Epoxy resin-based foamed body, carbon dioxide absorber, method for preparing epoxy resin-based foamed body, multilayer structure and method for producing same

Abstract

The present invention provides an epoxy resin-based foam, which is an epoxy resin-based foam (D) formed by foaming an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B); the amine curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, wherein the cyclic amine compound (a1) has an amine group bonded to a primary carbon atom.

Description

Technical Field

[0001] This invention relates to epoxy resin foam, carbon dioxide absorbent, method for manufacturing epoxy resin foam, multilayer structure, and method for manufacturing the same. Prior Technology

[0002] Epoxy resins possess excellent properties such as heat resistance, chemical resistance, adhesion, bonding strength, corrosion resistance, electrical insulation, and flexibility, and are widely used in various fields including coatings, civil engineering, electronic materials, and adhesive applications. Furthermore, research is underway to explore ways to impart heat insulation, sound insulation, and lightweight properties to epoxy resins through foaming. Regarding the technology of epoxy resin-based foams, for example, those described in Patent Documents 1 and 2 can be cited.

[0003] Patent Document 1 discloses an epoxy resin-based foaming composition, characterized by comprising the following components: (A) 100 parts by weight of liquid epoxy resin containing one or more epoxy groups per molecule; (B) 10-200 parts by weight of methacrylic acid resin with an average particle size of 300 μm or less; (C) 10-200 parts by weight of polyethylene resin with a melt index of 100 or less and an average particle size of 300 μm or less; (D) 0.5-20 parts by weight of latent curing agent for epoxy resin; (E) 0.5-20 parts by weight of foaming agent with a decomposition gas generation temperature of 100-220°C; and (F) 0.05-5 parts by weight of surfactant. This epoxy resin-based foaming composition not only provides a lightweight and highly rigid dense foam, but also enables it to firmly bond to oily metal surfaces and exhibits good heat resistance.

[0004] Patent Document 2 discloses a method for manufacturing an epoxy resin foam, characterized by comprising the following steps: when an epoxy resin composition consisting of epoxy resin (A) and a hardener (B) is hardened, a low molecular weight compound is generated by the reaction of epoxy resin (A) and hardener (B), and the low molecular weight compound is vaporized and foamed by the heat of reaction; and it is disclosed that according to the aforementioned manufacturing method, even without adding a foaming agent, and even without external heating, an epoxy resin foam having a uniform and dense bubble structure can be easily manufactured at the on-site construction level in an environment near the freezing point to room temperature. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-194780 [Patent Document 2] Japanese Patent Application Publication No. 2006-225438 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] Patent documents 1 and 2 did not investigate the carbon dioxide absorption capacity of epoxy resin foams. The present invention was made in view of the above circumstances, and provides an epoxy resin foam with improved carbon dioxide absorption capacity. [Methods for solving problems]

[0008] The inventors have conducted repeated and thorough research to solve the aforementioned problems. Therefore, they discovered that in an epoxy resin foam formed by foaming an epoxy resin composition containing an amine curing agent and epoxy resin, the aforementioned amine curing agent contains a reaction product of an amine compound containing a cyclic amine compound and carbon dioxide, and the aforementioned cyclic amine compound has an amine group bonded to a primary carbon atom. This improves the carbon dioxide absorption capacity of the epoxy resin foam, thus completing the present invention.

[0009] That is, according to the present invention, the following can be provided: epoxy resin foam, carbon dioxide absorbent, method for manufacturing epoxy resin foam, multilayer structure and method for manufacturing the same.

[0010] [1] An epoxy resin-based foam is an epoxy resin-based foam (D) formed by foaming an epoxy resin composition (C) containing an amine curing agent (A) and epoxy resin (B); The aforementioned amine-based curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, wherein the aforementioned cyclic amine compound (a1) has an amine group bonded to a primary carbon atom. [2] As mentioned above [1], the epoxy resin is a foam. The mass increase rate of the aforementioned amine compound, calculated using the following formula after standing in an air environment of 23°C and 50%RH for one week, is more than 15% by mass and less than 50% by mass. The mass increase rate of the amine compound [mass%] = 100 × mass increase of the amine compound (g) / (mass of the amine compound (g) + mass increase of the amine compound (g)). [3] As described in [1] or [2] above, the epoxy resin foam (D) absorbs more than 0.003 g / cm³ of carbon dioxide per unit volume. [4] The epoxy resin foam as described in any of [1] to [3] above, wherein the density of the aforementioned epoxy resin foam (D) is above 0.01 g / cm3 and below 0.80 g / cm3. [5] The epoxy resin described in any of [1] to [4] above is a foam, wherein the epoxy resin (B) mentioned above includes epoxy resins having an aromatic ring or alicyclic structure within the molecule. [6] The epoxy resin foam as described in any of [1] to [5] above, wherein the aforementioned cyclic amine compound (a1) comprises a compound represented by formula (1). [Chemistry 1] In formula (1) above, R1 to R4 each independently represent a hydrogen atom, or may have a hydrocarbon group with 1 or more carbon atoms and less than 10 substituents selected from at least one of amino, cyano and phenyl; R5 to R10 each independently represent a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and less than 4 carbon atoms; x and y each independently represent an integer of 0 or more and less than 6; x+y is 1 or more and less than 6; p and q each independently represent an integer of 0 or more and less than 4; and at least one of p and q is 1 or more. [7] The epoxy resin of any of the above [1] to [6] is a foam, wherein the number of amine groups in the aforementioned cyclic amine compound (a1) is 2 or more and 6 or less. [8] The epoxy resin is a foam as described in any of [1] to [7] above, wherein the cyclic structure of the aforementioned cyclic amine compound (a1) includes at least one selected from 5-membered rings and 6-membered rings. [9] The epoxy resin foam of any of the above [1] to [8] is wherein the aforementioned cyclic amine compound (a1) comprises at least one selected from bis(aminomethyl)cyclohexane and its derivatives, limonene diamine and its derivatives, and isophorone diamine and its derivatives.

[10] A carbon dioxide absorbent containing an epoxy resin foam (D) as described in any of [1] to [9] above.

[11] A method for manufacturing an epoxy resin-based foam includes the following steps: foaming an epoxy resin composition (C) containing an amine curing agent (A) and epoxy resin (B); The aforementioned amine-based curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, wherein the aforementioned cyclic amine compound (a1) has an amine group bonded to a primary carbon atom. After standing for one week in an air environment at 23°C and 50% RH, the mass increase rate of the aforementioned amine compound, calculated using the following formula, is between 15% and 50% by mass. The mass increase rate of the amine compound [mass%] = 100 × mass increase of the amine compound (g) / (mass of the amine compound (g) + mass increase of the amine compound (g)).

[14] A multilayer structure having an outer layer on at least one side of an epoxy resin foam as described in any of [1] to [9].

[15] As described above

[14] , the multilayer structure has, in sequence, an outer layer (Ia), a core layer composed of the aforementioned epoxy resin foam, and an outer layer (Ib).

[16] As described in the multilayer structure

[15] above, at least one of the aforementioned outer layers (Ia) and (Ib) is a fiber-reinforced composite material containing a matrix resin and reinforcing fibers.

[17] A method for manufacturing a multilayer structure, which is a method for manufacturing a multilayer structure as described above

[15] or

[16] , includes at least one step selected from steps (i) to (iii) below. Step (i): The aforementioned outer layer (Ia) or its precursor, the foamed layer (II) composed of the aforementioned epoxy resin composition (C) containing amine curing agent (A) and epoxy resin (B), and the aforementioned outer layer (Ib) or its precursor are stacked in sequence to form a laminate (i), and then the aforementioned foamed layer (II) is foamed; Step (ii): The aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are stacked sequentially to form a laminate (ii), and then the aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are integrated; Step (iii): After stacking the aforementioned outer layer (Ia) or its precursor with the aforementioned core layer to form a laminate (iii), the laminate (iii) is then stacked with the aforementioned outer layer (Ib) or its precursor and formed into a laminate. [Effects of the Invention]

[0011] According to the present invention, an epoxy resin-based foam with improved carbon dioxide absorption capacity can be provided. This foam is also useful as a core material for multilayer structures. Simple Explanation of the Diagram

[0012] [Figure 1] shows a cross-sectional schematic diagram of one embodiment of the multilayer structure of the present invention. Implementation

[0013] The embodiments for carrying out the present invention (hereinafter referred to as "the embodiments") will be described in detail below. The embodiments described below are illustrative of the present invention and do not limit the scope of the invention. The present invention can be appropriately modified within its scope. In the embodiments, any definition can be used, and combinations of preferred embodiments are considered more preferred. In the embodiments, the phrase "XX~YY" means "XX or more and YY or less".

[0014] [Epoxy Resin Foam] The epoxy resin foam of the present invention is an epoxy resin foam (D) formed by foaming an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B); wherein, the amine curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, and the cyclic amine compound (a1) has an amine group bonded to a primary carbon atom. The present invention relates to an epoxy resin-based foaming system with improved carbon dioxide absorption capacity.

[0015] In this embodiment, "improved carbon dioxide absorption capacity" means that it can absorb more carbon dioxide at low concentrations (approximately 0.04% by volume) in the air, and "primary carbon atom" means a carbon atom bonded to one other carbon atom. "Reusability" means the rate at which carbon dioxide absorption is maintained during a cycle test of carbon dioxide absorption and dissociation.

