JP7220061B2 - water-based ink - Google Patents

Description

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

In the field of commercial printing and industrial printing such as label printing used for product packaging printing and advertisements, PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), PP (polypropylene), NY (nylon), etc. 2. Description of the Related Art Solvent-based inks, UV curable inks, and the like have conventionally been used for printing on resin printing media. On the other hand, from the viewpoints of environmental load reduction, energy saving, safety, etc., as a printing method using water-based ink, utilization of an inkjet recording method, a flexographic printing method, and a gravure printing method is demanded.
In addition, from the viewpoint of weather resistance and water resistance of printed matter, water-based inks using pigments as colorants have become mainstream. However, since the resin print medium is non-absorbent and the water-based ink does not penetrate into the print medium, the pigment particles contained in the water-based ink remain on the surface of the print medium. Therefore, conventional water-based inks do not have sufficient fixability to the printing medium, and various attempts have been made to improve these problems.

For example, in Patent Document 1, 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, a latex binder, water and an organic solvent are added. and polymer-encapsulated pigment particles containing a carboxy-functional dispersant cross-linked around a pigment core by a cross-linking agent.
In Patent Document 2, for the purpose of providing a water-based inkjet ink that adheres well to a non-absorbent recording medium and is stable in ejection, a pigment, polymer fine particles having a core-shell structure, and two kinds of water-soluble inks with different boiling points are disclosed. A shell composed of an organic solvent and water and having an acid value of 50 to 200 mgKOH/g obtained by polymerizing the polymer fine particles having the core-shell structure with an unsaturated hydrophobic monomer and an unsaturated hydrophilic monomer. Aqueous inkjet inks are described which are composed of a resin and a core resin obtained by polymerizing an unsaturated hydrophobic monomer.
In Patent Document 3, for the purpose of providing an ink having good adhesion to a printing medium, etc., a dispersion solvent, particles of a first binder resin emulsified or suspended in the dispersion solvent and containing a colorant, and the above and particles of a second binder resin emulsified or suspended in a dispersion solvent, wherein the average particle diameter of the particles of the second binder resin is smaller than the average particle diameter of the particles of the first binder resin. ing.
Patent Document 4 discloses a water-based gravure ink containing a pigment, a polymer, a water-soluble organic solvent, a surfactant, and water for the purpose of providing a water-based gravure ink that has a low environmental impact and is capable of high-definition printing. The water-soluble organic solvent has a boiling point of 100° C. or higher and 260° C. or lower, and the aqueous gravure ink contains 10% by mass or more and 35% by mass or less of the water-soluble organic solvent and 50% by mass or more and 70% by mass or less of water. Gravure inks are described.

JP 2017-14491 A JP 2018-12829 A JP 2014-129497 A WO2017/047267

With the development of the packaging industry, the use of flexible packaging materials in the fields of commercial printing and industrial printing is progressing. Resin films such as PET and PP are mainly used as flexible packaging materials, and the resulting printed matter is required to have high adhesion to the resin film. On the other hand, in inkjet printing, it is necessary to improve the maintainability and ejection reliability to prevent clogging in the ink channels and nozzles. becomes. In order to improve the fixability between the ink coating film and the resin film, from the viewpoint of affinity with the resin film, the fixation aid polymer used in the ink should contain as few hydrophilic groups as possible such as carboxyl groups and should be hydrophobic. It is considered effective to increase However, when many hydrophobic groups are introduced into the fixing aid polymer to improve fixability, storage stability and redispersibility tend to decrease. With such restrictions on polymer design, it was difficult with the techniques of Patent Documents 1 to 4 to achieve both excellent fixability, storage stability, and redispersibility on various low water-absorbing printing media.
An object of the present invention is to provide a water-based ink that is excellent in fixability even on a low water-absorbing printing medium, storage stability and redispersibility, and a printing method using the water-based ink.

The present inventors have developed a water-based ink containing pigment-containing water-insoluble polymer particles A, pigment-free water-insoluble polymer particles B, and water, wherein the polymer particles A are crosslinked, and the polymer A polymer constituting 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 The inventors have found that the above problems can be solved by setting the content to a specific range. That is, the present invention relates to the following [1] and [2].
[1] Pigment-containing water-insoluble polymer particles A (hereinafter also referred to as “pigment-containing polymer particles A”), pigment-free water-insoluble polymer particles B (hereinafter also referred to as “polymer particles B”), and water A water-based ink containing
The polymer particles A are crosslinked water-insoluble polymer particles a containing a pigment,
The water-insoluble polymer P2 constituting the polymer particle 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 polymer P2 has a glass transition temperature of −30° C. or more and 40° C. or less,
A water-based ink in which the polymer particles B have a cumulant average particle size of 5 nm or more and 30 nm or less.
[2] A printing method, comprising printing on a low-absorbent printing medium using the water-based ink described in [1] above.

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

[Water-based ink]
The water-based ink of the present invention (hereinafter also simply referred to as "ink") is the ink described in [1] above.
The term "aqueous" means that water accounts for the maximum proportion in the medium.
"Low water absorption" is a concept including low water absorption and non-water absorption, and the amount of water absorption 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 / ^m2 or less. The water absorption is measured by the method described in Examples.
"Printing" is a concept that includes printing for recording characters and images.
In the present invention, the term "water-insoluble" of a polymer means that the amount dissolved in 100 g of water at 25°C is 10 g or less when the polymer reaches a constant weight after being dried at 105°C for 2 hours. do. When the polymer has an anionic group, the dissolution amount is the dissolution amount when the anionic group is 100% neutralized with sodium hydroxide. When the polymer has a cationic group, the dissolution amount is the It is the dissolution amount when the cationic group is 100% neutralized with hydrochloric acid.

