JP5279231B2 - Water-based ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink for inkjet recording superior in storage stability and curl suppression, and a curl-reducing method for printed matter using the same. <P>SOLUTION: The water-based ink for inkjet recording contains cross-linked polymer particles containing a coloring agent, of which the water content is 60 wt.% or less and the content of an anionic group neutralized with a base is 0.5 mmol/g or more to 1 g of the cross-linked polymer; and the curl-reducing method for printed matter comprises printing with an inkjet recording apparatus by using the water-based ink. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a water-based ink for ink-jet recording and a curl reduction method for printed matter using the same.

  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.

Patent Document 1 includes at least a colorant, an organic solvent, water and a polymer compound, a water content of 10 to 50% by mass, and an SP value of 9.0 to 12.0. The polymer compound has a content of 30% by mass or more, and the polymer compound has a plurality of side chains in the hydrophilic main chain, and can be cross-linked between the side chains by irradiation with active energy rays. Inkjet inks are disclosed and are said to be excellent in emission stability and curl characteristics.
Patent Document 2 discloses a method for producing an aqueous pigment dispersion in which a pigment and a resin having a carboxy group and a crosslinkable functional group are used and the crosslinkable functional group of the resin is reacted with a crosslinker to crosslink. The obtained aqueous pigment dispersion has good storage stability, and can form a coating film excellent in water resistance, durability and the like.
Patent Document 3 discloses an aqueous pigment dispersion in which a pigment is dispersed with a carboxy group-containing thermoplastic resin, the aqueous pigment dispersion having a carboxy group-containing thermoplastic resin crosslinked after the pigment is dispersed, It is said to be excellent in light resistance, water resistance, solvent resistance, stability over time, and the like.
However, the above-mentioned pigment dispersion or water-based ink is not satisfactory in terms of storage stability and curl suppression.

JP 2007-91910 A Japanese Patent Laid-Open No. 9-104834 International Publication No. 99/52966 Pamphlet

  An object of the present invention is to provide a water-based ink for inkjet recording excellent in storage stability and curl suppression, and a curl reduction method for printed matter using the same.

The present inventors can make a water-based ink for ink-jet recording excellent in storage stability and curl suppression by making the water content below a certain level and using crosslinked polymer particles and setting the amount of anion within a specific range. I found out.
That is, the present invention provides the following (1) and (2).
(1) An aqueous ink for inkjet recording containing crosslinked polymer particles containing a colorant, the water content being 60% by weight or less, and an anionic property neutralized with a base per 1 g of the crosslinked polymer A water-based ink for ink jet recording having a base amount of 0.5 mmol / g or more.
(2) A curl reduction method for printed matter printed by an ink jet recording apparatus using the water-based ink of (1).

  The water-based ink for ink-jet recording of the present invention can suppress curling with respect to plain paper, has excellent storage stability, and can increase the concentration of the colorant.

The water-based ink for ink-jet recording of the present invention is a water-based ink for ink-jet recording containing crosslinked polymer particles containing a colorant, the water content is 60% by weight or less, and a base per 1 g of the cross-linked polymer. The anionic group neutralized with is characterized by being 0.5 mmol / g or more.
Hereinafter, each component used in the present invention will be described.

[Colorant]
The colorant is not particularly limited, and pigments, hydrophobic dyes, water-soluble dyes (acid dyes, reactive dyes, direct dyes, etc.) can be used, but from the viewpoint of water resistance, storage stability and scratch resistance. Pigments and hydrophobic dyes are preferred. Among them, it is preferable to use a pigment in order to express the high weather resistance which has been recently demanded.
The pigment derivative can be used from the viewpoint of improving the dispersibility of the pigment, but it is preferably not used from the viewpoint of storage stability when the water content is 60% or less, and unless the present invention is impaired, It is preferable to determine the presence / absence of use and the amount of pigment derivative relative to the pigment based on a balance between both viewpoints.
The pigment derivative has a polar group, has a function as a surface treatment agent for organic pigments, and is used to promote pigment dispersion. Examples of polar groups include sulfonic acid groups, carboxy groups, phosphoric acid groups, sulfinic acid groups, amino groups, amide groups, and imide groups.
When the pigment and the hydrophobic dye are used in an aqueous ink, it is necessary to use a surfactant and a polymer to form fine particles that are stable in the ink. In particular, from the viewpoints of bleeding resistance, water resistance, and the like, it is preferable to include a pigment and / or a hydrophobic dye in the polymer particles.
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, metal oxide, metal sulfide, and metal chloride. Of these, carbon black is preferred particularly for black aqueous inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthoraquinone pigments, and quinophthalone pigments.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment Red, 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.
Examples of extender pigments include silica, calcium carbonate, and talc.

The hydrophobic dye is not particularly limited as long as it can be contained in the crosslinked polymer particles. The hydrophobic dye is dissolved in an amount of 2 g / L or more, preferably 20 to 500 g / L (25 ° C.) with respect to the organic solvent (preferably methyl ethyl ketone) used in the production of the polymer from the viewpoint of efficiently containing the dye in the polymer. What to do is desirable.
Examples of the hydrophobic dye include oil-soluble dyes and disperse dyes. Among these, oil-soluble dyes are preferable.
Examples of the oil-soluble dye include C.I. I. Solvent Black, C.I. I. Solvent Yellow, C.I. I. Solvent Red, C.I. I. Solvent Violet, C.I. I. Solvent Blue, C.I. I. Solvent Green, and C.I. I. One or more types of products selected from the group consisting of Solvent Orange are listed, which are commercially available from Orient Chemical Co., Ltd., BASF Corp. and others.
Examples of disperse dyes include C.I. I. Disperse Yellow, C.I. I. Disperse Orange, C.I. I. Disperse Red, C.I. I. Dispers Violet, C.I. I. Disperse Blue, C.I. I. One or more types of products selected from the group consisting of Disperse Green are listed. Of these, C.I. I. Solvent Yellow 29 and 30, C.I. I. Solvent Blue 70, C.I. I. Solvent Red 18 and 49, C.I. I. Solvent blacks 3 and 7 and nigrosine-based black dyes are preferred.
The above colorants can be used alone or in admixture of two or more at any ratio.

[Crosslinked polymer]
The crosslinked polymer used in the present invention is preferably a crosslinked polymer obtained by crosslinking the polymer with a crosslinking agent, and the polymer is preferably a water-insoluble polymer. Here, the water-insoluble polymer means that when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the dissolution amount is 10 g or less, preferably 5 g or less, more preferably 1 g or less. Is a polymer. When the polymer has a salt-forming group, the dissolution amount is a dissolution amount when the salt-forming group of the polymer is neutralized 100% with acetic acid or sodium hydroxide depending on the type.
Examples of the polymer to be used include polyester, polyurethane, and vinyl polymers. From the viewpoint of storage stability, vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are used. preferable.

