Ink set

Abstract

To provide an aqueous ink and an overcoat liquid with favorable ink storage stability, adhesion to substrates, resistance to scratching, and resistance to alcohol.SOLUTION: An ink set comprises an aqueous ink (A) containing a pigment and an aqueous overcoat liquid (B), wherein the aqueous ink (A) contains a water-insoluble polyester resin, and the aqueous overcoat liquid (B) contains a water-soluble polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink set comprising a water-based ink and an overcoat liquid that can be used on non-absorbent substrates. [Background technology]

[0002] After printing ink onto a non-absorbent substrate such as PET film or OPP film, a method of forming a protective layer on the surface of the printed layer using an overcoat liquid is being considered in order to improve the performance of the ink printing coating.

[0003] For example, Patent Document 1 describes an overcoat agent containing a binder resin and an isocyanate curing agent for forming a transparent protective layer to be placed on a printed layer, wherein the binder resin contains a polyester-based resin in an amount of 30% by mass or more of the entire binder resin, and the polyester-based resin contains structural units derived from a dibasic acid and a polyhydric alcohol in an amount of 50% by mass or more of the entire polyester-based resin, and either or both of the binder resin and the isocyanate curing agent have at least one cyclic structure selected from an aromatic group, an alicyclic group, and a pyranose group. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-138856 Summary of the Invention [Problem to be solved by the invention]

[0005] However, overcoat solutions using curing agents as described in patent documents have concerns about viscosity changes during storage. In addition, the overcoat solutions are non-aqueous and have unsatisfactory odors. To solve this problem, it is necessary to convert the ink and overcoat solution to aqueous systems. However, if they are converted to aqueous systems, the coated substrate is cooled by the heat of vaporization associated with the evaporation of water during the drying process after coating, which can lead to insufficient resin film formation and insufficient strength of the ink and overcoat coating. Furthermore, when applied to PET substrates that are thermally shaped or shrunk after printing, such as food trays made from amorphous polyethylene terephthalate (hereinafter also referred to as A-PET) or shrink film made from shrink PET, the amount of heat that can be applied during the drying process is limited, making it more difficult to achieve sufficient coating strength when converted to aqueous systems. Therefore, an object of the present invention is to provide a novel water-based ink and overcoat liquid that has good storage stability and gives a coating film on a printed matter that has good adhesion, scratch resistance, and alcohol resistance. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that when an ink set comprising a pigment-containing water-based ink (A) and a water-based overcoat liquid (B), wherein the water-based ink (A) contains a water-insoluble polyester resin and the water-based overcoat liquid (B) contains a water-soluble polyester resin, is used, the ink set has good storage stability, and the resulting printed matter has excellent coating film adhesion, scratch resistance, and alcohol resistance, and has completed the present invention. [Effects of the Invention]

[0007] According to the present invention, there are provided a water-based ink and an overcoat liquid which have good storage stability, adhesion to substrates, scratch resistance, and alcohol resistance. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0009] The ink set of the present disclosure is an ink set having a pigment-containing water-based ink (A) and a water-based overcoat liquid (B), characterized in that the water-based ink (A) contains a water-insoluble polyester resin and the water-based overcoat liquid (B) contains a water-soluble polyester resin. The term "aqueous system" means that an aqueous medium is used, and the aqueous medium means a medium in which water accounts for the largest proportion of the medium.

[0010] <Water-based ink (A)> The water-based ink (A) of the present disclosure is a water-based ink containing a pigment. Pigments used in the water-based ink (A) of the present disclosure include organic pigments and inorganic pigments, but the pigments used are not particularly limited.

[0011] Examples of organic pigments of the present disclosure include azo pigments such as benzidine and Hansa Yellow, azomethine pigments, methine pigments, anthraquinone pigments, phthalocyanine pigments such as phthalocyanine blue, perinone pigments, perylene pigments, diketopyrrolopyrrole pigments, thioindigo pigments, iminoisoindoline pigments, iminoisoindolinone pigments, quinacridone pigments such as quinacridone red and quinacridone violet, flavanthrone pigments, indanthrone pigments, anthrapyrimidine pigments, carbazole pigments, monoarylide yellow, diarylide yellow, benzimidazolone yellow, tolyl orange, naphthol orange, and quinophthalone pigments, but the present invention is not limited to these examples. These organic pigments may be used alone or in combination of two or more. Preferred organic pigments include, for example, CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green.

[0012] Examples of inorganic pigments of the present disclosure include titanium dioxide, antimony trioxide, zinc oxide, lithopone, white lead, red iron oxide, black iron oxide, iron oxide, chromium oxide green, carbon black, yellow lead, molybdenum red, ferric ferrocyanide (Prussian blue), ultramarine, and lead chromate; flat-shaped pigments such as mica, clay, aluminum powder, talc, and aluminum silicate; and extender pigments such as calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, and magnesium carbonate; but the present invention is not limited to these examples. These inorganic pigments may be used alone or in combination of two or more.

