JP2020084087A - Water based ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based ink having excellent fixability, storage stability and redispersibility even in printing on a low water absorption printing medium, and a printing method using the ink. A water-based ink containing a pigment-containing water-insoluble polymer particle A, a pigment-free water-insoluble polymer particle B, and water, wherein the polymer particle A is a pigment-containing polymer particle a. The water-insoluble polymer P2 constituting the polymer particles B contains a structural unit derived from (meth) acrylic acid and a structural unit derived from an aliphatic (meth) acrylate, and the glass transition of the polymer P2. A water-based ink having a temperature of -30 to 40 ° C. and an average cumulant particle size of the polymer particles B of 5 to 30 nm, and a printing method for printing on a low water absorption printing medium using the ink. [Selection diagram] None

Description

The present invention relates to a water-based ink and a printing method using the water-based ink.

PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), PP (polypropylene), NY (nylon), etc. in the field of commercial printing and industrial printing such as label printing used for product packaging printing and advertisement Conventionally, printing has been performed on the resin-made printing medium of (1) using solvent-based ink, UV curable ink, or the like. On the other hand, from the viewpoints of reduction of environmental load, energy saving, safety, etc., it is required to utilize an inkjet recording method, a flexographic printing method, and further a gravure printing method as a printing method using an aqueous ink.
From the viewpoint of weather resistance and water resistance of printed matter, water-based inks that use pigments as colorants have become mainstream. However, the resin print medium is non-water-absorbing and the water-based ink does not penetrate into the print medium, so that the pigment particles contained in the water-based ink remain on the surface of the print medium. Therefore, the conventional water-based ink is not sufficient in fixing property to the print medium, and various attempts have been made to improve these.

For example, Patent Document 1 discloses a latex binder, water, and an organic solvent for the purpose of providing a water-based inkjet ink that can be applied to a non-absorbent substrate to provide a print having good adhesion and the like. Inks are described that include a liquid medium that includes and polymer-encapsulated pigment particles that include a carboxy-functional dispersant that is cross-linked around the pigment core by a cross-linking agent.
Patent Document 2 discloses a pigment, polymer fine particles having a core-shell structure, and two types of water-soluble substances having different boiling points for the purpose of providing a water-based ink for inkjet that has good adhesion to a non-absorbent recording medium and stable ejection. A shell composed of an organic solvent and water, wherein the polymer fine particles having a core-shell structure have an acid value of 50 to 200 mgKOH/g obtained by polymerizing an unsaturated hydrophobic monomer and an unsaturated hydrophilic monomer. An aqueous inkjet ink is described which is composed of a resin and a core resin obtained by polymerizing an unsaturated hydrophobic monomer.
Patent Document 3 discloses a dispersion solvent, particles of a first binder resin which is emulsified or suspended in the dispersion solvent, and contains a colorant, for the purpose of providing an ink having good adhesion to a printing medium. An ink containing a second binder resin particle which is emulsified or suspended in a dispersion solvent, wherein the average particle diameter of the second binder resin particle is smaller than the average particle diameter of the first binder resin particle. ing.
Patent Document 4 discloses an aqueous gravure ink containing a pigment, a polymer, a water-soluble organic solvent, a surfactant and water for the purpose of providing an aqueous gravure ink that has a low environmental load and enables high-definition printing. The boiling point of the water-soluble organic solvent is 100° C. or more and 260° C. or less, the water-based gravure ink contains the water-soluble organic solvent in an amount of 10% by mass or more and 35% by mass or less, and the water in an amount of 50% by mass or more and 70% by mass or less. Gravure ink is listed.

JP, 2017-14491, A JP, 2008-12829, A JP, 2014-129497, A International publication 2017/047267

With the development of the packaging industry, the use of flexible packaging materials in the commercial printing and industrial printing fields is advancing. A resin film such as PET or PP is mainly used as the flexible packaging material, and the printed matter obtained is required to have high adhesion to the resin film. On the other hand, in inkjet printing, improvement in maintainability and ejection reliability in which clogging in an ink flow path or nozzle does not easily occur is required, and for that purpose, it is important that the ink has excellent storage stability and redispersibility. Becomes In order to improve the fixing property between the ink coating film and the resin film, from the viewpoint of the affinity with the resin film, the fixing aid polymer used in the ink does not contain a hydrophilic group such as a carboxy group as much as possible and has a hydrophobic property. It is considered effective to raise it. However, when many hydrophobic groups are introduced into the fixing aid polymer in order to improve the fixing property, the storage stability and redispersibility tend to decrease. While there are restrictions on such polymer design, it is difficult for the techniques of Patent Documents 1 to 4 to achieve both excellent fixability on various low water-absorbent printing media and storage stability and redispersibility.
An object of the present invention is to provide a water-based ink having excellent fixability, storage stability and redispersibility even in a low water-absorbent printing medium, and a printing method using the water-based ink.

The present inventor provides a water-based ink containing water-insoluble polymer particles A containing a pigment, water-insoluble polymer particles B not containing a pigment, and water, wherein the polymer particles A are cross-linked. The polymer forming the particles B contains a structural unit derived from (meth)acrylic acid and a structural unit derived from an aliphatic (meth)acrylate, and the glass transition temperature of the polymer and the cumulant average particle diameter of the polymer particles B are It has been found that the above problems can be solved by setting the specific range. That is, the present invention relates to the following [1] and [2].
[1] Water-insoluble polymer particles A containing a pigment (hereinafter also referred to as “pigment-containing polymer particles A”), water-insoluble polymer particles B containing no pigment (hereinafter also referred to as “polymer particles B”), and water A water-based ink containing and
The polymer particles A are obtained by crosslinking water-insoluble polymer particles a containing a pigment,
The water-insoluble polymer P2 constituting the polymer particles B contains a structural unit derived from (meth)acrylic acid (b-1) and a structural unit derived from an aliphatic (meth)acrylate (b-2),
The aliphatic (meth)acrylate (b-2) is 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and cyclohexyl (meth)acrylate. Is at least one selected from
The glass transition temperature of the polymer P2 is −30° C. or higher and 40° C. or lower,
An aqueous ink in which the cumulant average particle diameter of the polymer particles B is 5 nm or more and 30 nm or less.
[2] A printing method in which the water-based ink according to the above [1] is used to print on a low water absorbing print medium.

According to the present invention, it is possible to provide a water-based ink having excellent fixability, storage stability and redispersibility even in printing on a low water-absorption printing medium, and a printing method using the water-based ink.

[Water-based ink]
The water-based ink (hereinafter, also simply referred to as “ink”) of the present invention is the ink described in [1] above.
The term "water-based" means that water occupies the maximum proportion in the medium.
“Low water absorption” is a concept including low water absorption and non-water absorption, and the water absorption amount per surface area of the print medium at a contact time of 100 msec between the print medium and pure water is 0 g/m ² or more and 10 g/m ² or more. It means that it is m ² or less. The water absorption is measured by the method described in Examples.
“Printing” is a concept including printing for printing characters and images and printing.
In the present invention, the "water-insoluble" of a polymer means that when the polymer which has been dried at 105°C for 2 hours to reach a constant weight is dissolved in 100g of water at 25°C, the dissolved amount is 10g or less. To do. When the polymer has an anionic group, the amount of dissolution is the amount of dissolution when the anionic group is 100% neutralized with sodium hydroxide, and when the polymer has a cationic group, the amount of dissolution is It is the amount of dissolution when the cationic group is 100% neutralized with hydrochloric acid.

The ink of the present invention has excellent fixability, printing stability, and redispersibility even when printed on a low water-absorbent printing medium. The reason is not clear, but it is considered as follows.
In the present invention, the polymer particles B functioning as a fixing aid have a specific composition and characteristics in spite of having a carboxy group and further have a small particle size, so that the ink coating film formation is possible. It is possible to enhance the property and to exhibit excellent fixing property even in printing on a low water-absorption printing medium. Further, generally, when the particle size of the polymer particles functioning as a fixing aid is small, the storage stability and redispersibility of the ink are deteriorated due to depletion and aggregation. In the present invention, however, the pigment is the pigment-containing water-insoluble polymer particles A. In the ink, the polymer particles A are crosslinked. Therefore, it is considered that the polymer is strongly adsorbed or immobilized on the surface of the pigment, the aggregation of the pigment is suppressed, and as a result, the depletion aggregation is also suppressed. Further, since swelling of the polymer is also suppressed, it is considered that the synergistic effect of these can improve the fixability while maintaining excellent storage stability and redispersibility.

