JP2017082212A - Core-shell type modified pigment and aqueous pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core-shell type modified pigment having a plurality of resin layers as a shell layer that enables stable dispersion of a pigment in an aqueous medium and has good printing characteristics.SOLUTION: The core-shell type modified pigment has a layer of resin constituting a shell part present in a pigment being a core part. The layer of resin includes a first layer of an acrylic copolymer having an anionic group which comes into contact with the pigment and a second layer of an urethane resin having an anionic group which comes into contact with the first layer and constitutes the outermost layer. The urethane resin having an anionic group has a saturation adsorption amount in the range of 20-150%. An aqueous pigment dispersion contains the core-shell type modified pigment and an aqueous medium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a core-shell type modified pigment and an aqueous pigment dispersion.

  Inkjet recording systems have a growing tendency from home use to office use, photography use, and outdoor use, and the weather resistance (light) resistance and storage stability of printed matter are emphasized. The dyes that have been at the center of ink-jet recording colorants have many problems in terms of light resistance, and accordingly, development of water-based inks for ink-jet recording using pigments having excellent light resistance has been promoted.

The pigment is insoluble in water and is used as an aqueous pigment dispersion dispersed in an aqueous medium. For this reason, a technique for stably dispersing a pigment in an aqueous medium has been conventionally studied.
For example, a colored fine particle dispersion obtained by mixing a colorant and a resin and dispersing in water, wherein the fine particle has a core-shell structure of at least two layers, and a core that forms an inner core and at least formed outside thereof Among the shells of one layer, at least two or more each have a crosslinked structure, and a crosslinked colored fine particle dispersion having a core-shell structure with improved dispersion stability (see, for example, Patent Document 1), or the color of an aqueous ink for inkjet recording As a material, at least one having in the molecule at least one structure selected from a polymer containing a polymerizable unsaturated group soluble in a non-aqueous solvent, a carboxylic acid group, a sulfonic acid group, and a salt thereof on the pigment surface. It is known to use a modified pigment having a polymer obtained by copolymerizing a kind of polymerizable unsaturated monomer (see, for example, Patent Document 2). ).

Alternatively, as a method for producing colored resin particles in which a core colorant is encapsulated with a non-crosslinkable resin that is a shell, (1) at least a colorant (B) is dispersed in a synthetic resin (a) having an acid value Or a resin coloring step for dissolving to obtain a solid coloring compound, and (2) mixing at least water, an organic solvent for dissolving the synthetic resin (a), a base (b), and the solid coloring compound obtained in the resin coloring step. And a suspension step of obtaining a colorant suspension in which at least a part of the resin is dissolved by dispersion, and (3) a resin dissolved on the surface of the colorant in the colorant suspension obtained in the suspension step. It is described in paragraph 0023 of Document 3 that it can be obtained by a reprecipitation step in which components are deposited.
However, none of the documents discusses the influence of the coating amount of the resin serving as the shell on the printing characteristics.

JP 2004-269558 A JP 2009-235320 A JP-A-11-349870

  The problem to be solved by the present invention is to provide a core-shell modified pigment having a plurality of resin layers as a shell layer, which can stably disperse the pigment in an aqueous medium and has good printing characteristics.

  The present inventors provide a core-shell type modified pigment in which a resin layer serving as a shell portion is present in a pigment serving as a core portion, and the resin in the first layer that contains the pigment, that is, directly in contact with the pigment is a non-reactive anion. A core shell in which the resin serving as the shell portion is a two-layer resin, wherein the second layer resin that is in contact with the first layer and is the outermost layer is a urethane resin having an anionic group It has been found that type-modified pigments are excellent in dispersion stability, and that the amount of urethane resin having an anionic group affects printing characteristics, particularly marker resistance and printing density uniformity. The larger the amount of the urethane resin having an anionic group, the better the marker resistance, but the print density uniformity showing instability of ejection tends to be inferior.

  In contrast, the present inventors have found that an appropriate amount of urethane resin excellent in balance between marker resistance and printing density uniformity can be calculated from the saturated adsorption amount specified by colloid titration, and completed the present invention. Is.

  That is, the present invention provides a core-shell modified pigment in which a resin layer serving as a shell portion is present in a pigment serving as a core portion, wherein the resin layer has an anionic group in contact with the pigment. One layer and a second layer of a urethane resin having an anionic group in contact with the first layer and serving as the outermost layer, and the urethane resin having the anionic group is in a range of 20 to 150% of the saturated adsorption amount. A core-shell type modified pigment is provided.

  The present invention also provides an aqueous pigment dispersion containing the core-shell modified pigment described above and an aqueous medium.

  According to the present invention, it is possible to provide a pigment composition including a core-shell type modified pigment having a plurality of resin layers as a shell layer, which can stably disperse a pigment in an aqueous medium and has good printing characteristics.

(Pigment)
The pigment used in the present invention is at least one pigment selected from known and commonly used organic pigments or inorganic pigments. In addition, the present invention can be applied to either an untreated pigment or a treated pigment. Specifically, it can be dispersed in water or a water-soluble organic solvent, and a known inorganic pigment or organic pigment can be used. Examples of the inorganic pigment include carbon black produced by a known method such as iron oxide, a contact method, a furnace method, and a thermal method. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments, etc.), dye chelates (for example, basic dye chelate, acid dye chelate, etc.), nitro pigments, nitroso pigments, aniline black, and the like.

  For example, the pigment used in the black ink is carbon black, No. manufactured by Mitsubishi Chemical Corporation. 2300, no. 2200B, no. 995, no. 990, no. 900, no. 960, no. 980, no. 33, no. 40, No, 45, No. 45L, no. 52, HCF88, MA7, MA8, MA100, etc. are Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc. manufactured by Columbia, Regal 400R, Regal 330R, Regal 660R, Mull 660R, Mull 660R Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. are Color Black FW1, FW2, FW2V, FW18, FW200, S170, U , V, 1400U, Special Bla k 6, the 5, 4, 4A, NIPEX150, NIPEX160, NIPEX170, NIPEX180, NIPEX95, NIPEX90, NIPEX85, NIPEX80, NIPEX75 and the like.

  Specific examples of pigments used in yellow ink include C.I. 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, 185 and the like.

  Specific examples of pigments used in magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 150, 168, 176, 184, 185, 202, 209, 213 282, C.I. I. Pigment violet 19 and the like.

  Specific examples of pigments used for cyan ink include C.I. I. Pigment blue 1, 2, 3, 15, 15: 3, 15: 4, 15: 6, 16, 22, 60, 63, 66, and the like.

  The pigment preferably has a dispersed particle diameter of 1 μm or less after the dispersion treatment, more preferably 10 nm to 250 nm, and most preferably 50 nm to 200 nm. The pigment may be a solid solution, or two or more pigments may be mixed and used.

  Self-dispersing pigments may also be used. The self-dispersing pigment means a pigment that can be dispersed in an aqueous medium without a dispersant. Here, “dispersed or dissolved in an aqueous medium without a dispersant” means a state in which the surface is stably present in the aqueous medium due to the hydrophilic group on the surface without using a dispersant for dispersing the pigment. Means. Here, “stablely present in an aqueous medium” means stable in water (25 ° C., solid content 10% by weight) for 90 days without a dispersant (the change in the particle size of the pigment is within +/− 30%). It means that there is.

