Fiber-reinforced resin sheet

Abstract

The present invention provides a fiber-reinforced resin sheet with a high reinforcing fiber content and in which the reinforcing fibers are less prone to peeling. [Solution] The fiber-reinforced resin sheet 1 comprises a resin base material 11 made of a sheet-like thermoplastic resin, and reinforcing fibers 10 contained in the resin base material 11 in a state oriented in the same direction and with an average volume content of 30% to 70%. When the fiber-reinforced resin sheet 1 is divided into five equal parts in the thickness direction, each range is defined as the 1st to 5th ranges R1 to R5, in order from one surface of the sheet to the other surface, the reinforcing fibers 10 are contained in the resin base material 11 such that the volume content of the 1st range R1, the 3rd range R3, and the 5th range R5 is lower than the volume content of the 2nd range R2 and the 4th range R4.

Description

Technical Field

[0001] The present invention relates to a fiber-reinforced resin sheet in which a reinforcing fiber is contained in a resin base material.

Background Art

[0002] As an example of a fiber-reinforced resin sheet, the one described in Patent Document 1 below is known. The fiber-reinforced resin sheet of this Patent Document 1 includes a thermoplastic resin film and reinforcing fibers laminated on both surfaces of the resin film. The reinforcing fibers are laminated on both surfaces of the resin film so that the volume content rate (Vf) with respect to the fiber-reinforced resin sheet is 60 to 75% or more.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a relatively large amount of reinforcing fibers corresponding to a volume content rate of 60 to 75% are laminated on both surfaces of a resin film as in Patent Document 1 above, there is a possibility that the resin film may not be sufficiently impregnated into the reinforcing fibers. If the impregnation of the resin film into the reinforcing fibers is insufficient, problems such as peeling of the reinforcing fibers from the resin film may occur.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a fiber-reinforced resin sheet having a high content rate of reinforcing fibers and being difficult to cause peeling of the reinforcing fibers.

Means for Solving the Problems

[0006] To solve the above problems, the fiber-reinforced resin sheet of the present invention comprises a resin substrate made of a sheet-like thermoplastic resin and reinforcing fibers contained in the resin substrate in a state oriented in the same direction and with an average volume content of 30% to 70%. When the fiber-reinforced resin sheet is divided into five equal parts in the thickness direction, each range is defined as the 1st to 5th ranges in order from one surface to the other of the sheet, the reinforcing fibers are contained in the resin substrate such that the volume content of the 1st, 3rd, and 5th ranges is lower than the volume content of the 2nd and 4th ranges, the volume content of the 1st and 5th ranges is the average volume content plus -30 to -1%, the volume content of the 2nd and 4th ranges is the average volume content plus +1 to +25%, and the volume content of the 3rd range is the average volume content plus -20 to +20%.

[0007] In the fiber-reinforced resin sheet of the present invention, the volume content of reinforcing fibers in the first and fifth ranges, including the surface, is lower than the volume content of reinforcing fibers in the second and fourth ranges, which are further from the surface. With such a fiber-reinforced resin sheet, the resin component contained in the first and fifth ranges, which are closer to the surface, can be relatively increased. This allows the reinforcing fibers to be firmly bonded to the resin in the first and fifth ranges, preventing the reinforcing fibers from peeling off the sheet surface.

[0008] On the other hand, since the volume content in the second and fourth ranges, which are further from the surface, is relatively high, it is possible to keep the proportion of reinforcing fibers in the vicinity of the surface (first and fifth ranges) low, as described above, while increasing the overall proportion of reinforcing fibers in the sheet. This allows for the inclusion of a relatively large amount of reinforcing fibers in the sheet, corresponding to an average volume content of 30-70%.

[0009] Furthermore, since the volume content of the third and third central ranges, which are located between the second and fourth ranges, is relatively low, it is possible to sandwich layers with a high proportion of reinforcing fibers (second and fourth ranges) between layers with a high proportion of resin (first, third, and fifth ranges), thereby improving the integration of the resin and fibers. This makes it possible to obtain a high-strength, high-quality fiber-reinforced resin sheet that firmly holds the reinforcing fibers inside.

[0010] Preferably, the volume content of the first range and the fifth range is lower than the volume content of the third range.

[0011] In this embodiment, the proportion of resin contained in the first and fifth ranges closest to the surface can be maximized. Therefore, the possibility of defects such as reinforcing fibers peeling off from the sheet surface can be further reduced.

[0012] Conversely to the above embodiment, the volume content of the third range may be lower than the volume content of the first range and the fifth range.

