JP2015112805A - Method for molding composite material and molded article composed of composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a composite material, enabling a molded article having a high strength to be molded.SOLUTION: The method for molding a composite material related to the present invention comprises: a lamination step of molding a laminate 12 in which thermally expansive microspheres 11 having thermoplastic resin outer shells and including a volatile foaming agent inside the outer shells are interposed between a plurality of prepregs 10 obtained by impregnating a thermosetting resin or a thermoplastic resin to fibers; and a molding step of vaporizing the volatile foaming agent by heating the laminate 12 to expand the thermally expansive microspheres 11 and curing the prepregs 10.

Description

  The present invention relates to a method for molding a composite material including fibers and plastics. The present invention also relates to a molded article made of the composite material.

  When molding fiber reinforced plastics (hereinafter referred to as “FRP”), which is a composite material, thermally expandable microspheres are mixed into the thermosetting resin that is the matrix (matrix). There has been proposed a molding method for obtaining a molded product by heating (see Patent Document 1). According to this molding method, when the thermosetting resin is heated and cured, the thermally expansible microspheres expand to form a hollow portion in the FRP. For this reason, the density of the FRP is lowered, and the molded product can be reduced in weight.

  However, in this molding method, since the thermally expandable microspheres push the fibers and expand, the FRP is molded while the fibers are distorted. For this reason, the FRP obtained by this molding method is not transmitted to the fiber even when tension is applied, and sufficient tensile strength cannot be obtained. Patent Document 2 discloses a method of injection molding using a resin containing thermally expandable microspheres (thermally expandable microcapsules) in addition to fibers. However, in this method, only short fibers can be used, and sufficient tensile strength cannot be obtained because the fibers are not connected in the plane direction.

  Furthermore, Patent Document 3 proposes a molding method in which a thermosetting matrix resin containing thermally expandable microspheres (rigid lightweight particles) is sandwiched between reinforcing fiber sheets and heated. In this molding method, the thermosetting resin is infiltrated into the reinforcing fiber sheet with the force by which the heat-expandable microspheres expand, and then the thermosetting resin is cured. However, a separation membrane is provided between the thermosetting matrix resin and the reinforcing fiber sheet so that the thermally expandable microspheres do not flow into the reinforcing fiber sheet. According to such a configuration, since the heat-expandable microspheres do not flow into the reinforcing fiber sheet and the fibers are not distorted, it seems that a high-strength molded product can be obtained.

JP 2004-231811 A JP 2010-053351 A JP-A-8-302206

  However, in the method described in Patent Document 3, the thermosetting matrix resin must be pushed into the reinforcing fiber sheet side only by the expansion force of the thermally expandable microspheres. The resin needs to have a low viscosity. However, the low viscosity resin has lower strength after curing than the high viscosity resin. Therefore, high strength cannot be obtained with a molded product molded by this method.

  This invention is made | formed in view of such a situation, and it aims at providing the shaping | molding method of the composite material which can shape | mold a molded article with high intensity | strength.

  A method for molding a composite material according to an embodiment of the present invention includes a thermoplastic resin outer shell between a plurality of prepregs in which fibers are impregnated with a thermosetting resin or a thermoplastic resin. A laminating step for forming a laminate including a thermally expandable microsphere, which is a microsphere encapsulating a volatile foaming agent, and heating the laminate, whereby the volatile foaming agent is vaporized and the thermal expansion is performed. A molding step of expanding the conductive microsphere and curing the prepreg.

  According to this method, a molded product can be molded using the prepreg. Since the prepreg is impregnated with a resin in advance, a high-viscosity resin can be used as a matrix resin. If a resin having a high viscosity is used as the resin for the matrix, the strength of the plastic part of the molded product can be improved, and mixing of thermally expandable microspheres into the matrix can be suppressed. Further, since the density of the composite material is reduced by the expansion of the thermally expandable microsphere, the bending moment can be improved by increasing the second moment of section of the molded product. Thus, according to said method, the intensity | strength of a molded article can be improved.

