Method for molding a hollow molded article made of a fiber-reinforced resin

Abstract

To provide a molding method capable of simply and easily molding a hollow molded article made of a fiber-reinforced resin base material excellent in quality such as strength and homogeneity and accuracy at low cost without using a large-sized apparatus.SOLUTION: A molding method for a fiber-reinforced resin hollow molded article comprises the steps of: a) placing a fiber-reinforced resin base material on an inner surface of a molding die; b) placing a film-like bag member containing a thermally expandable microcapsule in a core space of the molding die, and filling an adjusting powder for adjusting a pressure during heating around the thermally expandable microcapsule; c) heating an interior of the molding die to a predetermined temperature to expand the thermally expandable microcapsule in the film-like bag member, and pressurizing the fiber-reinforced resin base material from the inside to form a resulting material into a shape of the molding die; and d) removing the film-like bag member and the adjusting powder from the inside of the fiber-reinforced resin base material.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a molding method for molding a molded article made of a fiber-reinforced resin. Specifically, it relates to a molding method for molding a hollow molded article made of a fiber-reinforced resin without using devices such as a hot press or an autoclave.

Background Art

[0002] As molding methods for molded articles made of fiber-reinforced resins, the following methods are known. i) A method in which a fiber-reinforced resin base material impregnated with a liquid thermosetting resin composition is placed in a mold, and then heated and pressurized to cure the resin, or a thermoplastic resin is melted and impregnated into the reinforcing fibers, and then the fiber-reinforced resin base material is placed in a mold and then heated and pressurized to be molded. ii) After impregnating a thermosetting resin composition into reinforcing fibers, the composition is semi-cured, or after melting a thermoplastic resin and impregnating it into reinforcing fibers, it is cooled and solidified into a sheet-like fiber-reinforced resin base material, so-called prepreg sheet or stampable sheet, and then heated and pressurized to be molded.

[0003] However, in those molding methods, in the heating and pressurizing step, heating and pressurizing devices such as a hot press and an autoclave are required. When manufacturing a large molded article, large-scale equipment is required, and a huge equipment investment is required.

[0004] Therefore, as a method capable of molding a large molded article made of a fiber-reinforced resin without a huge equipment investment, a prepreg sheet is laminated on the inner surface of an open mold, the whole is covered with a heat-resistant bagging material, and then the air between the bagging material and the mold inner surface is discharged to a vacuum state, and the prepreg sheet is heated and pressurized while being adhered to the inner surface of the open mold to be molded. However, in such a molding method, the pressure for adhering the prepreg sheet to the mold is due to atmospheric pressure, so the maximum is about 0.1 MPa, and there is a limit to obtaining a molded article with excellent accuracy and quality.

[0005] In addition, in Patent Document 1, when manufacturing a composite molded article having a surface layer portion formed into a predetermined shape by a fiber-reinforced resin composite material and a porous core, reinforcing fibers are arranged near the inner surface of the mold, and a mixture of thermally expandable particles such as thermally expandable microcapsules and a thermally fusible matrix resin is present in the core portion inside thereof. Then, a manufacturing method has been proposed in which the mold is heated to melt the matrix resin and form the surface layer portion while causing the thermally expandable particles to expand and foam. However, in such a manufacturing method, since it is necessary to impregnate the reinforcing fibers with the matrix resin melted by heating by the expansion force of the thermally expandable particles, it is difficult to set the heating conditions. Moreover, it is necessary to adopt a complicated configuration such as providing a separation layer made of a porous material (that is, a material having the property of allowing the melted matrix resin to pass through but not allowing the particles after the expansion of the thermally expandable particles to pass through).

[0006] Therefore, the applicant has proposed a method for manufacturing a molded article made of a fiber-reinforced resin using thermally expandable microcapsules that can obtain a molded article excellent in accuracy and quality by a simple operation without using a large-scale device (Patent Document 2). In such a manufacturing method, a fiber-reinforced resin base material in which a matrix resin is contained in reinforcing fibers is arranged on the inner surface of the lower mold, and a fluid powder mixture composed of thermally expandable microcapsules and other powders is filled in the core space portion of the mold on which the fiber-reinforced resin base material is arranged. The lower mold and the upper mold are sealed, and then the inside of the mold is heated to a predetermined temperature to expand the thermally expandable capsules, and the fiber-reinforced resin base material is pressed against the inner surface of the lower mold to manufacture a hollow molded article.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, although the method for manufacturing a fiber-reinforced resin hollow molded article according to Patent Document 2 can obtain a hollow molded article excellent in quality and accuracy without using a large-scale apparatus, since the heated and foamed (expanded) thermally expandable microcapsules are integrated with other powders and solidified, in the molding of a hollow molded article with a small (narrow) opening, it was difficult to take out such solidified powder mixture (that is, the mixture of expanded thermally expandable microcapsules and powder).

