Fiber-reinforced resin sheet

Abstract

To provide a fiber-reinforced resin sheet which has a high percentage content of reinforcement fibers and prevents peeling of the reinforcement fibers.SOLUTION: A fiber-reinforced resin sheet 1 includes a resin base material 11 composed of a sheet-like thermoplastic resin, and reinforcement fibers 10 which are aligned in the same direction, have an average volume percentage content of 30% or more and 70% or less and are contained in the resin base material 11. When each range when the fiber-reinforced resin sheet 1 is equally divided into five in a thickness direction is defined by first to fifth ranges R1 to R5, the reinforcement fibers 10 are contained in the resin base material 11 so that volume percentage contents of a first range R1, a third range R3 and a fifth range R5 are lower than volume percentage contents of a second range R2 and a fourth range R4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fiber-reinforced resin sheet in which reinforcing fibers are contained in a resin substrate. [Background technology]

[0002] One example of a fiber reinforced resin sheet is disclosed in the following Patent Document 1. The fiber reinforced resin sheet of Patent Document 1 includes a thermoplastic resin film and reinforcing fibers laminated on both sides of the resin film. The reinforcing fibers are laminated on both sides of the resin film so that the volume fraction (Vf) of the reinforcing fibers relative to the fiber reinforced resin sheet is 60 to 75% or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-103810 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a relatively large amount of reinforcing fibers, equivalent to a volume content of 60 to 75%, is laminated on both sides of a resin film as in Patent Document 1, the resin film may not sufficiently impregnate the reinforcing fibers. If the reinforcing fibers are not sufficiently impregnated with the resin film, problems such as peeling of the reinforcing fibers from the resin film may occur.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a fiber-reinforced resin sheet having a high content of reinforcing fibers and in which peeling of the reinforcing fibers is unlikely to occur. [Means for solving the problem]

[0006] In order 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 where the reinforcing fibers are oriented in the same direction and have an average volume content of 30% or more and 70% or less. When the fiber-reinforced resin sheet is divided into five equal parts in the thickness direction, and each of the five equal parts is defined as a first to fifth range from one surface to the other surface of the sheet, the reinforcing fibers are contained in the resin substrate such that the volume contents of the first range, the third range, and the fifth range are lower than the volume contents of the second range and the fourth range.

[0007] In the fiber-reinforced resin sheet of the present invention, the volume content of the reinforcing fibers in the first and fifth regions including the surface is lower than the volume content of the reinforcing fibers in the second and fourth regions away from the surface. With such a fiber-reinforced resin sheet, the resin components contained in the first and fifth regions close to the surface can be relatively increased, so that the reinforcing fibers can be firmly bonded to the resin in the first and fifth regions, and peeling of the reinforcing fibers from the sheet surface can be prevented.

[0008] On the other hand, since the volume content of the second and fourth ranges away from the surface is relatively high, it is possible to increase the proportion of reinforcing fibers in the sheet as a whole while keeping the proportion of reinforcing fibers near the surface (first and fifth ranges) low as described above, and to make the sheet contain a relatively large amount of reinforcing fibers equivalent to an average volume content of 30 to 70%.

[0009] Furthermore, because the volume fraction between the second and fourth regions, i.e., the central third region, is relatively low, layers with a high proportion of reinforcing fiber (second and fourth regions) can be sandwiched between layers with a high proportion of resin (first, third and fifth regions), improving the integrity of the resin and fiber. This makes it possible to obtain a high-strength, high-quality fiber-reinforced resin sheet with the reinforcing fiber firmly held inside.

[0010] Preferably, the volume fractions of the first range and the fifth range are lower than the volume fraction of the third range.

[0011] In this embodiment, the ratio of the resin contained in the first and fifth regions close to the surface can be maximized, which can further reduce the possibility of the reinforcing fibers peeling off from the sheet surface.

