Flat lightweight member and method for manufacturing the same

Abstract

In order to provide a flat, lightweight member having excellent mechanical properties in an end and excellent adhesion between core and skin, as well as favorable appearance and superior producibility, this flat, lightweight member is characterized by having: a skin layer that is arranged on the two surfaces of the flat, lightweight member; an end reinforcement layer that is disposed at the ends of the flat, lightweight member so as to make contact with both inner surfaces of the skin layer on the two surfaces; and a core layer that is arranged in a space enclosed by the skin layer and the end reinforcement layer, so as to make direct contact with the inner surfaces of the skin layer. The skin layer includes one or more layers composed of reinforcing fibers aligned in one direction and a first matrix resin. The end reinforcement layer includes a fiber-reinforced resin sheet, and the core layer includes heat-expandable particles and a second matrix resin.

Description

[Technical Field]

[0001] The present invention relates to a flat, lightweight member (fiber-reinforced resin molded product) consisting of a surface skin layer and an internal core layer, which can be used as a propeller blade, and a method for manufacturing the same. Specifically, the present invention relates to a flat, lightweight member made of fiber-reinforced resin that has excellent mechanical properties at the ends and adhesion between the core layer and the skin layer, as well as good appearance quality and productivity, and a method for manufacturing the same. [Background technology]

[0002] Fiber-reinforced resins are used in a wide range of industries due to their lightweight, high strength, and high rigidity. In particular, molded products using prepregs, which are intermediate materials made by impregnating long fibers such as reinforcing fibers with resin, are preferably used. Furthermore, sandwich structure materials, in which the skin layer is fiber-reinforced resin and the core layer is porous, are effectively used in transportation equipment such as aircraft, automobiles, and ships, as well as in the sports and leisure fields, due to their lightweight and toughness. As an example of a fiber-reinforced resin molded product having such a sandwich structure, a flat lightweight member is known, consisting of a skin layer made of a fiber-reinforced substrate and a core layer made of lightweight particles and matrix resin. Here, a flat lightweight member refers to a structure in which the circumference and cross-sectional shape change along the longitudinal direction, and mainly refers to a member that can be used as a propeller blade.

[0003] As such a flat, lightweight member, a propeller blade is known in which an upper prepreg and a lower prepreg are laminated and bonded in the thickness direction at the end. This flat, lightweight member is obtained by laminating the upper prepreg in one split mold and the lower prepreg in the other split mold, and then placing a foaming agent in the space formed by the two prepregs when the molds are joined. (For example, Patent Document 1)

[0004] Furthermore, a similar flat lightweight member is known in which the main part is composed of a skin layer, a core layer, and a separation layer, the peripheral part (the outer periphery of the flat lightweight member when viewed from the direction in which the projected area of ​​the flat lightweight member is largest) is composed of a skin layer and a core layer, and additional reinforcing fibers are placed in the parts corresponding to the leading edge and trailing edge when used as a propeller blade. In this flat lightweight member, a separation layer is placed between the core layer and the skin layer to suppress the passage of lightweight particles. The separation layer separates the lightweight particles from the matrix resin that constitutes the core layer, and impregnates only the matrix resin into the dry reinforcing fiber substrate that constitutes the skin layer, thereby forming the skin layer (for example, Patent Document 2).

[0005] Furthermore, techniques are known to use prepregs with regularly distributed notches across the entire in-plane surface, or preforms formed by laminating such prepregs, in order to obtain uniform mechanical properties and excellent dimensional stability of flat, lightweight members (for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-151876 [Patent Document 2] Japanese Patent Application Publication No. 8-276441 [Patent Document 3] Patent No. 5272418 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, flat lightweight members, as described above, in which the upper and lower prepregs are laminated and bonded together in the thickness direction at the ends, require a region at the end for laminating and bonding both prepregs. Therefore, it becomes necessary to place the high-density prepreg even in areas that should ideally be formed by a lightweight core layer, resulting in an increase in the weight of the flat lightweight member. Also, for similar reasons, the shape of flat lightweight members to which such a configuration can be applied was sometimes limited. On the other hand, if the structure is simply made by butting the ends of the prepregs together, the joint strength decreases, and the lightweight particles and matrix resin forming the core layer leak out of the flat lightweight member, impairing its appearance.

[0008] Furthermore, conventional flat lightweight members, in which the main part is composed of a skin layer, a core layer, and a separation layer, the peripheral part is composed of a skin layer and a core layer, and additional reinforcing fibers are placed in the areas corresponding to the leading edge and trailing edge as described above, have the problem that if the position of the separation layer is not appropriate, delamination may occur near the separation layer when used for a long period of time, and the core layer and skin layer cannot be firmly integrated.

[0009] Furthermore, conventional methods for manufacturing flat, lightweight components, in which a top prepreg is laminated into one split mold and a bottom prepreg into the other split mold, and a foaming agent is placed in the space formed by the two prepregs when the molds are joined, require the prepreg to be laminated onto the surface of a three-dimensional mold at room temperature, and then the mold is heated to harden the prepreg. This process requires considerable effort, special technology, and equipment, and the heating and cooling of the mold takes a long time, resulting in productivity problems.

[0010] In addition, conventional methods for manufacturing flat lightweight members, in which a portion of the matrix resin for the core layer is passed through a separation layer to impregnate and harden a dry reinforcing fiber substrate to form a skin layer, have been problematic. When the flat lightweight member has a three-dimensional shape rather than being a simple flat plate, the separation layers, which are positioned separately at the top and bottom, can shift during molding, making it difficult to obtain a flat lightweight member with good accuracy and low variability. Furthermore, positioning the reinforcing fibers for reinforcement is difficult, and they are prone to shifting during fiber-reinforced resin molding, which can cause the center of gravity of the flat lightweight member to change. Moreover, voids, or air bubbles, can form at the edges during the process of impregnating the reinforcing fibers with the matrix resin, which can lead to a decrease in mechanical properties and damage to the appearance of the finished product.

[0011] Thus, with the conventional technologies described above, it has been extremely difficult to obtain flat, lightweight members that have excellent mechanical properties at the edges, good adhesion between the core layer and the skin layer, and good appearance quality.

