JP2005041992A - Method for producing pigment dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pigment dispersion in which a commercially available pigment can be used and an aqueous coating or ink using the dispersion is excellent in long-term storage stability and provides a coating film or printed matter with a high optical density (OD), good scratch resistance and water resistance. <P>SOLUTION: The method for producing the pigment dispersion comprises: (1) a first step of neutralizing with a base a part or all of acid groups in a resin which has a weight average molecular weight (Mw) in the range of 9,000-80,000 and has acid groups and then emulsifying or suspending the resin into an aqueous medium to obtain a resin dispersion having an average particle size of the resin in the range of 0.01-1 μm; (2) a second step of adding a pigment to the resin obtained in the first step and then grinding the mixture; and (3) a third step of further finely-dividing the ground matter obtained in the second step with a homogenizer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a pigment dispersion useful as a raw material for producing water-based inks or water-based paints. More specifically, when used in water-based paints or water-based inks, the present invention is excellent in long-term storage stability, The present invention relates to a method for producing a pigment dispersion in which a printed matter exhibits a high optical density (OD) and is excellent in scratch resistance and water resistance.

Conventionally, pigment dispersions for water-based paints and water-based inks are produced by dispersing a pigment in an aqueous medium in the presence of a dispersant such as a surfactant in order to subdivide the pigment and uniformly disperse it in the aqueous medium. ing. For example, a resin such as a styrene-acrylic acid copolymer and a pigment are sprayed in an aqueous dispersion medium into a dispersion chamber at atmospheric pressure through a fine orifice under a liquid pressure of at least 1 × 10 ⁷ kg / m · sec ² . There has been proposed a production method for obtaining a pigment dispersion for inkjet ink by crushing and dispersing pigment particles. However, in order to obtain desired effects such as storage stability and clogging resistance, this pigment dispersion needs to be further filtered by centrifugal filtration and filter filtration to remove coarse pigments. There has been a problem that the manufacturing process becomes complicated and the manufacturing cost becomes high (for example, see Patent Document 1).

  Ink-jet ink pigments are obtained by grinding and dispersing the pigment in an aqueous carrier medium using a high-speed mill or the like in the presence of a surfactant such as a potassium salt of a phosphorylated ester of an alcohol having 8 to 18 carbon atoms. A method for producing a dispersion has been proposed. However, in this pigment dispersion, the surfactant remains in the aqueous medium, and the surfactant remaining in the aqueous medium is supplied while being contained in the aqueous paint or aqueous ink. The water-based paints and water-based inks used did not have sufficient long-term storage stability. In addition, there has been a problem that the optical density (OD) of an aqueous paint or aqueous ink coating or printed matter using this pigment dispersion is low and the water resistance is not sufficient (see, for example, Patent Document 2).

  Further, after a pigment that can be self-dispersed in water is dispersed in water using an ultrasonic homogenizer or the like, the water and solubility parameter (hereinafter referred to as SP) is 12 or less, and the surface tension at 25 ° C. is 40 mN / m. There has been proposed a method for producing a pigment dispersion for inkjet ink by mixing with less than a water-soluble organic compound. However, the pigment used in this method is not a normal pigment but a special pigment (a pigment that has been surface-modified and made self-dispersible in water). As a result, the pigment dispersion obtained by this method There has been a problem that the manufacturing cost becomes high (for example, see Patent Document 3).

JP 7-305006 A JP 10-176131 A Japanese Patent Laid-Open No. 11-228898

  The problem to be solved by the present invention is that a commercially available pigment can be used, and further, when used in a water-based paint or water-based ink, it has excellent long-term storage stability, and the resulting coating film or printed matter has a high optical density. It is to provide a pigment dispersion exhibiting (OD) and excellent in scratch resistance and water resistance.

