Method for manufacturing molded article

Abstract

This method for manufacturing a molded body comprises: a preparation step for preparing a chopped material that contains reinforcing fibers and is cut into a prescribed outer shape; a disposing step for a disposing the chopped material in a mold; and a molding step for obtaining a molded body from the chopped material disposed in the mold, by molding the chopped material with heat and pressure. In the preparation step, the chopped material is prepared such that the chopped material includes: a first chopped material in which an orientation direction, which is the orientation of the reinforced fiber with reference to the outer shape of the chopped material, is a first direction; and a second chopped material in which the orientation direction is a second direction, which is different from the first direction, with reference to the outer shape.

Description

Manufacturing method of molded body

[0001] The present disclosure relates to a method for producing a molded body.

[0002] Patent Document 1 discloses a fiber-reinforced resin article including a unidirectional fiber-reinforced resin sheet and a plurality of chopped sheets located on at least one surface of the unidirectional fiber-reinforced resin sheet.

[0003] Japanese Patent Application Laid-Open No. 2022-173292

[0004] For example, to mold complex shapes using fiber-reinforced resins, molding methods using chopped material, which is made by finely chopping prepreg, a sheet of reinforcing fibers impregnated with resin, are sometimes considered. For example, when chopped material has a square outer shape and the fiber direction of the reinforcing fibers is parallel to the sides of the square, accidental variations in the fiber direction distribution may occur when the chopped material is laid out in a mold. As a result, the fiber direction distribution of the final molded product may also vary, which may cause variations in the mechanical properties of the molded product. This can make product design using chopped material difficult, limiting its applications.

[0005] This disclosure describes a method for manufacturing a molded body that reduces the probability of large variations in the mechanical properties of the molded product due to accidental variations in the distribution of fiber direction when chopped material is laid out in a mold.

[0006] A method for manufacturing a molded body according to one aspect of the present disclosure includes a preparation step of preparing chopped material containing reinforcing fibers and cut to a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure. In the preparation step, chopped material is prepared so as to include a first chopped material having a first orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material, and a second chopped material having a second orientation direction, different from the first direction, based on the outer shape.

[0007] According to some aspects of the present disclosure, it is possible to reduce the probability that accidental variations in the distribution of fiber direction when chopped material is laid out in a mold will result in large variations in the mechanical properties of the molded product.

[0008] FIG. 1 is a flowchart showing an example of a method for manufacturing a molded body. FIG. 2 is a plan view showing an example of a first chopped material and a second chopped material. FIGS. 3(a), 3(b), and 3(c) are views showing an example of a preparation step in a method for manufacturing a molded body. FIGS. 4(a), 4(b), and 4(c) are views showing another example of the preparation step in a method for manufacturing a molded body. FIG. 5(a) is a view showing an example of an arrangement step in a method for manufacturing a molded body. FIG. 5(b) is a view showing an example of a molding step in a method for manufacturing a molded body. FIG. 5(c) is a view showing an example of a molded body obtained by the method for manufacturing a molded body. FIG. 6(a) is a plan view showing an example of a test piece cut out from a molded body obtained by the method for manufacturing a molded body. FIG. 6(b) is a schematic diagram showing an in-plane tensile test using a test piece. FIG. 7 is a view showing the average value and coefficient of variation of the relative tensile strength based on the results of the in-plane tensile test. FIG. 8 is a view showing the average value and coefficient of variation of the relative elastic modulus based on the results of the in-plane tensile test. 9(a) and 9(b) are plan views showing an example of chopped material having a specific outer shape prepared so that the orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material, is one type.

[0009] A method for manufacturing a molded body according to one aspect of the present disclosure includes a preparation step of preparing chopped material containing reinforcing fibers and cut to a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure. In the preparation step, chopped material is prepared so as to include a first chopped material having a first orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material, and a second chopped material having a second orientation direction, different from the first direction, based on the outer shape.

[0010] In a method for manufacturing a molded body according to one aspect of the present disclosure, the chopped material prepared in the preparation step includes a first chopped material and a second chopped material. The orientation direction, which is the direction of the reinforcing fibers based on the external shape of the chopped material, is a first direction for the first chopped material and a second direction different from the first direction for the second chopped material. This makes it less likely that accidental variations in the distribution of fiber orientation will occur when the first chopped material and the second chopped material are laid in a mold. Therefore, it is possible to reduce the probability that accidental variations in the distribution of fiber orientation will occur when the chopped material is laid in a mold, which will result in large variations in the mechanical properties of the molded product.

[0011] In some embodiments, the outer shape is square or rectangular, and in the disposing step, the chopped material may be disposed in the mold in a ratio of approximately equal amounts of the first chopped material and the second chopped material. In this case, chopped material having a square or rectangular outer shape can be used as the first chopped material and the second chopped material, which is less likely to cause accidental variations in the fiber direction distribution when laid out in the mold.

[0012] In some embodiments, the outer shape may be a square, and the minimum length of one side of the square may be 5 mm. As the length of one side of the square of the chopped material increases, the phenomenon of the fiber direction accidentally shifting in a particular direction tends to occur more easily over a wider area within the mold when the chopped material is laid out in the mold. Therefore, by using chopped material with a minimum side length of 5 mm, the above phenomenon can be effectively suppressed.

[0013] In some embodiments, the chopped material may be prepared by cutting a laminated prepreg, in which a plurality of prepregs are laminated so as to have a plurality of orientation directions, into a predetermined outer shape. In this case, since the chopped material is prepared using the laminated prepreg, the first chopped material and the second chopped material can be efficiently cut out.

