Polyester substrate recovery method

Abstract

Provided is a method for efficiently recovering polyester from a polyester composite material containing polyester and a resin material other than polyester. This polyester substrate recovery method comprises a step for inducing contact between: a polyester composite material containing a polyester substrate and an easily degradable crosslinked layer; and a solution containing an oxidant.

Description

Method for recovering polyester substrate

[0001] The present invention relates to a method for recovering polyester substrates.

[0002] Polyester is excellent in moldability, durability, and light weight, and is therefore used in a wide range of applications, including containers, industrial uses, and clothing. However, polyester is difficult to decompose, and the disposal of these products poses environmental pollution problems. Therefore, efforts to reuse polyester have been promoted in recent years.

[0003] On the other hand, PET beverage bottles are sometimes fitted with labels made of polystyrene, polypropylene, or polyethylene, or printed with inks containing these resins. Industrial films include release films with a polyester substrate laminated with silicone, and protective films with a polyester substrate and a protective layer made of an acrylic adhesive, a urethane adhesive, or a silicone adhesive and an acrylic resin or a melamine resin. Thus, there is a need for a method to efficiently recover only the polyester from products that combine polyester with other materials in a reusable form.

[0004] Patent Documents 1 and 2 describe the production of a laminate by forming an alkaline release layer and a pigment-containing ink layer on a resin substrate such as PET. The resin substrate can be recovered by contacting this laminate with an alkaline agent. In this recovery method, the alkaline release layer dissolves in a cleaning solution and can be easily separated from the resin substrate. However, the ink layer does not dissolve, so a separate step of sorting and separating the ink layer from the resin substrate is required to recover the resin substrate.

[0005] Patent Documents 3 and 4 describe a display label obtained by laminating high-quality paper onto a plastic housing such as PC-ABS via a readily degradable adhesive layer made of a polymer having a diacylhydrazine structure, and a heat insulating material obtained by laminating a polyurethane foam onto a similar plastic housing via a readily degradable adhesive layer made of a polymer having a diacylhydrazine structure. This readily degradable adhesive layer is stable in air but quickly decomposes upon reaction with an oxidizing agent such as sodium hypochlorite, allowing it to be easily separated from the plastic housing. However, because the laminated high-quality paper and polyurethane foam do not decompose, a separate process of sorting and separating the high-quality paper and polyurethane foam from the plastic housing is required to recover the plastic housing.

[0006] International Publication No. 2022 / 225018 International Publication No. 2023 / 074311 JP 2013-037067 A JP 2013-001692 A

[0007] An object of the present invention is to provide a method for efficiently recovering polyester from a polyester composite material containing polyester and other resin materials.

[0008] The present inventors have found that polyester can be efficiently recovered from a polyester composite material containing an easily decomposable cross-linked material layer that can be decomposed by an oxidizing agent, and have completed the present invention.

[0009] That is, the present invention includes the following aspects. <1> A method for recovering a polyester substrate, comprising a step of contacting a polyester composite material containing a polyester substrate and an easily decomposable crosslinked material layer with a solution containing an oxidizing agent. <2> The method for recovering a polyester substrate according to item 1, in which the easily decomposable crosslinked material layer is provided on the outermost surface of the polyester composite material. <3> The method for recovering a polyester substrate according to item 1 or 2, in which the easily decomposable crosslinked material layer is made of a crosslinked material containing a hydrazine structure represented by formula (1). -A １ -NH-NH-A ２ - (1) (In formula (1), A １ , A ２ are each a carbonyl group or a single bond, and A １ and A ２at least one of which is a carbonyl group.) <4> The method for recovering polyester substrates according to item 1 or 2, wherein the easily decomposable crosslinked material layer comprises a crosslinked material containing a siloxane structure or a poly(meth)acrylic acid ester structure. <5> The method for recovering polyester substrates according to item 1 or 2, wherein a printed layer is provided directly on the easily decomposable crosslinked material layer. <6> The method for recovering polyester substrates according to item 1 or 2, wherein the easily decomposable crosslinked material layer contains a pigment or a dye. <7> The method for recovering polyester substrates according to item 1 or 2, wherein a printed layer is provided between the polyester substrate and the easily decomposable crosslinked material layer. <8> The method for recovering polyester substrates according to item 1 or 2, wherein the polyester substrate is in a bottle shape. <9> The method for recovering polyester substrates according to item 1 or 2, wherein the polyester substrate is in a sheet shape. <10> A crosslinkable composition for forming an easily decomposable crosslinked material layer on a polyester substrate that is decomposed upon contact with a solution containing an oxidizing agent. <11> The composition according to item 10, characterized by containing an easily decomposable crosslinking agent represented by formula (2): (In formula (2), n≧0, k≧0, m≧0, p1≧1, p2≧1, p3≧1. R １ , R ２ , R ３ are each independently a divalent group containing a siloxane structure, or a hydrocarbon group which may have a substituent or a heteroatom. １ is a divalent or higher valent group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ２ is a divalent group containing a siloxane structure or a hydrocarbon group which may have a hetero atom. １ ~A ８ is a carbonyl group or a single bond, and A １ and A ２ At least one of A is a carbonyl group, ３ and A ４ At least one of A is a carbonyl group, ５ and A ６ At least one of A is a carbonyl group, ７ and A ８ At least one of the groups is a carbonyl group. １ , Q ２ , Q３ are each independently a reactive functional group, or hydrogen or halogen.) <12> A polyester composite comprising a polyester substrate and an easily decomposable crosslinked layer that is decomposable by an oxidizing agent.

[0010] According to the method of the present invention, polyester can be efficiently recovered from a polyester composite material containing polyester and other resin materials.

[0011] Fig. 1 is a cross-sectional view of a laminate in which an easily decomposable cross-linked material layer is provided on a polyester substrate; Fig. 2 is a cross-sectional view of a laminate in which an easily decomposable cross-linked material layer and a printed layer are provided on a polyester substrate; Fig. 3 is a cross-sectional view of a laminate in which a printed layer and an easily decomposable cross-linked material layer are provided on a polyester substrate; and Fig. 4 is a cross-sectional view of a laminate in which two easily decomposable cross-linked material layers are provided on a polyester substrate.

[0012] <<Polyester Substrate Recovery Method>> The polyester substrate recovery method of the present invention is characterized by including a step of contacting a polyester composite material including a polyester substrate and an easily decomposable cross-linked material layer with a solution containing an oxidizing agent. The easily decomposable cross-linked material layer is rapidly decomposed by the action of the oxidizing agent and peeled off from the polyester substrate, and dispersed or dissolved in the solution. As a result, the polyester substrate can be efficiently recovered.

[0013] <Polyester substrate> The polyester substrate is made of a polyester resin and supports an easily decomposable crosslinked layer. The polyester resin is not particularly limited as long as it is a polymer containing an ester bond, and examples thereof include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate, polybutylene naphthalate, polylactic acid, polyhydroxybutyric acid, polybutylene succinate, polycaprolactone, polyhydroxyalkanoic acid, and polyglycolic acid. In addition to the polyester resin, the polyester substrate may contain optional components such as an ultraviolet absorber, a lubricant, a release agent, a stabilizer, an antioxidant, an antistatic agent, a dye, and a pigment.

[0014] The shape of the polyester substrate is not particularly limited as long as it allows the formation of an easily decomposable cross-linked material layer thereon, and may be flat or non-flat. Specific examples of the shape of the polyester substrate include a bottle shape, a sheet shape, a tube shape, and a pipe shape.

[0015] <Easily decomposable crosslinked material layer> The easily decomposable crosslinked material layer is a layer made of a crosslinked material that is rapidly decomposed by the action of an oxidizing agent. The easily decomposable crosslinked material is not particularly limited in composition as long as it is decomposed by reaction with an oxidizing agent, and examples thereof include crosslinked polymers having a hydrazine structure or an azo structure that are easily decomposed by reaction with an oxidizing agent. Easily decomposable crosslinked materials having a hydrazine structure are preferred because they have excellent adhesion to polyester substrates and also excellent adsorption properties for dyes and pigments. The hydrazine structure can also be converted to an azo structure by a controlled oxidation reaction.

[0016] Among these easily decomposable crosslinked products, crosslinked products containing a hydrazine structure are preferred, and crosslinked products containing a hydrazine structure represented by formula (1) are more preferred. １ -NH-NH-A ２ - (1) In formula (1), A １ , A ２ are each a carbonyl group or a single bond, and A １ and A ２ At least one of A is a carbonyl group. １ and A ２ When one of the groups is a carbonyl group, it has the advantage of being easily decomposed with an oxidizing agent. １ and A ２ When both of the groups are carbonyl groups, there is an advantage that the decomposition products are easily dissolved in a solution.

[0017] Furthermore, the easily decomposable crosslinked product preferably contains a siloxane structure or a poly(meth)acrylic acid ester structure. When the easily decomposable crosslinked product contains a siloxane structure, it can be provided with properties such as sliding properties, releasability, antifouling properties, and chemical resistance. When the easily decomposable crosslinked product contains a poly(meth)acrylic acid ester structure, it can be provided with properties such as ink receptivity, adhesion, slight adhesion, and chemical resistance.

[0018] The crosslinkable composition is not particularly limited as long as it is a crosslinkable composition that can obtain the above-mentioned easily decomposable crosslinked product by a crosslinking reaction in the composition, but it preferably contains a crosslinking agent containing a hydrazine structure. As the crosslinking agent containing a hydrazine structure, a crosslinking agent containing a hydrazine structure represented by the above formula (1) is preferred, and an easily decomposable crosslinking agent represented by formula (2) is more preferred.

[0019] In formula (2), n≧0, k≧0, m≧0, p1≧1, p2≧1, and p3≧1. R １ , R ２ , R ３ are each independently a divalent group containing a siloxane structure, or a hydrocarbon group which may have a substituent or a heteroatom. １ is a divalent or higher valent group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ２ is a divalent group containing a siloxane structure or a hydrocarbon group which may have a hetero atom. １ ~A ８ is a carbonyl group or a single bond, and A １ and A ２ At least one of A is a carbonyl group, ３ and A ４ At least one of A is a carbonyl group, ５ and A ６ At least one of A is a carbonyl group, ７ and A ８ At least one of the groups is a carbonyl group. １ , Q ２ , Q ３ are each independently a reactive functional group, or hydrogen or halogen.

