Molded fiber-reinforced-resin object and method for producing said molded fiber-reinforced-resin object

Abstract

This molded fiber-reinforced-resin object comprises a main body and ribs.　The main body comprises continuous fibers and a heat-curable resin, and the ribs are composed of a heat-curable resin and short fibers having shorter fiber lengths than the continuous fibers. The main body includes a region extending in an in-plane direction thereof which does not contain the short fibers. Due to this configuration, it is possible to provide a molded fiber-reinforced-resin object with which a high reinforcing effect due to the high-strength ribs can be obtained.　This method for producing the molded fiber-reinforced-resin object involves using continuous fibers for the main body, using SMC-material-derived fibers for the ribs, and integrally molding the main body and the ribs by means of an RTM method. It is thus possible to produce a molded fiber-reinforced-resin object in which the main body is reinforced with high-strength ribs with no defects.

Description

Fiber-reinforced resin molded body and method for manufacturing the same

[0001] The present invention relates to a fiber-reinforced resin molded body and a method for manufacturing the fiber-reinforced resin molded body, and more particularly to a fiber-reinforced resin molded body in which a high reinforcing effect is obtained by ribs, and a method for manufacturing the fiber-reinforced resin molded body.

[0002] Fiber-reinforced resin moldings have excellent mechanical strength and are lighter than steel, allowing for significant weight reduction of vehicle bodies and the like, and are therefore used as alternatives to steel members.

[0003] To improve the mechanical performance of this fiber-reinforced resin molding, it is preferable that not only the volume fraction (Vf) of the reinforcing fibers is high, but also that the fiber length is long.Fiber-reinforced resin moldings reinforced with continuous fibers have excellent specific strength and specific rigidity.

[0004] Furthermore, the mechanical performance of a fiber-reinforced resin molded article can also be improved by its structure, and a fiber-reinforced resin molded article is generally provided with ribs or bosses that reinforce the main body portion.

[0005] Patent Document 1 discloses a fiber-reinforced resin molding in which the average fiber length of the reinforcing fibers in the boss portion is 10 to 20 mm and the fiber volume fraction (Vf) is 20 to 30%.

[0006] Japanese Patent Application Publication No. 2013-10254

[0007] However, since the mechanical properties of fiber-reinforced resin moldings are achieved by the mutual influence of the reinforcing fibers and the resin, it is necessary for the resin to penetrate sufficiently between the reinforcing fibers to connect them together, and therefore the ability of the resin to impregnate between the reinforcing fibers is important in the manufacturing process of fiber-reinforced resin moldings.

[0008] Therefore, if the thickness of the rib portion is thin or if its height is high, not only is it difficult for the reinforcing fibers to enter the grooves that form the rib portion, but it also becomes difficult for the resin to penetrate between the reinforcing fibers, making it difficult to form a rib portion with long fibers and a high fiber volume content and thereby obtain a high reinforcing effect.

[0009] The present invention has been made in consideration of the problems associated with the prior art, and its purpose is to provide a fiber-reinforced resin molding that provides a high reinforcing effect due to the high-strength rib portion, and a method for manufacturing such a fiber-reinforced resin molding.

[0010] As a result of extensive research into achieving the above object, the inventors discovered that the above object can be achieved by arranging continuous fibers in the main body forming portion of the mold, arranging sheet molding compound (SMC material) in the rib forming grooves, and integrally molding the main body portion and rib portion by resin transfer molding (RTM) method, thereby completing the present invention.

[0011] That is, the fiber-reinforced resin molding of the present invention includes a main body portion and a rib portion, wherein the main body portion contains continuous fibers and a thermosetting resin, the rib portion is made of short fibers having a fiber length shorter than that of the continuous fibers and the thermosetting resin, and the main body portion has an in-plane region that does not contain the short fibers.

