Method for manufacturing fiber-reinforced hollow molding

Abstract

To provide a fiber-reinforced hollow molding having good shapability and excellent strength characteristics.SOLUTION: Disclosed is a fiber-reinforced hollow molding 30 including a fiber-reinforced resin part 31 having a hollow part in its inside, wherein the fiber-reinforced resin part is molded by using a laminate prepared by laminating a plural pieces of resin-integrated fiber sheets comprising one-direction continuous fibers obtained by opening continuous fiber groups and arranging parallel to each other in one direction, with their surfaces having been adhered to and thermally fused with a thermoplastic resin powder which becomes a matrix. The laminate includes a first resin-integrated fiber sheet and a second resin-integrated fiber sheet with its longer direction of the one direction continuous fiber crossing with the first resin-integrated fiber sheet. The second resin-integrated fiber sheet is provided with slits, hence, with the slits, a part or all of the one direction continuous fiber is cut in the middle, and the thermoplastic resin is impregnated into the resin-integrated fiber sheet having been molded in the fiber-reinforced resin part, thus the laminate is integrated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced hollow molding. of Regarding the manufacturing method. [Background technology]

[0002] Carbon fiber, a reinforcing fiber material, is composited with various matrix resins, and the resulting fiber-reinforced plastics are now widely used in a variety of fields and applications. Composite materials with particularly high mechanical properties and impact resistance are in demand. Demand for hollow molded bodies, one type of composite material, is also increasing. While several molding methods exist for hollow molded bodies, one that has attracted attention is the internal pressure molding method, in which a laminate of resin fiber sheets, in which fibers and matrix resins are combined, is wound around a core material and a pressurized fluid, such as compressed air, is supplied to the inside of the wound laminate. This method simplifies the complicated process of stacking the prepared resin fiber sheets, and allows molding into any shape.

[0003] Patent Document 1 proposes the use of a sheet-like molding substrate, in which a nonwoven fabric made of a thermoplastic resin is layered on a sheet material in which reinforcing fibers are aligned in one direction, as a molding substrate for a pipe. Patent Document 2 discloses a method for producing a fiber-reinforced plastic with a core-sheath structure, in which a laminate including a cut prepreg substrate made of reinforcing fibers and a thermosetting resin is wound around a mandrel, a foamable resin (foam material) is injected into the area where the mandrel is de-cored, the laminate is pressed against a molding die by the foaming pressure of the foamable resin, and the foamable resin is cured, resulting in the laminate serving as the sheath and the foam material serving as the core. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-62818 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-273176 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the molding substrate described in Patent Document 1 contains a nonwoven fabric and therefore does not have good shapability. The laminate described in Patent Document 2 is also a prepreg substrate composed of reinforcing fibers and a thermosetting resin and therefore does not have good shapability. In addition, the manufacturing method described in Patent Document 2 utilizes the foaming pressure of the foamable resin, and requires many steps, making high-speed production difficult.

[0006] The present invention provides a fiber-reinforced hollow molding having good formability and excellent strength properties, and a method for producing the same. [Means for solving the problem]

[0007] The fiber-reinforced hollow molding of the present invention is a fiber-reinforced hollow molding including a fiber-reinforced resin part having a hollow part therein, The fiber-reinforced resin portion is molded using a laminate in which a plurality of resin-integrated fiber sheets are laminated, the resin-integrated fiber sheets being formed by adhering and heat-fusing a powder of a thermoplastic resin to the surface of unidirectional continuous fibers in which continuous fibers are spread and arranged in parallel in one direction, and forming a matrix. The laminate is a first resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers is the same as the axial direction of the fiber-reinforced hollow molding; a second resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers intersects with the first resin-integrated fiber sheet; a slit is formed in the second resin-integrated fiber sheet, and the unidirectional continuous fibers are partly or entirely separated by the slit; The present invention relates to a fiber-reinforced hollow molding product in which the resin-integrated fiber sheet molded in the fiber-reinforced resin part is impregnated with the thermoplastic resin, thereby integrating the laminate.

[0008] The method for producing a fiber-reinforced hollow molding of the present invention is a method for producing a fiber-reinforced hollow molding including a fiber-reinforced resin part having a hollow part therein, a step of placing a roll of a laminate on an elastic body, the laminate being formed by laminating a plurality of resin-integrated fiber sheets, each of which is formed by adhering and heat-fusing a powder of a thermoplastic resin that serves as a matrix to the surface of unidirectional continuous fibers that have been spread and aligned in parallel in one direction; and a step of supplying a pressurized fluid into the elastic body disposed in a mold to press the wound body against the mold, melting the thermoplastic resin by the heat of the mold, impregnating the resin-integrated fiber sheet with the thermoplastic resin, and integrating the wound body, The laminate is a first resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers is the same as the axial direction of the wound body; a second resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers intersects with the first resin-integrated fiber sheet; The present invention relates to a method for producing a fiber-reinforced hollow molding, wherein slits are formed in the second resin-integrated fiber sheet, so that some or all of the unidirectional continuous fibers are separated along the way by the slits. [Effects of the Invention]

