Binder component and water-based inkjet ink

Abstract

To provide an eco-friendly binder component for water-based inkjet ink, which can create a dry film that demonstrates superior adhesion and wear resistance on substrates composed of polypropylene, polyethylene, and polyester.SOLUTION: An binder component for water-based inkjet ink satisfies a following requirement (1) or the like. [Requirement (1)]: The binder component is an emulsion comprising emulsion particles composed of a polymer with a constitutional unit derived from styrene (i), a constitutional unit derived from isobornyl (meth)acrylate (ii), and a constitutional unit derived from an acrylate monomer such as ethyl acrylate (iii). A total content of the constitutional units (i) and (ii) is 60-90 mass%, and a mass ratio of the constitutional units (i), (ii), and (iii) is (i): (ii): (iii)=5-40: 20-70: 10-40.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder component for an aqueous inkjet ink, and an aqueous inkjet ink using the same. [Background technology]

[0002] Due to its increasing functionality, inkjet printing is now used in a wide range of applications, including personal, office, and commercial use, recording, color display, and color photography. Furthermore, in recent years, its range of application has expanded from traditional office consumer inkjet printers and wide-format inkjet printers for large-format printing to inkjet printers for industrial use. Because inkjet printing does not require image printing plates, it is suitable as a printing method that can produce small quantities of a wide variety of industrial printed materials on demand. In addition, due to environmental considerations, inkjet printing using aqueous inkjet inks has been actively proposed.

[0003] Industrial applications include, for example, sign displays, outdoor advertising, facility signs, displays, POP advertising, transit advertising, packaging, containers, labels, and the like. Examples of printing substrates (recording media) applicable to these applications include paper media such as paper, cardboard, photo paper, and inkjet paper; plastic media such as polyvinyl chloride, polyolefin, polyester, and nylon; and fabrics such as cotton cloth, ester cloth, nylon fabric, and nonwoven fabric. Furthermore, for industrial applications, on-demand printing that does not require a printing plate is mainstream, and high-speed printing suitability is required. Furthermore, since images recorded with aqueous inkjet inks containing dyes as colorants are poor in durability, such as water resistance and light resistance, aqueous inkjet inks containing pigments as colorants are used.

[0004] Therefore, in order to record printed images with improved durability, inkjet inks have been proposed that contain an acrylic or urethane binder component capable of forming a film (Patent Documents 1 and 2). It should be noted that in aqueous pigment inkjet inks, the pigment must be stably and finely dispersed. For this reason, pigment dispersions in which the pigment is stably and finely dispersed over time using a surfactant or polymer dispersant, and inkjet inks using such pigment dispersions have been proposed (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4157868 [Patent Document 2] Special Publication No. 2009-515007 [Patent Document 3] International Publication No. 2013 / 008691 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even the inkjet inks proposed in Patent Documents 1 to 3 are not necessarily sufficient in terms of adhesion of the recorded image to the substrate and durability such as abrasion resistance, and further performance improvements are required.

[0007] In light of recent trends in global warming, carbon dioxide emissions, resource issues, marine plastic issues, and the like, environmentally friendly technologies, such as those that support energy conservation, recycling, and use environmentally friendly materials, are becoming increasingly important. Under these circumstances, polymer dispersants synthesized using raw materials such as petroleum-derived monomers have been used as dispersants for dispersing pigments in conventional aqueous inkjet inks and aqueous pigment dispersions. In other words, images recorded with conventional aqueous inkjet inks are formed using materials derived from petroleum, and therefore, cannot necessarily be said to have been made using environmentally friendly technologies. In other words, while inkjet printing is used on printing substrates such as containers and labels made of biodegradable plastics such as polylactic acid and polyhydroxyalkanoic acid, there has been a problem in that environmentally friendly technologies have not been applied to images recorded on such printing substrates.

[0008] The present invention has been made in view of the problems associated with the prior art, and an object of the present invention is to provide a binder component for an environmentally friendly aqueous inkjet ink that is capable of forming a dried film that exhibits excellent adhesion and abrasion resistance to polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. Another object of the present invention is to provide an aqueous inkjet ink that uses this binder component and is capable of forming an image that is a dried film that exhibits excellent adhesion and abrasion resistance to polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. [Means for solving the problem]

[0009] According to the present invention, the following binder components are provided: [1] A binder component for aqueous inkjet inks that satisfies the following requirements (1) and (2): [Requirement (1)]: An emulsion containing emulsion particles made of a polymer having a structural unit (i) derived from styrene, a structural unit (ii) derived from isobornyl (meth)acrylate, and a structural unit (iii) derived from at least one acrylate monomer selected from the group consisting of ethyl acrylate, butyl acrylate, lauryl acrylate, and octadecyl acrylate, the total content of the structural unit (i) and the structural unit (ii) in the polymer is 60 to 90 mass %, In the polymer, the mass ratio of the structural unit (i), the structural unit (ii), and the structural unit (iii) is (i):(ii):(iii)=5 to 40:20 to 70:10 to 40; In the polymer, the total content of the structural unit (i), the structural unit (ii), and the structural unit (iii) is 80 mass % or more. [Requirement (2)]: The emulsion contains emulsion particles having a number average particle size of 50 to 250 nm, which are obtained by emulsion polymerization of a monomer component in the presence of a surfactant represented by the following general formula (1): The amount of the surfactant is 2 to 10 parts by mass relative to 100 parts by mass of the monomer component. RO-(CH2CH2O) n -SO3-X + ···(1) (In the general formula (1), R represents an organic group containing an alkyl chain having 8 to 18 carbon atoms, n represents a number from 1 to 40, and X + indicates an ammonium ion, an organic ammonium ion, a lithium ion, a sodium ion, or a potassium ion. [2] The binder component according to [1], wherein in the general formula (1), R is a group having one or more α,β-unsaturated bonds.

[0010] The present invention also provides the following aqueous inkjet ink. [3] A water-based inkjet ink comprising water, a water-soluble organic solvent, a colorant, and the binder component described in [1] or [2] above. [4] The aqueous inkjet ink according to [3] above, further comprising a polyethylene wax component. [5] The aqueous inkjet ink according to [3] or [4], wherein the colorant is a pigment dispersion containing a pigment, a pigment dispersant, and a dispersion medium containing water, and the pigment dispersant is a polymer that satisfies the following requirements (3) to (7): [Requirement (3)]: It has a structural unit (iv) derived from methacrylic acid and a structural unit (v) derived from a methacrylate derived from a biological material, and has an acid value of 30 to 250 mgKOH / g. [Requirement (4)]: The content of the structural unit (v) in the polymer is 50% by mass or more. [Requirement (5)]: The polymer has a number average molecular weight of 5,000 to 20,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 2.5 or less. [Requirement (6)]: At least a portion of the carboxy groups in the polymer are neutralized with an alkali. [Requirement (7)]: The methacrylate derived from a biological material is at least two selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. [6] The aqueous inkjet ink according to [5], wherein the pigment dispersant is an AB block copolymer having an A chain and a B chain, the A chain being a polymer block having a number average molecular weight of 3,000 to 10,000 and not having the structural unit (iv), and the B chain being a polymer block having the structural unit (iv). [7] The water-soluble organic solvent comprises propylene glycol and at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; The aqueous inkjet ink according to any one of [3] to [6] above, wherein the content of the water-soluble organic solvent is 3 to 30% by mass. [8] The aqueous inkjet ink according to any one of [3] to [7] above, which is used for printing on at least one printing substrate selected from the group consisting of polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. [9] The aqueous inkjet ink according to any one of [3] to [8], which has a viscosity at 25°C of 2.9 to 3.3 mPa·s. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an environmentally friendly binder component for an aqueous inkjet ink that is capable of forming a dry film that has excellent adhesion and abrasion resistance to polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. Another object of the present invention is to provide an aqueous inkjet ink that uses this binder component and is capable of forming an image that is a dry film that has excellent adhesion and abrasion resistance to polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Binder component for aqueous inkjet inks> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the binder component for an aqueous inkjet ink of the present invention (hereinafter also simply referred to as "binder component" or "binder") satisfies the following requirements (1) and (2).

