Method for manufacturing a fiber-reinforced resin article and fiber-reinforced resin article

Abstract

The present application provides an advantageous improvement in a method of manufacturing a fiber-reinforced resin article having at least a portion of a structure formed by a bent or curved wall surface, such as a hollow structure portion, a cross-sectional U-shaped structure portion. The method of manufacturing a fiber-reinforced resin article of the present application has a molding step of heating a prepreg preform together with a core formed of a wax material in a press mold to obtain a cured product, and a core removal step of removing the core from the cured product, the core having an expanded portion formed of a first wax material and a mold portion formed of a second wax material that is incompatible with the first wax material, the mold portion being disposed on a surface of the core, a portion reflecting a surface shape of the mold portion being formed on a surface of the cured product.

Description

Technical Field

[0001] This invention relates to a method for manufacturing fiber-reinforced resin articles and the fiber-reinforced resin articles themselves.

[0002] This application claims priority based on Japanese Patent Application No. 2021-069190 filed with the Japan Patent Office on April 15, 2021 and Japanese Patent Application No. 2021-106583 filed with the Japan Patent Office on June 28, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Fiber-reinforced plastic (FRP) is used in a variety of applications, including automotive reinforcement components, due to its lightweight and excellent mechanical properties, and its importance has been increasing in recent years.

[0004] A method has been proposed for manufacturing fiber-reinforced resin articles having a hollow structure and a U-shaped cross-section by heating and curing a prepreg preform together with a core formed of wax material in a pressing mold (Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2018 / 079824 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The main objective of this invention is to provide a beneficial improvement to a method for manufacturing fiber-reinforced resin articles having at least a portion of a structure formed by bent or flexed walls, such as a hollow structure or a U-shaped cross-section, by heating and curing a prepreg preform together with a core formed of wax material in a pressing mold.

[0010] The object of the present invention includes providing a technique for controlling the surface shape of the portion facing the core during molding in a fiber-reinforced resin article manufactured by the above method.

[0011] Problems solved by various embodiments of the present invention are sometimes disclosed, explicitly or implicitly, in this specification.

[0012] Methods for solving problems

[0013] According to one aspect of the present invention, a manufacturing method is provided for a fiber-reinforced resin article, comprising the following steps: a molding step in which a prepreg preform and a core formed of a wax material are heated together in a pressing mold to obtain a cured product; and a core removal step in which the core is removed from the cured product, the core having an expanded portion formed of a first wax material and an imprinted portion formed of a second wax material incompatible with the first wax material, the imprinted portion being disposed on the surface of the core, and a portion reflecting the surface shape of the imprinted portion being formed on the surface of the cured product.

[0014] According to another aspect of the present invention, a fiber-reinforced resin article is provided having a hollow structural portion having cavities and ribs formed on the walls of the cavities.

[0015] According to another aspect of the invention, a fiber-reinforced resin article is formed, the fiber-reinforced resin article having: a hollow structural portion having cavities and a rib pattern formed on the wall surface of the cavities.

[0016] According to another aspect of the invention, a fiber-reinforced resin article is formed, the fiber-reinforced resin article having: a hollow structural portion having cavities and a boss formed on the wall surface of the cavities.

[0017] The effects of the invention

[0018] A beneficial improvement is provided to the method of manufacturing a fiber-reinforced resin article having at least a portion of a structure formed by bent or flexed walls, such as a hollow structure or a U-shaped cross-section, by placing a prepreg preform together with a core formed of wax material in a pressing mold and curing it. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating a method for manufacturing fiber-reinforced resin articles according to an embodiment.

[0020] Figure 2 This is a schematic diagram of an FRP article that can be manufactured by the fiber-reinforced resin article manufacturing method according to the embodiments. Figure 2 (a) is a 3D diagram. Figure 2 (b) is a cross-sectional view.

[0021] Figure 3 This is a schematic diagram of a core that can be used in the fiber-reinforced resin article manufacturing method according to the embodiment. Figure 3 (a) is a 3D diagram. Figure 3 (b) is a cross-sectional view.

[0022] Figure 4A cross-sectional view of a prepreg preform manufactured in a manner that results in an internally configured core.

[0023] Figure 5 To indicate Figure 4 The diagram shows a cross-sectional view of the prepreg preform being inserted into the mold.

[0024] Figure 6 Indicates by Figure 4 The diagram shows a cross-sectional view of the cured prepreg obtained before the core is removed from the cavity.

[0025] Figure 7 For the reason Figure 4 The cross-sectional view of the FRP article obtained from the prepreg preform shown.

[0026] Figure 8 This is a schematic diagram of a core that can be used in the fiber-reinforced resin article manufacturing method according to the embodiment. Figure 8 (a) is a 3D diagram. Figure 8 (b) is a cross-sectional view.

[0027] Figure 9 This is a schematic diagram of a core that can be used in the FRP article manufacturing method according to the embodiment. Figure 9 (a) is a 3D diagram. Figure 9 (b) is a cross-sectional view.

