Resin decomposition liquid and decomposable resin composition

Abstract

To provide resin decomposition liquid which is excellent in industrial availability and practicality, and a decomposable resin composition including the same.SOLUTION: Resin decomposition liquid for decomposing a thermosetting resin cured product having a disulfide bond by cleaving the disulfide bond contains a reductant having a thiol group, a solvent having an SP value of 9.1 or more and 11.0 or less and at least one structure of a cyclic structure and a ketone structure, and a water-soluble carboxylic acid. A decomposable resin composition contains the resin decomposition liquid and a thermosetting resin cured product, wherein the thermosetting resin cured product is a cured product obtained by curing a main agent containing at least one kind selected from the group consisting of an epoxy compound and an isocyanate compound, and an amine-based curing agent having a disulfide bond.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a resin decomposing liquid that decomposes a cured thermosetting resin, and a decomposable resin composition containing the same. [Background technology]

[0002] Thermosetting resins such as epoxy resins and urea resins are generally used in a wide range of fields, including coatings, paints, primers, adhesives, and composite materials. While epoxy resins and urea resins exhibit excellent heat resistance, solvent resistance, and mechanical properties due to their crosslinked polymer network structure (crosslinked structure), their thermosetting nature makes the crosslinked structure difficult to decompose and dismantle after curing, resulting in poor recyclability and reworkability. Therefore, cured resin waste is difficult to recycle and is typically disposed of using environmentally hazardous methods such as landfilling and incineration, resulting in significant adverse effects on the entire ecosystem. To address these issues, various technologies for decomposing cured thermosetting resins and recycling the decomposed materials have been investigated.

[0003] For example, Patent Document 1 proposes an epoxy resin composition containing an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (-SS-) and a curing agent (B) capable of bonding with the epoxy groups; a cured epoxy resin obtained by curing the composition; an epoxy resin decomposable composition containing the epoxy resin monomer (A1) and a water-soluble biomolecular compound having a thiol group (-SH); and a recycled cured product obtained by curing the composition. The thiol group of the water-soluble biomolecular compound cleaves the disulfide bond in the cured epoxy resin, allowing the cured epoxy resin to be decomposed into a decomposable epoxy resin composition. Furthermore, the decomposable epoxy resin composition can be cured by heat treatment to obtain a recycled cured product. Thus, the epoxy resin composition described in Patent Document 1 allows for decomposition and recycling of the cured epoxy resin. The recycled cured product has the same mechanical strength as the cured product before recycling. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-168750 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, in Patent Document 1, when decomposing a cured epoxy resin material, a solution in which a water-soluble biomolecular compound is dissolved in an organic solvent such as chloroform is used as a resin decomposition liquid. Chloroform and other organic solvents exemplified in Patent Document 1 are toxic and hazardous substances and pose a significant burden to the human body and the environment, making them difficult to use industrially and leaving room for improvement.

[0006] Furthermore, even if a resin decomposing liquid is capable of decomposing a cured thermosetting resin, if the decomposition rate of the cured resin is slow and the decomposition takes a long time, the liquid is less practical and difficult to use industrially. Thus, although the decomposition rate is important for the practicality of a resin decomposing liquid, Patent Document 1 does not consider the decomposition rate.

[0007] The present disclosure has been made in view of the above points, and an object thereof is to provide a resin decomposing liquid that is highly industrially applicable and practical, and a decomposable resin composition containing the same. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to achieve the above-mentioned object, and have found that in a resin decomposition solution that decomposes a cured thermosetting resin having disulfide bonds (-SS-) by cleaving the disulfide bonds, industrial applicability can be ensured and the decomposition rate (in other words, practicality) can be improved by combining a reducing agent having a thiol group (-SH), a specific solvent that can dissolve the reducing agent and is easy to use industrially, and a third component.

[0009] The resin decomposing liquid of the present disclosure decomposes a cured thermosetting resin material by cleaving the disulfide bonds of the cured thermosetting resin material. The resin decomposing liquid comprises a reducing agent having a thiol group, a solvent containing an organic solvent having an SP value of 9.1 to 11.0 and having at least one structure selected from a cyclic structure and a ketone structure, and a water-soluble carboxylic acid. The resin decomposing liquid of the present disclosure may further comprise at least one amine selected from the group consisting of aromatic amines and aliphatic amines. The aromatic amine may comprise dimethylbenzylamine. The water-soluble carboxylic acid may comprise at least one selected from the group consisting of lactic acid, citric acid, and glutaric acid. The reducing agent having a thiol group may comprise glutathione. The organic solvent may comprise an alicyclic ketone. The cured thermosetting resin material may be a cured product obtained by curing a resin composition containing at least one compound selected from the group consisting of an epoxy compound and an isocyanate compound.

[0010] The decomposable resin composition of the present disclosure is a decomposable resin composition comprising the resin decomposing liquid and a cured thermosetting resin, wherein the cured thermosetting resin is a cured product obtained by curing a resin composition comprising a base agent containing at least one compound selected from the group consisting of epoxy compounds and isocyanate compounds, and an amine-based curing agent having a disulfide bond. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a resin decomposing liquid that is highly industrially applicable and practical, and a decomposable resin composition containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present embodiment will be described in detail below. The following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses. Note that each of the following components may be commercially available or synthetic.

[0013] <Resin decomposition liquid> The resin decomposition liquid according to this embodiment is a resin decomposition liquid that decomposes a cured thermosetting resin material (hereinafter also referred to as a "cured SS resin material") having disulfide bonds (-SS-) by cleaving (cutting) the disulfide bonds in the SS resin material.