[0016] Epoxy resin foam (D) can improve carbon dioxide absorption capacity by using an amine curing agent (A) containing the reaction product (a2) of an amine compound with carbon dioxide (a1) as a curing agent to harden the epoxy resin (B). The reason for this is not yet clear, but it is believed to be as follows. First, by heating the epoxy resin composition (C), an amine compound containing a cyclic amine compound (a1) and carbon dioxide are generated from the reaction product (a2). At this time, the epoxy resin composition (C) foams due to the generated carbon dioxide, and the generated amine compound reacts with the epoxy resin (B) to harden the epoxy resin composition (C), thereby obtaining an epoxy resin-based foam (D). That is, it is believed that the foam structure in epoxy resin foam (D) has a large surface area due to its porous structure. In addition, since it is a structure formed by the dissociation of carbon dioxide, it is a structure that easily absorbs carbon dioxide. Furthermore, cyclic amine compounds (a1) have an amine group bonded to a primary carbon atom. It is believed that such an amine system has low steric hindrance and readily absorbs carbon dioxide. Considering the above reasons, it is believed that epoxy resin foam (D) can improve carbon dioxide absorption capacity.

[0017] <Amine-based curing agent (A)> The amine-based curing agent (A) contains the reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide. Cyclic amine compounds (a1) are amine compounds with a cyclic structure. Regarding the cyclic structure of cyclic amine compounds (a1), examples include alicyclic hydrocarbon structures, aromatic hydrocarbon structures, and heterocyclic structures containing heteroatoms in the ring. Considering the viewpoint of improving the dissociation of cyclic amine compounds (a1) from carbon dioxide, alicyclic hydrocarbon structures are preferred. In this embodiment, alicyclic hydrocarbon structure refers to a ring structure composed of saturated or unsaturated carbon and hydrogen that is not aromatic, excluding heterocyclic structures containing heteroatoms in the ring. Furthermore, heterocyclic structure refers to a heterocyclic structure containing heteroatoms in the ring.

[0018] The cyclic structure of the cyclic amine compound (a1) is preferably selected from at least one of 5-membered and 6-membered rings, with 6-membered rings being more preferred, considering the viewpoint of improving reactivity and foaming properties with carbon dioxide. The cyclic amine compound (a1) containing a saturated 6-membered ring can also be any of the cis isomer, trans isomer, or mixture of cis and trans isomers. Furthermore, considering the improved reactivity and foaming properties with carbon dioxide, it is preferable that the cyclic amine compound (a1) has a single-ring structure. That is, it is preferable that the cyclic amine compound (a1) is a monocyclic compound. Regarding the alicyclic hydrocarbon structure of cyclic amine compounds (a1), examples include cyclopropane rings, cyclobutane rings, cyclopentane rings, cyclohexane rings, cycloheptane rings, and cyclooctane rings. Among the above ring structures, cyclopentane rings and cyclohexane rings are preferred, cyclohexane rings are even more preferred, and 1,3-substituted cyclohexane rings are even more preferred.

[0019] The number of amine groups in cyclic amine compounds (a1) is preferably 2 or more, considering the viewpoint of improving reactivity, curing properties and foaming properties with carbon dioxide. Furthermore, it is more ideal to have 6 or less, even more ideal to have 4 or less, even more ideal to have 3 or less, and even more ideal to have 2. Furthermore, regarding the amino group, considering the viewpoint of further improving reactivity, curing properties, and foaming properties with carbon dioxide, an amino group with a nitrogen-hydrogen bond is preferred, an amino group selected from at least one of the groups consisting of primary and secondary amino groups is preferred, and a primary amino group is even more preferred.

[0020] The cyclic amine compound (a1) preferably includes a compound represented by formula (1), and more preferably a compound represented by formula (1).

[0021] [Chemistry 2] In formula (1) above, R1 to R4 each independently represent a hydrogen atom, or may have a hydrocarbon group with 1 or more carbon atoms and less than 10 substituents selected from at least one of amino, cyano and phenyl; R5 to R10 each independently represent a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and less than 4 carbon atoms; x and y each independently represent an integer of 0 or more and less than 6; x+y is 1 or more and less than 6; p and q each independently represent an integer of 0 or more and less than 4; and at least one of p and q is 1 or more.

[0022] R1 to R4 are each independently a hydrogen atom, or may have a hydrocarbon group with 1 or more and 10 carbon atoms selected from at least one of amino, cyano, and phenyl substituents, preferably a hydrogen atom, or may have an alkyl group with 1 or more and 4 carbon atoms selected from at least one of amino, cyano, and phenyl substituents, more preferably a hydrogen atom, or may have an alkyl group with 1 or more and 4 carbon atoms selected from at least one of amino and cyano substituents, even more preferably a hydrogen atom, or may have an alkyl group with 2 or more and 4 carbon atoms selected from at least one of amino and cyano substituents, even more preferably a hydrogen atom. The number of carbon atoms in each of the hydrocarbon groups R1 to R4 is independently 1 or more, preferably 2 or more, furthermore, 10 or less, more ideally 5 or less, even more ideally 4 or less, and even more ideally 3 or less.

[0023] R5 to R10 are each independently a hydrogen atom or a hydrocarbon group having 1 or more but 4 or fewer carbon atoms, preferably a hydrogen atom or an alkyl group having 1 or more but 4 or fewer carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 or more but 3 or fewer carbon atoms, even more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. The number of carbon atoms in each of the hydrocarbon groups R5 to R10 is independently 1 or more and 4 or less, preferably 1 or 2, and more preferably 1.

[0024] p and q are each independently 0 or higher, preferably 1 or higher, furthermore, 4 or lower, more ideally 2 or lower, and even more ideally 1. However, at least one of p and q is 1 or higher.

[0025] x and y each independently represent an integer greater than 0 and less than 6, and x+y is greater than 1 and less than 6. Considering the improvement in carbon dioxide absorption and foaming properties, x+y is preferably greater than 2, more preferably greater than 3, and even more preferably greater than 4. Considering the further improvement in carbon dioxide absorption and foaming properties, it is ideally less than 5, and even more ideally 4. That is, alicyclic hydrocarbon structure with a 5-membered or 6-membered ring is preferred, with a 6-membered ring being even better. When x+y is 4, the preferred configuration is x = 1 and y = 3.

[0026] Regarding cyclic amine compounds (a1), considering the viewpoint of further improving reactivity, curing properties, and foaming properties with carbon dioxide, it is preferable to include at least one selected from the group consisting of o-phenylenediamine and its derivatives, m-phenylenediamine and its derivatives, p-phenylenediamine and its derivatives, bis(aminomethyl)cyclohexane and its derivatives, N-(2-aminoethyl)piperazine and its derivatives, limonene diamine and its derivatives, isophorone diamine and its derivatives, 2,5-diaminomethylfuran and its derivatives, and 2,5-bis(aminomethyl)tetrahydrofuran and its derivatives, including m-phenylenediamine... It is preferred to have at least one of the following groups: amines and their derivatives, bis(aminomethyl)cyclohexane and its derivatives, N-(2-aminoethyl)piperazine and its derivatives, limonenediamine and its derivatives, and isophoronediamine and its derivatives; it is even more preferred to have at least one selected from bis(aminomethyl)cyclohexane and its derivatives, limonenediamine and its derivatives, and isophoronediamine and its derivatives; bis(aminomethyl)cyclohexane and its derivatives are even more preferred; 1,3-bis(aminomethyl)cyclohexane and its derivatives are even more preferred; and 1,3-bis(aminomethyl)cyclohexane is even more desirable. Here, with regard to the various amine derivatives mentioned above, the following compounds can be listed as examples: compounds in which at least one hydrogen atom of the amino group is substituted by a hydrocarbon group having 1 or more and 10 or less carbon atoms, which may also have at least one substituent selected from the group consisting of amino, cyano, and phenyl; preferably substituted by an alkyl group having 1 or more and 4 or less carbon atoms, which may also have at least one substituent selected from the group consisting of amino and cyano; more preferably substituted by an alkyl group having 1 or more and 4 or less carbon atoms, which may also have at least one substituent selected from the group consisting of amino and cyano; and even more preferably substituted by an alkyl group having 2 or more and 4 or less carbon atoms, which may also have at least one substituent selected from the group consisting of amino and cyano. Furthermore, regarding the derivatives of the various amines mentioned above, the following compounds can be listed as examples: compounds in which at least a portion of the hydrogen atoms in the cyclic structure are replaced by a hydrocarbon group having 1 or more and 4 or fewer carbon atoms, preferably by an alkyl group having 1 or more and 3 or fewer carbon atoms, more preferably by a methyl or ethyl group, and even more preferably by a methyl group.

[0027] These cyclic amine compounds (a1) can be used alone or in combination of two or more.

[0028] The proportion of cyclic amine compounds (a1) in the amine compounds of the reaction product (a2) is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, more preferably 70 parts by mass or more, more preferably 80 parts by mass or more, more preferably 90 parts by mass or more, more ideally 95 parts by mass or more, and more preferably less than 100 parts by mass. Regarding amine compounds other than cyclic amine compounds (a1), examples include cyclic amine compounds other than cyclic amine compounds (a1); monoethanolamine, 2-amino-2-methyl-1-propanol, diethanolamine, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, ethylenediamine, N,N'-dimethylethylenediamine, diethylenetriamine, and other noncyclic aliphatic amine compounds.

