JP7287526B2 - Method for producing fiber-reinforced plastic molded article - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a fiber-reinforced plastic molded article.

Fiber reinforced plastics (FRP) moldings of hollow shape, U shape, etc., range from large ones such as aircraft fuselages and wings to small ones such as bicycle frames, tennis rackets, fishing rods and golf shafts. is widely used.

As a method for producing a hollow, U-shaped, or other fiber-reinforced plastic molded body, a prepreg in which fibers (filaments) are impregnated with a resin is placed around a core, and the core is removed after molding. method is known.
For example, a method has been proposed in which an FRP material is laminated on a wax mold, and after the molding is cured, the wax mold is melted and removed (Patent Document 1).
Further, a step of making a core with synthetic wax, a step of attaching a prepreg to the entire outer surface of the core, forming a wax discharge hole in the attached prepreg, heating the core and the prepreg, and thermosetting the prepreg. (Patent Document 2).

Furthermore, the steps of placing a prepreg containing a fiber reinforcement and a thermosetting resin around a solid mandrel material, curing the prepreg to form a fiber-reinforced plastic molding, and A method comprising the steps of melting the mandrel material to a liquid material at a temperature lower than the glass transition temperature of the molded article, discharging the liquid material, and cooling the fiber-reinforced plastic molded article. It has been proposed (Patent Document 3).
In addition, fluid is enclosed in a mandrel made of an easily deformable hollow body, and after winding a continuous resin-impregnated fiber bundle in a mesh shape around the mandrel, the internal pressure of the mandrel is increased while restraining it with a heated molding die. A method for curing the above resin has been proposed (Patent Document 4).

JP-A-4-7127 JP 2007-307853 A Japanese Patent Application Publication No. 2014-534914 JP-A-62-5842

In the method of Patent Literature 1, molding is performed by curing at room temperature, so that the curing time is long, resulting in a decrease in production efficiency. In addition, since hand lay-up is performed directly on the wax surface layer, wax may remain between filaments after the wax is melted and removed.
In the method of Patent Document 2, the core is melted and removed while curing the prepreg, so the number of steps is small. However, part of the core tends to be removed before the prepreg hardens sufficiently, and in the case of large-sized fiber-reinforced plastic moldings in particular, the shape is not stable, and voids and other gaps may occur in the molding. be. Therefore, it is difficult to efficiently obtain a high-quality fiber-reinforced plastic molded article, which is economically disadvantageous.

Furthermore, in the method of Patent Document 3, especially when the pressure is likely to be applied in one direction during mold clamping, such as a molding die having an upper mold and a lower mold, it is difficult to uniformly apply pressure to the mandrel material, and the standing surface ( Molding defects such as voids on the surface extending upward from the mold cavity bottom and chipping of corners are likely to occur.
Further, in the method of Patent Document 4, since a gas such as air is enclosed in the mandrel, the molding pressure tends to be low, and molding defects tend to occur on standing surfaces and corners.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a fiber-reinforced plastic molded article that can easily control the pressure of the core and can efficiently and economically produce a hollow fiber-reinforced plastic molded article. .

The present invention has the following configurations.
[1] A molding precursor in which a prepreg containing a thermosetting resin and fibers is arranged around a core containing a thermoplastic solid is heat-compressed using a molding die, and then the thermoplastic solid A method for producing a fiber-reinforced plastic molded article, in which a hollow-shaped fiber-reinforced plastic molded article is obtained by discharging an object.
[2] The method for producing a fiber-reinforced plastic molded article according to [1], wherein the volume of the core of the molding precursor is equal to or less than the volume of the hollow portion of the hollow shape.
[3] The method for producing a fiber-reinforced plastic molded article according to [1] or [2], wherein the thermoplastic solid is granular resin or powdery resin.
[4] The method for producing a fiber-reinforced plastic molded article according to [1] or [2], wherein the thermoplastic solid material is subjected to at least one of uneven processing, hole processing and groove processing.
[5] The method for producing a fiber-reinforced plastic molded article according to any one of [1] to [4], wherein voids are present inside the thermoplastic solid.
[6] The method for producing a fiber-reinforced plastic molded article according to any one of [1] to [5], wherein the thermoplastic solid is wax.

