Benzoxazine-based resin composition, prepreg, and method for producing resin composition

Abstract

To provide an advantageous method for producing a curable resin composition.SOLUTION: A resin composition according to the present disclosure contains: a compound (A) having a benzoxazine ring and an aldehyde group; and an aromatic amine compound (B). The amount of aldehyde groups is 50 mol% or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol%. The amount of a solvent contained in the resin composition is 0 wt.% or more and 68 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition containing a compound having a benzoxazine ring, a method for producing the same, a prepreg obtained from the resin composition, and a fiber composite material that is a cured product of the prepreg. [Background technology]

[0002] It is known that benzoxazine compounds are cured by the ring-opening polymerization of the benzoxazine ring and / or reaction with other compounds due to heat or other factors. For example, Patent Document 1 discloses a curable resin composition containing a benzoxazine compound, and films and prepregs using the same. Furthermore, Patent Document 2 discloses an imino group-containing benzoxazine resin that can be decomposed after curing. For example, by decomposing a cured product containing reinforcing fibers (reinforced fiber composite material), the decomposition products and reinforcing fibers can be recovered. The recovered decomposition products may be reusable as resin raw materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-148562 [Patent Document 2] International Publication No. 2023 / 204169 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional techniques have room for improvement in terms of making the manufacturing process for a benzoxazine-based resin composition or a prepreg containing the benzoxazine-based resin composition more advantageous (simple). There is also room for improvement in terms of increasing the solids concentration of the solution used to manufacture the benzoxazine-based resin composition or prepreg. One aspect of the present invention aims to realize a more advantageous (simple) manufacturing process for a benzoxazine-based resin composition or a prepreg containing the benzoxazine-based resin composition. Another aspect of the present invention aims to realize a high solids concentration of the solution used to manufacture the benzoxazine-based resin composition or prepreg.

[0005] Therefore, the present inventors have considered further improving the manufacturing process of Patent Document 2, and as a result of extensive investigation, have succeeded in designing a more advantageous manufacturing process. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a method for producing a prepreg according to one aspect of the present invention includes a step of mixing a resin composition containing a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B) with reinforcing fibers, In the production method, the amount of aldehyde groups is 50 mol % or more when the total amount of aldehyde groups and imino groups in the resin composition is taken as 100 mol %.

[0007] In order to solve the above-mentioned problems, a resin composition according to one aspect of the present invention is a resin composition including a compound (A) having a benzoxazine ring and an aldehyde group, and an aromatic amine compound (B), the amount of aldehyde groups is 50 mol % or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %, The amount of the solvent contained in the resin composition is 0% by weight or more and 68% by weight or less. [Effects of the Invention]

[0008] One aspect of the present invention provides a more advantageous (simple) production process for a benzoxazine-based resin composition or a prepreg containing the benzoxazine-based resin composition. It also enables the solids concentration of the solution used to produce the benzoxazine-based resin composition or prepreg to be increased. When the solids concentration of the solution is high, for example, evaporation of the solvent in the prepreg becomes easier. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows GPC charts (mobile phase: DMF) of the imino group-containing benzoxazine compounds of Production Examples 1 to 3. [Figure 2] 1 shows IR charts of the imino group-containing benzoxazine compounds of Production Examples 1 and 3 to 5 and Example 2. [Figure 3] 1 shows the results of measuring the melt viscosity of the imino group-containing benzoxazine compound of Production Example 3. [Figure 4] 1 shows GPC charts (mobile phase: chloroform) of the imino group-containing benzoxazine compounds of Production Examples 1, 3, and 5. [Figure 5] 1 is a GPC chart of the imino group-containing benzoxazine compound of Production Example 6 (mobile phase: lithium chloride-containing DMF). [Figure 6] 3 shows DMA curves of cured molded bodies of Examples 2 and 7. [Figure 7] 1 shows the results of measuring the melt viscosity of the imino group-containing benzoxazine compound (dry solid) of Production Example 6. [Figure 8] 3 shows DMA curves of cured molded bodies of Comparative Examples 1 to 3. [Figure 9] FIG. 1 shows the results of an amine decomposition evaluation test (decomposition evaluation 1) in each of the examples and comparative examples. [Figure 10] FIG. 1 shows the results of a hydrolysis evaluation test (degradation evaluation 2) in each of the examples and comparative examples. [Figure 11] FIG. 1 is a diagram illustrating a method for producing carbon fiber reinforced plastic (CFRP). [Figure 12]1 shows the decomposition state of the CFRP of Example 13 (decomposition evaluation 1), and the state of the r-CF and resin decomposition solution separated from the CFRP of Example 14. [Figure 13] 1 shows the decomposition state of the CFRP of Example 15 (decomposition evaluation 2). DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an example of an embodiment of the present invention will be described in detail, but the present invention is not limited thereto. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less."

[0011] In this specification, the aldehyde group refers to a -CH(=O) group, and the imino group refers to a -CH=N- group formed by a dehydration condensation reaction between an aldehyde group and an amino group. The resin composition in this specification may be in a solid state or in a solution state dissolved in a solvent.

[0012] 1. Overview of the Invention A conventional method for producing a prepreg includes the following steps (1) to (5).

[0013] (1) A benzoxazine resin having an aldehyde group at its terminal is reacted with an amine compound in a solution to prepare a polymer of the benzoxazine resin containing an imino group.

[0014] (2) The polymer obtained in (1) above is isolated from the solution.

[0015] (3) The polymer isolated in (2) above is dissolved again in a solvent.

[0016] (4) The solution obtained in (3) above is impregnated into reinforcing fibers.

[0017] (5) After impregnation, the solution is dried to obtain a prepreg.

[0018] However, the solubility of the polymer prepared in step (1) above in the solvent is often not sufficiently high. As a result, the concentration of the polymer isolated in step (2) above in the solution used in prepreg production is low, and a large amount of solvent must be removed in the drying process to obtain prepreg from reinforcing fibers impregnated with the polymer solution. In addition, many of the solvents that can be used in step (2) above have relatively high boiling points. For these reasons, the drying process in step (3) above often requires a long time.

[0019] Therefore, conventional prepreg manufacturing methods have room for improvement in the following respects. The process for producing a benzoxazine-based resin composition or a prepreg containing the benzoxazine-based resin composition is made more advantageous (simple). Increasing the solids concentration of the solution when producing a benzoxazine resin composition or prepreg, i.e., reducing the amount of solvent used.

[0020] On the other hand, the method for producing a prepreg according to one embodiment of the present invention does not require the step of preparing an imino group-containing benzoxazine resin, isolating it, and then redissolving it. Therefore, the production process is more advantageous (simpler) than conventional prepreg production methods. Furthermore, the method for producing a prepreg according to one embodiment of the present invention uses a resin composition containing a compound (monomer) having a benzoxazine ring and an aldehyde group, and an aromatic amine compound. Because the monomer has high solubility in solvents, a small amount of solvent is required; that is, the solids concentration of the solution used to produce the benzoxazine resin composition or prepreg is high.

[0021] [2. Resin composition] A resin composition according to one embodiment of the present invention contains a compound (A) having a benzoxazine ring and an aldehyde group, and an aromatic amine compound (B). The resin composition may be in the form of a solution dissolved in a solvent, or may be in the form of a solid.

[0022] (Compound (A) Having a Benzoxazine Ring and an Aldehyde Group) The number of aldehyde groups in the compound (A) having a benzoxazine ring and an aldehyde group according to one embodiment of the present invention is not particularly limited, but may usually be 2 to 5, preferably 2 to 3, and more preferably 2.

[0023] The compound (A) having a benzoxazine ring and an aldehyde group according to one embodiment of the present invention may be represented by the following general formula (I).

[0024] [ka]

[0025] [In the general formula (I), Ar 1 and Ar 2 represents a trivalent aromatic group derived from a phenol compound. In this specification, the term "aromatic group" refers to an organic group having at least one aromatic ring. Ar 1 and Ar 2 may be the same or different. 1 represents a divalent aromatic group. The divalent aromatic group may be a divalent aromatic group derived from the following general formula (IIa) or a divalent aromatic group represented by any one of general formulas (III) to (V). 1 , Ar 2 , and R 1 does not have a C=N group. The compound (A) having a benzoxazine ring and an aldehyde group according to one embodiment of the present invention can be produced, for example, by reacting a phenol compound, an aromatic diamine compound (Q), and an aldehyde compound.

[0026] The phenol compound is preferably a phenol compound having an aldehyde group. Examples of the phenol compound having an aldehyde group include 4-hydroxybenzaldehyde, 2-hydroxybenzaldehyde, vanillin, etc. Among them, from the viewpoint of ease of synthesis of compound (A), the phenol compound is preferably 4-hydroxybenzaldehyde and / or vanillin, and more preferably 4-hydroxybenzaldehyde.

[0027] The aromatic diamine compound (Q) may be an aromatic diamine compound represented by the following general formula (IIa) or an aromatic diamine compound containing a divalent aromatic group represented by any one of general formulas (III) to (V), or may be another aromatic diamine compound. Examples of other aromatic diamine compounds include 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 2,2'-dimethylbiphenyl-4,4'-diamine.

[0028] [ka]

[0029] [In general formula (IIa), the positional relationship of the main chain bonds excluding R bonded to the aromatic ring is meta or para. R is a substituent on the aromatic ring and represents an aliphatic group having 1 to 10 carbon atoms. The number of R is 0 or 1 or more, and when the number of R is 2 or more, they may be the same or different. m1 and m2 each represent 0 or 1.]

[0030] [ka]

[0031] [In general formula (III), an asterisk represents a bond. The positions of the main chain bonds excluding R, which are bonded to the two aromatic rings, are meta or para. L1 represents one or more of a single bond, an isopropylidene group, a sulfonyl group, a carbonyl group, and a 9,9-fluorenyl group. R is a substituent on the aromatic ring and represents an aliphatic group having 1 to 10 carbon atoms. The number of R in each aromatic ring is 0 or 1 or more. When the number of R is 2 or more, they may be the same or different. m3 and m4 each represent 0 or 1.]

