Aqueous inkjet ink

Abstract

To provide an aqueous inkjet ink which can record a high-quality image excellent in adhesiveness, abrasion resistance and alcohol resistance on a plastic medium (recording medium) such as polyethylene terephthalate and is excellent in storage stability and ejection stability.SOLUTION: An aqueous inkjet ink for printing on plastic media. A binder component and a crosslinking agent are contained, the binder component is an A-B block copolymer of methacrylate having a polymer chain A and a polymer chain B, the polymer chain A is a water-insoluble polymer block containing a constitutional unit derived from benzyl methacrylate or the like, the polymer chain B is a water-soluble polymer block in which all carboxyl groups are neutralized with an alkaline substance such as ammonia and ionized, and the crosslinking agent is a polymer containing a constitutional unit derived from an oxazoline compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous inkjet ink. [Background technology]

[0002] Due to its increasing functionality, inkjet printing methods are used in a wide range of applications, including personal, office, and commercial use, recording, color display, and color photography. Furthermore, in recent years, the scope of application has expanded from conventional office consumer inkjet printers and wide-format inkjet printers for large-format printing to industrial inkjet printers. Because inkjet printing methods do not require image printing plates, they are suitable as printing methods that can produce small quantities of a wide variety of industrial printed materials on demand. In addition, due to environmental considerations, inkjet printing methods using aqueous inkjet inks, which use aqueous solvents primarily composed of water as the liquid medium, have been actively proposed.

[0003] Industrial applications include, for example, sign displays, outdoor advertising, facility signs, displays, POP advertising, transit advertising, packaging, containers, and labels. Examples of media (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. For industrial applications, on-demand printing, which does not require a printing plate, is mainstream, and high-speed printing is required. Images recorded with aqueous inkjet inks containing dyes as colorants are poor in durability, such as water resistance and light resistance. For this reason, aqueous inkjet inks containing pigments as colorants are frequently used.

[0004] In order to record images with improved durability, inkjet inks have been proposed that contain acrylic or urethane binder components capable of forming a film (Patent Documents 1 and 2). Furthermore, in the case of aqueous inkjet inks that contain a pigment as a coloring material, the pigment must be stably and finely dispersed in the ink. For this reason, pigment dispersions in which the pigment is stably and finely dispersed using a surfactant or polymer dispersant, and inkjet inks prepared 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 with the water-based inks for inkjet printing proposed in Patent Documents 1 to 3, it has been difficult to record images that have excellent durability, such as adhesion and abrasion resistance, on plastic media.

[0007] The present invention has been made in view of the problems associated with the conventional techniques, and an object of the present invention is to provide an aqueous inkjet ink that has excellent storage stability and ejection stability and that is capable of recording high-quality images with excellent adhesion, abrasion resistance, and alcohol resistance on plastic media (recording media) such as polyethylene terephthalate. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided the following aqueous inkjet ink. [1] An aqueous inkjet ink for printing on plastic media, comprising a pigment, a pigment dispersant, a water-soluble organic solvent, a binder component, and a crosslinking agent, wherein the binder component is a methacrylate-based AB block copolymer having a polymer chain A and a polymer chain B, and having a number average molecular weight of 8,000 to 30,000 and a molecular weight distribution of 1.8 or less, wherein the polymer chain A is a water-insoluble polymer block containing 80% by mass or more of structural units derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and having a number average molecular weight of 5,000 to 20,000 and a molecular weight distribution of 1.6 or less, and wherein the polymer chain B contains 10 to 40% by mass of structural units derived from methacrylic acid, and 10 to 40% by mass of structural units derived from benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. an AB block copolymer in the form of a water-soluble polymer block having a number average molecular weight of 3,000 to 10,000, which contains 60 to 90% by mass of structural units derived from at least one compound selected from the group consisting of methacrylic acid, methacrylic acid, and isobornyl methacrylate, and which has a number average molecular weight of 3,000 to 10,000; all carboxy groups in the structural units derived from methacrylic acid have been ionized by neutralization with at least one first alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol; the AB block copolymer forms nanoparticles having a number average particle size of 20 to 200 nm; and the crosslinking agent is a water-soluble or water-dispersible polymer having a number average molecular weight of 1,000 to 50,000, which contains 15 to 90% by mass of structural units derived from at least one oxazoline compound selected from the group consisting of 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline. [2] The aqueous inkjet ink according to [1] above, further comprising a wax component dispersed in the form of particles having a number average particle diameter of 50 to 300 nm, the wax component being an olefin wax having a melting point of 80 to 150°C and containing carboxy groups in the polymer structure, and all of the carboxy groups in the olefin wax being neutralized with at least one second alkaline substance selected from the group consisting of sodium hydroxide, ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol. [3] The aqueous inkjet ink according to [1] or [2], wherein the water-soluble organic solvent comprises propylene glycol and at least one selected from the group consisting of diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and 3-methoxy-N,N-dimethylpropanamide, and the content of the water-soluble organic solvent is 3 to 30% by mass. [4] The aqueous inkjet ink according to any one of [1] to [3], wherein the plastic medium is a polyethylene terephthalate base material. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an aqueous inkjet ink that has excellent storage stability and ejection stability and that is capable of recording high-quality images with excellent adhesion, abrasion resistance, and alcohol resistance on plastic media (recording media) such as polyethylene terephthalate. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Water-based inkjet ink>

[0033] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the aqueous inkjet ink of the present invention is an aqueous ink for printing on plastic media, which is used to print images on plastic media (plastic recording media) by inkjet recording, and contains a pigment, a pigment dispersant, a water-soluble organic solvent, a binder component, and a crosslinking agent. Hereinafter, the aqueous inkjet ink of the present invention (hereinafter also simply referred to as "ink") will be described in detail.

[0011] (water) The ink of this embodiment is an aqueous ink containing water as an essential component. As the water, ion-exchanged water, distilled water, purified water, etc. are preferably used. The content of water in the ink is preferably 30 to 90 mass % based on the total amount of the ink.

