Fiber-reinforced resin sheets, fiber-reinforced composites and molded articles

Abstract

The fiber-reinforced resin sheet comprises: a thermoplastic resin film; and a plurality of reinforcing fibers, obtained by splitting fiber bundles of the reinforcing fibers and laminating them on both sides of the resin film in a state of being oriented in the same direction. The thickness of the resin film is 5 μm or more and 15 μm or less, and the area weight of the reinforcing fibers is 25 g / m². 2 Above 60g / m 2 The following conditions apply: the volume content of reinforcing fibers is 60% or more and 75% or less, and the thickness of the fiber-reinforced resin sheet is 30μm or more and 65μm or less.

Description

Technical Field

[0001] The present invention relates to fiber-reinforced resin sheets comprising a resin film and reinforcing fibers, fiber-reinforced composite materials formed using the fiber-reinforced resin sheets, and molded articles formed using the fiber-reinforced composite materials. Background Technology

[0002] As an example of fiber-reinforced resin sheets, a sheet as described in Patent Document 1 is known. The fiber-reinforced resin sheet (thermoplastic carbon fiber prepreg) of Patent Document 1 comprises split sheet-like carbon fibers and a pair of thermoplastic resin films overlapping both sides (one side and the other side) of the carbon fibers. This structure of fiber-reinforced resin sheet is manufactured by sandwiching the carbon fibers between the pair of resin films and applying pressure and heat. Specifically, for the fiber-reinforced resin sheet in Patent Document 1, there is a process of feeding the carbon fibers while they are split through a feed roller; and a process of overlapping thermoplastic resin films on both sides of the fed carbon fibers, pressing the resin films with rollers while heating them with a plate heater. This allows the resin films to soften and impregnate into the carbon fibers, resulting in the fiber-reinforced resin sheet with the aforementioned structure.

[0003] In the aforementioned Patent Document 1, the thickness of the resin film is preferably set to 8–55 μm. The reason for this is that the carbon fiber content (Vf value) in the fiber-reinforced resin sheet can be increased to 50–60%, thereby achieving high strength.

[0004] However, in Patent Document 1, since resin films are disposed on both sides of the carbon fiber (the carbon fiber is sandwiched between a pair of resin films), the resin content is inherently higher. In other words, to actually increase the carbon fiber content to 50-60% in Patent Document 1, a large amount of carbon fiber needs to be stacked between the pair of resin films. Therefore, even if the resin film is pressurized and heated during molding, the softened resin film may not fully penetrate the interior of the carbon fiber. If the resin film is not sufficiently impregnated, defects such as loose carbon fiber after molding may occur.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2020-122137 Summary of the Invention

[0008] The present invention was made in view of the above circumstances, and its object is to provide a fiber-reinforced resin sheet with a high content of reinforcing fibers and less prone to forming defects, thereby improving the mechanical properties of fiber-reinforced composite materials or molded articles.

[0009] As a technical solution to the above-mentioned problems, one aspect of the present invention relates to a fiber-reinforced resin sheet having a thickness of 30 μm or more and 65 μm or less, comprising: a thermoplastic resin film; and a plurality of reinforcing fibers obtained by splitting fiber bundles of the reinforcing fibers and stacking them on both sides of the resin film in a state of orientation in the same direction, wherein the thickness of the resin film is 5 μm or more and 15 μm or less, and the unit area weight of the reinforcing fibers is 25 g / m². 2 Above 60g / m 2 Hereinafter, the volume content of the reinforcing fiber is 60% or more and 75% or less. Attached Figure Description

[0010] Figure 1 This is a process diagram illustrating the method for manufacturing a molded article according to the first embodiment of the present invention.

[0011] Figure 2 This is a diagram showing the schematic structure of an apparatus for manufacturing fiber-reinforced resin sheets.

[0012] Figure 3 This is a diagram illustrating a method for forming fiber-reinforced composite materials by laminating fiber-reinforced resin sheets.

[0013] Figure 4A This is a cross-sectional view used to illustrate a method of forming molded articles from fiber-reinforced composite materials using a hot press.

[0014] Figure 4B It is a cross-sectional view showing the state of the hot press during mold closing.

[0015] Figure 4C This is a cross-sectional view showing the state after the hot press mold closing is complete.

[0016] Figure 5 This is a process diagram illustrating a method for manufacturing a molded article according to the second embodiment of the present invention.

[0017] Figure 6 This is a diagram illustrating a method for cutting short pieces of material from fiber-reinforced resin sheets.

[0018] Figure 7 This is a diagram illustrating a method for forming fiber-reinforced composite materials by laminating chopped materials.

[0019] Figure 8 This is a table showing the characteristics of embodiments of fiber-reinforced resin sheets.

[0020] Figure 9 This is a table showing the characteristics of comparative examples of fiber-reinforced resin sheets.

[0021] Figure 10 This is a table showing the characteristics of examples and comparative examples of fiber-reinforced composite materials. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0023] (1) First implementation method

[0024] Figure 1 This refers to the molded article 30 (representing the manufacture of the first embodiment of the present invention) Figure 4C The process diagram of the method is shown. In this first embodiment, the molded article 30 is a molded article (composite molded article) made of synthetic resin containing reinforcing fibers, through... Figure 1 The product is manufactured through each of the processes shown (S1 to S3). That is, the molded article 30 of the first embodiment is made from a resin sheet 1 containing molded fiber reinforced resin. Figure 2 The process S1 involves laminating fiber-reinforced resin sheets 1 to form fiber-reinforced composite material 10. Figure 3 The process S2 involves pressing the fiber-reinforced composite material 10 to form the molded article 30. Figure 4C It is manufactured through process S3. The details of each process are described below.