[0013] Preferably, the fiber-reinforced resin sheet has a thickness of 30 μm or more and 90 μm or less, and the void ratio, which is the ratio of voids to the cross-sectional area of ​​the fiber-reinforced resin sheet, is 10% or less.

[0014] Thin fiber-reinforced resin sheets with a thickness of 30 μm to 90 μm possess relatively high flexibility. Therefore, when molding composite molded products using such fiber-reinforced resin sheets as raw materials, the fluidity of the resin and fibers can be improved, thereby enhancing the formability of the composite molded products.

[0015] Furthermore, by reducing the void ratio to 10% or less, the strength and quality of the fiber-reinforced resin sheet can be further improved.

[0016] Here, the base resin may be a combination of a first resin film, a second resin film, and a third resin film that are sandwiched in a laminated state between a pair of rollers and pressurized and heated. In this case, the reinforcing fibers may include reinforcing fibers sandwiched between the first resin film and the second resin film and contained in the resin, and reinforcing fibers sandwiched between the second resin film and the third resin film and contained in the resin.

Advantages of the Invention

[0017] As described above, according to the present invention, it is possible to provide a fiber-reinforced resin sheet having a high content of reinforcing fibers and being difficult to cause peeling of the reinforcing fibers.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic cross-sectional view showing the structure of a fiber-reinforced resin sheet according to an embodiment of the present invention. [Figure 2] It is a side view schematically showing a manufacturing apparatus for manufacturing the above fiber-reinforced resin sheet. [Figure 3] It is a cross-sectional view schematically showing a state of opening a fiber bundle. [Figure 4] It is a table showing the characteristics of examples and comparative examples of the present invention.

Modes for Carrying Out the Invention

[0019] [Structure of Fiber-Reinforced Resin Sheet] FIG. 1 is a schematic cross-sectional view showing the structure of a fiber-reinforced resin sheet 1 according to an embodiment of the present invention. As shown in this figure, the fiber-reinforced resin sheet 1 includes a resin base material 11 made of a sheet-like thermoplastic resin and reinforcing fibers 10 contained in the resin base material 11. In other words, the fiber-reinforced resin sheet 1 is a thermoplastic composite material combining a thermoplastic resin and reinforcing fibers. Therefore, hereinafter, the fiber-reinforced resin sheet 1 will be abbreviated as FRTP sheet 1 as appropriate.

[0020] As the thermoplastic resin that is the material of the resin base material 11, that is, the matrix resin of the FRTP sheet 1, for example, polyamide (especially PA6, PAMXD6, PA9T, PA12), polyolefin, polyester, polyacetal, polyphenylene sulfide, polycarbonate, acrylic resin, acrylonitrile-butadiene-styrene copolymer (ABS), polyamideimide, polysulfone, polyphenylsulfone, polyetherimide, polyethersulfone, polyetheretherketone (PEEK), polyetherketoneketone, polyimide, polyarylate, fluororesin, liquid crystal polymer, thermoplastic epoxy resin, etc. can be used. Alternatively, a polymer alloy in which two or more of these thermoplastic resins are mixed may be used as the material of the resin base material 11. Also, the material of the resin base material 11 may be a thermoplastic resin each containing the above material examples, and they may be the same material as each other or different materials.

[0021] The FRTP sheet 1 is a sheet having a longitudinal direction orthogonal to the plane of FIG. 1 and having constant dimensions in the thickness direction D1 and the width direction D2. Hereinafter, one side in the thickness direction D1 corresponding to the upper side of FIG. 1 will be treated as "upper", and the other side in the thickness direction D1 corresponding to the lower side of FIG. 1 will be treated as "lower", but it is not intended to limit the posture of the FRTP sheet 1 during use.

[0022] The thickness T of the FRTP sheet 1, that is, the distance from the upper surface 1a to the lower surface 1b of the sheet 1, is set to be 30 μm or more and 90 μm or less. In a preferred embodiment, the thickness T is preferably 35 μm or more and 80 μm or less, and more preferably 35 μm or more and 70 μm or less.

[0023] The reinforcing fiber 10 is a continuous fiber oriented in the same direction. The reinforcing fibers 10 are all arranged so as to extend in a direction orthogonal to the plane of FIG. 1, that is, in the longitudinal direction of the FRTP sheet 1. That is, the reinforcing fibers 10 are contained in the resin base material 11 in a state aligned in the longitudinal direction of the FRTP sheet 1.

