1 to 24 carbon atoms, and fatty acids having 8 to 22 carbon atoms and polyhydric alcohols having 2 to 12 carbon atoms. and fatty acid esters such as dicarboxylic acid diesters composed of a dicarboxylic acid having 4 to 18 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms.
Examples of fatty acid monoesters composed of a fatty acid having 8 to 22 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms include isononyl isononanoate, isodecyl isononanoate, isotridecyl isononanoate, methyl laurate, isopropyl laurate, and lauric acid. Hexyl, 2-ethylhexyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, butyl stearate, 2-ethylhexyl stearate, isopropyl isostearate, methyl oleate, ethyl oleate, isopropyl oleate, isobutyl oleate , methyl linoleate, ethyl linoleate, isobutyl linoleate, methyl soybean oil, isobutyl soybean oil, methyl tall oil, isobutyl tall oil and the like.
Examples of fatty acid esters composed of a fatty acid having 8 to 22 carbon atoms and a polyhydric alcohol having 2 to 12 carbon atoms include propylene glycol monocaprate, trimethylolpropane tri-2-ethylhexanoate, and glyceryl tri-2-ethylhexanoate. etc.
Examples of the dicarboxylic acid diester comprising a dicarboxylic acid having 4 to 18 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms include diisopropyl adipate, diisopropyl sebacate and diethyl sebacate.

Higher alcohols include higher alcohols having 12 to 20 carbon atoms, such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol.

The oil phase of the emulsion ink of the present invention improves the dispersion stability of the pigment in the aqueous phase, narrows the particle size distribution width of the emulsion, and improves the initial fixability and print density, and is preferably Contains ester oil.
The ester oil is preferably a fatty acid monoester composed of a fatty acid having 8 to 22 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms, a fatty acid having 8 to 22 carbon atoms, and a polyhydric acid having 2 to 12 carbon atoms. fatty acid esters consisting of alcohols, and fatty acid esters such as dicarboxylic acid diesters consisting of a dicarboxylic acid having 4 to 18 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms, more preferably is a fatty acid monoester consisting of a fatty acid having 8 to 22 carbon atoms and a monohydric alcohol having 1 to 24 carbon atoms, more preferably a fatty acid having 8 to 18 carbon atoms and a monovalent more preferably a fatty acid monoester composed of a fatty acid having 8 to 18 carbon atoms and a monohydric alcohol having 1 to 12 carbon atoms, more preferably isononyl isononanoate, One or more selected from hexyl laurate, isopropyl myristate, and methyl oleate, more preferably hexyl laurate, still more preferably one or more selected from methyl laurate and hexyl laurate, and more More preferred is hexyl laurate.

When the oil phase of the emulsion ink of the present invention contains an ester oil, the content of the ester oil in the emulsion ink is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, even more preferably 60% by mass or more, still more preferably 65% by mass or more, and preferably 90% by mass or less, More preferably 80 mass % or less, still more preferably 75 mass % or less.

(emulsifier)
The oil phase of the emulsion ink of the present invention improves the dispersion stability of the pigment in the aqueous phase, narrows the particle size distribution width of the emulsion, and improves the initial fixability and print density, and is preferably Contains emulsifier.
The emulsifier is not particularly limited as long as it is contained in the oil phase and can emulsify the water phase to form a water-in-oil emulsion, but lipophilic emulsifiers such as surfactants and polymer dispersants are preferred.
As the lipophilic surfactant, a nonionic surfactant having an HLB value of 6 or less is preferred. Examples of the nonionic surfactant include sorbitan fatty acid esters such as sorbitan monooleate, sorbitan sesquioleate and sorbitan monostearate; polyoxyethylene sorbitan fatty acids such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; Ester; Glycerin fatty acid ester such as glycerol monostearate and glycerol monooleate; Polyoxyethylene glycerin fatty acid ester such as polyoxyethylene sorbitol fatty acid ester and polyoxyethylene glycerin vegetable oil fatty acid ester; Sucrose stearate, sucrose palmitic acid Ester, sucrose fatty acid ester such as sucrose oleate, sucrose erucate, sucrose laurate; polyethylene glycol fatty acid ester; polyglycerol condensed ricinoleate; polyoxyethylene alkyl ether; polyoxyethylene alkylphenyl ether polyoxyethylene alkylamine/fatty acid amide; polyoxyethylene polyoxypropylene alkyl ether, and the like.
The lipophilic surfactants may be used singly or in combination of two or more.

