JP6962636B2 - Aqueous pigment dispersion - Google Patents

Description

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

The inkjet recording method is a recording method in which ink droplets are directly ejected from a fine nozzle and adhered to a recording medium to obtain a printed matter or the like on which characters and images are recorded. This method is remarkably popular because it is easy to make full color and is inexpensive, and has many advantages such as plain paper can be used as a recording medium and non-contact with the recording medium. In recent years, in particular, from the viewpoint of weather resistance and water resistance of recorded materials, those using pigments as colorants have become mainstream.

By the way, in an aqueous pigment dispersion and an aqueous ink using the same, a functional group having a high affinity for water is imparted to the surface of the pigment, and the pigment is used as an aqueous medium or an ink vehicle without a dispersant or by using a polymer dispersant. It is used by being dispersed in. However, unlike inks that use dyes that dissolve uniformly in water-based media or ink vehicles, inks that use pigment dispersions have difficulty maintaining a dispersed state of pigment particles for a long period of time, and a polymer is used at the ink ejection nozzle portion. There is a demand for improvement in the decrease in ejection property due to the sticking of the ink and the pigment.
For example, in Patent Document 1, for the purpose of obtaining a pigment dispersion having excellent water resistance, stability over time, etc., a specific ratio of a carboxyl group-containing thermoplastic resin is used to disperse the pigment, and then the carboxy group-containing thermoplastic is obtained. An aqueous pigment dispersion liquid in which the resin is crosslinked with a cross-linking agent and the cross-linking agent / carboxy group-containing thermoplastic resin (effective solid content weight ratio) is 1/100 to 50/100 is disclosed. Further, it is disclosed that it is preferable to neutralize the thermoplastic resin with an organic amine having a boiling point of 200 ° C. or lower, and that the neutralization rate is preferably about 100 to 150%.

International Publication No. 1999/052966

The aqueous pigment dispersion of Patent Document 1 can obtain a strong film by three-dimensionally bonding a polymer dispersant that disperses a pigment with a cross-linking agent having a plurality of functional groups that react with a carboxy group in one molecule. Therefore, the stability of the ink can be ensured to some extent at room temperature. However, when the ink is stored at a high temperature for a longer period of time, the stability of the ink cannot be ensured, and the demand for reliability that has been increasing in recent years has not been satisfied.
Further, when the printed matter is held in a stacked state such as a printed matter using a recording medium having low water absorption such as coated paper, transfer may occur in the contact portion with the printed portion.
The present invention has excellent storage stability that can suppress solidification of pigments and polymers at the ink ejection nozzle while maintaining water resistance, which is an advantage of using pigments, and even if printed matter is held in a stacked state. An object of the present invention is to provide an aqueous pigment dispersion having excellent transfer resistance in which transfer does not occur in a contact portion, a method for producing the same, and a method for producing an aqueous ink.

In order to improve the water resistance of the water-based ink, it is a promising method to strengthen the adhesive force between the pigment particles or between the pigment particles and the recording medium after the ink droplets come into contact with the recording medium.
Therefore, as the performance of the water-based ink, the present inventors have formed a strong film in an environment where the ink droplets come into contact with the recording medium surface and the ink vehicle disappears from the vicinity of the pigment particles, as in (i) printing. Although it can be formed, it has low viscosity in an environment such as (ii) an ink ejection nozzle where even if a volatile component (for example, water) in the ink vehicle volatilizes, the volatile component remains. We aimed to obtain the performance that can maintain the fluid state of. Then, at least a part of the water-insoluble polymer having a carboxy group and a specific acid value is neutralized with an alkali metal hydroxide, and the pigment is watered with a polymer dispersant obtained by cross-linking with a water-insoluble polyfunctional epoxy compound. It has been found that the aqueous pigment dispersion dispersed in the above can achieve both the above-mentioned performance.
On the other hand, if the printed matter is held in a stacked state, transfer may occur in the contact portion with the printed portion. In particular, in printed matter using a recording medium having low water absorption such as coated paper, ink does not easily penetrate into the recording medium, and ink components such as pigments remain on the surface of the recording medium, so that transfer is likely to occur. In order to improve the transfer resistance of printed matter, it is necessary to increase the adhesive force between the pigment and the recording medium, and for that purpose, it is considered effective to increase the amount of the polymer used as the dispersant. However, when the amount of the polymer is increased, the polymer particles tend to adhere or aggregate to the nozzle in the vicinity of the discharge nozzle, and the discharge property tends to be deteriorated. From the above, there is an urgent need to develop a technology that can achieve both improvement in transfer resistance and improvement in ejection property while maintaining water resistance.

The present invention provides the following [1] to [3].
[1] An aqueous pigment dispersion containing a pigment and a polymer dispersant.
The polymer dispersant has a crosslinked structure obtained by reacting a water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. death,
At least a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide, and the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) is 0.5 or more and 1.8. Is below
A water-based pigment dispersion in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) exceeds −30 mgKOH / g and is 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage of "the molar equivalent of the alkali metal hydroxide / the molar equivalent of the carboxy group of the water-insoluble polymer (A) having a carboxy group", and the degree of cross-linking is "the molar equivalent of the water-insoluble polyfunctional epoxy compound". It is a percentage of "molar equivalent number of epoxy groups / molar equivalent number of carboxy groups of the water-insoluble polymer (A) having a carboxy group".

[2] An aqueous pigment dispersion having the following steps 1 to 3 and in which the acid value and neutralization degree of the water-insoluble polymer (A) in step 1 and the degree of cross-linking in step 3 satisfy the following condition 1. Production method.
Step 1: Neutralize the water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with an alkali metal hydroxide. Step 2: Neutralization obtained in Step 1. Step 3: Obtain the pigment aqueous dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium. Step 3: The pigment aqueous dispersion A obtained in step 2 is mixed with a water-insoluble polyfunctional epoxy. Step of cross-linking with a compound to obtain an aqueous pigment dispersion B containing a polymer dispersant which is a cross-linked water-insoluble polymer (A). Here, the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) Is 0.5 or more and 1.8 or less.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is more than -30 mgKOH / g and 130 mgKOH / g or less.
Here, the acid value, the degree of neutralization, and the degree of cross-linking are synonymous with the above [1].
[3] A method for producing a water-based ink, which comprises the steps 1 to 3 according to the above [2] and the following steps 4.
Step 4: A step of mixing the water-based pigment dispersion B obtained in step 3 with an organic solvent to obtain a water-based ink. The “water-based” means that water occupies the largest proportion in the medium for dispersing the pigment. Means that.

According to the present invention, while maintaining water resistance, which is an advantage of using a pigment, it has excellent storage stability capable of suppressing solidification of pigments and polymers at an ink ejection nozzle, and holds printed matter in a stacked state. However, it is possible to provide an aqueous pigment dispersion having excellent transfer resistance in which transfer does not occur in the contact portion, a method for producing the same, and a method for producing an aqueous ink.

[Aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion containing a pigment and a polymer dispersant.
The polymer dispersant has a crosslinked structure obtained by reacting a water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. death,
At least a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide, and the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) is 0.5 or more and 1.8. Is below
A water-based pigment dispersion in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) exceeds −30 mgKOH / g and is 130 mgKOH / g or less.
Here, the acid value, the degree of neutralization, and the degree of cross-linking are as described above.

The aqueous pigment dispersion of the present invention exhibits excellent storage stability that can suppress solidification of pigments and polymers at the ink ejection nozzle while maintaining water resistance, and also has excellent transfer resistance of printed matter, which is good printed matter. Can be suitably used as an aqueous pigment dispersion for flexo printing inks, gravure printing inks, or inkjet inks, and particularly preferably as an aqueous pigment dispersion for inkjet inks.
Further, the water-based ink using the water-based pigment dispersion of the present invention is preferably used as the water-based ink for inkjet recording because it is excellent in continuous ejection stability in the inkjet recording method and transfer resistance of printed matter.

The reason why the water-based pigment dispersion and the water-based ink of the present invention can exert the above-mentioned excellent effects is not clear, but it is considered as follows.
In the present invention, as the polymer dispersant, at least a part of the water-insoluble polymer (A) having a carboxy group is neutralized with an alkali metal hydroxide and crosslinked with a water-insoluble polyfunctional epoxy compound. A water-insoluble polymer having a carboxy group and having an acid value of 200 mgKOH / g or more has a high affinity with water, and a small amount of alkali metal hydroxide can appropriately neutralize a part of the carboxy group, resulting in strong charge repulsion. It is considered that the obtained material can enhance the dispersion stability of the pigment in an aqueous system.
Further, since the water-insoluble polyfunctional epoxy compound exists in the vicinity of the pigment surface to promote the cross-linking reaction, the polymer dispersant adsorbed on the pigment particles is more strongly adsorbed on the pigment particles, and the cross-linking is performed by the water-insoluble cross-linking agent. Since it has a structure, water insolubility is increased, and the polymer is hardly desorbed from the pigment, so that the storage stability of the water-based pigment dispersion and the water-based ink is improved.
Further, as described above, it is effective to increase the amount of the polymer dispersant in order to improve the transfer resistance of the printed matter. However, when the polymer dispersant according to the present invention is used, even if the amount of the polymer is increased, the nozzle can be used. It is considered that a printed matter having excellent transfer resistance can be obtained without deteriorating the ejection property because the agglomeration of the printed matter is suppressed.

