JP2023097073A - Method for producing pigment water dispersion - Google Patents

Abstract

To provide a method for producing a pigment water dispersion which can obtain a recorded article that is excellent in storage stability, solvent resistance and scratch resistance, and a method for producing aqueous ink.SOLUTION: There are provide [1] a method for producing a pigment water dispersion which includes a step 1 of mixing and dispersing a pigment, an anionic polymer (P) having an acid value of 100-300 mgKOH/g and an aqueous medium, and obtaining a pigment pre-dispersion containing pigment particles having an average particle diameter of 160 nm or less, a step 2 of mixing a radical-polymerizable monomer with a water dispersion of the anionic polymer (Q), and obtaining a pre-emulsion, and a step 3 of mixing the pigment pre-dispersion obtained in the step 1 with the pre-emulsion obtained in the step 2, emulsion-polymerizing the mixture, and obtaining a water dispersion of core-shell type polymer particles containing a pigment; and [2] a method for producing aqueous ink including adding an organic solvent to the pigment dispersion obtained in the method.SELECTED DRAWING: None

Description

The present invention relates to a method for producing an aqueous pigment dispersion and a method for producing a water-based ink.

The inkjet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and deposited on a recording medium to obtain a printed matter on which characters or images are recorded. This system has many advantages such as easy full-color printing, low cost, use of plain paper as a recording medium, and non-contact with the recording medium, and thus is remarkably popular. In particular, from the viewpoint of weather resistance and water resistance of printed matter, the use of pigments as colorants has become mainstream.
On the other hand, pigment water dispersions and water-based pigment inks have the problem of poor storage stability due to coarse particles derived from the pigment or polymer because the pigment particles are dispersed in the liquid.
Since the inkjet recording method is suitable for recording a wide variety of products in small quantities, the range of application of recording media is expanding. Along with the expansion of the application range, in addition to printing on high water absorption recording media such as plain paper, in commercial printing using low water absorption recording media such as coated paper and non-water absorption resin film, There is a demand for improved solvent properties.
In addition, especially in non-water-absorbent recording media, the pigment particles contained in the water-based ink remain on the surface of the recording medium because the water-based ink does not permeate the inside of the recording medium, resulting in poor scratch resistance of the resulting recorded matter. There's a problem.

Various proposals have been made to improve the properties of aqueous pigment dispersions and water-based pigment inks.
For example, Patent Document 1 discloses crosslinked core-shell polymer particles containing a pigment as an aqueous dispersion that can be used in aqueous inks for inkjet recording and is excellent in improving print density, improving glossiness, and suppressing bronzing. Disclosed is an aqueous dispersion comprising crosslinked core-shell polymer particles in which both the portion and the shell portion are crosslinked and having a specific weight ratio between the pigment and the crosslinked core-shell polymer.
Patent Document 2 describes a method for producing a colored fine particle dispersion used in water-based ink for inkjet recording, which provides an image excellent in abrasion resistance and gloss even on a low water-absorbing recording medium. Dispersion 2 is obtained by removing the organic solvent from Dispersion 1 of an active agent, water and an organic solvent, and emulsion polymerization of Dispersion 2 and a polymerizable monomer is performed to obtain a dispersion of colored fine particles. is disclosed.

JP 2008-88427 A JP 2016-27150 A

The aqueous pigment dispersions of Patent Documents 1 and 2 have room for improvement in terms of storage stability, solvent resistance of images obtained, and abrasion resistance.
An object of the present invention is to provide a method for producing an aqueous pigment dispersion and a method for producing a water-based ink, which are capable of obtaining recorded matter having excellent storage stability, solvent resistance, and abrasion resistance.

In the production of the aqueous pigment dispersion, the present inventors previously prepared a specific pigment pre-dispersion and a pre-emulsion in which a radically polymerizable monomer was dispersed in a polymer, mixed the two together, and emulsified to polymerize them. We have found that the above problems can be solved.
That is, the present invention provides the following [1] and [2].
[1] A method for producing an aqueous pigment dispersion, comprising the following steps 1 to 3.
Step 1: A pigment, an anionic polymer (P) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, and an aqueous medium are mixed and dispersed to obtain a pigment pre-dispersion containing pigment particles having an average particle size of 160 nm or less. Step 2: A step of mixing a radically polymerizable monomer with an aqueous dispersion of the anionic polymer (Q) to obtain a radically polymerizable monomer pre-emulsion Step 3: The pigment pre-dispersion obtained in Step 1 and , the pre-emulsion of the radically polymerizable monomer obtained in step 2 is mixed, a radical polymerization initiator is added, and the radically polymerizable monomer is emulsion-polymerized to obtain an aqueous dispersion of core-shell type polymer particles containing a pigment. [2] A method for producing a water-based ink, wherein an organic solvent is added to the aqueous pigment dispersion obtained by the method described in [1] above.

According to the present invention, it is possible to provide a method for producing an aqueous pigment dispersion and a method for producing a water-based ink, which are capable of obtaining recorded matter having excellent storage stability, solvent resistance, and abrasion resistance.

[Method for producing aqueous pigment dispersion]
The method for producing an aqueous pigment dispersion of the present invention is characterized by comprising the following steps 1 to 3.
Step 1: A pigment, an anionic polymer (P) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, and an aqueous medium are mixed and dispersed to obtain a pigment pre-dispersion containing pigment particles having an average particle size of 160 nm or less. Step 2: A step of mixing a radically polymerizable monomer with an aqueous dispersion of the anionic polymer (Q) to obtain a radically polymerizable monomer pre-emulsion Step 3: The pigment pre-dispersion obtained in Step 1 and , the pre-emulsion of the radically polymerizable monomer obtained in step 2 is mixed, a radical polymerization initiator is added, and the radically polymerizable monomer is emulsion-polymerized to obtain an aqueous dispersion of core-shell type polymer particles containing a pigment. Process for Obtaining Body The aqueous pigment dispersion obtained by the method of the present invention can be used for water-based inks for flexographic printing, gravure printing, and inkjet recording, and is particularly preferably used for water-based inks for inkjet recording.
In this specification, the term "aqueous" means that water accounts for the largest proportion in the medium in which the pigment is dispersed. Also, "recording" is a concept including printing for recording characters and images.

The aqueous pigment dispersion and water-based ink obtained by the method of the present invention are excellent in storage stability, and when ink jet recording is performed on a recording medium, recorded matter having excellent solvent resistance and abrasion resistance can be obtained. Although the reason is not clear, it is considered as follows.
In the pigment pre-dispersion element according to the present invention, the pigment is dispersed with an anionic polymer (P) having a high acid value, and the pigment is coated with the anionic polymer (P). In this state, a pre-emulsion in which a radically polymerizable monomer is dispersed in an anionic polymer (Q) is added and emulsion polymerization is carried out. Polymerization of the radically polymerizable monomer thus formed proceeds to form a pigment particle in which the core portion is coated with a polymer formed by emulsion polymerization of the radically polymerizable monomer, and the shell portion covering the core portion is an anionic polymer (P). It is thought that polymer particles containing a pigment having a core-shell structure are formed. As a result, the outermost shell of the polymer particles encapsulating the pigment was coated with an anionic polymer (P) having a high charge repulsion and a high acid value, and the pigment was a polymer formed by emulsion polymerization of radically polymerizable monomers. It is considered that the storage stability of the obtained aqueous pigment dispersion is improved because of the coating.
Furthermore, in the method of the present invention, since the pigment is coated with a polymer formed by emulsion polymerization of a radically polymerizable monomer, the film-forming property after recording on the recording medium is improved, and the solvent resistance and abrasion resistance are improved. It is considered to have excellent properties.

