Blade, method for manufacturing same, and flying body

Abstract

The present invention provides a blade capable of reducing the size of fragments generated when colliding with another object and being broken during rotation, and shortening a scattering distance of the fragments. The blade includes: a core material including a resin foam; and a skin material disposed on a surface of the core material, the skin material including a laminate in which a plurality of unidirectional reinforcement fiber layers are laminated, each of the layers including reinforcement fibers oriented and arranged in one direction and a matrix resin impregnated into the reinforcement fibers. Assuming that an angle in the direction from the root to the tip of the blade is 0° and a direction in which the blade moves during rotation is a direction in which the angle increases, the laminate includes a first alignment layer having a unidirectional reinforcement fiber layer in which the orientation direction of the reinforcement fibers is 10° to 65° inclusive, and a second alignment layer having a unidirectional reinforcement fiber layer in which the orientation direction of the reinforcement fibers is -65° to -10°.

Description

Blade, manufacturing method thereof, and projectile

[0001] The present invention relates to a blade, a manufacturing method thereof, and a flying object.

[0002] Blades that rotate or move through air or other fluids are used in wings and propellers of flying objects such as airplanes, helicopters, and drones, propellers of ships, and rotors (rotating bodies) such as windmill blades.

[0003] Patent Document 1 describes a blade made of composite materials to reduce weight. Patent Document 1 describes a blade having an outer portion made of a resin-impregnated preform made of a three-dimensional woven carbon fiber, and a blade core made of carbon fiber and resin disposed inside the outer portion. It also describes inserting a foam between the outer portion and the blade core to reduce the blade's weight. Patent Document 1 describes that the preform before resin impregnation is flexible and can be deformed to form an area into which the blade core can be inserted, while the outer portion after resin impregnation has impact resistance that can withstand impacts from solid objects. Patent Document 1 also uses thermosetting resins (epoxy resin and bismaleimide resin, respectively) for both the outer portion and the blade core, and a thermosetting resin (methacrylimide resin) for the foam.

[0004] Special Publication No. 2015-510469

[0005] As described in Patent Document 1, by using a fiber-reinforced resin for the outer portion of the blade, the impact resistance of the blade can be improved. However, no matter how much impact resistance is improved, when a blade rotating at high speed collides with another object, the blade will inevitably break. If large fragments resulting from the breakage fly far away, there is a risk of damaging surrounding objects or injuring people nearby.

[0006] The present invention has been made in consideration of the problems with the prior art described above, and aims to provide a blade that can reduce the size of the fragments that are generated when the blade collides with another object during rotation and breaks, and can shorten the distance that the fragments fly, as well as a method for manufacturing the same, and a flying object having such a blade.

[0007] One aspect of the present invention for solving the above problems relates to the blades described in [1] to

[12] below. [1] A blade having: a core material including a resin foam; and a skin material disposed on the surface of the core material, the skin material including a laminate formed of a plurality of unidirectional reinforcing fiber layers, the unidirectional reinforcing fiber layers including reinforcing fibers oriented in one direction and a matrix resin impregnated into the reinforcing fibers, wherein, when an angle from the root to the tip of the blade is defined as 0° and a direction in which the blade moves during rotation is defined as a direction in which the angle increases, the laminate includes a first orientation layer, which is the unidirectional reinforcing fiber layer, and a second orientation layer, which is the unidirectional reinforcing fiber layer, and an orientation direction of the reinforcing fibers of -65° to -10°. [2] The blade described in [1], wherein the laminate includes a third orientation layer, which is the unidirectional reinforcing fiber layer, and an orientation direction of the reinforcing fibers of -9° to 9°. [3] The blade according to [1] or [2], wherein the first orientation layer includes a layer in which the orientation direction of the reinforcing fibers is 10° or more and 35° or less. [4] The blade according to any of [1] to [3], wherein the second orientation layer includes a layer in which the orientation direction of the reinforcing fibers is -35° or more and -10° or less. [5] The blade according to any of [1] to [4], wherein the laminate has one layer of the first orientation layer and one layer of the second orientation layer on the outer side in the thickness direction of the core material. [6] The blade according to any of [1] to [5], wherein the ratio of the thickness of the first orientation layer and the second orientation layer to the thickness of the laminate is 70% or more and 100% or less. [7] The blade according to any of [1] to [6], wherein the ratio of the thickness of the unidirectional reinforcing fiber layer in which the orientation direction of the reinforcing fibers is -70° or more and 70° or less to the thickness of the laminate is 80% or more and 100% or less. [8] The blade according to any one of [1] to [7], wherein the core material is a resin foam having an expansion ratio of 1.1 to 15. [9] The blade according to any one of [1] to [8], wherein the core material is a resin foam of a thermoplastic resin, and the skin material is a laminate of the unidirectional reinforcing fiber layers formed by impregnating the reinforcing fibers with a thermoplastic resin.

[10] The blade according to any one of [1] to [9], wherein the core material is a resin foam containing polyolefin, and the skin material is a laminate of the unidirectional reinforcing fiber layers formed by impregnating the reinforcing fibers with polyolefin.

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

[10] , wherein the core material is a resin foam containing polypropylene, and the skin material is a laminate of the unidirectional reinforcing fiber layers formed by impregnating the reinforcing fibers with polypropylene.

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

[11] , wherein the reinforcing fibers are carbon fibers.

[0008] One aspect of the present invention for solving the above problems relates to a flying object according to the following item

[13] :

[13] A flying object having a blade according to any one of items [1] to

[12] .

[0009] One aspect of the present invention for solving the above problem relates to a blade manufacturing method according to

[14] below.

[14] A blade manufacturing method comprising the steps of: arranging, on a surface of a resin foam, a plurality of unidirectional fiber reinforced resin sheets, each sheet including reinforcing fibers oriented in one direction and a matrix resin or a material thereof impregnated into the reinforcing fibers; and molding the resin foam and the unidirectional fiber reinforced resin sheets, wherein, when a direction from the base to the tip of the blade is defined as 0° and a direction in which the blade moves during rotation is defined as a direction in which the angle increases, in the arranging step, the plurality of unidirectional fiber reinforced resin sheets are arranged so that the orientation direction of the reinforcing fibers is between 10° and 65°, and the unidirectional fiber reinforced resin sheets are arranged so that the orientation direction of the reinforcing fibers is between -65° and -10°.

[0010] According to the present invention, there are provided a blade that can reduce the size of fragments that are generated when the blade collides with another object during rotation and breaks, and can shorten the distance that the fragments fly, a method for manufacturing the blade, and a projectile having the blade.