[0012] Therefore, the object of the present invention is to focus on the above-mentioned problems and provide a flat, lightweight member that has excellent mechanical properties at the edges and adhesion between the core layer and the skin layer, as well as good appearance quality and productivity, and a method for manufacturing the same. [Means for solving the problem]

[0013] To solve the above problems, the present invention employs one of the following configurations. (1) A flat lightweight member comprising: a skin layer disposed on both surfaces of the flat lightweight member; an end reinforcing layer disposed at the end of the flat lightweight member so as to contact both inner surfaces of the skin layer on both surfaces; and a core layer disposed in the space surrounded by the skin layer and the end reinforcing layer so as to be in direct contact with the inner surface of the skin layer, wherein the skin layer comprises one or more layers made of reinforcing fibers aligned in one direction and a first matrix resin; the end reinforcing layer comprises a fiber-reinforced resin sheet; and the core layer comprises thermally expandable particles and a second matrix resin. (2) The flat lightweight member according to (1), characterized in that the fiber-reinforced resin sheet is made of reinforcing fibers aligned in one direction and a first matrix resin. (3) The flat lightweight member according to (1), characterized in that the fiber-reinforced resin sheet is a fiber-reinforced foam containing reinforcing fibers. (4) The flat lightweight member according to any one of (1) to (3), characterized in that the reinforcing fibers that have been raised from the skin layer have penetrated the core layer. (5) The flat lightweight member according to any one of (1) to (4), characterized in that the reinforcing fibers that have been raised from the end reinforcing layer have penetrated the core layer. (6) The flat lightweight member according to any one of (1) to (5), characterized in that the space enclosed by the skin layer and the end reinforcement layer is a closed space. (7) The flat lightweight member according to any one of (1) to (6), characterized in that the fiber-reinforced resin sheet in the end reinforcement layer has a rolled structure or a folded structure. (8) A method for manufacturing a flat, lightweight member using a double-sided mold consisting of an upper mold and a lower mold, A preparation step involves preparing one skin layer and the other skin layer using a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and preparing an edge reinforcement layer using a fiber-reinforced resin sheet. A first placement step involves placing the one skin layer on the lower mold heated to the molding temperature, and placing the end reinforcement layer on at least a portion of the peripheral edge of the one skin layer. A feeding step of placing a mixture of thermally expandable particles and a second matrix resin onto one of the skin layers, A second arrangement step involves further arranging the other skin layer on the upper surface of the first skin layer so that the end reinforcement layer comes into contact with at least a portion of the peripheral edge of the other skin layer. The process includes a mold closing step of closing the upper mold which has been heated to the molding temperature, Furthermore, a method for manufacturing a flat, lightweight member, characterized by comprising a step of expanding the volume of the thermally expandable particles to form a core layer. (9) A method for manufacturing a flat lightweight member using a double-sided mold composed of an upper mold and a lower mold, An end reinforcement layer made of a fiber-reinforced resin sheet is adhered to at least a part of the peripheral edge of one skin layer made of a prepreg composed of reinforcing fibers aligned in one direction and a first matrix resin, to prepare a skin layer with an end reinforcement layer, and to prepare the other skin layer made of the prepreg; a preparation step, A first placement step of placing the skin layer with an end reinforcement layer on the lower mold heated to a molding temperature, An input step of placing a mixture of thermally expandable particles and a second matrix resin on the one skin layer, A second placement step of further placing the other skin layer on the upper surface of the skin layer with an end reinforcement layer to bring the end reinforcement layer into contact with at least a part of the peripheral edge of the other skin layer, A mold closing step of closing the upper mold heated to a molding temperature, and having, Furthermore, a method for manufacturing a flat lightweight member, characterized by having a step of volume-expanding the thermally expandable particles to form a core layer. (10) The method for manufacturing a flat lightweight member according to (8) or (9) above, characterized in that the fiber-reinforced resin sheet is a prepreg composed of reinforcing fibers aligned in one direction and a first matrix resin. (11) The method for manufacturing a flat lightweight member according to (8) or (9) above, characterized in that the fiber-reinforced resin sheet is a fiber-reinforced foam containing reinforcing fibers. (12) The method for manufacturing a flat lightweight member according to any one of (8) to (11) above, characterized in that a cut prepreg is used as the prepreg. (13) The method for manufacturing a flat lightweight member according to any one of (8) to (12) above, characterized in that at least a part of the one skin layer corresponding to the inner surface of the flat lightweight member is fluffed up until the completion of the mold closing step. (14) The method for manufacturing a flat lightweight member according to any one of (8) to (13) above, characterized in that at least a part of the end reinforcement layer corresponding to the inner surface of the flat lightweight member is fluffed up until the completion of the mold closing step. [Effects of the Invention]

[0014] According to the flat lightweight member and its manufacturing method according to the present invention, a flat lightweight member can be obtained that has excellent mechanical properties at the ends and adhesion between the core layer and the skin layer, while also having good appearance quality and excellent productivity. [Brief explanation of the drawing]

[0015] [Figure 1] This shows a top view (a) and a cross-sectional view (b) in AA' of an example of the flat, lightweight member of the present invention. [Figure 2] This is a cross-sectional view (a) showing an example of a napped skin layer in an example of a flat, lightweight member of the present invention, and an enlarged view showing an example of a napped skin layer. [Figure 3] This is a cross-sectional view showing an example of the positional relationship between the skin layer, the end reinforcement layer, and the core layer in the flat lightweight member of the present invention. [Figure 4] This is a perspective top view showing an example of a closed space surrounded by a skin layer and an end reinforcement layer in a flat, lightweight member of the present invention. [Figure 5] This is an example of an end reinforcing layer having a rolled or folded structure in a flat, lightweight member of the present invention. [Figure 6] This figure shows the steps in the method for manufacturing a flat, lightweight member according to the present invention. [Figure 7] This figure shows the steps in an alternative manufacturing method for the flat, lightweight member of the present invention. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below, along with embodiments, with reference to the drawings.

[0017] The flat lightweight member according to the present invention has a skin layer disposed on both surfaces, an end reinforcing layer disposed at the end of the flat lightweight member so as to contact both inner surfaces of the skin layer on both surfaces, and a core layer disposed in the space enclosed by the skin layer and the end reinforcing layer so as to be in direct contact with the inner surface of the skin layer. The skin layer is formed using one or more layers of prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and includes one or more layers consisting of reinforcing fibers and the first matrix resin. The end reinforcing layer includes a fiber-reinforced resin sheet, and the core layer includes thermally expandable particles as lightweight particles and a second matrix resin.

[0018] Figure 1 shows one embodiment of the flat lightweight member of the present invention used as a propeller blade. Figure 1(a) shows a top view of the flat lightweight member 1, with the right side of the paper being the tip a and the left side being the root b. Figure 1(b) shows the AA' cross section of the flat lightweight member 1 (i.e., the cross section perpendicular to the longitudinal direction of the flat lightweight member 1). The flat lightweight member 1 mainly consists of skin layers 21 and 22, a core layer 30, and end reinforcement layers 40 and 41. The skin layers 21 and 22 are arranged on both surfaces of the flat lightweight member 1, the end reinforcement layers 40 and 41 are arranged at the ends (corresponding to the leading edge and trailing edge of the propeller blade) so as to contact the inner surfaces of the skin layers 21 and 22 on both surfaces, and the core layer 30 is arranged in the space surrounded by the skin layers 21 and 22 and the end reinforcement layers 40 and 41 so as to be in direct contact with the skin layers.