[0014] The resin decomposition liquid contains three essential components: a reducing agent having a thiol group (-SH), a solvent containing a specific organic solvent, and a water-soluble carboxylic acid.

[0015] (Reducing agents having thiol groups) A reducing agent having a thiol group (hereinafter also referred to as "SH reducing agent") has the action and function of cleaving and cutting disulfide bonds. Specific examples of SH reducing agents include water-soluble biomolecular compounds such as glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT). SH reducing agents (water-soluble biomolecular compounds) may be used alone or in combination of two or more types. From the viewpoint of improving the above-mentioned action and function, SH reducing agents preferably contain glutathione.

[0016] The content of the SH reducing agent in the resin decomposition liquid (the total content of each agent when two or more types are contained) is preferably 0.05% by mass or more, more preferably 0.09% by mass or more, relative to 100% by mass of the total amount of components contained in the resin decomposition liquid, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of improving the solubility of the resin after decomposition.

[0017] Since SH reducing agents are highly soluble in water, the content of the SH reducing agent can be appropriately determined depending on the amount of water in the resin decomposition liquid (the solvent that constitutes it). In the case of a two-phase (two-phase type) resin decomposition liquid containing an organic solvent and water (organic phase and aqueous phase), the content of the SH reducing agent (the total content of each when two or more types are contained) relative to the amount of water (100 mass%) in the resin decomposition liquid is preferably 0.13 mass% or more, more preferably 0.14 mass% or more, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 3 mass% or less, more preferably 1.5 mass% or less, and even more preferably 1 mass% or less, from the viewpoint of improving the solubility of the SH reducing agent.

[0018] (solvent) The solvent has the function of dissolving the SH reducing agent and the function of dissolving the decomposed resin. The solvent includes the specific organic solvents described below. Specifically, the resin decomposition liquid may be a non-aqueous system (organic phase, single-phase type) containing only an organic solvent, or a two-phase system (two-phase type) containing an organic solvent and water (organic phase and aqueous phase). Water can improve the solubility of the SH reducing agent. Organic solvents can improve the penetration of components into the cured SS resin. Among solvents, a two-phase system (two-phase type) containing an organic solvent and water (organic phase and aqueous phase) is preferred from the viewpoint of ensuring the effects and functions of both water and organic solvents. The following solvents may be used alone or in combination of two or more types.

[0019] The organic solvent is preferably one that is easy to use industrially. Examples of such organic solvents include organic solvents having an SP value (solubility parameter) of 9.1 or more and 11.0 or less (hereinafter also referred to as a "specific SP value") and having at least one structure selected from a cyclic structure and a ketone structure. In other words, an organic solvent that is easy to use industrially may be an organic solvent that has a specific SP value and only a cyclic structure, an organic solvent that has a specific SP value and only a ketone structure, or an organic solvent that has a specific SP value and only a cyclic structure and a ketone structure (hereinafter also referred to as a "cyclic ketone structure").

[0020] The SP value of the organic solvent is 9.1 or more and 11.0 or less, preferably 9.3 or more and 10.8 or less. For the resin decomposition liquid, an organic solvent having an SP value close to the SP value of an epoxy resin (10.8) or the SP value of a urea resin (10.0) is suitable. The SP value of the organic solvent may be a value measured by the method described in the examples below, or a generally known value may be used.

[0021] Furthermore, the organic solvent preferably has a solubility in water of 0.1 g / 100 mL or more, more preferably 0.5 g / 100 mL or more, and even more preferably 0.9 g / 100 mL or more. In other words, among organic solvents, those whose SP value and solubility in water satisfy the above ranges are preferred. A resin decomposing solution containing an organic solvent that satisfies the two physical properties of SP value and solubility in water can achieve good resin decomposition (bulk decomposition). The solubility in water of the organic solvent may be a value measured by the method described in the Examples below, or a commonly known value may be used.

[0022] Specific examples of organic solvents having the above physical properties and only a cyclic structure include tetrahydrofuran (THF). Specific examples of organic solvents having the above physical properties and only a ketone structure include methyl ethyl ketone. Specific examples of organic solvents having the above physical properties and only a cyclic ketone structure include alicyclic ketones. Alicyclic ketones are ketone compounds in which two hydrocarbon groups bonded via a carbonyl group are bonded to each other to form a cyclic structure. The hydrocarbon chain forming the cyclic structure may be a saturated hydrocarbon chain or an unsaturated hydrocarbon chain, but a saturated hydrocarbon chain is preferred. Specific examples of alicyclic ketones include cyclopentanone (CPN), cyclohexanone, cycloheptanone, cyclooctanone, trimethylcyclohexanone, etc. Among organic solvents that are easily used industrially, alicyclic ketones are preferred, and cyclopentanone is more preferred.

[0023] The content of solvent in the resin decomposition liquid (the total content of each solvent if two or more types are contained) is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total amount (100% by mass) of the components contained in the resin decomposition liquid, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 95% by mass or less, from the viewpoint of improving the solubility of the components contained in the resin decomposition liquid.

[0024] In the case of a two-phase (two-phase type) resin decomposition liquid containing an organic solvent and water (organic phase and aqueous phase), the blending ratio of the organic solvent to water (organic solvent:water) is preferably 20:80 or more and 90:10 or less, more preferably 30:80 or more and 90:10 or less, from the viewpoint of improving the above-mentioned actions and functions. Note that, from the viewpoint of dissolving the resin after decomposition in the organic phase, a solvent with a high blending ratio of organic solvent (low water content) is preferred, for example, 50:50 or more and 90:10 or less.