[0024] The reinforcing fibers 10 are widely dispersed within the resin substrate 11. As will be described in detail later, the distribution of the reinforcing fibers 10 has non-uniformity such that the density of the fibers varies along the thickness direction D1.

[0025] As the reinforcing fiber 10, carbon fiber, glass fiber, ceramic fiber, aramid fiber, basalt fiber, PBO fiber (poly(p-phenylenebenzoxazole) fiber), etc., can be used. Among these, carbon fiber is advantageous in improving the strength and corrosion resistance of the molded product. As the carbon fiber, it is preferable to use PAN (polyacrylonitrile) based carbon fiber, which has particularly high strength. When carbon fiber is used as the reinforcing fiber 10, it is preferable to set the fiber diameter to 5 μm or more and 12 μm or less.

[0026] The average volume content Vfa is defined as the percentage of the volume occupied by the reinforcing fibers 10 within the FRTP sheet 1, that is, the value obtained by dividing the volume of the reinforcing fibers 10 by the total volume of the FRTP sheet 1. The average volume content Vfa is set to be between 30% and 70%. In a preferred embodiment, the average volume content Vfa of the reinforcing fibers 10 is preferably between 30% and 65%, and more preferably between 30% and 60%.

[0027] The FRTP sheet 1 has a relatively small void ratio, which is the ratio of the area of ​​voids to the area of ​​the cross-section. Specifically, the void ratio of the FRTP sheet 1 is set to 10% or less. In a preferred embodiment, the void ratio is preferably 5% or less, and more preferably 3% or less.

[0028] [Distribution of reinforcing fibers] As shown in Figure 1, when the FRTP sheet 1 is divided into five equal parts in the thickness direction D1, each range is defined as the 1st to 5th ranges R1 to R5, from top to bottom. The 1st range R1 is the range that includes the top surface 1a of the FRTP sheet 1. The 5th range R5 is the range that includes the bottom surface 1b of the FRTP sheet 1. The 2nd range R2 is the range adjacent to the lower side of the 1st range R1. The 4th range R4 is the range adjacent to the upper side of the 5th range R5. The 3rd range R3 is the range that is located between the 2nd range R2 and the 4th range R4 and includes the center of the thickness direction D1 of the FRTP sheet 1. The thickness of each of the 1st to 5th ranges R1 to R5 is the value obtained by dividing the thickness T of the FRTP sheet 1 by 5, i.e., T / 5. The reinforcing fibers 10 are contained in the resin substrate 11 such that a specific magnitude relationship is established between the volume content of the reinforcing fibers 10 in these 1st to 5th ranges R1 to R5.

[0029] Specifically, the volume content of the reinforcing fibers 10 included in the first range R1 is defined as the first content Vf1, the volume content of the reinforcing fibers 10 included in the second range R2 is defined as the second content Vf2, the volume content of the reinforcing fibers 10 included in the third range R3 is defined as the third content Vf3, the volume content of the reinforcing fibers 10 included in the fourth range R4 is defined as the fourth content Vf4, and the volume content of the reinforcing fibers 10 included in the fifth range R5 is defined as the fifth content Vf5. In this case, the third content Vf3 is smaller than both the second content Vf2 and the fourth content Vf4. Also, both the first content Vf1 and the fifth content Vf5 are smaller than the third content Vf3. On the other hand, the first content Vf1 and the fifth content are approximately equal, and the second content Vf2 and the fourth content Vf4 are approximately equal. In other words, the following relationship of magnitude holds between the first to fifth content rates Vf1 to Vf5: (1) below.

[0030] [Mathematics 1] Vf2≒Vf4>Vf3>Vf1≒Vf5 ‥‥(1)

[0031] Thus, in this embodiment, the reinforcing fibers 10 are unevenly distributed in the resin substrate 11 such that the volume content of reinforcing fibers 10 (Vf1, Vf5) is lowest in the first range R1 and fifth range R5, which include the surface (upper and lower surfaces 1a, 1b) of the FRTP sheet 1, the volume content of reinforcing fibers 10 (Vf2, Vf4) is highest in the second range R2 and fourth range R4, which are one layer away from the surface, and the volume content of reinforcing fibers 10 (Vf3) in the central third range R3 is an intermediate value.