[0012] The present invention also provides a method for producing a fiber-reinforced resin molded product, which comprises the steps of: placing a fiber material in a mold; injecting a thermosetting resin composition into the cavity; and pressing the fiber material and the thermosetting resin composition together to impregnate the fiber material with the thermosetting resin composition and cure it. The placing step includes a process of locally placing an SMC material on a rib-forming groove of the mold; and a process of placing a continuous fiber material over the entire cavity that covers the SMC material and forms the main body.

[0013] According to the present invention, continuous fiber is used for the main body portion, and fiber derived from SMC material is used for the rib portion, and these are integrally molded by the RTM method, so that a fiber-reinforced resin molded product that provides a high reinforcing effect due to the high-strength ribs and a method for manufacturing the fiber-reinforced resin molded product can be provided.

[0014] FIG. 1 is a diagram illustrating a manufacturing process of a manufacturing method for a fiber-reinforced resin molded body of the present invention. FIG. 2 is a diagram illustrating an example of a mold used in the manufacturing method for a fiber-reinforced resin molded body of the present invention. FIG. 3 is a diagram illustrating a state in which stacked SMC materials collapse. FIG. 4 is a diagram illustrating a state in which a slide plate prevents lateral displacement of the SMC material. FIG. 5 is a graph showing viscosity changes in a mold of a thermosetting resin composition and a matrix resin of an SMC material. FIG. 6 is a cross-section showing an example of a fiber-reinforced resin molded body of the present invention. FIG. 7 is a diagram illustrating the relationship between the ratio of the height to the width of the SMC material and the filling rate into a rib forming groove.

[0015] <Method for manufacturing fiber-reinforced resin molded body> First, the method for manufacturing a fiber-reinforced resin molded body of the present invention will be described in detail. The method for manufacturing a fiber-reinforced resin molded body of the present invention is a method for manufacturing a fiber-reinforced resin molded body having a main body portion and a rib portion, and includes an arrangement step of arranging a fiber material in a mold, an injection step of injecting a thermosetting resin composition into the cavity, and a molding step of pressing the mold to impregnate the fiber material with the thermosetting resin composition and cure it, as shown in Figure 1.

[0016] (Placement process) The placement process is a process of placing two types of fiber materials in a mold, and in the present invention, sheet molding compound (hereinafter sometimes simply referred to as "SMC material") and continuous fiber material are used as the fiber materials.

[0017] The SMC material is a thermosetting molding material in which reinforcing fibers are impregnated with a matrix resin and processed into a sheet or plate shape with a thickness of 1 to 5 mm. Since the matrix resin has already been impregnated into the reinforcing fibers, there is no problem with impregnation.

[0018] In the present invention, in order to form the rib portion of the fiber-reinforced resin molding with SMC material, SMC material is locally placed directly above the rib-forming groove of the mold, and continuous fiber material is layered to cover this SMC material and over the entire cavity that forms the main body. Note that the continuous fiber material and SMC material may be placed in the mold in a pre-overlapping state.

[0019] It is also preferable that the volume of the SMC material placed directly above the rib forming groove is equal to or slightly larger than the volume of the rib forming groove.

[0020] Since the volume of the SMC material and the volume of the rib forming groove are approximately the same, the rib forming groove can be filled with SMC material without excess or deficiency, and the SMC material does not protrude into the main body portion, so that an area that does not contain fibers derived from the SMC material is formed in the in-plane direction of the main body portion, and the main body portion is reinforced with continuous reinforcing fibers, thereby improving the strength of the main body portion itself.

[0021] The SMC material placed directly above the rib forming groove is cut in the mold to match the width of the rib forming groove (the thickness of the rib), so the fiber length becomes shorter depending on the width of the rib forming groove.

[0022] Therefore, when pressed during the molding process described below, the SMC material can be easily pressed into the rib forming groove, forming a high-strength rib without defects. This high-strength rib can then reinforce the main body, allowing for the production of a highly rigid fiber-reinforced resin molded body.

[0023] The SMC material can be placed not only directly above the rib forming groove, but also inserted into the rib forming groove.