[0020] In a narrow sense, the term "crosslinking agent" can refer to a chemical substance that forms chemical bonds between polymers or within a polymer. In this specification, however, the term also refers to a chemical substance that can form chemical bonds between its own molecules, in addition to a chemical substance that forms chemical bonds between polymers or within a polymer.

[0021] <n, m, k in formula (2)> In formula (2), n and m are all 0 or more, but each independently is preferably 1 or more, more preferably 2 or more. When n is 1 or more, the compound has two or more hydrazine structures (-A-NH-NH-A-), thereby improving decomposition properties. There are no particular upper limits for n and m, but they can each be 50 or less.

[0022] In formula (2), k is 0 or more, preferably 1 or more, and more preferably 2 or more. When k is 1 or more, the crosslinkable composition containing the easily decomposable crosslinking agent can undergo three-dimensional crosslinking. The upper limit of k is not particularly limited, but can be 500 or less.

[0023] <R in formula (2) １ , R ２ , and R ３ > R １ , R ２ , and R ３ are each independently a divalent group containing a siloxane structure, or a hydrocarbon group which may have a substituent or a heteroatom.

[0024] The divalent group containing a siloxane structure contains an —Si—O— bond as a main skeleton. The main skeleton may be a linear structure, a branched structure, or a cyclic structure. The number of silicon atoms in the divalent group containing a siloxane structure is preferably 2 to 400, more preferably 4 to 200, and even more preferably 8 to 150.

[0025] In the siloxane structure, the hydrogen atoms bonded to the silicon atoms may be substituted. Specific examples of the substituent include alkyl groups, alkoxy groups, phenoxy groups, halogen atoms, amino groups, sulfo groups, cyano groups, and nitro groups.

[0026] Specific examples of divalent groups containing a siloxane structure include dimethyl silicone, diethyl silicone, ethyl methyl silicone, polymethyl silsesquioxane, and modified silicones obtained by modifying the hydrocarbon groups at the ends and / or side chains of these groups to contain heteroatoms such as N, S, O, and P.

[0027] R １ , R ２ , and R ３When is a hydrocarbon group, in order to achieve a good decomposition rate and solvent solubility, the number of carbon atoms therein is preferably 1 to 600, more preferably 3 to 100, and even more preferably 4 to 50. The hydrocarbon group may be a saturated or unsaturated hydrocarbon group, and may have any of a linear structure, a branched structure, and a cyclic structure.

[0028] The hydrocarbon group may have a substituent, specific examples of which include an alkoxy group, a phenoxy group, a halogen atom, an amino group, a sulfo group, a cyano group, and a nitro group.

[0029] The hydrocarbon group may contain heteroatoms. When heteroatoms are contained, the number thereof is preferably 1 to 300. The heteroatoms may be present in the main chain of the hydrocarbon group or in the side chain. Examples of heteroatoms include N, S, O, and P. Examples of structures containing heteroatoms contained in the hydrocarbon group include: The hydrocarbon group may not contain a heteroatom.

[0030] Specific examples of the hydrocarbon group include linear hydrocarbons such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, ether, urethane, urea, ester, thioether, carbonate, and amide, branched hydrocarbons such as isopropylene, isobutylene, 2,2-dimethylpropylene, and 2-ethyl-2-methylpropylene, cyclic hydrocarbons such as cyclohexylene, cyclopentylene, norbornenylene, phenylene, and naphthylene, PEG chains, and trivalent or tetravalent groups formed from these groups. The hydrogen atoms of these hydrocarbon groups may be substituted with the aforementioned substituents.

[0031] Specific examples of the hydrocarbon group include groups containing a poly(meth)acrylic acid ester structure. Examples of monomer units constituting the poly(meth)acrylic acid ester structure include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, norbornene acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, norbornene methacrylate, dimethylacrylamide, diethylacrylamide, isopropylacrylamide, 4-tert-butylcyclohexyl acrylate, diacetone acrylamide, and acryloylmorpholine.

[0032] <Z in formula (2) １ and Z ２ > In formula (2), Z １ Z is a divalent or higher valent group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ２ is a divalent group containing a siloxane structure or a hydrocarbon group which may have a hetero atom.

[0033] In formula (2), Z １ is a group containing a siloxane structure, Z １ is divalent when k=0, and is trivalent or more when k≧1. ２ When is a group containing a siloxane structure, its valency is divalent.

[0034] The group containing a siloxane structure contains an —Si—O— bond as a main skeleton. The main skeleton may be a linear structure, a branched structure, or a cyclic structure. The number of silicon atoms in the group containing a siloxane structure is preferably 2 to 400, more preferably 4 to 200, and even more preferably 8 to 150.

[0035] In the siloxane structure, the hydrogen atoms bonded to the silicon atoms may be substituted. Specific examples of the substituent include alkyl groups, alkoxy groups, phenoxy groups, halogen atoms, amino groups, sulfo groups, cyano groups, and nitro groups.

[0036] Specific examples of groups containing a siloxane structure include dimethyl silicone, diethyl silicone, ethyl methyl silicone, polymethyl silsesquioxane, and modified silicones obtained by modifying the hydrocarbon groups at the terminals and / or side chains of these groups to contain heteroatoms such as N, S, O, and P.

[0037] Z １ and Z ２ When is a hydrocarbon group, in order to achieve a good decomposition rate and solvent solubility, the number of carbon atoms therein is preferably 1 to 70,000, more preferably 5 to 30,000, and even more preferably 10 to 10,000. The hydrocarbon group has a saturated or unsaturated hydrocarbon group as the main skeleton, and may have a linear structure, a branched structure, or a cyclic structure.

[0038] The hydrocarbon group may have a substituent, specific examples of which include an alkoxy group, a phenoxy group, a halogen atom, an amino group, a sulfo group, a cyano group, and a nitro group.

[0039] The hydrocarbon group may contain heteroatoms such as N, S, O, and P. When heteroatoms are contained, the number thereof is preferably 1 to 10,000. The heteroatoms may be present in the main chain of the hydrocarbon group or in the side chain. Examples of structures containing heteroatoms contained in the hydrocarbon group include: The hydrocarbon group may not contain a heteroatom.

[0040] The hydrocarbon group may have a reactive functional group, such as a hydroxyl group, an amino group, a hydrazide group, a thiol group, an isoprenyl group, a crotonamide group, a crotonate group, a carboxylic acid, an acid anhydride group, a vinyl group, an allyl group, an acrylate group, a methacrylate group, an acrylamide group, a methacrylamide group, a hydroxysilyl group, an epoxy group, an oxetane group, an oxazoline group, an isocyanate group, a carbodiimide group, a methylol group, a silanol group, or an alkoxysilyl group.

[0041] Specific examples of the hydrocarbon group include linear hydrocarbons such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, ether, urethane, urea, ester, thioether, carbonate, and amide, branched hydrocarbons such as isopropylene, isobutylene, 2,2-dimethylpropylene, and 2-ethyl-2-methylpropylene, cyclic hydrocarbons such as cyclohexylene, cyclopentylene, norbornenylene, phenylene, and naphthylene, PEG chains, and trivalent or tetravalent groups formed from these groups. The hydrogen atoms of these hydrocarbon groups may be substituted with the aforementioned substituents.

[0042] Specific examples of the hydrocarbon group include groups containing a poly(meth)acrylic acid ester structure. Examples of monomer units constituting the poly(meth)acrylic acid ester structure include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, norbornene acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, norbornene methacrylate, dimethylacrylamide, diethylacrylamide, isopropylacrylamide, 4-tert-butylcyclohexyl acrylate, diacetone acrylamide, and acryloylmorpholine.

[0043] Z １ and Z ２ The structures of are independent of each other and may be the same or different. １ and Z ２ There may be multiple Z １ , Z ２ may be the same or different from each other. １ and Z ２ When the structures of Z are different from each other, the decomposition property and solvent solubility of the easily decomposable crosslinked product can be controlled by selecting a combination of the structures. １ and Z ２The following are examples of cases where the structures of Z are different from each other: １ and Z ２ Contains one or more of each. １ Includes 2 or more Z ２ Includes: Z １ Contains one or more of Z ２ Contains two or more. １ Contains two or more of Z ２ The combination of two or more Z includes, for example, a combination of a Z having high water solubility in the decomposition product and a Z having low water solubility in the decomposition product. In addition, the characteristics before decomposition include a combination of a Z having a high molecular weight and a Z having a low molecular weight, a combination of a hydrophilic Z and a hydrophobic Z, a combination of a Z having a high polarity and a Z having a low polarity, and a combination of a Z having a flexible structure and a Z having a rigid structure.

[0044] The easily decomposable crosslinking agent represented by formula (2) is Z １ or Z ２ It is preferable that the ring structure does not contain two or more ring structures. １ or Z ２ This is because, when the compound has a cyclic structure containing two or more Z groups, the solvent solubility may decrease. １ or Z ２ The cyclic structure containing two or more of R １ , R ２ , R ３ , Z １ , Z ２ Examples of the ring structure include a ring structure formed by bonding two or more of the following to each other.

[0045] In formula (2), R １ , R ２ , R ３ , Z １ , Z ２ It is preferable that at least one selected from the group consisting of is a group containing a siloxane structure or a poly(meth)acrylic acid ester structure. When a siloxane structure is contained, there are advantages in that the easily decomposable crosslinked product can be provided with properties such as sliding properties, releasability, antifouling properties, and chemical resistance, and in that compatibility with other additives having a siloxane structure is improved. １ , R ２ , R ３ , Z１ , Z ２ Preferably, at least two of the groups are groups containing a siloxane structure, and more preferably, at least three of the groups are groups containing a siloxane structure. When the poly(meth)acrylic acid ester structure is contained, the easily decomposable crosslinked product can be imparted with ink receptivity, adhesion, slight adhesion, chemical resistance, etc., and the time required to form the easily decomposable crosslinked product can be shortened in some cases. １ , Z ２ At least one of the groups is preferably a group containing a poly(meth)acrylic acid ester structure selected from the group consisting of １ is preferably a group containing a poly(meth)acrylic acid ester structure.