<Step 1>
In step 1, a pigment, an anionic polymer (P) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, and an aqueous medium are mixed and dispersed to obtain a pigment pre-dispersion containing pigment particles having an average particle size of 160 nm or less. It is the process of obtaining a body.

[Pigment]
The pigment used in the present invention may be either an inorganic pigment or an organic pigment.
Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black ink. Examples of carbon black include furnace black, lamp black, acetylene black, channel black and the like. White inks include metal oxides such as titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide.
Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
The hue is not particularly limited, and for achromatic inks, achromatic pigments such as white, black, and gray can be used, and for chromatic inks, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. can also be used.
The pigments may be used alone or in combination of two or more.

[Anionic polymer (P)]
The anionic polymer (P) (hereinafter also simply referred to as "polymer (P)") used in the present invention is an anionic polymer having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, and has pigment dispersibility.
Examples of the polymer (P) include vinyl polymers obtained by addition polymerization of vinyl monomers, polyesters, polyurethanes, and the like. Among these, vinyl-based polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are preferred from the viewpoint of pigment dispersion stability, storage stability, and the like. The polymer (P) may be appropriately synthesized or may be a commercially available product.

The polymer (P) may be either a water-soluble polymer or a water-insoluble polymer, but is more preferably a water-insoluble polymer from the viewpoint of the storage stability of the aqueous pigment dispersion obtained and the water-based ink using the same. Here, the term "water-insoluble polymer" refers to a polymer whose dissolved amount is less than 10 g when dissolved in 100 g of water at 25°C after drying at 105°C for 2 hours and reaching a constant weight. The dissolution amount is the dissolution amount when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.
As the polymer (P), a vinyl polymer obtained by copolymerizing a monomer mixture containing (a-1) an anionic monomer and (a-2) a hydrophobic monomer is preferable. This vinyl polymer has a structural unit derived from component (a-1) and a structural unit derived from component (a-2).

[(a-1) anionic monomer]
Examples of (a-1) anionic monomers include carboxylic acid monomers and sulfonic acid monomers, with carboxylic acid monomers being more preferred.
The carboxylic acid monomer includes one or more selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, preferably (meth)acrylic acid. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[(a-2) Hydrophobic Monomer]
(a-2) The “hydrophobicity” of the hydrophobic monomer means that the amount of the monomer dissolved in 100 g of deionized water at 25° C. until saturation is less than 10 g.
(a-2) Specific examples of the hydrophobic monomer include those described in paragraphs [0020] to [0022] of JP-A-2018-83938. Among these, an alkyl (meth)acrylate having an alkyl group having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, an aromatic group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms is preferably one or more selected from aromatic group-containing monomers having ethyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, styrene, α-methylstyrene, and benzyl (meth) acrylate More preferably one or more selected.

[(a-3) nonionic monomer]
The polymer (P) may further contain (a-3) a structural unit derived from a nonionic monomer. The (a-3) nonionic monomer is a monomer having a high affinity with water and water-soluble organic solvents, such as a monomer containing a hydroxyl group or a polyalkylene glycol chain.
Specific examples of the component (a-3) include those described in paragraph [0018] of JP-A-2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n=1 to 30) (meth)acrylate and polypropylene glycol (n=2 to 30) (meth)acrylate is preferable.
For the above components (a-1) to (a-3), the monomer components contained in each component can be used singly or in combination of two or more.

(Content of each structural unit in polymer (P))
The content of structural units derived from components (a-1) to (a-3) in the polymer (P) determines the storage stability of the resulting aqueous pigment dispersion and aqueous ink using the same, and the storage stability of the resulting recorded matter. From the standpoint of improving solvent resistance and scratch resistance, the followings are used.
The content of structural units derived from component (a-1) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 45% by mass or less, and more It is preferably 40% by mass or less, more preferably 35% by mass or less.
The content of structural units derived from component (a-2) is preferably 45% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, and preferably 90% by mass or less, and more It is preferably 85% by mass or less, more preferably 80% by mass or less.
(a-3) When a structural unit derived from component is contained, the content thereof is preferably 10% by mass or less.
The mass ratio of component (a-1) to component (a-2) [component (a-1)/component (a-2)] is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably is 0.2 or more, and is preferably 0.8 or less, more preferably 0.6 or less, and still more preferably 0.5 or less.

(Production of polymer (P))
The polymer (P) can be produced by copolymerizing a mixture of the above monomer components (a-1) to (a-3) by a known polymerization method. A solution polymerization method is preferable as the polymerization method.
Solvents used in the solution polymerization method are not limited, but polar solvents such as water, aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone and the like are preferred. more preferred.
At the time of polymerization, a known polymerization initiator or polymerization chain transfer agent can be used, and water-soluble azo compounds such as 4,4'-azobis(4-cyanovaleric acid) can be used as the polymerization initiator. Mercaptan compounds such as 3-mercaptopropionic acid are preferred as the polymerization chain transfer agent.
Preferred polymerization conditions vary depending on the type of polymerization initiator, etc., but the polymerization temperature is preferably 50 to 90° C., and the polymerization time is preferably 1 to 10 hours. Moreover, the polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

The weight-average molecular weight of the polymer (P) is preferably 3, from the viewpoint of improving the storage stability of the aqueous pigment dispersion obtained and the water-based ink using the same, and the solvent resistance and abrasion resistance of the obtained recorded matter. 000 or more, more preferably 8,000 or more, still more preferably 10,000 or more, even more preferably 12,000 or more, still more preferably 15,000 or more, and preferably 100,000 or less, more preferably is 80,000 or less, more preferably 60,000 or less.
The acid value of the polymer (P) is 100 mgKOH/g or more from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same, and the solvent resistance and scratch resistance of the obtained recorded matter. Yes, preferably 120 mgKOH/g or more, more preferably 130 mgKOH/g or more, still more preferably 140 mgKOH/g or more, still more preferably 220 mgKOH/g or more, and 300 mgKOH/g or less, preferably 280 mgKOH/g Below, more preferably 260 mgKOH/g or less, still more preferably 250 mgKOH/g or less.
The weight average molecular weight and acid value of the polymer (P) are measured by the methods described in Examples.

(Production of pigment pre-dispersion)
In step 1, a pigment, a polymer (P), and an aqueous medium are mixed and dispersed to obtain a pigment pre-dispersion containing pigment particles having an average particle size of 160 nm or less.
The pigment and polymer (P) are as described above.
The aqueous medium used here is not particularly limited, but one containing water as a main component is preferred. An organic solvent may be further added to the aqueous medium from the viewpoint of improving the wettability to the pigment and the adsorption of the polymer (P) to the pigment. As the organic solvent, aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 8 carbon atoms, ethers, esters, etc. are preferable, ketones having 4 to 8 carbon atoms are more preferable, and methyl ethyl ketone is preferable. More preferred. When a vinyl-based polymer is synthesized as the polymer (P) by a solution polymerization method, the solvent used in the polymerization may be used as it is.
The content of water in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more, from the viewpoint of environmental friendliness.
When an organic solvent is added, it is preferable to remove the organic solvent by a known method before performing step 3.

