Decomposition liquid of thermosetting resin and decomposition treatment method

Abstract

A decomposition liquid of a thermosetting resin according to the present disclosure comprises an alkali metal salt (A), a bicyclic amidine (B), and an organic solvent (Y), wherein: the ratio of the alkali metal salt (A) to the alkali metal salt (A) and the bicyclic amidine (B) is 20-70 mass% inclusive; and the ratio of the alkali metal salt (A) and the bicyclic amidine (B) to the alkali metal salt (A), the bicyclic amidine (B), and the organic solvent (Y) is 4-25 mass % inclusive.

Description

Thermosetting resin decomposition solution and decomposition treatment method

[0001] The present disclosure relates to a decomposition solution and a decomposition method for a thermosetting resin.

[0002] Thermosetting resins containing ester bonds include acid anhydride-cured epoxy resins and unsaturated polyester resins. As shown in Prior Art Documents 1 and 2, methods for chemically decomposing thermosetting or thermoplastic resins containing ester bonds include a method using an organic solvent and a basic inorganic compound or a basic organic compound as a decomposition liquid.

[0003] JP 2019-44100 A JP 2013-91727 A

[0004] However, prior art documents 1 and 2 do not make any detailed mention of the effects of the solvent and catalyst, or the combination and amount of catalysts added, on the decomposition behavior and decomposition rate. When these methods are used, the decomposition takes time, and therefore there is a problem in that it is necessary to shorten the decomposition time by taking advantage of the properties of the catalyst.

[0005] The present disclosure discloses a technique for solving the above-described problems, and aims to provide a thermosetting resin decomposition solution and a decomposition treatment method that can efficiently decompose a thermosetting resin containing an ester bond.

[0006] The decomposition liquid for a thermosetting resin according to the present disclosure comprises an alkali metal salt, a bicyclic amidine, and an organic solvent, and is characterized in that the ratio of the alkali metal salt to the alkali metal salt and the bicyclic amidine is 20% by mass or more and 70% by mass or less, and the ratio of the alkali metal salt and the bicyclic amidine to the alkali metal salt, the bicyclic amidine, and the organic solvent is 4% by mass or more and 25% by mass or less.

[0007] The method for decomposing a thermosetting resin according to the present disclosure includes the steps of: mixing an alkali metal salt, a bicyclic amidine, and an organic solvent; heating the mixed decomposition liquid at atmospheric pressure to a temperature higher than 100°C and equal to or lower than 200°C; and decomposing a thermosetting resin by contacting the decomposition liquid with the decomposition liquid, wherein the ratio of the alkali metal salt to the alkali metal salt and the bicyclic amidine is 20% by mass or more and 70% by mass or less, and the ratio of the alkali metal salt and the bicyclic amidine to the alkali metal salt, the bicyclic amidine, and the organic solvent is 4% by mass or more and 25% by mass or less.

[0008] According to the present disclosure, thermosetting resins can be efficiently decomposed under mild conditions.

[0009] 10 is a diagram showing the relationship between the decomposition residual rate of the decomposition liquid of the thermosetting resin and the relative time according to the first embodiment; FIG.

[0010] Embodiment 1. A decomposition liquid for a thermosetting resin according to embodiment 1 of the present disclosure is used mainly for a thermosetting resin containing an ester bond, and is composed of a composition including an alkali metal salt (A), a bicyclic amidine (B), and an organic solvent (Y).

[0011] 1 is a graph showing the relationship between the decomposition residual rate and the relative time for each composition of the decomposition solution for a thermosetting resin. Line I represents the decomposition residual rate for a thermosetting resin decomposition solution containing benzyl alcohol (BzOH) as the organic solvent (Y) and tripotassium phosphate (K phosphate), which is an alkali metal salt (A), as the catalyst. ３ P.O. ４ ) was used, and 4 parts by mass of K ３ P.O. ４ The graph shows the weight residual percentage (%) of the cured resin over time when the cured resin is decomposed using a decomposition solution containing 4 parts by mass of K. When the catalyst contains only alkali metal salt (A), the cured resin is effectively decomposed in the early stages of decomposition, but the decomposition rate decreases over time, and the decomposition rate becomes slower as the amount of resin remaining in the cured resin decreases. ３ P.O. ４ The time taken for the cured resin to be decomposed and disappear by the -BzOH decomposition solution was defined as 1, and the evaluation was made in terms of relative time.