As a result of intensive studies to solve the above problems, the present inventors have completed the following invention. That is, the present invention is (1) after neutralizing some or all of the acidic groups in the resin having an acidic group with a weight average molecular weight (Mw) in the range of 9,000 to 80,000 with a base. The first step of obtaining the resin dispersion having an average particle diameter in the range of 0.01 to 1 μm by emulsifying or suspending the resin in an aqueous medium and dispersing the resin.
(2) A second step of adding a pigment to the resin dispersion obtained in the first step and then grinding, and (3) a third step of further subdividing the ground product obtained in the second step using a homogenizer. A method for producing a pigment dispersion characterized by comprising:

  By using the pigment dispersion obtained by the production method of the present invention, a water-based paint or water-based ink excellent in long-term storage stability can be obtained. Moreover, the coating film or printed matter obtained from these water-based paints and water-based inks exhibits a high optical density (OD) and is excellent in scratch resistance and water resistance. Further, when used in ink for an ink jet printer, the ink has good storage stability even under high temperature storage, and has excellent clogging resistance before and after storage.

  The present invention is described in detail below. The resin having an acidic group used in the first step of the production method of the present invention is not particularly limited as long as it is a resin that can be emulsified or suspended in an aqueous medium and dispersed. Examples of such resins include acrylic resins, polyester resins, polyurethane resins, acrylic-polyurethane resins, water-dispersible alkyd resins, styrene-acrylic acid copolymers, styrene-maleic acid copolymers, and styrene-maleic acid copolymers. Polymers (including resins made from maleic acid that has been half-esterified or esterified as a raw material) are included. Furthermore, a vinyl acetate resin, a vinyl chloride resin, a vinyl pyrrolidone resin, and these copolymers are also mentioned. Among these, a styrene-maleic acid copolymer and a styrene-acrylic copolymer are particularly preferable.

  The resin having an acidic group preferably has a weight average molecular weight in the range of 9,000 to 80,000, particularly preferably in the range of 15,000 to 70,000. If the weight average molecular weight is within this range, when the pigment dispersion liquid dispersed with this resin is used as an ink for an ink jet printer, the storage stability is good, and the precipitated and dried and fixed ink quickly re-dissolves and returns. As a result, nozzle clogging is unlikely to occur and the scratch resistance after printing is also good.

  When the weight average molecular weight of the resin having an acidic group is less than 9,000, the initial dispersion is relatively easy, but the pigment in the pigment dispersion is likely to aggregate and settle with time, and storage stability. There is a problem that becomes bad. Further, since the molecular weight is low, the fixing property such as scratch resistance after printing tends to be inferior. On the other hand, when the weight average molecular weight exceeds 80,000, there are problems in initial dispersibility, precipitation, and re-dissolvability of the dried and fixed ink.

  The acid value of the resin having an acidic group is preferably in the range of 100 to 400 mgKOH / g. If the acid value is within this range, the resin is easily emulsified or suspended in an aqueous medium.

  What has SP of the resin which has the said acidic group exists in the range of 10-15, and what is in the range of 10.0-12.5 is especially preferable. If SP is in this range, the resin can be easily emulsified or suspended in an aqueous medium.

  Furthermore, it is more preferable that the correlation between the weight average molecular weight of the resin having an acidic group and the solubility parameter is within the range represented by the following formula.

［ただし、式中、ＳＰは溶解度パラメーターを、Ｍｗは重量平均分子量をそれぞれ表す。］

[Wherein, SP represents a solubility parameter, and Mw represents a weight average molecular weight. ]

  In the first step of the production method of the present invention, in order to obtain a resin dispersion, after neutralizing a part or all of the acidic groups in the resin having acidic groups with a base, an aqueous solution is used using a stirrer or the like. It can be easily produced by emulsifying or suspending in a medium. Further, if necessary, an aqueous medium dispersion can be obtained by dissolving a resin having an acidic group in an organic solvent, and then neutralizing with a base and emulsifying or suspending in an aqueous medium.

  Examples of the base include sodium hydroxide, potassium hydroxide, aqueous ammonia, and organic amine. Among these, potassium hydroxide is preferable from the viewpoint of the solubility of the resin and the storage stability of the pigment dispersion.