[0032] The volume content of the reinforcing fibers 10 in the first range R1 and the fifth range R5, i.e., the first content Vf1 and the fifth content Vf5, are set so that the difference between them and the average volume content Vfa of the FRTP sheet 1 is between -30% and -1%. This difference (-30 to -1%) is the difference when the difference when the first content Vf1 (fifth content Vf5) is greater than the average volume content Vfa is considered positive, and it is the value obtained by subtracting the average volume content Vfa from the first content Vf1 (fifth content Vf5). In other words, the first content Vf1 and the fifth content Vf5 are set to the average volume content Vfa plus -30 to -1%. In a preferred embodiment, the difference between the first content Vf1 (fifth content Vf5) and the average volume content Vfa is preferably between -25% and -3%, and more preferably between -20% and -5%.

[0033] The volume content of reinforcing fibers 10 in the second range R2 and the fourth range R4, i.e., the second content Vf2 and the fourth content Vf4, are set so that the difference from the average volume content Vfa of the FRTP sheet 1 is between +1% and +25%. This difference (+1 to +25%) is the difference when the difference is positive when the second content Vf2 (fourth content Vf4) is greater than the average volume content Vfa, and is the value obtained by subtracting the average volume content Vfa from the second content Vf2 (fourth content Vf4). In other words, the second content Vf2 and the fourth content Vf4 are set to the average volume content Vfa plus +1 to +25%. In a preferred embodiment, the difference between the second content Vf2 (fourth content Vf4) and the average volume content Vfa is preferably between +3% and +20%, and more preferably between +5% and +15%.

[0034] The volume content of reinforcing fibers 10 in the third range R3, i.e., the third content Vf3, is set such that the difference between it and the average volume content Vfa of the FRTP sheet 1 is between -20% and +20%. This difference (-20 to +20%) is the difference when the difference when the third content Vf3 is greater than the average volume content Vfa is considered positive, and it is the value obtained by subtracting the average volume content Vfa from the third content Vf3. In other words, the third content Vf3 is set to a value obtained by adding -20 to +20% to the average volume content Vfa. In a preferred embodiment, the difference between the third content Vf3 and the average volume content Vfa is preferably between -15% and +15%, and more preferably between -10% and +10%.

[0035] The numerical ranges for the first to fifth content rates Vf1 to Vf5 and the average volume content rate Vfa, as described above, can be summarized in Table 1 below.

[0036] [Table 1]

[0037] [Manufacturing method] An FRTP sheet 1 having the structure described above can be manufactured by the following method. Figure 2 is a schematic side view showing a manufacturing apparatus 20 for manufacturing an FRTP sheet 1. The manufacturing apparatus 20 shown in this figure comprises a film roller 21, a fiber roller 22, a pair of heating rollers 25, and a pair of cooling rollers 26.

[0038] The film roller 21 includes a first film delivery roller 21A for feeding the first resin film 31, a second film delivery roller 21B for feeding the second resin film 32, and a third film delivery roller 21C for feeding the third resin film 33. The first to third resin films 31 to 33 are tape-shaped resin films that form the original form of the resin substrate 11 (Figure 1) described above, and are made of appropriate thermoplastic resins corresponding to the material of the resin substrate 11. The materials of the first to third resin films 31 to 33 may be the same thermoplastic resin, or they may be different thermoplastic resins.

[0039] The thicknesses of the first to third resin films 31 to 33 are set to 3 μm or more and 35 μm or less, respectively. In a preferred embodiment, the thickness of each resin film 31 to 33 is preferably 5 μm or more and 20 μm or less, and more preferably 7 μm or more and 15 μm or less. The thicknesses of each resin film 31 to 33 may be the same or different. If the thicknesses are different, as an example, the thicknesses of the first and third resin films 31 and 33 may be made smaller than the thickness of the second resin film 32. In this case, it is preferable that the thicknesses of the first and third resin films 31 and 33 be set to a value exceeding 45% of the thickness of the second resin film 32.

[0040] The fiber roller 22 includes a first fiber delivery roller 22A for delivering the first reinforcing fiber 41 and a second fiber delivery roller 22B for delivering the second reinforcing fiber 42. The first reinforcing fiber 41 and the second reinforcing fiber 42 are continuous fibers extending along their delivery direction (in other words, the longitudinal direction of each resin film 31-33), and are incorporated into each of the resin films 31-33 during the manufacturing process to constitute the reinforcing fiber 10 (Figure 1) described above.

