Method for decrosslinking crosslinked elastomer, decrosslinked elastomer obtained by said method, rubber product comprising same and method for recrosslinking crosslinked elastomer

Abstract

A method for decrosslinking a crosslinked elastomer comprises heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B), thereby decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B).

Description

Method for depolymerizing a crosslinked elastomer, depolymerized elastomer obtained by the method, rubber product using the same, and method for re-crosslinking a crosslinked elastomer

[0001] The present invention relates to a method for depolymerizing a crosslinked elastomer, a depolymerized elastomer obtained by the method, a rubber product using the same, and a method for re-crosslinking a crosslinked elastomer.

[0002] Thermoplastic elastomer compositions are industrially extremely useful materials because they melt at the processing temperature during their molding process and can be molded by well-known resin molding methods. As such a thermoplastic elastomer composition, for example, in International Publication No. 2017 / 047274 (Patent Document 1), it has a side chain (a) containing a hydrogen-bonding crosslinking site having a carbonyl-containing group and / or a nitrogen-containing heterocycle, and an elastomeric polymer (A) having a glass transition point of 25°C or lower, and at least one elastomeric polymer component selected from the group consisting of an elastomeric polymer (B) in which a hydrogen-bonding crosslinking site and a covalent crosslinking site are contained in the side chain and the glass transition point is 25°C or lower, and clay having a content ratio of 20 parts by mass or less with respect to 100 parts by mass of the elastomeric component, and an α-olefin resin having no chemically-bonded crosslinking site. A thermoplastic elastomer composition is disclosed. Such a thermoplastic elastomer composition described in Patent Document 1 is excellent in terms of breaking strength and the like, and can be applied to various uses.

[0003] International Publication No. 2017 / 047274

[0004] However, regarding a conventional thermoplastic elastomer composition as described in Patent Document 1 above, which includes a crosslinked elastomer of a type in which a covalent crosslinking site is contained in the side chain, after using the composition for various uses, a treatment method that enables depolymerizing the crosslinking (covalent crosslinking site) of such a crosslinked elastomer and reusing the elastomeric polymer that was the raw material of the crosslinked elastomer has not been known so far.

[0005] The present invention has been made in view of the problems of the prior art, and an elastomeric polymer can be reused by efficiently crosslinking the covalent crosslinking sites in the crosslinked elastomer and easily plasticizing the crosslinked product. A method for crosslinking a crosslinked elastomer; a crosslinked elastomer obtained by the method; and a rubber product using the crosslinked elastomer; A method for re-crosslinking a crosslinked elastomer that enables reuse as a re-crosslinked product by re-crosslinking the crosslinked elastomer after crosslinking; The purpose is to provide.

[0006] As a result of intensive studies to achieve the above object, the inventors of the present invention heated an elastomer composition containing a crosslinked elastomer (A) having a covalent crosslinking site and water (B), and the crosslinked elastomer ( It has been found that the covalent crosslinking sites in A) can be crosslinked by the water (B), and that the crosslinked elastomer after use in various applications can be easily crosslinked and plasticized, and its reuse can be achieved. Thus, the present invention has been completed.

[0007] That is, the present invention provides the following aspects.

[0008] [1] A method for crosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having a covalent crosslinking site and water (B) to crosslink the covalent crosslinking site in the crosslinked elastomer (A) with the water (B).

[0009] [2] The method for crosslinking a crosslinked elastomer according to [1], wherein the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, and has a covalent crosslinking site that crosslinks the polymer molecules by covalent bonds.

[0010] [3] The method for crosslinking a crosslinked elastomer according to [1] or [2], wherein the crosslinked elastomer (A) is an elastomeric polymer (A1) having a hydrogen bonding crosslinking site and a covalent crosslinking site in a side chain and a glass transition point of 25 ° C. or lower.

[0011] [4] A method for decrosslinking a crosslinked elastomer according to any one of [1] to [3], wherein the covalent crosslinking site has at least one bond selected from the group consisting of amide, ester, urethane, urea, thiourethane, thioester, biuret, allophanate, and imide.

[0012] [5] A method for decrosslinking a crosslinked elastomer according to any one of [1] to [4], wherein the covalent crosslinking site has at least one bond selected from the group consisting of amides, esters, thioesters, and imides.

[0013] [6] A method for decrosslinking a crosslinked elastomer according to any one of [1] to [5], wherein the elastomer composition is heated under the conditions of heating temperature: 100 to 300°C and gauge pressure: 0.05 MPa or higher.

[0014] [7] A method for decrosslinking a crosslinked elastomer according to any one of [1] to [6], wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

[0015] [8] The method for decrosslinking a crosslinked elastomer according to [7], wherein the organic solvent (C) is at least one selected from the group consisting of sulfolane, N-methyl-2-pyrrolidone, N,N-dimethylimidazolidone, dimethyl sulfoxide, diglyme, monoglyme, toluene, xylene, mesitylene, tetralin (tetrahydronaphthalene), naphthalene, and chlorobenzene.

[0016] [9] The method for decrosslinking a crosslinked elastomer according to [7] or [8], wherein the catalyst (D) is at least one selected from the group consisting of an acid catalyst, a base catalyst, and a phase transfer catalyst.

[0017]

[10] A decrosslinked elastomer obtained by heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B), thereby decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B). (In the decrosslinked elastomer described in

[10] , it is preferable that the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having cyclic acid anhydride groups and a crosslinking agent having two or more functional groups in one molecule, and is a crosslinked elastomer having covalently crosslinked sites that crosslink the molecules of the polymer together by covalent bonds.)

[0018] Rubber products comprising the decrosslinked elastomer and / or its crosslinked product as described in

[11] and

[10] . (Note that the "crosslinked product of the decrosslinked elastomer" described in

[11] may be an elastomer recrosslinked by the recrosslinking method of the crosslinked elastomer described in any one of the following items

[12] to

[15] .)

[0019]

[12] A method for recrosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer, and then heating the decrosslinked elastomer composition containing the decrosslinked elastomer at a temperature of 100 to 280°C in an open system or under reduced pressure conditions to recrosslink the decrosslinked elastomer in the decrosslinked elastomer composition (for convenience, such a method for recrosslinking a crosslinked elastomer described in

[12] will be referred to as the "first method for recrosslinking a crosslinked elastomer" below).

[0020]

[13] The method for recrosslinking a crosslinked elastomer according to

[12] , wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

[0021]

[14] A method for recrosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer composition containing a decrosslinked elastomer, and then heating the decrosslinked elastomer composition, which includes a decrosslinked elastomer, in an open system or under reduced pressure conditions at a temperature above the boiling point of the water (B) to remove the water (B) present in the decrosslinked elastomer composition, and then adding a crosslinking agent to the obtained composition, which consists of a compound having at least one functional group from hydroxyl groups, thiol groups, amino groups, and imino groups in two or more molecules, thereby recrosslinking the decrosslinked elastomer with the crosslinking agent in the composition after the addition of the crosslinking agent (a method for recrosslinking a crosslinked elastomer as described in

[14] will, for convenience, be referred to below as the "second method for recrosslinking a crosslinked elastomer").

[0022]

[15] The method for recrosslinking a crosslinked elastomer according to

[14] , wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

[0023] According to the present invention, it is possible to provide a method for decrosslinking a crosslinked elastomer that can efficiently decrosslink the covalent crosslinking sites in the crosslinked elastomer, enabling the reuse of the elastomeric polymer as a decrosslinked product that can be easily plasticized; a decrosslinked elastomer obtained by this method; and rubber products using the decrosslinked elastomer; and a method for recrosslinking a crosslinked elastomer that enables reuse as a recrosslinked product by recrosslinking the crosslinked elastomer after decrosslinking.

[0024] This is a schematic diagram illustrating one form of the reaction scheme for a preferred embodiment of the re-crosslinking method for crosslinked elastomers of the present invention. This is a graph showing the IR spectrum of the elastomer constituting the sheet obtained in Synthesis Example 3 (IR spectrum of the crosslinked elastomer) and the IR spectrum of the elastomer constituting the solid content obtained in Example 4 (IR spectrum of the de-crosslinked elastomer). This is a graph showing the IR spectrum of the elastomer constituting the sheet obtained in Synthesis Example 4 (IR spectrum of the crosslinked elastomer), the IR spectrum of the elastomer constituting the solid content obtained in Example 7 (IR spectrum of the de-crosslinked elastomer), the IR spectrum of the elastomer constituting the sheet obtained in Example 8 (IR spectrum of the re-crosslinked elastomer), and the IR spectrum of the elastomer constituting the solid content obtained in Reference Example 1 (IR spectrum of the elastomer having maleic anhydride groups).

[0025] The present invention will be described in detail below with reference to its preferred embodiments. In this specification, unless otherwise specified, the notation "X to Y" for numerical values ​​X and Y means "X or greater and Y or less". If a unit is attached only to the numerical value Y in such notation, that unit shall also apply to the numerical value X.

[0026] <Method for De-crosslinking a Crosslinked Elastomer> The present invention provides a method for de-crosslinking a crosslinked elastomer, which involves heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to de-crosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B). Hereinafter, the crosslinked elastomer (A) having covalently crosslinked sites and the water (B) will be described separately.

[0027] <Cross-linked elastomer (A)> The cross-linked elastomer (A) according to the present invention has covalent cross-linking sites. Such a cross-linked elastomer (A) is not particularly limited as long as it has covalent cross-linking sites, but from the viewpoint of ease of obtaining raw materials, it is preferable that it is a cross-linked elastomer which is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a cross-linking agent having two or more functional groups in one molecule, and which has covalent cross-linking sites that cross-link the polymer molecules with each other by covalent bonds. In this invention, the term "covalent crosslinking site" refers to a site that crosslinks the molecules of the polymer constituting the main chain by covalent bonds. For example, if the crosslinked elastomer (A) is a reaction product of an elastomer polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, the site becomes a site that crosslinks the polymer molecules (molecules of the elastomer polymer) by covalent bonds formed by the reaction between the cyclic acid anhydride group and the functional groups of the crosslinking agent. (In other words, if the crosslinked elastomer (A) is a reaction product of an elastomer polymer having a cyclic acid anhydride group and the crosslinking agent, the "covalent crosslinking site" is a crosslinked portion (site) formed by crosslinking the molecules of the elastomer polymer with the crosslinking agent via bonds (covalent bonds: for example, bonds of amide, ester, urethane, urea, thiourethane, thioester, biuret, allophanate, imide, etc.) formed by the reaction between the cyclic acid anhydride group and the functional groups of the crosslinking agent.)

[0028] As such an elastomeric polymer having a cyclic acid anhydride group, it is preferable that the elastomeric polymer has a cyclic acid anhydride group as a functional group in the main chain or side chain, and it is particularly preferable that the elastomeric polymer has a cyclic acid anhydride group in the side chain. As an elastomeric polymer having a cyclic acid anhydride group in the main chain, polymers obtained by copolymerizing monomers that can introduce cyclic acid anhydride groups into the main chain, such as maleic anhydride, can be suitably used. An "elastomeric polymer having a cyclic acid anhydride group in the side chain" refers to an elastomeric polymer in which a cyclic acid anhydride group is chemically and stably bonded (covalently bonded) to the atoms forming the main chain of the polymer. For example, a polymer obtained by reacting an elastomeric polymer for forming the main chain (a polymer constituting the main chain) with a compound that can introduce a cyclic acid anhydride group (cyclic acid anhydrides such as succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, and their derivatives) can be suitably used. Furthermore, as an elastomeric polymer having such cyclic acid anhydride groups in its side chains, it is preferable that the elastomeric polymer has grafted cyclic acid anhydride groups in its side chains. The method for reacting the elastomeric polymer (the polymer constituting the main chain) with a compound that can introduce cyclic acid anhydride groups (cyclic acid anhydrides such as succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, and their derivatives) is not particularly limited, and known methods can be used as appropriate. Furthermore, as such cyclic acid anhydride groups, succinic anhydride groups, maleic anhydride groups, glutaric anhydride groups, and phthalic anhydride groups are preferred, and among these, maleic anhydride groups are more preferred from the viewpoint of being easily introduced into the polymer side chains and readily available industrially. Furthermore, commercially available elastomeric polymers having such cyclic acid anhydride groups may be used as appropriate.

[0029] Furthermore, the polymer constituting the main chain of the elastomeric polymer having the cyclic acid anhydride group (the polymer forming the main chain portion) can be any so-called elastomer. For example, a commonly known natural polymer or synthetic polymer with a glass transition temperature of room temperature (25°C) or lower can be suitably used. In this invention, the "glass transition temperature" is the glass transition temperature measured by differential scanning calorimetry (DSC). When measuring such a glass transition temperature, it is preferable to set the heating rate to 10°C / min. The "elastomeric polymer" referred to herein exhibits rubber-like elasticity at room temperature (around 25°C).

[0030] Furthermore, the main chain of such an elastomeric polymer having a cyclic acid anhydride group may contain monomer units (double bond-containing monomer units) that include double bonds in the region forming the main chain skeleton. Note that "double bond-containing monomer units" as used herein refers to monomer units that contain double bonds in the region forming the main chain skeleton (the region other than the side chain), not in the side chain portion. For example, monomer units derived from butadiene with the formula: -CH ２ -CH = CH - CH ２ The monomer unit represented by -, the monomer unit derived from isoprene, is formula -CH ２ -C(CH ３ ) = CH - CH ２ Examples include monomer units represented by -.

[0031] The polymer constituting the main chain of the elastomeric polymer having the cyclic acid anhydride group is preferably at least one selected from diene rubber, hydrogenated diene rubber, olefin rubber, possibly hydrogenated polystyrene elastomeric polymer, polyolefin elastomeric polymer, polyvinyl chloride elastomeric polymer, polyurethane elastomeric polymer, polyester elastomeric polymer, and polyamide elastomeric polymer. Furthermore, as the main chain of such an elastomeric polymer, at least one selected from the group consisting of diene rubber, hydrogenated diene rubber, and olefin rubber is preferred because it has good rubber elasticity.

[0032] Furthermore, if the elastomeric polymer having the cyclic acid anhydride group is an elastomeric polymer modified with maleic anhydride, it is more preferable that such maleic anhydride-modified elastomeric polymer has a maleation rate of 0.1 to 30% by mass. The upper limit of this numerical range of maleation rate is more preferably 20% by mass, and even more preferably 15% by mass. The lower limit of the numerical range of the maleation rate is more preferably 0.2% by mass, and even more preferably 0.5% by mass. In this specification, the value of "maleation rate" (unit: mass%) is the value obtained by employing the following [Method for measuring maleation rate].

[0033] [Method for Measuring Maleination Rate] First, 400 mg of the maleic anhydride-modified polymer to be measured is dissolved in 80 mL of tetrahydrofuran (hereinafter, for convenience, sometimes abbreviated as "THF") to obtain a THF solution for measurement. Next, the THF solution for measurement is titrated with a 0.1 mol / L potassium hydroxide ethanol solution (a standard solution for volumetric analysis: a 0.1 mol / L potassium hydroxide ethanol solution with correction: a commercially available product with a factor (characteristic value: correction value) to three or more decimal places may be used). Here, the endpoint (neutralization point) is determined by potentiometric titration using an instrument. The factor (characteristic value: correction value) of the 0.1 mol / L potassium hydroxide ethanol solution may be determined by titration with an oxalic acid standard solution, or, if a commercially available product with a known factor is used, the factor listed on the reagent (for example, the factor listed on the reagent's inspection report) may be used as is. Next, the same measurement (blank test) is performed, except that a maleic anhydride-modified polymer is not used, and the titration is performed to determine the volume (blank value) of ethanol solution of 0.1 mol / L potassium hydroxide per 80 mL of THF. Next, the acid value is calculated using the obtained titration value (volume) based on the "Acid Value Calculation Formula" below, and then the maleization rate (unit: mass%) is determined by using the obtained acid value to calculate the maleization rate based on the "Maleization Rate Calculation Formula" below. <Acid Value Calculation Formula> [Acid Value] = (A - B) × M １ ×C×f / S (wherein A represents the volume of 0.1 mol / L potassium hydroxide ethanol solution added to neutralize the measurement solution (titration value: mL), B represents the volume of 0.1 mol / L potassium hydroxide ethanol solution added in the blank test (titration value obtained by performing the same measurement except that maleic anhydride-modified polymer is not used (blank value: mL)), M １represents the molecular weight of potassium hydroxide (56.1 (constant)), C represents the concentration of potassium hydroxide in the ethanol solution of potassium hydroxide (0.1 mol / L (constant)), f represents the factor of the ethanol solution of potassium hydroxide (correction value: the factor described in the commercially available reagent (for example, the factor described in the inspection certificate of the reagent, etc.) can be used as it is), and S represents the mass of the maleic anhydride-modified polymer used in the measurement. The unit of the "acid value" obtained by such calculation is "mgKOH / g".) <Calculation formula for maleation rate> [Maleation rate] = [Acid value] ÷ M １ ×M ２ ÷1000×100÷2 (In the formula, the acid value represents the value obtained by the above "calculation formula for acid value" (unit: mgKOH / g), and M １ represents the molecular weight of potassium hydroxide (56.1 (constant)), and M ２ represents the molecular weight of maleic anhydride (98.1 (constant)). The unit of the "maleation rate" obtained by such calculation is "mass%".).

[0034] Furthermore, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, as described above, the crosslinking agent should have two or more functional groups in one molecule. By using such a crosslinking agent having two or more functional groups in one molecule, it becomes possible to efficiently form covalent crosslinking sites through the reaction between the cyclic acid anhydride groups of the elastomeric polymer and the functional groups. There are no particular limitations on the compounds that can be used as such crosslinking agents, and known crosslinking compounds having two or more functional groups in one molecule (for example, compounds described in Japanese Patent Application Publication No. 2017-57322 and Japanese Patent No. 5918878 that have two or more functional groups in one molecule) can be used as appropriate. Examples of such crosslinking agents include polyamine compounds having two or more amino groups and / or imino groups in one molecule (or a total of two or more if both amino and imino groups are present); polyol compounds having two or more hydroxyl groups in one molecule; polyisocyanate compounds having two or more isocyanate (NCO) groups in one molecule; polythiol compounds having two or more thiol groups (mercapto groups) in one molecule; and so on.

[0035] Such crosslinking agents are more preferably compounds that, through reaction with cyclic acid anhydride groups, can introduce at least one bond selected from the group consisting of amides, esters, urethanes, ureas, thiourethanes, thioesters, biuret, allophanates, and imides (hereinafter, such bond may be simply referred to as "bond (A)"). From the viewpoint of being easily decrosslinked by hydrolysis by reacting the bond (A) with water (B), amides, esters, urethanes, ureas, thiourethanes, thioesters, and imides are more preferred, amides, esters, thioesters, and imides are particularly preferred, and amides, esters, and thioesters are most preferred.

[0036] Furthermore, from the viewpoint of efficiently forming covalent crosslinking sites, such crosslinking agents are preferably compounds having two or more functional groups (hereinafter, such functional groups may be simply referred to as "functional group (A)") in one molecule, and among these, those having a nitrogen-containing heterocycle (at least one selected from a triazole ring, isocyanurate ring, thiadiazole ring, pyridine ring, imidazole ring, triazine ring, hydantoin ring, and oxopyrimidine ring are more preferably the nitrogen-containing heterocycle) are preferred. As such compounds, for example, those compounds having two or more functional groups in one molecule that are described in paragraph

[0049] of International Publication No. 2020 / 027109 can be appropriately used. Such compounds may be used individually or as a mixture of two or more.

