JP2019038893A - Aqueous ink and image forming method - Google Patents

Abstract

To provide aqueous ink containing metal nanoparticles, a resin and polyhydric alcohol which can enhance discharge stability of the aqueous ink, and brightness, scratch resistance and water resistance of the formed image.SOLUTION: Aqueous ink contains metal nanoparticles, a polymer dispersion agent which is adsorbable to the metal nanoparticles, anionic resin emulsion and a water-soluble organic solvent having a boiling point of 150°C or higher and 330°C or lower, and can be discharged by an inkjet method. A content of the water-soluble organic solvent is 20 mass% or more and 50 mass% or less based on the total mass of the aqueous ink. The water-soluble organic solvent contains polyhydric alcohol in an amount of 10 mass% or more and 50 mass% or less based on the total mass of the water-soluble organic solvent.SELECTED DRAWING: None

Description

  The present invention relates to a water-based ink and an image forming method.

  Aluminum pigments, pearl pigments, and the like are used for the purpose of developing metallic luster in recorded materials such as labels, packages, publicly printed materials, and photographs. These pigments are applied to the substrate as an ink composition by analog printing techniques including offset printing, gravure printing, screen printing, and the like, and form a region that emits a metallic gloss color in the recorded matter.

  In recent years, nano-sized particles containing metal such as gold, silver, and copper (hereinafter, also simply referred to as “metal nanoparticles”) are used to produce a recorded material with a high-definition region that emits a metallic luster color. A method has been developed in which a metallic luster layer containing the above-mentioned metal nanoparticles is formed on a substrate by being applied to the substrate surface.

  The water-based ink containing metal nanoparticles contains a water-soluble organic solvent as a wetting agent (humectant) that prevents a decrease in ejection stability due to drying of the water-based ink at the nozzle tip of the inkjet head. A polyhydric alcohol may be used as the water-soluble organic solvent. Patent Document 1 specifically describes an aqueous ink containing 93% by mass or more and 100% by mass or less of a polyhydric alcohol (glycerin or triethylene glycol) with respect to the total mass of the water-soluble organic solvent contained in the aqueous ink. Has been. Patent Document 2 discloses an aqueous ink containing a polyhydric alcohol (propylene glycol or 1,2-hexanediol) in an amount of 82% by mass to 92% by mass with respect to the total mass of the water-soluble organic solvent contained in the system ink. It is specifically described.

  The water-based ink containing metal nanoparticles may contain a fixing resin in order to improve the scratch resistance of the formed image. Patent Document 3 describes that as such a resin, a nonionic resin emulsion is used in order to suppress a decrease in specular gloss of an image formed by interaction with metal nanoparticles. Patent Document 4 describes that such a resin is selected in consideration of adhesiveness to a base material.

Japanese Patent Laying-Open No. 2015-193721 JP2012-101491A JP2013-203923A JP 2004-161852 A

  In an ink-jet ink containing metal nanoparticles, a polyhydric alcohol may be used as a humectant as described in Patent Document 1 and Patent Document 2. However, according to the study by the present inventors, in the water-based ink containing a resin in order to increase the scratch resistance of an image formed as described in Patent Document 3 and Patent Document 4, a polyhydric alcohol is further added. When it is contained, the ejection stability may be lowered, or the glitter (reflectance) of the formed image may be lowered. On the other hand, unless the water-based ink contains a resin, the scratch resistance and water resistance of the formed image cannot be sufficiently increased.

  The present invention has been made in view of the above problems, and in an aqueous ink containing metal nanoparticles, a resin, and a polyhydric alcohol, the discharge stability of the aqueous ink, and the glossiness, scratch resistance, and scratching of the formed image, and It is an object of the present invention to provide a water-based ink capable of enhancing water resistance and an image forming method using the water-based ink.

The above problem is solved by the following means.
[1] In a water-based ink that can be ejected by an ink jet method including metal nanoparticles, a polymer dispersant that can be adsorbed to the metal nanoparticles, an anionic resin emulsion, and a water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower. The content of the water-soluble organic solvent is 20% by mass to 50% by mass with respect to the total mass of the water-based ink, and the water-soluble organic solvent is 10% with respect to the total mass of the water-soluble organic solvent. An aqueous ink containing a polyhydric alcohol in an amount of not less than 50% by mass and not more than 50% by mass.
[2] The total content of the metal nanoparticles, the polymer dispersant, and the anionic resin emulsion is 1.0% by mass or more and 20% by mass or less based on the total mass of the water-based ink. ] Water-based ink as described in.
[3] The content of the anionic resin emulsion is 1.0% by mass to 15% by mass with respect to the total content of the metal nanoparticles and the polymer dispersant. 2] The water-based ink as described in 2].
[4] The water-based ink according to any one of [1] to [3], wherein the anionic resin emulsion has a zeta potential of −100 mV to −5 mV.
[5] The water-based ink according to any one of [1] to [4], wherein the anionic resin emulsion has a zeta potential of −90 mV to −10 mV.
[6] An image forming method including a step of discharging the water-based ink droplet according to any one of [1] to [5] from a nozzle of an inkjet head and landing on a substrate.

  According to the present invention, in a water-based ink containing metal nanoparticles, a resin and a polyhydric alcohol, the water-based ink capable of improving the discharge stability of the water-based ink and the glitter, scratch resistance and water resistance of the image formed, and An image forming method using water-based ink is provided.

  The present inventors have intensively studied in view of the above problems, and when the water-based ink containing the metal nanoparticles and the resin further contains a polyhydric alcohol, the polyhydric alcohol is adsorbed on the surface of the metal nanoparticle and dispersed in the ink. It has been found that by reducing the stability, the ejection stability and the glitter of the formed image are reduced.

  Although the mechanism of the above phenomenon is not clear, the following factors can be considered. That is, it is considered that the polyhydric alcohol is adsorbed on the surface of the metal nanoparticles and reduces the repulsion between the surface charges of the metal nanoparticles to facilitate aggregation of the metal nanoparticles.

  In addition, when a polyhydric alcohol is adsorbed on one metal nanoparticle with one hydroxy group in the molecule and adsorbed on another metal nanoparticle with another hydroxy group, the metal nanoparticle having the polyhydric alcohol as a crosslinking point is used. Another potential factor is the potential to form a crosslinked structure of the particles.

  Due to these actions, polyhydric alcohol is easily formed by agglomeration of metal nanoparticles, and the ejection stability (dispersion stability) decreases due to clogging of the nozzles of the inkjet head with the agglomerated metal nanoparticles. It is considered that the reduction in glitter due to the occurrence of the distribution of metal nanoparticles in the image is likely to occur.

  Based on the above findings, the present inventors controlled the amount of polyhydric alcohol contained in the water-based ink containing the metal nanoparticles and the resin emulsion to suppress a decrease in ejection stability (dispersion stability) and glitter due to the above-described action. It was found that by controlling to such an extent that it can be used as a water-based ink that has sufficiently high ejection stability and can enhance the glossiness of the formed image, and further studies and researches, the present invention has been completed.

