Method for recovering prepregs, fiber-reinforced plastics, and reinforcing fibers

Abstract

To provide a prepreg that can reduce damage to reinforced fibers and energy costs in the recycling process of fiber-reinforced plastic, fiber-reinforced plastic including the prepreg, and method for recycling reinforced fibers.SOLUTION: A prepreg comprises a resin composition comprising component (A): an epoxy resin and component (B): an aromatic amine compound including a disulfide bond, and reinforced fibers. A fiber-reinforced plastic comprises a cured product of the prepreg.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recovering prepregs, fiber reinforced plastics, and reinforcing fibers.

Background Art

[0002] Carbon fiber reinforced plastic (CFRP) containing carbon fibers and a matrix resin has been developed for a wide range of applications such as aircraft and automobiles as a metal substitute material because of its characteristics of being lightweight and high-strength compared to metals, and in recent years, its scope of application has been further expanding. As a molding material for obtaining CFRP, for example, a prepreg in which carbon fibers are impregnated with a matrix resin is known (for example, Patent Document 1). CFRP can be obtained by heating and pressing the prepreg for molding.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] From the perspective of circular economy, the demand for recyclability of CFRP is also increasing. If the matrix resin of used CFRP can be efficiently thermally decomposed, carbon fibers can be recovered with high efficiency while reducing damage to the carbon fibers and energy costs.

[0005] An object of the present invention is to provide a method for recovering prepregs, fiber reinforced plastics, and reinforcing fibers that can reduce damage to reinforcing fibers and energy costs when recovering from fiber reinforced plastics.

Means for Solving the Problems

[0006] The present invention includes the following configurations. [1] A prepreg comprising a resin composition containing the following component (A) and the following component (B), and reinforcing fibers. Component (A): An epoxy resin Component (B): An aromatic amine compound containing a disulfide bond [2] The prepreg according to [1], wherein the component (B) contains a compound represented by the following formula (1). (R 6 -) a Ar 1 -S-S-Ar 2 (-R 7 ) b ···(1) (However, in formula (1), Ar 1 and Ar 2 are each independently a divalent or higher aromatic group or heteroaromatic group which may have a substituent other than an amino group, and R 6 and R 7 are each independently NR 8 R 9 (R 8 , R 9 are each independently a hydrogen atom, an alkyl group or an aryl group.), or an aminoalkyl group in which at least one hydrogen atom is substituted with NR 10 R 11 (R 10 , R 11 are each independently a hydrogen atom, an alkyl group or an aryl group.), and a and b are each independently an integer of 1 to 5.) [3] The prepreg according to [1] or [2], wherein the component (B) contains at least one of 4,4'-diaminophenyldisulfide and 2,2'-diaminophenyldisulfide. [4] The prepreg according to any one of [1] to [3], wherein the blending amount of the component (B) is 5% by mass or more and 60% by mass or less based on the total mass of the resin composition. [5] The prepreg according to any one of [1] to [4], further comprising one or more components (C) selected from the compounds represented by the following formula (2).

[0007]

Chemical formula

[0008] (However, in equation (2), R 1 and R 2 (where c and d are independent substituents, and c and d are independent integers between 0 and 5.) [6] The prepreg according to [5], wherein the (C) component comprises triphenylphosphine triphenylborate. [7] The prepreg according to [5] or [6], wherein the amount of component (C) is 0.3% by mass or more and 20% by mass or less with respect to the total mass of the resin composition. [8] A prepreg according to any one of [5] to [7], further comprising one or more (D) components selected from the compounds represented by the following formula (3).

[0009] [ka]

[0010] (However, in equation (3), R 3 ~R 5 (Each of the nucleotides is an independent substituent, and e to g are independent integers from 0 to 5.) [9] The prepreg according to [8], wherein the component (D) comprises at least one selected from triphenylphosphine, tri-p-tolylphosphine, and tris(p-methoxyphenyl)phosphine.

[10] The prepreg according to [8] or [9], wherein the amount of component (D) is 0.5% by mass or more and 30% by mass or less with respect to the total mass of the resin composition.

[11] The prepreg according to any one of [1] to

[10] , wherein the reinforcing fibers include carbon fibers.

[12] The prepreg according to any one of [1] to

[11] , wherein the resin composition is cured by heating at 180°C for 4 hours, and then heated from 25°C to 400°C at a heating rate of 5°C / min, the decomposition temperature Td (°C) is 200°C or more and 400°C or less.

[13] The prepreg according to any one of [1] to

[12] , wherein in a DSC chart obtained by differential scanning calorimetry in which the resin composition is heated from -50°C to 400°C at a heating rate of 10°C / min, the peak top temperature T1 (°C) of the maximum peak is 70°C or more and 250°C or less.

