JP2018104545A - Aqueous pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion that has an excellent storage stability to inhibit solidification of a pigment and a polymer in an ink discharge nozzle while maintaining water resistance in which the advantage of using a pigment lies, and has an excellent transfer resistance to prevent the occurrence of transfer to a contact part even when the printed matters are held in a state that the printed matters are laid one upon another, to provide a method for producing the aqueous pigment dispersion and to provide a method for producing an aqueous ink.SOLUTION: The aqueous pigment dispersion includes a pigment and a polymer dispersant. In the aqueous pigment dispersion, the polymer dispersant has a crosslinking structure produced by reacting (A) a water-insoluble polymer having a carboxyl group and having an acid number of 200 to 320 mgKOH/g with a water-insoluble polyfunctional epoxy compound; at least a part of the carboxyl group of the water-insoluble polymer (A) is neutralized with an alkali metal hydroxide; the mass ratio (the pigment/the polymer dispersant) is 0.5 to 1.8; and the value of [(100-a neutralization degree-a crosslinking degree)/100]×(an acid number of the water-insoluble polymer (A))is more than -30 mgKOH/g to not more than 130 mgKOH/g.SELECTED DRAWING: None

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 ink jet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and attached to a recording medium to obtain a printed matter on which characters and images are recorded. This method is easily spread at full color and is inexpensive, and has a widespread use because it has a number of advantages in that plain paper can be used as a recording medium and it is non-contact with the recording medium. In recent years, in particular, those using pigments as colorants have become mainstream from the viewpoint of the weather resistance and water resistance of recorded matter.

By the way, in the water-based pigment dispersion and the water-based ink using the same, the pigment surface is provided with a functional group having a high affinity for water and the pigment is added to the water-based medium or the ink vehicle without using the dispersant or using the polymer dispersant. It is used by being dispersed in. However, an ink using a pigment dispersion is difficult to maintain a dispersed state of pigment particles over a long period of time, unlike an ink using a dye that dissolves uniformly in an aqueous medium or an ink vehicle. There is a demand for improvement in dischargeability reduction due to adhesion of pigments and pigments.
For example, in Patent Document 1, for the purpose of obtaining a pigment dispersion excellent in water resistance, stability with time, etc., a carboxy group-containing thermoplastic is obtained after dispersing a pigment with a specific proportion of a carboxyl group-containing thermoplastic resin. An aqueous pigment dispersion in which the resin is crosslinked with a crosslinking agent and the crosslinking agent / carboxy group-containing thermoplastic resin (effective solid content weight ratio) is 1/100 to 50/100 is disclosed. Furthermore, it is disclosed that the thermoplastic resin is preferably neutralized with an organic amine having a boiling point of 200 ° C. or less, and the neutralization rate is preferably about 100 to 150%.

International Publication No. 1999/052966

The aqueous pigment dispersion of Patent Document 1 can bond a polymer dispersing agent for dispersing a pigment three-dimensionally with a crosslinking agent having a plurality of functional groups that react with a carboxy group in one molecule to obtain a strong film. Therefore, the ink stability can be secured to some extent at room temperature. However, when the ink is stored for a long time at a high temperature, 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 such as a printed matter using a low water-absorbing recording medium such as coated paper is held in a stacked state, transfer may occur at a contact portion with the printing portion.
The present invention has excellent storage stability that can suppress the solidification of the pigment and polymer at the ink discharge nozzle while maintaining the water resistance, which is an advantage of using the pigment, and also holds the printed matter in a stacked state. It is an object of the present invention to provide an aqueous pigment dispersion excellent in transfer resistance in which no transfer occurs at 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 an effective technique to strengthen the adhesive force between the pigment particles or between the pigment particles and the recording medium after the ink droplet contacts the recording medium.
Therefore, the present inventors have set the performance of water-based inks as follows: (i) In an environment where ink droplets come into contact with the surface of the recording medium and the ink vehicle disappears from the vicinity of the pigment particles as in printing, a strong film is formed. (Ii) Low viscosity in an environment where the non-volatile component remains even if the volatile component (for example, water) in the ink vehicle volatilizes, such as the ink discharge nozzle portion. We aimed to obtain the performance that can maintain the fluid state. 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 water-treated with a polymer dispersant obtained by crosslinking reaction with a water-insoluble polyfunctional epoxy compound. It has been found that an aqueous pigment dispersion dispersed in can achieve both of the above performances.
On the other hand, if the printed materials are held in a stacked state, transfer may occur at the contact portion with the printing portion. In particular, in a printed matter using a low water-absorbing recording medium such as coated paper, the ink hardly penetrates into the recording medium, and ink components such as pigment remain on the surface of the recording medium, so that transfer tends to occur. In order to increase the transfer resistance of the printed material, it is necessary to increase the adhesion between the pigment and the recording medium. For this 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 adhere or aggregate to the nozzle in the vicinity of the discharge nozzle, and the discharge property tends to deteriorate. In view of the above, there has been an urgent need to develop a technology capable of achieving both improved transfer resistance and improved discharge while maintaining water resistance.

The present invention provides the following [1] to [3].
[1] A water-based 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 an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. And
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 from 0.5 to 1.8. And
An aqueous pigment dispersion in which the acid value, the degree of neutralization, and the degree of crosslinking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of the water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the degree of neutralization is a percentage ratio of “number of mole equivalents of alkali metal hydroxide / number of mole equivalents of carboxy group of water-insoluble polymer (A) having carboxyl group”, and degree of crosslinking is “of water-insoluble polyfunctional epoxy compound. It is a percentage of “number of molar equivalents of epoxy group / number of molar equivalents of carboxy group of water-insoluble polymer (A) having carboxy group”.

[2] An aqueous pigment dispersion having the following steps 1 to 3, wherein the acid value and neutralization degree of the water-insoluble polymer (A) in step 1 and the crosslinking degree in step 3 satisfy the following condition 1. Production method.
Step 1: Step of neutralizing 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 alkali metal hydroxide Step 2: Neutralization obtained in Step 1 Step of obtaining the pigment water dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium Step 3: The pigment water dispersion A obtained in Step 2 is converted into a water-insoluble polyfunctional epoxy. Step of obtaining a water-based pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) by crosslinking with a compound. Here, the mass ratio of pigment to the polymer dispersant (pigment / polymer dispersant) Is 0.5 or more and 1.8 or less.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the acid value, the degree of neutralization, and the degree of crosslinking are as defined in [1] above.
[3] A method for producing a water-based ink, comprising the steps 1 to 3 according to the above [2] and the following step 4.
Step 4: Step of mixing water-based pigment dispersion B obtained in step 3 with an organic solvent to obtain a water-based ink. “Water-based” means that water accounts for the largest proportion in the medium in which the pigment is dispersed. Means that.

