Recycled plastic substrate, and method for manufacturing the recycled plastic substrate.

Abstract

The object of the present invention is to provide a method for easily recovering plastic substrates from laminates comprising a plastic substrate and a coating layer consisting of a photocurable ink using a photopolymerization initiator in contact with the substrate, which has been difficult to recover until now, and to provide a recovered plastic substrate that maintains excellent quality even after heat regeneration, or to provide a method for producing such a recovered plastic substrate. [Solution] A recovered plastic substrate obtained by removing the film layer from a laminate having a plastic substrate and a film layer in contact with the plastic substrate, wherein the film layer is a cured product of a photocurable ink containing a photopolymerization initiator, and the content of the photopolymerization initiator is 10 to 1000 ppb in the total mass of the recovered plastic substrate.

Description

Technical Field

[0001] The present invention relates to a recovered plastic substrate obtained from a laminate containing a plastic substrate, and a method for producing the recovered plastic substrate.

Background Art

[0002] Compared with oxidative polymerization type, penetration drying type, and hot air drying type oil-based inks, photocurable inks have the convenience of instant curing, the property of being able to form a strong cured film, and the property of being non-VOC that does not contain petroleum-based volatile compounds. Therefore, they are widely used in the field of the packaging printing industry, from beverage and food packaging applications, pharmaceutical packaging applications, cosmetic packaging applications to general paper containers.

[0003] Particularly in the field of food packaging, as an ideal form of photocurable ink, an electron beam (hereinafter also referred to as "EB") curable ink that does not contain a photoinitiator and is safe and secure for the human body and the environment can be cited. However, due to the large initial equipment investment, it is difficult to say that it is common, and ultraviolet (hereinafter also referred to as "UV") curable ink is common in the market.

[0004] In recent years, it is known that there is a gradual shift to an LED curing type system using a UV-LED light source that saves power and suppresses the generation of ozone and heat, an energy-saving UV system using a single metal halide lamp that excludes the infrared region where heat is generated and the ultraviolet region where ozone is generated, and an energy-saving UV system that reduces the number of lamps of a conventional UV lamp from the usual 3 to 4 lamps to 1 lamp.

[0005] Energy-saving UV curable inks and varnishes designed to correspond to these new systems are particularly increasing in the switching from general oil-based inks in commercial printing in recent years, and performance equivalent to general oil-based inks, such as printing suitability and print quality, is required. Among these, an increasing number of energy-saving UV curable inks have received the certification of recycling suitability Class A as "recycling-compatible UV curable inks". However, not all UV systems in the market will be replaced by energy-saving UV systems, and conventional UV systems (many of which have a proven track record and are rated B for recyclability) are still frequently used. UV-curing inks are generally considered more difficult to recycle than general oil-based inks, with the exception of recyclable energy-saving UV-curing inks and some recyclable UV-curing inks. Separating printed materials with non-recyclable UV-curing or other light-curing inks to simplify recycling when collecting printed materials is considered extremely difficult, and almost impossible.

[0006] Similarly, for plastic substrates, which are non-absorbent substrates other than paper, there is an urgent need to develop methods that facilitate the recycling of these substrates. This is because, in recent years, UV curing equipment, UV-LED curing equipment, and EB curing equipment that do not generate much heat have been developed, making it possible to irradiate the substrate with light without causing thermal damage, even if the substrate thickness is small. As a result, the use of light-curing inks is increasing.

[0007] In particular, for plastic substrates, measures against marine pollution are required as part of global environmental protection, and the development of plastic recovery systems that prevent microplastics, which cause marine pollution, from flowing into the ocean is urgently needed. Compared to chemical recycling, which chemically decomposes and reuses recovered plastic, material recycling, which heats and pelletizes recovered plastic for reuse as recycled plastic, is simpler. However, if the photocurable ink is not detached from the substrate, the remaining ink enters the melting process of the substrate, causing problems such as the substrate becoming discolored, yellowing of the recycled plastic substrate due to components derived from the photoinitiator contained in the ink (often unreacted photoinitiator), and safety concerns such as the recycled plastic substrate not meeting the performance requirements for food applications. As a result, the uses of recycled substrates are likely to be limited. Therefore, developing a simple method to obtain recycled plastic without problems of discoloration, yellowing, and safety will lead to an increase in the efficiency of material recycling. To solve this safety issue, a specific initiator composition is desired in which the initiator sublimes during the plastic recycling process.

[0008] Furthermore, if recycled plastic free from discoloration, yellowing, and safety issues can be obtained from all forms of plastic substrates, including not only flexible packaging materials but also rigid plastic substrates such as PET bottles and their lids, nonwoven plastic substrates, and plastic substrates containing metal, then it will be possible to improve the efficiency of recycling, reduce the use of fossil resources, and ultimately contribute to reducing carbon dioxide emissions.

[0009] For example, Patent Document 1 discloses an organic solvent-based ink for a desorption layer that can be removed by alkaline treatment, a laminate such as a printed material containing the desorption layer using this ink, and a method for recycling this laminate. However, the disclosed ink is not a photocurable ink, and there is still no simple desorption method for photocurable inks.

[0010] Patent Document 2 mentions an aqueous anchoring agent for a desorption layer that can be removed by alkaline treatment, and laminates such as printed materials containing this desorption layer. However, the substrates to be desorbed are limited to paper and synthetic paper, and technology has not been established for non-absorbent substrates such as plastics.

[0011] Patent Document 3 describes a desorption technology when an aqueous anchoring agent is used on a plastic substrate, but without an anchoring agent, it is extremely difficult to achieve both ink performance and desorption properties. However, since adding an anchor layer, as described in reference 2 or 3, increases the process, the printing industry desires that the coating layer can be detached without using an anchoring agent. In other words, it is desirable to be able to recover the plastic substrate from a laminate in which the plastic substrate and a coating layer such as an ink layer are in direct contact.

[0012] The recycled plastic substrates are expected to be heated and reused (hereinafter also referred to as regenerated). There are concerns that components derived from photopolymerization initiators (in most cases, unreacted photopolymerization initiators) may cause yellowing of the recycled plastic substrates when heated, or that the recycled plastic substrates may not meet the standards for food use. Therefore, a specific initiator composition is desired in which the initiator sublimes as much as possible, and during the regeneration of the plastic. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2020-090627 [Patent Document 2] Japanese Patent Publication No. 2023-018605 [Patent Document 3] Japanese Patent Publication No. 2024-152215 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] The object of the present invention is to provide a method for easily recovering plastic substrates from laminates comprising a plastic substrate and a coating layer consisting of a photocurable ink using a photopolymerization initiator in contact with the substrate, which has been difficult to recover until now, and to provide a recovered plastic substrate that maintains excellent quality even after heat regeneration, or to provide a method for producing such a recovered plastic substrate. [Means for solving the problem]

[0015] The inventors of the present invention have conducted extensive research to solve the above problems and have found that the above problems can be solved by the following recycled plastic substrate or method for manufacturing the recycled plastic substrate, thereby completing the present invention.

[0016] In other words, embodiments of the present invention relate to the following. However, the present invention is not limited to the following embodiments and includes various embodiments. <1> A recovered plastic substrate obtained by removing the coating layer from a laminate having a plastic substrate and a coating layer in contact with the plastic substrate, The aforementioned film layer is a cured product of a photocurable ink containing a photopolymerization initiator. A recycled plastic substrate in which the content of the photopolymerization initiator is 10 to 1000 ppb in the total mass of the recycled plastic substrate.

[0017] <2> The above contains 80% by mass or more of a photopolymerization initiator whose mass loss rate by thermogravimetric analysis (heating conditions: 10°C / min) is 5% at a temperature of less than 290°C. <1> The recycled plastic substrates described.

[0018] <3> The photopolymerization initiator is a photopolymerization initiator having a peak absorption wavelength at 280-420 nm, as described above. <1> or <2> The recycled plastic substrates described.

[0019] <4>The recovered plastic substrate according to any one of <1> to <3> above, wherein the photoinitiator contains one or more selected from the group consisting of acylphosphine oxide compounds, dialkoxyacetophenone compounds, hydroxyketone compounds, oxime ester compounds, aminoketone compounds, thioxanthone compounds, coumarin compounds, and benzophenone compounds.

