JP2019056090A - Method for producing pigment water dispersion - Google Patents

Abstract

To provide a method for producing a pigment water dispersion which is excellent in adhesion, bending resistance and light resistance of a printed matter when being printed on a non water absorptive printing medium by being contained in aqueous ink, and aqueous ink containing the pigment water dispersion.SOLUTION: There are provided a method for producing a pigment water dispersion which includes: a step 1 of mixing and polymerizing a radical polymerizable monomer (a), a radical polymerization initiator (a) and an irreversible chain transfer agent to obtain an oligomer dispersion agent; a step 2 of mixing the oligomer dispersion agent obtained in the step 1 with water to obtain a pigment water dispersion; and a step 3 of mixing the pigment water dispersion obtained in the step 2 with a radical polymerizable monomer (b) to seed polymerize the mixed substance, and coating the pigment to obtain a pigment water dispersion; and aqueous ink containing the pigment water dispersion.SELECTED DRAWING: None

Description

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

  In the field of commercial label printing used for product packaging printing and advertisement, etc., resin printing such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), PP (polypropylene), NY (nylon) From the viewpoints of reducing environmental load, energy saving, safety, and the like for media, it is required to use an inkjet printing method or a flexographic printing method as a printing method using water-based ink. In particular, the inkjet printing method is a printing method in which ink droplets are directly ejected from a very fine nozzle onto a printing medium and adhered to obtain a printed matter on which characters and images are recorded. The inkjet printing method is remarkably widespread because it is easy to make full color and inexpensive, and has many advantages such as non-contact with the substrate. For this reason, attempts have been made to utilize the ink jet printing method for resin-made print media. However, since resin-made print media are non-water-absorbing, conventional ink jet printing inks do not have sufficient adhesion to the print media, and attempts have been made to improve adhesion.

For example, Patent Document 1 discloses a method for producing a colored fine particle dispersion used in an aqueous ink for inkjet recording, which can obtain a printed matter having scratch resistance when printed on a recording medium. A method for producing a colored fine particle dispersion comprising emulsion-polymerizing a dispersion containing a functional monomer, a surfactant, a polymerization initiator, and water, wherein the pigment is a pigment having a quinacridone skeleton, and the surfactant A method for producing a colored fine particle dispersion is described in which the agent is an anionic or nonionic surfactant and the polymerization initiator is an anionic or nonionic azo compound.
In Patent Document 2, an acid group-free ink-jet ink or the like using a carbodiimide compound that achieves good dispersion stability in a state where a polyacryl side chain is introduced into a carbodiimide compound and a pigment is dispersed. An acid group-free radical polymerizable unsaturated monomer containing at least one (meth) acrylic monomer is polymerized in the presence of an acid group-containing chain transfer agent to contain an acid group at one end of the molecule. A carbodiimide compound into which a polyacryl chain is introduced is obtained by obtaining a polyacryl compound and reacting an acid group at one end of the molecule of the polyacryl compound with a carbodiimide group of a carbodiimide compound having a specific carbodiimide equivalent. Have been described.
Non-Patent Document 1 describes a technique in which titanium oxide is dispersed in water with a macro-RAFT copolymer, and then a monomer and a polymerization initiator are added to polymerize the monomer to encapsulate titanium oxide. Yes.

JP-A-2006-27151 JP 2006-225431 A

Hawkett et al., Langmuir 2008, 24, 2140-2150, “Pigment Encapsulation by Emulsion Polymerization Using Macro-RAFT Copolymers”

However, it has been found that the methods of Patent Documents 1 and 2 do not have sufficient adhesion and bending resistance to non-water-absorbing print media. Further, in the technique of Non-Patent Document 1, there are many exposures of the pigment surface and the light resistance is not sufficient. For this reason, further improvements in adhesion to non-water-absorbing print media, bending resistance, and light resistance are required.
The present invention provides a method for producing a pigment water dispersion excellent in the adhesion, folding resistance, and light resistance of a printed matter even when printed on a non-water-absorbing print medium by being contained in a water-based ink, and the pigment water dispersion. An object is to provide a water-based ink containing a body.
In this specification, “print” is a concept including printing and printing for recording characters and images, and “printed material” is a concept including printed materials and printed materials on which characters and images are recorded. . “Non-water-absorbing” is a concept including low water-absorbing and non-water-absorbing, and the printing medium has a water absorption of 0 g / m ² or more and 10 g / m at a contact time of 100 msec between the printing medium and pure water. Means ² or less. The amount of water absorption is measured as a transition amount at a contact time of 100 msec of pure water using an automatic scanning absorption meter (for example, KM500win manufactured by Kumagai Riki Kogyo Co., Ltd.) at 23 ° C. and a relative humidity of 50%. Is done. Further, “aqueous” means that water accounts for the largest proportion in the medium contained in the ink.

The present inventors have found that the above problem can be solved by dispersing the pigment with an oligomer dispersant obtained using a specific chain transfer agent and then coating the pigment with a polymer produced by seed polymerization. It was.
That is, the present invention provides the following [1] and [2].
[1] A method for producing a pigment aqueous dispersion, comprising the following steps 1 to 3.
Step 1: A step of obtaining an oligomer dispersant by mixing a radical polymerizable monomer (a), a radical polymerization initiator (a), and an irreversible chain transfer agent to obtain an oligomer dispersant Step 2: Obtained in Step 1 with a pigment Step of mixing the obtained oligomer dispersant and water to obtain a pigment water dispersion Step 3: Mixing the pigment water dispersion obtained in Step 2 and the radical polymerizable monomer (b) to seed polymerization And a step of obtaining a pigment water dispersion by coating the pigment [2] A water-based ink comprising the pigment water dispersion obtained by the production method according to the above [1].

  According to the present invention, a method for producing a pigment aqueous dispersion having excellent adhesion, bending resistance, and light resistance of a printed matter even when printed on a non-water-absorbent printing medium by being contained in a water-based ink, and the pigment An aqueous ink containing an aqueous dispersion can be provided.

[Method for producing pigment aqueous dispersion]
This invention is a manufacturing method of the pigment water dispersion which has the following processes 1-3.
Step 1: A step of obtaining an oligomer dispersant by mixing a radical polymerizable monomer (a), a radical polymerization initiator (a), and an irreversible chain transfer agent to obtain an oligomer dispersant Step 2: Obtained in Step 1 with a pigment Step of mixing the obtained oligomer dispersant (hereinafter also referred to as “oligomer dispersant” or “oligomer component”) with water to obtain a pigment water dispersion Step 3: Pigment water dispersion obtained in Step 2 And radical polymerization monomer (b) are mixed, and seed polymerization is performed, and the pigment is coated to obtain a pigment aqueous dispersion. In the present invention, “irreversible chain transfer agent” means “reversible addition”. “Chain transfer agent that does not cause Reversible Addition Fragmentation Chain Transfer”.
In the present invention, “oligomer” means a polymer having a number average molecular weight of 300 to 6,000 and a weight average molecular weight of 700 to 20,000. In addition, the measurement of a number average molecular weight and a weight average molecular weight is measured by the gel permeation chromatography method as described in an Example.
Further, the “coating” in the pigment aqueous dispersion means that the entire surface of the pigment particles may not necessarily be coated with the polymer as long as the effect of the present invention is achieved. However, the adhesion, the bending resistance, and the light resistance are improved. From the viewpoint of improvement, it is preferable that the entire surface of the pigment particle is coated.

The pigment aqueous dispersion according to the present invention contains a pigment, an oligomer component containing a structural unit derived from the radical polymerizable monomer (a), and a polymer component containing a structural unit derived from the radical polymerizable monomer (b). Fine particles are dispersed in water as a main medium.
The form of the pigment fine particles includes a particle form in which the pigment is encapsulated in the polymer particles (so-called capsule type), a particle form in which the pigment is uniformly dispersed in the polymer particles, and the like. Among these, from the viewpoint of improving adhesion, bending resistance and light resistance, a particle form in which a pigment is included in polymer particles (so-called capsule type) is preferable.

