Method for producing aqueous pigment dispersions

Abstract

To provide a pigment aqueous dispersion which has excellent dispersion stability and storage stability under a high temperature condition as a pigment dispersion in which a pigment surface is coated with a polyurethane resin used in aqueous ink and a coating material.SOLUTION: A method for producing a pigment aqueous dispersion includes: a step 1 of dispersing a pigment in a mixed solution of a resin (A) having a carboxyl group and / or a carboxylate anion group, an aqueous solvent and water, and obtaining a pigment dispersion (X1); a step 2 of dispersing a mixture of the pigment dispersion (X1), a solvent solution of a polyurethane prepolymer having an isocyanate group, and a neutralizer in water, and obtaining a pigment dispersion (X2); and a step 3 of removing the aqueous solvent from the pigment dispersion (X2), and obtaining a pigment aqueous dispersion, wherein an acid value of the resin (A) is 10 mgKOH / g or more, and a weight ratio (aqueous solvent / water) of the aqueous solvent in the step 1 to the water is 85 / 15 to 95 / 5.SELECTED DRAWING: None

Description

Technical Field

[0003]

[0001] The present invention relates to a method for producing an aqueous pigment dispersion used in aqueous inks and paints.

Background Art

[0002] Pigments are usually used in an optimal dispersed state according to applications such as painting, image formation, writing instruments, etc. As methods for dispersing pigments, there are methods of dispersing using surfactants and polymer dispersants, methods of chemically modifying the pigment with an affinity group for the medium to disperse it, methods of coating the pigment with a resin containing an affinity group for the medium, and the like. Patent Document 1 discloses a method for producing an aqueous dispersion of each pigment (Pigment Blue 15:3, Pigment Red 122, Pigment Yellow 180, Carbon Black) coated with a styrene acrylic resin among the methods of coating pigments with a resin containing an affinity group for the medium. In addition, Patent Document 2 discloses a method for producing an aqueous dispersion of Pigment Yellow 74 coated with a styrene acrylic resin using methyl ethyl ketone and an ink.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the methods disclosed in Patent Document 1 and Patent Document 2, monoazo pigments such as Pigment Yellow 74 dissolve in ketone solvents, ester solvents, tetrahydrofuran, etc. whose SP value represented by the Fedors method is in the range of 8.0 to 10.0, and further, when stored for a long time under high temperature conditions, there is a problem that the primary particle diameter of the pigment increases due to crystal growth by recrystallization. The SP values ​​used in this specification were calculated using the method (Fedors method) described on pages 151-154 of Volume 14 of Polymer Engineering and Science, authored by Robert F. Fedors et al.

[0005] The present invention aims to provide an aqueous pigment dispersion in which the pigment surface is coated with a polyurethane resin used in aqueous inks and paints, and which has excellent dispersion stability and storage stability under high-temperature conditions. [Means for solving the problem]

[0006] In other words, the present invention is a method for producing an aqueous pigment dispersion, comprising: step 1, dispersing a pigment in a mixed solution of a resin (A) having carboxyl groups and / or carboxylate anion groups, an aqueous solvent, and water to obtain a pigment dispersion (X1); step 2, dispersing the pigment dispersion (X1) and a mixture of a solvent solution of a polyurethane prepolymer having isocyanate groups and a neutralizing agent in water to obtain a pigment dispersion (X2); and step 3, removing the aqueous solvent from the pigment dispersion (X2) to obtain an aqueous pigment dispersion, wherein the acid value of the resin (A) is 10 mg KOH / g or more, and the weight ratio of the aqueous solvent to the water in step 1 (aqueous solvent / water) is 85 / 15 to 95 / 5. [Effects of the Invention]

[0007] The present invention makes it possible to provide an aqueous pigment dispersion in which the pigment surface is coated with a polyurethane resin used in water-based inks and paints, and which has excellent dispersion stability and storage stability under high-temperature conditions. [Modes for carrying out the invention]

[0008] The present invention provides a method for producing an aqueous pigment dispersion, comprising: step 1, dispersing a pigment in a mixed solution of a resin (A) having carboxyl groups and / or carboxylate anion groups, an aqueous solvent, and water to obtain a pigment dispersion (X1); step 2, dispersing the pigment dispersion (X1) and a mixture of a solvent solution of a polyurethane prepolymer having isocyanate groups and a neutralizing agent in water to obtain a pigment dispersion (X2); and step 3, removing the aqueous solvent from the pigment dispersion (X2) to obtain an aqueous pigment dispersion, wherein the acid value of the resin (A) is 10 mg KOH / g or more, and the weight ratio of the aqueous solvent to the water in step 1 (aqueous solvent / water) is 85 / 15 to 95 / 5. The method for producing the aqueous pigment dispersion of the present invention will be described below.

[0009] [Step 1 to obtain the pigment dispersion (X1)] In step 1, a pigment is dispersed in a mixed solution of a resin (A) having carboxyl groups and / or carboxylate anion groups, an aqueous solvent, and water to obtain a pigment dispersion (X1). The mixed solution contains resin (A), an aqueous solvent, and water. In step 1, the pigment is dispersed in this aqueous solvent to obtain a pigment dispersion (X1).