  In the molding method, the laminate is molded using a mold having a first mold and a second mold facing each other in the molding step, and in the lamination step, the laminate is formed in the molding step. Depending on the amount of separation between the first mold and the second mold at each position in the surface direction, the amount of the heat-expandable microspheres at each position in the surface direction of the laminate (the heat interposed between the prepregs). The amount of expandable microspheres) may be increased or decreased. According to this method, a prepreg can be used even when the shape of the molded product is complicated, and a molded product having a desired shape can be obtained by using the first mold and the second mold facing each other. be able to.

  Moreover, in said shaping | molding method, you may adjust the thickness of the molded article obtained by heating the said laminated body by increasing / decreasing the magnitude | size of the pressure added to the said laminated body in the said formation process. According to this method, the thickness of the molded product can be set to an appropriate dimension even if one of the first mold and the second mold described above is not included even though the thermal expansion microsphere is included in the laminate. .

  In the molding method, when the thermally expandable microspheres are interposed between a plurality of prepregs in the stacking step, a sheet-like thermoplastic resin containing the thermally expandable microspheres is stacked on the prepreg. Also good. According to this method, the work of interposing the thermally expandable microspheres between the plurality of prepregs can be easily performed, and the amount of the thermally expandable microspheres can be easily adjusted.

  In the molding method, when the thermally expandable microsphere is interposed between a plurality of prepregs in the laminating step, a liquid thermosetting resin containing the thermally expandable microsphere is applied to the prepreg. May be. According to this method, the thermally expandable microspheres can be uniformly arranged in the plane direction.

  In the molding method, when the thermally expandable microspheres are interposed between a plurality of prepregs in the stacking step, the powdery thermally expandable microspheres may be dispersed on the surface of the prepreg. According to this method, the thermally expandable microspheres can be arranged by a very simple method.

  Further, the composite material molded product according to an embodiment of the present invention includes an FRP layer obtained by curing a prepreg in which fibers are impregnated with a thermosetting resin or thermoplastic resin for a matrix, and an outer layer of the thermoplastic resin. A hollow layer having a hollow portion formed by expansion of a thermally expandable microsphere which is a microsphere having a shell and containing a volatile foaming agent inside the outer shell is laminated. According to such a configuration, since the FRP layer is formed using the prepreg, a resin having a high viscosity can be used as the matrix resin. Therefore, it is possible to improve the strength of the plastic part of the FRP layer, and it is possible to suppress the thermal expansion microspheres from being mixed into the matrix in the manufacturing process. Moreover, the density of a molded product can be reduced by using a thermally expandable microsphere, thereby increasing the cross-sectional secondary moment and improving the bending strength. Therefore, according to said structure, the intensity | strength of a molded product can be improved.

  The molded product may have a plurality of the FRP layers and a plurality of the hollow layers. According to such a configuration, since the thickness per one hollow layer can be reduced, the hollow layer is hardly deformed, and the strength of the entire molded product can be improved.

  As described above, according to the method for molding a composite material described above, a molded product having high strength can be molded.

FIG. 1 is a view showing a molding method according to the first embodiment. FIG. 2 is a view showing a molding method according to the second embodiment. FIG. 3 is a view showing a molding method according to the third embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Below, the same code | symbol is attached | subjected to the element which is the same or it corresponds through all the drawings, and the overlapping description is abbreviate | omitted.

(First embodiment)
First, a method for molding a composite material according to the first embodiment will be described. FIG. 1 is a view showing a molding method according to this embodiment. The molding method according to the present embodiment includes a laminating process and a molding process. Hereinafter, the lamination process and the molding process will be described in order.