The pigment aqueous dispersion obtained by the production method of the present invention is contained in a water-based ink (hereinafter, also simply referred to as “ink”), so that even when printed on a non-water-absorbing print medium, the adhesion and resistance of the printed matter. There exists an effect that it is excellent in bendability and light resistance. The reason is not clear, but it is thought as follows.
First, the oligomer dispersant obtained in Step 1 of the present invention is polymerized using an irreversible chain transfer agent, and has a low molecular weight and a relatively wide molecular weight distribution. Therefore, it is excellent in the dispersibility with respect to a pigment, and is excellent also in the absorptivity of the radically polymerizable monomer used for seed polymerization in the following process 3. Then, after the oligomer dispersing agent having a low molecular weight and a wide molecular weight distribution is adsorbed on the surface of the pigment by the step 2, the oligomer dispersing agent on the pigment surface becomes a base material and absorbs the radical polymerizable monomer by the step 3 to perform seed polymerization. It is assumed that a polymer having a relatively high molecular weight is produced and the pigment is coated with the polymer.
When the printed material is bent, the pigment-polymer interface with low adhesion strength usually breaks down. In the present invention, since the oligomer component in the vicinity of the pigment has a low molecular weight and a relatively wide molecular weight distribution, the pigment follows the large deformation and maintains the adhesion to the oligomer component. Therefore, the bending resistance is greatly improved.
Furthermore, the oligomer component obtained in step 1 plasticizes the high molecular weight polymer component obtained in step 3, so that the polymer component also deforms following the surface form of the print medium, so that the adhesion of the printed matter is increased. Is thought to improve.
Further, in the present invention, since the pigment fine particles have a form in which the surface of the pigment particles is coated with a polymer, the pigment retains the adhesiveness with the polymer and the exposure of the pigment surface is suppressed. For this reason, it is considered that the pigment is inhibited from being decomposed by light and the light resistance is improved.

<Step 1>
Step 1 is a step in which a radical polymerizable monomer (a), a radical polymerization initiator (a), and an irreversible chain transfer agent are mixed and polymerized to obtain an oligomer dispersant. Thereby, an oligomer dispersant having a low molecular weight and a relatively wide molecular weight distribution can be obtained.

[Radically polymerizable monomer (a)]
The radical polymerizable monomer (a) used in the present invention is a group having an unsaturated double bond capable of radical polymerization, and includes a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. Examples include monomers having one or more selected. The radical polymerizable monomer (a) is a hydrophilic monomer (a-1) (hereinafter simply referred to as “monomer (a)” from the viewpoint of improving the dispersibility of the oligomer dispersant, adhesion, folding resistance and light resistance. -1) "). Examples of the monomer (a-1) include a monomer having an ionic functional group and a nonionic hydrophilic monomer having no ionic functional group, preferably a monomer having an ionic functional group.
In the present invention, the term “hydrophilic” means that the monomer can be dissolved in 100 g of ion-exchanged water at 25 ° C. in an amount of 10 g or more, and the dissolution amount is preferably 50 g or more. “Hydrophilic” in the case of an ionic functional group monomer means that the amount dissolved in 100 g of ion-exchanged water at 25 ° C. in a state in which the ionic functional group is neutralized is within the above range.

Examples of the monomer having an ionic functional group include a monomer having a cationic group and a monomer having an anionic group. From the viewpoint of the dispersibility of the oligomer dispersant, the adhesion, bending resistance and light resistance are improved. From the viewpoint, a monomer having an anionic group is preferable. Examples of the anionic group include dissociation of a carboxy group (—COOM ¹ ), a sulfonic acid group (—SO ₃ M ¹ ), a phosphoric acid group (—OPO ₃ M ¹ ₂ ), and the like to release hydrogen ions. Examples thereof include groups exhibiting acidity, or dissociated ionic forms thereof (—COO ⁻ , —SO ₃ ⁻ , —OPO ₃ ²⁻ , —OPO ₃ ⁻ M ¹ ), and the like. In the above chemical formula, M ¹ represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium.
Examples of the monomer having a carboxy group include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and 3-sulfopropyl (meth) acrylate.
Examples of the monomer having a phosphoric acid group include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, and the like.
Among these, preferably a monomer having a carboxy group, more preferably at least selected from (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and 2-methacryloyloxymethyl succinic acid. It is 1 type, More preferably, it is (meth) acrylic acid.
In this specification, “(meth) acrylic acid” means at least one selected from acrylic acid and methacrylic acid, and “(meth) acrylate” is at least one selected from acrylate and methacrylate. “(Meta)” in the following is also synonymous.

  The nonionic hydrophilic monomer is preferably a hydroxyalkyl (meth) acrylate such as 2-hydroxyethyl (meth) acrylate or 3-hydroxypropyl (meth) acrylate; polyethylene glycol (from the viewpoint of improving bending resistance; n = 2 to 30, n represents the average number of moles added of the oxyalkylene group (the same applies hereinafter) and polyalkylene glycol (meth) acrylates such as (meth) acrylate and polypropylene glycol (n = 2 to 30) (meth) acrylate; Alkoxypolyalkylene glycol (meth) acrylates such as methoxypolyethylene glycol (n = 1-30) (meth) acrylate; phenoxy (ethylene glycol / propylene glycol copolymer) (n = 1-30, ethylene glycol therein: n = 1 29) (meth) is at least one selected from acrylate, more preferably a polyalkylene glycol (meth) acrylate.

  Specific examples of commercially available nonionic hydrophilic monomers include NK ester M-20G, 40G, 90G, 230G, etc. (above, trade names of Shin-Nakamura Chemical Co., Ltd.), BLEMMER PE- 90, 200, 350, etc., Blemmer PME-100, 200, 400, etc., Blemmer PP-500, 800, 1000, etc., Blemmer AP-150, 400, 550, etc., Blemmer 50 PEP-300, Blemmer 50POEP-800B, Blemmer 43PAPE-600B, etc. (above, trade name of NOF Corporation) are mentioned.

From the viewpoint of the dispersibility of the oligomer dispersant, and the viewpoint of improving adhesion, bending resistance and light resistance, the radical polymerizable monomer (a) is further composed of a hydrophobic monomer (a-2) (hereinafter simply referred to as “ Monomer (a-2) ”) is preferably included.
In the present invention, “hydrophobic” means that the amount of the monomer that can be dissolved in 100 g of ion-exchanged water at 25 ° C. is less than 10 g. The amount of the hydrophobic monomer dissolved in 100 g of ion-exchanged water at 25 ° C. is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of the adsorptivity of the oligomer dispersant to the pigment.
The monomer (a-2) has a hydrophobic group and a group having an unsaturated double bond capable of radical polymerization in its structure. Examples of the hydrophobic group include one or more selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group, preferably selected from an aliphatic hydrocarbon group and an aromatic hydrocarbon group. One or more types. Examples of the group having an unsaturated double bond capable of radical polymerization include the same as those described above for the monomer (a-1), and a vinyl group is preferable.

The monomer (a-2) is preferably at least one selected from (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol and an aromatic group-containing monomer.
The (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 10 carbon atoms, more preferably an alkyl having 1 to 10 carbon atoms. Having an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, (Meth) acrylate having a linear alkyl group such as stearyl (meth) acrylate; isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isopentyl (meth) acrylate, isooctyl (meth) acrylate, It has a branched chain alkyl group such as isodecyl (meth) acrylate, isododecyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate (meta Acrylate; having an alicyclic alkyl group, such as cyclohexyl (meth) acrylate (meth) acrylate.
Among these, from the viewpoint of dispersibility of the oligomer dispersant, it is preferably at least one selected from methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. More preferably, it is methyl (meth) acrylate.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms which may have a substituent containing a hetero atom, more preferably a styrene monomer and an aromatic group-containing monomer. One or more selected from (meth) acrylates.
Examples of the styrene monomer include styrene and 2-methylstyrene, and examples of the aromatic group-containing (meth) acrylate include benzyl (meth) acrylate and phenoxyethyl (meth) acrylate. Among these, Preferably it is 1 or more types chosen from styrene and benzyl (meth) acrylate, More preferably, it is styrene.

  In the total amount of the radical polymerizable monomer (a), the total content of the monomers (a-1) and (a-2) is based on the viewpoint of dispersibility of the oligomer dispersant, as well as adhesion, bending resistance and light resistance. From the viewpoint of improving, preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 100% by mass, that is, only from the monomers (a-1) and (a-2). It is preferable to become.

The content of the monomer (a-1) is preferably within the total amount of the radically polymerizable monomer (a) from the viewpoint of dispersibility of the oligomer dispersant, and from the viewpoint of improving adhesion, bending resistance and light resistance. 15% by mass or more, more preferably 30% by mass or more, further preferably 45% by mass or more, still more preferably 50% by mass or more, and from the same viewpoint as described above, preferably 90% by mass or less, more preferably Is 80% by mass or less, more preferably 75% by mass or less, still more preferably 70% by mass or less, still more preferably 65% by mass or less, and still more preferably 60% by mass or less.
The content of the monomer (a-2) is preferably within the total amount of the radical polymerizable monomer (a) from the viewpoint of dispersibility of the oligomer dispersant, and from the viewpoint of improving adhesion, folding resistance and light resistance. 10% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, still more preferably 30% by mass or more, still more preferably 35% by mass or more, and still more preferably 40% by mass or more, And from a viewpoint similar to the above, Preferably it is 85 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 55 mass% or less, More preferably, it is 50 mass% or less.