  When neutralizing the acidic groups in the resin having acidic groups, it is preferable to add 0.2 to 2 equivalents of the base with respect to the total amount of acidic groups. By adding 0.2 to 2 equivalents of base to the total amount of acidic groups, the resin can be more stably emulsified or suspended in an aqueous medium. When one equivalent or more of a base is added, many resins are dissolved in an aqueous medium. However, a resin having a low acid value or a high molecular weight is not completely dissolved but remains emulsified or suspended. There are some, and in the case of such a resin, 1 equivalent or more of a base can be added.

  The aqueous medium is preferably water for reasons such as low viscosity, excellent safety, easy handling, low cost, and no odor. In the aqueous medium, a water-soluble organic solvent can be used in combination with water for the purpose of stabilizing the emulsion or suspension, improving dispersibility, and preventing drying.

  Examples of the water-soluble organic solvent include monohydric alcohols such as ethanol, propanol, butanol, hexanol, heptanol, and octanol; polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and polyethylene glycol. ; Etherified products of polyhydric alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether; N-methyl-2-pyrrolidone, 1,3-dimethylimidazolidinone And nitrogen-containing organic solvents.

  The average particle diameter of the resin having an acidic group in the resin dispersion obtained in the first step is preferably in the range of 0.01 to 1 μm, more preferably in the range of 0.01 to 0.8 μm. preferable. If the average particle diameter of the resin having an acidic group is within this range, the pigment dispersion of the resulting resin dispersion is good, and the storage stability of the pigment dispersion after pigment dispersion is also good.

  The pigment used in the second step of the production method of the present invention is not particularly limited, and examples thereof include carbon black such as furnace black, lamp black, acetylene black, and channel black; copper compound, iron compound, titanium oxide, and the like. Inorganic pigment, aniline black, phthalocyanine pigment, anthraquinone pigment, dioxazine pigment, quinacridone pigment, quinacridone quinone pigment, anthrapyrimidine pigment, ansanthrone pigment, indanthrone pigment, flavanthrone pigment, perylene Pigments, perinone pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, isoindoline pigments, benzimidazolone pigments, azo pigments, lake pigments, etc. Organic pigment; surface Processed pigments such as graft carbon treated with resins.

  As the pigment, any of dry powder and wet cake can be used. These pigments can be used alone or in combination of two or more.

  The pigment is preferably a pigment having a particle size of 25 μm or less, and particularly preferably a pigment having a particle size of 1 μm or less. If the particle diameter is in this range, the precipitation of the pigment is difficult to occur, and the pigment dispersibility and storage stability are good.

  The addition amount of the pigment is preferably in the range of 1 to 70% by mass with respect to the total amount of the pigment dispersion. When the addition amount is within this range, the pigment dispersion efficiency is good, and the coloring power of the obtained pigment dispersion is sufficient.

  Examples of the method of grinding the mixture of the resin dispersion and the pigment in the second step of the production method of the present invention include, for example, a dispersion stirrer, a high-pressure collision disperser, a kneader, a roll mill, an attritor, a media mill, and the like. And a method of grinding using a machine capable of giving a high shearing force and a high grinding force to the ground material. These machines used for grinding can be used in combination of two or more.

  Examples of the grinding medium used in the grinding method include glass, ceramic, metal, polymer resin beads, and the like. The grinding medium is preferably composed of particles, substantially spherical beads are preferred, the specific gravity is preferably as large as possible, and the size is as fine as possible. However, it is usually necessary to use a hard inert grinding medium for the media mill.

  By the second step of the production method of the present invention, the pigment that has been secondary-aggregated can be peptized into primary particles. The pigment dispersion obtained in the second step is used as a mill base.

  In the third step of the production method of the present invention, the mill base ground in the second step is further subdivided using a homogenizer. The homogenizer develops a cavitation phenomenon with high impact force and instantaneous high pressure. By the action of this homogenizer, the resin surrounding the pigment ground in the second step and the pigment particles can be simultaneously refined and dispersed, so that a pigment dispersion in a uniform state that is stable and does not reaggregate can be obtained. It is done.