[0011] FIG. 1 is a schematic perspective view of a drone according to one embodiment of the present invention. FIG. 2A is a plan view showing a blade of the drone shown in FIG. 1, and FIG. 2B is a cross-sectional view of the blade taken along line 2B-2B in FIG. 2A. FIG. 3A is a plan view of the blade, and FIG. 3B is an exploded view showing an exemplary layer configuration of the upper and lower skin and core materials that make up the blade. FIG. 4A is a plan view of a conventional blade having a fiber-reinforced resin skin material without a first orientation layer and a second orientation layer and a resin foam core material. FIG. 4B is a cross-sectional view of the blade taken along dashed line 4B-4B in FIG. 4A, showing the tip portion of the blade. FIG. 4C is a plan view of a blade according to this embodiment having a fiber-reinforced resin skin material with a first orientation layer and a second orientation layer and a resin foam core material. FIG. 4D is a cross-sectional view of the blade taken along dashed line 4D-4D in FIG. 4C, showing the tip portion of the blade. Fig. 5A is a partial cross-sectional view showing the state of the first orientation layer and the second orientation layer in the blade of this embodiment before collision, and Fig. 5B is a partial cross-sectional view showing the state of the first orientation layer and the second orientation layer in the blade of this embodiment after collision. Fig. 6A is an exemplary schematic diagram showing a process of arranging multiple sheets of unidirectional fiber-reinforced resin on the surface of a resin foam during blade manufacturing, and Fig. 6B is an exemplary schematic diagram showing a process of heating and pressurizing them to form them.

[0012] Fig. 1 is a schematic perspective view of a drone 100 (air vehicle) according to one embodiment of the present invention. As shown in Fig. 1, the drone 100 has a body 110, a plurality of blades 200, a plurality of arms 120 connecting the blades 200 to the body 110, and legs 130. By rotating each blade 200, the drone 100 can fly and move while flying.

[0013] The fuselage 110 has a lower body and an upper body joined by a plurality of bolts. In this embodiment, the fuselage 110 has a so-called monocoque structure in which stress is borne by the outer shells of the lower body and the upper body. Specifically, the lower body and the upper body are maintained in shape by lower and upper outer shells made of fiber-reinforced resin. Resin, preferably thermoplastic resin, reinforcing members are fused to the lower and upper outer shells on the inside of the housings of the lower and upper outer shells to increase the rigidity of the lower and upper bodies. The lower and upper bodies are joined to each other via the reinforcing members. This structure allows the fuselage 110 to be both lightweight and rigid.

[0014] 1. Blade 200 FIG. 2A is a plan view showing the blade 200 of the drone 100, and FIG. 2B is a cross-sectional view of the blade 200 taken along line 2B-2B in FIG. 2A.

[0015] 2A, the blade 200 has a plate-like shape. In this embodiment, two blades 200, each having the same shape, are fastened by a fastener at a center 210, which serves as the rotation axis, and are arranged rotationally symmetrically in opposite directions such that the angle between the blades is 180°.

[0016] 2A and 2B, the blade has a thin, flat shape. It has a cross-sectional shape in which one surface is convex and the other surface is concave. Hereinafter, the convex surface side will be referred to as the "front side," and the concave surface side will be referred to as the "back side."

[0017] 2A and 2B, the blade 200 has a thick main body portion 220 located at the front in the rotational direction and a thin flap portion 230 located at the rear in the rotational direction. The flap portion 230 preferably has a thickness equal to or less than half the thickness of the main body portion 220. A fastening hole (not shown) for attaching the blade 200 to a fastener is formed at one axial end of the blade 200.

[0018] Both the main body portion 220 and the flap portion 230 have a skin material 240 containing a fiber-reinforced resin and a core material 250 containing a resin foam filled inside the skin material 240 ( FIG. 2B ). The main body portion 220 and the flap portion 230 are integrally molded. "Integrated molding" means that the blade 200, which includes the main body portion 220 and the flap portion 230, is formed in a single molding process. The fact that the blade 200 is an integrally molded product can be confirmed by the absence of a joint (seam) between the main body portion 220 and the flap portion 230.

[0019] With this configuration, the core material 250 containing foam can reduce the weight of the blade 200, while the skin material 240 containing fiber-reinforced resin can impart rigidity to the blade 200. Therefore, the blade 200 is both lightweight and rigid in both the main body portion 220 and the flap portion 230.

[0020] Blade 200 may include components other than skin material 240 and core material 250, such as girders and voids (not shown). However, from the viewpoint of increasing the effect of breaking down fragments into smaller pieces and shortening the scattering distance, it is preferable not to include girders. Furthermore, from the viewpoint of increasing the rigidity of blade 200, it is preferable not to include voids.

[0021] The length of the blade 200 in the direction from the rotation axis toward the tip of the blade (the X direction in each figure; hereinafter simply referred to as the "tip direction"; the direction perpendicular to the tip direction in a plan view of the blade 200 (the Y direction in each figure) is also simply referred to as the "width direction," and the direction in which the skin material 240 and the core material 250 are layered (the Z direction in each figure) is also simply referred to as the "thickness direction") is preferably 20 cm or more and 50 cm or less, more preferably 25 cm or more and 45 cm or less, and even more preferably 30 cm or more and 40 cm or less. The length of the blade 200 in the width direction is preferably 20 mm or more and 80 mm or less, more preferably 25 mm or more and 70 mm or less, and even more preferably 30 mm or more and 60 mm or less.

[0022] Furthermore, the thickness of the blade 200 is preferably 0.3 mm or more and 20.0 mm or less, more preferably 3.0 mm or more and 15.0 mm or less, and even more preferably 3.5 mm or more and 12.0 mm or less.

[0023] The thickness of the flap portion 230 is preferably 0.3 mm to 10.0 mm, more preferably 0.4 mm to 7.0 mm, and even more preferably 0.5 mm to 5.0 mm. The maximum width of the flap portion 230 is preferably 1 / 10 to 2 times the maximum width of the main body portion 220, more preferably 1 / 7 to 1.5 times, and even more preferably 1 / 4 to 1 time.

[0024] The thickness of the skin material 240 is preferably 0.05 mm to 3.0 mm, more preferably 0.1 mm to 2.0 mm, and even more preferably 0.3 mm to 1.0 mm. The thickness of the skin material 240 in the main body 220 is not particularly limited, but may be the same as the thickness of the skin material 240 in the flap portion 230.

[0025] The thickness ratio between the skin material 240 and the core material 250 (skin material / core material) is preferably 1 / 25 or more and 2 / 1 or less, more preferably 1 / 20 or more and 1 / 1 or less, and even more preferably 1 / 15 or more and 1 / 2 or less. Note that in the above ratio, the thickness of the skin material 240 is the sum of the thicknesses of the two skin materials 240 that sandwich the core material 250 from above and below. Furthermore, the thicknesses of the skin material 240 and the core material 250 used to calculate the above ratio are values ​​obtained by measuring the thickness and width of the flap portion 230 at the measurement locations described above.

[0026] 2A and 2B , the widthwise length and thickness of the blade 200 and the flap portion 230 may vary depending on the location. In this specification, the widthwise length of the blade 200 refers to the widthwise length at the position where the widthwise length is greatest, and the widthwise length of the flap portion 230 refers to the widthwise length of the flap portion 230 at the position where the widthwise length of the blade 200 is measured. Furthermore, the thickness of the blade 200 refers to the thickness of the blade 200 at the thickest position on an imaginary line segment along which the widthwise length of the flap portion 230 is measured, and the thickness of the flap portion 230 refers to the thickness of the flap portion 230 at a position 2 mm from the rear end on the same imaginary line segment.

[0027] The skin material 240 includes a laminated body in which multiple unidirectional reinforcing fiber layers are stacked, each layer containing reinforcing fibers oriented in one direction and a matrix resin impregnated into the reinforcing fibers. The unidirectional reinforcing fiber layers increase the rigidity of the skin material 240, thereby increasing the rigidity of the blade 200.