[Vinyl polymer (hereinafter also simply referred to as “vinyl polymer”)]
The vinyl polymer includes (a) a salt-forming group-containing monomer (hereinafter also referred to as “(a) component”), (b) a macromer (hereinafter also referred to as “(b) component”) and / or (c) a hydrophobic monomer. A vinyl polymer obtained by copolymerizing a monomer mixture (hereinafter also referred to simply as “monomer mixture”) containing (hereinafter also referred to as “component (c)”) is preferable. This vinyl polymer has a structural unit derived from the component (a), a structural unit derived from the component (b) and / or a structural unit derived from the component (c). A more preferable vinyl polymer has a structural unit derived from the component (a) or a structural unit derived from the components (a) and (c) as a main chain, and water having a structural unit derived from the component (b) as a side chain. It is an insoluble vinyl-based graft polymer.

[(A) salt-forming group-containing monomer]
(A) The salt-forming group-containing monomer is used from the viewpoint of enhancing the storage stability of the resulting dispersion. Examples of the salt-forming group include a carboxy group, a sulfonic acid group, a phosphoric acid group, an amino group, and an ammonium group.
Examples of the salt-forming group-containing monomer include cationic monomers and anionic monomers described in JP-A-9-286939, paragraph [0022].
Representative examples of the cationic monomer include unsaturated amine-containing monomers and unsaturated ammonium salt-containing monomers. Among these, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide and vinylpyrrolidone are preferable.
Representative examples of anionic monomers include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like.
Examples of the unsaturated 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 unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, bis- (3-sulfopropyl) -itaconic acid ester, and the like. Examples of unsaturated phosphoric acid monomers include vinylphosphonic 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, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of storage stability and ejection stability.

[(B) Macromer]
(B) The macromer is used from the viewpoint of enhancing the storage stability of the crosslinked polymer particles containing a colorant. The macromer is preferably a macromer which is a monomer having a polymerizable unsaturated group having a number average molecular weight of 500 to 100,000, preferably 1,000 to 10,000. In addition, the number average molecular weight of (b) macromer is measured using polystyrene as a standard substance by gel chromatography using chloroform containing 1 mmol / L of dodecyldimethylamine as a solvent.
(B) Among the macromers, from the viewpoint of the storage stability of the crosslinked polymer particles containing a colorant, a styrenic macromer having a polymerizable functional group at one end, an aromatic group-containing (meth) acrylate macromer, And one or more selected from the group consisting of silicone macromers.
Examples of the styrenic macromer include a styrene monomer homopolymer or a copolymer of a styrene monomer and another monomer. Examples of the styrene monomer include styrene, 2-methylstyrene, vinyl toluene, ethyl vinyl benzene, vinyl naphthalene, chlorostyrene, 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. As an aromatic group-containing (meth) acrylate, an arylalkyl having 7 to 22 carbon atoms, preferably 7 to 18 carbon atoms, more preferably 7 to 12 carbon atoms, which may have a substituent containing a hetero atom. (Meth) acrylate having an aryl group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, more preferably 6 to 12 carbon atoms, which may have a group or a substituent containing a hetero atom In addition, examples of the substituent containing a hetero atom include a halogen atom, an ester group, an ether group, and a hydroxy group. Examples include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, and benzyl (meth) acrylate is particularly preferable.
The polymerizable functional group present at one end of the macromer is preferably an acryloyloxy group or a methacryloyloxy group, and the other monomer to be copolymerized is preferably acrylonitrile.
The content of the styrene monomer in the styrene macromer or the aromatic group-containing (meth) acrylate in the aromatic group-containing (meth) acrylate macromer is preferably 50% by weight from the viewpoint of increasing the affinity with the pigment. Above, more preferably 70% by weight or more.

(B) The macromer may have a side chain composed of another structural unit such as an organopolysiloxane. This side chain can be obtained, for example, by copolymerizing a silicone macromer having a polymerizable functional group at one end represented by the following formula (1).
_{CH 2 = C (CH 3)} -COOC 3 H 6 - [Si (CH _{3) 2} O] _{t -Si (CH 3) 3 (} 1)
(In the formula, t represents a number of 8 to 40).
Examples of commercially available styrenic macromers as component (b) include Toa Gosei Co., Ltd. trade names, AS-6 (S), AN-6 (S), HS-6 (S), and the like. It is done.

[(C) Hydrophobic monomer]
(C) The hydrophobic monomer is used from the viewpoint of improving the printing density. 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 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, methacrylate, or both.

The aromatic group-containing monomer has an aromatic group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, more preferably 6 to 12 carbon atoms, which may have a substituent containing a hetero atom. Vinyl monomers are preferable, and examples thereof include the styrene monomer (c-1 component) and the aromatic group-containing (meth) acrylate (c-2 component). The above-mentioned thing is mentioned as a substituent containing a hetero atom.
Among the components (c), a styrene monomer (c-1 component) is preferable from the viewpoint of improving printing density, and styrene and 2-methylstyrene are particularly preferable as the styrene monomer. The content of the component (c-1) in the component (c) is preferably 10 to 100% by weight, more preferably 20 to 80% by weight, from the viewpoint of improving printing density.
Moreover, as an aromatic group containing (meth) acrylate (c-2) component, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. are preferable. The content of the component (c-2) in the component (c) is preferably 10 to 100% by weight, more preferably 20 to 80% by weight, from the viewpoint of improving printing density and storage stability. Moreover, it is also preferable to use (c-1) component and (c-2) component together.

[(D) Hydroxyl-containing monomer]
The monomer mixture may further contain (d) a hydroxyl group-containing monomer (hereinafter also referred to as “component (d)”). (D) The hydroxyl group-containing monomer exhibits an excellent effect of enhancing storage stability.
As the component (d), for example, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyethylene glycol (n = 2 to 30, n represents the average number of added moles of oxyalkylene group. The same) (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, and the like. It is done. Among these, 2-hydroxyethyl (meth) acrylate, polyethylene glycol monomethacrylate, and polypropylene glycol methacrylate are preferable.

[(E) Monomer Represented by Formula (2)]
The monomer mixture may further contain (e) a monomer represented by the following formula (2) (hereinafter also referred to as “(e) component”).
CH ₂ = C (R ¹ ) COO (R ² O) _q R ³ (2)
Wherein R ¹ is a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, R ² is a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, and R ³ is A monovalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom or a phenyl group optionally having an alkyl group having 1 to 9 carbon atoms, q means the average number of moles added. , 1 to 60, preferably 1 to 30.)
(E) component expresses the outstanding effect of improving discharge property.
As a hetero atom contained in the monomer of Formula (2), a nitrogen atom, an oxygen atom, a halogen atom, and a sulfur atom are mentioned, for example.
Preferable examples of R ¹ include methyl group, ethyl group, (iso) propyl group and the like.
Preferred examples of the R ² O group include an oxyethylene group, an oxytrimethylene grave, an oxypropane-1,2-diyl group, an oxytetramethylene group, an oxyheptamethylene group, an oxyhexamethylene group, and two or more kinds thereof. Examples thereof include oxyalkanediyl groups having 2 to 7 carbon atoms (oxyalkylene groups).
Preferable examples of R ³ include an aliphatic alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, an alkyl group having 7 to 30 carbon atoms having an aromatic ring, and Preferable examples include an alkyl group having 4 to 30 carbon atoms having a heterocycle and an optionally substituted alkyl group having 1 to 8 carbon atoms.