[0014] In some embodiments, the preparation step may involve cutting prepreg offcuts into a predetermined shape to prepare chopped material, which allows for effective use of the prepreg offcuts.

[0015] A method for manufacturing a molded body according to another aspect of the present disclosure includes a preparation step of preparing chopped material containing reinforcing fibers and cut to a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure, wherein the outer shape is a shape that includes an acute angle portion, an obtuse angle portion, or an arc portion, and does not include a parallelogram other than a rhombus, and in the preparation step, the chopped material is prepared so that there is only one orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material.

[0016] In a method for manufacturing a molded body according to another aspect of the present disclosure, the chopped material prepared in the preparation step has only one orientation direction, which is the direction of the reinforcing fibers relative to the external shape of the chopped material. The external shape of the chopped material includes an acute angle, an obtuse angle, or an arc, and excludes parallelograms other than rhombuses. This makes it easier for the reinforcing fibers to take multiple different directions relative to the mold, depending on the orientation of the acute angle, obtuse angle, or arc relative to the mold. Therefore, when the chopped material is laid out in the mold, accidental variations in the fiber orientation distribution are less likely to occur. Therefore, it is possible to reduce the probability of large variations in the mechanical properties of the molded product due to accidental variations in the fiber orientation distribution when the chopped material is laid out in the mold.

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] The method for producing a molded body according to this embodiment involves producing a molded body by using chopped material containing reinforcing fibers and cut into a predetermined outer shape, followed by molding with heating and pressure to obtain a molded body from a molded body. One example of a method for producing a molded body is a molding process using prepreg as an intermediate substrate for carbon fibers. By using chopped prepreg material, the high volumetric fiber content of the prepreg can be inherited, making it easy to obtain high mechanical properties and providing excellent formability and moldability despite the relatively long fiber length. Examples of molded bodies obtained by this method for producing a molded body include CFRP (Carbon Fiber Reinforced Plastics). Such molded bodies can be used, for example, for aircraft parts.

[0019] Prepreg is a material in which fibers are impregnated with a base material (matrix). The base material here is, for example, a thermoplastic resin. The thermoplastic resin may be at least one of polyetheretherketone, polyimide, polyetherimide, polyamide, polycarbonate, polyphenylene sulfide, etc. The reinforcing material here is, for example, carbon fiber.

[0020] The molding method for obtaining a molded body using chopped thermoplastic prepreg material is also called the CTT (Chopped Fiber Tape Reinforced Thermoplastics) method. CTT stands for carbon fiber tape reinforced thermoplastic resin molded body. One example of the CTT method is the BMC-CTT method, which is similar to BMC (Bulk Molding Compound). The BMC-CTT method involves preparing chopped material cut from thermoplastic prepreg, weighing it, laying it out in a mold, and molding it under heat and pressure to obtain a molded body. Another example of the CTT method is the SMC-CTT method, which is a type of SMC (Sheet Molding Compound). The SMC-CTT method involves forming chopped material cut from thermoplastic prepreg into sheets, weighing the cut sheets, stacking them, charging them into a mold, and molding them under heat and pressure to obtain a molded body. The method for producing a molded body according to this embodiment can be applied to both the BMC-CTT method and the SMC-CTT method. The method for producing a molded body according to this embodiment will be described below using the BMC-CTT method as an example.

[0021] The steps of the method for manufacturing a molded body according to this embodiment will be described with reference to Figures 1 to 5(c). Figure 1 is a flowchart showing an example of the method for manufacturing a molded body. As shown in Figure 1, a preparation step is performed in step S10. In the preparation step, a chopped material containing reinforcing fibers and cut into a predetermined outer shape is prepared by cutting a prepreg.

[0022] In the preparation step, for example, chopped material is prepared to include a first chopped material having a first orientation direction, which is the orientation of the reinforcing fibers based on the external shape of the chopped material, and a second chopped material having a second orientation direction, which is different from the first orientation direction based on the external shape. Figure 2 is a plan view showing an example of the first chopped material and the second chopped material. As shown in Figure 2, the predetermined external shape of the chopped material may be square or rectangular. In Figure 2, hatching on the square indicates the orientation of the reinforcing fibers.

[0023] The orientation direction is the direction of the reinforcing fibers based on the external shape of the chopped material. "The orientation of the reinforcing fibers based on the external shape of the chopped material" means the extension direction of the reinforcing fibers based on the extension direction of one side of the external shape of the chopped material. The orientation direction can be expressed as the angle between the extension direction of one side of the external shape of the chopped material and the extension direction of the reinforcing fibers. "One side of the external shape of the chopped material" in the orientation direction is not particularly limited, but may be, for example, one side along the longitudinal direction of a sheet-like prepreg pulled out from a roll.

[0024] In the example of Figure 2, the orientation direction is the angle between one of the four sides of the square facing downward and the extension direction of the reinforcing fibers, and is shown as 0° and 45°. For example, when comparing chopped material 10 with a 0° orientation direction and chopped material (not shown) rotated 90°, the external shapes match and the reinforcing fiber orientation appears to differ by the angle (here, 90°) rotated. In this case, the orientation directions are not treated separately as 0° and 90°, but as a single type of "0°". When comparing chopped material 11 with a 45° orientation direction and chopped material (not shown) rotated 90°, the orientation directions are not treated separately as 45° and 135°, but as a single type of "45°". In other words, when the outer shape of the chopped material is the same before and after rotation, the orientation direction before rotation and the orientation direction after rotation are represented by the orientation direction with the smaller absolute value of the angle between the two. Note that the comparison of the chopped material before and after rotation is based on rotation within the same plane, but the same treatment can be applied to the comparison of the chopped material before and after flipping it over.

