JP2019019293A - Pigment water dispersion, and aqueous ink - Google Patents

Abstract

To provide a pigment water dispersion excellent in fixability to a resin printing medium and image density when mixed in ink and printed on the medium, and to provide aqueous ink containing the pigment water dispersion.SOLUTION: There are provided [1] a pigment water dispersion that is formed by dispersing a pigment (A) with a water-insoluble polymer (B), where the polymer (B) contains a constitutional unit derived from an itaconic acid (b-1) and a constitutional unit derived from a hydrophobic monomer (b-2), where at least a part of acid groups is neutralized; and [2] aqueous ink that contains 2 mass% or more and 15 mass% or less of the pigment water dispersion according to [1] in terms of a pigment.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion.

Resin printing media such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), PP (polypropylene), NY (nylon), etc. On the other hand, as a printing method using water-based ink, it is required to use an inkjet printing method or a flexographic printing method from the viewpoints of reducing environmental load, energy saving, safety, and the like.
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. Various inks containing pigments, aqueous media and polymers have been proposed as inks for inkjet printing.

For example, Patent Document 1 contains water, an organic solvent, an amine, and a polymer compound as an inkjet ink having printability on various recording media, and the polymer compound has (A) activity. It has a plurality of side chains capable of cross-linking by irradiating energy rays, and (B) at least one acidic group selected from acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid as a monomer unit Ink-jet inks having (C) an acid value of 50 or more and less than 250 and (D) a weight average molecular weight of 5,000 or more and less than 100,000 are described.
Patent Document 2 discloses an inkjet containing a carboxyl group-containing compound as an aqueous liquid for inkjet recording used in an inkjet recording apparatus using a synthetic rubber member in order to prevent precipitation of a metal compound contained in the synthetic rubber member. An aqueous recording liquid is described.

JP 2008-24830 A JP 2007-91837 A

However, Patent Document 1 uses a water-soluble resin as a polymer dispersant for dispersing a pigment, and Patent Document 2 uses a polymer that does not contain a structural unit derived from a hydrophobic monomer. Insufficient fixability and image density. For this reason, there is a demand for improvement in fixability to resin print media and image density.
An object of the present invention is to provide a pigment aqueous dispersion excellent in fixability to a resin print medium and image density when blended with ink and printed, and an aqueous ink containing the pigment aqueous dispersion.
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. . 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 an aqueous pigment dispersion in which a pigment is dispersed with a specific water-insoluble polymer.
That is, the present invention provides the following [1] and [2].
[1] A pigment aqueous dispersion in which a pigment (A) is dispersed with a water-insoluble polymer (B),
Pigment water in which the polymer (B) includes a structural unit derived from itaconic acid (b-1) and a structural unit derived from a hydrophobic monomer (b-2), and at least a part of the acid group is neutralized. Dispersion.
[2] A water-based ink containing the pigment aqueous dispersion according to [1] in an amount of 2% by mass to 15% by mass in terms of pigment.

  ADVANTAGE OF THE INVENTION According to this invention, when mix | blending with ink and printing, the pigment aqueous dispersion which is excellent in the fixability to a resin print medium and an image density, and the aqueous ink containing this pigment aqueous dispersion can be provided.

[Pigment water dispersion]
The pigment aqueous dispersion of the present invention is a pigment aqueous dispersion in which the pigment (A) is dispersed with a water-insoluble polymer (B) (hereinafter also simply referred to as “polymer (B)”). And a structural unit derived from itaconic acid (b-1) and a structural unit derived from the hydrophobic monomer (b-2), and at least a part of the acid group is neutralized.

The pigment aqueous dispersion of the present invention has an effect of being excellent in fixability to a resin print medium (hereinafter also simply referred to as “fixability”) and image density when blended in ink and printed. The reason is not clear, but it is thought as follows.
The polymer (B) according to the present invention includes a structural unit derived from itaconic acid (b-1) and a structural unit derived from a hydrophobic monomer (b-2). Therefore, in the polymer chain, a hydrophilic part having a high acid group density is locally formed by itaconic acid (b-1) and a hydrophobic part is formed by the hydrophobic monomer (b-2). Distribution bias occurs. This bias is more prominent than when one hydrophilic monomer is used for the acid group, the hydrophilic part increases the pigment dispersion ability of the polymer in the pigment aqueous dispersion, and the hydrophobic part is the resin. It is considered that the fixability to the print medium is improved.
In particular, the structural unit derived from itaconic acid (a-1) locally becomes a hydrophilic portion having a high acid group density, compared with the case where a hydrophilic monomer having one acid group is used. A sufficient dispersive force can be obtained even under low conditions, that is, under low ionicity. As a result, the pigment can be highly dispersed in an aqueous medium, so that the image density is considered to be remarkably improved.

<Pigment (A)>
The pigment (A) may be either an inorganic pigment or an organic pigment. If necessary, they can be used in combination with extender pigments.
Examples of inorganic pigments include carbon black and metal oxides, and carbon black is particularly preferable for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment Red, C.I. I. Pigment orange, C.I. I. Pigment violet, C.I. I. Pigment blue, and C.I. I. One or more types of products selected from Pigment Green are listed.
Examples of extender pigments include silica, calcium carbonate, and talc.
As the pigment (A), the above-mentioned pigments can be used alone or in admixture of two or more at any ratio.

The form of the pigment (A) dispersed in the polymer (B) in the pigment aqueous dispersion is preferably particles mainly composed of the pigment (A), more preferably at least the pigment (A) and the polymer (B). Thus, particles are formed. The particles are preferably particles in which the polymer (B) is adsorbed on the pigment (A) or particles containing the pigment (A) in the polymer (B). Among these, from the viewpoint of improving the dispersibility of the pigment, the polymer (B) particles containing the pigment (A) (hereinafter also simply referred to as “pigment-containing polymer (B) particles”) are preferable.
The pigment-containing polymer (B) particles are, for example, in the form of (capsule) particles in which the pigment (A) is encapsulated in the polymer (B), or particles in which the pigment (A) is uniformly dispersed in the polymer (B). Examples thereof include a particle form in which the pigment (A) is exposed on the surface of the polymer (B) particles, and a mixture thereof may be used. Among these, from the viewpoint of improving the dispersibility of the pigment, a pigment-encapsulated state in which the polymer (B) contains the pigment (A) is preferable.

<Water-insoluble polymer (B)>
The polymer (B) includes a structural unit derived from itaconic acid (b-1) (hereinafter also simply referred to as “monomer (b-1)”) and a hydrophobic monomer (b-2) (hereinafter simply referred to as “monomer (b-)”. 2) ”), and at least a part of the acid group is neutralized. The polymer (B) has a pigment dispersant that exhibits a pigment dispersing action and a function as a fixing agent for a printing medium.
Here, “water-insoluble” means that when a polymer that has been dried at 105 ° C. for 2 hours and reaches a constant weight is dissolved in 100 g of water at 25 ° C. until it is saturated, the amount of dissolution is less than 10 g. Meaning, the dissolution amount is preferably 5 g or less, more preferably 1 g or less. The amount of polymer (B) dissolved is the amount dissolved when the acid groups of the polymer (B) are neutralized with sodium hydroxide 100%.

[Monomer (b-1)]
Monomer (b-1) is itaconic acid. Itaconic anhydride can also be used as the monomer (b-1).
Further, in recent environmental protection problems, conversion from conventional petroleum-derived raw materials to plant-derived raw materials has been promoted. Since itaconic acid can be derived from plants, the dependence on petroleum can be reduced.

[Hydrophobic monomer (b-2)]
The monomer (b-2) is used as a monomer component of the polymer (B) from the viewpoint of improvement in fixability and image density.
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 improvement in fixability and image density.
The monomer (b-2) has at least a hydrophobic group and a polymerizable group 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. The polymerizable group is a group having an unsaturated double bond capable of radical polymerization, and includes at least one selected from a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group. Preferably, it is a vinyl group.