[0013] [Requirement (1)]: An emulsion containing emulsion particles made of a polymer having a structural unit (i) derived from styrene, a structural unit (ii) derived from isobornyl (meth)acrylate, and a structural unit (iii) derived from at least one acrylate monomer selected from the group consisting of ethyl acrylate, butyl acrylate, lauryl acrylate, and octadecyl acrylate, the total content of the structural units (i) and (ii) in the polymer is 60 to 90 mass%; In the polymer, the mass ratio of the structural unit (i), the structural unit (ii), and the structural unit (iii) is (i):(ii):(iii)=5-40:20-70:10-40; In the polymer, the total content of the structural units (i), (ii), and (iii) is 80 mass % or more.

[0014] [Requirement (2)]: The emulsion contains emulsion particles having a number average particle size of 50 to 250 nm, which are obtained by emulsion polymerization of a monomer component in the presence of a surfactant represented by the following general formula (1), and the amount of the surfactant is 2 to 10 parts by mass per 100 parts by mass of the monomer component.

[0015] RO-(CH2CH2O) n -SO3-X + ···(1) (In the general formula (1), R represents an organic group containing an alkyl chain having 8 to 18 carbon atoms, n represents a number from 1 to 40, and X + indicates an ammonium ion, an organic ammonium ion, a lithium ion, a sodium ion, or a potassium ion.

[0016] The structural unit (i) is a structural unit derived from styrene. Therefore, the structural unit (i) is a structural unit having an aromatic ring. By using a polymer containing a structural unit having an aromatic ring, adhesion to polyester-based substrates can be improved. Furthermore, since the glass transition temperature (Tg) of styrene homopolymers is as high as 100°C, the Tg of the polymer increases and the polymer itself hardens, thereby improving the durability of the formed film, such as abrasion resistance. Furthermore, emulsion particles can be stably formed during emulsion polymerization, thereby suppressing the generation of foreign matter. Furthermore, when a surfactant containing a group having an α,β-unsaturated bond in its structure (such as an allyl group or a maleic acid group) is used during emulsion polymerization, styrene has good copolymerizability with the α,β-unsaturated bond, so the surfactant can be included as a structural component of the polymer, with almost no unreacted surfactant remaining.

[0017] The structural unit (ii) is a structural unit derived from isobornyl (meth)acrylate. Because the Tg of a homopolymer of isobornyl (meth)acrylate is relatively high, the inclusion of a structural unit derived from isobornyl (meth)acrylate hardens the polymer itself, improving the durability of the resulting film, such as its abrasion resistance. The Tg of a homopolymer of isobornyl acrylate is 90°C, while the Tg of a homopolymer of isobornyl methacrylate is 155°C. Furthermore, because isobornyl (meth)acrylate has a large number of carbon atoms, the inclusion of structural unit (ii) improves adhesion to olefin-based substrates. Furthermore, the isobornyl group, which is the ester residue of isobornyl (meth)acrylate, is a residue obtained by esterifying borneol, which is obtained as camphene by isomerizing α-pinene obtained from pine resin or pine essential oil, with (meth)acrylic acid. That is, isobornyl (meth)acrylate is a carbon-neutral compound made from plant-derived materials and is environmentally friendly, so the binder component of this embodiment can contribute to preventing global warming.

[0018] The structural unit (iii) is a structural unit derived from at least one acrylate monomer selected from the group consisting of ethyl acrylate, butyl acrylate, lauryl acrylate, and octadecyl acrylate. The inclusion of this structural unit (iii) enables the polymer to be plasticized, thereby improving the film-forming properties of emulsion particles. The ethyl group, which is the ester residue of ethyl acrylate, is a residue of ethanol obtained by decomposing starch or sugar or by fermentation. The butyl group, which is the ester residue of butyl acrylate, is a residue of butanol obtained by biomass fermentation or the like. Lauryl acrylate and octadecyl acrylate are residues of long-chain alkyl alcohols obtained by fractionating fatty acids, which are hydrolyzates of fats and oils such as palm kernel oil and coconut oil, to separate long-chain alkanoic acids, which are then reduced with hydrogen. Therefore, the acrylate monomers obtained using these alcohols are carbon-neutral compounds made from plant-derived materials and are environmentally friendly. Therefore, the binder component of this embodiment can contribute to preventing global warming.

[0019] The total content of the structural units (i) and (ii) in the polymer is 60 to 90% by mass, preferably 65 to 85% by mass. If the total content of the structural units (i) and (ii) is less than 60% by mass, adhesion to the substrate and scratch resistance will be insufficient. On the other hand, if the total content of the structural units (i) and (ii) is more than 90% by mass, the Tg of the polymer will be too high, resulting in poor film-forming properties.

[0020] In the polymer, the mass ratio of the structural unit (i), the structural unit (ii), and the structural unit (iii) is (i):(ii):(iii) = 5-40:20-70:10-40. It is preferable that the content of the structural unit (ii) is higher than the content of the structural unit (i). The content of the structural unit (iii) in the polymer is 10-40% by mass, and preferably 10-30% by mass. If the content of the structural unit (iii) is less than 10% by mass, the contents of the structural units (i) and (ii) increase relatively, resulting in an excessively high Tg of the polymer and reduced film-forming properties. On the other hand, if the content of the structural unit (iii) exceeds 40% by mass, the film formed will be soft, resulting in reduced abrasion resistance and chemical resistance.

[0021] The total content of the structural units (i), (ii), and (iii) in the polymer is preferably 80% by mass or more, and more preferably 90% by mass or more. It is particularly preferable that the polymer is substantially composed of only the structural units (i), (ii), and (iii). If the total content of the structural units (i), (ii), and (iii) in the polymer is less than 80% by mass, the properties of the other structural units may become significant.

[0022] The polymer may contain other structural units in addition to the structural unit (i), the structural unit (ii), and the structural unit (iii). Examples of monomers constituting other structural units include alkyl (meth)acrylates such as methyl, propyl, isopropyl, butyl, isobutyl, t-butyl, hexyl, cyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl, octyl, 2-ethylhexyl, decyl, isodecyl, dodecyl, tetradecyl, hexadecyl, octadecyl, dicyclopentenyl, dicyclopentanyl, adamantyl, benzyl, tetrahydrofurfuryl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxybutyl, methoxyethyl, ethoxyethyl, butoxyethyl, ethoxyethoxyethyl, butoxyethoxyethyl, polyethylene glycol monomethyl ether, dimethylaminoethyl, diethylaminoethyl, trifluoromethyl, perfluoroalkyl, and polydimethylsiloxane; (meth)acrylic acid; and vinyl monomers such as styrene, vinyl toluene, vinyl naphthalene, vinyl acetate, vinyl chloride, and N-vinylpyrrolidone.

[0023] The binder component of the present embodiment is an emulsion containing emulsion particles obtained by emulsion polymerization of a monomer component containing the above-mentioned styrene, isobornyl (meth)acrylate, and an acrylate-based monomer in the presence of a surfactant represented by the following general formula (1):

[0024] RO-(CH2CH2O) n -SO3-X + ···(1) (In the general formula (1), R represents an organic group containing an alkyl chain having 8 to 18 carbon atoms, n represents a number from 1 to 40, and X + indicates an ammonium ion, an organic ammonium ion, a lithium ion, a sodium ion, or a potassium ion.

