Graft polymer, binder component, and water-based ink

Abstract

To provide a grafted polymer useful as a constituent material of a binder component of an aqueous ink capable of forming a coated film excellent in friction resistance, alcohol resistance, and adhesion to various substrates.SOLUTION: A grafted polymer includes a structural unit (1) derived from a polymer type monomer represented by formula (1), a structural unit (2) derived from styrene, a structural unit (3) derived from isobornyl (meth)acrylate, and a structural unit (4) derived from other monomers. A number average molecular weight of the polymer type monomer is 10,000 to 30,000, a number average molecular weight of the polymer type monomer is 1,000 to 10,000 and an acid value of the polymer type monomer is 30 to 200mgKOH / g. (In formula (1), R1 represents an alkyl group having 1 to 18 carbon atoms, R2 represents an isobornyl group, and R3 represents an ethyl group or a tetrahydrofurfuryl group.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a graft polymer, a binder component, and an aqueous ink. [Background technology]

[0002] In recent years, the development of environmentally friendly products has been in demand, and water-based inks have been attracting attention. In fields such as gravure printing, flexographic printing, and inkjet printing, there is a demand for water-based inks, and many studies are being conducted to transition from oil-based inks to water-based inks. Water-based inks, such as water-based gravure inks, water-based flexographic inks, and water-based inkjet inks, are used to print on packaging films such as plastic containers, labels, and packaging. Furthermore, these water-based inks are used as overcoats and clear varnishes to protect printed materials.

[0003] Images recorded on printed matter and films formed with clear varnish (hereinafter also referred to as "ink coating films" or "coating films") are required to have adhesion to the substrate as well as durability such as abrasion resistance, water resistance, chemical resistance, and solvent resistance. In order to improve the durability of coating films, for example, various binders for film formation and aqueous inks containing such binders have been proposed (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-131548 [Patent Document 2] International Publication No. 2020 / 213413 [Patent Document 3] Special Publication No. 2009-515007 Summary of the Invention [Problem to be solved by the invention]

[0005] While aqueous inks that are substantially free of volatile organic solvents have a small impact on the environment, the abrasion resistance of the coating film they form, particularly abrasion resistance under humid conditions (wet abrasion resistance), is often insufficient. For this reason, when printed materials recorded with aqueous inks are transported under humid conditions, problems such as peeling of the coating film have arisen.

[0006] In recent years, highly concentrated aqueous ethanol solutions have been used as disinfectants to remove viruses, including COVID-19. However, when a coating film formed with water-based ink is wiped off with an aqueous ethanol solution, problems have arisen, such as the coating film dissolving or peeling off from the substrate.

[0007] Conventionally, petroleum-derived materials have been the mainstream of materials for forming resins used as binders. However, in recent years, from the perspective of preventing global warming, there has been a demand for the development of carbon dioxide-recycling materials, such as those for reducing carbon dioxide and recycling carbon dioxide. For this reason, there is a demand for the components used in aqueous inks to be produced from non-petroleum-derived materials as much as possible.

[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 graft polymer that is useful as a constituent material of a binder component for aqueous inks, which is capable of forming a coating film that is excellent in abrasion resistance, alcohol resistance, and adhesion to various substrates.

[0009] Another object of the present invention is to provide a binder component for aqueous inks using the above-mentioned graft polymer, which is capable of forming coating films that are excellent in abrasion resistance, alcohol resistance, and adhesion to various substrates.A further object of the present invention is to provide a aqueous ink using the above-mentioned binder component, which is capable of forming coating films that are excellent in abrasion resistance, alcohol resistance, and adhesion to various substrates. [Means for solving the problem]

[0010] That is, according to the present invention, the following graft polymer is provided. [1] A graft polymer used as a binder component for aqueous inks, the graft polymer comprising 20 to 40% by mass of structural units (1) derived from a polymeric monomer represented by the following general formula (1), 5 to 50% by mass of structural units (2) derived from styrene, 5 to 50% by mass of structural units (3) derived from isobornyl (meth)acrylate, and 5 to 50% by mass of structural units (4) derived from at least one other monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, and octadecyl (meth)acrylate, and having a number average molecular weight of 10,000 to 30,000, wherein the number average molecular weight of the polymeric monomer is 1,000 to 10,000, and the acid value of the polymeric monomer is 30 to 200 mgKOH / g.

[0011] TIFF0007734116000001.tif55170 (In the general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, R2 represents an isobornyl group, and R3 represents an ethyl group or a tetrahydrofurfuryl group.)

[0012] The present invention also provides the following binder component. [2] A binder component for aqueous ink, comprising: a dispersion medium containing water; and emulsion particles dispersed in the dispersion medium, the emulsion particles being formed by neutralizing the carboxyl groups of the graft polymer described in [1] with an alkali, wherein the number average particle diameter of the emulsion particles is 50 to 200 nm. [3] The binder component according to [2], wherein the alkali is ammonia.

[0013] Furthermore, according to the present invention, there is provided the following aqueous ink. [4] A water-based ink containing water, a water-soluble organic solvent, and a binder component, wherein the binder component is the binder component described in [2] or [3] above. [5] The aqueous ink according to [4] above, further containing polyethylene wax. [6] The aqueous ink according to [4] or [5], wherein the water-soluble organic solvent is at least one selected from the group consisting of propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, 1,2-hexanediol, and glycerin. [7] The aqueous ink according to any one of [4] to [6], which is used for printing on at least one medium selected from the group consisting of polyolefin film, polyethylene terephthalate film, and vinyl chloride film. [8] The aqueous ink according to any one of [4] to [7] above, further comprising a colorant, wherein the colorant is a pigment dispersion containing a pigment and a dispersant that disperses the pigment, and the dispersant is a vinyl copolymer containing a structural unit derived from at least one acidic monomer selected from the group consisting of (meth)acrylic acid, maleic acid, and itaconic acid. [9] The aqueous ink according to [8], wherein the vinyl copolymer is a linear polymer having an acid value of 50 to 200 mgKOH / g and a number average molecular weight of 5,000 to 20,000, and comprising a structural unit derived from methacrylic acid, a structural unit derived from isobornyl (meth)acrylate, and a structural unit derived from at least one (meth)acrylate monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

