JP5629459B2 - Water-based ink for inkjet recording - Google Patents

Description

  The present invention relates to an aqueous ink for inkjet recording.

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 member and non-contact with the object to be printed.
In recent years, pigment-based inks in which pigments, polymers, and water are dispersed are mainly used as inks used in ink jet recording from the viewpoint of water resistance and weather resistance.

Various proposals have been made for improving the storage stability of pigment-based aqueous dispersions for inkjet recording and aqueous inks.
For example, Patent Document 1 discloses a first step in which a pigment is dispersed in an aqueous medium in advance using a surfactant and / or a water-soluble resin, a dispersion obtained in the first step, and a self-emulsification having a specific molecular weight. A method for producing an aqueous pigment dispersion comprising a second step of mixing a liquid obtained by dissolving a mold resin in a water-soluble solvent and fixing the self-emulsifying resin on the pigment surface is disclosed.
Patent Document 2 discloses a water-based ink containing crosslinked polymer particles containing a colorant, wherein the water content exceeds 60% by weight, the colorant content is 10% by weight or more, and the crosslinked polymer particles are A water-based ink for inkjet recording, which is obtained by crosslinking water-insoluble polymer particles containing a colorant with a crosslinking agent and has an anionic group neutralized with a base, is disclosed.

  However, the aqueous dispersions and aqueous inks of Patent Documents 1 and 2 are not fully satisfactory in redispersibility. Here, redispersibility refers to the property that, in the ink jet recording method, ink that has adhered to and dried around the nozzle holes that eject ink droplets is re-dissolved or re-dispersed in the ink. If the redispersibility is poor, coarse particles are generated in the ink, causing a problem that the discharge property is deteriorated.

JP 2000-239392 A JP 2009-108115 A

  An object of the present invention is to provide a water-based ink for inkjet recording excellent in redispersibility while satisfying print density and storage stability.

The inventors of the present invention are water-based inks obtained by dispersing a pigment using a water-soluble polymer having an anionic group and a water-insoluble polymer having an anionic group and then crosslinking the polymer. It has been found that a water-based ink having a specific amount of anionic group and crosslinking agent in a specific range is excellent in redispersibility while satisfying the printing density and storage stability.
That is, the present invention provides the following (1) to (2).
(1) A crosslinking agent having a functional group capable of reacting with the anionic group after the pigment is dispersed with the water-soluble polymer (x) having an anionic group and the water-insoluble polymer (y) having an anionic group. A water-based ink obtained by crosslinking the polymer, the amount of the crosslinking agent per 1 g of the polymer is 0.8 to 3.0 mmol equivalent / g, and the amount of the anionic group per 1 g of the polymer after the crosslinking treatment is 1. A water-based ink for inkjet recording, which is 5 to 3.0 mmol / g.
(2) The method for producing a water-based ink for inkjet recording according to (1), which comprises the following steps (I) to (III).
Step (I): A step of dispersing a pigment with a water-soluble polymer (x) having an anionic group and water to obtain an aqueous dispersion Step (II): An anionic group in the aqueous dispersion obtained in Step (I) A step of obtaining a dispersion containing polymer particles (A) containing a pigment by adding a water-insoluble polymer (y) having the following steps: Step (III): Crosslinking the dispersion obtained in step (II) Process to perform processing

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous ink for inkjet recording excellent in redispersibility can be provided, satisfy | filling printing density and storage stability.

The water-based ink for inkjet recording of the present invention can react with the anionic group after the pigment is dispersed with the water-soluble polymer (x) having an anionic group and the water-insoluble polymer (y) having an anionic group. A water-based ink obtained by crosslinking a polymer with a functional group-containing crosslinking agent, wherein the amount of the crosslinking agent per 1 g of the polymer is 0.8 to 3.0 mmol equivalent / g, and per 1 g of the polymer after the crosslinking treatment. The amount of the anionic group is from 1.5 to 3.0 mmol / g.
In the present invention, the “anionic group amount” means the total amount of the unneutralized anionic group after the crosslinking treatment and the anionic group amount neutralized with a base.
In addition, “aqueous” means that water accounts for the largest proportion (for example, 50% by weight or more in the medium) in the medium contained in the aqueous ink, and the medium may be only water. In addition, a mixed solvent of water and one or more organic solvents is also included.
In the present invention, by using a cross-linking agent having a functional group capable of reacting with an anionic group, the water-soluble polymer (x) having an anionic group and the water-insoluble polymer (y) having an anionic group are cross-linked. In addition, the water-soluble polymer (x) is prevented from detaching from the pigment to improve the storage stability, and further, by containing a specific amount of anionic group, the swelling property of the polymer after drying into water-based ink As a result, it is considered that redispersibility can be improved. The redispersibility is a measure of the dispersibility of the ink after drying, and is considered to correlate with the clogging of the inkjet ink sol.
Hereinafter, each component used in the present invention will be described.

<Pigment>
The pigment used in the present invention 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, metal oxide, metal sulfide, and metal chloride. In the black water-based ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
The hue of the organic pigment is not particularly limited, and any of chromatic pigments such as a red organic pigment, a yellow organic pigment, a blue organic pigment, an orange organic pigment, and a green organic pigment can be used.
Examples include phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, diazo pigments, and azo pigments.

For example, phthalocyanine pigments include C.I. I. Pigment green 7, 36, 37, pigment blue 16, 75, 15 and the like, and examples of the quinacridone pigment include C.I. I. Pigment violet 19, 42, C.I. I. Pigment Red 122, 192, 202, 207, 209 and the like, and examples of the dioxazine pigment include C.I. I. Pigment violet 23, 37, and the like, and examples of perylene pigments include C.I. I. Pigment red 190, 224, C.I. I. Pigment violet 29 and the like, and examples of perinone pigments include C.I. I. Pigment orange 43, C.I. I. Pigment Red 194 and the like, and examples of the thioindigo pigment include C.I. I. Pigment Red 88 and the like, and examples of the anthraquinone pigment include C.I. I. Pigment yellow 147 and the like, and examples of the diazo pigment include C.I. I. Pigment yellow 13, 83, 188 and the like, and examples of the azo pigment include C.I. I. Pigment red 187, 170, 48, 53, 247, C.I. I. Pigment yellow 74, 150, C.I. I. And CI Pigment Orange 64.
Solid solution pigments can also be used. Solid solution pigments include quinacridone solid solution pigments composed of unsubstituted quinacridone such as β-type and γ-type and dichloroquinacridone such as 2,9-dichloroquinacridone, 3,10-dichloroquinacridone, and 4,11-dichloroquinacridone. Can be mentioned.

<Definition of water-soluble polymer (x) and water-insoluble polymer (y)>
In the present invention, “water-soluble polymer (x) having an anionic group” (hereinafter also simply referred to as “water-soluble polymer (x)”) and “water-insoluble polymer (y) having an anionic group” (hereinafter simply referred to as “water-soluble polymer (x)”). The “water-insoluble polymer (y)”) is 10% neutralized with acetic acid or sodium hydroxide of 100% of the anionic groups of these polymers, and all of them are dissolved in 100 g of pure water at 25 ° C. The polymer is “water-soluble polymer (x)” in the present invention. In addition, when using a commercially available polymer, or when the polymer neutralized with a neutralizing agent other than acetic acid or sodium hydroxide at the time of synthesis is less than 100% neutralization, acetic acid or sodium hydroxide is added, The solubility is judged as 100% neutralization. The degree of neutralization can be determined by the method described later.
When the solubility test is performed and the polymer has a portion that does not dissolve at a neutralization degree of 100%, since pure water hardly penetrates into the polymer, the following procedure (specifically, the method of the example) Thus, the water-soluble polymer (x) and the water-insoluble polymer (y) can be separated.
That is, a polymer is dissolved in an organic solvent such as methyl ethyl ketone in advance, 100% neutralized product is dropped into pure water, and the aqueous dispersion having a concentration of 10% by weight is removed by centrifugation. The polymer separated and precipitated by “1” is defined as “water-insoluble polymer (y)”, and the dissolved polymer as “water-soluble polymer (x)”. However, the weight% of each of the “water-soluble polymer (x)” and “water-insoluble polymer (y)” in the polymer is rounded off to the first decimal place.

