Pigment aqueous dispersion

Abstract

To provide an aqueous pigment dispersion that is excellent in dispersion stability and re-dispersibility after long-term storage, and a water-based ink that is excellent in long-term dispersion stability and gives a recorded material excellent in substrate adhesion, scratch resistance, and solvent resistance.SOLUTION: The present invention relates to [1] an aqueous pigment dispersion of polyester resin particles containing a pigment, wherein the aqueous pigment dispersion contains 3-methyl-1,5-pentanediol as an alcohol component, which is a structural unit of the polyester resin, and [2] a water-based ink containing the aqueous pigment dispersion and a water-soluble organic solvent.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Inkjet recording is a recording method that directly ejects ink droplets from fine nozzles and adheres them to a recording medium to obtain a recorded material with text and images. This method has become extremely popular because it is easy and inexpensive to implement in full color, can use plain paper as a recording medium, and is contactless to the recording medium. In recent years, water-based pigment inks, which use pigments as colorants and polymers to disperse the pigments, have attracted attention from the perspective of providing weather resistance and water resistance to printed materials, as well as reducing the burden on the work environment and the natural environment. On the other hand, water-based pigment inks have problems with poor storage stability and dispensing performance due to coarse particles derived from pigments and polymers.

[0003] Therefore, various proposals have been made to improve storage stability and dispensing stability. For example, Patent Document 1 discloses an inkjet pigment ink containing a pigment and an aqueous polyester copolymer, which is an aqueous pigment ink for inkjet recording that has excellent long-term storage stability, in particular excellent intermittent ejection stability after a period of inactivity, and storage ejection stability when used again after being left for a long time with the ink reservoir and head separated, and can stably record images of good quality. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-60656 [Overview of the project] [Problems that the invention aims to solve]

[0005] In commercial and industrial printing, pigment aqueous dispersions and inks are generally supplied to the discharge nozzles via a main tank, a secondary tank, and an ink cartridge. However, the ink in the main tank is often stored for long periods. Therefore, dispersion stability and the ability to redisperse sediment that accumulates during long-term storage are required. On the other hand, inks printed on low-absorbent coated paper or non-absorbent resin films do not easily penetrate the substrate, resulting in problems such as poor adhesion to the substrate, abrasion resistance, and solvent resistance of the resulting recorded material. Conventional water-based inks, such as those described in Patent Document 1, suffer from insufficient redispersibility and scratch resistance of recorded materials, and improvements have been desired. The present invention aims to provide a pigment aqueous dispersion with excellent dispersion stability and redispersibility after long-term storage, and an aqueous ink that can produce a record with excellent long-term dispersion stability, substrate adhesion, abrasion resistance, and solvent resistance. [Means for solving the problem]

[0006] The inventors have found that by using a polyester resin having structural units derived from 3-methyl-1,5-pentanediol as the pigment dispersion polymer, the resulting aqueous pigment dispersion does not generate coarse particles due to aggregation even after long-term storage, and the aqueous ink containing it maintains good recording performance even after long-term storage, thus solving the above-mentioned problems. In other words, the present invention provides the following [1] and [2]. [1] A pigment aqueous dispersion of polyester resin particles containing a pigment, A pigment aqueous dispersion containing 3-methyl-1,5-pentanediol as an alcohol component that is a constituent unit of the polyester resin. [2] An aqueous ink containing the pigment aqueous dispersion described in [1] above and a water-soluble organic solvent. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pigment aqueous dispersion with excellent dispersion stability and redispersibility after long-term storage, and an aqueous ink that can produce a record with excellent long-term dispersion stability and excellent substrate adhesion, abrasion resistance, and solvent resistance. [Modes for carrying out the invention]

[0008] [Pigment aqueous dispersion] The present invention provides a pigment aqueous dispersion of polyester resin particles containing a pigment, wherein the polyester resin contains 3-methyl-1,5-pentanediol as an alcohol component which is a constituent unit of the polyester resin. In this specification, "pigment aqueous dispersion" means that water accounts for the largest proportion by mass in the medium used to disperse the pigment. Furthermore, "record" is a concept that includes printing and printing of text and images, while "record material" is a concept that includes printed materials and printed objects on which text and images are recorded. "Low liquid absorption" is a concept that includes both low liquid absorption and non-liquid absorption, where the amount of water absorbed by the recording medium during a 100 msec contact time with pure water is 0 g / m³. 2 More than 10g / m 2 This means the following:

[0009] The pigment aqueous dispersion of the present invention exhibits excellent dispersion stability and redispersibility after long-term storage, and the aqueous ink of the present invention exhibits excellent long-term dispersion stability, as well as excellent substrate adhesion, abrasion resistance, and solvent resistance, resulting in a recordable material. The reason for this is not entirely clear, but it is thought to be as follows. The pigment aqueous dispersion and aqueous ink of the present invention have a constituent unit derived from 3-methyl-1,5-pentanediol as a constituent unit of the polyester resin. Polyester resin is expected to enhance the affinity between images obtained by drying water-based inks and non-absorbent recording media, thereby improving substrate adhesion and abrasion resistance. Furthermore, because polyester resin does not swell easily in alcohols such as ethanol and isopropyl alcohol, it is expected to improve solvent resistance to alcohols and other solvents. Furthermore, since polyester resins have a structure in which alcohol and acid components form the main skeleton and ester groups are alternately bonded, it is thought that the relatively hydrophobic main skeleton contributes to the adsorption of pigments. In this case, 3-methyl-1,5-pentanediol is thought to have an excellent balance between the flexibility of the polyester resin's main skeleton and the adsorption to the pigment surface due to its hydrophobic side chains, as the methyl groups present in its side chains adsorb to the pigment like anchors. Therefore, the polyester resin adsorbed onto the pigment according to the present invention remains stable without partially detaching from the pigment even after long-term storage, and no coarse particles are generated due to aggregation. As a result, the pigment aqueous dispersion of the present invention exhibits excellent dispersion stability and redispersibility after long-term storage, and the aqueous ink of the present invention exhibits excellent long-term dispersion stability, making it possible to obtain recording materials with excellent substrate adhesion, abrasion resistance, and solvent resistance.