[0012] (pigment) The ink of this embodiment contains a pigment as a colorant from the viewpoints of water resistance, color development, color density, and clarity of the image. Known organic and inorganic pigments used in aqueous inkjet inks can be used as the pigment. Examples of organic pigments include chromatic pigments such as phthalocyanine-based, azo-based, azomethine azo-based, azomethine-based, anthraquinone-based, perinone-perylene-based, indigo-thioindigo-based, dioxazine-based, quinacridone-based, isoindoline-based, isoindolinone-based, diketopyrrolopyrrole-based, quinophthalone-based, and indanthrene-based 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-based pigments, iron oxide-based pigments, and spinel pigments.

[0013] Unless the printed matter (image) requires hiding power, it is preferable to use organic fine particle pigments. When a highly vivid and transparent printed matter 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 coarse particles with a particle size of more than 1.0 μm have been removed.

[0014] 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.

[0015] In inkjet printing applications, from the viewpoints of color development, dispersibility, weather resistance, and the like, yellow pigments such as CI Pigment Yellow 74, 83, 109, 128, 139, 150, 151, 154, 155, 180, 181, and 185; 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 are preferred.

[0016] 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 that have acidic groups such as carboxyl groups, sulfonic acid groups, and phosphate groups introduced onto the surface of the pigment particles, and these acidic groups are neutralized to make them more water-compatible, thereby enabling them to be dispersed in ink without the use of a pigment dispersant. In contrast, when using untreated pigments, surface-treated pigments, and encapsulated pigments, a pigment dispersant is used in combination.

[0017] The content of the pigment in the ink is preferably 0.1 to 25% by mass, and more preferably 0.2 to 20% by mass, based on the total amount of the ink.

[0018] (pigment dispersant) The ink of this embodiment contains a pigment dispersant for dispersing the pigment in the ink. For example, the ink can be prepared using a pigment dispersion containing a pigment dispersed using the pigment dispersant. A polymer-type pigment dispersant is preferably used as the pigment dispersant. Using a low-molecular-weight pigment dispersant such as a surfactant may result in somewhat insufficient pigment dispersion stability and increased foaming. The number-average molecular weight of the polymer used as the pigment dispersant is preferably 1,000 to 20,000. Furthermore, it is preferable to use a pigment dispersant in which a vinyl polymer having an acidic group and an acid value of 50 to 250 mg is neutralized with an alkaline substance.

[0019] The vinyl polymer preferably has an acidic group such as a carboxy group, a sulfonic acid group, or a phosphoric acid group. Neutralizing the acidic group with an alkaline substance makes it compatible with water, allowing 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.

[0020] The vinyl polymer may have other structural units besides the structural units derived from the monomer having an acidic group. Examples of the monomers constituting the other structural units include aromatic vinyl monomers such as styrene, vinyltoluene, and vinylnaphthalene; acrylate monomers such as butyl acrylate and 2-ethylhexyl acrylate; methacrylate monomers such as methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, dimethylaminoethyl methacrylate, and polyethylene glycol monomethyl ether methacrylate; vinyl ester monomers such as vinyl acetate; and heterocyclic vinyl monomers such as vinylpyridine and vinylimidazole.

[0021] 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.

[0022] 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 pigment adsorption may be insufficient and the strength of the printed film formed may be reduced. On the other hand, if the number-average molecular weight of the vinyl polymer is more than 20,000, the ink viscosity may increase excessively and the ink may tend to exhibit non-Newtonian viscosity, which may slightly reduce the ejection stability in the case of aqueous inkjet inks.

[0023] 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 less soluble in water even after neutralization with an alkaline substance, 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 carboxyl groups, which may slightly reduce the water resistance of the resulting printed film.

[0024] 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. Radical polymerization and living radical polymerization are preferred polymerization reactions. The resulting vinyl polymer can be converted into a pigment dispersant by neutralizing it with an alkaline substance. Alternatively, a solution of the pigment dispersant may be mixed with a pigment, and then the pigment dispersant is precipitated by adding it to a poor solvent or treating it with an acid, followed by treating or encapsulating the pigment to prepare a polymer-treated pigment.

[0025] The vinyl polymer may be any of polymers having a higher order structure such as a random copolymer, an AB block copolymer, an ABA block copolymer, a graft copolymer, a gradient copolymer, a star polymer, and a dendrimer.

[0026] The content of the pigment dispersant in the ink 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.

[0027] (Water-soluble organic solvent) The ink of this embodiment contains a water-soluble organic solvent. The ink of this embodiment is an ink used for printing on plastic media with low permeability. 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 to the plastic media. Furthermore, it is preferable to use a water-soluble organic solvent that can function as a leveling agent and also as a film-forming aid that improves the film-forming properties of the binder component in the ink.

[0028] 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.

[0029] If a large amount of water-soluble organic solvent remains in the printed film formed from the binder component in the ink applied to a plastic recording medium, the water resistance, adhesion to the recording medium, and abrasion resistance of the printed film may be slightly reduced. Furthermore, the organic solvent used to synthesize the binder component by a method such as solution polymerization may be directly blended into the ink. For this reason, it is preferable to use a water-soluble organic solvent with a certain degree of volatility. Based on the above, 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), 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 3-methoxy-N,N-dimethylpropanamide (boiling point 215°C).

[0030] 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 plastic media. 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 lead to a decrease in the ejection stability and storage stability of the ink. 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 formed printing film, which may lead to blocking and a slight decrease in physical properties such as water resistance and abrasion resistance of the image.