<Water-soluble polymer (x) having an anionic group>
Although there is no restriction | limiting in particular in water-soluble polymer (x) used for this invention, From a viewpoint which disperse | distributes a pigment efficiently, polyester, a polyurethane, a vinyl-type polymer etc. are mentioned. Among them, from the viewpoint of storage stability, a vinyl type obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound) is preferable, and (a) an anionic group-containing monomer (hereinafter referred to as “(a Vinyl) obtained by copolymerizing a monomer mixture (hereinafter also simply referred to as “monomer mixture (x)”) containing (b) a hydrophobic monomer (hereinafter also referred to as “component (b)”). A polymer is more preferable.

[(A) Anionic group-containing monomer]
(A) The anionic group-containing monomer is used from the viewpoint of enhancing the dispersibility of the resulting polymer particles. It is considered that if the dispersibility of the polymer particles is increased, the discharge property of the water-based ink is improved.
(A) As an anionic group containing monomer, a carboxylic acid group containing monomer, a sulfonic acid group containing monomer, a phosphoric acid group containing monomer, etc. are mentioned.
Examples of the carboxylic acid group-containing 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 group-containing monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.
As phosphoric acid group-containing monomers, vinyl phosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, etc. Is mentioned.
Among the anionic monomers, acrylic acid and methacrylic acid are more preferable from the viewpoint of dispersibility of the polymer particles, and acrylic acid is more preferable from the viewpoint of solubility in water.

[(B) Hydrophobic monomer]
(B) The hydrophobic monomer is used from the viewpoint of increasing the affinity of the polymer for the pigment. Examples of hydrophobic monomers include alkyl (meth) acrylates, aromatic group-containing monomers, and the like, and aromatic group-containing monomers are preferred from the viewpoint of increasing affinity with pigments and enhancing dispersibility and stability.
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 the present specification, “(iso or tertiary)” and “(iso)” mean both the case where these groups are present and the case where these groups are not present. Indicates. “(Meth) acrylate” indicates acrylate and / or methacrylate.
Examples of the aromatic group-containing monomer include styrene monomers and aromatic group-containing (meth) acrylates. As the styrenic monomer, styrene and 2-methylstyrene are preferable, and as the aromatic group-containing (meth) acrylate, benzyl (meth) acrylate and phenoxyethyl (meth) acrylate are preferable.

The water-soluble polymer (x) is preferably 10 to 50% by weight, more preferably 15% from the viewpoint of enhancing the storage stability and redispersibility of the polymer particles containing the pigment in the structural unit derived from the component (a). -40% by weight, more preferably 20-40% by weight.
The water-soluble polymer (x) preferably contains 50 to 90% by weight, more preferably 60 to 90% by weight, and still more preferably 60 to 80% by weight of the structural unit derived from the component (b). (B) As a structural unit derived from a component, the structural unit derived from a styrene-type monomer is preferable, and content of the structural unit derived from a styrene-type monomer is 50-in all the structural units of water-soluble polymer (x). 90% by weight is preferable, and 60 to 80% by weight is more preferable.
The water-soluble polymer (x) has a weight average molecular weight of preferably 1000 to 300,000, more preferably 2,000 to 200,000, from the viewpoint of dispersibility. In addition, the weight average molecular weight of this polymer can be measured by the method as described in an Example.
The acid value of the water-soluble polymer (x) is preferably 100 to 400 KOH mg / g, more preferably 150 to 300 KOH mg / g, still more preferably 170 to 280 KOH mg / g.
Examples of commercially available water-soluble polymers (x) include BASF Japan's Jonkrill (registered trademark) 57J, 60J, 61J, 63J, 70J, PD-96J, and 501J. .

<Water-insoluble polymer (y) having an anionic group>
Although there is no restriction | limiting in particular in the water-insoluble polymer (y) which has an anionic group used for this invention, From a viewpoint which disperse | distributes a pigment efficiently, polyester, a polyurethane, a vinyl-type polymer, etc. are mentioned. Among them, from the viewpoint of the storage stability, a vinyl type obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound) is preferable, and (a) an anionic group-containing monomer (the above ( a vinyl system obtained by copolymerizing a monomer mixture (hereinafter also referred to simply as “monomer mixture (y)”) containing (a) the same as component) and (b) a hydrophobic monomer (same as component (b) above). A polymer is more preferred.
The (a) salt-forming group-containing monomer in the water-insoluble polymer (y) is preferably a carboxylic acid monomer, more preferably acrylic acid or methacrylic acid, from the viewpoint of dispersibility of the polymer particles.
The (b) hydrophobic monomer in the water-insoluble polymer (y) is preferably styrene or benzyl (meth) acrylate, more preferably styrene, from the viewpoint of increasing the affinity of the polymer for the pigment.
Further, from the viewpoint of improving the storage stability of the water-based ink, the component (b) in the water-soluble polymer (x) and the water-insoluble polymer (y) is preferably the same.
Furthermore, it may have an optional structural unit derived from a macromer (hereinafter also referred to as “component (c)”), (a) a structural unit derived from the component, (b) a structural unit derived from the component, And the water-insoluble graft polymer containing all the structural units derived from the component (c) has a high affinity with the pigment, and is preferable because the pigment is contained in the water-insoluble polymer.

[(C) Macromer]
(C) A macromer is a compound having a polymerizable functional group at one end and a number average molecular weight of 500 to 100,000, and can be used from the viewpoint of increasing the affinity of a polymer for a pigment. If the affinity of the polymer for the pigment is increased, it is considered that the dispersion stability of the polymer particles is improved and the discharge property of the water-based ink is improved. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group. The number average molecular weight is 500 to 100,000, preferably 1,000 to 10,000. The number average molecular weight is measured using polystyrene as a standard substance by gel chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent.
(C) As a macromer, a styrenic macromer, an aromatic group-containing (meth) acrylate macromer, and a silicone macromer are preferable from the viewpoint of increasing the affinity of the polymer for the pigment.
Examples of the styrenic macromer include a styrene monomer homopolymer or a copolymer of a styrene monomer and another monomer. In the case of a copolymer, the content of the styrenic monomer is preferably 50% by weight or more, and more preferably 70% by weight or more from the viewpoint of increasing the affinity of the polymer for the pigment. Other monomers to be copolymerized include aromatic group-containing (meth) acrylates or acrylonitrile. Examples of the styrenic monomer include styrene and 2-methylstyrene.
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 aromatic group-containing (meth) acrylate-based macromer include a homopolymer of an aromatic group-containing (meth) acrylate or a copolymer thereof with another monomer. In the case of a copolymer, the content of the aromatic group-containing (meth) acrylate is preferably 50% by weight or more and more preferably 70% by weight or more from the viewpoint of increasing the affinity of the polymer for the pigment. The aromatic group-containing (meth) acrylate is a (meth) acrylate having an arylalkyl group having 7 to 12 carbon atoms or an aryl group, which may have a substituent containing a hetero atom, such as benzyl (meth). Examples include acrylate and phenoxyethyl (meth) acrylate, and benzyl (meth) acrylate is preferred. Examples of other monomers to be copolymerized include styrene monomers and acrylonitrile.
The macromer may be a silicone macromer, and examples of the silicone macromer include organopolysiloxane having a polymerizable functional group at one end.
As the (c) macromer in the water-insoluble polymer (y), from the viewpoint of increasing the affinity with the water-soluble polymer (x), a polymer of the same monomer as the (b) hydrophobic monomer in the water-soluble polymer (x) is used. It is preferably used, and more preferably a styrenic macromer.