[0028] Figure 10 To indicate Figure 9 The diagram shows an example of the core fabrication process in a cross-sectional view.

[0029] Figure 11 This is a schematic diagram of a core that can be used in the fiber-reinforced resin article manufacturing method according to the embodiment. Figure 11 (a) is a 3D diagram. Figure 11 (b) is a cross-sectional view.

[0030] Figure 12 This is a schematic diagram of a core that can be used in the fiber-reinforced resin article manufacturing method according to the embodiment. Figure 12 (a) is a 3D diagram. Figure 12 (b) is a cross-sectional view.

[0031] Figure 13 A cross-sectional view of a prepreg preform manufactured in a manner that results in an internally configured core.

[0032] Figure 14 For use Figure 12 The image shows a cross-sectional view of a fiber-reinforced resin article obtained from the core.

[0033] Figure 15 To indicate Figure 3 The diagram shows a cross-sectional view of the core surface covered by a barrier film.

[0034] Figure 16 A cross-sectional view showing the state in which the prepreg preform and the core, whose surface is covered by a barrier film, are inserted into the mold. Detailed Implementation

[0035] 1. Manufacturing method of fiber-reinforced resin articles

[0036] One embodiment of the present invention relates to a method for manufacturing fiber-reinforced resin articles (hereinafter also referred to as FRP articles).

[0037] The FRP article manufacturing method involved in the implementation method is as follows: Figure 1 The process flow is shown, including the next two steps.

[0038] (i) Molding process: The prepreg preform and the core formed of wax material are heated together in a pressing mold to obtain a cured product.

[0039] (ii) Core removal process, in which the core is removed from the solidified material.

[0040] The core has an expanded portion formed of a first wax material and an impression portion formed of a second wax material incompatible with the first wax material. The impression portion is disposed on the surface of the core, and a portion reflecting the surface shape of the impression portion is formed on the surface of the cured material obtained by the molding process.

[0041] Hereinafter, the method for manufacturing FRP articles according to the embodiments will be described in detail with reference to the accompanying drawings.

[0042] 1.1 Molding process

[0043] The molding process involves heating the prepreg preform and the core formed from wax material together in a pressing mold to obtain a cured product.

[0044] (Prepreg preform)

[0045] Prepreg preforms are made in advance outside of the pressing mold, using prepreg sheets or towed prepregs as the main material, and in a way that results in a near net shape.

[0046] When using prepreg sheets, two or more prepreg sheets may be stacked in part or all of the prepreg preform. A portion with multiple stacked prepreg sheets may contain two or more prepreg sheets of the same type, two or more prepreg sheets of different types, or both.

[0047] Prepreg preforms using prepreg sheets can have portions reinforced with towed prepreg.

[0048] Prepreg preforms can be formed partly or entirely from towed prepregs.

[0049] The fiber reinforcement used in prepregs can be various materials such as continuous fibers, chopped fibers, fabrics, nonwovens, and non-crimp fabrics.

[0050] Prepreg sheets with fiber reinforcement consisting of multiple continuous fiber bundles arranged in one direction are also called unidirectional prepregs (UD prepregs).

[0051] Prepreg sheets that use fabrics formed from continuous fiber bundles as fiber reinforcement are also known as fabric prepregs.

[0052] Prepreg sheets that use stacked bundles of short fibers as fiber reinforcement are called SMC (sheet molding compound).

[0053] Towed prepreg is a prepreg that uses a single continuous bundle of fibers as reinforcement.

[0054] Examples of fibers used as fiber reinforcement materials include carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, and metal fiber. Sometimes, two or more types of fibers are used together.

[0055] The thermosetting resins used in prepregs include, for example, epoxy resins, urea resins, vinyl ester resins (also known as epoxy acrylate resins), unsaturated polyesters, polyurethanes, and phenolic resins. Two or more thermosetting resins can be mixed for use.

[0056] The content of the thermosetting resin composition in the prepreg is not limited, but may be, for example, 15-60% by mass. This content can be 15-20% by mass, 20-25% by mass, 25-40% by mass, 40-50% by mass, 50-60% by mass, etc.

[0057] Thermosetting resin compositions can contain various additives, such as curing agents, thickeners, reactive diluents, flame retardants, defoamers, degassing agents, mold release agents, particulate fillers, colorants, silane coupling agents, and antibacterial agents.

[0058] (core)

[0059] The core has an expansion portion formed of a first wax material and an impression portion formed of a second wax material incompatible with the first wax material. The impression portion is disposed on the surface of the core.

[0060] Details of the first and second wax materials will be described later.

[0061] The overall shape of the core is roughly the same as the cavity formed by the hollow structure, for example, if an FRP article with a hollow structure is to be manufactured.