According to the method for producing a fiber-reinforced plastic molded article of the present invention, the core pressure can be easily controlled, and a hollow fiber-reinforced plastic molded article can be produced efficiently and economically.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing an example of heat compression molding in the method for producing a fiber-reinforced plastic molded article of the present invention; 1 is a schematic cross-sectional view showing a state in which a fiber-reinforced plastic molded article containing wax as a thermoplastic solid is obtained in the method for producing a fiber-reinforced plastic molded article of the present invention; FIG. 1 is a schematic cross-sectional view showing a state in which a discharge port for discharging wax is formed in a fiber-reinforced plastic molded article containing wax obtained in the method for producing a fiber-reinforced plastic molded article of the present invention; FIG. FIG. 3 is a schematic cross-sectional view showing a state after the wax is discharged through a discharge port formed in the fiber-reinforced plastic molded article encapsulating the wax obtained in the method for producing a fiber-reinforced plastic molded article of the present invention. 1 is a schematic diagram showing an example of the shape of a thermoplastic solid in the method for producing a fiber-reinforced plastic molded article of the present invention; FIG. 1 is a schematic diagram showing an example of the shape of a thermoplastic solid in the method for producing a fiber-reinforced plastic molded article of the present invention; FIG. 1 is a schematic diagram showing an example of the shape of a thermoplastic solid in the method for producing a fiber-reinforced plastic molded article of the present invention; FIG. 4 is a graph showing changes over time in internal pressure of cores in Examples and Comparative Examples of the present invention.

In the method for producing a fiber-reinforced plastic molded article of the present invention, a molding precursor in which a prepreg containing a thermosetting resin and fibers is arranged around a core containing a thermoplastic solid is heated by a molding die. After compression molding, the thermoplastic solid matter is discharged to obtain a hollow fiber-reinforced plastic molding.

A fiber-reinforced plastic molded article obtained by the method for producing a fiber-reinforced plastic molded article of the present invention is a hollow molded article having an outer layer made of fiber-reinforced plastic.
The thermoplastic solid material used in the present invention has a function as a core used when manufacturing a fiber-reinforced plastic molded article having a hollow shape or a U-shaped cross section. In addition, the thermoplastic solid used in the present invention does not show plasticity under the atmospheric temperature before heat and pressure molding, typified by room temperature (20 ° C.), but softens or melts and freely deforms during heat compression molding. It consists of substances that have the property of
The thermoplastic solid matter can be easily removed from the obtained molded article after hot compression molding, for example, by setting the temperature to a temperature equal to or lower than the heat distortion temperature of the molded article and equal to or higher than the melting point of the thermoplastic solid matter. can be done.

Substances constituting this thermoplastic solid include, for example, thermoplastic resins such as polyolefin, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, and acrylic resins, low melting point metals such as tin and indium, solder, Examples include fusible metals such as Wood alloys, Rose alloys, Lipovitz alloys, Newton alloys, low-melting glass, and waxes.
Among these, wax is used because it can have a melting point lower than the molding temperature of the prepreg, can be easily processed into a desired shape, has a low density, and can reduce the weight of the molding precursor. is preferred.

Natural wax such as paraffin wax and synthetic wax such as Fischer-Tropsch wax and polyethylene wax can be appropriately selected and used as the wax. As the wax, one type may be used alone, or two or more types may be used in combination. As the wax, it is preferable to use a lost-wax casting wax that melts at a relatively low temperature. The use of the lost wax casting wax tends to facilitate the removal of the wax after molding of the fiber-reinforced plastic molded article of the present invention.
The melting point (Tm) of these waxes preferably satisfies the relation of Tf-60≦Tm≦Tf with respect to the molding temperature (Tf) of the prepreg. If the melting point Tm is within the above range, it is possible to suppress the occurrence of molding defects and obtain a fiber-reinforced plastic molded article excellent in appearance. By setting the melting point Tm to preferably Tf-60 or higher, more preferably Tf-50 or higher, and even more preferably Tf-40 or higher, the wax is less likely to soften before hot compression molding, and the shape of the core is stabilized. Also, it is possible to suppress deterioration of the appearance of the fiber-reinforced plastic molded article caused by wrinkles in the prepreg before heat compression molding. By setting the melting point Tm to preferably Tf or less, more preferably Tf-10 or less, and even more preferably Tf-20 or less, the wax melts during hot compression molding, the internal pressure of the core tends to increase, and molding defects are suppressed. Cheap.

