JP2011126031A - Ink set for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set capable of providing a printed article which is excellent in printing density, suppressed in strike-through, and has high quality, and to provide a liquid composition included in the ink set which is excellent in material suitability with an inkjet print head and hardly changes pH during storing, and to provide an inkjet recording method. <P>SOLUTION: [1] The ink set for inkjet recording includes: a water-based ink containing an anionic coloring agent; and the liquid composition, and the liquid composition comprises a cationic polymer, a water-soluble organic solvent, an acid with an acid dissociation index (pKa) of 2-6 and organic amine with a base dissociation index (pKb) of 3-8, and does not contain an acid with the pKa of smaller than 2 or contains the acid of smaller than 0.5 wt.%, and its pH is 7-9. [2] The liquid composition is included in the ink set for inkjet recording. [3] The inkjet recording method is constituted by making the liquid composition stick to a recording medium by an inkjet system and performing recording by using the water-based ink containing the anionic coloring agent by an inkjet recording system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink set for ink jet recording, a liquid composition, and an ink jet recording method.

The ink jet recording system is a recording system in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle and attaching them to a recording member. This method is widely spread because it is easy to make full color and is inexpensive, and has many advantages such as the ability to use plain paper as a recording medium and non-contact with the substrate.
However, since the ink jet recording system prints on a recording medium such as paper by discharging a solution or dispersion of a colorant having a large amount of solvent, the ink permeates and spreads along the fiber of the paper and the like. There is a problem such as a decrease in sharpness, and in order to solve the problem, processing or the like is performed on a recording medium such as paper in advance.

For example, Patent Document 1 discloses an ink-jet liquid composition containing chitosan and a non-volatile organic acid for the purpose of improving high water resistance and suppressing bleeding.
Patent Document 2 contains at least an organic acid having a pKa of 4.5 or less, an organic amine compound, a water-soluble solvent, and water for the purpose of improving optical density, bleeding, etc., and the organic amine with respect to the organic acid. An ink jet liquid composition in which the ratio of the amount of compound added is in a specific range is disclosed.

JP 2005-248133 A JP 2006-35689 A

As a processing method for a recording medium used for ink jet recording, as described in Patent Document 1, a processing agent having a polarity opposite to that of the ink colorant is loaded into the printer together with the colored ink, and the processing agent is applied to the medium by an ink jet method. The method is used. In general, since the colorant is anionic, a cationic treating agent is widely used. However, the cationic treatment agent has a large change in physical properties such as pH during storage, which seems to corrode the print head of an ink jet printer that discharges this treatment agent, or the structural change of the cationic compound as a component. Therefore, there is a problem that stable printing is difficult.
The present invention includes an ink set that can provide a high-quality printed matter with excellent print density and little show-through, and an ink set that is excellent in material compatibility of an inkjet print head and has little pH change during storage. It is an object to provide a liquid composition and an inkjet recording method.

The inventor of the present invention uses an anionic colorant in an ink jet recording method, and if a cationic treatment agent is used, the ink jet print head is corroded and changes in physical properties such as pH occur. It was considered that the acid was included in the neutralization of the acid and the type of base used for pH adjustment. As a result, a liquid composition having a pH in a specific range, containing a cationic polymer, a water-soluble organic solvent, an acid having a specific pKa, an organic amine having a specific pKb, and substantially free of a strong acid, Excellent print material compatibility with ink jet print head, little change in pH during storage, and use of the liquid composition together with ink using an anionic colorant for ink jet recording, resulting in high print density and show-through suppression effect Was found to express.
That is, the present invention provides the following [1] to [3].
[1] An ink set for inkjet recording comprising an aqueous ink containing an anionic colorant and a liquid composition, wherein the liquid composition has a cationic polymer, a water-soluble organic solvent, and an acid dissociation index (pKa) of 2. An acid having a base dissociation index (pKb) of 3 to 8, an acid having a pKa of less than 2 or less than 0.5% by weight, and having a pH of 7 to 9 An ink set for inkjet recording.
[2] A liquid composition contained in the ink set for ink jet recording described in [1].
[3] An ink jet recording method in which the liquid composition of [2] is attached to a recording medium by an ink jet method and then recorded by an ink jet recording method using an aqueous ink containing an anionic colorant.

  According to the present invention, an ink set that has excellent print density and can provide a high-quality printed matter with little show-through, and an ink set that has excellent material compatibility with an inkjet print head and has little pH change during storage. The liquid composition contained and the inkjet recording method can be provided.

<Ink set for inkjet recording>
The ink set for ink jet recording of the present invention is an ink set for ink jet recording comprising a water-based ink containing an anionic colorant and a liquid composition, wherein the liquid composition comprises a cationic polymer, a water-soluble organic solvent, an acid. An acid having a dissociation index (pKa) of 2 to 6 and an organic amine having a base dissociation index (pKb) of 3 to 8, not containing an acid having a pKa of less than 2 or containing less than 0.5% by weight, Its pH is 7-9.
Hereinafter, each component used in the present invention will be described.

<Liquid composition for inkjet recording>
The liquid composition contained in the ink set for inkjet recording of the present invention has a cationic polymer, a water-soluble organic solvent, an acid having an acid dissociation index (pKa) of 2 to 6, and a base dissociation index (pKb) of 3 to 8. Contains an organic amine and does not contain an acid with a pKa of less than 2 or less than 0.5% by weight and has a pH of 7-9.

[Cationic polymer]
The inkjet recording liquid composition of the present invention contains a cationic polymer, and the cationic polymer preferably has a molecular weight of 1500 to 100,000.
Here, “cationic” of the cationic polymer means that when an unneutralized compound is dispersed or dissolved in pure water, the pH becomes higher than 7, or a compound having a quaternary ammonium salt or the like. When the counter ion is dispersed or dissolved in pure water as a hydroxide ion, the pH becomes higher than 7, or the compound or the like is insoluble in pure water, and the pH cannot be measured clearly. It means that the zeta potential of the dispersion dispersed in pure water becomes positive.

As the cationic polymer, a polymer having a cationic group such as a primary to tertiary amino group, an imino group, a quaternary ammonium base, or hydrazine is preferable, and a polymer having an amino group and / or an imino group is more preferable. The polymer is preferably a homopolymer of a monomer having a cationic group, a copolymer with another monomer, or a condensation polymer.
The cationic polymer is water-soluble from the viewpoint of efficiently reacting with the anionic polymer particles containing the colorant and improving the printing density of the aqueous dispersion or the ink containing the aqueous dispersion. Is preferred. Here, the water-soluble polymer means a polymer having a dissolution amount exceeding 10 g when the cationic polymer is dried at 105 ° C. for 2 hours and the polymer reaching a constant weight is dissolved in 100 g of water at 25 ° C. The dissolved amount is preferably 20 g or more, more preferably 100 g or more.