[0012] Lines II and III show the results of decomposition treatment of a cured material using a decomposition solution containing only 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU (registered trademark)) blended with the bicyclic amidine (B) catalyst. Line II shows the results of decomposition treatment of a cured material using a decomposition solution containing 4 parts by mass of DBU, and line III shows the results of decomposition treatment of a cured material using a decomposition solution containing 6 parts by mass of DBU. Although the initial decomposition rate of bicyclic amidine (B) is not as high as that of the alkali metal salt (A) catalyst, decomposition progresses at a constant rate and ultimately takes a shorter time than that of the alkali metal salt (A), with line III showing a relative value of 0.7.

[0013] Thus, the alkali metal salt (A) is particularly effective in the initial decomposition, while the bicyclic amidine (B) decomposes at a constant rate. We have found that by optimizing the combination of the alkali metal salt (A) and the bicyclic amidine (B) and their blending ratio, we can take advantage of the characteristics of each catalyst and improve the decomposition rate of the cured resin material.

[0014] That is, by forming a decomposition liquid that combines an alkali metal salt (A) and a bicyclic amidine (B) as catalysts, the decomposition reaction proceeds rapidly in the initial stage in accordance with the decomposition behavior of the alkali metal salt (A), while the decomposition rate does not decrease due to the effect of the bicyclic amidine (B). This makes it possible to shorten the decomposition treatment time, as shown by lines IV and V in Figure 1. Line IV shows the results of decomposition treatment of a cured material using a decomposition liquid containing 1 part by mass of DBU, and line III shows the results of decomposition treatment of a cured material using a decomposition liquid containing 3 parts by mass of DBU.

[0015] <Alkali Metal Salt> Examples of the alkali metal salt (A) include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, calcium hydroxide, barium hydroxide, rubidium hydroxide, and cesium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and barium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, alkali metal phosphates such as tripotassium phosphate, trisodium phosphate, potassium pyrophosphate, sodium pyrophosphate, potassium tripolyphosphate, sodium tripolyphosphate, and sodium tetrapolyphosphate, alkali metal silicates such as sodium orthosilicate, sodium metasilicate, and potassium silicate, and ammonia. As the alkali metal salt (A) in the present decomposition liquid, one type can be used alone, or two or more types can be used in combination.

[0016] <Bicyclic amidines> Examples of bicyclic amidines (B) include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), 3,3,6,9,9-pentamethyl-2,10-diazabicyclo[4.4.0]dec-1-ene, etc. As the bicyclic amidine (B) in the present decomposition liquid, one type can be used alone, or two or more types can be used in combination.

[0017] <Organic Solvent> The organic solvent (Y) preferably has a boiling point of 170°C or higher in order to suppress volatilization of the solvent during decomposition treatment. Furthermore, since the decomposition proceeds by cleaving the ester bonds in the resin and causing an exchange reaction with the hydroxyl groups in the solvent, the organic solvent is preferably a compound having one or more hydroxyl groups. Examples of alcohols include monohydric alcohols such as benzyl alcohol, diethylene glycol monomethyl ether, and diethylene glycol monobutyl ether; dihydric alcohols such as ethylene glycol, diethylene glycol, and propylene glycol; and polyhydric alcohols such as glycerin. The organic solvent (Y) in the decomposition liquid can be used alone or in combination of two or more.