1. Water-based ink One embodiment of the present invention based on the above idea is a water-based ink that can be ejected by an inkjet method including metal nanoparticles, a polymer dispersant that can be adsorbed to the metal nanoparticles, an anionic resin emulsion, and a water-soluble organic solvent. About. The water-soluble organic solvent includes a water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower. The content of the water-soluble organic solvent is 20% by mass or more and 50% by mass or less with respect to the total mass of the water-based ink. The water-soluble organic solvent contains a polyhydric alcohol in an amount of 10% by mass to 50% by mass with respect to the total mass of the water-soluble organic solvent.

1-1. Metal nanoparticles Metal nanoparticles are nano-sized metal particles.

  The metal that forms the metal nanoparticles may be any metal that exhibits a metallic luster when the metallic luster layer is formed.

  Examples of the metals include gold, silver, copper, nickel, palladium, platinum, aluminum, zinc, chromium, iron, cobalt, molybdenum, zirconium, ruthenium, iridium, tantalum, mercury, indium, tin, lead, and tungsten. Is included. Of these, gold, silver, copper, nickel, cobalt, tin, lead, chromium, zinc and aluminum are preferred because they can express high gloss and are inexpensive. Gold, silver, copper, tin, Chromium, lead and aluminum are more preferred, gold and silver are more preferred, and silver is particularly preferred. These metals can be used singly or in combination of two or more as an alloy or a mixture. Moreover, you may use combining the 2 or more types of metal nanoparticle from which the kind or composition of a metal differs. The metal nanoparticles only need to contain these metals as main components, may contain a small amount of other components inevitably contained, and are surface-treated with citric acid or the like to improve dispersion stability. Also good. Moreover, these metals may contain an oxide.

  The average particle diameter of the metal nanoparticles is not particularly limited, but is preferably 3 nm or more and 100 nm or less from the viewpoint of enhancing the dispersion stability and storage stability in the composition for producing the metallic luster layer, and 15 nm. More preferably, it is 50 nm or less. The average particle size of the metal nanoparticles can be a volume average particle size determined using a particle size distribution measuring apparatus based on a dynamic light scattering method.

  The content of the metal nanoparticles in the water-based ink is not particularly limited, but from the viewpoint of sufficiently improving the discharge stability (dispersion stability) of the water-based ink and the adhesion of the metal nanoparticles to the substrate, It is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 18% by mass or less, and further preferably 4% by mass or more and 15% by mass or less with respect to the total mass.

1-2. Polymer Dispersant The polymer dispersant is a compound having an adsorbing group that can be adsorbed on the surface of the metal nanoparticles and a hydrophilic structure.

  The polymer dispersant has an adsorbing group for adsorbing to the surface of the metal nanoparticles. The adsorbing group may be a functional group having a strong adsorbing force with respect to the surface of the metal particles. Examples of the adsorbing group include a primary to tertiary amino group, a quaternary ammonium group, a heterocyclic group having a basic nitrogen atom, a hydroxyl group, a carbonyl group, a carboxyl group, a phosphoric acid group, a sulfonic acid group, And thiol groups. The polymer dispersant can exhibit sufficient performance as a protective colloid of metal nanoparticles by having these adsorbing groups. The polymer dispersant preferably has an acid value. Examples of the polymer dispersant having an acid value include a polymer dispersant having a carboxyl group, a phosphate group, a sulfonate group, or the like as an adsorption group or a functional group. The acidic group is preferably a carboxyl group or a phosphate group, and more preferably a carboxyl group.

  The resin constituting the polymer dispersant is preferably a homopolymer or copolymer of a hydrophilic monomer. The copolymer of hydrophilic monomers may be a copolymer of hydrophilic monomers and hydrophobic monomers.

  Examples of hydrophilic monomers include monomers containing carboxyl groups or acid anhydride groups (such as (meth) acrylic acid, unsaturated polyvalent carboxylic acids such as maleic acid, and maleic anhydride), and alkylene oxide modified (meta). ) Acrylic acid ester monomers (such as ethylene oxide-modified (meth) acrylic acid alkyl esters). In the present invention, (meth) acryl means both or one of acrylic and methacrylic.

  Examples of hydrophobic monomers include (meth) acrylate monomers such as methyl (meth) acrylate and ethyl (meth) acrylate, styrene monomers such as styrene, α-methylstyrene and vinyltoluene, ethylene, propylene And α-olefin monomers such as 1-butene, and carboxylic acid vinyl ester monomers such as vinyl acetate and vinyl butyrate.

  When the polymer dispersant is a copolymer, it may be a random copolymer, an alternating copolymer, a block copolymer, a comb copolymer, or the like. Among these, from the viewpoint of further improving the dispersibility of the metal nanoparticles, the polymer dispersant is preferably a comb block copolymer.

  The comb-type block copolymer means a copolymer containing a linear polymer forming a main chain and another kind of polymer graft-polymerized to a structural unit derived from a monomer constituting the main chain. Preferred examples of the comb block copolymer include a long chain containing a structural unit derived from a (meth) acrylic acid ester and a side chain containing a polyalkylene oxide group (such as an ethylene oxide-propylene oxide copolymer group). Comb-type block copolymers containing a chain polyalkylene oxide group). In the comb-type block copolymer, since the graft-polymerized side chain causes steric hindrance, aggregation of metal nanoparticles can be further suppressed. Thereby, the dispersibility of the metal nanoparticles is increased, and thus it is easier to suppress ejection failure due to the aggregated metal nanoparticles.

  The polymer dispersant preferably has an acid value of 1 mgKOH / g or more and 100 mgKOH / g or less. When the acid value is 1 mgKOH / g or more, the polymer dispersant has a tendency to be hydrophilic, so that the dispersibility of the metal nanoparticles in the water-based ink can be improved, and the ejection stability (dispersion of the water-based ink) Stability) can also be increased. On the other hand, when the acid value is 100 mgKOH / g or less, it suppresses a remarkable decrease in ejection stability (dispersion stability) from the inkjet head due to swelling of the polymer dispersant in the inkjet head. You can also. From the above viewpoint, the acid value of the polymer dispersant is preferably 3 mgKOH / g or more and 80 mgKOH / g or less, more preferably 5 mgKOH / g or more and 60 mgKOH / g or less, and 7 mgKOH / g or more and 50 mgKOH / g. More preferably, it is as follows.

The acid value of the polymer dispersant may be measured according to JIS K 0070 using a stoichiometric method such as neutralization titration. Further, the type of the dispersant may be specified by Fourier transform infrared spectroscopy (FT-IR), ¹ H-NMR, and gas chromatography-mass spectrometry (GC / MS).

  The polymer dispersant preferably has a polyalkylene oxide structure in the molecule, and more preferably the above-described comb block copolymer having a polyalkylene oxide group in the side chain. The polyalkylene oxide structure moderately reduces the cohesiveness of the metal nanoparticles due to steric hindrance. Thereby, it is considered that the water-based ink (or metal nanoparticles in the water-based ink) spreads moderately on the substrate and can form a smoother and higher gloss image.

