JP7751533B2 - Actinic radiation curable resin composition and release layer - Google Patents

Description

The present invention relates to an actinic radiation-curable resin composition and a release layer.

In recent years, efforts to reduce waste plastic generation and promote advanced recycling have been actively considered in order to realize a carbon-neutral society. Methods for recycling waste plastic include chemical recycling, in which waste plastic is chemically broken down and reused as a raw material for chemical products, and material recycling, in which waste plastic is crushed and washed and reused as a raw material for plastic products.

Thermoplastic plastics such as polypropylene, polyethylene, polyethylene terephthalate, and nylon are widely used as packaging materials due to their moldability, light weight, impact resistance, transparency, and other characteristics. Plastic packaging materials are often printed with inks for the purposes of adding design and recording information, and inks containing organic solvents are primarily used. However, the organic solvents contained in inks are problematic as air pollutants. Furthermore, the organic solvents evaporated during the printing process require significant energy for detoxification and produce significant amounts of _CO2 . Therefore, there is a need to replace these inks with solvent-free or water-based inks.

Meanwhile, improving the recycling rate of plastic products and the number of times they are recycled requires improving the quality of the plastic waste itself. Therefore, it is important to obtain high-quality waste plastic raw materials free of dirt and impurities before undergoing recycling processes such as re-pelletization. From a recycling perspective, printed layers attached to plastic substrates are considered impurities. Recycling plastic substrates with printed layers attached as is can lead to problems such as poor appearance and reduced mechanical strength in the recycled plastic. Therefore, attempts have been made to remove printed layers attached to plastic substrates with alkaline aqueous solutions as a pretreatment for recycling. Improving the alkali solubility of the ink itself to improve deinking ability poses issues such as the durability of the printed layer, and re-dyeing and re-contamination of the plastic during the printed layer removal process. For this reason, efforts are being made to create a release layer between the plastic substrate and the printed layer that can be removed by alkaline aqueous solution treatment.

For example, Patent Document 1 proposes a technology for removing printed matter from the surface of a plastic substrate by treating it with an alkaline aqueous solution, as well as removing printed layers from laminates. However, this technology has the problem of requiring detoxification of the organic solvent that volatilizes during the process of forming the release layer.

Patent Documents 2 and 3 propose solvent-free actinic radiation-curable resin compositions that enable printed layers and labels to be removed from plastic containers by alkaline treatment. However, these techniques can result in printing defects when forming a printed layer on a cured product layer, insufficient adhesion to the plastic substrate, or insufficient removal of the printed layer and release layer from the plastic substrate when treated with an alkaline aqueous solution.

Patent No. 6638802 Patent No. 6742879 Patent No. 2999334

The present invention relates to a resin composition for forming a layer (detachment layer) that allows a printed layer to be easily removed from a plastic substrate. Its objective is to provide a solventless, actinic radiation-curable resin composition for forming a detachment layer that allows the printed layer to be easily separated from the plastic substrate by treatment with an alkaline aqueous solution, provides good printability for the printed layer, and has high adhesion to the substrate, as well as a detachment layer made from the cured product thereof.

The present inventors have completed the present invention as a result of extensive research aimed at solving the above-mentioned problems. Specifically, the present invention relates to the following (1) to (8). In this application, "(Numerical value 1) to (Numerical value 2)" indicates that the upper and lower limits are included.
(1) An actinic radiation-curable resin composition containing a carboxy group-containing monofunctional (meth)acrylate (A), a monofunctional (meth)acrylate having a cyclic skeleton without a carboxy group (B), and a di- or higher functional (meth)acrylate without a carboxy group (C), wherein the content of component (A) is 43% by weight or more and 65% by weight or less of the total amount of the actinic radiation-curable resin composition, and component (A) contains at least one selected from 2-(meth)acryloyloxyethyl hexahydrophthalic acid (A-1), 2-(meth)acryloyloxyethyl phthalic acid (A-2), and 2-(meth)acryloyloxypropyl hexahydrophthalic acid (A-3).
(2) The actinic radiation-curable resin composition according to the preceding item (1), wherein the total content of the components (A-1) to (A-3) is 50% by weight or more and 100% by weight or less, based on the total amount of the component (A).
(3) The actinic radiation-curable resin composition according to the preceding paragraph (1) or (2), wherein the content of the component (B) is 18% by weight or more and 45% by weight or less, and the content of the component (C) is 5% by weight or more and 20% by weight or less, based on the total amount of the actinic radiation-curable resin composition.
(4) The actinic radiation-curable resin composition according to any one of (1) to (3), wherein the component (B) contains at least one selected from the group consisting of isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, acryloylmorpholine, cyclic trimethylolpropane formal acrylate, and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate.
(5) The actinic radiation-curable resin composition according to any one of (1) to (4), which is an electron beam-curable resin composition.
(6) The actinic radiation-curable resin composition according to any one of (1) to (5), which is a coating composition for forming a release layer of a thermoplastic plastic substrate.
(7) The actinic radiation-curable resin composition according to the above (6), wherein the thermoplastic plastic substrate is a polyester or polyolefin substrate.
(8) A release layer formed from the actinic radiation-curable resin composition according to the above item (6) or (7).