[0018] In the thermosetting resin decomposition liquid according to the first embodiment of the present disclosure, the proportion of the alkali metal salt (A) in the alkali metal salt (A) and bicyclic amidine (B) is 20% by mass or more and 70% by mass or less. More preferably, it is 20% by mass or more and 50% by mass or less. If the proportion of the alkali metal salt (A) is less than 20% by mass, the initial decomposition rate decreases, and there is no difference in decomposition time compared to when only the bicyclic amidine (B) is used. If the proportion is more than 70% by mass, the effect of the bicyclic amidine (B) is not observed, and there is no significant difference compared to when only the alkali metal salt (A) is used. Furthermore, the proportion of the alkali metal salt (A) and bicyclic amidine (B) in the alkali metal salt (A), bicyclic amidine (B), and organic solvent (Y) is 4% by mass or more, more preferably 4% by mass or more and 25% by mass or less. Within this range, a homogeneous decomposition liquid is obtained, and the decomposition power for thermosetting resins is enhanced, thereby shortening the processing time.

[0019] <Additives> The thermosetting resin decomposition liquid of the present disclosure may contain other additives as needed. The additives are not particularly limited, and examples thereof include surfactants, antioxidants, rust inhibitors, viscosity modifiers, and antifoaming agents.

[0020] Next, a description will be given of a method for decomposing a thermosetting resin according to the first embodiment of the present disclosure. The method for decomposing a thermosetting resin according to the present disclosure includes the steps of mixing a decomposition liquid containing an alkali metal salt (A), a bicyclic amidine (B), and an organic solvent (Y) within the above-mentioned blending ratio range so as not to contain water, heating the mixed decomposition liquid at atmospheric pressure to a temperature exceeding 100°C and not exceeding 200°C, and bringing a thermosetting resin containing an ester bond into contact with the decomposition liquid to decompose it.

[0021] In the step of heating the mixed decomposition liquid at atmospheric pressure from more than 100°C to 200°C or less, the heating temperature is preferably equal to or higher than the glass transition temperature (Tg) of the cured product in order to rapidly promote decomposition, and is preferably equal to or lower than the boiling point of the organic solvent (Y) used in order to suppress volatilization of the organic solvent (Y). Furthermore, in order to achieve uniform and rapid mixing, heating may be performed while stirring using a stirrer.

[0022] In the step of decomposing a thermosetting resin containing an ester bond by contacting it with a decomposition liquid, the decomposition may be carried out while stirring using a stirrer to rapidly progress the decomposition. By carrying out the decomposition while stirring, the temperature of the decomposition liquid can be made uniform. Furthermore, convection in the decomposition liquid can physically remove post-decomposition deposits attached to the surface of the thermosetting resin to be decomposed.

[0023] In the method for decomposing a thermosetting resin disclosed herein, the step of decomposing a thermosetting resin containing an ester bond by contacting it with a decomposition liquid includes a step of contacting a resin product or part embedded with a thermosetting resin containing an ester bond with the decomposition liquid. In the step of contacting a resin product or part embedded with a thermosetting resin containing an ester bond with the decomposition liquid, the thermosetting resin containing an ester bond is decomposed and removed or peeled off from the resin product or part. The method for contacting a resin product or part embedded with a thermosetting resin with the decomposition liquid is not particularly limited, and preferred are immersing the resin product or part in the decomposition liquid or spraying the decomposition liquid onto the resin product or part.

[0024] Examples of thermosetting resins containing ester bonds that are decomposition targets include acid anhydride-cured epoxy resins and unsaturated polyester resins. The thermosetting resins can be used singly or in combination of two or more. When at least one thermosetting resin containing an ester bond is included, decomposition can proceed starting from the thermosetting resin containing an ester bond, so a thermosetting resin that does not contain an ester bond may also be included. Examples of thermosetting resins that do not contain ester bonds include amine-cured epoxy resins, phenol-cured epoxy resins, phenolic resins, melamine resins, polyimide resins, and polyamide resins.