[0010] <Polyester resin particles containing pigments> The pigments used in the present invention are included in the aqueous pigment dispersion and aqueous ink as polyester resin particles containing the pigment, from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion, the redispersibility after long-term storage, and the long-term dispersion stability of the aqueous ink of the present invention, as well as the adhesion to the substrate, abrasion resistance, and solvent resistance of the resulting recording material. In this specification, "polyester resin particles containing pigment" (hereinafter also referred to as "pigment-containing resin particles") includes particles in which the polyester resin contains the pigment, particles in which a portion of the pigment is exposed on the surface of particles made of polyester resin and pigment, particles in which the polyester resin is adsorbed onto a portion of the pigment, and mixed forms thereof, but the form of polyester resin particles containing pigment is more preferred.

[0011] [Pigments] The pigments used in this invention may be either inorganic or organic pigments, and lake pigments and fluorescent pigments may also be used. Furthermore, these may be used in combination with extender pigments as needed. Specific examples of inorganic pigments include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide, chromium oxide, and nacreous pigments. 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; 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 fluoranthene pigments.

[0012] The hue is not particularly limited, and any 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 C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. Examples of extender pigments include silica, calcium carbonate, talc, and the like. The above pigments can be used alone or in combination of two or more.

[0013] [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 polycondensing the alcohol component and the carboxylic acid component.

[0014] (Alcohol component) The alcohol component, which is a raw material monomer for the polyester resin, contains 3-methyl-1,5-pentanediol from the viewpoint of improving the dispersion stability of the pigment, improving redispersibility after long-term storage, long-term dispersion stability, substrate adhesion, and abrasion resistance, as well as from the viewpoint of improving the discharge performance of the ink using the pigment aqueous dispersion of the present invention after long-term storage. 3-methyl-1,5-pentanediol is thought to be stable because the methyl group in its side chain acts as an anchor, adsorbing to the pigment. This makes it difficult for the polyester resin to detach from the pigment even when stored for a long period of time, and it is believed that this can suppress the generation of coarse particles due to aggregation. From the same viewpoint as above, the content of 3-methyl-1,5-pentanediol in the alcohol component is preferably 5 mol% or more, more preferably 8 mol% or more, even more preferably 10 mol% or more, and preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less.

[0015] In the present invention, it is preferable to include, in addition to 3-methyl-1,5-pentanediol, one or more alcohol components selected from aromatic diols, aliphatic diols, and alicyclic diols, and more preferably one or more alcohol components selected from aromatic diols and aliphatic diols.

[0016] The aromatic diol is preferably one or more selected from alkylene oxide adducts of bisphenol A and hydrogenated bisphenol A, with hydrogenated bisphenol A being more preferred. The aliphatic diol is preferably one or more selected from 1,2-propanediol, 2,3-butanediol, 2,4-pentanediol, 2,5-hexanediol, 2,6-heptanediol, and 2,7-octanediol, more preferably one or more selected from 1,2-propanediol and 2,3-butanediol, and even more preferably 2,3-butanediol. As the alicyclic diol, one or more selected from 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol are preferred, with 1,4-cyclohexanediol being more preferred. From the above viewpoint, it is preferable that the polyester resin contains structural units derived from 3-methyl-1,5-pentanediol, alkylene oxide adducts of bisphenol A, hydrogenated bisphenol A, and one or more alcohol components selected from 2,3-butanediol.

[0017] The alkylene oxide adduct of bisphenol A refers to the entire structure obtained by adding an oxyalkylene group to 2,2-bis(4-hydroxyphenyl)propane. The alkylene oxide adduct of bisphenol A is preferably a compound represented by the following general formula (I), and two or more compounds within this range may be used in combination.

[0018] [ka]

[0019] In general formula (I), OR 1 , R 2 Each O independently represents an oxyalkylene group having 1 to 4 carbon atoms, preferably an oxyethylene group or an oxypropylene group. x and y are the number of moles of alkylene oxide added, and are independently positive numbers of 0 or greater. The average value of the sum of x and y is preferably 2 or greater, preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less, from the viewpoint of reactivity with the carboxylic acid component. Also, OR 1 and R 2 O may be the same or different in each case, but from the viewpoint of achieving the effects of the present invention, it is preferable that they be the same. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A or an ethylene oxide adduct of bisphenol A, with the propylene oxide adduct of bisphenol A being more preferred.

[0020] Hydrogenated bisphenol A is a hydrogenated bisphenol compound (2,2'-bis(4-hydroxycyclohexyl)propane). The content of one or more aromatic diols, aliphatic diols, and alicyclic diols in the alcohol component is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 15 mol% or more, and preferably 96 mol% or less, more preferably 95 mol% or less, even more preferably 94 mol% or less, even more preferably 92 mol% or less, and even more preferably 90 mol% or less.