[0020] <5>The recovered plastic substrate according to any one of <1> to <4> above, wherein the plastic substrate is any plastic substrate selected from the group consisting of polyethylene terephthalate, polypropylene, polyethylene, nylon, polyvinyl chloride, and polycarbonate.

[0021] <6>A method for recovering a plastic substrate from a laminate having a plastic substrate and a film layer in contact with the plastic substrate, the method including a step of detaching the film layer, wherein the film layer is a cured product of a photocurable ink containing a photoinitiator, and the content of the photoinitiator is 10 to 1000 ppb in the total mass of the recovered plastic substrate.

[0022] <7>The method for producing a recovered plastic substrate according to 6 above, wherein the photoinitiator contains 80% by mass or more of the total amount of the photoinitiator having a temperature at which the mass reduction rate in thermogravimetric analysis (heating rate: 10 ° C / min) is 5% and is less than 290 ° C.

Advantages of the Invention

[0023] According to the present invention, it is possible to easily recover a plastic substrate from a laminate including a plastic substrate and a film layer made of a photocurable ink using a photoinitiator in contact therewith, and to provide a recovered plastic substrate having excellent quality even after heat regeneration, or to provide a method for producing the recovered plastic substrate.

Modes for Carrying Out the Invention

[0024] The present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its spirit. Unless otherwise specified, "parts" refers to "parts by mass," and "%" refers to "mass%."

[0025] The recovered plastic substrate of the present invention is a recovered plastic substrate obtained by removing the coating layer from a laminate having a plastic substrate and a coating layer in contact with the plastic substrate, The aforementioned film layer is a cured product of a photocurable ink containing a photopolymerization initiator. The present invention is characterized in that the amount of photopolymerization initiator in the photopolymerizable ink remaining on the recovered plastic substrate is 10 to 1000 ppb of the total mass of the recovered plastic substrate.

[0026] While the layer formed from the cured product of light-curing inks offers excellent resistance to various substances, it is difficult to remove the film layer using simple methods. If a large amount of the film layer remains and the material is regenerated by heating, discoloration from the ink will occur, limiting its usability. Furthermore, in the case of light-curing inks containing photoinitiators, the remaining film layer contains components (residues and decomposition products) derived from the photoinitiator, and if the amount is large, it can lead to discoloration during regeneration and raise safety concerns for the regenerated material.

[0027] This invention has found that if a coating layer is removed from a laminate formed by printing or coating a photocurable ink in direct contact with a plastic substrate, and the photopolymerization initiator content in the recovered plastic substrate is 10 to 1000 ppb, then the regenerated material obtained by heating is free from coloring due to residual ink and discoloration due to residual initiator, and is a regenerated material with excellent safety.

[0028] The laminate for obtaining the recycled plastic substrate in the present invention will be described below.

[0029] <Coating layer, light-curing ink (hereinafter also simply referred to as "ink")> The photocurable ink used in the present invention comprises a photocurable component and a photopolymerization initiator.

[0030] There are two types of photopolymerization initiators: photoradical polymerization initiators and photocationic polymerization initiators. The photocurable component depends on the type of photopolymerization initiator. Examples include compounds having unsaturated ethylene groups that exhibit photoradical polymerization, or compounds having epoxy groups that exhibit photocationic polymerization. The photocurable component may be low molecular weight or high molecular weight. Furthermore, one or more photopolymerizable groups such as the unsaturated ethylene group and / or epoxy group are sufficient.

[0031] For light-curing inks, it is sufficient if an uncured film is formed by printing with a printing press or coating with a coating machine. Then, it is sufficient if this film can be cured by light to form a cured film layer.

[0032] When using a printing press, the light-curing ink is preferably at least one selected from the group consisting of light-curing offset printing ink, light-curing flexographic printing ink, and light-curing resin relief printing ink.

[0033] The coating layer can also be detached from the laminate by physical polishing. Alternatively, it can be detached from the laminate by contacting it with a liquid medium such as water, an organic solvent, an inorganic solvent, or a mixture thereof, causing it to swell or dissolve.

[0034] [Coloring agent] The light-curing ink used in the present invention may contain a colorant. At least one of pigments and dyes can be used as the colorant. From the viewpoint of lightfastness, pigments are preferred. There are no particular limitations on the pigments that can be used in the present invention; known pigments can be used. Both inorganic and organic pigments can be used. If the light-curing ink does not contain a coloring agent, it will become a varnish.

[0035] Examples of inorganic pigments include carbon blacks such as furnace black, lamp black, acetylene black, and channel black, as well as iron oxide and titanium dioxide.

[0036] Organic pigments include soluble azo pigments such as β-naphthol-based, β-oxynaphthoic acid-based, β-oxynaphthoic acid-based anilide-based, acetoacetate anilide-based, and pyrazolone-based pigments; Examples include insoluble azo pigments such as β-naphthol-based, β-oxynaphthoic acid-based anilide-based, acetoacetate anilide-based monoazo, acetoacetate anilide-based disazo, and pyrazolone-based pigments; phthalocyanine-based pigments such as copper phthalocyanine blue, halogenated (e.g., chlorinated or brominated) copper phthalocyanine blue, sulfonated copper phthalocyanine blue, and metal-free phthalocyanines; and polycyclic and heterocyclic pigments such as quinacridone-based, dioxazine-based, slene-based (pyrantrone, anthantrone, indanthrone, anthrapyrimidine, flavanthrone, thioindigo-based, anthraquinone-based, perinone-based, perylene-based, etc.), isoindolinone-based, metal complex-based, quinophthalone-based, and diketopyrrolopyrrole-based pigments.

[0037] More specifically, using the CI color index, examples of black pigments include CIPigment Black 1, 6, 7, 9, 10, 11, 28, 26, and 31.

[0038] Examples of white pigments include CIPigment White 5, 6, 7, 12, and 28.

[0039] Examples of yellow pigments include CIPigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 18, 24, 73, 74, 75, 83, 93, 95, 97, 98, 100, 108, 109, 110, 114, 120, 128, 129, 138, 139, 174, 150, 151, 154, 155, 167, 174, 176, 180, 185, and 213.

[0040] Examples of blue or cyan pigments include CIPigment Blue 1, 2, 14, 15, 15:1, 15:2, 15:3, 15:4, 60, and 62.

[0041] As red or crimson pigments, CIPigment RED 1, 3, 5, 19, 21, 22, 31, 38, 42, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 50, 52, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 83, 90, 104, 108, 11 Examples include 2, 114, 122, 144, 146, 148, 149, 150, 166, 168, 169, 170, 172, 173, 176, 177, 178, 184, 185, 187, 193, 202, 209, 214, 242, 254, 255, 264, 266, 269, and CIPigment Violet 19.

[0042] Examples of green pigments include CIPigment Green 1, 2, 3, 4, 7, 8, 10, 15, 17, 26, 36, 45, and 50.

[0043] Examples of purple pigments include CIPigment Violet 1, 2, 3, 4, 5:1, 12, 13, 15, 16, 17, 19, 23, 25, 29, 31, 32, 36, 37, 39, and 42. Examples of orange pigments include CIPigment Orange 13, 16, 20, 34, 36, 38, 39, 43, 51, 61, 63, 64, and 74.

[0044] In the present invention, the above pigments may be used individually or in combination of two or more types.

[0045] In the present invention, the above pigment can be used in any amount as long as the desired concentration can be reproduced on the surface of the printing substrate, and is preferably 5 to 60% by mass, and more preferably 10 to 50% by mass, relative to the total amount of ink.

[0046] [(meth)acrylate compounds] The photocurable ink used in the present invention preferably contains a compound containing an unsaturated ethylene group as a photocurable component, and more preferably contains a (meth)acrylate compound. In this specification, unless otherwise specified, "(meth)acryloyl," "(meth)acrylic acid," "(meth)acrylate," and "(meth)acryloyloxy" mean "acryloyl and / or methacryloyl," "acrylic acid and / or methacrylic acid," "acrylate and / or methacrylate," and "acryloyloxy and / or methacryloyloxy," respectively. Also, "PO" represents "propylene oxide" and "EO" represents "ethylene oxide." Furthermore, in EO-modified (X) and PO-modified (X), X represents the number of moles of EO and PO that have been modified, and in polyethylene glycol (Y) di(meth)acrylate, Y indicates the approximate molecular weight of the polyethylene glycol portion.

