JP5998747B2 - Aqueous pigment dispersion and inkjet ink - Google Patents

Description

  The present invention relates to an aqueous pigment dispersion having a low viscosity and excellent storage stability using titanium oxide as a pigment, and an aqueous inkjet ink having excellent concealability.

  The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. According to this method, there is an advantage that not only the noise of the apparatus to be used is small and the operability is good, but also colorization is easy and plain paper can be used as a recording member. It is widely used as an output machine in offices and homes.

  On the other hand, in industrial applications, it is expected to be used as an output machine for digital printing due to improvements in inkjet technology, and even for non-absorbable substrates (plastic substrates such as PVC and PET) using solvent inks and UV inks. Printing machines capable of printing have actually been marketed. However, in recent years, the demand for water-based inks has increased from the standpoint of environmental friendliness.

  In industrial applications, printing on transparent substrates such as PET films and printing on colored substrates are also required. When only process color ink is printed on these substrates, an image having poor color developability and visibility may be obtained due to the color influence of the substrate. In order to solve this, a method using white ink is known. That is, by printing with white ink before printing with color ink and forming an image with color ink thereon, an image with excellent color development and visibility can be obtained. Therefore, the practical application of white water-based inkjet ink has been desired.

  Examples of white pigments include titanium oxide, hollow particles, and organic white pigments. Titanium oxide is often used in terms of cost and concealment. However, even when titanium oxide is used, a large amount of pigment must be contained in the ink in order to exhibit sufficient hiding properties. As the viscosity of the ink increases as the pigment increases, an attempt to provide sufficient concealment may deviate from the dischargeable viscosity of the inkjet head and may not be suitable as an inkjet ink. In addition, a decrease in ink stability due to high concentration is also a problem, and the degree of freedom of the solvent used in the ink is limited.

  Patent Document 1 proposes an aqueous dispersion of titanium oxide that improves the dispersibility of titanium oxide by performing surface treatment of titanium oxide with an inorganic phosphoric acid compound, and is excellent in stability. However, this method has insufficient stability, and when a highly hydrophobic solvent is used for printing on a plastic substrate, pigment aggregation occurs in a short period of time, which is unsuitable for practical use. Patent Document 2 proposes an aqueous dispersion of titanium oxide that promotes the adsorption of the dispersed resin by performing a surface treatment of titanium oxide and has excellent dispersion stability. However, there is no description regarding the lowering of the viscosity of the dispersion, and it is considered that when this dispersion is used, it is impossible to produce a low-viscosity inkjet ink while exhibiting sufficient concealability.

JP 2002-348513 A JP 2011-225867 A

  An object of the present invention is to provide an aqueous pigment dispersion having a low viscosity and excellent storage stability using titanium oxide as a pigment, and an aqueous inkjet ink having excellent concealability.

  In order to improve the concealability of the water-based inkjet ink, it is necessary to increase the pigment concentration, but the viscosity increases as the pigment concentration increases. Therefore, the ink is not suitable for inkjet use. Thus, the pigment concentration (= hiding property) was a trade-off with the ink viscosity. In order to solve this problem, it was necessary to greatly reduce the viscosity of the pigment dispersion, to keep the ink at a low viscosity, and to contain the pigment in a high concentration. The present inventors have found that the viscosity of the pigment dispersion is lowered and the stability is improved by controlling the structure of the pigment dispersion resin.

That is, the present invention is an aqueous pigment dispersion containing at least water, titanium oxide, and a pigment dispersion resin,
The titanium oxide is a pigment surface treated with an organic compound,
The organic compound is any one of a polyhydric alcohol, an alkanolamine or a derivative thereof, an organosilicon compound, a higher fatty acid or a metal salt thereof, and an organometallic compound,
The pigment-dispersed resin further has an alkyl group having 10 to 36 carbon atoms.

Further, the present invention relates to the aqueous pigment dispersion, wherein the organic compound is an organosilicon compound.
Furthermore, the present invention relates to the aqueous pigment dispersion, wherein the acid value of the pigment dispersion resin is 50 to 400 mgKOH / g.

  Furthermore, the present invention relates to an aqueous inkjet ink characterized in that it contains at least the aqueous pigment dispersion and an alkanediol solvent and / or an alkylene glycol alkyl ether solvent.