Examples of the monomer (b-2) include aromatic group-containing monomers and (meth) acrylic acid alkyl esters.
Examples of the aromatic group-containing monomer include compounds having an aromatic ring and a polymerizable group. 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, such as a styrene monomer and an aromatic group-containing (meth) acrylic. Acid esters are more preferred. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
The styrenic monomer is preferably one or more selected from styrene, 2-methylstyrene, α-methylstyrene, and divinylbenzene, and more preferably styrene.
The aromatic group-containing (meth) acrylic acid ester is preferably one or more selected from benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, and more preferably benzyl (meth) acrylate.
Here, “(meth) acrylic acid” means one or more selected from acrylic acid and methacrylic acid. “(Meth) acrylate” means one or more selected from acrylate and methacrylate.

As a (meth) acrylic-acid alkylester, what has a C1-C22 alkyl group is preferable, and what has a C6-C18 alkyl group is more preferable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, Examples include 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, stearyl (meth) acrylate, and the like.
In the present specification, “(iso or tertiary)” and “(iso)” mean both cases where these prefixes are not present and cases where these prefixes are not present. , Indicates normal.

  The monomer (b-2) is preferably at least one selected from aromatic group-containing monomers and (meth) acrylic acid alkyl esters, more preferably aromatic group-containing, from the viewpoint of improvement in fixability and image density. It contains a monomer, more preferably one or more selected from a styrene monomer and an aromatic group-containing (meth) acrylic acid ester, still more preferably a styrene monomer, and still more preferably styrene.

The polymer (B) may further contain structural units derived from monomers other than the monomers (b-1) and (b-2).
Examples of other monomers include acid monomers other than itaconic acid and itaconic anhydride, and nonionic monomers containing a hydroxy group and a polyalkylene glycol chain. Specifically, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid and maleic acid; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; polyethylene glycol Polyalkylene glycol (meth) such as (meth) acrylate (n = 2 to 30, n represents the average number of added moles of oxyalkylene group, the same applies hereinafter), polypropylene glycol (n = 2 to 30) (meth) acrylate, etc. Acrylate; Alkoxypolyalkylene glycol (meth) acrylate such as methoxypolyethylene glycol (n = 1-30) (meth) acrylate; Phenoxy (ethylene glycol-propylene glycol copolymer) (n = 1-30, ethylene glycol therein) n = 1 to 29) (meth) acrylate.

  In the total amount of the monomer units constituting the polymer (B), the total content of the structural units derived from the monomers (b-1) and (b-2) is preferably 80 masses from the viewpoint of improvement in fixability and image density. % 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, it is preferably composed only of structural units derived from the monomers (b-1) and (b-2).

Monomer (b-1) in the content of each monomer in the monomer mixture at the time of polymer (B) production (content as an unneutralized amount; the same applies hereinafter) or the total amount of monomer units constituting the polymer (B) The content of the structural unit derived from and the structural unit derived from the monomer (b-2) is as follows from the viewpoint of improvement in fixability and image density.
The content of the monomer (b-1) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, still more preferably 10% by mass or more, and still more preferably 15% by mass. Or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less, and even more preferably. Is 45% by mass or less, more preferably 40% by mass or less, and still more preferably 35% by mass or less.
The content of the monomer (b-2) is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, still more preferably 55% by mass or more, and still more preferably 60% by mass. Or more, more preferably 65% by mass or more, and preferably 97% by mass or less, more preferably 95% by mass or less, still more preferably 90% by mass or less, still more preferably 85% by mass or less, and still more preferably. Is 80% by mass or less, more preferably 75% by mass or less.

  Since itaconic acid (b-1) is used in the present invention, pigment dispersibility can be achieved even when the content of the structural unit derived from the hydrophilic monomer in the polymer is low compared to the case where a hydrophilic monomer having one acid group is used. It is considered that the image density is improved. On the other hand, since the content of the structural unit derived from the hydrophobic monomer can be increased, the proportion of the hydrophobic portion in the polymer chain is increased, and the fixability to the resin print medium is also considered to be improved. From this viewpoint, the mass ratio [(b-1) / (b-2)] of the structural unit derived from the monomer (b-1) and the structural unit derived from the monomer (b-2) in the polymer (B) is preferable. Is at least 3/97, more preferably at least 5/95, even more preferably at least 10/90, even more preferably at least 15/85, even more preferably at least 20/80, even more preferably at least 25/75. And preferably 60/40 or less, more preferably 55/45 or less, still more preferably 50/50 or less, even more preferably 45/55 or less, still more preferably 40/60 or less, and even more preferably 35 / 65 or less.

  The number average molecular weight of the polymer (B) is preferably 500 or more, more preferably 1,000 or more, and still more preferably 1,300, from the viewpoint of improving the dispersibility of the pigment, and improving the fixability and image density. And preferably 100,000 or less, more preferably 50,000 or less, still more preferably 10,000 or less, still more preferably 8,000 or less, still more preferably 6,000 or less, and even more preferably. Is 2,000 or less. The number average molecular weight of the polymer (B) can be adjusted by the amount of the polymerization chain transfer agent. The number average molecular weight can be measured by the method described in Examples.

(Synthesis of polymer (B ′))
The polymer (B) is obtained by obtaining a water-insoluble polymer (B ′) from a monomer mixture containing the monomers (b-1) and (b-2) constituting the polymer (B), It is preferably obtained by a method of neutralizing at least a part. The water-insoluble polymer (B ′) is produced by copolymerizing the monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
In the present specification, the water-insoluble polymer (B) before neutralization is referred to as “water-insoluble polymer (B ′)” or “polymer (B ′)”.

Although there is no restriction | limiting in the solvent used by the solution polymerization method of a polymer (B '), Polar organic solvents, such as C1-C3 aliphatic alcohol, ketones, ethers, and esters, are preferable. Specific examples include 1,4-dioxane, methanol, ethanol, acetone, and methyl ethyl ketone. Among these, 1,4-dioxane is preferable.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, an azo compound is preferable, and 2,2′-azobis (isobutyronitrile), 4,4′- Azobis (4-carbovaleric acid) is more preferred. As the polymerization chain transfer agent, mercaptans are preferable, and 3-mercaptopropionic acid is more preferable.
Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 ° C. or higher and 90 ° C. or lower, and the polymerization time is preferably 1 hour or longer and 20 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer (B ′) can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained polymer (B ′) can remove unreacted monomers and the like by reprecipitation, membrane separation, chromatographic method, extraction method and the like.

The acid value of the polymer (B ′) is preferably 40 mgKOH / g or more, more preferably 70 mgKOH / g or more, still more preferably 100 mgKOH / g or more, still more preferably 150 mgKOH / g or more, still more preferably 180 mgKOH / g or more. And preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, still more preferably 250 mgKOH / g or less, and still more preferably 230 mgKOH / g or less.
In addition, the acid value of the polymer (B ′) is based on the method of JIS K 0070, as described in the examples, and only the solvent to be measured is mixed with acetone and toluene from the mixed solvent of ethanol and ether specified in JIS K 0070. It is measured by a method changed to a solvent (acetone: toluene = 4: 6 (volume ratio)). The acid value can also be obtained by calculation from the ratio of the monomer components at the time of synthesis of the polymer (B ′). However, when the polymer (B ′) has poor solubility in the acid value measurement solvent, the inside of the polymer chain It is considered that there is a structural unit derived from the monomer (b-1) that is taken in and does not come out, and the measured value by the above method tends to be lower than the calculated value.

  The number average molecular weight of the polymer (B ′) is preferably 500 or more, more preferably 1,000 or more, and still more preferably 1, from the viewpoint of improving the dispersibility of the pigment, and improving the fixability and image density. 300 or more, and preferably 100,000 or less, more preferably 50,000 or less, still more preferably 10,000 or less, still more preferably 8,000 or less, even more preferably 6,000 or less, even more Preferably it is 2,000 or less. The number average molecular weight of the polymer (B ′) can be adjusted by the amount of the polymerization chain transfer agent. The number average molecular weight can be measured by the method described in Examples.

[Method for producing pigment aqueous dispersion]
The pigment aqueous dispersion of the present invention is preferably produced by a method having the following step 1 and step 2 from the viewpoint of improvement in fixability and image density.
Step 1: A step of adding a neutralizing agent to the water-insoluble polymer (B ′) to obtain an aqueous dispersion of the water-insoluble polymer (B) Step 2: Adding the pigment (A) to the water dispersion obtained in Step 1 And dispersing the resulting pigment mixture to obtain a pigment aqueous dispersion in which the pigment (A) is dispersed with the water-insoluble polymer (B).

