Aqueous pigment dispersion

Abstract

To provide an aqueous pigment dispersion and an aqueous ink which are excellent in storage stability.SOLUTION: An aqueous pigment dispersion includes a pigment and a polyester resin containing a compound represented by formula (1). An aqueous ink includes the aqueous pigment dispersion and a water-soluble organic solvent. (X and Y individually denote a hydrogen atom or carboxy group or hydrocarbon group. However, at least one of X and Y is a carboxyl group.)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous pigment dispersion and an aqueous ink containing the same. [Background technology]

[0002] Inkjet recording is a method of printing characters and images by ejecting ink droplets from extremely fine nozzles directly onto a recording medium. This method has become extremely popular due to its many advantages, including the ease of full-color printing, low cost, the ability to use plain paper as a recording medium, and no contact with the substrate. In recent years, water-based pigment inks that use pigments as colorants and polymers to disperse the pigments have been attracting attention from the perspective of imparting weather resistance and water resistance to printed matter and reducing the burden on the working environment and the natural environment. On the other hand, water-based pigment inks have the problem that the pigments and polymers generate coarse particles, which deteriorate the storage stability and ejection properties.

[0003] Therefore, various proposals have been made to improve the storage stability and jetting properties of water-based pigment inks. For example, Patent Document 1 discloses a pigment water dispersion of a pigment-containing polyester resin, the pigment water dispersion containing 3-methyl-1,5-pentanediol as an alcohol component, which is a constituent unit of the polyester resin, and a water-based ink containing the same, for the purpose of providing a pigment water dispersion excellent in dispersion stability and redispersibility after long-term storage, and a water-based ink capable of obtaining recorded matter excellent in long-term dispersion stability, adhesion to substrates, abrasion resistance, and alcohol resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-151760 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the inkjet recording method used in commercial and industrial printing, water-based ink is generally supplied to the ejection nozzles via a main tank and a sub-tank. At this time, the ink in the main tank is often left for long periods of time. This causes a problem in that the ejection properties of the water-based ink (hereinafter also referred to as "ejection stability") deteriorate, especially when printing is resumed after a long pause. On the other hand, ink printed on low-absorbency coated paper or non-absorbent resin film is difficult to penetrate into the substrate, resulting in a problem of low scratch resistance of the resulting recorded matter. Conventional water-based inks such as those disclosed in Patent Document 1 are not sufficient in terms of ejection stability after being left unused for a long period of time and in terms of abrasion resistance of recorded matter, and there is room for improvement. The present invention relates to an aqueous pigment dispersion having excellent storage stability, and an aqueous ink having excellent ejection stability even after being left unused for a long period of time, and capable of obtaining recorded matter having excellent abrasion resistance and resistance to erosion by alcohol-containing liquids, i.e., excellent alcohol resistance, even when printed on a printing medium having low liquid absorption. [Means for solving the problem]

[0006] The present inventors have found that an aqueous pigment dispersion having a pigment and a polyester resin containing a compound having a specific structure as a carboxylic acid component has particularly excellent storage stability, and that an aqueous ink using the aqueous pigment dispersion has excellent ejection stability even after being left unused for an extended period of time, and further, that even when used on a printing medium with low liquid absorption, the recorded matter has excellent abrasion resistance and alcohol resistance. The present invention relates to the following [1] and [2]. [1] An aqueous pigment dispersion containing a pigment and a polyester resin, wherein a carboxylic acid component that is a structural unit of the polyester resin contains a compound represented by the following formula (1): [ka] (X and Y each represent a hydrogen atom, a carboxy group, or a hydrocarbon group, provided that at least one of X and Y is a carboxy group.) [2] A water-based ink containing the water-based pigment dispersion according to [1] above and a water-soluble organic solvent. Effect of the Invention

[0007] According to the present invention, it is possible to provide an aqueous pigment dispersion having excellent storage stability, and an aqueous ink having excellent ejection stability even after being left unused for a long period of time, and capable of obtaining recorded matter having excellent abrasion resistance and alcohol resistance even when printed on a printing medium having low liquid absorption. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based pigment dispersion] The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion containing a pigment and a polyester resin, in which a carboxylic acid component, which is a structural unit of the polyester resin, contains a compound represented by the following formula (1):

[0009] [ka]

[0010] In formula (1), X and Y each represent a hydrogen atom, a carboxy group, or a hydrocarbon group, provided that at least one of X and Y is a carboxy group.

[0011] In this specification, the term "water-based" means that water accounts for the largest proportion by mass of the medium in which the pigment is dispersed. In addition, "recording" is a concept that includes printing and printing out characters and images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters and images are recorded. "Low liquid absorption" is a concept including low liquid absorption and non-liquid absorption, and the amount of water absorption of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g / m 2 More than 10g / m 2 This means that:

[0012] The aqueous pigment dispersion of the present invention has excellent storage stability, and the aqueous ink using the aqueous pigment dispersion has excellent ejection stability even after being left unused for a long period of time, and further, even when printed on a printing medium with low liquid absorption, the recorded matter has excellent abrasion resistance and alcohol resistance. Although the reason for this is unclear, it is thought to be as follows. The polyester resin contained in the aqueous pigment dispersion of the present invention contains, among its constituent components, a constituent unit derived from the compound represented by the above formula (1) as a carboxylic acid component. Since the water-based ink of the present invention contains a polyester resin containing the compound represented by formula (1) as a constituent, it is believed that the adhesiveness imparting function derived from the compound represented by formula (1) acts between the recording medium and the components constituting the ink, such as the pigment, in the printed matter, thereby enhancing the scratch resistance of the printed matter. Furthermore, since the compound represented by formula (1) is highly hydrophobic as described above, it is believed that it has poor affinity with alcohol, which is a highly polar solvent, and therefore has excellent alcohol resistance.

[0013] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and may also be a lake pigment or a fluorescent pigment. If necessary, these pigments may also be used in combination with an extender pigment. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, pearlescent pigments, etc. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

[0014] There are no particular limitations on the hue, and any of achromatic pigments such as white, black, and gray; and chromatic organic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more product numbers selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of the extender pigment include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more kinds.

