Manufacturing method for FRP articles

Abstract

To provide a method for manufacturing FRP products using a novel molding process.SOLUTION: A method for manufacturing FRP products includes: preparing a molding die 10 having a thermosetting prepreg 2, a core 1 made of wax, and a molding cavity 12 that is connected to the outside through an opening 11; charging the molding die 10 with the prepreg 2 and core 1; vacuum bagging the charged molding die 10; and curing the prepreg 2 by heating the vacuum bagged molding die 10 under ambient pressure above atmospheric pressure. In the charging of the molding die, the prepreg 2 is sandwiched between a portion of the surface of the core 1 and the surface of the molding cavity 12, and the opening 11 is not blocked by the prepreg 2. At least a portion of the core 1 is melted by the heating described above.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing FRP articles, particularly a manufacturing method suitable for FRP pipes.

Background Art

[0002] Fiber Reinforced Plastic (FRP) is lightweight and has excellent mechanical properties, so it is used in various applications including reinforcement members for automobiles, and its importance has been increasing in recent years.

[0003] There is known a method for manufacturing a hollow FRP molded product in which a prepreg is placed in a mold together with a core made of solid wax, heated while being pressed by a press machine, and the prepreg is cured under the internal pressure generated as the wax melts (Patent Document 1). A method of forming a pipe made of FRTP (Fiber Reinforced Thermoplastic) by heating in an oven a material in which a prepreg having a thermoplastic resin matrix is interposed between a thermally expandable mandrel made of ultra-high molecular weight polyethylene and a copper pipe as an outer mold arranged outside the mandrel is known (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In methods where a wax core is melted in a sealed mold, the internal pressure of the molding cavity can become higher than the external pressure applied by the press, potentially causing the mold to open during molding. [Means for solving the problem]

[0006] The inventors have discovered that even when using an open-type mold, it is possible to manufacture hollow FRP articles with few voids by curing the prepreg under pressure using a wax core that melts during molding, thereby completing the present invention. According to one aspect of the present invention, a method for manufacturing an FRP article is provided, comprising: preparing a mold having a thermosetting prepreg, a core made of wax, and a molding cavity; charging the mold with the prepreg and the core; vacuum bagging the charged mold; and heating the vacuum bagged mold under atmospheric pressure above atmospheric pressure to cure the prepreg, wherein the mold has an opening connecting the molding cavity to the outside of the mold, and during the charging of the mold, the prepreg is sandwiched between a part of the surface of the core and the surface of the molding cavity, and the opening is not blocked by the prepreg, and at least a part of the core melts due to the heating. [Effects of the Invention]

[0007] A novel manufacturing method is provided that can be preferably used in the manufacture of hollow FRP articles. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic perspective view of the core. [Figure 2] Figure 2 is a schematic cross-sectional view showing a mold. [Figure 3] Figure 3 is a schematic perspective view showing how the prepreg is arranged around the core. [Figure 4]Figure 4 is a schematic cross-sectional view showing the process of charging the mold shown in Figure 2 with prepreg and core. [Figure 5] Figure 5 is a schematic perspective view showing how the core is wrapped in a polymer film and the prepreg is placed around it. [Figure 6] Figure 6 is a schematic cross-sectional view showing the process of charging the mold shown in Figure 2 with prepreg and core. [Figure 7] Figure 7 is a schematic cross-sectional view showing the vacuum bagging process of a mold charged with prepreg and core. [Figure 8] Figure 8 is a schematic cross-sectional view showing the piston inserted into the opening of the mold. [Figure 9] Figure 9 is a schematic cross-sectional view showing how a stopper formed from wax is used by wrapping it together with a core in a polymer film. [Modes for carrying out the invention]

[0009] Several embodiments of the present invention will be described below with reference to the drawings as appropriate. The dimensional ratios in the drawings are for illustrative purposes only and may differ from those of the actual components. In addition, identical components are indicated by the same reference numerals in the drawings, and descriptions of redundant components may be omitted.

[0010] 1. Manufacturing method of FRP articles One aspect of the present invention relates to a method for manufacturing an FRP article, comprising the following steps (a) to (d). (a) Prepare a mold having a core made of thermosetting prepreg and wax, and a molding cavity. (b) Charge the mold with the prepreg and the core. (c) Vacuum bagging the charged mold. (d) The vacuum bagged mold is heated under atmospheric pressure equal to or greater than atmospheric pressure to cure the prepreg. The details of each step (a) to (d) are as follows:

[0011] (a) Preparation of prepreg, core, and mold As starting materials, a thermosetting prepreg composed of a resin matrix containing a thermosetting resin and a fiber reinforcing material is prepared. The prepreg is cut into a predetermined shape.