(Process 1)
Step 1 is a step of adding a neutralizing agent to the polymer (B ′) to obtain an aqueous dispersion of the polymer (B). From the viewpoint of obtaining an aqueous dispersion having good dispersibility, first, the polymer (B ′) is dissolved in an organic solvent to obtain an organic solvent solution of the polymer (B ′), and then a neutralizer is added to the polymer ( It is preferable to obtain an aqueous dispersion of B).
Although there is no restriction | limiting in the organic solvent in which a polymer (B ') is dissolved, C1-C3 aliphatic alcohol, ketones, ethers, esters, etc. are preferable, the wettability to a pigment, a polymer (B') From the viewpoint of improving the solubility of the polymer and the adsorptivity of the polymer (B) to the pigment, a ketone having 4 to 8 carbon atoms is more preferable, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is still more preferable.
When the polymer (B ′) is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is.

<Neutralizing agent>
The neutralizing agent is preferably added so that the degree of neutralization of the polymer (B) is preferably 10 mol% or more and 60 mol% or less. Since itaconic acid (b-1) has two acid groups, the pigment can be highly dispersed in an aqueous medium even under conditions where the degree of neutralization is low compared to the case where a hydrophilic monomer having one acid group is used. And fixability and image density can be improved. From this viewpoint, the degree of neutralization of the polymer (B) is more preferably 15 mol% or more, still more preferably 20 mol% or more, and more preferably 55 mol% or less, still more preferably 50 mol% or less, More preferably, it is 40 mol% or less, More preferably, it is 30 mol% or less.
Here, the degree of neutralization is the value obtained by dividing the number of molar equivalents of the neutralizing agent by the number of molar equivalents of the acid groups of the polymer (B) (polymer (B ′)) before neutralization, that is, “moles of neutralizing agent”. The value of “number of equivalents / number of molar equivalents of acid groups of polymer (B ′)”. 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%.

Examples of the neutralizing agent include alkali metal hydroxides, ammonia, and organic amines. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, and sodium hydroxide is preferable. Examples of the organic amine include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine.
The neutralizing agent is preferably used as an aqueous neutralizing agent solution from the viewpoint of sufficiently and uniformly promoting neutralization. From the above viewpoint, the concentration of the neutralizing agent aqueous solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25%. It is below mass%.

(Process 2)
In step 2, the pigment (A) is added to the aqueous dispersion obtained in step 1, and the resulting pigment mixture is dispersed to obtain a pigment aqueous dispersion in which the pigment (A) is dispersed with the polymer (B). It is a process.
The mass ratio [(A) / (B)] of the pigment (A) to the polymer (B) in the pigment mixture is preferably 40/60 or more from the viewpoint of improving the dispersibility of the pigment, the fixability and the image density. More preferably 45/55 or more, still more preferably 50/50 or more, still more preferably 60/40 or more, still more preferably 70/30 or more, still more preferably 80/20 or more, and even more preferably 90 / 10 or more, more preferably 95/5 or more, and preferably 99.8 / 0.2 or less, more preferably 99.7 / 0.3 or less, still more preferably 99.5 / 0.5 or less. More preferably, it is 99/1 or less.

<Distributed processing>
In step 2, the pigment mixture is subjected to a dispersion treatment to obtain an aqueous pigment dispersion in which the pigment (A) is dispersed with the polymer (B). There is no particular limitation on the dispersion method. Although it is possible to atomize the pigment particles to a desired particle size only by dispersion due to shear stress, it is preferable to pre-disperse the pigment mixture and then apply this stress by applying further shear stress to obtain the desired pigment particles. It is preferable to control so that it may become a particle size.
The temperature in the preliminary dispersion in step 2 is preferably 0 ° C. or higher, and preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably 25 ° C. or lower, and the dispersion time is preferably 0.5 hours. More preferably, it is 0.8 hours or longer, and preferably 30 hours or shorter, more preferably 10 hours or shorter, still more preferably 5 hours or shorter.
When the pigment mixture is predispersed, commonly used mixing and stirring devices such as anchor blades and disper blades can be used, and among them, a high-speed stirring and mixing device is preferable.

Examples of means for imparting the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer (manufactured by Microfluidic), a media-type disperser such as a paint shaker and a bead mill. Examples of commercially available media type dispersers include Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd.), Pico Mill (manufactured by Hirota Iron Works Co., Ltd.), and the like. A plurality of these devices can be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When this dispersion is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the processing pressure and the number of passes.
The processing pressure is preferably 60 MPa or more, more preferably 100 MPa or more, still more preferably 130 MPa or more, and preferably 200 MPa or less, more preferably 180 MPa or less, from the viewpoints of productivity and economy.
The number of passes is preferably 5 or more, more preferably 10 or more, still more preferably 15 or more, and preferably 30 or less, more preferably 25 or less.

[Removal of organic solvent]
When an organic solvent is used in step 1, it is preferable to obtain a pigment aqueous dispersion by dispersing the pigment mixture in step 2 and then removing the organic solvent from the dispersion by a known method. . The organic solvent in the obtained pigment aqueous dispersion is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
Further, if necessary, a heating and stirring treatment can be performed before the organic solvent is distilled off.
The obtained pigment aqueous dispersion is obtained by dispersing the pigment (A) with the polymer (B), and preferably the particles of the polymer (B) containing the pigment (A) (pigment-containing polymer (B) particles) are aqueous. It is dispersed in the medium.

  The non-volatile component concentration (solid content concentration) of the pigment aqueous dispersion is preferably 10% by mass or more, more preferably 15%, from the viewpoints of pigment dispersibility, fixability and image density, and easy preparation of water-based ink. It is at least 30% by mass, and preferably at most 30% by mass, more preferably at most 25% by mass. The solid content concentration of the pigment aqueous dispersion is measured by the method described in Examples.

  The mass ratio [(A) / (B)] of the pigment (A) and the polymer (B) in the pigment aqueous dispersion is preferably 40/60 or more, more preferably from the viewpoint of improvement in fixability and image density. 45/55 or more, more preferably 50/50 or more, still more preferably 60/40 or more, still more preferably 70/30 or more, still more preferably 80/20 or more, still more preferably 90/10 or more, more More preferably 95/5 or more, and preferably 99.8 / 0.2 or less, more preferably 99.7 / 0.3 or less, still more preferably 99.5 / 0.5 or less, and still more preferably. Is 99/1 or less.

  The average particle diameter of the pigment-containing polymer (B) particles in the pigment aqueous dispersion is preferably 40 nm or more, more preferably 60 nm or more, from the viewpoint of reducing coarse particles, and from the viewpoint of improvement of fixability and image density. It is preferably 80 nm or more, more preferably 100 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less. The average particle diameter of the pigment-containing polymer (B) particles in the pigment aqueous dispersion is measured by the method described in Examples.

[Water-based ink]
The water-based ink of the present invention (hereinafter, also simply referred to as “ink”) contains the pigment aqueous dispersion from the viewpoint of improvement in fixability and image density.
The color of the ink of the present invention is not particularly limited, and chromatic colors such as C (cyan), M (magenta), Y (yellow), and a special color (S); no color such as K (black) and W (white) Coloring can be mentioned.
The content of the pigment aqueous dispersion in the ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more in terms of pigment from the viewpoint of improvement in fixability and image density. And more preferably 4% by mass or more, and preferably 20% by mass or less, more preferably 17% by mass or less, still more preferably 15% by mass or less, still more preferably 13% by mass or less, and still more preferably. It is 10 mass% or less.

  The mass ratio [(A) / (B)] of the pigment (A) to the polymer (B) in the ink is preferably 40/60 or more, more preferably 45/55, from the viewpoint of improvement in fixability and image density. More preferably, 50/50 or more, still more preferably 60/40 or more, still more preferably 70/30 or more, still more preferably 80/20 or more, still more preferably 90/10 or more, and even more preferably 95/5 or more, and preferably 99.8 / 0.2 or less, more preferably 99.7 / 0.3 or less, still more preferably 99.5 / 0.5 or less, and even more preferably 99 / 1 or less.

