Method for producing electron beam curable printed matter

Abstract

An object of the present invention is to provide a method for producing an electron beam curable printed matter and an electron beam curable ink set that can produce printed matter that is excellent in gloss and free of bleeding, wrinkles and streaks. [Solution] An ink set comprising an electron beam curable ink for an underlayer and an electron beam curable inkjet ink for an image layer, both of which contain an electron beam curable monomer, the surface tension A of the electron beam curable ink for the underlayer being 30 mN / m (25° C.) or less and the density being 1.22 to 2 g / cm 3 (25°C), wherein the electron beam curable inkjet ink for the image layer has a surface tension B minus A of 0 mN / m or more and 5 mN / m or less (25°C) and a density lower than that of the electron beam curable ink for the underlayer, and a production method for curing the electron beam curable ink for the underlayer and the electron beam curable inkjet ink for the image layer without provisionally curing the electron beam curable ink for the underlayer during printing.

Description

[Technical field]

[0001] The present invention relates to an electron beam curable ink set, in particular an ink set used in a printing method in which an underlayer is formed on a substrate, an image layer is formed thereon by inkjet printing, and then the underlayer and image layer are cured simultaneously by irradiating with an electron beam, and a method for producing a printed item using the ink set, and the ink set. [Background technology]

[0002] Electron beam curing is a technology that uses electron beams to crosslink and polymerize compounds that have ethylenic double bonds. Unlike UV curing, it does not contain photopolymerization initiators, so it has the advantage of not causing problems such as odors caused by residues and decomposition products, or migration of these products to the contents when used in packaging materials. However, compared to the widely used UV curing, the equipment is large and expensive, so it has not yet become widespread.

[0003] Inkjet printing is resource-saving and on-demand, and its range of applications has expanded in recent years. Accordingly, the substrates on which inkjet printing is performed are expanding to include a wide range of materials, such as paper, plastic films, and metals.

[0004] When inkjet printing is performed on the surface of an uncolored plastic film, a base layer is formed by printing a base ink such as white in a preset printing range in a solid or nearly solid area ratio, and then an image is printed on top of the base layer using colored inks such as yellow, magenta, cyan, and black by inkjet printing to form an image layer.

[0005] When printing images with UV-curable inkjet ink, conventionally, a manufacturing method has been put into practical use that uses a UV-curable ink containing a photopolymerization initiator for the base printing, or a heat-drying type gravure ink or flexographic ink to obtain a clear printed image. However, if all conventional inks are electron beam cured, the base layer must be cured first before the image layer is formed, otherwise bleeding (a phenomenon in which one overlapping color seeps into the other and mixes, resulting in a blurred image) will occur and the image will not be clear. In order to avoid this, the base layer must be cured first with an electron beam, which not only requires a larger installation space for the equipment, but also increases the cost of the equipment.

[0006] This problem is not limited to plastic films, but can also occur in inkjet printing using electron beam curable ink on other non-permeable substrates, when printing another ink on top of the underlying ink.

[0007] Therefore, the inventors proposed in Patent Document 1 a method for producing an electron beam curable inkjet printed product in a format in which an image is printed after solid printing, the method including a first step of preparing a substrate, a second step of printing an electron beam curable ink in a solid manner in a preset printing range of the substrate, a third step of subjecting the substrate to plasma treatment, a fourth step of inkjet printing a single-color or multiple-color electron beam curable inkjet ink of a different color from the ink in the second step by a single pass method, and a fifth step of irradiating the printed product with an electron beam.

[0008] According to the manufacturing method of Patent Document 1, a clear image can be obtained and there is no need to irradiate with an electron beam for each solid printing and inkjet ink printing; however, a separate plasma processing device is required, and the plasma curing is a method of increasing the viscosity (temporarily curing) of the solid-printed ink (base layer) near the surface so that it does not mix with the ink to be printed in the next inkjet print. Therefore, when the viscosity of the base layer surface increases, a wrinkled cured film sometimes occurs on the surface of the base layer, making it difficult to maintain surface smoothness, and in some cases, a highly glossy image cannot be obtained. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2022-112616 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide an electron beam curable ink set which can produce a printed matter that is high in gloss and free of bleeding or streaking without wrinkling, even when an underlayer is printed on a substrate, an image layer is inkjet-printed thereon, and then the underlayer and image layer are cured simultaneously by electron beam without plasma treatment, and a method for producing an electron beam curable printed matter using the ink set. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that by using an electron beam curable ink for the undercoat layer and an electron beam curable inkjet ink for the image layer having specific surface tensions and densities, excellent printed matter can be obtained by the following steps, and have completed the present invention.