[0047] The (meth)acrylate compounds that can be used in the present invention are not particularly limited as long as they have one or more (meth)acryloyl groups, and include monomers, oligomers, and polymers. Here, "monomer" refers to the smallest constituent compound for building oligomers and polymers, and "oligomer" refers to a polymer having constituent units based on 2 to 100 monomers.

[0048] Specific examples of (meth)acrylate compounds used in the present invention include the compounds listed below.

[0049] (monomer) 2-Ethylhexyl (meth)acrylate, 2-Hydroxyethyl (meth)acrylate, 2-Hydroxypropyl (meth)acrylate, β-Carboxyethyl (meth)acrylate, 4-Tert-Butylcyclohexinol (meth)acrylate, Tetrahydrofurfuryl acrylate, Alkoxylated Tetrahydrofurfuryl acrylate, Caprolactone (meth)acrylate, Lauryl (meth)acrylate, Stearyl (meth)acrylate, Isoamyl (meth)acrylate, 2-Phenoxyethyl (meth)acrylate, Isodecyl (meth)acrylate, 3,3,5-Trimethylcyclohexanol (meth)acrylate, Cyclohexyl ( Monofunctional (meth)acrylate monomers having one (meth)acryloyl group in their molecule, such as meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (oxyethyl) (meth)acrylate, 1,4-cyclohexanedimethanol (meth)acrylate, cyclic trimethylolpropaneformal (meth)acrylate, benzyl (meth)acrylate, EO-modified (2)nonylphenol acrylate, 2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, and 4-[2-(acryloyloxy)ethoxy]-4-oxobutanoic acid. 1,3-Butylene glycol di(meth)acrylate, 1,4-Butanediol di(meth)acrylate, 3-Methyl-1,5-Pentanediol di(meth)acrylate, 1,6-Hexanediol di(meth)acrylate, 1,9-Nonanediol di(meth)acrylate, 1,10-Decanediol di(meth)acrylate, 1,2-Dodecanediol di(meth)acrylate, Neopentyl glycol di(meth)acrylate, Polyethylene glycol (200) di(meth)acrylate, Polyethylene glycol (300) di(meth)acrylate, Polyethylene glycol (400) di(meth)acrylate, Polyethylene glycol (600) di(meth)acrylate, Neopentyl glycol di(meth)acrylate hydroxypivalate , dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, EO-modified (2) 1,6-hexanediol di(meth)acrylate, PO-modified (2) neopentyl glycol di(meth)acrylate, (neopentyl glycol-modified) trimethylolpropane di(meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, EO-modified (4) bisphenol A di(meth)acrylate, PO-modified (4) bisphenol A di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, dicyclopentanyl di(meth)acrylate, and other bifunctional (meth)acrylate monomers having two (meth)acryloyl groups in their molecules, Trifunctional (meth)acrylate monomers having three (meth)acryloyl groups in their molecule, such as trimethylolpropane tri(meth)acrylate, EO-modified (3) trimethylolpropane tri(meth)acrylate, EO-modified (6) trimethylolpropane tri(meth)acrylate, PO-modified (3) trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate. Tetrafunctional (meth)acrylate monomers having four acryloyl groups in their molecule, such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, EO-modified (4) pentaerythritol tetra(meth)acrylate, PO-modified (4) pentaerythritol tetra(meth)acrylate, EO-modified (4) ditrimethylolpropane tetra(meth)acrylate, and PO-modified (4) ditrimethylolpropane tetra(meth)acrylate. Pentafunctional (meth)acrylate monomers having five (meth)acryloyl groups in their molecule, such as dipentaerythritol penta(meth)acrylate, EO-modified (5) dipentaerythritol penta(meth)acrylate, and PO-modified (5) dipentaerythritol penta(meth)acrylate. Examples include six-functional (meth)acrylate monomers having six (meth)acryloyl groups in their molecule, such as dipentaerythritol hexa(meth)acrylate, EO-modified (6) dipentaerythritol hexa(meth)acrylate, and PO-modified (6) dipentaerythritol hexa(meth)acrylate.

[0050] (Oligomer) Examples include urethane acrylate oligomers such as aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers, acrylic ester oligomers, polyester acrylate oligomers, and epoxy acrylate oligomers, which have 1 to 15 (meth)acryloyl groups.

[0051] When the film layer is brought into contact with a liquid medium and swelled or dissolved to desorb it, it is preferable that the (meth)acrylate compound has a functional group that has affinity for the liquid medium. For example, when water or an alkaline aqueous solution is used as the liquid medium, it is preferable that the photo-ink contains a compound having a hydrophilic group. Examples of hydrophilic groups include carboxyl groups, phosphate groups, sulfonic acid groups, acidic groups such as phenolic hydroxyl groups, hydroxyl groups, and (poly)alkylene oxy groups. Among these, an acidic group is preferred. In a more preferred embodiment, it is preferable that the (meth)acrylate compound has the above-mentioned acidic group. If the (meth)acrylate compound has the above-mentioned acidic group, it is preferable that the (meth)acrylate compound has an acid value of 10 mg KOH / g or more.

[0052] Furthermore, in another preferred embodiment, even when using only (meth)acrylate compounds that do not have hydrophilic groups as the (meth)acrylate compound, a low-molecular-weight compound that does not have ethylenically unsaturated groups but has acidic groups, or a high-molecular-weight compound that does not have ethylenically unsaturated groups but has acidic groups, may be used in combination as an ink additive.

[0053] (Photopolymerization initiator) In the present invention, the ink contains a photopolymerization initiator. The photopolymerization initiator in the present invention is a compound that undergoes a chemical change and generates radicals or cations through the action of light or interaction with the electronically excited state of a sensitizing dye, and among these, a photoradical polymerization initiator is preferred from the viewpoint that polymerization can be initiated by light irradiation (also called exposure).

[0054] In the present invention, the above-mentioned photoradical polymerization initiator is not particularly limited, and known ones can be used. Specific examples include acylphosphine oxide compounds, dialkoxyacetophenone compounds, hydroxyketone compounds such as α-hydroxyalkylphenone compounds, oxime ester compounds, aminoketone compounds such as α-aminoalkylphenone compounds, thioxanthone compounds, coumarin compounds such as ketocoumarin compounds, and benzophenone compounds. Furthermore, the photopolymerization initiator may be used alone or in combination of two or more.

[0055] The photopolymerization initiator in the present invention preferably includes a photopolymerization initiator whose temperature at which the mass loss rate in thermogravimetric analysis (heating conditions: 10°C / min) becomes 5% is less than 290°C (hereinafter also referred to as "initiator below 290°C"), and more preferably, the photopolymerization initiator whose temperature at which the mass loss rate becomes 5% is less than 290°C constitutes 80% by mass or more of the total amount of the photopolymerization initiator. By using a photopolymerization initiator in the ink whose mass loss rate in thermogravimetric analysis (heating conditions: 10°C / min) is less than 290°C, sublimation of the photopolymerization initiator becomes more likely during the heat molding process in the recycling process of the recovered plastic substrate described later, thereby reducing the residue of the photopolymerization initiator in the recycled material. In particular, by including 80% by mass or more of a photopolymerization initiator whose mass loss rate is less than 290°C in the total amount of photopolymerization initiator, the residue of the photopolymerization initiator in the recycled material can be significantly reduced.

[0056] The photopolymerization initiator in the present invention preferably includes a photopolymerization initiator having a maximum absorption wavelength peak at 280 to 420 nm (hereinafter also referred to as "280 to 420 nm initiator"). By using a photopolymerization initiator with a maximum absorption wavelength peak at 280-420 nm as the photopolymerization initiator in the ink, good curability and adhesion of the ink can be achieved even when using an energy-saving LED curing system, which has become increasingly popular in recent years. In particular, by including 80% by mass or more of a photopolymerization initiator with a maximum absorption wavelength peak at 280-420 nm in the total amount of photopolymerization initiator, sufficient adhesion as a laminate can be ensured even when using an LED curing system.

