Water-based ink for inkjet recording.

Abstract

The present invention relates to an inkjet water-based ink that achieves both abrasion resistance of the printed area and suppression of pressure rise in the flow path without causing clogging of the filter provided in the flow path of an inkjet recording device. [Solution] An inkjet water-based ink containing a pigment and a fixing resin, wherein the fixing resin contains cross-linked polyurethane resin particles having a structure represented by the following formulas (1) to (4). JPEG2026091615000008.jpg5496

Description

Technical Field

[0001] The present invention relates to an aqueous ink for inkjet recording.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from a fine nozzle onto a recording medium and adhered thereto to obtain a printed matter on which characters and images are recorded. Different from the conventional recording methods, since it does not use a plate, it is widely used as on-demand printing that can handle small quantities and multiple varieties. In recent years, due to the demand for printing on conventional glossy paper and the demand for printing on recording media such as cotton broadcloth, matte coated paper, and resin films, various aqueous inks for inkjet recording have been developed.

[0003] Patent Document 1 describes an inkjet recording method in which an aqueous ink composition containing resin particles having a specific acid value, an amino alcohol having a specific boiling point, and a pigment as a colorant is ejected from an inkjet head having a circulation path for circulating the ink composition inside and used for recording, aiming to highly reconcile the water resistance and clogging recovery resistance of the recorded matter.

[0004] Patent Document 2 describes an inkjet recording method having an ink adhesion step in which a pigment printing ink composition containing specific resin particles, water, and a specific organic solvent is ejected from a nozzle of a liquid ejection part and adhered to a fabric, aiming to reconcile the ejection stability of the ink, rubbing resistance, and texture.

[0005] Patent Document 3 describes an inkjet ink composition containing a pigment, urethane resin particles having a crosslinkable group, a lubricant having a specific average particle size, water, and an organic solvent, aiming to improve the ejection stability and intermittent ejection characteristics during recording and to have good friction fastness.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-91822 [Patent Document 2] Japanese Patent Publication No. 2020-104362 [Patent Document 3] Japanese Patent Publication No. 2020-132829 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The urethane resin used as resin particles in Patent Documents 1 to 3 has a higher breaking energy compared to conventional acrylic resins, and when incorporated into an ink composition, it improves the abrasion resistance of the printed area on the recording medium.

[0008] However, as ink compositions containing urethane resin particles are used, coarse particles can become trapped in the filters within the inkjet recording device's flow channels, causing clogging and a gradual increase in pressure within the flow channels. If the pressure within the flow channels rises excessively, it can lead to filter damage.

[0009] The present invention relates to an inkjet water-based ink that prevents clogging of filters in the flow path of an inkjet recording device, and achieves both suppression of pressure rise in the flow path and improvement of abrasion resistance of the printed area. [Means for solving the problem]

[0010] In this invention, we have found that an inkjet recording water-based ink using cross-linked polyurethane resin particles, which are formed by cross-linking the surface of a urethane resin, as a fixing resin, achieves both abrasion resistance of the printed area and suppression of pressure rise in the flow path. The present invention relates to the following [1] to [3].

[0011] [1] An inkjet water-based ink containing a pigment and a fixing resin, wherein the fixing resin contains a crosslinked polyurethane resin having a structure represented by the following formulas (1) to (4). [ka] [2] A method for manufacturing an inkjet recording water-based ink, comprising the following steps. (Process 1) A step of adding a crosslinking agent to an aqueous dispersion of urethane resin, crosslinking the urethane resin particles in the aqueous dispersion of urethane resin, and obtaining an aqueous dispersion of crosslinked urethane resin. (Process 2) A step to obtain an inkjet water-based ink by mixing the crosslinked urethane resin aqueous dispersion obtained in step 1 with a dispersion liquid containing an aqueous pigment dispersion. [3] A printing apparatus equipped with a circulating head having a pressure chamber and a circulation path for circulating the water-based ink for inkjet recording in the pressure chamber, and an inkjet printing method for printing on a printing substrate using the water-based ink for inkjet recording described in [1]. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an inkjet water-based ink that suppresses pressure rise in the flow path and improves the abrasion resistance of the printed area without causing clogging of the filter provided in the flow path of the inkjet recording device. [Modes for carrying out the invention]

[0013] [Water-based ink for inkjet recording] The present invention provides an aqueous ink for inkjet recording (hereinafter also simply referred to as "aqueous ink") which contains a pigment and a fixing resin, wherein the fixing resin contains a crosslinked polyurethane resin having a structure represented by the following formulas (1) to (4). [ka]

[0014] The definitions of various terms used in this specification are shown below. "Printing" is a concept that includes printing and typesetting for recording characters and images, and "printed matter" is a concept that includes printed materials and typeset matter on which characters and images are recorded. "(Meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. "(Meth)acrylate" means at least one selected from the group consisting of acrylate and methacrylate.

[0015] The aqueous ink for inkjet recording of the present invention uses, as a fixing resin, crosslinked polyurethane resin particles having a crosslinked structure, particularly a crosslinked structure near the surface, whereby an ink film excellent in abrasion resistance, that is, printed matter can be obtained, and an increase in pressure in the flow path of the inkjet head can be suppressed.

[0016] The reason is not necessarily fully clear, but it is presumed as follows. By containing a urethane resin, it becomes possible to form an ink film excellent in abrasion resistance on the recording medium. However, when such an aqueous ink is passed through an inkjet head, a problem occurs in that the pressure increases in the flow path. This is because when the aqueous ink containing a urethane resin passes through the pores of the filter installed in the flow path, a local pressure increase occurs, and the dispersion solvent penetrates into the urethane resin and swells, resulting in a decrease in dispersion stability. As a result, it is considered that the urethane resins aggregate and clog the filter, causing an increase in the pressure in the flow path of the inkjet head. On the other hand, when using a urethane resin having a crosslinked structure formed by any of a crosslinking agent such as an epoxy compound, an aziridine compound, a carbodiimide compound, and a compound having an oxazoline group, since the crosslinked polyurethane resin forms a dense network structure on the surface of the resin dispersion, even when a local pressure increase occurs when passing through the filter installed in the ink flow path, the penetration of the dispersion solvent into the resin dispersion can be suppressed. Thereby, the swelling of the urethane resin and the aggregation of the urethane resins are suppressed, and an increase in the pressure in the inkjet head flow path is suppressed.

[0017] <Pigment> The pigment may be either an inorganic pigment or an organic pigment. Inorganic pigments include, for example, carbon black and metal oxides. For black inks, carbon black is preferred from the viewpoint of availability and cost-effectiveness. Specific examples of carbon black include furnace black, thermal black, acetylene black, and channel black. For white inks, examples include titanium dioxide, zinc oxide, silica, alumina, and metal oxides such as magnesium oxide. For white ink pigments, titanium dioxide is preferred from the viewpoint of availability and cost-effectiveness.

[0018] Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. For achromatic inks, achromatic pigments such as white, black, and gray can be used, while for chromatic inks, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. The aforementioned pigments can be used individually or in combination of two or more types.

[0019] Pigments are used in the form of pigments dispersed in a resin or surfactant having pigment-dispersing properties as a dispersant, or in the form of self-dispersing pigments dispersed without the use of a dispersant. Of these, from the viewpoint of improving print quality and abrasion resistance, the form of pigment-containing resin particles (hereinafter referred to as "pigment-containing resin particles") is preferred. Here, pigment-containing resin particles mean any of the following forms or mixtures thereof: particles consisting of the pigment and a resin having pigment-dispersing properties (hereinafter also referred to as "pigment-dispersing resin"), in which the pigment-dispersing resin encapsulates the pigment; particles consisting of pigment-dispersing resin and pigment, in which a portion of the pigment is exposed on the surface of the particles; or particles in which the pigment-dispersing resin is adsorbed onto a portion of the pigment.