[0037] Furthermore, from the viewpoint of high reactivity and ease of industrial availability, such crosslinking agents are preferably at least one compound selected from the group consisting of nitrogen-containing compounds having two or more of the functional group (A) in one molecule, oxygen-containing compounds having two or more of the functional group (A) in one molecule (e.g., diethylene glycol, neopentyl glycol, pentaerythritol), sulfur-containing compounds having two or more of the functional group (A) in one molecule, aliphatic compounds having two or more of the functional group (A) in one molecule (e.g., glycerin), and aromatic compounds having two or more of the substituent (A) in one molecule (compounds having an aromatic ring, e.g., benzenedimethanol, benzenetrimethanol). Note that these compounds may also have substituents other than the functional group (A).

[0038] Furthermore, such crosslinking agents include triazoles having two or more of the functional group (A) in one molecule; pyridines having two or more of the functional group (A) in one molecule; thiadiazoles having two or more of the functional group (A) in one molecule; imidazoles having two or more of the functional group (A) in one molecule; isocyanurates having two or more of the functional group (A) in one molecule; triazines having two or more of the functional group (A) in one molecule; hydantoins having two or more of the functional group (A) in one molecule; and a crosslinking agent having one or more of the functional group (A). It is preferable that the functional group (A) is at least one selected from the group consisting of: an oxopyrimidine having at least two of the functional group (A) in one molecule (more preferably a barbituric acid); a compound having two or more of the functional group (A) in one molecule and having an aromatic ring (such aromatic rings are more preferably benzene rings, naphthalene rings, indene rings, and anthracene rings); pentaerythritol; sulfamide; neopentyl glycol; glycerin; diethylene glycol; trimethylolpropane; and polyether polyols. It is more preferable that such a functional group (A) is at least one of a hydroxyl group, an amino group, and an imino group. Furthermore, triazoles, pyridines, thiadiazoles, imidazoles, isocyanurates, triazines, hydantoins, oxopyrimidines, and compounds having an aromatic ring that have the functional group (A) may also have other substituents other than the functional group (A).

[0039] From the viewpoint of having high industrial availability (easy to obtain) and allowing the elastomer to exhibit good rubber properties even after crosslinking, the following are preferred as crosslinking agents: tris(2-hydroxyethyl) isocyanurate (abbreviated as THI), 2,4-diamino-6-phenyl-1,3,5-triazine (benzoguanamine), 2,4-diamino-6-methyl-1,3,5-triazine (acetogyanamine), pentaerythritol, sulfamide, polyether polyol, benzenedimethanol, benzenetrimethanol, and diethylene glycol, with tris(2-hydroxyethyl) isocyanurate, benzenedimethanol, and benzenetrimethanol being more preferred.

[0040] Furthermore, the crosslinked elastomer (A) is not particularly limited, but it is preferable that it has a glass transition temperature of 25°C or lower, and more preferably that it is an elastomeric polymer (A1) that contains hydrogen bonding crosslinking sites and covalent bonding crosslinking sites in its side chains and has a glass transition temperature of 25°C or lower.

[0041] In this context, "side chain" refers to the side chains and terminals of an elastomeric polymer. Furthermore, with respect to the elastomeric polymer (A1), "the side chain contains hydrogen-bonding crosslinking sites and covalent crosslinking sites" is a concept that includes not only the case where the polymer's side chains contain both hydrogen-bonding crosslinking sites and covalent crosslinking sites by including both a side chain having a hydrogen-bonding crosslinking site (hereinafter, for convenience, sometimes referred to as "side chain (a')") and a side chain having a covalent crosslinking site (hereinafter, for convenience, sometimes referred to as "side chain (b)"), but also the case where the polymer's side chains contain both hydrogen-bonding crosslinking sites and covalent crosslinking sites by including a side chain having both hydrogen-bonding crosslinking sites and covalent crosslinking sites (a side chain containing both hydrogen-bonding crosslinking sites and covalent crosslinking sites in a single side chain: hereinafter, for convenience, sometimes referred to as "side chain (c)"). Furthermore, such elastomeric polymers may be appropriately selected and used from those described in Japanese Patent Publication No. 5918878 (for example, those described in paragraphs

[0032] to

[0145] of the said publication), which contain hydrogen-bonding crosslinking sites and covalent crosslinking sites in their side chains and have a glass transition temperature of 25°C or lower.

[0042] Thus, the elastomeric polymer (A1) has at least one of the following side chains: "a side chain containing a hydrogen-bonding crosslinking site (a') and a side chain containing a covalent crosslinking site (b)", and "a side chain containing a hydrogen-bonding crosslinking site and a covalent crosslinking site (c)". In this invention, it can also be said that side chain (c) functions as both side chain (a') and side chain (b). Each side chain will be briefly described below.

[0043] <Side chain (a'): Side chain containing hydrogen bonding crosslinking site> The side chain (a') containing hydrogen bonding crosslinking site has a group capable of forming crosslinks by hydrogen bonding (for example, a hydroxyl group, the hydrogen bonding crosslinking site included in side chain (a) described below, etc.), and any side chain that forms hydrogen bonds based on that group is acceptable, and its structure is not particularly limited. Here, the hydrogen bonding crosslinking site is a site that crosslinks polymers (elastomers) together by hydrogen bonding. Note that crosslinking by hydrogen bonding is only formed when there is a hydrogen acceptor (a group containing an atom with a lone pair of electrons, etc.) and a hydrogen donor (a group having a hydrogen atom covalently bonded to an atom with high electronegativity, etc.). Therefore, if neither a hydrogen acceptor nor a hydrogen donor is present between the side chains of elastomers, crosslinking by hydrogen bonding will not be formed. For this reason, a hydrogen bonding crosslinking site exists in the system only when both a hydrogen acceptor and a hydrogen donor are present between the side chains of elastomers. In this invention, the presence of both a portion that can function as a hydrogen acceptor (e.g., a carbonyl group) and a portion that can function as a hydrogen donor (e.g., a hydroxyl group) between the side chains of elastomers allows us to determine that the portion of the side chain that can function as a hydrogen acceptor and the portion that can function as a hydrogen donor are hydrogen bonding crosslinking sites.

[0044] From the viewpoint of forming stronger hydrogen bonds, the hydrogen-bonding crosslinking site in such a side chain (a') is more preferably the "side chain (a) containing a hydrogen-bonding crosslinking site having a carbonyl-containing group and / or a nitrogen-containing heterocycle" described later. Similarly, from the same viewpoint, the hydrogen-bonding crosslinking site in the side chain (a') is more preferably a hydrogen-bonding crosslinking site having a carbonyl-containing group and a nitrogen-containing heterocycle.

[0045] <Side chain (a): Side chain containing a hydrogen-bonding crosslinking site having a carbonyl-containing group and / or a nitrogen-containing heterocycle> The side chain (a) containing a hydrogen-bonding crosslinking site having a carbonyl-containing group and / or a nitrogen-containing heterocycle may have any other configurations, and is not particularly limited. A hydrogen-bonding crosslinking site having a carbonyl-containing group and / or a nitrogen-containing heterocycle is more preferable.

[0046] Such carbonyl-containing groups can be any group containing a carbonyl group and are not particularly limited. Specific examples include amides, esters, imides, carboxyl groups, carbonyl groups, and acid anhydride groups. Such carbonyl-containing groups may also originate from cyclic acid anhydride groups of elastomerous polymers having cyclic acid anhydride groups.

[0047] Furthermore, if the side chain (a) has a nitrogen-containing heterocycle, the nitrogen-containing heterocycle only needs to be introduced into the main chain directly or via an organic group, and its composition is not particularly limited. Such a nitrogen-containing heterocycle can be any heterocycle that contains a nitrogen atom, even if it contains heteroatoms other than a nitrogen atom, such as a sulfur atom, oxygen atom, phosphorus atom, etc. Known nitrogen-containing heterocycles (for example, those described in paragraphs

[0054] to

[0067] of Japanese Patent No. 5918878) can be used as appropriate. Such a nitrogen-containing heterocycle may also have substituents. Furthermore, a nitrogen-containing heterocycle similar to that described in the section on crosslinking agents is preferred. Such a nitrogen-containing heterocycle can be easily introduced into the side chain, for example, by using a compound having the functional group (A) and a nitrogen-containing heterocycle as a crosslinking agent.

[0048] Furthermore, if the side chain (a) contains both the carbonyl-containing group and the nitrogen-containing heterocycle, the carbonyl-containing group and the nitrogen-containing heterocycle may be introduced into the main chain as independent side chains, but it is preferable that the carbonyl-containing group and the nitrogen-containing heterocycle are introduced into the main chain as a single side chain linked to each other via different groups. Such a side chain (a) may be, for example, the structure described in paragraphs

[0068] to

[0081] of Japanese Patent No. 5918878.

[0049] Furthermore, as the side chain (a), it is preferable to react an elastomer polymer having a cyclic acid anhydride group as a side chain with a crosslinking agent of a type that reacts with the cyclic acid anhydride group to form hydrogen bonding crosslinking sites along with covalent crosslinking sites (a compound that forms both hydrogen bonding crosslinking sites and covalent crosslinking sites) to form hydrogen bonding crosslinking sites, thereby forming the side chain (a) of the polymer.

[0050] <Side chain (b): Side chain containing a covalent crosslinking site> "Side chain (b) containing a covalent crosslinking site" means a side chain that contains a site that crosslinks the polymer molecules constituting the main chain by covalent bonds (covalent crosslinking site: for example, a site that crosslinks polymers by a chemically stable bond (covalent bond), such as at least one bond selected from the group consisting of amides, esters, and thioesters, which can be formed by reacting an elastomer polymer having a cyclic acid anhydride group in its side chain with a crosslinking agent) (in this case, such a side chain becomes the crosslinking chain). Note that side chain (b) is a side chain containing a covalent crosslinking site, but if it has a covalent site and also a group capable of hydrogen bonding, and if it forms a crosslink by hydrogen bonding between side chains, it will be used as side chain (c) as described later. (Note that if neither a hydrogen donor nor a hydrogen acceptor capable of forming hydrogen bonds between the side chains of elastomers is present, for example, if only side chains containing ester groups (-COO-) exist in the system, hydrogen bonds will not be formed between the ester groups (-COO-), and therefore such groups will not function as hydrogen-bonding crosslinking sites. On the other hand, for example, carboxy When elastomers contain structures in their side chains that have both hydrogen donor sites and hydrogen acceptor sites, such as triazole rings or other hydrogen groups, hydrogen bonds are formed between the elastomer side chains, thus containing hydrogen-bonding crosslinking sites. Furthermore, for example, when ester groups and hydroxyl groups coexist between the side chains of elastomers, and hydrogen bonds are formed between the side chains by these groups, the sites that form these hydrogen bonds become hydrogen-bonding crosslinking sites. Therefore, depending on the structure of side chain (b) itself, and the types of substituents present in side chain (b) and other side chains, it may be used as side chain (c).

[0051] The side chain (b) containing such covalent crosslinking sites is not particularly limited, but it is preferable that it is a side chain formed by reacting an elastomeric polymer having cyclic acid anhydride groups in its side chains with a crosslinking agent, for example, using a compound that reacts with cyclic acid anhydride groups to form covalent crosslinking sites (a compound that generates covalent bonds). It is preferable that the crosslinking at the covalent crosslinking site of such a side chain (b) crosslinks polymer molecules with each other via the bond (A).

[0052] Compounds that generate such covalent bonds can be appropriately selected from the crosslinking agents and are not particularly limited, but examples include the polyamine compound; the polyol compound; the polyisocyanate compound; the polythiol compound; and so on. In this context, a compound that generates covalent bonds may be a compound that can introduce both hydrogen bonding crosslinking sites and covalent crosslinking sites, depending on the type of functional group the compound has and the degree to which the reaction proceeds when the compound is used in the reaction (for example, when a compound having three or more hydroxyl groups is used to form a covalent crosslinking site, depending on the degree to which the reaction proceeds, two hydroxyl groups may react with the functional group of an elastomer polymer having a functional group in its side chain, leaving the remaining hydroxyl group as a hydroxyl group, in which case a site that forms a hydrogen bonding crosslink can also be introduced). Therefore, the "compounds that generate covalent bonds" exemplified here may also include "compounds that form both hydrogen bonding crosslinking sites and covalent crosslinking sites." From this perspective, when forming side chain (b), a compound can be appropriately selected from among the "compounds that generate covalent bonds" according to the desired design, or the degree of reaction progress can be appropriately controlled to form side chain (b). If the compound that generates covalent bonds has a heterocycle, it becomes possible to produce hydrogen bonding crosslinking sites more efficiently at the same time, and it becomes possible to efficiently form a side chain having the covalent crosslinking site as side chain (c) described later. It should be noted that, due to its structure, side chain (c) can be said to be a preferred form of side chain such as side chain (a) and side chain (b). As for the polyamine compound, polyol compound, polyisocyanate compound, and polythiol compound that can be used as such "compounds that generate covalent bonds", known ones (for example, those described in paragraphs

[0094] to

[0106] of Japanese Patent No. 5918878) can be appropriately used.

[0053] <Side chain (c): Side chain containing both hydrogen-bonding and covalent-bonding sites> Such a side chain (c) is a side chain that contains both hydrogen-bonding and covalent-bonding sites within a single side chain. The hydrogen-bonding sites contained in such a side chain (c) are the same as the hydrogen-bonding sites described in side chain (a'), and are preferably the same as the hydrogen-bonding sites in side chain (a). Furthermore, the covalent-bonding sites contained in side chain (c) can be the same as the covalent-bonding sites in side chain (b) (and the preferred crosslinks can also be the same).

[0054] Such side chains (c) are preferably formed by reacting an elastomeric polymer having a cyclic acid anhydride group as a side chain with a compound that reacts with the cyclic acid anhydride group as a crosslinking agent to form both hydrogen-bonding and covalent crosslinking sites (compounds that introduce both hydrogen-bonding and covalent crosslinking sites). More preferably, such compounds that form both hydrogen-bonding and covalent crosslinking sites are heterocyclic polyols, heterocyclic polyamines, heterocyclic polythiols, etc. The same heterocyclic polyols, polyamines, and polythiols described above in "Compounds that generate covalent bonds" can be used as appropriate, except that they have heterocyclic rings (particularly preferably nitrogen-containing heterocyclic rings). In addition, known heterocyclic polyols, polyamines, and polythiols (for example, those described in paragraph

[0113] of Japanese Patent No. 5918878) can be used as appropriate.

[0055] (Regarding suitable structures for covalent crosslinking sites in side chains (b) to (c)) With respect to side chains (b) and / or (c), it is preferable that the crosslinking at the covalent crosslinking site contains a tertiary amino bond (-N<) and / or an ester bond (-COO-), and that these bonding sites also function as hydrogen bonding crosslinking sites. In this way, when the tertiary amino bond (-N<) and ester bond (-COO-) in a side chain having a covalent crosslinking site form hydrogen bonds with other side chains, the covalent crosslinking site containing such tertiary amino bond (-N<) and ester bond (-COO-) also has hydrogen bonding crosslinking sites and can function as side chain (c).

[0056] Furthermore, in the side chains (b) and (c), it is preferable that the crosslinking at the covalent crosslinking site is formed by the reaction of a cyclic acid anhydride group with at least one functional group selected from a hydroxyl group, an amino group, and an imino group.

[0057] Furthermore, in such side chains (b) and (c), it is more preferable that the crosslinks at the covalent crosslinking sites have the bond (A). Moreover, the crosslinks at the covalent crosslinking sites of side chain (b) and / or side chain (c) may be, for example, the same as the structure described in paragraphs

[0100] to

[0109] of Japanese Patent Application Publication No. 2017-206604 or the structure described in paragraphs

[0055] to

[0061] of International Publication No. 2019 / 027022.

[0058] As explained above, side chains (a'), (a), (b), and (c) were used as examples. However, the individual groups (structures) of such side chains in polymers can be confirmed using commonly used analytical methods such as NMR and IR spectroscopy.

[0059] The crosslinked elastomer (A) used in the present invention has covalent crosslinking sites (sites that crosslink the polymer molecules constituting the main chain through covalent bonds). Elastomers having such covalent crosslinking sites are generally difficult to plasticize, and by making them easier to plasticize through decrosslinking, they can be efficiently reused. On the other hand, hydrogen-bonding crosslinking sites are sites formed by crosslinking through hydrogen bonds, so it is possible to easily break those bonds (hydrogen bonds) when heated. Therefore, even if hydrogen-bonding crosslinking sites remain in the decrosslinked product obtained by decrosslinking the covalent crosslinking sites of the crosslinked elastomer (A), or if new hydrogen-bonding crosslinking sites are formed, it is considered that the hydrogen-bonding crosslinking sites do not have a significant effect on the fluidity (thermoplasticity) of the decrosslinked product when heated (it can be said that the effect is not so significant as to hinder processability). Therefore, the crosslinked elastomer (A) and its decrosslinked product may be in a form that has hydrogen-bonding crosslinking sites.

[0060] Furthermore, the method for obtaining the crosslinked elastomer (A) is not particularly limited. For example, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, a method is preferably employed in which the elastomeric polymer having the cyclic acid anhydride group in its side chain reacts with the crosslinking agent to obtain the reaction product. In this case, the conditions can be appropriately selected according to the type of crosslinking agent, etc., and the reaction can be carried out accordingly. Furthermore, when producing a crosslinked elastomer (A) consisting of the reactants suitable for use in the present invention, for example, a method may be employed in which the crosslinking agent is added while kneading the elastomer having cyclic acid anhydride groups in its side chains (occasionally mixed with other additives, etc.) at a temperature (for example, about 100 to 250°C) that allows the plasticization of the elastomeric polymer having cyclic acid anhydride groups in its side chains using a kneader, and the crosslinking agent is added while kneading the elastomeric polymer having cyclic acid anhydride groups in its side chains (occasionally mixed with other additives, etc.), and the reaction is carried out by kneading. Furthermore, there are no particular limitations on the method for producing such a crosslinked elastomer (A), and a method may be employed in which components to be used are appropriately selected to obtain a desired structure, and a method similar to known methods (for example, the method described in paragraphs

[0139] to

[0140] of Japanese Patent No. 5918878, etc.) is used.

[0061] <Water (B)> The water (B) used in the present invention is not particularly limited, but from the viewpoint of eliminating the influence of inorganic ions, it is preferable to use deionized water, ion-exchanged water, distilled water, pure water, supercritical water (water exceeding the critical temperature (374°C) and critical pressure (22.1 MPa)), or subcritical pressurized water (water at a temperature of approximately 100 to 374°C and a pressure of approximately 5 to 22 MPa).

[0062] Furthermore, taking as an example the case in which the covalent crosslinking site of the crosslinked elastomer is a bonding site formed by the reaction of a functional group of the crosslinking agent with a cyclic acid anhydride group, in the present invention, the water (B) reacts with the bonding site to cause a hydrolysis reaction of the bonding site (for example, if an ester bond is formed by the reaction of a functional group of the crosslinking agent with a cyclic acid anhydride group, a hydrolysis reaction of the ester bond is caused), thereby enabling the crosslinking to be decrosslinked. In this way, in order to cause a hydrolysis reaction, the present invention utilizes the water (B) as an essential component.

