Aqueous overcoat liquid

Abstract

To provide an aqueous overcoat liquid excellent in tape peeling resistance and nail scratching resistance of an obtained ink-coated film even in printing to a liquid-unabsorbable printing substrate, an ink set including the aqueous overcoat liquid and an ink, and a method for printing using the aqueous overcoat liquid.SOLUTION: [1] An aqueous overcoat liquid contains a polyester resin, a wax, a water-soluble organic solvent, and water, wherein a glass transition temperature of the polyester resin is 50°C or higher, and the water-soluble organic solvent includes polyhydric alcohol and polyhydric alcohol alkyl ether. [2] An ink set includes the aqueous overcoat liquid of the [1], and an ink. [3] A method for printing includes: a process 1 of forming an image onto a printing substrate by an inkjet recording method using the ink; and a process 2 of applying the aqueous overcoat liquid of the [1] onto a surface of the image formed in the process 1 to obtain a printed matter.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous overcoat liquid, an ink set containing the aqueous overcoat liquid and an ink, and a printing method using the aqueous overcoat liquid. [Background technology]

[0002] Inkjet printing is a method of ejecting ink droplets from minute nozzles and depositing them directly onto a printing substrate to produce printed matter with recorded characters and images. This printing method has become extremely popular due to its many advantages, including the ease and low cost of producing full-color images and the ability to use a variety of printing substrates, including plain paper, label paper, and synthetic resins.

[0003] As the applications of inkjet recording expand, there is a growing demand for its application in the label and packaging fields, which have been growing in recent years. In these fields, non-absorbent synthetic resin films such as polypropylene (PP) film and polyethylene terephthalate (PET) film are primarily used as printing substrates.

[0004] For example, Patent Document 1 discloses an aqueous ink set that aims to provide an ink set and printed matter that are excellent in print image quality and water abrasion resistance, and that contains a pretreatment liquid (I), an inkjet ink (II), and an overcoat liquid (III), wherein the pretreatment liquid (I) contains a flocculant (A), the inkjet ink (II) contains a pigment, a pigment dispersion resin (B), a water-soluble organic solvent, a surfactant, and water, the overcoat liquid (III) contains an acrylic resin emulsion (C), wax particles (D), and water, the acrylic resin emulsion (C) has an acid value of 5 to 65 mgKOH / g, and the wax particles (D) contain at least one wax selected from the group consisting of carnauba wax having a melting point of 80 to 90°C and montan wax having a melting point of 80 to 90°C. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-096217 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, if the coating film durability of the ink coating film of the obtained printed matter, particularly tape peel resistance and fingernail abrasion resistance when rubbed with a fingernail, is insufficient, the ink coating film will easily peel off from the non-liquid-absorbent printing substrate, which may result in a decrease in the aesthetic appeal of the printed matter and the display of inaccurate information. Therefore, when printing on non-liquid-absorbent printing substrates such as synthetic resin films, there is a strong demand for improved tape peel resistance and fingernail abrasion resistance when rubbed with a fingernail. However, the technique disclosed in Patent Document 1 has resulted in an ink coating film with insufficient tape peel resistance and fingernail abrasion resistance. An object of the present invention is to provide an aqueous overcoat liquid, an ink set containing the aqueous overcoat liquid and an ink, and a printing method using the aqueous overcoat liquid, which provide an ink coating film with excellent tape peel resistance and fingernail abrasion resistance even when printed on a non-liquid-absorbing printing substrate. [Means for solving the problem]

[0007] The present inventors have found that the above-described problems can be solved by providing an aqueous overcoat liquid containing a polyester resin, a wax, an organic solvent, and water, in which the polyester resin has a specific glass transition temperature and the organic solvent contains a specific organic solvent. That is, the present invention relates to the following [1] to [3]. [1] An aqueous overcoat liquid to be applied onto the surface of an image formed on a printing substrate, the aqueous overcoat liquid containing a polyester resin, a wax, a water-soluble organic solvent, and water, wherein the polyester resin has a glass transition temperature of 50°C or higher, and the water-soluble organic solvent contains a polyhydric alcohol and a polyhydric alcohol alkyl ether. [2] An ink set comprising the water-based overcoat liquid according to [1] above, and an ink containing crosslinked polymer particles containing a pigment and polymer particles not containing a pigment. [3] A printing method using the aqueous overcoat liquid described in [1] above, comprising the following steps 1 and 2: Step 1: A step of forming an image on a printing substrate by an inkjet recording method using an ink containing crosslinked polymer particles containing a pigment and polymer particles not containing a pigment. Step 2: A step of applying the aqueous overcoat liquid onto the surface of the image formed in step 1 to obtain a printed matter. [Effects of the Invention]

[0008] According to the present invention, there are provided an aqueous overcoat liquid, an ink set containing the aqueous overcoat liquid and an ink, and a printing method using the aqueous overcoat liquid, which provide an ink coating film with excellent tape peel resistance and fingernail abrasion resistance even when printed on a non-liquid-absorbing printing substrate. Furthermore, the aqueous overcoat liquid of the present invention provides an ink coating film with excellent alcohol abrasion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Water-based overcoat liquid] The aqueous overcoat liquid of the present invention is an aqueous overcoat liquid that is applied onto the surface of an image formed on a printing substrate, and contains a polyester resin, a wax, a water-soluble organic solvent, and water, wherein the polyester resin has a glass transition temperature of 50°C or higher, and the water-soluble organic solvent contains a polyhydric alcohol and a polyhydric alcohol alkyl ether.

[0010] In the present invention, the term "aqueous" in the term "aqueous overcoat liquid" means that water accounts for the largest proportion by mass of the medium contained in the aqueous overcoat liquid. In this specification, the term "non-absorbent" in the context of low-absorbent printing substrates is a concept that encompasses both low absorbency and non-absorbency, and refers to a printing substrate with a water absorption of 0 g / m when the printing substrate is in contact with pure water for 100 ms. 2 More than 10g / m 2 The water absorption amount can be measured using an automatic scanning absorbency meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23°C and a relative humidity of 50%, and is defined as the amount of water transferred in a contact time of 100 msec with pure water. Furthermore, "printing" is a concept that includes printing and printed letters on which characters and images are recorded, and "printed matter" is a concept that includes printed matter and printed letters on which characters and images are recorded.