[0057] Examples of acylphosphine oxide compounds include diphenylacylphenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, tris(phenyl(2,4,6-trimethylbenzoyl)phosphinic acid) polyethylene glycol ester, ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate, and bis(2,4,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0058] Examples of dialkoxyacetophenone compounds include 2,2-dimethoxy-2-phenylacetophenone, dimethoxyacetophenone, and diethoxyacetophenone.

[0059] Examples of α-hydroxyalkylphenone compounds include 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxymethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methylpropan-1-one, oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], and 2,3-dihydro-6-(2-hydroxy-2-methyl-1-oxopropyl)-1,1,3-trimethyl-3-[4-(2-hydroxy-2- Examples include mixtures of methyl-1-oxopropyl)phenyl]-1H-indene and 2,3-dihydro-5-(2-hydroxy-2-methyl-1-oxopropyl)-1,1,3-trimethyl-3-[4-(2-hydroxy-2-methyl-1-oxopropyl)phenyl]-1H-indene, 2-hydroxy-1-[4-[4-(2-hydroxy-2-methylpropynyl)benzyl]phenyl]-2-methylpropan-1-one, 2-hydroxy-1-[4-[4-(2-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropan-1-one, and 1-[4-(1,1-dimethylethyl)phenyl]-2-hydroxy-2-methylpropan-1-one.

[0060] Examples of oxime ester compounds include 1-[4-(phenylthio)phenyl]octane-1,2-dione,2-benzoyloxime, ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-,1-(o-acetyloxime), 3-cyclopentyl-1-(4-(phenylthio)phenyl)propane-1,2-dione-2-(o-benzoyloxime), and 1-[9-ethyl-6-(2-methylbenzoyl)-9H Examples include -carbazole-3-yl]-3-cyclopentylpropane-1-(o-acetyloxime), methanone, [8-[[(acetyloxy)imino][2-(2,2,3,3-tetrafluoropropoxy)phenyl]methyl]-11-(2-ethylhexyl)-11H-benzo[a]carbazole-5-yl]-,(2,4,6-trimethylphenyl), and 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime.

[0061] Examples of α-aminoalkylphenone compounds include 2-methyl-1-[4-(methoxythio)-phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, 1,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and 1-(9,9-dibutyl-9H-fluoren-2-yl)-2-methyl-2-morpho Examples include phosphate-4-yl-propan-1-one, polyethylene glycol di(β-4-[4-(2-dimethylamino-2-benzyl)butanonylphenyl]piperazine)propinate, 2-benzyl-2-dimethylamino-1-(4-piperidinylphenyl)-1-butanone, 1-(biphenyl-4-yl)-2-methyl-2-morpholinopropan-1-one, and 1-(biphenyl-4-yl)-2-methoxy-2-morpholinopropan-1-one.

[0062] Examples of thioxanthone compounds include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propylthioxanthone, 2-chlorothioxanthone, poly(oxy-1,4-butanediyl), α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]-, 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl]oxy}acetylpoly[oxy(1-methylethylene)])oxy]-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl]oxy}acetylpoly[oxy(1-methylethylene)])oxymethyl)propane.

[0063] Examples of ketocoumarin compounds include reaction products of 5,7-dimethoxy-3-(4-(sec-C10-C13-alkyl)-benzoyl)-2H-chromen-2-one.

[0064] Examples of benzophenone compounds include benzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(dimethylamino)benzophenone, [4-(methylphenylthio)phenyl]-phenylmethanone, 2-chloro-4phenyl-benzophenone, 1-{4-[(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylbenzenesulfonyl)propan-1-one, and polybutylene glycol bis(4-benzoylphenoxy)acetate.

[0065] The content of the photopolymerization initiator is preferably 1 to 20% by mass, and more preferably 5 to 15% by mass, relative to the total amount of ink.

[0066] [Other ingredients] In the present invention, the ink may, if necessary, contain, in addition to the above components, a photosensitizer, an amine compound, a resin, a polymerization inhibitor, a surface tension modifier, a wax, an extender pigment, a pigment dispersant, an antifoaming agent, an ultraviolet absorber, an antioxidant, an antistatic agent, and the like. (Amine compounds) In the present invention, the ink may contain an amine compound. There are no particular restrictions on the amine compound, and known amine compounds can be used. By using an amine compound as a component of a photocurable ink, it is expected that the effect of the hydrogen abstraction type photopolymerization initiator will be enhanced. Specific examples include, for instance, N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, ethyl 4-(dimethylamino)benzoate, N,N- Examples include dihydroxyethylaniline, triethylamine and N,N-dimethylhexylamine, poly(oxy-1,2-ethanediyl,α-[4-(dimethylamino)benzoyl]-ω-[[4-(dimethylamino)benzoyl]oxy]-, bis-N,N-[2-(4-dimethylaminobenzoyl)oxyethylene-1-yl]methylamine, poly(oxy-1,2-ethanediyl),α-[4-(dimethylamino)benzoyl]-ω-[[4-(dimethylamino)benzoyl]oxy]-, poly[oxy(methyl-1,2-ethanediyl),α-[4-(dimethylamino)benzoyl-ω-butoxy-, 2-butoxyethyl-4-(dimethylamino)benzoate, 2-(dimethylamino)ethylbenzoate, etc. The amine compounds may be used individually or in combination of two or more types.

[0067] (resin) In this invention, the ink may contain a resin. The inclusion of a resin mitigates the curing shrinkage of the coating film that occurs during curing, suppresses the shrinkage of the substrate, and improves adhesion. Furthermore, if the resin has an acid value of 10 mg KOH / g or higher, it promotes swelling in an alkaline aqueous solution, making peeling easier.

[0068] The resin may be used alone or in combination of two or more types. Furthermore, the resin content is preferably 1 to 20% by mass relative to the total mass of the ink.

[0069] Examples of resins include polyvinyl chloride, (meth)acrylic resin, styrene (meth)acrylic resin, epoxy resin, polyester resin, polyurethane resin, cellulose derivatives (e.g., ethylcellulose, cellulose acetate, nitrocellulose), vinyl chloride-vinyl acetate copolymer, polyamide resin, polyvinyl acetal resin, diallyl phthalate resin, non-phthalate allyl resin, alkyd resin, rosin-modified resin, petroleum resin, urea resin, and synthetic rubber such as butadiene-acrylonitrile copolymer. Among these, diallyl phthalate resin, polyester resin, and rosin-modified resin are more preferred from the viewpoint of dispersibility.

[0070] (Polymerization inhibitor) In the present invention, the ink may contain a polymerization inhibitor. Specific examples of polymerization inhibitors include 4-methoxyphenol, hydroquinone, methylhydroquinone, t-butylhydroquinone, 2,6-di-t-butyl-4-methylphenol, phenothiazine, copper dialkyldithiocarbamate complex, and aluminum salts of N-nitrosophenylhydroxylamine.

[0071] From the viewpoint of maintaining curability while improving ink stability, the content of the polymerization inhibitor is preferably 0.01 to 2% by mass relative to the total mass of the ink.

[0072] (wax) In the present invention, the ink may contain wax. The inclusion of wax can improve friction resistance, scratch resistance, anti-blocking properties, slipperiness, and scratch resistance. There are no particular restrictions on the wax used; known waxes can be used. Examples include natural waxes and synthetic waxes. Examples of natural waxes include carnauba wax, wood wax, lanolin, montan wax, paraffin wax, and microcrystalline wax. Examples of synthetic waxes include Fischertrop's wax, polyethylene wax, polypropylene wax, and polytetrafluoroethylene wax.

[0073] The wax content is preferably 0.1 to 5% by mass relative to the total mass of the ink.

[0074] (Extender pigments) In the present invention, the ink may contain an extender pigment. Examples of extender pigments include clay, talc, barium sulfate, calcium carbonate, heavy calcium carbonate, barium carbonate, magnesium carbonate, silica, and bentonite.