[0024] By inserting SMC material into the rib forming groove and arranging the missing SMC material directly above the rib forming groove, the amount of SMC material pushed into the rib forming groove from outside by the press can be reduced, and a rib portion without filling defects can be formed even in deep rib forming grooves.

[0025] The SMC material inserted into the rib-forming groove preferably has slits. The slitted SMC material bends in the rib-forming groove, improving the flowability of the matrix resin when it softens, facilitating the movement of the reinforcing fibers, and randomizing the orientation of the reinforcing fibers, thereby forming a rib without strength anisotropy.

[0026] The SMC material preferably has an average fiber length of 10 to 25 mm and a fiber volume fraction (Vf) of 20 to 50%. By containing fibers in the above ranges, the SMC material can achieve both rib strength and prevention of filling defects.

[0027] By using the above SMC material, it is possible to form a high-strength main body reinforced with continuous fibers and a high-strength rib portion which, although having a shorter fiber length than the above continuous fibers, has a longer fiber length and a higher fiber volume content (Vf) than the ribs of conventional fiber-reinforced resin moldings.

[0028] Therefore, in addition to the main body portion itself being highly strong, the fiber-reinforced resin molding can obtain a high reinforcing effect due to the high-strength rib portion, making it possible to produce a highly rigid fiber-reinforced resin molding.

[0029] It is preferable that the ratio (h / w) of the height (h) of the SMC material placed directly above the rib forming groove to the width (w1) in the thickness direction of the rib forming groove is 1 or more and 1.2 or less, and it is also preferable that the ratio (w1 / w2) of the width (w1) of the SMC material to the width (w2) of the rib forming groove is 1 to 2.

[0030] This allows all of the SMC material to be forced into the rib forming groove by pressing in the molding process described below, and the SMC material will not remain in the main body portion, resulting in an insufficient amount of SMC material being filled into the rib forming groove.As a result, the injected thermosetting resin composition that does not contain reinforcing fibers will not enter the rib forming groove, preventing a decrease in the fiber volume content of the rib portion.

[0031] The SMC material can be placed not only on the rib forming grooves but also in areas where complex shapes, such as boss forming areas, are formed, where continuous fibers are difficult to insert.

[0032] The matrix resin of the SMC material can be a thermosetting resin, which melts and remains in a liquid state up to a certain temperature, and hardens through a chemical reaction when the temperature exceeds the certain temperature, and examples of such a resin include vinyl ester resin, unsaturated polyester resin, and epoxy resin.

[0033] The continuous fiber material can be used as a preform in which a sheet-like continuous fiber material such as a woven fabric, knitted fabric, or unidirectional material (UD material) is pre-shaped into a product shape. However, from the viewpoint of the impregnation of the thermosetting resin material in the molding process described below, it is preferable that the preform is a continuous fiber material that is not impregnated with resin.

[0034] The reinforcing fibers of the continuous fiber material or SMC material may be any of carbon fiber, glass fiber, aramid fiber, flax fiber, and kenaf, but carbon fiber is preferred from the viewpoint of weight reduction.

[0035] (Injection Step) The injection step is a step of injecting a thermosetting resin composition into a cavity in a closed mold. In the method for producing a fiber-reinforced resin molded product of the present invention, the mold is not completely closed in the injection step, but rather the mold is closed while leaving a press allowance (gap) in the molding step so as not to crush the SMC material.

[0036] The thermosetting resin composition is then injected into the cavity containing the SMC material and continuous fibers from the side opposite the SMC material side of the continuous fibers. This allows the flow of the thermosetting resin composition to be unimpeded by the SMC material, allowing it to permeate the entire cavity and improving impregnation of the continuous fibers.

[0037] The thermosetting resin composition contains a thermosetting resin and a curing agent for the thermosetting resin. As described above, the thermosetting resin is a resin that undergoes a chemical reaction and hardens when heated above a predetermined temperature. Generally, before the chemical reaction, the thermosetting resin has a lower viscosity than a thermoplastic resin and is easily impregnated into a reinforcing fiber material, thereby enabling the reinforcing fibers to be firmly bonded to each other and shortening the takt time until molding.

