Fiber-reinforced resin molded article and method for producing the fiber-reinforced resin molded article

Abstract

The present invention provides a fiber-reinforced resin molded article with high strength and excellent productivity, and a method for producing the fiber-reinforced resin molded article. [Solution] The fiber-reinforced resin molded body of the present invention comprises a thermosetting resin and a fiber material, and includes a main body portion and a rib portion. Furthermore, since the main body portion has a bead, the rib portion is erected on the ridge line on the back side of the bead, the fiber material of the main body portion is continuous fiber, and the fiber material of the rib portion is short fiber with a shorter fiber length than the continuous fiber, the reinforcement by the bead shape of the main body portion and the reinforcement by the rib standing on the ridge line combine to provide a fiber-reinforced resin molded article with high strength and excellent productivity, as well as a method for manufacturing the fiber-reinforced resin molded article.

Description

Technical Field

[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 capable of obtaining a reinforcing effect by ribs and a method for manufacturing the fiber-reinforced resin molded body.

Background Art

[0002] Since the fiber-reinforced resin molded body is excellent in mechanical strength and lighter than steel, it can significantly reduce the weight of a vehicle body or the like, and thus is used as an alternative member to a steel member.

[0003] In order to improve the mechanical performance of this fiber-reinforced resin molded body, it is preferable not only that the volume content ratio (Vf) of the reinforcing fiber is high but also that the fiber length is long. A fiber-reinforced resin molded body reinforced with continuous fibers is excellent in specific strength and specific rigidity.

[0004] In addition, the mechanical performance of the fiber-reinforced resin molded body can also be improved depending on its structure. Generally, the fiber-reinforced resin molded body can be reinforced by providing ribs or the like on the main body portion. When the height of the rib is increased, the second moment of area of the cross section becomes large, and weight reduction can be achieved.

[0005] Patent Document 1 discloses a method for manufacturing a fiber-reinforced resin molded body in which an SMC material is inserted and filled into a reinforcing rib forming groove of a mold, a prepreg is then placed thereon, and the SMC material and the prepreg are heated and pressurized to be integrally cured. According to this manufacturing method, the rib portion itself can be strengthened.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, there are limits to how high the ribs can be made, and it is difficult to pre-insert SMC material into the grooves that form the tall, thin ribs when manufacturing fiber-reinforced resin molded products, resulting in reduced productivity.

[0008] This invention has been made in view of the problems of the prior art, and its objective is to provide a fiber-reinforced resin molded article that has high strength and excellent productivity, and a method for producing the fiber-reinforced resin molded article. [Means for solving the problem]

[0009] The inventors of the present invention have conducted extensive research to achieve the above objectives and have found that the objectives can be achieved by using continuous fibers for the reinforcing fibers of the main body and short fibers for the reinforcing fibers of the rib portion, forming a bead on the main body, and erecting the rib portion on the ridge line on the back side thereof. This has led to the completion of the present invention.

[0010] In other words, the fiber-reinforced resin molded body of the present invention comprises a thermosetting resin and a fiber material, and includes a main body portion and a rib portion. Furthermore, the main body portion has a bead, the rib portion is erected on the ridge line on the back side of the bead, the fiber material of the main body portion is continuous fiber, and the fiber material of the rib portion is short fiber with a shorter fiber length than the continuous fiber.

[0011] Furthermore, the present invention provides a method for manufacturing a fiber-reinforced resin molded article, comprising, in this order: an arrangement step of arranging a fiber material in a mold; an application step of applying a thermosetting resin composition to the cavity; and a molding step of pressing the fiber material and the thermosetting resin composition together to impregnate the fiber material with the thermosetting resin composition and cure it. Furthermore, the above mold has a fixed mold with a rib-forming groove and an expanded portion on the main body side of the rib-forming groove that widens toward the main body, and a movable mold with a bead-forming projection that extends in the longitudinal direction of the rib-forming groove, and this bead-forming projection is provided at a location opposite to the expanded portion. The above arrangement process includes a process of partially placing SMC material in the mold and a process of placing continuous fiber material over the placed SMC material and forming the entire cavity that constitutes the main body. The process of partially arranging the material described above is characterized by the process of arranging the SMC material in the fixed extension section described above. [Effects of the Invention]