  According to the present invention, it is possible to provide an aqueous pigment dispersion having a low viscosity and excellent storage stability using titanium oxide as a pigment, and an aqueous inkjet ink having excellent concealability.

  Hereinafter, the present invention will be described with reference to preferred embodiments.

  In the present invention, the viscosity of the pigment dispersion is lowered and the stability is improved by combining titanium oxide whose pigment surface is treated with an organic compound and a dispersion resin having an alkyl group having 10 to 36 carbon atoms. Titanium oxide with an untreated pigment surface has high hydrophilicity, and in a solvent-based dispersion, the hydrophilic group of the dispersed resin is adsorbed on titanium oxide, and the dispersion is considered to be stabilized. However, in the case of an aqueous dispersion, if the surface of the pigment of titanium oxide is hydrophilic, it has a strong affinity for water and adsorption of the dispersion resin is difficult to occur, and the dispersion cannot be stabilized. Therefore, in the present invention, the dispersion stability is improved by treating the pigment surface of titanium oxide with an organic compound to make it hydrophobic. Further, by selecting an alkyl group having 10 to 36 carbon atoms as the site where the dispersion resin adsorbs to titanium oxide, the degree of adsorption of the dispersion resin was increased, and the viscosity of the dispersion was reduced.

  First, the titanium oxide that is a pigment will be described. As the titanium oxide used in the present invention, either an anatase type or a rutile type can be used, but it is preferable to use a rutile type in order to improve the concealability of printed matter. Moreover, although what was manufactured by any methods, such as a chlorine method and a sulfuric acid method, it is more preferable to use the titanium oxide manufactured by the chlorine method because whiteness is high.

  In the present invention, titanium oxide having a pigment surface treated with an organic compound is used. The untreated titanium oxide surface has a myriad of hydroxyl groups, which causes the hydrophilicity of titanium oxide. The hydroxyl group is reacted with an organic compound, the hydroxyl group is eliminated from the pigment surface, and the titanium oxide is hydrophobized by covering with the organic compound.

  The organic compound for performing the surface treatment of titanium oxide is not particularly limited as long as titanium oxide can be hydrophobized, but polyhydric alcohol, alkanolamine or derivative thereof, organosilicon compound, higher fatty acid or metal salt thereof, organometallic Compounds and the like. Among these, organosilicon compounds are particularly preferable because the surface of titanium oxide can be highly hydrophobized. These organic compounds may be used alone or in combination of two or more. The treatment amount of the organic compound is preferably 0.1% by weight or more and 5% by weight or less with respect to titanium oxide. When the amount is less than this, the pigment surface is not sufficiently hydrophobized, and dispersion stability may not be maintained. On the other hand, when the amount is larger than this, organic substances may be detached from the pigment surface, which may adversely affect the properties of the dispersion.

  Examples of organosilicon compounds include organosilanes, organopolysiloxanes, and organosilazanes. Examples of organosilanes include amino silane compounds, epoxy silane compounds, (meth) acryl silane compounds, vinyl silane compounds, mercapto silane compounds, halogenated alkyl silane compounds, alkyl silane compounds, and phenyl silane compounds. . Examples of organopolysiloxanes include dimethylpolysiloxane, methylhydrogenpolysiloxane, and their alkyl-modified, ether-modified, epoxy-modified, and (meth) acryl-modified compounds. Examples of organosilazanes include alkyldisilazane and alkyltrisilazane. Among these, organopolysiloxanes are particularly preferable.

  Examples of other organic compounds include trimethylolethane, tripropanolethane, and pentaerythritol as the polyhydric alcohol. Examples of the alkanolamine include triethanolamine and tripropanolamine, and examples of the derivative include their hydrochlorides and organic acid salts. Examples of higher fatty acids include stearic acid and lauric acid, and examples of metal salts include magnesium salts and zinc salts thereof. Examples of the organometallic compound include a titanium coupling agent, an aluminum coupling agent, and a zirconium coupling agent.

