Composite fiber-reinforced resin and impact absorbing material

Abstract

Developed is a composite fiber-reinforced resin that has impact resistance against high-speed impacts and has a reusability property that is suitable for realizing a sustainable society.　Provided is a composite fiber-reinforced resin that, in addition to having the high strength and elasticity of a fiber-reinforced composite material, has a low initial elastic modulus and has excellent thermal decomposition resistance.

Description

Composite Fiber Reinforced Resin and Impact Absorbing Material

[0001] The present invention relates to a composite fiber reinforced resin and an impact absorbing material.

[0002] A fiber reinforced composite material obtained by compounding a base material and reinforcing fibers typified by carbon fiber reinforced plastics (CFRP: Carbon Fiber-Reinforced Plastics) is a material having low weight, high strength, and high elasticity. Such properties are largely based on the mechanical properties of reinforcing fibers such as carbon fiber, glass fiber, and aramid fiber. In particular, carbon fiber is known to have mechanical properties about 10 times that of iron in terms of specific strength obtained by dividing the strength by the mass of the material (Non-Patent Document 1). Due to such mechanical properties and chemical properties such as non-rusting, fiber reinforced composite materials are used as a substitute for metals in various fields ranging from sports and leisure goods, automobiles, houses, buildings, to aircraft.

[0003] On the other hand, since CFRP is formed by laminating reinforcing fibers such as carbon fiber, there are no fibers in the thickness direction, and it has poor impact resistance (Non-Patent Documents 2 and 3). Therefore, there is a problem that damage such as delamination between layers, resin cracking, and fiber breakage occurs inside CFRP due to an impact, and buckling or compressive failure easily occurs when a bending load or a compressive load is applied to the damaged portion.

[0004] In order to solve the above problems in CFRP, Patent Document 1 discloses a method of improving impact resistance by adhering an aromatic polyamide fiber reinforced resin sheet, which is an impact absorbing material, to both surfaces of a CFRP sheet so that the direction of the aramid fiber is inclined by ±30 to ±60° with respect to the impact load direction.

[0005] Further, Patent Document 2 discloses a problem that carbon fiber has poor compatibility with other conjugates in a method of imparting impact absorbency to CFRP by adhering an elastic polymer compound such as rubber to a carbon fiber woven fabric. After coating the strands of the carbon fiber woven fabric with a sizing agent, the sizing agent is melted by heat treatment to impregnate the inside of the strands of the carbon fiber woven fabric with the sizing agent to achieve bonding with an elastic polymer compound such as rubber.

[0006] As described above, conventional CFRP compensates for the low impact resistance of carbon fibers by bonding an impact-absorbing material to the surface of the carbon fibers. However, as mentioned earlier, carbon fibers have poor compatibility with other bonding materials, so conventional bonding methods using adhesives, etc., result in interfacial fracture at the bonding surface with the impact-absorbing material. Furthermore, the method described in Patent Document 2, which aims to solve this problem, involves many steps, leading to new problems such as increased manufacturing costs and extended manufacturing time.

[0007] Therefore, the present inventors have developed a composite fiber-reinforced resin in which three or more layers of prepregs such as CFRP are laminated so that the fiber directions of adjacent prepregs are different from each other, and a fiber sheet containing natural fibers is sandwiched between at least one of the prepregs (Patent Document 3). With this composite fiber-reinforced resin, it is possible to obtain an improved shock absorption effect while maintaining high strength and elasticity. With this invention, all of the above problems encompassed by conventional composite fiber-reinforced resins have been solved.

[0008] JP 8-197668 Patent No. 6531245 PCT / JP2024 / 011600

[0009] Toru Hiramatsu, "An Easy-to-Understand Introduction to Carbon Fiber Composites," Nikkan Kogyo Shimbun, 2015, Chapter 1. Kaoru Hasumi et al., "Development of Plastic Composite Materials for a Sustainable Circular Society," Chiba Prefectural Industrial Support Technology Research Library (FY2010); https: / / www.pref.chiba.lg.jp / sanken / kenkyuu / library / h22 / h22library.html. Masaru Kato, Keiichi Kutsusawa, 2012, Tohoku Bureau of Economy, Trade and Industry, FY2012 Next-Generation Manufacturing Base Processing Technology Survey Project, Machining Technology of Composite Materials (CFRP) and Heat-Resistant Alloys, 41-51.

[0010] In recent years, in order to realize a sustainable society, there has been a growing demand for the reusability of fiber-reinforced composite materials, which previously caused environmental pollution due to their disposal. However, the reuse of CFRP, a component of fiber-reinforced composite materials, presents a contradictory problem: it requires a large amount of thermal energy through high-temperature processing.

[0011] As described above, the composite fiber-reinforced resin disclosed in Patent Document 3 was able to solve the problems associated with conventional fiber-reinforced composite materials. However, a large amount of thermal energy was still required for reuse.

[0012] The present inventors pursued the improvement of shock absorption in the composite fiber-reinforced resin disclosed in Patent Document 3, and as a result of diligent research to solve the above problems, they have newly developed a composite fiber-reinforced resin in which a fiber sheet containing silk threads from a bagworm is used in the fiber layer, and this is placed between fiber-reinforced composite material layers with the fiber direction arranged in a predetermined direction and laminated.

[0013] The composite fiber-reinforced resin having the above configuration exhibits excellent thermal decomposition properties, reaching its thermal resistance limit and decomposing at a lower temperature than conventional fiber-reinforced composite materials. Furthermore, surprisingly, a significant decrease in the initial modulus of elasticity was observed, which was not confirmed in the composite fiber-reinforced resin disclosed in Patent Document 3. The initial modulus of elasticity corresponds to the proportionality constant in the deformation region satisfying Hooke's Law, representing the relationship where force and deformation are proportional when a sample is tensed, and is given as the slope of the initial gradient of the stress-strain curve. Generally, a smaller value indicates greater deformation in response to tensile stress, a softer property, and greater shock absorption. This indicates that the composite fiber-reinforced resin with the above configuration exhibits high shock absorption immediately after impact. The present invention is based on the above research and development results and includes the following:

[0014] (1) A composite fiber-reinforced resin comprising a fiber-reinforced composite material layer made of a fiber-reinforced composite material having a certain fiber direction, and a fiber layer comprising a fiber sheet containing cocoon silk, wherein the fiber-reinforced composite material layer is laminated in three or more consecutive layers such that the fiber-reinforced composite material constituting each adjacent layer has a different fiber direction, and the fiber layer is disposed between each of the three or more consecutive fiber-reinforced composite material layers. (2) The composite fiber-reinforced resin according to (1), wherein the intersection angle of the fiber directions in the fiber-reinforced composite material constituting each adjacent layer is 50 degrees to 90 degrees. (3) The composite fiber-reinforced resin according to (1) or (2), wherein the fiber layer consists of a plurality of identical and / or different fiber sheets. (4) The composite fiber-reinforced resin according to any one of (1) to (3), wherein the fiber sheet is a nonwoven fabric. (5) The composite fiber-reinforced resin according to any one of (1) to (4), wherein the fiber-reinforced composite material is a carbon fiber reinforced plastic (CFRP) prepreg. (6) A composite fiber-reinforced resin according to any one of (1) to (5), which is a three-dimensional structure. (7) An impact absorber comprising a composite fiber-reinforced resin according to any one of (1) to (6). This specification includes the disclosures of Japanese Patent Application No. 2024-167874, which forms the basis of the priority of this application.

[0015] The present invention provides a composite fiber-reinforced resin that, in addition to the high strength and elasticity of fiber-reinforced composite materials, has a remarkably low initial modulus of elasticity, and exhibits excellent impact resistance and thermal decomposition properties.

