JP2024020732A - Manufacturing method for frp products - Google Patents

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

Fiber Reinforced Plastic (FRP) is lightweight and has excellent mechanical properties, so it is used in a variety of applications including reinforcement for automobiles, and its importance has been increasing in recent years. It has become.

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

International Publication No. 2018/079824 Japanese Patent Application Publication No. 5-293908

In the method of melting the wax core in a closed mold, the internal pressure of the molding cavity becomes higher than the pressure applied from the outside by the press, which can cause the problem of the mold opening during molding.

The present inventors have discovered that even when an open mold is used, by using a wax core that melts during molding, the prepreg can be cured under pressure and a hollow FRP article with few voids can be manufactured. They discovered this and completed the present invention.
According to one aspect of the present invention, a mold having a thermosetting prepreg, a core made of wax, and a molding cavity is provided, the mold is charged with the prepreg and the core, and the charged vacuum bagging the mold; and curing the prepreg by heating the vacuum-bagged mold under an atmospheric pressure or higher, the mold having a mold cavity in the mold. It has an opening connected to the outside, and when charging 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 closed by the prepreg. There is provided a method for manufacturing an FRP article, wherein at least a portion of the core is melted by the heating.

A novel manufacturing method that can be preferably used for manufacturing hollow FRP articles is provided.

FIG. 1 is a perspective view schematically showing the core. FIG. 2 is a cross-sectional view schematically showing the mold. FIG. 3 is a perspective view schematically showing how the prepreg is arranged around the core. FIG. 4 is a cross-sectional view schematically showing how the mold shown in FIG. 2 is charged with prepreg and a core. FIG. 5 is a perspective view schematically showing how a core is wrapped with a polymer film and prepregs are arranged around it. FIG. 6 is a cross-sectional view schematically showing how the mold shown in FIG. 2 is charged with prepreg and a core. FIG. 7 is a cross-sectional view schematically showing vacuum bagging of a mold charged with prepreg and core. FIG. 8 is a cross-sectional view schematically showing how the piston is inserted into the opening of the mold. FIG. 9 is a cross-sectional view schematically showing how a plug made of wax is used by being wrapped with a polymer film together with a core.

Hereinafter, some embodiments of the present invention will be described with reference to the drawings as appropriate. The dimensional ratio in the drawings is for convenience of explanation and may differ from the actual one. In addition, in the drawings, the same configurations may be indicated using the same reference numerals, and the description of the overlapping configurations may be omitted.

1. Method for manufacturing an FRP article One aspect of the present invention relates to a method for manufacturing an FRP article including the following steps (a) to (d).
(a) Preparing a mold having a thermosetting prepreg, a core made of wax, and a molding cavity.
(b) charging the mold with the prepreg and the core;
(c) Vacuum bagging the charged mold.
(d) Curing the prepreg by heating the vacuum-bagged mold under atmospheric pressure or higher.
Details of each step (a) to (d) are as follows.

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

The core is formed of wax. The wax may contain a filler.
Depending on the curing properties of the prepreg resin matrix, the wax should have different melting temperatures. This is because, in the step (d) of curing the prepreg, it is preferable that the melting of the core begins 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 fluidity due to gelation.
For example, when molding an FRP pipe, a cylindrical core as shown in FIG. 1 is prepared.

FIG. 2 is a cross-sectional view of a mold used when molding 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 mold cavity 12 connected to the outside of the mold 10 through the opening 11. The mold 10 is a split mold consisting of two partial molds 13 and 14, and a molding cavity 12 is formed when these partial molds 13 and 14 are combined.
The number of partial molds that a mold has is not limited to two, and a mold consisting of three or more partial molds may be prepared.

(b) Charging the mold The prepared mold is charged with the prepared prepreg and core.
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.

When molding an FRP pipe using the core 1 and the mold 10, after placing the prepreg 2 around the core 1 as shown in FIG. is placed in the molding cavity 12 of.
The prepreg 2 may consist of a plurality of laminated prepreg sheets.

In a preferred example, the core 1 is wrapped with a polymer film 3 and the prepreg 2 is placed around it, as shown in FIG. 5, so that when the core melts during molding, the liquid wax does not flow into undesired areas. However, as shown in FIG. 6, a mold 10 may be charged with the core 1, polymer film 3, and prepreg 2.
Although it is a preferable embodiment to expose a portion of the core 1 to the outside of the mold 10 through the opening 11 as in the example shown in FIGS. 4 and 6, it is not essential.

The partial molds may be connected to each other by an appropriate method such as screwing or clamping.
The portion of the prepreg that is to be molded into a predetermined shape only needs to be placed within the molding cavity, and the portion that is not used for the product may be placed outside the molding cavity.