[0011] The aqueous overcoat liquid of the present invention provides an ink coating film with excellent tape peel resistance and fingernail abrasion resistance, even when printed on a non-liquid-absorbing synthetic resin film. The ink coating film also has excellent alcohol abrasion resistance. The reasons for this are not entirely clear, but are thought to be as follows. The aqueous overcoat liquid of the present invention contains a polyester resin having a glass transition temperature of 50° C. or higher. Because the glass transition temperature of the polyester resin is 50° C. or higher, which is sufficiently higher than room temperature, the polyester molecular chains are in a glassy state after the aqueous overcoat liquid dries, limiting thermal motion. This is thought to prevent entanglement of the molecules with the adhesive (glass transition temperature of approximately −50° C.) of tape or the like, resulting in good tape peel resistance. The aqueous overcoat solution of the present invention also contains a wax, which is believed to reduce the frictional resistance of the overcoat layer and thereby improve fingernail scratch resistance. Furthermore, the aqueous overcoat liquid contains a polyhydric alcohol and a polyhydric alcohol alkyl ether as a water-soluble organic solvent. The inclusion of a polyhydric alcohol is believed to suppress resin aggregation due to hydrophobic interactions, etc., thereby improving tape peel resistance and further improving alcohol abrasion resistance. Furthermore, the inclusion of a polyhydric alcohol alkyl ether is believed to enable the aqueous overcoat liquid to properly wet and spread on the surface of an image formed by inkjet printing, thereby improving tape peel resistance and further improving alcohol abrasion resistance.

[0012] [Polyester resin] The aqueous overcoat liquid of the present invention contains a polyester resin from the viewpoint of improving tape peel resistance. The polyester resin used in the aqueous overcoat liquid of the present invention contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and can be obtained by polycondensation of the alcohol component and the carboxylic acid component. That is, the polyester resin in the aqueous overcoat liquid of the present invention preferably contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component.

[0013] (alcohol content) From the viewpoint of improving the tape peel resistance of the resulting coating film, the alcohol component, which is a raw material monomer for the polyester resin, preferably contains one or more selected from aliphatic diols, aromatic diols, and alicyclic diols, and more preferably contains an aliphatic diol.

[0014] The aliphatic diol is preferably a linear aliphatic diol or an aliphatic diol having an alkyl group, particularly a methyl group, on the side chain. The carbon number of the aliphatic diol is preferably 2 or more and preferably 12 or less, more preferably 8 or less, and even more preferably 6 or less. Specifically, the aliphatic diol is preferably at least one selected from ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,3-butanediol, 2,4-pentanediol, neopentyl glycol, 2,5-hexanediol, 2,6-heptanediol, 2,7-octanediol, and 3-methyl-1,5-pentanediol, and more preferably at least one selected from ethylene glycol and neopentyl glycol. The aromatic diol may be at least one selected from alkylene oxide adducts of bisphenol A and hydrogenated bisphenol A. The alicyclic diol may be at least one selected from 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and hydrogenated bisphenol A.

[0015] The alcohol component, which is a raw material monomer for the polyester resin, may further contain an alcohol component other than the above-mentioned aliphatic diol, aromatic diol, and alicyclic diol. Examples of other alcohol components include glycerin, pentaerythritol, trimethylolpropane, sorbitol, and alkylene (having 2 to 4 carbon atoms) oxide adducts thereof (average number of added moles: 1 to 16).

[0016] The alcohol components may be used alone or in combination of two or more.

[0017] (carboxylic acid component) The carboxylic acid component, which is a raw material monomer for polyester resin, includes carboxylic acid, its acid anhydride, and its alkyl (having 1 to 3 carbon atoms) ester. From the viewpoint of improving the tape peel resistance of the resulting coating film, the carboxylic acid component preferably contains one or more selected from aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trivalent or higher polycarboxylic acids, more preferably one or more selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids, and even more preferably an aromatic dicarboxylic acid.

[0018] The aromatic dicarboxylic acid is preferably at least one selected from phthalic acid, isophthalic acid, and terephthalic acid, and more preferably at least one selected from isophthalic acid and terephthalic acid.

[0019] The aliphatic dicarboxylic acid is preferably a linear or branched aliphatic dicarboxylic acid, and the carbon number of the aliphatic dicarboxylic acid is preferably 2 or more, more preferably 4 or more, even more preferably 8 or more, and even more preferably 10 or more, and is preferably 22 or less, more preferably 18 or less, and even more preferably 16 or less. Examples of linear or branched aliphatic dicarboxylic acids include oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, succinic acids substituted with an aliphatic hydrocarbon group having from 1 to 20 carbon atoms, and anhydrides or alkyl esters thereof having from 1 to 3 carbon atoms. Examples of succinic acids substituted with an aliphatic hydrocarbon group having from 1 to 20 carbon atoms include dodecylsuccinic acid, dodecenylsuccinic acid, and octenylsuccinic acid. Among these, sebacic acid is preferred as the aliphatic dicarboxylic acid.

[0020] The alicyclic dicarboxylic acid is preferably at least one selected from cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid.

[0021] The trivalent or higher polycarboxylic acid is preferably one or more selected from trimellitic acid and pyromellitic acid, more preferably trimellitic acid. Furthermore, the trivalent or higher polycarboxylic acid is preferably trimellitic anhydride.

[0022] The carboxylic acid components can be used alone or in combination of two or more.

[0023] (Production of polyester resin) The polyester resin can be obtained by polycondensing an appropriate combination of the alcohol component and the carboxylic acid component, for example, by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere at a temperature of 150°C to 250°C, if necessary, using an esterification catalyst. Examples of the esterification catalyst include tin catalysts, titanium catalysts, and metal compounds such as antimony trioxide, zinc acetate, and germanium dioxide, among which tin catalysts are preferred from the viewpoint of esterification reaction efficiency. Preferred tin catalysts include dibutyltin oxide, tin(II) di(2-ethylhexanoate), and salts thereof, with tin(II) di(2-ethylhexanoate) being more preferred. If necessary, it is preferable to further use an esterification promoter such as gallic acid. It is also preferable to use a radical polymerization inhibitor such as 4-t-butylcatechol in combination.

[0024] (Physical properties of polyester resin) The number average molecular weight of the polyester resin is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more, from the viewpoint of improving the alcohol abrasion resistance of the resulting coating film, and is preferably 20,000 or less, more preferably 18,000 or less, and even more preferably 16,000 or less, from the viewpoint of improving the storage stability of the aqueous overcoat solution.

[0025] The glass transition temperature of the polyester resin is preferably 50°C or higher, more preferably 55°C or higher, from the viewpoint of appropriately softening the resulting coating film and improving tape peel resistance, and from the same viewpoint, is preferably 100°C or lower, more preferably 80°C or lower. The glass transition temperature is measured using a differential scanning calorimeter, specifically by the method described in the examples.

[0026] 〔wax〕 The aqueous overcoat liquid of the present invention contains a wax from the viewpoint of improving the fingernail scratch resistance of the resulting coating film. In this specification, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid when heated. Here, "semi-solid wax" means that the wax deforms and flows when force is applied to it, but can maintain a certain shape when no force is applied to it.