  Specific examples of the component (e) include methoxypolyethylene glycol (1 to 30: the value of q in the formula (2), the same applies hereinafter) (meth) acrylate, methoxypolytetramethylene glycol (1 to 30) ( (Meth) acrylate, ethoxy polyethylene glycol (1-30) (meth) acrylate, octoxy polyethylene glycol (1-30) (meth) acrylate, polyethylene glycol (1-30) (meth) acrylate 2-ethylhexyl ether, (iso) Propoxy polyethylene glycol (1-30) (meth) acrylate, butoxy polyethylene glycol (1-30) (meth) acrylate, methoxypolypropylene glycol (1-30) (meth) acrylate, methoxy (ethylene glycol / propylene glycol) Polymerization) (1 to 30, ethylene glycol therein: 1-29) (meth) acrylate. Among these, octoxypolyethylene glycol (1-30) (meth) acrylate and polyethylene glycol (1-30) (meth) acrylate 2-ethylhexyl ether are preferable.

Specific examples of commercially available (d) and (e) components include Shin-Nakamura Chemical Co., Ltd. polyfunctional acrylate monomer (NK ester) M-40G, 90G, 230G, and Nippon Oil & Fats Co., Ltd. BLEMMER series, PE-90, 200, 350, PME-100, 200, 400, 1000, PP-500, 800, 1000, AP-150, 400, 550, 800 , 50PEP-300, 50POEP-800B, 43PAPE600B, and the like.
The components (a) to (e) can be used alone or in admixture of two or more.

The content of the components (a) to (e) in the monomer mixture at the time of vinyl polymer production (content as an unneutralized amount; the same applies hereinafter) or derived from the components (a) to (e) in the vinyl polymer The content of the structural unit is as follows.
The content of component (a) is preferably 3 to 40% by weight, more preferably 4 to 30% by weight, and particularly preferably 5 to 25% by weight from the viewpoint of storage stability of the resulting dispersion.
The content of the component (b) is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, particularly from the viewpoint of enhancing the interaction with the pigment.
The content of the component (c) is preferably 5 to 98% by weight, more preferably 10 to 60% by weight, from the viewpoint of improving print density.
The content of component (d) is preferably 5 to 40% by weight, more preferably 7 to 20% by weight, from the viewpoint of storage stability of the resulting dispersion.
The content of the component (e) is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, from the viewpoint of improving dischargeability.
The total content of [component (a) + component (d)] in the monomer mixture is preferably 6 to 60% by weight, more preferably 10 to 50% by weight, from the viewpoint of storage stability of the resulting dispersion. is there. The total content of [component (a) + component (e)] is preferably 6 to 75% by weight, more preferably 13 to 50% by weight, from the viewpoint of storage stability and dischargeability of the resulting dispersion. . The total content of [(a) component + (d) component + (e) component] is preferably 6 to 60% by weight, more preferably from the viewpoint of storage stability and dischargeability of the resulting dispersion. 7 to 50% by weight.
The weight ratio of [(a) component / [(b) component + (c) component]] is preferably 0.01 to 1, more preferably from the viewpoint of dispersion stability and print density of the resulting dispersion. Is 0.02 to 0.67, more preferably 0.03 to 0.50.

(Production of polymer)
The polymer is produced by copolymerizing a monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is not particularly limited, but a polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be used by mixing with water. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol and propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable.
In the polymerization, azo compounds such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), t-butyl peroxyoctate, dibenzoyl oxide, etc. Known radical polymerization initiators such as organic peroxides 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.

Since the polymerization conditions of the monomer mixture vary depending on the type of radical polymerization initiator, monomer, and solvent used, it cannot be determined unconditionally. Usually, the polymerization temperature is preferably 30 to 100 ° C, more 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. Further, the obtained polymer can be purified by repeating reprecipitation or by removing unreacted monomers and the like by membrane separation, chromatographic method, extraction method and the like.

The weight average molecular weight of the polymer used in the present invention is preferably 5,000 to 500,000, more preferably 10,000 to 400,000, and more preferably 10,000 to 300,000, from the viewpoint of printing density and storage stability of the colorant. Preferred is 20,000 to 300,000. In addition, the weight average molecular weight of the polymer was measured by the method shown in the Examples.
When the polymer used in the present invention has (a) a salt-forming group derived from a salt-forming group-containing monomer, it is neutralized with a neutralizing agent. As the neutralizing agent, an acid or a base can be used depending on the type of the salt-forming group in the polymer. For example, hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid and other acids, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methylamine, dimethylamine , Bases such as trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine, and tributylamine.

The degree of neutralization of the salt-forming groups of the polymer before crosslinking the polymer is preferably 10 to 90%, more preferably 20 to 80%, from the viewpoint of storage stability and crosslinking efficiency, 80% is particularly preferable.
Here, the degree of neutralization can be determined by the following formula when the salt-forming group is an anionic group.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × polymer weight (g) / (56 × 1000)]} × 100
When the salt-forming group is a cationic group, it can be determined by the following formula.
{[Weight of neutralizer (g) / equivalent of neutralizer] / [amine value of polymer (HCL mg / g) × polymer weight (g) / (36.5 × 1000)]} × 100
The acid value and amine value can be calculated from the structural unit of the polymer. Alternatively, it can also be determined by a method in which a 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 is preferably used in order to appropriately crosslink the polymer. 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 cross-linking agent is preferably 2 to 6 from the viewpoint of controlling the molecular weight and improving storage stability. Preferred examples of the reactive functional group include one or more selected from the group consisting of a hydroxyl group, an epoxy group, an aldehyde group, an amino group, a carboxy group, an oxazoline group, and an isocyanate group.
From the viewpoint of efficiently crosslinking the surface of the polymer, the crosslinking agent has a dissolution amount of preferably 50 g or less, more preferably 40 g or less, and even more preferably 30 g or less when dissolved in 100 g of water at 25 ° C. .

Specific examples of the crosslinking agent include the following (a) to (f).
(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) Compounds having two or more aldehyde groups in the molecule: for example, polyaldehydes such as glutaraldehyde and glyoxal.
(D) Compounds having two or more amino groups in the molecule: for example, polyamines such as ethylenediamine and polyethyleneimine.

(E) Compounds having two or more carboxy groups in the molecule: for example, polyvalent carboxylic acids such as oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid and adipic acid.
(F) Compound having two or more oxazoline groups in the molecule: for example, a compound in which 2 or more, preferably 2 to 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
(G) Compound having two or more isocyanate groups in the molecule: for example, organic polyisocyanate or isocyanate group-terminated prepolymer.
Examples of organic polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; aromatic diisocyanates such as tolylene-2,4-diisocyanate and phenylene diisocyanate; alicyclic diisocyanates; aromatic Triisocyanate; and modified products such as urethane modified products thereof. The isocyanate group-terminated prepolymer can be obtained by reacting an organic polyisocyanate or a modified product thereof with a low molecular weight polyol or the like.
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.

