Aqueous Pigment Composition And Pigment Ink Patent Application (2025)

U.S. patent application number 15/039630 was filed with the patent office on 2017-06-08 for aqueous pigment composition and pigment ink. This patent application is currently assigned to DIC CORPORATION. The applicant listed for this patent is DIC CORPORATION. Invention is credited to Hiroyuki Fukui, Masaki Hosaka, Ryosuke Ohmura, Yuri Shoji, Masaki Watanabe.

AQUEOUS PIGMENT COMPOSITION AND PIGMENT INK

Abstract

An aqueous pigment composition contains a pigment, water, and anacrylic resin obtained by copolymerizing a silane coupling agenthaving an ethylenically unsaturated group and a polymerizablemonomer having an amide group. Relative to a total amount ofmonomers used in copolymerization, the acrylic resin uses 0.05% bymass or more and not more than 2% by mass of the silane couplingagent having an ethylenically unsaturated group, and 0.5% by massor more and not more than 5% by mass of the polymerizable monomerhaving an amide group.

Foreign Application Data

Claims

1. An aqueous pigment composition comprising a pigment, water, andan acrylic resin obtained by copolymerizing a silane coupling agenthaving an ethylenically unsaturated group and a polymerizablemonomer having an amide group, wherein, relative to a total amountof monomers used in copolymerization, the acrylic resin uses 0.05%by mass or more and not more than 2% by mass of the silane couplingagent having an ethylenically unsaturated group, and 0.5% by massor more and not more than 5% by mass of the polymerizable monomerhaving an amide group.

2. The aqueous pigment composition according to claim 1, whereinthe acrylic resin is dispersed in a water-soluble solvent and/orwater by using an emulsifier and has an average particle diameterin the range of 10 to 200 nm.

3. The aqueous pigment composition according to claim 1, wherein anamount of the acrylic resin relative to a total amount of theaqueous pigment composition is 7 to 10% by mass.

4. A pigment ink that uses the aqueous pigment compositionaccording to claim 1.

Description

TECHNICAL FIELD

[0001] The present invention relates to an aqueous pigmentcomposition and a pigment ink using the aqueous pigmentcomposition.

BACKGROUND ART

[0002] Pigment compositions that use pigments as colorants arebeing used in various indoor and outdoor applications owing topigments' superior lightfastness. The applications includeautomobile and building material paint applications, and inkapplications such as offset ink, gravure ink, flexo ink,silk-screen ink, and inkjet recording ink.

[0003] In particular, aqueous inks that use water as a main solventare favored since aqueous inks can reduce or avoid risk for fireand mutagenicity associated with solvent inks that use organicsolvents; thus, presently, development on the aqueous pigment inksis being actively pursued.

[0004] Since aqueous inks dry slower than solvent inks, there hasbeen a problem of a low print fixability when the printing mediumis plastic or metal that does not absorb water or coated paper orart paper having high hydrophobicity. However, merely improving thedrying property of aqueous ink is not favorable since ink with anexcessively high drying rate solidifies on the plate duringprinting and inhibits printing. Moreover, as for inkjet recordingink, images are recorded by discharging ink droplets from nozzlesas fine as several ten micrometers, and thus inks drying andsolidifying at the nozzle tips may directly damage dischargestability.

[0005] Another problem is the physical properties of the obtainedprint. In particular, when the printing medium is plastic, metal,coated paper, or art paper, for example, rubfastness tends to below compared to prints made on regular paper.

[0006] As an approach to improving rubfastness of aqueous inks,there has been known addition of binder resins to aqueous inks. Forexample, in PTL 1, the fixability of the aqueous inkjet ink isimproved by using a binder resin. PTL 2 discloses a composition ofa binder with which the dried and solidified inkjet recording inkat nozzle tips can be re-dispersed in the ink composition bysupplying ink in a liquid form (see PTL 2, paragraph 0031).

[0007] According to these approaches, the fixability of the printcan be improved, or the solidified ink can be re-dispersed in theink composition.

[0008] In the inkjet recording ink applications, the followingtechniques are known to improve the rubfastness of the imagesurface. That is, in order to improve the rubfastness of the imagesurface, an acrylic silicon resin is used or an acrylic siliconresin and a binder resin other than the acrylic silicon resin areused in combination (for example, see PTL 3 and PTL 4). Moreover, acopolymer having a mass-average molecular weight of 12,000 to35,000 and an acid value of 100 to 250 mgKOH/g and being preparedby copolymerizing 30 to 83% by mass of (.alpha.-methyl)styreneand/or an aromatic-group-containing (meth)acrylic acid ester as afirst monomer, 40 to 12% by mass of (meth)acrylic acid as a secondmonomer, and 30 to 5% by mass of an alkylene oxide group-containing(meth)acrylic acid ester represented by general formula 1 below asa third monomer is used (for example, refer to PTL 5).

CITATION LIST

Patent Literature

[0009] PTL 1: Japanese Unexamined Patent Application PublicationNo. 2011-12253

[0010] PTL 2: Japanese Unexamined Patent Application PublicationNo. 2007-197640

[0011] PTL 3: Japanese Unexamined Patent Application PublicationNo. 2008-284874

[0012] PTL 4: Japanese Unexamined Patent Application PublicationNo. 2013-194161

[0013] PTL 5: Japanese Unexamined Patent Application PublicationNo. 2013-91734

SUMMARY OF INVENTION

Technical Problem

[0014] An object of the present invention is to provide an aqueouspigment composition that can be applied to aqueous pigment inks,has an appropriate drying rate and excellent re-dispersibility, andoffers an image surface with excellent rubfastness even when aprinting medium is plastic or metal that does not absorb water orcoated paper or art paper having high hydrophobicity, forexample.

Solution to Problem

[0015] The inventors of the present invention have resolved theproblems described above by using, as a binder, an acrylic resinprepared by copolymerizing particular amounts of a silane couplingagent having an ethylenically unsaturated group and a polymerizablemonomer having an amide group.

[0016] In other words, the present invention provides an aqueouspigment composition that contains a pigment, water, and an acrylicresin obtained by copolymerizing a silane coupling agent having anethylenically unsaturated group and a polymerizable monomer havingan amide group. Relative to a total amount of monomers used incopolymerization, the acrylic resin uses 0.05% by mass or more andnot more than 2% by mass of the silane coupling agent having anethylenically unsaturated group, and 0.5% by mass or more and notmore than 5% by mass of the polymerizable monomer having an amidegroup.

[0017] The present invention also provides a pigment ink that usesthe aqueous pigment composition.

Advantageous Effects of Invention

[0018] According to the present invention, an aqueous pigmentcomposition is provided which can be applied to aqueous pigmentinks, has an appropriate drying rate and excellentre-dispersibility, and offers an image surface with excellentrubfastness even when a printing medium is plastic or metal thatdoes not absorb water or coated paper or art paper having highhydrophobicity, for example.