[0063] The crosslinked elastomer (A) and the water (B) contained in the elastomer composition according to the present invention have been described separately above. Next, the organic solvent (C) and the catalyst (D), which are components that can be suitably used in the elastomer composition, will be described.

[0064] <Organic solvent (C)> The elastomer composition according to the present invention may further contain an organic solvent (C) together with the crosslinked elastomer (A) and the water (B).

[0065] Examples of such organic solvents (C) include sulfolane, N-methyl-2-pyrrolidone (NMP), N,N-dimethylimidazolidone (DMI), dimethyl sulfoxide (DMSO), diglyme, monoglyme, toluene, chlorobenzene, xylene, mesitylene, tetralin (tetrahydronaphthalene), and naphthalene. Among these, sulfolane, NMP, DMI, DMSO, diglyme, monoglyme, toluene, xylene, mesitylene, tetralin (tetrahydronaphthalene), naphthalene, and chlorobenzene are preferred. Such organic solvents (C) may be used individually or in combination of two or more.

[0066] Furthermore, as such organic solvents (C), for example, when an acid catalyst is used as a catalyst (D), sulfolanes, NMP, DMI, and DMSO can be suitably used because they have properties such as readily dissolving water necessary for hydrolysis, being highly polar, and having high acid resistance.

[0067] Furthermore, when the elastomer composition is heated at a relatively high temperature, toluene, xylene, mesitylene, tetralin (tetrahydronaphthalene), naphthalene, and chlorobenzene (non-polar) are suitably used as the organic solvent (C) because they are non-reactive and have excellent heat resistance and acid resistance. However, when using these organic solvents (C), it is desirable to use a phase transfer catalyst (a suitable form of catalyst (D)) in combination, since water is hardly soluble in the organic solvent (C).

[0068] Furthermore, since the organic solvent (C) has high basic resistance, higher stability can be obtained when a basic catalyst is used, and therefore monoglyme and diglyme can be suitably used.

[0069] <Catalyst (D)> The elastomer composition according to the present invention may further contain catalyst (D) together with the crosslinked elastomer (A) and water (B).

[0070] The catalyst (D) can be any catalyst that can be used in a de-crosslinking reaction (hydrolysis reaction), and is not particularly limited. Known catalysts can be used as appropriate depending on the components in the elastomer component. Examples include acid catalysts, base catalysts, enzyme catalysts, metal catalysts, complex catalysts, organic catalysts, and phase transfer catalysts.

[0071] Examples of such acid catalysts include p-toluenesulfonic acid (TsOH), methanesulfonic acid (MsOH), trifluoroacetic acid, trifluoromethanesulfonic acid (TfOH), sulfuric acid, hydrochloric acid, phosphoric acid, Amberlyst (e.g., Amberlyst-15), zeolite (e.g., H-ZSM-5), silica-sulfonic acid carrier, and BF ３ ・Et ２ O, AlCl ３ FeCl ３ , Sc(OTf) ３ , Yb(OTf) ３ These are some examples.

[0072] The aforementioned base catalysts include NaOH, KOH, NaOH, LiOH, and Ba(OH) ２ Ca(OH)２ Triethylamine (TEA), pyridine, 4-dimethylaminopyridine (DMAP), diazabicycloundecene (DBU), diazabicyclononene (DBN), imidazole, MgO, CaO, Al ２ O ３ Examples include hydrotalcite.

[0073] Examples of the enzyme catalyst include lipase, protease, cellulase, amylase, and nuclease.

[0074] The metal catalyst and the complex catalyst are Zn ２＋ ,Cd ２＋ Fe ３＋ Examples include Zr(IV), Hf(IV) complexes, and metal-organic complexes (MOFs).

[0075] Examples of the aforementioned organic catalysts include DMAPs, N-heterocyclic carbenes (NHCs), and imidazoles.

[0076] Furthermore, examples of the phase transfer catalyst include tetrabutylammonium bromide (TBAB), tetrabutylammonium bisulfate (TBAHS), tetramethylammonium chloride, long-chain alkyltriphenylphosphonium bromide, and 18-crown-6. Such phase transfer catalysts are particularly suitable for use when an organic solvent (C) is utilized and the elastomer composition is a two-phase system of water and an organic solvent, as they enable efficient de-crosslinking reactions.

[0077] Furthermore, the catalyst (D) is not limited to the various catalysts described above, and other usable catalysts include, for example, photoacid and TiO2. ２ Examples include ZnO (photocatalyst).

[0078] Furthermore, from the viewpoint of efficient hydrolysis, such catalyst (D) is preferably at least one selected from the group consisting of acid catalysts, base catalysts, and phase transfer catalysts, and more preferably at least one selected from the group consisting of acid catalysts and phase transfer catalysts. It is preferable to appropriately select and use such catalyst (D) depending on the type of organic solvent used, etc., so that the reaction (hydrolysis) can proceed efficiently. Among such catalysts (D), when hydrolyzing a crosslinked site, for example, when the structure of the crosslinked site is bonded by a carboxylic acid ester (ester bond), it is preferable to use an acid catalyst from the viewpoint that the reaction of hydrolyzing the ester to a carboxylic acid can proceed more efficiently (considering that when a basic catalyst containing an alkali metal is used, it becomes a carboxylate salt first, and then needs to be treated with acid to become a carboxylic acid, it can be said that the crosslinking to the carboxylic acid form can be performed more efficiently in a single reaction). Among such acid catalysts, TsOH, MsOH, trifluoroacetic acid, TfOH, sulfuric acid, hydrochloric acid, and phosphoric acid are more preferred, and TsOH, MsOH, trifluoroacetic acid, and TfOH are even more preferred. Such catalysts (D) may be used individually or in combination of two or more. Furthermore, when the organic solvent (C) is one that hardly dissolves water (for example, solvents such as toluene, xylene, mesitylene, tetralin (tetrahydronaphthalene), naphthalene, and chlorobenzene), it is preferable to use the acid catalyst (for example, TsOH) and a phase transfer catalyst in combination as catalyst (D) from the viewpoint of more efficiently promoting the hydrolysis reaction.

[0079] The above describes components that can be suitably used in the composition together with the crosslinked elastomer (A) and water (B). Below, we will further describe the composition of the elastomer composition and other components that can be included in the composition.

[0080] <Elastomer Composition> In the method for decrosslinking a crosslinked elastomer of the present invention, the elastomer composition comprises the crosslinked elastomer (A) and the water (B).

[0081] In such an elastomer composition, the water (B) content is preferably 0.01 to 500 parts by mass (more preferably 0.1 to 400 parts by mass, even more preferably 0.2 to 300 parts by mass, particularly preferably 1 to 200 parts by mass, and most preferably 10 to 150 parts by mass) per 100 parts by mass of the crosslinked elastomer (A). Setting the water (B) content above the lower limit tends to allow for more efficient decomposition of the crosslinks by hydrolysis (de-crosslinking), while setting it below the upper limit tends to allow for minimization of the reaction vessel (space).

[0082] Furthermore, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and the crosslinking agent, the ratio of water (B) to the crosslinked elastomer (A) in the elastomer composition is preferably such that the amount of water (B) is 0.1 to 1000 moles (more preferably 0.2 to 800 moles, even more preferably 0.3 to 700 moles, and particularly preferably 0.5 to 600 parts by mass) per mole of functional groups of the crosslinking agent used in the production of the crosslinked elastomer (A). Setting the water (B) content ratio to above the lower limit tends to allow the reaction (hydrolysis reaction) that decrosslinks the covalently bonded crosslinked sites to proceed more efficiently, while setting it to below the upper limit tends to allow the reaction vessel (space) to be minimized.

[0083] Furthermore, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, it is preferable to include water (B) in a ratio of 0.1 to 1000 moles (more preferably 0.2 to 800 moles, and even more preferably 0.3 to 500 moles) per mole of cyclic acid anhydride groups contained in the elastomeric polymer having cyclic acid anhydride groups used in the production of the crosslinked elastomer (A). Setting the water (B) content ratio to above the lower limit tends to allow the reaction that decrosslinks the covalently bonded crosslinked sites (hydrolysis reaction) to proceed more efficiently, while setting it to below the upper limit tends to allow the reaction vessel (space) to be minimized.

[0084] In cases where the crosslinked elastomer (A) is a reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, the water content ratio (B) to the crosslinked elastomer (A) can be appropriately selected depending on the degree of reaction between the functional groups of the crosslinking agent used during production and the cyclic acid anhydride groups. This is because, in the reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, the crosslinked portion that is decrosslinked is the portion of the bond formed by the reaction between the functional groups of the crosslinking agent and the cyclic acid anhydride groups. For example, if, during the production of the reaction product, not all of the functional groups react but only some of them react to form crosslinks (bonds), and the remaining functional groups remain as functional groups in the reaction product, then water should be used in proportion to the molar amount of that bonded portion. On the other hand, from the viewpoint of making the reaction proceed more efficiently, it is preferable to use water in a proportion equivalent to or greater than (more preferably in excess of) the bonded portion of the crosslink in the portion that is decrosslinked. Considering these points, if the crosslinked elastomer (A) is a reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, the ratio of water (B) to the crosslinked elastomer (A) in the elastomer composition is preferably 1 mole or more (more preferably 10 moles or more, even more preferably 50 moles or more) per mole of functional groups of the crosslinking agent used in the production of the crosslinked elastomer (A), from the viewpoint of more efficiently promoting the decrosslinking reaction. Also, from a similar viewpoint, if the crosslinked elastomer (A) is a reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent, it is preferable to use water (B) in a ratio of 1 mole (equivalent) or more (more preferably 10 moles or more, even more preferably 50 moles or more) per mole of cyclic acid anhydride groups contained in the elastomeric polymer having cyclic acid anhydride groups.

[0085] Furthermore, in the method for decrosslinking a crosslinked elastomer of the present invention, from the viewpoint of enabling the reaction to decrosslink during heating to proceed more efficiently and reliably, it is preferable that the elastomer composition contains the organic solvent (C) and / or the catalyst (D) together with the crosslinked elastomer (A) and the water (B), and it is more preferable that it contains the organic solvent (C) and the catalyst (D) together with the crosslinked elastomer (A) and the water (B). Thus, it is even more preferable that the elastomer composition further contains the organic solvent (C) and the catalyst (D). In this way, when the elastomer composition contains the organic solvent (C) and the catalyst (D) together with the crosslinked elastomer (A) and the water (B), it is possible to proceed more efficiently with the decomposition of the crosslinks by hydrolysis (decrosslinking).

[0086] When the elastomer composition contains the organic solvent (C), the content of the organic solvent (C) is preferably 0.1 to 3000 parts by mass (more preferably 1 to 2000 parts by mass, even more preferably 3 to 1000 parts by mass, particularly preferably 5 to 800 parts by mass, and most preferably 10 to 500 parts by mass) per 100 parts by mass of the crosslinked elastomer (A). Setting the content of such organic solvent (C) above the lower limit makes it possible to swell or dissolve the crosslinked elastomer, and tends to allow the decomposition of the crosslinks by hydrolysis (de-crosslinking) to proceed more efficiently. On the other hand, setting it below the upper limit tends to minimize the complexity of the reaction vessel (space) and post-treatment.

[0087] When the elastomer composition contains the catalyst (D), the content of the catalyst (D) is preferably 0.01 to 300 parts by mass (more preferably 0.05 to 200 parts by mass, even more preferably 0.1 to 100 parts by mass, particularly preferably 0.5 to 80 parts by mass, and most preferably 1 to 50 parts by mass) per 100 parts by mass of the crosslinked elastomer (A). Setting the content of such catalyst (D) above the lower limit tends to allow for more efficient decomposition (de-crosslinking) of the crosslinked elastomer by hydrolysis, while setting it below the upper limit tends to allow for easier post-processing.

[0088] The elastomer composition according to the present invention may contain the crosslinked elastomer (A) and the water (B) (and may further contain the organic solvent (C) and / or the catalyst (D) as it is used), and its form is not particularly limited. For example, it may be obtained by adding the water (B) to a composition containing the crosslinked elastomer (A) to be decrosslinked (for example, a thermoplastic elastomer composition) (and may be obtained by adding the organic solvent (C) and / or the catalyst (D) together with the water (B) to a composition containing the crosslinked elastomer (A) (for example, a thermoplastic elastomer composition)). If such a composition containing the crosslinked elastomer (A) (the composition before adding the water (B)) is a thermoplastic elastomer composition, it may contain additives depending on the intended use of the composition, and may also contain components used in the production of the composition itself (for example, a thiram-based crosslinking accelerator). The components that such thermoplastic elastomer compositions may contain are not particularly limited, and components known in the field of thermoplastic elastomer compositions can be used as appropriate. Examples include reinforcing agents (fillers) such as carbon black and silica, hydrogen bonding reinforcing agents (fillers), fillers with introduced amino groups (hereinafter simply referred to as "amino group-introduced fillers"), amino group-containing compounds other than said amino group-introduced fillers, compounds containing metal elements (hereinafter simply referred to as "metal salts"), anti-aging agents, antioxidants, pigments (dyes), plasticizers (oils such as paraffin oil and phosphate esters), thixotropy-inducing agents, ultraviolet absorbers, flame retardants, solvents, surfactants (including leveling agents), fillers, dispersants, dehydrating agents, rust inhibitors, adhesion promoters, antistatic agents, and the like.

[0089] Furthermore, the thermoplastic elastomer composition containing the crosslinked elastomer (A) that is subject to such decrosslinking is not particularly limited, but may be in a similar form to known thermoplastic elastomer compositions containing an elastomeric polymer containing covalently crosslinked sites, such as the thermoplastic elastomer composition described in Japanese Patent No. 5918878, the thermoplastic elastomer composition described in International Publication No. 2017 / 047274, the thermoplastic elastomer composition described in International Publication No. 2017 / 188270, the conductive thermoplastic elastomer composition described in Japanese Patent Application Publication No. 2018-083894, and the thermoplastic elastomer composition described in Japanese Patent Application Publication No. 2021-134333. In addition, one embodiment of the thermoplastic elastomer composition containing such crosslinked elastomer (A) is, for example, a form containing the crosslinked elastomer (A), carbon black, a phosphorus-based plasticizer, and a thiram-based vulcanization accelerator.

[0090] Furthermore, the elastomer composition according to the present invention may be manufactured by employing a method that allows for obtaining a composition containing the crosslinked elastomer (A) and the water (B). For example, it may be manufactured by adding the crosslinked elastomer (A), the water (B), and (if necessary, further the organic solvent (C) and / or the catalyst (D)) to a container and mixing them. (In this case, the composition may be prepared separately and then introduced into a high-pressure reaction vessel to allow the reaction to proceed, or the production of the composition and the decrosslinking reaction may be carried out simultaneously in the high-pressure reaction vessel.) Moreover, in order to efficiently carry out the decrosslinking step described later, the elastomer composition according to the present invention may be prepared by, for example, introducing a component containing the crosslinked elastomer (A) to be decrosslinked (for example, the thermoplastic elastomer composition) into a kneader (adding other additives if necessary) to powderize it, and then putting the powder, water (B), and (if necessary, further the organic solvent (C) and / or the catalyst (D)) into a reaction vessel (for example, a high-pressure reaction vessel) and stirring (mixing) while heating.

[0091] When other additives are added, such other additives can be known additives used in the field of elastomer compositions, depending on the intended use of the composition containing the de-crosslinked product of the crosslinked elastomer (A) obtained after de-crosslinking. These additives can be similar to those described in the "Components that may be contained in the thermoplastic elastomer composition" section above (for example, antioxidants). In this way, by obtaining the elastomer composition according to the present invention, for example, by adding water (B) (and optionally the organic solvent (C) and / or the catalyst (D)) to the thermoplastic elastomer composition, the thermoplastic elastomer composition that has been used once can be easily plasticized by de-crosslinking the crosslinked elastomer in the composition, thereby enabling efficient reuse of the elastomer polymer.

[0092] <Regarding the decrosslinking process> In the present invention, the elastomer composition is heated to decrosslink the covalent crosslinked portions in the crosslinked elastomer (A) with water (B). In the present invention, if at least a portion of the covalent crosslinked portions in the crosslinked elastomer (A) is decrosslinked with water (B), it may be considered that the elastomer has been decrosslinked with water (B) (this is because, depending on the type of crosslinked elastomer, it may be possible to sufficiently plasticize the elastomer by decrosslinking only a portion of the covalent crosslinked portions. In this case, by decrosslinking a portion of the crosslinks, it is possible to improve plasticity and processability, thereby making it possible to reuse the elastomer. Thus, in the present invention, it is not necessarily required that all of the covalent crosslinked portions in the system be decrosslinked).

[0093] As an example of such de-crosslinking reactions, when the crosslink has an ester bond and the polymer has a carboxyl group adjacent to the ester bond (when the ester bond and the carboxyl group originate from a single cyclic anhydride group), a reaction in which water (B) is reacted with the ester bond to remove the crosslinking agent and generate a carboxyl group can be exemplified (a preferred embodiment of such a reaction will be described later using the reaction scheme shown in Figure 1, etc.).

[0094] Furthermore, from the viewpoint of enabling such de-crosslinking reactions to proceed more efficiently, it is preferable that the covalent crosslinking sites in the crosslinked elastomer (A) have at least one bond selected from the group consisting of amides, esters, urethanes, ureas, thiourethanes, thioesters, biuret, allophanates, and imides (the aforementioned bond (A)), and it is particularly preferable that they have at least one bond selected from the group consisting of amides, esters, thioesters, and imides (it is even more preferable that such bonds are formed by the reaction of a cyclic acid anhydride group with the functional group in the crosslinking agent). This is because such bonds can be easily decomposed (decomposed by hydrolysis, etc.) in water (B) due to their type.

[0095] Furthermore, while there are no particular limitations on the method of heating the elastomer composition, it is preferable to use a high-pressure reaction vessel for heating. Examples of such high-pressure reaction vessels include autoclaves, pressure vessels, portable reactors, metal sealed containers, and PTFE inner cylinder sealed containers, but autoclaves are preferred from the viewpoint of pressure resistance and safety. In addition, when the elastomer composition contains the catalyst (D), if an acid or alkali is present in the system due to the use of an acid catalyst or base catalyst, it is preferable to heat the composition using a PTFE inner cylinder sealed container or a PTFE inner cylinder autoclave from the viewpoint of preventing corrosion or dissolution of the container.

[0096] Furthermore, the temperature conditions when heating the elastomer composition are not particularly limited, as long as they are suitable for promoting de-crosslinking (temperature conditions that promote hydrolysis), but are preferably 100 to 300°C (more preferably 120 to 250°C, and even more preferably 150 to 230°C). Setting the heating temperature above the lower limit allows the de-crosslinking reaction to proceed more efficiently, which tends to result in a higher reaction rate. On the other hand, setting the temperature below the upper limit tends to allow the de-crosslinking reaction to proceed efficiently while suppressing thermal degradation of the polymer.

[0097] Furthermore, the pressure conditions when heating the elastomer composition are not particularly limited, as long as temperature conditions that allow decrosslinking to proceed (temperature conditions that allow hydrolysis to proceed) are adopted. However, it is preferable to set the gauge pressure to 0.05 MPa or higher (more preferably 0.1 to 10 MPa, and even more preferably 0.2 to 5 MPa). Setting such a gauge pressure above the lower limit allows the reaction to proceed rapidly. Also, setting such a gauge pressure below the upper limit tends to yield better results in terms of safety and degradation resistance.

