Method for manufacturing fiber-reinforced resin articles and fiber-reinforced resin articles

Abstract

The present invention provides a useful improvement which relates to a method for producing a fiber-reinforced resin article that at least partially has a hollow structure part.　A method for producing a fiber-reinforced resin article according to the present invention comprises: a molding step in which a prepreg preform that is provided with a core-containing part, within which a fusible core that is formed of a wax material is arranged, is arranged in a press mold and heated, thereby obtaining a cured product that has a hollow structure part; and a core removal step in which the fusible core is removed from the cured product. The prepreg preform is provided with a through hole in the core-containing part; and an elastomer plug is inserted into the through hole.

Description

Technical Field

[0001] The present invention mainly relates to a method for manufacturing a fiber reinforced resin article and a fiber reinforced resin article. This application claims priority based on International Application PCT / JP2021 / 011690 under the Patent Cooperation Treaty filed with the Japan Patent Office as the receiving office on March 22, 2021, and Japanese Patent Application No. 2021-069189 filed with the Japan Patent Office on April 15, 2021, and incorporates the content herein by reference.

Background Art

[0002] Fiber Reinforced Plastic (FRP) is used in various applications including reinforcement members for automobiles. A method has been proposed for manufacturing a fiber reinforced resin article having a hollow structure portion by heating and curing a prepreg preform together with a core made of a wax material in a press mold (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention aims to provide a useful improvement regarding a method for manufacturing a fiber reinforced resin article having at least a part of a hollow structure portion by heating and curing a prepreg preform together with a core made of a wax material in a press mold. The object of the present invention includes providing a technique useful for preventing the hollow structure portion from bulging and deforming after molding is completed and the press mold is opened. Problems addressed by each embodiment of the present invention may be disclosed explicitly or implicitly herein. [Means for solving the problem]

[0005] One aspect of the present invention provides a method for manufacturing a fiber-reinforced resin, comprising a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is disposed inside, in a press die and heating it to obtain a cured product having a hollow structure, and a core removal step of removing the fusible core from the cured product, wherein a through hole is formed in the core-enclosed portion of the prepreg premolded body and an elastomer plug is inserted into the through hole.

[0006] In another aspect of the present invention, a method for producing a fiber-reinforced resin is provided, comprising: a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is disposed inside, in a press die and heating it to obtain a cured product having a hollow structure; and a core removal step of removing the fusible core from the cured product, wherein a first through-hole and a second through-hole are formed in the prepreg premolded body in the core-enclosed portion, a first elastomer plug is inserted into the first through-hole, and a second elastomer plug is inserted into the second through-hole.

[0007] In yet another aspect of the present invention, a fiber-reinforced resin article is provided, having a hollow structure, a cavity formed in the hollow structure, a through hole leading from the internal space of the cavity to the outside, and an elastomer stopper that closes the through hole. [Effects of the Invention]

[0008] A useful improvement is provided to a method for manufacturing a fiber-reinforced resin article having at least a portion of a hollow structure, by placing a prepreg premolded body together with a core made of wax material in a press die and curing it. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a flowchart of a fiber-reinforced resin article manufacturing method according to an embodiment. [Figure 2] Figure 2 is a schematic perspective view of a fiber-reinforced resin article. [Figure 3] Figure 3 is a schematic cross-sectional view of a fiber-reinforced resin article. [Figure 4] Figure 4 is a cross-sectional view of the fusible core. [Figure 5] Figure 5 is a cross-sectional view of a prepreg premolded body that has been fabricated with a core positioned inside. [Figure 6] Figure 6 is a cross-sectional view showing an elastomer plug inserted into a through-hole in a prepreg premolded body that has been fabricated to have a core positioned inside. [Figure 7] Figure 7 is a cross-sectional view showing the prepreg premolded body being placed into the mold together with the fusible core. [Figure 8] Figure 8 is a cross-sectional view showing the prepreg premolded body being placed into the mold together with the fusible core. [Figure 9] Figure 9 shows how one end of a metal tube is inserted through an elastomer stopper, allowing wax to be discharged into a recovery container from the cavity in the hollow structure of the fiber-reinforced resin article through the metal tube. [Figure 10] Figure 10 shows that air is introduced into the cavity in the hollow structure of the fiber-reinforced resin article through a metal tube that penetrates one of the elastomer stoppers, while wax is discharged from the cavity into the recovery container through another metal tube that penetrates the other elastomer stopper. [Figure 11] Figure 11 is a cross-sectional view showing the structure of a partially fusible core. [Modes for carrying out the invention]

[0010] 1. Method for manufacturing fiber-reinforced resin articles One embodiment of the present invention relates to a method for producing fiber-reinforced resin articles (hereinafter also referred to as FRP articles). The FRP article manufacturing method according to the embodiment consists of the following two steps, as shown in the flow in FIG. 1. (i) A molding step of placing a prepreg preform provided with a core inclusion part having a fusible core made of a wax material inside in a press mold and heating it to obtain a cured product having a hollow structure part. (ii) A core removal step of removing the fusible core from the cured product. Hereinafter, the FRP article manufacturing method according to the embodiment will be described in detail while referring to the drawings.