  According to the present invention, while maintaining the water resistance, which is an advantage of using a pigment, it has excellent storage stability capable of suppressing the solidification of the pigment and polymer at the ink discharge nozzle, and holds the printed material in a stacked state. However, it is possible to provide an aqueous pigment dispersion excellent in transfer resistance in which no transfer occurs at the contact portion, a manufacturing method thereof, and an aqueous ink manufacturing method.

[Water-based 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 an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. And
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 from 0.5 to 1.8. And
An aqueous pigment dispersion in which the acid value, the degree of neutralization, and the degree of crosslinking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of the water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the acid value, the degree of neutralization, and the degree of crosslinking are as described above.

The water-based pigment dispersion of the present invention exhibits excellent storage stability capable of suppressing the solidification of the pigment and polymer at the ink discharge nozzle while maintaining water resistance, and is excellent in the transfer resistance of the printed matter, and is excellent in printed matter. Therefore, it can be suitably used as an aqueous pigment dispersion for flexographic ink, gravure printing ink, or inkjet ink, and particularly preferably used as an aqueous pigment dispersion for inkjet ink.
Further, the water-based ink using the water-based pigment dispersion of the present invention is preferably used as a water-based ink for ink-jet recording because it is excellent in continuous discharge stability in the ink-jet recording method and transfer resistance of printed matter.

The reason why the water-based pigment dispersion and water-based ink of the present invention can exhibit the excellent effects as described above is not clear, but is considered as follows.
In the present invention, a polymer dispersant obtained by neutralizing at least a part of the water-insoluble polymer (A) having a carboxy group with an alkali metal hydroxide and cross-linking with a water-insoluble polyfunctional epoxy compound is used. A water-insoluble polymer having a carboxyl group-containing acid value of 200 mgKOH / g or more has a high affinity with water, and an alkali metal hydroxide can neutralize a part of the carboxyl group appropriately with a small amount. It is considered that the dispersion stability of the pigment obtained in the aqueous system is improved.
In addition, since the water-insoluble polyfunctional epoxy compound is present in the vicinity of the pigment surface and causes the crosslinking reaction to proceed, the polymer dispersant adsorbed on the pigment particles is more strongly adsorbed on the pigment particles, and is further crosslinked by the water-insoluble crosslinking agent. Since it has a structure, water insolubility is increased and the polymer is not easily detached from the pigment, so that the storage stability of the aqueous pigment dispersion and the aqueous 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, the nozzle can be increased even if the polymer amount is increased. Therefore, it is considered that printed matter having excellent transfer resistance can be obtained without deteriorating the discharge property.

<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 can also be used. If necessary, they can be used in combination with extender pigments.
Specific examples of the inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, bengara and chromium oxide, and pearlescent pigments. Particularly for black ink, carbon black is preferred. 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, isoindoindigo pigments And polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and selenium 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 preferred 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 types of products selected from Pigment Green are listed.
Examples of extender pigments include silica, calcium carbonate, and talc.
The above pigments can be used alone or in admixture 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 aqueous pigment dispersion and the aqueous ink. Here, “containing a pigment” means a form in which a pigment is encapsulated in a polymer dispersant having a crosslinked structure obtained by a reaction between a water-insoluble polymer (A) having a carboxy group and 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, or a form in which the polymer dispersant is attached to the surface of the pigment. A mixture of In these, the form in which the pigment was included in the polymer dispersing agent which has 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. Then, it is preferably formed in an aqueous medium by crosslinking reaction with a water-insoluble polyfunctional epoxy compound in a state where the pigment is dispersed. In this case, the polymer dispersant is not isolated, but the condition 1 is determined from the monomer composition of the water-insoluble polymer (A), the type and amount of alkali metal hydroxide, the type and amount of water-insoluble polyfunctional epoxy compound, The condition of the polymer dispersant can be defined as satisfying the condition 1.
In the present invention, the use of an alkali metal hydroxide as a neutralizing agent increases the charge repulsive force developed after neutralization, and suppresses the occurrence of thickening or aggregation when the aqueous pigment dispersion or aqueous ink is stored. However, it is considered that the storage stability is improved to meet the high reliability demanded in recent years.

(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 a pigment dispersant that exhibits a pigment dispersing action. And a function as a fixing agent for a recording medium.
This water-insoluble polymer (A) is water-insoluble even after neutralizing a part of its carboxy group, as well as in an unneutralized state. Here, “water-insoluble polymer” means that the water-insoluble polymer is not transparent when dispersed in water. Even if the water dispersion of the water-insoluble polymer appears to be transparent visually, it is determined that the water-insoluble polymer is water-insoluble if a Tyndall phenomenon is observed by observation with laser light or normal light.

The acid value of the water-insoluble polymer (A) is derived from a 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, Preferably it is 300 mgKOH / g or less, More preferably, it is 270 mgKOH / g or less. When the acid value is in the above range, the amount of the carboxy group and the 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 in which a polymer is dissolved or swollen in an appropriate organic solvent (for example, MEK) and titrated.

The presence 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) a state where it is adsorbed on the pigment, There are ii) a pigment-encapsulated (capsule) state containing a pigment, and (iii) a form in which no pigment is adsorbed. From the viewpoint of the dispersion stability of the pigment, in the present invention, the state (i) or (ii) is preferable, and (ii) the pigment-encapsulated state containing the pigment is more preferable.
Examples of the water-insoluble polymer used for obtaining the polymer dispersant according to the present invention include polyesters, polyurethanes, and vinyl polymers. From the viewpoint of improving the storage stability of the aqueous pigment dispersion and the aqueous ink, vinyl is used. A vinyl polymer obtained by addition polymerization of monomers (vinyl compound, vinylidene compound, vinylene compound) is preferable.

  Examples of the water-insoluble polymer (A) used in the present invention include (a) a carboxy group-containing vinyl monomer (hereinafter also referred to as “component (a)”) and (b) a hydrophobic vinyl monomer (hereinafter referred to as “(b)”. A vinyl polymer obtained by copolymerizing a vinyl monomer mixture (hereinafter also simply referred to as “monomer mixture”) containing “component” is also preferable. This vinyl 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 aqueous pigment dispersion and the aqueous 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, 2-methacryloyloxymethyl succinic acid, and the like, but one kind selected from acrylic acid and methacrylic acid The above is preferable.

