JP3981396B2 - Method for producing aqueous pigment dispersion - Google Patents

Description

  The present invention relates to a method for producing a water-based pigment dispersion, and more specifically, a finely-stabilized water-based pigment dispersion that exhibits excellent gloss and scratch resistance when printed on special paper while satisfying a high printing density. The present invention relates to a method for producing a body, and an aqueous ink for inkjet recording.

  The ink jet recording method is a recording method in which characters and images are obtained by ejecting and adhering ink droplets directly from a very fine nozzle to a recording member. This method is remarkably widespread because it has many advantages of being easy to make full-color and inexpensive, using plain paper as a recording member, and being non-contact with the object to be printed. Among these, pigment-based inks have become mainstream from the viewpoint of light resistance and water resistance of printed matter. In recent years, glossiness and the like similar to those of dye-based inks are also required for pigment-based inks.

As a method for producing a pigment-based ink, a method is generally known in which a pigment is dispersed in a liquid medium such as water or an organic solvent in the presence of a dispersant.
For example, Patent Document 1 discloses that a fine grinding medium is used to disperse a pigment together with a dispersant using a high-speed mill. Here, a continuous medium recirculation fine grinding method and a mixed medium fine grinding method are shown as the fine grinding methods. However, in these methods, a slurry of the fine grinding media, liquid, pigment and dispersant is circulated in the system. After completion of the fine grinding, the pigment dispersion is separated from the fine grinding medium by a mechanical method such as sieving with a screen or filtration. However, this method has a problem that the time required for the separation is long and the yield of the pigment dispersion is also reduced.
Patent Document 2 discloses a method in which a pigment is added to a resin dispersion having a weight average molecular weight of 9,000 to 80,000, ground, and further subdivided with a homogenizer. However, since the resin used is a styrene-maleic acid copolymer or styrene-acrylic acid copolymer having a weight average molecular weight of 80,000 or less, a dispersion having excellent storage stability and glossiness cannot be obtained. There's a problem.

Japanese Patent Laid-Open No. 9-176543 JP 2005-41992 A

  The present invention relates to a method for producing a finely stabilized water-based pigment dispersion that exhibits excellent gloss and scratch resistance when printed on special paper while satisfying a high printing density, and water-based ink for inkjet recording It is an issue to provide.

That is, the present invention provides the following [1] and [2].
[1] (1) A water-insoluble polymer having a weight average molecular weight in the range of 90,000 to 400,000 and having a structural unit derived from an anionic monomer , and having a solubility in 100 g of water of 5 to 40% by weight at 20 ° C. An emulsion composition (A) containing a certain organic solvent, a neutralizing agent and water is mixed with the pigment (B), and the resulting mixture has a nonvolatile component ratio of 5 to 50% by weight, [organic solvent / water]. A first step of obtaining a preliminary dispersion having a weight ratio of 0.1 to 0.9;
(2) a second step of continuously dispersing the obtained preliminary dispersion using a media-type disperser and continuously separating the obtained dispersion-treated product and media particles; and (3) a homogenizer. The manufacturing method of the water-system pigment dispersion including the 3rd process of carrying out a dispersion process further using this.
[2] A water-based ink for ink jet recording containing the water-based pigment dispersion obtained by the method of [1].

According to the present invention, it is possible to efficiently produce a finely stabilized water-based pigment dispersion that exhibits excellent gloss and scratch resistance when printed on special paper while satisfying a high printing density. it can.
Moreover, the aqueous ink containing the obtained aqueous pigment dispersion can be suitably used for inkjet recording.

(Water-insoluble polymer)
In the method for producing an aqueous pigment dispersion of the present invention, a water-insoluble polymer is used from the viewpoint of obtaining excellent dischargeability with low viscosity.
Examples of water-insoluble polymers include water-insoluble vinyl polymers, water-insoluble ester polymers, water-insoluble urethane polymers, and the like. Among these, a water-insoluble vinyl polymer is preferable from the viewpoint of the stability of the aqueous dispersion.
In the present invention, the water-insoluble polymer means that when it is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the dissolved amount is 10 g or less, preferably 5 g or less, more preferably 1 g or less. A polymer. When the water-insoluble polymer has a salt-forming group, the above-mentioned dissolution amount refers to the dissolution amount when the salt-forming group of the water-insoluble polymer is neutralized 100% with acetic acid or sodium hydroxide, depending on the type.

(Water-insoluble graft polymer)
The water-insoluble polymer is a water-insoluble graft polymer from the viewpoint of developing a sufficient printing density, and the main chain is derived from at least a salt-forming group-containing monomer (a) [hereinafter sometimes referred to as component (a)] A polymer chain containing a unit and a structural unit derived from an aromatic ring-containing (meth) acrylate monomer (b) [hereinafter sometimes referred to as (b) component], and the side chain is at least a hydrophobic monomer (e) [hereinafter (e The polymer chain containing a structural unit derived from a component is sometimes preferred.
In the present invention, it is considered that the mobility of the salt-forming group can be increased by the main chain containing the structural unit derived from the component (a) and the structural unit derived from the component (b). As a result, when an aqueous dispersion of a water-insoluble graft polymer containing a pigment is ejected from a nozzle of an inkjet onto special paper (photographic paper, glossy paper), printing is performed by reducing the cohesiveness of the salt-forming groups. It is considered that the smoothness of the (printing) surface is increased and the gloss and scratch resistance of the printed matter (printed matter) are improved.

In the main chain, the structural unit derived from the component (a) is preferably obtained by polymerizing a salt-forming group-containing monomer. After polymerization of the polymer, a salt-forming group (anionic group, cationic group, etc.) may be introduced into the polymer chain. The structural unit derived from the component (a) is used to increase the dispersion stability of the polymer.
As the salt-forming group-containing monomer as component (a), (a-1) anionic monomer or (a-2) cationic monomer is preferable, and (a-1) anionic monomer is particularly preferable.

(A-1) Examples of the anionic monomer include one or more selected from the group consisting of an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylic acid ester, bis- (3-sulfopropyl) -itaconate, and the like. .
Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acrylic acid. And leuoxyethyl phosphate.
Among the above anionic monomers, an unsaturated carboxylic acid monomer is preferable, and acrylic acid or methacrylic acid is more preferable from the viewpoints of ink viscosity, dischargeability, and the like.

(A-2) Examples of the cationic monomer include unsaturated tertiary amine-containing vinyl monomers and / or unsaturated ammonium salt-containing vinyl monomers.
Examples of unsaturated tertiary amine-containing vinyl monomers include N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, vinylpyrrolidone, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-6-vinylpyridine, 5-ethyl-2-vinylpyridine and the like can be mentioned.
Examples of the unsaturated ammonium salt-containing vinyl monomer include N, N-dimethylaminoethyl (meth) acrylate quaternized product, N, N-diethylaminoethyl (meth) acrylate quaternized product, N, N-dimethylaminopropyl (meth) ) Acrylate quaternized product and the like.
Among the above cationic monomers, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and vinylpyrrolidone are preferable.
As used herein, “(meth) acrylate” means “acrylate”, “methacrylate”, or a mixture thereof.
The salt-forming group-containing monomers can be used alone or in combination of two or more.

  By combining the structural unit derived from the component (a) with the structural unit derived from the aromatic ring-containing (meth) acrylate monomer (b), it is possible to improve glossiness, scratch resistance and the like. (B) As a structural unit derived from a component, the structural unit represented by following formula (1) is preferable.

