Method for producing regenerated reinforced fibers

Abstract

Provided is a method for producing regenerated reinforcing fibers, whereby reinforcing fibers can be efficiently recovered from a fiber-reinforced resin material under relatively mild conditions. This method for producing regenerated reinforcing fibers comprises: a first step in which a fiber-reinforced resin material containing a resin and reinforcing fibers is treated with a treatment liquid, and at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid; and a second step in which the fiber-reinforced resin material is heated in a gas atmosphere at 150 DEG C or higher.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority based on Japanese patent application No. 2022-161820 filed in Japan on October 6, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a method for manufacturing regenerated reinforcing fibers. Background Art

[0004] Fiber reinforced plastics (FRP) using fibers such as glass fibers as reinforcement materials are lightweight, high-strength, and highly elastic materials, and are widely used in parts of small ships, automobiles, and railway vehicles. In addition, for the purpose of further lightweighting, high-strength, and high-elasticity, carbon fiber reinforced plastics (CFRP) using carbon fibers as reinforcement materials have been developed, and are used in parts of aircraft, automobiles, and the like.

[0005] In recent years, the amount of waste fiber-reinforced plastics after use has tended to increase, and research is being conducted on the development of recycling technologies for the same. As methods for recycling the reinforcing fibers of fiber-reinforced plastics, there are mainly a thermal decomposition method in which the resin component is removed by thermal decomposition through heat treatment and the reinforcing fibers are recovered, and a solvent method in which the resin component is removed by dissolving with a solvent and the reinforcing fibers are recovered. Among them, the solvent method is easy to recover the resin component, which is advantageous from the perspective of resource recycling.

[0006] As a thermal decomposition method, for example, patent document 1 discloses a method for producing a regenerated carbon fiber bundle, which is a method for obtaining the carbon fiber substrate as a regenerated carbon fiber bundle from a carbon fiber reinforced resin comprising a plurality of stacked fragment-shaped or sheet-shaped carbon fiber substrates and a matrix resin, wherein the carbon fiber reinforced resin is heated at 300 to 700° C. to thermally decompose the matrix resin to obtain a heat-treated product, and the heat-treated product is crushed in a direction in which the plurality of stacked fragment-shaped or sheet-shaped carbon fiber substrates are peeled off from each other to separate the plurality of fragment-shaped or sheet-shaped carbon fiber substrates while maintaining the fragment-shaped or sheet-shaped form, thereby obtaining a fragment-shaped or sheet-shaped regenerated carbon fiber bundle.

[0007] As a solvent method, for example, there are methods proposed in Patent Documents 2 and 3. Patent Document 2 proposes a method for manufacturing carbon fiber, which includes: immersing a carbon fiber composite material in an acidic aqueous solution, and extracting at least a portion of the resin portion of the carbon fiber composite material to obtain a roughly fibrous object; and immersing the roughly fibrous object in an alkaline aqueous solution, extracting at least a portion of the resin portion of the roughly fibrous object to obtain a fibrous object. In addition, Patent Document 3 proposes a carbon fiber recovery method, which includes a step of dissolving a base material of a carbon fiber reinforced plastic material using a dissolving solution containing phosphoric acid, the phosphoric acid concentration of the dissolving solution being 110% by mass or more, and the dissolving step is performed at a temperature of the dissolving solution of 200°C or more and 300°C or less.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2018 / 212016

[0011] Patent Document 2: Japanese Patent Application Publication No. 2019-136932

[0012] Patent Document 3: Japanese Patent Application Publication No. 2020-50704 Summary of the invention

[0013] Technical Problems to be Solved by the Invention

[0014] However, in the conventional thermal decomposition method, since the reinforcing fiber resin material is heated to a relatively high temperature, there is a possibility that the reinforcing fibers themselves to be recovered may be damaged.

[0015] In addition, in the conventional solvent method, the efficiency of removing the resin component is very low. For example, in the methods described in Patent Documents 1 and 2, the resin component is removed by cutting the fiber-reinforced resin material into pieces of about several centimeters in size in consideration of the penetration of the treatment liquid containing the solvent. If the fiber-reinforced resin material is cut into pieces in this way, the length of the regenerated reinforcing fiber recovered from the fiber-reinforced resin material will inevitably become shorter, making it difficult to maintain the performance of the reinforcing fiber contained in the fiber-reinforced resin material before recovery, and the use of the recovered reinforcing fiber is limited. On the other hand, in order to efficiently remove the resin component by the solvent method, it is required to perform a long-term treatment under harsh conditions such as high temperature.

[0016] Therefore, an object of the present invention is to provide a method for producing regenerated reinforcing fibers capable of efficiently recovering reinforcing fibers from a fiber-reinforced resin material under relatively mild conditions.

[0017] Technical means for solving technical problems

[0018] The present inventors have discovered in their research on recovering reinforcing fibers from fiber-reinforced resin materials that resin can be efficiently removed from fiber-reinforced resin materials under relatively mild conditions by combining a solvent method with a thermal decomposition method. Based on the above findings, the present inventors have conducted further research and have come up with the present invention.

[0019] The gist of the present invention is as follows.

[0020] (1) A method for producing a regenerated reinforcing fiber, comprising:

[0021] A first step of treating a fiber-reinforced resin material including a resin and reinforcing fibers with a treatment liquid so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid; and

[0022] In the second step, the fiber-reinforced resin material is heated in a gas atmosphere at 150° C. or higher.

[0023] (2) The method for producing regenerated reinforcing fibers according to (1), wherein the first step includes treating the fiber-reinforced resin material with an oxidizing treatment liquid containing an oxidant so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidizing treatment liquid.

[0024] (3) A method for producing regenerated reinforcing fibers according to (1), wherein the first step comprises: a first treatment of treating the fiber-reinforced resin material with an acidic solution containing an acid; and a second treatment of treating the fiber-reinforced resin material with an oxidizing treatment liquid containing an oxidant, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidizing treatment liquid.

[0025] (4) The method for producing regenerated reinforcing fibers according to (2) or (3), wherein the oxidizing agent contains an acid having oxidizing power.

[0026] (5) The method for producing a regenerated reinforcing fiber according to (4), wherein the acid having oxidizing power comprises one or more selected from the group consisting of nitric acid, a mixed acid of sulfuric acid and nitric acid, a mixed acid of nitric acid and hydrochloric acid (aqua regia), and a mixed solution of hydrogen peroxide and sulfuric acid.

[0027] (6) The method for producing regenerated reinforcing fibers according to any one of (2) to (5), wherein the oxidation treatment liquid further contains a polymerization inhibitor.

[0028] (7) The method for producing a regenerated reinforcing fiber according to (6), wherein the polymerization inhibitor includes one or more selected from the group consisting of nitrites and nitrite esters.

[0029] (8) The method for producing a regenerated reinforcing fiber according to any one of (3), wherein the acid includes one or more selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid.

