Method for producing electron beam-curable printed matter

Abstract

To provide a method for producing an electron beam-curable printed matter capable of obtaining a printed matter excellent in glossiness, free from smudging, wrinkles and streaks and an electron beam curable ink set.SOLUTION: There are provided: 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 electron beam-curable monomers, wherein the surface tension A of the electron beam-curable ink for the underlayer is 30 mN / m or less (25°C) and the density is 1.22 to 2 g / cm3 (25°C), and the electron beam-curable inkjet ink for the image layer has a value obtained by subtracting the A from its surface tension B of 0 mN / m or more and 5 mN / m or less (25°C) and a density smaller than that of the electron beam-curable ink for the underlayer; and a producing method in which the electron beam-curable ink for the underlayer and the electron beam-curable inkjet ink for the image layer are cured without temporarily curing the electron beam-curable ink for the underlayer during printing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electron beam curable ink set, and particularly to a method for producing a printed item using 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 the ink set. [Background technology]

[0002] Electron beam curing is a technology that uses electron beams to crosslink and polymerize compounds with ethylenic double bonds. Unlike UV curing, it does not contain a photopolymerization initiator, which has the advantage of eliminating the odor caused by residues and decomposition products, and when used in packaging materials, the migration of these products into the contents. 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 it is printed are expanding to include a wide range of materials, including 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 predetermined printing range in a solid or nearly solid area ratio, and then an image is printed thereon 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 to obtain clear printed images by using UV-curable ink containing a photopolymerization initiator for the base printing, or heat-drying gravure ink or flexographic ink. However, if all conventional inks are to be cured with electron beams, 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 addition, to avoid this, curing the base layer first with electron beams 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 when printing an ink on top of an underlying ink in inkjet printing using electron beam curable ink on other non-permeable substrates.

[0007] Therefore, the inventors have proposed, in Patent Document 1, a method for producing an electron beam curable inkjet printed matter 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 predetermined printing range of the substrate; a third step of subjecting the printed matter to plasma treatment; a fourth step of inkjet printing, by a single pass method, a single color or multiple colors of electron beam curable inkjet ink different from the ink used in the second step; and a fifth step of irradiating the printed matter with an electron beam.

[0008] According to the manufacturing method of Patent Document 1, printed matter with clear images can be obtained and there is no need to irradiate with electron beams for each solid printing and inkjet ink printing, but a separate plasma treatment device is required, and the plasma curing is performed by increasing the viscosity (temporarily curing) of the solid-printed ink (base layer) near the surface to prevent it from mixing 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 forms on the surface of the base layer, making it difficult to maintain surface smoothness and making it impossible to obtain printed matter with a high-gloss image. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-112616 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide an electron beam-curable ink set that can produce a printed matter that is wrinkle-free, has high gloss, and is free from bleeding and streaks, even when a base layer is printed on a substrate, an image layer is inkjet-printed thereon, and then the base layer and image layer are cured simultaneously with an 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 underlayer 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 is (1) A method for producing an electron beam curable printed matter, in which an undercoat layer and an image layer are formed on a substrate in the following order: (First step): A step of preparing a substrate; (Second step): A coating containing an electron beam curable monomer but not containing a 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 a temperature of 25°C in 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 but does not contain a photopolymerization initiator and satisfies the following conditions, on the printed surface of the electron beam curable ink for the underlayer obtained in the second step; (Condition) An electron beam curable inkjet ink for an image layer, wherein the density of the electron beam curable ink for the image layer 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 the 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. (3) An ink set comprising an electron beam curable ink for an underlayer and an electron beam curable inkjet ink for an image layer, wherein both inks contain an electron beam curable monomer but do not contain a photopolymerization initiator, and the electron beam curable ink for the underlayer has a surface tension A of 30 mN / m (25°C) or less and a density of 1.22 to 2 g / cm 3 (25°C), wherein the 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) when the surface tension A of the electron beam curable ink for the underlayer is subtracted from the surface tension B, and 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. is. [Effects of the Invention]

[0013] The present invention provides an electron beam-curable ink set that can produce a printed matter that is wrinkle-free, has high gloss, and is free from bleeding and streaks, 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. DETAILED DESCRIPTION OF THE INVENTION

[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 within the scope of the present invention. Furthermore, in this specification, the expression "a to b" in the description of a range of values ​​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 comprising an electron beam curable ink for an underlayer 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 underlayer.

[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 sometimes refer to "(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 the Wilhelmy method using a commonly used surface tensiometer (for example, the surface tensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.).

[0017] The present invention also relates to a method for producing an electron beam curable printed matter, in which an undercoat layer and an image layer are formed on a substrate in the following order: (First step): A step of preparing a substrate; (Second step): On the surface of the substrate, Contains electron beam curable monomers and no photoinitiators. Surface tension A is 30mN / m (25℃) or less, Density 1.22~2g / cm 3 (25℃) a step of printing an electron beam curable ink for the underlayer in a solid state 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 but does not contain a photopolymerization initiator and satisfies the following conditions, on the printed surface of the electron beam curable ink for the underlayer 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 the surface tension B of the electron beam curable inkjet ink for an image layer satisfies the following formula relative to the 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 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 that can serve 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 are described below. This prevents droplets of the image layer ink from sinking into the underlayer during printing, making it possible to obtain a highly glossy, non-bleeding printed product. Furthermore, because the underlayer is not temporarily cured, it is possible to obtain a printed product that does not wrinkle on the surface.