[(B) Hydrophobic vinyl monomer]
(B) The hydrophobic vinyl monomer 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 aqueous pigment dispersion and the aqueous ink. Examples of the hydrophobic vinyl monomer include alkyl (meth) acrylates having an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 22 carbon atoms, and aromatic group-containing monomers.
As the alkyl (meth) acrylic acid ester, those having an alkyl group having 1 to 22 carbon atoms are preferable, and those having an alkyl group having 6 to 18 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 include acrylate, isodecyl (meth) acrylate, isododecyl (meth) acrylate, and isostearyl (meth) acrylate.
The “(meth) acrylate” means one or more 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 hetero atom, is preferable, and a styrene monomer or an aromatic group-containing (meth) acrylate. Is more preferable.
As the styrene monomer, styrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and styrene and α-methylstyrene are more preferable.
Moreover, as an aromatic group containing (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. are preferable, and benzyl (meth) acrylate is more preferable.
(B) 2 or more types of said monomers may be used for a hydrophobic monomer, and a styrene-type monomer and an aromatic group containing (meth) acrylic acid ester may be used together.

[(C) Macromonomer]
(C) A 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 to 100,000, and 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). The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
(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 using polystyrene as a standard substance by gel permeation chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent.
(C) The macromonomer is preferably an aromatic group-containing monomer-based macromonomer or a silicone-based macromonomer from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the aqueous pigment dispersion and the aqueous ink. More preferred are monomer-containing macromonomers.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomers described in the above (b) hydrophobic monomer, styrene and benzyl (meth) acrylate are preferred, and styrene is preferred. More preferred.
Specific examples of the styrenic macromonomer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.), and the like.
Examples of the silicone macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[(D) Nonionic monomer]
From the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the aqueous pigment dispersion and aqueous ink, the water-insoluble polymer (A) is further referred to as (d) a nonionic monomer (hereinafter referred to as “component (d)”). Can be used as a monomer component.
Component (d) includes hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; polypropylene glycol (n = 2 to 30, n is an average addition of an oxyalkylene group Number of moles, the same applies hereinafter) (meth) acrylate, polyethylene glycol (n = 2 to 30) (meth) acrylate and other polyalkylene glycol (meth) acrylate, methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate Alkoxypolyalkylene glycol (meth) acrylates such as phenoxy (ethylene glycol / propylene glycol copolymer) (n = 1-30, ethylene glycol: n = 1-29 therein) (meth) acrylate, 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 NK Esters M-20G, 40G, 90G, and 230G from Shin-Nakamura Chemical Co., Ltd., Bremer PE-90 from NOF Corporation, 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, 50PEP-300, 50POEP-800B, 43PAPE-600B Etc.
The components (a) to (d) can be used alone or in admixture of two or more.
As described above, the water-insoluble polymer (A) having a carboxy group used in the present invention has a structural unit derived from one or more (a) carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, and 1 carbon atom. Contains a structural unit derived from at least one (b) hydrophobic vinyl monomer selected from a (meth) acrylate monomer having an alkyl group of 22 or less and an aromatic group-containing monomer having an aryl group of 6 to 22 carbon atoms It is preferable to be a vinyl polymer.

(Content of each component or structural unit in the 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, it is 50 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, it is 80 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. Hereinafter, it is more preferably 25% by mass or less, and further 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, still more preferably 15% by mass or more, and preferably 40% by mass. Hereinafter, it is more preferably 35% by mass or less, and further 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, More preferably, it is 1.5 or less, More preferably, it is 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, and further preferably 1.0 or less.
Random structure is preferable for the bonding mode of each component of the component (a), the component (b), the component (c), and the component (d). Even when the components (a) to (d) are each composed of a plurality of types, it is preferable that all the monomer types are bonded in a random structure. Although performance can be achieved 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 employ a polymerization method known to obtain a block structure such as group transfer polymerization, living radical polymerization, living anion polymerization, or living cation polymerization.

(Production 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 bulk polymerization method, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
Although there is no restriction | limiting in particular in the solvent used by a solution polymerization method, A polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be used by mixing with water. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, esters such as ethyl acetate, and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water, and methyl ethyl ketone or a mixed solvent of water and water are preferable.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used.
As polymerization initiators, azo compounds such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), t-butylperoxyoctate, benzoyl peroxide, etc. Known radical polymerization initiators such as organic peroxides can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.
As the polymerization chain transfer agent, known chain transfer agents such as mercaptans such as octyl mercaptan and 2-mercaptoethanol, and thiuram disulfides can be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent, etc. 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 longer, more preferably 2 hours or longer, and preferably 20 hours or shorter, more preferably 10 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatographic method, extraction method and the like.

From the viewpoint of improving the productivity of the aqueous dispersion of pigment-containing polymer particles, 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. % 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 within the above range, the adsorptive power to the pigment is sufficient and the dispersion stability can be expressed.
In addition, the measurement of a number average molecular weight can be performed by the method as described in an Example.

[Production of pigment-containing polymer particles]
Water-insoluble polymer particles (pigment-containing polymer particles) containing a pigment can be efficiently produced by a method having the following steps 1 to 3 as an aqueous dispersion.
Step 1: Step of neutralizing 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 alkali metal hydroxide Step 2: Neutralization obtained in Step 1 Step of obtaining the pigment water dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium Step 3: The pigment water dispersion A obtained in Step 2 is converted into a water-insoluble polyfunctional epoxy. Step of obtaining a water-based pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) by crosslinking with a compound