[0030] (9) The method for producing a regenerated reinforcing fiber according to (3) or (8), wherein the concentration of the acid in the acidic solution is 0.5 mol / L or more.

[0031] (10) The method for producing regenerated reinforcing fibers according to any one of (1) to (9), wherein in the second step, the fiber-reinforced resin material is heated in a gas atmosphere at 150° C. to 350° C.

[0032] (11) The method for producing regenerated reinforcing fibers according to any one of (1) to (10), wherein in the second step, the heating time is 60 minutes to 300 minutes.

[0033] (12) The method for producing a regenerated reinforcing fiber according to any one of (1) to (11), wherein the resin contains an epoxy resin.

[0034] (13) The method for producing a regenerated reinforcing fiber according to any one of (1) to (12), wherein the resin contains an amine-cured epoxy resin.

[0035] (14) The method for producing regenerated reinforcing fibers according to any one of (1) to (13), wherein the reinforcing fibers include carbon fibers.

[0036] Effects of the Invention

[0037] With the above configuration, an object of the present invention is to provide a method for producing regenerated reinforcing fibers, which can efficiently recover reinforcing fibers from a fiber-reinforced resin material under relatively mild conditions. DETAILED DESCRIPTION

[0038] Hereinafter, several examples of the method for producing the regenerated reinforcing fiber according to the preferred embodiment of the present invention will be described.

[0039] 1. First Implementation

[0040] Hereinafter, a method for producing regenerated reinforcing fibers according to a first embodiment of the present invention will be described. First, the method for producing regenerated reinforcing fibers according to the present invention comprises: a first step of treating a fiber-reinforced resin material containing a resin and reinforcing fibers with a treatment liquid so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid; and a second step of heating the fiber-reinforced resin material in a gas atmosphere at 150° C. or higher.

[0041] In addition, in the method for producing regenerated reinforcing fibers according to the present embodiment, the first step of the method for producing regenerated reinforcing fibers according to the present embodiment includes: a first treatment, treating the fiber-reinforced resin material with an acidic solution containing an acid; and a second treatment, treating the fiber-reinforced resin material with the oxidation treatment liquid containing an oxidant, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidation treatment liquid. Further, the method for producing regenerated reinforcing fibers according to the present embodiment includes a step (preparation step) of preparing the fiber-reinforced resin material before the first step and the second step. In addition, in this specification, "resin dissolution" includes not only the direct dissolution of the resin itself in the treatment liquid, but also the decomposition of the resin to generate a reactant, which is dissolved in the treatment liquid. Below, each step of the method for producing regenerated reinforcing fibers according to the present embodiment is described in sequence.

[0042] 1.1 Preparation process

[0043] First, before the first step, prepare a fiber-reinforced resin material. The fiber-reinforced resin material is a resin material reinforced by embedding reinforcing fibers in a matrix resin (also referred to as "resin"). Such fiber-reinforced resin materials are not particularly limited, and examples thereof include carbon fiber reinforced plastics (CFRP), glass fiber reinforced plastics (GFRP), glass-mat reinforced thermoplastics (GMT), aramid-fiber-reinforced plastics (AFRP), Kevlar fiber-reinforced plastics (KFRP), Dyneema fiber-reinforced plastics (DFRP), basalt fiber reinforced plastics, boron fiber reinforced plastics, and prepregs thereof. Among the above, the amount of carbon fiber reinforced plastic used is relatively large, and the energy consumption during the production of carbon fiber is large, so it is preferable to recover and reuse the used carbon fiber reinforced plastic and / or the carbon fiber in the prepreg.

[0044] In addition, the reinforcing fibers in the fiber-reinforced resin material may be present in the form of a fiber bundle (tow) obtained by pulling a plurality of reinforcing fibers in one direction, a woven fabric or non-woven fabric in which the fiber bundle of the reinforcing fibers is used for warp and weft, or in the form in which each reinforcing fiber is arranged in a random position and direction. In addition, the reinforcing fibers may be in a sheet form, in which case, for example, chopped fibers obtained by cutting a fiber bundle, a sheet-like woven fabric, etc. may be cited.

[0045] In addition, the resin in the fiber-reinforced resin material is not particularly limited, and may be, for example, a thermosetting resin or a thermoplastic resin. In addition, the thermosetting resin may be an uncured resin or a cured product.

[0046] Thermosetting resins are not particularly limited, and examples thereof include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, cyanate resins, polycarbonate resins, polyacetal resins, and the like. One of these resins may be used alone or two or more of them may be used in combination.

[0047] The thermoplastic resin is not particularly limited, and examples thereof include polyolefins, polyesters, polycarbonates, acrylic resins, acrylonitrile-butadiene-styrene copolymers, polyetherketones, and polyphenylene sulfide. One of these may be used alone or two or more of them may be used in combination.

[0048] The resin constituting the fiber-reinforced resin material preferably includes an epoxy resin. The epoxy resin can be efficiently decomposed in the oxidation step using a polymerization inhibitor described later and can be dissolved in the treatment liquid.

[0049] The epoxy resin having a phenol skeleton is not particularly limited, and examples thereof include bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, aliphatic epoxy resin, etc., and any one of them may be used alone or in combination of two or more.

[0050] In addition, the content of epoxy resin in the resin in the fiber-reinforced resin material is not particularly limited, and is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more. It is further preferred that the resin is essentially epoxy resin, and most preferably the resin is epoxy resin. Thus, it is easier to remove the resin from the fiber-reinforced resin material and recover the reinforcing fibers during the oxidation process.

[0051] In addition, in the present embodiment, the resin constituting the fiber-reinforced resin material preferably includes a resin having an alkaline structure. The resin having an alkaline structure can coordinate hydrogen ions (protons) in the acidic solution and swell in the first treatment of the first step described later. The oxidant can fully penetrate the swollen resin having an alkaline structure in the second treatment described later, resulting in the promotion of the dissolution of the resin into the treatment solution.

[0052] The basic structure of the resin is not particularly limited, and may include amide bonds, imide bonds, azo groups, diazo groups, urea bonds, carbamate bonds, peptide bonds, isocyanate groups, azido groups, etc., or chemical structures derived from them or similar chemical structures, etc. The resin having a basic structure may contain one or more of them. Among the above, the method according to this embodiment can be preferably used for swelling and decomposing a resin having a primary, secondary or tertiary amide bond as a basic structure.

[0053] In addition, the resin having an alkaline structure preferably contains a basic chemical bond in its main chain structure. Thus, in the first treatment of the first step, it can further swell by reacting with the chemical structure having an alkaline property, and in the oxidation step described later, it can promote the decomposition of the resin and the subsequent dissolution into the oxidation treatment solution. As resins having such an alkaline structure, amine-cured epoxy resins, urethane resins, polyimide resins, polyamides, melamine resins, aniline resins, urea resins, etc. can be listed, and the resin can contain one or more of them as resins having an alkaline structure.