[0029] The amine-based curing agent (A) may also contain components other than the reaction products (a2) of amine compounds that have not reacted with carbon dioxide. Regarding amine compounds that have not reacted with carbon dioxide, the aforementioned cyclic amine compound (a1) is ideal. For the preferred compound, similar to cyclic amine compounds (a1), it is preferably selected from at least one of the group consisting of o-phenylenediamine and its derivatives, m-phenylenediamine and its derivatives, p-phenylenediamine and its derivatives, bis(aminomethyl)cyclohexane and its derivatives, N-(2-aminoethyl)piperazine and its derivatives, limonene diamine and its derivatives, isophorone diamine and its derivatives, 2,5-diaminomethylfuran and its derivatives, and 2,5-bis(aminomethyl)tetrahydrofuran and its derivatives. It is more preferably selected from at least one of the group consisting of m-phenylenediamine and its derivatives, bis(aminomethyl)cyclohexane and its derivatives, and isophorone diamine and its derivatives. It is even more preferably selected from at least one of the group consisting of m-phenylenediamine, 1,3-bis(aminomethyl)cyclohexane, and isophorone diamine. The amine compound that does not react with carbon dioxide may be the same amine compound as the amine compound in the reaction product (a2), or it may be a different type of amine compound. The content of reaction product (a2) in the amine hardener (A) is preferably 50% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, more ideally 98% or more, and more preferably 100% or less, taking into account the viewpoint of improving carbon dioxide absorption and foaming properties. Furthermore, considering the improvement of the mechanical strength of the foam, the content of the reaction product (a2) in the amine hardener (A) is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more when the total amount of the amine hardener (A) is 100% by mass. It is also ideally 90% or less, even more ideally 80% or less, and even more ideally 70% or less.

[0030] The maximum dissociation temperature of carbon dioxide in the cyclic amine compound (a1) determined using the following method is preferably below 200°C, more preferably below 180°C, even more preferably below 160°C, and still more preferably below 150°C, even more preferably below 140°C, even more ideally below 135°C, and even more suitable below 130°C, considering the improvement of carbon dioxide dissociation properties and the reusability of epoxy resin-based foams. The lower limit of the above-mentioned maximum dissociation temperature of carbon dioxide is not particularly limited, but for example, it may be above 40°C. (method) A cyclic amine compound (a1) that has absorbed carbon dioxide was heated from 23°C to 250°C at a heating rate of 10°C / min. The temperature at which the heat of heat absorption accompanying the release of carbon dioxide reached its maximum was measured and defined as the maximum dissociation temperature of carbon dioxide. Here, the cyclic amine compound (a1) that has absorbed carbon dioxide can be prepared, for example, by placing 5 mmol of the cyclic amine compound (a1) in air at 23°C and 50% RH for 24 hours.

[0031] The acid dissociation constant (pKa) of the cyclic amine compound (a1) is preferably 8.0 or higher, more preferably 8.5 or higher, and even more preferably 9.0 or higher, considering the viewpoint of improving carbon dioxide dissociation and foaming properties. Furthermore, considering the viewpoint of improving carbon dioxide dissociation and foaming properties and the reusability of epoxy resin foams, it is ideally 12.0 or lower, more ideally 11.5 or lower, and even more ideally 11.0 or lower. The acid dissociation constant of cyclic amine compounds (a1) is obtained by means of the following determination method based on acid-base titration. (1) Dissolve 0.2 g of cyclic amine compound (a1) in 30 mL of purified water. (2) The acid dissociation constant (pKa) is calculated by titrating the solution obtained from (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration device (e.g., Kyoto Electronics Co., Ltd., AT-610). Furthermore, the temperature during the measurement was set to 25±2℃.

[0032] The molecular weight of the cyclic amine compound (a1) is preferably 110 or higher, more preferably 120 or higher, and even more preferably 130 or higher, considering the viewpoint of suppressing the weight reduction during heat treatment when carbon dioxide dissociates. Considering the viewpoint of further improving carbon dioxide absorption and foaming properties, it is ideally 200 or lower, more ideally 180 or lower, and even more ideally 175 or lower.

[0033] The maximum endothermic temperature of the cyclic amine compound (a1) determined by the following method is preferably above 130°C, more preferably above 140°C, and even more preferably above 150°C, considering the viewpoint of suppressing the weight reduction during heat treatment when carbon dioxide dissociates. Considering the viewpoint of further improving carbon dioxide absorption and foaming properties, it is ideally below 260°C, even more ideally below 230°C, even more ideally below 200°C, and even more ideally below 170°C. (method) The cyclic amine compound (a1) was heated from 23°C to 350°C at a heating rate of 10°C / min. The temperature at which the heat absorption accompanying the volatilization of the cyclic amine compound (a1) reached its maximum value was measured, and this temperature was defined as the maximum heat absorption temperature of the cyclic amine compound (a1).

[0034] The amine value of cyclic amine compounds (a1), considering improvements in carbon dioxide absorption and foaming properties, is preferably 400 mg KOH / g or higher, more preferably 500 mg KOH / g or higher, even more preferably 600 mg KOH / g or higher, and still more preferably 650 mg KOH / g or higher. Ideally, it should be below 1500 mg KOH / g, even more ideally below 1200 mg KOH / g, even more ideally below 1000 mg KOH / g, even more ideally below 900 mg KOH / g, even more ideally below 850 mg KOH / g, and even more suitablely below 800 mg KOH / g. The amine value indicates the amount of amine in the compound and refers to the number of mg of potassium hydroxide (KOH) equivalent to the amount of acid required to neutralize 1 g of the compound. The amine value can be determined according to JIS K7237-1995 using the following method. (1) Dissolve 0.1 g of cyclic amine compound (a1) in 20 mL of acetic acid. (2) The amine value is calculated by titrating the solution obtained from (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration device (e.g., Kyoto Electronics Co., Ltd., AT-610).

[0035] After the aforementioned amine compound was left to stand in an air environment of 23°C and 50%RH for one week, the mass increase rate of the aforementioned amine compound was calculated using the following formula. Considering the viewpoint of further improving the carbon dioxide absorption and foaming properties of epoxy resin foam (D), it is preferably 15% by mass or more, more preferably 18% by mass or more, even more preferably 20% by mass or more, even more preferably 23% by mass or more, further ideally 50% by mass or less, even more ideally 45% by mass or less, even more ideally 40% by mass or less, even more ideally 30% by mass or less, and even more ideally 28% by mass or less. The mass increase rate of the amine compound [mass%] = 100 × mass increase of the amine compound (g) / (mass of the amine compound (g) + mass increase of the amine compound (g)) Specifically, the mass increase rate of the aforementioned amine compounds can be determined using the methods described in the examples.

[0036] The amine-based curing agent (A) can be obtained by contacting an amine compound containing a cyclic amine compound (a1) with a gas containing carbon dioxide and allowing the amine compound to react with the carbon dioxide. The reaction product of an amine compound with carbon dioxide (a2) contains, for example, at least one of the following: carbamic acid, carbamate, carbonate, bicarbonate, etc., selected from the reaction products of a series of amine compounds with carbon dioxide.

[0037] <Epoxy Resin (B)> Epoxy resin (B) can also be any of the following: saturated or unsaturated aliphatic or alicyclic compounds, aromatic compounds, or heterocyclic compounds. Considering improvements in heat resistance, chemical resistance, curing properties, and mechanical strength, epoxy resins with aromatic or alicyclic structures within the molecule are preferred. Specific examples of such epoxy resins include: epoxy resins containing glycidylamine groups derived from m-phenylenediamine; epoxy resins containing glycidylamine groups derived from p-phenylenediamine; epoxy resins containing glycidylamine groups derived from 1,3-bis(aminomethyl)cyclohexane; epoxy resins containing glycidylamine groups derived from 1,4-bis(aminomethyl)cyclohexane; and epoxy resins containing glycidylamine groups derived from diaminodiphenylmethane. The epoxy resin comprises at least one of the following: epoxy resin having glycidylamine groups; epoxy resin having glycidylamine groups and / or glycidyloxy groups derived from p-aminophenol; epoxy resin having glycidyloxy groups derived from bisphenol A; epoxy resin having glycidyloxy groups derived from bisphenol F; epoxy resin having glycidyloxy groups derived from phenolic varnish; and epoxy resin having glycidyloxy groups derived from resorcinol. Two or more of the above epoxy resins can also be used in combination.

[0038] Of the above, considering the improvement of heat resistance, chemical resistance, and mechanical strength, for epoxy resin (B), it is preferable to use at least one of the following as the main component: epoxy resin with glycidylamine group derived from m-phenylenediamine, epoxy resin with glycidylamine group derived from p-phenylenediamine, epoxy resin with glycidyloxy group derived from bisphenol A, and epoxy resin with glycidyloxy group derived from bisphenol F. Considering the improvement of heat resistance, chemical resistance, and mechanical strength, as well as availability and economy, it is even more preferable to use epoxy resin with glycidyloxy group derived from bisphenol A as the main component. Furthermore, the term "main component" as used herein means that other components may be included without departing from the spirit of the present invention, and it means preferably 50 to 100% by mass of the whole, more preferably 70 to 100% by mass, and even more preferably 90 to 100% by mass.

[0039] The content of amine curing agent (A) in epoxy resin composition (C), in terms of the ratio of the number of active amine hydrogens in amine curing agent (A) to the number of epoxy groups in epoxy resin (B) (the aforementioned number of active amine hydrogens / the aforementioned number of epoxy groups), is preferably 0.5 or more, more preferably 0.8 or more, even more preferably 1.0 or more, even more preferably 1.1 or more, and even more preferably 1.2 or more, in view of improving the heat resistance, chemical resistance, curing properties and mechanical strength of epoxy resin foam (D). The content is preferably 2.0 or less, even more preferably 1.8 or less, even more preferably 1.5 or less, even more preferably 1.4 or less, and even more preferably 1.3 or less. Here, the active amine hydrogen number in the amine curing agent (A) refers to the sum of the active amine hydrogen number of the amine compound before reacting with carbon dioxide in the reaction product (a2) and the active amine hydrogen number of the amine compound contained in the amine curing agent (A) that has not reacted with carbon dioxide.