[0012] That is, the present invention provides (1) A method for producing an electron beam curable printed matter, comprising forming a base layer and an image layer on a substrate in the following order: (First step): preparing a substrate; (Second step): A coating material containing an electron beam curable monomer and no photopolymerization initiator, having a surface tension A of 30 mN / m (25°C) or less and a density of 1.22 to 2 g / cm is applied to the surface of the substrate. 3 a step of printing the electron beam curable ink for the undercoat layer at 25° C. in a thickness of 0.5 μm to 10 μm; (Third step): A step of inkjet printing, by a single pass method, an electron beam curable inkjet ink for an image layer, which contains an electron beam curable monomer and does not contain a photopolymerization initiator and satisfies the following conditions, on the printed surface of the electron beam curable ink for the undercoat layer obtained in the second step; (Condition) An electron beam curable inkjet ink for an image layer, the density of which is lower than the density of the electron beam curable ink for the underlayer, and the surface tension B of the electron beam curable inkjet ink for an image layer relative to the surface tension A of the electron beam curable ink for the underlayer, satisfies the following formula (1): 0mN / m(25℃) ≦[Surface tension B]-[Surface tension A]≦5mN / m(25℃) (1) (fourth step) a step of irradiating the inkjet printed surface with an electron beam to cure the electron beam curable ink for the underlayer and the electron beam curable inkjet ink for the image layer; (2) The method for producing an electron beam curable printed matter according to claim 1, wherein the substrate is a non-permeable substrate. It is. Effect of the Invention

[0013] The present invention provides an electron beam curable ink set that can produce a printed matter that is wrinkle-free, highly glossy, and free of bleeding or streaking, even when an underlayer is printed on a substrate, an image layer is inkjet-printed thereon, and the underlayer and image layer are cured simultaneously by electron beam curing without plasma treatment, and a method for producing an electron beam curable printed matter using the ink set. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail. Note that this embodiment is merely one embodiment of the present invention, and the present invention is not limited to this embodiment. Various modifications are possible without departing from the gist of the present invention. In addition, in this specification, the expression "a to b" in the explanation of a numerical range means not less than a and not more than b, unless otherwise specified.

[0015] The ink set of the present invention is an ink set including an electron beam curable ink for an undercoat layer and an electron beam curable inkjet ink for an image layer, Both inks contain electron beam curable monomers and do not contain photopolymerization initiators. The surface tension A of the electron beam curable ink for the undercoat layer is 30 mN / m (25° C.) or less, Density: 1.22~2g / cm 3 (25°C), a value obtained by subtracting a surface tension A of the electron beam curable ink for the undercoat layer from a surface tension B of the electron beam curable inkjet ink for the image layer is 0 mN / m or more and 5 mN / m or less (25° C.), The density of the electron beam curable inkjet ink for the image layer is lower than the density of the electron beam curable ink for the undercoat layer.

[0016] In the present invention, both the surface tension and density are measured at a measurement temperature of 25° C. Therefore, although the specification may state "(25° C.)", hereinafter, the measurement temperature may be omitted. The density is measured in accordance with JIS Z8804:2012, and the surface tension can be measured by, for example, the Wilhelmy method using a commonly used surface tensiometer (e.g., Kyowa Interface Science Co., Ltd., Surface Tensiometer CBVP-Z, etc.).

[0017] The present invention also relates to a method for producing an electron beam curable printed matter, comprising forming an undercoat layer and an image layer on a substrate in the following order: (First step): preparing a substrate; (Second step): On the surface of the substrate, Contains electron beam curable monomers and no photoinitiators. Surface tension A is 30 mN / m (25°C) or less. Density: 1.22~2g / cm 3 (25℃) A step of printing the electron beam curable ink for the undercoat layer in a solid form with a film thickness of 0.5 μm to 10 μm; (Third step): A step of inkjet printing, by a single pass method, an electron beam curable inkjet ink for an image layer, which contains an electron beam curable monomer and does not contain a photopolymerization initiator and satisfies the following conditions, on the printed surface of the electron beam curable ink for the undercoat layer obtained in the second step; (Condition) The density of the electron beam curable inkjet ink for the image layer is lower than the density of the electron beam curable ink for the underlayer, an electron beam curable inkjet ink for an image layer, wherein a surface tension B of the electron beam curable inkjet ink for an image layer satisfies the following formula relative to a surface tension A of the electron beam curable ink for an underlayer; 0mN / m(25℃) ≦[Surface tension B]-[Surface tension A]≦5mN / m(25℃) (1) (Fourth step) A step of irradiating the inkjet printed surface with an electron beam to cure the electron beam curable ink for the underlayer and the electron beam curable inkjet ink for the image layer.