[0032] [ka]

[0033] [In general formula (IV), an asterisk represents a bond. The positions of the main chain bonds excluding R, which are bonded to the three aromatic rings, are meta or para. L2 and L3 each represent an oxy group. R is a substituent on the aromatic ring and represents an aliphatic group having 1 to 10 carbon atoms. The number of R in each aromatic ring is 0 or 1 or more. When the number of R is 2 or more, they may be the same or different. m5 and m6 each represent 0 or 1.]

[0034] [ka]

[0035] [In general formula (V), an asterisk represents a bond. The positions of the main chain bonds excluding R, which are bonded to the four aromatic rings, are meta or para. L4 and L6 each represent an oxy group. L5 represents one or more of a single bond, an isopropylidene group, a sulfonyl group, a carbonyl group, and a 9,9-fluorenyl group. R is a substituent on the aromatic ring and represents an aliphatic group having 1 to 10 carbon atoms. The number of R in each aromatic ring is 0 or 1 or more. When the number of R is 2 or more, they may be the same or different. m7 and m8 each represent 0 or 1.] In other words, the aromatic diamine compound (Q) is represented by any one of the following general formulas (IIa) to (Va): In general formulas (IIa) to (Va), the definitions of L1 to L6, R, and m1 to m8 are the same as those in general formula (IIa) and general formulas (III) to (V).

[0036] [ka]

[0037] From the viewpoint of availability and ease of synthesis of the compound (A), the aromatic diamine compound (Q) is preferably 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 4-(aminomethyl)benzylamine, 3,3'-sulfonyldianiline, 4,4'-sulfonyldianiline, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 4,4 Preferably, the 3-(aminomethyl)benzylamine is at least one selected from the group consisting of m-xylene-α,α'-diamine, ...

[0038] The aldehyde compound is not particularly limited, but formaldehyde is preferred. As formaldehyde, paraformaldehyde, which is a polymer, or formalin, which is in the form of an aqueous solution, can be used.

[0039] In the production of compound (A), the molar ratio of the phenol compound to the aromatic diamine compound (Q) is preferably about 2:1, but may be 2.5 / 1 to 1.95 / 1. The molar ratio of the phenol compound to the aldehyde compound is preferably 1 / 1 to 1 / 20, more preferably 1 / 2 to 1 / 6. When the molar ratio of the phenol compound to the aldehyde compound is within the above range, a benzoxazine ring can be suitably produced.

[0040] A solvent can be used when producing the compound (A) having a benzoxazine ring and an aldehyde group according to one embodiment of the present invention. Examples of the solvent include halogenated solvents such as chloroform, non-halogenated aromatic hydrocarbon solvents such as toluene and xylene, ether solvents such as tetrahydrofuran (THF), cyclic diether solvents such as 1,4-dioxane and 1,3-dioxolane, highly polar and high-boiling solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N,N-diethylacetamide, N-methylcaprolactam, γ-butyrolactone, and dimethyl sulfoxide, and mixed solvents of non-halogenated hydrocarbon solvents and aliphatic alcohol solvents. Examples of aliphatic alcohol solvents include methanol, ethanol, propanol, and butanol (including structural isomers). To prevent side reactions, it is preferable to use a non-halogenated aromatic hydrocarbon solvent.

[0041] (Aromatic amine compound (B)) The number of amino groups in the aromatic amine compound (B) according to one embodiment of the present invention is not particularly limited, but may typically be 2 to 5, preferably 2 to 3, and more preferably 2. When the aromatic amine compound (B) according to one embodiment of the present invention is an aromatic diamine compound, it may be the same as or different from the aromatic diamine compound (Q). The aromatic diamine compound (B) may be an aromatic diamine compound represented by the above-mentioned general formula (IIa) or an aromatic diamine compound containing a divalent aromatic group represented by any of general formulas (III) to (V), or may be another aromatic diamine compound. Examples of other aromatic diamine compounds include 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 2,2'-dimethylbiphenyl-4,4'-diamine.

[0042] The aromatic amine compound (B) may be at least one compound selected from the group consisting of 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, and 9,9-bis(4-aminophenyl)fluorene.

[0043] 3. Method for producing resin composition A resin composition according to one embodiment of the present invention is produced by mixing a compound (A) having a benzoxazine ring and an aldehyde group with an aromatic amine compound (B). The compound (A) and the compound (B) are usually mixed in a solvent.

[0044] (Production of an imino group by reaction of compound (A) and compound (B)) A resin composition according to one embodiment of the present invention is a mixture of a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B). In this mixture, imino groups may be generated by a dehydration condensation reaction between the aldehyde group in compound (A) and the amino group in compound (B). In a resin composition according to one embodiment of the present invention, the amount of aldehyde groups is 50 mol% or more, where the total amount of aldehyde groups and imino groups in the resin composition is 100 mol%. In one embodiment of the present invention, the amount of aldehyde groups is preferably 55 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more, where the total amount of aldehyde groups and imino groups in the resin composition is 100 mol%. The resin composition according to one embodiment of the present invention may have an aldehyde group amount of 100 mol% and an imino group amount of 0 mol%. A high amount of aldehyde groups reduces the viscosity of the resin composition, making it easier to impregnate reinforcing fibers with the resin composition.

[0045] (Amount of imino groups in resin composition) A resin composition according to one embodiment of the present invention ultimately yields a cured product through a reaction such as cleavage of the benzoxazine ring. In one embodiment of the present invention, it is desirable that the amount of imino groups in the resin composition is increased immediately before the curing reaction of the benzoxazine ring occurs. In other words, it is desirable that the imino group-forming reaction by dehydration condensation proceeds to produce a resin composition with a high amount of imino groups. Before the curing reaction of the benzoxazine ring occurs, the amount of imino groups in the resin composition is preferably greater than 50 mol%, more preferably greater than 70 mol%, even more preferably greater than 80 mol%, and particularly preferably greater than 90 mol%, when the total amount of aldehyde groups and imino groups in the resin composition is taken as 100 mol%.

[0046] One embodiment of the present invention also includes a method for producing a resin composition having a high imino group content, which comprises heating a resin composition in a solution state until the amount of imino groups in the resin composition exceeds 50 mol %, assuming that the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %.

[0047] Furthermore, one embodiment of the present invention also includes a method for producing a resin composition having a high imino group content, which comprises heating a solid resin composition until the imino group content is 70 mol % or more, where the total content of aldehyde groups and imino groups in the resin composition is 100 mol %.

[0048] (Solvent in Resin Composition) The resin composition according to one embodiment of the present invention usually contains a solvent, but may also contain no solvent. In this specification, a resin composition containing a solvent may also be referred to as a varnish.

[0049] Examples of solvents contained in the resin composition according to one embodiment of the present invention include halogenated solvents such as chloroform, non-halogenated aromatic hydrocarbon solvents such as toluene and xylene, ether solvents such as tetrahydrofuran (THF), cyclic diether solvents such as 1,4-dioxane and 1,3-dioxolane, highly polar and high-boiling point solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N,N-diethylacetamide, N-methylcaprolactam, γ-butyrolactone, and dimethyl sulfoxide, and mixed solvents of non-halogenated hydrocarbon solvents and aliphatic alcohol solvents. Examples of aliphatic alcohol solvents include methanol, ethanol, propanol, and butanol (including structural isomers). To prevent side reactions, non-halogenated aromatic hydrocarbon solvents are preferred.

[0050] The amount of solvent contained in the resin composition according to one embodiment of the present invention is not particularly limited, but is typically 0% by weight or more and 95% by weight or less, preferably 0% by weight or more and 68% by weight or less, more preferably 10% by weight or more and 67% by weight or less, and even more preferably 20% by weight or more and 65% by weight or less, of the resin composition.

[0051] (reinforced fiber) The resin composition according to one embodiment of the present invention may further contain reinforcing fibers. The reinforcing fibers may be contained in the resin composition by impregnating the reinforcing fibers with the resin composition. Examples of the reinforcing fibers according to one embodiment of the present invention include inorganic fibers, organic fibers, metal fibers, and hybrid reinforcing fibers that combine these. The reinforcing fibers may be one type or two or more types.

[0052] Examples of inorganic fibers include carbon fibers, graphite fibers, silicon carbide fibers, alumina fibers, tungsten carbide fibers, boron fibers, and glass fibers. Examples of organic fibers include aramid fibers, high-density polyethylene fibers, and other common nylon fibers and polyester fibers. Examples of metal fibers include stainless steel and iron fibers. Examples of metal fibers include carbon-coated metal fibers, which are metal fibers coated with carbon. Among these, carbon fibers are preferred as the reinforcing fibers from the viewpoint of increasing the strength of the cured product.

[0053] Generally, the carbon fibers are subjected to a sizing treatment, but they may be used as they are, or, if necessary, fibers containing a small amount of sizing agent may be used, or the sizing agent may be removed by an existing method such as an organic solvent treatment or a heat treatment. Alternatively, the carbon fiber bundles may be opened in advance using air or a roller, and a treatment may be performed to facilitate impregnation of the resin between the single carbon fiber yarns.

[0054] (Other ingredients) A resin composition according to one embodiment of the present invention contains the compound (A) and the compound (B) as main components, and may contain other thermosetting resins, thermoplastic resins, and compounding agents as secondary components.

[0055] Other thermosetting resins include, for example, epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, silicon resins, melamine resins, urea resins, allyl resins, phenolic resins, unsaturated polyester resins, bismaleimide resins, alkyd resins, furan resins, polyurethane resins, and aniline resins.

[0056] Examples of the thermoplastic resin include a thermoplastic epoxy resin and a thermoplastic polyimide resin.