[0075] (Pigment dispersant) In the present invention, the ink preferably contains a pigment dispersant to improve pigment dispersibility. There are no particular restrictions on the pigment dispersant, and known pigment dispersants can be used. Among these, resin-type pigment dispersants having a basic functional group are preferred, and examples of the basic functional group include primary, secondary, or tertiary amino groups, and nitrogen-containing heterocycles such as pyridine, pyrimidine, and pyrazine. Furthermore, a fatty acid amine skeleton and / or a urethane skeleton are even more preferable as the framework constituting the resin-type pigment dispersant, as good pigment dispersibility can be easily obtained.

[0076] Examples of the aforementioned pigment dispersants include the Azisper series from Ajinomoto Fine Techno Co., Ltd. (Azisper PB821, PB822, PB824, etc.), the Solspers series from Lubrizol (Solsperse00, Solsperse32000, Solsperse38500, etc.), and the Disperbic series from Bic Chemie (BYK-162, BYK-168, BYK-183, etc.).

[0077] The content of the pigment dispersant is preferably 0.1 to 10% by mass, and more preferably 0.2 to 5% by mass, based on the total mass of the ink.

[0078] <Laminate> The laminate used in the present invention is a laminate having a plastic substrate and a film layer in contact with the plastic substrate, wherein the film layer is obtained by forming a film on the substrate with a photocurable ink containing a photopolymerization initiator and curing it with light.

[0079] In the present invention, the light-curable ink is, for example, printed or coated to form a film. In the present invention, the method for printing the light-curable ink is not particularly limited, but it is preferably one of the following: offset printing using light-curable offset printing ink, resin letterpress printing using light-curable resin letterpress printing ink, flexographic printing using light-curable flexographic printing ink, or gravure printing using light-curable gravure printing ink. Furthermore, there are no particular restrictions on the method of applying the light-curing ink, and known methods can be used. Specifically, these include roll coaters, gravure coaters, flexographic coaters, air doctor coaters, blade coaters, air knife coaters, squeeze coaters, impregnation coaters, transfer roll coaters, kiss coaters, curtain coaters, cast coaters, spray coaters, and die coaters.

[0080] There are no particular restrictions on the light source used for photocuring, and any known light source can be used. Specifically, examples include mercury lamps, xenon lamps, metal hydride lamps, excimer lamps, ultraviolet light-emitting diodes (UV-LEDs), ultraviolet laser diodes (UV-LDs), and other LEDs, as well as gas and solid-state lasers.

[0081] <Plastic substrate> The plastic substrate used in this invention is not particularly limited as it has little effect on the delamination mechanism of the coating layer, and known substrates can be used. Specifically, these include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), plastic substrates having an inorganic vapor-deposited layer such as aluminum, silica, or alumina, synthetic paper (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene resin (ABS), polycarbonate (PC), nylon (PA), and cellophane. Various additives such as antistatic agents, antifogging agents, and UV-blocking agents may be used in the substrate.

[0082] <Recycled plastic substrates> In the present invention, the recovered plastic substrate is obtained by peeling off the coating layer of a laminate containing a plastic substrate and a coating layer made of a cured product of a photocurable ink by contacting it with a liquid medium such as an alkaline aqueous solution (e.g., washing, drying), and the amount of photopolymerization initiator contained in the recovered plastic substrate is 10 ppb or more and 1000 ppb or less. Furthermore, when an anchor layer for detachment is used, or when a coating consisting of a photocurable ink designed to have particularly excellent detachment properties is used, the amount of photopolymerization initiator in the recovered plastic substrate will be less than 10 ppb, and will be classified as such.

[0083] <Method for manufacturing recycled plastic substrates> The method for producing recycled plastic substrates according to the present invention includes, for example, the following steps. Step 1: Detaching the coating layer from the laminate. Step 2: Separating the plastic substrate from which the coating layer has been detached (recovered plastic substrate) from the detached coating layer. Step 3: Process the recycled plastic substrate into a shape that can be reused by heat molding or other methods.

[0084] <Step 1: Detaching the coating layer from the laminate> In the present invention, desorption refers to the removal of the coating layer from a plastic substrate on which a coating layer has already been formed.

[0085] (A step in which the film layer is removed using an alkaline aqueous solution) The above-mentioned laminate is brought into contact with an alkaline aqueous solution in a treatment tank containing an alkaline aqueous solution, for example, to remove the coating layer. The desorption rate, which indicates the proportion of desorption, is known to improve with longer contact time with the liquid medium, but longer contact times are industrially disadvantageous. Generally, in order to desorb colored film layers such as inks and use them as colorless recycled plastic substrates, a desorption rate of 99% by mass or higher is preferable. By setting the following conditions, a substrate with a desorption rate of 99% by mass or higher can be efficiently obtained.

[0086] (Alkaline aqueous solution) In the present invention, the alkaline aqueous solution is an aqueous solution containing an alkaline compound, preferably containing 0.5 to 10% by mass of the alkaline compound, and more preferably 1 to 5% by mass. There are no particular limitations on the alkaline compound, but suitable examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonia, barium hydroxide (Ba(OH)2), sodium carbonate (Na2CO3), etc. Preferably, it is NaOH and / or KOH.

[0087] It is preferable to bring the laminate and the alkaline aqueous solution into contact while stirring. The stirring means are not particularly limited, and known stirring equipment such as general dispersers, radial flow turbine blades, axial flow turbine blades, paddle blades, propeller blades, anchor blades, and high-shear mixers can be used. The stirring speed is preferably 100 to 350 rpm, for example, on a 2L flask scale, depending on the shape and size of the stirring blades. Based on the content of the photopolymerization initiator in the recovered plastic substrate and the practicality of the desorption time, the stirring time is preferably 30 minutes to 24 hours, more preferably 30 minutes to 12 hours, and even more preferably 30 minutes to 6 hours.

[0088] <Step 2: Separating the plastic substrate from which the coating layer has detached (recovered plastic substrate) from the detached coating layer; Method for recovering the substrate> The present invention relates to a method for producing a recovered plastic substrate, which includes a step of separating the detached film layer after detaching the film layer from the laminate. The step of separating the detached film layer, for example, if detachment is performed in a treatment tank, is a step of separating and recovering the substrate from the treatment tank containing a mixture of the alkaline aqueous solution, fragments of the detached film layer, and the substrate after treating the laminate with an alkaline aqueous solution, and it is preferable to obtain the recovered plastic substrate in high purity. The method of recovering the substrate is not particularly limited, and for example, separation and recovery via a mesh or the like based on the size difference between the plastic substrate and the fragments of the film layer is preferred, and separation and recovery based on the difference in specific gravity is also preferred. Alternatively, separation and recovery can be appropriately performed by a combination of these, but it is particularly preferable to include a separation and recovery step based on the difference in specific gravity, and more preferably to use a combination of a separation and recovery step based on the difference in specific gravity and a separation and recovery step based on the difference in size. In the separation and recovery process based on specific gravity difference, it is preferable to recover only the substrate that floats in the alkaline aqueous solution within the treatment tank. It is also preferable that impurities and fragments of the coating layer in the alkaline aqueous solution settle, as this facilitates separation from the substrate and allows for more precise recovery of only the substrate. As a result, the physical properties and transparency of the recycled substrate after recovery are improved. The separation method based on specific gravity difference may be a conventionally known method, such as one using a fluidized bed or one using a centrifuge.

[0089] After the coating layer is detached from the laminate and the plastic substrate is recovered, the recovered plastic substrate can be obtained by washing and drying it with water. In this process, it is preferable that the recycled plastic substrate is free from any contaminants, including fragments of the detached coating layer.

[0090] (Amount of initiator remaining in recovered plastic substrates) The recovered plastic substrate can be washed with an organic solvent such as MEK, and the washing solution can be recovered, concentrated, and then its residual content measured by HPLC. This allows for the measurement of the photopolymerization initiator content in the total amount of recovered plastic substrate.

[0091] <Process 3: Processing of recycled plastic substrates into a form that can be reused; Recycling of recycled plastic substrates> The recovered plastic substrate can be heated and processed into pellets using an extruder or the like, and reused as recycled material. The use and form of the recycled material are not limited; it may be processed into a colorless, transparent film, or into a molded product with added colorants. The heating temperature is preferably 150 to 350°C, and more preferably 180 to 320°C.