At least part of the acid groups of the polymer (P) are preferably neutralized using a neutralizing agent. It is believed that this increases the charge repulsion generated after neutralization, suppresses aggregation of the pigment particles in the aqueous pigment dispersion and the water-based ink, and improves the dispersion stability of the pigment.
When neutralizing, it is preferable to neutralize so that the pH becomes 7 or more and 11 or less.
Examples of the neutralizing agent for the polymer (P) include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and water-soluble amines, preferably one selected from alkali metal hydroxides and ammonia. These are the above, more preferably alkali metal hydroxide, and still more preferably sodium hydroxide.
Moreover, the polymer (P) may be neutralized in advance.
The use equivalent of the neutralizing agent to the polymer (P) is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, from the viewpoint of improving dispersion stability. is 150 mol % or less, more preferably 120 mol % or less, still more preferably 100 mol % or less.
Here, the use equivalent of the neutralizing agent can be obtained by the following formula, where the polymer (P) before neutralization is defined as "polymer (P')".
Use equivalent of neutralizing agent (mol%) = [{adding mass of neutralizing agent (g) / equivalent of neutralizing agent} / [{acid value of polymer (P') (mgKOH/g) x polymer (P) Mass (g)} / (56 × 1,000)]] × 100

In the dispersion treatment in step 1, the pigment particles can be atomized to a desired particle size only by the main dispersion by shearing stress. , and preferably further dispersed.
As a dispersing machine used for pre-dispersion, generally used mixing and stirring devices such as anchor blades and disper blades can be used.
Means for imparting shear stress used for this dispersion include, for example, kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media type dispersers such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When dispersion treatment is performed using a high-pressure homogenizer, the average particle size of the pigment particles in the aqueous pigment dispersion can be adjusted by controlling the treatment pressure and the number of passes.
From the viewpoint of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

The resulting pigment predispersion is one in which pigment particles are dispersed in a water-based medium. Here, the form of the pigment particles is not particularly limited as long as at least the pigment and the polymer (P) form composite particles. Examples include a particle form in which the pigment is encapsulated in the polymer (P), a particle form in which the pigment is uniformly dispersed in the polymer (P), and a particle form in which the pigment is exposed on the surface of the polymer (P).
The mass ratio of the pigment to the total amount of the pigment and the polymer (P) in the pigment pre-dispersion [pigment/(pigment + polymer (P))] is such that the shell portion and the core portion are firmly bonded to form an aqueous pigment dispersion. From the viewpoint of increasing the solvent resistance of the Below, more preferably 0.98 or less, still more preferably 0.97 or less.

From the viewpoint of the dispersion stability of the pigment particles, the solid content concentration of the pigment pre-dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 18% by mass or more, and preferably 45% by mass or more. % by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.
The average particle size of the pigment particles in the pigment pre-dispersion is, from the viewpoint of improving the storage stability of the resulting aqueous pigment dispersion and water-based ink using the same, and the solvent resistance and abrasion resistance of the resulting recorded matter, It is 160 nm or less, preferably 140 nm or less, more preferably 120 nm or less, still more preferably 110 nm or less, and preferably 50 nm or more, more preferably 70 nm or more, still more preferably 80 nm or more.
The solid content concentration and average particle size of the pigment pre-dispersion are measured by the methods described in Examples.

<Step 2>
Step 2 is a step of mixing a radically polymerizable monomer with an aqueous dispersion of the anionic polymer (Q) to obtain a pre-emulsion of the radically polymerizable monomer.
In step 2, a pre-emulsion is obtained by previously dispersing the radically polymerizable monomer with the anionic polymer (Q), and in step 3, the pre-emulsion is mixed with the pigment pre-dispersion obtained in step 1, and a radical polymerization initiator is added. An aqueous dispersion of core-shell type polymer particles containing a pigment can be efficiently obtained by adding and emulsion polymerization without using a surfactant.

[Radical polymerizable monomer]
A radically polymerizable monomer is a monomer containing a radically polymerizable unsaturated double bond group. Examples of such groups include one or more selected from vinyl groups, allyl groups, acryloyl groups, methacryloyl groups, and the like.
The radically polymerizable monomer is preferably a hydrophobic monomer from the viewpoint of the storage stability of the resulting aqueous pigment dispersion. Such a hydrophobic radically polymerizable monomer has a hydrophobic group and a group having a radically polymerizable unsaturated double bond in its structure.
The hydrophobic radically polymerizable monomer includes one or more selected from (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol and aromatic group-containing monomers.

The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol is preferably a (meth)acrylate having an alkyl group having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, methyl (meth)acrylate, (meth)acrylates having a straight-chain alkyl group such as ethyl (meth)acrylate and butyl (meth)acrylate; (meth)acrylates having a branched-chain alkyl group such as 2-ethylhexyl (meth)acrylate; cyclohexyl (meth)acrylate, etc. (Meth)acrylates having an alicyclic alkyl group are more preferred, and at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate is further preferable.
The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, and at least one selected from styrene, 2-methylstyrene, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. is more preferred, and one or more selected from styrene and benzyl (meth)acrylate are even more preferred.
From the above viewpoints, the radically polymerizable monomer is one or more selected from (meth)acrylates having an alkyl group having 1 to 8 carbon atoms and vinyl monomers having an aromatic group having 6 to 22 carbon atoms. preferable.
As the radically polymerizable monomer, the above monomers may be used alone or in combination of two or more.

The amount of the radically polymerizable monomer is determined in the pre-emulsion in step 2 from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same, and the solvent resistance and abrasion resistance of the obtained recorded matter. , preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, further preferably 50% by mass or less is.

[Anionic polymer (Q)]
As the anionic polymer (Q) (hereinafter also referred to as "polymer (Q)"), the same anionic polymer (P) used in step 1 can be used.
That is, the polymer (Q) is preferably a vinyl polymer.
The vinyl polymer preferably contains (b-1) an anionic monomer-derived structural unit and (b-2) a hydrophobic monomer-derived structural unit, and further (b-3) a nonionic monomer-derived structural unit. It can contain structural units.
The specific examples and preferred examples of the above components (b-1) to (b-3), the contents and ratios of the structural units are the components (a-1) to (a-3) described in the column of the polymer (P). are the same as the specific examples, preferred examples, content and ratio of structural units.
The preferred weight average molecular weight and acid value of polymer (Q) are also the same as the preferred weight average molecular weight and acid value described in the column of polymer (P).

The method for producing the vinyl polymer is the same as the method for producing the polymer (P).
When the polymer (Q) is produced by solution polymerization, carboxyl groups are present on the surface of the polymer (Q) particles, so that the pH tends toward the acidic side, and viscosity increases and aggregation tend to occur. Therefore, it is preferable to neutralize using a neutralizing agent.
As the neutralizing agent for the polymer (Q), one or more selected from alkali metal hydroxides, water-soluble amines, and ammonia are preferred. That is, the polymer (Q) is preferably neutralized with one or more selected from alkali metal hydroxides, water-soluble amines and ammonia. From the viewpoint of solvent resistance, the neutralizing agent is more preferably ammonia or water-soluble amine, and still more preferably ammonia.
The amount of the neutralizing agent to be added is appropriately determined so that the pH of the polymer emulsion is in the range of 7.5 to 9.5, preferably 7.5 to 8.5.
The use equivalent of the neutralizing agent to the polymer (Q) is preferably 10 mol% or more, more preferably 15 mol% or more, from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same. , more preferably 20 mol % or more, and preferably 120 mol % or less, more preferably 100 mol % or less, still more preferably 90 mol % or less.
The difference between the acid value of the polymer (P) in step 1 and the acid value of the polymer (Q) in step 2 [acid value of polymer (P) - acid value of polymer (Q)] is the resulting aqueous pigment dispersion and its is preferably 170 mgKOH/g or less, more preferably 100 mgKOH/g or less, even more preferably 30 mgKOH/g or less, and 0 mgKOH/g, That is, it is even more preferable that the polymer (P) and the polymer (Q) have the same acid value.
Further, from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same, it is more preferable that the polymer (P) and the polymer (Q) are the same.