DESCRIPTION OF EMBODIMENTS

(Pigment)

[0019] The pigment used in the present invention is notparticularly limited, and common organic pigments and inorganicpigments used in aqueous gravure inks or aqueous inkjet recordinginks can be used. Both unprocessed pigments and processed pigmentscan be used. In printing using a plastic recording medium, whiteink is also used to enhance visibility in addition to yellow ink,cyan ink, magenta ink, black ink, etc.

[0020] Specifically, known inorganic pigments and organic pigmentsthat can be dispersed in water or water-soluble organic solventscan be used. Examples of the inorganic pigment include iron oxide,and carbon black prepared by known methods such as a contactmethod, a furnace method, and a thermal method. Examples of theorganic pigment include azo pigments (azo lake, insoluble azopigments, condensed azo pigments, chelate azo pigments, etc.),polycyclic pigments (for example, phthalocyanine pigments, perylenepigments, perinone pigments, anthraquinone pigments, quinacridonepigments, dioxazine pigments, thioindigo pigments, isoindolinonepigments, and quinophthalone pigments), dye chelates (for example,basic dye-type chelates and acidic dye-type chelates), nitropigments, nitroso pigments, and aniline black.

[0021] As the pigment used in black ink, examples of the carbonblack include No. 2300, No. 2200B, No. 900, No. 960, No. 980, No.33, No. 40, No. 45, No. 45L, No. 52, HCF88, MA7, MA8, and MA100produced by Mitsubishi Chemical Corporation, Raven 5750, Raven5250, Raven 5000, Raven 3500, Raven 1255, and Raven 700 produced byColumbian Chemicals Co., Regal 400R, Regal 330R, Regal 660R, MogulL, Mogul 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000,Monarch 1100, Monarch 1300, and Monarch 1400 produced by CabotCorporation, Color Black FW1, FW2, FW2V, FW18, FW200, 5150, 5160,and S170, Printex 35, U, V, and 1400U, Special Black 6, 5, 4, and4A, NIPEX 150, NIPEX 160, NIPEX 170, and NIPEX 180 produced byDEGUSSA AG.

[0022] Specific examples of the pigments used in yellow ink includeC.I. Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93,95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155,174, 180, and 185.

[0023] Specific examples of the pigments used in magenta inkinclude C.I. Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1,112, 122, 123, 146, 168, 176, 184, 185, 202, 209, 269, and 282, andC.I. Pigment Violet 19.

[0024] Specific examples of the pigments used in cyan ink includeC.I. Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 16, 22, 60, 63, and66.

[0025] Specific examples of the pigments used in white ink includesulfates and carbonates of alkaline earth metals, and silicas suchas fine powdered silicate and synthetic silicate, calcium silicate,alumina, alumina hydrates, titanium oxide, zinc oxide, talc, andclay. The inorganic white pigment may be surface-treated throughvarious surface-treatment methods.

[0026] The pigment is preferably subjected to a process that makesthe pigment satisfactorily dispersible in a water-soluble solventand/or water serving as a medium in order to stabilize the pigmentin the aqueous pigment composition.

[0027] Specifically, the pigment may be dispersed in awater-soluble solvent and/or water along with a common pigmentdispersing agent such as a polymer dispersing agent, a surfactant,or a pigment derivative by the dispersing method described below soas to form an aqueous pigment composition. Alternatively, adispersibility-imparting group (hydrophilic functional group and/ora salt thereof) may be bonded to a pigment surface either directlyor indirectly via an alkyl group, an alkyl ether group, an arylgroup, or the like so as to process the pigment into aself-dispersing pigment that disperses and/or dissolves in awater-soluble solvent and/or water without using a common pigmentdispersing agent, this self-dispersing pigment may be dispersed ina water-soluble solvent and/or water so as to form a pigmentdispersion, and this pigment dispersion may be blended with theaqueous pigment ink.

(Pigment Dispersing Agent)

[0028] The pigment dispersing agent used in the present inventionis not particularly limited, and a polymer dispersing agent, asurfactant, or a pigment derivative known in the art can beused.

[0029] Among the pigment dispersing agents, aqueous resins areparticularly preferable. Preferable examples include polyvinylalcohols, polyvinyl pyrrolidones, acrylic resins such as acrylicacid-acrylic acid ester copolymers, styrene-acrylic resins such asstyrene-acrylic acid copolymers, styrene-methacrylic acidcopolymers, styrene-methacrylic acid-acrylic acid ester copolymers,styrene-.alpha.-methylstyrene-acrylic acid copolymers, andstyrene-.alpha.-methylstyrene-acrylic acid-acrylic acid estercopolymers, styrene-maleic acid copolymers, styrene-maleicanhydride copolymers, vinylnaphthalene-acrylic acid copolymers, andsalts of the aqueous resins.

[0030] Examples of the compound used to form salts of thecopolymers include alkali metal hydroxides such as sodiumhydroxide, potassium hydroxide, and lithium hydroxide,diethylamine, ammonia, ethylamine, triethylamine, propylamine,isopropylamine, dipropylamine, butylamine, isobutylamine,triethanolamine, diethanolamine, aminomethylpropanol, andmorpholine. The amount of the compound used to form these salts ispreferably equal to or more than the neutralization equivalent ofthe copolymer.

[0031] Naturally, commercially available products can be used.Examples of the commercially available products include AJISPER PBseries produced by Ajinomoto Fine-Techno Co., Inc., Disperbykseries produced by BYK Chemie Japan, EFKA series produced by BASF,SOLSPERSE series produced by The Lubrizol Corporation Japan, andTEGO series produced by EVONIK Industries.

(Self-Dispersing Pigment)

[0032] A self-dispersing pigment that can be dispersed in anwater-soluble solvent or water without using a pigment dispersingagent is produced by performing a physical treatment or chemicaltreatment on a pigment so as to bond (graft) adispersibility-imparting group or an active species having adispersibility-imparting group to a surface of the pigment.Examples of the method include a vacuum plasma treatment, anoxidation treatment using hypohalous acid and/or hypohalite, anoxidation treatment using ozone, a wet oxidation method involvingoxidizing the pigment surface with an oxidizer in water, and amethod of bonding p-aminobenzoic acid to the pigment surface sothat a carboxyl group is bonded through a phenyl group.

[0033] An aqueous ink containing a self-dispersing pigment does nothave to contain a pigment dispersing agent and thus issubstantially free of bubbles caused by the pigment dispersingagent and can be easily prepared into an ink having excellentdischarge stability. Because a significant increase in viscositycaused by the pigment dispersing agent is suppressed, more pigmentcan be contained and the print density can be sufficientlyincreased or handling is facilitated. Due to these advantages, theself-dispersing pigment is particularly useful for an inkjetrecording ink that requires high concentration.

[0034] Commercially available products can be used as theself-dispersing pigment. Examples of the commercially availableproducts include MICROJET CW-1 (trade name, produced by OrientChemical Industries Co., Ltd.), and CAB-O-JET200 and CAB-O-JET300(trade name, produced by Cabot Corporation).