[0021] In addition, since the present invention simultaneously cures the undercoat layer and the image layer by a single electron beam irradiation, it does not require a large-scale device such as a plasma treatment device, 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 included 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, an oligomer thereof, or a combination thereof. 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, 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 bifunctional (meth)acrylate monomers and trifunctional or higher functional (meth)acrylate monomers. Examples of the bifunctional (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 dimethyloltricyclodecane 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, and dipropylene glycol diacrylate.

[0027] Examples of the tri- or higher functional (meth)acrylate monomers 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, Examples of the acrylate 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, and the electron beam curable ink for the underlayer 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 a white electron beam curable ink as the underlayer ink in order to give the substrate hiding properties and make the image printed thereafter stand out so as to obtain a clear printed matter, but other colors may also be used. If the substrate is opaque or colored, it is formed by solid printing of a clear primer ink or a primer ink of any color. The printing method for the ink for the undercoat layer 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 preferred, and 1.22 to 1.9 g / cm 3 is more preferable. In order to increase the density, a pigment or particle with a high density is added to the ink for the undercoat layer, for example, a metal oxide pigment such as titanium oxide if the undercoat layer is to be white, or zirconium oxide if the undercoat layer is clear. The density of the ink for the undercoat layer is 1.22 g / cm 3 By using inks with a weight of 2g / cm or more, it is possible to obtain high-gloss prints without bleeding or streaking, and 3 By using the following, a stable ink can be obtained that does not undergo sedimentation during long-term storage.

[0031] The ink for forming an 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 forming an undercoat layer (described later) can be made into a thin and uniform film. Furthermore, 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 the specified level.

[0032] The surface conditioner may be an acrylic, vinyl, silicone, fluorine, or acetylene glycol surface conditioner, with silicone and fluorine surface conditioners being preferred. 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 needed, 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 silicone-based surface conditioners include modified dimethylsiloxane skeletons, and polyether-modified siloxane-based surface conditioners are preferred. Polyethers include, for example, polyethylene oxide and polypropylene oxide. Typical examples of commonly used products include polyether-modified siloxanes such as BYK (registered trademark)-378, 348, and 349, and polyether-modified polydimethylsiloxanes such as BYK-UV3510 and UV3500, available from BYK-Chemie, and polyether-modified siloxane copolymers such as TEGO (registered trademark) GLIDE 450, 440, 435, 432, 410, 406, 130, 110, and 100, available 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 (manufactured by DIC Corporation), and the like.

[0035] The ink for the undercoat layer may contain a dispersant to improve the dispersibility of pigments and particles and the storage stability of the ink. The dispersant may be, for example, one or more selected from the group consisting of carbodiimide-based, polyester-based, polyamine-based, polyesteramine-based, phosphate ester-based, polyurethane-based, fatty acid amine-based dispersants, polyacrylate-based, polycaprolactone-based, polysiloxane-based, multi-chain polymer nonionic, and polymer ionic dispersants. Specific examples include EFKA PX4701 (manufactured by BASF), BYKJET-9150, BYKJET-9151, BYKJET-9170, DISPERBYK-168, DISPERBYK-190, DISPERBYK-198, DISPERBYK-2010, DISPERBYK-2012, and DISPERBYK-2015 (manufactured by BYK-Chemie). The dispersant can be contained 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 included 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 that form the image layer will spread excessively on 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 that form the image layer will not spread appropriately on the base layer, resulting in poor color development.

[0039] A surface conditioner may be added to the ink for the image layer to adjust the surface tension. The surface conditioner can be selected from the same ones as those used in the ink for the undercoat layer, and acrylic, vinyl, silicone, fluorine, and acetylene glycol surface conditioners can be used. Of these, silicone and fluorine surface conditioners are preferably used. The surface conditioner can be added at any concentration to adjust the surface tension as needed, 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 image layer.

[0040] In addition, from the viewpoint of preventing the ink for the image layer from sinking into the printed layer of the ink for the underlayer during printing, the density of the ink for the image layer is preferably lower than the density of the ink for the underlayer. 3 It is preferable that this 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 droplets of a typical inkjet ink that does not contain a large amount of metal or metal oxide, sinking into the underlying layer due to their density will be 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. The electron beam curable monomer 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 as desired with a colorant. The colorant may be any inorganic or organic pigment commonly 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 pigments are appropriately adjusted depending on the printing method and 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 contained 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.

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

[0046] The electron beam-curable ink compositions for both the undercoat layer ink and the image layer ink used in the present invention preferably 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 surface printed with 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 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 base layer is less than 0.5 μm, uneven printing, pinholes, etc. will occur, making it impossible to obtain a clear printed product. If the thickness exceeds 10 μm, the droplets of inkjet ink for the image layer that are ejected after printing the base layer in the third step will sink significantly into the base layer due to the force of impact, making it impossible to obtain a clear printed product.