[0054] The resin having a basic structure may include a basic structure in its side chain. Examples of such a resin include resins having the basic structure as described above in the side chains of various resin components described later.

[0055] In addition, the content of the resin having a basic structure in the resin in the fiber-reinforced resin material is not particularly limited, and is, for example, 20% by mass or more, preferably 50% by mass or more, and more preferably 70% by mass or more. It is further preferred that the resin is composed of a resin having an essentially basic structure, and it is most preferred that the resin is composed of a resin having an essentially basic structure. Thus, when the acid treatment step is performed, it is easier to remove the resin from the fiber-reinforced resin material and to recover the reinforcing fibers.

[0056] In addition, the fiber-reinforced resin material may be in the form of a sheet itself or in the form of cut pieces. In particular, the method according to this embodiment can remove the resin more efficiently, and thus can be appropriately applied to sheet-shaped fiber-reinforced resin materials, which have been difficult to recycle in the past.

[0057] In addition, the size of the fiber-reinforced resin material is not particularly limited. However, if the direction of the reinforcing fibers in the fiber-reinforced resin material is taken into consideration, the length of a piece of the fiber-reinforced resin material can be, for example, more than 100 mm, preferably more than 500 mm and less than 3000 mm. More specifically, as a fiber-reinforced resin material, for example, a stacked fiber-reinforced resin material sheet with a width of 1000 mm × 500 mm and a thickness of about 300 mm can also be used. The relatively large fiber-reinforced resin material as described above is difficult to penetrate into the treatment liquid, and the removal of the resin and the recovery of the reinforcing fibers are difficult. However, the method according to this embodiment can remove the resin more efficiently, and therefore can also be applied to relatively large fiber-reinforced resin materials.

[0058] 1.2 The first process

[0059] In the first step, the fiber-reinforced resin material is treated with a treatment liquid so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid. In this embodiment, specifically, the first step includes: a first treatment (acid treatment) in which the fiber-reinforced resin material is treated with an acidic solution containing an acid; and a second treatment (oxidation treatment) in which the fiber-reinforced resin material is treated with an oxidation treatment liquid containing an oxidant so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidation treatment liquid.

[0060] (i) First Process

[0061] In the first treatment, the prepared fiber-reinforced resin material is treated with an acidic solution containing an acid. In this way, by treating the fiber-reinforced resin material with an acidic solution containing an acid, at least a portion of the components that can be decomposed into acid in the resin of the fiber-reinforced resin material is decomposed and dissolved in the acidic solution. Alternatively, at least a portion of the components that can be dissolved in acid is dissolved in the acidic solution. As a result, in the second step described later, the oxidation treatment liquid can more easily penetrate into the resin, and the resin can be more efficiently dissolved in the oxidation treatment liquid.

[0062] In addition, when the fiber-reinforced resin material includes a resin having an alkaline structure, the fiber-reinforced resin material is treated with an acidic solution containing an acid, so that the hydrogen ions in the acidic solution are disposed with the resin component having an alkaline structure to form a salt, and as a result, the resin component having an alkaline structure and even the resin itself swell. As a result, the oxidant becomes easy to penetrate into the resin in the second treatment described later, and the decomposition and / or precipitation of the resin in the second treatment is promoted.

[0063] The acidic solution in this process contains at least an acid and optionally a solvent. As the acid, an inorganic acid or an organic acid or a mixture thereof can be used. As the inorganic acid, for example, sulfuric acid, hydrochloric acid, phosphoric acid, etc. can be listed, and one of them can be used alone or in combination of two or more. As phosphoric acid, for example, orthophosphoric acid, metaphosphoric acid, hypophosphorous acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, pyrophosphorous acid, etc. can be listed. As the organic acid, for example, formic acid, acetic acid, citric acid, succinic acid, oxalic acid, etc. can be listed.

[0064] Among the above, the resin component can also be appropriately swollen, and therefore the acid preferably contains one or more selected from the group consisting of inorganic acids, particularly sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid.

[0065] In addition, the acid dissociation constant pKa of the component with the largest molar concentration among the components contained in the acid is not particularly limited, and is preferably 5.0 or less, and more preferably 1.5 or less. In this way, since the pKa of the component with the largest molar concentration among the components contained in the acid is sufficiently small, it is easy to release hydrogen ions in an acidic solution, as a result, the above-mentioned effect can be further obtained. In addition, when the component with the largest molar concentration among the components contained in the acid has a plurality of acid dissociation constants, it is preferred that the first-order, i.e., smaller acid dissociation constant is the above-mentioned value.

[0066] The concentration of the acid contained in the acidic solution is not particularly limited, for example, 0.5 mol / L or more, preferably 1.0 mol / L or more, more preferably 3.5 mol / L or more. Thus, it is easy to release hydrogen ions in the acidic solution, as a result, the above-mentioned effect can be further obtained. In addition, the upper limit of the concentration of the acid is not limited as long as it can exist as an acidic solution, and it varies according to the type of the acid.

[0067] In addition, the acidic solution usually contains a solvent. The solvent is not particularly limited as long as it is miscible with the acid and chemically stable with respect to the acid, and for example, water and / or various organic solvents can be used.

[0068] The organic solvent is not particularly limited, and examples thereof include alcohol solvents, ether solvents, ketone solvents, aromatic hydrocarbons, halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and the like. One of these solvents may be used alone or two or more thereof may be used in combination.

[0069] Examples of the alcohol solvent include aliphatic alcohol solvents, aromatic alcohol solvents, glycol solvents, and other polyols such as glycerin.

[0070] Examples of the aliphatic alcohols include non-cyclic aliphatic alcohols such as 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-ethylhexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, dodecanol, methanol, and ethanol, and alicyclic alcohols such as cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, and 4-methylcyclohexanol.

[0071] Examples of the aromatic alcohol solvent include phenol, cresol, benzyl alcohol, and phenoxyethanol.

[0072] Examples of the glycol solvent include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol, polyethylene glycol (molecular weight 200 to 400), 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, 1,5-pentanediol, and dipropylene glycol.

[0073] Examples of the ether solvent include aliphatic ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether; cyclic ethers such as 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, and furan; and aromatic ethers such as anisole, phenethyl ether, diphenyl ether, and benzofuran.

[0074] Examples of the ketone solvent include acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, 2-hexanone, methyl isobutyl ketone, 2-heptanone, 4-heptanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, phorone, isophorone, acetylacetone, acetophenone, diethyl ketone, and diacetone alcohol.

[0075] Examples of the aromatic hydrocarbon include benzene, toluene, and xylene.

[0076] Examples of the halogenated aromatic hydrocarbon include o-chlorophenol and o-chlorobenzene.

[0077] Examples of the halogenated aliphatic hydrocarbon include chloroform and dichloromethane.