  In addition to surface treatment with an organic compound, it is also possible to treat with an inorganic compound in order to improve weather resistance and dispersion stability. Examples of inorganic compounds are compounds of silicon, aluminum, zirconium, tin, antimony and titanium, preferably hydrated oxides thereof. Among these, those treated with zirconium are preferable from the viewpoint of weather resistance and dispersion stability. The surface treatment with the inorganic compound is preferably performed before the surface treatment with the organic compound.

  The dispersed particle diameter of the titanium oxide of the present invention is preferably 100 to 400 nm from the viewpoints of the sedimentation property of the pigment and the concealability of the printed matter. If the particle size is 100 nm or less, the titanium oxide does not easily settle, but the concealability is lowered and the practicality as a white ink is lowered. On the other hand, at 400 nm or more, the concealability is sufficient, but sedimentation is likely to occur, which may cause clogging of the flow path in the printer and non-ejection. The average particle diameter of titanium oxide is more preferably 150 to 350 nm, and further preferably 200 nm to 300 nm.

  Titanium oxide surface-treated with such an organic compound can be obtained by a known technique, but is also commercially available and any can be used. Commercially available products are TYPEPEC CR-50-2, CR-57, CR-58-2, CR-60-2, CR-63, CR-Super-70, CR-90-2, CR-95, CR-953 , PC-3, PF-690, PF-691, PF-699, PF-711, PF-728, PF-736, PF-737, PF-739, PF-740, PF-742, R-980, UT -771 (all by Ishihara Sangyo). Among these, those treated with an organosilicon compound such as CR-63, PC-3, PF-691, PF-728, and PF-740 can be suitably used.

  The pigment dispersion resin used in the present invention is characterized by having an alkyl group having 10 to 36 carbon atoms. The type of resin is not particularly limited as long as it has an alkyl group having 10 to 36 carbon atoms. For example, an acrylic resin, a styrene acrylic resin, a maleic acid resin, a styrene maleic resin, a urethane resin, an ester resin, and the like can be given. Among these, it is preferable to use an acrylic resin or a styrene acrylic resin.

  Synthesis of resins having an alkyl group can be achieved by a method of condensing an alcohol or amine having an alkyl group to a functional group such as a carboxylic acid of the basic resin skeleton, or by using a monomer having an alkyl group during resin synthesis. And a method of synthesizing a resin having the following.

  As long as the alkyl group is in the range of 10 to 36 carbon atoms, either a straight chain or a branched chain can be used, but a straight chain is preferable. Linear alkyl groups include lauryl group (C12), myristyl group (C14), cetyl group (C16), stearyl group (C18), aralkyl group (C20), behenyl group (C22), lignoceryl group (C24), serotoyl Examples thereof include a group (C26), a montanyl group (C28), a meristyl group (C30), a dotriacontanoyl group (C32), a tetratriacontanoyl group (C34), a hexatriacontanoyl group (C36), and the like.

  In the present invention, the viscosity of the pigment dispersion and the viscosity stability are realized by setting the carbon number of the alkyl group of the pigment dispersion resin to 10 to 36. If the number of carbon atoms is less than 10, the viscosity stability is lowered and long-term operation becomes impossible, which is not suitable for practical use. On the other hand, if the number of carbon atoms is larger than 36, the viscosity of the pigment dispersion becomes too high, so that it is not suitable for inkjet applications. The alkyl group preferably has 12 to 30 carbon atoms, more preferably 18 to 24 carbon atoms.

  In the present invention, the acid value of the pigment dispersion resin is preferably 50 to 400 mgKOH / g. If the acid value is less than 50 mg KOH / g, the resin is difficult to dissolve in water, and the viscosity of the dispersion increases. Moreover, even when it is larger than 400 mgKOH / g, the interaction between the resins may be strengthened and the viscosity may be increased. The acid value of the pigment dispersion resin is preferably 100 to 350 mgKOH / g, and more preferably 150 to 300 mgKOH / g.

  Furthermore, by introducing an aromatic group into the pigment dispersion resin, it is possible to improve the pigment dispersibility and improve the dispersion stability. Examples of the aromatic group include phenyl group, naphthyl group, anthryl group, tolyl group, xylyl group, mesityl group, anisyl group and the like. Of these, a phenyl group and a tolyl group are preferable from the viewpoint of dispersion stability.