The present invention makes it possible to provide a solventless, actinic radiation-curable resin composition that allows a printed layer to be easily separated from a plastic substrate by treatment with an alkaline aqueous solution, and that forms a release layer that has good printability and high adhesion to the substrate, as well as a release layer made from the cured product of the resin composition.

In the present invention, the term "(meth)acrylate" refers to either or both of acrylate and methacrylate. Furthermore, the term "(meth)acryloyl group" refers to either or both of acryloyl and methacryloyl groups. For example, the term "isobornyl (meth)acrylate" refers to either or both of isobornyl acrylate and isobornyl methacrylate. Furthermore, the term "cured product" refers to a cured product of an actinic radiation-curable composition obtained by curing a resin composition by irradiating it with actinic radiation.

In the present invention, the term "solvent-free" refers to a composition that is substantially solvent-free. That is, in the present invention, a solvent-free live-beam curable resin composition refers to a live-beam curable resin composition in which the solvent content of the total amount of the live-beam curable resin composition is less than 2% by weight. While solvents used during synthesis of the components of the live-beam curable composition or during preparation of the composition may remain, it is preferable that they have been removed as much as possible, and it is more preferable that the composition contains substantially no solvent.

The actinic radiation-curable resin composition of the present invention contains a carboxyl group-containing monofunctional (meth)acrylate (A). The carboxyl group-containing monofunctional (meth)acrylate (A) is a compound containing one or more carboxyl groups, preferably 1 to 5, and one (meth)acryloyl group per molecule. The weight proportion of the carboxyl group-containing monofunctional (meth)acrylate (A) in the total amount of the actinic radiation-curable composition of the present invention is preferably 43% by weight or more and 65% by weight or less, more preferably 50% by weight or more and 63% by weight or less, and particularly preferably 51% by weight or more and 62% by weight or less. If it is more than 65% by weight, the printability of the release layer made of the cured resin may be reduced, while if it is less than 43% by weight, release properties during alkaline aqueous solution treatment may be reduced.

The actinic radiation-curable resin composition of the present invention contains at least one carboxy group-containing monofunctional (meth)acrylate (A) selected from 2-(meth)acryloyloxyethyl hexahydrophthalic acid (A-1), 2-(meth)acryloyloxyethyl phthalic acid (A-2), and 2-(meth)acryloyloxypropyl hexahydrophthalic acid (A-3). As the carboxy group-containing monofunctional (meth)acrylate (A), any of components (A-1) to (A-3) can be used alone, or two or more can be used in combination. Furthermore, the composition may contain a carboxy group-containing monofunctional (meth)acrylate (A) other than components (A-1) to (A-3). The total content of components (A-1) to (A-3) in the total amount of component (A) is preferably 50% by weight or more and 100% by weight or less, more preferably 75% by weight or more and 100% by weight or less, and particularly preferably 100% by weight. By ensuring that the total content of components (A-1) to (A-3) within the total amount of component (A) is 50% by weight or more and 100% by weight or less, an actinic radiation-curable resin composition can be obtained that can form a release layer that exhibits excellent adhesion to substrates, blocking resistance, printability, and release properties during alkaline aqueous solution treatment. Furthermore, from the standpoints of adhesion to substrates and release properties during alkaline aqueous solution treatment, it is preferable that the carboxyl group-containing monofunctional (meth)acrylate (A) contains 2-(meth)acryloyloxyethylhexahydrophthalic acid (A-1).

Carboxy group-containing monofunctional (meth)acrylates (A) other than components (A-1) to (A-3) are not particularly limited, but examples include acrylic acid, methacrylic acid, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl succinate, and ω-carboxy-polycaprolactone mono(meth)acrylate.