The cationic polymer is derived from a monomer having an amino group, an acid neutralized product of a monomer having an amino group, a quaternary ammonium salt obtained by quaternizing the monomer with a quaternizing agent, and the like. A polymer having structural units, polyethyleneimine, polyallylamine, polyvinylamine, poly (diallyldimethylammonium chloride), polyvinylpyridine, polyethyleneimine-epichlorohydrin reactant, polyamide-polyamine resin, polyamide-epichlorohydrin resin, chitosan, cationized starch, Polyamine sulfone, polyvinyl imidazole, polyamidine, dicyanamide polyalkylene polyamine condensate, polyalkylene polyamine dicyandiamide ammonium salt condensate, dicyandiamide formalin condensate, epichlorohydrin dia Kiruamin polycondensate, diallyl dimethyl ammonium chloride-SO ₂ copolymer, vinylpyrrolidone-vinylimidazole copolymer, and vinyl benzyl trimethylammonium chloride polymers and the like. Among these, a polymer having a structural unit derived from a monomer having an amino group, a polymer having a structural unit derived from a quaternary ammonium salt obtained by quaternizing the monomer with a quaternizing agent, polyethyleneimine, Polyallylamine is more preferred. In the case of a polymer having an amino group, an acid neutralized one is preferred.

Examples of the monomer having an amino group include (meth) acrylic acid esters having a dialkylamino group, and dialkylaminoethyl methacrylate having an alkyl group having 1 to 4 carbon atoms is preferable. Specific examples thereof include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, diisopropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate, diisobutylaminoethyl ( And (meth) acrylate, di-t-butylaminoethyl (meth) acrylate, and the like.
Examples of quaternary ammonium salt monomers obtained by quaternizing an amino group-containing monomer with a quaternizing agent include (meth) acryloyloxyethyltrialkyl (methyl or ethyl) ammonium salts and (meth) acryloyloxypropyltrimethyl. Alkyl (methyl or ethyl) ammonium salts are preferable, and (meth) acryloyloxyethyltrimethylammonium chloride and (meth) acryloyloxypropyltrimethylammonium chloride are more preferable.
Among the above cationic polymers, dialkylaminoethyl methacrylate having an alkyl group having 1 to 4 carbon atoms, particularly one having a structural unit derived from dimethylaminoethyl (meth) acrylate is particularly preferable.
The above cationic polymers can be used alone or in combination of two or more.
The content of the cationic polymer is preferably 1 to 15% by weight, more preferably 2 to 13% by weight, further preferably 3 to 12% by weight, and further preferably 4 to 10% by weight. When the content of the cationic polymer is 1% or more, agglomeration with an anionic ink is obtained, and a printed matter having a high print density and little show-through is obtained. When the content is 15% or less, the viscosity of the liquid composition is appropriately maintained, and the ejection from the head becomes good.

(Water-soluble organic solvent)
The liquid composition for inkjet recording of the present invention contains a water-soluble organic solvent.
The water-soluble organic solvent is not particularly limited as long as it is an organic solvent that can be uniformly mixed in water at an arbitrary ratio, but a solvent that does not affect the resin or adhesive of the print head is preferable.
Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-hexanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol and the like having 2 to 8 carbon atoms. Alkanediols, polyalkylene (2 to 4 carbon atoms) glycol alkyl (2 to 6 carbon atoms) ethers such as triethylene glycol monobutyl ether, polyethylene glycol, glycerin, dioxane, 2-pyrrolidone and the like. Among these, polyols such as ethylene glycol, diethylene glycol, polyethylene glycol, and glycerin are preferable, and glycerin is particularly preferable.
The content of the water-soluble organic solvent in the liquid composition is preferably 5 to 40% by weight, more preferably 10 to 35% by weight, and still more preferably 15 to 30% by weight from the viewpoint of ejection stability.

[Acid having an acid dissociation index (pKa) of 2 to 6]
In the liquid composition for inkjet recording of the present invention, an acid having an acid dissociation index (pKa) of 2 to 6 is used in order to prevent corrosion of a print head that discharges the liquid composition.
The acid dissociation index of the acid used here is 2 to 6, and 3 to 6 is preferable and 3 to 5 is more preferable from the viewpoints of the print density and the penetration property of the ink set.
In the present invention, the acid having a pKa of 2 to 6 contained in the ink jet recording liquid composition includes an acid used for neutralization of the cationic polymer and an acid derived from an anion used as a counter ion of the ammonium salt.
In addition, the acid dissociation index (pKa) in the present invention is a common logarithm value-logKa of the reciprocal of the acid dissociation constant (Ka), edited by the Chemical Society of Japan, Chemical Handbook, Basics, Revised 5th edition (issued by Maruzen Co., Ltd.) In the case where the value is not described, PH / ION METER F-23 (manufactured by Horiba, Ltd.) is used at 25 ° C. ", John Wilery (1980)".
Specific examples of acids having a pKa of 2 to 6 include malonic acid (pKa2.7), citric acid (pKa2.9), malic acid (pKa3.2), glycolic acid (pKa3.6), and lactic acid (pKa3.7). ), Gluconic acid (pKa 3.9), glutaric acid (pKa 4.1), acetic acid (pKa 4.6), propionic acid (pKa 4.7), uric acid (pKa 5.6) and the like. Among these, at least one selected from malonic acid, glycolic acid, lactic acid, gluconic acid, acetic acid, and uric acid is preferable from the viewpoints of corrosivity and printing density.
The content of the acid having a pKa of 2 to 6 is preferably 0.5 to 7% by weight, more preferably 0.8 to 6% by weight, still more preferably 1 to 5% by weight, still more preferably 2 to 4% by weight. It is.
When the acid content is 0.5% by weight or more, it is easy to obtain cohesiveness with an anionic ink, and it is easy to obtain a printed matter having a high print density and little show-through. If it is 7% by weight or less, the head is not corroded and the material compatibility is excellent. The ratio of the acid to the cationic polymer (cationic polymer / acid) is preferably from 1/1 to 1/20, and preferably from 1 / 1.2 to 1/20 from the viewpoint of improving printing density, see-through, and suppressing corrosiveness. / 10 is more preferable, and 1 / 1.5 to 1/5 is still more preferable.