[0012] Specifically, the volume contents of the first to fifth ranges are preferably as follows in relation to the average volume content of the entire sheet: the volume contents of the first and fifth ranges are preferably values ​​obtained by adding -30 to -1% to the average volume content, the volume contents of the second and fourth ranges are preferably values ​​obtained by adding +1 to +25% to the average volume content, and the volume content of the third range is preferably values ​​obtained by adding -20 to +20% to the average volume content.

[0013] Preferably, the fiber reinforced resin sheet has a thickness of 30 μm or more and 90 μm or less.

[0014] A thin fiber-reinforced resin sheet having a thickness of 30 μm or more and 90 μm or less has a relatively high flexibility, and therefore, when a composite molded product is molded using the fiber-reinforced resin sheet as a raw material, the flow properties of the resin and the fibers can be improved, and the formability of the composite molded product can be improved.

[0015] Preferably, the void ratio, which is the ratio of voids to the cross-sectional area of ​​the fiber reinforced resin sheet, is 10% or less.

[0016] In this way, when the void ratio is reduced to 10% or less, the strength and quality of the fiber reinforced resin sheet can be further improved. Effect 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 reinforcing fiber content and in which peeling of the reinforcing fibers is unlikely to occur. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a structure of a fiber-reinforced resin sheet according to one embodiment of the present [Diagram 2] FIG. 2 is a side view illustrating a manufacturing apparatus for manufacturing the fiber-reinforced resin sheet. [Diagram 3] FIG. 4 is a cross-sectional view illustrating a state in which a fiber bundle is opened. [Figure 4] 1 is a table showing characteristics of examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 one embodiment of the present invention. As shown in the figure, the fiber reinforced resin sheet 1 includes a resin substrate 11 made of a sheet-shaped thermoplastic resin and reinforcing fibers 10 contained in the resin substrate 11. In other words, the fiber reinforced resin sheet 1 is a thermoplastic composite material that combines a thermoplastic resin and reinforcing fibers. For this reason, hereinafter, the fiber reinforced resin sheet 1 will be appropriately abbreviated as FRTP sheet 1.

[0020] As the thermoplastic resin that is the material of the resin substrate 11, that is, the matrix resin of the FRTP sheet 1, for example, polyamide (particularly 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. may 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 substrate 11. In addition, the materials of the resin substrate 11 may be the same or different materials as long as each of them is a thermoplastic resin including the above-mentioned material examples.

[0021] The FRTP sheet 1 is a sheet whose longitudinal direction is perpendicular to the plane of the paper in Fig. 1 and has certain dimensions in the thickness direction D1 and width direction D2. In the following, one side in the thickness direction D1 corresponding to the upper part of Fig. 1 will be treated as the "upper" side, and the other side in the thickness direction D1 corresponding to the lower part of Fig. 1 will be treated as the "lower" side, but this is not intended to limit the position of the FRTP sheet 1 when it is in 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 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 fibers 10 are continuous fibers oriented in the same direction. The reinforcing fibers 10 are all arranged so as to extend in a direction perpendicular to the paper surface of Fig. 1, that is, in the longitudinal direction of the FRTP sheet 1. In other words, the reinforcing fibers 10 are contained in the resin substrate 11 in a state where they are 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 is non-uniform such that the fibers vary in density along the thickness direction D1.

[0025] As the reinforcing fiber 10, carbon fiber, glass fiber, ceramic fiber, aramid fiber, basalt fiber, PBO fiber (polyparaphenylenebenzoxazole fiber), etc. can be used. Among them, 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) 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 the ratio of the volume of the reinforcing fibers 10 in 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 30% or more and 70% or less. In a preferred embodiment, the average volume content Vfa of the reinforcing fibers 10 is preferably 30% or more and 65% or less, and more preferably 30% or more and 60% or less.