[0015] In the present invention, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has not been used for a long period of time, the pigment is preferably in a form in which it is dispersed using a polyester resin described below as a dispersant, and more preferably in the form of polyester resin particles containing the pigment. In the present invention, the term "polyester resin particles containing a pigment" refers to a concept including any one of particles comprising the pigment and a polyester resin whose constituent unit, a carboxylic acid component, contains a compound represented by formula (1), the polyester resin incorporating the pigment, particles comprising the polyester resin and a pigment, the pigment being partially exposed on the surface of the particle, and particles in which the polyester resin is adsorbed to a portion of the pigment, or a mixture of these. In addition, the polyester resin particles containing a pigment in the present invention are preferably contained in an aqueous medium as a dispersion. Since the rosin component constituting the compound represented by formula (1) has a rigid structure in which ring structures are linked, it is considered that the polyester resin used in the present invention has a resin chain with a lower mobility than a polyester resin whose carboxylic acid component is mainly composed of terephthalic acid, isophthalic acid, adipic acid, or the like. Furthermore, since the compound represented by formula (1) has a large number of carbon atoms constituting it and is therefore highly hydrophobic, it is considered that when the polyester resin in the present invention is used as a resin for dispersing a pigment, the resin is firmly adsorbed on the pigment surface and the effect of suppressing detachment acts, so that the pigment can be stably dispersed. As a result, the aqueous pigment dispersion of the present invention has high storage stability, and it is considered that by using the aqueous pigment dispersion having high storage stability, the aqueous ink of the present invention can maintain high ejection stability even after being unused for a long time.

[0016] The aqueous pigment dispersion of the present invention may be a mixture of pigment particles and the polyester resin particles of the present invention which do not contain a pigment, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, as well as from the viewpoint of improving the abrasion resistance and alcohol resistance of the resulting recorded matter. When the aqueous pigment dispersion of the present invention is a mixture of pigment particles and the polyester resin particles of the present invention that do not contain a pigment, the pigment particles may be contained in a resin other than the polyester resin of the present invention, or may be a so-called self-dispersing pigment that can be dispersed in an aqueous medium as pigment particles without using a resin.

[0017] <Polyester resin> The polyester resin contained in the aqueous pigment dispersion of the present invention (hereinafter also referred to as "polyester resin of the present invention") contains a structural unit derived from a compound represented by formula (1) as a carboxylic acid component. The polyester resin of the present invention also contains a structural unit derived from an alcohol component. The polyester resin of the present invention can be obtained by polycondensation of a carboxylic acid component containing a compound represented by formula (1) and an alcohol component. The polyester resin of the present invention is preferably water-insoluble. In this specification, a polyester resin being water-insoluble means that when a polyester resin that has been dried at 105° C. for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25° C., the amount of dissolution is 10 g or less. In addition, when the polyester resin is an anionic polymer, the amount of dissolution is the amount of dissolution when 100% of the anionic groups of the polymer are neutralized with sodium hydroxide.

[0018] (Carboxylic acid component) [Compound represented by formula (1)] The compound represented by formula (1) contained in the carboxylic acid component constituting the polyester resin of the present invention is a compound having a component derived from rosin and a component derived from a compound having a carbon-carbon double bond adjacent to a carboxy group. The compound represented by formula (1) can be obtained by the Diels-Alder reaction of rosin with a compound having a carbon-carbon double bond adjacent to a carboxy group. Specifically, the compound represented by formula (1) can be obtained by the Diels-Alder reaction of rosin as a raw material with fumaric acid, maleic acid, acrylic acid, or methacrylic acid. In the case where different functional groups are bonded to the carbon atoms in formula (1), the combination of the conformations is arbitrary. Specifically, in formula (1), even if X and H are interchanged at the carbon atom to which X and H are bonded, and even if Y and H are interchanged at the carbon atom to which Y and H are bonded, the carboxylic acid component constituting the polyester resin of the present invention can be obtained.

[0019] In the present invention, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the obtained recorded matter, the softening point of the compound represented by formula (1) is preferably 80° C. or more, more preferably 95° C. or more, even more preferably 100° C. or more, and is preferably 170° C. or less, even more preferably 160° C. or less, and even more preferably 150° C. or less.

[0020] Suitable examples of the compound represented by formula (1) include fumarated rosin, maleated rosin, acrylated rosin, methacrylated rosin, and the like. From the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has not been used for a long period of time, and from the viewpoint of improving the abrasion resistance and alcohol resistance of the resulting recorded matter, one or more types selected from maleated rosin and acrylated rosin are more preferred, and acrylated rosin is even more preferred. The compound represented by formula (1) may be prepared from rosin and the above-mentioned compound, or a commercially available product may be used. Commercially available products of the compound represented by formula (1) include maleic rosin such as Harima T-80 (softening point 80 to 90°C: catalog value) manufactured by Harima Chemical Industries Co., Ltd., and acrylic rosin such as Pine Crystal KE-604B (softening point 129°C) manufactured by Arakawa Chemical Industries Co., Ltd.

[0021] [Carboxylic acid components other than the compound represented by formula (1)] From the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, the polyester resin of the present invention preferably further contains, as the carboxylic acid component, a carboxylic acid component other than the compound represented by formula (1). That is, from the same viewpoint as above, the polyester resin of the present invention more preferably further contains, as the carboxylic acid component, one or more selected from aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids other than the compound represented by formula (1), and trivalent or higher polyvalent carboxylic acids. As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid and terephthalic acid are preferred, and terephthalic acid is more preferred. The aliphatic dicarboxylic acid may be unsaturated or saturated. The unsaturated aliphatic dicarboxylic acid may be fumaric acid or maleic acid, more preferably fumaric acid. The saturated aliphatic dicarboxylic acid may be adipic acid or succinic acid, more preferably adipic acid. As the alicyclic dicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid are preferred. As the trivalent or higher polyvalent carboxylic acid, trimellitic acid and pyromellitic acid are preferred. Also preferred is trimellitic anhydride. The carboxylic acid components may be used alone or in combination of two or more kinds. Among the above, it is preferable that the polyester resin of the present invention further contains terephthalic acid and fumaric acid as the carboxylic acid component, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time.