[Radical polymerization initiator (a)]
Examples of the radical polymerization initiator (a) (hereinafter, also simply referred to as “initiator (a)”) used in the present invention include 2,2′-azobis (isobutyronitrile) (AIBN), 2,2′-azobis. (4-methoxy-2,4-dimethylvaleronitrile) (V-70), 2,2′-azobis (2,4-dimethylvaleronitrile) (V-65), 1,1′-azobis (cyclohexane-1) -Azonitrile compounds such as (carbonitrile) (V-40), azoamidine compounds such as 2,2′-azobis [2- (2-imidazolin-2-yl) propane] (VA-061), 2,2′-azobis Azoamide compounds such as [2-methyl-N- (2-hydroxyethyl) propionamide] (VA-086) and 2,2′-azobis (N-butyl-2-methylpropionamide) (VAm-110) Azo polymerization initiators containing an azo group such as 4,4′-azobis (4-cyanovaleric acid); persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate; inorganic peroxides such as hydrogen peroxide Organic peroxides such as t-butylperoxyneoheptanoate, t-hexylperoxyneoheptanoate, di-t-butyl peroxide, benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide; organic Examples thereof include a redox polymerization initiator in which a peroxide and a reducing agent such as sodium sulfite, Rongalite, and ascorbic acid are combined.

  Initiator (a) is preferably an azo polymerization initiator, more preferably an oil-soluble azo polymerization initiator, more preferably an oil-soluble azo polymerization initiator, from the viewpoint of suppressing high molecular weight of the oligomer dispersant and improving adhesion. An azonitrile compound, more preferably 2,2′-azobis (isobutyronitrile) (AIBN), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) (V-70), It is at least one selected from 2,2′-azobis (2,4-dimethylvaleronitrile) (V-65) and 1,1′-azobis (cyclohexane-1-carbonitrile) (V-40).

The 10-hour half-life temperature of the initiator (a) is preferably 30 ° C. or higher from the viewpoint of suppressing side reactions and adjusting the molecular weight distribution, and improving the adhesion, bending resistance and light resistance. More preferably, it is 40 ° C. or more, more preferably 50 ° C. or more, and from the viewpoint of controlling the reaction at an appropriate temperature, preferably 100 ° C. or less, more preferably 90 ° C. or less, still more preferably 80 ° C. or less, more More preferably, it is 70 degrees C or less, More preferably, it is 60 degrees C or less.
In addition, you may use these polymerization initiators individually by 1 type or in combination of 2 or more types.

[Irreversible chain transfer agent]
As described above, the irreversible chain transfer agent means “a chain transfer agent that does not cause reversible addition fragmentation chain transfer”, and includes a trithiocarbonate structure (—S—C) contained in the RAFT agent. It is a chain transfer agent having no (= S) -S-), dithiocarbamate structure (-NC (= S) -S-) or dithiobenzoate structure. In the present invention, since the oligomer dispersant is obtained using an irreversible chain transfer agent, the molecular weight is low and the molecular weight distribution is relatively wide. Therefore, it is excellent in the dispersibility with respect to a pigment, it is excellent also in the absorptivity of the radically polymerizable monomer used for seed polymerization in the following process 3, and adhesiveness, bending resistance, and weather resistance can be improved.

The irreversible chain transfer agent is preferably a hydrophilic chain transfer agent from the viewpoint of improving adhesion, bending resistance and light resistance, and more preferably contains a thiol group or a haloalkyl group.
Examples of the thiol chain transfer agent containing a thiol group (hereinafter also simply referred to as “thiol chain transfer agent”) include hydroxy group-containing mercaptans such as 2-mercaptoethanol and 3-mercapto-1,2-propanediol; Carboxy group-containing mercaptans such as acetic acid, 3-mercaptopropionic acid and mercaptosuccinic acid; sulfonic acid group-containing mercaptans such as sodium 2-mercaptoethanesulfonate; 2,4-diphenyl-4-methyl-1-pentene; Alkyl mercaptans such as thiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol; cyclohexanethiol; thiophenol; methyl-3-mercaptopropionate, 2-ethylhexyl-3-mercaptopro Onato, mercaptopropionate such as n- octyl-3-mercaptopropionate and the like.
Examples of the chain transfer agent containing a haloalkyl group include carbon tetrachloride, carbon tetrabromide, methylene chloride, tribromoethane, bromotrichloroethane, and the like.

Among these, from the viewpoint of improving adhesion, bending resistance and light resistance, preferably a thiol chain transfer agent, and more preferably a thiol further containing an acidic group from the viewpoint of dispersibility of the oligomer dispersant. It is a chain transfer agent. Examples of the acidic group include groups that exhibit acidity by dissociating and releasing hydrogen ions, such as a carboxy group (—COOM ² ) and a sulfonic acid group (—SO ₃ M ² ), or their dissociated ion forms ( -COO ^-, -SO ₃ ^-) and the like. In the above chemical formula, M ² represents a hydrogen atom, an alkali metal, ammonium or organic ammonium.
The thiol chain transfer agent containing an acidic group is preferably at least one selected from a carboxy group-containing mercaptan and a sulfonic acid group-containing mercaptan, more preferably a carboxy group-containing mercaptan, and still more preferably 3-mercaptopropion. It is an acid.

The amount of the radically polymerizable monomer (a) is preferably 10% by mass or more, more preferably 20%, based on the entire polymerization reaction in Step 1, from the viewpoint of improving adhesion, bending resistance and light resistance. More preferably, it is 70 mass% or less, More preferably, it is 55 mass% or less, More preferably, it is 40 mass% or less.
The amount of the initiator (a) 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 radical polymerizable monomer (a). Yes, and preferably 15 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

  In step 1, the molar ratio of the total number of moles of the radical polymerizable monomer (a) to the total number of moles of the irreversible chain transfer agent [radical polymerizable monomer (a) / irreversible chain transfer agent] is an oligomer dispersant. Is preferably 3 or more, more preferably 5 or more, still more preferably 10 or more, still more preferably 13 or more, and preferably from the viewpoint of adjusting the molecular weight of the resin and improving adhesion, bending resistance and light resistance. Is 40 or less, more preferably 35 or less, still more preferably 30 or less, still more preferably 25 or less, still more preferably 20 or less, and still more preferably 18 or less.

  In step 1, the molar ratio of the total number of moles of initiator (a) to the total number of moles of irreversible chain transfer agent [radical polymerization initiator (a) / irreversible chain transfer agent] is the molecular weight of the oligomer dispersant. From the viewpoint of improving adhesion, bending resistance and light resistance, it is preferably 0.03 or more, more preferably 0.05 or more, still more preferably 0.07 or more, and preferably 1 Below, more preferably 0.7 or less, still more preferably 0.5 or less, still more preferably 0.3 or less, and still more preferably 0.1 or less.

As the polymerization method in Step 1, a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method can be used. Among these, 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, and esters. Among these, aliphatic alcohol, ketones, or a mixed solvent of these with water is preferable, and methyl ethyl ketone or a mixed solvent of it with water is preferable.
Moreover, when using 2 or more types of monomers as a radically polymerizable monomer (a), there is no restriction | limiting in the mode of a chain | linkage, Any polymerization modes, such as random, a block, and a graft, may be sufficient.

The preferred polymerization conditions vary depending on the initiator (a), the radical polymerizable monomer (a), the type of solvent, etc., but the polymerization temperature is preferably 30 ° C. or higher, more preferably 50 ° C. or higher, and even more preferably 70 ° C. or higher. And preferably 95 ° C. or lower, more preferably 80 ° C. or lower. 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 the completion of the polymerization reaction, the produced oligomer dispersant can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation.