[0018] In the present invention, solid printing refers to printing in which the area ratio of the ink covering the unit area of ​​the printing range is 80 to 100%.

[0019] The substrate used in the present invention may be any impermeable substrate, and may be any substrate capable of serving as a substrate for printed matter, such as plastic films and other plastic molded products, wood, metal, etc.

[0020] The ink set of the present invention is an ink set of an electron beam curable ink for the underlayer (hereinafter also referred to as "underlayer ink") and an inkjet ink for the image layer (hereinafter also referred to as "image layer ink"), which is described below. This allows the droplets of the image layer ink to be printed without sinking into the underlayer, resulting in a highly glossy printed product without bleeding. In addition, since the underlayer is not temporarily cured, a printed product without wrinkles on the surface can be obtained.

[0021] In addition, since the present invention simultaneously cures the undercoat layer and the image layer by a single electron beam irradiation, a large-scale device such as a plasma treatment device is not required, which results in cost reduction. Furthermore, since no photopolymerization initiator is used, problems such as odor and safety caused by the photopolymerization initiator itself or its decomposition products can be avoided.

[0022] [Electron beam curable ink for undercoat layer (undercoat layer ink)] The ink for the undercoat layer contained in the ink set of the present invention will be described in detail below.

[0023] The ink for the undercoat layer of the present invention contains an electron beam curable monomer.

[0024] The electron beam curable monomer is preferably a (meth)acrylate monomer, and may be a monofunctional (meth)acrylate monomer, a polyfunctional (meth)acrylate monomer, a urethane (meth)acrylate monomer, a polyester (meth)acrylate monomer, or an oligomer thereof, or a combination of these. In the present invention, the term "(meth)acrylate" is a concept that encompasses both acrylate and methacrylate.

[0025] Examples of the monofunctional (meth)acrylate monomer include 2-(2-vinyloxyethoxy)ethyl acrylate, (5-ethyl-1,3-dioxane-5-yl)methyl acrylate, isobornyl acrylate, 2-acryloyloxyethyl succinate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, and tridecyl acrylate. , 2-phenoxyethyl acrylate (PEA), bis(4-acryloxypolyethoxyphenyl)propane, oligoester acrylate, epoxy acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, cyclic trimethylolpropane formal acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, octyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, acrylate, 3,3,5-trimethylcyclohexyl acrylate, 4-t-butylcyclohexyl acrylate, isoamyl acrylate, stearyl acrylate, isostearyl acrylate, 2-ethylhexyl diglycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hydrophthalic acid, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, vinyl ether acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyphthalic acid, 2-acryloxyethyl-2-hydroxyethyl phthalic acid, lactone-modified acrylates, acryloylmorpholine, acrylamide, and substituted acrylamides (e.g., N-methylolacrylamide, and diacetone acrylamide).

[0026] Examples of the polyfunctional (meth)acrylate monomer include difunctional (meth)acrylate monomers and trifunctional or higher (meth)acrylate monomers. Examples of the difunctional (meth)acrylate monomer include polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate (NDDA), 1,10-decanediol diacrylate (DDDA), 3-methylpentanediol diacrylate (3MPDDA), neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, ethylene oxide ( EO) modified bisphenol A diacrylate, bisphenol A propylene oxide (PO) adduct diacrylate, ethoxylated bisphenol A diacrylate, hydroxyneopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylated dimethylol tricyclodecane diacrylate, polytetramethylene glycol diacrylate, alkoxylated cyclohexanone dimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycol diacrylate, cyclohexanone dimethanol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, dipropylene glycol diacrylate, and the like.

[0027] Examples of the trifunctional or higher (meth)acrylate monomer include trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol tetraacrylate, ethoxylated isocyanuric acid triacrylate, ε-caprolactone-modified tris-(2-acryloxyethyl)isocyanurate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated tris-(2-acryloxyethyl)isocyanurate, and the like. Examples of the monomer include methylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxy tetraacrylate, glycerin propoxy triacrylate, ethoxylated dipentaerythritol hexaacrylate, caprolactam-modified dipentaerythritol hexaacrylate, propoxylated glycerin triacrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated trimethylolpropane triacrylate.

[0028] The electron beam curable monomer is a liquid substance that also functions as a solvent in the ink. The electron beam curable ink for the undercoat layer can be used without containing any other solvents, but may also contain other organic solvents for the purpose of adjusting the viscosity of the ink, etc.