[0011] 1.1. Molding step The molding step is a step of placing a prepreg preform provided with a core inclusion part having a fusible core made of a wax material inside in a press mold and heating it to obtain a cured product.

[0012] (Prepreg preform) The prepreg preform is prepared in advance outside the press mold using a prepreg such as a prepreg sheet or a tow prepreg as the main material so as to have a near net shape. When a prepreg sheet is used, two or more prepreg sheets may be laminated in part or in whole of the prepreg preform. The part where a plurality of prepreg sheets are laminated may include two or more prepreg sheets of the same kind, or may include two or more different kinds of prepreg sheets, or both. The prepreg preform using a prepreg sheet may have a part reinforced with a tow prepreg. The prepreg preform may be formed entirely or in part only of tow prepregs.

[0013] The fiber reinforcing material used for the prepreg is various, such as continuous fibers, chopped fibers, woven fabrics, non-woven fabrics, non-crimp fabrics, etc. A prepreg sheet having a plurality of continuous fiber bundles arranged in parallel as a fiber reinforcing material is called a unidirectional prepreg (UD prepreg). A prepreg sheet that uses a fabric made of continuous fiber bundles as a fiber reinforcement material is called a cross prepreg. Prepreg sheets that use a mat formed by depositing chopped fiber bundles as a fiber reinforcement material are called SMC (sheet molding compound). Tow prepreg is a prepreg that uses a single continuous fiber bundle as a reinforcing material. Examples of fibers used in fiber reinforcement materials include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, and metal fibers. Two or more types of fibers may also be used in combination.

[0014] Examples of thermosetting resins used in prepregs include epoxy resins, urea resins, vinyl ester resins (also called epoxy acrylate resins), unsaturated polyesters, polyurethanes, and phenolic resins. Two or more thermosetting resins may be used in mixture form. The content of the thermosetting resin composition in the prepreg is not limited, but is, for example, 15 to 60% by mass. This content may be 15 to 20% by mass, 20 to 25% by mass, 25 to 40% by mass, 40 to 50% by mass, 50 to 60% by mass, etc. Various additives can be added to thermosetting resin compositions. Examples include reactive diluents, flame retardants, defoamers, defoaming agents, mold release agents, particulate fillers, colorants, and silane coupling agents.

[0015] The prepreg premolded body is manufactured such that a fusible core is positioned in a location corresponding to the cavity formed in the hollow structure of the FRP article to be manufactured. In other words, the prepreg premolded body is manufactured with a core-enclosed portion in which the fusible core is positioned on the inside, in the part that will become the hollow structure after curing. For example, when manufacturing a hollow FRP article 1 in the shape of a rectangular prism, as shown in Figures 2 and 3, where the top and bottom surfaces are square and the four sides are rectangular, a prepreg premolded body is produced by the procedure described below.

[0016] First, as shown in Figure 4, a fusible core 10 is prepared that has approximately the same shape and dimensions as the cavity inside the FRP article 1. The fusible core is formed from a wax material so that it can be completely melted and removed in a core removal process that takes place after the molding process. Details about the wax materials will be discussed later.

[0017] Next, as shown in Figure 5, a prepreg premolded body 20 with approximately the net shape is formed by arranging prepreg sheets around the fusible core 10. In this example, the entire prepreg premolded body 20 corresponds to the core encapsulation portion. When preparing the prepreg preformed body 20, a through hole H having an inner diameter of preferably 10 mm or less is formed in a portion of the prepreg sheet used as the material beforehand.

[0018] Finally, as shown in Figure 6, an elastomer plug P is inserted from the outside into the through hole H formed in the prepreg sheet. A gap may remain between the through-hole H and the elastomer plug P. This gap will be filled by the fluid deformation of the prepreg sheet when the prepreg premolded body 20 is cured. The elastomer stopper P is tapered in the direction opposite to the insertion direction into the through hole H. That is, the elastomer stopper P is inserted into the through hole H with the side having a larger cross-sectional area perpendicular to the insertion direction facing the fusible core 10. The reason for this is to prevent the elastomer stopper P from coming out due to the pressure inside the cavity after the molding process and before the wax is discharged.