<Lamination process>
As shown in FIG. 1A, the stacking step is a step of forming a stacked body 12 by interposing a thermally expandable microsphere 11 between a plurality of prepregs 10. The thermally expandable microsphere 11 is a microsphere in which a liquid hydrocarbon as a volatile foaming agent is encapsulated in an outer shell made of a thermoplastic resin. When the thermally expandable microsphere 11 reaches a certain temperature (expansion temperature) or higher, the internal hydrocarbons are vaporized, and the whole expands, for example, to a similarity ratio of about 10 times (volume ratio of about 1000 times). As the thermally expandable microsphere 11, Expancel (registered trademark) of Nippon Ferrite Co., Ltd., Advancel EM of Sekisui Chemical Co., Ltd., etc. can be used. Note that tetramethylsilane, CCl ₃ F, or the like may be used as a volatile foaming agent inside the thermally expandable microsphere 11.

  A general prepreg 10 can be used. However, the thermosetting resin used as the matrix has a high viscosity. As the matrix, for example, a bisphenol A type epoxy resin (viscosity: 500 to 5000 Pa · s) can be used. While high-viscosity resin is difficult to impregnate the fiber, the strength of the molded product can be improved by making the matrix resin high viscosity. Moreover, it can prevent that the thermally expansible microsphere 11 mixes in the prepreg 10 by making resin for matrixes into high viscosity. Furthermore, since the prepreg is obtained by impregnating a fiber with a resin in advance, there are almost no air bubbles inside. Therefore, according to the molding method using a prepreg, the amount of bubbles remaining in the molded product can be suppressed as compared with a molding method (see Patent Document 3) including a step of impregnating a fiber with a resin by foaming pressure. As a result, it is possible to suppress a decrease in strength of the molded product due to residual bubbles. In addition, the fiber used for the prepreg 10 may be arrange | positioned in one direction, may be a textile fabric, and material is not specifically limited.

  In the laminating step in the present embodiment, a method of spreading the powdery thermally expandable microspheres 11 on the surface of the prepreg 10 is adopted as a method of interposing the thermally expandable microspheres 11 between the plurality of prepregs 10. .

  However, as a method of interposing the thermally expandable microspheres 11 between the plurality of prepregs 10, a sheet-like thermoplastic resin (hereinafter referred to as “sheet-like resin”) including the thermally expandable microspheres 11 is used as the prepreg 10. A method of laminating may be employed. The sheet-like resin is obtained by adding the thermally expandable microsphere 11 to a thermoplastic resin (hereinafter referred to as “adhesive resin”) having a melting temperature lower than the expansion temperature of the thermally expandable microsphere 11 (for example, about 130 degrees). It can be obtained by forming it into a sheet and curing it. As the adhesive resin, EVA (ethylene vinyl acetate copolymer), PP (polypropylene), PA (polyamide), or the like can be used. When heat is applied to the sheet-like resin, the adhesive resin first melts, and then the thermally expandable microsphere 11 expands. Therefore, the adhesive resin does not hinder the expansion of the thermally expandable microsphere 11. In addition, since sheet-like resin can be piled up, it is effective when there is much quantity (intervening quantity) which interposes the thermally expansible microsphere 11 between several prepregs 10. FIG. Note that a thermosetting resin can be used as the adhesive resin instead of a thermoplastic resin. In this case, the sheet-like resin can be formed by spraying the thermally expandable microspheres 11 on one or both of the surfaces of the adhesive resin previously formed into a sheet-like shape.

  Further, as a method of interposing the thermally expandable microspheres 11 between the plurality of prepregs 10, a liquid thermosetting resin (hereinafter referred to as “liquid resin”) containing the thermally expandable microspheres 11 is added to the prepreg 10. You may employ | adopt the method of apply | coating. The liquid resin can be obtained by adding the thermally expandable microsphere 11 to a thermosetting resin that is liquid at room temperature (for example, RTM6 of Hexcel, USA). In addition, a liquid resin having a curing temperature equal to or higher than the expansion temperature of the thermally expandable microsphere 11 is used. When heat is applied to the liquid resin, the thermally expandable microsphere 11 is first expanded, and then the liquid thermosetting resin is cured. If a liquid resin is used, the thermally expandable microspheres 11 can be uniformly disposed on the entire surface of the prepreg 10. Note that the thermosetting resin is not limited to liquid, and may be in the form of a gel depending on the state of the resin.