[0038] The thermosetting resin may be the same as the matrix resin of the SMC material, or may be a different resin type from the matrix resin of the SMC material, such as epoxy resin, vinyl ester resin, or unsaturated polyester resin. Of these, epoxy resin is preferred because it has small cure shrinkage and excellent dimensional stability.

[0039] Examples of curing agents for epoxy resins include polyaddition curing agents having two or more active hydrogens and catalytic curing agents containing cations or anions, and examples of curing agents for vinyl ester resins and unsaturated polyester resins include organic peroxides.

[0040] The curing agent may be a two-component type that is mixed with the thermosetting resin immediately before curing the thermosetting resin, or a capsule-type curing agent. The capsule-type curing agent is a curing agent in which the curing agent component is encapsulated in microcapsules, and the capsules are broken by pressure or heat, causing the curing agent component to ooze out, thereby curing the thermosetting resin. This makes it possible to adjust the timing of the start of curing, and is therefore preferred.

[0041] (Molding step) The molding step is a step in which the mold that was closed in the injection step except for a pressing allowance is completely closed, and the thermosetting resin composition, fiber material, and SMC material are pressed and heated to cure the thermosetting resin composition and form a fiber-reinforced resin molded body.

[0042] The thermosetting resin composition injected into the cavity is spread throughout the cavity and impregnated into the continuous fiber material by pressing or vacuuming. The SMC material placed above the rib-forming groove is warmed and softened in a heated mold, and then pressed into the rib-forming groove. The thermosetting resin composition and the matrix resin of the SMC material are then thermally cured to form a fiber-reinforced resin molding.

[0043] (Mold) As shown in FIG. 2, the mold used in the method for producing a fiber-reinforced resin molded article of the present invention has a movable mold and a fixed mold having the rib-forming grooves.

[0044] The fixed-type rib-forming groove preferably has an opening that is rounded and widens like a funnel. This allows the SMC material to easily enter the rib-forming groove and prevents it from remaining in the main body. In particular, if the slide plate (described later) is also rounded, the SMC material can easily enter the rib-forming groove.

[0045] Furthermore, as shown in the top of Figure 2, it is preferable that the fixed mold has a length greater than or equal to the length of the rib forming groove and is provided with slide plates that are arranged on both sides along the rib forming groove and can move forward and backward into the cavity.

[0046] This slide plate protrudes into the cavity during the placement process and injection process, and is pushed into the mold during the molding process.

[0047] As mentioned above, the SMC material is in the form of a sheet with a thickness of 1 to 5 mm, and in order to fill the rib-forming groove with the correct amount of SMC material, it may be necessary to stack multiple sheets of SMC material. When pressed in the molding process, if the stacked SMC material shifts sideways and collapses, as shown in Figure 3, it becomes difficult to press it into the rib-forming groove.

[0048] By placing the stacked SMC material between two slide plates protruding from the mold, the SMC material is supported by the slide plates and prevented from shifting sideways, as shown on the left side of Figure 4, so that the SMC material can be reliably pushed into the rib forming groove.

[0049] The slide plate is preferably supported by a spring, which has a minimum strength sufficient to lift the slide plate and a spring constant sufficient to not lift the continuous fiber on the slide plate.

[0050] Because the slide plate is supported by a spring with the above spring constant, the protruding height of the slide plate is the same as or slightly higher than the height of the stacked SMC material, and the heated and softened SMC material does not leak out of the slide plate, making it possible to push all of the SMC material into the rib-forming groove.

[0051] Furthermore, since the slide plate cannot lift the continuous fibers, the SMC material enters the rib-forming groove and retreats into the mold as the amount of SMC material on the rib-forming groove decreases. As a result, as shown in the enlarged view on the right of Figure 4, the continuous fibers are not tightly clamped between the slide plate and the movable mold, and this does not reduce the ability of the thermosetting resin composition to impregnate the continuous fibers.