[0062] Here will Figure 2 The core setting model used in manufacturing a hollow FRP article 1 in the shape of a quadrangular prism with square upper and lower surfaces and rectangular four sides is shown, and the configuration example of the expansion part and the impression part is explained.

[0063] The core has the same overall shape as the cavity in FRP item 1, with a square top and bottom surface and four rectangular sides, forming a quadrangular prism.

[0064] In one example, such as Figure 3 As shown in the cross-sectional view, the core 10 may have a quadrangular prism-shaped expansion portion 12 and two plate-shaped impression portions 14 arranged to cover its upper and lower surfaces respectively. The expansion portion 12 is exposed on the side of the core 10.

[0065] In the core 10, the expansion portion 12 disposed at the center can be an expansion portion consisting of a single piece of the first wax material, or it can be an expansion portion consisting of multiple plates formed by stacking the first wax material.

[0066] The core 10 can be obtained by separately manufacturing the expansion portion 12 and the plurality of impression portions 14, and then assembling them. The expansion portion 12 and the impression portions 14 do not need to be glued to each other.

[0067] (Curing)

[0068] When manufacturing FRP articles with hollow structures, firstly, a prepreg is made such that a core is placed at the position corresponding to the cavity formed by the hollow structure. Next, the prepreg made in this way, together with the core placed inside it, is placed into a pressing mold.

[0069] Figure 4 For use in manufacturing Figure 2 The diagram shows a cross-sectional view of the prepreg preform prepared for FRP article 1. The prepreg preform 20 has a quadrangular prism shape and is provided with internal features... Figure 3 The core 10 of the structure shown.

[0070] In this specification, the temperature of the pressing mold used to cure the prepreg is called the molding temperature.

[0071] The molding temperature should be such that the prepreg preform can be cured in less than 1 hour, more preferably less than 40 minutes, and even more preferably less than 20 minutes.

[0072] The molding temperature can be, for example, above 100°C, above 120°C, and further above 130°C. The higher the molding temperature, the shorter the curing time required for the prepreg preform.

[0073] If the molding temperature exceeds 160°C, the options for the first and second wax materials become narrower. From the viewpoint of shortening the heating time required for the pressing mold and reducing energy consumption, the molding temperature can be below 150°C, and further below 140°C.

[0074] The temperature of the pressing mold is maintained at the molding temperature by the temperature control mechanism that is usually provided in the pressing molding machine before the prepreg is put into the machine.

[0075] Will Figure 4 The state shown is that the prepreg preform 20, together with the core 10, is placed into the pressing mold 100 formed by the lower mold 102 and the upper mold 104. Figure 5 middle.

[0076] The pressing mold 100 is pre-held at the molding temperature, so that the core 10 begins to heat up and expand immediately after being inserted into the pressing mold 100 along with the prepreg preform 20.

[0077] As the core 10 expands, the prepreg preform 20 is pressed against the inner surface of the pressing mold 100. In other words, the core 10 expands against the clamping force, thereby applying pressure generated within the pressing mold 100 to the prepreg preform 20.

[0078] FRP with fewer voids is produced by curing prepreg under pressure.

[0079] Here, the first wax material and the second wax material are explained as follows.

[0080] The softening temperature of the first wax material is lower than that of the second wax material. Between the softening temperatures of the first and second wax materials, there is a sufficient difference in the degree to which the second wax material in the mold portion remains unsoftened before the first wax material softens in the expansion portion.

[0081] This means that the expansion of the expansion section is the primary contributor to the pressure generation within the pressing mold. The pressure within the pressing mold rises sharply as a portion of the first wax material in the expansion section begins to soften.

[0082] Furthermore, before the prepreg preform loses its plasticity through the curing process, it also needs to begin to expand along with the softening of the first wax material.

[0083] One way to accelerate the softening of the first wax material is to lower its softening temperature.

[0084] Another method to accelerate the softening of the first wax material is to preheat the core to near its softening temperature before it is placed into the pressing mold. This can be achieved by placing the core, positioned inside the prepreg preform, into the oven according to the individual prepreg preforms during preheating.

[0085] These two methods can be used simultaneously.

[0086] The time from when the first wax material begins to soften until it melts into a highly fluid liquid is preferably long. When this time is sufficiently long, the prepreg solidifies before the first wax material melts, so that the molten first wax material does not flow into the gap between the prepreg and the pressing mold.

[0087] Considering the long softening and melting time, polyolefin waxes are preferred in the first wax material. Typical examples of polyolefin waxes are polyethylene wax and polypropylene wax. Suitable examples of polyolefin waxes include thermally decomposable polyethylene wax, which is a thermal decomposition product of polyethylene resin, and thermally decomposable polypropylene wax, which is a thermal decomposition product of polypropylene resin.

[0088] The second wax material preferably does not soften at the molding temperature, but this is not necessary. Heat from the pressing die is conducted to the impression section via the prepreg preform, so there is a time required from the time the pressing die is closed until the temperature of the impression section reaches the molding temperature. Therefore, if the first wax material softens quickly enough, the pressure inside the pressing die can rise before the second wax material softens in the impression section, even if the softening temperature of the second wax material is lower than the molding temperature.