[14] The prepreg according to [1] to

[13] , wherein the difference (Td-T1) between the peak top temperature T1 (°C) of the maximum peak in a DSC chart obtained by differential scanning calorimetry in which the resin composition is heated from -50°C to 400°C at a heating rate of 10°C / min and the decomposition temperature Td (°C) obtained when the resin composition is heated at 180°C for 4 hours to cure, and then heated from 25°C to 400°C at a heating rate of 5°C / min is 50°C or more. A fiber-reinforced plastic consisting of a cured prepreg described in any of

[15] [1] to

[14] .

[16] A method for recovering reinforcing fibers, comprising treating a fiber-reinforced plastic containing a matrix resin containing disulfide bonds and reinforcing fibers with heat or a reducing agent to decompose the matrix resin and extract the reinforcing fibers.

[17] The method for recovering reinforcing fibers according to

[16] , wherein the matrix resin comprises a cured epoxy resin.

[18] A method for recovering reinforcing fibers according to

[16] or

[17] , wherein the reinforcing fibers include carbon fibers. [Effects of the Invention]

[0011] According to a preferred embodiment of the present invention, the matrix resin can be easily decomposed by heating the fiber-reinforced plastic, and the reinforcing fibers and resin decomposition products can be recovered. Furthermore, it is possible to lower the temperature required for curing the matrix resin composition, thereby providing a prepreg and fiber-reinforced plastic that can reduce the energy cost required for molding the fiber-reinforced plastic and ensure moldability and mechanical properties by separating the curing temperature and thermal decomposition temperature of the matrix resin. [Modes for carrying out the invention]

[0012] 1. Prepreg One embodiment of the present invention relates to a prepreg. The prepreg according to this embodiment consists of a resin composition containing the following components (A) and (B), and reinforcing fibers. (A) Component: Epoxy resin (B) Component: Aromatic amine compound containing a disulfide bond

[0013] There are no particular limitations on the epoxy resin incorporated as component (A) in the resin composition. Any epoxy resin can be incorporated into the resin composition, such as bisphenol type epoxy resins like bisphenol A type epoxy resin and bisphenol F type epoxy resin, novolac type epoxy resin, or glycidylamine type epoxy resin. The component (A) incorporated into the resin composition may be one type or two or more types.

[0014] In the preferred example, at least a portion of the epoxy resin incorporated into the resin composition is a bisphenol-type epoxy resin, and in particular a bisphenol A-type epoxy resin. As is well known, bisphenol A type epoxy resin is a mixture mainly composed of the compound n=0 in the following formula (a), i.e., bisphenol A diglycidyl ether, with small amounts of components such as n=1. The average n in commercially available bisphenol A type epoxy resin that is liquid at room temperature is approximately 0.1 to 0.2.

[0015] [ka]

[0016] The amount of component (A) in the resin composition is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and also preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the resin composition. The preferred lower and upper limits of the amount of component (A) can be any combination, for example, 40 to 90% by mass is preferred.

[0017] The aromatic amine compound incorporated as component (B) in the resin composition functions as a curing agent for epoxy resins. Because aromatic amine compounds have aromatic rings, using them as curing agents yields fiber-reinforced plastics with excellent heat resistance and high mechanical strength. Furthermore, when aromatic amine compounds are used as curing agents, the curing temperature tends to be high and the curing reaction slow. However, the aromatic amine compound incorporated as component (B) contains disulfide bonds (-SS-) that are easily cleaved under heating or reducing conditions. Therefore, by cleaving the disulfide bonds through heat exposure or the addition of a reducing agent, the matrix resin of fiber-reinforced plastics can be easily decomposed at lower temperatures. As a result, damage to the reinforcing fibers and energy costs when recovering reinforcing fibers from fiber-reinforced plastics can be reduced.

[0018] The aromatic amine compound included as component (B) preferably contains a compound represented by the following formula (1). (R 6 -) a Ar 1 -SS-Ar 2 (-R 7 ) b ...(1) (However, in equation (1), Ar 1 and Ar 2 Each of these is a divalent or greater aromatic group or heteroaromatic group which may independently have substituents other than an amino group, and R 6 and R 7 Each of them independently 8 R 9 (R 8 , R 9 Each is independently a hydrogen atom, an alkyl group, or an aryl group. ), or at least one hydrogen atom is NR 10 R 11 (R 10 , R 11 Each of the following is independently a hydrogen atom, an alkyl group, or an aryl group. (The aminoalkyl group is substituted with , where a and b are independently integers from 1 to 5.)

