Aqueous ink for inkjet printing

Abstract

The present invention relates to a water-based ink for ink-jet printing, which is excellent in continuous ejection properties and also excellent in adhesion of an ink coating film of a printed material to a resin film (tape peeling resistance).SOLUTION: A water-based ink for ink-jet printing containing pigment-containing acrylic resin particles, a fixing resin, a water-soluble organic solvent and water, in which an acrylic resin A constituting the pigment-containing acrylic resin particles contains a constitutional unit derived from a cycloalkyl (meth) acrylate (a- 1) and a constitutional unit derived from an acid group-containing monomer (a- 2), and the fixing resin contains a polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet printing is a method of ejecting ink droplets from minute nozzles and depositing them directly onto a printing substrate to produce printed matter with recorded characters and images. This method has become extremely popular due to its many advantages, including ease of full-color printing, low cost, the ability to use a variety of printing substrates such as plain paper, label paper, and resin film, and non-contact with the substrate. In particular, from the perspective of weather resistance and water resistance of printed matter, the use of pigments as colorants has become mainstream.

[0003] For example, Patent Document 1 discloses an inkjet recording method that provides excellent image abrasion resistance and ink ejection stability, the inkjet recording method comprising the steps of recording an image on a recording medium using an aqueous ink and heating the recording medium, wherein the aqueous ink contains resin particles formed from a polyester resin and at least one surfactant selected from the group consisting of fluorine-based surfactants and silicone-based surfactants having an HLB value of 8 or less, and the content (mass %) of the surfactant is 0.15 to 0.50 times the mass ratio (times) of the content (mass %) of the resin particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-044752 Summary of the Invention [Problem to be solved by the invention]

[0005] In the industrial printing market, such as packaging printing for food products, resin films are primarily used as printing substrates from the perspective of durability. A particular issue with using resin films as printing substrates is the substrate adhesion, particularly tape peel resistance, of the ink coating of the resulting printed matter. If the tape peel resistance of the ink coating of the printed matter is insufficient, the ink coating is likely to peel off from the resin film, impairing the aesthetic appeal and information of the printed matter. Therefore, there is a demand for improved substrate adhesion (tape peel resistance) of the ink coating of the printed matter obtained when printing on resin films. In particular, when printing on resin films using aqueous inks, the ink coating formed by the aqueous ink needs to adhere sufficiently to the resin film. Furthermore, in the industrial printing market, such as packaging printing for food products, there is a demand for inks that can be printed efficiently from the perspective of packaging productivity, and there is a demand for inks that can be stably ejected when inkjet printing is performed continuously, i.e., inks with so-called continuous ejection properties. However, although the aqueous ink disclosed in Patent Document 1 discloses ink ejection stability in single printing, it sometimes fails to exhibit sufficient performance in terms of continuous ejection. Furthermore, when the aqueous ink disclosed in Patent Document 1 is used to print on a hydrophobic, non-liquid-absorbing resin film, it has been found that the ink coating film of the resulting printed matter has insufficient substrate adhesion (tape peel resistance). The present invention relates to a water-based ink for inkjet printing that has excellent continuous discharge properties and excellent substrate adhesion (tape peel resistance) of the ink coating film of a printed product on a resin film. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by a water-based ink for inkjet printing that contains pigment-containing acrylic resin particles, a fixer resin, a water-soluble organic solvent, and water, wherein the pigment-containing acrylic resin particles and the fixer resin have specific structures. The present invention relates to the following [1]. [1] A water-based ink for inkjet printing, comprising pigment-containing acrylic resin particles, a fixing resin, a water-soluble organic solvent, and water, wherein the acrylic resin A constituting the pigment-containing acrylic resin particles has a structural unit derived from a cycloalkyl(meth)acrylate (a-1) and a structural unit derived from a monomer (a-2) having an acid group, and the fixing resin comprises a polyester resin. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a water-based ink for inkjet printing that has excellent continuous discharge properties and excellent substrate adhesion (tape peel resistance) of the ink coating film of a printed product on a resin film. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Water-based ink for inkjet printing] The water-based ink for inkjet printing of the present invention (hereinafter also referred to simply as "water-based ink") contains pigment-containing acrylic resin particles (hereinafter also referred to as "pigment-containing acrylic resin particles"), a fixing resin, a water-soluble organic solvent, and water. The acrylic resin A constituting the pigment-containing acrylic resin particles has a structural unit derived from a cycloalkyl (meth)acrylate (a-1) and a structural unit derived from a monomer (a-2) having an acid group, and the fixing resin contains a polyester resin.

[0009] In the present invention, the term "aqueous system" means that water accounts for the largest proportion by mass of the liquid components. As the water, deionized water or distilled water is preferably used. In the present invention, the term "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid, and the term "alkyl (meth)acrylate" refers to alkyl acrylate and / or alkyl methacrylate. The term "non-liquid absorbing" in the context of the printing substrate of the present invention means that the amount of water absorption of the printing substrate when the printing substrate is in contact with pure water for 100 ms is 1 g / m 2 This means that: The term "hydrophobic" in the context of the printing substrate of the present invention means that the surface free energy (wetting tension) is 45 mN / m or less. The surface free energy (wetting tension) of the printing substrate is measured using a wetting tension test mixture (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in accordance with the wetting tension test method of JIS K6768:1999. In the present invention, "adhesion to substrate" means the tape peel resistance of the ink coating film of the printed matter obtained when used for printing on a hydrophobic, non-liquid-absorbing resin film, and may be simply referred to as "adhesion to substrate."

[0010] The water-based ink of the present invention has excellent continuous discharge properties and excellent substrate adhesion (tape peel resistance) of the ink coating film of the printed matter on the resin film. The reasons for this are not entirely clear, but are thought to be as follows. The polyester resin contained in the fixing resin is thought to enhance the affinity between the ink coating film obtained by drying the water-based ink and the resin film, thereby improving the adhesion of the ink coating film to the substrate in the resulting printed matter. On the other hand, because polyester resin exhibits high hydrophobic cohesive properties, when the water-based ink dries in the vicinity of the inkjet nozzle during inkjet printing, it can generate aggregates, which can deteriorate the continuous ejection of the water-based ink. In addition, due to its structure, there was an issue that it was difficult to adhere to polypropylene-based resin films. The acrylic resin A constituting the pigment-containing acrylic resin particles contained in the aqueous ink of the present invention contains a structural unit derived from cycloalkyl (meth)acrylate (a-1). Therefore, as the aqueous ink dries near the inkjet nozzle and the pigment-containing acrylic resin particles approach the polyester resin, the highly hydrophobic cycloalkyl ester moieties intervene in the aggregates of the polyester resin. Because the cycloalkyl ester moieties are bulky and lack the π-π stacking properties of aromatic rings, the formation of robust aggregates is suppressed, and when aqueous ink (water) is supplied again during continuous ejection, the aggregates are easily redispersed. This is thought to result in high continuous ejection performance. Furthermore, the cycloalkyl ester moiety of the cycloalkyl (meth)acrylate (a-1) is highly hydrophobic and has a high affinity for the resin film used as the printing substrate, improving the wettability of the pigment-containing acrylic resin particles to the resin film. Furthermore, van der Waals interactions can be efficiently generated between the resin film and the water-dispersible polymer main chain containing the structural unit derived from the cycloalkyl (meth)acrylate (a-1), which is thought to improve the substrate adhesion of the ink coating to the resin film.