[Acid with pKa less than 2]
On the other hand, the liquid composition for inkjet recording of the present invention substantially does not contain an acid having a pKa of less than 2 from the viewpoint of preventing corrosion of the print head that ejects ink and improving the print density. That is, it is not contained or even if contained, it is less than 0.5% by weight.
In the present invention, the acid having a pKa of less than 2 contained in the ink jet recording liquid composition includes an acid used for neutralization of a cationic polymer and an acid derived from an anion used as a counter ion of an ammonium salt.
An acid having a pKa of less than 2 corrodes the nozzle plate even if water repellent treatment is performed. Furthermore, since the cationic polymer neutralized with an acid having a pKa of less than 2 is highly soluble even when concentrated on the paper surface and easily permeates into the paper, the printing density may be increased if the liquid composition contains an acid having a pKa of less than 2. Is considered difficult to improve.
Examples of the acid having a pKa of less than 2 include hydrochloric acid (pKa: -8) and sulfuric acid (pKa: -5.2).
In the liquid composition of the present invention, the content of these so-called strong acids is preferably less than 0.1 wt%, more preferably less than 0.01 wt%, more preferably 0.001 wt% in the liquid composition. Less, more preferably less than 0.0001% by weight, and most preferably not contained.

[Organic amine having a base dissociation index (pKb) of 3 to 8]
In the liquid composition for inkjet recording of the present invention, an organic amine having a base dissociation index (pKb) of 3 to 8 is used in order to maintain the pH at 7 to 9 and suppress the pH change during storage.
The organic amine used here has a base dissociation index of 3 to 8, preferably 4 to 6.5, more preferably 5 to 6.5, from the viewpoints of the print density and back-through property of the ink set.
The base dissociation index (pKb) in the present invention is a common logarithm value-log Kb of the reciprocal of the base dissociation constant (Kb). Based on the pKa described in (Issuance), it is obtained from the following equation (1).
pKb = (14−pKa) (1)
If not listed in the chemical handbook, use PH / ION METER F-23 (manufactured by Horiba, Ltd.) at 25 ° C. ) ".
Specific examples of the amine having a pKb of 3 to 8 include dimethylamine, diethylamine, trimethylamine, triethylamine, ethylenediamine, N, N-dimethylethylenediamine, N-methylethanolamine, N-methyldiethanolamine, N, N-dimethylethanolamine, Examples thereof include organic amines such as N, N-diethylethanolamine, N, N-dibutylethanolamine, diethanolamine, triethanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, N, N-dimethylethylenediamine. Among these, alcohol amines are preferable from the viewpoints of corrosivity and printing density, and N, N-diethylethanolamine (pKb4.1), triethanolamine (pKb6.2), N, N-dimethylethylenediamine (pKb7.0). ) Is more preferable, and N, N-diethylethanolamine and triethanolamine are still more preferable.

The content of the organic amine having a pKb of 3 to 8 is preferably 0.1 to 5% by weight, more preferably 0.2 to 4.5% by weight, still more preferably 0.3 to 4% by weight, still more preferably. Is 0.4 to 3.5% by weight. When the organic amine content is 0.1% by weight or more, it is easy to adjust the pH of the acid-neutralized cationic polymer solution from the neutral to the alkaline region, and the head is not corroded and stored. The change of pH at the time can also be suppressed. On the other hand, when the content is 7% by weight or less, the viscosity of the liquid composition is appropriately maintained, and the ejection from the head becomes good.
The ratio of the organic amine to the cationic polymer (cationic polymer / organic amine) is preferably from 1/1 to 1/100, from the viewpoint of improving printing density, see-through, and suppressing corrosiveness, -1/70 is more preferable, and 1 / 1.5-1-40 is still more preferable.

[Liquid composition]
The liquid composition of the present invention is preferably substantially free of colorant. The specific colorant content is preferably 1% by weight or less, more preferably 0.1% by weight or less, and still more preferably 0.01% by weight or less. If the liquid composition does not substantially contain a colorant, it does not affect the hue of the ink when printed over the ink.
The water content in the liquid composition of the present invention is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and still more preferably 40 to 70% by weight.
The pH of the liquid composition of the present invention is 7.0 to 9.0, more preferably 7.2 to 8.8, and still more preferably 7.5 to 8.0. 5.
The preferred static surface tension (20 ° C.) of the liquid composition of the present invention is preferably 23 to 70 mN / m, more preferably 30 to 70 mN / m, and still more preferably 40 from the viewpoint of suppressing printing density and back-through. -70 mN / m.
The viscosity (20 ° C.) of the liquid composition of the present invention is preferably 2 to 20 mPa · s, more preferably 2.5 to 16 mPa · s, and further preferably 3.0 to 12 mPa · s.
The liquid composition of the present invention contains a dispersant, a surfactant, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, a rust inhibitor and the like that are usually used in a liquid composition ejected by an inkjet method. be able to.

[Aqueous ink containing anionic colorant]
The liquid composition of the present invention is used with an aqueous ink containing an anionic colorant.
(Anionic colorant)
There are no particular restrictions on the anionic colorant, and an anionic water-soluble dye, anionic colorant particles, and the like can be used. From the viewpoint of improving print density and print sharpness and suppressing back-through, “Colorant particles” are preferred.
Here, “anionic” means that when 1% by weight of an unneutralized substance with respect to pure water is dispersed or dissolved in pure water, the pH of the dispersion or the solution at 20 ° C. Is less than 7, or when the substance is insoluble in pure water and the pH cannot be measured clearly, the zeta potential of the dispersion dispersed in pure water is negative.

The anionic colorant particles are not particularly limited, but an anionic self-dispersing pigment in which a colorant such as a pigment and a hydrophobic dye is dispersed in an ink using an anionic surfactant or an anionic polymer. Anionic polymer particles containing an anionic self-dispersing pigment and a colorant are preferred, and “anionic polymer particles containing a colorant” are more preferred.
In the present specification, the term “colorant” refers to pigments and dyes, and examples thereof include anionic water-soluble dyes and anionic self-dispersing pigments.
The average particle diameter of the anionic colorant particles is preferably 40 to 200 nm, more preferably 50 to 150 nm, and still more preferably 60 to 100 nm from the viewpoint of printing density.
The average particle diameter of the anionic colorant particles is measured by a dynamic light scattering method, and specifically measured by the method of the example.