[0046] <Molecular weight of R and Z> In formula (2), R １ , R ２ , and R ３ and / or Z １ and Z ２ It is preferable that the molecular weight of at least one selected from the group consisting of is 200 or more. By adjusting the molecular weights of R and Z in this manner, the solubility of the easily decomposable crosslinking agent in a solvent can be improved. Furthermore, when a cured product is produced using the easily decomposable crosslinking agent, precipitation is suppressed, and a molded product with uniform composition and physical properties can be obtained.

[0047] R １ , R ２ , R ３ When two or more of any of R are present, only one of them may have a molecular weight of 200 or more. １ If there is one R １ The molecular weight of R may be 200 or more. １ , R ２ , and R ３ Preferably, the molecular weight of two or more selected from the group consisting of R １ , R ２ , and R ３ Preferably, the molecular weight of the copolymer is 200 or more.

[0048] Similarly, Z １ and Z２ When two or more of any of Z are present, only one of them may have a molecular weight of 200 or more. １ and Z ２ It is preferable that the molecular weight of R is 200 or more. １ , R ２ , and R ３ and Z １ and Z ２ It is particularly preferred that at least one selected from the group consisting of has a molecular weight of 200 or more.

[0049] The molecular weight is 200 or more, preferably 300 or more, more preferably 700 or more, and even more preferably 900 or more. There is no particular upper limit to the molecular weight, but it is generally 10,000 or less. When the molecular weight is within this range, the solubility of the easily decomposable crosslinking agent in a solvent can be improved. １ , R ２ , R ３ , Z １ , Z ２ The molecular weight can be determined, for example, by contacting a readily decomposable crosslinking agent with an oxidizing agent to obtain a decomposition product, followed by gel permeation chromatography (GPC), or by structural determination by NMR. When the molecular weight is determined by gel permeation chromatography (GPC), it is determined as a weight average molecular weight (Mw).

[0050] In formula (2), it is preferable that n ≥ 1 and k ≥ 1. In this case, the easily decomposable crosslinking agent becomes branched, enabling three-dimensional crosslinking.

[0051] In addition, in formula (2), n ≧ 1 and k ≧ 1, and Z １ The molecular weight of Z is preferably 200 or more, more preferably 300 or more, and even more preferably 700 or more. １ as the main skeleton and is a branched compound having two or more hydrazine-derived structures (-A-NH-NH-A-) in the side chain, making three-dimensional crosslinking possible.

[0052] In order to complicate the structure of the easily decomposable crosslinking agent, suppress crystallization, and improve solubility in a solvent, n≧2, m≧2, or m≧1 and k≧2 in formula (2), and Z １ or Z ２ It is preferable that a plurality of Z １ or Z ２ It is preferable that the molecular weight of at least one of the groups is 200 or more. １ or Z ２ It is more preferable that one or more of the Z groups have a molecular weight of 200 or more. １ or Z ２ It is even more preferable that the molecular weight of at least one of the above is 300 or more, and particularly preferably 700 or more.

[0053] <Q in formula (2) １ , Q ２ , and Q ３ In formula (2), Q １ , Q ２ , Q ３ are each independently a reactive functional group, or hydrogen or halogen. １ , Q ２ , Q ３ are R １ , R ２ , R ３ It bonds to the hydrazine structure (-A-NH-NH-A-) via

[0054] Examples of the reactive functional group include a hydroxyl group, an amino group, a thiol group, a hydrazide group, a carboxylic acid, an acid anhydride group, a vinyl group, an allyl group, an acrylate group, a methacrylate group, a crotonate group, an isoprenyl group, an acrylamide group, a methacrylamide group, a crotonamide group, an epoxy group, an oxetane group, an oxazoline group, an isocyanate group, a carbodiimide group, a methylol group, a silanol group, a hydroxysilyl group, and an alkoxysilyl group.

[0055] p1, p2, and p3 are each Q contained in the easily decomposable crosslinking agent １ , Q ２ , Q ３p1, p2, and p3 each represent a number of 1 or more, but each independently represents a number of 1 to 4, and more preferably 1 or 2. １ , Q ２ , Q ３ is a reactive functional group and p1, p2, and p3 are 2 or more, three-dimensional crosslinking becomes easy, and the strength and reliability of the crosslinked product are improved. １ Comrade, Q ２ Peer or Q ３ When the reactive functional groups are different from each other, it becomes easy to select various types of curable resins and crosslinking processes. Furthermore, when only specific reactive functional groups are crosslinked, the reactive functional groups not used in the crosslinking reaction can contribute to improving adhesion and solubility. When p1 = 1, p2 = 1, or p3 = 1, the decomposition rate is likely to be improved.

[0056] Q １ , Q ２ , Q ３ may be, independently of each other, hydrogen or a halogen, including fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0057] <A in formula (2) １ ~A ８ > A １ ~A ８ is a carbonyl group or a single bond. １ and A ２ At least one of A is a carbonyl group, ３ and A ４ At least one of A is a carbonyl group, ５ and A ６ At least one of A is a carbonyl group, ７ and A ８ At least one of the two A's on either side of -NH-NH- is a carbonyl group. When one of them is a carbonyl group, there is an advantage that the compound is easily decomposed with an oxidizing agent. When both are carbonyl groups, there is an advantage that the decomposition product is easily dissolved in a solution containing an oxidizing agent.

[0058] The easily decomposable crosslinking agent preferably has a weight average molecular weight of 300 to 2,000,000, more preferably 400 to 700,000. When the molecular weight is within these ranges, it becomes easy to adjust the crosslink density and solvent solubility.

[0059] The easily decomposable crosslinking agent is preferably liquid at 20 to 120° C., more preferably liquid at 30 to 60° C. In this case, it has excellent miscibility with other components when preparing a crosslinkable composition, and can suppress precipitation of other components during molding.

[0060] <Method for Synthesizing Crosslinking Agent Having a Hydrazine Structure> The method for synthesizing a crosslinking agent having a hydrazine structure is not particularly limited, and an easily decomposable crosslinking agent in which carbonyl groups are present on both sides of —NH—NH— can be obtained, for example, by reacting a hydrazide compound, a semicarbazide compound, or a carbazate compound with a carbonate compound, an isocyanate compound, an acid anhydride, an acid halide, or a cyclic ester compound; a reaction between hydrazine and a carboxylic acid ester; a reaction between hydrazine and a carbonate compound; or a reaction between hydrazine and an isocyanate compound.

[0061] Furthermore, an easily decomposable crosslinking agent in which a carbonyl group is present on one side of -NH-NH- can be obtained by, for example, reacting a hydrazide compound, a semicarbazide compound, or a carbazate compound with a compound having an unsaturated double bond such as an acrylate or a methacrylate, an epoxy compound, an oxetane compound, or cyanuric acid chloride; or by reacting a hydrocarbon having a hydrazino group with a carbonate compound, an isocyanate compound, an acid anhydride, an acid halide, or a cyclic ester compound.

[0062] Examples of hydrazide compounds used in the above synthesis method include lactic acid hydrazide, methacrylic acid hydrazide, sebacic acid dihydrazide, adipic acid dihydrazide, phthalic acid dihydrazide, salicylic acid dihydrazide, and trimellitic acid trihydrazide. Examples of carbonate compounds include allyl N-succinimidyl carbonate and C,C'-(oxydi-2,1-ethanediyl)bisN-succinimidyl carbonate. Examples of isocyanate compounds include 2-isocyanatoethyl methacrylate, hexamethylene diisocyanate, toluene diisocyanate, and polymethylene polyphenyl polyisocyanate. Examples of semicarbazide compounds include N-allylhydrazinecarboxamide, N,N'-1,6-hexanediylbis[hydrazinecarboxamide], 4,4'-isophoronebis(semicarbazide), and 4,4'-(1,3-phenylenebismethylene)bis(semicarbazide). Examples of carbazate compounds include allylcarbazate and C,C'-(oxydi-2,1-ethanediyl)biscarbazate. Examples of acid anhydrides include methacrylic anhydride, succinic anhydride, and pyromellitic dianhydride. Examples of acid halides include acrylic acid chloride, sebacic acid dichloride, adipic acid dichloride, phthalic acid dichloride, salicylic acid dichloride, and trimesic acid trichloride. Examples of cyclic ester compounds include propiolactone, butyrolactone, valerolactone, etc. Examples of carboxylic acid esters include ethyl lactate, methylparaben, monomethyl succinate, diethyl adipate, trimethyl trimellitate, etc.

[0063] <<Crosslinkable Composition>> The crosslinkable composition of the present invention is used to form an easily decomposable crosslinked layer on a polyester substrate, which is decomposed upon contact with a solution containing an oxidizing agent. Examples of such crosslinkable compositions include (i) crosslinkable compositions containing a component that is easily decomposable by an oxidizing agent, and (ii) crosslinkable compositions in which a structure that is easily decomposable by an oxidizing agent is formed in the molecular chain by a crosslinking reaction.

[0064] (i) In a crosslinkable composition containing a component that is easily decomposable by an oxidizing agent, the component that is easily decomposable by an oxidizing agent may be a crosslinking agent containing a hydrazine structure or an azo structure, and a crosslinking agent containing a hydrazine structure represented by the formula (1) is preferred, and an easily decomposable crosslinking agent represented by the formula (2) is more preferred. In the crosslinkable composition, the crosslinking agent containing a hydrazine structure may be used alone or in combination of two or more types.

[0065] (ii) In a crosslinkable composition in which a structure that is easily decomposable by an oxidizing agent is formed in the molecular chain by a crosslinking reaction, examples of components that form a structure that is easily decomposable by an oxidizing agent include a diazonio group, a crosslinking agent having a diazo group, a crosslinking agent having a hydrazino group, a crosslinking agent having a hydrazide group, a crosslinking agent having a semicarbazide group, and a crosslinking agent having a carbazate group.

[0066] The blending amounts of the non-reactive resin containing a hydrazine structure, the monofunctional curable resin containing a hydrazine structure, the crosslinking agent having a hydrazide group, and the crosslinking agent containing a hydrazine structure in the crosslinkable composition are preferably 1 to 99 wt %, more preferably 5 to 60 wt %, and even more preferably 10 to 45 wt %, of the total solid content. If the blending amount is less than 1 wt %, the chemical resistance of the easily decomposable crosslinked material layer tends to decrease, and if the blending amount is more than 99 wt %, it tends to be difficult to form a uniform film.