  The polyalkylene oxide structure is preferably a polyalkylene oxide structure (polyethylene oxide structure, polypropylene oxide structure and polybutylene oxide structure) having 3 to 6 carbon atoms. The polymer dispersant preferably has 3 or more and 80 or less polyalkylene oxide structures per molecule.

  The polymer dispersant preferably has a weight average molecular weight of 1,000 to 100,000, more preferably 2,000 to 50,000.

  Examples of commercially available polymer dispersants include DISPERBYK-102, DISPERBYK-187, DISPERBYK-190, DISPERBYK-191, DISPERBYK-194N, DISPERBYK-199, DISPERBYK-2015, and DISPERBYK-2069 (all manufactured by BYK Chemie, "DISPERBYK" is a registered trademark of the company), EFKA 6220 (manufactured by BASF, "EFKA" is a registered trademark of the company), Solsperse 32000, Solsperse 44000, Solsperse 46000 (manufactured by Lubrizol), Floren TG-750W (Kyoeisha Chemical) Etc.).

  The content of the polymer dispersant in the water-based ink is not particularly limited, but from the viewpoint of sufficiently improving the dispersibility of the metal nanoparticles in the water-based ink and the adhesion to the substrate, the total mass of the metal nanoparticles. On the other hand, it is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and further preferably 3% by mass or more and 8% by mass or less.

1-3. Anionic resin emulsion Anionic resin emulsion is a dispersion of anionic resin. The anionic resin emulsion can act as a fixing resin and enhance the adhesion of the metal nanoparticles to the substrate.

  Unlike an anionic resin, an anionic resin is unlikely to interact with metal nanoparticles, and the aggregation of metal nanoparticles via an anionic resin is unlikely to occur. Therefore, when an anionic resin is used as the fixing resin, it is possible to suppress a decrease in discharge stability (dispersion stability) of the water-based ink due to aggregation of metal nanoparticles.

  Moreover, an anionic resin can raise the abrasion resistance of the coating film formed into a film by making it react with a cationic flocculant on a base material, and bridge | crosslinking it. In addition, since anionic resins are less likely to form aggregates with metal nanoparticles than cationic resins, the density of the coating film is further increased, and the scratch resistance and water resistance of the coating film are further increased. Can do.

  In addition, since the anionic resin has a larger electrostatic repulsion than the nonionic resin, the dispersibility in the ink is more stable for a long time than the water-based ink containing the nonionic resin.

  Moreover, the resin which forms an emulsion has low solubility in water. Therefore, when an anionic resin emulsion is used as the fixing resin, the water resistance of the formed image can be increased.

  The anionic resin is preferably a resin having high affinity with the polymer dispersant, and is a (meth) acrylic resin, urethane resin, polyolefin resin, polyester resin, polyvinyl chloride resin (for example, polyvinyl chloride polymer, Vinyl chloride-vinylidene chloride copolymer), epoxy resin, polysiloxane resin, fluororesin, styrene copolymer (for example, styrene-butadiene copolymer, styrene- (meth) acrylate copolymer), and vinyl acetate A copolymer (for example, ethylene-vinyl acetate copolymer) can be appropriately selected and used. From the viewpoint of further improving the water resistance of the formed image, the anionic resin includes (meth) acrylic resin, urethane resin, polyolefin resin, polyester resin, polyvinyl chloride resin, epoxy resin, polysiloxane resin, fluororesin, It is preferably selected from styrene copolymers, vinyl acetate copolymers, and the like, and is preferably selected from urethane resins and (meth) acrylic resins.

  The aqueous solvent can be a mixed solvent of an organic solvent containing N-methylpyrrolidone (NMP) and propylene glycol dimethyl ether (DMPDG) and water.

  The (meth) acrylic resin can be obtained by polymerizing the monomer (b1) using the water-soluble initiator (b2) in an aqueous solution containing the polymer emulsifier (b3).

  Examples of the monomer (b1) include (meth) acrylic acid alkyl ester containing methyl (meth) acrylate and ethyl (meth) acrylate, (meth) acrylic acid alkoxyalkyl ester containing methoxybutyl (meth) acrylate and the like. , Aromatic vinyl compounds including styrene and α-methylstyrene, hydrolyzable silane group-containing vinyl compounds including vinyltriethoxysilane, and (meth) acrylamide compounds including N-methylolacrylamide.

  Examples of the water-soluble initiator (b2) include sodium persulfate, potassium persulfate, and ammonium persulfate.

  The polymer emulsifier (b3) may be a water-soluble resin, and a carboxyl group-containing polymer can be used. The carboxyl group-containing polymer is a homopolymer of a carboxy group-containing unsaturated monomer or a copolymer of a carboxy group-containing unsaturated monomer and another monomer. Examples of the carboxy group-containing unsaturated monomer include (meth) acrylic acid. Examples of the monomer copolymerizable with the carboxy group-containing unsaturated monomer include those similar to the monomer (b).

  The average particle size of the anionic resin emulsion is preferably 10 nm or more and 200 nm or less, and more preferably 30 nm or more and 100 nm or less. The average particle diameter of the anionic resin emulsion can be a volume average particle diameter determined using a particle size distribution measuring apparatus based on a dynamic light scattering method.

  From the viewpoint of further improving the dispersion stability of the anionic resin emulsion in the water-based ink and improving the ejection stability and storage stability of the water-based ink, the zeta potential of the anionic resin emulsion is from −100 mV to −5 mV. It is preferable that it is -90 mV or more and -10 mV or less. The zeta potential of the anionic resin emulsion can be an average value of zeta potentials obtained for 500 anionic resin emulsions using a zeta potential measuring device based on the electrophoretic light scattering method. The zeta potential of the anionic resin emulsion can be adjusted to a desired value by appropriately changing the salt concentration, the surfactant amount, the stirring strength and the like when preparing the anionic resin emulsion by a known method.

  The total solid content in the water-based ink is preferably 1.0% by mass or more and 20% by mass or less with respect to the total mass of the water-based ink. When the solid content is 20% by mass or less, the ejection stability of the water-based ink is further increased. When the solid content is 1.0% by mass or more, a sufficient amount of metal nanoparticles and an anionic resin emulsion are contained in the water-based ink, so that the glossiness, scratch resistance, and Water resistance is further increased. From the above viewpoint, the total solid content is more preferably 3% by mass or more and 15% by mass or less, and further preferably 5% by mass or more and 13% by mass or less with respect to the total mass of the water-based ink.

  The total solid content in the water-based ink can be the sum of the contents of the metal nanoparticles, the polymer dispersant, and the anionic resin emulsion (solid content) in the water-based ink.

  The solid content of the anionic resin emulsion in the water-based ink is preferably 1.0% by mass or more and 15% by mass or less based on the total mass of the metal nanoparticles and the polymer dispersant. When the solid content is 1.0% by mass or more, the scratch resistance and water resistance of the formed image can be further improved. When the solid content is 15% by mass or less, the glitter (reflectance) of the formed image can be further increased. From the above viewpoint, the solid content of the anionic resin emulsion in the water-based ink is preferably 1.0% by mass or more and 15% by mass or less based on the total mass of the metal nanoparticles and the polymer dispersant. The content is more preferably no less than 13% by mass and no greater than 13% by mass, and still more preferably no less than 5% by mass and no greater than 12% by mass.

