Patent Publication Number: US-11046028-B2

Title: Method for molding composite material

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application of International Application No. PCT/JP2017/021549, filed on Jun. 9, 2017. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a molding method for a molding composite material. Background Information 
     RTM (Resin Transfer Molding) molding method and CRTM (Compression Resin Transfer Molding) molding method are known from the prior art as molding methods for composite materials in which a fiber base material is impregnated with a resin. 
     In these molding methods, the fiber base material is placed in a cavity in a metal mold into which resin is injected, but the fiber base material restricts the flow. Attempts have thus been made to suppress the flow resistance; for example, Japanese Laid-Open Patent Application No. 2010-221642 (Patent Document 1) discloses the formation of a cavity between horizontal surfaces that is larger than the thickness of the article to be molded. 
     SUMMARY 
     However, besides the simple horizontal surfaces disclosed in the aforementioned prior art, in practice, the molding surfaces of a metal mold may take on complex shapes that correspond to the shapes of vehicle bodies, etc. 
     For this reason, even if the metal mold is controlled, for example, so that a gap of a prescribed interval is formed between the horizontal molding surfaces, there may be other locations where the gap is narrow, between inclined molding surfaces, for example. Since the flow resistance is high in such locations and the resin does not flow as easily compared with other locations, there is the risk that variations in the impregnation of the resin will occur. Variations in resin impregnation may cause a reduction in strength and rigidity, and may result in poor appearance, which is not preferable. 
     Therefore, the object of the present invention is to provide a molding method for composite materials that can suppress variations in resin impregnation. 
     In the molding method for molding a composite material according to the present invention which realizes the aforementioned object, a composite material is formed by disposing a fiber base material within a cavity formed inside a metal mold, injecting resin, and curing the resin. In the molding method for a composite material according to the present invention, the wettability of part of the fiber base material is enhanced, and one part of the fiber base material is disposed in a narrow portion where the gap constituting the cavity is smaller than other locations. 
     By means of the molding method for composite materials of the present invention, it is possible to suppress variations in resin impregnation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart illustrating a general overview of the molding method according to an embodiment. 
         FIG. 2  is a view schematically illustrating the process for enhancing wettability in a part of the fiber base material. 
         FIG. 3  is a view schematically illustrating the arrangement of the fiber base material in a metal mold. 
         FIG. 4  is a view schematically illustrating a state in which the fiber base material is disposed and the metal mold is closed. 
         FIG. 5  is a view schematically illustrating the injection of resin into the metal mold. 
         FIG. 6  is a view schematically illustrating a state in which the metal mold is further clamped after resin injection. 
         FIG. 7  is a view schematically illustrating the demolding of a molded article. 
         FIG. 8  is a view for explaining capillary action. 
         FIG. 9  is a view for explaining the relationship between the contact angle of a droplet and wettability. 
         FIG. 10  is a view for explaining the relationship between the contact angle of a droplet and wettability. 
         FIG. 11  is a view schematically illustrating the injection of resin accompanied by vacuum evacuation. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be explained below with reference to the appended drawings. The dimensional ratios of the drawings are exaggerated for the sake of explanatory clarity and may differ from actual ratios. 
     First Embodiment 
     As shown in  FIG. 1 , in the molding method for molding a composite material according to the present embodiment, wettability is enhanced in a portion of a preform (fiber base material) (Step S 1 ), and the preform is disposed in a metal mold (Step S 2 ). Thereafter, the metal mold is closed (Step S 3 ) and resin is injected into the metal mold (Step S 4 ). After the resin injection, the metal mold is further clamped (Step S 5 ). Thereafter, the resin is cured (Step S 6 ) and the composite material is demolded (Step S 7 ). Each step will be described below. 
     As shown in  FIG. 2 , in Step SI, an enhanced wettability portion  101  in which the wettability is enhanced is formed at an inclined portion of a preform  100  by means of irradiating a plasma or ultraviolet light thereon. Examples of factors that improve wettability include the addition of a hydrophilic functional group and substrate roughening. 
     The preform  100  has a configuration in which a plurality of fiber base materials  102  are stacked via an adhesive  103 , but is not limited in this way, and the preform may be composed of only one fiber base material  102 . The preform  100  is shaped in advance by means of preforming and is essentially trapezoidal in shape in the present embodiment. The enhanced wettability portion  101  is the portion that forms the legs of the trapezoidal shape. 
     In the present embodiment, wettability is partially enhanced in the state of the preform  100  obtained by shaping the fiber base material  102 , but the present invention is not limited in this way, and the wettability may be partially enhanced prior to the preforming. For example, before the fiber base material  102 , which is essentially flat prior to shaping by means of preforming, is cut to a prescribed size or after being cut, the wettability may be partially enhanced at a prescribed location of the essentially flat fiber base material  102 . 