[0022] (Content of the compound represented by formula (1) in the carboxylic acid component) The content of the compound represented by formula (1) in the carboxylic acid component constituting the polyester resin of the present invention is preferably 5 mol% or more, more preferably 8 mol% or more, even more preferably 10 mol% or more, even more preferably 15 mol% or more, even more preferably 20 mol% or more, even more preferably 25 mol% or more, even more preferably 30 mol% or more, from the viewpoint of improving the storage stability of the water-based pigment dispersion and the ejection stability of the water-based ink after a long time unused state, and from the viewpoint of improving the scratch resistance and alcohol resistance of the obtained recorded matter. And from the same viewpoint, it is preferably 100 mol% or less, more preferably 95 mol% or less, even more preferably 90 mol% or less, even more preferably 85 mol% or less, even more preferably 80 mol% or less. The molar ratio of the compound represented by formula (1) in the carboxylic acid component constituting the polyester resin of the present invention is expressed as the ratio of the molar equivalent of the carboxy group of the compound represented by formula (1) in the carboxylic acid component to the total molar equivalent of the carboxy group in the carboxylic acid component.

[0023] (Alcohol content) The alcohol component, which is a structural unit of the polyester resin of the present invention, preferably contains at least one selected from the group consisting of an aliphatic diol, an aliphatic triol, and an aromatic diol. Preferred examples of the aliphatic diol include ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 2,3-butanediol, 1,5-pentanediol, 2,4-pentanediol, neopentyl glycol, 1,2-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 2,6-heptanediol, 2,7-octanediol, 3-methyl-1,5-pentanediol, and hydrogenated bisphenol A and its alkylene (carbon number 2 to 4) oxide adducts (average added mole number 1 to 16). Preferred examples of the aliphatic triol include glycerin and trimethylolpropane. Among these, at least one selected from 1,2-propanediol, trimethylolpropane, and 3-methyl-1,5-pentanediol is more preferred.

[0024] The aromatic diol is preferably an alkylene oxide adduct of bisphenol A. The alkylene oxide adduct of bisphenol A means a compound in which an oxyalkylene group is added to 2,2-bis(4-hydroxyphenyl)propane, and specifically, a compound represented by the following general formula (I) is preferred. The alkylene oxide added to bisphenol A is preferably one or more selected from ethylene oxide and propylene oxide, and more preferably propylene oxide. As the aromatic diol, a propylene oxide adduct of bisphenol A is preferred.

[0025] [ka]

[0026] In the general formula (I), OR 1 , R 2 Each O independently represents an oxyalkylene group having 1 to 4 carbon atoms, and is preferably an oxyethylene group or an oxypropylene group. x and y are the number of moles of alkylene oxide added, and each is independently a positive number of 0 or more. From the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and is preferably 7 or less, more preferably 5 or less, and further preferably 3 or less. Also, OR 1 and R 2 Each O may be the same or different, but from the viewpoint of exerting the effects of the present invention, it is preferable that O is the same.

[0027] In the present invention, the alcohol component may further contain one or more selected from the group consisting of an aliphatic polyol having 4 or more hydroxyl groups and an alicyclic diol. Preferred examples of the aliphatic polyol having 4 or more hydroxyl groups include pentaerythritol and sorbitol. Preferred examples of the alicyclic diol include 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol, of which pentaerythritol 1,4-cyclohexanediol is more preferred.

[0028] The alcohol components may be used alone or in combination of two or more kinds.

[0029] (Production of polyester resin) The polyester resin of the present invention can be obtained by polycondensing the carboxylic acid component and the alcohol component in an appropriate combination, for example, by polycondensing the carboxylic acid component and the alcohol component in an inert gas atmosphere at a temperature of 150° C. to 250° C. using an esterification catalyst as necessary. Examples of the esterification catalyst include tin catalysts, titanium catalysts, and metal compounds such as antimony trioxide, zinc acetate, and germanium dioxide, and from the viewpoint of esterification reaction efficiency, tin catalysts are preferred. As the tin catalyst, dibutyltin oxide, tin(II) di(2-ethylhexanoate), and salts thereof are preferred, and tin(II) di(2-ethylhexanoate) is more preferred. If necessary, an esterification promoter such as gallic acid may be further used. A radical polymerization inhibitor such as 4-t-butylcatechol may also be used in combination.

[0030] The polyester resin of the present invention preferably has an acid group, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the abrasion resistance and alcohol resistance of the resulting recorded matter. Preferred examples of the acid group of the polyester resin of the present invention include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, etc. Among these, the carboxylic acid group is more preferred. The acid value of the polyester resin of the present invention is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, even more preferably 60 mgKOH / g or less, and even more preferably 40 mgKOH / g or less.

[0031]

[0043] The softening point of the polyester resin of the present invention is, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter, preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and is preferably 180°C or lower, more preferably 160°C or lower, even more preferably 150°C or lower.

[0032]

[0043] From the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter, the polyester resin of the present invention has a glass transition temperature of preferably 35°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and preferably 105°C or lower, more preferably 100°C or lower, even more preferably 95°C or lower.

[0033]

[0043] The weight average molecular weight of the polyester resin of the present invention is, from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter, preferably 4,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, and is preferably 30,000 or less, more preferably 20,000 or less, even more preferably 15,000 or less.