[(D) Nonionic monomer]
The monomer mixture may further contain (d) a nonionic monomer (hereinafter also referred to as “component (d)”).
(D) As a component, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyethyleneglycol (n = 2-30, n shows the average addition mole number of an oxyalkylene group. The same hereafter). (Meth) acrylate, polypropylene glycol (n = 2 to 30) (meth) acrylate, poly (ethylene glycol (n = 1 to 15) / propylene glycol (n = 1 to 15)) (meth) acrylate, methoxypolyethylene glycol ( 1-30) (meth) acrylate, methoxypolytetramethylene glycol (1-30) (meth) acrylate, ethoxypolyethylene glycol (1-30) (meth) acrylate, octoxypolyethylene glycol (1-30) (meth) acrylate , Polyethylene grease (1-30) (meth) acrylate 2-ethylhexyl ether, (iso) propoxypolyethylene glycol (1-30) (meth) acrylate, butoxypolyethylene glycol (1-30) (meth) acrylate, methoxypolypropylene glycol (1 -30) (meth) acrylate, methoxy (ethylene glycol / propylene glycol copolymer) (1-30, ethylene glycol: 1 to 29 therein) (meth) acrylate, and the like.

Specific examples of the commercially available component (d) include NK Esters M-40G, 90G, and 230G from Shin-Nakamura Chemical Co., Ltd., Bremer PE-90, 200, and 350 from Nippon Oil & Fats Co., Ltd. PME-100, 200, 400, 1000, PP-500, 800, 1000, AP-150, 400, 550, 800, 50PEP-300, 50POEP-800B, 43PAPE-600B, etc. Can be mentioned.
The components (a) to (d) can be used alone or in admixture of two or more.

The content of the structural unit derived from the components (a) to (d) in the water-insoluble polymer (y) is as follows.
The content of the structural unit derived from the component (a) is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, from the viewpoint of enhancing the storage stability and redispersibility of the polymer particles containing the pigment. More preferably, it is 15-30 weight%.
The content of the structural unit derived from the component (b) is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and still more preferably 30 to 70% by weight, from the viewpoint of increasing the affinity of the polymer for the pigment. %. In particular, the content of the structural unit derived from the styrene monomer is preferably 20 to 80% by weight and more preferably 30 to 70% by weight in all the structural units of the water-soluble polymer (x).
The content of the structural unit derived from the component (c) is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, from the viewpoint of increasing the affinity of the polymer for the pigment.
The content of the structural unit derived from the component (d) is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, from the viewpoint of enhancing the dispersibility of the polymer particles.
The weight average molecular weight of the water-insoluble polymer (y) is preferably from 5,000 to 500,000, more preferably from 10,000 to 400,000, from the viewpoint of improving the storage stability of the pigment aqueous dispersion and the water-based ink. 300,000 is more preferable, and 20,000 to 300,000 is particularly preferable. In addition, the weight average molecular weight of this polymer can be measured by the method as described in an Example.
The acid value of the water-insoluble polymer (y) is preferably 80 to 300 KOH mg / g, more preferably 90 to 200 KOH mg / g, and still more preferably 90 to 180 KOH mg / g.

(Production of polymer)
The water-soluble polymer (x) and water-insoluble polymer (y) used in the present invention (hereinafter collectively referred to simply as “polymer”) are a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsification method. It is produced by copolymerizing the monomer mixture by a known polymerization method such as a polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is preferably a polar organic solvent. When the polar organic solvent is miscible with water, it can be used by mixing with water. As the polar organic solvent, for example, aliphatic alcohols having 1 to 3 carbon atoms; ketones having 3 to 8 carbon atoms; esters such as ethyl acetate; or a mixed solvent of one or more of these with water.
In the polymerization, a known radical polymerization initiator such as an azo compound or an organic peroxide can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.
In the polymerization, a known polymerization chain transfer agent such as mercaptans such as octyl mercaptan and 2-mercaptoethanol and thiuram disulfide may be further added.
Although the polymerization conditions of the monomer mixture vary depending on the type of radical polymerization initiator, monomer, solvent, etc. used, it cannot be generally stated, but usually the polymerization temperature is preferably 30 to 100 ° C, more preferably 50 to 80 ° C. 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 polymer produced by a known method can be isolated. Further, the obtained polymer can be purified by removing the unreacted monomer and the like by re-precipitation by membrane separation, chromatographic method, extraction method or the like.

The polymer used in the present invention is preferably used after neutralizing an anionic group with a neutralizing agent. Examples of the neutralizing agent include volatile bases such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine, and non-volatile bases such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. Here, the volatile base refers to those having a boiling point of less than 130 ° C. under normal pressure, and the non-volatile base refers to those having a boiling point of 130 ° C. or higher under normal pressure. In these, a non-volatile base is preferable from a viewpoint of storage stability, and sodium hydroxide and potassium hydroxide are more preferable.
The neutralization degree of the anionic group of the polymer is preferably 10 to 300%, more preferably 20 to 200%, and further preferably 30 to 150%, from the viewpoint of dispersion stability of the polymer particles in the ink. preferable.
When the polymer is crosslinked, the average neutralization degree of the anionic group of the polymer before crosslinking is preferably 10 to 90% from the viewpoint of dispersion stability of the polymer particles in the ink, and is preferably 20 to 80%. It is more preferable that it is 30 to 70%.
Here, the average neutralization degree of the anionic group of the polymer can be obtained by the following formula (1).
Average neutralization degree of polymer (mol%) = {[weight (g) of neutralizing agent / equivalent of neutralizing agent] / [[acid value of water-soluble polymer (x) (KOH mg / g) × water-soluble polymer ( x) weight (g) + water-insoluble polymer (y) acid value (KOH mg / g) × water-insoluble polymer (y) weight (g)] / (56 × 1000)]} × 100) (1)
The acid value can be calculated by calculation from the structural unit of the polymer, or can be determined by a method in which the polymer is dissolved in an appropriate solvent (for example, methyl ethyl ketone) and titrated.

[Crosslinking agent]
In the present invention, as the crosslinking agent, a compound having two or more reactive functional groups in the molecule that react with the anionic group of the polymer is preferably used. The molecular weight of the cross-linking agent is preferably 120 to 2000, more preferably 150 to 1500, and particularly preferably 150 to 1000, from the viewpoint of easy reaction and storage stability of the resulting cross-linked polymer particles.
The number of reactive functional groups contained in the crosslinking agent is preferably 2 to 6, more preferably 2 to 3, from the viewpoint of controlling the molecular weight and improving storage stability. The reactive functional group is preferably at least one selected from a hydroxyl group, an epoxy group, an oxazoline group, and an amino group.
When the crosslinking agent is dissolved in 100 g of water at 25 ° C. from the viewpoint of efficiently crosslinking the polymer, the amount of the crosslinking agent is preferably 50 g or less, more preferably 40 g or less, and still more preferably 30 g or less.