[0020] From the viewpoint of improving the print density of the ink, the pigment content in the water-based ink is preferably 2.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 4.0% by mass or more. Furthermore, from the viewpoint of lowering the ink viscosity when the solvent evaporates and improving quick-drying fixation to the recording medium, storage stability of the ink, and discharge stability, the pigment content is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and even more preferably 7.0% by mass or less.

[0021] (Pigment-dispersed resin) Pigment dispersion resins are resins that have the ability to disperse pigments in an aqueous medium mainly composed of water. Examples of pigment dispersion resins include vinyl-based, polyester-based, and polyurethane-based resins. Of these, vinyl-based resins are preferred from the viewpoint of improving print quality and abrasion resistance. Vinyl-based resins are obtained by addition polymerization of vinyl monomers such as vinyl compounds, vinylidene compounds, and vinylene compounds.

[0022] From the viewpoint of improving print quality and abrasion resistance, it is preferable that the pigment dispersion resin has ionic groups. When the pigment dispersion resin is a vinyl resin, the ionic groups are present in the backbone of the pigment dispersion resin by ionic vinyl monomers having ionic groups (hereinafter simply referred to as "ionic vinyl monomers").

[0023] Furthermore, from the same viewpoint as described above, it is preferable that the pigment dispersion resin has hydrophobic groups. When the pigment dispersion resin is a vinyl resin, the hydrophobic groups are present in the backbone of the pigment dispersion resin by hydrophobic vinyl monomers having hydrophobic groups (hereinafter simply referred to as "hydrophobic vinyl monomers").

[0024] In other words, in the present invention, the pigment dispersion resin is preferably a vinyl resin containing structural units derived from ionic vinyl monomers and structural units derived from hydrophobic vinyl monomers.

[0025] From the same viewpoint as described above, the pigment dispersion resin may further have nonionic groups. If the pigment dispersion resin is a vinyl resin, the nonionic groups may be present in the backbone of the pigment dispersion resin by nonionic vinyl monomers having nonionic groups (hereinafter simply referred to as "nonionic vinyl monomers").

[0026] (Ionic vinyl monomer) Ionic vinyl monomers can be either anionic or cationic, but from the viewpoint of dispersion stability of pigment-containing resin particles, anionic monomers are preferred. The ionic group that exhibits anionic properties is preferably an acidic group, and as an acidic group, a carboxylic acid group is preferred from the viewpoint of dispersion stability of pigment-containing resin particles, as well as availability and cost-effectiveness. A specific example of a vinyl monomer having a carboxylic acid group is (meth)acrylic acid.

[0027] In the present invention, it is preferable that some or all of the ionic groups introduced by the ionic vinyl monomer in the pigment dispersion resin constituting the pigment-containing resin particles are neutralized with a basic compound or an acidic compound in order to obtain good dispersibility in an aqueous medium.

[0028] (Hydrophobic vinyl monomer) The term "hydrophobic" in "hydrophobic vinyl monomer" refers to a monomer that, when dissolved in 100g of deionized water at room temperature (25°C) until saturated, dissolves in less than 10g of water.

[0029] Examples of hydrophobic groups in hydrophobic vinyl monomers include alkyl groups, aromatic groups, and silicone groups. Examples of hydrophobic vinyl monomers include alkyl (meth)acrylates, aromatic group-containing monomers, aromatic group-containing macromonomers, and silicone-based macromonomers. Of these, aromatic group-containing monomers and aromatic group-containing macromonomers are preferred from the viewpoint of dispersion stability of pigment-containing resin particles, and aromatic group-containing monomers are more preferred.

[0030] Specific examples of hydrophobic vinyl monomers include styrene-based monomers such as styrene and α-methylstyrene, benzyl (meth)acrylate, and styrene macromers. From the viewpoint of availability and cost-effectiveness, styrene-based monomers are preferred, and styrene, α-methylstyrene, etc., are preferred.

[0031] (Nonionic vinyl monomer) Examples of nonionic groups in nonionic vinyl monomers include hydroxyl groups and polyoxyalkylene groups. Examples of nonionic vinyl monomers include hydroxyalkyl (meth)acrylates, polyalkylene glycol (meth)acrylates, alkoxy polyalkylene glycol (meth)acrylates, and phenoxy polyalkylene glycol (meth)acrylates.

[0032] Specific examples of nonionic vinyl monomers include polyethylene glycol (n=2-30) (meth)acrylate and phenoxy(ethylene glycol / propylene glycol copolymer) (meth)acrylate. The ionic vinyl monomer, hydrophobic vinyl monomer, and nonionic vinyl monomer can each be used individually or in combination of two or more.

[0033] (Content of each constituent unit in the pigment dispersion resin) From the viewpoint of improving the dispersion stability of pigment-containing resin particles, the content of constituent units derived from ionic vinyl monomers, hydrophobic vinyl monomers, and nonionic vinyl monomers in the pigment dispersion resin is as follows:

[0034] The content of constituent units derived from ionic vinyl monomer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0035] The content of constituent units derived from hydrophobic vinyl monomer is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% 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.

[0036] When a nonionic vinyl monomer is included, the content of constituent units derived from the monomer is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.

[0037] The mass ratio of ionic vinyl monomer to hydrophobic vinyl monomer [ionic vinyl monomer / hydrophobic vinyl monomer] is preferably 0.2 or higher, more preferably 0.3 or higher, and preferably 1.0 or lower, more preferably 0.8 or lower, and even more preferably 0.6 or lower, from the viewpoint of improving the dispersion stability and storage stability of the pigment-containing resin particles.

[0038] In the present invention, the content of constituent units derived from ionic vinyl monomers, hydrophobic vinyl monomers, and nonionic vinyl monomers in the pigment dispersion resin can be determined by measurement, or by the charging ratio of raw material monomers containing ionic vinyl monomers, hydrophobic vinyl monomers, and nonionic vinyl monomers during the production of the pigment dispersion resin.

[0039] (Manufacturing of pigment dispersion resins) When the pigment dispersion resin is a vinyl-based resin, it can be produced by polymerizing ionic vinyl monomers, hydrophobic vinyl monomers, and nonionic vinyl monomers using known methods.

[0040] The number-average molecular weight of the pigment-dispersing resin is preferably 9,000 or more, more preferably 12,000 or more, even more preferably 15,000 or more, and preferably 100,000 or less, more preferably 80,000 or less, even more preferably 50,000 or less, and even more preferably 30,000 or less, from the viewpoint of improving the dispersion stability of the pigment-containing resin particles.

[0041] From the viewpoint of improving the dispersion stability of pigment-containing resin particles, the acid value of the pigment dispersion resin is preferably 100 mg KOH / g or more, more preferably 150 mg KOH / g or more, even more preferably 200 mg KOH / g or more, and preferably 350 mg KOH / g or less, more preferably 300 mg KOH / g or less, and even more preferably 270 mg KOH / g or less.

[0042] The acid value of the pigment-dispersed resin can be determined by the method described in the examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, the acid value of vinyl resins with a cross-linked structure can also be calculated using the following formula. Acid value (mgKOH / g) of a crosslinked vinyl resin = [Acid value of vinyl resin before crosslinking (mgKOH / g) × [(100 - Crosslinking rate (mol%)) / 100]

[0043] Commercially available pigment dispersion resins may be used. Examples of commercially available pigment dispersion resins include styrene / acrylic resins such as "Joncryl 67," "Joncryl 611," "Joncryl 678," "Joncryl 680," "Joncryl 690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0044] (Manufacturing of pigment-containing resin particles) Resin particles containing pigments can be efficiently manufactured by a method comprising the following steps I and II. Step I: A step to obtain an aqueous dispersion of the pigment dispersion resin by neutralizing at least a portion of the carboxyl groups of the pigment dispersion resin with an alkali metal compound. Step II: A step to obtain an aqueous pigment dispersion of resin particles containing pigment dispersed in pigment dispersion resin, by dispersing the aqueous dispersion of pigment resin obtained in Step I with the pigment.