     The fiber base material  102  can be formed from, for example, carbon fiber, glass fiber, aramid fiber, polyamide (PA) fiber, polypropylene (PP) fiber, and acrylic fiber. The fiber base material  102  may have the structure, for example, of a woven fabric in which the fibers are combined vertically and horizontally. 
     The adhesive  103  is not particularly limited as long as the fiber base materials  102  can be bonded together; examples include thermoplastic resins, such as polyolefin resin, styrene resin, nylon resin and polyurethane resin, and thermosetting resins, such as epoxy resin, phenol resin and unsaturated polyester resin. 
     As shown in  FIG. 3 , in Step S 2 , the preform  100  is disposed in an opened metal mold  110 . The metal mold  110  includes a movable die  111  and a fixed die  112 . The preform  100  is pre-shaped so as to conform to the shape of the molding surface of the movable die  111  and the fixed die  112 , and is disposed along the molding surface of the fixed die  112  in Step S 2 . 
     The movable die  111  is connected to an unillustrated drive device equipped with a hydraulic cylinder, for example, and can freely move close to and away from the fixed die  112 . The movable die  111  is formed with a resin injection port  113 . 
     The fixed die  112  has a convex molding surface that opposes the concave molding surface of the movable die  111 . Alternatively, the movable die  111  may be provided with a convex molding surface, and the fixed die  112  with a concave molding surface. A sealing member  114  such as a gasket is provided on the outer perimeter of the fixed die  112 . The sealing member  114  may be provided on the outer perimeter of the movable die  111  instead of on the fixed die  112 . 
     As shown in  FIG. 4 , in Step S 3 , the movable die  111  is moved to approach the fixed die  112 , and the preform  100  is disposed inside the closed metal mold  110 . At this time, the cavity that is formed between the movable die  111  and the fixed die  112  is greater than the thickness of the composite material to be ultimately produced. 
     In addition, of the gaps that form the cavity, a gap t 1  between the inclined molding surfaces is smaller than a gap t 2  between the horizontal molding surfaces (t 1 &lt;t 2 ), and the space between the inclined molding surfaces forms a narrow portion  115  of the small gap tl. The enhanced wettability portion  101  is disposed in the narrow portion  115 . A relatively large gap portion 116  (other locations) of gap t 2  communicates with the resin injection port  113 . 
     As shown in  FIG. 5 , in Step S 4 , resin  120  is injected into the metal mold  110  through the injection port  113 . The resin  120  flows from the relatively large gap portion  116  to the narrow portion  115  and is impregnated in the preform  100 . 
     A thermosetting resin, for example, such as an epoxy resin or a phenol resin is used as the resin  120 . The epoxy resin typically used is a two-component type, which is used by mixing the primary agent and the curing agent. Generally, a bisphenol A type epoxy resin is used as the primary agent and an amine type is used as the curing agent, but no limitation is imposed thereby. The resin  120  is not limited to thermosetting resins, and thermoplastic resins may also be used. In addition, the resin  120  may contain a mold releasing agent. 
     As shown in  FIG. 6 , in Step S 5 , the metal mold  110  is further clamped. At this time, the metal mold  110  is clamped until the cavity and the thickness of the composite material to be ultimately produced become essentially the same. 
     As the pressure inside the metal mold  110  increases with further clamping in Step S 5 , the resin  120  becomes more reliably distributed throughout the entire preform  100 . 
     In Step S 6 , the resin  120  impregnated in the preform  100  is cured. If the resin  120  is a thermosetting resin, the resin  120  impregnated in the preform  100  can be cured by, for example, heating the metal mold  110  using a heating device such as a heater. 
     As shown in  FIG. 7 , in Step S 7 , the movable die  111  is moved so as to separate from the fixed die  112  to open the metal mold  110 , and a composite material  130 , which is the molded article, is demolded. 
     The composite material  130  has a relatively simple shape in the present embodiment, but no limitation is imposed thereby. For example, if the composite material  130  is manufactured as a frame component, such as a front side member or a pillar, or an outer panel component, such as a roof, which are used in automobile bodies, the composite material will have a correspondingly more complex shape. 
     The action and effects of the present embodiment will now be described. 
     The narrow portion  115 , being narrower than the relatively large gap portion  116 , has high flow resistance, which impedes the flow of the resin  120 . 
     However, in the present embodiment, the enhanced wettability portion  101  (portion of the fiber base material where the wettability has been enhanced) is disposed in the narrow portion  115 , and the capillary action is thereby enhanced in the narrow portion  115 , so that the resin  120  is readily drawn into the narrow portion  115 . Thus, the resin  120  is easily and entirely distributed, and impregnation variations can be suppressed. 
     With reference to  FIG. 8 , in general, the height h, up to which a liquid  1000  is drawn into a capillary tube  1100  by means of capillary action, can be expressed by Equation  1  below; when the wettability is enhanced and the contact angle θ (90°&gt;θ&gt;0) of Equation 1 becomes small, cos θ on the right side of the equation increases, so that the height h up to which the liquid  1000  is drawn increases. That is, with enhanced wettability, the liquid  1000  is more readily drawn into the capillary tube  1100 . Based on the same principle, the resin  120  is more readily drawn by arranging the enhanced wettability portion  101  in the narrow portion  115 . 
     