[0089] Before the prepreg preform loses its plasticity and before the second wax material in the mold softens, the surface of the prepreg preform deforms along the surface of the mold at the portion in contact with the mold due to the increased pressure within the die. As a result, a portion reflecting the surface shape of the mold is formed on the surface of the cured material.

[0090] For example, in making Figure 4 When the prepreg preform 20 shown is cured in the pressing mold, as Figure 6 As shown, the inner surface of the cured material 30 becomes flatter in the part that contacts the impression part 14 compared to the part that contacts the expansion part 12.

[0091] The reason for the poor flatness of the inner surface of the cured material 30 in the part that contacts the expansion portion 12 of the core 10 is that the pressure rise in the pressing mold 100 during the molding process is mainly caused by the softening of the surface of the expansion portion 12. Even when the softened surface of the expansion portion 12 is pressed, the shape of the inner surface of the prepreg preform 20 does not change significantly.

[0092] 1.2. Core Removal Process

[0093] Core removal process (ii) is the process of removing the core used in the molding process from the solidified material obtained from the molding process.

[0094] When the cured material has a hollow structure, the first wax material and the second wax material, which serve as the core material, are removed from the interior of the cavity formed by the hollow structure.

[0095] Although not limited, in one example, firstly, the solidified material is heated in an oven to melt the first and second wax materials inside the cavity. Then, a venting hole is made in the hollow structure using a piercing tool. The venting hole allows the molten first and second wax materials to be discharged out of the cavity.

[0096] Not only when the cured material has a hollow structure, but also when the cured material has an undercut portion, the core can be removed by melting the first wax material and the second wax material. When the cured material has neither a hollow structure nor an undercut portion, the core can be removed without melting it.

[0097] Will be through from Figure 6 A cross-section of the FRP article 1 obtained by removing the core 10 from the cavity of the solidified material 30 is shown. Figure 7 middle.

[0098] according to Figure 7 It can be understood that the flattening of the inner surface (wall of the cavity) of the FRP article 1, achieved by using the core 10 formed by the expansion portion 12 and the impression portion 14, helps to improve the wall thickness t of the FRP article 1. W Uniformity of the wall thickness t. W Improved uniformity can help reduce the unevenness of mechanical properties and strength of FRP article 1.

[0099] This effect becomes particularly pronounced when the prepreg preform 20 contains SMC. This is because the in-plane thickness of the SMC varies greatly across different prepreg sheets.

[0100] Since the first and second wax materials are incompatible with each other, it is easy to separate and reuse them.

[0101] When the melting points of the first wax material and the second wax material have a sufficient difference, they can be separated by melting only the material with the lower melting point.

[0102] When the specific gravity of the molten first wax material and the molten second wax material is different, they can be separated by the difference in specific gravity.

[0103] Waxes with hydrocarbons as the main component and waxes formed from organic compounds with polar groups are mostly incompatible with each other. Polar groups are functional groups containing carbon-oxygen or carbon-nitrogen bonds, such as hydroxyl, amino, amide, carbonyl, carboxyl, and ester groups (except for ether groups).

[0104] When a polyolefin wax is incorporated into the first wax material, it is preferable that a wax containing an organic compound with polar groups is incorporated into the second wax material.

[0105] 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.

[0106] 1.3. Various Implementation Methods

[0107] manufacture Figure 2 The core used in the FRP item 1 shown is not limited to those having Figure 3 The core of the structure shown.

[0108] In suitable examples, such as Figure 8 As shown, in addition to the upper and lower surfaces of the quadrangular prism-shaped expansion portion 12, the core may also have a structure in which all four sides are covered by the plate-shaped impression portion 14. Figure 8 Since the core 10 shown does not have a portion of the expansion portion 12 exposed to the surface, the overall flatness of the inner surface of the FRP article 1 manufactured using the core in the above method is improved.

[0109] Figure 9 The core 10 shown is Figure 8 In the modified example of the core shown, the entire surface of the expansion portion 12 is covered by the integrally formed impression portion 14.

[0110] Figure 9 The shown core 10 can be passed through Figure 10 Follow the steps shown to make it.

[0111] First, such as Figure 10 As shown in (a), a molding die M with an injection / discharge hole H is prepared, having an inner dimension slightly larger than the outer dimension of the core 10 to be manufactured.

[0112] Within the molding die M, through the injection / discharge hole H, such as Figure 10 As shown in (b), molten second wax material WM2 is injected. If the molding mold M is then moderately cooled, a portion of the second wax material solidifies on the wall of the molding mold M. The remaining, unsolidified second wax material is discharged from the molding mold M through the injection / extraction hole, thereby achieving the desired effect. Figure 10 As shown in (c), the impression portion 14 is formed.

