Pigment water dispersion

Abstract

To provide a pigment water dispersion capable of obtaining a recorded matter excellent in re-dispersibility, and excellent in scratch resistance and solvent resistance in a coated paper with low liquid absorption and a non-absorbent resin film and an aqueous ink containing the pigment water dispersion.SOLUTION: There are provided: a pigment water dispersion that contains polyester resin and a pigment and in which, in a chromatogram of a molecular weight distribution measured by gel permeation chromatography of the polyester resin, an area corresponding to a component having a molecular weight of 1000 or less is 5% or less of a total area; and an aqueous ink comprising the pigment water dispersion and an aqueous organic solvent.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pigment water dispersion and a water-based ink containing the pigment water dispersion. [Background technology]

[0002] Inkjet recording is a method of directly ejecting ink droplets from minute nozzles and depositing them on a recording medium to obtain a recorded matter with characters and images. This method has become extremely popular due to its many advantages, including the ease and low cost of producing full-color images, the ability to use plain paper as a recording medium, and the fact that it does not come into contact with the recording medium. 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 problems in that storage stability and ejection properties are deteriorated due to the generation of coarse particles resulting from insufficient dispersion stability of pigments and polymers. In addition, ink printed on low-absorbency coated paper or non-absorbent resin film is difficult to penetrate into the substrate, and thus the resulting recorded matter has poor abrasion resistance and solvent resistance.

[0003] Therefore, various proposals have been made to improve the ejection stability and abrasion resistance. Patent Document 1 discloses an aqueous ink for inkjet recording that has excellent ink ejection properties, excellent image fixation onto a non-absorbent recording medium, and excellent gloss of printed matter, even though it is an aqueous ink, and that contains pigment particles and polyester resin particles, the pigment particles contain the pigment and polyester resin (A) in a specific mass ratio, and the mass ratio of the pigment in the pigment particle to the total amount of the polyester resin (A) constituting the polyester resin particles and the polyester resin (B) constituting the polyester resin particles is within a specific range, with the object of providing an aqueous ink for inkjet recording that has excellent ejection properties, excellent image fixation onto a non-absorbent recording medium, and excellent gloss of printed matter, even though it is an aqueous ink. Patent Document 2 discloses an aqueous pigment dispersion of polyester resin particles containing a pigment, the aqueous pigment dispersion containing 3-methyl-1,5-pentanediol as an alcohol component, which is a constituent unit of the polyester resin, and an aqueous ink containing the aqueous pigment dispersion and a water-soluble organic solvent, with the objective of providing an aqueous pigment dispersion excellent in dispersion stability and redispersibility after long-term storage, and an aqueous ink capable of giving recorded matter excellent in long-term dispersion stability, as well as excellent in adhesion to a substrate, abrasion resistance, and solvent resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-28114 A [Patent Document 2] JP 2022-151760 A Summary of the Invention [Problem to be solved by the invention]

[0005] In commercial printing or industrial printing using an inkjet recording method, pigment water dispersions and inks are generally supplied to the ejection nozzles via a main tank, a sub-tank, and an ink cartridge, but the ink becomes concentrated near the ejection nozzles due to the evaporation of water and solvents. In concentrated inks, pigment particles tend to aggregate and are difficult to redisperse, resulting in a problem of poor ejection properties. On the other hand, inks printed on low-absorbency coated paper or non-absorbent resin films have the problem that the adhesive strength of the printed coating to the recording medium is insufficient, resulting in poor abrasion resistance of the resulting recorded matter. Moreover, in recent years, there has been a demand for improved solvent resistance so that printed matter can exhibit durability against solvents such as alcohol used for disinfection purposes. The water-based inks disclosed in Patent Documents 1 and 2 and conventional water-based inks are insufficient in terms of both redispersibility and abrasion resistance of recorded matter, and improvements thereto have been desired. An object of the present invention is to provide a pigment water dispersion which is excellent in redispersibility and which can give recorded matter which is excellent in abrasion resistance and solvent resistance on low-liquid-absorbent coated paper, non-liquid-absorbent resin film, and the like, and a water-based ink containing the pigment water dispersion. [Means for solving the problem]

[0006] The inventors have discovered that by using a polyester resin in which the area corresponding to components with a molecular weight of 1000 or less accounts for 5% or less of the total area in a molecular weight distribution chromatogram measured by gel permeation chromatography, the resin has high redispersibility and provides excellent abrasion resistance and solvent resistance of the coating surface after printing and drying, thereby solving the above-mentioned problems. That is, the present invention provides the following [1] and [2]. [1] A pigment water dispersion containing a polyester resin and a pigment, wherein in a chromatogram of the molecular weight distribution of the polyester resin measured by gel permeation chromatography, the area corresponding to components having a molecular weight of 1,000 or less accounts for 5% or less of the total area. [2] A water-based ink comprising the pigment water dispersion described in [1] above and a water-soluble organic solvent. Effect of the Invention