The number average molecular weight (Mn) of the oligomer dispersant obtained in Step 1 is 300 or more from the viewpoint of dispersibility of the oligomer dispersant, and from the viewpoint of improving adhesion, bending resistance and light resistance, Preferably it is 400 or more, more preferably 500 or more, and 6,000 or less, preferably 5,000 or less, more preferably 4,000 or less, still more preferably 3,000 or less, and even more preferably 2. , 1,000 or less, more preferably 1,000 or less.
The weight average molecular weight (Mw) of the oligomer dispersant obtained in Step 1 is 700 or more from the viewpoint of dispersibility of the oligomer dispersant, and from the viewpoint of improving adhesion, bending resistance and light resistance. Preferably it is 1,000 or more, More preferably, it is 1,300 or more, More preferably, it is 1,500 or more, And it is 20,000 or less, Preferably it is 15,000 or less, More preferably, it is 12,000 or less, Furthermore, Preferably it is 10,000 or less, More preferably, it is 8,000 or less, More preferably, it is 5,000 or less, More preferably, it is 3,000 or less, More preferably, it is 2,000 or less.
The molecular weight distribution (Mw / Mn) of the oligomer dispersant obtained in Step 1 is preferably 2 or more from the viewpoint of improving the dispersibility of the oligomer dispersant and improving the adhesion, folding resistance and light resistance. More preferably, it is 2.3 or more, more preferably 2.5 or more, and preferably 6 or less, more preferably 5 or less, still more preferably 4 or less, and still more preferably 3 or less.
In addition, the measurement of a weight average molecular weight, a number average molecular weight, and molecular weight distribution can be performed by the gel permeation chromatography method as described in an Example.

<Process 2>
Step 2 is a step of mixing the pigment, the oligomer dispersant obtained in Step 1 and water to obtain a pigment water dispersion. Thereby, a pigment can be disperse | distributed uniformly.
The method for obtaining the pigment aqueous dispersion is not particularly limited, but from the viewpoint of efficiently obtaining the pigment aqueous dispersion, a pigment mixture containing a pigment, an oligomer dispersant, and an aqueous medium (hereinafter also simply referred to as “pigment mixture”). ) Is preferably distributed.

[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. 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 of achromatic pigments such as white, black and gray; and chromatic pigments 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.
In addition, these pigments can be used individually by 1 type or in mixture of 2 or more types.

Among these, the pigment preferably contains an inorganic pigment, more preferably contains a metal oxide, more preferably contains titanium oxide, and more preferably from the viewpoint of improving adhesion, bending resistance and light resistance. Titanium oxide is preferable.
The particle shape of titanium oxide is granular, acicular, etc., and is not particularly limited, but the average primary particle size is preferably 40 nm or more, more preferably from the viewpoint of improving adhesion, bending resistance and light resistance. Is 100 nm or more, more preferably 150 nm or more, and from the same viewpoint as described above, it is preferably 400 nm or less, more preferably 350 nm or less, still more preferably 300 nm or less, and even more preferably 250 nm or less.
In addition, the average primary particle diameter of a titanium oxide is an arithmetic average of the major axis of a primary particle, and is measured by the method as described in an Example.

There are rutile type (tetragonal), anatase type (tetragonal), and brookite type (orthorhombic) in the crystal structure of titanium oxide. From the viewpoint of crystal stability and availability, rutile type titanium oxide is used. It is preferable.
Titanium oxide can be produced by a vapor phase method or a liquid phase method, but titanium oxide produced by a vapor phase method is more preferred because it is easy to obtain a highly crystalline material.
Although an untreated titanium oxide can be used, a surface-treated one is preferable from the viewpoint of obtaining good dispersibility. Examples of the surface treatment of titanium oxide include surface treatment with an inorganic substance such as alumina (Al ₂ O ₃ ) and zinc oxide, and surface treatment with an organic substance such as a titanium coupling agent, a silane coupling agent, and silicone oil.
Examples of commercial products of rutile titanium oxide include trade names of Ishihara Sangyo Co., Ltd .: Type R, CR, PF series, trade names of Sakai Chemical Industry Co., Ltd .: R series, trade names of Teika Co., Ltd. , MT series, trade names made by Titanium Industry Co., Ltd .: KURONOS KR series, trade names made by huntsmann: TR series, and the like.

(Aqueous medium)
The aqueous medium refers to a medium mainly composed of water. An organic solvent may be further added to the aqueous medium from the viewpoints of wettability to the pigment particles, solubility of the oligomer dispersant, and adsorptivity of the oligomer dispersant to the pigment particles. Examples of the organic solvent include aliphatic alcohols having 1 to 4 carbon atoms, ketones having 3 to 8 carbon atoms, ethers such as ethyl ether, propyl ether, butyl ether and tetrahydrofuran, and esters such as methyl acetate and ethyl acetate. Etc. Among these, from the viewpoint of the solubility of the oligomer dispersant and the adsorptivity of the oligomer dispersant to the pigment particles, a ketone having 4 to 6 carbon atoms is preferable, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is more preferable. . When the oligomer dispersant is synthesized 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, still more preferably 90% by mass or more, and still more preferably 95% by mass or more, from the viewpoint of environmental properties. .
When an organic solvent is added, it is preferable to remove the organic solvent by a known method before performing Step 3. The organic solvent in the obtained pigment aqueous dispersion is preferably substantially removed, but may remain as long as the effects of the present invention are 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.

(Neutralizer)
When using a monomer containing an ionic functional group as the radical polymerizable monomer (a), from the viewpoint of improving adhesion, folding resistance and light resistance, a neutralizing agent is further added, mixed, and ionized. It is preferable to neutralize at least a part of the functional group. Examples of the neutralizing agent include basic compounds such as alkali metal hydroxides and organic amines.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide and the like, and sodium hydroxide and potassium hydroxide are preferable.
Examples of the organic amine include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine. Among these, Preferably it is an alkali metal hydroxide, More preferably, it is sodium hydroxide. Further, the oligomer dispersant may be neutralized in advance.

The degree of neutralization of the oligomer dispersant is preferably 10 mol% or more, more preferably 15 mol% or more, and still more preferably 20 mol% or more, from the viewpoint of improving adhesion, bending resistance and light resistance. And from a viewpoint similar to the above, Preferably it is 100 mol% or less, More preferably, it is 70 mol% or less, More preferably, it is 50 mol% or less.
Here, the degree of neutralization is a value obtained by dividing the number of molar equivalents of the neutralizing agent by the number of molar equivalents of the ionic functional group of the oligomer dispersant before neutralization, that is, “number of molar equivalents of neutralizing agent / oligomer dispersant”. The number of molar equivalents of the ionic functional group. Originally, the degree of neutralization does not exceed 100 mol%, but in the present invention, it is calculated from the number of molar equivalents of the neutralizing agent. Therefore, when the neutralizing agent is used in excess, it exceeds 100 mol%.

(Distributed processing)
The dispersion treatment of the pigment mixture is not particularly limited, and the average particle diameter of the pigment particles can be atomized until a desired particle diameter is obtained only by dispersion applying shear stress. Preferably, however, the pigment mixture is predispersed. Thereafter, it is preferable to control the average particle size of the pigment particles to a desired particle size by applying a shear stress to the dispersion.
In the preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a disper blade, an ultrasonic disperser such as an ultrasonic homogenizer, or the like can be used. Among these, an ultrasonic disperser is preferable.

Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer, a media-type disperser such as a paint shaker and a bead mill. Among these, it is preferable to use a media-type disperser from the viewpoint of reducing the particle size of the pigment.
In the case of using a media type disperser, the material of the media is preferably a ceramic material such as zirconia or titania, a polymer material such as polyethylene or nylon, a metal, or the like, and zirconia is preferable from the viewpoint of wear. The diameter of the media is preferably 0.003 mm or more, more preferably 0.01 mm or more, still more preferably 0.03 mm or more, and preferably 0.5 mm or less from the viewpoint of sufficiently miniaturizing the pigment. More preferably, it is 0.3 mm or less, and still more preferably 0.1 mm or less.
The dispersion time is preferably 0.3 hours or more, more preferably 1 hour or more from the viewpoint of sufficiently miniaturizing the pigment, and preferably 200 hours or less from the viewpoint of the production efficiency of the pigment aqueous dispersion. More preferably, it is 50 hours or less.

The obtained pigment aqueous dispersion contains particles in which the oligomer dispersant is adsorbed on the pigment, and the particles are present in a state of being dispersed in the aqueous medium.
The nonvolatile component concentration (solid content concentration) of the pigment aqueous dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 45% by mass from the viewpoint of dispersion stability of the pigment aqueous dispersion. % Or less, more preferably 35% by mass or less.
The solid content concentration of the pigment aqueous dispersion is measured by the method described in Examples.
The content of the pigment in the pigment dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, from the viewpoint of dispersion stability of the pigment aqueous dispersion. Preferably it is 40 mass% or less, More preferably, it is 30 mass% or less, More preferably, it is 20 mass% or less.
The mass ratio of the pigment to the oligomer dispersant in the pigment aqueous dispersion (pigment / oligomer dispersant) is preferably 70/30 or more from the viewpoint of enhancing adsorption of the oligomer dispersant to the pigment surface and uniformly dispersing the pigment. , More preferably 75/25 or more, still more preferably 80/20 or more, still more preferably 85/15 or more, and preferably 99/1 or less, more preferably 97/3 or less, still more preferably 95 / 5 or less, more preferably 93/7 or less.