[0045] Furthermore, in the production of pigment-containing resin particles, the process may optionally include a step III in which the aqueous pigment dispersion obtained in step II is crosslinked with a crosslinking agent.

[0046] In the present invention, from the viewpoint of improving the dispersion stability of the pigment, it is preferable that the pigment dispersion resin constituting the pigment-containing resin particles has a crosslinked structure in at least a portion of it. The pigment dispersion resin having a crosslinked structure preferably further contains an ionic vinyl monomer, a hydrophobic vinyl monomer, and, if necessary, constituent units derived from the ionic vinyl monomer and hydrophobic vinyl monomer, as well as a compound having two or more functional groups that can react with the ionic vinyl monomer, i.e., a component derived from a crosslinking agent. In this invention, the amount of crosslinking agent-derived components in the pigment dispersion resin constituting the pigment-containing resin particles can be determined from the amount of resin used during its production.

[0047] When the pigment dispersion resin constituting the pigment-containing resin particles has a crosslinked structure, it is preferable that the pigment-containing resin particles be prepared using the aforementioned pigment, pigment dispersion resin, and crosslinking agent.

[0048] Examples of crosslinking agents include compounds having two or more functional groups that can react with the functional groups of the pigment dispersion resin. For example, when the pigment dispersion resin has a carboxyl group, from the viewpoint of improving the dispersion stability of the pigment, polyglycidyl ether compounds of polyhydric alcohols having hydrocarbon groups with 3 to 8 carbon atoms are preferred as crosslinking agents, pentaerythritol polyglycidyl ether and trimethylolpropane polyglycidyl ether are more preferred, and trimethylolpropane polyglycidyl ether is even more preferred.

[0049] In the present invention, the ratio of the molar equivalents of the crosslinking functional groups of the crosslinking agent to the molar equivalents of the ionic groups of the pigment dispersion resin, i.e., the crosslinking rate, is preferably 10 mol% or more, more preferably 30 mol% or more, and even more preferably 50 mol% or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 80 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less, from the viewpoint of improving the dispersion stability of the pigment-containing resin particles.

[0050] In the present invention, the mass ratio of the pigment dispersion resin to the pigment constituting the pigment-containing resin particles [content of pigment dispersion resin / content of pigment] is preferably 0.10 or more, more preferably 0.15 or more, even more preferably 0.20 or more, and preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.30 or less, from the viewpoint of improving the dispersion stability of the pigment-containing resin particles.

[0051] <Fixing resin> The fixing resin, in the inkjet recording method, fixes the atomized water-based ink that is ejected from the nozzle as ink droplets onto the recording medium. In this invention, a crosslinked polyurethane resin is used as the fixing resin. While fixing resins using urethane resins and crosslinked acrylic resins are known, prior art using crosslinked polyurethane resin is not known to date. In the present invention, the fixing resin is a crosslinked polyurethane resin, which is used as crosslinked polyurethane resin particles in an aqueous ink. The crosslinked polyurethane resin particles include crosslinked polyurethane resin particles having the structure represented by formulas (1) to (4) described later. Furthermore, crosslinked polyurethane resin is obtained by crosslinking urethane resin. Crosslinked polyurethane resin particles are obtained by using polyurethane resin as an aqueous dispersion of polyurethane resin particles and crosslinking the polyurethane resin particles.

[0052] To improve the water dispersion stability in the ink of the present invention, it is preferable to use a polyurethane having hydrophilic groups. As the hydrophilic groups, anionic groups, cationic groups, and nonionic groups can be used. Among these, it is preferable to use anionic groups or cationic groups as the hydrophilic groups.

[0053] Examples of anionic groups that can be used include carboxyl groups, carboxylate groups, sulfonic acid groups, and sulfonate groups. In particular, it is preferable to use carboxylate groups or sulfonate groups that are partially or entirely neutralized by a basic compound or the like in order to maintain good water dispersion stability.

[0054] More specifically, the polyurethane resin can be a reaction product of a polyol and a polyisocyanate. More specifically, a reaction product of a polyol and a polyisocyanate, including a polyol and a polyol having a hydrophilic group, can be used.

[0055] Polyurethane resins are obtained by polyaddition reaction of polyols and polyisocyanates using known methods.

[0056] There are no particular restrictions on the polyol as long as it is a compound having two or more hydroxyl groups in one molecule, and polyester polyols, polycarbonate polyols, and polyether polyols are used. Specifically, polyurethane resins include (i) polyester-based polyurethane resins, (ii) polycarbonate-based polyurethane resins, and (iii) polyether-based polyurethane resins, etc. The crosslinked polyurethane resin is preferably one or more selected from polyester-based polyurethane resins and polycarbonate-based polyurethane resins, with polycarbonate-based polyurethane resins being more preferred, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area.

[0057] (Polyol) (i) Polyester-based polyurethane resin Polyester-based polyurethane resins are obtained by polyaddition reaction between polyester polyol and polyisocyanate. The raw material, polyester polyol, is obtained by condensing a diol and a dicarboxylic acid. Examples of diols used include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 3-methyl-1,5-pentanediol, cyclohexanediol, and 1,6-hexanediol, all of which have 2 to 10 carbon atoms. Dicarboxylic acids include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and brassic acid, and aromatic dibasic acids such as isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid.

[0058] (ii) Polycarbonate-based polyurethane resin Polycarbonate-based polyurethane resins are obtained by polyaddition reaction between polycarbonate polyol and polyisocyanate. The raw material, polycarbonate polyol, is obtained by transesterifying a diol and a diester carbonate. Examples of diols include the same ones mentioned as raw material diols for polyester polyols.

[0059] (iii) Polyether-based polyurethane resin Polyether-based polyurethane resins are obtained by polyaddition reaction between a polyether polyol and a polyisocyanate. Examples of polyether polyols used as raw materials include polyether diols obtained by polymerizing 2 to 45 molecules, preferably 10 to 40 molecules, of alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, and tetramethylene glycol; and polymers obtained by ring-opening polymerization of cyclic ether compounds such as tetrahydrofuran and epichlorohydrin, either alone or in combination of two or more.

[0060] As the hydrophilic polyol, it is preferable to use one that has an anionic group, for example, 1,2-bis(hydroxymethyl)propionic acid or 1,2-bis(hydroxymethyl)butanoic acid can be used.

[0061] (Polyisocyanate) Examples of polyisocyanates include aliphatic diisocyanates, aliphatic diisocyanates with a cyclic structure, aliphatic diisocyanates with an aromatic ring, aromatic diisocyanates, and modified products of these diisocyanates (such as modified products containing carbodiimide, uretodione, and uretoimine).

[0062] Examples of aliphatic diisocyanates include tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0063] Examples of aliphatic diisocyanates having a cyclic structure include 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate.

[0064] Examples of aliphatic diisocyanates having an aromatic ring include xylylene diisocyanate and tetramethylxylylene diisocyanate.

[0065] Examples of aromatic diisocyanates include tolylene diisocyanate, phenylene diisocyanate, and diphenylmethane diisocyanate.

[0066] Among these, from the viewpoint of improving adhesion to recording media, abrasion resistance, water resistance, etc., aliphatic diisocyanates, aliphatic diisocyanates having a cyclic structure, and aromatic diisocyanates are preferred, and hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, tolylene diisocyanate, etc. are more preferred.