[0021] (Carboxylic acid component) The carboxylic acid components, which are raw material monomers for polyester resins, include carboxylic acids, their acid anhydrides, and their alkyl (1 to 3 carbon atoms) esters. Examples of carboxylic acid components include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and polycarboxylic acids with a valency of three or more. As aromatic dicarboxylic acids, phthalic acid, isophthalic acid, and terephthalic acid are preferred, with terephthalic acid being more preferred. Examples of aliphatic dicarboxylic acids include unsaturated and saturated aliphatic dicarboxylic acids. Preferred unsaturated aliphatic dicarboxylic acids are fumaric acid and maleic acid, with fumaric acid being more preferred. Preferred saturated aliphatic dicarboxylic acids are adipic acid and succinic acid, with adipic acid being more preferred. Preferred alicyclic dicarboxylic acids include cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid. As the polycarboxylic acid with a valency of 3 or higher, trimellitic acid and pyromellitic acid are preferred, and trimellitic anhydride is also preferred. The carboxylic acid components can be used individually or in combination of two or more.

[0022] From the viewpoint of exhibiting the effects of the present invention, the above carboxylic acid component preferably includes one or more selected from aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and polycarboxylic acids with a valency of three or more, and it is more preferable to use aromatic dicarboxylic acids and polycarboxylic acids with a valency of three or more in combination. From the above viewpoint, it is preferable that the polyester resin contains structural units derived from 3-methyl-1,5-pentanediol, one or more alcohol components selected from bisphenol A alkylene oxide adducts, hydrogenated bisphenol A, and 2,3-butanediol, and structural units derived from carboxylic acid components including aromatic dicarboxylic acids. It is more preferable that the polyester resin contains structural units derived from 3-methyl-1,5-pentanediol, one or more alcohol components selected from 3-methyl-1,5-pentanediol, bisphenol A alkylene oxide adducts, hydrogenated bisphenol A, and 2,3-butanediol, structural units derived from aromatic dicarboxylic acid components, and structural units derived from trivalent or higher polycarboxylic acid components.

[0023] (Manufacturing of polyester resin) Polyester resins can be obtained by polycondensing the alcohol component and the carboxylic acid component in appropriate combinations. For example, they can be produced by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere, using an esterification catalyst if necessary, at a temperature of 150°C to 250°C. Examples of esterification catalysts include tin catalysts, titanium catalysts, antimony trioxide, zinc acetate, and metal compounds such as germanium dioxide. From the viewpoint of esterification reaction efficiency, tin catalysts are preferred. Preferred tin catalysts include dibutyltin oxide, di(2-ethylhexanoate)tin(II), and their salts, with di(2-ethylhexanoate)tin(II) being more preferred. If necessary, esterification co-catalysts such as gallic acid may also be used. Furthermore, radical polymerization inhibitors such as 4-t-butylcatechol may be used in combination.

[0024] Polyester resins that have acidic groups are preferred from the viewpoint of improving the dispersion stability of pigments, as well as improving redispersibility after long-term storage, long-term dispersion stability, substrate adhesion, and abrasion resistance. The acid value of the polyester resin is preferably 10 mg KOH / g or more, more preferably 15 mg KOH / g or more, even more preferably 17 mg KOH / g or more, and even more preferably 23 mg KOH / g or more, and preferably 100 mg KOH / g or less, more preferably 80 mg KOH / g or less, even more preferably 60 mg KOH / g or less, even more preferably 40 mg KOH / g or less, even more preferably 34 mg KOH / g or less, and even more preferably 30 mg KOH / g or less. From the same viewpoint 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, even more preferably 140°C or lower, even more preferably 125°C or lower, and even more preferably 120°C or lower.

[0025] From the same viewpoint 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 45°C or higher, and preferably 100°C or lower, more preferably 98°C or lower, even more preferably 95°C or lower, even more preferably 80°C or lower, and even more preferably 70°C or lower. From the same viewpoint as above, the weight-average molecular weight of the polyester resin is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 12,000 or more, and preferably 100,000 or less, more preferably 80,000 or less, even more preferably 60,000 or less, and even more preferably 25,000 or less. The acid value, softening point, glass transition temperature, and weight-average molecular weight of the polyester resin can be measured by the method described in the examples. Furthermore, these properties can be adjusted to suit the desired characteristics by appropriately controlling the type of monomer used, the blending ratio, the polycondensation temperature, and the reaction time.

[0026] The polyester resin is preferably water-insoluble. Here, "water-insoluble" polyester resin means that when the polyester resin is dried at 105°C for 2 hours and the resulting constant weight is dissolved in 100g of water at 25°C, the amount dissolved is 10g or less, preferably 5g or less, and more preferably 1g or less. If the polyester resin has acidic groups, this amount of dissolution is the amount dissolved when the acidic groups are neutralized by 100 mol% with sodium hydroxide.

[0027] [Manufacturing of pigment-containing resin particles] Pigment-containing resin particles can be efficiently produced as a pigment aqueous dispersion by the method described in step 1 below. Furthermore, a crosslinking step can be performed as needed. Step 1: A process to obtain a pigment aqueous dispersion of polyester resin particles containing pigment by dispersing a pigment mixture containing pigment, polyester resin, water, and optionally a neutralizing agent, surfactant, etc.

[0028] (Process 1) Although the polyester resin has carboxyl groups derived from carboxylic acid components, it is more preferable that at least a portion of these carboxyl groups are neutralized with a neutralizing agent, from the viewpoint of improving the dispersion stability, substrate adhesion, and abrasion resistance of the resulting aqueous pigment dispersion and water-based ink. When neutralizing, it is preferable to neutralize the pigment aqueous dispersion so that its pH is between 7 and 11. Suitable neutralizing agents include sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred. Alternatively, the polyester resin may be neutralized beforehand. From the same viewpoint as above, the equivalent amount of neutralizing agent used is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and also preferably 150 mol% or less, more preferably 120 mol% or less, and even more preferably 100 mol% or less. The equivalent amount of neutralizing agent to be used can be calculated using the following formula. Amount of neutralizing agent used (mol%) = [{Mass of neutralizing agent added (g) / Equivalent amount of neutralizing agent} / [{Acid value of polyester resin before neutralization (mgKOH / g) × Mass of polyester resin before neutralization (g)} / (56 × 1,000)] × 100

[0029] The dispersion process in step 1 can be carried out by known methods. While it is possible to finely atomize pigment particles to the desired particle size by this dispersion alone using shear stress, it is preferable to pre-disperse the pigment mixture before this final dispersion from the viewpoint of obtaining a uniform aqueous pigment dispersion. For pre-dispersion, commonly used mixing and stirring devices such as anchor blades and disperser blades can be used as dispersers.