[0009] In the present invention, a laminate of resin-integrated fiber sheets is used to form a fiber-reinforced hollow molded body, and the laminate includes a first resin-integrated fiber sheet and a second resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers intersects with that of the first resin-integrated fiber sheet.Slits are formed in the second resin-integrated fiber sheet, and the slits separate some or all of the unidirectional continuous fibers along the way, thereby providing a fiber-reinforced hollow molded body with good formability and excellent strength properties. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1A is a schematic perspective view of a fiber-reinforced hollow molding according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of the same in FIG. 1A. [Figure 2]FIG. 2A is a schematic plan view illustrating a method for preparing a resin-integrated carbon fiber sheet used in molding a fiber-reinforced hollow molded body according to one embodiment of the present invention, and FIG. 2B is a schematic plan view illustrating a first resin-integrated carbon fiber sheet and a second resin-integrated carbon fiber sheet. [Figure 3] FIG. 3A is a schematic perspective exploded view illustrating an example of a laminate of resin-integrated carbon fiber sheets used to mold a fiber-reinforced hollow molded body according to one embodiment of the present invention, and FIG. 3B is a schematic explanatory view illustrating the winding direction of the laminate shown in FIG. 3A. [Figure 4] FIG. 4A is a schematic perspective exploded view illustrating another example of a laminate of resin-integrated carbon fiber sheets used in molding a fiber-reinforced hollow molded body according to one embodiment of the present invention, and FIG. 4B is a schematic explanatory view illustrating the winding direction of the laminate shown in FIG. 4A. [Figure 5] FIG. 5A is a schematic perspective exploded view illustrating another example of a laminate of resin-integrated carbon fiber sheets used in molding a fiber-reinforced hollow molded body according to one embodiment of the present invention, and FIG. 5B is a schematic explanatory view illustrating the winding direction of the laminate shown in FIG. 5A. [Figure 6] FIG. 6A is a schematic perspective view of an elastic body used in molding a fiber-reinforced hollow molded body according to one embodiment of the present invention, FIG. 6B is a schematic perspective view of the elastic body shown in FIG. 6A wound with a laminate of resin-integrated carbon fiber sheets, and FIG. 6C is a cross-sectional view of FIG. 6B. [Figure 7] 7A is a schematic plan view showing a state in which an elastic body wound with a laminate of resin-integrated carbon fiber sheets is placed in a molding die, and FIG. 7B is a cross-sectional view taken along line II of FIG. 7A. [Figure 8] FIG. 8 is a schematic perspective view of a resin-integrated carbon fiber sheet used for molding a fiber-reinforced hollow molded article according to one embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view of the resin-integrated carbon fiber sheet 1 in the thickness direction. [Figure 10] FIG. 10 is a schematic process diagram showing a method for producing a resin-integrated carbon fiber sheet used in producing a fiber-reinforced hollow molded article according to one embodiment of the present invention. [Figure 11]FIG. 11 is a schematic plan view of sheet A constituting the laminate used to mold the fiber-reinforced hollow molded articles A to E. As shown in FIG. [Figure 12] Figure 12A is a schematic plan view of B sheet I, which constitutes the laminate used to mold hollow molded body A; Figure 12B is a schematic plan view of B sheet II, which constitutes the laminate used to mold hollow molded body B; Figure 12C is a schematic plan view of B sheet III, which constitutes the laminate used to mold hollow molded body C; and Figure 12D is a schematic plan view of B sheet IV, which constitutes the laminate used to mold hollow molded body D. [Figure 13] FIG. 13 is a graph showing the test force-displacement measurement of the evaluation sample cut out from the hollow molded body A of Reference Example 1. [Figure 14] FIG. 14 is a graph showing the test force-displacement measurement of the evaluation sample cut out from the hollow molded body B of Reference Example 2. [Figure 15] FIG. 15 is a graph showing the test force-displacement measurement of the evaluation sample cut out from the hollow molded body C of Example 1. [Figure 16] FIG. 16 is a graph showing the test force-displacement measurement of the evaluation sample cut out from the hollow molded body D of Example 2. [Figure 17] FIG. 17 is a graph showing the test force-displacement measurement of the evaluation sample cut out from the hollow molded body E of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present inventors have proposed a method for molding a fiber-reinforced hollow molding product. To improve formability, the present inventors have used a resin-integrated fiber sheet (semipreg sheet) in which a group of unidirectional continuous fibers, which are spread and aligned in one direction, are thermally bonded to the surface of the unidirectional continuous fibers by attaching a thermoplastic resin powder matrix to the surface. Furthermore, to improve strength characteristics, they have proposed a laminate in which multiple resin-integrated fiber sheets are stacked so that the longitudinal directions of the unidirectional continuous fibers are different. Specifically, for example, a laminate was used in which, when molded into a fiber-reinforced hollow molding product, one sheet was stacked so that the longitudinal direction of the unidirectional continuous fibers was aligned with the axial direction of the fiber-reinforced hollow molding product, and another sheet was stacked so that the unidirectional continuous fibers were wound around the axis of the fiber-reinforced hollow molding product. The inventors have found that the strength characteristics of the resulting fiber-reinforced hollow molding product were insufficient. The new finding was that the unidirectional continuous fibers wound around the axis prevented the diametric expansion of the wound laminate when a pressurized fluid was supplied to the inside of the wound laminate to expand the diameter of the wound laminate. If the diameter of the wound body is insufficient, the transfer of heat from the molding die to the wound body and the melting of the thermoplastic resin will be insufficient, which will lead to the generation of voids and peeling, and to a decrease in strength characteristics.

[0012] The fiber-reinforced hollow molded article (hereinafter sometimes abbreviated as "hollow molded article") of the present invention is a hollow molded article including a fiber-reinforced resin part having a hollow part inside. The fiber-reinforced resin part is molded using a laminate in which multiple resin-integrated fiber sheets are stacked. The resin-integrated fiber sheet is a semi-preg sheet in which a thermoplastic resin powder (hereinafter sometimes referred to as "thermoplastic powder resin") that forms a matrix is ​​attached to the surface of unidirectional continuous fibers in which continuous fibers are spread and aligned in parallel in one direction, and then heat-fused. In the fiber-reinforced resin part molded using the laminate, the thermoplastic resin is impregnated throughout the resin-integrated fiber sheet.

[0013] The laminate used to form the hollow molded article includes a first resin-integrated fiber sheet and a second resin-integrated fiber sheet. The longitudinal direction of the unidirectional continuous fibers of the first resin-integrated fiber sheet is the same as the axial direction of the hollow molded article. Meanwhile, the unidirectional continuous fibers of the second resin-integrated fiber sheet intersect with the unidirectional continuous fibers of the first resin-integrated fiber sheet at a predetermined angle. Slits are formed in the second resin-integrated fiber sheet, and the unidirectional continuous fibers are partially or entirely separated along the length by the slits.

[0014] An example of the blow molded article of the present invention and a method for producing the same will be described in detail below with reference to the drawings.

[0015] [Hollow molded body] Fig. 1A is a schematic perspective view of a hollow molded body 30 according to one embodiment of the present invention, and Fig. 1B is a schematic cross-sectional view of Fig. 1A. The hollow molded body 30 includes a fiber-reinforced resin part 31 that is hollow in the longitudinal direction. The fiber-reinforced resin part 31 is formed by winding a laminate of resin-integrated carbon fiber sheets into a cylindrical shape, and heating during molding causes the thermoplastic resin that has been attached to the surfaces of the resin-integrated carbon fiber sheets and / or their vicinity to impregnate the resin-integrated carbon fiber sheets and penetrate and diffuse between the resin-integrated carbon fiber sheets, integrating them.