  In the present embodiment, the thermally expandable microspheres 11 are interposed between all the prepregs 10. That is, the laminate 12 has a plurality of layers made of the prepreg 10 and a plurality of layers made of the thermally expandable microsphere 11. However, the thermally expandable microspheres 11 do not have to be disposed between all the prepregs 10. For example, after a plurality of prepregs 10 are stacked, the thermally expandable microspheres 11 may be stacked on the surface thereof.

<Molding process>
The molding step is a step of heating the laminated body 12 to obtain a molded product. In the molding step of the present embodiment, as shown in FIG. 1A, a molding die 22 having a first die 20 and a second die 21 facing each other is used. In the present embodiment, the first mold 20 is a so-called upper mold, and the second mold is a so-called lower mold. Furthermore, in this embodiment, the molding surface 23 corresponding to the lower surface of the first mold 20 is formed in a flat shape, and the molding surface 24 corresponding to the upper surface of the second mold 21 is formed in a flat shape. In the molding process, first, the laminate 12 formed in the lamination process is disposed on the molding surface 24 of the second mold 21. As shown in FIG. 1A, the distance between the molding surface 24 of the second mold 21 and the molding surface 23 of the first mold 20 (the size of the space of the molding mold 22) is the thickness dimension (high) of the laminate 12. Larger than the dimension). Therefore, when the laminate 12 is disposed on the molding surface 24 of the second mold 21, the upper surface of the laminate 12 and the molding surface 23 of the first mold 20 are separated from each other.

  And in the state which has arrange | positioned the laminated body 12 to the 2nd type | mold 21, it puts into an autoclave (autoclave), heats the laminated body 12, and applies a pressure. If it does so, the liquid hydrocarbon in the thermally expansible microsphere 11 will vaporize, and the thermally expansible microsphere 11 will expand | swell. Thereby, the thickness dimension (height dimension) of the laminated body 12 increases, and as shown to (b) of FIG. 1, the upper surface of the laminated body 12 and the molding surface 23 of the 1st type | mold 20 contact | connect. That is, the lower surface of the laminate 12 is pressed against the molding surface 24 of the second mold 21 and the upper surface of the laminate 12 is pressed against the molding surface 23 of the first mold 20. And the prepreg 10 hardens | cures, maintaining this state, and the molded article 30 of a composite material is obtained.

  As described above, the molded product 30 molded by the molding method according to the present embodiment is cured with the upper surface and the lower surface in contact with the first mold 20 and the second mold 21, respectively. It can be finished to the state. According to the conventional molding method that does not use the thermally expandable microsphere 11, the member corresponding to the laminate 12 does not swell greatly, so the first mold 20 is not used, and the surface of the member is made of a film. A molding process is performed in the covered state. Therefore, unevenness is likely to occur particularly on the upper surface of the surface of the molded product 30. Thus, according to the molding method according to the present embodiment, the smoothness of the surface of the molded product 30 can be improved as compared with the conventional molding method that does not use the thermally expandable microsphere 11.

  Since the outer shell of the thermally expandable microsphere 11 is formed of a thermoplastic resin, the outer shell is melted and bonded to each other in the molding process. And when the molded article 30 cools, these will harden | cure and the hollow layer 31 which has the hollow part 33 formed by the thermally expansible microsphere 11 expanding will be formed. That is, the molded product 30 has the hollow layer 31 and the FRP layer 32 obtained by curing the prepreg 10. If the density of the molded product 30 having the hollow layer 31 is small and has the same weight, the thickness can be made larger than that of the molded product made of only the FRP layer 32. Thereby, the cross-sectional secondary moment of the molded product 30 can be increased and the bending strength can be improved.