[0009] An object of the present invention is to provide a molding method capable of simply and easily molding a hollow molded article made of a fiber-reinforced resin base material (containing a matrix resin) excellent in quality such as strength and homogeneity and accuracy at low cost without using a large-scale apparatus.

Means for Solving the Problems

[0010] In order to solve the above problems, the invention described in claim 1 is a molding method for molding a hollow molded article made of a fiber-reinforced resin base material in which reinforcing fibers and a matrix resin are mixed, wherein the fiber-reinforced resin base material is placed in a molding die Disposed on the inner surface and at the same time, A layer made of a release agent is formed inside a fiber-reinforced resin base material disposed on the inner surface of the molding die, inside the molding die (that is, inside the fiber-reinforced resin base material arranged on the inner surface of the molding die, hereinafter also referred to as the core space portion), a film-like bag member containing thermally expandable microcapsules is arranged, and around the thermally expandable microcapsules Of the layer made of the release agent formed inside after filling with adjustment powder for pressure adjustment during heating, the inside of the molding die is heated to a temperature equal to or higher than the thermal expansion start temperature and equal to or lower than the maximum expansion temperature of the thermally expandable microcapsules to expand the thermally expandable microcapsules in the film-like bag member, and the fiber-reinforced resin base material is molded into the shape of the molding die by pressurizing from the inside, and then, the film-like bag member and the adjustment powder are removed from the inside of the fiber-reinforced resin base material. A film-like bag member enclosing

[0011] ​The invention according to claim 2 is the invention according to claim 1, wherein the volume ratio of the adjusting powder filled into the forming mold is 50% to 100% of the volume obtained by subtracting the volume of the film-like bag member containing the thermally expandable microcapsules from the volume inside the forming mold.

[0012] The invention according to claim 3 is the invention according to claim 1 or 2, wherein the volume ratio of the film-like bag member containing the thermally expandable microcapsules to the adjusting powder is 99:1 to 50:50, and the volume of the film-like bag member containing the thermally expandable microcapsules and the adjusting powder And is 40% to 100% of the volume inside the forming mold.

[0013] The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the adjusting powder is composed of an organic powder, an inorganic powder, chopped fiber, or a mixture thereof.

Effect of the Invention

[0014] According to the molding method of the present invention, during heat molding, the pressure inside the fiber-reinforced resin base material can be increased by the thermally expandable microcapsules and the adjusting powder, and the fiber-reinforced resin base material can be strongly pressed against the inner surface of the molding mold. Therefore, it is possible to manufacture a highly accurate molded product (hollow molded product) that accurately traces the shape of the inner surface of the molding mold. Moreover, regardless of the shape of the hollow molded product (molded product made of a fiber-reinforced resin base material), the expanded microcapsules and the adjusting powder in a separated state can be separately removed from the inside of the hollow molded product after molding, so that the molding operation becomes extremely easy. In addition, according to the molding method of the present invention, the adjusting powder for adjusting the internal pressure during heating can be repeatedly reused, so that it can be implemented at low cost and the environmental load can be kept low.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0016] The method for molding a fiber-reinforced resin hollow molded article according to the present invention comprises disposing a fiber-reinforced resin base material on the inner surface of a molding die, and filling a film-like bag member containing thermally expandable microcapsules and adjustment powder into the interior (i.e., the core space portion) of the fiber-reinforced resin base material. After sealing the molding die, the interior of the molding die is heated to a predetermined temperature (equal to or higher than the thermal expansion start temperature and equal to or lower than the maximum expansion temperature) of the thermally expandable microcapsules to expand the thermally expandable microcapsules and press the fiber-reinforced resin base material against the inner surface of the molding die (pressing) to mold a hollow molded article made of fiber-reinforced resin. That is, the method for molding a fiber-reinforced resin hollow molded article according to the present invention includes the following steps a to d. a) Step of disposing a fiber-reinforced resin base material on the inner surface of a molding die b) A step of disposing a film-shaped bag member encapsulating thermally expandable microcapsules in a core space portion of a molding die, and filling an adjusting powder for pressure adjustment during heating around the thermally expandable microcapsules. c) A step of heating the inside of the molding die to a predetermined temperature to expand the thermally expandable microcapsules in the film-shaped bag member, and molding the fiber-reinforced resin base material into the shape of the molding die by pressurizing from the inside. d) A step of removing the film-shaped bag member and the adjusting powder from inside the fiber-reinforced resin base material.