[0031] (binder component) The ink of this embodiment contains a binder component. The binder component is a methacrylate-based AB block copolymer having a polymer chain A and a polymer chain B. The number-average molecular weight (Mn) of the AB block copolymer, calculated in terms of polystyrene, as measured by gel permeation chromatography (GPC) is 8,000 to 30,000, preferably 10,000 to 15,000. By using an AB block copolymer having a number-average molecular weight within the above range as the binder component, a printed film (image) with excellent adhesion and abrasion resistance can be formed. If the number-average molecular weight of the AB block copolymer is less than 8,000, the effect of improving the adhesion and abrasion resistance of the image will be insufficient. On the other hand, if the number-average molecular weight of the AB block copolymer exceeds 30,000, the viscosity of the ink may become excessively high. The AB block copolymer is a polymer with a relatively uniform molecular weight, with a molecular weight distribution (PDI = weight-average molecular weight (Mw) / number-average molecular weight (Mn)) of 1.8 or less, preferably 1.6 or less. If the PDI exceeds 1.8, the polymer will contain a large amount of polymers having number average molecular weights outside the above range.

[0032] The AB block copolymer is a methacrylate-based block copolymer. Polymer chain A is a water-insoluble (hydrophobic) polymer block, and polymer chain B is a polymer block that becomes water-soluble upon ionization. The AB block copolymer can be produced, for example, by living radical polymerization using an organic iodide as an initiator compound and an organic compound as a catalyst. In living radical polymerization using an organic iodide, the iodine atom serving as the terminal propagating group is preferably bonded to a tertiary carbon atom. For this reason, the content of structural units derived from methacrylate (methacrylic acid and methacrylic acid esters) in the AB block copolymer is preferably 90% by mass or more, and more preferably 100% by mass. Furthermore, a high content of structural units derived from methacrylate increases the glass transition temperature (Tg) of the AB block copolymer. Therefore, using an AB block copolymer with a high content of structural units derived from methacrylate as a binder component enables the recording of images with improved thermal properties, such as heat resistance. Furthermore, methacrylates have higher resistance to hydrolysis than acrylates (acrylic acid and acrylic acid esters), and are therefore less susceptible to hydrolysis even in aqueous liquid media, providing excellent stability.

[0033] The polymer chain A contains 80% by mass or more, preferably 95% by mass or more, of structural units (structural units A-1) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. The inclusion of structural units A-1 allows the glass transition temperature (Tg) of the polymer chain A to be preferably room temperature (25°C) or higher, more preferably 50°C or higher. Furthermore, the inclusion of structural units A-1 provides affinity, such as ππ stacking between aromatic rings and hydrophobic interactions, resulting in excellent adhesion to plastic recording media such as PET substrates, and enables the recording of images with improved durability, such as abrasion resistance.

[0034] The polymer chain A may further contain a structural unit (structural unit A-2) derived from a methacrylate other than benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. 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, and octadecyl methacrylate. , dicyclopentenyl methacrylate, dicyclopentanyl methacrylate, adamantyl 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.

[0035] The number average molecular weight (Mn) of the polymer chain A is 5,000 to 20,000, preferably 6,000 to 18,000, and more preferably 7,000 to 15,000. When the number average molecular weight of the polymer chain A is within the above range, an image (dried film) with excellent adhesion and abrasion resistance can be formed. If the number average molecular weight of the polymer chain A is less than 5,000, the adhesion of the image to the recording medium decreases. On the other hand, if the number average molecular weight of the polymer chain A exceeds 20,000, the polymerization rate of the polymer chain A decreases and the molecular weight distribution becomes broad.

[0036] The polymer chain A is a polymer block having a relatively uniform molecular weight. The molecular weight distribution (PDI) of the polymer chain A is 1.6 or less, preferably 1.5 or less, and more preferably 1.4 or less. If the molecular weight distribution (PDI) exceeds 1.6, the polymer chain A will contain many polymer blocks whose molecular weights are outside the above-mentioned range of number average molecular weight.

[0037] Polymer chain A is a water-insoluble polymer block that does not substantially dissolve in water. On the other hand, polymer chain B is a water-soluble polymer block that substantially dissolves in water. Therefore, in an AB block copolymer having polymer chain A and polymer chain B, preferably consisting essentially of only polymer chain A and polymer chain B, polymer chain A forms nanoparticles in water, while polymer chain B dissolves in water. In other words, the AB block copolymer is a so-called self-dispersing polymer.

[0038] The polymer chain B contains 10 to 40% by mass, preferably 15 to 30% by mass, of a structural unit (structural unit B-1) derived from methacrylic acid. That is, the polymer chain B is a polymer block having a carboxy group, which essentially contains a structural unit derived from methacrylic acid. The carboxy group derived from methacrylic acid is neutralized with a first alkaline substance and ionized, thereby making the polymer chain B soluble in water. If the content of the structural unit B-1 in the polymer chain B is less than 10% by mass, the polymer chain B is less soluble in water even after ionization. On the other hand, if the content of the structural unit B-1 in the polymer chain B is more than 40% by mass, the solubility of the polymer chain B becomes excessively high, resulting in an excessive increase in the viscosity of the ink and a decrease in the water resistance of the image. After the ink of this embodiment is applied to a recording medium, the carboxy group in the polymer chain B reacts with the crosslinker to form a three-dimensional network structure, which then hardens. Therefore, if the content of the structural unit B-1 in the polymer chain B is too high, the amount of crosslinker reacting with the carboxy group also becomes excessively large.

[0039] The polymer chain B further contains 60 to 90% by mass, preferably 70 to 85% by mass, of a structural unit (structural unit B-2) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. The total amount of the structural units B-1 and B-2 in the polymer chain B is preferably 80 to 100% by mass. By using a polymer chain B containing the structural unit B-2, it is possible to form an image with improved durability, such as improved adhesion to a recording medium and improved abrasion resistance. In addition to the structural units B-1 and B-2, the polymer chain B may further contain a structural unit derived from one of the other methacrylates described above.

