JP7748185B2 - Method for manufacturing fiber-reinforced hollow molding - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced hollow molding .

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 growing. There are several methods for molding hollow molded bodies, but one method 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 composited, is wrapped 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 tedious process of stacking the prepared resin fiber sheets, and allows molding into any shape.

Patent Document 1 proposes using a sheet-like molding substrate, consisting of a sheet material with reinforcing fibers aligned in one direction and a nonwoven fabric made of thermoplastic resin layered over it, as the base material for molding pipes. Patent Document 2 discloses a method for manufacturing fiber-reinforced plastic with a core-sheath structure, in which a laminate including a cut prepreg substrate made of reinforcing fibers and thermosetting resin is wrapped 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 mold using 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.

JP 2011-62818 A Japanese Patent Application Laid-Open No. 2008-273176

However, the molding substrate described in Patent Document 1 contains a nonwoven fabric, and therefore cannot be said to have good formability. The laminate described in Patent Document 2 is also a prepreg substrate composed of reinforcing fibers and a thermosetting resin, and therefore cannot be said to have good formability. Furthermore, 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.

The present invention provides a fiber-reinforced hollow molding that has good formability and excellent strength properties, and a method for producing the same.

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.

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.

In this invention, a laminate of resin-integrated fiber sheets is used to form a fiber-reinforced hollow molded article. 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 unidirectional continuous fibers are partially or entirely separated along the length by the slits. This allows for the provision of a fiber-reinforced hollow molded article with good formability and excellent strength properties.

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. 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. FIG. 3A is a schematic perspective exploded view illustrating an 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. 3B is a schematic explanatory view illustrating the winding direction of the laminate shown in FIG. 3A. Figure 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 Figure 4B is a schematic explanatory view illustrating the winding direction of the laminate shown in Figure 4A. Figure 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 of one embodiment of the present invention, and Figure 5B is a schematic explanatory view illustrating the winding direction of the laminate shown in Figure 5A. FIG. 6A is a schematic perspective view of an elastic body used in molding a fiber-reinforced hollow molding of one embodiment of the present invention, FIG. 6B is a schematic perspective view of the elastic body shown in FIG. 6A wrapped around a laminate of resin-integrated carbon fiber sheets, and FIG. 6C is a cross-sectional view of FIG. 6B. 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. FIG. 8 is a schematic perspective view of a resin-integrated carbon fiber sheet used in molding a fiber-reinforced hollow molded article according to one embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of the resin-integrated carbon fiber sheet 1 in the thickness direction. FIG. 10 is a schematic process diagram showing a method for producing a resin-integrated carbon fiber sheet used in the production of a fiber-reinforced hollow molded article according to one embodiment of the present invention. FIG. 11 is a schematic plan view of sheet A constituting the laminate used to mold the fiber-reinforced hollow moldings A to E. As shown in FIG. 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. 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. 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. 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. 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. 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.

To improve formability in molding fiber-reinforced hollow moldings, the inventors decided to use a resin-integrated fiber sheet (semi-preg sheet) in which a group of unidirectional continuous fibers is spread and aligned in one direction, with a thermoplastic resin powder matrix attached to the surface and heat-sealed. Furthermore, to improve strength characteristics, they decided to use a laminate in which multiple resin-integrated fiber sheets are stacked so that the longitudinal directions of the unidirectional continuous fibers differ. Specifically, for example, a laminate was used in which, when molded into a fiber-reinforced hollow molding, 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, and another sheet was stacked so that the unidirectional continuous fibers were wound around the axis of the fiber-reinforced hollow molding. The inventors discovered that the strength characteristics of the resulting fiber-reinforced hollow moldings were insufficient. The new findings were that the unidirectional continuous fibers wound around the axis prevented the diametric expansion of the wound body when pressurized fluid was supplied to the inside of the wound body of the laminate. If the diameter of the wound body is insufficient, heat transfer from the molding die to the wound body and melting of the thermoplastic resin will be insufficient, making voids and peeling more likely to occur and reducing strength characteristics. The inventors conducted extensive research to solve this problem, and have completed the invention described below.