[0098] Thus, when heating the elastomer composition, it is preferable to heat it under conditions of a heating temperature of 100 to 300°C and a gauge pressure of 0.05 MPa or higher. While other conditions besides the heating temperature and pressure are not particularly limited, it is preferable to thoroughly mix (stir) these components in order to efficiently bring the crosslinked elastomer (A) and the water (B) into contact and react with them.

[0099] Furthermore, the heating time when heating the elastomer composition varies depending on the conditions used during heating (heating temperature and gauge pressure) and the type of crosslinked elastomer, and cannot be uniquely determined, but it is preferable to heat it for 0.1 hours to 1 day (more preferably 0.5 to 15 hours, even more preferably 0.5 to 12 hours, and particularly preferably 1 to 12 hours) (however, such heating time may be 1 to 8 hours depending on the embodiment (for example, depending on the type of components in the composition)). In order to keep the heating time below the lower limit, it tends to be necessary to use higher heating temperatures and gauge pressures, although this varies depending on the type of crosslinked elastomer, crosslink density, etc. On the other hand, if the heating time exceeds the upper limit, depending on the conditions used during heating, it may be necessary to heat it further after the decrosslinking has completely progressed, which tends to reduce economic efficiency. Considering these points, it is desirable to set the heating temperature, pressure, and other conditions appropriately to satisfy the above heating time conditions. Furthermore, if, for example, the main chain structure is sensitive to heat and it is desirable to carry out the de-crosslinking reaction at relatively low temperatures and pressures, such temperature and pressure conditions may be adopted while extending the heating time to carry out the de-crosslinking reaction necessary to obtain the desired de-crosslinked elastomer.

[0100] Furthermore, if the crosslinked elastomer obtained by decrosslinking by heating in this manner is a reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent having two or more functional groups in one molecule, then basically, all or part of the covalent crosslinking sites of the crosslinked elastomer (A) will be converted into an elastomeric polymer in a form where the cyclic acid anhydride groups are converted into a structure (carboxyl group) obtained by the reaction of the cyclic acid anhydride groups with water (B). In addition, if the crosslinked elastomer (A) obtained by the present invention is a reaction product of the elastomeric polymer having cyclic acid anhydride groups and the crosslinking agent having two or more functional groups in one molecule, and all covalent crosslinking sites react with water (B), then it is possible to obtain a decrosslinked product of the crosslinked elastomer (A) obtained by the present invention that has a structure similar to that of the reaction product of the elastomeric polymer having cyclic acid anhydride groups and water (B). Thus, by performing a de-crosslinking process, it is also possible to form a de-crosslinked product (de-crosslinked elastomer) in which the bonding sites of the crosslinking agent in the covalent crosslinking sites of the crosslinked elastomer (A) are replaced with water (hydroxyl groups).

[0101] This reaction will be briefly explained with reference to Figure 1. Note that only the de-crosslinking reaction scheme proceeding as indicated by the arrow in "(1) De-crosslinking process" in Figure 1 will be explained here; all reaction schemes shown in Figure 1 will be described later. The crosslinked elastomer shown in Figure 1 is a reaction product of an elastomeric polymer having maleic anhydride groups and THI, which is suitably usable as a crosslinked elastomer according to the present invention (where the covalent crosslinking site is an ester bond (in the formula -COO-CH ２This schematically shows an elastomeric polymer having a structure with a bond (represented by -). When an elastomer composition containing such a reactant (crosslinked elastomer) and water is formed and heated, the covalent crosslinking sites (ester bond portions) are hydrolyzed, and a decrosslinked elastomer (in Figure 1, an elastomeric polymer having maleic acid groups) is formed. In the embodiment shown in Figure 1, all of the covalent crosslinking sites of the crosslinked elastomer are hydrolyzed by the water (B), and the elastomer after decrosslinking is an elastomeric polymer having maleic acid groups (a decrosslinked product in which the bonding sites of the crosslinking agent are replaced by water (hydroxyl groups)). Thus, when the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, depending on the degree of reaction, all or part of the covalent crosslinking sites may be converted into an elastomeric polymer in a form obtained by the reaction between the cyclic acid anhydride group and the water (B) (carboxyl group). In the embodiment shown in Figure 1, an example is shown in which all three ester bonds of the crosslinked elastomer in the figure have been hydrolyzed. However, depending on the degree of hydrolysis, it is conceivable that two of the ester bonds in the figure may be hydrolyzed, resulting in decomposition into two polymer molecules having maleic acid groups and one polymer molecule with the crosslinking agent still attached, or that only one bond in the figure may be hydrolyzed. The purpose of de-crosslinking is to make crosslinked elastomers having covalently crosslinked sites that are difficult to plasticize plasticizable, so that they can be reused by crosslinking them again while being remolded, etc. Therefore, it is sufficient if at least some of the crosslinked sites are de-crosslinked by hydrolysis and become plasticizable. Thus, in the present invention, de-crosslinking is sufficient if de-crosslinking occurs in all or part of the covalently crosslinked sites.

[0102] Furthermore, whether or not de-crosslinking has occurred in all or part of the covalent crosslinking site can be determined, for example, if the crosslinking has a specific structure (e.g., an ester bond), then by de-crosslinking with water (B), that structural part is converted to a different structure (e.g., a carboxyl group). This can be confirmed by measuring the elastomer before and after de-crosslinking using infrared absorption spectroscopy (IR measurement) to confirm the disappearance of the structure before de-crosslinking and the appearance of a new structure (a structure formed by the reaction of water (B) with a cyclic acid anhydride group). Alternatively, IR measurement can be performed on the elastomer before and after de-crosslinking, and the degree to which the absorption derived from the crosslinking structure decreases (decrease in peak intensity) before and after de-crosslinking can be confirmed to determine the extent of the de-crosslinking process. Furthermore, in some cases, it may be possible to determine whether or not de-crosslinking has occurred in all or part of the covalent crosslinked portion by checking whether or not there is a clear decrease in tensile strength (breaking strength) during heating (depending on the type of crosslinked elastomer, a clear decrease can be used to determine that de-crosslinking has occurred), whether or not plasticization is possible at a specific temperature (for example, a heating temperature of about 120°C) (if a crosslinked material that could not be plasticized becomes plasticizable through the de-crosslinking process, it can be determined that de-crosslinking has occurred), whether or not Mooney viscosity can be measured, and solubility in organic solvents.

[0103] Here, we will explain, for example, the case in which IR measurements are performed on the elastomer before and after decrosslinking, and the degree to which the absorption originating from the crosslinking structure decreases (the intensity of the absorption spectrum decreases) is confirmed to determine whether or not decrosslinking has occurred in all or part of the covalent crosslinking site, using the case where the crosslinked elastomer is a crosslinked elastomer as shown in Figure 1 as an example. The structure of the crosslinking sites in a crosslinked elastomer as shown in Figure 1 can be confirmed by IR measurement based on the presence or absence of absorption originating from the isocyanurate ester. If the decrease in the intensity of the absorption spectrum originating from such isocyanurate ester before and after decrosslinking is, for example, 33% or more (this decrease can be calculated by determining the ratio (%) of the difference to the spectral intensity before the reaction, which is obtained by subtracting the spectral intensity after the reaction from the spectral intensity before the reaction. Note that this decrease can also be considered as the reaction rate of the decrosslinking reaction), then, considering that the crosslinked elastomer shown in Figure 1 can have the structure of up to three crosslinking sites per molecule of crosslinking agent, it can be understood that, on average, at least one ester bond portion in each molecule of the crosslinked elastomer has been decrosslinked with respect to the three isocyanurate ester portions that form covalent crosslinks in each molecule. Similarly, with respect to the crosslinked elastomer shown in Figure 1, if the decrease in the magnitude of the absorption spectrum intensity derived from the isocyanurate ester (reaction rate) before and after the reaction is 67% or more, it can be understood that, on average, two or more isocyanurate ester portions of the crosslinked site have been decrosslinked in each molecule. Furthermore, if the decrease in the magnitude of the spectrum (reaction rate) is 80% or more, it can be understood that most of the crosslinks in the elastomer have been decrosslinked. Therefore, when confirming the degree of decrosslinking based on such a decrease (reaction rate), if the crosslinked elastomer has, for example, the structure shown in Figure 1, it may be confirmed that the reaction rate (decrease in absorption) is 33% or more (more preferably 67% or more, and even more preferably 80% or more) to confirm whether or not decrosslinking has occurred in all or part of the covalent crosslinked sites.Furthermore, based on this verification method, when considering heating conditions in the decrosslinking process, if the crosslinked elastomer has a structure such as that shown in Figure 1, it is preferable to perform the decrosslinking process by appropriately adjusting the heating conditions (heating temperature, gauge pressure, and heating time) during decrosslinking so that the reaction rate is preferably 33% or more (more preferably 67% or more, and even more preferably 80% or more). For example, if the design of the decrosslinked elastomer is such that the reaction rate is approximately 33% (40%, etc.), a relatively low gauge pressure may be used and heating may be performed at a relatively low temperature. Alternatively, if the design of the decrosslinked elastomer is such that the reaction rate is approximately 80% when using the same gauge pressure and heating temperature, a longer heating process (for example, several days) may be performed to allow the reaction to proceed to the desired design. Furthermore, when designing a decrosslinked elastomer with a reaction rate of approximately 80%, it is possible to expedite the reaction by adopting higher heating conditions and higher gauge pressures. In this way, the heating conditions can be appropriately changed according to the desired design, and the preferred heating conditions for the raw materials can be determined in advance using the results of IR measurements, etc., and the decrosslinking process can be carried out based on those conditions.

[0104] The method for decrosslinking the crosslinked elastomer of the present invention has been described above. Next, the decrosslinked elastomer of the present invention will be described.

[0105] <Decrosslinked Elastomer> The decrosslinked elastomer of the present invention is a decrosslinked product of the crosslinked elastomer (A), obtained by heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B), thereby decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B). (Note that the "elastomer composition" used to obtain the decrosslinked elastomer of the present invention is the same as that described in the decrosslinking method of the crosslinked elastomer of the present invention above (the preferred composition and preferred usage conditions are also the same). Therefore, the elastomer composition may further contain the organic solvent (C) and the catalyst (D).)

[0106] Such a de-crosslinked product of the crosslinked elastomer (A) can be prepared by using the de-crosslinking method for crosslinked elastomers of the present invention described above. In this case, the de-crosslinked product of the crosslinked elastomer (A) only needs to be one in which all or part of the covalent crosslinking sites in the crosslinked elastomer (A) have been de-crosslinked. For example, if the crosslinked elastomer (A) is a reaction product of an elastomer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, it is possible to have a structure similar to that of the reaction product of the elastomer having a cyclic acid anhydride group and water (B) (as a preferred form of such a structure, for example, the structure of the de-crosslinked elastomer obtained after the "(1) de-crosslinking step" in Figure 1 can be exemplified). In this case, it is preferable that the crosslinked elastomer (A) is a reaction product of an elastomer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, and has covalent crosslinking sites that crosslink the polymer molecules together by covalent bonds.

[0107] <Rubber Products> The rubber products of the present invention include the de-crosslinked elastomer and / or its crosslinked product described above. Such rubber products are not limited in any particular way, as long as they are based on known rubber products containing an elastomeric component, and the de-crosslinked elastomer and / or its crosslinked product described above are used in place of the elastomeric component.

[0108] Examples of such rubber products include daily necessities, automobile parts (e.g., hoses, belts, bushings, mounts, etc. in engine compartments), rubber parts in electrical appliances and industrial components, rubber for building materials, soundproofing rubber, rubber for automobile interior materials (instrument panels, etc.), and tires. Tires are a particularly suitable example of such rubber products. As for the method of manufacturing such rubber products, a method similar to that for manufacturing known rubber products can be appropriately employed, except that the decrosslinked elastomer of the present invention is used instead of known elastomeric components. For example, rubber products may be manufactured by employing a method to obtain rubber products such as tires containing a crosslinked product of the decrosslinked elastomer of the present invention by recrosslinking and / or sulfur crosslinking or peroxide crosslinking the decrosslinked elastomer of the present invention (by recrosslinking the functional groups in the decrosslinked elastomer, by sulfur crosslinking the elastomer if the main chain of the decrosslinked elastomer contains double bonds, or by crosslinking the decrosslinked elastomer with a peroxide), or by employing a method to obtain rubber products such as tires containing the decrosslinked elastomer of the present invention and / or its crosslinked product by adding the decrosslinked elastomer of the present invention to virgin rubber and then sulfur crosslinking or peroxide crosslinking it. In this way, rubber products in a form containing the decrosslinked elastomer of the present invention and / or its crosslinked product can be formed and used appropriately for various applications.

[0109] <First method for recrosslinking a crosslinked elastomer> The first method for recrosslinking a crosslinked elastomer of the present invention is a method in which an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) is heated to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer composition containing a decrosslinked elastomer, is heated in an open system or under reduced pressure conditions at a temperature of 100 to 280°C to recrosslink the decrosslinked elastomer in the decrosslinked elastomer composition.

[0110] The "crosslinked elastomer (A)", "water (B)", and "elastomer composition" used in this method are the same as those described in the above-mentioned method for decrosslinking the crosslinked elastomer of the present invention (the preferred materials and preferred usage conditions are also the same. For example, the elastomer composition may further contain the organic solvent (C) and the catalyst (D)). Furthermore, the step of "decrosslinking the covalent crosslinked sites in the crosslinked elastomer (A) with the water (B)" is the same as the method described as "Regarding the decrosslinking step" in the above-mentioned method for decrosslinking the crosslinked elastomer of the present invention (the preferred conditions are also the same).

[0111] The present invention relates to a method for re-crosslinking a de-crosslinked product (de-crosslinked elastomer) of a crosslinked elastomer (A) by using a de-crosslinked elastomer composition (a composition containing a de-crosslinked elastomer formed by heating the elastomer) obtained by heating the elastomer composition and de-crosslinking the covalently bonded crosslinked portions in the crosslinked elastomer (A) with water (B). This method makes it possible to efficiently form a re-crosslinked product after the crosslinked elastomer (A) has been de-crosslinked once, and makes it possible to reuse the crosslinked elastomer (A) as a re-crosslinked product.

[0112] Such a decrosslinked elastomer composition is a composition containing a decrosslinked elastomer formed by heating the crosslinked elastomer, and may contain, in addition to the decrosslinked product (decrosslinked elastomer) of the crosslinked elastomer (A) formed in the elastomer composition, water remaining in the decrosslinked elastomer (that which remained in the elastomer without reacting during heating and stirring), and components that formed covalent crosslinked sites (crosslinking agent generated by the decrosslinking of covalent crosslinked sites) that are generated (detached from the crosslinked portion) during the decrosslinking of the crosslinked elastomer (A). For example, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, decrosslinking proceeds as the crosslinking agent that formed covalent crosslinked sites is detached by hydrolysis, and hydroxyl groups derived from water (B) are bonded to the sites where the crosslinking agent was bonded. Therefore, during the decrosslinking, the crosslinking agent is generated in the composition along with the decrosslinked elastomer. Therefore, in such cases, the decrosslinked elastomer composition obtained by decrosslinking will contain the detached crosslinking agent (see Figure 1). Furthermore, if some of the water (B) used in the reaction during decrosslinking remains, the decrosslinked elastomer composition will also contain water (B).

[0113] Normally, when the elastomer composition is subjected to a decrosslinking process, it separates into two phases: one phase consisting of a mixture (solids) containing the decrosslinked elastomer, water, and a crosslinking agent, and another phase consisting of water. When the solids (the mixture containing the decrosslinked elastomer) are removed from the reaction vessel, the solids can be separated from the majority of the water, but some water and at least some of the crosslinking agent are thought to remain dispersed in the solids (the mixture containing the decrosslinked elastomer). Therefore, in the present invention, even when the solids (the mixture containing the decrosslinked elastomer) are removed from the reaction vessel and separated from the water for use, the solids are considered to be a composition containing the decrosslinked elastomer along with other components (water, crosslinking agent, etc.) and are referred to as the "decrosslinked elastomer composition."

[0114] In the present invention, a decrosslinked elastomer composition containing the decrosslinked elastomer is heated at a temperature of 100 to 280°C in an open system or under reduced pressure conditions to recrosslink the decrosslinked elastomer in the decrosslinked elastomer composition.

[0115] In the context of heating conditions, an "open system" means an atmosphere that allows vapors and other substances to move (be removed) from the de-crosslinked elastomer composition. This "open system" may be, for example, an atmospheric environment or an inert gas atmosphere. Furthermore, the reduced pressure conditions during heating are not particularly limited and only require a reduced pressure sufficient to remove vapors (water vapor) from the de-crosslinked elastomer composition. From the viewpoint of economy and workability, such heating conditions are preferably an open system (more preferably in the atmosphere).

[0116] Furthermore, as mentioned above, the temperature conditions during such heating should be such that 100 to 280°C (more preferably 120 to 250°C, even more preferably 140 to 230°C, and particularly preferably 150 to 230°C). By setting the heating temperature above the lower limit, it becomes possible to efficiently induce a crosslinking reaction using the remaining crosslinking agent in the composition while removing water from the composition. On the other hand, by setting the temperature below the upper limit, it becomes possible to more effectively suppress the decrosslinking reaction of the crosslinked portion and the deterioration of the polymer main chain.

[0117] Furthermore, by employing such a heating temperature, if water (B) remains in the decrosslinked elastomer composition, it becomes possible to remove the remaining water (B) while also removing any water that may be generated by heating (water that may be formed by the reaction between the decrosslinked elastomer and the crosslinking agent, or water that may be generated when the decrosslinked elastomer has two adjacent carboxyl groups (for example, a maleic acid group) and these groups undergo dehydration and cyclization to form an acid anhydride group), thereby enabling the crosslinking reaction to proceed efficiently. For example, if the crosslinked elastomer (A) is an elastomeric polymer having a cyclic acid anhydride group and two or more functional groups in one molecule In the case of a reaction product with a crosslinking agent having the above characteristics, if the decrosslinked elastomer is a decrosslinked product in which the site where the crosslinking agent was bonded at the covalent crosslinking site in the crosslinked elastomer (A) is replaced by a hydroxyl group derived from water (B) to become a carboxyl group (a decrosslinked elastomer in which the cyclic acid anhydride group is ring-opened to become two carboxyl groups), then it becomes possible to efficiently carry out a reaction in which the carboxyl group itself and / or the cyclic acid anhydride group that can be generated in the decrosslinked elastomer by heating reacts with the crosslinking agent to recrosslink (see Figure 1; Figure 1 will be described later). Furthermore, in the case of a de-crosslinked product (a de-crosslinked elastomer in which the cyclic acid anhydride group is ring-opened to form two carboxyl groups) in the covalent crosslinking site of the crosslinked elastomer (A), where the site to which the crosslinking agent was bonded has been replaced by a hydroxyl group derived from water (B), and the two carboxyl groups are to be cyclized to form an acid anhydride group for use in the crosslinking reaction, it is preferable to heat the product for about 3 hours using an oven under reduced pressure or atmospheric pressure at a temperature of about 160°C. This heating process makes it possible to efficiently cyclize the carboxyl group to form an acid anhydride group. The acid anhydride thus cyclized can efficiently react with the remaining crosslinking agent.

[0118] Furthermore, when the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, it is desirable to set the temperature condition of 100 to 280°C during heating to a temperature below the boiling point of the crosslinking agent within the temperature range of 100 to 280°C. By using such temperature conditions, it becomes possible to retain the crosslinking agent generated in the de-crosslinking reaction in the composition, and to involve such crosslinking agent in re-crosslinking.