[0040] The number average molecular weight (Mn) of the polymer chain B is 3,000 to 10,000, preferably 5,000 to 9,500. The polymer chain B is a water-soluble polymer block in which all carboxy groups in the structural units derived from methacrylic acid are neutralized and ionized with a first alkaline substance. The polymer chain B becomes water-soluble when all carboxy groups are neutralized and ionized with an alkaline substance. The first alkaline substance is at least one selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol.

[0041] After applying the ink to a recording medium using an inkjet printing method, drying forms a water-resistant coating film. Here, drying volatilizes the first alkaline substance, forming carboxyl groups and rendering the polymer chain B water-insoluble. Furthermore, the carboxyl groups formed by the evaporation of the first alkaline substance react with oxazoline groups in the oxazoline compound used as a crosslinking agent. This results in the formation of a three-dimensional network structure, resulting in a cured film. If some of the carboxyl groups in the polymer chain B are not neutralized with the first alkaline substance, the remaining carboxyl groups will react with the oxazoline groups in the ink, causing it to thicken and gel. Therefore, it is necessary to neutralize and ionize all carboxyl groups with the first alkaline substance, preventing them from substantially reacting with the oxazoline groups.

[0042] Furthermore, if the carboxyl groups in the polymer chain B are neutralized with an alkali metal hydroxide such as sodium hydroxide, these alkali metal hydroxides do not volatilize, and therefore, even when the coating film is dried, the carboxyl groups do not undergo a curing reaction with the oxazoline groups, and a cured film is not formed. Therefore, it is necessary to neutralize the carboxyl groups in the polymer chain B with at least one first alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol, which can volatilize at relatively low temperatures. From the viewpoints of volatility and basicity, the first alkaline substance is preferably dimethylaminoethanol.

[0043] It is necessary that all carboxy groups in the structural units derived from methacrylic acid in the polymer chain B are neutralized with the first alkaline substance. Specifically, the amount of the first alkaline substance relative to the carboxy groups is preferably 100 mol % or more, more preferably 105 mol % or more, and particularly preferably 110 mol % or more.

[0044] The AB block copolymer forms nanoparticles in the ink with a number-average particle diameter of 20 to 200 nm, preferably 30 to 120 nm. If the number-average particle diameter of the particles formed by the AB block copolymer is less than 20 nm, the viscosity of the ink becomes excessively high. On the other hand, if the number-average particle diameter of the particles exceeds 200 nm, clogging of the recording head of the inkjet recording device (printer) becomes more likely.

[0045] AB block copolymers can be produced by conventional methods. Because an AB block structure and a relatively narrow molecular weight distribution are required, it is preferable to produce (synthesize) AB block copolymers by living radical polymerization. Examples of living radical polymerization include the nitroxide method (NMP method), which utilizes the dissociation and binding of amine oxide radicals as a protecting group; atom transfer radical polymerization (ATRP), which uses heavy metals such as copper, ruthenium, nickel, and iron and ligands that form complexes with these heavy metals as catalysts and polymerization using halogen compounds as initiator compounds; reversible addition-fragmentation chain transfer polymerization (RAFT), which uses dithiocarboxylic acid esters or the like as initiator compounds and polymerization using addition-polymerizable monomers and radical initiators; the TERP method, which uses an organotellurium compound as an initiator compound and uses an organotellurium group as a protecting group to form a growing terminal; and reversible transfer catalyst polymerization (RTCP method, RCMP method), which uses iodine and / or an iodine compound as a polymerization initiator compound and a commercially available organic compound that can form radicals as a catalyst. Among these, the RTCP method and the RAFT method are preferred because they allow the structure and molecular weight of the methacrylate polymer to be controlled under mild conditions and do not require the removal of catalysts or protective group residues.

[0046] After forming polymer chain A, monomers that form polymer chain B are added to form polymer chain B, thereby obtaining the desired AB block copolymer. Polymer chain A may be formed after forming polymer chain B. However, if the polymerization rate of polymer chain B is not 100%, structural units derived from the remaining methacrylic acid used to form polymer chain B may be introduced into polymer chain A, causing polymer chain A to become water-soluble. For this reason, it is preferable to form polymer chain B after forming polymer chain A.

[0047] The polymerization method for producing the AB block copolymer may be any of bulk polymerization, suspension polymerization, and solution polymerization. Examples of organic solvents used during polymerization include hydrocarbon solvents, alcohol solvents, ester solvents, ketone solvents, ether solvents, glycol solvents, glycol ether solvents, glycol ester solvents, amide solvents, sulfoxide solvents, carbonate solvents, and ionic liquids. The formed AB block copolymer may be used as a solution, or a solid AB block copolymer may be isolated by evaporating the organic solvent or precipitating it in a poor solvent. Alternatively, an aqueous solution of the AB block copolymer may be obtained by solution polymerization using the water-soluble organic solvent to be contained in the ink, followed by adding an aqueous solution containing a first alkaline substance. The water-soluble organic solvent is preferably at least one selected from the group consisting of diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and dipropylene glycol monomethyl ether.

[0048] The content of the binder component (solids) in the ink per 100 parts by mass of pigment is preferably 50 to 505 parts by mass, and more preferably 100 to 400 parts by mass. If the content of the binder component per 100 parts by mass of pigment is less than 50 parts by mass, the resulting print film may be somewhat insufficient in adhesion to plastic media and abrasion resistance. On the other hand, if the content of the binder component per 100 parts by mass of pigment is more than 505 parts by mass, the pigment concentration will be relatively low, which may result in a slight decrease in the color development of the image.

[0049] (Crosslinking agent) The ink of this embodiment contains a crosslinking agent. The carboxyl groups in the AB block copolymer used as the binder component are neutralized by the first alkaline substance in the ink and ionized (-COO -When the ink applied to plastic media dries, the first alkaline substance evaporates, generating the original carboxyl group (-COOH). The generated carboxyl group reacts with the crosslinking agent to form a three-dimensional network structure and harden. This allows for the recording of a printing film (image) with excellent properties such as adhesion to the substrate, wet friction resistance, dry friction resistance, and alcohol resistance (alcohol rubbing resistance).