[0030] Dispersion machines used for this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersants 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 performing dispersion processing using a high-pressure homogenizer, the average particle size of pigment particles in the aqueous pigment dispersion can be adjusted by controlling the processing pressure and the number of passes. From the viewpoint of productivity and economic efficiency, the processing pressure is preferably 60 MPa to 300 MPa, and the number of passes is preferably 3 to 30.

[0031] If the pigment mixture contains an organic solvent, the pigment aqueous dispersion can be obtained by removing the organic solvent using known methods. The solid content concentration of the pigment aqueous dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the manufacture of the ink. The solid content concentration is measured by the method described in the examples. From the viewpoint of improving storage stability, the average particle size of the pigment-containing resin particles in the pigment aqueous dispersion is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and preferably 350 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and even more preferably 170 nm or less. The average particle size is measured by the method described in the examples.

[0032] (Content of each component in the pigment aqueous dispersion) The content of each component in the pigment aqueous dispersion of the present invention is as follows, from the viewpoint of improving the dispersion stability, substrate adhesion, and abrasion resistance of the resulting pigment aqueous dispersion and water-based ink. (Pigment content) The pigment content in the aqueous pigment dispersion is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and 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 pigment-containing resin particles in the pigment aqueous dispersion is preferably 3% by mass or more, more preferably 6% by mass or more, even more preferably 10% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0033] The polyester resin content in the pigment aqueous dispersion is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.

[0034] The mass ratio of pigment to the mass of pigment-containing resin particles in the pigment aqueous dispersion (pigment / pigment-containing resin particles) is preferably 0.2 or higher, more preferably 0.3 or higher, even more preferably 0.4 or higher, and preferably 0.9 or lower, more preferably 0.8 or lower, and even more preferably 0.7 or lower, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the manufacture of the ink. The aforementioned mass ratio (pigment / pigment-containing resin particles) can be calculated from the ratio of the amount of material added.

[0035] [Water-based ink] The water-based ink for inkjet recording according to the present invention is a water-based ink containing the pigment aqueous dispersion of the present invention and a water-soluble organic solvent. Here, "water-based" means that water makes up the largest proportion of the medium contained in the ink. The water-based ink of the present invention can be efficiently manufactured by mixing the pigment aqueous dispersion containing the pigment-containing resin particles obtained above, a water-soluble organic solvent, water, and, if necessary, various additives such as surfactants. There are no particular restrictions on the method of mixing the above components.

[0036] <Water-soluble organic solvents> The water-soluble organic solvent used may be a liquid or a solid at 25°C, but when the organic solvent is dissolved in 100 ml of water at 25°C, the amount dissolved must be 10 ml or more. From the viewpoint of improving the wetting spreadability of the ink, the boiling point of the water-soluble organic solvent is 100°C or higher, preferably 120°C or higher, more preferably 140°C or higher, even more preferably 150°C or higher, and 250°C or lower, preferably 245°C or lower, more preferably 240°C or lower, and even more preferably 235°C or lower. Examples of water-soluble organic solvents include glycol ethers such as alkylene glycol ethers, polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, and amide compounds. Among these, alkylene glycol ethers are preferred.

[0037] 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, dipropylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Among these, from the viewpoint of improving the wetting spread of the ink and improving the adhesion and abrasion resistance of the resulting printed material, 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, with diethylene glycol monoisobutyl ether being more preferred.

[0038] In the present invention, it is preferable to include propylene glycol in addition to alkylene glycol ether. Propylene glycol is thought to primarily suppress the evaporation of water from the ink nozzle and rapidly volatilize after recording, thereby forming a strong ink film with minimal drying steps and preventing the recording surface from adhering to the back surface.

[0039] <Surfactants> The ink of the present invention preferably contains a surfactant from the viewpoint of maintaining the surface tension of the ink appropriately and improving wettability to the recording medium. There are no particular restrictions on the surfactant, but nonionic surfactants are preferred, and silicone-based surfactants are more preferred. Examples of silicone-based surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone, but from the same viewpoint as above, polyether-modified silicone is preferred. 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, and lauryl PEG-9 polydimethylsiloxyethyl dimethicone. Examples of commercially available polyether-modified silicones include the following silicones manufactured by Shin-Etsu Chemical Co., Ltd.: KF-6011, KF-6012, KF-6013, KF-6015, KF-6016, KF-6017, KF-6028, KF-6038, KF-6043, etc.

[0040] In this invention, it is also preferable to use an acetylene glycol-based surfactant in addition to a silicone-based surfactant. Examples of commercially available acetylene glycol-based surfactants include the "Surfinol" series and "Orfin" series from Nisshin Chemical Industry Co., Ltd., and the "Acetylenel" series from Kawaken Fine Chemical Co., Ltd. The above-mentioned surfactants can be used individually or in combination of two or more. Other additives used in the water-based ink of the present invention include fixing aids, humectants, wetting agents, penetrating agents, viscosity modifiers, defoaming agents, preservatives, fungicides, and rust inhibitors. Examples of fixing aids include emulsions containing water-insoluble polymer particles, and examples of water-insoluble polymer particles include condensation resins such as polyurethane and polyester; and vinyl resin particles 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. Here, "water-insoluble" in water-insoluble polymer particles means that when the water-insoluble polymer particles are dried at 105°C for 2 hours and the polymer reaches a constant weight, the amount dissolved in 100g of water at 25°C is 10g or less, and the amount dissolved in the water-insoluble polymer particles is preferably 5g or less, more preferably 1g or less. If the water-insoluble polymer particles are anionic polymers, the amount dissolved is the amount dissolved when the anionic groups of the polymer are neutralized by 100 mol% with sodium hydroxide.