[0016] Figures A to D are conceptual diagrams showing the lamination patterns of fiber-reinforced composite material layers and fiber layers constituting the composite fiber-reinforced resin of the present invention. In the figures, 0101 to 0103, 0107, and 0108 represent fiber-reinforced composite material layers, 0104, 0105, and 0109 represent fiber layers consisting of fiber sheets containing cocoon silk threads, and 0106 represents a fiber layer consisting of fiber sheets not containing cocoon silk threads. Figures E and F are conceptual diagrams showing the lamination patterns of fiber-reinforced composite material layers and fiber layers constituting composite fiber-reinforced resins that do not fall under the composite fiber-reinforced resin of the present invention. In the figures, 0102' and 0103' represent fiber-reinforced composite material layers. The double-headed arrows in each fiber-reinforced composite material layer indicate the fiber direction of the reinforcing fibers contained in the fiber-reinforced composite material. This is a conceptual diagram showing the lamination configuration of fiber-reinforced composite material layers and fiber layers constituting the composite fiber-reinforced resin of the present invention used in Example 1. In the figure, 0201 to 0204 represent fiber-reinforced composite material layers, and 0205 and 0206 represent fiber layers consisting of fiber sheets containing bagworm silk. The double arrows in each fiber-reinforced composite material layer indicate the fiber direction of the reinforcing fibers contained in the fiber-reinforced composite material. The 90 degrees shown in the figure represent the intersection angle of the reinforcing fibers in the fiber-reinforced composite material in adjacent fiber-reinforced composite material layers 0203 and 0204. A shows the actual laminated structure produced in Example 1, and B shows its substantial laminated structure. This shows the laminated structure of the fiber-reinforced composite material used as a control in Example 1. The control fiber-reinforced composite material consists only of fiber-reinforced composite material layers and does not include a fiber layer. A shows the actual laminated structure produced in Example 1, and B shows its substantial laminated structure. Except for the absence of a fiber layer, the basic structure is the same as the laminated structure of the composite fiber-reinforced resin shown in Figure 2. This is a conceptual diagram showing the laminated structure of the fiber-reinforced composite material layer and fiber layer that constitute the comparative composite fiber-reinforced resin used in Example 1. A is a comparative composite fiber-reinforced resin having a similar laminated structure to the composite fiber-reinforced resin of the present invention shown in Figure 2A, in which the fiber-reinforced composite materials constituting each adjacent fiber-reinforced composite material layer all exhibit different fiber directions. B is a control fiber-reinforced composite material for the comparative composite fiber-reinforced resin shown in A, and has the same layer structure as Figure 4A, containing only fiber-reinforced composite material layers and no fiber layers. The 90 degrees shown in B represent the intersection angle of the reinforcing fibers in the fiber-reinforced composite material in adjacent fiber-reinforced composite material layers 0403 and 0404.Figure 5A shows the test force-stroke graphs for each composite fiber-reinforced resin in the puncture impact test of Example 1. a represents the composite fiber-reinforced resin of the present invention consisting of CFRP-90 / minomushi silk nonwoven fabric shown in Figure 2, b represents the fiber-reinforced composite material consisting only of CFRP-90 shown in Figure 3, c represents the comparative composite fiber-reinforced resin consisting of CFRP-90 / minomushi silk nonwoven fabric shown in Figure 4A, and d represents the comparative fiber-reinforced composite material consisting only of CFRP-90 shown in Figure 4B. Figure 5B is an enlarged view of the area indicated by the dashed-dotted line frame in Figure 5A, and further shows the linear approximation curves for a to d. This figure shows the results of the tensile test of Example 2. A shows the measurement results of the composite fiber-reinforced resin of the present invention having the laminated structure shown in Figure 2A, and B shows the measurement results of the fiber-reinforced composite material having the laminated structure shown in Figure 3A, which is a control of A. This figure shows the thermogravimetric (TG) results of Example 3. A shows the results for the entire test range, and B shows an enlarged view of the range indicated by the dashed frame in A. In the figure, the solid line represents the composite fiber-reinforced resin made of CFRP-90 / bagworm silk nonwoven fabric having the structure of the present invention, which was prepared in Example 1(a), and the dashed line represents the fiber-reinforced composite material made of only CFRP-90 for control, which was prepared in Example 1(b).

[0017] 1. Composite Fiber Reinforced Resin 1-1. Overview The first aspect of the present invention is a composite fiber reinforced resin. The composite fiber reinforced resin of the present invention comprises fiber reinforced composite material layers and fiber layers, and is characterized in that three or more layers are continuously laminated such that the fiber reinforced composite materials constituting each adjacent fiber reinforced composite material layer have different fiber directions, and fiber layers including fiber sheets containing bagworm silk threads are arranged between the layers.

[0018] The composite fiber-reinforced resin of the present invention can improve the reusability of fiber-reinforced composite materials due to its remarkably low initial modulus of elasticity and thermal decomposition properties, and can also provide high impact resistance due to its ability to absorb high-speed impacts.

[0019] 1-2. Composition 1-2-1. Components Below, we will specifically explain each component of the composite fiber-reinforced resin of the present invention and its definition.

[0020] In this specification, "composite fiber-reinforced resin" refers to a laminate in which multiple fiber-reinforced composite materials and fiber sheets are laminated together.

[0021] In this specification, "lamination" refers to a state in which sheet-like members having a planar structure are stacked in layers.

[0022] In this specification, "laminated structure" refers to a structure formed by laminating sheet-like members.

[0023] In this specification, "sheet-like member" refers to a member having a thin, flat structure. Examples include sheets, cloth, film, paper, membrane, etc. Sheet-like members are generally soft and variable, but are not limited in this specification and may be hard and / or immutable. The thickness of the sheet-like member is not limited. For example, we can list materials with thicknesses of 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, 350 μm or more, 400 μm or more, 450 μm or more, and 500 μm or more. We can also list materials with thicknesses of 5 mm or less, 4.5 mm or less, 4 mm or less, 3.5 mm or less, 3 mm or less, 2.5 mm or less, 2 mm or less, 1.5 mm or less, and 1 mm or less. Preferably, the thicknesses can be 100 μm to 5 mm, 150 μm to 4.5 mm, 200 μm to 4 mm, 250 μm to 3.5 mm, 300 μm to 3 mm, 350 μm to 2.5 mm, 400 μm to 2 mm, 450 μm to 1.5 mm, or 500 μm to 1 mm.

[0024] The composite fiber-reinforced resin of the present invention includes, as a sheet-like member, a fiber-reinforced composite material constituting a fiber-reinforced composite material layer and a fiber sheet constituting a fiber layer as essential components of the laminate. Furthermore, layers other than the fiber-reinforced composite material layer and the fiber layer (for example, metal foil, etc.) may be included on the surface and / or between the layers of the laminate.

[0025] In the composite fiber-reinforced resin of the present invention, the sheet-like members constituting each layer are, in principle, in complete contact with one another. However, non-contact areas may exist between some layers. Furthermore, the contact areas between layers may be bonded or not bonded. Preferably, all layers constituting the composite fiber-reinforced resin are completely bonded to each other.

[0026] The fiber-reinforced composite material layer and fiber layer in the composite fiber-reinforced resin of the present invention will be described in detail below.

[0027] (1) Fiber-reinforced composite layer In this specification, "fiber-reinforced composite layer" means a layer composed of fiber-reinforced composite material. In this specification, "fiber-reinforced composite material" means a material in which two or more different materials, namely reinforcing fibers and a matrix (base material), are integrated in a separated state without fusing with each other, and is also called a prepreg. Examples include carbon fiber-reinforced plastics (often referred to as "CFRP" or "CFRP prepreg" in this specification), glass fiber-reinforced plastics (often referred to as "GFRP" or "GFRP prepreg" in this specification), and aramid fiber-reinforced plastics (often referred to as "AFRP" or "AFRP prepreg" in this specification), in which reinforcing fibers are impregnated with resin.