(Water)

[0035] Water used in the present invention is a dispersing mediumof a pigment. Examples of the water that can be used include purewater and ultrapure water such as ion exchange water,ultrafiltration water, reverse osmosis water, and distilledwater.

[0036] Water may be used alone or a mixed solvent containing waterand a water-soluble solvent may be used. Examples of the solventinclude ketones such as acetone, methyl ethyl ketone, methyl butylketone, and methyl isobutyl ketone; alcohols such as methanol,ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, and2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and1,2-dimethoxyethane; glycols such as dimethylformamide,N-methylpyrrolidone, ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol,polyethylene glycol, and polypropylene glycol; diols such asbutanediol, pentanediol, hexanediol, and diols of the same family;glycol esters such as propylene glycol laurate; ethers ofdiethylene glycol monoethyl, diethylene glycol monobutyl, anddiethylene glycol monohexyl, and glycol ethers such as cellosolveincluding propylene glycol ether, dipropylene glycol ether, andtriethylene glycol ether; alcohols such as methanol, ethanol,isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,butyl alcohol, pentyl alcohol, and alcohols of the same family;sulfolane; lactones such as .gamma.-butyrolactone; lactams such asN-(2-hydroxyethyl) pyrrolidone; glycerin and derivatives thereof;and other various types of solvents known as water-soluble organicsolvents. These water-soluble organic solvents can be used alone oras a mixture of two or more.

[0037] The water-soluble organic solvent used is preferably ahigh-boiling-point water-soluble organic solvent since there is noneed for a debinding agent in the subsequent step. Examples of thehigh-boiling-point water-soluble organic solvent include glycolssuch as ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, polyethylene glycol, andpolypropylene glycol; diols such as butanediol, pentanediol,hexanediol, and diols of the same family; glycol esters such aspropylene glycol laurate; ethers of diethylene glycol monoethyl,diethylene glycol monobutyl, and diethylene glycol monohexyl, andglycol ethers such as cellosolve including propylene glycol ether,dipropylene glycol ether, and triethylene glycol ether; sulfolane;lactones such as .gamma.-butyrolactone; lactams such asN-(2-hydroxyethyl)pyrrolidone; glycerin and its derivatives; andother various types of solvents known as water-soluble organicsolvents. These water-soluble organic solvents can be used alone oras a mixture of two or more.

(Acrylic Resin Obtained by Copolymerizing a Silane Coupling AgentHaving an Ethylenically Unsaturated Group and a PolymerizableMonomer Having an Amide Group)

[0038] The acrylic resin obtained by copolymerizing a silanecoupling agent having an ethylenically unsaturated group and apolymerizable monomer having an amide group (hereinafter thisacrylic resin may be referred to as the acrylic resin (A); notethat for the purposes of the present invention, the "acrylic resin"is a general term for copolymers that contain a monomer having a(meth)acryloyl group as one of the raw materials, where the(meth)acryloyl group is a general term for an acryloyl group and amethacryloyl group) can be any acrylic resin that uses as rawmaterial polymerizable monomers a silane coupling agent having anethylenically unsaturated group and a polymerizable monomer havingan amide group.

[0039] Examples of the silane coupling agent having anethylenically unsaturated group include vinyltriethoxysilane,vinyltrimethoxysilane, p-styryltrimethoxysilane,3-methacryloxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane,3-methacryloxypropylmethyldiethoxysilane,3-methacryloxypropyltriethoxysilane, and3-acryloxypropyltrimethoxysilane.

[0040] The silane coupling agent having an ethylenicallyunsaturated group gives a crosslinked structure to the acrylicresin (A) to be obtained. In the present invention, in order todisplay a favorable binder function during printing, the amount ofthe silane coupling agent having an ethylenically unsaturated groupused is preferably 0.05% by mass or more but not more than 2% bymass relative to the total amount of monomers (this may contain amonomer that has plural ethylenically unsaturated groups in onemolecule, and may be a mixture of another vinyl monomer, a silanecoupling agent having an ethylenically unsaturated group, etc.)used as raw materials for copolymerization. The amount is morepreferably 0.05 to 1.5% by mass and most preferably 0.1 to 1.0% bymass.

[0041] The acrylic monomer having an amide group has an effect ofimproving re-dispersibility of the aqueous pigment composition ofthe present invention. The acrylic resin (A) strikes a good balancebetween hydrophilicity and hydrophobicity and is stable in awater-soluble solvent and/or water.

[0042] The acrylic monomer having an amide group may cause animbalance of hydrophilicity and hydrophobicity in the acrylic resin(A) and may generate a crosslinked structure if its content in theacrylic resin is excessively large, which leads to a tendency ofdecreasing re-solubility and decreasing rubfastness. Thus, thecontent of the acrylic monomer having an amide group is preferablynot more than 5% by mass relative to the total amount of themonomers used in copolymerization. Specifically, 0.5% by mass ormore but not more than 5% by mass of the acrylic monomer having anamide group is preferably used relative to the total amount of rawmaterial monomers used in copolymerization. The amount is morepreferably 0.5 to 4% by mass and most preferably 1.5 to 3% bymass.

[0043] Examples of the acrylic monomer having an amide groupinclude (meth)acrylamide, N-methyl(meth)acrylamide,N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide,N-methylol(meth)acrylamide, N-isopropyl(meth)acrylamide,N-butyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide,N,N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide,and hydroxyethyl(meth)acrylamide.

[0044] From the viewpoint of adhesion to plastic or metal that doesnot absorb water and highly hydrophobic coated paper or art paper,the acrylic resin (A) may contain a component whose molecularweight is difficult to measure because the component is insolublein tetrahydrofuran (THF) used as an eluent during gel permeationchromatography molecular-weight measurement.

[0045] The component insoluble in THF used as the eluent in gelpermeation chromatography molecular-weight measurement of acrylicresins such as the acrylic resin (A) can be deemed to have anumber-average molecular weight of at least 100,000 and amass-average molecular weight of at least 500,000.

[0046] As the other acrylic monomer used as the raw material of theacrylic resin (A), any known polymerizable monomers can be usedwithout limitation.

[0047] Examples thereof include (meth)acrylic acid ester monomerssuch as (meth)acrylic acid and alkali metal salts thereof, methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth) acrylate,2-ethylhexyl (meth) acrylate, benzyl (meth)acrylate, and cyclohexyl(meth)acrylate, amide-group-containing acrylic monomers such asacrylamide and N,N-dimethyl(meth)acrylamide, and acrylic monomerssuch as (meth) acrylonitrile, 2-dimethylaminoethyl (meth) acrylate,and glycidyl (meth)acrylate.

[0048] The monomer other than the acrylic monomers may be anymonomer that has an ethylenically unsaturated group that can bepolymerized with the acrylic monomers. Examples thereof includearomatic vinyl compounds such as styrene, .alpha.-methylstyrene,p-tert-butylstyrene, vinylnaphthalene, and vinylanthracene, vinylsulfonic acid compounds such as vinyl sulfonate and styrenesulfonate, and vinyl pyridine compounds such as 2-vinylpyridine,4-vinylpyridine, and naphthylvinylpyridine.