[0019] For example, in order to prevent the elastomer stopper from coming loose after the molding process, in addition to tapering the elastomer stopper as described above, or instead, a protrusion or recess may be provided on the side of the elastomer stopper. The material of the elastomer stopper is not limited, but may include, for example, acrylic rubber, fluororubber, silicone rubber, nitrile rubber, or butyl rubber.

[0020] (hardening) In this specification, the temperature of the press die used to cure the prepreg preform is referred to as the molding temperature. The molding temperature should be such that the prepreg premolded body can be cured in preferably 1 hour or less, more preferably 40 minutes or less, and even more preferably 20 minutes or less. The molding temperature can be, for example, 100°C or higher, and may be 120°C or higher, or even 130°C or higher. The higher the molding temperature, the shorter the time required for the prepreg premolding to harden. When the molding temperature exceeds 160°C, the range of wax materials available becomes limited. From the viewpoint of shortening the time required to heat the press die and reducing energy consumption, the molding temperature can be set to 150°C or lower, and even 140°C or lower.

[0021] The temperature of the press die is maintained at the molding temperature by the temperature control mechanism typically provided by the press molding machine, even before the prepreg premolding body is introduced. Figure 7 shows the prepreg premolded body 20, as shown in Figure 6, being placed into a press die 100 consisting of a lower die 102 and an upper die 104. Since the press die 100 is pre-heated to the molding temperature, the temperature rise and subsequent expansion of the fusible core 10 begin immediately after it is introduced into the press die 100 along with the prepreg pre-molded body 20. At this time, it is not necessary for the wax material in the fusible core 10 to soften or melt. As the fusible core 10 expands, the prepreg preform 20 is pressed against the inner surface of the press die 100. In other words, the pressure generated within the press die 100 as the fusible core 10 attempts to expand against the clamping force is applied to the prepreg preform 20. The higher the pressure, the fewer voids there will be in the FRP formed by the curing of the prepreg.

[0022] In one example, as shown in Figure 8, the press die 100 used in the molding process may include a cavity formed by a lower die 102, an upper die 104, and a slide core 106. The movement of the slide core 106 is controlled by a pressure control mechanism (not shown) using hydraulics or the like, and even if the fusible core 10 expands, the slide core 106 will not move until the pressure inside the mold reaches a predetermined value. When the pressure inside the press mold 100 is about to exceed the predetermined value, the slide core 106 moves horizontally to relieve the pressure. Controlling the molding pressure to stay within a certain range using such a press mold is advantageous for stabilizing the quality of FRP articles.

[0023] Here's a brief explanation of the wax materials: Since wax materials expand significantly when they soften or melt, it is preferable for the wax material to soften or melt during the molding process when high pressure is to be applied to the prepreg premolded body. In this case, it is necessary for the expansion due to the softening of the wax material to begin before the plasticity of the prepreg premolded body is lost due to the progression of hardening. One way to accelerate the softening of wax materials is to lower the softening temperature. Another way to accelerate the softening of the wax material is to preheat the fusible core before placing it in the press die, thereby bringing its temperature closer to the softening temperature of the wax material. When preheating the fusible core, simply place the prepreg premolded body together in an oven. These two methods can be employed simultaneously.

[0024] It is preferable that the time from when the wax material begins to soften until it melts and becomes a highly fluid liquid is long. When this time is sufficiently long, the prepreg premolded body hardens before the wax material melts, so the molten wax material does not flow into the gap between the prepreg premolded body and the press die.

[0025] Polyolefin waxes are preferred for use in wax materials due to their long softening and melting time. Typical examples of polyolefin waxes are polyethylene wax and polypropylene wax. Preferred examples of polyolefin waxes include pyrolysis-type polyethylene wax, which is a pyrolysis product of polyethylene resin, and pyrolysis-type polypropylene wax, which is a pyrolysis product of polypropylene resin.

[0026] In one example, the fusible core may consist of a first portion made of a first wax material having a melting point lower than the molding temperature, and a second portion made of a second wax material that is incompatible with the first wax material and has a melting point higher than the molding temperature. By adjusting the volume ratio of the first portion, which softens and expands in the press die, and the second portion, which does not soften in the press die, the pressure generated in the press die can be controlled.

[0027] When a polyolefin wax is blended into the first wax material, the second wax material preferably contains a wax that includes an organic compound having a polar group. This is because waxes mainly composed of hydrocarbons and waxes composed of organic compounds having a polar group are often incompatible with each other. Polar groups are functional groups (excluding ether groups) that contain a carbon-oxygen bond or a carbon-nitrogen bond, such as hydroxyl groups, amino groups, amide groups, carbonyl groups, carboxyl groups, and ester groups. Typical examples of waxes containing organic compounds with polar groups include waxes containing one or more organic compounds selected from hydroxy fatty acid amides, fatty acid amides, hydroxy fatty acid esters, and fatty acid esters.