[0025] (Forming of fiber-reinforced resin sheets)

[0026] Process S1 is forming Figure 2 The sheet forming process of the fiber-reinforced resin sheet 1 shown is described. The fiber-reinforced resin sheet 1 formed by this sheet forming process S1 is a unidirectional sheet (FRTP sheet) in which multiple reinforcing fibers 3 are impregnated in a thermoplastic resin film 2.

[0027] As the reinforcing fiber 3, carbon fiber, glass fiber, aramid fiber, ceramic fiber, etc. can be used. Among them, carbon fiber is beneficial for improving the strength and corrosion resistance of the molded product. As the carbon fiber, PAN (polyacrylonitrile) based carbon fiber with particularly high strength is preferred.

[0028] Examples of thermoplastic resins used as the material for resin film 2, i.e., the matrix resin of fiber-reinforced resin sheet 1, include polyamides (especially PA6 and PA9T), polyolefins, polyesters, polyacetals, polyphenylene sulfide, polycarbonate, acrylate resins, acrylonitrile-butadiene-styrene copolymer (ABS), polyamide-imide, polysulfone, polyphenylene sulfone, polyetherimide, polyethersulfone, polyetheretherketone, polyetherketoneketone, polyimide, polyarylate, fluoropolymers, liquid crystal polymers, and thermoplastic epoxy resins. Furthermore, polymer alloys that blend two or more of these thermoplastic resins can also be used as the material for resin film 2.

[0029] The resin film 2 is an extremely thin sheet (film) component with a certain thickness, formed from a thermoplastic resin. This resin film 2 is formed, for example, by extruding a thermoplastic resin. Furthermore, the thickness of the resin film 2 is set to be 5 μm or more and 15 μm or less.

[0030] Fiber-reinforced resin sheet 1 can use, for example Figure 2 The sheet manufacturing apparatus 50 shown is used to manufacture fiber-reinforced resin sheets 1 by continuously producing fiber-reinforced resin sheets 1 from bundles of reinforcing fibers, i.e., fiber bundles 3' and thermoplastic resin films 2.

[0031] Specifically, the sheet manufacturing apparatus 50 includes: multiple pairs (two pairs here) of heating rollers 51 arranged vertically; multiple pairs (two pairs here) of cooling rollers 522 arranged vertically on the lower side of the heating rollers 51; a pair of annular belts 54 suspended between the heating rollers 51 and the cooling rollers 52; a pair of pull-out rollers 55 located on the lower side of the annular belts 54; and a winding spool 56 disposed on the lower side of the pull-out rollers 55.

[0032] On both sides of the uppermost heating roller 51 are fiber-opening mechanisms (not shown) that open the fiber bundles 3' and spread them into a strip shape. These mechanisms continuously open the fiber bundles 3', thereby forming a large number of continuous reinforcing fibers 3 that are extended into a thin strip. Any mechanism capable of performing this process can be used, such as a mechanism that expands the fiber bundles by beating, a mechanism that expands the fiber bundles by blowing air, or a mechanism that expands the fiber bundles by applying ultrasound.

[0033] exist Figure 2 In the example described above, the fiber-opening mechanism has a mechanism for supplying the opened reinforcing fiber 3 to one side of the resin film 2 and a mechanism for supplying the opened reinforcing fiber 3 to the other side of the resin film 2. The former mechanism is configured to guide the reinforcing fiber 3 between one side of the resin film 2 and the heating roller 51 in contact with that side, while the latter mechanism is configured to guide the reinforcing fiber 3 between the other side of the resin film 2 and the heating roller 51 in contact with that side.

[0034] The heating roller 51 is a high-temperature roller heated by an electric heater or heating medium. The heating roller 51 clamps and heats the resin film 2 and the reinforcing fibers 3 introduced onto its two side surfaces via an annular belt 54, thereby continuously impregnating the reinforcing fibers 3 into the resin film 2. The reinforcing fibers 3 move in the same direction ( Figure 2 The resin membrane 2 is impregnated in a parallel arrangement (up and down direction).

[0035] The cooling roller 52 is a low-temperature roller that is cooled by a cooling medium or the like. The cooling roller 52 clamps and cools the resin film 2, which is impregnated with reinforcing fibers 3, from both sides by an annular belt 54, thereby fixing the reinforcing fibers 3 to the resin film 2. Accordingly, the resin film 2 (matrix resin) and the reinforcing fibers 3 are formed into an integral fiber-reinforced resin sheet 1.

[0036] The extraction roller 55 is a roller that pulls the formed fiber-reinforced resin sheet 1 downward while applying tension to it.

[0037] The winding spool 56 is used to wind the core material of the fiber-reinforced resin sheet 1. The winding spool 56 is driven to rotate by a drive source such as a motor, and the fiber-reinforced resin sheet 1 drawn out by the extraction roller 55 is wound in sequence, thereby assembling the fiber-reinforced resin sheet 1 into a roll.

[0038] Through the above processes, the fiber-reinforced resin sheet 1 is completed. The unit area weight of the reinforcing fibers 3 in the fiber-reinforced resin sheet 1, that is, the weight of the reinforcing fibers 3 impregnated in each unit area of ​​the resin film 2, is set to 25 g / m². 2 Above and 60g / m 2 In other words, the fiber-opening mechanism of the sheet manufacturing apparatus 50 described above supplies reinforcing fibers 3 to both sides of the resin film 2 at a predetermined density, such that the unit area weight of the reinforcing fibers 3 is 25 to 60 g / m². 2 It should be noted that, if necessary, the above-mentioned weight per unit area can be achieved by repeatedly performing the above series of processes (supplying reinforcing fibers 3 to both sides of the resin film 2 and impregnating them).