[0029] When the substrate is transparent, the underlayer ink can be formed by solid printing of a white electron beam curable ink as the underlayer ink in order to provide the substrate with concealing properties to enable the image to be printed thereafter to stand out, thereby obtaining a clear printed matter, but other colors may also be used. If the substrate is opaque or colored, it is formed by printing a clear undercoat ink or a solid undercoat ink of any color. The printing method for the undercoat layer ink is not particularly limited as long as the ink is electron beam curable, and various methods such as a roll coater, gravure coater, flexo coater, and inkjet can be used.

[0030] The density of the ink for the undercoat layer is 1.22 to 2 g / cm 3 is preferable, and 1.22 to 1.9 g / cm 3 is more preferred. In order to increase the density, pigments or particles having a high density are added to the ink for the undercoat layer, for example, metal oxide pigments such as titanium oxide if the color of the undercoat layer is to be white, or zirconium oxide if the color is clear. The density of the ink for the undercoat layer is 1.22 g / cm 3 By using inks with a weight of 2 g / cm or more, it is possible to obtain prints with high gloss and no bleeding or streaking. 3 By setting the following, a stable ink can be obtained that does not undergo component settling during long-term storage.

[0031] The ink for forming the undercoat layer used in the present invention preferably has a surface tension of 30 mN / m or less. By setting the surface tension to 30 mN / m, the undercoat layer formed by the electron beam curable ink for the undercoat layer described below can be made into a thin and uniform film. In addition, since the surface tension of the (meth)acrylate is generally known to be about 28 to 38 mN / m, if the surface tension of the ink exceeds 30 mN / m, a surface conditioner is added to adjust the surface tension to a predetermined level.

[0032] As the surface conditioner, acrylic, vinyl, silicone, fluorine, and acetylene glycol surface conditioners can be used, among which silicone and fluorine surface conditioners are preferably used. The surface conditioner can be added at any concentration to adjust the surface tension of the electron beam curable ink for the undercoat layer as necessary, but is preferably added in an amount of 0 to 5%, more preferably 0 to 1%, based on the total amount of the ink for the undercoat layer.

[0033] Specific examples of silicon-based surface conditioners include modified dimethylsiloxane skeletons, and among them, polyether-modified siloxane-based surface conditioners are preferred. Polyether refers to, for example, polyethylene oxide and polypropylene oxide. As general products, representative products from BYK-Chemie include polyether-modified siloxanes such as BYK (registered trademark)-378, 348, 349, polyether-modified polydimethylsiloxanes such as BYK-UV3510, UV3500, and polyether-modified siloxane copolymers such as TEGO (registered trademark) GLIDE 450, 440, 435, 432, 410, 406, 130, 110, 100 from Evonik.

[0034] As the fluorine-based surface tension adjuster, it is preferable to use a fluorine-modified polymer, and specific examples include BYK-3440 (manufactured by BYK-Chemie), Surflon S-241, S-242, S-243 (manufactured by AGC Seimi Chemical Co., Ltd.), Ftergent 215M (manufactured by Neos Corporation), Megafac F-251, F-430, F-444, F-477, F-553, F-554, F-556 (DIC Corporation), and the like.

[0035] The ink for undercoat layer can be added with a dispersant to improve the dispersibility of pigments and particles and the storage stability of ink.As the dispersant, for example, one or more selected from the group consisting of carbodiimide-based, polyester-based, polyamine-based, polyesteramine-based, phosphate-based, polyurethane-based, fatty acid amine-based dispersants, polyacrylate-based, polycaprolactone-based, polysiloxane-based, multi-chain polymer nonionic, and polymer ionic dispersants can be used, and specifically, EFKA PX4701 (manufactured by BASF), BYKJET-9150, BYKJET-9151, BYKJET-9170, DISPERBYK-168, DISPERBYK-190, DISPERBYK-198, DISPERBYK-2010, DISPERBYK-2012, DISPERBYK-2015 (BYK-Chemie) and the like can be mentioned. The dispersant can be included at any time within the range of the surface tension of the ink for the undercoat layer, but its concentration is preferably 0.01% or more from the viewpoint of dispersion stability, and preferably 10% or less from the viewpoint of stabilizing the surface tension of the ink for the undercoat layer.

[0036] [Electron beam curable inkjet ink for image layer (ink for image layer)] The inks for the image layer contained in the ink set of the present invention are described in detail below.

[0037] If the surface tension of the ink for the image layer is surface tension B and the surface tension of the ink for the underlayer is surface tension A, the value obtained by subtracting the surface tension A of the ink for the underlayer from the surface tension B of the ink for the image layer is preferably 0 mN / m or more and 5 mN / m or less, more preferably 0 mN / m or more and 4 mN / m or less, and even more preferably 0 mN / m or more and 3 mN / m or less.