[10] The aqueous ink according to any one of [4] to [9], which is for inkjet use. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a graft polymer useful as a constituent material of a binder component for an aqueous ink capable of forming a coating film excellent in abrasion resistance, alcohol resistance, and adhesion to various substrates. Furthermore, according to the present invention, it is possible to provide a binder component for an aqueous ink capable of forming a coating film excellent in abrasion resistance, alcohol resistance, and adhesion to various substrates, and an aqueous ink using the same. DETAILED DESCRIPTION OF THE INVENTION

[0015] <Graft polymer> Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments. One embodiment of the graft polymer of the present invention is a polymer used as a binder component for aqueous inks, which contains 20 to 40 mass% of structural units (1) derived from a polymeric monomer represented by the following general formula (1), 5 to 50 mass% of structural units (2) derived from styrene, 5 to 50 mass% of structural units (3) derived from isobornyl (meth)acrylate, and 5 to 50 mass% of structural units (4) derived from at least one other monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, and octadecyl (meth)acrylate, and has a number average molecular weight of 10,000 to 30,000. The number average molecular weight of the polymeric monomer constituting structural unit (1) is 1,000 to 10,000. The acid value of the polymeric monomer is 30 to 200 mgKOH / g. The graft polymer of this embodiment will be described in detail below.

[0016] TIFF0007734116000002.tif55170 (In the general formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, R2 represents an isobornyl group, and R3 represents an ethyl group or a tetrahydrofurfuryl group.)

[0017] The polymeric monomer represented by general formula (1) is a polymeric monomer having an unsaturated bond at one end. The polymeric monomer has a structural unit derived from methacrylic acid and an acid value derived from methacrylic acid of 30 to 200 mgKOH / g, preferably 50 to 150 mgKOH / g, and more preferably 60 to 100 mgKOH / g. Because it has a structural unit derived from methacrylic acid, the carboxyl group can be neutralized and ionized to form a water-soluble polymer. If the acid value of the polymeric monomer is less than 30 mgKOH / g, it becomes difficult to emulsify and disperse the graft polymer in water. On the other hand, if the acid value of the polymeric monomer exceeds 200 mgKOH / g, the graft polymer becomes too hydrophilic, resulting in a decrease in the water resistance of the resulting coating film.

[0018] The polymeric monomer has a structural unit derived from isobornyl methacrylate. The glass transition temperature (Tg) of a homopolymer of isobornyl methacrylate is 130°C or higher. In addition, since isobornyl methacrylate has an alicyclic hydrocarbon group, the use of a polymeric monomer having a structural unit derived from isobornyl methacrylate can result in a graft polymer capable of forming a coating film with excellent solvent resistance and alcohol resistance. Furthermore, since isobornyl methacrylate has a bulky structure, the use of a polymeric monomer having a structural unit derived from isobornyl methacrylate is expected to result in a graft polymer capable of forming a coating film with reduced shrinkage.

[0019] Isobornyl methacrylate is a monomer prepared using alcohol derived from plant materials obtained from pine resin or pine essential oil. Therefore, the graft polymer of this embodiment, which contains structural units derived from monomers prepared using plant-derived materials, is a material that can contribute to carbon neutrality. Isobornyl methacrylate is a material with a high biomass ratio. The biomass ratio is expressed as the ratio of plant-derived carbon atoms to the total carbon atoms of the compound. Isobornyl methacrylate has a total carbon number of 14, of which 10 are plant-derived. Therefore, the biomass ratio of isobornyl methacrylate can be calculated as "(10 / 14) × 100 = 71.4%."

[0020] In the polymeric monomer, the proportion of the structural units derived from isobornyl methacrylate is preferably 1 to 70% by mass, more preferably 5 to 50% by mass. If the proportion of the structural units derived from isobornyl methacrylate is less than 1% by mass, the effects of isobornyl methacrylate may not be fully exerted. On the other hand, if the proportion of the structural units derived from isobornyl methacrylate is more than 70% by mass, emulsification in water may be difficult.

[0021] The polymeric monomer has structural units derived from at least one of methacrylates, ethyl methacrylate and tetrahydrofurfuryl methacrylate. The Tg of the homopolymer of ethyl methacrylate and the Tg of the homopolymer of tetrahydrofurfuryl methacrylate are both 60°C or higher. Therefore, the inclusion of structural units derived from these methacrylates can improve the Tg of the graft polymer. Furthermore, the inclusion of an alkyl group with a small carbon number (an ethyl group) or a cyclic ether group (a tetrahydrofurfuryl group) allows for easy dispersion and emulsification in water. Furthermore, ethyl methacrylate can be produced from ethanol obtained by decomposing starch or sugar. Tetrahydrofurfuryl methacrylate can be produced from tetrahydrofurfuryl alcohol prepared by hydrogenating furfural obtained from corn cobs or the like. In other words, both ethyl methacrylate and tetrahydrofurfuryl methacrylate are suitable because they are environmentally friendly, plant-derived materials.

[0022] The polymeric monomer may further have a structural unit derived from a methacrylate (other methacrylate) other than the above-mentioned monomers. Specific examples of other methacrylates include methyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, trimethylcyclohexyl methacrylate, t-butylcyclohexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, isodecyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, hexadecyl methacrylate, octadecyl methacrylate, didecyl methacrylate, dimethyl ... Examples include clopentenyl methacrylate, dicyclopentanyl methacrylate, adamantyl methacrylate, benzyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, butoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, butoxyethoxyethyl methacrylate, polyethylene glycol monomethyl ether methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

[0023] Many of the other methacrylates mentioned above are petroleum-based materials. Therefore, from the viewpoint of environmental consideration, the proportion of structural units derived from other methacrylates in the polymer monomer is preferably 20% by mass or less, and more preferably 5% by mass or less.

[0024] The number-average molecular weight of the polymeric monomer is 1,000 to 10,000, preferably 3,000 to 8,000. If the number-average molecular weight of the polymeric monomer is less than 1,000, the molecular weight of the polymer chain that dissolves in water is small, making it difficult to disperse and emulsify it in water. On the other hand, if the number-average molecular weight of the polymeric monomer exceeds 10,000, the polymerization reactivity decreases, and the polymer may remain without being incorporated into the desired graft polymer. Furthermore, since the molecular weight of the polymer chain that dissolves in water is large, the viscosity of the emulsion obtained by dispersing and emulsifying it in water may increase. The number-average molecular weight in this specification is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0025] The content of the structural unit (1) derived from the polymeric monomer in the graft polymer is 20 to 40% by mass, preferably 25 to 35% by mass. If the content of the structural unit (1) is less than 20% by mass, the hydrophilic portion is reduced, making dispersion and emulsification in water difficult. On the other hand, if the content of the structural unit (1) is more than 40% by mass, the polymeric monomer is likely to remain unpolymerized during production of the graft polymer. This may result in reduced physical properties such as abrasion resistance and water resistance of the coating film formed using the graft polymer.