[0013] The water-based ink (A) of the present disclosure contains a water-insoluble polyester resin. That is, the water-based ink (A) is an aqueous dispersion containing a water-insoluble polyester resin, and is an aqueous dispersion containing a pigment and a water-insoluble polyester resin. In this specification, the term "water-insoluble polyester resin" does not strictly refer to a physicochemical substance, but includes those that are dispersible in water, and refers to commercially available products sold as water-insoluble polyester resins or water dispersions. The water-insoluble polyester resin of the present disclosure is in the form of an aqueous dispersion, and the average particle size of the water-insoluble polyester resin in the aqueous dispersion is preferably 85 nm or more, more preferably 90 nm or more, and even more preferably 100 nm or more. The average particle size of the polymer particles may be determined by the volume-based cumulant average particle size measured by dynamic light scattering.

[0014] The water-insoluble polyester resin of the present disclosure is not particularly limited as long as it satisfies the above physical properties, but it can be a polyester produced by polycondensation of an aromatic dicarboxylic acid or its ester, such as terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid, with a glycol, such as ethylene glycol, diethylene glycol, 1,4-butanediol, or neopentyl glycol. These polyesters can be produced by directly reacting an aromatic dicarboxylic acid with a glycol, or by transesterification of an alkyl ester of an aromatic dicarboxylic acid with a glycol followed by polycondensation, or by polycondensation of a diglycol ester of an aromatic dicarboxylic acid. Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene-2,6-naphthalate. These polyesters may be homopolymers or copolymers containing a third component. Commercially available products for use in the water-insoluble polyester resin of the present disclosure include Vylonal MD-1200, MD-1228, MD-1500, MD-2000, MD-1480, and MD-1985 manufactured by Toyobo MC Co., Ltd., and the Elitel series manufactured by Unitika Ltd.

[0015] The glass transition temperature of the water-insoluble polyester resin of the present disclosure is −20° C. or higher, preferably 0° C. or higher, and more preferably 10° C. or higher, from the viewpoint of blocking resistance, and is 80° C. or lower, preferably 60° C. or lower, and more preferably 40° C. or lower, from the viewpoint of fixability. The number average molecular weight (Mn) of the water-insoluble polyester resin of the present disclosure is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 12,000 or more, and is preferably 50,000 or less, and more preferably 20,000 or less, from the viewpoint of adhesion to substrates (particularly PET films and OPP films). The number average molecular weight of the water-insoluble polyester resin of the present disclosure can be measured using a known method, specifically, gel permeation chromatography (GPC) using tetrahydrofuran as an eluent. The number average molecular weight (Mn) of the water-insoluble polyester resin of the present disclosure can also be measured using the catalog value of a commercially available product.

[0016] The water-insoluble polyester resin of the present disclosure is preferably in the form of a water dispersion. The water-insoluble polyester resin of the present disclosure may contain a surfactant together with the water-insoluble polyester. As the surfactant contained in the water-insoluble polyester resin of the present disclosure, a conventionally known surfactant such as a nonionic surfactant, an anionic surfactant, a cationic surfactant, or an amphoteric surfactant can be used. These surfactants may be used alone or in combination of two or more.

[0017] The aqueous ink of the present disclosure may contain other binder resins besides the water-insoluble polyester resin, such as vinyl resins, (meth)acrylic resins, olefin resins, urethane resins, fluorine-containing resins, silicone resins, epoxy resins, phenoxy resins, phenolic resins, and xylene resins, as long as the object of the present disclosure is not impaired. The content of polymer particles composed of the water-insoluble polyester resin in 100% by mass of the binder resin contained in the ink of the present invention is preferably 70 to 100% by mass, more preferably 85% by mass or more, and even more preferably 95% by mass or more. The other binder resins are also preferably added as polymer particles composed of the resin.

[0018] The water-based ink (A) of the present disclosure is characterized by containing water as a medium, but may also contain a water-soluble organic solvent other than water. Specific examples of the water-soluble organic solvent used in the water-based ink (A) of the present disclosure include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and tert-butyl alcohol (preferably C 1-4 alcohol); glycols such as propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-hexanediol, dipropylene glycol, tripropylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; Glycerin; Ethylene glycol monoalkyl ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, etc.) 1-4 alkyl ether), propylene glycol monoalkyl ether (e.g., propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol monobutyl ether, propylene glycol monoisobutyl ether, etc.) 1-4 alkylene glycol monoalkyl ethers (preferably C alkyl ethers) 2-4 Alkylene glycol mono C 1-4 alkyl ethers); Diethylene glycol monoalkyl ethers (e.g., diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, etc.)1-4 alkyl ether), dipropylene glycol monoalkyl ether (e.g., dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monoisobutyl ether, etc.) 1-4 Dialkylene glycol monoalkyl ethers (preferably diC alkyl ethers) 2-4 Alkylene glycol mono C 1-4 alkyl ethers);

[0019] Polyethylene glycol monoalkyl ethers (e.g., polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polyethylene glycol monopropyl ether, polyethylene glycol monoisopropyl ether, polyethylene glycol monobutyl ether, polyethylene glycol monoisobutyl ether, etc.) 1-4 alkyl ether), polypropylene glycol monoalkyl ether (e.g., polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monopropyl ether, polypropylene glycol monoisopropyl ether, polypropylene glycol monobutyl ether, polypropylene glycol monoisobutyl ether, etc.) 1-4 alkyl ethers) (preferably polyC 2-4 Alkylene glycol mono C 1-4 alkyl ethers); Heterocycles such as 2-pyrrolidone and N-methyl-2-pyrrolidone; Ketones such as acetone and methyl ethyl ketone; The number of moles of alkylene oxide added to the polyalkylene glycol monoalkyl ether is preferably 2 to 10, and more preferably 2 to 4. The water-soluble organic solvent may be used alone or in combination of two or more kinds.