[0025] This surfactant is a nonionic-anionic surfactant having a nonionic moiety with a polyethylene glycol chain and an anionic moiety containing a sulfonate salt. Emulsion polymerization in the presence of such a surfactant reduces the precipitation of foreign matter such as "lumps," forms fine emulsion particles, and produces an emulsion with excellent storage stability. Furthermore, the resulting emulsion has low foaming properties, making it suitable as a binder component for aqueous inkjet inks.

[0026] The above-described emulsion, which is the binder component of this embodiment, can be obtained by emulsion polymerization of a monomer component in the presence of a specific surfactant represented by general formula (1), and cannot be substantially obtained by emulsion polymerization in the presence of other surfactants or by polymerization methods other than emulsion polymerization. Furthermore, it is substantially difficult or impossible to measure, using general equipment, the physical properties and characteristics of the emulsion particles of the binder component, which is an emulsion prepared by such methods, other than the particle size.

[0027] R in general formula (1) is an organic group containing an alkyl chain having 8 to 18 carbon atoms. Examples of the alkyl chain having 8 to 18 carbon atoms include linear or branched alkyl chains such as octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, octadecyl, and trimethyldecyl groups. R preferably has an alkyl chain directly ether-bonded to one end of an ethylene glycol chain. Specific examples of surfactants represented by general formula (1) include polyethylene glycol monododecyl ether sulfonate and polyethylene glycol monooctadecyl ether sulfonate. Furthermore, X in general formula (1) + From the viewpoint of maintaining the stability of the emulsion, ammonium ions and sodium ions are preferred.

[0028] In general formula (1), R is preferably a group having one or more α,β-unsaturated bonds. In other words, it is preferable to use a surfactant having a polymerizable group. By carrying out emulsion polymerization in the presence of such a surfactant, the resulting polymer contains a structure derived from the surfactant, making it possible to form emulsion particles that are stably emulsified in water. Furthermore, since the surfactant used is not liberated in the dispersion medium but is mostly incorporated into the resulting polymer, the ejection stability of aqueous inkjet inks containing this emulsion as a binder component can be improved.

[0029] Examples of the group having an α,β-unsaturated bond include a (meth)acryloyl group, an allyl group, a 1-methylethylene group, a maleic acid group, etc. Examples of the surfactant in which R is a group having one or more α,β-unsaturated bonds include a compound represented by the following formula (A).

[0030] TIFF0007732956000001.tif29170

[0031] Commercially available products of the compound (surfactant) represented by the above formula (A) include the Aqualon KH series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Latemul PD-104, PD-105 (manufactured by Kao Corporation); Adeka Reasop SR series, SR series (manufactured by Asahi Denka Co., Ltd.); and the like, under the following trade names.

[0032] The amount of surfactant represented by general formula (1) used during emulsion polymerization of the monomer components is 2 to 10 parts by mass, preferably 3 to 5 parts by mass, per 100 parts by mass of the monomer components. If the amount of surfactant is less than 2 parts by mass per 100 parts by mass of the monomer components, the resulting emulsion particles will be excessively large, foreign matter will be more likely to be generated, and the stability of the emulsion particles will be reduced. On the other hand, if the amount of surfactant is more than 10 parts by mass per 100 parts by mass of the monomer components, the water resistance of images recorded with ink containing the resulting emulsion as a binder component will be reduced, and the viscosity of the emulsion will become too high, which may result in severe foaming.

[0033] The number-average particle diameter of the emulsion particles contained in the emulsion is 50 to 250 nm, preferably 80 to 150 nm. If the number-average particle diameter of the emulsion particles is less than 50 nm, the viscosity of the ink containing this emulsion as a binder component may increase excessively. On the other hand, if the number-average particle diameter of the emulsion particles is more than 250 nm, the ink containing this emulsion as a binder component may be prone to clogging of the recording head.

[0034] The monomer components can be emulsion polymerized using water as the polymerization medium and a radical generator such as a water-soluble peroxide (e.g., potassium persulfate) or a water-soluble azo compound (e.g., 4,4'-azobis(4-cyanovaleric acid)). More specifically, examples include a method in which the surfactant described above is dissolved in water and the monomer components are added dropwise to polymerize; a method in which the surfactant is dissolved in the monomer components and the monomer components are added dropwise to polymerize; and a method in which the surfactant is dissolved in the monomer, added to water, and emulsified by stirring with a stirrer such as a disperser, followed by polymerization. Polymerization conditions can be set arbitrarily depending on the half-life temperature of the radical generator used, etc. Polymerization can also be performed by adding a catalyst to lower the polymerization temperature.

[0035] The polymerization may be conventionally known radical polymerization or living radical polymerization. Among these, emulsion polymerization of monomer components by living radical polymerization is preferred because it results in the formation of polymer emulsion particles with a more uniform molecular weight. Specific living radical polymerization methods include atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxide polymerization (NMP), organotellurium polymerization (TERP), reversible transfer catalyzed polymerization (RTCP), and reversible catalyst-mediated polymerization (RCMP).

[0036] Water used as a polymerization medium during emulsion polymerization may contain a high-boiling water-soluble organic solvent such as ethylene glycol or propylene glycol to prevent the emulsion from drying out. Other surfactants may also be used to stabilize the emulsion particles formed. The resulting emulsion may contain additives such as antifoaming agents, preservatives, leveling agents, pH adjusters, waxes, and mildew inhibitors.

[0037] From the viewpoint of further improving the abrasion resistance and adhesion of the coating to be formed, the number average molecular weight (Mn) of the polymer forming the emulsion particles is preferably 20,000 to 500,000, and more preferably 50,000 to 300,000. In this specification, the number average molecular weight (Mn) of the polymer is a value measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0038] The viscosity of the emulsion at 25°C is preferably 3 to 200 mPa·s, and more preferably 5 to 50 mPa·s. If the viscosity of the emulsion is too high, the viscosity of the ink containing this emulsion is likely to increase excessively, which may lead to problems such as poor ejection. From the viewpoint of improving the stability of the emulsion particles, the pH of the emulsion at 25°C is preferably 7 to 12, and more preferably 7.5 to 9.5. The surfactant represented by general formula (1) used during emulsion polymerization has a sulfonic acid group. Furthermore, since the stability of the emulsion particles is improved by neutralizing this sulfonic acid group, the liquid pH of the emulsion is preferably alkaline, in which salts are neutralized.

[0039] <Water-based inkjet ink> One embodiment of the aqueous inkjet ink of the present invention (hereinafter also simply referred to as "aqueous ink" or "ink") contains water, a water-soluble organic solvent, a colorant, and the binder component described above.

[0040] (water) The ink of this embodiment is a water-based inkjet ink and contains water as an essential component. Ion-exchanged water, distilled water, purified water, etc. are preferably used as the water. The content of water in the ink is preferably 30 to 90% by mass based on the total amount of the ink.

[0041] (Water-soluble organic solvent) The ink of this embodiment contains a water-soluble organic solvent. The ink of this embodiment is suitable for printing on substrates such as plastic films with low permeability, such as polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. For this reason, it is preferable to use a water-soluble organic solvent that not only functions as a humectant but also has good wettability with respect to the plastic film used as the printing substrate. Furthermore, it is preferable to use a water-soluble organic solvent that can function as a leveling agent for the surface of the printing substrate and also as a film-forming aid that improves the film-forming properties of the binder component.