[0025] In the example of Figure 2, the orientation direction of chopped material 10 (first chopped material) is, for example, a 0° direction (first direction) based on one of the four sides of the square that is on the bottom side of the page. The orientation direction of chopped material 11 (second chopped material) is, for example, a 45° direction (second direction) based on one of the four sides of the square that is on the bottom side of the page. The orientation direction of chopped material 10 is different from the orientation direction of chopped material 11.

[0026] The dimensions of the chopped material can be selected depending on the mechanical properties required for the molded product. This is because the fiber length in the chopped material is determined depending on the dimensions of the chopped material. In the chopped materials 10 and 11, the lower limit of the length of one side of the square may be 5 mm. For example, the length of one side of the square in the chopped materials 10 and 11 can be selected to be 5 mm, 10 mm, 15 mm, etc. The upper limit of the dimensions of the chopped material can be determined by physical constraints, such as the dimensions of the molded product or the mold.

[0027] 3(a), 3(b), and 3(c) are diagrams showing an example of a preparation step in a method for manufacturing a molded body. In the preparation steps shown in Fig. 3(a), 3(b), and 3(c), chopped materials 10 and 11 are prepared by cutting sheet-like prepregs, which are laminated with different reinforcing fiber orientations, in one cutting direction so as to have a predetermined outer shape.

[0028] As shown in Figure 3(a), for example, sheet-shaped prepregs 1 and 2 are used and laminated so that the reinforcing fibers are oriented in different directions. When prepreg 1 is unwound from a roll, the reinforcing fibers are oriented along a direction at 0° to the longitudinal direction. When prepreg 2 is unwound from a roll, the reinforcing fibers are oriented along a direction at 45° to the longitudinal direction. These prepregs 1 and 2 are laminated with their longitudinal directions aligned.

[0029] Next, as shown in Figure 3(b), the laminated prepregs 1 and 2 are cut in one cutting direction to obtain a predetermined outer shape. The one cutting direction means that the extension direction of the blade corresponding to the predetermined outer shape is not rotated relative to the prepreg in a planar view. With one cutting direction, the orientation of the predetermined outer shape relative to the prepreg is not rotated in a planar view, so the orientation direction of the chopped material corresponds to the orientation of the reinforcing fibers in each prepreg.

[0030] In the example of FIG. 3( b), prepregs 1 and 2 are stacked with their longitudinal directions aligned, and a square with the above-mentioned side length is cut out as the desired outer shape using a blade 3A parallel to the longitudinal direction of the prepregs 1 and 2 and a blade 3B perpendicular to the longitudinal direction of the prepregs 1 and 2. The orientation of the blades 3A and 3B is not rotated relative to the prepregs in a planar view. The cutting of the prepregs 1 and 2 with the blades 3A and 3B may be performed sequentially along one cut line at a time, or multiple cut lines may be performed at once. As a result, as shown in FIG. 3( c), chopped material 10 with an orientation direction of 0° and chopped material 11 with an orientation direction of 45° are obtained. Instead of cutting the prepregs 1 and 2 with the blades 3A and 3B, chopped material 10 and chopped material 11 may be obtained using, for example, a shredder configured for similar cutting.

[0031] 4(a), 4(b), and 4(c) are diagrams showing another example of the preparation step of the method for producing a molded body. In the preparation steps of Figures 4(a), 4(b), and 4(c), a sheet-like prepreg having a single reinforcing fiber orientation is cut in multiple cutting directions to obtain a predetermined outer shape, thereby preparing chopped material 10 having a first orientation direction and chopped material 11 having a second orientation direction.

[0032] As shown in Figure 4(a), for example, a sheet-like prepreg 1 drawn from a roll is used. In the prepreg 1 drawn from the roll, the orientation of the reinforcing fibers is along a direction of 0° relative to the longitudinal direction. In the state drawn from the roll, the prepreg 1 is a sheet-like prepreg with a single reinforcing fiber orientation.

[0033] In the example of FIG. 4( a), a prepreg 1 having a single reinforcing fiber orientation is cut in a first cutting direction. The first cutting direction refers to the extension direction of the blade corresponding to the predetermined outer shape set for the prepreg in a plan view so that the orientation direction is the first direction. For example, a prepreg 1 having a single reinforcing fiber orientation is cut into a square with the above-mentioned side length as the predetermined outer shape using a blade 3A parallel to the longitudinal direction of the prepreg 1 and a blade 3B perpendicular to the longitudinal direction of the prepreg 1. The prepreg 1 may be cut by the blades 3A and 3B sequentially along each cut line, or multiple cut lines at once. This results in a chopped material 10 with an orientation direction of 0°, as shown in FIG. 4( c).

[0034] In the example of FIG. 4(b), a prepreg 1 having a single reinforcing fiber orientation is cut in a second cutting direction. The second cutting direction refers to the extension direction of the blade corresponding to the predetermined outer shape set for the prepreg in a plan view so that the orientation direction is the second direction. The direction of blades 3C and 3D in FIG. 4(b) is the direction of blades 3A and 3B in FIG. 4(a) rotated 45° relative to the prepreg 1 in a plan view. For example, for a prepreg 1 having a single reinforcing fiber orientation, blade 3C is oriented at 45° relative to the longitudinal direction of the prepreg 1, and blade 3D is oriented at 135° relative to the longitudinal direction of the prepreg 1, to cut out a square with the above-mentioned side length as the predetermined outer shape. The cutting of the prepreg 1 with blades 3C and 3D may be performed sequentially along each cut line, or multiple cut lines may be performed at once. As a result, chopped material 11 having an orientation direction of 45° is obtained, as shown in FIG. 4(c).