(c) Vacuum bagging of the charged mold The mold charged with the core and prepreg is vacuum bagged.
Specifically, as shown in FIG. 7, a mold 10 charged with a core 1 and a prepreg 2 is covered with a bagging film 20 together with a breather cloth 21, a vacuum cap 22 is connected to a vacuum pump (not shown), The inside of the bagging film 20 is sucked. After closing the valve 23 so that the inside of the bagging film 20 is kept in a vacuum, the vacuum mouthpiece 22 and the vacuum pump are disconnected.

(d) Curing of prepreg The vacuum-bagged mold is placed in an autoclave and heated while being pressurized.
The pressure inside the autoclave is preferably 2 atmospheres or more, more preferably 3 atmospheres or more, and still more preferably 6 atmospheres or more. The pressure inside the autoclave may be, for example, 10 atmospheres or less, but is not limited thereto.
The temperature and heating time in the autoclave are set so that the prepreg is sufficiently cured.

As the core begins to melt, the liquid wax acts as a pressure medium, balancing the pressure inside the mold cavity with the pressure outside the mold. That is, 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 melting of the core begins before the resin matrix of the prepreg loses fluidity due to gelation. Since the prepreg is cured under pressure, a cured product with no voids and a good surface appearance can be obtained.
Since the internal pressure in the mold cavity does not exceed the pressure outside the mold, the mold will not open during molding.

In one example, a vacuum-bagged mold may be placed in an autoclave with the vacuum cap connected to the vacuum pump, and the inside of the bagging film covering the mold may be vacuum-sucked while the mold is heated in the autoclave. . This vacuum suction may continue throughout the heating of the mold, or may be temporary.

(e) Removal Once the prepreg has been cured, the mold is taken out from the autoclave, the bagging film is peeled off, the mold is opened, and the molded product (cured prepreg) is taken out.
Since the core is soft when the temperature of the molded product is higher than the melting temperature of the wax contained in the core, the core can be easily removed from the molded product. If the mold is opened after the wax has cooled until solidified, the core may be heated again after the molded product is taken out to soften it and then removed from the molded product.

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

Sheet prepregs of the same type can be laminated and used. When laminating UD prepregs, the fiber direction may be made the same between the plies, or cross ply or angle ply may be used, depending on requirements.
It is also possible to use a combination of different types of prepregs, that is, prepregs that differ in at least one of the form of the fiber reinforcing material, the type of fiber, the fiber content, and the matrix resin.

(2) Resin matrix of prepreg Typical examples of thermosetting resins used for the resin matrix of prepreg include, but are not limited to, epoxy resin, urea resin, vinyl ester resin, unsaturated polyester resin, polyurethane resin, and phenolic resin. It's not something you can do. These thermosetting resins can be used in combination of two or more types.
In addition to curing agents, the resin matrix contains thickeners, reactive diluents, low shrinkage agents, flame retardants, antifoaming agents, defoamers, mold release agents, particulate fillers, colorants, and silane coupling agents. Various additives may be added as necessary.

(3) Wax Since the working environment temperature is usually below 28°C, the wax used for the core is required not to melt at 28°C. For this reason, the melting temperature 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 melting temperature of the wax ensures that the core begins to melt before the prepreg resin matrix 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 still more preferably 100°C or lower.

There are no restrictions on the type of wax. Usable waxes include paraffin wax, petroleum wax such as microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, polypropylene wax, synthetic wax such as fatty acid amide wax, hydroxy fatty acid amide wax, fatty acid ester wax, and petroleum wax. This includes waxes such as oxidized paraffin wax and oxidized polyolefin wax, which are made by chemically modifying synthetic waxes, waxes made by blending these waxes with synthetic resins, and waxes made by blending different types of waxes.

(4) Polymer film Examples of methods for covering the core with a polymer film include the following.
・Wrap the core in polymer film and secure with heat-resistant tape to prevent the wrapped state from collapsing. It may be sealed, but it is not required. Instead of fixing with heat-resistant tape, adhesive may be used or fusion bonding may be used.
- Heat shrink the shrink tube with the core placed inside the shrink tube made of polymer, and then close both ends of the shrink tube 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 product of liquid rubber becomes a polymer film.
・Coat the raw material liquid of UV-curable elastomer on the surface of the core and cure it by UV irradiation. The cured product of the UV-curable elastomer becomes a polymer film.

The sealing effect will be higher if the polymer film is stretchable at the forming temperature. This elongation deformation may be elastic or plastic, or may have both properties.
Preferred materials for the polymer film include synthetic polymers such as polyolefins, polyamides, polyesters, polyurethanes, silicones, fluororubbers, and further include elastomers made of these polymers.

(5) Embodiment using a piston In one example, as shown in FIG. 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 mold cavity 12 are balanced via the piston 24.
The piston 24 also has the function of making it difficult for liquid wax to flow out into the gap between the mold 10 and the bagging film 20 when the core 1 melts. It takes time and effort to collect the wax that flows out.