<Water-insoluble polymer particles A containing pigment>
(Pigment)
The pigment used in the present invention is contained in the ink as the pigment-containing polymer particles A, and the polymer particles A are formed by crosslinking the polymer particles a containing the pigment (hereinafter, also referred to as “pigment-containing polymer particles a”). ..
The pigment may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment can also be used. If necessary, they may be used in combination with an extender pigment.
Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferable for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, channel black and the like.
Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments and chelate azo pigments; phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindo pigments. Examples thereof include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and slene pigments.
The hue is not particularly limited, and achromatic color pigments such as white, black and gray; chromatic color pigments such as yellow, magenta, cyan, blue, red, orange and green can be used.
Examples of extender pigments include silica, calcium carbonate, talc and the like.
The pigments may be used alone or in admixture of two or more.

(Polymer p1)
The polymer p1 constituting the pigment-containing polymer particles a is not particularly limited as long as it has at least pigment dispersibility.
From the viewpoint of dispersion stability of the pigment, the existing form of the polymer p1 in the ink is more preferably a pigment-encapsulated state in which the polymer p1 contains the pigment.

The polymer p1 preferably contains an ionic group from the viewpoint of improving the dispersion stability, fixability, storage stability and redispersibility of the pigment. Examples of the ionic groups, acid groups is preferred, a carboxyl group (-COOM), a sulfonic acid group (-SO ₃ M), dissociated hydrogen ions and phosphoric acid group (-OPO ₃ M ₂₎ is released group showing acidity by, or their dissociated ionic form ^{_{(-COO -, -SO 3 -,}} -OPO 3 2-, -OPO 3 - M) acid groups are more preferable. In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Among these, a carboxy group (—COOM) is preferable from the viewpoint of improving the dispersion stability, fixability, storage stability and redispersibility of the pigment.

The ionic group contained in the molecule of the polymer p1 is preferably one introduced into the polymer skeleton by the ionic monomer (a-1). That is, the polymer p1 preferably contains a structural unit derived from the ionic monomer (a-1). Examples of the polymer p1 include vinyl resins, polyester resins, polyurethane resins and the like. Among them, vinyl resins are preferable, and the raw material monomer (a) containing the ionic monomer (a-1) and the hydrophobic monomer (a-2) (hereinafter, also simply referred to as “raw material monomer (a)”) is used. A vinyl resin obtained by polymerization is more preferable. The vinyl resin contains a structural unit derived from the component (a-1) and a structural unit derived from the component (a-2). The vinyl resin may further contain a constitutional unit derived from the nonionic monomer (a-3) from the viewpoint of improving the dispersion stability, fixing property, storage stability and redispersibility of the pigment.

[Ionic monomer (a-1)]
The ionic monomer (a-1) is preferably a monomer having an acid group, such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. Monomers having a carboxy group; monomers having a sulfonic acid group such as styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth)acrylate; vinylphosphonic acid, vinyl phosphate, bis(methacryloxyethyl) ) Phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, and other monomers having a phosphoric acid group.
Among these, preferably a monomer having a carboxy group, more preferably at least selected from (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and 2-methacryloyloxymethylsuccinic acid. It is one type, and more preferably (meth)acrylic acid.
In the present specification, “(meth)acrylic acid” means at least one selected from acrylic acid and methacrylic acid, and “(meth)acrylate” is at least one selected from acrylate and methacrylate.

[Hydrophobic monomer (a-2)]
In the present invention, the “hydrophobicity” of the hydrophobic monomer (a-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until it is saturated, the dissolved amount is less than 10 g. .. The amount of the hydrophobic monomer (a-2) to be dissolved is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of adsorptivity to the pigment.

The hydrophobic monomer (a-2) is preferably at least one selected from (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol and an aromatic group-containing monomer.
The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, (Meth)acrylate having a linear alkyl group such as stearyl (meth)acrylate; isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, (Meth)acrylate having a branched chain alkyl group such as isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; cycloaliphatic alkyl such as cyclohexyl (meth)acrylate Examples thereof include a (meth)acrylate having a group. Among these, those having an alkyl group having 1 to 10 carbon atoms are more preferable, and those having an alkyl group having 1 to 8 carbon atoms are more preferable.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably a styrene-based monomer and an aromatic group-containing monomer. One or more selected from (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
Examples of the styrene-based monomer include styrene, α-methylstyrene and 2-methylstyrene, and examples of the aromatic group-containing (meth)acrylate include benzyl (meth)acrylate and phenoxyethyl (meth)acrylate. Among these, at least one selected from styrene, α-methylstyrene and benzyl (meth)acrylate is preferable.

The vinyl-based resin may include a structural unit derived from a macromonomer as the hydrophobic monomer (a-2). The macromonomer is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less, and is used as a monomer component of a vinyl resin from the viewpoint of dispersion stability of the pigment. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, more preferably a methacryloyloxy group.
The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by a gel permeation chromatography method using chloroform containing 1 mmol/L of dodecyldimethylamine as a solvent and polystyrene as a standard substance.
From the viewpoint of dispersion stability of the pigment, the macromonomers are preferably aromatic group-containing monomer-based macromonomers and silicone-based macromonomers, and more preferably aromatic group-containing monomer-based macromonomers.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomers described in the above-mentioned hydrophobic monomer, styrene and benzyl (meth)acrylate are preferable, and styrene is more preferable. ..
Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), HS-6(S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of the silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[Nonionic monomer (a-3)]
The nonionic monomer (a-3) is preferably 2-hydroxyethyl (meth)acrylate or 3-hydroxypropyl (meth) from the viewpoint of improving the dispersion stability, fixing property, storage stability and redispersibility of the pigment. ) Hydroxyalkyl (meth)acrylates such as acrylates; polyethylene glycol (n=2 to 30, n is the average number of moles of oxyethylene groups added, hereinafter, n is the average number of moles of oxyalkylene groups added). Polyalkylene glycol (meth)acrylate such as (meth)acrylate; methoxypolyethylene glycol (n=1 to 30) alkoxypolyalkylene glycol (meth)acrylate such as (meth)acrylate; phenoxy (ethylene glycol/propylene glycol copolymerization) ( n=1 to 30, ethylene glycol therein: n=1 to 29) at least one selected from (meth)acrylates, more preferably alkoxypolyalkylene glycol (meth)acrylates, and further preferably methoxypolyethylene glycol ( (Meth)acrylate.
Specific examples of the commercially available nonionic monomer (a-3) include NK ester M-40G, 90G, 230G (these are trade names of Shin-Nakamura Chemical Co., Ltd.) and Bremmer PE-90. , 200, 350, etc., Bremmer PME-100, 200, 400, etc., Bremmer 50PEP-300, Bremmer 50POEP-800B, etc. (above, trade name of NOF CORPORATION).

(Content of Each Component in Raw Material Monomer (a) or Content of Each Structural Unit in Vinyl Resin)
The content of the component (a-1) and the component (a-2) in the raw material monomer (a) (content as an unneutralized amount; the same applies hereinafter) or (in the vinyl resin) during the production of the vinyl resin. The contents of the constituent unit derived from the component a-1) and the constituent unit derived from the component (a-2) are as follows from the viewpoint of improving the dispersion stability of the pigment.
The content of the component (a-1) is preferably 5% by mass or more, more preferably 7% by mass or more, further preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass. % Or less, more preferably 20% by mass or less.
The content of the component (a-2) is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass. % Or less, more preferably 70% by mass or less.

(Manufacture of vinyl resin)
The vinyl-based resin is produced by copolymerizing a mixture of the raw material monomers (a) by a known polymerization method. For example, a solution polymerization method is preferred in which a mixture of the raw material monomers (a) is heated in a solvent together with a polymerization initiator, a polymerization chain transfer agent and the like to cause polymerization.
There is no limitation on the manner of chain of the polymerized monomers, and any polymerization manner such as random, block or graft may be used.
After the completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or evaporation of the solvent. Further, the obtained polymer can be purified by reprecipitation, membrane separation, chromatographic method, extraction method and the like to remove unreacted monomers and the like.