The hydrophilic _{group, -OM, -COOM, -SO 3 M} , -SO 2 M, -SO 2 NH 2, -RSO 2 M, -PO 3 HM, -PO 3 M 2, -SO 2 NHCOR, -NH ₃ and one or more hydrophilic groups selected from the group consisting of —NR ₃ , that is, an anionic hydrophilic functional group. Note that M in these formulas independently represents a hydrogen atom, an alkali metal, ammonium, a phenyl group which may have a substituent, or organic ammonium. R in these formulas independently represents an alkyl group having 1 to 12 carbon atoms or an aryl group which may have a substituent.

  The self-dispersing pigment is produced, for example, by bonding (grafting) the hydrophilic group to the surface of the pigment by subjecting the pigment to physical treatment or chemical treatment. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which oxidation is performed with an oxidizing agent in water, a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface, and the like. .

  Examples of the self-dispersing pigment include JP-A-8-3498, JP-T 2000-513396, JP-T 2008-524400, JP-T 2009-515007, JP-T 2010-537006, JP What processed the pigment by the method as described in Table 2012-500866 gazette etc. can be used. As the raw material for the self-dispersing pigment, both inorganic pigments and organic pigments can be used.

  As the pigment used in the present invention, either dry powder or wet cake can be used. Moreover, these pigments may be used independently and may be used in combination of 2 or more types.

The pigment used in the present invention is preferably a pigment having a primary particle size of 25 μm or less, particularly preferably a pigment having a primary particle size of 1 μm or less. When the particle diameter is within this range, pigment settling hardly occurs and the pigment dispersibility is good.
For the measurement of the particle diameter, for example, a value measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM) can be adopted.

(Acrylic copolymer having an anionic group)
The acrylic copolymer having an anionic group used in the present invention specifically includes a monomer having an anionic group such as (meth) acrylic acid and other ethylenically unsaturated monomers copolymerizable therewith. And a copolymer with a monomer. In the present invention, (meth) acrylic acid means a generic term for acrylic acid and methacrylic acid. In the case of various esters of (meth) acrylic acid, it is interpreted in the same manner as described above.

  As the other copolymerizable ethylenically unsaturated monomer described above, the hydrophobicity of the copolymer is further increased in the same acid value comparison, and the adsorption of the copolymer onto the pigment surface can be made stronger. For example, alkylstyrene such as styrene, α-methylstyrene, β-methylstyrene, 2,4-dimethylstyrene, α-ethylstyrene, α-butylstyrene, α-hexylstyrene, 4-chlorostyrene, 3-chlorostyrene, Halogenated styrene such as 3-bromostyrene, styrene monomers such as 3-nitrostyrene, 4-methoxystyrene, vinyltoluene, benzyl (meth) acrylate, phenyl (meth) acrylate, phenylethyl (meth) acrylate, phenylpropylene Ru (meth) acrylate, phenoxyethyl (meth) acrylate, etc. It is preferable to use a (meth) acrylic acid ester monomer having a benzene ring. Among these, it is particularly preferable to use a styrene monomer such as styrene, α-methylstyrene, or tert-butylstyrene.

  The copolymer in the present invention may be a copolymer containing a polymerization unit of (meth) acrylic acid and a polymerization unit of other copolymerizable ethylenically unsaturated monomer as essential polymerization units, Or a ternary copolymer of three or more with another copolymerizable ethylenically unsaturated monomer.

  Examples of the ethylenically unsaturated monomer include methyl acrylate, methyl methacrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, 2-ethylbutyl acrylate, 1,3-dimethyl Butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-methylbutyl methacrylate, pentyl methacrylate, heptyl methacrylate, maleic acid, maleic anhydride, nonyl methacrylate Acrylic acid esters and methacrylic acid esters such as 3-ethoxypropyl acrylate, 3-ethoxybutyl acrylate, dimethyl Acrylic ester derivatives such as aminoethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxybutyl acrylate, ethyl-α- (hydroxymethyl) acrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and methacryl Acid ester derivatives; aryl acrylates such as phenyl acrylate, benzyl acrylate, phenyl ethyl acrylate, phenyl ethyl methacrylate; and aralkyl acrylates; many such as diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, bisphenol A Monoacrylates or monomethacrylates of monohydric alcohols And dimethyl maleate, dialkyl maleate such as diethyl maleate, vinyl acetate and the like. One or more of these monomers can be added as monomer components.

  Even if the copolymer used in the present invention is a linear copolymer composed only of polymerized units of monoethylenically unsaturated monomers, various ethylenically unsaturated monomers having various crosslinking properties are used. It may be a copolymer containing a partially cross-linked partly crosslinked part.

  Examples of the ethylenically unsaturated monomer having such crosslinkability include glycidyl (meth) acrylate, divinylbenzene, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di ( Examples include poly (meth) acrylates of polyhydric alcohols such as (meth) acrylates, poly (oxyethyleneoxypropylene) glycol di (meth) acrylates, and tri (meth) acrylates of alkylene oxide adducts of glycerol.

  In the present invention, the reaction rate and the like of each monomer used is considered to be substantially the same, and the charging ratio of each monomer is regarded as the content ratio in terms of mass of the polymerization unit of each monomer. The copolymer in the present invention can be synthesized by various conventionally known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In this case, a known and usual polymerization initiator, chain transfer agent (polymerization degree adjusting agent), surfactant and antifoaming agent can be used in combination.

  Particularly preferred as the acrylic copolymer having an anionic group used in the present invention, among the copolymers, for example, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid ester- ( Styrenic monomers such as (meth) acrylic acid copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer, and styrene-acrylic acid copolymer containing (meth) acrylic acid as a raw material monomer Can be mentioned. (In the present invention, the “styrene-acrylic acid copolymer” is defined as “a copolymer containing a styrene monomer and (meth) acrylic acid as a raw material monomer” as described above. , General-purpose monomers other than styrene monomers and (meth) acrylic acid may be copolymerized)

  The use ratio of the styrene monomer that is the raw material of the styrene-acrylic acid copolymer is more preferably 50 to 98% by mass, and particularly preferably 70 to 90% by mass. When the use ratio of the styrene monomer is 50% by mass or more, the affinity of the styrene-acrylic acid copolymer to the pigment is good, and the dispersion stability of the aqueous pigment dispersion tends to be improved. Also, the plain paper recording characteristics of the aqueous inkjet recording ink obtained from the aqueous pigment dispersion are improved, the image recording density tends to increase, and the water resistance tends to improve. When the amount of the styrenic monomer is in the above range of 90% by mass or less, the dispersibility of the pigment coated with the styrene-acrylic acid copolymer in the aqueous medium can be favorably maintained. The dispersibility and dispersion stability of the pigment can be improved. Furthermore, the printing stability when used as an ink composition for inkjet recording is improved.

The styrene-acrylic acid copolymer is obtained by copolymerization of at least one of a styrene monomer, an acrylic acid monomer, and a methacrylic acid monomer, but it is preferable to use acrylic acid and methacrylic acid in combination. The reason is that the copolymerization at the time of resin synthesis is improved, the uniformity of the resin is improved, and as a result, the storage stability is improved, and a more finely divided pigment dispersion tends to be obtained. It is.
In the styrene-acrylic acid copolymer, the total during copolymerization of the styrene monomer, the acrylic acid monomer, and the methacrylic acid monomer is preferably 80% by mass or more based on the total monomer components.