(Process 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 to first dissolve the water-insoluble polymer (A) in an organic solvent and neutralize with an alkali metal hydroxide.
Although there is no restriction | limiting in the organic solvent in which water-insoluble polymer (A) is dissolved, C1-C3 aliphatic alcohol, ketones, ethers, esters, etc. are preferable, wettability to a pigment, dissolution of water-insoluble polymer From the viewpoint of improving the properties and the adsorption property of the water-insoluble polymer to the pigment, ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are more preferred, and methyl ethyl ketone is even more preferred.
When the water-insoluble polymer (A) is synthesized by a 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 the water resistance and storage stability of the resulting aqueous pigment dispersion and aqueous ink. It is preferable to neutralize so that the pH at this time is 7 or more and 11 or less.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, and sodium hydroxide and potassium hydroxide are preferable. Further, the water-insoluble polymer may be neutralized in advance.
In addition, neutralizing agents such as organic amines and organic phosphorus compounds are not preferable from the viewpoint of safety because of their specific odor and toxicity, and it is necessary to use a large amount in order to improve storage stability. Adverse effects such as excessively high ink viscosity occur.
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, more preferably 50% by mass or less, and 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 aqueous pigment dispersion and aqueous ink. More preferably, it is 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 number of molar equivalents of the alkali metal hydroxide by the number of molar equivalents of the carboxy group of the water-insoluble polymer (A), that is, “number of molar equivalents of alkali metal hydroxide / water-insoluble. It is a percentage (mol%) of the “number of mole equivalents of carboxy groups of the polymer (A)”. In the present invention, the degree of neutralization is calculated from the number of molar equivalents of the alkali metal hydroxide, and therefore exceeds 100 mol% when the alkali metal hydroxide is used in excess.

In step 1, in addition to the alkali metal hydroxide, a volatile basic compound can be used in combination. In the present invention, the volatile basic compound means an organic amine having a boiling point of 100 ° C. or less 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.
Although there is no restriction | limiting in particular about the usage-amount of a volatile basic compound, Preferably it is 5 mol% or more in conversion to the neutralization degree of the carboxy group of a water-insoluble polymer (A) even if it does not use at all or is used. More preferably, it is 10 mol% or more, and preferably 50 mol% or less, more preferably 30 mol% or less.
For the calculation of the neutralization degree of the present invention, only the amount of alkali metal hydroxide used is used, and the amount of volatile basic compound used is not used for the calculation of the neutralization degree of the present invention.

(Process 2)
Step 2 is a step of obtaining the pigment aqueous dispersion A by mixing and dispersing the neutralized water-insoluble polymer (A) obtained in Step 1 and the pigment in an aqueous medium.
Here, the “aqueous medium” means a medium in which water accounts for the maximum proportion in the medium in which the pigment is dispersed.

(Content of each component in the pigment mixture)
The content of each component in the pigment mixture in Step 2 is as follows from the viewpoint of water resistance, storage stability, dischargeability, and productivity of the aqueous pigment dispersion obtained.
The content of the pigment in the pigment mixture in 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 It is 30 mass% or less, More preferably, it is 20 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 mass% or less, More preferably, it is 7.0 mass% or less, More preferably, it is 6.0 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, still more 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. 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 from the viewpoint of low transferability and ink viscosity. It is 6 or more, more preferably 1.0 or more, and preferably 1.8 or less, more preferably 1.7 or less, and 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 only by the main dispersion until the desired particle size is reached, preferably the pigment mixture is pre-dispersed and further subjected to shear stress to perform the main dispersion. It is preferable to control the average particle size of the particles so as to have 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 predispersed, commonly used mixing and stirring devices such as anchor blades and disper blades can be used, and among them, a high-speed stirring and mixing device is preferable.

Examples of means for imparting the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer (manufactured by Microfluidic), a media-type disperser such as a paint shaker and a bead mill. Examples of commercially available media dispersers include Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd.), Picomill (manufactured by Asada Tekko Co., Ltd.), and the like. 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 this 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, still more 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. The organic solvent in the obtained pigment aqueous dispersion A is preferably substantially removed, but 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 heated and stirred before the organic solvent is distilled off.
The obtained pigment aqueous dispersion A is obtained by dispersing pigment-containing polymer particles in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited as long as the particles are formed at least from the pigment and the water-insoluble polymer (A). As described above, the pigment is included in the water-insoluble polymer (A). Preferably, it is in the form of particles made.

The non-volatile component concentration (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 preparation of the water-based ink. More preferably, it is 15 mass% or more, Preferably it is 30 mass% or less, More preferably, it is 25 mass% or less.
In addition, the solid content density | concentration of the pigment water dispersion A is measured by the method as described in an Example.
The average particle diameter of the pigment-containing polymer particles in the pigment aqueous dispersion A is preferably 50 nm or more, more preferably 60 nm or more, and still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving the discharge stability of the water-based ink. Further, it is preferably 200 nm or less, more preferably 170 nm or less, and still more preferably 140 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in the examples.

(Process 3)
In Step 3, from the viewpoint of improving the water resistance, storage stability, and dischargeability of the resulting aqueous pigment dispersion and aqueous ink, the pigment aqueous dispersion A obtained in Step 2 is treated with a water-insoluble polyfunctional epoxy compound (crosslinked). In this step, a water-based pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) is obtained.
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 particle is crosslinked to form a crosslinked structure in the surface layer portion of the pigment-containing polymer particle. 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 pigment surface.

(Water-insoluble polyfunctional epoxy compound)
When 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 water-based medium, The dissolved amount is preferably 50 g or less, more preferably 40 g or less, and still more preferably 35 g or less.
The water-insoluble polyfunctional epoxy compound preferably has a water content (mass ratio) of 50% or less, more preferably 40, from the viewpoints of water resistance, storage stability, and ejection properties of the resulting aqueous pigment dispersion and aqueous ink. % Or less, more preferably 35% or less. Here, the water content% (mass ratio) refers to the dissolution rate (%) when 10 parts by mass of an epoxy compound is dissolved in 90 parts by mass of water at room temperature of 25 ° C., more specifically, in the examples. It is measured by the method described.

As the water-insoluble polyfunctional epoxy compound, a compound having a plurality of epoxy groups in the molecule, preferably a glycidyl ether group is preferable, and a glycidyl ether compound of a polyhydric alcohol 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, from the viewpoint of easy reaction and the storage stability of the resulting crosslinked polymer. Preferably it is 2000 or less, More preferably, it is 1500 or less, More preferably, it is 1000 or less.
The number of epoxy groups of 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 a carboxy group to enhance the storage stability of the pigment-containing polymer particles. Is more preferable. Further, those having 5 or more epoxy groups in one molecule have poor market availability, 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 described 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 solubility 31%), glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether (water solubility 27). %), Polyglycidyl ethers such as sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether, and the like. Among these, one or two selected from trimethylolpropane polyglycidyl ether (water solubility 27%) and pentaerythritol polyglycidyl ether (water-insoluble) are preferable.