[0012] According to the present invention, the reinforcing fibers of the main body are made of continuous fibers, and the reinforcing fibers of the rib portion are made of short fibers, a bead is formed on the main body, and the rib portion is erected on the ridge line on the back side of the bead, thereby providing a fiber-reinforced resin molded article with high strength and excellent productivity, as well as a method for manufacturing the fiber-reinforced resin molded article. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing an example of a fiber-reinforced resin molded article of the present invention. [Figure 2] This figure illustrates the manufacturing process for the method of producing a fiber-reinforced resin molded article according to the present invention. [Figure 3] This diagram illustrates the arrangement of fiber materials during the arrangement process. [Figure 4] This diagram illustrates the state of filling the rib-forming grooves with SMC material. [Figure 5] This diagram illustrates the flow state of the short fibers in the rib section. [Figure 6] This figure shows the shapes of the fiber-reinforced resin molded articles produced in the examples and comparative examples. [Figure 7] These are load deflection diagrams of fiber-reinforced resin molded articles prepared in the examples and comparative examples. [Modes for carrying out the invention]

[0014] <Fiber-reinforced resin molded product> The fiber-reinforced resin molded article of the present invention contains a thermosetting resin and a fiber material, and as shown in Figure 1, comprises a main body portion and a rib portion, the rib portion being erected on the ridge line on the back side of the bead formed on the main body portion.

[0015] And the fibrous material of the main body part is continuous fiber, and the fibrous material of the rib part is short fiber with a fiber length shorter than that of the continuous fiber.

[0016] In addition to the main body part of the fiber-reinforced resin molded body of the present invention being reinforced with long continuous fibers, since this fiber forms beads while remaining continuous, the reinforcement by the continuous fiber and the reinforcement by the bead shape cooperate to improve the rigidity of the main body part itself.

[0017] Moreover, since the rib part is reinforced with short fibers, filling defects do not occur even if its height increases, and the fiber volume content (Vf) of the rib part can be increased, so the rigidity of the rib part itself is also high.

[0018] And in the fiber-reinforced resin molded body of the present invention, since the rib part stands on the back side ridge line of the bead of the main body part, the reinforcement by the bead shape of the main body part and the reinforcement by the rib standing on the ridge line cooperate to increase the second moment of area of the cross section of the fiber-reinforced resin molded body. Therefore, since the specific rigidity of the fiber-reinforced resin molded body of the present invention is extremely high, a significant weight reduction can be achieved.

[0019] <Manufacturing method of fiber-reinforced resin molded body> Next, the manufacturing method of the fiber-reinforced resin molded body of the present invention will be described in detail. The manufacturing method of the fiber-reinforced resin molded body of the present invention is a method for manufacturing the fiber-reinforced resin molded body, and is a method for manufacturing a fiber-reinforced resin molded body in which a rib part stands on the back side ridge line of a bead formed in the main body part using a thermosetting resin and a fibrous material.

[0020] As shown in FIG. 2, the manufacturing method of the present invention includes an arranging step of arranging a fibrous material in a mold, an applying step of applying a thermosetting resin composition to a cavity, and a molding step of pressing with the mold to impregnate the thermosetting resin composition into the fibrous material and curing it, in this order.

[0021] (Arranging step) The above arrangement process is a process of arranging fiber material inside the mold. Two types of fiber material are used as the fiber material: sheet molding compound (hereinafter sometimes simply referred to as "SMC material") and continuous fiber material, and these fiber materials are arranged inside the mold.

[0022] In the present invention, carbon fibers, glass fibers, and natural fibers such as hemp can be used as the fibers or continuous fibers that make up the SMC material.

[0023] Furthermore, the above-mentioned mold has a movable mold and a fixed mold. As shown in Figure 3, the fixed mold has a rib-forming groove and an expanded portion on the main body side of the rib-forming groove that widens toward the main body. The movable mold has a bead-forming protrusion formed at a location corresponding to the expanded portion of the rib-forming groove.

[0024] As shown in Figure 3, the arrangement process of the present invention comprises a process of partially arranging SMC material in the mold and a process of arranging continuous fiber material over the arranged SMC material and forming the main body cavity, wherein the partial arrangement process is a process of arranging SMC material in the expanded portion of the rib forming groove.