  In order to increase the solubility of the pigment-dispersed resin of the present invention in water, the acid group in the resin is preferably neutralized with a base. As the base, organic bases such as aqueous ammonia, dimethylaminoethanol, diethanolamine, and triethanolamine, and inorganic bases such as lithium hydroxide, sodium hydroxide, and potassium hydroxide can be used.

  The ratio of titanium oxide to pigment dispersion resin in the pigment dispersion of the present invention is preferably 2/1 to 100/1. When the ratio of the pigment dispersion resin is larger than 2/1, the viscosity of the pigment dispersion tends to increase. On the other hand, if it is less than 100/1, the dispersibility may be lowered and the stability may be lowered. The ratio of titanium oxide and pigment dispersion resin is more preferably 4/1 to 50/1, further preferably 5/1 to 25/1, and most preferably 10/1 to 20/1.

  Although the following method is mentioned as a manufacturing method of the pigment dispersion of this invention, It is not limited to this. First, a pigment is added to an aqueous medium in which a pigment dispersion resin and water are mixed, and after mixing and stirring, a dispersion treatment is performed using a disperser. Thereafter, the pigment dispersion can be obtained by performing centrifugation or filtration as necessary. As the disperser to be used, any wet disperser can be used, but it is preferable to use a bead mill.

  The pigment dispersion of the present invention can be used as an inkjet ink by adding additives such as an organic solvent, a binder resin, a surfactant, an antifoaming agent, a thickener, and a preservative.

  When used as an inkjet ink, the pigment concentration in the ink is preferably 5 to 25% by weight in order to achieve both concealability. When the pigment concentration is less than 5% by weight, sufficient concealment may not be obtained by one printing. On the other hand, if it is higher than 25% by weight, the viscosity of the ink becomes high, making it difficult to eject from the inkjet head, and long-term printing stability may be reduced. The pigment concentration in the ink is more preferably 8 to 20% by weight, and most preferably 10 to 15% by weight.

  In the inkjet ink of the present invention, an alkanediol solvent and / or an alkylene glycol alkyl ether solvent can be used as the organic solvent. By using these solvents, it is possible to improve the wettability of the ink with respect to the substrate and obtain a printed matter with good image quality.

  Alkanediol solvents include 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1, Examples include 5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, and the like. Among these, the use of 1,2-alkanediols such as 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol improves the wettability of the substrate. This is preferable because print quality can be improved. Furthermore, it is preferable to use 1,2-alkanediol having 4 to 6 carbon atoms.

  Dialkylene glycol alkyl ether solvents include diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether Dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol butyl methyl ether Ether and the like. Among these, alkylene glycol monoalkyl ether is preferable, and propylene glycol monoalkyl ether is more preferable.

  The alkanediol solvent and the alkylene glycol alkyl ether solvent are preferably contained in the ink in an amount of 10 to 40% by weight. When the amount is less than 10% by weight, the wettability of the ink with respect to the substrate becomes insufficient, and problems such as repellency may occur depending on the substrate. On the other hand, when the amount is more than 40% by weight, the viscosity becomes high, making it difficult to discharge from the ink jet head, and the long-term printing stability may be lowered. More preferably, it is contained in an amount of 20 to 35% by weight.

Further, other organic solvents can be used in combination for adjusting the moisture retention of the ink and the permeability to the substrate. Examples of other organic solvents include heterocyclic compounds such as 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyloxazolidinone, N-ethyloxazolidinone, γ-butyrolactone, and ε-caprolactone.

  In order to increase the resistance of the printed material, a binder resin can be further added in the present invention. Water-soluble resins and fine resin particles are generally known as binder resins for water-based inks. In general, resin fine particles have a higher molecular weight than water-soluble resins, and can achieve high resistance. In addition, the resin fine particles can lower the ink viscosity, and a larger amount of resin can be blended in the ink. Therefore, the resin fine particles are suitable for increasing the resistance of the ink-jet ink. Examples of the resin include acrylic, urethane, styrene butadiene, vinyl chloride, and polyolefin. In view of ink stability and printed material resistance, it is desirable to use acrylic resin fine particles.