[0025] In addition to the organic solvents that are easily industrially usable, other organic solvents may be contained within the scope of the present invention. Examples of other organic solvents include aromatic hydrocarbons, aliphatic hydrocarbons, and chlorinated aliphatic hydrocarbons. Specific examples of aromatic hydrocarbons include benzene, tert-butylbenzene, and chlorobenzene. Specific examples of aliphatic hydrocarbons include cyclohexane, n-hexane, n-pentane, and n-octane. Specific examples of chlorinated aliphatic hydrocarbons include carbon tetrachloride, dichloromethyl, and dichloroethane.

[0026] (Water-soluble carboxylic acid) Water-soluble carboxylic acids can improve the solubility of SH reducing agents and the antiseptic properties of resin decomposition solutions. They also function as a transfer catalyst (transporting SH reducing agents to the organic phase) and a pH adjuster. The water-soluble carboxylic acid is not particularly limited as long as it has a carboxyl group and an acid dissociation constant pKa (first-stage acid dissociation constant pKa1 for multiply ionized carboxylic acids) [temperature: room temperature (25°C), solvent: water] of 3 (3.0) to 4.5. Resin decomposition solutions containing water-soluble carboxylic acids with pKa (pKa1) within the above range can achieve good bulk decomposition properties and reduce damage caused by corrosion of metals (adherends). Specific examples of water-soluble carboxylic acids with pKa (pKa1) within the above range include lactic acid (pKa = 3.86), citric acid (pKa1 = 3.09), and glutaric acid (pKa1 = 4.13). Each water-soluble carboxylic acid may be used alone, or two or more types may be used in combination. From the viewpoint of improving the above-mentioned effects and functions, the water-soluble carboxylic acid preferably contains at least one of lactic acid, citric acid and glutaric acid, and more preferably contains lactic acid.

[0027] The content of the water-soluble carboxylic acid in the resin decomposition liquid (the total content of each when two or more types are contained) is preferably 0.05% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total amount of the components contained in the resin decomposition liquid, from the viewpoint of improving the above-mentioned actions and functions. The upper limit of the content is not particularly limited, and is, for example, 20% by mass or less.

[0028] (amine) In addition to the three essential components, the resin decomposition liquid may contain an amine. The amine acts and functions as a neutralizer and a catalytic converter. Specifically, the addition of an amine converts a water-soluble carboxylic acid into an amine salt, neutralizing the decomposition reaction system. This reduces corrosion damage to the metal (adherend), and the ionic liquid transports the SH reducing agent to the organic phase, accelerating the decomposition. Examples of amines include aromatic amines and aliphatic amines. In other words, the resin decomposition liquid may contain only aromatic amines, only aliphatic amines, or both aromatic and aliphatic amines as the fourth component. Examples of aromatic amines include amines having at least one monocyclic or fused aromatic ring, such as dimethylbenzylamine (BDMA). Examples of aliphatic amines include polyetherdiamine and polyoxypropylenediamine. The amines may be used alone or in combination. From the viewpoint of improving the above-mentioned effects and functions, the amine preferably contains an aromatic amine, and more preferably contains dimethylbenzylamine.

[0029] The content of amine in the resin decomposition liquid (the total content of each when two or more types are contained) may be determined appropriately depending on the content of water-soluble carboxylic acid, and from the viewpoint of improving the above-mentioned actions and functions, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to 100% by mass of the total amount of components contained in the resin decomposition liquid. The upper limit of the content may be determined appropriately depending on the content of water-soluble carboxylic acid and is not particularly limited, but from the viewpoint of suppressing a decrease in bulk decomposition ability due to an increase in the basicity of the resin decomposition liquid, it may be, for example, an amount sufficient to completely neutralize the water-soluble carboxylic acid (an amount in which the water-soluble carboxylic acid and the amine are equimolar). The upper limit of the content is, for example, 20% by mass or less.

[0030] (Other ingredients) In addition to the above three essential components and amine, the resin decomposing solution may contain a reducing agent other than the SH reducing agent (other reducing agent), a rust inhibitor, etc., within the scope of not impairing the object of the present invention. Rust inhibitors that are generally known in the art can be used.

[0031] Examples of other reducing agents include organic phosphorus compounds. Organic phosphorus compounds promote thiol-disulfide exchange reactions and act and function to re-reduce the SH reducing agent. Examples of organic phosphorus compounds include triphenylphosphine (TPP, an aromatic organic phosphorus compound having at least one monocyclic or fused aromatic ring). The other reducing agents may be used alone or in combination of two or more.

[0032] The content of other reducing agents in the resin decomposition liquid (the total content of each if two or more types are included) is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, relative to 100% by mass of the total amount of components contained in the resin decomposition liquid, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 20% by mass or less, from the viewpoint of improving the solubility of the resin after decomposition.

[0033] The resin decomposition liquid having the above-described structure can be produced by blending the above components in predetermined amounts and mixing them by a known method. The resin decomposition liquid may be non-aqueous (organic phase, one-phase type) or may be a two-phase system (two-phase type) containing an organic phase and an aqueous phase. A two-phase resin decomposition liquid may be produced, for example, by preparing a non-aqueous resin decomposition liquid and an aqueous resin decomposition liquid in advance and mixing the two liquids at a predetermined blending ratio. In this method, the blending ratio of the non-aqueous resin decomposition liquid (organic phase) to the aqueous resin decomposition liquid (aqueous phase) (non-aqueous resin decomposition liquid (organic phase):aqueous resin decomposition liquid (aqueous phase)) is, for example, about 100:5 to 100:20 (parts by mass).