The weight average molecular weight of the vinyl resin is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 30,000 or more, from the viewpoint of improving the fixability, and the dispersion stability of the pigment, From the viewpoint of storage stability and redispersibility, it is preferably 500,000 or less, more preferably 100,000 or less, still more preferably 70,000 or less. The weight average molecular weight can be measured by the method described in Examples.

(Crosslinking agent)
The pigment-containing polymer particle A is formed by crosslinking the pigment-containing polymer particle a, and preferably is formed by crosslinking the pigment-containing polymer particle a with a crosslinking agent. As a result, the polymer is strongly adsorbed or immobilized on the surface of the pigment, the aggregation of the pigment is suppressed, and as a result, the depletion aggregation is also suppressed, and the swelling of the polymer is also suppressed. It is thought that the property will improve.

The cross-linking agent is a polyfunctional compound, and it is preferable that the reactive functional group of the polyfunctional compound can react with the functional group of the polymer p1 constituting the pigment-containing polymer particles a to form a covalent bond. The covalent bond is preferably one or more selected from an ester bond, a thioester bond, an amide bond, an amino bond, an ether bond, a thioether bond, a carbonyl bond, a thiocarbonyl bond and a sulfonyl bond, more preferably an ester bond, It is one or more selected from a thioester bond and an amide bond.
The reactive functional group of the polyfunctional compound is not particularly limited as long as it can form the above-mentioned covalent bond.
When the polymer p1 contains a carboxy group, when the reactive functional group is at least one selected from an epoxy group, an isocyanate group, an aziridino group, an amino group and an oxazoline group, the reactive functional group is a carboxy group of the polymer p1. Can form a covalent bond in high yield by thermal reaction with. From this point of view, when the polymer p1 contains a carboxy group, it is preferably at least one selected from an epoxy group, an isocyanate group, an aziridino group, an amino group and an oxazoline group, and more preferably an epoxy group. The concept of the epoxy group includes a glycidyl group.
From the viewpoint of crosslinking the polyfunctional compound and the polymer p1 under the same conditions, the polyfunctional compound preferably has the same kind of reactive functional groups.

From the viewpoint of crosslinking efficiency, the polyfunctional compound having an epoxy group, that is, the polyfunctional epoxy compound, is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having two or more glycidyl ether groups, and further preferably It is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.
The molecular weight of the cross-linking agent is preferably 120 or more, more preferably 150 or more, further preferably 200 or more, and preferably 2 from the viewpoint of improving the easiness of reaction, fixability, storage stability and redispersibility. 1,000 or less, more preferably 1,500 or less, still more preferably 1,000 or less.
When the cross-linking agent is a polyfunctional epoxy compound, the epoxy equivalent of the cross-linking agent is preferably 90 or more, more preferably 100 or more, further preferably 110 or more, and preferably 300 or less, more preferably 200 or less. And more preferably 150 or less.
When the cross-linking agent is a polyfunctional epoxy compound, the number of epoxy groups in the cross-linking agent is 2 or more per molecule from the viewpoint of efficiently performing the cross-linking reaction to improve fixing property, storage stability and redispersibility. And preferably 6 or less per molecule, more preferably 4 or less, and further preferably 3 or less from the viewpoint of market availability.

Specific examples of the cross-linking agent include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl. Polyglycidyl ethers such as glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether and the like can be mentioned. Among these, at least one selected from trimethylolpropane polyglycidyl ether and pentaerythritol polyglycidyl ether is preferable, and trimethylolpropane polyglycidyl ether is more preferable.

[Production of Water-Insoluble Polymer Particle A Containing Pigment]
The pigment-containing polymer particles A are obtained by obtaining an aqueous dispersion of the pigment-containing polymer particles a (hereinafter, also referred to as pigment water dispersion (i)) and further reacting with a crosslinking agent to disperse the pigment-containing polymer particles A in water. It can be obtained as a body (I) (hereinafter, also referred to as a pigment water dispersion (I)).
The pigment water dispersion (i) is obtained by subjecting a pigment mixture containing, for example, the polymer p1, an organic solvent, a pigment, water, and optionally a neutralizing agent and a surfactant to a dispersion treatment to obtain a pigment-containing polymer particle a. It can be obtained by removing the organic solvent from the dispersion after obtaining the dispersion.
The organic solvent is not limited, but ketones, ethers, esters, and aliphatic alcohols having 1 to 3 carbon atoms are preferable, and the wettability to the pigment, the solubility of the polymer p1, and the pigment of the polymer p1 are used. From the viewpoint of improving the adsorptivity of 1, the ketone having 4 to 8 carbon atoms is more preferable, methyl ethyl ketone and methyl isobutyl ketone are still more preferable, and methyl ethyl ketone is still more preferable. When a vinyl resin is synthesized by the solution polymerization method as the polymer p1, the solvent used in the polymerization may be used as it is.

When the polymer p1 has an acid group, at least a part of the acid group is preferably neutralized with a neutralizing agent. In the case of neutralization, it is preferable that the pH is 7 or more and 11 or less.
Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia and various amines, and sodium hydroxide and ammonia are preferable. The neutralizing agent may be used alone or in combination of two or more. Further, the polymer p1 may be neutralized in advance.

The dispersion treatment method of the pigment mixture is not particularly limited, but it is preferable that the average particle diameter of the pigment-containing polymer particles a is controlled to a desired particle diameter by using a known kneader or disperser. The organic solvent is removed from the obtained dispersion-treated product by a known method to obtain the pigment water dispersion (i).

Then, a cross-linking agent is added to the obtained pigment water dispersion (i) to cross-link the pigment-containing polymer particles a to obtain the pigment water dispersion (I). At this time, the functional groups of the polymer p1 constituting the pigment-containing polymer particles a are crosslinked with a crosslinking agent.
For example, when the polymer p1 has a carboxy group, the crosslinking rate is from the viewpoint of improving fixability, storage stability and redispersibility, the molar equivalent of the crosslinking functional group of the crosslinking agent to the molar equivalent of the carboxy group of the polymer p1. The number ratio is preferably 10 mol% or more, more preferably 20 mol% or more, further preferably 30 mol% or more, still more preferably 40 mol% or more, and preferably 90 mol% or less, more preferably Is 80 mol% or less, more preferably 70 mol% or less.

From the same viewpoint as above, the temperature of the crosslinking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, further preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 85° C. or lower. , And more preferably 75° C. or lower.
The time of the crosslinking treatment is preferably 0.5 hours or more, more preferably 1 hour or more, still more preferably 1.5 hours or more, and preferably 12 hours or less, from the viewpoint of completion of the crosslinking reaction and economy. , More preferably 10 hours or less, further preferably 8 hours or less, still more preferably 5 hours or less.

The non-volatile component concentration (solid content concentration) of the pigment water dispersion (I) is preferably 10% by mass or more, more preferably from the viewpoint of improving the dispersion stability of the pigment water dispersion and facilitating the production of the ink. Is 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration of the pigment water dispersion (I) is measured by the method described in Examples.
From the viewpoint of dispersion stability, the content of the pigment in the pigment water dispersion (I) is preferably 5% by mass or more, more preferably 7% by mass or more, further preferably 10% by mass or more, and preferably Is 40% by mass or less, more preferably 30% by mass or less, and further preferably 20% by mass or less.
The mass ratio [pigment/crosslinked polymer p1] of the pigment to the crosslinked polymer p1 constituting the pigment-containing polymer particles A in the pigment water dispersion (I) is preferably 50/50 or more, more preferably 55/. It is 45 or more, more preferably 60/40 or more, and preferably 90/10 or less, more preferably 85/15 or less, still more preferably 80/20 or less.
The cumulant average particle diameter of the pigment-containing polymer particles A is preferably 40 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, still more preferably 80 nm, from the viewpoint of improving fixability, storage stability and redispersibility. It is above, and preferably 200 nm or less, more preferably 150 nm or less, still more preferably 120 nm or less. The average particle diameter can be measured by the method described in Examples.