[0041] A fiber opener 23, 24 is positioned downstream of the first fiber delivery roller 22A and the second fiber delivery roller 22B, respectively. The fiber opener 23 (24) opens the fiber bundle FB received from the corresponding fiber delivery roller 22A (22B) before opening, thereby forming a thin, strip-shaped first reinforcing fiber 41 (second reinforcing fiber 42). Any mechanism capable of such fiber opening can be used as the fiber opener 23 (24), and various mechanisms can be used, such as a mechanism that beats and spreads the fiber bundle, a mechanism that blows air on the fiber bundle to spread it, or a mechanism that blows ultrasonic waves on the fiber bundle to spread it. In other words, the first fiber delivery roller 22A (second fiber delivery roller 22B) sends the opened, strip-shaped first reinforcing fiber 41 (second reinforcing fiber 42) downstream by passing the fiber bundle FB through the fiber opener 23 (24).

[0042] As shown in Figure 3, the width of the fiber bundle FB before fiber opening is denoted as W1, and the width of the first reinforcing fiber 41 (second reinforcing fiber 42) after fiber opening, which has spread out into a strip shape, is denoted as W2. When the fiber bundle FB is a bundle with a circular cross-section as shown in Figure 3, the width W1 of the fiber bundle FB is synonymous with the diameter. In this embodiment, the fiber opening machine 23 (24) opens the fibers so that the width W2 of the first reinforcing fiber 41 (second reinforcing fiber 42) is 1.5 times or more and 6 times or less than the width W1 of the fiber bundle FB. That is, if the fiber opening ratio is the value obtained by dividing the width W2 by the width W1, in this embodiment, the fiber opening ratio is set to 1.5 times or more and 6 times or less. In a preferred embodiment, the fiber opening ratio is preferably 1.7 times or more and 5.5 times or less, and more preferably 2 times or more and 5 times or more.

[0043] The elements 31, 41, 32, 42, and 33, which are fed out from the film rollers 21 (21A-21C) and fiber rollers 22 (22A, 22B) described above, move toward the heating roller 25 while being aggregated so that they get closer to each other as they move downstream. There is no particular limit to the direction in which the elements are arranged, but Figure 2 illustrates a pattern in which the elements are arranged vertically, with the first resin film 31 placed at the top (and the third resin film 33 placed at the bottom). That is, the first resin film 31, the first reinforcing fiber 41, the second resin film 32, the second reinforcing fiber 42, and the third resin film 33 are fed toward the heating roller 25 in this order from top to bottom, and are guided so that the vertical distance between them decreases as they approach the heating roller 25. As a result, a laminate 100 is formed just upstream of the heating roller 25, in which the elements 31, 41, 32, 42, and 33 are stacked vertically.

[0044] As described above, in this embodiment, the feeding operation of the rollers 21 and 22 causes the first resin film 31 and the second resin film 32 to be positioned facing each other in the vertical direction, and the first reinforcing fiber 41 is sandwiched between the first and second resin films 31 and 32. Furthermore, the third resin film 33 is positioned facing the second resin film 32 from the opposite side (below) of the first resin film 31, and the second reinforcing fiber 42 is sandwiched between the second and third resin films 32 and 33. As a result, a laminate 100 is formed in which the first resin film 31, the first reinforcing fiber 41, the second resin film 32, the second reinforcing fiber 42, and the third resin film 33 are stacked in this order from top to bottom. At this point, before passing through the heating roller 25, the laminate 100 is a laminate in which the layers are simply overlapping, and the layers have not yet been bonded together.

[0045] The laminate 100 is sent downstream and introduced between a pair of heating rollers 25. The heating rollers 25 are high-temperature rollers heated by a heater (not shown). The laminate 100 is heated and pressurized by being sandwiched between these high-temperature heating rollers 25. Heating of the laminate 100 by the heating rollers 25 softens the first to third resin films 31 to 33. That is, the heating rollers 5 pressurize the laminate 100 in the thickness direction while heating the laminate 100 to a temperature at which each resin film 31 to 33 softens.

[0046] The heating and pressurizing described above softens the first to third resin films 31 to 33 while pressing them against the first and second reinforcing fibers 41 and 42. As a result, the first to third resin films 31 to 33 impregnate the first and second reinforcing fibers 41 and 42. Specifically, the softened first resin film 31 and second resin film 32 impregnate the first reinforcing fiber 41 from above and below, while the softened second resin film 32 and third resin film 33 impregnate the second reinforcing fiber 42 from above and below.