[0067] The aforementioned polyols and polyisocyanates can be used by using the compounds contained in each component individually or in combination of two or more.

[0068] (Manufacturing of polyurethane resin) In the polyaddition reaction of polyurethane resins, it is preferable to use polymerization catalysts such as amine compounds and organotin compounds. Specific examples of amine compounds include aliphatic diamines such as ethylenediamine, propylenediamine, and hexamethylenediamine; alicyclic diamines such as isophoronediamine; alkyl aromatic diamines such as xylylenediamine; and hydrazine. Among these, aliphatic diamines are preferred from the viewpoint of productivity, availability, and economic efficiency, and ethylenediamine is more preferred. Suitable reaction solvents include acetone, methyl ethyl ketone (MEK), tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. However, from the viewpoint of productivity, availability, and economic efficiency, acetone, MEK, and ethyl acetate are preferred. In polyaddition reactions, chain extenders may be used in combination as needed. The molecular weight can be increased by using chain extenders. Examples of chain extenders include polyols and polyamines.

[0069] Polyurethane resins may have a branched structure. Methods for forming a branched structure include synthesizing polyurethane using a monomer with three or more functions, or obtaining a linear polyurethane using a monomer with two functions and then reacting it with a compound with three or more functions that reacts with the terminal isocyanate or hydroxyl group.

[0070] The acid value of the crosslinked polyurethane resin according to the present invention before crosslinking is preferably 1 mg KOH / g or more, more preferably 10 mg KOH / g or more, even more preferably 20 mg KOH / g or more, and preferably 50 mg KOH / g or less, more preferably 40 mg KOH / g or less, and even more preferably 30 mg KOH / g or less, from the viewpoint of improving the dispersion stability of the crosslinked polyurethane resin particles in aqueous ink.

[0071] The crosslinked polyurethane resin according to the present invention is obtained by crosslinking the polyurethane. The crosslinked polyurethane resin has a structure represented by the following formulas (1) to (4). [ka]

[0072] The structures represented by formulas (1) to (4) are crosslinked structures present on part or all of the surface of crosslinked polyurethane resin particles. These crosslinked structures are formed by methods such as reacting the polyurethane resin with a bifunctional or more crosslinking agent after obtaining the polyurethane resin.

[0073] (The structure represented by equation (1)) The structure represented by formula (1) can be introduced by crosslinking a urethane resin using an epoxy compound as a crosslinking agent. In other words, the structure represented by formula (1) is derived from the epoxy compound. Specific examples of epoxy compounds include sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, phthalate diglycidyl ester, and polypropylene glycol diglycidyl ether. Of these, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area, glycidyl ether compounds of polyhydric alcohols having hydrocarbon groups with 3 to 8 carbon atoms are preferred, and one or more selected from glycidyl ether compounds of dihydric alcohols and glycidyl ether compounds of trihydric alcohols having hydrocarbon groups with 3 to 8 carbon atoms are more preferred. Therefore, the epoxy compound is preferably sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, or hydrogenated bisphenol A diglycidyl ether; more preferably trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, or hydrogenated bisphenol A diglycidyl ether; and even more preferably trimethylolpropane polyglycidyl ether or 1,6-hexanediol diglycidyl ether.

[0074] Examples of commercially available epoxy compounds include the following (all manufactured by Nagase ChemteX Corporation): Denacol EX-622 (sorbitol polyglycidyl ether (tetrafunctional), epoxy equivalent: 191 g / eq, water solubility: 0% by mass), Denacol EX-321 (trimethylolpropane polyglycidyl ether (mixture of bifunctional and trifunctional compounds), epoxy equivalent: 140 g / eq, water solubility: 27% by mass), Denacol EX-321L (Trimethylolpropane polyglycidyl ether (mixture of bifunctional and trifunctional), epoxy equivalent: 130 g / eq, water solubility: 0% by mass), Denacol EX-201 (resorcinol diglycidyl ether (bifunctional), epoxy equivalent: 117 g / eq, water solubility: 0% by mass), Denacol EX-201-IM (resorcinol diglycidyl ether (bifunctional), epoxy equivalent: 120 g / eq, water solubility: 0% by mass), Denacol EX-211 (neopentyl glycol diglycidyl ether (bifunctional), epoxy equivalent: 138 g / eq, water solubility: 0% by mass), Denacol EX-212 (1,6-Hexanediol diglycidyl ether (bifunctional), epoxy equivalent: 151 g / eq, water solubility: 0% by mass), Denacol EX-212L (1,6-Hexanediol diglycidyl ether (bifunctional), epoxy equivalent: 135 g / eq, water solubility: 0% by mass), Denacol EX-216L (Cyclohexanedimethanol diglycidyl ether, epoxy equivalent: 150 g / eq, water solubility: 0% by mass), Denacol EX-252 (Hydrogenated bisphenol A diglycidyl ether (bifunctional), epoxy equivalent: 213 g / eq, water solubility: 0% by mass), Denacol EX-721 (Diglycidyl phthalate (bifunctional), epoxy equivalent: 154 g / eq, water solubility: 0% by mass), Denacol EX-931 (polypropylene glycol diglycidyl ether (bifunctional), epoxy equivalent: 471 g / eq, water solubility: 0% by mass), Denacol EX-991L ((bifunctional), epoxy equivalent: 450 g / eq, water solubility: 0% by mass)

[0075] (The structure represented by equation (2)) The structure represented by formula (2) can be introduced by crosslinking a urethane resin using an aziridine compound as a crosslinking agent. In other words, the structure represented by formula (2) is derived from an aziridine compound. Aziridine compounds are specifically compounds that have two or more aziridine groups. Specific examples of aziridine compounds include 2,2-bishydroxymethylbutanoltris[3-(1-aziridinyl)propanate], 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane, 1-(aziridin-2-yl)-2-oxabuto-3-ene, 5-(aziridin-2-yl)-pento-1-ene, and (aziridin-2-yl)-buto-1-ene. From the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area, aziridine compounds having two to three aziridine groups and a molecular weight of 300 to 500 are preferred. The aziridine group equivalent of the aziridine compound is preferably 30 or more, more preferably 60 or more, even more preferably 100 or more, and preferably 1000 or less, more preferably 600 or less, and even more preferably 200 or less, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area. The aziridine group equivalent refers to the mass of the aziridine compound per mole of aziridine groups. A commercially available aziridine compound is, for example, Chemitite PZ33 (2,2-bishydroxymethylbutanoltris[3-(1-aziridinyl)propanate]; manufactured by Nippon Shokubai Co., Ltd.).

[0076] (The structure represented by equation (3)) The structure represented by formula (3) can be introduced by crosslinking a urethane resin using a carbodiimide compound as a crosslinking agent. In other words, the structure represented by formula (3) is derived from the carbodiimide compound. Carbodiimide compounds are specifically polycarbodiimide compounds that have two or more carbodiimide groups in one molecule. The carbodiimide group equivalent of the polycarbodiimide compound is preferably 200 or more, more preferably 250 or more, even more preferably 300 or more, and preferably 650 or less, more preferably 500 or less, and even more preferably 400 or less, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area. The carbodiimide group equivalent refers to the mass of the polycarbodiimide compound per mole of carbodiimide groups.

[0077] From the viewpoint of reactivity, stability, and ease of handling, the polycarbodiimide compound is preferably an aqueous polycarbodiimide compound having hydrophilic groups at its termini. The aqueous polycarbodiimide compound can be produced by forming an isocyanate-terminated polycarbodiimide through a condensation reaction involving decarboxylation of an organic diisocyanate compound, and then adding a known hydrophilic segment having a functional group that is reactive with isocyanate groups. Examples of commercially available polycarbodiimide compounds include Carbodilite E-02, Carbodilite E-03A, Carbodilite E-05, Carbodilite V-02, Carbodilite V-02-L2, and Carbodilite V-04 (all manufactured by Nisshinbo Chemical Co., Ltd., trade names).