[0028] As described above, the fiber-reinforced composite material in this specification corresponds to a sheet-like member and has a laminated structure.

[0029] The mass ratio of reinforcing fibers to matrix in the fiber-reinforced composite materials described herein is not particularly limited and may be any known ratio for fiber-reinforced composite materials. Generally, the reinforcing fibers and matrix may be present in the following ratios: 1:0.005 to 1:1, 1:0.01 to 1:0.8, 1:0.02 to 1:0.6, 1:0.025 to 1:0.4, 1:0.03 to 1:0.2, 1:0.035 to 1:0.15, 1:0.04 to 1:0.1, 1:0.045 to 1:0.09, 1:0.05 to 1:0.08, and 1:0.055 to 1:0.07.

[0030] A fiber-reinforced composite material layer is defined as a layer that forms a laminated end between layers of different types (e.g., fiber layers) or adjacent to layers of different types. A single fiber-reinforced composite material layer may be a single-layer structure consisting of one fiber-reinforced composite material, or it may be a multilayer structure consisting of multiple layers of different types of fiber-reinforced composite materials. A multilayer structure, as used here, refers to a structure in which fiber-reinforced composite materials are laminated with different configurations, such as the type of reinforcing fiber constituting the fiber-reinforced composite material (carbon fiber, glass fiber, aramid fiber, etc.), the orientation of the reinforcing fibers in the fiber-reinforced composite material (unidirectional arrangement, multidirectional arrangement, etc.), the intersection angle of the reinforcing fibers in the reinforced composite material (in the case of multidirectional arrangement), and the type of matrix. Therefore, if multiple layers of fiber-reinforced composite materials with the same configuration are laminated, it is not considered a multilayer structure, but rather a single-layer structure.

[0031] Furthermore, the types of fiber-reinforced composite materials constituting each layer of the fiber-reinforced composite material layer may be the same or different. The following describes the composition of the reinforcing fibers and matrix that make up the fiber-reinforced composite material.

[0032] (A) Reinforcement Fibers In this specification, "reinforcement fiber" refers to a fibrous base material in a fiber-reinforced composite material. Generally, a reinforcement fiber refers to a reinforcing material that provides strength to a fiber-reinforced composite material. The reinforcement fiber may be an inorganic fiber, an organic fiber, or a combination thereof.

[0033] Inorganic fibers include carbon fibers, glass fibers, metal fibers (stainless steel, titanium, copper, aluminum, nickel, iron, tungsten, molybdenum, etc.), and amorphous fibers (ceramic fibers, rock wool, basalt fibers, etc.). For example, carbon fibers are used as reinforcing fibers in the aforementioned CFRP prepreg, and glass fibers are used as reinforcing fibers in GFRP prepreg.

[0034] Organic fibers generally include synthetic fibers such as aramid, polyamide (including nylon), polyester, polyethylene, and acrylic. For example, in the aforementioned AFRP prepreg, aramid fibers serve as reinforcing fibers. Natural fibers such as plant fibers, animal fibers, and regenerated fibers may also be used.

[0035] Reinforcement fibers may be composed of a combination of multiple different fibers. In this case, a synergistic effect can be expected by combining reinforcement fibers with different physical properties.

[0036] The fiber-reinforced composite material constituting the fiber-reinforced composite material layer of the present invention has a certain fiber direction. Here, "fiber direction" refers to the orientation of the long fibers of the reinforcing fibers contained in the fiber-reinforced composite material, and in principle, it refers to the direction of the long axis. "Having a certain fiber direction" means that the fiber bundles of the reinforcing fibers have a certain orientation. The orientation of the reinforcing fibers is not limited. Multiple reinforcing fibers may be arranged in one direction, or they may be arranged in two or more directions.

[0037] In fiber-reinforced composite materials, an example of unidirectional arrangement of reinforcing fibers is UD material (unidirectional material), in which the reinforcing fibers are aligned linearly and arranged in a planar manner.

[0038] Examples of arranging reinforcing fibers in two directions include textiles such as woven fabrics and braided fabrics, and arrangements made by the filament winding molding method described later. A woven fabric is made by crossing warp and weft threads to form a flat surface (sheet). Specific examples of woven fabrics include plain weave, twill weave, and satin weave, but the arrangement of reinforcing fibers in fiber-reinforced composite materials may be any of these. Furthermore, the warp and weft threads cross each other at a predetermined intersection angle. In addition, in the filament winding molding method, two reinforcing fibers are wound around a core metal at a predetermined intersection angle. These intersection angles are not particularly limited in this specification. For example, the intersection angle on the acute side in actual angles may be 20 to 90 degrees, 30 to 85 degrees, 32 to 80 degrees, 35 to 78 degrees, 38 to 75 degrees, 40 to 70 degrees, 42 to 68 degrees, 45 to 65 degrees, 48 ​​to 60 degrees, 45 to 58 degrees, or 50 to 55 degrees.

[0039] (B) Matrix In this specification, “matrix” means the supporting substrate in a fiber-reinforced composite material. Although not limited to the matrix, the base material in a fiber-reinforced composite material is usually a polymer matrix. “Polymer matrix” includes either organic polymers or inorganic polymers, or both. Organic polymers include synthetic polymers and natural polymers.

[0040] In this specification, "synthetic polymer" refers to a polymer obtained by linking monomers through degeneration or addition polymerization reactions, and examples include synthetic resins and synthetic rubber.

[0041] "Synthetic resin" refers to an artificially produced polymer compound without rubber elasticity. It is a compound commonly referred to as "plastic", including thermosetting resins, thermoplastic resins, or combinations thereof. Although "plastic" strictly refers to thermoplastic resins, in this specification, it is broadly referred to as an alias for synthetic resin. Specific examples of thermosetting resins include, but are not limited to, epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, thermosetting polyurethanes, urea resins, melanin resins, polyimides, silicone resins, etc. Specific examples of thermoplastic resins include, but are not limited to, polyethylene, polypropylene, polyester, polystyrene, polyvinyl chloride, methacrylic resins, fluorine resins, polycarbonate, thermoplastic polyurethane, aromatic polyether ketone resins, polyphenylene sulfide resins, polyoxymethylene, acrylonitrile, polybutylene, polyamide, polyacetal, polyvinyl alcohol, polyglycol, polyethylene terephthalate, polyethylene succinate, polybutylene adipate, polybutylene adipate terephthalate, polybutylene succinate, polylactic acid, polyhydroxyalkanoate, polyhydroxybutyrate, etc.

[0042] "Synthetic rubber" refers to an artificially produced polymer compound having rubber elasticity. It is a compound commonly referred to as "elastomer", including thermosetting elastomers, thermoplastic elastomers, or combinations thereof. Specific examples of thermosetting elastomers include, but are not limited to, butadiene rubber, chloroprene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, nitrile rubber, silicone rubber, acrylic rubber, fluorine rubber, urethane rubber, etc.

[0043] In this specification, "natural polymer" refers to polymers existing in nature, such as proteins, polysaccharides, and natural resins. Specific examples of natural polymers composed of proteins include glue (including collagen and gelatin). Specific examples of natural polymers composed of polysaccharides include starch, cellulose, mannan, agar, etc. Further, specific examples of natural polymers composed of natural resins include lacquer, rosin, latex (natural rubber), shellac, etc.