[0042] Examples of the water-soluble organic solvent include alcohol-based solvents such as methanol, ethanol, and isopropanol; ketone-based solvents such as acetone; alkylene glycol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol; alkylene glycol monoalkyl ether-based solvents such as ethylene glycol methyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycerin-based solvents such as glycerin, diglycerin, and ethylene oxide adducts of glycerin; amide-based solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; urea-based solvents such as tetramethylurea and dimethylimidazolidinone; and carbonate-based solvents such as ethylene carbonate and dimethyl carbonate.

[0043] If a large amount of water-soluble organic solvent remains in the coating formed from the binder component, the water resistance, adhesion to the printing substrate, and abrasion resistance of the coating may decrease. For this reason, it is preferable to use a water-soluble organic solvent with a relatively high degree of volatility. From the above perspectives, the water-soluble organic solvent preferably contains propylene glycol (boiling point 188°C) and at least one selected from the group consisting of diethylene glycol monobutyl ether (boiling point 230°C), triethylene glycol monobutyl ether (boiling point 278°C), propylene glycol monomethyl ether (boiling point 121°C), propylene glycol monoethyl ether (boiling point 132.8°C), propylene glycol monopropyl ether (boiling point 150°C), dipropylene glycol monomethyl ether (boiling point 189.6°C), and tripropylene glycol monomethyl ether (boiling point 243°C).

[0044] The content of the water-soluble organic solvent in the ink is preferably 3 to 30% by mass, and more preferably 5 to 25% by mass, based on the total amount of ink. If the content of the water-soluble organic solvent is less than 3% by mass, the ink will dry easily and may not function as a leveling agent on the surface of the plastic film. On the other hand, if the content of the water-soluble organic solvent is more than 30% by mass, the viscosity of the ink will increase, which may reduce the ink's ejection properties and reduce the ink's stability. In addition, the binder component may precipitate or the pigment may aggregate. Furthermore, if the content of the water-soluble organic solvent is too high, the water-soluble organic solvent will tend to remain in the printing film, which may lead to blocking and reduce the physical properties of the image, such as water resistance and abrasion resistance.

[0045] (coloring agent) As the colorant, conventionally known dyes and pigments can be used. From the viewpoints of water resistance, color development, color density, and vividness, it is preferable to use a pigment. It is also preferable to use a pigment dispersion containing a pigment, a pigment dispersant, and a dispersion medium containing water as the colorant.

[0046] The pigment may be any of the conventional organic and inorganic pigments used in aqueous inkjet inks. Examples of organic pigments include chromatic pigments such as phthalocyanine, azo, azomethine azo, azomethine, anthraquinone, perinone-perylene, indigo-thioindigo, dioxazine, quinacridone, isoindoline, isoindolinone, diketopyrrolopyrrole, quinophthalone, and indanthrene pigments; and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. Examples of inorganic pigments include extender pigments, titanium oxide pigments, iron oxide pigments, and spinel pigments.

[0047] Unless the printed matter (image) requires hiding power, it is preferable to use organic fine particle pigments. When a printed matter that is highly vivid and transparent is required, it is preferable to use pigments that have been finely divided by wet grinding such as salt milling or dry grinding. Considering the avoidance of nozzle clogging, it is preferable to use organic pigments with a number average particle size of 0.2 μm or less, or inorganic pigments with a number average particle size of 0.4 μm or less, from which pigments with a particle size of more than 1.0 μm have been removed.

[0048] Specific examples of pigments, listed by Color Index (CI) number, are CI Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 97, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 175, 180, 181, 185, 191; CI Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, 73; and CI Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, 123, 14 4, 146, 147, 149, 150, 166, 168, 170, 176, 177, 180, 184, 185, 192, 202, 207, 214, 215, 216, 217, 220, 221, 223, 224, 226, 227, 228, 238, 240, 242, 254, 255, 264, 269, 272; CI Pigment Violet 19, 23, 29, 30, 37, 40, 50; CI Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22, 60, 64; CI Pigment Green 7, 36; CI Pigment Black 7; CI Pigment White 6; and the like.

[0049] Among these, yellow pigments such as CI Pigment Yellow 74, 83, 109, 128, 139, 150, 151, 154, 155, 180, 181, and 185 are preferred, as they are suitable for aqueous inkjet inks and have good color development, dispersibility, weather resistance, and the like; red pigments such as CI Pigment Red 122, 170, 176, 177, 185, and 269, and CI Pigment Violet 19 and 23; blue pigments such as CI Pigment Blue 15:3, 15:4, and 15:6; black pigments such as CI Pigment Black 7; and white pigments such as CI Pigment White 6.

[0050] The pigment may be any of the following: an untreated pigment; a self-dispersing pigment having functional groups introduced onto its surface; or a treated pigment that has been surface-treated with a surface treatment agent such as a coupling agent or an activator, or a polymer, or that has been encapsulated. Self-dispersing pigments are easily dispersible pigments in which acidic groups such as carboxyl groups, sulfonic acid groups, and phosphate groups have been introduced onto the surface of the pigment particles, and these acidic groups have been neutralized to make them more water-compatible, thereby enabling them to be dispersed in ink without the use of a pigment dispersant. In contrast, it is preferable to use a pigment dispersant in combination with untreated pigments, surface-treated pigments, and encapsulated pigments.

[0051] The pigment is preferably used as a pigment dispersion in the colorant, and a pigment dispersion containing a self-dispersing pigment is preferably used. Alternatively, a pigment dispersion in which the pigment is dispersed in a dispersion medium using a pigment dispersant, a surfactant, or the like can also be used. The pigment dispersant is preferably a vinyl polymer having a number-average molecular weight of 1,000 to 20,000 and an acid value of 50 to 250 mgKOH / g, neutralized with an alkali. This pigment dispersant is usually contained in the pigment dispersion in a finely dispersed or dissolved state.

[0052] The vinyl polymer preferably has an acidic group such as a carboxy group, a sulfonic acid group, or a phosphate group. Neutralizing the acidic group, such as a carboxy group, with an alkali makes it compatible with water and allows it to be finely dispersed or dissolved in the ink. The vinyl polymer having an acidic group has a structural unit derived from a monomer having an acidic group. Examples of the monomer having an acidic group include (meth)acrylic acid, (maleic anhydride), (itaconic anhydride), styrenecarboxylic acid, a monoester obtained by reacting a (meth)acrylate monomer having a hydroxyl group with a carboxylic anhydride, a dibasic acid, or a polycarboxylic acid, vinyl sulfonic acid, acrylamidomethylpropyne sulfonic acid, vinyl phosphoric acid, and methacryloyloxyethyl phosphoric acid.

[0053] Examples of monomers constituting a vinyl polymer other than the monomer having an acidic group include aromatic vinyl monomers such as styrene, vinyl toluene, and vinyl naphthalene; (meth)acrylate monomers such as butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; vinyl ester monomers such as vinyl acetate; and heterocyclic vinyl monomers such as vinyl pyridine and vinyl imidazole.

[0054] Specific examples of vinyl polymers include styrene-acrylic acid copolymer, styrene-maleic acid copolymer, styrene-ethyl acrylate-acrylic acid copolymer, styrene-acrylic acid-ethoxyethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-2-hydroxyethyl methacrylate copolymer, benzyl methacrylate-methacrylic acid copolymer, styrene-methacrylic acid-dimethylaminoethyl methacrylate-butyl acrylate copolymer, styrene-maleic acid-maleic acid polyethylene glycol propylene glycol monobutyl ether monoamine amidation copolymer, and styrene-methyl methacrylate-2-ethylhexyl methacrylate-methacrylic acid copolymer.