[0025] The thermosetting resin containing an ester bond may contain an inorganic material, which is not particularly limited, but may include metal oxide particles such as aluminum oxide, zinc oxide, indium tin oxide, magnesium oxide, beryllium oxide, and titanium oxide, metal nitride particles such as boron nitride, silicon nitride, and aluminum nitride, carbon compound particles such as silicon carbide, graphite, diamond, amorphous carbon, carbon black, and carbon fiber, and silica compound powders such as quartz and quartz glass.

[0026] The thermosetting resin containing an ester bond may be a sealing resin used in motors and power modules. The thermosetting resin decomposition solution disclosed herein does not contain water, which can prevent metal ionization. Therefore, when products using sealing resins, such as motors and power modules, are decomposed using this decomposition solution, valuable materials such as embedded metals can be recovered without degradation.

[0027] As described above, the thermosetting resin decomposition liquid according to the first embodiment contains an alkali metal salt (A), a bicyclic amidine (B), and an organic solvent (Y), and the ratio of the alkali metal salt (A) to the alkali metal salt (A) and the bicyclic amidine (B) is 20% by mass or more and 70% by mass or less, and the ratio of the alkali metal salt (A) and the bicyclic amidine (B) to the alkali metal salt (A), the bicyclic amidine (B), and the organic solvent (Y) is 4% by mass or more and 25% by mass or less. Therefore, by obtaining a uniform decomposition liquid, the decomposition power for thermosetting resins is increased and the processing time is shortened, and therefore the thermosetting resin can be efficiently decomposed under mild conditions.

[0028] Hereinafter, the present disclosure will be described in detail with reference to examples and comparative examples, but the present disclosure is not limited thereto.

[0029] Preparation of Thermosetting Resin Containing Ester Bonds: A liquid acid anhydride curing agent (HN2000, manufactured by Resonac) was added to a liquid bisphenol A epoxy resin (jER828US, manufactured by Mitsubishi Chemical Corporation) and stirred until dissolved to obtain a resin composition. This resin composition was heated at 130°C for 5 hours, 150°C for 5 hours, and 180°C for 5 hours to obtain a cured product.

[0030] <Decomposition Test> The prepared cured product was cut into 10 mm squares (10 x 10 x 1 mm) and immersed in 10 g of decomposition liquid to conduct a decomposition test. A decomposition liquid containing an alkali metal salt (A) and a bicyclic amidine (B) as catalysts and an organic solvent (Y) as solvent was prepared, and a sample tube containing the decomposition liquid was heated in an oil bath heated to 120°C. A 10 mm square resin piece whose weight had been measured in advance was placed in the heated sample tube and decomposed while being heated in an oil bath at 120°C.

[0031] The resin pieces treated for a certain period of time were collected from the sample tube and dried under reduced pressure at 120°C for 16 hours. The weight of the resin pieces after decomposition treatment was measured. The weight residual ratio of the resin pieces after treatment for a certain period of time was calculated from the weights of the resin pieces before and after decomposition. The decomposition time was determined by calculating the weight residual ratio of the sample after different treatment times.

[0032] Table 1 shows the blending ratios and decomposition characteristics of the decomposition liquids used in Examples 1 to 7 and Comparative Examples 1 to 10. Here, the amount of alkali metal salt (A) added in the total catalyst [mass %] = A / (A+B) × 100 was defined as Wa, and the amount of catalyst added in the total decomposition liquid [mass %] = (A+B) / (A+B+Y) × 100 was defined as Wb.

[0033]

[0034] <Preparation of Decomposition Solution> (Example 1) BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 1 part by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 3 parts by mass of the above with respect to the total weight of DBU.

[0035] (Example 2) BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 3 parts by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 3 parts by mass of the above with respect to the total weight of DBU.

[0036] (Example 3) BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 7 parts by mass based on the total weight of BzOH and K ３ P.O. ４A decomposition liquid was prepared by mixing 3 parts by mass of the above with respect to the total weight of DBU.

[0037] (Example 4) BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 3 parts by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 10 parts by mass of the compound and DBU with respect to the total weight of the compound.