[0044] In this specification, the method for manufacturing the fiber reinforced composite material is not particularly limited, and it may be manufactured by any existing method. For example, a press molding method in which a matrix and reinforcing fibers are placed in a preheated mold and cured while being pressed by a press machine, an internal pressure molding method in which compressed air is injected into the interior of a molded product for molding, a pultrusion molding method (drawing molding method) in which reinforcing fibers impregnated with a liquid matrix are drawn into a mold and heat-cured, a filament winding molding method in which reinforcing fibers impregnated with a liquid matrix are wound around a core metal (mandrel) and then heat-cured, an RTM molding method (resin transfer molding method) (including a vacuum-assisted VaRTM molding method) in which a preform obtained by preforming reinforcing fibers is placed in a mold composed of a male mold and a female mold, and after injecting and impregnating a liquid matrix, heat-curing is performed, an autoclave method, an injection molding method, a sheet winding method, etc. may be mentioned.

[0045] (2) Fiber layer In this specification, "fiber layer" refers to a layer composed of a fiber sheet in the composite fiber reinforced resin of the present invention.

[0046] A fiber layer is defined as a layer that forms a laminated end between layers of different types (e.g., fiber-reinforced composite material layers) or adjacent to layers of different types. A single fiber layer may be a single-layer structure consisting of one fiber sheet, or it may be a multi-layer structure. A multi-layer structure, as used here, refers to a structure in which different types of fiber sheets are laminated. For example, a fiber layer made by laminating two fiber sheets made of nonwoven fabric from silkworm silk and one fiber sheet made of Japanese paper placed between them is considered a multi-layer structure. On the other hand, if multiple layers of the same type of fiber sheet are laminated, it is not considered a multi-layer structure, but a single-layer structure. For example, a fiber layer made by laminating multiple fiber sheets made of nonwoven fabric from silkworm silk falls into this category.

[0047] In this specification, "fiber sheet" refers to a sheet-like constituent material in which multiple fiber bundles are arranged planarly in one direction or in two or more directions. A fiber sheet is a sheet-like member and has a structure that allows for lamination. The fiber layer may consist of one fiber sheet or multiple fiber sheets. For example, it may be composed of two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more fiber sheets laminated together. When the fiber layer is composed of multiple fiber sheets, each fiber sheet may be the same, different, or a combination thereof.

[0048] The fiber sheet may consist solely of natural fibers, or it may contain natural fibers as a main component, along with other components such as synthetic fibers or the matrix. The natural fibers contained in the fiber sheet may be derived from a single species or from multiple species. However, the fiber layer in the composite fiber-reinforced resin of the present invention is characterized in that at least one fiber sheet is composed of a fiber sheet containing bagworm silk as a natural fiber, preferably a fiber sheet made of bagworm silk.

[0049] In this specification, "natural fiber" refers to a fibrous natural polymer compound produced by living organisms, or an artificial fibrous polymer compound obtained by processing and spinning materials of biological origin. Examples of natural fibers include polypeptide fibers and cellulosic fibers.

[0050] In this specification, "polypeptide-based fiber" refers to a fibrous polymer compound whose main component is polypeptides, which make up proteins, and is also known as fibrous protein. These fibers are mainly derived from animal fibers and can be broadly classified into fibroin-derived fibers and keratin-derived fibers.

[0051] In this specification, "fibroin-derived fiber" refers to a fibrous polypeptide whose main component is fibroin protein (primarily fibroin H-chain protein). Examples include animal-derived natural fibers such as silk and spider silk obtained from the larvae of moths such as Psychidae, silkworms (Bombyx mori), or Saturniidae, or from the larvae of bees.

[0052] "Fibroin H-chain protein" refers to the main protein that constitutes fibroin, the fiber protein component of silk thread. In this specification, fibroin H-chain protein may be natural fibroin H-chain protein or artificial fibroin H-chain protein. "Natural fibroin H-chain protein" refers to fibroin H-chain protein that exists in nature. Natural fibroin H-chain protein is defined as a protein whose full-length amino acid sequence is identical to that of fibroin H-chain protein that exists in nature. Since natural fibroin H-chain protein is a protein encoded by the wild-type fibroin H-chain protein gene of various organisms, it is synonymous with "wild-type fibroin H-chain protein." "Artificial fibroin H-chain protein" refers to fibroin H-chain protein that does not exist in nature. This mainly refers to modified fibroin H-chain proteins, which are obtained by artificially modifying all or part of natural fibroin H-chain protein, mainly through genetic engineering technology. Modified fibroin H-chain proteins are composed of different amino acid sequences than wild-type fibroin H-chain protein. Modified fibroin H-chain proteins include, for example, mutant fibroin H-chain proteins in which one or more amino acids are added, deleted, and / or substituted into the amino acid sequence of a fibroin H-chain protein, and chimeric fibroin H-chain proteins in which the amino acid sequences of fibroin H-chain proteins from two or more different insects are fused.

[0053] In this specification, "keratin-derived fiber" refers to a fibrous polypeptide whose main component is keratin protein. Examples include animal hair and feathers. Specifically, examples include sheep's wool, goat's hair, llama's hair, horse's hair, camel's hair, fox's hair, raccoon's hair, chinchilla's hair, rabbit's hair, etc.

[0054] In this specification, "cellulose fibers" refers to fibrous polymer compounds whose main component is cellulose, a polysaccharide. These are fibers mainly derived from plant fibers, specifically including, for example, cotton, hemp, and paper. Paper includes Japanese paper, tissue paper (including Kimwipes®), and paper towels (including Kimtowels®). Other examples include regenerated fibers such as rayon, Tencel, Lyocell, and cupro, which are made from wood pulp.

[0055] "Bagworm" refers to the larvae of moths belonging to the family Psychidae in the order Lepidoptera. While moths of the Psychidae family are distributed worldwide, in principle, all larvae (bagworms) live in a nest they create by spinning silk threads themselves, weaving together natural materials such as leaves and branches. The nest is a sac-like structure capable of enclosing the entire body, and takes various forms such as spindle-shaped, cylindrical, or conical. Bagworms usually remain hidden within this nest, always accompanying it during feeding and movement, and pupation also generally occurs within the nest. The species of bagworm referred to in this specification are not limited. For example, genera such as Acanthopsyche, Anatolopsyche, Bacotia, Bambalina, Canephora, Chalioides, Dahlica, Diplodoma, Eumeta, Eumasia, Kozhantshikovia, Mahasena, Nipponopsyche, Paranarychia, Proutia, Psyche, Pteroma, Siederia, Striglocyrbasia, Taleporia, Theriodopteryx, and Trigonodoma exist, but the bagworms described herein may belong to any of these genera. Specific examples of bagworm species include the large bagworm (Eumeta japonica) and the small bagworm (Eumeta minuscula). The age of the bagworms described herein is not limited; any age from the first to the final instar is acceptable. However, larger bagworms are preferred if using fiber sheets containing thicker and longer bagworm silk threads. For example, within the same species, the final instar larva is preferable, and among males and females, the larger female is preferred. Within the Psychidae family, larger species are also preferred. Therefore, although not limited, the aforementioned *Psychidae japonica* and *Psychidae japonica* are suitable species for use as bagworms in this invention.

[0056] In this specification, "bagworm silk" refers to the protein-based thread spun by bagworms for nesting and migration. Bagworm silk is classified into monofilaments, spinned fibers, and aggregated fibers based on its structural form. In this specification, any of these fibers may be referred to as bagworm silk. While not limited to these, spinned fibers are preferred.

[0057] In this specification, "monofiber" refers to the smallest unit of fiber components, the filament, and is also called a monofilament. A monofiber consists of fibroin H-chain protein, which is a fibrous protein, and, in principle, does not contain sericin-like adhesive substances. Bagworm silk is spun from difilaments, as described below, and does not exist as a monofiber in its natural state. Usually, monofibers can be obtained by removing the adhesive substance covering the surface of the difilaments through artificial processing such as scouring.