[0028] 1-1-1. Reinforcing Fibers The type of reinforcing fiber is not particularly limited, and carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, and the like can be used. Of these, carbon fiber and aramid fiber are preferred because they have low density, particularly from the perspective of reducing the weight of the flap portion 230 and further increasing its specific rigidity. Carbon fiber, in particular, is less likely to peel at the interface with the matrix resin, making it easier to increase the strength of the blade 200. Furthermore, carbon fiber is less likely to crack when subjected to impact and is more likely to absorb stress, making the blade 200 less likely to break.

[0029] From the viewpoint of sufficiently enhancing the effect of improving rigidity, the average diameter of the reinforcing fibers is preferably 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less.

[0030] The length of the reinforcing fibers is usually 15 mm or more, preferably 20 mm or more, and more preferably 100 mm or more. In particular, the reinforcing fibers are preferably continuous fibers that are continuous from end to end of the unidirectional reinforcing fiber layer in the orientation direction of the reinforcing fibers. Furthermore, it is preferable that each reinforcing fiber is continuously arranged from end to end when the blade 200 is viewed in plan. The length of each reinforcing fiber can be determined by the distance from the front end to the rear end of the blade 200 at the position where the reinforcing fiber is arranged.

[0031] The reinforcing fibers may be subjected to a sizing treatment with a sizing agent.

[0032] Although the sizing agent is not particularly limited, modified polyolefins are preferred, and modified polyolefins containing metal carboxylates are more preferred. Modified polyolefins are, for example, polyolefins in which carboxylic acid groups, carboxylic anhydride groups, or carboxylic ester groups are grafted onto the polymer chains of unmodified polyolefins, and salts are formed between the functional groups and metal cations. These sizing agents may be derived from fossil fuels, biomass materials, or mixtures thereof.

[0033] The unmodified polyolefin is preferably an ethylene polymer having a content of structural units derived from ethylene of 50 mol% or more, or a propylene polymer having a content of structural units derived from propylene of 50 mol% or more. Examples of the ethylene polymer include an ethylene homopolymer and a copolymer of ethylene and an α-olefin having from 3 to 10 carbon atoms. Examples of the propylene polymer include a propylene homopolymer and a copolymer of propylene and ethylene or an α-olefin having from 4 to 10 carbon atoms. The unmodified polyolefin is preferably homopolypropylene, homopolyethylene, an ethylene-propylene copolymer, a propylene-1-butene copolymer, or an ethylene-propylene-1-butene copolymer.

[0034] The reinforcing fibers may be bundled into a fiber bundle. In this case, the number of single fibers per bundle of carbon fibers is preferably 100 to 100,000, and more preferably 1,000 to 50,000.

[0035] The content of the reinforcing fibers relative to the total mass of the skin material 240 is preferably 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 75% by mass or less, even more preferably 30% by mass or more and 70% by mass or less, and particularly preferably 35% by mass or more and 70% by mass or less.

[0036] The content of reinforcing fibers relative to the total volume of the skin material 240 is preferably 10% by volume or more and 70% by volume or less, more preferably 15% by volume or more and 60% by volume or less, and even more preferably 20% by volume or more and 60% by volume or less.

[0037] 1-1-2. Matrix Resin The matrix resin that holds the reinforcing fibers in the skin material 240 may be a thermoplastic resin or a thermosetting resin. The matrix resin may be a crystalline resin or a non-crystalline resin.

[0038] Examples of thermoplastic resins constituting the matrix resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and poly4-methyl-1-pentene, polyamide resins, polyester resins, polystyrene resins, thermoplastic polyimide resins, polyamideimide resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, acrylic resins, polyetherimide resins, polysulfone resins, polyether ketone resins, polyether ether ketone resins, polyarylate resins, polyether nitrile resins, vinyl chloride resins, ABS resins, and fluororesins. These thermoplastic resins may be derived from fossil fuels, biomass materials, or mixtures thereof.

[0039] Examples of thermosetting resins that constitute the matrix resin include epoxy resins, phenolic resins, melamine resins, urea resins, diallyl phthalate resins, silicone resins, urethane resins, furan resins, ketone resins, xylene resins, thermosetting polyimide resins, unsaturated polyester resins, and diallyl terephthalate resins. These thermosetting resins may be derived from fossil fuels, biomass materials, or mixtures thereof.

[0040] Among these, the matrix resin is preferably a thermoplastic resin from the viewpoint of enhancing the effects of fragmentation and shortening the scattering distance. As described below, it is believed that the skin material 240 of the present invention is more likely to absorb stress due to the misalignment (plastic deformation) of the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320. Therefore, when the matrix resin is a thermoplastic resin, the plastic deformation is easier than with a thermosetting resin, and the effects of fragmentation and shortening the scattering distance are more likely to be enhanced. Furthermore, from the viewpoint of making the blade 200 less susceptible to damage even when impacted by flying objects such as pebbles, a thermoplastic resin is preferred, with polyamide resin and polyolefin resin being more preferred. Furthermore, from the viewpoint of suppressing the deterioration of mechanical properties when the skin material 240 absorbs water, a polyolefin resin is more preferred, and a polypropylene resin is even more preferred.

[0041] The matrix resin may be a resin composition containing additives. Examples of additives include known fillers (inorganic fillers, organic fillers), pigments, dyes, weathering stabilizers, heat stabilizers, antistatic agents, antislip agents, antioxidants, antifungal agents, antibacterial agents, flame retardants, and softeners. For example, when the matrix resin is melted by laser irradiation to fuse the unidirectional reinforcing fiber layers together, the matrix resin is preferably a resin composition containing a dye that absorbs the laser at the irradiated wavelength. The dye may be any dye that absorbs light with a wavelength between 300 nm and 3000 nm, and is preferably carbon black.

[0042] The matrix resin may also contain other components such as resins other than those mentioned above and short fibers shorter than the carbon fibers mentioned above.

[0043] The content of the matrix resin relative to the total mass of the skin material 240 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, even more preferably 30% by mass or more and 70% by mass or less, and particularly preferably 30% by mass or more and 65% by mass or less.

[0044] The content of the matrix resin relative to the total volume of the skin material 240 is preferably 30% by volume or more and 90% by volume or less, more preferably 40% by volume or more and 85% by volume or less, and even more preferably 40% by volume or more and 80% by volume or less.

[0045] 1-1-3. Lamination of Unidirectional Reinforcing Fiber Layers The skin material 240 includes a laminate in which a plurality of unidirectional reinforcing fiber layers having reinforcing fibers with different orientation directions are laminated.

[0046] 3A is a plan view of the blade 200, and FIG. 3B is an exploded view showing an exemplary layer configuration of the upper and lower skin materials 240 and the core material 250 that make up the blade 200.