[0027] The wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum waxes such as paraffin wax and microcrystalline wax; vegetable waxes such as carnauba wax, candelilla wax and rice wax; and animal waxes such as lanolin and beeswax. Examples of synthetic waxes include synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax; silicone waxes; modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives; and acrylic waxes. Among these, one or more types selected from polyolefin waxes containing an olefin-based monomer as a main component and acrylic waxes are preferred, and one or more types selected from polyethylene waxes and acrylic waxes are more preferred. The waxes can be used alone or in combination of two or more.

[0028] The temperature at which the wax becomes liquid upon heating, i.e., the melting point of the wax, is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher, from the viewpoint of improving the fingernail scratch resistance of the resulting coating film, and from the same viewpoint, is preferably 160°C or lower, more preferably 150°C or lower, and even more preferably 145°C or lower.

[0029] The water-based overcoat liquid may contain wax in the form of wax particles. The wax particles are not particularly limited, and examples thereof include those in the form of a wax dispersion obtained by emulsifying wax with a known surfactant, such as a nonionic surfactant or an anionic surfactant. Examples of nonionic surfactants include ethylene oxide adducts of higher alcohols and ethylene oxide adducts of alkylated phenols. Examples of anionic surfactants include sulfates and phosphates based on ethylene oxide adducts of higher alcohols; and alkylated benzenesulfonates. Suitable examples of commercially available wax dispersions include the "Hi-Tec E" series and "Pertol E-351" manufactured by Toho Chemical Industry Co., Ltd., the "AQUACER" series manufactured by BYK, the "Cellosol" series manufactured by Chukyo Yushi Co., Ltd., the "Chemipearl" series manufactured by Mitsui Chemicals, Inc., and "ST200" manufactured by Nippon Shokubai Co., Ltd.

[0030] [Water-soluble organic solvent] The aqueous overcoat solution of the present invention contains a water-soluble organic solvent containing a polyhydric alcohol and a polyhydric alcohol alkyl ether from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that, when dissolved in 100 mL of water at 25°C, results in a dissolution volume of 10 mL or more.

[0031] (Polyhydric alcohol) As the polyhydric alcohol, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film, a diol is preferred, more preferably one or more selected from ethylene glycol, diethylene glycol, propylene glycol (1,2-propanediol), 1,3-propylene glycol, dipropylene glycol (isomer mixture), 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, triethylene glycol, polyethylene glycol, and polypropylene glycol, and even more preferably one or more selected from propylene glycol and dipropylene glycol.

[0032] (Polyhydric alcohol alkyl ether) As the polyhydric alcohol alkyl ether, a (poly)alkylene glycol monoalkyl ether is preferred from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film. Examples of the (poly)alkylene glycol monoalkyl ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol dimethyl ether, triethylene glycol monomethyl ether, and tripropylene glycol monomethyl ether. Among these, one or more selected from diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether are preferred.

[0033] SP value of polyhydric alcohol alkyl ether (unit: (cal / cm 3 ) 1 / 2) is preferably 8.3 or more, more preferably 8.5 or more, even more preferably 8.7 or more, and is preferably 9.8 or less, more preferably 9.6 or less, from the viewpoint of allowing the aqueous overcoat liquid to properly wet and spread on the surface of an image formed by inkjet printing and improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film. In this specification, the SP value is the Hildebrand solubility parameter, which is calculated by the following formula. SP value ((cal / cm 3 ) 1 / 2 )={(ΔH-RT)÷(M÷D)} 1 / 2 In the above formula, ΔH is the latent heat of vaporization (cal / mol), R is the gas constant (cal / K mol), T is the temperature (K), M is the molecular weight (g / mol), and D is the density (g / cm 3 ) are shown. The SP values above were calculated using R = 1.99 cal / K·mol and T = 298 K (25°C).

[0034] (Other water-soluble organic solvents) The aqueous overcoat solution may contain, as necessary, other water-soluble organic solvents in addition to the polyhydric alcohols and polyhydric alcohol alkyl ethers, such as polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether. Examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and ε-caprolactam. Examples of amides include formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide. Examples of amines include monoethanolamine, diethanolamine, triethanolamine, and triethylamine. Examples of sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol. In addition, for example, propylene carbonate, ethylene carbonate, etc. may also be contained.

[0035] [Surfactant] The aqueous overcoat liquid of the present invention may further contain a surfactant, preferably a nonionic surfactant, in order to improve the wettability on the surface of an image formed by an inkjet recording method and thereby improve the tape peel resistance and alcohol abrasion resistance of the resulting coating film. Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyalkylene alkyl ether surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone nonionic surfactants, and fluorine-based nonionic surfactants.

[0036] 〔water〕 The water-based overcoat solution of the present invention contains water. The water used in the aqueous overcoat solution of the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

[0037] The aqueous overcoat solution of the present invention may contain various additives such as a pH adjuster, a viscosity adjuster, an antifoaming agent, an antiseptic, and an anticorrosive as optional components depending on the intended use. In such cases, a portion of the water content may be replaced with the various additives.

[0038] (Composition of Water-Based Overcoat Solution) The content of the polyester resin in the aqueous overcoat liquid of the present invention is preferably 12% by mass or more, more preferably 14% by mass or more, and even more preferably 17% by mass or more, from the viewpoint of improving the tape peel resistance and fingernail abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 23% by mass or less.

[0039] The wax content in the aqueous overcoat liquid of the present invention is preferably 1.2% by mass or more, more preferably 1.4% by mass or more, and even more preferably 1.7% by mass or more, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 2.5% by mass or less.

[0040] The content of polyhydric alcohol in the aqueous overcoat liquid of the present invention is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 16% by mass or more, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 23% by mass or less.

[0041] The content of polyhydric alcohol alkyl ether in the aqueous overcoat liquid of the present invention is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film; and from the same viewpoint, it is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 4% by mass or less.

[0042] The content of the water-soluble organic solvent in the aqueous overcoat solution of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 27% by mass or less.

[0043] The mass ratio of the polyester resin to the wax (polyester resin / wax) in the aqueous overcoat solution of the present invention is preferably 3.0 or more, more preferably 5.0 or more, and even more preferably 7.0 or more, from the viewpoint of improving the tape peel resistance and fingernail abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 18.0 or less, more preferably 16.0 or less, and even more preferably 14.0 or less.

[0044] The mass ratio of the polyester resin to the water-soluble organic solvent (polyester resin / water-soluble organic solvent) in the aqueous overcoat liquid of the present invention is preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more, from the viewpoint of improving the tape peel resistance, fingernail abrasion resistance, and alcohol abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 1.6 or less, more preferably 1.4 or less, and even more preferably 1.2 or less.

[0045] The mass ratio of polyhydric alcohol to polyhydric alcohol alkyl ether (polyhydric alcohol / polyhydric alcohol alkyl ether) in the aqueous overcoat solution of the present invention is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 3.0 or more, from the viewpoint of improving the tape peel resistance and alcohol abrasion resistance of the resulting coating film, and from the same viewpoint, is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 7.0 or less.