1-4. Water-soluble organic solvent The water-soluble organic solvent can be any water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower, which is used for a humectant of water-based ink or viscosity adjustment.

  Examples of the water-soluble organic solvent include polyhydric alcohol, polyhydric alcohol derivative, alcohol, amide, ketone, keto alcohol, ether, nitrogen-containing solvent, sulfur-containing solvent, propylene carbonate, ethylene carbonate, and 1,3-dimethyl. 2-Imidazolidinone and the like are included.

  Examples of the polyhydric alcohol include glycerin, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, hexylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, trimethylolpropane, 1, 3-butanediol, 1,5-pentanediol, 1,2,6-hexanetriol and the like are included.

  Examples of the polyhydric alcohol derivatives include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol-n-propyl. Ether, diethylene glycol-n-butyl ether, diethylene glycol-n-hexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether, propylene glycol monomethyl ether, Propylene glycol monoethyl ether, propylene Recall-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol monomethyl ether, Examples include tripropylene glycol monoethyl ether, tripropylene glycol-n-propyl ether, and tripropylene glycol-n-butyl ether.

  Examples of the alcohol include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, and benzyl alcohol.

  Examples of the amide include dimethylformamide, dimethylacetamide and the like.

  Examples of the ketone include acetone.

  Examples of the keto alcohol include diacetone alcohol.

  Examples of the ether include tetrahydrofuran, dioxane and the like.

  Examples of the nitrogen solvent include pyrrolidone, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, and triethanolamine.

  Examples of the sulfur-containing solvent include thiodiethanol, thiodiglycol, thiodiglycerol, sulfolane, dimethyl sulfoxide, and the like.

  A water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower is less likely to volatilize by a nozzle of an inkjet head or the like, and can increase the moisture retention of the ink and improve the ejection stability (humidity retention).

  The content of the water-soluble organic solvent is 20% by mass or more and 50% by mass or less with respect to the total mass of the water-based ink. When the content is 20% by mass or more, even if the amount of the polyhydric alcohol is within the range described later, the ink ejection stability (moisturizing property) can be improved. When the content is 50% by mass or less, the dispersion stability is lowered due to the weakness of electrostatic repulsion due to the surface charge of the metal nanoparticles or polymer dispersant due to the water-soluble organic solvent having a relative dielectric constant lower than that of water. It is possible to suppress the discharge stability (dispersion stability) of the water-based ink and the brightness of the formed image. From the above viewpoint, the content of the water-soluble organic solvent is preferably 20% by mass or more and 50% by mass or less, more preferably 26% by mass or more and 45% by mass or less, with respect to the total mass of the water-based ink. More preferably, it is 30 mass% or more and 40 mass% or less.

  The water-soluble organic solvent includes a polyhydric alcohol. Since the polyhydric alcohol has particularly high moisturizing performance, even if the amount of the water-soluble organic solvent is 50% by mass or less with respect to the total mass of the water-based ink, the ink ejection stability (moisturizing property) can be further improved.

  The content of the polyhydric alcohol is 10% by mass or more and 50% by mass or less with respect to the total mass of the water-soluble organic solvent. When the content is 10% by mass or more, even if the amount of the water-soluble organic solvent is within the above-described range, the ink ejection stability (moisturizing property) can be improved. When the content is 50% by mass or less, a decrease in ink ejection stability (dispersion stability) and a decrease in brightness of the formed image due to adsorption of polyhydric alcohol on the surface of the metal nanoparticles are suppressed. can do. From the above viewpoint, the content of the polyhydric alcohol is preferably 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less with respect to the total mass of the water-soluble organic solvent. More preferably, it is 25 mass% or more and 35 mass% or less.

  In general, polyhydric alcohol is used to improve the ejection stability (moisturizing property) of water-based ink. On the other hand, in the present embodiment, unlike the prior arts such as Patent Document 1 and Patent Document 2, the amount of polyhydric alcohol is reduced to reduce the ink ejection stability (dispersion stability) and the formed image. On the other hand, the ink discharge stability (moisturizing property) is maintained by increasing the amount of the water-soluble organic solvent.

1-5. In addition, the water-based ink may contain a known surfactant (surface conditioner), thickener, leveling agent, preservative, and the like.

  Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates and fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols and polyoxy Nonionic surfactants such as ethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and silicone-based and fluorine-based surfactants are included.

  Examples of commercially available silicone surfactants include KF-351A, KF-352A, KF-642 and X-22-4272, manufactured by Shin-Etsu Chemical, BYK307, BYK345, BYK347 and BYK348, manufactured by Big Chemie ("BYK "Is a registered trademark of the same company), as well as TSF4452, manufactured by Toshiba Silicone.

  The content of the surfactant, thickener, leveling agent, preservative and the like can be, for example, 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the water-based ink.

  However, from the viewpoint of further increasing the reflectance of the metallic gloss layer, the upper ink is substantially composed of the metal nanoparticles adsorbed with the polymer dispersant, the emulsion and solvent of the anionic resin, and optionally the required amount. It preferably comprises a surfactant. The total content of the metal nanoparticles adsorbed by the polymer dispersant, the emulsion of the anionic resin, and the solvent is preferably 90% by mass or more and 100% by mass or less with respect to the total mass of the water-based ink. More preferably, it is at least 100% by mass.

1-6. Physical Properties From the viewpoint of further improving the ejection stability from the nozzles of the inkjet head, the viscosity of the water-based ink is preferably 1 cP or more and less than 100 cP, more preferably 1 cP or more and 50 cP or less, and 1 cP or more and 15 cP or less. More preferably.

  From the viewpoint of improving the ejection stability from the nozzles of the inkjet head, the surface tension of the water-based ink is preferably 20 mN / m or more and 50 mN / m or less. From the viewpoint of improving the wettability with respect to the substrate and making the formed image higher definition, the surface tension of the water-based ink is more preferably 20 mN / m or more and 35 mN / m or less. The surface tension of the water-based ink can be adjusted to the above range by changing the type or amount of the organic solvent or surfactant.

2. Image Forming Method Another aspect of the present invention based on the above idea relates to an image forming method using the aqueous ink.

2-1. Application of water-based ink The image forming method using the water-based ink includes a step of ejecting the water-based ink droplets from a nozzle of an inkjet head and landing on a substrate.

  The ejection method from the ink jet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion systems such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, and thermal inkjet type and bubble jet. Any of electric-thermal conversion methods such as Canon Inc. (registered trademark) type may be used.

  Among these, the ink jet head is preferably a piezo ink jet head having a nozzle diameter of 30 μm or less from the viewpoint of increasing the types of ink that can be used and making the image quality more precise.

  From the viewpoint of recording an image at a high speed, the ink jet recording method is preferably a one-pass type. The one-pass type ink jet recording method is a method in which when a substrate passes under one ink jet head unit, water-based ink droplets are ejected and landed on all pixels where dots should be formed in one pass. Means method.