[0016] The laminate used to form the hollow molded body 30 includes a first resin-integrated carbon fiber sheet and a second resin-integrated carbon fiber sheet, which will be described in detail later. Therefore, the fiber-reinforced resin portion 31 includes a first fiber-reinforced resin sheet 33a corresponding to the first resin-integrated carbon fiber sheet 1a and a second fiber-reinforced resin sheet 33b corresponding to the second resin-integrated carbon fiber sheet. The unidirectional continuous fibers of the first fiber-reinforced resin sheet 33a are oriented in the same direction as the longitudinal direction of the central axis 33 of the hollow molded body 30, while the unidirectional continuous fibers of the second fiber-reinforced resin sheet 33b are partially or entirely interrupted and wound around the central axis 33. In FIG. 1B, the first fiber-reinforced resin sheet 33a is indicated by dots to facilitate differentiation from the second fiber-reinforced resin sheet 33b.

[0017] In the second fiber-reinforced resin sheet 33b, the length of the cut fibers is preferably 1.5 times or less, and more preferably 1.2 times or less, the circumferential length of the hollow molded body, from the viewpoint of suppressing the occurrence of voids, peeling, and the like during the molding process of the hollow molded body 30 and suppressing a decrease in strength. On the other hand, from the viewpoint of improving the strength by the fibers of the second fiber-reinforced resin sheet 33b, the fiber length is preferably 0.5 times or more, and more preferably 0.7 times or more, the circumferential length of the hollow molded body.

[0018] 1, the laminate includes an overlap portion 32, but if the number of turns is two or more, the overlap portion 32 may be omitted. If the number of turns is one, the overlap portion 32 is required, and the width of the overlap portion is preferably 3 mm or more, and more preferably 10 mm or more.

[0019] When the second resin-integrated carbon fiber sheet used to mold the hollow molded body 30 has multiple slits that separate the unidirectional continuous fibers midway and the laminate has multiple windings, it is preferable, from the viewpoint of improving strength uniformity, that the unidirectional continuous fibers of the second fiber-reinforced resin sheet 33b be cut at positions that do not overlap in the thickness direction of the fiber-reinforced resin part 31 in a cross-sectional view perpendicular to the central axis 33 of the hollow molded body 30, as shown in Fig. 1B. In Fig. 1B, the cut fiber locations 33c are hatched, and thermoplastic resin flows into these locations and solidifies during molding of the hollow molded body 30.

[0020] The hollow molded body 30 preferably has a diameter (outer diameter) of 30 to 100 mm, a length of 50 to 5000 mm, and a thickness of 0.05 to 5 mm, more preferably 0.5 to 5 mm. The cross-sectional shape of the hollow molded body 30 is round, but is not limited to this and may be rectangular or the like.

[0021] The hollow molded body 30 is a straight pipe with a fixed diameter, but the hollow molded body of the present invention is not limited to this and may be a shaft, a frame, or any other hollow molded body of various shapes.

[0022] [Hollow Molded Product and Manufacturing Method Thereof] Next, an example of a method for producing a blown molded article of the present invention will be described. The example of a method for producing a blown molded article of the present invention includes the following steps. A process in which a roll of a laminate made of multiple resin-integrated fiber sheets, which are made by adhering a thermoplastic powder resin matrix to the surface of unidirectional continuous fibers that have been spread and aligned in one direction, is placed on an elastic body. a step of supplying a pressurized fluid into the elastic body placed in a mold to press the wound body against the mold, melting the thermoplastic resin by the heat of the mold, impregnating the resin-integrated fiber sheet with the thermoplastic resin, and integrating the wound body; The wound body may be disposed on the elastic body by winding the laminate around the elastic body, or by forming a wound body of the laminate and then disposing it on the elastic body.

[0023] The laminate contains the following two types of resin-integrated fiber sheets. (1) First resin-integrated fiber sheet The longitudinal direction of the unidirectional continuous fibers of the first resin-integrated sheet is the same as the axial direction of the hollow molded body. (2) Second resin-integrated fiber sheet The unidirectional continuous fibers of the second resin-integrated fiber sheet intersect with the first resin-integrated fiber sheet at a predetermined angle, and slits are formed in the second resin-integrated fiber sheet, so that some or all of the unidirectional continuous fibers are severed along the way by the slits.

[0024] In one example of the method for producing the hollow molded article of the present invention, first, a resin-integrated fiber sheet required for preparing the laminate is cut out from a long piece of resin-integrated fiber sheet. The longitudinal direction of the unidirectional continuous fibers in the long piece of resin-integrated fiber sheet is the MD direction.

[0025] The cut-out resin-integrated fiber sheets 11a and 11b are overlapped, for example, as shown in Figure 2A, and the overlapping portion 34 is cut out and used to prepare a laminate. As shown in Figure 2B, one sheet is used as is as the first resin-integrated fiber sheet 1a, and the other resin-integrated fiber sheet is formed with, for example, multiple slits 10a to form the second resin-integrated fiber sheet 1b. The external dimensions of the resin-integrated fiber sheets that make up the laminate can be adjusted either before or after the slits are formed.

[0026] 2B, each slit 10a is formed by cutting some of the unidirectional continuous fibers arranged in parallel, thereby dividing the continuous fibers in the middle. The length of the slit 10a is preferably 10 to 100 mm from the viewpoint of suppressing twisting during diameter expansion.

[0027] As shown in Fig. 2B, in the second resin-integrated fiber sheet, it is preferable that a plurality of slits 10a are formed in the second resin-integrated fiber sheet from the viewpoint of improving strength uniformity. Furthermore, from the viewpoint of improving strength uniformity, it is preferable that the slits 10a are formed periodically in the longitudinal direction of the unidirectional continuous fibers. From the viewpoint of suppressing a decrease in strength due to the occurrence of voids and peeling during molding, the distance L between adjacent slits 10a in the longitudinal direction of the continuous fibers is preferably 1.5 times or less, more preferably 1.2 times or less, the perimeter of the hollow molded article. On the other hand, from the viewpoint of improving the strength of the fibers of the second resin-integrated fiber sheet 1b, the distance L is preferably 0.5 times or more, more preferably 0.7 times or more, the perimeter of the hollow molded article.

[0028] In the second resin-integrated fiber sheet 1b, it is preferable that the parallelly arranged unidirectional continuous fibers are cut by any one of the multiple slits 10a, and all of the unidirectional continuous fibers are separated along the way.