[0034] (Basic compounds) From the viewpoint of improving the storage stability of the aqueous pigment dispersion and the ejection stability of the aqueous ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter, the aqueous pigment dispersion of the present invention preferably contains a basic compound for neutralizing the acid groups contained in the polyester resin of the present invention to impart an electric charge. In the case of neutralization, it is preferable to neutralize so that the pH of the water-based pigment dispersion of the present invention is from 7 to 10. The pH of the water-based pigment dispersion is measured by the method described in the examples. Examples of the neutralizing agent include basic compounds such as sodium hydroxide, potassium hydroxide, ammonia, and various amines. Of these, at least one selected from sodium hydroxide, potassium hydroxide, and ammonia is preferred, and sodium hydroxide is more preferred.

[0035] <Method of manufacturing water-based pigment dispersion> The water-based pigment dispersion of the present invention can be efficiently produced by a method having the following step 1. It is also preferable to carry out step 2 as necessary. Step 1 (pigment dispersion step): A step of dispersing a pigment mixture containing a pigment, a polyester resin, water, and, if necessary, a neutralizing agent, a surfactant, an organic solvent for dispersion treatment, etc., to obtain an aqueous pigment dispersion containing a pigment and polyester resin particles. Step 2 (concentration step): A step of removing the organic solvent used for the dispersion treatment from the aqueous pigment dispersion obtained in step I.

[0036] (Process 1) The dispersion treatment in step 1 can be carried out by a known method. Although the pigment particles can be atomized to a desired particle size only by main dispersion using shear stress, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion from the viewpoint of increasing the productivity of the aqueous pigment dispersion. As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used.

[0037] Examples of dispersing machines used in the dispersion include kneading machines such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersing machines such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When the dispersion treatment is carried out using a high-pressure homogenizer, the average particle size of the pigment particles in the aqueous pigment dispersion can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure of the high-pressure homogenizer is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

[0038] (Process 2) In the case where the pigment mixture obtained by the dispersion treatment contains an organic solvent used in the dispersion treatment, a step of removing the organic solvent by a known method can be carried out. In the case where the organic solvent used in the dispersion treatment may be allowed to continue to be contained in the ink, it may be left behind. From the viewpoint of improving the dispersion stability of the aqueous pigment dispersion and facilitating the production of the ink, the solid content concentration of the aqueous pigment dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration is measured by the method described in the Examples.

[0039] In the present invention, when the pigment is in the form of pigment-containing polyester resin particles, the average particle size of the pigment-containing polyester resin particles in the aqueous pigment dispersion of the present invention is, from the viewpoint of improving storage stability, preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, even more preferably 170 nm or less. The average particle size is measured by the method described in the Examples.

[0040] The pH of the water-based pigment dispersion of the present invention is, from the viewpoints of storage stability, reduced corrosiveness, and the like, preferably 7.0 or more, more preferably 7.2 or more, even more preferably 7.3 or more, and is preferably 11 or less, more preferably 10 or less, even more preferably 9 or less. The pH is measured by the method described in the Examples.

[0041] <Content of each component in water-based pigment dispersion> The contents of the various components in the water-based pigment dispersion of the present invention are as follows, from the viewpoints of improving the storage stability of the water-based pigment dispersion and the ejection stability of the water-based ink after it has been left unused for a long period of time, and from the viewpoints of improving the scratch resistance and alcohol resistance of the resulting recorded matter.

[0042] The content of the pigment in the aqueous pigment dispersion of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and is preferably 20% by mass or less, more preferably 18% by mass or less, even more preferably 15% by mass or less.

[0043] In the present invention, when the pigment is in the form of polyester resin particles containing a pigment, the content of the polyester resin particles containing a pigment in the aqueous pigment dispersion of the present invention is preferably 3 mass% or more, more preferably 6 mass% or more, even more preferably 10 mass% or more, and preferably 35 mass% or less, more preferably 30 mass% or less, even more preferably 25 mass% or less.

[0044] The content of the polyester resin of the present invention in the aqueous pigment dispersion of the present invention is preferably 1 mass % or more, more preferably 2 mass % or more, even more preferably 3 mass % or more, and is preferably 15 mass % or less, more preferably 12 mass % or less, even more preferably 10 mass % or less.

[0045] In the aqueous pigment dispersion of the present invention, the mass ratio of the pigment to the sum of the mass of the pigment and the mass of the polyester resin of the present invention [mass of pigment / (mass of pigment+mass of polyester resin of the present invention)] is, from the viewpoints of improving the dispersion stability and improving the storage stability of the aqueous pigment dispersion of the present invention, preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and is preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less. The mass ratio [pigment / (pigment+polyester resin of the present invention)] can be calculated from the charge amount ratio.

[0046] [Water-based ink] The water-based ink of the present invention contains the above-mentioned water-based pigment dispersion of the present invention and a water-soluble organic solvent. Here, "water-based ink" means that water accounts for the largest proportion of the medium contained in the ink.

[0047] <Water-soluble organic solvent> The water-soluble organic solvent in the water-based ink of the present invention may be liquid or solid at 25°C. However, when the water-soluble organic solvent is dissolved in 100 mL of water at 25°C, it is preferable that the amount of the dissolved water be 10 mL or more. From the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter, the boiling point of the water-soluble organic solvent is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 130°C or higher, even more preferably 140°C or higher, and is preferably 250°C or lower, more preferably 245°C or lower, even more preferably 240°C or lower, even more preferably 235°C or lower. Examples of the water-soluble organic solvent include glycol ethers such as alkylene glycol ethers, polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, amide compounds, etc. Among these, one or more selected from alkylene glycol ethers and polyhydric alcohols are preferred.

[0048] Examples of alkylene glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono(iso)butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono(iso)propyl ether, diethylene glycol mono(iso)butyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Of these, from the viewpoints of improving the ejection stability of the water-based ink of the present invention after heated storage, and further the abrasion resistance and alcohol resistance of recorded matter, one or more selected from diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol isobutyl ether, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether are preferred, and diethylene glycol monoisobutyl ether is more preferred.

[0049] In the present invention, it is preferable to contain propylene glycol in addition to the alkylene glycol ether. Propylene glycol primarily suppresses the evaporation of water from the ink nozzles, and by volatilizing quickly after recording, it is thought to form a strong ink film with a minimum drying process, thereby improving the abrasion resistance and alcohol resistance of the recorded material.