[0027] The FRTP sheet 1 has a relatively small void ratio, which is the ratio of the area of ​​voids to the cross section of the sheet. 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 FIG. 1, when the FRTP sheet 1 is divided into five equal parts in the thickness direction D1, the respective parts are defined as the first to fifth ranges R1 to R5 from the top. The first range R1 is a range including the upper surface 1a of the FRTP sheet 1. The fifth range R5 is a range including the lower surface 1b of the FRTP sheet 1. The second range R2 is a range adjacent to the lower side of the first range R1. The fourth range R4 is a range adjacent to the upper side of the fifth range R5. The third range R3 is a range located between the second range R2 and the fourth range R4 and including the center of the thickness direction D1 of the FRTP sheet 1. The thicknesses of the first to fifth ranges R1 to R5 are all the value obtained by dividing the thickness T of the FRTP sheet 1 by 5, that is, T / 5. The reinforcing fibers 10 are contained in the resin substrate 11 so that a specific magnitude relationship is established between the volume contents of the reinforcing fibers 10 in the first to fifth ranges R1 to R5.

[0029] Specifically, the volume content of the reinforcing fibers 10 included in the first range R1 is the first content Vf1, the volume content of the reinforcing fibers 10 included in the second range R2 is the second content Vf2, the volume content of the reinforcing fibers 10 included in the third range R3 is the third content Vf3, the volume content of the reinforcing fibers 10 included in the fourth range R4 is the fourth content Vf4, and the volume content of the reinforcing fibers 10 included in the fifth range R5 is the fifth content Vf5. In this case, the third content Vf3 is smaller than both the second content Vf2 and the fourth content Vf4. In addition, 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. That is, the first to fifth content rates Vf1 to Vf5 have a magnitude relationship as shown in the following formula (1).

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

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

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

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

[0034] The volume content of the reinforcing fibers 10 in the third range R3, that is, the third content Vf3, is set so that the difference from the average volume content Vfa of the FRTP sheet 1 is -20% or more and +20% or less. This difference (-20 to +20%) is the difference when the third content Vf3 is greater than the average volume content Vfa, and 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 -15% or more and +15% or less, and more preferably -10% or more and +10% or less.

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

[0036] [Table 1]

[0037] [Manufacturing method] The FRTP sheet 1 having the above-mentioned structure can be manufactured by the following method. Figure 2 is a side view that shows a schematic diagram of a manufacturing apparatus 20 for manufacturing the FRTP sheet 1. The manufacturing apparatus 20 shown in this figure includes 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-feeding roller 21A that feeds out the first resin film 31, a second film-feeding roller 21B that feeds out the second resin film 32, and a third film-feeding roller 21C that feeds out 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 base material 11 (FIG. 1) described above, and are made of an appropriate thermoplastic resin that corresponds to the material of the resin base material 11. The materials of the first to third resin films 31 to 33 may be the same thermoplastic resin or different thermoplastic resins.

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

[0040] The fiber roller 22 includes a first fiber-feeding roller 22A that feeds out a first reinforcing fiber 41, and a second fiber-feeding roller 22B that feeds out a second reinforcing fiber 42. The first reinforcing fiber 41 and the second reinforcing fiber 42 are continuous fibers extending along the feeding direction (in other words, the longitudinal direction of each of the resin films 31-33), and are contained in each of the resin films 31-33 during the manufacturing process to form the above-mentioned reinforcing fiber 10 (FIG. 1).

[0041] The first fiber delivery roller 22A and the second fiber delivery roller 22B are provided downstream with a fiber spreader 23, 24, respectively. The fiber spreader 23 (24) spreads the fiber bundle FB before being spread, received from the corresponding fiber delivery roller 22A (22B), to form a first reinforcing fiber 41 (second reinforcing fiber 42) spread in a thin band shape. The fiber spreader 23 (24) may be any mechanism capable of such a fiber spreading process, and may be any of various mechanisms, such as a mechanism for beating the fiber bundle to spread it, a mechanism for blowing the fiber bundle to spread it, or a mechanism for applying ultrasonic waves to the fiber bundle to spread it. In other words, the first fiber delivery roller 22A (second fiber delivery roller 22B) passes the fiber bundle FB through the fiber spreader 23 (24) to send out the spread band-shaped first reinforcing fiber 41 (second reinforcing fiber 42) downstream.