[0057] Examples of compounding agents include flame retardants, nucleating agents, antioxidants, antiaging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, flame retardant assistants, antistatic agents, antifogging agents, fillers, softeners, plasticizers, and colorants, as needed. These may be used alone or in combination of two or more. Reactive or non-reactive solvents may also be used.

[0058] [4. Prepreg] An embodiment of the present invention also includes a prepreg made of a resin composition containing the above-mentioned reinforcing fibers.

[0059] (Prepreg manufacturing method) A prepreg according to one embodiment of the present invention is produced by a production method including a step of mixing a resin composition containing a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B) with reinforcing fibers. In other words, a prepreg according to one embodiment of the present invention is produced by impregnating reinforcing fibers with a composition containing the compound (A) having a benzoxazine ring and an aldehyde group and the aromatic amine compound (B). Typically, the prepreg can be produced by impregnating reinforcing fibers with a mixture of the compound (A), the compound (B), and a solvent (known as a varnish by those skilled in the art).

[0060] When the total amount of aldehyde groups and imino groups in the resin composition is taken as 100 mol %, the amount of aldehyde groups is 50 mol % or more. Also, the amount of solvent in the resin composition is preferably 68 wt % or less.

[0061] Moreover, the method for producing a prepreg according to one embodiment of the present invention preferably includes the following steps. Step 1: A mixture containing a compound (A) having a benzoxazine ring and an aldehyde group, an aromatic amine compound (B), and a solvent is prepared. Step 2: The mixture obtained in step 1 is impregnated into the reinforcing fibers.

[0062] [5. Curing reaction of benzoxazine ring] A resin composition according to one embodiment of the present invention contains a benzoxazine ring derived from compound (A). This benzoxazine ring can undergo ring-opening polymerization and / or reaction with other compounds due to heat or the like to give a cured product. When the resin composition according to one embodiment of the present invention contains reinforcing fibers, a fiber-reinforced composite material can be obtained. In this specification, the term "fiber-reinforced composite material" is also referred to as a "fiber composite material."

[0063] The final heat treatment temperature required to completely cure the resin composition according to one embodiment of the present invention is usually 150°C or higher, but the curing reaction temperature is preferably 180°C or higher, more preferably 220°C or higher. Here, "completely cured" does not only refer to the state after all benzoxazine rings have reacted, but may also refer to the state after the benzoxazine rings have reacted to an extent that they can withstand use as a molded product. In order to prevent thermal decomposition of the resin composition during the curing reaction, the curing reaction is preferably carried out at 260°C or lower.

[0064] 6. Manufacturing method of fiber composite material (fiber composite materials) A fiber composite material can be obtained by impregnating reinforcing fibers with the resin composition according to one embodiment of the present invention, or by curing the prepreg according to one embodiment of the present invention.

[0065] (carbon fiber composite materials) When the reinforcing fibers in the prepreg according to one embodiment of the present invention are carbon fibers, a carbon fiber composite material can be obtained from the prepreg.

[0066] Carbon fiber composite materials are also called carbon fiber reinforced plastics (CFRP). There are no particular limitations on the method for producing carbon fiber composite materials, but for example, a method using prepreg, which is a sheet of carbon fiber impregnated with resin, or a method of impregnating carbon fiber (bundle-like or woven) with liquid resin may be used.

[0067] Although a carbon fiber composite material is used as an example here, as mentioned above, the reinforcing fibers that can be used are not limited to carbon fiber. The reaction is preferably carried out at 260°C or lower.

[0068] (Manufacturing method) One embodiment of the present invention also includes a method for producing a fiber composite material obtained by curing the prepreg. The method for producing the fiber composite material is not particularly limited, but the fiber composite material can be produced by a method including a step of producing the prepreg and then heating the prepreg to 150°C or higher. That is, the fiber composite material can be produced by a method including a step of producing a prepreg by the above-mentioned method and a step of heating the prepreg to 150°C or higher. The temperature to which the prepreg is heated is 150°C or higher, preferably 180°C or higher, and more preferably 220°C or higher. The temperature to which the prepreg is heated may be, for example, 300°C or lower.

[0069] The method for producing a fiber composite material may include, for example, a step of pre-curing a prepreg to obtain a pre-cured prepreg having a degree of cure of more than 0% to 99%, and a step of curing the pre-cured prepreg to obtain a fiber composite material. Here, in this specification, pre-curing means partially curing the prepreg.

[0070] The degree of cure of the pre-cured prepreg may be 99% or less, preferably 90% or less, and more preferably 80% or less.

[0071] While a fiber composite material made solely of a prepreg according to one embodiment of the present invention is given as an example here, a fiber composite material may also be produced by laminating together a prepreg according to one embodiment of the present invention and a prepreg obtained by impregnating reinforcing fibers with another resin or a composition thereof. The other resin is not particularly limited, and examples thereof include other thermosetting resins and thermoplastic resins listed in [2. Resin Composition]. The composition may contain the other resin as a main component and, in addition, other thermosetting resins (excluding the other resins), thermoplastic resins (excluding the other resins), and compounding agents listed in [2. Resin Composition]. That is, one embodiment of the present invention also includes a fiber composite material in which a fiber composite material obtained by impregnating reinforcing fibers with the above-mentioned resin composition and curing the resin composition is inseparably integrated with a fiber composite material obtained by impregnating reinforcing fibers with another resin or a composition thereof.

[0072] 7. Method for producing cured product One embodiment of the present invention also includes a method for producing a cured product, which includes a step of producing a resin composition and then heating the produced resin composition to 150°C or higher. That is, the production method includes a step of obtaining a resin composition and a step of heating the obtained resin composition to 150°C or higher. The heating temperature of the resin composition to obtain a cured product may be 150°C or higher, 180°C or higher, or 220°C or higher.

[0073] (Characteristics of the cured product) A prepreg or cured product obtained from a resin composition according to one embodiment of the present invention exhibits various excellent properties similar to those described in Patent Document 2 (WO2023 / 204169). A prepreg according to one embodiment of the present invention may be cured in a free-standing state. Herein, the term "free-standing state" refers to a state in which a free-standing shape is maintained. Furthermore, the term "free-standing shape" refers to any shape, such as a curved shape, that can be imparted after molding without the need for a physical support.

[0074] In this specification, the property of being able to cure in a free-standing state refers to the property that when a laminate containing prepreg having any desired shape, for example a curved shape, is heated in an oven or the like, the shape (free-standing shape) is maintained even after heating without the need for a physical support. Here, a laminate containing prepreg is also referred to as a prepreg laminate. Specifically, this property refers to the property that when one end of a prepreg laminate is fixed to the main surface of a flat object and the other end is left floating in the air and heated in an oven or the like, the pre-heating shape (for example, a curved shape) is maintained even after heating.

[0075] The freestanding property makes it possible to switch from autoclave molding to oven molding midway through molding the composite material. Unlike autoclave molding, oven molding allows the use of general-purpose auxiliary materials (heat resistance of about 180°C, in line with epoxy). Therefore, the freestanding property is preferable because it allows composite materials to be molded without the need for expensive auxiliary materials.

[0076] Furthermore, as described below, the cured product according to one embodiment of the present invention may be decomposed under acidic or basic conditions to give decomposition products soluble in a solvent. Furthermore, the decomposition products may be recovered and reused. For example, the decomposition solution (an acidic or basic solution containing the decomposition products) may be dried, or the decomposition solution may be mixed with a poor solvent to precipitate and obtain solids, thereby recovering the decomposition products from the solvent. The recovered decomposition products may then be reacted to obtain a cured product again.

[0077] When the cured product contains reinforcing fibers, both the decomposition product and the reinforcing fibers can be recovered and reused. Specifically, the decomposition product and the reinforcing fibers are first separated and recovered by filtration, centrifugation, or the like. The decomposition liquid containing the decomposition product is then dried, or the decomposition liquid is mixed with a poor solvent to precipitate and obtain the solid content, thereby recovering the decomposition product from the solvent. Alternatively, the recovered decomposition product can be mixed with reinforcing fibers and reacted to obtain a cured product containing reinforcing fibers again.

[0078] Furthermore, the above-described configuration allows the hardened material to be disassembled and reused, which can contribute to ensuring sustainable consumption and production patterns, and thus contribute to achieving and realizing Goal 12 of the Sustainable Development Goals (SDGs), "Responsible Consumption and Production."

[0079] 8. Method for Decomposing Fiber Composite Materials and Cured Materials The fiber composite material can be decomposed under acidic or basic conditions. One embodiment of the present invention also includes a method for decomposing the fiber composite material obtained by the above-mentioned production method, which comprises decomposing the fiber composite material under acidic or basic conditions.

[0080] Here, decomposition under acidic conditions refers to solvolysis. Decomposition under basic conditions, for example, involves adding a basic substance to an imino group to cause a cleavage reaction or a bond exchange reaction. Decomposition under acidic or basic conditions can cleave the imine bond in the fiber composite material to obtain a decomposition product. In this specification, solvolysis refers to the reaction of a solvent molecule with the imine bond to cleave the imine bond and obtain a decomposition product.

[0081] A method for solvolyzing a fiber composite material under acidic conditions includes contacting the fiber composite material with an acidic solution containing an acid and a solvent. Examples of the solvent in the acidic solution include water, tetrahydrofuran (THF), and mixtures thereof. Examples of the acid include acetic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0082] A method for decomposing a fiber composite material under basic conditions includes contacting the fiber composite material with an amine compound. The amine compound is not particularly limited, but examples thereof include aromatic monoamines such as aniline, aromatic diamines such as p-phenylenediamine, 1,3-bis(4-aminophenoxy)benzene (RODA), and 4,4'-isopropylidenebis[(4-aminophenoxy)benzene] (BAPP), aliphatic monoamines such as methylamine, ethylamine, and butylamine, and aliphatic diamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, and m-xylene-α,α'-diamine (mXDA).