[0029] As shown in FIG. 3A, a laminate 110 is formed by overlapping a first resin-integrated fiber sheet 1a with a second resin-integrated fiber sheet 1b. The first resin-integrated fiber sheet 1a and the second resin-integrated fiber sheet 1b are laminated so that the longitudinal directions of the unidirectional continuous fibers intersect. Arrow X indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers of the first resin-integrated fiber sheet 1a, and arrow Y indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers of the second resin-integrated fiber sheet 1b. As shown in FIG. 3B, the laminate 110 is wound around an elastic body 35 such that the longitudinal direction of the unidirectional continuous fibers of the first resin-integrated fiber sheet 1a forms an angle of 0° with the central axis 35a of the elastic body 35. The unidirectional continuous fibers of the second resin-integrated fiber sheet 1b are wound around the central axis 35a of the elastic body. The number of times of wrapping may be one or more. In the case of a single wrap, it is necessary to overlap the end of the wrap with the single wrap to provide an overlap.

[0030] FIG. 4A shows another example of a laminate. In FIG. 4A, a second resin-integrated fiber sheet 1b, laminated on a first resin-integrated fiber sheet 1a, has multiple slits 10b formed therein, each slit 10b cutting all of the parallel-arranged unidirectional continuous fibers. Therefore, the second resin-integrated fiber sheet is divided into multiple sheets. Each of the divided sheets is, for example, rectangular, with the fiber length shorter than the width of the second resin-integrated fiber sheet. As shown in FIG. 4B, the laminate 110 is wound around an elastic body 35a of the elastic body 35 so that the longitudinal angle of the unidirectional continuous fibers of the first resin-integrated fiber sheet 1a relative to the central axis 35a of the elastic body 35 is 0°. The unidirectional continuous fibers of the second resin-integrated fiber sheet 1b are wound around the central axis 35a of the elastic body. In this example, the diameter of the wound body can be expanded more easily than in the laminate shown in Figures 3A and 3B, and a higher strength can be ensured for the hollow molded body. The distance between adjacent slits 10b along the longitudinal direction of the continuous fibers is preferably 1.5 times or less, and more preferably 1.2 times or less, the outer periphery of the hollow molded body, from the viewpoint of suppressing a decrease in strength due to the occurrence of voids and peeling. On the other hand, from the viewpoint of improving the strength due to the fibers of the second resin-integrated fiber sheet 1b, the distance between the slits 10b is preferably 0.5 times or more, and more preferably 0.7 times or more, the outer periphery of the hollow molded body.

[0031] FIG. 5A shows another example of a laminate. As shown in FIG. 5A, two first resin-integrated fiber sheets 1a are arranged in the same layer, and two second resin-integrated fiber sheets 1b are arranged in the same layer. As shown in FIG. 5B, the laminate 110 is wound around the elastic body 35 so that the angle between the longitudinal direction of the unidirectional continuous fibers of the first resin-integrated fiber sheet 1a and the central axis 35a of the elastic body 35 is 0°. The unidirectional continuous fibers of the second resin-integrated fiber sheet 1b are wound around the central axis 35a of the elastic body. In this way, multiple first resin-integrated fiber sheets 1a and / or multiple second resin-integrated fiber sheets 1b may be used to form the same layer of the laminate 110, depending on the diameter (outer diameter) of the hollow molded body, the number of windings of the laminate, and the length of the resin-integrated fiber sheet.

[0032] In Figures 3A, 4A, and 5A, arrow X indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers constituting the first resin-integrated fiber sheet, and arrow Y indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers constituting the second resin-integrated fiber sheet. The absolute value of the angle (θ) of the unidirectional continuous fibers of the second resin-integrated fiber sheet relative to the unidirectional continuous fibers of the first resin-integrated fiber sheet is preferably 20° to 90° in terms of improving strength characteristics, and is preferably selected within this range depending on the mechanical properties required of the hollow molded article. In the laminates 110 described with reference to Figures 3 to 5, θ is 90°, and the fibers constituting the second resin-integrated fiber sheet 1b are wound circumferentially around the wound body. However, when θ is less than 90°, they are wound helically around the axis of the wound body.

[0033] In Figures 3A, 4A, and 5A, the laminate is wound so that the first resin-integrated fiber sheet 1a is on the outside (so that the second resin-integrated fiber sheet 1b is positioned on the elastic body side), but depending on the mechanical properties required of the hollow molded body, it may also be wound so that the second resin-integrated fiber sheet 1b is on the outside.

[0034] When the laminate has multiple windings, if the slits 10a and 10b overlap and are concentrated in a specific area when viewed in the thickness direction of the wound body, the strength of that area will be reduced compared to other areas. From the perspective of ensuring uniform strength, as shown in FIG. 6C , in a cross-sectional view perpendicular to the axial direction of the wound body 37, the multiple slits 10a are preferably dispersed in the circumferential direction around the axis, preferably formed in positions that do not overlap in the thickness direction of the wound body, and more preferably arranged at substantially equal intervals in the circumferential direction around the axis. Here, "substantially equal intervals" includes intervals within a range that can be considered to be strictly equal intervals and essentially the same, specifically, an error of ±10 mm. The same applies to the slits 10b.

[0035] Methods for forming the slits 10a and 10b include, but are not limited to, manual cutting with a cutter or pressing a rotating roller with a blade positioned at a predetermined position against the resin-integrated fiber sheet. In this example, to prepare the laminate, the long resin-integrated fiber sheet is cut into a predetermined shape and then the slits are formed. However, this is not limited to this method, and the slits may be formed in the long resin-integrated fiber sheet. The first resin-integrated fiber sheet and the second resin-integrated fiber sheet may be prepared from long resin-integrated fiber sheets of different compositions, either the same or different.

[0036] Fig. 6A is a schematic perspective view of an elastic body 35 used in internal pressure molding, Fig. 6B is a schematic perspective view of a wound body of a laminate of resin-integrated carbon fiber sheets placed on the elastic body 35, and Fig. 6C is a cross-sectional view of Fig. 6B. A jig 36 is attached to the tip of the elastic body 35 to seal the pressure fluid inside the elastic body. The elastic body is, for example, a tube made of fluororubber (heat resistance limit temperature 230°C) or silicone rubber (heat resistance limit temperature 230°C).