The actinic radiation-curable resin composition of the present invention contains a monofunctional (meth)acrylate (B) having a cyclic skeleton without a carboxy group. The monofunctional (meth)acrylate (B) having a cyclic skeleton without a carboxy group is a compound that does not have a carboxy group in one molecule, has a cyclic skeleton in one molecule, and further contains one (meth)acryloyl group in one molecule. The content of the monofunctional (meth)acrylate (B) having a cyclic skeleton without a carboxy group in the total amount of the actinic radiation-curable resin composition of the present invention is preferably 10% by weight or more but less than 57% by weight, more preferably 18% by weight or more but less than 45% by weight, and particularly preferably 23% by weight or more but less than 40% by weight. If it is more than 57% by weight, release properties during alkaline aqueous solution treatment may be impaired. If it is less than 10% by weight, there is a risk of poor adhesion to the substrate, reduced printability on the release layer, and reduced release properties from polyolefin-based substrates. The monofunctional (meth)acrylate (B) having a cyclic skeleton without a carboxy group can be used alone or in combination of two or more types.

Examples of monofunctional (meth)acrylates (B) having a cyclic skeleton without a carboxy group include, but are not limited to, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxyethylene oxide-modified (meth)acrylate, benzyl (meth)acrylate, acryloylmorpholine, dicyclopentenyl (meth)acrylate, cyclic trimethylolpropane formal acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl acrylate, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl acrylate, 1-adamantyl methacrylate, dicyclopentadieneoxyethyl (meth)acrylate, and glycerin carbonate acrylate. Among these, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, acryloylmorpholine, cyclic trimethylolpropane formal acrylate, and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate are preferred from the viewpoint of releasability during alkaline aqueous solution treatment, and isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and benzyl (meth)acrylate are particularly preferred from the viewpoint of achieving both good adhesion to the substrate and releasability during alkaline aqueous solution treatment.

The actinic radiation-curable resin composition of the present invention contains a difunctional or higher (meth)acrylate (C) that does not have a carboxy group. The difunctional or higher (meth)acrylate (C) that does not have a carboxy group is a compound that does not have a carboxy group in one molecule and contains two or more (meth)acryloyl groups in one molecule. The content of the difunctional or higher (meth)acrylate (C) that does not have a carboxy group in the total amount of the actinic radiation-curable resin composition of the present invention is preferably 0.1% by weight to 30% by weight, more preferably 5% by weight to 20% by weight, and particularly preferably 5% by weight to 15% by weight. If it is more than 30% by weight, poor adhesion to the substrate and poor release properties during alkaline aqueous solution treatment may occur. If it is less than 0.1% by weight, poor blocking resistance and reduced printability on the release layer may occur. The difunctional or higher (meth)acrylate (C) that does not have a carboxy group can be used alone or in combination of two or more types.

Examples of the difunctional or higher functional (meth)acrylate (C) that does not have a carboxy group include, but are not limited to, tricyclodecane dimethylol di(meth)acrylate, dioxane glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkylene oxide-modified bisphenol A di(meth)acrylate, caprolactone-modified hydroxypivalic acid neopentyl glycol di(meth)acrylate, and ethylene oxide-modified phosphoric acid di(meth)acrylate, trimethylol C2-C10 alkane tri(meth)acrylate such as trimethylolpropane tri(meth)acrylate and trimethyloloctane tri(meth)acrylate, and trimethylolpropane polyethoxy tri(meth)acrylate, trimethylolpropane polypropoxy tri(meth)acrylate, and trimethylolpropane polyethoxypolypropoxy tri(meth)acrylate. Examples of the alkylene oxide-modified trimethylolpropane tri(meth)acrylate include ethylene oxide-modified trimethylolpropane tri(meth)acrylate, tris[(meth)acroyloxyethyl]isocyanurate, pentaerythritol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol polyethoxytetra(meth)acrylate, pentaerythritol polypropoxytetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate. Of these, trifunctional (meth)acrylates are preferred from the viewpoints of adhesion to the substrate and imparting scratch resistance and blocking resistance to the cured film, and of the trifunctional (meth)acrylates, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are particularly preferred.

In addition to the components described above, the actinic radiation-curable resin composition of the present invention can optionally contain a (meth)acrylate (D) other than components (A) to (C). When a component other than components (A) to (C) is contained, it is preferable that the component does not reduce the properties of the cured product to an extent that it becomes unusable.

(D) (meth)acrylate other than components (A) to (C) may contain a photopolymerizable monomer, a photopolymerizable oligomer, etc. Examples of photopolymerizable oligomers include, but are not limited to, polyester (meth)acrylate oligomers, urethane (meth)acrylate oligomers, and epoxy (meth)acrylate oligomers.