[0017] In the molding method according to the present invention, it is preferable to form a layer made of a release agent inside the fiber-reinforced resin base material disposed on the inner surface of the molding die before molding. Examples of the method for forming the release agent layer include a method of attaching a release film made of a fluororesin film or the like to the inner surface of the fiber-reinforced resin base material, and a method of applying a release agent made of a fluororesin or the like to the inner surface of the fiber-reinforced resin base material.

[0018] <Molding Material for Hollow Molded Article Made of Fiber-Reinforced Resin> The thermally expandable microcapsules used in the molding method of the hollow molded article made of fiber-reinforced resin according to the present invention are a powder composed of particles encapsulating a volatile solvent inside a shell made of a thermoplastic resin. That is, a liquid, solid, or gas called a core substance is encapsulated inside a microcapsule which is a minute container. The average particle diameter of such thermally expandable microcapsules is 5 to 300 μm, preferably 5 to 150 μm. As the thermoplastic resin constituting the shell, a polyvinylidene chloride-based resin, an acrylic resin, or an AN (acrylonitrile)-based copolymer resin can be used. As the volatile solvent as the core substance, a low-boiling hydrocarbon or the like can be used. Note that the core substance may be a solid (powder) or a gas in addition to a liquid such as a volatile solvent.

[0019] In addition, as the adjustment powder, organic powder or inorganic powder with an average particle size of 1 to 200 μm, or chopped fibers with a fiber diameter of 1 to 20 μm, a length of 0.5 to 5 mm, preferably 1 to 3 mm, or a mixture thereof can be used. And the adjustment powder needs to have fluidity (be exhibited) without becoming sticky at the molding temperature. If the adjustment powder does not have fluidity, the filling operation will be difficult, and it will be unfavorable because it will hinder the transmission of the expansion force of the thermally expandable microcapsules to the fiber-reinforced resin base material. Note that having fluidity means that the adjustment powder 4 can slide down on an inclined plane of less than 90° and flow.

[0020] When using organic powder as the adjustment powder, as the organic powder, various cereal powders (such as wheat flour, rice flour, soybean flour, etc.), starches (such as potato starch, corn starch, etc.), fish powder, wasabi powder, wood powder, bamboo powder, etc. can be used. As the inorganic powder, powders such as sodium chloride, calcium carbonate, silica, alumina, talc, gypsum, silica sand, glass, etc. can be used, and pulverized powders of thermosetting resin products such as FRP can also be used. Note that although examples of the organic powder include those used for food and feed, etc., they are preferably easy to discard after use and can also be reused.

[0021] On the other hand, the film-shaped bag member is preferably formed of a synthetic resin film, and more preferably formed of a fluorine-based synthetic resin film. Since the molding temperature in the molding method according to the present invention is about 130 ± 10 °C, those having a heat resistance of about 140 °C to 150 °C can be preferably used. Examples of the fluorine-based synthetic resin film having such characteristics include films made of polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), etc.

[0022] In addition, as the release film or release agent for forming a release agent layer inside the fiber-reinforced resin base material disposed on the inner surface of the mold, films or coating agents made of fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF) can be mentioned.

[0023] In the molding method according to the present invention, when the thermally expandable microcapsules are heated, the thermoplastic resin constituting the shell softens, and the enclosed volatile solvent evaporates and gasifies, so that the pressure inside the thermally expandable microcapsules rises, and the volume of the thermally expandable microcapsules becomes 50 times or more. In the molding method according to the present invention, the thermally expandable microcapsules are used to press the fiber-reinforced resin base material against the inner surface of the molding die by the force of expansion due to heating to produce a molded article. The thermally expandable microcapsules used in the present invention start to expand their volume when the temperature rises to a predetermined temperature, and when the temperature is equal to or higher than the predetermined temperature, the thickness of the shell becomes thinner, and the gas of the volatile solvent permeates and diffuses to the outside of the microcapsules and has the property of shrinking. In the present invention, the temperature at which the thermally expandable microcapsules start to expand is referred to as the thermal expansion start temperature, and the temperature at which the volume of the thermally expandable microcapsules becomes maximum is referred to as the maximum expansion temperature.