[0011] <Acrylic resin particles containing pigment> The morphology of the pigment-containing acrylic resin particles in the water-based ink of the present invention includes a morphology in which the pigment is encapsulated by the acrylic resin A, a morphology in which the pigment is uniformly dispersed in the acrylic resin A, a morphology in which the pigment is exposed on the surface of the acrylic resin A particles, a morphology in which the acrylic resin A is adsorbed to the pigment, and mixtures of these.

[0012] (pigment) The pigment constituting the pigment-containing acrylic resin particles according to the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of inorganic pigments for white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. 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. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. The pigments can be used alone or in combination of two or more.

[0013] (Acrylic resin A) The acrylic resin A constituting the pigment-containing acrylic resin particles has a structural unit derived from a cycloalkyl(meth)acrylate (a-1) and a structural unit derived from a monomer (a-2) having an acid group. Because the acrylic resin A has a structural unit derived from a cycloalkyl(meth)acrylate (a-1) and a structural unit derived from a monomer (a-2) having an acid group, the water-based ink of the present invention has excellent continuous discharge properties and excellent adhesion of the printed coating film to the substrate.

[0014] [Cycloalkyl (meth)acrylate (a-1)] The number of carbon atoms in the cycloalkyl group of the cycloalkyl (meth)acrylate (a-1) is preferably 4 or more, more preferably 5 or more, from the viewpoint of improving the dispersion stability of the pigment and improving continuous dischargeability, and from the viewpoint of improving adhesion to the substrate, and is preferably 12 or less, more preferably 8 or less, and even more preferably 7 or less. The cycloalkyl(meth)acrylate (a-1) is preferably at least one selected from the group consisting of cyclopentyl(meth)acrylate, cyclohexyl(meth)acrylate, and cycloheptyl(meth)acrylate, more preferably cyclohexyl(meth)acrylate, and even more preferably cyclohexyl acrylate, from the viewpoint of improving the dispersion stability of the pigment to improve continuous dischargeability and improving adhesion to the substrate.

[0015] [Monomer (a-2) having an acid group] In the monomer (a-2) having an acid group, preferred examples of the acid group include a carboxy group (-COOH), a sulfonic acid group (-SO3H), and a phosphate group (-OPO3H2). Of these, a carboxy group is more preferred from the viewpoints of improving continuous dischargeability and improving adhesion to the substrate. The monomer having a carboxy group is preferably one or more selected from the group consisting of (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably (meth)acrylic acid, and even more preferably acrylic acid. Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and 3-sulfopropyl (meth)acrylate. Examples of the monomer having a phosphoric acid group include vinylphosphonic acid, vinyl phosphate, bis(methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, and diphenyl-2-methacryloyloxyethyl phosphate.

[0016] [Hydrophobic Monomer (a-3)] The acrylic resin A may further contain a structural unit derived from a hydrophobic monomer (a-3) from the viewpoint of improving the dispersion stability of the pigment to improve continuous dischargeability and improving adhesion to the substrate. The hydrophobic monomer (a-3) is preferably at least one selected from the group consisting of alkyl (meth)acrylates other than the above cycloalkyl (meth)acrylate (a-1) and aromatic group-containing (meth)acrylates. As the other alkyl (meth)acrylate, alkyl (meth)acrylates having an alkyl group having from 1 to 22 carbon atoms are preferred. Furthermore, as the aromatic group-containing (meth)acrylate, one or more selected from the group consisting of aryl group-containing (meth)acrylates having an aryl group having from 6 to 22 carbon atoms are preferred. That is, as the hydrophobic monomer (a-3), one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group having from 1 to 22 carbon atoms and aryl group-containing (meth)acrylates having an aryl group having from 6 to 22 carbon atoms are preferred.

[0017] Preferred examples of alkyl(meth)acrylates having an alkyl group having 1 to 22 carbon atoms include one or more selected from the group consisting of methyl acrylate (Tg: 8°C), ethyl acrylate (Tg: -20°C), propyl acrylate (Tg: 3°C), isopropyl acrylate (Tg: -3°C), butyl acrylate (Tg: -55°C), isobutyl acrylate (Tg: -33°C), hexyl acrylate (Tg: -57°C), 2-ethylhexyl acrylate (Tg: -70°C), octyl acrylate (Tg: -65°C), dodecyl acrylate (Tg: -3°C), and stearyl acrylate. Among these, from the viewpoint of improving the dispersion stability of the pigment to improve continuous dischargeability and improving adhesion to the substrate, more preferred is one or more selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, and isobutyl acrylate, even more preferred is one or more selected from the group consisting of methyl acrylate, butyl acrylate, and isobutyl acrylate, and even more preferred is butyl acrylate. Preferred examples of the aryl group-containing (meth)acrylate having an aryl group having from 6 to 22 carbon atoms include one or more selected from the group consisting of phenyl acrylate, benzyl acrylate (Tg: 6° C.), phenoxyethyl acrylate (Tg: −22° C.), and phenoxydiethylene glycol acrylate (Tg: −25° C.). Among these, benzyl acrylate is more preferred from the viewpoints of improving the dispersion stability of the pigment to improve continuous dischargeability and improving adhesion to the substrate. The values ​​in parentheses above indicate the glass transition temperature (Tg) when each monomer is made into a homopolymer.

[0018] The monomers contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more.

[0019] The acrylic resin A may contain structural units derived from monomers other than the monomers (a-1) to (a-3) described above, within the scope of not impairing the effects of the present invention. Examples of such other monomers include ionic monomers and nonionic monomers other than the monomers (a-1) to (a-3).

[0020] The acrylic resin A may be crosslinked as needed. That is, the acrylic resin A may have a crosslinked structure. When the acrylic resin A has a crosslinked structure, for example, a polyfunctional epoxy crosslinking agent can be used as the crosslinking agent. When the acrylic resin A has a crosslinked structure, the acrylic resin A having a crosslinked structure preferably has a structural unit derived from the monomer (a-1), a structural unit derived from the monomer (a-2), and a structural unit derived from a crosslinking agent, and more preferably has a structural unit derived from the monomer (a-1), a structural unit derived from the monomer (a-2), and a structural unit derived from a crosslinking agent. Furthermore, the acrylic resin A having a crosslinked structure may further have a structural unit derived from the monomer (a-3) as necessary.

[0021] (Content of each structural unit in acrylic resin A) The content of cycloalkyl (meth)acrylate (a-1) in the raw material monomers constituting the acrylic resin A, or the content of structural units derived from cycloalkyl (meth)acrylate (a-1) in all structural units of the acrylic resin A, is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 40% by mass or more, still more preferably 55% by mass or more, from the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, and is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.

[0022] The content of the monomer (a-2) having an acid group in the raw material monomers constituting the acrylic resin A, or the content of the structural units derived from the monomer (a-2) having an acid group in all structural units of the acrylic resin A, is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, still more preferably 25% by mass, from the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 33% by mass or less, and still more preferably 30% by mass or less.