The volume of the core containing the thermoplastic solid material used in the present invention is preferably equal to or less than the volume of the hollow portion of the hollow shape after molding. When the molding precursor of the fiber-reinforced plastic molding is heat-compressed, the volume of the thermoplastic solid expands due to the temperature rise, and the internal pressure of the core increases. If there is a possibility that the volume expansion of the thermoplastic solid is large and the internal pressure of the core becomes excessive and molding defects may occur, the volume of the thermoplastic solid is preliminarily adjusted to the hollow shape of the hollow shape after molding. The internal pressure of the core is controlled by making it smaller than the volume of the core. The volume of the thermoplastic solid can be appropriately changed depending on the selection of various materials for the thermoplastic solid and the conditions of the molding temperature.

As a method for reducing the volume of the thermoplastic solid, there is a method of making the thermoplastic solid into a granular resin or a powdery resin, and the thermoplastic solid is subjected to at least uneven processing, drilling and grooving. A method of applying one, forming voids inside a thermoplastic solid, is preferred. These methods are appropriately selected according to the target inner pressure of the core. In addition, even if the volume of the thermoplastic solid is the same as the volume of the hollow part of the hollow shape after molding, by applying a method for reducing the volume of the thermoplastic solid, the internal pressure of the core can be reduced. It is possible to make the rising behavior of .DELTA.

An example of the method for producing a fiber-reinforced plastic molded article of the present invention will be described in detail below with reference to the drawings. It should be noted that the dimensions and the like in each drawing are examples, and the present invention is not necessarily limited to those shown in each drawing, and can be implemented with appropriate modifications within the scope of not changing the gist of the invention.

The method for producing a fiber-reinforced plastic molded article according to the present embodiment includes the following molding steps, and further includes a step of discharging thermoplastic solids such as wax described below.
In the method for producing a fiber-reinforced plastic molded article of the present embodiment, the case of using wax as the thermoplastic solid is exemplified. Further, in the method for producing a fiber-reinforced plastic molded article of the present embodiment, a case where the core is made of wax and a barrier layer surrounding the wax is exemplified.
Molding step: As shown in FIG. 1, a molding precursor 5 having a prepreg 4 arranged around a core 3 containing a wax 1 in a barrier layer 2 is formed by a molding die 10 to at least partly remove the wax 1. Hot compression molding is performed while melting.
Step of discharging thermoplastic solids: As shown in FIGS. 2A to 2C, the wax 1 is discharged from the fiber-reinforced plastic molding 6 obtained after the molding step.
In this example, a rectangular tube-shaped fiber-reinforced plastic molding 6 used for pipes and the like is manufactured.

(Molding process)
FIG. 1 is a cross-sectional view taken in a direction perpendicular to the length direction of the mold 10 for molding.
In the molding process of this embodiment, first, as shown in FIG. Heat compression molding. As a result, the prepreg 4 is cured to obtain a fiber-reinforced plastic molding 6 containing the core 3 as shown in FIG. 2A. When arranging the prepreg 4 around the core 3, the prepreg 4 is arranged along the outer surface of the core 3 (along with the outer shape of the core 3).

A method for forming the core 3 is not particularly limited. As a method of forming the core 3, for example, the wax 1, which has been molded into a predetermined shape in advance with a mold, is covered with a film that forms the barrier layer 2, and the ends of the film are adhered or heat-sealed. A method of forming the barrier layer 2 by pressing and sealing the wax 1 in the barrier layer 2 to form the core 3 can be exemplified. In addition, the wax 1 preliminarily formed into a predetermined shape is placed in the shrink tube, and the shrink tube is heat-shrunk to adhere to the wax 1, and both ends of the shrink tube are heat-sealed to seal the barrier. A method of forming the layer 2 to form the core 3 may be employed. The method using a shrink tube is advantageous in that the barrier layer 2 easily conforms to the shape of the wax 1 and can be easily sealed. Alternatively, the core 3 may be formed by melting and filling wax in the barrier layer 2 obtained by blow molding into a predetermined shape, and sealing the opening of the barrier layer 2 by heat-sealing.
Alternatively, the liquid rubber to be the barrier layer 2 may be applied to the entire circumference of the wax 1 , the liquid rubber may be dried to form the barrier layer 2 , and the core 3 may be formed. As another method, liquid rubber is applied to the entire circumference of the wax 1, and then a nonwoven fabric serving as a fiber reinforcing material is attached to the surface to which the liquid rubber is applied. A method of forming the barrier layer 2 made of and forming the core 3 may be employed.