[0046] The content of colorant in the aqueous overcoat liquid of the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably 0% by mass, i.e., it is even more preferable that the aqueous overcoat liquid of the present invention does not contain any colorant. If the content of the colorant in the water-based overcoat liquid of the present invention is within the above range, when printing is carried out using the water-based overcoat liquid together with an ink for ink-jet recording, an image can be formed without affecting the hue of the ink.

[0047] The aqueous overcoat liquid of the present invention is preferably used for printing on non-liquid-absorbing printing substrates, and more preferably for printing on synthetic resin films. The water-based overcoat solution of the present invention has the above-mentioned characteristics, and therefore, when printed on a non-liquid-absorbing synthetic resin film, the resulting coating film has improved coating durability. Examples of synthetic resin films include transparent synthetic resin films, such as polyester films such as polyethylene terephthalate films; vinyl chloride films; polyolefin films such as polypropylene films and polyethylene films; and polyamide films such as nylon films. These synthetic resin films may be oriented films such as biaxially oriented films and uniaxially oriented films, or may be unoriented films. It is preferable to use synthetic resin films that have been subjected to surface treatment such as corona discharge treatment.

[0048] [Ink set] The ink set of the present invention contains the above-described water-based overcoat liquid of the present invention and an inkjet recording ink described below.

[0049] <Inkjet recording ink>

[0033] The inkjet recording ink in the ink set of the present invention, together with the above-described aqueous overcoat liquid of the present invention, constitutes the ink set of the present invention. From the viewpoint of obtaining excellent coating film durability when using a non-liquid-absorbing recording medium, the inkjet recording ink preferably contains crosslinked polymer particles containing a pigment and polymer particles not containing a pigment. Furthermore, when the inkjet recording ink contains water, it is more preferable that water accounts for the largest proportion by mass of the liquid components in the ink, i.e., the inkjet recording ink is more preferably a water-based ink.

[0050] [Pigments] The pigment for the inkjet recording ink of the present invention may be any of known organic pigments and inorganic pigments. One type of pigment may be used alone, or two or more types may be used in combination, and mixed crystals may also be used. Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, etc. Carbon black produced by known methods such as a contact method, a furnace method, or a thermal method can also be used as the inorganic pigment. Examples of organic pigments include azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, and aniline black. As the pigment, hollow particles such as hollow resin particles and hollow inorganic particles can also be used. Luster pigments such as gold and silver pigments or metallic pigments can also be used.

[0051] Specific examples of pigments for black inks include inorganic pigments such as carbon black (CI Pigment Black 7); copper, iron (CI Pigment Black 11), and titanium oxide (CI Pigment Black 35); and organic pigments such as aniline black (CI Pigment Black 1). Specific examples of pigments for white ink include inorganic pigments such as titanium oxide (CI Pigment White 6). Specific examples of pigments for chromatic inks include one or more product numbers selected from the group consisting of CI Pigment Yellow, CI Pigment Orange, CI Pigment Red, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green.

[0052] The pigment in the inkjet recording ink of the present invention may be in the form of a pigment dispersed with a polymer dispersant or a surfactant as a dispersant, or in the form of a self-dispersing pigment dispersed without the use of a dispersant. The polymer dispersant may be either a water-soluble polymer or a water-insoluble polymer. Here, regarding the "water-soluble" and "water-insoluble" of a polymer, when a resin that has reached a constant weight after drying at 105°C for 2 hours is dissolved in 100 g of water at 25°C until saturation is reached, if the dissolved amount exceeds 10 g, it is judged to be "water-soluble," and if it is 10 g or less, it is judged to be "water-insoluble." Furthermore, as described below, if the polymer has anionic groups, the dissolved amount is the amount dissolved when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

[0053] Specific examples of the form of the pigment in the inkjet recording ink of the present invention, from the viewpoint of improving the dispersion stability of the pigment, include (a) a form in which a water-soluble resin is adsorbed onto the surface of the pigment, (b) a form in which a water-soluble surfactant or a water-dispersible surfactant is adsorbed onto the surface of the pigment, (c) a form in which a hydrophilic functional group is chemically or physically introduced onto the surface of the pigment and the pigment is dispersed without using a pigment dispersing resin or a surfactant, and (d) a form in which the pigment is coated with a pigment dispersing resin, etc. Among these, from the same viewpoint as above, the form of the pigment in the inkjet recording ink is preferably one or more forms selected from form (c) and form (d), and more preferably form (d).

[0054] When the pigment in the inkjet recording ink is in the form (d), the pigment dispersing resin is preferably water-insoluble. Furthermore, when the form of the pigment in the inkjet recording ink is form (d), the form in which the pigment is coated with the pigment dispersing resin includes a form in which the pigment is encapsulated in the pigment dispersing resin, a form in which the pigment is uniformly dispersed in the pigment dispersing resin, a form in which the pigment is exposed from the surface of the pigment dispersing resin particles, a form in which the pigment dispersing resin is adsorbed to the pigment, and the like. When the pigment in the inkjet recording ink is in the form (d), the pigment dispersing resin preferably has anionic properties in order to improve the dispersion stability of the pigment. The anionic group may be a group that dissociates to release a hydrogen ion, such as a carboxyl group (-COOM), a sulfonic acid group (-SO3M), or a phosphate group (-OPO3M2), or a group in the form of a dissociated ion (-COO - , -SO 3- , -OPO3 2- , (-OPO3M) - In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0055] Furthermore, when the pigment in the inkjet recording ink has the form (d), the pigment is preferably coated with a pigment dispersing resin having a crosslinked structure. In the form in which the pigment is coated with a pigment dispersing resin having a crosslinked structure, the pigment dispersing resin preferably has a structure containing a polymer component having a linear two-dimensional structure, which may have branched chains, and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a polymer having a linear two-dimensional structure, which may have branched chains, being transformed into a three-dimensional structure by the component derived from the crosslinking agent. The inkjet recording ink is preferably an ink containing pigment-containing crosslinked polymer particles and pigment-free polymer particles, that is, the ink set of the present invention preferably includes the above-mentioned water-based overcoat liquid of the present invention, and an ink containing pigment-containing crosslinked polymer particles and pigment-free polymer particles.

[0056] When the inkjet recording ink is in the form (d), the type of pigment dispersing resin used to disperse the pigment is not particularly limited. Specific examples of pigment dispersing resins include (meth)acrylic resins, styrene / (meth)acrylic resins, maleic acid resins, styrene / maleic acid resins, urethane resins, and polyester resins. Among these, from the viewpoint of improving the dispersion stability of the pigment, the pigment dispersing resin is preferably at least one selected from the group consisting of (meth)acrylic resins, styrene / (meth)acrylic resins, urethane resins, and polyester resins, and more preferably at least one selected from the group consisting of (meth)acrylic resins and styrene / (meth)acrylic resins. In this specification, "(meth)acrylic" means acrylic or methacrylic. The pigment dispersing resin may be synthesized by a known method or may be a commercially available product. The pigment dispersing resin may be used alone or in combination of two or more.

