JP7370176B2 - Water-based pigment dispersion - Google Patents

Description

The present invention relates to an aqueous pigment dispersion and a method for producing the aqueous pigment dispersion.

In the field of commercial and industrial printing, such as label printing used for product packaging printing and advertising, we use PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), PP (polypropylene), NY (nylon), etc. Conventionally, printing has been performed on resin print media using solvent-based inks, UV-curable inks, or the like. On the other hand, water-based inks that use pigments as colorants have become mainstream from the viewpoints of reducing environmental impact, saving energy, and safety, as well as improving the weather resistance and water resistance of printed matter.

For example, Patent Document 1 discloses an aqueous pigment dispersion composition for inkjet recording consisting of a pigment, a water-soluble resin, a water-soluble organic solvent, and water for the purpose of providing an aqueous pigment dispersion composition for inkjet recording having scratch resistance and the like. A dispersion composition, wherein the water-soluble resin is composed of a first resin and a second resin, and the first resin and the second resin each independently contain an acrylic resin, a styrene/acrylic resin, or a styrene/malein resin. An aqueous pigment dispersion composition for inkjet, etc., which is made of at least one selected from the resin group consisting of acid-based resins and urethane-based resins, is disclosed.
Patent Document 2 discloses that polymer particles containing a colorant are coated with a crosslinking agent for the purpose of providing an aqueous dispersion for inkjet recording with excellent dispersibility and an aqueous ink for inkjet recording that has excellent fixability to recording paper. An aqueous dispersion of crosslinked polymer particles formed by crosslinking, wherein the polymer constituting the colorant-containing polymer particles is represented by a constitutional unit derived from the salt-forming group-containing monomer (a) and a specific formula. The monomer (b) contains a structural unit derived from polypropylene glycol mono(meth)acrylate (b) and a structural unit derived from one or more nonionic monomers (c) selected from monomers represented by a specific formula. Disclosed is an aqueous dispersion for inkjet recording containing a polymer having a difference in solubility parameters of (c) within a specific range, and an aqueous ink for inkjet recording containing the aqueous dispersion.
Patent Document 3 discloses water-insoluble crosslinked polymer particles containing a colorant, and core-shell polymer particles or crosslinked polymer particles containing a colorant, for the purpose of providing an aqueous inkjet recording ink with excellent print density, an aqueous dispersion used in the ink, etc. An aqueous dispersion for inkjet recording containing polymer particles and an aqueous ink for inkjet recording containing the aqueous dispersion are disclosed.

Japanese Patent Application Publication No. 2011-144271 Japanese Patent Application Publication No. 2012-1675 Japanese Patent Application Publication No. 2008-63500

However, resin print media are non-water-absorbing and the water-based ink does not penetrate into the print medium, so the pigment particles contained in the water-based ink remain on the surface of the print medium. Therefore, adhesion to resin print media and scratch resistance are insufficient, and improvements in these are required. In addition, a method of adding a polymer emulsion as a fixing agent to ink is known as a method of improving adhesion and scratch resistance, but when a water-based ink with a high content of polymer emulsion is used for non-water-absorbing printing media, It was found that the dispersion stability of the pigment decreased, and the storage stability and print density of the ink tended to decrease.
In the technique of Patent Document 1, the two different resins used in the aqueous pigment dispersion composition are both water-soluble resins, so the storage stability is insufficient and the print density is low. The technique disclosed in Patent Document 2 does not have sufficient scratch resistance against non-water-absorbing printing media. In the technology of Patent Document 3, since the inkjet recording water dispersion contains water-insoluble crosslinked polymer particles containing a colorant and core-shell polymer particles or crosslinked polymer particles, the storage stability is insufficient and the print density is low. . In this way, it satisfies all of the recently increasing demands for improved storage stability of water-based pigment dispersions and inks, improved adhesion and scratch resistance of printed matter when printed on non-water-absorbing printing media, and high print density. This has not yet been achieved.
The present invention provides a water-based pigment dispersion that has excellent storage stability and can be used in water-based inks to obtain printed matter that has excellent adhesion and scratch resistance to non-water-absorbing printing media and has high print density; An object of the present invention is to provide a method for producing the aqueous pigment dispersion.

When a polymer emulsion is blended into a water-based ink, it is possible to strengthen the adhesive force between pigment particles or between pigment particles and a printing medium, and it is possible to improve adhesion and scratch resistance. On the other hand, storage stability decreases, and after the ink droplets come into contact with the print medium, phase separation occurs between the pigment dispersant and the emulsion polymer, causing local aggregation of pigment particles. , the smoothness of the coating film surface decreases, causing a decrease in print density.
Therefore, the present inventors have discovered that it is possible to maintain excellent storage stability, while at the same time preventing the pigment particles from locally agglomerating in an environment where the ink vehicle dries on the surface of the printing medium, such as during printing. Aiming to obtain performance that can maintain strong adhesion between particles or between pigment particles and printing media, we have developed a new resin that contains two types of (meth)acrylic resins that have acid groups and different glass transition temperatures. It has been found that the above problems can be solved by dispersing pigments with a polymer dispersant made by crosslinking seed resin with a crosslinking agent via acid groups.

That is, the present invention provides the following [1] to [3].
[1] An aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant,
The polymer dispersant contains (meth)acrylic resin A and (meth)acrylic resin B having acid groups,
The glass transition temperature of the (meth)acrylic resin A is 80°C or more and 140°C or less,
The glass transition temperature of the (meth)acrylic resin B is -50°C or more and 40°C or less,
An aqueous pigment dispersion in which at least the (meth)acrylic resin A and the (meth)acrylic resin B are crosslinked with a crosslinking agent C via their respective acid groups.
[2] A method for producing an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant,
The polymer dispersant contains (meth)acrylic resin A and (meth)acrylic resin B having acid groups,
The glass transition temperature of the (meth)acrylic resin A is 80°C or more and 140°C or less,
The glass transition temperature of the (meth)acrylic resin B is -50°C or more and 40°C or less,
A method for producing an aqueous pigment dispersion, comprising a step of crosslinking the (meth)acrylic resin A and the (meth)acrylic resin B with a crosslinking agent C via their respective acid groups.
[3] A water-based ink containing the water-based pigment dispersion described in [1] above.

According to the present invention, an aqueous pigment dispersion is excellent in storage stability, and when used in an aqueous ink, it is possible to obtain printed matter having excellent adhesion and scratch resistance to non-water-absorbing printing media and high print density. An object of the present invention is to provide a method for producing the aqueous pigment dispersion.

[Aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant, and the polymer dispersant includes (meth)acrylic resin A having an acid group and (meth)acrylic resin A and (meth)acrylic resin A having an acid group. Contains acrylic resin B, the (meth)acrylic resin A has a glass transition temperature of 80°C or more and 140°C or less, and the (meth)acrylic resin B has a glass transition temperature of -50°C or more and 40°C or less. At least the (meth)acrylic resin A and the (meth)acrylic resin B are crosslinked with a crosslinking agent C via their respective acid groups.
Note that the term "aqueous medium" refers to a medium in which water accounts for the largest proportion of the pigment-dispersing medium.
The aqueous pigment dispersion of the present invention has excellent storage stability, and when used in a water-based ink, it is possible to obtain printed matter that has excellent adhesion and scratch resistance to non-water-absorbing printing media and has high print density. It can be suitably used as an aqueous pigment dispersion for flexographic printing ink, gravure printing ink, or inkjet ink, and is particularly preferably used as an aqueous pigment dispersion for inkjet ink.