[0035] In the preparation process, instead of directly cutting out the sheet-like prepreg pulled out from the roll, chopped material may be prepared by cutting out scraps of the sheet-like prepreg pulled out from the roll. Note that pulling out the prepreg from the roll is not essential in the preparation process. For example, already cut sheet-like prepreg may be obtained and used. The prepreg scraps are, for example, the portions remaining after a portion for producing another molded body is cut out from the sheet-like prepreg pulled out from the roll. The prepreg scraps may be, for example, die-cut materials. The die-cut materials have a shape corresponding to the outer shape of the other molded body in a plan view, and are components for forming a pre-molded laminate by stacking multiple die-cut materials. The prepreg scraps may also be the portions remaining after a portion for producing another molded body is cut out from the sheet-like prepreg pulled out from the roll with scissors or the like. By preparing chopped material from prepreg scraps, the portions remaining after the other die-cut materials are cut out are recycled rather than discarded, thereby enabling effective use of the prepreg scraps. The prepreg sheet scraps drawn from the roll here are scraps of laminated prepregs, in which multiple prepregs 1 and 2 are stacked to include multiple orientation directions, like the prepregs 1 and 2 described above. This allows chopped materials 10 and 11 including multiple orientation directions to be cut out from the laminated prepreg scraps. The prepreg scraps may also be the portion remaining after a portion for producing another molded body is cut out from a single unlaminated sheet of prepreg.

[0036] As shown in Figures 1 and 5(a), step S12 is an arrangement process in which the chopped material is arranged in a mold. In the arrangement process, the chopped materials 10 and 11 are weighed and spread out in the mold 4. In the arrangement process, for example, the chopped materials 10 and 11 may be arranged in the mold 4 with the chopped materials 10 and 11 in approximately equal amounts, and the chopped materials 10 and 11 may be leveled by hand and spread out in the mold 4. As a result, the chopped materials 10 and 11 become a pre-molded laminate. Note that "approximately equal amounts of chopped material 10 and chopped material 11" may refer to the weight ratio of the chopped materials 10 and 11 being approximately equal, or the volume ratio of the chopped materials 10 and 11 being approximately equal.

[0037] As shown in Figures 1, 5(b), and 5(c), step S14 is a molding process in which a molded body 7 is obtained from the chopped materials 10, 11. In the molding process, the molded body 7 is obtained from the chopped materials 10, 11 placed in a mold 4 by molding (e.g., press molding) involving heating and pressure. In the molding process, the molded body 7 is formed, for example, by sandwiching the pre-molded laminate between preheated upper mold 5 and lower mold 6 and press molding it. The molded body 7 obtained by the molded body manufacturing method is subjected to machining (e.g., trimming), painting, etc., as necessary. Preheating of the mold 4 is not essential in the molding process.

[0038] For example, in chopped material with a square outer shape, if the fiber direction of the reinforcing fibers is parallel to the sides of the square, accidental variations in the fiber direction distribution may occur when the chopped material is laid in a mold. As a result, variations in the fiber direction distribution of the final molded product may occur, resulting in variations in the mechanical properties (e.g., strength and modulus) of the molded product. This may make it difficult to design products using chopped material, limiting their applications. To achieve the intended fiber orientation distribution of the pre-molded laminate, measures to control the initial placement of the chopped material in the mold are considered, such as automatically feeding and placing the chopped material into the mold using a mechanical device, or manually adjusting the fiber direction distribution using a jig. However, there are problems such as increased costs for introducing the mechanical device and increased cycle time due to the increased time required to prepare the pre-molded laminate.

[0039] In this regard, according to the manufacturing method of a molded body as described above, the chopped materials prepared in the preparation step include chopped material 10 and chopped material 11. The orientation direction, which is the direction of the reinforcing fibers based on the external shape of chopped materials 10 and 11, is a 0° direction (first direction) based on one of the four sides of the square on the page, for chopped material 10, and a 45° direction (second direction different from the first direction) based on one of the four sides of the square on the page, for chopped material 11. This makes it less likely that accidental variations will occur in the distribution of the fiber direction when chopped materials 10 and 11 are laid out in a mold.

[0040] For example, when the chopped materials 10, 11 are laid out in the mold 4, the edges of the outer shapes of the chopped materials 10, 11 may be oriented along the inner wall surface of the mold 4, or the edges of the outer shapes of the chopped materials 10, 11 may come into contact with each other inside the mold 4 and become aligned. Even if the chopped materials 10, 11 behave in this way, for example, if the orientation directions of adjacent chopped materials 10, 11 are 0° and 45°, respectively, the bias in the orientation of the reinforcing fibers is reduced compared to when the orientation directions of adjacent chopped materials are the same. Therefore, it is possible to reduce the probability that accidental variations in the distribution of fiber orientations when the chopped materials 10, 11 are laid out in the mold, which will increase the variation in the mechanical properties (e.g., strength and elastic modulus) of the molded product.

[0041] Furthermore, it is possible to omit the introduction of a mechanical device or the like for controlling the initial placement of the chopped materials 10, 11 in the mold 4 so as to suppress accidental variations in the distribution of fiber directions when, for example, laying the chopped materials 10, 11 in the mold. It is possible to suppress the distribution of the orientation of the reinforcing fibers from being biased in a particular direction while maintaining the aspect ratio of the external shape of the chopped materials 10, 11 (for example, maintaining it as a square).

[0042] In the above-described method for manufacturing a molded body, the chopped materials 10, 11 have a square or rectangular outer shape, and in the arrangement step, the chopped materials 10, 11 are arranged in the mold in approximately equal amounts. This makes it possible to use chopped materials 10, 11 having a square or rectangular outer shape as chopped materials that are less likely to cause accidental variations in the distribution of fiber direction when laid out in the mold 4.