[0025] The above-mentioned SMC material is a thermosetting molded material obtained by laminating sheets of reinforcing fibers, impregnating them with a matrix resin composition, and processing them into a plate shape. In the present invention, the SMC material is cut to match the width of the expanded portion of the rib-forming groove so that its volume is equal to or slightly larger than the volume of the rib-forming groove.

[0026] Therefore, the length of the reinforcing fibers in the SMC material is shorter than the continuous fibers mentioned above, and longer than the thickness of the rib-forming groove, thus achieving both good filling of the rib-forming groove and improved rib strength.

[0027] The reinforcing fibers of the above-mentioned SMC material preferably have an average fiber length of 10 to 25 mm, and the fiber volume content (Vf) of the SMC material preferably has a value of 20 to 50%.

[0028] As described above, the SMC material is cut to match the width of the expansion section. By partially positioning it in the fixed expansion section, it is pressed into and filled into the rib-forming groove by the pressing process in the molding process described later, thereby forming a high-strength rib without filling defects.

[0029] In this invention, "partially arranged in the expanded portion" means excluding the arrangement of SMC material across the entire in-plane direction of the fixed type, including the expanded portion, and does not mean that it does not extend even slightly in the in-plane direction from the expanded portion.

[0030] Preferably, the slope of the extended portion is formed as a flat surface. If the inclined surface of the expansion section is formed as a flat surface, the main surface of the plate-shaped SMC material can be placed in contact with the flat surface of the expansion section, allowing heat from the mold to be efficiently transferred to the SMC material.

[0031] SMC material is formed by impregnating a laminate of sheets made of reinforcing fibers with a matrix resin composition. The matrix resin composition melts into a liquid state up to a predetermined temperature, and above that temperature, it undergoes a chemical reaction to form a thermosetting resin.

[0032] Examples of the matrix resin composition include monomers and oligomers that form vinyl ester resins, unsaturated polyester resins, epoxy resins, etc., as well as additives such as curing agents and thickeners.

[0033] As shown in Figure 4, when this SMC material softens due to the heat of the mold, the adhesive force between the sheets weakens, and the outermost sheet that makes up the lower main surface in contact with the plane of the expanded part slides down into the rib-forming groove along the inclined plane of the expanded part, and the other sheets are dragged along by the sheet that has slid down and sequentially slide down into the rib-forming groove.

[0034] Therefore, since the reinforcing fibers of the SMC material do not buckle due to pressing during the molding process, the reinforcing fibers do not get stuck midway through the rib-forming groove. This allows the reinforcing fibers to fill the rib-forming groove all the way to the bottom, and also increases the fiber volume content (Vf) of the rib-forming groove, thereby improving the strength of the rib itself.

[0035] In this invention, the above-mentioned SMC material is cut and used, so the cross-sectional shape of the SMC material is usually rectangular.

[0036] In such SMC material, if the angle between the plane constituting the inclined surface of the expanded section and the height direction of the rib-forming groove is 45°, that is, if the angle between the two inclined surfaces of the expanded section is 90°, then both the main surface and the cut surface of the SMC material come into contact with the entire inclined surface of the expanded section. As a result, heat from the mold is efficiently transferred to the SMC material, and the sheet slides easily into the rib-forming groove.

[0037] Furthermore, when an SMC material with a rectangular cross-section is placed in the expansion section, its upper side protrudes towards the main body section. This increases the stroke required for the movable mold to push the SMC material during the molding process, making it easier to push the SMC material into the rib-forming groove.

[0038] In this case, if the movable bead-forming protrusion has a plane at its apex that is perpendicular to the depth direction of the rib-forming groove, as shown in Figure 4, this plane presses the SMC material straight in the depth direction of the rib-forming groove, making it difficult for the SMC material to shift laterally. Therefore, it is possible to suppress the occurrence of appearance defects where the upper sheet of the SMC material in the lamination direction shifts laterally and protrudes laterally from the expanded portion towards the main body.

[0039] Furthermore, as shown in Figure 4, if the extension portion has a step at the connection point with the main body, even if the upper sheet of the SMC material in the lamination direction shifts laterally and is about to protrude from the rib forming groove, it will catch on the step, preventing the upper sheet from protruding towards the main body. This allows for the formation of a fiber-reinforced resin molded body with a good appearance in which the short fibers do not exist outside the bead of the main body. That is the case.