<Pigment>
The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment may also be used. In addition, if necessary, they can be used in combination with extender pigments.
Specific examples of the inorganic pigment include carbon black, titanium oxide, iron oxide, red iron oxide, metal oxides such as chromium oxide, and pearl luster pigments. Especially for black ink, carbon black is preferable. 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 isoind. Examples thereof include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and slen pigments.
The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used.
Specific examples of preferable organic pigments include C.I. I. Pigment Yellow, C.I. I. Pigment Red, C.I. I. Pigment Orange, C.I. I. Pigment Violet, C.I. I. Pigment Blue and C.I. I. One or more product numbers selected from Pigment Green can be mentioned.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.
The above pigments can be used alone or in combination of two or more.

In the present invention, the pigment is preferably present as water-insoluble polymer particles containing the pigment (hereinafter, also referred to as “pigment-containing polymer particles”) in the water-based pigment dispersion and the water-based ink. Here, "containing a pigment" means a form in which a pigment is encapsulated in a polymer dispersant having a crosslinked structure obtained by reacting a water-insoluble polymer (A) having a carboxy group with a water-insoluble polyfunctional epoxy compound. , A form in which a part of the pigment is encapsulated in the polymer dispersant and a part of the pigment is exposed from the polymer dispersant, a form in which the polymer dispersant is adhered to the surface of the pigment, and the like. Also included is a mixture of. Among these, a form in which a pigment is encapsulated in a polymer dispersant having a crosslinked structure is preferable.

<Polymer dispersant>
The polymer dispersant used in the present invention is prepared from a water-insoluble polymer (A) having a carboxy group, and at least a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide. After that, it is preferable that the pigment is formed in an aqueous medium by carrying out a cross-linking reaction with a water-insoluble polyfunctional epoxy compound in a dispersed state. In this case, the polymer dispersant is not isolated, but condition 1 is determined by the monomer composition of the water-insoluble polymer (A), the type and amount of alkali metal hydroxide used, and the type and amount of water-insoluble polyfunctional epoxy compound used. The state of the polymer dispersant can be defined as satisfying the condition 1.
In the present invention, by using an alkali metal hydroxide as a neutralizing agent, the charge repulsive force generated after neutralization becomes large, and when an aqueous pigment dispersion or an aqueous ink is stored, thickening and aggregation are suppressed. However, it is considered that the storage stability is improved to the extent that the high reliability demanded in recent years can be met.

(Water-insoluble polymer (A))
The water-insoluble polymer (A) having a carboxy group for preparing the polymer dispersant used in the present invention (hereinafter, also simply referred to as "water-insoluble polymer (A)") is used as a pigment dispersant exhibiting a pigment dispersion action. And a function as a fixing agent on a recording medium.
This water-insoluble polymer (A) is water-insoluble not only in an unneutralized state but also after a part of its carboxy group is neutralized. Here, the "water-insoluble polymer" means that when the water-insoluble polymer is dispersed in water, it does not become transparent. Even if the aqueous dispersion of the water-insoluble polymer looks transparent visually, it is judged to be water-insoluble if the Tyndall phenomenon is observed by observation with laser light or normal light.

The acid value of the water-insoluble polymer (A) is derived from the carboxy group, but is 200 mgKOH / g or more, preferably 210 mgKOH / g or more, more preferably 220 mgKOH / g or more, and 320 mgKOH / g or less. It is preferably 300 mgKOH / g or less, more preferably 270 mgKOH / g or less. When the acid value is in the above range, the amount of the carboxy group and its neutralized carboxy group is sufficient, and the storage stability and the transfer resistance are improved.
The acid value of the water-insoluble polymer (A) can be calculated from the mass ratio of the constituent monomers. It can also be determined by a method of dissolving or swelling the polymer in a suitable organic solvent (for example, MEK) and titrating it.

The present form of the polymer dispersant obtained by reacting the water-insoluble polymer (A) in the water-based pigment dispersion and the water-based ink with the water-insoluble polyfunctional epoxy compound is (i) in a state of being adsorbed on the pigment, (i). There are ii) a pigment-containing (capsule) state containing a pigment, and (iii) a form in which the pigment is not adsorbed. From the viewpoint of the dispersion stability of the pigment, the state of (i) or (ii) is preferable in the present invention, and (ii) the pigment-encapsulating state containing the pigment is more preferable.
Examples of the water-insoluble polymer used to obtain the polymer dispersant according to the present invention include polyester, polyurethane, vinyl-based polymer, etc., and vinyl is used from the viewpoint of improving the storage stability of the water-based pigment dispersion and the water-based ink. A vinyl polymer obtained by addition polymerization of a monomer (vinyl compound, vinylidene compound, vinylene compound) is preferable.

The water-insoluble polymer (A) used in the present invention includes (a) a carboxy group-containing vinyl monomer (hereinafter, also referred to as “component (a)”) and (b) a hydrophobic vinyl monomer (hereinafter, “(b)). A vinyl-based polymer obtained by copolymerizing a vinyl monomer mixture containing (also referred to as “component”) (hereinafter, also simply referred to as “monomer mixture”) is preferable. This vinyl-based polymer has a structural unit derived from the component (a) and a structural unit derived from the component (b).

[(A) Carboxy group-containing vinyl monomer]
(A) The carboxy group-containing vinyl monomer is used as a monomer component of the water-insoluble polymer from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based pigment dispersion and the water-based ink. As the carboxy group-containing vinyl monomer, a carboxylic acid monomer is used.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid, and one selected from acrylic acid and methacrylic acid. The above is preferable.

[(B) Hydrophobic vinyl monomer]
The hydrophobic vinyl monomer (b) is preferably used as a monomer component of the water-insoluble polymer (A) from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based pigment dispersion and the water-based ink. Examples of the hydrophobic vinyl monomer include an alkyl group having 1 to 22 carbon atoms, an alkyl (meth) acrylate having an aryl group having 6 to 22 carbon atoms, and an aromatic group-containing monomer.
As the alkyl (meth) acrylic acid ester, those having an alkyl group having 1 or more and 22 or less carbon atoms are preferable, and those having an alkyl group having 6 or more and 18 or less carbon atoms are more preferable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth). Acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isoamyl (meth) acrylate, isooctyl (meth) Examples thereof include acrylate, isodecyl (meth) acrylate, isododecyl (meth) acrylate, and isostearyl (meth) acrylate.
In addition, "(meth) acrylate" means one or more kinds selected from acrylate and methacrylate. "(Meta)" in the following is also synonymous.

As the aromatic group-containing monomer, a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a heteroatom, is preferable, and a styrene-based monomer and an aromatic group-containing (meth) acrylate Is more preferable.
As the styrene-based monomer, styrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and styrene and α-methylstyrene are more preferable.
Further, as the aromatic group-containing (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate and the like are preferable, and benzyl (meth) acrylate is more preferable.
(B) As the hydrophobic monomer, two or more of the above-mentioned monomers may be used, or a styrene-based monomer and an aromatic group-containing (meth) acrylic acid ester may be used in combination.

[(C) Macromonomer]
(C) The macromonomer (hereinafter, also referred to as “component (c)”) is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less, and is an aqueous pigment dispersion of pigment-containing polymer particles. From the viewpoint of improving dispersion stability in the body and water-based ink, it can be used as a monomer component of the water-insoluble polymer (A). As the polymerizable functional group present at one end, an acryloyloxy group or a methacryloyloxy group is preferable, and a methacryloyloxy group is more preferable.
(C) 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 dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
As the macromonomer, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferable, and aromatic groups are preferable from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the aqueous pigment dispersion and the aqueous ink. The containing monomer-based macromonomer is more preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in (b) Hydrophobic Monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene is preferable. More preferable.
Specific examples of the styrene-based macromonomer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of the silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[(D) Nonionic monomer]
The water-insoluble polymer (A) is further referred to as (d) a nonionic monomer (hereinafter, also referred to as “component (d)” from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based pigment dispersion and the water-based ink. Can be used as a monomer component.
As the component (d), hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; polypropylene glycol (n = 2 to 30, n is the average addition of oxyalkylene groups). The number of moles is shown. The same applies hereinafter.) Polyalkylene glycol (meth) acrylate such as (meth) acrylate and polyethylene glycol (n = 2 to 30) (meth) acrylate, methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate. Examples thereof include alkoxypolyalkylene glycol (meth) acrylates such as, phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycols: n = 1 to 29) (meth) acrylates and the like. Among these, polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy (ethylene glycol / propylene glycol copolymer) (meth) acrylate are preferable, and polypropylene glycol (n = 2 to 30) (meth) acrylate is preferable. More preferred.