[0067] The crosslinkable composition can contain a crosslinking agent having a diazonio group, a diazo group, a hydrazino group, a hydrazide group, a semicarbazide group, a carbazate group, or a hydrazine structure or azo structure, as well as a curable resin, a polymerization initiator, a solvent, a dye, a pigment, a surfactant, an ink fixing aid, a surfactant, and the like.

[0068] <Curable Resin> When the crosslinkable composition contains a crosslinking agent having an azo group or a crosslinking agent containing a hydrazine structure, the curable resin is not particularly limited as long as it has a structure that reacts with the reactive functional group of the crosslinking agent to crosslink, and examples of such curable resins include curable resins having a reactive functional group at their terminals, such as a mercapto group, a hydroxyl group, an amino group, a hydrazide group, a carboxylic acid, an acid anhydride group, a vinyl group, an allyl group, an acrylate group, a methacrylate group, a crotonate group, an isoprenyl group, an acrylamide group, a methacrylamide group, a crotonamide group, an epoxy group, an oxetane group, an oxazoline group, an isocyanate group, a carbodiimide group, a methylol group, a silanol group, a hydroxysilyl group, or an alkoxysilyl group.

[0069] When the crosslinkable composition contains a crosslinking agent having a hydrazino group, the curable resin is not particularly limited as long as it has a structure that crosslinks by a reaction with the hydrazino group to form a hydrazine structure represented by the formula (1), and examples thereof include curable resins having a reactive functional group at the end, such as a carbonate group, an isocyanate group, an acid anhydride group, or a cyclic ester group.

[0070] When the crosslinkable composition contains a crosslinking agent having a hydrazide group, a crosslinking agent having a semicarbazide group, or a crosslinking agent having a carbazate group, the curable resin is not particularly limited as long as it has a structure that crosslinks by reacting with these groups to form a hydrazine structure represented by formula (1), and examples of the curable resin include curable resins having a reactive functional group at their terminals, such as a carbonate group, an isocyanate group, an acid anhydride group, a cyclic ester group, an acrylate group, a methacrylate group, a crotonate group, an isoprenyl group, an acrylamide group, a methacrylamide group, a crotonamide group, an epoxy group, an oxetane group, or a cyanuric chloride group.

[0071] When the crosslinkable composition contains a crosslinking agent having a diazonio group or a crosslinking agent having a diazo group, the curable resin is not particularly limited as long as it has a structure that crosslinks by reacting with these groups to form an azo structure, and examples of such curable resins include curable resins having a reactive functional group containing an unsaturated double bond at the end, such as a phenoxy group, a phenol group, an anilino group, an aniline group, or a naphthol group.

[0072] The curable resin may have only one type of reactive functional group or may have two or more types of reactive functional groups, and the number of reactive functional groups present in the curable resin is preferably two or more.

[0073] The main skeleton of the curable resin is preferably a hydrocarbon group which may have a heteroatom, or a group containing a siloxane structure. The main skeleton of the hydrocarbon group may be saturated or unsaturated, and may have a linear structure, a branched structure, or a cyclic structure. The hydrocarbon group constituting the main skeleton of the curable resin may contain heteroatoms such as N, S, O, and P. When heteroatoms are contained, the number thereof is preferably 1 to 10,000. Examples of structures containing heteroatoms contained in the main skeleton of the curable resin include: and the like. The hydrocarbon group may not contain a heteroatom. The main skeleton of the group containing a siloxane structure may have a linear structure, a branched structure, or a cyclic structure. The number of silicon atoms in the group containing a siloxane structure is preferably 2 to 400, more preferably 4 to 200, and even more preferably 8 to 150.

[0074] Specific examples of the hydrocarbon group constituting the main skeleton of the curable resin include linear hydrocarbons such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, ether, urethane, urea, ester, thioether, carbonate, and amide, branched hydrocarbons such as isopropylene, isobutylene, 2,2-dimethylpropylene, and 2-ethyl-2-methylpropylene, cyclic hydrocarbons such as cyclohexylene, cyclopentylene, norbornenylene, phenylene, and naphthylene, PEG chains, and trivalent or tetravalent groups of these groups. The hydrogen atoms of these hydrocarbon groups may be substituted with the aforementioned substituents.

[0075] The curable resin is preferably one that is liquid at 40° C. or below, one that dissolves in a water-soluble organic solvent, or one that dissolves in an acid or alkaline aqueous solution. By using such a curable resin, the decomposition rate of the easily decomposable crosslinked material layer can be improved.

[0076] The molecular weight of the curable resin is preferably 100 to 2,000,000, more preferably 200 to 700,000. The curable resin may be a thermosetting resin or a photocurable resin. The amount of the curable resin in the crosslinkable composition is preferably 0.1 to 95 wt % of the total solid content, more preferably 1 to 80 wt %.

[0077] <Polymerization Initiator> The polymerization initiator is not particularly limited as long as it is a compound that can catalyze the crosslinking reaction of the crosslinking agent or the curable resin, and either a thermal polymerization initiator or a photopolymerization initiator can be used. Examples of the polymerization initiator include radical generators such as alkylphenone compounds, benzoin compounds, benzophenone compounds, oxime ester compounds, and phosphine compounds; base generators such as oxime ester compounds, ammonium compounds, benzoin compounds, dimethoxybenzyl urethane compounds, and orthonitrobenzyl urethane compounds; acid generators such as onium salts, halogen-containing compounds, diazomethane compounds, sulfone compounds, and sulfonic acid compounds; tin compounds such as dibutyltin dilaurate and dibutyltin diacetate; bismuth compounds such as bismuth octoate; titanium compounds such as tetraoctyl titanate and titanium ethyl acetoacetate; zirconium compounds such as zirconium monoacetylacetate and zirconium tetraacetylacetate; amines such as triethylenediamine and 1,4-diazabicyclo[2,2,2]octane (DABCO); platinum compounds such as chloroplatinic acid and alkenylsiloxane platinum complexes; iron complexes; and cobalt complexes. The amount of the polymerization initiator in the composition is preferably 0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the curable resin.

[0078] <Solvent> Examples of the solvent include water and organic solvents, such as ether solvents, amide solvents, hydrocarbon solvents, alcohol solvents, ester solvents, aldehyde solvents, ketone solvents, and solvents containing carbon atoms, such as solvents containing carbon atoms and hetero atoms.

[0079] Examples of ether-based solvents include propylene glycol monomethyl ether, anisole, 4-methylanisole, diisopropyl ether, diethyl ether, dibutyl ether, tetrahydrofuran, dimethoxyethane, cyclopentyl methyl ether, and tert-butyl methyl ether. Examples of amide-based solvents include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of hydrocarbon-based solvents include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and cyclohexane, and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, and chlorobenzene. Examples of alcohol-based solvents include methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol monomethyl ether. Examples of ester-based solvents include ethyl acetate, butyl acetate, and propylene glycol monomethyl ether acetate. Examples of aldehyde-based solvents include formaldehyde and acetaldehyde. Examples of ketone solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of solvents containing carbon atoms and heteroatoms include acetonitrile and dimethyl sulfoxide. The blending amount of the solvent in the crosslinkable composition is preferably 5 to 99% by weight, and more preferably 20 to 95% by weight.

[0080] The solvents listed above may be used alone or in combination of two or more. The boiling point of the solvent is preferably 150°C or less, more preferably 130°C or less, and even more preferably 110°C or less. When the boiling point is within these ranges, the solvent can be removed by heating for a relatively short time. The amount of solvents in the crosslinkable composition having a boiling point of more than 150°C is preferably less than 10% by weight. Within this range, the solvent can be removed at a relatively low temperature after the crosslinkable composition is applied to the polyester substrate, so that PET bottles or shrink films with low heat resistance can be selected as the polyester substrate.

[0081] <Dyes> Examples of dyes include direct dyes, vat dyes, sulfur dyes, naphthol dyes, reactive dyes, acid dyes, acid mordant dyes, disperse dyes, cationic dyes, and fluorescent brighteners. From the viewpoint of dissolution rate in a solution containing an oxidizing agent, direct dyes, reactive dyes, acid dyes, and cationic dyes are preferred. Examples of chromophores include nitro-based, azo-based, stilbene-based, carbonium-based, quinoline-based, methine-based, thiazole-based, quinoneimine-based, anthraquinone-based, indigoid-based, and phthalocyanine-based dyes. Azo-based dyes are preferred because they can be decomposed in a solution containing an oxidizing agent. Furthermore, dyes preferably have functional groups such as sulfonic acid groups, carboxylic acid groups, amino groups, and hydroxyl groups. Such dyes are easily chemically adsorbed to the easily decomposable crosslinked layer containing a hydrazine structure and tend to have excellent solvent resistance and fastness. The amount of dye is preferably 0.1 to 50 wt % of the total solids content of the crosslinkable composition, and more preferably 1 to 20 wt %.

[0082] <Pigments> Examples of pigments include organic pigments such as nitro pigments, nitroso pigments, azo pigments, dye lake pigments, phthalocyanine pigments, threne pigments, quinacridone pigments, dioxazine pigments, and isoindolinone pigments; inorganic pigments such as oxide pigments, hydroxide pigments, sulfide pigments, selenide pigments, ferrocyanide pigments, chromate pigments, sulfate pigments, carbonate pigments, silicate pigments, phosphate pigments, carbon pigments, and metal powder pigments; mineral pigments; and natural pigments such as natural dye lake pigments. Preferred organic pigments include azo pigments that can be decomposed in a solution containing an oxidizing agent, and pigments having functional groups such as sulfonic acid groups, carboxylic acid groups, amino groups, and hydroxyl groups. Pigments having such functional groups tend to be chemically adsorbed to the readily decomposable crosslinked material layer containing a hydrazine structure and are easily dispersed in a solution containing an oxidizing agent after the readily decomposable crosslinked material layer is decomposed. Preferred inorganic pigments include carbon pigments and metal powder pigments that can be chemically adsorbed to the readily decomposable crosslinked material layer containing a hydrazine structure. The average particle size of the pigment is preferably 0.005 to 1000 μm, more preferably 0.01 to 200 μm, and the amount of the pigment is preferably 0.1 to 50% by weight, more preferably 1 to 20% by weight, of the total solid content of the crosslinkable composition.