[0078] Among the above, it is also easy to mix with acid, and it is preferred that the solvent contains water in order to properly dissociate the hydrogen ions in the acid. In addition, the solvent may also be a mixed solvent of water and an organic solvent miscible with water. As an organic solvent miscible with water, for example, alcoholic solvents, ketone solvents, etc. may be listed.

[0079] The content of the solvent contained in the acidic solution is not particularly limited, and may be the remainder of other components such as the acid.

[0080] The fiber-reinforced resin material is treated using the acid solution as described above. The temperature of the acid solution during the treatment is not particularly limited, and is, for example, 0°C to 100°C, preferably 50°C to 100°C.

[0081] The time for the treatment with the acid solution is not particularly limited, but is 5 minutes to 1200 minutes after the target temperature is reached, and preferably 10 minutes to 120 minutes after the target temperature is reached.

[0082] In addition, the treatment using an acidic solution may be carried out under normal pressure, under reduced pressure, or under pressure. In the case of the treatment using an acidic solution under pressure, for example, the treatment may be carried out in an atmosphere of 0.11 MPa to 7.0 MPa, particularly 0.11 MPa to 2.0 MPa. In addition, if safety and economy are taken into consideration, the treatment using an acidic solution is preferably carried out under normal pressure.

[0083] In addition, the treatment of the fiber-reinforced resin material using the acidic solution is not particularly limited, and can be carried out by immersing the fiber-reinforced resin material in the acidic solution, or by spraying the acidic solution onto the fiber-reinforced resin material using a sprayer or the like, and any method that allows the acidic solution to contact the fiber-reinforced resin material can be used. In addition, the acidic solution can also be stirred during the treatment using the acidic solution. In addition, the fiber-reinforced resin material can also be fixed by a fixing device to maintain the fiber bundle of the fiber-reinforced resin material.

[0084] In addition, in this step, the first treatment may be omitted.

[0085] (ii) Second Process

[0086] In the second treatment, the fiber-reinforced resin material is treated with an oxidation treatment liquid containing an oxidant, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidation treatment liquid. In addition, the treatment liquid in this step contains at least an oxidant, and optionally a polymerization inhibitor and a solvent.

[0087] In the fiber-reinforced resin material treated with the acid solution in the first treatment, the oxidant easily penetrates into the resin, and as a result, in the second treatment, the resin is efficiently decomposed and / or precipitated by the treatment with the oxidizing treatment solution. In particular, in the case where the resin includes a resin having an alkaline structure, the resin swells by the acid treatment, and as a result, the oxidant easily penetrates into the resin.

[0088] As the oxidant, there is no particular limitation, and examples thereof include nitric acid, hot concentrated sulfuric acid, a mixed acid of sulfuric acid and nitric acid, a mixed acid of nitric acid and hydrochloric acid (aqua regia), a mixed solution of hydrogen peroxide and sulfuric acid, perchloric acid, chloric acid, hypochlorous acid, chlorous acid, perbromic acid, bromic acid, hypobromous acid, bromous acid, periodic acid, iodic acid, hypoiodous acid, iodous acid and other acids with oxidizing power, their alkali (earth) metal salts, oxygen, ozone, hydrogen peroxide, acetone peroxide (the reactant of hydrogen peroxide and acetone), and other oxygen-based oxidants, chlorine, chlorine dioxide, bromine, fluorine, iodine and other halogen-based oxidants, and the like, and one of them can be used alone or in combination of two or more thereof. In addition, examples of alkali metal elements include lithium, sodium, potassium, rubidium, cesium, and francium, and examples of alkaline earth metals include calcium, strontium, barium, and radium.

[0089] Among the above, the oxidant preferably contains an acid having oxidizing power from the viewpoint of being relatively easy to handle and being able to stabilize the liquid properties of the oxidation treatment solution. In particular, from the viewpoint of the efficiency of decomposition of the resin, the oxidant more preferably contains one or more selected from the group consisting of nitric acid, a mixed acid of sulfuric acid and nitric acid, a mixed acid of nitric acid and hydrochloric acid (aqua regia), and a mixed solution of hydrogen peroxide and sulfuric acid, and particularly preferably contains a mixed solution of nitric acid or hydrogen peroxide and sulfuric acid.

[0090] The concentration of the oxidant in the oxidation treatment liquid is not particularly limited and can be appropriately set according to the amount of resin in the fiber-reinforced resin material to be treated. However, for example, when the oxidant is an acid having oxidizing power, the concentration of the oxidant in the oxidation treatment liquid is, for example, 5 mass % or more and 80 mass % or less, preferably 20 mass % or more and 50 mass % or less.

[0091] In addition, the oxidation treatment liquid preferably contains a polymerization inhibitor. In this way, the oxidation treatment liquid contains a polymerization inhibitor in addition to the oxidant, so that the resin can be more efficiently decomposed and dissolved in the treatment liquid. The details of the phenomenon generated in this treatment are not certain, but the inventors speculate as follows.

[0092] First, generally, the resin in the fiber-reinforced resin material can be reduced in molecular weight by using an oxidant to cleave the molecular chain in the resin. Then, the hydroxyl group and carboxyl group generated by the oxidation reaction and the polar group caused by the oxidant are introduced into the resin, whereby the resin becomes easily soluble in the oxidation treatment liquid. In combination with the above, the resin is dissolved in the treatment liquid.

[0093] On the other hand, the present inventors paid attention to the fact that a part of the resin of the reinforcing fiber resin material remains after the above-mentioned oxidation reaction. Furthermore, the present inventors conducted intensive research, and as a result, the present inventors recognized that in the oxidation reaction of the resin using the oxidant, a repolymerization reaction may also occur in parallel with the above-mentioned decomposition reaction. Furthermore, it was found that by including the oxidant and the polymerization inhibitor in the oxidation treatment liquid, the resin can be dissolved to a greater extent than when no polymerization inhibitor is added.

[0094] The polymerization inhibitor is not particularly limited as long as it can inhibit the repolymerization of the decomposed product of the resin, and examples thereof include nitrites such as alkali metal or alkaline earth metal salts of nitrous acid, nitrite esters, hydroquinone, oxoquinone, 4-tert-butylcatechol, tert-butylhydroquinone, 1,4-benzoquinone, dibutylated hydroxytoluene, 1,1-diphenyl-2-picrylhydrazyl free radical, mequinol, phenothiazine, etc., and one of them can be used alone or in combination of two or more. Examples of the alkali metal include sodium, potassium, cesium, rubidium, etc. Examples of the alkaline earth metal include beryllium, magnesium, calcium, strontium, and barium. Examples of the nitrite include methyl nitrite, ethyl nitrite, amyl nitrite, isoamyl nitrite, isobutyl nitrite, isopropyl nitrite, tert-butyl nitrite, n-butyl nitrite, and n-propyl nitrite.