The aqueous pigment dispersion of the present invention has excellent storage stability, and when used in a water-based ink, it can improve both adhesion to non-water-absorbing printing media, scratch resistance, and print density. Although the reason is not certain, it is thought to be as follows.
In the aqueous pigment dispersion of the present invention, it is presumed that the pigment is dispersed in an aqueous medium with the polymer dispersant adsorbed or immobilized on the surface of the pigment. The polymer dispersant contains (meth)acrylic resin A having a high glass transition temperature and (meth)acrylic resin B having a low glass transition temperature. (Meth)acrylic resin A and (meth)acrylic resin B, which have similar polymer structures, exist on the pigment surface in a compatible, rather than exclusive, state, so that there is a difference between resin A and resin B. It is thought that they are cross-linked by a cross-linking agent via their respective acid groups and are in an integrated state. As a result, it is thought that the polymer dispersant is strongly adsorbed or immobilized on the pigment surface, stably dispersing the pigment, and improving storage stability. Furthermore, the effect of improving adhesion to non-water-absorbing printing media by (meth)acrylic resin B with a low glass transition temperature is complementary to the effect of improving scratch resistance with (meth)acrylic resin A having a high glass transition temperature. It is also assumed that phase separation of the resin is unlikely to occur during coating film formation and drying of the ink vehicle, resulting in a coating film with a smooth surface and improved print density.

<Pigment>
The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. Further, if necessary, extender pigments can be used in combination with these pigments.
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 preferred for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
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, and isoindo 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 above pigments can be used alone or in combination of two or more.

<Polymer dispersant>
The polymer dispersants used in the present invention are (meth)acrylic resin A with a high glass transition temperature (hereinafter also referred to as "high Tg resin A") and (meth)acrylic resin B (hereinafter referred to as "high Tg resin A") with a low glass transition temperature. (also referred to as "low Tg resin B").
The presence of the polymer dispersant in the aqueous pigment dispersion is as follows: the polymer dispersant is adsorbed to the pigment, the pigment is encapsulated (capsule) in which the polymer dispersant contains the pigment, and the polymer dispersant is present in the pigment. There is a form in which it is not adsorbed. From the viewpoint of dispersion stability of the pigment, in the present invention, a form in which the pigment is contained in a polymer dispersant, that is, a form of polymer particles containing the pigment is preferable, and a state in which the pigment is contained in a polymer dispersant is more preferable. preferable.

The glass transition temperature of the high Tg resin A is 80°C or higher, preferably 85°C or higher, more preferably 90°C or higher, and The temperature is preferably 95°C or higher, and from the viewpoint of adhesion, the temperature is 140°C or lower, preferably 130°C or lower, more preferably 120°C or lower, even more preferably 110°C or lower.
The glass transition temperature of the low Tg resin B is -50°C or higher, preferably -40°C or higher, more preferably -30°C or higher, from the viewpoint of storage stability of the aqueous pigment dispersion, adhesion, and print density. , more preferably -20°C or higher, even more preferably -10°C or higher, and 40°C or lower, preferably 30°C or lower, more preferably 20°C or lower, even more preferably 10°C or lower.
The glass transition temperature can be measured by the measuring method described in Examples. The glass transition temperature is calculated from the mass fraction of each monomer component in high Tg resin A or low Tg resin B and the glass transition temperature of a homopolymer of each monomer component based on the Fox formula. You can ask for it.

The difference between the glass transition temperature of high Tg resin A and the glass transition temperature of low Tg resin B is preferably 40°C or more from the viewpoint of storage stability of the aqueous pigment dispersion, adhesion, scratch resistance, and print density. , more preferably 60°C or higher, even more preferably 80°C or higher, and preferably 190°C or lower, more preferably 170°C or lower, even more preferably 150°C or lower, even more preferably 130°C or lower, even more preferably is below 110°C.

The mass ratio [A/(A+B)] of the content of high Tg resin A to the total content of high Tg resin A and low Tg resin B in the aqueous pigment dispersion determines the storage stability of the aqueous pigment dispersion, and From the viewpoint of adhesion, scratch resistance and print density, it is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, even more preferably 0.4 or more, and is 0.9 or less, more preferably 0.8 or less, still more preferably 0.7 or less, even more preferably 0.6 or less.

The mass ratio [A/pigment] of the high Tg resin A to the pigment content in the aqueous pigment dispersion is preferably 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000. It is 1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and preferably 0.9 or less, more preferably 0.7 or less, and still more preferably 0.5 or less.

The mass ratio of the content of low Tg resin B to the content of pigment in the aqueous pigment dispersion [B/pigment] is preferably set from the viewpoint of storage stability, adhesion, and print density of the aqueous pigment dispersion. It is 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and preferably 0.7 or less, more preferably 0.6 or less, and still more preferably 0.5 or less.

The high Tg resin A and the low Tg resin B each have an acid group from the viewpoint of storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and print density. It is preferable that some of the acid groups of each of the high Tg resin A and the low Tg resin B are neutralized with a neutralizing agent described below. It is thought that the charge repulsion force developed after neutralization increases, suppressing aggregation of pigment particles in the aqueous pigment dispersion, suppressing thickening, and improving storage stability.
Examples of the acid group include groups that become acidic by dissociating and releasing hydrogen ions, such as a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), and a phosphoric acid group (-OPO ₃ M ₂ ). , or their dissociated ionic forms (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M), and the like. In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Among these, a carboxy group (-COOM) is preferred from the viewpoint of storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and print density.

The acid value of the high Tg resin A is preferably 50 mgKOH/g or more, more preferably 100 mgKOH/g or more, still more preferably 150 mgKOH/g or more, and even more preferably from the viewpoint of storage stability and print density of the aqueous pigment dispersion. is 200 mgKOH/g or more, and preferably 300 mgKOH/g or less, more preferably 280 mgKOH/g or less, even more preferably 260 mgKOH/g, and even more preferably 250 mgKOH/g.
The acid value of the low Tg resin B is preferably 50 mgKOH/g or more, more preferably 70 mgKOH/g or more, still more preferably 90 mgKOH/g or more, and even more preferably from the viewpoint of storage stability and print density of the aqueous pigment dispersion. is 100 mgKOH/g or more, and preferably 260 mgKOH/g or less, more preferably 230 mgKOH/g or less, even more preferably 200 mgKOH/g or less, even more preferably 160 mgKOH/g or less, even more preferably 140 mgKOH/g or less. It is.
When the acid value is in the above range, the amount of acid groups and their neutralized acid groups is sufficient, and the dispersion stability of the pigment is ensured. It is also preferable from the viewpoint of the balance between the affinity between the polymer dispersant and the aqueous medium and the interaction between the polymer dispersant and the pigment.
The acid value can be calculated from the mass ratio of the constituent monomers. It can also be determined by a method in which high Tg resin A or low Tg resin B is dissolved or swollen in a suitable organic solvent (for example, methyl ethyl ketone) and then titrated.

From the viewpoints of storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and print density, the polymer dispersant is designed to allow at least high Tg resin A and low Tg resin B to form crosslinking agent C through their respective acid groups. It has a cross-linked structure.

[Crosslinking agent C]
In the present invention, from the viewpoint of storage stability, adhesion, scratch resistance, and print density of the aqueous pigment dispersion, at least high Tg resin A and low Tg resin B are crosslinked with crosslinking agent C via their respective acid groups. has been done.
From the viewpoint of efficiently reacting the acid groups of high Tg resin A and the acid groups of low Tg resin B in a medium mainly composed of water, the water solubility (mass ratio) of crosslinking agent C is as follows: Preferably it is 50% or less, more preferably 40% or less, still more preferably 35% or less. Here, the water solubility % (mass ratio) refers to the dissolution rate (%) when 10 parts by mass of the crosslinking agent C is dissolved in 90 parts by mass of water at room temperature of 25°C.