[0028] 1.2. Core Removal Process The core removal step (ii) is a step in which the core used in the molding step is removed from the cured product obtained in the molding step. If the pressure inside the cavity remains high even after the molding process is complete and the press die has been opened, the hollow structure of the hardened material is prone to swelling and deformation. To prevent this, it is preferable to immediately pierce one end of the metal tube 200 through the elastomer stopper P as soon as the upper die is lifted, as shown in Figure 9, to reduce the pressure inside the cavity. By connecting the other end of the metal tube 200 to the recovery container 300, the internal pressure of the cavity can be safely reduced.

[0029] As a variation, the press die 100 may be provided with a through-hole for passing the metal tube 200 through, and before lifting the upper die, the metal tube 200 may be pierced through this through-hole into the hardened material 30 inside the press die 100 to reduce the pressure inside the cavity. In this modified embodiment, the timing of piercing the metal tube 200 may be after or before the die opens.

[0030] To completely remove the wax material from the hollow structure of the cured product, one can, for example, heat the FRP article in an oven to completely melt the fusible core inside the hollow structure. When discharging the wax material through the metal tube 200, it is preferable to heat at least a portion of the metal tube to prevent the wax from solidifying inside the metal tube.

[0031] To shorten the time required for wax material discharge, multiple through-holes can be provided in the hollow structure of the cured product. Air can be introduced into the cavity through some of these through-holes while the wax is discharged out of the cavity through the other through-holes. The through-holes may be created after the molding process using a drill or hole saw.

[0032] In one example, as shown in Figure 10, air can be introduced into the cavity through a metal tube 201 inserted into an elastomer stopper P1 that seals a through-hole in the hollow structure of the cured product 30, while the wax in the cavity can be discharged through a metal tube 202 inserted into an elastomer stopper P2 that seals another through-hole. The number of through-holes sealed by elastomer stopper P1 and the number of through-holes sealed by elastomer stopper P2 are not limited to one, but may be two or more.

[0033] The end of the metal tube 201 that is not inserted into the cavity is open to the atmosphere. However, when air flows into the cavity through the metal tube 201, pressure loss occurs, which can cause the pressure inside the cavity to become lower than atmospheric pressure. To minimize this pressure loss, it is preferable that the metal tube 201 be as short as possible and that its inner diameter be as large as possible.

[0034] The example shown in Figure 10 may be modified to allow pressurized gas to flow into the cavity through the metal tube 201. For example, the end of the metal tube 201 that is not inserted into the cavity can be connected to a compressor to supply pressurized air to the cavity. Alternatively, instead of a compressor, a gas cylinder can be connected to supply pressurized inert gas (e.g., nitrogen gas) to the cavity. In the embodiment in which gas is introduced into the cavity using the metal tube 201, it is not essential to use the metal tube 202 for wax discharge; the wax may be discharged from the cavity through a through hole formed in the cured product after the molding process.

[0035] 1.3. Various Embodiments Various additives can be added to the fusible core used in the FRP article manufacturing method according to the embodiment, as needed. For example, a fusible core can be inductively heated by adding particles of a material that generates heat under a high-frequency electromagnetic field. Examples of such materials include ferromagnetic materials, ferrimagnetic materials, and conductive materials. Examples of ferromagnetic materials include iron, nickel, cobalt, iron alloys, nickel alloys, cobalt alloys, permalloy, and many types of steel. Examples of ferrimagnetic materials include magnetite, nickel-zinc ferrite, manganese-zinc ferrite, and copper-zinc ferrite. Examples of conductive materials include copper, aluminum, and brass.

[0036] In another example, a fusible core can be made microwave-heatable by adding particles of a material that has the property of absorbing microwaves and generating heat. Examples of such materials include silicon carbide, ferrite, barium titanate, anatase titanium oxide, graphite, and carbon black. Induction heating or microwave heating of the fusible core can preferably be performed when preheating the fusible core outside the press mold.

[0037] When a fusible core is provided with a first part and a second part, a coloring agent such as a pigment or dye can be used to make them visually distinguishable by the difference in color. The coloring agent may be added to either the first part or the second part, or to both. By making the first and second parts different in color, it is possible to prevent mistakes in the placement of the first and second parts when assembling a fusible core, for example. In the process of separating the first and second wax materials by melting the first and second parts after the core removal process, it is advantageous if the first and second parts have different colors.