<Step 3>
In step 3, the pigment pre-dispersion obtained in step 1 and the radically polymerizable monomer pre-emulsion obtained in step 2 are mixed, and a radical polymerization initiator is added to emulsify the radically polymerizable monomer. This is a step of polymerizing to obtain an aqueous dispersion of core-shell type polymer particles containing a pigment.

[Radical polymerization initiator]
As the radical polymerization initiator (hereinafter, also simply referred to as “polymerization initiator”), those used in ordinary emulsion polymerization can be used. Specifically, persulfates such as potassium persulfate and ammonium persulfate; inorganic peroxides such as hydrogen peroxide; organic peroxides such as t-butyl hydroperoxide; azo polymerization initiator; redox polymerization initiation agents and the like. Among these, from the viewpoint of promoting the polymerization of the radically polymerizable monomer and improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same, and the solvent resistance and scratch resistance of the obtained recorded matter, A water-soluble azo polymerization initiator is preferred.

Examples of water-soluble azo polymerization initiators include anionic azo polymerization initiators and nonionic azo polymerization initiators such as hydroxy group-containing azoamide compounds. more preferred.
Examples of anionic azo polymerization initiators include azobiscarboxylic acids having 8 to 16 carbon atoms such as 1,1′-azobis (cyclohexane-1-carboxylic acid), 4,4′-azobis (4- cyanovaleric acid), 2,2'-azobis (4-cyanovaleric acid), 4,4'-azobis (2-cyanopentanoic acid) and other azobiscyanocarboxylic acids having 8 to 16 carbon atoms, and these Carboxy group-containing azo compounds such as salts can be mentioned. Among these, carboxy group-containing azo compounds are preferred, and at least one selected from azobiscyanocarboxylic acids having 10 to 14 carbon atoms and salts thereof is more preferred, and 4,4′-azobis(4-cyanovaleric acid ) and salts thereof are more preferred.

In step 3, polymerization chain transfer agents such as mercaptans and xanthogens can be used as long as they do not impair the effects of the present invention.
The amount of the polymerization initiator is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more with respect to 100 parts by mass of the radically polymerizable monomer. is 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less.

[Emulsion polymerization]
In the emulsion polymerization in step 3, the pigment pre-dispersion obtained in step 1 and the radical polymerizable monomer pre-emulsion obtained in step 2 are mixed, the polymerization initiator is added, and a surfactant is added. It can be done without addition.
At the time of emulsion polymerization, water may be added as a dispersion medium as necessary, and organic solvents such as alcohols and ketones may also be added as necessary. The proportion of water in the entire dispersion medium is preferably 50% by mass or more, more preferably 65% by mass or more, and even more preferably 75% by mass or more.
There are no particular restrictions on the conditions for emulsion polymerization, and the emulsion polymerization can be carried out in a conventional manner.
The polymerization temperature for emulsion polymerization varies depending on the type of polymerization initiator, but from the viewpoint of reactivity, it is preferably 55° C. or higher, more preferably 70° C. or higher, and from the viewpoint of the molecular weight distribution of the resulting polymer, it is preferably is 90° C. or less, more preferably 85° C. or less.
The polymerization atmosphere is preferably a nitrogen atmosphere or an inert gas atmosphere such as argon.
After the emulsion polymerization, it is preferable to age for 0.5 hours or more while maintaining the polymerization temperature.

The mass ratio of the radically polymerizable monomer to the pigment [radically polymerizable monomer/pigment] during emulsion polymerization is determined from the viewpoint of improving the storage stability and scratch resistance of the obtained aqueous pigment dispersion and the aqueous ink using the same. , preferably 1.0 or more, more preferably 1.3 or more, still more preferably 1.5 or more, and preferably 2.5 or less, more preferably 1.9 or less, still more preferably 1.7 or less is.

[Core-shell polymer particles containing pigment]
The pigment-containing core-shell type polymer particles obtained in step 3 have a structure in which the core portion contains (encloses) the pigment in a polymer formed by emulsion polymerization of radically polymerizable monomers in the pre-emulsion, and the shell portion However, it is believed that the anionic polymer (P) in the pigment pre-dispersion has a structure covering the core portion.
The glass transition temperature (Tg) of the core polymer constituting the pigment-containing core-shell polymer particles is preferably 40°C or higher, more preferably 50°C or higher, still more preferably 60°C or higher, and preferably 120°C. °C or lower, more preferably 100 °C or lower, still more preferably 90 °C or lower, and even more preferably 80 °C or lower.

The glass transition temperature can be calculated from the mass ratio of monomers in each polymer portion according to the following Fox formula.
1/Tg=( _W1 / _Tg1 )+( _W2 / _Tg2 )+...+( _Wm / _Tgm )
_W1 + _W2 +... _Wm =1
In the Fox formula, Tg is the glass transition temperature of the polymer, Tg ₁ , Tg _{2 ,} . W ₁ , W ₂ , . . . , W _m represent the mass ratio of each polymerized monomer.
As the glass transition temperature of each polymerization monomer in the Fox formula, for example, the values described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

The average particle diameter of the pigment-containing core-shell polymer particles is, from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion and the water-based ink using the same, and the solvent resistance and abrasion resistance of the obtained recorded matter, It is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 90 nm or more, and preferably 200 nm or less, more preferably 160 nm or less, still more preferably 130 nm or less.
The average particle size of the polymer particles is measured by the method described in Examples.

<Step 4>
Step 4 is a step of cross-linking the pigment-containing core-shell polymer particles obtained in Step 3 with an epoxy cross-linking agent to obtain pigment-containing crosslinked core-shell polymer particles.
Step 4 is an optional step, but forms a crosslinked structure in the shell portion of the core-shell polymer particles by subjecting a part of the anionic groups of the polymer constituting the pigment-containing core-shell polymer particles to a cross-linking treatment. As a result, it is believed that the polymer (Q), which is considered to be adsorbed on the surface of the core-shell polymer particles, can be strongly integrated with the core-shell polymer particles after step 3 is completed. Aggregation of particles is suppressed, and as a result, the storage stability of the resulting water dispersion and water-based ink is further improved, and the solvent resistance and abrasion resistance of the resulting recorded matter are also considered to be further improved.

[Epoxy cross-linking agent]
As the epoxy cross-linking agent, a polyfunctional epoxy compound having two or more epoxy groups in the molecule is preferable, a compound having two or more glycidyl ether groups is more preferable, and a polyhydric alcohol having a hydrocarbon group having 3 or more and 4 or less carbon atoms is used. More preferred are polyglycidyl ether compounds.
The epoxy equivalent weight (g/eq) of the epoxy cross-linking agent is preferably 90 or more, more preferably 100 or more, and preferably 300 or less, more preferably 200 or less.
Preferable examples of the cross-linking agent include one or more selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether.

The degree of crosslinking of the shell polymer in step 4 is preferably 10 mol % or more, more preferably 20 mol % or more, and still more preferably 30 mol %, from the viewpoint of improving the solvent resistance and scratch resistance of the obtained recorded matter. and preferably 70 mol % or less, more preferably 60 mol % or less, still more preferably 50 mol % or less.
Here, the degree of cross-linking is the apparent degree of cross-linking calculated from "the number of molar equivalents of epoxy groups in the epoxy cross-linking agent/the number of molar equivalents of anionic groups (carboxy groups) in the polymer before cross-linking".
The temperature of the cross-linking treatment is preferably 50° C. or higher, more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 92° C. or lower, from the viewpoint of cross-linking reaction efficiency.