Specific examples of the crosslinking agent include the following (a) to (d).
(A) Compound having two or more hydroxyl groups in the molecule: for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol 1,6-hexanediol, neopentyl alcohol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, glucose and the like.
(B) Compound having two or more epoxy groups in the molecule: for example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether Polyglycidyl ethers such as trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether.
(C) a compound having two or more oxazoline groups in the molecule: for example, a compound in which two or more, preferably 2-3 oxazoline groups are bonded to an aliphatic group or an aromatic group, more specifically 2 , 2′-bis (2-oxazoline), 1,3-phenylenebisoxazoline, bisoxazoline compounds such as 1,3-benzobisoxazoline, and terminal oxazoline groups obtained by reacting the compound with a polybasic carboxylic acid A compound having
(D) Compounds having two or more amino groups in the molecule: for example, polyamines such as ethylenediamine and polyethyleneimine.
Among these, (b) a compound having two or more epoxy groups in the molecule is preferable, and ethylene glycol diglycidyl ether and trimethylolpropane polyglycidyl ether are particularly preferable.

[Water-based ink for inkjet recording]
The aqueous ink of the present invention is obtained by dispersing a pigment with a water-soluble polymer (x) having an anionic group and a water-insoluble polymer (y) having an anionic group, and then having a functional group that reacts with the anionic group. It can be obtained by crosslinking the water-soluble polymer (x) and the water-insoluble polymer (y) with an agent.
By using a water-soluble polymer (x) having an anionic group and a water-insoluble polymer having an anionic group as a dispersant, the printing density is excellent. This is presumably because the pigment is finely dispersed by the water-soluble polymer (x) and aggregation is suppressed by the water-insoluble polymer (y).
By crosslinking the water-soluble polymer (x) and the water-insoluble polymer (y), the anionic groups of the water-soluble polymer (x), the anionic groups of the water-insoluble polymer (y), and the water-soluble polymer (x) It is considered that the anionic group and the anionic group of the water-insoluble polymer (y) are crosslinked.

The water-based ink for inkjet recording is required to be excellent in redispersibility after drying the ink from the viewpoint of ink dischargeability and the like.
The amount of the anionic group per 1 g of the polymer after the crosslinking treatment is 1.5 to 3.0 mmol / g from the viewpoint of the storage stability and redispersibility of the ink. Here, the polymer after the crosslinking treatment refers to the total amount of the water-soluble polymer (x) and the water-insoluble polymer (y).
That is, when [anionic group amount / (total amount of water-soluble polymer (x) and water-insoluble polymer (y))] is less than 1.5 mmol / g, the polymer is difficult to swell in water and redispersibility is not good. When it exceeds 3.0 mmol / g, the storage stability becomes insufficient. From the viewpoint of redispersibility and storage stability, the anionic group amount is preferably 1.8 to 2.5 mmol / g, more preferably 2.0 to 2.5 mmol / g.
The amount of anionic group can be measured by the method described in the examples, and is the total amount of an anionic group neutralized with an unneutralized anionic group and a base.
Since the water-soluble polymer (x) is used together with the water-insoluble polymer (y) as the polymer of the crosslinked polymer particles containing the pigment, the polymer, particularly the water-soluble polymer (x), is prevented from being detached from the pigment and stored. It is important to increase stability. Ink with poor storage stability causes polymer particles to aggregate when the ink is solidified, and redispersibility also decreases.

The amount of crosslinking agent per 1 g of polymer, that is, [the amount of crosslinking agent used / (total amount of water-soluble polymer (x) and water-insoluble polymer (y))] is 0.8 to 3.0 mmol equivalent / g. . When the amount of the crosslinking agent is less than 0.8 mmol equivalent / g, crosslinking is insufficient, and when it exceeds 3.0 mmol / g, redispersibility is insufficient. From the viewpoint of redispersibility and crosslinkability of the ink, the amount of the crosslinking agent is preferably 1.0 to 2.5 mmol equivalent / g, more preferably 1.2 to 2.5 mmol equivalent / g.
Here, the molar equivalent is a value obtained by dividing the weight of the crosslinking agent by the equivalent of the crosslinking agent (molecular weight / number of functional groups that react with an anionic group (carboxy group) in one molecule of the crosslinking agent).

In order to improve the redispersibility, the amount of the anionic group may be increased. However, since the present invention uses the water-insoluble polymer (y), the amount of the anionic group needs to be set to a certain level. Furthermore, in order to increase the storage stability, the amount of the crosslinking agent may be increased, but the crosslinked anionic group does not contribute to the redispersibility. Therefore, in order to improve redispersibility while satisfying storage stability, the amount of anionic group and the amount of crosslinking agent need to be within a certain range.
The use amount of the crosslinking agent is preferably 1/100 to 50/100, more preferably 5/100 to 40/100 in terms of weight ratio of [crosslinking agent / polymer] from the viewpoint of storage stability and redispersibility. 5/100 to 30/100 is more preferable, and 10/100 to 25/100 is particularly preferable.
The crosslinking rate (mol%) of the crosslinked polymer obtained from the following formula (2) is preferably 10 to 90 mol%, more preferably 20 to 80 mol%, still more preferably, from the viewpoints of storage stability and redispersibility. 30 to 70 mol%. The crosslinking rate can be determined by calculation from the amount of the crosslinking agent used and the number of moles of the reactive group, the amount of polymer used and the number of moles of the reactive group of the polymer that can react with the reactive group of the crosslinking agent.
Crosslinking rate (mol%) = [number of moles of reactive group of crosslinking agent / number of moles of reactive group capable of reacting with crosslinking agent of polymer] × 100 (2)
In the formula (2), “the number of moles of the reactive group of the crosslinking agent” is obtained by multiplying the number of moles of the crosslinking agent used by the number of functional groups that react with the carboxy group in one molecule of the crosslinking agent.

The weight ratio of the pigment to the water-soluble polymer (x) [pigment / water-soluble polymer (x)] is preferably 12 to 25, more preferably 12 to 22, more preferably 12 to 20, from the viewpoint of dispersion stability. 12-18 are more preferable and 12-15 are still more preferable. The weight ratio of the pigment to the water-insoluble polymer (y) [pigment / water-insoluble polymer (y)] is preferably 1 to 20, preferably 1 to 10 from the viewpoint of dispersion stability of the polymer particles (A) in the ink. More preferably, 1-6 are still more preferable.
The weight ratio of the pigment to the total amount [(x) + (y)] of the water-soluble polymer (x) and the water-insoluble polymer (y) used for dispersion [pigment / [(x) + (y)]] is the print density. From the viewpoint of improvement, 50/50 to 95/5 is preferable, 60/40 to 95/5 is more preferable, and 70/30 to 95/5 is still more preferable.
The weight ratio of the water-insoluble polymer (y) to the water-soluble polymer (x) [water-insoluble polymer (y) / water-soluble polymer (x)] is 2 from the viewpoint of ink print density, storage stability, and redispersibility. 0.0-5.0 are preferable, 2.5-5.0 are more preferable, 3.0-5.0 are still more preferable, and 3.0-4.0 are still more preferable.
The average degree of neutralization before cross-linking of the polymer is preferably 70 mol% or less from the viewpoint of the storage stability of the ink due to the cross-linking reaction, and 30 mol% or more from the viewpoint of the redispersibility of the ink due to salt neutralization of the carboxy group. Is preferable, 30 to 70 mol% is preferable, and 30 to 60 mol% is more preferable. The average neutralization degree can be calculated by the method described in Examples.