[0007] According to the present invention, it is possible to provide a pigment water dispersion which is excellent in redispersibility and which can give recorded matter which is excellent in abrasion resistance and solvent resistance on low-liquid-absorbent coated paper, non-liquid-absorbent resin film, and the like, and a water-based ink containing the pigment water dispersion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Pigment water dispersion] The pigment water dispersion of the present invention (hereinafter also simply referred to as "pigment water dispersion") is a pigment water dispersion containing a polyester resin and a pigment, and in the polyester resin, the area corresponding to components having a molecular weight of 1,000 or less accounts for 5% or less of the total area in a chromatogram of molecular weight distribution measured by gel permeation chromatography (hereinafter also simply referred to as "GPC"). In this specification, the term "pigment water dispersion" 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:

[0009] The pigment water dispersion of the present invention can provide a pigment water dispersion that is excellent in redispersibility and can give recorded matter that is excellent in abrasion resistance and solvent resistance on a low-absorbency recording medium such as a low-absorbency coated paper or a non-absorbent resin film, and a water-based ink containing the pigment water dispersion. The reason for this is not clear, but is thought to be as follows. When the polyester resin contained in the pigment water dispersion is a polyester resin in which the area corresponding to components with a molecular weight of 1000 or less is 5% or less of the total area in a chromatogram of the molecular weight distribution measured by GPC, the amount of the polyester resin not adsorbed to the pigment is reduced because the low molecular weight components with poor adsorption power to the pigment are reduced, and the effect of the so-called depletion aggregation action that occurs when the ink is concentrated is reduced, and the aggregation of the pigment particles is suppressed, thereby enabling high redispersibility to be exhibited. In addition, the polyester resin increases the affinity between the coating film obtained by drying the water-based ink and the low liquid-absorbent recording medium, improving the abrasion resistance, and further, since the polyester resin is difficult to swell in alcohols such as ethanol and isopropyl alcohol, the solvent resistance to alcohol and the like is improved. In particular, by including a polyester resin with a reduced amount of low molecular weight components, the weakening of the printed coating film is suppressed, resulting in a coating film with excellent abrasion resistance and solvent resistance.

[0010] <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, and pearlescent pigments. In particular, carbon black is preferred for black inks. 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.

[0011] 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. In the pigment water dispersion and water-based ink of the present invention, from the viewpoint of exerting the effects of the present invention, it is preferable to use an inorganic pigment, in particular carbon black, as the pigment.

[0012] (Pigment-containing polyester resin particles) The pigment and polyester resin used in the present invention are preferably in the form of polyester resin particles containing a pigment, from the viewpoints of improving the redispersibility of the pigment water dispersion and improving the abrasion resistance of a coating film obtained from an aqueous ink using the pigment water dispersion of the present invention to a low liquid-absorbent recording medium and solvent resistance. The polyester resin will be described later. In this specification, "polyester resin particles containing a pigment" (hereinafter also referred to as "pigment-containing resin particles") includes particles in a form in which the polyester resin contains the pigment, in a form in which part of the pigment is exposed on the surface of a particle consisting of the polyester resin and the pigment, in a form in which the polyester resin is adsorbed to part of the pigment, and particles in a mixture of these forms, with the form of polyester resin particles containing the pigment being more preferred.

[0013] <Polymer a constituting polyester resin particles containing pigment> The polymer constituting the pigment-containing polyester resin particles (hereinafter also referred to as "polymer a") is not particularly limited as long as it has at least the ability to disperse the pigment, but is preferably a water-insoluble polymer. Here, the term "water-insoluble" for polymer a means that when the polymer is dried at 105° C. for 2 hours and reaches a constant weight, and then dissolved in 100 g of water at 25° C., the amount of dissolution is 10 g or less, and the amount of dissolution of polymer a is preferably 5 g or less, and more preferably 1 g or less. When polymer a is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

[0014] <Polyester resin> The polyester resin used in the present invention contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and can be obtained by polycondensation of the alcohol component and the carboxylic acid component.

[0015] (Alcohol content) The alcohol component, which is a raw material monomer for the polyester resin, preferably contains one or more selected from the group consisting of aliphatic diols, aromatic diols, and alicyclic diols, and more preferably contains one or more selected from the group consisting of aliphatic diols and aromatic diols, from the viewpoints of improving the dispersion stability of the pigment and improving the redispersibility, abrasion resistance, and the like of a water-based ink using the pigment water dispersion of the present invention after it has been concentrated, and of improving the ejection properties of the ink after long-term storage.

[0016] As the aliphatic diol, a linear diol and an aliphatic diol having an alkyl group on the side chain are preferred. As the alkyl group on the side chain, a methyl group is more preferred. As a specific example of the aliphatic diol, one or more selected from the group consisting of 1,2-propanediol, 2,3-butanediol, 2,4-pentanediol, 2,5-hexanediol, 2,6-heptanediol, 2,7-octanediol, and 3-methyl-1,5-pentanediol are preferred, one or more selected from the group consisting of 1,2-propanediol, 2,3-butanediol, and 3-methyl-1,5-pentanediol are more preferred, and 1,2-propanediol and 3-methyl-1,5-pentanediol are even more preferred.