  As a method for producing the styrene-acrylic acid copolymer, a usual polymerization method can be employed, and a method of performing a polymerization reaction in the presence of a polymerization catalyst such as solution polymerization, suspension polymerization, bulk polymerization, etc. It is done. Examples of the polymerization catalyst include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), Examples thereof include benzoyl peroxide, dibutyl peroxide, butyl peroxybenzoate, and the amount used is preferably 0.1 to 10.0% by mass of the vinyl monomer component.

  The styrene-acrylic acid copolymer may be a random copolymer or a graft copolymer. As the graft copolymer, a copolymer of polystyrene or a nonionic monomer copolymerizable with styrene and styrene is used as a trunk or branch, and a copolymer of acrylic acid, methacrylic acid and other monomers including styrene is branched. Or the graft copolymer used as a trunk can be shown as the example. The styrene-acrylic acid copolymer may be a mixture of the graft copolymer and the random copolymer.

  In the present invention, the weight average molecular weight of the acrylic copolymer having an anionic group is preferably in the range of 2000 to 40000. For example, also when using the said styrene-acrylic-acid type copolymer, it is preferable that the weight average molecular weight exists in the range of 5000-20000, and it is more preferable that it exists in the range of 5000-18000. Especially, it is especially preferable that it exists in the range of 5500-15000. Here, the weight average molecular weight is a value measured by a GPC (gel permeation chromatography) method, and is a value converted to a molecular weight of polystyrene used as a standard substance.

  When the acrylic copolymer having an anionic group used in the present invention is a styrene-acrylic acid copolymer, it has a carboxyl group derived from an acrylic acid monomer and a methacrylic acid monomer, but the acid value thereof is 10 to 400 ( mgKOH / g), preferably 50 to 300 (mgKOH / g). When the acid value is 300 (mgKOH / g) or less, the aggregation of the pigment tends to be less likely to occur.

The acid value here is a value measured in accordance with Japanese Industrial Standard “K 0070: 1992. Test method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products”. , The amount (mg) of potassium hydroxide required to completely neutralize 1 g of resin.
When the acid value is too low, pigment dispersion and storage stability are lowered, and when an aqueous ink for inkjet recording described later is prepared, printing stability is deteriorated, which is not preferable. If the acid value is too high, the water resistance of the colored recording image is lowered, which is also not preferable. In order to make the copolymer within the range of the acid value, (meth) acrylic acid may be included and copolymerized so as to be within the range of the acid value.

(Basic compound)
In the present invention, the basic compound is used for the purpose of neutralizing the anionic group. Known compounds can be used as the basic compound, for example, alkali metal hydroxides such as potassium and sodium; carbonates of alkali metals such as potassium and sodium; carbonates such as alkaline earth metals such as calcium and barium; Inorganic basic compounds such as ammonium hydroxide, amino alcohols such as triethanolamine, N, N-dimethanolamine, N-aminoethylethanolamine, dimethylethanolamine, NN-butyldiethanolamine, morpholine, N -Organic basic compounds such as morpholines such as methylmorpholine and N-ethylmorpholine, and piperazine such as N- (2-hydroxyethyl) piperazine and piperazine hexahydrate.

  Although the neutralization rate of the anionic group using these is not particularly limited, it is generally carried out in a range of 80 to 120%. In the present invention, the neutralization rate is a numerical value indicating how much the compounding amount of the basic compound is relative to the amount required for neutralization of all carboxyl groups in the acrylic copolymer having the anionic group. And is calculated by the following equation.

(Method for forming first layer of acrylic copolymer having anionic group)
The method for forming the first layer of the acrylic copolymer shell having an anionic group on the pigment as the core portion is not particularly limited and can be carried out by a known dispersion method. For example, media mill dispersion methods using media such as paint shakers, bead mills, sand mills, ball mills, medialess dispersion methods using ultrasonic homogenizers, high pressure homogenizers, nanomizers, optimizers, etc., roll mills, Henschel mixers, pressure kneaders And kneading and dispersing methods that give a strong shearing force, such as intensive mixers, Banbury mixers, and planetary mixers. Among these, the kneading dispersion method is preferred because it is a method of refining pigment particles by applying a strong shearing force to a mixture having a high solid content concentration containing a pigment with a kneader.
Hereinafter, a modified pigment in which only the first layer of the resin serving as the shell is formed on the pigment that is the core portion may be referred to as a core-shell single-layer modified pigment, and an acrylic copolymer having an anionic group is used as the resin. The core-shell single layer modified pigment may be referred to as a core-shell single layer modified pigment A.

  In the kneading dispersion method, a pigment, an acrylic copolymer having an anionic group, a basic compound, and, if necessary, a water-soluble organic solvent are charged and kneaded. In addition, there is no particular limitation on the charging order at this time, and the entire amount may be simultaneously charged and kneading may be started, or a small amount of each may be charged. For example, an acrylic copolymer having an anionic group and a basic compound The order of preparation may be changed depending on the raw material, for example, a water-soluble organic solvent is charged after charging the pigment and the pigment. The amount of each raw material charged can be within the above-mentioned range.

  In order to give a strong shearing force, which is a merit of the kneading dispersion method, to the mixture, it is preferable to knead the mixture at a high solid content ratio, and a higher shearing force can be applied to the mixture. As a solid content ratio, 20-100 mass% is preferable, 30-90 mass% is more preferable, 40-80 mass% is the most preferable. If the amount is less than 20% by mass, the viscosity of the mixture decreases, so that the kneading is not sufficiently performed, and the pigment may be insufficiently crushed. And by increasing the solid content ratio in this way, the viscosity of the kneaded product during kneading is kept moderately high, the share of the kneaded product from the kneading machine during kneading is increased, and the pulverization of the pigment in the kneaded product and the pigment The coating with the acrylic copolymer having the anionic group can proceed simultaneously.

  The amount of the acrylic copolymer having an anionic group with respect to the pigment may be any resin amount, but is generally preferably 1 to 100% by weight, more preferably 5 to 50% by weight, and further preferably 10 to 30% by weight. Preferably, 2.5 to 20% by weight is most preferable.

  The temperature at the time of kneading can be appropriately adjusted in consideration of temperature characteristics such as the glass transition point of the acrylic copolymer having an anionic group to be used so that a sufficient shearing force is applied to the kneaded product. For example, when the acrylic copolymer having an anionic group is a styrene-acrylic acid copolymer, it is preferably performed in a range lower than the glass transition point and having a temperature difference from the glass transition point of less than 50 ° C. By kneading in such a temperature range, there is no shortage of shear force due to a decrease in the viscosity of the kneaded product accompanying the melting of the resin due to an increase in the kneading temperature.

  The kneading apparatus used in the kneading step may be any apparatus capable of generating a high shearing force with respect to a mixture having a high solid content ratio, and may be selected from known kneading apparatuses as described above. Although it is possible, it is preferable to use a kneading apparatus having a stirring tank and stirring blades and capable of sealing the stirring tank, rather than using an open type kneader that does not have a stirring tank such as two rolls. It is preferable to use a kneading apparatus having a stirring tank and stirring blades. Examples of such an apparatus include a Henschel mixer, a pressure kneader, a Banbury mixer, and a planetary mixer. A planetary mixer is particularly suitable. In the present invention, the kneading is preferably carried out in a state where the pigment concentration and the solid content concentration of the pigment and the resin are high. Compared with a two-roller, etc., a mixer can be kneaded in a wide range of viscosity, and an aqueous medium can be added and distilled off under reduced pressure, making it easy to adjust the viscosity and load shear force during kneading. It is.