<Step 3>
Step 3 is a step of mixing the pigment aqueous dispersion obtained in Step 2 and the radical polymerizable monomer (b), seed polymerization, and coating the pigment to obtain a pigment aqueous dispersion.
In the seed polymerization method in step 3, the radical polymerizable monomer (b) is added to and mixed with the radical polymerizable monomer (b) using the particles obtained by adsorbing the oligomer dispersant to the pigment obtained in step 2 as a seed. Is absorbed and radical polymerization occurs in the seed.

[Radically polymerizable monomer (b)]
The radical polymerizable monomer (b) preferably contains a hydrophobic monomer (b-1) from the viewpoint of the dispersion stability of the pigment aqueous dispersion, and from the viewpoint of improving adhesion, bending resistance and light resistance. More preferably, it contains one or more selected from (meth) acrylates having a hydrocarbon group derived from an aliphatic alcohol and an aromatic group-containing monomer. Specific examples of the (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol and the aromatic group-containing monomer include the same as the above-mentioned radical polymerizable monomer (a). Among them, (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol is preferable from the viewpoint of dispersion stability of the pigment aqueous dispersion and from the viewpoint of improving adhesion, bending resistance and light resistance. Yes, more preferred is a (meth) acrylate having an alkyl group having 1 to 8 carbon atoms, and still more preferred is a (meth) acrylate having an alkyl group having 1 to 6 carbon atoms.
As the radical polymerizable monomer (b), one of the above monomers may be used alone, or two or more thereof may be used.

The radical polymerizable monomer (b) contains, in addition to the hydrophobic monomer (b-1), a monomer having an anionic group such as a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer, or a monomer having a cationic group. You can also. Among these, Preferably it is a monomer which has an anionic group, More preferably, it is a carboxylic acid monomer, More preferably, it is (meth) acrylic acid.
Further, if necessary, the polyalkylene glycol (meth) acrylate, the alkoxy polyalkylene glycol (meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymer) (n = 1 to 30, ethylene glycol therein: n = 1 to 29) (meth) acrylate or the like can also be used.
The content of monomers other than the hydrophobic monomer (b-1) is radically polymerizable from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and improving the adhesion, bending resistance and light resistance. In the total amount of the monomer (b), it is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less.
There is no restriction | limiting in particular in the addition method of a radically polymerizable monomer (b), It can carry out by well-known methods, such as a monomer dripping method, a monomer batch charging method, and a pre-emulsion method. Among these, the monomer dropping method is preferable. The dropping of the radical polymerizable monomer (b) is preferably continuous dropping from the viewpoint of polymerization control, and the dropping rate is preferably 3 hours or more, more preferably as the time for dropping the total amount of the radical polymer monomer (b). Is 12 hours or longer, and preferably 48 hours or shorter, more preferably 24 hours or shorter.

[Radical polymerization initiator (b)]
In step 3, it is preferable to use a radical polymerization initiator (b) (hereinafter also simply referred to as “initiator (b)”). Any initiator (b) can be used as long as it is used in ordinary emulsion polymerization, but a water-soluble polymerization initiator is preferred. Specifically, persulfates such as potassium persulfate and ammonium persulfate; inorganic peroxides such as hydrogen peroxide; organic peroxides such as t-butyl hydroperoxide; 4,4′-azobis (4-cyano Examples include azo polymerization initiators such as valeric acid) and 2,2-azobis (2-amidinopropane) dihydrochloride; redox polymerization initiators and the like. Among these, an azo polymerization initiator is preferable from the viewpoint of promoting polymerization of the radical polymerizable monomer (b) and improving adhesion, bending resistance, and light resistance.

Examples of the azo polymerization initiator include anionic azo polymerization initiators and nonionic azo polymerization initiators. Examples of the anionic azo polymerization initiator include azobiscarboxylic acid having 8 to 16 carbon atoms such as 1,1′-azobis (cyclohexane-1-carboxylic acid), 4,4′-azobis (4-cyano). Azobiscyanocarboxylic acids having 8 to 16 carbon atoms, such as valeric acid), 2,2′-azobis (4-cyanovaleric acid), 4,4′-azobis (2-cyanopentanoic acid), and salts thereof Carboxy group-containing azo compounds such as
Nonionic azo polymerization initiators include 2,2′-azobis [2-methyl-N- [1,1′-bis (hydroxymethyl) -2-hydroxyethyl] propionamide], 2,2′-. Hydroxy such as azobis [2-methyl-N- [1,1′-bis (hydroxymethyl) ethyl] propionamide], 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] And group-containing azoamide compounds. Among these, an anionic azo polymerization initiator is preferable, a carboxy group-containing azo compound is more preferable, and at least one selected from azobiscyanocarboxylic acids having 10 to 14 carbon atoms and salts thereof is more preferable. A seed, and more preferably at least one selected from 4,4′-azobis (4-cyanovaleric acid) and salts thereof.

In step 3, a chain transfer agent may be used as long as the effects of the present invention are not impaired. For example, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, n-octyl mercaptan; xanthogens such as dimethylxanthogen disulfide and diisobutylxanthogen disulfide; dipentene, indene, 1,4-cyclohexadiene, dihydrofuran, xanthene Can be mentioned.
In step 3, a surfactant may be added to increase the polymerization stability. As the surfactant, a known surfactant such as anionic or nonionic for emulsion polymerization can be used.

In step 3, it is preferable to use water as a dispersion medium for seed polymerization.
The ratio of water in the entire dispersion medium is preferably 50% by mass or more, more preferably 65% by mass or more, still more preferably 75% by mass or more, and still more preferably 80% by mass or more.
From the viewpoint of improving the dispersibility of the pigment, an arbitrary organic solvent can be added in addition to water.
Examples of organic solvents that can be used include alcohols and ketones having 1 to 6 carbon atoms, ethers, amides, aromatic hydrocarbons, and aliphatic hydrocarbons having 5 to 10 carbon atoms. Can be mentioned. Among these, a polar solvent having an oxygen atom having 1 to 5 carbon atoms is preferable. Specific examples include methanol, ethanol, acetone, and methyl ethyl ketone, with methyl ethyl ketone being preferred.
The ratio of water to these organic solvents is not particularly limited, but from the viewpoint of improving the dispersibility of the pigment, the mass ratio of organic solvent to water (organic solvent / water) is preferably 0.05 or more, more preferably Is 0.08 or more, more preferably 0.10 or more, still more preferably 0.12 or more, and preferably 0.40 or less, more preferably 0.35 or less, still more preferably 0.30 or less, More preferably, it is 0.25 or less.

The polymerization temperature of the seed polymerization is appropriately adjusted depending on the decomposition temperature of the polymerization initiator, but from the viewpoint of reactivity, it is preferably 50 ° C or higher, more preferably 60 ° C or higher, still more preferably 70 ° C or higher, and From the viewpoint of the molecular weight distribution of the obtained polymer, it is preferably 90 ° C. or lower, more preferably 85 ° C. or lower.
The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 10 hours or less, more preferably 5 hours or less.
The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon from the viewpoint of reactivity.

The amount of the radically polymerizable monomer (b) is preferably 5% by mass or more, more preferably 10%, based on the entire polymerization reaction in Step 3, from the viewpoint of improving adhesion, bending resistance and light resistance. It is at least mass%, more preferably at least 15 mass%, and preferably at most 40 mass%, more preferably at most 30 mass%, still more preferably at most 25 mass%.
The mass ratio of the radical polymerizable monomer (b) to the pigment [radical polymerizable monomer (b) / pigment] is preferably 0. 0 at the time of seed polymerization from the viewpoint of improving adhesion, bending resistance and light resistance. It is 3 or more, more preferably 0.7 or more, still more preferably 1.0 or more, and preferably 2.0 or less, more preferably 1.7 or less, still more preferably 1.5 or less.
The mass ratio of the radical polymerizable monomer (b) to the oligomer dispersant (radical polymerizable monomer (b) / oligomer dispersant) is from the viewpoint of improving adhesion, bending resistance and light resistance, during seed polymerization, Preferably it is 1 or more, More preferably, it is 5 or more, More preferably, it is 10 or more, Preferably it is 50 or less, More preferably, it is 30 or less, More preferably, it is 20 or less.
The amount of the initiator (b) is preferably 0.01 parts by mass or more, more preferably from the viewpoint of improving adhesion, bending resistance and light resistance with respect to 100 parts by mass of the radical polymerizable monomer (b). Is 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, still more preferably 0.5 parts by weight or more, and preferably 5 parts by weight or less, more preferably 3 parts by weight or less. Is 1 part by mass or less.

