Blade, projectile and manufacturing method thereof

Abstract

The present invention provides a blade in which the specific rigidity of a flap part is further increased. This blade has a thick body part and a thin flap part integrally formed in the rear end of the body part. The flap part has a skin material containing a fiber-reinforced thermoplastic resin, and a core material containing a thermoplastic resin foam filled inside the skin material.

Description

[Technical field]

[0001] The present invention relates to a blade, a projectile, and a method for manufacturing the same. [Background technology]

[0002] 2. Description of the Related Art Blades that rotate 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] For blades, a shape having a thicker front end in the direction of movement and a thinner flap portion at the rear end is considered to be preferable because it reduces resistance when the blade moves and makes it easier to generate lift.

[0004] Incidentally, blades are required to have a rigidity that can withstand resistance during movement. At the same time, there is also a demand for lighter blades for the purpose of reducing fuel consumption, etc. As a method for satisfying these demands, a configuration in which the surface of a core material made of a resin foam is covered with a fiber-reinforced resin material is known (for example, Patent Document 1). In the blade described in Patent Document 1, the flap portion is formed only from a fiber-reinforced resin material, and such a configuration is considered to be effective from the viewpoint of increasing the rigidity of the flap portion, which is thin and prone to breaking. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-177704 A Summary of the Invention [Problem to be solved by the invention]

[0006] It is thought that a blade having a configuration as described in Patent Document 1 has both the rigidity due to the fiber-reinforced resin material and the light weight due to the resin foam. However, according to the knowledge of the present inventors, the rigidity per weight of the flap portion of the blade described in Patent Document 1 (hereinafter, also referred to as "specific rigidity") cannot be said to be sufficient.

[0007] The present invention has been made in consideration of the problems with the conventional technology described above, and has an object to provide a blade having a flap portion with improved specific rigidity, and a manufacturing method thereof. [Means for solving the problem]

[0008] A blade according to one embodiment of the present invention for solving the above problems is a blade having a thick main body and a thin flap portion integrally formed at a rear end of the main body. The flap portion has a skin material including a fiber-reinforced thermoplastic resin, and a core material including a thermoplastic resin foam filled inside the skin material.

[0009] A manufacturing method for a blade according to another embodiment of the present invention for solving the above problems is a manufacturing method for a blade having a thick main body portion and a thin flap portion integrally formed at a rear end of the main body portion, the method including the steps of: preparing a thermoplastic resin foam and a fiber-reinforced thermoplastic resin that sandwiches the thermoplastic resin foam from above and below; and hot-pressing the thermoplastic resin foam and the fiber-reinforced thermoplastic resin to mold the blade so that the flap portion includes a skin material containing fiber-reinforced thermoplastic resin and a thermoplastic resin foam filled inside the skin material. Effect of the Invention

[0010] According to the present invention, a blade having a flap portion with increased specific rigidity and a method for manufacturing the same are provided. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic perspective view of a drone according to one embodiment of the present invention. [Diagram 2] FIG. 2A is a plan view showing one of the blades of the drone shown in FIG. 1, and FIG. 2B is a cross-sectional view of the blade taken along line AA in FIG. 2A. [Diagram 3] 3A and 3B are schematic diagrams showing a manufacturing method of the blade of the drone shown in FIG. 1. [Figure 4] 4A and 4B are schematic diagrams showing another manufacturing method of the blade of the drone shown in FIG. 1. [Diagram 5] 5A and 5B are schematic cross-sectional views showing how a blade is manufactured from a thermosetting resin. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Drone and its blades] Fig. 1 is a schematic perspective view of a drone 100 according to an embodiment of the present invention. As shown in Fig. 1, the drone 100 has a body 110, a plurality of blades 200, and a foot 120, and is capable of flying and moving while flying by rotating each of the blades 200. In this embodiment, the drone 100 has four blades 200, all of which have the same shape.

[0013] [blade] FIG. 2A is a plan view showing one of the blades 200 possessed by the drone 100, and FIG. 2B is a cross-sectional view of the blade 200 cut along line AA in FIG. 2A.

[0014] 2A, blade 200 has a central portion 210 that serves as a rotation axis, and a pair of plate-like wing portions 220 extending from the central axis. The pair of (two) wing portions 220 each have the same shape and are arranged in opposite directions from central portion 210 such that the angle between them is 180°.

[0015] 2A and 2B, the blade 200 has a thick main body 230 disposed in the front in the rotation direction (which is also the direction in which the blades 220 move, and hence will be referred to as the "movement direction" hereinafter), and a thin flap 240 disposed in the rear in the rotation direction (movement direction). The flap 240 is preferably a portion whose thickness is 1 / 2 or less of the thickness of the main body 230.

[0016] Both the main body portion 230 and the flap portion 240 have a skin material 250 containing a fiber-reinforced thermoplastic resin, and a core material 260 containing a thermoplastic resin foam filled inside the skin material 250. The main body portion 230 and the flap portion 240 are integrally molded. Note that integrally molded means that the blade 200 having the main body portion 230 and the flap portion 240 is formed in a single molding process. It can be confirmed that the blade 200 is an integrally molded product by the fact that there is no joint (seam) between the main body portion 230 and the flap portion 240.