  By increasing the glass transition temperature (Tg) of the binder resin, it is possible to improve resistance such as abrasion resistance and chemical resistance, preferably in the range of 50 to 120 ° C, more preferably in the range of 80 to 100 ° C. It is good to do. When the temperature is lower than 50 ° C., sufficient resistance cannot be obtained, and the ink coating film may be peeled off from the printed matter in practical use. In addition, when the temperature is higher than 120 ° C., the coating film becomes very hard, and cracking and cracking may occur on the printed surface when the printed material is bent.

  The content of the binder resin in the ink as described above is in the range of 2% by weight or more and 30% by weight or less of the total weight of the ink in solid content, more preferably in the range of 3% by weight or more and 20% by weight or less. Particularly preferably, it is in the range of 6 wt% or more and 15 wt% or less.

  Further, a surfactant can be further added to improve the image quality of the printed matter. Examples of the surfactant include a silicon-based surfactant, a fluorine-based surfactant, and an acetylenic diol-based surfactant. Among these, it is preferable to use a silicon-based surfactant from the viewpoint of printing stability. The content of the surfactant is preferably in the range of 0.05% by weight to 2% by weight.

  In the present invention, not only a single color but also an ink set combining color inks such as cyan, magenta, yellow, and black can be used. When used as an ink set, finely adjust the composition between the inks, align the viscosity and surface tension, etc., and evenly spread and dry on the base material during printing, so that the print quality is uniform. Can be further improved.

  The substrate for printing the ink-jet ink of the present invention is not particularly limited, but paper substrates such as fine paper, coated paper, art paper, cast paper, synthetic paper, polycarbonate, hard vinyl chloride, soft vinyl chloride, polystyrene, polystyrene foam, Plastic substrates such as PMMA, polypropylene, polyethylene, and PET, metal substrates such as stainless steel, glass, and wood can be used. These substrates that are not white can be printed with white ink first and then with color ink to improve the color developability of the printed matter.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “parts” and “%” are based on weight unless otherwise specified.

The titanium oxide used in the present invention is as follows.
Taipei PE CR-60-2 (Aluminum / polyhydric alcohol treatment, manufactured by Ishihara Sangyo Co., Ltd.)
Taipei PF-711 (Silicon, aluminum / polyhydric alcohol treatment, manufactured by Ishihara Sangyo Co., Ltd.)
Typep CR-63 (Silicon, aluminum / organosilicon compound treatment, manufactured by Ishihara Sangyo Co., Ltd.)
Taipei PF-740 (zirconium, aluminum / organosilicon compound treatment, manufactured by Ishihara Sangyo Co., Ltd.)
Typep CR-60 (aluminum treatment, manufactured by Ishihara Sangyo Co., Ltd.)
Typeke CR-80 (Silicon, aluminum treatment, manufactured by Ishihara Sangyo Co., Ltd.)

(Example 1)
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 93.4 parts of butanol and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., and a mixture of 95 parts of lauryl methacrylate, 5 parts of acrylic acid, and 6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over 2 hours to carry out a polymerization reaction. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, 0.6 parts of V-601 (manufactured by Wako Pure Chemical Industries) was added, and the reaction was further continued at 110 ° C. for 1 hour to obtain a dispersion resin 1 solution. Further, after cooling to room temperature, 37.1 parts of dimethylaminoethanol was added for neutralization, and 100 parts of water was added to make it aqueous. Thereafter, the mixture was heated to 100 ° C. or more, butanol was azeotroped with water, butanol was distilled off, and the nonvolatile content was adjusted to 50%. As a result, an aqueous solution of the dispersion resin 1 having a nonvolatile content of 50% was obtained.

  After predispersing 60 parts of Typeke CR-60-2 as a pigment, 12 parts of an aqueous solution of Dispersing Resin 1 and 28 parts of water with a disper, a 0.6 L dyno mill filled with 1800 g of zirconia beads having a diameter of 0.5 mm was used. This dispersion was used for 2 hours to obtain an aqueous pigment dispersion of the present invention. At this time, the ratio of the non-volatile component between the pigment and the dispersion resin is pigment / dispersion resin (non-volatile component) = 10/1.