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

[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 (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 Corporation, density: 1.05 g / cm 3 ), Monomer 4: (5-ethyl-1,3-dioxan-5-yl)methyl acrylate (Osaka Organic Chemical Industry, 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 (manufactured by 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 (Mitsubishi Chemical Corporation, density: 1.67 g / cm 3 ), Fluorine-based surface conditioner: Megafac F-477 (DIC Corporation, 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] <Surface tension measurement> 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 7.6 g of zirconium oxychloride octahydrate, 0.36 g of yttrium acetate tetrahydrate, and 48.0 g of distilled water was added to a solution containing 7.4 g of triethanolamine, 2.8 g of octanoic acid, and 2.2 g of 12-hydroxystearic acid, followed by 6 ml of 28% aqueous ammonia. The resulting mixture was hydrothermally treated in an autoclave at 290°C for 2 hours. After hydrothermal treatment, the supernatant was removed, and the white precipitate was dispersed in methanol using an ultrasonic cleaner, then centrifuged, and the supernatant was removed again. This washing process was repeated three times, followed by vacuum drying at room temperature overnight, yielding 3.58 g of a white powder of carboxylic acid-coated zirconium oxide.

[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, and after removing the ceramic beads, the mixture was filtered through a 10 μm filter to obtain a white ink dispersion 1 for undercoat layer.

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

[0059] "Undercoat layer ink dispersion Clear 1" Monomer 1 of the undercoat layer ink dispersion liquid 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 formulation shown in Table 1, and then kneaded and filtered in the same manner as for the undercoat layer ink dispersion liquid white 1, to obtain undercoat layer ink dispersion liquid 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 primer 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 1 hour using a three-one motor stirrer to prepare primer 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 methods for preparing the ink dispersions for the image layer, Black 1 to Black 6, will be described.

[0064] "Image layer ink dispersion liquid 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, and after removing the ceramic beads, the mixture was filtered through a 10 μm filter to obtain ink dispersion liquid black 1 for the image layer.

[0065] "Image layer ink dispersion liquid Black 2 to Black 5" Monomer 1 of the black ink dispersion for imaging layer 1 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. Then, the mixture was kneaded and filtered in the same manner as the black ink dispersion for imaging layer 1, to obtain black ink dispersions for imaging layer 2 to black 5.

[0066] "Image layer ink dispersion liquid black 6" Monomer 1 in 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 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 image layer ink dispersions, Black 1 to Black 6, obtained above, according to the formulations shown in Table 4, and the mixture was stirred for 1 hour using a three-one motor stirrer to prepare image layer inks 1 to 9 with adjusted surface tension. The surface tension and density of each of the resulting inks for the image layers are shown in Table 4.

[0068] [Table 3]

[0069] [Table 4]

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

[0071] [Table 5]

[0072] [Table 6]

[0073] [Table 7]

[0074] The printed matter of Example 9 was produced by the following method: The base layer ink 6 was solid-printed to a thickness of 3 μm and an area ratio of 100% on a plastic film (Lumirror, manufactured by Toray Industries, Inc., count: #50-T60) using a bar coater. Immediately after coating, a Kyocera KJ-4A inkjet head filled with each of the image layer inks was used to print 100 characters (10 characters vertically and 10 characters horizontally) of 3- to 12-point Mincho and Gothic fonts and outline characters at a resolution of 600 dpi using a single-pass inkjet printing method. Within 5 seconds, the base layer ink and image layer ink were cured by irradiating 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. Each of the obtained prints was visually inspected to confirm that there were no streaks or wrinkles on the printed surface of the ink for the undercoat layer.

[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 across the entire print Rating ×: 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 printed matter 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 image layer on the surface of the base layer, and no sinking of the ink for the image layer into the interior, and the image appears clear. Evaluation △: The ink for the image layer sunk into the base layer, and the image color development was poor. Evaluation: ×: The ink for the image layer was smeared on the surface of the base layer, and the image was 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, and the following checks were carried out on the printed matter. The undercoat layer ink 1 was solid-printed 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 (Lumilar, 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, using a Kyocera inkjet head KJ-4ARH filled with the image layer ink 1, 100 characters (10 characters vertically x 10 characters horizontally) of 3 to 12 point Mincho and Gothic fonts and cut-out characters were printed on the obtained coating film using single-pass inkjet printing at a resolution of 600 dpi, 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 the printed matter of Reference Example 1. The resulting printed matter 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): A step of preparing a substrate; (Second step): Applying a coating of the base material to the surface of the base material. 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 underlayer in a solid form to 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 but does not contain a photopolymerization initiator and satisfies the following conditions, on the printed surface of the electron beam curable ink for the underlayer 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 forming an image layer, wherein the surface tension B of the electron beam curable inkjet ink for forming 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 an impermeable substrate.

3. An ink set comprising an electron beam curable ink for an underlayer 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 to 2 g / cm ３ (25°C), The surface tension B of the electron beam curable inkjet ink for the image layer is a value obtained by subtracting the surface tension A of the electron beam curable ink for the undercoat layer from the surface tension B 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 underlayer; Electron beam curable ink set.

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