[0026] The graft polymer contains a structural unit (2) derived from styrene. The polymeric monomer described above is a monomer component that constitutes the side chain (graft chain) of the graft polymer, while styrene is a monomer component that constitutes the main chain of the graft polymer. The inclusion of the structural unit (2) derived from styrene improves the Tg of the main chain and introduces an aromatic ring, making it possible to form a coating film with improved adhesion to polyesters such as polyethylene terephthalate. The content of the structural unit (2) derived from styrene in the graft polymer is 5 to 50% by mass, preferably 10 to 40% by mass. If the content of the structural unit (2) is less than 5% by mass, the effect of introducing the structural unit (2) cannot be obtained. On the other hand, if the content of the structural unit (2) is more than 50% by mass, styrene may remain.

[0027] The graft polymer contains a structural unit (3) derived from isobornyl (meth)acrylate. Isobornyl (meth)acrylate is a monomer component that constitutes the main chain of the graft polymer. The inclusion of the structural unit (3) derived from isobornyl (meth)acrylate improves the Tg of the main chain and introduces a bulky isobornyl group, which is expected to improve the alcohol resistance of the formed coating film and suppress shrinkage of the coating film. The content of the structural unit (3) derived from isobornyl (meth)acrylate in the graft polymer is 5 to 50% by mass, preferably 10 to 40% by mass. If the content of the structural unit (3) is less than 5% by mass, the effects of introducing the structural unit (3) cannot be obtained. On the other hand, if the content of the structural unit (3) exceeds 50% by mass, the Tg of the main chain becomes too high and the structural unit (3) may not polymerize during the production of the graft polymer and may remain. Isobornyl (meth)acrylate is also preferred because it is an environmentally friendly, plant-derived material.

[0028] The graft polymer contains a structural unit (4) derived from at least one other monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, and octadecyl (meth)acrylate. The other monomer is a monomer component that constitutes the main chain of the graft polymer. The inclusion of this structural unit (4) can adjust the Tg of the main chain of the graft polymer, improve polymerizability, and improve properties such as alcohol resistance of the resulting coating film. The content of the structural unit (4) in the graft polymer is 5 to 50% by mass, preferably 6 to 35% by mass, and more preferably 7 to 20% by mass. By ensuring that the content of the structural unit (4) is 5% by mass or more, copolymerization with the polymer monomer and isobornyl (meth)acrylate can be improved, thereby increasing the polymerization rate. Note that if the content of the structural unit (4) exceeds 50% by mass, the properties of the other monomer become apparent, making it difficult to exhibit the properties of styrene or isobornyl (meth)acrylate. As the other monomer, it is preferable to use an esterification reaction product of a plant-derived alcohol and (meth)acrylic acid.

[0029] The graft polymer may further contain structural units (other structural units) other than the structural units (1) to (4). As the monomers constituting the other structural units, vinyl monomers other than the above-mentioned monomers can be used. The content of the other structural units in the graft polymer is preferably 10% by mass or less.

[0030] The number-average molecular weight of the graft polymer is 10,000 to 30,000, preferably 15,000 to 25,000. If the number-average molecular weight of the graft polymer is less than 10,000, the physical properties of the formed coating film will be insufficient, and physical properties such as abrasion resistance will decrease. On the other hand, if the number-average molecular weight of the graft polymer is more than 30,000, the viscosity will tend to increase excessively during polymerization, making production difficult.

[0031] The polymeric monomer has an unsaturated bond at one end that can undergo radical polymerization. Due to steric hindrance, this unsaturated bond is known to be difficult to copolymerize with tertiary radicals generated from methacrylates, but to copolymerize with secondary radicals generated from vinyl monomers, acrylates, etc. The desired graft polymer can be obtained by copolymerizing a polymeric monomer having such an unsaturated bond at one end with each of the monomers that make up the structural units (2) to (4).

[0032] Polymeric monomers can be produced, for example, by using a chain transfer agent such as α-bromomethylacrylic acid or its ester; (ii) a cobalt catalyst such as cobalt porphyrin or cobalt(II) acetylacetonate; or (iii) dehydrobromination of the bromoisobutyrate ester group introduced at the terminal by the action of a strong base. Among these, (i) producing polymeric monomers using a chain transfer agent such as α-bromomethylacrylic acid or its ester is preferred because it eliminates the need to remove catalysts such as cobalt. Polymerization of various monomers in an organic solvent using α-bromomethylacrylic acid or the like can yield an organic solvent solution of the polymeric monomer. Using a water-soluble organic solvent is preferred because the resulting solution can be used directly in the next step. Alternatively, the polymer obtained by solution polymerization can be precipitated in a poor solvent, filtered, and washed with water to obtain an aqueous paste. The resulting aqueous paste may then be dried to produce a solid polymeric monomer.

[0033] The graft polymer can be obtained by radical polymerization of a polymeric monomer and another monomer. Specifically, the polymeric monomer is first dissolved in an organic solvent, preferably a water-soluble organic solvent, to obtain a solution of the polymeric monomer. Next, the graft polymer can be obtained by radical polymerization with another monomer in the organic solvent in the presence of a radical generator.

[0034] Examples of the water-soluble organic solvent include alcohol-based solvents such as methanol, ethanol, propanol, isopropanol alcohol, furfuryl alcohol, and tetrahydrofuranol; glycol-based solvents such as ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether; amide-based solvents such as dimethylformamide, dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; urea-based solvents such as tetramethylurea and 1,3-dimethylimidazoline; sulfur-containing solvents such as dimethyl sulfoxide and sulfolane; and polyhydric alcohols such as propylene glycol, 1,2-hexanediol, and glycerin. Among these, alcohol-based solvents such as isopropanol and glycol-based solvents such as diethylene glycol monobutyl ether are preferred.

[0035] Examples of radical generators include peroxides such as benzoyl peroxide and lauroyl peroxide; azo-based initiators such as azobisisobutyronitrile; etc. In the presence of these radical generators, radical polymerization is carried out by setting the total content of monomers in the polymerization reaction solution to preferably 40 to 80 mass%, more preferably 50 to 75 mass%, and particularly preferably 60 to 70 mass%. This allows the production of the desired graft polymer.