(In the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² may have a substituent, which has 7 to 22 carbon atoms, preferably 7 to 18 carbon atoms, and more preferably 7 carbon atoms. An arylalkyl group having 12 to 12 carbon atoms, or an aryl group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and more preferably 6 to 12 carbon atoms, which may have a substituent.

Specific examples of R ² include a benzyl group, a phenethyl group (phenylethyl group), a phenoxyethyl group, a diphenylmethyl group, and a trityl group.
The arylalkyl group or the substituent that the aryl group may have may include a hetero atom, and examples of the hetero atom include a nitrogen atom, an oxygen atom, and a sulfur atom. Specific examples of the substituent include preferably an alkyl group, an alkoxy group or an acyloxy group, a hydroxyl group, an ether group, an ester group, a nitro group and the like having 1 to 9 carbon atoms.

The structural unit represented by the formula (1) is preferably obtained by polymerizing a monomer represented by the following formula (1-1).
CH ₂ = CR ¹ COOR ² (1-1)
(Wherein R ¹ and R ² are the same as described above.)
Specifically, benzyl (meth) acrylate, phenyl (meth) acrylate, 2-phenylethyl (meth) acrylate, phenoxyethyl (meth) acrylate, 1-naphthalyl acrylate, 2-naphthalyl (meth) acrylate, phthalimidomethyl ( And (meth) acrylate, p-nitrophenyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, 2-acryloyloxyethyl phthalate, and the like. . Of these, benzyl (meth) acrylate is preferred. These can be used alone or in combination of two or more.

In the main chain, from the viewpoint of improving storage stability, printing density, etc., (meth) acrylate (c-1) having 1 to 22 carbon atoms (hereinafter referred to as (c-1) component) Or a structural unit derived from the monomer (c-2) represented by the following formula (2) (hereinafter sometimes referred to as (c-2) component) [hereinafter collectively referred to as (c) component] It may be.
^{_{CH 2 = C (R 3)}} -R 4 (2)
(In the formula, R ³ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ⁴ represents an aromatic ring-containing hydrocarbon group having 6 to 22 carbon atoms.)
Specifically, the structural unit derived from (meth) acrylate having an alkyl group having 1 to 22 carbon atoms is methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tarsha Lee) Butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (meth) It can be obtained by polymerizing acrylate, behenyl (meth) acrylate or the like.
In the present specification, “(iso or tertiary)” and “(iso)” are the case where the branched structure represented by “iso” or “tertiary” is present or absent, that is, “ Both “normal” are shown.
In the formula (2), R ³ is preferably a hydrogen atom or a methyl group. As the monomer represented by the formula (2), styrene, vinylnaphthalene, α-methylstyrene, vinyltoluene, ethyl are used from the viewpoint of printing density and the like. One or more selected from vinylbenzene, 4-vinylbiphenyl and 1,1-diphenylethylene are preferred. Among these, from the viewpoint of printing density, storage stability, and the like, a styrene monomer that is at least one selected from the group consisting of styrene, α-methylstyrene, and vinyltoluene is more preferable.

The main chain contains a structural unit derived from a nonionic (meth) acrylate monomer (d) (hereinafter sometimes referred to as component (d)) to improve glossiness, print density, ejection stability, etc. From the viewpoint of making it.
As the nonionic (meth) acrylate monomer (d), a nonionic monomer represented by the following formula (3) is preferable.
^{_{CH 2 = C (R 5)}} COO (R 6 O) n R 7 (3)
(In the formula, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ⁶ represents an alkylene group having 2 to 18 carbon atoms, n represents an average number of added moles, 1 to 30 and R ⁷ represents hydrogen. (A phenyl group which may have an atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 1 to 8 carbon atoms is preferred.)
In formula (3), from the viewpoint of polymerizability and the like, R ⁵ is preferably a hydrogen atom, a methyl group or the like, and R ⁶ is an ethylene group having 2 to 4 carbon atoms, a trimethylene group, a propane-1,2-diyl group, A tetramethylene group or the like is preferable. R ⁵ is preferably an ethylene group from the viewpoint of improving ejection properties, glossiness, and the like, and a trimethylene group, a propane-1,2-diyl group, or a tetramethylene group is preferable from the viewpoint of improving the printing density. n is preferably a number from 2 to 25, more preferably a number from 4 to 23, from the viewpoint of printing density, storage stability, and the like. At least two of the n R ^{6 s} may be the same or different, and if they are different, either block addition or random addition may be used.
R ⁷ is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms, from the viewpoints of high printing density, good storage stability, and the like. Moreover, the phenyl group which may have a C1-C8 alkyl group is preferable.
Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, tert-butyl group, hexyl group, octyl group, and 2-ethylhexyl group.

  Specific examples of the nonionic monomer represented by the formula (3) include hydroxyethyl methacrylate, methoxypolyethylene glycol mono (meth) acrylate; polyethylene glycol mono (meth) acrylate; methoxypolypropylene glycol mono (meth) acrylate; polypropylene glycol Examples include mono (meth) acrylate; ethylene glycol / propylene glycol (meth) acrylate; poly (ethylene glycol / propylene glycol) mono (meth) acrylate; octoxypolyethylene glycol / polypropylene glycol mono (meth) acrylate, and the like. These can be used alone or in combination of two or more.

In the main chain, the weight ratio of (a) a structural unit derived from a salt-forming group-containing monomer (calculated as an unneutralized amount; the same applies hereinafter) and (b) a structural unit derived from an aromatic ring-containing (meth) acrylate monomer [(a The content of the structural unit derived from the component / the content of the structural unit derived from the component (b) is 1/1 to 1/20 from the viewpoint of improving the glossiness, scratch resistance, etc. when printed. It is preferably 1 / 1.5 to 1/15, more preferably 1/2 to 1/10. Particularly within this range, it is possible to give excellent gloss to dedicated paper printing.
In the water-insoluble graft polymer used in the present invention, the content of the structural units derived from the components (a) to (d) in the main chain is as follows.
From the viewpoint of improving the dispersibility of the water-insoluble graft polymer, the content of the structural unit derived from the component (a) is preferably 3 to 30% by weight, more preferably 5 to 20% by weight, and 5 to 15% by weight. Is particularly preferred.
The content of the structural unit derived from the component (b) is preferably 10 to 80% by weight, more preferably 15 to 75% by weight, and particularly preferably 20 to 70% by weight from the viewpoint of improving glossiness, scratch resistance and the like. The content of the constituent unit derived from the component (c-1) is preferably 0 to 30% by weight, more preferably 0 to 15% by weight from the viewpoint of improving dispersion stability. The content of the structural unit derived from the component (c-2) is preferably 0 to 30% by weight, and more preferably 0 to 15% by weight, from the viewpoint of improving the printing density, marker resistance and the like. Further, the content of the structural unit derived from the component (c) is preferably 0 to 40% by weight, and more preferably 0 to 20% by weight from the viewpoint of improving dispersion stability, printing density, and the like.
The content of the structural unit derived from the component (d) is preferably 0 to 60% by weight, and more preferably 10 to 50% by weight, from the viewpoint of improving the printing density, glossiness, ejection stability and the like.

The water-insoluble graft polymer used in the present invention contains a structural unit derived from the hydrophobic monomer (e) in the side chain from the viewpoint of sufficiently containing the colorant in the water-insoluble graft polymer particles and improving the printing density. .
In the side chain, the content of the structural unit derived from the component (e) is preferably 60% by weight or more, from the viewpoint of sufficiently containing the colorant in the water-insoluble graft polymer particles and improving the printing density. % Or more is more preferable, and 90% by weight or more is particularly preferable.
Examples of the hydrophobic monomer (e) include vinyl monomers, and styrene monomers are particularly preferable. Examples of the styrenic monomer include styrene, α-methylstyrene, vinyltoluene, and the like. Among these, styrene is preferable. A side chain containing a structural unit derived from a styrenic monomer can be obtained by copolymerizing a styrenic macromer having a polymerizable functional group at one end (hereinafter referred to as a styrenic macromer).