[0057] The number average molecular weight of the pigment dispersing resin is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. The number average molecular weight is measured by the method described in the Examples. The acid value of the pigment dispersing resin is preferably 5 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 80 mgKOH / g or more, and preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, even more preferably 300 mgKOH / g or less. When the pigment is in a form coated with a pigment dispersing resin having a crosslinked structure, the acid value of the pigment dispersing resin having a crosslinked structure that coats the pigment is preferably 2 mgKOH / g or more, more preferably 20 mgKOH / g or more, even more preferably 40 mgKOH / g or more, and is preferably 320 mgKOH / g or less, more preferably 200 mgKOH / g or less, even more preferably 120 mgKOH / g or less. The acid value of the pigment dispersing resin and the acid value of the pigment dispersing resin having a crosslinked structure can be determined by the method described in the Examples, but can also be calculated from the mass ratio of the constituent monomers.

[0058] [Fixing resin] The inkjet recording ink of the present invention preferably contains a resin that functions as a fixing aid (also referred to as a "fixing resin"). The fixing resin is preferably in the form of a resin that does not coat the pigment, and more preferably in the form of resin particles that do not contain a pigment. That is, the fixing resin is preferably polymer particles that do not contain a pigment. The fixing resin is not particularly limited and can be appropriately selected depending on the purpose. Specific examples of the fixing resin include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene / butadiene resin, vinyl chloride resin, styrene / acrylic resin, and acrylic silicone resin. The ink can be obtained by mixing a particulate fixing resin with a colorant, water, an organic solvent, etc. The fixing resin may be a synthesized resin or a commercially available product. The fixing resin may be used alone or in combination of two or more.

[0059] 〔wax〕 The inkjet recording ink of the present invention may contain wax from the viewpoint of improving the durability of the coating film. As the wax for the ink jet recording ink, the same waxes as those exemplified for the water-based overcoat liquid are preferably used.

[0060] 〔water〕 The inkjet recording ink contains water. The water used in the inkjet recording ink is preferably pure water or ion-exchanged water from the viewpoint of preventing contamination with unintended substances.

[0061] [Water-soluble organic solvent] The inkjet recording ink of the present invention may further contain a water-soluble organic solvent. Suitable examples of the water-soluble organic solvent for the inkjet recording ink include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds, similar to the water-soluble organic solvents exemplified for the aqueous overcoat liquid. Among these, the water-soluble organic solvent for the inkjet recording ink is preferably at least one selected from polyhydric alcohols and polyhydric alcohol alkyl ethers, and more preferably at least one selected from propylene glycol, diethylene glycol monoisobutyl ether, and diethylene glycol monoethyl ether.

[0062] [Surfactant] The inkjet recording ink may further contain a surfactant, preferably a nonionic surfactant, from the viewpoint of improving wettability to a recording medium and improving coating durability. Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyalkylene alkyl ether surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone nonionic surfactants, fluorine nonionic surfactants, etc. Among these, one or more selected from acetylene glycol surfactants and silicone nonionic surfactants are preferred, and one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol and its ethylene oxide adduct, and polyether-modified silicone are more preferred. Commercially available nonionic surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd., the "Silface SAG" series manufactured by Nissin Chemical Industry Co., Ltd., and the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd. The surfactants can be used alone or in combination of two or more.

[0063] The inkjet recording ink may contain various additives as optional components depending on the application, such as a pH adjuster, a viscosity adjuster, an antifoaming agent, an antiseptic, and an anticorrosive agent. In such cases, a portion of the water may be replaced with the various additives.

[0064] (Composition of inkjet recording ink) From the viewpoint of improving the image density of printed matter, the content of the pigment in the inkjet recording ink is preferably 2% by mass or more, more preferably 2.5% by mass or more, even more preferably 3% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 7% by mass or less.

[0065] When the inkjet recording ink contains a pigment dispersing resin, the content of the pigment dispersing resin in the ink is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more, from the viewpoint of pigment dispersion stability, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of improving the image density of printed matter.

[0066] When the inkjet recording ink contains a pigment dispersion resin, the mass ratio of the pigment content to the pigment dispersion resin content in the ink [pigment / pigment dispersion resin] is preferably 0.30 or more, more preferably 0.50 or more, and even more preferably 0.70 or more, from the viewpoint of improving the image density of the printed matter, and is preferably 1.00 or less, more preferably 0.90 or less, and even more preferably 0.80 or less, from the viewpoint of the dispersion stability of the pigment.

[0067] When the inkjet recording ink contains a fixing resin, the content of the fixing resin in the ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of improving the coating durability, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, from the viewpoint of improving the image density of the printed matter.

[0068] When the inkjet recording ink contains a wax, the content of the wax in the ink is, from the viewpoint of improving the durability of the coating film, preferably 0.3% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.8% by mass or more, and is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less.

[0069] When the inkjet recording ink contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the ink is, from the viewpoint of improving coating durability, preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and still more preferably 20% by mass or less.

[0070] From the viewpoint of environmental friendliness, the water content in the inkjet recording ink is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, and still more preferably 60% by mass or more, and is preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0071] [Printing method] The printing method of the present invention is a method of forming an image on a recording medium by inkjet recording using the above-mentioned inkjet recording ink, and then applying the above-mentioned aqueous overcoat liquid onto the surface of the image. The recording method of the present invention preferably includes the following steps 1 and 2. A printing method using the aqueous overcoat liquid according to claim 1 or 2, comprising the following steps 1 and 2: Step 1: A step of forming an image on a printing substrate by an inkjet recording method using an ink containing crosslinked polymer particles containing a pigment and polymer particles not containing a pigment. Step 2: A step of applying the aqueous overcoat liquid onto the surface of the image formed in step 1 to obtain a printed matter.

[0072] (Process 1) Step 1 is a step of forming an image on a recording medium by an inkjet recording method using the inkjet recording ink. The printing substrate used in the present invention is preferably a non-liquid-absorbing printing substrate, and more preferably a synthetic resin film.As the synthetic resin film, as described above, a transparent synthetic resin film can be used, for example, a polyester film such as a polyethylene terephthalate film; a vinyl chloride film; a polyolefin film such as a polypropylene film or a polyethylene film; a polyamide film such as a nylon film.These synthetic resin films can be oriented films such as a biaxially oriented film or a uniaxially oriented film, or can be unoriented films.In addition, it is preferable to use these synthetic resin films that have been surface-treated, such as by corona discharge treatment. The ink for inkjet recording is loaded into a known inkjet recording device, and an image can be formed by being deposited as ink dots on the surface of the image formed in step 1. The inkjet recording device can be of any type, such as a thermal type or a piezo type.

