Fiber-reinforced resin sheet and method for producing the same

Abstract

To provide a fiber-reinforced resin sheet that has a thin structure but exhibits resistance to delamination of the reinforcing fibers.SOLUTION: A fiber-reinforced resin sheet 1 includes: a thermoplastic first resin layer 11, a thermoplastic second resin layer 12, and a thermoplastic third resin layer 13, laminated in the thickness direction and welded together; and reinforcing fibers 10, dispersed and incorporated within each of the first to third resin layers 11-13, and aligned in the same direction. The fiber-reinforced resin sheet has a thickness (d) of 20 μm or more and 200 μm or less. The reinforcing fibers 10 have a volume content of 30% or more and 70% or less.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 layer. [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 is a relatively thin fiber reinforced resin sheet having a thickness of 30 to 65 μm, and 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 which is thin but in which peeling of the reinforcing fibers is unlikely to occur. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a fiber-reinforced resin sheet according to one aspect of the present invention is a fiber-reinforced resin sheet having a thickness of 20 μm or more and 200 μm or less, comprising a thermoplastic first resin layer, a second resin layer, and a third resin layer that are laminated in the thickness direction and welded to each other, and reinforcing fibers that are dispersed and contained in each of the first to third resin layers and oriented in the same direction, and the volume content of the reinforcing fibers is 30% or more and 70% or less.

[0007] According to the present invention, since each of the three resin layers welded together contains reinforcing fibers, it is possible to improve the integrity of each resin layer with the reinforcing fibers and prevent problems such as the reinforcing fibers peeling off from the resin layers. This makes it possible to obtain a high-strength, high-quality fiber-reinforced resin sheet that has a relatively small thickness of 20 to 200 μm but firmly holds a relatively large amount of reinforcing fibers inside, equivalent to a volume content of 30 to 70%.

[0008] 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.

[0009] 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.

[0010] A method for producing a fiber-reinforced resin sheet according to another aspect of the present invention includes a first arrangement step of arranging continuous first reinforcing fibers opened from a fiber bundle between a first thermoplastic resin film and a second thermoplastic resin film, a second arrangement step of arranging a third resin film so as to face the second resin film from the opposite side of the first resin film, and arranging continuous second reinforcing fibers opened from a fiber bundle between the third resin film and the second resin film, and an impregnation step of softening the first to third resin films by heating so that the first to third resin films are impregnated with the first reinforcing fibers and the second reinforcing fibers.

[0011] According to this manufacturing method, a sheet similar to the above-mentioned fiber-reinforced resin sheet of the invention can be appropriately manufactured. That is, the first resin film and the second resin film arranged opposite to each other with the first reinforcing fiber sandwiched therebetween are heated and softened, so that the first resin film and the second resin film can be impregnated into the first reinforcing fiber. Similarly, the second resin film and the third resin film arranged opposite to each other with the second reinforcing fiber sandwiched therebetween are heated and softened, so that the second resin film and the third resin film can be impregnated into the second reinforcing fiber. As a result, a high-strength and high-quality fiber-reinforced resin sheet having three resin layers corresponding to the first to third resin films and reinforcing fibers contained in the three resin layers can be manufactured.

[0012] Preferably, the impregnation step is a step of collectively heating the laminate of the resin films and the carbon fibers formed through the first and second arrangement steps.

[0013] In this embodiment, the first resin film, the first reinforcing fiber, the second resin film, the second reinforcing fiber, and the third resin film are laminated in this order, and then the formed laminate is heated together. This allows the processes of softening each resin film and impregnating each reinforcing fiber to be carried out simultaneously, thereby improving the manufacturing efficiency of the fiber-reinforced resin sheet.

[0014] Preferably, the first to third resin films have a thickness of 3 μm or more and 35 μm or less.

[0015] In this way, when the thickness of each resin film is set to 3 to 35 μm, the fiber reinforced resin sheet including the resin film can be formed thin, and the thickness can be kept within the desired value (20 to 200 μm).

[0016] Preferably, the first reinforcing fibers and the second reinforcing fibers are spread to have a width that is 1.5 times or more and 6 times or less the width of the fiber bundle.