[0040] In the manufacturing method of the present invention, as described above, the SMC material slides down from one slope of the expanded portion into the rib-forming groove, and slides down less easily from the other slope. As a result, as shown in Figure 5, the flow direction of the short fibers is not uniform but anisotropic. In such a rib portion, the strength against lateral stress differs between the left and right sides.

[0041] When a fiber-reinforced resin molded body has multiple ribs, by alternating the arrangement direction of the SMC material so that the flow direction of the short fibers alternates between adjacent ribs, a high-strength fiber-reinforced resin molded body without strength anisotropy can be produced.

[0042] (Granting process) The above application process involves applying a thermosetting resin composition to the cavity of a mold in which fiber material is placed.

[0043] The thermosetting resin composition may be poured onto the continuous fibers arranged in the fixed mold with the movable mold open, or it may be injected into the cavity from the side of the continuous fibers, with the mold closed while leaving a press allowance (gap) in the molding process so as not to crush the SMC material.

[0044] By applying the thermosetting resin composition from the side of the continuous fibers, the flow of the thermosetting resin composition is not obstructed by the SMC material, allowing it to spread throughout the entire cavity and improving its impregnation into the continuous fibers.

[0045] The above thermosetting resin composition contains a curing agent in addition to the monomers and oligomers that constitute the thermosetting resin. Thermosetting resins, as described above, are resins that harden through a chemical reaction when a certain temperature is exceeded. Generally, before the chemical reaction occurs, they have a lower viscosity than thermoplastic resins and are easily impregnated into reinforcing fiber materials. This allows for strong bonding of reinforcing fibers and shortens the cycle time until molding.

[0046] As the thermosetting resin mentioned above, a resin similar to the matrix resin of the SMC material can be used, and the resin type may differ from that of the SMC material. Examples include epoxy resin, vinyl ester resin, and unsaturated polyester resin. Among these, epoxy resin is preferable because it exhibits low curing shrinkage and excellent dimensional stability.

[0047] Examples of curing agents for epoxy resins include polyaddition curing agents having two or more active hydrogen atoms, and catalytic curing agents containing cations or anions. Examples of curing agents for vinyl ester resins and unsaturated polyester resins include organic peroxides.

[0048] Furthermore, the curing agents mentioned above include two-component curing agents that are mixed with the thermosetting resin immediately before curing, and capsule-type curing agents. The capsule-type curing agent is a curing agent in which the curing agent component is encapsulated in microcapsules. The capsules are broken by pressure or heat, and the curing agent component seeps out, curing the thermosetting resin. This allows for adjustment of the curing start timing, making it a preferred choice.

[0049] (molding process) The molding process involves completely closing the mold, pressing and heating a fiber material impregnated with a thermosetting resin composition, and curing the thermosetting resin composition to form a fiber-reinforced resin molded body.

[0050] The thermosetting resin composition applied to the cavity is spread throughout the cavity and impregnated into the continuous fiber material by pressing and vacuuming. In addition, the SMC material placed in the fixed expansion section is heated and softened by a heated mold, and then pressed into the rib-forming groove.

[0051] When the mold is completely closed, if the gap between the fixed expansion portion and the movable bead-forming protrusion is the same as the thickness of the continuous fibers, the SMC material is blocked by the continuous fibers, preventing it from overflowing outside the bead of the main body, and preventing short fibers derived from the SMC material from overflowing onto the main body side outside the bead. As a result, a fiber-reinforced resin molded body with a good appearance can be formed in which the short fibers are not present outside the bead of the main body.

[0052] Then, by thermosetting the above-mentioned thermosetting resin composition and the matrix resin of the above-mentioned SMC material, the fiber-reinforced resin molded article of the present invention can be formed. [Examples]

[0053] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0054] [Examples] (Placement process) As shown in Figure 3, a fixed mold having a rib-forming groove with a width of 2 mm and a depth of 20 mm, and an expansion section with a clamping angle of 90° on the main body side of the rib-forming groove, and a movable mold having a bead-forming protrusion opposite the expansion section of the fixed mold were used. SMC materials were arranged with the orientation of adjacent SMC material sheets changed so that the main surface of the SMC material abuts against the plane of the expansion section, and then a continuous fiber material was placed on top of the SMC material.