[0119] Furthermore, heating at a temperature of 100 to 280°C in an open system or under reduced pressure conditions is preferably carried out while kneading the decrosslinked elastomer composition. The method of kneading is not particularly limited, and for example, a method of kneading using known equipment such as rolls, kneaders, mixers, Banbury mixers, extruders, and universal agitators can be employed.

[0120] Furthermore, the step of recrosslinking the decrosslinked elastomer in the decrosslinked elastomer composition by heating the decrosslinked elastomer composition containing the decrosslinked elastomer at a temperature of 100 to 280°C in an open system or under reduced pressure conditions is as follows: Step (1) of heating the decrosslinked elastomer composition in an open system or under reduced pressure conditions at a temperature of 100 to 280°C for a relatively long time while kneading (the heating time will vary depending on the amount of water (B) remaining in the composition, the type of crosslinking agent, and the heating temperature used, and in some cases it may be possible to recrosslink with heating and kneading for about 1 minute, so the time until recrosslinking can be achieved should be appropriately set within a heating time of 1 minute or more, and there are no particular limitations, but preferably 10 minutes or more, more preferably 15 minutes or more) to recrosslink the decrosslinked elastomer; or, The process is preferably one of the following steps: (2) Heating the decrosslinked elastomer composition in an open system or under reduced pressure at a temperature of 100 to 280°C to remove the water (B) contained in the composition, and then separately heating the composition obtained after removing the water (B) at a temperature of 100 to 280°C (preferably selected from the range of 140 to 280°C) to recrosslink the decrosslinked elastomer.

[0121] When such process (1) is adopted, by kneading at a temperature of 100 to 280°C and continuing to heat for a relatively long time (preferably 10 minutes or more, more preferably 15 minutes or more), water (water used for decrosslinking remaining in the composition, or in some cases, water generated when cyclic acid anhydride groups are formed from the two carboxyl groups of the decrosslinked elastomer by heating) is removed from the decrosslinked elastomer composition, and then the crosslinking reaction proceeds by such heating, making it possible to recrosslink the composition. Furthermore, when process (2) is adopted, first, the water (B) can be removed by heating at a temperature of 100 to 280°C (the heating time for removing such water (B) will be described later), and then the composition after the removal of the water (B) can be recrosslinked by heating while processing it into a specific shape, for example by hot pressing. Thus, by employing process (1) and continuing heating at a temperature of 100 to 280°C for a long period of time, the decrosslinked elastomer may be recrosslinked. Alternatively, by employing process (2), the residual water (B) may be removed from the decrosslinked elastomer composition by heating at a temperature of 100 to 280°C, and then the decrosslinked elastomer may be recrosslinked by subjecting the composition after the removal of water (B) to a separate heating process at a temperature of 100 to 280°C. When employing such process (2), it is also possible to obtain the composition after the removal of water (B), pass it through the flow process, and then perform a separate recrosslinking process. Furthermore, the step of removing water (B) in step (2) may be carried out by heating until it is recognized that the water (B) has been sufficiently evaporated and removed, based on the amount of water (B) remaining in the decrosslinked elastomer composition, etc. The heating time is not particularly limited and may be set appropriately to achieve the objective depending on the amount of water (B) remaining, the heating temperature used, etc. For example, it is preferable to set the heating time to an appropriate time within the range of 10 seconds to 30 minutes (for example, depending on conditions such as the type of composition, it may be conceivable that it may take about 30 minutes to remove water (B)) (more preferably in the range of 10 seconds to less than 15 minutes, and even more preferably in the range of 10 seconds to less than 10 minutes) (in some cases it may be possible to set it to a short time of about 10 seconds to 1 minute).The heating time can be appropriately changed depending on the equipment used during kneading (type and capacity of the kneader, etc.). Furthermore, when step (2) is adopted, if the decrosslinked elastomer is a decrosslinked product in which the portion to which the crosslinking agent was bonded in the covalent crosslinked portion of the crosslinked elastomer (A) has been replaced by a hydroxyl group derived from the water (B) to form a carboxyl group (a decrosslinked elastomer in which the cyclic acid anhydride group portion has been ring-opened to form two carboxyl groups), then it is preferable to heat the mixture during the removal of the water (B) to ring-close the two carboxyl groups to form a cyclic acid anhydride group, so that the composition after the removal of the water (B) contains an elastomer having a cyclic acid anhydride group (depending on the type of crosslinking agent present in the system, for example, heating under reduced pressure or atmospheric pressure at a temperature of about 160°C for about 60 to 300 minutes).

[0122] Here, the heating temperature of the composition after the removal of water (B) in step (2) (the heating temperature for re-crosslinking) can be set appropriately within the range of 100 to 280°C and is not particularly limited, but it is desirable to set the temperature to 120 to 280°C (more preferably 140 to 280°C). Such temperatures are suitable heating temperatures used when molding elastomers, and such heating makes it possible to efficiently carry out the crosslinking reaction by the crosslinking agent present in the decrosslinked elastomer composition. Such heating may be carried out while performing pressure pressing or the like in the molding process.

[0123] In this way, by heating the de-crosslinked elastomer composition containing the de-crosslinked elastomer at a temperature of 100 to 280°C in an open system or under reduced pressure conditions, the de-crosslinked elastomer in the de-crosslinked elastomer composition can be re-crosslinked, thereby obtaining a re-crosslinked elastomer (re-crosslinked elastomer).

[0124] <Second method for recrosslinking a crosslinked elastomer> The second method for recrosslinking a crosslinked elastomer of the present invention involves heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer composition containing a decrosslinked elastomer, and then heating the decrosslinked elastomer composition, which contains a decrosslinked elastomer obtained by decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), in an open system or under reduced pressure conditions at a temperature above the boiling point of the water (B) to remove the water (B) present in the decrosslinked elastomer composition. After that, a crosslinking agent consisting of a compound having at least one functional group from hydroxyl groups, thiol groups, amino groups, and imino groups in two or more molecules is added to the obtained composition, and the decrosslinked elastomer is recrosslinked with the crosslinking agent in the composition after the addition of the crosslinking agent.

[0125] In this second crosslinking method for the crosslinked elastomer of the present invention, the components used; the conditions for decrosslinking the covalent crosslinked sites in the crosslinked elastomer (A) with water (B) (conditions for obtaining the decrosslinked elastomer composition); conditions such as an open system or reduced pressure; etc., are the same as those described in the first crosslinking method for the crosslinked elastomer of the present invention.

[0126] In the second crosslinking method for a crosslinked elastomer of the present invention, first, the decrosslinked elastomer composition is heated in an open system or under reduced pressure conditions at a temperature above the boiling point of water (B) to remove the water (B) present in the decrosslinked elastomer composition. By removing water (B) from the decrosslinked elastomer composition in this way, the crosslinking reaction can be carried out more efficiently during recrosslinking. The temperature conditions during such heating only need to be above the boiling point of water (B), and there are no particular restrictions on other conditions. However, if the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, it is desirable to set the temperature above the boiling point of water (B) and below the boiling point of the crosslinking agent. By setting such temperature conditions, it is possible to retain the crosslinking agent generated in the decrosslinking reaction in the composition, and such crosslinking agent can also be involved in the recrosslinking. Furthermore, it is desirable that the step of removing the water (B) from the decrosslinked elastomer composition be the same as the step of removing the water (B) in step (2) described in the first crosslinked elastomer recrosslinking method of the present invention.

[0127] Furthermore, in the second crosslinking method for the crosslinked elastomer of the present invention, a crosslinking agent comprising a compound having at least two of at least one functional group from among hydroxyl groups, thiol groups, amino groups, and imino groups in one molecule is added to the composition obtained by removing the water (B) by heating. Such a crosslinking agent comprising a compound having at least one functional group from among hydroxyl groups, thiol groups, amino groups, and imino groups in one molecule is the same as the "compound having at least two of at least one functional group from among hydroxyl groups, thiol groups, amino groups, and imino groups in one molecule" described as a suitable crosslinking agent in the decrosslinking method for the crosslinked elastomer of the present invention described above (the same applies to the preferred compounds). Examples of such crosslinking agents include triazoles, pyridines, thiadiazoles, imidazoles, isocyanurates, triazines, hydantoins, oxopyrimidines, and compounds having aromatic rings, which have two or more functional groups in one molecule, at least one of the functional groups selected from hydroxyl groups, thiol groups, amino groups, and imino groups (such functional groups may be simply referred to as "functional group (A)" as described above). Furthermore, as such a crosslinking agent, at least one compound selected from the group consisting of nitrogen-containing compounds having two or more of the functional group (A) in one molecule, oxygen-containing compounds having two or more of the functional group (A) in one molecule (e.g., diethylene glycol, neopentyl glycol, pentaerythritol), sulfur-containing compounds having two or more of the functional group (A) in one molecule, aliphatic compounds having two or more of the functional group (A) in one molecule (e.g., glycerin), and aromatic compounds (compounds having aromatic rings) having two or more of the substituent (A) in one molecule can be suitably used.

[0128] From the viewpoint of high thermal stability of the reactants, tris(2-hydroxyethyl) isocyanurate (abbreviated as THI), 2,4-diamino-6-phenyl-1,3,5-triazine (benzoguanamine), 2,4-diamino-6-methyl-1,3,5-triazine (acetoguanamine), pentaerythritol, 4,4'-diaminodiphenylmethane, xylylenediamine, phenylenediamine, polyether polyol, benzenetrimethanol, benzenedimethanol, and diethylene glycol are preferred as such crosslinking agents.

[0129] Furthermore, the amount of crosslinking agent added to the composition obtained by removing the water (B) can be appropriately set according to the type of component to be recrosslinked, etc., and is not particularly limited. However, for example, if there is a target number of moles of covalently crosslinked sites (for example, the number of moles of covalently crosslinked sites that the crosslinked elastomer (A) had before decrosslinking may be the design objective), it is preferable to use 0.01 to 3 equivalents (more preferably 0.1 to 1.5 equivalents) of the crosslinking agent relative to the number of moles of covalently crosslinked sites. Setting the content ratio of such crosslinking agent above the lower limit tends to allow the reaction that forms crosslinks with the crosslinking agent (crosslinking reaction) to proceed more efficiently, while setting it below the upper limit tends to suppress the decrease in crosslink density more effectively (because depending on the type of crosslinking agent, if there is too much, the amount of crosslinking agent that is penetrating increases and the crosslink density may decrease). The amount of crosslinking agent added can be appropriately changed according to the intended use after recrosslinking, etc., and is not particularly limited.

[0130] Furthermore, while there are no particular limitations on the method for re-crosslinking the de-crosslinked elastomer with the crosslinking agent in the composition after the addition of the crosslinking agent, it is preferable to employ a method of heating to a temperature at which the crosslinking agent reacts to promote the crosslinking reaction. The heating temperature for promoting such a crosslinking reaction varies depending on the type of crosslinking agent and is not particularly limited, but it is preferably 100 to 280°C (more preferably 120 to 250°C, and even more preferably 150 to 230°C). Setting the heating temperature above the lower limit makes it possible to efficiently induce the crosslinking reaction, while setting it below the upper limit makes it possible to more effectively suppress the de-crosslinking reaction of the crosslinked portion and the deterioration of the polymer main chain.

[0131] The crosslinking agent may be added while heating the composition. In this case, the heating temperature of the composition at the time of addition may be set to the temperature at which the crosslinking reaction proceeds, allowing the crosslinking reaction to proceed simultaneously with the addition of the crosslinking agent. Alternatively, the heating temperature of the composition at the time of addition may be set to a temperature at which the crosslinking reaction does not proceed (preferably a heating temperature at which the crosslinking reaction does not proceed but plasticization of the composition is possible (this will vary depending on the type of crosslinking agent, etc., but for example, a heating temperature of around 100°C)), and the crosslinking agent may be added. After that, the composition to which the crosslinking agent has been added may be heated to the temperature at which the crosslinking reaction proceeds to allow the crosslinking reaction to proceed.

[0132] In this way, by re-crosslinking the de-crosslinked elastomer with the crosslinking agent in the composition after the addition of the crosslinking agent, a re-crosslinked elastomer (re-crosslinked elastomer) can be efficiently obtained.

[0133] <Preferred Embodiments of the Re-crosslinking Method for the First and Second Crosslinked Elastomers> Hereinafter, preferred embodiments of the re-crosslinking method for crosslinked elastomers (re-crosslinking method for the first and second crosslinked elastomers) of the present invention will be described with reference to Figure 1. Figure 1 is a schematic diagram illustrating one form of the reaction scheme of a preferred embodiment of the re-crosslinking method for crosslinked elastomers of the present invention. As shown in Figure 1, the de-crosslinking of crosslinked elastomers and the re-crosslinking of de-crosslinked elastomers can be repeated. Therefore, Figure 1 can also be said to be a schematic diagram illustrating a preferred form in which these elastomers are recycled as raw materials and products, and crosslinked elastomers are reused.

[0134] The crosslinked elastomer shown in Figure 1 is a reaction product of an elastomeric polymer having maleic anhydride groups and THI, which can be suitably used as a crosslinked elastomer according to the present invention (where the covalent crosslinking site is an ester bond (in the formula -COO-CH ２ This schematically shows an elastomeric polymer having a structure with a bond represented by -. Such a crosslinked elastomer may be one that has been used as a molded article.

[0135] In the embodiment shown in Figure 1, first, in the "(1) De-crosslinking step," an elastomer composition containing a crosslinked elastomer and water is formed and heated in order to hydrolyze the crosslinked elastomer. For this purpose, for example, the crosslinked elastomer and water may be placed in a reaction vessel (preferably a high-pressure reaction vessel such as an autoclave) (if necessary, an organic solvent and / or catalyst may also be added to the reaction vessel), and the formation of the elastomer composition containing the crosslinked elastomer and water and the heating step may be carried out simultaneously by heating while stirring. By stirring and heating in the reaction vessel in this way, the formation of the composition and the subsequent hydrolysis reaction can be carried out efficiently, making it possible to hydrolyze the covalent crosslinking sites of the crosslinked elastomer. By hydrolyzing the covalent crosslinking sites in this way, de-crosslinking becomes possible, and a de-crosslinked elastomer can be obtained. In addition, such de-crosslinking is essentially done in such a way that crosslinked elastomers having covalently linked crosslinked sites that are difficult to plasticize can be made plasticizable and reused in molding processes, etc. Depending on the type of crosslinked elastomer, it is not necessarily required that all of the covalently linked crosslinked sites be de-crosslinked; it is sufficient if at least some of the covalently linked crosslinked sites are de-crosslinked. In the embodiment shown in Figure 1, the crosslinked elastomer shown in the figure has all of its covalently linked crosslinked sites (the three ester bond portions) hydrolyzed, resulting in a de-crosslinked elastomer having maleic acid groups as shown in Figure 1.

[0136] Furthermore, in the embodiment shown in Figure 1, the decrosslinked elastomer is in a state where it coexists with the crosslinking agent (THI) produced by hydrolysis during the decrosslinking process. For example, if the "(1) decrosslinking process" is carried out in a high-pressure reaction vessel, and the decrosslinked elastomer is removed after the heating is stopped and the mixture is cooled to room temperature, the decrosslinked elastomer usually separates into two phases: a solid phase containing the decrosslinked elastomer and water. If only the solid phase is removed and washed, the resulting solid phase will be a composition containing the decrosslinked elastomer, a small amount of water, and the crosslinking agent that remains even after such washing.

[0137] Therefore, in the embodiment shown in Figure 1, in the "(2) Re-crosslinking step," the solid content obtained in the de-crosslinking step (de-crosslinked elastomer composition (which may include water and residual crosslinking agent)) is heated at a temperature above the boiling point of water to dehydrate it, and the remaining crosslinking agent in the system is used as is, or a crosslinking agent is added to the dehydrated composition to allow the crosslinking reaction to proceed, thereby forming crosslinks again and obtaining a re-crosslinked elastomer (crosslinked elastomer). When using the solid content obtained after the de-crosslinking step in the re-crosslinking step, the amount of residual crosslinking agent in the solid content will differ depending on the degree of washing, the type of de-crosslinked elastomer, the type of crosslinking agent that formed the crosslinks, etc. Therefore, depending on these circumstances and the intended design of the crosslinked elastomer to be formed after re-crosslinking (design of crosslink density, etc.), the re-crosslinking step should be carried out appropriately by either not adding a crosslinking agent, or by adjusting the amount of crosslinking agent added.

[0138] As explained above, the reaction scheme shown in Figure 1 can be repeatedly recycled. Therefore, by using such a re-crosslinking method, it is possible to repeatedly reuse the crosslinked elastomer as a re-crosslinked product by de-crosslinking and then re-crosslinking it. It should be noted that the re-crosslinking method for crosslinked elastomers of the present invention is not limited to the embodiment shown in Figure 1, but any method that can carry out each of the steps described in the first and second re-crosslinking methods for crosslinked elastomers described above is acceptable, and other forms may be used as appropriate, such as by changing the type of crosslinked elastomer.

[0139] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0140] <Synthesis Example 1, Examples 1-3 and Comparative Example 1> (Synthesis Example 1: Synthesis of Crosslinked Elastomer) <Preparation Step of Uncrosslinked Thermoplastic Elastomer Composition> 70 g of elastomer consisting of maleic anhydride-modified ethylene-butene copolymer (abbreviated as "maleinized EBM", product name "Tafmer MH5020" manufactured by Mitsui Chemicals, Inc., maleination rate: 1.0% by mass, crystallinity 4%) was placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes under the conditions of temperature: 100°C and rotation speed: 50 rpm. Subsequently, under a temperature of 100°C, 0.917 g of tris(2-hydroxyethyl) isocyanurate (abbreviated as "THI," trade name "Tanac P" manufactured by Nissei Sangyo Co., Ltd.) as a crosslinking agent (1 equivalent relative to the number of moles of maleic anhydride groups in the maleated EBM) was added to the plasticized elastomer as described above, and the mixture was kneaded at a rotation speed of 50 rpm for 5 minutes to prepare an uncrosslinked thermoplastic elastomer composition. Note that, under a temperature of 100°C, the reaction between the maleic anhydride groups and the hydroxyl groups in THI basically does not proceed.

[0141] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0142] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleated EBM and THI. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of maleic anhydride groups.

[0143] Here, the IR spectrum of the components constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, a component of 1783 cm⁻¹ originated from maleic anhydride. －１ The peak was barely observed (compared to the peak of the IR spectrum of the raw material maleic anhydride-modified ethylene-butene copolymer, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of THI with maleic anhydride groups. As demonstrated in Comparative Example 1 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 1 did not plasticize even when kneaded at 120°C in a kneader.

[0144] (Example 1) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 1 was placed in a 100cc pressurized kneader and pulverized to prepare 50g of powdered crosslinked elastomer. Next, 50g of powdered crosslinked elastomer and 50g of water were placed in a 100cc autoclave (with a stirrer), sealed, and heated for 6 hours at a heating temperature of 180°C and a gauge pressure of 0.8 MPa to allow the decrosslinking reaction to proceed. During this heating, the 50g of powdered crosslinked elastomer and 50g of water were heated while being stirred. Furthermore, the amount of water added to the autoclave for heating was 369 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (THI) used in the production of the crosslinked elastomer (50 g) used in the decrosslinking process, and 545 moles per mole of maleic anhydride groups in the maleated EBM used in the production of the crosslinked elastomer (50 g) used in the decrosslinking process. Subsequently, the mixture was cooled to room temperature (approximately 25°C) to obtain a composition containing solids including the decrosslinked product of the crosslinked elastomer (decrosslinked elastomer) and water. This composition was separated into a water phase and a solids phase.