  Examples of the homogenizer include a high-speed homomixer, a line homogenizer, an ultrasonic homogenizer, and a high-pressure homogenizer. Of these, an appropriate model can be arbitrarily used in combination with one or more models in consideration of the viscosity of the mill base and the particle diameter of the target pigment.

  In addition, in the second step or the third step of the production method of the present invention, if necessary, a drying inhibitor such as thiourea or ethylene urea; a pH adjuster such as potassium dihydrogen phosphate or sodium dihydrogen phosphate; Fungicides or rust inhibitors such as benzoic acid, dichlorophene, hexachlorophene, sorbic acid, hydroxybenzoic acid ester, ethylenediaminetetraacetic acid, benzotriazole; nonionic and anionic surfactants or polymer pigment dispersants, etc. Can also be added.

  By passing through the first to third steps of the production method of the present invention as described above, when used in a water-based paint or water-based ink, it has excellent long-term storage stability and the resulting coating film or printed matter has a high optical density (OD). And a pigment dispersion having excellent scratch resistance and water resistance can be produced.

  The pigment dispersion obtained by the production method of the present invention can be used as it is as a coloring material such as water-based ink or water-based paint. If necessary, a vehicle can be added and redispersed to obtain a water-based ink or water-based paint.

  EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the scope of these examples. The raw materials used are those manufactured by Dainippon Ink & Chemicals, Inc. unless otherwise specified. “Parts” and “%” represent “parts by mass” and “% by mass”, respectively, unless otherwise specified. Furthermore, all of the water used in the examples and comparative examples is ion-exchanged water.

Further, each device used in Examples and Comparative Examples is as follows.
(mixer)
Device name "Three One Motor (HEIDON600G)" manufactured by Shinto Science Co., Ltd.

(6-cylinder sand grinder)
Device name "OSG-29" manufactured by Imex Corporation

(Dispersing stirrer)
Device name made by Tokushu Kika Kogyo Co., Ltd. “TK Homodisper 2.5”

(Ultrasonic homogenizer)
Device name “US-1200” manufactured by Nippon Seiki Seisakusho Co., Ltd.

(High pressure homogenizer)
Device name made by Nanomizer Co., Ltd. “Nanomaker 200”

<Example 1>
Styrene-maleic acid half ester (product name “DSS-11” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 180 mg KOH / g, weight average molecular weight: 18,000, SP: 11.1) 15 parts, triethanol Mix and stir 3.5 parts of amine (an amount corresponding to 0.5 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 81.5 parts of water at 55 ° C. using a stirrer. Thus, a milky white resin dispersion (R-1) was obtained. The particle diameter of the resin in this resin dispersion (R-1) was 0.05 μm.

  Next, 85 parts of resin dispersion (R-1) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-1).

  70 parts of the mill base (M-1) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-1). .

  Further, 36 parts of the pigment dispersion (D-1) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (1).

<Example 2>
15 parts of styrene-maleic acid half ester-methyl methacrylate (product name “DSS-24” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 166 mg KOH / g, weight average molecular weight: 9,000, SP: 11.6) , 2.12 parts of potassium hydroxide (an amount corresponding to 0.85 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 82.88 parts of water were mixed at 70 ° C. using a stirrer. By stirring, a milky white resin dispersion (R-2) was obtained. The particle diameter of the resin in this resin dispersion (R-2) was 0.63 μm.

  Next, 85 parts of resin dispersion (R-2) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-2).

  70 parts of the mill base (M-2) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-2). .

  Furthermore, 36 parts of the pigment dispersion (D-2) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (2).

<Example 3>
15 parts of styrene-acrylic resin (product name “DSS-19” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 384 mg KOH / g, weight average molecular weight: 37,000, SP: 11.7), potassium hydroxide 2 By mixing and stirring at 70 ° C. using 30 g of 30 parts (an amount corresponding to 0.40 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 82.70 parts of water, A milky white resin dispersion (R-3) was obtained. The particle diameter of the resin in this resin dispersion (R-3) was 0.74 μm.