Specific examples of the commercially available component (d) include Shin Nakamura Chemical Industry Co., Ltd.'s NK Ester M-20G, 40G, 90G, 230G, etc., NOF Corporation's Blemmer PE-90, and the same. 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B, 43PAPE-600B And so on.
The above-mentioned components (a) to (d) can be used alone or in combination of two or more.
As described above, the water-insoluble polymer (A) having a carboxy group used in the present invention has one or more (a) structural units derived from one or more (a) carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, and one carbon number. Contains a structural unit derived from one or more (b) hydrophobic vinyl monomers selected from a (meth) acrylate monomer having an alkyl group of 22 or more and an aromatic group-containing monomer having an aryl group of 6 to 22 carbon atoms. It is preferably a vinyl-based polymer.

(Content of each component or constituent unit in monomer mixture or polymer)
The content of the component (a) is preferably 20% by mass or more, more preferably 25% by mass or more, further preferably 30% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less. , More preferably 50% by mass or less.
The content of the component (b) is preferably 15% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and preferably 70% by mass or less, more preferably 75% by mass or less. , More preferably 80% by mass or less.
When the component (c) is contained, the content of the component (c) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, and preferably 30% by mass or more. Below, it is more preferably 25% by mass or less, still more preferably 20% by mass or less.
When the component (d) is contained, the content of the component (d) is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and preferably 40% by mass or more. Hereinafter, it is more preferably 35% by mass or less, still more preferably 30% by mass or less.

The mass ratio of [component (a) / component (b)] is preferably 0.3 or more, more preferably 0.35 or more, still more preferably 0.40 or more, and preferably 2.0 or less. It is more preferably 1.5 or less, still more preferably 1.0 or less.
When the component (c) is contained, the mass ratio of [(a) component / [(b) component + (c) component]] is preferably 0.01 or more, more preferably 0.05 or more, and further. It is preferably 0.10 or more, and preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.0 or less.
A random structure is preferable for the binding mode of the component (a), the component (b), the component (c), and the component (d) for each component. Even when the components (a) to (d) are each composed of a plurality of types or more, it is preferable that all the monomer species are bonded in a random structure. Although the performance can be exhibited even with a block structure, the procedure for obtaining the water-insoluble polymer (A) becomes complicated, which is not preferable.
That is, in the present invention, it is preferable not to adopt a polymerization method known to obtain a block structure such as group transfer polymerization, living radical polymerization, living anionic polymerization, and living cationic polymerization.

(Manufacture of water-insoluble polymer (A))
The water-insoluble polymer (A) is produced by copolymerizing the monomer mixture by a known polymerization method such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is not particularly limited, but a polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be mixed with water and used. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, and esters such as ethyl acetate. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable, and methyl ethyl ketone or a mixed solvent of it and water is preferable.
At the time of polymerization, a polymerization initiator or a polymerization chain transfer agent can be used.
Examples of the polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), t-butylperoxyoctate, benzoyl peroxide and the like. A known radical polymerization initiator such as the organic peroxide of Azobisisobutyria can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per 1 mol of the monomer mixture.
As the polymerization chain transfer agent, known chain transfer agents such as octyl mercaptan, mercaptans such as 2-mercaptoethanol, and thiuram disulfides can be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent and the like used, but usually the polymerization temperature is preferably 30 ° C. or higher, more preferably 50 ° C. or higher, and preferably 95 ° C. or lower. More than 80 ° C. The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 20 hours or less, more preferably 10 hours or less. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation and solvent distillation. Further, the obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatographic method, extraction method and the like.

The solid content concentration of the water-insoluble polymer solution is preferably 30% by mass or more, more preferably 40% by mass or more, and preferably 70% by mass from the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles. % Or less, more preferably 65% by mass or less.
The number average molecular weight of the water-insoluble polymer (A) is preferably 2,000 or more, more preferably 5,000 or more, and preferably 20,000 or less, more preferably 18,000 or less. The weight average molecular weight is preferably 6,000 or more, more preferably 8,000 or more, and preferably 80,000 or less, more preferably 40,000 or less. When the molecular weight of the polymer is in the above range, the adsorption force to the pigment is sufficient and dispersion stability can be exhibited.
The number average molecular weight can be measured by the method described in Examples.

[Manufacture of pigment-containing polymer particles]
The water-insoluble polymer particles containing a pigment (pigment-containing polymer particles) can be efficiently produced as an aqueous dispersion by a method having the following steps 1 to 3.
Step 1: Neutralize the water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with an alkali metal hydroxide. Step 2: Neutralization obtained in Step 1. Step 3: Obtain the pigment aqueous dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium. Step 3: The pigment aqueous dispersion A obtained in Step 2 is mixed with a water-insoluble polyfunctional epoxy. Step of cross-linking with a compound to obtain an aqueous pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A).

(Step 1)
Step 1 is a step of neutralizing the water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with an alkali metal hydroxide.
The method for producing the water-insoluble polymer (A) is as described above.
In step 1, it is preferable that the water-insoluble polymer (A) is first dissolved in an organic solvent and neutralized with an alkali metal hydroxide.
The organic solvent for dissolving the water-insoluble polymer (A) is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters and the like are preferable, and wettability to pigments and dissolution of the water-insoluble polymer are preferable. From the viewpoint of improving the properties and the adsorptivity of the water-insoluble polymer to the pigment, a ketone having 4 or more and 8 or less carbon atoms is more preferable, a methyl ethyl ketone and a methyl isobutyl ketone are more preferable, and a methyl ethyl ketone is even more preferable.
When the water-insoluble polymer (A) is synthesized by the solution polymerization method, the solvent used in the polymerization may be used as it is.

At least a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide from the viewpoint of water resistance, storage stability and the like of the obtained water-based pigment dispersion and water-based ink. It is preferable to neutralize the pH at this time so that it is 7 or more and 11 or less.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide, but sodium hydroxide and potassium hydroxide are preferable. Moreover, the water-insoluble polymer may be neutralized in advance.
Neutralizers such as organic amines and organophosphorus compounds have a peculiar odor and toxicity, which is not preferable from the viewpoint of safety, and it is necessary to use a large amount in order to improve storage stability. There are adverse effects such as the viscosity of the ink becoming too high.
The alkali metal hydroxide is preferably used as an aqueous solution from the viewpoint of sufficiently and uniformly promoting neutralization. From the above viewpoint, the concentration of the aqueous solution is preferably 3% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 25% by mass or less. ..
The degree of neutralization of the carboxy group of the water-insoluble polymer (A) is preferably 20 mol% or more, more preferably 25 mol% or more, from the viewpoint of water resistance and storage stability of the obtained water-based pigment dispersion and water-based ink. It is more preferably 30 mol% or more, and preferably 80 mol% or less, more preferably 75 mol% or less, still more preferably 72 mol% or less.
Here, the degree of neutralization is a value obtained by dividing the molar equivalent number of the alkali metal hydroxide by the molar equivalent number of the carboxy group of the water-insoluble polymer (A), that is, "molar equivalent number of the alkali metal hydroxide / water insoluble". It is a percentage (mol%) of "the molar equivalent number of the carboxy group of the polymer (A)". In the present invention, since the degree of neutralization is calculated from the molar equivalent number of the alkali metal hydroxide, it exceeds 100 mol% when the alkali metal hydroxide is excessively used.

In step 1, in addition to the alkali metal hydroxide, a volatile basic compound can also be used in combination. In the present invention, the volatile basic compound means an organic amine having a boiling point of 100 ° C. or lower at atmospheric pressure, and specific examples of the volatile basic compound include ammonia, trimethylamine, triethylamine and the like. Among these, ammonia is preferable from the viewpoint of high volatility.
The amount of the volatile basic compound used is not particularly limited, but it is not used at all, or even if it is used, it is preferably 5 mol% or more in terms of the degree of neutralization of the carboxy group of the water-insoluble polymer (A). , More preferably 10 mol% or more, and preferably 50 mol% or less, more preferably 30 mol% or less.
Only the amount of alkali metal hydroxide used is used in the calculation of the degree of neutralization of the present invention, and the amount of the volatile basic compound used is not used in the calculation of the degree of neutralization of the present invention.