[0041] (Content of each component in the water-based ink of the present invention) The content of each component in the aqueous ink of the present invention is as follows, from the viewpoint of improving the long-term dispersion stability of the aqueous ink and obtaining a record with excellent substrate adhesion, abrasion resistance, and solvent resistance. (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 2.5% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. The content of pigment-containing resin particles in the water-based ink is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0042] The polyester resin content in the water-based ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 6% by mass or less. The mass ratio of pigment to the mass of pigment-containing resin particles in the water-based ink (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 preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less.

[0043] The total content of 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 preferably 45% by mass or less, more preferably 42% by mass or less, and even more preferably 40% by mass or less. The content of the surfactant in the water-based ink 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 preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The water content in the water-based ink is preferably 50% by mass or more, more preferably 54% by mass or more, more preferably 58% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0044] (Physical properties of the water-based ink of the present invention) The viscosity of the water-based ink at 32°C is preferably 2 mPa·s or higher, more preferably 2.5 mPa·s or higher, and more preferably 12 mPa·s or lower, more preferably 9 mPa·s or lower, and even more preferably 7 mPa·s or lower, from the viewpoint of improving long-term dispersion stability, substrate adhesion, abrasion resistance, etc. The pH of the water-based ink is preferably 7.0 or higher, more preferably 7.2 or higher, even more preferably 7.3 or higher, and preferably 11 or lower, more preferably 10 or lower, and even more preferably 9 or lower, from the viewpoint of storage stability and reduced corrosiveness.

[0045] The water-based ink of the present invention is preferable for use in inkjet recording because it can produce recordings with excellent filtration properties after long-term storage, as well as excellent adhesion to the substrate, abrasion resistance, and solvent resistance. The ink of the present invention can be loaded into a known inkjet recording device such as a piezo-type device and ejected as ink droplets onto a low-liquid-absorption recording medium to record images and the like. Examples of low-liquid-absorbent recording media include low-liquid-absorbent coated paper, art paper, and non-liquid-absorbent resin films. Examples of coated paper include general-purpose glossy paper and multi-color foam gloss paper. Examples of resin films include transparent synthetic resin films, such as polyester, polyvinyl chloride, polyolefin, and nylon films. These films may be biaxially oriented, uniaxially oriented, or unoriented. Among these, polyester films and stretched polypropylene films are preferred, and corona-discharge treated polyethylene terephthalate (PET) films and corona-discharge treated biaxially oriented polypropylene (OPP) films are more preferred. [Examples]

[0046] The measurement methods for each physical property in the manufacturing examples, examples, and comparative examples are as follows.

[0047] (1) 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)]. (2) Softening point of polyester resin Using a flow tester (Shimadzu Corporation, product name: CFT-500D), 1 g of sample was heated at a heating rate of 6°C / min while a load of 1.96 MPa was applied by a plunger and extruded through a nozzle with a diameter of 1 mm and a length of 1 mm. The amount of plunger descent of the flow tester was plotted against temperature, and the temperature at which half of the sample flowed out was defined as the resin softening point.

[0048] (3) Glass transition temperature (Tg) of polyester resin Using a differential scanning calorimeter (manufactured by Perkin Elmer, trade name: Pyris 6 DSC), the temperature was raised to 200 °C, and the sample cooled from that temperature to 0 °C at a cooling rate of 10 °C / min was then heated at a heating rate of 10 °C / min. The temperature at the intersection of the extension of the baseline below the maximum peak temperature of the endotherm and the tangent showing the maximum slope from the rising part of the peak to the apex of the peak was taken as the glass transition temperature (Tg) of the resin.

[0049] (4) Weight average molecular weight (Mw) of the polyester resin A solution prepared by dissolving the polyester resin 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., trade name: FP-200) to remove insoluble components and used as the sample solution. Tetrahydrofuran was flowed as the molecular weight measurement dissolution solution at a flow rate of 1 mL / min, and the column was stabilized in a constant temperature 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 the gel chromatography method [GPC apparatus (CO-8010) manufactured by Tosoh Corporation, analytical columns: "GMHXL" + "G3000HXL"]. The calibration curve was prepared using several types of monodisperse polystyrenes [monodisperse polystyrene manufactured by Tosoh Corporation; 2.63×103, 2.06×10 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)] as standard samples.

[0050] (5) Average particle size of the pigment dispersion The average particle size of a pigment aqueous dispersion 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 integration cycles. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, a pigment aqueous dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5), and the solid content concentration was 2 × 10⁻⁶. -4 Water was added to the solution to a mass percentage, and the mixture was stirred using a magnetic stirrer at 25°C for 1 hour.

[0051] (6) Solid content concentration 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 ml polypropylene container (φ: 40 mm, height: 30 mm). Approximately 1.0 g of the sample was added and mixed, then weighed. The mixture was maintained at 105°C for 2 hours to remove volatile components, and then left in the desiccator for another 15 minutes. The mass was then measured. The mass of the sample after removal of volatile components was taken as the solid content, and the solid content concentration was obtained by dividing it by the mass of the added sample.

[0052] (7) pH The pH of the pigment aqueous dispersion and ink at 20°C was measured using a benchtop pH meter (Horiba, Ltd., product name: F-71) equipped with a pH electrode (Horiba, Ltd., product name: 6337-10D).