(Crosslinking 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 the pigment water dispersion A, and then the carboxy group of the water-insoluble polymer. A water-insoluble polyfunctional epoxy compound is partially reacted to form a cross-linked structure to obtain an aqueous pigment dispersion B in which a pigment is dispersed in an aqueous medium with a polymer dispersant obtained in the system. At that time, from the viewpoint of improving storage stability and transfer resistance while maintaining the water resistance of the water-based pigment dispersion and water-based ink obtained, an alkali metal is added in an amount satisfying the following condition 1, preferably further satisfying condition 2. A compound and a water-insoluble polyfunctional epoxy compound are used.

[Condition 1]
Condition 1 is that the value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of 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 “number of molar equivalents of alkali metal hydroxide / number of molar equivalents of carboxy groups of water-insoluble polymer (A) having carboxy groups”, and the degree of crosslinking is “water-insoluble It is the percentage (mol%) of the molar equivalent number of the epoxy group of the functional epoxy compound / the molar equivalent number of the carboxyl group of the water-insoluble polymer (A) having a carboxyl group.
Condition 1 indicates the amount of unneutralized carboxy group of the polymer dispersant in the pigment dispersion necessary for enhancing the ejection stability and the storage stability, and the acid value and neutralization of the water-insoluble polymer (A). The degree is determined by the degree of crosslinking. In other words, the condition 1 represents the acid value of the water-insoluble polymer (A) after neutralization and crosslinking.
If the value of Condition 1 exceeds -30 mgKOH / g and is 130 mgKOH / g or less, the charge amount on the pigment surface is sufficient when the pigment dispersion is prepared using the polymer, and the water content of the polymer dispersant is Insolubility is sufficient, and high ejection stability and storage stability can be expressed.
The value of Condition 1 is preferably −20 mgKOH / g or more, more preferably −10 mgKOH / g or more, further preferably −5 mgKOH / g or more, and preferably 120 mgKOH / g or less, more preferably 110 mgKOH / g or less. More preferably, it is 100 mgKOH / g or less.

[Condition 2]
Condition 2 is that the value of [(degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less.
Condition 2 indicates the degree of cross-linking necessary to increase storage stability. In other words, Condition 2 represents the acid value of the insoluble polymer (A) reduced by crosslinking. In order to improve the storage stability of the pigment particles in the aqueous pigment dispersion, it is preferable to satisfy the condition of the degree of crosslinking in addition to the above conditions.
If the value of Condition 2 is 30 mgKOH / g or more, the water insolubility of the polymer dispersant can be sufficiently increased, the adsorption to the pigment becomes strong, and the storage stability can be improved. On the other hand, if the value of condition 2 is 180 mgKOH / g or less, the hydrophobicity of the polymer dispersant is sufficient and can be strongly adsorbed to the pigment, and the amount of carboxy anion 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, further preferably 80 mgKOH / g or more, and preferably 170 mgKOH / g or less, more preferably 160 mgKOH / g or less, still more preferably Is 150 mgKOH / g or less.
In addition, since it is difficult to measure the actually reacted amount of the water-insoluble polyfunctional epoxy compound to be reacted with the carboxy group of the water-insoluble polymer (A), the epoxy group of the water-insoluble polyfunctional epoxy compound used is difficult to measure. The number of moles is expressed in terms of an acid value per 1 g of the water-insoluble polymer (A) used for dispersing the pigment.

The crosslinking reaction between the water-insoluble polyfunctional epoxy compound and the carboxy group of the polymer dispersant (water-insoluble polymer (A)) is performed after dispersing the pigment with the water-insoluble polymer (A).
The reaction temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, further preferably 60 ° C. or higher, still more preferably 65 ° C. or higher, and preferably 95 ° C. from the viewpoint of completion of the reaction and economy. It is 90 degrees C or less, More preferably, it is 90 degrees C or less.
In addition, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, still more preferably 2 hours or more, even more preferably 3 hours or more, from the same viewpoint as described above, and preferably It is 12 hours or less, more preferably 10 hours or less, still more preferably 8 hours or less, and even more preferably 6 hours or less.
The degree of crosslinking 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 crosslinking is the apparent degree of crosslinking calculated from the acid value of the polymer and the equivalent of the epoxy group of the crosslinking agent. That is, the degree of crosslinking is a percentage (mol%) of “number of molar equivalents of epoxy groups of water-insoluble polyfunctional epoxy compound / number of molar equivalents of carboxy groups of water-insoluble polymer (A)”.

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

The pH of the pigment aqueous dispersion B is preferably 8.0 or more. A high pH means that dissociation of the anionic group is promoted and the amount of charge of the pigment aqueous dispersion B is large, leading to an increase in the stability of the pigment aqueous dispersion B.
The pH of the pigment aqueous dispersion B is more preferably 8.5 or more, and the upper limit of the pH is not particularly limited, but 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 members of a printer or printing machine using the ink. Therefore, the pH of the pigment aqueous 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 20 ° C.
Although there is no restriction | limiting in particular in the measuring method of pH, The pH measuring method using a glass electrode is prescribed | regulated to JISZ8802, and this method is preferable from a simple and accurate point. Specifically, it is measured by the method described in the examples.

In the aqueous pigment dispersion of the present invention, 1 to 10% by mass of glycerin, polyethylene glycol or the like as a moisturizing agent may be blended to prevent drying, or additives such as an antifungal agent may be blended.
The above additives may be blended when the pigment is dispersed with the water-insoluble polymer (A), or may be blended after the pigment is dispersed or after the crosslinking reaction.

[Method for producing aqueous pigment dispersion]
The method for producing a water-based pigment dispersion of the present invention has the following steps 1 to 3, and the acid value and the degree of neutralization of the water-insoluble polymer (A) in step 1 and the degree of crosslinking in step 3 satisfy the following conditions. 1 is satisfied.
Step 1: Step of neutralizing 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 alkali metal hydroxide Step 2: Neutralization obtained in Step 1 Step of obtaining the pigment water dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium Step 3: The pigment water dispersion A obtained in Step 2 is converted into a water-insoluble polyfunctional epoxy. Step of obtaining a water-based pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) by crosslinking with a compound. Here, the mass ratio of pigment to the polymer dispersant (pigment / polymer dispersant) Is 0.5 or more and 1.8 or less.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the acid value, the degree of neutralization, and the degree of crosslinking are as defined above.