The crosslinking agent C is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having a glycidyl ether group, and even more preferably a polyhydric alcohol having a hydrocarbon group having 3 or more and 8 or less carbon atoms. It is a glycidyl ether compound.
The molecular weight of the crosslinking agent C is preferably 120 or more, more preferably 150 or more, even more preferably 200 or more, and preferably 2,000 or less, from the viewpoint of reaction ease and storage stability of the aqueous pigment dispersion. , more preferably 1,500 or less, still more preferably 1,000 or less.
The epoxy equivalent of the crosslinking agent C is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, still more preferably 150 or less.
The number of epoxy groups in crosslinking agent C is 2 or more per molecule, preferably 6 or less per molecule, from the viewpoint of efficiently reacting with acid groups and improving the storage stability of the aqueous pigment dispersion. From the viewpoint of availability, it is more preferably 4 or less.

Specific examples of crosslinking agent C include diethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether (water solubility 31%), glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether (water solubility 27%), Sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether (water solubility 0%), resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, hydrogenated bisphenol A Examples include polyglycidyl ethers such as type diglycidyl ether. Among these, one or more selected from diethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, and cyclohexanedimethanol diglycidyl ether are preferred, and trimethylolpropane polyglycidyl ether is more preferred. preferable.

The degree of crosslinking [[number of molar equivalents of crosslinkable functional groups of crosslinking agent C]/[number of molar equivalents of average acid groups of high Tg resin A and low Tg resin B]] is a measure of the storage stability of the aqueous pigment dispersion; In addition, from the viewpoint of adhesion, scratch resistance, and print density, it is preferably 0.20 or more, more preferably 0.25 or more, even more preferably 0.30 or more, even more preferably 0.35 or more, and Preferably it is 0.70 or less, more preferably 0.65 or less, still more preferably 0.60 or less, even more preferably 0.55 or less, still more preferably 0.50 or less.
The degree of crosslinking in the present invention is the degree of crosslinking calculated from the equivalent weight of acid groups calculated from the average acid values of high Tg resin A and low Tg resin B and the equivalent weight of crosslinkable functional groups of crosslinking agent C. The average acid value of high Tg resin A and low Tg resin B is a weighted average value weighted by the content (mass %) of each (meth)acrylic resin in the aqueous pigment dispersion.

The crosslinked structure of the polymer dispersant preferably has three or more branched structures represented by the following formula (1).

(In formula (1), X represents a group represented by the following formula (2) or (3), and A represents a group represented by X or an ethyl group.)

(In formula (2), P represents the molecular chain of high Tg resin A or the molecular chain of low Tg resin B, and * represents the bonding site with the quaternary carbon atom in formula (1).)

(In formula (3), P and * are the same as above.)

In the present invention, at least the high Tg resin A chain and the low Tg resin B chain are crosslinked via the crosslinking agent C, but the high Tg resin A chains are also crosslinked, and the low Tg resin B chains are also crosslinked. It may be crosslinked via Agent C.

[(meth)acrylic resin A and (meth)acrylic resin (B)]
High Tg resin A and low Tg resin B are based on structural units derived from carboxyl group-containing monomers and hydrophobic monomers, respectively, from the viewpoint of storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and print density. Preferably, it contains a structural unit, and may further contain a structural unit derived from at least one monomer selected from macromonomers and nonionic monomers.

(carboxy group-containing monomer)
Carboxy group-containing monomers are monomers for high Tg resin A and low Tg resin B from the viewpoint of improving the dispersion stability of the pigment, the storage stability of the aqueous pigment dispersion, and the adhesion, scratch resistance, and printing density. Preferably, it is used as a component. As the carboxy group-containing monomer, a carboxylic acid monomer is used.
Examples of the carboxylic acid monomer include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid, etc., but (meth)acrylic acid is preferable. .
In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

(hydrophobic monomer)
The hydrophobic monomer improves the adsorption of the polymer dispersant to the pigment, improving the dispersion stability of the pigment, the storage stability of the aqueous pigment dispersion, and the adhesion, scratch resistance, and printing density. , is preferably used as a monomer component of high Tg resin A and low Tg resin B.
As used herein, "hydrophobic" means that when a monomer is dissolved in 100 g of ion-exchanged water at 25° C. to saturation, the amount of the monomer dissolved is less than 10 g. The amount of the hydrophobic monomer dissolved is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of adsorption of the polymer dispersant to the pigment.
The hydrophobic monomer is preferably at least one selected from aromatic group-containing monomers and (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols.
In this specification, "(meth)acrylate" is at least one selected from acrylate and methacrylate.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 or more and 22 or less carbon atoms, which may have a substituent containing a hetero atom, such as a styrene monomer, an aromatic group-containing (meth) Acrylates are more preferred. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
As the styrene monomer, styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene are preferred, and styrene and α-methylstyrene are more preferred.
As the aromatic group-containing (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. are preferable, and benzyl (meth)acrylate is more preferable.
As the hydrophobic monomer, two or more of the above monomers may be used, or a styrene monomer and an aromatic group-containing (meth)acrylate may be used in combination.

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, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, (meth)acrylates having branched alkyl groups such as isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; alicyclic alkyls such as cyclohexyl (meth)acrylate Examples include (meth)acrylates having groups. Among these, those having an alkyl group having 1 or more and 10 or less carbon atoms are more preferable, and those having an alkyl group having 1 or more and 8 or less carbon atoms are even more preferable.

(macromonomer)
The macromonomer is a compound with a number average molecular weight of 500 or more and 100,000 or less and has a polymerizable functional group at one end, and is a monomer component of high Tg resin A and low Tg resin B from the viewpoint of improving the dispersion stability of the pigment. It can be used as The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. Note that the number average molecular weight is measured by gel permeation chromatography using chloroform containing 1 mmol/L of dodecyldimethylamine as a solvent and using polystyrene as a standard substance.
As the macromonomer, from the viewpoint of pigment dispersion stability, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferred, and aromatic group-containing monomer-based macromonomers are more preferred.
Aromatic group-containing monomers The aromatic group-containing monomers constituting the macromonomer include the aromatic group-containing monomers described above for hydrophobic monomers, with styrene and benzyl (meth)acrylate being preferred, and styrene being more preferred. .
Specific examples of commercially available styrenic macromonomers include AS-6(S), AN-6(S), and HS-6(S) (trade name of Toagosei Co., Ltd.).
Examples of silicone macromonomers include organopolysiloxanes having a polymerizable functional group at one end.

(Nonionic monomer)
The nonionic monomer can be used as a monomer component of the high Tg resin A and the low Tg resin B from the viewpoint of pigment dispersion stability.
Nonionic monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polypropylene glycol (n = 2 to 30, n is the average added mole of oxypropylene groups) The following n indicates the average number of added moles of the oxyalkylene group.) (meth)acrylate, polyethylene glycol (n = 2 to 30) Polyalkylene glycol (meth)acrylate such as (meth)acrylate; methoxy Alkoxypolyalkylene glycol (meth)acrylate such as polyethylene glycol (n = 1 to 30) (meth)acrylate; phenoxy (ethylene glycol/propylene glycol copolymerization) (n = 1 to 30, among which ethylene glycol: n = 1 -29) (meth)acrylate, etc. Among these, polypropylene glycol (n=2-30) (meth)acrylate, phenoxy (ethylene glycol/propylene glycol copolymer) (meth)acrylate are preferred, and polypropylene glycol (n=2-30) (meth)acrylate is preferred. More preferred.
Specific examples of commercially available nonionic monomers include NK Ester M-20G, 40G, 90G, and 230G from Shin-Nakamura Chemical Co., Ltd., and Blenmar PE-90 and 200 from NOF Corporation. , 350 etc., PME-100, 200, 400 etc., PP-500, 800, 1000 etc., AP-150, 400, 550 etc., 50PEP-300, 50POEP-800B, 43PAPE-600B etc. can be mentioned.