[0042] As shown in FIG. 3, the width of the fiber bundle FB before spreading is W1, and the width of the first reinforcing fibers 41 (second reinforcing fibers 42) after spreading, which spreads in a band shape, is W2. When the fiber bundle FB is a bundle having a circular cross section as shown in FIG. 3, the width W1 of the fiber bundle FB is synonymous with the diameter. In this embodiment, the spreader 23 (24) performs spreading so that the width W2 of the first reinforcing fibers 41 (second reinforcing fibers 42) is 1.5 to 6 times the width W1 of the fiber bundle FB. That is, when the value obtained by dividing the width W2 by the width W1 is set as the spreading ratio, in this embodiment, the spreading ratio is set to 1.5 to 6 times. In a preferred embodiment, the spreading ratio is preferably 1.7 to 5.5 times, and more preferably 2 to 5 times.

[0043] The elements 31, 41, 32, 42, and 33 sent from the film roller 21 (21A to 21C) and the fiber roller 22 (22A, 22B) described above are gathered together so that the distance between them becomes closer toward the downstream side, and move toward the heating roller 25. There is no particular limitation on the direction in which the elements are arranged, but FIG. 2 illustrates a pattern in which the elements are arranged vertically, with the first resin film 31 arranged at the top (the third resin film 33 arranged 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 sent toward the heating roller 25 in a state of being arranged in this order from the top, and are guided so that the vertical interval between them becomes shorter as they approach the heating roller 25. As a result, a laminate 100 in which the elements 31, 41, 32, 42, and 33 are stacked vertically is formed immediately upstream of the heating roller 25.

[0044] In this manner, in this embodiment, the first resin film 31 and the second resin film 32 are disposed opposite to each other in the vertical direction by the above-described feeding operation of the rollers 21 and 22, and the first reinforcing fiber 41 is sandwiched between the first and second resin films 31 and 32. In addition, the third resin film 33 is disposed so as to face 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 laminated in this order from above. At this point before passing through the heating roller 25, the laminate 100 is a laminate in which the layers are merely overlapped, and the layers are not yet bonded to each other.

[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. The heating of the laminate 100 by the heating rollers 25 softens the first to third resin films 31-33. That is, the heating rollers 5 pressurize the laminate 100 in the thickness direction while heating the laminate 100 to a temperature at which the resin films 31-33 soften.

[0046] The above-mentioned heating and pressurization softens the first to third resin films 31-33 while pressing them against the first and second reinforcing fibers 41, 42. This causes the first to third resin films 31-33 to impregnate the first and second reinforcing fibers 41, 42. That is, the softened first resin film 31 and second resin film 32 impregnate the first reinforcing fiber 41 from above and below, and 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 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. This causes the softened first to third resin films 31 to 33 to harden again, and the resin films 31 to 33 are bonded (welded) to each other. This forms a single resin layer in which the first to third resin films 31 to 33 are integrated, that is, the resin substrate 11 (FIG. 1).

[0048] In order to prevent the laminate 100 from sticking to the heating roller 25 or the cooling roller 26 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] Through the above-mentioned processes, the FRTP sheet 1 is manufactured. That is, the FRTP sheet 1 (FIG. 1) is manufactured, which includes a sheet-like resin base material 11 of a predetermined thickness and reinforcing fibers 10 dispersed and contained in the resin base material 11. In other words, the resin base material 11 is formed by the first to third resin films 31 to 33 that are softened and then hardened and integrated, the reinforcing fibers 10 in the upper half of the sheet are formed by the first reinforcing fibers 41 that are sandwiched between the first and second resin films 31, 32 and contained in the resin, and the reinforcing fibers 10 in the lower half of the sheet are formed by the second reinforcing fibers 42 that are sandwiched between the second and third resin films 32, 33 and contained in the resin.