[0038] In a configuration in which the wax material melts in at least a portion of the fusible core during the molding process, a partially fusible core may be used instead of a fusible core. As illustrated in the cross-sectional view in Figure 11, the partially fusible core 14 consists of a fusible core (fusible portion) 10 made of wax material and an outer shell 12 covering the fusible core. When the wax material melts in the fusible core (fusible portion), the outer shell prevents the molten wax material from entering the gap between the prepreg premolded body and the press die.

[0039] In order to prevent the outer shell 12 from rupturing when the fusible core (fusible portion) 10 deforms or expands during the molding process, the material of the outer shell 12 of the partially fusible core 14 must be able to undergo tensile deformation at the molding temperature. This tensile deformation may be elastic, plastic, or have both properties. Therefore, preferred materials for the outer shell 12 are, but are not limited to, organic materials, and in particular, resin materials. Preferred materials for the outer shell include synthetic polymers such as polyolefins, polyamides, polyesters, polyurethanes, silicones, and fluororubber, and further include elastomers made of these polymers.

[0040] When manufacturing the partially fusible core 14, for example, the fusible core (fusible portion) 10 is wrapped in a polymer film prepared for the outer shell 12 and sealed by adhesion or fusion. The outer shell 12 can also be formed using a shrink tube made of the above polymer. A shrink tube with a fusible core (fusible portion) inside is heat-shrunk, and then both ends of the shrink tube are heat-sealed.

[0041] The outer shell 12 can also be formed using a low-temperature curing liquid rubber made of the above polymer. The liquid rubber is applied to the surface of the fusible core (fusible part) 10 and cured at a temperature in which the wax does not melt. The outer shell 12 can also be formed from a UV-curable elastomer. A UV-curable elastomer is a UV-curable resin in which the cured product becomes an elastic material like rubber. Examples include UV-curable silicone rubber and UV-curable urethane acrylate. UV-curable elastomers are suitable as outer shell materials because they can be cured in a short time even at room temperature.

[0042] 1.4. Scope of Application The FRP article manufacturing method according to this embodiment is also applicable when manufacturing large FRP articles from two or more partial prepreg premolded bodies. In an FRP article manufactured by the FRP article manufacturing method according to the embodiment, the FRP may be molded in such a way that a composite is formed between it and a part made of a material other than FRP, such as metal.

[0043] 2.FRP goods Another embodiment of the present invention is an FRP article manufactured by the FRP article manufacturing method according to the embodiment described with reference to specific examples in Section 1 above. The hollow FRP article 1 shown in Figure 2 consists entirely of a single hollow structure, and as shown in Figure 3, its interior is hollow. The FRP article 1 has a through hole H' that leads from the internal space of the hollow to the outside, and this through hole H' is sealed with an elastomer plug P. This structure is due to the fact that the FRP article 1 was manufactured by the manufacturing method according to the embodiment.

[0044] In FRP article 1, the entire elastomer stopper P is tapered in the direction from the internal space of the cavity outwards. In one example, instead of being tapered, or in addition to being tapered, the elastomer stopper P may have protrusions or recesses on its sides.