[0078] (The structure represented by equation (4)) The structure represented by formula (4) can be introduced by crosslinking a urethane resin using a compound having an oxazoline group as a crosslinking agent. In other words, the structure represented by formula (4) is a structure derived from a compound having an oxazoline group. Compounds containing oxazoline groups are specifically compounds in which two to three oxazoline groups are bonded to an aliphatic or aromatic group. Examples include bisoxazoline compounds such as 2,2'-bis(2-oxazoline), 1,3-phenylenebisoxazoline, and 1,3-benzobisoxazoline, and compounds having terminal oxazoline groups obtained by reacting these compounds with polybasic carboxylic acids.

[0079] (Polyfunctional oxazoline compounds) A polyfunctional oxazoline compound is a compound having two or more oxazoline groups in its molecule. A polymer containing two or more oxazoline groups (hereinafter also referred to as an "oxazoline group-containing polymer") is preferred as the polyfunctional oxazoline compound. From the viewpoint of increasing reactivity, the number-average molecular weight of the oxazoline group-containing polymer is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. Examples of oxazoline group-containing polymers include polymers with an acrylic backbone, polymers with a styrene / acrylic backbone, polymers with a styrene backbone, and polymers with an acrylonitrile / styrene backbone.

[0080] The oxazoline group equivalent of the oxazoline group-containing polymer is preferably 100 or more, more preferably 170 or more, even more preferably 200 or more, and preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less, from the viewpoint of providing an inkjet water-based ink that achieves both excellent intermittent ejection stability and excellent storage stability. Note that the oxazoline group equivalent refers to the mass of the oxazoline group-containing polymer per mole of oxazoline groups. Examples of commercially available oxazoline group-containing polymers include the "Epocross WS" series, such as "Epocross WS-300," "Epocross WS-500," and "Epocross WS-700" (all manufactured by Nippon Shokubai Co., Ltd., and are water-soluble).

[0081] The crosslinked polyurethane resin according to the present invention has a structure represented by formulas (1) to (4) above. That is, the crosslinked polyurethane resin has a urethane bond that forms the main skeleton, an ether bond derived from the crosslinking agent, a divalent amino group (-NH-), and a divalent hydrocarbon group which may have one or more selected from the group consisting of oxygen atoms and nitrogen atoms.

[0082] The crosslinked polyurethane resin according to the present invention is preferably one or more selected from a crosslinked polyurethane resin crosslinked with a glycidyl ether compound of a polyhydric alcohol having hydrocarbon groups having 3 to 8 carbon atoms, and a urethane resin crosslinked with an aziridine compound having 2 to 3 aziridine groups and a molecular weight of 300 to 500, from the viewpoint of suppressing pressure rise in the flow channel and improving the abrasion resistance of the printed part. It is more preferable that the material be one or more selected from polyurethane resins and polyurethane resins crosslinked with an aziridine compound having two to three aziridine groups and a molecular weight of 300 to 500; it is even more preferable that the material be one or more selected from crosslinked polyurethane resins crosslinked with a glycidyl ether compound of a divalent alcohol having hydrocarbon groups having 3 to 8 carbon atoms and crosslinked polyurethane resins crosslinked with a glycidyl ether compound of a trivalent alcohol having hydrocarbon groups having 3 to 8 carbon atoms; and even more preferable that the material is a polyurethane resin crosslinked with a glycidyl ether compound of a trivalent alcohol having hydrocarbon groups having 3 to 8 carbon atoms. Furthermore, from the viewpoint of suppressing pressure rise in the flow channel and improving the abrasion resistance of the printed area, the crosslinked polyurethane resin according to the present invention is preferably one or more crosslinked polyurethane resins selected from the structures represented by formulas (1) to (4) above, specifically from the structures represented by formula (1) and formula (2), and more preferably the crosslinked polyurethane resin with the structure represented by formula (1).

[0083] In the crosslinked polyurethane resin according to the present invention, the crosslinking rate of the polyurethane resin by the crosslinking agent is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and even more preferably 15 mol or more, from the viewpoint of suppressing pressure rise in the flow channel, and from the viewpoint of improving the abrasion resistance of the printed part, it is preferably 90 mol or less, more preferably 75 mol or less, even more preferably 70 mol or less, even more preferably 60 mol or less, even more preferably 50 mol or less, and even more preferably 30 mol or less. Here, the crosslinking ratio is determined by the ratio of the number of molar equivalents of the crosslinking functional groups of the crosslinking agent to the number of molar equivalents of ionic groups determined from the acid value of the polyurethane resin before crosslinking. Furthermore, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed portion, it is preferable that part or all of the surface of the crosslinked polyurethane resin particles has a structure represented by formula (1) or formula (2), and it is more preferable that part or all of the surface of the crosslinked polyurethane resin particles has a structure represented by formula (1).

[0084] The average particle size of the crosslinked polyurethane resin is preferably 40 nm or more, more preferably 50 nm or more, even more preferably 60 nm or more, and preferably 100 nm or less, more preferably 90 nm or less, and even more preferably 80 nm or less, from the viewpoint of suppressing pressure rise in the flow channel and improving the abrasion resistance of the printed part.

[0085] The content of cross-linked polyurethane resin particles in the water-based ink is preferably 1.5% by mass or more, more preferably 3.0% by mass or more, even more preferably 4.0% by mass or more, even more preferably 5.0% by mass or more, and preferably 15.0% by mass or less, more preferably 12.0% by mass or less, and even more preferably 9.0% by mass or less, from the viewpoint of suppressing pressure rise in the flow path and improving the abrasion resistance of the printed area, from the viewpoint of improving quick-drying fixation to the recording medium and long-term fixation, and from the viewpoint of improving the storage stability and discharge stability of the water-based ink.

[0086] The aforementioned crosslinked polyurethane resin particles are obtained by reacting a polyurethane resin particle aqueous dispersion with a crosslinking agent. For this reason, the crosslinked polyurethane resin particles have the structure represented by formulas (1) to (4) on part or all of their surface. In other words, they have a layer on their surface with a high crosslink density. For this reason, when an aqueous ink containing crosslinked polyurethane resin particles is passed through an inkjet recording device, the crosslinked polyurethane resin particles are less likely to swell in the ink flow path and are less likely to clog the filter provided in the circulating print head. On the other hand, polyurethane resin particles that do not have the structure represented by formulas (1) to (4) on their surface have a low crosslink density on their surface. Therefore, when an aqueous ink containing these polyurethane resin particles is passed through an inkjet head, the pressure locally increases as it passes through the pores of the filter, causing the ink components to penetrate into the polyurethane resin particles and swell.

[0087] When acrylic resins are used as fixing resins for water-based inkjet recording, the problem of filter clogging does not occur. However, because their breaking energy is lower than that of polyurethane resins, the printed area has poor abrasion resistance when printed on recording media such as cotton broadcloth. On the other hand, the crosslinked polyurethane resin according to the present invention has a higher breaking energy than acrylic resins. Therefore, the printed area printed on a recording media using water-based ink containing the crosslinked polyurethane resin has excellent abrasion resistance, thus achieving both abrasion resistance of the printed area and suppression of pressure rise in the flow path.