[0083] <Ink Fixing Aid> An ink fixing aid can be added when the easily decomposable crosslinked material layer is used as a primer, etc. Examples of ink fixing aids include swelling fixing types such as gelatin, polyvinyl alcohol, polyvinylpyrrolidone, and polyurethane, and pore-forming types such as alumina, silica, titanium oxide, and zirconia oxide, and although not particularly limited, hydrophilic ones are preferred. The ink fixing aid is preferably present in an amount of 1 to 80 wt %, and more preferably 3 to 20 wt %, of the total solids content of the crosslinkable composition.

[0084] <Surfactant> Examples of surfactants include siloxane-based compounds such as polyether-modified polydimethylsiloxane, polyether-modified siloxane, polyetherester-modified hydroxyl group-containing polydimethylsiloxane, polyether-modified acrylic group-containing polydimethylsiloxane, polyester-modified acrylic group-containing polydimethylsiloxane, perfluoropolydimethylsiloxane, perfluoropolyether-modified polydimethylsiloxane, and perfluoropolyester-modified polydimethylsiloxane; polyether-based compounds such as polyoxyethylene alkylphenyl ether, propylene oxide polymer, and ethylene oxide polymer; carboxylic acids such as coconut oil fatty acid amine salts and gum rosin; ester-based compounds such as castor oil sulfates, phosphate esters, alkyl ether sulfates, sorbitan fatty acid esters, sulfonate esters, and succinate esters; and sulfonate compounds such as alkylarylsulfonic acid amine salts and dioctyl sodium sulfosuccinate. The amount of surfactant is preferably 0.01 to 10 wt % of the total solids content of the crosslinkable composition, and more preferably 0.1 to 5 wt %.

[0085] <Method for producing easily decomposable cross-linked layer> The easily decomposable cross-linked layer can be produced by laminating a cross-linkable composition on a polyester substrate and cross-linking the cross-linkable composition. Examples of methods for laminating a cross-linkable composition on a polyester substrate include a method of applying the cross-linkable composition to a polyester substrate. Specific application methods include bar coating, spin coating, spray coating, dip coating, nozzle coating, gravure coating, reverse roll coating, die coating, air doctor coating, blade coating, rod coating, curtain coating, knife coating, transfer roll coating, squeeze coating, impregnation coating, kiss coating, calendar coating, extrusion coating, screen printing, inkjet printing, flexographic printing, offset printing, pad printing, water transfer, pressure-sensitive transfer, and in-mold molding. Another example of a method for laminating a cross-linkable composition is a method of bonding a polyester substrate with a film or sheet made of the cross-linkable composition.

[0086] Preferred methods for laminating the crosslinkable composition on a sheet-shaped polyester substrate include gravure coating, die coating, screen printing, inkjet printing, flexographic printing, and offset printing. Preferred methods for laminating the crosslinkable composition on a bottle-shaped polyester substrate include spray coating, dip coating, screen printing, pad printing, inkjet printing, flexographic printing, water transfer, pressure-sensitive transfer, and in-mold molding. A bottle-shaped laminate can also be obtained by laminating an easily decomposable crosslinked material layer on a sheet-shaped polyester substrate, molding it into a pipe shape, and covering and heating the bottle-shaped polyester substrate to integrate them.

[0087] The crosslinkable composition may be laminated on only one side of the polyester substrate, or may be laminated on both sides simultaneously or sequentially. When laminated on both sides, the crosslinkable compositions laminated on both sides may have the same composition or different compositions.

[0088] The crosslinking method of the crosslinkable composition includes light irradiation and heating. Specific crosslinking conditions are not particularly limited. When crosslinking is performed by light irradiation, the crosslinking conditions are 100 to 2000 mJ / cm.２ When crosslinking is performed by heating, the heating temperature is preferably 40 to 200° C., and more preferably 80 to 120° C. The heating time is preferably 0.5 to 180 minutes, and more preferably 0.5 to 10 minutes.

[0089] The thickness of the readily decomposable cross-linked material layer after cross-linking is not particularly limited, but is preferably 0.01 to 30 μm, and more preferably 0.05 to 20 μm. Within this range, both the strength of the readily decomposable cross-linked material layer and the decomposition removal speed of the readily decomposable cross-linked material layer can be achieved.

[0090] The easily decomposable cross-linked material layer may be formed directly or indirectly on the polyester substrate. Furthermore, the easily decomposable cross-linked material layer may be formed on the outermost surface of the polyester composite material, or may be formed as an intermediate layer. Furthermore, multiple easily decomposable cross-linked material layers may be laminated on the polyester substrate. The multiple easily decomposable cross-linked material layers may have the same composition or different compositions. An example of an easily decomposable cross-linked material layer formed directly on the polyester substrate is a structure in which a printing layer or receiving layer made of an easily decomposable cross-linked material is formed directly on the polyester substrate. An example of an easily decomposable cross-linked material layer formed on the outermost surface of a polyester composite is a structure in which a release layer, a weak adhesive layer, a printing layer, or a protective layer made of an easily decomposable cross-linked material is formed on the polyester substrate directly or via a printing layer.

[0091] 1 shows an example of a structure in which a print layer 11 made of an easily decomposable crosslinked material is formed directly on a polyester substrate 1. The print layer 11 may contain a pigment or dye.

[0092] Figure 2 shows an example of a structure in which a receiving layer 12 made of an easily decomposable crosslinked material is formed directly on a polyester substrate 1. A print layer 13 can be further laminated directly on the receiving layer 12. The receiving layer 12 may function as a primer for fixing the print layer 13 to the polyester substrate. The print layer 13 is formed from a crosslinkable composition containing any pigment, dye, and binder. This crosslinkable composition may contain the easily decomposable crosslinking agent described above.

[0093] Layers other than the easily decomposable crosslinked material layer, such as the printing layer 13 and the printing layer 14, may be formed from a composition containing a binder or dispersant that is soluble or dispersible in water, an acidic aqueous solution, an alkaline aqueous solution, acetone, alcohol, or other water-soluble organic solvent. Examples of such binders and crosslinking agents include those containing a hydrophilic group such as a carboxylic acid group, a sulfonic acid group, a hydroxyl group, or an amino group, and those containing a polyethylene glycol structure or a propylene glycol structure.

[0094] An example of an easily decomposable cross-linked material layer being indirectly formed on a polyester substrate is a structure in which a print layer and a protective layer made of an easily decomposable cross-linked material are formed in this order on a polyester substrate. Figure 3 shows an example of a structure in which a print layer 14 and a protective layer 15 made of an easily decomposable cross-linked material are formed on a polyester substrate 1. The print layer 14 is formed from a cross-linkable composition containing any pigment, dye, binder, etc. This cross-linkable composition may contain the above-mentioned easily decomposable cross-linking agent. The protective layer 15 has the function of protecting the print layer 14.

[0095] Figure 4 shows an example of a structure in which a print layer 2 (16) made of an easily decomposable cross-linked material is formed directly on a polyester substrate 1. A protective layer 2 (17) made of an easily decomposable cross-linked material can be laminated directly on top of the print layer 2 (16) made of an easily decomposable cross-linked material. The print layer 2 (16) made of an easily decomposable cross-linked material and the protective layer 2 (17) made of an easily decomposable cross-linked material may be formed of the same easily decomposable cross-linked material, or may be formed of different easily decomposable cross-linked materials.

[0096] The easily decomposable cross-linked material layer may be present on at least a portion of the surface of the polyester substrate, or may be present on the entire surface. For example, in the embodiment shown in Figure 1, the printing layer 11 made of the easily decomposable cross-linked material may be present on a portion of the surface of the polyester substrate. Furthermore, in the embodiments shown in Figures 2 and 3, the receiving layer and protective layer made of the easily decomposable cross-linked material may each be present on the entire surface of the polyester substrate.

[0097] In addition to the easily decomposable crosslinked layer, the polyester composite may include any layer such as a print layer, a gas barrier layer, a receiving layer, a protective layer, etc. These layers are preferably soluble or dispersible in water, an acidic aqueous solution, an alkaline aqueous solution, or a water-soluble organic solvent such as acetone or alcohol.

[0098] <Decomposition of Easily Decomposable Crosslinked Products> The oxidizing agent used in the step of contacting the polyester composite with a solution containing an oxidizing agent is not particularly limited as long as it is an oxidizing agent other than molecular oxygen. Examples of oxidizing agents include sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, ammonium hypochlorite, hydrogen peroxide, peracetic acid, m-chloroperbenzoic acid, perbenzoic acid, ammonium hypobromite, calcium hypobromite, potassium hypobromite, sodium hypobromite, and ozone. These may be used alone or in combination of two or more. Of these, water-soluble salts such as sodium hypochlorite and sodium hypobromite, and ozone water are preferred. These oxidizing agents are preferably used by dissolving them in an aqueous solution. The solution containing an oxidizing agent may also contain an alkali agent such as sodium hydroxide or potassium hydroxide, an organic solvent such as ethanol, methanol, isopropanol, or tetrahydrofuran, or a surfactant such as alkylbenzenesulfonate, alkyl sulfate ester salt, alkyl ether carboxylate, polyoxyethylene alkyl ether, glycerin fatty acid ester, alkyltrimethylammonium salt, or alkylcarboxybetaine. The concentration of the oxidizing agent in the solution is preferably 0.001 to 50% by weight, more preferably 0.01 to 5% by weight, and even more preferably 0.01 to 3% by weight.

[0099] The temperature condition when the polyester composite is brought into contact with the solution containing the oxidizing agent is preferably 100°C or less, more preferably 15 to 50°C. The time condition is preferably 60 minutes or less, more preferably 10 minutes or less. If necessary, the mixture may be shaken or stirred during the reaction with the oxidizing agent. The specific method for bringing the polyester composite into contact with the solution containing the oxidizing agent is not particularly limited, and examples include a method of immersing the polyester composite in the solution containing the oxidizing agent, and a method of spraying or dropping the solution containing the oxidizing agent onto the polyester composite.

[0100] In the step of contacting the polyester composite with the solution containing an oxidizing agent, if the polyester composite is in a sheet form, it is preferable to contact the polyester composite with the solution containing an oxidizing agent in that form without cutting, etc. If the polyester composite is in a bottle, tube, or pipe shape, it is preferable to mechanically crush the polyester composite before contacting it with the solution containing an oxidizing agent.