[0050] The crosslinking agent is a water-soluble or water-dispersible polymer containing structural units derived from at least one oxazoline compound selected from the group consisting of 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline. In other words, the crosslinking agent is a polymer containing oxazoline groups that react with carboxy groups. The urethane bond formed by the reaction of the carboxy groups with the oxazoline groups is believed to improve the adhesion of images to plastic media. Furthermore, because the polymer used as the crosslinking agent contains polar oxazoline groups, it can be dissolved or dispersed in water.

[0051] In the polymer used as a crosslinking agent, the content of structural units derived from an oxazoline compound is 15 to 90% by mass, preferably 30 to 60% by mass. If the content of structural units derived from an oxazoline compound is less than 15% by mass, the number of crosslinking points will be small, making it difficult to sufficiently improve the physical properties of the coating film (image) formed. On the other hand, it may be difficult to produce (synthesize) a polymer with a content of structural units derived from an oxazoline compound of more than 90% by mass. Note that the polymer used as a crosslinking agent usually further contains structural units derived from monomers such as styrene, acrylic acid esters, and methacrylic acid esters in addition to the structural units derived from an oxazoline compound.

[0052] The number-average molecular weight (Mn) of the polymer used as the crosslinking agent is 1,000 to 50,000, preferably 10,000 to 30,000. Because the polymer has a relatively high molecular weight, the crosslinking points are close to the binder component and readily react, and the resulting printed film can have improved adhesion to the substrate. If the number-average molecular weight of the polymer is less than 1,000, the crosslinking reaction will be insufficient. On the other hand, if the number-average molecular weight of the polymer exceeds 50,000, the viscosity of the ink will increase excessively.

[0053] The crosslinking agent (polymer) may be obtained by polymerizing a monomer component containing 2-vinyl-2-oxazoline or 2-isopropenyl-2-oxazoline, or may be commercially available, such as the "Epocross" series manufactured by Nippon Shokubai Co., Ltd.

[0054] The preferred content of crosslinking agent in the ink varies depending on the amount of carboxy groups in the binder component. Specifically, the content of crosslinking agent (solid content) in the ink per 100 parts by mass of binder component (solid content) is preferably 5 to 100 parts by mass, and more preferably 10 to 50 parts by mass. If the content of crosslinking agent per 100 parts by mass of binder component is less than 5 parts by mass, crosslinking may be insufficient, and adhesion to plastic media and abrasion resistance may be somewhat insufficient. On the other hand, if the content of crosslinking agent per 100 parts by mass of binder component is more than 100 parts by mass, the properties of the polymer used as the crosslinking agent may be more likely to be reflected in the coating film properties.

[0055] (wax component) The ink of this embodiment preferably further contains a wax component. The wax component is present in a molten state in the coating film, and either bleeds out after drying or remains in a particulate state. This forms fine irregularities on the image surface, imparting slipperiness and further improving the abrasion resistance of the image.

[0056] The wax component is an olefin wax such as polyethylene wax or polypropylene wax, which has a carboxy group in its polymer structure. The carboxy group may be introduced by oxidation, by copolymerization of an unsaturated carboxylic acid such as acrylic acid, or by grafting a compound such as maleic anhydride through radical addition. The acid value of the wax component is preferably 10 to 100 mgKOH / g.

[0057] All carboxy groups in the wax component (olefin wax) are neutralized with a second alkaline substance. Neutralization and ionization of the carboxy groups allow the wax component to disperse in a particulate form. The second alkaline substance is at least one selected from the group consisting of sodium hydroxide, ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol. The second alkaline substance is preferably sodium hydroxide or dimethylaminoethanol. The wax component can be obtained, for example, by emulsifying and dispersing a wax (polymer) in an organic solvent by adding an aqueous solution containing the second alkaline substance while heating the organic solvent in the presence of an optional surfactant. The organic solvent is then removed under normal or reduced pressure. Therefore, using ammonia as the second alkaline substance can easily volatilize, resulting in deionization and precipitation of the wax. Furthermore, using 2-amino-2-methyl-1-propanol as the second alkaline substance can easily cause dehydration condensation of the amino and carboxy groups. However, ammonia and 2-amino-2-methyl-1-propanol can be used to adjust the pH after removing the organic solvent.

[0058] The wax component is present in the ink in a particulate dispersed state. The number-average particle diameter of the wax component measured by light scattering is preferably 50 to 300 nm, and more preferably 60 to 200 nm. If the number-average particle diameter of the wax component is less than 50 nm, the viscosity of the ink may become too high. On the other hand, if the number-average particle diameter of the wax component exceeds 300 nm, clogging may occur in the recording head of the inkjet recording device (printing machine).

[0059] The melting point of the olefin wax (polymer) used as the wax component is preferably 80 to 150°C, and more preferably 100 to 130°C. If the melting point of the olefin wax is too low, it may melt and become less viscous, becoming cloudy and failing to fully exhibit its performance. Furthermore, the ink may be more likely to aggregate during storage.

[0060] 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 amount of the ink.

[0061] (Other additives) The ink may contain other components (other additives) in addition to the above-mentioned components, such as surfactants, preservatives, organic solvents other than the above-mentioned water-soluble organic solvents, leveling agents, surface tension adjusters, pH adjusters, UV absorbers, light stabilizers, antioxidants, dyes, fillers, thickeners, viscosity adjusters, antifoaming agents, antifungal agents, antistatic agents, metal fine particles, and magnetic powders.