[0113] Next, the molten first wax material WM1 is injected through the injection / extraction port H. Figure 10 As shown in (d), it is injected into the molding mold M. At this time, the temperature of the first wax material WM1 becomes the temperature at which the second wax material in the mold section 14 does not melt.

[0114] After the first wax material WM1 solidifies to form the expanded part 12, as... Figure 10 As shown in (e), the core 10 is removed from the molding die M.

[0115] Finally, the remaining holes in the impression part 14 are filled with a second wax material. Figure 10 The core 10 is thus completed by filling it in as shown in (f).

[0116] The method for manufacturing this core is also convenient when the core has a complex shape or a curved surface.

[0117] Figure 11 The core 10 shown is Figure 8 In another variation of the core shown, a quadrangular prism-shaped low-expansion portion 16 formed of a second wax material is disposed at the center. Multiple plate-shaped expansion portions 12 are arranged to cover the upper surface, lower surface, and four sides of the low-expansion portion 16, respectively, and multiple plate-shaped impression portions 14 are further disposed on their outer sides. The expansion portions 12 are not exposed on the surface of the core 10.

[0118] exist Figure 11 The reason for arranging a low-expansion portion 16 in the center of the core 10 shown is to reduce the volume ratio of the expansion portion 12 in the core 10, so that the expansion amount of the core 10 during the molding process will not become too large.

[0119] Figure 12 The core 10 shown is Figure 8 In other variations of the core shown, a cross groove G is provided on the surface of the impression portion 14 on both the upper and lower surfaces.

[0120] The purpose of the cross groove G is to form cross-shaped ribs on the wall surface inside the cavity of the FRP article 1 to be manufactured. For example... Figure 13 As shown, Figure 12The core shown is disposed in the inner prepreg preform 20, and its shape does not follow the inner surface of the cross groove G, and its upper and lower surfaces are flat.

[0121] During the molding process, a portion of the prepreg material constituting the prepreg preform 20 flows into the interior of the cross groove G. Especially when the prepreg preform 20 contains SMC, the interior of the groove is easily and fully filled with prepreg material.

[0122] In one example, during the production of the prepreg preform 20, the interior of the cross groove G can be pre-filled with prepreg material prepared separately from the prepreg preform 20.

[0123] Figure 13 The FRP item 1 shown in the cross-section is for use. Figure 12 The article manufactured from the core 10 shown has ribs R formed in a cross shape on the top and bottom surfaces of the cavity.

[0124] Figure 12 The pattern of the grooves shown in the core 10 is just one example. It is not limited to the pattern of grooves formed on the surface of the impression section for setting ribs on FRP articles; it can be a variety of patterns such as rectangular grid patterns, triangular grid patterns, radial patterns, striped patterns, etc. It is also possible to set multiple areas on the surface of the impression section with different groove patterns.

[0125] The depth of the grooves can be the same or different across different grooves. It is not necessary for any groove to have a constant depth.

[0126] By forming ribs, it is possible to reduce the weight of FRP articles while maintaining rigidity.

[0127] The surface of the mold part may have a recess for forming a boss on the wall surface inside the cavity of the FRP article to be manufactured, in addition to the groove for forming ribs, or instead of the groove for forming ribs.

[0128] The core can be fitted with various additives as needed.

[0129] In one example, by adding particles of a material that has the property of heating under a high-frequency electromagnetic field to the first wax material, the expansion portion can be inductively heated. Examples of such materials include strongly magnetic materials, ferrimagnetic materials, and conductive materials. Examples of strongly magnetic materials include iron, nickel, cobalt, iron alloys, nickel alloys, cobalt alloys, permalloy, and various 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.

[0130] In another example, by adding particles of a material that has the property of absorbing microwaves and generating heat to the first wax material, the expanded portion can be microwave-heated. Examples of such materials include silicon carbide, ferrite, barium titanate, anatase titanium dioxide, graphite, and carbon black.

[0131] Induction heating or microwave heating of the expansion section is preferably performed when the expansion section is preheated outside the pressing mold.

[0132] In one example, to enable induction heating or microwave heating of the entire core, particles of a material that generates heat under a high-frequency electromagnetic field or particles of a material that absorbs microwaves and generates heat can be added to both the first and second wax materials. If this is done, induction heating or microwave heating can be used to melt the entire core during the core removal process.

[0133] In one example, to enable visual identification of the first wax material and the second wax material by their different colors, a colorant such as a pigment or dye can be used. The colorant can be added to either the first wax material or the second wax material, or to both.

[0134] By making the first wax material and the second wax material different colors, it is possible to prevent errors, such as those between the expansion portion and the impression portion, during core assembly.

[0135] After the core removal process, it is appropriate for the first wax material and the second wax material to have different colors during the separation process.

[0136] In one instance, the core can be used after the surface has been covered with a barrier film.

[0137] Figure 15 Indicates will Figure 3 The core shown is covered by a barrier film. The barrier film 18 is tightly fitted to the core 10 and conforms to the surface of the core 10.