[0010] Resin (A) has a carboxyl group and / or a carboxylate anion group. Examples of resin (A) include polyurethane resin, polyester resin, and styrene-acrylic resin, which are obtained by reacting a polyol component with a polyisocyanate component. Of these, polyurethane resin is preferred from the viewpoint of abrasion resistance. Examples of polyol components include branched aliphatic diols, polyester polyols, and polyols having carboxyl groups in their side chains.

[0011] Examples of branched aliphatic diols include 1,2-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, and 1,2-, 1,3-, or 2,3-butanediol. Among these, neopentyl glycol is preferred.

[0012] Examples of polyester polyols include condensed polyester polyols, which are polycondensates of an alcohol component and a carboxylic acid component, as well as polylactone polyols and castor oil-based polyols. Among these, condensed polyester polyols are preferred. In particular, it is preferable that the polyester polyol is a polycondensate of an alcohol component and a carboxylic acid component, the alcohol component is an alcohol component containing a branched aliphatic diol, and the carboxylic acid component is a carboxylic acid component containing an aliphatic dicarboxylic acid.

[0013] The alcohol component constituting the condensed polyester polyol is preferably a diol (hereinafter referred to as a low molecular weight diol) with a number average molecular weight or chemical formula weight (Mn) of less than 500, and is an aliphatic dihydric alcohol having 2 to 8 carbon atoms [linear diols (ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol, etc.) and branched aliphatic diols (1,2-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 1,2-, Examples include: 1,3- or 2,3-butanediol (etc.); alicyclic dihydric alcohols with 6 to 10 carbon atoms (e.g., 1,4-bis(hydroxymethyl)cyclohexane and 2,2-bis(4-hydroxycyclohexyl)propane); aromatic ring-containing dihydric alcohols with 8 to 20 carbon atoms (e.g., m- or p-xylylene glycol, bis(hydroxyethyl)benzene, bis(hydroxyethoxy)benzene); AO adducts of bisphenol (bisphenol A, bisphenol S, and bisphenol F, etc.), AO adducts of dihydroxynaphthalene, and bis(2-hydroxyethyl)terephthalate, etc.). Low molecular weight diols may be used individually or in combination of two or more. Among these, an alcohol component containing a branched aliphatic diol is preferred. Of these, 3-methyl-1,5-pentanediol is preferred.

[0014] The carboxylic acid component constituting the condensed polyester polyol is preferably a carboxylic acid component containing a dicarboxylic acid. Examples include aliphatic dicarboxylic acids having 2 to 15 carbon atoms [oxalic acid, succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, maleic acid, and fumaric acid, etc.], aromatic dicarboxylic acids having 8 to 12 carbon atoms [phthalic acid, terephthalic acid, and isophthalic acid, etc.], and ester-forming derivatives thereof [acid anhydrides, lower alkyl esters (dimethyl esters and diethyl esters, etc.), acid halides (acid chlorides, etc.)]. One type of dicarboxylic acid may be used alone, or two or more types may be used in combination. Among these, the aliphatic dicarboxylic acid component is preferred, and adipic acid is more preferred.

[0015] Examples of condensed polyester polyols include polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyhexamethylene isophthalate diol, polyneopentylene adipate diol, polyethylene propylene adipate diol, polyethylene butylene adipate diol, polybutylene hexamethylene adipate diol, poly(polyoxytetramethylene) adipate diol, poly(3-methylpentylene adipate) diol, polyethylene azelate diol, polyethylene sebacate diol, polybutylene azelate diol, and polybutylene sebacate diol. Polyester polyols may be used individually or in combination of two or more.

[0016] Polylactone polyols are polyadditions of lactones to the low molecular weight diols mentioned above, and examples of lactones include lactones having 4 to 12 carbon atoms (e.g., γ-butyrolactone, γ-valerolactone, and ε-caprolactone). Specific examples of polylactone polyols include, for example, polycaprolactone diol, polyvalerolactone diol, and polycaprolactone triol.

[0017] Castor oil-based polyols include castor oil and modified castor oil modified with a polyol or an alkylene oxide (AO). The modified castor oil can be produced by transesterification of castor oil and a polyol and / or AO addition. Examples of castor oil-based polyols include castor oil, trimethylolpropane-modified castor oil, pentaerythritol-modified castor oil, and ethylene oxide (EO) (4 to 30 moles) adducts of castor oil, etc.

[0018] Examples of polyols having a carboxyl group in the side chain include compounds containing a carboxyl group and having 2 to 10 carbon atoms [dialkylolalkanoic acids (e.g., 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolheptanoic acid, and 2,2-dimethyloloctanoic acid)] and salts obtained by neutralizing these compounds with a neutralizing agent. From the viewpoint of the dispersion stability of the pigment aqueous dispersion, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and salts thereof are preferable, and more preferable are neutral salts of 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid with ammonia or an amine compound having 1 to 20 carbon atoms.

[0019] Examples of the polyisocyanate component include aromatic polyisocyanates having 6 to 20 carbon atoms (excluding carbon in the isocyanate group, the same applies hereinafter) having two or more isocyanate groups, aliphatic polyisocyanates having 2 to 18 carbon atoms, alicyclic polyisocyanates having 4 to 15 carbon atoms, aromatic aliphatic polyisocyanates having 8 to 15 carbon atoms, and derivatives of these polyisocyanates (e.g., isocyanurate compounds). The polyisocyanate component may be used alone or in combination of two or more.