[0019] [Skin layer] The skin layer in the present invention is mainly formed using a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and includes one or more layers containing reinforcing fibers and the first matrix resin.

[0020] Here, the inner surface of the skin layer refers to the surface located on the inner side of the flat lightweight member within the skin layer. Unless otherwise specified, "surface" hereafter refers to the outer surface of the flat lightweight member.

[0021] In the present invention, it is preferable that the thickest portion of the skin layer constituting one surface of the flat lightweight member is formed from two or more prepregs, and more preferably has four or more prepregs. That is, such portion preferably has two or more layers containing reinforcing fibers and a first matrix resin, and more preferably has four or more layers.

[0022] The thickness of the skin layer of the present invention is preferably 0.1 mm to 10 mm, more preferably 0.2 mm to 5 mm, and even more preferably 0.4 mm to 2 mm. Having a thickness within the above preferred range facilitates uniform heat transfer to the interior of the laminate during molding, resulting in a flat, lightweight member with excellent appearance.

[0023] The skin layer may also be formed using a prepreg having two or more orientation directions, more preferably a prepreg having three or more orientation directions. This results in a skin layer having two or more, more preferably three or more orientation directions. Such a prepreg can be obtained by preparing multiple prepregs in which the reinforcing fibers are aligned in one direction, and laminating them so that the orientation directions of the reinforcing fibers are offset. When the longitudinal direction of the flat lightweight member is the 0-degree direction, for example, preferred lamination configurations include a lamination configuration including two types, 0 degrees and 90 degrees; a lamination configuration including three types, 0 degrees and ±45 degrees; a lamination configuration including three types, 0 degrees and ±30 degrees; and a lamination configuration including four types, 0 degrees, ±45 degrees and 90 degrees.

[0024] Furthermore, from the viewpoint of achieving both impact characteristics and rigidity, it is preferable to use one or more layers of unidirectional prepregs, which are prepregs in which reinforcing fibers are aligned in one direction, and one or more layers of woven prepregs, which are prepregs in which continuous fibers are woven, for the skin layer. In particular, it is a preferred embodiment to have a woven prepreg on the outermost surface of the flat lightweight member, and a unidirectional prepreg inside it, with the fiber direction being the longitudinal direction of the flat lightweight member, thereby creating a flat lightweight member with a woven base material of reinforcing fibers on the outermost surface and a skin layer having unidirectionally arranged reinforcing fibers on the inside. With such a configuration, when used as a propeller blade, the woven base material derived from the woven prepreg can suppress the fracture of the flat lightweight member due to the impact of flying objects, while the reinforcing fibers derived from the unidirectional prepreg can bear the tensile stress applied in the longitudinal direction of the flat lightweight member.

[0025] [End reinforcement layer] In this invention, the end reinforcement layer is positioned on the periphery of the flat lightweight member. In this invention, the periphery of the flat lightweight member refers to the surrounding area when the flat lightweight member is projected from above (i.e., the outer periphery of the flat lightweight member when viewed from the direction that maximizes the projected area). Furthermore, the inner surface of the end reinforcement layer refers to the surface of the end reinforcement layer that is located on the inner side of the flat lightweight member.

[0026] The edge reinforcement layer in the present invention includes a fiber-reinforced resin sheet.

[0027] The fiber-reinforced resin sheet is preferably composed of a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin. The fiber-reinforced resin sheet is preferably composed of two or more layers of prepreg, and more preferably of four or more layers. With such a fiber-reinforced resin sheet, the edge reinforcement layer will include one or more layers consisting of reinforcing fibers aligned in one direction and a first matrix resin.

[0028] On the other hand, the fiber-reinforced resin sheet of the edge reinforcement layer is also preferably a fiber-reinforced foam (porous body) containing reinforcing fibers. Examples of such fiber-reinforced foams include sandwich structures (for example, described in International Publication No. 14 / 162873) and nonwoven fabrics in which a thermoplastic resin is impregnated on one side and reinforcing fibers are exposed on the other side (for example, described in Japanese Patent Publication No. 2014-172201).

[0029] Depending on the dimensions of the flat, lightweight member, the cross-sectional area of ​​the end reinforcement layer of the present invention is 1 mm² in a cross section perpendicular to the contour direction of the peripheral edge. 2 1200mm or more 2 Preferably, it is less than 5 mm, and more preferably 5 mm 2 500mm or more 2 The following is the result: By setting the thickness to have such a cross-sectional area, it becomes easier to uniformly transfer heat to the interior of the laminate (i.e., throughout the entire thickness of the end reinforcement layer), and consequently, a flat, lightweight member with an excellent appearance can be obtained.

[0030] The end reinforcement layer of the present invention preferably has a fiber orientation in a direction along the contour of the peripheral edge. For example, by creating an elongated laminate in which the reinforcing fibers are oriented in the longitudinal direction using a fiber-reinforced resin sheet, and then arranging the laminate along the contour of the peripheral edge of a desired flat lightweight member, the fiber orientation can be made in a direction along the contour of the peripheral edge of the flat lightweight member.

[0031] [Core Layer] Unlike conventional flat, lightweight members that have a separation layer between the skin layer and the core layer, the core layer in this invention is in direct contact with the skin layer. This configuration allows the core layer and the skin layer to be firmly integrated, making it less likely for delamination to occur near the separation layer even after long-term use.

[0032] The core layer in this invention is formed from a lightweight resin and a second matrix resin. The weight ratio of lightweight particles (thermally expandable particles) to the second matrix in the core layer is preferably in the range of 5% to 100%, and more preferably in the range of 10% to 40%, when the weight of the second matrix resin is set to 100%. Setting the weight of lightweight particles to 5% or more reduces the specific gravity of the core layer, making it easier to exhibit lightweight properties. Setting it to 10% or more reduces the partial "resin richness" that occurs when the second matrix resin separates from the lightweight particles, resulting in a more homogeneous structure for the core layer and reducing variations in the center of gravity. On the other hand, setting it to 100% or less allows the second matrix resin to be present between the lightweight particles, causing them to crosslink, making the core layer rigid and able to maintain its shape. If it is greater than 100%, the crosslinking between the lightweight particles will be insufficient, making the core layer brittle and prone to deformation. Furthermore, by keeping the amount below 40%, the second matrix resin can surround the lightweight particles, thereby suppressing the occurrence of cracks in the core layer and maintaining good mechanical properties of the core layer over a long period of time.

[0033] [Fiber-reinforced resin sheet] The fiber-reinforced resin sheet used in the present invention mainly consists of reinforcing fibers and a first matrix resin.

[0034] The reinforcing fibers in the fiber-reinforced resin sheet may be continuous or discontinuous. There are no particular limitations on the form of the fiber-reinforced resin sheet, but from the viewpoint of mechanical properties, it is preferable to use a prepreg as the fiber-reinforced resin sheet. Furthermore, from the viewpoint of lightweight properties, it is preferable to use a fiber-reinforced resin foam as the fiber-reinforced resin sheet.