Lipophilic polymer dispersants include polyester polyimines, polyester polyamines, polyalkylolaminoamides and their salts, polyether polyamines, hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, high-molecular-weight poly Carboxylic acid salt, long-chain polyaminoamide and polar acid ester salt, high molecular weight unsaturated acid ester, modified polyurethane, modified poly(meth)acrylate, polyether ester type anionic surfactant, naphthalenesulfonic acid formalin condensate salt, Examples include polyoxyethylene alkyl phosphate, polyoxyethylene nonylphenyl ether, stearylamine acetate, and the like. Among these, one or more selected from polyester polyimine, polyester polyamine, polyalkylolaminoamide and its salt, and polyether polyamine are preferable, and polyester polyimine is more preferable. You may use these individually by 1 type or in combination of 2 or more types.

The polyester polyimine preferably comprises an amide or salt formed by reacting a polyalkyleneimine, such as polyethyleneimine, with a polyester having carboxyl groups, such as a polymer of hydroxystearic acid or a polymer of cyclic esters. , a dispersant having a graft structure in which two or more polyester chains are bonded as branches to a polyalkyleneimine chain as a trunk. When the water-insoluble organic solvent contains ester oil, the interaction between the dispersed phase droplet particles is suppressed by the steric repulsion in the oil phase of the polyester chain of the polyester polyimine, and the dispersed phase droplet particles coalesce. It is thought that by suppressing the first, the particle size distribution width of the emulsion can be made narrower, and the initial fixability and print density can be improved.
Examples of commercially available lipophilic polymer dispersants include Solsperse (trade name) series manufactured by Nippon Lubrizol; Efka (trade name) series manufactured by Efka CHEMICALS; ) series; Ajinomoto Co., Inc. Ajisper (trade name) series and the like.

When the oil phase of the emulsion ink of the present invention contains an emulsifier, the content of the emulsifier in the emulsion ink is preferably 0.3% by mass or more, more preferably 0% by mass, from the viewpoint of improving initial fixability and print density. 7% by mass or more, more preferably 1% by mass or more, and from the viewpoint of adjusting the viscosity of the emulsion ink, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. , more preferably 5% by mass or less, and even more preferably 3% by mass or less.

In the present invention, the oil phase improves the dispersion stability of the pigment in the aqueous phase, narrows the particle size distribution width of the emulsion, and improves the initial fixability and printing density. It is preferably agent-free.

[Method for producing 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 them, from the viewpoint of improving the dispersion stability of the pigment in the water phase, narrowing the particle size distribution width of the emulsion, and improving the initial fixability and print density, the water-based medium in which the pigment is dispersed in the water-based medium It is preferably obtained by a method including a step of emulsifying a pigment dispersion (hereinafter also referred to as "aqueous pigment dispersion") in an oil phase.
The "aqueous medium" in the water-based 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 by the vinyl polymer (a) having a non-crosslinked carboxyl group, the aqueous pigment dispersion is preferably efficiently produced by a method including the following step 1.
Step 1: A step of dispersing a pigment mixture containing a pigment, a vinyl polymer (a) having a carboxy group, and water to obtain an aqueous pigment dispersion in which the pigment is dispersed in an aqueous medium with the vinyl polymer (a).