Examples of the styrenic macromer include a styrene homopolymer having a polymerizable functional group at one end, or a copolymer of styrene and another monomer having a polymerizable functional group at one end, and having at one end. As the polymerizable functional group, an acryloyloxy group or a methacryloyloxy group is preferable. Examples of other monomers copolymerized with styrene include (meth) acrylic acid esters, aromatic ring-containing (meth) acrylates, acrylonitrile and the like.
In the side chain or in the styrenic macromer, the content of the structural unit derived from the styrenic monomer is the largest, and from the viewpoint of sufficiently containing the colorant in the water-insoluble graft polymer particles and improving the printing density, preferably 60 % By weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more.
The number average molecular weight of the styrenic macromer is preferably 1,000 to 10,000, more preferably 2,000 to 8,000, from the viewpoint of keeping the viscosity low while increasing the copolymerization ratio in order to enhance the storage stability. preferable.
The number average molecular weight of the styrenic macromer can be measured by gel permeation chromatography using polystyrene as a standard substance and tetrahydrofuran containing 50 mmol / L acetic acid as a solvent.
Examples of commercially available styrenic macromers include trade names of Toa Gosei Co., Ltd., AS-6, AS-6S, AN-6, AN-6S, HS-6, HS-6S, and the like.

  In the water-insoluble graft polymer used in the present invention, a main chain comprising a structural unit derived from a salt-forming group-containing monomer (a) and a structural unit derived from an aromatic ring-containing (meth) acrylate monomer (b), and a hydrophobic monomer (e ) The weight ratio [main chain / side chain] to the side chain containing the structural unit derived from is preferably 1/1 to 20/1 in order to improve the printing density, glossiness, scratch resistance and the like. 3/2 to 15/1 is more preferable, and 2/1 to 10/1 is particularly preferable. (The polymerizable functional group is calculated as contained in the side chain. The same applies hereinafter)

The water-insoluble graft polymer used in the present invention can further have a side chain composed of another constituent unit, for example, an organopolysiloxane side chain. This side chain is preferably obtained, for example, by copolymerizing a silicone macromer having a polymerizable functional group at one end, which is represented by the following formula (4).
CH ₂ = C (CH ₃ ) -COOC ₃ H _6- [Si (CH ₃ ) ₂ -O] _t -Si (CH ₃ ) ₃ (4)
(Wherein t represents a number of 8 to 40)

The water-insoluble graft polymer used in the present invention comprises a monomer mixture containing a salt-forming group-containing monomer (a), an aromatic ring-containing (meth) acrylate monomer (b), and a hydrophobic monomer (e) such as a styrenic macromer. It can be obtained by polymerization. Further, the monomer mixture is copolymerized with a monomer mixture containing (c) component monomer and / or nonionic (meth) acrylate monomer (d) (hereinafter collectively referred to as “monomer mixture”). What is obtained is preferred.
The content of the components (a) to (e) in the monomer mixture, or the content of the structural units derived from the components (a) to (e) present in the main chain or side chain in the water-insoluble graft polymer are as follows: It is as follows.
The content of the salt-forming group-containing monomer (a) (content as an unneutralized amount; the same applies hereinafter), or the content of the structural unit derived from the component (a) present in the main chain in the water-insoluble graft polymer, From the viewpoint of improving the dispersion stability of the resulting dispersion and the glossiness of the printed matter, it is preferably 3 to 30% by weight, more preferably 3 to 20% by weight, and particularly preferably 5 to 15% by weight.
The content of the component (b) or the content of the structural unit derived from the component (b) present in the main chain in the water-insoluble graft polymer is 10 from the viewpoint of improving the gloss, scratch resistance, etc. of the printed matter. -80 wt% is preferable, 15-70 wt% is more preferable, and 20-60 wt% is particularly preferable.
The content of the component (c) or the content of the structural unit derived from the component (c) is preferably 0 to 40% by weight, and 0 to 20% by weight from the viewpoint of printing density, dispersion stability, marker resistance and the like. Further preferred.
The content of the component (d) or the content of the structural unit derived from the component (d) is preferably 0 to 60% by weight, more preferably 10 to 50% by weight from the viewpoints of ejection stability, glossiness, print density, and the like. preferable.
The content of the component (e) or the content of the structural unit derived from the component (e) present in the side chain in the water-insoluble graft polymer is 5 to 50% by weight from the viewpoint of improving the print density of the printed matter. 5 to 40% by weight is more preferable, and 5 to 35% by weight is particularly preferable.

Weight ratio of [(a) component content / (e) component content] in the monomer mixture, or [(a) component unit content / (e) in the water-insoluble graft polymer] The content ratio of the component-derived constituent unit] is preferably from 1/5 to 2/1, and more preferably from 1/4 to 2/1, from the viewpoints of dispersion stability, print density, and the like.
Weight ratio of [(b) component / (d) component] in the monomer mixture, or content of [(b) component-derived structural unit / (d) component-derived structural unit in the water-insoluble graft polymer] The weight ratio of [Amount] is preferably 5/1 to 1/2, and more preferably 4/1 to 1/2 from the viewpoints of glossiness, print density, and the like.

The water-insoluble graft polymer used in the present invention is used by neutralizing a salt-forming group derived from a salt-forming group-containing monomer with a neutralizing agent described later. The degree of neutralization of the salt-forming group is preferably 10 to 200%, more preferably 20 to 150%, and particularly preferably 30 to 100%. Moreover, when neutralizing excessively at the time of preliminary dispersion | distribution, the neutralization degree can also be adjusted by using the neutralizing agent which can be removed by a concentration process.
The degree of neutralization can be determined by the following formula when the salt-forming group is an anionic group.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × polymer weight (g) / (56 × 1000)]} × 100
When the salt-forming group is a cationic group, the degree of neutralization can be determined by the following formula.
[[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [amine value of polymer (HCL mg / g) × weight of polymer (g) / (36.5 × 1000)]] × 100
The acid value and the amine value can be calculated from the structural unit of the water-insoluble graft polymer, but can also be determined using a method in which the polymer is dissolved in an appropriate solvent (for example, methyl ethyl ketone) and titrated.
From the viewpoint of dispersion stability, the acid value of the polymer is preferably 30 (KOHmg / g) or more, and more preferably 40 (KOHmg / g) or more. Further, from the viewpoint of developing a high printing density, it is preferably 200 (KOHmg / g) or less, and more preferably 150 (KOHmg / g) or less.

(Production of water-insoluble graft polymer)
The water-insoluble graft polymer used in the present invention is produced by copolymerizing a monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is preferably a polar organic solvent. 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 such as methanol, ethanol, and propanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable.

Although the polymerization conditions of the monomer mixture vary depending on the type of radical polymerization initiator, monomer, solvent, etc. to be used and cannot be determined unconditionally, the polymerization temperature is usually preferably 30 to 100 ° C., more preferably 50 The polymerization time is preferably 1 to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced water-insoluble graft polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained water-insoluble graft polymer can be purified by repeating reprecipitation or removing unreacted monomers by membrane separation, chromatographic methods, extraction methods, and the like.