The polymer used in the present invention has a reactive group (crosslinkable functional group) capable of reacting with a crosslinking agent. Preferred examples of the combination of both are as follows.
When the reactive group of the polymer is an anionic group such as a carboxy group, a sulfonic acid group, a sulfuric acid group, a phosphonic acid group, or a phosphoric acid group, the cross-linking agents are the above (a), (b), (d) and (f ) Compounds are preferred. When the reactive group of the polymer is an amino group, the crosslinking agent is preferably the compounds (b), (c) and (e). When the reactive group of the polymer is a hydroxyl group, the crosslinking agent is preferably the compounds (c) and (e). When the reactive group of the polymer is an isocyanate group or an epoxy group, the crosslinking agent is preferably the compounds (a), (d) and (e).
Among the above combinations, the crosslinking agent preferably has a functional group that reacts with the anionic group of the polymer from the viewpoint of controlling the polymer so as to impart an appropriate crosslinking structure. (B) 2 in the molecule A combination with a compound having one or more epoxy groups is particularly preferred.

The polymer having an anionic group such as a carboxy group, a sulfonic acid group, and a phosphoric acid group, an amino group, a hydroxyl group, an isocyanate group, an epoxy group, etc. as a reactive group (crosslinkable functional group) capable of reacting with the crosslinking agent, In the production of the polymer, it can be produced by copolymerizing a polymerizable monomer composition containing the monomer having the reactive group.
As a polymer having a salt-forming group such as an anionic group or an amino group as a reactive group capable of reacting with the crosslinking agent, a polymer obtained by copolymerizing the above-mentioned salt-forming group-containing monomer can be used. Moreover, as a polymer which has a hydroxyl group as a reactive group which can react with a crosslinking agent, the polymer which copolymerized the above-mentioned hydroxyl-containing monomer can be used.
As a polymer having an epoxy group as a reactive group capable of reacting with a crosslinking agent, a monomer having an epoxy group, specifically, a polymer copolymerized with glycidyl (meth) acrylate can be used. As a polymer having an isocyanate group as a reactive group capable of reacting with a crosslinking agent, (i) a monomer having an isocyanate group, for example, a polymer copolymerized with isocyanate ethyl (meth) acrylate, (ii) an unsaturated polyester polyol and an isocyanate A polymer obtained by copolymerizing the resulting isocyanate-terminated prepolymer can be used.

[Crosslinked polymer particles containing colorant]
Crosslinked polymer particles containing a colorant (hereinafter also referred to as “colorant-containing crosslinked polymer particles” or simply “crosslinked polymer particles”) are used to suppress curling and improve storage stability.
The colorant-containing crosslinked polymer particles of the present invention are characterized by containing 0.5 mmol / g or more of an anionic group neutralized with a base per 1 g of the crosslinked polymer.
Specific examples of the anionic group neutralized with a base include carboxy ion (—COOM ¹ ), sulfonate ion (—SO ₃ M ¹ ), phosphate ion (—PO ₃ M ¹ ₂ ) and the like.
In the above chemical formula, M ¹ may be the same or different, and alkali metals such as lithium, sodium and potassium; ammonium; monomethylammonium group, dimethylammonium group, trimethylammonium group; monoethylammonium group; Organic ammonium and the like.
Examples of the base include alkali hydroxides such as sodium hydroxide, alkaline earth hydroxides, organic amines such as amines and triethanolamine, basic amino acids, and the like.
The anionic group neutralized with the base is considered to dissociate and contribute to the stability of the colorant-containing crosslinked polymer particles by charge repulsion between the ions of the anion.

From the viewpoint of improving stability due to charge repulsion between the colorant-containing crosslinked polymer particles, the amount of anionic group neutralized with a base per 1 g of the crosslinked polymer is 0.5 mmol / g or more, preferably 0.7 mmol. / G or more, more preferably 1.0 mmol / g or more, and the upper limit is preferably 5 mmol / g or less, more preferably 3 mmol / g or less, still more preferably 2 mmol / g or less, particularly preferably 1.5 mmol / g or less. It is. From these viewpoints, preferably 0.5 to 5 mmol / g, more preferably 0.7 to 3 mmol / g, more preferably 0.7 to 2 mmol / g, still more preferably 0.7 to 1.5 mmol / g, Most preferably, it is 1.0-1.5 mmol / g. Within the above range, the storage stability is high even in a water-based ink having a high pigment concentration and a small water content.
As a method for producing a colorant-containing crosslinked polymer particle, from the viewpoint of storage stability, using a colorant and a polymer, Step I for obtaining polymer particles containing a colorant, and the colorant obtained in Step I are used. A method is preferred in which the polymer particles contained are mixed with a cross-linking agent and the polymer is cross-linked to obtain the cross-linked polymer particles.

The manufacturing method by the said process I and the process II can be performed by the following process (1)-(3), for example.
Step (1): Step of obtaining a dispersion of polymer particles containing a colorant by dispersing a mixture containing a polymer, an organic solvent, a colorant, water and, if necessary, a neutralizing agent Step (2) : A step of removing the organic solvent from the dispersion obtained in step (1) to obtain an aqueous dispersion of polymer particles containing a colorant. Step (3): the colorant obtained in step (2). A step of obtaining an aqueous dispersion of a colorant-containing crosslinked polymer particle by crosslinking the polymer of the contained polymer particle with a crosslinking agent

In step (1), the 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 and mixed with the obtained organic solvent solution. A method for obtaining an oil-in-water type dispersion is preferred. 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 polymer is 2 to 2% by weight. It is preferably 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.
The weight ratio of the colorant amount to the total amount of the polymer and the colorant [colorant / (polymer + colorant)] is preferably 55/100 to 90/100 from the viewpoint of storage stability. / 100 to 85/100 is more preferable.
When the polymer has a salt-forming group, it is preferable to use a neutralizing agent. There is no particular limitation on the degree of neutralization when neutralizing with a neutralizer. Usually, it is preferable that the liquid dispersion of the finally obtained water dispersion is neutral, for example, pH is 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the polymer. Examples of the neutralizing agent include those described above. Further, the 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. Preferably, the amount dissolved in 100 g of water at 20 ° C. is preferably 5 g or more, more preferably 10 g or more, more specifically preferably 5 to 80 g, more preferably 10 to 50 g, especially Methyl ethyl ketone and methyl isobutyl ketone are preferred.

There is no restriction | limiting in particular in the dispersion method of the mixture in process (1). Although the average particle size of the polymer particles can be atomized only by the main dispersion until the desired particle size is reached, it is preferably pre-dispersed and then subjected to further dispersion by applying a shear stress to obtain the average particle size of the polymer particles. It is preferable to control the diameter to a desired particle diameter. The dispersion in the step (1) is preferably 5 to 50 ° C, more preferably 10 to 35 ° C, and the dispersion time is preferably 1 to 30 hours, more preferably 2 to 25 hours.
When preliminarily dispersing the mixture, a commonly used mixing and stirring device such as an anchor blade can be used. Among the mixing and stirring apparatuses, high-speed stirring and mixing apparatuses such as Ultra Disper [Asada Steel Co., Ltd., trade name], Ebara Milder [Ebara Manufacturing Co., Ltd., trade name], TK Homomixer [Primix Co., Ltd., trade name] are preferable. .
As means for applying the shear stress of this dispersion, for example, a kneader such as a roll mill, a bead mill, a kneader, an extruder, a high-pressure homogenizer (Izumi Food Machinery Co., Ltd., trade name), a minilab 8.3H type (Rannie Co., trade name) Examples thereof include chamber type high-pressure homogenizers such as homo-valve type high-pressure homogenizers, microfluidizers (trade name), and nanomizers (trade name). A plurality of these devices can be combined. Among these, a high-pressure homogenizer is preferable from the viewpoint of reducing the particle size of the pigment.