  Next, 85 parts of resin dispersion (R-3) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) were mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads were added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-3).

  70 parts of the mill base (M-3) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-3).

  Further, 36 parts of the pigment dispersion (D-3) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (3).

<Example 4>
After mixing and stirring 76 parts of the resin dispersion (R-1) obtained in Example 1 and 24 parts of a wet cake (solid content 48%) of a blue pigment (product name “FASTOGEN BLUE GBK”), The mill base (M-4) was obtained by grinding with a dispersion stirrer for 2 hours.

  70 parts of the mill base (M-4) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-4). .

  Further, 36 parts of the pigment dispersion (D-4) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (4).

<Example 5>
Styrene-maleic acid half ester (product name “DSS-25” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 116 mg KOH / g, weight average molecular weight: 42,000, SP: 11.0) 15 parts, hydroxylated 1.57 parts of potassium (amount corresponding to 0.90 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 83.43 parts of water are mixed and stirred at 70 ° C. using a stirrer. As a result, a translucent resin dispersion (R-5) was obtained. The particle diameter of the resin in this resin dispersion (R-5) was 0.51 μm.

  Next, 85 parts of resin dispersion (R-5) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-5).

  70 parts of the mill base (M-5) obtained above and 30 parts of water were mixed and stirred, and treated 5 times using a high-pressure homogenizer with a liquid pressure of 147 MPa to obtain a pigment dispersion (D-5).

  Furthermore, 36 parts of the pigment dispersion (D-5) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (5).

<Example 6>
Styrene-maleic acid half ester (product name “DSS-13” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 189 mg KOH / g, weight average molecular weight: 3,7000, SP: 11.1) 15 parts, hydroxylated 1.70 parts of potassium (an amount corresponding to 0.60 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 83.3 parts of water are mixed and stirred at 55 ° C. using a stirrer. As a result, a milky white resin dispersion (R-6) was obtained. The particle diameter of the resin in this resin dispersion (R-6) was 0.33 μm.

  Next, 85 parts of resin dispersion (R-6) and 15 parts of magenta pigment (product name “SYMULER SUPER MAGENTA RG”) were mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads were added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-6).

  70 parts of the mill base (M-6) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-6).

  Further, 36 parts of the pigment dispersion (D-6) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (6).

<Example 7>
15 parts of styrene-acrylic resin (product name “DSS-21” manufactured by Gifu Shellac Co., Ltd., acid value: 250 mg KOH / g, weight average molecular weight: 23,000, SP: 11.7), potassium hydroxide 1 .69 parts (an amount corresponding to 0.45 equivalent to the total amount of acidic groups in styrene-acrylic) and 83.31 parts of water were mixed and stirred at 65 ° C. using a stirrer to give a milky white resin. A dispersion (R-7) was obtained. The particle diameter of the resin in this resin dispersion (R-7) was 0.05 μm.

  Next, 85 parts of resin dispersion (R-7) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) were mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads were added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-7).

  70 parts of the mill base (M-7) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-7). .

  Further, 36 parts of the pigment dispersion (D-7) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (7).

<Example 8>
Styrene-maleic acid half ester (product name “DSS-23” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 237 mg KOH / g, weight average molecular weight: 65,000, SP: 11.1) 15 parts, hydroxylated 1.99 parts of potassium (an amount corresponding to 0.56 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 83.01 parts of water are mixed and stirred at 65 ° C. using a stirrer. As a result, a translucent resin dispersion (R-8) was obtained. The particle diameter of the resin in this resin dispersion (R-8) was 0.04 μm.

  Next, 85 parts of resin dispersion (R-8) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-8).

  70 parts of the mill base (M-8) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-8). .

  Further, 36 parts of the pigment dispersion (D-8) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (8).