The weight average molecular weight of the water-insoluble graft polymer thus obtained is preferably 90,000 to 400,000 from the viewpoints of pigment dispersion stability, water resistance, dischargeability, and the like, and 120,000 to 350,000. More preferably, it is 000.
The weight-average molecular weight of the water-insoluble graft polymer was determined by gel chromatography using dimethylformamide in which 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide were dissolved as a solvent, and polystyrene as a standard substance. Can be measured.

(Organic solvent)
In the present invention, an organic solvent having a solubility in 100 g of water of 5 to 40% by weight, preferably 10 to 30% by weight at 20 ° C. is used.
When the organic solvent is used, the dispersion stability of the pigment in the obtained aqueous pigment dispersion can be improved. Thus, the dispersion stability of the pigment is improved because part of the organic solvent dissolves in water, and when the emulsion composition and the pigment are mixed, the organic solvent dissolved in water wets the pigment surface, This is considered to be due to the improvement of the adsorptivity of the insoluble graft polymer to the pigment surface.
Examples of the organic solvent include alcohol solvents, ketone solvents, ether solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, halogenated aliphatic hydrocarbon solvents, and the like. For example, as an alcohol solvent, 1-butanol (solubility in 100 g of water is 7.8% by weight at 20 ° C. according to “Solvent Handbook” edited by Teruzo Asahara (Kodansha, published in 1976); 2-butanol (solubility in 100 g of water is 12.5% by weight at 20 ° C.) and the like. Examples of the ketone solvent include methyl ethyl ketone (solubility in 100 g of water is 22.6% by weight at 20 ° C.). Among these organic solvents, methyl ethyl ketone is preferable from the viewpoint of safety and operability of solvent removal in post-treatment. These organic solvents can be used individually or in mixture of 2 or more types.

(Neutralizer)
As the neutralizing agent, it can be neutralized using an acid or a base depending on the kind of the salt-forming group in the water-insoluble graft polymer, hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, Uses acids such as glycolic acid, gluconic acid, glyceric acid, bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, trimethylamine, triethanolamine it can.

(Emulsified composition (A))
The emulsified composition (A) used in the present invention contains a water-insoluble polymer such as a water-insoluble graft polymer, an organic solvent, a neutralizing agent and water.
The amount of the water-insoluble polymer is preferably 0.1 to 160 parts by weight, more preferably 0.5 to 100 parts by weight, still more preferably 1 with respect to 100 parts by weight of water, from the viewpoint of the stability of the emulsion composition. ~ 50 parts by weight. The content of the water-insoluble polymer in the emulsion composition is preferably 1 to 20% by weight from the viewpoint of the stability of the emulsion composition.
The content of water in the emulsified composition is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, from the viewpoints of stability of the emulsified composition and ease of compatibility of the pigment.
Further, the content of the neutralizing agent in the emulsified composition is appropriately adjusted so that the liquid property of the finally obtained aqueous pigment dispersion is neutral, for example, pH is 4.5 to 10. be able to. When the salt-forming group of the water-insoluble graft polymer is anionic, it is preferably adjusted to a pH such as 7-10.
There are no particular restrictions on the method of mixing and preparing the emulsified composition, but if the water-insoluble polymer is dissolved or dispersed in an organic solvent and then mixed with water and a neutralizing agent, a part of the water-insoluble polymer is dissolved in the organic solvent. And a uniform emulsion composition is preferable. The mixing temperature of each component is not particularly limited, but is usually preferably 5 to 50 ° C.
The emulsion composition obtained by mixing each component becomes an oil-in-water emulsion composition having water as a continuous phase.

(Pigment (B))
As the pigment (B), both organic pigments and inorganic pigments can be used. If necessary, they can be used in combination with extender pigments.
Examples of the organic pigment 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 chromatic pigments such as a red organic pigment, a yellow organic pigment, a blue organic pigment, an orange organic pigment, and a green orange organic pigment can be used.
Specific examples of preferred organic pigments include C.I. I. Pigment Yellow 13, 17, 74, 83, 97, 109, 110, 120, 128, 139, 151, 154, 155, 174, 180; I. Pigment Red 48, 57: 1, 122, 146, 176, 184, 185, 188, 202; I. Pigment violet 19, 23; C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 60; I. One or more types of products selected from the group consisting of CI Pigment Green 7 and 36 are listed.
Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. Among these, carbon black is particularly preferable as the black water-based ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of extender pigments include silica, calcium carbonate, and talc.

As the pigment, a so-called self-dispersing pigment can also be used. The self-dispersing pigment is an aqueous medium without using a surfactant or a resin by binding one or more of an anionic hydrophilic group or a cationic hydrophilic group to the surface of the pigment directly or through another atomic group. Means a pigment that is dispersible. Here, the anionic hydrophilic group is particularly preferably a carboxyl group (—COOM ¹ ) or a sulfonic acid group (—SO ₃ M ¹ ) (wherein M ¹ is a hydrogen atom, an alkali metal, or ammonium), As the cationic hydrophilic group, a quaternary ammonium group is preferable.
In order to convert a normal pigment into a self-dispersing pigment, the necessary amount of the above anionic hydrophilic group or cationic hydrophilic group is changed to a known method, for example, a method of introducing a carboxyl group with an acid, or thermal decomposition of a persulfuric acid compound. It may be chemically bonded to the pigment surface by a method of introducing a sulfone group by a method, a method of introducing the anionic hydrophilic group by a diazonium salt compound having a carboxyl group, a sulfone group, an amino group or the like.
The above pigments can be used alone or in admixture of two or more.

  The amount of the pigment is preferably 1 to 90 parts by weight, more preferably 5 to 80 parts by weight, and still more preferably 10 to 100 parts by weight with respect to 100 parts by weight of the emulsified composition from the viewpoint of inclusion in the printing density and the water-insoluble graft polymer. 70 parts by weight. The amount ratio of the water-insoluble graft polymer to the pigment is preferably 20 to 1,000 parts by weight, more preferably 50 parts by weight of the pigment with respect to 100 parts by weight of the solid content of the water-insoluble graft polymer from the viewpoint of increasing the printing density. It is -900 weight part, More preferably, it is 100-800 weight part.

(Production of water-based pigment dispersion)
In the production of an aqueous pigment dispersion, (1) a first step of mixing the emulsified composition (A) and the pigment (B) to obtain a preliminary dispersion, (2) the obtained preliminary dispersion is used as a media type disperser A second step of continuously dispersing and continuously separating the dispersion-treated product is used, and (3) a third step of further dispersing treatment is performed using a homogenizer.

(First step)
In the first step, a mixture (hereinafter simply referred to as “mixture”) obtained by mixing the emulsified composition (A) and the pigment (B) was dispersed, and the pigment was uniformly dispersed in the emulsified composition. This is a process aimed at obtaining a preliminary dispersion and adsorbing the neutralized water-insoluble polymer to the pigment.
The order of mixing the emulsified composition (A) and the pigment (B) is not particularly limited, but it is easy to mix the pigment and the emulsified composition from the viewpoint of increasing productivity in consideration of the bulk density of the pigment. From this viewpoint, it is preferable to add the pigment (B) to the emulsion composition (A).
On the other hand, for example, when an organic solvent in which a water-insoluble polymer is dissolved and the pigment are mixed without using the emulsified composition (A), it is difficult to uniformly disperse the pigment in the organic solvent. It is difficult to obtain an emulsion composition in which is uniformly dispersed. Moreover, even if water and a pigment are mixed in advance and then an organic solvent in which a water-insoluble polymer is dissolved is added and mixed, it is difficult to obtain an emulsified composition in which the pigment is uniformly dispersed.