[0020] Examples of aromatic polyisocyanates having 6 to 20 carbon atoms include 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate (TDI), 4,4'- or 2,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate, 4,4',4''-triphenylmethane triisocyanate, m- or p-isocyanatophenylsulfonyl isocyanate, crude MDI, and the like.

[0021] Examples of aliphatic polyisocyanates having 2 to 18 carbon atoms include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, and the like.

[0022] Examples of alicyclic polyisocyanates having 4 to 15 carbon atoms include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis(2-isocyanatoethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5- or 2,6-norbornane diisocyanate, and the like.

[0023] Examples of aromatic aliphatic polyisocyanates having 8 to 15 carbon atoms include m- or p-xylylene diisocyanate (XDI), α,α,α',α'-tetramethylxylylene diisocyanate (TMXDI), and the like.

[0024] From the viewpoint of initial dispersibility and mechanical strength of the polyurethane resin, it is preferable to include an aliphatic isocyanate as the polyisocyanate component. As the aliphatic isocyanate, aliphatic polyisocyanates having 2 to 18 carbon atoms and alicyclic polyisocyanates having 4 to 15 carbon atoms are preferred, alicyclic polyisocyanates having 4 to 15 carbon atoms are more preferred, and IPDI and hydrogenated MDI are even more preferred.

[0025] Resin (A) has an acid value of 10 mgKOH / g or higher. When the acid value of resin (A) is 10 mgKOH / g or higher, the solubility of resin (A) in a mixed solvent of aqueous solvent and water becomes sufficient. Therefore, the initial dispersibility of particles contained in the aqueous pigment dispersion is excellent, and storage stability is also good. The acid value of resin (A) is preferably 20 mg KOH / g or higher. It may also be 40 mg KOH / g or lower. The acid value of resins can be measured by the method specified in JIS K0070 (1992 edition).

[0026] Resin (A) preferably has isocyanate groups, and preferably has an isocyanate group content of 0.5% by weight or more, and more preferably 2.0% by weight or more. The isocyanate group content may also be 3.0% by weight or less. If resin (A) has isocyanate groups, it can react with the urethane prepolymer (P) contained in the solvent solution (B) of the urethane prepolymer added in step 2, increasing the molecular weight and thus the mechanical strength of the resin, which improves abrasion resistance when used in water-based inks or paints.

[0027] In step 1, the weight ratio of aqueous solvent to water (aqueous solvent / water) should be set to 85 / 15 to 95 / 5. Examples of aqueous solvents include alcohol-based solvents, glycol-based solvents, and glycol ether-based solvents. Examples of alcohol-based solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, and isopentanol. Examples of glycol-based solvents include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, and 1,2-hexanediol. Examples of glycol ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and triethylene glycol monobutyl ether. Isopropanol or propylene glycol are preferred as aqueous solvents. The weight ratio of aqueous solvent to water (aqueous solvent / water) is more preferably 88 / 12 to 92 / 8.

[0028] The SP value (Fedors method) of the mixed solvent of aqueous solvent and water is preferably 12.0 to 17.0, and more preferably 12.7 to 16.7. When the weight ratio of aqueous solvent to water (aqueous solvent / water) is within the preferred range and the SP value of the mixed solvent is within the above range, resin (A) can be dissolved. The SP value of a mixed solvent is calculated as the weight average of the SP values ​​of the aqueous solvent and water.

[0029] In step 1, resin (A) is added to a mixed solvent of aqueous solvent and water and stirred to obtain a mixed solution. A neutralizing agent may be added during this mixing. Adding a neutralizing agent makes it easier to disperse the carboxyl groups of resin (A) as salts in the aqueous solvent. Examples of neutralizing agents include ammonia, organic amines having 1 to 20 carbon atoms, and hydroxides of alkali metals (such as sodium, potassium, and lithium). Examples of organic amines include primary amines such as monomethylamine, monoethylamine, monobutylamine, monoethanolamine, and 2-amino-2-methyl-1-propanol; secondary amines such as dimethylamine, diethylamine, dibutylamine, diethanolamine, and N-methyldiethanolamine; and tertiary amines such as trimethylamine, triethylamine, dimethylethylamine, and triethanolamine. Of these, organic amines are preferred, and triethylamines are more preferred. The neutralization rate of the carboxyl group by the neutralizing agent is preferably 20-100%, more preferably 60-100%, from the viewpoint of dispersion stability. After adding the neutralizing agent to the mixed solution, stir until it is uniformly dissolved to obtain a homogeneous mixed solution.

[0030] In step 1, the pigment is dispersed in the above mixed solution to obtain a pigment dispersion (X1). Examples of pigments used in step 1 include conventionally known organic and inorganic pigments (for example, white pigments, black pigments, gray pigments, red pigments, brown pigments, yellow pigments, green pigments, blue pigments, purple pigments and metallic pigments, naturally occurring organic pigments, synthetic organic pigments, nitroso pigments, nitro pigments, pigment-type azo pigments, azo lakes made from water-soluble dyes, azo lakes made from poorly soluble dyes, lakes made from basic dyes, lakes made from acid dyes, xanthan lakes, anthraquinone lakes, pigments and phthalocyanine pigments from vat dyes, and organic pigments such as daylight fluorescent pigments).