[0012] The core is formed of wax. The wax may contain a filler. Depending on the curing characteristics of the resin matrix of the prepreg, the melting temperature that the wax should have is different. This is because in step (d) of curing the prepreg, it is preferable that the melting of the core starts before the resin matrix of the prepreg gels. Gelation means that the thermosetting resin components contained in the resin matrix react to form a three-dimensional crosslinked structure, and the resin matrix loses its fluidity due to gelation. For example, when forming an FRP pipe, a columnar core as shown in FIG. 1 is prepared.

[0013] FIG. 2 is a cross-sectional view of a mold used when forming an FRP pipe using the core 1 shown in FIG. 1. As shown in FIG. 2, the mold 10 has an opening 11 and a molding cavity 12 connected to the outside of the mold 10 through the opening 11. The mold 10 is a split mold composed of two sub-molds 13, 14, and the molding cavity 12 is formed when these sub-molds 13, 14 are combined. The number of sub-molds that the mold has is not limited to two, and a mold composed of three or more sub-molds may be prepared.

[0014] (b) Charging of the mold The prepared mold is charged with the prepared prepreg and core. The charging is performed such that the prepreg is sandwiched between a part of the surface of the core and the surface of the molding cavity, and the opening of the mold is not blocked by the prepreg.

[0015] When forming an FRP pipe using a core 1 and a mold 10, the prepreg 2 is placed around the core 1 as shown in Figure 3, and then placed together with the core 1 inside the molding cavity 12 of the mold 10 as shown in Figure 4. Prepreg 2 may consist of multiple laminated prepreg sheets.

[0016] In a preferred example, to prevent the liquefied wax from flowing to undesirable locations when the core melts during molding, the core 1 may be wrapped in a polymer film 3 as shown in Figure 5, with prepreg 2 placed around it, and the mold 10 may be charged with the core 1, polymer film 3, and prepreg 2 as shown in Figure 6. As shown in the example in Figures 4 and 6, it is a preferred but not essential configuration to allow a portion of the core 1 to protrude outside the mold 10 through the opening 11.

[0017] The individual parts can be joined together using appropriate methods such as screws or clamps. The prepreg only needs to have the portion to be molded into a predetermined shape located within the molding cavity; the portion not used in the product may extend outside the molding cavity.

[0018] (c) Charged molded vacuum bagging The mold, charged with the core and prepreg, is vacuum bagged. Specifically, as shown in Figure 7, the mold 10, which has been charged with core 1 and prepreg 2, is covered with bagging film 20 together with breather cloth 21, and a vacuum nozzle 22 is connected to a vacuum pump (not shown) to suck air from the inside of the bagging film 20. After closing valve 23 to maintain a vacuum inside the bagging film 20, the connection between the vacuum nozzle 22 and the vacuum pump is disconnected.

[0019] (d) Curing of the prepreg The vacuum-bagged mold is placed in an autoclave and heated under pressure. The pressure inside the autoclave is preferably 2 atmospheres or more, more preferably 3 atmospheres or more, and even more preferably 6 atmospheres or more. The pressure inside the autoclave may be, for example, 10 atmospheres or less, but is not limited to that. The temperature and heating time inside the autoclave are set to ensure that the prepreg is sufficiently cured.

[0020] As the core begins to melt, the liquefied wax acts as a pressure medium, balancing the pressure inside the molding cavity with the pressure outside the mold. In other words, the prepreg is pressed against the inner surface of the mold with a pressure equal to the pressure outside the mold. It is preferable that the core melting begins before the resin matrix of the prepreg loses its fluidity due to gelation. Since the prepreg hardens under pressure, a cured product without voids and with a good surface appearance can be obtained. Since the internal pressure of the molding cavity does not exceed the external pressure of the mold, the mold will not open during molding.

[0021] In one example, with the vacuum nozzle still connected to the vacuum pump, the vacuum-bagged mold may be placed in an autoclave, and while the mold is being heated in the autoclave, vacuum suction may be applied to the inside of the bagging film covering the mold. This vacuum suction may be continued throughout the heating of the mold, or it may be temporary.

[0022] (e) Take out Once the prepreg has cured, remove the mold from the autoclave, peel off the bagging film, open the mold, and remove the molded product (cured prepreg). When the temperature of the molded product is higher than the melting point of the wax contained in the core, the core is soft, allowing it to be easily removed from the molded product. If the mold is opened after the wax has cooled and solidified, the core can be reheated to soften it after removing the molded product, and then removed from the molded product.