[0038] (Example 5) BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using TBD as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and 1 part by mass based on the total weight of TBD, and the amount of TBD blended was BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 3 parts by mass of the hydroxybenzoate and TBD with respect to the total weight of the hydroxybenzoate and TBD.

[0039] (Example 6) BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using TBD as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and 3 parts by mass based on the total weight of TBD, and the amount of TBD blended was BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 3 parts by mass of the hydroxybenzoate and TBD with respect to the total weight of the hydroxybenzoate and TBD.

[0040] (Example 7) BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU and TBD as catalytic bicyclic amidines (B),３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and 3 parts by mass based on the total weight of DBU and TBD, and the amount of DBU blended was BzOH and K ３ P.O. ４ and 3 parts by mass based on the total weight of DBU and TBD, and the amount of TBD blended was BzOH and K ３ P.O. ４ A decomposition liquid was prepared by blending 3 parts by mass of DBU and TBD with 3 parts by mass of DBU and TBD in total.

[0041] Comparative Example 1: BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using K ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 4 parts by mass of the above with respect to the total weight of the above.

[0042] Comparative Example 2: BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using K ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 6 parts by mass of the above with respect to the total weight of the above.

[0043] Comparative Example 3: BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using K ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 13 parts by mass of the above with respect to the total weight of the above.

[0044] Comparative Example 4 A decomposition liquid was prepared using BzOH as the organic solvent (Y) and DBU as the bicyclic amidine catalyst (B) in an amount of 4 parts by mass of DBU based on the total weight of BzOH and DBU.

[0045] Comparative Example 5 A decomposition liquid was prepared using BzOH as the organic solvent (Y) and DBU as the bicyclic amidine catalyst (B) in an amount of 6 parts by mass of DBU based on the total weight of BzOH and DBU.

[0046] Comparative Example 6 A decomposition liquid was prepared using BzOH as the organic solvent (Y) and DBU as the bicyclic amidine catalyst (B) in an amount of 13 parts by mass of DBU based on the total weight of BzOH and DBU.

[0047] Comparative Example 7 A decomposition liquid was prepared using BzOH as the organic solvent (Y) and DBU as the bicyclic amidine catalyst (B) in an amount of 23 parts by mass of DBU based on the total weight of BzOH and DBU.

[0048] Comparative Example 8: BzOH was used as the organic solvent (Y) and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 0.5 parts by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 4 parts by mass of the above with respect to the total weight of DBU.

[0049] Comparative Example 9: BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４ Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 1 part by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 2 parts by mass of the above with respect to the total weight of DBU.

[0050] Comparative Example 10: BzOH was used as the organic solvent (Y), and K was used as the alkali metal salt of the catalyst (A). ３ P.O. ４Using DBU as the catalytic bicyclic amidine (B), ３ P.O. ４ The amount of BzOH and K ３ P.O. ４ and DBU, and the amount of DBU blended was 6 parts by mass based on the total weight of BzOH and K ３ P.O. ４ A decomposition liquid was prepared by mixing 2 parts by mass of the above with respect to the total weight of DBU.

[0051] Example 1 is a mixed catalyst, and by combining an initially effective catalyst (alkali metal salt (A)) and a catalyst (bicyclic amidine (B)) that allows linear decomposition, the alkali metal salt (A) improves the initial decomposition rate, and the bicyclic amidine (B) allows linear decomposition to proceed until the end of decomposition, as shown by line IV in Figure 1. ３ P.O. ４ The decomposition time is 0.64 times longer than that of Comparative Example 1, in which the simple substance is used as a catalyst and the total catalyst amount Wb in the decomposition solution is the same.

[0052] Similarly, the decomposition time was 0.77 times longer than that of Comparative Example 4, which uses DBU alone as the catalyst for the bicyclic amidine (B) and has the same total catalyst amount Wb in the decomposition solution. Although Example 1 has a Wb of 4 mass%, the decomposition time (0.64 relative to Comparative Example 1) is equivalent to the decomposition times of Comparative Example 6, in which the Wb is 13 mass%, and Comparative Example 7, in which the Wb is 23 mass% (0.67 and 0.62 relative to Comparative Example 1, respectively), demonstrating that the decomposition reaction can be accelerated with a small amount of catalyst.