The prepreg 4 is a molding composite material containing fibers and thermosetting resin. As the prepreg 4, for example, a UD (uni-directional) material in which fibers are aligned in one direction, a cloth material in which fibers are woven, a nonwoven fabric made of fibers, a sheet molding compound (SMC) in which fibers are chopped, and other fiber reinforcing materials. , a sheet-like prepreg impregnated with an uncured thermosetting resin.
The fibers are not particularly limited, and examples thereof include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, metal fibers and the like. Among these, carbon fiber is preferable from the viewpoint that performance required for the fiber-reinforced plastic molded body 6, such as shape stability and mechanical strength, can be easily exhibited. As the fibers, one type may be used alone, or two or more types may be used in combination.

Thermosetting resins are not particularly limited, and examples thereof include epoxy resins, urea resins, vinyl ester resins, unsaturated polyesters, polyurethanes, and phenol resins. As the thermosetting resin, one type may be used alone, or two or more types may be used in combination.

In addition, the content of the thermosetting resin (hereinafter referred to as "resin content") with respect to the total mass of the prepreg 4 is preferably 15 to 50% by mass, more preferably 20 to 45% by mass, and further 25 to 40% by mass. preferable. If the resin content is 15% by mass or more, it is possible to sufficiently secure the adhesiveness between the fibers and the thermosetting resin. On the other hand, if the resin content is 50% by mass or less, the flame retardancy of the fiber-reinforced plastic molding 6 is further improved.

The prepreg 4 may contain optional components (additives) other than the fibers and the thermosetting resin, if necessary. Examples of such optional components include flame retardants (e.g., phosphorus-containing epoxy resins, red phosphorus, phosphazene compounds, phosphates, phosphate esters, etc.), silicone oils, wetting and dispersing agents, antifoaming agents, Defoaming agents, natural waxes, synthetic waxes, metal salts of straight-chain fatty acids, acid amides, esters, mold release agents such as paraffins, crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc , powders such as barium sulfate, inorganic fillers such as glass fibers and carbon fibers, coloring agents such as carbon black and red iron oxide, and silane coupling agents.
Also, the content of the optional component with respect to the total mass of the prepreg 4 is preferably 0 to 25% by mass, more preferably 1 to 20% by mass, and even more preferably 1 to 15% by mass.

The form of the molded precursor 5 is not particularly limited, and for example, a form in which two sheet-like prepregs 4 are arranged so as to wrap the entire core 3 can be mentioned.

A molding die 10 of this example is for manufacturing a rectangular tube-shaped fiber-reinforced plastic molding 6 and includes a lower die 12 and an upper die 14 . A concave portion 12 a is formed on the upper surface side of the lower mold 12 . A convex portion 14 a that fits into the concave portion 12 a of the lower mold 12 is formed on the lower surface side of the upper mold 14 . In the molding die 10, the lower mold 12 and the upper mold 14 are brought close to each other and clamped to form a cavity having a shape complementary to the shape of the desired fiber-reinforced plastic molded body 6 (recess 12a and protrusion 12a). A space formed by the portion 14a) is formed.

It is sufficient for the molding die 10 to have an opening/closing mechanism, and a high-pressure press may not be used. That is, at the stage where the lower mold 12 and the upper mold 14 are brought close to each other and the molds are clamped, the pressure applied to the molding precursor 5 does not necessarily have to be sufficiently high. Even if the pressure applied to the molded precursor 5 at the stage of mold clamping is insufficient, the wax 1 melts during heat compression molding as described later, and the internal pressure of the core 3 increases, so that the molded precursor 5 is sufficiently pressed. pressure is applied. Therefore, the occurrence of molding defects can be suppressed, and a fiber-reinforced plastic molded article 6 with high dimensional accuracy can be obtained.