As the colorant contained in the anionic colorant particles, pigments, hydrophobic dyes and the like can be used, but pigments are preferred.
The pigment may be either an inorganic pigment or an organic pigment. If necessary, they can be used in combination with extender pigments.
Examples of the inorganic pigment include carbon black and metal oxide, and carbon black is particularly preferable for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Specific examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
The hue is not particularly limited, and any chromatic pigment such as red, yellow, blue, 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 products selected from the group consisting of pigment green are listed. Among these, quinacridone pigments are preferable from the viewpoint of color developability.
Moreover, solid solution pigments, such as a quinacridone solid solution pigment, can also be used suitably. The quinacridone solid solution pigment includes β-type and γ-type unsubstituted quinacridone and 2,9-dimethylquinacridone (CI Pigment Red 122), or β-type and γ-type unsubstituted quinacridone and 2,9- It consists of dichloroquinacridone such as dichloroquinacridone, 3,10-dichloroquinacridone, and 4,11-dichloroquinacridone. The quinacridone solid solution pigment is preferably a solid solution pigment composed of a combination of unsubstituted quinacridone (CI Pigment Violet 19) and 2,9-dichloroquinacridone (CI Pigment Red 202).

In the present invention, a self-dispersing pigment can also be used. Self-dispersing pigments are those in which one or more hydrophilic functional groups (anionic hydrophilic groups such as carboxy groups and sulfonic acid groups, or cationic hydrophilic groups such as quaternary ammonium groups) are directly or other atomic groups. It means a pigment that can be dispersed in an aqueous medium without using a surfactant or a resin by binding to the surface of the pigment. Here, examples of the “other atomic group” include an alkanediyl group having 1 to 12 carbon atoms, a phenylene group, or a naphthylene group. When used for anionic colorant particles, the hydrophilic functional group is preferably an anionic hydrophilic group such as a carboxy group or a sulfonic acid group. In order to make the pigment a self-dispersing pigment, for example, a necessary amount of the hydrophilic functional group may be chemically bonded to the pigment surface by a conventional method.
The amount of the hydrophilic functional group is not particularly limited, but is preferably 100 to 3,000 μmol per 1 g of the self-dispersing pigment, and preferably 200 to 700 μmol per 1 g of the self-dispersing pigment when the hydrophilic functional group is a carboxy group.
The above pigments can be used alone or in admixture of two or more at any ratio.

[Anionic polymer particles containing colorant]
As anionic colorant particles, anionic polymer particles containing a colorant can be preferably used.
(Anionic polymer)
The anionic polymer used for the anionic polymer particles is preferably a water-insoluble polymer from the viewpoint of improving the print density of the aqueous dispersion and ink. Here, the “water-insoluble polymer” refers to a polymer that has been dried at 105 ° C. for 2 hours and has reached a constant weight and dissolved in 100 g of water at 25 ° C., and its dissolved amount is 10 g or less. The dissolved amount is preferably 5 g or less, more preferably 1 g or less. In the case of an anionic polymer, the dissolution amount is the dissolution amount when the anionic group of the polymer is neutralized 100% with sodium hydroxide.
Examples of polymers used include polyesters, polyurethanes, and vinyl polymers. From the viewpoint of ink storage stability, vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds). Polymers are preferred.

  The anionic vinyl polymer includes a monomer mixture (a) an anionic monomer (hereinafter also referred to as “(a) component”) and (b) a hydrophobic monomer (hereinafter also referred to as “(b) component”) ( In the following, a vinyl polymer obtained by copolymerizing a simple monomer mixture) is preferred. This vinyl polymer has a structural unit derived from the component (a) and a structural unit derived from the component (b). Especially, what contains the structural unit derived from (c) macromer (henceforth "(c) component") is preferable.

[(A) Anionic monomer]
(A) The anionic monomer is used as a monomer component of the anionic polymer from the viewpoint of stably dispersing the anionic polymer particles containing the colorant in the ink.
Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of the sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and 3-sulfopropyl (meth) acrylate.
Examples of the phosphoric acid monomer include vinyl phosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, and the like.
Among the anionic monomers, a carboxylic acid monomer is preferable and acrylic acid and methacrylic acid are more preferable from the viewpoint of dispersion stability of the anionic polymer particles in the ink.

[(B) Hydrophobic monomer]
(B) The hydrophobic monomer is used as a monomer component of the anionic polymer from the viewpoint of dispersion stability of the aqueous dispersion. Examples of the hydrophobic monomer include alkyl (meth) acrylates and aromatic group-containing monomers.
As the alkyl (meth) acrylate, those having an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms are preferable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meta) ) Acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) Examples include decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, and (iso) stearyl (meth) acrylate.
In addition, “(iso or tertiary)” and “(iso)” mean both cases where these groups are not present and indicate normal when these groups are not present. “(Meth) acrylate” indicates acrylate and / or methacrylate.

As the aromatic group-containing monomer, a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, is preferable, and a styrene monomer or an aromatic group-containing (meth) acrylate. Is more preferable.
As the styrenic monomer, styrene, 2-methylstyrene, and divinylbenzene are preferable, and styrene is more preferable.
Moreover, as an aromatic group containing (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. are preferable, and benzyl (meth) acrylate is more preferable.
(B) As for the hydrophobic monomer, two or more kinds of the above-mentioned monomers can be used, but it is preferable to use a styrene monomer and an aromatic group-containing (meth) acrylate in combination, and benzyl (meth) acrylate and styrene are used in combination. More preferably.

[(C) Macromer]
(C) The macromer is a compound having a polymerizable functional group at one end and a number average molecular weight of 500 to 100,000, and from the viewpoint of storage stability of the anionic polymer particles in the ink, the monomer component of the anionic polymer Used as The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
(C) The number average molecular weight of the macromer is preferably 1,000 to 10,000. The number average molecular weight is measured using polystyrene as a standard substance by a gel chromatography method using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent.
(C) As the macromer, from the viewpoint of dispersion stability of the anionic polymer particles in the ink, an aromatic group-containing monomer-based macromer and a silicone-based macromer are preferable, and an aromatic group-containing monomer-based macromer is more preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromer include the aromatic group-containing monomers described in the above (b) hydrophobic monomer, styrene and benzyl (meth) acrylate are preferable, and styrene is more preferable. preferable.
Specific examples of the styrenic macromer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of the silicone macromer include organopolysiloxane having a polymerizable functional group at one end.