[0043] In the above-described method for manufacturing a molded body, the chopped material 10, 11 has a square outer shape, with the minimum side length of 5 mm. As the length of each square of the chopped material 10, 11 increases, the fiber orientation tends to be accidentally biased in a particular direction over a wider area within the mold when the chopped material 10, 11 is laid out in the mold. Therefore, by using chopped material 10, 11 with a minimum side length of 5 mm, the above phenomenon can be effectively suppressed.

[0044] Incidentally, the larger the dimensions of the chopped material, the longer the fiber length in the chopped material can be. Therefore, it becomes easier to improve the mechanical properties (e.g., tensile strength) of the molded product. However, the larger the dimensions of the chopped material, the more likely it is that when the chopped material is laid out in a mold, the phenomenon of the fiber direction accidentally being biased in a particular direction tends to occur over a wider area within the mold. Therefore, by applying the manufacturing method for a molded product of the present disclosure, the increase in the variation in the fiber direction distribution is suppressed, making the above phenomenon less likely to occur. As a result, there is more room to increase the dimensions of the chopped material, making it easier to improve the mechanical properties of the molded product.

[0045] In the above-described method for manufacturing a molded body, in the preparation step, a laminated prepreg, in which a plurality of prepregs are laminated so as to include a plurality of orientation directions, is cut into a predetermined outer shape to prepare chopped material. In this way, since the chopped material is prepared using the laminated prepreg, chopped material 10, 11 can be efficiently cut out.

[0046] In the above-described method for manufacturing a molded body, in the preparation step, prepreg offcuts may be cut into a predetermined outer shape to prepare chopped materials 10, 11. In this case, the prepreg offcuts can be effectively utilized.

[0047] Next, the effects of the method for manufacturing a molded body according to this embodiment will be further explained with reference to examples, but the method for manufacturing a molded body according to the present disclosure is not limited to the following examples.

[0048] [Example] Fig. 6(a) is a plan view showing an example of a test piece cut out from a molded body obtained by the molded body manufacturing method. Fig. 6(b) is a schematic diagram showing an in-plane tensile test using the test piece. In the example, a CFRP test piece as shown in Fig. 6(a) was produced. The test piece is a specimen for evaluating the mechanical properties (elastic modulus and tensile strength) of a molded body produced by the above-mentioned molded body manufacturing method.

[0049] Scraps of four layers of laminated prepreg, consisting of alternating layers of prepreg whose reinforcing fibers were oriented at 0° to the longitudinal direction and prepreg whose reinforcing fibers were oriented at 45° to the longitudinal direction, were used to cut out square first and second chopped materials with the specified external shapes. The laminated prepreg used to cut out the first and second chopped materials did not need to be scraps. The orientation direction of the first chopped material was 0°, and the orientation direction of the second chopped material was 45°. The blade direction and spacing were set so that the side length of the square was 5 mm in Example 1, 10 mm in Example 2, and 15 mm in Example 3. The cut-out material was sieved according to the side length of the square to extract squares with the corresponding side length, and other small pieces were separated. Any chopped material that remained stacked in two or more layers was removed. The first chopped material and the second chopped material were cut out from the laminated prepreg using portions containing approximately equal amounts of prepreg with an orientation direction of 0° and prepreg with an orientation direction of 45°.

[0050] The first chopped material and the second chopped material were weighed, placed in a mold, and evenly distributed by hand to form a pre-molded laminate. The first chopped material and the second chopped material placed in the mold were sandwiched between preheated upper and lower molds and press-molded with heat and pressure. After cooling, the molded body 7 was demolded to obtain a 2 mm thick molded body.

[0051] As shown in Fig. 6(a), eight test pieces 8 each having a width of 25 mm, a length of 180 mm, and a thickness of 2 mm were cut out from the molded body 7. For each of Examples 1 to 3, 16 test pieces 8 were cut out from two molded bodies 7. For each of Examples 1 to 3, an in-plane tensile test was performed in which the test pieces 8 were pulled in the longitudinal direction, as shown in Fig. 6(b).

[0052] For Comparative Examples 1 to 3, only the first chopped material was used without using the second chopped material, and the molded body 107 was produced in the same manner as in Examples 1 to 3, and 16 test pieces 108 were cut out from two molded bodies 107. In Example 1 and Comparative Example 1, the length of one side of a square was 5 mm, in Example 2 and Comparative Example 2, the length of one side of a square was 10 mm, and in Example 3 and Comparative Example 3, the length of one side of a square was 15 mm. For each of Comparative Examples 1 to 3, an in-plane tensile test was performed in which the test piece 108 was pulled in the longitudinal direction, as shown in FIG. 6(b).

[0053] In the in-plane tensile test, the elastic modulus and tensile strength were calculated from the measured values ​​of load, strain, etc. for test pieces 8 and 108 of the chopped material of the same size. For each of Examples 1 to 3, the average values ​​of the relative elastic modulus and relative tensile strength and the coefficients of variation of the relative elastic modulus and relative tensile strength were determined for 16 test pieces 8. For each of Comparative Examples 1 to 3, the average values ​​of the relative elastic modulus and relative tensile strength and the coefficients of variation of the relative elastic modulus and relative tensile strength were determined for 16 test pieces 108.