[0055] The number-average molecular weight of the vinyl polymer is preferably 1,000 to 20,000, more preferably 3,000 to 15,000, and particularly preferably 5,000 to 13,000. If the number-average molecular weight of the vinyl polymer is less than 1,000, the ink may have insufficient pigment adsorption and the strength of the resulting printed film may be reduced. On the other hand, if the number-average molecular weight of the vinyl polymer is more than 20,000, the ink may have an excessively high viscosity and may be prone to exhibiting non-Newtonian viscosity, resulting in reduced ejection stability.

[0056] The acid value of the vinyl polymer is preferably 50 to 250 mgKOH / g, more preferably 75 to 150 mgKOH / g, and particularly preferably 85 to 130 mgKOH / g. If the acid value of the vinyl polymer is less than 50 mgKOH / g, it will be difficult to dissolve in water even after neutralization with alkali, and its function as a pigment dispersant may be insufficient. On the other hand, if the acid value of the vinyl polymer is more than 250 mgKOH / g, its water solubility may be too high. This may result in an excessive increase in ink viscosity and an increase in the amount of hydrophilic acidic groups such as carboxy groups, which may reduce the water resistance of the resulting printed film.

[0057] Vinyl polymers can be synthesized according to conventional methods. For example, vinyl polymers can be obtained by bulk polymerization of a monomer alone, emulsion polymerization, or solution polymerization using a water-soluble organic solvent for inkjet inks in the presence of an azo initiator such as azobisisobutyronitrile or a peroxide initiator such as benzoyl peroxide. The resulting vinyl polymer can then be neutralized with an alkaline substance to form a pigment dispersant. Alternatively, a solution of the pigment dispersant may be mixed with the pigment and then added to a poor solvent or treated with an acid to precipitate the pigment dispersant, thereby treating or encapsulating the pigment to prepare a polymer-treated pigment. Living radical polymerization is preferred as a polymerization method for producing vinyl polymers. The vinyl polymer may be any polymer with a higher structure, such as a random copolymer, block copolymer, graft copolymer, gradient copolymer, star polymer, or dendrimer.

[0058] The pigment dispersant is preferably a polymer that satisfies the following requirements (3) to (7).

[0059] [Requirement (3)]: It has a structural unit (iv) derived from methacrylic acid and a structural unit (v) derived from a methacrylate derived from a biological material, and has an acid value of 30 to 250 mgKOH / g.

[0060] [Requirement (4)]: The content of the structural unit (v) in the polymer is 50 mass % or more.

[0061] [Requirement (5)]: The number average molecular weight of the polymer is 5,000 to 20,000, and the molecular weight distribution (weight average molecular weight / number average molecular weight) is 2.5 or less.

[0062] [Requirement (6)]: At least a portion of the carboxy groups in the polymer are neutralized with an alkali.

[0063] [Requirement (7)]: The methacrylate derived from a biological material is at least two selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate.

[0064] If the acid value of the polymer (pigment dispersant) is less than 30 mgKOH / g, the polymer may be less soluble in water. On the other hand, if the acid value of the polymer is more than 250 mgKOH / g, the water solubility becomes too high, which may result in an excessive increase in ink viscosity or a decrease in the water resistance of the image. It is more preferable that the acid value of the polymer is 50 to 150 mgKOH / g.

[0065] The polymer dissolves in water when at least a portion of the carboxyl groups in the polymer structure is neutralized with an alkali. Examples of alkali that can be used include ammonia, organic amines such as dimethylaminoethanol, and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Among these, ammonia is preferred because of its high drying properties.

[0066] The content of the structural unit (v) derived from a biological material in the polymer is 50% by mass or more, preferably 80% by mass or more. By including a large amount of the structural unit (v) derived from a biological material, the polymer can be made environmentally friendly. The biological material-derived methacrylate is at least two selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. Tetrahydrofurfuryl methacrylate is a methacrylate using an alcohol (tetrahydrofurfuryl alcohol), which is a hydrogenated product of furfural obtained from corn cobs, etc. The tetrahydrofurfuryl ring and isobornyl group are easily adsorbed to the pigment, thereby improving the dispersibility of the pigment. Furthermore, these methacrylates have a structure similar to that of the constituent monomers of the polymer forming the emulsion particles contained in the binder component (emulsion), making them suitable from the standpoint of compatibility.

[0067] The polymer may have other structural units in addition to the structural unit (iv) and the structural unit (v). The monomer that constitutes the other structural units is preferably a methacrylate monomer, since this allows for structural control by living radical polymerization.

[0068] The number-average molecular weight (Mn) of the polymer is 5,000 to 20,000, preferably 7,000 to 13,000. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the polymer is 2.5 or less. If the number-average molecular weight (Mn) of the polymer is less than 5,000, the polymer may have low adsorption to the pigment and may be easily detached after dispersion, resulting in reduced dispersibility. On the other hand, if the number-average molecular weight (Mn) of the polymer exceeds 20,000, the viscosity of the ink may increase excessively.

[0069] The polymers used as pigment dispersants can be produced, for example, by radical polymerization in the presence of an azo-based radical generator or a peroxide-based radical generator through solution polymerization using an organic solvent. The organic solvent is preferably the same water-soluble organic solvent as that used in the aqueous inkjet ink. After polymerization, an aqueous solution containing an alkali is added to neutralize and ionize at least a portion of the carboxyl groups, allowing the polymer to be dissolved in water.

[0070] The structure of the polymer may be any of a random structure, a block structure, and a graft structure. Among these, the polymer used as a pigment dispersant is preferably an AB block copolymer having an A chain and a B chain. The A chain is preferably a polymer block having a number average molecular weight of 3,000 to 10,000 and not having the structural unit (iv). The B chain is preferably a polymer block having the structural unit (iv).

[0071] The A chain is a water-insoluble polymer block that does not have a carboxy group. Therefore, the water-insoluble A chain strongly adsorbs or accumulates on the pigment, encapsulating the pigment, making it difficult for the polymer to detach from the pigment, and allowing the pigment to be stably dispersed in the dispersion medium for a long period of time. The number-average molecular weight (Mn) of the A chain is 3,000 to 10,000, preferably 5,000 to 8,000. If the number-average molecular weight (Mn) of the A chain is less than 3,000, the adsorption to the pigment may be reduced. On the other hand, if the number-average molecular weight (Mn) of the A chain is more than 10,000, the polymer itself tends to become water-insoluble, and may not exhibit adsorption to the pigment.

[0072] The above-mentioned AB block copolymers are preferably produced by polymerization methods with living properties, such as living anionic polymerization, living cationic polymerization, and living radical polymerization. Among these, living radical polymerization is preferred from the viewpoints of conditions, materials, and equipment. Among living radical polymerization methods, the RTCP method and RCMP method, which use an organic compound as a catalyst and an organic iodide as a polymerization initiator, are preferred. These methods use relatively safe, commercially available compounds, do not use heavy metals or special compounds, and are advantageous in terms of cost and purification. Furthermore, by using tertiary iodine as the growing terminal, precise block structures can be easily formed using standard equipment.

[0073] Either the A chain or the B chain may be polymerized first. However, if the B chain is polymerized first, methacrylic acid may remain in the polymerization system. In this case, a structural unit derived from methacrylic acid may be introduced into the A chain that is polymerized subsequently. For this reason, it is preferable to polymerize the A chain first, and then polymerize the B chain.

[0074] (Method of manufacturing pigment dispersion liquid) The pigment dispersion can be produced by dispersing the pigment in a dispersion medium using the pigment and pigment dispersant described above according to a conventional method. The pigment content in the pigment dispersion is preferably 1 to 30% by mass, and more preferably 10 to 25% by mass, for organic pigments. Furthermore, the pigment content is preferably 5 to 70% by mass, and more preferably 30 to 50% by mass, for inorganic pigments. The pigment dispersant content is preferably 5 to 100 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the pigment.