[0049] As the other acrylic monomer, a monomer having an aromaticgroup, such as styrene or benzyl (meth)acrylate, is particularlypreferable from the viewpoint of compatibility with thepigment.

[0050] The acrylic resin (A) is dispersed in a water-solublesolvent and/or water, and may take various dispersion forms.Dispersion forms are roughly categorized into (1) dispersions inwhich the acrylic resin (A) is dispersed in an aqueous medium byusing an emulsifier, and (2) dispersions in which the acrylic resin(A) having a hydrophilic group is dispersed in an aqueousmedium.

[0051] Examples of the acrylic resin (A) dispersed in the aqueousmedium by using an emulsifier (1) include an acrylic resin (A)water-dispersed by stirring the acrylic resin (A), an emulsifier,and water, and a product of emulsion-polymerizing the acrylicmonomer in the presence of an emulsifier in an aqueous medium.

[0052] Examples of the emulsifier that can be used inwater-dispersing the acrylic resin (A) by stirring and adding anemulsifier include nonionic emulsifiers such as polyoxyethylenealkyl ether, polyoxyethylene alkyl phenyl ether, andpolyoxyethylene-polyoxypropylene copolymers, anionic emulsifierssuch as alkyl sulfuric acid ester salt, alkyl benzene sulfonic acidsalt, polyoxyethylene alkyl ether sulfuric acid ester salt, andpolyoxyethylene alkyl phenyl ether sulfuric acid ester salt, andcationic emulsifiers such as quaternary ammonium salt. Relative to100 parts by mass of the monomers, 20 parts by mass or less of theemulsifier is preferably used, and more preferably 5 to 15 parts bymass of the emulsifier is used since a print with excellentwaterproofness is obtained.

[0053] As the emulsifier that can be used in conducting emulsionpolymerization, any of the nonionic emulsifiers, anionicemulsifiers, and cationic emulsifiers listed as the emulsifiersthat can be used in water-dispersing the acrylic resin (A) can beused. Preferably, 10 parts by mass or less of the emulsifier isused relative to 100 parts by mass of the monomers, and the amountis more preferably 2 to 5 parts by mass since a print withexcellent waterproofness is obtained.

[0054] Among the emulsion polymerization methods described above, aradical emulsion polymerization method that uses a radicalpolymerization initiator is particularly convenient. Examples ofthe radical polymerization initiator used in this method includepersulfates such as potassium persulfate, sodium persulfate, andammonium persulfate, azo compounds such as2,2'-azobisisobutyronitrile and dimethyl-2,2'-azobisisobutyrate,organic peroxides such as benzoyl peroxide andtert-butylperoxy-2-ethylhexanoate, and redox initiators such as acombination of an organic peroxide, such as cumene hydroperoxide,and a reducing agent such as iron oxide. The amount of theseradical polymerization initiators used relative to the total massof 100 parts by mass of the monomers is usually 0.01 to 5 parts bymass and is preferably 0.05 to 2 parts by mass.

[0055] In addition to the acrylic monomers, emulsifier, and radicalpolymerization initiator described above, if needed, various chaintransfer agents, pH adjustors, and the like are used in combinationso as to conduct emulsion polymerization for 0.1 to 10 hours in thetemperature range of 5 to 100.degree. C. and preferably 50 to90.degree. C. in 100 to 500 parts by mass of water relative to thetotal mass of 100 parts by mass of the monomers. As a result, thetarget acrylic resin (A) can be obtained.

[0056] Examples of the acrylic resin (A) having a hydrophilic groupdispersed in an aqueous medium (2) among the acrylic resins (A)used in the present invention include those acrylic resins having ahydrophilic group such as an anionic group, a cationic group, or anonionic group, dispersed in aqueous media.

[0057] Examples of the anionic group include a carboxyl group, aphosphoric acid group, an acidic phosphoric acid ester group, aphosphorous acid group, a sulfonic acid group, and a sulfinic acidgroup, and any of these groups is preferably used after beingneutralized with a basic compound.

[0058] Examples of the basic compound used to neutralize theanionic group include methylamine, dimethylamine, trimethylamine,ethylamine, diethylamine, triethylamine, 2-aminoethanol,2-dimethylaminoethanol, ammonia, sodium hydroxide, potassiumhydroxide, tetramethylammonium hydroxide, tetra-n-butylammoniumhydroxide, and trimethylbenzylammonium hydroxide.

[0059] Examples of the cationic group include a primary aminogroup, a secondary amino group, a tertiary amino group, and anammonium hydroxide group. These groups are preferably neutralizedwith an acidic compound.

[0060] Examples of the acidic compound used to neutralize thecationic group include formic acid, acetic acid, propionic acid,lactic acid, phosphoric acid monomethyl ester, methanesulfonicacid, benzenesulfonic acid, dodecylbenzenesulfonic acid,hydrochloric acid, sulfuric acid, and nitric acid.

[0061] Examples of the nonionic group include groups havingpolyether chains such as polyoxyethylene and polyoxypropylene.

[0062] The acrylic resin (A) having a hydrophilic group can beproduced by using an acrylic monomer having a hydrophilic group asa part of the other acrylic monomer used in the production methodthat involves copolymerizing a silane coupling agent having anethylenically unsaturated group and the other acrylic monomer, forexample.

[0063] Examples of the acrylic monomer having a hydrophilic groupinclude various carboxyl-group-containing acrylic monomers andtheir alkali metal salts such as (meth)acrylic acid and2-carboxyethyl (meth)acrylate, varioustertiary-amino-group-containing (meth)acrylamides such asN,N-dimethyl(meth)acrylamide, and varioustertiary-amino-group-containing (meth)acrylic acid esters and theirquaternaried compounds such as dimethylaminoethyl (meth)acrylate.Among these, (meth)acrylic acid or dimethylaminoethyl(meth)acrylate is preferable. These can be used alone or incombination.

[0064] As the method for preparing the acrylic resin (A) having ahydrophilic group by using the acrylic monomers described above,various polymerization methods may be named. Among these, asolution radical polymerization method that uses an organic solventis most convenient. Examples of the organic solvent used in thismethod include aliphatic and alicyclic hydrocarbons such asn-hexane, n-heptane, n-octane, cyclohexane, and cyclopentane;aromatic hydrocarbons such as toluene, xylene, and ethylbenzene;esters such as ethyl acetate, n-butyl acetate, n-amyl acetate,ethylene glycol monomethyl ether acetate, ethylene glycol monoethylether acetate, and ethylene glycol monobutyl ether acetate;alcohols such as methanol, ethanol, iso-propanol, n-butanol,iso-butanol, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol mono-n-butyl ether, propyleneglycol monomethyl ether, propylene glycol mono-n-propyl ether, anddiethylene glycol monobutyl ether; ketones such as acetone, methylethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, andcyclohexanone; ethers such as dimethoxyethane, tetrahydrofuran,dioxane, ethylene glycol dimethyl ether, ethylene glycol dibutylether, diethylene glycol dimethyl ether, and diethylene glycoldibutyl ether; and N-methylpyrrolidone, dimethylformamide,dimethylacetamide, and ethylene carbonate. These can be used aloneor in combination.