[0083] In the decomposition step, heating may be performed. The heating temperature may be, for example, 40 to 180° C. The heating time may be 5 minutes to 350 hours. In the decomposition step, stirring may be performed as appropriate.

[0084] The cured product obtained by curing the resin composition can also be decomposed under acidic or basic conditions. One embodiment of the present invention also includes a method for decomposing the cured product, which includes a step of decomposing the cured product under acidic or basic conditions. Here, the cured product may be obtained by curing the resin composition in the prepreg obtained by the above-mentioned "method for producing a prepreg." Decomposition under acidic conditions and decomposition under basic conditions are the same as the decomposition of the above-mentioned fiber composite material, so a description thereof will be omitted here.

[0085] [9. Cured molded body] A cured molded product can be obtained by curing and molding a resin composition according to one embodiment of the present invention. In this specification, the term "cured molded product" refers to a molded product having a degree of cure of 1 to 100%. In other words, the term "cured molded product" also encompasses molded products that are only partially cured. As shown in the examples below, the degree of cure can be calculated from the ratio of the areas of the exothermic peaks obtained from the DSC curves of the uncured resin and the uncured molded product or the cured molded product. Here, the term "uncured molded product" refers to a molded product having a degree of cure of less than 1%.

[0086] The size and shape of the cured molded product are not particularly limited, and examples thereof include a film, sheet, plate, block, etc. The cured molded product may have other layers (e.g., an adhesive layer) in addition to the layer made of the resin composition described above.

[0087] From the viewpoint of heat resistance, the glass transition temperature of the cured molded product is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 220° C. or higher. There is no particular upper limit to the glass transition temperature of the cured molded product, but it can be, for example, 400° C. or lower.

[0088] The thermal stability of the cured molded product can be evaluated by its 5% weight loss temperature (Td5), which is preferably 250°C or higher, more preferably 300°C or higher, and even more preferably 320°C or higher.

[0089] From the viewpoint of mechanical properties, the tensile modulus of the cured molded product is preferably 10 GPa or less, more preferably 8 GPa or less, and even more preferably 5 GPa or less, and from the viewpoint of ease of handling, the tensile modulus of the cured molded product is preferably 0.1 GPa or more, more preferably 0.5 GPa or more, and even more preferably 1 GPa or more.

[0090] The tensile breaking strength of the cured molded body is preferably 5 MPa or more, more preferably 10 MPa or more, and even more preferably 50 MPa or more, from the viewpoint of resistance to breaking.

[0091] From the viewpoint of mechanical properties, the tensile elongation at break of the cured molded product is preferably 1% or more, more preferably 3% or more, and even more preferably 5% or more.

[0092] The method for molding the cured molded article is not particularly limited, and examples thereof include a method in which the above-mentioned resin composition is dissolved in a solvent and the resulting solution is cast onto a substrate to form the molded article (casting method), and a method in which the above-mentioned thermosetting resin or composition is pressed and molded (pressing method). Examples of solvents used in the casting method include N,N-dimethylformamide (DMF), tetrahydrofuran (THF), chloroform, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N,N-diethylacetamide, N-methylcaprolactam, γ-butyrolactone, cyclohexanone, dimethyl sulfoxide, cyclopentanone, 1,4-dioxane, and 1,3-dioxolane. The pressure used in the pressing method is not particularly limited, and may be, for example, 0.1 to 5.0 MPa.

[0093] The curing temperature of the cured molded body (the highest temperature when the temperature is gradually increased) is not particularly limited, but is preferably 200 to 300°C, more preferably 210 to 280°C, and even more preferably 220 to 260°C.

[0094] The cured molded article may contain reinforcing fibers from the viewpoint of improving the mechanical strength of the cured molded article. Examples of the reinforcing fibers that can be used include the same reinforcing fibers that can be contained in the resin composition described above. The cured molded article can also be used as a fiber composite material. The cured molded article described above may be molded into a prepreg, and the prepreg may be used to produce a fiber composite material.

[0095] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0096] <Summary> As a result of investigations by the present inventors, it has become possible to produce prepregs using a more advantageous process by impregnating reinforcing fibers with "a mixture of a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B), the mixture having a predetermined amount of aldehyde groups."

[0097] That is, one embodiment of the present invention is as follows. <1> The method includes a step of mixing a resin composition containing a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B) with reinforcing fibers, the amount of aldehyde groups is 50 mol% or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol%; Prepreg manufacturing method. <2> The resin composition is in a solution state. <1> A method for producing the prepreg described in <3> The amount of solvent in the resin composition is 68% by weight or less. <2> A method for producing the prepreg described in <4> The compound (A) has 2 to 5 aldehyde groups, and the compound (B) has 2 to 5 amino groups. <1> ~ <3> 1. A method for producing a prepreg according to any one of claims 1 to 9. <5> The compound (A) having a benzoxazine ring and an aldehyde group is represented by the following general formula (I): <1> ~ <4> 1. A method for producing a prepreg according to any one of claims 1 to 9.

[0098] [ka]

[0099] [In the general formula (I), Ar 1 and Ar 2 represents a trivalent aromatic group derived from a phenolic compound, and Ar 1 and Ar 2 may be the same or different, and R 1 represents a divalent aromatic group. 1 , Ar 2 , and R 1 does not have a C=N group. <6> the aromatic amine compound (B) is at least one compound selected from the group consisting of 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, and 9,9-bis(4-aminophenyl)fluorene; <1> ~ <5> 1. A method for producing a prepreg according to any one of claims 1 to 9. <7> <1> ~ <6> 1. A method for producing a fiber composite material, comprising the step of producing a prepreg by the method according to any one of the above items 1 to 5, and then heating the prepreg to 150°C or higher. <8> A resin composition comprising a compound (A) having a benzoxazine ring and an aldehyde group, and an aromatic amine compound (B), the amount of aldehyde groups is 50 mol % or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %, The amount of solvent contained in the resin composition is 0% by weight or more and 68% by weight or less. Resin composition. <9> The compound (A) has 2 to 5 aldehyde groups, and the compound (B) has 2 to 5 amino groups. <8> The resin composition according to claim 1. <10> The compound (A) having a benzoxazine ring and an aldehyde group is represented by the following general formula (I): <8> or <9> The resin composition according to claim 1.

[0100] [ka]

[0101] [In the general formula (I), Ar 1 and Ar 2 represents a trivalent aromatic group derived from a phenolic compound, and Ar 1 and Ar 2 may be the same or different, and R 1 represents a divalent aromatic group. 1 , Ar 2 , and R 1 does not have a C=N group. <11> the aromatic amine compound (B) is at least one compound selected from the group consisting of 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, and 9,9-bis(4-aminophenyl)fluorene; <8> ~ <10> The resin composition according to any one of the above. <12> containing reinforcing fibers, <8> ~ <11> The resin composition according to any one of the above. <13> <12> A prepreg comprising the resin composition according to claim 1. <14> <8> ~ <12> a method for producing a resin composition having a high imino group content, the method comprising heating the resin composition according to any one of the preceding items in a solution state until the amount of imino groups becomes more than 50 mol % when the total amount of aldehyde groups and imino groups in the resin composition is taken as 100 mol %. <15> <8> ~ <12> a method for producing a resin composition having a high imino group content, the method comprising heating a solid resin composition according to any one of the above items until the amount of imino groups becomes 70 mol % or more, where the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %. <16> <8> ~ <12> The resin composition according to any one of the above items, or <14> or <15> 1. A method for producing a cured product, comprising the step of producing a resin composition having a high imino group content as described in claim 1, and then heating the composition to 150°C or higher. <17> <13> 1. A method for producing a fiber composite material, comprising the step of producing the prepreg according to claim 1, and then heating the prepreg to 150°C or higher. <18> <1> ~ <6> 10. A method for decomposing a cured product obtained by curing the resin composition in the prepreg obtained by the production method according to any one of 9. to 10. above, comprising a step of decomposing the cured product under acidic or basic conditions. <19> <7> or <17> A method for decomposing a fiber composite material, comprising the step of decomposing the fiber composite material obtained by the manufacturing method described in 1. under acidic or basic conditions. <20> <8> ~ <12> 10. A method for decomposing a cured product obtained by curing the resin composition according to any one of the above items 1 to 9, wherein the cured product is decomposed under acidic or basic conditions. [Example]

[0102] An embodiment of the present invention will be described below. In the following description, the term "cured film" refers to a cured molded article.

[0103] [Test method] <Structural analysis of benzoxazine compounds> The molecular structure of the benzoxazine compound was analyzed. Specifically, a nuclear magnetic resonance spectrometer (NMR, Bruker, AVANCEIII 400MHz) was used, and the measurement was performed at room temperature with 16 accumulations. 1 H-NMR measurements were carried out.

[0104] <GPC measurement of benzoxazine compounds - 1> The molecular weight of the benzoxazine compounds was measured using a gel permeation chromatograph (GPC) (Shimadzu Corporation, Prominence UFLC). The mobile phase was DMF containing 0.01 mol / L lithium chloride, and three TSKgel GMHHR-M columns (Tosoh Corporation) connected in series were used. The flow rate was 1 mL / min, the injection volume was 20 μL, and the column temperature was 40°C. A UV detector was used for detection, and polystyrene was used as the calibration curve sample.

[0105] <GPC measurement of benzoxazine compounds - 2> The molecular weight of the benzoxazine compound was measured using GPC (HLC-8320GPC, manufactured by Tosoh Corporation). Chloroform was used as the mobile phase, and a TSKgel SuperHM-N column manufactured by Tosoh Corporation was used. A UV detector was used for detection, and polystyrene was used as the sample for the calibration curve.

[0106] <Curing start temperature, curing heat generation peak top, heat generation amount measurement> The DSC curve was measured using a differential scanning calorimeter (DSC, Hitachi High-Tech Science Corporation, DSC7000X) under conditions of a nitrogen flow rate of 40 mL / min and 5°C / min. Next, the degree of cure was calculated from the heat generated by the ring-opening of benzoxazine using the following formula.