[0073] (Process 2) Step 2 is a step of applying the water-based overcoat liquid onto the surface of the image formed in step 1. The method for applying the aqueous overcoat liquid onto the surface of the image formed in step 1 is not particularly limited, and preferred methods include immersion, roller coating, spray coating, brush coating, and coating by inkjet recording, etc. Among these, roller coating is more preferred from the viewpoint of being able to apply the aqueous overcoat liquid simply and uniformly. Specific examples of rollers used for roller application include offset gravure coaters, gravure coaters, doctor coaters, bar coaters, blade coaters, flexo coaters, and roll coaters. Of these, bar coaters are more preferred.

[0074] The amount of the aqueous overcoat liquid applied is preferably 5.0 g / m from the viewpoint of improving the durability of the coating film. 2 More preferably, 6.0 g / m 2 More preferably, 7.0 g / m 2 From the same viewpoint as above, it is preferably 20.0 g / m 2 or less, more preferably 18.0 g / m 2 More preferably 16.0 g / m or less 2 The following is the result. [Example]

[0075] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0076] [Measurement method] (1) Number average molecular weight (Mn) of the polymer The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H," "TSKgel SuperAW3000," and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights, "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (both manufactured by Tosoh Corporation) The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring the mixture with a magnetic stirrer at 25°C for 10 hours, and filtering the mixture through a syringe filter "DISMIC-13HP" (manufactured by Advantech Co., Ltd., pore size: 0.2 μm, material: PTFE).

[0077] (2) Measurement of the acid value of the polymer The resin was dissolved in a titration solvent (toluene:acetone = 2:1 (volume ratio)) mixed with toluene and acetone in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0078] (3) Measurement of the glass transition temperature of polymers Using a differential scanning calorimeter (TA Instruments Japan, "Q-100"), 0.01-0.02 g of sample was weighed into an aluminum pan and heated from room temperature (20 °C) to 200 °C at a heating rate of 10 °C / min, then cooled to 0 °C at a cooling rate of 10 °C / min. The sample was then heated to 180 °C at a heating rate of 10 °C / min, and the glass transition temperature was determined as the temperature at the intersection of the extension of the baseline below the maximum endothermic peak temperature and the tangent line showing the maximum slope from the rising part of the peak to the peak apex.

[0079] (4) Measurement of solid concentration Using an infrared moisture meter ("FD-230" manufactured by Kett Electric Laboratory Co., Ltd.), 5 g of the measurement sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and the moisture content (mass%) of the measurement sample was measured, and the solid content (mass%) was calculated using the following formula. Solid concentration (mass%) = 100 - moisture content of measurement sample (mass%)

[0080] (5) Measurement of the average particle size of pigment-containing polymer particles Cumulant analysis was performed using a laser particle analysis system (Otsuka Electronics Co., Ltd., "ELS-8000") to measure the average particle size. -3 The dispersion was diluted with water to a mass % (solid content equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion medium, and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing polymer particles in the aqueous dispersion.

[0081] (Production of pigment dispersion resin) Production Example 1-1 (Production of Water-Insoluble Polymer P-1) A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. In a reaction vessel, 10 parts of methyl ethyl ketone (hereinafter also referred to as "MEK"), 0.2 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the monomer mixture were placed and mixed, and the inside of the vessel was thoroughly purged with nitrogen gas. Meanwhile, a mixture of the remaining monomer mixture (90% of the monomer mixture), 0.13 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo-based radical polymerization initiator was placed in a dropping funnel. The monomer mixture in the reaction vessel was heated to 65°C under a nitrogen atmosphere with stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C from the end of the dropping, a solution of 0.1 parts of the polymerization initiator in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours, followed by drying under reduced pressure to obtain water-insoluble polymer P-1 (number average molecular weight: 19,000, acid value: 240 mgKOH / g).

[0082] Production Example 1-2 (Production of Water-Insoluble Polymer P-2) A water-insoluble polymer P-2 (number average molecular weight: 18,000, acid value: 91 mgKOH / g) was obtained in the same manner as in Production Example 1-1, except that the monomer composition in Production Example 1-1 was changed to that shown in Table 1.

[0083] [Table 1]

[0084] (Preparation of aqueous dispersion of pigment-free polymer particles) Production Example 2 (Production of aqueous dispersion of polymer particles 1 containing no pigment) In a reaction vessel equipped with a dropping funnel, the monomers shown in "Initial Charge Monomer Solution" in Table 2, sodium polyoxyethylene alkyl ether sulfate ("Latemul E-118B" manufactured by Kao Corporation) (hereinafter referred to as "Latemul E-118B") as a surfactant, potassium persulfate (manufactured by Fujifilm Wako Pure Chemical Industries) as a polymerization initiator, and ion-exchanged water were mixed and purged with nitrogen gas to obtain an initial charge monomer solution. Furthermore, the monomers, surfactants, polymerization initiator, and ion-exchanged water shown in "Monomer Solution to Be Added" in Table 2 were mixed to obtain a dropping monomer solution, which was placed in the dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the initial monomer solution in the reaction vessel was heated from room temperature to 80°C over 30 minutes while stirring. While maintaining the temperature at 80°C, the monomer in the dropping funnel was gradually added dropwise to the reaction vessel over 3 hours. After the addition was completed, the mixture was stirred for 1 hour while maintaining the temperature inside the reaction vessel. The mixture was then filtered through a 200 mesh filter to obtain an aqueous dispersion of pigment-free polymer particles 1 (solids concentration: 44.1%). The resin constituting the pigment-free polymer particles 1 had a number average molecular weight of 18,000 and an acid value of 16 mgKOH / g.

[0085] [Table 2]

[0086] (Preparation of aqueous dispersion of pigment-containing polymer particles) Production Example 3-1 (Preparation of aqueous dispersion of pigment-containing polymer particles Bk-1) 100 parts of the water-insoluble polymer P-1 obtained in Production Example 1-1 (pigment dispersion resin) was mixed with 78.6 parts of MEK, and 41.2 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide content: 16.9%) was added as a neutralizer to neutralize (neutralization degree: 40 mol%). 800 parts of ion-exchanged water was then added, followed by 100 parts of black pigment (CB, CI Pigment Black 7 (carbon black), Cabot Chemical Company, "Monarch 717"), and the mixture was stirred for 60 minutes at 20°C using a disperser (Asada Iron Works, Inc., "Ultra Disperser") with the disperser blade rotating at 7000 rpm. The resulting mixture was then dispersed in a Microfluidizer (Microfluidics, Inc., product name) for 10 passes at 200 MPa. Next, 250 parts of ion-exchanged water was added to the resulting dispersion and stirred. After that, MEK was removed under reduced pressure at 60°C, and some of the water was further removed until the pigment concentration reached 10%. 35.7 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) was added as a crosslinker, and the mixture was sealed. It was heated at 70°C for 5 hours while stirring with a stirrer, and then cooled to room temperature to obtain an aqueous dispersion of pigment-containing polymer particles Bk-1 (crosslinking rate: 60 mol%) (solids concentration: 23.4%, pigment content: 9.7%, acid value: 96 mgKOH / g (calculated value)).