[0054] The elastic modulus was measured by drawing a graph with tensile stress on the vertical axis and strain on the horizontal axis, and the slope of the linear approximation in the strain range of 0.1% to 0.3% was used. The tensile strength was the maximum tensile stress. The tensile stress was calculated by dividing the tensile load (testing machine load) of the tensile testing machine by the initial cross-sectional area of ​​the test piece. The strain was calculated by dividing the elongation between the gauge points measured with a video extensometer (gauge length: 50 mm) by the initial gauge point distance. The coefficient of variation [%] of relative tensile strength was calculated by dividing the standard deviation of the tensile strength [MPa] by the average value of the tensile strength [MPa] and multiplying the result by 100. The coefficient of variation [%] of the relative elastic modulus was calculated by dividing the standard deviation of the elastic modulus [GPa] by the average value of the elastic modulus [GPa] and multiplying the result by 100.

[0055] 7 is a diagram showing the average value and coefficient of variation of the relative tensile strength based on the results of the in-plane tensile test. In Fig. 7, the average value of the tensile strength (relative tensile strength) based on the average tensile strength of Example 2 is shown as a bar graph on the left vertical axis, and the coefficient of variation of the relative tensile strength is shown as a plot on the right vertical axis. In Fig. 7, the upper end of the error bars for the Example and Comparative Example indicate the maximum value among the relative tensile strengths, and the lower end indicates the minimum value among the relative tensile strengths.

[0056] 7, when comparing the coefficient of variation of the relative tensile strength between Example 2 and Comparative Example 2, and between Example 3 and Comparative Example 3, Example 2 is smaller than Comparative Example 2, and Example 3 is smaller than Comparative Example 3. From this, it was found that the variation in tensile strength was reduced by mixing chopped material with orientation directions of 0° and 45°. The reason for this is presumably that, for example, even if the edge portion of the outer shape of the chopped material is aligned with the inner wall surface of the mold, the fiber direction is less likely to be biased in the direction of the edge of the outer shape of the chopped material, thereby reducing the variation in the mechanical properties of the molded body 7.

[0057] When the coefficient of variation of the relative tensile strength is compared between Example 1 and Comparative Example 1, Comparative Example 1 was equal to or less than Example 1. From this, it is presumed that when the length of one side of the square outer shape of the chopped material is 5 mm, the small outer shape of the chopped material makes it difficult to manifest the influence of the fiber direction of the chopped material, and the variation in the mechanical properties of the molded bodies 7, 107 is small in both Example 1 and Comparative Example 1.

[0058] In addition, the average value of the relative tensile strength was smaller when comparing Comparative Example 2 to Example 2, and Comparative Example 3 to Example 3. The reason why the average value of the relative tensile strength was large in Comparative Examples 2 and 3 is presumed to be that, for example, the sides of the outer shape of the chopped material are aligned with the inner wall surface of the mold, so that the fiber direction along the tensile direction becomes dominant in test piece 108, increasing the relative tensile strength and raising the average value. Therefore, the fact that the average value of the relative tensile strength in Examples 2 and 3 is smaller than that of Comparative Examples 2 and 3 means that there are many test pieces 8 in Examples 2 and 3 whose relative tensile strength is close to the average value, and is presumed not to simply mean a decrease in relative tensile strength.

[0059] 8 is a diagram showing the average value and coefficient of variation of the relative elastic modulus based on the results of the in-plane tensile test. In Fig. 8, the average value of the elastic modulus (relative elastic modulus) based on the average value of the elastic modulus of Example 2 is shown as a bar graph on the left vertical axis, and the coefficient of variation of the relative elastic modulus is shown as a plot on the right vertical axis. In Fig. 8, the error bars for the Example and Comparative Example each indicate the maximum value of the relative elastic modulus at the top and the minimum value at the bottom.

[0060] 8, when comparing the coefficient of variation of the relative elastic modulus between Example 1 and Comparative Example 1, and between Example 3 and Comparative Example 3, Example 1 was smaller than Comparative Example 1, and Example 3 was smaller than Comparative Example 3. From this, it was found that the variation in the elastic modulus was reduced by mixing approximately equal amounts of chopped material with orientation directions of 0° and 45°. The reason for this is presumably that, for example, even if the edge portions of the outer shape of the chopped material are aligned with the inner wall surface of the mold, the fiber direction is less likely to be biased in the direction of the edge portions of the outer shape of the chopped material, thereby reducing the variation in the mechanical properties of the molded body 7.

[0061] Incidentally, the coefficient of variation of the relative modulus of elasticity increased when comparing Comparative Example 2 with Example 2. It is possible that the coefficient of variation of the relative modulus of elasticity in Comparative Example 2 was accidentally small. For example, in Comparative Example 2, the number of test pieces 108 whose fiber direction was along the tensile direction was close to 16, and the fiber direction along the tensile direction in test piece 108 became particularly dominant, which may have resulted in an accidentally small calculated coefficient of variation of the relative modulus of elasticity. In this case, if the significant bias is eliminated by retesting, for example, by preparing additional molded bodies 7 and 107 and further increasing the number of test pieces 8 and 108, it is considered that there is room to reduce the probability of the coefficient of variation (variation) of the relative modulus of elasticity increasing by mixing approximately equal amounts of chopped materials with orientation directions of 0° and 45°, even when one side of the square is 10 mm.

[0062] [Modifications] The present disclosure is not limited to the above-described embodiments and examples.

[0063] In the above-described embodiment, the outer shape of the chopped materials 10, 11 is a square, for example. However, as another example, it may be a rectangular (oblong) shape.