  20 parts of the obtained aqueous pigment dispersion, 20 parts of fixing resin (styrene acrylic resin emulsion, Tg 80 ° C., Nv. 40%), 10 parts of 1,2-butanediol, 10 parts of 1,2-hexanediol Then, 5 parts of diethylene glycol monobutyl ether and 35 parts of water were sequentially added to the mixing vessel while stirring with a disper, and stirred until sufficiently uniform to prepare an ink jet ink. The viscosity of this ink was 5 mPa · s.

(Viscosity measurement of dispersion)
The viscosity of the pigment dispersion was measured using an E-type viscometer (TVE-20L, manufactured by Toki Sangyo Co., Ltd.) at 25 ° C. and a rotation speed of 50 rpm. When the measured viscosity was 5 mPa · s or less, it was judged as ◎, when it was 5 to 12 mPa · s, it was judged as ○, and when it was 12 mPa · s or more (out of the measurement range), it was judged as ×.

(Viscosity stability of dispersion and ink)
The pigment dispersion and ink-jet ink were stored in a thermostat at 70 ° C. and accelerated over time, and then the change in viscosity of the ink before and after aging was evaluated.
A: Viscosity change rate after storage for two weeks is less than ± 10% ○: Viscosity change rate after storage for one week is less than ± 10% ×: Viscosity change rate after storage for one week is ± 10 or more

(Concealment of printed matter)
The prepared inkjet ink was filled into an inkjet printer VJ-1608HSJ (an inkjet printer manufactured by Muto Kogyo Co., Ltd.), and a solid image was printed on a transparent PET film. After printing the ink on the substrate, it was dried by heating at 70 ° C. for 3 minutes to obtain a printed matter for evaluation. The concealability was evaluated by measuring the transmission density of this printed matter with a Macbeth TR-924 densitometer. The evaluation criteria at this time are as follows.
◎: Transmission density is 0.6 or more ○: Transmission density is 0.45 or more and less than 0.6 ×: Transmission density is less than 0.3

(Examples 2-14, Comparative Examples 1-12)
Dispersing resins 2 to 13 were prepared in the same manner as in Example 1 according to the composition described in Table 1. Using the obtained dispersion resin, an aqueous pigment dispersion was prepared in the same manner as in Example 1 with the pigment dispersion resin and titanium oxide described in Table 2, and this aqueous pigment dispersion was used in the same manner as in Example 1. An inkjet ink was prepared and evaluated. In addition, when viscosity became high at the time of ink-jet ink preparation, water was added and the viscosity was adjusted to 5 mPa · s.
CR-60 and CR-80 are titanium oxides that are not pigment-treated with an organic compound.

  As a result of the evaluation, in Examples 1 to 14, a pigment dispersion resin having an alkyl group having 10 to 36 carbon atoms is used, and the pigment dispersion is reduced in viscosity by using a surface treated with an organic compound as titanium oxide. In addition, the viscosity stability is also good. Moreover, the ink using this has high concealability. Further, higher effects can be obtained by adjusting the acid value of the pigment-dispersed resin and introducing an aromatic group.

  On the other hand, regarding the comparative example, the pigment-dispersed resin does not have an alkyl group having 10 to 36 carbon atoms or does not use titanium oxide surface-treated with an organic compound, so any performance is low compared to the examples. It is the result.

Claims (4)

An aqueous pigment dispersion containing at least water, titanium oxide, and a pigment dispersion resin, wherein the titanium oxide has a pigment surface treated with an organic compound,
The organic compound is any one of a polyhydric alcohol, an alkanolamine or a derivative thereof, an organosilicon compound, a higher fatty acid or a metal salt thereof, and an organometallic compound,
Further, the pigment dispersion resin has an alkyl group having 10 to 36 carbon atoms, and is an aqueous pigment dispersion.   The aqueous pigment dispersion according to claim 1, wherein the organic compound is an organosilicon compound.   The aqueous pigment dispersion according to claim 1 or 2, wherein the acid value of the pigment dispersion resin is 50 to 400 mgKOH / g.   An aqueous inkjet ink comprising at least the aqueous pigment dispersion according to any one of claims 1 to 3, and an alkanediol solvent and / or an alkylene glycol alkyl ether solvent.