[0019] Ar1 and Ar 2 The aromatic group or heteroaromatic group is a group from which two or more hydrogen atoms have been removed from an aromatic ring or heteroaromatic ring, and may have substituents other than an amino group. Ar 1 and Ar 2 The aromatic ring or heteroaromatic ring constituting it is not particularly limited, and examples include a benzene ring, a naphthyl ring, and a triazine ring, with a benzene ring being preferred from the viewpoint of reactivity. Ar 1 and Ar 2 These may be the same group or different groups, and are preferably arylene groups which may have substituents other than amino groups, more preferably phenylene groups which may have substituents other than amino groups, and are particularly preferably unsubstituted phenylene groups from the viewpoint of reactivity and dispersibility in the matrix of aromatic amine compounds. Ar 1 and Ar 2 Other substituents that may be present are not particularly limited, and examples include alkyl groups, aryl groups, carboxyl groups, alkoxy groups, alkoxycarbonyl groups, cyano groups, hydroxyl groups, amide groups, and halogens.

[0020] R 8 and R 9 Specific examples include, for instance, hydrogen atoms, methyl groups, ethyl groups, n-propyl groups, i-propyl groups, n-butyl groups, i-butyl groups, t-butyl groups, phenyl groups, and benzyl groups. 8 and R 9 They may be the same or different. NR 8 R 9Examples include unsubstituted amino groups; primary amino groups such as N-methylamino group, N-ethylamino group, Nn-propylamino group, Ni-propylamino group, Nn-butylamino group, Ni-butylamino group, Nt-butylamino group, N-phenylamino group, and N-benzylamino group; and secondary amino groups such as N,N'-dimethylamino group, N,N'-diethylamino group, N,N'-di-n-propylamino group, N,N'-di-i-propylamino group, N,N'-di-n-butylamino group, N,N'-di-i-butylamino group, N,N'-di-t-butylamino group, N,N'-diphenylamino group, N,N'-dibenzylamino group, N,N'-methylethylamino group, and N,N'-methylphenylamino group. Among these, unsubstituted amino groups, N-methylamino groups, N-ethylamino groups, and N-phenylamino groups are more preferred from the viewpoint of reactivity, improved adhesion to reinforcing fibers, and suppression of organic acid gas generation.

[0021] R 10 and R 11 Specific examples include, for instance, hydrogen atoms, methyl groups, ethyl groups, and phenyl groups. 10 and R 11 They may be the same or different. R 6 and R 7 The aminoalkyl group has NR 10 R 11 The number of these is not limited, but from the viewpoint of decomposing the hardened fiber-reinforced plastic and making it easier to extract the fibers, it is preferable to have one. At least one hydrogen atom is NR 10 R 11Examples of aminoalkyl groups substituted with methyl include aminomethyl group, 1-aminoethyl group, 2-aminoethyl group, 1-amino-n-propyl group, 2-amino-n-propyl group, 3-amino-n-propyl group, 1-amino-i-propyl group, 2-amino-i-propyl group, 1-amino-n-butyl group, 2-amino-n-butyl group, 3-amino-n-butyl group, 4-amino-n-butyl group, 1-amino-s-butyl group, 2-amino-s-butyl group, 3-amino-s-butyl group, N-methylaminomethyl group, N-ethylaminomethyl group, N-phenylaminomethyl group, 1-(N-methylamino)ethyl group, 2-(N-methylamino)ethyl group, 1-(N-phenylamino)ethyl group, 2-(N-phenylamino)ethyl group, N,N'-dimethylaminomethyl group, 1-(N,N'-dimethylamino)ethyl group, and 2-(N,N'-dimethylamino)ethyl group. Among these, aminoalkyl groups that are not substituted with amino groups are preferred from the viewpoint of preventing a decrease in physical strength after molding, and aminomethyl groups, 1-aminoethyl groups, 2-aminoethyl groups, 1-amino-n-propyl groups, 2-amino-n-propyl groups, 3-amino-n-propyl groups, 1-amino-i-propyl groups, and 2-amino-i-propyl groups are more preferred.

[0022] a is preferably an integer between 1 and 3, and is particularly preferred to be 1 from the viewpoint of decomposing the hardened fiber-reinforced plastic and making it easier to extract the fibers. b is preferably an integer between 1 and 3, and is particularly preferred at 1 from the viewpoint of decomposing the hardened fiber-reinforced plastic to facilitate the extraction of fibers. a and b may be the same number or they may be different numbers.

[0023] The compound represented by formula (1) is more preferably the compound represented by formula (11) below, and even more preferably the compound represented by formula (12) below. However, R in formula (12) 61 , R 62 , R 71 , R 72 R in equation (1) 8 , R 9 It is the same as this.