Details of Steps 1 to 3 and Condition 1 are as described above.
From the viewpoint of improving transfer resistance, the mass ratio of the pigment to the mass of the polymer dispersant (pigment / polymer dispersant) is from 0.5 to 1.8.
Here, the mass of the polymer dispersant is the total amount of the mass of the water-insoluble polymer (A) used for the production of the polymer dispersant and the mass of the water-insoluble polyfunctional epoxy compound.
The portion of the polymer dispersant of the present invention that contributes to the storage stability of the aqueous pigment dispersion is a carboxy anion, not an alkali metal ion that is a counter cation thereof. Therefore, in calculating the mass of the polymer dispersant, The portion of the alkali metal ion that is the counter cation is not counted, 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, and still more preferably 1. from the viewpoint of improving transfer resistance and practically low viscosity. 3 or less, and preferably 0.6 or more, more preferably 0.8 or more, and still more preferably 1.0 or more.

[Method for producing water-based ink]
The manufacturing method of the water-based ink of the present invention is a manufacturing method having the steps 1 to 3 and the following step 4 and preferably satisfying the following condition 2.
Step 4: Step of mixing water-based pigment dispersion B obtained in Step 3 and an organic solvent to obtain a water-based ink Condition 2: [(degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) Of 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 a water-based ink. However, 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 includes one or more organic solvents having a boiling point of 90 ° C. or higher, and is preferably an organic solvent having a boiling point weighted average value of 250 ° C. or lower. The weighted average value of the boiling point 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 alcohol, polyhydric alcohol alkyl ether, nitrogen-containing heterocyclic compound, amide, amine, sulfur-containing compound and the like. Among these, at least one selected from polyhydric alcohol and polyhydric alcohol alkyl ether is preferable, and is selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, and diethylene glycol diethyl ether. 1 or more types are more preferable, and 1 or more types chosen from glycerol, a triethylene glycol, and a trimethylol propane are still more preferable.

In the method for producing a water-based ink of the present invention, if necessary, a humectant, a wetting agent, a penetrating agent, a dispersant, a surfactant, a viscosity modifier, an antifoaming agent, a preservative, ordinarily used in a water-based ink. Various additives such as an antifungal agent and an antirust agent can be added, and further a filtration treatment with a filter or the like can be performed.
The content of each component of the water-based ink obtained by the production method of the present invention and the ink physical properties are as follows.

(Pigment content)
The content of the pigment in the aqueous ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and further preferably 2.5% by mass or more from the viewpoint of improving the printing density of the aqueous ink. is there. From the viewpoint of lowering the ink viscosity during solvent volatilization and improving the ejection stability and storage stability, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and even more 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, 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, and 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, 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, and more preferably 12% by mass or less from the viewpoint of dischargeability.

(Water-based ink properties)
From the viewpoint of improving the storage stability of the ink, the viscosity at 32 ° C. of the water-based ink is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and further preferably 5.0 mPa · s. s or more, and preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and even more preferably 7.0 mPa · s or less.
From the viewpoint of improving the storage stability of the ink, 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. And from a viewpoint of member tolerance and skin irritation, pH becomes like this. Preferably it is 11.0 or less, More preferably, it is 10.0 or less, More preferably, it is 9.5 or less.

[Inkjet recording method]
The aqueous ink of the present invention can be loaded in a known ink jet recording apparatus and ejected as ink droplets onto a recording medium to record an image or the like.
As the ink jet recording apparatus, there are a thermal type and a piezo type, and it is more preferable to use the ink as a piezo type aqueous ink for ink jet recording.
Examples of the recording medium that can be used include plain paper with high water absorption, coated paper and film with low water absorption. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper, and examples of the film include a polyester film, a polyvinyl chloride film, a polypropylene film, and a polyethylene film.
The water-based ink of the present invention is remarkably effective in transfer resistance on printed matter printed on a recording medium such as coated paper and film having low water absorption. 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 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., reagent special grade) and A solution obtained by dissolving lithium bromide (manufactured by Tokyo Chemical Industry Co., Ltd., reagent) so as to have a concentration of 60 mmol / L and 50 mmol / L was used as an eluent, and a gel chromatography method [GPC apparatus manufactured by Tosoh Corporation (HLC-8120GPC) was used. ), A column manufactured by Tosoh Corporation (TSK-GEL, α-M × 2), flow rate: 1 mL / min], using monodisperse polystyrene having a known molecular weight as a standard substance.

(2) Measurement of average particle diameter of water-insoluble polymer particles and pigment-containing polymer particles Measurement was performed by cumulant analysis 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 between incident light and a detector of 90 °, and the number of integrations of 100. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. It diluted with water so that a measurement density | concentration might be 5 * 10 < ^-3 >% (solid content concentration conversion).

(3) Measurement of solid content concentration of pigment aqueous dispersion In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate constant in a desiccator was weighed, and a sample of about 1. After adding 0 g and mixing, the sample was accurately weighed and maintained at 105 ° C. for 2 hours to remove volatiles, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removal of 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 Constant temperature at which room temperature was 25 ° C., 90 parts by mass of ion exchange water and 10 parts by mass of crosslinking agent were added to a glass tube (25 mmφ × 250 mmh), and the glass tube was adjusted to a water temperature of 25 ° C. It left still in the tank for 1 hour. Next, the glass tube was vigorously shaken for 1 minute, and then allowed to stand again in a thermostatic bath for 10 minutes. Subsequently, the undissolved material was weighed and the water solubility (mass%) was calculated.

<Preparation of water-insoluble polymer (A)>
Preparation Example 1
46 parts of methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent), 94 parts of benzyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd., reagent), styrene macromer (manufactured by Toagosei 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 NOF Corporation, trade name: Blemmer PP-800, propylene oxide average added mole number 13, terminal : Hydroxyl group) 40 parts were mixed to prepare a monomer mixture. In a reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent) and 10% of the monomer mixture were mixed and sufficiently substituted with nitrogen gas.
Meanwhile, in the dropping funnel, the remaining 90% of the monomer mixture, 0.27 part of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (trade name: V-65, manufactured by Wako Pure Chemical Industries, Ltd.) , 2,2′-azobis (2,4-dimethylvaleronitrile)) 2.2 parts of a mixed solution, and the temperature of the monomer mixture in the reaction vessel was increased to 65 ° C. with stirring in a nitrogen atmosphere, The mixed solution in the dropping funnel was dropped over 3 hours. After 2 hours at 65 ° C. from the end of the dropping, a solution in which 0.3 part of the polymerization initiator was dissolved in 5 parts of MEK was added, and further aged at 65 ° C. for 2 hours and at 70 ° C. for 2 hours. An average molecular weight: 11,000) solution was obtained.