[0039] The volume fraction (Vf) of the reinforcing fiber 3, i.e., the volume occupied by the reinforcing fiber 3 divided by the total volume of the fiber-reinforced resin sheet 1, is set to be 60% or more and 75% or less. That is, the reinforcing fiber 3, at the aforementioned unit area weight (25-60 g / m²), is used. 2 The fiber 3 is impregnated into a resin film 2 with a thickness of 5 to 15 μm, thereby reinforcing the fiber 3 by setting the volume content to 60 to 75%.

[0040] By ensuring that the unit area weight and volume content of the reinforcing fibers are within the aforementioned ranges, the thickness of the fiber-reinforced resin sheet 1 is set to be 30 μm or more and 65 μm or less. This thickness of fiber-reinforced resin sheet 1 provides high flexibility without hindering its assembly into rolls.

[0041] (Forming of fiber-reinforced composite materials)

[0042] If the fiber-reinforced resin sheet 1 is formed as described above, the process proceeds to the next step, S2. Step S2 is a sheet lamination process for forming the fiber-reinforced composite material 10 by laminating the fiber-reinforced resin sheet 1. In this sheet lamination process S2, as... Figure 3 As shown, a plate-shaped fiber-reinforced composite material 10 with a thickness of about a few millimeters (e.g., 2 mm) is formed by stacking multiple substrate sheets 1A cut into a specified shape from fiber-reinforced resin sheet 1 with an angular difference between them when viewed from above, with their fiber direction X. It should be noted that the fiber direction X is the orientation direction of the reinforcing fibers 3 contained in the substrate sheet 1A (fiber-reinforced resin sheet 1).

[0043] Specifically, in the sheet lamination process S2, the fiber-reinforced resin sheet 1 (a long strip of fiber-reinforced resin sheet 1 rolled into a roll) formed in the sheet forming process S1 is cut into multiple substrate sheets 1A with appropriate shapes and sizes. Then, the multiple substrate sheets 1A are laminated along the thickness direction. At this time, the substrate sheets 1A are laminated in such a way that the fiber directions X of adjacent substrate sheets 1A in the thickness direction are staggered. In other words, the multiple substrate sheets 1A must be laminated in a manner where the angle of the fiber direction X, viewed from above, is different between adjacent sheets.

[0044] Figure 3 This illustrates an example of multiple rectangular substrate sheets 1A being stacked with each sheet staggered by 45° when viewed from above, oriented at an angle of the fiber direction X. Specifically, the multiple substrate sheets 1A stacked in the sheet lamination process S2 include: a first substrate sheet 1Aa with an angle of 0° in the fiber direction X; a second substrate sheet 1Ab with an angle of 45° in the fiber direction X; a third substrate sheet 1Ac with an angle of 90° in the fiber direction X; and a fourth substrate sheet 1Ad with an angle of 135° in the fiber direction X.

[0045] After the substrate sheets 1A are laminated in the above-described state, the substrate sheets 1A are further pressed and heated, for example, along the thickness direction, to perform a process of thermally bonding the substrate sheets 1A together. This forms a plate-shaped fiber-reinforced composite material 10 in which multiple substrate sheets 1A are integrally laminated. The number of laminated substrate sheets 1A is set such that the thickness of the fiber-reinforced composite material 10 is approximately a few millimeters.

[0046] (Pressed molding)

[0047] If the forming of the fiber-reinforced composite material 10 is completed as described above, the process moves to the next step, S3. Step S3 involves using... Figure 4A The pressing process shown in ~C involves using a hot press 60 to press the fiber-reinforced composite material 10 to form a molded article 30 of a specified shape.

[0048] Specifically, in pressing process S3, such as Figure 4A As shown, multiple sheet-shaped fiber-reinforced composite materials 10 are prepared and stacked in the mold of a hot press 60 while being stacked along the thickness direction. The fiber-reinforced composite materials 10 are all sheets formed by the above-described stacking process S2 and have a thickness of about a few millimeters.

[0049] like Figure 4A As shown, the hot press 60 includes a punch 61 and a die 62. The die 62 is a mold (female mold) having a recess 62a capable of accommodating the fiber-reinforced composite material 10. The punch 61 is a mold (male mold) having a base 61a and an insertion portion 61b protruding from the lower surface of the base 61a. The fiber-reinforced composite materials 10 are arranged in a stacked state within the recess 62a of the die 62. A heater (not shown) is installed in the die 62 for heating the fiber-reinforced composite material 10 within the recess 62a to a high temperature.

[0050] If the fiber-reinforced composite material 10 is loaded into the pressing mold as described above, the molded product 30 is formed by pressing the punch 61 into the die 62 while heating the fiber-reinforced composite material 10. Specifically, the fiber-reinforced composite material 10 is raised to a specified temperature by heating the die 62 using the heater described above, and with the insertion portion 61b of the punch 61 inserted into the recess 62a of the die 62, the punch 61 is pressed downward by a pressure device (not shown), thereby pressurizing the fiber-reinforced composite material 10 (see reference). Figure 4B The heating and pressurization cause the fiber-reinforced composite material 10 to soften and deform.

[0051] Figure 4C This indicates that the punch 61 is pressed to the end of its stroke. In this state, the space defined between the punch 61 and the die 62 (i.e., the forming cavity) is filled with the deformed fiber-reinforced composite material 10. That is, by deforming the fiber-reinforced composite material 10 into a shape corresponding to the forming cavity, a molded article 30 made of fiber-reinforced resin can be obtained. After a specified cooling period, the molded article 30 is removed from the die 62 with the punch 61 pulled out.

[0052] (Effects, etc.)

[0053] As explained above, in the first embodiment of the present invention, a fiber-reinforced composite material 10, which is formed by laminating multiple fiber-reinforced resin sheets 1 (substrate sheets 1A), is used as the molding material for the molded article 30. Furthermore, each fiber-reinforced resin sheet 1 is a sheet containing reinforcing fibers 3 at a volume content of 60 to 75%. Therefore, it has the advantage of being able to manufacture a molded article 30 with good formability and high strength.