[0047] When the angle from the root of blade 200 (the portion where blade 200 is attached to body portion 110) toward the tip is defined as 0°, and the direction in which blade 200 moves during rotation is defined as the direction in which the angle increases, the laminate has a first orientation layer 310 that is a unidirectional reinforcing fiber layer in which the orientation direction of reinforcing fibers is 10° or more and 65° or less, and a second orientation layer 320 that is a unidirectional reinforcing fiber layer in which the orientation direction of reinforcing fibers is -65° or more and -10° or less. The first orientation layer 310 and the second orientation layer 320 are layers that break down fragments generated upon collision of blade 200 into small pieces and shorten the scattering distance of the fragments. Furthermore, the first orientation layer 310 and the second orientation layer 320 orient the reinforcing fibers at a predetermined angle relative to the tip direction of blade 200, thereby increasing the strength of blade 200 in the width direction.

[0048] A unidirectional reinforcing fiber layer is a layer containing a matrix resin and reinforcing fibers oriented in the same direction within the same layer. Therefore, a layer in which the reinforcing fibers are oriented in one direction and a layer in which the reinforcing fibers are oriented in a different direction are different unidirectional reinforcing fiber layers. When a unidirectional reinforcing fiber layer is manufactured by continuously stacking multiple layers so that the reinforcing fibers are oriented in the same direction, observing the cross section of the skin material 240 reveals that the reinforcing fibers in the lower layer form a single reinforcing fiber cluster, while the reinforcing fibers in the upper layer form a different reinforcing fiber cluster. Even if layers with reinforcing fibers oriented in the same direction are continuously arranged in the stacking direction, if they are formed as separate layers during manufacturing and the clusters of reinforcing fibers are observed as separate clusters in the cross section (i.e., matrix resin-rich regions are observed between the clusters of reinforcing fibers above and below), these are considered to be different unidirectional reinforcing fiber layers.

[0049] FIG. 4A is a plan view showing a conventional blade 400 having a fiber-reinforced resin skin material 440 that does not have a first orientation layer 310 or a second orientation layer 320, and a resin foam core material 450, and FIG. 4B is a cross-sectional view of the blade 400 taken along dashed line 4B-4B in FIG. 4A, which is the tip portion of the blade 400.

[0050] When the rotating blade 400 collides with another object, the front side of the tip of the blade 400 in the direction of rotation (the region indicated by S in FIG. 4A ) comes into contact with the object first. At this time, stress is generated in the blade 400 in the width direction (in the −90° direction) from region S toward the opposite side of the direction of rotation. The skin material 440 made of fiber-reinforced resin has high rigidity and is therefore resistant to plastic deformation. For this reason, the skin material 440 is prone to brittle fracture during a collision, and it is thought that cracks 410 in the direction of stress will occur preferentially in the skin material 440 ( FIG. 4A ).

[0051] When blade 400 breaks, it is believed that skin material 440 and core material 450 break along crack 410. Therefore, when blade 400 breaks, thick and large fragments 420 are likely to be generated ( FIG. 4B ), while the layered structure of skin material 440 and core material 450 remains intact. These fragments 420 are heavy, and their scattering speed is not likely to decrease even when subjected to air resistance, so they tend to scatter far away.

[0052] FIG. 4C is a plan view showing blade 200 of this embodiment, which has skin material 240 having first alignment layer 310 and second alignment layer 320, and core material 250, and FIG. 4D is a cross-sectional view of blade 200 taken along dashed line 4D-4D in FIG. 4C, which is the tip portion of blade 200.

[0053] 5A is a partial cross-sectional view showing the state of the first orientation layer 310 and the second orientation layer 320 of the blade 200 of this embodiment before collision, and FIG. 5B is a partial cross-sectional view showing the state of the first orientation layer 310 and the second orientation layer 320 of the blade 200 of this embodiment after collision. The orientation direction of the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320 is tilted toward the 0° direction relative to 90°. Therefore, when stress in the -90° direction occurs during a collision, the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320 tend to shift within the layer in the stress direction (so that the orientation direction of the reinforcing fibers becomes closer to the 0° direction) ( FIGS. 5A and 5B ), and it is thought that this shift (plastic deformation) makes it easier to absorb stress.

[0054] Therefore, in blade 200 of this embodiment, it is thought that cracks are unlikely to occur in skin material 240 upon impact, and cracks 412 occur preferentially in core material 250. Furthermore, the portion of core material 250 near the interface with skin material 240 is likely to be crushed and hardened by pressure applied during manufacturing, and is therefore relatively resistant to cracking, so in this embodiment, cracks 412 occur preferentially in the tip direction or width direction in the center of core material 250 ( FIG. 4C ).

[0055] As a result, when blade 200 breaks, it is believed that core material 250 breaks preferentially along crack 412. Therefore, when blade 200 breaks, relatively thin fragments 422 are likely to be produced. Furthermore, due to the above-mentioned misalignment of the reinforcing fibers, delamination occurs between each unidirectional reinforcing fiber layer in skin material 240, and fragments 424 of the thin skin material layer are also likely to be produced. These fragments 422 and 424 are lightweight and thin, so they experience significant air resistance and are unlikely to fly far.

[0056] In this way, by constructing the skin material 240 using the first orientation layer 310 and the second orientation layer 320, it is believed that it is possible to reduce the size of the fragments 422 and 424 that are generated when the blade 200 collides with another object during rotation and is broken, and to shorten the distance that these fragments fly.

[0057] The first orientation layer 310 and the second orientation layer 320 are layers in which the reinforcing fibers are inclined toward the tip (0° direction). Therefore, these layers suppress deflection of the blade 200 toward the tip during rotation (bending of the blade 200 toward the tip and displacement of the tip in the thickness direction), thereby also having the effect of increasing the durability of the blade 200. From the viewpoint of more effectively achieving both the reduction of fragmentation and the shortening of scattering distance through the above-mentioned action, and the suppression of deflection of the blade 200, the orientation direction of the reinforcing fibers in the first orientation layer 310 is preferably 10° or more and 50° or less. Furthermore, from the viewpoint of further enhancing the effect of reducing fragmentation and the shortening of scattering distance, the orientation direction of the reinforcing fibers in the first orientation layer 310 is more preferably 10° or more and 35° or less. Similarly, the orientation direction of the reinforcing fibers in the second orientation layer 320 is preferably -50° or more and -10° or less, and more preferably -35° or more and -10° or less. Furthermore, the angle between the orientation directions of the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320 is preferably less than 90° (acute angle), more preferably 80° or less, and even more preferably 70° or less. When the angle between the orientation directions of the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320 is less than 90°, the reinforcing fibers in the first orientation layer 310 and the second orientation layer 320 are more likely to be displaced (plastically deformed), which further enhances the effect of reducing the fragments and shortening the scattering distance. Note that this angle is the angle between the orientation directions of the reinforcing fibers in the layer of the first orientation layer 310 with the smallest orientation direction of the reinforcing fibers and the layer of the second orientation layer 320 with the largest orientation direction of the reinforcing fibers.

[0058] On the other hand, from the viewpoint of more effectively suppressing deflection of the blade 200, the laminate preferably includes a third orientation layer 330 that is a unidirectional reinforcing fiber layer in which the orientation direction of the reinforcing fibers is between -9° and 9°. The third orientation layer 330 is a layer in which the reinforcing fibers are oriented in the tip direction, and suppresses deflection of the blade 200 in the tip direction. The orientation direction of the reinforcing fibers in the third orientation layer 330 is preferably between -5° and 5°, and more preferably between -3° and 3°.