  From the viewpoint of recording an image by a one-pass ink jet recording method, the ink jet head is preferably a line head type. The line head type ink jet head means an ink jet head having a length equal to or greater than the width of the printing range in a direction orthogonal to the substrate transport direction. The line head type inkjet head may be composed of a single head having a length longer than the width of the printing range, or a combination of a plurality of heads so as to be longer than the width of the printing range. But you can. From the viewpoint of higher definition of the formed image, the plurality of heads form a plurality of rows in a direction perpendicular to the conveyance direction of the substrate, and the heads in each row are nozzles for the substrate. It is preferable to arrange so that the emission positions are different.

2-2. Application of pretreatment liquid The water-based ink may be landed on a region of the substrate to which the pretreatment liquid is applied. At this time, by using a liquid composition that can form a cationic pretreatment layer when applied to the substrate as the pretreatment liquid, the anionic resin composition in the landed aqueous ink is crosslinked and aggregated, The scratch resistance of the formed image can be further increased.

  For example, the pretreatment liquid may be a liquid composition containing a cationic resin, a cationic surfactant, a polyvalent metal salt or an organic acid (hereinafter collectively referred to as “aggregating agent”). . The cationic resin, the cationic surfactant, and the polyvalent metal salt can aggregate anionic components (such as an anionic resin emulsion) in the aqueous ink by salting out. The organic acid can aggregate anionic components in the water-based ink due to pH fluctuation.

  Examples of the cationic resin include polyallylamine, polyvinylamine, polyethyleneimine, and polydiallyldimethylammonium chloride.

  Examples of the polyvalent metal salt include water-soluble salts such as calcium salt, magnesium salt, aluminum salt, and zinc salt.

  Examples of the organic acids include formic acid, acetic acid, propionic acid, isobutyric acid, oxalic acid, fumaric acid, malic acid, citric acid, malonic acid, succinic acid, maleic acid, benzoic acid, 2-pyrrolidone-5-carboxylic acid , Lactic acid, acrylic acid and derivatives thereof, methacrylic acid and derivatives thereof, and compounds having a carboxyl group including acrylamide and derivatives thereof, sulfonic acid derivatives, and phosphoric acid and derivatives thereof.

  The flocculant is preferably a polyvalent metal salt or an acid because it has a low molecular weight and easily diffuses into the water-based ink, and can flocculate the water-based ink at a higher speed. Furthermore, since the safety is higher and the compatibility with the crosslinked resin is higher, the flocculant is more preferably an acid.

  The range of the content (amount) of the flocculant applied to the substrate is not limited, and can be appropriately set according to the composition of the water-based ink, the amount of the water-based ink, the type of the pigment flocculant, and the like. For example, it is preferable that the mass of the flocculant is 3% by mass or more and 50% by mass or less with respect to the mass of the image to be formed.

  In addition, when using an acid, it is preferable that the addition amount of an acid is an amount which adjusts the pH of a process liquid to below the neutralization equivalent of the anion component contained in aqueous ink. Further, when the anion component is a compound having a carboxyl group, the first dissociation constant of the acid is preferably 3.5 or less from the viewpoint of making image bleeding more difficult.

  The pretreatment liquid may contain a resin. The resin can improve the scratch resistance of the formed image.

  The resin can be a resin used as a fixing resin, (meth) acrylic resin, urethane resin, polyolefin resin, polyvinyl chloride resin (for example, polyvinyl chloride polymer, vinyl chloride-vinylidene chloride copolymer), And a vinyl acetate copolymer (for example, ethylene-vinyl acetate copolymer) can be appropriately selected and used. From the viewpoint of facilitating aggregation of the water-based ink, the resin is preferably a cationic resin or a nonionic resin, and more preferably a cationic resin. The polyolefin resin may have a polar group such as a halogen atom (such as chlorine) and a carboxyl group.

  The resin can be a polyurethane resin, for example, when it is desired to further improve the water resistance of the image, and a polyolefin-based resin when it is desired to further improve the adhesion of the image to a hydrophobic substrate such as polyethylene and polypropylene. Can do.

  When the resin is an emulsion, the average particle size of the resin fine particles is preferably 10 nm or more and 10 μm or less, more preferably 10 nm or more and 1 μm or less, further preferably 10 nm or more and 500 nm or less, and more preferably 10 nm or more. The thickness is more preferably 300 nm or less, and further preferably 10 nm or more and 200 nm or less. The average particle size can be measured by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, etc., but the measurement by the dynamic light scattering method is simple and the particle size region is Accurate measurement.

  The content of the resin in the pretreatment liquid is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less with respect to the total mass of the pretreatment liquid.

  The solvent of the pretreatment liquid is preferably water, but may optionally contain the water-soluble organic solvent described above for the water-based ink depending on the application method and the like.

  The application method of the pretreatment liquid is not particularly limited, and the pretreatment liquid may be applied to the surface of the substrate using a roll coater or a spin coater, or spray coating, dipping method, screen printing, gravure printing, offset. The pretreatment liquid may be applied to the surface of the substrate by a method such as printing, or the pretreatment liquid may be landed on the surface of the substrate by an inkjet method. Among these, the inkjet method is preferable from the viewpoint of forming a finer recorded matter.

The amount of the pretreatment liquid is not particularly limited and can be adjusted as appropriate. For example, when the flocculant is a polyvalent metal salt, the amount of the polyvalent metal salt is preferably 0.1 g / m ² or more and 20 g / m ² or less. When the flocculant is an acid, it is preferable that the amount of acid is not more than the neutralization equivalent of the anion component in the water-based ink.

  The amount of the flocculant can be measured by a known method. For example, when the pigment flocculant is a polyvalent metal salt, the content can be measured by ICP emission analysis, and when the pigment flocculant is an acid, the content can be measured by high performance liquid chromatography (HPLC).

  After application of the pretreatment liquid or water-based ink, the substrate may be dried. Drying can be performed by known methods such as infrared lamp drying, hot air drying, back heat drying, and reduced pressure drying. From the viewpoint of further improving the efficiency of drying, it is preferable to dry the substrate by combining two or more of these drying methods.

  Drying may be performed both after application of the pretreatment liquid and after application of the water-based ink. However, from the viewpoint of more sufficiently aggregating the water-based ink with the pretreatment liquid, drying is performed after application of the pretreatment liquid. It is preferable to dry completely or after applying water-based ink to a sufficient degree (water remains).

2-3. Substrate The substrate is not particularly limited, and may be a paper substrate with high water absorption, or a substrate with low water absorption such as a gravure or coated paper for offset printing, or a film, plastic board (soft vinyl chloride, hard Non-water-absorbing substrates such as vinyl chloride, acrylic plates, polyolefins, etc.), glass, tiles and rubbers may be used. Of these, low water-absorbing substrates and non-water-absorbing substrates, particularly preferably films, are difficult to form images using water-based inks. In such substrates, the present invention uses water-based inks. It is possible to form an image less than the liquid by sufficiently pinning.