<Water-insoluble polymer particles B containing no pigment>
From the viewpoint of improving fixability, storage stability and redispersibility, the water-insoluble polymer particles B containing no pigment (polymer particles B) have a polymer (P) (polymer P2) constituting the polymer particles B (meta) A polymer having a structural unit derived from acrylic acid (b-1) and a structural unit derived from an aliphatic (meth)acrylate (b-2), and having a glass transition temperature of polymer P2 of -30°C or higher and 40°C or lower, The cumulant average particle diameter of the particles B is 5 nm or more and 30 nm or less.
In the present invention, the “water-insoluble” of the polymer P2 is as described above. The dissolution amount of the polymer P2 is the dissolution amount when the carboxy group of the polymer P2 is 100% neutralized with sodium hydroxide.

[(Meth)acrylic acid (b-1)]
The (meth)acrylic acid (b-1) is at least one selected from acrylic acid and methacrylic acid from the viewpoint of improving fixability, storage stability and redispersibility, and is preferably methacrylic acid.

[Aliphatic (meth)acrylate (b-2)]
The aliphatic (meth)acrylate (b-2) is a 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate from the viewpoint of improving fixability, storage stability and redispersibility. , Tert-butyl (meth)acrylate and cyclohexyl (meth)acrylate, preferably 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate and cyclohexyl (meth)acrylate. It is at least one type, and more preferably 2-ethylhexyl (meth)acrylate.

[Aromatic group-containing monomer (b-3)]
The polymer P2 may include a structural unit derived from a monomer other than the (meth)acrylic acid (b-1) and the aliphatic (meth)acrylate (b-2). Examples of the other monomer include an ionic monomer other than (meth)acrylic acid, a hydrophobic monomer having an aromatic group, or a nonionic monomer, and among them, a hydrophobic monomer having an aromatic group (hereinafter, referred to as “aromatic group”). The containing monomer (b-3)" is also preferable.
Examples of the aromatic group-containing monomer (b-3) include the above-mentioned styrene-based monomer, aromatic group-containing (meth)acrylate, aromatic group-containing monomer-based macromonomer and the like. Among them, aromatic group-containing (meth)acrylates are preferable, and benzyl (meth)acrylates are more preferable, from the viewpoint of improving fixability, storage stability and redispersibility.

As described above, the polymer P2 is preferably a structural unit derived from (meth)acrylic acid (b-1), a structural unit derived from an aliphatic (meth)acrylate (b-2), and an aromatic group-containing monomer ( b-3)-derived constitutional unit, and more preferably, (meth)acrylic acid (b-1)-derived constitutional unit, 2-ethylhexyl (meth)acrylate, and n-butyl (meth)acrylate. And a structural unit derived from at least one monomer selected from cyclohexyl (meth)acrylate and a structural unit derived from an aromatic group-containing (meth)acrylate, and more preferably (meth)acrylic acid ( It contains a structural unit derived from b-1), a structural unit derived from 2-ethylhexyl (meth)acrylate, and a structural unit derived from benzyl (meth)acrylate.

The content of the structural unit derived from (meth)acrylic acid (b-1) in the polymer P2 is preferably 1% by mass or more, more preferably 3% from the viewpoint of improving fixability, storage stability and redispersibility. It is at least mass%, more preferably at least 7 mass%, and preferably at most 30 mass%, more preferably at most 20 mass%, even more preferably at most 15 mass%.
The content of the structural unit derived from the aliphatic (meth)acrylate (b-2) in the polymer P2 is preferably 10% by mass or more, and more preferably from the viewpoint of improving fixability, storage stability and redispersibility. It is 20% by mass or more, more preferably 30% by mass or more, and preferably 90% by mass or less, more preferably 75% by mass or less, still more preferably 60% by mass or less.
When the polymer P2 contains a constituent unit derived from the aromatic group-containing monomer (b-3), the content of the constituent unit derived from the aromatic group-containing monomer (b-3) in the polymer P2 is preferably 5% by mass. Or more, more preferably 10 mass% or more, still more preferably 20 mass% or more, still more preferably 30 mass% or more, and preferably 80 mass% or less, more preferably 70 mass% or less, further preferably 60 mass% or less. It is not more than mass %.

The mass ratio of (meth)acrylic acid (b-1) and aliphatic (meth)acrylate [(meth)acrylic acid (b-1)/aliphatic (meth)acrylate (b-2)] is preferably 0. 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, still more preferably 0.2 or more, and preferably 2 or less, more preferably 1 or less, still more preferably 0.8. Or less, more preferably 0.6 or less, still more preferably 0.4 or less.

The total content of the structural unit derived from the (meth)acrylic acid (b-1) and the structural unit derived from the aliphatic (meth)acrylate (b-2) in the polymer P2 is preferably 10% by mass or more, more preferably 20 mass% or more, more preferably 30 mass% or more, still more preferably 40 mass% or more, and preferably 90 mass% or less, more preferably 80 mass% or less, further preferably 70 mass% or less, More preferably, it is 60 mass% or less.

The polymer P2 is a raw material monomer (b) containing (meth)acrylic acid (b-1) and an aliphatic (meth)acrylate (hereinafter, also simply referred to as “raw material monomer (b)”), like the vinyl resin. It can be produced by copolymerizing the mixture of 1) by a known polymerization method. For example, a solution polymerization method in which a mixture of the raw material monomers (b) is heated in a solvent together with a polymerization initiator, a polymerization chain transfer agent and the like to perform polymerization is preferable.
Examples of the polymerization initiator include azo compounds such as 2,2′-azobisisobutyronitrile and 2,2′-azobis(2,4-dimethylvaleronitrile); tert-butylperoxyoctoate, benzoyl peroxide, etc. Known radical polymerization initiators such as organic peroxides can be used. Among them, 4,4'-azobis(4-cyanovaleric acid), and one or more ionic groups selected from 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide] The polymerization initiator having is preferable.
The amount of the radical polymerization initiator is preferably 0.001 mol or more and 5 mol or less per 1 mol of the raw material monomer (b).

The weight average molecular weight of the polymer P2 is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 30,000 or more, still more preferably 50,000 or more, from the viewpoint of improving fixability. And from the viewpoint of dispersion stability, storage stability and redispersibility of the pigment, it is preferably 500,000 or less, more preferably 300,000 or less, still more preferably 200,000 or less, still more preferably 100,000 or less. Is. The weight average molecular weight of the polymer P2 can be measured by the method described in Examples.

The glass transition temperature of the polymer P2 is −30° C. or higher, preferably −10° C. or higher, more preferably 10° C. or higher, further preferably 20° C., from the viewpoint of improving fixability, storage stability and redispersibility. It is above, and 40 °C or less, preferably 37 °C or less, more preferably 33 °C or less. The glass transition temperature can be calculated based on the Fox equation from the mass fraction of each monomer component in the polymer P2 and the value of the glass transition temperature of the homopolymer of each monomer component. It can also be measured using a differential scanning calorimeter.

The cumulant average particle diameter of the polymer particles B is 5 nm or more, preferably 7 nm or more, more preferably 10 nm or more, further preferably 15 nm or more, from the viewpoint of improving fixability, storage stability and redispersibility. And it is 30 nm or less, preferably 27 nm or less, more preferably 25 nm or less, and further preferably 23 nm or less. The average particle diameter is measured by the method described in Examples.

[Production of polymer particles B containing no pigment]
The polymer particles B containing no pigment (polymer particles B) may be appropriately synthesized or may be commercially available products, but are preferably used as an aqueous dispersion.
When obtaining the aqueous dispersion (II) of the polymer particles B, the polymer P2 forming the polymer particles B is preferably neutralized with a neutralizing agent.
The aqueous dispersion (II) of the polymer particles B is obtained by obtaining the polymer P2 by a known polymerization method, stirring the mixture containing the polymer P2, water, and optionally a neutralizing agent while heating, After that, the temperature can be lowered; it can be produced by a method of dispersing a mixture containing the polymer P2, an organic solvent, a neutralizing agent, and water to obtain a dispersion, and then removing the organic solvent from the dispersion. .. Above all, from the viewpoint of workability, a method of stirring the mixture containing the polymer P2, water, and the neutralizing agent while heating and then lowering the temperature is preferable.