  When the pigment (A) and the polymer (B) form the pigment-containing polymer (B) particles, the pigment-containing polymer (B) particles in the ink should not swell or shrink, or aggregate between the particles. The average particle size of the pigment-containing polymer (B) particles in the ink is preferably the same as the average particle size in the pigment aqueous dispersion. The preferable aspect of the average particle diameter of the pigment-containing polymer (B) particles in the ink is the same as the preferable aspect of the average particle diameter in the pigment aqueous dispersion. The average particle diameter of the pigment-containing polymer (B) particles in the ink is also measured by the same method as described in the examples.

<Organic solvent (C)>
The ink of the present invention preferably further contains an organic solvent (C) from the viewpoint of improvement in fixability and image density. The boiling point of the organic solvent (C) is preferably 90 ° C or higher, more preferably 120 ° C or higher, still more preferably 150 ° C or higher, still more preferably 180 ° C or higher, and preferably lower than 250 ° C, more preferably 240 degrees C or less, More preferably, it is 230 degrees C or less, More preferably, what is 220 degrees C or less is preferable.
In addition, when using 2 or more types of organic solvents together as an organic solvent (C), the boiling point of an organic solvent (C) is a weighted average value weighted by content (mass%) of each organic solvent.

The ink of the present invention preferably contains a polyhydric alcohol as the organic solvent (C) from the viewpoint of improvement in fixability and image density. The polyhydric alcohol is preferably a compound having a boiling point of 90 ° C. or higher and lower than 250 ° C.
Examples of the polyhydric alcohol include ethylene glycol (boiling point 197 ° C.), propylene glycol (boiling point 188 ° C.), 1,2-butanediol (boiling point 193 ° C.), 1,2-pentanediol (boiling point 206), 1,2 -1,2-alkanediols such as hexanediol (boiling point 223 ° C); diethylene glycol (boiling point 244 ° C), polyethylene glycol, dipropylene glycol (boiling point 232 ° C), 1,3-propanediol (boiling point 210 ° C), 1, 3-butanediol (boiling point 208 ° C.), 1,4-butanediol (boiling point 230 ° C.), 3-methyl-1,3-butanediol (boiling point 203 ° C.), 1,5-pentanediol (boiling point 242 ° C.), 2-methyl-2,4-pentanediol (boiling point 196 ° C.), 1,2,6-hexanetriol (boiling point 1 8 ° C.), 1,2,4-butanetriol (boiling point 190 ° C.), 1,2,3-butanetriol (boiling point 175 ° C.), petriol (boiling point 216 ° C.), and the like.
Further, compounds having a boiling point of 250 ° C. or higher such as 1,6-hexanediol (boiling point 250 ° C.), triethylene glycol (boiling point 285 ° C.), tripropylene glycol (boiling point 273 ° C.), glycerin (boiling point 290 ° C.) May be used in combination with a compound having a temperature of less than 250 ° C.

As the organic solvent (C), an organic solvent other than the polyhydric alcohol may be used. Examples of the organic solvent other than the polyhydric alcohol include glycol ethers, alcohols other than the polyhydric alcohols, alkyl ethers of the alcohols, nitrogen-containing heterocyclic compounds such as N-methyl-2-pyrrolidone, amides, amines, and sulfur-containing compounds. Etc. These organic solvents can be used individually by 1 type or in mixture of 2 or more types.
The organic solvent (C) is preferably a polyhydric alcohol, more preferably one or more selected from propylene glycol, diethylene glycol and glycerin, and more preferably propylene glycol.

  The content of the organic solvent (C) in the ink is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more, from the viewpoint of improvement in fixability and image density. The amount is preferably 40% by mass or less, more preferably 30% by mass or less, and still more preferably 20% by mass or less.

<Water-insoluble polymer (D) particles>
The ink of the present invention is preferably an aqueous dispersion of particles of a water-insoluble polymer (D) other than the polymer (B) (hereinafter also simply referred to as “polymer (D)”), from the viewpoint of improvement in fixability and image density. Containing. The polymer (D) particles have a function as a fixing aid.
Here, “water-insoluble” has the same meaning as “water-insoluble” in the polymer (B). When the polymer which has been dried at 105 ° C. for 2 hours and reaches a constant weight is dissolved in 100 g of water at 25 ° C. until it is saturated, the amount of the polymer (D) dissolved is preferably 5 g or less, more preferably 1 g or less. . When the polymer (D) is an anionic polymer, the dissolution amount is the dissolution amount when the anionic group of the polymer is neutralized 100% with sodium hydroxide. When the polymer (D) is a cationic polymer, the dissolution amount is the dissolution amount when the cationic group of the polymer is neutralized 100% with hydrochloric acid.
The polymer (D) includes a structural unit derived from the hydrophilic monomer (d-1) (hereinafter, also simply referred to as “monomer (d-1)”) and a hydrophobic monomer (d) from the viewpoint of improvement in fixability and image density. -2) (hereinafter, also simply referred to as “monomer (d-2)”).
Examples of the polymer (D) include acrylic polymers, polyesters, polyurethanes and the like. Among these, an acrylic polymer is preferable from the viewpoint of improvement in fixability and image density.

[Hydrophilic monomer (d-1)]
The monomer (d-1) has an amount of 10 g or more that can be dissolved in 100 g of ion-exchanged water at 25 ° C. from the viewpoint of improvement in fixability and image density.
The monomer (d-1) is preferably a monomer having one or more acid groups, more preferably at least one selected from a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
The number of acid groups in the monomer (d-1) is preferably 1 or more and 3 or less, more preferably 1 or more and 2 or less, and still more preferably 2.
Examples of the 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 sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and 3-sulfopropyl (meth) acrylate.
Examples of the phosphoric acid monomer include vinyl phosphonic acid, vinyl phosphate, bis (methacryloyloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, and the like.
Among these, from the viewpoint of improvement in fixability and image density, a carboxylic acid monomer is preferable, and acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and 2-methacryloyl are more preferable. It is 1 or more types chosen from oxymethyl succinic acid, More preferably, it is 1 or more types chosen from acrylic acid, methacrylic acid, and itaconic acid, More preferably, itaconic acid is used.

[Hydrophobic monomer (d-2)]
As a monomer (d-2), the aromatic group containing monomer, (meth) acrylic-acid alkylester, etc. which were mentioned by the above-mentioned hydrophobic monomer (b-2) are mentioned.
The monomer (d-2) is preferably an aromatic group-containing monomer, more preferably one or more selected from a styrene monomer and an aromatic group-containing (meth) acrylic ester, and more preferably a styrene monomer. More preferably, it is styrene.

The polymer (D) may contain a structural unit derived from another monomer other than the monomers (d-1) and (d-2) from the viewpoint of improvement in fixing property and image density. Examples of other monomers include the aforementioned nonionic monomers and macromonomers.
In the total amount of the monomer units constituting the polymer (D), the total content of the structural units derived from the monomers (d-1) and (d-2) is preferably 80 masses from the viewpoint of improvement in fixability and image density. % 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, it is preferably composed only of structural units derived from the monomers (d-1) and (d-2).

  As the aqueous dispersion of polymer (D) particles, a synthesized product or a commercially available product may be used. For example, “Neocryl A-1127” (manufactured by DSM Coating Resins, anionic self-crosslinking aqueous vinyl resin), “Jonkrill 390”, “Jonkrill 7100”, “Johnkrill 734”, “Johnkrill 538” (above, Examples thereof include dispersions such as acrylic resins such as BASF Japan Ltd., and vinyl chloride-acrylic resins such as “Viniblanc 701” (Nisshin Chemical Industry Co., Ltd.).

Monomer (d-1) in the content of each monomer in the monomer mixture (content as an unneutralized amount; the same applies hereinafter) or the total amount of monomer units constituting the polymer (D) during the production of the polymer (D) The content of the structural unit derived from the monomer and the structural unit derived from the monomer (d-2) is as follows from the viewpoint of improvement in fixability and image density.
The content of the monomer (d-1) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, still more preferably 10% by mass or more, and still more preferably 15% by mass. Or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less, and even more preferably. Is 45% by mass or less, more preferably 40% by mass or less, and still more preferably 35% by mass or less.
The content of the monomer (d-2) is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, still more preferably 55% by mass or more, and still more preferably 60% by mass. Or more, more preferably 65% by mass or more, and preferably 97% by mass or less, more preferably 95% by mass or less, still more preferably 90% by mass or less, still more preferably 85% by mass or less, and still more preferably. Is 80% by mass or less, more preferably 75% by mass or less.