The fiber-reinforced hollow molded article (hereinafter sometimes referred to as "hollow molded article") of the present invention is a hollow molded article including a fiber-reinforced resin part with an internal hollow portion. 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 matrix of thermoplastic resin powder (hereinafter sometimes referred to as "thermoplastic powder resin") is adhered to the surface of unidirectional continuous fibers in which continuous fibers are spread and aligned in one direction, and then heat-fused. In the fiber-reinforced resin part molded using the laminate, the entire resin-integrated fiber sheet is impregnated with the thermoplastic resin.

The laminate used to form the hollow molded body 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 body. 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, which separate some or all of the unidirectional continuous fibers midway.

Below, an example of the hollow molded article of the present invention and its manufacturing method will be described in detail with reference to the drawings.

[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 portion 31 that is hollow in the longitudinal direction. The fiber-reinforced resin portion 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 and/or the vicinity of the resin-integrated carbon fiber sheets to impregnate the resin-integrated carbon fiber sheets, and then penetrate and diffuse between the resin-integrated carbon fiber sheets, integrating them.

The laminate used to form the hollow molded body 30 includes a first resin-integrated carbon fiber sheet (described in detail below) and a second resin-integrated carbon fiber sheet (described in detail below). 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. Note that in FIG. 1B, the first fiber-reinforced resin sheet 33a is marked with dots to facilitate differentiation from the second fiber-reinforced resin sheet 33b.

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 30, from the viewpoint of suppressing the occurrence of voids, peeling, etc. 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 of 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.

In the hollow molded body 30 shown in Figure 1, the laminate includes an overlap portion 32, but if the number of turns is two or more, the overlap portion 32 is not necessary. 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.

When the second resin-integrated carbon fiber sheet used to mold the hollow molded body 30 has multiple slits that partially separate the unidirectional continuous fibers and the laminate has multiple windings, it is preferable, from the perspective 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 portion 31 in a cross-sectional view perpendicular to the central axis 33 of the hollow molded body 30, as shown in Figure 1B. In Figure 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.

The diameter (outer diameter) of the hollow molded body 30 is preferably 30 to 100 mm, the length is preferably 50 to 5000 mm, and the thickness is preferably 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, etc.

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

[Hollow Molded Article 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 of placing a wound laminate, which is made of multiple resin-integrated fiber sheets that have been heat-fused by adhering a thermoplastic powder resin matrix to the surfaces of unidirectional continuous fibers that have been spread and aligned in one direction, on an elastic body; - A process of supplying pressure fluid into the inside of the elastic body placed inside a mold to press the wound laminate 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 laminate. The wound laminate can be placed on the elastic body by wrapping the laminate around the elastic body, or by forming a wound laminate and then placing it on the elastic body.

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 those of the first resin-integrated fiber sheet at a predetermined angle. 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.

In one example of a method for producing a hollow molded article of the present invention, first, the 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.

The cut 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 the 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.

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

As shown in FIG. 2B, in the second resin-integrated fiber sheet, it is preferable that multiple slits 10a be formed in the second resin-integrated fiber sheet from the perspective of improving strength uniformity. Furthermore, from the perspective of improving strength uniformity, it is preferable that the slits 10a be formed periodically in the longitudinal direction of the unidirectional continuous fibers. From the perspective of suppressing strength reduction due to void generation and peeling during molding, the distance L between adjacent slits 10a along the longitudinal direction of the continuous fibers is preferably 1.5 times or less, and more preferably 1.2 times or less, the circumferential length of the hollow molded body. On the other hand, from the perspective of improving strength due to the fibers of the second resin-integrated fiber sheet 1b, the distance L is preferably 0.5 times or more, and more preferably 0.7 times or more, the circumferential length of the hollow molded body.

In the second resin-integrated fiber sheet 1b, it is preferable that the parallel-arranged unidirectional continuous fibers are cut by one of the multiple slits 10a, so that all of the unidirectional continuous fibers are severed along the way.

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 35a of the elastic body 35 so 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. 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 multiple. In the case of a single wrap, it is necessary to overlap the end of the wrap with the single wrap to create an overlap.

Figure 4A shows another example of a laminate. In Figure 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 Figure 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 is expanded more easily than in the laminate shown in Figures 3A and 3B, making it possible to ensure higher strength 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 circumferential length 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 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 circumferential length of the hollow molded body.