[0035] [Prepreg] The prepreg used in this invention mainly consists of reinforcing fibers and a first matrix resin.

[0036] The preferred volume content of the reinforcing fibers as a prepreg is preferably 40% or more and 80% or less, more preferably 45% or more and 75% or less, and still more preferably 50% or more and 70% or less.

[0037] The amount of reinforcing fibers contained in the prepreg, as the basis weight of the reinforcing fibers in the form of a sheet, is 50 g / m 2 or more and 1000 g / m 2 or less. If the basis weight is too small, voids where no reinforcing fibers exist may occur in the plane of the prepreg. By setting the basis weight to be not less than the lower limit value of the above preferred range, voids that serve as fracture initiation points can be eliminated. Also, if the basis weight is not more than the upper limit of the above preferred range, heat can be uniformly transferred to the inside during preheating for molding. The basis weight is more preferably 100 g / m 2 or more and 600 g / m 2 or less, and still more preferably 150 g / m 2 or more and 400 g / m 2 or less.

[0038] The measurement of the basis weight of the reinforcing fibers is carried out by cutting out a 10 cm square area from the sheet of reinforcing fibers, measuring its mass, and dividing by the area. The measurement is performed 10 times at different sites of the sheet of reinforcing fibers, and the average value is adopted as the basis weight of the reinforcing fibers.

[0039] [Reinforcing Fibers] In the present invention, examples of reinforcing fibers used in fiber-reinforced resin sheets, prepregs, and fiber-reinforced foams include organic fibers such as aramid fibers, polyethylene fibers, and poly(p-phenylene benzoxide) oxadol (PBO) fibers; inorganic fibers such as glass fibers, carbon fibers, silicon carbide fibers, alumina fibers, tyranno fibers, basalt fibers, and ceramic fibers; metallic fibers such as stainless steel fibers and steel fibers; and other types of fibers such as boron fibers, natural fibers, and modified natural fibers. Among these, carbon fibers are particularly lightweight, possess excellent properties in specific strength and specific modulus, and also have excellent heat resistance and chemical resistance, making them suitable for components such as automobile panels and aircraft propulsion system blades where weight reduction is desired. Among these, PAN-based carbon fibers, which easily yield high-strength carbon fibers, are preferred.

[0040] [Matrix resin] In the flat, lightweight member of the present invention, the first matrix resin and the second matrix resin are in a cured state.

[0041] Examples of the first matrix resin used in the prepreg of the present invention include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, and cyanate resins, as well as thermoplastic resins such as polyamide resins, polyacetal resins, polyacrylate resins, polysulfone resins, acrylic butadiene styrene (ABS) resins, polyester resins, acrylic resins, polybutylene terephthalate (PBT) resins, polyethylene terephthalate (PET) resins, polyethylene resins, polypropylene resins, polyphenylene sulfide (PPS) resins, polyether ether ketone (PEEK) resins, liquid crystal polymers, vinyl chloride, polytetrafluoroethylene and other fluororesins, and silicones. Among these, thermosetting resins are particularly preferred. Because the first matrix resin is a thermosetting resin, the prepreg has tackiness at room temperature. Therefore, even when the skin layer is composed of multiple prepregs, these layers are integrated by adhesion, and the molded product can be formed while maintaining the intended laminated structure.

[0042] Examples of the second matrix resin used in the core layer of the present invention include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, and cyanate resins, as well as thermoplastic resins such as polyamide resins, polyacetal resins, polyacrylate resins, polysulfone resins, acrylic butadiene styrene (ABS) resins, polyester resins, acrylic resins, polybutylene terephthalate (PBT) resins, polyethylene terephthalate (PET) resins, polyethylene resins, polypropylene resins, polyphenylene sulfide (PPS) resins, polyether ether ketone (PEEK) resins, liquid crystal polymers, vinyl chloride, polytetrafluoroethylene and other fluororesins, and silicones. Among these, the use of thermosetting resins is particularly preferred. Because the second matrix resin is a thermosetting resin, the hardened matrix resin surrounds the lightweight particles of the core layer, forming a porous structure. This prevents deformation and expansion of the core layer even when heat is applied to the flat, lightweight member.

[0043] In the first matrix resin and the second matrix resin of the present invention, it is preferable that the glass transition temperature of the first matrix resin is higher than that of the second matrix resin.

[0044] [Lightweight particles] The lightweight particles relating to the flat lightweight member of the present invention refer to thermally expandable resin particles that undergo volume expansion when heated during molding, and thermally expandable particles that are already in a thermally expanded state but can be compressed by pressurization.

[0045] When thermally expandable particles are mixed with a second matrix resin and heated, they undergo volume expansion. If the second matrix resin is a thermosetting resin, the curing of the thermosetting resin forms a lightweight, porous core layer. If the second matrix resin is a thermoplastic resin, the solidification of the molten thermoplastic resin during cooling, or the binding of the softened thermoplastic resin, forms a lightweight, porous core layer.

[0046] The volume expansion coefficient α (%) of a mixture of thermally expandable particles and a second matrix resin is given by V1 (cm³) of the volume of the mixture before expansion. 3 ), the volume after expansion is V2(cm 3 When ), it is expressed by the following equation (1). α = 100 × (V2 - V1) ÷ V1 ... (1)

[0047] In the core layer, the volume expansion coefficient α is preferably in the range of 30% to 2000%, although this varies depending on the weight ratio of thermally expandable particles to the second matrix resin and the heating conditions during molding.

[0048] Examples of thermally expandable particles include polyacrylonitrile copolymers, polymethacrylonitrile copolymers, polyvinylidene chloride copolymers, polystyrene or polystyrene copolymers, polyolefins, and polyphenylene oxide copolymers. Preferably, these are capsule-shaped particles containing a thermally expandable gas. In particular, thermally expandable particles using low-boiling-point hydrocarbons as the thermally expandable gas are preferred because they have a large volume expansion coefficient and allow for the formation of a lightweight core layer.

[0049] The size of the thermally expandable particles is preferably in the range of 1 μm to 1 mm in average particle size before volume expansion. By setting the average particle size to 1 μm or more, leakage of thermally expandable particles onto the surface of the flat, lightweight member due to resin flow during molding can be suppressed. Furthermore, by setting it to 1 mm or less, the thermally expandable particles penetrate even into the thin-walled portion of the core layer, making the core layer lighter and reducing density unevenness between the thermally expandable particles and the second matrix resin in the core layer.

[0050] Examples of such thermally expandable particles include "Matsumoto Microspheres" (registered trademark) manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., "Expancell" (registered trademark) manufactured by Nobel Co., Ltd., and "Eslenbeads" manufactured by Sekisui Chemical Co., Ltd., but the present invention is not limited to these products.