[0050] <Surfactant> The water-based ink of the present invention preferably contains a surfactant from the viewpoints of maintaining the surface tension of the ink at an appropriate level and improving the wettability of the ink to a recording medium. The surfactant is not particularly limited, but a nonionic surfactant is preferred, and a silicone-based surfactant is more preferred. Examples of silicone surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone, with polyether-modified silicone being preferred from the same viewpoint as above. Specific examples of polyether-modified silicones include PEG-3 dimethicone, PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG / PPG-20 / 22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, lauryl PEG-9 polydimethylsiloxyethyl dimethicone, and the like. Commercially available examples of polyether-modified silicones include silicones KF-6011, KF-6012, KF-6013, KF-6015, KF-6016, KF-6017, KF-6028, KF-6038, and KF-6043 manufactured by Shin-Etsu Chemical Co., Ltd.

[0051] In the present invention, in addition to the silicone surfactant, an acetylene glycol surfactant can be used. Commercially available examples of acetylene glycol surfactants include the "Surfynol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd. The above surfactants can be used alone or in combination of two or more.

[0052] Other additives that may be used in the water-based ink of the present invention include fixing aids, humectants, wetting agents, penetrating agents, viscosity adjusters, defoamers, preservatives, antifungal agents, and rust inhibitors. The fixing aid may be an emulsion containing water-insoluble polymer particles. Examples of the water-insoluble polymer particles include particles of condensation resins such as polyurethane resins and polyester resins other than the polyester resin of the present invention; and particles of vinyl resins such as (meth)acrylic resins, styrene resins, styrene-(meth)acrylic resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins. In addition, polyurethane resins having the structure of the polyester resin of the present invention as a constituent unit, specifically, polyurethane resins having a polyester diol compound having a compound represented by formula (1) as a constituent unit and a (poly)isocyanate compound as constituent units, are not included in the polyester resin of the present invention.

[0053] <Contents of each component in the water-based ink of the present invention> The contents of each component in the water-based ink of the present invention are as follows, from the viewpoint of improving the ejection stability of the water-based ink after it has been left unused for a long period of time, and from the viewpoint of improving the scratch resistance and alcohol resistance of the resulting recorded matter. (Pigment content) The pigment content in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0054] The total content of the pigment in the water-based ink and the content of the polyester resin of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

[0055] The content of the polyester resin of the present invention in the water-based ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less.

[0056] From the viewpoint of facilitating the production of the water-based ink, the mass ratio of the pigment to the sum of the mass of the pigment and the mass of the polyester resin of the present invention [mass of pigment / (mass of pigment+mass of polyester resin of the present invention)] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and is preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less.

[0057] The total content of water-soluble organic solvents in the water-based ink is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and is preferably 45% by mass or less, more preferably 42% by mass or less, even more preferably 40% by mass or less.

[0058] The water content in the water-based ink is preferably 45% by mass or more, more preferably 50% by mass or more, more preferably 55% by mass or more, and preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0059] <Physical properties of the water-based ink of the present invention> From the viewpoint of improving ejection stability, the viscosity of the water-based ink of the present invention at 32°C is preferably 2 mPa s or more, more preferably 2.5 mPa s or more, and preferably 12 mPa s or less, more preferably 9 mPa s or less, and even more preferably 7 mPa s or less.

[0060] From the viewpoint of improving ejection stability, the average particle size of the water-based ink is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 170 nm or less. The average particle size is measured by the method described in the Examples.

[0061] The water-based ink of the present invention has high ejection stability even after being unused for a long period of time, and further has high abrasion resistance and alcohol resistance of the resulting recorded matter, and is therefore preferably used for inkjet recording. The water-based ink of the present invention can be loaded into a known ink jet recording device such as a piezoelectric type, and ejected as ink droplets onto a low liquid-absorbent recording medium to record an image or the like. Examples of low-absorbency recording media include low-absorbency coated paper, art paper, and non-absorbent resin films. Examples of coated paper include general-purpose glossy paper and multi-color form glossy paper. Examples of the resin film include transparent synthetic resin films, such as polyester, polyvinyl chloride (PVC), polyolefin, and nylon films. These films may be biaxially oriented, uniaxially oriented, or non-oriented films, and may be corona discharge-treated. Among these, polyester films and oriented polypropylene films are preferred, and corona discharge-treated polyethylene terephthalate (PET) films, corona discharge-treated biaxially oriented polypropylene (OPP) films, and white polyvinyl chloride films are more preferred. EXAMPLES

[0062] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each property value was measured and evaluated by the following methods. The methods for measuring the various physical properties in the Production Examples, Examples and Comparative Examples are as follows.

[0063] (1) Polyester resin, softening point of compound represented by formula (1) Using a flow tester (Shimadzu Corporation, product name: CFT-500D), 1 g of the sample was heated at a temperature increase rate of 6°C / min, while applying a load of 1.96 MPa with the plunger, and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. The plunger descent amount of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was determined as the softening point of the polyester resin and the compound represented by formula (1).

[0064] (2) Glass transition temperature (Tg) of polyester resin Using a differential scanning calorimeter (Perkin Elmer, product name: Pyris 6 DSC), the sample was heated to 200°C, cooled from that temperature at a rate of 10°C / min to 0°C, and then heated again at a rate of 10°C / min. The glass transition temperature (Tg) of the polyester resin was determined as the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the top of the peak.

[0065] (3) Acid value of polyester resin The acid value of the polyester resin was measured according to the neutralization titration method described in JIS K0070-1992, except that the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene=1:1 (volume ratio)].