[0095] Among the above, the polymerization inhibitor preferably includes one or more selected from the group consisting of nitrites and nitrite esters, and more preferably includes one or more selected from the group consisting of sodium nitrite, potassium nitrite, ethyl nitrite and amyl nitrite. Thus, the resin can be dissolved in the oxidation treatment solution more efficiently.

[0096] The concentration of the polymerization inhibitor in the oxidation treatment liquid is not particularly limited and can be appropriately set according to the amount of resin in the fiber-reinforced resin material to be treated. However, for example, the concentration of the polymerization inhibitor in the treatment liquid is, for example, 0.010 mass % or more and 20 mass % or less, preferably 0.20 mass % or more and 5.0 mass % or less. Thus, the oxidation reaction of the resin by the oxidant is not hindered, and the repolymerization reaction of the low-molecular-weight resin can be sufficiently suppressed.

[0097] In addition, the oxidation treatment solution usually contains a solvent. The solvent is not particularly limited as long as it is stable to the oxidant and polymerization inhibitor used and can be mixed with these components. For example, water and various organic solvents listed as solvents for the above-mentioned acidic solution can be used alone or in combination of two or more.

[0098] The solvent contained in the oxidation treatment liquid preferably includes water or an organic solvent contained in the solvent of the above-mentioned acidic solution. In the case where the acidic solution includes multiple solvents, the oxidation treatment liquid preferably includes one or more of these multiple solvents. Thus, when the oxidation treatment liquid is brought into contact with the fiber-reinforced resin material, it is possible to more reliably suppress the occurrence of unintended side reactions or to more reliably suppress the unintended shrinkage of the swollen fiber-reinforced resin material.

[0099] In addition, from the viewpoint of ease of handling and promotion of the oxidation reaction by the oxidant, the oxidation treatment liquid preferably contains water or a mixed solvent of an organic solvent miscible with water and water, and more preferably contains water.

[0100] The content of the solvent contained in the oxidation treatment liquid is not particularly limited, and may be the remainder of other components such as the oxidizing agent.

[0101] The oxidation treatment liquid is preferably neutral or acidic, more preferably acidic, so that when the oxidation treatment liquid is brought into contact with the fiber-reinforced resin material, the fiber-reinforced resin material treated with the acidic solution can be prevented from being neutralized and the resin can be prevented from being unintentionally cured and / or deposited.

[0102] Specifically, the pH of the treatment liquid at 25° C. is, for example, 5.0 or less, preferably 2.0 or less, and more preferably 1.5 or less.

[0103] The oxidation treatment liquid may contain an acid. Thus, as such an acid capable of adjusting the pH of the oxidation treatment liquid, the acids listed in the second treatment can be cited, and these acids can be used alone or in combination of two or more.

[0104] The fiber-reinforced resin material is treated using the oxidation treatment liquid as described above. The temperature of the treatment liquid during the treatment is not particularly limited, and is, for example, 0°C to 100°C, preferably 50°C to 100°C.

[0105] The time for the treatment with the oxidation treatment solution is not particularly limited, but is 5 minutes to 1200 minutes after the target temperature is reached, and preferably 10 minutes to 120 minutes after the target temperature is reached.

[0106] In addition, the treatment with the oxidizing treatment liquid may be carried out under normal pressure, under reduced pressure, or under pressure. When the treatment with the treatment liquid is carried out under pressure, for example, the treatment may be carried out in an atmosphere of 0.11 MPa to 7.0 MPa, particularly 0.11 MPa to 2.0 MPa. In addition, in consideration of safety and economy, the treatment with the oxidizing treatment liquid is preferably carried out under normal pressure.

[0107] In addition, the treatment of the fiber-reinforced resin material using the oxidation treatment liquid is not particularly limited, and can be carried out by immersing the fiber-reinforced resin material in the oxidation treatment liquid, or by spraying the oxidation treatment liquid onto the fiber-reinforced resin material using a sprayer or the like, and any method that allows the oxidation treatment liquid to contact the fiber-reinforced resin material can be used. In addition, the oxidation treatment liquid can also be stirred during the treatment using the oxidation treatment liquid. In addition, the fiber-reinforced resin material can also be fixed by a fixing device to maintain the fiber bundle of the fiber-reinforced resin material.

[0108] (iii) Cleaning

[0109] Next, cleaning is performed as needed. Cleaning can be performed by bringing the cleaning liquid into contact with the fiber-reinforced resin material. Specifically, in the above-mentioned second treatment, the oxidation treatment liquid can be replaced by the cleaning liquid. However, the temperature of the cleaning liquid and the cleaning time during cleaning can be appropriately set.

[0110] As the cleaning liquid, water and various organic solvents listed as the solvent for the above-mentioned acidic solution can be used alone or in combination of two or more. In addition, as the organic solvent, in addition to the above-mentioned solvents, the following ester solvents and amide solvents can also be used.

[0111] Examples of the ester solvent include methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, pentyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, 3-methoxybutyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, benzyl acetate, methyl propionate, ethyl propionate, and butyl propionate. , isoamyl propionate, methyl lactate, ethyl lactate, butyl lactate, methyl butyrate, ethyl butyrate, butyl butyrate, isoamyl butyrate, isobutyl isobutyrate, ethyl isovalerate, isoamyl isovalerate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, γ-butyrolactone, diethyl oxalate, dibutyl oxalate, diethyl malonate, methyl salicylate, ethylene glycol diacetate, tributyl borate, trimethyl phosphate, triethyl phosphate, etc.

[0112] Examples of the amide solvent include formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, caprolactam, and carbamates.

[0113] In addition, the cleaning liquid may contain an alkaline substance. By using the alkaline substance to neutralize and adjust the liquid properties, the residual resin component and its reactants in the fiber-reinforced resin material can be removed. Thus, a fibrous object containing reinforcing fibers can be obtained.

[0114] As the alkaline substance, for example, inorganic alkaline substances such as hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, etc. of lithium, alkali metals, and alkaline earth metals, and amine compounds such as dimethylamine and diethylamine can be listed, and one of them can be used alone or in combination of two or more. As the alkali metal, for example, sodium, potassium, cesium, rubidium, etc. can be listed. As the alkaline earth metal, for example, beryllium, magnesium, calcium, strontium, barium, etc. can be listed.

[0115] The above first treatment, second treatment and cleaning treatment can be performed multiple times as needed. In addition, the order of each treatment can be changed as needed. For example, the cleaning process can be performed after repeating the first treatment and the second treatment multiple times. In addition, for example, the second treatment can be performed after performing the first treatment multiple times, and then the cleaning process can be performed the required number of times. Or, for example, the first treatment, the second treatment and the cleaning process can be performed the required number of times in sequence.

[0116] In addition, in the present embodiment, the acidic solution of the first treatment and the oxidizing treatment solution of the second treatment can be considered to correspond to the treatment solution in the present invention.