[0037] Fig. 7A is a schematic plan view showing a state in which an elastic body 35 on which a wound body 37 of a laminate of resin-integrated carbon fiber sheets is arranged is placed in a molding die, and Fig. 7B is a cross-sectional view taken along line II in Fig. 7A. The molding die is composed of a lower die 40 and an upper die 39. For example, a laminate 110 of resin-integrated carbon fiber sheets is wound around the surface of the elastic body 35 to form the wound body 37. Alternatively, the laminate 110 may be wound to form a preform, which is then placed on the elastic body.

[0038] The elastic body 35 with the wound body 37 arranged thereon is placed in a molding die, and pressurized fluid is supplied from an air supply port 41 fixed to one end of the elastic body 35 to expand the elastic body. This causes the wound body 37 to expand as well, and the elastic body presses the wound body 37 against the die. The wound body 37 pressed against the die is heated by the die, and the thermoplastic resin on the surface of the resin-integrated carbon fiber sheet that constitutes the wound body 37 melts. The molten thermoplastic resin impregnates the resin-integrated carbon fiber sheet, penetrates and diffuses between the resin-integrated carbon fiber sheets, and impregnates the entire wound body 37, integrating the wound body. The temperature of the die begins, for example, after the wound body 37 is placed in the die. Next, the die is cooled, for example, by water cooling, and then demolded. This results in a hollow molded body including a fiber-reinforced resin portion.

[0039] When the resin-integrated carbon fiber sheet laminate 110 is wound around the elastic body 35, the unidirectional continuous fibers constituting the second resin-integrated fiber sheet are wound around the elastic body 35 in the circumferential direction. The unidirectional continuous fibers constituting the resin-integrated fiber sheet do not stretch by themselves. Therefore, if the unidirectional continuous fibers of the second resin-integrated fiber sheet were completely continuous over the entire length in the longitudinal direction, the radial expansion of the elastic body 35 and, consequently, the expansion of the wound body 37 would be hindered. However, because the second resin-integrated carbon fiber sheet has slits, the portions where the slits are formed expand radially, facilitating the radial expansion of the wound body. As a result, the wound body can be pressed against the mold and heated sufficiently, suppressing the occurrence of voids and peeling, and ensuring sufficient strength for practical use for the hollow molded body.

[0040] Examples of the pressure fluid supplied to the inside of the elastic body include compressed air. The internal pressure of the pressure fluid is preferably 0.1 to 2 MPa, and the mold temperature T is preferably Tm (melting temperature of the thermoplastic resin) + 20°C ≦ T ≦ 350°C. The heat molding time is preferably 30 seconds to 30 minutes, and the cooling time is preferably 1 to 10 minutes. Cooling is carried out until the mold temperature reaches, for example, 60°C or less.

[0041] [Resin-integrated fiber sheet] Next, the resin-integrated fiber sheet used to manufacture a hollow molded body will be described. The resin-integrated fiber sheet used to manufacture a hollow molded body preferably contains crosslinked fibers in a direction intersecting the unidirectional continuous fibers, and the thermoplastic resin integrates the continuous fibers with the crosslinked fibers. The resin-integrated fiber sheet may further contain auxiliary threads arranged in the other direction on the continuous fibers. The auxiliary threads maintain a constant orientation of the unidirectional continuous fibers, and examples of auxiliary threads include glass fiber, aramid fiber, polyester fiber, nylon fiber, and vinylon fiber.

[0042] The main fiber component of the resin-integrated fiber sheet used in the present invention is unidirectional continuous fibers that are spread and aligned in parallel in one direction, and is unidirectional long fibers. The secondary fiber component is preferably crosslinked fibers aligned in a direction intersecting with the unidirectional continuous fibers. The content of the main component is preferably 75 to 99 mass%, and the content of the secondary component is preferably 1 to 25 mass%, assuming that the total mass of the fibers contained in the resin-integrated fiber sheet is 100 mass%. The thermoplastic resin is preferably in powder form and applied onto the unidirectional continuous fibers and crosslinked fibers, heat-fused to at least the surface of the unidirectional continuous fibers, and integrates the unidirectional continuous fibers and the crosslinked fibers. Because the unidirectional continuous fibers and the crosslinked fibers are integrated by the heat-fused thermoplastic resin, this sheet is easy to handle and easy to operate during lamination (including lamination involving winding) and molding.

[0043] The resin-integrated fiber sheet is a semipreg formed by adhering a thermoplastic powder resin matrix to the surface of unidirectional continuous fibers and then heat-fusing the fibers. When molded, the thermoplastic resin on the surface of the semipreg is easily impregnated into the resin-integrated fiber sheet and easily penetrates and diffuses uniformly between the resin-integrated fiber sheets. This results in excellent formability (moldability) and suppressed void formation.

[0044] When the total of the unidirectional continuous fibers and crosslinked fibers is taken as 100% by mass, the unidirectional continuous fibers preferably account for 75 to 99% by mass, more preferably 80 to 97% by mass, and even more preferably 85 to 97% by mass. The crosslinked fibers preferably account for 1 to 25% by mass, more preferably 3 to 20% by mass, and even more preferably 3 to 15% by mass. When the mass proportions are within the above ranges, the integrity of the unidirectional continuous fibers is high, resulting in a resin-integrated fiber sheet with high tensile strength in the width direction.

[0045] The fiber volume (Vf) of the resin-integrated fiber sheet is preferably 25 to 70% by volume and the thermoplastic resin 30 to 75% by volume, more preferably 35 to 60% by volume of fiber and 40 to 65% by volume of resin. This allows the resin component of the resin-integrated fiber sheet to be used as the matrix resin component of the hollow molded article. In other words, there is no need to add a new resin when producing the hollow molded article. The mass per unit area of ​​the resin-integrated fiber sheet is 20 to 1000 g / m 2 is preferable, and more preferably 50 to 500 g / m 2 is.

[0046] The fiber is preferably at least one selected from carbon fiber, glass fiber, and high-modulus fibers with a modulus of elasticity of 380 cN / dtex or more. Examples of high-modulus fibers include aramid fiber, particularly para-aramid fiber (modulus: 380-980 cN / dtex), polyarylate fiber (modulus: 600-741 cN / dtex), heterocyclic polymer (PBO, modulus: 1060-2200 cN / dtex), high-molecular-weight polyethylene fiber (modulus: 883-1413 cN / dtex), and polyvinyl alcohol fiber (PVA, strength: 14-18 cN / dtex) (Encyclopedia of Fibers, p. 522, March 25, 2002, Maruzen). These fibers are useful as resin-reinforced fibers. Carbon fiber is particularly useful.