  The mass ratio [(d-1) / (d-2)] of the structural unit derived from the monomer (d-1) and the structural unit derived from the monomer (d-2) in the polymer (D) is the fixability and image density. From the viewpoint of improvement, preferably 3/97 or more, more preferably 5/95 or more, still more preferably 10/90 or more, still more preferably 15/85 or more, still more preferably 20/80 or more, and even more preferably. Is 25/75 or more, and preferably 60/40 or less, more preferably 55/45 or less, still more preferably 50/50 or less, even more preferably 45/55 or less, and even more preferably 40/60 or less. More preferably, it is 35/65 or less.

(Production of aqueous dispersion of polymer (D) particles)
When the monomer (d-1) has one or more acid groups, the aqueous dispersion of the polymer (D) particles is a monomer containing the monomers (d-1) and (d-2) constituting the polymer (D). It is preferable to obtain a water-insoluble polymer (D ′) from the mixture, and then neutralize at least a part of the acid groups with a neutralizing agent and disperse it in an aqueous medium. The water-insoluble polymer (D ′) is produced by copolymerizing the monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
In the present invention, the water-insoluble polymer (D) before neutralization is referred to as “water-insoluble polymer (D ′)” or “polymer (D ′)”.

Although there is no restriction | limiting in the solvent used by the solution polymerization method of a polymer (D '), Polar organic solvents, such as C1-C3 aliphatic alcohol, ketones, ethers, and esters, are preferable. Specific examples include 1,4-dioxane, methanol, ethanol, acetone, and methyl ethyl ketone. Among these, 1,4-dioxane is preferable.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, an azo compound is preferable, and 2,2′-azobis (isobutyronitrile) is more preferable. As the polymerization chain transfer agent, mercaptans are preferable, and 3-mercaptopropionic acid is more preferable.
Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 ° C. or higher and 90 ° C. or lower, and the polymerization time is preferably 1 hour or longer and 20 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer (D ′) can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained polymer (D ′) can remove unreacted monomers and the like by reprecipitation, membrane separation, chromatographic method, extraction method and the like.

The acid value of the polymer (D ′) is preferably 40 mgKOH / g or more, more preferably 70 mgKOH / g or more, still more preferably 100 mgKOH / g or more, still more preferably 150 mgKOH / g or more, still more preferably 180 mgKOH / g or more. And preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, still more preferably 250 mgKOH / g or less, and still more preferably 230 mgKOH / g or less.
In addition, the acid value of a polymer (D ') is measured by the method similar to the above-mentioned polymer (B'). The acid value can also be obtained by calculation from the ratio of monomer components at the time of production of the polymer (D ′). However, when the polymer (D ′) has poor solubility in the acid value measurement solvent, the inside of the polymer chain It is considered that there is a structural unit derived from the monomer (d-1) that is taken in and does not come out, and the measured value by the above method tends to be lower than the calculated value.

  The number average molecular weight of the polymer (D ′) is preferably 500 or more, more preferably 1,000 or more, still more preferably 1,300 or more, and preferably 100 from the viewpoint of improvement in fixability and image density. 000 or less, more preferably 50,000 or less, still more preferably 10,000 or less, even more preferably 8,000 or less, still more preferably 6,000 or less, and even more preferably 2,000 or less. The number average molecular weight of the polymer (D ′) can be adjusted by the amount of the polymerization chain transfer agent. The number average molecular weight can be measured by the method described in Examples.

〔dispersion〕
When the monomer (d-1) has one or more acid groups, an aqueous dispersion of polymer (D) particles is produced by a method of adding a neutralizing agent to the polymer (D ′) and dispersing it in an aqueous medium. It is preferable to do. Thereby, at least a part of the acid group contained in the structural unit derived from the monomer (d-1) is neutralized with the neutralizing agent, and at least a part of the acid group forms a salt, which is excellent in dispersibility. You can get a body.
The aqueous medium contains water as a main component. The content of water in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass or less from the viewpoint of improving the dispersibility of the polymer and from the viewpoint of environmental safety. Yes, more preferably 100% by mass. As water, deionized water, ion-exchanged water or distilled water is preferably used. Examples of components other than water include alcohol solvents such as methanol, ethanol, isopropanol, and butanol; ketone solvents such as acetone and methyl ethyl ketone; and organic solvents that dissolve in water such as ether solvents such as tetrahydrofuran.

Examples of the neutralizing agent include alkali metal hydroxides, ammonia, organic amines, etc. Among these, alkali metal hydroxides are preferable. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, and sodium hydroxide is preferable.
The degree of neutralization is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 20 mol% or more, and even more preferably 25 mol% or more, from the viewpoint of improving the dispersibility of the aqueous dispersion. And preferably 50 mol% or less, more preferably 45 mol% or less, still more preferably 40 mol% or less, still more preferably 35 mol% or less, and still more preferably 30 mol% or less.
Here, the degree of neutralization refers to the value obtained by dividing the number of molar equivalents of the neutralizing agent by the number of molar equivalents of the acid groups of the polymer (D) (polymer (D ′)) before neutralization, that is, “moles of neutralizing agent”. The number of equivalents / the number of molar equivalents of acid groups of the polymer (D ′) ”. 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%.

From the viewpoint of reducing coarse particles, the average particle size of the polymer (D) particles in the aqueous dispersion is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, and preferably 400 nm or less. More preferably, it is 300 nm or less, More preferably, it is 200 nm or less, More preferably, it is 100 nm or less, More preferably, it is 80 nm or less, More preferably, it is 60 nm or less. An average particle diameter is measured by the method as described in an Example.
The non-volatile component concentration (solid content concentration) of the aqueous dispersion of polymer (D) particles is preferably 10% by mass or more, more preferably 20% by mass from the viewpoint of improving dispersibility and facilitating ink preparation. It is above, and is preferably 40% by mass or less, more preferably 30% by mass or less. The solid content concentration of the aqueous dispersion of polymer (D) particles is measured by the method described in Examples.

[Bridge]
In the aqueous dispersion of the polymer (D) particles, the polymer (D) is preferably a cross-linked polymer from the viewpoint of improvement in fixability and image density. The crosslinked polymer is formed by crosslinking the polymer (D) with a crosslinking agent.
In the case where the hydrophilic monomer (d-1) has one or more acid groups, the crosslinking agent has at least two reactive groups that react with the acid groups in the molecule from the viewpoint of improvement in fixability and image density. The compound which has is preferable. The molecular weight of the crosslinking agent is preferably 120 or more, more preferably 150 or more, and preferably 2,000 or less, more preferably 1,500 or less, from the viewpoints of reactivity, fixability and image density improvement. More preferably, it is 1,000 or less, More preferably, it is 500 or less.
The number of reactive groups contained in the crosslinking agent is preferably 2 or more and 4 or less, more preferably 2 or more and 3 or less, and still more preferably, from the viewpoint of efficiently performing the type of acid group of the polymer (D) and the crosslinking reaction. 2. Examples of the reactive group include an epoxy group, an oxazoline group, a hydroxy group, an amino group, and an isocyanate group, and among these, an epoxy group is preferable.

The crosslinking agent having an epoxy group is preferably a polyhydric alcohol glycidyl ether, and preferably has a group derived from a polyhydric alcohol.
The number of carbon atoms of the polyhydric alcohol is preferably 2 or more, more preferably 4 or more, still more preferably 6 or more, and preferably 14 or less, more preferably 10 from the viewpoint of improvement in fixability and image density. Hereinafter, it is more preferably 8 or less.
Examples of the polyhydric alcohol include alkylene glycols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol; 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol And alkanediols such as neopentyl glycol; trimethylolpropane; pentaerythritol and the like.