[0036] Furthermore, when a polymeric monomer is obtained in the form of an aqueous paste or a solid, a graft polymer can be obtained by emulsion polymerization. For example, a polymeric monomer, water, and an alkali are mixed, and the carboxyl group of the polymeric monomer is neutralized and ionized to prepare an aqueous solution of the polymeric monomer. Subsequently, another monomer is added in the presence of a radical generator and polymerized to obtain a graft polymer. Alternatively, another monomer is added to the aqueous solution of the polymeric monomer, and then the mixture is dispersed to form dispersed particles. A graft polymer can also be obtained by polymerization using a radical generator. In addition to the organic radical generators described above, inorganic radical generators such as potassium persulfate and ammonium persulfate can also be used as the radical generator.

[0037] <Binder component> The above-described graft polymer can be used to obtain a binder component for aqueous ink. That is, one embodiment of the binder component of the present invention is a binder component for aqueous ink, which is an emulsion containing a dispersion medium containing water and emulsion particles dispersed in the dispersion medium. The emulsion particles are particles formed by neutralizing the carboxy groups of the above-described graft polymer with an alkali.

[0038] The number-average particle diameter of the emulsion particles contained in the binder component of this embodiment is 50 to 200 nm, preferably 60 to 150 nm. If the number-average particle diameter of the emulsion particles is less than 50 nm, the viscosity of the binder component (emulsion) will be excessively high. On the other hand, if the number-average particle diameter of the emulsion particles is more than 200 nm, when used in an aqueous ink for inkjet printing, clogging of the recording head may occur and the ink ejection performance may become unstable. Furthermore, the emulsion particles may settle. The number-average particle diameter of the emulsion particles in this specification is a value measured using a dynamic light scattering particle size distribution analyzer.

[0039] To produce the binder component of this embodiment, the graft polymer described above is mixed with water in which an alkali has been dissolved, and the carboxyl groups in the graft polymer are neutralized and ionized with the alkali. As a result, the graft chains are dissolved in water, and the graft polymer is dispersed and emulsified in water to form emulsion particles, thereby obtaining the desired binder component.

[0040] Examples of alkalis that can be used include ammonia, organic amines such as triethylamine, dimethylaminoethanol, and aminomethylpropanol, and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Considering the water resistance of the coating film to be formed, volatile ammonia is preferred, as it easily reverts to a water-insoluble carboxyl group upon drying.

[0041] <Water-based ink> An aqueous ink can be obtained by using the binder component described above. That is, one embodiment of the aqueous ink of the present invention is an ink containing water, a water-soluble organic solvent, and a binder component. The binder component is the binder component described above. The aqueous ink of this embodiment can form a transparent coating (film), and therefore can be suitably used as an overprint varnish (OP varnish). OP varnish is an aqueous ink used for the purposes of coating the surface of a substrate with a transparent film to protect it, or coating the surface of a printed material to prevent color transfer, peeling, scratches, etc., thereby improving the durability of the printed material.

[0042] The content of the binder component (solid content) in the aqueous ink is preferably 2 to 10% by mass. The water-soluble organic solvent may be any of the water-soluble organic solvents described above. From the viewpoints of improving drying and leveling properties and adjusting viscosity, it is particularly preferred to use at least one selected from the group consisting of propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, 1,2-hexanediol, and glycerin. The content of the water-soluble organic solvent in the aqueous ink is preferably 5 to 35% by mass.

[0043] The aqueous ink may further contain various additives, such as antifoaming agents, leveling agents, surfactants, wax components, crosslinking agents, fillers, UV absorbers, antioxidants, light stabilizers, preservatives, antibacterial agents, viscosity adjusters, anti-scratch agents, surface tension adjusters, and pH adjusters.

[0044] The aqueous ink preferably further contains a wax component, and the wax component is preferably a polyethylene wax. The wax component is oriented near the surface of the coating film. Therefore, by using an aqueous ink containing a wax component, the tape releasability, wet rub resistance, dry rub resistance, and alcohol resistance of the formed coating film can be further improved.

[0045] Examples of polyethylene wax include emulsions in which low-molecular-weight to high-molecular-weight polyethylene is dispersed and emulsified in water using an emulsifier, and emulsions in which the carboxy groups of oxidized polyethylene or polyethylene (meth)acrylic acid copolymer are neutralized and then dispersed and emulsified in water. The content of the wax component (solid content) in the aqueous ink is preferably 0.1 to 5% by mass.

[0046] The aqueous ink can be produced by a conventional method. For example, first, the components are blended and stirred and mixed using a disperser or the like to obtain a mill base. Then, if necessary, the obtained mill base is filtered to remove particles, foreign matter, dust, etc., to obtain the desired aqueous ink.

[0047] Because the aqueous ink contains a binder component using the aforementioned graft polymer, it can form a coating film that adheres well to plastic media. Suitable plastic media include polyolefin films, polyethylene terephthalate films, and vinyl chloride films. Examples of polyolefins that form the polyolefin film include polyethylene, polypropylene, ethylene-propylene copolymers, propylene-butene copolymers, cycloolefins, polyethylene polyvinyl alcohol, and polyethylene ethyl acrylate. Multilayer films formed from these polyolefins may also be used. The film may be stretched or unstretched. The film surface may be untreated or may be subjected to surface treatments such as corona discharge treatment, plasma treatment, flame treatment, chemical treatment, and matte finish. A conventionally known plasticizer may be blended into the vinyl chloride film.

[0048] The aqueous ink of this embodiment preferably further contains a colorant. Dyes and pigments can be used as colorants. Of these, pigments are preferred from the viewpoints of lightfastness and water resistance. Examples of pigments that can be used include self-dispersing pigments having acidic groups on their surfaces and pigment dispersions in which the pigment is dispersed with a dispersant. Of these, it is preferred to use a pigment dispersion containing a pigment and a dispersant that disperses the pigment as the colorant. Self-dispersing pigments require the addition of acidic groups to the pigment particle surfaces, which can be costly and can also lead to the ink being more susceptible to coarse particles being mixed in.

[0049] As the pigment, conventionally known organic pigments and inorganic pigments can be used. Specific examples of pigments include 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, and 191; CI Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, and 73; and CI Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, 123, 144, 146, 147, and 1 49, 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, 58; CI Pigment Black 7; CI Pigment White 6; and the like.