[0047] The thickness of one of the resin-integrated fiber sheets is preferably 20 to 1000 μm, more preferably 50 to 500 μm. Resin-integrated fiber sheets with a thickness in this range are easy to mold. The thickness of one of the resin-integrated fiber sheets is measured in a state where the unidirectional continuous fibers are completely impregnated with the thermoplastic resin.

[0048] The thermoplastic resin may be, but is not limited to, a polyamide resin, a polycarbonate resin, a polypropylene resin, a polyester resin, a polyethylene resin, an acrylic resin, a phenoxy resin, a polystyrene resin, a polyimide resin, or a polyether ether ketone (PEEK) resin.

[0049] The resin adhesion state of the resin-integrated fiber sheet of the present invention is preferably such that the powder resin melts and solidifies and adheres near the surfaces of unidirectional continuous fibers (hereinafter also referred to as "spread sheet") in which continuous fibers are spread and arranged in parallel in one direction, and the resin does not impregnate the inside of the spread sheet or only slightly impregnates a part of it. In this state, when a plurality of resin-integrated fiber sheets are stacked and a hollow molded body is formed, the resin easily spreads throughout the entire spread sheet, which is preferable.

[0050] In the case of carbon fibers, the width of the spread sheet is preferably 0.1 to 5.0 mm per 1,000 constituent fibers. Specifically, the width of the spread sheet is approximately 0.1 to 1.5 mm per 1,000 constituent fibers for large tows such as 50K or 60K, and approximately 0.5 to 5.0 mm per 1,000 constituent fibers for regular tows such as 12K or 15K. Here, K indicates 1,000 constituent fibers. Unspread tows sold by carbon fiber manufacturers are spread to form easy-to-use spread sheets, which can be supplied for molding various hollow molded articles. The carbon fiber bundles (tows) supplied for producing a resin-integrated fiber sheet preferably have 5,000 to 50,000 fibers per bundle, and 10 to 280 of these carbon fiber bundles (tows) are preferably supplied to the spreading means. When multiple carbon fiber bundles (tows) are supplied and spread to form a single sheet in this way, the spaces between the carbon fiber bundles (tows) are likely to split, but if crosslinked fibers with various orientations are bonded and fixed to the spread sheet with resin, splitting between the tows can also be prevented.

[0051] The average length of the crosslinked fibers is preferably 1 mm or more, more preferably 5 mm or more. If the average length of the crosslinked fibers is within the above range, the carbon fiber sheet will have high strength in the width direction and excellent handleability.

[0052] [Method of manufacturing resin-integrated fiber sheet] The method for producing the resin-integrated fiber sheet used in producing the hollow molded article of the present invention includes, for example, the following steps: A carbon fiber sheet will be taken as an example of the spread fiber sheet. (1) When a group of carbon fiber filaments is spread by at least one means selected from passing through a plurality of rolls, passing through a spreading bar, and air spreading, and arranged in parallel in one direction, crosslinked fibers are generated from the group of carbon fiber filaments during or after spreading, or crosslinked fibers are dropped onto a carbon fiber sheet during or after spreading. The crosslinked fibers are formed in an area of ​​10 mm2 of the carbon fiber sheet. 2The number of carbon fiber filaments is set to an average of one or more per 15,000 filaments. When the carbon fiber filaments are spread by passing them through a roll or a spreading bar, tension can be applied to the carbon fiber filaments to generate crosslinked fibers from the carbon fiber filaments during spreading. The tension of the carbon fiber filaments can be, for example, in the range of 2.5 to 30 N per 15,000 filaments. When air spreading is employed, it is preferable to subsequently generate crosslinked fibers using a roll or a spreading bar. When crosslinked fibers are generated from the carbon fiber filaments, the crosslinked fibers are intertwined with the carbon fibers constituting the carbon fiber sheet. Here, intertwining includes entanglement. For example, some or all of the crosslinked fibers are present in the carbon fiber sheet and are three-dimensionally intertwined with the carbon fibers arranged in one direction. (2) Powdered resin is applied to the opened carbon fiber sheet. (3) The powder resin is heated and melted in a pressure-free state (without pressure), and then cooled to cause the resin to be partially present on at least a part of the surface of the carbon fiber sheet. At this time, the crosslinked fibers are bonded and fixed to the carbon fiber sheet by the resin on the surface.

[0053] Fig. 8 is a schematic perspective view of a resin-integrated carbon fiber sheet 1 used to produce a hollow molded article according to one embodiment of the present invention, and Fig. 9 is a schematic cross-sectional view in the thickness and width directions of the resin-integrated carbon fiber sheet 1. Crosslinked fibers 3 are oriented in various directions on the surface of unidirectional continuous fibers 2, which are formed by spreading continuous fibers and arranging them in parallel in one direction. Resin 4 is melted and solidified and adheres near the surface of the unidirectional carbon fibers 2, and the resin 4 does not impregnate the interior of the unidirectional carbon fibers 2 (spread fiber sheet), or only partially impregnates the interior. The resin 4 adheres and fixes the crosslinked fibers 3 to the surface of the unidirectional carbon fibers 2.

[0054] As shown in Figure 9, crosslinked fibers 3a and 3b are present on the surface of the unidirectional carbon fiber 2 (spread sheet). All of the crosslinked fibers 3a are present on the surface of the unidirectional carbon fiber 2. Some of the crosslinked fibers 3b are present on the surface of the unidirectional carbon fiber 2, and some are inside and intertwined with the carbon fibers. Resin 4 adheres and fixes the crosslinked fibers 3 to the surface of the unidirectional carbon fiber 2. The surface of the unidirectional carbon fiber 2 (spread sheet) has parts where the resin 4 is attached and parts 5 where the resin is not attached. When multiple resin-integrated carbon fiber sheets 1 are heated in a stacked state and molded into a fiber-reinforced hollow molding, the parts 5 where the resin is not attached serve as paths for the air inside the fiber sheet to escape, and when pressurized, the resin on the surface easily penetrates the entire spread sheet. As a result, the resin 4 becomes the matrix resin of the fiber-reinforced hollow molding.

[0055] 10 is a schematic process diagram showing a method for producing a resin-integrated carbon fiber sheet used to produce a hollow molded article according to one embodiment of the present invention. A group of carbon fiber filaments (tow) 8 is drawn from a number of supply bobbins 7 (only one is shown in FIG. 7, the others are omitted) and spread by passing it between spreading rolls 21a-21j (roll spreading process 23). Air spreading may be used instead of roll spreading. The spreading rolls may be fixed or rotating, or may vibrate in the width direction.