[0024] [ka]

[0025] Examples of aromatic amine compounds for component (B) include 2,2'-diaminophenyl disulfide, 4,4'-diaminophenyl disulfide, 4,4'-diaminophenyl disulfide, 3,4'-diaminophenyl disulfide, 3,4,3',4'-tetraaminophenyl disulfide, decaaminophenyl disulfide, 4,4'-bis(N,N'-methyl)aminophenyl disulfide, 4,4'-bis(N-methyl-N-phenyl)aminophenyl disulfide, 3-(N,N-diethyl)-4'-(N',N'-diphenyl)aminophenyl disulfide, 4,4'-diaminomethylphenyl disulfide, 3-(1-aminoethyl)-4'-aminophenyl disulfide, 3-{1-(N,N-dimethylamino)ethyl)}-4'-aminophenyl disulfide, and their salts. Examples of the salt include alkali metal salts such as lithium, potassium, sodium, cesium, and rubidium. From the viewpoint of reactivity, stability, mechanical properties, and availability, it is preferable that at least one of 4,4'-diaminophenyl disulfide and 2,2'-diaminophenyl disulfide is used. The component (B) incorporated into the resin composition may be one type or two or more types.

[0026] (B) The amount of component (B) blended is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, relative to the total mass of the resin composition, from the viewpoint of promoting curing and increasing the number of decomposable bonds. From the viewpoint of the strength of the cured product, it is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less. The preferred lower and upper limits of the amount of component (B) blended can be arbitrarily combined, for example, 10 to 50% by mass is preferred.

[0027] The amount of component (B) is the ratio of the number of moles of epoxy groups in component (A) (a) to the number of moles of active hydrogen in component (B) (b) ((a) / (b) (molar ratio)), which from the viewpoint of shortening the curing time is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. From the viewpoint of the strength of the cured product, it is preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.2 parts by mass or less. The preferred lower and upper limits of the (a) / (b) (molar ratio) can be arbitrarily combined, for example, 0.9 to 1.2 is preferred.

[0028] In addition to components (A) and (B), it is preferable that the resin composition further contains one or more compounds selected from those represented by the following formula (2) as component (C).

[0029] [ka]

[0030] However, in equation (2), R 1 and R 2 c and d are independent substituents, and c and d are independent integers between 0 and 5.

[0031] R 1 and R 2 The substituents are not particularly limited and include, for example, alkyl groups, aryl groups, carboxyl groups, alkoxy groups, alkoxycarbonyl groups, cyano groups, hydroxyl groups, amide groups, and halogens. c is preferably an integer between 0 and 3, and particularly preferably 0. When c is 2 or greater, there are multiple R 1 They may be the same or different from each other. d is preferably an integer between 0 and 3, and particularly preferably 0. When d is 2 or greater, there are multiple R 1 They may be the same or different from each other. c and d may be the same number or they may be different numbers.

[0032] Examples of component (C) include triphenylphosphine triphenylborate and trisparamethylphenylphosphine triphenylborate, with triphenylphosphine triphenylborate being preferred. The (C) component incorporated into the resin composition may be one type or two or more types.

[0033] The inclusion of component (C) tends to result in a lower curing temperature and a more rapid curing reaction. As a result, the molding temperature can be lowered, making it easier to suppress thermal decomposition of the matrix resin during molding. Although this mechanism is not entirely clear, it is speculated that: Component (C), triphenylborate (TPB), is stabilized by complex formation with triphenylphosphine (TPP), and the unpaired electrons of the oxygen atom of the epoxy are attracted to the empty orbital of the boron atom of TPB, activating it and promoting nucleophilic attack of the aromatic amine compound of component (B) onto the epoxy.

[0034] (C) The amount of component (C) is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to the total mass of the resin composition, from the viewpoint of shortening the curing time. Furthermore, from the viewpoint of improving the strength of the cured product, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. The preferred lower and upper limits of the amount of component (C) can be arbitrarily combined, for example, 0.5 to 10% by mass is preferred.

[0035] The amount of component (C) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of component (B), from the viewpoint of improving reactivity through catalytic effect, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, from the viewpoint of thermal stability at the temperature to which it is exposed during the manufacturing process of the resin composition or prepreg. The preferred lower and upper limits of the amount of component (C) can be arbitrarily combined, for example, 5 to 40 parts by mass per 100 parts by mass of component (B) is preferred.

[0036] When component (C) is incorporated into the resin composition, it is preferable to further incorporate one or more compounds selected from the compounds represented by the following formula (3) as component (D) into the resin composition. (D) The inclusion of component (D) allows for adjustment to prevent the curing temperature from dropping too low, and is thought to have the effect of suppressing the reaction of the matrix resin due to heating during the manufacturing process of the prepreg.

[0037] [ka]

[0038] However, in equation (3), R 3 ~R 5 Each of these is an independent substituent, and e to g are independent integers from 0 to 5.

[0039] R 3 ~R 5 The substituents are not particularly limited and include, for example, alkyl groups, aryl groups, carboxyl groups, alkoxy groups, alkoxycarbonyl groups, cyano groups, hydroxyl groups, amide groups, and halogens. Among these, alkyl groups and alkoxy groups are preferred, methyl groups, t-butyl groups, methoxy groups, and t-butoxy groups are more preferred, and methyl groups and methoxy groups are particularly preferred. e is preferably an integer between 0 and 3, and particularly preferably 0 or 1. f is preferably an integer between 0 and 3, and particularly preferably 0 or 1. g is preferably an integer between 0 and 3, and particularly preferably 0 or 1. e to f may be the same number or they may be different numbers.