[0034] The resin decomposition liquid is highly suitable for industrial use because it contains an organic solvent that is easy to use industrially as a solvent for dissolving the SH reducing agent. Furthermore, the resin decomposition liquid contains a water-soluble carboxylic acid (and, if necessary, an amine), which neutralizes the decomposition reaction system, reducing damage caused by corrosion of the adherend and surrounding objects (especially metals), and accelerating the decomposition of the cured SS resin by transporting the SH reducing agent to the organic phase. In other words, the resin decomposition liquid is also highly practical. Therefore, the resin decomposition liquid is suitable for decomposing (dismantling) the cured SS resin described below, particularly cured resins obtained by curing a resin composition containing at least one of an epoxy compound and an isocyanate compound.

[0035] The method of using the resin decomposition solution (method of decomposing a cured SS resin) is not particularly limited, and examples include contacting a cured SS resin with the resin decomposition solution by immersion, application, or the like. This method generates a decomposition reaction product, a hydroxy thiol compound containing a hydroxy group (-OH) and a thiol group (-SH), in the organic phase. For example, when a two-phase resin decomposition solution containing an organic solvent and water (organic phase and aqueous phase) is used, contacting a cured SS resin with the resin decomposition solution cleaves the dynamic disulfide bonds in the thermosetting resin through a thiol-disulfide exchange reaction and exchanges them with SH bonds of the SH reducing agent. This allows the residue of the decomposition product of the cured SS resin (the decomposable resin composition described below) to dissolve in the organic phase. Meanwhile, for example, the exchange product produced by an SH reducing agent or the like can be dissolved in the aqueous phase due to the presence of hydrophilic groups.

[0036] From the viewpoint of practicality, the viscosity of the resin decomposition liquid is preferably about 0.5 to 3 mPa·s at 25° C. The pH of the resin decomposition liquid is preferably about 4 to 9, more preferably about 6 to 8, from the viewpoint of neutralizing the system and reducing damage caused by metal corrosion.

[0037] <Cured thermosetting resin> The thermosetting resin cured product (SS resin cured product, first (before decomposition) resin cured product) according to this embodiment is a cured product obtained by curing a resin composition (adhesive, hereinafter also referred to as "SS resin composition") having disulfide bonds. The disulfide bonds of the SS resin cured product can be cleaved (cut) by a resin decomposition liquid, and the bonded structure can be easily dismantled. Therefore, the SS resin composition can be said to be an adhesive that has easy dismantling properties. In this specification, the "easy dismantling" of a resin composition (adhesive) refers to the property that the cured resin can be dismantled safely and easily (under relatively mild conditions without the use of toxic or deleterious substances) and that no adhesive residue (resin residue) remains after dismantling, or if any remains, it is minimal.

[0038] The SS resin composition contains a base agent and an amine-based curing agent having a disulfide bond. For example, the SS resin composition may contain a base agent without a disulfide bond and an amine-based curing agent having a disulfide bond, or a base agent with a disulfide bond and an amine-based curing agent having a disulfide bond. This results in a cured thermosetting resin (cured SS resin) that contains disulfide bonds when the SS resin composition is cured.

[0039] (Main ingredient) The base agent contains at least one of an epoxy compound and an isocyanate compound, which act and function as the main matrix of the SS resin composition (adhesive). In other words, the base agent may contain only an epoxy compound, only an isocyanate compound, or both an epoxy compound and an isocyanate compound as the main matrix.

[0040] The epoxy compound (main matrix) may be any known epoxy compound that is liquid or solid at room temperature, depending on the application. The epoxy compound may have a disulfide bond or may not have a disulfide bond. Examples of epoxy compounds having a disulfide bond include bis(4-glycidyloxyphenyl)disulfide [BGPDS], 1,2-bis((oxiran-2-ylmethoxy)methyl)disulfane, 1,2-bis(4-(oxiran-2-ylmethoxy)cyclohexyl)disulfane, and 1,2-bis(4-(oxiran-2-ylmethoxy)phenyl)disulfane. Examples of epoxy compounds not having a disulfide bond include bifunctional epoxy compounds containing two epoxy groups, such as bisphenol A epoxy resin, bisphenol F epoxy resin, diglycidyl ether of bisphenol A (DGEBA), ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. The epoxy compounds may be used alone or in combination of two or more. Among the epoxy compounds, aromatic epoxy compounds having at least one monocyclic or condensed aromatic ring are preferred.

[0041] The isocyanate compound (main matrix) may be any known isocyanate compound that is liquid or solid at room temperature, depending on the application. Among these, aliphatic or alicyclic isocyanate compounds are preferred from the viewpoint of pot life. Examples of such isocyanate compounds (not having a disulfide bond) include HDI (hexamethylene diisocyanate), MDI (diphenylmethane diisocyanate), TODI (4,4'-diisocyanato-3,3'-dimethylbiphenyl), and polymers thereof. Each of the isocyanate compounds may be used alone, or two or more types may be used in combination. Among isocyanate compounds, those having two or more isocyanate groups per molecule are preferred.

[0042] The content of the main matrix in the base agent (the total content of each when two or more types are included) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, relative to 100% by mass of the total amount of components included in the base agent, from the viewpoint of improving the above-mentioned actions and functions. The upper limit of the content is not particularly limited, and the base agent may be composed of only the main matrix (100% by mass), or when other components are included, from the viewpoint of improving adhesive performance, it is, for example, 90% by mass or less, 80% by mass or less.

[0043] Alternatively, a main matrix may be combined with an amine having a disulfide bond (hereinafter also referred to as "SS amine") to introduce a disulfide bond into the main matrix (to impart bulk degradability), thereby forming a base resin having a disulfide bond. Examples of SS amines include aromatic amines having a disulfide bond, which are described below as amine-based curing agents. In this case, the content of SS amine in the base resin (the total content of each when two or more types are included) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to 100% by mass of the total amount of components contained in the base resin, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 30% by mass or less, from the viewpoint of improving bulk degradability.