[0053] Manufacturing Examples 1-7, Comparative Manufacturing Example 1 (Manufacturing of polyester resins P1-P7 and CP1) The raw material monomers other than trimellitic anhydride and the esterification catalyst shown in Table 1 were placed in a 10 L four-necked flask equipped with a nitrogen inlet tube, stirrer, and thermocouple. The mixture was heated to 235°C under a nitrogen atmosphere and then polycondensed at 235°C for 6 hours. Next, the temperature was lowered to 210°C, trimellitic anhydride as shown in Table 1 was added, and the mixture was reacted at 210°C for 1 hour. Then, the reaction was carried out under reduced pressure of 10 kPa at 210°C until the softening point shown in Table 1 was reached, yielding polyester resins P1-P7 and CP1. The results are shown in Table 1.

[0054] [Table 1]

[0055] Manufacturing examples 8-14, 18 (Manufacturing of polyester resins P8-P14, P18) As shown in Table 2, each raw material monomer other than trimellitic anhydride and the esterification catalyst were placed in a 10 L four-necked flask equipped with a thermometer, fractionation column, stainless steel stirring rod, a drop-flow condenser with a dehydration tube, and a nitrogen inlet tube. Under a nitrogen atmosphere and using a mantle heater, the temperature was raised to 185°C and the reaction was carried out for 5 hours. After that, the temperature was gradually raised to 220°C at a rate of 5°C / hour, and then the pressure inside the flask was further reduced and maintained at 8.3 kPa for 1 hour. After that, it was cooled to 200°C and returned to atmospheric pressure, then trimellitic anhydride was added, the temperature was raised to 220°C and maintained for 1 hour, and then the pressure inside the flask was further reduced to 8.3 kPa and the reaction was carried out until the softening point reached the temperature shown in Table 2 to obtain polyester resins P8-P14 and P18. The results are shown in Table 2.

[0056] Manufacturing Examples 15, 16, 17 (Manufacturing of polyester resins P15, P16, and P17) As shown in Table 2, each raw material monomer other than trimellitic anhydride, along with the esterification catalyst, was placed in a 10 L four-necked flask equipped with a thermometer, fractionation column, stainless steel stirring rod, a drop-flow condenser with a dehydration tube, and a nitrogen inlet tube. Under a nitrogen atmosphere and using a mantle heater, the mixture was heated to 185°C and reacted for 5 hours. After that, the temperature was gradually increased to 235°C at a rate of 5°C / hour, and the pressure inside the flask was further reduced and maintained at 8.3 kPa for 1 hour. Subsequently, the mixture was cooled to 200°C and returned to atmospheric pressure. Trimellitic anhydride was then added, the temperature was raised to 220°C and maintained for 1 hour, and then the pressure inside the flask was further reduced to 8.3 kPa. The mixture was reacted until the softening point reached the temperature shown in Table 2 to obtain polyester resins P15, P16, and P17. The results are shown in Table 2.

[0057] [Table 2]

[0058] Example 1 (Preparation of Pigment Aqueous Dispersion 1 of Pigment-Containing Resin Particles) (1) Step 1 (Pigment Dispersion Step 1) In a 2L container, 66.7 parts of polyester resin P1 obtained in Production Example 1 were dissolved in 198.6 parts of MEK, and a 5N sodium hydroxide aqueous solution was added to neutralize 85 mol% of the acid value of polyester resin P1. Furthermore, 390.5 parts of deionized water were added dropwise over 30 minutes, and the mixture was stirred and mixed at 1,500 r / min using a disperser blade at 10-15°C for 15 minutes. Next, 100 parts of carbon black (Cabot Monarch 717) were added, and the mixture was stirred and mixed at 10-15°C at 6,500 r / min using a disperser blade for 2 hours to obtain a preliminary dispersion. The obtained preliminary dispersion was filtered through a 200-mesh filter, diluted with 36.1 parts of deionized water, and then subjected to a 15-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer (Microfluidics, high-pressure homogenizer, product name: M-110EH-30XP) to obtain an aqueous dispersion of pigment-containing resin particles. (2) Process 2 (concentration process) The entire amount of the pigment aqueous dispersion obtained in step 1 was placed in a 2 L round-bottom flask, and deionized water was added to achieve a solid content concentration of 15%. Using a rotary distillation apparatus (Tokyo Rikakikai Co., Ltd., rotary evaporator, product name: N-1000S), the mixture was maintained at a rotation speed of 50 r / min in a 32°C warm bath at a pressure of 0.09 MPa (abs) for 3 hours to remove the organic solvent. Furthermore, the warm bath was adjusted to 62°C, and the pressure was reduced to 0.07 MPa (abs) to concentrate the mixture until the solid content 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 high-speed refrigerated centrifuge (Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20°C). The liquid layer was then filtered through a 5 μm pore size membrane filter (Sartorius, product name: Minisart), and diluted with water to a solid content concentration of 22% to obtain a pigment aqueous dispersion 1 of pigment-containing resin particles (solid content concentration: 22%, pigment: 13.2%, polyester resin: 8.8%).

[0059] Examples 2-52, Comparative Examples 1 and 2 (Preparation of Pigment Aqueous Dispersions of Pigment-Containing Resin Particles) Pigment aqueous dispersions 2-52 and comparative aqueous dispersions 1 and 2 of pigment-containing resin particles were obtained in the same manner as in Example 1, except that the conditions shown in Tables 3 and 4 were changed.

[0060] The dispersion stability and redispersibility after long-term storage were evaluated for the obtained pigment aqueous dispersions 1-52 and comparative aqueous dispersions 1 and 2 using the method described below. The results are shown in Tables 3 and 4.