[0047] The laminate 100, which has been discharged from the heating roller 25, is then introduced between a pair of cooling rollers 26. The cooling rollers 26 are low-temperature rollers cooled by a cooler (not shown). The laminate 100 is cooled and pressurized by being sandwiched between these low-temperature cooling rollers 26. As a result, the softened first to third resin films 31 to 33 harden again, and the resin films 31 to 33 are bonded (welded) together. This forms a single resin layer, i.e., a resin substrate 11 (Figure 1), in which the first to third resin films 31 to 33 are integrated.

[0048] Furthermore, in order to prevent the laminate 100 from sticking to the heating roller 25 or cooling roller 26 as described above, a release film or release sheet may be placed between the surface (resin film) of the laminate 100 and each roller 25, 26.

[0049] The FRTP sheet 1 is manufactured through the above process. Specifically, the FRTP sheet 1 (Figure 1) is manufactured, comprising a sheet-like resin substrate 11 of a predetermined thickness and reinforcing fibers 10 dispersed and contained in the resin substrate 11. In other words, the resin substrate 11 is formed by first to third resin films 31 to 33 that are softened, then hardened and integrated; the reinforcing fibers 10 of the upper half of the sheet are formed by first reinforcing fibers 41 contained in the resin and sandwiched between first and second resin films 31 and 32; and the reinforcing fibers 10 of the lower half of the sheet are formed by second reinforcing fibers 42 contained in the resin and sandwiched between second and third resin films 32 and 33.

[0050] Furthermore, due to the process in which two sets of reinforcing fibers 41 and 42 are sandwiched between three resin films 31 to 33, the density of the reinforcing fibers 10 naturally decreases near the surface (upper and lower surfaces) of the resin substrate 11 and in the central part of the resin substrate 11. In particular, the density of the reinforcing fibers 10 decreases significantly near the surface of the resin substrate 11. Conversely, the density of the reinforcing fibers 10 increases near the position corresponding to the boundary between the resin films 31 to 33. This variation in the density of the reinforcing fibers 10 establishes the relative magnitudes of the first to fifth content rates Vf1 to Vf5 as shown in equation (1) or Table 1 above.

[0051] Downstream of the cooling roller 26, a winding roller 28 is positioned to wind up the FRTP sheet 1. That is, after the FRTP sheet 1 is led out from the cooling roller 26, it is wound up by the winding roller 28 and bundled into a roll.

[0052] [Effects and Effects] As described above, in this embodiment, the FRTP sheet 1 has a lower volume content of reinforcing fibers 10 in the first range R1 and fifth range R5, including the surface (upper and lower surfaces 1a and 1b) (first and fifth content Vf1 and Vf5), than in the second range R2 and fourth range R4, which are further from the surface (second and fourth content Vf2 and Vf4). With such an FRTP sheet 1, the resin component contained in the first range R1 and fifth range R5, which are closer to the surface, can be relatively increased, so the reinforcing fibers 10 can be firmly bonded to the resin in the first range R1 and fifth range R5, and the reinforcing fibers 10 can be prevented from peeling off from the sheet surface.

[0053] On the other hand, the volume content in the second range R2 and the fourth range R4, which are further from the surface (second and fourth content Vf2 and Vf4), is relatively high. Therefore, as described above, the proportion of reinforcing fibers 10 near the surface (first range R1 and fifth range R5) can be kept low while increasing the overall proportion of reinforcing fibers 10 in the sheet, allowing the sheet to contain a relatively large amount of reinforcing fibers, corresponding to an average volume content Vfa of 30-70%.

[0054] Furthermore, in this embodiment, the volume content of the third range R3, which is furthest from the surface (third range content Vf3), is the second lowest after the volume content of the first range R1 and fifth range R5 (first and fifth range content Vf1, Vf5) described above. In other words, the resin components contained in the first range R1 and fifth range R5, which are close to the surface, and the third range R3 in the center are greater than the resin components contained in the other second range R2 and fourth range R4. As a result, layers with a high proportion of reinforcing fibers 10 (second and fourth ranges R2, R4) can be sandwiched between layers with a high proportion of resin (first, third, and fifth ranges R1, R3, R5), thereby improving the integrity of the resin and fibers. Therefore, a high-strength and high-quality FRTP sheet 1 can be obtained that firmly holds the reinforcing fibers 10 inside.

[0055] Furthermore, in this embodiment, a method is employed to manufacture the FRTP sheet 1 having the structure described above, which involves alternately laminating resin films and reinforcing fibers and then heating them. Specifically, the first resin film 31, the first reinforcing fiber 41, the second resin film 32, the second reinforcing fiber 42, and the third resin film 33 are laminated in this order, and the formed laminate 100 is subjected to processing such as heating with a heating roller 25, thereby manufacturing the FRTP sheet 1. This method has the advantage that it is possible to appropriately manufacture the FRTP sheet 1 having the structure described above, in which the content of reinforcing fibers 10 differs depending on each range in the thickness direction D1 (first to fifth ranges R1 to R5).