[0056] After the fiber-spreading step, the spread tow is nipped between nip rolls 9a and 9b and passed between multiple bridge rolls 12a-12b placed between them. A tension of, for example, 2.5 to 30 N per 15,000 tows (corresponding to a group of carbon fiber filaments supplied from one supply bobbin) is applied to generate crosslinked fibers (crosslinked fiber generating step 24). The bridge rolls may rotate or vibrate in the width direction. The bridge rolls may be, for example, multiple rolls with matte, textured, or mirrored surfaces, and the bridge rolls may be positioned in a bent state relative to the group of carbon fiber filaments, or may be fixed, rotated, vibrated in the width direction, or a combination of these to generate crosslinked fibers. 13a-13g are guide rolls.

[0057] Then, dry powder resin 15 is sprinkled on the surface of the spread sheet from powder supply hopper 14, supplied into heating device 16 in a pressure-free state and heated, the dry powder resin 15 is melted, and cooled between guide rolls 13e-13g. Then, dry powder resin 18 is sprinkled on the back surface of the spread sheet from powder supply hopper 17, supplied into heating device 19 in a pressure-free state and heated, the dry powder resin 18 is melted, cooled, and taken up by take-up roll 20 (powder resin application process 25). Dry powder resins 15 and 18 are, for example, polypropylene resin (melting point: 150 to 165°C), and the temperatures in heating devices 16 and 19 are, for example, +5 to +60°C of the melting point, softening point, or fluidization point of the dry powder resin, and the residence times are, for example, 4 seconds each. This increases the strength in the width direction of the carbon fiber spread sheet.

[0058] The powder resin can be applied by powder coating, electrostatic coating, spraying, fluidized bed dipping, etc. The powder coating method in which the powder resin is dropped onto the surface of the spread carbon fiber sheet is preferred. For example, the powder resin in the form of dry powder is sprinkled on the surface of the spread carbon fiber sheet.

[0059] The advantages of the present invention can be summarized as follows: (1) The resin-integrated carbon fiber sheet is different from nonwoven fabric or prepreg substrates in that it has high flexibility and is therefore excellent in formability and moldability. (2) By forming slits in the second resin-integrated carbon fiber sheet, the continuous fibers oriented in the winding direction of the wound body of the laminate are cut in the middle, which facilitates the expansion of the elastic body and the expansion of the diameter of the wound body placed thereon. As a result, the wound body can be pressed against the mold and heated sufficiently, which suppresses the occurrence of voids and peeling, and makes it possible to ensure a hollow molded body with sufficient strength for practical use. (3) Unlike prepreg or semipreg substrates made of thermosetting resins, resin-integrated carbon fiber sheets can be directly molded. In other words, there is no need to soften the resin to form a wound body or to expand the diameter of the wound body. The shaping of the resin-integrated carbon fiber sheet and the impregnation of the thermoplastic resin into the entire fiber sheet and its penetration and diffusion into the resin-integrated carbon fiber sheet can be performed almost simultaneously. (4) In the present invention, since no additional resin other than the resin contained in the resin-integrated carbon fiber sheet is required, the molding time can be shortened and a hollow molded body with a thin fiber-reinforced resin portion can also be produced. [Example]

[0060] The present invention will be specifically described below using examples, but the present invention is not limited to the following examples.

[0061] Example 1 (1) Unopened carbon fiber tow The carbon fiber unspread tow used was manufactured by Mitsubishi Chemical Corporation, product number: PYROFILE TR 50S15L, shape: regular tow filament 15K (15,000 filaments), single fiber diameter 7 μm. An epoxy compound was attached to the carbon fibers of this carbon fiber unspread tow as a sizing agent.

[0062] (2) Means for spreading unspread tow The fibers were spread using the spreading means shown in Fig. 10 (spreading process). In the spreading process, the tension of the carbon fiber filaments (tow) was 15 N per 15,000 filaments. In this way, a spread sheet having 15,000 carbon fiber filaments and a spread width of 500 mm was obtained. The crosslinked fiber was 3.3% by mass.

[0063] (3) Semipreg [Semi-preg 1] Polyphenylene sulfide (PPS) resin (melting point: 290°C, manufactured by Polyplastics Co., Ltd.) was used as the dry powder resin. 2The temperature in the heating devices 16 and 19 was 220°C, and the residence time was 8 seconds (powder resin application step). The mass of the obtained resin-integrated fiber sheet (long object) was 132.4 g / m 2 The thickness was 0.2 mm, the fiber volume (Vf) was 50% by volume, and the dry powder resin (thermoplastic resin) was 50% by volume. [Semi-preg 2] The same procedure was repeated except that the amount of dry powder resin applied was changed to 124.1 g / m 2 A resin-integrated fiber sheet (long object) was produced with a thickness of 0.2 mm, a fiber volume (Vf) of 35% by volume, and a dry powder resin (thermoplastic resin) content of 65% by volume.

[0064] (4) Laminate A long resin-integrated fiber sheet was cut to a predetermined shape, and slits were made as necessary to obtain Sheet A (width 460 mm, MD length 320 mm (longitudinal length of the carbon fiber), no slits) shown in Figure 11 and Sheets B I to IV (width 320 mm, MD length 460 mm (longitudinal length of the carbon fiber)) shown in Figures 12A to 12D, respectively. Sheet B II shown in Figure 12B was divided into five sections along the longitudinal direction of the carbon fiber (L1 = 90 mm, L2 = 100 mm), Sheet B III shown in Figure 12C was divided into four sections along the longitudinal direction of the carbon fiber (L3 = 140 mm, L4 = 40 mm), and Sheet B IV shown in Figure 12D had 60 mm long slits formed at 90 mm intervals (L5) along the longitudinal direction of the carbon fiber. Sheets B I to IV were each stacked on top of Sheet A so that the longitudinal direction of the carbon fibers in Sheet A and Sheets B I to IV were perpendicular to each other, thereby obtaining two-layer laminates A to E (see Table 1).

[0065] Next, internal pressure molding was carried out under the following conditions using the apparatus shown in Fig. 7 to form a hollow molded body, and both ends were cut off by 10 mm to remove burrs, to obtain the hollow molded bodies of Reference Examples 1 and 2 and Examples 1 to 3 shown in the following Table 1 (number of windings: 4, diameter: 35 mm, length: 300 mm, outer periphery: 109 mm, overlap width: 24 mm). The laminate was wound so that Sheet A was on the outside. Elastic body diameter: 30mm Mold temperature: 315℃ Air pressure: 0.6 MPa Heat molding time: 5 minutes Water cooling time: 5 minutes After cooling, the air line was cut off and the hollow molded body was demolded.