When dispersing the mixture, the non-volatile component ratio of the mixture is preferably 5% by weight or more, more preferably 8% by weight from the viewpoint of increasing the dispersion force and shearing force and reducing the pigment particle size to increase production efficiency. % Or more, more preferably 10% by weight or more. From the viewpoint of reducing the viscosity of the mixture to obtain a preliminary dispersion having a uniform composition and facilitating separation from the media particles, the non-volatile component ratio of the mixture is preferably 50% by weight or less, more preferably 40%. The weight is adjusted to be not more than% by weight, more preferably not more than 35% by weight. From the above, the nonvolatile component ratio of the mixture is preferably 5 to 50% by weight, more preferably 8 to 40% by weight, and still more preferably 10 to 35% by weight.
Here, the “nonvolatile component ratio” means a value obtained based on the following formula.
Nonvolatile component ratio (% by weight) = [(total weight of water-insoluble polymer having salt-forming group, neutralizing agent and pigment) / (total weight of emulsified composition and pigment)] × 100

The weight ratio of [organic solvent / water] (value at the time of dispersion of the mixture) decreases as the amount of the organic solvent dissolved in water relatively decreases and the pigment surface tends to be difficult to wet sufficiently. .1 or more, preferably 0.2 or more.
Further, if the weight ratio of [organic solvent / water] is increased, the pigment can be sufficiently wetted. However, on the other hand, the viscosity of the mixture is increased, and uniform mixing and dispersion tend to be difficult. There is also a tendency for oil-type emulsified compositions to phase invert to water-in-oil. Therefore, from the viewpoint of suppressing the viscosity of the mixture to such an extent that the mixture can be uniformly dispersed and suppressing phase inversion from the oil-in-water type to the water-in-oil type, the weight ratio of [organic solvent / water] is 0.9 or less. Even when the non-volatile component ratio is increased, the viscosity of the mixture tends to increase, so that it is preferably 0.8 or less. From the above, the weight ratio of [organic solvent / water] is 0.1 to 0.9, preferably 0.2 to 0.8.
In addition, when dispersing the mixture, from the viewpoint of reducing the content of coarse particles after the first step and improving the adsorptivity between the water-insoluble polymer and the pigment, the weight ratio of [organic solvent / water] and non-volatile components The pre-dispersion process may be performed twice or more by gradually reducing the rate. The number of preliminary dispersion treatments is preferably 10 times or less, more preferably 5 times or less, from the viewpoint of complexity and productivity.

In the first step, a commonly used mixing and stirring device such as an anchor blade can be used. Among the mixing and stirring devices, Ultra Disper (Asada Tekko Co., Ltd., trade name), Ebara Milder (Ebara Manufacturing Co., Ltd., trade name), TK homomixer, TK pipeline mixer, TK homojetter, TK homomic line flow, High-speed agitation and mixing devices such as Fillmix (Primix Co., Ltd., trade name), Clear Mix (M Technique Co., trade name), and K-D Mill (Kinetic Dispersion Co., trade name) are preferred.
In addition, after the mixture is predispersed in the first step, if the resulting predispersion has a large number of coarse particles, a shearing force stronger than the stirring force is applied as necessary to obtain a desired particle size. It is also possible to atomize or remove coarse particles with a centrifuge. In the manufacturing process, the dispersion process and the centrifugal separation process are continuously performed during the transfer from the first process to the second process, while the continuous dispersion process of one pass or more is added by a high-pressure homogenizer having a high atomization effect. The method etc. which transfer to 2 processes are illustrated.

(Second step)
The second step is a step intended to further disperse the pigment by continuously dispersing the preliminary dispersion obtained in the first step using a media type disperser, and was obtained. This is a step of continuously separating the dispersed product and the media particles.
The media-type disperser used in the second step uses media particles (microbeads), and can provide shearing force, collision force, and grinding force that can disperse and atomize to near the primary particles of the pigment. Is preferred.
A media-type disperser retains media particles in a dispersion chamber (mill) and disperses the pre-dispersion flowing through the dispersion while applying dispersion energy such as pulverization, shearing, and collision with the media particles. The treated product is separated by centrifugation or the like, and only the dispersed treatment product is allowed to flow out of the dispersion chamber.
Examples of such media-type dispersers include Star Mill (Ashizawa Finetech Co., Ltd., trade name), Ultra Apex Mill (Kotobuki Kogyo Co., Ltd., trade name), and Pico Mill (Asada Tekko Co., Ltd., trade name). , DCP Superflow, Cosmo (Nippon Eirich Co., Ltd., trade name), MSC Mill (Mitsui Mining Co., Ltd., trade name), and other known dispersers.

A typical media-type disperser includes, for example, a plurality of agitator disks (rotors) mounted on a drive shaft in a cylindrical dispersion chamber having a liquid supply port, and a large number of media particles are built in the internal space. It has a structure. A liquid mixture containing an emulsion composition (A) and a pigment (B) containing a water-insoluble polymer having a salt-forming group, an organic solvent, a neutralizing agent, and water while rotating the agitator disk by rotating the drive shaft When (slurry) is continuously introduced from the liquid supply port into the dispersion chamber, a strong shearing force is applied to the media particles and the mixed solution, and the pigment (B) is pulverized and finely dispersed in the mixed solution. The mixed liquid in which the pigment (B) is finely dispersed is separated from the media particles and conveyed to the outside from a liquid discharge port provided in the upper part of the dispersion chamber.
As a method for separating the mixed liquid from the media particles, a centrifugal separation method or a method in which a screen and centrifugal separation are combined can be employed.
As described above, there are a circulation method and a continuous method as an operation method in which the dispersion process and the separation process are performed simultaneously and continuously. As a circulation method, for example, there is a method in which a tank of one tank and a media-type disperser are installed, and a circulation system is formed by piping to perform a circulation path (one tank circulation method, see FIG. 1). In addition, as a continuous method, a method in which two tanks and a media-type disperser are installed and passed by the catch ball method, a method in which the passed liquid is returned to the original tank again, and the same pass operation is repeated ( Examples include a liquid return method using two tanks (see FIG. 2), and a method in which a required number of media type dispersers are arranged in series to perform one pass. Among these, the continuous method is preferable, in which the distribution of the number of passes when the dispersion liquid passes through the media type disperser hardly occurs. In the case where the media type dispersers are arranged in series, it is preferable to install a cooler at the outlet of the disperser because the liquid temperature after the dispersion treatment increases.

Examples of the material of the media particles used in the media-type disperser include high-hardness metals such as steel and chromium alloys, high-hardness ceramics such as alumina, zirconia, zircon, and titania, and polymers such as glass, ultra high molecular weight polyethylene, and nylon. Materials and the like.
Since the magnitude of the shearing force, collision force, and pulverizing force for atomizing the pigment increases as the specific gravity of the media particles increases, among them, ceramic media particles having a relatively large specific gravity are preferable. From the viewpoint of wear resistance, zirconia, titania and the like are more preferable. Moreover, you may use the media particle manufactured by the high frequency induction thermal plasma method from a viewpoint of reducing the contamination generate | occur | produced from a media particle more.
As the particle size (diameter) of the media particles used in the media-type disperser, a desired size can be used. However, the smaller the particle size of the media particles, the less contamination occurs from the media. The particle size of the media particles is preferably 0.25 mm or less, more preferably 0.20 mm or less, from the viewpoint of separating the media particles and the pigment dispersion, preferably 0.01 mm or more, and 0.03 mm. The above is more preferable.