[0054] Specifically, in the first embodiment described above, a fiber-reinforced resin sheet 1 is formed by laminating reinforcing fibers 3 on both sides of a relatively thin resin film 2 of 5 to 15 μm, and the weight per unit area of ​​the reinforcing fibers 3 relative to the resin film 2 is set to 25 to 60 g / m². 2 Accordingly, it is possible to prevent poor forming of the fiber-reinforced resin sheet 1, and to increase the volume content (Vf value) of the reinforcing fibers 3 in the sheet 1 to 60-75%.

[0055] That is, in the structure of reinforcing fibers 3 stacked on both sides of the resin membrane 2, even without excessively increasing the stacking amount of reinforcing fibers 3 on each surface (one side or the other side) of the resin membrane 2, it is possible to achieve an overall density of 25-60 g / m³. 2 The unit area weight. Therefore, by heating and pressurizing during molding, the reinforcing fibers 3 can be fully impregnated into each surface of the resin film 2, thereby improving the bonding strength between the resin film 2 and the reinforcing fibers 3. Moreover, since the resin film 2 is only 5 to 15 μm thick, it softens rapidly upon heating, allowing the reinforcing fibers 3 to reliably impregnate into the interior of the resin film 2. This prevents defects such as loosening of the reinforcing fibers 3 after molding. Furthermore, under these conditions, a fiber-reinforced resin sheet 1 with a high volume content (Vf value) of 60 to 75% is achieved, resulting in a significant improvement in the strength of molded articles formed using the fiber-reinforced resin sheet 1 (the strength of the fiber-reinforced composite material 10 and the molded article 30 formed using it).

[0056] In particular, in the first embodiment described above, when the fiber-reinforced composite material 10 is formed from the fiber-reinforced resin sheet 1, multiple fiber-reinforced resin sheets 1 are stacked in a state where they have an angular difference from each other when viewed from above, with the fiber direction X (the orientation direction of the reinforcing fiber 3). Therefore, the reinforcing effect of the reinforcing fiber 3 can be exerted on the fiber-reinforced composite material 10 from multiple different directions, and the mechanical properties of the fiber-reinforced composite material 10 and the molded article 30 can be improved.

[0057] It should be noted that in the first embodiment described above, when the fiber-reinforced composite material 10 is formed from the fiber-reinforced resin sheet 1 (substrate sheet 1A), multiple fiber-reinforced resin sheets 1 are stacked in such a way that the fiber direction X between adjacent sheets must be different (for example, the fiber directions X are staggered by 46°). However, the fiber directions X can also be stacked with every other sheet staggered.

[0058] (2) Second Implementation

[0059] Figure 5 This is a process diagram illustrating a method for manufacturing a molded article according to the second embodiment of the present invention. The molded article of this second embodiment is similar to the molded article 30 of the first embodiment described above. Figure 4C Similarly, it is a molded article (composite molded article) made of synthetic resin containing reinforcing fibers, through... Figure 5 It is manufactured through the processes shown (S11 to S14).

[0060] (Forming of fiber-reinforced resin sheets)

[0061] Process S11 is forming Figure 2 The sheet forming process of the fiber-reinforced resin sheet 1 shown is as follows: In this sheet forming process S11, a unidirectional sheet (FRTP sheet) comprising a thermoplastic resin film 2 and a large number of reinforcing fibers 3 impregnated in the resin film 2 in a parallel arrangement in the same direction is formed as the fiber-reinforced resin sheet 1. The thickness of the resin film 2 is 5 to 15 μm, and the unit area weight of the reinforcing fibers 3 is 25 to 60 g / m². 2 The volume content of reinforcing fiber 3 is 60-75%, and the thickness of fiber-reinforced resin sheet 1 is 30-65 μm. Since the steps of this sheet forming process S11 are the same as those of the sheet forming process S1 in the first embodiment described above, its detailed description is omitted.

[0062] (Preparation of short-cut materials)

[0063] If the forming of the fiber-reinforced resin sheet 1 is completed as described above, the process proceeds to the next step, S12. Step S12 involves cutting out the fiber-reinforced resin sheet 1. Figure 6 The chopped material 1B shown is produced in a chopped material manufacturing process. In this chopped material manufacturing process S12, a large number of rectangular chopped materials 1B of a specified size can be produced by cutting the fiber-reinforced resin sheet 1 along its length and width directions. Specifically, the chopped material 1B is produced through the following steps.

[0064] First, such as Figure 6 As shown, slits C1 extending along the length direction are formed. That is, while feeding the fiber-reinforced resin sheet 1 along the length direction, a plurality of slits C1 continuously extending along the length direction are formed in section I midway along its conveying path. The slits C1 can be formed, for example, using a cutting device containing a plurality of blades arranged at equal intervals in the width direction of the fiber-reinforced resin sheet 1.

[0065] Next, in the following section II, a slit C2 is formed that extends continuously from one end of the fiber-reinforced resin sheet 1 in the width direction to the other end. The slit C2 can be formed, for example, using a rotary cutter. The slit C2 is formed each time the fiber-reinforced resin sheet 1 is fed out a fixed distance along its length. Accordingly, a large number of rectangular stubs 1B are cut out, each stub having a short side corresponding to the length of the spacing between the slits C1 and a long side corresponding to the length of the spacing between the slits C2.

[0066] As described above, the fiber-reinforced resin sheet 1 is a thermoplastic resin sheet containing a large number of reinforcing fibers 3 oriented in its length direction. Therefore, each chopped material 1B cut from this fiber-reinforced resin sheet 1 also contains a large number of reinforcing fibers 3 oriented in its length direction (the direction of the long side). That is, the chopped material 1B has a thermoplastic resin film 2 and a large number of reinforcing fibers 3 impregnated into the resin film 2 (matrix resin) in a state of being oriented in the same direction.