[0138] Figure 16 This indicates that the prepreg preform 20, together with the core 10 covered by the barrier film 18, is placed into the pressing mold 100.

[0139] The purpose of the barrier film 18 is to prevent the first wax material from leaking into the gap between the prepreg preform 20 and the pressing mold when the first wax material forming the expansion portion 12 melts before the prepreg preform 20 is cured.

[0140] To prevent breakage due to core expansion, the barrier membrane is made of a material capable of elongation at the molding temperature. This elongation can be elastic, plastic, or a combination of both.

[0141] Therefore, while there is no limitation on the preferred material for the barrier membrane, it is an organic material, particularly a resin material. Preferred materials for the barrier membrane include synthetic polymers such as polyolefins, polyamides, polyesters, polyurethanes, silicones, and fluororubbers, and further include elastomers formed from these polymers.

[0142] The thickness of the barrier membrane is not limited as long as it is within the range that can achieve the above purpose. For example, it can be 0.05 to 1 mm, less than 0.5 mm, or even less than 0.1 mm.

[0143] In one example, the barrier film can be formed by thermally shrinking a shrink tube formed of polymer around the core.

[0144] In another example, the barrier film can be formed by coating the surface of the core with liquid rubber and allowing it to dry.

[0145] In another example, the barrier film can also be formed from a UV-curable elastomer.

[0146] The liquid barrier membrane material is preferably coated onto the core surface by spraying.

[0147] 1.4. Scope of Application

[0148] The scope of application of the FRP article manufacturing method according to the embodiments is not limited to the manufacture of FRP articles of the specific shapes illustrated in the above description. The FRP article manufacturing method according to the embodiments can be applied to the manufacture of so-called FRP articles having at least a portion of a structure formed by bent or flexed walls.

[0149] Typical examples of structures formed by bent or curved walls include hollow structures, cylindrical structures, U-shaped cross-section structures, and L-shaped cross-section structures. Various undercuts also mostly have bent or curved walls within the structure.

[0150] The FRP article manufacturing method described in the embodiments can also be applied to the situation where large-sized FRP articles are manufactured from two or more partial prepreg preforms.

[0151] In an FRP article manufactured by the FRP article manufacturing method according to the embodiments, FRP can be molded in such a way as to form a composite with a component made of a material other than FRP such as metal.

[0152] 1.5. Summary of Implementation Methods

[0153] The embodiments of the present invention include the following, but are not limited thereto.

[0154] [Embodiment 1] A manufacturing method for a fiber-reinforced resin article includes: a molding step in which a prepreg preform and a core formed of a wax material are heated together in a pressing mold to obtain a cured product; and a core removal step in which the core is removed from the cured product, the core having an expanded portion formed of a first wax material and an imprinted portion formed of a second wax material incompatible with the first wax material, the imprinted portion being disposed on the surface of the core, and a portion reflecting the surface shape of the imprinted portion being formed on the surface of the cured product.

[0155] [Embodiment 2] According to the manufacturing method of Embodiment 1, the expansion portion is not exposed on the surface of the core.

[0156] [Embodiment 3] According to the manufacturing method of Embodiment 1 or 2, the core further has a low expansion portion formed of the second wax material.

[0157] [Embodiment 4] According to any one of Embodiments 1 to 3, the core has a groove for forming ribs provided on the surface of the impression portion.

[0158] [Embodiment 5] According to any one of Embodiments 1 to 3, the core has a groove pattern for forming rib patterns provided on the surface of the impression portion.

[0159] [Embodiment 6] According to the manufacturing method of Embodiment 5, the groove pattern includes one or more selected from rectangular grid patterns, triangular grid patterns, radial patterns and stripe patterns.

[0160] [Embodiment 7] According to any one of Embodiments 1 to 6, the core has a recess for forming a boss provided on the surface of the impression portion.

[0161] [Embodiment 8] According to the manufacturing method of any one of Embodiments 1 to 3, the surface of the above-mentioned mold portion is flat.

[0162] [Embodiment 9] According to any one of Embodiments 1 to 3, the core has protrusions or recesses provided on the surface of the impression portion.

[0163] [Embodiment 10] According to any one of Embodiments 1 to 9, in the manufacturing method, before the above molding process, the surface of the core is covered by a barrier film.

[0164] [Embodiment 11] According to the manufacturing method of any one of Embodiments 1 to 10, the prepreg preform contains SMC.

[0165] [Embodiment 12] According to any one of Embodiments 1 to 11, the core is preheated before the molding process described above.

[0166] [Embodiment 13] According to the manufacturing method of any one of Embodiments 1 to 12, the first wax material described above contains a polyolefin wax.

[0167] [Embodiment 14] According to the manufacturing method of Embodiment 13, the first wax material described above contains polypropylene wax as the polyolefin wax described above.