[0017] It is believed that in an aliphatic diol having a methyl group on the side chain, the methyl group on the side chain adsorbs to the pigment like an anchor, making it difficult for the polyester resin to detach from the pigment even when the polyester resin is stored for a long period of time, making the polyester resin stable and suppressing the generation of coarse particles due to aggregation. When 1,2-propanediol and 3-methyl-1,5-pentanediol are used in combination, the content of 3-methyl-1,5-pentanediol in the alcohol component is, from the same viewpoint as above, preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less. When 1,2-propanediol and 3-methyl-1,5-pentanediol are used in combination, the content of 1,2-propanediol in the alcohol component is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, and preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less.

[0018] The aromatic diol is preferably one or more selected from the group consisting of an alkylene oxide adduct of bisphenol A and hydrogenated bisphenol A, and more preferably an alkylene oxide adduct of bisphenol A. The alkylene oxide adduct of bisphenol A is a compound having a structure 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, and two or more of these compounds may be used in combination within the scope of the compound. [ka] 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. The alkylene oxide adduct of bisphenol A is preferably at least one selected from the group consisting of a propylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A. When an alkylene oxide adduct of bisphenol A is used, the content of the alkylene oxide adduct of bisphenol A in the alcohol component is, from the viewpoint of manifesting the effects of the present invention, preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, still more preferably 90 mol % or more, and preferably 100 mol % or less.

[0019] The alicyclic diol is preferably at least one selected from the group consisting of 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and hydrogenated bisphenol A, and more preferably 1,4-cyclohexanediol.

[0020] The alcohol component, which is a raw material monomer for the polyester resin, may contain an alcohol component other than the aliphatic diol, aromatic diol, and alicyclic diol. Examples of other alcohol components include glycerin, pentaerythritol, trimethylolpropane, sorbitol, and alkylene (having 2 to 4 carbon atoms) oxide adducts thereof (average number of moles added: 1 to 16). The alcohol components can be used alone or in combination of two or more.

[0021] (Carboxylic acid component) The carboxylic acid component, which is a raw material monomer of the polyester resin, includes carboxylic acid, its acid anhydride, and its alkyl (having 1 to 3 carbon atoms) ester. The carboxylic acid component, which is a structural unit of the polyester resin, preferably contains one or more selected from the group consisting of aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trivalent or higher polycarboxylic acids, from the viewpoint of improving redispersibility and abrasion resistance after concentration of an aqueous ink using the pigment water dispersion of the present invention, and from the viewpoint of improving the ejection properties of the ink after long-term storage. More preferably, the polyester resin contains one or more selected from the group consisting of aromatic dicarboxylic acids and aliphatic dicarboxylic acids. The aromatic dicarboxylic acid is preferably at least one selected from the group consisting of phthalic acid, isophthalic acid, and terephthalic acid, and more preferably terephthalic acid. The aliphatic dicarboxylic acid is preferably a linear or branched aliphatic dicarboxylic acid, and the number of carbon atoms is preferably 2 or more, more preferably 4 or more, even more preferably 8 or more, and still more preferably 10 or more, and is preferably 22 or less, more preferably 16 or less. Examples of linear or branched aliphatic dicarboxylic acids include oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, succinic acid substituted with an aliphatic hydrocarbon group having 1 to 20 carbon atoms, or anhydrides or alkyl esters thereof having 1 to 3 carbon atoms. Examples of succinic acid substituted with an aliphatic hydrocarbon group having 1 to 20 carbon atoms include dodecylsuccinic acid, dodecenylsuccinic acid, and octenylsuccinic acid. Among these, fumaric acid is preferred. The alicyclic dicarboxylic acid is preferably at least one selected from the group consisting of cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid. As the trivalent or higher polyvalent carboxylic acid, at least one selected from the group consisting of trimellitic acid and pyromellitic acid is preferred, and trimellitic anhydride is also preferred. The carboxylic acid components may be used alone or in combination of two or more kinds.

[0022] (Production of polyester resin) The polyester resin can be obtained by polycondensing the alcohol component and the carboxylic acid component in an appropriate combination, for example, by polycondensing the alcohol component and the carboxylic acid 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.

[0023] (Physical properties of polyester resin) The polyester resin preferably has an acid group, from the viewpoints of improving the dispersion stability of the pigment and improving the redispersibility after long-term storage, long-term dispersion stability, abrasion resistance, etc. of a water-based ink using the pigment water dispersion of the present invention. The acid value of the polyester resin is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, even more preferably 60 mgKOH / g or less, still more preferably 40 mgKOH / g or less, even more preferably 35 mgKOH / g or less. From the same viewpoints as above, the softening point of the polyester resin is preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and preferably 180°C or lower, more preferably 160°C or lower, even more preferably 150°C or lower.

[0024] From the same viewpoints as above, the glass transition temperature of the polyester resin is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower. From the same viewpoints as above, the weight average molecular weight of the entire polyester resin is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 9,000 or more, still more preferably 11,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, even more preferably 60,000 or less, and still more preferably 40,000 or less. From the same viewpoints as above, the number average molecular weight of the entire polyester resin is preferably 2,000 or more, more preferably 2,500 or more, even more preferably 3,000 or more, and preferably 10,000 or less, more preferably 9,000 or less, even more preferably 8,000 or less. The acid value, softening point, glass transition temperature, weight average molecular weight, and number average molecular weight of the polyester resin can be measured by the method described in the Examples. These physical properties can be adjusted as desired by appropriately adjusting and selecting the type and blending ratio of the monomers used, the polycondensation temperature, the reaction time, and the purification method for removing low molecular weight components.