[0107] Cure degree [%] = 100 - {(heat generation after curing) / (heat generation before curing) × 100} Here, the calorific value before curing represents the area of ​​the exothermic peak in the DSC curve of the uncured resin, and the calorific value after curing represents the area of ​​the exothermic peak in the DSC curve of the cured film.

[0108] <Glass transition temperature (Tg) of cured film> The Tg of the uncured and cured films was measured using a dynamic viscoelasticity measuring device (DMA, manufactured by TA Instruments, RSA G2, tensile mode) at a frequency of 1 Hz and a heating rate of 5°C / min. The extrapolated glass transition onset temperature (the intersection of the straight line extrapolated from the baseline before the inflection point to the higher temperature side and the tangent to the inflection point) obtained from the DMA curve was used as the Tg in this example.

[0109] <Infrared absorption spectrum (IR) measurement> Shimadzu Corporation's IRAffinity-1 was used at room temperature and 600 cm -1 ~4000cm -1 Infrared absorption spectrum measurement was carried out under the condition of 32 accumulations within the measurement range.

[0110] <Melt viscosity measurement> Using a rheometer (model: ARES-G2, manufactured by TA Instruments), the sample was sandwiched between 25 mm parallel plates and measured at a heating rate of 2°C / min.

[0111] <Glass transition temperature (Tg) of fiber-reinforced composite materials> The Tg values ​​of the uncured and cured films were measured using a dynamic viscoelasticity measuring device (DMA, TA Instruments, DMA Q850, cantilever mode) at a frequency of 1 Hz and a heating rate of 5°C / min. The extrapolated glass transition onset temperature (the intersection of the straight line extrapolated from the baseline before the inflection point to the higher temperature side and the tangent to the inflection point) obtained from the DMA curve was used as the Tg value in this example.

[0112] <Cured film degradability evaluation 1> The cured film and hexamethylenediamine were added to various organic solvents and then heated and stirred. After heating and stirring, the state of the mixture was observed and the decomposition rate was evaluated according to the following criteria. A: Dissolved (evaluated as degradable). B: Not dissolved (evaluated as not degradable).

[0113] <Degradability evaluation of cured film 2> The cured film was added to a 2M aqueous HCl solution / THF (1 / 3, v / v) and then heated and stirred at 55° C. After heating and stirring, the state was observed, and decomposition was evaluated according to the following criteria. A: Dissolved (evaluated as degradable). B: Not dissolved (evaluated as not degradable).

[0114] 〔material〕 The materials used in the production of the imino group-containing benzoxazine compound are shown below.

[0115] (phenolic compounds with aldehyde groups) 4-Hydroxybenzaldehyde (Fujifilm Wako Pure Chemical Industries, Ltd.) (aromatic diamine compounds) 4,4'-Diaminodiphenyl ether (Seika Corporation) 2,2-bis[4-(4-aminophenoxy)phenyl]propane (Seika Corporation) (Other compounds) Paraformaldehyde (Fujifilm Wako Pure Chemical Industries, Ltd.) The materials used in the benzoxazine compound decomposition evaluation 1 are shown below.

[0116] (amine compounds) Hexamethylenediamine (Toray Industries) <Production of aldehyde group-containing benzoxazine compound> [Production Example 1] 4,4'-Diaminodiphenyl ether (58.4692 g, 0.2000 mol), paraformaldehyde (25.2302 g, 0.8402 mol), 4-hydroxybenzaldehyde (48.8505 g, 0.4000 mol), and toluene (174.0641 g) were added to a reaction vessel equipped with a stirrer and reacted under reflux for 6 hours. The resulting reaction solution (A) was cooled to room temperature and then added dropwise to stirred hexane (600 mL), yielding a viscous precipitate. After removing the supernatant, the resulting precipitate was dried in a vacuum dryer at 110 °C under reduced pressure for 15 hours to obtain aldehyde-containing benzoxazine compound (a). The molecular weight of the resulting aldehyde group-containing benzoxazine compound (a) was measured by GPC, and it was found that the weight average molecular weight (Mw) was 1,168 and the number average molecular weight (Mn) was 927. 1 By measuring by H-NMR (deuterated solvent: DMSO-d6), a decrease in the peak of the aldehyde group of 4-hydroxybenzaldehyde at 9.8 ppm and the generation of peaks of the benzoxazine ring at 4.7 ppm and 5.5 ppm were observed. The former confirmed that the raw material was consumed, and the latter confirmed that benzoxazine compound (a) had been synthesized.

[0117] <Mixing of imino group-containing benzoxazine compound raw materials 1> [Production Example 2] The obtained benzoxazine compound (a) (7.01 g, 0.0142 mol), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (4.11 g, 0.0100 mol), and 1,3-dioxolane (13.58 g) were added to a reaction vessel equipped with a stirrer, and the mixture was stirred at room temperature for 5 minutes to 2 hours. 1 H-NMR measurements (heavy solvent: DMSO-d6) revealed a decrease in the aldehyde-terminated (raw material) peak at 9.8 ppm and the generation of an imino-group (product) peak at 8.5 ppm over time, confirming that the raw material was sufficiently unreacted within this time range. The integrals of each peak, assuming the integral of benzoxazine at 5.5 ppm as 1, are shown in Table 1. GPC measurements using DMF containing 0.01 mol / L lithium chloride as the mobile phase revealed multiple peaks higher in molecular weight than the raw material aldehyde-containing benzoxazine, confirming the increase in imino-group-containing benzoxazine monomers (monomers) and oligomers (dimers-trimers) over time. The GPC chart is shown in Figure 1.

[0118] [Table 1]

[0119] <Drying of imino group-containing benzoxazine compound raw material mixed varnish 1> [Production Example 3] The varnish prepared in Production Example 2 was mixed for 30 minutes, and 1.953 g of the varnish was placed in an aluminum container and heated in a vacuum oven at 30°C for vacuum drying. The drying was stopped after 1 hour when the amount of evaporation had become relatively constant. The weight after drying was 1.034 g, and 87% of the solvent had evaporated. 1H-NMR measurements (heavy solvent: CDCl3) showed that, when the integral value of benzoxazine at 5.4 ppm was taken as 1, the integral value of the aldehyde terminal at 9.8 ppm was 0.26, and the integral value of the imino group at 8.3 ppm was 0.22. GPC measurements revealed that, compared to after mixing and dissolution, multiple peaks were observed on the higher molecular weight side than the raw aldehyde group-containing benzoxazine, confirming an increase in imino group-containing benzoxazine monomers (monomers) and oligomers (dimers to trimers). The GPC chart is shown in Figure 1. This means that the reaction of the imino group-containing benzoxazine progresses upon heating. IR measurements revealed a peak at 1684 cm -1 1614 cm when the aldehyde C=O stretching peak intensity is set to 1 -1 The imine C=N stretching peak intensity was 0.73. The IR chart is shown in Figure 2.

[0120] [Production Example 4] In the same manner as in Production Example 3, 1.972 g of varnish was placed in an aluminum container and heated at 70°C in a vacuum oven without vacuuming. The drying was stopped after 1.5 hours when the amount of evaporation became relatively constant. The weight after drying was 1.153 g, and 76% of the solvent had evaporated. 1 By H-NMR measurement (heavy solvent: CDCl3), the integral value of the aldehyde terminal at 9.8 ppm was 0.17, and the integral value of the imino group at 8.3 ppm was 0.39, assuming that the integral value of benzoxazine at 5.4 ppm was 1. IR measurement revealed that the integral value of the imino group at 1684 cm -1 1614 cm when the aldehyde C=O stretching peak intensity is set to 1 -1 The imine C=N stretching peak intensity was 1.01. Compared to Production Example 3, the amount of aldehyde was reduced and the imino group content was increased, confirming that the reaction of the imino group-containing benzoxazine proceeded upon heating. The IR chart is shown in Figure 2.

[0121] <Heating of mixed dry solid of imino group-containing benzoxazine compound raw material 1> [Production Example 5] The dried solid obtained in Production Example 3 was further heated in an oven at 140°C for 30 minutes.1 By H-NMR measurement (heavy solvent: CDCl3), the integral value of the aldehyde terminal at 9.8 ppm was 0.15, and the integral value of the imino group at 8.3 ppm was 0.39, assuming that the integral value of benzoxazine at 5.4 ppm was 1. IR measurement revealed that the integral value of the imino group at 1684 cm -1 1614 cm when the aldehyde C=O stretching peak intensity is set to 1 -1 The imine C=N stretching peak intensity was 1.03. Compared to Production Example 3, the amount of aldehyde decreased and the imino group content increased, confirming that the reaction of the imino group-containing benzoxazine proceeded upon heating. The IR chart is shown in Figure 2. The GPC chart using chloroform as the mobile phase is shown in Figure 4.

[0122] [Table 2]

[0123] <Mixing of imino group-containing benzoxazine compound raw materials 2 and drying of varnish 2> [Production Example 6] Into a reaction vessel equipped with a stirrer, Solution A: benzoxazine compound (a) (2.00 g, 0.039 mol) obtained in Production Example 1 and 1,3-dioxolane (3.41 g), and Solution B: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (1.67 g, 0.0041 mol) and 1,3-dioxolane (2.84 g) were added, and the mixture was stirred at room temperature for 5 minutes. 1 H-NMR measurement (heavy solvent: DMSO-d6) revealed a peak at 9.8 ppm for the aldehyde terminal (raw material) and a peak at 8.5 ppm for the imino group (product), confirming that the raw material was sufficiently unreacted. 1H-NMR analysis (deuterated solvent: DMSO-d6) revealed that the integral of the aldehyde terminal at 9.8 ppm was 0.62, and the integral of the imino group at 8.3 ppm was 0.04, assuming that the integral of the benzoxazine at 5.4 ppm was 1. The aldehyde group content was 95 mol%, and the imino group content was 5 mol%. Figure 5 shows a GPC chart using DMF containing 0.01 mol / L lithium chloride as the mobile phase.