  In the kneading step, the water-soluble organic solvent such as high surface tension glycols and diols such as polyhydric alcohols functioning as a wetting agent may be used in combination.

The core shell single layer modified pigment A is obtained by the kneading dispersion method. When the core-shell single layer-type modified pigment A is obtained by the kneading and dispersing method as described above, it is used as it is in the step of forming a second layer of urethane resin having the following anionic group by diluting with water as it is.
In the case of diluting with water, for example, if a kneading apparatus having a stirring tank and stirring blades and capable of sealing the stirring tank is used, it is possible to add water as it is after the kneading dispersion method. The water used here may be used in combination with water or a water-soluble organic solvent.

(water)
As the water used in the present invention, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. In addition, the generation of mold or bacteria can be prevented when long-term storage of aqueous pigment dispersions obtained by using ultraviolet rays or water sterilized by addition of hydrogen peroxide, inks using the same, etc. Therefore, it is preferable.

(Water-soluble organic solvent)
In the present invention, a water-soluble organic solvent may be used in combination with water as necessary. Examples of the water-soluble organic solvent include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, and 2-methoxyethanol. Alcohols such as tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, etc .; amides such as dimethylformamide, N-methylpyrrolidone, etc., and especially those having 3 to 6 carbon atoms It is preferable to use a compound selected from the group consisting of a ketone and an alcohol having 1 to 5 carbon atoms.

  Also, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol with high viscosity; diols such as butanediol, pentanediol, hexanediol, and diols of the same family Glycol esters such as propylene glycol laurate; glycol ethers such as cellosolve including diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl ethers, propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; methanol; Ethanol, isopropyl alcohol, 1-propano , 2-propanol, 1-butanol, 2-butanol, butyl alcohol, pentyl alcohol, and alcohols such as homologues thereof; or sulfolane; lactones such as γ-butyrolactone; 2-pyrrolidinone, N- (2 -Lactams such as -hydroxyethyl) pyrrolidone; glycerin and its derivatives, polyoxyethylene benzyl alcohol ether and the like can also be used as a wetting agent used at the time of pigment dispersion.

  These water-soluble organic solvents can be used alone or in combination. Among them, polyhydric alcohols such as glycols and diols having high boiling point and low volatility and high surface tension are particularly preferably used as wetting agents, and glycols such as diethylene glycol and triethylene glycol are particularly preferable.

  The core-shell single layer-modified pigment A paste obtained in this way, depending on the application, is usually adjusted to have a pigment concentration of 10 to 50% by mass. The step of forming the second layer is easy and preferable.

Specifically, for example, after preparing a pigment kneaded product in a kneader having a stirring tank as described above, water is added to the stirring tank, mixed, and if necessary, stirred to directly dilute the aqueous pigment. Dispersions can be produced. Further, the aqueous pigment dispersion can be prepared by mixing the solid pigment dispersion and water with another stirrer equipped with a stirring blade and stirring as necessary.
Regarding water mixing, the required amount may be mixed at once with respect to the pigment kneaded material, but dilution with water is more efficient when the required amount is added continuously or intermittently. As a result, the aqueous pigment dispersion can be prepared in a shorter time. Although there is no particular limitation on the dissolution time and superheat temperature, in order to ensure sufficient solubility of the kneaded product and uniformity of the resulting dispersion, the acrylic copolymer having an anionic group may be decomposed, It is preferable that the temperature is high for a long time as long as the stability of the dispersion is not impaired.

  Further, the aqueous pigment dispersion obtained in this way may be further subjected to a dispersion treatment by a disperser. There are no particular restrictions on the disperser that can be used at this time. Paint shaker, bead mill, roll mill, sand mill, ball mill, attritor, basket mill, sand mill, sand grinder, dyno mill, disper mat, SC mill, spike mill, agitator mill, juice Examples include mixers, high-pressure homogenizers, ultrasonic homogenizers, nanomizers, dissolvers, dispersers, high-speed impeller dispersers, kneaders, and planetary mixers.

(Urethane resin having an anionic group)
Next, a second layer of urethane resin having an anionic group is formed on the core-shell single layer modified pigment A.
Hereinafter, "the core-shell pigment having the first layer of the resin in contact with the pigment as the shell and the second layer of the resin as the outermost layer in contact with the first layer" is a core-shell two-layer modified pigment. The first layer of the acrylic copolymer having an anionic group in contact with the pigment and the urethane having the anionic group in contact with the first layer and serving as the outermost layer in the pigment of the present invention The “core-shell modified pigment containing the second layer of resin” may be referred to as “core-shell two-layer modified pigment A”.
Specifically, the urethane resin having an anionic group used in the present invention has a polyol and a polyisocyanate having an anionic group such as a carboxy group or a sulfonic acid group, and a general-purpose anionic group as required. And urethane resins obtained by reacting no polyol or chain extender.

Examples of the polyol having a carboxy group used in the present invention include esters obtained by reaction of polyhydric alcohols and polybasic acid anhydrides, 2,2-dimethylol lactic acid, 2,2-dimethylol propionic acid, 2, And dihydroxyalkanoic acids such as 2-dimethylolbutanoic acid and 2,2-dimethylolvaleric acid. Preferable compounds include 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid. Among them, dimethylolpropionic acid or dimethylolbutanoic acid is easily available and preferable.
Examples of the polyol having a sulfonic acid group include dicarboxylic acids such as 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, and 5 [4-sulfophenoxy] isophthalic acid, and salts thereof, and the low molecular weight. The polyester polyol obtained by making a polyol react is mentioned.

Examples of the diisocyanate used in the present invention include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, and 4,4-cyclohexylmethane. Examples thereof include alicyclic diisocyanate compounds such as diisocyanate, aromatic aliphatic diisocyanate compounds such as xylylene diisocyanate and tetramethylxylene diisocyanate, aromatic diisocyanates such as toluylene diisocyanate and phenylmethane diisocyanate.
Among these, an aliphatic diisocyanate compound or an alicyclic diisocyanate is preferable from the viewpoint that light discoloration of a printed image hardly occurs.

Moreover, as a polyol which does not have a general purpose anionic group, polyester polyol, polyether polyol, polyhydroxy polycarbonate, polyhydroxy polyacetal, polyhydroxy polyacrylate, polyhydroxy polyester amide, and polyhydroxy polythioether are mentioned, for example. Of these, polyester polyol, polyether polyol and polyhydroxy polycarbonate are preferred. One of these polyols may be reacted, or several may be mixed and reacted.
In addition to the polyol, a low molecular weight diol may be used in combination as appropriate for the purpose of adjusting the film hardness of the printed matter. Examples include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and the like.

  Examples of the chain extender used in the present invention include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,4-bis (β-hydroxyethoxy) benzene. Diols such as 1,4-cyclohexanediol and xylylene glycol, polyamine, propylenediamine, xylylenediamine, isophoronediamine, 4,4′-diaminodiphenylmethane, tolylenediamine, 4,4′-diaminodicyclohexylmethane, etc. One kind or two or more kinds of diamines can be used.