[0066] (4) Weight average molecular weight (Mw) of polyester resin A solution of polyester resin dissolved in chloroform to a concentration of 0.5 g / 100 mL was filtered using a fluororesin filter with a pore size of 2 μm (manufactured by Sumitomo Electric Industries, Ltd., product name: FP-200) to remove insoluble components, and a sample solution was prepared. Tetrahydrofuran was passed as a molecular weight measurement dissolving solution at a flow rate of 1 mL per minute, and the column was stabilized in a thermostatic bath at 40° C. 100 μL of the above sample solution was injected therein to measure the weight average molecular weight. The weight-average molecular weight of the sample was calculated based on a calibration curve prepared in advance using gel chromatography (GPC apparatus (CO-8010) manufactured by Tosoh Corporation, analytical column: "GMHXL" + "G3000HXL"). The calibration curve was prepared using several types of monodisperse polystyrene (monodisperse polystyrene manufactured by Tosoh Corporation; 2.63 x 103, 2.06 x 10 4 , 1.02×10 5 (Mw): Monodisperse polystyrene manufactured by GL Sciences Inc.; 2.10×10 3 , 7.00×10 3 , 5.04×10 4 (Mw)] was used as a standard sample.

[0067] (5) Average particle size of water-based pigment dispersion Using a laser particle analysis system (Otsuka Electronics Co., Ltd., product name: ELS-8000), the average particle size of the water-based pigment dispersion was measured by dynamic light scattering, and calculated by cumulant analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements, and the refractive index of water (1.333) was entered as the refractive index of the dispersion solvent. For the measurement sample, the water-based pigment dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5) and the solids concentration was 2 x 10 -4 Water was added so as to obtain the desired mass %, and the mixture was stirred at 25° C. for 1 hour using a magnetic stirrer.

[0068] (6) Solid content concentration 10.0 g of sodium sulfate, which had been kept constant in a desiccator, was weighed out into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample was added and mixed, then weighed, and the mixture was kept at 105°C for 2 hours to remove volatile matter, and the mixture was left in the desiccator for another 15 minutes and the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content, and was divided by the mass of the sample added to obtain the solid content concentration.

[0069] (7) pH The pH of the aqueous pigment dispersion at 20° C. was measured using a tabletop pH meter (manufactured by Horiba, Ltd., product name: F-71) equipped with a pH electrode (manufactured by Horiba, Ltd., product name: 6337-10D).

[0070] (8) Ink viscosity The viscosity was measured at 32° C. using an E-type viscometer (model: TV-25, manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34'×R24, rotation speed 100 rpm).

[0071] Production Examples 1 to 7, and Comparative Production Example 1 (Production of Polyester Resins P1 to P7 and CP1) Into a 10 L four-neck flask equipped with a thermometer, a stainless steel stirring rod, a rectification column into which 95°C hot water was flowed, a downflow condenser having a dehydration tube, and a nitrogen inlet tube, the raw material monomers other than fumaric acid (FA) (carboxylic acid components and alcohol components), di(tin(II)2-ethylhexanoate) as an esterification catalyst, and gallic acid were placed as shown in Table 1, and the temperature was raised to 235°C using a mantle heater while stirring (300 rpm) under a nitrogen atmosphere and atmospheric pressure, and the reaction was carried out for 5 hours, after which the pressure in the flask was reduced to 8.3 kPa and maintained for 1 hour. After that, it was cooled to 180°C and returned to atmospheric pressure, then fumaric acid (FA) and 4-t-butylcatechol were added and the temperature was raised to 210°C and reacted for 1 hour, after which the pressure inside the flask was lowered to 8.3 kPa and the reaction was continued until the softening point reached the temperature shown in Table 1, to obtain polyester resins P1 to P7 and CP1. The results are shown in Table 1.

[0072] The details of the components shown in Table 1 are as follows: (Carboxylic acid component) ·TPA: Terephthalic acid FA: Fumaric acid Compound represented by formula (1): Arakawa Chemical Industries, Ltd., product name "Pine Crystal KE-604B" (acrylated rosin, softening point 129°C) (Alcohol content) 1,2-PD: 1,2-propanediol ·TMP: Trimethylolpropane ·BPA-PO: Polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane ·MPD: 3-Methyl-1,5-pentanediol

[0073] [Table 1]

[0074] Example I-1 (Preparation of Water-Based Pigment Dispersion 1) (1) Step 1 (pigment dispersion step) In a 2L vessel, 66.7g of polyester resin P1 was dissolved in 198.6g of methyl ethyl ketone (MEK), and then 6.70g of 5N aqueous sodium hydroxide solution (85% neutralized by mole) was added. 390.5g of ion-exchanged water was added dropwise over 30 minutes, and the mixture was stirred and mixed at 10-15°C for 15 minutes at 1,500 r / min using a disperser blade. Next, 100 g of carbon black (manufactured by Cabot Corporation, product name: Monarch 717) was added, and the mixture was stirred and mixed at 10 to 15° C. for 2 hours at 6,500 r / min using a disperser blade to obtain a preliminary dispersion. The obtained preliminary dispersion was filtered through a 200 mesh filter and diluted with 36.1 g of ion-exchanged water. The mixture was then subjected to 15 passes of dispersion treatment at a pressure of 150 MPa using a Microfluidizer (Microfluidics Corporation, high-pressure homogenizer: M-110EH-30XP) to obtain an aqueous dispersion of pigment-containing polyester resin particles. (2) Process 2 (concentration process) The entire amount of the aqueous dispersion obtained in step 1 was placed in a 2 L eggplant flask, ion-exchanged water was added so that the solid concentration was 15%, and the organic solvent was removed by holding the mixture at a pressure of 0.09 MPa (abs) for 3 hours in a warm bath adjusted to 32°C at a rotation speed of 50 r / min using a rotary distillation apparatus (Tokyo Rikakikai Co., Ltd., rotary evaporator: N-1000S). The temperature of the warm bath was further adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration reached 25%, to obtain a concentrate. The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r / min for 20 minutes using a centrifuge (Hitachi Koki Co., Ltd., high-speed refrigerated centrifuge: himac CR22G, set temperature 20°C). The liquid phase was then filtered through a membrane filter with a pore size of 5 μm (Sartorius, Minisart) and diluted with water to a solids concentration of 22%, yielding an aqueous pigment dispersion 1 of pigment-containing polyester resin particles (pigment: 13.2%, polyester resin: 8.8%).