[(D) Nonionic monomer]
The monomer mixture preferably further contains (d) a nonionic monomer (hereinafter also referred to as “component (d)”).
(D) As a component, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2-30, n shows the average addition mole number of an oxyalkylene group. The same hereafter). Polyalkylene glycol (meth) acrylates such as (meth) acrylate, alkoxypolyalkylene glycol (meth) acrylates such as methoxypolyethylene glycol (1-30) (meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymer) (1 to 1) 30, ethylene glycol: 1 to 29) (meth) acrylate and the like therein. Among these, polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy (ethylene glycol / propylene glycol copolymer) (meth) acrylate are preferable, and polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy ( More preferably, ethylene glycol / propylene glycol copolymer) (meth) acrylate is used in combination.

Specific examples of the commercially available component (d) include NK Esters M-20G, 40G, and 90G from Shin-Nakamura Chemical Co., Ltd., Bremer PE-90, 200, and 200 from NOF Corporation. 350, PME-100, 200, 400, etc., PP-500, 800, etc., AP-150, 400, 550, 50PEP-300, 50POEP-800B, 43PAPE-600B, and the like.
The components (a) to (d) can be used alone or in admixture of two or more.

Content (a) to (c) component in the monomer mixture of the above components (a) to (c) at the time of vinyl polymer production (content as an unneutralized amount; the same applies hereinafter) or vinyl polymer The content of the structural unit derived from is as follows.
The content of the component (a) is preferably 3 to 40% by weight, more preferably 4 to 30% by weight, and particularly preferably 5 from the viewpoint of stably dispersing the anionic polymer particles containing the colorant in the ink. ~ 25% by weight.
The content of component (b) is preferably 5 to 98% by weight, more preferably 10 to 80% by weight, from the viewpoint of dispersion stability of the anionic polymer particles in the aqueous dispersion.
The content of the component (c) is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, from the viewpoint of dispersion stability of the anionic polymer particles in the aqueous dispersion.
The weight ratio of [(a) component / [(b) component + (c) component]] is from the viewpoint of dispersion stability of the anionic polymer particles containing the colorant in the ink and the printing density of the ink. , Preferably 0.01 to 1, more preferably 0.02 to 0.67, still more preferably 0.03 to 0.50.

(Production of anionic polymer)
The anionic polymer is produced by copolymerizing a monomer mixture by a known polymerization method. As the polymerization method, a solution polymerization method is preferable.
Although there is no restriction | limiting in the solvent used by the solution polymerization method, Polar organic solvents, such as C1-C3 aliphatic alcohol, ketones, ethers, and esters, are preferable, specifically, methanol, ethanol, acetone, and methyl ethyl ketone. And methyl ethyl ketone is preferred.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, 2,2′-azobis (2,4-dimethylvaleronitrile) is preferable, and the polymerization chain transfer agent is used. Is preferably 2-mercaptoethanol.

Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 to 80 ° C., and the polymerization time is preferably 1 to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. In addition, unreacted monomers and the like can be removed from the obtained polymer by reprecipitation, membrane separation, chromatographic methods, extraction methods and the like.
The weight average molecular weight of the anionic polymer used in the present invention is preferably 5,000 to 500,000 from the viewpoint of dispersion stability of the anionic polymer particles containing the colorant in the ink and the printing density of the ink, 10,000 to 400,000 are more preferable, 10,000 to 300,000 are more preferable, and 20,000 to 200,000 are more preferable. In addition, the measurement of a weight average molecular weight can be performed by the method as described in an Example.

[Production of Anionic Polymer Particles Containing Colorant]
Anionic polymer particles containing a colorant can be efficiently produced by a method having the following steps (1) and (2) as an aqueous dispersion.
Step (1): A step of dispersing a mixture containing an anionic polymer, an organic solvent, a colorant, and water to obtain a dispersion of anionic polymer particles containing a colorant Step (2): Step (1) The organic solvent is removed from the dispersion obtained in step 1) to obtain an aqueous dispersion of anionic polymer particles containing a colorant.

Process (1)
In step (1), an anionic polymer is first dissolved in an organic solvent, and then a colorant, water, and, if necessary, a neutralizing agent and a surfactant are added to the obtained organic solvent solution and mixed. A method of obtaining an oil-in-water type dispersion is preferred. Although there is no restriction | limiting in the order added to the organic solvent solution of an anionic polymer, It is preferable to add in order of a neutralizing agent, water, and a coloring agent.
Although there is no restriction | limiting in the organic solvent in which an anionic polymer is dissolved, C1-C3 aliphatic alcohol, ketones, ethers, esters, etc. are preferable and methyl ethyl ketone is preferable. When the anionic polymer is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is.
When using a neutralizing agent, it is preferable to neutralize so that pH may be 7-11. Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and various amines. Further, the anionic polymer may be neutralized in advance.
From the viewpoint of dispersion stability, the neutralization degree of the anionic group of the anionic polymer is preferably 10 to 300%, more preferably 20 to 200%, and still more preferably 30 to 150%.
Here, the degree of neutralization is obtained by dividing the molar equivalent of the neutralizing agent by the molar amount of the anionic group of the anionic polymer.

In the mixture, the colorant is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, the organic solvent is preferably 10 to 70% by weight, more preferably 10 to 50% by weight, and the anionic polymer is The amount is preferably 2 to 40% by weight, more preferably 3 to 20% by weight, and water is preferably 10 to 70% by weight, more preferably 20 to 70% by weight.
From the viewpoint of dispersion stability, the weight ratio of the amount of the colorant to the amount of the anionic polymer [colorant / anionic polymer] is preferably 50/50 to 90/10, and 70/30 to 85 / More preferably, it is 15.

There is no restriction | limiting in particular in the dispersion method of the mixture in process (1). Although the average particle diameter of the anionic polymer particles containing the colorant can be atomized only by the main dispersion until the desired particle diameter is reached, preferably after pre-dispersion, the main dispersion is further subjected to shear stress. It is preferable to control the average particle size of the anionic polymer particles containing the colorant to a desired particle size. The temperature in the dispersion in the step (1) is preferably 0 to 40 ° C, more preferably 5 to 30 ° C, and the dispersion time is preferably 1 to 30 hours, and more preferably 2 to 25 hours.
When the mixture is predispersed, a generally used mixing and stirring device such as an anchor blade or a disper blade, particularly a high-speed stirring and mixing device is preferable.
Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer (trade name), a media-type disperser such as a paint shaker and a bead mill. Examples of commercially available media dispersers include Ultra Apex Mill (trade name, manufactured by Kotobuki Industries Co., Ltd.), Pico Mill (trade name, manufactured by Asada Tekko Co., Ltd.), and the like. A plurality of these devices can be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the anionic polymer particles containing a colorant.