The ink of the present invention has excellent fixability even when printed on a low water-absorbing printing medium, and has excellent storage stability and redispersibility. Although the reason is not clear, it is considered as follows.
In the present invention, the polymer particles B functioning as a fixing aid have a specific composition and properties in spite of having a carboxyl group, and have a small particle size. It is possible to improve fixing properties even when printing on a low water-absorbing printing medium. Generally, when the particle size of the polymer particles that function as a fixing aid is small, the storage stability and redispersibility of the ink deteriorate due to depletion aggregation. and the polymer particles A are crosslinked. Therefore, it is believed that the polymer is strongly adsorbed or immobilized on the surface of the pigment, suppressing aggregation of the pigment and, as a result, suppressing depletion aggregation. Furthermore, since the swelling of the polymer is also suppressed, it is thought that the synergistic effect of these can improve 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 pigment-containing polymer particles A, and the polymer particles A are obtained by cross-linking pigment-containing polymer particles a (hereinafter also referred to as "pigment-containing polymer particles a"). .
Pigments may be either inorganic pigments or organic pigments, and lake pigments and fluorescent pigments may also be used. In addition, if necessary, they can be used in combination with an extender pigment.
Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide and chromium oxide, and pearl luster pigments. Carbon black is particularly preferred for black ink. 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; Examples include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.
The hue is not particularly limited, and achromatic pigments such as white, black and gray; and chromatic pigments such as yellow, magenta, cyan, blue, red, orange and green can be used.
Examples of extender pigments include silica, calcium carbonate, and talc.
The pigments may be used alone or in combination 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 the dispersion stability of the pigment, the polymer p1 is more preferably present in the ink in a pigment-encapsulated state in which the pigment is contained in the polymer p1.

The polymer p1 preferably contains an ionic group from the viewpoint of improving the dispersion stability, fixability, storage stability and redispersibility of the pigment. The ionic group is preferably an acid group, and a carboxy group (--COOM), a sulfonic acid group (--SO ₃ M), a phosphate group (--OPO ₃ M ₂ ), etc. dissociate to release hydrogen ions. More preferred are acid groups such as groups exhibiting acidity, or their dissociated ionic forms (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M). In the above chemical formula, M represents a hydrogen atom, alkali metal, ammonium or organic ammonium. Among these, a carboxy group (--COOM) is preferred 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 introduced into the polymer skeleton by the ionic monomer (a-1). That is, the polymer p1 preferably contains structural units derived from the ionic monomer (a-1). Examples of the polymer p1 include vinyl-based resins, polyester-based resins, polyurethane-based resins, and the like. Among them, vinyl-based resins are preferable, and a raw material monomer (a) containing an ionic monomer (a-1) and a hydrophobic monomer (a-2) (hereinafter also simply referred to as "raw material monomer (a)") is used together. A vinyl-based resin obtained by polymerization is more preferable. The vinyl resin contains a structural unit derived from component (a-1) and a structural unit derived from component (a-2). From the viewpoint of improving the dispersion stability, fixability, storage stability and redispersibility of the pigment, the vinyl resin may further contain a structural unit derived from the nonionic monomer (a-3).

[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, 2-methacryloyloxymethylsuccinic acid, etc. Monomers having a carboxyl group; monomers having a sulfonic acid group such as styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-sulfopropyl (meth)acrylate; vinylphosphonic acid, vinylphosphate, bis(methacryloxyethyl) ) monomers having a phosphoric acid group such as phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate.
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 1 type, more preferably (meth)acrylic acid.
As used herein, "(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 the amount dissolved in 100 g of deionized water at 25° C. until the monomer is saturated is less than 10 g. . The dissolved amount of the hydrophobic monomer (a-2) is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of adsorption to the pigment.

The hydrophobic monomer (a-2) is preferably at least one selected from (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols and aromatic group-containing monomers.
The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, (meth)acrylates having a linear alkyl group such as stearyl (meth)acrylate; isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, (meth)acrylates having a branched chain alkyl group such as isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; alicyclic alkyl such as cyclohexyl (meth)acrylate group-containing (meth)acrylates, and the like. 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, more preferably a styrene-based monomer and an aromatic group-containing monomer. It is one or more selected from (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
Styrenic monomers include styrene, α-methylstyrene, 2-methylstyrene and the like, and aromatic group-containing (meth)acrylates include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate and the like. Among these, one or more selected from styrene, α-methylstyrene and benzyl (meth)acrylate are preferred.