[0031] Examples of specific organic and inorganic pigments are given below. Examples of white pigments include inorganic pigments such as titanium dioxide, zinc oxide, zinc sulfide, antimony oxide, and zirconium oxide. In addition to inorganic pigments, hollow resin microparticles and polymer microparticles can also be used.

[0032] Examples of pigments for magenta include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, and CI Pigment Red 222.

[0033] Pigments for yellow are not particularly limited, but examples include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 128, CI Pigment Yellow 138, and Pigment Yellow 180.

[0034] Pigments for cyan are not particularly limited, but examples include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, and CI Pigment Green 7.

[0035] The pigment content in the pigment dispersion (X1) is preferably 5 to 15% by weight from the viewpoint of dispersion stability. Furthermore, other components such as penetrating agents may be added when obtaining the pigment dispersion (X1).

[0036] Penetrants play a role in promoting the penetration of printing ink into permeable media. Surfactants and the like can be used as penetrants.

[0037] Examples of surfactants that can be used as penetrating agents include amphoteric surfactants and nonionic surfactants. Examples of amphoteric surfactants include lauryldimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, polyoctyl polyaminoethylglycine, and other imidazoline derivatives.

[0038] Nonionic surfactants include ether-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyalkylene alkyl ether (polyoxypropylene polyoxyethylene alkyl ether); ester-based surfactants such as polyoxyethylene oleic acid, polyoxyethylene oleic acid ester, polyoxyethylene distearate ester, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; and other fluorine-containing surfactants such as fluorine alkyl esters and perfluoroalkyl carboxylates. Acetylene alcohol-based surfactants, acetylene glycol-based surfactants, and silicone-based surfactants can also be used. Among these, nonionic surfactants are preferred, and a specific product name is Naroacty-CL-100 (polyoxyalkylene alkyl ether manufactured by Sanyo Chemical Industries, Ltd.). The content of these surfactants is preferably in the range of 0.01% to 10% by weight, and more preferably 0.1% to 5% by weight, based on the total weight of the resulting aqueous pigment dispersion.

[0039] [Step 2 to obtain the pigment dispersion (X2)] In step 2, a mixture of the pigment dispersion (X1), a solvent solution (B) of a urethane prepolymer having an isocyanate group, and a neutralizing agent is dispersed in water to obtain a pigment dispersion (X2).

[0040] The solvent solution (B) of the urethane prepolymer having an isocyanate group contains the urethane prepolymer (P) and the solvent. The urethane prepolymer (P) is obtained by reacting a polyol component and a polyisocyanate component in a heating facility and has isocyanate groups at its terminals. Examples of polyol components include the polyol components described in section (A) of resins, polycarbonate diols, and polyether diols. It is preferable to use low molecular weight diols and polyols having carboxyl groups in their side chains as the polyol components. 1,4-butanediol is preferred as the low molecular weight diol. Furthermore, 2,2-dimethylolpropionic acid (DMPA) is preferred as the polyol having a carboxyl group in its side chain.

[0041] Examples of polycarbonate polyols include polycarbonate diols produced by condensing the above-mentioned low molecular weight diol with a low molecular weight carbonate compound (for example, dialkyl carbonates with an alkyl group having 1 to 6 carbon atoms, alkylene carbonates having an alkylene group with 2 to 6 carbon atoms, and diaryl carbonates having an aryl group with 6 to 9 carbon atoms) while undergoing a de-alcoholization reaction. Two or more types of low molecular weight diols and alkylene carbonates may be used in combination. A trivalent or higher alcohol may be used instead of, or together with, the above-mentioned low molecular weight diol.

[0042] Specific examples of polycarbonate diols include aliphatic polycarbonates such as polyhexamethylene carbonate diol, polypentamethylene carbonate diol, 3-methyl-5-pentane-carbonate diol, polytetramethylene carbonate diol, and poly(tetramethylene / hexamethylene) carbonate diol (for example, a diol obtained by condensing 1,4-butanediol and 1,6-hexanediol with a dialkyl carbonate while de-alcoholizing). Aromatic polycarbonates include poly1,4-xylylene carbonate diol, bisphenol A type polycarbonate diol, and bisphenol F type polycarbonate diol.

[0043] Commercially available polycarbonate diols include Ethanol UH-200 (polycarbonate diol made from hexanediol: manufactured by Ube Industries, Ltd.), Nipponran 980R [polyhexamethylene carbonate diol with Mn=2,000, manufactured by Nippon Polyurethane Industries, Ltd.], Kuraray Polyol C-3090 [poly(3-methyl-5-pentanediol / hexamethylene) carbonate diol with Mn=3,000], and T4672 [poly(tetramethylene / hexamethylene) carbonate diol with Mn=2,000, manufactured by Asahi Kasei Chemicals Corporation].

[0044] Examples of polyetherdiols include aliphatic polyetherdiols and aromatic ring-containing polyetherdiols.

[0045] Examples of aliphatic polyether diols include polyoxyethylene polyols [polyethylene glycol (hereinafter abbreviated as PEG) etc.], polyoxypropylene polyols [polypropylene glycol etc.], polyoxyethylene / propylene polyols and polytetramethylene ether glycol.