[0023] When the acrylic resin A further contains a structural unit derived from a hydrophobic monomer (a-3), the content of the hydrophobic monomer (a-3) in the raw material monomers constituting the acrylic resin A or the content of the structural unit derived from the hydrophobic monomer (a-3) in all structural units of the acrylic resin A is, from the viewpoint of improving continuous dischargeability and improving substrate adhesion, preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 20% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and still more preferably 40% by mass or less.

[0024] (Production of acrylic resin A) The acrylic resin A can be produced by copolymerizing raw material monomers including the above-mentioned monomers (a-1) to (a-3) by a known polymerization method.

[0025] From the viewpoint of improving continuous dischargeability and improving adhesion to a substrate, the acid value of the acrylic resin A is preferably 40 mgKOH / g or more, more preferably 80 mgKOH / g or more, and is preferably 300 mgKOH / g or less, more preferably 260 mgKOH / g or less, and even more preferably 240 mgKOH / g or less. The acid value of the acrylic resin A is measured by the method described in the examples.

[0026] The weight average molecular weight of the acrylic resin A is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 15,000 or more, from the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, and is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight average molecular weight of the acrylic resin A is measured by the method described in the examples.

[0027] (Neutralizer) The acid groups of the acrylic resin A may be neutralized with a neutralizing agent, which is thought to increase the charge repulsion force of the acid groups that occurs after neutralization, thereby suppressing aggregation of the pigment-containing acrylic resin particles in the aqueous dispersion of the present invention, further improving dispersion stability and continuous dischargeability. The neutralizing agent is preferably one or more selected from the group consisting of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds.

[0028] From the viewpoint of improving continuous dischargeability, the degree of neutralization of the acid groups of the acrylic resin A is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, and is preferably less than 100 mol%, more preferably 90 mol% or less, even more preferably 80 mol% or less. Here, the degree of neutralization can be calculated by the following formula (1) as the equivalent amount of neutralizer used relative to the acid groups of acrylic resin A. When the equivalent amount of neutralizer used is 100 mol% or less, it is synonymous with the degree of neutralization. When the equivalent amount of neutralizer used exceeds 100 mol%, it means that the neutralizer is in excess relative to the carboxyl groups of acrylic resin A, and in this case the degree of neutralization of acrylic resin A is considered to be 100 mol%. Equivalent amount of neutralizing agent used (mol%) = [{mass of neutralizing agent added (g) / equivalent amount of neutralizing agent} / [{acid value of acrylic resin A (mg KOH / g) × mass of acrylic resin A (g)} / (56 × 1000)]] × 100 (1)

[0029] (Method of manufacturing pigment-containing acrylic resin particles) Acrylic resin particles containing a pigment (pigment-containing acrylic resin particles) can be efficiently produced as an aqueous pigment-containing acrylic resin particle dispersion (hereinafter also referred to as "aqueous pigment dispersion") by a process including the following Step 1. Step 1: Dispersing a pigment mixture containing pigment, acrylic resin A, and water

[0030] Step 1 is preferably carried out by, for example, dispersing a pigment mixture containing a pigment, acrylic resin A, an organic solvent, water, and, as necessary, a neutralizing agent, a surfactant, and the like to obtain a pigment dispersion, and then removing the organic solvent from the pigment dispersion by a known method. The dispersion treatment in step 1 can be carried out by a known method using a kneading machine such as a roll mill or kneader, a high-pressure homogenizer such as a Microfluidizer (manufactured by Microfluidics), a paint shaker, a media-type disperser such as a bead mill, or the like.

[0031] In the present invention, the solids concentration of the aqueous pigment dispersion obtained by the process including step 1 is, from the viewpoints of productivity of the aqueous ink, improving continuous ejection properties, and improving adhesion to the substrate, preferably 7% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

[0032] In the present invention, the content of the pigment in the aqueous pigment dispersion obtained by the steps including step 1 is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, from the viewpoints of productivity of the aqueous ink, improving continuous ejection ability, and print density.

[0033] In the present invention, the mass ratio of the pigment content to the total content of the pigment and acrylic resin in the aqueous pigment dispersion obtained by a process including step 1 [pigment / (pigment+acrylic resin)] is preferably 0.45 or more, more preferably 0.50 or more, even more preferably 0.55 or more, from the viewpoint of improving continuous dischargeability and improving substrate adhesion, and is preferably 0.80 or less, more preferably 0.75 or less, even more preferably 0.70 or less, and still more preferably 0.65 or less.

[0034] In the present invention, the average particle size of the pigment-containing acrylic resin particles in the aqueous pigment dispersion obtained by the steps including step 1 is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 90 nm or more, from the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, and is preferably 400 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less. The average particle size of the pigment-containing acrylic resin particles in the water-based pigment dispersion of the present invention is measured by the method described in the Examples.

[0035] In the present invention, the viscosity at 20°C of the aqueous pigment dispersion obtained by a process including step 1 is preferably 1 mPa s or more, more preferably 1.5 mPa s or more, even more preferably 2 mPa s or more, and is preferably 15 mPa s or less, more preferably 10 mPa s or less, even more preferably 5 mPa s or less, from the viewpoint of productivity of the aqueous ink. The viscosity of the water-based pigment dispersion of the present invention at 20° C. is determined by the method described in the examples.

[0036] <Fixing resin> (polyester resin) The water-based ink of the present invention contains a polyester resin as a fixing resin from the viewpoint of improving adhesion to a substrate. In the present invention, the polyester resin contained in the fixing resin contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and can be obtained by polycondensation of the alcohol component and the carboxylic acid component.

[0037] (alcohol content) The alcohol component, which is a raw material monomer for the polyester resin, contains at least one selected from the group consisting of an aliphatic diol, an aromatic diol, an alicyclic diol, and a trihydric or higher polyhydric alcohol, from the viewpoint of improving adhesion to a substrate. Among these, it is preferable to contain an aliphatic diol, and it is more preferable to contain an aliphatic diol and a trihydric or higher polyhydric alcohol.

[0038] The aliphatic diol is preferably a linear diol or an aliphatic diol having an alkyl group on the side chain. The alkyl group on the side chain is more preferably a methyl group. Specific examples of the aliphatic diol include one or more selected from the group consisting of 1,2-propanediol (propylene glycol), 2,3-butanediol, 2,4-pentanediol, 2,5-hexanediol, 2,6-heptanediol, 2,7-octanediol, and 3-methyl-1,5-pentanediol, more preferably one or more selected from the group consisting of 1,2-propanediol, 2,3-butanediol, and 3-methyl-1,5-pentanediol, and even more preferably 1,2-propanediol and 3-methyl-1,5-pentanediol.

[0039] A preferred example of the aromatic diol is an alkylene oxide adduct of bisphenol A. The alkylene oxide adduct of bisphenol A is a compound having a structure in which an oxyalkylene group is added to 2,2-bis(4-hydroxyphenyl)propane, and specifically, a compound represented by the following general formula (I) is preferred, and two or more types of such compounds may be used in combination.

[0040] [ka]

[0041] In the general formula (I), OR 1 , R 2Each O independently represents an oxyalkylene group having 1 to 4 carbon atoms, and is preferably an oxyethylene group or an oxypropylene group. x and y are the number of moles of alkylene oxide added, and each independently is a positive number of 0 or more. From the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and is preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. Also, OR 1 and R 2 Each O may be the same or different. Examples of the alkylene oxide adduct of bisphenol A include a propylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol A.