[0040] Examples of component (D) include triphenylphosphine, tri-p-tolylphosphine, tris(p-methoxyphenyl)phosphine, and tris(pt-butoxyphenyl)phosphine, and it is preferable that it be at least one selected from triphenylphosphine, tri-p-tolylphosphine, and tris(p-methoxyphenyl)phosphine. The component (D) incorporated into the resin composition may be one type or two or more types.

[0041] The amount of component (D) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, relative to the total mass of the resin composition, from the viewpoint of providing thermal stability at the temperature to which the resin composition and prepreg are exposed during the manufacturing process, and improving reaction control so that the reaction of the resin composition separates into multiple peaks and broadens. Furthermore, from the viewpoint of preventing the reaction temperature from rising due to reaction suppression and delaying the time until the completion of the reaction, it is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. The preferred lower and upper limits of the amount of component (D) can be arbitrarily combined, for example, 0.5 to 20% by mass is preferred.

[0042] The amount of component (D) is preferably 70 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 120 parts by mass or more, per 100 parts by mass of component (C), from the viewpoint of providing thermal stability at the temperature to which the resin composition or prepreg is exposed during the manufacturing process. Furthermore, from the viewpoint of controlling the temperature increase due to reaction suppression and adjusting the time until the reaction is completed, it is preferably 150 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 300 parts by mass or less. The preferred lower and upper limits of the amount of component (D) can be arbitrarily combined, for example, 90 to 200 parts by mass per 100 parts by mass of component (C) is preferred.

[0043] In addition to components (A) to (D), optional components may be added to the resin composition. Optional components, though not limited to them, include other curing agents, antioxidants, internal release agents, low-shrinkage agents, colorants, flame retardants, and modifiers made of rubber, elastomers, or thermoplastic resins.

[0044] The flame retardants that can be incorporated into the resin composition are not particularly limited, but preferred examples include non-halogenated flame retardants. Examples of non-halogenated flame retardants are not limited to inorganic phosphorus-based flame retardants such as red phosphorus, organophosphorus-based flame retardants such as phosphate esters, organophosphates, phosphonates, and phosphinates, nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, and isocyanuric acid compounds, silicone-based flame retardants, inorganic flame retardants such as metal hydroxides and metal oxides, and organometallic salt-based flame retardants such as ferrocene and acetylacetone metal complexes. In a preferred example, the resin composition may contain either or both an organophosphorus-based flame retardant and a nitrogen-based flame retardant.

[0045] Other preferred curing agents include aromatic polyamines, such as xylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, phenylenediamine, and dimethylthiotoluenediamine. Among these, diaminodiphenylmethane and diaminodiphenylsulfone are particularly preferred. Examples of diaminodiphenylsulfone include 3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone.

[0046] When a resin composition is heated at 180°C for 4 hours to cure, and then heated from 25°C to 400°C at a heating rate of 5°C / min, the decomposition temperature Td (°C) is preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 300°C or higher. If the decomposition temperature Td is above the lower limit, the curing reaction and the decomposition reaction can be easily separated, resulting in a prepreg and fiber-reinforced plastic that can ensure moldability and mechanical properties. The decomposition temperature Td is preferably 600°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. If the decomposition temperature Td is below the upper limit, damage due to decomposition of carbon fibers used as reinforcing fibers and the generation of large amounts of gas due to decomposition other than disulfide bonds in the matrix resin tend to be suppressed. The preferred lower and upper limits of the decomposition temperature Td can be arbitrarily combined, for example, 250 to 400°C is preferred.

[0047] In a DSC chart obtained by differential scanning calorimetry (DSC) in which the resin composition is heated from -50°C to 400°C at a heating rate of 10°C / min, the peak top temperature T1 (°C) of the maximum peak is preferably 70°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. If the peak top temperature T1 is above the lower limit, the progress of the curing reaction due to heat exposure in the manufacturing process of the prepreg is easily suppressed. The peak top temperature T1 is preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 150°C or lower. If the peak top temperature T1 is below the upper limit, the decomposition temperature and separation of the matrix resin of the fiber-reinforced composite material are easily achieved, and prepregs and fiber-reinforced plastics that can ensure moldability and mechanical properties are easily obtained. The preferred lower and upper limits of the peak top temperature T1 can be arbitrarily combined, for example, 70 to 250°C is preferred.

[0048] The difference between the decomposition temperature Td and the peak top temperature T1 (Td-T1) is preferably 50°C or higher, more preferably 80°C or higher, even more preferably 120°C or higher, and particularly preferably 150°C or higher. If the difference (Td-T1) is above the lower limit, the curing reaction and the decomposition reaction can be separated, and the resulting prepreg and fiber-reinforced plastic tend to have moldability and mechanical properties. The difference (Td-T1) can be, for example, 220°C or lower.