[0055] The SMC material (matrix resin: vinyl ester resin, gel time 85 seconds @ 140°C, cure time 93 seconds @ 140°C, fiber volume content (Vf): 45%) was cut to an average fiber length of 25 mm before use.

[0056] (Granting process) A two-component thermosetting resin composition (gel time 35 seconds at 120°C, cure time 60 seconds at 120°C), consisting of epoxy resin and a hardener, was applied to the mold.

[0057] (molding process) The mold was closed and pressed to cure the thermosetting resin composition and the matrix resin of the SMC material, obtaining a fiber-reinforced resin molded body having the shape shown in Figure 6 and two parallel rib sections. The main body of this fiber-reinforced resin molded body is 150 mm x 150 mm, and the combined height of the bead and rib sections is 25 mm.

[0058] [Comparative Example] A fiber-reinforced resin molded body having two parallel rib sections was obtained in the same manner as in Example 1, except that a movable mold without a bead-forming protrusion was used.

[0059] <Rating> In the central part of the above fiber-reinforced resin molded body (between the two rib sections), the bottom surface area is 800 mm². 2 The failure mode was measured by applying load using a cylindrical indenter. The evaluation results are shown in Table 1, and the load deflection diagram is shown in Figure 7.

[0060] [Table 1]

[0061] From Table 1 and the graph in Figure 7, the fiber-reinforced resin molded article of the present invention, which has ribs erected on the ridge line on the back side of the bead, had a maximum load of 1.3 times or more and specific energy absorption of 9 times or more compared to the comparative fiber-reinforced resin molded article which had ribs but did not form ribs on the main body. Furthermore, while the continuous fibers delaminated in the comparative example, delamination did not occur in the example even when the continuous fibers themselves fractured, and it was confirmed that the strength improved dramatically as the fracture mode changed. [Explanation of Symbols]

[0062] 1. Main body 11 Bead 12 continuous fibers 2 Rib section 21 SMC material 22 sheets (short fibers) 3 Movable type 31 Bead-forming protrusion 4 Fixed type 41 Rib-forming groove 42 Expansion section 43 steps

Claims

1. A fiber-reinforced resin molded body comprising a thermosetting resin and a fiber material, and having a main body portion and a rib portion, The main body part described above has a bead, The above-mentioned rib portion is erected on the ridge line on the back side of the bead. The fiber material of the main body is a continuous fiber, A fiber-reinforced resin molded article characterized in that the fibrous material of the rib portion is short fiber with a shorter fiber length than the continuous fiber.

2. The above bead has multiple rib portions formed on the ridge line on the back side, The fiber-reinforced resin molded body according to 1, characterized in that the flow direction of the short fibers described above alternates between adjacent rib sections.

3. The fiber-reinforced resin molded body according to 1, characterized in that the short fibers described above are not present outside the bead of the main body.

4. A method for producing a fiber-reinforced resin molded article according to any one of the above claims 1 to 3, The process of placing fiber material inside the mold, A step of applying a thermosetting resin composition to the 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. The above mold has a fixed mold with a rib-forming groove and an expanded portion on the main body side of the rib-forming groove that widens toward the main body, and a movable mold with a bead-forming projection that extends in the longitudinal direction of the rib-forming groove, and this bead-forming projection is provided at a location opposite to the expanded portion. The above arrangement process includes a process of partially placing SMC material in the mold and a process of placing continuous fiber material over the placed SMC material and forming the entire cavity that constitutes the main body. A method for manufacturing a fiber-reinforced resin molded article, characterized in that the above-mentioned partial arrangement process is a process of arranging the above-mentioned SMC material in the above-mentioned fixed-type expansion portion.

5. The cross-sectional shape of the above SMC material is rectangular. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the angle between the two inclined surfaces constituting the above-mentioned extension is 90°.

6. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the movable bead-forming protrusion has a plane at its apex that is perpendicular to the depth direction of the rib-forming groove.

7. The method for manufacturing a fiber-reinforced resin molded article according to claim 4, characterized in that the extension portion has a step difference with the main body portion at the connection point with the main body portion.

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