In the step (2), an aqueous dispersion of polymer particles containing a colorant can be obtained by distilling off the organic solvent from the obtained dispersion by a known method to form an aqueous system. The organic solvent in the aqueous dispersion containing the obtained polymer particles is preferably substantially removed, but may remain as long as the purpose of the present invention is not impaired, and may be removed again after crosslinking as necessary. That's fine. The amount of the residual organic solvent is preferably 0.1% by weight or less, and more preferably 0.01% by weight or less.
The obtained aqueous dispersion of polymer particles containing the colorant is one in which the solid content of the polymer containing the colorant is dispersed in water as the main solvent. Here, the form of the polymer particles is not particularly limited as long as the particles are formed of at least a colorant and a polymer. For example, a particle form in which a colorant is included in a polymer, a particle form in which a colorant is uniformly dispersed in a polymer, a particle form in which a colorant is exposed on the surface of a polymer particle, and the like are included.

In the step (3), from the viewpoint of saturation and storage stability, it is preferable to obtain a colorant-containing crosslinked polymer particle by mixing a polymer particle containing a colorant and a crosslinking agent to crosslink the polymer. Specifically, a method of mixing an aqueous dispersion of polymer particles containing a colorant and a crosslinking agent to crosslink the polymer to obtain an aqueous dispersion of the colorant-containing crosslinked polymer particles is preferable. It is preferable from the viewpoint of crosslinking efficiency and surface crosslinking that the polymer is water-insoluble and the amount of the crosslinking agent dissolved in water is as described above.
In step (3), the catalyst, solvent, temperature, and time can be appropriately selected and determined depending on the crosslinking agent used. The crosslinking reaction time is preferably 0.5 to 10 hours, more preferably 1 to 5 hours, and the crosslinking reaction temperature is preferably 40 to 95 ° C.
The amount of the crosslinking agent (compound having two or more reactive functional groups in the molecule) is preferably 0.3 / 100 to 50/100 in terms of weight ratio of [crosslinking agent / polymer] from the viewpoint of storage stability. 0.3 / 100 to 35/100 is more preferable, 2/100 to 30/100 is more preferable, 5/100 to 25/100 is still more preferable, and 5/100 to 20/100 is particularly preferable.
From the viewpoint of improving the stability of the crosslinked polymer particles, the crosslinking agent has a functional group that reacts with the anionic group of the polymer, and the amount of the crosslinking agent used is calculated in terms of the amount of anionic group per gram of the polymer. It is preferably an amount that reacts with 0.1 to 3 mmol / g of the anionic group of the polymer, more preferably an amount that reacts with 0.2 to 2.5 mmol / g, and 0.4 to 2.5 mmol / g. More preferably, the amount reacts with g, more preferably the amount reacts with 0.7 to 2.5 mmol / g, and particularly preferably the amount reacts with 0.7 to 2.0 mmol / g. An amount that reacts with 0.7 to 1.5 mmol / g is most preferable.
In addition, the polymer crosslinking step may be performed by mixing a dispersion of polymer particles containing the colorant obtained in step (1) and a crosslinking agent. In this case, an aqueous dispersion of the colorant-containing crosslinked polymer particles is obtained by performing the step of removing the organic solvent from the dispersion of the crosslinked polymer particles obtained in the crosslinking step in the same manner as in the step (2). be able to.

Here, the crosslinking rate (mol%) of the crosslinked polymer obtained from the following formula (3) is preferably 10 to 80 mol%, more preferably 20 to 80 mol%, and still more preferably 30 from the viewpoint of storage stability. ~ 60 mol%. The crosslinking rate is a value that can be obtained 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 × 100 / number of moles of reactive group capable of reacting with crosslinking agent of polymer] (3)
In Formula (3), “the number of moles of the reactive group of the crosslinking agent” is a value obtained by dividing the weight of the crosslinking agent to be used by the equivalent of the reactive group. That is, the number of moles of the crosslinking agent used is multiplied by the number of reactive groups in one molecule of the crosslinking agent.
The weight ratio of the colorant amount to the total amount of the crosslinked polymer and the colorant [colorant / (crosslinked polymer + colorant)] is preferably 55/100 to 90/100 from the viewpoint of storage stability. More preferably, the ratio is 70/100 to 85/100.

[Aqueous ink containing colorant-containing crosslinked polymer particles]
The water-based ink for ink-jet recording of the present invention is a hydrophilic organic solvent usually used for water-based ink for ink-jet recording, in an aqueous dispersion containing the colorant-containing crosslinked polymer particles obtained in the steps (1) to (3). It can be prepared by adding a wetting agent, a penetrating agent, a dispersing agent, a viscosity modifier, an antifoaming agent, an antifungal agent, an antirust agent and the like.
The content of the colorant in the water-based ink is preferably 3 to 30% by weight, more preferably 4 to 30% by weight, more preferably 6 to 25% by weight, from the viewpoint of printing density and storage stability, and 8 to 20%. % By weight is more preferable, and 10 to 15% by weight is particularly preferable. In addition, the content of the colorant in the aqueous dispersion before preparing the water-based ink is preferably 10 to 50% by weight, and more preferably 15 to 40% by weight from the viewpoints of print density and storage stability. By using the crosslinked polymer particles containing the colorant used in the present invention, the water content is 60% by weight or less, and the storage stability is excellent even when the colorant has a high concentration.
The content of the colorant-containing crosslinked polymer particles in the water-based ink is preferably 5 to 50% by weight and more preferably 10 to 40% by weight from the viewpoints of curl suppression and storage stability.
The average particle size of the colorant-containing crosslinked polymer particles is preferably 10 to 500 nm, more preferably 30 to 300 nm, and particularly preferably 50 to 200 nm, from the viewpoint of preventing clogging of the printer nozzle and storage stability. . The average particle size is measured by the method described in the examples.
The water content in the water-based ink is 60% by weight or less, preferably 20 to 60% by weight, more preferably 30 to 60% by weight, still more preferably 30 to 57% by weight, from the viewpoint of curling suppression. -55 wt% is particularly preferred.
The content of the hydrophilic organic solvent in the water-based ink is preferably 10% by weight or more, more preferably 10 to 35% by weight, from the viewpoint of suppressing curling and maintaining storage stability while suppressing an increase in viscosity. 15 to 35% by weight is more preferable.