[0061] (Dispersion stability) Within one day of production, the pigment aqueous dispersion was diluted with deionized water to a solid content concentration of 0.25%, weighed into a screw-cap tube (model: No. 5, manufactured by Maruemu Co., Ltd.), and stirred at 25°C for 1 hour using a magnetic stirrer to obtain pigment aqueous dispersion (α). The obtained pigment aqueous dispersion (α) was injected into a dynamic light scattering particle size distribution analyzer (manufactured by Nippon Integris LLC, product name: AccuSizer780APS) using a 5 mL syringe, and the number of particles was measured at a measurement temperature of 25°C using the particle counting method. The particle size measurement range for the particle counting method is 0.51 μm to 483.42 μm. The number of coarse particles was calculated as the number of particles 0.5 μm or larger per 1 mL of a pigment aqueous dispersion with a solid content of 20%. Next, the pigment aqueous dispersion, which had been left at room temperature for 6 months, was diluted with deionized water in the same manner as described above to obtain pigment aqueous dispersion (β). The number of particles in the obtained aqueous dispersion (β) was also measured in the same manner. The particle number increase rate (%) was calculated using the following formula. Particle count increase rate (%) = [Number of particles 0.5 μm or larger per 1 mL of pigment aqueous dispersion (β) with a solid content of 20% / Number of particles 0.5 μm or larger per 1 mL of pigment aqueous dispersion (α) with a solid content of 20% - 1] × 100 [Evaluation Criteria] 5. The particle number increase rate is less than 5%. 4. The particle number increase rate is 5% or more but less than 10%. 3. The particle number increase rate is between 10% and 100%. 2: The particle number increase rate is between 100% and 1000%. 1: The particle number increase rate is 1000% or more. The smaller the particle number increase rate, the better the storage stability of the pigment aqueous dispersion. If the evaluation result is 3 or higher, the dispersion stability is sufficient, and the amount of coarse particles does not pose a practical problem.

[0062] (Evaluation of redispersibility after long-term storage) 40 g of the pigment aqueous dispersions obtained in the examples from Tables 3 and 4 were placed in a 50 ml resealable glass screw tube, sealed, and left upright at room temperature for 6 months. After that, the screw tube was turned on its side and rotated at 100 rpm for 1 hour around its central axis to redisperse the particles. The solid content of the pigment dispersion after redispersion was measured, and the percentage was calculated by comparing it to the solid content before long-term storage to evaluate the redispersibility. [Evaluation Criteria] 5: The solid content is 99% or more. 4. The solid content is 97% or more but less than 99%. 3: The solid content is 95% or more but less than 97%. 2: The solid content is 93% or more but less than 95%. 1: The solid content is less than 93%. If the evaluation result is 3 or higher, the redistribution is at an acceptable level.

[0063] [Table 3]

[0064] [Table 4]

[0065] Tables 3 and 4 show that the pigment aqueous dispersions obtained in the examples exhibit superior dispersion stability and redispersibility after long-term storage compared to the pigment aqueous dispersions obtained in the comparative examples.

[0066] Examples 53-104, Comparative Examples 3,4 (Manufacturing of water-based inks 1-52, 103, 104) Using the pigment aqueous dispersions 1-52 and comparative aqueous dispersions 1-2 obtained from the pigment-containing resin particles in Examples 1-52 and Comparative Examples 1 and 2, each component was mixed according to the formulations shown in Tables 5 and 6. The resulting mixture was filtered through a 5 μm pore size membrane filter (product name: Minisart) to obtain aqueous inks (solid content concentration: 6.7%, pigment: 4.0%, polyester resin: 2.7%) 1-52, 103, and 104. The details of the components listed in Tables 5 and 6 are as follows. iBDG: Diethylene glycol monoisobutyl ether • PG: Propylene glycol • KF6011: Alkylene glycol-modified polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd., product name "KF-6011"

[0067] The obtained water-based inks were evaluated for continuous dispensing performance or filtration rate after long-term storage, as well as substrate adhesion, abrasion resistance, and solvent (ethanol) resistance, using the methods described below. The results are shown in Tables 5 and 6.

[0068] (Evaluation of continuous dispensing performance after long-term storage) Water-based ink stored in a sealed container at 25°C for 6 months (long-term storage water-based ink) was prepared. Next, the above long-term storage water-based ink was filled into an inkjet printer equipped with a rubber heater (manufactured by Ricoh Co., Ltd., product name: IPSIO SG 2010L), and a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., product name: Lumirror® T60 #75, water absorption capacity 2.3g / m²) heated to 60°C was used. 2 A solid color image was printed onto the paper. This printing process was repeated 100 times, and the prints from the 30th, 50th, and 100th printings were visually inspected for printing defects such as smudging, and evaluated according to the following criteria. [Evaluation Criteria] 5: No printing smudges are visible even in the 100th print. 4: Slight smudging was observed in the 100th print run. 3: Smudging was clearly observed in printed materials from the 100th printing onwards. 2: Smudging was observed in printed materials from the 50th printing onwards. Smudging was observed in prints from 1:30 onwards. If the evaluation result is 3 or higher, the continuous dispensing capability is sufficient.

[0069] (Evaluation of filtration rate after long-term storage) An open-system container was prepared by attaching a 5μm pore size membrane filter (Sartorius, product name: Minisart). 50.0g of each water-based ink, left at room temperature for 6 months (long-term stagnant ink 3), was placed inside, and the time required from the moment of insertion until the entire volume of ink flowed through was measured. [Evaluation Criteria] 5. The total flow time is less than 15 minutes. 4. The total flow time is 15 minutes or more but less than 30 minutes. 3: The total flow time is 30 minutes or more but less than 45 minutes. 2: The total flow time is 45 minutes or more but less than 60 minutes. 1. The entire volume does not flow through even after 60 minutes. If the evaluation result is 3 or higher, the filtration rate is at an acceptable level.