[0066] [Table 1]

[0067] [evaluation] (Thickness measurement) Evaluation samples 50 mm long were cut out from the end and center of each of the hollow molded bodies A to E. The minimum thickness and average thickness of each sample were measured, and the results are shown in Table 2 below. The thickness was measured using a micrometer, and the average thickness was calculated by averaging measurements taken at five points. The measurements were performed after the evaluation samples were left to stand in an atmosphere of 23°C and 50% humidity for 48 hours or more.

[0068] (Strength measurement) Evaluation samples measuring 50 mm in length were cut from the end and center of each hollow molded body A to E, and compression tests were performed in the diameter direction of the evaluation samples. The compression tests were performed in accordance with JIS K7181 using a precision universal testing machine (Shimadzu Corporation, Model: AG-50kNXplus). The evaluation samples were placed on a table and pressed with a φ50 mm disk. Measurements were performed after the evaluation samples were left in an atmosphere of 23°C and 50% humidity for at least 48 hours. Table 2 below shows the maximum load, maximum load stroke, and maximum stress (force at the moment of buckling). Figures 13 to 17 are test force-displacement measurement graphs for evaluation samples cut from the hollow molded bodies of Reference Examples 1 and 2 and Examples 1 to 3, respectively. In Figures 13 to 17, a indicates the measurement results at the center of the hollow molded body, and b indicates the measurement results at the end of the hollow molded body.

[0069] [Table 2]

[0070] As shown in Table 2, the hollow molded bodies of Examples 1 to 3 have higher maximum stress (compression strength) and improved strength characteristics than the hollow molded bodies of Reference Examples 1 and 2. In particular, the hollow molded bodies of Examples 1 and 2, in which Sheet A is divided into multiple pieces, have improved strength characteristics. [Industrial Applicability]

[0071] The hollow molded article of the present invention may be a pipe, shaft, frame, etc., and may have a cross section of a circular hollow, a rectangular hollow, or various other shapes. The present invention can be widely applied to general industrial uses such as building materials, sporting goods, windmills, bicycles, automobiles, railways, ships, aviation, and space. [Explanation of symbols]

[0072] 1. Resin-integrated carbon fiber sheet 1a First resin-integrated carbon fiber sheet 1b Second resin-integrated carbon fiber sheet 2. Unidirectional carbon fiber 3,3a,3b crosslinked fiber 4. Resin 5 Areas where resin is not attached 6 Opening device 7 Supply bobbin 8 Carbon fiber filament group (carbon fiber unopened tow) 9a, 9b Nip roll 10a, 10b Slit 11a, 11b Resin-integrated carbon fiber sheet 12a-12b Bridge Roll 13a-13g guide roll 14,17 Powder supply hopper 15,18 Dry powder resin 16,19 Heating device 20 Winding Roll 21a-21j Spreading roll 23 Roll opening process 24 Cross-linked fiber generation process 25 Powder resin application process 30 Hollow molded body 31 Fiber reinforced resin part 32 Overlapped part of resin-integrated carbon fiber sheet 33 Central axis of hollow molding 34 Overlap 35 Elastic Body 35a Central axis of elastic body 36 Jig 37 Rolled laminate of resin-integrated carbon fiber sheet 39 Upper mold 40 Lower mold 41 Air supply port 110 Laminate

Claims

1. A method for producing a fiber-reinforced hollow molded body including a fiber-reinforced resin part having a hollow part therein, a step of placing a roll of a laminate on an elastic body, the laminate being formed by laminating a plurality of resin-integrated fiber sheets, each of which is formed by adhering and heat-fusing a powder of a thermoplastic resin that serves as a matrix to the surface of unidirectional continuous fibers that have been spread and aligned in parallel in one direction; a step of supplying a pressurized fluid into the elastic body arranged in a mold to expand the diameter of the wound body and press it against the mold, the wound body pressed against the mold is heated by the mold and the thermoplastic resin is melted by the heat of the mold, the thermoplastic resin is impregnated into the resin-integrated fiber sheet, and the wound body is integrated with the resin-integrated fiber sheet, The resin-integrated fiber sheet contains crosslinked fibers in various directions and in a direction intersecting the unidirectional continuous fibers, and the thermoplastic resin integrates the unidirectional continuous fibers and the crosslinked fibers, but does not contain a thermosetting resin; The laminate is a first resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers is the same as the axial direction of the wound body; a second resin-integrated fiber sheet in which the longitudinal direction of the unidirectional continuous fibers intersects with the longitudinal direction of the unidirectional continuous fibers of the first resin-integrated fiber sheet, a slit is formed in the second resin-integrated fiber sheet, and the unidirectional continuous fibers are partly or entirely separated by the slit; The method for producing a fiber-reinforced hollow molding, wherein the first resin-integrated fiber sheet has no slits formed therein.

2. 2. The method for manufacturing a fiber-reinforced hollow molding according to claim 1, wherein a plurality of slits that cut all of the unidirectional continuous fibers are formed in the second resin-integrated fiber sheet, dividing the second resin-integrated fiber sheet into a plurality of sheets, and the fiber length of the sheets is shorter than the widthwise length of the second resin-integrated fiber sheet.

3. a plurality of the slits are formed in the second resin-integrated fiber sheet, 3. The method for producing a fiber-reinforced hollow molding according to claim 1, wherein the plurality of slits are formed along the longitudinal direction of the unidirectional continuous fibers at intervals of 0.5 to 1.5 times the outer circumferential length of the fiber-reinforced hollow molding.

4. a plurality of the slits are formed in the second resin-integrated fiber sheet, The method for producing a fiber-reinforced hollow molding according to any one of claims 1 to 3, wherein, in a cross-sectional view perpendicular to the axial direction of the fiber-reinforced hollow molding, the plurality of slits are distributed in a circumferential direction around the axis.

5. The absolute value of the angle of the orientation direction of the unidirectional continuous fibers of the second resin-integrated fiber sheet relative to the orientation direction of the unidirectional continuous fibers of the first resin-integrated fiber sheet is 20° or more and 90° or less. The method for manufacturing a fiber-reinforced hollow molding according to any one of claims 1 to 4.

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