[0101] The easily decomposable cross-linked product is oxidized by contact with an oxidizing agent, and the decomposition products are N ２ , carboxylic acids, alcohols, amines, etc. may be produced. Specific examples of carboxylic acids include succinic acid, malonic acid, adipic acid, phthalic acid, trimellitic acid, and polyacrylic acid. Specific examples of alcohols include ethylene glycol, diethylene glycol, triethylene glycol, hexanediol, pentitol, pentaerythritol, polyethylene glycol, polyvinyl alcohol, resorcinol, and phenol novolac. Specific examples of amines include hexamethylenediamine, pentamethylenediamine, isophoronediamine, toluenediamine, and diaminodiphenylmethane. Decomposition products can be confirmed by NMR, IR spectra, etc.

[0102] The method for evaluating the decomposition property of the easily decomposable crosslinked material upon contact with an oxidizing agent is not particularly limited, but after immersing a polyester composite material in a 1.5% aqueous solution of sodium hypochlorite for 2 minutes, the surface is visually observed, and it is preferable that the easily decomposable crosslinked material layer peels off, and it is more preferable that the easily decomposable crosslinked material layer dissolves.

[0103] When the polyester composite includes a non-easily degradable printing layer, protective layer, receiving layer, etc., it is preferable that these dissolve or disperse in the solution upon contact with an oxidizing agent-containing solution. If they can be dissolved or dispersed in an oxidizing agent-containing solution, the step of separating and recovering the non-easily degradable printing layer, protective layer, receiving layer, etc. can be omitted. If the non-easily degradable printing layer, protective layer, receiving layer, etc. does not dissolve in an oxidizing agent-containing solution but can be dissolved or dispersed in water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent, the polyester substrate can be efficiently recovered by a step of dissolving the printing layer, etc. with these solutions and a step of decomposing the easily degradable crosslinked layer with an oxidizing agent-containing solution.

[0104] Furthermore, a polyester composite material having a slightly adhesive layer made of an easily decomposable crosslinked product formed on a polyester substrate can be used as an adhesive protective film. Such a protective film can be easily peeled off from an adherend, and the polyester substrate can be efficiently recovered by contacting the peeled protective film with a solution containing an oxidizing agent.

[0105] After the step of contacting the polyester composite material including the polyester substrate and the easily decomposable crosslinked layer with the solution containing an oxidizing agent, fine solid components may be removed by centrifugation or filtration. Furthermore, solvent substitution, washing, etc. may also be performed. By undergoing these steps, a high-purity polyester substrate can be recovered.

[0106] The present invention will be described below with reference to examples, but is not limited to the following examples. Hereinafter, "parts" and "%" mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

[0107] (1) Preparation of Crosslinkable Compositions (Production Example 1) Crosslinkable Composition 1 Easily decomposable crosslinking agents A and B, a curable resin, a polymerization initiator, and a solvent were mixed in the weight ratios shown in Table 1.

[0108] Easily decomposable crosslinking agent A was produced by the following method. 22.2 g of dimethyl sulfoxide and 1.00 g of 4,4'-hexyl disemicarbazide were mixed in a 50 ml recovery flask at 40°C, and 1.89 g of N-(allyloxycarbonyloxy)succinimide was added dropwise thereto, followed by stirring at room temperature for 4 hours. The reaction solution was added dropwise to 300 g of acetonitrile to obtain a white solid, which was further washed with acetonitrile and dried in a vacuum dryer at room temperature, yielding Easily Decomposable Crosslinking Agent A having the structure of Formula (A) in an 89% yield.

[0109] 1H-NMR (DMSO, δppm) 1.22 (4H, S, C ６ H １２ ), 1.36 (4H, t, C ６ H １２ ), 2.95-3.00 (4H, m, C ６ H １２ ), 4.49-4.51 (4H, m, CH ２ ), 5.19 (2H, d, CH=CH ２ ), 5.28-5.33 (2H, m, CH=CH ２ ), 5.85-5.94 (2H, m, CH=CH ２ ), 6.30 (2H, s, NH), 7.65 (2H, S, NHNH), 8.83 (2H, S, NHNH)

[0110] Easily decomposable crosslinking agent B was produced by the following method. 11.1 g of poly(acrylic acid hydrazide) with a molecular weight of approximately 1,000 and 138 g of dimethyl sulfoxide were mixed in a 300 ml recovery flask, and 5.0 g of 2-isocyanatoethyl methacrylate was added dropwise at room temperature. After stirring for 4 hours, 10.6 g of succinic anhydride was added and stirred for an additional 2 hours. The reaction liquid was added dropwise to 1,651 g of methyl isobutyl ketone, and the resulting solid was dried in a vacuum dryer at 50°C, yielding Easily Decomposable Crosslinking Agent B having the structure of Formula (B) in a 60% yield.

[0111] 1 H-NMR (DMSO, δppm) 1.55 (20H, br, main chain CH ２ ), 2.11 (10H, br, main chain CH), 1.88 (9H, s, CH ３ ), 2.46 (28H, br, COCH ２ CH２ CO), 3.47-3.51 (6H, m, NCH ２ ), 4.04-4.08 (6H, m, OCH ２ ), 5.67 (3H, d, C=CH ２ ), 6.06 (3H, d, C=CH ２ ), 6.43 to 6.52 (3H, m, CONHC), 9.82 (20H, br, NHNH), 12.12 (7H, br, COOH)

[0112] (Production Example 2) Crosslinkable Composition 2 Rhodamine B (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to crosslinkable composition 1 to prepare crosslinkable composition 2. Rhodamine B was added in an amount of 1 wt % based on the total solid content.

[0113] (Production Example 3) Crosslinkable Composition 3 Crosslinkable Composition 3 was prepared by blending Acid Blue 9 (manufactured by Tokyo Chemical Industry Co., Ltd.) into Crosslinkable Composition 1. Acid Blue 9 was blended so as to account for 1 wt % of the total solid content.

[0114] (Production Example 4) Crosslinkable Composition 4 Easily decomposable crosslinking agents D to E, a polymerization initiator, and a solvent were mixed in the weight ratios shown in Table 2.

[0115]

[0116] Easily decomposable crosslinking agent D was prepared by the following method. In a 100 mL three-neck flask, 1.8 g of sodium 5-sulfoisophthalic acid dihydrazide was dissolved in 40 g of methyl sulfoxide, and 3.4 g of diethyl 2-isocyanatoglutarate was added and stirred overnight at 80°C. The reaction mixture was allowed to cool to room temperature, then diluted with 100 g of purified water. The aqueous layer was washed three times with 90 g of ethyl acetate and then concentrated. The resulting residue was dried under vacuum. The resulting pale orange solid was transferred to a 30 mL recovery flask, to which 4.6 g of hydrazine monohydrate was added and stirred at room temperature for 4 hours. The reaction mixture was added dropwise to 200 g of methanol, resulting in the precipitation of a white solid. The resulting solid was collected by filtration and dried under vacuum, yielding the compound of formula (C) in a 93% yield.

[0117] In a 100 mL recovery flask, 2.9 g of the compound of formula (C) was dissolved in 33 g of dimethyl sulfoxide, and 4.1 g of N-allyloxycarbonyloxysuccinimide was added. The mixture was stirred overnight at room temperature. The reaction solution was transferred to a separatory funnel and diluted with 105 g of pure water. The resulting aqueous layer was washed three times with 80 g of methylene chloride and then concentrated to obtain a pale orange solid. This solid was washed three times with 150 g of methylene chloride and then vacuum dried to obtain the compound of formula (D) in an 83% yield.

[0118]

[0119] 1H-NMR (DMSO, δppm) 1.72-1.94 (4H, m, CH ２ ), 2.19 (4H, br, C=OCH ２ ), 4.26 (2H, q, C=OCH), 4.50 to 4.55 (8H, m, OCH ２ ), 5.20 (4H, dd, C=CH ２ ), 5.31 (4H, dd, C=CH ２ ), 5.87 to 5.95 (2H, m, CH=C), 6.69 (2H, br, NC=ONHC), 8.18 (2H, s, NC=ONHN), 8.28 (2H, s, benzene ring), 8.30 (1H, s, benzene ring ), 9.06 (2H, s, OC=ONH), 9.24 (2H, s, OC=ONH), 9.69 (2H, s, CC=ONH), 9.89 (2H, br, CC=ONH), 10.40 (2H, br, CC=ONH)

[0120] Easily decomposable crosslinking agent E was prepared by the following method. 10 g of polymethyl acrylate (UMM-1001, manufactured by Soken Chemical & Engineering Co., Ltd.) with a molecular weight of approximately 1000 and a hydroxyl group at one end was mixed with 13 g of acetonitrile and 3.5 g of triethylamine in a 100 ml recovery flask, and 4.7 g of di(N-succinimidyl)carbonate was added and stirred overnight at room temperature. Next, 1.8 g of methacrylic acid hydrazide was added and stirred for another overnight at room temperature. The reaction solution was washed four times with 50 g of pure water, after which 70 g of ethanol was added and the solvent and residual water were distilled off, yielding a decomposable compound having the structure of formula (E) in a 77% yield.

[0121] In the formula, R represents a hydrocarbon group.

[0122] 1H-NMR (DMSO, δppm) 1.4-1.9 (22H, m, CH ２ ), 1.86 (3H, s, CH ３ ), 2.19-2.41 (11H, m, CH), 3.58 (33H, br, OCH ３ ), 5.44 (1H, br, C=CH ２ ), 5.72 (1H, br, C=CH ２ ), 9.09 (1H, br, NHNH), 9.87 (1H, br, NHNH)

[0123] (Production Example 5) Crosslinkable Composition 5 Crosslinkable Composition 5 was prepared by blending 32 parts by weight of DENA DISPER RED 002DD (manufactured by Nagase & Co., Ltd.), a pigment water dispersion with a solids content of 20%, with 100 parts by weight of Crosslinkable Composition 4.

[0124] (Production Example 6) Crosslinkable Composition 6 Pure water was added to Crosslinkable Composition 4 so that the solid content would be 33%, and then Reactive Red 120 (manufactured by Sigma Aldrich) was blended to prepare Crosslinkable Composition 6. Reactive Red 120 was blended in an amount of 0.5 wt % relative to the total solid content.