(Step 1)
Specifically, step 1 is a method (1) of dispersing a pigment mixture obtained by mixing a previously prepared aqueous dispersion of vinyl polymer (a) with a pigment; pigment, vinyl polymer (a), organic solvent , Water, and if necessary, a neutralizer, a surfactant, etc., are dispersed to obtain a dispersion, and then the organic solvent is removed from the dispersion by the method (2) or the like. is preferred. Among them, the method (1) is preferable from the viewpoint of improving initial fixability and print density.

In the case of method (1), it is preferable to have the following step 1-1 before step 1.
Step 1-1: Some of the carboxy groups of the polymer (a) having carboxy groups are neutralized with a neutralizing agent to obtain an aqueous dispersion of the vinyl polymer (a) (hereinafter referred to as "aqueous polymer dispersion (D)"). the process of obtaining

Examples of the neutralizing agent used for neutralizing the polymer (a) in step 1-1 include alkali metal compounds such as alkali metal hydroxides, ammonia, and the like. Above all, it improves the dispersion stability of the pigment in the aqueous phase, improves the dispersion stability of the aqueous phase with respect to the oil phase, narrows the particle size distribution width of the emulsion, and improves the initial fixability and print density. from the viewpoint of allowing the be. The neutralizing agent is preferably used as an aqueous solution from the viewpoint of sufficiently and uniformly promoting neutralization.
The degree of neutralization of the polymer (a) improves the dispersion stability of the pigment in the aqueous phase, improves the dispersion stability of the aqueous phase with respect to the oil phase, and narrows the particle size distribution width of the emulsion, From the viewpoint of improving the initial fixability and print density, the It is 85 mol% or less, more preferably 80 mol% or less, still more preferably 70 mol% or less, even more preferably 60 mol% or less, still more preferably 50 mol% or less, and even more preferably 45 mol% or less.
Here, the degree of neutralization of the polymer (a) can be determined by the following formula. If the degree of neutralization exceeds 100 mol % in the following formula, it means that the neutralizing agent is excessive with respect to the carboxy groups of the vinyl polymer (a). degree is taken as 100 mol %.
Degree of neutralization (mol%) = [{additional mass of neutralizing agent (g)/equivalent weight of neutralizing agent}/[{acid value of vinyl polymer (a) (mgKOH/g) x mass of vinyl polymer (a) (g)}/(56.1×1,000)]]×100

In the dispersion treatment in step 1, the pigment particles can be atomized to a desired particle size only by the main dispersion by shearing stress. , and preferably further dispersed.
As a dispersing machine used for pre-dispersion, generally used mixing and stirring devices such as anchor blades and disper blades can be used.
Means for imparting shear stress used for this dispersion include, for example, 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 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 later is also adjusted. be able to.
The treatment pressure is preferably 60 MPa or more and 300 MPa or less from the viewpoint of productivity and economy.
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 aqueous pigment dispersion can be obtained by removing the organic solvent by a known method. The organic solvent in the resulting aqueous pigment dispersion is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of 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 vinyl polymer (a′), the water-based pigment dispersion is prepared after step 1, preferably after step 1-1 and step 1, and further including step 2 below. It is preferably obtained by
Step 2: A water-based pigment dispersion obtained by adding a cross-linking agent to the water-based pigment dispersion obtained in step 1, cross-linking the polymer (a) with the cross-linking agent, and dispersing the pigment in the vinyl polymer (a′). the process of obtaining

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

The non-volatile component concentration (solid content concentration) of the water-based pigment dispersion is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably, from the viewpoint of improving dispersion stability and facilitating ink production. is 35% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. The solid content concentration of the water-based pigment dispersion is measured by the method described in Examples.

The cumulant average particle size of the pigment particles in the water-based pigment dispersion is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, and even more preferably 80 nm or more, from the viewpoint of improving initial fixability and print density. , more preferably 90 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, even more preferably 130 nm or less, even more preferably 120 nm or less, and even more preferably less than 100 nm. The cumulant average particle size of the water-based pigment dispersion is measured by the method described in Examples.