[0168] [Embodiment 15] According to the manufacturing method of Embodiment 13 or 14, the first wax material described above contains polyethylene wax as the polyolefin wax described above.

[0169] [Embodiment 16] According to the manufacturing method of any one of Embodiments 13 to 15, the above-mentioned second wax material contains an organic compound having a polar group.

[0170] [Embodiment 17] According to any one of Embodiments 1 to 16, in the manufacturing method, either or both of the first wax material and the second wax material contain a colorant to enable visual identification of the first wax material and the second wax material.

[0171] [Embodiment 18] According to any one of Embodiments 1 to 17, the above-mentioned expansion portion contains particles of a material that has the property of generating heat under a high-frequency electromagnetic field.

[0172] [Embodiment 19] According to any one of Embodiments 1 to 17, the above-mentioned expansion portion contains particles of a material that has the property of absorbing microwaves and generating heat.

[0173] [Embodiment 20] A fiber-reinforced resin article is manufactured using the manufacturing method described in any one of Embodiments 5 to 7.

[0174] [Embodiment 21] A fiber-reinforced resin article has: a hollow structural portion having cavities and ribs formed on the wall surface of the cavities.

[0175] [Embodiment 22] A fiber-reinforced resin article has: a hollow structural portion having cavities and a rib pattern formed on the wall surface of the cavities.

[0176] [Embodiment 23] According to the fiber-reinforced resin article of Embodiment 22, the rib pattern includes one or more selected from rectangular grid patterns, triangular grid patterns, radial patterns and stripe patterns.

[0177] [Embodiment 24] The fiber-reinforced resin article according to any one of Embodiments 21 to 23 has a protrusion formed on the wall surface of the cavity.

[0178] [Embodiment 25] A fiber-reinforced resin article has: a hollow structural portion having cavities and a protrusion formed on the wall surface of the cavity.

[0179] 2. Experimental Results

[0180] The following describes the results of experiments conducted by the inventors.

[0181] 2.1. Experiment 1

[0182] Create a hollow cuboid with external dimensions of 300mm × 100mm × 30mm as an FRP item.

[0183] Short-cut carbon fiber stacks are impregnated with epoxy acrylate resin to form SMC (Structured MC STR120N131 manufactured by Mitsubishi Chemical Corporation) with a fiber content of 53% by mass and a thickness of about 2 mm. Two sheets of this SMC are overlapped, cut into a predetermined shape, and bent to produce a prepreg preform with an almost net shape.

[0184] When manufacturing the prepreg preform, a separately prepared cuboid core is placed inside it with its surface covered by a barrier film. The core is made of a pyrolytic polypropylene wax with a melting point of 123°C [VISCOL (registered trademark) manufactured by Sanyo Chemical Industries, Ltd.], and is molded to a size that fits perfectly inside the prepreg preform when the barrier film covers its surface. The barrier film is a nylon stretch film [Stretchlon (registered trademark) 800 manufactured by Airtech Corporation].

[0185] The prepreg with the core inside is placed into a mold preheated to the molding temperature and heated to cure. The molding temperature is 140°C and the molding time is 10 minutes.

[0186] The cured material removed from the mold is heated to 150°C in an oven to melt the wax forming the core. Then, a 10mm diameter discharge hole is drilled in the cured material to allow the wax to drain out.

[0187] The resulting hollow cuboid has a good appearance, and its shape and size are as designed.

[0188] The arithmetic mean roughness (reference length 50 mm) of the central part of the wall of the cavity (approximately 300 mm × 100 mm) was measured using a surface roughness measuring machine [SURFCOM 1400LCD, Tokyo Seimitsu Co., Ltd. (registered trademark)]. The result was 45 μm.

[0189] 2.2. Experiment 2

[0190] The core used was changed, but otherwise the same procedure was followed as in Experiment 1 to produce a hollow cuboid formed of FRP.

[0191] The core used in Experiment 2 was developed using... Figure 10 The process shown results in a structure in which the entire surface of the expanded portion formed by the thermally decomposable polypropylene wax is tightly covered by an impression layer formed by other waxes incompatible with the wax.

[0192] The thermally decomposable polypropylene wax is the same as the thermally decomposable polypropylene wax used in Experiment 1.

[0193] The impression portion is formed using a synthetic wax (ITOWAX J-530 manufactured by Ito Oil Co., Ltd.) with a melting point of 142°C, with N,N'-ethylene-bis-12-hydroxystearylamide as the main component. The thickness of the impression portion is approximately 2 mm.

[0194] The outer dimensions of the core are roughly the same as those of the core made in Experiment 1.

[0195] The resulting hollow cuboid has a good appearance, and its shape and size are as designed.

[0196] The arithmetic mean roughness of the cavity wall was measured using the same procedure as in Experiment 1, and the result was 12 μm.