[0024] In the molding method according to the present invention, the thermally expandable microcapsules having the above-described characteristics are filled in the interior (i.e., the core space portion) of the fiber-reinforced resin base material disposed on the inner surface of the sealed molding die in an unexpanded (unheated) state, and by heating to a temperature equal to or higher than the thermal expansion start temperature and equal to or lower than the maximum expansion temperature, the pressure inside the sealed space (i.e., the core space portion) can be increased to approximately 0.5 MPa or more. Since the pressure inside the shell of the thermally expandable microcapsules is about 3 MPa at maximum expansion, it is also possible to increase the pressure to that level. In the molding method according to the present invention, the internal pressure inside the sealed space (i.e., the core space portion) is usually 0.1 to 0.6 MPa, but it is also possible to make it 1 MPa or more by increasing the amount of the thermally expandable microcapsules to be filled.

[0025] In the molding method according to the present invention, the pressure generated as the thermally expandable microcapsules expand can be adjusted by the amount of the thermally expandable microcapsules, the filling amount of the adjusting powder filled in the core space portion, and the like. Further, various types of thermally expandable microcapsules are commercially available, and those of the low to medium temperature expansion type with a thermal expansion start temperature of 80 to 110°C and a maximum expansion temperature of 115 to 140°C to those of the medium to high temperature expansion type with a thermal expansion start temperature of 115 to 140°C and a maximum expansion temperature of 170 to 200°C are available. Furthermore, those of the ultra-high temperature expansion type with a thermal expansion start temperature of 180 to 230°C and a maximum expansion temperature of 210 to 275°C are also commercially available. In the molding method according to the present invention, it is necessary to select the type of the thermally expandable microcapsules and select the molding temperature in consideration of the appropriate molding temperature of the fiber-reinforced resin base material and the like.

[0026] On the other hand, as the reinforcing fiber used for the fiber-reinforced resin base material, glass fiber, carbon fiber, aramid fiber, etc. can be preferably used. Also, boron fiber, ceramic fiber, silicon carbide fiber, etc. obtained by processing those fibers may be used. And those fiber bundles obtained by aligning those reinforcing fibers in one direction to form rovings or yarns, or cloths obtained by weaving or knitting the fibers, impregnated with the matrix resin, can be suitably used as the fiber-reinforced resin base material. Furthermore, it is also possible to use a fiber-reinforced resin base material in which chopped fibers obtained by cutting the fibers are mixed with the matrix resin.

[0027] In addition, examples of the matrix resin used for the fiber-reinforced resin base material include various thermosetting resins and thermoplastic resins. When a thermosetting resin is used as the matrix resin, unsaturated polyester resin, epoxy resin, phenolic resin, vinyl ester resin, etc. can be preferably used as the thermosetting resin. The thermosetting resin is usually used as a resin composition added with a curing agent or the like, and is often used as a liquid resin composition. A material obtained by impregnating reinforcing fibers with such a liquid resin composition composed of a thermosetting resin can be used as the fiber-reinforced resin base material. Further, when a material obtained by impregnating reinforcing fibers with such a liquid thermosetting resin composition is used as the fiber-reinforced resin base material, a semi-cured thermosetting resin composition or the like can be used as a prepreg sheet. It is also possible to use other commercially available prepreg sheets.

[0028] On the other hand, when a thermoplastic resin is used as the matrix resin, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacetal (POM), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), etc. can be preferably used as the thermoplastic resin. It is possible to use, as the fiber-reinforced resin base material, a material obtained by impregnating reinforcing fibers with a liquid composition composed of such a thermoplastic resin. In that case, a semi-cured thermoplastic resin composition or the like can be used as a prepreg sheet. For example, it is also possible to use a commercially available stamperable sheet.