[0045] 3. Summary of Embodiments Embodiments of the present invention include, but are not limited to, the following. [Embodiment 1] A method for manufacturing fiber-reinforced resin, comprising a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is arranged inside, in a press die and heating it to obtain a cured product having a hollow structure, and a core removal step of removing the fusible core from the cured product, wherein a through hole is formed in the core-enclosed portion of the prepreg premolded body and an elastomer plug is inserted into the through hole. [Embodiment 2] The manufacturing method according to Embodiment 1, wherein the elastomer stopper is tapered in part and inserted into the through hole with the side having a larger cross-sectional area perpendicular to the insertion direction toward the fusible core. [Embodiment 3] The manufacturing method according to Embodiment 1 or 2, wherein the elastomer stopper has a projection or recess on its side surface. [Embodiment 4] A manufacturing method according to any one of Embodiments 1 to 3, wherein in the core removal step, one end of a metal tube is pierced through the elastomer stopper, and all or part of the wax material is discharged from the cavity formed in the hollow structure of the hardened product through the metal tube. [Embodiment 5] The manufacturing method according to Embodiment 4, wherein in the core removal step, at least a portion of the metal tube is heated. [Embodiment 6] A manufacturing method according to Embodiment 4 or 5, wherein the other end of the metal tube is connected to a collection container. [Embodiment 7] A manufacturing method according to any one of Embodiments 1 to 3, wherein in the core removal step, one end of a metal tube is pierced through the elastomer stopper, and gas is introduced into the cavity formed in the hollow structure of the hardened product through the metal tube. [Embodiment 8] The manufacturing method according to Embodiment 7, wherein the other end of the metal tube is open to the atmosphere. [Embodiment 9] The manufacturing method according to Embodiment 7, wherein the gas is pressurized. [Embodiment 10] A manufacturing method according to any one of Embodiments 1 to 9, wherein in the molding step, the wax material is softened in at least a portion of the fusible core. [Embodiment 11] A manufacturing method according to any one of Embodiments 1 to 10, wherein in the molding step, the wax material melts in at least a portion of the fusible core. [Embodiment 12] A manufacturing method according to Embodiment 10 or 11, wherein the fusible core has a first portion made of a first wax material and a second portion made of a second wax material that is incompatible with the first wax material, and the second wax material does not soften in the molding process. [Embodiment 13] A manufacturing method according to Embodiment 12, wherein one of the first wax material and the second wax material mainly consists of a hydrocarbon, and the other contains an organic compound having a polar group. [Embodiment 14] A manufacturing method according to any one of Embodiments 1 to 13, wherein the fusible core contains particles of a material that has the property of generating heat under a high-frequency electromagnetic field. [Embodiment 15] A manufacturing method according to any one of Embodiments 1 to 13, wherein the fusible core contains particles of a material having the property of absorbing microwaves and generating heat. [Embodiment 16] A manufacturing method according to any one of Embodiments 1 to 15, wherein the fusible core is preheated before the molding step. [Embodiment 17] A manufacturing method according to any one of Embodiments 1 to 16, wherein in the prepreg premolded body, the fusible core is arranged inside the core-enclosing portion without being covered by the outer shell. [Embodiment 18] A method for manufacturing a fiber-reinforced resin, comprising: a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is disposed inside, in a press die and heating it to obtain a cured product having a hollow structure; and a core removal step of removing the fusible core from the cured product, wherein a first through hole and a second through hole are formed in the prepreg premolded body in the core-enclosed portion, a first elastomer plug is inserted into the first through hole, and a second elastomer plug is inserted into the second through hole. [Embodiment 19] The manufacturing method according to Embodiment 18, wherein both the first elastomer stopper and the second elastomer stopper are tapered in part, and both are inserted into the through hole with the side having a larger area of ​​the cross-section perpendicular to the insertion direction toward the fusible core. [Embodiment 20] A manufacturing method according to Embodiment 18 or 19, wherein both the first elastomer stopper and the second elastomer stopper have protrusions or recesses on their sides. [Embodiment 21] A manufacturing method according to any of Embodiments 18 to 20, wherein in the core removal step, one end of the first metal tube is pierced through the first elastomer stopper, and one end of the second metal tube is pierced through the second elastomer stopper, and while gas is introduced into the cavity formed in the hollow structure of the cured product through the first metal tube, all or part of the wax material is discharged from the cavity through the second metal tube. [Embodiment 22] The manufacturing method according to Embodiment 21, wherein in the core removal step, at least a portion of the second metal tube is heated. [Embodiment 23] A manufacturing method according to Embodiment 21 or 22, wherein the other end of the second metal tube is connected to a collection container. [Embodiment 24] A manufacturing method according to any one of embodiments 21 to 23, wherein the other end of the first metal tube is open to the atmosphere. [Embodiment 25] A manufacturing method according to any one of Embodiments 21 to 23, wherein the gas is pressurized. [Embodiment 26] A manufacturing method according to any one of Embodiments 18 to 25, wherein in the molding step, the wax material is softened in at least a portion of the fusible core. [Embodiment 27] A manufacturing method according to any one of Embodiments 18 to 26, wherein in the molding step, the wax material melts in at least a portion of the fusible core. [Embodiment 28] A manufacturing method according to Embodiment 26 or 27, wherein the fusible core has a first portion made of a first wax material and a second portion made of a second wax material that is incompatible with the first wax material, and the second wax material does not soften in the molding process. [Embodiment 29] A manufacturing method according to Embodiment 28, wherein one of the first wax material and the second wax material mainly consists of a hydrocarbon, and the other contains an organic compound having a polar group. [Embodiment 30] A manufacturing method according to any one of Embodiments 18 to 29, wherein the fusible core contains particles of a material that has the property of generating heat under a high-frequency electromagnetic field. [Embodiment 31] A manufacturing method according to any one of Embodiments 18 to 29, wherein the fusible core contains particles of a material having the property of absorbing microwaves and generating heat. [Embodiment 32] A manufacturing method according to any one of embodiments 18 to 31, wherein the fusible core is preheated before the molding step. [Embodiment 33] A manufacturing method according to any one of Embodiments 18 to 32, wherein in the prepreg premolded body, the fusible core is arranged inside the core-enclosing portion without being covered by the outer skin. [Embodiment 34] A fiber-reinforced resin article having a hollow structure, a cavity formed in the hollow structure, a through hole leading from the internal space of the cavity to the outside, and an elastomer stopper that closes the through hole. [Embodiment 35] A fiber-reinforced resin article according to Embodiment 34, wherein at least a portion of the elastomer stopper is tapered in a direction toward the outside from the internal space of the cavity. [Embodiment 36] A fiber-reinforced resin article according to Embodiment 34 or 35, wherein the elastomer stopper has a projection or recess on its side surface.