[0059] The number of these layers is not particularly limited. From the viewpoint of reducing the weight of the blade 200, it is preferable that the number of reinforcing fiber layers constituting the laminate is small. Specifically, it is preferable that the laminate has only one first orientation layer 310 and only one second orientation layer 320 on both the front and back sides, that is, on the outer side in the thickness direction, of the core material 250. When the third orientation layer 330 is included, it is preferable that the laminate has only one third orientation layer 330 on both the front and back sides, that is, on the outer side in the thickness direction, of the core material 250. In this embodiment, the skin material 240 has one each of the first orientation layer 310, the second orientation layer 320, and the third orientation layer 330 on the front side of the blade 200 (upward in the plane of FIG. 2B ), and one each of the first orientation layer 310, the second orientation layer 320, and the third orientation layer 330 on the back side of the blade 200 (downward in the plane of FIG. 2B ).

[0060] The laminate may have multiple layers of any one or more of the first orientation layer 310, the second orientation layer 320, and the third orientation layer 330. When multiple layers are included, the number of each layer is preferably 2 to 4, more preferably 2 to 3, and even more preferably 2. When the laminate has multiple first orientation layers 310, the multiple first orientation layers 310 may include multiple layers in which the orientation direction of the reinforcing fibers is the same, or may include layers in which the orientation directions are different. Similarly, when the laminate has multiple second orientation layers 320, the multiple second orientation layers 320 may include multiple layers in which the orientation direction of the reinforcing fibers is the same, or may include layers in which the orientation directions are different. Similarly, when the laminate has multiple third orientation layers 330, the multiple third orientation layers 330 may include multiple layers in which the orientation direction of the reinforcing fibers is the same, or may include layers in which the orientation directions are different.

[0061] In addition, from the viewpoint of enhancing the effect of shortening the scattering distance of fragments, the ratio of the thickness of the first orientation layer 310 and the second orientation layer 320 to the total thickness of the laminate is preferably 70% or more, and more preferably 70% or more and 100% or less. The greater the ratio of the thickness of the first orientation layer 310 and the second orientation layer 320, the more likely it is that when stress in the -90° direction occurs during a collision, the reinforcing fibers of the first orientation layer 310 and the second orientation layer 320 will be displaced in the stress direction within the layer (so that the orientation direction of the reinforcing fibers is closer to the 0° direction) (Figures 5A and 5B), and this displacement (plastic deformation) is thought to make it easier to absorb stress.

[0062] The arrangement of these layers is not particularly limited. For example, the position of the third alignment layer 330 is not particularly limited, but it is preferably arranged between the first alignment layer 310 and the second alignment layer 320 and the core material 250, or arranged outside the first alignment layer 310 and the second alignment layer 320.

[0063] The laminate may be composed solely of a reinforcing fiber layer in which the reinforcing fibers do not form a woven or knitted fabric (hereinafter simply referred to as a "non-woven fabric layer"). Alternatively, the laminate may include a reinforcing fiber layer in which the reinforcing fibers form a woven or knitted fabric (hereinafter simply referred to as a "woven fabric layer"). However, non-woven fabric layers are more susceptible to displacement of the reinforcing fibers during a collision than woven fabric layers. Therefore, it is preferable that the laminate include more non-woven fabric layers than woven fabric layers. Specifically, the ratio of the thickness of the non-woven fabric layers to the thickness of the laminate is preferably 50% to 100%, more preferably 80% to 100%, even more preferably 90% to 100%, and most preferably 100%, i.e., the laminate is composed solely of non-woven fabric layers and does not include a woven fabric layer.

[0064] The laminate may also have layers different from the first orientation layer 310, the second orientation layer 320, and the third orientation layer 330. When the laminate has such different layers, the layers may be unidirectional reinforcing fiber layers or other layers, but are preferably unidirectional reinforcing fiber layers. The unidirectional reinforcing fiber layer as the different layer is a unidirectional reinforcing fiber layer having a different orientation direction of the reinforcing fibers from those of the first orientation layer 310, the second orientation layer 320, and the third orientation layer 330. The other layers may be reinforcing fiber layers or resin layers that are not unidirectional reinforcing fiber layers. However, from the viewpoint of increasing the strain in the width direction of the skin material 240 due to stress during a collision and suppressing brittle fracture in the width direction ( FIG. 4B ), it is preferable that the laminate have as its main constituent layers unidirectional reinforcing fiber layers whose reinforcing fiber orientation direction is between −70° and 70°. Specifically, the ratio of the thickness of the unidirectional reinforcing fiber layers in which the reinforcing fibers are oriented at an angle of -70° to 70° to the thickness of the laminate is preferably 80% to 100%, more preferably 90% to 100%, even more preferably 95% to 100%, and most preferably 100%, i.e., the laminate is composed solely of unidirectional reinforcing fiber layers in which the reinforcing fibers are oriented at an angle of -70° to 70°. Furthermore, it is preferable that there are no other layers between the unidirectional reinforcing fiber layers. The absence of other layers between the unidirectional reinforcing fiber layers makes the above-mentioned interlayer delamination more likely to occur, resulting in the generation of fragments 424 of the thin skin material 240 layer. Furthermore, it is preferable that the reinforcing fibers contained in the unidirectional reinforcing fiber layers are not integrated with the reinforcing fibers contained in adjacent unidirectional reinforcing fiber layers by being woven with stitch yarn. Since the reinforcing fibers contained in the unidirectional reinforcing fiber layer are not integrated with the reinforcing fibers contained in the adjacent unidirectional reinforcing fiber layer by being woven with stitch threads, the above-mentioned interlayer delamination is likely to occur, and fragments 424 of the thin skin material layer are likely to occur.

[0065] The skin material 240 may have layers other than the laminate described above. For example, the skin material 240 may have a surface protection layer or an adhesive layer that bonds the laminate and the core material 250 together.

[0066] The skin material 240 may have the same or different layer configuration of the laminate on the front side and the back side of the blade 200. When the layer configuration is the same, the skin material 240 may have symmetrical laminates on the front side and the back side of the blade 200 (i.e., the layers are laminated in the same order from the core material 250 side toward the surface side) or may have asymmetrical laminates.

[0067] The thickness of the skin material 240 is not particularly limited, but is preferably 0.1 mm to 2.0 mm, and more preferably 0.3 mm to 1.0 mm. The thicker the skin material 240, the more rigid the blade can be, making it less likely to bend during rotation. The thinner the skin material 240, the lighter the blade 200 can be.

[0068] 1-2 Core Material 250 The core material 250 includes a resin foam. The resin foam may be a thermoplastic resin foam or a thermosetting resin foam.

[0069] Examples of thermoplastic resins constituting the foam include polyolefin resins such as polyethylene, polypropylene, polybutene, and poly4-methyl-1-pentene, polyamide resins, polyester resins, polystyrene resins, thermoplastic polyimide resins, polyamideimide resins, polycarbonate resins, polyphenylene ether resins, polyphenylene sulfide resins, polyacetal resins, acrylic resins, polyetherimide resins, polysulfone resins, polyetherketone resins, polyetheretherketone resins, polyarylate resins, polyethernitrile resins, vinyl chloride resins, ABS resins, urethane resins, and fluororesins. These thermoplastic resins may be derived from fossil fuels, biomass materials, or mixtures thereof.