[0044] In addition to the main matrix (and SS amine, if necessary), the base material may contain a monofunctional epoxy compound containing one epoxy group, a coupling agent, etc., within the scope that does not impair the object of the present invention.

[0045] The monofunctional epoxy compound acts and functions to improve the decomposition rate of the cured SS resin. Examples of the monofunctional epoxy compound include aromatic epoxy compounds having at least one monocyclic or condensed aromatic ring. Examples include phenyl glycidyl ether, o-phenylphenol glycidyl ether, p-sec-butylphenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, 2,3-propylphenyl glycidyl ether, and dibromophenyl glycidyl ether.

[0046] The content of the monofunctional epoxy compound in the base resin (the total content of each compound when two or more types are included) is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of the total amount of components included in the base resin, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 10% by mass or less from the viewpoint of improving adhesive performance.

[0047] Coupling agents act to improve adhesion to adherends. Examples of coupling agents include silane coupling agents and titanate coupling agents. Examples include trimethoxysilylpropylsuccinic anhydride, 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, vinyltriethoxysilane, aminotriethoxysilane, 3-isocyanatopropyltriethoxysilane, mercaptopropyltrimethoxysilane, 5-norbornenecarboxypropyl(trimethoxy)silane, 3-methacryloxypropyltrimethoxysilane, alkoxysilyl group-containing acrylic polymers, and alkoxysilyl group-containing silicone oligomers. Each coupling agent may be used alone, or two or more types may be used in combination.

[0048] The content of coupling agent in the main agent (the total content of each when two or more types are included) is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to 100% by mass of the total amount of components contained in the main agent, from the viewpoint of improving the above-mentioned effects and functions, and is preferably 1% by mass or less from the viewpoint of improving adhesive performance.

[0049] The main component of the SS resin composition having the above-mentioned structure can be produced by blending the above-mentioned components in predetermined amounts and mixing them by a known method.

[0050] (amine-based curing agent) The amine-based curing agent has a disulfide bond. The amine-based curing agent has the effect and function of introducing a disulfide bond (imparting bulk degradability) to a resin composition (adhesive). The amine-based curing agent includes, for example, an aromatic amine having a disulfide bond and at least one monocyclic or fused aromatic ring. Examples of aromatic amines having a disulfide bond (hereinafter also referred to as "SS aromatic amines") include diamines such as 2,2'-dithiodianiline (2,2'-DTDA), 4,4'-dithiodianiline (4,4'-DTDA), cystamine, cystine dimethyl ester, and cystine diethyl ester. The SS aromatic amines may be used alone or in combination of two or more. Among the SS aromatic amines, 2,2'-dithiodianiline (2,2'-DTDA) and 4,4'-dithiodianiline (4,4'-DTDA) are more preferred.

[0051] The content of SS aromatic amine in the amine curing agent (the total content of each when two or more types are contained) is preferably 25% by mass or more, more preferably 30% by mass or more, relative to 100% by mass of the total amount of components contained in the amine curing agent, from the viewpoint of improving the bulk decomposition property of the resin decomposition liquid. The upper limit of the content is not particularly limited, and the resin may be composed solely of SS aromatic amine (100% by mass), or when other components are contained, it is, for example, 70% by mass or less, from the viewpoint of improving adhesive performance and bulk decomposition property.

[0052] The introduction rate of disulfide bonds in the SS resin composition (introduction rate, content of SS aromatic amine in the resin composition) is preferably 15% by mass or more, more preferably 35% by mass or more, relative to 100% by mass of the total amount of components contained in the SS resin composition, from the viewpoint of improving the bulk decomposition property of the resin decomposition liquid, and is preferably 50% by mass or less from the viewpoint of improving adhesive performance and bulk decomposition property.

[0053] The amine-based curing agent may contain an aromatic amine having no disulfide bond. The aromatic amine having no disulfide bond acts and functions to liquefy the amine-based curing agent. Examples of aromatic amines having no disulfide bond include diamines such as diaminodiphenylmethane (DDM), ethylenedimine, diethylenetriamine, triethylenetetramine, and norbornanediamine; and secondary amines of polyaspartic acid esters.

[0054] The amine-based curing agent may contain, in addition to the aromatic amine, a curing accelerator, a solvent, etc., to the extent that the object of the present invention is not impaired.

[0055] The curing accelerator acts to improve the curing rate of the aromatic amine. Examples of the curing accelerator include tertiary amine compounds, imidazoles, and phosphorus compounds. Examples of the tertiary amine compounds include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, triethylenediamine, and 1,8-diazabicyclo[5,4,0]-7-undecene. Examples of imidazoles include 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-ethyl-5-methylimidazole, 1-benzyl-2-methylimidazole, 1-isobutyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 2-methylimidazole azine, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-ethyl-5-methylimidazole. Examples of phosphorus-based compounds include organic phosphorus-based compounds having three organic groups, such as dicyclohexylphenylphosphine, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, cyclohexyldiphenylphosphine, triphenylphosphine, triphenylphosphine-triphenylboron complex (TPP-S), and tetraphenylphosphonium-tetraphenylborate. Each of the curing accelerators may be used alone, or two or more types may be used in combination. Among the curing accelerators, phosphorus-based compounds are preferred, and triphenylphosphine-triphenylboron complex is more preferred.

[0056] The content of the curing accelerator in the amine-based curing agent (the total content of each accelerator when two or more types are contained) is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, relative to 100% by mass of the total amount of the components contained in the amine-based curing agent, from the viewpoint of improving the above-mentioned actions and functions, and is preferably 50% by mass or less from the viewpoint of extending the pot life.