  Specific examples of the crosslinking agent include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and 1,4-butanediol. Diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,8-octanediol diglycidyl ether, 1,10-decanediol diglycidyl ether, 1,12-dodecanediol diglycidyl ether, 1,14-tetradecanediol Diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, neopentyl glycol diglycidyl ether, etc. Esters diglycidyl ether; trihydric alcohol polyglycidyl ethers such as trimethylolpropane polyglycidyl ether; tetravalent alcohol polyglycidyl ethers such as pentaerythritol polyglycidyl ether, and the like. Among these, Preferably it is 1 or more types chosen from 1, 6- hexanediol diglycidyl ether and a trimethylol propane polyglycidyl ether, More preferably, it is 1, 6-hexanediol diglycidyl ether.

  Specific examples of the glycidyl ether type crosslinking agent of polyhydric alcohol that can be obtained commercially include Denacol EX-810 (ethylene glycol diglycidyl ether), Denacol EX-811 (ethylene glycol diglycidyl ether), Denacol EX-911 ( Propylene glycol diglycidyl ether), Denacol EX-850 (diethylene glycol diglycidyl ether), Denacol EX-851 (diethylene glycol diglycidyl ether), Denacol EX-941 (polypropylene glycol diglycidyl ether, n = 2 (catalog value)), Denacol EX-920 (polypropylene glycol diglycidyl ether, n = 3 (catalog value)), Denacol EX-212 (1,6-hexanediol diglycidyl ether) ), Denacol EX-216 (1,4-cyclohexanedimethanol diglycidyl ether), Denacol EX-211 (Neopentyl glycol diglycidyl ether), Denacol EX-321 (Trimethylolpropane polyglycidyl ether), and L -Series (low chlorine product) (manufactured by Nagase ChemteX Corporation), Epolite 40E (ethylene glycol diglycidyl ether), Epolite 100E (diethylene glycol diglycidyl ether), Epolite 1600 (1,6-hexanediol diglycidyl ether) (Above, manufactured by Kyoeisha Chemical Co., Ltd.), Rica Resin DME-100 (1,4-cyclohexanedimethanol diglycidyl ether) (manufactured by Shin Nippon Chemical Co., Ltd.) and the like.

When the polymer (D) is a crosslinked polymer, the average particle size of the aqueous dispersion of the polymer (D) particles is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, from the viewpoint of reducing coarse particles. Also, it is preferably 400 nm or less, more preferably 300 nm or less, still more preferably 200 nm or less, still more preferably 100 nm or less, still more preferably 80 nm or less, and still more preferably 60 nm or less. An average particle diameter is measured by the method as described in an Example.
The polymer (D) particles preferably do not cause swelling or shrinkage of the particles and aggregation between the particles. The average particle diameter of the polymer (D) particles in the ink is the average particle diameter in the aqueous dispersion. Is preferably the same. The preferred average particle diameter of the polymer (D) particles in the ink is the same as the preferred average particle diameter of the aqueous dispersion. The average particle diameter of the polymer (D) particles in the ink is also measured by the same method as described in the examples.

  The content of the aqueous dispersion of the polymer (D) particles in the ink is preferably 3% by mass or more, more preferably 5% by mass or more, and still more preferably in terms of solid content, from the viewpoint of improvement in fixability and image density. Is 7% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

(Other ingredients)
In addition to the above-mentioned components, the ink of the present invention includes various commonly used surfactants, humectants, wetting agents, penetrating agents, viscosity modifiers, antifoaming agents, antiseptics, antifungal agents, rust inhibitors, and the like. Additives can be added.

(Surfactant)
The ink of the present invention preferably further contains a surfactant from the viewpoint of improvement in fixability and image density. Examples of the surfactant include a nonionic surfactant, a silicone-based surfactant, and a fluorine-based surfactant, and a nonionic surfactant is more preferable.
Any nonionic surfactant may be used as long as it can be used in water-based inks. For example, polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanols. Examples include amides. Among these, polyoxyalkylene alkyl ether type surfactants and acetylene glycol surfactants are preferable, from surfactants of alkylene oxide adducts of alcohols having 6 to 30 carbon atoms, and acetylene glycol surfactants. One or more selected are more preferable, and from the viewpoint of improvement in fixing property and image density, a combination of an alkylene oxide adduct of an alcohol having 6 to 30 carbon atoms and an acetylene glycol surfactant are used in combination. Is more preferable.

  The content of the surfactant in the ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more, from the viewpoint of improvement in fixability and image density. Preferably, it is 5 mass% or less, More preferably, it is 4 mass% or less, More preferably, it is 3 mass% or less.

(Manufacture of water-based ink)
In the ink of the present invention, the pigment aqueous dispersion, if necessary, water, an organic solvent (C), an aqueous dispersion of polymer (D) particles, a surfactant, and other components are mixed and stirred. Can be obtained by:
The water content in the ink is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less. More preferably, it is 70 mass% or less.

(Water-based ink properties)
The viscosity of the ink at 25 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, still more preferably 4.0 mPa · s or more, and preferably 12 mPa · s or less, more preferably Is 9.0 mPa · s or less, more preferably 7.0 mPa · s or less, and still more preferably 6.0 mPa · s or less. The viscosity of the ink is measured by the method described in the examples.

  The pH at 25 ° C. of the ink is preferably 7.0 or more, more preferably 7.5 or more, from the viewpoint of increasing the image density. Moreover, from a viewpoint of member tolerance and skin irritation, pH becomes like this. Preferably it is 11.0 or less, More preferably, it is 10.0 or less, More preferably, it is 9.5 or less. The pH of the ink is measured by the method described in the examples.

(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 because a printed matter having excellent fixability and image density can be obtained even when printed on a resin printing medium. In view of the excellent fixability and image density in ink jet printing, it is preferably used as an aqueous ink for ink jet printing.

In the ink jet printing method using the water-based ink, a serial head method, a line head method, or the like can be used, but an ink jet recording apparatus having a line head type recording head is preferably used. The recording head of the line head type is a recording head that is as long as the width of the printing medium. The recording head is fixed, the printing medium is moved in the transport direction, and the nozzle head of the recording head is linked with this movement. An image or the like can be recorded by ejecting ink droplets and attaching them to a print medium.
Examples of the printing medium include low water-absorbing printing media such as art paper and coated paper, and non-water-absorbing resin printing media such as synthetic resin films. Among these, a resin print medium is preferable from the viewpoint of improvement in fixability and image density. Further, a water-absorbing print medium such as plain paper or high-quality paper can also be used as the print medium.

Examples of the resin printing medium include polyester films such as polyethylene terephthalate films; polyvinyl chloride films; polyolefin films such as polypropylene films and polyethylene films; and synthetic resin films such as polyamide films such as nylon films. These films may be a biaxially stretched film, a uniaxially stretched film, or an unstretched film. Among these, a polyolefin film is preferable and a polypropylene film is more preferable.
The thickness of the resin print medium is not particularly limited, and may be a thin film having a thickness of 1 μm or more and less than 20 μm. However, from the viewpoint of suppressing the appearance defect of the print medium and availability, it is preferably 20 μm or more, more preferably 50 μm or more. More preferably, it is 80 μm or more, and preferably 200 μm or less, more preferably 170 μm or less, and still more preferably 150 μm or less.
Commercially available synthetic resin films include Lumirror P60, Lumirror T60 (above, manufactured by Toray Industries, Inc., polyethylene terephthalate), Dazai FE2001 (produced by Phutamura Chemical Co., Ltd., corona-treated polyethylene terephthalate), PVC80BP (produced by Lintec Corporation, chloride). Vinyl), KAINUS KEE70CA (manufactured by Lintec Corporation, polyethylene), Dazai FOA (manufactured by Futamura Chemical Co., Ltd., corona-treated biaxially oriented polypropylene (OPP)), YUPO SG90 PAT1 (manufactured by Lintec Corporation, polypropylene), Bonil RX (King Human Film & Chemicals Co., Ltd. nylon).

In the following production examples, examples and comparative examples, “%” is “% by mass” unless otherwise specified.
Each physical property was measured by the following method.

[Acid value of water-insoluble polymer]
The acid value of the water-insoluble polymer was measured based on the method of JIS K 0070. However, only the measurement solvent was changed from a mixed solvent of ethanol and ether specified in JIS K 0070 to a mixed solvent of acetone and toluene (acetone: toluene = 4: 6 (volume ratio)).