[0064] In the above-described embodiment, the orientation directions when the chopped material includes the first chopped material and the second chopped material are exemplified as 0° and 45°, but are not limited to these. For example, angles such as 30° and 60° are also acceptable. Furthermore, the orientation direction is not limited to the first and second directions. In addition to the first chopped material and the second chopped material, chopped material may be prepared so as to include a third chopped material whose orientation direction is a third direction different from the first and second directions. Similarly, chopped material may be prepared so as to include a fourth chopped material, a fifth chopped material, etc.

[0065] In the above-described embodiment and modified example, the orientation direction, which is the orientation of the reinforcing fibers based on the external shape of the chopped material, is two or more different directions. However, this is not limited to these examples. In the present disclosure, as long as the external shape of the chopped material is a specific shape, there may be only one orientation direction based on the external shape of the chopped material. The specific shape is a shape that includes an acute angle, an obtuse angle, or an arc, and does not include a parallelogram other than a rhombus. For chopped material with this external shape, the preparation process may involve preparing the chopped material so that there is only one orientation direction, which is the orientation of the reinforcing fibers based on the external shape of the chopped material. Figures 9(a) and 9(b) are plan views showing an example of chopped material with a specific external shape prepared so that there is only one orientation direction, which is the orientation of the reinforcing fibers based on the external shape of the chopped material. As shown in Figure 9(a), the specific external shape of the chopped material 12 may be, for example, a circle having an arc portion 12a. The arc portion 12a is a curved portion of a circle. The arc portion 12a may be a curved portion corresponding to any section of the circle. As shown in Fig. 9(b) , the specific outer shape of the chopped material 13 may be a rhombus. As an example, the rhombus has an acute angle portion 13a and an obtuse angle portion 13b.

[0066] Here, "there is only one type of orientation direction, which is the direction of the reinforcing fibers based on the external shape of the chopped material" means that when chopped material 12 and chopped material 13 are rotated or turned over in a plan view, the external shapes and the orientation of the reinforcing fibers match. In this case, the orientation direction is treated as being one type. When chopped material such as chopped material 12 and chopped material 13 is used, the external shape includes an acute angle portion 13a, an obtuse angle portion 13b, or an arc portion 12a, so that, for example, the acute angle portion 13a, the obtuse angle portion 13b, or the arc portion 12a can take multiple directions along the inner wall surface of the mold.

[0067] For example, when the apex of the acute-angled portion 13a abuts the inner wall surface of the mold, rotation around the apex of the acute-angled portion 13a tends to result in a variety of orientations of the reinforcing fibers, even if there is only one orientation direction, depending on the rotation around the apex of the acute-angled portion 13a, compared to a square or rectangular shape having only right-angled portions. This also applies to when the apex of the obtuse-angled portion 13b abuts the inner wall surface of the mold and when any point on the arc portion 12a abuts the inner wall surface of the mold. The same is also true when the acute-angled portion 13a, the obtuse-angled portion 13b, or the arc portion 12a does not abut the inner wall surface of the mold, for example, when the arc portions 12a of adjacent chopped material 12 abut each other, when one side of adjacent chopped material 13 abuts the acute-angled portion 13a of another chopped material 13, or when one side of adjacent chopped material 13 abuts the obtuse-angled portion 13b of another chopped material 13. Therefore, the orientation of chopped material 12 and chopped material 13 relative to the inner wall surface of the mold becomes diverse, and the orientation of the reinforcing fibers is less likely to become biased compared to when rectangular chopped material is used, for example, even within a rectangular shape where the orientation of the reinforcing fibers is only one type in the longitudinal direction.

[0068] Furthermore, in chopped material 13 having a diamond-shaped outer shape and a single orientation direction of 0°, the fiber length can be uniform. For example, in chopped material having a rectangular or square outer shape and two or more orientation directions, the fiber length of the reinforcing fibers in the outer shape of the chopped material may vary between long and short portions depending on the orientation direction. Specifically, in rectangular or square chopped material, if the orientation direction is 0°, the fiber length is equal to one side of the rectangle or square. However, if the orientation direction is parallel to the diagonal, the fiber length becomes longer the closer to the diagonal of the rectangle or square, and shorter the farther from the diagonal of the rectangle or square. In contrast, in chopped material 13 having a diamond-shaped outer shape and an orientation direction parallel to one side of the diamond, the fiber length of the reinforcing fibers in the outer shape is uniform, equal to one side of the diamond, and no long or short portions occur. In this way, by using chopped material 13 having a diamond-shaped outer shape and an orientation direction parallel to one side of the diamond, it is possible to omit the process of mixing chopped material with two or more different orientation directions when diversifying the orientation direction of the reinforcing fibers in the mold, and it is possible to prevent the fiber length of the reinforcing fibers in the outer shape of the chopped material from being partially shortened depending on the orientation direction. Furthermore, since the outer shape is diamond-shaped, all four sides are of equal length, so the synergistic effect of this uniform fiber length and the effect of preventing bias in the orientation of the reinforcing fibers can further suppress variation in the mechanical properties of the molded body.

[0069] As described above, in the manufacturing method for a molded body using chopped materials 12, 13, the chopped materials 12, 13 prepared in the preparation step have only one orientation direction, which is the direction of the reinforcing fibers based on the external shape of the chopped materials 12, 13. The external shape of the chopped materials 12, 13 includes an acute angle portion 13a, an obtuse angle portion 13b, or an arc portion 12a, and excludes parallelograms other than rhombuses. This makes it easier for the reinforcing fibers to take multiple different directions based on the orientation of the acute angle portion 13a, the obtuse angle portion 13b, or the arc portion 12a relative to the mold. Therefore, when the chopped materials 12, 13 are laid out in the mold, accidental variations in the fiber direction distribution are less likely to occur. Therefore, the probability of large variations in the mechanical properties of the molded product due to accidental variations in the fiber direction distribution when the chopped materials 12, 13 are laid out in the mold can be reduced.