  In the present invention, the obtained polymer can be further subjected to a crosslinking treatment from the viewpoint of improving adhesion, bending resistance and light resistance. As the crosslinking agent, compounds having a reactive functional group such as two or more epoxy groups in the molecule, such as ethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, and the like are preferable.

The non-volatile component concentration (solid content concentration) of the pigment aqueous dispersion of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably from the viewpoint of dispersion stability of the pigment water dispersion. Is 50% by mass or less, more preferably 45% by mass or less.
The solid content concentration of the pigment aqueous dispersion is measured by the method described in the examples.
In the pigment water dispersion according to the present invention, the mass ratio of pigment to polymer (pigment / polymer) is preferably 15/85 or more, more preferably 20 from the viewpoint of improving adhesion, bending resistance and light resistance. / 80 or more, more preferably 25/75 or more, still more preferably 30/70 or more, and preferably 80/20 or less, more preferably 70/30 or less, still more preferably 60/40 or less, and even more. Preferably it is 50/50 or less. Here, the mass of the polymer is the total amount of the oligomer dispersant used in Step 2 and the polymer obtained by seed polymerization in Step 3.
The calculation of the mass ratio (pigment / polymer) can determine the mass of the pigment and polymer from the amount of raw materials charged during production, thermogravimetry (TG), and the like.

The coating state of the pigment fine particles in the pigment aqueous dispersion according to the present invention with the polymer can be confirmed by observing the water dispersion with an electron microscope.
From the viewpoint of improving adhesion, bending resistance and light resistance, the polymer coverage representing the degree of pigment coating with the polymer is preferably 93% or more, more preferably 95% or more, still more preferably 97% or more, Even more preferably, it is 99% or more and 100% or less. When the coverage is 100%, the raw material pigment is completely coated with the polymer, and when it is 0%, it is not coated.
For example, when the pigment is titanium oxide, the coverage is the sum of the atomic fractions of titanium, aluminum, and zinc on the particle surface by X-ray photoelectron spectroscopy (XPS) of the raw material pigment, titanium oxide and pigment fine particles (hereinafter referred to as the following) , Also referred to as “atomic fraction such as titanium”), and can be calculated by the following formula (1).
Polymer coverage (%) = {1- (surface titanium atom fraction of pigment fine particles) / (surface titanium atom fraction of titanium oxide)} × 100 (1)

When black pigments and chromatic pigments are used, the average particle size of the pigment fine particles in the pigment aqueous dispersion suppresses an increase in ink viscosity during concentration, and improves adhesion, bending resistance and light resistance. , Preferably 10 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, still more preferably 50 nm or more, still more preferably 60 nm or more, still more preferably 75 nm or more, still more preferably 80 nm or more, still more preferably 100 nm or more, more preferably 150 nm or more, still more preferably 200 nm or more, and from the same viewpoint as described above, preferably 600 nm or less, more preferably 500 nm or less, still more preferably 400 nm or less, still more preferably 300 nm. It is as follows.
When using a white pigment, the average particle size of the pigment fine particles in the pigment aqueous dispersion suppresses an increase in ink viscosity when concentrating, and improves adhesion, folding resistance and light resistance. In view of the above, it is preferably 100 nm or more, more preferably 150 nm or more, further preferably 200 nm or more, and preferably 600 nm or less, more preferably 500 nm or less, still more preferably 400 nm or less, and still more preferably 300 nm or less. .
The average particle diameter of the pigment fine particles is measured by the method described in the examples.
The pigment fine particles in the pigment water dispersion preferably do not cause swelling or shrinkage of the particles or aggregation between the particles. The average particle diameter of the pigment fine particles in the aqueous ink described later is determined in the pigment water dispersion. It is preferable that the average particle size is the same. The preferable average particle diameter of the pigment fine particles in the water-based ink is the same as the preferable average particle diameter of the aqueous pigment dispersion. The average particle diameter of the pigment fine particles in the water-based ink is also measured by the same method as the average particle diameter of the pigment fine particles in the pigment aqueous dispersion described in the Examples.

[Water-based ink]
The ink of the present invention contains the pigment aqueous dispersion, and can be obtained by adding or mixing the pigment aqueous dispersion as it is or further with water. In addition, various additions such as commonly used organic solvents, surfactants, wetting agents, penetrating agents, viscosity modifiers, antifoaming agents, antifungal agents, rustproofing agents, UV absorbers, etc., may be added to the ink as necessary. An agent can be added.

The ink of the present invention preferably contains an organic solvent.
Examples of the organic solvent include polyhydric alcohol, polyhydric alcohol alkyl ether, polyhydric alcohol aryl ether, cyclic carbonate, nitrogen-containing heterocyclic compound, amide, amine, and sulfur-containing compound. Among these, Preferably it is 1 or more types chosen from a polyhydric alcohol and a polyhydric alcohol alkyl ether, More preferably, it is diethylene glycol, propylene glycol, dipropylene glycol, 1,2-butanediol, 1,2-hexanediol, One or more selected from glycerin, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.
The ink of the present invention preferably further contains a surfactant.
Examples of the surfactant include nonionic surfactants, anionic surfactants, amphoteric surfactants, silicone surfactants, and fluorine surfactants. Among these, it is preferably at least one selected from nonionic surfactants and silicone surfactants.

The content of each component and the ink physical properties in the ink of the present invention are as follows from the viewpoint of improving adhesion, bending resistance and light resistance.
The pigment content in the water-based ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, still more preferably 2% by mass or more, and preferably 20% by mass from the viewpoint of printing density. Hereinafter, it is more preferably 15% by mass or less, and further preferably 10% by mass or less.
The mass ratio of pigment to polymer (pigment / polymer) in the water-based ink is preferably 15/85 or more, more preferably 20/80 or more, still more preferably 25/75 or more, and even more preferably 30/70 or more. And, it is preferably 80/20 or less, more preferably 70/30 or less, further preferably 60/40 or less, and still more preferably 50/50 or less. Here, the mass of the polymer is the total amount of the oligomer dispersant used in step 2 and the polymer produced by seed polymerization in step 3.
The content of the organic solvent in the water-based ink is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more from the viewpoint of storage stability, and the same viewpoint as described above. Therefore, it is preferably 50% by mass or less, more preferably 45% by mass or less, and still more preferably 40% by mass or less.
The water content in the water-based ink is preferably 30% by mass or more, more preferably 35% by mass or more, and still more preferably 40% by mass or more from the viewpoint of reducing environmental burden, and from the viewpoint of storage stability. Preferably, it is 80 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 60 mass% or less.

(Water-based ink properties)
The pH of the water-based ink at 20 ° C. is preferably 5.5 or more, more preferably 6.0 or more, and still more preferably 6.5 or more, from the viewpoint of improving adhesion, bending resistance and light resistance. And from a viewpoint of member tolerance and skin irritation, Preferably it is 11.0 or less, More preferably, it is 10.0 or less, More preferably, it is 9.5 or less, More preferably, it is 9.0 or less.
The pH of the water-based ink at 20 ° C. is measured by the method described in the examples.
The viscosity of the water-based ink at 20 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and still more preferably 3.5 mPa, from the viewpoint of improving adhesion, bending resistance and light resistance. S or more, more preferably 4.0 mPa · s or more, and from the same viewpoint as described above, preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and even more preferably 7.0 mPa · s. s or less.

(Inkjet printing method)
The ink of the present invention can be used as a water-based ink for flexographic printing, gravure printing, or inkjet printing, and is excellent in adhesion, folding resistance, and light resistance in inkjet printing. It is preferably used as a water-based ink. Although it can be used in an ink jet printing method for printing on a water-absorbing print medium such as plain paper or high-quality paper or a print medium such as ink jet dedicated paper, it has excellent adhesion, folding resistance, and light resistance. The ink jet printing method for printing on a low water-absorbing print medium such as coated paper or a non-water-absorbing print medium such as a synthetic resin film can be suitably used.
The print medium is preferably a synthetic resin film from the viewpoint of improving adhesion, bending resistance and light resistance. Examples of the synthetic resin film include a polyester film, a vinyl chloride film, a polypropylene film, a polyethylene film, and a nylon film. These films may be subjected to surface treatment such as corona treatment as necessary.