[0017] In this embodiment, the first reinforcing fibers and the second reinforcing fibers that are sufficiently opened and strip-shaped can be contained in each resin film, which can facilitate thinning of the fiber-reinforced resin sheet. Effect of the Invention

[0018] As described above, according to the present invention, it is possible to provide a fiber reinforced resin sheet which is thin but in which peeling of the reinforcing fibers is unlikely to occur. [Brief description of the drawings]

[0019] [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 invention. [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

[0020] [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 this figure, the fiber reinforced resin sheet 1 includes a first resin layer 11, a second resin layer 12, and a third resin layer 13 laminated in the thickness direction, and reinforced fibers 10 contained in these first to third resin layers 11 to 13. The first to third resin layers 11 to 13 are all made of thermoplastic resin. In other words, the fiber reinforced resin sheet 1 is a thermoplastic composite material that combines a thermoplastic resin and reinforced fibers. For this reason, hereinafter, the fiber reinforced resin sheet 1 will be abbreviated as FRTP sheet 1 as appropriate.

[0021] The first resin layer 11, the second resin layer 12, and the third resin layer 13 are laminated in this order in the thickness direction of the FRTP sheet 1. In the following, with reference to Fig. 1, one side in the thickness direction of the FRTP sheet 1, which is the side from the second resin layer 12 to the first resin layer 11, is referred to as the "upper", and the other side in the thickness direction, which is the side from the second resin layer 12 to the third resin layer 13, is referred to as the "lower". However, this is not intended to limit the position of the FRTP sheet 1 when in use.

[0022] The first to third resin layers 11 to 13 are welded to one another. That is, the lower surface 11b of the first resin layer 11 is welded to the upper surface 12a of the second resin layer 12, and the lower surface 12b of the second resin layer 12 is welded to the upper surface 13a of the third resin layer 13, thereby bonding the first to third resin layers 11 to 13 to one another and forming an integrated body.

[0023] As the thermoplastic resin which is the material of the first to third resin layers 11 to 13, that is, the matrix resin of the FRTP sheet 1, for example, polyamide (particularly PA6, 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 first to third resin layers 11 to 13. In addition, the materials of the first to third resin layers 11 to 13 may be the same material or different materials as long as each of them is a thermoplastic resin including the above-mentioned material examples.

[0024] The thickness d of the FRTP sheet 1, that is, the distance from the upper surface 11a of the first resin layer 11 to the lower surface 13b of the third resin layer 13, is set to 20 μm or more and 200 μm or less. In a preferred embodiment, the thickness d is preferably 30 μm or more and 150 μm or less, and more preferably 40 μm or more and 100 μm or less.

[0025] The reinforcing fiber 10 is dispersed and contained in each of the first to third resin layers 11. That is, the reinforcing fiber 10 has a fiber group contained in the first resin layer 11, a fiber group contained in the second resin layer 12, and a fiber group contained in the third resin layer 13. Furthermore, the reinforcing fiber 10 may have a fiber group arranged at the boundary between the first resin layer 11 and the second resin layer 12 and contained in both the resin layers 11, 12, and a fiber group arranged at the boundary between the second resin layer 12 and the third resin layer 13 and contained in both the resin layers 12, 13.

[0026] The reinforcing fibers 10 are all arranged to extend in a direction perpendicular to the plane of the paper in Fig. 1. That is, the reinforcing fibers 10 are continuous fibers oriented in the same direction inside each of the resin layers 11-13. The orientation direction of the reinforcing fibers 10 (direction perpendicular to the plane of the paper) coincides with the longitudinal direction of the FRTP sheet 1. In other words, the reinforcing fibers 10 are contained in each of the resin layers 11-13 in a state where they are aligned in the longitudinal direction of the FRTP sheet 1.

[0027] As the reinforcing fiber 10, carbon fiber, glass fiber, ceramic fiber, aramid 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.

[0028] The volume content of the reinforcing fibers 10, that is, the value (Vf) obtained by dividing the volume occupied by the reinforcing fibers 10 by the total volume of the FRTP sheet 1, is set to 30% or more and 70% or less. In a preferred embodiment, the volume content of the reinforcing fibers 10 is preferably 35% or more and 65% or less, and more preferably 50% or more and 60% or less.

[0029] 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.

[0030] [Manufacturing method] The FRTP sheet 1 having the above-mentioned structure can be manufactured by the following manufacturing method. Fig. 2 is a side view that shows a schematic diagram of a manufacturing apparatus 20 that manufactures 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.

[0031] The film roller 21 includes a first film-feeding roller 21A for feeding out the first resin film 31, a second film-feeding roller 21B for feeding out the second resin film 32, and a third film-feeding roller 21C for feeding out the third resin film 33. The first resin film 31 is a tape-shaped resin film that serves as the original form of the above-mentioned first resin layer 11 (FIG. 1). The second resin film 32 is a tape-shaped resin film that serves as the original form of the above-mentioned second resin layer 12. The third resin film 33 is a tape-shaped resin film that serves as the original form of the above-mentioned third resin layer 13. The first to third resin films 31 to 33 are made of appropriate thermoplastic resins that correspond to the materials of the first to third resin layers 11 to 13. The materials of the first to third resin films 31 to 33 may be the same thermoplastic resin or different thermoplastic resins.