The acid value of the polymer P2 is preferably 10 mgKOH/g or more, more preferably 30 mgKOH/g or more, even more preferably 50 mgKOH/g or more, even more preferably 70 mgKOH/g or more, and preferably 200 mgKOH/g or less, It is more preferably 150 mgKOH/g or less, still more preferably 100 mgKOH/g or less, still more preferably 90 mgKOH/g or less. The acid value of the polymer P2 is measured by the method described in the examples.

The temperature for stirring the mixture is preferably 60° C. or higher, more preferably 70° C. or higher, further preferably 80° C. or higher, and preferably 100° C. or lower, more preferably 95° C. or lower. The stirring time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 3 hours or more, and preferably 30 hours or less, more preferably 15 hours or less, further preferably 10 hours or less. is there.

The neutralizing agent used for producing the aqueous dispersion (II) of the polymer particles B is preferably a hydroxide of an alkali metal such as lithium hydroxide, sodium hydroxide or potassium hydroxide; ammonia; ethylamine, diethylamine, trimethylamine, triethylamine. , Organic amines such as triethanolamine, and more preferably sodium hydroxide and triethanolamine. The neutralizing agent may be used alone or in combination of two or more.
From the viewpoint of dispersion stability of the polymer particles B, the equivalent amount (mol %) of the neutralizing agent is preferably 10 mol% or more, more preferably 30 mol% or more, still more preferably 50 mol% or more, even more preferably It is 70 mol% or more, and from the same viewpoint as described above, it is preferably 160 mol% or less, more preferably 130 mol% or less, still more preferably 110 mol% or less. The equivalent amount of the neutralizing agent used can be calculated by the following formula.
Equivalent amount of the neutralizing agent (mol %)=[{added mass of neutralizing agent (g)/equivalent amount of neutralizing agent}/[{acid value of polymer P2 (mgKOH/g)×mass of polymer P2 (g) }/(56×1,000)]]×100

[Manufacture of water-based ink]
The ink of the present invention is preferably obtained by mixing the pigment aqueous dispersion (I) and the aqueous dispersion liquid (II) of the polymer particles B. From the viewpoint of improving fixability, storage stability and redispersibility, the ink preferably further contains a water-soluble organic solvent.

<Water-soluble organic solvent>
The water-soluble organic solvent may be liquid or solid at room temperature (25°C). The water-soluble organic solvent refers to an organic solvent in which the dissolved amount is 10 ml or more when the organic solvent is dissolved in 100 ml of water at 25°C.
The water-soluble organic solvent preferably contains at least one organic solvent having a boiling point of 90°C or higher. The weighted average value of the boiling points of the water-soluble organic solvents is preferably 150°C or higher, more preferably 180°C or higher, and preferably 240°C or lower, more preferably 220°C or lower, and further preferably 200°C or lower. ..
Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines and sulfur-containing compounds. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable, and ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, diethylene glycol diethyl ether, and diethylene glycol. One or more selected from monobutyl ether is more preferable, and one or more selected from propylene glycol and diethylene glycol monobutyl ether is further preferable.

The ink of the present invention further comprises, if necessary, a moisturizer, a wetting agent, a penetrant, a surfactant, a viscosity modifier, an antifoaming agent, an antiseptic agent, an antifungal agent, an anticorrosive agent and the like which are usually used in water-based inks. It is possible to add various additives described in 1 above and further perform a filtering treatment with a filter or the like.
The content of each component of the water-based ink and the physical properties of the ink are as follows.

(Content of each component in the water-based ink)
The content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, from the viewpoint of printing density, and the ink viscosity at the time of solvent volatilization is From the viewpoint of lowering and improving fixability, storage stability and redispersibility, it is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less.
The content of the pigment-containing polymer particles A in the water-based ink is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 7% by mass or more, from the viewpoint of improving print density and fixability. From the viewpoint of reducing the ink viscosity, it is preferably 15% by mass or less, more preferably 13% by mass or less, and further preferably 10% by mass or less.
The content of the polymer particles B in the water-based ink is preferably 0.3% by mass or more, more preferably 1% by mass or more, further preferably 2% by mass or more, from the viewpoint of improving fixability, and the solvent. From the viewpoint of lowering the ink viscosity at the time of volatilization and improving storage stability and redispersibility, it is preferably 7% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less.
The content of the water-soluble organic solvent in the water-based ink is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, from the viewpoint of ink viscosity, storage stability and redispersibility. And preferably 47% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less.
The content of water in the water-based ink is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, from the viewpoint of fixability, storage stability and redispersibility. , Preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less.

The mass ratio [pigment/(total solid content of the water-based ink)] of the pigment in the total solid content in the water-based ink is preferably 0.1 or more, from the viewpoint of improving fixability, storage stability and redispersibility. It is preferably 0.2 or more, more preferably 0.3 or more, and preferably 0.8 or less, more preferably 0.7 or less, still more preferably 0.6 or less, still more preferably 0.5 or less. Is.

(Physical properties of water-based ink)
The viscosity of the water-based ink at 32° C. is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, and further preferably 5 mPa·s or more from the viewpoint of improving fixability, storage stability and redispersibility. , And preferably 12 mPa·s or less, more preferably 9 mPa·s or less, further preferably 7 mPa·s or less. The viscosity of the water-based ink can be measured using an E-type viscometer.
The pH of the water-based ink is preferably 7.0 or more, more preferably 7.2 or more, further preferably 7.5 or more, and preferably 11 or less, more preferably from the viewpoint of member resistance and skin irritation. Is 10 or less, more preferably 9.5 or less. The pH of the water-based ink can be measured by a conventional method.

[Printing method]
The ink of the present invention has excellent fixability even in printing on a low water-absorbent printing medium, and since it has excellent storage stability and redispersibility, it can be suitably used for flexographic printing, gravure printing, or inkjet printing, Since it is excellent in ejection reliability in inkjet printing, it is particularly preferably used for inkjet ink.
Inkjet printing can be performed by loading a known inkjet recording device and ejecting it as ink droplets onto a print medium to record an image or the like.
The ink jet recording apparatus includes a thermal type and a piezo type, but it is more preferable to use it as a piezo type aqueous ink for ink jet recording.
Examples of print media that can be used include plain paper, coated paper, and resin film. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper. The resin film is preferably at least one selected from polyester film, polypropylene film, polyethylene film and polyvinyl chloride film. The resin film may use a corona-treated base material.
Examples of commonly available resin films include Lumirror T60 (Toray Co., Ltd., polyester), PVC80BP (Lintec Co., vinyl chloride), DGS-210WH (Roland DG Co., vinyl chloride), transparent PVC RE-137 (Vinyl chloride manufactured by Mimaki Engineering Co., Ltd.), Kainus KEE70CA (Polyethylene manufactured by Lintec Co., Ltd.), Yupo SG90 PAT1 (Polypropylene manufactured by Lintec Co., Ltd.), FOR, FOA (all manufactured by Futamura Chemical Co., Ltd., Polypropylene), Bonile RX (Konjin Film & Chemicals Co., Ltd., nylon), Emblem ONBC (Unitika Co., Ltd., nylon) and the like.

The print medium is preferably a low water-absorbent print medium from the viewpoint of fixability.
From the viewpoint of fixability and print image quality, the water absorption amount of the low-water-absorption printing medium in contact with pure water for 100 ms is preferably 1 g/m ² or more, more preferably 2 g/m ² or more, and preferably Is 8 g/m ² or less, more preferably 6 g/m ² or less. The water absorption amount is measured by the method described in Examples using an automatic scanning liquid absorption meter.

The printing method using the inkjet recording method preferably includes a step of discharging the ink droplets onto the print medium by the inkjet recording method to perform printing, and then drying the ink droplets landed on the print medium.
In the drying step, the surface temperature of the print medium is preferably 25° C. or higher, more preferably 30° C. or higher, still more preferably 50° C. or higher, from the viewpoint of improving print image quality, and suppressing deformation of the print medium by heat. From the viewpoint of energy reduction, the temperature is preferably 100°C or lower, more preferably 85°C or lower, and further preferably 70°C or lower.