[0046] 4. Experimental Results A hollow rectangular prism measuring 72mm x 36mm x 20mm made of FRP was prototyped using the following procedure. A prepreg premolded body with nearly the net shape was produced by cutting a 2mm thick SMC (STR120N131, manufactured by Mitsubishi Chemical Corporation) sheet into a predetermined shape, forming a cylindrical through-hole with an inner diameter of 6mm in a portion of it, and then bending it further. When fabricating the prepreg premolded body, a partially fusible core, prepared in a separate process, was placed inside it.

[0047] The partially fusible core consists of a fusible portion (fusible core) made of a synthetic wax (ITOHWAX E-70G, manufactured by Ito Oil Co., Ltd.) containing a higher fatty acid ester with a melting point of 68°C, covered with an outer shell formed using a 7 μm thick nylon 6 film. It was manufactured to form a rectangular parallelepiped that fits perfectly inside the prepreg premolded body. A silicone rubber stopper was inserted into the through-hole made in the SMC. This silicone rubber stopper was a frustoconical tapered stopper with an upper base diameter of 6 mm, a lower base diameter of 10 mm, and a height of 4 mm, and was inserted into the through-hole so that the lower base faced the core.

[0048] The prepreg premolded body, with the side containing the through-hole facing upwards, was placed in a mold preheated to the same temperature as the molding temperature, along with the core enclosed inside, and cured by heating and pressurizing. The molding temperature was 140°C and the molding time was 10 minutes. Immediately after the molding was completed, the upper mold was lifted and one end of a stainless steel tube with an outer diameter of 2 mm and an inner diameter of 1 mm was inserted into a silicone rubber stopper. Molten wax flowed from inside the molded product through the stainless steel tube into a container connected to the other end of the stainless steel tube.

[0049] Although the present invention has been described above with reference to specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described herein can be modified in various ways within the scope in which the effects of the invention are achieved, and can be combined with features described in other embodiments to the extent that is feasible. [Industrial applicability]

[0050] The inventions disclosed herein, without limitation, can be preferably used when manufacturing parts (including structural components) for automobiles, ships, railway vehicles, aircraft and other transportation equipment, as well as various sporting goods, including bicycle frames, tennis rackets and golf shafts, using fiber-reinforced resins. [Explanation of symbols]

[0051] 1. Fiber-reinforced resin articles 10 fusible cores 12 Hull 14 Partially Fusible Cores 20 Prepreg preforms 30 Cured product 100 press molds 102 Lower mold 104 Upper mold 106 Slide Core 200, 201, 202 Metal Tubes 300 collection containers H, H´ through hole P, P1, P2 elastomer stoppers WM wax materials

Claims

1. A method for manufacturing a fiber-reinforced resin, comprising a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is arranged inside, in a press die and heating it to obtain a cured product having a hollow structure, and a core removal step of removing the fusible core from the cured product, wherein a through hole is formed in the core-enclosed portion of the prepreg premolded body and an elastomer plug is inserted into the through hole.

2. The manufacturing method according to claim 1, wherein the elastomer stopper is tapered in part and inserted into the through hole with the side having a larger cross-sectional area perpendicular to the insertion direction toward the fusible core.

3. The manufacturing method according to claim 1 or 2, wherein the elastomer stopper has a projection or recess on its side surface.

4. The manufacturing method according to any one of claims 1 to 3, wherein in the core removal step, one end of the metal tube is pierced through the elastomer stopper, and all or part of the wax material is discharged from the cavity formed in the hollow structure of the cured product through the metal tube.

5. The manufacturing method according to claim 4, wherein in the core removal step, at least a portion of the metal tube is heated.

6. The manufacturing method according to claim 4 or 5, wherein the other end of the metal tube is connected to a collection container.

7. The manufacturing method according to any one of claims 1 to 3, wherein in the core removal step, one end of the metal tube is pierced through the elastomer stopper, and gas is introduced into the cavity formed in the hollow structure of the hardened material through the metal tube.