[0056] Specifically, when the first resin film 31 and the second resin film 32, which are positioned opposite each other with the first reinforcing fiber 41 in between, are heated and softened, the first resin film 31 and the second resin film 32 impregnate the first reinforcing fiber 41. Similarly, when the second resin film 32 and the third resin film 33, which are positioned opposite each other with the second reinforcing fiber 42 in between, are heated and softened, the second resin film 32 and the third resin film 33 impregnate the second reinforcing fiber 42. As a result, an FRTP sheet 1 can be manufactured comprising a resin base material 11 formed by welding and integrating each of the resin films 31 to 33, and reinforcing fibers 10 contained within it. In this process, the proportion of resin naturally increases near the surface and in the center of the sheet, while the proportion of fibers naturally increases elsewhere. As a result, the desired relative size relationship of the reinforcing fibers 10 in each of the five equally divided ranges (1st to 5th ranges R1 to R5) along the thickness direction D1 can be established, thereby improving the quality and strength of the FRTP sheet 1.

[0057] Furthermore, the method of this embodiment, in which a laminate 100 of resin film and reinforcing fibers is sandwiched between heating rollers 25, is advantageous for thinning the FRTP sheet 1 and also facilitates the integration of the resin and fibers. Therefore, even when manufacturing a relatively thin FRTP sheet 1 having a thickness T of 30 to 90 μm as in this embodiment, it is possible to firmly hold a relatively large amount of reinforcing fibers 10 corresponding to an average volume content Vfa of 30 to 70% inside. In addition, since the resin is sufficiently impregnated into the reinforcing fibers 10, the occurrence of voids inside the FRTP sheet 1 can be suppressed, and the void ratio of the FRTP sheet 1 can be reduced to 10% or less. When a composite molded product is formed using a thin FRTP sheet 1 with a low void ratio containing a large amount of reinforcing fibers 10 in this way, the strength of the composite molded product can be increased, and even composite molded products with relatively complex shapes can be molded well. In other words, according to this embodiment, it is possible to manufacture a high-quality FRTP sheet 1 that contributes to improving the strength and moldability of composite molded products.

[0058] [Examples] Figure 4 shows the results obtained by actually manufacturing FRTP sheets 1 using the methods of the embodiments described above, as Examples 1 and 2. Specifically, FRTP sheets 1 were manufactured under two different conditions, varying the thickness of the first to third resin films 31 to 33 and the fiber opening ratio of the first and second reinforcing fibers 41 and 42, and the resulting products were designated as Examples 1 and 2. In Example 1, the thickness of the first to third resin films 31 to 33 was set to 7 μm, and the fiber opening ratio of the first and second reinforcing fibers 41 and 42 was set to 2. In Example 2, the thickness of the first to third resin films 31 to 33 was set to 15 μm, and the fiber opening ratio of the first and second reinforcing fibers 41 and 42 was set to 2.2. In both Examples 1 and 2, polyamide 6 (PA6) was used as the material for the first to third resin films 31 to 33, and PAN-based carbon fiber was used as the material for the first and second reinforcing fibers 41 and 42. The PAN-based carbon fiber used had a fiber diameter of 7 μm, a fiber count of 12,000, and a fineness of 800 Tex.

[0059] Figure 4 also shows Comparative Examples 1 and 2. In Comparative Examples 1 and 2, the materials of the first to third resin films 31 to 33 and the first and second reinforcing fibers 41 and 42 are the same as in Examples 1 and 2, but the film thickness or fiber opening ratio differs from Examples 1 and 2. Specifically, in Comparative Example 1, the fiber opening ratio of the first and second reinforcing fibers 41 and 42 was set to 1 (no opening). In Comparative Example 2, the thickness of the first to third resin films 31 to 33 was set to 50 μm, and the fiber opening ratio of the first and second reinforcing fibers 41 and 42 was set to 3.