[0020] Among these, from the viewpoint of preventing adhesion due to drying during printing and reducing the drying load during printing, it is preferable to include a water-soluble organic solvent having a boiling point of 150° C. or higher but lower than 200° C. (preferably 180° C. or higher but lower than 195° C.). Specific examples include glycols with boiling points of 150° C. or higher but lower than 200° C., such as propylene glycol and 1,2-butanediol, dialkylene glycol monoalkyl ethers with boiling points of 150° C. or higher but lower than 200° C., such as diethylene glycol monomethyl ether and dipropylene glycol monomethyl ether, and dialkylene glycol dialkyl ethers with boiling points of 150° C. or higher but lower than 200° C., such as dipropylene glycol dimethyl ether.

[0021] Moreover, from the viewpoint of promoting film formation and improving coating strength, the water-soluble organic solvent preferably contains a water-soluble organic solvent having a boiling point of 200° C. or more and less than 400° C. (preferably 200° C. or more and 300° C. or less). Specific examples include triethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, tripropylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono-n-butyl ether, propylene glycol monophenyl ether, tripropylene glycol mono-n-butyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and diethylene glycol dibutyl ether.

[0022] As the water-soluble organic solvent used in the water-based ink (A) of the present disclosure, it is more preferable to use a water-soluble organic solvent having a boiling point of 150°C or more but less than 200°C in combination with a water-soluble organic solvent having a boiling point of 200°C or more but less than 400°C.

[0023] The water-based ink (A) of the present disclosure may contain a surfactant in addition to the surfactant contained in the water-insoluble polyester resin. The surfactant added to the water-based ink (A) of the present disclosure is not particularly limited, but known surfactants such as acetylene-based, silicone-based, fluorine-based, Pluronic-based, and alcohol alkoxylate-based surfactants can be used. Commercially available products may be used as the acetylene surfactant, and specific examples include the Surfynol series (manufactured by Evonik), the Olfine series (manufactured by Nissin Chemical Industry Co., Ltd.), and the Acetylenol series (manufactured by Kawaken Fine Chemicals Co., Ltd.). Examples of silicone surfactants include polyether-modified siloxanes, polyether-modified polydimethylsiloxanes, etc. Commercially available products may be used as the silicone surfactants, and specific examples include the Silface series (manufactured by Nissin Chemical Industry Co., Ltd.), the KF series (manufactured by Nissin Chemical Industry Co., Ltd.), BYK-345, 347, 348, 349, 3450, 3451, 3455, and 3480 (all manufactured by BYK). Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains, etc. Commercially available products may be used as the fluorine-based surfactants, and specific examples include the Surflon series (manufactured by AGC Seiko Chemical Co., Ltd.) and Megafac F series (manufactured by DIC Corporation). Pluronic surfactants are nonionic surfactants formed by block copolymerization of hydrophilic polyoxyethylene and hydrophobic polyoxypropylene groups. Commercially available Pluronic surfactants may be used, including the Adeka Pluronic series (manufactured by ADEKA Corporation) and polyoxyethylene polyoxypropylene glycol (160 E.O.) (30 P.O.) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Commercially available products may be used as the alcohol alkoxylate surfactant, and specific examples include DYNWET800 (manufactured by BYK) and Adekatal LB series (manufactured by ADEKA). The surfactants may be used alone or in combination of two or more.

[0024] The water-based ink (A) of the present disclosure may contain other compounds in addition to the pigment, water-insoluble polyester resin, and surfactant, such as film-forming aids, UV absorbers, UV inhibitors, fillers, leveling agents, dispersants, thickeners, wetting agents, plasticizers, stabilizers, antioxidants, and crosslinkers.