[0053] Example 2 is a mixed catalyst, and as shown by line V in Figure 1, the decomposition time is 0.57 times that of Comparative Example 1. Furthermore, the decomposition time of Example 2 (0.57 times that of Comparative Example 1) is improved over the decomposition time of Comparative Example 2 (0.95 times that of Comparative Example 1) in which only alkali metal salt (A) was blended, and the decomposition time of Comparative Example 5 (0.71 times that of Comparative Example 1) in which only bicyclic amidine (B) was blended, both of which had the same total catalyst amount Wb. The decomposition time of Example 2 is 0.60 times that of Comparative Example 2 and 0.80 times that of Comparative Example 5.

[0054] Example 3 is a mixed catalyst, and the decomposition time is 0.52 times that of Comparative Example 1.

[0055] Example 4 is a mixed catalyst, and the decomposition time is 0.45 times that of Comparative Example 1. The decomposition time of Example 4 (0.45 times that of Comparative Example 1) is also improved over the decomposition time of Comparative Example 3 (0.94 times that of Comparative Example 1) in which only alkali metal salt (A) was blended, and the decomposition time of Comparative Example 6 (0.67 times that of Comparative Example 1) in which only bicyclic amidine (B) was blended, both of which had the same total catalyst amount Wb. The decomposition time of Example 4 is 0.48 times that of Comparative Example 3 and 0.67 times that of Comparative Example 6.

[0056] In Examples 5 and 6, the catalyst for bicyclic amidine (B) was changed from DBU to TBD, and the decomposition time was shortened by 0.38 times in Example 5 compared to Comparative Example 1, and by 0.38 times in Example 6 compared to Comparative Example 2, which is more effective than DBU in shortening the decomposition time.

[0057] In Example 7, DBU and TBD are used in combination as a catalyst for the bicyclic amidine (B), and the decomposition can proceed in a shorter time even when Wb is low compared to Example 4. Therefore, it is also effective to combine multiple types of catalysts for the alkali metal salt (A) and / or the bicyclic amidine (B).

[0058] K, which is an alkali metal salt (A) ３ P.O. ４ In Comparative Examples 1 to 3, in which a simple substance was used as a catalyst, the catalyst was effective in the initial stage of decomposition, but the decomposition rate decreased as the decomposition progressed. In Comparative Examples 2 and 3, in which the total catalyst amount Wb in the decomposition solution was increased compared to Comparative Example 1, the decomposition time was shortened, but the difference between Comparative Examples 2 and 3 was small, and the effect decreased once a certain amount was exceeded.

[0059] In Comparative Examples 4 to 7, in which DBU, a bicyclic amidine (B), was used as a catalyst, resin decomposition proceeded linearly. In Comparative Examples 5 to 7, in which the total catalyst amount Wb in the decomposition solution was increased compared to Comparative Example 4, the decomposition time was shortened. The difference in the total catalyst amount Wb between Comparative Example 5 and Comparative Example 4 was 2% by mass, but the decomposition time was shortened by 0.86 times. On the other hand, the difference in the total catalyst amount Wb between Comparative Example 6 and Comparative Example 7 was 10% by mass, but the decomposition time was 0.93 times. Therefore, K ３ P.O. ４As in the case of using the compound, the effect becomes smaller when the amount added exceeds a certain amount.

[0060] Comparative Example 8 is a mixed catalyst, but the amount of alkali metal salt (A) added to the entire catalyst, Wa, is 11.1 mass%, Wa<20 mass%, and the decomposition time is equivalent to that of Comparative Example 4, which uses DBU alone (0.83 mass% for Comparative Example 1). Comparative Example 10 is a mixed catalyst, but the amount of alkali metal salt (A) added to the entire catalyst, Wa, is 75 mass%, Wa>70 mass%, and the decomposition time is equivalent to that of Comparative Example 4, which uses DBU alone (0.82 mass% for Comparative Example 1). ３ P.O. ４ This is 0.93 times that of the single catalyst in Comparative Example 2. Therefore, it cannot be said that these catalysts have a significant effect on the single catalysts, and when 20 mass %≦Wa≦70 mass %, they are effective in shortening the decomposition time as a mixed catalyst.