[0017] The thickness of the main body 230 is preferably 1 mm or more and 20 mm or less, more preferably 1.5 mm or more and 15 mm or less, and even more preferably 2 mm or more and 10 mm or less. The maximum width (maximum width in the moving direction of the blade 200) of the main body 230 is preferably 1 / 20 or more and 1 / 2 or less of the length of the wing 220, more preferably 1 / 10 or more and 1 / 3 or less, and even more preferably 1 / 7 or more and 1 / 4 or less. The length of the wing 220 in a flying object having multiple blades such as the drone 100 of this embodiment may be determined by the maximum takeoff weight (total of the aircraft weight and the transport weight) and the number of blades used. For example, in the case of a takeoff weight of 25 kg and 16 blades (two blades, eight rotors), the length of the wing 220 is preferably 20 mm or more and 40 mm or less. In the rotating blade 200 of this embodiment, the length of the wing 220 is the value obtained by dividing the length of the line segment connecting both ends of the blade in the length direction by 2.

[0018] The flap portion 240 preferably has a thickness of 0.3 mm to 10.0 mm, more preferably 0.4 mm to 7 mm, and even more preferably 0.5 mm to 5 mm. The maximum width of the flap portion 240 (the maximum width in the moving direction of the blade 200) is preferably 1 / 10 to 2 times the maximum width of the main body portion, more preferably 1 / 7 to 1.5 times, and even more preferably 1 / 4 mm to 1 times the maximum width.

[0019] 2A and 2B, the thickness and width of the main body 230 and the flap 240 may vary depending on the location. In this specification, the thickness of the flap 240 is measured at a position 2 mm from the rear end on a virtual line segment in the forward and backward direction of movement that passes through the part where the wing 220 is at its maximum thickness, and the thickness of the main body 230 is measured at the thickness of the thickest part of the wing 220. The maximum width of the main body 230 is the length of a part that has a thickness exceeding 1 / 2 the maximum thickness of the wing 220 on a virtual line segment in the forward and backward direction of rotation that passes through the maximum width part, and the width of the flap 240 is the length obtained by subtracting the maximum width of the main body from the maximum width of the wing 220.

[0020] In addition, when the core material 260 is formed by extruding a melt-kneaded resin composition into a die as in Patent Document 1, it is usually difficult to fill the inside of the thin flap portion as described above. In contrast, as described below, a sandwich-shaped material is prepared in which a thermoplastic resin foam is sandwiched between fiber-reinforced thermoplastic resin, which is the material of the skin material 250, and the material is heat-pressed from above and below to form the blade 200 in which the core material 260 is sufficiently filled inside the flap portion 240. In order to ensure sufficient moldability by heat pressing, both the skin material 250 and the core material 260 use a thermoplastic resin as the resin.

[0021] Generally, light weight and rigidity are contradictory physical properties, and as light weight improves, rigidity tends to decrease, and as rigidity improves, light weight tends to decrease. For example, as described in Patent Document 1, when the flap portion is formed only from a fiber-reinforced resin material, the rigidity of the flap portion increases, but the weight of the flap portion increases due to the relatively heavy reinforcing fibers, so the specific rigidity does not increase significantly. As such, no invention has been made in the past that focuses on achieving both light weight and rigidity in the flap portion 240.

[0022] In contrast, in this embodiment, a core material 260 made of a foamed thermoplastic resin is also disposed inside the flap portion 240. With this configuration, the weight of the flap portion 240 is reduced by the foamed core material 260, while rigidity is imparted by the fiber-reinforced resin skin material 250. Therefore, the flap portion 240 can be made both lightweight and rigid.

[0023] The thickness ratio of the skin material 250 and the core material 260 in the flap portion 240 may be set in consideration of the specific rigidity. For example, the thickness ratio of the skin material 250 and the core material 260 (skin material / core material) is preferably 1 / 25 to 2 / 1, more preferably 1 / 20 to 1 / 1, and even more preferably 1 / 10 to 1 / 2. In the above ratio, the thickness of the skin material 250 is the sum of the thicknesses of the two skin materials 250 that sandwich the core material 260 from above and below. The thicknesses of the skin material 250 and the core material 260 for calculating the above ratio are values ​​obtained by measuring the thickness and width of the flap portion 240 at the measurement points described above.

[0024] The thickness of the skin material 250 in the flap portion 240 is preferably 0.05 mm to 3 mm, more preferably 0.1 mm to 2 mm, and even more preferably 0.3 mm to 1 mm. The thickness of the skin material 250 in the main body portion 230 is not particularly limited, but may be the same as the thickness of the skin material 250 in the flap portion 240.

[0025] (skin material) The skin material 250 includes a fiber-reinforced thermoplastic resin. The type of reinforcing fiber in the fiber-reinforced thermoplastic resin 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 from the viewpoint of low density, particularly reducing the weight of the flap portion 240 and further increasing its specific rigidity, and carbon fiber is more preferred from the viewpoint of further increasing the specific rigidity of the flap portion 240.