(Content of each component in aqueous dispersion of core-shell type polymer particles containing pigment (pigment aqueous dispersion))
The content of each component in the aqueous pigment dispersion obtained by the method of the present invention determines the storage stability of the aqueous pigment dispersion obtained and the water-based ink using the same, and the solvent resistance and scratch resistance of the obtained recorded matter. From the viewpoint of improvement, it is as follows.

The solid content concentration of the aqueous pigment dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass. 30% by mass or less, more preferably 30% by mass or less.
The content of the pigment in the aqueous pigment dispersion is preferably 4% by mass or more, more preferably 6% by mass or more, still more preferably 7% by mass or more, and is preferably 25% by mass or less, more preferably 20% by mass. % by mass or less, more preferably 15% by mass or less.
The content of the (crosslinked) polymer in the aqueous pigment dispersion is preferably 6% by mass or more, more preferably 10% by mass or more, more preferably 12% by mass or more, and preferably 30% by mass or less and more It is preferably 25% by mass or less, more preferably 20% by mass or less.

[Method for producing water-based ink]
The method for producing a water-based ink of the present invention is a method of adding an organic solvent to the aqueous pigment dispersion obtained by the method of the present invention.
The organic solvent preferably has a boiling point of 110° C. or higher, preferably 150° C. or higher, and preferably 240° C. or lower, more preferably 220° C. or lower, from the viewpoint of improving the storage stability of the water-based ink. things are preferred. Specific examples include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.
Examples of polyhydric alcohols include ethylene glycol, propylene glycol, 1,2-alkanediols such as 1,2-butanediol, diethylene glycol, dipropylene glycol, 1,3-propanediol and 1,4-butanediol. .
Specific examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, diethylene glycol mono butyl ether and the like.

In the method for producing a water-based ink of the present invention, water, surfactants, and other additives such as humectants and viscosity modifiers can be mixed, if necessary.
Examples of surfactants include nonionic surfactants, anionic surfactants, amphoteric surfactants, etc. Nonionic surfactants are preferred, and polyether-modified silicone surfactants and acetylene glycol-based surfactants are preferred. etc. are more preferable.
Specific examples of polyether-modified silicone surfactants include PEG-9 dimethicone, PEG-9 PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone and the like.
Acetylene glycol surfactants include acetylene glycol having 8 to 22 carbon atoms and ethylene adducts of the acetylene glycol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol and Ethylene oxide adducts thereof are preferred.

(Content of each component in water-based ink)
The content of each component in the water-based ink obtained by the method of the present invention is as follows from the viewpoint of improving the storage stability and the solvent resistance and scratch resistance of the resulting recorded matter.
(Pigment content)
The content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and is preferably 12% by mass or less, more preferably 10% by mass. Below, it is more preferably 8 mass % or less.
(Content of pigment-containing (crosslinked) polymer particles)
The total content of the pigment-containing (crosslinked) polymer particles in the water-based ink is preferably 2% by mass or more, more preferably 4% by mass or more, and still more preferably 6% by mass. and preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.
The mass ratio (pigment/polymer) of the pigment and the polymer (the total amount of the polymer (P), the polymer (Q), and the polymer produced by polymerization of the radically polymerizable monomer) in the water-based ink is preferably 0.1 or more. It is more preferably 0.2 or more, still more preferably 0.3 or more, and preferably 2 or less, more preferably 1 or less, and still more preferably 0.8 or less.

(Organic solvent content)
The content of the organic solvent in the water-based ink is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass. % or less, more preferably 30 mass % or less.
(water content)
The water content in the water-based ink is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass. 75% by mass or less, more preferably 75% by mass or less.

(Inkjet recording method)
Examples of recording media for inkjet recording using the water-based ink according to the present invention include low water-absorbing recording paper such as plain paper and coated paper, and non-water-absorbing resin films such as PET film and polypropylene film. . The water-based ink according to the present invention is excellent in storage stability, and even when recording on a low-absorbent or non-absorbent recording medium, a recorded matter excellent in solvent resistance and abrasion resistance can be obtained.

In the following Preparation Examples, Production Examples, Examples and Comparative Examples, "parts" and "%" are "mass parts" and "mass%" unless otherwise specified. In addition, the measuring method of each physical property etc. is as follows.

(1) Measurement of weight-average molecular weight (Mw) of polymer A gel was prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent. By permeation chromatography [manufactured by Tosoh Corporation, GPC apparatus (HLC-8320GPC), columns manufactured by Tosoh Corporation (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H), flow rate: 0.5 mL / min], Monodisperse polystyrene kits with known molecular weights as standard materials [manufactured by Tosoh Corporation, PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40) , F-4, A-5000, A-500)].
A measurement sample was obtained by mixing 0.1 g of the polymer with 10 mL of the eluent in a glass vial, stirring at 25° C. for 10 hours, and filtering through a syringe filter (manufactured by Advantech, DISMIC-13HP, PTFE, 0.2 μm). used things.

(2) Measurement of acid value of polymer According to the neutralization titration method described in JIS K0070-1992, the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone: toluene = 1: 1 (volume ratio)] to measure the acid value of the polymer.

(3) Measurement of average particle size of pigment particles in pigment pre-dispersion and pigment-containing core-shell polymer particles in pigment aqueous dispersion Laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., trade name: ELS-8000) was used to measure the particle size by the dynamic light scattering method and calculated by the cumulant method analysis.
The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 90°, and 100 integration times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, the dispersion was weighed into a screw tube (manufactured by Maruem Co., Ltd., No. 5), water was added so that the solid content concentration was 2 × 10 ^-4 % by mass, and the mixture was stirred at 25°C for 1 hour. used things.

(4) Measurement of Solid Content Concentration of Dispersion 10.0 g of sodium sulfate was weighed to a constant weight in a desiccator into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of a sample was added thereto. After addition and mixing, it was weighed, held at 105° C. for 2 hours to remove volatiles, then left in a desiccator for an additional 15 minutes and weighed. The mass of the sample after removal of the volatile matter was defined as the solid content, and the mass of the added sample was divided to obtain the solid content concentration.

Preparation Example 1-1 (Preparation of anionic polymer P1)
31 parts of acrylic acid and 69 parts of styrene were mixed to prepare a monomer mixture. 5 parts of methyl ethyl ketone (MEK), 0.25 parts of 3-mercaptopropionic acid (polymerization chain transfer agent), and 10% of the above-mentioned monomer mixture were added and mixed in a reaction vessel, and the mixture was sufficiently replaced with nitrogen gas.
On the other hand, in the dropping funnel, the remaining 90% of the monomer mixture, 2.25 parts of the polymerization chain transfer agent, 75 parts of MEK, and an azo radical polymerization initiator (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V- 501,4,4′-azobis(4-cyanovaleric acid)) is added, and under a nitrogen atmosphere, the monomer mixture in the reaction vessel is heated to 77° C. while stirring, and added dropwise. The mixture in the funnel was added dropwise over 5 hours. After the completion of dropping, a solution obtained by dissolving 0.5 parts of the polymerization initiator in 5 parts of MEK was added, and further reacted at 77° C. for 2 hours. 900) was obtained.
Table 1 shows the results.

Preparation Examples 1-2 to 1-5 (Preparation of Anionic Polymers P2 to P5)
Solutions of anionic polymers P2 to P5 were prepared in the same manner as in Preparation Example 1-1, except that the amounts of acrylic acid, styrene, and 3-mercaptopropionic acid were changed as shown in Table 1. got Table 1 shows the results.