  Further, the molded product 30 of the present embodiment has a structure in which the hollow layers 31 and the FRP layers 32 are alternately stacked. In other words, the molded product 30 has a large number of hollow layers 31. When a force is applied to the surface of the hollow layer 31, the portion where the force is applied is easily deformed, such as a depression, and when the thickness is large, the amount of deformation is large. Become. Therefore, even if the ratio occupied by the hollow layer 31 in the molded product 30 is the same, for example, compared to the case where the hollow layer 31 is formed of a single layer, it is formed of a large number of layers as in this embodiment. However, since the thickness per layer can be reduced, it is difficult to deform and high strength can be obtained.

(Second Embodiment)
Next, a molding method according to the second embodiment will be described. FIG. 2 is a view showing a molding method according to this embodiment. The molding method according to the present embodiment is the first in that the concave portion 25 is mainly formed in the first mold 20 and the molding surface 23 of the first mold 20 and the molding surface 24 of the second mold 21 have different shapes. Different from the embodiment.

  In the laminating process of the present embodiment, the heat at each position in the surface direction of the laminate 12 according to the amount of separation between the first mold 20 and the second mold 21 at each position in the surface direction of the laminate 12 in the molding process. Increase or decrease the amount of interstitial microspheres 11. In the present embodiment, as shown in FIG. 2A, the recess 25 is formed in the central portion of the first mold 20. Therefore, the distance between the molding surface 23 of the first mold 20 and the molding surface 24 of the second mold 21 is greater in the central portion of the molding die 22 than in other portions. In this case, as shown in FIG. 2A, more thermally expandable microspheres 11 are interposed in the central portion of the laminate 12 than in other portions.

  After the laminated body 12 is formed in this way, when the laminated body 12 is heated in the molding process, the central portion of the laminated body 12 swells greatly as shown in FIG. That is, the part corresponding to the recessed part 25 of the 1st type | mold 20 among the laminated bodies 12 expand | swells greatly. As described above, the molded product 30 has a complicated shape by increasing or decreasing the amount of the thermally expansible microspheres 11 depending on the shape of the mold 22 (the distance between the portions of the mold 22). However, the molded product 30 can be molded by the laminate 12 in which the prepreg 10 is arranged without being interrupted in the plane direction, that is, the laminate 12 in which the fibers are arranged without being interrupted in the plane direction. Therefore, the strength of the molded product 30 can be improved.

  In addition, when increasing the intervention amount of the thermally expansible microsphere 11 in the center part of the laminated body 12, it can concentrate only on the layer of the thermally expansible microsphere 11 and can increase the intervention amount of the center part. However, as described above, since the strength decreases as the thickness of each layer of the thermally expandable microsphere 11 increases, the thermally expandable microsphere 11 is distributed in the same distribution in each layer of each thermally expandable microsphere 11. It is desirable to arrange.

(Third embodiment)
Next, a molding method according to the third embodiment will be described. FIG. 3 is a view showing a molding method according to this embodiment. The molding method according to the present embodiment is different from that of the first embodiment mainly in that the molding die 22 does not have the first die 20.

  In the stacking process of the present embodiment, the stacked body 12 is formed in which the thermally expandable microspheres 11 are interposed between the plurality of prepregs 10 as in the case of the first embodiment.

  In the molding step, the laminate 12 formed in the lamination step is disposed on the molding surface 24 of the second mold 21. However, as described above, the mold 22 used in the present embodiment has the second mold 21, but does not have the first mold 20. Therefore, even if the thickness of the laminate 12 is increased by heating the laminate 12, there is no member that is in contact with the upper surface of the laminate 12 and regulates expansion.