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

[Nonionic monomer (a-3)]
As the nonionic monomer (a-3), from the viewpoint of improving the dispersion stability, fixability, storage stability and redispersibility of the pigment, preferably 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) ) Hydroxyalkyl (meth)acrylates such as acrylates; Polyethylene glycol (n = 2 to 30, n indicates the average number of added moles of oxyethylene groups. Hereinafter, n indicates the average number of added moles of the oxyalkylene groups.) Polyalkylene glycol (meth) acrylate such as (meth) acrylate; Alkoxypolyalkylene glycol (meth) acrylate such as methoxy polyethylene glycol (n = 1 to 30) (meth) acrylate; Phenoxy (ethylene glycol / propylene glycol copolymerization) ( n = 1 to 30, wherein ethylene glycol: n = 1 to 29) at least one selected from (meth)acrylates, more preferably alkoxypolyalkylene glycol (meth)acrylates, more preferably methoxypolyethylene glycol ( meth) acrylate.
Specific examples of commercially available nonionic monomers (a-3) include NK Ester M-40G, 90G, 230G (these are trade names of Shin-Nakamura Chemical Co., Ltd.), Blenmer PE-90. , 200, 350, etc., Blenmer PME-100, 200, 400, etc., Blenmer 50PEP-300, Blenmer 50POEP-800B, etc. (these are trade names 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 components (a-1) and (a-2) in the raw material monomer (a) (the content as an unneutralized amount; the same shall apply hereinafter) or in the vinyl resin ( From the viewpoint of improving the dispersion stability of the pigment, the contents of the constituent units derived from the component (a-1) and the constituent units derived from the component (a-2) are as follows.
The content of component (a-1) is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass. % or less, more preferably 20 mass % or less.
The content of component (a-2) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass. % or less, more preferably 70 mass % or less.

(Manufacture of vinyl resin)
A vinyl resin is produced by copolymerizing a mixture of 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 polymerize.
There are no restrictions on the chain mode of polymerizable monomers, and any polymerization mode such as random, block, or graft may be used.
After completion of the polymerization reaction, the polymer produced can be isolated from the reaction solution by known methods such as reprecipitation and solvent distillation. The obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatography, extraction, or the like.

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

(crosslinking agent)
Pigment-containing polymer particles A are obtained by cross-linking pigment-containing polymer particles a, preferably by cross-linking pigment-containing polymer particles a with a cross-linking agent. As a result, the polymer is strongly adsorbed or immobilized on the surface of the pigment, suppressing aggregation of the pigment, resulting in suppression of depletion aggregation, and further suppressing swelling of the polymer. It is thought that the quality will improve.

The cross-linking agent is a polyfunctional compound, and the reactive functional group of the polyfunctional compound preferably reacts 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 covalent bond described above.
When the polymer p1 contains a carboxy group, the reactive functional group is one or more selected from an epoxy group, an isocyanate group, an aziridino group, an amino group and an oxazoline group, and the reactive functional group is the 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 one or more selected from an epoxy group, an isocyanate group, an aziridino group, an amino group and an oxazoline group, and more preferably an epoxy group. In addition, the concept of an epoxy group includes a glycidyl group.
The polyfunctional compound preferably has the same type of reactive functional groups from the viewpoint of cross-linking between the polyfunctional compound and the polymer p1 under the same conditions.

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

Specific examples of cross-linking agents include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, and neopentyl. Polyglycidyl ethers such as glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether and the like are included. Among these, one or more selected from trimethylolpropane polyglycidyl ether and pentaerythritol polyglycidyl ether are preferred, and trimethylolpropane polyglycidyl ether is more preferred.

[Production of water-insoluble polymer particles 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 an aqueous pigment dispersion (i)) and further reacting with a cross-linking agent to obtain an aqueous dispersion of the pigment-containing polymer particles A. It can be obtained as a body (I) (hereinafter also referred to as an aqueous pigment dispersion (I)).
Aqueous pigment dispersion (i) is obtained, for example, by dispersing a pigment mixture containing polymer p1, an organic solvent, a pigment, water, and optionally a neutralizer, a surfactant, etc., to obtain pigment-containing polymer particles a. It can be obtained by removing the organic solvent from the dispersion after obtaining the dispersion.
Although the organic solvent is not limited, ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms, etc. are preferable, and the wettability to the pigment, the solubility of the polymer p1, and the pigment of the polymer p1 From the viewpoint of improving the adsorptivity of , ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are more preferred, and methyl ethyl ketone is even more preferred. When a vinyl resin is synthesized as the polymer p1 by a solution polymerization method, the solvent used in the polymerization may be used as it is.

When the polymer p1 has acid groups, at least part of the acid groups are preferably neutralized using a neutralizing agent. When neutralizing, it is preferable to neutralize so that the pH becomes 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, preferably sodium hydroxide and ammonia. Neutralizing agents can be used alone or in combination of two or more. Moreover, the polymer p1 may be neutralized in advance.

The method for dispersing the pigment mixture is not particularly limited, but it is preferable to control the average particle size of the pigment-containing polymer particles a to a desired particle size using a known kneader, disperser, or the like. An aqueous pigment dispersion (i) can be obtained by removing the organic solvent from the obtained dispersion treated product by a known method.

Next, a cross-linking agent is added to the resulting aqueous pigment dispersion (i) to cross-link the pigment-containing polymer particles a, thereby obtaining the aqueous pigment dispersion (I). At this time, the functional groups of the polymer p1 constituting the pigment-containing polymer particles a are crosslinked with the crosslinking agent.
For example, when the polymer p1 has a carboxy group, the cross-linking ratio is the molar equivalent number of the cross-linkable functional group of the cross-linking agent with respect to the number of molar equivalents of the carboxy group of the polymer p1, from the viewpoint of improving fixability, storage stability and redispersibility. The number ratio is preferably 10 mol% or more, more preferably 20 mol% or more, still more 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.

The temperature of the cross-linking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, still more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 85° C. or lower, from the same viewpoint as described above. , and more preferably 75°C or less.
The time for the cross-linking treatment is preferably 0.5 hours or longer, more preferably 1 hour or longer, still more preferably 1.5 hours or longer, and preferably 12 hours or shorter, from the viewpoint of completion of the cross-linking reaction and economy. , more preferably 10 hours or less, still more preferably 8 hours or less, and even more preferably 5 hours or less.

The non-volatile component concentration (solid content concentration) of the aqueous pigment dispersion (I) is preferably 10% by mass or more, more preferably 10% by mass or more, from the viewpoint of improving the dispersion stability of the aqueous pigment 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 aqueous pigment dispersion (I) is measured by the method described in Examples.
From the viewpoint of dispersion stability, the content of the pigment in the aqueous pigment dispersion (I) is preferably 5% by mass or more, more preferably 7% by mass or more, and still more preferably 10% by mass or more. is 40% by mass or less, more preferably 30% by mass or less, and still more 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 aqueous pigment dispersion (I) is preferably 50/50 or more, more preferably 55/ 45 or more, more preferably 60/40 or more, and preferably 90/10 or less, more preferably 85/15 or less, and even more preferably 80/20 or less.
The cumulant average particle size 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, and even more preferably 80 nm, from the viewpoint of improving fixability, storage stability, and redispersibility. and preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 120 nm or less. The average particle size 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 pigment-free water-insoluble polymer particles B (polymer particles B) contain the polymer P2 (polymer P2) that constitutes the polymer particles B. The polymer P2 contains a structural unit derived from acrylic acid (b-1) and a structural unit derived from an aliphatic (meth)acrylate (b-2), and the glass transition temperature of the polymer P2 is −30° C. or higher and 40° C. or lower, and the polymer The cumulant average particle size of the particles B is 5 nm or more and 30 nm or less.
In the present invention, the "water-insoluble" polymer P2 is as described above. The dissolved amount of the polymer P2 is the dissolved amount when the carboxy groups of the polymer P2 are 100% neutralized with sodium hydroxide.

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

[Aliphatic (meth)acrylate (b-2)]
Aliphatic (meth)acrylates (b-2) are 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate from the viewpoint of improving fixability, storage stability and redispersibility. , tert-butyl (meth)acrylate and cyclohexyl (meth)acrylate, preferably selected from 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, and cyclohexyl (meth)acrylate At least one, more preferably 2-ethylhexyl (meth)acrylate.

[Aromatic group-containing monomer (b-3)]
The polymer P2 may contain structural units derived from monomers other than (meth)acrylic acid (b-1) and aliphatic (meth)acrylate (b-2). Other monomers include ionic monomers other than (meth)acrylic acid, hydrophobic monomers having aromatic groups, and nonionic monomers. Among them, hydrophobic monomers having aromatic groups (hereinafter referred to as "aromatic group Containing monomer (b-3)”) is preferred.
Examples of the aromatic group-containing monomer (b-3) include the aforementioned styrene-based monomers, aromatic group-containing (meth)acrylates, aromatic group-containing macromonomers, and the like. Among them, aromatic group-containing (meth)acrylates are preferred, and benzyl (meth)acrylate is more preferred, from the viewpoint of improving fixability, storage stability and redispersibility.

As described above, the polymer P2 preferably comprises a (meth)acrylic acid (b-1)-derived structural unit, an aliphatic (meth)acrylate (b-2)-derived structural unit, and an aromatic group-containing monomer ( b-3)-derived structural units, more preferably (meth) acrylic acid (b-1)-derived structural units, 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate , and at least one monomer-derived structural unit selected from cyclohexyl (meth)acrylate, and a structural unit derived from an aromatic group-containing (meth)acrylate, 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% by mass, from the viewpoint of improving fixability, storage stability and redispersibility. % by mass or more, more preferably 7% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.
The content of the aliphatic (meth)acrylate (b-2)-derived structural unit in the polymer P2 is preferably 10% by mass or more, more preferably 10% by mass or more, 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, and even more preferably 60% by mass or less.
When the polymer P2 contains structural units derived from the aromatic group-containing monomer (b-3), the content of the structural units derived from the aromatic group-containing monomer (b-3) in the polymer P2 is preferably 5% by mass. above, more preferably 10% by mass or more, still more preferably 20% by mass or more, still more preferably 30% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass % by mass or less.

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 Below, more preferably 0.6 or less, still more preferably 0.4 or less.

The total content of structural units derived from (meth)acrylic acid (b-1) and aliphatic (meth)acrylate (b-2) in polymer P2 is preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and more More preferably, it is 60% by 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)") in the same manner as the vinyl resin described above. ) by a known polymerization method. For example, a solution polymerization method in which a mixture of the raw material monomers (b) is heated together with a polymerization initiator, a polymerization chain transfer agent, etc. in a solvent and polymerized is preferred.
Examples of the polymerization initiator include azo compounds such as 2,2′-azobisisobutyronitrile and 2,2′-azobis(2,4-dimethylvaleronitrile); tert-butyl peroxyoctoate, benzoyl peroxide, etc. A known radical polymerization initiator such as an organic peroxide of can be used. Among them, one or more ionic groups selected from 4,4′-azobis(4-cyanovaleric acid) and 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamide] is preferred.
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, even more preferably 30,000 or more, and even more preferably 50,000 or more, from the viewpoint of improving fixability. 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, even more preferably 200,000 or less, and even more preferably 100,000 or less. is. The weight average molecular weight of polymer P2 can be measured by the method described in Examples.

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

The cumulant average particle size of the polymer particles B is 5 nm or more, preferably 7 nm or more, more preferably 10 nm or more, and still more 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, still more preferably 23 nm or less. The average particle size is measured by the method described in Examples.

[Production of Polymer Particles B Not Containing Pigment]
As the pigment-free polymer particles B (polymer particles B), appropriately synthesized ones or commercially available products may be used, but it is preferable to use them as an aqueous dispersion.
When obtaining the aqueous dispersion (II) of the polymer particles B, the polymer P2 constituting the polymer particles B is preferably neutralized with a neutralizing agent.
Aqueous dispersion (II) of polymer particles B is obtained by obtaining polymer P2 by a known polymerization method, then stirring while heating a mixture containing polymer P2, water and, if necessary, a neutralizing agent, A method in which the temperature is then lowered; a method in which a mixture containing polymer P2, an organic solvent, a neutralizer, and water is subjected to dispersion treatment to obtain a dispersion, and then the organic solvent is removed from the dispersion; . Among them, from the viewpoint of ease of work, a method of stirring while heating a mixture containing polymer P2, water, and a neutralizing agent 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, still more preferably 50 mgKOH/g or more, still 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 polymer P2 is measured by the method described in Examples.

The temperature at which the mixture is stirred is preferably 60° C. or higher, more preferably 70° C. or higher, still more 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 longer, more preferably 1 hour or longer, still more preferably 3 hours or longer, and preferably 30 hours or shorter, more preferably 15 hours or shorter, and still more preferably 10 hours or shorter. be.

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

[Production of water-based ink]
The ink of the present invention is preferably obtained by mixing the pigment water dispersion (I) and the polymer particle B water dispersion (II). 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.). A water-soluble organic solvent is an organic solvent that dissolves in an amount of 10 ml or more when dissolved in 100 ml of water at 25°C.
The water-soluble organic solvent preferably contains one or more organic solvents having a boiling point of 90° C. or higher. The weighted average boiling point of the water-soluble organic solvent is preferably 150°C or higher, more preferably 180°C or higher, and is preferably 240°C or lower, more preferably 220°C or lower, and still more preferably 200°C or lower. .
Examples of water-soluble organic solvents 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 even more preferable.

Further, the ink of the present invention may optionally contain moisturizing agents, wetting agents, penetrating agents, surfactants, viscosity modifiers, antifoaming agents, preservatives, antifungal agents, antirust agents, etc., which are commonly used in water-based inks. Various additives can be added, and filtration treatment can be performed using 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 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, and still more preferably 5% by mass or more, from the viewpoint of print density. From the viewpoint of lowering the content and improving fixability, storage stability and redispersibility, the content is preferably 15% by mass or less, more preferably 10% by mass or less, and even 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 still more preferably 7% by mass or more, from the viewpoint of improving print density and fixability. From the viewpoint of reducing ink viscosity, the content is preferably 15% by mass or less, more preferably 13% by mass or less, and even more 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, and still more preferably 2% by mass or more, from the viewpoint of improving fixability. From the viewpoint of lowering the ink viscosity when volatilized and improving storage stability and redispersibility, the content is preferably 7% by mass or less, more preferably 5% by mass or less, and even more 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, and still more preferably 15% by mass or more, from the viewpoint of ink viscosity, storage stability, and redispersibility. Yes, and preferably 47% by mass or less, more preferably 45% by mass or less, and even 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, and still more preferably 50% by mass or more, from the viewpoints of fixability, storage stability, and redispersibility, and , preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

From the viewpoint of improving fixability, storage stability, and redispersibility, the mass ratio of the pigment in the total solid content of the water-based ink [pigment/(total solid content of the water-based ink)] is preferably 0.1 or more, and more preferably 0.2 or more, more preferably 0.3 or more, and preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less, and even 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 still more 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, and still more preferably 7 mPa·s or less. The viscosity of water-based ink can be measured using an E-type viscometer.
The pH of the water-based ink is preferably 7.0 or higher, more preferably 7.2 or higher, still more preferably 7.5 or higher, and preferably 11 or lower, more preferably, from the viewpoint of member resistance and skin irritation. is 10 or less, more preferably 9.5 or less. The pH of water-based ink can be measured by a conventional method.

[Print method]
The ink of the present invention has excellent fixability even in printing on low water-absorbing printing media, and has excellent storage stability and redispersibility, so 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 preferable to use it as an inkjet ink.
Ink jet printing can be performed by loading a known ink jet recording apparatus and ejecting ink droplets onto a print medium to record an image or the like.
As an inkjet recording apparatus, there are a thermal type and a piezo type, but it is more preferable to use a piezo type ink jet recording water-based ink.
Usable print media include plain paper, coated paper, and resin film. Examples of coated paper include general-purpose glossy paper, multicolor foam gloss paper, and the like. The resin film is preferably at least one selected from polyester film, polypropylene film, polyethylene film and polyvinyl chloride film. A corona-treated substrate may be used for the resin film.
Examples of commonly available resin films include Lumirror T60 (manufactured by Toray Industries, Inc., polyester), PVC80BP (manufactured by Lintec Corporation, vinyl chloride), DGS-210WH (manufactured by Roland DG Co., Ltd., vinyl chloride), and transparent. PVC RE-137 (manufactured by Mimaki Engineering Co., Ltd., vinyl chloride), Cainus KEE70CA (manufactured by Lintec Corporation, polyethylene), YUPO SG90 PAT1 (manufactured by Lintec Corporation, polypropylene), FOR, FOA (both manufactured by Futamura Chemical Co., Ltd., Polypropylene), Bonyl RX (manufactured by Kohjin Film & Chemicals Co., Ltd., nylon), Emblem ONBC (manufactured by Unitika Ltd., nylon), and the like.

From the viewpoint of fixability, the print medium is preferably a low water absorption print medium.
The water absorption amount of the low-absorbent printing medium at a contact time of 100 ms with pure water is preferably 1 g/m ² or more, more preferably 2 g/m ² or more, from the viewpoint of fixability and print image quality. is 8 g/m ² or less, more preferably 6 g/m ² or less. The amount of water absorption 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 printing medium by the inkjet recording method for printing, and then drying the ink droplets that have landed on the printing medium.
In the drying step, the surface temperature of the print medium is preferably 25° C. or higher, more preferably 30° C. or higher, and still more preferably 50° C. or higher, from the viewpoint of improving print image quality, and suppresses deformation of the print medium due to heat. and energy reduction, the temperature is preferably 100° C. or lower, more preferably 85° C. or lower, and even more preferably 70° C. or lower.

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

(1) Measurement of weight-average molecular weight of polymer Gel permeation chromatography using a solution obtained by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent. Method [Tosoh Corporation GPC device (HLC-8320GPC), Tosoh Corporation column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H), flow rate: 0.5 mL / min] molecular weight as a standard substance Known monodisperse polystyrene kits [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].
A sample to be measured was obtained by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and using a syringe filter (DISMIC-13HP PTFE 0.2 μm, Advantech Co., Ltd.). and used after filtration.

(2) Measurement of Cumulant Average Particle Size Cumulant analysis was performed using a laser particle analysis system “ELS-8000” (manufactured by Otsuka Electronics Co., Ltd.) to measure the cumulant average particle size. The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and 100 integration times, and 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 % (converted to solid concentration).

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

(4) Measurement of 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, measurements were made according to JIS K0070.

(5) Water absorption amount of the print medium at a contact time of 100 msec between the 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 50% relative humidity Below, the amount of transfer at a pure water contact time of 100 msec was measured and taken as the water absorption amount at 100 msec. Measurement conditions are shown below.
"Spiral Method"
Contact Time (seconds): 0.010 to 1.0
Pitch (mm): 7
Length Per Sampling (degree): 86.29
Start Radius (mm): 20
End Radius (mm): 60
Min Contact Time (ms): 10
Max Contact Time (ms): 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 charge monomer solution" listed 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 mixture was replaced with nitrogen gas to obtain an "initial charge monomer solution".
On the other hand, the monomer, organic solvent, polymerization initiator (2,2'-azobis (2,4-dimethylvaleronitrile) shown in "dropping monomer solution 1" in Table 1; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., commercial Name: V-65), and the polymerization chain transfer agent were mixed to obtain "dropping monomer solution 1", which was placed in the dropping funnel 1 and replaced with nitrogen gas.
Further, the monomers shown in the "dropping monomer solution 2" listed in Table 1, the organic solvent, the polymerization initiator, and the polymerization chain transfer agent are mixed to obtain the "dropping monomer solution 2", which is placed in the dropping funnel 2. Then, nitrogen gas replacement was performed.
Under a nitrogen atmosphere, the "initial charged monomer solution" in the reaction vessel was maintained at 77°C while stirring, and the "dropping 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 vessel over 2 hours. After the dropwise addition was completed, the mixed solution in the reaction vessel was stirred at 77°C for 0.5 hour. 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 for 1 hour at 77°C.
The preparation, addition and aging of the polymerization initiator solution were carried out five more times. Then, the reaction solution in the reaction vessel was maintained at 80° C. for 1 hour, and MEK was added to obtain a solution of polymer p1-1 (solid 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: manufactured by Toagosei Co., Ltd., trade name: AS-6S (effective content: 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 added moles of ethylene oxide: 4, terminal: methoxy group)

<Preparation of Pigment Water Dispersion (I)>
Preparation Example 1-1
315.2 g of the polymer p1-1 solution (solid concentration: 40.8%) obtained in Production Example 1-1 was mixed with 121.4 g of methyl ethyl ketone (MEK) to obtain an MEK solution of polymer p1-1. The MEK solution of the polymer p1-1 is put into a disper having a receiver with a volume of 3 L, and while stirring at 1,400 rpm, 893.8 g of ion-exchanged water, 44.6 g of a 5N sodium hydroxide aqueous solution, and 25 % ammonia aqueous solution was added to adjust the use equivalent of the neutralizing agent using sodium hydroxide to 78.8 mol% and the use equivalent of the neutralizing agent using ammonia to 21.2 mol%. The mixture was stirred at 1,400 rpm for 15 minutes while cooling in a water bath at 1,400°C. Then, 300 g of carbon black (trade name: MONARCH717, manufactured by Cabot Corporation) was added as a black pigment, and the mixture was stirred at 20° C. and 7,000 rpm for 3 hours. Further, 399.6 g of ion-exchanged water is added, and the resulting pigment mixture is subjected to dispersion treatment using a microfluidizer "M-110EH-30XP" (manufactured by Microfluidics) at a pressure of 150 MPa for 20 passes to obtain a dispersed product ( 1) (solid concentration: 21%) was obtained.
2,000 g of the obtained dispersed product (1) was placed 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 Rikaki Co., Ltd. ) was used to remove the organic solvent by maintaining a pressure of 0.09 MPa for 3 hours in a hot bath adjusted to 32° C. at a rotational speed of 50 rpm. Further, the hot bath was adjusted to 62° C., the pressure was lowered to 0.07 MPa, and the mixture was concentrated to a solid content concentration of 25%.
The resulting concentrate was put into a 500 ml angle rotor, and centrifuged at 7000 rpm for 20 minutes using a high-speed refrigerated centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20 ° C.). Filtration was performed through a 5 μm membrane filter “Minisart” (manufactured by Sartorius) to obtain an aqueous dispersion (i-1) of black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the obtained aqueous dispersion (i-1) (containing 17.2 g of carbon black and 7.4 g of polymer p1-1), and Proxel LVS (Arch Chemicals Japan Co., Ltd. Product: antifungal agent, effective content 20%) 0.22 g, epoxy cross-linking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Co., Ltd., product name: Denacol EX321L, epoxy 0.27 g of equivalent weight 129) was added and 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 was 22% to obtain an aqueous dispersion (I-1) of black pigment-containing polymer particles A1. The average particle size of the aqueous 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 black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the obtained aqueous dispersion (i-1) (containing 17.2 g of carbon black and 7.4 g of polymer p1-1), and Proxel LVS (Arch Chemicals Japan Co., Ltd. Product: antifungal agent, effective content 20%) 0.22 g, epoxy cross-linking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Co., Ltd., product name: Denacol EX321L, epoxy 0.89 g of equivalent weight 129) was added and 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 was 22% to obtain an aqueous dispersion (I-2) of black pigment-containing polymer particles A2. The average particle size of the aqueous 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 black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the obtained aqueous dispersion (i-1) (containing 17.2 g of carbon black and 7.4 g of polymer p1-1), and Proxel LVS (Arch Chemicals Japan Co., Ltd. Product: antifungal agent, effective content 20%) 0.22 g, epoxy cross-linking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Co., Ltd., product name: Denacol EX321L, epoxy 1.3 g of equivalent weight 129) was added and 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 was 22% to obtain an aqueous dispersion (I-3) of black pigment-containing polymer particles A3. The average particle size of the aqueous 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 black pigment-containing polymer particles a1.
13.7 g of ion-exchanged water was added to 100 g of the obtained aqueous dispersion (i-1) (containing 17.2 g of carbon black and 7.4 g of polymer p1-1), and Proxel LVS (Arch Chemicals Japan Co., Ltd. 0.22 g of antifungal agent, active ingredient 20%) 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 was 22% to obtain an aqueous dispersion (I-C1) of black pigment-containing polymer particles AC1. The average particle size of the aqueous 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 raw material monomer (b). Into the reaction vessel, 5 parts of methyl ethyl ketone (MEK) and 10% of the mixed liquid of the raw material monomer (b) were put and mixed, and the nitrogen gas was sufficiently replaced.
On the other hand, in the dropping funnel, the remainder of the mixture 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'- 1.5 parts of azobis(4-cyanovaleric acid)) was added, and the temperature of the mixture in the reaction vessel was raised to 77°C while stirring under a nitrogen atmosphere. dripped. After completion of dropping, a solution of 0.5 parts of the polymerization initiator dissolved 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 weight average molecular weight, measured acid value, and calculated glass transition temperature of the obtained polymer P2-1.

Production Examples 2-2 to 2-10 and Comparative Production Examples 2-1 to 2-3
In Production Example 2-1, Polymers 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. A solution of C1-P2-C3 was obtained. Table 2 shows the weight average molecular weight and acid value of each polymer P2 obtained, and the calculated glass transition temperature.

<Preparation of aqueous dispersion (II) of polymer particles B>
Preparation Example 2-1
79.0 parts of ion-exchanged water and 5N sodium hydroxide aqueous solution (sodium hydroxide Solid content 16.9%, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd., for volumetric titration) 6.6 parts are added, and the equivalent amount of sodium hydroxide used is the number of moles of carboxy groups of polymer P2-1 of sodium hydroxide. Neutralization was carried out so that the molar ratio was 100 mol %. The resulting mixture was heated at 90° C. for 5 hours while stirring at 150 rpm to form an aqueous dispersion (II-1) of polymer particles B1 (cumulant average particle size 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 in the same manner as in Preparation Example 2-1 except that in Preparation Example 2-1, 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. Aqueous dispersions (II-2) to (II-13) of B2 to B13 and aqueous dispersions (II-C1) to (II-C4) of BC1 to BC4 (both of which had a solid concentration of 20%) were obtained.

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

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 are added and mixed, The raw material monomer mixture obtained 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 monomers. . A KPS aqueous solution obtained by dissolving 2.7 parts of potassium persulfate (KPS) in 165 parts of ion-exchanged water was put into a dropping funnel, and then the inside of the reaction vessel was replaced with nitrogen. Under a nitrogen atmosphere, the raw material monomer emulsion in the reaction vessel was kept at 70° C. while 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 performed at 70° C. for 1 hour.
Purification was performed using a dialysis membrane (manufactured by Spectrum 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 with an evaporator 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 2.8 parts of B3 and 11.4 parts of water), 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 part of a surfactant (trade name "Surfinol 440", manufactured by Evonik Industries) and 15.6 parts of ion-exchanged water are mixed, and the resulting mixture is passed through a 1.2 μm membrane filter (Sartorius). (trade name: Minisart) to obtain Ink 1.

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 were changed to those shown in Tables 4 and 5.

<Preparation of printed matter>
An inkjet printer (manufactured by Ricoh Co., Ltd., product name: IPSIO SG 2010L) is equipped with a rubber heater, filled with each water-based ink obtained in the printer, and heated to 60 ° C. Biaxially stretched polyethylene terephthalate film (Toray Industries, Inc. Product name: Lumirror T60, water absorption 2.3 g/m ² ) (hereinafter also referred to as “PET”), biaxially stretched anti-fogging polypropylene film (manufactured by Futamura Chemical Co., Ltd., product type: AF-662, anti-fogging 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”) ), and the resulting printed matter was dried on a hot plate heated to 60° C. for 6 minutes to obtain a printed matter. The printed matter obtained was evaluated by the method described later.

<Evaluation>
(Storage stability)
Each water-based ink was stored in an environment of 60° C. for 28 days, and the rate of change in cumulant average particle size and the rate of change in viscosity of each water-based ink before and after storage were evaluated according to the following evaluation criteria. The smaller the absolute values of the rate of change in average particle size and the rate of change in viscosity, the better the storage stability. The results are shown in Tables 4 and 5.
[Change rate of cumulant average particle size]
For each aqueous 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 rate of change in the average particle size [= (the cumulant average particle size after storage diameter)/(average cumulant particle size before storage)×100] was calculated.
[Ink viscosity change rate]
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 rate of change in viscosity [= (ink viscosity after storage) / (before storage ink viscosity)×100] was calculated.
〔Evaluation criteria〕
A: The rate of change in average particle size is within ±5% and the rate of change in viscosity is within ±5%.
B: Of the rate of change in average particle size and viscosity, the larger rate of change is more than ±5% and within ±10%.
C: Of the rate of change in average particle size and viscosity, the larger rate of change is more than ±10% and within ±15%.
D: Of the rate of change of average particle size and viscosity, the larger rate of change is more than ±15% and within ±20%.
E: The rate of change in average particle size is more than ±20%, or the rate of change in viscosity is more than ±20%.

(Redispersibility)
10 μL of each water-based ink was dropped onto a slide glass using a micropipette and allowed to stand in an environment of 60° C. and 40% RH for 24 hours to evaporate and dry the water-based ink.
Next, 200 μL of a redispersibility evaluation vehicle was dropped onto the solid matter remaining on the slide glass, and after 5 minutes, the redispersibility of the solid matter was visually observed and evaluated according to the following evaluation criteria. When the solids are redispersed, the less the solids remain, the better the redispersibility. The results are shown in Tables 4 and 5.
The vehicle for redispersibility evaluation was prepared by adding 28% propylene glycol (PG), 4% diethylene glycol monobutyl ether (BDG), and ion-exchanged water, weighing so that the total amount was 100%, and using a magnetic stirrer. Prepared by stirring and mixing well.
〔Evaluation criteria〕
A: Solids were uniformly redispersed and no residue was found.
B: Solid matter was re-dispersed, but there was a residue.
C: Solids were not redispersed.

(Fixability)
Evaluation was performed by a test method according to JIS K6854-3. A double-sided tape (manufactured by Nichiban Co., Ltd., trade name "Nicetak (registered trademark)", adhesive strength: 04) is attached to the printed surface of the PET, OPP and PVC printed matter, and a test piece with a width of 15 mm and a length of 20 mm is attached. cut to fit. Using a tensile tester "RTC-1150A" (manufactured by Orientec Co., Ltd.), both the print medium part at the tip of the test piece and the double-sided tape part are sandwiched between the arms, and a T-shaped tension is applied at a speed of 300 mm / min. did the test. The load was measured every 20 μm in length, and the value obtained by averaging the load values from 25 mm to 125 mm was taken as the value of tensile strength, which was evaluated according to the following evaluation criteria. The higher the tensile strength value, the better the fixability. The results are shown in Tables 4 and 5.
〔Evaluation criteria〕
A: The value of tensile strength was 2.0N 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.

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

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

Claims (6)

A water-based ink containing pigment-containing water-insoluble polymer particles A, pigment-free water-insoluble polymer particles B, and water,
The polymer particles A are crosslinked 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), a structural unit derived from an aliphatic (meth)acrylate (b-2), and an aromatic group. and a structural unit derived from the monomer (b-3) ,
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 content of the structural unit derived from the (meth)acrylic acid (b-1) is 5% by mass or more and 20% by mass or less,
The content of structural units derived from the aromatic group-containing monomer (b-3) is 20% by mass or more and 60% by mass or less,
The mass ratio of the structural unit derived from the (meth) acrylic acid (b-1) and the structural unit derived from the aliphatic (meth) acrylate (b-2) [(meth) acrylic acid (b-1) / aliphatic (meth)acrylate (b-2)] is 0.2 or more and 2 or less,
The polymer P2 has a glass transition temperature of −30° C. or more and 40° C. or less,
A water-based ink in which the polymer particles B have a cumulant average particle size of 5 nm or more and 30 nm or less. 2. The water-based ink according to claim 1, wherein the content of the structural unit derived from the aliphatic (meth)acrylate (b-2) in the polymer P2 is 20 % by mass or more and 75 % by mass or less. 3. The water-based ink according to claim 1, wherein the polymer P2 has an acid value of 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 any one of claims 1 to 3, wherein the content of the polymer particles B is 0.3% by mass or more and 7% by mass or less. 5. The polymer according to any one of claims 1 to 4 , wherein 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, wherein the water-based ink according to any one of claims 1 to 5 is used for printing on a low water-absorbing printing medium.