(6) Embodiment utilizing expansion of the core In one example, in step (d) of curing the prepreg, the prepreg may be pressed against the surface of the molding cavity by thermal expansion of the core before melting of the core begins. . To this end, when charging the mold, the gap between the prepreg and the surface of the molding cavity should be made sufficiently small.
In another example, as shown in FIG. 9, a plug 25 made of wax whose melting temperature is higher than that of the wax constituting the core 1 but lower than the molding temperature is formed with the polymer film 3 together with the core 1. It can also be used wrapped. Since the plug 25 closes the opening 11 of the mold 10, the internal pressure of the mold cavity 12 continues to rise even after the core 1 begins to melt in step (d) of curing the prepreg. When the wax constituting the plug 25 begins to melt, the plug 25 can no longer close the opening 11 of the mold 10, and the internal pressure of the molding cavity 12 decreases until it balances with the pressure outside 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 the wax constituting the plug 25 can be easily separated after molding.

(7) Embodiment that does not use an autoclave Instead of an autoclave, the prepreg may be cured by placing a vacuum-bagged mold in an oven (inside normal pressure: 1 atm) that does not have a pressure mechanism. The pressure applied to the prepreg during curing is 1 atm, which has the effect of suppressing the generation of voids. Furthermore, if the expansion of the core is also used to pressurize the prepreg in the method described in item (6) above, the generation of voids can be more effectively suppressed.

3. Summary of Embodiments Preferred embodiments of the invention include, but are not limited to:
[Embodiment 1] Preparing a mold having a core made of thermosetting prepreg and wax, and a molding cavity, charging the mold with the prepreg and the core, and vacuuming the charged mold. and curing the prepreg by heating the vacuum-bagged mold under atmospheric pressure or higher, the mold having an opening connecting the mold cavity to an exterior of the mold. In charging 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. . A method for producing an FRP article, wherein at least a portion of the core is melted by the heating.
[Embodiment 2] The manufacturing method according to Embodiment 1, wherein the core is wrapped with a polymer film before charging the mold.
[Embodiment 3] The manufacturing method according to Embodiment 1 or 2, wherein the mold is charged so that a part of the core comes out of the mold through the opening.
[Embodiment 4] The manufacturing method according to Embodiment 1 or 2, wherein in charging the mold, the opening is closed with a piston.
[Embodiment 5] The manufacturing method according to any one of Embodiments 1 to 4, wherein melting of the core by the heating starts before the resin matrix of the prepreg gels.
[Embodiment 6] The manufacturing method according to any one of Embodiments 1 to 5, wherein the melting temperature of the wax is within the range of 30 to 120°C.
[Embodiment 7] The manufacturing method according to any one of Embodiments 1 to 6, wherein the atmospheric pressure is 2 atm or more and may be 10 atm or less.
[Embodiment 8] The manufacturing method according to any one of Embodiments 1 to 7, wherein an autoclave is used for the heating.
[Embodiment 9] The manufacturing method according to any one of Embodiments 1 to 6, wherein an oven having no pressure mechanism is used for the heating.
[Embodiment 10] The manufacturing method according to any one of Embodiments 1 to 9, wherein while the heating is performed, continuous or temporary vacuum suction is performed inside the bagging film covering the mold.

Although the present invention has been described above based on specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described in this specification can be variously modified within the scope where the effects of the invention can be achieved, and the features described in other embodiments may be modified to the extent that it is practicable. Can be combined.

1 core
10 Molding mold 11 Opening 12 Molding cavity 13 Partial mold (upper mold)
14 Partial mold (lower mold)
20 Bagging film 21 Breather cloth 22 Vacuum cap 23 Valve 24 Piston 25 Plug

Claims (10)

providing a mold having a thermoset prepreg, a core made of wax, and a mold cavity;
charging the mold with the prepreg and the core;
vacuum bagging the charged mold; and
Curing the prepreg by heating the vacuum-bagged mold under atmospheric pressure or higher,
The mold has an opening that connects the mold cavity to the outside of the mold,
In charging 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,
At least a portion of the core is melted by the heating;
Method for manufacturing FRP articles. 2. The method of claim 1, wherein the core is wrapped with a polymer film before charging the mold. 3. The manufacturing method according to claim 1, wherein the mold is charged so that a part of the core comes out of the mold through the opening. 3. The manufacturing method according to claim 1, wherein in charging the mold, the opening is closed with a piston. The manufacturing method according to any one of claims 1 to 4, wherein melting of the core by the heating begins before the resin matrix of the prepreg gels. The manufacturing method according to any one of claims 1 to 5, wherein the melting temperature of the wax is within the range of 30 to 120°C. The manufacturing method according to any one of claims 1 to 6, wherein the atmospheric pressure is 2 atmospheres or more. The manufacturing method according to any one of claims 1 to 7, wherein an autoclave is used for the heating. The manufacturing method according to any one of claims 1 to 6, wherein an oven without a pressure mechanism is used for the heating. The manufacturing method according to any one of claims 1 to 9, wherein while the heating is performed, continuous or temporary vacuum suction is performed inside a bagging film covering the mold.

Images