[0075] Examples I-2 to I-7 and Comparative Example I-1 Water-based pigment dispersions 2 to 7 and C1 of pigment-containing polyester resin particles were obtained in the same manner as in Example I-1, except that the amounts of polyester resin and aqueous sodium hydroxide solution added were changed as shown in Table 2.

[0076] Example I-8 In Example I-3, 100 g of ion-exchanged water was used instead of 100 g of carbon black, and the solid content concentration was adjusted to 26%, but the same procedure was followed as in Example I-3 to obtain an aqueous dispersion 8 of polyester resin particles that did not contain a pigment (pigment: 0%, polyester resin: 26%). Into a glass container were mixed 500 g of CAB-O-JET200 (self-dispersible carbon black manufactured by Cabot Corporation) (solid content 20%: carbon black 100 g, water 400 g) and 257 g of the aqueous dispersion 8 of pigment-free polyester resin particles obtained in Example I-8 (pigment-free polyester resin particles 66.8 g, water 190.2 g) to obtain aqueous pigment dispersion 8 containing pigment-free polyester resin particles and pigment particles.

[0077] The storage stability of the obtained water-based pigment dispersions 1 to 8 and C1 was evaluated by the following method. The results are shown in Table 2.

[0078] (Evaluation of storage stability) Within one day after production, the aqueous pigment dispersions of the Examples and Comparative Examples were diluted with ion-exchanged water to a solids concentration of 0.25%, weighed into a screw tube (model number: No. 5, manufactured by Maruemu Co., Ltd.), and stirred with a magnetic stirrer at 25°C for 1 hour to obtain a sample (α) for measuring the number of coarse particles. The obtained sample (α) for measuring the number of coarse particles was injected into a dynamic light scattering particle size distribution analyzer (manufactured by Japan Entegris LLC, product name: AccuSizer780APS) using a 5 mL syringe, and the number of particles was measured at a measurement temperature of 25°C by a number counting method. The measurement range of particle size by the number counting method is 0.51 μm to 483.42 μm. The number of coarse particles was defined as the number of particles of 0.51 μm or more per mL of an aqueous pigment dispersion with a solid content of 20%. Next, the aqueous pigment dispersion was left at 60° C. for 4 weeks, which was a condition simulating the storage state of the aqueous pigment dispersion, and diluted with ion-exchanged water in the same manner as above to obtain a sample (β) for measuring the number of coarse particles. The number of particles of 0.51 μm or more was also measured for the obtained sample (β) for measuring the number of coarse particles by the number counting method using the above-mentioned measuring device. The rate of increase in the number of coarse particles (%) was calculated by the following formula, and the rate of increase in the number of coarse particles was ranked according to the following criteria. Increase rate of coarse particle number (%) = [[Number of particles of 0.51 μm or more per 1 mL of aqueous pigment dispersion (β) with a solid content of 20%]] / [Number of particles of 0.51 μm or more per 1 mL of aqueous pigment dispersion (α) with a solid content of 20%]] - 1] x 100 [Evaluation Criteria] 4: The increase in the number of coarse particles is less than 5%. 3: The increase rate of the number of coarse particles is 5% or more and less than 10%. 2: The increase rate in the number of coarse particles is 10% or more and less than 100%. 1: The increase in the number of coarse particles is 100% or more. The smaller the rate of increase in the number of coarse particles, the more excellent the storage stability of the water-based pigment dispersion.

[0079] [Table 2]

[0080] From Table 2, it can be seen that the water-based pigment dispersions obtained in the Examples have a smaller increase rate in the number of coarse particles and are superior in storage stability compared to the water-based pigment dispersions obtained in the Comparative Examples.

[0081] Examples II-1 to II-8 and Comparative Example II-1 (Production of Water-Based Inks 1 to 8 and C1) As shown in Table 3, the aqueous pigment dispersion, the water-soluble organic solvent, the surfactant, and the ion-exchanged water were mixed, and the resulting mixture was filtered through a membrane filter having a pore size of 5 μm (Minisart, manufactured by Sartorius) to obtain aqueous inks 1 to 8 and C1.

[0082] Details of the components shown in Table 3 are as follows: (Organic solvent) iBDG: Diethylene glycol monoisobutyl ether ·PG: Propylene glycol (Surfactant) KF-6011: Shin-Etsu Chemical Co., Ltd., product name "KF-6011", silicone surfactant (alkylene glycol modified polydimethylsiloxane)

[0083] The resulting water-based ink was evaluated for ejection stability, abrasion resistance, and alcohol resistance after being left unused for a long period of time by the following methods. The results are shown in Table 3.

[0084] (Evaluation of ejection stability after a long period of unused state) The water-based inks obtained in the examples and comparative examples were stored for 4 weeks at 60° C., simulating conditions of long-term storage. In an environment of room temperature 25±1° C. and relative humidity 50±5%, a direct T-shirt printer (manufactured by Mastermind Corporation, product name: MMP8130, 4-color model) was filled with the water-based inks stored under the above-mentioned conditions of 60° C. and 4 weeks, a nozzle check pattern was printed on plain paper, and the number of missing nozzles was visually counted. If there were 11 or more missing nozzles, cleaning was performed, the nozzle check pattern was printed again, and the number of missing nozzles was measured. This procedure was repeated until the number of missing nozzles was 10 or less. [Evaluation Criteria] 4: The initial nozzle check pattern shows 10 or fewer missing nozzles. 3: The nozzle check pattern after the first cleaning has 10 or fewer missing nozzles. 2: The nozzle check pattern after the second cleaning has 10 or fewer missing nozzles. 1: More than 10 missing nozzles are found in the nozzle check pattern after the second cleaning. An evaluation result of 3 or more indicates excellent ejection stability after being left unused for a long period of time, while an evaluation result of 2 or less indicates poor ejection stability after being left unused for a long period of time.