[0051] In this invention, only one type of thermally expandable particle may be used as the lightweight particle, or a mixture of multiple types of thermally expandable particles may be used. Furthermore, the thermally expandable particles may be used alone, or they may be used in combination with particles that do not expand with heat, such as glass beads.

[0052] [More Preferred Embodiments of the Invention] In the flat, lightweight member of the present invention, it is preferable that the reinforcing fibers, which are raised from the skin layer, penetrate into the core layer.

[0053] Figure 2 shows one embodiment of the flat lightweight member of the present invention, where Figure 2(a) is a cross-sectional view showing an example of the napped skin layer of the flat lightweight member 1, and Figure 2(b) is an enlarged view of an example of the napped skin layer in the flat lightweight member 1. In Figure 2(b), the skin layer 22, napped reinforcing fibers 200, core layer 30, and the fiber-reinforced portion 300 of the core layer, which is partially reinforced by the intrusion of napped reinforcing fibers, are shown.

[0054] Here, the term "napped" refers to a state in which one or more reinforcing fibers protrude out of plane from the surface (the side with the largest surface area) of the fiber-reinforced resin sheet, prepreg, or fiber-reinforced foam. The lower limit of the length of the protruding reinforcing fibers is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. If it falls below the lower limit, there is a concern that the reinforcing fibers that have penetrated the core layer may fall out. The upper limit of the length of the protruding reinforcing fibers is preferably 100 mm or less, more preferably 50 mm or less, and even more preferably 10 mm or less. If it exceeds the upper limit, there is a possibility that the reinforcing fibers may break during the napped process. Here, the length of the napped reinforcing fibers is determined by embedding and polishing the region including the boundary between the skin layer and the core layer as shown in Figure 2(b), and then measuring the length of the reinforcing fibers that have penetrated the core layer by cross-sectional observation. It is preferable that the napped reinforcing fibers are continuously connected from the skin layer to the core layer, and this configuration can strengthen the adhesion between the skin layer and the core layer.

[0055] Furthermore, in the flat lightweight member of the present invention, it is also preferable that the reinforcing fibers, which are raised from the end reinforcing layer, penetrate into the core layer.

[0056] The napped reinforcing fibers are preferably connected continuously from the end reinforcement layer to the core layer, and this configuration allows for strong adhesion between the end reinforcement layer and the core layer.

[0057] The method for raising the nap of the reinforcing fibers will be described later.

[0058] In the flat lightweight member of the present invention, it is preferable that the space enclosed by the skin layer and the end reinforcement layer is a closed space. That is, it is preferable that the periphery of the core layer is covered by the skin layer and the end reinforcement layer.

[0059] Figure 3 shows an example of a cross-section of the flat lightweight member of the present invention (a cross-section in the same direction as the AA' cross-section shown in Figure 1). In Figure 3(a), the skin layers 21 and 22 completely reach both ends c and d of the flat lightweight member, and the entire surface of the flat lightweight member is covered with the skin layers 21 and 22. In Figure 3(b), the end reinforcement layers 40 and 41 are exposed on the surface of the flat lightweight member. Furthermore, in Figure 3(c), one end c of the flat lightweight member is covered with the skin layer 23, and the end reinforcement layer 41 is exposed on the surface of the flat lightweight member at the other end d. In addition, in Figure 3(d), the skin layers 21 and 22 completely reach both ends of the flat lightweight member, and furthermore, the skin layers 21 and 22 merge between the two ends of the flat lightweight member (between the one end c and the other end d) to form an internal reinforcement layer 25. This internal reinforcement layer 25 can be formed by partially increasing the thickness of the skin layer, by placing a prepreg laminate separate from the skin layer between the skin layers 21 and 22, by placing reinforcing fibers with the same configuration as the end reinforcement layer between the skin layers 21 and 22, or by placing a component with the shape of an internal reinforcement layer, formed by arranging reinforcing fibers such as prepreg around a core, between the skin layers 21 and 22. A cross section with such an internal reinforcement layer can bear a large amount of shear load applied to the cross section, making it a preferred embodiment with excellent mechanical properties. Here, in all of Figures 3(a) to (d), it can be seen that the entire surface of the flat lightweight member is covered with skin layers 21 and 22 and end reinforcement layers 40 and 41, and the region enclosed by skin layers 21 and 22 and end reinforcement layers 40 and 41 is closed. In addition, one closed region is formed between the skin layer and the end reinforcement layer in Figures 3(a) to (c), and two closed regions are formed in Figure 3(d).

[0060] Figure 4 is an example of a perspective top view of the flat lightweight member of the present invention, illustrating the closed space 50 and its contour 500 in which the core layer of the present invention is arranged. The closed space 50 is located inside the surface of the flat lightweight member 1 and is composed of the closed region described in Figure 3, extending from the tip a to the base b in Figure 4. Furthermore, at the tip a and base b, the closed space 50 is closed by the skin layer and the end reinforcement layer, or by the skin layer and a laminate of a prepreg other than the skin layer. Therefore, the core layer of the present invention, which is arranged in the closed space 50, is not exposed on the surface of the flat lightweight member 1.

[0061] Figure 4(a) illustrates a case where the flat lightweight member of the present invention has one closed space. Figure 4(b) illustrates a case where the flat lightweight member of the present invention has two closed spaces parallel to each other from the tip a to the base b. Figure 4(c) illustrates a case where the flat lightweight member of the present invention has three closed spaces discontinuously from the tip a to the base b. In Figures 4(b) and (c), the spaces between the multiple closed spaces are internal reinforcement layers formed by the unification of skin layers. These can be formed by partially increasing the thickness of the skin layers, or by placing a prepreg laminate separate from the skin layers 21 and 22 between the skin layers 21 and 22, or by placing reinforcing fibers with the same configuration as the end reinforcement layer between the skin layers 21 and 22, or by placing a component with the shape of an internal reinforcement layer, formed by arranging reinforcing fibers such as prepreg around a core, between the skin layers 21 and 22.

[0062] In the flat lightweight member of the present invention, it is preferable that an end reinforcing layer is provided along the entire peripheral edge. With such a configuration, the mechanical properties at the end of the flat lightweight member are improved, and leakage of lightweight particles forming the core layer and the second matrix to the surface of the flat lightweight member can be suppressed.

[0063] In the flat lightweight member of the present invention, as described above, it is preferable that the reinforcing fibers, which are raised from the skin layer and end reinforcement layer, penetrate into the core layer. To achieve this configuration, it is preferable to use a cut prepreg as at least a portion of the prepreg used to constitute the skin layer and end reinforcement layer. This is particularly suitable when the flat lightweight member has a change in thickness or a complex three-dimensional shape.

[0064] A prepreg with cuts is a prepreg having cuts that are regularly distributed throughout the entire plane, and the continuous reinforcing fibers that make up the prepreg are cut at the locations where the cuts are present. Such regularly distributed cuts can be provided, for example, by the method described in Patent Document 3 mentioned above.