[0038] If the value obtained by subtracting the surface tension A from the surface tension B is less than 0 mN / m, i.e., if the surface tension B of the ink for the image layer is smaller than the surface tension A of the ink for the base layer, the droplets of the inkjet ink forming the image layer will spread excessively over the base layer, causing the image to bleed. If the value obtained by subtracting the surface tension A from the surface tension B exceeds 5 mN / m, the droplets of the inkjet ink forming the image layer will not spread adequately over the base layer, resulting in poor color development.

[0039] A surface modifier may be added to the ink for the image layer in order to adjust the surface tension. The surface conditioner may be selected from the same ones as those used in the ink for the undercoat layer, and may be an acrylic, vinyl, silicone, fluorine, or acetylene glycol surface conditioner. Of these, it is preferable to use a silicone or fluorine surface conditioner. The surface conditioner can be added at any concentration so as to adjust the surface tension as necessary, but is preferably added at 0 to 5%, more preferably 0 to 1%, based on the total amount of the ink for the image layer.

[0040] In order to prevent the ink for the imaging layer from sinking into the printed layer of the ink for the underlayer during printing, the ink for the imaging layer has a density smaller than that of the ink for the underlayer. In order to obtain a sufficient design by using a coloring material, the ink for the imaging layer has a density of 0.9 g / cm. 3 More preferably, it is equal to or greater than this.

[0041] The ink for the image layer has a density of 1.22 g / cm 3 Since the droplets are sufficiently large, it is believed that for typical inkjet ink droplets that do not contain large amounts of metal or metal oxide, sinking into the underlying layer due to their density is sufficiently suppressed.

[0042] The ink for the image layer contains an electron beam curable monomer. The electron beam curable monomer is preferably a (meth)acrylate monomer, similar to the electron beam curable ink for the undercoat layer, and may be a monofunctional (meth)acrylate monomer, a polyfunctional (meth)acrylate monomer, a urethane (meth)acrylate monomer, a polyester (meth)acrylate monomer, or an oligomer thereof, or a combination thereof.

[0043] The ink for the image layer can be colored arbitrarily with a coloring material. The coloring material may be any inorganic or organic pigment that is generally used in conventional ink compositions, such as carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, titanium oxide, chromium oxide, viridian, titanium cobalt green, ultramarine blue, Prussian blue, cobalt blue, diketopyrrolopyrrole, anthraquinone, benzimidazolone, anthrapyrimidine, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, threne pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, aluminum paste, silica, calcium carbonate, magnesium carbonate, clay, precipitated barium sulfate, and pearl pigments. The content and dispersed particle size of these are appropriately adjusted according to the printing method and its purpose.

[0044] The ink for the image layer may contain a dispersant similar to that used in the ink for the undercoat layer in order to improve the dispersibility of the pigment and the storage stability of the ink. As the dispersant, one or more of the dispersants used in the ink for the undercoat layer may be selected and used. The dispersant can be included at any time within the range of the surface tension of the ink for the undercoat layer, but the concentration is preferably 0.01% or more from the viewpoint of dispersion stability, and is preferably 10% or less from the viewpoint of stabilizing the surface tension of the ink for the undercoat layer.

[0045] [Other components of the ink for the base layer and the ink for the image layer] The electron beam curable ink compositions of both the ink for the undercoat layer and the ink for the image layer used in the present invention may further contain additives such as defoamers, waxes, non-reactive polymers, silane coupling agents, antistatic agents, etc., as necessary, within the range satisfying the density and surface tension of each ink. The concentration of such additives is preferably 0% or more and 10% or less, from the viewpoint of dispersion stability.

[0046] It is preferable that the electron beam curable ink compositions of both the undercoat layer ink and the image layer ink used in the present invention do not contain a photopolymerization initiator from the viewpoints of odor due to decomposition products, safety, etc. The photopolymerization initiator refers to a photopolymerization initiator used in general ultraviolet-curable inks.

[0047] [Method of manufacturing electron beam curable printed matter] The method for producing an electron beam curable printed matter of the present invention comprises a first step of preparing a substrate, a second step of solid printing the electron beam curable ink for the underlayer on the surface of the substrate, a third step of inkjet printing the electron beam curable ink for the image layer by a single pass method on the printed surface of the electron beam curable ink for the underlayer obtained in the second step, and a fourth step of irradiating the inkjet-printed surface with an electron beam to cure the electron beam curable ink for the underlayer and the electron beam curable inkjet ink for the image layer.

[0048] The solid printing with the ink for the undercoat layer in the second step can be performed by using various printing methods such as a roll coater, a gravure coater, a flexo coater, or an inkjet.