  The urethane resin is produced, for example, by reacting the polyol and the polyisocyanate in the absence of a solvent or in the presence of an organic solvent. Next, the urethane resin having an anionic group formed by neutralization using the basic compound or the like is mixed with an aqueous medium to make it aqueous, and if necessary, mixed with a chain extender. It can be produced by reacting.

  The reaction between the polyol and the polyisocyanate is preferably carried out, for example, in an equivalent ratio of the isocyanate group of the polyisocyanate to the hydroxyl group of the polyol in the range of 0.8 to 2.5, 0.9 to It is more preferable to carry out in the range of 1.5.

  In the present invention, the urethane resin having an anionic group preferably has a weight average molecular weight in the range of 5,000 to 500,000, more preferably 10,000 to 200,000. It is particularly preferable to use those having a viscosity of 1,000,000 to 100,000.

  Here, the weight average molecular weight is a value measured by a GPC (gel permeation chromatography) method, and is a value converted to a molecular weight of polystyrene used as a standard substance.

  Moreover, as said urethane resin, it is preferable to use what has an acid value of the range of 0-150 (mgKOH / g), and it is the range of 10-100 (mgKOH / g), and a urethane resin is favorable. It is preferable for improving the water dispersion stability.

The acid value here is a value measured in accordance with Japanese Industrial Standard “K 0070: 1992. Test method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products”. , The amount (mg) of potassium hydroxide required to completely neutralize 1 g of resin.
If the acid value is too low, the pigment dispersion and storage stability may be lowered, and if the acid value is too high, the water resistance of the formed image may be lowered. In order to make the copolymer within the range of the acid value, a polyol having a carboxy group may be included and copolymerized so as to be within the range of the acid value.

  As the basic compound used for neutralization, a basic compound used for the purpose of neutralizing the anionic group described above can be used.

(Method for forming second layer of urethane resin having an anionic group)
As a method for forming the second layer of urethane resin having an anionic group on the core-shell single layer modified pigment A, the first layer of the acrylic copolymer shell having an anionic group on the pigment as the core portion described above is used. Although it can be carried out by a known dispersion method as in the case of the formation method, the dispersion method in which a very strong shearing force is applied, on the contrary, peels off the first layer of the shell of the acrylic copolymer having an anionic group encapsulating the pigment. A somewhat mild dispersion method is preferred because it can result. Preferred dispersion methods include stirring using a stirring blade, media mill dispersion using media such as paint shaker, bead mill, sand mill, ball mill, and media using ultrasonic homogenizer, high-pressure homogenizer, nanomizer, optimizer, etc. And a less dispersion method.

(Colloidal titration)
The urethane resin having an anionic group has 40% or more of the saturated adsorption amount with respect to the core-shell two-layer modified pigment.
In the present invention, the saturated adsorption amount is calculated by a colloid titration method. The colloid titration method is a method for measuring the charge amount of various polymers in the solution and the surface charge amount of the colloidal particles. As a titrant, cationic polymer: poly-DADMAC (polydimethylallyl ammonium chloride), MGCh (methyl) Glycol chitosan), anionic polymer: Polymer electrolytes such as Pes-Na (polyethylene sulfonate sodium), PVSK (polyvinyl potassium sulfate) are generally used. In the present invention, poly-DADMAC (polydimethylallyl ammonium chloride), which is a cationic polymer, was used as the titrant because the target to be titrated was an anionic resin. The titration apparatus used was a particle charge meter PCD-04 (Spectres).

In the colloid titration method, when the target to be titrated is an anionic resin, the streaming potential before titration shows a negative value, and when the target to be titrated is a cationic resin, the streaming potential before titration shows a positive value. Since all the resins used in the present invention are resins having an anionic group, the streaming potential before titration shows a negative value.
When the polymer electrolyte as the titrant is dropped into an aqueous solution containing only the resin having an anionic group, the cation and the anion react to form an ion aggregate. In this way, the potential is lowered by neutralizing the charge of the anion. It can be judged that the amount of the titrant dropped when the potential reaches zero is equal to the amount of neutralization of all anionic charges in the aqueous solution.
From the drop amount V when the potential reaches zero and the concentration N of the titrant, the charge amount Q [C / g] per 1 g of the aqueous solution containing the resin having an anionic group is obtained by the following formula (1). It is done.

In the above formula (1), the symbols are as follows.
Q: Charge [C] per gram of an aqueous solution containing a resin having an anionic group
V: Amount of titrant consumed [L]
c: Concentration of titrant [N]
F: Faraday coefficient [96485 C / eq])
m: aqueous solution containing a resin having an anionic group [g]

From the weight of the resin having an anionic group in the aqueous solution, the charge amount per 1 g of the resin having an anionic group can be determined. If the resins have the same structure and the same acid value, the charge amount Q is proportional to the aqueous solution concentration of the resin. The slope of the proportional line is gentler as the acid value of the resin is lower, and is steeper as the acid value is higher. This is shown in FIG. In FIG. 1, a graph A represented by reference numeral 1 is a graph of a styrene-acrylic acid copolymer used in the examples described later, and a graph B represented by reference numeral 2 represents urethane used in the examples described later. It is a graph of resin.
In the core-shell type modified pigment, since the charge amount Q per 1 g of the resin having an anionic group by the colloid titration of the core-shell type modified pigment is constant, it has a proportional relationship with the weight of the organic polymer layer. Show.

On the other hand, in the core-shell two-layer modified pigment A, the charge amount Q per 1 g of the resin having an anionic group by the colloid titration does not show a proportional relationship with the weight of the resin layer. This is shown in FIG. In FIG. 2, a graph C represented by reference numeral 4 shows a behavior different from that of the formula (1) and has an inflection point P.
Theoretically, since a proportional relationship is shown with respect to the weight of the resin layer, the charge amount Q with respect to the total amount of the acrylic copolymer having an anionic group and the urethane resin having an anionic group is It should be obtained as a graph A + B represented by 3. However, the second layer of the urethane resin having an anionic group that is in contact with the shell of the acrylic copolymer having the anionic group is formed so as to cover the acrylic copolymer having the anionic group. For this reason, the anionic charge of the acrylic copolymer coated with the urethane resin is not neutralized, and an increase in the sample charge amount according to the amount of the added urethane resin is not observed. It is presumed that the graph C shows a behavior different from that of the equation (1). Further, after exceeding the inflection point P, the same graph as the slope of the graph B similar to the formula (1) is obtained, which is the same as that of the urethane resin having an anionic group in which the inflection point P is the outermost layer. It is presumed that the adsorption amount of the two layers is saturated and the urethane resin having an anionic group is released and present in the aqueous solution without being adsorbed thereafter.
That is, when the charge amount Q indicating the inflection point P is applied to the formula (1), the calculated amount of the urethane resin having an anionic group is estimated as the saturated adsorption amount for the core-shell two-layer modified pigment A. The

  In the present invention, when the urethane resin having an anionic group is 20% or more of the saturated adsorption amount with respect to the core-shell two-layer modified pigment A, the printing characteristics are good. In addition, when the urethane resin is added beyond the inflection point P, which is the saturated adsorption amount, if the amount exceeds 150% of the saturated adsorption amount, the core-shell two layers that are not significantly affected by the free urethane resin present A type-modified pigment A can be obtained. In addition, as described above, the core-shell two-layer modified pigment A can be formed by the dispersion method for both the first layer and the second layer, and can be used as an aqueous dispersion as it is after drying. However, even if it is used as an aqueous dispersion, it is preferable that the amount exceeding 150% of the saturated adsorption amount is less affected by the free urethane resin. The range of the urethane resin is more preferably 30 to 120%, and most preferably 40 to 110%.