[Measurement of number average molecular weight of water-insoluble polymer]
Gel permeation chromatography [GPC apparatus “HLC-8120GPC” (eluents) were prepared by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Tosoh Co., Ltd.) column “TSK-GEL, α-M” (manufactured by Tosoh Co., Ltd., flow rate: 1 mL / min) was measured using polystyrene having a known molecular weight as a standard substance.

[Average particle diameter of pigment-containing polymer (B) particles or polymer (D) particles in an aqueous dispersion]
The cumulant average particle diameter was measured under the following measurement conditions using a dynamic light scattering particle size measuring instrument “Zetasizer Nano ZS” (manufactured by Malvern). The obtained cumulant average particle diameter was defined as the average particle diameter of the pigment-containing polymer (B) particles or polymer (D) particles in the aqueous dispersion.
(Measurement condition)
Solid content concentration: 0.1%
Measurement temperature: 25 ° C
Medium: Water Measuring cell: Glass Cuvette
Laser specification: He-Ne, 4mW, 633nm
Detection optical system: NIBS, 173 ° C.
Number of measurements: 10 times Isothermal time: 5 minutes Analysis software: Zeta Sizer Software 6.2
Analysis method: General Purpose Mode (cumulant method)

[Solid content concentration of aqueous dispersion]
Using an infrared moisture meter “FD-230” (manufactured by Kett Scientific Laboratory Co., Ltd.), 5 g of an aqueous dispersion was measured at a drying temperature of 150 ° C. in a measurement mode 96 (monitoring time 2.5 minutes / variation width 0.05%). It dried on conditions, and measured the water | moisture content (%) of the water dispersion. The solid content concentration was calculated according to the following formula.
Solid content concentration (%) = 100-M
M: Water content of water dispersion (%) = [(W−W ₀ ) / W] × 100
W: Sample mass before measurement (initial sample mass)
W ₀ : Sample weight after measurement (absolute dry weight)

[Measurement of viscosity of water-based ink]
The viscosity was measured at 25 ° C. using an E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., using standard cone rotor 1 ° 34 ′ × R24, rotation speed 50 rpm).

[Measurement of pH of water-based ink]
The pH of the aqueous ink at 25 ° C. was measured using a desktop pH meter “F-71” (manufactured by Horiba, Ltd.) using a pH electrode “6337-10D” (manufactured by Horiba, Ltd.).

(Synthesis of polymer (B ′))
Synthesis Example 1-1
In a 200 mL two-necked round bottom flask equipped with a thermometer and a reflux apparatus, 9 g of itaconic acid, 21 g of styrene, 55 g of 1,4-dioxane (solvent), 4,4′-azobis (4-carbovaleric acid) “V -501 "(manufactured by Wako Pure Chemical Industries, Ltd., polymerization initiator) and 0.55 g of 3-mercaptopropionic acid (manufactured by Tokyo Chemical Industry Co., Ltd., polymerization chain transfer agent) were added and mixed with a magnetic stirrer. . The mixture was bubbled with nitrogen for 10 minutes, then warmed to 85 ° C. in a water bath and stirred for 30 minutes. Thereafter, the temperature was kept at 85 ° C. for 8 hours to complete the reaction. Thereafter, the solvent was distilled off at 80 ° C. and 20 kPa, followed by drying at 80 ° C. and 8 kPa for 8 hours to obtain a polymer (B′1) having an acid value of 237 mgKOH / g and a number average molecular weight of 1,500.

Synthesis Examples 1-2 to 1-3
Polymers (B′2) and (B′3) were obtained in the same manner as in Synthesis Example 1 except that the amounts of itaconic acid and styrene were changed to the mass ratio shown in Table 1 in Synthesis Example 1-1. It was. The acid value and number average molecular weight are shown in Table 1.

Synthesis Examples 1-4 to 1-5
Polymers (B′4) and (B′5) were synthesized in the same manner as in Synthesis Example 1-1 except that the amount of 3-mercaptopropionic acid in Synthesis Example 1-1 was changed to 0.45 g and 0.05 g, respectively. Obtained. The acid value and number average molecular weight are shown in Table 1.

Synthesis Example 1-6
A polymer (B′6) was obtained in the same manner as in Synthesis Example 1-1 except that in Synthesis Example 1-1, butyl acrylate was used instead of styrene. The acid value and number average molecular weight are shown in Table 1.

Comparative Synthesis Example 1-1
A polymer (B′7) was obtained in the same manner as in Synthesis Example 1-1 except that in Synthesis Example 1-1, acrylic acid was used instead of itaconic acid. The acid value and number average molecular weight are shown in Table 1.

Comparative Synthesis Example 1-2
A polymer (B′8) was obtained in the same manner as in Synthesis Example 1-1 except that styrene was not used in Synthesis Example 1-1. The acid value and number average molecular weight are shown in Table 1.

In Table 1, “BA” is butyl acrylate.

(Manufacture of pigment aqueous dispersion)
Example 1-1
(Process 1)
1.4 g of the polymer (B′1) obtained in Synthesis Example 1-1 was dissolved in 10 g of methyl ethyl ketone, and an amount of 5N sodium hydroxide aqueous solution as a neutralizing agent in a neutralization degree of 20 mol% and ion exchange 24 g of water was added, and the mixture was stirred and mixed at 2,000 rpm for 15 minutes at 10 to 15 ° C. using a disper blade to obtain an aqueous dispersion of polymer (B1).
(Process 2)
Subsequently, C.I. I. Pigment Violet 19 “Inkjet Magenta E5B02” (manufactured by Clariant) 45 g and C.I. I. 25 g of Pigment Red 122 “6111T” (manufactured by Dainichi Seika Kogyo Co., Ltd.) was added, and the mixture was stirred and mixed at 7,000 rpm for 3 hours at 10 to 15 ° C. using a disper blade. The obtained pigment mixture was filtered through 200 mesh, and subjected to 20-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer “M-110K” (manufactured by Microfluidics, high-pressure homogenizer). Methyl ethyl ketone was removed from the obtained dispersion-treated product at 60 ° C. under reduced pressure, a part of water was further removed, and after centrifugation, the liquid layer portion was filtered with a filter having a pore diameter of 5 μm (manufactured by Sartorius Stedim Biotech). The coarse particles were removed to obtain an aqueous dispersion.
Further, 80 g of this aqueous dispersion, 5.0 g of glycerin (manufactured by Kao Corporation), 0.2 g of 1,2-benzisothiazol-3 (2H) -one “Proxel XL2” (manufactured by Avicia Corporation), 14 of ion-exchanged water 8 g was mixed, sterilized at 70 ° C. for 1 hour, cooled to room temperature, and filtered through a filter having a pore size of 5 μm to obtain an aqueous dispersion of pigment-containing polymer (B1) particles (pigment aqueous dispersion). 1) [solid content concentration 20%, average particle size 103 nm] was obtained.

Examples 1-2 to 1-10 and Comparative Examples 1-1 to 1-2
In Example 1-1, the pigment was prepared in the same manner as in Example 1-1 except that the polymer (B ′), the degree of neutralization, or the mass ratio [pigment (A) / polymer (B)] shown in Table 2 was changed. Aqueous dispersions 2 to 10 and C1 to C2 were obtained. The solid content concentration of each pigment aqueous dispersion was 20%.

In Table 2, “BA” is butyl acrylate.

(Synthesis of polymer (D ′))
Synthesis Example 2-1
In a 200 mL two-necked round bottom flask equipped with a thermometer and a reflux apparatus, 9 g of itaconic acid, 21 g of styrene, 45 g of 1,4-dioxane (solvent), 2,2-azobis (isobutyronitrile) (Wako Pure Chemical Industries, Ltd.) Co., Ltd., polymerization initiator) 0.50 g, 3-mercaptopropionic acid (Tokyo Kasei Kogyo Co., Ltd., polymerization chain transfer agent) 0.30 g was added and mixed with a magnetic stirrer. The mixture was bubbled with nitrogen for 10 minutes, then warmed to 77 ° C. in a water bath and stirred for 30 minutes. Thereafter, the temperature was kept at 77 ° C. for 16 hours to complete the reaction. Thereafter, the solvent was distilled off at 70 ° C. and 20 kPa, followed by drying at 70 ° C. and 8 kPa for 8 hours to obtain a polymer (D′ 1) having an acid value of 220 mgKOH / g and a number average molecular weight of 1,600. The mass ratio [(d-1) / (d-2)] of the polymer (D′ 1) was 30/70.