[0032] The thickness 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 thickness of each of the resin films 31 to 33 may be the same or different from each other.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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. The process of forming the laminate 100 in this manner corresponds to the "first arrangement step" and the "second arrangement step" in the present invention.

[0037] 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.

[0038] 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.

[0039] The above-mentioned heating and pressurization pressurize the first to third resin films 31 to 33 against the first and second reinforcing fibers 41, 42 while softening them. As a result, the first to third resin films 31 to 33 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. The process of impregnating the reinforcing fibers 41, 42 with the resin films 31 to 33 in this manner corresponds to the "impregnation step" in the present invention.

[0040] 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 31-33 to harden again, and the resin films 31-33 are bonded (welded) to each other.

[0041] 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.

[0042] Through the above-mentioned processes, the FRTP sheet 1 is manufactured. That is, the FRTP sheet 1 (FIG. 1) is manufactured, which includes the first to third resin layers 11 to 13 welded together and the reinforcing fibers 10 dispersed and contained in each of the resin layers 11 to 13. The first to third resin layers 11 to 13 are layers derived from the first to third resin films 31 to 33, and the reinforcing fibers 10 are a collection of the first and second reinforcing fibers 41, 42. In other words, the first resin layer 11 is formed by the first resin film 31 that has been softened and then hardened, the second resin layer 12 is formed by the second resin film 32 that has been softened and then hardened, and the third resin layer 13 is formed by the third resin film 33 that has been softened and then hardened. In addition, the upper half of the reinforcing fiber 10 is formed by the first reinforcing fiber 41 sandwiched between the first and second resin films 31, 32 and contained in the resin, and the lower half of the reinforcing fiber 10 is formed by the second reinforcing fiber 42 sandwiched between the second and third resin films 32, 33 and contained in the resin.

[0043] 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.

[0044] [Effects] As described above, in this embodiment, 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 treatment such as heating by the heating roller 25, thereby producing the FRTP sheet 1. The FRTP sheet 1 produced in this manner has the property that, despite its thinness, the reinforcing fibers are unlikely to peel off.

[0045] That is, the first resin film 31 and the second resin film 32 arranged opposite to each other with the first reinforcing fiber 41 interposed therebetween 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 interposed therebetween 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 a high-strength and high-quality FRTP sheet 1 including the first to third resin layers 11 to 13 corresponding to the first to third resin films 31 to 33 and the reinforcing fibers 10 contained in each of the resin layers 11 to 13.

[0046] Specifically, since the first to third resin layers 11 to 13, which are welded together, each contain the reinforcing fibers 10, the integrity of each resin layer 11 to 13 and the reinforcing fibers 10 can be improved, and defects such as the reinforcing fibers 10 peeling off from the resin layers 11 to 13 can be prevented. Therefore, even when a relatively thin FRTP sheet 1 having a thickness d of 20 to 200 μm is manufactured as in this embodiment, a relatively large amount of reinforcing fibers 10 corresponding to a volume content (Vf) 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-walled FRTP sheet 1 with a low void ratio containing many reinforcing fibers 10 in this way, the strength of the composite molded product can be increased, and even a composite molded product having a relatively complicated shape can be molded well. That is, according to this embodiment, it is possible to manufacture a high-quality FRTP sheet 1 that contributes to improving the strength and moldability of a composite molded product.

[0047] Furthermore, in this embodiment, after 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, the formed laminate 100 is heated all at once by the heating roller 25. Therefore, the processes of softening each of the resin films 31 to 33 and impregnating each of the reinforcing fibers 41, 42 can be performed simultaneously, thereby improving the manufacturing efficiency of the FRTP sheet 1.

[0048] In addition, in this embodiment, the first to third resin films 31-33 have a thickness of 3 to 35 μm, so that the FRTP sheet 1 including the resin films 31-33 can be formed thin, and the thickness d can be kept within the desired value (20 to 200 μm).

[0049] Furthermore, in this embodiment, the fiber bundles FB that are opened at a fiber opening ratio of 1.5 to 6 times are used as the first reinforcing fibers 41 and the second reinforcing fibers 42. Therefore, the resin films 31 to 33 can contain the band-like first reinforcing fibers 41 and the second reinforcing fibers 42 that are sufficiently opened, which can promote thinning of the FRTP sheet 1.

[0050] [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 2.8. 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. 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.