[0075] A pigment dispersion can be prepared by finely dispersing the pigment in a mixture of a pigment, a pigment dispersant, and a dispersion medium containing water using a paint shaker, ball mill, attritor, sand mill, horizontal media mill, colloid mill, roll mill, or the like. It is preferable to remove coarse particles from the pigment dispersion using a centrifuge or filter. Other additives may also be added as needed.

[0076] (binder component) The ink of this embodiment contains the binder component for aqueous inkjet inks described above. When the colorant is a dye, the content of the binder component (solid content) in the ink is preferably 20 to 505 parts by mass per 100 parts by mass of the dye. On the other hand, when the colorant is a pigment, the content of the binder component (solid content) in the ink is preferably 50 to 505 parts by mass, more preferably 100 to 400 parts by mass, per 100 parts by mass of the pigment. If the amount of solid content of the binder component per 100 parts by mass of the pigment is less than 50 parts by mass, the resulting printed film may have slightly insufficient adhesion to the plastic film and abrasion resistance. On the other hand, if the amount of solid content of the binder component per 100 parts by mass of the pigment is more than 505 parts by mass, the pigment concentration is relatively low, which may result in a slight decrease in the color development of the image.

[0077] (wax component) The ink can further contain a wax component. Examples of wax components include polyethylene-based wax components, polyolefin-based wax components, and silicone-based wax components. Among these, it is preferable to use a polyethylene-based wax component (wax emulsion). Because wax components have a high affinity for plastic films, adding a wax component can form a printed film with superior adhesion. Furthermore, the wax component easily phase-separates from the binder component and bleeds to the surface, further improving the abrasion resistance of the printed film. Furthermore, because polyethylene-based wax components are highly hydrophobic, they can form a printed film with superior durability.

[0078] The wax component is preferably used in the form of a dispersion in water. The content of the wax component in the ink is preferably 0.1 to 2.5% by mass, and more preferably 0.3 to 1.5% by mass, based on the total mass of the ink.

[0079] (Other additives) The ink may further contain other conventionally known components, such as surfactants, preservatives, organic solvents other than the above-mentioned water-soluble organic solvents, leveling agents, surface tension adjusters, pH adjusters, ultraviolet absorbers, light stabilizers, antioxidants, fillers, thickeners, antifoaming agents, antifungal agents, antistatic agents, metal fine particles, and magnetic powders.

[0080] The surface tension of the ink can be controlled by adding a surfactant to the ink. Examples of surfactants include silicone-based, acetylene glycol-based, fluorine-based, alkylene oxide-based, and hydrocarbon-based surfactants. Among these, silicone-based, acetylene glycol-based, and fluorine-based surfactants are preferred. Surfactants generally cause ink to foam or to be repelled by the film surface. Furthermore, since the use of surfactants can cause pigments to aggregate, it is preferable to adjust the amount of surfactant added. The content of surfactant in the ink is preferably 0 to 3.5% by mass, and more preferably 0.01 to 2.0% by mass, based on the total amount of ink.

[0081] Examples of preservatives include sodium benzoate, benzimidazole, thiabendazole, potassium sorbitanate, sodium sorbitanate, sodium dehydroacetate, thiazosulfamide, and pyridinethiol oxide. The content of the preservative in the ink is preferably 0.05 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass, based on the total mass of the ink.

[0082] When the colorant is a dye, the content of the dye in the ink is preferably 0.5 to 30.0% by mass, based on the total mass of the ink. When the colorant is a pigment, the content of the pigment in the ink is preferably 0.1 to 25.0% by mass, and more preferably 0.2 to 20% by mass, based on the total mass of the ink. From the viewpoint of improving the water resistance, light resistance, color development, etc. of the printed film (image) to be formed, it is preferable to use a pigment as the colorant.

[0083] (Ink properties) The viscosity of the ink is adjusted to an appropriate level, taking into consideration the type of pigment, etc., so that the ink can be ejected from the nozzles of the recording head by inkjet printing. For example, the viscosity of ink containing organic pigments is preferably 2 to 10 mPa·s. Furthermore, the viscosity of ink containing inorganic pigments is preferably 5 to 30 mPa·s.

[0084] In particular, the viscosity of the ink at 25°C is preferably 2.9 to 3.3 mPa·s, and more preferably 3.0 to 3.2 mPa·s. By keeping the ink viscosity within the above range (i.e., low viscosity), it is possible to use the ink in commercially available inkjet recording devices equipped with existing recording heads, without the need for a recording head that can handle high viscosities. The binder component used in the ink is an emulsion, and the polymer content dissolved in the liquid medium is low. Therefore, by using the binder component, the ink viscosity can be kept within the above range.

[0085] The pH of the ink is preferably 7.0 to 10.0, and more preferably 7.5 to 9.5. If the pH of the ink is less than 7.0, the binder component (polymer) may be more likely to precipitate and the pigment may be more likely to aggregate. On the other hand, if the pH of the ink is more than 10.0, the ink may be difficult to handle due to its strong alkalinity.

[0086] The surface tension of the ink is set appropriately depending on the performance of the inkjet recording device, etc. For example, the surface tension of the ink is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0087] (Printing base material) By using the ink of this embodiment, it is possible to form a printed film (image) that has high adhesion to a printing substrate such as a plastic film and excellent abrasion resistance. Examples of plastics that can be used as a constituent material of the plastic film include polyolefin resins, polyester resins, polyamide resins, polyvinyl halide resins, cellulose resins, polystyrene resins, polymethacrylate resins, polyacrylonitrile resins, polycarbonate resins, polyimide resins, polyvinyl acetal resins, and polyvinyl alcohol resins.

[0088] Examples of polyolefin resins include low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, polyα-olefin, polyethylene vinyl acetate, polyethylene vinyl alcohol, and polycycloolefin. Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polylactic acid. Examples of polyamide resins include nylon 6, nylon 66, and nylon 610. Examples of polyvinyl halide resins include polyvinyl chloride, polyvinylidene chloride, and polyfluoroethylene.

[0089] It is preferable to print on a polyolefin-based resin film, which is inexpensive and easily available, and which is generally difficult to form a printed film with excellent adhesion and abrasion resistance on, and it is preferable to print on a polyethylene-based resin film or a polypropylene-based resin film. Furthermore, from the viewpoints of durability, cost, etc., it is also preferable to print on a polyester-based resin film. The ink of this embodiment is suitable as an ink for inkjet printing on a printing substrate such as a polypropylene-based substrate, a polyethylene-based substrate, or a polyester-based substrate.

[0090] The plastic film may be unstretched or may be stretched by uniaxial stretching, biaxial stretching, or the like. The surface (printed surface) of the plastic film may be untreated or may be subjected to surface treatment such as plasma treatment, corona treatment, radiation treatment, or silane coupling treatment. The plastic film may have a single-layer structure or a multi-layer structure, and may be subjected to aluminum vapor deposition or transparent vapor deposition. The thickness of the plastic film is preferably 1 to 500 μm, more preferably 5 to 200 μm. The plastic film may be colored with a pigment or dye, or may contain a reinforcing filler such as carbon black, silica, calcium carbonate, glass fiber, or cellulose nanofiber.