[0070] Examples of the thermosetting resin that constitutes the foam include epoxy resin, phenolic resin, melamine resin, urea resin, diallyl phthalate resin, silicone resin, urethane resin, furan resin, ketone resin, xylene resin, thermosetting polyimide resin, unsaturated polyester resin, diallyl terephthalate resin, etc. These thermosetting resins may be derived from fossil fuels, may be derived from biomass raw materials, or may be a mixture thereof.

[0071] The matrix resin of the skin material 240 and the resin constituting the foam in the core material 250 are preferably the same type of resin. In this specification, "same type of resin" means that the bonding method between the structural units (repeating units) in the main chain of the resins is the same between the resins. For example, when the matrix resin of the skin material 240 is a polyamide resin, the thermoplastic resin constituting the foam in the core material 250 is preferably also a polyamide resin. When the matrix resin of the skin material 240 is a polyolefin resin, the thermoplastic resin constituting the foam in the core material 250 is preferably also a polyolefin resin. Resins of the same type have a high affinity for each other and tend to intermix at the interface between the skin material 240 and the core material 250. This intermixing can increase the bonding strength between the skin material 240 and the core material 250. In this specification, "same type of resin" means that these resins account for 50% by mass or more of the total mass of the matrix resin and the thermoplastic resin constituting the foam.

[0072] Furthermore, it is preferable that the matrix resin of the skin material 240 and the resin constituting the foam in the core material 250 are compatible with each other. This allows these resins to be compatible during the molding of the blade, thereby increasing the bonding strength between the skin material 240 and the core material 250. Note that "compatible" means that these resins (three types of resins, two types of matrix resins and one resin constituting the foam, if the matrix resins contained in the upper and lower skin materials 240 are different) are combined to a temperature higher than the melting points of all the resins, mixed, and then cooled to 25°C to form a single phase.

[0073] Furthermore, the difference in melting point between the thermoplastic resin that is the matrix resin of the skin material 240 and the thermoplastic resin that constitutes the foam in the core material 250 is preferably within 10°C. If the matrix resins contained in the upper and lower skin materials 240 are different, the difference in melting point between either matrix resin and the thermoplastic resin that constitutes the foam may be within 10°C, but it is preferable that the difference in melting point between both matrix resins and the thermoplastic resin that constitutes the foam be within 10°C. During hot press molding, it is desirable to heat both resins to a temperature at which they can sufficiently flow and deform. At this time, if the melting points of both resins are close to each other, they will flow sufficiently and easily mix and dissolve. Furthermore, setting the heating temperature to match the resin with a higher melting point can prevent deterioration of the other resin and collapse of the foam shape.

[0074] The glass transition temperature (Tg) of the resin constituting the foam is not particularly limited, but is preferably −50° C. or higher and 160° C. or lower, and more preferably −20° C. or higher and 80° C. or lower. The higher the Tg, the greater the rigidity of blade 200. The lower the Tg, the more likely it is that crack 412 ( FIG. 4C ) will occur in the center of core material 250 upon impact, making it easier to break down fragments generated upon impact of blade 200 into smaller pieces and shortening the distance the fragments will fly.

[0075] The density of the foam is preferably 0.2 g / cc or more and 0.6 g / cc or less, and more preferably 0.25 g / cc or more and 0.4 g / cc or less. The cells in the foam may be closed cells or open cells. Of these, closed cells are preferred because they have higher strength.

[0076] The expansion ratio of the foam is preferably 1.1 to 15, more preferably 1.1 to 10, even more preferably 1.1 to 5, and particularly preferably 1.1 to 4. The lower the density of the foam or the higher the expansion ratio, the more easily the blade 200 can be molded and the lighter the blade 200 can be. The higher the density of the foam or the lower the expansion ratio, the less likely the blade 200 to have poor appearance during molding.

[0077] The thickness of the core material 250 is not particularly limited, but is preferably 2 mm to 20 mm, and more preferably 4 mm to 12 mm. The thicker the core material 250, the less likely it is to deform, and the thinner the core material 250, the lighter it can be. The thickness of the core material 250 is measured at the position where the thickness of the blade 200 described above is measured.

[0078] 2. Blade Manufacturing Method The method for manufacturing the blade 200 is not particularly limited. For example, the blade 200 can be manufactured by arranging a plurality of unidirectional fiber-reinforced resin sheets 650 on the surface of a resin foam 660 (arranging step), and then molding the sheets by heating and pressurizing them as necessary (molding step). Fig. 6A is an exemplary schematic diagram showing the arrangement step, and Fig. 6B is an exemplary schematic diagram showing the molding step.

[0079] (Placing Step) In the placing step, resin foam 660 and unidirectional fiber-reinforced resin sheet 650 are prepared, each having a planar shape that is substantially identical to or similar to the shape of blade 200 when viewed from the same direction. Here, resin foam 660 may be flat, or a flat resin foam 660 formed by press molding or the like into a shape that is substantially identical to or similar to the shape of blade 200 in three dimensions may be used. The shapes and sizes of resin foam 660 and sheet 650 do not need to completely match the shape and size of blade 200. The shapes and sizes of resin foam 660 and sheet 650 to be prepared should be determined taking into account deformation due to resin flow during molding and the like, and such that sheet 650 covers the entire periphery of resin foam 660 when blade 200 is molded.

[0080] The resin foam 660 may be a foam of the resin that is the material of the core material 250. The expansion ratio of the foam varies depending on the location on the blade, but at the location of the maximum thickness of the blade, it is almost maintained before and after the next process (hot pressing).

[0081] The sheet 650 is a unidirectional fiber-reinforced resin sheet including reinforcing fibers oriented in one direction and a matrix resin impregnated into the reinforcing fibers. Specifically, the sheet 650 is a sheet-like fiber-reinforced resin formed by impregnating the reinforcing fibers of the skin material 240 with the matrix resin or the matrix resin. When a thermosetting resin is used as the matrix resin, a prepreg impregnated with the uncured material may be placed in this step.

[0082] In this process, a unidirectional fiber-reinforced resin sheet 650 formed so that the orientation direction of the reinforcing fibers is 10° to 65° in plan view and a unidirectional fiber-reinforced resin sheet 650 formed so that the orientation direction of the reinforcing fibers is -65° to -10° in plan view are arranged. Depending on the layer configuration of the laminate, a unidirectional fiber-reinforced resin sheet 650 formed so that the orientation direction of the reinforcing fibers is -9° to 9° in plan view may be prepared, or other sheets may be prepared. The orientation direction of the reinforcing fibers in these sheets 650 may be the same as the orientation direction of the reinforcing fibers in each layer of the laminate. Note that the orientation and dispersion state of the reinforcing fibers are substantially maintained before and after the next process (molding).

[0083] The multiple sheets 650 are arranged on the front and back sides of the resin foam 660 in the same order as the layer structure of the laminate in the blade 200 .

[0084] The sheet 650 may be placed in direct contact with the resin foam 660, or may be placed between the sheet 650 and the resin foam 660 via an adhesive layer, depending on the bonding form between the skin material 240 and the core material 250.