[0050] Furthermore, due to the process in which the two sets of reinforcing fibers 41, 42 are sandwiched between the three resin films 31-33, the density of the reinforcing fibers 10 naturally becomes low near the surface (top and bottom surfaces) of the resin substrate 11 and in the center 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 positions corresponding to the boundaries of the resin films 31-33. The density of the reinforcing fibers 10 thus obtained establishes the magnitude relationship of the first to fifth content rates Vf1-Vf5 as shown in the above formula (1) or Table 1.

[0051] A winding roller 28 that winds up the FRTP sheet 1 is disposed downstream of the cooling roller 26. 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 assembled into a roll.

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

[0053] On the other hand, since the volume contents (second and fourth contents Vf2, Vf4) of the second range R2 and the fourth range R4 away from the surface are relatively high, it is possible to increase the proportion of the reinforcing fibers 10 in the entire sheet while keeping the proportion of the reinforcing fibers 10 in the vicinity of the surface (first range R1 and fifth range R5) low as described above, and it is possible to contain a relatively large amount of reinforcing fibers in the sheet, equivalent to an average volume content Vfa of 30 to 70%.

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

[0055] In addition, as a method for manufacturing the FRTP sheet 1 having the above-mentioned structure, in this embodiment, a method is adopted in which resin films and reinforcing fibers are alternately laminated and heated. That is, the first resin film 31, the first reinforcing fibers 41, the second resin film 32, the second reinforcing fibers 42, and the third resin film 33 are laminated in this order, and the formed laminate 100 is subjected to a process such as heating by 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 above-mentioned structure in which the content of the reinforcing fibers 10 varies depending on each range (first to fifth ranges R1 to R5) in the thickness direction D1.

[0056] That is, the first resin film 31 and the second resin film 32 arranged opposite to each other with the first reinforcing fiber 41 in between are heated and softened, so that the first resin film 31 and the second resin film 32 are impregnated into the first reinforcing fiber 41. Similarly, the second resin film 32 and the third resin film 33 arranged opposite to each other with the second reinforcing fiber 42 in between are heated and softened, so that the second resin film 32 and the third resin film 33 are impregnated into the second reinforcing fiber 42. This makes it possible to manufacture the FRTP sheet 1 including the resin base material 11 formed by welding and integrating the resin films 31 to 33, and the reinforcing fiber 10 contained therein. At this time, the proportion of resin naturally becomes higher near the surface and in the center of the sheet, and the proportion of fiber naturally becomes higher in other areas. As a result, the desired magnitude relationship described above can be established for the volume content of the reinforcing fibers 10 in each of five equally divided ranges (first to fifth ranges R1 to R5) in the thickness direction D1, thereby improving the quality and strength of the FRTP sheet 1.

[0057] In addition, the method of this embodiment in which the laminate 100 of the resin film and the reinforcing fibers is sandwiched between the heating rollers 25 is advantageous for thinning the FRTP sheet 1, and also makes it easy to improve the integrity of the resin and the fibers. Therefore, even when manufacturing a relatively thin FRTP sheet 1 having a thickness T of 30 to 90 μm as in this embodiment, a relatively large number of reinforcing fibers 10 corresponding to an average volume content Vfa of 30 to 70% can be firmly held inside the FRTP sheet. In addition, since the reinforcing fibers 10 are sufficiently impregnated with the resin, it is possible to prevent the generation of voids inside the FRTP sheet 1, and the void ratio of the FRTP sheet 1 can be reduced to 10% or less. And, when a composite molded product is molded using a thin FRTP sheet 1 with a low void ratio containing a large number of reinforcing fibers 10 in this way, the strength of the composite molded product can be increased, and even a composite molded product with a relatively complicated shape can be molded well. That is, according to this embodiment, a high-quality FRTP sheet 1 that contributes to improving the strength and moldability of the composite molded product can be manufactured.