[0040] The epoxy resin composition (C) may also contain other components such as fillers, plasticizers and other modifiers, thixotropic agents and other flow modifiers, pigments, leveling agents, tackifiers, elastomer microparticles, curing accelerators, foam stabilizers, and chemical foaming agents, depending on the application. However, considering the viewpoint of effectively obtaining the effects of the present invention, the total amount of amine curing agent (A) and epoxy resin (B) in epoxy resin composition (C) is preferably 50% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. Furthermore, the upper limit is 100% by mass.

[0041] The amount of carbon dioxide absorbed per unit volume of the epoxy resin foam (D), considering the viewpoint of further improving carbon dioxide absorption capacity, is preferably 0.003 g / cm³ or more, more preferably 0.005 g / cm³ or more, even more preferably 0.010 g / cm³ or more, even more preferably 0.020 g / cm³ or more, and even more preferably 0.025 g / cm³ or more. Since a higher absorption rate is generally better, there is no particular upper limit, but for example, it may be 0.10 g / cm³ or less. Specifically, the aforementioned carbon dioxide absorption rate can be determined using the method described in the examples.

[0042] The density of the epoxy resin foam (D), considering the improvement of mechanical strength, is preferably 0.01 g / cm³ or higher, more preferably 0.05 g / cm³ or higher, even more preferably 0.10 g / cm³ or higher, and still more preferably 0.13 g / cm³ or higher. Considering further improvements in thermal insulation, sound insulation, and lightweight properties, it is ideally 0.80 g / cm³ or lower, even more preferably 0.60 g / cm³ or lower, even more preferably 0.50 g / cm³ or lower, and still even more preferably 0.45 g / cm³ or lower. Specifically, the density of the epoxy resin foam (D) can be determined using the method described in the examples.

[0043] <Preparation Method of Epoxy Resin Composition (C)> There are no particular restrictions on the preparation method of epoxy resin composition (C). It can be manufactured by mixing amine curing agent (A), epoxy resin (B), and other components as needed using known methods and apparatus.

[0044] [Manufacturing Method of Epoxy Resin-Based Foam] The method for manufacturing an epoxy resin foam of the present invention includes the following steps: foaming an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B); wherein the amine curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, and the cyclic amine compound (a1) has an amine group bonded to a primary carbon atom. According to the method for manufacturing epoxy resin-based foam of the present invention, a foam with improved carbon dioxide absorption capacity can be obtained. The reasons for believing that the method for manufacturing the epoxy resin-based foam of the present invention can achieve the same effect are the same as those for the aforementioned reasons for achieving the effect of the epoxy resin-based foam of the present invention. The components and their ideal states used in the manufacturing method of the epoxy resin foam of the present invention are the same as those in the epoxy resin foam of the present invention described above.

[0045] In the step of foaming the epoxy resin composition (C), for example, by heating the epoxy resin composition (C), a cyclic amine compound (a1) and carbon dioxide are generated from the reaction product (a2). The carbon dioxide causes the epoxy resin composition (C) to foam, and the epoxy resin composition (C) hardens due to the reaction of the amine compound containing the cyclic amine compound (a1) with the epoxy resin (B). In this way, an epoxy resin-based foam (D) can be obtained. The heating temperature and heating time in the step of foaming the epoxy resin composition (C) can be appropriately selected. However, considering the reaction rate, productivity, and prevention of raw material decomposition, a temperature of 50~250℃ is preferred, 100~200℃ is more preferred, and 120~180℃ is even more preferred. Furthermore, the reaction time is preferably 10 minutes to 12 hours, and more preferably 15 minutes to 4 hours.

[0046] The method for manufacturing an epoxy resin foam of the present invention preferably includes the following steps: before the step of foaming the epoxy resin composition (C), the amine compound containing the cyclic amine compound (a1) is contacted with a gas containing carbon dioxide at a concentration of 0.01% by volume or more and 10% by volume or less, so that the amine compound reacts with the carbon dioxide to obtain the reaction product (a2). The aforementioned carbon dioxide concentration is preferably 0.02% by volume or higher, more preferably 0.03% by volume or higher, further ideally 5% by volume or lower, more ideally 1% by volume or lower, even more ideally 0.5% by volume or lower, and even more ideally 0.1% by volume or lower. Furthermore, an air-based gas concentration of 0.01% by volume or higher and 10% by volume or lower is even more suitable. The reaction product (a2) is the reaction product of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, such as containing at least one of carbamic acid, carbamate, carbonate, bicarbonate, etc., selected from the reaction products of a amine compound and carbon dioxide.

[0047] Carbon dioxide absorbent The carbon dioxide absorbent of the present invention contains the aforementioned epoxy resin-based foam (D). Because the carbon dioxide absorbent of the present invention contains the epoxy resin-based foam (D), its carbon dioxide absorption capacity is improved. The content of epoxy resin foam (D) in the carbon dioxide absorbent of the present invention is, from the viewpoint of improving carbon dioxide absorption capacity, such that when the total amount of carbon dioxide absorbent is 100% by mass, it is 60% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and ideally, it is 100% by mass or less.

[0048] The carbon dioxide absorbent of this invention has a good absorption capacity for carbon dioxide from the air, and therefore can be ideally used in the technology of direct absorption of carbon dioxide from the air (DAC). Furthermore, the carbon dioxide absorbent of the present invention can be ideally used, for example, to recover low concentrations of carbon dioxide of 0.01% to 1% by volume.

[0049] The carbon dioxide absorbent of the present invention may appropriately contain components other than epoxy resin-based foam (D) without impairing the effect of the invention. Examples of components other than epoxy resin-based foam (D) include compounds capable of absorbing carbon dioxide other than epoxy resin-based foam (D), degradation inhibitors, defoamers, antioxidants, and desiccants for removing moisture (magnesium sulfate, molecular sieves, etc.).

[0050] [Multi-layer structure] The multilayer structure system of the present invention has an outer layer on at least one side of the aforementioned epoxy resin foam. There are no particular restrictions on the materials used to form the outer layer of a multi-layered structure; examples include metals, resins, and fiber-reinforced composites. For metals, examples include stainless steel, aluminum, iron, copper, and other alloys; for resins, examples include thermoplastic resins, cured thermosetting resins, and cured ray-cured resins.

[0051] Regarding the fiber-reinforced composite material constituting the outer layer, examples include fiber-reinforced composite materials containing a matrix resin and reinforcing fibers. Regarding the matrix resin, examples include cured thermoplastic resins, cured thermosetting resins, and cured energy-cured resins. Considering the need to improve the adhesion between the outer layer and the epoxy resin foam that forms the core layer, a cured thermosetting resin is preferable as the matrix resin, and a cured epoxy resin composition is even better. The epoxy resin composition used as a precursor to the matrix resin may have the same composition as the aforementioned epoxy resin composition (C), or it may be different, but it is preferably a non-foaming epoxy resin composition. That is, it is ideal that the epoxy resin composition used as a precursor to the matrix resin contains at least epoxy resin and epoxy resin curing agent, and does not contain the reaction product of amine compound and carbon dioxide. The content of the reaction product of amine compound and carbon dioxide in the epoxy resin composition is preferably 5% by mass or less, more preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0% by mass.

[0052] Regarding the form of reinforcing fibers used in fiber-reinforced composites, short fibers, long fibers, and continuous fibers can be listed. Among these, considering the ease of forming the multilayer structure into the desired shape, long fibers or continuous fibers are preferred, with continuous fibers being even better. Furthermore, in this specification, short fibers refer to fibers with a length of 0.1 mm or more but less than 10 mm, and long fibers refer to fibers with a length of 10 mm or more but less than 100 mm. Also, continuous fibers refer to fiber bundles with a fiber length exceeding 100 mm.

[0053] In terms of the shape of continuous fibers, various forms such as unidirectional (UD) materials, woven fabrics, non-woven fabrics, and felts can be listed, which are formed by arranging monofilaments or multiple fibers in a unidirectional or alternating manner. Among these, considering the manufacture of fiber-reinforced composite materials for outer layers, the form of monofilaments, fabrics, non-woven fabrics, or felts is preferred, and fabrics are even more preferred.

[0054] In continuous fibers, there is no particular limitation on the average fiber length of the continuous fiber bundle, but from the perspective of forming and processing, it is preferred to be 1 to 10,000 m, and more preferably 100 to 10,000 m. The average fineness of the continuous fiber bundle, considering the viewpoints of formability and ease of obtaining high strength and high elastic modulus, is preferably 50~2000 tex (g / 1000m), more preferably 200~1500 tex, and even more preferably 500~1500 tex. Furthermore, the average tensile modulus of continuous fiber bundles is preferably 50~1000 GPa.