[Manufacture of water-based ink for inkjet recording]
The method for producing the aqueous ink for ink jet recording of the present invention is not particularly limited, but after obtaining an aqueous dispersion by the method having the following steps (I) to (III), it is used as an aqueous ink as it is or later as necessary. A water-based ink can be efficiently produced by adding an additive or the like usually used for a water-based ink.
Step (I): A step of dispersing a pigment with a water-soluble polymer (x) having an anionic group and water to obtain an aqueous dispersion Step (II): An anionic group in the aqueous dispersion obtained in Step (I) A step of obtaining a dispersion containing polymer particles (A) containing a pigment by adding a water-insoluble polymer (y) having the following steps: Step (III): Crosslinking the dispersion obtained in step (II) Process to perform processing

Process (I)
Step (I) is a step of dispersing the pigment with the water-soluble polymer (x) to obtain an aqueous dispersion. First, the water-soluble polymer (x), the pigment, water, and, if necessary, a neutralizing agent, A method of mixing a surfactant, an organic solvent and the like to obtain a mixture and dispersing the mixture with a disperser is preferable.
In the mixture, the colorant is preferably 5 to 50% by weight, more preferably 7 to 40% by weight, and the organic solvent is preferably 2 to 40% by weight, more preferably 3 to 30% by weight, and the water-soluble polymer (x ) Is preferably 0.2 to 10% by weight, more preferably 0.3 to 8% by weight, and water is preferably 20 to 90% by weight, more preferably 30 to 90% by weight. The weight ratio of the pigment to the water-soluble polymer (x) is as described above.
When neutralizing with a neutralizing agent, it is preferable to neutralize so that the finally obtained aqueous dispersion has a pH of 7-11. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, and various amines. Further, the water-soluble polymer (x) may be neutralized in advance.

There is no restriction | limiting in particular in the dispersion method of the mixture in process (I). Although the average particle size of the pigment particles can be atomized only by the main dispersion until the desired particle size is obtained, preferably the pre-dispersion is performed, and then the main dispersion is further performed by applying a shear stress to obtain the average particle size of the pigment particles. It is preferable to control the diameter to a desired particle diameter. 5-50 degreeC is preferable, as for the temperature in dispersion | distribution of process (I), 5-35 degreeC is more preferable, 1-30 hours is preferable and dispersion time is more preferable 1-25 hours.
When pre-dispersing the mixture, commonly used mixing and stirring devices such as anchor blades and disper blades, such as Ultra Disper, Desperm (Asada Tekko Co., Ltd., trade name), Milder (Ebara Manufacturing Co., Ltd.) High-speed agitation and mixing devices such as TK Homomixer, TK Pipeline Mixer, TK Homojetter, TK Homomic Line Flow, and Fillmix (hereinafter, Primix Co., Ltd., trade name) are preferred.
Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill, a kneader, and an extruder, and a high pressure homogenizer represented by a high pressure homogenizer (Izumi Food Machinery Co., Ltd., trade name), a microfluidizer (Microfluidics). Company name, Nanomizer (Yoshida Kikai Kogyo Co., Ltd., trade name), Optimizer, Starburst (Sugino Machine Co., Ltd., trade name) and other chamber type high-pressure homogenizers, paint shakers, bead mills and other media-type dispersers Is mentioned. Commercially available media-type dispersers include Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd., trade name), Picomill (manufactured by Asada Tekko Co., Ltd., trade name), Dino Mill (manufactured by Shinmaru Enterprises Co., Ltd., trade name), etc. Is mentioned. A plurality of these devices can be combined. Among these, it is preferable to use a media-type disperser from the viewpoint of reducing the particle diameter of the pigment particles and stabilizing the dispersion.

Process (II)
Step (II) is a step of adding a water-insoluble polymer (y) to the water dispersion obtained in step (I) and further dispersing to obtain a dispersion containing polymer particles (A) containing a pigment. . In the step (II), from the viewpoint of the storage stability of the obtained water-based ink, the water dispersion obtained in the step (I), a water-insoluble polymer (y), an organic solvent, and a water-insoluble polymer containing water ( The dispersion of y), ie, “emulsion of water-insoluble polymer (y) containing an organic solvent” is mixed and dispersed to obtain an emulsified dispersion containing polymer particles (A) containing a colorant. More preferably, it is a process.
In the dispersion obtained in step (II), the colorant is preferably 5 to 50% by weight, more preferably 6 to 40% by weight, and the water-insoluble polymer (y) is preferably 1 to 40% by weight, More preferably, the water-soluble polymer (x) is preferably 0.1 to 20% by weight, more preferably 0.2 to 10% by weight, and the organic solvent is preferably 3 to 50% by weight, 30% by weight is more preferable, and water is preferably 30 to 90% by weight, more preferably 50 to 85% by weight, and the pH (20 ° C.) is preferably adjusted to 7 to 10. The weight ratio of the pigment to the water-insoluble polymer (y) is as described above.

Here, as a method for preparing an emulsion of a water-insoluble polymer (y) containing an organic solvent, first, the water-insoluble polymer (y) is dissolved in an organic solvent, then charged in the order of a neutralizing agent and water. A method of adding a surfactant and the like and stirring and mixing until an oil-in-water emulsion (emulsion) having a desired average particle diameter is obtained. If it is difficult to emulsify, mechanical force such as a high-speed stirrer or a disperser may be applied as necessary, and the average particle size is preferably adjusted to be in the range of 0.01 to 2 μm. .
Moreover, as a preparation method of the dispersion in an emulsified state, a phase inversion method, a normal phase method, or the like can be used. In that case, (i) a mixed solution of water and a neutralizing agent is prepared, and a mixed solution of a water-insoluble polymer (y) and an organic solvent is dropped therein; (ii) a water-insoluble polymer (y) in water And a method of dropping a mixture of an organic solvent and a neutralizing agent. The temperature during emulsification is preferably 40 ° C. or less, more preferably 30 ° C. or less, from the viewpoint of the particle size and viscosity stability of the polymer particles obtained.
As each component ratio in the emulsion, the organic solvent is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, and the water-insoluble polymer (y) (solid content) is preferably 2 to 40%. % By weight, more preferably 3 to 30% by weight, and water is preferably 50 to 90% by weight, more preferably 55 to 85% by weight.

The amount of the neutralizing agent is used so that the amount of the anionic group neutralized with a base (calculated value) per 1 g of the polymer of the water-based ink finally obtained is within the above range. Further, the anionic polymer may be neutralized in advance.
Examples of the organic solvent include alcohol solvents such as ethanol, isopropanol and isobutanol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and diethyl ketone, and ether solvents such as dibutyl ether, tetrahydrofuran and dioxane. You may use these individually or in combination of 2 or more types.
The amount of the organic solvent dissolved in 100 g of water is preferably 5 g or more, more preferably 10 g or more at 20 ° C., and methyl ethyl ketone and methyl isobutyl ketone are preferred.