[0085] (Evaluation of Scratch Resistance) A direct T-shirt printer (Mastermind, product name: MMP8130, 4-color model) with an A4-sized film heater (Kawai Electric Manufacturing Co., Ltd.) attached was filled with the water-based inks of the Examples and Comparative Examples. A white polyvinyl chloride film (PVC, 3M Japan, product name: IJ180-10) was prepared as a printing substrate. The printing substrate was heated from below with a film heater set at a temperature of 50°C, and a solid image was printed with a duty of 100% in the printing mode: white fabric direct, 1440 x 1440 dpi, and the print was dried by heating in a constant temperature dryer at 80°C for 5 minutes to prepare a print for evaluation. The 100% solid printed surface of the obtained print for evaluation was applied to a cellulose nonwoven fabric (manufactured by Asahi Kasei Fibers Corporation, product name: BEMCOT (registered trademark) M3-II) at 100 g / cm 2 After rubbing, the printed surface was visually inspected for damage (scratches), and the abrasion resistance was evaluated according to the following criteria. [Evaluation Criteria] 4: There are no scratches on the printed surface, and no reduction in gloss is observed. 3: There are no scratches on the printed surface, but the glossiness has decreased visually. 2: There are scratches on the printed surface, but the film surface is not exposed. 1: The printed surface has peeled off and the area of ​​exposed film is less than 50% of the printed area. The higher the evaluation criterion value, the fewer scratches on the printed surface and the better the abrasion resistance.

[0086] (Evaluation of alcohol resistance) The same printed matter used in the evaluation of the abrasion resistance was prepared as a printed matter for evaluation of alcohol resistance. Furthermore, aqueous ethanol solutions were prepared with concentrations ranging from 10 to 100% by mass in increments of 10% by mass. The ethanol solution was soaked into a Johnson & Johnson cotton swab, and a load of 5 g was applied to a solid print, which was rubbed back and forth 10 times across the printed surface. When no change occurred to the printed surface during the test, the ethanol concentration in the ethanol solution was used to evaluate the alcohol resistance according to the following criteria. [Evaluation Criteria] 5: The ethanol concentration is 100%. 4: The ethanol concentration is greater than 70% and less than 100%. 3: The ethanol concentration is greater than 50% and less than 70%. 2: The ethanol concentration is greater than 30% and less than 50%. 1: The ethanol concentration is less than 30%. A higher value on the evaluation scale indicates higher alcohol resistance.

[0087] [Table 3]

[0088] From Table 3, it can be seen that the aqueous inks obtained in the Examples have superior ejection stability after being unused for a long period of time compared to the aqueous inks obtained in the Comparative Examples. It can also be seen that the aqueous inks obtained in the Examples can provide recorded matter with superior abrasion resistance and alcohol resistance compared to the aqueous inks obtained in the Comparative Examples, even when printed on printing media with low liquid absorption.

Claims

1. An aqueous pigment dispersion containing a pigment and a polyester resin, The aqueous pigment dispersion contains a carboxylic acid component, which is a structural unit of the polyester resin, containing a compound represented by the following formula (1): 【Chemical 1】 (X and Y each represent a hydrogen atom, a carboxy group, or a hydrocarbon group, provided that at least one of X and Y is a carboxy group.)

2. The water-based pigment dispersion according to claim 1 , wherein the compound represented by formula (1) is an acrylated rosin.

3. 2. The water-based pigment dispersion of claim 1, wherein the pigment is in the form of pigment-containing polyester resin particles.

4. 4. The water-based pigment dispersion according to claim 1, wherein the content of the compound represented by formula (1) in the carboxylic acid component that is a structural unit of the polyester resin is 5 mol % or more and 100 mol % or less.

5. The aqueous pigment dispersion according to claim 1 or 3, wherein the alcohol component that is a structural unit of the polyester resin comprises at least one selected from the group consisting of an aliphatic diol, an aliphatic triol, and an aromatic diol.

6. 4. The aqueous pigment dispersion according to claim 1, further comprising, as a carboxylic acid component which is a structural unit of the polyester resin, at least one selected from the group consisting of an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid other than the compound represented by formula (1), and a trivalent or higher polycarboxylic acid.

7. The water-based pigment dispersion according to claim 1 or 3, wherein the polyester resin has an acid value of 5 mgKOH / g or more and 100 mgKOH / g or less.

8. The water-based pigment dispersion according to claim 1 or 3, wherein the polyester resin has a glass transition temperature of 35°C or higher and 105°C or lower.

9. A water-based ink comprising the water-based pigment dispersion according to claim 1 or 3 and a water-soluble organic solvent.

10. The water-based ink described in claim 9, used for inkjet recording.

11. A water-based ink as described in claim 9, used for printing on a low-absorbency recording medium.

12. A pigment-containing polyester resin particle, comprising: The polyester resin particles contain a pigment, and the carboxylic acid component, which is a structural unit of the polyester resin, contains a compound represented by the following formula (1): 【Chemistry 2】 (X and Y each represent a hydrogen atom, a carboxy group, or a hydrocarbon group, provided that at least one of X and Y is a carboxy group.) 13. A method for producing polyester resin particles containing the pigment according to claim 12, comprising: A method for producing pigment-containing polyester resin particles, comprising the following steps 1 and 2: Step 1: A step of obtaining a polyester resin by polycondensing a carboxylic acid component containing at least a compound represented by the following formula (1) with an alcohol component: Step 2: A step of dispersing a pigment mixture containing a pigment, the polyester resin obtained in Step 1, and water to obtain an aqueous pigment dispersion containing polyester resin particles containing a pigment. 【Chemistry 3】 (X and Y each represent a hydrogen atom, a carboxy group, or a hydrocarbon group, provided that at least one of X and Y is a carboxy group.)

14. A water-based ink containing polyester resin particles containing the pigment described in claim 12 and a water-soluble organic solvent.

Images