The aqueous pigment dispersion preferably comprises pigment-containing polymer particles or pigment-containing crosslinked polymer particles dispersed in an aqueous medium. The forms of the pigment-containing polymer particles and the pigment-containing crosslinked polymer particles are not particularly limited as long as the particles are formed of at least a pigment and a non-crosslinked vinyl polymer (a) or a vinyl polymer (a') having a crosslinked structure. As described above, it is preferably in the form of particles in which the pigment is encapsulated in the vinyl polymer (a) or the vinyl polymer (a').
The water-based pigment dispersion may contain 1% by mass or more and 10% by mass or less of glycerin, polyethylene glycol, or the like as a humectant to prevent drying, and may also contain additives such as antifungal agents.
The above additives may be blended when dispersing the pigment in the vinyl polymer (a), or may be blended after dispersing the pigment or after crosslinking.

In the present invention, when the aqueous phase of the emulsion ink contains the aforementioned surfactant, water-soluble organic solvent, or optional component, the water-based pigment dispersion and, if necessary, the surfactant, water-soluble organic solvent, Alternatively, an emulsion ink can be prepared by mixing optional components or adjusting the water content to prepare an aqueous phase component, and then mixing and emulsifying the aqueous phase component and the oil phase component.
The mixing mass ratio [aqueous phase component/oil phase component] of the aqueous phase component and the oil phase component is preferably 5/95 or more, more preferably 10, from the viewpoint of productivity and obtaining a stable emulsion. /90 or more, more preferably 15/85 or more, even more preferably 20/80 or more, and preferably 45/55 or less, more preferably 40/60 or less, even more preferably 35/65 or less, and even more Preferably it is 30/70 or less.

The emulsion ink of the present invention may optionally contain moisturizing agents, wetting agents, penetrating agents, viscosity modifiers, antifoaming agents, preservatives, antifungal agents, and antirust agents that are commonly used in water-in-oil emulsion inks. It is possible to add various additives such as, and further perform filtration treatment using a filter or the like.

The cumulant average particle size of the pigment particles in the aqueous phase of the emulsion ink of the present invention is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, and still more preferably 50 nm or more, from the viewpoint of improving initial fixability and print density. It is preferably 80 nm or more, even 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, even more preferably 120 nm or less, still more preferably less than 100 nm.
The cumulant average particle size of the pigment particles in the aqueous phase of the emulsion ink of the present invention is obtained by, for example, centrifuging the emulsion ink under conditions that can maintain the dispersed state of the pigment particles in the aqueous phase, demulsifying, and removing the water phase. It can be determined by separating the 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 centrifugal separation conditions that can maintain the dispersed state of the pigment particles in the aqueous phase can be set by confirming the dispersed state of the pigment particles before and after the centrifugal separation treatment with an electron microscope.

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, still more preferably 7 mPa·s or more, and even more preferably 9 mPa·s or more. From the viewpoint of using the ink for inkjet recording, the viscosity is preferably 20 mPa·s or less, more preferably 17 mPa·s or less, even more preferably 15 mPa·s or less, even more preferably 13 mPa·s or less, and even more preferably 11 mPa·s or less. is.
The viscosity of the emulsion ink is measured by the method described in Examples.

The emulsion ink of the present invention is preferably used for inkjet recording from the viewpoint that it is excellent in initial fixability even in printing by an inkjet recording method and a printed matter having a high print density can be obtained. An image or the like can be recorded by loading the emulsion ink into a known inkjet recording apparatus and ejecting the ink as ink droplets onto a printing medium.
The print media to be used include highly water-absorbing plain paper, low water-absorbing coated paper, and non-water-absorbing resin film. Examples of coated paper include general-purpose glossy paper, multicolor foam gloss paper, and the like. The resin film is preferably at least one selected from polyester film, polyvinyl chloride film, polypropylene film and polyethylene film. A corona-treated substrate may be used for the resin film.
Among these, plain paper is preferable from the viewpoint of initial fixability and print density.

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

(1) Measurement of acid value of vinyl polymer (a) and vinyl polymer (a') (capacity ratio)] was measured according to JIS K0070.