[0062] The inclusion of a surfactant allows the surface tension of the ink to be maintained at a predetermined value. Examples of surfactants include silicone-based surfactants, acetylene glycol-based surfactants, fluorine-based surfactants, alkylene oxide-based surfactants, and hydrocarbon-based surfactants. Among these, silicone-based surfactants, acetylene glycol-based surfactants, and fluorine-based surfactants are preferred. Surfactants generally cause ink to foam or to be repelled by the surface of plastic media (films). Furthermore, adding a surfactant can cause pigments to aggregate, so it is preferable to appropriately adjust the amount of surfactant added. The content of surfactant in the ink is preferably 3.5% by mass or less, and more preferably 0.01 to 2.0% by mass, based on the total amount of ink.

[0063] 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.

[0064] (Water-based inkjet ink) The ink of this embodiment can be prepared using, for example, a pigment dispersion containing a pigment dispersed using a pigment dispersant. The pigment dispersion can be prepared using, for example, a pigment, a pigment dispersant, water, and a water-soluble organic solvent. The content of the organic pigment in the pigment dispersion is preferably 1 to 30% by mass, and more preferably 10 to 25% by mass. The content of the inorganic pigment in the pigment dispersion is preferably 5 to 70% by mass, and more preferably 30 to 50% by mass.

[0065] The pigment dispersion can be prepared according to a conventionally known method. For example, a pigment dispersion can be obtained by processing a mixture of a pigment, a pigment dispersant, water, and a water-soluble organic solvent using a paint shaker, a ball mill, an attritor, a sand mill, a horizontal media mill, a colloid mill, a roll mill, or the like to finely disperse the pigment. The resulting pigment dispersion is preferably processed using a centrifuge or a filter to remove coarse particles. Furthermore, other additives may be added as necessary.

[0066] The desired ink can be obtained by mixing the resulting pigment dispersion with the other components. For example, the components are mixed in predetermined amounts and then thoroughly stirred using a disperser or the like. The mixture is then passed through a filter to remove coarse particles and dust, thereby obtaining the ink.

[0067] The physical properties of the ink are usually adjusted appropriately to match the performance of the inkjet recording device used. For example, the viscosity is adjusted to an appropriate level depending on the type of pigment, etc., so that the ink can be ejected from the nozzles of the recording head by inkjet printing. The viscosity of ink containing organic pigments is preferably 2 to 10 mPa·s. The viscosity of ink containing inorganic pigments is preferably 5 to 30 mPa·s.

[0068] The pH of the ink is preferably 8.0 to 10.0, and more preferably 8.5 to 9.5. If the pH of the ink is less than 8.0, the binder component is likely to precipitate, and the binder component and the crosslinker may react in the ink, or the pigment may aggregate. On the other hand, if the pH of the ink is more than 10.0, the ink becomes too alkaline and may become difficult to handle.

[0069] The surface tension of the ink is set appropriately depending on the performance of the inkjet recording device, etc. The surface tension of the ink is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0070] (Printing base material) The ink of this embodiment is a water-based inkjet ink for printing on plastic media, and can record a high-quality printed film (image) with excellent adhesion, abrasion resistance, and alcohol resistance on plastic media.

[0071] Examples of plastics constituting plastic media such as plastic films 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. 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.

[0072] The plastic film may be unstretched or may be stretched by uniaxial stretching, biaxial stretching, or the like. The surface (printing 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.

[0073] The plastic medium is preferably a polyethylene terephthalate (PET) substrate. By using the ink of this embodiment, an image can be formed as a printed film with particularly good adhesion to PET. Furthermore, since PET film has good heat resistance, the drying temperature of the ink can be increased. In addition to PET film, shrinkable PET film can also be used as the PET substrate.

[0074] The ink of this embodiment is applicable to inkjet printing and can be applied to inkjet recording devices equipped with recording heads such as thermal heads and piezo heads. Furthermore, by using the inkjet recording method, images can be recorded (printed) on various printing substrates, including plastic media. Furthermore, the ink of this embodiment is suitable not only for inkjet printing, but also as an ink for gravure printing and flexographic printing, as an ink for paints, and as an ink for water-based writing implements such as markers. [Example]

[0075] 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.

[0076] <Production of binder components> Synthesis Example 1 A reaction vessel was charged with 289.4 parts of diethylene glycol monobutyl ether (BDG) (hereinafter, solvent content: 50%), 1.5 parts of iodine, 5.5 parts of 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", Fujifilm Wako Pure Chemical Industries, Ltd.) (V-70), 0.05 parts of N-iodosuccinimide (NIS), 154.6 parts of benzyl methacrylate (BzMA), and 14.6 parts of 2-hydroxyethyl methacrylate (HEMA). The mixture was stirred with nitrogen bubbling, and polymerization was carried out at 45 °C for 4 hours to synthesize polymer (A chain). A portion of the reaction solution was sampled and measured for solids content, which was 37.3%. The polymerization conversion calculated from the solids content was approximately 100%. The polystyrene-equivalent number average molecular weight (Mn) of the A chain measured by GPC using tetrahydrofuran (THF) as a developing solvent was 9,100, and the polydispersity index (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.19.

[0077] The resulting A-chain solution was cooled to 40°C, and then 92.5 parts of BzMA and 22.6 parts of methacrylic acid (MAA) were added. Polymerization was continued at 40°C for 4 hours to form a polymer (B-chain), yielding an AB block copolymer. Solid content measurements and residual monomer analysis by gas chromatography confirmed that the polymerization was nearly complete. A portion of the reaction solution was sampled and measured to find that the solid content was approximately 50%, and the polymerization conversion was approximately 100%. The resulting AB block copolymer had an Mn of 14,500 and a PDI of 1.23. The GPC peak shifted to a higher molecular weight side than the A-chain peak, confirming the formation of an AB block copolymer. The Mn of the B-chain was 5,400. A portion of the reaction solution was added to methanol, and the precipitate was filtered, washed with methanol, and dried to obtain a resin. The acid value of the resin, measured by titration with an ethanolic 0.1 mol / L potassium hydroxide solution, was 51.6 mg KOH / g.