[0049] Various types of reinforcing fibers can be used depending on the application and purpose of the fiber-reinforced plastic. Examples include carbon fibers (including graphite fibers; the same applies hereinafter), aramid fibers, silicon carbide fibers, alumina fibers, boron fibers, tungsten carbide fibers, and glass fibers. From the viewpoint of the mechanical properties of the fiber-reinforced plastic, carbon fibers and glass fibers are preferred, and carbon fibers are particularly preferred.

[0050] 2. Method for manufacturing prepregs The prepreg can be manufactured by impregnating the aforementioned components with a matrix resin using a known method to create reinforcing fibers. For example, a prepreg can be obtained by supplying a reinforcing fiber substrate to a film surface coated with a predetermined amount of resin composition, such as on a release paper, and then passing it through a pressing roll to impregnate the reinforcing fiber substrate with the resin composition. Alternatively, a prepreg can be obtained by coating a reinforcing fiber substrate with a predetermined amount of resin composition, then, if necessary, sandwiching the reinforcing fiber substrate between release paper or the like, and passing it through a pressing roll to impregnate the reinforcing fiber substrate with the resin composition.

[0051] The form of the reinforcing fiber substrate is not particularly limited, and examples include woven fabrics, nonwoven fabrics, a sheet-like form in which continuous fibers are aligned in one direction, and a sheet-like form in which short fibers (bundles) of continuous fibers cut to a certain length are randomly piled up. The basis weight of the reinforced fiber base material is 10 g / m². 2 More than 4000g / m 2 The following is possible: The basis weight of a single sheet of reinforcing fiber substrate prepreg may be, for example, 10 g / m² if it is a sheet aligned in one direction.2 More than 300g / m 2 For sheets that are randomly piled up, the following is 500g / m² 2 More than 2000g / m 2 The following is also acceptable.

[0052] From the viewpoint of improving the adhesion between the reinforcing fibers and the matrix resin and improving the mechanical properties of the fiber-reinforced plastic, the content of the matrix resin composition in the prepreg is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and even more preferably 15 to 50% by mass, relative to the total mass of the prepreg.

[0053] From the viewpoint of improving the adhesion between the reinforcing fibers and the matrix resin and improving the mechanical properties of the fiber-reinforced plastic, the volume content of reinforcing fibers in the prepreg is preferably 30 to 85 volume%, more preferably 35 to 80 volume%, and even more preferably 40 to 80 volume% relative to the total volume of the prepreg.

[0054] As described above, the prepreg according to this embodiment uses an aromatic amine compound containing a disulfide bond as a curing agent. Therefore, the disulfide bond can be cleaved by heat exposure or the addition of a reducing agent, allowing the matrix resin to be decomposed at a lower temperature compared to when other curing agents are used. As a result, damage to the reinforcing fibers and energy costs during the recovery of the reinforcing fibers are reduced, and the reinforcing fibers can be recycled efficiently. Furthermore, by incorporating components (C) and (D), the difference between the curing temperature of the prepreg and the thermal decomposition temperature of the matrix resin becomes even larger, making it even easier to suppress the thermal decomposition of the matrix resin during the process of obtaining the prepreg and fiber-reinforced plastic.

[0055] 3. Fiber-reinforced plastics Another embodiment of the present invention relates to fiber-reinforced plastics. The fiber-reinforced plastic according to this embodiment is a cured product of the prepreg according to this embodiment. By heating and pressurizing the prepreg according to this embodiment to cure it, a fiber-reinforced plastic made from the cured product can be manufactured. Molding methods include press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, sheet wrap molding, and RTM (Resin Transfer Molding), VaRTM (Vacuum assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion), which involve impregnating reinforcing fiber filaments or preforms with a matrix resin composition and curing to obtain molded products. Press molding and autoclave molding are preferred, and press molding is particularly preferred when combining components (A) to (C) because it improves the curing speed.

[0056] The applications of fiber-reinforced plastics are not particularly limited and include structural materials for aircraft, automobiles and other vehicles, ships, buildings, sports equipment such as golf shafts, fishing rods, and tennis rackets, and general industrial products such as wind turbines and rollers.

[0057] Methods for producing the fiber-reinforced plastic according to the embodiment include autoclave molding, vacuum bag molding, and press molding. When producing the fiber-reinforced plastic by press molding, it is preferable to include a step of heating and pressurizing a preform, which has been pre-shaped using the prepreg of the embodiment or a prepreg laminate obtained by laminating the prepreg, by placing it in a mold that has been pre-adjusted to a molding temperature.