(Step 2)
Step 2 is a step of mixing and dispersing the neutralized water-insoluble polymer (A) obtained in Step 1 and the pigment in an aqueous medium to obtain a pigment aqueous dispersion A.
Here, the "aqueous medium" means a medium in which water occupies the largest proportion among the media in which the pigment is dispersed.

(Content of each component in pigment mixture)
The content of each component in the pigment mixture in step 2 is as follows from the viewpoints of water resistance, storage stability, dischargeability, and productivity of the obtained aqueous pigment dispersion.
The content of the pigment in the pigment mixture in the step 2 is preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 4% by mass or more, and preferably 35% by mass or less, more preferably 35% by mass or less. It is 30% by mass or less, more preferably 20% by mass or less.
The content of the water-insoluble polymer (A) in the pigment mixture is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 3.0% by mass or more, and preferably. It is 8.0% by mass or less, more preferably 7.0% by mass or less, still more preferably 6.0% by mass or less.
The content of the organic solvent in the pigment mixture is preferably 5% by mass or more, more preferably 7% by mass or more, further preferably 10% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass. % Or less, more preferably 25% by mass or less.
The content of water in the pigment mixture is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or more. Hereinafter, it is more preferably 75% by mass or less.

The mass ratio of the pigment to the water-insoluble polymer (A) in the pigment mixture [pigment / water-insoluble polymer (A)] is preferably 0.5 or more, more preferably 0. It is 6 or more, more preferably 1.0 or more, and preferably 1.8 or less, more preferably 1.7 or less, still more preferably 1.5 or less.

(Dispersion treatment of pigment mixture)
In step 2, there is no particular limitation on the dispersion method for obtaining the dispersion. Although the average particle size of the pigment particles can be atomized to a desired particle size only by the main dispersion, preferably, after the pigment mixture is pre-dispersed, the main dispersion is further applied by applying shear stress to perform the main dispersion of the pigment particles. It is preferable to control the average particle size of the above to a desired particle size.
The temperature in step 2, particularly the temperature in the preliminary dispersion, is preferably 0 ° C. or higher, preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably 25 ° C. or lower, and the dispersion time is preferably 0. .5 hours or more, more preferably 0.8 hours or more, preferably 30 hours or less, more preferably 10 hours or less, still more preferably 5 hours or less.
When the pigment mixture is pre-dispersed, a commonly used mixing and stirring device such as an anchor blade and a dispenser blade can be used, and among them, a high-speed stirring and mixing device is preferable.

Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidic (manufactured by Microfluidic), and a media type disperser such as a paint shaker and a bead mill. Examples of commercially available media-type dispersers include Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd.) and Pico Mill (manufactured by Asada Iron Works Co., Ltd.). A plurality of these devices can be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When the main dispersion is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the processing pressure and the number of passes.
From the viewpoint of productivity and economy, the treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, further preferably 130 MPa or more, and preferably 200 MPa or less, more preferably 180 MPa or less.
The number of passes is preferably 3 or more, more preferably 10 or more, and preferably 30 or less, more preferably 25 or less.

In step 2, an aqueous dispersion of pigment-containing polymer particles (pigment aqueous dispersion A) can be obtained by removing the organic solvent from the dispersion obtained above by a known method. It is preferable that the organic solvent in the obtained aqueous pigment dispersion A is substantially removed, but it may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
If necessary, the dispersion can be heat-stirred before distilling off the organic solvent.
The obtained pigment aqueous dispersion A is one in which pigment-containing polymer particles are dispersed in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited, and at least the particles may be formed by the pigment and the water-insoluble polymer (A), but as described above, the pigment is contained in the water-insoluble polymer (A). It is preferably in the form of particles.

The concentration of the non-volatile component (solid content concentration) of the obtained pigment aqueous dispersion A is preferably 10% by mass or more from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of the aqueous ink. It is more preferably 15% by mass or more, preferably 30% by mass or less, and more preferably 25% by mass or less.
The solid content concentration of the aqueous pigment dispersion A is measured by the method described in Examples.
The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion A is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. It is more preferably 200 nm or less, more preferably 170 nm or less, still more preferably 140 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.

(Step 3)
In step 3, the pigment aqueous dispersion A obtained in step 2 is crosslinked with a water-insoluble polyfunctional epoxy compound (crosslinking) from the viewpoint of improving the water resistance, storage stability, and ejection property of the obtained aqueous pigment dispersion and the aqueous ink. This is a step of obtaining an aqueous pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) by cross-linking with an agent).
Here, the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) is 0.5 or more and 1.8 or less.
In this step, a part of the carboxy group of the water-insoluble polymer (A) constituting the pigment-containing polymer particles is crosslinked to form a crosslinked structure on the surface layer portion of the pigment-containing polymer particles. That is, the polymer dispersant according to the present invention is prepared from the water-insoluble polymer (A) and the water-insoluble polyfunctional epoxy compound on the surface of the pigment.

(Water-insoluble polyfunctional epoxy compound)
The water-insoluble polyfunctional epoxy compound used in the present invention is dissolved in 100 g of water at 20 ° C. from the viewpoint of efficiently reacting with the carboxy group of the water-insoluble polymer (A) in a medium mainly composed of water. The dissolved amount is preferably 50 g or less, more preferably 40 g or less, still more preferably 35 g or less.
The water-insoluble polyfunctional epoxy compound has a water content (mass ratio) of preferably 50% or less, more preferably 40, from the viewpoint of water resistance, storage stability, and ejection property of the obtained water-based pigment dispersion and water-based ink. % Or less, more preferably 35% or less. Here, the water content% (mass ratio) means the dissolution rate (%) when 10 parts by mass of the epoxy compound is dissolved in 90 parts by mass of water at room temperature of 25 ° C., and more specifically, in Examples. Measured by the method described.

As the water-insoluble polyfunctional epoxy compound, a compound having a plurality of epoxy groups, preferably a glycidyl ether group in the molecule is preferable, and a polyhydric alcohol glycidyl ether compound having a hydrocarbon group having 3 to 8 carbon atoms is more preferable. ..
The molecular weight of the water-insoluble polyfunctional epoxy compound is preferably 120 or more, more preferably 150 or more, still more preferably 200 or more, and from the viewpoint of ease of reaction and storage stability of the obtained crosslinked polymer. It is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less.
The number of epoxy groups in the water-insoluble polyfunctional epoxy compound is preferably 2 to 6 per molecule, preferably 3 to 6 per molecule, from the viewpoint of efficiently reacting with the carboxy group to improve the storage stability of the pigment-containing polymer particles. Is more preferable. Further, those having 5 or more epoxy groups in one molecule are poorly available on the market, and therefore, those having 3 or 4 epoxy groups in one molecule are more preferable from the viewpoint of achieving both reactivity and economy.
From the same viewpoint as above, the epoxy equivalent of the water-insoluble polyfunctional epoxy compound is preferably 100 or more, more preferably 110 or more, still more preferably 120 or more, and preferably 300 or less, more preferably 270 or less. More preferably, it is 250 or less.

Specific examples of the water-insoluble polyfunctional epoxy compound include polypropylene glycol diglycidyl ether (water content 31%), glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether (water content 27%). %), Sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether and other polyglycidyl ethers. Among these, one or two selected from trimethylolpropane polyglycidyl ether (water content 27%) and pentaerythritol polyglycidyl ether (water insoluble) are preferable.

(Crosslink reaction)
In the present invention, a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal compound to disperse the pigment to obtain a pigment aqueous dispersion A, and then the carboxy group of the water-insoluble polymer is further obtained. A part of the above is reacted with a water-insoluble polyfunctional epoxy compound to form a crosslinked structure, and the pigment is dispersed in an aqueous medium with a polymer dispersant obtained in the system to obtain an aqueous pigment dispersion B. At that time, from the viewpoint of improving the storage stability and transfer resistance while maintaining the water resistance of the obtained aqueous pigment dispersion and the aqueous ink, the alkali metal is in an amount satisfying the following condition 1, preferably further condition 2. Compounds and water-insoluble polyfunctional epoxy compounds are used.