Figure 5A shows another example of a laminate. As shown in Figure 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 Figure 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 adjustments made from long resin-integrated fiber sheets.

3A, 4A, and 5A, arrow X indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers that make up the first resin-integrated fiber sheet, and arrow Y indicates the longitudinal direction (orientation direction) of the unidirectional continuous fibers that make up the second resin-integrated fiber sheet. From the perspective of improving strength characteristics, the absolute value of the angle (θ) 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 preferably 20° or more and 90° or less. It is preferable to select an appropriate angle within this range depending on the mechanical properties required of the hollow molded article. In all of the laminates 110 described using Figures 3 to 5, θ is 90°, and the fibers that make up 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.

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 product, it may also be wound so that the second resin-integrated fiber sheet 1b is on the outside.

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 Figure 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 about the axis, and are preferably formed in positions that do not overlap in the thickness direction of the wound body, and are more preferably arranged at substantially equal intervals in the circumferential direction about the axis. Here, "substantially equal intervals" includes intervals within a range that can be considered to be substantially the same as strictly equal intervals, and specifically means an error of ±10 mm. The same applies to the slits 10b.

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, but this is not limited to this method; slits may also 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.

Figure 6A is a schematic perspective view of an elastic body 35 used for internal pressure molding, Figure 6B is a schematic perspective view of a wound laminate of resin-integrated carbon fiber sheets placed on the elastic body 35, and Figure 6C is a cross-sectional view of Figure 6B. A jig 36 is attached to the tip of the elastic body 35 to seal the pressurized 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).

Figure 7A is a schematic plan view showing an elastic body 35 on which a wound body 37 of a resin-integrated carbon fiber sheet laminate is placed in a molding die, and Figure 7B is a cross-sectional view taken along line I-I in Figure 7A. The molding die is composed of a lower die 40 and an upper die 39. For example, a wound body 37 is formed by wrapping a resin-integrated carbon fiber sheet laminate 110 around the surface of the elastic body 35. Alternatively, the laminate 110 may be wound into a preform, which is then placed on the elastic body.

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 it 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 makes up the wound body 37 melts. The molten thermoplastic resin impregnates the resin-integrated carbon fiber sheet, permeates 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. The die is then cooled, for example, by water cooling, and then demolded. This results in a hollow molded body containing a fiber-reinforced resin portion.

When the resin-integrated carbon fiber sheet laminate 110 is wound around the elastic body 35, the unidirectional continuous fibers that make up the second resin-integrated fiber sheet are wound circumferentially around the elastic body 35. The unidirectional continuous fibers that make up the resin-integrated fiber sheet do not stretch themselves. Therefore, if the unidirectional continuous fibers of the second resin-integrated fiber sheet were completely continuous along their entire length, the radial expansion of the elastic body 35 and, ultimately, the expansion of the wound body 37 would be hindered. However, because the second resin-integrated carbon fiber sheet has slits, the slit portions expand radially, facilitating 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 delamination and ensuring sufficient strength for practical use in the hollow molded body.

Examples of the pressurized fluid supplied to the inside of the elastic body include compressed air. The internal pressure of the pressurized 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 drops to, for example, 60°C or below.

[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.

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 amount of 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, integrating 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.

The resin-integrated fiber sheet is a semipreg made by adhering a matrix thermoplastic powder resin to the surface of unidirectional continuous fibers and then heat-fusing them. When molded, this semipreg allows the thermoplastic resin on the surface to easily impregnate the resin-integrated fiber sheet and easily penetrate and diffuse uniformly between the resin-integrated fiber sheets. This results in excellent formability (moldability) and suppresses the occurrence of voids.

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.

The fiber volume (Vf) of the resin-integrated fiber sheet is preferably 25 to 70 volume % and the thermoplastic resin is preferably 30 to 75 volume %, more preferably 35 to 60 volume % fiber and 40 to 65 volume % resin. This allows the resin component of the resin-integrated fiber sheet to be used as the matrix resin component of the hollow molded body. In other words, no additional resin is required when producing the hollow molded body. The mass per unit area of the resin-integrated fiber sheet is preferably 20 to 1,000 g/ ^m² , more preferably 50 to 500 g/ ^m² .