[0052] After all of the SMC material placed on the rib forming groove has been pushed into the rib forming groove, the slide plate is completely retracted and stored within the mold and does not protrude into the cavity, so no marks are left by the slide plate on the fiber reinforced resin molded body and the appearance of the fiber reinforced resin molded body is not affected.

[0053] The spring supporting the slide plate can be further supported by a push-up pin, as shown in the bottom of Figure 2. This allows the spring to be set to push down to a position even lower than the surface of the mold where the main body is formed, forming a convex shape originating from the slide plate storage area in the fiber-reinforced resin molded body, and creating a shape that serves as a reference position for secondary processing such as bonding.

[0054] Furthermore, by connecting the push-up pins to an ejector plate and using them as an ejection mechanism for the fiber reinforced resin molded body, it is possible to suppress warping of the fiber reinforced resin molded body when it is removed from the mold.

[0055] It is preferable that the temperature of the rib-forming groove portion and the other portions of the mold are separately controlled.

[0056] The thermosetting resin composition is injected into the cavity in a liquid state, while the SMC material placed on the rib-forming groove is in a solid state and is heated in the mold to soften and then harden. As a result, as shown in Figure 5, there may be a discrepancy in the hardening timing between the thermosetting resin composition and the matrix resin of the SMC material.

[0057] For example, if the thermosetting resin composition hardens to form the main body and then the matrix resin of the SMC material hardens to form the rib, a joint that is not completely integrated between the main body and the rib may occur, resulting in a so-called cold joint between the main body and the rib, which significantly reduces the reinforcing effect of the rib.

[0058] This cold joint is likely to occur when the resin in the thermosetting resin composition and the matrix resin in the SMC material are of different resin types, or when their molecular weights or molecular structures are different.

[0059] By separately adjusting the temperature of the rib-forming groove portion and other portions, as shown by the arrows in Figure 5, the matrix resin of the SMC material can be softened early, and the resin of the thermosetting resin composition and the matrix resin of the SMC material can be hardened almost simultaneously after they have both been in a liquid state.

[0060] This makes it possible to integrally mold the main body and the rib portion while preventing the occurrence of cold joints, and also makes it possible to shorten the tact time.

[0061] <Fiber-reinforced resin molded article> The fiber-reinforced resin molded article of the present invention has a main body portion and a rib portion. A schematic cross-sectional view showing one example of the fiber-reinforced resin molded article of the present invention is shown in Fig. 6 .

[0062] The fiber-reinforced resin molding can be produced by the above-mentioned method for producing a fiber-reinforced resin molding. Accordingly, the main body portion includes continuous fibers and a thermosetting resin, and the rib portion is made of short fibers derived from an SMC material and having a fiber length shorter than that of the continuous fibers, and a thermosetting resin.

[0063] Furthermore, since the SMC material that forms the rib portion enters the rib forming grooves without excess or deficiency to form the rib portion, no SMC material remains in the main body portion, and as a result, the main body portion has an area that does not contain the short fibers in its in-plane direction, as shown in Figure 6.

[0064] Therefore, the fiber-reinforced resin molding of the present invention has high strength because the main body is reinforced with long continuous fibers.

[0065] Furthermore, since the rib portion is formed from a material derived from the SMC material, its fiber volume fraction (Vf) and average fiber length are the same as those of the SMC material, so the fiber volume fraction (Vf) of the rib portion is 20 to 50%, and the average fiber length is 10 to 25 mm, providing high strength.

[0066] Furthermore, by inserting the above-mentioned SMC material into the rib forming groove, it is possible to form a rib portion with a large height-to-thickness ratio (height / thickness), which makes it difficult to impregnate the reinforcing fibers with thermosetting resin using a press.