[0070] (Evaluation of substrate adhesion) An inkjet printer equipped with a rubber heater (manufactured by Ricoh Co., Ltd., product name: IPSIO SG 2010L) was filled with various water-based inks, and a solid image was printed onto polyethylene terephthalate (PET) film (product name: Lumirror T60 #75) heated to 60°C. The resulting print was then placed on a hot plate heated to 60°C and dried for 3 minutes, and after cooling to 25°C, an evaluation print of polyethylene terephthalate was obtained. This print was then evaluated using the grid test method in accordance with JIS K5400. Specifically, 11 vertical and horizontal cuts were made on the printed surface of the polyethylene terephthalate evaluation printout using a utility knife, reaching the substrate, creating 100 grid patterns. Cellophane tape was then firmly pressed onto the grid areas, and the ends of the tape were peeled off in one swift motion at a 45° angle. The state of the grid was then compared to the state before the test, and the substrate adhesion was evaluated according to the following evaluation criteria. [Evaluation Criteria] 5: More than 90% of the material remains intact without being peeled off. 4: Between 80% and 90% of the total remains without being peeled off. 3: Between 50% and 80% of the total remains without being peeled off. 2: Between 30% and 50% of the total remains without being peeled off. 1: Less than 30% of the total remains without being peeled off. If the evaluation result is 3 or higher, the adhesion to the substrate is sufficient.

[0071] (Evaluation of abrasion resistance) The printed surface of the same evaluation print used in the aforementioned substrate adhesion evaluation was coated with 100 g / cm² of cellulose nonwoven fabric (manufactured by Asahi Kasei Fibers Corporation, product name: Bencot® M3-II). 2 The material was rubbed back and forth 50 times under a load. After rubbing, the damage (scratches) to the printed surface was visually observed, and the abrasion resistance was evaluated according to the following evaluation criteria. [Evaluation Criteria] 5: The printed surface is free of scratches, and no decrease in glossiness is observed. 4: There are no scratches on the printed surface, but a decrease in glossiness is visible to the naked eye. 3: Although there are scratches on the printed surface, the film surface is not exposed. 2: The printed surface has peeled off, and the area of ​​the exposed film is less than 50% of the printed area. 1: The printed surface has peeled off, and the exposed film area is 50% or more of the printed area. The higher the numerical value in the evaluation criteria below, the fewer scratches there are on the printed surface, and the better the abrasion resistance. An evaluation result of 3 or higher indicates sufficient abrasion resistance.

[0072] (Evaluation of solvent resistance (ethanol)) The same evaluation printout used in the aforementioned evaluation of substrate adhesion was prepared. In addition, ethanol aqueous solutions were prepared at concentrations ranging from 10% to 100% by mass in 5% by mass increments. The ethanol aqueous solution was soaked into Johnson & Johnson's Johnson cotton swabs, and a 5g load was applied to the polyethylene terephthalate evaluation printout, rubbing the printed surface back and forth 10 times. The ethanol concentration in the ethanol aqueous solution was measured when no change occurred on the printed surface during the test, and the solvent resistance was evaluated according to the following evaluation criteria. [Evaluation Criteria] 5. The ethanol concentration is 100%. 4. The ethanol concentration is between 70% and 100%. 3. The ethanol concentration is between 50% and less than 70%. 2: The ethanol concentration is 30% or more but less than 50%. 1: The ethanol concentration is less than 30%. If the evaluation result is 3 or higher, the solvent resistance is sufficient.

[0073] [Table 5]

[0074] [Table 6]

[0075] Tables 5 and 6 show that the water-based inks obtained in the examples exhibit superior continuous ejection performance and filtration performance after long-term storage, as well as superior dispersion stability during long-term storage, compared to the water-based inks obtained in the comparative examples. Furthermore, the water-based inks obtained in the examples yield recordings with superior substrate adhesion, abrasion resistance, and solvent resistance in inkjet printing compared to the water-based inks obtained in the comparative examples.

Claims

1. A pigment aqueous dispersion for water-based inks, comprising polyester resin particles containing pigment, The polyester resin is a polycondensate of an alcohol component and a carboxylic acid component, and the alcohol component contains 3-methyl-1,5-pentanediol. A water-based ink pigment aqueous dispersion wherein the average particle size of the polyester resin particles containing the aforementioned pigment is 60 nm or more and 350 nm or less.

2. The aqueous pigment dispersion for water-based ink according to claim 1, wherein the acid value of the polyester resin is 10 mg KOH / g or more and 100 mg KOH / g or less.

3. The aqueous pigment dispersion for water-based ink according to claim 1 or 2, wherein the polyester resin has a glass transition temperature of 35°C or higher and 100°C or lower.

4. The aqueous pigment dispersion for water-based ink according to any one of claims 1 to 3, wherein the alcohol component contains one or more selected from aromatic diols, aliphatic diols, and alicyclic diols, in addition to 3-methyl-1,5-pentanediol.

5. A water-based ink pigment aqueous dispersion according to any one of claims 1 to 4, wherein the polyester resin contains structural units derived from 3-methyl-1,5-pentanediol and structural units derived from a carboxylic acid component including an aromatic dicarboxylic acid.

6. The aqueous pigment dispersion for water-based ink according to any one of claims 1 to 5, wherein the pigment content in the aqueous pigment dispersion for water-based ink is 2% by mass or more and 20% by mass or less.

7. A water-based ink pigment aqueous dispersion according to any one of claims 1 to 6, wherein the mass ratio of pigment to pigment-containing polyester resin particles (pigment / pigment-containing polyester resin particles) is 0.2 or more and 0.9 or less.

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

9. The aqueous ink according to claim 8, for use with inkjet recording.

Images