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 higher. Examples of high-modulus fibers include aramid fiber, particularly para-aramid fiber (modulus of elasticity: 380-980 cN/dtex), polyarylate fiber (modulus of elasticity: 600-741 cN/dtex), heterocyclic polymer (PBO, modulus of elasticity: 1060-2200 cN/dtex), high-molecular-weight polyethylene fiber (modulus of elasticity: 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.

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. Note that the thickness of one of the resin-integrated fiber sheets is measured when the thermoplastic resin has been completely impregnated into the unidirectional continuous fibers.

The thermoplastic resin may be, but is not limited to, polyamide resin, polycarbonate resin, polypropylene resin, polyester resin, polyethylene resin, acrylic resin, phenoxy resin, polystyrene resin, polyimide resin, and polyether ether ketone (PEEK) resin.

The resin adhesion state of the resin-integrated fiber sheet of the present invention is such that the powder resin melts and solidifies and adheres near the surface of the unidirectional continuous fibers (hereinafter also referred to as the "spread sheet"), in which continuous fibers have been spread and aligned in parallel in one direction, and the resin does not impregnate the interior of the spread sheet, or only slightly impregnates some of it. This state is preferable because it makes it easier for the resin to spread throughout the entire spread sheet when multiple resin-integrated fiber sheets are stacked and a hollow molded body is formed.

For carbon fiber, 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 can be 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 the production of resin-integrated fiber sheets are preferably 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 in this way to form a single sheet, the carbon fiber bundles (tows) are prone to splitting apart, 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.

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

[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 carbon fiber filaments are spread and arranged in parallel in one direction by at least one means selected from passing through multiple rolls, passing through a spreading bar, and air spreading, crosslinked fibers are generated from the 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 an average of one or more ^per 10 mm2 area of the carbon fiber sheet. When spreading carbon fiber filaments by passing through rolls or a spreading bar, crosslinked fibers can be generated from the carbon fiber filaments during spreading by applying tension to the carbon fiber filaments. 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 used, 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 that are aligned 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.

Figure 8 is a schematic perspective view of a resin-integrated carbon fiber sheet 1 used to manufacture a hollow molded article according to one embodiment of the present invention, and Figure 9 is a schematic cross-sectional view of the resin-integrated carbon fiber sheet 1 in the thickness-width direction. The unidirectional continuous fibers 2 are formed by spreading continuous fibers and arranging them in parallel in one direction. On the surface of the fibers, bridging fibers 3 are oriented in various directions. Resin 4 melts and solidifies and adheres to the surface of the unidirectional carbon fibers 2. 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 bridging fibers 3 to the surface of the unidirectional carbon fibers 2.

As shown in Figure 9, bridging fibers 3a and 3b are present on the surface of the unidirectional carbon fiber 2 (spread sheet). All of the bridging fibers 3a are present on the surface of the unidirectional carbon fiber 2. Some of the bridging fibers 3b are present on the surface of the unidirectional carbon fiber 2, while some are present inside and intertwined with the carbon fibers. Resin 4 adheres and fixes the bridging fibers 3 to the surface of the unidirectional carbon fiber 2. The surface of the unidirectional carbon fiber 2 (spread sheet) has areas where resin 4 is attached and areas 5 where 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 areas 5 where resin is not attached serve as paths for air to escape from the fiber sheet. This makes it easier for the resin on the surface to impregnate the entire spread sheet when pressurized. As a result, resin 4 becomes the matrix resin for the fiber-reinforced hollow molding.

Figure 10 is a schematic process diagram showing a method for producing a resin-integrated carbon fiber sheet used to produce a hollow molded body according to one embodiment of the present invention. A group of carbon fiber filaments (tows) 8 is pulled out from multiple supply bobbins 7 (only one is shown in Figure 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.

After the opening process, the opened tow is nipped between nip rolls 9a and 9b and passed between multiple bridge rolls 12a-12b placed between them. A tension of 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 generation process 24). The bridge rolls may rotate or vibrate widthwise. The bridge rolls may be multiple rolls with, for example, matte, textured, or mirrored surfaces. The bridge rolls are positioned in a bent state relative to the group of carbon fiber filaments, or may be fixed, rotated, vibrated widthwise, or a combination of these to generate crosslinked fibers. 13a-13g are guide rolls.