[0067] Specifically, by setting the ratio of the height to the thickness of the rib portion (height / thickness) to be between 20 and 50, the rib portion can be made thin and lightweight, yet tall and has a reinforcing effect, thereby achieving both lightness and strength.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0069] Using a mold having the shape shown in FIG. 2, an SMC material (matrix resin: vinyl ester resin, gel time 85 seconds @ 140°C, cure time 93 seconds @ 140°C) with a fiber volume content (Vf) of 45% was cut to an average fiber length of 25 mm and inserted into a rib-forming groove having a width (w2) of 2 mm and a depth of 100 mm.

[0070] Furthermore, the above SMC material was placed directly above the rib forming groove with varying ratios (h / w) of the height (h) to the width (w1) in the thickness direction of the rib forming groove, and continuous fiber material was placed on top of that.

[0071] The mold was closed, and the temperature of the rib-forming groove portion was set 20°C higher than the temperature of the other portions. Then, a two-component thermosetting resin composition (gel time 35 seconds @ 120°C, cure time 60 seconds @ 120°C) containing an epoxy resin and a curing agent was injected into the mold, and pressed to cure the thermosetting resin composition and the matrix resin of the SMC material, thereby obtaining a fiber-reinforced resin molded body.

[0072] <Evaluation> (Presence or absence of filling defects in the rib portion) Figure 7 shows the relationship between the ratio (h / w1) of the SMC material placed directly above the rib forming groove to the width (w1) in the thickness direction of the rib forming groove and the filling rate of the SMC material in the rib portion.

[0073] From FIG. 7, it can be seen that when the (h / w1) of the SMC material is 1.2 or less, the entire rib forming groove can be filled with the SMC material.

[0074] (Presence or absence of cold joints) The fiber reinforced resin moldings were observed to check for the presence or absence of any unintegrated joints between the main body portion and the rib portion. All fiber reinforced resin moldings were found to be completely integrated.

[0075] REFERENCE SIGNS LIST 1 fiber reinforced resin molded body 11 main body portion 111 continuous fiber 12 rib portion 121 short fiber 2 SMC material 3 continuous fiber material 4 movable mold 41 sealing member 5 fixed mold 51 rib forming groove 6 slide plate 61 spring 62 push-up pin 7 ejector pin 71 push-up pin 72 ejector plate 73 hydraulic cylinder

Claims

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4. A method for manufacturing a fiber-reinforced resin molded article comprising a main body and a rib portion, The process of placing fiber material inside the mold, An injection process in which a thermosetting resin composition is injected into a cavity, The process includes, in this order, a molding step of pressing the above-mentioned fiber material and the above-mentioned thermosetting resin composition, impregnating the fiber material with the thermosetting resin composition, and curing it. A method for manufacturing a fiber-reinforced resin molded article, characterized in that the above arrangement step comprises a process of locally arranging SMC material on the rib-forming grooves of a mold, and a process of arranging continuous fiber material over the SMC material and throughout the cavity forming the main body.

5. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the above arrangement step further includes a step of inserting the SMC material into the rib-forming groove of the mold before the step of placing the SMC material on the rib-forming groove.

6. The volume of the rib-forming groove in the mold and the volume of the SMC material placed in the rib-forming groove are the same. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the ratio (h / w) of the height (h) of the SMC material to the width (w) in the thickness direction of the rib forming groove is 1.2 or less, and the width (w) is 10 mm or more.

7. The above mold includes a slide plate that can move back and forth within the above cavity, The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the slide plate has a length greater than or equal to the length of the rib-forming groove and is arranged on both sides along the rib-forming groove.

8. The method for manufacturing a fiber-reinforced resin molded article according to claim 6, characterized in that the process of placing the SMC material on the rib-forming groove is the process of placing the SMC material between the slide plates.

9. The above slide plate is supported by a spring, Up to the injection process described above, it protrudes into the cavity described above. The method for manufacturing a fiber-reinforced resin molded article according to claim 6, characterized in that the article is pressed into the mold in the molding process described above.

10. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the temperature of the rib-forming groove portion and other portions of the mold are controlled separately.