[0051] Fig. 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, 42 are the same as those in Examples 1 and 2, but the film thickness and the spread ratio are different from those in Examples 1 and 2. Specifically, in Comparative Example 1, the thicknesses of the first to third resin films 31 to 33 were all 10 µm, and the spread ratios of the first and second reinforcing fibers 41, 42 were all 1 (non-spread). In Comparative Example 2, the thicknesses of the first to third resin films 31 to 33 were all 50 µm, and the spread ratios of the first and second reinforcing fibers 41, 42 were all 1.5.

[0052] 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) of the obtained FRTP sheet 1, the volume content (Vf) of the reinforcing fibers 10, and the void ratio were all within the ranges specified in the above embodiment (sheet thickness 20 to 200 μm, Vf 30 to 70%, void ratio 10% or less). Specifically, the sheet thickness was 60 μm in Example 1 and 89 μm in Example 2. Vf was 60% in Example 1 and 50% 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 the reinforcing fibers 10 peeling off (fuzzing) was not particularly observed.

[0053] In contrast, in Comparative Examples 1 and 2, the sheet thickness, Vf, or void ratio fell outside the specified range. Specifically, in Comparative Example 1, the void ratio was 12%, which is larger than the specified range (10% or less). This is believed to be due to the use of unspread reinforcing fibers with a spreading ratio of 1. In Comparative Example 2, the sheet thickness was 210 μm, which is larger than the specified range (20 to 200%), and the Vf was 28%, which is smaller than the specified range (30 to 70%). This is believed to be due to the use of a resin film with a thickness of 50 μm.

[0054] The above results confirmed the advantages of producing the FRTP sheet 1 by the method of the above embodiment.

[0055] [Variations] In the above embodiment, the five elements of 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 then the formed laminate 100 is collectively heated by the heating roller 25, but the heating method is not limited to this. For example, a laminate in which only some of the above five elements are laminated may be first heated, and then the remaining elements may be laminated and heated again.

[0056] The manufacturing method similar to the above embodiment can be similarly applied to the case of manufacturing a FRTP sheet with a different number of layers. For example, it is possible to manufacture a FRTP sheet with fewer layers than the above embodiment, that is, a FRTP sheet containing reinforcing fibers inside two resin layers, by a method similar to the above embodiment. In this case, a FRTP sheet is manufactured by sandwiching one layer of reinforcing fibers between two layers of resin film and heating the laminate obtained thereby. This makes it possible to obtain a FRTP sheet having a first resin layer and a second resin layer and reinforcing fibers dispersed and contained in both resin layers. [Explanation of symbols]

[0057] 1 Fiber reinforced plastic sheet (FRTP sheet) 10 Reinforced Fiber 11 First resin layer 12 Second resin layer 13 Third resin layer 31 First resin film 32 Second resin film 33 Third resin film 41 First reinforcement fiber 42 Second reinforcing fiber FB Fiber bundle

Claims

1. A fiber reinforced resin sheet having a thickness of 20 μm or more and 200 μm or less, a first thermoplastic resin layer, a second thermoplastic resin layer, and a third thermoplastic resin layer that are laminated in a thickness direction and welded to each other; The reinforcement fiber is dispersed and contained in each of the first to third resin layers and oriented in the same direction, The fiber reinforced resin sheet, wherein the volume content of the reinforcing fibers is 30% or more and 70% or less.

2. The fiber reinforced resin sheet according to claim 1, 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.

3. A first arrangement step of arranging continuous first reinforcing fibers opened from a fiber bundle between a first thermoplastic resin film and a second thermoplastic resin film; A second arrangement step of arranging a thermoplastic third resin film so as to face the second resin film from the opposite side of the first resin film, and arranging continuous second reinforcing fibers opened from a fiber bundle between the third resin film and the second resin film; and an impregnation step of softening the first to third resin films by heating so that the first to third resin films are impregnated into the first reinforcing fibers and the second reinforcing fibers. A method for producing a fiber-reinforced resin sheet.

4. In the method for producing a fiber-reinforced resin sheet according to claim 3, The impregnation step is a step of collectively heating a laminate of the resin films and the carbon fibers formed through the first and second arrangement steps, in the method for producing a fiber-reinforced resin sheet.

5. In the method for producing a fiber-reinforced resin sheet according to claim 3 or 4, The method for producing a fiber reinforced resin sheet, wherein the first to third resin films have a thickness of 3 μm or more and 35 μm or less.

6. In the method for producing a fiber-reinforced resin sheet according to claim 3 or 4, The manufacturing method of a fiber reinforced resin sheet, characterized in that the first reinforcing fibers and the second reinforcing fibers are spread so as to have a width of 1.5 times or more and 6 times or less than that of the fiber bundle.

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