[0025] The pigment aqueous dispersion of the present invention contains a polyester resin and a pigment, and in a chromatogram of the molecular weight distribution of the polyester resin measured by gel permeation chromatography (GPC), the area corresponding to components having a molecular weight of 1,000 or less accounts for 5% or less of the total area.

[0026] It is preferable that the low-molecular-weight component of the polyester resin contains few components with a molecular weight of 1,000 or less, from the viewpoints of redispersibility of a concentrated ink obtained by concentrating an aqueous ink using the pigment water dispersion of the present invention, abrasion resistance to a low-liquid-absorbent recording medium, and solvent resistance.

[0027] In terms of redispersibility of concentrated ink, abrasion resistance to a low-absorbent recording medium, and solvent resistance, the polyester resin contained in the pigment water dispersion of the present invention has an area corresponding to components having a molecular weight of 1,000 or less that is 5% or less of the total area in a chromatogram of molecular weight distribution measured by gel permeation chromatography, preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, and still more preferably 1% or less.

[0028] <Method for reducing low molecular weight components in polyester resin> The low molecular weight components of the polyester resin can be reduced by adjusting the production conditions of a known production method, but can also be reduced by commonly known methods such as dialysis, gel filtration, ultrafiltration, precipitation, etc. From the viewpoints of cost and versatility, the method for reducing the low molecular weight components of the polyester resin is preferably one or more selected from the group consisting of adjustment of production conditions, ultrafiltration, and precipitation.

[0029] (Production of pigment-containing resin particles) The pigment-containing resin particles can be efficiently produced as a pigment aqueous dispersion by a method including the following step 1. If necessary, a crosslinking step can be further carried out. Step 1: A step of dispersing a pigment mixture containing a pigment, a polymer a, water, and, if necessary, a neutralizing agent, a surfactant, etc., to obtain a pigment water dispersion of polyester resin particles containing a pigment (pigment-containing resin particles).

[0030] ≪Process 1≫ Polymer a preferably has a carboxy group derived from a carboxylic acid component, and from the viewpoint of improving the dispersion stability, abrasion resistance, etc. of the resulting pigment water dispersion and of the water-based ink using the pigment water dispersion of the present invention, it is more preferable that at least a part of the carboxy group is neutralized with a neutralizing agent. In the case of neutralization, it is preferable to neutralize so that the pH is 7 or more and 10 or less. The pH is measured by the method described in the Examples. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, and one or more selected from the group consisting of sodium hydroxide and ammonia are preferred. Polymer a may be neutralized in advance. From the same viewpoints as above, the amount of the neutralizing agent used is preferably 20 mol % or more, more preferably 40 mol % or more, even more preferably 50 mol % or more, and is preferably 200 mol % or less, more preferably 150 mol % or less, even more preferably 120 mol % or less. Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where polymer a before neutralization is "polymer a'". Equivalent amount of neutralizing agent used (mol%)=[{weight of neutralizing agent added (g) / equivalent amount of neutralizing agent} / [{acid value of polymer a' (mg KOH / g) × weight of polymer a' (g)} / (56 × 1,000)]] × 100

[0031] 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, from the viewpoint of obtaining a uniform pigment aqueous dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main 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.

[0032] 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 pigment aqueous dispersion can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure 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.

[0033] When the pigment mixture contains an organic solvent, the organic solvent can be removed by a known method to obtain a pigment aqueous dispersion. From the viewpoint of improving the dispersion stability of the pigment water dispersion and facilitating the production of the ink, the solid content concentration of the pigment water 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. From the viewpoint of improving storage stability and redispersibility, the average particle size of the pigment-containing resin particles in the pigment water dispersion is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 170 nm or less, and still more preferably 150 nm or less. The average particle size is measured by the method described in the Examples. From the viewpoints of storage stability, reduced corrosiveness, etc., the pH of the pigment water dispersion at 20° C. is 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.

[0034] <Content of each component in pigment water dispersion> The contents of the respective components in the pigment water dispersion of the present invention are as follows, from the viewpoint of improving the dispersion stability, redispersibility, abrasion resistance, etc. of the resulting pigment water dispersion and of a water-based ink using the pigment water dispersion. The content of the pigment in the pigment water 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, still more preferably 8% by mass or more, even more preferably 10% by mass or more, and is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. The content of the pigment-containing resin particles in the pigment water dispersion of the present invention is preferably 3% by mass or more, more preferably 6% by mass or more, even more preferably 10% by mass or more, still more preferably 13% by mass or more, even more preferably 15% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. The content of the polyester resin (polymer a) in the pigment water dispersion of the present invention is preferably 1 mass % or more, more preferably 2 mass % or more, even more preferably 3 mass % or more, still more preferably 4 mass % or more, and is preferably 15 mass % or less, more preferably 12 mass % or less, and even more preferably 10 mass % or less.