  Examples of generally available synthetic resin films include Lumirror T60 (manufactured by Toray Industries, Inc., polyethylene terephthalate), PVC80BP (manufactured by Lintec Corporation, vinyl chloride), Kainus KEE70CA (manufactured by Lintec Corporation, polyethylene), YUPO SG90. PAT1 (made by Lintec Co., Ltd., polypropylene), Bonil RX (made by Kojin Film & Chemicals Co., Ltd., nylon), etc. are mentioned.

Preferably, the ink jet printing method includes a step of drying ink droplets that have landed on the print medium after the ink droplets have been ejected onto the print medium for printing.
In the drying step, the printing medium surface temperature is preferably 25 ° C. or higher, more preferably 30 ° C. or higher, from the viewpoint of improving print quality, and from the viewpoint of suppressing deformation of the printing medium due to heat and reducing energy, Preferably it is 100 degrees C or less, More preferably, it is 80 degrees C or less, More preferably, it is 50 degrees C or less.

  In the following Examples and Comparative Examples, “%” is “% by mass” unless otherwise specified.

(1) Measurement of number average molecular weight, weight average molecular weight and molecular weight distribution of oligomer dispersant Liquid obtained by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively. As an eluent, gel chromatography method (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, column (TSKgel SuperAWM-3000, TSKgel superAW3000, TSKgel guardcolumn SuperAW-H) manufactured by Tosoh Corporation, flow rate: 0.5 mL / min) ], As a standard substance, monodispersed polystyrene kits [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F -4, A-5000, A-500), manufactured by Tosoh Corporation].
In Example 2, the measurement was performed using a mixture of oligomer dispersant A1 and oligomer dispersant A2 at a mass ratio (1/1).

(2) Measurement of average primary particle diameter of titanium oxide The average primary particle diameter of titanium oxide is 500 titanium oxide primary particles by image analysis using a transmission electron microscope “JEM-2100” (manufactured by JEOL Ltd.). Were randomly extracted to measure the particle diameter, and the average was calculated as the arithmetic average particle diameter. In addition, when the titanium oxide had a major axis and a minor axis, the major axis was used for calculation.

(3) Measurement of Solid Content Concentration of Pigment Water Dispersion and Pigment Water Dispersion Using an infrared moisture meter “FD-230” (manufactured by Kett Scientific Laboratory), 5 g of a measurement sample was dried at a temperature of 150 ° C. and a measurement mode. After drying under the condition of 96 (monitoring time 2.5 minutes / variation width 0.05%), the moisture (%) of the measurement sample was measured, and the solid content concentration was calculated by the following formula.
Solid content concentration (%) = 100- (moisture content of measurement sample (%))

(4) Average particle size of pigment aqueous dispersion Using a laser diffraction / scattering type particle size distribution measuring device “LA-920” manufactured by Horiba, Ltd., distilled water is added to the measurement cell, and the absorbance falls within an appropriate range. The volume median particle size (D ₅₀ ) was measured by concentration.

(5) Viscosity measurement of water-based ink Viscosity at 20 ° C. using E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1 ° 34 ′ × R24, rotation speed 50 rpm) Was measured.

(6) Measurement of pH of water-based ink Water system at 20 ° C. using a desktop pH meter “F-71” (manufactured by Horiba, Ltd.) using a pH electrode “6337-10D” (manufactured by Horiba, Ltd.) The pH of the ink was measured.

Example 1
(1) Production of pigment aqueous dispersion 1 (step 1)
In a 200 mL four-necked round bottom flask equipped with a thermometer and a reflux apparatus, 100 g of methyl ethyl ketone, 33.9 g of acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as monomer (a-1), and styrene as monomer (a-2) 26 g (manufactured by Wako Pure Chemical Industries, Ltd.), 5.4 g of 3-mercaptopropionic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as the irreversible chain transfer agent, and 2,2′-azobis (2) as the initiator (a) , 4-dimethylvaleronitrile) (trade name: V-65, manufactured by Wako Pure Chemical Industries, Ltd.) 1.0 g was added and mixed with a magnetic stirrer for 10 minutes to obtain a mixture. The mixture was bubbled with nitrogen for 10 minutes, then warmed to 77 ° C. in a water bath and stirred for 5 hours to complete the polymerization reaction. Thereafter, the reaction solution was poured into 1 L of n-hexane and reprecipitated. Then, it was dried at 80 ° C. and 8 kPa for 8 hours to obtain an oligomer dispersant A1 having a number average molecular weight of 600 and a weight average molecular weight of 1,700 in a yield of 99%.

(Process 2)
In a 200 mL glass beaker, 90 g of ion-exchanged water, 2 g of the oligomer dispersant A1 obtained in Step 1, 0.22 g of sodium hydroxide (corresponding to the degree of neutralization of the oligomer dispersant A1: 30 mol%), titanium oxide (as a pigment) Product name: JR-405, Rutile type, alumina (Al) treatment, average primary particle size 210 nm) 22 g was added, and an ultrasonic disperser (made by Nippon Seiki Seisakusho Co., Ltd.) was stirred with a magnetic stirrer. For 20 minutes. Then, after mixing and dispersing at 20 ° C. for 8 hours using a bead mill type disperser (manufactured by Kotobuki Kogyo Co., Ltd., Ultra Apex Mill, model: UAM-05, media particles: zirconia beads, particle size: 50 μm), 200 mesh The zirconia beads were removed with a wire mesh, and the concentration was adjusted with ion-exchanged water to obtain pigment aqueous dispersion 1 (solid content concentration 20%).

(Process 3)
Next, in a 100 mL two-necked flask equipped with a septum seal and a three-way cock, 60 g of the pigment aqueous dispersion 1 obtained in Step 2 and 4,4′-azobis (4-cyanoyoshin) as an initiator (b) were used. 0.10 g of herbic acid (made by Wako Pure Chemical Industries, Ltd., trade name: V-501, water-soluble azo polymerization initiator) was added and bubbled with nitrogen for 10 minutes. Next, a 20 mL Hamilton gas tight syringe containing 14 g of methyl methacrylate was set in a micro syringe pump MSP-3D (manufactured by ASONE Corporation). The eggplant-shaped flask was placed in a 70 ° C. water bath, and methyl methacrylate as a radical polymerizable monomer (b) was added dropwise to the reaction solution at a rate of 1.0 mL / h. After completion of the dropping, a polymerization reaction was carried out at 80 ° C. for 2 hours. Then, using a rotary distillation apparatus “Rotary evaporator N-1000S” (manufactured by Tokyo Rika Kikai Co., Ltd.), adjusting the number of revolutions to 50 rpm and the warm bath to 60 ° C. until the solid content concentration becomes 40% at a pressure of 0.07 MPa. Concentration gave a pigment aqueous dispersion 1 [solid content concentration: 40%, mass ratio (pigment / polymer) = 42/58].

(2) Production of aqueous ink 1 8 g of pigment aqueous dispersion 1 and 13 g of ion-exchanged water were placed in a glass container, and stirred for 10 minutes with a magnetic stirrer. Next, while continuing stirring with a magnetic stirrer, 0.2 g of propylene glycol, Surfynol 104PG-50 (Air Products Japan, acetylene-based nonionic surfactant, propylene glycol solution, effective content 50%) 0.2 g The mixture was further stirred with a magnetic stirrer for 1 hour. Thereafter, filtration was performed using a 5 μm disposal membrane filter (manufactured by Sartorius Co., Ltd., Mini Sarto) to obtain an aqueous ink 1. The pH of the ink 1 was 8.2. The ink 1 was printed by the following method, and the printed matter was evaluated.

Example 2
According to Table 1-1, it carried out similarly to the process 1 of Example 1, and obtained oligomer dispersing agent A2. The physical property values of the oligomer dispersant A2 are shown in Table 1-1.
Next, in the same manner as in Step 2 and Step 3 of Example 1, except that 1 g of each of the oligomer dispersant A1 and the oligomer dispersant A2 was used instead of the oligomer dispersant A1 in Step 2 of Example 1, pigment water Dispersion 2 and aqueous ink 2 were obtained.