[0088] <Water-soluble organic solvents> From the viewpoint of obtaining printed materials with excellent ejection stability and adhesion to recording media, the aforementioned water-based ink preferably contains a water-soluble organic solvent with a boiling point of 100°C or higher and 300°C or lower. Water-soluble organic solvents may be liquid or solid at room temperature (25°C). A water-soluble organic solvent is defined as an organic solvent whose solubility is 10 mL or more when dissolved in 100 mL of water at 25°C. From the viewpoint of obtaining printed materials with excellent discharge stability and adhesion to recording media, the boiling point of the water-soluble organic solvent is preferably 110°C or higher, more preferably 120°C or higher, and preferably 300°C or lower, more preferably 290°C or lower. Here, boiling point refers to the standard boiling point (boiling point at 1 atmosphere), and when two or more water-soluble organic solvents are used, the weighted average value is used, weighted by the content (mass%) of each water-soluble organic solvent.

[0089] Examples of water-soluble organic solvents include glycol ethers, polyhydric alcohols, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, and alkanolamines. Of these, glycol ethers and polyhydric alcohols are more preferred from the viewpoint of obtaining printed materials with excellent ejection stability and adhesion to recording media. From the viewpoint of obtaining printed materials with excellent ejection stability and adhesion to recording media, alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers are preferred as glycol ethers, and alkylene glycol monoalkyl ethers are more preferred. From the viewpoint of obtaining printed materials with excellent ejection stability and adhesion to recording media, the number of carbon atoms in the alkyl group of the glycol ether is 1 or more, preferably 2 or more, more preferably 3 or more, and preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. The alkyl group may be linear or branched.

[0090] Specific examples of alkylene glycol monoalkyl ethers include ethylene glycol monoisopropyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, and diethylene glycol monobutyl ether. Of these, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monoisobutyl ether are preferred from the viewpoint of availability and cost-effectiveness, and diethylene glycol monoisobutyl ether is more preferred from the viewpoint of quick drying. For recording media that require time for ink drying, such as non-permeable recording media like resin films, a water-soluble organic solvent using diethylene glycol monoisobutyl ether is preferred.

[0091] From the viewpoint of availability and economic efficiency, preferred polyhydric alcohols include propylene glycol, diethylene glycol, dipropylene glycol, alkanediols with 2 to 6 carbon atoms such as 1,2-hexanediol, glycerin, and polypropylene glycol with a molecular weight of 500 to 1000, with propylene glycol and dipropylene glycol being more preferred.

[0092] From the viewpoint of improving the discharge stability of the water-based ink, the content of water-soluble organic solvent in the water-based ink is preferably 5.0% by mass or more, more preferably 10.0% by mass or more, even more preferably 15.0% by mass or more, and preferably 60.0% by mass or less, more preferably 50.0% by mass or less, even more preferably 40.0% by mass or less, and even more preferably 30.0% by mass or less.

[0093] <Surfactants> As for the surfactant, nonionic surfactants are preferred from the viewpoint of the wetting and spreading properties of the ink on the recording medium, and one or more selected from acetylene glycol-based surfactants and silicone-based surfactants are more preferred, and using acetylene glycol-based surfactants and silicone-based surfactants in combination is even more preferred.

[0094] (Acetylene glycol-based surfactant) Examples of acetylene glycol-based surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol, as well as their ethylene oxide adducts. The sum of the average number of moles of ethylene oxy groups (EO) added to the ethylene oxide adduct is preferably 0 or more, preferably 20 or less, and more preferably 10 or less. The hydrophilic-lipophilic balance (HLB) of the acetylene glycol-based surfactant is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, from the viewpoint of solubility in water-based inks, and preferably 14 or less, more preferably 10 or less, and even more preferably 6 or less, from the viewpoint of ink wetting and spreading properties on recording media. 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.

[0095] (Silicone-based surfactant) Examples of silicone-based surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone. Of these, polyether-modified silicone is preferred from the viewpoint of ink wetting and spreading properties on recording media. The HLB of the polyether-modified silicone surfactant is preferably 8 or higher, more preferably 10 or higher, and even more preferably 13 or higher, from the viewpoint of solubility in water-based inks. The HLB can be determined by the Griffin method. Commercially available polyether-modified silicone surfactants include the KF series from Shin-Etsu Chemical Co., Ltd., the Silface SAG series from Nisshin Chemical Industry Co., Ltd., and the BYK series from BIC Chemie Japan Co., Ltd. Among these, the KF series from Shin-Etsu Chemical Co., Ltd. is preferred.

[0096] The surfactant content in the water-based ink is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, from the viewpoint of improving the wettability of the ink and improving the uniformity of the image when printed on a recording medium. Furthermore, from the viewpoint of improving the uniformity of the image when printed on a recording medium and improving the ejection stability of the water-based ink, it is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

[0097] <Water> Distilled water, deionized water, pure water, and purified water are used as the water content. The water content is the remainder after subtracting the content of pigment, fixing resin, and other optional components from the water-based ink. The water content in the water-based ink is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of improving the ejection stability and storage stability of the water-based ink. Furthermore, from the viewpoint of improving the quick-drying fixation, long-term fixation, and image uniformity of the printed material on the recording medium, it is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0098] <Other ingredients> In addition to the components mentioned above, the water-based ink of the present invention may contain additives such as commonly used penetrating agents, dispersing agents, viscosity modifiers, defoaming agents, preservatives, fungicides, and rust inhibitors.

[0099] [Method for manufacturing water-based ink for inkjet recording] The aqueous ink of the present invention is prepared by adding the aforementioned pigment, fixing resin, and other components, dispersing them by a known method, and, if necessary, removing coarse particles by filtration.

[0100] The aqueous ink of the present invention is preferably discharged from a circulation head having a pressure chamber and a circulation path for circulating the aqueous ink for inkjet recording within the pressure chamber. The aqueous ink can suppress pressure rise in the flow path because it does not cause clogging of the filter provided in the circulation print head within the inkjet recording device.

[0101] [Inkjet recording method] The present invention relates to an inkjet printing method comprising a printing apparatus equipped with a circulation head having a pressure chamber and a circulation path for circulating an inkjet recording aqueous ink in the pressure chamber, and a method of printing on a printing substrate using the inkjet recording aqueous ink. Specifically, the inkjet printing method involves attaching a container filled with aqueous ink to an inkjet recording apparatus equipped with the circulation head, and forming a printed material by spraying the aqueous ink onto the printing substrate. The inkjet printing method may also include a step of drying the printed material after printing on the printing substrate. Inkjet recording apparatuses include thermal and piezo types, but the piezo type is preferred. That is, the aqueous ink of the present invention is preferably used for piezo type inkjet recording.

[0102] (Printing base material) The water-based ink of the present invention is applicable to any substrate. Therefore, suitable recording media include paper, cloth (fabric), and resin films. Specific examples of paper include glossy paper, matte coated paper, and gloss coated paper. Specific examples of cloth include cotton, polyester, and nylon. Specific examples of resin films include polyester film, polyvinyl chloride film, polypropylene film, polyethylene film, and nylon film. These films may be subjected to surface treatments such as corona treatment as needed. [Examples]

[0103] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way by these examples. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. [Methods for measuring various physical properties] (1) Number average molecular weight of pigment dispersion resin D1 The results were obtained by gel permeation chromatography. The measurement conditions are shown below. GPC device: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation. Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits 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)] (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of resin was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter "DISMIC-13HP" (PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0104] (2) Non-volatile component concentration (solid content concentration) Approximately 10 g of sodium sulfate, which had been stabilized in a desiccator, was accurately weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm). Approximately 1 g of the sample was added and mixed, then accurately weighed again. The mixture was maintained at 105°C for 2 hours to remove volatile components, and then left in the desiccator for another 15 minutes before being accurately weighed again. The mass of the sample after removal of volatile components was taken as the solid content, and the concentration of non-volatile components (solid content concentration) was obtained by dividing it by the mass of the added sample.