Examples of the method of heat-compression molding the molding precursor 5 with the molding die 10 include the following methods. After the prepreg 4 is arranged around the core 3 to form the molded precursor 5, the molded precursor 5 is preliminarily shaped at room temperature into a shape substantially the same as the cavity shape of the mold 10 for molding. Reform. Next, the molding precursor 5 (preform) is placed in the recess 12a of the lower mold 12 of the preheated molding die 10, and the molding die 10 is clamped to perform hot compression molding, thereby forming the prepreg 4. Harden.

In addition, the hot compression molding method is not limited to the above method. For example, the following RTM (resin transfer molding) method may be employed. Specifically, instead of the prepreg, a fiber reinforcing material (fabric) that is not impregnated with a thermosetting resin is arranged around the core 3, and the core 3 and the fiber reinforcement are placed in the recess 12a of the lower mold 12. The material is placed and the molding die 10 is clamped. Next, an uncured thermosetting resin is injected into the molding die 10 to impregnate the fiber reinforcing material with the thermosetting resin.

In the present invention, it is preferable to use a thermoplastic solid that melts below the molding temperature for the core. In this way, the molding precursor can be heat-compression-molded while at least part of the thermoplastic solid contained in the barrier layer is melted in the core.
In this example, the heat of the molding die 10 is transmitted to the prepreg 4 and also to the wax 1 through the barrier layer 2, so that at least part of the wax 1 is melted.

Since the wax 1 expands when heated and further expands greatly when melted, the internal pressure of the core 3 increases during hot compression molding. Further, since the wax 1 melted in the barrier layer 2 flows, the internal pressure of the entire core 3 becomes uniform. Since the inner pressure of the core 3 becomes uniform, pressure is uniformly applied to the prepreg 4 also in directions other than the vertical direction in which the lower mold 12 and the upper mold 14 of the molding die 10 are closed in the heat compression molding.

Since the wax 1 is housed in the barrier layer 2 of the core 3 , leakage of the melted wax 1 to the outside of the prepreg 4 is suppressed. In addition, since the barrier layer 2 is flexible and can be stretched, it can allow deformation of the outer shape of the core 3 due to the flow of the wax 1 . Therefore, when the expansion of the wax 1 increases the internal pressure, the core 3 expands. As a result, even if a gap is formed between the core 3 and the prepreg 4 arranged around it, the gap is filled by the deformation of the core 3 . Moreover, even if a gap is formed between the molding surface and the prepreg 4 at the corners in the molding die 10, the prepreg 4 is pressed against the molding surface as the core 3 deforms (expands). fills the voids. In this way, the prepreg 4 is tightly and without gap between the core 3 and the molding surface of the molding die 10, so that the occurrence of molding defects is suppressed. As a result, bending of the standing surface, wrinkles, voids, etc. are particularly difficult to occur, and a fiber-reinforced plastic molded body 6 having a predetermined thickness and high dimensional accuracy can be obtained. Even when manufacturing a fiber-reinforced plastic molded body 6 having right-angled corners, the corners of the molding die 10 are sufficiently filled with the prepreg 4, and the corners are raised along the molding surface of the molding die 10. Accurately square.

During hot compression molding, if the internal pressure of the core 3 caused by the expansion of the wax 1 becomes too much larger than the clamping pressure of the molding die 10, the molding die 10 will open. Further, if the internal pressure of the core 3 becomes excessive, it may cause breakage of the barrier layer 2 and opening of the fibers of the prepreg 4, leading to poor molding. As a countermeasure, the volume of the wax 1 is previously made smaller than the volume of the hollow portion of the hollow shape after molding, and the internal pressure of the core 3 due to volume expansion is controlled. It is preferable that the volume of the wax 1, which is previously reduced, is equal to the volume of the wax 1 expanded during molding and the volume of the hollow portion.