[0025] The content of the pigment contained in 100 parts by mass of the water-based ink (A) of the present disclosure is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, from the viewpoint of sufficiently coloring the print or image formed with the water-based ink, and is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, from the viewpoint of forming a uniform coating film. The content of the pigment contained in 100 parts by mass of the nonvolatile content of the water-based ink (A) of the present disclosure is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, from the viewpoint of sufficiently coloring the print or image formed with the water-based ink, and is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 65 parts by mass or less, from the viewpoint of forming a uniform coating film. Known methods can be used to calculate the non-volatile content. For example, the non-volatile content may be calculated by subtracting the mass of volatile components from the total mass of the aqueous ink dispersion, as shown in Equation 1 below. Alternatively, as described in the Examples, 1 g of the aqueous ink dispersion may be weighed and dried in a hot air dryer at 110°C for 1 hour, and the resulting residue may be used to calculate the non-volatile content, as shown in Equation 2 below. Formula 1: [Non-volatile content in aqueous ink dispersion (mass%)] = ([Total mass of aqueous ink dispersion - Mass of volatile components] ÷ [Total mass of aqueous ink dispersion]) × 100 Equation 2: [Non-volatile content in aqueous ink dispersion (mass%)] = ([mass of residue] ÷ [mass of aqueous ink dispersion (1 g)]) × 100

[0026] In the aqueous ink (A) of the present disclosure, water accounts for the largest proportion in the medium, and the water content per 100 parts by mass of the medium may be 60 parts by mass or more, preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and particularly preferably 95 parts by mass or more. The water-based ink (A) of the present disclosure may contain a water-soluble organic solvent other than water in the medium, but the content of the water-soluble organic solvent other than water in 100 parts by mass of the medium is preferably 40 parts by mass or less, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. The content of the water-insoluble polyester resin contained in 100 parts by mass of the water-based ink (A) of the present disclosure is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, from the viewpoint of sufficient coloring of prints or images formed with the water-based ink, and is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, from the viewpoint of handleability. The content of the water-insoluble polyester resin contained in 100 parts by mass of the non-volatile content of the water-based ink (A) of the present disclosure is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more, from the viewpoint of sufficient coloring of prints or images formed with the water-based ink, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, from the viewpoint of forming a uniform coating film.

[0027] The content of water contained in 100 parts by mass of the water-based ink (A) of the present disclosure may be 35 parts by mass or more, preferably 40 parts by mass or more, and more preferably 45 parts by mass or more, and may be 70 parts by mass or less, preferably 65 parts by mass or less, and more preferably 60 parts by mass or less. The content of the water-soluble organic solvent in 100 parts by mass of the water-based ink (A) of the present disclosure may be 30 parts by mass or more, 35 parts by mass or more, or 40 parts by mass or more, or 65 parts by mass or less, preferably 60 parts by mass or less, and more preferably 55 parts by mass or less. The content of the water-soluble organic solvent having a boiling point of 150°C or more and less than 200°C in 100 parts by mass of the water-based ink (A) of the present disclosure may be 20 parts by mass or more, 25 parts by mass or more, or 30 parts by mass or more, or 50 parts by mass or less, preferably 30 parts by mass or less, and more preferably 25 parts by mass or less. The content of the water-soluble organic solvent having a boiling point of 200°C or higher and lower than 400°C per 100 parts by mass of the water-based ink (A) of the present disclosure is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. The content of the surfactant in 100 parts by mass of the water-based ink (A) of the present disclosure may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, or 3.0 parts by mass or less, preferably 2.0 parts by mass or less, and more preferably 1.5 parts by mass or less.

[0028] <Water-based overcoat solution (B)> The water-based overcoat liquid (B) of the present disclosure is characterized by being an aqueous medium using water as the medium, and preferably further contains a water-soluble polyester resin. The term "water-soluble polyester resin" in the present disclosure does not strictly refer to a physicochemical resin, but includes those that are soluble or finely dispersed in water, and is intended to include commercially available products sold as water-soluble polyester resins. The water-soluble polyester resin of the present disclosure is preferably a water-soluble polyester resin having a sulfonate group introduced therein, a water-soluble polyester resin having a carboxylic acid group introduced therein, etc. Examples of the sulfonate group include alkali metal salts of sulfonic acid represented by -SO3Na and SO3K. Examples of commercially available water-soluble polyester resins include water-soluble polyester resins having sulfonate groups introduced therein (manufactured by GOO Chemical Co., Ltd., trade names: PLASCOAT Z-221, Z-446, Z-456, Z-565, Z-880, Z-3310, RZ-105, RZ-570, etc.), water-soluble polyester resins having carboxylic acid groups introduced therein (manufactured by GOO Chemical Co., Ltd., trade names: PLASCOAT Z-730, Z-760, etc.), and water-soluble polyester resins having a naphthalene skeleton (manufactured by GOO Chemical Co., Ltd., trade names: PLASCOAT Z-592, Z-687, Z-690, etc.).

[0029] The water-soluble polyester resin of the present disclosure also includes those in a form finely dispersed in water, and the average particle size of the water-soluble polyester resin finely dispersed in water is preferably 80 nm or less, and may be 75 nm or less. The average particle size of the polymer particles may be the volume-based cumulant average particle size measured by dynamic light scattering. The water-soluble polyester resin of the present disclosure has a glass transition temperature of preferably 0°C or higher, more preferably 20°C or higher, from the viewpoint of blocking resistance, and preferably 70°C or lower, more preferably 50°C or lower, from the viewpoint of adhesion to a substrate.