As described above, the high Tg resin A and the low Tg resin B each preferably contain a structural unit derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, an aromatic group-containing monomer, and an aliphatic group-containing monomer. A vinyl polymer containing a structural unit derived from one or more hydrophobic monomers selected from (meth)acrylates having a hydrocarbon group derived from alcohol, and further derived from at least one monomer selected from macromonomers and nonionic monomers. It may also be a vinyl polymer containing the following structural units.
High Tg resin A is preferably a vinyl polymer containing structural units derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, and structural units derived from aromatic group-containing monomers.
From the viewpoint of adjusting the glass transition temperature, the low Tg resin B preferably contains structural units derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, and structural units derived from aromatic group-containing monomers. It is a vinyl polymer containing a (meth)acrylate-derived structural unit having a hydrocarbon group derived from an aliphatic alcohol.

(Content of each monomer in raw material monomer or content of each structural unit in high Tg resin A and low Tg resin B)
During the production of high Tg resin A, the content of each monomer in the raw material monomer (content as unneutralized amount; the same applies hereinafter) or the content of the constituent units derived from each monomer in high Tg resin A is the content of the pigment. From the viewpoint of improving dispersion stability, the following is true.
The content of the carboxy group-containing monomer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less. , more preferably 40% by mass or less.
The content of the hydrophobic monomer is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, More preferably, it is 80% by mass or less.

The content of each monomer in the raw material monomer or the content of the constituent units derived from each monomer in low Tg resin B during the production of low Tg resin B is as follows from the viewpoint of improving the dispersion stability of the pigment. be.
The content of the carboxy group-containing monomer is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less. , more preferably 20% by mass or less.
The content of the hydrophobic monomer is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and preferably 95% by mass or less, more preferably 93% by mass or less, More preferably, it is 90% by mass or less.
When using an aromatic group-containing monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol as a hydrophobic monomer, the aromatic group-containing monomer and a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol are used. From the viewpoint of adjusting the glass transition temperature, the mass ratio of the content of the aromatic group-containing monomer to the total content is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. , and is preferably 0.7 or less, more preferably 0.6 or less, even more preferably 0.5 or less.

The high Tg resin A and the low Tg resin B are produced by copolymerizing the raw material monomers using a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, solution polymerization is preferred.
The weight average molecular weights of high Tg resin A and low Tg resin B are each preferably 3,000 or more, more preferably 5,000 or more, even more preferably 7,000 or more, and preferably 100,000 or less. , more preferably 80,000 or less, still more preferably 60,000 or less. When the weight average molecular weight of the high Tg resin A or the low Tg resin B is within the above range, the adsorption power to the pigment is sufficient and dispersion stability can be exhibited.
The weight average molecular weight can be measured by the method described in Examples.

The mass ratio of the pigment in the total solid content of the aqueous pigment dispersion [pigment/(total solid content of the aqueous pigment dispersion)] determines the storage stability, adhesion, scratch resistance, and printing density of the aqueous pigment dispersion. From this point of view, it is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and preferably 0.8 or less, more preferably 0.7 or less, still more preferably 0. 6 or less.

[Method for producing aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention crosslinks (meth)acrylic resin A (high Tg resin A) and (meth)acrylic resin B (low Tg resin B) with crosslinking agent C via their respective acid groups. It is obtained by a manufacturing method including a step of.
Examples of methods for dispersing the pigment in an aqueous medium include a method of dispersing a pigment mixture containing the pigment, high Tg resin A, and low Tg resin B; It can be produced by a method of dispersing one of the two and then adding the other.
The high Tg resin A and the low Tg resin B may each be used as a dispersion in which resin particles are dispersed in an aqueous medium, and may contain a dispersant such as a surfactant as necessary. The dispersion may be appropriately synthesized or a commercially available product.

The aqueous pigment dispersion of the present invention is preferably produced efficiently by a method having the following steps 1 and 2 from the viewpoint of storage stability, adhesion, scratch resistance, and print density of the aqueous pigment dispersion. .
Step 1: A step of dispersing a pigment mixture containing a pigment, (meth)acrylic resin A, and (meth)acrylic resin B to obtain a dispersion.Step 2: The dispersion obtained in step 1, Crosslinking step using crosslinking agent C

In step 1, (meth)acrylic resin A and (meth)acrylic resin B, which have different glass transition temperatures but similar polymer structures, are adsorbed together on the pigment in a compatible state, and each (meth)acrylic resin It is presumed that the resin is bound by the pigment. Then, in step 2, the acid groups of the two types of (meth)acrylic resin A and (meth)acrylic resin B that exist in such an adsorbed state are crosslinked by crosslinking agent C, thereby making the pigment surface more solid. considered to be bound by.

(Step 1)
In step 1, first, high Tg resin A and low Tg resin B are dissolved in an organic solvent, and then pigment, water, and if necessary, a neutralizing agent, a surfactant, etc. are added to the obtained organic solvent solution. A method of adding and mixing to obtain an oil-in-water dispersion is preferred. Although there is no restriction on the order in which the high Tg resin A and the low Tg resin B are added to the organic solvent solution, it is preferable to add water, the neutralizing agent, and the pigment in this order.
There is no restriction on the organic solvent in which the high Tg resin A and the low Tg resin B are dissolved, but aliphatic alcohols having 1 or more and 3 or less carbon atoms, ketones, ethers, esters, etc. are preferable. From the viewpoint of improving the solubility of the meth)acrylic resin and the adsorption of the (meth)acrylic resin to the pigment, a ketone having 4 or more and 8 or less carbon atoms, such as methyl ethyl ketone, is more preferable. When high Tg resin A and low Tg resin B are synthesized by a solution polymerization method, the solvent used in the polymerization may be used as is.

Some of the acid groups in each of the high Tg resin A and low Tg resin B are treated with a neutralizing agent from the viewpoint of storage stability, adhesion, scratch resistance, print density and productivity of the aqueous pigment dispersion. It is preferable to neutralize it by When neutralizing, it is preferable to neutralize so that the pH becomes 7 or more and 11 or less.
Examples of neutralizing agents include alkali metal hydroxides and ammonia. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, with sodium hydroxide and potassium hydroxide being preferred. The neutralizing agent is preferably an alkali metal hydroxide from the viewpoints of storage stability of the aqueous pigment dispersion, as well as adhesion and print density. Further, the high Tg resin A and the low Tg resin B may be neutralized in advance.
The neutralizing agent is preferably used as a neutralizing agent aqueous solution from the viewpoint of promoting neutralization sufficiently and uniformly.
The equivalent amount of the neutralizing agent used is preferably 10 mol% or more, more preferably 30 mol% or more, from the viewpoint of storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and print density. Preferably it is 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less.
Here, the equivalent amount of the neutralizing agent used can be determined by the following formula. When the equivalent amount of the neutralizing agent used is 100 mol% or less, it has the same meaning as the degree of neutralization, and when the equivalent amount of the neutralizing agent used exceeds 100 mol% in the following formula, the neutralizing agent is high Tg resin A and This means that it is in excess of the acid groups of low Tg resin B, and the degree of neutralization of high Tg resin A and low Tg resin B at this time is considered to be 100 mol%.
Equivalent amount of neutralizing agent used (mol%) = [{Added mass of neutralizing agent (g)/Equivalent weight of neutralizing agent}/[{Average acid value of high Tg resin A and low Tg resin B (mgKOH/g )×Mass (g) of high Tg resin A and low Tg resin B}/(56×1,000)]×100