[0046] Commercially available aliphatic polyether diols include PTMG1000 [polytetramethylene ether glycol with Mn=1,000, manufactured by Mitsubishi Chemical Corporation], PTMG2000 [polytetramethylene ether glycol with Mn=2,000, manufactured by Mitsubishi Chemical Corporation], PTMG3000 [polytetramethylene ether glycol with Mn=3,000, manufactured by Mitsubishi Chemical Corporation], PTGL3000 [modified PTMG with Mn=3,000, manufactured by Hodogaya Chemical Co., Ltd.], and Sannix Diol GP-3000 [polypropylene ether triol with Mn=3,000, manufactured by Sanyo Chemical Industries, Ltd.].

[0047] Examples of aromatic polyether diols include polyols having a bisphenol skeleton, such as EO adducts of bisphenol A [e.g., 2-mol EO adduct of bisphenol A, 4-mol EO adduct of bisphenol A, 6-mol EO adduct of bisphenol A, 8-mol EO adduct of bisphenol A, 10-mol EO adduct of bisphenol A, and 20-mol EO adduct of bisphenol A] and propylene oxide (PO) adducts of bisphenol A [e.g., 2-mol PO adduct of bisphenol A, 3-mol PO adduct of bisphenol A, 5-mol PO adduct of bisphenol A], as well as EO or PO adducts of resorcinol.

[0048] Suitable solvents include those that are substantially inactive with isocyanate groups (acetone, ketones such as ethyl methyl ketone, esters, ethers, amides, and alcohols). Of these, tetrahydrofuran is preferred. The solvent containing the urethane prepolymer (P) described above is a solvent solution (B) of a urethane prepolymer having an isocyanate group.

[0049] The acid value of the urethane prepolymer (P) is preferably 10 mg KOH / g or higher. When the acid value of the urethane prepolymer is 10 mg KOH / g or higher, the particle size after dispersion is small and the particle size distribution is sharp.

[0050] The isocyanate group content of the urethane prepolymer (P) is preferably 0.5% by weight or more, and more preferably 1.0% by weight or more. It may also be 3.0% by weight or less. If the isocyanate group content of the urethane prepolymer (P) is 1.0% by weight or more, it reacts with the resin (A), resulting in a stronger coating film.

[0051] In step 2, the pigment dispersion (X1) and a solvent solution (B) of a urethane prepolymer having an isocyanate group are mixed, and then a neutralizing agent is added to obtain a mixture. A pigment dispersion (X2) is obtained by adding water while stirring the mixture to homogenize it, and dispersing the mixture in water.

[0052] As a neutralizing agent, the neutralizing agents listed in step 1 can be used, and it is preferable to use an organic amine. A more preferable option is triethylamine. A neutralizing agent is added to neutralize the carboxyl groups remaining in the resin (A) and the carboxyl groups in the urethane prepolymer (P) contained in the solvent solution (B) of the urethane prepolymer, thereby producing a salt. The neutralization rate of the carboxyl groups by the neutralizing agent is preferably 20-100%, more preferably 60-100%, from the viewpoint of the dispersion stability of the resin (A) and the urethane prepolymer (P).

[0053] [Step 3: Obtaining an aqueous pigment dispersion] In step 3, the aqueous solvent is removed from the pigment dispersion (X2) to obtain an aqueous pigment dispersion. In step 3, the solvent contained in the urethane prepolymer solvent solution (B) used in step 2 is removed along with the aqueous solvent. Aqueous solvents and their removal can be carried out by any combination of reduced pressure and heating. Furthermore, the isocyanate group is reacted with water, and then more water is added to adjust the solid content concentration to the desired range. As a result of removing the aqueous solvent and solvent in step 3, an aqueous pigment dispersion is obtained in which the pigment is coated with resin and dispersed in water.

[0054] In the obtained aqueous pigment dispersion, the particle size (primary particle size) of the pigment particles coated with resin (hereinafter also referred to as resin-coated pigment particles) is preferably 100 to 200 nm. Particle size refers to the cumulant mean diameter. Particle size can be measured and determined using a light scattering particle size distribution analyzer [for example, the "DLS-8000" manufactured by Otsuka Electronics Co., Ltd.]. When the particle size is within the above range, the primary particle size does not become too large, making it easy to disperse in water and providing excellent dispersion stability and storage stability under high-temperature conditions.

[0055] The aqueous pigment dispersion obtained by the method for producing aqueous pigment dispersions of the present invention can be used in applications such as aqueous inks and paints.

[0056] When using a pigment aqueous dispersion as an aqueous ink, other components may be added as needed. For example, one or more penetrating agents, crosslinking agents, viscosity modifiers, defoaming agents, preservatives, degradation inhibitors, stabilizers, antifreeze agents, and water may be included.

[0057] Water-based ink can be manufactured by mixing and stirring a pigment aqueous dispersion with the components described above. During mixing, all components may be mixed simultaneously, or each component may be added and mixed in stages. The solid content concentration in the water-based ink is preferably 3 to 70% by weight, and more preferably 7 to 60% by weight.

[0058] Water-based inks can be used for offset printing, letterpress printing, gravure printing, screen printing, inkjet recording, and more.