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

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

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 using thermosetting resins, resin-integrated carbon fiber sheets can be directly molded. That is, there is no need to soften the resin to form a wound body or to expand the diameter of the wound body. Shaping into a resin-integrated carbon fiber sheet and impregnation of the thermoplastic resin into the entire fiber sheet and penetration and diffusion between the resin-integrated carbon fiber sheets 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 be produced.

The present invention will be specifically explained using the following examples. Note that the present invention is not limited to the following examples.

Example 1
(1) Unopened Carbon Fiber Tow The unopened carbon fiber 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 unopened carbon fiber tow as a sizing agent.

(2) Means for spreading unspread tow The unspread tow was 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 15K carbon fiber filaments and a spread width of 500 mm was obtained. The crosslinked fiber was 3.3% by mass.

(3) Semipreg [Semipreg 1]
Polyphenylene sulfide (PPS) resin (melting point: 290°C, manufactured by Polyplastics Co., Ltd.) was used as the dry powder resin. An average of 28.2 g of this resin was applied to one side of 1 ^m2 of carbon fiber, for a total of 56.4 g on both sides. The 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/ ^m2 , the thickness was 0.2 mm, the fiber volume (Vf) was 50 vol%, and the dry powder resin (thermoplastic resin) was 50 vol%.
[Semi-preg 2]
A resin-integrated fiber sheet (long object) was prepared in the same manner as above, except that the amount of dry powder resin applied was changed, with a weight of 124.1 g/ ^m2 , a thickness of 0.2 mm, a fiber volume (Vf) of 35 vol%, and a dry powder resin (thermoplastic resin) content of 65 vol%.

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

Next, internal pressure molding was carried out under the following conditions using the apparatus shown in Figure 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.
・Diameter of elastic body: 30 mm
Mold temperature: 315°C
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.

[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.

(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 diametric direction of the evaluation sample. The compression tests were performed in accordance with JIS K7181 using a precision universal testing machine (Shimadzu Corporation, Model: AG-50kNXplus). The evaluation sample was placed on a platform and pressed with a φ50 mm disk. Measurements were performed after the evaluation sample was 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.

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 strength characteristics of the hollow molded bodies of Examples 1 and 2, in which Sheet A is divided into multiple pieces, are improved.

The hollow molded articles of the present invention include pipes, shafts, frames, etc., and can have cross sections of circular or rectangular hollows, as well as various other shapes. The present invention can be widely applied to general industrial applications such as building materials, sporting goods, wind turbines, bicycles, automobiles, railways, ships, aviation, and space.

1 Resin-integrated carbon fiber sheet 1a First resin-integrated carbon fiber sheet 1b Second resin-integrated carbon fiber sheet 2 Unidirectional carbon fibers 3, 3a, 3b Cross-linked fibers 4 Resin 5 Portion to which resin is not attached 6 Spreading device 7 Supply bobbin 8 Carbon fiber filament group (carbon fiber unspread tow)
9a, 9b Nip rolls 10a, 10b Slits 11a, 11b Resin-integrated carbon fiber sheets 12a-12b Bridge rolls 13a-13g Guide rolls 14, 17 Powder supply hoppers 15, 18 Dry powder resin 16, 19 Heating device 20 Winding rolls 21a-21j Spreading roll 23 Roll spreading process 24 Crosslinked fiber generating process 25 Powder resin application process 30 Hollow molded body 31 Fiber reinforced resin portion 32 Overlap portion of resin-integrated carbon fiber sheet 33 Central axis of hollow molded body 34 Overlap portion 35 Elastic body 35a Central axis of elastic body 36 Jig 37 Wound body of resin-integrated carbon fiber sheet laminate 39 Upper mold 40 Lower mold 41 Air supply port 110 Laminate

Claims (5)

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 a plurality of resin-integrated fiber sheets formed by adhering and heat-fusing a thermoplastic resin powder as a matrix to the surfaces 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. 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. 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. 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. 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.