[0065] Various compounds can be used as the radical polymerizationinitiator in the solution radical polymerization method describedabove. Representative examples thereof include various azocompounds such as 2,2'-azobis(isobutylnitrile) and2,2'-azobis(2,4-dimethylvaleronitrile); and various peroxides suchas tert-butyl peroxypivalate, tert-butyl peroxybenzoate, andtert-butyl peroxy-2-ethylhexanoate.

[0066] When the monomers, polymerization initiators, and organicsolvents mentioned above are used and a solution radicalpolymerization method is employed, a target acrylic resin (A)having a hydrophilic group can be prepared.

[0067] Various methods are available as the method for dispersingthe acrylic resin (A) having a hydrophilic group in an aqueousmedium; among these, a phase-inversion emulsification method ispreferably used to conduct dispersing.

[0068] The phase-inversion emulsification method is a method thatinvolves mixing an aqueous medium and an organic solvent solutionof an acrylic resin (A) having a hydrophilic group neutralized witha basic compound or an acidic compound as needed, so as to disperse(phase inversion emulsification) the acrylic resin (A) in theaqueous medium, and then removing the organic solvent as needed.During this method, an emulsifier can be used as needed as long asthe object of the present invention is achieved.

[0069] As the emulsifier, any of the nonionic emulsifiers, anionicemulsifiers, and cationic emulsifiers listed above as theemulsifier that can be used to water-disperse the acrylic resin (A)can be used.

[0070] The media listed as the water-soluble solvent and/or waterdescribed above can be used as the aqueous medium.

[0071] As the organic solvent, those organic solvents that arelisted as the organic solvents that can be used in the solutionradical polymerization of the acrylic resin (A) can be directlyused. In particular, esters, ketones, and ethers are preferable.The aqueous medium may contain one or more organic solvents, andthe ratio used in the aqueous medium is preferably 30% by mass orless, more preferably 15% by mass or less, yet more preferably 5%by mass or less, and most preferably zero. The ratio of the organicsolvent is preferably 1% by mass or more if any organic solvent isused.

[0072] The acrylic resin (A) may be polymerized by decreasing thenumber of radicals generated from the polymerization initiatorrelative to the silane coupling agent having an ethylenicallyunsaturated group and the other acrylic monomer (vinyl monomers mayalso be used in combination) present in the polymerization system,for example. Examples of the method for decreasing the number ofradicals generated includes (1) a method that involves decreasingthe amount of the polymerization initiator used, (2) a method thatinvolves performing polymerization at low temperature, and (3) amethod that involves a longer polymerization time. Any one of orcombination of these is effective. Specific examples of the method(2) that involves performing polymerization at low temperatureinclude (i) a method of polymerization using a redox initiator at apolymerization temperature of 50.degree. C. or less in order toobtain an acrylic resin (A) dispersed in an aqueous medium by usinga dispersing agent such as an emulsifier, and (ii) a method ofpolymerization at a polymerization temperature of 80.degree. C. orless in order to obtain an acrylic resin (A) dispersed in anaqueous medium, the acrylic resin (A) being an acrylic resin havinga hydrophilic group.

[0073] The particle diameter of the acrylic resin (A) is notparticularly limited. For example, particles having an averageparticle diameter in the range of 10 to 200 nm as measured byMicrotrac Particle Size Analyzer UPA-EX150 produced by Nikkiso Co.,Ltd., are preferable.

[0074] In addition, resins that are known to be other binders mayalso be used as long as the scope of the present invention is notimpaired.

(Method for Producing Aqueous Pigment Composition)

[0075] In the present invention, an aqueous pigment composition forpigment ink can be produced by a known method without specificlimitations.

[0076] One example of such a method involves stirring and mixingthe pigment, a pigment dispersing agent, water, the acrylic resin(A), and, if needed, various additives, dispersing and kneading theresulting mixture by using a disperser or a kneader such as a beadmill, an ultrasonic homogenizer, a high-pressure homogenizer, apaint shaker, a ball mill, a roll mill, a sand mill, a sandgrinder, a Dyno mill, a Dispermat, an SC mill, a nanomizer, or thelike, adding and mixing the rest of the materials thereto, andadjusting the viscosity to an appropriate level.

[0077] The composition can also be prepared by adding awater-soluble solvent and/or water, the acrylic resin (A), and, ifneeded, various additives to a self-dispersing pigment or ahigh-concentration dispersion (mill base) preliminarily prepared byusing the disperser described above, mixing and stirring theresulting mixture, and diluting the resulting mixture to a desiredviscosity.

[0078] The aqueous pigment composition of the present invention canbe diluted to a desired concentration and used in variousapplications including pigment ink applications such as offset ink,gravure ink, flexo ink, and silk screen ink, inkjet recording inkapplications, and automobile and building material paintapplications.

[0079] In particular, when an acrylic resin of the presentinvention prepared by copolymerizing a silane coupling agent havingan ethylenically unsaturated group and a polymerizable monomerhaving an amide group is used, the composition becomes suitable foruse as an aqueous gravure ink, aqueous flexo ink, or aqueous inkjetink for use with various printing paper such as art paper, coatedpaper, high-quality paper, special inkjet paper having absorbinglayers for inkjet ink, and resin substrates (plates, sheets, andfilms are included) formed of hydrophobic resins such aspolystyrene, acrylonitrile-butadiene-styrene copolymers (ABSresins), vinyl chloride such as soft vinyl chloride and hard vinylchloride, polyethylene terephthalate (PET), polymethacrylate(PMMA), polypropylene, polyethylene, and polycarbonate.

(Aqueous Gravure Ink)

[0080] When the aqueous pigment composition of the presentinvention is to be applied to aqueous gravure ink, a water-solublesolvent and/or water, a binder resin, etc., are further added, andif needed, a defoaming agent, a leveling agent, and other additivesmay be added to produce the ink.

(Solvent for Aqueous Gravure Ink)

[0081] Examples of the solvent used in the aqueous gravure ink ofthe present invention that contains water as a base includealcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol,and N-propyl alcohol, glycols such as ethylene glycol and propyleneglycol, and glycol ethers such as butyl cellosolve, propyleneglycol monomethyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, and diethylene glycol monobutylether.

(Additives for Aqueous Gravure Ink)

[0082] The aqueous gravure ink of the present invention may furthercontain, if needed, bases such as ammonia, triethylamine,aminomethylpropanol, monoethanolamine, diethylaminoethanol, sodiumhydroxide, and potassium hydroxide, fine powdered silica such asgas-phase-method silica, wet-method silica, organically treatedsilica, and alumina-treated silica, other binder resins, adefoaming agent, a leveling agent, an antibacterial agent, anantifungal agent, a preservative, an adhesion-imparting agent, awax, etc.