In the following Production Examples, Preparation Examples, Examples and Comparative Examples, “parts” and “%” are “parts by mass” and “mass %” unless otherwise specified.

(1) Measurement of weight average molecular weight of polymer Gel permeation chromatography using N,N-dimethylformamide in which phosphoric acid and lithium bromide were dissolved at concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent. By a method [GPC device (HLC-8320GPC, manufactured by Tosoh Corporation), column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5 mL/min] as a standard substance. Known monodisperse polystyrene kit [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation].
The measurement sample was prepared by mixing 0.1 g of the polymer in a glass vial with 10 mL of the eluent, stirring the mixture with a magnetic stirrer at 25° C. for 10 hours, and using a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantech Co., Ltd.). What was filtered with.

(2) Measurement of Cumulant Average Particle Diameter Cumulant analysis was performed using a laser particle analysis system “ELS-8000” (manufactured by Otsuka Electronics Co., Ltd.) to measure the cumulant average particle diameter. The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and an integration number of 100 times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The concentration of the measurement sample was 5×10 ⁻³ % (in terms of solid content concentration).

(3) Measurement of solid content concentration Into a 30 ml polypropylene container (φ=40 mm, height=30 mm) was weighed out 10.0 g of sodium sulfate that was constant-weighted in a desiccator, and about 1.0 g of the sample was added thereto. After mixing, the mixture was accurately weighed, kept at 105° C. for 2 hours to remove volatile matter, and left to stand in a desiccator at room temperature (25° C.) for another 15 minutes, and then weighed. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration.

(4) Measurement of polymer acid value In JIS K0070, the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of ethanol and toluene [ethanol:toluene=1:1 (volume ratio)]. Other than that was measured according to JIS K0070.

(5) Water absorption amount of print medium at contact time of 100 msec between print medium and pure water Using an automatic scanning liquid absorption meter "KM500win" (manufactured by Kumagai Riki Kogyo Co., Ltd.), conditions of 23°C and relative humidity of 50% The amount of transfer of pure water at a contact time of 100 msec was measured under the conditions below, and was taken as the water absorption amount of 100 msec. The measurement conditions are shown below.
"Spiral Method"
Contact Time (sec): 0.010 ~ 1.0
Pitch (mm): 7
Length Per Sampling(degree):86.29
Start Radius (mm): 20
End Radius (mm):60
Min Contact Time (msec): 10
Max Contact Time (msec): 1,000
Sampling Pattern :50
Number of Sampling Points :19
"Square Head"
Slit Span (mm): 1
Slit Width(mm):5

<Production of polymer p1>
Production Example 1-1
In a reaction vessel equipped with two dropping funnels 1 and 2, the monomers shown in the "initial charging monomer solution" shown in Table 1, an organic solvent (methyl ethyl ketone (hereinafter, also referred to as "MEK")), a polymerization chain transfer agent ( 2-mercaptoethanol) was added and mixed, and the atmosphere was replaced with nitrogen gas to obtain an "initial charged monomer solution".
On the other hand, the monomer, organic solvent, and polymerization initiator (2,2′-azobis(2,4-dimethylvaleronitrile) shown in “Dropped monomer solution 1” shown in Table 1; manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., product Name: V-65), and the above-mentioned polymerization chain transfer agent were mixed to obtain "Drop monomer solution 1", which was placed in the dropping funnel 1 and subjected to nitrogen gas replacement.
Further, the monomer shown in "Dropped monomer solution 2" in Table 1 is mixed with the organic solvent, the polymerization initiator, and the polymerization chain transfer agent to obtain "Dropped monomer solution 2", which is placed in the dropping funnel 2. Then, nitrogen gas replacement was performed.
Under an atmosphere of nitrogen, the "initial charged monomer solution" in the reaction vessel was maintained at 77°C with stirring, and the "dropped monomer solution 1" in the dropping funnel 1 was gradually dropped into the reaction vessel over 3 hours. Then, the "dropping monomer solution 2" in the dropping funnel 2 was gradually dropped into the reaction container over 2 hours. After the dropping was completed, the mixed solution in the reaction vessel was stirred at 77° C. for 0.5 hours. Next, a polymerization initiator solution was prepared by dissolving 0.6 parts of the polymerization initiator in 27.0 parts of MEK, added to the mixed solution, and aged by stirring at 77°C for 1 hour.
The polymerization initiator solution was prepared, added and aged 5 more times. Next, the reaction solution in the reaction vessel was maintained at 80° C. for 1 hour, MEK was added to obtain a solution of polymer p1-1 (solid content concentration 40.8%). The weight average molecular weight of the obtained polymer p1-1 was 52,700.

The details of the monomers in Table 1 are as follows.
Styrene-based macromonomer: Toagosei Co., Ltd., trade name: AS-6S (effective concentration: 50%, number average molecular weight: 6,000, terminal: methacryloyl group, segment: styrene)
M-40G: Methoxy polyethylene glycol monomethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-40G (average number of moles of ethylene oxide added: 4, terminal: methoxy group)

<Preparation of pigment water dispersion (I)>
Preparation Example 1-1
315.2 g of the polymer p1-1 solution (solid content concentration 40.8%) obtained in Production Example 1-1 was mixed with 121.4 g of methyl ethyl ketone (MEK) to obtain a MEK solution of the polymer p1-1. The MEK solution of the polymer p1-1 was charged into a disper having a receiver having a volume of 3 L, and ion-exchanged water 893.8 g, 5N sodium hydroxide aqueous solution 44.6 g, and 25 while stirring under conditions of 1,400 rpm. % Aqueous ammonia solution (3.4 g) to adjust the equivalent amount of the neutralizing agent with sodium hydroxide to 78.8 mol% and the equivalent amount of the neutralizing agent with ammonia to 21.2 mol%. The mixture was stirred at 1,400 rpm for 15 minutes while cooling with a water bath at ℃. Next, 300 g of carbon black (trade name: MONARCH717, manufactured by Cabot Corporation) as a black pigment was added, and the mixture was stirred at 20° C. and 7,000 rpm for 3 hours. Further, 399.6 g of ion-exchanged water was added, and the obtained pigment mixture was subjected to 20-pass dispersion treatment at a pressure of 150 MPa using a Microfluidizer "M-110EH-30XP" (manufactured by Microfluidics) to obtain a dispersion treatment product ( 1) (solid content concentration 21%) was obtained.
2,000 g of the obtained dispersion treated product (1) was put in a 4 L eggplant flask, 800 g of ion-exchanged water was added (solid content concentration 15%), and a rotary distillation apparatus "rotary evaporator N-1000S" (Tokyo Rika Kikai Co., Ltd.) was used. Manufactured by K.K.) at a rotation speed of 50 rpm in a warm bath adjusted to 32° C. and maintained at a pressure of 0.09 MPa for 3 hours to remove the organic solvent. Further, the temperature of the hot bath was adjusted to 62° C., the pressure was lowered to 0.07 MPa, and the mixture was concentrated until the solid content concentration became 25%.
The obtained concentrate was put into a 500 ml angle rotor and centrifuged at 7,000 rpm for 20 minutes using a high-speed cooling centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20°C), and then the liquid layer portion was separated. A 5 μm membrane filter “Minisart” (manufactured by Sartorius) was filtered to obtain an aqueous dispersion (i-1) of the black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the resulting water dispersion (i-1) (including 17.2 g of carbon black and 7.4 g of polymer p1-1), and further Proxel LVS (Arch Chemicals Japan Ltd.). Product: 0.22 g of antifungal agent, effective content 20%), epoxy crosslinking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase Chemtex Co., Ltd., trade name: Denacol EX321L, epoxy so that the crosslinking rate becomes 15 mol %. 0.27 g of equivalent weight 129) was added, and the mixture was stirred at 70° C. for 2 hours. After cooling to 25° C., the mixture was filtered through the 5 μm filter, and ion-exchanged water was further added so that the solid content concentration was 22% to obtain an aqueous dispersion (I-1) of the black pigment-containing polymer particles A1. The average particle size of the water dispersion (I-1) was 94.7 nm.