[0058] In this specification, "spun silk fibers" refer to silk threads spun by bagworms. Bagworm spinning fibers are composed of difilaments, which are pairs of two single fibers. This form is based on the fact that when spinning, two single fibers extruded from the spinning openings located on the left and right sides of the bagworm are joined together by a sericin-like adhesive substance. In this specification, when "spun silk" is used together with "spun silk" as in "spun silk threads of bagworms," ​​it generally refers to spinning fibers.

[0059] In this specification, "compound fiber" refers to a fiber composed of multiple fiber bundles, also known as a multifilament. It is what is commonly called raw silk, and in principle is composed of multiple single fibers, but in this specification, it also includes cases where it is composed of multiple single fibers and spinning fibers, or multiple spinning fibers. In this specification, compound fibers may also include mixed fibers that are a mixture of fibers other than cocoon silk, such as silkworm silk, but unless otherwise specified, in this specification, it usually refers to compound fibers composed only of cocoon silk. Compound fibers are twisted by a twisting process to become stronger silk threads. However, in this specification, compound fibers include not only twisted threads but also untwisted threads that exhibit a soft and smooth texture.

[0060] Furthermore, bagworm fibers are classified into nest silk and scaffold silk depending on the form of the silk they spin. In this specification, when referring to bagworm silk, either type of silk may be used. Scaffold silk is preferred.

[0061] In this specification, "scaffolding silk" refers to silk spun by bagworms for the purpose of movement, and it functions as a scaffold to prevent them from falling from branches, leaves, etc., while moving. Bagworms use this scaffolding silk as a foothold, and move in the direction of travel by hooking the claws of both their legs onto it. To make it easier for bagworms to hook their left and right legs, and to distribute the load on the silk and the fixing points of the silk to both sides, the scaffolding silk is spun in a zigzag pattern. Scaffolding silk is thicker and mechanically stronger than the nesting silk described later.

[0062] In this specification, "nest silk" refers to the silk that makes up the nest, which is spun to bind together leaf fragments and twigs, and to create a comfortable environment on the inner wall of the nest, which is the living area.

[0063] The fiber sheet may be composed of either woven or nonwoven fabric. While not limited to woven fabric, nonwoven fabric is preferred.

[0064] A "nonwoven fabric" refers to a sheet-like web in which fibers are oriented in one direction or randomly, and the fibers are bonded together by entanglement and / or fusion and / or adhesion, resulting in a finished fabric-like material. For example, paper is a nonwoven fabric made of cellulose fibers. Fiber sheets containing bagworm silk, or fiber sheets made of bagworm silk, are also preferably nonwoven fabrics.

[0065] In this specification, nonwoven fabrics may be manufactured by existing methods. Examples include dry methods, wet methods, spunbond methods, meltblown methods, thermal bonding methods, impregnation chemical bonding methods, spray chemical bonding methods, needle punching methods, spunlace methods, and composite methods combining these methods. The method used to manufacture these nonwoven fabrics may be determined appropriately according to the properties and / or fiber length of the fibers constituting each fiber layer. For example, for nonwoven fabrics made of synthetic fibers, methods such as impregnation chemical bonding methods and spray chemical bonding methods, which chemically bond fibers together using synthetic resin as an adhesive, thermal bonding methods, which weld fibers together by heating, meltblown methods, which spin fine fibers of 1d to 10d using high-temperature air ejected from around a spinning nozzle with molten resin and simultaneously laminate them, and spunlace methods, which entangle fibers by spraying a high-pressure water stream onto a web, can be used.

[0066] Furthermore, nonwoven fabrics made from bagworm silk can be manufactured, for example, by the methods disclosed in Japanese Patent Publication No. 2020-045381 or Japanese Patent Publication No. 2023-165754. The method disclosed in Japanese Patent Publication No. 2020-045381 involves placing bagworms on a solvent-soluble substrate or a heat-meltable substrate, allowing them to spin scaffolding silk, then dissolving the solvent-soluble substrate with a solvent, or dissolving the heat-meltable substrate by heating, and recovering the remaining scaffolding silk as a nonwoven fabric. The method disclosed in Japanese Patent Publication No. 2023-165754 involves placing bagworms on a substrate, allowing them to spin scaffolding silk, then spraying or applying a wetting solution such as ethanol, an aqueous solution, or an organic solvent to the surface of the substrate, and finally peeling the scaffolding silk from the substrate as a nonwoven fabric and recovering it.

[0067] If the fiber sheet contains a matrix in addition to natural fibers, the matrix may be impregnated into the fiber sheet or coated onto one or both sides of the fiber sheet surface.

[0068] 1-2-2. Structure The composite fiber-reinforced resin of the present invention is a laminate comprising a fiber-reinforced composite material layer and a fiber layer, both made of a fiber-reinforced composite material having a certain fiber direction.

[0069] The present invention provides a composite fiber-reinforced resin characterized by having three or more layers of fiber-reinforced composite material laminated in a continuous manner, such that the fiber-reinforced composite material constituting each adjacent fiber-reinforced composite material layer has a different fiber direction from one another, and having fiber layers containing a fiber sheet containing bagworm silk threads arranged between these layers.

[0070] In this specification, "three or more consecutive layers" means that three or more layers of fiber-reinforced composite material having different fiber directions are laminated consecutively. Therefore, even if three or more layers of fiber-reinforced composite material are laminated consecutively, if the fiber directions of the fiber-reinforced composite material constituting each layer coincide in two adjacent layers, the continuity between those layers is lost. The layers subject to continuity are the fiber-reinforced composite material layers, and other layers (e.g., fiber layers) present between the fiber-reinforced composite material layers are not subject to continuity.

[0071] In this specification, "adjacent" means that two fiber-reinforced composite material layers are located adjacent to each other with a fiber layer in between.

[0072] In this specification, "so that the fiber directions are different from each other" means that, in the case of fiber-reinforced composite materials in which the reinforcing fibers are arranged in one direction, such as UD materials, the fiber directions of the reinforcing fibers contained between two fiber-reinforced composite material layers do not coincide. Furthermore, in the case of fiber-reinforced composite materials in which the reinforcing fibers are arranged in two or more fiber directions, such as fiber-reinforced composite materials manufactured by the filament winding molding method, it also means that at least one of the multiple fiber directions of the reinforcing fibers contained between two fiber-reinforced composite material layers does not coincide.

[0073] In fiber-reinforced composite material layers, the requirement that the fiber-reinforced composite materials constituting each layer have different fiber directions applies when a fiber layer containing a fiber sheet with cocoon silk threads is placed between two adjacent fiber-reinforced composite material layers. Therefore, when a fiber layer containing a fiber sheet with cocoon silk threads is not placed between two fiber-reinforced composite material layers, for example, when a fiber layer made of a fiber sheet other than cocoon silk threads is placed between two fiber-reinforced composite material layers, or when two layers of different types of fiber-reinforced composite material layers are directly laminated, the fiber directions of the fiber-reinforced composite materials constituting those fiber-reinforced composite material layers may be the same or different. Furthermore, for example, even when the composite fiber-reinforced resin of the present invention includes three fiber-reinforced composite material layers, from the first to the third layer, and a fiber layer containing a fiber sheet with cocoon silk threads is placed between each layer, it is sufficient that the fiber directions of the reinforcing fibers in two adjacent layers, i.e., the first and second layers, or the second and third layers of the fiber-reinforced composite material layers, are different, and the fiber directions of the first and third layers may be perfectly aligned. Of course, the fiber directions of all three layers may be arranged to be different.