[0078] At room temperature, a mixture of 17.5 parts of 28% aqueous ammonia (amount relative to carboxy groups: 110 mol%) and 561.1 parts of ion-exchanged water was added to neutralize and emulsify the mixture, yielding binder component V-1. In the following examples, the amount of water was adjusted so that the polymer content was 25%. A portion was sampled and diluted 10 times with water, and the pH measured with a pH meter was 8.9. The number-average particle size of the polymer particles measured using a dynamic light scattering particle size distribution analyzer (trade name "Nicomp 380", manufactured by Entegris) was 76.3 nm.

[0079] (Comparative Synthesis Examples 1 and 2) Binder components HV-1 and HV-2 were obtained in the same manner as in Synthesis Example 1 above, except that the types and amounts (unit: parts) of various materials shown in Table 1 were used.

[0080] TIFF2026037034000001.tif190170

[0081] (Synthesis Examples 2 to 10, Synthesis Comparative Examples 3 to 7) Binder components V-2 to 10 and HV-3 to 7 were obtained in the same manner as in Synthesis Example 1, except that various materials were used in the types and amounts (unit: parts) shown in Tables 2 to 4. The meanings of the abbreviations in Tables 2 to 4 are as follows. CHMA: Cyclohexyl methacrylate THFMA: Tetrahydrofurfuryl methacrylate IBXMA: Isobornyl methacrylate LMA: Lauryl methacrylate MMA: Methyl methacrylate DMAE: Dimethylaminoethanol AMP: 2-amino-2-methyl-1-propanol MPA: 3-Methoxy-N,N-dimethylpropanamide PPG: Propylene glycol monopropyl ether

[0082] TIFF2026037034000002.tif211170

[0083] TIFF2026037034000003.tif183170

[0084] TIFF2026037034000004.tif234170

[0085] <Production of pigment dispersants> (Production Example 1) 100 parts of BDG were placed in a reaction vessel and heated to 80°C with nitrogen bubbling. 20 parts of styrene (St), 15 parts of methyl methacrylate (MMA), 15 parts of ethyl methacrylate (EMA), 20 parts of 2-ethylhexyl methacrylate (2EHMA), 15 parts of 2-hydroxyethyl methacrylate (HEMA), 15 parts of MAA, and 1.5 parts of 2,2-azobisisobutyronitrile (AIBN) were placed in a separate reaction vessel and stirred to prepare a homogeneous monomer solution. 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 13,200, a PDI of 2.15, and an acid value of 65.2 mgKOH / g. The aqueous solution of pigment dispersant G-1 had a pH of 8.7 and a solids content of 36.5%.

[0086] (Production Example 2) A reaction vessel was charged with 283.1 parts of BDG, 59.6 parts of THFMA, 59.6 parts of IBXMA, 2.5 parts of iodine, 4.6 parts of V70, and 0.1 parts of NIS. The mixture was heated to 45°C while bubbling nitrogen, and polymerization was carried out for 4 hours to form the A chain. A portion of the reaction solution was sampled and analyzed by GPC. The A chain had an Mn of 4,000, a PDI of 1.19, and a polymerization rate of approximately 100%.

[0087] A mixture of 119 parts THFMA and 30.2 parts MAA was added, and polymerization was carried out at 45°C for 4 hours to form the B chain, yielding an AB block copolymer. The GPC peak shifted to a higher molecular weight side than the A chain peak, confirming the formation of an AB block copolymer. The Mn of the B chain was 4,100. The AB block copolymer had an Mn of 8,100, a PDI of 1.22, and an acid value of 73.0 mgKOH / g. The conversion rate calculated from the solid content was approximately 100%. The acid value of the B chain, calculated taking the conversion rate into account, was 132.0 mgKOH / g.

[0088] After cooling the reaction solution 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%.

[0089] <Production of aqueous inkjet ink> Example 1 864 parts of ion-exchanged water, 411 parts of an aqueous solution of pigment dispersant G-1 (150 parts polymer), and 600 parts of CI Pigment Blue 15:3 (PB15:3, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were mixed and thoroughly stirred using a dissolver to obtain a mixture. The resulting mixture was dispersed at a peripheral speed of 7 m / s using a horizontal media disperser (trade name "Dynomill 0.6 Liter Multilab," manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.5 mm) 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. Ion-exchanged water was added to adjust the concentration to obtain a blue, aqueous pigment dispersion B-1 with a pigment concentration of 14%.

[0090] 16.0 parts of binder component V-1, 28.6 parts of pigment dispersion B-1, 10.0 parts of propylene glycol (PG), 7.5 parts of a crosslinker (a polymer crosslinker containing approximately 50% structural units derived from 2-isopropenyl-2-oxazoline, trade name "Epocross WS-700" manufactured by Nippon Shokubai Co., Ltd., Mn approximately 20,000, solids content 25%) (WS700), 0.5 parts of a surfactant (trade name "Silface SAG503A" manufactured by Nissin Chemical Co., Ltd.) (503A), and 37.4 parts of ion-exchanged water were mixed, thoroughly stirred, and then filtered through a 5 μm pore membrane filter to obtain Ink I-1, an aqueous inkjet ink. The viscosity of the resulting Ink I-1 at 25°C was 3.4 mPa·s and the pH was 8.5. The number-average particle size of the particles in Ink I-1 was 111.0 nm.

[0091] Example 2 517.5 parts of ion-exchanged water, 182.5 parts of an aqueous solution of pigment dispersant G-2 (75.0 parts polymer), and 300 parts of CI Pigment Blue 15:3 (PB15:3, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were mixed and thoroughly stirred using a dissolver to obtain a mixture. The resulting mixture was dispersed at a peripheral speed of 7 m / s using a horizontal media disperser (trade name "Dynomill 0.6 Liter Multilab," manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.5 mm) 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. Ion-exchanged water was added to adjust the concentration to obtain a blue aqueous pigment dispersion B-2 with a pigment concentration of 14%.