[0042] Examples of the alicyclic diol include cyclohexanediol and hydrogenated bisphenol A.

[0043] The trihydric or higher polyhydric alcohol is preferably one or more selected from the group consisting of glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sorbitan, and more preferably trimethylolpropane.

[0044] When the polyester resin contains an aliphatic diol as an alcohol component, the content of the aliphatic diol in the alcohol component constituting the polyester resin, or the content of the aliphatic diol-derived structural units in all structural units derived from the alcohol components of the polyester resin, is preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, and is 100 mol% or less, preferably 99 mol% or less, more preferably 97 mol% or less, even more preferably 95 mol% or less, from the viewpoint of improving adhesion to the substrate.

[0045] When the polyester resin contains a trihydric or higher polyhydric alcohol as an alcohol component, the content of the trihydric or higher polyhydric alcohol in the alcohol component constituting the polyester resin, or the content of the trihydric or higher polyhydric alcohol-derived structural units in all structural units derived from the alcohol components of the polyester resin, is preferably 1 mol% or more, more preferably 3 mol% or more, even more preferably 5 mol% or more, and is preferably 20 mol% or less, more preferably 15 mol% or less, even more preferably 10 mol% or less, from the viewpoint of improving adhesion to the substrate.

[0046] (carboxylic acid component) Examples of carboxylic acid components constituting polyester resins include dicarboxylic acids and trivalent or higher polycarboxylic acids. In the present invention, the carboxylic acid component includes not only carboxylic acids but also their anhydrides and alkyl esters having 1 to 3 carbon atoms. In other words, when the name of a carboxylic acid is mentioned in this specification, it is understood that the anhydrides and alkyl esters having 1 to 3 carbon atoms of the carboxylic acid are also mentioned.

[0047] Dicarboxylic acids include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid, preferably isophthalic acid and terephthalic acid, and more preferably terephthalic acid.

[0048] Examples of aliphatic dicarboxylic acids include fumaric acid, adipic acid, sebacic acid, maleic acid, azelaic acid, succinic acid, and succinic acid substituted with a hydrocarbon group having 1 to 20 carbon atoms, and fumaric acid is preferred. Specific examples of succinic acid substituted with a hydrocarbon group having 1 to 20 carbon atoms include dodecylsuccinic acid, dodecenylsuccinic acid, and octenylsuccinic acid.

[0049] Examples of the alicyclic dicarboxylic acid include cyclohexanedicarboxylic acid. Examples of trivalent or higher polycarboxylic acids include trimellitic acid, 2,5,7-naphthalenetricarboxylic acid, and pyromellitic acid. The carboxylic acid component may be used alone or in combination of two or more.

[0050] Among the above, the carboxylic acid component constituting the polyester resin preferably contains an aromatic dicarboxylic acid, more preferably contains an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid, and even more preferably contains terephthalic acid and fumaric acid, from the viewpoint of improving adhesion to a substrate.

[0051] When the polyester resin contains an aromatic dicarboxylic acid as a carboxylic acid component, the content of aromatic dicarboxylic acid in the carboxylic acid component constituting the polyester resin or the content of structural units derived from aromatic dicarboxylic acid in all structural units derived from carboxylic acid components of the polyester resin is, from the viewpoint of improving substrate adhesion, preferably 70 mol% or more, more preferably 75 mol% or more, even more preferably 80 mol% or more, and is 100 mol% or less, preferably 98 mol% or less, more preferably 95 mol% or less. When the polyester resin contains an aliphatic dicarboxylic acid as a carboxylic acid component, the content of the aliphatic dicarboxylic acid in the carboxylic acid component constituting the polyester resin or the content of the aliphatic dicarboxylic acid-derived structural units in all structural units derived from the carboxylic acid component of the polyester resin is preferably 2 mol% or more, more preferably 5 mol% or more, and is preferably 30 mol% or less, more preferably 25 mol% or less, and even more preferably 20 mol% or less, from the viewpoint of improving adhesion to the substrate.

[0052] The equivalent ratio (COOH groups / OH groups) of the carboxyl groups (COOH groups) of the carboxylic acid component to the hydroxyl groups (OH groups) of the alcohol component constituting the polyester resin is preferably 0.7 or more, more preferably 0.8 or more, from the viewpoint of improving substrate adhesion, and is preferably 1.3 or less, more preferably 1.2 or less.

[0053] From the viewpoint of improving the dispersion stability of resin particles in water and improving adhesion to substrates, the acid value of the polyester resin is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and is preferably 50 mgKOH / g or less, more preferably 40 mgKOH / g or less, even more preferably 35 mgKOH / g or less. The acid value of the polyester resin is measured by the method described in the examples.

[0054] From the viewpoint of improving adhesion to the substrate, the weight average molecular weight of the polyester resin is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and is preferably 50,000 or less, more preferably 30,000 or less, even more preferably 20,000 or less. The weight average molecular weight of the polyester resin is measured by the method described in the examples.

[0055] From the viewpoint of improving adhesion to the substrate, the glass transition temperature of the polyester resin is preferably 35°C or higher, more preferably 45°C or higher, and even more preferably 50°C or higher, and is preferably 65°C or lower, and more preferably 60°C or lower. The glass transition temperature of the polyester resin is measured using a differential scanning calorimeter, specifically by the method described in the examples.

[0056] From the viewpoint of improving adhesion to the substrate, the softening point of the polyester resin is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, and is preferably 165°C or lower, and more preferably 130°C or lower. The softening point of the polyester resin is measured by the method described in the examples.

[0057] The polyester resins may be used alone or in combination of two or more. When two or more types of polyester resins are used in combination, the acid value, weight average molecular weight, glass transition temperature and softening point are measured for each of the two or more types of mixture by the methods described in the examples. The acid value, weight average molecular weight, glass transition temperature, and softening point of the polyester resin can all be obtained as desired by appropriately adjusting the types and blending ratios of raw material monomers used in the production of the polyester resin, the polycondensation temperature, and the reaction time.

[0058] (Production of polyester resin) The polyester resin can be obtained by polycondensing the alcohol component and the carboxylic acid component, for example, by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere at a temperature of 120°C or higher and 250°C or lower, optionally using an esterification catalyst. Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolamine. If necessary, an esterification promoter such as 3,4,5-trihydroxybenzoic acid (gallic acid), and a radical polymerization inhibitor such as 4-tert-butylcatechol may also be used.

[0059] In the present invention, the polyester resin includes not only unmodified polyester resins but also polyester resins modified to such an extent that their properties are not substantially impaired. Examples of modified polyester resins include polyester resins grafted or blocked with phenol, urethane, epoxy, or the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, etc., and composite resins having two or more resin units including a polyester unit.

[0060] Furthermore, the fixing resin in the present invention may contain resins other than polyester resins, such as styrene-acrylic copolymers, epoxy resins, polycarbonates, polyurethanes, etc., within the scope of not impairing the effects of the present invention. The fixing resin may contain optional components such as reinforcing fillers such as fibrous substances, antioxidants, antiaging agents, and other additives, as long as the effects of the present invention are not impaired. The content of polyester resin in the fixing resin in the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and preferably 100% by mass or less.