(Use as Aqueous Gravure Ink)

[0083] The obtained aqueous gravure ink is diluted to anappropriate viscosity at the time of printing, and printed onvarious printing paper and plastic films by a gravure printingtechnique. As the diluting solution, one or a mixture of water anda lower alcohol such as methanol, ethanol, normal propyl alcohol,or isopropyl alcohol can be used. The mass ratio for dilution ispreferably 100:0 to 60:40 from the viewpoint of emission ofvolatile organic compounds.

[0084] The pigment in the aqueous gravure ink is preferablycontained at a ratio of 1 to 50% by mass relative to the total massof the ink since this amount is sufficient for ensuring the inkdensity and coloring power. In order for the acrylic resin (A) toobtain satisfactory gloss after printing and resin coating filmproperties, the resin solid content in the ink composition ispreferably 5 to 50% by mass. If the resin solid content is lessthan 5% by mass, sufficient gloss and resin coating film propertiescannot be obtained, and at a content exceeding 50% by mass,sufficient flowability and leveling properties are rarelyobtained.

(Aqueous Ink for Inkjet Recording)

[0085] When the aqueous pigment composition of the presentinvention is to be applied to inkjet recording ink, a water-solublesolvent and/or water, other binder resins, etc., are further added,and a humectant (drying inhibitor), a penetrant, a surfactant, andother additives may be added according to the desirable physicalproperties to produce the ink.

[0086] After the ink is prepared, a centrifugal separation orfiltration step may be added.

(Humectant)

[0087] The humectant is added to prevent ink from drying. Thehumectant content in the ink in order to prevent drying ispreferably 3 to 50% by mass. The humectant used in the presentinvention is not particularly limited, and a humectant that hasmiscibility with water and offers an effect of preventing the headof an inkjet printer from clogging is preferable. Examples thereofinclude glycerin, ethylene glycol, diethylene glycol, triethyleneglycol, polyethylene glycol having a molecular weight of 2000 orless, propylene glycol, dipropylene glycol, tripropylene glycol,1,3-propylene glycol, isopropylene glycol, isobutylene glycol,1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,mesoerythritol, and pentaerythritol. Among these, propylene glycoland 1,3-butyl glycol are preferably contained to offer safety andexcellent effects on ink drying properties and dischargeperformance.

(Penetrant)

[0088] The penetrant is added to improve the penetrating propertyinto a recording medium and to adjust the dot diameter on arecording medium.

[0089] Examples of the penetrant include lower alcohols such asethanol and isopropyl alcohol, ethylene oxide adducts of alkylalcohols such as ethylene glycol hexyl ether and diethylene glycolbutyl ether, and propylene oxide adducts of alkyl alcohols such aspropylene glycol propyl ether.

[0090] The penetrant content in the ink is preferably 0.01 to 10%by mass.

(Surfactant)

[0091] The surfactant is added to adjust the ink properties such assurface tension. The surfactants that can be used therefor are notparticularly limited, and various anionic surfactants, nonionicsurfactants, cationic surfactants, and amphoteric surfactants canbe named as the example. Among these, anionic surfactants andnonionic surfactants are preferable.

[0092] Examples of the anionic surfactants include alkylbenzenesulfonic acid salts, alkylphenyl sulfonic acid salts,alkylnaphthalene sulfonic acid salts, higher aliphatic acid salts,sulfuric acid ester salts of higher aliphatic acid esters, sulfonicacid salts of higher aliphatic acid esters, sulfuric acid estersalts and sulfonic acid salts of higher alcohol ethers, higheralkyl sulfosuccinic acid salts, polyoxyethylene alkyl ethercarboxylic acid salts, polyoxyethylene alkyl ether sulfuric acidsalts, alkyl phosphoric acid salts, and polyoxyethylene alkyl etherphosphoric acid salts. Specific examples thereof includedodecylbenzene sulfonic acid salts, isopropylnaphthalene sulfonicacid salts, monobutylphenylphenol monosulfonic acid salts,monobutylbiphenyl sulfonic acid salts, and dibutylphenylphenoldisulfonic acid salts.

[0093] Examples of the nonionic surfactants include polyoxyethylenealkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylenealiphatic acid esters, sorbitan aliphatic acid esters,polyoxyethylene sorbitan aliphatic acid esters, polyoxyethylenesorbitol aliphatic acid esters, glycerin aliphatic acid esters,polyoxyethylene glycerin aliphatic acid esters, polyglycerinaliphatic acid esters, sucrose aliphatic acid esters,polyoxyethylene alkyl amines, polyoxyethylene aliphatic acidamides, aliphatic acid alkylolamides, alkyl alkanol amides,acetylene glycol, oxyethylene adducts of acetylene glycol, andpolyethylene glycol-polypropylene glycol block copolymers. Amongthese, polyoxyethylene nonyl phenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylenealkyl ethers, polyoxyethylene aliphatic acid esters, sorbitanaliphatic acid esters, polyoxyethylene sorbitan aliphatic acidesters, aliphatic acid alkylolamides, acetylene glycol, oxyethyleneadducts of acetylene glycol, and polyethylene glycol-polypropyleneglycol block copolymers are preferable.

[0094] As other surfactants, the following can also be used:silicone surfactants such as polysiloxane oxyethylene adducts;fluorine surfactants such as perfluoroalkyl carboxylic acid salts,perfluoroalkyl sulfonic acid salts, and oxyethylene perfluoroalkylethers; and bio-surfactants such as spiculisporic acid,rhamnolipid, and lysolecithin.

[0095] These surfactants can be used alone or as a mixture of twoor more. Considering the dissolution stability of the surfactants,etc., the HLB is preferably in the range of 7 to 20. When asurfactant is to be added, the amount of the surfactant addedrelative to the total mass of the ink is preferably in the range of0.001 to 2% by mass, more preferably in the range of 0.001 to 1.5%by mass, and yet more preferably in the range of 0.01 to 1% bymass. When the amount of the surfactant added is less than 0.001%by mass, the effects of adding the surfactant are not likely to beobtained, and at a content exceeding 2% by mass, issues such asimage blurring readily occur.

(Other Additives)

[0096] If needed, a preservative, a viscosity adjusting agent, a pHadjusting agent, a chelating agent, a plasticizer, an antioxidant,an ultraviolet absorber, etc., can be added.

(Use as Inkjet Recording Ink)

[0097] The amount of the pigment in the inkjet recording ink ispreferably 1 to 20% by mass from the viewpoint of necessity ofobtaining a sufficient image density and in order to obtainpigment's dispersion stability in the ink. The amount of theacrylic resin (A) contained in the inkjet ink composition ispreferably 3 to 15% by mass, more preferably 5 to 12% by mass, andmost preferably 7 to 10% by mass on a resin solid content basis inorder to obtain good gloss after printing and resin coating filmproperties. At a content less than 3% by mass, sufficient gloss andresin coating film properties cannot be obtained. At a content morethan 12% by mass, nozzles of an inkjet printer clog due to dryingof the ink near the nozzles and thus such a content is notsuitable.