[0049] The thickness of the underlayer formed by the underlayer ink in the second step is preferably 0.5 to 10 μm, more preferably 0.6 to 8 μm, and even more preferably 0.8 to 6 μm. If the thickness of the underlayer is less than 0.5 μm, uneven printing and pinholes will occur, preventing a clear print. If the thickness exceeds 10 μm, the droplets of the inkjet ink for the image layer that are ejected after printing the underlayer in the third step will sink significantly into the underlayer due to the force of impact, preventing a clear print.

[0050] The electron beam irradiation in the fourth step is preferably performed within 5 seconds after the ink for the image layer lands, since if it exceeds 5 seconds, the landed inkjet ink may bleed, making it difficult to obtain a clear image. In order to avoid inhibition of polymerization by oxygen, the oxygen concentration is preferably 1,000 ppm or less, and more preferably 500 ppm or less. EXAMPLES

[0051] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by weight" and "%" means "% by weight".

[0052] The raw materials used in the present invention are as follows: Monomer 1: 2-(2-vinyloxyethoxy)ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd., density: 1.04 g / cm 3 ), Monomer 2: 1,6-hexanediol diacrylate (Shin-Nakamura Chemical Co., Ltd., density: 1.01 g / cm 3 ), Monomer 3: Dipropylene glycol diacrylate (Daicel-Allnex, density: 1.05 g / cm 3 ), Monomer 4: (5-ethyl-1,3-dioxane-5-yl)methyl acrylate (Osaka Organic Chemical Industry Co., Ltd., density: 1.09 g / cm 3 ), Monomer 5: Isobornyl acrylate (Osaka Organic Chemical Industry Co., Ltd., density: 0.997 g / cm 3 ), Monomer 6: 2-Acryloyloxyethyl succinate (Kyoeisha Chemical Co., Ltd., density: 1.23 g / cm 3 ), Monomer 7: Ethylene oxide modified bisphenol A diacrylate (manufactured by Daicel-Allnex Corporation, product name: EBECRYL150, density: 1.14 g / cm 3 ) Dispersant: EFKA PX4701 (BASF, density: 1.11 g / cm 3 ), Titanium oxide: TITONE R-25 (manufactured by Sakai Chemical Industry Co., Ltd., density: 4.23 g / cm 3 ), Carbon black: MA-7 (manufactured by Mitsubishi Chemical Corporation, density: 1.67 g / cm 3 ), Fluorine-based surface conditioner: Megafac F-477 (DIC, density: 1.18 g / cm 3 ), Silicone surface conditioner: BYK-UV3510 (manufactured by BYK Chemie, density: 1.04 g / cm 3 ).

[0053] <Density measurement> The density of the ink for the undercoat layer and the ink for the image layer described in the examples and comparative examples was measured at 25° C. using a hydrometer and a pycnometer.

[0054] <Measurement of surface tension> The surface tension of each dispersion and each ink described in the examples and comparative examples was measured at 25° C. by the Wilhelmy method using a surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science).

[0055] <Preparation of zirconium oxide> A mixed solution of 7.6g of zirconium oxychloride octahydrate, 0.36g of yttrium acetate tetrahydrate and 48.0g of distilled water was added to a solution containing 7.4g of triethanolamine, 2.8g of octanoic acid and 2.2g of 12-hydroxystearic acid, and then 6ml of 28% aqueous ammonia was added. The resulting mixture was subjected to hydrothermal treatment at 290°C for 2 hours in an autoclave. After the hydrothermal treatment, the supernatant was removed, and the white precipitate was dispersed in methanol using an ultrasonic cleaner, centrifuged, and the supernatant was removed again. This washing process was repeated three times, and then vacuum dried at room temperature for a day and night to obtain 3.58g of white powder of zirconium oxide coated with carboxylic acid.

[0056] <Preparation of Ink Dispersion for Undercoat Layer> Hereinafter, the methods for preparing the undercoat layer ink dispersions White 1 to White 6 and Clear 1 will be described.

[0057] "Undercoat layer ink dispersion white 1" 73 parts of Monomer 1, 24 parts of titanium oxide, and 3 parts of dispersant were kneaded together with ceramic beads in a paint shaker for 2 hours. After removing the ceramic beads, the mixture was filtered through a 10 μm filter to obtain an undercoat layer ink dispersion white 1.

[0058] "Undercoat layer ink dispersion White 2 to White 6" Monomer 1 of the undercoat layer ink dispersion white 1 was changed to a monomer shown in Table 1, and the monomer, dispersant, and titanium oxide were mixed in the ratio shown in Table 1. The mixture was then kneaded and filtered in the same manner as for the undercoat layer ink dispersion white 1, to obtain undercoat layer ink dispersion white 2 to white 6.