[0092] Next, a water-based inkjet ink, ink I-2, was obtained in the same manner as in Example 1, except that the pigment dispersion B-2 was used instead of the pigment dispersion B-1. The viscosity of the resulting ink I-2 at 25°C was 3.4 mPa·s, the pH was 8.6, and the number-average particle size of the particles in ink I-2 was 99.1 nm.

[0093] (Examples 3 to 16, Comparative Examples 1 to 8) Aqueous inkjet inks I-3 to I-16 and Inks HI-1 to HI-8 were obtained in the same manner as in Example 1, except that the types and amounts of various materials shown in Tables 5 to 7 were used. The meanings of the abbreviations in Tables 5 to 7 are as follows: WS300: Polymer crosslinker containing approximately 80% of structural units derived from 2-isopropenyl-2-oxazoline, trade name "Epocross WS-300", manufactured by Nippon Shokubai Co., Ltd., Mn approximately 40,000, solid content 10% W-1: Self-dispersing emulsion of wax component and polyethylene oxide, neutralized with DMEA, glass transition temperature 81°C, solid content 40%, pH 8.8, number average particle size 88.0nm W-2: Self-dispersing emulsion of wax component and polyethylene oxide, neutralized with sodium hydroxide, glass transition temperature 130°C, solid content 20%, pH 8.9, number average particle size 180nm

[0094] TIFF2026037034000005.tif130170

[0095] TIFF2026037034000006.tif115170

[0096] TIFF2026037034000007.tif115170

[0097] <Evaluation> The following items were evaluated, and the results are shown in Table 8.

[0098] (Storage stability) The prepared ink was placed in a dryer at 70°C and left for one day and one week. After being left for one day and one week, the viscosity of the ink and the number average particle diameter of the particles in the ink were measured, and the storage stability of the ink was evaluated according to the evaluation criteria shown below. ○: No change in either the viscosity of the ink or the number average particle size of the particles in the ink ×: There is a significant change in at least one of the viscosity of the ink and the number average particle size of the particles in the ink.

[0099] (printing) An inkjet printer equipped with a plate heater (product name "MMP825H", manufactured by Mastermind) and a recording medium (polyethylene terephthalate (PET) film, manufactured by Futamura Chemical Co., Ltd., 50 μm) were prepared. Images were recorded on the recording medium by the inkjet method using the prepared inks to obtain printed matter. Specifically, the recording medium was heated using a plate heater to a surface temperature of 55°C, and then each ink was applied and printed. The recording medium was then dried in a thermostatic chamber at 90°C for 10 minutes to record the image and obtain a printed matter.

[0100] (Discharge stability) The occurrence of ejection defects (ink dots not ejecting or ink dots scattering) during printing was observed, and the ink ejection stability was evaluated according to the following evaluation criteria. ○: No discharge failure occurred. △: A small amount of splashing was observed in addition to ink droplets during ejection. ×: Discharge stopped midway, or scattering of dots was observed.

[0101] (Appearance of printed matter) 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.

[0102] (adhesion) Cellophane tape was pressed firmly against the image and then peeled off. The degree of peeling of the image from the PET film 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.

[0103] (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 was moved back and forth over the surface of the image 100 times with a weight of 500 g, and a wet rub test was conducted in which a water-soaked white cloth was moved back and forth over the surface of the image 100 times with a weight of 200 g. After the 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 evaluation criteria shown below. ◎: 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.

[0104] (alcohol resistant) A 70% aqueous solution of ethanol was dropped onto the surface of the image and left for 10 seconds. After that, a cotton swab was swiped back and forth across the surface of the image. The number of times the cotton swab was swiped back and forth until the image (coating) 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 ×: Peeled off immediately - less than 5 times

[0105] TIFF2026037034000008.tif188170 [Industrial Applicability]

[0106] The inks of the present invention are suitable for outdoor display printing and for high volume, high speed ink jet printing.

Claims

1. 1. A water-based inkjet ink for printing on plastic media, comprising: Contains a pigment, a pigment dispersant, a water-soluble organic solvent, a binder component, and a crosslinking agent, the binder component is a methacrylate-based AB block copolymer having a polymer chain A and a polymer chain B, a number average molecular weight of 8,000 to 30,000, and a molecular weight distribution of 1.8 or less; the polymer chain A is a water-insoluble polymer block containing 80% by mass or more of structural units derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and having a number average molecular weight of 5,000 to 20,000 and a molecular weight distribution of 1.6 or less; the polymer chain B is a water-soluble polymer block having a number average molecular weight of 3,000 to 10,000, which contains 10 to 40% by mass of structural units derived from methacrylic acid and 60 to 90% by mass of structural units derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and in which all of the carboxy groups in the structural units derived from methacrylic acid have been neutralized and ionized with at least one first alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol; the AB block copolymer forms nanoparticles having a number average particle size of 20 to 200 nm; The aqueous inkjet ink comprises a water-soluble or water-dispersible polymer having a number average molecular weight of 1,000 to 50,000, and containing 15 to 90 mass % of structural units derived from at least one oxazoline compound selected from the group consisting of 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline.

2. Further containing a wax component dispersed in the form of particles having a number average particle diameter of 50 to 300 nm, the wax component is an olefin wax having a carboxy group in its polymer structure and a melting point of 80 to 150°C; 2. The aqueous inkjet ink according to claim 1, wherein all of the carboxy groups in the olefin wax are neutralized with at least one second alkaline substance selected from the group consisting of sodium hydroxide, ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol.

3. the water-soluble organic solvent contains propylene glycol and at least one selected from the group consisting of diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and 3-methoxy-N,N-dimethylpropanamide; 3. The aqueous inkjet ink according to claim 1, wherein the content of the water-soluble organic solvent is 3 to 30% by mass.

4. 3. The aqueous inkjet ink according to claim 1, wherein the plastic medium is a polyethylene terephthalate base material.

Images