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

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

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

<Manufacture of pigment aqueous dispersion A>
Production Example 1
25 parts of 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 5N aqueous sodium hydroxide solution (sodium hydroxide solid content 16.9%, 5.1 parts of 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 in the water-insoluble polymer a1 was 32% (medium (32% safety). Furthermore, 400 parts of ion-exchanged water was added, and 30 parts of a cyan pigment (CI Pigment Blue 15: 3, manufactured by DIC Corporation, trade name: TGR-SD) was added, and Disper (Asada Tekko Co., Ltd.) was added. Manufactured by Ultra Disper (trade name), and the Disper blade was stirred at 7,000 rpm for 60 minutes at 20 ° C.
The obtained mixture was subjected to 10-pass dispersion treatment with a microfluidizer (trade name, manufactured by Microfluidics) at a pressure of 150 MPa. After adding 250 parts of ion-exchanged water to the obtained dispersion and stirring, MEK was completely removed at 60 ° C. under reduced pressure, a part of water was further removed, and a 5 μm filter (acetylcellulose membrane, outer diameter). : Pigment water dispersion A1 having a solid content concentration of 20% by filtering with a 25 mL needleless syringe (made by Terumo Corporation) attached with 2.5 cm, manufactured by Fuji Film Co., Ltd., and removing coarse particles. Got. The results are shown in Table 2.

Production 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. A pigment water dispersion A2 was obtained in the same manner as in Production Example 1, except that 8.1 parts (neutralization degree 32%) was used instead of 0.1 part. The results are shown in Table 2.

Production Examples 3-6
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 changed to 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 polymers a3 to a7 obtained by drying the polymer solution obtained in Preparation Example shown in Table 2 under reduced pressure were used. Pigment water dispersions A7 to A11 were obtained in the same manner as in Production Example 1 except that the amount of sodium hydroxide aqueous 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 changed to the amount shown in Table 2. The results are shown in Table 2.

Production Examples 15-16
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 the 5N sodium hydroxide aqueous 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 polymer a8 or a9 obtained by drying the polymer solution obtained in Preparation Example shown in Table 2 under reduced pressure was used. Pigment water dispersions A17 and A18 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 19-20
In Production Example 2, pigment water dispersions A19 and A20 were obtained in the same manner as in Production Example 2 except that the neutralizing agent and amount shown in Table 2 were used instead of the 5N aqueous sodium hydroxide solution. The results are shown in Table 2.
KOH used as a neutralizing agent is a 5N potassium hydroxide aqueous solution (potassium hydroxide solid content 21.9%, manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration), and TEA is triethylamine (purity 99%). , Wako Pure Chemical Industries, Ltd., reagent grade).

Production Example 21
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: Monarch 880, manufactured by Cabot Specialty Chemicals) was used instead of 30 parts of cyan pigment in Production Example 2. The results are shown in Table 2.

<Production of water-based pigment dispersion B>
Example 1
100 parts of pigment aqueous dispersion A2 obtained in Production Example 2 (solid content 20%) are taken into a glass bottle with a screw cap, and trimethylolpropane polyglycidyl ether (as a crosslinking agent having three epoxy groups in one molecule) ( Nagase ChemteX Corporation, Denacol EX-321, molecular weight 302, epoxy equivalent 140 g / eq., Water content 27%) 0.96 part (crosslinking degree 40 mol%) was added and sealed, and 70 with stirring with a stirrer. Heat at 5 ° C. for 5 hours. After 5 hours, the temperature was lowered to room temperature, and filtered with a 25 mL needleless syringe (Terumo Corporation) attached with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation). An aqueous pigment dispersion B2 was obtained.

Examples 2-4
In Example 1, instead of the pigment water dispersion A2 obtained in Production Example 2, filtration was performed in the same manner as in Example 1 except that the pigment water dispersion obtained in Production Example shown in Table 3 was used. Pigment water dispersions B3, B4 and B7 were obtained.

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

Examples 5-16
In Example 1, as shown in Table 4, 100 parts (20% solid content) of the pigment aqueous dispersion A obtained in each production example was placed in a glass bottle with a screw cap, and the above-mentioned Denacol EX-321 was used as a crosslinking agent. The amount shown in Table 4 was added and 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 pigment water dispersions B10 to B20, B23, B25, and B27.

Example 17
In Example 1, 100 parts (solid content 20%) of the pigment aqueous dispersion A2 obtained in Production Example 2 is taken in a glass bottle with a screw cap, and pentaerythritol is used as a crosslinking agent having four epoxy groups in one molecule. Polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-411, epoxy equivalent 229 g / eq., Water-soluble) was added 1.57 parts (crosslinking degree 40%) and sealed, and stirred at 70 ° C. with a stirrer. 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 Pigment Water 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 amount of Denacol EX-321 shown in Table 4 was added and sealed. The mixture was heated at 70 ° C. for 5 hours while stirring with a stirrer. Then, it filtered similarly to Example 1 and obtained the pigment water dispersion B for a comparison.

Comparative Example 12
100 parts (solid content 20%) of pigment aqueous dispersion A2 obtained in Production Example 2 is taken into a glass bottle with a screw cap and polyglycerin polyglycidyl ether as a water-soluble crosslinking agent having two epoxy groups in one molecule. 1.25 parts (crosslinking degree 40%) of Nagase ChemteX Corporation, Denacol EX-521, epoxy equivalent 183 g / eq., Water-soluble) was added and sealed, and heated at 70 ° C. for 5 hours while stirring with a stirrer. did. Then, it filtered like Example 1, and obtained the pigment water dispersion B29 for a comparison.