[0067] The dimensions of the chopped material 1B are set to be appropriate, taking into account the material's shapeability and other properties in the pressing process (S14) described later. Specifically, the chopped material 1B is formed into a rectangular shape with a short side length of 2 mm or more and 50 mm or less, and a long side length of 2 mm or more and 80 mm or less. As a suitable example, the chopped material 1B is formed into a rectangular shape of 5 × 20 mm. It should be noted that the thickness of the chopped material 1B is the same as the thickness of the fiber-reinforced resin sheet 1, which is 30 μm or more and 65 μm or less.

[0068] (Forming of fiber-reinforced composite materials)

[0069] If the chopped material 1B is fabricated as described above, the process moves to the next step, S13. Step S13 involves forming the material by stacking the chopped materials 1B together. Figure 7 The fiber-reinforced composite material 20 shown is a chopped material lamination process. In this chopped material lamination process S13, a large number of chopped materials 1B are arranged in a two-dimensional and random manner on the upper surface of a carrier sheet 21 made of thermoplastic resin and then laminated and fixed, thereby forming the fiber-reinforced composite material 20. Specifically, the fiber-reinforced composite material 20 is formed by the following steps.

[0070] First, such as Figure 7As shown, while the carrier sheet 21 is fed out along its length, a large number of chopped materials 1B are dispersed on the upper surface of the carrier sheet 21. This dispersion of the chopped materials 1B can be achieved, for example, using a dropping device that vibrates the chopped materials 1B and causes them to fall from above the carrier sheet 21. Furthermore, by repeatedly performing the dropping operation of the chopped materials 1B using the dropping device at multiple positions along the conveying direction of the carrier sheet 21, the density and number of layers of the chopped materials 1B on the carrier sheet 21 gradually increase. That is, by repeatedly performing the dropping operation of the chopped materials 1B using the aforementioned dropping device in multiple intervals XI, XII, XIII... along the length direction of the carrier sheet 21, a large number of chopped materials 1B are stacked on the carrier sheet 21 in such a way that the fiber direction of the reinforcing fibers 3 contained in each chopped material 1B (in other words, the length direction of the chopped materials 1B) is dispersed in various directions on the horizontal plane, and multiple chopped materials 1B are stacked in the thickness direction.

[0071] Next, a heating roller (not shown) is used to pressurize and heat the carrier sheet 21 and the chopped material 1B thereon, causing the carrier sheet 21 and the chopped material 1B to integrate with each other. That is, by using the aforementioned heating roller to pressurize and heat, the carrier sheet 21 and the chopped material 1B are bonded together (melt-bonded), and the stacked chopped materials 1B are bonded together (melt-bonded). Through this bonding, a sheet is formed in which the carrier sheet 21 and a large number of chopped materials 1B are integrated. Then, this sheet is cut into a suitable shape and size to obtain a fiber-reinforced composite material 20. The thickness of the fiber-reinforced composite material 20, that is, the total thickness of the carrier sheet 21 and the chopped material 1B stacked thereon, is set to about a few millimeters (e.g., 2 mm). In other words, the number of stacked chopped material 1B sheets is set to a number that makes the thickness of the fiber-reinforced composite material 20 about a few millimeters.

[0072] As the material for the carrier sheet 21, a thermoplastic resin that is essentially the same as the matrix resin (i.e., resin film 2) of the chopped material 1B can be used. However, as long as it is a thermoplastic resin, various materials of carrier sheet 21 can be used, and carrier sheet 21 made of a different material than the matrix resin of the chopped material 1B can also be used.

[0073] It should be noted that, in Figure 7The example illustrates the fabrication of fiber-reinforced composite material 20 by laminating chopped material 1B only on the upper surface of carrier sheet 21. However, chopped material 1B can also be lamination on both sides of carrier sheet 21. In this case, the chopped material 1B is sequentially laminated and fixed onto the upper and lower surfaces of carrier sheet 21 (i.e., the chopped material 1B is arranged multiple times and randomly, and then pressurized and heated). Specifically, after laminating and fixing the chopped material 1B onto the upper surface of carrier sheet 21, carrier sheet 21 is flipped so that the lower surface of carrier sheet 21 faces upward. In this state, the chopped material 1B is laminated and fixed. This process is repeated to fabricate fiber-reinforced composite material 20 with chopped material 1B laminated on both sides of carrier sheet 21.

[0074] (Pressed molding)

[0075] If the fiber-reinforced composite material 20 is formed as described above, the process moves to the next step, S14. Step S14 involves using... Figure 4A The pressing process shown in ~C involves using a hot press 60 to press the fiber-reinforced composite material 20 to form a molded article 30 of a specified shape. Since the steps of this pressing process S14 are the same as those of the pressing process S3 in the first embodiment described above, a detailed description of it is omitted.

[0076] (Effects, etc.)

[0077] As explained above, in the second embodiment of the present invention, a fiber-reinforced composite material 20 comprising a large amount of chopped material 1B cut and stacked from the fiber-reinforced resin sheet 1 is used as the molding material for the molded article 30. Furthermore, the fiber-reinforced resin sheet 1 is a sheet containing reinforcing fibers 3 at a volume content of 60 to 75%. Therefore, similar to the first embodiment described above, it has the advantage of being able to manufacture a molded article 30 with good formability and high strength.