The method for dispersing the mixture in the step (II) is not particularly limited as in the step (I), and the average particle size of the polymer particles can be atomized until the desired particle size is obtained only by this dispersion, After the preliminary dispersion, the main dispersion may be performed by applying a shear stress. The temperature in the dispersion in the step (II) is preferably 5 to 50 ° C, more preferably 5 to 35 ° C, and the dispersion time is preferably 1 to 30 hours, more preferably 2 to 25 hours.
When preliminarily dispersing the mixture, the above-described mixing and stirring device or the like is preferably used.
Examples of means for imparting the shear stress of this dispersion include the kneader, the high-pressure homogenizer, and the media-type disperser. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle diameter of the polymer particles (A) and stabilizing the dispersion.

(Solvent removal step)
In the water-based ink production method, as an optional step, after step (II), the organic solvent is distilled off from the dispersion containing the polymer particles (A) obtained in step (II) by a known method. By making an aqueous system, an aqueous dispersion of polymer particles (A) can be obtained. This step may be performed after step (II).
The organic solvent in the aqueous dispersion of the obtained polymer particles (A) is preferably substantially removed, but may remain as long as the object of the present invention is not impaired, and the crosslinking step is performed later. In such a case, it may be additionally removed after cross-linking if necessary. The amount of the residual organic solvent in the aqueous dispersion of the polymer particles (A) finally obtained 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 polymer particles (A) is one in which the solid content of the polymer is dispersed in water as a main medium. Here, the form of the polymer particles (A) is not particularly limited as long as the particles are formed of at least a pigment and a polymer. For example, a particle form in which the pigment is included in the polymer, a particle form in which the pigment is uniformly dispersed in the polymer, a particle form in which the pigment is exposed on the polymer particle surface, and the like are included.

Process (III)
Step (III) is a step of subjecting the dispersion containing the polymer particles (A) obtained in step (II) to a crosslinking treatment. When the dispersion containing the polymer particles (A) obtained in the step (II) or the dispersion obtained in the step (II) contains an organic solvent, the organic solvent is removed from the dispersion. By adding a crosslinking agent to the aqueous dispersion of the obtained polymer particles (A), an aqueous dispersion containing crosslinked polymer particles obtained by crosslinking the water-soluble polymer (x) and the water-insoluble polymer (y) can be obtained. . In step (III), the viscosity of the water-based ink is reduced, the printing density is improved, and the crosslinking is performed so that the amount of the crosslinking agent per 1 g of the polymer is within the above-mentioned range from the viewpoint of storage stability and redispersibility. It is necessary.
When the polymer is crosslinked by mixing the dispersion of polymer particles (A) containing the pigment obtained in the step (II) and a crosslinking agent, the dispersion of the crosslinked polymer particles obtained in the crosslinking step is performed. An aqueous dispersion can also be obtained by performing the step of removing the organic solvent from the body in the same manner as the solvent removal step.

[Composition, physical properties, etc. of water-based ink]
The content of the pigment in the water-based ink of the present invention is preferably 3 to 20% by weight, more preferably 4 to 20% by weight, still more preferably 4 to 15% by weight, from the viewpoints of print density and storage stability. Particularly preferred is 4 to 13 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.
To the water-based ink, additives such as a wetting agent, a penetrating agent, a dispersant, a viscosity modifier, an antifoaming agent, an antifungal agent, and a rust-preventing agent that are usually used for water-based inks can be added. For example, as penetrants, alkanediols having 2 to 8 carbon atoms such as 1,2-hexanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, triethylene glycol mono Examples of polyalkylene (2 to 4 carbon atoms) glycol alkyl (2 to 6 carbon atoms) ethers such as butyl ether and wetting agents include glycerin, dioxane, and 2-pyrrolidone.
The surface tension (20 ° C.) of the aqueous ink of the present invention is preferably 23 to 50 mN / m, more preferably 23 to 45 mN / m, and further preferably 25 to 45 mN / m.
The viscosity (20 ° C.) of the water-based ink is preferably 2 to 20 mPa · s, more preferably 2.5 to 16 mPa · s, and further preferably 2.5 to 12 mPa, in order to maintain good ejection reliability. -S.
The ink jet recording method to which the water-based ink of the present invention is applied is not particularly limited, but is suitable for a piezo ink jet printer suitable for discharging a dispersion containing a dispersible colorant such as a pigment or polymer particles.

  In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified. The weight average molecular weight of the polymer, the water-insoluble / water-soluble ratio of the polymer, the average particle size of the pigment-containing crosslinked polymer particles, the measurement of the anionic group amount of the aqueous dispersion, and the storage stability and redispersibility of the water-based ink. Evaluation was performed by the following method.

(1) Weight average molecular weight of polymer Gel chromatography method [Tosoh Corporation] using a solution in which phosphoric acid and lithium bromide were dissolved in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. It was measured using polystyrene 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.

(2) Water-insoluble / water-soluble ratio of polymer (i) In the case of water-soluble polymer (1) Water-soluble polymer (1) (Joncrill 61J, (a) acrylic acid / (b) styrene = 25/75 (weight ratio ), An aqueous solution of BASF Japan Ltd., weight average molecular weight 16000, neutralized product of ammonia 100%), pure water was added and all polymer solutions having a polymer concentration of 10% by weight were dissolved.
(Ii) In the case of the water-insoluble polymer P1 A 5N sodium hydroxide aqueous solution is added to the methyl ethyl ketone solution of the water-insoluble polymer (2) obtained in Production Example 1 to obtain 100% neutralization, and 10 g is measured in terms of polymer pure content. I took it. This was dropped into pure water, a part of methyl ethyl ketone and water was removed with a rotary evaporator, and the dispersion with a polymer concentration of 10% by weight was centrifuged, and the settled part was a water-insoluble polymer (y-2). Assuming that the dissolved portion is a water-soluble polymer (x-2), the ratio of water-insoluble polymer (y-2) / water-soluble polymer (x-2) is 100/0 when the first decimal place is rounded off.
(Iii) In the case of the water-insoluble polymer P2 A 5N sodium hydroxide aqueous solution is added to the methyl ethyl ketone solution of the water-insoluble polymer (3) obtained in Production Example 2 to make it 100% neutralized. I took it. This was dropped into pure water, a part of methyl ethyl ketone and water was removed with a rotary evaporator, and the dispersion with a polymer concentration of 10% by weight was centrifuged, and the settled part was a water-insoluble polymer (y-2). When the dissolved portion was the water-soluble polymer (x-2), the ratio of water-insoluble polymer (y-2) / water-soluble polymer (x-2) was 99/1.
Table 2 shows the water-insoluble / water-soluble ratio of the polymer used for each example. In Table 1, the amount of water-soluble polymer (x) is the amount of water-soluble polymer (x-1) + (x-2), and the amount of water-insoluble polymer (y) is the amount of water-insoluble polymer (y-1). ) + (Y−2).

(3) Measurement of average particle diameter of pigment-containing crosslinked polymer particles Measurement was performed using a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The measurement concentration was about 5 × 10 ⁻³ wt%.

(4) Measurement of anionic group amount of pigment-containing crosslinked polymer particles in ink (measuring conditions)
Apparatus: Kyoto Denshi Kogyo Co., Ltd., potentiometric automatic titrator, AT-610
Reagent: 0.1N-NaOH manufactured by Wako Pure Chemical Industries, Ltd., 0.1 mol / L sodium hydroxide (for volume analysis), 0.1N-HCl manufactured by Wako Pure Chemical Industries, Ltd., 0 .1 mol / L hydrochloric acid (for volumetric analysis) was used.
(Measuring method)
Weigh accurately so as to be 5 g of water-based ink, add ion-exchanged water to 50 ml, add 6 ml (excess amount) of 0.1N NaOH and stir for 30 minutes to make all anionic groups Na salt.
0.1N-HCl is added dropwise at a rate of 0.1 ml every 30 seconds while stirring, and the pH is measured. Starting from the neutralization point (inflection point 1) where the excess alkali is neutralized, the neutralization point (inflection point 2) from the most acidic among the subsequent neutralization inflection points is the end point. The amount of anionic group (carboxy group) was calculated from the amount of 0.1 N HCl used between the inflection point 2 and the inflection point 1, and was determined as the number of moles per gram of polymer. The measurement was performed at 20 ° C.