[0124] A varnish was prepared, heated in a vacuum oven at 30°C, and vacuum dried for 30 minutes. 1 H-NMR analysis (using DMSO-d6 as a heavy solvent) revealed that the integral of the aldehyde terminal at 9.8 ppm was 0.31, and the integral of the imino group at 8.3 ppm was 0.25, assuming that the integral of the benzoxazine at 5.4 ppm was 1. The aldehyde group content was 55 mol%, and the imino group content was 45 mol%. GPC analysis revealed multiple peaks on the higher molecular weight side than the starting aldehyde-containing benzoxazine, confirming an increase in imino-containing benzoxazine monomers (monomers) and oligomers (dimers-trimers). The GPC chart is shown in Figure 5. This indicates that the reaction of the imino-containing benzoxazine proceeds upon heating.

[0125] <Tracking the hardening reaction of a mixed, dried solid of imino-group-containing benzoxazine compound raw materials 1> Example 1 DSC analysis of the dried solid obtained in Production Example 3 confirmed a curing initiation temperature of 157°C, a curing exothermic peak of 221°C, and a calorific value of 159 J / g. Figure 3 shows the melt viscosity of the solid. The viscosity dropped sharply from 90°C, and the gap between the two parallel plates used to hold the sample increased. The viscosity increased to 130°C, then decreased again. It reached its lowest melt viscosity at 170°C and then increased again. From these results, it is inferred that the behavior in each temperature range is as follows: from room temperature to 100°C, the melting of raw materials, solvent evaporation, and reaction of the imino-group-containing benzoxazine occur primarily; from 100°C to 130°C, the reaction of the imino-group-containing benzoxazine and the resulting increase in viscosity occur primarily. Furthermore, from 130°C to 160°C, the viscosity decrease is inferred to be primarily due to melting of the imino-group-containing benzoxazine. Furthermore, it is presumed that at temperatures above 160°C, curing of the imino group-containing benzoxazine occurs primarily.

[0126] <Curing of mixed dried solid of imino group-containing benzoxazine compound raw materials 1> Example 2 Based on the curing behavior of Example 1, the dried solid obtained in Production Example 3 was placed in a 125 μm-thick PI film mold (4 cm × 6 cm) and pressed together with a Teflon (registered trademark) sheet (release paper) and a stainless steel plate to obtain a cured film. A MINI TEST PRESS-10 (manufactured by Toyo Seiki Co., Ltd.) was used as the press. The processing conditions for obtaining the cured film were melting at 100°C for 5 minutes, pressing at an actual pressure of 6.875 MPa for 30 minutes, and then heating at 190°C for 2 hours and 220°C for 1 hour. DSC measurement of this film-like cured product showed no exothermic peak, indicating a degree of cure of 100%. DMA measurement revealed a Tg of 231°C. The elastic modulus at room temperature was 3.2 GPa. The DMA curve is shown in Figure 6. IR measurement revealed a peak at 1684 cm -1 1614 cm when the aldehyde C=O stretching peak intensity is set to 1 -1The imine C=N stretching peak intensity was 1.44. Compared to Production Examples 3 to 5, the amount of aldehyde was further reduced and the imino group content was increased, confirming that the reaction of the imino group-containing benzoxazine proceeded further during the curing heating process. The IR chart is shown in Figure 2.

[0127] [Table 3]

[0128] <Preparation of imino group-containing benzoxazine prepreg and CFRP 1> Example 3 According to Production Example 2, a 45 wt% solution obtained by mixing for 30 minutes was mixed with a plain weave material (basis weight: 195 g / m) of carbon fiber (IMS60-6K manufactured by Teijin). 2 The weight of the solution in the prepreg was approximately 60 wt%, and the weight of the carbon fiber was approximately 40 wt%.

[0129] Example 4 The prepreg obtained in Example 3 was heated in a vacuum oven at 30° C. and vacuum dried for 30 minutes.

[0130] Example 5 Four 7.5 cm square pieces were cut out from the prepreg obtained in Example 4 and laminated to obtain a prepreg laminate. Next, together with a Teflon (registered trademark) sheet (release paper) and a stainless steel plate, the prepreg was pressed at 100°C under an actual pressure of 6.875 MPa for 30 minutes, and then heated to 190°C for 2 hours and then to 220°C for 1 hour to obtain a carbon fiber reinforced composite material (fiber composite material). The press used was a MINI TEST PRESS-10 (manufactured by Toyo Seiki Co., Ltd.). DMA measurement revealed that the Tg of the obtained composite material was 231°C.

[0131] <Tracking the hardening reaction of a mixed, dried solid of imino-group-containing benzoxazine compound raw materials 2> Example 6 DSC analysis of the dried solid obtained in Production Example 6 confirmed that the curing initiation temperature was 132°C, the curing exothermic peak was 204°C, and the calorific value was 150 J / g. Figure 7 shows the melt viscosity measurement results for the same solid. After a viscosity decrease at 80°C, the gap between the two parallel plates used to sandwich the sample widened at 100°C. The viscosity increased up to 150°C, and then decreased again at 190°C. Based on these results, the behavior in each temperature range is presumed to be primarily due to melting of the raw materials, solvent evaporation, and reaction of the imino group-containing benzoxazine from room temperature to 100°C. Furthermore, it is presumed that the reaction of the imino group-containing benzoxazine and the increase in viscosity due to the increase in imino group-containing benzoxazine occur primarily from 100°C to 150°C. Furthermore, it is presumed that the viscosity decrease from 150°C to 190°C is primarily due to melting of the imino group-containing benzoxazine. Furthermore, it is presumed that at temperatures above 190°C, curing of the imino group-containing benzoxazine occurs primarily.

[0132] <Hardening of mixed dried solid of imino group-containing benzoxazine compound raw materials 2> Example 7 Based on the curing behavior of Example 6, the dried solid obtained in Production Example 6 was placed in a 125 μm-thick PI film mold (4 cm × 6 cm) and pressed together with a Teflon® sheet (release paper) and a stainless steel plate to obtain a cured film. An AYSR-10 press (Kando Metal Industries) was used. The processing conditions for obtaining the cured film were melting at 90°C for 1 minute, followed by pressing at 220°C at an actual pressure of 3.2 MPa for 1 hour while increasing the temperature. DSC measurement of this cured film indicated no exothermic peak and a degree of cure of 100%. DMA measurement of this cured film indicated a Tg of 316°C. The elastic modulus at room temperature was 3.4 GPa. The DMA curve is shown in Figure 6.

[0133] Comparative Example 1 A known benzoxazine compound, 3,3'-(methylene-1,4-diphenylene)bis(3,4-dihydro-2H-1,3-benzoxazine)(Pd) (manufactured by Shikoku Kasei Co., Ltd.), was placed in a 125 μm-thick PI film mold (6 cm × 4 cm) and pressed together with a Teflon® sheet (release paper) and a stainless steel plate to obtain a cured film. A MINI TEST PRESS-10 (manufactured by Toyo Seiki Co., Ltd.) was used as the press. The cured film was obtained by pressing at 5 MPa for 30 minutes at 180°C, 30 minutes at 200°C, and 2 hours at 220°C, with the temperature increasing. DMA measurement revealed that the Tg of this cured film was 180°C. The elastic modulus at room temperature was 3.9 GPa. The DMA curve is shown in Figure 8.

[0134] Comparative Example 2 Manufacturing process: 1,3-bis(4-aminophenoxy)benzene (6.0000 g, 0.0205 mol), paraformaldehyde (2.5886 g, 0.0862 mol), 4-hydroxybenzaldehyde (5.0128 g, 0.0410 mol), and toluene (31.7366 g) were added to a reaction vessel equipped with a stirrer and reacted under reflux for 6 hours. The resulting reaction solution (A) was cooled to room temperature and then added dropwise to stirred hexane (500 mL), yielding a viscous precipitate. After removing the supernatant, the precipitate was washed with methanol (500 mL), stirred, and filtered. The resulting precipitate was dried in a vacuum dryer at room temperature under reduced pressure for 2 hours to obtain the reaction intermediate benzoxazine compound (b).

[0135] Next, the resulting benzoxazine compound (b) (5.0000 g, 0.0086 mol), 1,3-bis(4-aminophenoxy)benzene (2.3809 g, 0.0081 mol), and chloroform (17.2220 g) were added to a reaction vessel equipped with a stirrer and reacted under reflux for 2 hours. After cooling the resulting reaction solution (B) to room temperature, 20 mL of chloroform was added, and the mixture was added dropwise to stirred methanol (300 mL) and filtered. This process was repeated once more, and the mixture was dried in a vacuum dryer at 85 °C under reduced pressure for 1.5 hours to obtain the target imino group-containing benzoxazine compound (c).

[0136] The imino group-containing benzoxazine compound (c) obtained by the above process was dissolved in 1,4-dioxane to prepare a benzoxazine solution (27 wt%). A PP plate (substrate) was fixed on a smooth glass plate, and the benzoxazine solution was cast onto the substrate using a glass rod. A Teflon (registered trademark) sheet was used to adjust the thickness. Thereafter, to prevent the solvent from volatilizing rapidly, the substrate onto which the benzoxazine solution had been cast was covered with a tray and allowed to stand overnight.

[0137] A cured film was obtained from the resulting cast film under the following processing conditions: The cast film was heated in an oven at 50°C for 30 minutes, 75°C for 30 minutes, and 90°C for 30 minutes. The resulting free-standing film was then pressed at 2 MPa while increasing the temperature: 95°C for 1 hour, 120°C for 1 hour, 150°C for 1 hour, 190°C for 2 hours, and 220°C for 1 hour. The AYSR-10 (Kando Metal Industries) press was used.