[0026] The reinforcing fibers may be long fibers oriented randomly or in one direction and having a length of 15 mm or more, or short fibers oriented randomly or in one direction and having a length of less than 15 mm, or a combination of these. From the viewpoint of further improving the specific rigidity of the flap portion 240, it is preferable that the skin material 50 contains reinforcing fibers oriented in one direction. In this case, the long fibers may be oriented in only one direction, or multiple layers having different orientation directions of the long fibers may be formed in the skin material 250, or the long fibers may be woven. Alternatively, blocks formed of long fibers oriented in one direction may be arranged in the skin material 250 so that the orientation direction of the long fibers in each block is random. Of these, from the viewpoint of improving the shapeability during manufacturing, it is preferable that multiple layers having the same or different orientation directions of the long fibers are formed in the skin material 250, or that the long fibers are woven.

[0027] From the viewpoint of sufficiently enhancing the effect of improving rigidity, the reinforcing fibers preferably have an average diameter of 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less.

[0028] The unmodified polyolefin is preferably an ethylene-based polymer having a content of 50 mol% or more of structural units derived from ethylene, or a propylene-based polymer having a content of 50 mol% or more of structural units derived from propylene. Examples of the ethylene-based polymer include an ethylene homopolymer and a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms. Examples of the propylene-based polymer include a propylene homopolymer and a copolymer of propylene and ethylene or an α-olefin having 4 to 10 carbon atoms. The unmodified polyolefin is preferably a homopolypropylene, a homopolyethylene, an ethylene-propylene copolymer, a propylene-1-butene copolymer, or an ethylene-propylene-1-butene copolymer.

[0029] The content of the reinforcing fibers relative to the total mass of the skin material 250 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 65% by mass or less, and particularly preferably 35% by mass or more and 60% by mass or less.

[0030] The content of the reinforcing fibers relative to the total volume of the skin material 250 is preferably 10 volume % or more and 70 volume % or less, more preferably 15 volume % or more and 60 volume % or less, and even more preferably 20 volume % or more and 60 volume % or less.

[0031] The material of the matrix resin that holds the reinforcing fibers in the skin material 250 is not particularly limited as long as it is a thermoplastic resin, and the matrix resin may be either a crystalline resin or a non-crystalline resin.

[0032] Examples of the thermoplastic 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.

[0033] Among these, polyamide resin and polyolefin resin are preferred because they are less likely to be damaged when struck by flying objects such as pebbles, thereby increasing the reliability of the blade 200. From the viewpoint of suppressing the deterioration of mechanical properties when the skin material 250 absorbs water, polyolefin resin is more preferred, and polypropylene resin is even more preferred.

[0034] The matrix resin may be a resin composition containing an additive. Examples of the additive 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 and bonded to the base to form the heat-conductive portion 116, the matrix resin is preferably a resin composition containing a dye that absorbs the laser of the irradiated wavelength. The dye may be any dye that absorbs light of any wavelength between 300 nm and 3000 nm, and is preferably carbon black.

[0035] As will be described in the manufacturing method below, in this embodiment, a thermoplastic resin foam is sandwiched between two upper and lower fiber-reinforced thermoplastic resin sheets, which are then hot-pressed to form the blade 200. At this time, the types of thermoplastic resin compositions contained in the two upper and lower fiber-reinforced thermoplastic resin sheets can be made different from each other, so that the types of matrix resins contained in the upper and lower skin materials 250 can be made different from each other. However, it is preferable that the types of matrix resins contained in the upper and lower skin materials 250 are the same.

[0036] The matrix resin may also contain other components, such as resins other than those mentioned above and short fibers having a length shorter than that of the carbon fibers mentioned above.

[0037] The content of the matrix resin relative to the total mass of the skin material 250 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 35% by mass or more and 70% by mass or less, and particularly preferably 40% by mass or more and 65% by mass or less.

[0038] The content of the matrix resin relative to the total volume of the skin material 250 is preferably 30 volume % or more and 90 volume % or less, more preferably 40 volume % or more and 85 volume % or less, and even more preferably 40 volume % or more and 80 volume % or less.

[0039] (Core material) The core material 260 is a thermoplastic resin foam.

[0040] The type of thermoplastic resin constituting the above-mentioned thermoplastic resin foam is not particularly limited, and examples of the thermoplastic resin that can be used include polyolefin resins including 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.

[0041] In addition, the thermoplastic resin which is the matrix resin of the skin material 250 and the thermoplastic resin which constitutes the foam in the core material 260 are preferably the same type of resin. In this specification, the term "same type of resin" means that the bonding method between the structural units (repeating units) in the main chain of the resin is common between the resins. For example, when the matrix resin of the skin material 250 is a polyamide resin, the thermoplastic resin which constitutes the foam in the core material 260 is preferably also a polyamide resin, and when the matrix resin of the skin material 250 is a polyolefin resin, the thermoplastic resin which constitutes the foam in the core material 260 is preferably also a polyolefin resin. Resins of the same type have high affinity with each other, and the two are easily mixed at the interface between the skin material 250 and the core material 260, and the above-mentioned mixing can increase the bonding strength between the skin material 250 and the core material 260. In addition, in this specification, the term "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 which constitutes the foam.