Preparation Example 2-1 (Preparation of water dispersion P1-D1 of anionic polymer P1)
The solution of the anionic polymer P1 obtained in Preparation Example 1 was dried under reduced pressure, and 80 parts of it was added with 255 parts of ion-exchanged water and a 5N sodium hydroxide aqueous solution (sodium hydroxide solid content: 16) as an alkali metal compound (neutralizing agent). .9%) was added and neutralized so that the ratio of the number of moles of sodium hydroxide to the number of moles of carboxyl groups of the anionic polymer P1 was 80 mol% (degree of neutralization: 80 mol%). . The resulting aqueous solution was heated at 90° C. for 5 hours while stirring at 150 rpm to obtain a water dispersion P1-D1 (solid concentration: 20%) of anionic polymer P1. Table 2 shows the results.

Preparation Examples 2-2 to 2-3, 2-6 to 2-9 (Preparation of aqueous dispersions of anionic polymers P1 to P5 (P1-D2, P1-D3, P2-D1 to P5-D1))
In Preparation Example 2-1, the anionic polymer water Dispersions P1-D2, P1-D3, P2-D1 to P5-D1 were obtained. Table 2 shows the results.

Preparation Example 2-4 (Preparation of Aqueous Dispersion P1-D4 of Anionic Polymer P1)
The anionic polymer P1 solution obtained in Preparation Example 1 was dried under reduced pressure, and 311 parts of ion-exchanged water and 9.3 parts of an aqueous ammonia solution (ammonia concentration: 25%) as a neutralizing agent were added to 80 parts thereof to obtain a water-insoluble Neutralization was carried out so that the ratio of the number of moles of ammonia to the number of moles of carboxyl groups in the polymer (P1) was 40 mol % (degree of neutralization: 40 mol %). The resulting aqueous solution was stirred at 150 rpm and heated at 90° C. for 5 hours to obtain a water dispersion P1-D4 (solid concentration: 20%) of anionic polymer P1. Table 2 shows the results.

Preparation Example 2-5 (Preparation of water dispersion P1-D5 of anionic polymer P1)
The anionic polymer P1 solution obtained in Preparation Example 1 was dried under reduced pressure, and 311 parts of ion-exchanged water and 17.8 parts of triethanolamine as a neutralizing agent were added to 80 parts of it to obtain carboxyl of the water-insoluble polymer (P1). Neutralization was carried out so that the ratio of the number of moles of triethanolamine to the number of moles of groups was 35 mol % (degree of neutralization: 35 mol %). The resulting aqueous solution was heated at 90° C. for 5 hours while being stirred at 150 rpm to obtain a water dispersion P1-D5 (solid concentration: 20%) of anionic polymer P1. Table 2 shows the results.

Production Example 1-1 (Step 1: Production of Pigment Pre-dispersion i-1)
Aqueous dispersion P1-D1 of anionic polymer P1 obtained in Preparation Example 2-1 26.3 parts, ion-exchanged water 538 parts, MEK 47 parts, cyan pigment (PB15:3, manufactured by DIC Corporation, C.I. 100 parts of Pigment Blue 15:3) was mixed and stirred for 60 minutes at 20° C. using a disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper) under the condition of rotating the disper blade at 7,000 rpm. The resulting mixture was subjected to 10 passes of dispersion treatment with a microfluidizer (manufactured by Microfluidics, trade name) at a pressure of 200 MPa to obtain a dispersion treated product.
MEK was distilled off from the obtained dispersed product under reduced pressure, a part of water was further removed, and a 25 mL needleless syringe ( Terumo Corporation) to remove coarse particles to obtain a pigment pre-dispersion i-1 containing pigment particles with a solid concentration of 22%.
The mass ratio of the pigment in the pigment particles [pigment/(pigment+anionic polymer (P))] was 0.95, and the average particle diameter of the pigment particles was 90 nm. Table 3 shows the results.

Production Examples 1-2 to 1-7 (Step 1: Production of pigment pre-dispersions i-2 to i-7)
Pigment particles were prepared in the same manner as in Production Example 1-1, except that in Production Example 1-1, the type and amount of the anionic polymer aqueous dispersion and the amounts of ion-exchanged water and MEK were changed as shown in Table 3. Pigment predispersions i-2 to i-7 containing were obtained. Table 3 shows the results.

Production Example 1-8 (Step 1: Production of pigment pre-dispersion i-8)
Reactive surfactant (KH-05, Daiichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon KH-05, ether sulfate ester salt, active ingredient concentration: 100%) 11.1 parts, ion-exchanged water 483 parts, MEK42 parts, cyan pigment (PB15:3, C.I. Pigment Blue 15:3) 100 parts were mixed, and using Disper (manufactured by Asada Iron Works Co., Ltd., trade name: Ultra Disper), Production Example 1-1 and Similarly, a pigment pre-dispersion i-8 (solid concentration: 22%) containing pigment particles dispersed with a reactive surfactant was obtained.
The mass ratio of the pigment in the pigment particles [pigment/(pigment+reactive surfactant)] was 0.90, and the average particle diameter of the pigment particles was 105 nm. Table 3 shows the results.

Production Example 1-9 (Step 1: Production of pigment predispersion i-9)
Aqueous dispersion P1-D1 of anionic polymer P1 obtained in Preparation Example 2-1 26.3 parts, ion-exchanged water 335 parts, MEK 335 parts, cyan pigment (PB15: 3, CI Pigment Blue 15: 3) 100 parts were mixed and stirred for 60 minutes at 20° C. using a disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper) under the condition of rotating the disper blade at 7,000 rpm. The resulting mixture was subjected to one-pass dispersion treatment at a pressure of 50 MPa using a microfluidizer (manufactured by Microfluidics, trade name) to obtain a dispersion treated product.
MEK was distilled off from the obtained dispersed product under reduced pressure, a part of water was further removed, and a 25 mL needleless syringe ( Terumo Corporation) to remove coarse particles to obtain a pigment pre-dispersion i-9 containing pigment particles with a solid concentration of 22%.
The mass ratio of the pigment in the pigment particles [pigment/(pigment+anionic polymer (P))] was 0.95, and the average particle diameter of the pigment particles was 188 nm. Table 3 shows the results.

Production Example 2-1 (Step 2: Production of pre-emulsion E-1)
15.3 parts of the aqueous dispersion P1-D1 of the anionic polymer obtained in Preparation Example 2-1 as the anionic polymer (Q) in a plastic container (acid value of anionic polymer P1: 240 mg KOH / g, degree of neutralization: 80 mol%, neutralizer: NaOH), 14.3 parts of cyclohexyl methacrylate as a radically polymerizable monomer, 6.1 parts of methyl methacrylate, and 15.3 parts of ion-exchanged water are mixed and shaken to prepare pre-emulsion E-1. got Table 4 shows the results.

Production Examples 2-2 to 2-12 (Step 2: Production of pre-emulsions E-2 to E-12)
In Production Example 2-1, as the anionic polymer (Q), the water dispersion of the anionic polymer and the radically polymerizable monomer were changed as shown in Table 4. In the same manner as in Production Example 2-1, Pre-emulsions E-2 to E-12 were obtained. Table 4 shows the results.

Production Example 2-13 (Step 2: Production of pre-emulsion E-13)
Except for mixing 0.6 parts of a reactive surfactant (trade name: Aqualon KH-05), 30.0 parts of ion-exchanged water, 14.3 parts of cyclohexyl methacrylate, and 6.1 parts of methyl methacrylate instead of the anionic polymer. obtained a pre-emulsion E-13 in the same manner as in Production Example 2-1. Table 4 shows the results.