  Examples of the film include known plastic films. Specific examples of the plastic film include polyester films such as polyethylene terephthalate, polyethylene films including high-density polyethylene films and low-density polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, ethylene / vinyl acetate copolymer Includes biodegradable films such as coalescence (EVA) film, polyvinyl chloride (PVC) film, polyvinyl alcohol (PVA) film, polyacrylic acid (PAA) film, polycarbonate film, polyacrylonitrile film, and polylactic acid film . In order to impart gas barrier properties, moisture proof properties, and fragrance retention properties, polyvinylidene chloride may be coated on one or both surfaces of the film, or a metal oxide may be deposited. Further, the film may be subjected to an antifogging process. The film may be subjected to corona discharge and ozone treatment.

  The film may be an unstretched film or a stretched film.

  The film may be a multilayer substrate in which a layer such as a PVA coat is provided on the surface of an absorbent substrate such as paper so that a region to be recorded is non-absorbable.

  The thickness of the film is preferably less than 0.25 mm.

  Hereinafter, although the specific Example of this invention is described with a comparative example, this invention is not limited to these.

1. 1. Material 1-1. Solvent The following solvents were used.
H ₂ O: Water TEGMME: Triethylene glycol monomethyl ether (boiling point: 248 ° C.)
EGMME: Ethylene glycol monomethyl ether (boiling point: 124 ° C)
EGMMEAc: Ethylene glycol monomethyl ether acetate (boiling point: 152 ° C.)
tEGMBE: Tetraethylene glycol monobutyl ether (boiling point: 304 ° C.)
(Hereinafter polyhydric alcohol)
Gly: Glycerin EG: Ethylene glycol PG: Propylene glycol

1-2. Metal nanoparticle dispersion <Silver nanoparticle dispersion 1>
To a 1 L separable flask having a flat stirring blade and a baffle plate, 7.2 g of DISPERBYK-190 (manufactured by Big Chemie, acid value of 10 mgKOH / g) as a dispersant, and 252 g of ion-exchanged water were added. Stirring was performed to dissolve DISPERBYK-190. Subsequently, 62 g of silver nitrate (manufactured by Toyo Chemical Co., Ltd.) dissolved in 252 g of ion-exchanged water was charged into the separable flask with stirring. Thereafter, the separable flask was placed in a water bath and heated and stirred until the temperature of the solution was stabilized at 70 ° C. Then, using a syringe pump, 157 g of dimethylaminoethanol (manufactured by Wako Pure Chemical Industries, Ltd.) as a reducing agent was added dropwise to the separable flask over 48 minutes, and the stirring was continued for 1 hour while maintaining the temperature at 70 ° C. A reaction solution containing nanoparticles was obtained.

  The obtained reaction liquid was put into a stainless steel cup, and 2 L of ion exchange water was further added, and then the pump was operated to perform ultrafiltration. After the solution in the stainless steel cup decreased, ion-exchanged water was added again, and purification was repeated until the filtrate had a conductivity of 100 μS / cm. Thereafter, the filtrate was concentrated to obtain a silver nanoparticle dispersion 1 having a solid content of 30 wt%.

  The ultrafiltration device used was an ultrafiltration module AHP1010 (manufactured by Asahi Kasei Co., Ltd., molecular weight cut off: 50000, number of membranes used: 400), and a tube pump (manufactured by Masterflex) connected by a Tygon tube. . It was 55 nm when the average particle diameter of the silver nanoparticle in the obtained silver nanoparticle dispersion liquid 1 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method.

1-3. Resin emulsion The following resin emulsion was used.
<Anionic resin emulsion 1>
(Synthesis of polyester glycol 1)
A flask equipped with a dehydrator was charged with 10 g of terephthalic acid, 190 g of isophthalic acid and 170 g of adipic acid as acid components, 32 g of ethylene glycol and 510 g of neopentyl glycol as glycol components, and used as a reaction catalyst. After adding 0.2 g of tetraisopropyl titanate, a condensation reaction was performed at 220 ° C. until the acid value became 1.0 or less and the water content became 0.05% or less, whereby polyester glycol 1 was obtained.

(Preparation of anionic resin emulsion 1)
To a four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube is added 488 g of polyester glycol 1, 13 g of trimethylolpropane, 88 g of dimethylolpropionic acid, 252 g of isophorone diisocyanate, and 670 g of methyl ethyl ketone. And a reaction at 75 ° C. for 4 hours to obtain a methyl ethyl ketone solution of a urethane prepolymer. The solution was cooled to 40 ° C., neutralized by adding 40 g of triethylamine, and then emulsified and dispersed using a homogenizer while gradually adding 1850 g of ion-exchanged water, and further stirred for 1 hour. Thereafter, the solvent was removed in an environment of reduced pressure and 50 ° C., and ion-exchanged water was further added to obtain an anionic resin emulsion 1 made of polyurethane having a solid content of about 20%. It was 40 nm when the average particle diameter of the resin particle of the emulsion 1 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method. Using a zeta potential measurement device (ELSZ1000, manufactured by Otsuka Electronics Co., Ltd.), the zeta potential based on the electrophoretic light scattering method of the resin particles of Emulsion 1 was -25 mV.

<Anionic resin emulsion 2>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 990 g of ion-exchanged water and 4.4 g of sodium lauryl sulfate, and the temperature was raised to 70 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 70 ° C., and 2.2 g of potassium persulfate was added as a polymerization initiator. After dissolution, 500 g of ion-exchanged water was added in advance to 3.3 g of sodium lauryl sulfate, 22 g of acrylamide, 480 g of styrene, An emulsion prepared by adding 520 g of butyl acrylate and 33 g of methacrylic acid under stirring was continuously dropped into the reaction solution over 3 hours. After completion of the dropping, aging was performed for 3 hours at the same temperature. The obtained emulsion of resin particles was cooled to room temperature, and then ion-exchanged water and ammonia water were added to obtain a resin particle emulsion 2 having a solid content of 20%. It was 70 nm when the average particle diameter of the resin particle of the emulsion 2 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method. Using a zeta potential measurement device (ELSZ1000, manufactured by Otsuka Electronics Co., Ltd.), the zeta potential based on the electrophoretic light scattering method of the resin particles of Emulsion 2 was measured to be −5.5 mV.

<Anionic resin emulsion 3>
To a polymerization vessel equipped with a stirrer and a heat insulation jacket, 1000 g of ion-exchanged water was added and vigorously stirred while introducing nitrogen. Next, after completely replacing the air in the vessel with nitrogen, the solution temperature was raised to 60 ° C., 0.1 g of ammonium persulfate as a polymerization initiator, 5 g of Na ₂ CO ₃ as a salt, and as a surfactant. Of 0.1 g of di (2-ethylhexyl) sodium sulphosuccinate was added. Next, 50 g of n-butyl acrylate, 50 g of methyl methacrylate, and 2 g of acrylic acid were added dropwise as monomers, and 3 g of acrylic acid was further added after completion. Then, after stirring for 2 hours, the polymerization was completed, neutralization, centrifugation, and ultrafiltration were performed to remove the remaining surfactant and the like, and an anionic resin emulsion 3 was prepared. It was 60 nm when the average particle diameter of the resin particle of the emulsion 3 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method. Using a zeta potential measurement device (ELSZ1000, manufactured by Otsuka Electronics Co., Ltd.), the zeta potential based on the electrophoretic light scattering method of the resin particles of Emulsion 3 was −38 mV.