<Example 9>
15 parts of styrene-maleic acid half ester (product name “RS-88” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 104 mg KOH / g, weight average molecular weight: 41,500, SP: 10.6), hydroxylated 1.25 parts of potassium (an amount corresponding to 0.80 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 83.75 parts of water are mixed and stirred at 65 ° C. using a stirrer. As a result, a translucent resin dispersion (R-9) was obtained. The particle diameter of the resin in this resin dispersion (R-9) was 0.30 μm.

  Next, 85 parts of resin dispersion (R-9) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-9).

  70 parts of the mill base (M-9) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-9). .

  Furthermore, 36 parts of the pigment dispersion (D-9) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (9).

<Comparative Example 1>
85 parts of the resin dispersion liquid (R-1) obtained in Example 1 and 15 parts of a magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) were mixed and stirred, and 0.3 mmφ ceramic beads were added to this mixture. After adding 500 parts, it grind | pulverized for 9 hours with the 6 cylinder type sand grinder. After the grinding, the ceramic beads were separated to obtain a pigment dispersion (D-C1).

  36 parts of pigment dispersion (D-C1), 18 parts of glycerin and 46 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (C1).

<Comparative example 2>
15 parts of styrene-maleic acid half ester same as that used in Example 1, 7.0 parts of triethanolamine (amount corresponding to 1.0 equivalent with respect to the total amount of acidic groups in styrene-maleic acid half ester) And 78 parts of water was mixed and stirred at 55 ° C. using a stirrer to obtain a light yellow transparent resin aqueous solution (R-C2). The resin in this aqueous resin solution (R-C2) was in a dissolved state.

  Next, 85 parts of an aqueous resin solution (R-C2) and 15 parts of a magenta pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to the mixture. After that, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-C2).

  70 parts of the mill base (M-C2) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-C2). .

  Further, 36 parts of the pigment dispersion (D-C2) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (C2).

<Comparative Example 3>
Styrene-maleic acid half ester (product name “DSS-17” manufactured by Gifu Shellac Manufacturing Co., Ltd., acid value: 167 mg KOH / g, weight average molecular weight: 7,900, SP: 11.5) 15 parts, hydroxylated 1. Stir 1.47 parts of potassium (an amount corresponding to 0.59 equivalent to the total amount of acidic groups in the styrene-maleic acid half ester) and 83.53 parts of water at 65 ° C. using a stirrer. Thus, a translucent resin dispersion (R-C3) was obtained. The particle diameter of the resin in this resin dispersion (R-C3) was 0.05 μm.

  Next, 85 parts of resin dispersion (R-C3) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-C3).

  70 parts of the mill base (M-C3) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-C3). .

  Further, 36 parts of the pigment dispersion (D-C3) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (C3).

<Comparative example 4>
Styrene-maleic acid half ester “DSS-16 (manufactured by Gifu Shellac Manufacturing Co., Ltd.)” (acid value 205 mg KOH / g, weight average molecular weight 110,000, SP 11.1) 15 parts, TEA 4.50 parts (styrene- A translucent resin dispersion (by an amount corresponding to 0.58 equivalent to the total amount of acidic groups in the maleic acid half ester) and 80.5 parts of water at 65 ° C. using a stirrer. R-C4) was obtained. The particle diameter of the resin in this resin dispersion (R-C4) was 0.005 μm.

  Next, 85 parts of resin dispersion (R-C4) and 15 parts of magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to this mixture. After the addition, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-C4).

  70 parts of the mill base (M-C4) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-C4).

  Further, 36 parts of the pigment dispersion (D-C4) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (C4).

<Comparative Example 5>
Styrene-maleic acid (product name “GSM1001” manufactured by Gifu Shellac Co., Ltd.), acid value: 472 mg KOH / g, weight average molecular weight: 12,400, SP: 14.4) 15 parts, potassium hydroxide 5.66 A transparent resin aqueous solution by mixing and stirring at 75 ° C. using a stirrer with 79 parts of water (an amount corresponding to 0.80 equivalent to the total amount of acidic groups in styrene-maleic acid) and 79.34 parts of water. (R-C5) was obtained. The resin in this aqueous resin solution (R-C5) was in a dissolved state.