[0042] In addition, it is preferable that the thermoplastic resin that is the matrix resin of the skin material 250 and the thermoplastic resin that constitutes the foam in the core material 260 are compatible. This allows these resins to be compatible during hot press molding, thereby further increasing the bonding strength between the skin material 250 and the core material 260. Note that being compatible means that the combination of resins forms a single phase when these thermoplastic resins (three types, two types of matrix resins and a thermoplastic resin that constitutes the foam, in the case where the matrix resins contained in the upper and lower skin materials 250 are different from each other) are heated to a temperature higher than the melting points of all the resins, mixed, and then cooled to 25°C.

[0043] In addition, the difference in melting point between the thermoplastic resin that is the matrix resin of the skin material 250 and the thermoplastic resin that constitutes the foam in the core material 260 is preferably within 10°C. When the matrix resins contained in the upper and lower skin materials 250 are different from each other, 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 is within 10°C. During the heat press molding, it is desirable to heat the two resins to a temperature at which they can flow sufficiently and deform. At this time, if the melting points of the two are close to each other, the two will flow sufficiently and be easily mixed and dissolved. In addition, it is also possible to prevent deterioration of the other resin and collapse of the foam shape by setting the heating temperature according to the resin with a higher melting point.

[0044] The density of the foam is preferably 0.2 g / cc or more and 0.6 g / cc or less, 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.

[0045] The expansion ratio of the foam is preferably 1.3 to 5 times, and more preferably 2 to 4 times.

[0046] [Blade manufacturing method] Blade 200 can be manufactured by a step (step 1) of preparing a foam 260a of thermoplastic resin (hereinafter simply referred to as "foam 260a") and two fiber-reinforced thermoplastic resin sheets 250a that sandwich foam 260a from above and below, and a step (step 2) of hot pressing them to form a blade. Fig. 3A is a schematic diagram showing step 1, and Fig. 3B is a schematic diagram showing step 2.

[0047] (Preparation process (Process 1)) In step 1, the foam 260a and the sheet 250a can be formed so that the shape viewed in the vertical direction (pressing direction) is substantially the same as or similar to the shape of the blade 200 viewed from the same direction. When it is desired to change the thickness of the skin material 250 between the main body portion 230 and the flap portion 240, a sheet 250a for the main body portion 230 and a sheet 250a for the flap portion 240 may be prepared separately. However, from the viewpoint of preventing the sheet from being displaced during heat pressing, it is preferable to use a sheet 250a having a shape that combines the main body portion 230 and the flap portion 240, and to make the thickness of the skin material 250 the same between the main body portion 230 and the flap portion 240.

[0048] However, as described in step 2, in the embodiment shown in Fig. 3, during the heat pressing, the foam 260a is caused to flow inside the mold in a direction from the main body portion 230 toward the rear end of the flap portion 240, and a part of it is discharged from the rear end of the flap portion 240 to the outside of the blade 200 (outside the sheet 250a). From the viewpoint of reducing the amount of foam 260a that is unnecessary in the molded blade 200 by this discharge, it is preferable that the shape of the foam 260a seen in the vertical direction is smaller than the shape of the blade 200, and in particular, it is preferable that the width of the foam 260a in the front-rear direction at the part that becomes the flap portion 240 (the width in the moving direction of the blade 200) is smaller than the width of the flap portion 240 to be formed ("X" in Fig. 3A).

[0049] In addition, from the viewpoint of preventing the formation of gaps inside the formed blade 200 that are not filled with foam 260a, it is preferable that the shape and size of foam 260a in areas other than the area that will become flap portion 240 (such as the area that will become main body portion 230) be the same as or slightly smaller than the shape and size of the area to be formed.

[0050] The thickness of the foam 260a may be such that the volume of the foam 260a is greater than the volume of the core material of the blade 200 to be formed.

[0051] On the other hand, as described in step 2, in the embodiment shown in FIG. 3, the front end 252a of the sheet 250a is wrapped around the front of the foam 260a on the front surface of the blade 200 to suppress the discharge of the foam 260a from the front end. Therefore, it is preferable that the shape of the sheet 250a in the part that becomes the main body 230 is a shape that extends forward of the main body 230 and is enlarged by the amount of the front end 252a that is wrapped around the front. The front end 252a of the two upper and lower sheets 250a that are wrapped around are brought close to each other and abut against each other during heat pressing, and are fused together. Therefore, the front end 252a of the sheets 250a do not need to be in contact with each other in this step.

[0052] In addition, from the viewpoint of preventing dimensional deviations in blade 200 and wrinkles in skin material 250 due to excess sheet 250a, it is preferable that the shape and size of sheet 250a in areas other than the front of the area that will become main body 230 (such as the area that will become flap portion 240) be the same as the shape and size of the area to be formed.