The peripheral speed of the tip of the agitator disk (rotor) of the media type dispersing machine is not particularly limited, but is preferably 4 m / s or more, and more preferably 6 m / s or more. In the case of 4 m / s or more, the mixing and dispersing state in the dispersion chamber can be kept good, and the centrifugal force necessary to separate the media particles and the dispersion-treated product can be obtained.
The apparent filling rate of the media particles in the dispersion chamber of the media type dispersing machine is preferably in the range of 50 to 100% by volume based on the space in the dispersion chamber. When the amount is 50% by volume or less, the effects of pulverization, shearing, and collision with the media are reduced, and the pigment dispersion effect is reduced.

As the operating conditions for dispersing the pigment, the above-mentioned circulation type or continuous type media dispersion machine, media particles, the particle size of the media particles, the circumferential speed of the rotor, the filling rate of the media particles, etc. are appropriately selected and dispersed. The net power is preferably 0.3 to 4 [kw / kg] per 1 kg of the preliminary dispersion obtained in the first step so that the energy required for the dispersion is not too small or excessively dispersed. 0.3-3 [kw / kg] is more preferable. Moreover, it is preferable to disperse | distribute so that it may become the range of 0.1-2 [kwh / kg] as net integrated power, The range of 0.1-1.5 [kwh / kg] is more preferable, 0.2 The range of -1.5 [kwh / kg] is more preferable. Here, the net power means the power obtained by subtracting the idling power from the actual load power to the disperser, and the idling power means the power without the media particles and the dispersion medium. The net accumulated power is obtained by multiplying the net power [kw] by the processing time [h].
In addition, it is necessary to pay attention to the manner in which the dispersion energy is applied. From the viewpoint of setting the treatment flow rate to an appropriate range and preventing changes in the particle size and viscosity of the pigment dispersion due to heat generation, the average per pass in the dispersion chamber The residence time is preferably in the range of 30 seconds to 10 minutes. Further, the total average residence time obtained by multiplying the average residence time by the number of passes is preferably in the range of 5 to 100 minutes, depending on the capacity and size of the disperser. The average residence time here means a value obtained by dividing the spatial volume [L] excluding the volume of media particles in the dispersion chamber by the processing flow rate [L / h].
Although the temperature at the time of a dispersion process is not specifically limited, 5-60 degreeC is preferable.

(Third step)
The third step is a step aimed to further disperse using a homogenizer and to crush and stabilize the pigment aggregate. In the second step, atomization can be performed to a desired particle size by a media type disperser, but the surface area and surface energy of the pigment increase with the atomization of the pigment. Since the pigment starts to reagglomerate in an attempt to reduce the surface energy, a dispersion treatment is required to break up the pigment aggregate and stabilize the pigment particles.
The homogenizer stabilizes the pigment particles by pulverizing the pigment aggregate and suppressing reaggregation by developing a cavitation phenomenon with high impact force and instantaneous high pressure.
Examples of the homogenizer include an ultrasonic homogenizer and a high-pressure homogenizer. When using an ultrasonic homogenizer, it is desirable to carry out dispersion treatment after evacuation, defoaming, and deaeration, and a high-pressure homogenizer is more preferable from the viewpoint of the efficiency of use of the dispersed energy to be input.

Examples of commercially available high-pressure homogenizers that can be used include high-pressure homogenizers (Izumi Food Machinery Co., Ltd., trade name), homovalve type high-pressure homogenizers represented by Minilab 8.3H (Rannie Co., trade name), and microfluidizer ( Microfluidics, trade name), Nanomizer (Yoshida Kikai Kogyo Co., Ltd., trade name), Ultimateizer (Sugino Machine Co., trade name), Genus PY (Shiramizu Chemical Co., Ltd., trade name), DeBEE2000 (Japan EE Co., Ltd., Chamber type high-pressure homogenizer, etc.
From the viewpoint of suppressing reaggregation of pigment particles and achieving dispersion stabilization, the dispersion pressure is preferably 20 MPa or more, and more preferably 50 MPa or more. From the same point of view, the number of processing passes is at least 1 pass or more, preferably 3 passes or more, more preferably 5 passes or more. As the operation method for passing, like the media-type disperser in the second step, there are a circulation method and a continuous method, and a continuous method is more preferable from the viewpoint of hardly generating a pass number distribution.
Although the temperature at the time of a dispersion process is not specifically limited, 5-80 degreeC is preferable.
Further, from the viewpoint of printing performance such as prevention of clogging of the nozzle of the printer, dispersion stability, glossiness, and image clarity, the average particle diameter of the pigment is preferably 0.01 to 0.5 μm, more preferably 0.03 to 0.03. Dispersion treatment is performed until the thickness becomes 0.3 μm, particularly preferably 0.05 to 0.2 μm.
The average particle diameter was measured using a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd., at a temperature of 25 ° C., an angle between incident light and a detector of 90 °, an integration count of 100 times, and water refraction. The ratio can be measured using uniform microparticles (average particle size 204 nm) manufactured by Seradyn as a standard substance.

By performing the first to third steps, a finely divided and stabilized pigment dispersion can be obtained, but it is preferable to remove the organic solvent from the viewpoint of further stabilization.
The removal of the organic solvent can be performed by a general method such as distillation under normal pressure or reduced pressure, and it is preferable to remove coarse particles by filtration or centrifugation. As described above, the aqueous pigment dispersion of the present invention can be obtained.
In general, the non-volatile component of the water-based pigment dispersion is preferably adjusted to 1 to 30% by weight, and more preferably 3 to 25% by weight, from the viewpoints of print density and ejection stability.
Further, this water-based pigment may be used as it is as a water-based ink, but wetting agents, penetrants, dispersants, viscosity modifiers, antifoaming agents, antifungal agents, rust-proofing agents and the like that are usually used in water-based inks for inkjet recording May be added. The aqueous pigment dispersion obtained by the production method of the present invention can be suitably used for an aqueous ink for inkjet recording.

  In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.

(Production Example 1)
In a 5 L reaction vessel, 81.8 g of methyl ethyl ketone, 0.31 g of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of 2000 g of the monomer mixture shown in Production Example 1 are mixed and mixed thoroughly with nitrogen gas. A mixed solution was obtained.
On the other hand, the remaining 90% of the monomer mixture shown in Production Example 1 was charged into a dropping funnel, and 2.78 g of a polymerization chain transfer agent (2-mercaptoethanol), 736.4 g of methyl ethyl ketone and 2,2′-azobis (2,4 -Dimethylvaleronitrile) 18.2g was mixed and nitrogen gas substitution was fully performed, and the mixed solution was obtained.
While stirring the mixed solution in the reaction vessel under a nitrogen atmosphere, the temperature was raised to 75 ° C., and the mixed solution in the dropping funnel was dropped over 5 hours. After 2 hours at 75 ° C. from the end of dropping, a solution prepared by dissolving 16.4 g of 2,2′-azobis (2,4-dimethylvaleronitrile) in 218.2 g of methyl ethyl ketone was added, and further at 75 ° C. for 2 hours, 80 ° C. For 2 hours to obtain a polymer solution.

(Production Example 2)
In Production Example 1, the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the reaction vessel was changed from 0.31 g to 0.45 g, and the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the dropping funnel was 2 The same operation as in Production Example 1 was carried out except that the composition was changed from 0.78 g to 4.09 g and the monomer mixture was changed to the composition shown in Production Example 2.
(Production Example 3)
In Production Example 1, the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the reaction vessel is changed from 0.31 g to 0.255 g, and the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the dropping funnel is 2 The same operation as in Production Example 1 was carried out except that the monomer mixture was changed from 0.78 g to 2.29 g, and the monomer mixture was changed to the composition shown in Production Example 3.
(Production Example 4)
In Production Example 1, the amount of methyl ethyl ketone charged into the reaction vessel is 81.8 g to 90.0 g, the amount of the polymerization chain transfer agent (2-mercaptoethanol) is 0.31 g to 0.273 g, and the polymerization chain charged to the dropping funnel Manufactured except that the amount of transfer agent (2-mercaptoethanol) was changed from 2.78 g to 2.50 g, the amount of methyl ethyl ketone was changed from 736.4 g to 728.2 g, and the monomer mixture was changed to the composition shown in Production Example 4. The same operation as in Example 1 was performed.