[0035] The mass ratio of the pigment to the mass of the pigment-containing resin particles in the pigment water dispersion of the present invention (pigment / pigment-containing resin particles) is, from the viewpoint of improving the dispersion stability of the pigment water dispersion and of facilitating the production of the ink, 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-containing resin particles) can be calculated from the charge amount ratio.

[0036] [Water-based ink] The water-based ink of the present invention contains the pigment water dispersion of the present invention and a water-soluble organic solvent. Here, "water-based" means that water accounts for the largest proportion by mass of the medium contained in the ink. The water-based ink of the present invention can be efficiently produced by mixing the above-obtained pigment water dispersion containing the pigment-containing resin particles, a water-soluble organic solvent, and, as necessary, water and various additives such as a surfactant. There is no particular limitation on the method for mixing the above components.

[0037] <Water-soluble organic solvent> The water-soluble organic solvent used in the water-based ink of the present invention may be liquid or solid at 25°C. When the water-soluble organic solvent is dissolved in 100 mL of water at 25°C, the amount of the dissolved water is 10 mL or more. The water-soluble organic solvents may be used alone or in combination of two or more. From the viewpoints of improving the wetting and spreading properties of the ink and improving the abrasion resistance of the resulting printed 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, still more preferably 140° C. or higher, and preferably 250° C. or lower, more preferably 245° C. or lower, even more preferably 240° C. or lower, and still more preferably 235° C. or lower. When two or more water-soluble organic solvents are used as the water-soluble organic solvent, the boiling point of the water-soluble organic solvent is a weighted average value weighted by the content (mass %) of each water-soluble organic solvent. Examples of the water-soluble organic solvent include glycol ethers such as alkylene glycol ethers, polyhydric alcohols such as ethylene glycol, 1,2-propanediol, and glycerin, amide compounds, etc. Among these, alkylene glycol ethers are preferred.

[0038] 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. Among these, from the viewpoints of improving the wetting and spreading properties of the ink and improving the abrasion resistance of the resulting printed matter, preferred are one or more selected from the group consisting of 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, more preferred are one or more selected from the group consisting of propylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and diethylene glycol monoisobutyl ether, and even more preferred are one or more selected from the group consisting of propylene glycol monobutyl ether, propylene glycol monopropyl ether, and dipropylene glycol monomethyl ether.

[0039] The water-based ink of the present invention preferably contains 1,2-propanediol in addition to the alkylene glycol ether. It is believed that 1,2-propanediol mainly functions to suppress the evaporation of water from the ink nozzle and to quickly volatilize after recording, thereby forming a strong ink film with a minimum drying process and preventing adhesion between the recorded surface and the back surface of the recorded surface.

[0040] <Surfactant> The water-based ink of the present invention may contain a surfactant from the viewpoints of maintaining an appropriate surface tension of the ink, improving the wettability of the ink to the recording medium, and improving the scratch resistance of the resulting printed matter. When the water-based ink of the present invention contains a surfactant, there are no particular limitations, but it preferably contains a nonionic surfactant, and more preferably contains a silicone-based surfactant. 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-6 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.

[0041] In the water-based ink of the present invention, it is also preferable to use an acetylene glycol surfactant in addition to the silicone surfactant. 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.

[0042] 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 and polyester; and 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.

[0043] <Content of each component in water-based ink> The content of each component in the water-based ink of the present invention is as follows, from the viewpoint of improving the dispersion stability, abrasion resistance, etc. of the water-based ink of the present invention. The pigment content in the water-based ink of the present invention 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. The content of pigment-containing resin particles in the water-based ink 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. The content of the polyester resin (polymer a) in the water-based ink of the present invention 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. The total content of water-soluble organic solvents in the water-based ink of the present invention 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. The water content in the water-based ink of the present invention is preferably 45% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and is preferably 85% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0044] From the viewpoint of facilitating the production of the water-based ink, the mass ratio of the pigment to the mass of the pigment-containing resin particles in the water-based ink of the present invention (pigment / pigment-containing resin particles) 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.

[0045] From the viewpoints of maintaining an appropriate surface tension of the ink, improving its wettability to a recording medium, and improving the scratch resistance of the resulting printed matter, the content of the silicone surfactant in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less.

[0046] <Physical properties of the water-based ink of the present invention> 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, from the viewpoint of improving long-term dispersion stability, abrasion resistance, etc. The viscosity of the water-based ink of the present invention at 32°C can be measured using an E-type viscometer. From the viewpoint of improving storage stability, the average particle size of the water-based ink of the present invention 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 of the water-based ink of the present invention is measured by the method described in the Examples.

[0047] The redispersibility of the water-based ink of the present invention can be evaluated by comparing the absorbance at a specific wavelength of the water-based ink immediately after preparation (absorption wavelength 550 nm for black ink, absorption wavelength 500 nm for white ink, and maximum absorption wavelength for color inks) with the absorbance at a specific wavelength of the ink obtained by concentrating the water-based ink and then redispersing it. In other words, if there is a small change in absorbance at a specific wavelength before and after concentrating the water-based ink, this means that the pigment-containing resin particles are dispersed as uniformly in the ink obtained by concentrating the water-based ink and then redispersing it, just as they were before the concentration, and it is clear that the redispersibility is excellent. In other words, the greater the rate of change (%) in absorbance at a specific wavelength before and after concentration of the water-based ink (100 x absorbance at a specific wavelength after concentration / absorbance at a specific wavelength before concentration), the better the redispersibility, and this value is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and still more preferably 95% or more. The rate of change in absorbance at a specific wavelength before and after concentration of the water-based ink, which serves as an index of redispersibility, is measured and evaluated by the method described in the examples.