[0061] (Production of aqueous polyester resin dispersion) The fixing resin of the present invention is preferably used as an aqueous fixing resin dispersion when preparing an aqueous ink. That is, in the present invention, the fixing resin is preferably used as an aqueous polyester resin dispersion when preparing an aqueous ink. The aqueous polyester resin dispersion is preferably produced by a method of dispersing a resin containing a polyester resin in water. Examples of methods for obtaining an aqueous polyester resin dispersion include a method in which a resin containing a polyester resin is added to water and then subjected to a dispersion treatment using a disperser or the like, and a method in which water is gradually added to a solution of a resin containing a polyester resin and then subjected to phase inversion emulsification. Among these, the method in which phase inversion emulsification is performed is preferred.

[0062] A preferred phase inversion emulsification method is to first dissolve a resin containing a polyester resin in an organic solvent to obtain a solution of a resin containing a polyester resin, then add water to the solution to invert the phase, and then remove the organic solvent. As the organic solvent for dissolving the resin including the polyester resin, from the viewpoint of dissolving the resin including the polyester resin and facilitating removal from the emulsion, a dialkyl ketone having an alkyl group having 1 to 3 carbon atoms, such as acetone or methyl ethyl ketone, is preferred, and methyl ethyl ketone is more preferred.

[0063] When the polyester resin particles contain multiple types of polyester resins or resins other than polyester resins, the multiple types of polyester resins may be mixed in advance before dissolving in the organic solvent, or the polyester resin may be mixed with the other resin, or these resins may be added simultaneously to the organic solvent and dissolved to obtain a resin solution containing the polyester resin.

[0064] The mass ratio of the organic solvent to the resin containing the polyester resin [organic solvent / resin] is preferably 30 / 100 or more, more preferably 50 / 100 or more, even more preferably 70 / 100 or more, from the viewpoint of dissolving the resin and facilitating phase inversion to water, and is preferably 500 / 100 or less, more preferably 300 / 100 or less, even more preferably 200 / 100 or less, and even more preferably 150 / 100 or less.

[0065] In the present invention, when the polyester resin contains an acid group, it is preferably neutralized with a basic compound from the viewpoint of improving the dispersion stability of the resin particles in water. Examples of the basic compound include metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonia; and various organic amines, and preferably at least one selected from sodium hydroxide, potassium hydroxide, and ammonia, more preferably sodium hydroxide. The basic compound is preferably used as an aqueous solution. The degree of neutralization of the polyester resin, represented by the following formula (1), is preferably 50 mol % or more, more preferably 55 mol % or more, and preferably 100 mol % or less, more preferably 85 mol % or less, and even more preferably 80 mol % or less. Degree of neutralization = {[basic compound added (g) / equivalent of basic compound (g / mol)] / [[acid value of polyester resin (mg KOH / g) × mass of polyester resin (g)] / (56 × 1000 (mg KOH / mol))]} × 100 (1)

[0066] The dissolution of the resin containing the polyester resin in the organic solvent and the subsequent addition of the aqueous solution of the basic compound are usually carried out at a temperature not higher than the boiling point of the organic solvent.

[0067] The temperature when adding water to a resin solution containing a polyester resin is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 25°C or higher, from the viewpoint of the stability of phase inversion emulsification, and is preferably 80°C or lower, and more preferably 75°C or lower. From the viewpoint of improving the productivity of the aqueous polyester resin dispersion, the amount of water added is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, and is preferably 900 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 300 parts by mass or less, relative to 100 parts by mass of the resin constituting the polyester resin particles.

[0068] After the phase inversion emulsification, it is preferable to remove the organic solvent from the dispersion obtained by the phase inversion emulsification in order to remove unnecessary components. The method for removing the organic solvent is not particularly limited, and any method can be used. The aqueous polyester resin dispersion may be filtered through a wire mesh or the like to remove coarse particles, etc. When the organic solvent is removed, water is also reduced azeotropically together with the organic solvent, and therefore, water may be added to adjust the solid content concentration.

[0069] From the viewpoint of productivity of the aqueous ink and improving adhesion to the substrate, the solids concentration of the aqueous polyester resin dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The solids concentration of the aqueous polyester resin dispersion is measured by the method described in the examples.

[0070] From the viewpoint of improving continuous dischargeability and substrate adhesion, the average particle size of the polyester resin particles in the aqueous polyester resin dispersion is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, and is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. The average particle size of the polyester resin particles in the aqueous polyester resin dispersion is measured by the method described in the Examples.

[0071] <Water-soluble organic solvent> The water-soluble organic solvent is an organic solvent that can be mixed with water in any ratio. The water-soluble organic solvents can be used alone or in combination of two or more. Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, the water-soluble organic solvent preferably contains at least one selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, from the viewpoints of improving continuous dischargeability and improving substrate adhesion.

[0072] Examples of polyhydric alcohols include alkanediols such as ethylene glycol, propylene glycol (1,2-propanediol), 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol; polyalkylene glycols such as diethylene glycol and triethylene glycol; glycerin; and trimethylolpropane. Among these, the polyhydric alcohol is preferably one or more selected from the group consisting of propylene glycol, 1,2-hexanediol, triethylene glycol, and glycerin, and more preferably propylene glycol.

[0073] Examples of polyhydric alcohol alkyl ethers include (poly)alkylene glycol monoalkyl ethers such as monoalkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers; and (poly)alkylene glycol dialkyl ethers such as monoalkylene glycol dialkyl ethers and dialkylene glycol dialkyl ethers. Among these, the polyhydric alcohol alkyl ether is preferably a (poly)alkylene glycol monoalkyl ether, and more preferably a dialkylene glycol monoalkyl ether. The alkylene oxide group of the polyhydric alcohol alkyl ether may be at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group, with an ethylene oxide group being more preferred. The alkyl group of the polyhydric alcohol alkyl ether preferably has 2 or more and 8 or less carbon atoms.

[0074] The (poly)alkylene glycol monoalkyl ether is preferably one or more selected from the group consisting of ethylene glycol monoalkyl ethers such as ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol monoisobutyl ether, and ethylene glycol mono-n-hexyl ether; diethylene glycol monoalkyl ethers such as diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monoisobutyl ether, and diethylene glycol mono-n-hexyl ether; triethylene glycol monoalkyl ethers such as triethylene glycol monobutyl ether; propylene glycol monoalkyl ethers such as propylene glycol mono-n-propyl ether; dipropylene glycol monoalkyl ethers; tripropylene glycol monoalkyl ethers; and ethylene glycol aryl ethers such as ethylene glycol monobenzyl ether. Among these, the (poly)alkylene glycol monoalkyl ether is preferably diethylene glycol monoalkyl ether, and more preferably diethylene glycol mono-n-butyl ether.

[0075] Examples of the (poly)alkylene glycol dialkyl ether include diethylene glycol dialkyl ethers such as diethylene glycol methyl ethyl ether and diethylene glycol diethyl ether.

[0076] From the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, the water-soluble organic solvent preferably contains one or more solvents selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, more preferably contains one or more solvents selected from the group consisting of polyhydric alcohols and (poly)alkylene glycol monoalkyl ethers, even more preferably contains one or more solvents selected from the group consisting of polyhydric alcohols and dialkylene glycol monoalkyl ethers, and still more preferably contains one or more solvents selected from the group consisting of propylene glycol and diethylene glycol mono-n-butyl ether.