[0050] The pigment may be mixed by any of the following methods: mixing powdered pigments, mixing paste-like pigments, or mixing to form a solid solution during pigmentation. Fillers such as zinc oxide, zirconium oxide, silica, and mica can also be used. Furthermore, carbon nanotubes, graphite, graphene, carbon nanohorns, carbon nanoribbons, carbon fullerenes, carbon-based quantum dots, and nanodiamonds can also be used.

[0051] Pigments suitable for aqueous inks, from the standpoints of color development, dispersibility, weather resistance, etc., include CI Pigment Yellow 74, 83, 109, 128, 139, 150, 151, 154, 155, 180, 181, 185; CI Pigment Red 122, 170, 176, 177, 185, 269; CI Pigment Violet 19, 23; CI Pigment Blue 15:3, 15:4, 15:6; CI Pigment Black 7; and CI Pigment White 6.

[0052] The pigment may be an untreated pigment, a pigment surface-treated with a pigment derivative, or a pigment surface-treated or encapsulated with a surface treatment agent such as a coupling agent or an activator, or a polymer. It is preferable to use organic fine particle pigments unless hiding power is required. Furthermore, when high clarity and transparency are required, it is preferable to use pigments that have been finely milled by wet or dry grinding such as salt milling. To prevent nozzle clogging during printing, it is preferable to remove pigments with particle diameters exceeding 1.0 μm. The number-average particle diameter of organic pigments is preferably 0.2 μm or less. The number-average particle diameter of inorganic pigments is preferably 0.4 μm or less.

[0053] Dispersants for dispersing pigments include surfactants such as nonionic, anionic, cationic, amphoteric, and betaine; and polymer dispersants such as vinyl, ether, ester, and urethane dispersants. Among these, vinyl polymers are preferred. Polymer dispersants have higher molecular weights than surfactants, resulting in better pigment adsorption. Furthermore, portions of the polymer adsorb to the pigment at multiple points, and even if the adsorbed portions detach, other portions remain adsorbed, making the polymer less likely to detach from the pigment overall, thereby improving pigment dispersibility. Furthermore, vinyl polymers can be designed to meet various requirements. Among these, vinyl copolymers containing structural units derived from at least one acidic monomer selected from the group consisting of (meth)acrylic acid, maleic acid, and itaconic acid are preferred as dispersants. The carboxy groups in these vinyl copolymers can be neutralized with alkali to ionize them and then dissolved in water for use. The carboxy groups can also be adsorbed onto the pigment.

[0054] Dispersants can be produced by copolymerizing the above-mentioned acidic monomers having a carboxy group with other vinyl monomers capable of radical polymerization. Examples of other vinyl monomers capable of radical polymerization include styrene-based monomers such as styrene and vinyltoluene; the above-mentioned (meth)acrylate monomers; and monoesters and diesters of maleic acid and itaconic acid. Dispersants can also be used that contain an acid anhydride such as maleic anhydride or itaconic anhydride as a constituent component, polymerize the above-mentioned vinyl monomers, and then react with a monoalcohol or a monoamine. Specifically, polymers obtained by reacting an acid anhydride obtained by copolymerizing styrene and maleic anhydride with polyethylene glycol polypropylene glycol monomethyl ether monoamine or the like can be used as dispersants.

[0055] The vinyl copolymer used as a dispersant is preferably a linear polymer containing structural units derived from methacrylic acid, structural units derived from isobornyl (meth)acrylate, and structural units derived from at least one (meth)acrylate monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate. Furthermore, the acid value of this vinyl copolymer (linear polymer) is preferably 50 to 200 mgKOH / g, and the number-average molecular weight is preferably 5,000 to 20,000. This vinyl copolymer (linear polymer) has a similar composition to the graft polymer that constitutes the binder component, and is therefore highly compatible. Therefore, when the pigment dispersion and the binder component are mixed, problems such as separation and precipitation are unlikely to occur, and printing defects such as color unevenness and streaks are unlikely to occur, resulting in an aqueous ink.

[0056] Examples of the linear polymer structure include a random structure, a gradient structure, an AB diblock structure, and an ABA triblock structure. Among these, it is preferable to use a linear polymer with an AB diblock structure having an A block that is substantially insoluble in water and a B block that is soluble in water as a dispersant. The A block that is substantially insoluble in water is adsorbed to the pigment, and the B block that has a structural unit derived from methacrylic acid dissolves in water as the carboxy group is neutralized with an alkali.

[0057] The pigment dispersion can be prepared by dispersing the pigment using the above-mentioned pigment and dispersant according to a conventionally known method. The organic pigment content in the pigment dispersant is preferably 1 to 30 mass %, more preferably 10 to 25 mass %. The inorganic pigment content in the pigment dispersion is preferably 5 to 70 mass %, more preferably 30 to 50 mass %. The viscosity of the pigment dispersion is preferably 2 to 100 mPa·s when an organic pigment is used. It is preferably 5 to 200 mPa·s when an inorganic pigment is used.

[0058] The aqueous ink of this embodiment is useful as an aqueous ink for a variety of applications. Specific examples include aqueous gravure inks, aqueous flexographic inks, aqueous paints, aqueous coating agents, aqueous stationery inks, and aqueous inkjet inks. In particular, the aqueous ink of this embodiment is suitable as an aqueous inkjet ink. The graft polymer constituting the binder component has a hydrophilic moiety in its graft chain, and therefore has extremely high stability in water. Therefore, the aqueous ink of this embodiment containing the binder component obtained using this graft polymer has excellent ejection stability, which is one of the properties required for inkjet printing. Furthermore, printed matter obtained using the aqueous ink of this embodiment has good adhesion to substrates and excellent abrasion resistance and alcohol resistance. [Example]

[0059] 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.

[0060] <Production of binder components> (Production Example 1) [Polymer-type monomer IMAC-1] 104 parts of diethylene glycol monobutyl ether (BDG), 15 parts of isobornyl methacrylate (IBXMA), 70 parts of tetrahydrofurfuryl methacrylate (THFMA), 15 parts of methacrylic acid (MAA), and 4 parts of ethyl α-bromomethyl acrylate (EBMA) were placed in a reaction vessel and heated to 80 ° C. while bubbling nitrogen. When the temperature reached 72 ° C., 0.3 parts of dimethyl 2,2'-azobis(2-methylpropionate) (V-601) (trade name "V-601", Fujifilm Wako Pure Chemical Industries, Ltd.) was added and polymerized for 8 hours to obtain a solution of the polymeric monomer IMAC-1.