[0087] Production Example 3-2 (Preparation of aqueous dispersion of pigment-containing polymer particles Bk-2) In Production Example 3-1, the water-insoluble polymer P-2 obtained in Production Example 1-2 was used as the pigment dispersing resin, and a water dispersion of pigment-containing polymer particles Bk-2 was obtained in the same manner, except that crosslinking treatment with a crosslinking agent was not performed.

[0088] [Table 3]

[0089] (Production of Water Dispersion of Polyester Resin) Production Example 4-1 (Production of Water Dispersion of Polyester Resin PES-1) (1) Manufacture of polyester resin PES-1 A 10-L four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser with a dehydration tube, and a nitrogen inlet tube was charged with the raw material monomers (alcohol components and carboxylic acid components other than trimellitic anhydride), an esterification catalyst (tin(II) di(2-ethylhexanoate)), and an esterification co-catalyst (gallic acid) shown in Table 4, and the mixture was heated to 235°C using a mantle heater while stirring (300 rpm) under a nitrogen atmosphere and atmospheric pressure. After reaction for 5 hours, the pressure in the flask was reduced to 8.3 kPa, and the mixture was stirred for 1 hour. After that, the mixture was cooled to 180°C and returned to atmospheric pressure, after which trimellitic anhydride and 4-t-butylcatechol were added, the temperature was raised to 210°C, and the mixture was allowed to react for 1 hour. After that, the pressure inside the flask was reduced to 8.3 kPa, and the mixture was allowed to react for a further 2 hours to obtain polyester resin PES-1. (2) Preparation of aqueous dispersion of polyester resin PES-1 80 parts of the polyester resin PES-1 obtained in (1) and 120 parts of MEK were further mixed, and 1.0 part of a 5N aqueous sodium hydroxide solution (sodium hydroxide content: 16.9%) was added as a neutralizing agent to neutralize the mixture. Next, 400 parts of ion-exchanged water was added to the resulting solution, and after stirring, the MEK was removed at 60°C under reduced pressure, and then some of the water was removed to obtain an aqueous dispersion of polyester resin PES-1 (solid concentration: 40.0%).

[0090] Production Examples 4-2 and 4-3 (Production of Water Dispersion of Polyester Resin PES-2 and Water Dispersion of Polyester Resin PES-3) A water dispersion of polyester resin PES-2 and a water dispersion of polyester resin PES-3 were obtained in the same manner as in Production Example 4-1, except that the raw material monomers were changed as shown in Table 4.

[0091] [Table 4]

[0092] (Preparation of Water-Based Ink) Preparation Example 1-1 (Preparation of Water-Based Ink Ink-1) To obtain the composition of the water-based ink shown in Table 5 (total 100 parts), 32.9 parts of an aqueous dispersion of pigment-containing polymer particles Bk-1 obtained in Production Example 3-1 (solid content concentration: 23.4%, pigment content: 9.7%), 11.3 parts of an aqueous dispersion of pigment-free polymer particles 1 obtained in Production Example 2 (solid content concentration: 44.1%), 11.5 parts of propylene glycol, 3.5 parts of diethylene glycol monoisobutyl ether, and acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name PG-100) were mixed. A water-based ink, Ink-1, was obtained by mixing and stirring 1.0 part of Surfynol 104-PG50 (a propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content 50%), 0.2 parts of a silicone surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: SAG-005), and 39.5 parts of ion-exchanged water, and filtering the mixture through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate).

[0093] Preparation Examples 1-2 and 1-3 (Preparation of Water-Based Inks Ink-2 and Ink-3) Water-based inks Ink-2 and Ink-3 were obtained in the same manner as in Preparation Example 1-1, except that the composition of the water-based ink was changed to the conditions shown in Table 5.

[0094] (Preparation of Water-Based Overcoat Solution) Preparation Example 2-1 (Preparation of Water-Based Overcoat Solution OC-1) To obtain the aqueous overcoat liquid composition shown in Table 5 (100 parts in total), 50 parts of the aqueous dispersion of polyester resin PES-1 obtained in Production Example 4-1 (solid content concentration: 40.0%), 5.7 parts of wax ("Pertol E-351" manufactured by Toho Chemical Industry Co., Ltd. (solid content 35%)), 20.0 parts of propylene glycol, 3.0 parts of diethylene glycol monoisobutyl ether, and 21.3 parts of ion-exchanged water were mixed and stirred, and the mixture was filtered through a membrane filter (manufactured by Sartorius, trade name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous overcoat liquid OC-1.

[0095] Preparation Examples 2-2 to 2-20 (Preparation of Water-Based Overcoat Solutions OC-2 to OC-20) Water-based overcoat solutions OC-2 to OC-20 were obtained in the same manner as in Preparation Example 2-1, except that the composition of the water-based overcoat solution in Preparation Example 2-1 was changed to the conditions shown in Table 5. The water-based overcoat solution OC-19 in Preparation Example 2-19 is a water-based overcoat solution containing no wax, and the water-based overcoat solution OC-20 in Preparation Example 2-20 is a water-based overcoat solution containing no polyhydric alcohol alkyl ether.

[0096] Examples 1 to 20 and Comparative Examples 1 to 2 The aqueous inks and aqueous overcoat solutions obtained in Preparation Examples 1-1 to 1-3 and 2-1 to 2-20 were combined to form aqueous ink sets as shown in Table 5, and printed materials were produced by the following steps 1 and 2. Using the resulting printed materials, tape peel resistance, fingernail scratch resistance, and alcohol scratch resistance were evaluated by the following methods (1) to (3). The results are shown in Table 5.

[0097] (Process 1) Using a water-based ink, an image was formed on an A4-sized polypropylene film (manufactured by Futamura Chemical Co., Ltd., trade name: FOR-AQ, non-absorbent printing substrate) as a non-absorbent printing substrate by the following inkjet recording method. In an environment with a temperature of 25±1°C and a relative humidity of 30±5%, a printing evaluation device (manufactured by Tritec Corporation) equipped with an inkjet head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) was filled with water-based ink. The settings were head voltage 26V, frequency 10 kHz, ejection liquid volume 12 pL, head temperature 32°C, resolution 600 dpi, pre-ejection flushing count 200 shots, and negative pressure -4.0 kPa. The recording medium was fixed to the conveying table under reduced pressure with the longitudinal direction of the recording medium aligned with the conveying direction. A printing command was transferred to the printing evaluation device, and a solid image was printed at 100% duty. (Process 2) Next, a water-based overcoat liquid was applied onto the surface of the obtained solid image using a bar coater No. 3 to obtain a printed matter.