[0023] 2. Various Embodiments (1) Prepreg Various prepregs can be used, including unidirectional prepregs (UD prepregs), woven prepregs, nonwoven prepregs, SMC (sheet molding compound), and tow prepregs. Typical examples of fibers used as fiber reinforcement in prepregs are carbon fibers, glass fibers, and aramid fibers, but prepregs using natural fibers such as plant fibers can also be preferably used. The fiber content of the prepreg is, for example, in the range of 30 to 70 wt%.

[0024] Multiple sheets of the same type of prepreg can be laminated and used. When laminating UD prepregs, the fiber direction may be aligned between the plies, or cross-ply or angle-ply materials may be used, as required. It is also possible to use a combination of different prepregs, that is, prepregs that differ in at least one aspect, such as the form of the fiber reinforcement, the type of fiber, the fiber content, or the matrix resin.

[0025] (2) Prepreg resin matrix Typical examples of thermosetting resins used in the resin matrix of prepregs include epoxy resins, urea resins, vinyl ester resins, unsaturated polyester resins, polyurethane resins, and phenolic resins, but are not limited to these. Two or more of these thermosetting resins can be used in combination. In addition to the curing agent, various additives may be added to the resin matrix as needed, such as thickeners, reactive diluents, low-shrinkage agents, flame retardants, defoamers, defoaming agents, mold release agents, particulate fillers, colorants, and silane coupling agents.

[0026] (3) Wax Since the working environment temperature is usually below 28°C, the wax used in the core must not melt at 28°C. For this reason, the melting point of the wax is preferably 30°C or higher. The wax is required to melt at a temperature lower than the molding temperature. The lower the melting temperature of the wax, the more reliably the core will begin to melt before the resin matrix of the prepreg gels. Since the temperature at which the resin matrix gels is often higher than 120°C, the melting temperature of the wax is preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower.

[0027] There are no limitations on the type of wax. Usable waxes include petroleum waxes such as paraffin wax and microcrystalline wax, synthetic waxes such as Fischer-Tropsch wax, polyethylene wax, polypropylene wax, fatty acid amide wax, hydroxy fatty acid amide wax, and fatty acid ester wax, waxes such as oxidized paraffin wax and oxidized polyolefin wax obtained by chemically modifying petroleum wax or synthetic wax, waxes obtained by blending these waxes with synthetic resins, and waxes obtained by blending different waxes.

[0028] (4) Polymer film Methods for covering the core with a polymer film include the following: • Wrap the core in polymer film and secure it with heat-resistant tape to prevent it from collapsing. Sealing is possible but not required. Instead of heat-resistant tape, adhesive or fusion bonding may be used. The core is placed inside a shrink tube made of polymer, the shrink tube is heat-shrunk, and then both ends of the shrink tube are sealed by fusion. A low-temperature curing liquid rubber is applied to the surface of the core and cured at a temperature that does not melt the core. The cured liquid rubber becomes a polymer film. The raw material liquid for the UV-curable elastomer is applied to the surface of the core and cured by UV irradiation. The cured product of the UV-curable elastomer becomes a polymer film.

[0029] The sealing effect is enhanced when the polymer film is tensile and deformable at the molding temperature. This tensile deformation may be elastic, plastic, or possess both properties. Preferred materials for polymer films include synthetic polymers such as polyolefins, polyamides, polyesters, polyurethanes, silicones, and fluororubber, and furthermore, elastomers made from these polymers.

[0030] (5) A configuration using a piston In one example, as shown in Figure 8, when charging the mold 10, a piston 24 made of a material that does not melt at all or hardly melts at the molding temperature may be inserted into the opening 11. In step (d) of curing the prepreg, after the core begins to melt, the pressure outside the mold 10 and the pressure inside the molding cavity 12 are balanced via the piston 24. The piston 24 also serves to prevent liquid wax from flowing out into the gap between the mold 10 and the bagging film 20 when the core 1 melts. Recovering the wax that does flow out is time-consuming.

[0031] (6) Embodiments that utilize core expansion In one example, in step (d) of curing the prepreg, the prepreg may be pressed against the surface of the molding cavity by the thermal expansion of the core before the core begins to melt. To achieve this, the gap between the prepreg and the surface of the molding cavity should be made sufficiently small when charging the mold. In another example, as shown in Figure 9, a stopper 25 made of wax with a melting temperature higher than that of the wax constituting the core 1 but lower than the molding temperature can be used, wrapped together with the core 1 in the polymer film 3. Since the stopper 25 seals the opening 11 of the mold 10, in step (d) of curing the prepreg, the internal pressure of the molding cavity 12 continues to rise even after the melting of the core 1 has begun. When the wax constituting the stopper 25 begins to melt, the stopper 25 can no longer seal the opening 11 of the mold 10, and the internal pressure of the molding cavity 12 decreases until it balances with the external pressure of the mold 10. It is preferable that the wax constituting the core 1 and the wax constituting the stopper 25 are incompatible with each other so that they can be easily separated after molding.