Step (2)
In the step (2), an aqueous dispersion of anionic polymer particles containing a colorant can be obtained by distilling off the organic solvent from the obtained dispersion by a known method. The organic solvent in the aqueous dispersion containing the anionic polymer particles containing the obtained colorant is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by weight or less, and more preferably 0.01% by weight or less.
If necessary, the dispersion can be heated and stirred before the organic solvent is distilled off.
The obtained aqueous dispersion of anionic polymer particles containing a colorant is one in which the solid content of the polymer containing a colorant is dispersed in water as a main medium. Here, the form of the polymer particles is not particularly limited as long as the particles are formed of at least a colorant and an anionic polymer. For example, a particle form in which a colorant is encapsulated in the polymer, a particle form in which a colorant is uniformly dispersed in the polymer, a particle form in which a colorant is exposed on the polymer particle surface, and the like are included. Is also included.

[Ink containing an anionic colorant]
The ink containing the anionic colorant of the present invention includes a wetting agent, a penetrating agent, a dispersant, a surfactant, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, a rust preventing agent and the like that are usually used in the ink. Can be added.
The content of each component in the ink of the present invention is as follows.
The content of the anionic colorant particles used in the ink of the present invention is preferably 1 to 40% by weight, more preferably 2 to 30% by weight, and more preferably 4 to 20% from the viewpoint of increasing the printing density of the water-based ink. % By weight, more preferably 5 to 15% by weight.
The content of the colorant contained in the anionic colorant particles used in the ink of the present invention is preferably 1 to 25% by weight, more preferably in the ink (B), from the viewpoint of increasing the print density of the water-based ink. It is 2 to 20% by weight, more preferably 4 to 15% by weight, still more preferably 5 to 12% by weight.
The water content is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and still more preferably 40 to 70% by weight.
The preferred surface tension (20 ° C.) of the ink of the present invention is 23 to 50 mN / m, more preferably 23 to 45 mN / m, and still more preferably 25 to 40 mN / m.
In order to maintain good ejection reliability, the viscosity (20 ° C.) of the ink of the present invention is preferably 2 to 20 mPa · s, more preferably 2.5 to 16 mPa · s, and still more preferably 3.0. ˜12 mPa · s.

<Ink set for inkjet recording>
The ink set for ink jet recording of the present invention is characterized by including the water-based ink containing the anionic colorant and the liquid composition of the present invention.
The ink cartridge for each color of the ink jet printer is filled with the water-based ink containing the liquid composition of the present invention and the anionic colorant, respectively, and ink droplets are ejected from each ejection nozzle corresponding to each ink cartridge. Can be printed.

<Inkjet recording method>
The inkjet recording method of the present invention is characterized in that after the liquid composition of the present invention is attached to a recording medium by an inkjet method, recording is performed by an inkjet recording method using an aqueous ink containing an anionic colorant. To do.
By recording the liquid composition on a recording medium before recording by an ink jet recording method, the printing density is high even when printing on plain paper. It is possible to obtain a high-quality printed matter that is excellent in properties and has less show-through. In this case, the time from when the liquid composition is attached to the recording medium to when recording by the ink jet recording method is not particularly limited.
The method of attaching the liquid composition to the recording medium is an ink jet method, and it is preferable to use a piezo ink jet printer.
In addition, an ink jet recording method for printing on a recording medium using an aqueous ink containing an anionic colorant is not limited, but a piezo ink jet printer is preferably used.

The ink jet recording apparatus used in the present invention can have any ejection surface, but preferably has a nickel-fluorine resin plated nozzle plate. In the ink jet recording method of the present invention, a liquid composition is used. Further, it is preferable to discharge from an ink jet recording apparatus having a nozzle plate having a discharge surface plated with nickel-fluorine resin.
A nozzle plate of an ink jet printer is provided with a plurality of nozzle holes including a funnel-shaped portion that is largely open on the back surface side and an orifice portion that is narrowly open on the front surface side. This nozzle plate is formed of various metals, ceramics, photosensitive resin, and the like. The discharge surface (nozzle hole and its surrounding portion) is preferably subjected to water repellency treatment by eutectoid plating using nickel-fluorine resin from the viewpoint of ink repellency. When the nozzle plate is plated with nickel-fluorine resin, in the liquid composition of the present invention, the corrosion of the print head can be effectively suppressed, so that ejection is stable and high quality printed matter is obtained. Can do.
This water repellent treatment can be performed, for example, by electroplating a nickel electroformed plate having ink discharge nozzles in a nickel plating solution in which a fluorine-based resin such as polytetrafluoroethylene (PTFE) is dispersed. .
In addition, there is no restriction | limiting in particular about the other structure of an inkjet recording method, A well-known method is employable.

  In the inkjet recording method of the present invention, the recording medium to be used is not particularly limited, and examples thereof include plain paper, foam paper, coated paper, transparent film, etc., but so-called plain paper and foam paper such as copy paper and bond paper are used. From the standpoint of clarifying the effect of significantly improving the print density and suppressing the back-through.

  In the following preparation examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified. The weight average molecular weight of the cationic polymer, the cationization density, the change in pH of the liquid composition, the measurement of the material compatibility of the ink jet print head, and the evaluation are performed by the following methods. For the water-based ink set, the following ink jet recording is performed. Printing was carried out by the method, and the print density and the penetration property were evaluated.

(1) Measurement of weight average molecular weight (Mw) (1-1) Weight average molecular weight of cationic polymer 0.15 mol / L Gel permeation chromatography method using 1% aqueous solution of Na ₂ SO ₄ in acetic acid [Tosoh Corporation It was measured using polyethylene glycol as a standard substance with a company-made GPC apparatus (HLC-8120GPC), a column (TSK-GEL, α-M × 2) manufactured by Tosoh Corporation, and a flow rate of 1 mL / min.
(1-2) Weight average molecular weight of anionic polymer Gel permeation chromatography using a 60 mmol / L H ₃ PO ₄ , 50 mmol / L LiBr solution of dimethyl sulfoxide as a developing solvent [GPC apparatus manufactured by Tosoh Corporation (HLC-8120GPC) And Tosoh Corporation column (TSK-GEL, α-M × 2), flow rate: 1 mL / min], using polystyrene as a standard substance.