[0074] In this specification, "different fiber directions" means that the fiber directions of adjacent fiber-reinforced composite material layers do not coincide with each other, but it is preferable that the intersection angle (actual angle) between fibers is 50 to 90 degrees, 52 to 88 degrees, 54 to 85 degrees, 56 to 80 degrees, 58 to 78 degrees, 60 to 75 degrees, 62 to 70 degrees, or 64 to 68 degrees on the acute angle side.

[0075] In the composite fiber-reinforced resin of the present invention, the number of fiber-reinforced composite material layers may be 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 12 or more, and 14 or more, as well as 100 or fewer, 80 or fewer, 60 or fewer, 50 or fewer, 40 or fewer, 30 or fewer, 20 or fewer, and 15 or fewer. In the case of 4 or more layers, it is not necessary for all layers to exhibit the above characteristics, that is, for three or more consecutive fiber-reinforced composite material layers, the fiber-reinforced composite material constituting each adjacent fiber-reinforced composite material layer to have different fiber orientations. For example, in a composite fiber-reinforced resin containing 5 fiber-reinforced composite material layers, all 5 layers may satisfy the above requirement, or only 3 layers may satisfy the requirement, and the remaining 2 layers may not. On the other hand, the number of fiber-reinforced composite material layers that satisfy the above requirement is not particularly limited as long as it is 3 or more, and may be within the range of the above number of layers.

[0076] In the composite fiber-reinforced resin of the present invention, the number of fiber layers may be 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 12 or more, and 14 or more, as well as 100 or fewer, 80 or fewer, 60 or fewer, 50 or fewer, 40 or fewer, 30 or fewer, 20 or fewer, and 15 or fewer. Of these, 2 or more layers are fiber layers containing fiber sheets with cocoon silk threads, and in principle, they are required to be arranged between layers that satisfy the requirements of the aforementioned three or more consecutive fiber-reinforced composite material layers. However, as long as the composite fiber-reinforced resin contains at least three fiber-reinforced composite material layers that satisfy the above requirements and two fiber layers arranged between those layers that satisfy the above requirements, the arrangement and composition of other fiber layers are not limited. For example, a fiber layer containing a fiber sheet with cocoon silk threads may be arranged in the uppermost and / or lowermost layer of the composite fiber-reinforced resin, i.e., at the end of the laminate.

[0077] Figure 1 shows an example of the structure of the composite fiber-reinforced resin of the present invention. A is a structure comprising three fiber-reinforced composite material layers (0101, 0102, 0103) with different fiber directions of adjacent fiber-reinforced composite materials, and two fiber layers (0104, 0105) arranged between these layers and comprising a fiber sheet containing cocoon silk threads, B is a structure comprising a fiber layer in which a fiber sheet containing cocoon silk threads (0105) and a fiber sheet not containing cocoon silk threads (0106) are laminated, and C is a structure in which the fiber-reinforced composite material layer (01 Adjacent to 03), a structure is further laminated with fiber-reinforced composite material layers (0107) such that the fiber directions of adjacent fiber-reinforced composite materials are different, and no fiber layers are placed between these layers. D is a structure that includes four fiber-reinforced composite material layers (0101, 0102, 0103, 0108) with different fiber directions of adjacent fiber-reinforced composite materials, and three fiber layers (0104, 0105, 0109) placed between these layers and including a fiber sheet containing cocoon silk thread. Other examples include a structure that includes five fiber-reinforced composite material layers that satisfy the above requirements and four fiber layers placed between each of these layers that satisfy the above requirements, or a structure that includes six fiber-reinforced composite material layers that satisfy the above requirements and five fiber layers placed between each of these layers that satisfy the above requirements.

[0078] On the other hand, structures similar to the composite fiber-reinforced resin of the present invention but not corresponding to the composite fiber-reinforced resin of the present invention include, for example, the structures shown in E and F of Figure 1. The composite fiber-reinforced resin of E includes three fiber-reinforced composite material layers (0101, 0102', 0103') and two fiber layers (0104, 0105) arranged between these layers and containing fiber sheets containing cocoon silk threads. However, the fiber orientation of the second and third fiber-reinforced composite material layers (0102', 0103') is reversed compared to A, resulting in the first layer (0101) and the second layer (0102') having the same fiber orientation, thus failing to satisfy the condition that adjacent fiber-reinforced composite materials have different fiber orientations. Furthermore, the composite fiber-reinforced resin of F, like D, includes four fiber-reinforced composite material layers with adjacent fiber directions differing, but a fiber layer (0106) consisting of a fiber sheet without cocoon silk threads is placed between the second layer (0102) and the third layer (0103). Therefore, it does not satisfy the conditions of three fiber-reinforced composite material layers with adjacent fiber directions differing, and fiber layers including two fiber sheets containing cocoon silk threads placed between each of these layers.

[0079] The shape of the composite fiber-reinforced resin of the present invention is not limited as long as it has a laminated structure including a fiber-reinforced composite material layer and a fiber layer. For example, it may be a planar shape such as a plate or sheet, or it may be a three-dimensional shape that forms any three-dimensional structure. The three-dimensional structure can be formed by laminating it onto the surface of a mold during the formation process (manufacturing process), or it can be formed into a desired shape by plastic deformation after being manufactured as a planar laminate.

[0080] 1-3. Applications As shown in the examples described later, the composite fiber-reinforced resin of the present invention possesses not only the strength and elasticity of conventional composite fiber-reinforced resins such as CFRP, but also a remarkably low initial modulus of elasticity and excellent thermal decomposition properties. Taking advantage of these physical properties, it can be used, for example, as a substitute material in known structures made of resin. It is suitable for use as a base material for structures that are expected to be subjected to strong impacts, especially high-speed impacts. For example, it can be used as a structure for sports equipment such as tennis and badminton rackets, hockey and lacrosse sticks, golf shafts, pole vault poles, and helmets. In addition, it can be used as a structure for sports equipment such as snowboards, skis, ski poles, climbing poles, and fishing rods, as well as for structures such as bumpers, guards, fuel tanks, frames, rims, and body panels in mobile bodies such as cars, motorcycles, bicycle frames, ships, aircraft, and drones, as well as for structures or reinforcements of buildings, structures of electrical products, or various housings.

[0081] 1-4. Effects Conventional composite fiber reinforced polymers (CFRP) have a problem in that, due to the properties of carbon fibers, they have a very high modulus of elasticity and are susceptible to large impact loads.

[0082] Because the composite fiber-reinforced resin of the present invention has a low initial modulus of elasticity, it absorbs and mitigates high-speed impacts, thus reducing impact loads compared to CFRP. Therefore, the composite fiber-reinforced resin of the present invention is expected to be used in sports equipment, sports machinery, and sports equipment structures that are used in direct contact with people.

[0083] Furthermore, in static physical property tests, the composite fiber-reinforced resin of the present invention showed no difference from the results of CFRP alone, which is a fiber-reinforced composite material that does not contain a fiber layer, and no material degradation due to the composite with a fiber layer was observed.

[0084] Furthermore, thermogravimetric analysis (TG) of the present invention showed that the composite fiber-reinforced resin exhibited faster weight loss upon heating than CFRP alone, suggesting high thermal decomposition properties. This property facilitates the recycling of waste CFRP, which is currently an environmental problem, making it possible to produce environmentally friendly CFRP.

[0085] 2. Shock Absorbing Material 2-1. Overview A second aspect of the present invention is a shock absorbing material. The shock absorbing material of the present invention is characterized by containing the composite fiber-reinforced resin of the first aspect.