[0030] The number average molecular weight (Mn) of the water-soluble polyester resin of the present disclosure is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 15,000 or more from the viewpoint of blocking resistance, and is preferably 50,000 or less, more preferably 40,000 or less, even more preferably 30,000 or less, and even more preferably 25,000 or less from the viewpoint of adhesion to the substrate. The number average molecular weight of the water-soluble polyester resin of the present disclosure can be measured using a known method, specifically, gel permeation chromatography (GPC) using tetrahydrofuran as an eluent. The number average molecular weight of the water-soluble polyester resin of the present disclosure can also be measured using a catalog value of a commercially available product. The weight-average molecular weight (Mw) of the water-soluble polyester resin of the present disclosure is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 15,000 or more from the viewpoint of blocking resistance, and is preferably 50,000 or less, more preferably 40,000 or less, even more preferably 30,000 or less, and even more preferably 25,000 or less from the viewpoint of adhesion to the substrate. The weight-average molecular weight of the water-soluble polyester resin of the present disclosure can be measured using a known method, specifically, gel permeation chromatography (GPC) using tetrahydrofuran as an eluent. The weight-average molecular weight of the water-soluble polyester resin of the present disclosure can also be measured using the catalog value of a commercially available product.

[0031] The aqueous overcoat liquid (B) of the present disclosure is characterized by containing water as a medium, but may also contain a water-soluble organic solvent other than water, specific examples of which include the water-soluble organic solvents described above in the section on the aqueous ink (A). The aqueous overcoat liquid (B) of the present disclosure may contain a surfactant in addition to the water-soluble polyester resin. The surfactant used in the aqueous overcoat liquid (B) is not particularly limited, but may be, for example, a known surfactant such as an acetylene-based, silicone-based, fluorine-based, Pluronic-based, or alcohol alkoxylate-based surfactant. Specific examples of the surfactant include the surfactants described for the aqueous ink (A). The aqueous overcoat solution (B) of the present disclosure may contain other compounds in addition to the water-soluble polyester resin and surfactant, such as pigments, film-forming aids, UV absorbers, UV inhibitors, fillers, leveling agents, dispersants, thickeners, wetting agents, plasticizers, stabilizers, antioxidants, crosslinking agents, and antiblocking agents.

[0032] The content of the water-soluble polyester resin contained in 100 parts by mass of the aqueous overcoat liquid (B) of the present disclosure is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, and from the viewpoint of handleability, is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less, and may be 30 parts by mass or less. The content of water contained in 100 parts by mass of the aqueous overcoat liquid (B) of the present disclosure may be 50 parts by mass or more, preferably 60 parts by mass or more, and more preferably 70 parts by mass or more, and may be 90 parts by mass or less, preferably 85 parts by mass or less, and more preferably 80 parts by mass or less. The content of the water-soluble organic solvent contained in 100 parts by mass of the aqueous overcoat liquid (B) of the present disclosure may be 0.5 parts by mass or more, 1.0 parts by mass or more, or 2.0 parts by mass or more, or 15 parts by mass or less, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less. The content of the surfactant contained in 100 parts by mass of the aqueous overcoat liquid (B) of the present disclosure may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, or 3.0 parts by mass or less, preferably 2.0 parts by mass or less, and more preferably 1.5 parts by mass or less. The content of other compounds contained in 100 parts by mass of the aqueous overcoat liquid (B) of the present disclosure is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and may be 0 parts by mass.

[0033] <Base material> The substrate to which the water-based ink (A) and water-based overcoat liquid (B) of the present disclosure are applied is not particularly limited, but it is preferable that they be applied onto a non-absorbent substrate. In the present disclosure, the term "non-absorbent substrate" refers to a substrate that has no or almost no ink absorption capacity. In other words, the term encompasses both non-absorbent and low ink absorption. Non-absorbent can be evaluated by the absorbency of pure water. More specifically, this refers to a water absorption per surface area of ​​the printing medium of 0 g / m to 10 g / m when the printing medium is in contact with pure water for 100 ms. The water absorption can be measured using an automatic scanning absorptivity meter. Examples of non-liquid-absorbing substrates according to the present disclosure include metal substrates and resin substrates. Specific examples of resin substrates include polyvinyl chloride substrates, polyethylene terephthalate substrates, polycarbonate substrates, polystyrene substrates, polyurethane substrates, polyethylene substrates, polypropylene substrates, and acrylic resin substrates. From the viewpoint of adhesion when using the ink set according to the present disclosure, polyethylene terephthalate substrates are preferred. Examples of polyethylene terephthalate substrates of the present disclosure include amorphous polyethylene terephthalate (A-PET), crystalline polyethylene terephthalate (C-PET), and glycol-modified polyethylene terephthalate (G-PET). From the viewpoint of use as a tray, it is preferable to use amorphous polyethylene terephthalate (A-PET).

[0034] <Ink set> The ink set of the present disclosure is an ink set having a water-based ink (A) containing a pigment and a water-based overcoat liquid (B). The ink set of the present disclosure is not particularly limited as long as it comprises a water-based ink (A) and a water-based overcoat (B) applied to a substrate. As for the method of applying the water-based ink (A) and the water-based overcoat (B) to the substrate, the water-based ink (A) and the water-based overcoat (B) may be applied by the same method or by different methods.