(2) Measurement of weight-average molecular weight of vinyl polymer (a) Using a solution obtained by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, Gel permeation chromatography method [GPC device (model: HLC-8320GPC, manufactured by Tosoh Corporation), columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H, above, trade names manufactured by Tosoh Corporation), flow rate : 0.5 mL/min], monodisperse polystyrene kits with known molecular weights [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288 , F-40, F-4, A-5000, A-500), above, trade names manufactured by Tosoh Corporation].
A sample to be measured was obtained by mixing 0.1 g of polymer (a) with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and applying a syringe filter (trade name: DISMIC-13HP, membrane filter material : Hydrophilic PTFE, pore size 0.2 μm, manufactured by Advantech).

(3) Measurement of solid content concentration 10.0 g of sodium sulfate that has been made constant in a desiccator is weighed into a 30 mL polypropylene container (φ = 40 mm, height = 30 mm), and about 1.0 g of a sample is added thereto. After mixing, the mixture was accurately weighed, maintained at 105° C. for 2 hours to remove volatile matter, allowed to stand in a desiccator at room temperature (25° C.) for 15 minutes, and weighed. The mass of the sample after removing the volatile matter was defined as the solid content, and the mass of the added sample was divided to obtain the solid content concentration.

(4) Measurement of Cumulant Average Particle Size A 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 size. The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and the number of accumulation times of 100, and the refractive index of water (1.333) was input as the refractive index of the dispersion medium. The concentration of the measurement sample was 5×10 ⁻³ % (converted to solid concentration).

(5) Measurement of emulsion particle size ( _D10 , _D50 , and _D90 )
It was measured using a laser diffraction/scattering particle size measuring device "Mastersizer 3000" (manufactured by Malvern Panalytical). From the obtained particle diameter with a small particle diameter distribution, the particle diameter D at which the cumulative volume frequency is ₁₀ %, the particle diameter D at which the cumulative volume frequency is ₅₀ %, and the particle diameter D at which the cumulative volume frequency is 90% Asked for ₉₀ . The measurement sample was prepared by adding hexyl laurate (trade name: EXEPAL HL, manufactured by Kao Corporation, viscosity at 20°C: 6.8 mPa s) to the emulsion ink, and adjusting the concentration to give a scattering intensity of 5 to 15%. Using. Measurement was performed under the conditions of a particle refractive index of 1.59 (absorption rate of 0.1, density of 1 g/cm ³ ) and a dispersion medium refractive index of 1.44.

(6) Viscosity of water-in-oil emulsion ink 25 ° C. using an E-type viscometer (model: TV-25, manufactured by Toki Sangyo Co., Ltd., using standard cone rotor 1 ° 34' × R24, rotation speed 50 rpm) The viscosity was measured at

<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. In a reaction vessel, 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 are added and mixed, and the nitrogen gas is sufficiently replaced. went to
On the other hand, the remaining raw material monomer (90%), 0.27 parts of the polymerization chain transfer agent, 40 parts of MEK and an azo radical polymerization initiator (trade name: V-65, FUJIFILM Wako Pure Chemical Industries, Ltd.) were added to the dropping funnel. 2,2′-azobis(2,4-dimethylvaleronitrile) (hereinafter referred to as “V-65”) was added, and the raw material monomer in the reaction vessel was added under a nitrogen atmosphere. The temperature was raised to 65° C. with stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After stirring for 2 hours from the end of dropping while maintaining the contents in the reaction vessel at 65° C., a solution of 0.15 parts of the polymerization initiator dissolved in 2.5 parts of MEK was added, and the mixture was further heated at 65° C. for 2 hours and 70°C. C. for 2 hours to obtain a solution of polymer (a1) having a carboxy group. Table 1 shows the weight average molecular weight and acid value.

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 amounts of raw material monomers charged were changed as shown in Table 1. Table 1 shows the weight average molecular weight and acid value.