  Subsequently, in a state where the laminate 12 is disposed on the molding surface 24 of the second mold 21, the laminate 12 is placed in an autoclave, and the laminate 12 is heated and pressure is applied. However, in this embodiment, the thickness of the molded product 30 obtained by heating the laminated body 12 is adjusted by increasing / decreasing the magnitude of the pressure applied to the laminated body 12. If the pressure at the time of heating is large, the expansion coefficient of the thermally expandable microsphere 11 is small. That is, if the pressure applied to the laminate 12 is reduced, the thickness of the molded product 30 can be increased, and if the pressure applied to the laminate 12 is increased, the thickness of the molded product 30 can be reduced. Thus, if the pressure applied to the laminate 12 is increased or decreased in the molding step, the thickness of the molded product 30 can be adjusted within a predetermined range even when the molding die 22 does not have the first die 20. Can do. In addition, since there exists a suitable range in the pressure at the time of hardening the prepreg 10, a pressure is increased / decreased within the range.

  The embodiments have been described above with reference to the drawings. However, the specific configuration is not limited to these embodiments, and the present invention can be applied even if there is a design change or the like without departing from the scope of the invention. included.

  Although the case where the matrix of the prepreg 10 is a thermosetting resin has been described above, the matrix may be a thermoplastic resin. Even if the matrix is a thermoplastic resin, the molded product 30 can be obtained by the same molding method as in the case where the matrix is a thermosetting resin. Examples of thermoplastic resins that can be used for the matrix include PEI (polytailimide), PPS (polyphenylene sulfide), PEEK (polyetheretherketone), and nylon 66.

  According to the method for molding a composite material according to the present invention, a molded product having high strength can be molded. Therefore, it is useful in the technical field of composite materials.

DESCRIPTION OF SYMBOLS 10 Prepreg 11 Thermal expansion microsphere 12 Laminated body 20 1st type | mold 21 2nd type | mold 22 Molding die 23 Molding surface (1st type)
24 Molding surface (second mold)
30 Molded product 31 Hollow layer 32 FRP layer 33 Hollow part

Claims (8)

Thermal expansion is a microsphere that has a thermoplastic resin outer shell between a plurality of prepregs in which fibers are impregnated with a thermosetting resin or a thermoplastic resin, and a volatile foaming agent is included inside the outer shell. A laminating process for forming a laminated body with microspheres interposed therebetween;
A molding method of a composite material, comprising: heating the laminated body to vaporize the volatile foaming agent to expand the thermally expandable microsphere and to cure the prepreg. Forming the laminate using a mold having a first mold and a second mold facing each other in the molding step;
In the laminating step, the thermal expansion at each position in the plane direction of the laminate according to the amount of separation between the first mold and the second mold at each position in the plane direction of the laminate in the molding step. The shaping | molding method of Claim 1 which increases / decreases the intervention amount of a property microsphere.   The shaping | molding method of Claim 1 which adjusts the thickness of the molded article obtained by heating the said laminated body by increasing / decreasing the magnitude | size of the pressure applied to the said laminated body in the said shaping | molding process.   2. The molding method according to claim 1, wherein a sheet-like thermoplastic resin containing the thermally expandable microspheres is stacked on the prepreg when the thermally expandable microspheres are interposed between the plurality of prepregs in the laminating step. .   The molding according to claim 1, wherein a liquid thermosetting resin containing the thermally expandable microsphere is applied to the prepreg when the thermally expandable microsphere is interposed between the plurality of prepregs in the laminating step. Method.   2. The molding method according to claim 1, wherein the thermally expandable microspheres are dispersed on the surface of the prepreg when the thermally expandable microspheres are interposed between the plurality of prepregs in the stacking step.   An FRP layer obtained by curing a prepreg in which fibers are impregnated with a thermosetting resin or thermoplastic resin for a matrix, and an outer shell of a thermoplastic resin, and a volatile foaming agent is included inside the outer shell. A composite article formed by laminating a hollow layer having a hollow portion formed by expansion of a thermally expandable microsphere that is a microsphere.   The molded article according to claim 7, wherein the molded article has a plurality of the FRP layers and a plurality of the hollow layers.

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