(Use)
The core-shell two-layer modified pigment A of the present invention is obtained as an aqueous dispersion. By drying this, it may be used as a composition of the core-shell bilayer pigment and the released resin, or the aqueous dispersion is diluted as it is to the desired pigment concentration, and the paint field for automobiles and building materials, It can be used for various applications such as printing ink field such as offset ink, gravure ink, flexo ink, silk screen ink, etc., or ink jet recording ink field.
When drying, it is preferable to dry with a hot air dryer, a vacuum dryer or the like. It is also possible to distribute the pigment paste without completely drying it.

When the core-shell type modified pigment of the present invention is applied to an ink for ink jet recording, an acrylic copolymer having an aqueous group and a water-soluble solvent and / or water, and an anionic group for binder purposes, depending on the desired physical properties. It is prepared by adding a coalescence or the like and adding a drying inhibitor, a penetrating agent, or other additives as required for the desired physical properties.
Centrifugation or filtration may be added during or after the ink preparation.

(Drying inhibitor)
The drying inhibitor is added for the purpose of preventing ink drying. The content of the drying inhibitor in the ink is preferably 3 to 50% by mass. The drying inhibitor used in the present invention is not particularly limited, but those that are miscible with water and can prevent clogging of the head of an inkjet printer are preferred. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol mono-n-butyl ether, polyethylene glycol having a molecular weight of 2000 or less, 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, pentaerythritol, and the like. Among them, the inclusion of propylene glycol and 1,3-butyl glycol has safety and excellent effects in ink drying properties and ejection performance.
The drying inhibitor may be the same compound as the above-mentioned wetting agent used in the aqueous pigment dispersion. Therefore, when a wetting agent is already used in the aqueous pigment dispersion, it can also serve as a drying inhibitor.

(Penetration agent)
The penetrant is added for the purpose of improving the permeability to a recording medium and adjusting the dot diameter on the recording medium.
Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether. The penetrant content in the ink is preferably 0.01 to 10% by mass.

(Surfactant)
The surfactant is added to adjust ink properties such as surface tension. The surfactant that can be added for this purpose is not particularly limited, and examples include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, anionic surfactants and nonionic surfactants are preferred.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonates of the above, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol disulfate. , And the like salts.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Polyethylene glycol polypropylene glycol block copolymer, etc. Among them, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid Preference is given to alkylolamide, acetylene glycol, oxyethylene adducts of acetylene glycol and polyethylene glycol polypropylene glycol block copolymers.

  Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin and the like can also be used.

  These surfactants can be used alone or in combination of two or more. When the surfactant is added, the addition amount is preferably in the range of 0.001 to 2% by mass, more preferably 0.001 to 1.5% by mass, based on the total mass of the ink. More preferably, it is in the range of 01 to 1% by mass. When the addition amount of the surfactant is less than 0.001% by mass, the effect of adding the surfactant tends to be not obtained, and when it exceeds 2% by mass, problems such as blurring of the image are likely to occur. .

  Moreover, antiseptic | preservative, a viscosity modifier, a pH adjuster, a chelating agent, a plasticizer, antioxidant, an ultraviolet absorber etc. can be added as needed.

(recoding media)
The recording medium of the water-based ink for inkjet recording is not particularly limited, and is an absorbent recording medium such as copy paper (PPC paper) generally used in a copying machine, a recording medium having an ink absorbing layer, There may be a non-water-absorbing recording medium that does not have absorptivity, a hard-absorbing recording medium that has a low water-absorbing property, and the like.

  Examples of the absorbent recording medium include plain paper, fabric, cardboard, wood, and the like. Further, examples of the recording medium having an absorption layer include inkjet dedicated paper, and specific examples thereof include, for example, Pictrico Pro Photo Paper from Pictorico Co., Ltd.

  Examples of non-water-absorbing recording media that do not have ink absorbency include those used for food packaging materials and the like, and known plastic films can be used. Specific examples include polyester films such as polyethylene terephthalate and polyethylene naphthalate, polyolefin films such as polyethylene and polypropylene, polyamide films such as nylon, polystyrene films, polyvinyl alcohol films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, A polylactic acid film etc. are mentioned. In particular, a polyester film, a polyolefin film, and a polyamide film are preferable, and polyethylene terephthalate, polypropylene, and nylon are more preferable. Moreover, the above-mentioned film coated with polyvinylidene chloride or the like for imparting a barrier property may be used, and if necessary, a film in which a deposited layer of a metal oxide such as aluminum or a metal oxide such as silica or alumina is used in combination. May be.

The plastic film may be an unstretched film, but may be stretched in a uniaxial or biaxial direction. Further, the surface of the film may be untreated, but those subjected to various treatments for improving adhesive properties such as corona discharge treatment, ozone treatment, low temperature plasma treatment, flame treatment, glow discharge treatment and the like are preferable.
The film thickness of the plastic film is appropriately changed according to the use. For example, in the case of a flexible packaging application, the film thickness is 10 μm to 100 μm as having flexibility, durability, and curl resistance. Preferably there is. More preferably, it is 10 micrometers-30 micrometers. Specific examples thereof include Pyrene (registered trademark) manufactured by Toyobo Co., Ltd.

  Art paper such as printing paper, coated paper, lightweight coated paper, finely coated paper, and the like can be used as a recording medium having low ink water absorption and poor absorbability. These hardly absorbent recording media are those in which a coating layer is provided by applying a coating material on the surface of high-quality paper, neutral paper, etc. that are generally not surface-treated mainly composed of cellulose. Oji Paper Co., Ltd. “OK Everlight Coat” manufactured by Nippon Paper Industries Co., Ltd., “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., “OK Coat L” manufactured by Oji Paper Co., Ltd., and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. , Etc. Lightweight coated paper (A3), Oji Paper Co., Ltd. “OK Top Coat +” and Nippon Paper Industries Co., Ltd. “Aurora Coat” coated paper (A2, B2), Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Mitsubishi and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries, Ltd., and the like.

(Acrylic copolymer having an anionic group (SA1))
As the acrylic copolymer having an anionic group, a styrene-acrylic acid copolymer (SA1) was used. Specifically, it is a resin in a powder form (diameter 1 mm or less) produced by solution polymerization, and in the monomer composition ratio, styrene / acrylic acid / methacrylic acid / butyl acrylate = 83 / 7.35 / 9.55 / A styrene acrylic acid copolymer (SA1) having 0.1 (mass ratio), a weight average molecular weight of 11,000 and an acid value of 120 mgKOH / g was used.