Production Example 2-14 (Step 2: Production of pre-emulsion E-14)
Pre-emulsion E-14 was prepared in the same manner as in Production Example 2-1, except that 14.3 parts of cyclohexyl methacrylate, 6.1 parts of methyl methacrylate, and 30.6 parts of ion-exchanged water were mixed without using an anionic polymer. However, it separated into two phases as soon as the stirring was finished, and a stable pre-emulsion could not be obtained. Table 4 shows the results.

Production Example 3-1 (Step 3: Production of Aqueous Dispersion I-1 of Core-Shell Polymer Particles Containing Pigment)
In a separable flask, 60.3 parts of the pigment pre-dispersion i-1 obtained in Production Example 1-1 and 51.0 parts of the pre-emulsion E-1 obtained in Production Example 2-1 were added and stirred. , the nitrogen gas was sufficiently replaced.
On the other hand, 0.4 parts of 4,4′-azobis(4-cyanovaleric acid) (radical polymerization initiator), 4.2 parts of deionized water, and 0.2 parts of 25% aqueous ammonia solution are mixed and stirred in a glass vessel. By doing so, an aqueous solution of a radical polymerization initiator was obtained.
Add 4.8 parts of the resulting radical polymerization initiator aqueous solution to the dropping funnel, raise the temperature of the mixture in the separable flask container to 80° C. under a nitrogen atmosphere while stirring, and drop the radical polymerization initiator aqueous solution in the dropping funnel. was added dropwise over 3 hours to emulsion polymerize the radically polymerizable monomer in the pre-emulsion E-1.
After the dropping of the radical polymerization initiator aqueous solution was completed, the mixture was aged at 80°C for 1 hour, cooled to 25°C, filtered through a 5 μm filter (acetyl cellulose membrane, manufactured by Fuji Film Co., Ltd.), and the solid content concentration was adjusted with deionized water. The content was adjusted to 25% (pigment: 8.6%, polymer: 16.4%) to obtain an aqueous dispersion I-1 of core-shell type polymer particles containing pigment.

The obtained pigment-containing core-shell polymer particles have a structure in which the core portion contains (encloses) the pigment in a polymer obtained by emulsion polymerization of the radically polymerizable monomer in the pre-emulsion E-1, and the shell portion However, it has a structure in which the anionic polymer in the pigment pre-dispersion coats the core. The glass transition temperature (Tg) of the core polymer constituting the pigment-containing polymer particles was 72°C. Table 5 shows the results.
Here, the Tg of the core polymer is obtained by the above FOX formula from the Tg when each of the radically polymerizable monomers in the pre-emulsion E-1 is homopolymerized to form a homopolymer, and the composition ratio of the radically polymerizable monomers. calculated using
The Tg of the core polymer in the following production examples was calculated in the same manner as described above.

Production Examples 3-2 to 3-18, Comparative Production Examples 3-1 to 3-2 (Step 3: Aqueous Dispersions of Core-Shell Polymer Particles Containing Pigments I-2 to I-18, CI-1 to CI- 2 manufacturing)
Aqueous dispersion of pigment-containing core-shell polymer particles in the same manner as in Production Example 3-1, except that in Production Example 3-1, the type and blending amount of the pre-emulsion were changed as shown in Table 5 or Table 6. Forms I-2 to I-18, CI-1 to CI-2 were obtained. Tables 5 and 6 show the results.

Production Example 3-19 (Step 4: Production of Aqueous Dispersion I-19 of Core-Shell Crosslinked Polymer Particles Containing Pigment)
1,6-hexanediol diglycidyl ether (manufactured by Nagase ChemteX Corporation, product name: Denacol EX-212L , Epoxy equivalent: 135) 0.86 parts (an amount corresponding to 40 mol% of the total number of moles of the carboxyl groups of the anionic polymer (P) and the anionic polymer (Q)) was added. After that, the temperature was raised to 90° C. and the reaction was carried out for 2 hours. After the temperature was lowered to 25° C., the mixture was filtered through a 5 μm filter and the solid content concentration was adjusted to 25% with deionized water to obtain an aqueous dispersion I-19 of core-shell type crosslinked polymer particles containing a pigment.
In this core-shell type crosslinked polymer particle, only the shell portion was crosslinked (degree of crosslinking: 40 mol %), and the polymer Tg of the core portion was 72°C. At this time, the Tg and composition ratio of the components forming the crosslinked structure are not substituted into the FOX formula. Table 5 shows the results.

Comparative Production Example 3-3 (Production of Water Dispersion CI-3 of Polymer Particles Containing Pigment)
Pigment pre-dispersion i-8 dispersed with the reactive surfactant obtained in Production Example 1-8 in a separable flask 63.7 parts, pre-emulsion E-10 obtained in Production Example 2-10 51.0 After adding and stirring, the nitrogen gas was sufficiently replaced.
After that, in the same manner as in Comparative Production Example 3-1, an aqueous solution of a radical initiator was added dropwise, the radical polymerizable monomer was emulsion-polymerized, aged, filtered, and the solid content concentration was adjusted to 25% with ion-exchanged water. An aqueous dispersion CI-3 of polymer particles containing a pigment was obtained.
These pigment-containing polymer particles were not core-shell type polymer particles, and the Tg of the polymer constituting the particles was 72°C. Table 6 shows the results.

Comparative Production Example 3-4 (Production of Water Dispersion CI-4 of Core-Shell Polymer Particles Containing Pigment)
In a separable flask, 67.4 parts of the pigment pre-dispersion i-3 obtained in Production Example 1-3 and 51.0 parts of the pre-emulsion E-13 obtained in Production Example 2-13 were added and stirred. Sufficient nitrogen gas replacement was performed.
After that, in the same manner as in Comparative Production Example 3-1, an aqueous solution of a radical initiator was added dropwise, the radical polymerizable monomer was emulsion-polymerized, aged, filtered, and the solid content concentration was adjusted to 25% with ion-exchanged water. An aqueous dispersion CI-4 of core-shell type polymer particles containing a pigment was obtained.
The Tg of the core polymer of the core-shell type polymer particles was 72°C.
Table 6 shows the results.

Comparative Production Example 3-5 (Production of Water Dispersion CI-5 of Core-Shell Polymer Particles Containing Pigment)
In a separable flask, 67.4 parts of the pigment pre-dispersion i-3 obtained in Production Example 1-3 is filtered through a 5 μm filter, and the solid content is adjusted to 25% with ion-exchanged water. An aqueous dispersion CI-5 of polymer particles containing was obtained. Table 6 shows the results.
Comparative Production Example 3-5 is an example without step 3.

Comparative Production Example 3-6
Production Example 3-1 (Production of Water Dispersion CI-6 of Core-Shell Polymer Particles Containing Pigment)
In a separable flask, 60.3 parts of the pigment pre-dispersion i-1 obtained in Production Example 1-1 and 51.0 parts of pre-emulsion E-14 obtained in Production Example 2-14 were added and stirred. , the nitrogen gas was sufficiently replaced.
After that, an aqueous radical initiator solution was added dropwise in the same manner as in Comparative Production Example 3-1. After completion of dropping, the mixture was aged at 80° C. for 1 hour. After the temperature was lowered to 25° C., the contents were checked, and it was found that the unreacted monomer and the aqueous pigment dispersion were separated, and the polymerization had not progressed.
This example shows that emulsion polymerization does not proceed unless the anionic polymer (Q) is used during pre-emulsion production.