  Next, 85 parts of an aqueous resin solution (R-C5) and 15 parts of a magenta color pigment (product name “SYMULER SUPER MAGENTA RG”) are mixed and stirred, and 500 parts of 0.3 mmφ ceramic beads are added to the mixture. After that, it was ground for 6 hours with a 6-cylinder sand grinder. After the grinding, the ceramic beads were separated to obtain a mill base (M-C5).

  70 parts of the mill base (M-C5) obtained above and 30 parts of water were mixed and stirred, and subdivided for 3 hours using an ultrasonic homogenizer at an output of 15 W to obtain a pigment dispersion (D-C5). .

  Further, 36 parts of the pigment dispersion (D-C5) obtained above, 17 parts of glycerin and 47 parts of water were mixed and filtered through a 1 μm filter to obtain an aqueous ink (C5).

The resin dispersions and water-based inks obtained in Examples and Comparative Examples were evaluated by the following methods.
(Measurement of average particle diameter of resin in resin dispersion)
At 25 ° C., the average particle size of the resin in the resin dispersion was measured using a device name “UPA150” manufactured by Microtrack Co., Ltd.
(Viscosity of water-based ink)
At 25 ° C., the viscosity of the water-based ink was measured under the measurement conditions of rotor: 1 ° 34 ′ × R24, rotation speed: 100 min ⁻¹ using a device name “ELD viscometer” manufactured by Toki Sangyo Co., Ltd. .

(Storage stability of water-based ink)
The water-based inks obtained in Examples and Comparative Examples were sealed in glass sample bottles and stored at 50 ° C. for 14 days, then left in a constant temperature water bath at 25 ° C. and returned to room temperature. The aggregation of pigment particles in the aqueous ink after storage was observed using an optical microscope, and storage stability was evaluated according to the following criteria.
◎: No aggregates, ○: Some aggregates, but most have no aggregates,
Δ: Small amount of aggregates, ×: Many aggregates (preparation of printed sample)
The aqueous ink obtained in Examples and Comparative Examples was filled in an ink cartridge of an ink jet printer (product name “Inkjet Printer MJ-510C” manufactured by Seiko Epson Corporation), and “KJ” manufactured by KOKUYO Corporation. -1110N ").

(Clogging resistance)
The water-based inks obtained in Examples and Comparative Examples were stored at 40 ° C. for 2 days, and print samples were prepared by the above method using the water-based ink stored at 40 ° C. Next, the missing dot generated in the printing part of the produced printing sample was observed, and clogging resistance was evaluated according to the following criteria.
◎: No missing dots, ○: Less than 2 missing dots,
Δ: Less than 5 missing dots, ×: More than 5 missing dots

(Print density)
The optical density (OD) of the printed portion of the printed sample prepared above was measured using a Macbeth reflection densitometer (device name “RD-918” manufactured by Macbeth). From the obtained optical density (OD) value, the following criteria were used for evaluation.
A: 1.40 or more, B: 1.35 or more and less than 1.40,
Δ: 1.30 or more and less than 1.35, ×: less than 1.30

(Abrasion resistance)
A print sample was prepared by the above method and allowed to stand for 2 hours, and then the print surface was rubbed strongly with a finger, and the scratch resistance was evaluated according to the following criteria.
○: No decrease in density on the printed surface was observed, and the non-printed surface was not smudged.
Δ: The density of the printed surface hardly decreases, but the non-printed surface is slightly stained
X: The density of the printed surface is lowered, and the stain on the non-printed surface is noticeable.

(water resistant)
The print sample was immersed in water for 10 minutes, and the density of the printed part after immersion was measured. From the difference between the concentration after immersion and the concentration before immersion, water resistance was evaluated according to the following criteria.
○: Density difference is 0.06 or less, Δ: Density difference is over 0.06 and less than 0.1
X: Concentration difference is 0.1 or more

The evaluation results of the examples are shown in Table 1, and the evaluation results of the comparative examples are shown in Table 2.