FIG. 3 shows an example in which a rectangular parallelepiped wax 1 is perforated as one method of reducing the volume of the wax 1 . Here, the wax 1 is provided with two through holes 1a penetrating in the height direction (vertical direction to close the lower mold 12 and the upper mold 14), and the vertical direction of the wax 1 (upper surface 1b and lower surface 1c of the wax 1). The figure shows the case where they are formed at equal intervals in the long side direction). The through hole 1a has openings on the upper surface 1b and the lower surface 1c of the wax 1. As shown in FIG. The openings of the through holes 1a are arranged at equal intervals on the upper surface 1b and the lower surface 1c of the wax 1. As shown in FIG. In this example, the wax 1 melted from the surface layer due to heating during molding flows into the through holes 1a, and the volume of the wax 1 inside the core 3 is reduced compared to when the wax 1 is solid. An increase in the internal pressure of the child 3 is suppressed. Further, by appropriately adjusting the diameter, number, depth, etc. of the through-holes 1a, it is possible to control the rise behavior of the internal pressure of the core 3. FIG.

FIG. 4 shows an example in which the surface layer of the rectangular parallelepiped wax 1 is grooved as one method of reducing the volume of the wax 1 . Here, in the surface layer of the wax 1 (the layer on the upper surface 1b side), two grooves 1d extending along the entire length of the wax 1 in the longitudinal direction (long side direction of the upper surface 1b and the lower surface 1c of the wax 1) are formed. The figure shows the case where they are formed at regular intervals in the horizontal direction (the short side direction of the upper surface 1b and the lower surface 1c of the wax 1). The groove 1d is recessed from the upper surface 1b toward the lower surface 1c in a cross section perpendicular to the longitudinal direction of the wax 1. As shown in FIG. In this example, the wax 1 melted from the surface layer due to heating during molding flows into the groove 1d, and the volume of the wax 1 inside the core 3 is reduced compared to when the wax 1 is solid. An initial increase in internal pressure of the core 3 can be suppressed. By appropriately adjusting the shape, size (width, depth), number, etc. of the grooves 1d, it is possible to control the internal pressure rise behavior of the core 3. FIG.

FIG. 5 shows an example in which a space 1 e is formed inside a rectangular parallelepiped wax 1 as one method of reducing the volume of the wax 1 . Here, a case where a space 1e is formed inside the wax 1 is shown. The space 1e has a rectangular parallelepiped shape. In this example, when the wax 1 melts due to heating during molding, the volume of the wax 1 inside the core 3 decreases compared to when the wax 1 is solid, so the internal pressure of the core 3 increases. rise can be suppressed. By appropriately adjusting the position, shape, size, number, etc. of the spaces 1e, it is possible to control the internal pressure rise behavior of the core 3 .

In hot compression molding, only a part of the wax 1 may be melted, or the whole may be melted. The wax 1 is melted by heat conduction from the mold 10 for molding. Since the wax 1 has a low thermal conductivity, only the surface layer of the wax 1 melts particularly when the core 3 has a large volume and the molding time is short.
In order to improve the molding cycle in hot compression molding, it is necessary to heat the prepreg 4 efficiently. It takes time to raise the temperature of the prepreg 4 so that heat is consumed to melt the wax 1 of the core 3 . From the viewpoint of improving the molding cycle, it is preferable to melt only the surface layer of the wax 1 in the hot compression molding. Further, when only the surface layer of the wax 1 is melted, even if the melted wax 1 leaks out from the barrier layer 2, the melted amount is small. Therefore, since the wax 1 leaking out of the molding die 10 is rapidly cooled and solidified, the adverse effects caused by the leakage of the wax 1 can be minimized.

(Step of discharging thermoplastic solids)
The wax 1 is discharged from the fiber-reinforced plastic molding 6 obtained after the molding process. As a method for discharging the wax 1, the wax 1 is discharged to the outside of the fiber-reinforced plastic molded body 6 at a temperature equal to or lower than the thermal deformation temperature of the fiber-reinforced plastic molded body 6 and at a temperature equal to or higher than the melting point of the wax 1 after hot compression molding. method is preferred. Specifically, it is preferable to set the temperature to the melting point of the wax 1 plus 20 degrees or more because the discharge is promoted.
Specifically, for example, as shown in FIG. 2B, after the discharge holes 7 are formed in the fiber-reinforced plastic molded body 6, the fiber-reinforced plastic molded body 6 is heated at a temperature not higher than the heat deformation temperature and not less than the melting point of the wax 1. heat to Thereby, as shown in FIG. 2C, the melted wax 1 is discharged from the discharge hole 7 to the outside of the fiber-reinforced plastic molding 6 . By melting the wax 1, the wax 1 can be discharged even if the diameter of the discharge hole 7 is small.