[0055] Regarding the materials used to reinforce the fibers, examples include inorganic fibers such as carbon fiber, glass fiber, basalt fiber, metal fiber, boron fiber, and ceramic fiber; and organic fibers such as polyarylamide fiber, polyoxymethylene fiber, aromatic polyamide fiber, poly(p-phenylene benzobis(oxo)azole fiber, and ultra-high molecular weight polyethylene fiber. Among these, inorganic fibers are more ideal from the perspective of achieving high strength. From the perspective of lightweight, high strength, and high modulus of elasticity, at least one fiber from the group consisting of carbon fiber, glass fiber, and basalt fiber is preferred. From the perspective of strength and lightweight, carbon fiber is even more preferred. Regarding carbon fibers, examples include polyacrylonitrile-based carbon fibers and pitch-based carbon fibers. Additionally, carbon fibers derived from plant materials such as lignin and cellulose can also be used.

[0056] Reinforcing fibers can also be treated with a treatment agent. Examples of treatment agents include surface treatment agents or bundling agents. Of the aforementioned surface treatment agents, silane coupling agents are preferred. Examples include silane coupling agents containing vinyl groups, silane coupling agents containing amino groups, silane coupling agents containing epoxy groups, silane coupling agents containing (meth)acrylate groups, and silane coupling agents containing mercapto groups.

[0057] Regarding the aforementioned bundlers, examples include carbamate-based bundlers, epoxy-based bundlers, acrylic-based bundlers, polyester-based bundlers, vinyl ester-based bundlers, polyolefin-based bundlers, polyether-based bundlers, and carboxylic acid-based bundlers, etc., and one of these or a combination of two or more of these can be used. Regarding combinations of two or more bundlers, examples include carbamate / epoxy-based bundlers, carbamate / acrylic-based bundlers, carbamate / carboxylic acid-based bundlers, etc.

[0058] The amount of the aforementioned treatment agent, considering the viewpoint of improving the interfacial adhesion between the reinforcing fiber and the matrix resin and further improving the strength and impact resistance, is preferably 0.001 to 5% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.5 to 2% by mass, relative to the reinforcing fiber.

[0059] For reinforcing fibers, commercially available products can also be used. Examples of commercially available continuous carbon fiber products include TORAY CA CLOTH manufactured by TORAY (Stock) Co., Ltd., including "CO6142", "CO6151B", "CO6343", "CO6343B", "CO6347B", "CO6644B", "CK6244C", "CK6273C", "CK6261C", "UT70" series, "UM46" series, "BT70" series, "T300" series, "T300B" series, "T400HB" series, "T700SC" series, "T800SC" series, "T800HB" series, "T1000GB" series, "M35JB" series, and "M4" series. The series includes "M46JB", "M50JB", "M55J", "M55JB", "M60JB", "M30SC", "Z600GT", etc.; TORAYCA silk includes "T300", "T300B", "T400HB", "T700SC", "T800SC", "T800HB", "T830HB", "T1000GB", "T100GC", "M35JB", "M40JB", "M46JB", "M50JB", "M55J", "M5 Various series including "5JB", "M60JB", "M30SC", and "Z600"; and Tenax series manufactured by Teijin Co., Ltd., including "HTA40", "HTS40", "HTS45", "HTS45P12", "STS40", "UTS50", "ITS50", "ITS55", "IMS40", "IMS60", "IMS65", "IMS65P12", "HMA35", "UMS40", "UMS45", and "UMS55". The product lines include: "HTS40" series, "HTS40MC" series, etc.; Teijin Holdings' Tenax "HTA40" series, "HTS40" series, "HTS45" series, "HTS45P12" series, "STS40" series, "UTS50" series, "ITS50" series, "ITS55" series, "IMS40" series, "IMS60" series, "IMS65" series, "IMS65P12" series, "HMA35" series, "UMS40" series, "UMS45" series, "UMS55" series, "HTS40MC" series, etc.Mitsubishi Chemical Co., Ltd. produces PYROFIL carbon fiber fabrics including "TR3110M", "TR3523M", "TR3524M", "TR6110HM", "TR6120HM", "TRK101M", "TRK510M", "TR3160TMS", "TRK979PQRW", "TRK976PQRW", "TR6185HM", and "TRK180M", as well as SGL's "50K NCF0° / 90°" carbon fiber fabrics, and Mitsubishi Chemical Co., Ltd.'s PYROFIL "HT", "IM", and "HM" series, GRAFIL "HT" series, and "DIALEAD" series carbon fiber bundles.

[0060] When the outer layer is a fiber-reinforced composite material, the volume fraction of the reinforcing fibers in the outer layer, considering the need for high strength and high modulus of elasticity, is preferably 0.10 or higher, more preferably 0.20 or higher, even more preferably 0.30 or higher, and still more preferably 0.40 or higher. Furthermore, considering impact resistance and processability, it is preferably 0.85 or lower, more preferably 0.80 or lower, and even more preferably 0.70 or lower. The volume fraction Vf of the reinforcing fibers in the outer layer can be calculated by the following formula. Vf = {Mass of reinforcing fiber (g) / Specific gravity of reinforcing fiber} ÷ [{Mass of reinforcing fiber (g) / Specific gravity of reinforcing fiber} + {Mass of matrix resin (g) / Specific gravity of matrix resin}]

[0061] <Composition of Multi-layered Structures> The multilayer structure of the present invention can have an outer layer on at least one side of the aforementioned epoxy resin foam, but considering the improvement of mechanical strength, it is more ideal to have an outer layer on both sides of the aforementioned epoxy resin foam. That is, as shown in FIG1, the multilayer structure of the present invention having an outer layer (Ia), a core layer composed of the aforementioned epoxy resin foam, and an outer layer (Ib) in sequence is more ideal. Figure 1 is a cross-sectional schematic diagram showing one embodiment of the multilayer structure 100 of the present invention, where 1a is the outer layer (Ia), 1b is the outer layer (Ib), and 2 is the core layer. The outer layers (Ia) and (Ib) can be made of the same material or different materials. The multilayer structure of the present invention, considering the improvement of mechanical strength and lightweight, has an outer layer (Ia), a core layer composed of the aforementioned epoxy resin foam, and an outer layer (Ib) in sequence. It is more ideal that at least one of the outer layers (Ia) and (Ib) is a fiber-reinforced composite material containing a matrix resin and reinforcing fibers, and it is more suitable that both the outer layers (Ia) and (Ib) are fiber-reinforced composite materials.

[0062] <Manufacturing Methods of Multi-Layer Structures> There are no particular limitations on the manufacturing method of the multilayer structure of the present invention, and known methods can be used. For example, in the manufacturing method of the multilayer structure 100 shown in Figure 1, which has an outer layer (Ia), a core layer composed of the aforementioned epoxy resin foam, and an outer layer (Ib) in sequence, it is more ideal to include at least one step selected from steps (i) to (iii) below, from the perspective of improving manufacturing efficiency. Step (i): The aforementioned outer layer (Ia) or its precursor, the foamed layer (II) composed of the aforementioned epoxy resin composition (C) containing amine curing agent (A) and epoxy resin (B), and the aforementioned outer layer (Ib) or its precursor are stacked in sequence to form a laminate (i), and then the aforementioned foamed layer (II) is foamed; Step (ii): The aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are stacked sequentially to form a laminate (ii), and then the aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are integrated; Step (iii): After stacking the aforementioned outer layer (Ia) or its precursor with the aforementioned core layer to form a laminate (iii), the laminate (iii) is then stacked with the aforementioned outer layer (Ib) or its precursor and formed into a laminate.

[0063] (Step (i)) In step (i), the aforementioned outer layer (Ia) or its precursor, the foamed layer (II) composed of the aforementioned epoxy resin composition (C) containing amine curing agent (A) and epoxy resin (B), and the aforementioned outer layer (Ib) or its precursor are stacked in sequence to form a laminate (i), and then the aforementioned foamed layer (II) is foamed. In step (i), together with the foaming of the foamable layer (II), the outer layer (Ia), the core layer obtained by foaming the foamable layer (II), and the outer layer (Ib) are integrated. Furthermore, the precursors of the outer layer (Ia) and the outer layer (Ib) are transformed into the outer layer (Ia) and the outer layer (Ib) respectively together with the foaming of the foamable layer (II).

[0064] "The precursor of the outer layer" refers to, for example, when the outer layer is a fiber-reinforced composite containing a matrix resin and reinforcing fibers, a reinforcing fiber prepreg made by impregnating the reinforcing fibers with a matrix resin precursor. The reinforcing fiber prepreg can be a commercially available prepreg or one made using known methods such as RTM (Resin Transfer Molding) molding or hand lay-up molding. The reinforced fiber prepreg preferably comprises a matrix resin precursor selected from at least one of thermosetting resins and energy-curing resins, and reinforcing fibers; more preferably, it comprises a thermosetting resin and reinforcing fibers; and even more preferably, it comprises an epoxy resin composition and reinforcing fibers. The matrix resin precursor and its ideal form are as described above.

[0065] The aforementioned laminate (i) can be manufactured, for example, by coating one side of the outer layer (Ia) or its precursor with an epoxy resin composition (C) to form a foamed layer (II), and then laminating the outer layer (Ib) or its precursor onto the foamed layer (II). Alternatively, the foamed layer (II) can be pre-prepared by pre-reacting the epoxy resin composition (C) and shaping it into a sheet, and then the outer layer (Ia) or its precursor, the foamed layer (II) shaped into a sheet, and the outer layer (Ib) or its precursor can be laminated sequentially. From the viewpoint of improving the manufacturing efficiency of the multilayer structure of the present invention, the aforementioned laminate (i) is preferably made using pre-made outer layers (Ia) and (Ib). In the fabrication of the laminate (i), precursors for outer layers (Ia) and (Ib) can also be used, and the conversion of the precursors for the outer layers into foamed outer layers and foamed layers (II) is carried out simultaneously in step (i) because it requires long-term heating at high temperatures.