[0077] (Various additives) The water-based ink of the present invention may contain various additives such as surfactants, humectants, wetting agents, wetting and penetrating agents, viscosity adjusters, antifoaming agents, preservatives, antifungal agents, and anticorrosive agents, as required.

[0078] [Surfactant] Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants. Of these, nonionic surfactants are preferred. Examples of nonionic surfactants include polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorine surfactants. Among these, from the viewpoints of improving continuous dischargeability, defoaming properties, and wettability to resin films, one or more surfactants selected from the group consisting of acetylene glycol-based surfactants and silicone-based surfactants are preferred, and acetylene glycol-based surfactants are more preferred. Examples of acetylene glycol surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide adducts of these acetylene diols. Examples of commercially available acetylene glycol surfactants include the "Surfynol" series and the "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd. Examples of silicone surfactants include polyether-modified silicones. Examples of commercially available silicone surfactants include the KF series (KF-353, KF-355A, KF-642, KF-6011, etc.) manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd., and the BYK series manufactured by BYK Japan K.K.

[0079] (Water-based ink manufacturing) The water-based ink of the present invention can be produced by mixing pigment-containing acrylic resin particles, a fixing resin, a water-soluble organic solvent, water, and, if necessary, various additives such as a surfactant. More specifically, the water-based ink of the present invention can be produced by mixing an aqueous pigment dispersion containing the above-mentioned pigment-containing acrylic resin particles, an aqueous polyester resin dispersion containing the above-mentioned polyester resin as the fixing resin, a water-soluble organic solvent, water, and, if necessary, various additives such as a surfactant.

[0080] (Contents and properties of each component of water-based ink) The content of pigment-containing acrylic resin particles in the water-based ink of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, from the viewpoints of improving continuous dischargeability, improving adhesion to the substrate, and print density, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

[0081] From the viewpoint of print density, the content of the pigment in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 12% by mass or less, more preferably 9% by mass or less, even more preferably 6% by mass or less.

[0082] From the viewpoint of improving continuous jetting properties and improving adhesion to the substrate, the content of acrylic resin A in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 8% by mass or less, more preferably 6% by mass or less, even more preferably 4% by mass or less.

[0083] The mass ratio of the pigment content to the total content of the pigment and acrylic resin A in the water-based ink of the present invention [pigment / (pigment+acrylic resin A)] is preferably 0.45 or more, more preferably 0.50 or more, even more preferably 0.55 or more, from the viewpoint of improving adhesion to the substrate, and is preferably 0.75 or less, more preferably 0.70 or less, even more preferably 0.65 or less.

[0084] From the viewpoint of improving continuous ejection properties and improving adhesion to the substrate, the content of the fixing resin in the water-based ink of the present invention is preferably 0.5% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.

[0085] The mass ratio of the content of the pigment-containing acrylic resin particles to the total content of the pigment-containing acrylic resin particles and the fixing resin in the water-based ink of the present invention [pigment-containing acrylic resin particles / (pigment-containing acrylic resin particles+fixing resin)] is preferably 0.45 or more, more preferably 0.50 or more, even more preferably 0.55 or more, from the viewpoint of improving continuous dischargeability and improving adhesion to the substrate, and is preferably 0.75 or less, more preferably 0.70 or less, even more preferably 0.65 or less.

[0086] The mass ratio of the pigment content to the total content of the pigment and fixing resin in the water-based ink of the present invention [pigment / (pigment+fixing resin)] is preferably 0.35 or more, more preferably 0.40 or more, even more preferably 0.45 or more, and is preferably 0.65 or less, more preferably 0.60 or less, even more preferably 0.55 or less, from the viewpoint of improving adhesion to the substrate.

[0087] From the viewpoint of improving continuous ejection properties and improving adhesion to the substrate, the content of the water-soluble organic solvent in the water-based ink of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

[0088] When the water-based ink of the present invention contains a surfactant, the content of the surfactant in the water-based ink of the present invention is, from the viewpoint of improving continuous ejection properties and improving adhesion to the substrate, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is preferably 2% by mass or less, more preferably 1.5% by mass or less, even more preferably 1% by mass or less.

[0089] From the viewpoint of improving continuous jetting properties and improving adhesion to a substrate, the water content in the water-based ink of the present invention is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, and is preferably 92.5% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0090] The average particle size of the pigment-containing acrylic resin particles in the water-based ink of the present invention is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 100 nm or more, from the viewpoint of improving continuous jetting properties and improving adhesion to the substrate, and is preferably 200 nm or less, more preferably 180 nm or less, even more preferably 150 nm or less. The average particle size of the pigment-containing acrylic resin particles in the water-based ink of the present invention is measured by the method described in the Examples.

[0091] The viscosity of the water-based ink of the present invention at 20°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The viscosity of the water-based ink is measured by the method described in the examples.

[0092] The water-based ink of the present invention is a water-based ink for inkjet printing, and can be loaded into a known inkjet printing device and ejected as ink droplets onto a printing substrate such as a resin film described below to print an image, etc. The ink droplet ejection method can be any of a piezoelectric method, a thermal method, and an electrostatic method.

[0093] The water-based ink of the present invention has excellent substrate adhesion to resin films, and is therefore preferably used in printing using resin films as printing substrates. Examples of resin films include transparent synthetic resin films, such as polyester films such as polyethylene terephthalate films; vinyl chloride films; polyolefin films such as polypropylene films and polyethylene films; and polyamide films such as nylon films. These resin films may be oriented films such as biaxially oriented films and uniaxially oriented films, or unoriented films. Furthermore, from the viewpoint of improving adhesion to substrates, it is preferable to use these resin films that have been subjected to surface treatment such as corona discharge treatment. Among these, resin films having a surface free energy of 45 mN / m or less are preferred, and one or more selected from the group consisting of polyester film, oriented polypropylene film, and polyethylene film are more preferred, and one or more selected from the group consisting of corona discharge-treated polyethylene terephthalate (PET) film, corona discharge-treated biaxially oriented polypropylene (OPP) film, corona discharge-treated polyethylene (PE) film, etc. are even more preferred. [Example]

[0094] In the following Production Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring and calculating each physical property are as follows.

[0095] (Measurement method) [Measurement of acid value of acrylic resin A and polyester resin] Acrylic resin A or polyester resin was dissolved in a titration solvent consisting of a mixture of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0096] [Measurement of weight average molecular weight of acrylic resin A and polyester resin] The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kit with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (Tosoh Corporation) Measurement sample: 0.1 g of acrylic resin A or polyester 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 with a syringe filter "DISMIC-13HP" (PTFE, 0.2 μm, manufactured by ADVANTEC) before use.