<Anionic resin emulsion 4>
Similar to the preparation of anionic resin emulsion 3 except that 50 g of n-butyl acrylate, 50 g of methyl methacrylate, 2 g of acrylic acid and 5 g of sodium styrenesulfonate were used as monomers, the amount of salt and surfactant and The anionic resin emulsion 4 was adjusted by appropriately adjusting the stirring speed and the like. It was 60 nm when the average particle diameter of the resin particle of the emulsion 4 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method. Using a zeta potential measuring device (ELSZ1000, manufactured by Otsuka Electronics Co., Ltd.), the zeta potential based on the electrophoretic light scattering method of the resin particles of the emulsion 4 was −53 mV.

<Anionic resin emulsion 5>
As in the preparation of anionic resin emulsion 3, except that 50 g of n-butyl acrylate, 50 g of methyl methacrylate, 2 g of acrylic acid, and 5 g of Aqualon HS-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were used as monomers. Anionic resin emulsion 5 was prepared by appropriately adjusting the amount of salt and surfactant and the stirring speed. It was 60 nm when the average particle diameter of the resin particle of the emulsion 5 was measured using the particle size distribution measuring apparatus based on the dynamic light scattering method. Using a zeta potential measuring device (ELSZ1000, manufactured by Otsuka Electronics Co., Ltd.), the zeta potential based on the electrophoretic light scattering method of the resin particles of the emulsion 5 was measured to be −68 mV.

<Cationic resin emulsion>
To a 1 liter round bottom flask equipped with an overhead stirrer, thermocouple, condenser and inlet for addition of monomer and initiator was added 230 g deionized water, 5.0 g 50% Cavasol W7 M TL (Wacker Chemie, “Cavasol” ”Was added to the company, 0.83 g of 0.15% iron sulfate solution, and 20 g of 50% [3- (methacrylolamino) propyl] -trimethylammonium chloride solution, and stirring was started. After heating the flask to 82 ° C, 85g deionized water and 9.4g 70% Tergitol 15-S-40 (Union Carbide, "Tergitol" is a registered trademark of the company) as a surfactant A monomer emulsion was prepared by adding to a suitable container and stirred. After the surfactant was dissolved in water, 30 g of styrene was slowly added to the stirred mixture. Thereafter, 100 g of methyl methacrylate (MMA) and 70 g of 2-ethylhexyl acrylate were added to the mixture. A catalyst solution was also prepared by adding 1.1 g Vazo 56 as radical polymerization initiator and 50 g deionized water.

  At a reaction temperature of 82 ° C., 27 g of the monomer emulsion is rinsed with 10 g of deionized water, followed by 5 g of 50% Cavasol W7 M TL and 5 g of water, followed by 0.25 g of Vazo. An initiator solution of 56 and 10 g of water was added. The temperature was maintained at 77 ° C. or higher and reacted for 20 minutes. Thereafter, the monomer emulsion was supplied at a rate of 3.4 g / min for 90 minutes while the temperature was increased to 82 ° C., and at the same time, the catalyst was supplied at a rate of 0.46 g / min for 110 minutes. At the end of the monomer emulsion feed, 8.0 g of deionized water was added as rinse water. At the end of the catalyst feed, 2.0 g of rinse water was added. Thereafter, the reaction was further continued at 82 ° C. for 30 minutes. While holding, 2 g Tergitol 15-S-40 as surfactant and 10 g water were mixed and added to 0.1 g Vazo 56 and 10 g water to obtain a mixture. After the 30 minute hold was complete, the mixture was added to the kettle at a rate of 1.1 g / min for 20 minutes. At this time, 1.0 g of MMA was also added to the kettle. After the addition of the mixture was completed, the mixture was kept for 30 minutes for further reaction. Thereafter, the reaction solution was cooled to room temperature, filtered through a 100 mesh bag and a 325 mesh bag in this order, and then diluted twice with deionized water to obtain a cationic resin emulsion having a solid content of 20%.

1-4. Additives The following additives were used.
PVA: Polyvinyl alcohol 2000 (Thickener) manufactured by Kanto Chemical Co., Inc.
Megafuck: DIC Corporation, Megafuck F410 (leveling agent)
Proxel: Arch Chemical Company, Proxel GXL (preservative)

2. Preparation of water-based ink According to the composition shown in Tables 1 to 3 (units of each component are mass%), after mixing the above components, ADVATEC Teflon ("Teflon" is a registered trademark of DuPont) 3 μm membrane filter The aqueous ink 1 to the aqueous ink 30 were prepared. In addition, the numerical value described in the column of “metal nanoparticles” and various resins in Tables 1 to 3 indicates a value in terms of solid content. The numerical value described in “content of water-soluble organic solvent” is the amount of water-soluble organic solvent (unit: mass%) relative to the total mass of the water-based ink, and the numerical value described in “boiling point of water-soluble organic solvent” is water-soluble. The boiling point of organic organic solvent (unit: ° C), the numerical value described in “Ratio of polyhydric alcohol” is the amount of polyhydric alcohol (unit: mass%) relative to the total mass of water-soluble organic solvent, “solid content concentration” The numerical value described in is the amount (unit: mass%) of the solid content (metal nanoparticles, polymer dispersant and resin emulsion) relative to the total mass of the water-based ink, and the numerical value described in “PB ratio” is the amount of metal nanoparticles and high The amount (unit: mass%) of the resin emulsion with respect to the total content of the molecular dispersant is shown.

3. 3. Image formation 3-1. Substrates Using water-based inks 1 to 30, images were formed on the following substrates.
PET: Lamy Corporation, WPG2-24
Coated paper: Lamy Corporation, WRG3-36

3-2. Image formation conditions An image was formed on each of the substrates using an inkjet image forming apparatus having a piezo inkjet nozzle.

  The ink jet recording apparatus has an ink tank, an ink supply pipe, an ink supply tank immediately before the ink jet head, a filter, and a piezo type ink jet head in this order from the upstream side to the downstream side where the ink flows. It was.

  The inkjet head is driven under the conditions that the droplet amount is 14 pl, the printing speed is 0.5 m / sec, the ejection frequency is 10.5 kHz, and the printing rate is 100%, and any one of the water-based ink 1 to the water-based ink 30 is driven. Images 1 to 30 were produced by discharging and landing on the treatment agent and drying at 80 ° C. for about 5 minutes.

4). Evaluation Images 1 to 30 were evaluated according to the following criteria.