[0066] In step (i), the heating temperature and heating time for foaming the foamable layer (II) can be appropriately selected, for example, the same conditions as those used in the step of foaming the epoxy resin composition (C) described above can be used.

[0067] When foaming the foamed layer (II), in order to improve the interlayer adhesion between the outer layer and the core layer obtained by foaming the foamed layer (II), a hot press or similar device can be used to apply pressure simultaneously with heating. There are no particular restrictions on the pressure conditions, but they are usually in the range of 0.1 to 5 MPa.

[0068] (Step (ii)) In step (ii), the aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are stacked in sequence to form a laminate (ii), and then the aforementioned outer layer (Ia) or its precursor, the aforementioned core layer, and the aforementioned outer layer (Ib) or its precursor are integrated. The aforementioned stack (ii) can be fabricated using a pre-made core layer and by sequentially stacking an outer layer (Ia) or its precursor, a core layer, and an outer layer (Ib) or its precursor. The outer layer or its precursor used in step (ii) is the same as that described in step (i). From the perspective of improving the manufacturing efficiency of multilayer structures, the aforementioned stacked body (ii) is preferably made by prefabricating outer layers (Ia) and outer layers (Ib), and then stacking the outer layers (Ia), core layer, and outer layers (Ib) in sequence.

[0069] Regarding the method of integrating the outer layer (Ia) or its precursor, the core layer, and the outer layer (Ib) or its precursor of the laminate (ii), a method of applying heating conditions to the laminate (ii) can be cited. By applying these heating conditions, the precursors of the outer layer (Ia) and the outer layer (Ib) are transformed into the outer layer (Ia) and the outer layer (Ib) respectively and integrated with the core layer. Alternatively, a hot press or the like can be used to pressurize simultaneously with heating. The ideal heating and pressurizing conditions in this case are the same as in step (i).

[0070] (Step (iii)) In step (iii), after the aforementioned outer layer (Ia) or its precursor is laminated with the aforementioned core layer and integrated to form a laminate (iii), the laminate (iii) is laminated with the aforementioned outer layer (Ib) or its precursor and integrated to form a laminate. The aforementioned laminate (iii) can be manufactured, for example, by laminating an outer layer (Ia) or its precursor onto a single side of the core layer and applying heating conditions. By applying these heating conditions, the precursor of the outer layer (Ia) transforms into the outer layer (Ia) and integrates with the core layer. Alternatively, a hot press or similar device can be used to apply pressure simultaneously with heating. The ideal heating and pressurizing conditions in this case are the same as in step (i). Next, the aforementioned outer layer (Ib) or its precursor can be laminated on the core side of the laminate (iii) and integrated using the same method as the outer layer (Ia) to create the desired multilayer structure.

[0071] Among the aforementioned steps (i) to (iii), considering the viewpoints of improving manufacturing efficiency and improving the interlayer adhesion of the obtained multilayer structure, the manufacturing method of the multilayer structure including step (i) is more ideal. The multi-layer structure of this invention has high mechanical strength and is lightweight, so in addition to being used as a carbon dioxide absorbent, it can be used primarily as a secondary structural material for aircraft, as well as automotive components, building components, panel components, electronic and electrical components, housings, etc. [Example]

[0072] The present invention will now be described by way of examples, but the present invention is not limited to the scope of the examples. Furthermore, in this embodiment, various measurements are performed using the following methods.

[0073] (Acid dissociation constant (pKa) of amine compounds) The acid dissociation constant of amine compounds is determined using the following method. (1) Dissolve 0.2g of the amine compound in 30mL of purified water. (2) The acid dissociation constant (pKa) is calculated by titrating the solution obtained from (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration apparatus (manufactured by Kyoto Electronics Co., Ltd., AT-610). Furthermore, the temperature during the measurement was set to 25±2℃.

[0074] (Amine value of amine compounds) The amine value was determined in accordance with JIS K7237-1995 using the following determination method. (1) Dissolve 0.1g of the amine compound in 20mL of acetic acid. (2) The amine value is calculated by titrating the solution obtained from (1) above with a 0.1N perchloric acid-acetic acid solution using an automatic potentiometric titration apparatus (manufactured by Kyoto Electronics Co., Ltd., AT-610).

[0075] (Maximum endothermic temperature of amine compounds) For amine compounds, the following DSC measurement was performed to determine the maximum endothermic temperature of the amine compound. First, for the amine compound, differential scanning calorimetry (DSC) was performed using a DTG-60 (manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 23–350 °C, a heating rate of 10 °C / min, and a nitrogen atmosphere. From the resulting DSC curve, the temperature at which the endothermic heat accompanying the volatilization of the amine compound reaches its maximum value was calculated, and this temperature was defined as the maximum endothermic temperature of the amine compound.

[0076] (Maximum dissociation temperature of carbon dioxide (CO2) in amine compounds) A carbon dioxide concentration meter and petri dishes were placed inside a desiccator (internal dimensions: 370mm × 260mm × 272mm) that could be opened and closed. Then, an amine compound (5 mmol) was added to the petri dish inside the desiccator, the door was immediately closed, and the amine compound was left to stand in the desiccator at 23°C and 50% RH for 24 hours. Furthermore, the initial concentration of carbon dioxide was adjusted to approximately 400 ppm. Next, the amine compound was removed from the desiccator, yielding an amine compound that had absorbed carbon dioxide. For the amine compound that had absorbed carbon dioxide, DSC measurement was performed as follows to determine the maximum carbon dioxide dissociation temperature of the amine compound. First, for the amine compound, differential scanning calorimetry (DSC) was performed using a DTG-60 (manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 23–250 °C, a heating rate of 10 °C / min, and a nitrogen atmosphere. From the resulting DSC curve, the temperature at which the heat absorption accompanying the release of carbon dioxide reached its maximum value was calculated, and this temperature was defined as the maximum carbon dioxide dissociation temperature of the amine compound.

[0077] In the examples and comparative examples described in Table 1, the following were used in relation to the amine compounds and epoxy resins.

[0078] (amine compounds) MXDA: m-Phenylenediamine (manufactured by Mitsubishi Gas Chemical Co., Ltd.) 1,3-BAC: 1,3-bis(aminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.) AEP: N-(2-aminoethyl)piperazine (manufactured by Tokyo Chemical Industry Co., Ltd.) PACM: 4,4'-Methylenebis(cyclohexylamine) (manufactured by Tokyo Chemical Industry Co., Ltd.) IPDA: Isophorone diamine (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0079] (Epoxy resin) Bis-A type epoxy resin: Bisphenol A type liquid epoxy resin (Mitsubishi Chemical Co., Ltd. "JER828", Bisphenol A diglycidyl ether, epoxy equivalent 186g / equivalent)

[0080] Example 1 (Manufacturing and Evaluation of Epoxy Resin-Based Foam) (1) Absorption of carbon dioxide by amine compounds (Preparation of reaction product (a2) of amine compounds and carbon dioxide) Add 5 mmol of the amine compound MXDA to a container inside the desiccator, and immediately close the desiccator door. Then, place the MXDA in the desiccator at 23°C and 50% RH for one week. This allows the MXDA to react with carbon dioxide in the air to form MXDA carbonate. Here, to prevent uneven reaction, the container containing the amine compound is shaken appropriately to avoid the formation of unreacted MXDA. Furthermore, the initial concentration of carbon dioxide in the desiccator is adjusted to 400 ppm. Next, the mass increase of MXDA was measured, and the mass increase rate of the amine compound was calculated using the following formula. The mass increase rate of the amine compound [mass%] = 100 × mass increase of the amine compound (g) / (initial mass of the amine compound (g) + mass increase of the amine compound (g))

[0081] (2) Preparation of epoxy resin composition Calculate the number of active amine hydrogens of the initial MXDA in (1) above, and weigh the bis-A type epoxy resin in such a way that the number of active amine hydrogens / the number of epoxy groups in the epoxy resin becomes the value recorded in Table 1. Next, the MXDA carbonate obtained in (1) and the bis-A type epoxy resin were mixed by stirring in a disperser at 3000 rpm for 5 minutes to obtain the epoxy resin composition.

[0082] (3) Manufacturing of epoxy resin foam The epoxy resin composition obtained in (2) was placed in a mold with a length × width × height of 7 × 12 × 2.1 cm, and heated using a hot air dryer at a heating temperature of 150°C for 30 minutes to harden and foam the epoxy resin composition. Thus, an epoxy resin foam was obtained. The obtained epoxy resin foam was evaluated as follows. The results are shown in Table 1.

[0083] (Evaluation of foaming properties) The foaming properties of epoxy resin components are evaluated by the density of the epoxy resin foam. Lower density indicates better foaming properties. The density of epoxy resin foam is calculated from the mass and volume of the foam.

[0084] (Evaluation of carbon dioxide absorption capacity) The obtained epoxy resin foam and a carbon dioxide concentration meter were placed in an openable and closable dryer (internal dimensions: 370mm×260mm×272mm). The carbon dioxide absorption per unit volume of the epoxy resin foam (g / cm3) was calculated by the difference (C2-C1) between the carbon dioxide concentration C1 in the dryer 1000 minutes after the epoxy resin foam was placed in the dryer and the maximum carbon dioxide concentration C2 in the dryer between the time of placement and the time of placement. Furthermore, the dryer is set to an air environment of 23°C and 50%RH, with the initial carbon dioxide concentration adjusted to 400ppm.