8. The manufacturing method according to claim 7, wherein the other end of the metal tube is open to the atmosphere.

9. The manufacturing method according to claim 7, wherein the gas is pressurized.

10. The manufacturing method according to any one of claims 1 to 9, wherein in the molding step, the wax material is softened in at least a portion of the fusible core.

11. The manufacturing method according to any one of claims 1 to 10, wherein in the molding step, the wax material melts in at least a portion of the fusible core.

12. The manufacturing method according to claim 10 or 11, wherein the fusible core has a first portion made of a first wax material and a second portion made of a second wax material that is incompatible with the first wax material, and the second wax material does not soften in the molding process.

13. The manufacturing method according to claim 12, wherein one of the first wax material and the second wax material mainly consists of a hydrocarbon and the other contains an organic compound having a polar group.

14. The manufacturing method according to any one of claims 1 to 13, wherein the fusible core contains particles of a material having the property of generating heat under a high-frequency electromagnetic field.

15. The manufacturing method according to any one of claims 1 to 13, wherein the fusible core contains particles of a material having the property of absorbing microwaves and generating heat.

16. The manufacturing method according to any one of claims 1 to 15, wherein the fusible core is preheated before the molding step.

17. The manufacturing method according to any one of claims 1 to 16, wherein in the prepreg premolded body, the fusible core is arranged inside the core-encapsulating portion without being covered by an outer shell.

18. A method for manufacturing a fiber-reinforced resin, comprising: a molding step of placing a prepreg premolded body, which has a core-enclosed portion in which a fusible core made of wax material is arranged inside, in a press die and heating it to obtain a cured product having a hollow structure; and a core removal step of removing the fusible core from the cured product, wherein a first through-hole and a second through-hole are formed in the prepreg premolded body in the core-enclosed portion, a first elastomer plug is inserted into the first through-hole, and a second elastomer plug is inserted into the second through-hole.

19. The manufacturing method according to claim 18, wherein both the first elastomer stopper and the second elastomer stopper are tapered in at least a portion, and both are inserted into the first through-hole and the second through-hole, respectively, with the side having a larger cross-sectional area perpendicular to the insertion direction facing the fusible core.

20. The manufacturing method according to claim 18 or 19, wherein both the first elastomer stopper and the second elastomer stopper have protrusions or recesses on their sides.

21. The manufacturing method according to any one of claims 18 to 20, wherein in the core removal step, one end of the first metal tube is pierced through the first elastomer stopper, and one end of the second metal tube is pierced through the second elastomer stopper, and while gas is introduced into the cavity formed in the hollow structure of the cured product through the first metal tube, all or part of the wax material is discharged from the cavity through the second metal tube.

22. The manufacturing method according to claim 21, wherein in the core removal step, at least a portion of the second metal tube is heated.

23. The manufacturing method according to claim 21 or 22, wherein the other end of the second metal tube is connected to a collection container.

24. The manufacturing method according to any one of claims 21 to 23, wherein the other end of the first metal tube is open to the atmosphere.

25. The manufacturing method according to any one of claims 21 to 23, wherein the gas is pressurized.

26. The manufacturing method according to any one of claims 18 to 25, wherein in the molding step, the wax material is softened in at least a portion of the fusible core.

27. The manufacturing method according to any one of claims 18 to 26, wherein in the molding step, the wax material melts in at least a portion of the fusible core.

28. The manufacturing method according to claim 26 or 27, wherein the fusible core has a first portion made of a first wax material and a second portion made of a second wax material that is incompatible with the first wax material, and the second wax material does not soften in the molding process.

29. The manufacturing method according to claim 28, wherein one of the first wax material and the second wax material mainly consists of a hydrocarbon and the other contains an organic compound having a polar group.

30. The manufacturing method according to any one of claims 18 to 29, wherein the fusible core contains particles of a material having the property of generating heat under a high-frequency electromagnetic field.

31. The manufacturing method according to any one of claims 18 to 29, wherein the fusible core contains particles of a material having the property of absorbing microwaves and generating heat.

32. The manufacturing method according to any one of claims 18 to 31, wherein the fusible core is preheated before the molding step.

33. The manufacturing method according to any one of claims 18 to 32, wherein in the prepreg premolded body, the fusible core is arranged inside the core-encapsulating portion without being covered by an outer shell.

34. It has a hollow structure, a cavity formed in the hollow structure, a through hole leading from the internal space of the cavity to the outside, and an elastomer stopper that closes the through hole. At least a portion of the elastomer stopper is tapered in a direction toward the outside from the internal space of the cavity, A fiber-reinforced resin article in which the gap between the through hole and the elastomer stopper is sealed with a cured material.

35. The fiber-reinforced resin article according to claim 34, wherein the elastomer stopper has a projection or recess on its side.

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