[0117] 1.3 Second process

[0118] In the second step, the fiber-reinforced resin material is heated in a gas atmosphere at 150°C or higher. In the first step, at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid. In the first step, the resin contained in the fiber-reinforced resin material is reduced in molecular weight due to decomposition, etc., and the surface area of ​​the resin in contact with the external air is increased due to the precipitation of the resin itself. For the fiber-reinforced resin material in such a state, by heating in a gas atmosphere at 150°C or higher, the resin remaining in the fiber-reinforced resin material is easily decomposed and / or melted, and as a result, a regenerated reinforcing fiber from which the resin is fully removed can be obtained.

[0119] Generally, when obtaining regenerated reinforcing fibers by thermal decomposition, the resin is removed by treatment at a temperature of 500°C or higher. In such a case, the reinforcing fibers themselves present in the fiber-reinforced resin material may be damaged by heat. Furthermore, when removing the resin by thermal decomposition, the resin such as the curable resin is temporarily cured by heat and then decomposed. Such curing of the resin actually hinders the decomposition of the resin, thereby hindering the removal.

[0120] In contrast, in the present embodiment, at least a portion of the resin is decomposed in the first step, so that the resin is less likely to solidify than when a simple thermal decomposition method is used. Furthermore, since at least a portion of the resin is decomposed in the first step, the resin can be decomposed and removed even at a relatively low temperature, and damage to the reinforcing fibers due to heat can be suppressed.

[0121] The heating temperature in this step may be within the above range, preferably 150° C. to 600° C., more preferably 150° C. to 350° C., and even more preferably 200° C. to 300° C. This can more reliably suppress damage to the obtained regenerated reinforcing fibers due to heat, and can more reliably remove the resin.

[0122] The heating time is not particularly limited, but is 30 minutes to 1500 minutes after reaching the target temperature, preferably 60 minutes to 300 minutes after reaching the target temperature. Thus, damage to the obtained regenerated reinforcing fiber due to heat can be suppressed, and the resin can be removed more reliably.

[0123] In addition, the gas present in the surrounding atmosphere in this step is not particularly limited, and may include, for example, inert gas such as nitrogen, rare gas, air, and / or water vapor. Among the above, the gas present in the surrounding atmosphere preferably includes air.

[0124] The heat treatment may be performed under normal pressure, under reduced pressure, or under increased pressure. In addition, the heat treatment is preferably performed under normal pressure in consideration of safety and economic efficiency.

[0125] In addition, the fiber-reinforced resin material may be fixed and heated as needed, thereby allowing the reinforcing fibers contained in the fiber-reinforced resin material to be dried while maintaining their shapes and arrangement directions.

[0126] Thus, regenerated reinforcing fibers can be obtained. In the method for producing regenerated reinforcing fibers according to the present embodiment, at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid in the first step. Moreover, in the first step, the resin contained in the fiber-reinforced resin material is reduced in molecular weight due to decomposition, etc., and the surface area of ​​the resin in contact with the external air is increased due to the precipitation of the resin itself. For the fiber-reinforced resin material in such a state, by heating in a gas atmosphere of 150° C. or more and 350° C. or less, the resin remaining in the fiber-reinforced resin material is easily decomposed and / or melted, and as a result, regenerated reinforcing fibers from which the resin is fully removed can be obtained.

[0127] Furthermore, compared with the conventional solvent method and thermal decomposition method, the first step and the second step can be performed at a relatively low temperature, that is, under mild conditions. Thus, damage to the obtained regenerated reinforcing fibers can be prevented, and the energy required for the production of the regenerated reinforcing fibers can be significantly reduced.

[0128] In addition, in this embodiment, the first process includes: a first treatment, treating the fiber-reinforced resin material using an acidic solution containing an acid; and a second treatment, treating the fiber-reinforced resin material using an oxidizing treatment liquid containing an oxidant, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidizing treatment liquid.

[0129] In this way, by treating the fiber-reinforced resin material with an acidic solution containing an acid, at least a portion of the components that can be decomposed into acid contained in the resin of the fiber-reinforced resin material is decomposed and dissolved in the acidic solution. Alternatively, at least a portion of the components that can be dissolved in acid is dissolved in the acidic solution. As a result, in the second step described later, the oxidation treatment liquid can more easily penetrate into the resin, and the resin can be dissolved in the oxidation treatment liquid more efficiently.

[0130] Furthermore, according to the present embodiment, the resin can be removed efficiently, so unlike the past, it is not necessary to dissolve the resin after cutting the fiber-reinforced resin material into small pieces. That is, even for relatively large fiber-reinforced resin materials, the resin can be removed uniformly and efficiently by using the method according to the present embodiment.

[0131] Furthermore, the resin dissolved in each process can also be recovered and reused.

[0132] 2. Second Implementation

[0133] Hereinafter, a method for producing a regenerated reinforcing fiber according to a second embodiment of the present invention will be described. In the following description, the method for producing a regenerated reinforcing fiber according to the second embodiment of the present invention will be described mainly with respect to matters different from the first embodiment described above, and description of the same matters will be omitted.

[0134] The manufacturing method of the regenerated reinforcing fiber according to the present embodiment is different from the first embodiment in that, in the first step, the fiber-reinforced resin material is treated with a treatment liquid containing a solvent and optionally a catalyst, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid. That is, in the first embodiment, an oxidizing treatment liquid containing an oxidant is used as the main treatment liquid, but the oxidant is not necessarily used in the present invention. Therefore, in the present embodiment, including the form of the first embodiment, the treatment liquid that can be used as a solvent method is fully described. In addition, the above-mentioned preparation step and the second step are the same, so only the first step is described below.

[0135] First, in the present embodiment, in the first step, the fiber-reinforced resin material is treated with a treatment liquid containing a solvent and optionally a catalyst, so that at least a part of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid.

[0136] The solvent is a main component of the treatment liquid. As the solvent, there is no particular limitation as long as it can dissolve the resin of the fiber-reinforced resin material or its reactant in this process, and for example, water and / or various organic solvents can be used. As various organic solvents, the solvents exemplified in the first treatment of the first embodiment can be used alone or in combination of two or more.

[0137] The content of the solvent contained in the treatment liquid is not particularly limited, but may be, for example, 0.01 mass % to 100 mass %, 40 mass % to 60 mass %, or 80 mass % to 100 mass %.

[0138] In addition, the treatment liquid may also contain a catalyst. The catalyst is not particularly limited as long as it has the function of catalyzing the dissolution of the resin in the fiber-reinforced resin material, and for example, acidic substances and alkaline substances can be cited. These substances can improve the solubility of the resin in the solvent by, for example, adding hydrogen ions or hydroxide ions to the functional groups of the resin components or decomposing the resin. In particular, when the solvent contains a protic solvent, especially when it contains water, the catalytic effect of the acidic substance and the alkaline substance is further improved.