[0057] The solvent acts and functions to lower the viscosity of the amine-based curing agent. Examples of the solvent include water, alcohols, cyclic ethers, and ketones. Examples of the alcohols include methanol, ethanol, propanol, butanol, propylene glycol monomethyl ether, and benzyl alcohol. Examples of the cyclic ethers include tetrahydrofuran and dioxane. Examples of the ketones include ethyl methyl ketone, methyl isobutyl ketone, and 2-heptanone. Each of the solvents may be used alone, or two or more types may be used in combination.

[0058] The content of the solvent in the amine curing agent (the total content of each solvent when two or more types are contained) is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total amount of the components contained in the amine curing agent, from the viewpoint of improving the above-mentioned actions and functions, and is preferably 20% by mass or less from the viewpoint of improving adhesive performance.

[0059] The amine-based curing agent for the SS resin composition having the above-mentioned structure can be produced by blending the above-mentioned components in predetermined amounts and mixing them by a known method.

[0060] The method and conditions for curing the SS resin composition (obtaining a cured SS resin) are not particularly limited, and known methods and conditions can be used as appropriate. Examples include mixing the base agent and amine-based curing agent all at once or in a predetermined ratio, and then leaving the mixture to cure at room temperature (approximately 25°C) for 0.5 to 3 days with stirring as needed, or heating the mixture at 90 to 200°C for 30 minutes to 10 hours. The blending ratio of the base agent to the amine-based curing agent is not particularly limited. For example, in the case of an epoxy adhesive containing an epoxy compound in the base agent, the ratio of the number of moles of epoxy groups in the base agent to the number of moles of amino groups (-NH2) in the amine-based curing agent (molar ratio, epoxy groups / NH2) can be adjusted appropriately to approximately 1.0. In the case of an isocyanate adhesive containing an isocyanate compound in the base resin, the ratio of the number of moles of isocyanate groups (-NCO) contained in the base resin to the number of moles of amino groups (-NH2) contained in the amine curing agent (molar ratio, NCO / NH2) can be appropriately adjusted to about 1.0. In this way, a cured SS resin (cured epoxy resin, cured urea resin) can be obtained from the SS resin composition (epoxy adhesive, isocyanate adhesive).

[0061] <Degradable resin composition> The decomposable resin composition according to this embodiment contains the resin decomposition liquid and the cured SS resin (a cured product of the SS resin composition, a first (before decomposition) cured thermosetting resin). The decomposable resin composition may be such that at least one disulfide bond (-SS-) in the cured SS resin is cleaved by the action and function of the thiol group (-SH) contained in the resin decomposition liquid, resulting in decomposition and disintegration of the cured SS resin. In other words, the decomposable resin composition may contain a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH), which are decomposition reaction products.

[0062] The decomposable resin composition can be cured by heat treatment to obtain a cured resin product (a second (decomposed) thermosetting resin cured product described below). Therefore, the decomposable resin composition can be reused as a cured resin product by curing it, and an environmentally friendly recycling system can be established.

[0063] The method and conditions for curing the decomposable resin composition (to obtain a second thermosetting resin cured product) are not particularly limited, and known methods and conditions can be appropriately adopted. Examples include a method in which the decomposable resin composition (a liquid containing a hydroxythiol compound) is poured into a desired mold and left to stand at room temperature (about 25°C) for about 0.5 to 3 days to cure, and a method in which the composition is heated at about 90°C to 250°C for about 30 minutes to 10 hours.

[0064] <Second (decomposed) cured thermosetting resin> The second thermosetting resin cured product is a cured product obtained by curing the above-mentioned decomposable resin composition containing the decomposition reaction product of the first thermosetting resin cured product (SS resin cured product). The second thermosetting resin cured product has a resin network structure containing disulfide bonds (-SS-), i.e., a resin network structure common to the SS resin cured product, and therefore has mechanical strength equivalent to that of the SS resin cured product. Note that only the disulfide bonds are decomposed by the resin decomposition solution, and the other skeletal parts in the second thermosetting resin cured product, which is obtained by polymerizing these decomposition reaction products to a higher molecular weight, may have a higher molecular weight than the SS resin cured product.

[0065] The cured second thermosetting resin may contain a hydroxy thiol compound. In other words, the cured second thermosetting resin may contain unreacted thiol groups (-SH) that were not disulfidized when the decomposable resin composition was cured ... disulfidized at 2500 cm by Fourier transform infrared spectroscopy (FT-IR), for example. -1 It may also be one in which an absorption band derived from a thiol group is detected nearby.

[0066] In addition to the above components, the second thermosetting resin cured product may contain the above curing accelerators and the like to the extent that the object of the present invention is not impaired.

[0067] <Other embodiments> The first thermosetting resin cured product (SS resin cured product) and the second thermosetting resin cured product may be in the form of carbon fiber reinforced plastic (CFRP) containing carbon fiber. [Example]

[0068] The present disclosure will be described below based on examples. Note that the present disclosure is not limited to the following examples, and the following examples can be modified or changed based on the spirit of the present disclosure, and are not excluded from the scope of the present disclosure. "%" in the tables means "% by mass" unless otherwise specified.