[0070] The outer shape including an acute angle portion is not limited to a rhombus. For example, it may be a triangle, or a star shape such as a five-pointed star or a twelve-pointed star. The outer shape including an obtuse angle portion is not limited to a rhombus. For example, it may be a polygon other than a parallelogram, such as a regular pentagon or a regular octagon. The outer shape including an arc portion is not limited to a circle. For example, it may be a semicircle or a fan shape. The arc portion may be a curved portion of a semicircle or a fan shape. The arc portion may be a curved portion of a shape with curved corners like a puzzle piece.

[0071] Although a thermoplastic resin is exemplified as the base material (matrix), a thermosetting resin may also be used as the base material. Examples of thermosetting resins include epoxy, phenol, vinyl ester, unsaturated polyester, cyanate ester, BMI, and polyimide. Furthermore, carbon, ceramics, and metals may also be used as the base material. Furthermore, while carbon fiber is exemplified as the reinforcing material, this is not limiting. For example, inorganic fibers such as glass fiber, boron fiber, and silicon carbide fiber may also be used, or organic fibers such as aramid fiber, polyarylate fiber, PBO fiber, and high-strength polyethylene fiber may also be used.

[0072] Although the manufacturing method for a molded body has been described using the BMC-CTT method as an example, the manufacturing method for a molded body can also be applied to the SMC-CTT method. In this case, for example, chopped material is placed and stacked on a surface plate or the like manually or using a mechanical device, and the chopped material is welded together to form a pre-laminate, which is then cut into a predetermined shape, stacked, and placed in a mold to form a pre-molded laminate.

[0073] As described above, the present disclosure can reduce the probability of significant variation in the mechanical properties of molded products due to accidental variations in the fiber direction distribution when chopped material is laid in a mold. This prevents the design of products using chopped material from becoming difficult and prevents the use of chopped material from becoming limited. In other words, it is possible to expand the range of applications for products using chopped material. Furthermore, when chopped material is prepared by cutting prepreg scraps into a predetermined shape, it is possible to effectively utilize the prepreg scraps. This can contribute to Goal 12 of the Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."

[0074] The constituent elements of various aspects of the present disclosure are described below. [1] A method for producing a molded body, comprising: a preparation step of preparing chopped material containing reinforcing fibers and cut into a predetermined outer shape; an arrangement step of placing the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material placed in the mold by molding with heat and pressure, wherein the preparation step prepares the chopped material to include first chopped material having a first orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material, and second chopped material having a second orientation direction, which is different from the first direction based on the outer shape. [2] The outer shape is square or rectangular, and the arrangement step places the chopped material in the mold in a ratio of the first chopped material to the second chopped material so that the ratio is approximately equal. [3] The method for producing a molded body described in [1], wherein the outer shape is square, and the lower limit of the length of one side of the square is 5 mm. [4] The method for manufacturing a molded body according to any one of [1] to [3], wherein in the preparation step, the chopped material is prepared by cutting a laminated prepreg, in which a plurality of prepregs are laminated so as to include a plurality of orientation directions, into the predetermined outer shape. [5] The method for manufacturing a molded body according to any one of [1] to [4], wherein in the preparation step, the chopped material is prepared by cutting an offcut of a prepreg into the predetermined outer shape. [6] A method for manufacturing a molded body, comprising: a preparation step of preparing chopped material containing reinforcing fibers and cut out to a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure, wherein the outer shape is a shape that includes an acute angle portion, an obtuse angle portion, or a circular arc portion, and parallelograms other than rhombuses are excluded, and in the preparation step, the chopped material is prepared so that there is only one orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material.

[0075] REFERENCE SIGNS LIST 1, 2 Prepreg 4 Mold 7 Molded body 10 Chopped material (first chopped material) 11 Chopped material (second chopped material) 12, 13 Chopped material 12a Arc portion 13a Acute angle portion 13b Obtuse angle portion

Claims

1. A method for manufacturing a molded body, comprising: a preparation step of preparing chopped material containing reinforcing fibers and cut to a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure, wherein in the preparation step, the chopped material is prepared so as to include first chopped material in which the orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material, is a first direction, and second chopped material in which the orientation direction, based on the outer shape, is a second direction different from the first direction.

2. A method for manufacturing a molded body as described in claim 1, wherein the outer shape is square or rectangular, and in the placing step, the chopped material is placed in a mold in a ratio of approximately equal amounts of the first chopped material and the second chopped material.

3. The method for producing a molded product according to claim 1, wherein the outer shape is a square, and the lower limit of the length of one side of the square is 5 mm.

4. A method for manufacturing a molded body as described in claim 1 or 2, wherein in the preparation step, the chopped material is prepared by cutting a laminated prepreg, in which multiple prepregs are stacked so as to include multiple orientation directions, into the specified outer shape.

5. A method for manufacturing a molded body according to claim 1 or 2, wherein in the preparation step, the chopped material is prepared by cutting prepreg scraps into the predetermined outer shape.

6. A method for manufacturing a molded body, comprising: a preparation step of preparing chopped material containing reinforcing fibers and cut into a predetermined outer shape; an arrangement step of arranging the chopped material in a mold; and a molding step of obtaining a molded body from the chopped material arranged in the mold by molding involving heating and pressure, wherein the outer shape is a shape that includes an acute angle portion, an obtuse angle portion, or a circular arc portion, and parallelograms other than rhombuses are excluded, and in the preparation step, the chopped material is prepared so that there is only one orientation direction, which is the direction of the reinforcing fibers based on the outer shape of the chopped material.

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