[0065] Cut prepregs can be used in conjunction with regular prepregs that do not have cuts, where the reinforcing fibers are simply continuous fibers, to form skin layers or edge reinforcement layers.

[0066] With a prepreg that has been cut, openings and misalignments are more likely to occur at the cut insertion points, improving the extensibility of the prepreg in the direction of the reinforcing fibers. In addition, as the prepreg flows during compression molding, the cut insertion points open up and the fiber bundles of reinforcing fibers separate, making the prepreg more flexible and increasing its fluidity. By configuring the prepreg to flow in this way, the reinforcing fibers reach to the edges, reducing the area of ​​excess resin, and making it possible to obtain a flat, lightweight member with excellent mechanical properties and appearance. From the viewpoint of fluidity, it is preferable to make cuts throughout the entire thickness of the prepreg.

[0067] Using pre-cut prepreg in the skin layer is preferable because it facilitates the raising of the reinforcing fibers, allowing them to penetrate the core layer and form a strong adhesive surface. Furthermore, since the ends of the raised reinforcing fibers can penetrate into the core layer, the fibers can penetrate deep into the core layer, thereby strengthening the adhesion between the core layer and the skin layer.

[0068] As the skin layer, an integrated laminate of a prepreg without cuts and a prepreg with cuts may be used. In this case, it is preferable to place the prepreg with cuts on the contact surface with the core layer. This embodiment is preferable because the prepreg without cuts exhibits excellent mechanical properties while the prepreg with cuts strengthens the adhesion between the core layer and the skin layer.

[0069] Using pre-cut prepreg for the end reinforcement layer is preferable because, as the end reinforcement layer is pressed against the end contour of the flat lightweight member and deforms due to the expansion of the core layer, tension in the fiber direction can be suppressed, thereby suppressing the occurrence of "resin-rich" areas and voids, and improving the appearance quality and mechanical properties at the ends. Preferably, the fiber direction of the reinforcing fibers in the end reinforcement layer is in the direction along the end contour of the flat lightweight member.

[0070] In the present invention, it is preferable that the flat, lightweight member has a fiber-reinforced resin sheet in a rolled or folded structure in the end reinforcement layer.

[0071] Figure 5(a) shows an example of a rolled structure, and Figure 5(b) shows an example of a folded structure. The end reinforcement layer having a rolled structure can be easily adjusted in thickness and cross-sectional area by adjusting the amount of fiber-reinforced resin sheet such as prepreg that is rolled up, and it is also easy to manufacture, so it is particularly suitable for use when the ends of flat lightweight members have a rounded shape. On the other hand, the end reinforcement layer having a folded structure can be easily adjusted in thickness by adjusting the width of folding the fiber-reinforced resin sheet such as prepreg or by adjusting the number of folds, and it is easier to make the thickness thinner than that of the rolled structure, so it is particularly suitable for use when the ends of flat lightweight members have a sharp shape. In other words, in Figures 3(a) to (d), it is preferable that the end reinforcement layer 40 has a rolled structure, and it is preferable that the end reinforcement layer 41 has a folded structure.

[0072] [Manufacturing method] The present invention relates to a method for manufacturing a flat lightweight member, which uses a double-sided mold consisting of an upper mold and a lower mold, and comprises a preparation step of preparing one skin layer and the other skin layer using a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and preparing an end reinforcement layer using a fiber-reinforced resin sheet; a first placement step of placing the one skin layer in the lower mold heated to a molding temperature and placing the end reinforcement layer on at least a part of the peripheral edge of the one skin layer; a filling step of placing a mixture of lightweight particles (thermally expandable particles) and a second matrix resin on the inner surface of the one skin layer (the inner surface of the skin layer in the final flat lightweight member); a second placement step of further placing the other skin layer on the upper surface of the one skin layer and bringing the end reinforcement layer into contact with at least a part of the peripheral edge of the other skin layer; and a mold closing step of closing the upper mold heated to a molding temperature, and further comprising a step of expanding the volume of the lightweight particles to form a core layer.

[0073] Figure 6 shows the steps in the manufacturing method of the flat lightweight member of the present invention, in which the flat lightweight member is formed using a double-sided mold in which a cavity with the shape of the flat lightweight member is formed on the mating surface of the upper and lower molds.

[0074] Figure 6(a) shows the preparation process, in which one skin layer 22, the other skin layer 21, and the end reinforcement layers 40 and 41 are prepared.

[0075] The skin layers 21 and 22 can be manufactured, for example, by cutting prepreg cut pieces having a desired shape and desired fiber orientation from a sheet of prepreg, and then laminating the prepreg cut pieces as needed. Alternatively, they can be manufactured by laminating a sheet of prepreg in a desired fiber orientation and then cutting it into a desired shape.

[0076] The end reinforcement layer can be manufactured, for example, by laminating fiber-reinforced resin sheets to a predetermined thickness and then cutting them into a long, narrow strip of a predetermined width, or by pultrusion or extrusion molding to produce a long, narrow, string-like member.

[0077] If the end reinforcement layer has a rolled structure, it can be produced, for example, by winding a single fiber-reinforced resin sheet sequentially from the end. Alternatively, it can also be produced by folding a single fiber-reinforced resin sheet and then winding it. Separately, a rolled structure can also be obtained from multiple fiber-reinforced resin sheets laminated together using a similar procedure.

[0078] If the end reinforcement layer has a foldable structure, it can be manufactured, for example, by folding a single fiber-reinforced resin sheet in half or thirds, and then folding it again. Alternatively, for example, a thin, flattened roll structure can be made from a single fiber-reinforced resin sheet, and then folded. In addition, a foldable structure can be obtained from multiple fiber-reinforced resin sheets laminated together using a similar procedure.

[0079] When using prepreg as the fiber-reinforced sheet, it can be manufactured by laminating long, narrow sheets of prepreg or tape-shaped prepreg slit tapes. Similarly, when using fiber-reinforced foam as the fiber-reinforced sheet, it can be manufactured by cutting sheet-shaped fiber-reinforced foam into long, narrow strips.

[0080] Next, Figure 6(b) shows the first placement step. In this step, one skin layer 22 is placed in the lower mold 82 heated to the molding temperature, and the end reinforcement layers 40 and 41 are placed on at least a portion of the peripheral edge of the one skin layer 22. The molding temperature set as the temperature of the lower mold depends on the types of the first and second matrix resins, but when thermosetting resins are used, it is preferable to set the temperature in the range of 80°C to 230°C. Setting it above 80°C promotes the reaction of the matrix resin, and setting it below 230°C suppresses the decomposition of the matrix resin. Furthermore, since the manufacturing method of the present invention does not require raising or lowering the temperature of the mold, the manufacturing time can be shortened compared to conventional methods that involve raising or lowering the temperature of the mold.