[0059] "Undercoat layer ink dispersion clear 1" Monomer 1 of the undercoat layer ink dispersion white 1 was changed to a monomer shown in Table 1, and titanium oxide was changed to zirconium oxide. The monomer and zirconium oxide were mixed in the ratio shown in Table 1, and then kneaded and filtered in the same manner as for the undercoat layer ink dispersion white 1, to obtain undercoat layer ink dispersion clear 1.

[0060] <Preparation of ink for undercoat layer> A fluorine-based surface conditioner or a silicon-based surface conditioner was added to the seven types of undercoat layer ink dispersions obtained above, White 1 to White 6 and Clear 1, according to the formulations shown in Table 2, and the mixture was stirred for one hour using a three-one motor stirrer to prepare undercoat layer inks 1 to 9 with adjusted surface tension. The surface tension and density of each of the resulting undercoat layer inks are shown in Table 2.

[0061] [Table 1]

[0062] [Table 2]

[0063] <Preparation of Ink Dispersion for Image Layer> Hereinafter, the preparation methods of black 1 to black 6 of the ink dispersions for the image layer will be described.

[0064] "Image layer ink dispersion black 1" 88 parts of Monomer 1, 9 parts of carbon black, and 3 parts of dispersant were kneaded together with ceramic beads in a paint shaker for 2 hours. After removing the ceramic beads, the mixture was filtered through a 10 μm filter to obtain an ink dispersion black 1 for image layer.

[0065] "Image layer ink dispersion Black 2 to Black 5" Monomer 1 of the ink dispersion liquid black 1 for imaging layer was changed to a monomer shown in Table 3, and the monomer, dispersant, and carbon black were mixed in the formulation shown in Table 3. The mixture was kneaded and filtered in the same manner as the ink dispersion liquid black 1 for imaging layer, to obtain ink dispersion liquids black 2 to black 5 for imaging layer.

[0066] "Image layer ink dispersion black 6" Monomer 1 of the black ink dispersion 1 for imaging layer was changed to a monomer shown in Table 3, and zirconium oxide was added in addition to carbon black. The monomer, dispersant, carbon black, and zirconium oxide were mixed in the formulation shown in Table 3, and then kneaded and filtered in the same manner as for the black ink dispersion 1 for imaging layer, to obtain a black ink dispersion 6 for imaging layer.

[0067] <Preparation of ink for image layer> A fluorine-based surface conditioner or a silicon-based surface conditioner was added to the six types of ink dispersions for the image layer, Black 1 to Black 6, obtained above, according to the formulations shown in Table 4, and the inks were stirred for one hour using a three-one motor stirrer to prepare inks for the image layer, 1 to 9, with adjusted surface tensions. The surface tension and density of the resulting ink for each image layer are listed in Table 4.

[0068] [Table 3]

[0069] [Table 4]

[0070] <Creating printed materials> Printed matter was prepared as Examples 1 to 8, Examples 10 to 18, and Comparative Examples 1 to 3 by the following method. Each of the inks for the undercoat layer was printed on a plastic film (Lumirror, manufactured by Toray Industries, Inc., number: #50-T60) as a substrate by a single-pass inkjet printing method at a resolution of 600 dpi with a thickness as shown in Tables 5 to 7, with a solid area ratio of 100%, and then, immediately after coating, a Kyocera inkjet head KJ-4A filled with each of the inks for the image layer was used to print 100 characters (10 characters vertically x 10 characters horizontally) of 3 to 12 point mixed hiragana and kanji in Ming and Gothic fonts and cut-out characters by a single-pass inkjet printing method at a resolution of 600 dpi. Within 5 seconds, the ink for the undercoat layer and the ink for the image layer were irradiated with an electron beam under conditions of an acceleration voltage of 90 kV, an absorbed dose of 30 kGy, and an oxygen concentration of 300 ppm to cure the ink for the undercoat layer and the ink for the image layer, to prepare a printed matter. Each of the obtained prints was visually inspected to confirm that there were no streaks or wrinkles on the printed surface of the undercoat layer ink.

[0071] [Table 5]

[0072] [Table 6]

[0073] [Table 7]

[0074] The printed matter of Example 9 was prepared by the following method: The ink 6 for the undercoat layer was printed solidly on a plastic film (Lumirror manufactured by Toray Industries, Inc., number: #50-T60) as a substrate, with a film thickness of 3 μm and an area ratio of 100% using a bar coater, and then immediately after the application, 100 characters (10 characters vertically x 10 characters horizontally) of 3 to 12 point Ming and Gothic fonts and cut characters were printed by single-pass inkjet printing at a resolution of 600 dpi using an inkjet head KJ-4A manufactured by Kyocera Corporation filled with each of the inks for the image layer, and then within 5 seconds, an electron beam was irradiated under conditions of an acceleration voltage of 90 kV, an absorbed dose of 30 kGy, and an oxygen concentration of 300 ppm to cure the ink for the undercoat layer and the ink for the image layer, thereby preparing a printed matter. Each of the obtained prints was visually inspected to confirm that there were no streaks or wrinkles on the printed surface of the undercoat layer ink.