[Condition 1]
Condition 1 is that the value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) exceeds −30 mgKOH / g and is 130 mgKOH / g or less.
Here, the degree of neutralization is the percentage (mol%) of "the molar equivalent of the alkali metal hydroxide / the molar equivalent of the carboxy group of the water-insoluble polymer (A) having a carboxy group", and the degree of cross-linking is "water-insoluble many". The molar equivalent of the epoxy group of the functional epoxy compound / the molar equivalent of the carboxy group of the water-insoluble polymer (A) having a carboxy group ”is a percentage (mol%).
Condition 1 indicates the amount of unneutralized carboxy groups of the polymer dispersant in the pigment dispersion required to enhance discharge stability and storage stability, and the acid value and neutralization of the water-insoluble polymer (A). It is determined by the degree and degree of cross-linking. In other words, Condition 1 represents the acid value of the water-insoluble polymer (A) after neutralization and cross-linking.
When the value of Condition 1 exceeds -30 mgKOH / g and 130 mgKOH / g or less, the amount of charge on the pigment surface is sufficient when the pigment dispersion is prepared using the polymer, and the water of the polymer dispersant is sufficient. Insolubility is also sufficient, and high discharge stability and storage stability can be exhibited.
The value of condition 1 is preferably -20 mgKOH / g or more, more preferably -10 mgKOH / g or more, still more preferably -5 mgKOH / g or more, and preferably 120 mgKOH / g or less, more preferably 110 mgKOH / g or less. , More preferably 100 mgKOH / g or less.

[Condition 2]
Condition 2 is that the value of [(crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less.
Condition 2 indicates the degree of cross-linking required to enhance storage stability. In other words, condition 2 represents the acid value of the insoluble polymer (A) reduced by cross-linking. In the aqueous pigment dispersion, in order to improve the storage stability of the pigment particles, it is preferable to satisfy the condition of the degree of cross-linking in addition to the above-mentioned conditions.
When the value of Condition 2 is 30 mgKOH / g or more, the water insolubility of the polymer dispersant can be sufficiently enhanced, the adsorption to the pigment becomes strong, and the storage stability can be enhanced. On the other hand, when the value of Condition 2 is 180 mgKOH / g or less, the hydrophobicity of the polymer dispersant is sufficient and can be strongly adsorbed on the pigment, and the amount of carboxy anions present in the aqueous pigment dispersion is also sufficient. Aggregation can be suppressed.
The value of condition 2 is preferably 40 mgKOH / g or more, more preferably 60 mgKOH / g or more, still more preferably 80 mgKOH / g or more, and preferably 170 mgKOH / g or less, more preferably 160 mgKOH / g or less, still more preferable. Is 150 mgKOH / g or less.
Since it is difficult to actually measure the amount of the water-insoluble polyfunctional epoxy compound that reacts with the carboxy group of the water-insoluble polymer (A), the epoxy group of the water-insoluble polyfunctional epoxy compound used is used. The number of moles is expressed in terms of the acid value per 1 g of the water-insoluble polymer (A) used to disperse the pigment.

The cross-linking reaction between the water-insoluble polyfunctional epoxy compound and the carboxy group of the polymer dispersant (water-insoluble polymer (A)) is carried out after the pigment is dispersed in the water-insoluble polymer (A).
The reaction temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 60 ° C. or higher, even more preferably 65 ° C. or higher, and preferably 95 ° C. or higher from the viewpoint of reaction completion and economic efficiency. ° C or lower, more preferably 90 ° C or lower.
From the same viewpoint as above, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 2 hours or more, still more preferably 3 hours or more, and preferably. It is 12 hours or less, more preferably 10 hours or less, still more preferably 8 hours or less, still more preferably 6 hours or less.
The degree of cross-linking of the crosslinked water-insoluble polymer is preferably 5 mol% or more, more preferably 10 mol% or more, still more preferably 15 mol% or more, and preferably 80 mol% or less, more preferably 70 mol. % Or less, more preferably 60 mol% or less.
The degree of cross-linking is an apparent degree of cross-linking calculated from the acid value of the polymer and the equivalent of the epoxy group of the cross-linking agent. That is, the degree of cross-linking is a percentage (mol%) of "the molar equivalent of the epoxy group of the water-insoluble polyfunctional epoxy compound / the molar equivalent of the carboxy group of the water-insoluble polymer (A)".

The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion B is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. It is more preferably 200 nm or less, more preferably 170 nm or less, still more preferably 140 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.
The average particle size of the pigment-containing polymer particles in the water-based ink is the same as the average particle size in the pigment aqueous dispersion B, and the preferred average particle size is the average particle size in the pigment aqueous dispersion. It is the same as the aspect.

The pH of the aqueous pigment dispersion B is preferably 8.0 or higher. A high pH means that the dissociation of the anionic group is promoted and the amount of charge of the pigment aqueous dispersion B is large, which leads to an increase in the stability of the pigment aqueous dispersion B.
The pH of the aqueous pigment dispersion B is more preferably 8.5 or more, and the upper limit of the pH is not particularly limited. However, when the pH exceeds 11, the pH of the ink obtained from the pigment dispersion becomes too high. This is not preferable because it adversely affects the members of the printer or printing machine that uses the ink. Therefore, the pH of the aqueous pigment dispersion B is more preferably 10.5 or less.
The pH of the pigment dispersion is measured with the obtained pigment dispersion as it is, and the temperature is set to 20 ° C.
The pH measuring method is not particularly limited, but a pH measuring method using a glass electrode is defined in JIS Z8802, and this method is preferable from the viewpoint of simplicity and accuracy. Specifically, it is measured by the method described in Examples.

The aqueous pigment dispersion of the present invention may contain 1 to 10% by mass of glycerin, polyethylene glycol or the like as a moisturizer to prevent drying, or may contain an additive such as a fungicide.
The above additive may be blended when the pigment is dispersed in the water-insoluble polymer (A), or may be blended after the pigment is dispersed or after the cross-linking reaction.

[Manufacturing method of aqueous pigment dispersion]
The method for producing an aqueous pigment dispersion of the present invention has the following steps 1 to 3, and the acid value and neutralization degree of the water-insoluble polymer (A) in step 1 and the degree of cross-linking in step 3 are the following conditions. Satisfy 1.
Step 1: Neutralize the water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with an alkali metal hydroxide. Step 2: Neutralization obtained in Step 1. Step 3: Obtain the pigment aqueous dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium. Step 3: The pigment aqueous dispersion A obtained in step 2 is mixed with a water-insoluble polyfunctional epoxy. Step of cross-linking with a compound to obtain an aqueous pigment dispersion B containing a polymer dispersant which is a cross-linked water-insoluble polymer (A). Here, the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) Is 0.5 or more and 1.8 or less.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is more than -30 mgKOH / g and 130 mgKOH / g or less.
Here, the acid value, the degree of neutralization, and the degree of cross-linking are synonymous with the above.

Details of steps 1 to 3 and condition 1 are as described above.
The mass ratio of the pigment (pigment / polymer dispersant) to the mass of the polymer dispersant is 0.5 or more and 1.8 or less from the viewpoint of improving transfer resistance.
Here, the mass of the polymer dispersant is the total mass of the water-insoluble polymer (A) used in the production of the polymer dispersant and the mass of the water-insoluble polyfunctional epoxy compound.
In the calculation of the mass of the polymer dispersant, the part of the polymer dispersant of the present invention that contributes to the storage stability of the aqueous pigment dispersion is the carboxy anion, not the alkali metal ion that is the counter cation thereof. The portion of the alkali metal ion which is the counter cation is not included, and the sum of the mass of the water-insoluble polymer (A) and the mass of the water-insoluble polyfunctional epoxy compound is used as described above.
The value of the mass ratio (pigment / polymer dispersant) is preferably 1.7 or less, more preferably 1.5 or less, still more preferably 1. It is 3 or less, preferably 0.6 or more, more preferably 0.8 or more, still more preferably 1.0 or more.

[Manufacturing method of water-based ink]
The method for producing a water-based ink of the present invention includes the above steps 1 to 3 and the following steps 4, and is preferably a production method that further satisfies the following condition 2.
Step 4: Mix the water-based pigment dispersion B obtained in Step 3 with an organic solvent to obtain a water-based ink. Step Condition 2: [(Crosslinkability) / 100] × (Acid value of water-insoluble polymer (A)) The value of is 30 mgKOH / g or more and 180 mgKOH / g or less.
The details of condition 2 are as described above.

Step 4 is a step of mixing the pigment aqueous dispersion B obtained in Step 3 with an organic solvent to obtain an aqueous ink, but the mixing method is not particularly limited.
The organic solvent is used from the viewpoint of improving the storage stability of the water-based ink. The organic solvent used here preferably contains one kind or two or more kinds of organic solvents having a boiling point of 90 ° C. or higher, and an organic solvent having a weighted average value of boiling points of 250 ° C. or lower is preferable. The weighted average value of the boiling points of the organic solvent is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and preferably 240 ° C. or lower, more preferably 220 ° C. or lower, still more preferably 200 ° C. or lower.
Specific 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 preferable, and ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, and diethylene glycol diethyl ether are selected. One or more are more preferable, and one or more selected from glycerin, triethylene glycol, and trimethylolpropane are further preferable.