As the hydrophilic organic solvent, the amount dissolved in 100 g of water is preferably 50 g or more at 25 ° C., more preferably 60 g or more, and the saturated vapor pressure (20 ° C.) is preferably 0.001 to 1 kPa. The hydrophilic organic solvent functions as a component that suppresses breaking of hydrogen bonds of paper by water.
Examples of the hydrophilic organic solvent include monoalkyl ethers of one or more alkylene glycols selected from monoalkylene glycol, dialkylene glycol, and trialkylene glycol.
The alkylene group of the alkylene glycol is preferably an alkylene group having 2 to 4 carbon atoms, that is, an ethylene group, a propylene group or a butylene group, and these may be the same or different in one molecule. The alkyl group of the monoalkyl ether includes an alkyl group having 1 to 4 carbon atoms, that is, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, and a t-butyl group. Groups are preferred.
Among these, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, tetraethylene glycol mono-n-butyl ether, or dipropylene glycol monobutyl ether is particularly preferable.
Said hydrophilic organic solvent can be used individually or in mixture of 2 or more types.
The surface tension (20 ° C.) of the aqueous ink of the present invention is preferably 25 to 50 mN / m, more preferably 27 to 45 mN / m. Further, the viscosity (20 ° C.) at a solid content of 10% by weight of the water-based ink is preferably 2 to 12 mPa · s, more preferably 2.5 to 10 mPa · s, in order to maintain good dischargeability. The pH of the water-based ink is preferably 4-10.

[Method for reducing curling of printed matter]
In the curl reduction method for printed matter of the present invention, by printing water-based ink containing colorant-containing crosslinked polymer particles with an ink jet recording apparatus, it is possible to obtain a printed matter in which curling is suppressed and the print density is excellent. it can.
The color to be printed is not limited to a single color of cyan, magenta, and yellow, but may be a multi-order color such as a secondary color or a tertiary color of blue, red, or green.
The substrate to be printed is not particularly limited, and both commonly available plain paper and special paper can be used, but plain paper is preferably used from the viewpoint of exerting the effects of the present invention.
The applicable inkjet recording apparatus is not limited, but is particularly suitable for a piezoelectric inkjet printer. Further, it is suitable for a printer capable of high-speed printing, for example, 3 to 150 sheets / minute, preferably 5 to 100 sheets / minute, and more preferably 10 to 100 sheets / minute. is there.

In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified. In addition, the measuring methods of a weight average molecular weight, an average particle diameter, and a viscosity are as follows.
(1) Weight average molecular weight of polymer Gel chromatography using N, N-dimethylformamide containing 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide as a solvent [GPC apparatus (HLC- 8120GPC), a column manufactured by Tosoh Corporation (TSK-GEL, α-M × 2), flow rate: 1 mL / min], using polystyrene as a standard substance.
(2) Measurement of average particle diameter of colorant-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%.
(3) Viscosity measurement Using RE-type viscometer “RE80” manufactured by Toki Sangyo Co., Ltd., using a standard rotor (1 ° 34 ′ × R24), measuring temperature 20 ° C., measuring time 1 minute, rotation speed 100 rpm It measured on condition of this.

Production Examples 1-4
In a reaction vessel, 20 parts of MEK (methyl ethyl ketone), 0.03 part of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of 200 parts of the monomer mixture shown in Table 1 were mixed and mixed, and nitrogen gas substitution was sufficient. To obtain a mixed solution.
On the other hand, the remaining 90% of the monomer mixture shown in Table 1 was charged into a dropping funnel, and 0.27 part of the polymerization chain transfer agent, 60 parts of MEK, and a radical polymerization initiator (2,2′-azobis (2,4-dimethyl). Valeronitrile)) 1.2 parts were added and mixed, and nitrogen gas substitution was sufficiently performed to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 3 hours. After 2 hours at 65 ° C. from the end of the dropping, a solution in which 0.3 part of the radical polymerization initiator was dissolved in 5 parts of MEK was added, and further aged at 65 ° C. for 2 hours and at 70 ° C. for 2 hours to obtain a vinyl polymer (P -1 to P-4) A solution was obtained. Table 1 shows the weight average molecular weight and acid value of the obtained polymer. The acid value (KOHmg / g) of the polymer can be calculated from the ratio of methacrylic acid and the molecular weight.

The details of the monomers shown in Table 1 are as follows.
Styrene macromer: manufactured by Toa Gosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group / polyethylene glycol monomethacrylate (ethylene oxide average added mole number = 9): Shin-Nakamura Chemical Product name: NK ester M-90G
Polypropylene glycol monomethacrylate (average number of moles of propylene oxide added = 9): manufactured by NOF Corporation, trade name: BLEMER PP-500

Example 1
25 parts of polymer obtained by drying the polymer (P-1) solution obtained in Production Example 1 under reduced pressure was mixed with 78.6 parts of MEK, and quinacridone pigment (CI Pigment Violet 19, Clariant) was mixed therein. 100 parts by Japan Co., Ltd., trade name: Hostaperm Red E5B02) and mixed well, and then 7.0 parts and 6.0 parts (neutralization degree 60%) of 5N sodium hydroxide aqueous solution and 25% aqueous ammonia solution, respectively. In addition, using a disper (Ultra Disper, manufactured by Asada Tekko Co., Ltd.), the disper blade was rotated at 7000 rpm at 20 ° C. and stirred for 60 minutes. The obtained mixture was diluted with ion-exchanged water so as to be a 20% aqueous solution, and it was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics).
After adding 250 parts of ion-exchanged water to the obtained dispersion and stirring, MEK was completely removed at 60 ° C. under reduced pressure, a part of the water was further removed, and a 5 μm filter (acetylcellulose membrane, outer diameter). : 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) A pigment-containing vinyl system having a solid content concentration of 20% by filtering with a 25 mL needleless syringe (Terumo Co., Ltd.) attached to remove coarse particles. An aqueous dispersion of polymer particles was obtained.
Next, to 40 g of the obtained aqueous dispersion, a crosslinking agent (trade name: Denacol EX321, epoxy equivalent 140, about 27 g (25 ° C.) dissolved in 100 g of water, Nagase ChemteX, so that the crosslinking rate is 40 mol%, 0.177 g) was added and 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 Photo Film Co., Ltd.) to obtain an aqueous dispersion of pigment-containing crosslinked polymer particles.
To 62.5 parts of the obtained pigment-containing crosslinked polymer particle aqueous dispersion, 10 parts of water, 26.2 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 ( Avicia Co., Ltd.) (0.3 parts) was mixed so that the water content was 60%.
By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles A water-based ink was obtained.

(Calculation of crosslinking rate of crosslinked polymer particles)
Calculation of the crosslinking rate (mol%) of the crosslinked polymer particles was performed by the above formula (3) (the same applies to the following examples).
In Example 1, 0.177 part of a crosslinking agent (Denacol EX-321, epoxy equivalent 140) was reacted with 1.6 part of the water-insoluble polymer. Therefore, the number of moles of reactive groups in the cross-linking agent is 0.177 / 140 = 0.00126.
Here, since the crosslinking agent (Denacol EX-321) reacts with the carboxy group, the number of moles of the reactive group of the polymer that can react with the crosslinking agent is the number of moles of methacrylic acid (molecular weight 86) that the polymer has. .6 × 0.17 / 86 = 0.002.
Therefore, the crosslinking rate of the water-insoluble crosslinked polymer particles is 0.00126 × 100 / 0.0032 = 40 (mol%).
The amount (mmol / g) of anionic group neutralized with a base per gram of the crosslinked polymer is 111/56 × 0.6 × (1 because the acid value of the polymer is 111 and the degree of neutralization is 60%. .6 / 1.777) = 1.07 mmol / g.
The amount of the crosslinking agent used is an amount that reacts with 0.00126 / 1.6 × 1000 = 0.79 mmol / g in terms of anionic group amount per 1 g of the polymer.