[0078] In particular, in the second embodiment described above, a large number of short-cut materials 1B are prepared to be cut into rectangular shapes with short sides of 2 to 50 mm in length and long sides of 2 to 80 mm in length. The short-cut materials 1B are stacked in a state where the fiber direction of the reinforcing fibers 3 contained in each short-cut material 1B is randomly oriented in two dimensions, thereby forming a fiber-reinforced composite material 20. Therefore, the mechanical properties of the fiber-reinforced composite material 20 can be endowed with sufficient isotropy (quasi-isotropy), and a good reinforcement effect using the reinforcing fibers 3 can be obtained.

[0079] It should be noted that in the second embodiment described above, a large amount of chopped material 1B is laminated and fixed on a carrier sheet 21 made of thermoplastic resin to form the fiber-reinforced composite material 20. However, the carrier sheet 21 may be omitted. That is, as the fiber-reinforced composite material 20, a composite material formed solely of chopped material 1B laminated and fixed together may also be formed.

[0080] (3) Examples

[0081] Next, the method described in the first or second embodiment above will be discussed. Figure 1 Process S1 or Figure 5 An example of fiber-reinforced resin sheet 1 manufactured by process S11) will be described here. The example described here uses... Figure 2 The sheet manufacturing apparatus 50 shown produces a fiber-reinforced resin sheet 1 under the following manufacturing conditions.

[0082] (Manufacturing conditions)

[0083] Membrane material: Nylon 9T (PA9T)

[0084] Film forming conditions: Extrusion forming is carried out at a forming temperature of 290–310°C.

[0085] Roller temperature: 280℃

[0086] Conveyor line speed: 20m / min

[0087] Here, membrane material and membrane forming conditions refer to the material and forming conditions of resin membrane 2, roller temperature refers to the temperature of heating roller 51 in sheet manufacturing apparatus 50, and conveying line speed refers to the speed at which reinforcing fiber 3 is fed to resin membrane 2 in sheet manufacturing apparatus 50.

[0088] In the fabrication of this embodiment, one of the following materials 1 to 3 is used as the reinforcing fiber 3.

[0089] (Materials for reinforcing fibers)

[0090] Material 1: Carbon fiber with a diameter of 7μm, a fiber count of 12,000, and a fineness of 800 tex

[0091] Material 2: Carbon fiber with a fiber diameter of 5μm, a fiber count of 24,000, and a fineness of 1030tex.

[0092] Material 3: Carbon fiber with a fiber diameter of 7μm, a fiber count of 15,000, and a fineness of 1000tex.

[0093] Using reinforcing fiber 3 formed from one of the materials 1 to 3 described above, and manufacturing fiber-reinforced resin sheet 1 under the manufacturing conditions described above, a fiber-reinforced resin sheet 1 was obtained. Figure 8 Examples 1 to 8 are shown. Figure 8 In Examples 1-8, parameters for film thickness, weight per unit area, volume content, and sheet thickness are shown. It should be noted that film thickness refers to the thickness (μm) of the resin film 2, and weight per unit area refers to the weight per unit area of ​​the reinforcing fiber 3 relative to the resin film 2 (g / m²). 2 Volume content refers to the volume content (%) of reinforcing fiber 3 in fiber-reinforced resin sheet 1, and sheet thickness refers to the measured value of the thickness (μm) of fiber-reinforced resin sheet 1.

[0094] like Figure 8 As shown, in Examples 1 to 8, the thickness of the resin film 2 is all within the range of 5 to 15 μm, and the unit area weight of the reinforcing fiber 3 is all within the range of 25 to 60 g / m². 2 Within the specified range, the volume content of reinforcing fiber 3 is all within the range of 60-75%, and the thickness of fiber-reinforced resin sheet 1 is all within the range of 30-65 μm. It should be noted that, in the following description, these ranges are collectively referred to as the target range.

[0095] Here, focusing on the relationship between the unit area weight of the resin film 2 and the reinforcing fiber 3, roughly speaking, there is a relationship that the greater the thickness of the resin film 2, the greater the unit area weight of the reinforcing fiber 3. That is, the unit area weight of the resin film 2 with a thickness of 10 mm (Examples 2, 3, 6) is on average greater than that with a thickness of 5 mm (Examples 1, 8), and the unit area weight of the resin film 2 with a thickness of 15 mm (Examples 4, 5, 7) is on average greater than that with a thickness of 10 mm (Examples 2, 3, 6). Furthermore, as a result of adjusting the unit area weight of the reinforcing fiber 3 according to the thickness of the resin film 2, the volume content of the reinforcing fiber 3 is within the aforementioned target range (60-75%), and the thickness of the fiber-reinforced resin sheet 1 is also within the aforementioned target range (30-65 μm).

[0096] Figure 8 The results of confirming whether molding defects occurred in each embodiment are also shown. Figure 8 As shown, no molding defects were found in Examples 1 to 8 (the defects 1 to 3 described later were not found in any of them). That is, it can be seen that Examples 1 to 8 are excellent materials for fiber-reinforced composite materials because no molding defects occurred and the volume content of reinforcing fiber 3 is as high as 60% or more.

[0097] on the other hand, Figure 9In this paper, several examples of poor forming or insufficient fiber content (reinforcing fiber 3 volume content less than 60%) are shown as Comparative Examples 1 to 5. Specifically, in Comparative Examples 1 to 5, any one of the parameters—film thickness, weight per unit area, volume content, and sheet thickness—exceeds the aforementioned target range (the values ​​in the gray background cells represent parameters exceeding the target range), and due to this deviation, poor forming (Defects 1 to 3) or insufficient fiber content occurs. It should be noted that Defect 1 is a defect caused by weak bonding between the reinforcing fiber 3 and the resin film 2, resulting in the peeling of the reinforcing fiber 3; Defect 2 is a defect where the density of the reinforcing fiber 3 is significantly uneven in the sheet width direction; and Defect 3 is a defect occurring in the resin film 2 itself (the resin film 2 before the reinforcing fiber 3 is impregnated).