[0085] (Molding Process) Next, resin foam 660 and multiple sheets 650 placed on the surface of resin foam 660 are molded. For example, resin foam 660 and multiple sheets 650 may be placed inside a mold ( FIG. 6A ; the placing process may also be performed inside the mold), and then heated and pressurized to fuse resin foam 660 and sheets 650 together, and to fuse multiple sheets 650 together. In this case, if the resin used to make resin foam 660 (the resin that constitutes the foam in core material 250) and the resin impregnated in sheets 650 (the matrix resin of skin material 240) are the same type of resin, resin foam 660 and sheets 650 are easily fused together, and the bonding strength between skin material 240 and core material 250 is increased.

[0086] The heating temperature is not particularly limited. For example, when resin foam 660 and sheet 650 contain thermoplastic resins, the heating temperature is preferably −20° C. or higher and 50° C. or lower than the melting points of these thermoplastic resins (when they contain different types of thermoplastic resins, the melting point of the thermoplastic resin with the highest melting point), more preferably −10° C. or higher and 30° C. or lower, and even more preferably 0° C. or higher and 20° C. or lower. When resin foam 660 and sheet 650 contain thermosetting resins, the heating temperature is preferably 0° C. or higher and 50° C. or lower than the temperatures at which both of these thermosetting resins harden, more preferably 0° C. or higher and 30° C. or lower, and even more preferably 0° C. or higher and 20° C. or lower.

[0087] The pressure of the pressurization is not particularly limited. For example, the pressure of the pressurization can be 0.2 MPa or more and 10 MPa or less, preferably 0.3 MPa or more and 7 MPa or less, and more preferably 0.5 MPa or more and 5 MPa or less.

[0088] The time for the heating and pressurization is not particularly limited. For example, the time for the heating and pressurization can be set so that the holding time at the set temperature is from 1 second to 10 minutes, preferably from 5 seconds to 5 minutes, and more preferably from 10 seconds to 1 minute.

[0089] The above heating and pressurization are preferably performed by rapidly cooling the mold. Rapid cooling can prevent melting of the foam of the core material 250 while ensuring adhesion to the skin material 240. For example, the cooling rate is preferably 0.1°C / min or more and 100°C / min or less, more preferably 1°C / min or more and 50°C / min or less, and even more preferably 5°C / min or more and 30°C / sec or less.

[0090] After the blade 200 is removed from the mold, post-processing such as drilling a hole for inserting a rotating shaft can be performed as needed.

[0091] 3. Other Embodiments The above-described embodiment is merely an example of the present invention, and the present invention is not limited to the above-described embodiment. Needless to say, various other embodiments are possible within the scope of the concept of the present invention.

[0092] For example, in the above embodiment, the blades were described using rotor blades for drones as an example, but the type of blade is not limited to this, and the present invention can be applied to various blades that move inside a fluid (gas or liquid) to generate a predetermined force, such as propellers for airplanes and ships, rotor blades for helicopters, wings such as the main wings and tail fins of airplanes, rotor blades for wind turbines, etc. Among these, the present invention is preferably used as rotor blades for flying objects such as drones, helicopters, and flying cars, because the flap portion can be made thin and has excellent specific rigidity.

[0093] The flying object having a blade according to the above-described embodiment may be a manned flying object or an unmanned flying object.

[0094] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the descriptions in the examples.

[0095] 1. Blade Fabrication A UD sheet (manufactured by Mitsui Chemicals, Inc., product name TAFNEX, fiber volume fraction (Vf) 50%, thickness 0.15 mm) composed of unidirectionally oriented continuous carbon fibers impregnated with a polypropylene matrix resin was prepared as the skin material. This UD sheet was punched into the shape shown in Figure 3A using a Thomson blade to produce a unidirectional fiber-reinforced resin sheet for the skin material. The direction of blade rotation (counterclockwise in Figure 3A) was set as the direction of increasing angle, and the unidirectional fiber-reinforced resin sheets for each blade were fabricated so that the orientation direction of the reinforcing fibers in the unidirectional fiber-reinforced resin sheet was the same as the orientation direction of the reinforcing fibers in each layer of the skin material listed in Table 1. For example, when producing Blade 1, three types of unidirectional fiber reinforced resin sheets for the skin material were produced, with the orientation directions of the reinforcing fibers being 15°, −15°, and 0° (referred to as Sheet (15), Sheet (−15), and Sheet (0), respectively). Note that, since the skin material was to be disposed on both the front and back sides of the blade, two unidirectional fiber reinforced resin sheets for the skin material were produced corresponding to each layer of the skin material.

[0096] A polypropylene foam (manufactured by Mitsui Chemicals Tohcello, Inc., trade name: Paronia, expansion ratio: 3, thickness: 8 mm) was prepared as the core material. This polypropylene foam sheet was punched into a rectangle using a Thomson blade and press-molded into the shape shown in Figure 3A to produce a resin foam for the core material that was three-dimensionally approximately the same shape as the blade.

[0097] The unidirectional fiber reinforced resin sheets prepared for each blade were stacked so as to have the layer configuration shown in Table 1, and the sheets were welded together using a lamp heater to prepare a laminate for the skin material. For example, for Blade 1, three unidirectional fiber reinforced resin sheets for the skin material were stacked in the order of Sheet (15), Sheet (-15), and Sheet (0), and the sheets were welded together using a lamp heater to prepare a laminate for the skin material to be placed on the front side of the blade. Similarly, a laminate for the skin material to be placed on the back side of the blade was also prepared.

[0098] A laminate for the skin material to be placed on the back side of the blade, a resin foam for the core material, and a laminate for the skin material to be placed on the front side of the blade were placed in this order in a press mold heated to 200° C. At this time, the two laminates placed on both sides of the resin foam for the core material were placed so that the outermost layer shown in Table 1 was on the outside, so that the skin material had the layer configuration shown in Table 1. For example, in Blade 1, the two laminates for the skin material placed on both sides of the resin foam for the core material were placed so that sheet (15) was on the outside and sheet (0) was on the side of the resin foam for the core material.

[0099] The mold was then closed and held at 200°C for 1 minute, and then cooled, and when the mold temperature reached 60°C or less, the mold was opened to obtain Blade 1. Blade 1 had a length of 320 mm in the tip direction (the direction from the base of the blade to the tip; X direction in Figure 3A ), a maximum width of 65 mm in the width direction (the direction perpendicular to the major axis direction in a plan view of the blade; Y direction in Figure 3A ), and a maximum thickness of 7.7 mm.

[0100] The same procedure was repeated to obtain blades 2 to 10.

[0101]

[0102] 2. Evaluation of Blade The produced blade was rotatably mounted on a motor and the following evaluations were carried out.

[0103] 2-1. Scattering Distance of Fragments An aluminum plate measuring 150 mm in length, 400 mm in width, and 10 mm in thickness was brought close to a blade rotating at a rotation speed of 3000 rpm with a cylinder diameter of 32 mm and an air pressure of 0.4 MPa, and the flat surface of the aluminum plate was collided with the blade. Of the blade fragments broken by the collision, the fragment that flew farthest from the center of rotation of the blade was measured, and this was taken as the scattering distance of the fragments.