[0048] The water-based ink of the present invention is preferably used for inkjet recording because it has excellent redispersibility after long-term storage and can provide recorded matter having excellent abrasion resistance and solvent resistance. 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, polyolefin, and nylon films. These films may be biaxially oriented, uniaxially oriented, or non-oriented films, and may be corona discharge-treated. Among these, polyethylene terephthalate (PET) films, polypropylene (PP) films, and polyvinyl chloride (PVC) films are preferred, and corona discharge-treated polyethylene terephthalate films, corona discharge-treated biaxially oriented polypropylene films, and white polyvinyl chloride films are more preferred. EXAMPLES

[0049] The methods for measuring the various physical properties in the Production Examples, Examples and Comparative Examples are as follows.

[0050] (1) Measurement of the acid value of polyester resin The acid value of the 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)].

[0051] (2) Measurement of the softening point of polyester resin 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 extruding the sample 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 resin.

[0052] (3) Measurement of glass transition temperature (Tg) of polyester resin Using a differential scanning calorimeter (Perkin Elmer, product name: Pyres 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 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.

[0053] (4) Measurement of weight average molecular weight and number average molecular weight of polyester resin The weight average molecular weight and number average molecular weight of the polyester resin were calculated by collecting data on the molecular weight distribution curve using a gel permeation chromatography measuring device [Tosoh Corporation, GPC device (HLC-8320GPC), Tosoh Corporation columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H), flow rate: 0.5 mL / min] with a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to a concentration of 60 mmol / L and 50 mmol / L, respectively, as the eluent, and converting the data into the molecular weight distribution curve using a monodisperse polystyrene kit with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), Tosoh Corporation] as a standard substance. The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and filtering with a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantec Co., Ltd.).

[0054] (5) Measurement of the content of components with molecular weight of 1,000 or less From the molecular weight distribution curve obtained during the measurement of the weight average molecular weight and number average molecular weight of the polyester resin (4), the total area I1 of the molecular weight distribution curve over the entire molecular weight measurement range and the area I2 of the molecular weight distribution curve corresponding to a molecular weight of 1000 or less were calculated, and the proportion of the area corresponding to a molecular weight of 1000 or less was calculated using the following formula. Content of components with molecular weight of 1000 or less (%) = (I2 / I1) x 100 The upper limit of the molecular weight measurement range was the exclusion limit molecular weight of the column used in the analysis, and the lower limit was 1 / 10 of the number average molecular weight of the standard sample used to create the calibration curve. The molecular weight distribution curve was obtained using an RI (differential refractive index) detector.

[0055] (6) Measurement of solids 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 thereto 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 15 minutes, after which 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 (mass%).

[0056] (7) Measurement of average particle size of pigment water dispersion and water-based ink The average particle size of the pigment water dispersion and the water-based ink was measured by dynamic light scattering using a laser particle analysis system (Otsuka Electronics Co., Ltd., product name: ELS-8000), 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 samples, the pigment water dispersion and the water-based ink were weighed into a screw tube (Maruemu Co., Ltd., No. 5) and the solids concentration was 2×10 -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.

[0057] (8) pH measurement The pH of the pigment aqueous 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).

[0058] (Production of polyester resin) Manufacturing Example 1 Into a 10 L four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser with a dehydration tube, and a nitrogen inlet tube, the raw material monomers (alcohol components and carboxylic acid components) other than fumaric acid (FA), an esterification catalyst (tin(II) di(2-ethylhexanoate)), and an esterification promoter (gallic acid) shown in Table 1 were placed, and the temperature was raised to 235°C using a mantle heater while stirring (300 rpm) under a nitrogen atmosphere and atmospheric pressure. The reaction was carried out for 5 hours, after which the pressure in the flask was reduced to 8.3 kPa and the mixture was stirred 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 in the flask was reduced to 8.3 kPa and the reaction was continued until the softening point reached the temperature shown in Table 1, yielding polyester resin P1. The results of measuring the resin physical properties are shown in Table 1.

[0059] Manufacturing Example 2 Polyester resin P2 was obtained in the same manner as in Production Example 1, except that the conditions in Production Example 1 were changed to those shown in Table 1. The results are shown in Table 1.