Examples 3 to 16 and Comparative Examples 1 to 3
According to Table 1-1 to 1-3, it carried out similarly to the process 1 of Example 1, and obtained oligomer dispersing agent A3-A16 and dispersing agent C1-C3. Tables 1-1 to 1-3 show physical property values of the oligomer dispersants A3 to A16 and the dispersants C1 to C3.
Then, instead of the oligomer dispersant A1 in Step 2 of Example 1, the oligomer dispersants A3 to A16 shown in Table 2 in Examples 3 to 16 and the dispersants C1 to C3 shown in Table 2 in Comparative Examples 1 to 3 were used. Except having used, it carried out similarly to the process 2 and the process 3 of Example 1, and obtained the pigment water dispersion 3-16 and C1-C3, and the water-system ink 3-16 and C1-C3.

Example 17
Example 1 is the same as Example 1 except that a cyan pigment (CI Pigment Blue 15: 3, manufactured by Dainichi Seika Kogyo Co., Ltd.) was used instead of titanium oxide JR-405 as the pigment in Step 2 of Example 1. The same was done.

In addition, each notation of Table 1-1 to 1-3 and Table 2 is as follows.
[Monomer (a-1)]
AA: acrylic acid MAA: methacrylic acid PEGMA: polyethylene glycol methacrylate (number average molecular weight: 360)
[Monomer (a-2)]
St: Styrene MMA: Methyl methacrylate [Radical polymerization initiator (a)]
V-65: 2,2′-azobis (2,4-dimethylvaleronitrile)
V-70: 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile)
V-40: 1,1′-azobis (cyclohexane-1-carbonitrile)
[Irreversible chain transfer agent]
3MP: 3-mercaptopropionic acid [reversible chain transfer agent]
RAFT: 2-{[(butylsulfanyl) carbonothioyl] sulfanyl} propanoic acid [others]
CTA: irreversible chain transfer agent or reversible chain transfer agent

<Evaluation of water-based ink>
(Printing method, inkjet recording method)
Printing evaluation device (manufactured by Tritech Co., Ltd.) equipped with an inkjet head (Kyocera Corporation KJ4B-QA06NTB-STDV, piezo type, 2656 nozzles) in an environment of temperature 25 ± 1 ° C. and relative humidity 30 ± 5% Then, the water-based ink shown in Table 2 was filled.
Set head voltage 26V, frequency 20kHz, proper amount of discharge liquid 18pl, head temperature 32 ° C, resolution 600dpi, pre-discharge flushing 200 shots, negative pressure -4.0kPa, the direction in which the longitudinal direction of the print medium is the same as the transport direction In addition, the printing medium was fixed to the conveyance platform under reduced pressure. A print command was transferred to the print evaluation apparatus, and a 100% duty image was printed.
As a printing medium, a polyester film (Lumirror T60 # 50, thickness 50um) manufactured by Toray Industries, Inc. is used. After printing, the film is dried by heating at 40 ° C. for 20 minutes with a constant temperature dryer (DVS602 manufactured by Yamato Scientific Co., Ltd.). The printed matter for evaluation was obtained.

(Adhesion)
Double-sided tape (manufactured by 3M Japan, Scotch (R) strong double-sided tape, PSD-30) is applied to the non-printed surface of the evaluation printed matter, and 50 g on a stainless steel plate (manufactured by ASONE, SUS304, 300 mm × 300 mm). Strongly pasted at / cm ² . Next, using a cutter knife on the printing surface, make 11 notches at 2 mm intervals to reach the substrate to make 100 grids, and 50 g of adhesive tape (product number: CT-12M, manufactured by Nichiban Co., Ltd.) on the grids. / cm ² strongly pressure-bonded in a stretch peeling at an angle of the edge of tape 45 °, to count the number of squares that were not peeled off the printing surface. The results are shown in Table 2.

(Bending resistance)
The evaluation printed material is bent inward at 50 g / cm ² for 30 seconds, reopened, and the damaged image is wiped off with a soft cloth, and the maximum value of the width (mm) of the image defect is an index of the bending resistance of the printed material. It was. The smaller the maximum image defect width, the better the bending resistance of the printed matter. The results are shown in Table 2.

(Light resistance)
The printed matter for evaluation is placed in a sunshine weather meter “WEL-SUN-DC-B” (manufactured by Suga Test Instruments Co., Ltd., light source: carbon arc lamp, irradiation time 48 hours), and a light resistance test is performed. Sex was evaluated.
The amount of hue change is determined by measuring the optical reflection density of the printed matter using an optical densitometer (Gretag Macbeth), and measuring L ^* a ^* b ^* before and after irradiation with a color difference meter (made by Gretag Macbeth). Thus, the hue change amount ΔE was calculated to evaluate the light resistance. The smaller the hue change amount, the better the light resistance. The results are shown in Table 2.
Hue variation _{^{ΔE = [(L * 1 -L}} * 2) 2 + (a * 1 -a * 2) 2 + (b * 1 -b * 2) 2] 1/2
(L ^* a ^* b ^* values before irradiation: L ^* ₁ , a ^* ₁ , b ^* ₁ )
(L ^* a ^* b ^* values after irradiation: L ^* ₂ , a ^* ₂ , b ^* ₂ )

The annotations in Table 2 are as follows.
* 1: In Step 2 of Example 1, a mixture of oligomer dispersant A1 and oligomer dispersant A2 at a mass ratio (1/1) was used.
* 2: The 10-hour half-life temperature (° C) of the initiator (a).
As described above, Examples and Comparative Examples other than Example 17 use titanium oxide as a pigment, and Example 17 uses a cyan pigment.

From Table 2, the water-based inks of Examples 1 to 17 were excellent in adhesion, folding resistance and light resistance as compared with Comparative Examples 1 to 3.
Since Comparative Example 1 was radical polymerization by heat without using the initiator (a) in Step 1, the yield of the dispersant was low, and the number average molecular weight and the weight average molecular weight of the dispersant were high. Therefore, compared with Examples 1-17, it is inferior to all of adhesiveness, bending resistance, and light resistance.
Since the comparative example 2 does not use the chain transfer agent, the number average molecular weight and the weight average molecular weight of the dispersant are high, and it is inferior to any of adhesion, bending resistance and light resistance as compared with Examples 1-17.
In Comparative Example 3, since the RAFT agent is used as the chain transfer agent, the molecular weight distribution of the dispersant is narrow, and the adhesion, bending resistance, and light resistance are inferior to those of Examples 1-17.

  The pigment aqueous dispersion obtained by the production method of the present invention is excellent in the adhesion, bending resistance, and light resistance of a printed matter even when printed on a non-water-absorbing print medium by being contained in an aqueous ink.

Claims (10)

The manufacturing method of the pigment water dispersion which has the following processes 1-3.
Step 1: A step of obtaining an oligomer dispersant by mixing a radical polymerizable monomer (a), a radical polymerization initiator (a), and an irreversible chain transfer agent to obtain an oligomer dispersant Step 2: Obtained in Step 1 with a pigment Step of mixing the obtained oligomer dispersant and water to obtain a pigment water dispersion Step 3: Mixing the pigment water dispersion obtained in Step 2 and the radical polymerizable monomer (b) to seed polymerization And coating the pigment to obtain a pigment aqueous dispersion   The manufacturing method of the pigment water dispersion of Claim 1 whose molecular weight distribution (Mw / Mn) measured by the gel permeation chromatography method of the oligomer dispersing agent obtained at the process 1 is 2-5.   The method for producing a pigment aqueous dispersion according to claim 1 or 2, wherein the irreversible chain transfer agent contains a thiol group or a haloalkyl group.   The manufacturing method of the pigment water dispersion in any one of Claims 1-3 in which the said irreversible chain transfer agent contains a thiol group.   The method for producing an aqueous pigment dispersion according to claim 3 or 4, wherein the irreversible chain transfer agent further has an acidic group.   The method for producing a pigment aqueous dispersion according to any one of claims 1 to 5, wherein the radical polymerization initiator (a) is an azo polymerization initiator containing an azo group.   In step 1, the molar ratio of the total number of moles of the radical polymerizable monomer (a) to the total number of moles of the irreversible chain transfer agent [radical polymerizable monomer (a) / irreversible chain transfer agent] is 5 or more. The method for producing a pigment aqueous dispersion according to any one of claims 1 to 6, which is 30 or less.   In step 1, the molar ratio of the total number of moles of the radical polymerization initiator (a) to the total number of moles of the irreversible chain transfer agent [radical polymerization initiator (a) / irreversible chain transfer agent] is 0. The method for producing a pigment aqueous dispersion according to any one of claims 1 to 7, which is from 05 to 0.5.   The manufacturing method of the pigment aqueous dispersion in any one of Claims 1-8 in which the said pigment contains a titanium oxide.   A water-based ink comprising a pigment aqueous dispersion obtained by the production method according to claim 1.