(5) Storage stability The screw tube was filled with ink, sealed, and stored in a thermostatic bath at 70 ° C. for 2 weeks. The average particle size before and after storage was measured by the method (3) above, and the change rate (%) of the average particle size was determined by the following formula to evaluate ink storage stability. The storage stability is better when the value is closer to 100%.
Change rate of average particle diameter (%) = [[average particle diameter after storage (nm) −average particle diameter before storage (nm)] / [initial average particle diameter (nm)]] × 100
〔Evaluation criteria〕
A: Change rate (%) of average particle size is less than 105% B: Change rate (%) of average particle size is 105 or more and less than 110% C: Change rate (%) of average particle size is 110% or more

(6) Redispersibility After 0.1 g of ink was placed in a petri dish and allowed to dry at 40 ° C. for 24 hours, 2 cc of the “mixed solution” used in the preparation of the aqueous ink of Example 1 (6) was added for 5 minutes. The mixture was allowed to stand and further shaken at 60 rpm for 5 minutes, and then the redispersibility was evaluated according to the following criteria.
A: The mixed solution is colored in pigment color, and no undissolved material is seen.
B: The mixed solution is colored in pigment color, but there are slight fine undissolved substances.
C: The mixed solution is slightly colored in pigment color, but there are fine undissolved substances.
D: The mixed solution is not colored in pigment color, and a large undissolved product exists.

Production Example 1 (Production of water-insoluble polymer P1)
21 parts of methacrylic acid (component (a)), 39 parts of styrene (component (b)), styrene macromer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, solid content 50%, component (c)) 20 parts ( 10 parts as an effective component), phenoxy polyethylene glycol polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: BLEMMER 43PAPE-600B, ethylene oxide average addition mole number = 6, propylene oxide average addition mole number = 6, (d-1 ) Component) 15 parts, polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: BLEMMER PP-800, propylene oxide average added mole number = 13, (d-2) component) 15 parts are mixed, and monomer mixture Was prepared.
In a reaction vessel, 10 parts of methyl ethyl ketone (hereinafter referred to as “MEK”), 0.025 part of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of the monomer mixture are mixed and sufficiently mixed with nitrogen gas. Substitution was performed to obtain a mixed solution.
On the other hand, the remaining 90% of the monomer mixture, 0.225 parts of the polymerization chain transfer agent, 30 parts of MEK, and radical polymerization initiator (2,2′-azobis (2,4-dimethylvaleronitrile) were added to the dropping funnel. ) 0.6 parts of the mixed solution was added, and the monomer mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was dropped over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution in which 0.15 part of the polymerization initiator was dissolved in 2.5 parts of MEK was added, and further aged at 65 ° C. for 2 hours and at 70 ° C. for 2 hours, and further MEK 57.5 A part of the mixture was added and stirred for 30 minutes, and the solution of the water-insoluble polymer P1 ((a) / (b) / (c) / (d-1) / (d-2) = 25/35/10/15/15 (weight) Ratio), solid content 40%, weight-average molecular weight of water-insoluble polymer P1: 100,000, water-insoluble / water-soluble ratio = 100/0, acid value 137). The composition and weight average molecular weight of the obtained polymer are shown in Table 1.

Production Example 2 (Production of water-insoluble polymer P2)
In the same manner as in Production Example 1, a monomer mixed solution shown in Table 1 was prepared, and using the monomer mixed solution, in the same manner as in Production Example 1, a solution ((a) / (b) / ( c) / (d-1) / (d-2) = 25/35/10/15/15 (weight ratio), solid content 40%, weight average molecular weight of water-insoluble polymer P2: 100,000, water Insoluble / water-soluble ratio = 99/1, acid value 162). The composition and weight average molecular weight of the obtained polymer are shown in Table 1.

Example 1
(1) Preparation of Pigment Water Dispersion Water-soluble polymer (1) (trade name: Jonkrill 61J: Copolymer made by BASF Japan Ltd., styrene / acrylic acid = 75/25 (weight ratio), weight average molecular weight 16000 Acid value 195) 773.0 g of ion-exchanged water, 9.9 g of 25% aqueous ammonia solution and 101 g of MEK were added to 30.0 g of 31.85% aqueous solution to obtain an aqueous solution of water-soluble polymer (1).
To the obtained aqueous solution of water-soluble polymer (1), C.I. I. 150 g of Pigment Yellow 74 (trade name: FY615, manufactured by Dainichi Seika Kogyo Co., Ltd.) was added, mixed for 1 hour at 20 ° C. using a disper blade, and further 532 g of ion-exchanged water was added to obtain a preliminary dispersion.
Using 1596 g of the obtained preliminary dispersion using a bead mill type disperser (trade name: Ultra Apex Mill UAM-05, manufactured by Kotobuki Industries Co., Ltd.), using zirconia beads having a particle diameter of 0.05 mm as media particles, Dispersion treatment by a circulation method is performed for 60 minutes (total average residence time in the mill: 10 minutes) under the conditions of a bead filling rate of 70% by volume, a stirring blade peripheral speed of 8 m / s, and a circulation flow rate of 200 cc / min. An aqueous dispersion dispersed with the polymer (1) was obtained.
(2) Preparation of emulsion of water-insoluble polymer To 82.6 g of the solution of water-insoluble polymer P1 obtained in Production Example 1, 8.2 g of MEK was added, and 10.8 g of 5N aqueous sodium hydroxide solution and 120. 1 g was added and mixed with a stirrer to prepare an emulsion of the water-insoluble polymer (2).
(3) Dispersion treatment of mixture of pigment aqueous dispersion and water-insoluble polymer emulsified liquid While mixing the aqueous dispersion obtained by dispersing the pigment with the water-soluble polymer (1) obtained in (1) above with a stirrer, An emulsion of the water-insoluble polymer (2) obtained in (2) was added to obtain a mixture.
The obtained mixture was subjected to dispersion treatment using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics, pressure: 150 MPa, continuous system of 10 passes) to obtain a dispersion.