4-1. Brightness Using a spectrophotometer (U-4100) manufactured by Hitachi High-Technologies, the reflectance of images 1 to 38 is measured in the range of 380 nm to 780 nm, and based on the reflectance at 550 nm, the following criteria are used. The glitter of images 1 to 38 was evaluated.
A: Reflectance is 45% or more O: Reflectance is 35% or more and less than 45% Δ: Reflectance is 25% or more and less than 35% ×: Reflectance is less than 25%

4-2. Scratch resistance After recording, the recorded matter was left at room temperature for 1 day. Then, according to JIS K5701 (ISO 11628), using a Gakushin type friction fastness tester AB-301 (manufactured by Tester Sangyo Co., Ltd.), a white cotton cloth for friction (Kanakin 3) under the conditions of a load of 450 g and a friction frequency of 90 times. No.) and the pattern part were rubbed together. The surface state of the image (pattern) after rubbing was visually observed, and scratch resistance was evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: The surface of the image was not scratched at all.
◯: There were 1 to 4 scratches on the surface of the image.
(Triangle | delta): The surface of the image had 5-10 scratches.
X: Scratches were observed at 11 or more locations on the surface of the image.

4-3. Water resistance The ink supply tank of the inkjet image forming apparatus is filled with water-based ink 1 to water-based ink 30. At room temperature, the droplet volume is 42 pl, the printing speed is 0.5 m / sec, the ejection frequency is 10.5 kHz, and the printing rate is 100%. An image was formed under the following conditions. The obtained coating film was immersed in water for 24 hours, and a decrease in reflectance (550 nm) was evaluated.
◎: Reflectance decrease is within 5% ◯: Reflectance decrease is 5% or more and less than 15% △: Reflectance decrease is 15% or more and less than 20% ×: Reflectance decrease is 25% or more

4-4. Discharge stability The ink supply tank of the inkjet image forming apparatus is filled with water-based ink 1 to water-based ink 30. At room temperature, the droplet volume is 42 pl, the printing speed is 0.5 m / sec, the ejection frequency is 10.5 kHz, and the printing rate is 100. %, Ink composition droplets were ejected continuously for 8 hours to land on the substrate.
During 8 hours of continuous ejection, the number of missing dots, flying bends, and ink splashes on the substrate was observed visually, and based on the total number of times, the ejection stability of the ink composition was evaluated according to the following criteria: did.
◎ The number of missing dots, flying bends and ink splashes was less than 10 ○ The number of missing dots, flying bends and ink splashes was more than 10 and less than 15 △ Dot missing, flying bends and ink splashes Number of times was 15 times or more and less than 20 times × Number of missing dots, flying bends and ink splashes was 20 times or more

  Table 4 shows the evaluation results. The same evaluation was made regardless of whether an image was formed on PET or coated paper.

  A metal nanoparticle, a polymer dispersant that can be adsorbed to the metal nanoparticle, an anionic resin emulsion, and a water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower. Water-based ink 1 containing 20% by mass or more and 50% by mass or less of the total mass, and the water-soluble organic solvent contains polyhydric alcohol in an amount of 20% by mass or more and 50% by mass or less based on the total mass of the water-soluble organic solvent. -Aqueous ink 21 has high ejection stability, and image 1 to image 21 formed using these aqueous inks were also high in glitter, scratch resistance and water resistance.

  In particular, the water-based ink 11 to the water-based ink 21 whose solid content is 1.0% by mass or more and 20% by mass or less with respect to the total mass of the water-based ink have the scratch resistance and water resistance of the formed images 11 to 21. While improving, the discharge stability could be further improved.

  In addition, the water-based ink 15 to the water-based ink 21 in which the content of the anionic resin emulsion is 1.0% by mass to 15% by mass with respect to the total content of the metal nanoparticles and the polymer dispersant is formed. It was possible to further improve the glitter of the formed images while improving the scratch resistance and water resistance of the images 15 to 21 and the ejection stability.

  On the other hand, the image 22 formed using the water-based ink 22 containing no metal nanoparticles had lower glitter.

  Further, the image 23 formed using the water-based ink 23 not containing the anionic resin emulsion, and the image 24 formed using the water-based ink 24 containing the cationic resin emulsion instead of the anionic resin emulsion are scratch resistant. And water resistance was lower.

  The water-based ink 25 containing no water-soluble organic solvent, the water-based ink 26 containing a water-soluble organic solvent having a boiling point of 150 ° C. or less, and the content of the water-soluble organic solvent is 20% by mass with respect to the total mass of the water-based ink. The less water-based ink 27 had low ejection stability, and the nozzles of the inkjet head were likely to be clogged.

  In addition, the water-based ink 28 having a water-soluble organic solvent content of more than 50% by mass with respect to the total mass of the water-based ink has low ejection stability and is likely to clog the nozzles of the inkjet head, and is formed. The brightness of the image was also low. This is presumably because the water-soluble organic solvent weakens the electrostatic repulsion due to the surface charge of the metal nanoparticles or the polymer dispersant, and the dispersion stability of the water-based ink is lowered.

  In addition, the water-based ink 29 in which the content of the polyhydric alcohol is less than 10% by mass with respect to the total mass of the water-soluble organic solvent has low ejection stability and easily causes clogging of the nozzles of the inkjet head.

  Further, the water-based ink 30 having a polyhydric alcohol content of more than 50% by mass with respect to the total mass of the water-soluble organic solvent is low in ejection stability and easily causes clogging of the nozzles of the inkjet head, and is formed. The brightness of the image was also low. This is presumably because the aggregation of the metal nanoparticles was caused by the polyhydric alcohol and the dispersion stability of the water-based ink was lowered.

  The water-based ink of the present invention is excellent in ejection stability and can form an image excellent in glitter, scratch resistance and water resistance. Therefore, the present invention is expected to expand the range of application of glittering recorded materials and contribute to the advancement and spread of technology in the same field.

Claims (6)

In a water-based ink that can be ejected by an inkjet method including metal nanoparticles, a polymer dispersant that can be adsorbed to the metal nanoparticles, an anionic resin emulsion, and a water-soluble organic solvent having a boiling point of 150 ° C. or higher and 330 ° C. or lower,
The content of the water-soluble organic solvent is 20% by mass or more and 50% by mass or less with respect to the total mass of the water-based ink,
The water-soluble organic solvent contains a polyhydric alcohol in an amount of 10% by mass to 50% by mass with respect to the total mass of the water-soluble organic solvent.
Water-based ink.   The total content of the metal nanoparticles, the polymer dispersant, and the anionic resin emulsion is 1.0% by mass or more and 20% by mass or less with respect to the total mass of the water-based ink. Water-based ink.   The content of the anionic resin emulsion is 1.0% by mass or more and 15% by mass or less with respect to the total content of the metal nanoparticles and the polymer dispersant. Water-based ink.   The water-based ink according to any one of claims 1 to 3, wherein a zeta potential of the anionic resin emulsion is -100 mV or more and -5 mV or less.   5. The water-based ink according to claim 1, wherein the anionic resin emulsion has a zeta potential of −90 mV to −10 mV.   An image forming method, comprising: discharging the water-based ink droplet according to any one of claims 1 to 5 from a nozzle of an inkjet head to land on a substrate.