[0138] The above corresponds to the manufacturing process described in Patent Document 2. DMA measurement results showed that the Tg of this film-like cured product was 233°C. The elastic modulus at room temperature was 3.6 GPa. The DMA curve is shown in Figure 8.

[0139] Comparative Example 3 Manufacturing process: In a reaction vessel equipped with a stirrer, 160.0000 g (0.5473 mol) of 1,3-bis(4-aminophenoxy)benzene, 69.0298 g (2.2987 mol) of paraformaldehyde, 133.6745 g (1.0946 mol) of 4-hydroxybenzaldehyde, and 846.3099 g of toluene were added and reacted under reflux for 6 hours. The resulting reaction solution (C) was cooled to room temperature and then dried using an evaporator at 60°C under reduced pressure to obtain the reaction intermediate benzoxazine compound (d).

[0140] Next, 321.0320 g (0.5491 mol) of benzoxazine compound (d), 107.0070 g (0.3660 mol) of 1,3-bis(4-aminophenoxy)benzene, and 998.7577 g of chloroform were added to a reaction vessel equipped with a stirrer and reacted under reflux for 7 hours. The resulting reaction solution (D) was cooled to room temperature and then dried under reduced pressure using an evaporator and a vacuum dryer. The dried product was then washed in methanol and filtered. This process was repeated once more, and the mixture was dried under reduced pressure using a vacuum dryer at 25°C for 2 hours, 30°C for 6 hours, and 40°C for 2 hours to obtain the desired imino group-containing benzoxazine compound (e).

[0141] The imino group-containing benzoxazine compound (e) obtained by the above process was dissolved in 1,3-dioxolane to prepare a benzoxazine solution (50 wt%). A Nitoflon film No. 900UL (substrate) was fixed onto a smooth glass plate, and the benzoxazine solution was cast onto the substrate using a glass rod. A Teflon (registered trademark) sheet was used to adjust the thickness. The substrate onto which the benzoxazine solution had been cast was then covered with a tray to prevent the solvent from volatilizing too quickly, and allowed to stand overnight.

[0142] A cured film was obtained from the obtained cast film under the following processing conditions. Cured film: The cast film was heated using a vacuum laminator at 50°C for 30 minutes, 70°C for 30 minutes, 80°C for 2 hours, and 120°C for 1 hour. The resulting free-standing film was then pressed at 2 MPa while increasing the temperature: at 150°C for 1 hour, at 190°C for 2 hours, and at 220°C for 1 hour. The pressing machine used was an AYSR-10 (Kando Metal Industries).

[0143] The above corresponds to the manufacturing process described in Patent Document 2. DMA measurement results showed that the Tg of this film-like cured product was 325°C. The elastic modulus at room temperature was 3.7 GPa. The DMA curve is shown in Figure 8.

[0144] (Conclusion) The cured films of Examples 2 and 7 were found to have higher Tg and better heat resistance than the cured film of Comparative Example 1. Their heat resistance is comparable to that of the cured films of Comparative Examples 2 and 3 produced by the multi-stage manufacturing process described in Patent Document 2.

[0145] From the above, it can be said that the cured product of the benzoxazine compound containing a dynamic covalent bond according to one embodiment of the present invention realizes a more advantageous production process and also exhibits excellent heat resistance.

[0146] <Degradability evaluation of cured films of dried solid mixtures of imino group-containing benzoxazine compound raw materials 1> The physical properties of each Example and Comparative Example are shown in Table 4 below. The results of the amine decomposition evaluation test (decomposition evaluation 1) for each Example and Comparative Example are shown in Figure 9. In Figure 9, the cylindrical object that can be seen in common in the containers of all Examples and Comparative Examples is a stirrer. Evaluation criteria A Amine decomposition. B Amine not decomposed.

[0147] Example 8 In a reaction vessel equipped with a stirrer, the film-like cured product (0.008 g) of the imino group-containing benzoxazine compound obtained in Example 7, hexamethylenediamine (0.4 g), and 1 mL of NMP were added, and the mixture was reacted at 170°C for 1 minute.

[0148] Example 9 Into a reaction vessel equipped with a stirrer, the film-like cured product (0.008 g) of the imino group-containing benzoxazine compound obtained in Example 7, hexamethylenediamine (0.4 g), and 1 mL of DMF were added, and the mixture was reacted at 100°C for 15 minutes.

[0149] Comparative Example 4 Into a reaction vessel equipped with a stirrer, the film-like cured product (0.008 g) of the imino group-containing benzoxazine compound obtained in Comparative Example 3, hexamethylenediamine (0.4 g), and 1 mL of NMP were added, and the mixture was reacted at 170°C for 1 minute.

[0150] Comparative Example 5 Into a reaction vessel equipped with a stirrer, the film-like cured product (0.008 g) of the imino group-containing benzoxazine compound obtained in Comparative Example 3, hexamethylenediamine (0.4 g), and 1 mL of DMF were added, and the mixture was reacted at 100°C for 15 minutes.

[0151] Table 4 and FIG. 9 reveal that the cured films of Examples 8 and 9 exhibit amine decomposability. Although these cured films are cured products obtained from a resin composition containing a benzoxazine compound equivalent to a thermosetting resin, it is believed that they exhibited decomposability due to the dynamic covalent bond (imine bond) introduced into the structure undergoing an imine exchange reaction with the added amine. The presence of decomposability under the evaluation conditions of this example means that the cured product of the benzoxazine compound, in other words, the cured product of the thermosetting resin, can be chemically decomposed to produce low molecular weight compounds. Therefore, it is believed that the cured product obtained from the resin composition according to one embodiment of the present invention can also be recycled, for example, by chemical recycling.

[0152] On the other hand, it was found that the cured films of Comparative Example 4 (decomposition conditions corresponding to Example 8) and Comparative Example 5 (decomposition conditions corresponding to Example 9) did not exhibit amine decomposition. It is thought that not only this Comparative Example but also general cured products of thermosetting resins do not exhibit decomposition under the evaluation conditions of this Example because they do not have dynamic covalent bonds.

[0153] <Degradability evaluation of cured films of mixed dry solids of imino group-containing benzoxazine compound raw materials 2> The physical properties of each example and comparative example are shown in Table 4 below. The results of the hydrolysis evaluation test (degradability evaluation 2) for each example and comparative example are shown in Figure 10. In Figure 10, the cylindrical object that can be seen in common in the containers of all examples and comparative examples is a stirrer. Evaluation criteria A Hydrolyzed. B Not hydrolyzed.

[0154] Example 10 A reaction vessel equipped with a stirrer was charged with the film-like cured product (0.003 g) of the imino group-containing benzoxazine compound obtained in Example 7 and 2 M aqueous HCl solution / THF (1 / 3, v / v) (1.4816 g), and the mixture was reacted at 55°C for 18 hours.

[0155] Comparative Example 6 A film-like cured product (0.003 g) of the imino group-containing benzoxazine compound obtained in Comparative Example 3 and 2 M aqueous HCl solution / THF (1 / 3, v / v) (1.4816 g) were placed in a reaction vessel equipped with a stirrer, and the mixture was reacted at 55°C for 18 hours.

[0156] Table 4 and FIG. 10 reveal that the cured film of Example 10 exhibits hydrolysis. Although this cured film is a cured product obtained from a resin composition containing a benzoxazine compound equivalent to a thermosetting resin, it is believed that the hydrolysis was due to the dynamic covalent bond (imine bond) introduced into the main chain. The hydrolysis under the evaluation conditions of this example means that the cured product of the benzoxazine compound, in other words, the cured product of the thermosetting resin, can be chemically decomposed to produce low molecular weight compounds. Therefore, it is believed that the cured product obtained from the resin composition according to one embodiment of the present invention can also be recycled, for example, by chemical recycling.

[0157] On the other hand, it was found that the cured film of Comparative Example 6 did not exhibit hydrolysis. It is thought that not only this Comparative Example but also general cured products of thermosetting resins do not exhibit hydrolysis under the evaluation conditions of this example because they do not have dynamic covalent bonds.

[0158] [Table 4]

[0159] (Conclusion) From the above, it is believed that a cured product of a benzoxazine compound containing a dynamic covalent bond according to one embodiment of the present invention exhibits amine decomposition and hydrolysis. Therefore, it is believed that a cured product using a resin composition containing a benzoxazine compound according to one embodiment of the present invention as a thermosetting resin can be recycled by decomposing the cured resin. Furthermore, it is believed that a carbon fiber composite material using a resin composition containing a benzoxazine compound according to one embodiment of the present invention as a thermosetting resin can be recycled not only for the resin but also for the carbon fiber by decomposing the cured resin component.

[0160] <Preparation of imino group-containing benzoxazine prepreg and CFRP 2> Example 11 Solution A: benzoxazine compound (a) (37.10 g, 0.0726 mol) obtained in Production Example 1 and 1,3-dioxolane (60.53 g), and Solution B: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (31.32 g, 0.0762 mol) and 1,3-dioxolane (51.10 g) were added to a reaction vessel equipped with a stirrer, and the mixture was stirred at room temperature for 5 minutes to obtain a raw material mixture solution of an imino group-containing benzoxazine compound. Carbon fiber (T300-6K manufactured by Toray Industries, Inc.) (fineness: 396 Tex, density: 1.76 g / cm) was poured into the solution bath into which the raw material mixture solution had been poured. 3 ) and wound around a drum rotating at a speed of 8 m / min at a width feed rate of 18.35 mm / min to produce a unidirectional prepreg (fiber basis weight: 145 g / m2) with a width of 20 cm and a length of 100 cm. 2 ) was produced.

[0161] This process was repeated three times to obtain three unidirectional prepregs, each 20 cm wide and 100 cm long. Five 15 cm pieces were cut out of each prepreg, yielding a total of 15 15 cm square prepregs. The solution weight in the prepreg was approximately 60 wt%, and the carbon fiber weight was approximately 40 wt%.