EXAMPLES

[0098] The present invention will now be described in detailthrough Examples. The present invention is not limited by Examplesbelow within the gist of the present invention. In examples below,"g" and "% by mass" are on a mass basis unless otherwise noted.

Synthetic Example 1: Method for Producing Acrylic Resin (A-1)

[0099] Into a four-necked flask equipped with a stirrer, athermometer, a condenser, and a nitrogen inlet tube, 16 g of Newcol707SF (anionic emulsifier produced by Nippon Nyukazai Co., Ltd.),6.5 g of NOIGEN TDS-200D (nonionic emulsifier produced by DKS Co.,Ltd.), and 220 g of deionized water were placed. The resultingmixture was heated to 80.degree. C. under a nitrogen stream, and anaqueous solution prepared by dissolving 0.8 g of ammoniumpersulfate in 16 g of deionized water was added thereto. A mixedliquid containing 60 g of 2-ethylhexyl acrylate, 100 g of styrene,27 g of methyl methacrylate, 0.4 g of3-methacryloxypropyltrimethoxysilane, 3 g of acrylamide, and 6 g ofmethacrylic acid was added thereto dropwise over 3 hours. Aftercompletion of dropwise addition, the reaction was carried out for 2hours, and the resulting product was cooled to 25.degree. C.,neutralized with 1.5 g of a 28% by mass ammonia water, and combinedwith deionized water so that the non-volatile component content was45% by mass. As a result, an acrylic resin water dispersion (A-1)having a glass transition temperature (Tg) of 30.degree. C. and anaverage particle diameter of 60 nm was obtained.

Synthetic Examples 2 and 3: Method for Producing Acrylic Resins(A-2 and A-3)

[0100] Synthesis was conducted on the same scale as SyntheticExample 1 except that the amounts of the materials placed in termsof % by mass were as shown in Table 1. As a result, acrylicresin-based resin water dispersions (A-2 and A-3) were obtained.The unit of the figures in the table is % by mass.

Comparative Synthetic Examples 1 to 5: Method for Producing AcrylicResins (HA-1 to HA-5)

[0101] Synthesis was conducted on the same scale as SyntheticExample 1 and Synthetic Example 2 except that the amounts of thematerials placed in terms of % by mass were as shown in Table 1. Asa result, acrylic resin-based resin water dispersions (HA-1 toHA-5) were obtained. The unit of the figures in the table is % bymass.

TABLE-US-00001 TABLE 1 Synthetic Synthetic Synthetic Example 1Example 2 Example 3 Resin sample A-1 A-2 A-3 Resin Styrene 53.453.4 53.3 composition 2-Ethylhexyl acrylate 30.9 30.9 30.8 Methylmethacrylate 11.0 9.5 10.9 Acrylamide 1.5 3.0 1.5 Methacrylic acid3.0 3.0 3.0 3-Methacryloxypropyl- 0.2 0.2 0.5 trimethoxysilaneTotal 100.0 100.0 100.0 Glass transition 30.degree. C. 35.degree.C. 35.degree. C. temperature (Tg) Average particle 60 nm 60 nm 50nm diameter

TABLE-US-00002 TABLE 2 Comparative Comparative ComparativeComparative Comparative Synthetic Synthetic Synthetic SyntheticSynthetic Example 1 Example 2 Example 3 Example 4 Example 5 Resinsample HA-1 HA-2 HA-3 HA-4 HA-5 Resin Styrene 53.5 53.4 53.5 53.452.4 composition 2-Ethylhexyl acrylate 31.0 30.9 31.0 30.9 30.4Methyl methacrylate 12.5 12.5 11.0 7.5 10.8 Acrylamide 0.0 0.0 1.55.0 1.5 Methacrylic acid 3.0 3.0 3.0 3.0 2.9 3-Methacryloxypropyl-0.0 0.2 0.0 0.2 2.0 trimethoxysilane Total 100.0 100.0 100.0 100.0100.0 Glass transition 35.degree. C. 34.degree. C. 35.degree. C.35.degree. C. 35.degree. C. temperature (Tg) Average particle 45 nm50 nm 50 nm Broad 55 nm diameter

(Method for Producing Pigment Dispersion)

(Method for Producing Pigment Dispersion J1)

[0102] Into a 200 ml polyethylene bottle, 25 g of TEGO Disperse750W (solid content: 40% by mass) produced by EVONIK Industries asa pigment dispersing agent, 15 g of diethylene glycol monobutylether, 15 g of triethylene glycol, 35 g of distilled water, 10 g ofcarbon black #960 produced by Mitsubishi Chemical Corporation, and150 g of 0.5 mm zirconia beads were placed, and the resultingmixture was dispersed for 4 hours with a paint conditioner. As aresult, a pigment dispersion (J1) was obtained.

(Method for Producing Pigment Dispersion J2)

[0103] A commercially available pigment dispersion, CAB-O-JET300produced by Cabot Japan, was used as a pigment dispersion (J2).

(Method for Producing Pigment Dispersion J3)

<Synthesis of Styrene-(Meth)Acrylic Acid Copolymer>

[0104] Into a reactor of an automatic polymerization apparatus(polymerization tester DSL-2AS model produced by Todoroki SangyoCo., Ltd.) equipped with a stirrer, a dropping device, atemperature sensor, and a refluxing device equipped with a nitrogenintroducing device in an upper part, 1,200 g of isopropyl alcohol(IPA) was placed, and the interior of the reactor was purged withnitrogen under stirring. The temperature was elevated to 80.degree.C. while maintaining a nitrogen atmosphere in the reactor, and thena mixed liquid containing 75.0 g of 2-hydroxyethyl methacrylate,260.8 g of methacrylic acid, 400.0 g of styrene, 234.2 g of benzylmethacrylate, 30.0 g of glycidyl methacrylate, and 80.0 g ofPERBUTYL (registered trademark) O (active ingredient: t-butylperoxy 2-ethylhexanate, produced by NOF Corporation) was addeddropwise from the dropping device over 4 hours. After completion ofdropwise addition, the reaction was continued at the sametemperature for 15 hours, and then a portion of IPA was distilledaway under a reduced pressure to control the solid componentcontent to 42.5%. As a result, a styrene-(meth)acrylic acidcopolymer (B) having an acid value of 170 was obtained.