Preparation Example 1-2
The pigment was dispersed in the same manner as in Preparation Example 1-1 to obtain an aqueous dispersion (i-1) of the black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the resulting water dispersion (i-1) (including 17.2 g of carbon black and 7.4 g of polymer p1-1), and further Proxel LVS (Arch Chemicals Japan Ltd.). Product: 0.22 g of antifungal agent, effective content 20%), epoxy crosslinking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase Chemtex Co., Ltd., trade name: Denacol EX321L, epoxy so that the crosslinking rate is 50 mol %. 0.89g of equivalent weight 129) was added, and it stirred at 70 degreeC for 2 hours. After cooling to 25° C., the mixture was filtered through the 5 μm filter, and ion-exchanged water was added so that the solid content concentration became 22% to obtain an aqueous dispersion (I-2) of the black pigment-containing polymer particles A2. The average particle size of the water dispersion (I-2) was 92.1 nm.

Preparation Example 1-3
The pigment was dispersed in the same manner as in Preparation Example 1-1 to obtain an aqueous dispersion (i-1) of the black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the resulting water dispersion (i-1) (including 17.2 g of carbon black and 7.4 g of polymer p1-1), and further Proxel LVS (Arch Chemicals Japan Ltd.). Product: 0.22 g of antifungal agent, effective content 20%), epoxy crosslinking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase Chemtex Co., Ltd., trade name: Denacol EX321L, epoxy so that the crosslinking rate becomes 75 mol %. 1.3g of equivalent weight 129) was added, and the mixture was stirred at 70° C. for 2 hours. After cooling to 25° C., the mixture was filtered through the 5 μm filter, and ion-exchanged water was added so that the solid content concentration became 22% to obtain an aqueous dispersion (I-3) of black pigment-containing polymer particles A3. The average particle size of the water dispersion (I-3) was 93.4 nm.

Preparation Example 1-4
The pigment was dispersed in the same manner as in Preparation Example 1-1 to obtain an aqueous dispersion (i-1) of the black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the resulting water dispersion (i-1) (including 17.2 g of carbon black and 7.4 g of polymer p1-1), and further Proxel LVS (Arch Chemicals Japan Ltd.). (Production: antifungal agent, effective content 20%) 0.22 g was added, and the mixture was stirred at 70° C. for 2 hours. After cooling to 25° C., the mixture was filtered through the 5 μm filter, and ion-exchanged water was further added so that the solid content concentration was 22% to obtain an aqueous dispersion (I-C1) of black pigment-containing polymer particles AC1. The average particle size of the water dispersion (I-C1) was 96.4 nm.

<Production of polymer P2>
Production Example 2-1
12 parts of methacrylic acid, 15 parts of 2-ethylhexyl methacrylate, 33 parts of benzyl methacrylate, and 40 parts of benzyl acrylate were mixed to prepare a mixed solution of the raw material monomer (b). Into a reaction vessel, 5 parts of methyl ethyl ketone (MEK) and 10% of a mixed liquid of the raw material monomer (b) were put and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, the rest of the mixed liquid of the raw material monomer (b), 75 parts of MEK, and an azo radical polymerization initiator (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., trade name: V-501, 4, 4'- A mixture of 1.5 parts of azobis(4-cyanovaleric acid)) was added, and the mixture in the reaction vessel was heated to 77° C. under a nitrogen atmosphere while stirring, and the mixture in the dropping funnel was allowed to take 5 hours. Was dropped. After the dropping was completed, a solution prepared by dissolving 0.5 part of the polymerization initiator in 5 parts of MEK was added, and the mixture was further reacted at 77° C. for 2 hours to obtain a solution of water-insoluble polymer P2-1.
Table 2 shows the measured values of the weight average molecular weight and acid value of the obtained polymer P2-1 and the calculated values of the glass transition temperature thereof.

Production Examples 2-2 to 2-10 and Comparative Production Examples 2-1 to 2-3
Polymer P2-2 to P2-10 and polymer P2- were prepared in the same manner as in Production Example 2-1, except that the type or amount of the raw material monomer (b) was changed to those shown in Table 2 in Production Example 2-1. A solution of C1-P2-C3 was obtained. Table 2 shows the measured weight average molecular weight and acid value of each polymer P2, and the calculated glass transition temperature.

<Preparation of Polymer Particle B Aqueous Dispersion (II)>
Preparation Example 2-1
29.0 parts of the polymer P2-1 obtained by drying the solution of the polymer P2-1 obtained in Production Example 2-1 under reduced pressure was added with 79.0 parts of ion-exchanged water and a 5N sodium hydroxide aqueous solution (sodium hydroxide). 6.6 parts of solid content 16.9%, FUJIFILM Wako Pure Chemical Industries, Ltd., for volumetric titration) was added, and the equivalent of sodium hydroxide used was sodium hydroxide based on the number of moles of the carboxy group of the polymer P2-1. It neutralized so that it might become 100 mol% in the ratio of the number of moles. By heating the obtained mixture at 90° C. for 5 hours while stirring at 150 rpm, an aqueous dispersion liquid (II-1) of polymer particles B1 (cumulant average particle diameter of polymer particles B1: 10 nm, solid content concentration 20) %) was obtained.

Preparation Examples 2-2 to 2-13 and Comparative Preparation Examples 2-1 to 2-4
Polymer particles were prepared in the same manner as in Preparation Example 2-1 except that the type of polymer P2, the amount of ion-exchanged water, or the amount of 5N sodium hydroxide aqueous solution was changed to those shown in Table 3 in Preparation Example 2-1. Aqueous dispersions (II-2) to (II-13) of B2 to B13 and aqueous dispersions (II-C1) to (II-C4) of BC1 to BC4 (solid content concentration 20%) were obtained.

Preparation Example 2-14
In Preparation Example 2-1, the polymer P2-1 was used as the polymer P2-3, the amount of ion-exchanged water was 79.2 parts, and 5N sodium hydroxide aqueous solution 6.6 parts was added to triethanolamine (purity 98% or more, Tokyo Kasei Co., Ltd. (Manufactured by Kogyo Co., Ltd.) except that the amount was changed to 5.0 parts to obtain an aqueous dispersion liquid (II-14) of polymer particles B14 (solid content concentration 20%) by the same method as in Preparation Example 2-1.

Comparative Preparation Example 2-5
In a reaction vessel equipped with a dropping funnel, 20 parts of n-butyl acrylate, 80 parts of benzyl methacrylate, 1.9 parts of sodium dodecylbenzenesulfonate, 8.7 parts of hexadecane, and 550 parts of ion-exchanged water were added and mixed, The resulting raw material monomer mixture was irradiated with ultrasonic waves for 3 minutes at an output of 300 W and a frequency of 20 kHz using an ultrasonic disperser "US300T" (manufactured by Nippon Seiki Seisakusho Co., Ltd.) to obtain an emulsion of the raw material monomer. .. An aqueous KPS solution prepared by dissolving 2.7 parts of potassium persulfate (KPS) in 165 parts of ion-exchanged water was placed in a dropping funnel, and then the atmosphere in the reaction vessel was replaced with nitrogen. Under a nitrogen atmosphere, the emulsion of the raw material monomer in the reaction vessel was maintained at 70° C. with stirring, and the KPS aqueous solution in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After completion of dropping, aging was carried out at 70° C. for 1 hour.
Purification was performed using a dialysis membrane (Spectra Laboratories, trade name: Spectra/Pore 3 Dialysis Membrane, molecular weight cutoff: 3,500). An aqueous dispersion (II-C5) of polymer particles BC5 was obtained by removing water so that the solid content concentration was 20% (cumulant average particle diameter of polymer particles BC5: 123 nm, solid content concentration 20%). ). The dried polymer particles BC5 had a weight average molecular weight of 210,000 and a glass transition temperature of 25°C.