[0060] [Table 1]

[0061] The details of the components shown in Table 1 are as follows: (Alcohol content) 1,2-PD: 1,2-propanediol MPD: 3-methyl-1,5 pentanediol BPA-PO: Polyoxypropylene (2.2)-2,2-bis(4-hydroxyphenyl)propane TMP: Trimethylolpropane (Carboxylic acid component) TPA: Terephthalic acid FA: Fumaric acid

[0062] (Step for removing low molecular weight components) Manufacturing Examples 1-1 to 1-3 80g of polyester resin P1 was dissolved in 120g of methyl ethyl ketone (MEK) to obtain a polyester resin solution with a solid content concentration of 40% by mass. Then, the polyester resin solution was dropped into 10 times the amount of ethanol (2000g) at a rate of 10g / min while stirring the ethanol. After the dropwise addition was completed, the organic solvent was removed by vacuum filtration using a membrane filter (pore size 5μm, manufactured by Merck Millipore), and the residue on the membrane filter was dried in a vacuum dryer at 80°C for 48 hours to obtain a purified polyester resin A1. The same procedure was repeated except that the solids concentration of the MEK resin solution of the polyester resin was changed to 20% by mass and 10% by mass, to obtain purified polyester resins A2 and A3, respectively. The physical properties of the purified polyester resins A1 to A3 are shown in Table 2.

[0063] Manufacturing Examples 1-4 to 1-6 The same operations as in Production Examples 1-1 to 1-3 were carried out, except that the polyester resin was changed to P2, to obtain purified polyester resins A4, A5, and A6, respectively. The physical properties of purified polyester resins A4 to A6 are shown in Table 2.

[0064] [Table 2]

[0065] (Preparation of Pigment Water Dispersion) Example I-1 (1) Step 1 (pigment dispersion step) In a 2L vessel, 66.7g of purified polyester resin A1 was dissolved in 198.6g of methyl ethyl ketone (MEK), and then 6.46g 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 disper 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 then 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 pigment dispersion of polyester resin particles containing a pigment. (2) Process 2 (concentration process) The entire amount of the pigment 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% by mass, and the organic solvent was removed by using a rotary distillation apparatus (Tokyo Rikakikai Co., Ltd., rotary evaporator: N-1000S) at a rotation speed of 50 r / min while heating in a warm bath adjusted to 32°C and maintaining a pressure of 0.09 MPa (abs) for 3 hours. Furthermore, the warm bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration was 25% by mass, 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 cooling centrifuge: iMac CR22G, set temperature 20°C), and the liquid phase was filtered through a membrane filter with a pore size of 5 μm (Sartorius, Minisart) and diluted with water to a solid content concentration of 22 mass%, to obtain an aqueous dispersion 1 of polyester resin particles containing a pigment (pigment: 13.2 mass%, polyester resin: 8.8 mass%) (hereinafter referred to as "pigment aqueous dispersion 1"). The redispersibility of the obtained pigment aqueous dispersion 1 was evaluated. The results are shown in Table 3.

[0066] Examples I-2 to I-6 and Comparative Examples I-1 to I-2 Pigment water dispersions 2 to 6 and C1 to C2 were produced in the same manner as in Example I-1, except that in Example I-1, the type of polyester resin and the amount of sodium hydroxide aqueous solution added in step 1 were changed to the conditions shown in Table 3, and the redispersibility was evaluated in the same manner as in Example I-1. The results are shown in Table 3.

[0067] <Evaluation of redispersibility> A water-based ink for redispersion testing was obtained by adding 30.3 parts of an aqueous dispersion of polyester resin particles containing a pigment described below (4 parts as the pigment content in the water-based ink), 40 parts of 1,2-propanediol, and ion-exchanged water to a total amount of 100 parts. The absorbance of the resulting ink immediately after preparation and after concentration were measured as described below to determine the rate of change in absorbance, i.e., redispersibility (unit: %), and the redispersibility of the ink was evaluated. (i) Measurement of absorbance immediately after preparation The aqueous ink for redispersibility testing was diluted 2,500-fold with ion-exchanged water to prepare a sample for measuring absorbance within 24 hours after preparation (sample immediately after preparation). Using a spectrophotometer (manufactured by Hitachi, Ltd., model number: U-3010), the absorbance of the black ink was measured at an absorption wavelength of 550 nm, the absorbance of the white ink at an absorption wavelength of 500 nm, and the absorbance of each color ink at its maximum absorption wavelength was measured, and the absorbance immediately after preparation was calculated using the following formula. Absorbance immediately after preparation = (absorbance at the specific wavelength above according to the ink color of the sample immediately after preparation x 2500) (ii) Measurement of absorbance after concentration 2 g of the water-based ink for redispersibility test was added to a screw tube No. 6 (manufactured by Maruemu Co., Ltd.), and the tube was left uncovered at 40°C and 25% RH for 12 hours to evaporate the liquid components of the water-based ink. Ion-exchanged water was added to the solid matter remaining at the bottom of the screw tube so that the mass was 2 g, and the tube was stirred at 150 rpm for 1 minute. The resulting solution was then diluted 2500 times with ion-exchanged water to serve as a measurement sample for absorbance after concentration (sample after concentration). The absorbance at the specific wavelength corresponding to the color of the ink was measured using a spectrophotometer, and the absorbance after concentration was calculated using the following formula. Absorbance after concentration = (absorbance at the specific wavelength above according to the ink color of the concentrated sample x 2500) The redispersibility was evaluated by calculating the rate of change in absorbance at a specific wavelength before and after concentration of the water-based ink, that is, the redispersibility (unit: %) according to the following formula, and judged. Redispersibility (%) = 100 x absorbance after concentration / absorbance immediately after preparation The closer the value is to 100, the better the redispersibility is.