[0061] A portion of the sampled solution was dried at 180°C and measured for solid content, which was 50.0%, confirming that most of the polymer had polymerized. The polystyrene-equivalent number average molecular weight (Mn) measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the developing solvent was 5,500, and the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.76. The sampled solution was poured into methanol, a poor solvent, and the precipitate was washed and dried to obtain a solid. A portion of the obtained solid was dissolved in a mixed solution of toluene / ethanol = 1 / 1 (volume ratio), and the acid value was measured by titration with 0.1N potassium hydroxide ethanol solution using a phenolphthalein ethanol solution as an indicator. The measured acid value was 97.8 mgKOH / g. 1 H-NMR analysis confirmed that EBMA acts as a chain transfer agent and that the product contains structural units derived from IBXMA, THFMA, and MAA. Furthermore, the presence of peaks at 5.54 ppm and 6.10 ppm confirmed that the product is a polymeric monomer with an unsaturated bond introduced at its terminal.

[0062] [Binder component IRR-1] 47.7 parts of BDG, 120 parts of IMAC-1 solution, 70 parts of styrene, 35 parts of tetrahydrofurfuryl acrylate (THFA), 35 parts of isobornyl acrylate (IBXA), and 2 parts of 1,1,3,3-tetramethylbutylperoxyethylhexanoate (trade name "Perocta O", NOF Corporation) were placed in a reaction vessel and heated to 75°C while bubbling nitrogen, allowing polymerization for 8 hours to yield a polymer-containing liquid. The solids content measured after polymerization was 64.7%, confirming that most of the polymerization had occurred. The Mn of the resulting polymer was 25,200, the PDI was 3.5, and the GPC peak shape was unimodal.

[0063] A mixture of 7.0 parts of 28% aqueous ammonia and 488.3 parts of water was added to the resulting polymer-containing liquid to obtain binder component IRR-1, a dispersion containing emulsion particles. The resulting dispersion (IRR-1) was translucent. The number-average particle diameter of the emulsion particles in the dispersion was measured using a dynamic light scattering particle size distribution analyzer (product name "nanoSAQRA", manufactured by Otsuka Electronics Co., Ltd.) and was found to be 58.6 nm. The pH of the dispersion was 8.9, the solids content was 25.3%, and the viscosity, measured using a Brookfield viscometer, was 111 mPa·s.

[0064] (Production Examples 2 to 14, Comparative Production Examples 1 to 5) Polymeric monomers IMAC-2 to 9, HMAC-1 to 4, and binder components IRR-2 to 14, and HRR-1 to 5 were obtained in the same manner as in Production Example 1, except for the formulations shown in Tables 1 to 4. The amount of ammonia used was 1.1 moles of MAA. The meanings of the abbreviations in the tables are as follows: EMA: Ethyl methacrylate ·LA: Lauryl acrylate SA: Stearyl acrylate

[0065] TIFF0007734116000003.tif191170

[0066] TIFF0007734116000004.tif203170

[0067] TIFF0007734116000005.tif210170

[0068] TIFF0007734116000006.tif209170

[0069] (Comparative Production Example 6) 140.7 parts of water and 30 parts of acrylic resin (styrene / ethyl acrylate / acrylic acid copolymer (Mn 5,000, PDI 2.3, acid value 260 mgKOH / g)) were placed in a reaction vessel and stirred. 9.3 parts of 28% aqueous ammonia were added to dissolve the acrylic resin in the water, and the mixture was heated to 78°C. 1.5 parts of potassium persulfate were then added, followed by a monomer mixture of 35 parts of Stearoyl Stearate and 35 parts of butyl acrylate, which was added dropwise over 2 hours. The mixture was aged for 4 hours to obtain a styrene-acrylic emulsion (binder component HRR-6) containing acrylic resin as a protective colloid. The resulting emulsion was a slightly yellowish, translucent liquid with a solids content of 40.3%, a pH of 8.3, a viscosity of 230 mPa·s, and a number-average particle size of 89.6 nm.

[0070] <Preparation of pigment dispersant> (Preparation Example 1) 100 parts of BDG were placed in a reaction vessel and heated to 78°C with stirring. 20 parts of THFMA, 30 parts of IBXMA, 15 parts of lauryl methacrylate (LMA), 15 parts of stearyl methacrylate (StMA), 20 parts of MAA, and 3 parts of V-601 were placed in a separate vessel and homogenized to obtain a monomer solution. The resulting monomer solution was added dropwise to the reaction vessel over 2 hours and then polymerized for 6 hours to obtain a polymer-containing liquid. A portion of the liquid was sampled and measured for solids content of 50.1%, confirming that most of the polymerization had occurred. The polymer's Mn was 16,000 and PDI was 2.01. A mixture of 15.5 parts of 28% aqueous ammonia and 34.5 parts of ion-exchanged water was added to dissolve the polymer, yielding pigment dispersant D-1 with a solids content of 40.3%, pH 8.9, and viscosity of 2.65 Pa·s.

[0071] (Preparation Example 2) 100 parts of polyethylene glycol propylene glycol monomethyl ether monoamine (trade name "Genamine M," manufactured by Clariant, amine value 26.2 mg KOH / g) and 0.5 parts of pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (trade name "ADK STAB AO-60," manufactured by ADEKA Corporation) were placed in a reaction vessel and stirred. 20 parts of styrene / maleic anhydride copolymer (Mn 2,100, PDI 2.3, acid value 480 mg KOH / g) were added, and the mixture was heated to 100°C and homogenized. The reaction was allowed to proceed for 4 hours until the amine value reached "0," after which a mixture of 10 parts of 28% aqueous ammonia and 110 parts of ion-exchanged water was gradually added. This resulted in pigment dispersant D-2, containing a unimodal polymer with Mn 12,000 and PDI 1.6, a solids content of 50.0%, and a pH of 7.9.