[0081] In the first placement step, one skin layer may be placed in the lower mold in a planar state, or it may be pre-formed into a three-dimensional shape before being placed in the lower mold. Alternatively, a linear end reinforcement layer may be placed while bending it along the periphery of one skin layer, or it may be placed after being pre-bent along the shape of the periphery. In particular, when a thermosetting resin is used as the first matrix resin, the skin layer and the end reinforcement layer are integrated by the tack of the prepreg, making it easier and preferable to position the end reinforcement layer.

[0082] Next, Figure 6(c) shows the filling process. This process involves placing a mixture 90 of lightweight particles (thermally expandable particles) and a second matrix resin onto the inner surface of one of the skin layers 22. During the filling process, care must be taken to prevent the mixture of lightweight particles and the second matrix resin from flowing out of the skin layer beyond the end reinforcement layer. Therefore, it is preferable that the mixture does not adhere to the end reinforcement layer at the point where it comes into contact with the other skin layer. By filling the mixture of lightweight particles and the second matrix resin inside the peripheral edge and keeping it inside the peripheral edge, it is possible to prevent the lightweight particles from flowing out from between the end reinforcement layer and the skin layer onto the surface of the flat lightweight member. Furthermore, it is preferable to fill the mixture of lightweight particles and the second matrix resin so as to coat the entire inner surface of one of the skin layers, in order to obtain a homogeneous core layer.

[0083] In the input process, it is preferable to preheat the mixture of lightweight particles and the second matrix resin. By using this method, the viscosity of the mixture of lightweight particles and the second matrix resin is reduced, which shortens the input time and makes it easier to adjust the amount to be added. The mixture of lightweight particles and the second matrix resin can be preheated using an oven or microwave oven.

[0084] Furthermore, Figure 6(d) shows the second placement step. In this step, the other skin layer 21 is further placed on the upper surface of the first skin layer 22, so that the end reinforcement layers 40 and 41 come into contact with at least a portion of the peripheral edge of the other skin layer 22. In the second placement step, the other skin layer may be placed in the lower mold in a planar state, or it may be pre-formed into a three-dimensional shape before being placed in the lower mold. In particular, when a thermosetting resin is used as the first matrix resin, the skin layer and the end reinforcement layer are integrated by the tack of the prepreg, making it easier and preferable to position the end reinforcement layer.

[0085] Figure 6(e) shows the mold closing process, which involves closing the upper mold 81 that has been heated to the molding temperature. In the mold closing process, one skin layer, the end reinforcement layer, and the other skin layer are pressed together and integrated. It is preferable to set the temperature of the upper mold to the same temperature as the lower mold, but this is not limited to the manufacturing method of the flat lightweight member of the present invention. Furthermore, the cavity can be evacuated during the mold closing process. Using such a method is preferable because it reduces voids in the skin layer and end reinforcement layer, improving the mechanical properties of the flat lightweight member, and prevents the generation of air bubbles on the surface, thus obtaining a flat lightweight member with excellent appearance quality. The mold closing process is completed when the double-sided mold, consisting of the upper and lower molds, is completely closed.

[0086] As shown in Figure 6(f), the lightweight particles, which are thermally expandable particles, begin to expand in volume after reaching a predetermined temperature, forming a core layer. Due to the expansion of the lightweight particles, the skin layer and the edge reinforcement layer are pressed against the mold cavity by the core layer and subjected to pressure. Subsequently, by curing and demolding as shown in Figure 6(g), a flat, lightweight member of excellent quality can be obtained.

[0087] The present invention relates to a method for manufacturing a flat lightweight member using a double-sided mold consisting of an upper mold and a lower mold, comprising: a preparation step of preparing a skin layer with an end reinforcement layer and another skin layer using a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, wherein the end reinforcement layer is bonded to the peripheral edge of one skin layer; a first placement step of placing the skin layer with the end reinforcement layer in the lower mold heated to a molding temperature; a filling step of placing a mixture of lightweight particles and a second matrix resin on the inner surface of the one skin layer; a second placement step of further placing the other skin layer in the lower mold and bringing the end reinforcement layer into contact with the peripheral edge of the one skin layer; and a mold closing step of closing the upper mold heated to a molding temperature, further characterized in that the lightweight particles are expanded in volume to form a core layer.

[0088] Figure 7 shows each step in more detail, but in this method as well, fiber-reinforced resin is molded using a double-sided mold in which a cavity in the shape of a flat, lightweight member is formed at the mating surface of the upper and lower molds.

[0089] Figure 7(a) shows the preparation process, which involves preparing a skin layer with end reinforcement layers, in which end reinforcement layers 40 and 41 made of fiber-reinforced resin sheets are bonded to at least a portion of the peripheral edge of one skin layer 22, which is made of a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and the other skin layer 21 made of prepreg.

[0090] The skin layer and the edge reinforcement layer can each be manufactured by the methods described above. A skin layer with an edge reinforcement layer can be manufactured by bonding the edge reinforcement layer to the periphery of one of the skin layers. When a thermosetting resin is used as the first matrix resin, the skin layer and the edge reinforcement layer can be bonded by the tack of the prepreg. When a thermoplastic resin is used as the first matrix resin, the edge reinforcement layer and one of the skin layers can be bonded by heating them to the melting temperature of the thermoplastic resin, pressing them together, and then cooling them. Alternatively, the edge reinforcement layer can be bonded to one of the skin layers using a resin adhesive or a resin adhesive film.

[0091] Figure 7(b) shows the first placement process, Figure 7(c) shows the loading process, Figure 7(d) shows the second placement process, and Figure 7(e) shows the mold closing process. These processes can be carried out in the same manner as described in Figure 6 above, and by going through these processes, a flat, lightweight member of excellent quality can be obtained.

[0092] In the method for manufacturing a flat, lightweight member according to the present invention, it is preferable to use a cut prepreg as the prepreg. Using a cut prepreg for the skin layer is preferable because it facilitates the raising of the reinforcing fibers, and the raised reinforcing fibers penetrate deep into the core layer to form a strong adhesive surface. Alternatively, an integrated laminate of a non-cut prepreg and a cut prepreg may be used as the skin layer. In this case, it is preferable to place the cut prepreg on the side that contacts the core layer. This embodiment is preferable because the non-cut prepreg exhibits excellent mechanical properties while the cut prepreg strengthens the adhesion between the core layer and the skin layer.

[0093] Using pre-cut prepreg for the end reinforcement layer is preferable because, as the end reinforcement layer is pressed against the end contour of the flat lightweight member and deforms due to the expansion of the core layer, tension in the fiber direction can be suppressed, thereby suppressing the occurrence of "resin-rich" areas and voids, and improving the appearance quality and mechanical properties at the ends. Preferably, the fiber direction of the reinforcing fibers in the end reinforcement layer is in the direction along the end contour of the flat lightweight member.