[0105] (3) Acid value of polyurethane resin particles, acrylic resin particles, and pigment dispersion resin D1 Two g of 50% MEK solution samples of each resin were accurately weighed, diluted with 50 g of deionized water, and 3 mL of 0.1 N sodium hydroxide / ethanol solution was added to obtain titration samples. The titration samples were titrated with 0.1 N hydrochloric acid using a potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610). After measuring the pH inflection points at two locations, the number of moles of hydrochloric acid used was calculated from the difference in the amount of 0.1 N hydrochloric acid added between the two points. The acid value (mgKOH / g) of each resin was calculated from the ratio of the number of moles of hydrochloric acid used to the solid content of each resin.

[0106] (4) Measurement of the average particle size of crosslinked polyurethane resin particles, crosslinked acrylic resin particles, and pigment aqueous dispersions Using a laser particle analysis system (ELS-8000, manufactured by Otsuka Electronics Co., Ltd.), the average particle size of crosslinked polyurethane resin particles, crosslinked acrylic resin particles, and pigment aqueous dispersions was measured by dynamic light scattering and calculated by cumulant analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integration cycles. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. Crosslinked polyurethane resin particles, crosslinked acrylic resin particles, and pigment aqueous dispersions were weighed into screw tubes (No. 5, manufactured by Maruemu Co., Ltd.) 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.

[0107] [Manufacturing Example 1-1] (Manufacturing of an aqueous dispersion of urethane resin particles A-1) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 14.0 parts of polycarbonate polyol (product name: UH CARB-100, manufactured by Ube Industries, Ltd., molecular weight 1,000) as the polyol component, 6.2 parts of hexamethylene diisocyanate (reagent name: 1,6-diisocyanate hexane, manufactured by Tokyo Chemical Industry Co., Ltd.) as the diisocyanate component, and 43.6 parts of MEK were added and reacted at 75°C for 1 hour. Then, 1.3 parts of dimethylolpropionic acid, 1.0 part of triethylamine, and 10 parts of MEK were added and reacted at 75°C for 1 hour to obtain a MEK solution containing the prepolymer. Next, this solution was cooled to 45°C, ion-exchanged water and 0.2 parts of diethylenetriamine were mixed, and the solvent was removed by vacuum distillation at 50°C for 2 hours to obtain an aqueous dispersion of urethane resin particles A-1 (solid content concentration 35%, acid value 25 mg KOH / g).

[0108] [Manufacturing Example 1-2] (Manufacturing of aqueous dispersion of urethane resin particles A-2) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 9.8 parts of polyester polyol (trade name: P-2011, manufactured by Mitsubishi Chemical Corporation, molecular weight 1000) as the polyol component, 7.2 parts of tolylene diisocyanate (trade name: Coronate T-80, manufactured by Tosoh Corporation) as the diisocyanate component, and 50 parts of MEK were added and reacted at 75°C for 1 hour. Then, 1.2 parts of dimethylolpropionic acid, 0.5 parts of 1,4-butanediol, 0.2 parts of triethylamine, and 10 parts of MEK were added and reacted at 75°C for 1 hour to obtain a MEK solution containing the prepolymer. Next, this solution was cooled to 45°C, ion-exchanged water and 1.1 parts of ethylenediamine were mixed, and the solvent was removed by vacuum distillation at 50°C for 2 hours to obtain an aqueous dispersion of urethane resin particles A-2 (solid content concentration 35%, acid value 25 mg KOH / g).

[0109] [Manufacturing Example 1-3] (Manufacturing of aqueous dispersion of urethane resin particles A-3) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 14.6 parts of polyether polyol (trade name: PTMG1000, manufactured by Mitsubishi Chemical Corporation, molecular weight 1000) as the polyol component, 4.1 parts of isophorone diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) as the diisocyanate component, and 50 parts of MEK were added and reacted at 75°C for 1 hour. Then, 1.2 parts of dimethylolpropionic acid, 0.2 parts of triethylamine, and 10 parts of MEK were added and reacted at 75°C for 1 hour to obtain a MEK solution containing the prepolymer. Next, this solution was cooled to 45°C, ion-exchanged water and 0.6 parts of ethylenediamine were mixed, and the solvent was removed by vacuum distillation at 50°C for 2 hours to obtain an aqueous dispersion of urethane resin particles A-3 (solid content concentration 35%, acid value 25 mg KOH / g).

[0110] [Manufacturing Example 2-1] (Manufacturing of aqueous dispersion of cross-linked polyurethane resin particles B-1) To 285.71 parts (100 parts solids) of an aqueous dispersion of urethane resin particles A-1 obtained in Production Example 1-1, 0.57 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-321L, epoxy equivalent: 129) were added as a crosslinking agent to achieve a degree of crosslinking of 10 mol%, and then 116.01 g of deionized water was added and mixed. The mixture was then heated at 80°C for 7 hours with stirring to react the carboxyl groups in urethane resin A-1 with the epoxy groups in trimethylolpropane polyglycidyl ether. The mixture was then cooled to 25°C and filtered through a 5 μm pore size filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain an aqueous dispersion of crosslinked polyurethane resin particles B-1 (solids concentration: 25%, crosslinking rate: 10 mol%, average particle size: 68 nm) that did not contain pigment.

[0111] [Manufacturing Example 2-2] to [Manufacturing Example 2-9] (Manufacturing of aqueous dispersions of cross-linked polyurethane resin particles B-2 to B-9) Aqueous dispersions of crosslinked polyurethane resin particles B-2 to B-9 (solid content concentration 25%) were produced in the same manner as in Production Example 2-1, except that the type of urethane resin particles, the type and amount of crosslinking agent were changed as shown in Table 1. Table 1 shows the crosslinking ratio and average particle size of crosslinked polyurethane resin particles B-2 to B-9. [Table 1]

[0112] [Manufacturing Example 2-10] (Manufacturing of aqueous dispersion of cross-linked acrylic resin particles B-10) 100 parts (solid content concentration: 44%) of acrylic resin particles (BASF, trade name: Joncryl8211, Tg: 60℃, acid value: 26 mg KOH / g) were placed in a screw-top glass bottle. 0.84 parts (crosslinking rate: 30%) of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, trade name: Denacol EX-321, epoxy equivalent: 140 g / eq.) and 79 parts of deionized water were added as crosslinking agents. The bottle was then sealed tightly and heated at 70℃ for 5 hours while stirring with a stirrer. After 5 hours, the mixture was cooled to room temperature and filtered using a 25 mL needleless syringe (Terumo Corporation) fitted with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, Fujifilm Corporation) to obtain an aqueous dispersion of crosslinked acrylic resin particles B-10 (solid content concentration: 25%, acid value: 18 mg KOH / g, average particle size: 108 nm).

[0113] [Manufacturing Example 3-1] (Manufacturing of Pigment Dispersion 1) (1) Synthesis of pigment-dispersed resin D1 A monomer mixture was prepared by mixing 31 parts acrylic acid and 69 parts styrene. In a reaction vessel, 10 parts MEK, 0.2 parts 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the monomer mixture were added and mixed, and the vessel was thoroughly purged with nitrogen gas. Separately, a dropping funnel was filled with the remaining monomer mixture (90% of the monomer mixture), 0.13 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) as a radical polymerization initiator. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours had elapsed since the end of the dropwise addition while maintaining the temperature at 65°C, a solution of 0.1 parts of the polymerization initiator dissolved in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours before being dried under reduced pressure to obtain pigment dispersion resin D1 (number average molecular weight: 19,000, acid value: 240 mg KOH / g).