[0092] (Amount of initiator remaining in recycled material) The effects of the present invention can also be confirmed by the amount of initiator remaining after heat processing. While it is preferable that no initiator remains detected in the recovered plastic substrate of the present invention after heat processing, it can be used depending on the application if the amount is 100 ppb or less. The amount of initiator remaining in the recycled material was measured by Soxhlet extraction of the obtained recycled material with an organic solvent such as MEK, followed by concentration of the solution and analysis by HPLC or other methods. [Examples]

[0093] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited in any way by the following examples. In the examples and comparative examples, "parts" and "%" represent "parts by mass" and "mass%", respectively.

[0094] <Synthesis of rosin-modified resin 1> A reaction mixture was obtained by charging 25.0 parts of gum rosin and 13.0 parts of maleic anhydride into a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heating it at 180°C for 1 hour while blowing in nitrogen gas. Subsequently, the completion of the Diels-Alder addition reaction was confirmed by gas chromatography-mass spectrometry of the reaction mixture. Next, 38.0 parts of benzoic acid, 18.0 parts of pentaerythritol, 9.0 parts of glycerin, and 0.1 parts of p-toluenesulfonic acid monohydrate as a catalyst were added to the above reaction mixture, and a dehydration condensation reaction was carried out at 240°C for 9 hours to obtain rosin-modified resin 1. The acid value of rosin-modified resin 1 was 36, and the weight-average molecular weight (Mw) in polystyrene equivalent, measured by GPC, was 27,200.

[0095] <Preparation of light-curing resin varnish 1> As (meth)acrylate compounds, 69.5 parts of TMPTA(PO) and 6.5 parts of TMPTA(EO) were mixed and heated to 100°C while stirring. Then, 25.0 parts of rosin-modified resin 1 were mixed in and dissolved while maintaining the temperature at 100°C to prepare photocurable resin varnish 1.

[0096] <Preparation of light-curing resin varnish 2> As (meth)acrylate compounds, 69.5 parts of DPHA and 6.5 parts of TMPTA(EO) were mixed and heated to 100°C while stirring. Then, 25.0 parts of resin 2 were mixed in and dissolved while maintaining the temperature at 100°C to prepare photocurable resin varnish 2.

[0097] (Ink manufacturing example 1 (UV ink 1)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 3.0 parts of 379 as a photopolymerization initiator, and 51.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0098] (Ink manufacturing example 2 (UV ink 2)) (Photocurable offset printing ink, Photocurable resin relief printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 0.5 parts of 379 as a photopolymerization initiator, and 53.5 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to prepare the ink.

[0099] (Ink manufacturing example 3 (UV ink 3)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 10.0 parts of 379 as a photopolymerization initiator, and 44.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0100] (Ink manufacturing example 4 (UV ink 4)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 2.0 parts of 910 as a photopolymerization initiator, and 52.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0101] (Ink manufacturing example 5 (UV ink 5)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together. As (meth)acrylate compounds, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed together. As a photopolymerization initiator, 10.0 parts of DEABP were mixed together. As an amine compound, 3.0 parts of EDB were mixed together. As an amine compound, 41.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer. The mixture was then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to prepare the ink.

[0102] (Ink manufacturing example 6 (UV ink 6)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 10.0 parts of TPO as a photopolymerization initiator, and 44.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to prepare the ink.

[0103] (Ink manufacturing example 7 (UV ink 7)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together. As (meth)acrylate compounds, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed together. As a photopolymerization initiator, 10.0 parts of DETX were mixed together. As an amine compound, 3.0 parts of EDB were mixed together. As a photocurable resin varnish, 41.0 parts of the mixture were mixed and stirred using a butterfly mixer. The mixture was then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to produce an ink.

[0104] (Ink manufacturing example 8 (UV ink 8)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed together. As (meth)acrylate compounds, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed together. As a photopolymerization initiator, 10.0 parts of 4MBP were mixed together. As an amine compound, 3.0 parts of EDB were mixed together. As an amine compound, 41.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer. The mixture was then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to prepare the ink.

[0105] (Ink manufacturing example 9 (UV ink 9)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed, along with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 10.0 parts of 184 as a photopolymerization initiator, and 44.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0106] (Ink manufacturing example 10 (UV ink 10)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed; as (meth)acrylate compounds, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed; as photopolymerization initiators, 7.0 parts of 379 and 3.0 parts of TX were mixed; as an amine compound, 3.0 parts of EDB was mixed; and 41.0 parts of photocurable resin varnish 1 were mixed. After stirring and mixing using a butterfly mixer, the mixture was dispersed using a three-roll mixer so that the maximum particle size was 7.5 μm or less to prepare the ink.

[0107] (Ink manufacturing example 11 (UV ink 11)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra and 3.0 parts of BA-2550 were mixed; as (meth)acrylate compounds, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed; as photopolymerization initiators, 9.0 parts of 379 and 1.0 part of TX were mixed; as an amine compound, 3.0 parts of EDB was mixed; and 41.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer, and then dispersed using a three-roll mixer so that the maximum particle size was 7.5 μm or less to prepare the ink.

[0108] (Ink manufacturing example 12 (UV ink 12)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 15.0 parts of Permanent Yellow BHS, 6.0 parts of (meth)acrylate compounds TMPTA(EO), 18.0 parts of DiTMPTA, and 7.0 parts of DPHA, 3.0 parts of 379 as a photopolymerization initiator, and 51.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0109] (Ink manufacturing example 13 (UV ink 13)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 20.0 parts of Permanent Rubine L5B-01 was mixed with 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA as (meth)acrylate compounds, 3.0 parts of 379 as a photopolymerization initiator, and 51.0 parts of photocurable resin varnish 1. The mixture was stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to a maximum particle size of 7.5 μm or less to prepare the ink.

[0110] (Ink manufacturing example 14 (UV ink 14)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 20.0 parts of Heliogen Blue D7088, 6.0 parts of (meth)acrylate compounds TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA, 3.0 parts of 379 as a photopolymerization initiator, and 51.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer, and then dispersed using a three-roll mixer so that the maximum particle size was 7.5 μm or less to prepare the ink.

[0111] (Ink manufacturing example 15 (UV ink 15) (Photocurable flexographic printing ink)) As colorants, 15.0 parts of RAVEN 1080 Ultra and 1.0 part of BA-2550 were added; as (meth)acrylate compounds, 40.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were added; as a photopolymerization initiator, 3.0 parts of 379 were added; and as a pigment dispersant, 6.0 parts of Solsperse24000 were added. These were stirred and mixed using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less. Subsequently, 15.0 parts of SC6640 as a (meth)acrylate compound were added and stirred and mixed using a butterfly mixer to produce another ink.

[0112] (Ink manufacturing example 16 (UV ink 16)) (Photocurable offset printing ink (varnish), Photocurable resin relief printing ink (varnish)) As an extender pigment, 15.0 parts of calcium carbonate, 6.0 parts of (meth)acrylate compounds TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA, 10.0 parts of TPO as a photopolymerization initiator, and 49.0 parts of photocurable resin varnish 1 were mixed and stirred using a butterfly mixer, and then dispersed using a three-roll mixer so that the maximum particle size was 7.5 μm or less to prepare an ink (varnish).

[0113] (Ink manufacturing example 17 (UV ink 17)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) As a coloring agent, 17.0 parts of RAVEN 1080 Ultra, 3.0 parts of BA-2550, 6.0 parts of TMPTA(EO), 13.0 parts of DiTMPTA, and 7.0 parts of DPHA were mixed together. As a photopolymerization initiator, 3.0 parts of 379 and 51.0 parts of photocurable resin varnish 2 were mixed and stirred using a butterfly mixer, and then dispersed using a three-roll mixer to produce an ink with a maximum particle size of 7.5 μm or less.

[0114] (Ink manufacturing example 18 (UV ink 18)) (Photocurable offset printing ink, Photocurable resin letterpress printing ink) The ink used in Manufacturing Example 1 of Patent No. 2989735 was prepared and designated as UV ink 17.