[0098] [Evaluation method] (1) Evaluation of tape peel resistance Tape (Cellotape (registered trademark), 18 mm wide, CT-18S, manufactured by Nichiban Co., Ltd.) was applied to the printed matter obtained above, and the edge of the tape was quickly peeled off at a 90° angle. The image area after peeling was binarized using a print density value that was half the print density value of the solid image area before tape peeling as a threshold value, and the peeled and non-peeled areas were calculated by image analysis. The area ratio of the non-peeled areas was calculated as the coating film remaining rate (%) after the tape peeling test. The higher the value, the better the tape peel resistance, and if it is 70% or more, there is no problem in practical use.

[0099] (2) Evaluation of fingernail scratch resistance The print obtained above was rubbed back and forth with a fingernail 50 times. The area of the solid image with remaining coating after rubbing was calculated by image analysis, and the image after rubbing was binarized using a print density value that was half the print density value of the solid image before the fingernail scratch resistance test. The remaining and non-remaining areas of the coating were calculated by image analysis, and the area ratio of the remaining coating area was calculated as the fingernail scratch resistance (%). The higher the value, the better the resistance to fingernail abrasion, and a value of 70% or more is acceptable for practical use.

[0100] (3) Evaluation of alcohol abrasion resistance The print obtained above was rubbed back and forth 50 times with a cotton swab soaked in 70% ethanol aqueous solution. The area of the solid image with remaining coating after rubbing was calculated using image analysis, and the image area after rubbing was binarized using a print density value that was half the print density value of the solid image area before the alcohol rub resistance test. The area with and without remaining coating was calculated using image analysis, and the area ratio of the remaining coating area was calculated as the alcohol rub resistance (%). The higher the value, the better the resistance to alcohol abrasion, and a value of 70% or higher is acceptable for practical use.

[0101] The notations in Table 5 are as follows: <Composition of water-based ink> (pigment) Carbon black: Cabot Chemical Company, trade name "Monarch 717", CB, CI Pigment Black 7 (carbon black) (surfactant) Surfynol 104-PG50: Manufactured by Nissin Chemical Industry Co., Ltd., product name "Surfynol 104-PG50", acetylene glycol surfactant (2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol, active ingredient 50%) SAG-005: Nissin Chemical Industry Co., Ltd., product name "SAG-005", Nissin Chemical Industry Co., Ltd., product name: SAG-005, silicone surfactant, <Composition of water-based overcoat solution> (wax) Pertol E-351: Toho Chemical Industry Co., Ltd., trade name "Pertol E-351", polyethylene wax emulsion (wax emulsion dispersed with a nonionic surfactant), melting point 130°C, particle size 150 nm, solid content 35% Hi-Tech E-6500: Toho Chemical Industry Co., Ltd., product name "Hi-Tech E-6500", polyethylene wax emulsion (wax emulsion dispersed with a nonionic surfactant), melting point 140°C, particle size 80nm, solids concentration 35% ST200: Manufactured by Nippon Shokubai Co., Ltd., product name "ST200", (wax emulsion composed of acrylic polymer), melting point 46°C, particle size 171nm, solid content 40% (Polyhydric alcohol alkyl ether) Diethylene glycol monoisobutyl ether: SP value 8.7 Tripropylene glycol monomethyl ether: SP value 9.1 Propylene glycol monopropyl ether: SP value 9.4 Diethylene glycol monobutyl ether: SP value 8.9 Dipropylene glycol monomethyl ether: SP value 9.6

[0102] [Table 5]

[0103] Table 5 shows that the aqueous overcoat liquids of the Examples have excellent storage stability, and that the recorded materials obtained using the aqueous overcoat liquids of the Examples have excellent coating durability (tape peel resistance, fingernail abrasion resistance, and alcohol abrasion resistance). On the other hand, Comparative Example 1 shows that the absence of wax in the aqueous overcoat solution results in poor fingernail scratch resistance, and Comparative Example 2 shows that the absence of polyhydric alcohol alkyl ether in the aqueous overcoat solution results in poor tape peel resistance. [Industrial Applicability]

[0104] According to the present invention, it is possible to provide an aqueous overcoat liquid, an ink set containing the aqueous overcoat liquid and an ink, and a printing method using the aqueous overcoat liquid, which provide an ink coating film that has excellent tape peel resistance and fingernail abrasion resistance even when printed on a non-liquid-absorbing printing substrate.

Claims

1. A water-based overcoat liquid applied onto the surface of an image formed on a printing substrate, The composition contains a polyester resin, a wax, a water-soluble organic solvent, and water, The glass transition temperature of the polyester resin is 50°C or higher, The water-based overcoat liquid, wherein the water-soluble organic solvent contains a polyhydric alcohol and a polyhydric alcohol alkyl ether.

2. 2. The water-based overcoat liquid according to claim 1, wherein the number average molecular weight of the polyester resin is 5,000 or more and 20,000 or less.

3. 3. The water-based overcoat liquid according to claim 1, wherein the content of the polyester resin in the water-based overcoat liquid is 12% by mass or more and 30% by mass or less.

4. 3. The water-based overcoat liquid according to claim 1, wherein the content of the wax in the water-based overcoat liquid is 1.2% by mass or more.

5. 3. The aqueous overcoat liquid according to claim 1, wherein the polyhydric alcohol is at least one selected from the group consisting of propylene glycol and dipropylene glycol.

6. 3. The aqueous overcoat liquid according to claim 1, wherein the content of the polyhydric alcohol in the aqueous overcoat liquid is 10% by mass or more and 30% by mass or less.

7. 3. The water-based overcoat liquid according to claim 1, wherein the polyhydric alcohol alkyl ether has an SP value of 8.3 or more and 9.8 or less.

8. 3. The aqueous overcoat liquid according to claim 1, wherein the polyhydric alcohol alkyl ether is at least one selected from the group consisting of diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether.

9. 3. The water-based overcoat liquid according to claim 1, wherein the content of the polyhydric alcohol alkyl ether in the water-based overcoat liquid is 10% by mass or less.

10. 3. The water-based overcoat liquid according to claim 1, wherein the polyester resin contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, the alcohol component contains an aliphatic diol, and the carboxylic acid component contains an aromatic dicarboxylic acid.

11. 3. The water-based overcoat liquid according to claim 1, which is used for printing on a synthetic resin film.

12. An ink set comprising the water-based overcoat liquid according to claim 1 or 2, and an ink containing crosslinked polymer particles containing a pigment and polymer particles not containing a pigment.

13. A printing method using the aqueous overcoat liquid according to claim 1 or 2, comprising the following steps 1 and 2: Step 1: A step of forming an image on a printing substrate by an inkjet recording method using an ink containing pigment-containing crosslinked polymer particles and pigment-free polymer particles. Step 2: A step of applying the aqueous overcoat liquid onto the surface of the image formed in step 1 to obtain a printed matter.

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