[0125] (Production Example 7) Crosslinkable Composition 7 Easily decomposable crosslinking agent F, a curable resin, a polymerization initiator, a solvent, and a surfactant were mixed in the weight ratios shown in Table 3.

[0126]

[0127] Easily decomposable crosslinking agent F was prepared by the following method. 10 g of a carbinol-modified polydimethylsiloxane (KF-6000, manufactured by Shin-Etsu Chemical Co., Ltd.) with a molecular weight of approximately 1000, 16 g of acetone, and 6.5 g of triethylamine were mixed in a 100 ml recovery flask, and 6.0 g of di(N-succinimidyl) carbonate was added and stirred overnight at room temperature. 47 g of chloroform and 3.1 g of 4-pentenoic acid hydrazide were added to the reaction solution, and the mixture was stirred overnight at room temperature. This reaction solution was transferred to a separatory funnel, and 140 g of chloroform was added. The organic layer was then washed three times with 140 g of pure water. After washing, the organic layer was distilled off, yielding a decomposable compound having the structure of formula (F) in a 98% yield.

[0128] In the formula, R represents a hydrocarbon group.

[0129] 1H-NMR (CDCl ３ , δppm) 0.06 (76H, br, CH ３ ), 2.29-2.46 (8H, m, CH ２ CH ２ ), 4.96-5.10 (4H, m, CH=CH ２ ), 5.76-5.94 (2H, m, CH=CH ２ ), 7.74 (2H, br, NHNH), 8.41 (2H, br, NHNH)

[0130] (Production Example 8) Crosslinkable Composition 8 Easily decomposable crosslinking agent G, a curable resin, a polymerization initiator, a solvent, and a surfactant were mixed in the weight ratio shown in Table 4.

[0131] Easily decomposable crosslinking agent G was prepared by the following method. 2.0 g of 3-mercaptopropanehydrazide was dissolved in 26 g of THF in a 100 ml recovery flask, and 3.0 g of poly(hexamethylene diisocyanate) (Sigma-Aldrich) was added dropwise thereto, followed by stirring overnight at room temperature. The precipitated white solid was collected by decantation and dried in a vacuum dryer, yielding a decomposable compound having the structure of formula (G) in a yield of 94%.

[0132]

[0133] 1H-NMR (DMSO, δppm) 1.24-1.50 (24H, m, CH ２ ), 2.41 (6H, t, C=OCH ２ ), 2.67 (6H, t, SCH ２ ), 2.97-3.10 (12H, m, NCH ２ ), 6.26 (3H, s, NH), 7.67 (3H, s, NH), 8.21 (2H, br, NH), 9.50 (3H, s, NH)

[0134] (Production Example 9) Crosslinkable Composition 9 Easily decomposable crosslinking agent B, a curable resin, a polymerization initiator, a solvent, and a surfactant were mixed in the weight ratios shown in Table 5.

[0135] (Production Example 10) Crosslinkable composition 10 An ethyl acetate solution of readily decomposable crosslinking agent H, a curable resin, a polymerization initiator, and a surfactant were mixed in the weight ratios shown in Table 6.

[0136]

[0137] An ethyl acetate solution of readily decomposable crosslinker H was prepared as follows. 7.8 g of dehydrated acetonitrile, 0.7 g of triethylamine, and 0.28 g of 2-hydroxyethyl carbazate were mixed in a 20 ml recovery flask, and 0.36 g of methacrylic anhydride was added dropwise while cooling on ice. After stirring at room temperature for 2 hours, the solvent was removed using an evaporator. The residue was transferred to a 200 ml recovery flask, and 25 g of ethyl acetate, 30 g of butyl acrylate, 8.6 g of 2-ethylhexyl acrylate, and 2.98 g of diethylacrylamide were added and mixed. The mixture was heated to 80°C, and 0.12 g of azobis(isobutyronitrile) was added in small portions. After stirring overnight, the mixture was returned to room temperature and ethyl acetate was added to a solids content of 40% to obtain an ethyl acetate solution of a decomposable compound having the structure of formula (H). The average molecular weight of formula (H) was confirmed to be 650,000 by GPC.

[0138]

[0139] 1H-NMR (DMSO, δppm) 0.83-0.93 (420H, m, CH ３ ), 1.02-1.13 (60H, m, CH ３ ), 1.25-1.41 (360H, m, OCH), 1.42-1.88 (490H, m, CH, CH ２ , C.H. ３ ), 2.19-2.42 (130H, m, CH), 3.29-3.43 (40H, m, NCH ２ ), 3.57 (2H, dd, C=CH ２ ), 5.24 (2H, dd, C=CH ２ ), 5.82-5.92 (2H, br, HOCH ２ ), 3.99-4.43 (242H, m, O=COCH ２ ), 9.02 (1H, br, NH), 9.77 (1H, br, NH)

[0140] (Production Example 11) Crosslinkable Composition 11 Easily decomposable crosslinking agent I, a curable resin, a polymerization initiator, and a pigment were mixed in the weight ratio shown in Table 7.

[0141]

[0142] Easily decomposable crosslinker I was prepared as follows. 70 g of 6-hydroxyhexanoic acid hydrazide and 206 g of γ-butyrolactone were mixed in a 500 ml recovery flask and stirred at 100°C for 4 days. The reaction mixture was then added dropwise to 700 g of acetone to precipitate a solid. The resulting solid was transferred to a 2 L recovery flask, and 1.5 L of dehydrated acetonitrile and 100 g of triethylamine were added and stirred at 0°C. 212 g of a 40 wt % acetonitrile solution of acryloyl chloride was added dropwise and stirred at room temperature for 1 hour. After removing the solvent to a certain extent using an evaporator, 1 L of chloroform was added, followed by three separations with 500 ml of ion-exchanged water. The organic layer, washed with water, was concentrated using an evaporator to obtain a decomposable compound having the structure of formula (I) in a 34% yield.

[0143]

[0144] 1H-NMR (DMSO, δppm) 1.30-1.38 (2H, m, CH ２ ), 1.48-1.65 (4H, m, CH ２ ), 1.77-1.88 (2H, m, CH ２ ), 2.06-2.23 (4H, m, O=CCH ２ ), 4.06 to 4.13 (4H, m, O=COCH ２ ), 5.91-5.97 (2H, m, C=CH), 6.10-6.24 (2H, m, C=CH ２ ), 6.27-6.38 (2H, m, C=CH ２ ), 9.70 (2H, br, NHNH)

[0145] (2) Preparation of Polyester Composite Material (Example 1) Crosslinkable composition 1 was applied by dip coating onto a PET film (Lumirror T60, manufactured by Toray Industries, Inc., thickness 188 μm), dried, and then cured with UV light to form an easily decomposable crosslinked material layer with a thickness of 10 μm on the film. Furthermore, a print layer was formed on the easily decomposable crosslinked material layer. The print layer was formed using an inkjet printer (PIXUS TS3130S, manufactured by Canon) equipped with a water-based ink cartridge (BC-345, BC-346).

[0146] Comparative Example 1 A print layer was formed directly on a PET film by the method described in Example 1.

[0147] (Example 2) A print layer was directly formed on a PET film by the method described in Example 1. Furthermore, crosslinkable composition 1 was applied onto the print layer by dip coating, dried, and then cured with UV light to form an easily decomposable crosslinked layer having a thickness of 10 μm.

[0148] Example 3 Crosslinkable composition 2 was printed on a PET film (Lumirror T60 manufactured by Toray Industries, Inc., thickness 188 μm) using an inkjet printer B10 manufactured by BENTSAI Corporation, and after drying, was cured with UV light to form an easily decomposable crosslinked layer having a thickness of 7 μm on the film.

[0149] Example 4 Crosslinkable composition 3 was printed on a PET film (Lumirror T60 manufactured by Toray Industries, Inc., thickness 188 μm) using an inkjet printer B10 manufactured by BENTSAI Corporation, and after drying, was cured with UV light to form an easily decomposable crosslinked layer having a thickness of 7 μm on the film.

[0150] (Example 5) The crosslinkable composition 1 was applied by dip coating onto a PET film (Lumirror T60 manufactured by Toray Industries, Inc., thickness 188 μm), dried, and then UV-cured to form an easily decomposable crosslinked material layer with a thickness of 10 μm on the film. Furthermore, a print layer was formed on the easily decomposable crosslinked material layer. The print layer was formed using an inkjet printer B10 manufactured by BENTSAI Corporation equipped with the solvent-based ink BENTSAI BT-2580P2.

[0151] Example 6 An easily decomposable crosslinked layer having a thickness of 8 μm was formed on the curved surface of a PET bottle by flexographically printing the crosslinkable composition 5. An EasyProof made by Matsuo Sangyo Co., Ltd. was used for printing, and after printing, the layer was cured by UV irradiation.

[0152] Example 7 Crosslinkable composition 6 was printed on a PET bottle using an inkjet printer B10 manufactured by BENTSAI Corporation, and then cured with UV light to form an easily decomposable crosslinked layer of 18 μm on the curved surface of the bottle.

[0153] (Example 8) Crosslinkable composition 7 was applied to a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm) by bar coating, dried, and then UV-cured to form an easily decomposable crosslinked layer with a thickness of 0.9 μm on the film. When a 180-degree peel strength test was performed on each of the PET film and the easily decomposable crosslinked layer using Nitto 31B tape (19 mm wide), the easily decomposable crosslinked layer had a smaller peel strength. Because this easily decomposable crosslinked layer has a silicone structure, it exhibited non-adhesion to the test tape.

[0154] (Example 9) The crosslinkable composition 8 was applied to a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm) by bar coating, dried, and then UV-cured to form an easily decomposable crosslinked layer with a thickness of 0.6 μm on the film. When a 180-degree peel strength test was performed on each of the PET film and the easily decomposable crosslinked layer using Nitto 31B tape (19 mm wide), the easily decomposable crosslinked layer had a smaller peel strength. Because this easily decomposable crosslinked layer has a silicone structure, it exhibited non-adhesion to the test tape.

[0155] (Example 10) Crosslinkable composition 9 was applied to a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm) by bar coating, dried, and then UV-cured to form an easily decomposable crosslinked layer with a thickness of 0.4 μm on the film. When a 180-degree peel strength test was performed on each of the PET film and the easily decomposable crosslinked layer using Nitto 31B tape (19 mm wide), the easily decomposable crosslinked layer had a smaller peel strength. Because this easily decomposable crosslinked layer has a silicone structure, it exhibited non-adhesion to the test tape.