The dispersion treatment of the pigment mixture is preferably carried out by applying shear stress and controlling the average particle size of the pigment particles to a desired particle size.
Examples of means for applying shear stress include kneading machines such as roll mills and kneaders; high-pressure homogenizers such as microfluidizers; media-type dispersing machines such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When performing dispersion treatment using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the treatment pressure and the number of passes.
From the viewpoint of productivity and economy, the processing pressure is preferably 60 MPa or more and 300 MPa or less. Further, the number of passes is preferably 3 or more and 20 or less.
In step 1, it is preferable to obtain an aqueous dispersion by further removing the organic solvent from the dispersion by a known method. Although it is preferable that the organic solvent in the obtained aqueous dispersion is substantially removed, it may remain as long as the object of the present invention is not impaired. The amount of residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
Furthermore, if necessary, the dispersion can be heated and stirred before distilling off the organic solvent.

(Step 2)
Step 2 is a step of crosslinking the dispersion obtained in Step 1 using crosslinking agent C.
Step 2 provides an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant having a crosslinked structure.
In the present invention, in Step 1, a part of the acid groups possessed by the high Tg resin A and the low Tg resin B are neutralized to disperse the pigment to obtain a dispersion, and then in Step 2, the high Tg resin A water-based pigment dispersion in which a part of each acid group of resin A and low Tg resin B is reacted with cross-linking agent C to form a cross-linked structure, and the pigment is dispersed in an aqueous medium using a polymer dispersant having a cross-linked structure. It is preferable to do so.
A part of the acid groups of each of high Tg resin A and low Tg resin B constituting the polymer dispersant are crosslinked with crosslinking agent C, and between the high Tg resin A chain and the low Tg resin B chain, high Tg resin A It is thought that a crosslinked structure is formed between the chains and between the B chains of the low Tg resin.

In step 2, it is preferable that the dispersion obtained in step 1 and crosslinking agent C are mixed and crosslinked.
The temperature of the crosslinking treatment is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and preferably 90°C or lower, more preferably from the viewpoint of completion of the crosslinking reaction and economical efficiency. is below 80°C.
The crosslinking treatment time is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 3 hours or more, and preferably 12 hours or less, from the viewpoint of completion of the crosslinking reaction and economical efficiency. Preferably it is 10 hours or less, more preferably 7 hours or less.

The aqueous pigment dispersion of the present invention may contain 1% by mass or more and 10% by mass or less of glycerin, triethylene glycol, etc. as a humectant to prevent drying, or may contain additives such as antifungal agents. It's okay. The additive may be blended when dispersing the pigment, or may be blended after the pigment is dispersed or after the crosslinking reaction.

The aqueous pigment dispersion of the present invention is preferably one in which pigment-containing polymer particles are dispersed in an aqueous medium containing water as the main medium. Here, the form of the polymer particles containing the pigment may be such that the particles are formed of at least the pigment and the polymer. That is, it is sufficient that particles are formed of at least a pigment, high Tg resin A, and low Tg resin B. For example, it includes a particle form in which a pigment is encapsulated in a polymer, a particle form in which a pigment is uniformly dispersed in a polymer, a particle form in which a pigment is exposed on the surface of a polymer particle, and mixtures thereof are also included.

The nonvolatile component concentration (solid content concentration) of the aqueous pigment dispersion of the present invention is preferably 10% by mass or more, more preferably is 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.
The solid content concentration of the aqueous pigment dispersion is measured by the method described in Examples.
The average particle size of the aqueous pigment dispersion is determined in order to reduce coarse particles, improve the storage stability of the aqueous pigment dispersion, as well as adhesion, scratch resistance, and printing density, and also when used as an aqueous pigment dispersion for inkjet inks. is preferably 50 nm or more, more preferably 60 nm or more, even more preferably 70 nm or more, and preferably 200 nm or less, more preferably 160 nm or less, still more preferably 150 nm or less, from the viewpoint of improving the ejection stability of water-based ink. It is.
The average particle size of the aqueous pigment dispersion is measured by the method described in Examples.
Further, the average particle diameter of the water-based ink is preferably the same as the average particle diameter of the water-based pigment dispersion, and the preferred embodiment of the average particle diameter of the water-based ink is the same as the preferred embodiment of the average particle diameter of the water-based pigment dispersion. It is.

[Water-based ink]
The aqueous pigment dispersion of the present invention is preferably used by being included in a water-based ink (hereinafter also referred to as "aqueous ink" or "ink"). Thereby, the storage stability of the water-based ink, as well as the adhesion to non-water-absorbing printing media, scratch resistance, and print density can be improved. The aqueous pigment dispersion of the present invention can be used as is as an aqueous ink, but from the viewpoint of improving the storage stability, adhesion, scratch resistance, and print density of the aqueous ink, it may further contain an organic solvent. preferable. The organic solvent preferably has a boiling point of 90° C. or more and 250° C. or less from the same viewpoint as above.
Examples of the organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and the like. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred, including ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, diethylene glycol monobutyl ether, and diethylene glycol. One or more types selected from diethyl ether are more preferable, and one or more types selected from propylene glycol and diethylene glycol monobutyl ether are even more preferable.

The water-based ink may further contain an aqueous dispersion of polymer particles containing no pigment from the viewpoint of improving adhesion and the like. An aqueous dispersion of pigment-free polymer particles can function as a fusing aid.
Polymers constituting the polymer particles that do not contain pigments include condensation polymers such as polyurethane resins and polyester resins; acrylic resins, styrene resins, styrene-acrylic resins, butadiene resins, styrene-butadiene resins, and vinyl chloride. Examples include vinyl polymers such as vinyl acetate resins, acrylic silicone resins, and vinyl acetate resins.
The aqueous dispersion of polymer particles containing no pigment may be appropriately synthesized or a commercially available product.

The water-based ink may be further treated with various types of moisturizers, wetting agents, penetrants, surfactants, viscosity modifiers, antifoaming agents, preservatives, anti-mold agents, rust preventive agents, etc. that are normally used in water-based inks, as necessary. Additives can be added and further filtration treatment using a filter or the like can be performed.
The content of each component of the water-based ink and the physical properties of the ink are as follows.

(Pigment content)
The pigment content in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more from the viewpoint of printing density, and the content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. From the viewpoint of reducing the content and improving storage stability, 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.
(Total content of pigment and polymer dispersant)
The total content of pigment and polymer dispersant in the water-based ink is preferably 2% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more, from the viewpoint of adhesion and scratch resistance. From the viewpoint of lowering the ink viscosity when the solvent evaporates and improving storage stability, the content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.
(Content of organic solvent)
The content of the organic solvent in the water-based ink is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, from the viewpoints of storage stability, adhesion, and print density of the water-based ink. The content is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.
(Water content)
The content of water in the water-based ink is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of storage stability, adhesion, and print density of the water-based ink. The content is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less.

The mass ratio of pigment in the total solid content of the water-based ink [pigment/(total solid content of the water-based ink)] is preferably 0 from the viewpoint of storage stability, adhesion, scratch resistance, and print density of the water-based ink. .2 or more, more preferably 0.3 or more, still more preferably 0.4 or more, and preferably 0.8 or less, more preferably 0.7 or less, still more preferably 0.6 or less.