(4) Removal of organic solvent The dispersion obtained in (3) above was subjected to removal of MEK, ammonia and some water using a hot water heating medium under reduced pressure, and a 5 μm filter (acetylcellulose membrane, outer diameter). : 2.5 cm, manufactured by Fujifilm Co., Ltd.) and filtered with a 25 mL needleless syringe (manufactured by Terumo Co., Ltd.) to remove coarse particles, thereby obtaining an uncrosslinked aqueous dispersion having a solid content concentration of 31%. Obtained. The average neutralization degree of this polymer was 40 mol% when calculated from the formula (1).
That is, a specific gravity of 5N sodium hydroxide (10.8 g) 1.185, an acid value of 195 of a water-soluble polymer (31.85% aqueous solution 30.0 g), an acid of a water-insoluble polymer (solid content 40%, 82.6 g) When the value 137 is put into the formula (1) and calculated, the average degree of neutralization of the polymer is determined as follows.
195 x 9.5 + 137 x 33 = 6374
[5 × 0.0108 / 1.185 / (6374/56000)] × 100 = 40 mol%
(5) Crosslinking step of aqueous dispersion 40 g of the aqueous dispersion obtained in the above (4) (composition in 12.4 g of solid content is 9.7 g of pigment (78%), 2.1 g of water-insoluble polymer (17%) ), Water-soluble polymer 0.6 g (5%)), ion-exchanged water 2.5 g and a crosslinking agent (trimethylolpropane polyglycidyl ether, trade name: Denacol EX321, manufactured by Nagase ChemteX Corporation, epoxy equivalent 130, water 0.51 g of an amount dissolved in 100 g (about 27 g (25 ° C.)) was added, and the mixture was stirred at 90 ° C. for 1 hour. After stirring, the mixture was cooled and filtered using a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Film Co., Ltd.), and the solid content concentration was 30% (pigment concentration 22.5%). An aqueous dispersion of pigment-containing crosslinked polymer particles was obtained.
The amount of the crosslinking agent per 1 g of the polymer is 1.45 mmol equivalent / g (= 0.51 / 130 / 2.7).

(6) Preparation of ink The mixed solution was 3.0 g of 1,2-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd., solubility parameter 13.15) as a water-soluble organic solvent, 2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd., Solubility parameter 13.66) 3.0 g, Glycerin (product of Kao Corporation, solubility parameter 19.40) 5.0 g, Triethylene glycol monobutyl ether (trade name: Butyltriglycol, Nippon Emulsifier Co., Ltd., solubility parameter 10. 21) 24.0 g, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) 0.5 g as a nonionic surfactant, 0.5 g of Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (Abisia shares) as a preservative Made by company) 0.3g and 19.3g of ion-exchanged water are magnetic stars. The resulting mixture was stirred for 15 minutes at room temperature to obtain a “mixed solution”.
Next, while stirring 44.4 g of the aqueous dispersion obtained in (5) above with a magnetic stirrer, 55.6 g of the mixed solution was added, and the mixture was filtered through a 5 μm filter (cellulose acetate membrane, manufactured by Sartorius). A water-based ink having a pigment content of 10.0% was obtained.

Example 2
In the crosslinking step of Example 1 (5), solids were obtained in the same manner as in Examples 1 (1) to (5) except that ion-exchanged water was changed to 2.2 g and the crosslinking agent (Denacol EX321) was changed to 0.38 g. An aqueous dispersion of pigment-containing crosslinked polymer particles having a partial concentration of 30% was obtained. Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6). The results are shown in Table 2.
Example 3
In the preparation of the water-insoluble polymer emulsion of Example 1 (2), Example 1 (except that MEK was changed to 8.2 g, 5N sodium hydroxide aqueous solution 9.5 g, and ion-exchanged water 121.2 g). In the same manner as in 1) to (5), an aqueous dispersion of pigment-containing crosslinked polymer particles having a solid content concentration of 30% was obtained. Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6). The results are shown in Table 2. The reason why the amount of carboxy increased compared to Example 1 is considered to be that the degree of neutralization was low and the reaction rate of the crosslinking agent was decreased.

Example 4
In the crosslinking step of Example 1 (5), solids were obtained in the same manner as in Examples 1 (1) to (5), except that ion-exchanged water was changed to 2.9 g and the crosslinking agent (Denacol EX321) was changed to 0.66 g. An aqueous dispersion of pigment-containing crosslinked polymer particles having a partial concentration of 30% was obtained. Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6). The results are shown in Table 2.
Example 5
In the preparation of the water-insoluble polymer emulsion of Example 1 (2), the water-insoluble polymer was changed to P2, and in the crosslinking step of Example 1 (5), 3.0 g of ion-exchanged water and a crosslinking agent (Denacol) were used. Except for changing EX321) to 0.69 g, an aqueous dispersion of pigment-containing crosslinked polymer particles having a solid content concentration of 30% was obtained in the same manner as in Examples 1 (1) to (5). Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6). The results are shown in Table 2.

Comparative Example 1
In the crosslinking step of Example 1 (5), the solid content concentration was the same as in Examples 1 (1) to (5) except that the ion-exchanged water was changed to 1.3 g and the crosslinking agent (Denacol EX321) was changed to 0 g. An aqueous dispersion of 30% pigment-containing crosslinked polymer particles was obtained. Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6). The results are shown in Table 2.
Comparative Example 2
In the preparation of the water-insoluble polymer emulsion of Example 1 (2), MEK was changed to 8.2 g, 5N sodium hydroxide aqueous solution was 16.3 g, and ion-exchanged water was changed to 115.6 g. In the crosslinking step, a pigment having a solid content concentration of 30% was obtained in the same manner as in Examples 1 (1) to (5) except that the ion-exchanged water was changed to 2.2 g and the crosslinking agent (Denacol EX321) was changed to 0.38 g. An aqueous dispersion of contained crosslinked polymer particles was obtained. Using this aqueous dispersion, an aqueous ink was obtained in the same manner as in Example 1 (6).

From Table 2, it can be seen that the water-based inks of Examples 1 to 5 of the present invention have excellent redispersibility and excellent storage stability. Since Comparative Example 1 was not cross-linked, the storage stability was poor, it aggregated, and the redispersibility was also lowered.
In addition, by using an inkjet printer (Seiko Epson Corporation, model number: EM-930C, piezo type), water-based inks of Examples and Comparative Examples are commercially available high-quality plain paper (Xerox Corporation, trade name: XEROX 4200). (Print condition = paper type: plain paper, mode setting: fine), leave it at 25 ° C for 24 hours, and then print the density with a Macbeth densitometer (product number: Spectroeye). In addition, when a total of five points at the four corners were measured and the average value was obtained, the print density of the water-based ink of the example was 1.05 or higher and all were high.

Claims (6)

After the pigment is dispersed with the water-soluble polymer (x) having an anionic group and the water-insoluble polymer (y) having an anionic group, the polymer is a crosslinking agent having a functional group capable of reacting with the anionic group. Is a water-based ink obtained by crosslinking treatment, the amount of the crosslinking agent per 1 g of the polymer is 1.2 to 3.0 mmol equivalent / g, and the amount of the anionic group per 1 g of the polymer after the crosslinking treatment is 1.8 to 3 Water-based ink for inkjet recording, which is 0.0 mmol / g.   The water-based ink for inkjet recording according to claim 1, wherein a weight ratio of [water-insoluble polymer (y) / water-soluble polymer (x)] is 2.0 to 5.0.   The aqueous ink for inkjet recording according to claim 1 or 2, wherein the average neutralization degree of the anionic group of the polymer before crosslinking is 10 to 90 mol%.   The water-based ink for inkjet recording according to any one of claims 1 to 3, wherein the water-insoluble polymer (y) is a graft polymer. The manufacturing method of the water-based ink for inkjet recording in any one of Claims 1-4 which has following process (I)-(III).
Step (I): A step of dispersing a pigment with a water-soluble polymer (x) having an anionic group and water to obtain an aqueous dispersion Step (II): An anionic group in the aqueous dispersion obtained in Step (I) A step of obtaining a dispersion containing polymer particles (A) containing a pigment by adding a water-insoluble polymer (y) having the following steps: Step (III): Crosslinking the dispersion obtained in step (II) Process to perform processing   Step (II) mixes and disperses the water dispersion obtained in Step (I) and the water-insoluble polymer (y) containing water-insoluble polymer (y), an organic solvent, and water. The manufacturing method of the water-based ink for inkjet recording of Claim 5 which is a process.