[0162] Example 12 The prepreg obtained in Example 11 was laminated to form 15 layers. The obtained prepreg laminate was sandwiched between two Nitoflon sheets (release paper) (white rectangles written above and below the prepreg laminate in Figure 11), wrapped in a PI (polyimide) film (dotted rectangle surrounding the prepreg laminate and Nitoflon sheets in Figure 11), and arranged as shown in Figure 11. These were (1) heated at 30°C under vacuum conditions for 30 minutes in a press molding machine, (2) pressed at 0.7 MPa under vacuum conditions and held at 90°C for 3 minutes, (3) pressed at 1.4 MPa under vacuum conditions and heated to 95°C, (4) pressed at 2 MPa under vacuum conditions and heated to 150°C, and (5) cooled to 100°C. After that, the secondary materials (glass fiber, bagging film, breather cloth, and sealant tape) were removed, and a stainless steel plate was used as the base plate. The mixture was then pressed at 2 MPa and heated at 220° C. for 1 hour to harden it. The materials used are listed below. Stainless steel plate 2mm thick Glass fiber manufactured by Airtech, product name: BleederLeaseE Bagging film, manufactured by Airtech, product name: Strechlon 800 (SL800) Breather Cross, manufactured by Takayasu Co., Ltd., product name: Arafnon OSE-135 Sealant tape, Airtech, AT-200Y Base plate 3mm thick Nitoflon sheet, manufactured by Nitto Denko Corporation, product name: 9700UL PI film, 75 microns thick The press used was AYSR-10 (Kamito Metal Industries).

[0163] <Degradability evaluation of imino group-containing benzoxazine CFRP 1> Example 13 A 1 cm square test piece (0.3816 g) (estimated resin amount: 0.1546 g, estimated carbon fiber weight: 0.2270 g) was cut from the plate-shaped CFRP obtained in Example 12 using a diamond cutter, and hexamethylenediamine (7.7284 g) and 20 mL of NMP were added, followed by a reaction at 170°C for a total of 30 minutes. Disassembly criteria: A The hardened resin component has completely dissolved, and the carbon fiber has unraveled. B: Most of the hardened resin components have dissolved, discoloring the solution, but some of the carbon fibers still retain their shape. C The cured resin component is partially dissolved, discoloring the solution, but most of the carbon fibers maintain their shape. D The hardened resin component is not dissolved at all, and the solution is not colored. The decomposition process is shown in Figure 12.

[0164] Example 14 The resin decomposition solution obtained in Example 13 was filtered to recover carbon fibers. The fibers were then washed in acetone for 2 hours and filtered. This process was repeated twice, and the resulting carbon fibers were dried in a vacuum oven at 100°C for 5 hours to obtain recycled carbon fibers (r-CF). The appearance of the r-CF and resin decomposition solution separated from the CFRP is shown in Figure 12.

[0165] In Example 13, it was confirmed that the resin cured product component of the CFRP was completely decomposed and the carbon fibers were untangled, so the evaluation was given as A. In Example 14, it was found that r-CF can be recovered by decomposing CFRP.

[0166] <Degradability evaluation of imino group-containing benzoxazine CFRP 2> Example 15 A 1 cm square test piece (0.3869 g) (estimated resin amount: 0.1499 g, estimated carbon fiber weight: 0.2190 g) was cut from the plate-shaped CFRP obtained in Example 12 using a diamond cutter, and a 2 M aqueous HCl solution / THF (1 / 3, v / v) (81.4880 g) was added thereto, followed by a reaction at 55°C for a total of 300 hours. Disassembly criteria: The cured resin component is completely dissolved and the carbon fibers are unraveled. Most of the cured resin component is dissolved, the solution is colored, but some of the carbon fibers maintain their shape. Some of the cured resin component is dissolved, the solution is colored, but most of the carbon fibers maintain their shape. The cured resin component is not dissolved at all and no coloring of the solution is observed. The state of decomposition is shown in Fig. 13.

[0167] From Example 15, although some of the carbon fibers maintained their shape, since most of the resin cured product component of the CFRP could be decomposed, the evaluation was B.

[0168] (Conclusion) As described above, for the CFRP having a cured product of an imino group-containing benzoxazine compound as a matrix resin according to an embodiment of the present invention, the carbon fibers can be recycled due to the amine decomposability and hydrolysis of the cured resin component.

[0169] <Glass transition temperature of CFRP> [Example 16] For the plate-shaped CFRP obtained in Example 12, which was cut out with a diamond cutter and post-cured at 250 °C for 30 minutes in an oven, the glass transition temperature Tg was determined using a dynamic viscoelasticity measuring device. Tg was 220 °C.

[0170] It was found that the CFRP having a cured product of a benzoxazine compound containing a dynamic covalent bond as a matrix resin according to an embodiment of the present invention exhibits excellent heat resistance, similar to the cured resin film.

[0171] <Interlaminar shear strength of CFRP> [Example 17] The plate-shaped CFRP obtained in Example 12 was cut out with a diamond cutter, and a short beam shear (SBS) test was performed using a universal testing machine (AG-10TB, manufactured by SHIMADZU Corporation). The test piece size and test conditions complied with ASTM D2344, and the interlaminar shear strength of the CFRP was determined from the following formula.

[0172] Interlaminar shear strength [MPa] = 3 × Interlaminar shear load [N] / (4 × Test piece width [mm] × Test piece thickness [mm]) The interlaminar shear strength was 85 MPa.

[0173] <Flexural modulus and flexural strength of CFRP> [Example 18] The plate-shaped CFRP obtained in Example 12 was cut out with a diamond cutter, and a flexural test was performed using a universal testing machine (INSTRON 5982, manufactured by INSTRON Corporation) and a deflection meter (CDP-50MT, Tokyo Measuring Instrument Laboratory). The test piece size and test conditions complied with ASTM D7264. The flexural modulus was 102 MPa and the flexural strength was 1444 MPa.

Industrial Applicability

[0174] One aspect of the present invention can be used in the field of using thermosetting resins.

Claims

1. The method includes a step of mixing a resin composition containing a compound (A) having a benzoxazine ring and an aldehyde group and an aromatic amine compound (B) with reinforcing fibers, the amount of aldehyde groups in the resin composition is 50 mol % or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %.

2. The method for producing a prepreg according to claim 1 , wherein the resin composition is in a solution state.

3. The method for producing a prepreg according to claim 2, wherein the amount of solvent in the resin composition is 68% by weight or less.

4. 2. The method for producing a prepreg according to claim 1, wherein the compound (A) has 2 to 5 aldehyde groups and the compound (B) has 2 to 5 amino groups.

5. 2. The method for producing a prepreg according to claim 1, wherein the compound (A) having a benzoxazine ring and an aldehyde group is represented by the following general formula (I): 【Chemical 1】 [In the general formula (I), Ar １ and Ar ２ represents a trivalent aromatic group derived from a phenol compound, and Ar １ and Ar ２ may be the same or different, and R １ represents a divalent aromatic group. １ , Ar ２ , and R １ does not have a C═N group.

6. The aromatic amine compound (B) is 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3- (aminomethyl) benzylamine, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, and 9,9-bis (4-aminophenyl) fluorene. At least one compound selected from the group consisting of fluorene, the method for producing a prepreg according to claim 1.

7. A method for producing a fiber composite material, comprising the step of producing a prepreg by the method according to claim 1 and then heating the prepreg to 150°C or higher.

8. A resin composition comprising a compound (A) having a benzoxazine ring and an aldehyde group, and an aromatic amine compound (B), the amount of aldehyde groups is 50 mol% or more when the total amount of aldehyde groups and imino groups in the resin composition is 100 mol%, A resin composition, wherein the amount of solvent contained in the resin composition is 0% by weight or more and 68% by weight or less.

9. The resin composition according to claim 8, wherein the compound (A) has 2 to 5 aldehyde groups and the compound (B) has 2 to 5 amino groups.

10. The resin composition according to claim 8, wherein the compound (A) having a benzoxazine ring and an aldehyde group is represented by the following general formula (I): 【Chemistry 2】 [In the general formula (I), Ar １ and Ar ２ represents a trivalent aromatic group derived from a phenol compound, and Ar １ and Ar ２ may be the same or different, and R １ represents a divalent aromatic group. １ , Ar ２ , and R １ does not have a C═N group.

11. The aromatic amine compound (B) is 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3- (aminomethyl) benzylamine, 3,3'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, and 9,9-bis (4-aminophenyl) fluorene. At least one compound selected from the group consisting of fluorene, the resin composition according to claim 8.

12. The resin composition according to claim 8, further comprising reinforcing fibers.

13. A prepreg comprising the resin composition according to claim 12.

14. A method for producing a resin composition having a high imino group content, comprising heating the resin composition according to any one of claims 8 to 12 in a solution state until the amount of imino groups becomes more than 50 mol % when the total amount of aldehyde groups and imino groups in the resin composition is taken as 100 mol %.

15. A method for producing a resin composition having a high imino group content, comprising heating a solid resin composition according to any one of claims 8 to 12 until the amount of imino groups in the resin composition is 70 mol % or more, where the total amount of aldehyde groups and imino groups in the resin composition is 100 mol %.

16. A method for producing a cured product, comprising the step of producing the resin composition according to any one of claims 8 to 12 and then heating the composition to 150°C or higher.

17. A method for producing a fiber composite material, comprising the step of producing the prepreg according to claim 13 and then heating the prepreg to 150°C or higher.

18. A method for decomposing a cured product obtained by curing a resin composition in a prepreg obtained by the production method according to any one of claims 1 to 6, comprising a step of decomposing the cured product under acidic or basic conditions.

19. A method for decomposing a fiber composite material, comprising the step of decomposing the fiber composite material obtained by the production method according to claim 7 or 17 under acidic or basic conditions.

20. A method for decomposing a cured product obtained by curing the resin composition according to any one of claims 8 to 12, comprising a step of decomposing the cured product under acidic or basic conditions.

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