[0058] One method for recovering reinforcing fibers according to the embodiment is to treat a fiber-reinforced plastic containing a matrix resin with disulfide bonds and reinforcing fibers with heat or a reducing agent to decompose the matrix resin and extract the reinforcing fibers. When decomposing by heat, the temperature can be, for example, 200°C to 600°C or 250°C to 400°C. This recovery method can be applied to fiber-reinforced plastics to which the above-described embodiments are applied as the matrix resin and reinforcing fibers. [Examples]

[0059] 4. Experimental Results The present invention will be specifically described below with reference to experimental examples, but the present invention is not limited to the following description.

[0060] The materials used in this experiment are listed below. [(A) component] A-1: Bisphenol A type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER(registered trademark) 828, epoxy equivalent weight 184-194, liquid) A-2: Bisphenol F type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER(registered trademark) 807, epoxy equivalent weight 160-175, liquid) A-3: Phenol novolac type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER(registered trademark) 152, epoxy equivalent weight 176-178, liquid)

[0061] [(B) Component] B-1: 4,4'-Diaminophenyl disulfide (manufactured by Tokyo Chemical Industry Co., Ltd., standard name 4,4'-Dithiodianiline, purity >98.0%, molecular weight 248.36, solid) B-2: 2,2'-Diaminophenyl disulfide (manufactured by Tokyo Chemical Industry Co., Ltd., trade name 2,2'-Dithiodianiline, purity >98.0%, molecular weight 248.36, solid)

[0062] [(C) component] C-1: Triphenylphosphine triphenylborate (manufactured by Hokko Chemical Industry Co., Ltd., trade name TPP-S, molecular weight 504.4, solid)

[0063] [(D) component] D-1: Triphenylphosphine (manufactured by Hokko Chemical Industry Co., Ltd., registered trademark TPP-FP, molecular weight 262.3, solid) D-2: Tri-p-tolylphosphine (manufactured by Hokko Chemical Industry Co., Ltd., registered trademark TPTP, molecular weight 304.0, solid) D-3: Tris(p-methoxyphenyl)phosphine (manufactured by Hokko Chemical Industry Co., Ltd., registered trademark TPAP, molecular weight 352.0, solid)

[0064] [(B') component: Hardener other than component (B)] B'-1:4,4'-Diaminodiphenylsulfone (manufactured by Seika Corporation, trade name SEIKACURE-S, molecular weight 248.3, solid) B'-2: 4,4'-Diaminodiphenylsulfone (manufactured by Tokyo Chemical Industry Co., Ltd., trade name Bis(4-aminophenyl)Sulfone, molecular weight 248.3, solid)

[0065] [Experimental Example 1] 100 parts by mass of component A-1, 33 parts by mass of component B-1, 3 parts by mass of component C-1, and 3 parts by mass of component D-1 were weighed into a container, stirred using a planetary stirring and defoaming device Mazelstar KK-2000 (manufactured by Kurabo Corporation), and then the solid components were uniformly dispersed using a three-roll mill to obtain a resin composition.

[0066] [Experimental Examples 2-13] A resin composition was obtained in the same manner as in Experimental Example 1, except that the composition of each component was changed as shown in Table 1.

[0067] [Evaluation Method] (1) Evaluation of thermal decomposition behavior The resin composition for each example was sandwiched between two smooth stainless steel plates that had been treated with a fluorine-based release agent, along with a spacer (made of polytetrafluoroethylene, thickness: approximately 100 μm). The plates were then heated in a hot air circulating constant temperature furnace at a rate of 2 °C / min from 25 °C to 180 °C. After maintaining the temperature of the stainless steel plates at 180 °C for 4 hours, they were cooled to obtain a cured resin sheet. Next, the cured resin sheet was heated using a thermomechanical analyzer (hereinafter referred to as "TMA") under the conditions of a temperature range of 25°C to 400°C, a heating rate of 5°C / min, and a probe load of 0.02N, and the change in the thickness of the cured resin sheet at that time was measured. When the cured resin sheet exhibited thermal decomposition within the measurement temperature range, a temporary expansion due to decomposition was observed, after which the probe sank into the resin, resulting in a thickness of virtually zero. The onset temperature at which this temporary expansion began was defined as the decomposition temperature Td (°C). On the other hand, when the cured resin sheet exhibited non-degradability within the measurement temperature range, the change in the thickness of the cured resin sheet was only slightly reduced by the probe weight above Tg.

[0068] (2) Evaluation of curing reactivity based on exothermic behavior Using a differential scanning calorimetry (DSC), the resin compositions of each example were heated from -50°C to 400°C at a heating rate of 10°C / min to cure, and the exothermic behavior was measured. In the DSC chart of the resin composition, the peak top temperature T1 (°C) of the maximum peak and the endpoint temperature T2, where the reaction occurring at the maximum peak terminates and forms with the baseline, were determined. Regarding the maximum peak, even if it was multi-peaked, it was treated the same as a single peak if it could be considered as a series of reaction processes.