In the method for producing a water-based ink of the present invention, if necessary, a moisturizer, a wetting agent, a penetrant, a dispersant, a surfactant, a viscosity modifier, a defoaming agent, a preservative, which are usually used for the water-based ink, Various additives such as antifungal agents and antiseptic agents can be added, and further filtration treatment with a filter or the like can be performed.
The content and physical characteristics of each component of the water-based ink obtained by the production method of the present invention are as follows.

(Pigment content)
The content of the pigment in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 2.5% by mass or more, from the viewpoint of improving the printing density of the water-based ink. be. Then, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization and improving ejection stability and storage stability, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and further preferably 7.0% by mass. % Or less.
(Content of water-insoluble polymer)
The content of the water-insoluble polymer in the water-based ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, still more preferably 2.5% by mass or more, and further, from the viewpoint of storage stability and fixability. From the viewpoint of transfer resistance, it is more preferably 5% by mass or more, and from the viewpoint of storage stability and fixability, it is preferably 15% by mass or less, more preferably 12% by mass or less, still more preferably 9% by mass. % Or less, more preferably 6% by mass or less from the viewpoint of dischargeability.
(Total content of pigment and water-insoluble polymer)
The total content of the pigment and the water-insoluble polymer in the water-based ink is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 9% by mass or more, and further, from the viewpoint of storage stability and fixability. From the viewpoint of transfer resistance, it is more preferably 11% by mass or more, and from the viewpoint of storage stability and fixability, it is preferably 20% by mass or less, more preferably 17% by mass or less, still more preferably 15% by mass. % Or less, more preferably 12% by mass or less from the viewpoint of dischargeability.

(Physical characteristics of water-based ink)
The viscosity of the water-based ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, still more preferably 5.0 mPa · s or more, from the viewpoint of improving the storage stability of the ink. It is s or more, preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and further preferably 7.0 mPa · s or less.
The pH of the water-based ink is preferably 7.0 or more, more preferably 7.2 or more, and further preferably 7.5 or more, from the viewpoint of improving the storage stability of the ink. From the viewpoint of member resistance and skin irritation, the pH is preferably 11.0 or less, more preferably 10.0 or less, and further preferably 9.5 or less.

[Inkjet recording method]
The water-based ink of the present invention can be loaded into a known inkjet recording device and ejected as ink droplets onto a recording medium to record an image or the like.
The inkjet recording apparatus includes a thermal type and a piezo type, but it is more preferable to use it as a piezo type water-based ink for inkjet recording.
Examples of the recording medium that can be used include high water absorption plain paper, low water absorption coated paper and film. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper, and examples of the film include polyester film, polyvinyl chloride film, polypropylene film, polyethylene film and the like.
The water-based ink of the present invention is remarkably effective in transfer resistance on printed matter printed on recording media such as low water-absorbent coated paper and film. Here, "low water absorption" is a concept including low liquid absorption and non-liquid absorption. For example, the water absorption of the recording medium at a contact time of 100 msec between the recording medium and pure water is 0 g / m. It means that it is ² or more and less than 10 g / m ^2.

In the following preparation examples, production examples, examples and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.

(1) Measurement of number average molecular weight of water-insoluble polymer N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography), phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) and Gel chromatography method using a solution prepared by dissolving lithium bromide (manufactured by Tokyo Kasei Kogyo Co., Ltd., reagent) at concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent [GPC apparatus manufactured by Toso Co., Ltd. (HLC-8120 GPC) ), Column manufactured by Toso Co., Ltd. (TSK-GEL, α-M × 2), flow velocity: 1 mL / min], using monodisperse polystyrene with a known molecular weight as a standard substance.

(2) Measurement of average particle size of water-insoluble polymer particles and pigment-containing polymer particles Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25 ° C., an angle of 90 ° between the incident light and the detector, and 100 times of integration, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. It was diluted with water so that the measured concentration was 5 × 10 ^-3 % (converted to solid content concentration).

(3) Measurement of solid content concentration of pigment aqueous dispersion Weigh 10.0 g of sodium sulfate homogenized in a desiccator into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), and sample about 1. After adding 0 g and mixing, the mixture was accurately weighed, maintained at 105 ° C. for 2 hours to remove volatiles, and left in a desiccator for another 15 minutes to measure the mass. The mass of the sample after removing the volatile matter was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

(4) Measurement of water content of epoxy compound At room temperature of 25 ° C, 90 parts by mass of ion-exchanged water and 10 parts by mass of cross-linking agent were added to a glass tube (25 mmφ × 250 mmh), and the glass tube was adjusted to a constant temperature of 25 ° C. It was allowed to stand in the tank for 1 hour. Then, the glass tube was vigorously shaken for 1 minute and then allowed to stand again in a constant temperature bath for 10 minutes. Then, the undissolved material was weighed and the water content (mass%) was calculated.

<Preparation of water-insoluble polymer (A)>
Preparation Example 1
Methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 46 parts, benzyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 94 parts, styrene macromer (manufactured by Toa Synthetic Co., Ltd., trade name: AS-6S, number average Molecular weight: 6,000, solid content concentration 50%) 40 parts (20 parts as solid content), polypropylene glycol monomethacrylate (manufactured by Nichiyu Co., Ltd., trade name: Blemmer PP-800, average number of moles of propylene oxide added 13, terminal : A hydroxyl group) 40 parts were mixed to prepare a monomer mixed solution. In the reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the above-mentioned monomer mixture were put and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, in the dropping funnel, the remaining 90% of the monomer mixture, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65). , 2,2'-Azobis (2,4-dimethylvaleronitrile)) 2.2 parts of the mixture was added, and the temperature was raised to 65 ° C. while stirring the monomer mixture in the reaction vessel under a nitrogen atmosphere. The mixed solution in the dropping funnel was dropped over 3 hours. After 2 hours have passed at 65 ° C. from the end of the dropping, a solution in which 0.3 part of the polymerization initiator is dissolved in 5 parts of MEK is added, and the mixture is further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours to obtain a water-insoluble polymer a1 (number). A solution having an average molecular weight of 11,000) was obtained.

Preparation Examples 2-4
In Preparation Example 1, a solution of the water-insoluble polymers a2 to a4 was obtained in the same manner as in Preparation Example 1 except that the amounts of methacrylic acid and benzyl acrylate were set to the amounts shown in Preparation Examples 2 to 4 in Table 1. The results are shown in Table 1.

Preparation Example 5
Acrylic acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 38.5 parts, styrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 152.5 parts, α-methylstyrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 9 The parts were mixed to prepare a monomer mixed solution. In the reaction vessel, 20 parts of MEK, 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were placed and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, the remaining 90% of the monomer mixed solution, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK and 2.2 parts of the azo radical polymerization initiator (V-65) were put into the dropping funnel, and thereafter. Obtained a solution of the water-insoluble polymer a5 (number average molecular weight: 11,000) in the same manner as in Preparation Example 1.

Preparation Examples 6-9
In Preparation Example 5, solutions of water-insoluble polymers a6 to a9 were obtained in the same manner as in Preparation Example 5, except that the amounts of acrylic acid, styrene, and α-methylstyrene were set to the amounts shown in Table 1. The results are shown in Table 1.

<Manufacturing of aqueous pigment dispersion A>
Manufacturing example 1
25 parts of the water-insoluble polymer a1 obtained by drying the polymer solution obtained in Preparation Example 1 under reduced pressure was mixed with 78.6 parts of MEK, and further, a 5N sodium hydroxide aqueous solution (sodium hydroxide solid content 16.9%, 5.1 parts (manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration) was added and neutralized so that the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the water-insoluble polymer a1 was 32% (middle). 32% sum). Further, 400 parts of ion-exchanged water was added, and 30 parts of cyan pigment (CI Pigment Blue 15: 3, manufactured by DIC Co., Ltd., trade name: TGR-SD) was added therein, and Disper (Asada Iron Works Co., Ltd.) was added. The disper blade was stirred at 20 ° C. under the condition of 7,000 rpm for 60 minutes using (manufactured by Ultra Disper: trade name).
The obtained mixture was subjected to 10-pass dispersion treatment with a microfluidics (manufactured by Microfluidics, trade name) at a pressure of 150 MPa. 250 parts of ion-exchanged water was added to the obtained dispersion, and after stirring, MEK was completely removed at 60 ° C. under reduced pressure, and a part of water was further removed to remove a 5 μm filter (acetyl cellulose film, outer diameter). : A pigment aqueous dispersion A1 with a solid content concentration of 20% by filtering with a needleless syringe (manufactured by Terumo Corporation) with a capacity of 25 mL and equipped with 2.5 cm (manufactured by Fujifilm Co., Ltd.) to remove coarse particles. Got The results are shown in Table 2.