(Comparative Production Example 1)
In Production Example 1, the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the reaction vessel was changed from 0.31 g to 0.62 g, and the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the dropping funnel was 2 The same operation as in Production Example 1 was carried out except that the monomer mixture was changed to the composition shown in Comparative Production Example 1 from 0.78 g to 5.56 g.
(Comparative Production Example 2)
In Production Example 1, the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the reaction vessel was changed from 0.31 g to 0.20 g, and the amount of the polymerization chain transfer agent (2-mercaptoethanol) charged in the dropping funnel was 2 The same operation as in Production Example 1 was carried out except that the monomer mixture was changed to the composition shown in Comparative Production Example 2 from 0.78 g to 1.80 g.

  The weight average molecular weight of the obtained polymer was determined as a polystyrene-reduced weight average molecular weight by gel chromatography using 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide-containing dimethylformamide as a solvent. The results are shown in Table 1.

The details of the compounds shown in Table 1 are as follows.
Polyethylene glycol monomethacrylate (ethylene oxide average addition mole number: 9): Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-90G
Polypropylene glycol monomethacrylate (propylene oxide average added mole number: 12): manufactured by NOF Corporation, trade name: Blemmer PP-800
Styrene macromer: manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group, stearyl methacrylate: manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK ester S

Example 1
112 g of the polymer obtained by drying the polymer solution obtained in Production Example 1 under reduced pressure was dissolved in 634 g of methyl ethyl ketone, and 25.5 g (neutralization degree 75%) of a neutralizer (5N aqueous sodium hydroxide solution) and ions The salt-forming group was neutralized by adding 1900 g of exchange water to obtain an emulsified composition. Then, 335 g of yellow pigment: diazo pigment (CI Pigment Yellow 74 [PY74], manufactured by Sanyo Color Co., Ltd., trade name: FY7413) was added and mixed with a disper blade at 20 ° C. for 1 hour to obtain a preliminary dispersion. (First step).
Next, 3006.5 g of the obtained pre-dispersion was used as a media particle having a particle size of 0.05 mm using an Ultra Apex Mill: Model UAM-1 (Koto Kogyo Co., Ltd., Media Disperser, trade name). Dispersion treatment by a circulation method was performed for 2 hours (total average residence time in the mill: 15 minutes) under the conditions of zirconia beads, bead filling rate of 80%, stirring blade peripheral speed of 12 m / s, and circulation flow rate of 500 cc / min. The net power given to 1 kg of the preliminary dispersion was 2.0 kw / kg, and the net integrated power was 0.5 kwh / kg (second step) (one tank circulation system, see FIG. 1).
Next, in order to further stabilize the dispersion, a dispersion process was carried out by a 10-pass continuous system at a pressure of 180 MPa using a microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, product name) (third step). ).
To the resulting dispersion mixture, 1503 g of ion-exchanged water was added and stirred, and then methyl ethyl ketone was removed using a 60 ° C. hot water heating medium under reduced pressure, a part of the water was further removed, and a 5 μm filter (acetyl) was added. By filtering with a 25 mL needleless syringe (made by Terumo Corporation) with a cellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd., and removing coarse particles, the solid content concentration is 20%. An aqueous pigment dispersion was obtained.
40 parts of the resulting aqueous pigment dispersion, 10 parts of glycerin, 7 parts of triethylene glycol monobutyl ether (TEGMBE), 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (manufactured by Avicia Corporation) 3 parts and 41.7 parts of ion-exchanged water were mixed, and the resulting mixture was mixed with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) with a capacity of 25 mL. The aqueous ink shown in Table 2 was obtained by filtering with a syringe without a needle and removing coarse particles.

(Example 2)
A water-based ink was obtained in the same manner as in Example 1 except that the polymer of Production Example 2 was used instead of the polymer of Production Example 1 used in Example 1.
(Example 3)
A water-based ink was obtained in the same manner as in Example 1 except that the polymer of Production Example 3 was used instead of the polymer of Production Example 1 used in Example 1.
(Example 4)
A water-based ink was obtained in the same manner as in Example 1 except that the polymer of Production Example 4 was used instead of the polymer of Production Example 1 used in Example 1.

(Example 5)
Example 1 except that the yellow pigment used in Example 1 was changed to a magenta pigment: unsubstituted quinacridone pigment (CI Pigment Violet 19 [PV19], manufactured by Clariant Japan, trade name: Hostaperm Red E5B02) The same operation was performed to obtain a water-based ink.
(Example 6)
Except for changing the yellow pigment used in Example 1 to a cyan pigment: phthalocyanine pigment (CI Pigment Blue 15: 4 [PB15: 4], manufactured by Toyo Ink Manufacturing Co., Ltd., trade name: LIONOGEN BLUE BGJ) The same operation as in Example 1 was performed to obtain a water-based ink.
(Example 7)
In Example 5, the same operation as in Example 5 was carried out except that methyl ethyl ketone in the first step was changed to 852 g, ion-exchanged water was changed to 1682 g, and the weight ratio of [methyl ethyl ketone / water] was changed to 0.51. Ink was obtained.

(Example 8)
A water-based ink was obtained in the same manner as in Example 1 except that the particle size of the media beads was changed from 0.05 mmφ to 0.2 mmφ in the second step of Example 1.
Example 9
A water-based ink was obtained in the same manner as in Example 1 except that the microfluidizer was changed to an optimizer (trade name, manufactured by Sugino Machine Co., Ltd.) in the third step of Example 1.
(Example 10)
The circulation dispersion treatment time in the second step of Example 1 was changed from 2 hours to 4 hours (total average residence time in the mill: 30 minutes), and the net integrated power given to 1 kg of the preliminary dispersion was 1.0 kwh / A water-based ink was obtained in the same manner as in Example 1 except that the weight was kg.
(Example 11)
A water-based ink was obtained in the same manner as in Example 1 except that the operation method in the second step of Example 1 was changed from a circulation method to a continuous method (liquid return method using two tanks, see FIG. 2).

(Comparative Example 1)
A water-based ink was obtained in the same manner as in Example 1 except that the polymer of Comparative Production Example 1 was used instead of the polymer of Production Example 1 used in Example 1.
(Comparative Example 2)
A water-based ink was obtained in the same manner as in Example 1 except that the polymer of Comparative Production Example 2 was used instead of the polymer of Production Example 1 used in Example 1.
(Comparative Example 3)
A water-based ink was obtained in the same manner as in Example 1 except that the dispersion process in the second step was not performed in Example 1.
(Comparative Example 4)
A water-based ink was obtained in the same manner as in Example 4 except that the dispersion process in the second step was not performed in Example 4.
(Comparative Example 5)
A water-based ink was obtained in the same manner as in Example 5 except that the dispersion process in the third step was not performed in Example 5. In this water-based ink, pigments aggregated and storage stability was poor.
(Comparative Example 6)
The same operation as in Example 1 was performed except that the weight ratio of [methyl ethyl ketone / water] in the first step was changed from 0.33 to 1.0 in Example 1. However, the viscosity increased in the middle of the second step by the bead mill, and dispersion was impossible.