[0097] [Softening point of polyester resin] Using a flow tester "CFT-500D" (Shimadzu Corporation), 1 g of sample was heated at a temperature increase rate of 6°C / min, while a load of 1.96 MPa was applied by the plunger, and the sample was extruded from a nozzle 1 mm in diameter and 1 mm in length. The plunger depression distance of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

[0098] [Glass transition temperature of polyester resin] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan Co., Ltd.), 0.02 g of sample was weighed into an aluminum pan, heated to 200°C, and then cooled from 200°C to 0°C at a rate of 10°C / min to prepare a sample for measurement. The temperature was then increased at a rate of 10°C / min, and the calorific value was measured. The peak temperature with the largest peak area among the observed endothermic peaks was defined as the maximum endothermic peak temperature, and the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the peak apex was defined as the glass transition temperature.

[0099] [Measurement of solids concentration] Approximately 10 g of sodium sulfate was weighed out and placed in a 30 mL polypropylene container (φ=40 mm, height=30 mm) at a constant weight in a desiccator. Approximately 1 g of the sample was added and mixed, and the mass was then weighed. The mixture was then maintained at 105°C for 2 hours to remove volatiles, and the mixture was then left in the desiccator for 15 minutes before being weighed again. The mass of the sample after volatiles removal was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration (%).

[0100] [Measurement of average particle size of water-based pigment dispersion, water-based polyester resin dispersion, and water-based ink] Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle diameter was taken as the average particle diameter of the aqueous pigment dispersion, aqueous polyester resin dispersion, or aqueous ink. The measurement sample had a particle concentration of 5 × 10 -3 The dispersion was diluted with water to a concentration of 1.333 (solids concentration). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0101] [Viscosity of Water-Based Pigment Dispersion and Water-Based Ink] The aqueous pigment dispersion and the aqueous ink were measured at 20°C using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34' x R24, rotation speed 50 rpm).

[0102] (Production of acrylic resin A) Production Example 1-1 (Production of Acrylic Resin A1) A reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank was initially charged with 0.96 parts of acrylic acid and 2.74 parts of cyclohexyl acrylate as raw material monomers, and 5.54 parts (one-tenth of the total amount of the raw material monomers and the polymerization solvent) of methyl ethyl ketone (hereinafter referred to as "MEK") as a polymerization solvent, and the mixture was stirred for 10 minutes while maintaining the temperature of the reaction vessel at 77°C. Next, a mixture of 8.67 parts acrylic acid and 24.59 parts cyclohexyl acrylate as raw monomers, 49.85 parts MEK as polymerization solvent (9 / 10 of the total amount of raw monomers and polymerization solvent), 0.56 parts 2,2'-azobis(isobutyronitrile) as polymerization initiator, and 0.41 parts 3-mercaptopropionic acid as chain transfer agent was continuously added to the reaction vessel over a period of 5 hours. After the addition was completed, the polymerization reaction was carried out for 1 hour, and then the mixture was cooled to room temperature to terminate the polymerization reaction, yielding a MEK solution of acrylic resin A1 (resin solids concentration 40%). The physical properties of the resulting acrylic resin A1 are shown in Table 1.

[0103] Production Examples 1-2 to 1-13, 1-21 (Production of Acrylic Resins A2 to A13, A21) An MEK solution of acrylic resin A (resin solids concentration: 40%) was obtained in the same manner as in Production Example 1-1, except that the monomer composition constituting acrylic resin A in Production Example 1-1 was changed to the conditions shown in Table 1. Acrylic resins A5 to A10 obtained in Production Examples 5 to 10 further used hydrophobic monomer (a-3) as a raw material monomer. Acrylic resin A21 obtained in Production Example 1-21 did not use cycloalkyl (meth)acrylate as a raw material monomer, but used styrene instead. The physical properties of each acrylic resin A obtained are shown in Table 1.

[0104] (Production of Water-Based Pigment Dispersion) Production Example 2-1 (Production of Water-Based Pigment Dispersion D1) To 41.7 parts of the MEK solution of acrylic resin A1 obtained in Production Example 1-1 (resin solids concentration: 40%), 0.6 parts of MEK, 8.5 parts of a 5N aqueous sodium hydroxide solution (neutralization degree: 60 mol%), and 163.6 parts of deionized water were added, and 25.0 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 15:3) were further added to obtain a pigment mixed solution (ratio of the pigment mass to the total mass of the pigment and acrylic resin A [pigment / (pigment + acrylic resin A)] = 0.60). The resulting pigment mixture was mixed using a disper blade at 7000 rpm and 20°C for 1 hour, and then further dispersed using a Microfluidizer (high-pressure homogenizer, manufactured by Microfluidics, product name: M-140K) for 10 passes at a pressure of 180 MPa to obtain a pigment dispersion. From the resulting pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed and centrifuged. The liquid layer was then filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding aqueous dispersion D1 of pigment-containing acrylic resin particles (total concentration of pigment and acrylic resin A1: 20%). The physical properties of the resulting aqueous pigment dispersion D1 are shown in Table 1.

[0105] Production Examples 2-2 to 2-13, 2-21 (Production of Water-Based Pigment Dispersions D2 to D13, D21) Aqueous dispersions of each pigment-containing acrylic resin particle (total concentration of pigment and acrylic resin A: 20%, degree of neutralization of resin: 60 mol%) were obtained in the same manner as in Production Example 2-1, except that the type of acrylic resin A in Production Example 2-1 was changed to the corresponding acrylic resin A as shown in Table 1. The physical properties of each aqueous pigment dispersion obtained are shown in Table 1.

[0106] [Table 1]

[0107] (Production of polyester resin) Production Example 3-1 (Production of Polyester Resin P1) A 10-L four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser with a dehydration tube, and a nitrogen inlet tube was charged with the raw material monomers (alcohol components and carboxylic acid components) other than fumaric acid shown in Table 2, an esterification catalyst (tin(II) di(2-ethylhexanoate)), and an esterification co-catalyst (gallic acid). The mixture was heated to 235°C using a mantle heater under a nitrogen atmosphere and atmospheric pressure with stirring (300 rpm). The reaction was carried out for 5 hours, after which the pressure in the flask was reduced to 8.3 kPa and the mixture was stirred for 1 hour. After that, it was cooled to 180°C and returned to atmospheric pressure, then fumaric acid and a polymerization inhibitor (4-tert-butylcatechol) were added, the temperature was raised to 210°C, and the reaction was carried out for 1 hour. After that, the pressure inside the flask was reduced to 8.3 kPa, and the reaction was continued until the softening point reached the temperature shown in Table 2, thereby obtaining polyester resin P1. The physical properties of the obtained polyester resin P1 are shown in Table 2.

[0108] Production Examples 3-2 to 3-3 (Production of Polyester Resins P2 to P3) In Production Example 3-1, Each polyester resin was obtained in the same manner as in Production Example 3-1, except that the monomer composition constituting the polyester resin was changed as shown in Table 2. The physical properties of each polyester resin obtained are shown in Table 2.

[0109] (Production of aqueous polyester resin dispersion) Production Example 4-1 (Production of Water-Based Polyester Resin Dispersion C1) 20 parts of polyester resin P1 obtained in Production Example 3-1 and 20 g of MEK were added to a 1-liter four-neck flask equipped with a nitrogen inlet tube, reflux condenser, stirrer "Three-One Motor BL300" (manufactured by Shinto Scientific Co., Ltd.), and thermocouple. The mixture was stirred at 60°C for 4 hours to obtain a resin solution of P1. Subsequently, 1.78 parts of 5N aqueous sodium hydroxide solution (neutralization degree 72 mol%) was added with stirring at 30°C and stirred for 30 minutes. 47 parts of deionized water were added dropwise at a rate of 20 mL / min with stirring at 30°C to induce phase inversion emulsification. The mixture was then heated to 60°C, and the pressure was gradually reduced from 80 kPa to 30 kPa to distill off methyl ethyl ketone and further distill off some of the water, yielding aqueous polyester resin dispersion C1 (solids concentration 30%). The physical properties of each aqueous polyester resin dispersion C1 are shown in Table 2.