[0029] In addition, in the molding method according to the present invention, by using biodegradable fibers or biodegradable resins as the reinforcing fibers, thermoplastic resin, and thermosetting resin used for the fiber-reinforced resin base material, it is also possible to reduce the environmental load when treating the molded product after use as waste.

[0030] <Mold for molding a hollow molded article made of fiber-reinforced resin> In the molding method according to the present invention, various molds such as metal molds and ceramic molds can be preferably used as the molding mold. Further, as the heating means of the molding mold, known means such as an electric heater, a method of heating by providing a conduit for a heat medium, a high-frequency induction heating method, and a radiation heating method can be used. Furthermore, a cooling means such as switching cooling water or cooling oil to a heat medium and passing it through a conduit can be provided in the molding mold, and by using a molding mold provided with a cooling means in addition to the heating means, it is possible to obtain a molded article having a better gloss surface.

[0031] <Method for molding a hollow molded article made of fiber-reinforced resin> Hereinafter, an embodiment of the method for molding a hollow molded article made of fiber-reinforced resin according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a molding mold (metal mold) used for molding, and FIGS. 2 and 3 show a state of molding a hollow molded article made of fiber-reinforced resin using the metal mold. The metal mold M in the present embodiment is composed of an upper mold 5a and a lower mold 5b, has a rectangular parallelepiped cavity with chamfered corners in an R shape, and has an injection port G for a molding material provided on the side of the cavity. The metal mold M can be sealed by screwing a flange Fa formed on the outer periphery of the upper mold 5a and a flange Fb formed on the outer periphery of the lower mold 5b, and screwing a flange Fg of the injection port G and a lid material L.

[0032] When molding a hollow molded article made of fiber-reinforced resin, first, a fiber-reinforced resin base material (such as a prepreg) 1 is disposed in close contact with the inner surfaces of the upper mold 5a and the lower mold 5b. Thereafter, the upper mold 5a and the lower mold 5b are joined, and the metal mold M is assembled by screwing the flange Fa of the upper mold 5a and the flange Fb of the lower mold 5b. Further, a release film 6 (such as one formed in a bag shape) made of a fluororesin film is disposed (stuck) in close contact with the inside (inner surface) of the fiber-reinforced resin base material 1 disposed on each inner surface of the upper mold 5a and the lower mold 5b thus integrated.

[0033] Thereafter, the core space portion 7 (inside the release film 6) of the mold M is filled with the film-like bag member 2 containing the thermally expandable microcapsules 3 and the adjustment powder 4. At this time, the film-like bag member 2 containing the thermally expandable microcapsules 3 is arranged so as to be positioned near the center (near the center in the vertical, front-rear, and left-right directions) of the adjustment powder 4. For example, using a thread (such as a tag or a fishing line) or an adhesive tape, after positioning the film-like bag member 2 containing the thermally expandable microcapsules 3 near the center inside the release film 6 (that is, the core space portion 7), the mold M is arranged with the injection port G on the upper side, and the adjustment powder 4 is filled around the film-like bag member 2. Alternatively, the mold M is arranged with the injection port G on the upper side, and with the film-like bag member 2 containing the thermally expandable microcapsules 3 suspended from above the injection port G, the adjustment powder 4 is filled around the film-like bag member 2. In the molding method according to the present invention, it is preferable to arrange the film-like bag member 2 containing the thermally expandable microcapsules 3 near the center (near the center in the vertical, front-rear, and left-right directions) of the core space portion 7. However, it is not necessary to strictly arrange the film-like bag member 2 at the center of the core space portion 7. As long as the adjustment powder with a thickness of 10 mm or more exists around the arranged film-like bag member 2, there is no particular problem even if the film-like bag member 2 after arrangement is deviated from the center of the core space portion 7.

[0034] FIG. 2 shows a state in which the core space portion 7 of the mold M is filled with the film-like bag member 2 containing the thermally expandable microcapsules 3 and the adjustment powder 4, and the core space portion 7 is in a state of being filled without gaps by the adjustment powder 4 and the film-like bag member 2 (containing the thermally expandable microcapsules 3).