Example 2
The quinacridone pigment of Example 1 was replaced with dimethylquinacridone pigment (CI Pigment Red 122, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name Chromofine Red 6111T), and the polymer obtained in Production Example 2 (P- 2) and the neutralization degree was adjusted to 51%. Further, an aqueous dispersion of pigment-containing crosslinked polymer particles (solid content 20%) was obtained in the same manner as in Example 1 except that the crosslinking rate was 49 mol%.
To 62.5 parts of an aqueous dispersion (solid content 20%) of the obtained pigment-containing crosslinked polymer particles, 36.2 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (made by Avicia Co., Ltd.) (0.3 parts) was mixed so that the water content was 50%.

(Calculation of crosslinking rate of crosslinked polymer particles)
In Example 2, 1.666 parts of a water-insoluble polymer was reacted with 0.266 parts of a crosslinking agent (Denacol EX-321, epoxy equivalent 140). Therefore, the number of moles of the reactive group of the cross-linking agent is 0.266 / 140 = 0.0019.
The number of moles of the reactive group of the polymer that can react with the cross-linking agent is the number of moles of methacrylic acid (molecular weight 86) of the polymer, and is 1.6 × 0.21 / 86 = 0.039.
Therefore, the crosslinking rate of the water-insoluble crosslinked polymer particles is 0.0019 × 100 / 0.0039 = 49 (mol%).
The amount (mmol / g) of anionic group neutralized with a base per gram of the crosslinked polymer is 137/56 × 0.51 × (1 because the acid value of the polymer is 137 and the degree of neutralization is 51%. .6 / 1.866) = 1.07 mmol / g.
The amount of the crosslinking agent used is an amount that reacts with 0.0019 / 1.6 × 1000 = 1.2 mmol / g in terms of the amount of anionic group per gram of polymer.

Example 3
The pigment was obtained in the same manner as in Example 1 except that the quinacridone pigment of Example 1 was changed to a cyan pigment (CI Pigment Blue 15: 3, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name Chromofine Blue 6335JC). An aqueous dispersion (solid content 20%) of the contained crosslinked polymer particles was obtained.
To 62.5 parts of an aqueous dispersion (solid content 20%) of the obtained pigment-containing crosslinked polymer particles, 36.2 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (made by Avicia Co., Ltd.) (0.3 parts) was mixed so that the water content was 50%.

Example 4
The quinacridone pigment of Example 1 was replaced with a cyan pigment (CI Pigment Blue 15: 3, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name Chromofine Blue 6335JC), and the polymer (P -3), the aqueous dispersion of pigment-containing crosslinked polymer particles (solid content 20%), except that the degree of neutralization was adjusted to 49% and the degree of crosslinking was further adjusted to 51 mol%, in the same manner as in Example 1. Got. To 62.5 parts of an aqueous dispersion (solid content 20%) of the obtained pigment-containing crosslinked polymer particles, 36.2 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (made by Avicia Co., Ltd.) (0.3 parts) was mixed so that the water content was 50%.

(Calculation of crosslinking rate of crosslinked polymer particles)
In Example 4, 0.308 parts of a crosslinking agent (Denacol EX-321, epoxy equivalent 140) is reacted with 1.6 parts of a water-insoluble polymer. Therefore, the number of moles of reactive groups of the cross-linking agent is 0.308 / 140 = 0.0002.
The number of moles of the reactive group of the polymer that can react with the cross-linking agent is the number of moles of methacrylic acid (molecular weight 86) that the polymer has, and is 1.6 × 0.23 / 86 = 0.743.
Therefore, the crosslinking rate of the water-insoluble crosslinked polymer particles is 0.0022 × 100 / 0.0043 = 51 (mol%).
The amount (mmol / g) of anionic group neutralized with a base per gram of the crosslinked polymer is 150/56 × 0.49 × (1 because the acid value of the polymer is 150 and the degree of neutralization is 49%. .6 / 1.908) = 1.10 mmol / g.
The amount of the crosslinking agent used is an amount that reacts with 0.0022 / 1.6 × 1000 = 1.38 mmol / g in terms of anionic group amount per 1 g of the polymer.

Example 5
A water-based ink was obtained in the same manner as in Example 3 except that the amount of water in the water-based ink of Example 3 was adjusted so that the amount of triethylene glycol monobutyl ether was reduced to 60%.

Example 6
Instead of the quinacridone pigment of Example 1, a yellow pigment (CI Pigment Yellow 74, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name: First Yellow 615) was used, and the polymer obtained in Production Example 2 ( P-2) and after stirring with a disper during the preparation of the dispersion, 1500 g of the dispersion was added to a bead mill (beads: zirconia, bead filling rate: 85%, bead weight: 1560 g, flow rate 200 g / min, circumference Speed: 20 m / second, rotation speed: 3,525 rotations / minute for 45 minutes) and microfluidizer (manufactured by Microfluidics) using a 10-pass dispersion treatment at a pressure of 200 MPa. A water-based ink was obtained in the same manner as in Example 1 except that the amount of the crosslinking agent was 0.218 parts and the water content was 50% when preparing the water dispersion.

(Calculation of crosslinking rate of crosslinked polymer particles)
In Example 6, 0.218 part of a crosslinking agent (Denacol EX-321, epoxy equivalent 140) was reacted with 1.6 part of the water-insoluble polymer. Therefore, the number of moles of reactive groups in the cross-linking agent is 0.218 / 140 = 0.00156.
The number of moles of the reactive group of the polymer that can react with the cross-linking agent is the number of moles of methacrylic acid (molecular weight 86) of the polymer, and is 1.6 × 0.21 / 86 = 0.039.
Therefore, the crosslinking rate of the water-insoluble crosslinked polymer particles is 0.00156 × 100 / 0.0039 = 40 (mol%).
The amount (mmol / g) of anionic group neutralized with a base per gram of the crosslinked polymer is 137/56 × 0.6 × (1) because the acid value of the polymer is 137 and the degree of neutralization is 60%. .6 / 1.818) = 1.29 mmol / g.
The amount of the crosslinking agent used is an amount that reacts with 0.00156 / 1.6 × 1000 = 0.98 mmol / g in terms of anionic group amount per 1 g of the polymer.

Example 7
Instead of the cyan pigment of Example 5, a cyan pigment (CI Pigment Blue 15: 4, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name Chromofine Blue 6337JC) was used. Thus, a water-based ink was obtained.