Synthesis Example 2-2
A polymer (D′ 2) having an acid value of 211 mgKOH / g and a number average molecular weight of 1,700 was obtained in the same manner as in Synthesis Example 2-1, except that itaconic acid was changed to acrylic acid in Synthesis Example 2-1.

(Production of aqueous dispersion of polymer (D) particles)
Production Example 1
Into a glass bottle having pressure resistance, 15.4 g of the polymer (D′ 1) obtained in Synthesis Example 2-1, 1.5 g of 5N sodium hydroxide aqueous solution, 23.1 g of ion-exchanged water, and a stirrer bar are placed, and the lid is closed. Then, the mixture was stirred for 1 hour in a 90 ° C. water bath and dispersed.
Thereafter, the temperature was returned to room temperature, and 1.1 g of Denacol EX-212L (trade name, Nagase ChemteX Corporation, 1,6-hexanediol diglycidyl ether) and 1.49 g of ion-exchanged water were added as a crosslinking agent at room temperature. Stir for 30 minutes. Thereafter, the mixture was stirred in a water bath at 70 ° C. for 3 hours to crosslink the polymer (D) to obtain an aqueous dispersion (solid content concentration 30%, average particle diameter 45 nm) of polymer (D1) particles as crosslinked polymer particles. The mass ratio [(d-1) / (d-2)] of the polymer (D1) was 30/70. The degree of neutralization was 30 mol%.

Production Example 2
An aqueous dispersion of polymer (D2) particles that are crosslinked polymer particles [solid content concentration of 30] in the same manner as in Production Example 1, except that the polymer (D′ 1) was changed to the polymer (D′ 2) in Production Example 1. %, Average particle size 47 nm]. The mass ratio [(d-1) / (d-2)] of the polymer (D2) was 30/70. The degree of neutralization was 30 mol%.

(Manufacture of water-based ink)
Example 2-1
24 g of propylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.), Surfynol 104PG-50 (trade name, manufactured by Air Products and Chemicals, propylene glycol solution of acetylene glycol nonionic surfactant, effective content 50%) 1.50 g , Emulgen 120 (trade name, manufactured by Kao Corporation, polyoxyethylene lauryl ether, ether-based nonionic surfactant) 1.50 g and ion-exchanged water 29.96 g are mixed, and 15 minutes at room temperature using a magnetic stirrer. Stir to obtain a mixed solution.
Next, 46.67 g of the aqueous dispersion (pigment aqueous dispersion 1) of the pigment-containing polymer (B1) particles obtained in Example 1-1 (7 g in terms of pigment in 100 g of ink) was stirred with a magnetic stirrer. Then, the mixed solution was mixed. Further, 30.1 g of an aqueous dispersion of the polymer (D1) particles obtained in Production Example 1 (9 g in terms of solid content in 100 g of ink) was stirred and mixed while dropping with a dropper. Finally, the mixture was filtered through a filter having a pore diameter of 1.2 μm (manufactured by Sartorius) to obtain an ink. Table 3 shows the evaluation results of the obtained ink.

Examples 2-2 to 2-15 and comparative examples 2-1 to 2-2
Ink was obtained in the same manner as in Example 2-1, except that the composition shown in Table 3 was changed to Example 2-1. Table 3 shows the evaluation results of the obtained ink.

<Evaluation of water-based ink>
[OPP film fixability]
The obtained ink was filled into an ink injection port at the top of the head of an inkjet printer “IPSiO GX5000” (trade name, manufactured by Ricoh Co., Ltd.) via a silicon tube. A solid print pattern (size: 204 mm wide × 275 mm long) is produced by Photoshop (registered trademark) (manufactured by Adobe), and the OPP film “FOA # 30” (discharge amount is 14 g / m ² ) ( A solid product was printed on the product name (Futamura Chemical Co., Ltd.) and dried for 60 minutes at a temperature of 50 ° C. and a relative humidity of 30% to obtain a printed matter. The printed material was subjected to 30 reciprocations by applying a load of 1.5 kg to the cellulose nonwoven fabric “Bencot M-3II” (manufactured by Asahi Kasei Co., Ltd.) using the bottom surface of the weight (bottom surface area 78.5 cm ² ). The image density on the surface of the Bencot before and after rubbing was measured using a reflection densitometer “RD-915” (manufactured by Gretag Macbeth). The image density difference before and after rubbing was calculated, and the fixability to the OPP film was evaluated from the calculated value. The smaller the calculated value, the better the fixability to the OPP film.

[Image density]
Using the printer used in the fixing property evaluation, solid printing was performed on the OPP film “FOA # 30” (trade name, manufactured by Futamura Chemical Co., Ltd.) under the same conditions as the printing conditions, and the temperature was 25 ° C. and the relative humidity was 50%. After standing for 1 day under the conditions, any ten locations were measured using an optical densitometer SpectroEye (manufactured by Gretag Macbeth), and the average value was determined. The image density was evaluated from the average value. The larger the average value, the better the image density.

In addition, each notation in Table 3 is as follows.
PG: Propylene glycol * 1: Content (mass%) of pigment aqueous dispersion in ink in terms of pigment
* 2: Content (mass%) of the aqueous dispersion of polymer (D) particles in the ink in terms of solid content

From Table 3, it can be seen that Examples 2-1 to 2-15 are superior in both fixability to an OPP film and image density as compared with Comparative Examples 2-1 to 2-2.
Since Comparative Example 2-1 uses acrylic acid having one acid group as the hydrophilic monomer, the fixability and the image density are inferior.
Since Comparative Example 2-2 does not use a hydrophobic monomer, the fixability and the image density are inferior.

  The pigment aqueous dispersion of the present invention is excellent in fixability to a resin print medium and image density when blended in ink and printed. The water-based ink containing the pigment aqueous dispersion can be suitably used for inkjet printing.

Claims (10)

A pigment aqueous dispersion in which the pigment (A) is dispersed with a water-insoluble polymer (B),
Pigment water in which the polymer (B) includes a structural unit derived from itaconic acid (b-1) and a structural unit derived from a hydrophobic monomer (b-2), and at least a part of the acid group is neutralized. Dispersion.   The mass ratio [(A) / (B)] of the pigment (A) and the water-insoluble polymer (B) in the pigment aqueous dispersion is 50/50 or more and 99.5 / 0.5 or less. The pigment aqueous dispersion described.   The mass ratio [(b-1) / (b-2)] of the structural unit derived from the itaconic acid (b-1) and the structural unit derived from the hydrophobic monomer (b-2) in the polymer (B) is The pigment water dispersion according to claim 1 or 2, which is 5/95 or more and 50/50 or less.   The pigment water dispersion according to any one of claims 1 to 3, wherein the polymer (B) has a number average molecular weight of 1,000 or more and 10,000 or less.   The pigment water dispersion according to any one of claims 1 to 4, wherein the degree of neutralization of the polymer (B) is 20 mol% or more and 50 mol% or less.   The pigment water dispersion according to any one of claims 1 to 5, wherein the hydrophobic monomer (b-2) contains an aromatic group-containing monomer. The manufacturing method of the pigment water dispersion in any one of Claims 1-6 which has the following process 1 and process 2.
Step 1: A step of adding a neutralizing agent to the water-insoluble polymer (B ′) to obtain an aqueous dispersion of the water-insoluble polymer (B) Step 2: Adding the pigment (A) to the water dispersion obtained in Step 1 And dispersing the resulting pigment mixture to obtain a pigment aqueous dispersion in which the pigment (A) is dispersed with the water-insoluble polymer (B).   An aqueous ink containing the pigment aqueous dispersion according to any one of claims 1 to 6 in an amount of 2% by mass to 15% by mass in terms of pigment.   The aqueous ink according to claim 8, further comprising a polyhydric alcohol as the organic solvent (C). Furthermore, it contains an aqueous dispersion of water-insoluble polymer (D) particles,
The water-based ink according to claim 8 or 9, wherein the polymer (D) comprises a structural unit derived from a hydrophilic monomer (d-1) and a structural unit derived from a hydrophobic monomer (d-2).