Water-based inks were prepared by the following method using the aqueous pigment dispersions obtained in Production Examples, and the storage stability, solvent (ethanol) resistance, and abrasion resistance were evaluated. Tables 5 and 6 show the results.

<Preparation of water-based ink>
In a 100 mL screw tube, 46.6 parts of the aqueous dispersion I-1 of core-shell type polymer particles containing the pigment obtained in Production Example 3-1, 4.0 parts of diethylene glycol monoisobutyl ether (iBDG), 20 parts of propylene glycol. 0 part, polyether-modified silicone activator (PEG-11 methyl ether dimethicone, manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-6011) 0.7 part and ion-exchanged water 28.7 parts were added, and the mixture was stirred at room temperature for 15 minutes. A mixed solution was obtained by stirring. Then, it was filtered through a filter with a pore size of 5.0 μm to obtain water-based ink 1 (pigment content: 4.0%).
For water-based inks 2 to 19 and 21 to 25, the amount of aqueous dispersion of pigment-containing (core-shell type) polymer particles and the amount of ion-exchanged water are such that the pigment content in the water-based ink is 4.0%. A water-based ink was prepared in the same manner as described above, except that .
A water-based ink was not prepared for the water dispersion CI-6.

(Method for evaluating storage stability)
The water-based inks 1 to 19 and 21 to 25 obtained above were stored in a constant temperature room at 70° C. for 7 days, and then the average particle size was measured. The average particle size change rate after storage at 70° C. for 7 days was calculated by the following formula (rounded down to the nearest decimal point), and the storage stability was evaluated according to the following evaluation criteria.
Average particle size change rate (%) = [(average particle size after storage/average particle size before storage) -1] x 100
(Evaluation criteria)
5: The absolute value of the average particle size change rate is less than 5%.
4: The absolute value of the average particle diameter change rate is 5% or more and less than 15%.
3: The absolute value of the average particle diameter change rate is 15% or more and less than 30%.
2: The absolute value of the average particle size change rate is 30% or more and less than 50%.
1: The absolute value of the average particle size change rate is 50% or more, or the water-based ink has lost fluidity and the average particle size cannot be measured.
If the evaluation result is 3 or more, there is no problem in actual use.

(Evaluation of printing on resin film (PVC))
An inkjet printer (manufactured by Ricoh Co., Ltd., product name: IPSiO GX 2500, piezo type) is filled with the water-based inks 1 to 19 and 21 to 25 obtained above, and a polyvinyl chloride (PVC) film (product name: 3M An A4 solid image was printed on ^TM Scotchcal ^TM graphic film IJ40-10R (white gloss). Then, it was dried in a drier at 80° C. for 5 minutes and allowed to stand for one day in an environmental room with a room temperature of 25° C. and a relative humidity of 50% to obtain a print for evaluation. Solvent resistance (ethanol) resistance and scratch resistance of the obtained prints were evaluated by the following methods.

(Evaluation method for solvent (ethanol) resistance)
Attach cotton (AATCC CROCKMETER SQUARES) moistened with 70% ethanol aqueous solution to Gakushin tester (manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd., product name: RT-300), and rub 100 reciprocations with a load of 200 g. did the test. Capture the scratched portion of the print as an image, binarize it with 8 bits and a threshold of 90 using Image J software, and use the following formula to calculate the ratio of the area where color remains after the scratch (color retention rate). was calculated, and the ethanol resistance was evaluated according to the following evaluation criteria.
Color retention rate (%) = [number of dots counted as black/(number of dots counted as black + number of dots counted as white)] x 100
(Evaluation criteria)
8: The color retention rate is 90% or more.
7: The color retention rate is 80% or more and less than 90%.
6: The color retention rate is 70% or more and less than 80%.
5: The color retention rate is 60% or more and less than 70%.
4: The color retention rate is 50% or more and less than 60%.
3: The color retention rate is 40% or more and less than 50%.
2: The color retention rate is 20% or more and less than 40%.
1: Color retention rate is less than 20%.
If the evaluation result is 4 or more, there is no problem in practical use, but 6 or more is preferable.

(Method for evaluating abrasion resistance)
A scratch test was performed on the evaluation printed matter obtained above using an AB-201 Sutherland type ink lab tester (manufactured by Tester Sangyo Co., Ltd.). A cellulose nonwoven fabric (trade name: BEMCOT M-3, manufactured by Asahi Kasei Corp.) as a friction material was rubbed 10 times (back and forth) with a weight of 900 g on the bottom surface (bottom surface area: 50 cm ² ). The condition of the printed surface of the rubbed printed material was visually confirmed and evaluated according to the following evaluation criteria.
(Evaluation criteria)
4: Scratches on the printed surface could not be confirmed, and there was no change in the surface condition of the printed surface before and after rubbing.
3: Scratches on the printed surface were observed, but the surface of the printed medium was not exposed.
2: Scratches on the printed surface were observed, and part of the surface of the printed medium was exposed.
1: The entire surface of the printing medium was exposed at the rubbed portion.
If the evaluation result is 3 or more, there is no problem in practical use, but 4 or more is preferable.

From Tables 5 and 6, water-based inks 1 to 19 of Examples are superior to water-based inks 21 to 25 of Comparative Examples in terms of storage stability, solvent resistance, and scratch resistance. I know you can.

Claims (8)

A method for producing an aqueous pigment dispersion, comprising the following steps 1 to 3.
Step 1: A pigment, an anionic polymer (P) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, and an aqueous medium are mixed and dispersed to obtain a pigment pre-dispersion containing pigment particles having an average particle size of 160 nm or less. Step 2: A step of mixing a radically polymerizable monomer with an aqueous dispersion of the anionic polymer (Q) to obtain a radically polymerizable monomer pre-emulsion Step 3: The pigment pre-dispersion obtained in Step 1 and , the pre-emulsion of the radically polymerizable monomer obtained in step 2 is mixed, a radical polymerization initiator is added, and the radically polymerizable monomer is emulsion-polymerized to obtain an aqueous dispersion of core-shell type polymer particles containing a pigment. the process of getting a body 2. The method for producing an aqueous pigment dispersion according to claim 1, wherein the anionic polymer (P) has a weight average molecular weight of 3,000 or more and 100,000 or less. The mass ratio of the pigment to the total amount of the pigment and the anionic polymer (P) [pigment/(pigment + anionic polymer (P)] is 0.82 or more and 0.99 or less. A method for producing an aqueous pigment dispersion. Claims 1 to 1, wherein the radically polymerizable monomer is one or more selected from a (meth)acrylate having an alkyl group having 1 to 8 carbon atoms and a vinyl monomer having an aromatic group having 6 to 22 carbon atoms. 4. A method for producing an aqueous pigment dispersion according to any one of 3. Production of the aqueous pigment dispersion according to any one of claims 1 to 4, wherein the anionic polymer (Q) is neutralized with one or more selected from alkali metal hydroxides, water-soluble amines, and ammonia. Method. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 5, wherein the glass transition temperature (Tg) of the core polymer constituting the pigment-containing core-shell polymer particles is 40°C or higher and 120°C or lower. . 7. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 6, further comprising the following step 4.
Step 4: A step of cross-linking the pigment-containing core-shell polymer particles obtained in Step 3 with an epoxy cross-linking agent to obtain pigment-containing core-shell crosslinked polymer particles. A method for producing a water-based ink, comprising adding an organic solvent to the aqueous pigment dispersion obtained by the method according to any one of claims 1 to 7.