[0098] For example, in Comparative Example 1, although the unit area weight of the reinforcing fiber 3 was within the aforementioned target range, the thickness of the resin film 2 was greater than the aforementioned target range (more than 15 μm), resulting in a fiber deficiency where the volume content of the reinforcing fiber 3 was lower than the aforementioned target range (60-75%). This means that when fiber-reinforced composite materials are formed using fiber-reinforced resin sheet 1, the strength of the fiber-reinforced composite material cannot be sufficiently improved.

[0099] In Comparative Example 2, the weight per unit area of ​​reinforcing fiber 3 is greater than the target range mentioned above (exceeding 60 g / m²). 2 Therefore, defect 1, which causes the reinforcing fiber 3 to peel off, occurred. It is believed that this is due to the resin content of the resin film 2 being too low relative to the amount of reinforcing fiber 3.

[0100] In Comparative Example 3, both the thickness of the resin film 2 and the unit area weight of the reinforcing fiber 3 were below the aforementioned target range. Therefore, both defects 2 (excessive unevenness in fiber density in the width direction) and 3 (formation defects of the resin film 2) occurred. Furthermore, the thickness of the fiber-reinforced resin sheet 1 also exceeded the aforementioned target range.

[0101] In Comparative Examples 4 and 5, the weight per unit area of ​​reinforcing fiber 3 was less than the target range mentioned above (below 60 g / m²). 2 Therefore, defect 2, which resulted in excessive unevenness of fiber density in the width direction, occurred. In addition, in Comparative Example 5, fiber deficiency occurred, where the volume content of reinforcing fiber 3 was too low (less than 60%).

[0102] Conversely, based on the above explanation, in order to fully increase the content of reinforcing fiber 3 while ensuring formability, the above parameters need to be controlled within the target range.

[0103] Next, examples and comparative examples of fiber-reinforced composite materials will be described. Here, 2 mm thick plate-shaped fiber-reinforced composite materials formed using the fiber-reinforced resin sheet 1 of the above-described examples or comparative examples are used as Examples 9-11 and Comparative Examples 6 and 7. Their respective characteristics are shown below. Figure 10 .

[0104] Example 9 is based on the first embodiment described above ( Figure 3 The fiber-reinforced composite material 10 is obtained by laminating the fiber-reinforced resin sheet 1 of Example 6 using the method described above. That is, the fiber-reinforced composite material 10 of Example 9 is a fiber-reinforced composite material formed by laminating multiple fiber-reinforced resin sheets 1 of Example 6 in a manner that staggers each fiber direction X by 45° (quadriaxial lamination), and is a plate-shaped composite material with a thickness of 2 mm.

[0105] Example 10 is the same as Example 9, except that the sheet used as the material is the fiber-reinforced resin sheet 1 of Example 4.

[0106] Comparative Example 6 is the same as Example 9, except that the sheet used as the material is the fiber-reinforced resin sheet 1 of Comparative Example 1.

[0107] Example 11 is based on the second embodiment described above ( Figure 7 The fiber-reinforced composite material 20 is obtained by laminating the fiber-reinforced resin sheet 1 of Example 6 above using the method described above. That is, the fiber-reinforced composite material 20 of Example 11 is a fiber-reinforced composite material formed by laminating a large number of short-cut materials 1B in rectangular shape (here, 5×20mm) cut from multiple fiber-reinforced resin sheets 1 of Example 6 onto the upper surface of the carrier sheet 21, and is a plate-shaped composite material with a thickness of 2mm.

[0108] Comparative Example 7 is the same as Example 11, except that the sheet used as the material is the fiber-reinforced resin sheet 1 of Comparative Example 1.

[0109] Since Examples 9, 10, and Comparative Example 6 are fiber-reinforced composite materials 10 formed solely from fiber-reinforced resin sheet 1, the volume content of reinforcing fibers 3 in these fiber-reinforced composite materials 10 is the same as the volume content of reinforcing fibers 3 in the fiber-reinforced resin sheet 1 (Examples 6, 4, and Comparative Example 1) used as the material. On the other hand, since Examples 11 and Comparative Example 7 are fiber-reinforced composite materials 20 formed by laminating chopped material 1B of fiber-reinforced resin sheet 1 onto carrier sheet 21, the volume content of reinforcing fibers 3 in these fiber-reinforced composite materials 20 is slightly less than the volume content of reinforcing fibers 3 in the fiber-reinforced resin sheet 1 (Example 6 and Comparative Example 1) used as the material before forming. This is because the amount of resin component increased corresponding to the amount in the carrier sheet 21.

[0110] Tensile and bending tests were performed on Examples 9-11 and Comparative Examples 6 and 7, and the tensile strength and tensile modulus, as well as the bending strength and bending modulus, were measured, respectively. The tensile test was conducted by stretching a test piece with a width of 25 mm, a length of 250 mm, and a thickness of 2 mm along its length. The bending test was conducted by subjecting a test piece with a width of 15 mm, a length of 100 mm, and a thickness of 2 mm to a so-called four-point bending. The results of each test are shown below. Figure 10 As shown in the figure, in terms of tensile strength and flexural strength, through Figure 3 The molded articles obtained by the method of the first embodiment shown (quadaxial sheet lamination) (Examples 9, 10, Comparative Example 6) are higher than those obtained by... Figure 7 The molded article obtained by the method of the second embodiment shown (layering of chopped materials) is (Example 11, Comparative Example 7). It is believed that this is because the reinforcing fibers 3 contained in the former case are on average longer than those in the latter case. On the other hand, regarding the latter, although the length of the reinforcing fibers 3 contained is shorter, sufficient randomness is imparted in the fiber direction, thus enabling high isotropy of mechanical properties.