[0061] Comparative Example 9 is a mixed catalyst, but the total catalyst amount Wb in the decomposition solution is 3 mass%, Wb < 4 mass%, and the decomposition time is 0.93 times that of Comparative Example 1. Therefore, when Wb is 4 mass% or less, the mixed catalyst is effective in shortening the decomposition time. A decomposition solution composed of Wa and Wb within the thus determined ranges allows for more efficient decomposition with a smaller amount of catalyst than when used alone.

[0062] From the above examples and comparative examples, it can be seen that a thermosetting resin decomposition liquid containing an alkali metal salt (A), a bicyclic amidine (B), and an organic solvent (Y), in which the ratio of the alkali metal salt (A) to the alkali metal salt (A) and the bicyclic amidine (B) is 20% by mass or more and 70% by mass or less, and the ratio of the alkali metal salt (A) and the bicyclic amidine (B) to the alkali metal salt (A), the bicyclic amidine (B), and the organic solvent (Y) is 4% by mass or more and 25% by mass or less, can obtain a homogeneous decomposition liquid, increase the decomposition ability for the thermosetting resin, shorten the treatment time, and enable the thermosetting resin to be efficiently decomposed under mild conditions. Furthermore, the ratio of the alkali metal salt (A) to the alkali metal salt (A) and the bicyclic amidine (B) is more preferably 20% by mass or more and 50% by mass or less.

[0063] Although various exemplary embodiments are described in this application, the various features, aspects, and functions described in the embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, modifications of at least one component, additions, or omissions, as well as extraction of at least one component and combinations with other components, are also contemplated.

[0064] A: alkali metal salt, B: bicyclic amidine, Y: organic solvent.

Claims

1. containing an alkali metal salt, a bicyclic amidine, and an organic solvent, a ratio of the alkali metal salt to the alkali metal salt and the bicyclic amidine is 20% by mass or more and 70% by mass or less; a ratio of the alkali metal salt and the bicyclic amidine to the alkali metal salt, the bicyclic amidine, and the organic solvent is 4% by mass or more and 25% by mass or less; A decomposition liquid for thermosetting resins, characterized in that

2. 2. The decomposition liquid for thermosetting resins according to claim 1, wherein the alkali metal salt comprises at least one selected from the group consisting of potassium hydroxide, sodium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, and potassium carbonate.

3. The decomposition liquid for thermosetting resins according to claim 1, wherein the bicyclic amidine contains one or more selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

4. The decomposition liquid for thermosetting resins according to claim 2, wherein the bicyclic amidine contains one or more selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

5. 5. The decomposition liquid for thermosetting resins according to claim 1, wherein the organic solvent has a boiling point of 170° C. or higher and has a hydroxyl group.

6. 6. The decomposition liquid for thermosetting resins according to claim 5, wherein the organic solvent contains at least one selected from the group consisting of benzyl alcohol, ethylene glycol, and propylene glycol.

7. mixing an alkali metal salt, a bicyclic amidine, and an organic solvent; heating the mixed decomposition liquid to a temperature exceeding 100°C and not exceeding 200°C at atmospheric pressure; a step of decomposing a thermosetting resin by contacting the thermosetting resin with the decomposition liquid; and a ratio of the alkali metal salt to the alkali metal salt and the bicyclic amidine is 20% by mass or more and 70% by mass or less; a ratio of the alkali metal salt and the bicyclic amidine to the alkali metal salt, the bicyclic amidine, and the organic solvent is 4% by mass or more and 25% by mass or less; A method for decomposing a thermosetting resin, comprising: