Core material and method for producing core material, skin-core structure, and structural member

Abstract

To provide a core material capable of adjusting thickness and density of a cell wall according to characteristics required for a structural member to be an application target, after shaping into a core material, or a skin-core structure.SOLUTION: A core material consists of an assembly of hollow columnar cells partitioned by cell walls, in which the cell walls include a fiber substrate composed of stacked dispersed fibers (Cf), and within the cell walls, the fiber substrate is compressed in the out-of-plane direction and the fibers (Cf) are bonded together by resin (Cr), and the cell walls have the ability to expand in the out-of-plane direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a core material for use in a skin-core structure. [Background technology]

[0002] Skin-core structures, which use a core material consisting of an aggregate of hollow cylindrical cells separated by cell walls, have excellent mechanical properties such as light weight and high rigidity, and are therefore widely used in structural components and building materials for aircraft, ships, etc. Core materials include aluminum honeycomb cores and FRP honeycomb cores made of reinforcing fibers and matrix resins. Of these, aramid honeycomb cores, which are made by impregnating aramid fiber nonwoven fabric with phenolic resin, are primarily used as FRP honeycomb cores for aircraft and other flying objects, which have a strong demand for lightweight construction.

[0003] Core materials are often required to have multiple properties, such as shear properties, impact properties, etc., in addition to light weight and mechanical properties. For example, when a sandwich structure is created by bonding skin materials to the surface of a core material, a phenomenon known as core crushing can occur, in which the cell walls buckle due to slippage of the skin materials.

[0004] To prevent core crushing, it is necessary to improve the strength of the core material without sacrificing its light weight as much as possible. As a technology that meets this requirement, Patent Document 1 proposes a core material in which a porous structure of fiber-reinforced resin is used for the cell walls, thereby increasing the thickness of the cell walls while suppressing weight increase. Furthermore, Patent Document 2 proposes a core material in which a sheet material in which discontinuous reinforcing fibers are dispersed in the cell walls is used, thereby increasing the strength without increasing the thickness of the cell walls. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2023 / 167334 [Patent Document 2] International Publication No. 2023 / 167335 Summary of the Invention [Problem to be solved by the invention]

[0006] In the core materials described in Patent Documents 1 and 2, the thickness and density of the cell walls are basically determined before the overall shape of the core material is formed, i.e., before it is processed into a shape consisting of an aggregate of hollow columnar cells. On the other hand, if the thickness and density of any part of the cell walls of the core material could be adjusted after the overall shape of the core material is formed, it would be possible to design more precise skin-core structures and structural members using them.

[0007] The present invention aims to provide a core material that, after being shaped into a core material or a skin-core structure, allows the thickness and density of the cell walls to be adjusted according to the required characteristics of the structural component to which it is applied. [Means for solving the problem]

[0008] To solve this problem, the present invention provides a core material consisting of an aggregate of hollow columnar cells separated by cell walls, the cell walls including a fiber base material formed by stacking dispersed fibers (Cf), and within the cell walls, the fiber base material is compressed in the out-of-plane direction and the fibers (Cf) are bonded together by resin (Cr), and the cell walls have the ability to expand in the out-of-plane direction.

[0009] Another aspect of the present invention is a method for producing a core material having a structure consisting of an aggregate of hollow columnar cells separated by cell walls, the method comprising the steps of: compressing a fiber substrate consisting of stacked dispersed fibers (Cf) in the out-of-plane direction, and bonding the fibers (Cf) together with a resin (Cr) to produce a sheet substrate; and shaping the sheet substrate into a structure consisting of an aggregate of hollow columnar cells.

[0010] Yet another aspect of the present invention is a skin-core structure formed by bonding the above-mentioned core material to a skin material. [Effects of the Invention]

[0011] The present invention allows greater flexibility in the manufacturing process of core materials or skin-core structures, allowing for more precise design of structural members using these. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagram showing one embodiment of a core material of the present invention. [Figure 2] Enlarged schematic diagram of the cell wall [Figure 3] Schematic diagram for explaining the method for measuring the two-dimensional orientation angle of fibers [Figure 4] FIG. 2 is a schematic diagram showing how the density of the cell walls varies in the in-plane direction of the core material. [Figure 5] Schematic diagram showing an aspect in which the thickness and density of at least some cell walls vary in the in-plane direction of the cell walls. [Figure 6] Schematic diagram showing one embodiment of a sandwich structure [Figure 7] Schematic diagram showing the stacking and molding state in the evaluation of the buckling resistance of the core material DETAILED DESCRIPTION OF THE INVENTION

[0013] <Core material> The core material of the present invention will be described below with reference to the drawings as appropriate, but the present invention is not limited to these drawings. However, as will be easily understood by those skilled in the art, the description of the embodiments shown in the drawings can also function as a description of the core material of the present invention as a general concept.

[0014] In this specification, the core material refers to a structural material consisting of an aggregate of hollow, columnar cells (hereinafter, sometimes simply referred to as "cells") defined by cell walls. Such core materials are typically used as skin-core structures in which skin materials are bonded to at least one, preferably both, of the core openings where the cells are open. Therefore, in this specification, the above structural materials are collectively referred to as "core materials," regardless of whether or not they are ultimately bonded to skin materials.

[0015] The shape of the cell opening (the cross-sectional shape perpendicular to the axial direction of the columnar cells) is not particularly limited, and may be polygonal (e.g., triangular, rectangular, hexagonal), circular, or elliptical. However, a regular hexagon is preferred from the viewpoint of impact resistance. That is, the core material preferably has a honeycomb structure. The diameter of the smallest circle that completely encompasses the shape of the cell opening is preferably 2 to 20 mm, more preferably 3 to 16 mm. When the cell shape is a regular hexagon, the length of one side of the regular hexagon is generally 3 mm to 20 mm. However, from the viewpoint of the contact point with the adhesive described below, the length of one side of the regular hexagon is preferably 3 mm to 10 mm, more preferably 3 mm to 8 mm. Furthermore, it is also preferable to form a cell assembly by combining multiple polygonal cell shapes or by combining cell shapes of different sizes, because this reduces the variation in properties within the core material and provides shape-forming capabilities to accommodate complex skin-core structures. Combinations of multiple polygonal cell shapes include, for example, a truncated icosahedron that combines a pentagon and a hexagon, or a curved shape using a part of either, which are preferable because they allow the core opening surface to have a curved shape such as a sphere.

[0016] 1 is a schematic diagram showing one embodiment of a core material 1 of the present invention, along with an enlarged image of only the fiber substrate 2 that constitutes the cell walls 3. The core material 1 has a structure formed by an aggregate of hollow columnar cells, each having a regular hexagonal opening, that are partitioned by the cell walls 3.

[0017] As shown in Figure 2, the cell walls 3 contain a fibrous base material 2 composed of dispersed fibers (Cf) 4 stacked one on top of the other. The fibers (Cf) 4 constituting the fibrous base material 2 are discontinuous fibers. The number-average fiber length of the fibers (Cf) is preferably 1 mm or more and 10 mm or less, more preferably 2 mm or more and 8 mm or less, and even more preferably 3 mm or more and 6 mm or less. By setting the number-average fiber length within this range, it becomes easier to increase the spacing between the fibers (Cf), which makes it easier to exhibit the expandability described below.

[0018] Furthermore, if such fibers (Cf) are randomly dispersed within the cell walls, the concentration variations of the fibers (Cf) and resin (Cr) within the cell walls are small, and isotropy is improved, which is preferable.

[0019] Examples of the fibers (Cf) constituting the fiber substrate 2 include carbon fibers, glass fibers, aramid fibers, alumina fibers, silicon carbide fibers, boron fibers, metal fibers, natural fibers, and mineral fibers, and these may be used alone or in combination. Among these, PAN-based, pitch-based, and rayon-based carbon fibers, which have high specific strength and specific rigidity, are preferred. Glass fibers are preferred for economic efficiency, and a combination of carbon and glass fibers is preferred for balancing mechanical properties and economic efficiency. Aramid fibers are preferred for improving impact absorption and formability. A combination of carbon and aramid fibers is also preferred for balancing mechanical properties and impact absorption. Fibers coated with metals such as nickel, copper, and ytterbium can also be used for improving electrical conductivity.

[0020] In particular, it is preferable to use fibers with a tensile modulus of 200 GPa or more as the fiber (Cf). Using fibers with a tensile modulus of 200 GPa or more in the fiber substrate increases the restoring force of the fiber (Cf) to its original state, making it easier for the sheet substrate to expand and advantageous for forming a porous structure. Examples of fibers with a tensile modulus of 200 GPa or more include para-aramid fiber, boron fiber, carbon fiber, and graphite fiber. Among these, it is preferable to use carbon fiber, which has no water absorption problem and excellent strength and elastic modulus. Commercially available carbon fibers include "TORAYCA (registered trademark)" T800S-24K, "TORAYCA (registered trademark)" T300-3K, "TORAYCA (registered trademark)" M55J-6K, and "TORAYCA (registered trademark)" T700S-12K (all manufactured by Toray Industries, Inc.).

[0021] When carbon fibers are used as the fibers (Cf), the tensile modulus of the carbon fibers is preferably in the range of 200 to 600 GPa. The tensile modulus of the carbon fibers is affected by the crystallinity of the graphite structure that constitutes the carbon fibers, and the higher the crystallinity, the higher the modulus. Furthermore, the higher the crystallinity, the higher the electrical conductivity. This range is preferable because the fiber-reinforced composite material has a high level of balance between electrical conductivity, rigidity, and strength. A more preferred range of modulus is 230 to 400 GPa, and even more preferably 260 to 370 GPa. Here, the tensile modulus of the fibers is a value measured in accordance with JIS R7601-2006.

[0022] Within the cell walls 3, the fiber substrate 2 is compressed in the out-of-plane direction, with the fibers (Cf) bonded together by the resin (Cr). Because the fiber substrate contained in the cell walls is compressed in the out-of-plane direction and the fibers (Cf) are bonded together by the resin (Cr), when the resin (Cr) softens, the bonds between the fibers (Cf) are released, allowing the fiber substrate to expand in the out-of-plane direction due to the restoring force that attempts to return it to its original thickness. In this case, as shown in FIG. 2(A), the resin (Cr) 5 only needs to bond at least the intersections of the dispersed fibers (Cf) 4. Another preferred embodiment is shown in FIG. 2(B), in which the resin (Cr) 5 coats the fibers (Cf) 4 while bonding them together. This means that the surfaces of the fibers (Cf) 4 and the fiber substrate 2 are not exposed by the resin (Cr) 5. In other words, the fibers (Cf) 4 and the fiber substrate 2 form a wire-like coating with the resin (Cr) 5. This improves the shape stability and mechanical properties of the cell walls. In this embodiment, the coating thickness of the resin (Cr) is preferably 1 μm or more. Furthermore, as shown in FIG. 2(C), the fibers (Cf) 4 may be bonded together by the resin (Cr) 5 filling substantially all of the voids inside the fiber substrate 2. This embodiment is preferable from the viewpoint of widening the adjustment range of the expansion amount of the cell walls (described later) and increasing the degree of design freedom.

[0023] The resin (Cr) may be a thermoplastic resin or a thermosetting resin. Examples of thermoplastic resins include polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyolefins such as polyethylene, polypropylene, polybutylene, and modified polypropylene; polyamides such as polyoxymethylene, polyamide 6 and polyamide 66; polycarbonate; polymethyl methacrylate; polyvinyl chloride; polyarylene sulfides such as polyphenylene sulfide; polyphenylene ethers; modified polyphenylene ethers; polyimides; polyamideimides; polyetherimides; polysulfones; modified polysulfones; polyethersulfones; polyarylene ether ketones such as polyketones, polyether ketones, polyether ether ketones, and polyether ketone ketones; polyarylates; polyether nitriles; and phenoxy resins. These thermoplastic resins may also be copolymers, modified resins, and / or blends of two or more types. Among these, at least one amorphous thermoplastic resin selected from the group consisting of polycarbonate (PC), polyphenylene ether (PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PES), and polyarylate (PAR) is more preferred in terms of heat resistance and mechanical properties. The use of an amorphous thermoplastic resin is preferred because it allows the cell walls to expand at a lower heating temperature after forming the core shape by the stretching or corrugating method compared to crystalline resins. The heating temperature is preferably between −20°C and +80°C, and more preferably between −10°C and +50°C, relative to the glass transition temperature of the resin used.

[0024] Examples of thermosetting resins include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, urea resins, melamine resins, thermosetting polyimide resins, BT resins, cyanate ester resins, bismaleimide resins, benzoxazine resins, copolymers, modified products, and / or blends of two or more of these. Among these, in terms of heat resistance and mechanical properties, at least one thermosetting resin selected from the group consisting of epoxy resins, phenolic resins, benzoxazine resins, BT resins, cyanate ester resins, bismaleimide resins, and polyimide resins is more preferred.

[0025] Furthermore, the resin (Cr) may contain other fillers or additives as appropriate depending on the application, etc., within the scope of not impairing the object of the present invention. Examples include inorganic fillers, flame retardants, conductivity imparting agents, crystal nucleating agents, ultraviolet absorbers, antioxidants, vibration dampers, antibacterial agents, insect repellents, deodorizing agents, coloring inhibitors, heat stabilizers, release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, foam control agents, and coupling agents.

[0026] From the viewpoint of improving the flame retardancy of the core material, the LOI (Limiting Oxygen Index) value of the resin (Cr) is preferably 26% or more, more preferably 30% or more. The LOI value can be measured, for example, according to JIS K7201-2 (2007). Examples of resins with an LOI value of 26% or more include polyarylene sulfide resins, polyetherimide resins, polyethersulfone resins, polyarylene ether ketone resins, polyimide resins, and phenolic resins. This LOI value range may be achieved by adding a flame retardant to the resin. For example, a resin composition in which a flame retardant is added to an epoxy resin is preferred because it can achieve high adhesive strength between the skin material and the core material. Phosphorus-based flame retardants, nitrogen-based flame retardants, and inorganic flame retardants are preferably used as flame retardants.

[0027] Flammability can be evaluated based on Advisory Circular (AC) 25.853-1a(1)i "Flammability Requirements for Aircraft Seat Cushions" published by the Federal Aviation Administration, using the burn time measured in accordance with FAR 25.853 Appendix F of the U.S. Federal Aviation Regulations (FAR). According to FAR 25.853 Appendix F, a test specimen is fixed with its long side vertical, and a flame is applied to the center of the bottom edge of the specimen from a position 19 mm directly below using a burner. The burn time is the time it takes for a flame to emerge from the specimen after 60 seconds of heating. The burn time of the core material after the ignition source has been extinguished should be 30 seconds or less, preferably 15 seconds or less.

[0028] A high elastic modulus is required for the core material to exhibit high buckling resistance. The elastic modulus of the cell walls is preferably 1 GPa or more at room temperature (20°C ± 15°C), and more preferably 1 GPa or more at the molding temperature of the skin-core structure. Here, the elastic modulus refers to the storage modulus measured by dynamic mechanical analysis (DMA) in accordance with JIS-K7244-5:1999, with the cell walls sampled from the core material and the thickness direction of the core material (the axial direction of the cell walls) as the longitudinal direction of the test piece. In this case, the molding temperature for the skin-core structure is typically 120 to 180°C, and in the examples of the present application, the storage modulus is measured at room temperature and 180°C.

[0029] The fibers (Cf) constituting the fiber substrate are preferably dispersed in the form of single filaments. Dispersing the fibers in the form of single filaments increases the number of contact points between the fibers, making the sheet substrate more likely to expand. This is also preferable from the viewpoint of improving uniformity, as it also suppresses variations in the physical properties of the sheet substrate.

[0030] The average value of the two-dimensional orientation angle (hereinafter simply referred to as "two-dimensional orientation angle") in the in-plane direction of the cell walls of the fibers (Cf) is preferably 10 to 80°, more preferably 20 to 70°, and even more preferably 30 to 60°. In other words, the closer the two-dimensional orientation angle is to 45°, the more preferable it is. The more the two-dimensional orientation angle deviates from 45°, the more bundled fibers are suggested to be present. When fibers are bundled in a fibrous substrate, it is difficult to ensure isotropy, and it may be difficult to impregnate the fiber bundles with resin.

[0031] The two-dimensional orientation angle will be explained using the drawings. FIG. 3 is a schematic diagram showing the dispersion state of the fiber (Cf) 4 constituting the fiber substrate 2 when only the fiber (Cf) 4 is observed from a direction perpendicular to the cell wall. Focusing on the fiber monofilaments, the fiber (Cf) monofilament 4a intersects with the fiber (Cf) monofilaments 4b to 4g. Here, "intersection" refers to a state in which the fiber monofilament of interest is observed intersecting with other fiber monofilaments in the observed two-dimensional plane; the fiber 4a and the fibers 4b to 4g do not necessarily need to be in contact with each other. The two-dimensional orientation angle is defined as the angle θ between two intersecting fiber (Cf) monofilaments in this two-dimensional plane, and is between 0° and 90°. There are no particular limitations on the method for obtaining a two-dimensional plane from the sheet substrate or core material to measure the two-dimensional orientation angle. For example, a method of observing the fiber orientation from the surface of a sample cut out from the sheet substrate or core material can be used. Then, the average two-dimensional orientation angle is calculated from the obtained two-dimensional plane using the following steps I and II. I. The two-dimensional orientation angles of all intersecting fiber single yarns (for example, fiber single yarn 4a in FIG. 3) are measured for one randomly selected fiber single yarn, and the average value is calculated. If there are many fiber single yarns intersecting the selected fiber single yarn, the average value measured for 20 randomly selected intersecting fiber single yarns is used instead. II. Repeat the measurement in I above five times focusing on another reinforcing fiber single yarn, and calculate the average value.

[0032] The cell walls constituting the core material of the present invention have out-of-plane expandability. "Out-of-plane expandability" refers to the property of the cell walls being able to increase in thickness by heating after the core material's overall shape is formed, i.e., after it is processed into a shape consisting of an aggregate of hollow cylindrical cells. The out-of-plane expandability of the cell walls differs from the thermal expansion that occurs when the constituent fibers (Cf) and resin (Cr) are heated; rather, it is a change in the out-of-plane direction caused by the cell walls increasing their porosity. If the cell walls have expandability, then expanding them after forming a predetermined cell shape, such as a honeycomb structure, can form a porous structure within the cell walls or increase the porosity of an existing porous structure. This expandability typically occurs when the resin (Cr) softens or melts, releasing the bonds between the fibers (Cf).

[0033] To achieve expandability, the fiber (Cf) / resin (Cr) ratio in the cell wall calculated from the following formula 1 is preferably 10 to 100%, more preferably 15 to 60%, and even more preferably 20 to 45%. [Formula 1] Fiber (Cf) / Resin (Cr) ratio [%] = {Fiber (Cf) area [mm 2 ] / Resin (Cr) area [mm 2 ]}×100 Here, the area of the fiber (Cf) and the area of the resin (Cr) refer to the total area of the fiber (Cf) and the total area of the resin (Cr), respectively, in the cross section of the sheet substrate. The area of the fiber (Cf) and the area of the resin (Cr) can be calculated from an image obtained by cutting out a sheet substrate, embedding it in a thermosetting resin such as epoxy, polishing the surface corresponding to the edge of the cross section of the sheet substrate, and observing an area of approximately 500 to 1000 μm wide with an optical microscope or an electron microscope.

[0034] To impart expandability to the cell walls, the cell walls of the core material are joined together with an adhesive, and the glass transition point of the adhesive is preferably set to be equal to or higher than the glass transition point of the resin (Cr). The glass transition point of the adhesive is more preferably 10°C or higher, and even more preferably 20°C or higher, than the glass transition point of the resin (Cr).

[0035] More preferably, the glass transition point of the adhesive is higher than the temperature at which the thermal expansion coefficient becomes 5% (this is the expansion starting temperature), which is the relationship between the heating temperature and the cell wall size (thickness) measured in accordance with JIS-K7197:1997 using cell walls cut out from the core material and expressed by the following formula 2. [Formula 2] Thermal expansion coefficient of cell wall [%] = {(cell wall thickness at heating temperature tn - cell wall thickness before heating t1) / cell wall thickness before heating t1} × 100 The adhesive used for joining the cell walls preferably has a glass transition point of 150° C. or higher, more preferably 180° C. or higher, and even more preferably 200° C. or higher. By using such an adhesive, peeling of the cell walls during the process of forming the core material can be suppressed, and the heat resistance of the core material can also be improved.

[0036] The amount of adhesive to be applied is not particularly limited as long as the cell walls are sufficiently bonded to each other, but is preferably 5 to 80 g / m 2 is preferable, and 10 to 50 g / m 2 More preferably, 15 to 30 g / m 2 More preferably, 5 g / m 2 If it is less than 80g / m, the adhesive strength may be insufficient due to uneven application of adhesive between cell walls. 2 If it exceeds this, the effect of the increased weight of the core material will be more pronounced.

[0037] When the resin (Cr) is softened or melted under no load and the cell walls 3 are completely expanded in the out-of-plane direction in the shaped core material, the dimensional change rate of the cell walls in the in-plane direction is preferably ±10% or less. If the change rate is within this range, wrinkling and breakage of the cell walls due to expansion can be suppressed.

[0038] From the viewpoint of increasing the degree of freedom in designing the properties to be imparted to the core material, it is preferable that the ratio t2 / t1 of the thickness t2 after expansion of the sheet substrate to the thickness t1 before expansion be 1.05 to 30. t2 / t1 is more preferably 1.5 to 20, and even more preferably 3.0 to 10.

[0039] The core material of the present invention can adjust the thickness and density of the cell walls by expanding any portion of the cell walls. For example, as shown in Figure 4, in the in-plane direction of the core material as a whole, the cell walls 3 near the center remain as pre-expansion cell walls 6, while the cell walls around the periphery are expanded (expanded cell walls 7), creating a region in which the cell wall thickness varies in the in-plane direction of the core material as a whole. For example, if only the peripheral portion of the core material is expanded, the shear properties of the peripheral portion are improved, making it possible to suppress core crush, a problem in manufacturing skin-core structures. This eliminates the need for conventional countermeasures such as forming tapered portions or reinforcing, thereby reducing core material loss, eliminating work processes, and reducing weight. In this way, the core material of the present invention can be designed to vary the cell wall thickness and density in the in-plane direction of the core material as a whole after shaping.

[0040] It is also preferable to form regions in which the thickness and density of the cell walls vary in the out-of-plane direction when viewing the core material as a whole, i.e., in the in-plane direction of the cell walls. For example, as shown in Figure 5, if each cell wall 3 near the opening of the core material is expanded to make it thicker (to form expanded cell wall 7), this is preferable because the contact area with the skin material increases and high adhesive strength is exhibited. In this way, the core material of the present invention can be designed so that the thickness and density of at least some of the cell walls after shaping vary in the in-plane direction of the cell walls.

[0041] <Core material manufacturing method> As an example, the core material of the present invention can be produced by a manufacturing method including the steps of: compressing a fiber substrate composed of stacked dispersed fibers (Cf) in the out-of-plane direction, bonding the fibers (Cf) together with a resin (Cr) to form a sheet substrate; and shaping the sheet substrate into a structure consisting of an aggregate of hollow columnar cells.

[0042] The fiber substrate can be produced by dispersing the fibers (Cf) in strands and / or approximately single fibers in advance. Examples of such methods include dry processes such as the airlaid method, in which the fibers (Cf) are dispersed into a sheet by an air flow, and the carding method, in which the fibers (Cf) are mechanically combed to shape them into a sheet, and a wet process such as the Radlite method, in which the fibers (Cf) are stirred in water to make paper.

[0043] It is more preferable to manufacture the fiber substrate by a wet process. With a wet process, the proportion of fiber (Cf) in the fiber substrate can be easily adjusted by adjusting the concentration of the input fiber, the flow rate (flow rate) of the dispersion, and the speed of the mesh conveyor. For example, by slowing the speed of the mesh conveyor relative to the flow rate of the dispersion, the orientation of the fibers in the resulting fiber substrate becomes less likely to be oriented in the take-up direction, making it possible to manufacture a bulky fiber substrate.

[0044] When producing the fiber base material, it is also preferable to mix a powder or fiber-shaped matrix resin component with the fibers (Cf) beforehand.It is also preferable to mix a resin component to seal the fibers (Cf) that make up the fiber base material.

[0045] The sheet substrate can be produced by applying softened or molten resin (Cr) to the fiber substrate produced as described above, applying pressure, and impregnating the fiber substrate with resin (Cr). More specifically, a preferred example of a method is to heat a laminate in which resin (Cr) is arranged on both sides of the fiber substrate in the thickness direction, and then impregnate the fiber substrate with resin (Cr). Alternatively, a method may be used in which the viscosity of the resin component is reduced using a solvent, and the fiber substrate is then impregnated with the resin, and then the solvent alone is volatilized or evaporated.

[0046] As equipment for impregnating the fiber substrate with the resin (Cr), a press molding machine such as a double belt press can be suitably used. Although productivity can be improved by using an intermittent press system in which two or more machines, one for heating and one for cooling, are arranged in parallel, a double belt press, which can easily perform continuous processing, is excellent in terms of continuous productivity.

[0047] The process of forming the sheet substrate into a structure consisting of an aggregate of hollow columnar cells preferably includes a step of adhering a plurality of the sheet substrates with an adhesive. More specifically, this process can be carried out by a spreading method or a corrugating method. The adhesive used to adhere the sheet substrates to each other in the spreading method or the corrugating method is the same as that used for joining cell walls, and therefore will not be described again.

[0048] When shaping the core material using the spreading method, adhesive is applied in the same stripe pattern to the sheet substrate manufactured in this manner, and the sheet substrates are stacked and the adhesive is hardened to bond each layer at the stripe portions, after which spreading is performed.

[0049] The method for applying the adhesive is not particularly limited, and examples include a method of applying the adhesive in a stripe using a dispenser with an adjustable discharge amount, a method of attaching the adhesive to the convex portions of a roller with concaves and convexes formed thereon and then bringing the substrate into contact with the roll to transfer the adhesive, and a method of applying the adhesive to the substrate via a screen plate with partial through-holes formed therein. Coating with a roller or screen plate is preferred from the viewpoint of workability, as the coating is repeated in the same pattern at equal intervals in the stripe shape.

[0050] The sheet substrates coated with the adhesive in stripes are stacked so that adjacent sheet substrates are offset by half a pitch. The stacking may be done manually or automatically by a robot or the like.

[0051] After laminating the sheet substrates, the adhesive is cured. The adhesive is generally cured by heating. The heating method is not limited, but examples include a method in which the laminate is placed between the hot plates of a press molding machine having hot plates with built-in heaters and heated while being pressed, and a method in which the laminate is placed in a chamber where the temperature is maintained by circulating hot air.

[0052] Then, by gripping and pulling (stretching) the edges of the laminate of sheet substrates, with each layer bonded at the striped portions coated with adhesive, a hollow columnar structure partitioned by the sheet material is formed, i.e., hollow columnar cells with the sheet material as the cell walls are formed.

[0053] Examples of stretching methods include attaching grippers to both outermost layers of the laminate and pulling it, or inserting a pin or the like into the space (columnar cell) where the cells are formed inside the outermost layer of the laminate and pulling it. When pulling, it is preferable to pull evenly so as not to apply excessive tension to any part of the laminate. Therefore, it is preferable to adjust the pulling speed depending on the degree of opening of the laminate. From the viewpoint of reducing the rigidity of the sheet substrate and improving stretchability, it is also preferable to pull the laminate in a heated state.

[0054] In the corrugation method, a sheet substrate is first folded into a corrugated sheet, and then multiple corrugated sheets are stacked and bonded together with an adhesive, with the valleys and peaks offset by half the wave pitch, to form a block. The resulting stack is then heated and pressurized to form hollow columnar structures defined by the sheet substrate. In other words, hollow columnar cells are formed with the sheet material as cell walls.

[0055] The method for bending the sheet substrate into a corrugated plate is not limited, but examples include passing the sheet substrate between a pair of gears or placing the sheet substrate between a pair of molds with corresponding concave and convex shapes and applying pressure to the substrate.

[0056] The method of applying adhesive to each valley and peak of the corrugated sheet, the method of laminating the corrugated sheets, and the method of curing the adhesive for each layer are not particularly limited, and examples thereof include methods similar to the spreading method.

[0057] The core material of the present invention can preferably be further subjected to a process of heating the cell walls entirely or partially to expand the cell walls and adjust the thickness to a desired value. The core material after the cell walls have been expanded in this manner is also one embodiment of the present invention.

[0058] When expanding the cell walls, the heating method is not particularly limited, but the same method as in the curing process described above can be exemplified. Among these, from the viewpoint of uniformly heating the structure consisting of an aggregate of hollow columnar cells, a method of placing the core material in a chamber where the temperature is maintained by circulating hot air is preferred. In this case, from the viewpoint of uniform heating, it is preferable to place the core material so that the hot air passes in the thickness direction of the core material (the direction through the cells). The heating temperature in the expansion process is preferably equal to or higher than the heating temperature in the stretching process described above, and more preferably 150°C or higher.

[0059] <Skin-core structure> As mentioned above, the core material of the present invention is preferably used as a skin-core structure in which a skin material is bonded to at least one, preferably both, surfaces of the core opening where the prismatic cells are open. Hereinafter, in this specification, a particularly preferred embodiment in which skin materials are bonded to both surfaces of the core material will be referred to as a "sandwich structure," especially among skin-core structures. Figure 6 is a schematic diagram showing one embodiment of such a sandwich structure 8. In Figure 6, the core material 1 and the skin material 9 are depicted in a separated state to clarify the structure of the skin-core structure 8. The sandwich structure 8 is constructed by bonding a skin material 9 to the open end surface of the core material 1.

[0060] The skin material preferably contains a resin. If the resin (Sr) of the skin material is a thermoplastic resin, it is preferable to bond the skin material to the core material while heating and pressurizing it at a temperature above the melting point of the resin (Sr). The fibers (Sf) and resin (Sr) that make up the skin material can be selected in the same way as the fibers (Cf) and resin (Cr) that make up the core material (sheet material) described above.

[0061] In a preferred embodiment, the skin material is a fiber-reinforced composite material containing fiber (Sf) and resin (Sr). In this case, the fiber-reinforced composite material serving as the skin material is preferably formed from a prepreg in which a reinforcing fiber substrate containing fiber (Sf) as the reinforcing fiber is impregnated with resin (Sr). The form of the reinforcing fiber is not limited in terms of shape or arrangement, and can be, for example, unidirectional, random, sheet-like, mat-like, woven, or braided. Among these, two-dimensional woven fabrics are preferably used, and although the weave is not particularly limited, plain weave, twill weave, leno weave, and satin weave are preferred. Plain weave structures are particularly suitable because they make it easy to produce thin skin materials.

[0062] There are no particular limitations on the method for bonding the skin material and core material, and examples include bonding with an adhesive or heat welding. For example, an adhesive sheet and a skin material or its precursor prepreg can be placed on both sides of the core opening, and then bonded to the core material while being heated and cured. When the resin (Sr) is a thermosetting resin, examples include the co-bond method, in which the skin material is first cured and then bonded to the core material using an adhesive, and the co-cure method, in which the uncured resin (Sr) is cured and bonded to the core material simultaneously. The co-cure method is preferred because it requires fewer steps than the co-bond method.

[0063] When joining a core material to a skin material, the core material only contacts the skin material at the open ends of the cell walls, making it difficult to achieve a strong bond. To achieve high adhesive strength, it is necessary to control the fluidity of the adhesive or the resin in the skin material, form a resin pool called a fillet, and use the side surfaces of the cell walls for bonding. The core material of the present invention expands near the open ends, i.e., near the area that contacts the skin material when bonding to the skin material, to create a porous structure. This allows the cell walls to be thickened while maintaining mass and strength, thereby increasing the contact area with the skin material and achieving high adhesive strength. Furthermore, a portion of the adhesive or resin (Sr) in the skin material can flow into the porous structure of the core material, further strengthening the bond between the skin material and the core material.

[0064] When expanding the cell walls, the core material may be expanded before bonding to the skin material, or after bonding to the skin material. Alternatively, the expansion may be performed simultaneously with bonding to the skin material. In this case, the core material is heated and pressurized above the softening or melting point of the resin (Cr) of the core material to bond to the skin material, causing the fiber (Cf) to expand the sheet substrate, forming a porous structure at the bonded area between the core material and the skin material.

[0065] When expanding the cell walls after bonding the skin material, it is preferable to use an adhesive that has similar properties to the adhesive used to bond the cell walls described above in relation to the resin (Cr).

[0066] In order to expand the cell walls while maintaining the honeycomb shape, it is preferable that the elastic modulus of the adhesive layer bonding the cell walls together at the expansion temperature of the core material be higher than the elastic modulus of the resin (Cr) at the same temperature. The elastic modulus of each material at the expansion temperature can be measured by cutting out a section of the core material where the cell walls are bonded together via an adhesive, and measuring it in tapping mode using an atomic force microscope (AFM) with the measurement field set to the expansion temperature. [Example]

[0067] 1.Material [Carbon fiber 1] A copolymer consisting mainly of polyacrylonitrile was spun, calcined, and surface-oxidized to obtain continuous carbon fibers with a total of 12,000 single fibers. The properties of this continuous carbon fiber are as follows:

[0068] Single fiber diameter: 7 μm Specific gravity: 1.8 Tensile strength: 4600 MPa Tensile modulus: 220GPa [PEI resin] Polyetherimide resin (SABIC "ULTEM" (registered trademark) 1000) with a basis weight of 17 g / m 2 A resin film was prepared.

[0069] [PC resin] Polycarbonate resin (Mitsubishi Engineering Plastics Corporation's "Iupilon" (registered trademark) H-4000) with a basis weight of 16 g / m 2 A resin film was prepared.

[0070] [PEKK resin] Polyether ketone ketone resin ("KEPSTAN" (registered trademark) 6002 manufactured by Arkema Co., Ltd.) with a basis weight of 17 g / m 2 A resin film was prepared.

[0071] [Carbon fiber substrate 1] Carbon fiber 1 was cut to 6 mm using a cartridge cutter to obtain chopped carbon fiber. A dispersion liquid with a concentration of 0.1% by mass consisting of water and a surfactant (Nacalai Tesque, Inc., Polyoxyethylene Lauryl Ether (trade name)) was prepared, and a carbon fiber substrate was produced using this dispersion liquid, chopped carbon fiber, and a carbon fiber substrate production device. The production device was equipped with a cylindrical container with a diameter of 1000 mm having an opening cock at the bottom of the container as a dispersion tank, and a linear transport section (inclined angle 30°) connecting the dispersion tank and a papermaking tank. A stirrer was attached to the opening on the top surface of the dispersion tank, and chopped carbon fiber and dispersion liquid (dispersion medium) could be introduced through the opening. The papermaking tank was equipped with a mesh conveyor with a 500 mm wide papermaking surface at the bottom, and this mesh conveyor was connected to a conveyor capable of transporting the carbon fiber substrate (papermaking substrate). Papermaking was performed with a carbon fiber concentration in the dispersion liquid of 0.05% by mass. The paper-made carbon fiber substrate was dried in a drying oven at 200°C for 30 minutes to obtain a carbon fiber substrate 1. The resulting weight per unit area was 20 g / m 2 It was.

[0072] [Sheet substrate 1] A laminate was produced in which the carbon fiber substrate 1 was used as the carbon fiber substrate and the PEI resin was used as the resin film, arranged in the order of [resin film / carbon fiber substrate / resin film]. Next, the sheet substrate 1 was obtained through the following steps (I) to (IV). (I) The laminate was placed in a press mold cavity preheated to 380°C, the mold was closed, and held for 120 seconds. (II) Next, a pressure of 8 MPa was applied and maintained for 10 minutes. (III) The cavity temperature was cooled to 80°C while maintaining the pressure. (IV) The mold was opened and the sheet substrate was removed.

[0073] Density 1.42g / cm 3 Thus, a sheet substrate 1 having a thickness of 38 μm was obtained.

[0074] [Sheet substrate 2] A PC resin film was used as the resin film, and a density of 1.37 g / cm was obtained in the same manner as in Sheet Base Material 1, except that the temperature of the press molding die was set to 280°C. 3 Thus, a sheet substrate 2 having a thickness of 38 μm was obtained.

[0075] [Sheet substrate 3] A sheet substrate with a density of 1.44 g / cm was fabricated in the same manner as Sheet Base Material 1, except that PEKK resin was used as the resin film. 3 Thus, a sheet substrate 1 having a thickness of 38 μm was obtained. Sheet substrate 3 was obtained.

[0076] [Sheet substrate 4] The obtained sheet substrate 1 was heated in a hot air oven at an atmospheric temperature of 220°C for 30 minutes, and expanded to a thickness 2.0 times that of sheet substrate 1, resulting in a density of 0.71 g / cm 3 Thus, a sheet substrate 4 having a thickness of 76 μm was obtained.

[0077] [Sheet substrate 5] The obtained sheet substrate 1 was heated for 20 minutes in a hot air oven at an atmospheric temperature of 270°C, and expanded to a thickness 5.2 times that of sheet substrate 1, resulting in a density of 0.27 g / cm 3 Thus, a sheet substrate 5 having a thickness of 200 μm was obtained.

[0078] [Prepreg 1 used as skin material] Epoxy resin (Huntsman Advanced Materials Co., Ltd.'s "Araldite (registered trademark)" MY721: 40 parts by mass, Japan Epoxy Resins Co., Ltd.'s "Epikote (registered trademark)" 828: 35 parts by mass, "Epikote (registered trademark)" 1001: 25 parts by mass, "Epikote (registered trademark)" 154: 25 parts by mass) and polyethersulfone (Sumitomo Chemical Co., Ltd.'s "Sumikaexcel (registered trademark)" PES The epoxy resin composition was then kneaded in a kneader with 5 parts by mass of polyethersulfone (5003P) under heating to uniformly dissolve the polyethersulfone. Polyamide particles (13 parts by mass of "Amilan (registered trademark)" SP-500, manufactured by Toray Industries, Inc.) and a curing agent (36 parts by mass of "Seikacure (registered trademark)" S, manufactured by Seika Corporation) were then added to the kneader to prepare an uncured epoxy resin composition, from which an epoxy resin film was produced using a knife coater. The composition was then superimposed on both sides of a carbon fiber fabric, and the resin composition was impregnated while heating and pressurizing using heat rolls to produce prepreg 1 with a fiber volume content of 60%. The carbon fiber fabric used was plain weave fabric CF6273H (193 g / m²) made of Torayca (registered trademark) T700G-12K carbon fiber (12,000 fibers, tensile strength of 4.9 GPa, tensile modulus of elasticity of 240 GPa, tensile elongation of 2.1%) manufactured by Toray Industries, Inc. 2 ) was used.

[0079] 2. Evaluation Method [Evaluation of the area ratio (bonding area ratio) occupied by cell walls on the core opening surface] The open surface of the core material was photographed using an optical microscope, and a randomly selected 50mm x 50mm area on the photograph was image processed using an image processing device (KEYENCE: CV-3000) to evaluate the area ratio (adhesion area ratio) occupied by the cell walls on the open surface.

[0080] [Measurement of climbing drum peel strength] A sandwich structure in which a skin material was bonded to a honeycomb core (hereinafter referred to as a "honeycomb sandwich structure") was produced according to the following procedures (1) and (2). (1) Sample stacking Prepreg 1 was laminated in a two-ply symmetrical configuration of (±45°) / (0° / 90°) on the top and bottom of the core opening of each honeycomb core (the outermost layer was at ±45° with respect to the honeycomb core). (2) Forming honeycomb sandwich structure samples The following steps (a) to (d) were carried out.

[0081] (a) A preform in which prepregs are laminated as skin materials 9 on a honeycomb core (core material) 1 is placed on an aluminum tool plate 16 coated with a mold release agent.

[0082] (b) A Teflon film 10, silicone rubber 11, and bleeder 12 were laminated in this order on the surface of the prepreg, and the whole was covered with a nylon backing film 13. A sealant 15 was placed between an aluminum tool plate 16 and the nylon bag film 13 to form an airtight space. Thereafter, the inside of the nylon backing film 13 (hereinafter abbreviated as the system) was suctioned with a vacuum nozzle 14 to maintain a vacuum, and the system was then placed in an autoclave.

[0083] (c) The pressure inside the autoclave is increased to 0.15 MPa, then the pressure inside the system is returned to normal pressure, and then the pressure inside the autoclave is increased to 0.30 MPa, after which the temperature is started to be increased.

[0084] (d) The pressure inside the autoclave is maintained at 0.30 MPa until molding is complete, and the temperature is raised to 180°C at 1.5°C / min., and then left at 180°C for 2 hours to harden the resin and bond it to the honeycomb core. After that, the temperature is lowered to room temperature at 2°C / min. to form a honeycomb sandwich structure.

[0085] A sample was cut out from the above honeycomb sandwich structure, and the climbing drum peel strength between the skin panel on the aluminum tool plate side and the honeycomb core was measured according to ASTM D1781.

[0086] [Buckling resistance of honeycomb core] A honeycomb sandwich structure was formed in the same manner as in (2) of [Measurement of climbing drum peel strength] above.

[0087] The core retention rate during molding was measured according to the following procedures (1) to (4), and the buckling resistance of the cell walls of the honeycomb core was evaluated according to the following three levels.

[0088] Good: Core retention rate is 99% or higher.

[0089] fair: Core retention is less than 99% and greater than or equal to 90%.

[0090] Bad: Core retention rate is less than 90%. (1) Two plies of prepreg 1 (±45°) / (0° / 90°) are placed on the top and bottom of each honeycomb core whose peripheral edges have been chamfered to a 45° angle, and then laminated. (2) Measure the horizontal and vertical dimensions A and B of the top surface before molding (as shown in Figure 7B). (3) Measure the horizontal and vertical dimensions a and b of the top surface after molding (as shown in Figure 7C). (4) Core retention rate (%) = (a × b) × 100 / (A × B) [Compression strength] Samples were cut from the skin-core structure described above and tested in accordance with MIL-STD-401 to measure compressive strength (tested by stabilized compression).

[0091] 3. Fabrication of Honeycomb Core-Honeycomb Sandwich Structure The honeycomb cores and sandwich structures produced in the examples and comparative examples will be described below.

[0092] [Example 1] Honeycomb core Sheet substrate 1 was cut into multiple pieces, each with a width of 1.9 mm, a pitch of 7.3 mm, and a basis weight of 20 g / m. 2The epoxy adhesive was applied in stripes. In the lamination process, the sheet substrates 1 coated with the adhesive were laminated while being shifted by half a pitch to obtain a laminate. In the curing process, the obtained laminate was sandwiched between aluminum plates, placed in a hot air oven with an ambient temperature of 180°C, and heated for 3 hours to cure the adhesive. In the spreading process, after curing, a gripping portion made of aluminum foil was joined to the outermost layer of the laminate, and the laminate was spread while being heated in a hot air oven with an ambient temperature of 210°C. Through the spreading process, a core material with a cell pitch of 3.2 mm (core material thickness (axial direction of the cell wall) 12.7 mm, mass per unit volume 39 kg / m) was obtained. 3 ) was produced.

[0093] The obtained core material was heated for 30 minutes in a hot air oven with the atmospheric temperature set to 230°C as an expansion process, to obtain a honeycomb core with a cell wall thickness increased by 2.8 times.

[0094] Honeycomb sandwich structure A honeycomb sandwich structure having a laminate structure of [prepreg laminate / adhesive film / honeycomb core / adhesive film / prepreg laminate] was fabricated from the honeycomb core obtained by the above method and a two-ply prepreg laminate using prepreg 1. The evaluation results of the obtained honeycomb core and honeycomb sandwich structure are shown in Table 1.

[0095] [Example 2] Honeycomb core In the expansion step, the same procedure as in Example 1 was carried out except that the atmospheric temperature was set to 270° C. and the heating time was set to 20 minutes, and a honeycomb core with a cell wall thickness increased by 5.2 times was obtained.

[0096] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0097] [Example 3] Honeycomb core The honeycomb core obtained in Example 1 was used, and the same procedures were carried out as for the honeycomb core of Example 1, except that an insulating plate was placed in the center of the honeycomb core to sandwich it, making it difficult to heat the central part of the honeycomb core. A honeycomb core was obtained in which the thickness of the cell walls at the peripheral part of the honeycomb core was 2.8 times greater.

[0098] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0099] [Example 4] Honeycomb core Using the honeycomb core obtained in Example 1, the release film / honeycomb core was placed on a heating plate at a temperature of 230°C, in that order, and heated for 3 minutes. After that, the release film / honeycomb core was removed from the heating plate and allowed to cool. Similarly, the honeycomb core was turned upside down and the other side was heated. This resulted in a honeycomb core in which only the cell walls near the open surfaces of the core material had expanded by 2.8 times, as shown in Figure 5.