[0053] The foam 260a may be any foam of thermoplastic resin as the material of the above-mentioned core material 260. The expansion ratio of the foam is almost maintained before and after the next process (heat pressing).

[0054] The sheet 250a may be a sheet-shaped fiber-reinforced resin obtained by impregnating reinforcing fibers, which are the material of the skin material 250, with a matrix resin, which is the material of the skin material 250 described above. From the viewpoint of further improving the specific rigidity, the sheet-shaped fiber-reinforced resin is preferably a unidirectional material in which the reinforcing fibers are oriented in one direction. The orientation and dispersion state of the reinforcing fibers are maintained before and after the next process (heat pressing).

[0055] The sheet 250a may be a single-layer sheet-like material, or may be a laminate of multiple sheet-like materials. The multiple sheet-like materials may have the same or different orientation angles of the reinforcing fibers. The multiple sheet-like materials may also be a woven fabric in which multiple sheet-like materials cut into strips are woven. Of these, from the viewpoint of improving the shapeability, a woven fabric in which multiple sheet-like materials are woven is preferable.

[0056] (Step 2: Forming the blade) Next, the foam 260a and the two sheets 250a, one above the other and the other below, that sandwich the foam 260a are placed in a mold (FIG. 3A). At this time, the front end of the sheet 250a is wrapped around the front of the foam 260a.

[0057] By heat pressing in this state, the foam 260a softens and flows, and the two upper and lower sheets 250a are fused to each other, resulting in a blade 200 in which the outer surface 250 made of fiber-reinforced thermoplastic resin surrounds the outer surface and the core material 260 made of foamed thermoplastic resin is positioned inside.

[0058] At this time, in the embodiment shown in FIG. 3, the surplus of the thermoplastic resin foam that has flowed by the heat press is caused to flow so that it is more easily discharged from the rear end of the flap portion 240 than from the front end of the main body portion 230. For example, as shown in FIG. 3A, by wrapping the sheet 250a around the front of the foam 260a, it is possible to make it difficult for the foam 260a that has softened and flowed to be discharged to the outside from the front end. Also, as shown in FIG. 3A, by making the width of the foam 260a at the portion that becomes the flap portion 240 smaller than the width of the flap portion 240 to be formed, it is possible to make the foam 260a more easily flow to the rear end of the flap portion 240 and more easily discharged from the rear end of the flap portion 240.

[0059] Then, the softened and flowing foam 260a flows between the upper and lower sheets 250a in the thin flap portion 240, filling the flap portion 240 up to the rear end, and the excess is discharged to the outside from the rear end of the flap portion 240. This discharged foam 260a forms a thin, needle-like burr 270a protruding from the tip of the flap portion 240 (FIG. 3B). This protruding burr 270a can be easily cut off, making deburring easy.

[0060] 3, during the heat pressing, more of the excess foam 260a is discharged from the rear end of the flap portion 240. This allows the excess foam 260a to be easily turned into thin needle-like burrs 270a, which can be easily cut off to easily smooth the shape of the blade 200 and improve the appearance.

[0061] In contrast, in the embodiment shown in FIG. 4, when most of the excess foam 260a is removed from the front end of the flap portion 240, the excess foam 260a discharged from the front end of the main body portion 230 during heat pressing flows along the surface of the sheet 250a in the main body portion 230, forming a solidified burr 270b on the surface of the skin material 250 (FIGS. 4A and 4B). It is easier to remove the needle-like burr 270a shown in FIG. 3A and FIG. 3B than to remove the solidified burr 270b on the surface (when the foam 260a and the sheet 250a contain the same type of thermoplastic resin, they are likely to fuse to each other, so that it is easier to remove the needle-like burr 270a). Therefore, from the viewpoint of reducing the manufacturing cost associated with the removal of the burr 270b, the embodiment shown in FIG. 3 is preferable. However, the specific rigidity of the blade 200 manufactured in the embodiment shown in FIG. 3 and the blade 200 manufactured in the embodiment shown in FIG. 4 is almost the same, and both can be used in practice.

[0062] When the blade 200 moves through air or other fluids, the relative movement of the fluid along the surface of the blade 200 greatly affects the performance of the blade 200, so it is necessary to smooth the surface of the blade 200 to suppress the above-mentioned unexpected relative movement of the fluid. For example, if the surface of the blade 200 is highly rough and turbulence occurs near the surface of the blade 200, the flight of a drone or the like equipped with the blade 200 may become unstable. By facilitating the smoothing of the surface of the blade 200 using the method of the present embodiment, the manufacturing cost of the blade can also be suppressed.

[0063] The temperature during heat pressing is preferably a temperature that is -20°C or more and 50°C or less than the melting point of the thermoplastic resin contained in the foam 260a and the fiber-reinforced thermoplastic resin (when these contain different types of thermoplastic resins, the melting point of the thermoplastic resin with the highest melting point), more preferably a temperature that is -10°C or more and 30°C or less, and even more preferably a temperature that is 0°C or more and 20°C or less.