[0072] <Water-based ink (1): Water-based overprint inkjet ink> Example 1 A mixture of 61.9 parts ion-exchanged water, 15.8 parts IRR-1 (25.3% solids), 1.8 parts oxidized polyethylene wax emulsion (40% solids, trade name "Hitex E-4A", Toho Chemical Industry Co., Ltd.), 5 parts 1,2-hexanediol, 15 parts propylene glycol, and 0.5 parts silicone surfactant (trade name "SAG-503A", Nissin Chemical Industry Co., Ltd.) was thoroughly mixed using a disper mixer and then filtered through a hydrophilic PTFE membrane filter (5 μm) to obtain a colorant-free aqueous ink. The resulting aqueous ink had a viscosity of 3.5 mPa·s, a pH of 8.6, and a surface tension of 28.7 mN / m.

[0073] (Examples 2 to 10, Comparative Examples 1 to 5) A water-based ink containing no colorant was obtained in the same manner as in Example 1 above, except that the binder components shown in Table 5 were used.

[0074] <Production of printed matter (1)> An inkjet printer equipped with a plate heater (product name "MMP825H", manufactured by Mastermind) and a printing substrate (OPP film (polypropylene film, manufactured by Futamura Chemical Co., Ltd., thickness 50 μm)) were prepared. A cartridge filled with aqueous ink was loaded into the inkjet printer. An image was then recorded on the printing substrate using the inkjet recording method to obtain a printed matter. Specifically, the printing substrate was heated with a plate heater to a surface temperature of 55°C, and then aqueous ink was applied. The substrate was then dried in a thermostatic chamber at 90°C for 10 minutes to obtain a printed matter.

[0075] <Rating (1)> The following evaluations were carried out, and the results are shown in Table 5.

[0076] (filterability) The state of filtration through the membrane filter during preparation of the aqueous ink was observed, and the filterability of the ink was evaluated according to the following evaluation criteria. ○: No clogging occurred. ×: Clogging occurred.

[0077] (Discharge stability) The ink ejection state during printing was observed, and the ink ejection stability was evaluated according to the following evaluation criteria. ◯: No ejection failure occurred. ×: Discharge ceased during printing, or scattering of dots was observed.

[0078] (Printed material) The appearance of the printed matter was visually observed and evaluated according to the following evaluation criteria. ◯: No streaks or unevenness were observed, and the print was uniform. ×: Streaks and unevenness were observed.

[0079] (adhesion) Cellophane tape was pressed firmly against the recorded 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. ◎: 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.

[0080] (Rubbing resistance (dry and wet friction resistance)) A dry rub test was conducted using a Gakushin-type rub fastness tester (product name "RT-300", manufactured by Daiei Scientific Co., Ltd.) in which a dry white cloth with a weight of 500 g was applied was moved back and forth 100 times over the surface of the image. Similarly, a wet rub test was conducted in which a water-moistened white cloth with a weight of 200 g was applied was moved back and forth 100 times over the surface of the image. After each rub test, the degree of peeling of the image was visually observed, and the rub resistance of the image (dry rub resistance and wet rub resistance) was evaluated according to the following evaluation criteria. ◎: 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.

[0081] (alcohol resistant) A 70% aqueous solution of ethanol was dropped onto the recorded image. After leaving it for 10 seconds, the image was rubbed back and forth with a cotton swab several times. The number of times the image was rubbed back and forth until it peeled off was counted, and the alcohol resistance of the image was evaluated according to the following evaluation criteria. ◎: 20 or more times ○: Less than 10 to 20 times △: Less than 5-10 times ×: Less than 5 times

[0082] TIFF0007734116000007.tif121170

[0083] <Water-based ink (2): Water-based pigment inkjet ink> Example 11 93.5 parts of pigment dispersant D-1 and 333.4 parts of ion-exchange water were mixed and homogenized to obtain a solution. 150 parts of copper phthalocyanine pigment (PB-15:3, trade name "Cyanine Blue A220JC", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) was added to the resulting solution and stirred for 30 minutes using a disperser to obtain a mill base. The resulting mill base was dispersed using a horizontal media disperser (trade name "Dynomill 0.6 Liter ECM Type", manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.5 mm) at a peripheral speed of 7 m / s to thoroughly disperse the pigment. After centrifugation (7,500 rpm, 20 minutes), the mixture was filtered through a 10 μm membrane filter to remove coarse particles. Ion-exchange water was added to adjust the concentration, yielding a blue pigment dispersion with a pigment concentration of 14%.

[0084] The number-average particle size of the pigment in the pigment dispersion was measured using a particle size analyzer (NICOMP 380ZLS-S, manufactured by International Business Corporation) and was found to be 105.9 nm, confirming that the pigment was finely dispersed. The viscosity (25°C) of the pigment dispersion, measured at 60 rpm using an E-type viscometer, was 3.58 mPa·s, and the pH was 8.8. The pigment dispersion was stored at 70°C for one week. After storage, the number-average particle size of the pigment in the pigment dispersion was 106.3 nm, and the viscosity was 3.56 mPa·s. This confirmed that the storage stability of the pigment dispersion was excellent.

[0085] Four parts of pigment, 4 parts of IRR-5 (as solids), 0.1 part of an acetylene-based surfactant (trade name "Surfynol S465" manufactured by Nissin Chemical Industry Co., Ltd.), 0.7 parts of a wax dispersion (ethylene-acrylic acid ionomer, trade name "Chemipearl W300" manufactured by Mitsui Chemicals, Inc.), 12 parts of propylene glycol, and water (the remainder making a total of 100 parts) were mixed and thoroughly stirred. The mixture was then filtered through a 10 μm pore membrane filter to obtain an aqueous ink. No clogging occurred during filtration. The number-average particle size of the pigment in the resulting aqueous ink was 103.3 nm. The viscosity of the aqueous ink was 3.40 mPa·s, and the pH was 8.64.

[0086] (Examples 12 to 14, Comparative Example 6) Aqueous inks were obtained in the same manner as in Example 11, except that the binder components shown in Table 6 were used.

[0087] <Production of printed matter (2)> A printed matter was obtained in the same manner as in "Production of printed matter (1)" above, except that a PET film (polyethylene terephthalate film, manufactured by Futamura Chemical Co., Ltd., 60 μm) was used as the printing substrate.

[0088] <Evaluation (2)> The following evaluations were carried out, and the results are shown in Tables 6 and 7.