Urethane (meth)acrylate oligomers are obtained by reacting polyhydric alcohols, polyisocyanates, and hydroxyl group-containing (meth)acrylates.

Examples of polyhydric alcohols include alkylene glycols having 1 to 10 carbon atoms, such as polybutadiene glycol, hydrogenated polybutadiene glycol, polyisoprene glycol, hydrogenated polyisoprene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, ethylene glycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol; triols such as trimethylolpropane and pentaerythritol; and alcohols having a cyclic skeleton, such as tricyclodecane dimethylol and bis-[hydroxymethyl]cyclohexane; and mixtures of these polyhydric alcohols with polybasic acids (e.g., cobalt, methylpropyl ... Examples include polyester polyols obtained by reacting polyols with carboxylic acids such as citric acid, phthalic acid, hexahydrophthalic anhydride, terephthalic acid, adipic acid, azelaic acid, and tetrahydrophthalic anhydride; caprolactone alcohols obtained by reacting polyhydric alcohols with ε-caprolactone; polycarbonate polyols (such as polycarbonate diols obtained by reacting 1,6-hexanediol with diphenyl carbonate); and polyether polyols (such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene oxide-modified bisphenol A).

Examples of organic polyisocyanates include isophorone diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and dicyclopentanyl isocyanate.

Examples of hydroxyl group-containing (meth)acrylates that can be used include hydroxy C2-C4 alkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, dimethylolcyclohexyl mono(meth)acrylate, hydroxycaprolactone (meth)acrylate, and hydroxyl group-terminated polyalkylene glycol (meth)acrylate.

Any epoxy (meth)acrylate oligomer obtained by reacting a glycidyl ether-type epoxy compound with (meth)acrylic acid can be used. Preferred glycidyl ether-type epoxy compounds for obtaining epoxy (meth)acrylates include diglycidyl ethers of bisphenol A or its alkylene oxide adducts, diglycidyl ethers of bisphenol F or its alkylene oxide adducts, diglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, diglycidyl ethers of hydrogenated bisphenol F or its alkylene oxide adducts, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and polypropylene glycol diglycidyl ether.

The actinic radiation-curable resin composition of the present invention may optionally contain a photopolymerization initiator (F). When the photopolymerization initiator (F) is contained, the content of the photopolymerization initiator (F) in the total amount of the actinic radiation-curable resin composition of the present invention is preferably 0.05% by weight or more and 10% by weight or less, and more preferably 1% by weight or more and 5% by weight or less. If the content is more than 10% by weight, the transparency of the cured resin layer may be impaired, and initiator decomposition products contained in the cured product may migrate to other substrates, contaminating the substrate or contents. If the content is less than 0.05% by weight, curability and adhesion may be impaired. Photopolymerization initiators may be used alone or in combination of two or more types.

The photopolymerization initiator (F) contained in the actinic radiation-curable resin composition of the present invention is not particularly limited, and examples thereof include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184; manufactured by BASF), 2-hydroxy-2-methyl-[4-(1-methylvinyl)phenyl]propanol oligomer (Esacure ONE; manufactured by Lambarty), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959; manufactured by BASF), 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl)phenyl]propanol oligomer} (Esacure ONE; manufactured by Lambarty), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Esacure 2959; manufactured by BASF), 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl)phenyl]propanol oligomer} (Esacure ONE; manufactured by Lambarty), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one} (Esacure 2959; manufactured by BASF), 1-[4-(2-hydroxy-2-methyl)phenyl]propanol oligomer} (Esacure ONE; manufactured by Lambarty), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one} (Esacure 29 {4-(methylthio)phenyl}-2-methyl-propan-1-one (Irgacure 127; manufactured by BASF), 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651; manufactured by BASF), 2-hydroxy-2-methyl-1-phenyl-propan-1-one (DAROCUR 1173; manufactured by BASF), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (Irgacure 907; manufactured by BASF), ; manufactured by BASF), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-chlorothioxanthone, 2,4-diethylthioxanthone (Kayacure DETX-S; manufactured by Nippon Kayaku Co., Ltd.), 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone, 1,2-octanedione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)] (IRGACURE OXE01; manufactured by BASF), and a mixture of oxyphenylacetic acid 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenylacetic acid 2-(2-hydroxyethoxy)ethyl ester (IRGACURE 754; manufactured by BASF).

The actinic radiation-curable resin composition of the present invention may contain additives such as antioxidants, thixotropy-imparting agents, antifoaming agents, surface tension modifiers, silane coupling agents, polymerization inhibitors, leveling agents, antistatic agents, surface lubricants, fluorescent brighteners, and light stabilizers (e.g., hindered amine compounds, etc.) as needed. In the present invention, the amount of solvent is less than 2% by weight of the total amount of actinic radiation-curable resin composition. This is because containing a large amount of solvent requires equipment for volatilizing and detoxifying the organic solvent during the film-forming process and has a negative effect on curability. Here, the amount of solvent is preferably 1% by weight or less, and more preferably 0.1% by weight or less, of the total amount of actinic radiation-curable resin composition.

When the above-mentioned various additives are contained in the actinic radiation-curable resin composition, the content of the various additives in the total amount of the actinic radiation-curable resin composition is preferably 0.01% by weight or more and 3% by weight or less, more preferably 0.01% by weight or more and 1% by weight or less, and particularly preferably 0.02% by weight or more and 0.5% by weight or less.

The actinic radiation-curable resin composition of the present invention can be obtained by mixing and dissolving the above components at room temperature to 80°C, and impurities may be removed by filtration or other procedures, if necessary. It is preferable to appropriately adjust the component ratios of the actinic radiation-curable resin composition of the present invention so that the viscosity at 25°C is in the range of 1 to 10,000 mPa·s. Furthermore, from the perspective of coatability to substrates, it is more preferable to appropriately adjust the component ratios so that the viscosity at 25°C is in the range of 1 to 6,000 mPa·s, even more preferably a viscosity at 25°C in the range of 1 to 300 mPa·s, and even more preferably a viscosity at 25°C in the range of 1 to 100 mPa·s. If the viscosity is higher than 10,000 mPa·s, coatability to substrates may be impaired.

The method for applying the actinic radiation-curable resin composition of the present invention to a substrate is not particularly limited, but examples include silk screen printing, gravure printing, offset printing, flexographic printing, roller coater, brush coating, spraying, knife jet coater, inkjet printing, pad printing, gravure offset printing, die coater, bar coater, spin coater, comma coater, impregnation coater, dispenser, and metal mask methods.

The actinic radiation-curable resin composition of the present invention can be cured by irradiation with actinic radiation such as electron beams (EB) or ultraviolet rays (UV). The means for irradiating actinic radiation is not particularly limited, but examples include metal halide light sources, high-pressure mercury light sources, low-pressure mercury light sources, UV-LED light sources, and electron beam irradiation devices. From the perspective of reducing the odor of the cured product and the risk of component migration to the substrate, etc., it is preferable not to include a photopolymerization initiator in the actinic radiation-curable resin composition and to cure it by irradiation with electron beams (EB). Furthermore, from the perspective of improving surface curability, it is preferable to irradiate with actinic radiation in a nitrogen atmosphere.

To remove the release layer formed from the cured product of the actinic radiation-curable resin composition of the present invention from a plastic substrate, immersion in an alkaline aqueous solution is preferred. The conditions for removing the release layer and printed layer from the plastic substrate are preferably a concentration of 1 to 10% by weight, and more preferably 1 to 5% by weight. A concentration higher than 10% by weight can significantly damage the plastic substrate itself due to hydrolysis. A concentration lower than 1% by weight can result in a longer release time or insufficient release properties. The immersion temperature is preferably 20 to 80°C, more preferably 30 to 60°C. The immersion time is 1 minute to 24 hours, and even more preferably 1 minute to 12 hours. After rinsing and drying, the removal rate of the printed layer is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. To improve efficiency, physical stimulation such as circulating rinsing, crushing the printed material or laminate, stirring, or ultrasonic waves may be applied.

By providing a release layer made of a cured product of the actinic radiation-curable resin composition of the present invention on a plastic substrate, it is possible to remove impurities such as printed layers from the plastic substrate by immersing it in an alkaline aqueous solution, and then by rinsing with water and drying, a high-quality recycled plastic substrate suitable for recycling can be obtained.

The actinic radiation-curable resin composition of the present invention can be applied to substrates preferably made of thermoplastic plastics, including polyolefin substrates such as polyethylene and polypropylene, polyester substrates such as polyethylene terephthalate and polylactic acid, polycarbonate substrates, polystyrene substrates, various substrates such as polystyrene-based resins, polyamide substrates, polyvinyl chloride substrates, and polyvinylidene chloride substrates, cellophane substrates, and film or sheet substrates made from composite materials of these. Among these, polyolefin substrates and polyester substrates are preferred. Substrates for sealants, such as unstretched polyethylene substrates, unstretched polypropylene substrates, and unstretched polyester substrates, may also be used.

The above substrates may be coated with a metal oxide or the like by vapor deposition and/or with polyvinyl alcohol or the like. Furthermore, if necessary, substrates may be treated with additives such as antistatic agents and ultraviolet protection agents, or the surface of the substrate may be corona-treated or low-temperature plasma-treated.

When multiple substrates are laminated to obtain a laminate, an adhesive layer may be provided if necessary. Examples of adhesive layers include, but are not limited to, anchor agent layers, molten resin layers, urethane adhesive layers, and acrylic adhesive layers. From the perspective of recyclability, an adhesive layer that dissolves or swells when immersed in an alkaline aqueous solution is preferred, resulting in detachment of the adhesive layer from the substrate adjacent to the adhesive layer. Methods for forming the adhesive layer include, but are not limited to, extrusion lamination, dry lamination, and non-solvent lamination. From an environmental perspective, non-solvent lamination is preferred.

The configuration of the substrate and laminate thereof formed with a detachment layer obtained by curing the actinic radiation-curable resin composition of the present invention is not particularly limited, but examples include the following configurations: "substrate/detachment layer/substrate," "substrate/detachment layer/printed layer," "substrate/detachment layer/adhesive layer/substrate," "substrate/detachment layer/printed layer/adhesive layer/substrate," "substrate/detachment layer/printed layer/adhesive layer/detachment layer/substrate," "substrate/detachment layer/adhesive layer/detachment layer/substrate," "substrate/detachment layer/adhesive layer/detachment layer/substrate," "substrate/detachment layer/printed layer/detachment layer/substrate," "substrate/detachment layer/printed layer/detachment layer/substrate," "substrate/detachment layer/adhesive layer/detachment layer/substrate."

The colored or colorless (clear) ink used to form the printed layer is not particularly limited, but examples include water-based ink, solvent-based ink, UV-curable ink, and electron beam-curable ink. The method for forming the printed layer is not particularly limited, but examples include printing methods such as screen printing, offset printing, flexographic printing, gravure printing, and inkjet printing.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

(Preparation of actinic radiation-curable resin composition)
The resin compositions of Examples 1 to 19 and Comparative Examples 1 to 13 were prepared by heating and mixing at 80°C in the compounding ratios shown in Tables 1 and 2. The components used in preparing the resin compositions are shown in Table 3. The viscosity of the resulting resin compositions was measured at 25°C using an E-type viscometer (TV-25, manufactured by Toki Sangyo Co., Ltd., measuring cone: 1°34 x R24, rotation speed: 20 to 1 rpm).

The following evaluations were carried out using the obtained compositions of Examples 1 to 19 and Comparative Examples 1 to 13.

(Step A: Preparation of PET film with release layer)
The resin compositions of Examples 1 to 19 and Comparative Examples 1 to 13 were coated onto the corona-treated surface of polyethylene terephthalate (PET) film E5102 manufactured by Toyobo Co., Ltd. using a bar coater #3.
The coated surface of each of the resin compositions of Examples 1 to 16 and Comparative Examples 1 to 13 was irradiated with ultraviolet light at an irradiation intensity of 200 mW/ ^cm² and an integrated light dose of 500 mJ/ ^cm² using a high-pressure mercury lamp (80 W/cm², ozone-free) under a nitrogen atmosphere to cure the resin compositions, thereby obtaining PET films with release layers made of the cured products of the resin compositions of Examples 1 to 16 and Comparative Examples 1 to 13. Furthermore, the resin compositions of Examples 17 to 19 were irradiated with electron beams (EB) at an acceleration voltage of 100 kV and a dose of 50 kGy using an electron beam (EB) irradiation device manufactured by Hamamatsu Photonics KK to cure the resin compositions, thereby obtaining PET films with release layers made of the cured products of the resin compositions of Examples 17 to 19.

(Step B: Creation of printed matter using water-based ink)
The aqueous ink described in Example 1 of JP-A No. 2020-125382 was applied to the detachment layer of the PET film with a detachment layer obtained by process A using bar coater #3, and dried at 70°C for 3 minutes to create a printed matter of "PET substrate/detachment layer/printed layer (using aqueous ink)".

(Step C: Creation of printed matter using oil-based ink)
PX-30 ink (colorant: carbon black, main solvent: xylene) manufactured by Mitsubishi Pencil Co., Ltd. was applied to the release layer of the PET film with a release layer obtained by process A using bar coater #3, and dried at 70°C for 3 minutes to prepare a printed matter of "PET substrate/release layer/printed layer (using oil-based ink)".

(Step D: Preparation of OPP film with release layer)
The resin compositions of Examples 1 to 19 and Comparative Examples 1 to 13 were coated onto the corona-treated surface of biaxially oriented polypropylene (OPP) film P2102 manufactured by Toyobo Co., Ltd. using a bar coater #3.
The coated surfaces of the resin compositions of Examples 1 to 16 and Comparative Examples 1 to 13 were irradiated with ultraviolet light at an irradiation intensity of 200 mW/ ^cm² and an integrated light dose of 500 mJ/ ^cm² using a high-pressure mercury lamp (80 W/cm², ozone-free) under a nitrogen atmosphere to cure the resin compositions, thereby obtaining OPP films with release layers made of the cured products of the resin compositions of Examples 1 to 16 and Comparative Examples 1 to 13. Furthermore, the resin compositions of Examples 17 to 19 were irradiated with electron beams (EB) at an acceleration voltage of 100 kV and a dose of 50 kGy using an electron beam (EB) irradiation device manufactured by Hamamatsu Photonics KK to cure the resin compositions, thereby obtaining OPP films with release layers made of the cured products of the resin compositions of Examples 17 to 19.

(Step E: Creation of printed matter using water-based ink)
The aqueous ink described in Example 1 of JP-A No. 2020-125382 was applied to the detachment layer of the OPP film with a detachment layer obtained by process D using bar coater #3, and dried at 70°C for 3 minutes to create a printed matter of "OPP substrate/detachment layer/printed layer (using aqueous ink)".

(Process F: Creation of printed matter using oil-based ink)
PX-30 ink (colorant: carbon black, main solvent: xylene) manufactured by Mitsubishi Pencil Co., Ltd. was applied to the release layer of the OPP film with a release layer obtained by process D using bar coater #3 and dried at 70°C for 3 minutes to produce a printed matter of "OPP substrate/release layer/printed layer (using oil-based ink)".

(Adhesion to substrate: Adhesion to PET)
Cellotape (registered trademark) was adhered to the release layer surface of the PET film with the release layer obtained in step A, and then the tape was peeled off vigorously to check for peeling. The adhesiveness was evaluated based on the ratio of the peeled area to the adhesive area.
◯: The release layer was not peeled off at all.
Δ: The area where the detachment layer peeled off was less than 20%.
x: The area where the detachable layer peeled off was 20% or more and less than 80%.
XX: The area where the detachment layer peeled off was 80% or more.

(Adhesion to substrate: Adhesion to OPP)
Cellotape (registered trademark) was adhered to the release layer surface of the OPP film with the release layer obtained in step D, and then the tape was peeled off vigorously to check for peeling. The adhesiveness was evaluated based on the ratio of the peeled area to the adhesive area.
◯: The release layer was not peeled off at all.
Δ: The area where the detachment layer peeled off was less than 20%.
×: The area where the detachment layer peeled off was 20% or more.
XX: The area where the detachment layer peeled off was 80% or more.

(Blocking resistance)
The PET film with the release layer obtained in step A was cut into a size of 5 cm x 5 cm, folded so that the release layers faced each other, and left to stand in an environment of 40°C for 12 hours while applying a load of 500 g/ ^cm2 . After that, the blocking resistance was evaluated based on the state when the load was removed. The results are shown in Table 2.
◯: The folded surfaces separated within 1 minute after the load was removed. △: The folded surfaces separated within 10 minutes after the load was removed. ×: The folded surfaces remained in close contact for 10 minutes or more after the load was removed.

(Suitable for ink printing: water-based ink)
The printability of the release layer was evaluated based on the appearance of the printed layer obtained in step B. The results are shown in Tables 4 and 5.
◯: No defects in appearance were observed. ×: Defects in appearance such as repelling, surface roughness, and reduced gloss were observed.

(Suitable for ink printing: oil-based ink)
The printability of the release layer was evaluated based on the appearance of the printed layer obtained in step C. The results are shown in Tables 4 and 5.
◯: No defects in appearance were observed. ×: Defects in appearance such as repelling, surface roughness, and reduced gloss were observed.

(Removal: PET substrate, water-based ink)
The printed matter obtained in step B was cut into a 2 cm x 2 cm piece, immersed in 20 g of a 2% aqueous sodium hydroxide solution, and left to stand for 120 minutes at 50°C, and the detachment properties of the detachment layer and printed layer from the substrate were evaluated. The time it took for all of the detachment layers and printed layers to detach from the substrate, and the evaluation results, are shown in Tables 4 and 5.
When the printed layer was detached from the detachable layer but the detachable layer remained on the substrate, the test was continued, and the time until all of the detachable layer was detached from the substrate was measured.
◯: All of the detachable layers and printed layers were detached from the substrate within 60 minutes. Δ: All of the detachable layers and printed layers were detached from the substrate within 120 minutes. ×: All of the detachable layers and printed layers were not detached from the substrate.