(Comparative Example 7)
The circulation dispersion treatment time in the second step of Example 1 was changed from 2 hours to 20 minutes (total average residence time in the mill: 2.5 minutes), and the net integrated power given to 1 kg of the preliminary dispersion was changed to 0. A water-based ink was obtained in the same manner as in Example 1 except that the amount was changed to 08 kwh / kg.
(Comparative Example 8)
The dispersion treatment time in the second step of Example 1 was changed from 2 hours to 12 hours (total average residence time in the mill: 90 minutes), and the net integrated power given to 1 kg of the preliminary dispersion was 3.0 kwh / kg. A water-based ink was obtained in the same manner as in Example 1 except that the water-based ink was used.
(Comparative Example 9)
In the second step of Example 4, a continuous-type media disperser that continuously disperses and continuously separates the media particles is used as a batch-type media disperser (manufactured by Imex Corporation: Sand Grinder MODEL 6TSG-1 / 4), 230 g of the pre-dispersion obtained in the first step and 1.9 kg of zirconia beads having a particle size of 0.05 mm were charged as media particles in the 1 L pot container, and under stirring, the stirring blade peripheral speed was 8 m / s. Batch dispersion treatment was performed for 30 minutes under the conditions (total average residence time in the mill: 30 minutes). The net power applied to 1 kg of the preliminary dispersion was 1.1 kw / kg, and the net integrated power was 0.55 kwh / kg. In addition, since the 1 L pot is not a closed container, the dispersion and beads described above were charged as a condition to prevent spillage, and the volume ratio was set to 3: 7 (corresponding to a bead filling ratio of 70%) (batch method, FIG. 3). reference).
Then, a third step similar to that in Example 4 was performed, 115 g of ion-exchanged water was added to the obtained dispersion mixture, and the same operation was performed thereafter to obtain a water-based ink.

Next, the performance of the ink obtained in each of Examples 1 to 10 and Comparative Examples 1 to 9 was measured according to the following method. The results are shown in Tables 2 and 3.
The meanings of the abbreviations of the dispersing devices in Tables 2 and 3 are as follows.
BM: Bead mill (Kotobushi Industries Co., Ltd., media type disperser, trade name: Ultra Apex Mill)
SG: Sand grinder (made by IMEX: Sand grinder MODEL 6TSG-1 / 4)
MF: Microfluidizer (Microfluidics, homogenizer, trade name)
ULT: Optimizer (Sugino Machine Co., Ltd., homogenizer, trade name)

(1) Storage stability (viscosity change)
The viscosity before and after heating for 30 days in a constant temperature bath at 60 ° C. was measured with an E-type viscometer [manufactured by Toki Sangyo Co., Ltd., model number: RE80 type], and evaluated based on the following evaluation criteria.
〔Evaluation criteria〕
○: Less than 5% of viscosity change rate before and after heating left Δ: 5% or more and less than 8% of viscosity change rate before and after heating left ×: 8% or more of viscosity change rate before and after heating left (2) Storage stability (grain Diameter change)
The average particle size before and after heating for 30 days in a 60 ° C. thermostat was measured with a laser particle analysis system ELS-8000 (cumulant analysis) from Otsuka Electronics Co., Ltd., and evaluated based on the following evaluation criteria. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent.
〔Evaluation criteria〕
○: Less than 10% of the particle size change rate before and after heating left Δ: 10% or more and less than 20% of the particle size change rate before and after heating left ×: 20% or more of the particle size change rate before and after heating left (3) Print density Using an inkjet printer (Seiko Epson Corporation, model number: PX-V600), print on plain paper (plain paper, Xerox Co., Ltd., trade name: Premium-Multipurpose) with solid printing [printing conditions: paper type; plain paper , Mode setting; photo], and left at 25 ° C. for 24 hours, the printing density was measured 5 times (25 ° C.) with a Macbeth densitometer (product number: RD914, manufactured by Gretag Macbeth), and the average value was obtained.
(4) Glossiness Using the printer, solid printing is performed on special paper (photo paper <gloss>, manufactured by Seiko Epson Corporation, trade name: KA450PSK) [printing conditions: paper type; photo print paper, mode setting: photo] , After standing for 24 hours at 25 ° C, measure the gloss of 20 ° five times (25 ° C) with a gloss meter (Nippon Denshoku Co., Ltd., trade name: HANDY GLOSSMETER, product number: PG-1). Asked.
(5) Scratch resistance Using the printer, solid printing was performed on the dedicated paper and dried at 25 ° C. for 24 hours, and then the print surface was rubbed strongly with fingers. The degree of printing was evaluated based on the following evaluation criteria.
〔Evaluation criteria〕
○: Almost no printing is obtained and the surroundings are not stained. Δ: The printing is slightly scratched, the surroundings are slightly stained, and the fingers are also slightly stained. X: The printing is scraped considerably, the surroundings are considerably dirty, and the fingers are considerably stained.

  From Tables 2 and 3, the aqueous inks of the examples have excellent gloss and scratch resistance when printed on special paper while satisfying the printing density in plain paper printing compared to the aqueous inks of the comparative examples. It turns out that it expresses.

It is the schematic of the 1 tank circulation system used in Examples 1-10. 10 is a schematic diagram of a liquid return method using two tanks used in Example 11. FIG. 10 is a schematic diagram of a batch method used in Comparative Example 9. FIG.

Claims (9)

(1) A water-insoluble polymer having a weight average molecular weight in the range of 90,000 to 400,000 and having a structural unit derived from an anionic monomer , an organic solvent having a solubility in 100 g of water of 5 to 40% by weight at 20 ° C. The emulsion composition (A) containing the neutralizing agent and water and the pigment (B) are mixed, and the resulting mixture has a nonvolatile component ratio of 5 to 50% by weight, and the weight ratio of [organic solvent / water]. A first step of obtaining a pre-dispersion which is 0.1 to 0.9;
(2) a second step of continuously dispersing the obtained preliminary dispersion using a media-type disperser and continuously separating the obtained dispersion-treated product and media particles; and (3) a homogenizer. The manufacturing method of the water-system pigment dispersion including the 3rd process of carrying out a dispersion process further using this.   The method for producing an aqueous pigment dispersion according to claim 1, wherein the media particles used in the second step have a particle size of 0.01 to 0.25 mm.   3. The dispersion according to claim 1, wherein the net integrated power is dispersed in a range of 0.1 to 2 [kwh / kg] per 1 kg of the preliminary dispersion using a media type dispersing machine in the second step. A method for producing an aqueous pigment dispersion.   The method for producing an aqueous pigment dispersion according to claim 1, wherein the operation method in the second step is a circulation method or a continuous method.   The method for producing an aqueous pigment dispersion according to any one of claims 1 to 4, wherein the homogenizer used in the third step is a high-pressure homogenizer.   The manufacturing method of the aqueous pigment dispersion in any one of Claims 1-5 which adds and mixes a pigment (B) to an emulsion composition (A) in a 1st process.   The method for producing an aqueous pigment dispersion according to any one of claims 1 to 6, wherein the organic solvent in the first step is methyl ethyl ketone.   The water-insoluble polymer is a water-insoluble graft polymer, and the main chain includes at least a structural unit derived from the salt-forming group-containing monomer (a) and a structural unit derived from the aromatic ring-containing (meth) acrylate monomer (b). The method for producing an aqueous pigment dispersion according to any one of claims 1 to 7, wherein the side chain is a polymer chain containing at least a structural unit derived from the hydrophobic monomer (e).   A water-based ink for inkjet recording, comprising the water-based pigment dispersion obtained by the method according to claim 1.

Images