[0032] (7) A mode without using an autoclave Instead of an autoclave, the prepreg may be cured by placing a vacuum-bagged mold in an oven without a pressurizing mechanism (internal pressure: 1 atmosphere). Although the pressure applied to the prepreg during curing is 1 atmosphere, this method is effective in suppressing void formation. Furthermore, if the expansion of the core is also used to pressurize the prepreg using the method described in section (6) above, void formation can be suppressed more effectively.

[0033] 3. Summary of Embodiments Preferred embodiments of the present invention include, but are not limited to, the following. [Embodiment 1] A method for manufacturing an FRP article, comprising: preparing a mold having a thermosetting prepreg, a core made of wax, and a molding cavity; charging the mold with the prepreg and the core; vacuum bagging the charged mold; and heating the vacuum bagged mold under atmospheric pressure above atmospheric pressure to cure the prepreg, wherein the mold has an opening connecting the molding cavity to the outside of the mold, and during the charging of the mold, the prepreg is sandwiched between a part of the surface of the core and the surface of the molding cavity, and the opening is not blocked by the prepreg, and at least a part of the core melts due to the heating. [Embodiment 2] A manufacturing method according to Embodiment 1, wherein the core is wrapped in a polymer film before the mold is charged. [Embodiment 3] A manufacturing method according to Embodiment 1 or 2, wherein the charging of the mold is performed such that a portion of the core exits the mold through the opening. [Embodiment 4] A manufacturing method according to Embodiment 1 or 2, wherein the opening is closed with a piston during the charging of the mold. [Embodiment 5] A manufacturing method according to any one of Embodiments 1 to 4, wherein the melting of the core by heating begins before the resin matrix of the prepreg gels. [Embodiment 6] A manufacturing method according to any one of Embodiments 1 to 5, wherein the melting temperature of the wax is in the range of 30 to 120°C. [Embodiment 7] A manufacturing method according to any of Embodiments 1 to 6, wherein the ambient pressure is 2 atmospheres or more and may be 10 atmospheres or less. [Embodiment 8] A manufacturing method according to any one of Embodiments 1 to 7, wherein an autoclave is used for the heating. [Embodiment 9] A manufacturing method according to any one of Embodiments 1 to 6, wherein an oven without a pressurizing mechanism is used for heating. [Embodiment 10] A manufacturing method according to any one of Embodiments 1 to 9, wherein continuous or temporary vacuum suction is performed on the inside of the bagging film covering the mold while the heating is being performed.

[0034] 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. [Explanation of Symbols]

[0035] 1 core 10 mold 11 Aperture 12 molded cavities 13 Partial mold (upper mold) 14 Partial mold (lower mold) 20 Bagging film 21 Breather Cross 22 Vacuum nozzles 23 valves 24 pistons 25 stoppers

Claims

1. To prepare a mold having a core made of thermosetting prepreg and wax, and a molding cavity, The mold is charged with the prepreg and the core. The charged mold is vacuum bagged, and The vacuum-bagged mold is heated under atmospheric pressure above atmospheric pressure to cure the prepreg. Includes, The mold has an opening that connects the molding cavity to the outside of the mold, In the charging of the mold, the prepreg is sandwiched between a portion of the core surface and the surface of the molding cavity, and the opening is not blocked by the prepreg, and the opening is closed by a piston. The heating causes at least a portion of the core to melt. A method for manufacturing FRP articles.

2. The manufacturing method according to claim 1, wherein the core is wrapped in a polymer film before the mold is charged.

3. The manufacturing method according to claim 1 or 2, wherein the melting of the core by heating begins before the resin matrix of the prepreg gels.

4. The manufacturing method according to claim 1 or 2, wherein the melting temperature of the wax is in the range of 30 to 120°C.

5. The manufacturing method according to claim 1 or 2, wherein the ambient pressure is 2 atmospheres or more.

6. The manufacturing method according to claim 1 or 2, wherein an autoclave is used for the heating.

7. The manufacturing method according to claim 1 or 2, wherein an oven without a pressurizing mechanism is used for the heating.

8. The manufacturing method according to claim 1 or 2, wherein continuous or temporary vacuum suction is performed on the inside of the bagging film covering the mold while the heating is being performed.

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