[0035] Then, as shown in Fig. 2, a film-like bag member 2 (containing thermally expandable microcapsules 3) is placed near the center of the core space portion 7 of the mold M, and after filling the surrounding with the adjusting powder 4, the ends of the release film 6 in a bag shape are sealed tightly without gaps using a sealing tape, thereby blocking the inside and outside of the release film 6. After that, a flat donut-shaped rubber packing material 10 is interposed on the flange Fg on the outer periphery of the injection port G of the assembled mold M, and a disc-shaped lid L is screwed on by a fastening member 9 to seal the mold M. Then, in order to closely adhere the fiber-reinforced resin base material 1 to the inner surface of the mold M (upper mold 5a and lower mold 5b) together with the release film 6, the air between the release film 6 and the fiber-reinforced resin base material 1, and between the fiber-reinforced resin base material 1 and the mold M (upper mold 5a and lower mold 5b) is vacuum-sucked from a vacuum suction port (not shown).

[0036] As described above, after filling the core space portion 7 with the film-like bag member 2 (containing thermally expandable microcapsules 3) and the adjusting powder 4, the inside of the mold M is heated at a predetermined temperature (equal to or higher than the thermal expansion start temperature of the thermally expandable microcapsules 3 and equal to or lower than the maximum expansion temperature). By heating the inside of the mold M in a state where the core space portion 7 is filled with the film-like bag member 2 and the adjusting powder 4 in this way, the thermally expandable microcapsules 3 expand, and it becomes possible to increase the pressure inside the core space portion 7 along with the expansion. Specifically, it becomes possible to increase the pressure inside the core space portion 7 to about 0.1 to 0.6 MPa. Therefore, compared with the conventional molding method (that is, a method of discharging the air between the bagging material and the mold inner surface to a vacuum state, closely adhering the prepreg sheet to the inner surface of the open mold, and heating and pressurizing using atmospheric pressure for molding), it becomes possible to apply a pressing force several times to about 10 times greater. And by increasing the pressure inside the core space portion 7 in this way and strongly pressing (pressing) the fiber-reinforced resin base material 1 against the inner surfaces of the upper mold 5a and the lower mold 5b, it becomes possible to obtain a highly accurate molded product (hollow molded product) that exactly follows the shape of the inner surfaces of the upper mold 5a and the lower mold 5b.

[0037] Figure 3 shows the state after heating the inside of the mold M. By heating the inside of the mold M, the thermally expandable microcapsules 3 expand and the film-like bag member 2 expands. As a result, the filled adjustment powder 4 has a high bulk density and is tightly filled in the entire core space portion 7.

[0038] And as described above, after pressing the fiber-reinforced resin base material 1 sufficiently against the inner surfaces of the upper mold 5a and the lower mold 5b, the inside of the mold M is cooled, and the film-like bag member 2 (containing the thermally expandable microcapsules 3) and the adjustment powder 4 are taken out from the inside of the core space portion 7. At this time, since the adjustment powder 4 is not bonded to the fiber-reinforced resin base material 1 by the release film 6 and is also not bonded to the film-like bag member 2, the adjustment powder 4 and the film-like bag member 2 can be taken out separately and very easily from the inside of the core space portion 7.

[0039] In the above-described molding method, the volume ratio of the adjustment powder 4 and the film-like bag member 2 filled in the core space portion 7 is not particularly limited. However, in order to exhibit good thermal conductivity and fluidity in the adjustment powder 4 during heating and obtain a good molded product (a highly accurate molded product that is homogeneous and exactly follows the shape of the inner surface of the mold M), the filling amount (volume ratio) of the adjustment powder 4 in the core space portion 7 is preferably 50% to 100% of the volume obtained by subtracting the volume of the film-like bag member 2 containing the thermally expandable microcapsules 3 from the core space portion 7. Further, the ratio (volume ratio) of the film-like bag member 2 containing the thermally expandable microcapsules 3 to the adjustment powder 4 is such that microcapsules 3: adjustment powder 4 = 99:1 to 50:50, and the volume of the film-like bag member 2 containing the thermally expandable microcapsules 3 and the adjustment powder 4 is preferably 40% to 100% of the volume of the core space portion 7.

Example

[0040] Hereinafter, the molding method according to the present invention will be described in detail by way of examples. However, the molding method according to the present invention is not limited to the embodiments in any way, and can be appropriately changed as necessary without departing from the spirit of the present invention.