[0094] In the method for manufacturing a flat lightweight member according to the present invention, it is preferable to fluff the inner surface of at least one of the skin layers before the completion of the mold closing process. In particular, it is preferable to fluff the reinforcing fibers on the inner surface of at least one of the skin layers during the loading process. The reinforcing fibers on the inner surface of the skin layer can be fluffed by loading the mixture of lightweight particles and the second matrix resin so as to coat the entire inner surface of one of the skin layers using a spatula or the like. Alternatively, the reinforcing fibers on the inner surface of the skin layer can be fluffed by applying the mixture of lightweight particles and the second matrix resin while allowing it to flow from the high part to the low part of one of the skin layers by gravity. Preheating the mixture of lightweight particles and the second matrix resin is preferable as it allows for effective utilization of gravity-induced flow. The preheating temperature depends on the molding temperature and the expansion start temperature of the lightweight particles, but is preferably 40°C to 180°C, and more preferably 70°C to 130°C. By setting the viscosity above the lower limit of the preferred range, the viscosity of the second matrix resin decreases, allowing the resin to flow. By setting it below the upper limit, the thermal expansion of the lightweight particles is suppressed, allowing sufficient time to apply the resin during the input process.

[0095] In the manufacturing method of the flat lightweight member according to the present invention, it is preferable to raise the reinforcing fibers on the inner surface of the end reinforcement layer before the completion of the mold closing process. In particular, when fiber-reinforced foam is used as the end reinforcement layer, the reinforcing fibers contained in the fiber-reinforced foam are raised by the springback of the reinforcing fibers contained in the fiber-reinforced foam when the foam is heated in the mold, and these reinforcing fibers penetrate into the core layer, thereby firmly integrating the core layer and the end reinforcement layer. [Industrial applicability]

[0096] The method for manufacturing a flat, lightweight member according to the present invention can be applied to the manufacture of any flat, lightweight member, and the resulting flat, lightweight member can be suitably used, for example, as a propeller blade structure in transportation equipment such as aircraft, automobiles, and ships, or in the sports and leisure fields. [Explanation of Symbols]

[0097] 1. Flat lightweight member 21, 22, 23 Skin layers 200 Skin layer brushed reinforced fibers 30 core layers 300 The fiber reinforcement section of the core layer where the napped reinforcing fibers of the skin layer have partially penetrated. 40, 41 End reinforcement layers 50 Closed space 500 Contour of a closed space 81 Upper mold 82 Lower mold 90 mixture

Claims

1. A flat lightweight member comprising: a skin layer disposed on both surfaces of the flat lightweight member; an end reinforcing layer disposed at the end of the flat lightweight member so as to contact both inner surfaces of the skin layer on both surfaces; and a core layer disposed in the space enclosed by the skin layer and the end reinforcing layer so as to be in direct contact with the inner surface of the skin layer, wherein the skin layer comprises one or more layers made of reinforcing fibers aligned in one direction and a first matrix resin; the end reinforcing layer comprises a fiber-reinforced resin sheet; and the core layer comprises thermally expandable particles and a second matrix resin, wherein reinforcing fibers raised from the skin layer penetrate into the core layer.

2. The flat lightweight member according to claim 1, characterized in that the fiber-reinforced resin sheet comprises reinforcing fibers aligned in one direction and a first matrix resin.

3. The flat, lightweight member according to claim 1, characterized in that the fiber-reinforced resin sheet is a fiber-reinforced foam containing reinforcing fibers.

4. The flat lightweight member according to any one of claims 1 to 3, characterized in that the reinforcing fibers raised from the skin layer are made of cut prepreg.

5. The flat lightweight member according to any one of claims 1 to 4, characterized in that the reinforcing fibers that have been raised from the end reinforcing layer have penetrated the core layer.

6. The flat lightweight member according to any one of claims 1 to 5, characterized in that the space enclosed by the skin layer and the end reinforcement layer is a closed space.

7. The flat lightweight member according to any one of claims 1 to 6, characterized in that the fiber-reinforced resin sheet in the end reinforcement layer has a rolled structure or a folded structure.

8. A method for manufacturing a flat, lightweight member using a double-sided mold consisting of an upper mold and a lower mold, A preparation step involves preparing one skin layer and the other skin layer using a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, and preparing an edge reinforcement layer using a fiber-reinforced resin sheet. A first arrangement step involves placing the one skin layer on the lower mold heated to the molding temperature, and placing the end reinforcement layer on at least a portion of the peripheral edge of the one skin layer. A feeding step of placing a mixture of thermally expandable particles and a second matrix resin onto the one skin layer, A second arrangement step involves further arranging the other skin layer on the upper surface of the first skin layer so that the end reinforcement layer comes into contact with at least a portion of the peripheral edge of the other skin layer. The process includes a mold closing step of closing the upper mold which has been heated to the molding temperature, Furthermore, a method for manufacturing a flat, lightweight member, characterized by comprising a step of expanding the volume of the thermally expandable particles to form a core layer.

9. A method for manufacturing a flat, lightweight member using a double-sided mold consisting of an upper mold and a lower mold, A preparation step involves bonding an edge reinforcement layer, made of a fiber-reinforced resin sheet, to at least a portion of the peripheral edge of one skin layer, which is made of a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin, thereby preparing a skin layer with an edge reinforcement layer, and also preparing the other skin layer, which is made of the prepreg. A first placement step involves placing the skin layer with the end reinforcement layer into the lower mold heated to the molding temperature, A feeding step of placing a mixture of thermally expandable particles and a second matrix resin onto the one skin layer, A second arrangement step involves further arranging the other skin layer on the upper surface of the skin layer with the end reinforcement layer so that the end reinforcement layer comes into contact with at least a portion of the peripheral edge of the other skin layer. The process includes a mold closing step of closing the upper mold which has been heated to the molding temperature, Furthermore, a method for manufacturing a flat, lightweight member, characterized by comprising a step of expanding the volume of the thermally expandable particles to form a core layer.

10. The method for manufacturing a flat lightweight member according to claim 8 or 9, characterized in that the fiber-reinforced resin sheet is a prepreg consisting of reinforcing fibers aligned in one direction and a first matrix resin.

11. The method for manufacturing a flat lightweight member according to claim 8 or 9, characterized in that the fiber-reinforced resin sheet is a fiber-reinforced foam containing reinforcing fibers.

12. A method for manufacturing a flat lightweight member according to any one of claims 8 to 11, characterized in that a pre-cut prepreg is used as the prepreg.

13. A method for manufacturing a flat lightweight member according to any one of claims 8 to 12, characterized in that at least one of the skin layers, the portion corresponding to the inner surface of the flat lightweight member, is made to fluff up by the completion of the mold closing process.

14. A method for manufacturing a flat lightweight member according to any one of claims 8 to 13, characterized in that the portion of the end reinforcing layer corresponding to the inner surface of the flat lightweight member is made to nap before the completion of the mold closing process.

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