[0058] [Example] The results obtained by actually manufacturing the FRTP sheet 1 by the method of the embodiment described above are shown in FIG. 4 as Examples 1 and 2. That is, the FRTP sheet 1 was manufactured under two conditions in which the thicknesses of the first to third resin films 31 to 33 and the opening ratios of the first and second reinforcing fibers 41 and 42 were different, and the results obtained were named Examples 1 and 2, respectively. In Example 1, the thicknesses of the first to third resin films 31 to 33 were all 7 μm, and the opening ratios of the first and second reinforcing fibers 41 and 42 were all 2. In Example 2, the thicknesses of the first to third resin films 31 to 33 were all 15 μm, and the opening ratios of the first and second reinforcing fibers 41 and 42 were all 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 fibers were 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, 12,000 fibers, and a fineness of 800 Tex.

[0059] 4 also shows Comparative Examples 1 and 2. In Comparative Examples 1 and 2, the materials of the first to third resin films 31-33 and the first and second reinforcing fibers 41, 42 are the same as those in Examples 1 and 2, but the film thickness or the spreading ratio is different from that in Examples 1 and 2. Specifically, in Comparative Example 1, the spreading ratios of the first and second reinforcing fibers 41, 42 were both set to 1 (non-spread). In Comparative Example 2, the thicknesses of the first to third resin films 31-33 were all set to 50 μm, and the spreading ratios of the first and second reinforcing fibers 41, 42 were all set to 3.

[0060] As shown in FIG. 4, in Examples 1 and 2, the film thickness and the fiber spreading ratio were all within the ranges specified in the above embodiment (film thickness 3 to 35 μm, fiber spreading 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 were all within the ranges specified in 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. In addition, in both Examples 1 and 2, the phenomenon of peeling of the reinforcing fibers 10 (fuzzing) was not particularly observed.

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

[0062] The above results confirmed the superiority of the FRTP sheet 1 of the above embodiment.

[0063] [Variations] In the above embodiment, the volume content of the third range R3 (third content Vf3) is larger than the volume content of the first range R1 and the fifth range R5 (first and fifth content Vf1, Vf5) and smaller than the volume content of the second range R2 and the fourth range R4 (second and fourth content Vf2, Vf4), but the third content Vf3 only needs to be smaller than the second and fourth content Vf2, Vf4, and the relationship between the third content Vf3 and the first and fifth content Vf1, Vf5 is not particularly limited. For example, the third content Vf3 may be equal to the first and fifth content Vf1, Vf5, or may be smaller than the first and fifth content Vf1, Vf5. However, when the third content rate Vf3 is made larger than the first and fifth content rates Vf1, Vf5 as in the above embodiment, the proportion of resin contained in the first and fifth ranges R1, R5 close to the surface can be made the highest, thereby further reducing the possibility of the reinforcing fiber 10 peeling off from the sheet surface. [Explanation of symbols]

[0064] 1 Fiber reinforced plastic sheet (FRTP sheet) 10 Reinforced Fiber 11 Resin substrate R1 1st range R2 Second range R3 3rd range R4 4th range R5 5th range

Claims

1. A fiber reinforced resin sheet, A resin substrate made of a sheet-like thermoplastic resin; Reinforcing fibers are contained in the resin substrate in a state where they 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, each range is defined as a first to a fifth range from one surface to the other surface of the sheet, and the reinforcing fibers are contained in the resin base material so that the volume contents of the first range, the third range, and the fifth range are lower than the volume contents of the second range and the fourth range. A fiber-reinforced resin sheet.

2. The fiber reinforced resin sheet according to claim 1, A fiber reinforced resin sheet, wherein the volume content of the first range and the volume content of the fifth range are lower than the volume content of the third range.

3. The fiber reinforced resin sheet according to claim 2, the volume content of the first range and the volume content of the fifth range are values ​​obtained by adding −30 to −1% to the average volume content, the volume content of the second range and the volume content of the fourth range are values ​​obtained by adding +1 to +25% to the average volume content, A fiber reinforced resin sheet, wherein the volume content in the third range is a value obtained by adding −20 to +20% to the average volume content.

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.

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

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