In addition, the weight average molecular weight in this invention is a value measured by GPC (gel permeation * chromatography) method, and is a value converted into the molecular weight of the polystyrene used as a standard substance. The measurement was carried out with the following equipment and conditions.
Liquid feed pump: LC-9A
System controller: SLC-6B
Auto injector: S1L-6B
Detector: RID-6A
Data processing software manufactured by Shimadzu Corporation: Sic480II data station (manufactured by System Instruments).
Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R400M (manufactured by Hitachi Chemical Co., Ltd.)
Elution solvent: THF
Elution flow rate: 2 ml / min
Column temperature: 35 ° C

(Urethane resin having an anionic group (U1))
As the urethane resin having an anionic group, a urethane resin (U1) synthesized by the following method was used. That is, in a nitrogen-substituted container equipped with a thermometer, a nitrogen gas introduction tube, and a stirrer, 103.07 parts by mass of 2,2-dimethylolpropionic acid and 233.91 parts by mass of isophorone diisocyanate were used as organic solvents. In the presence of 336.98 parts by mass of methyl ethyl ketone to produce a urethane prepolymer having isocyanate groups at both molecular ends, followed by 178.91 parts by mass of methyl ethyl ketone and “PTMG2000” (polyoxytetra Methylene glycol, number average molecular weight 2,000, average added mole number (n in general formula (I); 27.5) 621.19 parts by mass were added, and the reaction was further continued.
When the weight average molecular weight of the reaction product reaches the range of 35,000 to 39,000, the reaction is terminated by adding 6.91 parts by mass of methanol, and 199.99 parts by mass of methyl ethyl ketone is further added as a diluent solvent. Thus, an organic solvent solution of urethane resin was obtained.
Next, 83.66 parts by mass of a 50% by mass potassium hydroxide aqueous solution is added to the organic solvent solution of the urethane resin to neutralize part or all of the carboxyl groups of the polyurethane, and further 4241.35 parts by mass of water. In addition, by sufficiently stirring, an aqueous dispersion of urethane resin having a weight average molecular weight of 37,000 and an acid value of 55 was obtained.
Finally, the aqueous dispersion of urethane resin was aged and removed, and the non-volatile content was adjusted by adding water to obtain an aqueous solution of urethane resin (U1) having a non-volatile content of 20% by mass.

(Method for producing aqueous dispersion (AD) of core-shell two-layer modified pigment (A))
Example 1
(Method for forming first layer of acrylic copolymer having anionic group)
10 parts by mass of a styrene-acrylic acid copolymer (SA1) and 50 parts by mass of “FASTOGEN Super Magenta RY (DIC)” as a quinacridone pigment, a planetary mixer (trade name: Chemical Mixer ACM04LVTJ- B, manufactured by Aikosha Seisakusho Co., Ltd., heated the jacket, and after the contents reached 80 ° C., kneading was performed at a rotational speed of 80 rotations / minute and a revolution speed of 25 rotations / minute. . After 5 minutes, 35 parts by mass of triethylene glycol and 3.5 parts by mass of a 34% by mass aqueous potassium hydroxide solution were added. The amount of water at this time is 3.8% by mass with respect to the solid content. Kneading was continued until 120 minutes after the current value of the planetary mixer showed the maximum current value, and a mixture was obtained.
80 parts by mass of the obtained mixture was taken out from the jacket, cut into a 1 cm square, and then put into a commercially available juicer mixer. 81 parts by mass of ion-exchanged water was added thereto, mixed and diluted with a mixer for 10 minutes, and dispersed in ion-exchanged water.
Further, ion-exchanged water and triethylene glycol are added, and a core-shell single-layer modified pigment in which only the first layer of the acrylic copolymer (SA1) having an anionic group having a quinacridone pigment concentration of 15.5% by mass is formed ( An aqueous dispersion (S1) of S1) was obtained.

(Method for forming second layer of urethane resin having an anionic group)
To the aqueous dispersion (S1) of the core-shell single layer modified pigment (S1), an aqueous solution of urethane resin (U1) having a solid content concentration of 20% was added and stirred with a stirrer. The organic polymer layer has a first layer of an acrylic copolymer (SA1) having an anionic group in contact with the pigment, and a urethane resin (U1 having an anionic group in contact with the first layer and serving as the outermost layer) The aqueous dispersion of the core-shell bilayer-type modified pigment in which the second layer of) was formed was obtained.

(Calculation method of saturated adsorption by the inflection point of colloid titration method)
(Method for preparing test solution A of acrylic copolymer (SA1) having an anionic group)
Add 50 g of styrene-acrylic acid copolymer (SA1), 178 g of ion-exchanged water, and 22 g of 34% by mass potassium hydroxide (KOH) aqueous solution, stir well while heating, and have a resin solid content of 20% by mass. An aqueous solution was obtained. Pure water and potassium chloride (hereinafter referred to as KCl) aqueous solution were added to the obtained aqueous solution to prepare a resin aqueous solution having a resin concentration of 0.15% by mass and a KCl concentration of 0.5% by mass.
A resin aqueous solution having a KCl concentration of 0.5% by mass and resin concentrations of 0.3%, 0.6%, and 0.9% by mass was prepared in the same manner.

(Method for preparing test solution B of urethane resin (U1) having an anionic group)
Pure water and potassium chloride (hereinafter referred to as KCl) aqueous solution were added to the aqueous solution of the urethane resin (U1) to prepare a resin aqueous solution having a resin concentration of 0.15% by mass and a KCl concentration of 0.5% by mass.
A resin aqueous solution having a KCl concentration of 0.5% by mass and resin concentrations of 0.3%, 0.6%, and 0.9% by mass was prepared in the same manner.

(Colloidal titration method Calibration curve creation)
A particle charge meter PCD-04 (Spectris) was used as the colloid titration apparatus. Using a sample cell made of Teflon (Teflon is a registered trademark) and a moving piston, a flow potential in a range of ± 2500 mV was measured with a platinum electrode of the sample cell. The sample was placed in a cell, and after confirming that the potential was negative, it was titrated with a titrant having a positive charge (0.01 N, Poly-DADMAC). The amount of charge was titrated based on the potential difference caused by the movement of the sample cell and the moving piston, that is, the flow potential of the liquid.
The titration was terminated when the streaming potential exceeded zero (potential became positive).
From the drop amount V when the potential reached zero and the concentration c of the titrant, the charge amount Q [C / g] per 1 g of the test solution was determined by the following equation (1). 1 g of a resin aqueous solution having a known concentration is titrated in advance, and from a correlation with the amount of charge per 1 g of the test solution, a calibration curve graph A (corresponding to symbol 1) and a calibration curve graph B (corresponding to symbol 2) shown in FIG. n ≧ 4, r ² ≧ 0.90).

Q: Charge amount per gram of test solution [C / g]
V: Amount of titrant consumed [L]
c: Concentration of titrant [N]
F: Faraday coefficient [96485 C / eq])
m: aqueous solution containing a resin having an anionic group [g]

(Calculation of saturated adsorption amount of urethane resin second layer by inflection point of colloid titration method)
To the aqueous dispersion of the core-shell two-layer modified pigment obtained in Example 1, pure water and an aqueous potassium chloride solution were added to prepare a solution having a pigment concentration of 3% by mass and a KCl concentration of 0.5% by mass. Colloidal titration was performed.
The horizontal axis is plotted as the ratio of the urethane resin to the pigment weight [R / P], and the vertical axis is plotted as the amount of charge per 1 g of the test solution, and at least from the origin so that the contribution ratio r ² by the least square method is 0.95 or more. Four or more measurement points (including the origin) were selected to obtain a linear approximation formula (2). (Fig. 3, reference 5)

Y: Charge amount per gram of test solution [C / g]
(R / P): urethane resin content ratio to pigment weight A: slope of linear approximation calculated from least square method B: intercept of linear approximation calculated from least square method

  Two or more measurement points were selected when the inflection point appeared and the slope changed thereafter and became a straight line almost coincident with the slope of the calibration curve B of the urethane resin, and a linear approximation formula (3) was obtained. (Fig. 3, reference 6)

Y: Charge amount per gram of test solution [C / g]
(R / P): Urethane content ratio to pigment weight C: slope of linear approximation calculated from least square method D: intercept of linear approximation calculated from least square method

  The intersection of the linear approximation formula (2) and the linear approximation formula (3) was defined as an inflection point P (symbol 7 in FIG. 3), which was the end point of the shell formation of the second layer using urethane resin. (See Figure 3)

  From the inflection point P of the obtained graph, the saturated adsorption amount of the urethane resin (U1) was 0.12 g with respect to 1 g of the pigment. This is the saturated adsorption amount.