[0069] [1. Consideration of solvent type and blending ratio] <Production of resin decomposition liquid (reference example)> A resin decomposition solution was prepared by mixing a solvent containing water and the organic solvent shown in Table 1 in the proportions shown in Table 1 with glutathione (reduced form, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; the same applies hereinafter) as a reducing agent having a thiol group and triphenylphosphine (TPP, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; the same applies hereinafter) as another reducing agent in the amounts (parts by mass) shown in Table 1. Note that blank spaces in the table indicate that no compound was added (the same applies hereinafter). Each Reference Example is a two-phase resin decomposition solution containing an organic phase and an aqueous phase (two-phase type). The physical properties of the organic solvents shown in the table are listed as commonly known values ​​for SP value and solubility in water. The glutathione content relative to the water content refers to the glutathione content (% by mass) relative to the water content (100% by mass) in the resin decomposition solution.

[0070] <Production of Resin Composition (Epoxy Adhesive)> (Main ingredient) The base resin was produced by mixing 66.7 parts by mass of JER828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation, bifunctional epoxy) and 7.4 parts by mass of DEX146 (p-tert-butylphenyl glycidyl ether, manufactured by Nagase ChemteX Corporation, monofunctional epoxy) as epoxy compounds, 25.2 parts by mass of 2,2'-DTDA (2,2'-dithiodianiline, aromatic amine having a disulfide bond), and 0.7 parts by mass of SLA-187 (glycidoxypropyltrimethoxysilane).

[0071] (amine-based curing agent) An amine-based curing agent was produced by mixing 39.1 parts by mass of KH-AA (aromatic amine, manufactured by Nippon Kayaku Co., Ltd., product name: KAYAHARD AA), 48.8 parts by mass of TPP-S (triphenylphosphine triphenylborate, manufactured by Hokko Chemical Co., Ltd.), and 12.1 parts by mass of BENA (benzyl alcohol).

[0072] (Resin composition) Finally, the amine-based curing agent and the main component (epoxy compound) were blended so that the ratio of the number of moles of epoxy groups in the main component to the number of moles of amino groups (-NH2) contained in the amine-based curing agent (molar ratio, epoxy groups / NH2) was 1.0, and the two components were mixed to obtain a resin composition (epoxy adhesive) containing the main component and the amine-based curing agent and having disulfide bonds.

[0073] <Evaluation of resin decomposition solution> (Bulk degradability) The resulting resin composition was heated at 160°C for 1 hour to cure, yielding a cured thermosetting resin having disulfide bonds (cured epoxy resin, bulk). 50 mg of the bulk was immersed in 3 g of each resin decomposition solution, heated to 60°C, and stirred at 300 rpm. The bulk was then visually inspected and the time (maximum 24 hours) until the bulk was completely dissolved in the resin decomposition solution was measured. Bulk decomposition was evaluated according to the following evaluation criteria. The results are shown in Table 1. A score of 2 or higher was considered acceptable for bulk decomposition.

[0074] (Bulk degradability evaluation criteria) 5 points: Completely dissolved within 3 hours (no resin residue was found, same below) (passed). 4 points: Completely dissolved within more than 3 hours and within 6 hours (passed). 3 points: Completely dissolved within 10 hours but over 6 hours (passed). 2 points: Completely dissolved within 24 hours but over 10 hours (passed). 1 point: Not completely dissolved within 24 hours (bulk (resin residue) was observed) (failure).

[0075] [Table 1]

[0076] <Discussion of Table 1> Comparison of Reference Examples 1 to 6 confirmed that, among organic solvents having a cyclic structure, a ketone structure, or both, resin decomposition solutions containing organic solvents having physical properties such as an SP value of 9.1 or more and 11.0 or less and / or a solubility in water of 0.1 g / 100 mL or more can achieve good bulk decomposition properties. Comparison of Reference Examples 6 to 14 confirmed that good bulk decomposition properties could be obtained by setting the blending ratio of organic solvent to water (organic solvent:water) in the range of 20:80 or more and 90:10 or less.

[0077] [2. Examination of the effects of adding carboxylic acids and amines] <Production of Resin Decomposition Solution (Example)> A two-phase (two-phase type) resin decomposition liquid containing an organic phase and an aqueous phase was produced by mixing a solvent containing water and cyclopentanone (CPN) in the proportions shown in Table 2, glutathione as a reducing agent having a thiol group, TPP as another reducing agent, a water-soluble carboxylic acid shown in Table 2, and an amine shown in Table 2 in the amounts (parts by mass) shown in Table 2, respectively.

[0078] The pH of the resin decomposition liquid shown in the table means the pH measured at room temperature (25°C) before the evaluation of bulk decomposition ability (after the preparation of the resin decomposition liquid). The amines listed in Table 2 are shown below. · BDMA: Dimethylbenzylamine (aromatic amine). D230: Manufactured by HUNTSMAN, product name: JEFFAMINE (registered trademark) D-230, polyether diamine, polyoxypropylene diamine (aliphatic amine).

[0079] <Evaluation of resin decomposition solution> A resin composition (epoxy adhesive) was produced in the same manner as above, and the bulk decomposition property of the resin decomposition liquid was evaluated using the obtained resin composition in the same manner as above. The evaluation results are shown in Table 2.

[0080] [Table 2]

[0081] <Discussion of Table 2> A comparison of Comparative Example 1 with Examples 1 to 6 confirmed that the decomposition rate (in other words, practicality) of the resin decomposition liquid was improved when water-soluble carboxylic acid was further included. A comparison of Example 1 with Examples 7 and 8 confirmed that a fast decomposition rate was maintained even when an amine was further added to adjust the pH of the resin decomposition solution to a value close to neutral. Furthermore, in Examples 7 and 8, the decomposition reaction system was neutralized, which is expected to reduce damage caused by corrosion of the adherend and surrounding objects (especially metals).