[0064] The pressure during the heat pressing is preferably 0.2 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more and 7 MPa or less, and even more preferably 0.5 MPa or more and 5 MPa or less.

[0065] The time for the heat press is preferably 1 second to 10 minutes, more preferably 5 seconds to 5 minutes, and even more preferably 10 seconds to 1 minute, at a set temperature.

[0066] After the hot pressing, it is preferable to rapidly cool the mold. Rapid cooling can prevent the foam from melting while ensuring adhesion to the skin material. For example, the cooling rate is preferably 0.1° C. / min to 100° C. / min, more preferably 1° C. / min to 50° C. / min, and even more preferably 5° C. / min to 30° C. / sec.

[0067] 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 necessary.

[0068] When a core is formed from a thermosetting resin, the thermosetting resin 260b before hardening, which is the material of the core, is introduced by flowing it inside the skin material 250b arranged inside the mold (FIG. 5A). However, in this method, the viscosity of the thermosetting resin 260b before hardening is low, which causes too much change in the weight of the charged material, and sealing is required in the foaming process, so that it is necessary to bond the thin flap portion 240 with the skin material, and it is not possible to form a flap portion having a resin foam core material sandwiched between the skin materials 250, and only the flap portion 240b consisting of only the upper and lower skin materials 250 can be formed (FIG. 5B). In order to form a flap portion having a fiber-reinforced resin skin material and a core material containing a foam filled inside the skin material, both the fiber-reinforced resin and the foam material must contain a thermoplastic resin.

[0069] [Other embodiments] It should be noted that 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.

[0070] For example, in the above embodiment, the blades are described using the 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, flying cars, and ships, rotor blades for helicopters, wings such as the main and tail wings of airplanes, and rotor blades for windmills, etc. Among these, the present invention can be preferably used as rotor blades for flying objects such as drones, helicopters, and flying cars, since the flap portion can be made thin and the specific rigidity is excellent.

[0071] In another embodiment of the present invention, a flying object having a blade according to the above embodiment is provided. In such a flying object, the flap portion can be thinned and the specific rigidity is excellent, so that the takeoff weight can be improved. In addition, in the flying object, the blade is preferably a rotor. The flying object may be manned or unmanned. EXAMPLES

[0072] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0073] 1. Blade Preparation 1-1. Making Blade 1 A unidirectional carbon fiber reinforced resin sheet (manufactured by Mitsui Chemicals, Inc., product name TAFNEX, fiber volume fraction (Vf) 50%, thickness 0.16 mm) was prepared as the material for the skin, which was made by impregnating long carbon fibers oriented in one direction with a polypropylene matrix resin. Using a Thomson blade, this unidirectional carbon fiber reinforced resin sheet was punched into the shape shown in FIG. 2A to produce a fiber reinforced thermoplastic resin sheet for the skin. The punched shape had a length of 700 mm in the long axis direction (left and right direction in FIG. 2A), a maximum width of 60 mm in the short axis direction (up and down direction in FIG. 2A), and a surface area of ​​250 cm. 2 In addition, two types of sheets were obtained: a sheet punched out so that the unidirectionally oriented carbon fibers were oriented in the long axis direction (hereinafter referred to as "sheet (horizontal)"), and a sheet punched out so that the unidirectionally oriented carbon fibers were oriented in the short axis direction (hereinafter referred to as "sheet (vertical)").

[0074] A polypropylene foam sheet (manufactured by Mitsui Chemicals Tocello, Inc., product name Paronia, density 0.3 g / cc, expansion ratio 3 times, thickness 5 mm) was prepared as the material for the core material. This polypropylene foam sheet was punched out using a Thomson blade to obtain a thermoplastic resin foam for the core material. The punched shape was a shape in which the width of the part that became the flap part was shortened by 7.6 mm compared to the shape shown in Figure 2A. The surface area was 210 cm2. 2 It was.

[0075] Two sheet sets were prepared by stacking three sheets for the skin material in the order of sheet (horizontal)-sheet (vertical)-sheet (horizontal), and the thermoplastic resin foam for the core material was sandwiched between these two sheet sets from above and below and placed inside a mold. Then, using a 50t press machine, it was hot-press molded under conditions of a mold temperature of 175°C, a mold clamping force of 10t, and a mold clamping time of 1 minute, and then the mold was quenched to 50°C to obtain blade 1.

[0076] 1-2. Making Blade 2 As a fiber-reinforced thermoplastic resin sheet for the skin material, a sheet (horizontal) having a shape in which the width of main body portion 230 was extended forward by 2 mm with respect to the shape shown in FIG. 2A (hereinafter referred to as “sheet (horizontal / long)”) was obtained.