[0059] When using an aqueous pigment dispersion as a paint, other components may be added as needed. For example, it may contain one or more crosslinking agents, catalysts, viscosity modifiers, defoaming agents, wetting agents, film-forming aids, leveling agents, preservatives, degradation inhibitors, stabilizers, and antifreeze agents, as well as at least one resin selected from the group consisting of urethane resins, acrylic resins, and polyester resins other than the resin contained in the aqueous pigment dispersion.

[0060] The paint can be used as a water-based paint composition for building materials or architectural painting, and as a water-based paint for automobiles. The coating film can be obtained, for example, by coating a substrate (plastic film, coated paper for printing, corrugated cardboard, fabric, etc.) and then heating and / or curing it as necessary.

[0061] This specification discloses the following:

[0062] This disclosure (1) includes a step 1 of dispersing a pigment in a mixed solution of a resin (A) having carboxyl groups and / or carboxylate anion groups, an aqueous solvent, and water to obtain a pigment dispersion (X1), Step 2 involves dispersing a mixture of the pigment dispersion (X1), a solvent solution (B) of a urethane prepolymer having an isocyanate group, and a neutralizing agent in water to obtain a pigment dispersion (X2). The step includes removing the aqueous solvent from the pigment dispersion (X2) to obtain an aqueous pigment dispersion, The acid value of the aforementioned resin (A) is 10 mg KOH / g or more. This is a method for producing an aqueous pigment dispersion in which the weight ratio of the aqueous solvent to the water (aqueous solvent / water) in step 1 is 85 / 15 to 95 / 5.

[0063] Disclosure (2) is a method for producing an aqueous pigment dispersion according to Disclosure (1), wherein the neutralizing agent is an organic amine.

[0064] The present disclosure (3) is a method for producing an aqueous pigment dispersion according to the present disclosure (1) or (2), wherein the resin (A) is a polyurethane resin obtained by reacting a polyol component and a polyisocyanate component, the polyol component is a polyol component containing a branched aliphatic diol, a polyester polyol and a polyol having a carboxyl group in its side chain, and the polyisocyanate component is a polyisocyanate component containing an aliphatic isocyanate.

[0065] This disclosure (4) is a method for producing an aqueous pigment dispersion according to this disclosure (3), wherein the polyester polyol is a polycondensate of an alcohol component and a carboxylic acid component, the alcohol component is an alcohol component containing a branched aliphatic diol, and the carboxylic acid component is a carboxylic acid component containing an aliphatic dicarboxylic acid.

[0066] Disclosure (5) is a method for producing an aqueous pigment dispersion according to any of Disclosures (1) to (4), wherein the SP value (Fedors method) of the mixed solvent of aqueous solvent and water used in step 1 is 12.0 or more and 17.0 or less. [Examples]

[0067] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" means parts by weight.

[0068] <Method for measuring acid value> The acid value was measured using the method specified in JIS K0070 (1992 edition).

[0069] <Method for measuring isocyanate group content> The isocyanate group content was measured by the method specified in JIS K1603-1.

[0070] <Manufacturing Example 1> In a simple pressurized reaction apparatus equipped with a stirrer and a heating device, 69.3 parts of polyester polyol A [Kuraray Polyol P-2010 (methylpentanediol adipic acid copolymer), manufactured by Kuraray Co., Ltd.], 0.8 parts of neopentyl glycol, 4.8 parts of 2,2-dimethylolpropionic acid (DMPA) as a polyol component having carboxyl groups in the side chain, and 25.1 parts of isophorone diisocyanate (IPDI) as a polyisocyanate component were charged and stirred at 70°C for 12 hours to carry out a urethane reaction to obtain a resin (A-1) having carboxyl groups.

[0071] <Manufacturing Example 2> A resin (A-2) containing carboxyl groups was obtained in the same manner as in Production Example 1, except that the amount of raw materials used was changed to those listed in Table 1. Resin (A-2) has an isocyanate group content of 0% and is not a prepolymer.

[0072] <Comparative Manufacturing Example 1> In a reaction vessel equipped with a condenser, thermometer, stirrer, and nitrogen inlet, 548.9 parts of 1,6-hexanediol, 597.9 parts of adipic acid, and 2 parts of titanium diisopropoxybistriethanolamine as a condensation catalyst were added, and the reaction was carried out at 200°C under a nitrogen stream for 3 hours while distilling off the water produced. The reaction was then carried out at 200°C for 6 hours under reduced pressure of 0.5 to 2.5 kPa. When the acid value fell below 1 mg KOH / g, the reaction product was removed from the reaction vessel to obtain polyester polyol B with a hydroxyl value of 56.1 mg KOH / g. Next, 75.7 parts of polyester polyol B, 0.5 parts of neopentyl glycol, 2.2 parts of 2,2-dimethylolpropionic acid (DMPA) as a polyol component having carboxyl groups in its side chains, and 21.5 parts of isophorone diisocyanate (IPDI) as a polyisocyanate component were charged into a simple pressurized reactor equipped with a stirrer and a heating device. The mixture was stirred at 70°C for 12 hours to carry out the urethane reaction and obtain a resin (A'-1) having carboxyl groups.