Manufacturing example 2
In Production Example 1, instead of the polymer a1 solution obtained in Preparation Example 1, 25 parts of the polymer a2 obtained by drying the polymer solution obtained in Preparation Example 2 under reduced pressure was used, and a 5N sodium hydroxide aqueous solution 5 was used. An aqueous pigment dispersion A2 was obtained in the same manner as in Production Example 1 except that 8.1 parts (neutralization degree 32%) were used instead of 1 part. The results are shown in Table 2.

Production Examples 3 to 6
In Production Example 2, pigment aqueous dispersions A3 to A6 were obtained in the same manner as in Production Example 2 except that 30 parts of the cyan pigment was used as the amount shown in Table 2. The results are shown in Table 2.

Production Examples 7 to 11
In Production Example 1, instead of the polymer a1 solution obtained in Preparation Example 1, 25 parts of the polymers a3 to a7 obtained by drying the polymer solution obtained in the preparation example shown in Table 2 under reduced pressure was used, and 5N was used. A7 to A11 pigment aqueous dispersions were obtained in the same manner as in Production Example 1 except that the amount of the aqueous sodium hydroxide solution and the degree of neutralization were as shown in Table 2. The results are shown in Table 2.

Production Examples 12-14
In Production Example 11, pigment aqueous dispersions A12 to A14 were obtained in the same manner as in Production Example 11 except that 30 parts of the cyan pigment was used in the amount shown in Table 2. The results are shown in Table 2.

Production Examples 15 to 16
In Production Example 11, pigment aqueous dispersions A15 and A16 were obtained in the same manner as in Production Example 11 except that the amount of 5N aqueous sodium hydroxide solution and the degree of neutralization were as shown in Table 2. The results are shown in Table 2.

Production Examples 17-18
In Production Example 1, instead of the polymer a1 solution obtained in Preparation Example 1, 25 parts of the polymer a8 or a9 obtained by drying the polymer solution obtained in the preparation example shown in Table 2 under reduced pressure was used, and 5N water was used. A17 and A18 pigment aqueous dispersions were obtained in the same manner as in Production Example 1 except that the amount of the aqueous sodium oxide solution was as shown in Table 2. The results are shown in Table 2.

Production Examples 19 to 20
In Production Example 2, pigment aqueous dispersions A19 and A20 were obtained in the same manner as in Production Example 2 except that the neutralizing agent and the amount shown in Table 2 were used instead of the 5N aqueous sodium hydroxide solution. The results are shown in Table 2.
The KOH used as a neutralizing agent was a 5N potassium hydroxide aqueous solution (potassium hydroxide solid content 21.9%, manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration), and TEA was triethylamine (purity 99%). , Wako Pure Chemical Industries, Ltd., special grade reagent).

Production example 21
In Production Example 2, a pigment aqueous dispersion A21 was obtained in the same manner as in Production Example 2, except that 30 parts of carbon black pigment (CB: manufactured by Cabot Specialty Chemicals, Monarch880) was used instead of 30 parts of cyan pigment. The results are shown in Table 2.

<Manufacturing of aqueous pigment dispersion B>
Example 1
100 parts (solid content 20%) of the pigment aqueous dispersion A2 obtained in Production Example 2 is placed in a glass bottle with a screw cap, and trimethylolpropane polyglycidyl ether (trimethylolpropane polyglycidyl ether) as a cross-linking agent having three epoxy groups in one molecule ( Made by Nagase ChemteX Corporation, Denacol EX-321, molecular weight 302, epoxy equivalent 140 g / eq., Water content 27%) 0.96 parts (crosslinkability 40 mol%) was added and sealed, and 70 while stirring with a stirrer. It was heated at ° C. for 5 hours. After 5 hours, the temperature is lowered to room temperature, and the mixture is filtered with a needleless syringe (manufactured by Terumo Corporation) having a capacity of 25 mL and equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Co., Ltd.). , Water-based pigment dispersion B2 was obtained.

Examples 2-4
In Example 1, the pigment aqueous dispersion obtained in Production Example 2 was replaced with the pigment aqueous dispersion obtained in Table 3, and the mixture was filtered in the same manner as in Example 1. , Pigment aqueous dispersions B3, B4 and B7 were obtained.

Comparative Examples 1 to 4
In Example 1, the pigment aqueous dispersion obtained in each production example was filtered in the same manner as in Example 1 except that the pigment aqueous dispersion obtained in the production example shown in Table 3 was used for comparison. Pigment aqueous dispersions B1, B5, B6 and B8 for use were obtained.

Examples 5-16
In Example 1, as shown in Table 4, 100 parts (solid content 20%) of the pigment aqueous dispersion A obtained in each production example was placed in a glass bottle with a screw cap, and the Denacol EX-321 was used as a cross-linking agent. The amount shown in Table 4 was added, the mixture was sealed, and the mixture was heated at 70 ° C. for 5 hours while stirring with a stirrer. After 5 hours, the temperature was lowered to room temperature and filtered in the same manner as in Example 1 to obtain aqueous pigment dispersions B10 to B20, B23, B25 and B27.

Example 17
In Example 1, 100 parts (solid content 20%) of the aqueous pigment dispersion A2 obtained in Production Example 2 was placed in a glass bottle with a screw cap, and pentaerythritol was used as a cross-linking agent having four epoxy groups in one molecule. Add 1.57 parts (crosslinkability 40%) of polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-411, epoxy equivalent 229 g / eq., Water-soluble), seal it tightly, and stir with a stirrer at 70 ° C. Was heated for 5 hours. After 5 hours, the temperature was lowered to room temperature and filtered in the same manner as in Example 1 to obtain an aqueous pigment dispersion B28.

Comparative Examples 5-11
As shown in Table 4, 100 parts (solid content 20%) of the pigment aqueous dispersion A obtained in the production example was placed in a glass bottle with a screw cap, and the Denacol EX-321 was added in the amount shown in Table 4 and sealed. Then, the mixture was heated at 70 ° C. for 5 hours while stirring with a stirrer. Then, the mixture was filtered in the same manner as in Example 1 to obtain a pigment aqueous dispersion B for comparison.

Comparative Example 12
100 parts (solid content 20%) of the pigment aqueous dispersion A2 obtained in Production Example 2 is placed in a glass bottle with a screw cap, and polyglycerin polyglycidyl ether is used as a water-soluble cross-linking agent having two epoxy groups in one molecule. (Manufactured by Nagase ChemteX Corporation, Denacol EX-521, epoxy equivalent 183 g / eq., Water-soluble) was added in an amount of 1.25 parts (crosslinkability 40%), sealed, and heated at 70 ° C. for 5 hours while stirring with a stirrer. bottom. Then, the mixture was filtered in the same manner as in Example 1 to obtain a pigment aqueous dispersion B29 for comparison.

<Evaluation test for water-based ink>
(Preparation of water-based ink)
Using each of the aqueous pigment dispersions obtained in Examples and Comparative Examples, the pigment concentration was 5%, glycerin (manufactured by Kao Co., Ltd., concentrated glycerin for cosmetics) 5%, and triethylene glycol (Wako Pure Chemical Industries, Ltd.) with respect to the entire aqueous ink. 7% acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd., 10 mol of ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol) 0.5% Then, add ion-exchanged water, weigh to 100% of the total amount, stir with a magnetic stirrer and mix well, and mix well with a 1.2 μm filter (acetyl cellulose film, outer diameter: 2.5 cm, Fuji Film Co., Ltd.). Water-based ink was obtained by filtering with a needleless syringe having a capacity of 25 mL and equipped with (manufactured by the company).
Using the obtained water-based ink, the following tests 1 to 5 were performed and evaluated. The results are shown in Tables 3 and 4.