[0104] The scattering distance of fragments from each blade was evaluated according to the following criteria: ⊚ The scattering distance of fragments was less than 7.5 m. ◯ The scattering distance of fragments was 7.5 m or more but less than 20.0 m. × The scattering distance of fragments was 20.0 m or more.

[0105] 2-2. Maximum Mass of Fragments The mass of all fragments of the blade that broke off in the same test as the fragment scattering distance was measured, and the mass of the largest fragment was recorded as the maximum mass of the fragments.

[0106] The maximum mass of the fragments of each blade was evaluated according to the following criteria: ◎ The maximum mass of the fragments was less than 0.5 g ○ The maximum mass of the fragments was 0.5 g or more and less than 4.0 g × The maximum mass of the fragments was 4.0 g or more

[0107] 2-3. Deflection An image of the blade rotating at 3000 rpm taken from a direction perpendicular to the rotation axis was superimposed on an image of the blade not rotating taken from a direction perpendicular to the rotation axis. The deviation (mm) of the tip of the blade between the two images was then calculated. Because the captured image was reduced in size compared to the actual size, the calculated deviation was converted to the actual blade size using the following formula to obtain the amount of deflection: Amount of deflection = (actual motor diameter / motor diameter in the image not rotating) x (deviation width of tip)

[0108] The amount of deflection of each blade was evaluated according to the following criteria: A: The amount of deflection was less than 15 mm. B: The amount of deflection was 15 mm or more but less than 17 mm. C: The amount of deflection was 17 mm or more.

[0109] The evaluation results for each blade are shown in Table 2.

[0110]

[0111] As is clear from Tables 1 and 2, Blades 1 to 7, which are laminates whose skin material includes a first orientation layer that is a unidirectional reinforcing fiber layer with an orientation direction of the reinforcing fibers of 10° to 65° and a second orientation layer that is a unidirectional reinforcing fiber layer with an orientation direction of the reinforcing fibers of -65° to -10°, exhibited little deflection, a short fragment scattering distance, and a small maximum fragment mass. Among these, Blades 1 and 2, which are laminates whose skin material includes a first orientation layer that is a unidirectional reinforcing fiber layer with an orientation direction of the reinforcing fibers of 10° to 35° and a second orientation layer that is a unidirectional reinforcing fiber layer with an orientation direction of the reinforcing fibers of -35° to -10°, exhibited a more significant short fragment scattering distance and a small maximum fragment mass. Blade 10, which includes a first orientation layer but no second orientation layer, exhibited a small effect of absorbing stress due to misalignment of the reinforcing fibers, resulting in a long fragment scattering distance.

[0112] Furthermore, when images of the blades breaking were taken and observed, it was found that in Blade 1, the core material broke perpendicular to the thickness direction, causing the upper and lower skin materials to separate and fly apart. On the other hand, in Blade 9, both the upper and lower skin materials and the core material broke in the thickness direction, causing fragments of the core material attached to the upper and lower skin materials to fly apart.

[0113] This application claims priority from Japanese Patent Application No. 2024-089110, filed May 31, 2024, and Japanese Patent Application No. 2024-176450, filed October 8, 2024. The entire contents of the specification, claims, and drawings of those applications as originally filed are incorporated herein by reference.

[0114] The blades of the present invention generate small fragments upon impact and the fragments fly a short distance. Therefore, the present invention is expected to improve the safety of blades and contribute to the further spread of flying objects and wind power generation using such blades.

[0115] REFERENCE SIGNS LIST 100 drone 110 body 120 arms 130 feet 200 blade 210 center 220 main body 230 flap 240 skin material 250 core material 310 first orientation layer 320 second orientation layer 330 third orientation layer 400 blade 410, 412 cracks 420, 422, 424 fragments 440 skin material 450 core material 650 sheet 660 resin foam

Claims

1. A blade having: a core material containing a resin foam; and a skin material arranged on the surface of the core material, the skin material including a laminate formed of a plurality of unidirectional reinforcing fiber layers each including reinforcing fibers oriented in one direction and a matrix resin impregnated into the reinforcing fibers, wherein when the angle from the root to the tip of the blade is defined as 0° and the direction in which the blade moves during rotation is defined as the direction in which the angle increases, the laminate includes a first orientation layer which is the unidirectional reinforcing fiber layer in which the orientation direction of the reinforcing fibers is 10° or more and 65° or less, and a second orientation layer which is the unidirectional reinforcing fiber layer in which the orientation direction of the reinforcing fibers is -65° or more and -10° or less.

2. The blade according to claim 1, wherein the laminate includes a third orientation layer, which is a unidirectional reinforcing fiber layer in which the orientation direction of the reinforcing fibers is between -9° and 9°.

3. The blade according to claim 1, wherein the first orientation layer includes a layer in which the orientation direction of the reinforcing fibers is 10° or more and 35° or less.

4. The blade according to claim 1, wherein the second orientation layer includes a layer in which the orientation direction of the reinforcing fibers is between -35° and -10°.

5. The blade according to claim 1, wherein the laminate has one layer of the first orientation layer and one layer of the second orientation layer on the outer side of the core material in the thickness direction.

6. The blade according to claim 1, wherein the ratio of the thickness of the first orientation layer and the second orientation layer to the thickness of the laminate is 70% or more and 100% or less.

7. A blade as set forth in claim 1, wherein the ratio of the thickness of the unidirectional reinforcing fiber layers in which the orientation direction of the reinforcing fibers is between -70° and 70° to the thickness of the laminate is between 80% and 100%.

8. The blade according to claim 1, wherein the core material is a resin foam with an expansion ratio of 1.1 to 15 times.

9. A blade as set forth in claim 1, wherein the core material is a resin foam of a thermoplastic resin, and the skin material is a laminate of the unidirectional reinforcing fiber layer in which the reinforcing fibers are impregnated with a thermoplastic resin.

10. A blade as claimed in claim 1, wherein the core material is a resin foam containing polyolefin, and the skin material is a laminate of the unidirectional reinforcing fiber layer in which the reinforcing fiber is impregnated with polyolefin.

11. A blade as set forth in claim 1, wherein the core material is a resin foam containing polypropylene, and the skin material is a laminate of the unidirectional reinforcing fiber layer in which the reinforcing fiber is impregnated with polypropylene.

12. The blade according to claim 1, wherein the reinforcing fibers are carbon fibers.

13. A flying object having a blade according to any one of claims 1 to 12.

14. A method for manufacturing a blade, comprising the steps of: arranging, on the surface of a resin foam, a plurality of unidirectional fiber reinforced resin sheets, each sheet comprising reinforcing fibers oriented in one direction and a matrix resin or a material thereof impregnated into the reinforcing fibers; and molding the resin foam and the unidirectional fiber reinforced resin sheets, wherein, when the direction from the base to the tip of the blade is defined as 0° and the direction in which the blade moves when rotating is defined as the direction in which the angle increases, in the arranging step, the plurality of unidirectional fiber reinforced resin sheets are arranged so that the orientation direction of the reinforcing fibers is between 10° and 65°, and the unidirectional fiber reinforced resin sheets are arranged so that the orientation direction of the reinforcing fibers is between -65° and -10°.

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