[0100] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0101] [Example 5] Honeycomb core A honeycomb core (core material thickness 12.7 mm, cell wall thickness 61 μm, mass per unit volume 38 kg / m) was prepared in the same manner as in Example 1, except that sheet base material 2 was used as the sheet base material, the ambient temperature in the curing process was 130°C, and the ambient temperature in the expansion process was 150°C. 3 ) was obtained.

[0102] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0103] [Example 6] Honeycomb core A honeycomb core (core material thickness 12.7 mm, cell wall thickness 68 μm, mass per unit volume 39 kg / m) was prepared in the same manner as in Example 1, except that sheet base material 3 was used as the sheet base material and the atmospheric temperature during the expansion process was set to 170°C. 3 ) was produced.

[0104] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0105] [Example 7] Honeycomb core A honeycomb core (thickness of core material: 12.7 mm, mass per unit volume: 39 kg / m) was prepared in the same manner as in Example 1, except that sheet base material 4 was used as the sheet base material. 3 ) was produced.

[0106] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0107] [Comparative Example 1] Honeycomb core Aramid honeycomb (manufactured by Showa Aircraft Industry Co., Ltd., model number: SAH1 / 8-3.0, core thickness 12.7 mm, mass per unit volume 48 kg / m 3 ) was used as the honeycomb core.

[0108] Honeycomb sandwich structure Using this honeycomb core, a honeycomb sandwich structure was produced in the same manner as in the honeycomb sandwich structure of Example 1. Table 1 shows the evaluation results of the obtained honeycomb core and honeycomb sandwich structure.

[0109] Comparative Example 2 Honeycomb core An attempt was made to manufacture a honeycomb core in the same manner as in Example 1, except that sheet base material 5 was used as the sheet base material, but during the expansion process, some parts of the sheet base materials (cell walls) peeled off from each other. Furthermore, even in the parts where the sheet base materials (cell walls) were bonded to each other, the rigidity of the sheet base material was high, making it difficult to deform the sheet base material to a shape with a cell pitch of 3.2 mm.

[0110] [Table 1] [Industrial Applicability]

[0111] The core material and skin-core structure of the present invention can be suitably used as structural members for automobile interior and exterior materials, solar cell reinforcements, sports equipment structures, aircraft interior materials, flying vehicle structures, satellite casings, transport boxes, and the like. [Explanation of symbols]

[0112] 1: Core material 2: Fiber base material 3: Cell wall 4: Fiber (Cf) 4a-4g: Fiber (Cf) single yarn 5: Resin (Cr) 6: Cell wall before expansion 7: Cell wall after expansion 8: Skin-core structure (sandwich structure) 9: Skin material (prepreg) 10: Teflon (registered trademark) film 11: Silicone rubber 12: Breeder 13: Nylon bag film 14: Vacuum nozzle 15: Sealant 16: Aluminum tool plate A: Width of core material before molding B: Length of core material before molding a: Width of core material after molding b: longitudinal dimension of core material after molding

Claims

1. A core material comprising an aggregate of hollow columnar cells partitioned by cell walls, The cell walls include a fiber substrate formed by stacking dispersed fibers (Cf), Within the cell walls, the fibers (Cf) are bonded together by resin (Cr) while the fiber base material is compressed in the out-of-plane direction, and the cell walls have expandability in the out-of-plane direction. A core material.

2. 2. The core material according to claim 1, wherein the expandability in the out-of-plane direction is exhibited by releasing the bonds between the fibers (Cf) due to softening or melting of the resin (Cr).

3. 3. The core material according to claim 2, wherein in the cell assembly, cell walls are bonded together with an adhesive, and the glass transition point of the adhesive is equal to or higher than the glass transition point of the resin (Cr).

4. 4. The core material according to claim 3, wherein the adhesive has a glass transition temperature of 150°C or higher.

5. 5. The core material according to claim 2, wherein the dimensional change rate of the cell walls in the in-plane direction when the cell walls are heated in an unloaded state to soften or melt the resin (Cr) and maximize the expansion of the cell walls in the out-of-plane direction is ±10% or less.

6. 4. The core material according to claim 1, wherein the fiber (Cf) / resin (Cr) ratio in the cell wall calculated from the following formula 1 is 10 to 100%. [Formula 1] Fiber (Cf) / Resin (Cr) ratio [%] = {Area of fiber (Cf) [mm ２ ] / area of resin (Cr) [mm ２ ]×100

7. 4. The core material according to claim 1, wherein the average value of the two-dimensional orientation angle of the fibers in the cell walls is 10 to 80 degrees.

8. 4. The core material according to claim 1, wherein the ratio (t2 / t1) of the thickness t1 before expansion to the thickness t2 after expansion of the cell walls is 1.05 to 30.

9. The resin (Cr) is at least one amorphous thermoplastic resin selected from the group consisting of polycarbonate (PC), polyphenylene ether (PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone (PES) and polyarylate (PAR). The core material according to any one of claims 1 to 3.

10. 4. The core material according to claim 1, wherein there are regions in which the thickness of the cell walls varies in the in-plane direction when the core material is viewed as a whole.

11. 4. The core material according to claim 1, wherein at least some of the cell walls constituting the core material have portions where the thickness and density of the cell walls vary in the in-plane direction of the cell walls.

12. A method for manufacturing a core material having a structure consisting of an aggregate of hollow columnar cells partitioned by cell walls, comprising: A step of producing a sheet substrate by binding the fibers (Cf) together with a resin (Cr) in a state where a fiber substrate formed by stacking dispersed fibers (Cf) is compressed in an out-of-plane direction; a step of forming the sheet substrate into a structure consisting of an aggregate of hollow columnar cells; A method for manufacturing a core material having the above structure.

13. The method for manufacturing a core material according to claim 12, wherein the shaping step includes a step of adhering a plurality of the sheet substrates with an adhesive, and the glass transition point of the adhesive is higher than or equal to the glass transition point of the resin (Cr).

14. The method for manufacturing a core material according to claim 13, wherein the adhesive has a glass transition temperature of 150°C or higher.

15. The method for producing a core material according to any one of claims 12 to 14, wherein the shaping is carried out by a spreading method or a corrugating method.

16. The method for manufacturing a core material according to any one of claims 12 to 14, further comprising the step of heating at least a portion of the cell walls by heating to expand the cell walls.

17. A skin-core structure obtained by joining a skin material to the open surface of the core material according to any one of claims 1 to 3.

18. A structural member used as an automobile interior / exterior material, a solar cell reinforcement body, a structural material for sporting goods, an aircraft interior material, a flying object structural material, an artificial satellite housing, or a transport box, comprising the core material according to any one of claims 1 to 3 or the skin-core structure according to claim 17.

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