Preparation example 3
37.0 parts of methacrylic acid, 33.0 parts of benzyl acrylate, 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 ”) 40.0 parts (20.0 parts as solid content), polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: Blemmer PP-800, propylene oxide average added mole number 13, terminal: hydroxyl group) (hereinafter referred to as "PP-800") was mixed with 10.0 parts to prepare a raw material monomer. 10 parts of MEK, 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the raw material monomers were added and mixed in a reaction vessel, and nitrogen gas was sufficiently replaced.
On the other hand, a mixture of the remainder (90%) of the raw material monomer, 0.27 parts of the polymerization chain transfer agent, 40 parts of MEK, and 1.1 parts of an azo radical polymerization initiator (V-65) was put into a dropping funnel. Then, in the same manner as in Preparation Example 1, a solution of polymer (a3) having a carboxy group was obtained. Table 1 shows the weight average molecular weight and acid value.

<Production of aqueous polymer dispersion (D) (step 1-1)>
Production Example 1-1
After drying the polymer solution obtained in Preparation Example 1 under reduced pressure, 316.0 parts of ion-exchanged water was added to 80.0 parts of the polymer (a1) obtained by pulverizing, and 5N sodium hydroxide (Fuji Film Co., Ltd.) was used as a neutralizing agent. Reagent manufactured by Kojunyaku Co., Ltd.) 30.4 parts of an aqueous solution was added so that the ratio of the number of moles of sodium hydroxide to the number of moles of carboxyl groups in the polymer (a1) was 60 mol% (degree of neutralization: 60 mol%). Then, it was neutralized and dispersed by heating at 90° C. for 5 hours while stirring at 150 rpm to obtain an aqueous polymer dispersion (D1) (solid concentration: 20%).

Production Examples 1-2 to 1-8
Aqueous polymer dispersions (D2) to (D8) (solid concentration: 19.8-20.1% and degree of neutralization: 30-90 mol%) was obtained.

<Production of aqueous pigment dispersion (i) (step 1)>
Production example 2-1
As shown in Table 3, 109.9 parts of the aqueous polymer dispersion (D1) obtained in Production Example 1-1, 400.0 parts of ion-exchanged water, a black pigment (carbon black, trade name: MONARCH717, Cabot Corporation) 100.0 parts of DBP oil absorption 53 mL/100 g) was added, and using a disper (manufactured by Asada Iron Works Co., Ltd., trade name: Ultra Disper), the disper blade was rotated at 7,000 rpm at 20 ° C. for 60 minutes. Stirred. The resulting mixture was subjected to 10 passes of dispersion treatment with a microfluidizer (manufactured by Microfluidics, trade name) at a pressure of 200 MPa to obtain a dispersion treated product.
The obtained dispersed product was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), After removing coarse particles, an aqueous pigment dispersion (i-1) having a solid content concentration of 20% (pigment content: 16.6%, polymer (a) content: 3.4%) was obtained. .

Production Examples 2-2 to 2-8
Aqueous pigment dispersions i-2 to i-8 were prepared in the same manner as in Production Example 2-1, except that the type and amount of the aqueous polymer dispersion (D) were changed as shown in Table 3. got

<Production of aqueous pigment dispersion (step 2)>
Production Example 3-1
As shown in Table 4, 100.0 parts (solid content concentration 20%) of the aqueous pigment dispersion (i-1) obtained in Production Example 2-1 was placed in a glass bottle with a screw cap, and the aqueous pigment dispersion ( Trimethylolpropane polyglycidyl ether (trade name: Denacol EX-321) is used as a cross-linking agent so that 50 mol% of all carboxy groups of the polymer (a1) in i-1) are cross-linked (degree of cross-linking: 50 mol%). , manufactured by Nagase Chemtex Co., Ltd., epoxy equivalent: 139, water solubility: 27%) (hereinafter referred to as "EX-321") 0.63 parts was added and sealed, and stirred with a stirrer at 70 ° C. for 5 minutes. Heated for hours. After 5 hours, the temperature was lowered to room temperature, and a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used. Filtration, concentration under reduced pressure so that the content of the pigment in the resulting aqueous pigment dispersion is 36.0%, water-based black pigment dispersion (hereinafter also referred to as "black pigment dispersion") Bk -I (mass ratio [pigment/vinyl polymer (a′)]=4.1, solid content concentration: 44.8%, cumulant average particle size: 96 nm) was obtained.