(2) Measurement of pH change amount of liquid composition 80 g of the liquid composition was prepared, and divided into two, and one of them was stored in a thermostat adjusted to 70 ° C for 2 days. The liquid composition left at room temperature and the liquid composition stored at 70 ° C. were placed in a thermostatic bath at 25 ° C. and allowed to stand for 1 hour, and the temperature of the liquid composition was adjusted to 25 ° C. Using PH / ION METER F-23 (manufactured by Horiba, Ltd.), three-point calibration of standard solutions (pH 4.01, pH 6.86, pH 9.10), and then measuring the pH of each liquid composition at 25 ° C. did. The smaller the difference in pH value between before and after standing, the better the pH change suppressing effect.
(3) Material compatibility of ink jet print head of liquid composition 3 g of the liquid composition obtained in Examples and Comparative Examples is put into a screw tube, and Epson head (ejection surface of ink jet nozzle: nickel-fluororesin plating) is put on it. After dipping and storing at 70 ° C. for 2 days, the ejection surface of the inkjet nozzle was visually observed and evaluated according to the following evaluation criteria.
〔Evaluation criteria〕
A: The discharge surface is not corroded.
B: The discharge surface is corroded by 10% or more in area.
C: The discharge surface is corroded by 50% or more in area.

(4) Inkjet recording method First, the liquid compositions obtained in the examples and comparative examples were placed on the black head of an inkjet printer (manufactured by Seiko Epson Corporation, model number: EM-930C, piezo method) through a silicon tube. The ink inlet was filled. Next, a solid print pattern (width 204 mm × length 275 mm) was created by Photoshop (trade name, manufactured by Adobe) and printed on plain paper (Nip55: manufactured by Nippon Paper Industries Co., Ltd.) with a solid duty of 100%. Applied.
Next, the ink obtained in Production Example 1 was similarly filled into the ink injection port above the black head of the ink jet printer (EM-930C) via a silicon tube. Next, a solid print pattern (size: horizontal 204 mm x vertical 275 mm) was created by Photoshop (trade name, manufactured by Adobe), solid duty 100% and 10%, and the letter “轟” (font: MS Akira) In the morning, the character size: 12) was printed on the plain paper coated with the liquid composition 1, and ink jet recording was performed (printing condition = paper type: photo paper, mode setting: black, photo, bidirectional).

(5) Measurement of print density The prints obtained in the examples and comparative examples were allowed to stand at 25 ° C. and 50% humidity for 24 hours, and then the print density on the print surface was measured. For the measurement of the print density, a Macbeth densitometer (manufactured by Gretag Macbeth, product number: RD914) was used, and the numerical value of the color density component of magenta printed at Duty 100% was read (measurement conditions: observation light source D65, observation field of view 2 degrees, Concentration standard DIN 16536). The number of times of measurement was changed, and 5 points were selected at random from the portion printed in the forward path of bidirectional printing, and 5 points were selected from the portion printed on the return path, and an average value of a total of 10 points was obtained. A larger measured value is better.
(6) Evaluation of see-through property The print density on the back side of the portion printed with Duty 100% of the printed matter obtained in Examples and Comparative Examples was measured. The measurement was performed in the same manner as the above (6) measurement of printing density. The smaller the measured value, the better.

Example 1 (Production of liquid composition 1)
(1) Synthesis of cationic polymer (polydimethylaminoethyl methacrylate) 200 parts of dimethylaminoethyl methacrylate (made by Wako Pure Chemical Industries, Ltd., special grade reagent) were weighed, and 10 parts of methyl ethyl ketone and a chain transfer agent ( 2-mercaptopropionic acid) 0.4 part and 10% of the monomer liquid were added and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, in the dropping funnel, the remaining 90% of the monomer liquid, 3.6 parts of the chain transfer agent, methyl ethyl ketone 90, and a polymerization initiator (made by Wako Pure Chemical Industries, Ltd., trade names: V-65, 2, 2 ′ -A solution mixture containing 4.0 parts of azobis (2,4-dimethylvaleronitrile)) was added, and the mixture was heated to 75 ° C while stirring the mixed solution in the reaction vessel in a nitrogen atmosphere. Was added dropwise over 3 hours. After 2 hours at 75 ° C. from the end of the dropwise addition, a solution prepared by dissolving 0.15 part of the polymerization initiator in 2.5 parts of methyl ethyl ketone was added, and the mixture was further aged at 75 ° C. for 2 hours and 80 ° C. for 2 hours. A 50% solution of ethyl methacrylate (polymer weight average molecular weight: 7000) was obtained.
(2) Production of liquid composition As cationic polymer, 100 parts of 50% solution of polydimethylaminoethyl methacrylate synthesized in (1) above, 33.17 parts of malonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as acid, 215 parts of ion-exchanged water was added, and methyl ethyl ketone was distilled off with an evaporator adjusted to 60 ° C. with warm water to obtain a 20% polydimethylaminoethyl methacrylate glycolic acid neutralized product.
30.0 parts of the neutralized product, 10.0 parts of glycerin (manufactured by Kao Corporation), 5.0 parts of polyethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd., first grade reagent, average molecular weight 600) and ion exchange water The mixture was stirred with a tic stirrer and further stirred at room temperature for 15 minutes to obtain a mixed solution. Here, the blending amount of ion-exchanged water is an amount adjusted so that the total amount of the mixed solution and the neutralized product is 100 parts.
Next, as an organic amine, triethanolamine is added with stirring with a magnetic stirrer until the pH becomes 8.4, and the liquid composition is filtered through a 1.2 μm filter (cellulose acetate membrane, manufactured by Sartorius). Product 1 was obtained.

Examples 2 to 10 and Comparative Examples 1 to 9 (Production of liquid compositions 2 to 19)
In Example 1 (2), liquid compositions 2 to 19 were obtained in the same manner as in Example 1 except that the cationic polymer, acid, and organic amine were changed to the substances and amounts shown in Tables 1 and 2, respectively. It was.
The polyethyleneimine used in Example 7 is a reagent manufactured by Wako Pure Chemical Industries, Ltd., and has a weight average molecular weight of 10,000, and the polyallylamine used in Example 8 is a product number PAA-05 manufactured by Nitto Boseki Co., Ltd. And the weight average molecular weight is 5000.
As mentioned above, pH of the obtained liquid composition was measured, and the said pH change inhibitory effect was evaluated after that. The results are shown in Tables 1 and 2.