  Based on the saturated adsorption amount, an aqueous dispersion of the core-shell two-layer modified pigment (A1) in which the content of the urethane resin (U1) is 0.10 g with respect to 1 g of the pigment (83% with respect to the saturated adsorption amount) ( AD1) was obtained.

(Example 2)
As a method for forming the second layer of the urethane resin having an anionic group, Example 1 except that zirconia beads (1.25 mm diameter) were added and the mixture was shaken for 30 minutes with a paint shaker instead of stirring with a stirrer. Similarly, an aqueous dispersion (AD2) of the core-shell two-layer modified pigment (A2) was obtained.

(Example 3)
An aqueous dispersion (AD3) of the core-shell two-layer modified pigment (A3) was obtained in the same manner as in Example 1 except that the urethane resin (U1) that was 42% of the saturated adsorption amount of the urethane resin (U1) was used. .

(Comparative Example 1)
An aqueous dispersion (HD1) of the core-shell two-layer modified pigment (H1) was obtained in the same manner as in Example 1 except that the urethane resin (U1) that was 166% of the saturated adsorption amount of the urethane resin (U1) was used. .

(Comparative Example 2)
An aqueous dispersion (HD2) of the core-shell single layer modified pigment (H2) was obtained in the same manner as in Example 1 except that the urethane resin (U1) was not used.

(Measurement of zeta potential of core-shell type modified pigment)
Whether or not the core-shell two-layer modified pigment obtained in Examples and Comparative Examples has two layers was determined by zeta potential.
The aqueous dispersion (AD1) of the core-shell two-layer modified pigment (A1) obtained in Example 1 was diluted 1000 times with a 10 mM KCl aqueous solution, and pH = 7 ± 0 using Zetasizer Nano ZSP (Malvern). The zeta potential was measured in the range of .3. The average value measured at three points was adopted as the zeta potential.
Similarly, the data potentials of the aqueous dispersions of the core-shell bilayer modified pigment obtained in Examples 2-3 and Comparative Examples 1-2 were measured.
The zeta potential when the acrylic copolymer (SA1) having an anionic group is the outermost layer is −40 mV, and the zeta potential when the urethane resin (U1) having an anionic group is the outermost layer. The potential is -50 mV. Based on this value, when the zeta potential is close to −40 mV, the second layer of the urethane resin having an anionic group is not formed, and the first layer of the acrylic copolymer is the outermost layer. When the potential was close to −50 mV, it was judged that the second layer of urethane resin having an anionic group was formed and became the outermost layer.
The results are shown in Table 1.

(Preparation of water-based pigment ink)
Using the aqueous dispersion of the core-shell two-layer modified pigment obtained in Examples and Comparative Examples, water-based inks (A1) to (A3) and (H1) to (H2) for inkjet recording having a pigment concentration of 6% by mass were prepared. Produced. The composition is as follows.
Water dispersion of core-shell type modified pigment: 50 parts by mass 2-pyrrolidinone: 8 parts by mass Triethylene glycol: 4 parts by mass Triethylene glycol mono-n-butyl ether: 8 parts by mass Purified glycerin: 3 parts by mass Surfynol 440 (Air Products (Made by company): 0.5 mass part ion-exchange water: 26.5 mass parts

(Print density uniformity test)
Each inkjet recording water-based ink was filled in a cartridge of a commercially available inkjet printer, and a specific pattern was printed on a dedicated inkjet paper in a draft mode. In the same image of the obtained printed matter, the highest color density and the lowest color density were measured with a Spectroscan from X-Rite. A value (c * / L *) obtained by dividing c * (saturation) by L * (brightness) is calculated from the obtained colorimetric result, and the ratio of (c * / L *) at the two measurement points. Were evaluated according to the following criteria. The results are shown in Table 2.

(Criteria)
◎: (c * / L *) ratio is less than 5% ○: (c * / L *) ratio is less than 10% ×: (c * / L *) ratio is 10% or more

(Marker resistance test)
A straight line of 2 cm in total including a printed part of 1 cm of an evaluation pattern printed by an ink jet printer was continuously overlaid with an alkaline aqueous fluorescent pen three times, and the part drawn on the blank paper part was a colorimetric system (micro-haze manufactured by BYK). plus), the magenta OD was measured (1). Similarly, a blank paper portion not including a printing portion was overlaid three times with a fluorescent pen, and magenta OD was measured (2). The difference ([(1)-(2)]) between the two points was used as the evaluation value. The results are shown in Table 2.

(Criteria)
○: OD difference is less than 0.1 ×: OD difference is 0.1 or more

As a result, all of Examples 1 to 3 using the core-shell modified pigment obtained in the present invention were excellent in the balance between the marker resistance and the printing density uniformity.
On the other hand, Comparative Example 1 is an example in which the urethane resin was blended in excess of the saturated adsorption amount, but color unevenness occurred in the print density uniformity test. This is presumed that part of the blended urethane resin was present in the ink in a free manner, resulting in uneven color. On the other hand, Comparative Example 2 is an example in which no urethane resin was blended, but this was inferior to the marker resistance test.

It is a graph showing the relationship between the charge amount Q and the aqueous solution density | concentration of anionic resin. It is a graph showing the relationship between the charge amount Q and the aqueous dispersion of a core-shell two-layer modified pigment. It is the graph which showed the calculation method of the saturated adsorption amount by the inflection point of the colloid titration method.

1: Graph A of styrene-acrylic acid copolymer used in Examples
2: Graph B of urethane resin used in Examples
3: Graph A + B obtained by adding the graph A and the graph B
4: Graph C of aqueous dispersion of core-shell two-layer modified pigment
5: Graph of linear approximation formula (2) 6: Graph of linear approximation formula (3) 7: Inflection point P

Claims (4)

A core-shell type modified pigment in which a pigment layer as a core portion has a resin layer as a shell portion,
The resin layer includes a first layer of an acrylic copolymer having an anionic group in contact with the pigment, and a second layer of a urethane resin having an anionic group in contact with the first layer and serving as the outermost layer. The core-shell modified pigment, wherein the urethane resin having an anionic group is in the range of 20 to 150% of the saturated adsorption amount. The core-shell type modification according to claim 1, wherein the acrylic copolymer having an anionic group is a styrene-acrylic acid copolymer having an acid value of 10 to 400 and is contained in an amount of 1 to 100% by weight based on the pigment. Pigments. The core-shell modified pigment according to claim 1, wherein the urethane resin having an anionic group has an acid value of 0 to 150 and is contained in an amount of 1 to 100% by weight based on the pigment. An aqueous pigment dispersion comprising the core-shell modified pigment according to any one of claims 1 to 3 and an aqueous medium.

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