[0082] [3. Confirmation of bulk decomposition of cured urea resin (bulk)] <Production of Resin Decomposition Solution (Example)> In the same manner as in Example 9 shown in Table 2, a non-aqueous (organic phase, one-phase type) resin decomposition liquid (9) was produced.

[0083] <Production of Resin Composition (Isocyanate-Based Adhesive)> (Main ingredient) The isocyanate compound used as the base was XF800 [HDI (hexamethylene diisocyanate) modified polyisocyanate (aliphatic), a mixture of HDI oligomer and HDI-based polyisocyanate, manufactured by Vencorex, product name: Tolonate XF800] weighed out in the amount (parts by mass) shown in Table 3.

[0084] (amine-based curing agent) 2,2'-DTDA (2,2'-dithiodianiline, an aromatic amine having a disulfide bond) or F420 (a secondary amine of polyaspartic acid ester, manufactured by Feiyang Co., Ltd., product name: FEISPARTICF420) was weighed out in the amounts (parts by mass) shown in Table 3, or a mixture of both in the amounts (parts by mass) shown in Table 3 was used as the amine-based curing agent.

[0085] (Resin composition) Finally, the two were blended and mixed so that the ratio (molar ratio, NCO / NH2) of the number of moles of isocyanate groups (-NCO) in the main component (isocyanate compound) to the number of moles of amino groups (-NH2) contained in the amine curing agent was 1.0, thereby obtaining resin compositions (isocyanate adhesives) No. 1 to No. 6 containing the main component and the amine curing agent.

[0086] The Tg (DSC method) of the resin compositions shown in the tables was measured using an X-DSC7000 manufactured by Hitachi High-Tech Science Corporation under measurement temperature conditions of 25°C to 200°C with a temperature increase rate of 16°C / min. The amount of 2,2'-DTDA in the amine curing agent refers to the content (mass%) of 2,2'-DTDA relative to 100% by mass of the total amount of components contained in the amine curing agent. The introduction rate (introduction rate) of S-S bonds in the resin composition refers to the content (mass%) of 2,2'-DTDA relative to 100% by mass of the total amount of components contained in the resin composition.

[0087] <Evaluation of resin decomposition solution> (Bulk degradability) The resulting resin composition was allowed to stand at 25°C for 24 hours to cure, yielding a cured thermosetting resin having disulfide bonds (cured urea resin, bulk). 50 mg of the bulk was immersed in 3 g of resin decomposition liquid (9), heated to 60°C, and stirred at 300 rpm. The bulk was then visually inspected and the time (maximum 24 hours) until the bulk was completely dissolved in the resin decomposition liquid (9) was measured. Bulk decomposition was evaluated according to the above evaluation criteria. The results are shown in Table 3. A score of 2 or higher was considered acceptable for bulk decomposition.

[0088] [Table 3]

[0089] <Discussion of Table 3> A comparison of isocyanate adhesive No. 1 with Nos. 2 to 5 confirmed that resin decomposition liquid (9) exhibited good bulk decomposition properties for the bulk into which SS bonds had been introduced. Comparing No. 2 to No. 5 and No. 6, which are isocyanate-based adhesives, it was confirmed that the resin decomposing solution (9) exhibits good bulk decomposition properties for bulks in which the introduction ratio of SS bonds is, for example, 15% by mass or more.

[0090] (summary) The resin decomposition liquid of the present disclosure contains a reducing agent having a thiol group, a specific solvent that can dissolve the reducing agent and is easy to use industrially, and a water-soluble carboxylic acid. As a result, it has good bulk decomposition properties for cured resins such as epoxy adhesives and isocyanate adhesives, which are thermosetting resins having disulfide bonds, and is therefore highly suitable for industrial use. The resin decomposing solution of the present disclosure decomposes the above-mentioned cured resin within 24 hours (preferably within 10 hours, more preferably within 6 hours, and even more preferably within 3 hours), and is therefore highly practical. [Industrial Applicability]

[0091] As described above, the present disclosure is suitable for a resin decomposing liquid that decomposes a cured thermosetting resin having a disulfide bond.

Claims

1. A resin decomposing liquid that decomposes a cured thermosetting resin material by cleaving disulfide bonds in the cured thermosetting resin material, the resin decomposing liquid comprising: A resin decomposition liquid characterized by comprising a reducing agent having a thiol group, a solvent containing an organic solvent having an SP value of 9.1 or more and 11.0 or less and having at least one structure selected from a cyclic structure and a ketone structure, and a water-soluble carboxylic acid.

2. 2. The resin decomposing solution according to claim 1, further comprising at least one amine selected from the group consisting of aromatic amines and aliphatic amines.

3. 3. The resin decomposing solution according to claim 2, wherein the aromatic amine includes dimethylbenzylamine.

4. 2. The resin decomposing solution according to claim 1, wherein the water-soluble carboxylic acid includes at least one selected from the group consisting of lactic acid, citric acid, and glutaric acid.

5. 2. The resin decomposing solution according to claim 1, wherein the reducing agent having a thiol group includes glutathione.

6. 2. The resin decomposing solution according to claim 1, wherein the organic solvent contains an alicyclic ketone.

7. The resin decomposing liquid according to claim 1, wherein the thermosetting resin cured product is a cured product obtained by curing a resin composition containing at least one compound selected from the group consisting of an epoxy compound and an isocyanate compound.

8. A decomposable resin composition comprising the resin decomposing liquid according to any one of claims 1 to 7 and a cured thermosetting resin, The decomposable resin composition is characterized in that the thermosetting resin cured product is a cured product obtained by curing a resin composition containing a base agent containing at least one selected from the group consisting of epoxy compounds and isocyanate compounds, and an amine-based curing agent having a disulfide bond.

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