[0085] (Examples 2-4 and Comparative Example 1) The amine compounds were changed to those shown in Table 1, and otherwise the same procedure as in Example 1 was followed to obtain epoxy resin foams. The above evaluations were performed on the obtained epoxy resin foams. The results are shown in Table 1.

[0086] [Table 1]

[0087] As shown in Table 1, the epoxy resin foam of the embodiments has a higher carbon dioxide absorption capacity compared to the foam of the comparative examples. That is, it can be seen that the epoxy resin foam of the present invention can improve carbon dioxide absorption capacity.

[0088] Example 5 (Fabrication and Evaluation of Multi-layer Structures) The multilayer structure shown in Figure 1, consisting of an outer layer (Ia), a core layer composed of an epoxy resin foam, and an outer layer (Ib) stacked sequentially, was fabricated using the following method and evaluated. (1) Fabrication of carbon fiber reinforced composite material for outer layers (Ia) and (Ib) 100g of bisphenol A type liquid epoxy resin (OLIN "DER332") and 19g of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, Mitsubishi Gas Chemical Co., Ltd., cis isomer / trans isomer ratio = 77 / 23) were mixed to prepare an epoxy resin composition. The epoxy resin composition was then impregnated into carbon fiber fabric (SGL "50K NCF0° / 90°", 300g / m², 0.33mm thick, 6ply) using hand-lamination at room temperature to create a carbon fiber composite substrate. Next, the carbon fiber composite substrate was placed in an aluminum upper and lower mold preheated to 130°C in an oven, the mold was quickly closed, and the mixture was heated for 3 minutes to harden the epoxy resin composition, resulting in a carbon fiber reinforced composite material with an outer layer consisting of carbon fiber fabric and the hardened epoxy resin composition as a matrix resin. Two outer layers of carbon fiber reinforced composite material were made using the same method. The thickness of the carbon fiber reinforced composite is 2mm, and the volume fraction Vf of the carbon fiber in the carbon fiber reinforced composite is 0.49. (2) Preparation of epoxy resin composition (C) For the amine curing agent (A), 5.94 g (32.96 mmol) of the reaction product (a2) obtained in Example 1, namely the carbonate of m-phenylenediamine, and 2.99 g (21.95 mmol) of m-phenylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used. For the epoxy resin (B), 40.90 g of bisphenol A type liquid epoxy resin (Mitsubishi Chemical Co., Ltd. "jER828", bisphenol A diglycidyl ether, epoxy equivalent 186 g / equivalent) was used. They were stirred and mixed in a disperser at 3000 rpm for 5 minutes to obtain epoxy resin composition (C). The ratio of the number of active amine hydrogens in the amine curing agent (A) to the number of epoxy groups in the epoxy resin (B) is 1 / 1. (3) Fabrication of multi-layer structures A spacer with a thickness of 10 mm is placed on the carbon fiber reinforced composite material for the outer layer (Ia) prepared in (1) above. The epoxy resin composition (C) prepared in (2) above is coated inside the spacer to form a foamed layer (II). Further, the carbon fiber reinforced composite material for the outer layer (Ib) is stacked on the spacer (fabrication of the laminate (i)), and the foamed layer (II) is foamed by heating at 80°C for 30 minutes to form a multilayer structure consisting of the outer layer (Ia), the core layer composed of epoxy resin foam, and the outer layer (Ib) stacked in sequence. (4) Evaluation of multi-layered structures For the multilayer structure fabricated in (3) above, the mechanical strength and specific gravity were determined using the following method. The results are shown in Table 2. (Mechanical strength) The bending test was conducted using an Autograph (Shimadzu Corporation "AG-Xplus 100kN") at a temperature of 23°C, a support spacing of 80 mm, and a test speed of 5 mm / min. The bending strength (MPa), specific strength (N·m / kg), bending modulus (GPa), maximum test force (N), and displacement (mm) were measured. (proportion) The measurement was performed using an electronic hydrometer (ALFAMIRAGE, Ltd., "MDS-300").

[0089] [Table 2] Bending strength (MPa) Specific gravity (g / cm3) Specific strength (N·m / kg) Flexural modulus (GPa) Maximum test force (N) Displacement (mm) 33.8 0.63 54 1.23 815 8.7

[0090] Example 6 (Fabrication of Multilayer Structures and Evaluation of Interlayer Adhesion) The multilayer structure shown in Figure 1, consisting of an outer layer (Ia), a core layer composed of an epoxy resin foam, and an outer layer (Ib), was fabricated using the following method, and the interlayer adhesion was evaluated. (1) Fabrication of carbon fiber reinforced composite material for outer layers (Ia) and (Ib) The outer layers (Ia) and (Ib) of the carbon fiber reinforced composite were prepared using the same method as in Example 5. (2) Preparation of epoxy resin composition (C) For the amine curing agent (A), 1.35 g (7.49 mmol) of the reaction product (a2) obtained in Example 1, namely the carbonate of m-phenylenediamine, and 0.68 g (4.99 mmol) of m-phenylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used. For the epoxy resin (B), 9.30 g of bisphenol A type liquid epoxy resin (Mitsubishi Chemical Co., Ltd. "jER828", bisphenol A diglycidyl ether, epoxy equivalent 186 g / equivalent) was used. They were stirred and mixed in a disperser at 3000 rpm for 5 minutes to obtain epoxy resin composition (C). The ratio of the number of active amine hydrogens in the amine curing agent (A) to the number of epoxy groups in the epoxy resin (B) is 1 / 1. (3) Fabrication of multi-layered structures (test specimens described in JIS K6851:1994) On the carbon fiber reinforced composite material for the outer layer (Ia) prepared in (1) above, an epoxy resin composition (C) prepared in (2) above is coated with a thickness of 1 mm, and heated at 60°C for 45 minutes to form a foamed layer (II). Further, the carbon fiber reinforced composite material for the outer layer (Ib) is stacked on top of the foamed layer (II) (fabrication of the laminate (i)), and heated at 130°C for 15 minutes to foam the foamed layer (II), thus forming a multilayer structure consisting of an outer layer (Ia), a core layer composed of an epoxy resin foam, and an outer layer (Ib) stacked sequentially. This multilayer structure is the test piece shape described in JIS K6851:1994, and three test pieces are prepared using the same method. (4) Evaluation of interlayer adhesion Using the multilayer structure (test piece) prepared in (3) above, a tensile test was conducted using an Autograph (Shimadzu Corporation "AG-Xplus 100kN") at 23°C and a test speed of 1 mm / min, in accordance with JIS K6851:1994, to determine the maximum shear stress (MPa). The average value of the three test results is shown in Table 3. A higher value indicates higher interlayer adhesion.

[0091] Example 7 In Example 6, for the amine curing agent (A), 1.35 g (7.49 mmol) of the reaction product (a2) obtained in Example 1, namely the carbonate of m-phenylenediamine, and 0.71 g (4.99 mmol) of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated using the same method as in Example 6. The results are shown in Table 3.

[0092] Example 8 In Example 6, for the amine curing agent (A), 1.13 g (6.27 mmol) of the reaction product (a2) obtained in Example 1, namely the carbonate of m-phenylenediamine, and 1.06 g (6.22 mmol) of isophorone diamine (IPDA, manufactured by EVONIK) were used. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated using the same method as in Example 6. The results are shown in Table 3.

[0093] Examples 9-11 For the outer layers (Ia) and (Ib), iron material (Paltec "SS400 single-sided sandblasting", 25mm×100mm×1.6mm thickness) was prepared. In Example 6, the aforementioned iron material was used for the outer layers (Ia) and (Ib). For the amine curing agent (A), m-phenylenediamine and the reaction product (a2) obtained in Example 1, i.e., the carbonate of m-phenylenediamine, were used in the proportions shown in Table 3. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated in the same manner as in Example 6. The results are shown in Table 3.

[0094] Example 12 For the outer layers (Ia) and (Ib), iron material (Paltec "SS400 single-sided sandblasting", 25mm×100mm×1.6mm thickness) was prepared. In Example 7, the aforementioned iron material was used for the outer layers (Ia) and (Ib). For the amine curing agent (A), 1,3-bis(aminomethyl)cyclohexane and the carbonate of the reaction product (a2) obtained in Example 1, namely m-phenylenediamine, were used in the proportions described in Table 3. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated using the same method as in Example 7. The results are shown in Table 3.

[0095] Example 13 For the outer layers (Ia) and (Ib), iron material (Paltec "SS400 single-sided sandblasting", 25mm×100mm×1.6mm thickness) was prepared. In Example 8, the aforementioned iron material was used for the outer layers (Ia) and (Ib). For the amine curing agent (A), isophorone diamine and the carbonate of the reaction product (a2) obtained in Example 1, namely m-phenylenediamine, were used in the proportions described in Table 3. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated in the same manner as in Example 8. The results are shown in Table 3.

[0096] Example 14 In Example 13, the reaction product (a2) obtained in Example 4, namely isophorone diamine carbonate, was used instead of the reaction product (a2) obtained in Example 1. Regarding the amine curing agent (A), isophorone diamine and isophorone diamine carbonate were used in the proportions shown in Table 3. Otherwise, the fabrication of the multilayer structure and the evaluation of interlayer adhesion were performed using the same method as in Example 13. The results are shown in Table 3. Furthermore, since 1 mol of carbon dioxide and 1 mol of water were added to the isophorone diamine carbonate per mol of isophorone diamine, the molar mass was calculated to be 232.31 g / mol.