[0115] <Preparation of anchoring agent> (Anchor agent 1) 99.0 parts of resin 3 and 1.0 part of polyethylene wax (Chemipearl W500, manufactured by Mitsui Chemicals, Inc.) were added and stirred in a disperser for 10 minutes to obtain an aqueous anchoring agent (AC1).

[0116] The notation for the materials used in the examples is explained below. [Coloring agent] ·Permanent Yellow BHS: Manufactured by Clariant, Permanent Yellow BHS (CIPigment Yellow 174) ·Permanent Rubine L5B-01: Manufactured by Clariant, Permanent Rubine L5B-01 (CIPigment Red 57:1) ·HELIOGEN BLUE D7088: Manufactured by BASF, HELIOGEN BLUE D7088(CIPigment Blue 15:3) ·Raven 1080 Ultra: Made by Bilra Carbon, Raven 1080 Ultra Powder (CIPigment Black 7) • BA-2550: Manufactured by Morimura Shoji Co., Ltd., Alkali Blue Toner BA-2550 (CIPigment Blue 61) [Body pigments] • Calcium carbonate: Manufactured by Shiraishi Calcium Co., Ltd. [(meth)acrylate compounds] • TMPTA(EO): BASF, LAROMER LR8863, trimethylolpropaneethylene oxide-modified triacrylate • TMPTA(PO): Manufactured by Changxing Chemical Co., Ltd., ETEMER 2381, Trimethylolpropanepropylene oxide-modified triacrylate • DiTMPTA: Manufactured by Daicel Ornex, EBECRYL1142, ditrimethylolpropanetetraacrylate • DPHA: MIWON Corporation, MIRAMER M600, Dipentaerythritol Hexaacrylate • SC6640: MIWON Corporation, MIRAMER SC6640, 4-[2-(acryloyloxy)ethoxy]-4-oxobutanoic acid [resin] Resin 1: Rosin-modified resin 1 Resin 2: Osaka Soda Co., Ltd. Daiso Dap A (acid value 2 mg KOH / g, glass transition temperature 150℃) Resin 3: Seikoh PMC's Hyros X X436 (acid value 33 mg KOH / g, glass transition temperature 21°C) [Photopolymerization initiator] • 379: Omnirad 379, manufactured by IGM RESINS, 1,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, a photopolymerization initiator with a mass loss rate of 5% at a temperature of less than 290°C (temperature increase condition: 10°C / min) and a maximum absorption wavelength peak between 280 and 420 nm. • 910: Omnipol910, manufactured by IGM REGINS, polyethylene glycol di(β-4-[4-(2-dimethylamino-2-benzyl)butanonylphenyl]piperazine)propinate, a photopolymerization initiator with a mass loss rate of 5% at a temperature of less than 290°C (temperature increase conditions: 10°C / min) and a maximum absorption wavelength peak between 280 and 420 nm. • DEABP: Manufactured by Chemark Chemical, CHEMARK DEABP, 4,4'-bis(dimethylamino)benzophenone, a photopolymerization initiator with a mass loss rate of 5% at a temperature of less than 290°C (temperature increase conditions: 10°C / min), and a maximum absorption wavelength peak between 280 and 420 nm. • 4MBP: Manufactured by Sohkuni Jitsugyo Co., Ltd., SB-PI 712, a photopolymerization initiator whose mass loss rate in thermogravimetric analysis (heating conditions: 10°C / min) is 5% at a temperature of less than 290°C and which does not have a peak in the maximum absorption wavelength range of 280-420 nm. • 184: Omnirad184, 1-hydroxycyclohexylphenyl ketone, manufactured by IGM RESINS. A photopolymerization initiator whose mass loss rate by thermogravimetric analysis (heating conditions: 10°C / min) is less than 290°C and which does not have a peak at a maximum absorption wavelength between 280 and 420 nm. • TX: OmnipolTX, manufactured by IGM REGINS, poly(oxy-1,4-butanediyl), α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]-, a photopolymerization initiator with a mass loss rate of 5% at a temperature of 290°C or higher (temperature increase conditions: 10°C / min), and a peak of maximum absorption wavelength between 280 and 420 nm. • DETX: CHEMARK DETX, manufactured by Chemark Chemical, is a photopolymerization initiator with a mass loss rate of 5% at a temperature of less than 290°C (temperature increase conditions: 10°C / min) and a maximum absorption wavelength peak between 280 and 420 nm. • TPO: CHEMARK TPO, manufactured by Chemark Chemical, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, a photopolymerization initiator with a mass loss rate of 5% at a temperature of less than 290°C (temperature increase conditions: 10°C / min), and a maximum absorption wavelength peak between 280 and 420 nm. [Amine compounds] • EDB: CHEMARK EDB, manufactured by Chemark Chemical, ethyl-4-(dimethylamino)benzoate [Pigment dispersant] • Solsperse 24000: Manufactured by Lubrizol, Solsperse 24000

[0117] [Table 1]

[0118] [Table 1]

[0119] [Table 1]

[0120] [Table 1]

[0121] <Printing of anchoring agent onto substrate> Comparative Example 5 involved applying an anchoring agent to a substrate using a bar coater (No. 4, manufactured by Yasuda Seiki Co., Ltd.). The material was then dried in a 60-degree oven for 10 minutes to create a laminate with an anchoring layer on the substrate.

[0122] <Ink and varnish printing> Examples 1-30 and Comparative Examples 1-4, 6, and 7 were prepared by printing the inks shown in Table 1 onto the substrate using an RI tester (a simple printing press manufactured by Akira Seisakusho Co., Ltd., which can print offset printing inks, flexographic printing inks, and resin relief printing inks) at an ink gauge of 0.25 mL. Then, half of the printed material was cured using an ultraviolet curing device manufactured by I-Graphics Co., Ltd. (160 W / cm² metal halide lamp) at a conveyor speed of 30 m / min to obtain a laminate with the film layers in this order on the substrate. The other half of the printed material was cured using a Panasonic LED UD-80 (8 W / cm² 2 The coating was cured under the condition of a conveyor speed of 30 m / min, and a laminate having the coating layers in this order was obtained on the substrate. In Example 31, a mixture of 90 parts ink 16 and 10 parts ink 6 was used to color the ink 16 (varnish). Using an RI tester (a simple printing press manufactured by Akira Seisakusho Co., Ltd., which can print offset printing inks, flexographic printing inks, and resin relief printing inks), 0.25 mL of ink gauge was printed over the entire surface of the substrate. Then, half of the printed material was cured using an I-Graphics ultraviolet curing device (160 W / cm² metal halide lamp) at a conveyor speed of 30 m / min to obtain a laminate with the film layers in this order on the substrate. The other half of the printed material was cured using a Panasonic LED UD-80 (8 W / cm²). 2 The coating was cured under the condition of a conveyor speed of 30 m / min, and a laminate having the coating layers in this order was obtained on the substrate. Comparative Example 5 involved printing the sample inks shown in Table 1 onto the entire surface of a laminate having an anchor layer on a prepared substrate using an RI tester (a simple printing machine manufactured by Akira Seisakusho Co., Ltd., which can print offset printing inks, flexographic printing inks, and resin relief printing inks) with an ink gauge of 0.25 mL. Then, half of the printed material was cured using an ultraviolet curing device manufactured by I-Graphics Co., Ltd. (160 W / cm² metal halide lamp) at a conveyor speed of 30 m / min, obtaining a laminate having an anchor layer and an ink layer in that order on the substrate. The other half of the printed material was cured using a Panasonic LED UD-80 (8 W / cm² 2 The coating was cured under the condition of a conveyor speed of 30 m / min, and a laminate was obtained having an anchor layer and an ink layer on the substrate in that order.