[0156] (Example 11) Crosslinkable composition 9 was applied by bar coating onto the easily decomposable crosslinked material layer of the polyester composite obtained in Example 4 so that the film thickness after curing was 0.5 μm, and after drying, it was UV-cured to form a second easily decomposable crosslinked material layer. When a PET film was placed on the second easily decomposable crosslinked material layer of the obtained polyester composite and slid horizontally by hand, it could be moved with less force than when two PET films were stacked on top of each other. It is believed that the second easily decomposable crosslinked material layer exhibited good sliding properties because it had a silicone structure.

[0157] (Example 12) The crosslinkable composition 10 was applied by bar coating onto a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm), and then dried and cured for 2 minutes at 110° C. to form an easily decomposable crosslinked material layer with a thickness of 20 μm on the film. The obtained easily decomposable crosslinked material layer had slight adhesiveness and could be attached to an acrylic film or a TAC film, but could also be easily peeled off.

[0158] Example 13 A print layer was formed on the easily decomposable crosslinked layer of the polyester composite material obtained in Example 12 using an inkjet printer (PIXUS TS3130S, manufactured by Canon) equipped with a water-based ink cartridge (BC-345, BC-346).

[0159] Example 14 The crosslinkable composition 11 was flexographically printed on a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm) and then irradiated with UV light to form an easily decomposable crosslinked layer having a thickness of 5 μm on the film. Flexiproof 100UV, manufactured by Matsuo Sangyo Co., Ltd., was used for printing and UV irradiation.

[0160] Comparative Example 2 A solvent-based ink, BENTSAI BT-2580P2, was printed on a PET film using an inkjet printer B10 manufactured by BENTSAI Corporation, and then dried to directly form a 7 μm thick printed layer.

[0161] (3) Evaluation of Polyester Composite Material (3-1) Chemical Resistance Test The surface of the polyester composite material was wiped with a nonwoven fabric soaked in water or ethanol, and evaluated according to the following criteria: ○: No peeling of the readily decomposable cross-linked material layer and the printed layer ×: Peeling of the readily decomposable cross-linked material layer or the printed layer

[0162] (3-2) Polyester substrate recovery test The polyester composite materials prepared in each example and comparative example were immersed in a solution containing an oxidizing agent at room temperature for 3 minutes. The solution was then drained and the polyester substrate was recovered. Evaluation was performed visually and classified according to the following criteria: ○: All layers on the polyester substrate were dissolved or uniformly dispersed, and only the polyester substrate could be easily recovered. △: All layers were peeled off from the polyester substrate, but some layers did not dissolve or uniformly disperse, and some of them were mixed into the recovered polyester substrate. ×: The easily decomposable cross-linked layer or printed layer remained on the polyester substrate, and only the polyester substrate could not be recovered.

[0163] The following solutions a, b, and c were used as solutions containing an oxidizing agent: (Solution a) 1.5% aqueous solution of sodium hypochlorite (Solution b) A solution obtained by diluting kitchen bleach containing sodium hypochlorite manufactured by Kaneyo Soap Co., Ltd. three times with Solmix AP-1 manufactured by Japan Alcohol Sales Co., Ltd., which contains ethanol as its main ingredient (Solution c) A solution obtained by diluting kitchen bleach containing sodium hypochlorite manufactured by Kaneyo Soap Co., Ltd. three times with propylene glycol monomethyl ether

[0164]

[0165] The polyester composite materials of Examples 1 to 14 exhibited excellent chemical resistance. It was also confirmed that the easily decomposable cross-linked layer dissolved or peeled off upon reaction with an oxidizing agent, allowing the PET substrate to be recovered.

[0166] The polyester composite material of Comparative Example 1 had poor chemical resistance. In Example 1, in which the easily decomposable cross-linked material layer was used as a primer, the chemical resistance was improved even though the printing layer was the same as in Comparative Example 1, and it was confirmed that the easily decomposable cross-linked material layer was able to fix the ink.

[0167] Although the polyester composite material of Comparative Example 2 was water resistant, it had poor alcohol resistance, and the polyester substrate could not be recovered using a solution containing an oxidizing agent. In Example 5, although the printing layer was the same as that of Comparative Example 2, the printing layer could be peeled off from the polyester substrate by decomposition of the easily decomposable cross-linked layer.

[0168] The present invention may include, for example, the following aspects. <1> A method for recovering a polyester substrate, comprising a step of contacting a polyester composite material containing a polyester substrate and an easily decomposable cross-linked material layer with a solution containing an oxidizing agent. <2> The method for recovering a polyester substrate according to item 1, in which the easily decomposable cross-linked material layer is provided on the outermost surface of the polyester composite material. <3> The method for recovering a polyester substrate according to item 1 or 2, in which the easily decomposable cross-linked material layer is made of a cross-linked material containing a hydrazine structure represented by formula (1). -A １ -NH-NH-A ２ - (1) (In formula (1), A １ , A ２ are each a carbonyl group or a single bond, and A １ and A ２at least one of which is a carbonyl group.) <4> The method for recovering a polyester substrate according to any one of items 1 to 3, wherein the easily decomposable crosslinked material layer comprises a crosslinked material containing a siloxane structure or a poly(meth)acrylic acid ester structure. <5> The method for recovering a polyester substrate according to any one of items 1 to 4, wherein a printed layer is provided directly on the easily decomposable crosslinked material layer. <6> The method for recovering a polyester substrate according to any one of items 1 to 5, wherein the easily decomposable crosslinked material layer contains a pigment or a dye. <7> The method for recovering a polyester substrate according to any one of items 1 to 6, wherein a printed layer is provided between the polyester substrate and the easily decomposable crosslinked material layer. <8> The method for recovering a polyester substrate according to any one of items 1 to 7, wherein the polyester substrate is in a bottle shape. <9> The method for recovering a polyester substrate according to any one of items 1 to 8, wherein the polyester substrate is in a sheet shape. <10> A crosslinkable composition for forming an easily decomposable crosslinked material layer on a polyester substrate that is decomposed upon contact with a solution containing an oxidizing agent. <11> The composition according to item 10, characterized by containing an easily decomposable crosslinking agent represented by formula (2). (In formula (2), n≧0, k≧0, m≧0, p1≧1, p2≧1, p3≧1. R １ , R ２ , R ３ are each independently a divalent group containing a siloxane structure, or a hydrocarbon group which may have a substituent or a heteroatom. １ is a divalent or higher valent group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ２ is a divalent group containing a siloxane structure or a hydrocarbon group which may have a hetero atom. １ ~A ８ is a carbonyl group or a single bond, and A １ and A ２ At least one of A is a carbonyl group, ３ and A ４ At least one of A is a carbonyl group, ５ and A ６ At least one of A is a carbonyl group, ７ and A ８ At least one of the groups is a carbonyl group. １, Q ２ , Q ３ are each independently a reactive functional group, or hydrogen or halogen.) <12> A polyester composite comprising a polyester substrate and an easily decomposable crosslinked layer that is decomposable by an oxidizing agent.

[0169] REFERENCE SIGNS LIST 1 Polyester substrate 11 Printing layer made of easily decomposable cross-linked material 12 Receiving layer made of easily decomposable cross-linked material 13 Printing layer 1 14 Printing layer 2 15 Protective layer made of easily decomposable cross-linked material 16 Printing layer 2 made of easily decomposable cross-linked material 17 Protective layer 2 made of easily decomposable cross-linked material

Claims

1. A method for recovering a polyester substrate, comprising the step of bringing a polyester composite material including a polyester substrate and an easily decomposable crosslinked layer into contact with a solution containing an oxidizing agent.

2. The method for recovering a polyester substrate according to claim 1, wherein the easily decomposable crosslinked layer is provided on the outermost surface of the polyester composite material.

3. The method for recovering the polyester base material according to claim 1 or 2, wherein the easily decomposable crosslinked material layer is composed of a crosslinked material containing a hydrazine structure represented by the formula (1). -A １ -NH-NH-A ２ - (1) (In the formula (1), A １ , A ２ is each a carbonyl group or a single bond, and at least one of A １ and A ２ is a carbonyl group.) 4. The method for recovering a polyester substrate according to any one of claims 1 to 3, wherein the easily decomposable crosslinked layer is composed of a crosslinked product including a siloxane structure or a poly(meth)acrylate structure.

5. The method for recovering a polyester substrate according to any one of claims 1 to 4, wherein a printing layer is directly provided on the easily decomposable crosslinked layer.

6. The method for recovering a polyester substrate according to any one of claims 1 to 5, wherein the easily decomposable crosslinked layer contains a pigment or a dye.

7. The method for recovering a polyester substrate according to any one of claims 1 to 4, wherein a printing layer is provided between the polyester substrate and the easily decomposable crosslinked layer.

8. The method for recovering a polyester substrate according to any one of claims 1 to 7, wherein the polyester substrate has a bottle shape.

9. The method for recovering a polyester substrate according to any one of claims 1 to 7, wherein the polyester substrate has a sheet shape.

10. A crosslinkable composition for forming an easily decomposable crosslinked layer that is formed on a polyester substrate and decomposed by contact with a solution containing an oxidizing agent.

11. The composition according to claim 10, characterized in that it contains a readily decomposable crosslinking agent represented by formula (2). (In formula (2), ・n≧0, k≧0, m≧0, p1≧1, p2≧1, p3≧1. ・R １ , R ２ , R ３ are each independently a divalent group containing a siloxane structure, or a hydrocarbon group which may have a substituent or a hetero atom. ・Z １ is a divalent or higher group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ・Z ２ is a divalent group containing a siloxane structure, or a hydrocarbon group which may have a hetero atom. ・A １ to A ８ is a carbonyl group or a single bond, and at least one of A １ and A ２ is a carbonyl group, at least one of A ３ and A ４ is a carbonyl group, at least one of A ５ and A ６ is a carbonyl group, at least one of A ７ and A ８ is a carbonyl group. ・Q １ , Q ２ , Q ３ are each independently a reactive functional group, or hydrogen or a halogen.) 12. A polyester composite material including a polyester substrate and an easily decomposable crosslinked layer that is decomposed by an oxidizing agent.

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