[0145] Next, the solid component was extracted from the composition formed in the autoclave as described above by filtration, dried under reduced pressure at 50°C for 1 hour, and then the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid component. As a result of this measurement, the peak top of 1740 cm was found in the IR spectrum of the component constituting the sheet before decrosslinking (crosslinked elastomer obtained in Synthesis Example 1). －１ Almost no absorption of isocyanurate esters was observed in the vicinity, at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, and a shift in the peak top was confirmed. From this shift in the absorption peak in the IR spectrum, it is inferred that when the crosslinked elastomer, a reaction product of maleated EBM and THI, is heated with water, a hydrolysis reaction proceeds, and the THI in the reaction product is replaced by water (with hydroxyl groups), resulting in a decrosslinked elastomer.

[0146] Furthermore, as demonstrated in Examples 2 and 3 described later, the decrosslinked elastomer obtained in Example 1 was plasticizable at 120°C or 100°C, and the resulting sheet was moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 1, which could not be plasticized at 120°C, became plasticizable at 120°C or 100°C after the decrosslinking process clearly demonstrates that the crosslinked elastomer was decrosslinked.

[0147] These results clearly indicate that the solid content obtained in Example 1 is a composition containing de-crosslinked products (de-crosslinked elastomers) of the crosslinked elastomer.

[0148] (Example 2) <Re-crosslinking process> First, a composition containing solids including a de-crosslinked elastomer and water was obtained in the same manner as in Example 1. Next, the solids were removed from this composition by filtration. Then, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm.

[0149] Next, using a pressure press heated to 200°C, 50g of the plasticized solid material as described above was placed into a mold measuring 15cm in length, 15cm in width, and 2mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15cm in length, 15cm in width, and 2mm in thickness.

[0150] It is clear that the heating during this hot pressing process utilizes the remaining crosslinking agent (THI) in the solid content to initiate a crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated EBM and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of THI and maleic acid groups or maleic anhydride groups (it is possible that the maleic acid groups are dehydrated and cyclized to become maleic anhydride groups upon heating). When the IR spectra of the components constituting the obtained sheet were measured, the 1710 cm⁻¹ point, which was present in the IR spectrum of the decrosslinked elastomer before recrosslinking, was found to be present in the IR spectrum. －１ The absorption of nearby dicarboxylic acids has almost disappeared, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer, a component of the sheet, has a crosslink structure similar to that formed by the reaction between the hydroxyl groups of THI and the maleic anhydride groups. Thus, the IR spectrum results clearly showed that the sheet obtained in Example 2 contains a crosslinked elastomer as a component.

[0151] Furthermore, the solid content used for molding the sheet in Example 2 was the same as the solid content (de-crosslinked elastomer) obtained in Example 1, and was plasticized in a kneading process at 120°C. Therefore, in this example, it was confirmed that the de-crosslinked elastomer obtained in Example 1 is plasticizable at 120°C.

[0152] (Example 3) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 1. Next, the solids were removed from this composition by filtration. Then, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. After that, 0.3225 g of THI (0.5 equivalents relative to the number of moles of maleic anhydride groups in the maleated EBM of the crosslinked elastomer raw material) was added and kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0153] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0154] It is clear that the heating during this hot pressing process utilizes the crosslinking agent (THI) present in the uncrosslinked composition to initiate the crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated EBM and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of THI and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectra of the components constituting the obtained sheet were measured, the 1710 cm⁻¹ point, which was present in the IR spectrum of the decrosslinked elastomer before recrosslinking, was found to be present in the IR spectrum. －１ The absorption of nearby dicarboxylic acids has almost disappeared, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer, a component of the sheet, has a crosslink structure similar to that formed by the reaction between the hydroxyl groups of THI and the maleic anhydride groups.

[0155] Furthermore, the solid content used for molding the sheet in Example 3 was the same as the solid content (de-crosslinked elastomer) obtained in Example 1, and was plasticized in a kneading process at 100°C. Therefore, in this example, it was confirmed that the de-crosslinked elastomer obtained in Example 1 is plasticizable even at 100°C.

[0156] (Comparative Example 1) When 50 g of the sheet obtained in Synthesis Example 1 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the crosslinked elastomer constituting the sheet obtained in Synthesis Example 1 cannot be plasticized at a temperature of 120°C.

[0157] [Evaluation of the properties of sheets obtained in Synthesis Example 1, Examples 1-3 and Comparative Example 1] <Confirmation of plasticization feasibility> The sheets (elastomers) obtained in Synthesis Example 1, Examples 2-3 and Comparative Example 1, and the solid content (elastomer) obtained in Example 1 were evaluated for plasticization feasibility when kneaded in a kneader (product name "Laboplastmill Micro" manufactured by Toyo Seiki Co., Ltd., capacity: 100 cc) at a temperature of 120°C and a rotation speed of 20 rpm for 5 minutes. The results are shown in Table 1. In the table, "Possible" is written for materials that can be plasticized, and "Not Possible" is written for materials that cannot be plasticized.

[0158] <Measurement of JIS-A Hardness> The JIS-A hardness was measured using the sheets obtained in Synthesis Example 1 and Examples 2-3, respectively, as follows. First, the sheets were punched out into a 29 mm diameter disc shape, and seven sheets were stacked together to prepare a measurement sample with a height (thickness) of 12.5 ± 0.5 mm. Using the measurement sample obtained in this way, the JIS-A hardness was measured in accordance with JIS K6253 (published in 2012). The results obtained are shown in Table 1.

[0159] <Measurement of 100% Modulus (unit: MPa), 300% Modulus (unit: MPa), Breaking Strength (unit: MPa), and Breaking Elongation (unit: %)> Using the sheets obtained in Synthesis Example 1 and Examples 2-3, dumbbell-shaped test specimens were punched out from the sheets, and tensile tests were performed using a tensile testing machine in accordance with JIS K6251, under the conditions of temperature: room temperature (approximately 25°C) and tensile speed: 500 mm / min. The 100% modulus (unit: MPa), 300% modulus (unit: MPa), breaking strength (unit: MPa), and breaking elongation (unit: %) were measured. The obtained results are shown in Table 1.

[0160] In Comparative Example 1, since a powder was obtained without plasticization, it was not possible to measure JIS-A hardness, 100% modulus (unit: MPa), 300% modulus (unit: MPa), breaking strength (unit: MPa), and breaking elongation (unit: %) for the product obtained in Comparative Example 1.

[0161]

[0162] As is clear from the results shown in Table 1, the crosslinked elastomer obtained in Synthesis Example 1 did not plasticize at 120°C and was confirmed to turn into powder during the kneading process at 120°C (see Comparative Example 1). On the other hand, in Example 1, the crosslinked elastomer obtained in Synthesis Example 1 was decrosslinked, and from the results of confirming whether the elastomer obtained after decrosslinking could be plasticized, it was confirmed that the elastomer could be modified into a state that could be plasticized and processed by the decrosslinking process described in Example 1 (see Examples 1 and 2-3).

[0163] Furthermore, the crosslinked elastomer (re-crosslinked product) obtained in Example 2 was obtained by decrosslinking and then recrosslinking the crosslinked elastomer obtained in Synthesis Example 1. Here, the hardness and tensile strength of the crosslinked elastomer obtained in Example 2 were approximately 98% (= (47 / 48) × 100) of the hardness and approximately 87% (= (4.23 / 4.89) × 100) of the hardness and tensile strength of the crosslinked elastomer obtained in Synthesis Example 1, respectively, when decrosslinked and then recrosslinked, the hardness recovered to approximately 98% and the tensile strength recovered to approximately 87% of the original material, the crosslinked elastomer obtained in Synthesis Example 1. Similarly, the hardness and tensile strength of the crosslinked elastomer obtained in Example 3 were found to have recovered to approximately 102% (= (49 / 48) × 100) of the hardness and approximately 91% (= (4.46 / 4.89) × 100) of the tensile strength, compared to the hardness and tensile strength of the crosslinked elastomer obtained in Synthesis Example 1.

[0164] Thus, it was found that by re-crosslinking the de-crosslinked elastomer obtained in Example 1, the hardness and fracture strength can be sufficiently restored based on the original crosslinked elastomer material (the crosslinked elastomer obtained in Synthesis Example 1) before de-crosslinking and re-crosslinking. Therefore, it was found that according to the present invention, the covalent crosslinked portions in the crosslinked elastomer can be efficiently de-crosslinked and made easily plasticizable for processing, and then re-crosslinked to make it usable as a crosslinked elastomer, thus enabling efficient reuse of the crosslinked elastomer.

[0165] <Synthesis Examples 2-3, Examples 4-6 and Comparative Example 2> (Synthesis Example 2: Synthesis of Maleinated Hydrogenated SBR) First, 70 g of the raw material polymer, hydrogenated styrene-butadiene copolymer (hydrogenated SBR: ENEOS Material Co., Ltd., product name: NT120), was placed in a pressurized kneader (Toyo Seiki Seisakusho Co., Ltd., product name: Laboplastmill (using R100 mixer)) and kneaded for 60 seconds at a temperature of 90°C and a rotation speed of 50 rpm. Next, 7 g of maleic anhydride (Tokyo Chemical Industries Co., Ltd.), 3.5 g of tris(2-ethylhexyl) phosphate (Daihachi Chemical Industry Co., Ltd., product name "TOP"), and 0.7 g of an antioxidant (Ouchi Shinko Chemical Co., Ltd., product name "Norac 6C") were placed in the pressurized kneader and kneaded for a further 10 minutes at a temperature of 90°C and a rotation speed of 50 rpm, after which the mixture was released. The mixture released in this manner was again placed into a pressurized kneader (manufactured by Toyo Seiki Seisakusho, product name: Laboplast Mill (using R100 mixer)) and kneaded for 30 minutes at a temperature of 250°C and a rotation speed of 50 rpm before being released. The mixture released in this manner was dried under reduced pressure at 160°C for 3 hours, and the unreacted maleic anhydride was removed by distillation to obtain hydrogenated SBR modified with maleic anhydride (abbreviated as "maleinized hydrogenated SBR"). The maleination rate of the obtained maleinized hydrogenated SBR was found to be 2.4% by mass.

[0166] (Synthesis Example 3) <Preparation Step for Uncrosslinked Thermoplastic Elastomer Composition> 5.625 g of maleic anhydride-modified ethylene-butene copolymer (abbreviated as "maleinized EBM", trade name "Tafmer MH5040" manufactured by Mitsui Chemicals, Inc., maleination rate: 2.2% by mass, crystallinity 4%) and 39.375 g of maleinated hydrogenated SBR (maleination rate: 2.4% by mass) obtained in Synthesis Example 2 were placed in a 100 cc pressurized kneader and kneaded for 2 minutes at a temperature of 180°C and a rotation speed of 50 rpm to plasticize and obtain a mixture. Subsequently, 18 g of carbon black N339 (manufactured by Tokai Carbon Co., Ltd.), 6.75 g of tris(2-ethylhexyl) phosphate (product name "TOP" manufactured by Daihachi Chemical Industry Co., Ltd.) as a plasticizer (oil), 1.35 g of tetrabutylthiuram disulfide (product name "Noxellar TBTN" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as a vulcanization accelerator, and 0.45 g of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (product name "Nocrack 6C" manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant were added to the plasticized mixture, kneaded for 8 minutes, and released to obtain the mixture.

[0167] Next, 69.96 g of the mixture was placed in a pressurized kneader (capacity: 100 cc) at a temperature of 100°C, 0.93 g of THI (product name "Tanac P" manufactured by Nissei Sangyo Co., Ltd.) (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the composition) was added, and the mixture was kneaded for 5 minutes at a temperature of 100°C and a rotation speed of 50 rpm to obtain an uncrosslinked thermoplastic elastomer composition.

[0168] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0169] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleated EBM and THI, and a crosslinked elastomer which is a reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of maleic anhydride groups.

[0170] Here, the IR spectrum of the composition constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, 1783 cm⁻¹ was found to be derived from maleic anhydride. －１ The peak was barely observed (compared to the peaks in the IR spectra of the raw materials, maleic anhydride-modified ethylene-butene copolymer and maleated hydrogenated SBR, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of THI with maleic anhydride groups (see Figure 2). As demonstrated in Comparative Example 2 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 3 did not plasticize even when kneaded at 120°C in a kneader.

[0171] (Example 4) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 3 was placed in a 100cc pressurized kneader and pulverized to prepare 50g of powdered crosslinked elastomer. Next, 50g of powdered crosslinked elastomer and 50g of water were placed in a 100cc autoclave (with a stirrer), sealed, and heated for 6 hours at a heating temperature of 180°C and a gauge pressure of 0.8 MPa to allow the decrosslinking reaction to proceed. During this heating, the 50g of powdered crosslinked elastomer and 50g of water were heated while being stirred. Furthermore, the amount of water added to the autoclave for heating was 369 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (THI) used in the production of the crosslinked elastomer (50 g) used in the decrosslinking process, and also 369 moles per mole of maleic anhydride when considered based on the total amount of maleic anhydride groups in the maleated EBM and maleated hydrogenated SBR used in the production of the crosslinked elastomer (50 g) used in the decrosslinking process. Subsequently, the mixture was cooled to room temperature (approximately 25°C) to obtain a composition containing solids including the decrosslinked product of the crosslinked elastomer (decrosslinked elastomer) and water. This composition was separated into a water phase and a solids phase.

[0172] Next, the solid component was extracted from the composition formed in the autoclave as described above by filtration, dried under reduced pressure at 50°C for 1 hour, and then the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid component. As a result of this measurement, the peak top of 1740 cm was found in the IR spectrum of the component constituting the sheet before decrosslinking (crosslinked elastomer obtained in Synthesis Example 3). －１ The absorption of isocyanurate esters in the vicinity almost disappears at 1710 cm. －１Absorption of nearby dicarboxylic acids was confirmed, and a shift in the peak top was observed. For reference, Figure 2 shows the IR spectra of the elastomer constituting the sheet obtained in Synthesis Example 3 (IR spectrum of the crosslinked elastomer) and the elastomer constituting the solid content obtained in Example 4.

[0173] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is the reaction product of maleated EBM and THI, underwent a hydrolysis reaction upon heating with water, and the THI in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Examples 5 and 6 described later, the decrosslinked elastomer obtained in Example 4 was plasticizable at 100°C or 120°C, and the sheet became moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 3, which could not be plasticized at 120°C, became plasticizable at 100°C or 120°C after the decrosslinking process clearly indicates that the crosslinked elastomer was decrosslinked in Example 4.

[0174] (Example 5) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 4. Next, the solids were extracted from this composition by filtration. Then, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm.

[0175] Next, using a pressure press heated to 200°C, 50g of the plasticized solid material as described above was placed into a mold measuring 15cm in length, 15cm in width, and 2mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15cm in length, 15cm in width, and 2mm in thickness.

[0176] It is clear that the heating during this hot pressing process utilizes the remaining crosslinking agent (THI) in the solid content to initiate the crosslinking reaction, and that the sheet components include crosslinked elastomers with a structure similar to that of the reaction product of maleated EBM and THI, and crosslinked elastomers with a structure similar to that of the reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomers include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectra of the components constituting the obtained sheet were measured, the IR spectrum showed that the 1710 cm⁻¹ point, which was present in the IR spectrum of the decrosslinked elastomer, was also present. －１ The absorption of nearby dicarboxylic acids has almost disappeared, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of THI and the maleic anhydride group.

[0177] Furthermore, the solid components used in molding the sheet in Example 5 were the same as those in the decrosslinked elastomer obtained in Example 4, and were plasticized in a kneading process at 120°C. Therefore, in this example, it was confirmed that the decrosslinked elastomer obtained in Example 4 is plasticizable at 120°C.

[0178] (Example 6) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 4. Next, the solids were removed from this composition by filtration. Then, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. After that, 0.332 g of THI (0.5 equivalents relative to the total number of moles of maleic anhydride groups in the maleated EBM and maleated hydrogenated SBR, which are the raw materials for the crosslinked elastomer) was added and kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0179] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0180] It is clear that the heating during hot pressing utilizes the crosslinking agent (THI) present in the uncrosslinked composition to initiate the crosslinking reaction, and that the sheet components include crosslinked elastomers with a structure similar to that of the reaction product of maleated EBM and THI, and crosslinked elastomers with a structure similar to that of the reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomers include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectra of the components constituting the obtained sheet were measured, the IR spectrum showed that the 1710 cm⁻¹ point, which was present in the IR spectrum of the decrosslinked elastomer, was also present. －１ The absorption of nearby dicarboxylic acids has almost disappeared, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of THI and the maleic anhydride group.

[0181] (Comparative Example 2) When 50 g of the sheet obtained in Synthesis Example 3 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the composition constituting the sheet obtained in Synthesis Example 3 cannot be plasticized at a temperature of 120°C.

[0182] [Evaluation of the properties of sheets obtained in Synthesis Example 3, Examples 4-6 and Comparative Example 2] Using the same methods as described in "Evaluation of the properties of sheets obtained in Synthesis Example 1, Examples 1-3 and Comparative Example 1" above, the sheets obtained in Synthesis Example 3, Examples 5-6 and Comparative Example 2 were subjected to "confirmation of plasticization feasibility," "measurement of JIS-A hardness," and "measurement of 100% modulus (unit: MPa), 300% modulus (unit: MPa), breaking strength (unit: MPa), and breaking elongation (unit: %)." The results are shown in Table 2. Note that in Comparative Example 2, since the material could not be processed into a sheet and a powder was obtained, these measurements could not be performed on the product obtained in Comparative Example 2.

[0183]

[0184] As is clear from the results shown in Table 2, the crosslinked elastomer obtained in Synthesis Example 3 did not plasticize at 120°C and was confirmed to turn into powder during the plasticization process at 120°C (see Comparative Example 2). On the other hand, in Example 4, the crosslinked elastomer obtained in Synthesis Example 3 was decrosslinked, and from the results of confirming whether the elastomer obtained after decrosslinking could be plasticized, it was confirmed that the elastomer could be modified into a state that could be plasticized and processed by the decrosslinking process described in Example 4 (see Examples 4 and 5-6).

[0185] Furthermore, the crosslinked elastomer (re-crosslinked product) obtained in Example 5 was obtained by decrosslinking and then recrosslinking the crosslinked elastomer obtained in Synthesis Example 3. Here, the hardness and tensile strength of the crosslinked elastomer obtained in Example 5 were found to have recovered to approximately 90% (= (57 / 63) × 100) of the hardness and approximately 81% (= (18.9 / 23.3) × 100) of the tensile strength, using the hardness and tensile strength of the crosslinked elastomer (original material) obtained in Synthesis Example 3 as a reference. Similarly, the hardness and tensile strength of the crosslinked elastomer obtained in Example 6 were found to have recovered to approximately 97% (= (61 / 63) × 100) of the hardness and approximately 89% (= (20.8 / 23.3) × 100) of the tensile strength, using the hardness and tensile strength of the crosslinked elastomer (original material) obtained in Synthesis Example 3 as a reference. Furthermore, since the difference between Example 5 and Example 6 is the presence or absence of the crosslinking agent, it was found that when the crosslinked elastomer obtained in Synthesis Example 3 is decrosslinked and then recrosslinked, it is possible to restore it to a state closer to the original material by adding a crosslinking agent.