<Evaluation test of water-based ink>
(Preparation of water-based ink)
Using each aqueous pigment dispersion obtained in Examples and Comparative Examples, the pigment concentration is 5% with respect to the entire aqueous ink, glycerin (made by Kao Corporation, concentrated glycerin for cosmetics) 5%, triethylene glycol (Wako Pure Chemical Industries, Ltd.) 7%, acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd., ethylene oxide 10 mol adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol) 0.5% Add ion-exchanged water, weigh so that the total amount becomes 100%, stir with a magnetic stirrer and mix well, and use a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, Fujifilm Corporation) A water-based ink was obtained by filtration through a needleless syringe having a capacity of 25 mL equipped with (manufactured by 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 (Ejectability evaluation)
The ink-jet printer (Seiko Epson Corporation, model number: EM-930C, piezo method) is loaded with the water-based ink obtained above, and the entire surface is printed on 100 sheets of XEROX plain paper 4200 (fine mode). The printed matter on the first sheet was observed, and the number of white lines (corresponding to the number of nozzles not ejected) was counted. Next, after performing the nozzle cleaning operation, another 100 sheets of solid printing is performed, the 100th printed material is observed again, the number of white lines generated is measured per discharge nozzle width, and discharged according to the following criteria. Sex was evaluated.
(Evaluation criteria)
A: No white line is generated in the 100th printed material and the 200th printed material B: No more than 2 white lines are generated in the 100th printed material and the 200th printed material C: In the 100th printed material or the 200th printed material 3-5 white lines generated D: 6 or more white lines generated on the 100th or 200th printed matter

Test 2 (storage stability evaluation)
Each water-based ink was sealed in a screw tube made by Marum Co., Ltd. and allowed to stand in a temperature-controlled room set at 20 ° C. and 60 ° C. for 1 week, and the average particle size was measured. The rate of increase was calculated.
Average particle diameter increase rate (%) = [(average particle diameter of ink after storage−average particle diameter of water dispersion used for ink preparation) / average particle diameter of water dispersion used for ink preparation] × 100
As the average particle size increase rate is smaller, aggregation is suppressed and storage stability is excellent.
The 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 gelation

Test 3 (Fixability evaluation)
Plain paper (Oce Corp., plain paper Engineering Bond paper) was attached to the bottom surface (1 inch × 1 inch) of a stainless steel weight weighing 460 g with double-sided tape. Next, the plain paper affixed to the bottom surface of the weight is placed on the printed surface of the plain paper printed material obtained in Test 1 so that the printed surface is 4 inches wide. Rubbing was performed 10 times. Thereafter, the value output as the black optical density of plain paper affixed 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.
If the optical density value is 0.05 or less, sufficient fixability to a low water-absorbing recording medium can be obtained and put to practical use, and 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 0.00. 10 or more

Test 4 (Water resistance evaluation)
Using the printing pattern used in Test 1 (evaluation of ejection properties), coated paper (Oji Paper Co., Ltd., OK top coat, water absorption: 4.9 g / m ² ) instead of plain paper was 4 cm x 4 cm. After printing a solid print pattern and leaving it for 24 hours in an environment of temperature 23 ° C. and humidity 50%, the printed surface is rubbed 10 times with a cotton swab soaked in ion exchange water (manufactured by Johnson & Johnson, 100% natural cotton). The water resistance test was conducted. In the evaluation, the print density of the rubbed portion was measured before rubbing, the print density of the rubbed portion after rubbing was measured again, and the water resistance was evaluated based on 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.
The 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)
The same printing pattern as used in Test 4 was printed on coated paper (Oji Paper Co., Ltd., OK Top Coat) under the same conditions as in Test 4 (water resistance evaluation), and the temperature was 23 ° C and the humidity was 50%. For 24 hours, coated paper (Oji Paper Co., Ltd., OK top coat, water absorption: 4.9 g / m ² ) and overlaid with 200 g of weight for 24 hours in an environment of 23 ° C. and 50% humidity. After being allowed to stand, the print density of the overlaid coated paper was measured and evaluated by the difference from the print density before being overlaid which had been measured in advance.
Print density difference = (print density after stacking)-(print density before stacking)
The closer the print density difference is to 0, the less ink transfer and the better the transfer resistance.
Transferability 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 inks of the examples are superior in terms of ejection performance, storage stability, fixability, water resistance, transfer resistance and performance balance compared to the water-based inks of the examples.

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 an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound. And
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 from 0.5 to 1.8. And
An aqueous pigment dispersion in which the acid value, the degree of neutralization, and the degree of crosslinking of the water-insoluble polymer (A) satisfy the following condition 1.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of the water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the degree of neutralization is a percentage ratio of “number of mole equivalents of alkali metal hydroxide / number of mole equivalents of carboxy group of water-insoluble polymer (A) having carboxyl group”, and degree of crosslinking is “of water-insoluble polyfunctional epoxy compound. It is a percentage of “number of molar equivalents of epoxy group / number of molar equivalents of carboxy group of water-insoluble polymer (A) having carboxy group”. The water-based pigment dispersion according to claim 1, further satisfying the following condition 2.
Condition 2: The value of [(degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less.   The water-based pigment dispersion according to claim 1 or 2, wherein the water-insoluble polyfunctional epoxy compound is a glycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.   The water-insoluble polymer (A) is a (meth) acrylate monomer having a structural unit derived from one or more carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, an alkyl group having 1 to 22 carbon atoms, and the number of carbon atoms The aqueous system according to any one of claims 1 to 3, which is a vinyl polymer containing a structural unit derived from at least one hydrophobic vinyl monomer selected from aromatic group-containing monomers having 6 to 22 aryl groups. Pigment dispersion.   The aqueous pigment dispersion according to any one of claims 1 to 4, which is for inkjet recording. A method for producing an aqueous pigment dispersion, comprising the following steps 1 to 3, wherein the acid value and neutralization degree of the water-insoluble polymer (A) in step 1 and the crosslinking degree in step 3 satisfy the following condition 1.
Step 1: Step of neutralizing 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 alkali metal hydroxide Step 2: Neutralization obtained in Step 1 Step of obtaining the pigment water dispersion A by mixing and dispersing the water-insoluble polymer (A) and the pigment in an aqueous medium Step 3: The pigment water dispersion A obtained in Step 2 is converted into a water-insoluble polyfunctional epoxy. Step of obtaining a water-based pigment dispersion B containing a polymer dispersant which is a crosslinked water-insoluble polymer (A) by crosslinking with a compound. Here, the mass ratio of pigment to the polymer dispersant (pigment / polymer dispersant) Is 0.5 or more and 1.8 or less.
Condition 1: The value of [(100−degree of neutralization−degree of crosslinking) / 100] × (acid value of water-insoluble polymer (A)) is more than −30 mgKOH / g and not more than 130 mgKOH / g.
Here, the acid value, the degree of neutralization, and the degree of crosslinking are as defined in claim 1. A method for producing a water-based ink, comprising the steps 1 to 3 according to claim 6 and the following step 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: [(crosslinking degree) / 100] × (acid value of water-insoluble polymer (A)) is 30 mgKOH / g or more and 180 mgKOH / g or less.