[0114] (2) Production of Pigment Aqueous Dispersion 1 100 parts of pigment dispersion resin D1 and 78.6 parts of MEK were mixed, and then 41.2 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide content: 16.9%) were added as a neutralizing agent to neutralize the mixture (degree of neutralization: 40 mol%). 800 parts of deionized water were then added, and 400 parts of black pigment (CI Pigment Black 7, manufactured by Cabot, product name: Monarch 717) were added to this mixture. The mixture was stirred for 60 minutes at 20°C with the disperser blades rotating at 7000 rpm using a disperser (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disperser). The resulting mixture was dispersed in 10 passes at a pressure of 200 MPa using a high-pressure disperser (manufactured by Microfluidics, product name: Microfluidizer MF-140K).

[0115] To the obtained dispersion, 250 parts of deionized water were added and stirred. MEK was then completely removed under reduced pressure at 60°C, and some of the water was further removed until the pigment concentration was 15%. Then, 35.7 parts of Denacol EX-321 were added as an epoxy crosslinking agent, the container was sealed, and heated at 70°C for 5 hours while stirring with a stirrer. After cooling to room temperature, a pigment aqueous dispersion 1 (crosslinking rate: 60 mol%, solid content concentration: 20%, pigment concentration: 14.9%, average particle size: 99 nm) was obtained.

[0116] [Example 1] (Preparation of water-based ink I1) To obtain the ink composition shown in Table 2 (total of 100 parts), use 33.6 parts of the pigment aqueous dispersion 1 obtained in Production Example 3-1 (solids concentration: 20%, pigment concentration: 14.9%, average particle size: 99 nm), 30.0 parts of the aqueous dispersion of crosslinked polyurethane resin particles (solids concentration: 25.0%), 15.0 parts of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 5.0 parts of dipropylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and acetylene glycol-based surfactant. 0.4 parts of surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., product name: Surfinol 104PG50, effective content 50%), 0.1 parts of polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-6011, effective content 100%), and 15.9 parts of deionized water were mixed and thoroughly stirred, and then filtered through a membrane filter (manufactured by Sartorius, product name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink I1.

[0117] [Examples 2-11 and Comparative Examples 1,2] (Preparation of water-based inks I2-I11, IC1 and IC2) Water-based inks I2 to I11, IC1, and IC2 were prepared in the same manner as in Example 1, except that the cross-linked resin particles and water-soluble organic solvents shown in Table 2 were changed.

[0118] [Table 2]

[0119] Using the aqueous inks I1-I11, IC1, and IC2 from Examples 1-11 and Comparative Examples 1 and 2, the following evaluations of abrasion resistance and pressure changes during long-term circulation were conducted. The results are shown in Table 3. (1) Method for evaluating abrasion resistance (Printing process) In an environment with a temperature of 25±1℃ and a relative humidity of 30±5%, a printing evaluation device (manufactured by Trytech Co., Ltd.) equipped with an inkjet head (Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) was filled with water-based ink. The printing evaluation device was set to the following conditions: head voltage 26V, frequency 15kHz, head temperature 32℃, ejected droplet volume 5pL, resolution 600×600dpi, number of pre-ejection flushings 200 times, and negative pressure -4.0kPa. An A4-sized film heater (manufactured by Kawai Electric Works Co., Ltd.) was fixed on the transport table, and the printing substrate shown in Table 3 was fixed on the heater with double-sided tape in an orientation where the longitudinal direction of the recording medium and the transport direction were the same. The heater intensity was adjusted so that the temperature of the area where the water-based ink would land reached 50°C, as measured by an infrared radiation thermometer MT-4 (manufactured by Raytec Co., Ltd.). A print command was then transmitted to the print evaluation device, and a 10cm print pattern with a 60% duty cycle in the transport direction was inkjet printed to obtain an inkjet printed material for abrasion resistance evaluation. The following materials were used as printing substrates: Cotton broadcloth: Manufactured by Irozome Co., Ltd., Product name: Cotton broadcloth 40 with mercerization PET film: Manufactured by Toray Industries, Inc., Product name: Lumirror #25-T60

[0120] (Heating process) The obtained inkjet printed materials were placed in a constant-temperature dryer adjusted to the temperatures shown in Table 3. The temperature of the inkjet printed surface on the printing substrate was measured using the infrared radiation thermometer to confirm that the inkjet printed surface of the printing medium was maintained at each temperature for 5 minutes. After that, the material was returned to room temperature (23±1°C) to obtain the printed material. The obtained printed material was then subjected to an evaluation of its abrasion resistance.

[0121] (Evaluation of abrasion resistance) The aforementioned inkjet printed materials were evaluated for abrasion resistance in accordance with JIS L0849:2013 using a Type II friction tester and a colorfast grayscale. Dry friction fastness of Grade 3 or higher was considered acceptable, Grade 3-4 or higher was considered excellent, and Grade 4 or higher was considered even better.

[0122] (2) Method for evaluating pressure changes A water-based ink is passed through a diaphragm pump with a nylon filter (10 μm mesh, 5 cm cross-sectional area) at one point along the flow path. 2 A circulation path equipped with ( ) was run at a flow rate of 100 L / min for two weeks. For each water-based ink, the pressure change (%) after two weeks of circulation (pressure after two weeks / pressure 24 hours after the start of circulation) was calculated relative to the pressure 24 hours after the start of circulation, and the pressure change was evaluated. A pressure change (%) closer to 100% was considered superior, and a pressure change of 110% or less was considered practically usable. [Table 3]

[0123] As is clear from Table 3, the aqueous inks I1 to I11 of Examples 1 to 11 are superior to the aqueous inks IC1 and IC2 of Comparative Examples 1 and 2 in terms of abrasion resistance and pressure change resistance.

Claims

1. A water-based ink for inkjet recording, comprising a pigment and a fixing resin, wherein the fixing resin comprises cross-linked polyurethane resin particles having a structure represented by the following formulas (1) to (4). 【Chemistry 1】

2. The water-based ink for inkjet recording according to claim 1, wherein the acid value of the crosslinked polyurethane resin particles before crosslinking is 1 mg KOH / g or more and 30 mg KOH / g or less.

3. The water-based inkjet recording ink according to claim 1, wherein part or all of the surface of the crosslinked polyurethane resin particles has a structure represented by formulas (1) to (4).

4. The water-based inkjet recording ink according to claim 1, wherein the polyurethane resin of the crosslinked polyurethane resin particles is one or more selected from polycarbonate-based polyurethane resins and polyester-based polyurethane resins.

5. The water-based inkjet recording ink according to claim 1, wherein the crosslinked polyurethane resin particles are a urethane resin crosslinked with one or more selected from a glycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms and an aziridine compound having two to three aziridine groups and a molecular weight of 300 to 500.

6. The water-based inkjet recording ink according to claim 1, wherein the pigment is in the form of resin particles containing the pigment.

7. The inkjet recording aqueous ink according to claim 1, which is discharged from a circulation head having a pressure chamber and a circulation path for circulating the inkjet recording aqueous ink in the pressure chamber.

8. A method for manufacturing water-based ink for inkjet recording, including the following steps. (Step 1) A step of adding a crosslinking agent to an aqueous dispersion of urethane resin, crosslinking the urethane resin particles in the aqueous dispersion of urethane resin, and obtaining an aqueous dispersion of crosslinked urethane resin. (Step 2) A step to obtain an inkjet water-based ink by mixing the crosslinked urethane resin aqueous dispersion obtained in step 1 with a dispersion liquid containing an aqueous pigment dispersion.

9. A printing apparatus comprising a circulating head having a pressure chamber and a circulation path for circulating water-based ink for inkjet recording within the pressure chamber, and an inkjet printing method for printing on a printing substrate using the water-based ink for inkjet recording described in any one of claims 1 to 6.

10. The inkjet printing method according to claim 9, wherein the printing substrate is paper, cloth, or film.

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