[0035] <Printing method> Methods for applying the water-based ink (A) containing the pigment of the present disclosure to a substrate include digital printing methods and analog printing methods, but it is preferable to adopt a digital printing method from the perspective of responding to small-lot production. The digital printing method of the present disclosure includes an inkjet printing method, etc. In other words, the pigment-containing water-based ink (A) is preferably an ink for digital printing, and more preferably an ink for inkjet printing. Methods for applying the water-based overcoat liquid (B) of the present disclosure include digital printing methods and analog printing methods, but from the viewpoint of productivity, it is preferable to employ analog printing methods. The analog printing method of the present disclosure includes offset lithography printing, flexography printing, gravure printing, screen printing, etc. In other words, the aqueous overcoat liquid (B) is preferably an ink for analog printing, more preferably an ink for gravure printing.

[0036] <Drying method> After applying the water-based ink (A) and overcoat liquid (B) of the present disclosure to a substrate, they may be heated to promote drying. To prevent shrinkage of the substrate, the drying temperature is preferably 100°C or less, more preferably 80°C or less, and even more preferably 60°C or less.

[0037] <Printed material> The ink set of the present disclosure comprises step (1) of applying a pigment-containing water-based ink (A) to a substrate, and step (2) of applying an ink set containing a water-based overcoat liquid (B) to the substrate, thereby making it possible to obtain a printed material with good adhesion to the substrate, scratch resistance, and alcohol resistance, and it is preferable to include step (2) after step (1). The water-based ink (A) containing the pigment of the present disclosure may be in direct contact with the substrate, or another layer may be present between the two layers. From the viewpoint of productivity, direct contact is preferred, and from the viewpoint of adhesion, an easy-adhesion layer (primer layer) or the like may be present between the two layers. "Direct" means that there is no other layer between the two layers. A printed material printed using the ink set of the present disclosure is preferably a laminate having a substrate, an ink layer (A) using a pigment-containing water-based ink (A), and an overcoat layer (B) using a water-based overcoat liquid (B) laminated in this order. The layers may be in direct contact with each other, or other layers may be present between them, but it is preferred that the overcoat layer (B) be the outermost layer.

[0038] <Application> The printed matter of the present disclosure can be used as various containers after undergoing a molding process. Examples of containers of the present disclosure include food containers and packaging containers for miscellaneous goods, and examples of food containers include food trays used for fresh foods, prepared foods, and the like. [Example]

[0039] The present invention will now be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0040] <Glass transition temperature of resin> The glass transition temperature (Tg) of the resin contained in the aqueous resin dispersion was calculated based on the glass transition temperature of the homopolymer of each monomer used in the monomer component constituting the resin, according to the Fox equation shown below.

[0041] 1 / Tg A =Σ(Wm / Tgm) / 100 [In the formula, Tg A indicates the glass transition temperature (absolute temperature: K) of the resin, Wm indicates the content (mass%) of monomer m in all monomer components constituting the resin, and Tgm indicates the glass transition temperature (absolute temperature: K) of a homopolymer of monomer m.]

[0042] <Acid value of resin> The acid value of the resin contained in the aqueous resin dispersion was obtained by approximating the number of mg of potassium hydroxide required to neutralize the acid groups present in 1 g of the monomer component constituting the resin. <Nonvolatile content of aqueous resin dispersion> The nonvolatile content of the aqueous resin dispersion was calculated based on the following formula by weighing 1 g of the aqueous resin dispersion, drying it in a hot air dryer at 110°C for 1 hour, and using the resulting residue as the nonvolatile content. Formula: [Non-volatile content in aqueous resin dispersion (mass%)] = ([mass of residue] ÷ [mass of aqueous resin dispersion (1 g)]) × 100

[0043] <Average particle size> The measurement temperature was 25±0.5°C, and an autocorrelation function was determined by the photon correlation method using a multi-analyte nanoparticle size measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: nanoSAQLA), which is a particle size measurement device using the dynamic light scattering method, to determine the cumulant average particle size.

[0044] Example 1 -Adjusting the overcoat liquid- An overcoat solution was obtained by mixing 16.2 parts of pure water, 80.0 parts of PLASCOAT R-565 (a binder resin manufactured by GOO Chemical Industry Co., Ltd., water-soluble polyester resin A, active ingredient concentration 25%), 3.0 parts of diethylene glycol monobutyl ether (an organic solvent), and 0.8 parts of BYK-348 (a silicone surfactant manufactured by BYK-Chemie) in a homodisper at 1000 rpm and filtering through a 3 μm filter [Advantec Co., Ltd., MCP-3-C10S]. In the overcoat solution obtained in Example 1, the nonvolatile content of water-soluble polyester resin A was 20% by mass, the diethylene glycol monobutyl ether was 3% by mass, and the nonvolatile content of BYK-348 was 0.5% by mass.