[0097] [Table 3] Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Resin composition (C) Amine-based hardener (A) Reaction product (a2) MXDA carbonate (g) 1.35 1.35 1.13 1.13 1.35 1.58 1.35 1.13 IPDA carbonate (g) 1.16 Amine compounds that have not reacted with carbon dioxide MXDA(g) 0.68 0.85 0.68 0.51 1,3-BAC(g) 0.71 0.71 IPDA(g) 1.06 1.06 1.28 Reaction product (a2) / Amine compound that did not react with carbon dioxide (mol ratio) 60 / 40 60 / 40 50 / 50 50 / 50 60 / 40 70 / 30 60 / 40 50 / 50 40 / 60 Epoxy Resin (B) jER828(g) 9.3 9.3 9.3 9.3 9.3 9.3 9.3 9.3 9.3 Types of outer layers (Ia) and (Ib) CFRP CFRP CFRP iron iron iron iron iron iron Maximum shear stress (MPa) 11.1 3.6 9.9 11.5 11.1 8.7 9.9 4.9 3.6

[0098] Examples 15-17, 19 In Example 10, the outer layers (Ia) and (Ib) were changed to the materials described in Table 4. Otherwise, the multilayer structure was fabricated and the interlayer adhesion was evaluated using the same method as in Example 10. The results are shown in Table 4.

[0099] Example 18 (1) Fabrication of glass fiber reinforced composite material for outer layers (Ia) and (Ib) 100g of bisphenol A type liquid epoxy resin (OLIN "DER332") and 19g of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, Mitsubishi Gas Chemical Co., Ltd., cis / trans isomer ratio = 77 / 23) were mixed to prepare an epoxy resin composition. Using Va-RTM molding at room temperature, the prepared epoxy resin composition was impregnated onto a 16cm × 16cm plain woven glass cloth (CENTRAL GLASS FIBER "ERW320-554A", 0.3mm thick) to create a prepreg. The prepreg was then heat-cured in a 60°C hot air dryer for 15 hours to produce a 2mm thick glass fiber reinforced composite material for the outer layer. (2) Preparation of epoxy resin composition (C), fabrication of multilayer structure and evaluation of interlayer adhesion In Example 10, the outer layers (Ia) and (Ib) were replaced with the aforementioned glass fiber reinforced composite material. Otherwise, the preparation of the epoxy resin composition (C), the fabrication of the multilayer structure, and the evaluation of interlayer adhesion were carried out using the same method as in Example 10. The results are shown in Table 4.

[0100] [Table 4] Example 10 Example 15 Example 16 Example 17 Example 18 Example 19 Resin composition (C) Amine-based hardener (A) Reaction product (a2) MXDA carbonate (g) 1.35 1.35 1.35 1.35 1.35 1.35 Amine compounds that have not reacted with carbon dioxide MXDA(g) 0.68 0.68 0.68 0.68 0.68 0.68 Reaction product (a2) / Amine compound that did not react with carbon dioxide (mol ratio) 60 / 40 60 / 40 60 / 40 60 / 40 60 / 40 60 / 40 Epoxy Resin (B) jER828(g) 9.3 9.3 9.3 9.3 9.3 9.3 Types of outer layers (Ia) and (Ib) iron copper SUS Al GFRP CFRP Maximum shear stress (MPa) 11.1 3.0 2.4 1.9 6.7 8.2

[0101] The details of the outer layer recorded in Table 4 are as follows. Copper: STANDARD TESTPIECE (stock) JIS K6850 test piece "C1020P-1 / 2H", 25mm × 100mm × 2mm thickness SUS:STANDARD TESTPIECE manufactures JIS K6850 test piece "SUS304-2B", 25mm × 100mm × 2mm thickness. Al:STANDARD TESTPIECE (stock) manufactures JIS K6850 test piece "A1050P-H24", 25mm × 100mm × 2mm thickness. GFRP: The glass fiber reinforced composite material prepared in Example 18 CFRP: Carbon fiber reinforced composite material prepared in Example 5 [Industrial applicability]

[0102] According to the present invention, an epoxy resin-based foam with improved carbon dioxide absorption capacity can be provided. This foam is also useful as a core material for multilayer structures.

[0103] 100: Multi-layer structure 1a, 1b: Outer layer 2: Epoxy resin foam (core layer)

Claims

1. An epoxy resin-based foam, comprising an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B) foamed to form an epoxy resin-based foam (D); wherein the amine curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, and a cyclic amine compound (a1') that has not reacted with carbon dioxide, wherein the content of the reaction product (a2) in the amine curing agent (A) is 30% to 90% by mass when the total amount of the amine curing agent (A) is 100% by mass, and the cyclic amine compound (a1) has an amine group bonded to a primary carbon atom.

2. If the epoxy resin in claim 1 is a foam, wherein, The mass increase rate of the amine compound after standing in an air environment of 23°C and 50%RH for 1 week is calculated using the following formula. If it is more than 15% by mass and less than 50% by mass, the mass increase rate of the amine compound [mass%] = 100 × mass increase of amine compound (g) / (mass of amine compound (g) + mass increase of amine compound (g)).

3. If the epoxy resin in request item 1 or 2 is a foam, wherein, The amount of carbon dioxide absorbed per unit volume of the epoxy resin foam (D) is above 0.003 g / cm3.

4. If the epoxy resin in request item 1 or 2 is a foam, wherein, The density of the epoxy resin foam (D) is above 0.01 g / cm3 and below 0.80 g / cm3.

5. If the epoxy resin in request item 1 or 2 is a foam, wherein, The epoxy resin (B) comprises epoxy resins having an aromatic ring or alicyclic structure within the molecule.

6. If the epoxy resin in request item 1 or 2 is a foam, wherein, The cyclic amine compound (a1) comprises a compound represented by the following formula (1), in which R1 to R4 each independently represent a hydrogen atom, or may have a hydrocarbon group with 1 or more carbon atoms and 10 or less having a substituent selected from at least one of amino, cyano and phenyl; R5 to R10 each independently represent a hydrogen atom or a hydrocarbon group with 1 or more carbon atoms and 4 or less; x and y each independently represent an integer of 0 or more and 6 or less; x+y is 1 or more and 6 or less; p and q each independently represent an integer of 0 or more and 4 or less; and at least one of p and q is 1 or more.

7. If the epoxy resin in request item 1 or 2 is a foam, wherein, The cyclic amine compound (a1) has 2 or more but less than 6 amino groups.

8. If the epoxy resin in request item 1 or 2 is a foam, wherein, The cyclic structure of the cyclic amine compound (a1) includes at least one selected from 5-membered rings and 6-membered rings.

9. If the epoxy resin in request item 1 or 2 is a foam, wherein, The cyclic amine compound (a1) comprises at least one selected from bis(aminomethyl)cyclohexane and its derivatives, limonene diamine and its derivatives, and isophorone diamine and its derivatives.

10. A carbon dioxide absorbent comprising an epoxy resin-based foam (D) as claimed in any one of claims 1 to 9.

11. A method for manufacturing an epoxy resin-based foam, comprising the following steps: foaming an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B); wherein the amine curing agent (A) contains a reaction product (a2) of an amine compound containing a cyclic amine compound (a1) and carbon dioxide, and a cyclic amine compound (a1') that has not reacted with carbon dioxide, wherein the content of the reaction product (a2) in the amine curing agent (A) is 30% to 90% by mass when the total amount of the amine curing agent (A) is 100% by mass, and the cyclic amine compound (a1) has an amine group bonded to a primary carbon atom.

12. The method for manufacturing an epoxy resin foam as claimed in claim 11 further includes the following step: prior to the step of foaming the epoxy resin composition (C), the amine compound is contacted with a gas having a carbon dioxide concentration of 0.01% by volume or more and 10% by volume or less, thereby reacting the amine compound with the carbon dioxide to obtain the reaction product (a2).

13. The method for manufacturing an epoxy resin-based foam as described in claim 11 or 12, wherein, The mass increase rate of the amine compound after standing in an air environment of 23°C and 50%RH for 1 week is calculated using the following formula. If it is more than 15% by mass and less than 50% by mass, the mass increase rate of the amine compound [mass%] = 100 × mass increase of amine compound (g) / (mass of amine compound (g) + mass increase of amine compound (g)).

14. A multilayer structure having an outer layer on at least one side of an epoxy resin foam as claimed in any one of claims 1 to 9.

15. As in request item 14, a multi-layered structure, wherein, The multilayer structure system has, in sequence, an outer layer (Ia), a core layer composed of the epoxy resin foam, and an outer layer (Ib).

16. As in request item 15, a multi-layered structure, wherein, At least one of the outer layers (Ia) and (Ib) is a fiber-reinforced composite material containing a matrix resin and reinforcing fibers.

17. A method for manufacturing a multilayer structure, comprising at least one step selected from steps (i) to (iii) below: Step (i): sequentially laminating an outer layer (Ia) or its precursor, a foamed layer (II) composed of an epoxy resin composition (C) containing an amine curing agent (A) and an epoxy resin (B), and the outer layer (Ib) or its precursor to form a laminate (i), and then foaming the foamed layer (II); Step (ii): sequentially laminating an outer layer (Ia) or its precursor, the core layer, and the outer layer (Ib) or its precursor to form a laminate (ii), and then integrating the outer layer (Ia) or its precursor, the core layer, and the outer layer (Ib) or its precursor; Step (iii): After stacking the outer layer (Ia) or its precursor with the core layer to form a laminate (iii), the laminate (iii) is then stacked with the outer layer (Ib) or its precursor and integrated with it.

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