(Water-based ink physical properties)
From the viewpoint of storage stability, the viscosity of the water-based ink at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 5 mPa·s or more, and preferably 12 mPa·s or less, More preferably it is 9 mPa·s or less, and still more 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 aqueous ink at 20° C. is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher, from the viewpoint of storage stability. Further, from the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less. The pH of the water-based ink at 20° C. can be measured by a conventional method.

The water-based ink can be suitably used as a flexographic printing ink, a gravure printing ink, or an inkjet ink, and is particularly preferably used as an inkjet ink. It can be loaded into a known inkjet recording device and ejected as ink droplets onto a print medium to record an image or the like.
Inkjet recording devices include thermal type and piezo type, and it is more preferable to use the aqueous ink containing the aqueous pigment dispersion of the present invention as a piezo type aqueous ink for inkjet recording.
Examples of the printing medium used include highly water-absorbent plain paper, low water-absorbent coated paper, and non-water-absorbent resin film. Examples of the 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, polyvinyl chloride film, polypropylene film, and polyethylene film. For the resin film, a corona-treated base material may be used.
Commonly available resin films include, for example, Lumirror T60 (manufactured by Toray Industries, Ltd., polyester), PVC80B P (manufactured by Lintec Corporation, vinyl chloride), DGS-210WH (manufactured by Roland DG Corporation, vinyl chloride), transparent PVC RE-137 (manufactured by Mimaki Engineering Co., Ltd., vinyl chloride), Kynas 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 Kojin Film & Chemicals Co., Ltd., nylon), Emblem ONBC (manufactured by Unitika Co., Ltd., nylon), and the like.

In the following Preparation Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.
In addition, various physical properties of the dispersions obtained in the Preparation Examples, Examples, and Comparative Examples were measured and evaluated by the following methods.

(1) Measurement of weight average molecular weight of (meth)acrylic resin A and (meth)acrylic resin B Phosphoric acid and lithium bromide are added to N,N-dimethylformamide at concentrations of 60 mmol/L and 50 mmol/L, respectively. Using the solution dissolved in the above as an eluent, gel permeation chromatography [GPC apparatus (model: HLC-8320GPC, manufactured by Tosoh Corporation), columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn SuperAW-H, Tosoh Corporation) Co., Ltd. product name), flow rate: 0.5 mL/min], a monodisperse polystyrene kit with a known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A- 1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), all trade names manufactured by Tosoh Corporation].
For the measurement sample, 0.1 g of (meth)acrylic resin A or (meth)acrylic resin B was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and passed through a syringe filter ( A product filtered through a membrane filter (trade name: DISMIC-13HP, membrane filter material: hydrophilic PTFE, pore size 0.2 μm, manufactured by Advantech Co., Ltd.) was used.

(2) Measurement of average particle size of aqueous pigment dispersion The cumulant average particle size measured using a laser particle analysis system (model: ELS-8000, Otsuka Electronics Co., Ltd.) (cumulant analysis) is It was taken as the average particle size. The measurement conditions were a temperature of 25° C., an angle of 90° between the incident light and the detector, and 100 integrations, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was usually about 5×10 ⁻³ %.

(3) Measurement of solid content concentration 10.0 g of sodium sulfate, which had been made constant in a desiccator, was weighed into a 30 mL polypropylene container (φ = 40 mm, height = 30 mm), and about 1.0 g of the sample was added thereto. After mixing, the mixture was accurately weighed, maintained at 105° C. for 2 hours to remove volatile components, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removal of volatile matter was taken as solid content, and the solid content concentration was obtained by dividing by the mass of the added sample.

(4) Measurement of acid value of (meth)acrylic resin A and (meth)acrylic resin B before crosslinking In JIS K0070, the measurement solvent is changed from a mixed solvent of ethanol and ether to a mixed solvent of ethanol and toluene. Measurement was performed according to JIS K0070, except that the ratio was changed to [ethanol:toluene=1:1 (volume ratio)].

(5) Measurement of glass transition temperature of (meth)acrylic resin A and (meth)acrylic resin B The temperature was raised to 200°C using a differential scanning calorimeter (trade name: Pyris 6 DSC, manufactured by Perkin Elmer). , the sample was cooled from that temperature to -30°C at a cooling rate of 10°C/min, and then heated at a heating rate of 10°C/min. The temperature at the intersection with the tangent line showing the maximum inclination to the apex was defined as the glass transition temperature (Tg).
Note that the measurement sample (meth)acrylic resin A or (meth)acrylic resin B was dried under reduced pressure and then dried at -10°C using a freeze dryer (model: FDU-2100, manufactured by Tokyo Rikakikai Co., Ltd.). The sample was freeze-dried for 9 hours.

<Preparation of (meth)acrylic resin A and (meth)acrylic resin B>
Preparation example 1-1
A raw material monomer was prepared by mixing 30 parts of acrylic acid, 40 parts of styrene, and 30 parts of α-methylstyrene. In a reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.2 parts of 3-mercaptopropionic acid (polymerization chain transfer agent), and 10% of the raw material monomers were placed and mixed, and the mixture was thoroughly purged with nitrogen gas.
Meanwhile, in a dropping funnel, the remaining raw material monomers (90% of the raw material monomers), 1.8 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., Add 1.7 parts of the mixture (product name: V-501, 4,4'-azobis(4-cyanovaleric acid)) and heat the monomer mixture in the reaction vessel to 65°C while stirring under a nitrogen atmosphere. The temperature was raised, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C from the end of the dropwise addition, a solution of 0.3 part of the polymerization initiator dissolved in 5 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and at 70°C for 2 hours, and diluted with MEK to form a solid. A solution of acrylic resin A1 (glass transition temperature: 121° C., acid value: 240 mgKOH/g, weight average molecular weight: 16,500) with a concentration of 50% was obtained.

Preparation Examples 1-2 to 1-7 and Preparation Examples 2-1 to 2-6
Each (meth)acrylic resin was obtained in the same manner as in Preparation Example 1-1 except that the raw material monomer composition was changed as shown in Table 1.

<Manufacture of water-based pigment dispersion and water-based ink>
Example 1
[Manufacture of water-based pigment dispersion]
(Step 1)
66.7 parts of the solution of acrylic resin A2 obtained in Preparation Example 1-2 and 66.7 parts of the solution of acrylic resin B2 obtained in Preparation Example 2-2 were mixed, and 30 parts of the 5N aqueous sodium hydroxide solution was added. .4 parts were added to neutralize acrylic resin A2 and acrylic resin B2 so that the equivalent amount of the neutralizing agent used was 60 mol%.
Next, 570 parts of ion-exchanged water (W1) was added, and carbon black pigment (C.I. Pigment Black 7, manufactured by Cabot Specialty Chemicals, trade name: Monarch 717) (hereinafter referred to as "M717") was added. ) and stirred for 60 minutes using a disper (manufactured by Asada Tekko Co., Ltd., trade name: Ultra Disper) at 20° C. with the disper blade rotating at 7,000 rpm to obtain a pigment mixture.
The obtained pigment mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa using a microfluidizer (manufactured by Microfluidics, trade name) to obtain a dispersion.
After adding 278 parts of ion-exchanged water (W2) to the obtained dispersion and stirring, MEK was removed at 60°C under reduced pressure, some of the water was removed, and filtered with a pore size of 5 μm (acetyl cellulose membrane, A dispersion with a solid content concentration of 25% (outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) is filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) to remove coarse particles. d-1) was obtained. The average particle size was 99 nm.
(Step 2)
100 parts of the dispersion (d-1) obtained in step 1 was placed in a glass bottle with a screw cap, and trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Co., Ltd., trade name: Denacol EX-321L, epoxy 1.66 parts of equivalent weight 129) (hereinafter referred to as "EX321L") was added, the mixture was tightly stoppered, and the mixture was heated at 70° C. for 5 hours while stirring with a stirrer. After that, the temperature was lowered to room temperature, and after filtration with a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a filter with a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Film Corporation), the ion By diluting with exchanged water, an aqueous pigment dispersion (D-1) having a solid content concentration of 25% was obtained. The average particle size was 100 nm.

[Manufacture of water-based ink]
Using the obtained aqueous pigment dispersion (D-1), the pigment concentration relative to the entire aqueous ink was 4.0%, propylene glycol (hereinafter referred to as "PG") was 20.0%, and diethylene glycol monobutyl ether ( 10.0% of polyether-modified silicone activator (PEG-11 methyl ether dimethicone, trade name: KF6011, manufactured by Shin-Etsu Chemical Co., Ltd.) as a surfactant (hereinafter referred to as "BDG"). Add ion-exchanged water, weigh the total amount to 100%, stir with a magnetic stirrer to mix well, and filter the resulting mixture using the 5 μm filter and needleless syringe in the same manner. A water-based ink (I-1) was obtained by removing coarse particles.

Examples 2 to 11
Each water-based pigment was prepared in the same manner as in Example 1, except that the types and degree of crosslinking of (meth)acrylic resin A, (meth)acrylic resin B, and crosslinking agent C were changed as shown in Tables 2 and 3. Dispersions (D-2) to (D-11) and water-based inks (I-2) to (I-11) were obtained.
In addition, the crosslinking agent C in Table 3 is as follows.
EX850L: Diethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-850L, epoxy equivalent 145)
EX216L: Cyclohexane dimethanol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-216L, epoxy equivalent 150)
EX212L: 1,6-hexanediol diglycidyl ether (manufactured by Nagase ChemteX Co., Ltd., trade name: Denacol EX-212L, epoxy equivalent: 135)

Example 12
[Manufacture of water-based pigment dispersion]
(Step 1)
Add 32.4 parts of a 5N aqueous sodium hydroxide solution to 106.7 parts of the solution of acrylic resin A2 obtained in Preparation Example 1-2, and adjust the amount of acrylic resin A2 so that the equivalent amount of the neutralizing agent used is 60 mol%. neutralized.
Next, 570 parts of ion-exchanged water (W1) was added, 100 parts of carbon black pigment (M717) was added thereto, and a disper blade was heated at 20°C using a disper (manufactured by Asada Tekko Co., Ltd., trade name: Ultra Disper). The mixture was stirred for 60 minutes while rotating at 7,000 rpm to obtain a pigment mixture.
The obtained pigment mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa using a microfluidizer (manufactured by Microfluidics, trade name) to obtain a dispersion.
After adding 278 parts of ion-exchanged water (W2) to the obtained dispersion and stirring, MEK was removed at 60°C under reduced pressure, some of the water was removed, and filtered with a pore size of 5 μm (acetyl cellulose membrane, A dispersion with a solid content concentration of 25% (outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) is filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) to remove coarse particles. d'-12) was obtained. The average particle size was 105 nm.
Next, after drying 26.7 parts of the solution of acrylic resin B3 obtained in Preparation Example 2-3 under reduced pressure, 4.0 parts of a 5N aqueous sodium hydroxide solution and 22.7 parts of ion-exchanged water were added to the powder. In addition, an aqueous solution of acrylic resin B3 having a solid content concentration of 25% was obtained. The aqueous solution was added to the dispersion (d'-12) to obtain a dispersion (d-12) with a solid content concentration of 25%. The average particle size was 104 nm.
(Step 2)
100 parts of the obtained dispersion (d-12) was placed in a glass bottle with a screw cap, 1.99 parts of trimethylolpropane polyglycidyl ether (EX321L) was added as a crosslinking agent C, the cap was tightly capped, and the bottle was heated at 70°C while stirring with a stirrer. The mixture was heated for 5 hours. Thereafter, the temperature was lowered to room temperature, and the solid was filtered through a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a filter with a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Film Corporation). An aqueous pigment dispersion (D-12) having a concentration of 25% was obtained. The average particle size was 105 nm.

[Manufacture of water-based ink]
A water-based ink (I-12) was obtained in the same manner as in Example 1, except that the water-based pigment dispersion (D-12) was used instead of the water-based pigment dispersion (D-1).

Comparative examples 1 to 4
Each aqueous pigment dispersion was made in the same manner as in Example 1, except that (meth)acrylic resin A, (meth)acrylic resin B, and the type and degree of crosslinking of the crosslinking agent were changed as shown in Tables 2 and 4. Inks (D-C1) to (D-C4) and water-based inks (I-C1) to (I-C4) were obtained.

Comparative example 5
After drying the solution of acrylic resin A2 obtained in Preparation Example 1-2 under reduced pressure, 7.6 parts of a 5N aqueous sodium hydroxide solution and 35.3 parts of ion-exchanged water were added to 12.6 parts of the powder. An aqueous solution of acrylic resin A2 having a solid content concentration of 25% was obtained. To the aqueous solution, add 2.78 parts of trimethylolpropane polyglycidyl ether (EX321L) as the crosslinking agent C and 8.3 parts of ion-exchanged water, seal the solution, and heat at 70°C for 5 hours while stirring with a stirrer. Thus, an aqueous solution of crosslinked acrylic resin A2 was obtained (solid content concentration 25%).
Next, 22.3 parts of an aqueous solution of crosslinked acrylic resin A2 was added to 100 parts of the aqueous pigment dispersion (D-C2) obtained in Comparative Example 2, and the aqueous pigment dispersion (D-C5) was prepared. Obtained. The average particle size was 103 nm.
A water-based ink (I-C5) was obtained in the same manner as in Example 1, except that the water-based pigment dispersion (D-C5) was used instead of the water-based pigment dispersion (D-1).

Comparative example 6
A water-based ink (I-C6) was produced in the same manner as in Example 1, except that the pigment dispersion (d-2) obtained in Step 1 of Example 2 was used instead of the water-based pigment dispersion (D-1). I got it.

<Evaluation test of water-based pigment dispersion>
Test 1 (evaluation of storage stability)
Each aqueous pigment dispersion obtained in Examples and Comparative Examples was filled into a screw tube, sealed, and stored for 7 days in a thermostatic chamber set at a temperature of 70°C. The average particle diameter before and after storage was measured by the method described in (2) above, and the average particle diameter maintenance rate was calculated from the following formula. The results are shown in Tables 3 and 4. The closer the average particle diameter maintenance rate is to 100%, the smaller the amount of pigment particle aggregation and the better the storage stability.
Average particle size maintenance rate (%) = [average particle size of aqueous pigment dispersion after storage/average particle size of aqueous pigment dispersion before storage] x 100

<Water-based ink evaluation test>
Tests 2 to 4 below were conducted and evaluated using each of the water-based inks obtained in Examples and Comparative Examples. The results are shown in Tables 3 and 4.

Test 2 (evaluation of print density)
Coat each water-based ink with bar coater No. 4 (manufactured by As One Corporation) on a polyester film (manufactured by Toray Industries, Inc., trade name: Lumirror T60, thickness 75 μm) and heated at 60° C. for 10 minutes. Then, after being left at 25°C for 24 hours, a total of 5 points at the center and four corners of the obtained printed matter (5.1 cm x 8.0 cm) were measured using a Macbeth densitometer (manufactured by Gretag Macbeth, product number: Spectroeye). Then, the average value was calculated. The larger the value, the better the print density.

Test 3 (evaluation of adhesion)
A cellophane tape (manufactured by Nichiban Co., Ltd., tape width 18 mm x 4 cm) was applied to the coating film of the printed matter obtained in the above print density evaluation, and after leaving it for 1 minute, the tape was applied in a direction perpendicular to the coating film. The peeled area of the coated film was visually confirmed from the state of the coated film after being pulled and peeled off, and when the entire surface of the coated film was peeled off, the peeled area was defined as 100%, and the peeled area was evaluated based on the following evaluation criteria. A score of 3 or more on the following evaluation criteria indicates excellent adhesion.
〔Evaluation criteria〕
4: There was no peeling of the coating film.
3: The peeled area of the coating film was less than 20%.
2: The peeled area of the coating film was 20% or more and less than 40%.
1: The peeled area of the coating film was 40% or more.

Test 4 (evaluation of scratch resistance)
Regarding the printed matter obtained in the evaluation of print density, a Sutherland type ink lab tester AB-201 (manufactured by Tester Sangyo Co., Ltd.) was used to apply cotton (manufactured by Asahi Kasei Corporation, product name: Bencot) as a friction material between the printed matter and the weight. (BEMCOT) M-3) was placed on the bottom of a weight (bottom area: 4 cm ² ), and a printed matter was rubbed 10 times (back and forth) under a load of 1,000 g to perform a scratch test on printed matter. The scratched printed matter was visually evaluated according to the following evaluation criteria.
〔Evaluation criteria〕
4: No scratches could be visually confirmed.
3: Only scratches were visually confirmed.
2: Scratches were visually confirmed, and the film surface was exposed in part of the scratched area.
1: The film surface was exposed over the entire scratched area.

From Tables 3 and 4, in Examples 1 to 12, the polymer dispersant contained high Tg resin A and low Tg resin B, and some of the acid groups of each of high Tg resin A and low Tg resin B were It can be seen that because it is cross-linked with cross-linking agent C, it has excellent storage stability and achieves both excellent adhesion and scratch resistance as well as high print density.
On the other hand, in Comparative Examples 1 and 3, the polymer dispersant did not contain low Tg resin B, so the adhesion was inferior to Examples 1 to 12.
Since Comparative Examples 2 and 4 do not contain high Tg resin A, their scratch resistance is inferior to Examples 1 to 12.
In Comparative Example 5, only low Tg resin B was used as a polymer dispersant during pigment dispersion, and an aqueous solution of crosslinked high Tg resin A was added during ink preparation, and the pigment was dispersed in the low Tg resin B. Since the high Tg resin A and the low Tg resin B are not crosslinked with each other, the print density is low and the scratch resistance is poor.
It can be seen that in Comparative Example 6, both the high Tg resin A and the low Tg resin B as polymer dispersants were not crosslinked, so the storage stability was poor, the print density was low, and the scratch resistance was poor.

According to the present invention, by using the ink as a water-based ink which has excellent storage stability, it is possible to obtain printed matter having high print density while maintaining excellent adhesion and scratch resistance to non-water-absorbing printing media.

Claims (12)

An aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant,
The polymer dispersant contains (meth)acrylic resin A and (meth)acrylic resin B having acid groups,
The (meth)acrylic resin A is a vinyl polymer containing a structural unit derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from a styrene monomer, ) The content of structural units derived from the carboxyl group-containing monomer in the acrylic resin A is 5% by mass or more and 40% by mass or less,
The (meth)acrylic resin B has a structural unit derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, a structural unit derived from a styrene monomer, and a hydrocarbon group derived from an aliphatic alcohol. (meth)acrylate-derived structural units, and the content of the structural units derived from the carboxy group-containing monomer in the (meth)acrylic resin B is 5% by mass or more and 40% by mass or less,
The glass transition temperature of the (meth)acrylic resin A is 80°C or more and 140°C or less,
The glass transition temperature of the (meth)acrylic resin B is -50°C or more and 40°C or less,
An aqueous pigment dispersion in which at least the (meth)acrylic resin A and the (meth)acrylic resin B are crosslinked with a crosslinking agent C via their respective acid groups. The aqueous pigment dispersion according to claim 1, wherein the content of the structural unit derived from the styrene monomer in the (meth)acrylic resin A is 50% by mass or more and 95% by mass or less. The mass ratio of the content of the styrene monomer to the total content of the styrene monomer and the (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol, which constitute the (meth)acrylic resin B, is 0.1 or more and 0. 7 or less, the aqueous pigment dispersion according to claim 1 or 2. The aqueous pigment dispersion according to any one of claims 1 to 3 , wherein the difference between the glass transition temperature of the (meth)acrylic resin A and the glass transition temperature of the (meth)acrylic resin B is 40°C or more and 190°C or less. body. The aqueous pigment dispersion according to any one of claims 1 to 4 , wherein the (meth)acrylic resin A has an acid value of 50 mgKOH/g or more and 300 mgKOH/g or less. The aqueous pigment dispersion according to any one of claims 1 to 5 , wherein the (meth)acrylic resin B has an acid value of 50 mgKOH/g or more and 260 mgKOH/g or less. The mass ratio of the content of (meth)acrylic resin A to the total content of (meth)acrylic resin A and (meth)acrylic resin B in the aqueous pigment dispersion [A/(A+B)] is 0. The aqueous pigment dispersion according to any one of claims 1 to 6 , which has a molecular weight of 1 or more and 0.9 or less. The degree of crosslinking [[number of molar equivalents of crosslinkable functional groups of crosslinking agent C]/[number of molar equivalents of average acid groups of (meth)acrylic resin A and (meth)acrylic resin B]] is 0.20 or more The aqueous pigment dispersion according to any one of claims 1 to 7 , which has a molecular weight of 0.70 or less. The aqueous pigment dispersion according to any one of claims 1 to 8 , wherein the crosslinking agent C is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 or more and 8 or less carbon atoms. A method for producing an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium using a polymer dispersant, the method comprising:
The polymer dispersant contains (meth)acrylic resin A and (meth)acrylic resin B having acid groups,
The (meth)acrylic resin A is a vinyl polymer containing a structural unit derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from a styrene monomer, ) The content of structural units derived from the carboxyl group-containing monomer in the acrylic resin A is 5% by mass or more and 40% by mass or less,
The (meth)acrylic resin B has a structural unit derived from one or more carboxy group-containing monomers selected from acrylic acid and methacrylic acid, a structural unit derived from a styrene monomer, and a hydrocarbon group derived from an aliphatic alcohol. (meth)acrylate-derived structural units, and the content of the structural units derived from the carboxy group-containing monomer in the (meth)acrylic resin B is 5% by mass or more and 40% by mass or less,
The glass transition temperature of the (meth)acrylic resin A is 80°C or more and 140°C or less,
The glass transition temperature of the (meth)acrylic resin B is -50°C or more and 40°C or less,
A method for producing an aqueous pigment dispersion, comprising a step of crosslinking the (meth)acrylic resin A and the (meth)acrylic resin B with a crosslinking agent C via their respective acid groups. The method for producing an aqueous pigment dispersion according to claim 10 , comprising the following steps 1 and 2.
Step 1: A step of dispersing a pigment mixture containing a pigment, (meth)acrylic resin A, and (meth)acrylic resin B to obtain a dispersion.Step 2: The dispersion obtained in step 1, Crosslinking step using crosslinking agent C A water-based ink containing the water-based pigment dispersion according to any one of claims 1 to 9 .