[0077] Two sheet sets were prepared in which three sheets for the skin material were stacked in the order of sheet (horizontal / long)-sheet (vertical)-sheet (horizontal), and the foamed thermoplastic resin for the core material was sandwiched between these two sheet sets from above and below and placed inside the mold. At that time, the sheet (horizontal / long) was placed on the outermost side of the upper and lower sheet sets, and the front end of the sheet (horizontal / long) was wrapped around the front of the foamed thermoplastic resin for the core material. However, the front ends of the two upper and lower sheets (horizontal / long) that were wrapped around were not in contact when they were placed in the mold. Thereafter, hot press molding and quenching were performed in the same manner as for Blade 1, and Blade 2 was obtained.

[0078] 1-3. Making Blade 3 A unidirectional carbon fiber reinforced resin sheet (manufactured by Mitsui Chemicals, Inc., product name TAFNEX, fiber volume fraction (Vf) 50%, thickness 0.16 mm) made of unidirectionally oriented long carbon fibers impregnated with a polypropylene matrix resin was cut into a long and narrow tape shape with a width of 12.5 mm. This tape was woven into a woven fabric so that the opening ratio was 0.38% and the spacing between the warp and weft threads was about 0.05 mm to about 1 mm on average. Using a Thomson blade, this woven fabric was punched into a sheet (horizontal) shape and a sheet (horizontal / long) shape (hereinafter referred to as "sheet (woven)" and "sheet (woven / long)", respectively).

[0079] Two sheet sets, each consisting of one sheet (woven) and one sheet (woven / long), were prepared and the foamed thermoplastic resin for the core material was sandwiched between these two sheet sets from above and below and placed inside the mold. At that time, the sheet (woven / long) was placed on the outermost side of the upper and lower sheet sets, and the front end of the sheet (woven / long) was wrapped around the front of the foamed thermoplastic resin for the core material. However, the front ends of the wrapped upper and lower sheets (woven / long) were not in contact when placed in the mold. Thereafter, similar to Blade 1, hot press molding and quenching were performed to obtain Blade 3.

[0080] 1-4. Making Blade 4 A unidirectional carbon fiber reinforced resin sheet (manufactured by Mitsui Chemicals, Inc., product name TAFNEX, fiber volume fraction (Vf) 50%, thickness 0.16 mm) consisting of unidirectionally oriented long carbon fibers impregnated with a polypropylene matrix resin was punched out with a Thomson blade into the shape of the flap and the shape of the main body of the blade shown in Figure 2A. At that time, two types of sheets were obtained for the flap and the main body, respectively: a sheet punched out so that the unidirectionally oriented carbon fibers were oriented in the long axis direction (hereinafter referred to as "sheet (horizontal-flap)" and "sheet (horizontal-main body)"), and a sheet punched out so that the unidirectionally oriented carbon fibers were oriented in the short axis direction (hereinafter referred to as "sheet (vertical-flap)" and "sheet (vertical-main body)").

[0081] For the flap section, nine sheet laminates were prepared, with seven sheets (vertical, flaps) sandwiched between two sheets (horizontal, flaps), and for the main section, nine sheet assemblies, each consisting of three sheets stacked in the order of sheet (horizontal, main body)-sheet (vertical, main body)-sheet (horizontal, main body), were stacked on top of each other, for a total of 27 sheet laminates. These were placed inside a mold and subjected to hot press molding and quenching in the same manner as for blade 1, to obtain blade 4.

[0082] 2. Evaluation 2-1. Specific rigidity of the flap In order to eliminate the variation in measurement values ​​due to the measurement position, the specific rigidity of the flap portion of each blade was calculated by measuring and calculating the following thickness.

[0083] (Thickness measurement) The resin used for embedding was a mixture of a base material (Epofix resin, manufactured by Struers; a mixture of 60-90% by mass of 2,2-bis(4-glycidyloxyphenyl)propane and 40-10% by mass of aliphatic (C12-14) glycidyl ether) and a hardener (Epofix hardener, manufactured by Struers; 100% by mass of triethylenetetramine) in a weight ratio of base material:hardener = 25:3. Each blade and the above mixed resin were placed in an embedding container with a diameter of 40 mm and hardened at room temperature for 12 hours to obtain a blade embedded in resin.

[0084] Each resin-embedded blade was cut to expose the cross section, and the exposed cross section was roughly polished using a Struers Tegramin-20 polisher, changing the polishing plate to #500, #1000, and #2000 in that order. The polishing conditions were a load of 10N for 2 minutes, and each time the plate was washed with sufficient water to remove polishing debris. Then, for the final polishing, the polishing plate / diamond suspension was changed to MD-Largo / Diapro Allegro-Largo9, and polishing was performed for 3 minutes at a load of 10N, and then changed to MD-Dac / Diapro NAP R1, and polishing was performed for 10 minutes at a load of 10N.

[0085] The cross section of the blade was observed at a magnification of 20x using a microscope (Keyence VHX-6000). The average thicknesses of the upper and lower surface materials and the thickness of the core material were measured at the location where the blade was at its widest and 2mm from the rear end of the flap.