[0123] The substrates used in the examples are as follows: • PP: Polypropylene sheet manufactured by Okamoto Co., Ltd. • PE: Manufactured by Futamura Chemical Co., Ltd., Taiko FC • PET: Manufactured by Toyobo Co., Ltd. (Lishine) • Vapor deposition: VM-PET manufactured by Toray Film Processing Co., Ltd. Synthetic paper: Manufactured by Yupo Corporation, New Yupo FGS • PVC: Manufactured by Lintec Corporation, PVC80C P • PS: Manufactured by Oishi Sangyo Co., Ltd., Styrofoam PC: Polycarbonate film manufactured by AS ONE Corporation • ABS: ABS resin sheet manufactured by Morino Kako Co., Ltd. • Nylon: Manufactured by Unitika Ltd., emblem • Cellophane: Manufactured by Futamura Chemical Co., Ltd., PL

[0124] <Initiating agent ratio 1> Regarding the proportion of initiator in the ink used in each example and comparative example, Mark with a circle (〇) if the proportion of initiators below 290℃ is 80% by mass or more. Mark with an X if the proportion of initiators below 290°C is less than 80% by mass. These are shown in Table 1.

[0125] <Initiator ratio 2> Regarding the proportion of initiator in the ink used in each example and comparative example, Mark with a circle (〇) if the initiator ratio for 280-420 nm is 80% by mass or more. Mark with an X if the initiator ratio for 280-420 nm is less than 80% by mass. These are shown in Table 1.

[0126] The adhesion properties of UV-printed laminates and LED-printed laminates obtained by UV printing and LED printing were evaluated. The results are shown in Table 1.

[0127] <Evaluation of adhesion of printed laminates> Adhesive tape (18mm wide cellophane tape manufactured by Nichiban Co., Ltd.) was applied to the ink surface of the fabricated laminate, and peeling was performed in a 90-degree vertical direction. The adhesion to the substrate was evaluated based on the percentage of the area where the ink film layer was peeled off from the plastic substrate. ○ and △ are practically preferable, and ○ is particularly preferable. ○: The peeling of the ink film layer from the substrate is 0% or more and less than 30%. △: The ink coating layer is peeled off from the substrate by 30% or more but less than 40%. ×: More than 40% of the ink film layer peels off from the substrate.

[0128] The following evaluations were performed using UV-printed laminates obtained by UV printing. The results are shown in Table 1.

[0129] <Regarding the conditions for detachment> In Examples 1-31 and Comparative Examples 1-7, the printed material was cut into 1.5 cm squares. For desorption, 1.5 L of a 2.0% sodium hydroxide aqueous solution at 70°C was added to a 2 L flask, and the sample was added to a total weight of 10% of the aqueous solution. The mixture was stirred at 300 rpm for 60 minutes. After desorption was complete, the substrate was removed, and the ink fragments were washed away with water using a metal sieve with a 2.0 mm mesh. The plastic fragments obtained after washing are referred to as the recovered plastic substrate.

[0130] The recovered plastic substrates were evaluated for their performance using the following method. The results are shown in Table 1.

[0131] <Evaluation of residual initiator content in recycled plastic substrates> After Soxhlet extraction using MEK, the solution was concentrated and analyzed by HPLC (Shimadzu Corporation) to measure the residual concentration of the photopolymerization initiator.

[0132] <Evaluation of detachment of recovered plastic substrates, and detachment rate> A PET substrate printed at 100% was prepared, and a PET substrate without printing was also prepared. 1.0% by weight of the printed PET substrate was added to the unprinted PET substrate, and the mixture was heated and melted. An injection plate (Shibaura Industrial Machinery, EC75SX) was created and used as a reference. Next, each of the obtained recycled plastic substrates was heated and melted to create an injection plate (Shibaura Industrial Machinery, EC75SX), and the desorption ratio was confirmed by comparing the color with the reference. A circle (〇) indicates a practically preferable result. ○: Products that can be judged by visual inspection to have a desorption rate equivalent to or higher than that of the standard product. ×: Products that can be judged by visual inspection to have a lower detachment rate than the standard product.

[0133] <Manufacturing of recycled materials> The recovered substrate was pelletized at 300°C using TEX25 (manufactured by Japan Steel Works, Ltd.) to produce recycled material. <Evaluation of the amount of initiator remaining in recycled materials> The recycled material was subjected to Soxhlet extraction with MEK, the solution was concentrated, and the residual concentration of the photopolymerization initiator was measured by HPLC (Shimadzu Corporation). ○ and △ are practically preferable, and ○ is particularly preferable. ○: Not detected △: Detectable at levels below 100 ppb ×: More than 100 ppb detected

[0134] <Evaluation of the color of recycled materials> Injection plates made using recycled materials were compared to injection plates made using virgin materials. ○ and △ are practically preferable, and ○ is particularly preferable. ○: The largest difference between the L, b, and a values ​​is less than 5. △: The largest difference between the L value, b value, and a value is between 5 and 7. ×: The largest difference between the L, b, and a values ​​is 7 or greater.

[0135] Examples 1-31 yielded practical results in all evaluation items. Comparing Examples 1-6 and Comparative Examples 1-4, Comparative Examples 1 and 2 had short processing times for the desorption step, resulting in insufficient desorption and a residual initiator content exceeding 1000 ppb in the recovered plastic substrate. As a result, both the color of the recycled material and the residual initiator content in the recycled material were unacceptable. Comparative Examples 3 and 4 showed sufficient desorption, with an initiator content of less than 10 ppb, but the processing time was extremely long, making them impractical. On the other hand, Examples 1-6 had a practical desorption time, and the residual initiator content in the recovered plastic substrate was in the range of 10-1000 ppb. As a result, both the color of the recycled material and the residual initiator content in the recycled material were satisfactory. Comparative Example 5 is a laminate having a desorption anchor layer, in which desorption proceeded sufficiently, and the initiator content became less than 10 ppb. Comparative Example 6 was an example using an ink with low deleaching properties, resulting in insufficient deleaching of the film layer and a residual initiator amount exceeding 1000 ppb in the recovered plastic substrate. As a result, both the color of the recycled material and the residual initiator amount in the recycled material were unsatisfactory. In Comparative Example 7, because the ink had very high deleaching properties, deleaching proceeded sufficiently, and the initiator content became less than that specified in the present application.

[0136] From the above, it has been found that the present invention makes it possible to easily recover plastic substrates from laminates containing a plastic substrate and a film layer made of a photocurable ink using a photopolymerization initiator in contact with the substrate, which has been considered difficult until now, and provides recovered plastic substrates that maintain excellent quality even after heat regeneration.

Claims

1. A recovered plastic substrate obtained by removing the coating layer from a laminate having a plastic substrate and a coating layer in contact with the plastic substrate, The aforementioned film layer is a cured product of a photocurable ink containing a photopolymerization initiator. A recovered plastic substrate in which the content of the photopolymerization initiator is 10 to 1000 ppb in the total mass of the recovered plastic substrate.

2. The recovered plastic substrate according to claim 1, wherein the photopolymerization initiator comprises 80% by mass or more of the total amount of the photopolymerization initiator, wherein the temperature at which the mass loss rate in thermogravimetric analysis (heating conditions: 10°C / min) becomes 5% is less than 290°C.

3. The recycled plastic substrate according to claim 1 or 2, wherein the photopolymerization initiator is a photopolymerization initiator having a peak with a maximum absorption wavelength in the range of 280 to 420 nm.

4. The recycled plastic substrate according to claim 1 or 2, wherein the photopolymerization initiator comprises one or more selected from the group consisting of acylphosphine oxide compounds, dialkoxyacetophenone compounds, hydroxyketone compounds, oxime ester compounds, aminoketone compounds, thioxanthone compounds, coumarin compounds, and benzophenone compounds.

5. The recycled plastic substrate according to claim 1 or 2, wherein the plastic substrate is a plastic substrate selected from the group consisting of polyethylene terephthalate, polypropylene, polyethylene, nylon, polyvinyl chloride, and polycarbonate.

6. A method for manufacturing a recycled plastic substrate, comprising the step of detaching the coating layer from a laminate having a plastic substrate and a coating layer in contact with the plastic substrate, The aforementioned film layer is a cured product of a photocurable ink containing a photopolymerization initiator. A method for producing a recycled plastic substrate, wherein the content of the photopolymerization initiator is 10 to 1000 ppb in the total mass of the recycled plastic substrate.

7. A method for producing a recovered plastic substrate according to claim 6, wherein the photopolymerization initiator comprises 80% by mass or more of the total amount of the photopolymerization initiator, wherein the temperature at which the mass loss rate in thermogravimetric analysis (heating conditions: 10°C / min) becomes 5% is less than 290°C.

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