A method for forming the discharge holes 7 in the fiber-reinforced plastic molded body 6 is not particularly limited, and examples thereof include drilling, hole sawing, and the like.
A method for heating the core 3 and the fiber-reinforced plastic molding 6 is not particularly limited, and examples thereof include oven heating and infrared heating.

In the case of the long fiber-reinforced plastic molded body 6 as in this example, the fiber-reinforced plastic molded body 6 is further provided with an air blow hole in addition to the discharge hole 7 to the extent that the quality of the product is not adversely affected. The discharge of the wax 1 from the discharge hole 7 may be accelerated by blowing air through the nozzle. Further, by arranging a string in advance in the core 3 and pulling out the string when the wax 1 is discharged, the discharge of the wax 1 can be promoted.
The barrier layer 2 in the fiber-reinforced plastic molded body 6 may be pulled out as necessary, or left as it is in the fiber-reinforced plastic molded body 6 .

In the method for producing a fiber-reinforced plastic molded article of the present invention described above, hot compression molding is performed using a core containing a thermoplastic solid material such as wax. By melting at least a part of the thermoplastic solid matter during compression molding, the internal pressure of the core can be sufficiently increased. It is possible to suppress the progress of hardening of the prepreg in a state where voids exist in the prepreg. In addition, the internal pressure of the core can be controlled by setting the volume of the core containing the thermoplastic solid to be equal to or less than the volume of the hollow portion of the hollow shape after molding. Before hot compression molding, the thermoplastic solid is hard to soften and the shape of the core is stable, so wrinkles are less likely to occur in the prepreg before hot compression molding, and wrinkles are suppressed in fiber-reinforced plastic moldings. can. As described above, it is possible to suppress the occurrence of molding defects even in a large-sized fiber-reinforced plastic molded article, and to efficiently and economically produce a hollow-shaped fiber-reinforced plastic molded article having an excellent appearance.

The method for producing the fiber-reinforced plastic molded article of the present invention is not limited to the method described above. For example, the method described above is a method for manufacturing a fiber-reinforced plastic molded article having a rectangular cylindrical shape, but it may be a method for manufacturing a fiber-reinforced plastic molded article having a U-shaped cross section.
In this case, a molding precursor is formed in which a part of the core is exposed and the other part is covered with prepreg, and heat compression molding is performed in a state where a part of the core is in contact with the molding surface of the molding die. I do. Further, in discharging thermoplastic solids such as wax, it is not necessary to provide a discharge hole in the fiber-reinforced plastic molding.

EXAMPLES The present invention will be further described with reference to examples below, but the present invention is not limited by the following description.

[Internal pressure of core, surface temperature and center temperature of wax]
The inner pressure of the core in hot compression molding was measured by attaching a piezoelectric pressure sensor so that the surface position was the same as the end surface of the lower mold. Also, the surface temperature and center temperature of the wax in the core were measured with a thermocouple.

[ Reference example 1]
As the wax 1, a synthetic wax (product name “File-A-Wax Green”, manufactured by Freeman Manufacturing & Supply Company, melting point Tm: 117°C, density: 0.9 g/cm3) is used, and this wax 1 is a polyolefin shrink. The shrink tube is placed in a tube (thickness: 15 μm; melting point Tb: 145° C.), and the shrink tube is heat-shrunk to adhere to the wax 1, and both ends of the shrink tube are heat-sealed to form a shrink tube. A core 3 was produced by forming a barrier layer 2 consisting of
The shape of the wax 1 was a rectangular parallelepiped with a length of 100 mm, a width of 50 mm and a height of 24 mm. 18 through-holes 1a each having a diameter of 6 mm were formed in the wax 1 in the same direction as in FIG. As a result, the weight of the wax 1 was reduced by about 10% compared to before the drilling process.
Next, as the prepreg 4, a prepreg (manufactured by Mitsubishi Rayon Co., Ltd., product name “TR3110 360 GMP”; resin content: 40% by mass) in which a fiber reinforcing material made of carbon fiber is impregnated with an epoxy resin is used. After being arranged so as to cover the entire circumference of the element 3, it was preliminarily shaped at room temperature to have substantially the same shape as the cavity shape of the molding die 10 to obtain a molding precursor 5 (preform).
Next, the molding precursor 5 was placed in the concave portion 12a of the lower mold 12 of the molding die 10, and the molding die 10 was clamped. Heat compression molding was carried out at an average molding temperature of 140° C. from mold closing to mold opening for a molding time of 5 minutes to produce a fiber-reinforced plastic molded body 6 enclosing the core 3 .
Next, a discharge hole 7 (diameter: 10 mm) for discharging wax was formed in the fiber-reinforced plastic molding 6 by drilling.
Next, the core 3 and the fiber-reinforced plastic molding 6 were heated to 130° C. by heating in an oven to melt the wax 1 and discharge it through the discharge hole 7 to obtain a fiber-reinforced plastic molding 6 in the shape of a rectangular tube.