       
         
           
             
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     In Equation 1, θ: contact angle, σ: surface tension, τ: capillary tube radius, γ: specific gravity of the liquid. 
     In contrast to the relatively large gap portion  116 , the narrow portion  115  is positioned on the downstream side of the flow direction of the resin  120 ; but since the flow of the resin  120  is reduced on the downstream side due to energy loss on the upstream side due to flow resistance, etc., so that it is particularly difficult for the resin  120  to flow. 
     However, in the present embodiment, since the enhanced wettability portion  101  is disposed in the narrow portion  115  on the downstream side and the drawing of the resin  120  is increased due to capillary action, the resin  120  is more readily distributed, even on the downstream side, and variations in impregnation can be suppressed particularly effectively. 
     As long as the wettability can be enhanced in a portion of the preform  100  (fiber base material), the invention is not limited to the partial irradiation with a plasma or ultraviolet light, as in the present embodiment; for example, a sizing agent may be applied locally. 
     However, when an attempt is made to locally increase wettability with a sizing agent, for example, the preform  100  requires masking, which is time- and labor-intensive. 
     In contrast, partial irradiation is sufficient if a plasma or ultraviolet light is used, so that it is possible easily to increase the wettability over a prescribed range. 
     In the present embodiment, the wettability is enhanced after the preform  100  is formed, so that, compared to the case in which the wettability of the fiber base material  102  is enhanced prior to preforming, the period from enhancing the wettability to injection of the resin  120  (Step S 4 ) can be made short. 
     Therefore, it is possible to inject the resin  120  while the wettability is maintained, and the effect of the enhanced wettability portion  101  is not easily impaired. 
     As shown in  FIGS. 9 and 10 , the degree of wettability can be determined from the size of the contact angle θ of a droplet  1001  that is dropped onto the base material, wherein, the greater the contact angle θ, the lower the wettability, and the smaller the contact angle θ, the higher the wettability. 
     Second Embodiment 
     As shown in  FIG. 11 , a metal mold  210  that is different from that of the first embodiment is used in the second embodiment. In addition, the present embodiment is different from the first embodiment in that the narrow portion  115  is vacuum-pumped in Step S 4  for injecting the resin  120 . Since the other device configurations and steps of the present embodiment are essentially the same as in the first embodiment, the redundant explanations are omitted. 
     The metal mold  210  has a movable die  211  that is different from the first embodiment. A vacuum port  217  that communicates with the narrow portion  115  is formed on the molding surface of the movable die  211 . The invention is not limited to such a form, and it is sufficient if the vacuum port  217  is formed on the molding surface of at least one of the movable die  211  and the fixed die  112 . 
     The vacuum port  217  communicates with a vacuum pump  218 . In addition, a pin-shaped opening/closing member  219  is provided so as be capable of freely moving close to or away from the vacuum port  217 . The vacuum pump  218  evacuates the narrow portion  115  through the vacuum port  217 . At this time, the opening/closing member  219  is separated from the vacuum port  217 , and the vacuum port  217  is opened. 
     In the resin injection Step S 4  of the present embodiment, the resin  120  is injected in a state in which the narrow portion  115  is vacuum-pumped and set to a more negative pressure than the other location  116 . 
     Before the resin  120  flows and reaches the vacuum port  217 , the opening/closing member  219  is pushed in to approach the vacuum port  217  and closes the vacuum port  217 . Therefore, the resin  120  does not flow into the vacuum port  217 . 
     In the present embodiment, since the resin  120  is injected while the narrow portion  115  is set to a more negative pressure than the other location  116 , the resin  120  is drawn into the narrow portion  115  and is more easily distributed throughout, variations in impregnation can be more reliably prevented. 
     In addition, since the resin  120  is prevented from flowing into the vacuum port  217  by the opening/closing member  219 , demolding is a simple matter and unnecessary deburring can be avoided. 
     The present invention is not limited to the embodiment described above, and various modifications are possible within the scope of the claims. 
     For example, the present invention is not limited to the molding method referred to as CRTM (Compression Resin Transfer Molding) molding method, as is illustrated in  FIG. 1  of the present embodiment above, and may include the RTM (Resin Transfer Molding) molding method, in which full clamping is carried out in Step S 3  of  FIG. 1 . 
     In this case, in Step S 3 , clamping is carried out until the cavity dimension of the metal mold  110  is essentially equal to the thickness of the composite material  130 , and the resin curing Step S 6  is carried out without carrying out the further clamping Step S 5  after the resin injection Step S 4 .