[0073] Table 1 shows the raw materials, acid value, isocyanate group content, and solubility in a mixed solvent of aqueous solvent and water used to produce the carboxyl group resins obtained in each production example and comparative production example. Solubility in mixed solvents was determined by mixing 100g of each mixed solvent shown in Table 1, such as a mixed solvent of isopropyl alcohol (IPA) and water (weight ratio IPA:water = 90:10) and a mixed solvent of propylene glycol (PG) and water (weight ratio PG:water = 90:10), with 25g of a mixture of a resin containing carboxyl groups and an amount of organic amine sufficient to neutralize 100% of the carboxyl groups. If the solution was clear, it was judged to be highly solubility; if the solution became cloudy, it was judged to be low solubility.

[0074] [Table 1]

[0075] <Manufacturing Example 3> In a simple pressurized reactor equipped with a stirrer and heating device, 67.2 parts of ethanol UH-200 (polycarbonate diol made from hexanediol: manufactured by Ube Industries, Ltd.), 0.5 parts of 1,4-butanediol (a low molecular weight diol), 4.8 parts of 2,2-dimethylolpropionic acid (DMPA) as a polyol component having carboxyl groups in its side chain, 27.5 parts of dicyclohexylmethane-4,4-diisocyanate (hydrogenated MDI) as a polyisocyanate component, and 100 parts of tetrahydrofuran as an organic solvent for the reaction were charged and stirred at 70°C for 12 hours to carry out the urethane formation reaction, obtaining a tetrahydrofuran solution (B-1) (solid content concentration 50% by weight) of a urethane prepolymer having isocyanate groups. The acid value of the urethane prepolymer having isocyanate groups was 20 mg KOH / g, and the isocyanate group content was 1.0% by weight.

[0076] <Example 1> In the vessel of a pigment disperser (TSU-6U, manufactured by AIMEX Co., Ltd.), 25 parts of a mixed solvent of 22.5 parts isopropyl alcohol (IPA) and 2.5 parts water (weight ratio IPA:water = 90:10), 5 parts of the carboxyl group-containing resin (A-1) prepared in Production Example 1, and 0.18 parts of triethylamine as a neutralizing agent were added, and the mixture was stirred until uniformly dissolved. Then, 10 parts of pigment PY74 (Yellow No. 71, manufactured by Dainichi Seika Kogyo Co., Ltd.), 0.5 parts of Naroacty CL-100 (manufactured by Sanyo Chemical Industries, Ltd.) as a penetrating agent, and 100 parts of glass beads (ASGB-320, manufactured by AS ONE Corporation) were added, and the mixture was dispersed for 4 hours while passing 4°C cooling water through the jacket to obtain a pigment dispersion (X1). To the obtained pigment dispersion (X1), 20 parts of the tetrahydrofuran solution of the urethane prepolymer prepared in Production Example 3 (B-1) and 0.36 parts of triethylamine as a neutralizing agent were added and homogenized. Then, 80 parts of water were added while stirring at 200 rpm to disperse the mixture and obtain pigment dispersion (X2). The obtained pigment dispersion (X2) was subjected to distillation to remove IPA and tetrahydrofuran under reduced pressure at 60°C for 2 hours, and the glass beads were removed by filtration. The mixture was then allowed to stand at 60°C for 3 hours to allow the reaction between the isocyanate group and water to proceed, after which water was added to adjust the solid content to 25% by weight to obtain the aqueous pigment dispersion (R-1).

[0077] <Examples 2-10> Pigment aqueous dispersions (R-2) to (R-10) were obtained in the same manner as in Example 1, except that the amount of raw materials used was changed to those listed in Table 2.

[0078] <Comparative Examples 1-4> Pigment aqueous dispersions (R'-1) to (R'-4) were obtained in the same manner as in Example 1, except that the amount of raw materials used was changed to those listed in Table 2.

[0079] <Method for measuring particle size> The particle size of resin-coated pigment particles contained in the aqueous pigment dispersions (R-1) to (R-10) and (R'-1) to (R'-4) was measured using a light scattering particle size distribution analyzer [DLS-8000 manufactured by Otsuka Electronics Co., Ltd.], and the resulting cumulant average diameter was defined as the particle size.

[0080] <Method for measuring viscosity> The viscosity of the aqueous pigment dispersions (R-1) to (R-10) and (R'-1) to (R'-4) was measured using the following measuring device and conditions. Equipment: MCR92 (manufactured by Anton Paar) Jig: 50mm cone plate Shear rate: 200 1 / s Measurement temperature: 25℃

[0081] <Method for evaluating storage stability> The aqueous pigment dispersions (R-1) to (R-10) and (R'-1) to (R'-4) were subjected to an accelerated drying test in a circulating air dryer [SPH-201 from ESPEC Corporation] at 70°C for one week. The particle size and viscosity after removal were measured using the method described above. The rate of change (100 × (measured value after accelerated test - measured value before accelerated test) / measured value before accelerated test) was calculated from the measured particle size and viscosity before and after the accelerated test. The rate of change (%) of particle size and viscosity is shown in Table 2 (storage stability). A rate of change of 10% or less for both particle size and viscosity is considered to be at a practical level. ○: Particle size and viscosity change rate within ±10% ×: Particle size and viscosity change rate is greater than ±10%

[0082] <Manufacturing of printing inks (S-1) to (S-10), (S'-1) to (S'-4)> Forty parts of the aqueous pigment dispersions (R-1) to (R-10) and (R'-1) to (R'-4) obtained in Examples 1 to 10 or Comparative Examples 1 to 4, 28.5 parts of propylene glycol, 1.5 parts of triethylene glycol as a penetrating agent, and 30 parts of water were placed in a container and mixed for 10 minutes to prepare printing inks (S-1) to (S-10) and comparative printing inks (S'-1) to (S'-4).