[0075] The obtained prints were evaluated for glossiness and bleeding using the evaluation methods described below, and prints that were evaluated as "good" for both glossiness and bleeding were determined to be good products.

[0076] <Evaluation of gloss> The obtained prints were visually inspected and evaluated according to the following criteria. The evaluation results of the prints of Examples 1 to 18 and Comparative Examples 1 to 3 are shown in Tables 5 to 7. Evaluation: Good: High gloss over the entire surface of the print Evaluation: ×: Low gloss and dull

[0077] <Evaluation of bleeding> The obtained images were observed visually and with a magnifying glass and evaluated according to the following criteria. The evaluation results of the prints of Examples 1 to 18 and Comparative Examples 1 to 3 are shown in Tables 5 to 7. Evaluation ◯: There is no bleeding of the ink for the imaging layer on the surface of the base layer, and no sinking of the ink for the imaging layer into the interior, and the image appears clear. Evaluation Δ: The ink for the image layer sunk into the inside of the base layer, and the color development of the image was poor. Evaluation: ×: The ink for the image layer is bled onto the surface of the base layer, and the image is not clear.

[0078] <Reference Example 1: Pre-cured print> The ink for the undercoat layer was solid-printed and temporarily cured by plasma treatment, and then the ink for the image layer was printed on the printed matter, which was then checked as follows. The ink 1 for the undercoat layer was printed solidly at a thickness of 3 μm and an area ratio of 100% using a single-pass inkjet printing method at a resolution of 600 dpi on a plastic film (Lumirror, manufactured by Toray Industries, Inc., count: #50-T60) as a substrate, using a Kyocera inkjet head KJ-4ARH. The ink was then pre-cured by irradiating it with plasma generated at an output of 0.1 kW using a corona discharge generator (processing station: 220 mm wide aluminum type 3 electrode, high-frequency power supply AGF-B10PT, high-voltage transformer HTF-B10 (manufactured by Kasuga Electric Co., Ltd.)) in a nitrogen gas atmosphere with an oxygen concentration of 1,000 ppm. Next, a Kyocera inkjet head KJ-4ARH filled with the image layer ink 1 was used to print 100 characters (10 characters vertically x 10 characters horizontally) of 3 to 12 point Mincho and Gothic fonts and cut-out characters at a resolution of 600 dpi using a single-pass inkjet printing method, and then within 5 seconds, the print was cured by irradiating it with an electron beam under conditions of an acceleration voltage of 90 kV, an absorbed dose of 30 kGy, and an oxygen concentration of 300 ppm, to produce a printed matter of Reference Example 1. The obtained print was visually inspected, and streaks and wrinkles were observed on the printed surface of the ink for the undercoat layer.

Claims

1. A method for producing an electron beam curable printed matter, comprising forming an undercoat layer and an image layer on a substrate in the following order: (First step): preparing a substrate; (Second step): Applying a coating material to the surface of the substrate. Contains electron beam curable monomers and no photoinitiators. Surface tension A is 30 mN / m (25°C) or less, Density: 1.22 to 2 g / cm ３ (25°C). A step of printing the electron beam curable ink for the undercoat layer in a solid form with a film thickness of 0.5 μm or more and 10 μm or less; (Third step): A step of inkjet printing, by a single pass method, an electron beam curable inkjet ink for an image layer, which contains an electron beam curable monomer and does not contain a photopolymerization initiator and meets the following conditions, on the printed surface of the electron beam curable ink for the undercoat layer obtained in the second step; (Condition) The density of the electron beam curable inkjet ink for the image layer is lower than the density of the electron beam curable ink for the undercoat layer, an electron beam curable inkjet ink for forming an image layer, wherein a surface tension B of the electron beam curable inkjet ink for forming an image layer satisfies the following formula (1) relative to a surface tension A of the electron beam curable ink for forming an undercoat layer; 0mN / m (25℃) ≦[Surface tension B] - [Surface tension A]≦5mN / m (25℃) (1) (Fourth step) A step of irradiating the inkjet printed surface with an electron beam to cure the electron beam curable ink for the underlayer and the electron beam curable inkjet ink for the image layer.

2. The method for producing an electron beam curable printed matter according to claim 1 , wherein the substrate is a non-permeable substrate.

Images