[0041] [Example] Using a mold M composed of an upper mold 5a and a lower mold 5b as shown in FIG. 1, a hollow molded article was manufactured using a fiber-reinforced resin substrate, a film-like bag member containing thermally expandable microcapsules, and the following as adjustment powder. In this molding, the ratio (volume ratio) of the filling amount of the film-like bag member 2 containing thermally expandable microcapsules to the filling amount of the adjustment powder was adjusted to 50:50. [Molding Materials] · Fiber-reinforced resin substrate: Carbon fiber-reinforced epoxy resin prepreg impregnated with a 130°C curing type epoxy resin varnish on a carbon fiber cloth · Thermally expandable microcapsules: Expancel (registered trademark) 031-40DU manufactured by Expancel, heat expansion start temperature 80 - 90°C, maximum expansion temperature 125 - 135°C, average particle diameter = 10 - 16μm · Film-like bag member: Fluorine-based synthetic resin film · Adjustment powder: Dried kudzu starch (average particle diameter = about 30μm)

[0042] [Manufacture of Molded Article] The carbon fiber-reinforced epoxy resin prepreg impregnated with the epoxy resin varnish, which is the fiber-reinforced resin substrate 1, was placed in close contact with the inner surfaces of the upper mold 5a and the lower mold 5b of the mold M. Then, the upper mold 5a and the lower mold 5b were joined, and the mold M was assembled by screwing the flange Fa of the upper mold 5a and the flange Fb of the lower mold 5b. Further, a fluorine-based resin film (formed in a bag shape), which is a release film 6, was placed in close contact with the inside of the carbon fiber-reinforced epoxy resin prepreg disposed on each inner surface of the upper mold 5a and the lower mold 5b integrated in this way.

[0043] Thereafter, the core space portion 7 (inside the fluororesin film) of the integrated mold M was filled with the film-like bag member 2 containing thermally expandable microcapsules and starch powder as an adjusting powder. At that time, the film-like bag member 2 was adjusted to be located near the center of the starch powder (near the center in the vertical, horizontal, and lateral directions). Also, the combined volume of the film-like bag member 2 (containing the thermally expandable microcapsules 3) and the starch powder was adjusted to be about 80% of the volume of the core space portion 7.

[0044] After filling the core space portion 7 of the mold M with the film-like bag member 2 and the starch powder as described above, the ends of the bag-shaped fluororesin film as the release film 6 were sealed without gaps using a sealing tape. And in that state, a flat doughnut-shaped rubber packing material 10 was interposed between the flange Fg on the outer periphery of the injection port G of the assembled mold M, and a disc-shaped lid L was screwed on to seal the mold M. Further, in the sealed mold M, the air between the release film 6 and the fiber-reinforced resin base material 1 (carbon fiber-reinforced epoxy resin prepreg), and between the fiber-reinforced resin base material 1 and the mold M (the upper mold 5a and the lower mold 5b) was vacuum-sucked.

[0045] Thereafter, the inside of the mold M was heated at a predetermined temperature. That is, after raising the temperature of the core space portion 7 to 80°C and holding it in that state for 30 minutes, the temperature of the core space portion 7 was raised to 130°C and held in that state for 60 minutes. The internal pressure of the core space portion during that time was 0.3 to 0.5 MPa.

[0046] As described above, after heating the inside of the mold M, the inside of the mold M was sufficiently cooled (naturally cooled), the lid L was removed, and the film-like bag member 2 (containing the expanded thermally expandable microcapsules 3) and the arrowroot powder were removed from the core space portion 7. When removing them, since the inner surface of the carbon fiber reinforced epoxy resin prepreg was covered with the release film 6, the arrowroot powder was not bonded to the carbon fiber reinforced epoxy resin prepreg and was not bonded to the fluorine-based synthetic resin film which is the film-like bag member 2 either. Therefore, the arrowroot powder and the film-like bag member 2 could be easily removed separately from the small-diameter inlet G. After removing the arrowroot powder and the film-like bag member 2 from the core space portion 7 of the mold M in this way, the mold M was disassembled, and the cured carbon fiber reinforced epoxy resin prepreg was removed from the inside of the mold M to obtain a molded product (see Fig. 5). The obtained molded product (hollow molded product) was highly accurate, accurately tracing the shapes of the inner surfaces of the upper mold 5a and the lower mold 5b.