[0091] The ink of this embodiment can be applied to an inkjet printer equipped with a recording head such as a thermal head or a piezo head, and can record (print) images on various substrates, including the plastic films mentioned above, using an inkjet recording method. In addition to the plastic films mentioned above, other substrates that can be used include paper, photographic paper, glossy photographic paper, fibers, fabrics, ceramics, metals, and molded objects. The recorded image (printed film) is a so-called dried film that has high saturation, high color development, adhesion, and excellent durability, such as abrasion resistance. By using the ink of this embodiment, it is possible to obtain a printed item on which an environmentally friendly, carbon-neutral dried film containing components derived from biological materials is formed. [Example]

[0092] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0093] <Binder manufacturing> Synthesis Example 1 252 parts of ion-exchanged water were placed in a reaction vessel and heated to 78°C while bubbling nitrogen. In a separate vessel, 30 parts of styrene (St), 60 parts of isobornyl acrylate (IBXA), 10 parts of lauryl acrylate (LA), and 3 parts of polyethylene glycol monododecyl ether sulfonate ammonium salt (LA-12) (trade name "Hitenol LA-12" manufactured by Daiichi Kogyo Yakuhin Co., Ltd.) were placed and mixed uniformly to prepare a monomer mixture. IBXA is an acrylate of borneol obtained by isomerizing α-pinene obtained from pine resin or pine essential oil, and is an acrylate of a plant-derived alcohol. LA is an acrylate of dodecanol obtained by hydrogen reduction of lauric acid obtained by fractionating fatty acids, which are hydrolyzed from oils such as palm oil and coconut oil. 3 parts of potassium persulfate (KPS) were added to the reaction vessel, and the prepared monomer mixture was added dropwise over 2 hours. Polymerization was carried out at 78°C for 4 hours to obtain a bluish-white emulsion, Binder E-1. No lumps (precipitates) were observed on the wall surfaces. Filtration through a 200-mesh filter revealed no residue. A sample was dried in a dryer at 150°C, and the solid content calculated from the residue at the time of reaching a constant weight was 29.9%. The pH of the emulsion was adjusted to 9.0 by adding 0.1 mol / L aqueous sodium hydroxide solution. The number-average particle size of the emulsion particles measured using a dynamic light scattering particle size distribution analyzer (product name "nanoSAQRA", manufactured by Otsuka Electronics Co., Ltd.) was 120.0 nm.

[0094] 10g of emulsion was placed in a 20mL sample bottle and shaken 30 times. Foaming was observed after shaking, but disappeared after 1 minute. Below, the evaluation was made as follows: if foaming did not disappear after shaking, it was marked "X", if foaming disappeared after 1 minute, it was marked "△", and if little foaming occurred even after shaking, it was marked "〇".

[0095] (Synthesis Examples 2 to 8, Synthesis Comparative Examples 1 to 5) Binders E-2 to E-8 and H-1 to E-5, which are polymer emulsions, were obtained in the same manner as in Synthesis Example 1, except that the formulations shown in Tables 1 and 2 were used. The meanings of the abbreviations in Tables 1 and 2 are as follows. IBXMA: Isobornyl methacrylate (a methacrylate of borneol obtained as camphene by isomerizing α-pinene obtained from pine resin and pine essential oil, an acrylate of plant-derived alcohol) EA: Ethyl acrylate (acrylate of ethanol obtained by fermentation) BA: Butyl acrylate (acrylate of butanol obtained by fermentation) StA: Stearyl acrylate (an acrylate of stearyl alcohol obtained by fractionating fatty acids, which are hydrolyzed products of oils such as palm oil and coconut oil, and then hydrogenating the resulting stearic acid) KH-10: Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (trade name "Aqualon KH-10", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) POELA: Poly(n=23) polyethylene glycol monolauryl ether

[0096] TIFF0007732956000002.tif158170

[0097] TIFF0007732956000003.tif134170

[0098] <Production of pigment dispersants> (Production Example 1) 100 parts of diethylene glycol monobutyl ether (BDG) was placed in a reaction vessel and heated to 80°C with nitrogen bubbling. In a separate vessel, 20 parts of ethyl methacrylate (EMA), 30 parts of IBXMA, 30 parts of tetrahydrofurfuryl methacrylate (THFMA), 20 parts of methacrylic acid, and 1.5 parts of 2,2-azobisisobutyronitrile (AIBN) were added and stirred to prepare a homogeneous monomer solution. EMA is a methacrylate of ethanol obtained by fermentation. THFMA is a methacrylate of furfuryl alcohol obtained from corn. The prepared monomer solution was added dropwise to the reaction vessel over 2 hours. One hour after the dropwise addition, 1.5 parts of AIBN was added, and the reaction was continued for an additional 5 hours at 80°C. After cooling, a mixture of 11.6 parts of 28% aqueous ammonia and 62.7 parts of ion-exchanged water was added to dissolve the polymer in water, yielding a light brown, transparent polymer solution, pigment dispersant G-1. The resulting pigment dispersant G-1 (polymer) had an Mn of 12,600, a PDI (=Mw / Mn) of 2.05, and an acid value of 130.0 mgKOH / g. The aqueous solution of pigment dispersant G-1 had a pH of 8.7 and a solids content of 36.5%.

[0099] (Production Example 2) A reaction vessel was charged with 283.1 parts of BDG, 59.6 parts of THFMA, 59.6 parts of IBXMA, 2.0 parts of iodine, 3.6 parts of 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), and 0.1 parts of N-iodosuccinimide (NIS), and the mixture was heated to 45°C while bubbling nitrogen. Polymerization was carried out at 45°C for 4 hours to form A chains. The Mn of the A chains measured by GPC was 5,100, the PDI was 1.21, and the polymerization rate was approximately 100%.

[0100] Next, a mixture of 119 parts THFMA and 30.2 parts methacrylic acid was added, and polymerization was carried out at 45°C for 4 hours to form B chains. GPC analysis confirmed that the A chain peak shifted to the higher molecular weight side, confirming the formation of an AB block copolymer in which B chains extended from A chains. The Mn of the AB block copolymer was 10,700, the PDI was 1.31, and the Mn of the B chain was 5,600 (=10,700 - 5,100). The conversion rate calculated from the solid content was approximately 100%. The acid value of the AB block copolymer was 73.0 mgKOH / g, and the acid value of the B chain calculated taking the conversion rate into account was 132.0 mgKOH / g.

[0101] After the reaction mixture was cooled to room temperature, a mixture of 23.4 parts of 28% aqueous ammonia and 118.5 parts of water was added to dissolve the polymer in water, yielding a pale brown, transparent polymer solution, Pigment Dispersant G-2, which had a pH of 9.2 and a solids content of 41.1%.

[0102] <Ink manufacturing> Example 1 To 864 parts of ion-exchanged water, 411 parts of an aqueous solution of pigment dispersant G-1 (150 parts of polymer) and 600 parts of CI Pigment Blue 15:3 (PB15:3, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were added, and the mixture was thoroughly stirred and mixed using a dissolver to obtain a mixture. The resulting mixture was dispersed using a horizontal media disperser (trade name "Dynomill 0.6 Liter Multilab," manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.5 mm) at a peripheral speed of 7 m / s to thoroughly disperse the pigment in the mill base. After centrifugation (7,500 rpm, 20 minutes), the mixture was filtered through a 10 μm membrane filter to remove coarse particles. The concentration was adjusted by adding ion-exchanged water to obtain aqueous pigment dispersion B-1 with a pigment concentration of 14%.

[0103] Binder E-1 was diluted with water to obtain a binder solution with a solids content of 25%. 16.0 parts of the resulting binder solution, 28.6 parts of pigment dispersion B-1, 18.0 parts of propylene glycol, 0.5 parts of surfactant (product name "Silface SAG503A" manufactured by Nissin Chemical Co., Ltd.), 0.7 parts of polyethylene wax, and 36.2 parts of water were mixed, thoroughly stirred, and then filtered through a 5 μm pore membrane filter to obtain Ink I-1. The viscosity of the resulting Ink I-1 at 25°C was 3.2 mPa·s.