The abbreviations of the devices in Table 1 and Table 2 respectively represent the following.
SG: 6 cylinder sand grinder SD: Dispersing stirrer UH: Ultrasonic homogenizer HPH: High pressure homogenizer

  From the results shown in Table 1, the aqueous inks of Examples 1 to 9 obtained by the production method of the present invention had high print quality with high print density, and good scratch resistance and water resistance. Further, even when these water-based inks were stored at a high temperature for a long period of time, there was no aggregation and sedimentation of the pigment particles, and no solid matter was deposited. Further, even when used in ink for an ink jet printer, there was no problem such as clogging, and high quality printing was possible.

  The water-based ink of Comparative Example 1 is an example in which the subdivision by the homogenizer in the third step of the production method of the present invention was not performed. This water-based ink has problems in clogging and storage stability, and cannot be used as an ink for an ink jet printer.

  The water-based ink of Comparative Example 2 is an example in which the resin in the resin dispersion obtained in the first step of the production method of the present invention is dissolved and the resin dispersion is not emulsified or suspended. This water-based ink has good scratch resistance and clogging properties, but has problems in printing density, water resistance and storage stability.

  The water-based ink of Comparative Example 3 is an example in which the resin having an acidic group has a weight average molecular weight of less than 9,000. This water-based ink has some problems in printing density, scratch resistance, water resistance, clogging property and storage stability.

  The water-based ink of Comparative Example 4 is an example in which the weight average molecular weight of the resin having an acidic group exceeds 80,000. With this water-based ink, the print density, scratch resistance and water resistance were good, but there were some problems with clogging and storage stability.

  In the aqueous ink of Comparative Example 5, the resin in the resin dispersion obtained in the first step of the production method of the present invention is dissolved, the resin dispersion is not emulsified or suspended, and the resin having an acidic group is used. This is an example in which the acid value and SP deviate from the values defined in the present invention. This water-based ink has problems in clogging and storage stability, and cannot be used as an ink for an ink jet printer.

  The pigment dispersion obtained by the production method of the present invention can be used for ink for writing instruments, water-based paints, pigment printing agents, dyeing agents and the like in addition to ink for inkjet printers.

FIG. 1 is a graph showing the correlation between SP and the weight average molecular weight of resins having acidic groups used in Examples and Comparative Examples.

Claims (6)

(1) The weight average molecular weight (Mw) is in the range of 9,000 to 80,000, and after neutralizing some or all of the acidic groups in the resin having acidic groups with a base, the resin is treated with an aqueous medium. A first step of obtaining a resin dispersion in which the average particle size of the resin is in the range of 0.01 to 1 μm by emulsifying or suspending in
(2) A second step of adding a pigment to the resin dispersion obtained in the first step and then grinding, and (3) a third step of further subdividing the ground product obtained in the second step using a homogenizer. A method for producing a pigment dispersion, comprising: The method for producing a pigment dispersion according to claim 1, wherein a resin having an acid value in the range of 100 to 400 mgKOH / g is used as the resin having an acidic group. The method for producing a pigment dispersion according to claim 1 or 2, wherein a resin having a solubility parameter (SP) in the range of 10 to 15 is used as the resin having an acidic group. The method for producing a pigment dispersion according to claim 1, 2 or 3, wherein a resin having a correlation between a weight average molecular weight and a solubility parameter is within a range represented by the following formula as the resin having an acidic group.

[Wherein, SP represents a solubility parameter, and Mw represents a weight average molecular weight. ] The method for producing a pigment dispersion according to any one of claims 1 to 4, wherein the amount of the base used is in the range of 0.2 to 2 equivalents relative to the total amount of acidic groups in the resin having acidic groups. . The method for producing a pigment dispersion according to any one of claims 1 to 5, wherein the resin having an acidic group is a styrene-maleic acid copolymer or a styrene-acrylic acid copolymer.

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