[0186] Thus, it was found that by subjecting the decrosslinked elastomer obtained in Example 4 to a recrosslinking process, it is possible to sufficiently restore the hardness and fracture strength of the original crosslinked elastomer material (the crosslinked elastomer obtained in Synthesis Example 3) before decrosslinking and recrosslinking. Therefore, it was found that according to the present invention, the covalent crosslinking sites in a crosslinked elastomer can be efficiently decrosslinked and made easily plasticizable for processing, and then recrosslinked to make it usable as a crosslinked elastomer, thus enabling efficient reuse of crosslinked elastomers.

[0187] <Synthesis Examples 4-5, Examples 7-12 and Comparative Examples 3-4> (Synthesis Example 4) <Preparation Step for Uncrosslinked Thermoplastic Elastomer Composition> 70 g of maleated hydrogenated SBR (maleinization rate: 2.4% by mass) obtained in Synthesis Example 2 and 0.7 g of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (product name "Nocrack 6C" manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant were placed in a pressurized kneader (capacity: 100 cc) at a temperature of 60°C and kneaded for 30 seconds at a rotation speed of 50 rpm to plasticize the mixture. Subsequently, 1.38 g of THI (product name "Tanac P" manufactured by Nissei Sangyo Co., Ltd.) (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the composition) was added to the plasticized mixture and kneaded for 5 minutes at a temperature of 60°C and a rotation speed of 50 rpm to obtain an uncrosslinked thermoplastic elastomer composition. Furthermore, at a temperature of 60°C, the reaction between the maleic anhydride group and the hydroxyl group in THI does not generally proceed.

[0188] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0189] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleinated hydrogenated SBR and THI. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of maleic anhydride groups.

[0190] Here, the IR spectrum of the composition constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, 1783 cm⁻¹ was found to be derived from maleic anhydride. －１ The peak was barely detectable (compared to the peak of the IR spectrum of the raw material maleinated hydrogenated SBR, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of THI with maleic anhydride groups. For reference, Figure 3 shows the IR spectrum of the elastomer constituting the sheet obtained in Synthesis Example 4 (IR spectrum of the crosslinked elastomer). Furthermore, as demonstrated in Comparative Example 3 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 4 did not plasticize even when kneaded at 120°C in a kneader.

[0191] (Synthesis Example 5) <Preparation Step for Uncrosslinked Thermoplastic Elastomer Composition> 50 g of maleated hydrogenated SBR (maleinization rate: 2.4% by mass) obtained in Synthesis Example 2 and 0.5 g of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (product name "Nocrack 6C" manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant were placed in a 100 cc pressurized kneader and kneaded for 2 minutes at a temperature of 180°C and a rotation speed of 50 rpm to plasticize and obtain a mixture. Then, 15 g of carbon black N339 (manufactured by Tokai Carbon Co., Ltd.) and 7.5 g of aroma oil T-DAE (manufactured by ENEOS Corporation) as a plasticizer (oil) were added to the plasticized mixture and kneaded for 8 minutes, after which the mixture was released to obtain a mixture.

[0192] Next, 71.54 g of the mixture was placed in a pressurized kneader (capacity: 100 cc) at a temperature of 60°C, and 0.965 g of THI (product name "Tanac P" manufactured by Nissei Sangyo Co., Ltd.) (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the composition) was added. The mixture was kneaded for 5 minutes at a temperature of 60°C and a rotation speed of 50 rpm to obtain an uncrosslinked thermoplastic elastomer composition.

[0193] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0194] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleinated hydrogenated SBR and THI. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction of hydroxyl groups of THI with maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of maleic anhydride groups.

[0195] Here, the IR spectrum of the composition constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, 1783 cm⁻¹ was found to be derived from maleic anhydride. －１ The peak was barely detectable (compared to the peak of the IR spectrum of the raw material maleinated hydrogenated SBR, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of THI with maleic anhydride groups. As demonstrated in Comparative Example 4 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 5 did not plasticize even when kneaded at 120°C in a kneader.

[0196] (Example 7) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 4 was placed in a 100cc pressurized kneader and pulverized to prepare 20g of powdered crosslinked elastomer. Next, 20g of powdered crosslinked elastomer, 6g of water, 54g of N-methylpyrrolidone, and 3.42g of p-toluenesulfonic acid monohydrate were placed in a 100cc PTFE inner cylindrical sealed container (with a stirring bar), sealed, and heated at a heating temperature of 180°C for 10 hours to allow the decrosslinking reaction to proceed. The amount of water added to the PTFE inner cylindrical sealed container for heating was 75.9 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (THI) used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process, and also 75.9 moles per mole of maleic anhydride groups in the maleated hydrogenated SBR used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process. The mixture was then cooled to room temperature (approximately 25°C) to obtain a composition containing solids including the decrosslinked product of the crosslinked elastomer (decrosslinked elastomer) and water (components in the liquid phase). The resulting composition was separated into a liquid phase (the liquid phase described here is a phase containing water, specifically an aqueous solution containing water, N-methylpyrrolidone, and p-toluenesulfonic acid) and a solid phase.

[0197] Next, the solid component was extracted from the composition formed in the PTFE cylindrical sealed container as described above by filtration, dried under reduced pressure at 100°C for 1 hour, and then the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid component. As a result of this measurement, the peak top of 1740 cm was found in the IR spectrum of the component constituting the sheet before decrosslinking (the crosslinked elastomer obtained in Synthesis Example 4). －１ The absorption of isocyanurate esters in the vicinity almost disappears at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, confirming a shift in the peak top. The IR spectrum of the elastomer constituting the solid content obtained in Example 7 is shown in Figure 3.

[0198] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is the reaction product of maleinated hydrogenated SBR and THI, underwent a hydrolysis reaction when heated with water, and the THI in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Example 8 described later, the decrosslinked elastomer obtained in Example 7 was plasticizable even at 100°C, and the sheet became moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 4, which could not be plasticized at 120°C, became plasticizable at 100°C after the decrosslinking process clearly indicates that the crosslinked elastomer was decrosslinked in Example 7.

[0199] (Reference Example 1) <Water Removal Process> First, a composition containing solids including de-crosslinked products of the crosslinked elastomer (de-crosslinked elastomer) and water was obtained in the same manner as in Example 7. Next, the solids were removed from this composition by filtration, and then the water was removed by heating at 160°C for 180 minutes and drying under reduced pressure to obtain solids. To confirm the structure of the elastomer contained in the water-removed solids obtained in this way, the IR spectrum was measured using FT-IR, and in the obtained IR spectrum, 1780 cm⁻¹ was observed. －１Absorption of nearby maleic anhydride groups was confirmed, indicating that the elastomer in the composition contains maleic anhydride groups. The IR spectrum of the elastomer constituting the solid content obtained in Reference Example 1 is shown in Figure 3.

[0200] (Example 8) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 7. Next, the solids were removed from this composition by filtration. This process was repeated until the amount of solids reached 50 g or more. Next, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. Then, 0.985 g of THI (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the maleated hydrogenated SBR, the raw material for the crosslinked elastomer) was added and kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0201] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0202] It is clear that the heating during such hot pressing utilizes the crosslinking agent (THI) present in the uncrosslinked composition to initiate a crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of THI and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectrum of the components constituting the obtained sheet was measured, the IR spectrum showed 1710 cm⁻¹.－１ The absorption of nearby dicarboxylic acids almost disappears, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of THI and the maleic anhydride group (i.e., it is a re-crosslinked elastomer). The IR spectra of the components constituting the sheet obtained in Example 8 are shown in Figure 3.

[0203] (Example 9) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 4 was placed in a 100cc pressurized kneader and pulverized to prepare 20g of powdered crosslinked elastomer. Next, 20g of powdered crosslinked elastomer, 6g of water, 54g of xylene, 0.9g of p-toluenesulfonic acid monohydrate, and 0.18g of tetrabutylammonium bisulfate (TBAHS) were placed in a 100cc PTFE inner cylindrical sealed container (with a stirring bar), sealed, and heated at a heating temperature of 180°C for 6 hours to allow the decrosslinking reaction to proceed. The amount of water added to the PTFE inner cylindrical sealed container for heating was 75.9 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (THI) used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process, and also 75.9 moles per mole of maleic anhydride groups in the maleated hydrogenated SBR used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process. The mixture was then cooled to room temperature (approximately 25°C) to obtain a composition containing solids including the decrosslinked product of the crosslinked elastomer (decrosslinked elastomer) and water (components in the liquid phase). The resulting composition was separated into a liquid phase (the liquid phase described here is a phase containing water, specifically an aqueous solution containing water, xylene, p-toluenesulfonic acid, and TBAHS) and a solid phase.

[0204] Next, the solid component was extracted from the composition formed in the PTFE cylindrical sealed container as described above by filtration, dried under reduced pressure at 100°C for 1 hour, and then the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid component. As a result of this measurement, the peak top of 1740 cm was found in the IR spectrum of the component constituting the sheet before decrosslinking (the crosslinked elastomer obtained in Synthesis Example 4). －１ The absorption of isocyanurate esters in the vicinity disappears at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, confirming a shift in the peak top.

[0205] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is a reaction product of maleated HSBR and THI, underwent a hydrolysis reaction when heated with water, and the THI in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Example 10 described later, the decrosslinked elastomer obtained in Example 9 was plasticizable even at 100°C, and the sheet became moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 4, which could not be plasticized at 120°C, became plasticizable at 100°C after the decrosslinking process clearly demonstrates that the crosslinked elastomer was decrosslinked in Example 9.

[0206] (Example 10) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 7. Next, the solids were removed from this composition by filtration. This process was repeated until the amount of solids reached 50 g or more. Next, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. Then, 0.985 g of THI (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the maleated hydrogenated SBR, the raw material for the crosslinked elastomer) was added and kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0207] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0208] It is clear that the heating during such hot pressing utilizes the crosslinking agent (THI) present in the uncrosslinked composition to initiate a crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of THI and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectrum of the components constituting the obtained sheet was measured, the IR spectrum showed 1710 cm⁻¹. －１ The absorption of nearby dicarboxylic acids almost disappears, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of THI and the maleic anhydride group (i.e., it is a re-crosslinked elastomer).

[0209] (Example 11) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 5 was placed in a 100cc pressurized kneader and pulverized to prepare 20g of powdered crosslinked elastomer. Next, 20g of powdered crosslinked elastomer, 6g of water, 54g of N-methylpyrrolidone, and 3.42g of p-toluenesulfonic acid monohydrate were placed in a 100cc PTFE inner cylindrical sealed container (with a stirring bar), sealed, and heated at a heating temperature of 180°C for 10 hours to allow the decrosslinking reaction to proceed. The amount of water added to the PTFE inner cylindrical sealed container for heating was 100.7 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (THI) used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process, and also 100.7 moles per mole of maleic anhydride groups in the maleated hydrogenated SBR used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process. The mixture was then cooled to room temperature (approximately 25°C) to obtain a composition containing solids including the decrosslinked product of the crosslinked elastomer (decrosslinked elastomer) and water (components in the liquid phase). The obtained composition was separated into a liquid phase (the liquid phase described here is a phase containing water, specifically an aqueous solution containing water, N-methylpyrrolidone, and p-toluenesulfonic acid) and a solid phase.

[0210] Next, the solid component was extracted from the composition formed in the PTFE cylindrical sealed container as described above by filtration, dried under reduced pressure at 100°C for 1 hour, and then the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid component. As a result of this measurement, the peak top of 1740 cm was present in the IR spectrum of the component constituting the sheet before decrosslinking (crosslinked elastomer obtained in Synthesis Example 5). －１ The absorption of isocyanurate esters in the vicinity almost disappears at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, confirming a shift in the peak top.

[0211] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is the reaction product of maleated HSBR and THI, underwent a hydrolysis reaction upon heating with water, and the THI in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Example 12 described later, the decrosslinked elastomer obtained in Example 11 was plasticizable at 100°C, and the sheet became moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 5, which could not be plasticized at 120°C, became plasticizable at 100°C after the decrosslinking process clearly indicates that the crosslinked elastomer was decrosslinked in Example 11.

[0212] (Example 12) <Re-crosslinking process> First, a composition containing solids including the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer and water was obtained in the same manner as in Example 11. Next, the solids were removed from this composition by filtration. This process was repeated until the amount of solids reached 50 g or more. Next, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. Then, 0.665 g of THI (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the maleated hydrogenated SBR, the raw material for the crosslinked elastomer) was added and kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0213] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0214] It is clear that the heating during such hot pressing utilizes the crosslinking agent (THI) present in the uncrosslinked composition to initiate a crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated hydrogenated SBR and THI. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of THI and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectrum of the components constituting the obtained sheet was measured, the IR spectrum showed 1710 cm⁻¹. －１ The absorption of nearby dicarboxylic acids almost disappears, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since absorption of isocyanurate ester was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of THI and the maleic anhydride group (i.e., it is a re-crosslinked elastomer).

[0215] (Comparative Example 3) When 50 g of the sheet obtained in Synthesis Example 4 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the composition constituting the sheet obtained in Synthesis Example 4 cannot be plasticized at a temperature of 120°C.

[0216] (Comparative Example 4) When 50 g of the sheet obtained in Synthesis Example 5 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the composition constituting the sheet obtained in Synthesis Example 5 cannot be plasticized at a temperature of 120°C.

[0217] [Evaluation of the properties of sheets obtained in Synthesis Examples 4-5, Examples 7-12, and Comparative Examples 3-4] Using the same methods as described in "Evaluation of the properties of sheets obtained in Synthesis Example 1, Examples 1-3, and Comparative Example 1" above, the sheets obtained in Synthesis Examples 4-5, Examples 8, 10, and 12 were subjected to "confirmation of plasticization feasibility," "measurement of JIS-A hardness," and "measurement of 100% modulus (unit: MPa), 300% modulus (unit: MPa), breaking strength (unit: MPa), and breaking elongation (unit: %)." In addition, the compression set was measured for the sheets obtained in Synthesis Examples 4-5 and Examples 8, 10, and 12 as follows. These results are shown in Table 3. Note that in Comparative Examples 3-4, the materials could not be processed into sheets and only powdered material was obtained, so these measurements could not be performed on the products obtained in Comparative Examples 3-4.

[0218] <Measurement of Compression Set> The compression set (C-Set) of the sheets obtained in Synthesis Examples 4-5 and Examples 8, 10, and 12 was measured as follows. First, using the sheets obtained by employing the same method as described in each example, for each synthesis example and example to be measured, the sheets were punched out into a 29 mm diameter disc shape, seven sheets were stacked together, and a height (thickness) of 12.5 ± 0.5 mm was prepared to make a measurement sample. Next, using the obtained measurement sample and a "Vulcanized Rubber Compression Set Tester SCM-1008L" manufactured by Dumbbell Co., Ltd. as the compression device, the measurement sample was compressed by 25% using a dedicated jig, and the compression set (unit: %) after being left at 70°C for 22 hours was determined in accordance with JIS K6262 (published in 2013).

[0219]

[0220] As is clear from the results shown in Table 3, the crosslinked elastomers obtained in Synthesis Examples 4 and 5 did not plasticize at 120°C and were confirmed to turn into powder during the plasticization process at 120°C (see Comparative Examples 3 and 4). On the other hand, regarding Examples 7, 9, and 11, in Examples 7 and 9 the crosslinked elastomer obtained in Synthesis Example 4 was decrosslinked, and in Example 11 the crosslinked elastomer obtained in Synthesis Example 5 was decrosslinked. Considering the results of the confirmation of whether the elastomers obtained after decrosslinking could be plasticized (see Table 3), it was confirmed that the elastomers could be modified into a state that could be plasticized and processed by the decrosslinking process described in Examples 7, 9, and 11 (see Examples 7, 9, and 11).

[0221] Furthermore, the crosslinked elastomer (re-crosslinked product) obtained in Example 8 was obtained by de-crosslinking and then re-crosslinking the crosslinked elastomer obtained in Synthesis Example 4, the crosslinked elastomer (re-crosslinked product) obtained in Example 10 was obtained by de-crosslinking and then re-crosslinking the crosslinked elastomer obtained in Synthesis Example 4, and the crosslinked elastomer (re-crosslinked product) obtained in Example 12 was obtained by de-crosslinking and then re-crosslinking the crosslinked elastomer obtained in Synthesis Example 5. Here, it was found that the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Example 8 recovered to approximately 96% (= (50 / 52) × 100) of the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 4 (the original material), with the recovery rate being approximately 85% (= (4.0 / 4.7) × 100) of the fracture strength and approximately 98% (= {(100 - 15) / (100 - 13)} × 100) of the compression set. Furthermore, the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Example 10 were found to have recovered to approximately 98% (= (51 / 52) × 100) of the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 4 (the original material), with a recovery rate of approximately 91% (= (4.3 / 4.7) × 100) of the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 4 (the original material). Furthermore, it was found that the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Example 12 recovered to approximately 87% (= (53 / 61) × 100) of the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 5 (the original material), approximately 86% (= (18.2 / 21.2) × 100) of the fracture strength, and approximately 76% (= {(100 - 35) / (100 - 15)} × 100) of the compression set.

[0222] Thus, it was found that by subjecting the decrosslinked elastomers obtained in Examples 7, 9, and 11 to the recrosslinking process described in Examples 8, 10, and 12, respectively, it is possible to sufficiently restore the hardness, fracture strength, and compression set of the original crosslinked elastomer material (one of the crosslinked elastomers obtained in Synthesis Examples 4 and 5) before decrosslinking and recrosslinking. Therefore, it was found that according to the present invention, the covalent crosslinked portions in the crosslinked elastomer can be efficiently decrosslinked and made easily plasticizable for processing, and then recrosslinked to make it usable as a crosslinked elastomer, thus enabling efficient reuse of the crosslinked elastomer.

[0223] <Synthesis Examples 6-7, Examples 13-16 and Comparative Examples 5-6> (Synthesis Example 6) <Preparation Step for Uncrosslinked Thermoplastic Elastomer Composition> 70 g of maleated hydrogenated SBR (maleinization rate: 2.4% by mass) obtained in Synthesis Example 2 and 0.7 g of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (product name "Nocrack 6C" manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant were placed in a pressurized kneader (capacity: 100 cc) at a temperature of 60°C and kneaded for 30 seconds at a rotation speed of 50 rpm to plasticize the mixture. Subsequently, 1.18 g of benzenedimethanol (manufactured by Tokyo Chemical Co., Ltd.) (1 equivalent relative to the total number of moles of maleic anhydride groups in the composition) was added to the plasticized mixture and kneaded for 5 minutes at a temperature of 60°C and a rotation speed of 50 rpm to obtain an uncrosslinked thermoplastic elastomer composition. Furthermore, at a temperature of 60°C, the reaction between maleic anhydride groups and hydroxyl groups in benzenedimethanol generally does not proceed.

[0224] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0225] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleinated hydrogenated SBR and benzenedimethanol. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction between the hydroxyl groups of benzenedimethanol and the maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of the maleic anhydride groups.