[0083] <Method for evaluating abrasion resistance> Printing inks (S-1) to (S-10) or comparative printing inks (S'-1) to (S'-4) were applied to coated printing paper [high-grade art paper manufactured by Mitsubishi Paper Mills Ltd.] using a bar coater so that the thickness after drying was 1 μm. The paper was dried at 70°C for 2 minutes to prepare test pieces (2 cm x 6 cm) on which pigment and printing ink were coated onto the coated printing paper. The prepared test specimens were attached to the measurement area of ​​a speed-variable friction measuring instrument [Trinity Labs Tribomaster μv1000]. A 1cm x 1cm cotton cloth (No. 3) was attached to the indenter with double-sided tape, and a 200g load was applied. The friction was performed 100 times back and forth with a friction stroke of 2cm and a friction speed of 2400mm / min. The color transfer density on the cotton cloth (No. 3) side of the indenter was measured at 9 points using a spectrophotometer [X-rite 938], and the average of the measurement results was taken as the color transfer density. The color transfer density was evaluated according to the following criteria, and the results are shown in Table 2. The lower the color transfer density, the better the abrasion resistance. ◎: Dye migration concentration 0.10 or less ○: Transfer concentration greater than 0.10 and 0.15 or less. △: Transfer staining concentration greater than 0.15 and less than or equal to 0.20 ×: Transfer concentration greater than 0.20 and less than or equal to 0.30 A transfer staining concentration of 0.15 or less is considered to be at a practical level.

[0084] The aqueous pigment dispersions of Examples 1-10 exhibited excellent initial dispersibility and storage stability. Furthermore, the inks using the aqueous pigment dispersions of Examples 1 and 2 also showed excellent abrasion resistance. In Example 3, where the resin (A-2) dissolved in the mixed solvent of aqueous solvent and water used in Step 1 is not a prepolymer, the resin (A-2) did not react with the urethane prepolymer (B-1) produced in Production Example 3. As a result, the molecular weight was lower and the mechanical strength was inferior compared to Examples 1 and 2, resulting in a difference in abrasion resistance, although it was still at a practical level. Comparative Example 1's aqueous pigment dispersion (R'-1), in which a resin (A'-1) that does not dissolve in the mixed solvent of aqueous solvent and water used in Step 1 was dispersed with a pigment, and Comparative Examples 2-4's aqueous pigment dispersions (R'-2)-(R'-4), in which the weight ratio of aqueous solvent to water (aqueous solvent / water) in Step 1 was outside the range of 85 / 15-95 / 5, showed insufficient initial dispersibility or storage stability.

[0085] [Table 2] [Industrial applicability]

[0086] The present invention provides a method for producing an aqueous pigment dispersion that yields an aqueous pigment dispersion with excellent dispersion stability and storage stability under high-temperature conditions. The obtained aqueous pigment dispersion can be suitably used as a printing ink or paint.

Claims

1. Step 1 involves dispersing a pigment in a mixed solution of a resin (A) having carboxyl groups and / or carboxylate anion groups, an aqueous solvent, and water to obtain a pigment dispersion (X1), Step 2 involves dispersing a mixture of the pigment dispersion (X1), a solvent solution (B) of a urethane prepolymer having an isocyanate group, and a neutralizing agent in water to obtain a pigment dispersion (X2). The step includes removing the aqueous solvent from the pigment dispersion (X2) to obtain an aqueous pigment dispersion, The acid value of the aforementioned resin (A) is 10 mg KOH / g or more. The weight ratio of the aqueous solvent to the water in step 1 (aqueous solvent / water) is 85 / 15 to 95 / 5. The boiling point of the aqueous solvent is lower than the boiling point of water. A method for producing an aqueous pigment dispersion, wherein in step 3, the aqueous solvent is removed by at least one of reduced pressure and heating.

2. The method for producing an aqueous pigment dispersion according to claim 1, wherein the neutralizing agent is an organic amine.

3. A method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the resin (A) is a polyurethane resin obtained by reacting a polyol component and a polyisocyanate component, the polyol component is a polyol component containing a branched aliphatic diol, a polyester polyol, and a polyol having a carboxyl group in its side chain, and the polyisocyanate component is a polyisocyanate component containing an aliphatic isocyanate.

4. The method for producing an aqueous pigment dispersion according to claim 3, wherein the polyester polyol is a polycondensate of an alcohol component and a carboxylic acid component, the alcohol component is an alcohol component containing a branched aliphatic diol, and the carboxylic acid component is a carboxylic acid component containing an aliphatic dicarboxylic acid.

5. A method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the SP value (Fedors method) of the mixed solvent of the aqueous solvent and water used in step 1 is 12.0 or more and 17.0 or less.

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