(Removal: PET substrate, oil-based ink)
The printed matter obtained in step C was cut into a 2 cm x 2 cm piece, immersed in 20 g of a 2% aqueous sodium hydroxide solution, and left to stand for 120 minutes at 50°C, and the detachment properties of the release layer and printed layer from the substrate were evaluated. The time it took for all of the release layers and printed layers to detach from the substrate, and the evaluation results, are shown in Tables 4 and 5.
When the printed layer was detached from the detachable layer but the detachable layer remained on the substrate, the test was continued, and the time until all of the detachable layer was detached from the substrate was measured.
◯: All of the detachable layers and printed layers were detached from the substrate within 60 minutes. Δ: All of the detachable layers and printed layers were detached from the substrate within 120 minutes. ×: All of the detachable layers and printed layers were not detached from the substrate.

(Removal: OPP substrate, water-based ink)
The printed matter obtained in step E was cut into a 2 cm x 2 cm piece, immersed in 20 g of a 2% aqueous sodium hydroxide solution, and left to stand for 120 minutes at 50°C, and the detachment properties of the detachment layer and printed layer from the substrate were evaluated. The time it took for all of the detachment layer and printed layer to detach from the substrate, and the evaluation results, are shown in Tables 4 and 5.
When the printed layer was detached from the detachable layer but the detachable layer remained on the substrate, the test was continued, and the time until all of the detachable layer was detached from the substrate was measured.
◯: All of the detachable layers and printed layers were detached from the substrate within 60 minutes. Δ: All of the detachable layers and printed layers were detached from the substrate within 120 minutes. ×: All of the detachable layers and printed layers were not detached from the substrate.

(Releasability: OPP base material, oil-based ink)
The printed matter obtained in step F was cut into a 2 cm x 2 cm piece, immersed in 20 g of a 2% aqueous sodium hydroxide solution, and left to stand for 120 minutes at 50°C, and the detachment properties of the detachment layer and printed layer from the substrate were evaluated. The time it took for all of the detachment layers and printed layers to detach from the substrate, and the evaluation results, are shown in Tables 4 and 5.
When the printed layer was detached from the detachable layer but the detachable layer remained on the substrate, the test was continued, and the time until all of the detachable layer was detached from the substrate was measured.
◯: All of the detachable layers and printed layers were detached from the substrate within 60 minutes. Δ: All of the detachable layers and printed layers were detached from the substrate within 120 minutes. ×: All of the detachable layers and printed layers were not detached from the substrate.

Claims (7)

An actinic radiation-curable resin composition containing a carboxy group-containing monofunctional (meth)acrylate (A), a monofunctional (meth)acrylate having a cyclic skeleton and no carboxy group (B), and a bifunctional or higher functional (meth)acrylate and no carboxy group (C), wherein the content of component (A) is 43% by weight or more and 65% by weight or less of the total amount of the actinic radiation-curable resin composition, and component (A) contains at least one selected from 2-(meth)acryloyloxyethyl hexahydrophthalic acid (A-1), 2-(meth)acryloyloxyethyl phthalic acid (A-2), and 2-(meth)acryloyloxypropyl hexahydrophthalic acid (A-3) ,
A solvent-free actinic radiation curable resin composition that is a coating composition for forming a release layer on a thermoplastic plastic substrate . The actinic radiation-curable resin composition according to claim 1, wherein the total content of components (A-1) to (A-3) is 50% by weight or more and 100% by weight or less of the total amount of component (A). The actinic radiation-curable resin composition according to claim 1 or 2, wherein the content of component (B) is 18% by weight or more and 45% by weight or less, and the content of component (C) is 5% by weight or more and 20% by weight or less, based on the total amount of the actinic radiation-curable resin composition. The actinic radiation-curable resin composition according to claim 3, wherein component (B) contains at least one selected from isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, acryloylmorpholine, cyclic trimethylolpropane formal acrylate, and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate. The actinic radiation-curable resin composition according to claim 1 or 2, which is an electron beam-curable resin composition. 3. The actinic radiation-curable resin composition according to claim 1 , wherein the thermoplastic plastic substrate is a polyester or polyolefin substrate. A release layer formed from the actinic radiation-curable resin composition according to claim 1 or 2 .