Preparation Example 1 (Preparation of an aqueous dispersion of anionic polymer particles containing a colorant)
(1) Synthesis of anionic polymer 58 parts of benzyl methacrylate, 42 parts of methacrylic acid, 20 parts of styrene, 40 parts of styrene macromer (manufactured by Toagosei Co., Ltd., trade name: AS-6S) (solid content 50%), polypropylene glycol methacrylate (NOF Corporation, trade name: Blenmer PP-800) 30 parts, phenoxypoly (ethylene glycol propylene glycol) methacrylate (NOF Corporation, trade name: Blemmer 43PAPE-600B) 30 parts are mixed, and monomer mixture Was prepared.
In a reaction vessel, 18 parts of methyl ethyl ketone, 0.03 part of a chain transfer agent (2-mercaptoethanol) and 10% of the monomer mixture were mixed and sufficiently substituted with nitrogen gas.
Meanwhile, in the dropping funnel, the remaining 90% of the monomer mixture, 0.27 part of the chain transfer agent, 42 parts of methyl ethyl ketone, and a polymerization initiator (trade name: V-65, 2, manufactured by Wako Pure Chemical Industries, Ltd.) A mixed solution containing 1.2 parts of 2′-azobis (2,4-dimethylvaleronitrile) was added, and the temperature was raised to 75 ° C. while stirring the mixed solution in the reaction vessel under a nitrogen atmosphere. The mixed solution in the funnel was added dropwise over 3 hours. After 2 hours at 75 ° C. from the end of dropping, a solution in which 0.3 part of the polymerization initiator was dissolved in 5 parts of methyl ethyl ketone was added, and further aged at 75 ° C. for 2 hours and at 80 ° C. for 2 hours. Weight average molecular weight: 100,000).
(2) Preparation of aqueous dispersion of anionic polymer particles containing colorant 45 parts of polymer obtained by drying the polymer solution obtained in (1) under reduced pressure was dissolved in 300 parts of methyl ethyl ketone, A 10.2 part 5N aqueous sodium hydroxide solution, 12.2 parts 25% aqueous ammonia, and 1150 parts ion-exchanged water are added as a compatibilizing agent, and a magenta pigment (product number: Chromofine Red 6111T, manufactured by Dainichi Seika Kogyo Co., Ltd.) After adding 135 parts and mixing for 1 hour at 7000 rpm and 20 ° C. using a disperse blade, the obtained dispersion is microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, trade name, model M-140K). Then, a further 15-pass dispersion treatment was performed at a pressure of 180 MPa.
Methyl ethyl ketone was removed from the obtained dispersion at 60 ° C. under reduced pressure, a part of water was further removed, and the mixture was centrifuged, and the filter (manufactured by Sartorius, mini-Salto syringe filter, pore size: 5 μm, material: cellulose acetate) ) To remove coarse particles, and an aqueous dispersion of anionic polymer particles containing a colorant (solid content concentration: 20.0%, average particle size 100 nm) was obtained.

Production Example 1 (Manufacture of ink)
The aqueous dispersion for inkjet recording (1) obtained in Preparation Example 1 was prepared so as to be 7.5 parts in terms of solid content and 5.6 parts in terms of pigment content.
1,2-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 2.0 parts, 2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) 2.0 parts, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) 0.5 Part, Olfine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 0.5 part, glycerin (manufactured by Kao Corporation) 20.0 parts, triethylene glycol monobutyl ether (trade name: butyl triglycol, manufactured by Nippon Emulsifier Co., Ltd.) 2 0.0 part, 0.2 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) and ion-exchanged water were mixed while stirring with a magnetic stirrer, and further stirred at room temperature for 15 minutes to obtain a mixed solution. Here, the blending amount of the ion exchange water is an amount adjusted so that the total amount of the mixed solution and the water dispersion (1) for ink jet recording is 100 parts.
Next, while stirring the prepared aqueous dispersion for ink jet recording (1) with a magnetic stirrer, the above mixed solution was added, and the mixture was filtered through a 1.2 μm filter (cellulose acetate film, manufactured by Sartorius). Got.

Examples 11 to 20 and Comparative Examples 10 to 18 (ink set and ink jet recording)
The liquid compositions obtained in Examples 11 to 20 or Comparative Examples 10 to 18 and the ink obtained in Production Example 1 were attached to an ink jet printer as an ink set, and ink jet recording was performed by the above-described method. And the penetration property was evaluated. The results are shown in Tables 1 and 2.

Comparative Example 19 (ink set and inkjet recording)
In Example 11, the water-based ink obtained in Production Example 1 was printed on a foam paper not coated with the liquid composition. The results are shown in Table 2.

  From Table 1 and Table 2, the liquid composition of the example has less pH change than the liquid composition of the comparative example, excellent material compatibility with the ink jet print head, and ink using the liquid composition of the example It can be seen that the set and ink jet recording methods are superior in print density and have less show-through than the comparative example.

Claims (8)

  An ink set for inkjet recording comprising an aqueous ink containing an anionic colorant and a liquid composition, wherein the liquid composition has a cationic polymer, a water-soluble organic solvent, and an acid dissociation index (pKa) of 2 to 6. An ink containing an acid and an organic amine having a base dissociation index (pKb) of 3 to 8, a pKa of less than 2 or less than 0.5% by weight, and a pH of 7 to 9 Ink set for recording.   The liquid composition contains 1 to 15% by weight of a cationic polymer, 0.5 to 7% by weight of an acid having a pKa of 2 to 6, and 0.1 to 5% by weight of an organic amine having a pKb of 3 to 8, The ink set for inkjet recording according to claim 1.   The ink set for inkjet recording according to claim 1 or 2, wherein the acid having a pKa of 2 to 6 is at least one selected from malonic acid, glycolic acid, lactic acid, gluconic acid, acetic acid, and uric acid.   The inkjet according to any one of claims 1 to 3, wherein the organic amine having a pKb of 3 to 8 is at least one selected from N, N-diethylethanolamine, triethanolamine, and N, N-dimethylethylenediamine. Ink set for recording.   The ink set for inkjet recording according to any one of claims 1 to 4, wherein the cationic polymer has a structural unit derived from a dialkylaminoethyl methacrylate having an alkyl group having 1 to 4 carbon atoms.   The liquid composition contained in the ink set for inkjet recording in any one of Claims 1-5.   An ink jet recording method, wherein the liquid composition according to claim 6 is adhered to a recording medium by an ink jet method, and then recorded by an ink jet recording method using an aqueous ink containing an anionic colorant.   The ink jet recording method according to claim 7, wherein the liquid composition is discharged from an ink jet recording apparatus having a nozzle plate having a discharge surface plated with nickel-fluorine resin.