[0060] As shown in Figure 4, in Examples 1 and 2, both the film thickness and fiber opening ratio fell within the specified range of the above embodiment (film thickness 3 to 35 μm, fiber opening ratio 1.5 to 6 times). As a result, the thickness (sheet thickness) T of the obtained FRTP sheet 1, the average volume content Vfa of the reinforcing fibers 10, and the void ratio all fell within the specified range of the above embodiment (sheet thickness 30 to 90 μm, average volume content 30 to 70%, void ratio 10% or less). Specifically, the sheet thickness T was 66.6 μm in Example 1 and 85.4 μm in Example 2. The average volume content Vfa was 68.5% in Example 1 and 47.3% in Example 2. The void ratio was 0% in both Examples 1 and 2. Furthermore, in both Examples 1 and 2, no peeling (fuzzing) of the reinforcing fibers 10 was particularly observed.

[0061] In contrast, in Comparative Examples 1 and 2, the sheet thickness T, average volume content Vfa, or void ratio fell outside the specified range. Specifically, in Comparative Example 1, the sheet thickness T was 109.9 μm, which is greater than the specified range (30-90 μm), the average volume content Vfa was 80.9%, which is greater than the specified range (30-70%), and the void ratio was 12%, which is greater than the specified range (10% or less). This is thought to be due to the use of unopened reinforcing fibers with a fiber opening ratio of 1. In Comparative Example 2, the sheet thickness T was 179.6 μm, which is greater than the specified range, and the average volume content Vfa was 16.5%, which is smaller than the specified range. This is thought to be due to the use of a resin film with a thickness of 50 μm.

[0062] Based on the above results, the superiority of the FRTP sheet 1 of the above embodiment was confirmed.

[0063] [Differentiation] In the above embodiment, the volume content of the third range R3 (third content Vf3) is greater than the volume content of the first range R1 and the fifth range R5 (first and fifth content Vf1, Vf5), and less than the volume content of the second range R2 and the fourth range R4 (second and fourth content Vf2, Vf4). However, the third content Vf3 only needs to be less than the second and fourth content Vf2, Vf4, and the relative magnitudes with the first and fifth content Vf1, Vf5 are not particularly limited. For example, the third content Vf3 may be equal to the first and fifth content Vf1, Vf5, or it may be less than the first and fifth content Vf1, Vf5. However, if the third content Vf3 is made larger than the first and fifth content Vf1 and Vf5 as in the above embodiment, the proportion of resin contained in the first and fifth ranges R1 and R5, which are close to the surface, can be made the highest, thus further reducing the possibility of defects such as the reinforcing fibers 10 peeling off from the sheet surface. [Explanation of symbols]

[0064] 1. Fiber-reinforced resin sheet (FRTP sheet) 10 Reinforced Fibers 11 Resin substrate R1 First Range R2 Second Range R3 Third Range R4 4th range R5 5th range

Claims

1. A fiber-reinforced resin sheet, A resin substrate made of a sheet-like thermoplastic resin, The resin substrate contains reinforcing fibers that are oriented in the same direction and have an average volume content of 30% to 70%. When the fiber-reinforced resin sheet is divided into five equal parts in the thickness direction, and each of these parts is defined as the 1st to 5th ranges, sequentially from one surface to the other of the sheet, the reinforcing fibers are contained in the resin substrate such that the volume content of the 1st, 3rd, and 5th ranges is lower than the volume content of the 2nd and 4th ranges. The volume content in the first range and the fifth range is the average volume content plus -30% to -1%. The volume content in the second range and the fourth range is a value obtained by adding +1 to +25% to the average volume content. A fiber-reinforced resin sheet in which the volume content in the third range is a value obtained by adding -20% to +20% to the average volume content.

2. In the fiber-reinforced resin sheet according to claim 1, A fiber-reinforced resin sheet in which the volume content of the first range and the fifth range is lower than the volume content of the third range.

3. In the fiber-reinforced resin sheet according to claim 1, A fiber-reinforced resin sheet in which the volume content of the third range is lower than the volume content of the first range and the fifth range.

4. In the fiber-reinforced resin sheet according to any one of claims 1 to 3, A fiber-reinforced resin sheet having a thickness of 30 μm or more and 90 μm or less, and having a void ratio of 10% or less, which is the ratio of voids to the cross-sectional area of ​​the fiber-reinforced resin sheet.

5. In the fiber-reinforced resin sheet according to any one of claims 1 to 3, The base resin is formed by bonding together a first resin film, a second resin film, and a third resin film that are sandwiched in a laminated state between a pair of rollers, pressurized, and heated. The fiber-reinforced resin sheet comprises reinforcing fibers sandwiched between the first resin film and the second resin film and contained within the resin, and reinforcing fibers sandwiched between the second resin film and the third resin film and contained within the resin.

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