[0139] As the acidic substance, an inorganic acid, an organic acid, or a salt thereof, or a mixture thereof can be used. As the inorganic acid, for example, nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, etc. can be listed, and one of them can be used alone or in combination of two or more. As the phosphate, for example, orthophosphate, metaphosphate, hypophosphite, phosphite, hypophosphite, pyrophosphate, trimetaphosphate, tetrametaphosphate, pyrophosphite, etc. can be listed. As the organic acid, for example, formic acid, acetic acid, citric acid, succinic acid, oxalic acid, etc. can be listed.

[0140] Examples of the salt of an inorganic acid or an organic acid include alkali metal (eg, sodium, potassium, cesium, rubidium, etc.) and / or alkaline earth metal (eg, beryllium, magnesium, calcium, strontium, barium, etc.) salts of the above-mentioned inorganic acid or organic acid.

[0141] Among the above, inorganic acids, particularly nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid are preferred because they are easily available and can easily contribute to promoting the dissolution of the resin.

[0142] In addition, when the treatment liquid contains an acidic substance as a catalyst, the content of the acidic substance can be appropriately selected according to the type of acidic substance used, the type of solvent in the treatment liquid, and the resin in the fiber-reinforced resin material to be treated, but the content of the acidic substance in the treatment liquid can be, for example, greater than 0.01 mass % and less than 100 mass %, in particular, greater than 10 mass % and less than 50 mass %.

[0143] As the alkaline substance, for example, inorganic alkaline substances such as hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, etc. of lithium, alkali metals, and alkaline earth metals, and amine compounds such as dimethylamine and diethylamine can be listed, and one of them can be used alone or in combination of two or more. As the alkali metal, for example, sodium, potassium, cesium, rubidium, etc. can be listed. As the alkaline earth metal, for example, beryllium, magnesium, calcium, strontium, barium, etc. can be listed.

[0144] Among the above, hydroxides, carbonates and bicarbonates of alkali metals are preferred because they are easily available and can easily help promote the dissolution of the resin component. More specifically, the alkaline substance preferably includes one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium bicarbonate and potassium carbonate.

[0145] In addition, when the treatment liquid contains an alkaline substance as a catalyst, the content of the alkaline substance can be appropriately selected according to the type of alkaline substance used, the type of solvent in the treatment liquid, and the resin component in the fiber-reinforced resin material being the target, but the content of the alkaline substance in the treatment liquid 200 can be, for example, greater than 0.01 mass % and less than 100 mass %, particularly greater than 10 mass % and less than 50 mass %.

[0146] The temperature of the treatment liquid during the treatment is not particularly limited and varies depending on the type of the treatment liquid, but is, for example, 30° C. to 300° C., preferably 50° C. to 100° C.

[0147] The treatment time using the treatment liquid is not particularly limited, but is 1 minute or more and 1440 minutes or less after the target temperature is reached, and preferably 10 minutes or more and 60 minutes or less after the target temperature is reached.

[0148] In addition, the treatment using the treatment liquid may be carried out under normal pressure, under reduced pressure, or under pressure. When the treatment using the treatment liquid is carried out under pressure, for example, the treatment may be carried out in an atmosphere of 0.11 MPa to 7.0 MPa, particularly 0.11 MPa to 2.0 MPa. In addition, if safety and economy are taken into consideration, it is preferred to carry out the treatment using the treatment liquid under normal pressure.

[0149] In addition, the treatment of the fiber-reinforced resin material using the treatment liquid is not particularly limited, and can be performed by immersing the fiber-reinforced resin material in the treatment liquid, or by spraying the treatment liquid onto the fiber-reinforced resin material using a sprayer or the like, and any method that allows the treatment liquid and the fiber-reinforced resin material to contact can be used. In addition, the treatment liquid can also be stirred during the treatment using the treatment liquid. In addition, the fiber-reinforced resin material can also be fixed by a fixing device to maintain the fiber bundle of the fiber-reinforced resin material.

[0150] As described above, after the treatment of the fiber-reinforced resin material with the treatment liquid as the first step described above, the cleaning treatment described in the first embodiment may be performed.

[0151] In addition, the processing of the fiber reinforced resin material using the above processing solution can also be carried out multiple times. In this case, the processing solution used in each processing can also have different compositions. In addition, the cleaning process as described in the first embodiment can also be carried out between each processing.

[0152] The fiber-reinforced resin material subjected to the treatment of the fiber-reinforced resin material with the treatment liquid as the above-mentioned first step is supplied to the second step in the same manner as in the first embodiment, and regenerated reinforcing fibers are obtained.

[0153] In the second embodiment described above, at least a part of the resin of the fiber-reinforced resin material is also dissolved in the treatment liquid in the first step. In addition, in the first step, the resin contained in the fiber-reinforced resin material is reduced in molecular weight due to decomposition, etc., and the surface area of ​​the resin in contact with the external air is increased due to the precipitation of the resin itself. For the fiber-reinforced resin material in such a state, by heating in a gas atmosphere of 150° C. or above, the resin remaining in the fiber-reinforced resin material is easily decomposed and / or melted, and as a result, a regenerated reinforcing fiber from which the resin is fully removed can be obtained.

[0154] Furthermore, similarly to the first embodiment, in the present embodiment, the first step and the second step can be performed at a relatively low temperature, that is, under mild conditions, compared to the conventional solvent method and thermal decomposition method.

[0155] Example

[0156] Hereinafter, the present invention will be further specifically described by way of examples, but the present invention is not limited to these examples.

[0157] 1. Manufacture of recycled reinforcing fibers

[0158] (Example 1)

[0159] (1) Preparation process

[0160] First, a carbon fiber reinforced resin material is prepared as a sample. The carbon fiber resin material used is a sheet material with a length of about 30 cm, a width of 5 cm, and a thickness of about 1 mm. In addition, the resin constituting the carbon fiber reinforced resin material is an amine-cured epoxy resin.

[0161] (2) First process

[0162] (i) First treatment (acid treatment)

[0163] Next, the carbon fiber reinforced resin material was immersed in a 40 wt% (5.3 mol / L) sulfuric acid aqueous solution heated to 80°C for 1 hour. During the immersion, the temperature of the sulfuric acid aqueous solution was maintained at 80°C.

[0164] (ii) Second treatment (oxidation treatment)

[0165] Next, 0.5% by mass of sodium nitrite was added to a 40% by mass (8.0 mol / L) nitric acid aqueous solution to obtain an oxidation treatment solution. The concentration of nitric acid in the oxidation treatment solution was 39.8% by mass, and the concentration of sodium nitrite was 0.50% by mass. The carbon fiber reinforced resin material was immersed in the treatment solution heated to 80°C for 60 minutes. During the immersion, the temperature of the oxidation treatment solution was maintained at 80°C.