[0226] Here, the IR spectrum of the composition constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, 1783 cm⁻¹ was found to be derived from maleic anhydride. －１ The peak was barely detectable (compared to the peak of the IR spectrum of the raw material maleinated hydrogenated SBR, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１ Since ester absorption was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of benzenedimethanol with maleic anhydride groups. As demonstrated in Comparative Example 5 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 6 did not plasticize even when kneaded at 120°C in a kneader.

[0227] (Synthesis Example 7) <Preparation Step for Uncrosslinked Thermoplastic Elastomer Composition> 50 g of maleated hydrogenated SBR (maleinization rate: 2.4% by mass) obtained in Synthesis Example 2 and 0.5 g of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (product name "Nocrack 6C" manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant were placed in a 100 cc pressurized kneader and kneaded for 2 minutes at a temperature of 180°C and a rotation speed of 50 rpm to plasticize and obtain a mixture. Then, 15 g of carbon black N339 (manufactured by Tokai Carbon Co., Ltd.) and 7.5 g of aroma oil T-DAE (manufactured by ENEOS Corporation) as a plasticizer (oil) were added to the plasticized mixture and kneaded for 8 minutes, after which the mixture was released to obtain a mixture.

[0228] Next, 71.54 g of the mixture was placed in a pressurized kneader (capacity: 100 cc) at a temperature of 60°C, and 1.159 g of benzenedimethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the composition) was added. The mixture was kneaded for 5 minutes at a temperature of 60°C and a rotation speed of 50 rpm to obtain an uncrosslinked thermoplastic elastomer composition.

[0229] <Sheet preparation process (crosslinking process by heating)> Next, using a pressure press heated to 200°C, 50 g of the thermoplastic elastomer composition obtained as described above was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. After pressurizing (hot pressing) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes, a water-cooled cooling press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The pressed composition was then removed from the mold to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0230] It is clear that the heating during such hot pressing causes a crosslinking reaction to proceed within the composition, and that the thermoplastic elastomer composition constituting the sheet contains a crosslinked elastomer which is a reaction product of maleinated hydrogenated SBR and benzenedimethanol. Furthermore, it is clear from the types of raw materials that the crosslinked sites of the obtained crosslinked elastomer include sites that crosslink via ester bonds formed by the reaction between the hydroxyl groups of benzenedimethanol and the maleic anhydride groups (covalent crosslinked sites), as well as carboxyl groups formed by ring-opening of the maleic anhydride groups.

[0231] Here, the IR spectrum of the composition constituting the obtained sheet was measured using a Fourier transform infrared spectrophotometer (FT-IR, product name "Nicolet IS10" manufactured by Thermo Scientific). In the IR spectrum, 1783 cm⁻¹ was found to be derived from maleic anhydride. －１ The peak was barely detectable (compared to the peak of the IR spectrum of the raw material maleinated hydrogenated SBR, the component constituting the sheet showed 1783 cm⁻¹). －１ The peak has almost completely disappeared), peak top 1740 cm －１ Since ester absorption was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has crosslinks formed by the reaction of hydroxyl groups of benzenedimethanol with maleic anhydride groups. As demonstrated in Comparative Example 6 described later, the composition containing the crosslinked elastomer obtained in Synthesis Example 7 did not plasticize even when kneaded at 120°C in a kneader.

[0232] (Example 13) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 6 was placed in a 100cc pressurized kneader and pulverized to prepare 20g of powdered crosslinked elastomer. Next, 20g of powdered crosslinked elastomer, 6g of water, 54g of xylene, and 0.9g of p-toluenesulfonic acid monohydrate were placed in a 100cc PTFE inner cylindrical sealed container (with a stirring bar), sealed, and heated at a heating temperature of 180°C for 6 hours to allow the decrosslinking reaction to proceed. The amount of water added to the PTFE inner cylindrical sealed container for heating was 75.9 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (benzenedimethanol) used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process, and also 75.9 moles per mole of maleic anhydride groups in the maleated hydrogenated SBR used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process. Subsequently, the mixture was cooled to room temperature (approximately 25°C) to obtain a composition consisting of a viscous liquid containing the decrosslinked product (decrosslinked elastomer) of the crosslinked elastomer.

[0233] Next, the composition (viscous liquid) formed in the PTFE cylindrical sealed container as described above was added dropwise to acetone while stirring, the solid was extracted by filtration, and after drying under reduced pressure at 100°C for 1 hour, the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid. As a result of this measurement, the peak top of 1740 cm was present in the IR spectrum of the component constituting the sheet before decrosslinking (crosslinked elastomer obtained in Synthesis Example 6). －１ The ester absorption at this position almost disappears, at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, confirming a shift in the peak top.

[0234] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is a reaction product of maleinated hydrogenated SBR and benzenedimethanol, underwent a hydrolysis reaction upon heating with water, and the benzenedimethanol in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Example 14 described later, the decrosslinked elastomer obtained in Example 13 was plasticizable even at 60°C, and the sheet was moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 6, which could not be plasticized at 120°C, became plasticizable at 60°C after the decrosslinking process, clearly demonstrates that the crosslinked elastomer was decrosslinked in Example 13.

[0235] (Example 14) <Re-crosslinking process> First, a composition consisting of a viscous liquid containing the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer was obtained in the same manner as in Example 13. Next, this composition was added dropwise to acetone with stirring, the solids were removed by filtration, and the solids were removed from the composition (viscous liquid) by vacuum drying at 100°C for 1 hour. This process was repeated until the amount of solids reached 50 g or more. Next, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 60°C and a rotation speed of 20 rpm. Then, 0.845 g of benzenedimethanol (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the maleated hydrogenated SBR, the raw material for the crosslinked elastomer) was added, and the mixture was kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0236] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0237] It is clear that the heating during this hot pressing process utilizes the crosslinking agent (benzenedimethanol) present in the uncrosslinked composition to initiate the crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated hydrogenated SBR and benzenedimethanol. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of benzenedimethanol and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectrum of the components constituting the obtained sheet was measured, the IR spectrum showed 1710 cm⁻¹. －１ The absorption of nearby dicarboxylic acids almost disappears, and the 1783 cm⁻¹ derived from maleic anhydride is also present. －１ The peak was barely visible, with a peak height of 1740 cm. －１ Since ester absorption was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl groups of benzenedimethanol and the maleic anhydride groups (i.e., it is a re-crosslinked elastomer).

[0238] (Example 15) (Decrosslinking process) A sheet containing the crosslinked elastomer obtained by the method used in Synthesis Example 7 was placed in a 100cc pressurized kneader and pulverized to prepare 20g of powdered crosslinked elastomer. Next, 20g of powdered crosslinked elastomer, 6g of water, 54g of xylene, 0.9g of p-toluenesulfonic acid monohydrate, and 0.18g of tetrabutylammonium bisulfate (TBAHS) were placed in a 100cc PTFE inner cylindrical sealed container (with a stirring bar), sealed, and heated at a heating temperature of 180°C for 6 hours to allow the decrosslinking reaction to proceed. The amount of water added to the PTFE inner cylindrical sealed container for heating was 100.7 moles per mole of functional groups (hydroxyl groups) of the crosslinking agent (1,4-benzenedimethanol) used in the production of the crosslinked elastomer (50 g) used in the decrosslinking process, and 100.7 moles per mole of maleic anhydride groups in the maleated hydrogenated SBR used in the production of the crosslinked elastomer (20 g) used in the decrosslinking process. The mixture was then cooled to room temperature (approximately 25°C) to obtain a composition consisting of a viscous liquid containing the decrosslinked product (decrosslinked elastomer) of the crosslinked elastomer.

[0239] Next, the composition formed in the PTFE cylindrical sealed container as described above was added dropwise to acetone while stirring, the solid was extracted by filtration, and after drying under reduced pressure at 100°C for 1 hour, the IR spectrum was measured using FT-IR to confirm the structure of the elastomer contained in the obtained solid. As a result of this measurement, the peak top of 1740 cm was present in the IR spectrum of the component constituting the sheet before decrosslinking (crosslinked elastomer obtained in Synthesis Example 7). －１ The absorption of esters in the vicinity disappears, at 1710 cm. －１ Absorption of nearby dicarboxylic acids was observed, confirming a shift in the peak top.

[0240] From the shift in the absorption peak in this IR spectrum, it is inferred that the crosslinked elastomer, which is the reaction product of maleated HSBR and 1,4-benzenedimethanol, underwent a hydrolysis reaction upon heating with water, and the 1,4-benzenedimethanol in the reaction product was replaced (with hydroxyl groups) by water, resulting in a decrosslinked elastomer. As demonstrated in Example 16 described later, the decrosslinked elastomer obtained in Example 15 was plasticizable at 100°C, and the sheet was moldable. Thus, the fact that the crosslinked elastomer obtained in Synthesis Example 7, which could not be plasticized at 120°C, became plasticizable at 100°C after the decrosslinking process clearly demonstrates that the crosslinked elastomer was decrosslinked in Example 15.

[0241] (Example 16) <Re-crosslinking process> First, a composition consisting of a viscous liquid containing the de-crosslinked product (de-crosslinked elastomer) of the crosslinked elastomer was obtained in the same manner as in Example 15. Next, this composition was added dropwise to acetone with stirring, the solids were removed by filtration, and the solids were removed from the composition (viscous liquid) by vacuum drying at 100°C for 1 hour. This process was repeated until the amount of solids reached 50 g or more. Next, 50 g of the obtained solids were placed in a 100 cc pressurized kneader and plasticized by kneading for 2 minutes at a temperature of 100°C and a rotation speed of 20 rpm. Then, 0.57 g of 1,4-benzenedimethanol (1.0 equivalent relative to the total number of moles of maleic anhydride groups in the maleated hydrogenated SBR, the raw material for the crosslinked elastomer) was added, and the mixture was kneaded for 5 minutes at a rotation speed of 50 rpm to prepare an uncrosslinked composition.

[0242] Next, using a pressure press heated to 200°C, 50 g of the uncrosslinked composition, plasticized as described above, was placed into a mold measuring 15 cm in length, 15 cm in width, and 2 mm in thickness. The mold was then pressurized (hot press) at a temperature of 200°C, a working pressure of 18 MPa, and a pressing time of 30 minutes. After that, a water-cooled press was performed at a working pressure of 18 MPa and a pressing time of 2 minutes. The sheet was then removed from the mold after pressing to prepare a sheet measuring 15 cm in length, 15 cm in width, and 2 mm in thickness.

[0243] It is clear that the heating during hot pressing utilizes the crosslinking agent (1,4-benzenedimethanol) present in the uncrosslinked composition to initiate the crosslinking reaction, and that the sheet contains a crosslinked elastomer with a structure similar to that of the reaction product of maleated hydrogenated SBR and 1,4-benzenedimethanol. Furthermore, it is clear that the crosslinked sites of the obtained crosslinked elastomer include sites (covalent crosslinked sites) that crosslink via ester bonds formed by the reaction between the hydroxyl groups of 1,4-benzenedimethanol and maleic acid groups or maleic anhydride groups (which may have been dehydrated by heating to become maleic anhydride groups). When the IR spectrum of the components constituting the obtained sheet was measured, the IR spectrum showed 1783 cm⁻¹, which originates from maleic anhydride. －１ No peak was observed, with a peak height of 1740 cm. －１ Since ester absorption was confirmed at a nearby location, it was found that the crosslinked elastomer in the composition has a crosslink structure similar to that formed by the reaction between the hydroxyl group of 1,4-benzenedimethanol and the maleic anhydride group (i.e., it is a re-crosslinked elastomer).

[0244] (Comparative Example 5) When 50 g of the sheet obtained in Synthesis Example 6 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the composition constituting the sheet obtained in Synthesis Example 6 cannot be plasticized at a temperature of 120°C.

[0245] (Comparative Example 6) When 50 g of the sheet obtained in Synthesis Example 7 was placed in a 100 cc pressurized kneader and kneaded for 5 minutes at a temperature of 120°C and a rotation speed of 20 rpm, it did not plasticize and turned into powder, making it impossible to mold it into a sheet. From these results, it was confirmed that the composition constituting the sheet obtained in Synthesis Example 7 cannot be plasticized at a temperature of 120°C.

[0246] [Evaluation of the properties of sheets obtained in Synthesis Examples 6-7, Examples 13-16, and Comparative Examples 5-6] Using the same methods as described in "Evaluation of the properties of sheets obtained in Synthesis Examples 4-5, Examples 7-12, and Comparative Examples 3-4" above, the sheets obtained in Synthesis Examples 6-7, Example 14, and Example 16 were subjected to the following measurements: "Confirmation of plasticization feasibility," "Measurement of JIS-A hardness," "Measurement of 100% modulus (unit: MPa), 300% modulus (unit: MPa), breaking strength (unit: MPa), and breaking elongation (unit: %)," and "Measurement of compression set." The results are shown in Table 4. Note that in Comparative Examples 5-6, the materials could not be processed into sheets and only powdered material was obtained; therefore, these measurements could not be performed on the products obtained in Comparative Examples 5-6.

[0247]

[0248] As is clear from the results shown in Table 4, it was confirmed that the crosslinked elastomers obtained in Synthesis Examples 6 and 7 did not plasticize at 120°C and turned into powder during the plasticization process at 120°C (see Comparative Examples 5 and 6). On the other hand, regarding Examples 13 and 15, in Example 13, the crosslinked elastomer obtained in Synthesis Example 6 was decrosslinked, and in Example 15, the crosslinked elastomer obtained in Synthesis Example 7 was decrosslinked. Considering the results of the confirmation of whether the elastomers obtained after decrosslinking could be plasticized (see Table 4), it was confirmed that the elastomers could be modified into a state that could be plasticized and processed by the decrosslinking process described in Examples 13 and 15 (see Examples 13 and 15).

[0249] Furthermore, the crosslinked elastomer (re-crosslinked product) obtained in Example 14 was obtained by de-crosslinking and then re-crosslinking the crosslinked elastomer obtained in Synthesis Example 6, and the crosslinked elastomer (re-crosslinked product) obtained in Example 16 was obtained by de-crosslinking and then re-crosslinking the crosslinked elastomer obtained in Synthesis Example 7. Here, it was found that the hardness, breaking strength, and compression set of the crosslinked elastomer obtained in Example 14 recovered to approximately 98% (= (42 / 43) × 100) of the hardness, breaking strength to approximately 107% (= (3.2 / 3.0) × 100) of the hardness, breaking strength to approximately 94% (= {(100 - 32) / (100 - 28)} × 100) of the compression set, based on the hardness, breaking strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 6 (original material). Furthermore, it was found that the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Example 16 recovered to approximately 87% (= (53 / 61) × 100) of the hardness, fracture strength, and compression set of the crosslinked elastomer obtained in Synthesis Example 7 (the original material), approximately 97% (= (18.1 / 18.6) × 100) of the fracture strength, and approximately 97% (= {(100-17) / (100-14)} × 100) of the compression set.

[0250] Thus, it was found that by applying the re-crosslinking process described in Examples 14 and 16 to the de-crosslinked elastomers obtained in Examples 13 and 15, it is possible to sufficiently restore the hardness, fracture strength, and compression set of the original crosslinked elastomer material (one of the crosslinked elastomers obtained in Synthesis Examples 6 and 7) before de-crosslinking and re-crosslinking. Therefore, it was found that according to the present invention, the covalent crosslinked portions in a crosslinked elastomer can be efficiently de-crosslinked and made easily plasticizable for processing, and then re-crosslinked to make it usable as a crosslinked elastomer, thus enabling efficient reuse of crosslinked elastomers.

[0251] As described above, the present invention provides a method for decrosslinking a crosslinked elastomer that efficiently decrosslinks the covalently bonded crosslinked portions in the crosslinked elastomer, enabling the reuse of the elastomeric polymer as a decrosslinked product that can be easily plasticized; a decrosslinked elastomer obtained by this method; and rubber products using the decrosslinked elastomer; as well as a method for recrosslinking a crosslinked elastomer that enables its reuse as a recrosslinked product by recrosslinking the crosslinked elastomer after decrosslinking. Therefore, the decrosslinking method of the present invention is particularly useful as a processing method when reusing crosslinked elastomers.

Claims

1. A method for decrosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B), thereby decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B).

2. The method for decrosslinking a crosslinked elastomer according to claim 1, wherein the crosslinked elastomer (A) is a reaction product of an elastomeric polymer having a cyclic acid anhydride group and a crosslinking agent having two or more functional groups in one molecule, and is a crosslinked elastomer having covalent crosslinking sites that crosslink the polymer molecules together by covalent bonds.

3. The method for decrosslinking a crosslinked elastomer according to claim 1, wherein the crosslinked elastomer (A) is an elastomeric polymer (A1) having hydrogen-bonding crosslinking sites and covalent crosslinking sites in its side chains and having a glass transition temperature of 25°C or lower.

4. A method for decrosslinking a crosslinked elastomer according to claim 1, wherein the covalent crosslinking site has at least one bond selected from the group consisting of amide, ester, urethane, urea, thiourethane, thioester, biuret, allophanate, and imide.

5. The method for decrosslinking a crosslinked elastomer according to claim 1, wherein the covalent crosslinking site has at least one bond selected from the group consisting of amides, esters, thioesters, and imides.

6. The method for decrosslinking a crosslinked elastomer according to claim 1, wherein the elastomer composition is heated under the conditions of heating temperature: 100 to 300°C and gauge pressure: 0.05 MPa or higher.

7. The method for decrosslinking a crosslinked elastomer according to claim 1, wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

8. The method for decrosslinking a crosslinked elastomer according to claim 7, wherein the organic solvent (C) is at least one selected from the group consisting of sulfolane, N-methyl-2-pyrrolidone, N,N-dimethylimidazolidone, dimethyl sulfoxide, diglyme, monoglyme, toluene, xylene, mesitylene, tetralin, naphthalene, and chlorobenzene.

9. The method for decrosslinking a crosslinked elastomer according to claim 7, wherein the catalyst (D) is at least one selected from the group consisting of an acid catalyst, a base catalyst, and a phase transfer catalyst.

10. A decrosslinked elastomer, which is a decrosslinked product of the crosslinked elastomer (A), obtained by heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B), thereby decrosslinking the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B).

11. A rubber product comprising the decrosslinked elastomer and / or crosslinked product thereof as described in claim 10.

12. A method for recrosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer composition containing a decrosslinked elastomer, and heating the decrosslinked elastomer composition, which contains a decrosslinked elastomer, in an open system or under reduced pressure conditions at a temperature of 100 to 280°C to recrosslink the decrosslinked elastomer in the decrosslinked elastomer composition.

13. The method for recrosslinking a crosslinked elastomer according to claim 12, wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

14. A method for recrosslinking a crosslinked elastomer, comprising heating an elastomer composition containing a crosslinked elastomer (A) having covalently crosslinked sites and water (B) to decrosslink the covalently crosslinked sites in the crosslinked elastomer (A) with the water (B), thereby obtaining a decrosslinked elastomer composition containing a decrosslinked elastomer, and then heating the composition in an open system or under reduced pressure conditions at a temperature above the boiling point of the water (B) to remove the water (B) present in the decrosslinked elastomer composition, and then adding a crosslinking agent to the obtained composition, which consists of a compound having at least one functional group from hydroxyl groups, thiol groups, amino groups, and imino groups in two or more molecules, thereby recrosslinking the decrosslinked elastomer with the crosslinking agent in the composition after the addition of the crosslinking agent.

15. The method for recrosslinking a crosslinked elastomer according to claim 14, wherein the elastomer composition further comprises an organic solvent (C) and a catalyst (D).

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