[0086] The composite fiber-reinforced resin of the first embodiment possesses not only the high strength and elasticity of conventional composite fiber-reinforced resins, but also a remarkably low initial modulus of elasticity and excellent thermal decomposition properties. The impact-absorbing material of the present invention utilizes the impact resistance against high-speed impacts and reusability based on these properties of the composite fiber-reinforced resin of the first embodiment. The impact-absorbing material of the present invention can be used as a component that provides the physical properties of conventional composite fiber-reinforced resins and high impact resistance to structures and parts where conventional composite fiber-reinforced resins could not be used due to their low impact resistance, and the reuse of composite fiber-reinforced resins can contribute to the realization of a sustainable society and the resolution of environmental pollution problems.

[0087] 2-2. Structure In this specification, "impact absorption" refers to the property of absorbing the impact force generated when an object collides at a certain speed.

[0088] In this specification, "impact absorbing material" refers to a material that has a long stress generation time at the impact surface when objects collide. Impact absorbing materials can reduce the maximum impact force during a collision by converting impact energy into other forms of energy. These other forms of energy include, for example, deformation energy, vibration energy, and thermal energy.

[0089] The impact-absorbing material of the present invention contains the composite fiber-reinforced resin of the first embodiment as a main component. The content of the composite fiber-reinforced resin of the first embodiment in the impact-absorbing material of the present invention is not particularly limited as long as it is within a range that maintains and / or exhibits the impact resistance of the composite fiber-reinforced resin. For example, it may be 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 8% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 92% by mass or more, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass or more, or 100% by mass.

[0090] If the shock-absorbing material of the present invention contains other components, the type of those components is not limited. Preferably, the components do not reduce the impact resistance of the composite fiber-reinforced resin of the first embodiment, and it is preferable that the components do not reduce the impact resistance and instead provide higher impact resistance through a synergistic effect. Examples include polymer foams such as polyurethane foam and polystyrene (expanded polystyrene), glass wool, carbon wool, natural rubber, synthetic rubber, metal springs, organic polymer springs, hydrogels, and airbags. In the shock-absorbing material of the present invention, the composite fiber-reinforced resin of the first embodiment may be in direct or indirect contact with the other components. In the case of direct contact, the two may be bonded together or they may be separable and non-bonded.

[0091] <Example 1> (Objective) To verify the impact absorption properties of the composite fiber-reinforced resin of the present invention.

[0092] (Material) ・CFRP prepreg: PAN-based CF, mass: 150g / m 2 Thickness: 0.124mm, CF mass: 200g / m 2 High-toughness epoxy resin content: 25 wt% Nonwoven fabric made from the silk of the giant bagworm: Mass: Approximately 0.57 g / m² per sheet 2 Thickness: Approximately 0.005 mm per sheet

[0093] The nonwoven fabric of bagworm silk was obtained by a method similar to that disclosed in Example 1 of Japanese Patent Application Publication No. 2023-165754. Specifically, bagworms were placed on the surface of a substrate with a sufficient amount of food leaves, and after they were allowed to spin a sufficient amount of scaffolding silk on the surface, a 70% ethanol aqueous solution was applied to the bagworm silk on the substrate, and after confirming that it was sufficiently wet, the bagworm silk was peeled off the substrate to recover the nonwoven fabric of bagworm silk. After recovery, it was dried and used in this example.

[0094] (Method) (1) Composition of each test specimen (a) CFRP / bagworm silk nonwoven fabric (Figure 2) ・Fiber-reinforced composite material layer: Four CFRP prepregs (Figure 2A: 0201, 0202, 0203, 0204) were laminated. At this time, the CFRP prepregs of the first layer (0201) and the second layer (0202), and the third layer (0203) and the fourth layer (0204) were laminated so that the actual angle (fiber intersection angle) when the fiber directions of the reinforcing fibers intersect was 90° (Figure 2A). On the other hand, the fiber directions of the reinforcing fibers of the second layer (0202) and the third layer (0203) were laminated so that they were perfectly aligned. Therefore, in this embodiment, the laminated structure of the fiber-reinforced composite material layers is such that the first layer (0201) and the second layer (0202), and the third layer (0203) and the fourth layer (0204) are mirror images of each other with respect to the fiber direction. Fiber layer: Ten sheets each of bagworm silk nonwoven fabric (Figure 2A: 0205, 0206) were placed between two prepreg layers (Figure 2A: between 0201 / 0202 and between 0203 / 0204).

[0095] In the above laminated configuration, since the second layer (0202) and the third layer (0203) of the fiber-reinforced composite material are identical in terms of fiber direction and material, the second layer (0202) and the third layer (0203) are not considered as two separate fiber-reinforced composite material layers, but rather as a single fiber-reinforced composite material layer (0202 / 0203).

[0096] Therefore, the specimen essentially has a structure consisting of five layers, as shown in Figure 2B, in which three layers (0201, 0202 / 0203, 0204) are continuously laminated so that the fiber-reinforced composite materials constituting each adjacent fiber-reinforced composite material layer have a fiber direction with a fiber intersection angle of 90° to each other, and fiber layers (0205, 0206) consisting of 10 fiber sheets made of bagworm silk nonwoven fabric are placed between each layer.

[0097] (b) CFRP-90 (Control: Fiber-reinforced composite material layer only) (Figure 3) The basic structure of the fiber-reinforced composite material layer is the same as in (a). However, as shown in Figure 3A, this test specimen does not include a fiber layer. Therefore, as shown in Figure 3B, it has a structure in which a total of three layers (0301, 0302 / 0303, 0304) are laminated, in which the fiber-reinforced composite material constituting each adjacent fiber-reinforced composite material layer is laminated so that the fiber direction of each layer is at a fiber intersection angle of 90°.

[0098] (c) CFRP / bagworm silk nonwoven fabric (for comparison) (Figure 4A) ・Fiber-reinforced composite material layer: Four CFRP prepregs (0401, 0402, 0403, 0404) were laminated. At this time, the CFRP prepregs in each adjacent layer were laminated so that the actual angle (fiber intersection angle) when the fiber directions of the reinforcing fibers intersect was 90° (Figure 4B). ・Fiber layer: Ten sheets each of bagworm silk nonwoven fabric (Figure 4A: 0405, 0406) were placed between two prepreg layers (Figure 4A: between 0401 / 0402, between 0403 / 0404).

[0099] In the above laminated structure, the fiber directions of the second layer (0402) and the third layer (0403) of the fiber-reinforced composite material layer are different from (a) and do not coincide. Therefore, the second layer (0402) and the third layer (0403) are independent fiber-reinforced composite material layers.

[0100] As described above, the test specimen of this comparative example, as shown in Figure 4A, has four layers (0401, 0402, 0403, 0404) of fiber-reinforced composite material stacked continuously such that the fiber directions of the fiber-reinforced composite material constituting each adjacent fiber-reinforced composite material layer are at a fiber intersection angle of 90° to each other. However, the fiber layers (0405, 0406) composed of 10 fiber sheets made of bagworm silk nonwoven fabric are arranged only between two layers (0401 / 0402, 0403 / 0404) and are not arranged between three consecutive layers of fiber-reinforced composite material. Therefore, although it is similar in structure to (a), which is the composite fiber-reinforced resin of the present invention, it does not satisfy the constituent requirements of the composite fiber-reinforced resin of the present invention.

[0101] (d) CFRP-90 (Comparative control: Fiber-reinforced composite material layer only) (Figure 4B) The basic structure of the fiber-reinforced composite material layer is the same as in (c). However, as shown in Figure 4B, this test specimen does not include the fiber layer.