Production Examples 3-2 to 3-6, 3-9, 3-10
In Production Example 3-1, the type of aqueous pigment dispersion (i) and the amount of cross-linking agent were changed as shown in Table 4, and in Production Examples 3-9 and 3-10, Black pigment dispersions Bk-II to Bk-VI, Bk-IX and Bk-X were obtained in the same manner, except that the pigment content was changed to 33.0%.

Production Examples 3-7, 3-8
In Production Examples 3-1 and 3-4, water-based pigment dispersion (i-1) and water-based pigment dispersion (i-4) are each taken in a glass bottle with a screw cap, and 0.63 parts or 0 of EX-321 Same as Production Examples 3-1 and 3-4, except that the same amount of ion-exchanged water was added instead of 99 parts, and the pigment content in the resulting aqueous pigment dispersion was 33.0%. Black pigment dispersions Bk-VII and Bk-VIII were obtained by the procedure of .

<Production of water-in-oil emulsion ink>
Example 1
A water-in-oil emulsion ink Bk-1 was obtained by the following procedure so that the pigment content in the resulting water-in-oil emulsion ink was 6.0%.
16.7 parts of the black pigment dispersion Bk-I obtained in Production Example 3-1, Surfynol 465 (trade name, 2,4,7,9-tetramethyl-5-decyne-4, EO adduct of 7-diol, EO average added moles: 10, HLB: 13, manufactured by Nissin Chemical Industry Co., Ltd.) 2.0 parts, glycerin (concentrated glycerin for cosmetics, manufactured by Kao Corporation) 2.0 parts and 1.8 parts of ion-exchanged water were mixed to prepare an aqueous phase component.
Separately, 74.5 parts of hexyl laurate (trade name: Excepar HL (ester oil), manufactured by Kao Corporation) as a water-insoluble organic solvent, and Solsperse 11200 (trade name, polymer dispersant, effective content 50%) as an emulsifier. , manufactured by Lubrizol) were mixed to prepare an oil phase component.
Using a homogenizer (trade name: ULTLRA-TURRAX, model: T25 digital, shaft generator (model: S25N-25F), both manufactured by IKA Japan Co., Ltd.), the oil phase component was stirred at 5,000 rpm. The aqueous phase components were added dropwise while stirring. After that, the mixture was stirred at 12,000 rpm for 30 minutes to obtain a water-in-oil emulsion ink Bk-1 shown in Table 5.

Examples 2 to 10 and Comparative Examples 1 and 2
Water-in-oil emulsion inks shown in Table 5 were obtained in the same manner as in Example 1, except that the types or amounts of the components constituting the water phase component and the oil phase component were changed as shown in Table 5.

<Evaluation test of water-in-oil emulsion ink>
Initial fixability and print density were evaluated using the emulsion inks obtained in Examples and Comparative Examples. Table 5 shows the results.

[Evaluation of Initial Fixability]
An inkjet printer (trade name: Business Printer PX-105, manufactured by Seiko Epson Corporation) was filled with each of the obtained emulsion inks and printed on plain paper (trade name: Xerox A solid image of 1 cm×1 cm was printed on business 4200 copy paper (manufactured by Fuji Xerox Co., Ltd.). One minute after printing, a load of 500 g was applied to a cellulose non-woven fabric "BENCOT (registered trademark) M3-II" (manufactured by Asahi Kasei Corp.) using the bottom surface of a weight (bottom surface area: 50 cm ² ), and the printed surface was swung five times. It was rubbed back and forth. The initial fixability of the image was evaluated according to the following criteria from the degree of staining of the ink transferred to the nonwoven fabric made of cellulose.
(Evaluation criteria)
A: There was no dirt on the cellulose nonwoven fabric.
B: The cellulose nonwoven fabric was almost free from stains.
C: The cellulose nonwoven fabric was slightly stained.
D: The cellulose nonwoven fabric was markedly soiled.
If the above evaluation criteria is A or B, it is suitable for practical use. If the above evaluation criteria is C, it is a level that can be used in practice. If the above evaluation criteria is D, actual use may be difficult.