[0110] Production Examples 4-2 to 4-3 (Production of Water-Based Polyester Resin Dispersions C2 to C3) Each aqueous polyester resin dispersion (each had a solids concentration of 30% and a degree of neutralization of the resin of 72 mol%) was obtained in the same manner as in Production Example 4-1, except that the type of polyester resin in Production Example 4-1 was changed to the corresponding polyester resin as shown in Table 2. The physical properties of each aqueous polyester resin dispersion obtained are shown in Table 2.

[0111] [Table 2]

[0112] (Water-based ink manufacturing) Example 1 (Production of Water-Based Ink 1) To obtain the ink composition shown in Table 3, 8.3 parts of aqueous pigment dispersion D1 (pigment content: 5 parts) as the total pigment and acrylic resin A1, 5.0 parts of aqueous polyester resin dispersion C1 (polyester resin content), 9.0 parts of propylene glycol, 4.0 parts of diethylene glycol monobutyl ether, 0.5 parts of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 465 (ethylene oxide (12 moles) adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content: 100%)), and deionized water were added to make a total of 100 parts of the aqueous ink. The mixture was stirred and then filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink 1. The physical properties of the resulting aqueous ink 1 are shown in Table 3.

[0113] Examples 2 to 17 and Comparative Examples 1 to 2 (Production of Water-Based Inks 2 to 17, 21 to 22) Each water-based ink was obtained in the same manner as in Example 1, except that the composition of the water-based ink was changed as shown in Table 3. The physical properties of each water-based ink obtained are shown in Table 3.

[0114] The water-based inks 1 to 17 and 21 to 22 obtained in the above examples and comparative examples were evaluated for continuous dischargeability and substrate adhesion by the methods described below. The evaluation results are shown in Table 3.

[0115] <Evaluation of continuous ejection> Each water-based ink was loaded into an inkjet ejection evaluation device (ImageXpert's "Jetexpert") equipped with an inkjet recording head (Fujifilm's "Samba G3L," piezo type) under an environment of 25±1°C temperature and 30±5% relative humidity. The head voltage, frequency, and negative pressure were set to 30 V, 50 kHz, a push-pull drive waveform, a 2.5 pL ejection volume, and -4.0 kPa negative pressure. An ink ejection command was transmitted to the ejection evaluation device, and the number of nozzles ejecting each water-based ink correctly was counted. Continuous ejection was performed under the same conditions for 15 minutes, and the number of nozzles ejecting correctly after 15 minutes was reconfirmed. The nozzle failure rate (%) was calculated using the following formula to evaluate continuous ejection. The smaller the nozzle failure rate (%), the better the ejection stability. Nozzle missing rate (%) = 100 - (number of nozzles that discharge normally after 15 minutes of continuous discharge / number of nozzles that discharge normally at the beginning) x 100

[0116] <Evaluation of adhesion to substrate> A printing evaluation device (Seiko Epson Corporation, inkjet printer, PX105, piezo type) was used, and an A4-sized film heater (Kawai Electric Manufacturing Co., Ltd.) was fixed to the printing substrate discharge area so that the area where the ink was injected could be heated to 50°C. The printing substrate used was the resin film shown below cut to A4 size. The cartridges of the printing evaluation device were filled with each of the aqueous inks from the Examples and Comparative Examples in an environment of 25±1°C temperature and 30±5% relative humidity. A 50mm x 50mm solid image was printed using 100% ink duty, and then dried for 3 minutes on a film heater set to 60°C to obtain a print. A 50mm long, 15mm wide tape, "Nice Tack No. 4" (registered trademark) (manufactured by Nichiban Co., Ltd.), was applied to the printed surface of the resulting print, covering a 4cm area with a 1cm margin. A T-peel test was performed using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd., product name: RTC-1150A). The peel strength (N / 15mm), an indicator of substrate adhesion, was measured and the substrate adhesion was evaluated according to the following criteria. A peel strength of 1.0N / 15mm or greater was considered to indicate excellent substrate adhesion. (Printing base material) OPP film: Polypropylene film, manufactured by Futamura Chemical Co., Ltd., product number: FOR-AQ, thickness: 20 μm PET film: Polyester (polyethylene terephthalate) film, manufactured by Toray Industries, Inc., product number: Lumirror, thickness: 38 μm

[0117] [Table 3]

[0118] Table 3 confirms that the water-based inks of Examples 1 to 17 have excellent continuous discharge properties and also excellent substrate adhesion of the ink coating film of the printed matter obtained when printing on resin films such as polypropylene film and polyester film. The water-based ink of Comparative Example 1 had poor continuous dischargeability and poor substrate adhesion to polypropylene film because the acrylic resin A did not have a structural unit derived from cycloalkyl(meth)acrylate (a-1). Furthermore, the water-based ink of Comparative Example 2 had poor substrate adhesion to polypropylene films and polyester films because the acrylic resin A did not contain a structural unit derived from cycloalkyl (meth)acrylate (a-1) and did not contain a polyester resin. [Industrial Applicability]

[0119] According to the present invention, it is possible to obtain a water-based ink for inkjet printing that has excellent continuous discharge properties and excellent substrate adhesion (tape peel resistance) of the ink coating film of a printed product on a resin film.

Claims

1. The ink contains pigment-containing acrylic resin particles, a fixing resin, a water-soluble organic solvent, and water, the acrylic resin A constituting the acrylic resin particles containing the pigment has a structural unit derived from a cycloalkyl(meth)acrylate (a-1) and a structural unit derived from a monomer (a-2) having an acid group, The water-based ink for ink-jet printing, wherein the fixing resin comprises a polyester resin.

2. 2. The water-based ink for ink-jet printing according to claim 1, wherein the cycloalkyl(meth)acrylate (a-1) is at least one selected from the group consisting of cyclopentyl(meth)acrylate, cyclohexyl(meth)acrylate, and cycloheptyl(meth)acrylate.

3. 3. The water-based ink for ink-jet printing according to claim 1, wherein a content of the structural units derived from the cycloalkyl(meth)acrylate (a-1) in all structural units of the acrylic resin A is 15% by mass or more and 85% by mass or less.

4. 3. The water-based ink for ink-jet printing according to claim 1, wherein the acrylic resin A has an acid value of 40 mgKOH / g or more and 300 mgKOH / g or less.

5. 3. The water-based ink for ink-jet printing according to claim 1, wherein the polyester resin has an acid value of 5 mgKOH / g or more.

6. 3. The water-based ink for ink-jet printing according to claim 1, wherein the content of the fixing resin in the water-based ink is 0.5% by mass or more and 15% by mass or less.

7. The water-based ink for ink-jet printing according to claim 1 or 2, which is used for printing on a resin film as a printing substrate.

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