[0069] Table 1 shows the composition and evaluation results of each component in each experimental example.

[0070] [Table 1] Note that in Experimental Example 5 in Table 1, "103 / 254" for T1 indicates the peak top temperature T1 of each of the two maximum peaks, and in Experimental Example 5 in Table 1, T2 indicates the temperature T2 obtained from the maximum peak where T1 is 254°C.

[0071] As shown in Table 1, no thermal decomposition was observed in the resin composition of Experimental Example 13, in which component (B') was added instead of component (B), whereas thermal decomposition was observed in the resin compositions of Experimental Examples 1 to 12, in which component (B) was added to component (A). Furthermore, a comparison of experimental examples 3 and 4 with experimental examples 1 and 2 revealed that by incorporating components (C) and (D), the curing reaction proceeded at a lower temperature, and the difference between the curing temperature and the decomposition temperature became larger.

Claims

1. A prepreg comprising a resin composition containing component (A) below, component (B) below, and one or more components (C) selected from the compounds represented by formula (2) below, and reinforcing fibers. (A) Component: Epoxy resin (B) Component: Aromatic amine compound containing a disulfide bond 【Chemistry 1】 (However, in formula (2), R1 and R2 are each independent substituents, and c and d are each independent integers from 0 to 5.)

2. The prepreg according to claim 1, wherein the (B) component comprises a compound represented by the following formula (1). (R ６ -) ａ Ar １ -S-S-Ar ２ (-R ７ ) ｂ ・・・(1) (However, in Formula (1), Ar １ and Ar ２ are each independently an aromatic group or heteroaromatic group having a valence of 2 or more which may have a substituent other than an amino group, R ６ and R ７ are each independently NR ８ R ９ (R ８ and R ９ are each independently a hydrogen atom, an alkyl group or an aryl group.), or an aminoalkyl group in which at least one hydrogen atom is substituted with NR １０ R １１ (R １０ and R １１ are each independently a hydrogen atom, an alkyl group or an aryl group.), and a and b are each independently an integer of 1 to 5.)

3. The prepreg according to claim 1, wherein component (B) comprises at least one of 4,4'-diaminophenyl disulfide and 2,2'-diaminophenyl disulfide.

4. The prepreg according to claim 1, wherein the amount of component (B) is 5% by mass or more and 60% by mass or less with respect to the total mass of the resin composition.

5. The prepreg according to claim 1, wherein the (C) component comprises triphenylphosphine triphenylborate.

6. The prepreg according to claim 1, wherein the amount of component (C) is 0.3% by mass or more and 20% by mass or less with respect to the total mass of the resin composition.

7. The prepreg according to claim 1, further comprising one or more (D) components selected from compounds represented by the following formula (3). 【Chemistry 2】 (However, in equation (3), R ３ ~R ５ (Each of these is an independent substituent, and e to g are independent integers from 0 to 5.)

8. The prepreg according to claim 7, wherein the component (D) comprises at least one selected from triphenylphosphine, tri-p-tolylphosphine, and tris(p-methoxyphenyl)phosphine.

9. The prepreg according to claim 7, wherein the amount of component (D) is 0.5% by mass or more and 30% by mass or less with respect to the total mass of the resin composition.

10. The prepreg according to claim 1, wherein the reinforcing fibers include carbon fibers.

11. The prepreg according to claim 1, wherein the resin composition is cured by heating at 180°C for 4 hours, and then heated from 25°C to 400°C at a heating rate of 5°C / min, the decomposition temperature Td (°C) is 200°C or more and 400°C or less.

12. The prepreg according to claim 1, wherein in a DSC chart obtained by differential scanning calorimetry in which the resin composition is heated from -50°C to 400°C at a heating rate of 10°C / min, the peak top temperature T1 (°C) of the maximum peak is 70°C or more and 250°C or less.

13. The prepreg according to claim 1, wherein the difference (Td-T1) between the peak top temperature T1 (°C) of the maximum peak in a DSC chart obtained by differential scanning calorimetry performed by heating the resin composition from -50°C to 400°C at a heating rate of 10°C / min and the decomposition temperature Td (°C) obtained when the resin composition is cured by heating at 180°C for 4 hours and then heated from 25°C to 400°C at a heating rate of 5°C / min is 50°C or more.

14. A fiber-reinforced plastic comprising a cured prepreg according to any one of claims 1 to 13.

15. A method for recovering reinforcing fibers, comprising treating the fiber-reinforced plastic described in Claim 14 with heat or a reducing agent to decompose the matrix resin and extract the reinforcing fibers.

16. The method for recovering reinforcing fibers according to claim 15, wherein the matrix resin includes a cured epoxy resin.

17. The method for recovering reinforcing fibers according to claim 15, wherein the reinforcing fibers include carbon fibers.

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