[0047] [Comparative Example] A mixed powder was obtained by mixing the same thermally expandable microcapsules as in the example and the same arrowroot powder as in the example so that the volume ratio was 1:1. Then, a molded product of the comparative example was obtained in the same manner as in the example, except that the above-mentioned mixed powder was filled in the core space portion 7 of the mold M instead of filling the film-like bag member 2 and the arrowroot powder as the adjusting powder 4. When filling the core space portion 7 of the mold M with the mixed powder, the volume of the mixed powder was adjusted to be about 80% of the volume of the core space portion 7 in the same manner as in the example. The obtained molded product (hollow molded product) was highly accurate, accurately tracing the shapes of the inner surfaces of the upper mold 5a and the lower mold 5b. However, since the mixed powder (thermally expandable microcapsules and arrowroot powder) was cured integrally in the core space portion 7, it was difficult to remove.

[0048] <Modification Example of the Method for Molding a Fiber Reinforced Resin Hollow Molded Product> The method for molding a fiber-reinforced resin hollow molded article according to the present invention is not limited to the aspects of each of the above-described embodiments at all. The mold, the film-like bag member, the thermally expandable microcapsules, the material and shape of the adjusting powder, and the configuration such as the molding procedure and molding conditions can be appropriately changed as necessary without departing from the gist of the present invention. For example, the molding method according to the present invention is not limited to being performed in a state where the core space portion is completely filled (or substantially filled) with the adjusting powder and the film-like bag member (containing the thermally expandable microcapsules) as in the above embodiment. As shown in FIG. 6, it can also be changed to be performed in a state where about 30 to 40% of the space is left in the core space portion. Further, the molding method according to the present invention is not limited to using a mold provided with an injection port for the molding material on the side of the cavity as in the above embodiment. As shown in FIG. 7, it may be possible to use a mold or the like provided with an injection port for the molding material above the cavity, and the material and shape of the molding die can be appropriately changed as necessary.

Industrial Applicability

[0049] Since the method for molding a fiber-reinforced resin hollow molded article according to the present invention has the excellent effects as described above, it can be suitably used as a method for easily molding a highly accurate hollow molded article made of fiber-reinforced resin.

Explanation of Signs

[0050] 1 ··· Fiber-reinforced resin base material 2 ··· Film-like bag member 3 ··· Thermally expandable microcapsules 4 ··· Adjusting powder 5a ··· Upper mold 5b ··· Lower mold 6 ··· Release film 7 ··· Core space portion 9 ··· Fastening member 10 ··· Rubber packing material S ··· Fiber-reinforced resin hollow molded article M, M’ ··· Mold (molding die)

Claims

1. A molding method for molding a hollow molded article made of a fiber-reinforced resin base material in which reinforcing fibers and a matrix resin are mixed, wherein the fiber-reinforced resin base material is disposed on the inner surface of a molding die, and a layer made of a release agent is formed inside the fiber-reinforced resin base material disposed on the inner surface of the molding die. A film-like bag member containing thermally expandable microcapsules is disposed inside the molding die, and after filling an adjustment powder for pressure adjustment during heating around the film-like bag member containing the thermally expandable microcapsules, the inside of the molding die is heated to a temperature equal to or higher than the thermal expansion start temperature and equal to or lower than the maximum expansion temperature of the thermally expandable microcapsules to expand the thermally expandable microcapsules, and the fiber-reinforced resin base material is pressurized from the inside to be molded into the shape of the molding die, and then, the film-like bag member and the adjustment powder are removed from inside the fiber-reinforced resin base material. A method for molding a hollow molded article made of a fiber-reinforced resin, characterized by this.

2. The volume ratio of the adjustment powder filled into the inside of the molding die is 50% to 100% of the volume obtained by subtracting the volume of the film-like bag member containing the thermally expandable microcapsules from the volume of the inside of the molding die. The method for molding a hollow molded article made of a fiber-reinforced resin according to Claim 1, characterized by this.

3. The volume ratio of the film-like bag member containing the thermally expandable microcapsules and the adjustment powder is 99:1 to 50:50, and the volume of the film-like bag member containing the thermally expandable microcapsules and the adjustment powder is 40% to 100% of the volume of the inside of the molding die. The method for molding a hollow molded article made of a fiber-reinforced resin according to Claim 1 or 2, characterized by this.

4. The adjustment powder is composed of an organic powder, an inorganic powder, chopped fibers, or a mixture thereof. The method for molding a hollow molded article made of a fiber-reinforced resin according to any one of Claims 1 to 3, characterized by this.

Images