[0045] [Preparation of Water-Based Ink (Water-Based White Ink)] -Preparation of titanium oxide dispersion- A 250 mL plastic container was charged with 40.77 parts of pure water, 4.13 parts of DISPERBYK-190 (manufactured by BYK Japan, polyalkylene glycol group-containing acrylic water-soluble polymer, acid value 10 mg KOH / g, active ingredient concentration 40%) as a dispersant, and 55.00 parts of JR-403 (manufactured by Teika Corporation, rutile-type titanium dioxide, primary particle diameter 250 nm) as titanium dioxide. Subsequently, 100 parts of 0.1 mm diameter zirconia beads were added as dispersion media. The plastic container was sealed and subjected to a paint shaker treatment for 300 minutes. The zirconia beads were then suction filtered through a 7 μm mesh paper filter to obtain Titanium Dioxide Dispersion 1, with a rutile-type titanium dioxide concentration of 55%.

[0046] Next, 16.9 parts of pure water, 15.0 parts of propylene glycol, 12.0 parts of dipropylene glycol monomethyl ether, and 3.0 parts of diethylene glycol monobutyl ether as water-soluble organic solvents, 27.3 parts of the titanium oxide dispersion 1 described above, 25.0 parts of Vylonal MD-2000 (manufactured by Toyobo Co., Ltd., water-insoluble polyester resin A, active ingredient concentration 40%) as a binder resin, and 0.8 parts of BYK-348 (manufactured by BYK Japan, silicone surfactant) as a surfactant were mixed in a homodisper at 1000 rpm and filtered through a 3 μm filter [Advantec Co., Ltd., MCP-3-C10S] to obtain a water-based ink. In the water-based ink obtained in Example 1, the non-volatile content of titanium oxide dispersion 1 was 15% by mass, the non-volatile content of water-insoluble polyester resin A was 10% by mass, the propylene glycol content was 15% by mass, the dipropylene glycol monomethyl ether content was 12% by mass, and the diethylene glycol monobutyl ether content was 3% by mass.

[0047] <Production Example 1> [Preparation of Acrylic Emulsion] A flask equipped with a dropping funnel, a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser was charged with 536 parts of deionized water. A pre-emulsion for the first stage of addition, consisting of 326 parts of deionized water, 160 parts of a 25% aqueous solution of an emulsifier (manufactured by ADEKA Corporation, trade name: ADEKA REASORB SR-10), 632 parts of cyclohexyl methacrylate, 208 parts of 2-ethylhexyl acrylate, 150 parts of 2-hydroxyethyl methacrylate, and 10 parts of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine (manufactured by ADEKA Corporation, trade name: Adeka STAB LA-87), was prepared. 74 parts of this pre-emulsion, equivalent to 5% of the total amount of all monomer components, was added to the flask. The temperature was raised to 70°C while slowly blowing in nitrogen gas, and 30 parts of a 5% aqueous solution of ammonium persulfate was added to initiate polymerization. Thereafter, the remainder of the pre-emulsion for dropping and 30 parts of a 5% aqueous solution of ammonium persulfate were added dropwise uniformly into the flask over 180 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 70°C for 60 minutes, and the pH was adjusted to 8 by adding 25% aqueous ammonia to terminate the polymerization. The resulting reaction solution was cooled to room temperature and then filtered through a 300-mesh wire mesh to prepare an emulsion. The nonvolatile content of this emulsion was 50%, the acid value derived from the carboxyl groups of the resin emulsion particles was 0 mgKOH / g, and the glass transition temperature of the resin constituting the resin emulsion particles contained in the emulsion was 32°C. The minimum film-forming temperature was 40°C, and the average particle size was 200 nm.

[0048] <Examples 2 to 6 and Comparative Examples 1 to 8> An overcoat liquid, a titanium oxide dispersion, and an aqueous ink were prepared in the same manner as in Example 1, except that the types and ratios of the components contained in the overcoat liquid and the aqueous ink, and the base material were changed according to Table 1. The numerical values ​​for each component in Table 1 indicate the content (mass %) of the non-volatile content of each component in the aqueous ink.

[0049] <Creating inkjet prints> The water-based inks prepared in the above Examples and Comparative Examples were filled into a print evaluation device, jetXpert (manufactured by imageXpert Co., Ltd.), equipped with an inkjet printhead (manufactured by SII Printec Co., Ltd., product number RC1536), in air at a temperature of 25±1°C and a relative humidity of 30±5%. Next, the print evaluation device was set to a droplet volume of 40 pL (picoliters), a head temperature of 32°C, and a resolution of 360 dpi. A corona-treated PET film (manufactured by Futamura Chemical Co., Ltd., product name: Taiko Polyester Film FE2001) was used as the substrate, with the longitudinal direction of the corona-treated PET film aligned with the transport direction. A solid image was printed onto the corona-treated PET film using the above aqueous ink in a single pass using an inkjet recording method at a coverage of 100% (40 pL, 360 × 360 dpi). The printed corona-treated PET film was then dried immediately for 60 seconds in a dryer at 60°C, yielding a print. An overcoat liquid was applied to this print using bar coater #3, and immediately thereafter dried in a dryer at 60° C. for 60 seconds to obtain a test sheet.