[0086] The unidirectional carbon fiber reinforced resin sheets were layered to have the same structure as the skin material of the flap portion and hot press molded under the same conditions as the blade 1 to obtain test material 1, and the flexural modulus of test piece 2, the polypropylene foam sheet, was measured by a bending test in accordance with ISO178 (2010). The flexural modulus of test piece 1 (skin material) was 60,000 MPa, and the flexural modulus of test piece 2 (core material) was 300 MPa.

[0087] Based on these measurements, the bending rigidity D of the flap was calculated using the following formula. It was also calculated from the shape of the flap and the density of each material. The specific rigidity was calculated by dividing the rigidity D by the weight of the flap. The results are shown in Table 1.

[0088]

number

[0089]

number

[0090]

number

[0091]

number

[0092] In the above formulas, D s is the bending stiffness of the skin material, D0 is the bending stiffness of the axial force generated in the skin material, D c indicates the bending stiffness of the core material. E s is the bending modulus of the skin material (60000Mpa), E c is the bending modulus of the core material (300Mpa) s is the thickness of the skin, t c is the thickness of the core material. However, since the blade 4 does not have a core material, D c is 0.

[0093] The results are shown in Table 1. The values ​​shown in Table 1 are approximate values ​​for the shape of the flap portion such that the length in the major axis direction is 100 mm, the maximum width in the minor axis direction is 2 mm, and the thickness is 0.6 mm.

[0094] 2-2. Burrs on the front end The front end of each blade was visually inspected to determine whether or not there were any burrs on the surface of the skin. The results are shown in Table 1.

[0095] [Table 1]

[0096] As is clear from Table 1, the specific rigidity of the flap portion is increased by configuring the flap portion to have a skin material containing a fiber-reinforced thermoplastic resin and a core material containing a thermoplastic resin foam filled inside the skin material.

[0097] This application claims priority to Japanese Application No. 2021-185621, filed on November 15, 2021, and the contents of the specification, claims and drawings of that application are incorporated by reference into this application. [Industrial Applicability]

[0098] The blade according to the present invention has a high specific rigidity in the flap portion. Therefore, the present invention is expected to increase the durability of the blade in various applications, promote the use and further development of the blade, and contribute to the development of various fields in which the blade is used. [Explanation of symbols]

[0099] 100 Drones 110 Torso 120 Foot 200 Blades 210 Center 220 Wing 230 Main body 240 Flap section 240b Flap section 250 Skin material 250a fiber reinforced thermoplastic sheet 252a Forward end 250b Skin material 260 Core material 260a Thermoplastic resin foam 260b Thermosetting resin before curing

Claims

1. A blade having a thick main body and a thin flap portion integrally formed at the rear end of the main body, The flap portion has a skin material including a fiber-reinforced thermoplastic resin and a core material including a foamed thermoplastic resin filled inside the skin material, There is no joint between the main body and the flap. blade.

2. The blade according to claim 1 , wherein the flap portion has a thickness of 0.3 mm or more and 10.0 mm or less.

3. The skin material includes a fiber-reinforced polyolefin resin, The core material includes a polyolefin resin foam. A blade according to claim 1 or 2.

4. The blade according to any one of claims 1 to 3, wherein the thermoplastic resin contained in the skin material and the thermoplastic resin constituting the foam in the core material are mutually compatible.

5. 5. The blade according to claim 1, wherein the difference in melting point between the thermoplastic resin contained in the skin material and the thermoplastic resin constituting the foam in the core material is within 10° C.

6. The main body portion has a skin material including a fiber-reinforced thermoplastic resin, and a core material including a foam of a thermoplastic resin filled inside the skin material, The core material of the flap portion is the same as the core material of the main body portion and is disposed continuously from the main body portion. A blade according to any one of claims 1 to 5.

7. A flying object having a blade according to any one of claims 1 to 6.

8. A method for manufacturing a blade having a thick main body portion and a thin flap portion integrally formed at a rear end of the main body portion, comprising the steps of: A step of preparing a thermoplastic resin foam and a fiber-reinforced thermoplastic resin sandwiching the thermoplastic resin foam from above and below; and hot pressing the thermoplastic resin foam and the fiber-reinforced thermoplastic resin so that the flap portion includes a skin material containing a fiber-reinforced thermoplastic resin and a thermoplastic resin foam filled inside the skin material, thereby forming the blade without providing a joint between the main body portion and the flap portion. How the blade is manufactured.

9. 9. The method for manufacturing a blade according to claim 8, wherein in the forming step, the excess of the thermoplastic resin foam flowed by the heat press is caused to flow so as to be more easily discharged from the rear end of the flap portion than from the front end of the main body portion.

10. The method for manufacturing a blade according to claim 8 or 9, wherein in the preparing step, the fiber-reinforced thermoplastic resin is prepared such that a width of the flap portion in the front-rear direction is shortened.

11. In the preparation step, the fiber-reinforced thermoplastic resin is prepared in a shape in which the front of the main body portion is extended and enlarged, In the forming step, the front of the stretched fiber-reinforced thermoplastic resin is wrapped around the front of the thermoplastic resin foam, and then the heat pressing is performed. A method for manufacturing a blade according to any one of claims 8 to 10.

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