Comparative Example 1
An aqueous dispersion of pigment-containing vinyl polymer particles having a solid content concentration of 20% was obtained in the same manner as in Example 7 except that the crosslinking was not performed. To 62.5 parts of an aqueous dispersion of the obtained pigment-containing vinyl polymer particles, 15 parts of water, 7 parts of triethylene glycol monobutyl ether, 14.2 parts of glycerin, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 Part, 0.3 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) was mixed so that the water content was 65%.
By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles A water-based ink was obtained.
Comparative Example 2
Instead of the polymer (P-1), the polymer (P-4) obtained in Production Example 4 was used, and instead of the cyan pigment, a yellow pigment (CI Pigment Yellow 74, Dainichi Seika Kogyo Co., Ltd.) Comparison was made except that the product was treated with a bead mill and a microfluidizer after being stirred with a disperser in the same manner as in Example 6 during the preparation of the dispersion. A water-based ink was obtained in the same manner as in Example 1.
Comparative Example 3
Instead of the polymer (P-1), the polymer (P-4) obtained in Production Example 4 was used, and instead of the cyan pigment, dimethylquinacridone pigment (CI Pigment Red 122, Dainichi Seika Kogyo Co., Ltd.) A water-based ink was obtained in the same manner as in Comparative Example 1 except that company-made product name: Chromofine Red 6111T) was used.

Comparative Example 4
A water-based ink was obtained in the same manner as in Example 2 except that the crosslinking agent was not used.
Comparative Example 5
An aqueous dispersion of pigment-containing vinyl polymer particles having a solid content concentration of 20% was obtained in the same manner as in Example 2 except that the crosslinking was not performed. To 31.3 parts of the obtained pigment-containing vinyl polymer particle aqueous dispersion, 40 parts of water, 7 parts of triethylene glycol monobutyl ether, 20.4 parts of glycerin, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 Part, 0.3 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) was mixed so that the water content was 65%.
By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles A water-based ink was obtained.
Comparative Example 6
An aqueous dispersion of pigment-containing vinyl polymer particles having a solid content concentration of 20% was obtained in the same manner as in Example 2 except that the crosslinking was not performed. To 31.3 parts of the obtained pigment-containing vinyl polymer particle aqueous dispersion, 25 parts of water, 36.2 parts of triethylene glycol monobutyl ether, 6.2 parts of glycerin, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) ) 1 part and 0.3 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) were mixed so that the water content was 50%.
By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles A water-based ink was obtained.
Comparative Example 7
An aqueous dispersion of pigment-containing vinyl polymer particles having a solid content concentration of 20% was obtained in the same manner as in Example 2 except that the degree of neutralization of the polymer was 20% and no crosslinking was performed. To 31.3 parts of the obtained pigment-containing vinyl polymer particle aqueous dispersion, 40 parts of water, 7 parts of triethylene glycol monobutyl ether, 20.4 parts of glycerin, Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 Part, 0.3 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) was mixed so that the water content was 65%.
By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 5.0 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles A water-based ink was obtained.

Next, the storage stability and curl of the inks obtained in each Example and each Comparative Example were evaluated by the following methods. The results are shown in Table 2.
(1) Storage stability The inks described in the sealed examples are allowed to stand at 70 ° C. for one week, and the rate of change thereof is measured by the method for measuring the average particle diameter and viscosity of the pigment-containing crosslinked polymer particles. It was evaluated according to the criteria.
◯: Change rate of average particle size and viscosity is within ± 10% Δ: Change rate of average particle size and viscosity exceeds ± 10% and within ± 15% ×: Change rate of average particle size and viscosity is ± 15 %: Within ± 20% XX: Change rate of average particle diameter and viscosity exceeds ± 20% (2) Evaluation of curl suppression Printer manufactured by Seiko Epson Corporation (model number: EM-930C, piezo method) The solid ink on the top and bottom and left and right margins is 1.5 cm on the commercially available high-quality plain paper (product name: XEROX P, manufactured by Xerox Co., Ltd.) (printing condition = paper type: plain paper, Mode setting: Fine], and after standing for 1 week under conditions of 23 ° C. and 50% RH, the average value of the floating heights (cm) of the four corners of the printed matter was calculated.
(3) Evaluation of printing density Using a printer (model number: EM-930C) manufactured by Seiko Epson Corporation, the water-based ink described in the examples was solid on commercially available high-quality plain paper (Xerox P, trade name: XEROX P). After printing (printing condition = paper type: plain paper, mode setting: fine) and leaving at 25 ° C. for 24 hours, print density (5.1 cm) with a Macbeth densitometer (Gretag Macbeth, product number: Spectroeye) A total of 5 points including the center and four corners of (× 8.0 cm) were measured, and the average value was obtained.

In Examples 1 to 6, the pigment concentration is high, the printing density is excellent, the water content is low, the curl suppression effect is excellent, and the storage stability is also excellent. The pigment of Example 7 contains a pigment derivative, but the storage stability is at a practical level.
Comparative Examples 1 to 3 are inferior in curl suppression and storage stability because the polymer is not crosslinked and the water content is high.
In Comparative Example 4, although the amount of water is low and curling is suppressed, the storage stability is very poor.
Comparative Example 5 has good storage stability, but has a high water content and is inferior in curling suppression.
Comparative Example 6 has a curl suppressing effect but is inferior in storage stability.
In Comparative Example 7, the amount of anionic group neutralized with a base is low, the water content is high, and curl suppression and storage stability are poor.
When Example 2 and Comparative Example 4 are compared, it can be seen that the Example of the present invention has an excellent curl suppressing effect even when the same water content is 50%.
The colorant-containing crosslinked polymer particles prepared by replacing Denacol EX-321 (trimethylolpropane polyglycidyl ether, bifunctional or trifunctional) of Example with Denacol EX-411 (pentaerythritol polyglycidyl ether, tetrafunctional) It was further excellent in storage stability.

Claims (10)

An aqueous ink for inkjet recording containing crosslinked polymer particles containing a colorant, wherein the water content is 50 to 60% by weight , the hydrophilic organic solvent is contained by 10% by weight or more, and the crosslinked polymer An aqueous ink for inkjet recording, wherein the amount of anionic group neutralized with a base is 0.5 mmol / g or more per 1 g of polymer.   The aqueous ink for inkjet recording according to claim 1, wherein the content of the anionic group neutralized with a base is 0.5 to 5 mmol / g.   The water-based ink for inkjet recording according to claim 1 or 2, wherein the content of the colorant is 4 to 30% by weight.   The weight ratio of the amount of the colorant to the total amount of the crosslinked polymer and the colorant [colorant / (crosslinked polymer + colorant)] is 55/100 to 90/100. Water-based ink for inkjet recording.   The water-based ink for inkjet recording according to any one of claims 1 to 4, wherein the crosslinked polymer particles containing a colorant are obtained by crosslinking the polymer in the polymer particles containing a colorant with a crosslinking agent. .   The water-based ink for inkjet recording according to claim 5, wherein the polymer is a water-insoluble vinyl-based graft polymer.   The crosslinking agent has a functional group that reacts with the anionic group of the polymer, and the amount of the crosslinking agent used is an amount that reacts with 0.1 to 3 mmol / g in terms of the amount of anionic group per 1 g of the polymer. The water-based ink for inkjet recording according to claim 5 or 6.   The aqueous ink for inkjet recording according to any one of claims 5 to 7, wherein the amount of the crosslinking agent used is 0.3 / 100 to 50/100 in a weight ratio of [crosslinking agent / polymer]. The water-based ink for inkjet recording according to any one of claims 1 to 8, wherein the amount of the hydrophilic organic solvent dissolved in 100 g of water is 50 g or more at 25 ° C.   A curl reduction method for printed matter printed by an ink jet recording apparatus using the water-based ink according to claim 1.