[0104] Example 2 To 517.5 parts of ion-exchanged water, 182.5 parts of an aqueous solution of pigment dispersant G-2 (75.0 parts of polymer) and 300 parts of CI Pigment Blue 15:3 (PB15:3, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were added, and the mixture was thoroughly stirred and mixed with a dissolver to obtain a mixture. Then, except for using the obtained mixture, an aqueous pigment dispersion B-2 with a pigment concentration of 14% was obtained in the same manner as in Example 1 described above.

[0105] Furthermore, except for using the obtained pigment dispersion B-2, ink I-2 was obtained in the same manner as in Example 1. The viscosity of the obtained ink I-1 at 25°C was 2.9 mPa s.

[0106] (Examples 3 to 9, Comparative Examples 1 to 3) Inks I-2 to I-9 and HI-1 to HI-3 were obtained in the same manner as in Example 1 above, except that the materials shown in Tables 3 and 4 were used.

[0107] <Evaluation> An inkjet printer equipped with a plate heater (product name "MMP825H", manufactured by Mastermind) and the following printing substrate were prepared. Then, an image was recorded by inkjet recording using the prepared ink to obtain a printed matter. Specifically, the substrate to be printed was heated using a plate heater to a surface temperature of 55°C, and then each ink was applied and printed, and the substrate was dried for 10 minutes in a thermostatic chamber heated to 90°C to obtain a printed product. [Printing base material] OPP film (polypropylene film, manufactured by Futamura Chemical Co., Ltd., 50 μm) PET film (polyethylene terephthalate film, manufactured by Futamura Chemical Co., Ltd., 50 μm)

[0108] (Discharge stability) The ink ejection state during printing was visually observed, and the ink ejection stability was evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. ◯: No discharge defects were observed. △: A small amount of splashing was observed in addition to ink droplets. ×: Discharge stopped midway, or scattering of dots was observed.

[0109] (Printed material) The appearance of the printed matter (image) was visually observed, and the condition of the printed matter was evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. ◯: No streaks or unevenness were observed, and the print was uniform. ×: Streaks and unevenness were observed.

[0110] (adhesion) Cellophane tape was pressed firmly against the image and then peeled off. The degree of peeling of the image from the printing substrate was visually observed, and the adhesion of the image was evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. ◎: No peeling at all. ◯: Slight peeling. △: The peeled area was smaller than the non-peeled area. ×: The peeled area was larger than the non-peeled area.

[0111] (dry and wet friction resistance) A dry rub test was carried out using a Gakushin type rub fastness tester (product name "RT-300", manufactured by Daiei Kagakusha) by moving a dry white cloth with a weight of 500 g back and forth over the surface of the image 100 times. A wet friction test was also carried out in which a white cloth moistened with water was rubbed back and forth over the surface of the image 100 times with a weight of 200 g. The degree of peeling of the image after the rub test was visually observed, and the dry rub resistance and wet rub resistance of the image were evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. ◎: No peeling at all. ○: Slight peeling. △: The peeled area was smaller than the non-peeled area. ×: The peeled area was larger than the non-peeled area.

[0112] (Ethanol resistance) A 70% aqueous ethanol solution was dropped onto the image surface and left for 10 seconds. After leaving it, the image surface was rubbed back and forth with a cotton swab, and the number of times the image (coating) peeled off was counted. The ethanol resistance of the image was then evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. ◎: 20 or more times 〇: 10 or more times but less than 20 times △: 5 to less than 10 times ×: Peeled off immediately - less than 5 times

[0113] TIFF0007732956000004.tif109170

[0114] TIFF0007732956000005.tif109170 [Industrial Applicability]

[0115]

[0023] The binder of the present invention can provide an environmentally friendly, low-viscosity aqueous inkjet ink that can form a dried film of an image or the like that has excellent adhesion and abrasion resistance to polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates. The aqueous inkjet ink of the present invention is suitable for outdoor display printing and high-volume, high-speed printing, and is also useful as an aqueous flexographic printing ink, an aqueous paint, an aqueous writing instrument ink, and the like.

Claims

1. A binder component for an aqueous inkjet ink that satisfies the following requirements (1) and (2): [Requirement (1)]: An emulsion containing emulsion particles made of a polymer having a structural unit (i) derived from styrene, a structural unit (ii) derived from isobornyl (meth)acrylate, and a structural unit (iii) derived from at least one acrylate monomer selected from the group consisting of ethyl acrylate, butyl acrylate, lauryl acrylate, and octadecyl acrylate, In the polymer, the total content of the structural unit (i) and the structural unit (ii) is 60 to 90 mass %, In the polymer, the mass ratio of the structural unit (i), the structural unit (ii), and the structural unit (iii) is (i):(ii):(iii)=5 to 40:20 to 70:10 to 40; In the polymer, the total content of the structural unit (i), the structural unit (ii), and the structural unit (iii) is 90 mass % or more. [Requirement (2)]: The emulsion contains emulsion particles having a number average particle size of 50 to 250 nm, which are obtained by emulsion polymerization of a monomer component in the presence of a surfactant represented by the following general formula (1): The amount of the surfactant is 2 to 10 parts by mass based on 100 parts by mass of the monomer component. R-O-(CH ２ CH ２ O) ｎ -SO ３ -X ＋ ・・・(1) (In the general formula (1), R represents an organic group containing an alkyl chain having 8 to 18 carbon atoms, n represents a number from 1 to 40, and X ＋ represents an ammonium ion, an organic ammonium ion, a lithium ion, a sodium ion, or a potassium ion)

2. The binder component described in claim 1, wherein the polymer is substantially composed of only the structural unit (i), the structural unit (ii), and the structural unit (iii).

3. 2. The binder component according to claim 1, wherein in the general formula (1), R is a group having one or more α,β-unsaturated bonds.

4. An aqueous inkjet ink comprising water, a water-soluble organic solvent, a colorant, and the binder component of claim 1.

5. The aqueous inkjet ink according to claim 4, further comprising a polyethylene wax component.

6. the colorant is a pigment dispersion containing a pigment, a pigment dispersant, and a dispersion medium containing water, 5. The aqueous inkjet ink according to claim 4, wherein the pigment dispersant is a polymer that satisfies the following requirements (3) to (7): [Requirement (3)]: The polymer has a structural unit (iv) derived from methacrylic acid and a structural unit (v) derived from a methacrylate derived from a biological material, and has an acid value of 30 to 250 mgKOH / g. [Requirement (4)]: The content of the structural unit (v) in the polymer is 50% by mass or more. [Requirement (5)]: The polymer has a number average molecular weight of 5,000 to 20,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 2.5 or less. [Requirement (6)]: At least a portion of the carboxy groups in the polymer are neutralized with an alkali. [Requirement (7)]: The methacrylate derived from a biological material is at least two selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate.

7. the pigment dispersant is an A-B block copolymer having an A chain and a B chain; the A chain is a polymer block that does not have the structural unit (iv) and has a number average molecular weight of 3,000 to 10,000, The aqueous inkjet ink according to claim 6, wherein the B chain is a polymer block having the structural unit (iv).

8. the water-soluble organic solvent comprises propylene glycol and at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; 8. The aqueous inkjet ink according to claim 4, wherein the content of the water-soluble organic solvent is 3 to 30% by mass.

9. The aqueous inkjet ink according to any one of claims 4 to 7, which is used for printing on at least one printing substrate selected from the group consisting of polypropylene-based substrates, polyethylene-based substrates, and polyester-based substrates.

10. The aqueous inkjet ink according to any one of claims 4 to 7, which has a viscosity at 25°C of 2.9 to 3.3 mPa·s.

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