[0166] (iii) Cleaning

[0167] Next, the reaction product was neutralized with a 10% by mass sodium hydrogen carbonate aqueous solution, and thereafter the fibrous material (carbon fiber) obtained from the carbon fiber reinforced resin material was washed with purified water.

[0168] (3) Second step (heating step)

[0169] Next, the fibrous material obtained by washing was heated at 350° C. for 1 hour, and the regenerated reinforcing fiber according to Example 1 was obtained.

[0170] (Example 2)

[0171] Regenerated reinforcing fibers according to Example 2 were obtained in the same manner as in Example 1, except that sodium nitrite was not contained in the oxidation treatment liquid in the second treatment.

[0172] (Example 3)

[0173] Regenerated reinforcing fibers according to Example 3 were obtained in the same manner as in Example 2 except that the neutralization of the reaction product with a 10 mass % sodium hydrogen carbonate aqueous solution was omitted in the washing step.

[0174] (Example 4)

[0175] Regenerated reinforcing fibers according to Example 4 were obtained in the same manner as in Example 3 except that the acid treatment step was omitted.

[0176] (Comparative Example 1)

[0177] Regenerated reinforcing fibers according to Comparative Example 1 were obtained in the same manner as in Example 2 except that the drying step was performed instead of the second step. In the drying step, the fibrous material obtained by washing was dried at 110° C. for 1 hour.

[0178] (Comparative Example 2)

[0179] Regenerated reinforcing fibers according to Comparative Example 2 were obtained in the same manner as in Comparative Example 1, except that the neutralization of the reaction product with a 10 mass % sodium hydrogen carbonate aqueous solution was omitted in the washing step.

[0180] (Comparative Example 3)

[0181] Regenerated reinforcing fibers according to Comparative Example 3 were obtained in the same manner as in Comparative Example 2 except that the acid treatment step was omitted.

[0182] 2. Evaluation of recycled reinforcing fibers

[0183] The amount of residual resin in the obtained regenerated carbon fibers according to Examples 1 to 4 and Comparative Examples 1 to 3 and the original carbon fibers used for the carbon fiber reinforced resin material as a reference example were evaluated by thermogravimetric analysis (TGA).

[0184] Specifically, first, the regenerated carbon fibers according to Examples 1 to 4 and Comparative Examples 1 to 3 were heated at a heating rate of 10°C / min while nitrogen was circulated at a flow rate of 200 ml / min, and were kept at 200°C for 15 minutes in order to wait for the weight change caused by the convection of the sample to stop. Next, the weight reduction of the regenerated carbon fibers during this period was measured by heating from 200°C to 600°C at a heating rate of 10°C / min. In addition, for the amount of resin in the untreated carbon fiber reinforced resin material, the volume content was 50%, and the specific gravity of the epoxy resin was set to 1.1 to 1.4 g / cm 3 In the case of , it is approximately 37 to 43% by mass. The results are shown in Table 1 together with the experimental conditions.

[0185] [Table 1]

[0186] Table 1

[0187]

[0188] As shown in Table 1, it can be confirmed that the resin can be efficiently removed from the carbon fiber reinforced resin material in Examples 1 to 4. Specifically, the regenerated carbon fibers according to Examples 1 and 2 have a smaller amount of residual resin than the regenerated carbon fibers according to Comparative Example 1, the regenerated carbon fibers according to Example 3 have a smaller amount of residual resin than the regenerated carbon fibers according to Comparative Example 2, and the regenerated carbon fibers according to Example 4 have a smaller amount of residual resin than the regenerated carbon fibers according to Comparative Example 3. It can be seen that the resin can be efficiently removed from the carbon fiber reinforced resin material by sequentially performing the second step as a heat treatment after the first step as a treatment using a solution. In particular, in Examples 1 and 2, a weight reduction rate close to the weight reduction rate of the original carbon fibers performed as a reference example was observed, and it was confirmed that almost all the resin was removed.

[0189] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to these examples. It should be understood by those skilled in the art that various variations or modifications can be conceived within the scope of the technical concept described in the claims, and these obviously belong to the technical scope of the present invention.

Claims

1. A method for producing a regenerated reinforcing fiber, comprising: A first step of treating a fiber-reinforced resin material including a resin and reinforcing fibers with a treatment liquid so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the treatment liquid; and In the second step, the fiber-reinforced resin material is heated in a gas atmosphere at 150° C. or higher.

2. The method for producing a regenerated reinforcing fiber according to claim 1, wherein: The first step includes treating the fiber-reinforced resin material with an oxidation treatment liquid containing an oxidizing agent to dissolve at least a portion of the resin of the fiber-reinforced resin material in the oxidation treatment liquid.

3. The method for producing a regenerated reinforcing fiber according to claim 1, wherein: The first step includes: a first treatment, treating the fiber-reinforced resin material with an acidic solution containing an acid; and a second treatment, treating the fiber-reinforced resin material with an oxidizing treatment liquid containing an oxidant, so that at least a portion of the resin of the fiber-reinforced resin material is dissolved in the oxidizing treatment liquid.

4. The method for producing a regenerated reinforcing fiber according to claim 2 or 3, wherein: The oxidizing agent includes an acid having oxidizing power.

5. The method for producing a regenerated reinforcing fiber according to claim 4, wherein: The acid having oxidizing power includes at least one selected from the group consisting of nitric acid, a mixed acid of sulfuric acid and nitric acid, a mixed acid of nitric acid and hydrochloric acid, namely, aqua regia, and a mixed solution of hydrogen peroxide and sulfuric acid.

6. The method for producing a regenerated reinforcing fiber according to claim 2 or 3, wherein: The oxidation treatment solution further contains a polymerization inhibitor.

7. The method for producing a regenerated reinforcing fiber according to claim 6, wherein: The polymerization inhibitor includes one or more selected from the group consisting of nitrites and nitrite esters.

8. The method for producing a regenerated reinforcing fiber according to claim 3, wherein: The acid includes one or more selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid.

9. The method for producing a regenerated reinforcing fiber according to claim 3, wherein: The concentration of the acid in the acidic solution is 0.5 mol / L or more.

10. The method for producing a regenerated reinforcing fiber according to claim 1, wherein: In the second step, the fiber-reinforced resin material is heated in a gas atmosphere at 150° C. or higher and 350° C. or lower.

11. The method for producing a regenerated reinforcing fiber according to claim 1, wherein: In the second step, the heating time is 60 minutes to 300 minutes.

12. The method for producing a regenerated reinforcing fiber according to claim 2 or 3, wherein: The resin includes epoxy resin.

13. The method for producing a regenerated reinforcing fiber according to claim 3, wherein: The resin comprises an amine-cured epoxy resin.

14. The method for producing a regenerated reinforcing fiber according to claim 1, wherein: The reinforcing fibers include carbon fibers.

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