Test 1 (Evaluation of dischargeability)
Inkjet printer (manufactured by Seiko Epson Corporation, model number: EM-930C, piezo method) is loaded with the water-based ink obtained above, and 100 sheets of plain paper 4200 manufactured by XEROX are printed on 100 sheets (fine mode). The number of white lines (corresponding to the number of non-ejected nozzles) was measured by observing the printed matter on the first sheet. Next, after performing the nozzle cleaning operation, 100 sheets of solid printing are performed on the entire surface, the 100th printed matter is observed again, the number of white lines generated is measured per nozzle width, and the printed matter is ejected according to the following criteria. Gender was evaluated.
(Evaluation criteria)
A: No white line is generated on the 100th and 200th printed matter B: No white line is generated on the 100th and 200th printed matter C: No white line is generated on the 100th or 200th printed matter C: 100th or 200th printed matter 3 to 5 white lines generated D: 6 or more white lines generated on the 100th or 200th printed matter

Test 2 (evaluation of storage stability)
Each water-based ink is sealed in a screw tube manufactured by Maruemu Corporation and allowed to stand in a thermostatic chamber set at 20 ° C. and 60 ° C. for 1 week, respectively, and then the average particle size is measured and the average particle size is measured from the following formula. The rate of increase was calculated.
Average particle size increase rate (%) = [(Average particle size of ink after storage-Average particle size of aqueous dispersion used for ink preparation) / Average particle size of aqueous dispersion used for ink preparation] × 100
The smaller the average particle size increase rate, the more the aggregation is suppressed and the better the storage stability.
Storage stability was evaluated according to the following criteria.
(Evaluation criteria)
A: Average particle size increase rate is less than 7% B: Average particle size increase rate is 7% or more and less than 15% C: Average particle size increase rate is 15% or more and less than 30% D: Average particle size increase rate is 30% or more Or gelling

Test 3 (fixation evaluation)
Plain paper (Oce, plain paper Engineering Bond paper) was attached to the bottom surface (1 inch x 1 inch) of a stainless steel weight weighing 460 g with double-sided tape. Next, the printed surface of the plain paper obtained in Test 1 was placed so that the printed surface and the plain paper attached to the bottom surface of the weight were in contact with each other, and the width was 4 inches with respect to the solid printed portion. It was rubbed back and forth 10 times. Then, the value output as the black optical density of the plain paper attached to the bottom surface of the weight was measured with the Macbeth densitometer in the same manner as described above, and the average value was obtained.
When the value of the optical density is 0.05 or less, sufficient fixability to a low water absorption recording medium can be obtained and practical use can be obtained, preferably 0.03 or less.
Fixability was evaluated according to the following criteria.
(Evaluation criteria)
A: Optical density value is less than 0.03 B: Optical density value is 0.03 or more and less than 0.05 C: Optical density value is 0.05 or more and less than 0.10 D: Optical density value is 0. 10 or more

Test 4 (water resistance evaluation)
Using the printing pattern used in Test 1 (Evaluation of ejection property), instead of plain paper, coated paper (Oji Paper Co., Ltd., OK top coat, water absorption: 4.9 g / m ² ) was used for 4 cm x 4 cm. After printing a solid print pattern and leaving it in an environment with a temperature of 23 ° C and a humidity of 50% for 24 hours, the printed surface is rubbed 10 times with a cotton stick (manufactured by Johnson End Johnson, 100% natural cotton) immersed in ion-exchanged water, and the printed matter is printed. Water resistance test was performed. In the evaluation, the print density of the rubbed portion was measured before rubbing, the print density of the rubbed portion was measured again after rubbing, and the water resistance was evaluated by the difference.
(Evaluation criteria)
Print density difference = (Print density before rubbing)-(Print density after rubbing)
The closer the print density difference is to 0, the less ink is peeled off and the better the water resistance.
Water resistance was evaluated according to the following criteria.
(Evaluation criteria)
A: Print density difference is less than 0.20 B: Print density difference is 0.20 or more and less than 0.50 C: Print density difference is 0.50 or more and less than 0.80 D: Print density difference is 0.80 or more or Paper exposure

Test 5 (Evaluation of transfer resistance)
Under the same conditions as in Test 4 (water resistance evaluation), one sheet of the same printing pattern used in Test 4 was printed on coated paper (Oji Paper Co., Ltd., OK top coat), and the temperature was 23 ° C and the humidity was 50%. 24 hours in an environment with a temperature of 23 ° C and a humidity of 50% with a 200 g weight placed on top of coated paper (Oji Paper Co., Ltd., OK top coat, water absorption: 4.9 g / m ^2). After being left to stand, the print density of the laminated coated paper was measured and evaluated by the difference from the pre-measured print density before stacking.
Print density difference = (Print density after overlaying)-(Print density before overlaying)
The closer the print density difference is to 0, the less ink is transferred and the better the transfer resistance.
Transcription was evaluated according to the following criteria.
(Evaluation criteria)
A: Optical density difference is less than 0.03 B: Optical density difference is 0.03 or more and less than 0.05 C: Optical density difference is 0.05 or more and less than 0.10 D: Optical density difference is 0.10 or more

From Tables 3 and 4, it can be seen that the water-based ink of the example is superior in ejection property, storage stability, fixability, water resistance, transfer resistance and performance balance as compared with the water-based ink of the example.

Claims (8)

An aqueous pigment dispersion containing a pigment and a polymer dispersant.
The polymer dispersant has a crosslinked structure obtained by reacting a water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. death,
The water-insoluble polymer (A) is a (meth) acrylate monomer having one or more carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, and an alkyl group having 1 to 22 carbon atoms and a carbon number of carbon atoms. A vinyl-based polymer containing a structural unit derived from one or more hydrophobic vinyl monomers selected from aromatic group-containing monomers having 6 or more and 22 or less aryl groups.
The water-insoluble polyfunctional epoxy compound is a polyhydric alcohol glycidyl ether compound having a hydrocarbon group having 3 to 8 carbon atoms.
At least a part of the carboxy group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide, and the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) is 0.5 or more and 1.8. Is below
A water-based pigment dispersion in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) exceeds −30 mgKOH / g and is 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage of "the molar equivalent of the alkali metal hydroxide / the molar equivalent of the carboxy group of the water-insoluble polymer (A) having a carboxy group", and the degree of cross-linking is "the molar equivalent of the water-insoluble polyfunctional epoxy compound". It is a percentage of "molar equivalent number of epoxy groups / molar equivalent number of carboxy groups of the water-insoluble polymer (A) having a carboxy group", and the water-insoluble polymer (A) is water-insoluble after neutralization. The aqueous pigment dispersion according to claim 1, further satisfying the following condition 2.
Condition 2: The value of [(crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less. The method 1 or 2 according to claim 1 or 2, wherein the mass ratio of [the structural unit derived from the carboxy group-containing vinyl monomer / the structural unit derived from the hydrophobic vinyl monomer] in the water-insoluble polymer (A) is 0.3 or more and 2.0 or less. Aqueous pigment dispersion. The water-based pigment dispersion according to any one of claims 1 to 3, wherein the pigment is in the form of water-insoluble polymer particles containing the pigment, and the average particle size thereof is 70 nm or more and 140 nm or less. The aqueous pigment dispersion according to any one of claims 1 to 4, which is used for inkjet recording. A method for producing an aqueous pigment dispersion, which comprises the following steps 1 to 3 and in which the acid value and neutralization degree of the water-insoluble polymer (A) in step 1 and the degree of cross-linking in step 3 satisfy the following condition 1.
Step 1: A step of neutralizing a water-insoluble polymer (A) having a carboxy group and having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with an alkali metal hydroxide. A structural unit derived from one or more carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, a (meth) acrylate monomer having an alkyl group having 1 or more and 22 or less carbon atoms, and an aryl group having 6 or more and 22 carbon atoms or less. It is a vinyl-based polymer containing a structural unit derived from one or more hydrophobic vinyl monomers selected from the aromatic group-containing monomers having.
Step 2: The neutralized water-insoluble polymer (A) obtained in Step 1 and the pigment are mixed and dispersed in an aqueous medium to obtain a pigment aqueous dispersion A. Step 3: The pigment obtained in Step 2. A step of cross-linking the aqueous dispersion A with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A). Here, the water-insoluble polyfunctional epoxy The compound is a polyhydric alcohol glycidyl ether compound having a hydrocarbon group having 3 or more and 8 or less carbon atoms, and the mass ratio of the pigment to the polymer dispersant (pigment / polymer dispersant) is 0.5 or more and 1.8. It is as follows.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is more than -30 mgKOH / g and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage of "the molar equivalent of the alkali metal hydroxide / the molar equivalent of the carboxy group of the water-insoluble polymer (A) having a carboxy group", and the degree of cross-linking is "the molar equivalent of the water-insoluble polyfunctional epoxy compound". It is a percentage of "molar equivalent number of epoxy groups / molar equivalent number of carboxy groups of the water-insoluble polymer (A) having a carboxy group" , and the water-insoluble polymer (A) is water-insoluble after neutralization. A method for producing a water-based ink, which comprises steps 1 to 3 according to claim 6 and the following steps 4.
Step 4: A step of mixing the aqueous pigment dispersion B obtained in Step 3 with an organic solvent to obtain an aqueous ink. The method for producing a water-based ink according to claim 7, further satisfying the following condition 2.
Condition 2: The value of [(crosslinking degree) / 100] × (acid value of the water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less.