[0068] [Table 3]

[0069] Examples II-1 to II-10 and Comparative Examples II-1 to II-2 The pigment water dispersion, water-soluble organic solvent, surfactant, and ion-exchanged water were mixed in the ratios shown in Table 4, and the resulting mixture was filtered through a membrane filter with a pore size of 5 μm (Minisart, manufactured by Sartorius) to obtain water-based inks 1 to 10 and C1 to C2. The obtained water-based inks 1 to 10 and C1 to C2 were used to evaluate the abrasion resistance and solvent resistance. The results are shown in Table 4.

[0070] <Evaluation of abrasion resistance> A direct T-shirt printer (Mastermind Co., Ltd., product name: MMP8130, 4-color specification) was filled with the water-based ink obtained in the examples or comparative examples. An A4-sized film heater (Kawai Electric Manufacturing Co., Ltd.) was fixed to the printer, and a white polyvinyl chloride film (PVC, 3M Japan Co., Ltd., product name: IJ180-10) was prepared as a printing substrate, and the film was heated from the bottom at a set temperature of 50°C, and the printing mode (white fabric direct, 1440 x 1440 dpi) was set to not discharge printing during printing. A solid image was printed with a duty of 100%, and the obtained print was immediately heated and dried for 5 minutes in a constant temperature dryer at 80°C to obtain a print for evaluation. The printed surface of the evaluation print is coated with 100 g / cm of cellulose nonwoven fabric (manufactured by Asahi Kasei Fibers Corporation, product name: BEMCOT M3-II). 2 The print surface was rubbed 50 times at a speed of 1 m / min under a load of 0.01 mm. After rubbing, damage (scratches) on the print surface was visually observed, and the rub resistance was evaluated according to the following evaluation 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 a decrease in gloss is observed. 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 total printed area. The higher the evaluation criterion value, the fewer scratches on the printed surface and the better the abrasion resistance. <Evaluation of Solvent Resistance> The printed surface of the evaluation print produced in the <Evaluation of abrasion resistance> above was rubbed with a cotton swab (manufactured by Johnson & Johnson) soaked in 70% by mass of ethanol aqueous solution at a rate of 5 g / cm. 2 The surface condition of the printed surface after rubbing was visually observed, and the solvent resistance was evaluated according to the following criteria. (Evaluation Criteria) 5: The printed coating film has not peeled off from the substrate. 4: The peeled area is less than 10%. 3: The peeled area is 10% or more and less than 30%. 2: The peeled area is 30% or more and less than 50%. 1: Peeled area is 50% or more. The larger the evaluation criterion value, the smaller the peeled area and the more excellent the solvent resistance.

[0071] [Table 4]

[0072] The details of the components shown in Table 4 are as follows: (Water-soluble organic solvent) iBDG: Diethylene glycol monoisobutyl ether BDG: Diethylene glycol monobutyl ether BFG: Propylene glycol monobutyl ether PFG: Propylene glycol monopropyl ether MFDG: Dipropylene glycol monomethyl ether 1,2-PD: 1,2-propanediol (Surfactant) KF-6011: Alkylene glycol modified polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.

[0073] From Tables 3 and 4, it can be seen that the pigment water dispersions of the Examples have good redispersibility, and the water-based inks using the pigment water dispersions have excellent abrasion resistance and solvent resistance and exhibit high coating strength.

Claims

1. A pigment water dispersion containing a polyester resin and a pigment, In a chromatogram of the molecular weight distribution of the polyester resin measured by gel permeation chromatography, the area corresponding to components having a molecular weight of 1,000 or less accounts for 5% or less of the total area of ​​the pigment aqueous dispersion.

2. The pigment water dispersion according to claim 1 , wherein the pigment and the polyester resin are in the form of pigment-containing polyester resin particles.

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

4. The pigment water dispersion according to claim 1, wherein the glass transition temperature of the polyester resin is 35°C or higher and 100°C or lower.

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

6. The water-based ink according to claim 5, which is for ink-jet recording.

7. A water-based ink comprising a pigment water dispersion according to any one of claims 1 to 4 and a water-soluble organic solvent.

8. Pigment-containing polyester resin particles, wherein in a chromatogram of the molecular weight distribution of the polyester resin measured by gel permeation chromatography, the area corresponding to components with a molecular weight of 1,000 or less is 5% or less of the total area.

9. Pigment-containing polyester resin particles as described in claim 8, which contain terephthalic acid and fumaric acid as carboxylic acid components that are constituent units of the polyester resin.

10. Pigment-containing polyester resin particles as described in claim 8, for use in a water-based ink for inkjet recording.

11. A water-based ink for inkjet recording containing the pigment-containing polyester resin particles described in claim 8.

12. The water-based ink for inkjet recording according to claim 11, which is used on a low-liquid-absorbency recording medium.

13. A method for producing a pigment aqueous dispersion as described in claim 1, comprising a step of reducing low molecular weight components of a polyester resin using at least one method selected from dialysis, gel filtration, ultrafiltration and precipitation to obtain a polyester resin in which the area corresponding to components with a molecular weight of 1,000 or less is 5% or less of the total area in a chromatogram of molecular weight distribution measured by gel permeation chromatography.