[0197] 2.3. Experiment 3

[0198] The wax used for the expansion part of the core was changed from a thermally decomposable polypropylene wax to a thermally decomposable polyethylene wax with a melting point of 107°C [Sanyo Chemical Industry Co., Ltd. Sunwax (registered trademark) 151-P]. Otherwise, the same procedure as in Experiment 2 was followed to produce a hollow cuboid formed of FRP.

[0199] The resulting hollow cuboid has a good appearance, and its shape and size are as designed.

[0200] The arithmetic mean roughness of the cavity wall was measured using the same procedure as in Experiment 1, and the result was 10 μm.

[0201] 2.4. Experiment 4

[0202] The expansion part of the core was formed by mixing a wax material of thermally degradable polypropylene wax [VISCOL (registered trademark) manufactured by Sanyo Chemical Industry Co., Ltd.] and thermally degradable polyethylene wax [sunwax151-P manufactured by Sanyo Chemical Industry Co., Ltd.] in a weight ratio of 1:1. Otherwise, the same procedure as in Experiment 2 was followed to produce a hollow cuboid formed of FRP.

[0203] The resulting hollow cuboid has a good appearance, and its shape and size are as designed.

[0204] The walls of the cavity are flatter than the walls of the cavity in the FRP item made in Experiment 1.

[0205] The present invention has been described above based on specific embodiments, but these embodiments are given as examples and are not intended to limit the scope of the invention. The embodiments described in this specification can be modified in various ways to achieve the effects of the invention, and can be combined with features described through other embodiments to the extent that they are feasible.

[0206] Industry availability

[0207] The invention disclosed in this specification is preferably used, for example, in the manufacture of components (including structural components) for automobiles, ships, railway vehicles, aircraft, unmanned aerial vehicles, and other transportation equipment, bicycle frames, and various sporting goods including tennis rackets and golf clubs using fiber-reinforced resins.

[0208] Explanation of symbols

[0209] 1. Fiber Reinforced Resin (FRP) Items

[0210] 10 cores

[0211] 12 Expansion section

[0212] 14. Imprinting Section

[0213] 16 Low Expansion Section

[0214] 18. Barrier membrane

[0215] 20 Prepreg Preform

[0216] 30 cured product

[0217] 100 Pressing Mold

[0218] 102 Lower mold

[0219] 104 Upper mold.

Claims

1. A manufacturing method for a fiber-reinforced resin article, comprising: a molding step of heating a prepreg preform and a core formed of a wax material together in a pressing mold to obtain a cured product; and a core removal step of removing the core from the cured product, the core having an expanded portion formed of a first wax material and an imprinted portion formed of a second wax material incompatible with the first wax material, the first wax material having a lower softening temperature than the second wax material, the imprinted portion being disposed on the surface of the core, and a portion reflecting the surface shape of the imprinted portion being formed on the surface of the cured product.

2. In the manufacturing method according to claim 1, the expanded portion is not exposed on the surface of the core.

3. The manufacturing method according to claim 1 or 2, wherein the core further comprises a low-expansion portion formed of the second wax material.

4. The manufacturing method according to claim 1 or 2, wherein the core has a groove for forming ribs provided on the surface of the impression portion.

5. The manufacturing method according to claim 1 or 2, wherein the core has a groove pattern for forming a rib pattern disposed on the surface of the impression portion.

6. The manufacturing method according to claim 5, wherein the groove pattern comprises one or more selected from rectangular grid patterns, triangular grid patterns, radial patterns, and stripe patterns.

7. The manufacturing method according to claim 1 or 2, wherein the core has a recess for forming a boss provided on the surface of the impression portion.

8. The manufacturing method according to claim 1 or 2, wherein the surface of the impression portion is flat.

9. The manufacturing method according to claim 1 or 2, wherein the core has protrusions or recesses disposed on the surface of the impression portion.

10. The manufacturing method according to claim 1 or 2, wherein the surface of the core is covered with a barrier film prior to the molding process.

11. The manufacturing method according to claim 1 or 2, wherein the prepreg preform comprises SMC.

12. The manufacturing method according to claim 1 or 2, wherein the core is preheated prior to the molding process.

13. The manufacturing method according to claim 1 or 2, wherein the first wax material contains a polyolefin wax.

14. The manufacturing method according to claim 13, wherein the first wax material contains polypropylene wax as the polyolefin wax.

15. The manufacturing method according to claim 13, wherein the first wax material contains polyethylene wax as the polyolefin wax.

16. The manufacturing method according to claim 13, wherein the second wax material contains an organic compound having a polar group.

17. The manufacturing method according to claim 1 or 2, wherein either or both of the first wax material and the second wax material contain a colorant to enable visual identification of the first wax material and the second wax material.

18. The manufacturing method according to claim 1 or 2, wherein the expanded portion contains particles of a material having the property of generating heat under a high-frequency electromagnetic field.

19. The manufacturing method according to claim 1 or 2, wherein the expanded portion contains particles of a material having the property of absorbing microwaves and generating heat.

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