<Preparation of Pigment Dispersion J3>

[0105] Into a mixing tank equipped with a cooling jacket, 360 g ofFastogen Blue TGR (.beta.-type copper phthalocyanine pigment (C.I.Pigment Blue 15:3) produced by DIC Corporation), 170 g ofstyrene-(meth)acrylic acid copolymer (B), 61 g of a 25% aqueoussodium hydroxide solution, 83 g of isopropyl alcohol, and 1000 g ofion exchange water were placed, and the resulting mixture wasstirred and mixed with a three-one motor for 1 hour. The resultingmixture was sent through a dispersing apparatus filled withzirconia beads having a diameter of 0.3 mm (SC Mill SC 100/32Model, produced by Mitsui Mining Co., Ltd.) and dispersed by acirculation mode (a mode with which the dispersion discharged fromthe dispersing apparatus was returned to the mixing tank). Duringthe dispersing step, the temperature of the dispersion wascontrolled to 30.degree. C. or lower by causing cold water to passthrough the cooling jacket, and dispersing was conducted for 4hours by fixing the rotor peripheral speed of the dispersingapparatus to 11.25 m/sec. After completion of dispersing, thedispersion raw liquid was removed from the mixing tank, the mixingtank and the dispersing apparatus channels were washed with 1500 gof water, and the water was combined with the dispersion raw liquidto obtain a mill dispersion.

[0106] The mill dispersion was placed in a glass distillator, andall of isopropyl alcohol and a portion of water were distilledaway. The resulting mixture was allowed to cool to roomtemperature, 2% hydrochloric acid was added dropwise under stirringto control pH to 3.5, and then the solid component was filtered outwith a Nutsche type filter and washed with water.

[0107] The wet cake was placed in a container, a 25% aqueous sodiumhydroxide solution was added to control pH to 9.0, andre-dispersing was conducted with a disper (T.K. HOMODISPER 20Model, produced by Tokushu Kika Kogyo Co., Ltd.). After acentrifugal separation step (6000 G, 30 minutes), ion exchangewater was added to obtain a pigment dispersion (J3) having a solidcontent of 18%.

Example 1: Method for Producing Aqueous Pigment Ink

[0108] A black pigment ink was prepared by adding 20 g of theacrylic resin water dispersion (A-1) obtained in Synthetic Example1, 20 g of distilled water, and 10 g of propylene glycol to 50 g ofthe pigment dispersion (J1) as the pigment dispersion, and stirringthe resulting mixture.

Example 2: Method for Producing Aqueous Pigment Ink

[0109] An aqueous pigment ink was obtained as in Example 1 exceptthat the composition was as shown in Table 3.

Examples 3 and 4: Method for Producing Aqueous Pigment Ink

[0110] An aqueous pigment ink was obtained as in Examples 1 and 2except that the composition was as shown in Table 3. Nipacide IBproduced by Clariant was used as a preservative, and TEGO WET KL245 produced by EVONIK Industries was used as a surfactant.

Comparative Examples 1 to 5: Method for Producing Aqueous PigmentInk

[0111] An aqueous pigment ink was obtained as in Examples exceptthat the composition was as shown in Table 4.

(Evaluation Method)

(Test Printing 1)

[0112] Aqueous pigment inks obtained in Examples and ComparativeExamples were applied onto art paper "OK Kinfuji Plus" produced byOji Paper Co., Ltd., by using a bar coater #4, and dried for 30seconds in a dryer at 60.degree. C. so as to obtain prints.

(Wet Rubfastness Test)

[0113] "Bemcot AP-2" produced by OZU CORPORATION was fixed to ahead portion of "Rubbing Tester" produced by Taisei Rikagaku Kogyo,impregnated with 100 .mu.L of distilled water, and reciprocatedto-and-fro ten times under a 500 g load on each of the printsobtained in Test Printing 1 so as to rub the prints. Evaluation wasconducted by visual inspection of images on art paper shown inFIGS. 1 to 3. Since the degree of rubbing in this test is strongerthan typically expected, a moderate degree of image exfoliationstill indicates good results.

(Re-Dissolving Test)

[0114] Each of the obtained aqueous pigment inks of Examples andComparative Examples was applied to a slide glass to a thickness of4 .mu.m by using a bar coater and dried for 1 hour in a dryer at32.degree. C. to prepare a test plate. The test plate was immersedin 35 g of a test solution containing 20 g of distilled water and10 g of propylene glycol for 5 minutes at room temperature, theslide glass was reciprocated 10 times in the test solution, andwhether re-dissolving occurs was confirmed by visualinspection.

[0115] Samples in which no coloring components were found on therecovered slide glass and a moderate amount of insoluble residuewas observed in the test solution were rated "Good: AA". Samples inwhich a large amount of insoluble matter was found on the slideglass or in the test solution and no coloring of the test solutionwas observed were rated "Poor: F". Evaluation was made based onthis criteria in the tables.

(Inkjet Printing Test)

[0116] Each of the obtained aqueous pigment inks was printed onregular paper (npi high-grade) produced by NIPPON PAPER INDUSTRIESCO., LTD., by using a commercially available inkjet printer PX-105produced by Seiko Epson Corporation to check whether printing canbe conducted smoothly.

TABLE-US-00003 TABLE 3 Example 1 Example 2 Example 3 Example 4Example 5 Resin sample A-1 A-1 A-1 A-2 A-3 AM content in resin 1.51.5 1.5 3 1.5 SC content in resin 0.2 0.2 0.2 0.2 0.5 Amount ofresin sample (g) 20 22 22 21 21 Pigment dispersion/amount (g) J1/50J2/15 J3/34 J3/34 J3/34 Distilled water 20 33 16.0 16.0 16.3Propylene glycol 10 30 13 13 13 Triethylene glycol -- -- 5 5 5Glycerin -- -- 10 10 10 Triethanol amine -- -- 0.2 0.2 0.2 NipacideIB -- -- 0.1 0.1 0.1 Tego WET KL 245 -- -- 0.4 0.4 0.4 Total 100100 100 100 100 Wet rubfastness AA AA AA AA AA Re-dissolvingproperty AA AA AA AA AA

TABLE-US-00004 TABLE 4 Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Resin sample HA-1 HA-2 HA-3 HA-4 HA-5 AM content in resin0 0 1.5 5.0 1.5 SC content in resin 0 0.2 0 0.2 2.0 Amount of resinsample (g) 21 21 21 24 21 Pigment dispersion/ J3/34 J3/34 J3/34J3/34 J3/ 34 amount (g) Distilled water 16.2 16.1 16.4 13.2 16.3Propylene glycol 13 13 13 13 13 Triethylene glycol 5 5 5 5 5Glycerin 10 10 10 10 10 Triethanol amine 0.2 0.2 0.2 0.2 0.2Nipacide IB 0.1 0.1 0.1 0.1 0.1 Tego WET KL 245 0.4 0.4 0.4 0.4 0.4Total 100 100 100 100 100 Wet rubfastness AA AA B B B Re-dissolvingproperty F F F F F

BRIEF DESCRIPTION OF DRAWINGS

[0117] FIG. 1 is a photograph of a print evaluated in Examples (wetrubfastness test). The state shown in FIG. 1 is rated good(AA).

[0118] FIG. 2 is a photograph of a print evaluated in Examples (wetrubfastness test). The state shown in FIG. 2 is rated insufficient(B).

[0119] FIG. 3 is a photograph of a print evaluated in Examples (wetrubfastness test). The state shown in FIG. 3 is rated poor (F).

* * * * *