[ Reference example 2]
The shape of the wax 1 is a rectangular parallelepiped having a length of 100 mm, a width of 50 mm and a height of 24 mm. It was formed. As a result, a fiber-reinforced plastic molded article 6 having a rectangular tubular shape was obtained in the same manner as in Reference Example 1, except that the weight of the wax 1 was reduced by about 10% compared to before the grooving.

[ Reference example 3]
Wax 1 was formed as follows. In a rectangular parallelepiped wax of 50 mm long, 50 mm wide and 24 mm high, a hole of 30 mm long, 20 mm wide and 10 mm high is formed from the side toward the center and parallel to the upper and lower surfaces of the rectangular parallelepiped. Two pieces of hollow wax having a weight reduced by about 10% compared to before processing were prepared. Next, the surfaces of the hollow wax having the holes formed thereon (the surfaces having the openings of the holes) were welded together to form a wax 1 having a space 1e inside as shown in FIG. A rectangular tubular fiber-reinforced plastic molding 6 was obtained in the same manner as in Reference Example 1 except that this wax 1 was used.

[ Reference Example 4]
In the same manner as in Reference Example 1, except that the number of through-holes 1a formed in the wax 1 was set to 9 and the weight of the wax 1 was reduced by about 5% compared to before the hole-making process, a fiber-reinforced rectangular tubular shape was obtained. A plastic molding 6 was obtained.

[ Reference Example 5 ]
A fiber-reinforced plastic molding 6 in the form of a square tube was obtained in the same manner as in Reference Example 1, except that the shape of the wax 1 was a solid rectangular parallelepiped with a length of 100 mm, a width of 50 mm, and a height of 24 mm.

FIG. 6 shows the change behavior of the internal pressure of the core over time during a molding time of 5 minutes from mold closing to mold opening. The vertical axis indicates the value obtained by dividing the measured pressure by the initial pressure, with the pressure when the mold is closed at the start of molding as the initial pressure. When each example and comparative example were compared, all of examples 1 to 4 showed a gentle upward curve compared to comparative example 1. In addition, Example 4 exhibited a rise behavior between Example 1 and Comparative Example 1, and was able to control the rise behavior of the internal pressure of the core.

1 wax (thermoplastic solid)
2 barrier layer 3 core 4 prepreg 5 molding precursor 6 fiber-reinforced plastic molding 7 discharge hole 10 molding die 12 lower die 14 upper die

Claims (5)

A method for producing a fiber-reinforced plastic molded article having a hollow portion,
A prepreg containing a thermosetting resin and fibers is arranged around a core containing a wax portion made of wax, and heat-compressed using a molding die, and then the wax portion is melted and discharged. A method for producing a hollow-shaped fiber-reinforced plastic molded article, comprising forming a hollow portion, wherein only the surface layer of the wax portion melts in the heat compression molding. 2. The manufacturing method according to claim 1, wherein the volume of wax contained in said wax portion is smaller than the volume of said hollow portion before said heat compression molding. 3. The manufacturing method according to claim 1, wherein said core comprises said wax portion and a barrier layer surrounding said wax portion. 4. The manufacturing method according to any one of claims 1 to 3, wherein the wax portion is subjected to at least one of uneven processing, boring processing and groove processing. The manufacturing method according to any one of claims 1 to 4, wherein voids are present inside the wax portion.

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