[0050] <Evaluation method for overcoat liquid and ink> -Storage stability of ink- The ink was placed in a sealed container and stored in a thermostatic chamber at 50°C for one week, after which the rate of change in ink viscosity was evaluated using the following formula. The ink viscosity was measured using a TP-200 E-type viscometer (manufactured by Toki Sangyo Co., Ltd.). [Evaluation criteria] ○: Viscosity change rate is less than 15% △: Viscosity change rate is 15% or more but less than 30% ×: Viscosity change rate is 30% or more -Adhesion- An adhesive tape (Nichiban Co., Ltd., Cellotape (registered trademark) No. 405, 24 mm wide) was applied to the overcoat-coated surface of the test sheet at room temperature, left to stand for 1 minute, and then peeled off in a 180° direction. [Evaluation criteria] 〇: The printed image does not peel off at all △: 1 to 20% of the printed image peels off.

[0051] ×: 21 to 100% of the printed image peeled off. -Scratch resistance- The overcoat-coated surface of the test sheet was scratched with a fingernail, and the state of the coating film was then evaluated. [Evaluation criteria] 〇: The printed image does not peel off at all △: The printed image peels off a little. ×: Printed image peels off easily -Alcohol resistance- A 50% aqueous solution of ethanol was applied to the overcoat-coated surface of the test sheet, and the condition of the coating film was evaluated after rubbing with Kimwipe. [Evaluation criteria] 〇: The printed image does not peel off at all △: The printed image peels off a little. ×: Printed image peels off easily

[0052] [Table 1]

[0053] [Table 2]

[0054] The abbreviations in each table have the following meanings. <Resin> Water-insoluble polyester resin A: Vylonal MD-2000 manufactured by Toyobo Co., Ltd. (solid content 40% by mass, glass transition temperature 67°C, number average molecular weight 18,000 (catalog value), hydroxyl value 6 KOH mg / g, acid value <2 KOH mg / g, average particle size 134 nm) Water-insoluble polyester resin B: Vylonal MD-1480 manufactured by Toyobo Co., Ltd. (solid content 25% by mass, glass transition temperature 20°C, number average molecular weight 15,000 (catalog value), hydroxyl value 6 KOH mg / g, acid value 3 KOH mg / g, average particle size 114 nm) Water-soluble polyester resin A: Goo Chemical Co., Ltd. Pluscoat R-565 (solid content 25% by mass, glass transition temperature 64°C, molecular weight 15,000 (catalog value), acid value <5 KOH mg / g, contains -SO3Na groups, average particle size 22 nm) Water-soluble polyester resin B: Goo Chemical Co., Ltd. Pluscoat RZ-105 (solid content 25% by mass, glass transition temperature 52°C, molecular weight 16,000 (catalog value), acid value <5 KOH mg / g, contains -SO3Na groups, average particle size 19 nm) Water-soluble polyester resin C: PLASCOAT Z-880 manufactured by GOO CHEMICAL CO., LTD. (solid content 25% by mass, glass transition temperature 20°C, molecular weight 15,000, acid value <5 KOH mg / g, contains -SO3 Na groups, average particle size 70 nm) Acrylic emulsion: Production example 1 (solid content 50% by mass, glass transition temperature 32°C) Urethane emulsion: Superflex 150 manufactured by Daiichi Kogyo Seiyaku (solid content 30% by mass, glass transition temperature 40°C)

[0055] <Organic solvents> PG: Propylene glycol (boiling point 187°C) DPM: Dipropylene glycol methyl ether (boiling point 188°C) DEGBE: Diethylene glycol monobutyl ether (boiling point 230°C) <Surfactant> BYK-348: BYK-348 manufactured by BYK Japan, a silicone surfactant

[0056] <Base material> Substrate A: Futamura Chemical Co., Ltd. Taiko Polyester Film FE-2001 (corona-treated polyester film) Substrate B: Toyobo Space Clean S7561 (corona-treated, heat-shrinkable polyester film) Base material C: NOACRYSTAL-V (A-PET sheet) manufactured by RC Topla Co., Ltd.

Claims

1. The ink set comprises a pigment-containing water-based ink (A) and a water-based overcoat liquid (B), wherein the water-based ink (A) contains a water-insoluble polyester resin, and the water-based overcoat liquid (B) contains a water-soluble polyester resin.

2. The ink set of claim 1 applied to a polyethylene terephthalate substrate.

3. 2. The ink set according to claim 1, wherein the water-based ink (A) is for digital printing.

4. 2. The ink set according to claim 1, wherein the water-based overcoat liquid (B) is for analog printing.

5. 2. The ink set according to claim 1, wherein the ink (A) is a white ink.

6. A printed matter obtained using the ink set according to any one of claims 1 to 5.

7. A tray obtained using the printed matter according to claim 6.

8. A method for producing a printed matter, comprising the steps of: (1) applying a water-based ink (A) containing a pigment to a polyethylene terephthalate substrate; and (2) applying an ink set containing a water-based overcoat liquid (B) to the substrate.

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