[0111] When the molded articles obtained by the method of the first embodiment (quadriaxial sheet lamination) (Examples 9, 10 and Comparative Example 6) are compared with each other, the strength (tensile strength, flexural strength) and elastic modulus (tensile modulus, flexural modulus) of Examples 9 and 10 are higher than those of Comparative Example 6. It is believed that the main reason is that the volume content of reinforcing fiber 3 in Examples 9 and 10 is higher than that in Comparative Example 6.

[0112] Similarly, when comparing the molded articles obtained by the method of the second embodiment (layering of chopped materials) (Example 11, Comparative Example 7), the strength and elastic modulus of Example 11 are higher than those of Comparative Example 7. It is believed that the main reason for this is the difference in the volume content of the reinforcing fiber 3.

[0113] As can be seen from the above, compared with the fiber-reinforced composite material formed from the fiber-reinforced resin sheet of the comparative example, the fiber-reinforced composite material formed from the fiber-reinforced resin sheet of the embodiment has superior mechanical properties.

[0114] (4) Overview of the implementation method

[0115] The inventions included in the above embodiments are summarized as follows.

[0116] One aspect of the present invention relates to a fiber-reinforced resin sheet having a thickness of 30 μm or more and 65 μm or less, comprising: a thermoplastic resin film; and a plurality of reinforcing fibers obtained by splitting fiber bundles of the reinforcing fibers and stacking them on both sides of the resin film in a state of being oriented in the same direction, wherein the thickness of the resin film is 5 μm or more and 15 μm or less, and the unit area weight of the reinforcing fibers is 25 g / m². 2 Above 60g / m 2 Hereinafter, the volume content of the reinforcing fiber is 60% or more and 75% or less.

[0117] According to this configuration, a fiber-reinforced resin sheet is formed by laminating reinforcing fibers on both sides of a relatively thin resin film of 5–15 μm, and the weight per unit area of ​​the reinforcing fibers relative to the resin film is set to 25–60 g / m². 2 Therefore, it can prevent poor forming of fiber-reinforced resin sheets and increase the volume content of reinforcing fibers in the sheet to 60-75%.

[0118] That is, by stacking reinforcing fibers on both sides of the resin membrane, even without excessively increasing the amount of reinforcing fibers stacked on each surface (one side or the other side) of the resin membrane, an overall strength of 25–60 g / m² can be achieved. 2 The unit area weight is [not specified]. Therefore, through heating and pressurization during molding, the reinforcing fibers can be fully impregnated into all surfaces of the resin film, improving the bonding strength between the resin film and the reinforcing fibers. Furthermore, since the resin film is only 5–15 μm thick, it softens rapidly upon heating, allowing the reinforcing fibers to reliably penetrate into the interior of the resin film. This prevents defects such as loosening of the reinforcing fibers after molding. Moreover, by achieving a high volume content of 60–75% in the fiber-reinforced resin sheet under these conditions, the strength of molded articles formed using this fiber-reinforced resin sheet is significantly improved.

[0119] One aspect of the present invention relates to a fiber-reinforced composite material, which is formed by stacking the above-mentioned fiber-reinforced resin sheets in the thickness direction. A plurality of the fiber-reinforced resin sheets are stacked on top of each other with an angular difference between them when viewed from above, i.e., the orientation direction of the reinforcing fibers.

[0120] Based on this structure, the reinforcing effect of the reinforcing fibers can be utilized from multiple different directions in the fiber-reinforced composite material, thereby improving the mechanical properties of the fiber-reinforced composite material.

[0121] Another aspect of the present invention relates to a fiber-reinforced composite material which is formed by stacking a plurality of short-cut materials cut from the above-mentioned fiber-reinforced resin sheet in the thickness direction. The plurality of short-cut materials are each formed into a rectangular shape with a short side length of 2 mm or more and 50 mm or less and a long side length of 2 mm or more and 80 mm or less, and are stacked in a state where the orientation direction of the reinforcing fibers, i.e. the fiber direction, is randomly oriented in two dimensions (claim 3).

[0122] Based on this structure, the mechanical properties of fiber-reinforced composite materials can be endowed with sufficient isotropy (quasi-isotropy), and good reinforcement effect can be obtained by utilizing the reinforcing fibers.

[0123] Another aspect of the present invention relates to a molded article formed using the above-described fiber-reinforced composite material.

[0124] This structure allows for a significant improvement in the strength of the molded product.

Claims

1. A fiber-reinforced resin sheet, characterized in that, The fiber-reinforced resin sheet, having a thickness of 30 μm or more and 65 μm or less, comprises: Thermoplastic resin films; and Multiple reinforcing fibers are obtained by opening fiber bundles and are stacked on both sides of the resin film in a state of being oriented in the same direction. The thickness of the resin film is greater than 5 μm and less than 15 μm. The reinforcing fiber has a unit area weight of 25 g / m². 2 Above 60g / m 2 the following, The volume content of the reinforcing fiber is more than 60% and less than 75%.

2. A fiber-reinforced composite material, characterized in that: A fiber-reinforced composite material formed by stacking multiple fiber-reinforced resin sheets as described in claim 1 in the thickness direction. Multiple fiber-reinforced resin sheets are stacked on top of each other with an angular difference between them when viewed from above, i.e., the orientation direction of the reinforcing fibers.

3. A fiber-reinforced composite material, characterized in that: A fiber-reinforced composite material formed by stacking multiple short-cut materials cut from the fiber-reinforced resin sheet of claim 1 in the thickness direction. The plurality of chopped materials are each formed into a rectangular shape with a short side length of 2 mm or more and 50 mm or less, and a long side length of 2 mm or more and 80 mm or less, and are stacked in a state of random orientation in two dimensions with the orientation direction of the reinforcing fibers, i.e. the fiber direction.

4. A molded article, characterized in that, It is formed using the fiber-reinforced composite material as described in claim 2 or 3.

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