[0102] (2) Preparation of composite fiber-reinforced resins For the test specimens (a) and (c), in order to impregnate the fiber layer with epoxy resin, each was placed in a stainless steel mold (t=5mm: 2 pieces) and held at 100°C for 10 minutes in a high-temperature hot press (AS ONE: H400-05). The same method was used for the test specimens (b) and (d). Next, in order to cure the epoxy resin, a pressure of approximately 2.5 MPa was maintained at 120°C for 120 minutes. After curing, the mold was removed and the material was allowed to cool slowly to obtain each test specimen with a thickness of approximately 0.5 mm.

[0103] Next, using an ultrasonic cutter (Sonotec: SF-3140 | SF-3400II), the pressed test pieces (a) to (d) were cut to 60 mm. 2 It was cut into a rectangular shape.

[0104] (3) Puncture Impact Test Conditions The surface impact strength of each test specimen was measured by a puncture impact test using a puncture impact testing machine (Shimadzu Corporation: HITS-PX). Each test specimen prepared in (1) above was placed on a test specimen support stand and fixed with a clamping plate. At room temperature (approximately 25°C), a hemispherical striker with a diameter of 20 mm was struck perpendicularly to the central surface of the test specimen at a loading speed of 10 m / sec. The displacement was measured from the point when the striker struck and the test force became 0 or greater until the point when the test force became 0.

[0105] Furthermore, the spring constant when a central load was applied to a flat plate was calculated as the slope of the curve within a range of approximately 5% to 40% of the test force. In the range in which the slope was calculated, vibrations were generated in the test specimen or the entire apparatus because the striker was in high-speed contact with the test specimen, affecting the test force data. Therefore, data within a range of two vibration cycles was used for the calculation. The slope indicates the initial modulus of elasticity, and a smaller slope value indicates softerness, i.e., higher shock absorption.

[0106] (Results) Figure 5 shows the results of the puncture impact test, and Table 1 shows the spring constant and R of each test specimen. 2 Show the value.

[0107]

[0108] Figure 5A shows the relationship between the test force from the striker impact (0 mm) to the stroke of 5 mm, and Figure 5B shows an enlarged view of the stroke range from 1 mm to 3.5 mm, indicated by the dashed-dotted line frame in Figure 5A.

[0109] In Figure 5 and Table 1, test piece a represents a composite fiber-reinforced resin made of CFRP-90 / bagworm silk nonwoven fabric of the present invention having the configuration of (a) above, test piece b represents a fiber-reinforced composite material made only of CFRP-90 having the configuration of (b) above, test piece c represents a comparative composite fiber-reinforced resin made of CFRP-90 / bagworm silk nonwoven fabric having the configuration of (c) above, and test piece d represents a comparative fiber-reinforced composite material made only of CFRP-90 having the configuration of (d) above.

[0110] The graph in Figure 5A clearly shows that the initial modulus of elasticity in the composite fiber-reinforced resin of test specimen a, which has the configuration of the present invention, is significantly lower than that of other composite fiber-reinforced resins. Furthermore, as shown in Table 1, the spring constant, which represents the slope of the linear approximation curve for each test specimen calculated between strokes of 1.35 mm and 3.5 mm, was significantly smaller only for the composite fiber-reinforced resin a, which has the configuration of the present invention, compared to other composite fiber-reinforced resins. As mentioned above, a smaller slope value indicates greater deformation under tensile stress, a softer property, and greater shock absorption capacity. On the other hand, in test specimen c, which has a similar layer structure to test specimen a, but in which the fiber directions of the two adjacent fiber-reinforced composite material layers are different, the slope (spring constant) value was almost the same as that of test specimens b and d, which consist of CFRP alone. In other words, this characteristic is obtained only when the fiber directions of three or more adjacent fiber-reinforced composite material layers are different, and a fiber layer containing a silkworm silk fiber sheet is arranged between those layers.

[0111] From the above results, it has been demonstrated that the composite fiber-reinforced resin having the configuration of the present invention has a significantly lower initial modulus of elasticity than composite fiber-reinforced resins or fiber-reinforced composite materials with other configurations. This suggests that the composite fiber-reinforced resin of the present invention has high impact resistance in the initial stages of a collision.

[0112] <Example 2> (Objective) To verify the strength obtained by tensile testing, which is one of the static property evaluations of the composite fiber-reinforced resin of the present invention.

[0113] (Method) The test specimens used were those of the composite fiber-reinforced resin (a) and (b) prepared in Example 1. However, the size of the test specimens was 15 mm × 140 mm.

[0114] A desktop precision universal testing machine, Autograph AGS-X (Shimadzu Corporation), was used for the measurements. The tensile test conditions were based on JIS K7127 (Plastics - Test methods for tensile properties). The load cell used was 5kN, the tensile speed was 5mm / min, the chuck clamping pressure was 0.4MPa or 0.1MPa, and the distance between chucks was 40mm. Each measurement was performed twice.

[0115] (Results) Figure 6 shows the results. The shapes of the SS curves, which show the relationship between strain and stress, were almost the same for both specimens A and B, and almost no difference was observed. This indicates that the tensile strength of the composite fiber-reinforced resin (A) having the structure of the present invention is no different from that of the control fiber-reinforced composite material (B) consisting only of CFRP. In other words, it suggests that placing a fiber layer containing a nonwoven fabric of cocoon silk threads between layers of reinforced fiber composite material does not affect the tensile strength.

[0116] <Example 3> (Objective) To verify the thermal decomposition properties of the composite fiber-reinforced resin of the present invention.

[0117] (Method) The test specimens used were the composite fiber-reinforced resin specimens (a) and (b) prepared in Example 1. The thermal decomposition properties of each specimen were investigated using thermogravimetric analysis (TG). A Thermo Plus TG8120 (Rigaku Corporation) was used for the measurement. Each specimen (a) and (b) (approximately 2 mg) was placed on a 5 mm diameter aluminum pan and measured in a 200 mL / min "air" stream at a heating rate of 10 °C / min.

[0118] (Results) Figure 7 shows the results. The composite fiber-reinforced resin of the present invention (a), shown by the solid line, showed a faster weight loss during heating between 350°C and 450°C than the fiber-reinforced composite material of CFRP alone (b). This indicates that the composite fiber-reinforced resin of the present invention has superior thermal decomposition properties compared to the fiber-reinforced composite material alone. In other words, the composite fiber-reinforced resin of the present invention can suppress the amount of thermal energy required for high-temperature processing during the recycling of CFRP. All publications, patents and patent applications cited herein are incorporated herein by direct reference.

Claims

1. A composite fiber-reinforced resin comprising a fiber-reinforced composite material layer made of a fiber-reinforced composite material having a certain fiber direction, and a fiber layer comprising a fiber sheet containing bagworm silk thread, wherein the fiber-reinforced composite material layer is laminated in three or more consecutive layers such that the fiber-reinforced composite materials constituting each adjacent layer have different fiber directions, and the fiber layer is disposed between each of the three or more consecutive fiber-reinforced composite material layers.

2. The composite fiber-reinforced resin according to claim 1, wherein the intersection angle of the fiber directions in the fiber-reinforced composite material constituting each of the adjacent layers is 50 degrees to 90 degrees.

3. The composite fiber-reinforced resin according to claim 1 or 2, wherein the fiber layer consists of a plurality of identical and / or different fiber sheets.

4. The composite fiber-reinforced resin according to any one of claims 1 to 3, wherein the fiber sheet is a nonwoven fabric.

5. The composite fiber-reinforced resin according to any one of claims 1 to 4, wherein the fiber-reinforced composite material is a carbon fiber reinforced plastic (CFRP) prepreg.

6. A composite fiber-reinforced resin according to any one of claims 1 to 5, which is a three-dimensional structure.

7. An impact absorbing material comprising a composite fiber-reinforced resin according to any one of claims 1 to 6.

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