<Water-based ink>
Example 1
37.2 parts of the aqueous dispersion (I-2) obtained in Preparation Example 1-2, 14.2 parts of the aqueous dispersion (II-3) of polymer particles B3 obtained in Preparation Example 2-3 (polymer particles B3 2.8 parts, water 11.4 parts included), propylene glycol (hereinafter, also referred to as "PG") 28.0 parts, diethylene glycol monobutyl ether (hereinafter, also referred to as "BDG") 4.0 parts, acetylene. 1.0 parts of a surfactant (trade name "Surfynol 440", manufactured by Evonik Industries Co., Ltd.) and 15.6 parts of ion-exchanged water were mixed, and the resulting mixed solution was a membrane filter of 1.2 μm (Sartorius). Ink 1 was obtained by filtration with a product name: Minisart.

Examples 2-19 and Comparative Examples 1-6
Inks 2 to 19 and C1 to C6 were obtained in the same manner as in Example 1 except that the ink compositions shown in Tables 4 and 5 were changed.

<Preparation of printed matter>
A biaxially stretched polyethylene terephthalate film (Toray Industries, Inc.) in which an inkjet printer (manufactured by Ricoh Co., Ltd., product name: IPSIO SG 2010L) is equipped with a rubber heater, each of the water-based inks obtained in the printer is filled, and heated to 60° C. Product name: Lumirror T60, water absorption 2.3 g/m ² ) (hereinafter also referred to as “PET”), biaxially stretched anti-fog treated polypropylene film (Futamura Chemical Co., Ltd., product type: AF-662, anti-fog) Great, water absorption 2.4 g/m ² (hereinafter also referred to as “OPP”), and polyvinyl chloride (manufactured by Lintec Corporation, PVC80BP, water absorption 1.4 g/m ² ) (hereinafter also referred to as “PVC”). A solid image is printed on each of the above (1) and the printed surface is dried for 6 minutes on a hot plate heated to 60° C. to obtain a printed material. The obtained printed matter was evaluated by the method described below.

<Evaluation>
(Storage stability)
Each water-based ink was stored in an environment of 60° C. for 28 days, and evaluated based on the following evaluation criteria from the change rate of the cumulant average particle diameter and the change rate of viscosity of each water-based ink before and after storage. The smaller the absolute value of the change rate of the average particle diameter and the change rate of the viscosity, the better the storage stability. The results are shown in Tables 4 and 5.
[Change rate of cumulant average particle size]
For each water-based ink before and after storage, the cumulant average particle size was measured using a particle size measuring device “ELSZ-2000S” (manufactured by Otsuka Electronics Co., Ltd.), and the change rate of the average particle size [= (cumulant average particle after storage Diameter)/(cumulant average particle size before storage)×100] was calculated.
[Change rate of ink viscosity]
For each water-based ink before and after storage, the ink viscosity at 25° C. was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.), and the change rate of viscosity [= (ink viscosity after storage)/(before storage) Ink viscosity)×100] was calculated.
〔Evaluation criteria〕
A: The change rate of the average particle size is within ±5%, and the change rate of the viscosity is within ±5%.
B: Among the change rates of the average particle diameter and the viscosity, the one with a larger change rate is more than ±5% and within ±10%.
C: The larger change rate of the average particle diameter and the change rate of viscosity is more than ±10% and within ±15%.
D: The change rate of the average particle size and the change rate of the viscosity is greater than ±15% and within ±20%.
E: The change rate of the average particle size is more than ±20%, or the change rate of the viscosity is more than ±20%.

(Redispersibility)
10 μL of each water-based ink was dropped on a slide glass using a micropipette, and left in an environment of 60° C. and 40% RH for 24 hours to evaporate and dry the water-based ink.
Then, 200 μL of the vehicle for redispersibility evaluation was dropped on the solid matter remaining on the slide glass, and the redispersibility of the solid matter after 5 minutes was visually observed and evaluated according to the following evaluation criteria. When redispersing the solid matter, the smaller the residue of the solid matter, the better the redispersibility. The results are shown in Tables 4 and 5.
The vehicle for redispersibility evaluation was prepared by adding 28% of propylene glycol (PG), 4% of diethylene glycol monobutyl ether (BDG) and ion-exchanged water, and measuring the total amount to 100% with a magnetic stirrer. Stir well and mix well to prepare.
〔Evaluation criteria〕
A: The solid matter was uniformly redispersed and there was no residue.
B: The solid matter was redispersed, but there was a residue.
C: Solid matter was not redispersed.

(Fixability)
The evaluation was performed by a test method according to JIS K6854-3. A double-sided tape (manufactured by Nichiban Co., Ltd., trade name "Nystack (registered trademark)", adhesive strength: 04) was attached to the printing surface of the PET, OPP and PVC printed matter, and a test piece having a width of 15 mm and a length of 20 mm was obtained. I cut it to be. Using a tensile tester "RTC-1150A" (manufactured by Orientec Co., Ltd.), the print medium portion at the tip of the test piece and the double-sided tape portion are both sandwiched by an arm, and a T-shaped tension is obtained at a speed of 300 mm/min. The test was conducted. The measurement of the load was performed every 20 μm in length, and the value obtained by averaging the values of the load of 25 mm to 125 mm was taken as the value of tensile strength, and evaluated according to the following evaluation criteria. The larger the value of tensile strength, the better the fixability. The results are shown in Tables 4 and 5.
〔Evaluation criteria〕
A: The value of tensile strength was 2.0 N or more.
B: The value of tensile strength was 1.25 or more and less than 2.0N.
C: The value of tensile strength was 0.5 or more and less than 1.25N.
D: The value of tensile strength was less than 0.5N.

From Tables 4 and 5, it can be seen that Examples 1 to 19 are superior in fixability, storage stability and redispersibility as compared with Comparative Examples 1 to 6.
In Comparative Example 1, it can be seen that the storage stability and redispersibility are inferior because the polymer particles AC1 containing the pigment do not have a crosslinked structure.
In Comparative Example 2, the pigment-free polymer particles BC1 do not contain a constitutional unit derived from the aliphatic (meth)acrylate (b-2), so that the fixability is inferior.
In Comparative Example 3, since the polymer particles BC5 containing no pigment do not contain the structural unit derived from the (meth)acrylic acid (b-1), the redispersibility is inferior.
In Comparative Examples 4 and 5, since the glass transition temperatures of the polymer particles BC2 and BC3 containing no pigment are less than −30° C. and more than 40° C., respectively, it can be seen that the fixability is poor.
In Comparative Example 6, the fixability is inferior because the cumulant average particle size of the polymer particles BC4 containing no pigment is more than 30 nm.

According to the present invention, it is possible to provide a water-based ink having excellent fixability and excellent storage stability and redispersibility even in printing on a low water-absorbent printing medium, and a printing method using the water-based ink.

Claims (7)

A water-based ink containing water-insoluble polymer particles A containing a pigment, water-insoluble polymer particles B not containing a pigment, and water,
The polymer particles A are obtained by crosslinking the polymer particles a containing a pigment,
The water-insoluble polymer P2 constituting the polymer particles B contains a structural unit derived from (meth)acrylic acid (b-1) and a structural unit derived from an aliphatic (meth)acrylate (b-2),
The aliphatic (meth)acrylate (b-2) is 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and cyclohexyl (meth)acrylate. Is at least one selected from
The glass transition temperature of the polymer P2 is −30° C. or higher and 40° C. or lower,
An aqueous ink in which the cumulant average particle diameter of the polymer particles B is 5 nm or more and 30 nm or less. The water-based ink according to claim 1, wherein the content of the constituent unit derived from the aliphatic (meth)acrylate (b-2) in the polymer P2 is 10% by mass or more and 90% by mass or less. The water-based ink according to claim 1, wherein the acid value of the polymer P2 is 10 mgKOH/g or more and 200 mgKOH/g or less, and the polymer P2 is neutralized with a neutralizing agent. The water-based ink according to claim 1, wherein the content of the polymer particles B is 0.3% by mass or more and 7% by mass or less. The water-based ink according to claim 1, wherein the polymer P2 further includes a constituent unit derived from an aromatic group-containing monomer (b-3). 6. The polymer p1 constituting the pigment-containing polymer particles a contains a carboxy group, and the polymer p1 is crosslinked with a compound having two or more epoxy groups in the molecule. Water based ink. A printing method comprising printing on a low water-absorption print medium using the water-based ink according to claim 1.