[Evaluation of Print Density]
A printed matter obtained under the same conditions as the initial fixability evaluation was allowed to stand for one day under the same environment as the printing conditions. The printing density of the printed material after being left for one day was measured using an optical densitometer (trade name: SpectroEye, manufactured by GretagMacbeth). The measurement was carried out at arbitrary 10 locations by changing the measurement location of the printed matter, and the average value was defined as the print density and evaluated according to the following criteria. (Evaluation criteria)
A: The average value of print density is 1.10 or more.
B: The average value of print density is 1.00 or more and less than 1.10.
C: The average value of print density is 0.95 or more and less than 1.00.
D: The average print density is less than 0.95.
The higher the print density, the better. If the above evaluation criteria is A or B, it is suitable for practical use. If the above evaluation criteria is C, it is a level that can be used in practice. If the above evaluation criteria is D, actual use may be difficult.

From Table 5, it can be seen that Examples 1 to 10 are superior to Comparative Examples 1 and 2 in both initial fixability and print density.

According to the emulsion ink and the method for producing the emulsion ink of the present invention, it is possible to obtain a printed matter having excellent initial fixability and high printing density. Moreover, the emulsion ink of the present invention is useful for inkjet recording.

Claims (8)

A water-in-oil emulsion ink having an aqueous phase in an oil phase,
the aqueous phase contains a pigment;
The water-in-oil emulsion ink has a water content of 10% by mass or more and 25% by mass or less,
A water-in-oil emulsion ink in which the particle size distribution width of the emulsion represented by the following formula (1) is 2.0 or less.
Emulsion particle size distribution width = (D ₉₀ - D ₁₀ )/D ₅₀ (1)
(In formula (1), D ₁₀ , D ₅₀ and D ₉₀ represent particle diameters corresponding to cumulative volume frequencies of 10%, 50% and 90%, respectively, calculated from the smaller emulsion particle diameter.) 2. The water-in-oil emulsion ink according to claim 1, wherein the aqueous phase further contains a polymeric dispersant A. Polymer dispersant A is a vinyl polymer (a′) having a crosslinked structure containing a structure derived from the vinyl polymer (a) having a carboxyl group and a structure derived from a crosslinker,
3. A water-in-oil emulsion ink according to claim 2, wherein said cross-linking agent is a polyfunctional epoxy compound. 4. The water-in-oil emulsion ink according to any one of claims 1 to 3, wherein the oil phase contains an ester oil. The water-in-oil emulsion ink according to any one of claims 1 to 4, wherein the emulsion has a particle diameter _D50 of 1.5 µm or less. The water-in-oil emulsion ink according to any one of claims 1 to 5, which is for inkjet recording. 7. The method for producing a water-in-oil emulsion ink according to any one of claims 1 to 6, comprising emulsifying an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium in an oil phase. 8. The method for producing a water-in-oil emulsion ink according to claim 7, wherein the water-based pigment dispersion is obtained by a method comprising steps 1-1 and 1 below.
Step 1-1: Part of the carboxy groups of the polymer (a) having carboxy groups is neutralized with a neutralizing agent to obtain an aqueous dispersion of the polymer (a) Step 1: Obtained in step 1-1 After the aqueous dispersion of the polymer (a) and the pigment are mixed to obtain a pigment mixture, the pigment mixture is subjected to a dispersion treatment so that the pigment is dispersed in an aqueous medium with the polymer (a) having a carboxy group. Step of obtaining an aqueous pigment dispersion