[0089] (Storage stability) The number average particle size of the pigment in the ink and the viscosity of the ink were measured immediately after preparation (initial stage) and after storage for 1 week at 70° C. The storage stability of the ink was also evaluated according to the following evaluation criteria. ◯: The rate of change in the number average particle size of the pigment and the viscosity of the ink after storage was both within ±5%. △: The rate of change in the number average particle size of the pigment after storage was within ±5%, but the rate of change in the viscosity of the ink was 10% or more. ×: The rate of change in the number average particle diameter of the pigment after storage exceeded ±5%, or the rate of change in the viscosity of the ink was 10% or more.

[0090] In addition, in the same manner as in the above-mentioned "Evaluation (1)", the filterability, ejection stability, printed matter, adhesion, dry rub resistance, wet rub resistance, and alcohol resistance were evaluated.

[0091] TIFF0007734116000008.tif63170

[0092] TIFF0007734116000009.tif57170

[0093] When a similar evaluation was carried out using a vinyl chloride film as the printing substrate instead of the PET film, the same results were obtained.

[0094] <Water-based ink (3): Water-based gravure ink> Example 15 A container was charged with 150 parts of ion-exchanged water, 162 parts of a quinacridone pigment (PR-122, product name "6111", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 28 parts of pigment dispersant D-2, 10 parts of a polyethylene wax dispersion (product name "Chemipearl W500", manufactured by Mitsui Chemicals, Inc.), 2 parts of an antifoaming agent (product name "Tegoformex 805N", manufactured by Evonik), and 20 parts of calcium carbonate (product name "Scallop Powder S", manufactured by NC Corporation). The mixture was mixed using a disperser and then thoroughly dispersed using the horizontal media disperser described above.

[0095] 580 parts of IRR-11, 31 parts of ion-exchanged water, 4 parts of a surfactant (trade name "Tegowet 500", manufactured by Evonik), 8 parts of a thickener (trade name "SN Thickener 623N", manufactured by San Nopco), and 2 parts of an antifoaming agent were mixed. The mixture was diluted with ion-exchanged water so that the viscosity measured with Zahn cup #4 was 14 seconds at 25°C, to obtain a water-based gravure ink for coating.

[0096] (Examples 16 to 18, Comparative Example 7) Water-based gravure inks were obtained in the same manner as in Example 15, except that the binder components shown in Table 8 were used.

[0097] <Manufacturing of coated products> Anilox roll (cell volume: 4.5cm 3 / m 2 The aqueous gravure ink was applied to the substrate film using a flexographic hand proofer equipped with a flexographic proofer. The ink was then dried at 25°C for 48 hours to form a coating on the substrate film, yielding a coated product for testing.

[0098] <Rating (3)> The following evaluations were carried out, and the results are shown in Table 8.

[0099] (blocking resistance) A heat-shrinkable plastic film (HST, manufactured by Gunze Co., Ltd.) and the prepared test coated product were laminated so that the untreated side of the plastic film was in contact with the coated surface of the coated product, and a pressure of 7 kg / cm was applied. 2 The coated film was left in a thermostatic chamber at 40°C for 24 hours with a load of 10 ... ⊚: No transfer of the coating film to the untreated surface and no peeling resistance. ◯: There was almost no transfer of the coating film to the untreated surface, but slight peeling resistance was felt. Δ: Some transfer of the coating film to the untreated surface was observed, and some resistance to peeling was felt. Δ×: Transfer of the coating film to the untreated surface was observed, and resistance to peeling was felt. ×: Severe transfer of the coating film to the untreated surface was observed, and severe peeling resistance was felt.

[0100] In addition, adhesion, dry rub resistance, wet rub resistance, and alcohol resistance were evaluated in the same manner as in the above-mentioned "Evaluation (1)."

[0101] TIFF0007734116000010.tif56170 [Industrial Applicability]

[0102] The graft polymer of the present invention is useful as a constituent component used in binder components for aqueous inks such as aqueous inkjet inks.

Claims

1. A graft polymer used as a binder component for aqueous ink, A polymer having a number average molecular weight of 10,000 to 30,000, comprising 20 to 40% by mass of structural units (1) derived from a polymeric monomer represented by the following general formula (1), 5 to 50% by mass of structural units (2) derived from styrene, 5 to 50% by mass of structural units (3) derived from isobornyl (meth)acrylate, and 5 to 50% by mass of structural units (4) derived from at least one other monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, lauryl (meth)acrylate, and octadecyl (meth)acrylate: the polymeric monomer has a structural unit derived from methacrylic acid, a structural unit derived from isobornyl methacrylate, and a structural unit derived from at least one methacrylate selected from ethyl methacrylate and tetrahydrofurfuryl methacrylate, the number average molecular weight of the polymeric monomer is 1,000 to 10,000; The acid value of the polymeric monomer is 30 to 200 mgKOH / g. (In the general formula (1), R １ represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R ２ represents an isobornyl group, and R ３ represents an ethyl group or a tetrahydrofurfuryl group)

2. A binder component for a water-based ink, comprising: a dispersion medium comprising water; and emulsion particles formed by neutralizing the carboxy groups of the graft polymer according to claim 1 with an alkali, the emulsion particles being dispersed in the dispersion medium; The binder component has emulsion particles having a number average particle size of 50 to 200 nm.

3. The binder component of claim 2 wherein the alkali is ammonia.

4. Contains water, a water-soluble organic solvent, and a binder component, An aqueous ink, wherein the binder component is the binder component according to claim 2 or 3.

5. 5. The aqueous ink of claim 4, further comprising a polyethylene wax.

6. 5. The aqueous ink according to claim 4, wherein the water-soluble organic solvent is at least one selected from the group consisting of propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, 1,2-hexanediol, and glycerin.

7. The aqueous ink according to claim 4, which is used for printing on at least one medium selected from the group consisting of polyolefin film, polyethylene terephthalate film, and vinyl chloride film.

8. Further containing a colorant, the colorant is a pigment dispersion containing a pigment and a dispersant that disperses the pigment, 5. The aqueous ink according to claim 4, wherein the dispersant is a vinyl copolymer containing structural units derived from at least one acidic monomer selected from the group consisting of (meth)acrylic acid, maleic acid, and itaconic acid.

9. The vinyl copolymer is A structural unit derived from methacrylic acid and a structural unit derived from isobornyl (meth)acrylate, and a structural unit derived from at least one (meth)acrylate monomer selected from the group consisting of ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

9. The aqueous ink according to claim 8, which is a linear polymer having an acid value of 50 to 200 mgKOH / g and a number average molecular weight of 5,000 to 20,000.

10. The aqueous ink according to claim 4, which is for ink-jet printing.

Images